Publications & Presentations - Archive

This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the $2\times {10}^{-4}\lesssim \left|\Delta m_{41}^2\right|\lesssim 0.3{\mathrm{eV}}^2$ mass range. The resulting limits on ${\sin }^{2}2{\theta }_{14}$ are improved by approx imately a factor of 2 over previous results and constitute the most stringent constraints to date in the $\left|\Delta m_{41}^2\right|\lesssim 0.2{\mathrm{eV}}^2$ region.

Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti)neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on ${\sin }^{2}2{\theta }_{\mu e}$ are set over 6 orders of magnitude in the sterile mass-squared splitting $\Delta m_{41}^2$. The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for $\Delta m_{41}^2<0.8{\mathrm{eV}}^2$ at $95\%{\mathrm{CL}}_s$.

Modern cosmological simulations have reached the trillion-element scale, rendering data storage and subsequent analysis formidable tasks. To address this circumstance, we present a new MPI-parallel approach for analysis of simulation data while the simulation runs, as an alternative to the traditional workflow consisting of periodically saving large data sets to disk for subsequent `offline' analysis. We demonstrate this approach in the compressible gasdynamics/N-body code Nyx, a hybrid MPI+OpenMP code based on the BoxLib framework, used for large-scale cosmological simulations. We have enabled on-the-fly workflows in two different ways: one is a straightforward approach consisting of all MPI processes periodically halting the main simulation and analyzing each component of data that they own ('in situ'). The other consists of partitioning processes into disjoint MPI groups, with one performing the simulation and periodically sending data to the other 'sidecar' group, which post-processes it while the simulation continues ('in-transit'). The two groups execute their tasks asynchronously, stopping only to synchronize when a new set of simulation data needs to be analyzed. For both the in situ and in-transit approaches, we experiment with two different analysis suites with distinct performance behavior: one which finds dark matter halos in the simulation using merge trees to calculate the mass contained within iso-density contours, and another which calculates probability distribution functions and power spectra of various fields in the simulation. Both are common analysis tasks for cosmology, and both result in summary statistics significantly smaller than the original data set. We study the behavior of each type of analysis in each workflow in order to determine the optimal configuration for the different data analysis algorithms.

The disappearance of reactor ν¯e observed by the Daya Bay experiment is examined in the framework of a model in which the neutrino is described by a wave packet with a relative intrinsic momentum dispersion σrel. Three pairs of nuclear reactors and eight antineutrino detectors, each with good energy resolution, distributed among three experimental halls, supply a high-statistics sample of ν¯e acquired at nine different baselines. This provides a unique platform to test the effects which arise from the wave packet treatment of neutrino oscillation. The modified survival probability formula was used to fit Daya Bay data, providing the first experimental limits: 2.38⋅10−17<σrel<0.23. Treating the dimensions of the reactor cores and detectors as constraints, the limits are improved: 10−14≲σrel<0.23, and an upper limit of σrel<0.20 is obtained. All limits correspond to a 95\% C.L. Furthermore, the effect due to the wave packet nature of neutrino oscillation is found to be insignificant for reactor antineutrinos detected by the Daya Bay experiment thus ensuring an unbiased measurement of the oscillation parameters sin22θ13 and Δm232 within the plane wave model.

NVRAM-based Burst Buffers are an important part of the emerging HPC storage landscape. The National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory recently installed one of the first Burst Buffer systems as part of its new Cori supercomputer, collaborating with Cray on the development of the DataWarp software. NERSC has a diverse user base comprised of over 6500 users in 700 different projects spanning a wide variety of scientific computing applications. The use-cases of the Burst Buffer at NERSC are therefore also considerable and diverse. We describe here performance measurements and lessons learned from the Burst Buffer Early User Program at NERSC, which selected a number of research projects to gain early access to the Burst Buffer and exercise its capability to enable new scientific advancements. To the best of our knowledge this is the first time a Burst Buffer has been stressed at scale by diverse, real user workloads and therefore these lessons will be of considerable benefit to shaping the developing use of Burst Buffers at HPC centers.

We present DES14X3taz, a new hydrogen-poor superluminous supernova (SLSN-I) discovered by the Dark Energy Survey (DES) supernova program, with additional photometric data provided by the Survey Using DECam for Superluminous Supernovae. Spectra obtained using Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy on the Gran Telescopio CANARIAS show DES14X3taz is an SLSN-I at z = 0.608. Multi-color photometry reveals a double-peaked light curve: a blue and relatively bright initial peak that fades rapidly prior to the slower rise of the main light curve. Our multi-color photometry allows us, for the first time, to show that the initial peak cools from 22,000 to 8000 K over 15 rest-frame days, and is faster and brighter than any published core-collapse supernova, reaching 30% of the bolometric luminosity of the main peak. No physical ⁵⁶Ni-powered model can fit this initial peak. We show that a shock-cooling model followed by a magnetar driving the second phase of the light curve can adequately explain the entire light curve of DES14X3taz. Models involving the shock-cooling of extended circumstellar material at a distance of ≃400 {\text{}}{R}_⊙ are preferred over the cooling of shock-heated surface layers of a stellar envelope. We compare DES14X3taz to the few double-peaked SLSN-I events in the literature. Although the rise times and characteristics of these initial peaks differ, there exists the tantalizing possibility that they can be explained by one physical interpretation.

Haplotyping of human chromosomes is a prerequisite for cataloguing the full repertoire of genetic variation. We present a microfluidics-based, linked-read sequencing technology that can phase and haplotype germline and cancer genomes using nanograms of input DNA. This high-throughput platform prepares barcoded libraries for short-read sequencing and computationally reconstructs long-range haplotype and structural variant information. We generate haplotype blocks in a nuclear trio that are concordant with expected inheritance patterns and phase a set of structural variants. We also resolve the structure of the EML4-ALK gene fusion in the NCI-H2228 cancer cell line using phased exome sequencing. Finally, we assign genetic aberrations to specific megabase-scale haplotypes generated from whole-genome sequencing of a primary colorectal adenocarcinoma. This approach resolves haplotype information using up to 100 times less genomic DNA than some methods and enables the accurate detection of structural variants.

SN 2012dn is a super-Chandrasekhar mass candidate in a purportedly normal spiral (SAcd) galaxy, and poses a challenge for theories of type Ia supernova diversity. Here we utilize the fast and highly parametrized spectrum synthesis tool, SYNAPPS, to estimate relative expansion velocities of species inferred from optical spectra obtained with six facilities. As with previous studies of normal SN Ia, we find that both unburned carbon and intermediate-mass elements are spatially coincident within the ejecta near and below 14 000 km s⁻¹. Although the upper limit on SN 2012dn's peak luminosity is comparable to some of the most luminous normal SN Ia, we find a progenitor mass exceeding ∼1.6 M_⊙ is not strongly favoured by leading merger models since these models do not accurately predict spectroscopic observations of SN 2012dn and more normal events. In addition, a comparison of light curves and host-galaxy masses for a sample of literature and Palomar Transient Factory SN Ia reveals a diverse distribution of SN Ia subtypes where carbon-rich material remains unburned in some instances. Such events include SN 1991T, 1997br, and 1999aa where trace signatures of C III at optical wavelengths are presumably detected.

We use observed UV through near-IR spectra to examine whether SN 2011fe can be understood in the framework of Branch-normal Type Ia supernovae (SNe Ia) and to examine its individual peculiarities. As a benchmark, we use a delayed-detonation model with a progenitor metallicity of Z_⊙/20. We study the sensitivity of features to variations in progenitor metallicity, the outer density profile, and the distribution of radioactive nickel. The effect of metallicity variations in the progenitor have a relatively small effect on the synthetic spectra. We also find that the abundance stratification of SN 2011fe resembles closely that of a delayed-detonation model with a transition density that has been fit to other Branch-normal SNe Ia. At early times, the model photosphere is formed in material with velocities that are too high, indicating that the photosphere recedes too slowly or that SN 2011fe has a lower specific energy in the outer ≈0.1 M_⊙ than does the model. We discuss several explanations for the discrepancies. Finally, we examine variations in both the spectral energy distribution and in the colours due to variations in the progenitor metallicity, which suggests that colours are only weak indicators for the progenitor metallicity, in the particular explosion model that we have studied. We do find that the flux in the U band is significantly higher at maximum light in the solar metallicity model than in the lower metallicity model and the lower metallicity model much better matches the observed spectrum.

This research investigates thermal conductivity properties of Cu/Zr alloys combined with diamond particles to form a composite that possess superior thermal conductivity. This article describes the use of a theoretical calculation and finite element analysis to compare to previously published experimental observations. Both theoretical calculations and finite element analysis indicate that experimental results cannot be explained solely by an improved interface between the matrix and diamond particles, as originally suggested. This study shows that the experimental results, theoretical calculations, and finite element analysis are in agreement when the thermal conductivity of the matrix is adjusted to compensate for the amount of zirconium lost to the interface. This finding can be used to predict the thermal conductivity of a composite material composed of a Cu/Zr matrix with diamond particles.

We report a new measurement of electron antineutrino disappearance using the fully constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9 x 10^5 GW,ton a day, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six radioactive calibration sources reduced the background by a factor of 2 for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission.

We describe an algorithm for identifying point-source transients and moving objects on reference-subtracted optical images containing artifacts of processing and instrumentation. The algorithm makes use of the supervised machine learning technique known as Random Forest. We present results from its use in the Dark Energy Survey Supernova program (DES-SN), where it was trained using a sample of 898,963 signal and background events generated by the transient detection pipeline. After reprocessing the data collected during the first DES-SN observing season (2013 September through 2014 February) using the algorithm, the number of transient candidates eligible for human scanning decreased by a factor of 13.4, while only 1.0% of the artificial Type Ia supernovae (SNe) injected into search images to monitor survey efficiency were lost, most of which were very faint events. Here we characterize the algorithm’s performance in detail, and we discuss how it can inform pipeline design decisions for future time-domain imaging surveys, such as the Large Synoptic Survey Telescope and the Zwicky Transient Facility. An implementation of the algorithm and the training data used in this paper are available at at http://portal.nersc.gov/project/dessn/autoscan.

The Daya Bay experiment consists of functionally identical antineutrino detectors immersed in pools of ultrapure water in three well-separated underground experimental halls near two nuclear reactor complexes. These pools serve both as shields against natural, low-energy radiation and as water Cherenkov detectors that efficiently detect cosmogenic muons using arrays of photomultiplier tubes. Each pool is covered by a plane of resistive plate chambers as an additional means of detecting muons. The design, construction, operation, and performance of these muon detectors are described.

The fabrication, testing and modeling of thermal annealed pyrolytic graphite (TPG) encapsulated heat spreaders was explored for potential use in the cooling of microelectronic devices. The 60 mm diameter, 5 mm thick heat spreaders were created using field-assisted sintering technology (FAST). The TPG encapsulated heat spreaders were compared to their simple aluminum and copper versions through both experimental measurements and numerical calculations. The results show that TPG encapsulated heat spreaders yield lower and more uniform surface temperatures when exposed to identical heating conditions. Heat spreaders such as these should be considered for cooling the next generation of high power density microelectronic devices.

This document presents the results from the Distances subgroup of the Cosmic Frontier Community Planning Study (Snowmass 2013). We summarize the current state of the field as well as future prospects and challenges. In addition to the established probes using Type Ia supernovae and baryon acoustic oscillations, we also consider prospective methods based on clusters, active galactic nuclei, gravitational wave sirens and strong lensing time delays.

We estimate systematic errors due to K-corrections in standard photometric analyses of high-redshift Type Ia supernovae. Errors due to K-correction occur when the spectral template model underlying the light curve fitter poorly represents the actual supernova spectral energy distribution, meaning that the distance modulus cannot be recovered accurately. In order to quantify this effect, synthetic photometry is performed on artificially redshifted spectrophotometric data from 119 low-redshift supernovae from the Nearby Supernova Factory, and the resulting light curves are fit with a conventional light curve fitter. We measure the variation in the standardized magnitude that would be fit for a given supernova if located at a range of redshifts and observed with various filter sets corresponding to current and future supernova surveys. We find significant variation in the measurements of the same supernovae placed at different redshifts regardless of filters used, which causes dispersion greater than ~0.05 mag for measurements of photometry using the Sloan-like filters and a bias that corresponds to a 0.03 shift in w when applied to an outside data set. To test the result of a shift in supernova population or environment at higher redshifts, we repeat our calculations with the addition of a reweighting of the supernovae as a function of redshift and find that this strongly affects the results and would have repercussions for cosmology. We discuss possible methods to reduce the contribution of the K-correction bias and uncertainty.

We present near-infrared synthetic spectra of a delayed-detonation hydrodynamical model and compare them to observed spectra of four normal Type Ia supernovae ranging from day +56.5 to day +85. This is the epoch during which supernovae are believed to be undergoing the transition from the photospheric phase, where spectra are characterized by line scattering above an optically thick photosphere, to the nebular phase, where spectra consist of optically thin emission from forbidden lines. We find that most spectral features in the near-infrared can be accounted for by permitted lines of Fe II and Co II. In addition, we find that [Ni II] fits the emission feature near 1.98 μm, suggesting that a substantial mass of ⁵⁸Ni exists near the center of the ejecta in these objects, arising from nuclear burning at high density.

The bottleneck for cellular 3D electron microscopy is feature extraction (segmentation) in highly complex 3D density maps. We have developed a set of criteria, which provides guidance regarding which segmentation approach (manual, semi-automated, or automated) is best suited for different data types, thus providing a starting point for effective segmentation.

A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines from six 2.9~GWth nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512~m and 561~m) and one far (1579~m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10−3 eV2<|Δm241|<0.3 eV2 range. The relative spectral distortion due to electron antineutrino disappearance was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin22θ14 cover the 10−3 eV2≲|Δm241|≲0.1 eV2 region, which was largely unexplored

A new measurement of the θ13 mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely different systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of θ13 measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GWth reactors, the rate deficit observed at the far hall is interpreted as sin22θ13=0.083±0.018 in the three-flavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain sin22θ13=0.089±0.008 as the final result for the six-antineutrino-detector configuration of the Daya Bay experiment.

Molecular dynamics simulations employing reactive potentials were used to determine the activation barriers to the dissolution of the amorphous SiO2 surface in the presence of a 2 nm overlayer of water. The potential of mean force calculations of the reactions of water molecules with 15 different starting Q4 sites (Qi is the Si site with i bridging oxygen neighbors) to eventually form the dissolved Q0 site were used to obtain the barriers. Activation barriers for each step in the dissolution process, from the Q4 to Q3 to Q2 to Q1 to Q0 were obtained. Relaxation runs between each reaction step enabled redistribution of the water above the surface in response to the new Qi site configuration. The rate-limiting step observed in the simulations was in both the Q32 reaction (a Q3 site changing to a Q2 site) and the Q21 reaction, each with an average barrier of ∼14.1 kcal mol(-1). However, the barrier for the overall reaction from the Q4 site to a Q0 site, averaged over the maximum barrier for each of the 15 samples, was 15.1 kcal mol(-1). This result is within the lower end of the experimental data, which varies from 14-24 kcal mol(-1), while ab initio calculations using small cluster models obtain values that vary from 18-39 kcal mol(-1). Constraints between the oxygen bridges from the Si site and the connecting silica structure, the presence of pre-reaction strained siloxane bonds, and the location of the reacting Si site within slight concave surface contours all affected the overall activation barriers.

We present a sample of normal Type Ia supernovae (SNe Ia) from the Nearby Supernova Factory data set with spectrophotometry at sufficiently late phases to estimate the ejected mass using the bolometric light curve. We measure ⁵⁶Ni masses from the peak bolometric luminosity, then compare the luminosity in the ⁵⁶Co-decay tail to the expected rate of radioactive energy release from ejecta of a given mass. We infer the ejected mass in a Bayesian context using a semi-analytic model of the ejecta, incorporating constraints from contemporary numerical models as priors on the density structure and distribution of ⁵⁶Ni throughout the ejecta. We find a strong correlation between ejected mass and light-curve decline rate, and consequently ⁵⁶Ni mass, with ejected masses in our data ranging from 0.9 to 1.4 M_⊙. Most fast-declining (SALT2 x₁ < -1) normal SNe Ia have significantly sub-Chandrasekhar ejected masses in our fiducial analysis.

SN 2011fe was the nearest and best-observed type Ia supernova in a generation, and brought previous incomplete datasets into sharp contrast with the detailed new data. In retrospect, documenting spectroscopic behaviors of type Ia supernovae has been more often limited by sparse and incomplete temporal sampling than by consequences of signal-to-noise ratios, telluric features, or small sample sizes. As a result, type Ia supernovae have been primarily studied insofar as parameters discretized by relative epochs and incomplete temporal snapshots near maximum light. Here we discuss a necessary next step toward consistently modeling and directly measuring spectroscopic observables of type Ia supernova spectra. In addition, we analyze current spectroscopic data in the parameter space defined by empirical metrics, which will be relevant even after progenitors are observed and detailed models are refined.

A measurement of the energy dependence of antineutrino disappearance at the Daya Bay Reactor Neutrino Experiment is reported. Electron antineutrinos from six GW reactors were detected with six detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls. Using 217 days of data, 41589 (203809 and 92912) antineutrino candidates were detected in the far hall (near halls). An improved measurement of the oscillation amplitude and the first direct measurement of the mass-squared difference is obtained using the observed rates and energy spectra in a three-neutrino framework. 

This value obtained is consistent with measured by muon neutrino disappearance, supporting the three-flavor oscillation model.

Full Author List:

F.P. An, A.B. Balantekin, H.R. Band, W. Beriguete, M. Bishai, S. Blyth, R.L. Brown, I. Butorov, G.F. Cao, J. Cao, R. Carr, Y.L. Chan, J.F. Chang, Y. Chang, C. Chasman, H.S. Chen, H.Y. Chen, S.J. Chen, S.M. Chen, X.C. Chen, X.H. Chen, Y. Chen, Y.X. Chen, Y.P. Cheng, J.J. Cherwinka, M.C. Chu, J.P. Cummings, J. de Arcos, Z.Y. Deng, Y.Y. Ding, M. Diwan, E. Draeger, X.F. Du, D.A. Dwyer, W.R. Edwards, S.R. Ely, J.Y. Fu, L.Q. Ge, R. Gill, M. Gonchar, G.H. Gong, H. Gong, Y.A. Gornushkin, W.Q. Gu, M.Y. Guan, X.H. Guo, R.W. Hackenburg, R.L. Hahn, G.H. Han, S. Hans,M. He, K.M. Heeger, Y.K. Heng, P. Hinrichs, J. Hor, Y.B. Hsiung, B.Z. Hu, L.J. Hu, L.M. Hu, T. Hu, W. Hu, E.C. Huang, H.X. Huang, H.Z. Huang, X.T. Huang, P. Huber, G. Hussain, Z. Isvan, D.E. Jaffe, P. Jaffke, S. Jetter, X.L. Ji, X.P. Ji, H.J. Jiang, J.B. Jiao, R.A. Johnson, L. Kang, S.H. Kettell, M. Kramer, K.K. Kwan, M.W. Kwok, T. Kwok, W.C. Lai, W.H. Lai, K. Lau, L. Lebanowski, J. Lee, R.T. Lei, R. Leitner,A. Leung, J.K.C. Leung, C.A. Lewis, D.J. Li, F. Li, G.S. Li, Q.J. Li, W.D. Li, X.N. Li, X.Q. Li, Y.F. Li, Z.B. Li, H. Liang, C.J. Lin, G.L. Lin, S.K. Lin, Y.C. Lin, J.J. Ling, J.M. Link, L. Littenberg, B. Littlejohn,D.W. Liu, H. Liu, J.C. Liu, J.L. Liu, S.S. Liu, Y.B. Liu, C. Lu, H.Q. Lu, K.B. Luk, Q.M. Ma, X.B. Ma, X.Y. Ma, Y.Q. Ma, K.T. McDonald, M.C. McFarlane, R.D. McKeown, Y. Meng, I. Mitchell, Y. Nakajima, J. Napolitano, D. Naumov, E. Naumova, I. Nemchenok, H.Y. Ngai, W.K. Ngai, Z. Ning, J.P. Ochoa-Ricoux, A. Olshevski, S. Patton, V. Pec, J.C. Peng, L.E. Piilonen, L. Pinsky, C.S.J. Pun, F.Z. Qi, M. Qi, X. Qian, N. Raper, B. Ren, J. Ren, R. Rosero, B. Roskovec, X.C. Ruan, B.B. Shao, H. Steiner, G.X. Sun, J.L. Sun, Y.H. Tam, H.K. Tanaka, X. Tang, H. Themann, S. Trentalange, O. Tsai, K.V. Tsang, R.H.M. Tsang, C.E. Tull, Y.C. Tung, B. Viren, V. Vorobel, C.H. Wang, L.S. Wang, L.Y. Wang, L.Z. Wang, M. Wang, N.Y. Wang, R.G. Wang, W. Wang, W.W. Wang, Y.F. Wang, Z. Wang, Z. Wang, Z.M. Wang, D.M. Webber, H.Y. Wei, Y.D. Wei, L.J. Wen, K. Whisnant, C.G. White, L. Whitehead, T.S. Wise, H.L.H. Wong, S.C.F. Wong, E. Worcester, Q. Wu, D.M. Xia, J.K. Xia, X. Xia, Z.Z. Xing, J. Xu, J.L. Xu, J.Y. Xu, Y. Xu, T. Xue, J. Yan, C.G. Yang, L. Yang, M.S. Yang, M. Ye, M.F. Yeh, Y.S. Yeh, B.L. Young, G.Y. Yu, J.Y. Yu, Z.Y. Yu, S.L. Zang, L. Zhan, C. Zhang, F.H. Zhang, J.W. Zhang, Q.M. Zhang, S.H. Zhang, Y.C. Zhang, Y.H. Zhang, Y.M. Zhang, Y.X. Zhang, Z.J. Zhang, Z.P. Zhang, Z.Y. Zhang, J. Zhao, Q.W. Zhao, Y.B. Zhao, L. Zheng, W.L. Zhong, L. Zhou, Z.Y. Zhou, H.L. Zhuang, J.H. Zou

Modelling and mitigation of damage are crucial for safe and economical operation of high-power laser facilities. Experiments at the National Ignition Facility use a variety of targets with a range of laser energies spanning more than two orders of magnitude (~14 kJ to ~1.9 MJ). Low-energy inertial confinement fusion experiments are used to study early-time x-ray load symmetry on the capsule, shock timing, and other physics issues. For these experiments, a significant portion of the target is not completely vaporized and late-time (hundreds of ns) simulations are required to study the generation of debris and shrapnel from these targets. Damage to optics and diagnostics from shrapnel is a major concern for low-energy experiments. We provide the first full-target simulations of entire cryogenic targets, including the Al thermal mechanical package and Si cooling rings. We use a 3D multi-physics multi-material hydrodynamics code, ALE-AMR, for these late-time simulations. The mass, velocity, and spatial distribution of shrapnel are calculated for three experiments with laser energies ranging from 14 to 250 kJ. We calculate damage risk to optics and diagnostics for these three experiments. For the lowest energy re-emit experiment, we provide a detailed analysis of the effects of shrapnel impacts on optics and diagnostics and compare with observations of damage sites.

Molecular dynamics simulations using a dissociative water potential were applied to study transport of excess protons in water and determine the applicability of this potential to describe such behavior. While originally developed for gas-phase molecules and bulk liquid water, the potential is transferrable to nanoconfinement and interface scenarios. Applied here, it shows proton behavior consistent with ab initio calculations and empirical models specifically designed to describe proton transport. Both Eigen and Zundel complexes are observed in the simulations showing the Eigen–Zundel–Eigen-type mechanism. In addition to reproducing the short-time rattling of the excess proton between the two oxygens of Zundel complexes, a picosecond-scale lifetime was also found. These longer-lived H3O+ ions are caused by the rapid conversion of the local solvation structure around the transferring proton from a Zundel-like form to an Eigen-like form following the transfer, effectively severing the path along which the proton can rattle. The migration of H+ over long times (>100 ps) deviates from the conventional short-time multiexponentially decaying lifetime autocorrelation model and follows the t–3/2 power-law behavior. The potential function employed here matches many of the features of proton transport observed in ab initio molecular dynamics simulations as well as the highly developed empirical valence bond models, yet is computationally very efficient, enabling longer time and larger systems to be studied.

 Radiative transfer studies of Type Ia supernovae (SNe Ia) hold the promise of constraining both the density profile of the SN ejecta and its stratification by element abundance which, in turn, may discriminate between different explosion mechanisms and progenitor classes. Here we analyse the Type Ia SN 2010jn (PTF10ygu) in detail, presenting and evaluating near-ultraviolet (near-UV) spectra from the Hubble Space Telescope and ground-based optical spectra and light curves. SN 2010jn was discovered by the Palomar Transient Factory (PTF) 15 d before maximum light, allowing us to secure a time series of four near-UV spectra at epochs from -10.5 to +4.8 d relative to B-band maximum. The photospheric near-UV spectra are excellent diagnostics of the iron-group abundances in the outer layers of the ejecta, particularly those at very early times. Using the method of `Abundance Tomography' we derive iron-group abundances in SN 2010jn with a precision better than in any previously studied SN Ia. Optimum fits to the data can be obtained if burned material is present even at high velocities, including significant mass fractions of iron-group elements. This is consistent with the slow decline rate (or high `stretch') of the light curve of SN 2010jn, and consistent with the results of delayed-detonation models. Early-phase UV spectra and detailed time-dependent series of further SNe Ia offer a promising probe of the nature of the SN Ia mechanism.

Molecular dynamics simulations were conducted to determine the response of a vitreous silica surface in contact with water to radiation damage. The defects caused by radiation damage create channels that promote high H⁺ mobility and result in significantly higher concentration and deeper penetration of H⁺ in the silica subsurface. These subsurface H⁺ hop between acidic sites such as SiOH₂⁺ and Si–(OH)–Si until subsequent radiation ruptures siloxane bridges and forms subsurface non-bridging oxygens (NBOs); existing excess H⁺ readily bonds to these NBO sites to form SiOH. The high temperature caused by irradiation also promotes the diffusion of molecular H₂O into the subsurface, and although H₂O does not penetrate as far as H⁺, it readily reacts with ruptured bridges to form 2SiOH. These SiOH sites are thermally stable and inhibit the reformation of bridges that would otherwise occur in the absence of water. In addition to this reduction of self-healing, the presence of water during the self-irradiation of silica may cause an increase in the glass’s proton conductivity.

In supernova (SN) spectroscopy relatively little attention has been given to the properties of optically thick spectral lines in epochs following the photosphere's recession. Most treatments and analyses of post-photospheric optical spectra of SNe assume that forbidden-line emission comprises most if not all spectral features. However, evidence exists that suggests that some spectra exhibit line profiles formed via optically thick resonance-scattering even months or years after the SN explosion. To explore this possibility, we present a geometrical approach to SN spectrum formation based on the "Elementary Supernova" model, wherein we investigate the characteristics of resonance-scattering in optically thick lines while replacing the photosphere with a transparent central core emitting non-blackbody continuum radiation, akin to the optical continuum provided by decaying 56Co formed during the explosion. We develop the mathematical framework necessary for solving the radiative transfer equation under these conditions and calculate spectra for both isolated and blended lines. Our comparisons with analogous results from the Elementary Supernova code SYNOW reveal several marked differences in line formation. Most notably, resonance lines in these conditions form P Cygni-like profiles, but the emission peaks and absorption troughs shift redward and blueward, respectively, from the line's rest wavelength by a significant amount, despite the spherically symmetric distribution of the line optical depth in the ejecta. These properties and others that we find in this work could lead to misidentification of lines or misattribution of properties of line-forming material at post-photospheric times in SN optical spectra.

ABSTRACT: We report an improved measurement of the neutrino mixing angle $\theta_{13}$ from the Daya Bay Reactor Neutrino Experiment. We exclude a zero value for $\sin^22\theta_{13}$ with a significance of 7.7 standard deviations. Electron antineutrinos from six reactors of 2.9 GW$_{\rm th}$ were detected in six antineutrino detectors deployed in two near (flux-weighted baselines of 470 m and 576 m) and one far (1648 m) underground experimental halls. Using 139 days of data, 28909 (205308) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to the expected number of antineutrinos assuming no oscillations at the far hall is $0.944\pm 0.007({\rm stat.}) \pm 0.003({\rm syst.})$. An analysis of the relative rates in six detectors finds $\sin^22\theta_{13}=0.089\pm 0.010({\rm stat.})\pm0.005({\rm syst.})$ in a three-neutrino framework.

Full Author List:

F. P. An, Q. An, J. Z. Bai, A. B. Balantekin, H. R. Band, W. Beriguete, M. Bishai, S. Blyth, R. L. Brown, G. F. Cao, J. Cao, R. Carr, W. T. Chan, J. F. Chang, Y. Chang, C. Chasman, H. S. Chen, H. Y. Chen, S. J. Chen, S. M. Chen, X. C. Chen, X. H. Chen, X. S. Chen, Y. Chen, Y. X. Chen, J. J. Cherwinka, M. C. Chu, J. P. Cummings, Z. Y. Deng, Y. Y. Ding, M. V. Diwan, E. Draeger, X. F. Du, D. Dwyer, W. R. Edwards, S. R. Ely, S. D. Fang, J. Y. Fu, Z. W. Fu, L. Q. Ge, R. L. Gill, M. Gonchar, G. H. Gong, H. Gong, Y. A. Gornushkin, W. Q. Gu, M. Y. Guan, X. H. Guo, R. W. Hackenburg, R. L. Hahn, S. Hans, H. F. Hao, M. He, Q. He, K. M. Heeger, Y. K. Heng, P. Hinrichs, Y. K. Hor, Y. B. Hsiung, B. Z. Hu, T. Hu, H. X. Huang, H. Z. Huang, X. T. Huang, P. Huber, V. Issakov, Z. Isvan, D. E. Jaffe, S. Jetter, X. L. Ji, X. P. Ji, H. J. Jiang, J. B. Jiao, R. A. Johnson, L. Kang, S. H. Kettell, M. Kramer, K. K. Kwan, M. W. Kwok, T. Kwok, C. Y. Lai, W. C. Lai, W. H. Lai, K. Lau, L. Lebanowski, J. Lee, R. T. Lei, R. Leitner, J. K. C. Leung, K. Y. Leung, C. A. Lewis, F. Li, G. S. Li, Q. J. Li, W. D. Li, X. B. Li, X. N. Li, X. Q. Li, Y. Li, Z. B. Li, H. Liang, C. J. Lin, G. L. Lin, S. K. Lin, Y. C. Lin, J. J. Ling, J. M. Link, L. Littenberg, B. R. Littlejohn, D. W. Liu, J. C. Liu, J. L. Liu, Y. B. Liu, C. Lu, H. Q. Lu, A. Luk, K. B. Luk, Q. M. Ma, X. B. Ma, X. Y. Ma, Y. Q. Ma, K. T. McDonald, M. C. McFarlane, R. D. McKeown, Y. Meng, D. Mohapatra, Y. Nakajima, J. Napolitano, D. Naumov, I. Nemchenok, H. Y. Ngai, W. K. Ngai, Y. B. Nie, Z. Ning, J. P. Ochoa-Ricoux, A. Olshevski, S. Patton, V. Pec, J. C. Peng, L. E. Piilonen, L. Pinsky, C. S. J. Pun, F. Z. Qi, M. Qi, X. Qian, N. Raper, J. Ren, R. Rosero, B. Roskovec, X. C. Ruan, B. B. Shao, K. Shih, H. Steiner, G. X. Sun, J. L. Sun, N. Tagg, Y. H. Tam, H. K. Tanaka, X. Tang, H. Themann, Y. Torun, S. Trentalange, O. Tsai, K. V. Tsang, R. H. M. Tsang, C. E. Tull, Y. C. Tung, B. Viren, V. Vorobel, C. H. Wang, L. S. Wang, L. Y. Wang, L. Z. Wang, M. Wang, N. Y. Wang, R. G. Wang, W. Wang, X. Wang, Y. F. Wang, Z. Wang, Z. M. Wang, D. M. Webber, H. Y. Wei, Y. D. Wei, L. J. Wen, K. Whisnant, C. G. White, L. Whitehead, Y. Williamson, T. Wise, H. L. H. Wong, E. T. Worcester, F. F. Wu, Q. Wu, J. B. Xi, D. M. Xia, Z. Z. Xing, J. Xu, J. L. Xu, Y. Xu, T. Xue, C. G. Yang, L. Yang, M. Ye, M. Yeh, Y. S. Yeh, B. L. Young, Z. Y. Yu, L. Zhan, C. Zhang, F. H. Zhang, J. W. Zhang, Q. M. Zhang, S. H. Zhang, Y. C. Zhang, Y. H. Zhang, Y. X. Zhang, Z. J. Zhang, Z. P. Zhang, Z. Y. Zhang, J. Zhao, Q. W. Zhao, Y. B. Zhao, L. Zheng, W. L. Zhong, L. Zhou, Z. Y. Zhou, H. L. Zhuang, J. H. Zou

The nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s^–1) provides a unique opportunity to study the early evolution of a "normal" SN Ia, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s^–1. This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I λ7774 absorption features detected within 5 days post-explosion indicates the presence of O I with expansion velocities from 11,500 to 21,000 km s^–1. The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta.

The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for the neutrino mixing angle θ₁₃ with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GW_th reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With 55 days of data, 10416 (80376) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is  R=0.940 ±0.011( stat) ± 0.004( syst). A rate-only analysis finds sin² 2 θ₁₃ - 0.092 ± 0.016( stat}) ± 0.005(syst) in a three-neutrino framework.

Full Author list: F. P. An, J. Z. Bai, A. B. Balantekin, H. R. Band, D. Beavis, W. Beriguete, M. Bishai, S. Blyth, R. L. Brown, G. F. Cao, J. Cao, R. Carr, W. T. Chan, J. F. Chang, Y. Chang, C. Chasman, H. S. Chen, H. Y. Chen, S. J. Chen, S. M. Chen, X. C. Chen, X. H. Chen, X. S. Chen, Y. Chen, Y. X. Chen, J. J. Cherwinka, M. C. Chu, J. P. Cummings, Z. Y. Deng, Y. Y. Ding, M. V. Diwan, L. Dong, E. Draeger, X. F. Du, D. A. Dwyer, W. R. Edwards, S. R. Ely, S. D. Fang, J. Y. Fu, Z. W. Fu, L. Q. Ge, V. Ghazikhanian, R. L. Gill, J. Goett, M. Gonchar, G. H. Gong, H. Gong, Y. A. Gornushkin, L. S. Greenler, W. Q. Gu, M. Y. Guan, X. H. Guo, R. W. Hackenburg, R. L. Hahn, S. Hans, M. He, Q. He, W. S. He, K. M. Heeger, Y. K. Heng, P. Hinrichs, T. H. Ho, Y. K. Hor, Y. B. Hsiung, B. Z. Hu, T. Hu, T. Hu, H. X. Huang, H. Z. Huang, P. W. Huang, X. Huang, X. T. Huang, P. Huber, Z. Isvan, D. E. Jaffe, S. Jetter, X. L. Ji, X. P. Ji, H. J. Jiang, W. Q. Jiang, J. B. Jiao, R. A. Johnson, L. Kang, S. H. Kettell, M. Kramer, K. K. Kwan, M. W. Kwok, T. Kwok, C. Y. Lai, W. C. Lai, W. H. Lai, K. Lau, L. Lebanowski, J. Lee, M. K. P. Lee, R. Leitner, J. K. C. Leung, K. Y. Leung, C. A. Lewis, B. Li, F. Li, G. S. Li, J. Li, Q. J. Li, S. F. Li, W. D. Li, X. B. Li, X. N. Li, X. Q. Li, Y. Li, Z. B. Li, H. Liang, J. Liang, C. J. Lin, G. L. Lin, S. K. Lin, S. X. Lin, Y. C. Lin, J. J. Ling, J. M. Link, L. Littenberg, B. R. Littlejohn, B. J. Liu, C. Liu, D. W. Liu, H. Liu, J. C. Liu, J. L. Liu, S. Liu, X. Liu, Y. B. Liu, C. Lu, H. Q. Lu, A. Luk, K. B. Luk, T. Luo, X. L. Luo, L. H. Ma, Q. M. Ma, X. B. Ma, X. Y. Ma, Y. Q. Ma, B. Mayes, K. T. McDonald, M. C. McFarlane, R. D. McKeown, Y. Meng, D. Mohapatra, J. E. Morgan, Y. Nakajima, J. Napolitano, D. Naumov, I. Nemchenok, C. Newsom, H. Y. Ngai, W. K. Ngai, Y. B. Nie, Z. Ning, J. P. Ochoa-Ricoux, A. Olshevski, A. Pagac, S. Patton, C. Pearson, V. Pec, J. C. Peng, L. E. Piilonen, L. Pinsky, C. S. J. Pun, F. Z. Qi, M. Qi, X. Qian, N. Raper, R. Rosero, B. Roskovec, X. C. Ruan, B. Seilhan, B. B. Shao, K. Shih, H. Steiner, P. Stoler, G. X. Sun, J. L. Sun, Y. H. Tam, H. K. Tanaka, X. Tang, H. Themann, Y. Torun, S. Trentalange, O. Tsai, K. V. Tsang, R. H. M. Tsang, C. Tull, B. Viren, S. Virostek, V. Vorobel, C. H. Wang, L. S. Wang, L. Y. Wang, L. Z. Wang, M. Wang, N. Y. Wang, R. G. Wang, T. Wang, W. Wang, X. Wang, X. Wang, Y. F. Wang, Z.Wang, Z.Wang, Z. M.Wang, D. M.Webber, Y. D.Wei, L. J.Wen, D. L.Wenman, K. Whisnant, C. G. White, L. Whitehead, C. A. Whitten Jr., J. Wilhelmi, T. Wise, H. C. Wong, H. L. H. Wong, J. Wong, E. T. Worcester, F. F. Wu, Q. Wu, D. M. Xia, S. T. Xiang, Q. Xiao, Z. Z. Xing, G. Xu, J. Xu, J. Xu, J. L. Xu, W. Xu, Y. Xu, T. Xue, C. G. Yang, L. Yang, M. Ye, M. Yeh, Y. S. Yeh, K. Yip, B. L. Young, Z. Y. Yu, L. Zhan, C. Zhang, F. H. Zhang, J. W. Zhang, Q. M. Zhang, K. Zhang, Q. X. Zhang, S. H. Zhang, Y. C. Zhang, Y. H. Zhang, Y. X. Zhang, Z. J. Zhang, Z. P. Zhang, Z. Y. Zhang, J. Zhao, Q. W. Zhao, Y. B. Zhao, L. Zheng, W. L. Zhong, L. Zhou, Z. Y. Zhou, H. L. Zhuang, J. H. Zou

We present photometry and spectroscopy of the peculiar Type II supernova (SN) SN 2010jp, also named PTF10aaxi. The light curve exhibits a linear decline with a relatively low peak absolute magnitude of only −15.9 (unfiltered), and a low radioactive decay luminosity at late times, which suggests a low synthesized nickel mass of M (⁵⁶ Ni) ≲ 0.003  M_⊙. Spectra of SN 2010jp display an unprecedented triple-peaked Hα line profile, showing (1) a narrow (full width at half-maximum >rsim800 km s⁻¹) central component that suggests shock interaction with dense circumstellar material (CSM); (2) high-velocity blue and red emission features centred at −12 600 and +15 400 km s⁻¹, respectively; and (3) very broad wings extending from −22 000 to +25 000 km s⁻¹. These features persist over multiple epochs during the ∼100 d after explosion. We propose that this line profile indicates a bipolar jet-driven explosion, with the central component produced by normal SN ejecta and CSM interaction at mid and low latitudes, while the high-velocity bumps and broad-line wings arise in a non-relativistic bipolar jet. Two variations of the jet interpretation seem plausible: (1) a fast jet mixes ⁵⁶Ni to high velocities in polar zones of the H-rich envelope; or (2) the reverse shock in the jet produces blue and red bumps in Balmer lines when a jet interacts with dense CSM. Jet-driven Type II SNe are predicted for collapsars resulting from a wide range of initial masses above 25 M_⊙, especially at subsolar metallicity. This seems consistent with the SN host environment, which is either an extremely low-luminosity dwarf galaxy or the very remote parts of an interacting pair of star-forming galaxies. It also seems consistent with the apparently low ⁵⁶Ni mass that may accompany black hole formation. We speculate that the jet survives to produce observable signatures because the star’s H envelope was very low mass, having been mostly stripped away by the previous eruptive mass-loss indicated by the Type IIn features in the spectrum. http://dx.doi.org/10.1111/j.1365-2966.2011.20104.x

While a white dwarf (WD) is, from a theoretical perspective, the most plausible primary star of a Type Ia supernova (SN Ia), many other candidates have not been formally ruled out. Shock energy deposited in the envelope of any exploding primary contributes to the early SN brightness and, since this radiation energy is degraded by expansion after the explosion, the diffusive luminosity depends on the initial primary radius. We present a new non-detection limit of the nearby SN Ia 2011fe, obtained at a time that appears to be just 4 hr after explosion, allowing us to directly constrain the initial primary radius (R_p ). Coupled with the non-detection of a quiescent X-ray counterpart and the inferred synthesized ⁵⁶Ni mass, we show that R_p 0.02 R _☉ (a factor of five smaller than previously inferred), that the average density of the primary must be ρ _p > 10⁴ g cm^–3, and that the effective temperature must be less than a few × 10⁵ K. This rules out hydrogen-burning main-sequence stars and giants. Constructing the helium-burning and carbon-burning main sequences, we find that such objects are also excluded. By process of elimination, we find that only degeneracy-supported compact objects—WDs and neutron stars—are viable as the primary star of SN 2011fe. With few caveats, we also restrict the companion (secondary) star radius to R _c  0.1 R _☉, excluding Roche-lobe overflowing red giant and main-sequence companions to high significance.

http://dx.doi.org/10.1088/2041-8205/744/2/L17

We present convincing evidence of unburned carbon at photospheric velocities in new observations of five Type Ia supernovae (SNe Ia) obtained by the Nearby Supernova Factory. These SNe are identified by examining 346 spectra from 124 SNe obtained before +2.5 days relative to maximum. Detections are based on the presence of relatively strong C II λ6580 absorption "notches" in multiple spectra of each SN, aided by automated fitting with the SYNAPPS code. Four of the five SNe in question are otherwise spectroscopically unremarkable, with ions and ejection velocities typical of SNe Ia, but spectra of the fifth exhibit high-velocity (v > 20, 000 km s^–1) Si II and Ca II features. On the other hand, the light curve properties are preferentially grouped, strongly suggesting a connection between carbon-positivity and broadband light curve/color behavior: three of the five have relatively narrow light curves but also blue colors and a fourth may be a dust-reddened member of this family. Accounting for signal to noise and phase, we estimate that 22⁺¹⁰ _{– 6}% of SNe Ia exhibit spectroscopic C II signatures as late as –5 days with respect to maximum. We place these new objects in the context of previously recognized carbon-positive SNe Ia and consider reasonable scenarios seeking to explain a physical connection between light curve properties and the presence of photospheric carbon. We also examine the detailed evolution of the detected carbon signatures and the surrounding wavelength regions to shed light on the distribution of carbon in the ejecta. Our ability to reconstruct the C II λ6580 feature in detail under the assumption of purely spherical symmetry casts doubt on a "carbon blobs" hypothesis, but does not rule out all asymmetric models. A low volume filling factor for carbon, combined with line-of-sight effects, seems unlikely to explain the scarcity of detected carbon in SNe Ia by itself. http://dx.doi.org/10.1088/0004-637X/743/1/27

Type Ia supernovae are thought to result from a thermonuclear explosion of an accreting white dwarf in a binary system^{1, 2}, but little is known of the precise nature of the companion star and the physical properties of the progenitor system. There are two classes of models^{1, 3}: double-degenerate (involving two white dwarfs in a close binary system^{2, 4}) and single-degenerate models^{5, 6}. In the latter, the primary white dwarf accretes material from a secondary companion until conditions are such that carbon ignites, at a mass of 1.38 times the mass of the Sun. The type Ia supernova SN 2011fe was recently detected in a nearby galaxy⁷. Here we report an analysis of archival images of the location of SN 2011fe. The luminosity of the progenitor system (especially the companion star) is 10–100 times fainter than previous limits on other type Ia supernova progenitor systems^{8, 9, 10}, allowing us to rule out luminous red giants and almost all helium stars as the mass-donating companion to the exploding white dwarf.

Type Ia supernovae have been used empirically as `standard candles' to demonstrate the acceleration of the expansion of the Universe even though fundamental details, such as the nature of their progenitor systems and how the stars explode, remain a mystery. There is consensus that a white dwarf star explodes after accreting matter in a binary system, but the secondary body could be anything from a main-sequence star to a red giant, or even another white dwarf. This uncertainty stems from the fact that no recent type Ia supernova has been discovered close enough to Earth to detect the stars before explosion. Here we report early observations of supernova SN 2011fe in the galaxy M101 at a distance from Earth of 6.4 megaparsecs. We find that the exploding star was probably a carbon-oxygen white dwarf, and from the lack of an early shock we conclude that the companion was probably a main-sequence star. Early spectroscopy shows high-velocity oxygen that slows rapidly, on a timescale of hours, and extensive mixing of newly synthesized intermediate-mass elements in the outermost layers of the supernova. A companion paper uses pre-explosion images to rule out luminous red giants and most helium stars as companions to the progenitor. http://dx.doi.org/10.1038/nature10644

On 2011 May 31 UT a supernova (SN) exploded in the nearby galaxy M51 (the Whirlpool Galaxy). We discovered this event using small telescopes equipped with CCD cameras and also detected it with the Palomar Transient Factory survey, rapidly confirming it to be a Type II SN. Here, we present multi-color ultraviolet through infrared photometry which is used to calculate the bolometric luminosity and a series of spectra. Our early-time observations indicate that SN 2011dh resulted from the explosion of a relatively compact progenitor star. Rapid shock-breakout cooling leads to relatively low temperatures in early-time spectra, compared to explosions of red supergiant stars, as well as a rapid early light curve decline. Optical spectra of SN 2011dh are dominated by H lines out to day 10 after explosion, after which He i lines develop. This SN is likely a member of the cIIb (compact IIb) class, with progenitor radius larger than that of SN 2008ax and smaller than the eIIb (extended IIb) SN 1993J progenitor. Our data imply that the object identified in pre-explosion Hubble Space Telescope images at the SN location is possibly a companion to the progenitor or a blended source, and not the progenitor star itself, as its radius (~1013 cm) would be highly inconsistent with constraints from our post-explosion spectra. http://dx.doi.org/10.1088/2041-8205/742/2/L18

A variable charge potential is developed that is suitable for the simulations of energy conversion materials FeF₂ and FeF₃. Molecular dynamics simulations using this potential show that the calculated structural and elastic properties of both FeF₂ and FeF₃ are in good agreement with experimental data. Such a transferability of this potential rests in the fact that the difference in the bond characteristic between FeF₂ and FeF₃ is properly accounted for by the variable charge approach. The calculated equilibrium charges are also in excellent agreement with first-principles Bader charges. Surface energies obtained by the variable charge method are closer to the first-principles data than are fixed charge models, indicating the importance of variable charge method for the simulations of the surface. A significant decrease in atomic charges is observed only for the outermost one or two layers, which is also observed in the first-principles calculations.

We present the discovery and follow-up observations of a broad-line Type Ic supernova (SN), PTF 10bzf (SN 2010ah), detected by the Palomar Transient Factory (PTF) on 2010 February 23. The SN distance is 218 Mpc, greater than GRB 980425/SN 1998bw and GRB 060218/SN 2006aj, but smaller than the other SNe firmly associated with gamma-ray bursts (GRBs). We conducted a multi-wavelength follow-up campaign with Palomar 48 inch, Palomar 60 inch, Gemini-N, Keck, Wise, Swift, the Allen Telescope Array, Combined Array for Research in Millimeter-wave Astronomy, Westerbork Synthesis Radio Telescope, and Expanded Very Large Array. Here we compare the properties of PTF 10bzf with those of SN 1998bw and other broad-line SNe. The optical luminosity and spectral properties of PTF 10bzf suggest that this SN is intermediate, in kinetic energy and amount of ⁵⁶Ni, between non-GRB-associated SNe like 2002ap or 1997ef, and GRB-associated SNe like 1998bw. No X-ray or radio counterpart to PTF 10bzf was detected. X-ray upper limits allow us to exclude the presence of an underlying X-ray afterglow as luminous as that of other SN-associated GRBs such as GRB 030329 or GRB 031203. Early-time radio upper limits do not show evidence for mildly relativistic ejecta. Late-time radio upper limits rule out the presence of an underlying off-axis GRB, with energy and wind density similar to the SN-associated GRB 030329 and GRB 031203. Finally, by performing a search for a GRB in the time window and at the position of PTF 10bzf, we find that no GRB in the interplanetary network catalog could be associated with this SN. http://dx.doi.org/10.1088/0004-637X/741/2/76

Stellar rotation periods measured from single-age populations are critical for investigating how stellar angular momentum content evolves over time, how that evolution depends on mass, and how rotation influences the stellar dynamo and the magnetically heated chromosphere and corona. We report rotation periods for 40 late-K to mid-M star members of the nearby, rich, intermediate-age (~600 Myr) open cluster Praesepe. These rotation periods were derived from ~200 observations taken by the Palomar Transient Factory of four cluster fields from 2010 February to May. Our measurements indicate that Praesepe's mass-period relation transitions from a well-defined singular relation to a more scattered distribution of both fast and slow rotators at ~0.6 M _sun. The location of this transition is broadly consistent with expectations based on observations of younger clusters and the assumption that stellar spin-down is the dominant mechanism influencing angular momentum evolution at 600 Myr. However, a comparison to data recently published for the Hyades, assumed to be coeval to Praesepe, indicates that the divergence from a singular mass-period relation occurs at different characteristic masses, strengthening the finding that Praesepe is the younger of the two clusters. We also use previously published relations describing the evolution of rotation periods as a function of color and mass to evolve the sample of Praesepe periods in time. Comparing the resulting predictions to periods measured in M35 and NGC 2516 (~150 Myr) and for kinematically selected young and old field star populations suggests that stellar spin-down may progress more slowly than described by these relations. http://dx.doi.org/10.1088/0004-637X/740/2/110

We present ground-based and Hubble Space Telescope optical and infrared observations of Swift XRF 100316D/SN 2010bh. It is seen that the optical light curves of SN 2010bh evolve at a faster rate than the archetype gamma-ray burst supernova (GRB-SN) 1998bw, but at a similar rate to SN 2006aj, an SN that was spectroscopically linked with XRF 060218, and at a similar rate to the non-GRB associated Type Ic SN 1994I. We estimate the rest-frame extinction of this event from our optical data to be E(B - V) = 0.18 ± 0.08 mag. We find the V-band absolute magnitude of SN 2010bh to be M_V = -18.62 ± 0.08, which is the faintest peak V-band magnitude observed to date for spectroscopically confirmed GRB-SNe. When we investigate the origin of the flux at t - t ₀ = 0.598 days, it is shown that the light is not synchrotron in origin, but is likely coming from the SN shock breakout. We then use our optical and infrared data to create a quasi-bolometric light curve of SN 2010bh, which we model with a simple analytical formula. The results of our modeling imply that SN 2010bh synthesized a nickel mass of M _Ni ≈ 0.1 M _sun, ejected M _ej ≈ 2.2 M _sun, and has an explosion energy of E _k ≈ 1.4 × 10⁵²erg. Thus, while SN 2010bh is an energetic explosion, the amount of nickel created during the explosion is much less than that of SN 1998bw and only marginally more than SN 1994I. Finally, for a sample of 22 GRB-SNe we check for a correlation between the stretch factors and luminosity factors in the R band and conclude that no statistically significant correlation exists.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 11709. http://dx.doi.org/10.1088/0004-637X/740/1/41

We present extensive photometric and spectroscopic observations of PTF1 J071912.13+485834.0, an outbursting AM CVn system discovered by the Palomar Transient Factory (PTF). AM CVn systems are stellar binaries with some of the smallest separations known and orbital periods ranging from 5 to 65 minutes. They are believed to be composed of a white dwarf accretor and a (semi-)degenerate He-rich donor and are considered to be the helium equivalents of cataclysmic variables (CVs). We have spectroscopically and photometrically identified an orbital period of 26.77 ± 0.02 minutes for PTF1 J071912.13+485834.0 and found a super-outburst recurrence time of greater than 65 days along with the presence of "normal" outbursts—rarely seen in AM CVn systems but well known in super-outbursting CVs. We present a long-term light curve over two super-cycles as well as high-cadence photometry of both outburst and quiescent stages, both of which show clear variability. We also compare both the outburst and quiescent spectra of PTF1 J071912.13+485834.0 to other known AM CVn systems, and use the quiescent phase-resolved spectroscopy to determine the origin of the photometric variability. Finally, we draw parallels between the different subclasses of SU UMa-type CVs and outbursting AM CVn systems. We conclude by predicting that the PTF may more than double the number of outbursting AM CVn systems known, which would greatly increase our understanding of AM CVn systems. http://dx.doi.org/10.1088/0004-637X/739/2/68

We present optical and near-infrared photometry, as well as ground-based optical spectra and Hubble Space Telescope ultraviolet spectra, of the Type Ia supernova (SN) 2001ay. At maximum light the Si II and Mg II lines indicated expansion velocities of 14,000 km s^–1, while Si III and S II showed velocities of 9000 km s^–1. There is also evidence for some unburned carbon at 12,000 km s^–1. SN 2001ay exhibited a decline-rate parameter of Δm ₁₅(B) = 0.68 ± 0.05 mag; this and the B-band photometry at t +25 day past maximum make it the most slowly declining Type Ia SN yet discovered. Three of the four super-Chandrasekhar-mass candidates have decline rates almost as slow as this. After correction for Galactic and host-galaxy extinction, SN 2001ay had M_B = –19.19 and M_V = –19.17 mag at maximum light; thus, it was not overluminous in optical bands. In near-infrared bands it was overluminous only at the 2σ level at most. For a rise time of 18 days (explosion to bolometric maximum) the implied ⁵⁶Ni yield was (0.58 ± 0.15)/α M _☉, with α = L _max/E _Ni probably in the range 1.0-1.2. The ⁵⁶Ni yield is comparable to that of many Type Ia SNe. The "normal" ⁵⁶Ni yield and the typical peak optical brightness suggest that the very broad optical light curve is explained by the trapping of γ rays in the inner regions. http://dx.doi.org/10.1088/0004-6256/142/3/74