Propagations of massive graviton in the deformed Ho\v{r}ava-Lifshitz gravity

We study massive graviton propagations of scalar, vector, and tensor modes in the deformed Ho\v{r}ava-Lifshitz gravity by introducing Lorentz-violating mass term. It turns out that vector and tensor modes are massively propagating on the Minkowski spacetime background. However, adding the mass term does not cure a ghost instability in the Ho\v{r}ava scalar.Comment: 17 pages, version with projectability requirement, to appear in PR

ReaxFF Reactive Force Field for the Y-Doped BaZrO_3 Proton Conductor with Applications to Diffusion Rates for Multigranular Systems

Proton-conducting perovskites such as Y-doped BaZrO3 (BYZ) are promising candidates as electrolytes for a proton ceramic fuel cell (PCFC) that might permit much lower temperatures (from 400 to 600 °C). However, these materials lead to relatively poor total conductivity (∼10^−4 S/cm) because of extremely high grain boundary resistance. In order to provide the basis for improving these materials, we developed the ReaxFF reactive force field to enable molecular dynamics (MD) simulations of proton diffusion in the bulk phase and across grain boundaries of BYZ. This allows us to elucidate the atomistic structural details underlying the origin of this poor grain boundary conductivity and how it is related to the orientation of the grains. The parameters in ReaxFF were based entirely on the results of quantum mechanics (QM) calculations for systems related to BYZ. We apply here the ReaxFF to describe the proton diffusion in crystalline BYZ and across grain boundaries in BYZ. The results are in excellent agreement with experiment, validating the use of ReaxFF for studying the transport properties of these membranes. Having atomistic structures for the grain boundaries from simulations that explain the overall effect of the grain boundaries on diffusion opens the door to in silico optimization of these materials. That is, we can now use theory and simulation to examine the effect of alloying on both the interfacial structures and on the overall diffusion. As an example, these calculations suggest that the reduced diffusion of protons across the grain boundary results from the increased average distances between oxygen atoms in the interface, which necessarily leads to larger barriers for proton hopping. Assuming that this is the critical issue in grain boundary diffusion, the performance of BYZ for multigranular systems might be improved using additives that would tend to precipitate to the grain boundary and which would tend to pull the oxygens atoms together. Possibilities might be to use a small amount of larger trivalent ions, such as La or Lu or of tetravalent ions such as Hf or Th. Since ReaxFF can also be used to describe the chemical processes on the anode and cathode and the migration of ions across the electrode-membrane interface, ReaxFF opens the door to the possibility of atomistic first principles predictions on models of a complete fuel cell

Integrability of N=6 Chern-Simons Theory at Six Loops and Beyond

We study issues concerning perturbative integrability of N=6 Chern-Simons theory at planar and weak `t Hooft coupling regime. By Feynman diagrammatics, we derive so called maximal-ranged interactions in the quantum dilatation generator, originating from homogeneous and inhomogeneous diagrams. These diagrams require proper regularization of not only ultraviolet but also infrared divergences. We first consider standard operator mixing method. We show that homogeneous diagrams are obtainable by recursive method to all orders. The method, however, is not easily extendable to inhomogeneous diagrams. We thus consider two-point function method and study both operator contents and spectrum of the quantum dilatation generator up to six loop orders. We show that, of two possible classes of operators, only one linear combination actually contributes. Curiously, this is exactly the same combination as in N=4 super Yang-Mills theory. We then study spectrum of anomalous dimension up to six loops. We find that the spectrum agrees perfectly with the prediction based on quantum integrability. In evaluating the six loop diagrams, we utilized remarkable integer-relation algorithm (PSLQ) developed by Ferguson, Baily and Arno.Comment: 1+39 pages, 12 figures, references added, minor structural changes, typos correcte

The Effect of Periodic Silane Burst on the Properties of GaN on Si (111) Substrates

The periodic silane burst technique was employed during metalorganic chemical vapor deposition of epitaxial GaN on AlN buffer layers grown on Si (111). Periodic silicon delta doping during growth of both the AlN and GaN layers led to growth of GaN films with decreased tensile stresses and decreased threading dislocation densities, as well as films with improved quality as indicated by x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The possible mechanism of the reduction of tensile stress and the dislocation density is discussed in the paper.Singapore-MIT Alliance (SMA

On the Effect of Quantum Interaction Distance on Quantum Addition Circuits

We investigate the theoretical limits of the effect of the quantum interaction distance on the speed of exact quantum addition circuits. For this study, we exploit graph embedding for quantum circuit analysis. We study a logical mapping of qubits and gates of any $\Omega(\log n)$-depth quantum adder circuit for two $n$-qubit registers onto a practical architecture, which limits interaction distance to the nearest neighbors only and supports only one- and two-qubit logical gates. Unfortunately, on the chosen $k$-dimensional practical architecture, we prove that the depth lower bound of any exact quantum addition circuits is no longer $\Omega(\log {n})$, but $\Omega(\sqrt[k]{n})$. This result, the first application of graph embedding to quantum circuits and devices, provides a new tool for compiler development, emphasizes the impact of quantum computer architecture on performance, and acts as a cautionary note when evaluating the time performance of quantum algorithms.Comment: accepted for ACM Journal on Emerging Technologies in Computing System

Decoherence Driven Quantum Transport

We propose a new mechanism to generate a dc current of particles at zero bias based on a noble interplay between coherence and decoherence. We show that a dc current arises if the transport process in one direction is maintained coherent while the process in the opposite direction is incoherent. We provide possible implementations of the idea using an atomic Michelson and an atomic Aharonov-Bohm interferometer.Comment: 4 pages, 3 figure

The Impact of Duty Cycle Workflow on Sign-Out Practices: A Qualitative Study of an Internal Medicine Residency Program in Maryland, USA

OBJECTIVES: Although JCAHO requires a standardised approach to handoffs, and while many standardised protocols have been tested, sign-out practices continue to vary. We believe this is due to the variability in workflow during inpatient duty cycle. We investigate the impact of such workflows on intern sign-out practices. DESIGN: We employed a prospective, grounded theory mixed-method design. SETTING: The study was conducted at a residency programme in the mid-Atlantic USA. Two observers randomly evaluated three types of daily sign-outs for 1 week every 3 months from September 2013 to March 2014. The compliance of each observed behaviour to JCAHO\u27s Handoff Communication Checklist was recorded. PARTICIPANTS: Thirty one interns conducting 134 patient sign-outs were observed randomly among the 52 in the programme. RESULTS: In the 06:00 to 07:00 sign-back, the night-cover focused on providing information on overnight events to the day interns. In the 11:00 to 12:00 sign-out, the night-cover focused on transferring task accountability to a day-cover intern before departure. In the 20:00 to 21:00 sign-out, the day interns focused on transferring responsibility of their patients to a night-cover. CONCLUSION: Different sign-out periods had different emphases regarding information exchange, personal responsibility and task accountability. Sign-outs are context-specific, implying that across-the-board standardised sign-out protocols are likely to have limited efficacy and compliance. Standardisation may need to be relative to the specific type and purpose of each sign-out to be supported by interns

Evaluation of House Staff Candidates for Program Fit: A Cohort-Based Controlled Study

Background: Medical school academic achievements do not necessarily predict house staff job performance. This study explores a selection mechanism that improves house staff-program fit that enhances the Accreditation Council for Graduate Medical Education Milestones performance ratings. Objective: Traditionally, house staff were selected primarily on medical school academic performance. To improve residency performance outcomes, the Program designed a theory-driven selection tool to assess house staff candidates on their personal values and goals fit with Program values and goals. It was hypothesized cohort performance ratings will improve because of the intervention. Methods: Prospective quasi-experimental cohort design with data from two house staff cohorts at a university-based categorical Internal Medicine Residency Program. The intervention cohort, comprising 45 house staff from 2016 to 2017, was selected using a Behaviorally Anchored Rating Scales (BARS) tool for program fit. The control cohort, comprising 44 house staff from the prior year, was selected using medical school academic achievement scores. House staff performance was evaluated using ACGME Milestones indicators. The mean scores for each category were compared between the intervention and control cohorts using Student\u27s t-tests with Bonferroni correction and Cohen\u27s d for effect size. Results: The cohorts were no different in academic performance scores at time of Program entry. The intervention cohort outperformed the control cohort on all 6 dimensions of Milestones by end-PGY1 and 3 of 6 dimensions by mid-PGY3. Conclusion: Selecting house staff based on compatibility with Residency Program values and objectives may yield higher job performance because trainees benefit more from a better fit with the training program

Structural analysis of metalorganic chemical vapor deposited AlN nucleation layers on Si (111)

AlN nucleation layers are being investigated for growth of GaN on Si. The microstructures of high-temperature AlN nucleation layers grown by MOCVD on Si (111) substrates with trimethylaluminium pre-treatments have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The AFM results show that with TMA pre-treatments, AlN grows in a pseudo-2-dimensional mode because the lateral growth rate of AlN is increased, and the wetting property of the AlN on silicon is improved. Also, no amorphous SiNx layer was observed at the interface with TMA pre-treatments and AlN films with good epitaxial crystalline quality were obtained. Transmission electron diffraction patterns revealed that the AlN and Si have the crystallographic orientation relationship AlN [0001]âSi[111] and AlN[11 2 0] âSi[110]. High resolution transmission electron microscopy indicates a 5:4 lattice matching relationship for AlN and Si along the Si [110] direction. Based on this observation, a lattice matching model is proposed.Singapore-MIT Alliance (SMA