Lowering of the Kinetic Energy in Interacting Quantum Systems

Interactions never lower the ground state kinetic energy of a quantum system. However, at nonzero temperature, where the system occupies a thermal distribution of states, interactions can reduce the kinetic energy below the noninteracting value. This can be demonstrated from a first order weak coupling expansion. Simulations (both variational and restricted path integral Monte Carlo) of the electron gas model and dense hydrogen confirm this and show that in contrast to the ground state case, at nonzero temperature the population of low momentum states can be increased relative to the free Fermi distribution. This effect is not seen in simulations of liquid He-3.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett., June, 200

SORDOR pulses: expansion of the Böhlen–Bodenhausen scheme for low-power broadband magnetic resonance

A novel type of efficient broadband pulse, called second-order phase dispersion by optimised rotation (SORDOR), has recently been introduced. In contrast to adiabatic excitation, SORDOR-90 pulses provide effective transverse 90∘ rotations throughout their bandwidth, with a quadratic offset dependence of the phase in the x,y plane. Together with phase-matched SORDOR-180 pulses, this enables the Böhlen–Bodenhausen broadband refocusing approach for linearly frequency-swept pulses to be extended to any type of 90$^∘$/180$^∘$ pulse–delay sequence. Example pulse shapes are characterised in theory and experiment, and an example application is given with a $^{19}$F-PROJECT experiment for measuring relaxation times with reduced distortions due to J-coupling evolution

Is the daily use of public transport facilities an enhanced epidemiological risk for diagnosing COVID-19 among healthcare workers with mild respiratory symptoms?

Introduction: Many people in Switzerland think that the daily use of the public transport facilities, during a pandemic peak wave, could be associated with an enhanced risk for Covid-19. Objectives: To investigate the association between the daily use of the public transport and acquisition of Covid-19 in Zurch during a peak wave of the pandemics. Methods: Retrospective cohort analysis of hospital-own databases at the Balgrist University Hospital in Zurich, between 1 October and 31 December 2020. We specifically interviewed our healthcare workers (HCW) about the use of public transport (with mandatory masking). Results: During the three most intensive months of the 2nd wave, we investigated 376 episodes of Covid-19-compatible respiratory symptoms and exposures among our HCW (median age 37 years), of which 94 (25%) revealed a positive PCR result for Covid-19. Overall, 225 HCW (225/376;60%) reportedly used the public transport (train, bus, tramway). In group comparison, the HCWs using the public transport system acquired no more Covid-19 than using a private transport (58/225 vs. 36/151;Pearson-chi2-test;p = 0.67). We added a logistic regression model with the outcome “Covid-19 infection” to adjust for the case-mix of different localizations or opportunities of potential contamination such as a documented exposure in the hospital, among the team members, in the family, or after a close contact to a PCR-confirmed case. In the multivariate results, using the public transport was irrelevant concerning the acquisition of Covid- 19 (odds ratio (OR) 0.98, 95%CI 0.59-1.62), in contrast, for example, to being exposed to a sick team member (OR 2.28, 95%CI 1.20-4.34). Conclusion: In Zurich, the daily use of public transport was not associated with an additional risk of being diagnosed with Covid-19 among the young population of HCWs, not even during the peak of a pandemic wave. Other factors are more relevant

Coulomb Interactions via Local Dynamics: A Molecular--Dynamics Algorithm

We derive and describe in detail a recently proposed method for obtaining Coulomb interactions as the potential of mean force between charges which are dynamically coupled to a local electromagnetic field. We focus on the Molecular Dynamics version of the method and show that it is intimately related to the Car--Parrinello approach, while being equivalent to solving Maxwell's equations with freely adjustable speed of light. Unphysical self--energies arise as a result of the lattice interpolation of charges, and are corrected by a subtraction scheme based on the exact lattice Green's function. The method can be straightforwardly parallelized using standard domain decomposition. Some preliminary benchmark results are presented.Comment: 8 figure

Statistical Mechanics of the Fluctuating Lattice Boltzmann Equation

We propose a new formulation of the fluctuating lattice Boltzmann equation that is consistent with both equilibrium statististical mechanics and fluctuating hydrodynamics. The formalism is based on a generalized lattice-gas model, with each velocity direction occupied by many particles. We show that the most probable state of this model corresponds to the usual equilibrium distribution of the lattice Boltzmann equation. Thermal fluctuations about this equilibrium are controlled by the mean number of particles at a lattice site. Stochastic collision rules are described by a Monte Carlo process satisfying detailed balance. This allows for a straightforward derivation of discrete Langevin equations for the fluctuating modes. It is shown that all non-conserved modes should be thermalized, as first pointed out by Adhikari et al.; any other choice violates the condition of detailed balance. A Chapman-Enskog analysis is used to derive the equations of fluctuating hydrodynamics on large length and time scales; the level of fluctuations is shown to be thermodynamically consistent with the equation of state of an isothermal, ideal gas. We believe this formalism will be useful in developing new algorithms for thermal and multiphase flows.Comment: Submitted to Physical Review E-11 pages Corrected Author(s) field on submittal for

A Comparison of the Technological Maturation of SmallSat Propulsion Systems from 2018 to 2020

The maturity in small spacecraft technology is indicated by the continued growth in the number of missions, mission complexity, and the expansion of smallsat subsystem capability. Identified development paths include the consideration of systems and components with flight heritage on larger spacecraft to meet the needs of smaller platforms, the conception of novel technologies specifically designed for small spacecraft, and the incremental improvements every 1-2 years in components where the underlying technology remains unchanged. Progress of overall smallsat technology development is captured in the most recent 2020 State-of-the-Art Small Spacecraft Technology (SoA) report, the objective of which is to assess and provide an overview on the current development status across all subsystem architectures. The SoA report contains a variety of surveys covering device performance, capabilities, and flight history, as presented in publicly available literature. The focus of these surveys is on devices or systems that can be commercially procured or appear on a path towards commercial availability. The work toward the 2020 edition of the report was managed by NASA’s Small Spacecraft Systems Virtual Institute (S3VI) and performed by several contractor staff. The S3VI is jointly funded by NASA’s Space Technology Mission Directorate and Science Mission Directorate. Technological advancement varies across subsystems, and smallsat propulsion technology has had a rapid increase in quantity and type in the last few years that is documented in the SoA report. The extensive efforts made by industry, academia, and government entities to develop and mature small spacecraft propulsive technologies suggest a range of devices with diverse capabilities will become more readily available in near future. While the report uses the NASA Technology Readiness Level scale to measure technical maturity, the “In-Space Propulsion” chapter implemented a novel classification system that recognized Progress towards Mission Infusion (PMI) as an early indicator of the efficacy of the manufacturers’ approach to system maturation and mission infusion. Readers of this paper are highly encouraged to refer to the “In-Space Propulsion” chapter for further information on the PMI classifications. A driving trend captured in the SoA report is that smallsat missions are becoming more complex in the anticipation of using smallsats to collect lunar and deep space science. Smallsat propulsive technology must mature operationally to meet the needs of the increasing smallsat mission complexity. This paper will expand upon the progression of technical maturation identified in the “In-Space Propulsion” chapter presented in the 2020 report and compare these developmental achievements to the “Propulsion” chapter in the 2018 SoA report. By making these comparisons, the reader will be able to measure the degree of advancement in smallsat propulsion technology that has been made in the last few years, understand the specific development approaches propulsion engineers encounter, and learn about the current trends in smallsat propulsion

Stationary Black Holes with Static and Counterrotating Horizons

We show that rotating dyonic black holes with static and counterrotating horizon exist in Einstein-Maxwell-dilaton theory when the dilaton coupling constant exceeds the Kaluza-Klein value. The black holes with static horizon bifurcate from the static black holes. Their mass decreases with increasing angular momentum, their horizons are prolate.Comment: 4 pages, 6 figure

Differentiation between Parkinson disease and other forms of Parkinsonism using support vector machine analysis of susceptibility-weighted imaging (SWI): initial results

Objectives: To diagnose Parkinson disease (PD) at the individual level using pattern recognition of brain susceptibility-weighted imaging (SWI). Methods: We analysed brain SWI in 36 consecutive patients with Parkinsonism suggestive of PD who had (1) SWI at 3T, (2) brain 123I-ioflupane SPECT and (3) extensive neurological testing including follow-up (16 PD, 67.4 ± 6.2years, 11 female; 20 OTHER, a heterogeneous group of atypical Parkinsonism syndromes 65.2 ± 12.5years, 6 female). Analysis included group-level comparison of SWI values and individual-level support vector machine (SVM) analysis. Results: At the group level, simple visual analysis yielded no differences between groups. However, the group-level analyses demonstrated increased SWI in the bilateral thalamus and left substantia nigra in PD patients versus other Parkinsonism. The inverse comparison yielded no supra-threshold clusters. At the individual level, SVM correctly classified PD patients with an accuracy above 86%. Conclusions: SVM pattern recognition of SWI data provides accurate discrimination of PD among patients with various forms of Parkinsonism at an individual level, despite the absence of visually detectable alterations. This pilot study warrants further confirmation in a larger cohort of PD patients and with different MR machines and MR parameters. Key Points: • Magnetic resonance imaging data offers new insights into Parkinson's disease • Visual susceptibility-weighted imaging (SWI) analysis could not discriminate idiopathic from atypical PD • However, support vector machine (SVM) analysis provided highly accurate detection of idiopathic PD • SVM analysis may contribute to the clinical diagnosis of individual PD patients • Such information can be readily obtained from routine MR dat

Using Information from Rendezvous Missions for Best-Case Appraisals of Impact Damage to Planet Earth Caused by Natural Objects

The Asteroid Threat Assessment Project (ATAP), a part of NASAs Planetary Defense Coordination Office (PDCO) has the responsibility to appraise the range of surface damage by potential asteroid impacts on land or water. If a threat is realized, the project will provide appraisals to officials empowered to make decisions about potential mitigation actions. This paper describes a scenario for assessment of surface damage when characterization of an asteroid had been accomplished by a rendezvous mission that would be conducted by the international planetary defense community. It is shown that the combination of data from ground and in-situ measurements on an asteroid provides knowledge that can be used to pin-point its impact location and predict the level of devastation it would cause. The hypothetical asteroid 2017 PDC with a size range of 160 to 290 m in diameter to be discussed at the PDC 2017 is used as an example. In order of importance for appraising potential damage, information required is: (1) where will the surface impact occur? (2) what is the mass, shape and size of the asteroid and what is its entry state (speed and entry angle) at the 100 km atmospheric pierce point? And (3) is the asteroid a monolith or a rubble pile? If it is a rubble pile, what is its structure and heterogeneity from the surface and throughout its interior? Item (1) is of first order importance to determine levels of devastation (loss of life and infrastructure damage) because it varies strongly on the impact location. Items (2) and (3) are used as inputs for ATAPs simulations to define the level of surface hazards: winds, overpressure, thermal exposure; all created by the deposition of energy during the objects atmospheric flight, andor cratering. Topics presented in this paper include: (i) the devastation predicted by 2017 PDCs impact on land based on initial observations using ATAPs risk assessment capability, (ii) how information corresponding to items (1) to (3) could be obtained from a rendezvous mission, and (iii) how information from a rendezvous mission could be used, along with that from ground observations and data from the literature to provide input for a new risk analysis capability that is emerging from ATAPs research. It is concluded that this approach would result in the creation of an appraisal of the threat from 2017 PDC with the least uncertainty possible, herein called the best-case

Variational Density Matrix Method for Warm Condensed Matter and Application to Dense Hydrogen

A new variational principle for optimizing thermal density matrices is introduced. As a first application, the variational many body density matrix is written as a determinant of one body density matrices, which are approximated by Gaussians with the mean, width and amplitude as variational parameters. The method is illustrated for the particle in an external field problem, the hydrogen molecule and dense hydrogen where the molecular, the dissociated and the plasma regime are described. Structural and thermodynamic properties (energy, equation of state and shock Hugoniot) are presented.Comment: 26 pages, 13 figures. submitted to Phys. Rev. E, October 199