Structural and electronic properties of new "122" pnictogen-free superconductor SrPd2Ge2 as compared with SrNi2Ge2 and SrNi2As2: first principles calculations

Very recently the new low-temperature (TC ~ 3K) superconductor (SC) SrPd2Ge2 has been reported. This compound is isostructural with curently intensively studied group of so-called "122" SC's (based on tetragonal AM2Pn2 phases, where A are Sr, Ba; M are d metals and Pn are pnictogens: As or P), but it is pnictogen-free. Here, by means of first-principle FLAPW-GGA calculations, we have studied the electronic structure of new SC SrPd2Ge2. The band structure, total and partial densities of states and Fermi surface topology for SrPd2Ge2 are evaluated and discussed in comparison with those of isostructural SrNi2Ge2 and SrNi2As2 phases.Comment: 9 pages, 3 figure

Low-temperature nonequilibrium transport in a Luttinger liquid

The temperature-dependent nonlinear conductance for transport of a Luttinger liquid through a barrier is calculated in the nonperturbative regime for $g=1/2-\epsilon$, where $g$ is the dimensionless interaction constant. To describe the low-energy behavior, we perform a leading-log summation of all diagrams contributing to the conductance which is valid for $|\epsilon| << 1$. With increasing external voltage, the asymptotic low-temperature behavior displays a turnover from the $T^{2/g-2}$ to a universal $T^2$ law.Comment: 13 pages RevTeX 3.0, accepted by Physical Review

Hamiltonian Description of Composite Fermions: Magnetoexciton Dispersions

A microscopic Hamiltonian theory of the FQHE, developed by Shankar and myself based on the fermionic Chern-Simons approach, has recently been quite successful in calculating gaps in Fractional Quantum Hall states, and in predicting approximate scaling relations between the gaps of different fractions. I now apply this formalism towards computing magnetoexciton dispersions (including spin-flip dispersions) in the $\nu=1/3$, 2/5, and 3/7 gapped fractions, and find approximate agreement with numerical results. I also analyse the evolution of these dispersions with increasing sample thickness, modelled by a potential soft at high momenta. New results are obtained for instabilities as a function of thickness for 2/5 and 3/7, and it is shown that the spin-polarized 2/5 state, in contrast to the spin-polarized 1/3 state, cannot be described as a simple quantum ferromagnet.Comment: 18 pages, 18 encapsulated ps figure

Hamiltonian theory of gaps, masses and polarization in quantum Hall states: full disclosure

I furnish details of the hamiltonian theory of the FQHE developed with Murthy for the infrared, which I subsequently extended to all distances and apply it to Jain fractions \nu = p/(2ps + 1). The explicit operator description in terms of the CF allows one to answer quantitative and qualitative issues, some of which cannot even be posed otherwise. I compute activation gaps for several potentials, exhibit their particle hole symmetry, the profiles of charge density in states with a quasiparticles or hole, (all in closed form) and compare to results from trial wavefunctions and exact diagonalization. The Hartree-Fock approximation is used since much of the nonperturbative physics is built in at tree level. I compare the gaps to experiment and comment on the rough equality of normalized masses near half and quarter filling. I compute the critical fields at which the Hall system will jump from one quantized value of polarization to another, and the polarization and relaxation rates for half filling as a function of temperature and propose a Korringa like law. After providing some plausibility arguments, I explore the possibility of describing several magnetic phenomena in dirty systems with an effective potential, by extracting a free parameter describing the potential from one data point and then using it to predict all the others from that sample. This works to the accuracy typical of this theory (10 -20 percent). I explain why the CF behaves like free particle in some magnetic experiments when it is not, what exactly the CF is made of, what one means by its dipole moment, and how the comparison of theory to experiment must be modified to fit the peculiarities of the quantized Hall problem

Optical manipulation of silicon microparticles in biological environments

Manipulation of micron-scale silicon particles has been investigated with optical tweezers implemented using a two-dimensional scanning trap driven with acousto-optic modulators. Spheres of latex, Poly(methyl methacrylate) (PMMA), silica, and silver-coated PMMA have been utilized to calibrate transverse trapping forces. The goal of this work is to non-invasively manipulate 10-20μm silicon-based devices in and around cells

Observation of Orbitally Excited B_s Mesons

We report the first observation of two narrow resonances consistent with states of orbitally excited (L=1) B_s mesons using 1 fb^{-1} of ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. We use two-body decays into K^- and B^+ mesons reconstructed as B^+ \to J/\psi K^+, J/\psi \to \mu^+ \mu^- or B^+ \to \bar{D}^0 \pi^+, \bar{D}^0 \to K^+ \pi^-. We deduce the masses of the two states to be m(B_{s1}) = 5829.4 +- 0.7 MeV/c^2 and m(B_{s2}^*) = 5839.7 +- 0.7 MeV/c^2.Comment: Version accepted and published by Phys. Rev. Let

Origin of defect-related green emission from ZnO nanoparticles: effect of surface modification

We investigated the optical properties of colloidal-synthesized ZnO spherical nanoparticles prepared from 1-octadecene (OD), a mixture of trioctylamine (TOA) and OD (1:10), and a mixture of trioctylphosphine oxide (TOPO) and OD (1:12). It is found that the green photoluminescence (PL) of samples from the mixture of TOA/OD and TOPO/OD is largely suppressed compared with that from pure OD. Moreover, it is found that all spherical nanoparticles have positive zeta potential, and spherical nanoparticles from TOA/OD and TOPO/OD have a smaller zeta potential than those from OD. A plausible explanation is that oxygen vacancies, presumably located near the surface, contribute to the green PL, and the introduction of TOA and TOPO will reduce the density of oxygen vacancies near the surfaces. Assuming that the green emission arises due to radiative recombination between deep levels formed by oxygen vacancies and free holes, we estimate the size of optically active spherical nanoparticles from the spectral energy of the green luminescence. The results are in good agreement with results from TEM. Since this method is independent of the degree of confinement, it has a great advantage in providing a simple and practical way to estimate the size of spherical nanoparticles of any size. We would like to point out that this method is only applicable for samples with a small size distribution

Impact of exposure to patients with COVID-19 on residents and fellows: An international survey of 1420 trainees

Objectives To determine how self-reported level of exposure to patients with novel coronavirus 2019 (COVID-19) affected the perceived safety, training and well-being of residents and fellows. Methods We administered an anonymous, voluntary, web-based survey to a convenience sample of trainees worldwide. The survey was distributed by email and social media posts from April 20th to May 11th, 2020. Respondents were asked to estimate the number of patients with COVID-19 they cared for in March and April 2020 (0, 1-30, 31-60, >60). Survey questions addressed (1) safety and access to personal protective equipment (PPE), (2) training and professional development and (3) well-being and burnout. Results Surveys were completed by 1420 trainees (73% residents, 27% fellows), most commonly from the USA (n=670), China (n=150), Saudi Arabia (n=76) and Taiwan (n=75). Trainees who cared for a greater number of patients with COVID-19 were more likely to report limited access to PPE and COVID-19 testing and more likely to test positive for COVID-19. Compared with trainees who did not take care of patients with COVID-19, those who took care of 1-30 patients (adjusted OR [AOR] 1.80, 95% CI 1.29 to 2.51), 31-60 patients (AOR 3.30, 95% CI 1.86 to 5.88) and >60 patients (AOR 4.03, 95% CI 2.12 to 7.63) were increasingly more likely to report burnout. Trainees were very concerned about the negative effects on training opportunities and professional development irrespective of the number of patients with COVID-19 they cared for. Conclusion Exposure to patients with COVID-19 is significantly associated with higher burnout rates in physician trainees

Microflares and the Statistics of X-ray Flares

This review surveys the statistics of solar X-ray flares, emphasising the new views that RHESSI has given us of the weaker events (the microflares). The new data reveal that these microflares strongly resemble more energetic events in most respects; they occur solely within active regions and exhibit high-temperature/nonthermal emissions in approximately the same proportion as major events. We discuss the distributions of flare parameters (e.g., peak flux) and how these parameters correlate, for instance via the Neupert effect. We also highlight the systematic biases involved in intercomparing data representing many decades of event magnitude. The intermittency of the flare/microflare occurrence, both in space and in time, argues that these discrete events do not explain general coronal heating, either in active regions or in the quiet Sun.Comment: To be published in Space Science Reviews (2011