Atomic Effective Pseudopotentials for Semiconductors

We derive an analytic connection between the screened self-consistent effective potential from density functional theory (DFT) and atomic effective pseudopotentials (AEPs). The motivation to derive AEPs is to address structures with thousands to hundred thousand atoms, as given in most nanostructures. The use of AEPs allows to bypass a self-consistent procedure and to address eigenstates around a certain region of the spectrum (e.g., around the band gap). The bulk AEP construction requires two simple DFT calculations of slightly deformed elongated cells. The ensuing AEPs are given on a fine reciprocal space grid, including the small reciprocal vector components, are free of parameters, and involve no fitting procedure. We further show how to connect the AEPs of different bulk materials, which is necessary to obtain accurate band offsets. We derive a total of 20 AEPs for III-V, II-VI and group IV semiconductors and demonstrate their accuracy and transferability by comparison to DFT calculations of strained bulk structures, quantum wells with varying thickness, and semiconductor alloys.Comment: 10 pages, 5 figures, submitted to PR

Jamming Transition In Non-Spherical Particle Systems: Pentagons Versus Disks

We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on experiments with monodisperse photoelastic particles with static friction coefficient μ≈1. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, Znr, reaches 3, and the dependence of Znr on the packing fraction ϕ changes again when Znr reaches 4. (2) Though the packing fractions ϕc1 and ϕc2 at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of ϕc1 and ϕc2 for pentagons are around 1% smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution

Jamming Transition In Non-Spherical Particle Systems: Pentagons Versus Disks

We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on experiments with monodisperse photoelastic particles with static friction coefficient μ≈1. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, Znr, reaches 3, and the dependence of Znr on the packing fraction ϕ changes again when Znr reaches 4. (2) Though the packing fractions ϕc1 and ϕc2 at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of ϕc1 and ϕc2 for pentagons are around 1% smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution

Improving Influenza Vaccination Rates Among Children Through Provider and Staff Education

Children younger than five are more likely to develop severe medical complications from the influenza virus. As of June 4th, 2021, the Centers for Disease Control and Prevention (CDC) reported 199 pediatric flu-related deaths for the 2019-2020 influenza season; seventy-eight percent of these deaths occurred in children who had not received a flu vaccination. The CDC annually recommends influenza (Flu) vaccination for all children ages 6 months through 18 years. Any child 6 months to 8 years old who had not received a previous dose of the flu vaccine or whose influenza vaccination history is unknown was recommended to receive a total of two doses of the vaccine four weeks apart. A quality improvement project was performed at three primary care clinics in Northeast Mississippi to improve flu vaccination rates among children 6 months to 18 years old

Globular domain of the prion protein needs to be unlocked by domain swapping to support prion protein conversion

Prion diseases are fatal transmissible neurodegenerative diseases affecting many mammalian species. The normal prion protein (PrP) converts into a pathological aggregated form, PrPSc, which is enriched in the β-sheet structure. While the high resolution structure of the normal PrP was determined, the structure of the converted form of PrP remains inaccessible to high resolution techniques. In order to map the PrP conversion process we introduced disulfide bridges into different positions within the globular domain of PrP, tethering selected secondary structure elements. The majority of tethered PrP mutants exhibited increased thermodynamic stability, nevertheless they converted efficiently. Only the disulfides which tether subdomain B1-H1-B2 to subdomain H2-H3 prevented PrP conversion in vitro and in prion infected cell cultures. Reduction of disulfides recovered the ability of these mutants to convert, demonstrating that the separation of subdomains is an essential step in conversion. Formation of disulfide-linked proteinase K-resistant dimers in fibrils composed of a pair of single cysteine mutants supports the model based on domain-swapped dimers as the building blocks of prion fibrils. In contrast to previously proposed structural models of PrPSc suggesting conversion of large secondary structure segments, we provide evidence for the conservation of secondary structure elements of the globular domain upon PrP conversion. Previous studies already showed that dimerization is the rate-limiting step in PrP conversion. We show that separation and swapping of subdomains of the globular domain is necessary for conversion. Therefore, we propose that domain-swapped dimer of PrP precedes amyloid formation and represents a potential target for therapeutic intervention

Deuterated Ammonia in Galactic Protostellar Cores

We report on a survey of \nh2d towards protostellar cores in low-mass star formation and quiescent regions in the Galaxy. Twenty-three out of thirty-two observed sources have significant (\gsim 5\sigma) \nh2d emission. Ion-molecule chemistry, which preferentially enhances deuterium in molecules above its cosmological value of \scnot{1.6}{-5} sufficiently explains these abundances. NH2D/NH3 ratios towards Class 0 sources yields information about the ``fossil remnants'' from the era prior to the onset of core collapse and star formation. We compare our observations with predictions of gas-phase chemical networks.Comment: 16 Pages, 7 Figures, Accepted to Ap.J., to appear in the June 20, 2001 editio

A Spectral Line Survey of Selected 3 mm Bands Toward Sagittarius B2(N-LMH) Using the NRAO 12 Meter Radio Telescope and the BIMA Array I. The Observational Data

We have initiated a spectral line survey, at a wavelength of 3 millimeters, toward the hot molecular core Sagittarius B2(N-LMH). This is the first spectral line survey of the Sgr B2(N) region utilizing data from both an interferometer (BIMA Array) and a single-element radio telescope (NRAO 12 meter). In this survey, covering 3.6 GHz in bandwidth, we detected 218 lines (97 identified molecular transitions, 1 recombination line, and 120 unidentified transitions). This yields a spectral line density (lines per 100 MHz) of 6.06, which is much larger than any previous 3 mm line survey. We also present maps from the BIMA Array that indicate that most highly saturated species (3 or more H atoms) are products of grain chemistry or warm gas phase chemistry. Due to the nature of this survey we are able to probe each spectral line on multiple spatial scales, yielding information that could not be obtained by either instrument alone.Comment: 35 pages, 15 figures, to be published in The Astrophysical Journa

Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy

The Supernova / Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the dark energy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled measurements. We describe a self-consistent reference mission design for building a Type Ia supernova Hubble diagram and for performing a wide-area weak gravitational lensing study. A 2-m wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The SNAP mission will obtain high-signal-to-noise calibrated light-curves and spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A wide-field survey covering one thousand square degrees resolves ~100 galaxies per square arcminute. If we assume we live in a cosmological-constant-dominated Universe, the matter density, dark energy density, and flatness of space can all be measured with SNAP supernova and weak-lensing measurements to a systematics-limited accuracy of 1%. For a flat universe, the density-to-pressure ratio of dark energy can be similarly measured to 5% for the present value w0 and ~0.1 for the time variation w'. The large survey area, depth, spatial resolution, time-sampling, and nine-band optical to NIR photometry will support additional independent and/or complementary dark-energy measurement approaches as well as a broad range of auxiliary science programs. (Abridged)Comment: 40 pages, 18 figures, submitted to PASP, http://snap.lbl.go

Multiband tight-binding theory of disordered ABC semiconductor quantum dots: Application to the optical properties of alloyed CdZnSe nanocrystals

Zero-dimensional nanocrystals, as obtained by chemical synthesis, offer a broad range of applications, as their spectrum and thus their excitation gap can be tailored by variation of their size. Additionally, nanocrystals of the type ABC can be realized by alloying of two pure compound semiconductor materials AC and BC, which allows for a continuous tuning of their absorption and emission spectrum with the concentration x. We use the single-particle energies and wave functions calculated from a multiband sp^3 empirical tight-binding model in combination with the configuration interaction scheme to calculate the optical properties of CdZnSe nanocrystals with a spherical shape. In contrast to common mean-field approaches like the virtual crystal approximation (VCA), we treat the disorder on a microscopic level by taking into account a finite number of realizations for each size and concentration. We then compare the results for the optical properties with recent experimental data and calculate the optical bowing coefficient for further sizes