819 research outputs found
Official Misconduct, Exoneree Race, and the Length of Time from False Conviction to Exoneration
We investigated the interaction of official misconduct (OM) committed by criminal justice officials and race of the defendant in the context of the length of time from conviction to exoneration. We included in our study cases from 1989 to 2020 from the National Registry of Exonerations (NRE), which compiles in its database exonerations accomplished both with and without DNA evidence. Analysis revealed that there does exist an interaction effect of OM and race of the defendant. The timeframe from conviction to exoneration was longest when the case involved both OM and a Black exoneree. Our results indicate that official misconduct and exoneree race, as well as the interaction of these two variables, are important factors in the exoneration timeframe
Huge excitonic effects in layered hexagonal boron nitride
The calculated quasiparticle band structure of bulk hexagonal boron nitride
using the all-electron GW approximation shows that this compound is an
indirect-band-gap semiconductor. The solution of the Bethe-Salpeter equation
for the electron-hole two-particle Green function has been used to compute its
optical spectra and the results are found in excellent agreement with available
experimental data. A detailed analysis is made for the excitonic structures
within the band gap and found that the excitons belong to the Frenkel class and
are tightly confined within the layers. The calculated exciton binding energy
is much larger than that obtained by Watanabe {\it et al} using a Wannier model
to interpret their experimental results and assuming that h-BN is a
direct-band-gap semiconductor.Comment: 4 pages, 3 figure
BN domains included into carbon nanotubes: role of interface
We present a density functional theory study on the shape and arrangement of
small BN domains embedded into single-walled carbon nanotubes. We show a strong
tendency for the BN hexagons formation at the simultaneous inclusion of B and N
atoms within the walls of carbon nanotubes. The work emphasizes the importance
of a correct description of the BN-C frontier. We suggest that BN-C interface
will be formed preferentially with the participation of N-C bonds. Thus, we
propose a new way of stabilizing the small BN inclusions through the formation
of nitrogen terminated borders. The comparison between the obtained results and
the available experimental data on formation of BN plackets within the single
walled carbon nanotubes is presented. The mirror situation of inclusion of
carbon plackets within single walled BN nanotubes is considered within the
proposed formalism. Finally, we show that the inclusion of small BN plackets
inside the CNTs strongly affects the electronic character of the initial
systems, opening a band gap. The nitrogen excess in the BN plackets introduces
donor states in the band gap and it might thus result in a promising way for
n-doping single walled carbon nanotubes
Theoretical Study of One-dimensional Chains of Metal Atoms in Nanotubes
Using first-principles total-energy pseudopotential calculations, we have
studied the properties of chains of potassium and aluminum in nanotubes. For BN
tubes, there is little interaction between the metal chains and the tubes, and
the conductivity of these tubes is through carriers located at the inner part
of the tube. In contrast, for small radius carbon nanotubes, there are two
types of interactions: charge-transfer (dominant for alkali atoms) leading to
strong ionic cohesion, and hybridization (for multivalent metal atoms)
resulting in a smaller cohesion. For Al-atomic chains in carbon tubes, we show
that both effects contribute. New electronic properties related to these
confined atomic chains of metal are analyzed.Comment: 12 pages + 3 figure
Elimination of unoccupied state summations in it ab initio self-energy calculations for large supercells
We present a new method for the computation of self-energy corrections in large supercells. It eliminates the explicit summation over unoccupied states, and uses an iterative scheme based on an expansion of the Green's function around a set of reference energies. This improves the scaling of the computational time from the fourth to the third power of the number of atoms for both the inverse dielectric matrix and the self-energy, yielding improved efficiency for 8 or more silicon atoms per unit cell
Curvature, hybridization, and STM images of carbon nanotubes
The curvature effects in carbon nanotubes are studied analytically as a
function of chirality. The pi-orbitals are found to be significantly
rehybridized in all tubes, so that they are never normal to the tubes' surface.
This results in a curvature induced gap in the electronic band-structure, which
turns out to be larger than previous estimates. The tilting of the pi-orbitals
should be observable by atomic resolution scanning tunneling microscopy
measurements.Comment: Four pages in revtex format including four epsfig-embedded figures.
The latest version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/hybrid.pd
Stochastic Heterostructures in B/N-Doped Carbon Nanotubes
Carbon nanotubes are one-dimensional and very narrow. These obvious facts
imply that under doping with boron and nitrogen, microscopic doping
inhomogeneity is much more important than for bulk semiconductors. We consider
the possibility of exploiting such fluctuations to create interesting devices.
Using self-consistent tight-binding (SCTB), we study heavily doped highly
compensated nanotubes, revealing the spontaneous formation of structures
resembling chains of random quantum dots, or nano-scale diode-like elements in
series. We also consider truly isolated impurities, revealing simple scaling
properties of bound state sizes and energies.Comment: 4 pages RevTeX, 4 PostScript figure
Model for the on-site matrix elements of the tight-binding hamiltonian of a strained crystal: Application to silicon, germanium and their alloys
We discuss a model for the on-site matrix elements of the sp3d5s*
tight-binding hamiltonian of a strained diamond or zinc-blende crystal or
nanostructure. This model features on-site, off-diagonal couplings between the
s, p and d orbitals, and is able to reproduce the effects of arbitrary strains
on the band energies and effective masses in the full Brillouin zone. It
introduces only a few additional parameters and is free from any ambiguities
that might arise from the definition of the macroscopic strains as a function
of the atomic positions. We apply this model to silicon, germanium and their
alloys as an illustration. In particular, we make a detailed comparison of
tight-binding and ab initio data on strained Si, Ge and SiGe.Comment: Submitted to Phys. Rev.
Publishing a Master’s Thesis: A Guide for Novice Authors
Publication of original research, clinical experiences, and critical reviews of literature are vital to the growth of the genetic counseling field, delivery of genetic counseling services, and professional development of genetic counselors. Busy clinical schedules, lack of time and funding, and training that emphasizes clinical skills over research skills may make it difficult for new genetic counselors to turn their thesis projects into publications. This paper summarizes and elaborates upon a presentation aimed at de-mystifying the publishing process given at the 2008 National Society of Genetic Counselors Annual Education Conference. Specific topics include familiarizing prospective authors, particularly genetic counseling students, with the basics of the publication process and related ethical considerations. Former students’ experiences with publishing master’s theses also are described in hopes of encouraging new genetic counselors to submit for publication papers based on their thesis projects
Suppression of electron-electron repulsion and superconductivity in Ultra Small Carbon Nanotubes
Recently, ultra-small-diameter Single Wall Nano Tubes with diameter of have been produced and many unusual properties were observed, such as
superconductivity, leading to a transition temperature , much
larger than that observed in the bundles of larger diameter tubes.
By a comparison between two different approaches, we discuss the issue
whether a superconducting behavior in these carbon nanotubes can arise by a
purely electronic mechanism. The first approach is based on the Luttinger Model
while the second one, which emphasizes the role of the lattice and short range
interaction, is developed starting from the Hubbard Hamiltonian. By using the
latter model we predict a transition temperature of the same order of magnitude
as the measured one.Comment: 7 pages, 3 figures, to appear in J. Phys.-Cond. Ma
- …