3,049 research outputs found
Planar Dirac Electron in Coulomb and Magnetic Fields: a Bethe ansatz approach
The Dirac equation for an electron in two spatial dimensions in the Coulomb
and homogeneous magnetic fields is an example of the so-called quasi-exactly
solvable models. The solvable parts of its spectrum was previously solved from
the recursion relations. In this work we present a purely algebraic solution
based on the Bethe ansatz equations. It is realised that, unlike the
corresponding problems in the Schr\"odinger and the Klein-Gordon case, here the
unknown parameters to be solved for in the Bethe ansatz equations include not
only the roots of wave function assumed, but also a parameter from the relevant
operator. We also show that the quasi-exactly solvable differential equation
does not belong to the classes based on the algebra .Comment: LaTex, 12 pages, no figure
Charged particles in external fields as physical examples of quasi-exactly solvable models: a unified treatment
We present a unified treatment of three cases of quasi-exactly solvable
problems, namely, charged particle moving in Coulomb and magnetic fields, for
both the Schr\"odinger and the Klein-Gordon case, and the relative motion of
two charged particles in an external oscillator potential. We show that all
these cases are reducible to the same basic equation, which is quasi-exactly
solvable owing to the existence of a hidden algebraic structure. A
systematic and unified algebraic solution to the basic equation using the
method of factorization is given. Analytic expressions of the energies and the
allowed frequencies for the three cases are given in terms of the roots of one
and the same set of Bethe ansatz equations.Comment: RevTex, 15 pages, no figure
The Sac1 Lipid Phosphatase Regulates Cell Shape Change and the JNK Cascade during Dorsal Closure in Drosophila
AbstractThe Sac1 lipid phosphatase dephosphorylates several phosphatidylinositol (PtdIns) phosphates and, in yeast, regulates a diverse range of cellular processes including organization of the actin cytoskeleton and secretion [1]. We have identified mutations in the gene encoding Drosophila Sac1. sac1 mutants die as embryos with defects in dorsal closure (DC). DC involves the migration of the epidermis to close a hole in the dorsal surface of the embryo occupied by the amnioserosa. It requires cell shape change in both the epidermis and amnioserosa and activation of a Jun N-terminal kinase (JNK) MAPK cascade in the leading edge cells of the epidermis [2]. Loss of Sac1 leads to the improper activation of two key events in DC: cell shape change in the amnioserosa and JNK signaling. sac1 interacts genetically with other participants in these two events, and our data suggest that loss of Sac1 leads to upregulation of one or more signals controlling DC. This study is the first report of a role for Sac1 in the development of a multicellular organism
A Comparison of the Intrinsic Shapes of Two Different Types of Dwarf Galaxies: Blues Compact Dwarfs and Dwarf Ellipticals
We measure the apparent shapes for a sample of 62 blue compact dwarf galaxies
(BCDs), and compare them with the apparent shapes for a sample of 80 dwarf
elliptical galaxies (dEs). The BCDs are flatter, on average, than the dEs, but
the difference is only marginally significant. We then use both non-parametric
and parametric techniques to determine possible distributions of intrinsic
shapes for the BCDs. The hypothesis that BCDs are oblate spheroids can be ruled
out with a high confidence level (), but the hypothesis that they are
prolate spheroids cannot be excluded. The apparent shapes of BCDs are totally
consistent with the hypothesis that they are triaxial ellipsoids. If the
intrinsic axis ratios, and , are distributed according to a
Gaussian with means and and standard deviation ,
we find the best-fitting distribution for BCDs has , while that for dEs has . Our results are consistent with the hypothesis that BCDs
have a close evolutionary relation with dEs.Comment: total 23 pages, 9 figures, and 1 Table, submitted to ApJ on Sep 19
1997. Email addresses: [email protected],
[email protected], [email protected],
[email protected], [email protected]
Predicting Opioid Use Outcomes in Minoritized Communities
Machine learning algorithms can sometimes exacerbate health disparities based
on ethnicity, gender, and other factors. There has been limited work at
exploring potential biases within algorithms deployed on a small scale, and/or
within minoritized communities. Understanding the nature of potential biases
may improve the prediction of various health outcomes. As a case study, we used
data from a sample of 539 young adults from minoritized communities who engaged
in nonmedical use of prescription opioids and/or heroin. We addressed the
indicated issues through the following contributions: 1) Using machine learning
techniques, we predicted a range of opioid use outcomes for participants in our
dataset; 2) We assessed if algorithms trained only on a majority sub-sample
(e.g., Non-Hispanic/Latino, male), could accurately predict opioid use outcomes
for a minoritized sub-sample (e.g., Latino, female). Results indicated that
models trained on a random sample of our data could predict a range of opioid
use outcomes with high precision. However, we noted a decrease in precision
when we trained our models on data from a majority sub-sample, and tested these
models on a minoritized sub-sample. We posit that a range of cultural factors
and systemic forms of discrimination are not captured by data from majority
sub-samples. Broadly, for predictions to be valid, models should be trained on
data that includes adequate representation of the groups of people about whom
predictions will be made. Stakeholders may utilize our findings to mitigate
biases in models for predicting opioid use outcomes within minoritized
communities
A de Haas-van Alphen study of the filled skutterudite compounds PrOsAs and LaOsAs
Comprehensive magnetic-field-orientation dependent studies of the
susceptibility and de Haas-van Alphen effect have been carried out on single
crystals of the filled skutterudites PrOsAs and LaOsAs
using magnetic fields of up to 40~T. Several peaks are observed in the
low-field susceptibility of PrOsAs, corresponding to cascades of
metamagnetic transitions separating the low-field antiferromagnetic and
high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments
show that the Fermi-surface topologies of PrOsAs in its PMM phase
and LaOsAs are very similar. In addition, they are in reasonable
agreement with the predictions of bandstructure calculations for
LaOsAs on the PrOsAs lattice. Both observations suggest
that the Pr 4 electrons contribute little to the number of itinerant
quasiparticles in the PMM phase. However, whilst the properties of
LaOsAs suggest a conventional nonmagnetic Fermi liquid, the effects
of direct exchange and electron correlations are detected in the PMM phase of
PrOsAs. For example, the quasiparticle effective masses in
PrOsAs are found to decrease with increasing field, probably
reflecting the gradual suppression of magnetic fluctuations associated with
proximity to the low-temperature, low-field antiferromagnetic state
Orientation preference maps in Microcebus murinus reveal size-invariant design principles in primate visual cortex
Orientation preference maps (OPMs) are a prominent feature of primary visual cortex (V1) organization in many primates and carnivores. In rodents, neurons are not organized in OPMs but are instead interspersed in a ââsalt and pepperââ fashion, although clusters of orientation-selective neurons have been reported. Does this fundamental difference reflect the existence of a lower size limit for orientation columns (OCs) below which they cannot be scaled down with decreasing V1 size? To address this question, we examined V1 of one of the smallest living primates, the 60-g prosimian mouse lemur (Microcebus murinus). Using chronic intrinsic signal imaging, we found that mouse lemur V1 contains robust OCs, which are arranged in a pinwheel-like fashion. OC size in mouse lemurs was found to be only marginally smaller compared to the macaque, suggesting that these circuit elements are nearly incompressible. The spatial arrangement of pinwheels is well described by a common mathematical design of primate V1 circuit organization. In order to accommodate OPMs, we found that the mouse lemur V1 covers one-fifth of the cortical surface, which is one of the largest V1-to-cortex ratios found in primates. These results indicate that the primate-type visual cortical circuit organization is constrained by a size limitation and raises the possibility that its emergence might have evolved by disruptive innovation rather than gradual change
Disentangling the link between supplemental feeding, population density, and the prevalence of pathogens in urban stray cats
Background Supplemental feeding of free-roaming animals, including wildlife and feral or stray animals, is well known to have a substantial impact on various aspects of animal ecology including habitat use, activity patterns, and host-pathogen interactions. Among them, an increased population density (PD) of animals receiving supplemental food raises concerns regarding the transmission of pathogens in these host populations. The primary aim of this study was to investigate how supplemental feeding is associated with host PD and prevalence of pathogens with different transmission modes in urban stray cats. We hypothesized that supplemental feeding would be positively associated with host PD and the prevalence of pathogens with density-dependent transmission modes compared with pathogens with transmission modes that are considered relatively density-independent. Methods This study was conducted in six districts in Seoul, Republic of Korea which were selected based on different degrees of supplemental feeding and cat caretaker activity (CCA). The PD of stray cats was estimated by mark-recapture surveys. Stray cat blood samples (N = 302) were collected from stray cats by local animal hospitals from each district performing the trap-neuter-release which tested for eight pathogens with different transmission modes (feline immunodeficiency virus, feline leukemia virus (FeLV), feline panleukopenia virus, feline calicivirus, feline herpesvirus-1, Bartonella henselae, hemoplasma, and Toxoplasma gondii) with molecular or serological assays. Associations between the prevalence of each pathogen and PD, CCA, and sex of cats were statistically analyzed. Results In contrast to initial predictions, the cat PD was generally higher in low CCA districts. The prevalence of (FeLV), which is transmitted through direct contact, was significantly higher in areas with a high CCA, conforming to our hypothesis. On the other hand, the prevalence of feline parvovirus, which can be spread by environmental transmission, was higher in low CCA districts. The remaining six pathogens did not show any association with the CCA; however, they had a unique association with the PD or the sex of the stray cats. Discussion Our findings suggest that in addition to influencing the PD, supplemental feeding may affect the prevalence of pathogens in urban animals by mechanisms such as increased aggregation and/or altered foraging strategies, with different consequences depending on the transmission mode of each pathogen
Coronary CTA and Quantitative Cardiac CT Perfusion (CCTP) in Coronary Artery Disease
We assessed the benefit of combining stress cardiac CT perfusion (CCTP)
myocardial blood flow (MBF) with coronary CT angiography (CCTA) using our
innovative CCTP software. By combining CCTA and CCTP, one can uniquely identify
a flow limiting stenosis (obstructive-lesion + low-MBF) versus MVD
(no-obstructive-lesion + low-MBF. We retrospectively evaluated 104 patients
with suspected CAD, including 18 with diabetes, who underwent CCTA+CCTP. Whole
heart and territorial MBF was assessed using our automated pipeline for CCTP
analysis that included beam hardening correction; temporal scan registration;
automated segmentation; fast, accurate, robust MBF estimation; and
visualization. Stenosis severity was scored using the CCTA
coronary-artery-disease-reporting-and-data-system (CAD-RADS), with obstructive
stenosis deemed as CAD-RADS>=3. We established a threshold MBF
(MBF=199-mL/min-100g) for normal perfusion. In patients with CAD-RADS>=3,
28/37(76%) patients showed ischemia in the corresponding territory. Two
patients with obstructive disease had normal perfusion, suggesting collaterals
and/or a hemodynamically insignificant stenosis. Among diabetics, 10 of 18
(56%) demonstrated diffuse ischemia consistent with MVD. Among non-diabetics,
only 6% had MVD. Sex-specific prevalence of MVD was 21%/24% (M/F). On a
per-vessel basis (n=256), MBF showed a significant difference between
territories with and without obstructive stenosis (165 +/- 61 mL/min-100g vs.
274 +/- 62 mL/min-100g, p <0.05). A significant and negative rank correlation
(rho=-0.53, p<0.05) between territory MBF and CAD-RADS was seen. CCTA in
conjunction with a new automated quantitative CCTP approach can augment the
interpretation of CAD, enabling the distinction of ischemia due to obstructive
lesions and MVD
- âŠ