Thermodynamics of Random Ferromagnetic Antiferromagnetic Spin-1/2 Chains

Using the quantum Monte Carlo Loop algorithm, we calculate the temperature dependence of the uniform susceptibility, the specific heat, the correlation length, the generalized staggered susceptibility and magnetization of a spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings, down to very low temperatures. Our data show a consistent scaling behavior in all the quantities and support strongly the conjecture drawn from the approximate real-space renormalization group treatment.A statistical analysis scheme is developed which will be useful for the search of scaling behavior in numerical and experimental data of random spin chains.Comment: 13 pages, 13 figures, RevTe

Random Exchange Quantum Heisenberg Chains

The one-dimensional quantum Heisenberg model with random $\pm J$ bonds is studied for $S=\frac{1}{2}$ and $S=1$. The specific heat and the zero-field susceptibility are calculated by using high-temperature series expansions and quantum transfer matrix method. The susceptibility shows a Curie-like temperature dependence at low temperatures as well as at high temperatures. The numerical results for the specific heat suggest that there are anomalously many low-lying excitations. The qualitative nature of these excitations is discussed based on the exact diagonalization of finite size systems.Comment: 13 pages, RevTex, 12 figures available on request ([email protected]

Anatomical study of Momordica charantia L. from Bangladesh

Recent investigation on the root, stem, leaf and petiole anatomy of Momordica charantia L. completed the detailed anatomical study of the genus Momordica from Bangladesh. Root has tetrach vascular bundles where thick patches of sclerenchyma cells encompassed the vessel cells. Five angular ridges and furrows are visible through stem transverse section typical to Cucurbitaceae. Total nine open, bicollateral fibro-vascular bundles are observed in stem crosssection where three large are in the center and others each are under the ridges. Midrib of the leaf is characterized by several double and scarcely seated stalkless globular cystoliths in the lower epidermis. Configuration of petiole is octagonal in shape with eight ridges where seven fibro vascular bundles situated as a ring. Stem and leaf has multicellular, unisireate blunt ended conical shaped trichomes where petiole has similar trichomes with both blunt and pointed head

Fisher information comparison between a monolithic and a fiber-optic light guide in a modular gamma camera

Single-photon emission computed tomography (SPECT) performed with a pinhole collimator often suffers from parallax error due to depth-of-interaction uncertainty. One possible way to reduce the parallax error for a new generation of SPECT pinhole cameras would be to incorporate fiber optics to control the spread of light and improve 3D position estimation. In this work, we have developed a Monte Carlo simulation for an SiPMbased modular gamma camera that incorporates a fiber optic-plate as a light guide. We have created a custom photon transport code written in Swift and we perform the computationally taxing components on a GPU using Metal. This code includes refraction according to Snell's law as well as reflection according to Fresnel's laws at material boundaries. The plate is modeled as a hexagonally-packed array of individual fibers. We also include the scintillation statistics of NaI(Tl) and the detection efficiency of the silicon photomultipliers. We use the simulation code to create mean-detector-response functions (MDRFs) from which Fisher information on event positioning can be assessed. We compare planar detectors with different light guides to determine the effects of the fiber optics. We model three geometries; one that only uses a monolithic light guide, one that only has a fiber-optic plate, and one that has a monolithic light guide and a fiber-optic plate in combination. The spatial resolutions are compared by using Fisher Information Matrices to calculate the Craḿer-Rao Lower Bounds on position estimate variances. © 2022 SPIE.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

A read-out strategy for high-resolution large-area SiPM-based modular gamma-ray cameras

Ongoing developments in the field of molecular imaging have increased the need for gamma-ray detectors with better spatial resolution, while maintaining a large detection area. One approach to improve spatial resolution is to utilize smaller light sensors for finer sampling of scintillation light distribution. However, the number of required sensors per camera must increase significantly, which in turn increases the complexity of the imaging system. Examples of challenges that arise are the analog-to-digital conversion of large numbers of channels, and a bottleneck effect that results from transferring large amounts of raw list-mode data to an acquisition computer. Here we present the design of a read-out electronics system that addresses these challenges. The read-out system, which is designed for a 10"× 10"SiPM-based scintillation gamma-ray camera, can process up to 162 light-sensor signals per event. This is achieved by implementing 1-bit and non-uniform 2-bit sigma-delta modulation analogto-digital conversion, and an on-board processing system with a large number of input/output user pins and relatively high processing power. The processor is a system-on-a-module that also has SDRAM, which allows us to buffer raw list-mode data on board. The bottleneck effect is avoided by buffering event data on the camera module, and only transferring it when the main acquisition computer requests it. This design can be adapted for other crystal/sensor configurations, and can be scaled for a different number of channels. © 2022 SPIE.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Mature students in higher education: Academic performance and intellectual ability

Mature students are sometimes said to be deficient in the basic skills needed for effective studying in higher education or to be impaired by age-related intellectual deficits. However, the research literature on the academic performance of mature students contains no good evidence that mature students perform any less well than younger students on courses of study in higher education. Moreover, the idea that normal ageing impairs the capacity for learning in higher education is most questionable: even the oldest mature students can obtain good results when assessed by means of both examinations and coursework

Sewage pollution: mitigation is key for coral reef stewardship

Coral reefs are in decline worldwide, and land-derived sources of pollution, including sewage, are a major force driving that deterioration. This review presents evidence that sewage discharge occurs in waters surrounding at least 104 of 112 reef geographies. Studies often refer to sewage as a single stressor. However, we show that it is more accurately characterized as a multiple stressor. Many of the individual agents found within sewage, specifically freshwater, inorganic nutrients, pathogens, endocrine disrupters, suspended solids, sediments, and heavy metals, can severely impair coral growth and/or reproduction. These components of sewage may interact with each other to create as-yet poorly understood synergisms (e.g., nutrients facilitate pathogen growth), and escalate impacts of other, non-sewage-based stressors. Surprisingly few published studies have examined impacts of sewage in the field, but those that have suggest negative effects on coral reefs. Because sewage discharge proximal to sensitive coral reefs is widespread across the tropics, it is imperative for coral reef-focused institutions to increase investment in threat-abatement strategies for mitigating sewage pollution