821 research outputs found
Automation, regulation, and collaboration: Threats and opportunities for clinical medical physics careers in diagnostic imaging and nuclear medicine.
Thermodynamics of the Antiferromagnetic Heisenberg Model on the Checkerboard Lattice
Employing numerical linked-cluster expansions (NLCEs) along with exact
diagonalizations of finite clusters with periodic boundary condition, we study
the energy, specific heat, entropy, and various susceptibilities of the
antiferromagnetic Heisenberg model on the checkerboard lattice. NLCEs, combined
with extrapolation techniques, allow us to access temperatures much lower than
those accessible to exact diagonalization and other series expansions. We find
that the high-temperature peak in specific heat decreases as the frustration
increases, consistent with the large amount of unquenched entropy in the region
around maximum classical frustration, where the nearest-neighbor and
next-nearest neighbor exchange interactions (J and J', respectively) have the
same strength, and with the formation of a second peak at lower temperatures.
The staggered susceptibility shows a change of character when J' increases
beyond 0.75J, implying the disappearance of the long-range antiferromagnetic
order at zero temperature. For J'=4J, in the limit of weakly coupled crossed
chains, we find large susceptibilities for stripe and Neel order with
Q=(pi/2,pi/2) at low temperatures with antiferromagnetic correlations along the
chains. Other magnetic and bond orderings, such as a plaquette valence-bond
solid and a crossed-dimer order suggested by previous studies, have also been
investigated.Comment: 10 pages, 13 figure
How does linguistic knowledge contribute to short-term memory?:Contrasting effects of impaired semantic knowledge and executive control
Illiquidity Premia in Asset Returns: An Empirical Analysis of Hedge Funds, Mutual Funds, and US Equity Portfolios
We establish a link between illiquidity and positive autocorrelation in asset returns among a sample of hedge funds, mutual funds, and various equity portfolios. For hedge funds, this link can be confirmed by comparing the return autocorrelations of funds with shorter vs. longer redemption-notice periods. We also document significant positive return-autocorrelation in portfolios of securities that are generally considered less liquid, e.g., small-cap stocks, corporate bonds, mortgage-backed securities, and emerging-market investments. Using a sample of 2,927 hedge funds, 15,654 mutual funds, and 100 size- and book-to-market-sorted portfolios of US common stocks, we construct autocorrelation-sorted long/short portfolios and conclude that illiquidity premia are generally positive and significant, ranging from 2.74% to 9.91% per year among the various hedge funds and fixed-income mutual funds. We do not find evidence for this premium among equity and asset-allocation mutual funds, or among the 100 US equity portfolios. The time variation in our aggregated illiquidity premium shows that while 1998 was a difficult year for most funds with large illiquidity exposure, the following four years yielded significantly higher illiquidity premia that led to greater competition in credit markets, contributing to much lower illiquidity premia in the years leading up to the Financial Crisis of 2007â2008
An Assessment of the Impacts of Construction Projects on the Environment in the Gaza Strip
The aim of this study is to assess the most common impacts of construction projects on the environment in the Gaza Strip and propose the best solutions in curbing down the adverse impacts. To achieve this aim, a structured survey, in the form of a questionnaire was conducted to identify the most critical and important impacts of construction projects on the environment. Environmental impacts were categorized into three safeguard subjects: ecosystems, natural resources, and public impacts. The results showed that dust generation, noise pollution, operations with vegetation removal, and air pollution are the most significant environmental impacts of construction sites in the Gaza Strip. In addition, the public impacts are the most important category that affects the environment in the Gaza Strip. Furthermore, the results demonstrated that the necessity of taking measures to protect labors and residents who are living near to construction sites. It is recommended to enhance the knowledge and awareness of construction participants to the environmental impacts of construction projects and enact strict laws to curb down the adverse impacts of construction projects. In addition, the researchers should look for alternative methods for construction to mitigate the adverse impacts of construction projects on the environment. The results of this study can help decision makers to identify major construction impacts on the environment and make environmentally friendly construction plans in the early stages of construction. Keywords: Environment, Construction projects, EIA, Gaza Strip
Discrimination of prostate cancer cells and non-malignant cells using secondary ion mass spectrometry
This communication utilises Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) combined with multivariate analysis to obtain spectra from the surfaces of three closely related cell lines allowing their discrimination based upon mass spectral ions
Spin Transport in a Mott Insulator of Ultracold Fermions
Strongly correlated materials are expected to feature unconventional
transport properties, such that charge, spin, and heat conduction are
potentially independent probes of the dynamics. In contrast to charge
transport, the measurement of spin transport in such materials is highly
challenging. We observed spin conduction and diffusion in a system of ultracold
fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong
interactions, spin diffusion is driven by super-exchange and
doublon-hole-assisted tunneling, and strongly violates the quantum limit of
charge diffusion. The technique developed in this work can be extended to
finite doping, which can shed light on the complex interplay between spin and
charge in the Hubbard model.Comment: 16 pages, 10 figure
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