Electronic Excitations and Correlation Effects in Metals

Theoretical descriptions of the spectrum of electronic excitations in real metals have not yet reached a fully predictive, "first-principles" stage. In this paper we begin by presenting brief highlights of recent progress made in the evaluation of dynamical electronic response in metals. A comparison between calculated and measured spectra - we use the loss spectra of Al and Cs as test cases - leads us to the conclusion that, even in "weakly-correlated" metals, correlation effects beyond mean-field theory play an important role. Furthermore, the effects of the underlying band structure turn out to be significant. Calculations which incorporate the effects of both dynamical correlations and band structure from first principles are not yet available. As a first step towards such goal, we outline a numerical algorithm for the self-consistent solution of the Dyson equation for the one-particle Green's function. The self-energy is evaluated within the shielded-interaction approximation of Baym and Kadanoff. Our method, which is fully conserving, is a finite-temperature scheme which determines the Green's function and the self-energy at the Matsubara frequencies on the imaginary axis. The analytical continuation to real frequencies is performed via Pade approximants. We present results for the homogeneous electron gas which exemplify the importance of many-body self-consistency.Comment: 32 pages, 6 figures; "Fifty Years of the Correlation Problem", invited paper, to be published in Mol.Phy

Nuclear Shell Structure and Chaotic Dynamics in Hexadecapole Deformation

The effect of an axially symmetric hexadecapole term is investigated in a strongly deformed quadrupole potential. While the system is nonintegrable and shows significant chaotic behaviour classically, the quantum mechanical treatment not only produces a general smoothing effect with regard to chaos but even yields a pronounced shell structure at certain hexadecapole strength parameter values for oblate and prolate deformation.Comment: RevTeX + 4 figs. available from the authors, to appear in Phys.Rev.

Beam quality improvement of high-power semiconductor lasers using laterally inhomogeneous waveguides

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 113, 221107 (2018) and may be found at https://doi.org/10.1063/1.5054645.High-brightness vertical broad-area edge-emitting (HiBBEE) semiconductor lasers in the 1060 nm wavelength range with excellent beam quality in both lateral and vertical directions are presented. An approach to modify the thresholds of the transverse lateral modes of ridge-waveguide (RW) lasers is investigated. It has been experimentally shown that inhomogeneities in both sides of the ridges increase optical losses of the higher-order lateral modes as compared to the fundamental mode. The resulting enhancement in the contrast of the optical losses favors the emission of the fundamental mode and improves the beam quality. Reference RW HiBBEE lasers with a 15 μm wide conventional ridge and a 2.0 mm long cavity provide laterally multi-lateral mode emission which is typical for RW lasers with such wide and homogeneous ridges. On the other hand, RW HiBBEE lasers with triangular-shaped corrugations in both sides of 15 μm wide ridges provide single-lateral mode emission across a wide current range and improve the lateral M2 factor by more than a factor of 2 in the investigated current range. The corrugated RW HiBBEE lasers provide an almost 2 times higher brightness than the reference RW lasers

The value-added of investable hedge fund indices

This paper empirically investigates the risk and performance of three types of alternative beta products over the January 2002 to September 2009 time period: funds of hedge funds (FHFs), investable hedge fund indices (IHFIs), and hedge fund replication strategies (HFRS). We show that IHFIs are true alternative beta products with high correlations and beta to noninvestable hedge fund indices. Our results further suggest that, in a best case scenario, IHFIs outperform FHFs and HFRS on a risk-adjusted basis. However, in the worst case scenario, IHFIs underperform both investments. If we take the average of all IHFIs, we find they perform equally well as FHFs. Hence, IHFIs constitute a solid alternative to FHF investments, while costing substantially less, and offering generally more transparency and liquidity. We propose that fee-sensitive investors especially should consider taking a core-satellite approach to their hedge fund portfolio, with the core represented by cheap passive hedge fund beta through IHFIs, and the satellite represented by more expensive and actively managed alphagenerating FHFs. --Hedge funds,investable hedge fund indices,alternative beta,funds of hedge funds,hedge fund replication,Omega ratio

Density of States of GaAs-AlGaAs Heterostructures Deduced from Temperature Dependend Magnetocapacitance Measurements

Abstract We have analyzed the density of states of a two dimensional electron gas in a GaAs- AlGaAs hetereostructure by measuring the magnetocapacitance in magnetic fields up to 6 Tesla at temperatures below 10 K. The experimental data are well described by a Gaussian-like density of states where the linewidth à is proportional to B

Alcohol consumption in heroin users, methadone-substituted and codeine-substituted patients - Frequency and correlates of use

This retrospective study aims to determine whether there is a difference in the additional consumption of alcohol between addicts treated with methadone or dihydrocodeine (DHC) and untreated addicts injecting heroin. 1,685 patients admitted for opioid withdrawal between 1991 and 1997 were reviewed. Cross-reference tables and multiple logistic regression analyses were carried out. 28% of patients take more than 40 g of alcohol daily (on average 176 g). We found that patients who are treated with methadone or DHC drink alcohol significantly more often daily than the heroin-dependent patients (p<0.01). Using multiple regression analyses, the results were confirmed. Additionally, we found that co-abuse of alcohol was predicted by male gender, longer duration of drug use, additional daily consumption of tetrahydrocannabinol and daily consumption of benzodiazepines. Alcohol consumption by opioid-addicted patients treated with methadone or DHC presents a serious medical problem. Co-abuse of alcohol will receive more attention Copyright (C) 2003 S. Karger AG, Basel

Density of States in Landau Level Tails of GaAs-AlxGa1-xAs Heterostructures

From an analysis of the thermally activated resistivity as a function of the magnetic field in the quantum Hall regime we deduced the position of the Fermi energy in the mobility gap as a function of the filling factor and therefore the density of states. The measured density of states is best described by a Gaussian like profile superimposed on a constant background

Effects of Evidence-Based Fall Reduction Programing on the Functional Wellness of Older Adults in a Senior Living Community: A Clinical Case Study.

BACKGROUND: Older adults at a high risk of falls may be referred to a physical therapist. A physical therapy episode of care is designed for the transition of an older adult from a high fall risk to a moderate to low fall risk. However, these episodes of care are limited in time and duration. There is compelling evidence for the efficacy of group-based exercise classes to address risk, and transitioning an older adult from physical therapy to a group-based program may be an effective way to manage risk through the continuum of care. OBJECTIVES: The purpose of this study was to translate research findings into a real world setting, and demonstrate the efficacy of integrating evidence-based fall prevention exercises into pre-existing exercise classes at a senior living facility as a proof of concept model for future programing. METHODS: Twenty-four participants aged 65 years and older living in a senior living community and the community were stratified into group-based exercise classes. Cutoff scores from functional outcome measures were used to stratify participants. Exercises from The Otago Exercise Program were implemented into the classes. Functional outcome measures collected included the 10-Meter Walk Test, 30-Second Sit to Stand, and Timed Up and Go (TUG). Number of falls, hospitalizations, and physical therapy episodes of care were also tracked. Data were compared to a control group in a different senior living community that offered classes with similar exercises aimed at improving strength and mobility. The classes were taught by an exercise physiologist and were of equal duration and frequency. RESULTS: Participants demonstrated significant improvements in all functional outcome measures. TUG mean improved from 13.5 to 10.4 s (p = 0.034). The 30-Second Sit to Stand mean improved from 10.5 to 13.4 (p = 0.002). The 10-Meter Walk Test improved from 0.81 to 0.98 m/s (p \u3c 0.0001). Participants did not experience any falls or hospitalizations, and two participants required physical therapy episodes of care. CONCLUSION: Implementing an evidence-based fall reduction program into a senior living program has a positive effect on strength, balance, fall risk, gait speed, fall rate, hospitalizations, and amount of physical therapy intervention