Modeling of Covalent Bonding in Solids by Inversion of Cohesive Energy Curves

We provide a systematic test of empirical theories of covalent bonding in solids using an exact procedure to invert ab initio cohesive energy curves. By considering multiple structures of the same material, it is possible for the first time to test competing angular functions, expose inconsistencies in the basic assumption of a cluster expansion, and extract general features of covalent bonding. We test our methods on silicon, and provide the direct evidence that the Tersoff-type bond order formalism correctly describes coordination dependence. For bond-bending forces, we obtain skewed angular functions that favor small angles, unlike existing models. As a proof-of-principle demonstration, we derive a Si interatomic potential which exhibits comparable accuracy to existing models.Comment: 4 pages revtex (twocolumn, psfig), 3 figures. Title and some wording (but no content) changed since original submission on 24 April 199

Design and validation of Segment - freely available software for cardiovascular image analysis

<p>Abstract</p> <p>Background</p> <p>Commercially available software for cardiovascular image analysis often has limited functionality and frequently lacks the careful validation that is required for clinical studies. We have already implemented a cardiovascular image analysis software package and released it as freeware for the research community. However, it was distributed as a stand-alone application and other researchers could not extend it by writing their own custom image analysis algorithms. We believe that the work required to make a clinically applicable prototype can be reduced by making the software extensible, so that researchers can develop their own modules or improvements. Such an initiative might then serve as a bridge between image analysis research and cardiovascular research. The aim of this article is therefore to present the design and validation of a cardiovascular image analysis software package (Segment) and to announce its release in a source code format.</p> <p>Results</p> <p>Segment can be used for image analysis in magnetic resonance imaging (MRI), computed tomography (CT), single photon emission computed tomography (SPECT) and positron emission tomography (PET). Some of its main features include loading of DICOM images from all major scanner vendors, simultaneous display of multiple image stacks and plane intersections, automated segmentation of the left ventricle, quantification of MRI flow, tools for manual and general object segmentation, quantitative regional wall motion analysis, myocardial viability analysis and image fusion tools. Here we present an overview of the validation results and validation procedures for the functionality of the software. We describe a technique to ensure continued accuracy and validity of the software by implementing and using a test script that tests the functionality of the software and validates the output. The software has been made freely available for research purposes in a source code format on the project home page <url>http://segment.heiberg.se</url>.</p> <p>Conclusions</p> <p>Segment is a well-validated comprehensive software package for cardiovascular image analysis. It is freely available for research purposes provided that relevant original research publications related to the software are cited.</p

Lithium in Blanco1: Implications for Stellar Mixing

We obtain lithium abundances for G and K stars in Blanco 1, an open cluster with an age similar to, or slightly younger than, the Pleiades. We critically examine previous spectroscopic abundance analyses of Blanco 1 and conclude that while there were flaws in earlier work, it is likely that Blanco 1 is close in overall metallicity to the older Hyades cluster and more metal-rich than the Pleiades. However, we find Blanco 1 has Li abundances and rotation rates similar to the Pleiades, contradicting predictions from standard stellar evolution models, in which convective pre-main sequence (PMS) Li depletion should increase rapidly with metallicity. If the high metallicity of Blanco 1 is subsequently confirmed, our observations imply (1) that a currently unknown mechanism severely inhibits PMS Li depletion, (2) that additional non-standard mixing modes, such as those driven by rotation and angular momentum loss, are then responsible for main sequence Li depletion between the ages of Blanco 1 and the Hyades, and (3) that in clusters younger than the Hyades, metallicity plays only a minor role in determining the amount of Li depletion among G and K stars. These conclusions suggest that Li abundance remains a useful age indicator among young (less than 700 Myr) stars even when metallicities are unknown. If non-standard mixing is effective in Population I stars, the primordial Li abundance could be significantly larger than present day Population II Li abundances, due to prior Li depletion.Comment: 18 pages, 3 figs. To appear in ApJ Vol. 511 (Jan 20 1999

Beneficial cumulative effects of old parental age on offspring fitness

Old parental age is commonly associated with negative effects on offspring life-history traits. Such parental senescence effects are predicted to have a cumulative detrimental effect over successive generations. However, old parents may benefit from producing higher quality offspring when these compete for seasonal resources. Thus, old parents may choose to increase investment in their offspring, thereby producing fewer but larger and more competitive progeny. We show that Caenorhabditis elegans hermaphrodites increase parental investment with advancing age, resulting in fitter offspring who reach their reproductive peak earlier. Remarkably, these effects increased over six successive generations of breeding from old parents and were subsequently reversed following a single generation of breeding from a young parent. Our findings support the hypothesis that offspring of old parents receive more resources and convert them into increasingly faster life histories. These results contradict the theory that old parents transfer a cumulative detrimental ‘ageing factor’ to their offspring

Electronic and Structural Properties of a 4d-Perovskite: Cubic Phase of SrZrO3_3

First-principles density functional calculations are performed within the local density approximation to study the electronic properties of SrZrO$_3$, an insulating 4d-perovskite, in its high-temperature cubic phase, above 1400 K, as well as the generic 3d-perovskite SrTiO$_3$, which is also a d^0-insulator and cubic above 105 K, for comparison reasons. The energy bands, density of states and charge density distributions are obtained and a detailed comparison between their band structures is presented. The results are discussed also in terms of the existing data in the literature for both oxides.Comment: 5 pages, 2 figure

Response to GH Treatment After Radiation Therapy Depends on Location of Irradiation

OBJECTIVES: Cancer survivors with GH deficiency (GHD) receive GH therapy (GHT) after 1+ year observation to ensure stable tumor status/resolution. HYPOTHESIS: Radiation therapy (RT) to brain, spine, or extremities alters growth response to GHT. AIM: Identify differences in growth response to GHT according to type/location of RT. METHODS: The Pfizer International Growth Database was searched for cancer survivors on GHT for ≥5 years. Patient data, grouped by tumor type, were analyzed for therapy (surgery, chemotherapy, RT of the focal central nervous system, cranial, craniospinal, or total body irradiation [TBI] as part of bone marrow transplantation), sex, peak stimulated GH, age at GHT start, and duration from RT to GHT start. Kruskal-Wallis test and quantile regression modeling were performed. RESULTS: Of 1149 GHD survivors on GHT for ≥5 years (male 733; median age 8.4 years; GH peak 2.8 ng/mL), 431 had craniopharyngioma (251, cranial RT), 224 medulloblastoma (craniospinal RT), 134 leukemia (72 TBI), and 360 other tumors. Median age differed by tumor group (P < 0.001). Five-year delta height SD score (SDS) (5-year ∆HtSDS; median [10th-90th percentile]) was greatest for craniopharyngioma, 1.6 (0.3-3.0); for medulloblastoma, 5-year ∆HtSDS 0.9 (0.0-1.9); for leukemia 5-year ∆HtSDS, after TBI (0.3, 0-0.7) versus without RT (0.5, 0-0.9), direct comparison P < 0.001. Adverse events included 40 treatment-related, but none unexpected. CONCLUSIONS: TBI for leukemia had significant impact on growth response to GHT. Medulloblastoma survivors had intermediate GHT response, whereas craniopharyngioma cranial RT did not alter GHT response. Both craniospinal and epiphyseal irradiation negatively affect growth response to GH therapy compared with only cranial RT or no RT

Detection of the Li I 6104 Angstroem transition in the Population II star HD 140283

Lithium is one of the few primordially produced elements. The value of the primordial Li is taken to be that observed in metal--poor dwarfs, where it is not contaminated by stellar Li sources which act on longer time scales. The atmospheric abundance is currently derived from the LiI 6707 Angstroem resonance transition and the validity of the models employed has been questioned (Kurucz 1995). In this letter we report the first detection of the Li I 6104 Angstroem 2^2P - 3^2D subordinate transition in the prototype population II star HD 140283. The same Li abundance of (Li/H) =1.4x10^{-10} is found consistent with both the resonance and subordinate lines. The two lines form at different depths in the atmosphere implying that the 1-D homogeneous atmospheric models used in the abundance determination are essentially correct. When coupled with the standard big bang yields, the Li in the halo dwarfs provides two solutions for the baryon-to-photon ratio \eta_{10}= n_{b}/n_{\gamma} x 10^{10}and for the present baryon density \Omega_b h_{70}^2=0.0748\eta_{10}: a) a first solution at \eta_{10} about 1.8, consistent with the \eta_{10} implied by the high deuterium values D/H\approx 2 x 10^{-4}observed in some quasar absorption systems (Webb et al 1997) and b) a second solution at \eta_{10} about 4 which is consistent, within the errors, with the low deuterium D/H =3.4x10^{-5} measured in other quasar absorption systems (Burles & Tytler 1998).Comment: To appear in ApJ Letters, 11 pages 3 figures, uses aasms4.st

Third-order relativistic many-body calculations of energies and lifetimes of levels along the silver isoelectronic sequence

Energies of 5l_j (l= s, p, d, f, g) and 4f_j states in neutral Ag and Ag-like ions with nuclear charges Z = 48 - 100 are calculated using relativistic many-body perturbation theory. Reduced matrix elements, oscillator strengths, transition rates and lifetimes are calculated for the 17 possible 5l_j-5l'_{j'} and 4f_j-5l_{j'} electric-dipole transitions. Third-order corrections to energies and dipole matrix elements are included for neutral Ag and for ions with Z60. Comparisons are made with available experimental data for transition energies and lifetimes. Correlation energies and transition rates are shown graphically as functions of nuclear charge Z for selected cases. These calculations provide a theoretical benchmark for comparison with experiment and theory.Comment: 8 page

Chemical dissociation of human awareness: focus on non-competitive NMDA receptor antagonists

Since the mid-1950s the pharmaceutical industry has developed a number of chemicals, including phencyclidine, ketamine and related arylcyclohexylamines (PCE and TCP), dizocilpine (MK-801), N-allylnormetazocine [ NANM, (±)SKF-10,047], etoxadrol, dioxadrol and its enantiomers dexoxadrol and levoxadrol, which produce a constellation of unusual behavioral effects in animals and man. The compounds best studied in humans are phencyclidine and ketamine. They produce a remarkable dose-dependent dissociation of awareness. All of these substances are now known to be non-competitive antagonists of NMDA receptors of glutamic acid. They act in the NMDA receptor ion channel. One can conclude, on the basis of the effects observed with these agents, that glutamic acid and related excitatory amino acids are extremely important in the maintenance of human awareness.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68872/2/10.1177_026988119200600312.pd

The non-LTE line formation of neutral carbon in late-type stars

We investigate the non-Local Thermodynamic Equilibrium (non-LTE) line formation of neutral carbon in late-type stars in order to remove some of the potential systematic errors in stellar abundance analyses employing C I features. The statistical equilibrium code MULTI was used on a grid of plane-parallel 1D MARCS atmospheric models. Within the parameter space explored, the high-excitation C I lines are stronger in non-LTE due to the combined effect of line source function drop and increased lower level population; the relative importance of the two effects depends on the particular combination of Teff, log g, [Fe/H] and [C/Fe] and on the analysed C I line. As a consequence, the non-LTE abundance corrections are negative and can be substantially so, for example ~-0.4 dex in halo turn-off stars at [Fe/H]~-3. The magnitude of the non-LTE corrections is rather insensitive to whether inelastic H collisions are included or not. Our results have implications on studies of nucleosynthetic processes and on Galactic chemical evolution models. When applying our calculated corrections to recent observational data, the upturn in [C/O] at low metallicity might still be present (thus apparently still necessitating contributions from massive Pop. III stars for the carbon production), but at a lower level and possibly with a rather shallow trend of ~-0.2 dex/dex below [O/H]~-1Comment: Accepted for publication in A&A, 19 pages, 2 tables, 11 figures, aa.cls v6.0 include