bluuebunny/crossref_metadata_2025 huggingface dataset:
Classification du Spectre d'Arc du Sélénium (Sel) entre 3 900 et 11 844 cm-1
Authors: C Morillon  , J Vergès
Published: January 2007

The spectrum emitted by an electrodeless discharge tube filled with pure80Se has been newly investigated by Fourier transform spectroscopy. The observations have led to a list of wavenumbers and estimated intensities for 360 lines in the range 3 900 to 11 844 cm-1. The values of the known energy levels involved in the observed transitions have been improved by exploiting the high wavenumber accuracy, 3 × 10-3cm-1. The fine structures of the 4p3(4S)nd5Dand3Dterms have been improved and 3 levels withJ=0 are new. The fine structures of the 4p3(4S)nf5Fand5Fterms, which were not resolved in previous studies, are given fromn=4 ton=6. It is shown that the principal quantum numbersnare in error by one unit in the compilation Atomic Energy Levels Vol. II (1952). Finally, the very regular 4p3(4S)nf5F5series yields for the principal ionization energy of Se I the value:

IP = 78 658.12 ± 0.1 cm-1(9.747 ± 0.001 eV).
Additions to the Displaced Term System of Be I
Authors: Lennart Johansson
Published: January 2007

The wavelengths of 27 new lines of Be I have been measured and 24 new levels have been established, most of which belong to the displaced system 2pnl. The series 2sns1Sand 2snd1Dhave been extended, the former indicating a possible disturbance from 2p21S0.
Lifetimes of Excited Levels in Some Important Ion-molecules Part I: NH+, OH+and SH+
Authors: J Brzozowski  , N Elander  , P Erman  , M Lyyra
Published: January 2007

The spectra of NH+, OH+and SH+in the range 3 000-5 000 Å have been studied at 0.2-0.4 Å FWHM resolution using the High-Frequency Deflection technique. Radiative lifetimes of low-lying excited electronic states in these molecules were simultaneously measured and found to be of the magnitude of 400-1 100 ns.
Transition Probabilities, Correlation Functions and Dielectric Permittivity Tensors for Semi-bounded and Bounded Nonequilibrium Plasmas
Authors: I P Yakimenko  , A G Zagorodny
Published: January 2007

The spectral tensors of current fluctuations in the systems of uncorrelated particles and the linear response functions are derived on the basis of the transition-probability approach to the theory of nonequilibrium plasmas, semi-bounded or bounded in one direction. The typical cases of non-equilibrium systems are considered, including the presence of directed particle flows, external force fields and temperature anisotropy. Also discussed is the statement of the boundary value problem for the fluctuation fields in a plasma half-space and a plasma layer under the condition that the particles suffer specular reflection near the boundaries. The results obtained are assigned for building the correlation theory of electromagnetic processes in a bounded nonequilibrium plasma.
The Elastic p+d Reaction at Ep=185 MeV
Authors: P C Gugelot  , J Källne  , P-U Renberg
Published: January 2007

The differential cross section of the reaction p+d → p+d has been measured for deuteron angles θ, 4.1 ⩽θ⩽ 51° (in the c.m. frame). The results are compared with other data and discussed in view of model predictions.
Possible Results of Including Spatial Effects in Forrester's World Dynamics Model
Authors: Douglas H McQueen
Published: January 2007

Possible spatial effects in an extended world dynamics model including diffusion are discussed. The rate equations are similar to those describing autocatalytic chemical reactions, which exhibit spatial inhomogeneities under certain conditions. The extended world dynamics model should exhibit similar spatial structure due to strong positive feedback loops (autocatalytic steps).
The Effect of Simultaneous Acceleration and Fragmentation on the Composition of the Iron Group of Low-energy Cosmic Rays
Authors: S Lindstam
Published: January 2007

The effect of simultaneous acceleration and fragmentation on the charge composition of the iron group 21⩽Z⩽26 is investigated. A pure 56Fe source is assumed and several acceleration mechanisms and potential path length distributions are applied. The iron particles are injected at 40 MeV/nucleon and accelerated to 300 and 1 000 MeV/nucleon. It is found that the ratio N(21⩽Z⩽25)/N(Fe) depends only weakly on the energy at which matter is traversed. It is, however, a good measure of the amount of matter traversed. The ratio N(Ti)/N(Cr) depends on the acceleration mechanism to a degree which makes it possible to distinguish between different acceleration mechanisms from measurements.
Nuclear Spins of165Lu,168mLu and172Lu
Authors: C Ekström  , W Hogervorst  , S Ingelman  , G Wannberg
Published: January 2007

The nuclear spins of some neutron-deficient lutetium isotopes have been measured using the atomic-beam magnetic resonance method. The following results have been obtained:165Lu (12 min)I= 1/2,168mLu (6.7 min)I= 3 and172Lu (6.7 d)I= 4. The spin values are discussed within the framework of the Nilsson model.
Equilibrium Charge-state Distributions of Heavy-ion Beams after Passage through Carbon Foils
Authors: J Heinemeier  , P Hvelplund  , J Østgård Olsen  , F R Simpson
Published: January 2007

Equilibrium charge distributions have been measured for beams of59Pr,64Gd,71Lu,80Hg,81Tl, and82Pb ions, which were sent through thin carbon foils (≈ 4 μg/cm2) at beam energies ranging from 300 keV to 1 000 keV. Corrections were made for energy loss in the carbon foils, partly by means of direct measurements and partly by means of theoretical electronic-and nuclear-stopping cross sections for the forward-directed beam. The main purpose of the present work has been to extend existing data on equilibrium charge-state fractions. Similarities in the measured equilibrium charge-state distributions for the rare earths Pr, Gd, and Lu, and also the fact that only a weak shell effect around Hg was found, suggest that the charge distributions of one heavy atom could be used for neighbouring atoms (or group of atoms) within the same period.
Experimental Observables and the Fission Barrier
Authors: H J Specht
Published: January 2007

The experimental evidence supporting the double humped character of the fission barrier in actinide nuclei is reviewed and compared with theoretical predictions. The discussion covers the properties of spontaneously fissioning isomers, intermediate structure in fission cross sections, the systematics of fission barrier heights, and the implications of a possible octupole deformation at the second barrier for fragment mass distributions.
Bevalac: Status of the Machine and of the Physics Research Program
Authors: Earl K Hyde
Published: January 2007

The Bevalac is briefly described and its schedule for completion is given. The Physics Research Program to be carried out with heavy ion beams with energy in the range 0.250 to 2.1 GeV/nucleon is described.
Experiments Concerning the Synthesis of Superheavy Elements
Authors: C Spèhan
Published: January 2007

Experiments made at Orsay to synthesize superheavy elements by heavy ion induced reactions are described, and the results are presented. An attempt to explain the negative results obtained is presented, based on the mechanisms of the reaction involved: interaction barrier, critical distance of approach, deep inelastic transfers.
Review of Recent SHE Predictions
Authors: A Sobiczewski
Published: January 2007

Recent predictions for lifetimes of superheavy (A≈ 300) and super-superheavy (A300) nuclei are reviewed. Various factors affecting the predicted lifetimes and the uncertainties in these predictions are discussed.
Theoretical Estimates of Spontaneous-Fission Half-Lives for Superheavy Elements Based on the Modified-Oscillator Model
Authors: J Randrup  , S E Larsson  , P Möller  , A Sobiczewski  , A Lukasaik
Published: January 2007

The stability problem for the superheavy elements has been reconsidered based on the use of the shape-dependent droplet model and the modified-oscillator potential. The effect of axial asymmetry on the barrier heights is included. A semi-empirical inertial-mass function is employed. Alternatively the inertial-mass parameters are calculated microscopically. The spontaneous-fission half-lives are calculated with these inertials. Both of the latter were renormalized to give optimal agreement with experimental half-lives in the actinide region. The resulting spontaneous-fission half-lives in the SHE region are somewhat shorter than those of most previous estimates, predicting, for example, around 105 years as the total half-live for the most stable nucleus 294110.
Preliminary Study of Additional Effects with Bearing on the Barrier Heights for Superheavy Elements
Authors: S E Larsson  , G Leander  , I Ragnarsson  , J Randrup
Published: January 2007

The effects of the simultaneous presence of monopole and quadrupole pairing interactions on the fission barriers for heavy and superheavy elements are considered. The first barrier for light Th isotopes is found to be raised by 1 MeV, while heavier actinide nuclei seem to be less affected by the inclusion of quadrupole pairing. For the superheavy elements, the inclusion of quadrupole pairing tends to increase the barriers considerably. Moreover, the Coulomb energy, associated with the non-homogeneous charge distribution of the modified oscillator model, is compared with the liquid-drop value and with value emerging from a self-consistent calculation based on the Skyrme interaction. The shell effect, which may be several MeV in magnitude, appears to be highly sensitive to model assumptions concerning the forces between neutrons and protons.
The Search for Superheavy Elements in Nature
Authors: G Herrmann
Published: January 2007

A review is given of the methods used in the search for superheavy elements in nature and of the results obtained. It is concluded that there is no convincing evidence for the presence of such elements in nature.
Superheavies in Nature – Where and How to Look
Authors: Matti Nurmia
Published: January 2007

In searching for superheavy elements in nature it is usually assumed that the SHE (1) follows the chemistry of its lighter homolog and (2) decays by spontaneous fission. The sensitivity of SHE detection can be substantially improved by replacing these assumptions by a consideration of the geo-chemical fractionation processes, and by using a mass spectrometer. A good candidate for a search would be element 112, eka-mercury. It is expected to be more volatile and more noble than Hg so that it may behave like a heavy rare gas and be concentrated in the earth's atmosphere.
Complete and Incomplete Fusion in Heavy-Ion Collisions
Authors: M Lefort
Published: January 2007

This is a survey of the work done at Orsay on the accelerator ALICE, on reactions induced by very heavy ions. (Ar to Kr). It deals mainly with the questions of complete fusion and very inelastic exchanges of nucleons which are relevant to the problem of nuclear viscosity. New results are presented on the very inelastic processes which produce light fragments in Ar-induced reactions on Ni and Th targets. The angular and mass correlation has been verified between the light and the heavy partner, and it is now entirely proven that a large amount of energy is dissipated into intrinsic excitations. Measured cross sections for complete fusion are compiled and a number of comments are given on the limitation for fusion in relation to critical angular momenta and critical distances of approach. For reactions induced by krypton and copper ions, the fusion barrier is higher than the interaction barrier. Below the fusion barrier, peculiar phenomena occur, named "quasi-fission". The fusion barrier is explained in terms of a cut-off in the lowlℏpopulation for partial waves of the incoming ion, due to friction forces.
Superfluid versus Viscous Descent from Saddle to Scission
Authors: S Bjørnholm
Published: January 2007

The spectrum of mass yields from spontaneous fission and thermal neutron induced fission of even nucleides sometimes shows a fine structure, indicating a preference for doubly even mass divisions. This occurs only when the fissility parameter is relatively small. For a given nuclide, the fine structure is more pronounced when the total kinetic energy carried away by the fragments is larger than average. The preference for doubly even mass divisions is interpreted as the preservation of superfluidity, i.e. of the paired configuration, during the descent from saddle to scission. Conversely, loss of fine structure means excitation of quasiparticles during the descent. Alternative models for the saddle-to-scission transition are discussed in relation to the observed variance in the number of neutrons evaporated from a single fragment, under the constraint of a fixed total kinetic energy and a fixed mass ratio. It is concluded that fine structure in the mass yields may also occur, when the total kinetic energy is much lower than average.
Quantum Theory of Dissipation for Nuclear Collective Motion
Authors: Arthur K Kerman  , Steven E Koonin
Published: January 2007

We present a theory of energy dissipation in heavy ion and fission process. Beginning with the time-independent coupled channels generator coordinate equations, a statistical treatment leads to a quantal equation in the collective coordinates and excitation energy. Assumptions of adiabaticity lead to a momentum coupled Schroedinger-like equation for the statistical wave-function. This equation describes, in a statistical manner, quantum mechanical collective motion, including dissipation. Therefore, average inelastic cross sections or fragment excitation energies may be obtained. Of course, phenomenologically known functions such as the nuclear mass parameter or potential energy surface can be simply utilized. The new dissipation function (like all the others) is determined by averages of microscopically calculable quantities. Numerical result for a model calculation exhibiting the structure of the equation are presented.
Quantum Mechanical Motion in a Multidimensional Space of Deformation (Barrier Penetration)
Authors: Hans-Christian Pauli
Published: January 2007

In the first part, calculated lifetimes for spontaneous fission from the ground and from the isomer state are presented. The agreement reached with experiments correponds to the crude approximations done, but is better than expected. The calculations are based on the shell correction approach for the potential energy and on the cranking model for the collective mass. In the second part we discuss the behaviour of the so-called least action trajectories: there are two of them, one for symmetric and one for asymmetric shapes. The systematic behaviour of the dynamic barriers and of the peak-to-peak ratio of the fission fragment mass distribution and their correlation with the experimental in formation support this point of view.
An Alternative Thermonuclear n-Capture Path to the Superheavy Island
Authors: Heiner W Meldner  , John Nuckolls  , Lowell Wood
Published: January 2007

Thermonuclear neutron-capture approaches to heavy transuranium element synthesis are investigated. Certain feature of capture experiments using thermonuclear macro-explosives are re-analyzed in view of recent results of nuclear shell-structure theory and theoretical developments in laser-energized fusion micro-explosions. The micro-explosion conditions for prompt multiple neutron capture are estimated for the simplest moderation techniques. We speculate on some practical neutor-capture paths to the superheavy island, especially a hybrid approach, using both macro-and micro-explosion events.
Activation of sphingosine‐1‐phosphate receptor S1P5 inhibits oligodendrocyte progenitor migration
Authors: Novgorodov Alexander S. , El‐Awani Mazen , Bielawski Jacek , Obeid Lina M. , Gudz Tatyana I.
Published: January 2007

Sphingosine‐1‐phosphate (S1P) acts as an extracellular ligand for a family of G‐protein coupled receptors that are crucial in cell migration. S1P5 is exclusively expressed in oligodendrocytes and oligodendrocyte precursor cells (OPCs), which migrate considerable distances during brain development. The current studies suggest a physiological role for S1P and S1P5 in regulation of OPC migration. mRNA expression levels of S1P2 and S1P5 are comparable in OPCs, but S1P binding specifically to the S1P5 receptor blocked OPC migration (IC50 = 29 nM). Thus, knocking down S1P5 using siRNA prevented the S1P‐induced decrease in OPC migration, whereas knocking down S1P2 did not have any effect. S1P‐induced modulation of OPC migration was insensitive to pertussis toxin, suggesting that S1P5‐initiated signaling is not mediated by the Gαi‐protein coupled pathway. Furthermore, S1P5 appears to engage the Gα12/13 protein coupled Rho/ROCK signaling pathway to impede OPC migration. To modulate OPC motility, extracellular S1P could be derived from the export of intracellular S1P generated in response to glutamate treatment of OPCs. These studies suggest that S1P could be a part of the neuron‐oligodendroglial communication network regulating OPC migration and may provide directional guidance cues for migrating OPCs in the developing brain.—Novgorodov A. S., El‐Alwani, M., Bielawski, J., Obeid, L. M., Gudz T. I. Activation of sphingosine‐1‐phosphate receptor S1P5 inhibits oligodendrocyte progenitor migration. FASEB J. 21, 1503–1514 (2007)
Functional relevance of DNA polymorphisms within the promoter region of the prion protein gene and their association to BSE infection
Authors: Kashkevich Kseniya , Humeny Andreas , Ziegler Ute , Groschup Martin H. , Nicken Petra , Leeb Tosso , Fischer Christine , Becker Cord-Michael , Schiebel Katrin
Published: January 2007

Transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative diseases that can occur spontaneously or can be caused by infection or mutations within the prion protein gene PRNP. Nonsynonymous DNA polymorphisms within the PRNP gene have been shown to influence susceptibility/resistance to infection in sheep and humans. Analysis of DNA polymorphisms within the core promoter region of the PRNP gene in four major German bovine breeds resulted in the identification of both SNPs and insertion/deletion (indel) polymorphisms. Comparative genotyping of both controls and animals that tested positive for bovine spongiform encephalopathy (BSE) revealed a significantly different distribution of two indel polymorphisms and two SNPs within Braunvieh animals, suggesting an association of these polymorphisms with BSE susceptibility. The functional relevance of these polymorphisms was analyzed using reporter gene constructs in neuronal cells. A specific haplotype near exon 1 was identified that exhibited a significantly lower expression level. Genotyping of nine polymorphisms within the promoter region and haplotype calculation revealed that the haplotype associated with the lowest expression level was underrepresented in the BSE group of all breeds compared to control animals, indicating a correlation of reduced PRNP expression and increased resistance to BSE.—Kashkevich K., Humeny, A., Ziegler, U., Groschup, M. H., Nicken, P., Leeb, T., Fischer, C., Becker, C.‐M., Schiebel K. Functional relevance of DNA polymorphisms within the promoter region of the prion protein gene and their association to BSE infection. FASEB J. 21, 1547–1555 (2007)
Scent may signal fighting ability in male Iberian rock lizards
Authors: Martín José , López Pilar
Published: January 2007

Intrasexual competition favours the evolution of conspicuous fighting ability badges. However, in spite of the fact that chemoreception is important in sexual selection of many animals, such as lizards, the role of chemical signals in males' contests is relatively unknown. Here, we show that proportions of cholesterol in femoral gland secretions of male Iberian rock lizards were related to their body size (which confers a competitive advantage in fights). Males discriminated chemically and responded aggressively to cholesterol stimuli presented on swabs. Moreover, we experimentally increased cholesterol in the scent of males, and staged encounters in neutral cages between two unfamiliar and size-matched males. Focal males lost more agonisitic interactions against males manipulated with cholesterol than in control tests. We suggest that differences in scent composition may reliably signal fighting ability in many lizard species, which would help to avoid the costs of fighting.
Expanding the polypeptide backbone: hydrogen-bonded conformations in hybrid polypeptides containing the higher homologues of α-amino acids
Authors: Chatterjee Sunanda , Roy Rituparna Sinha , Balaram P
Published: January 2007

Half a century has passed since the hydrogen-bonded secondary structures of polypeptides and proteins were first recognized. An extraordinary wealth of conformational information is now available on peptides and proteins, which are formed of α-amino acid residues. More recently, the discovery of well-folded structures in oligopeptides containing β-amino acids has focused a great deal of current interest on the conformational properties of peptides constructed from higher homologues (ω) of α-amino acids. This review examines the nature of intramolecularly hydrogen-bonded conformations of hybrid peptides formed by amino acid residues, with a varying number of backbone atoms. The β-turn, a ubiquitous structural feature formed by two residue (αα) segments in proteins and peptides, is stabilized by a 10-atom (C10) intramolecular 4→1 hydrogen bond. Hybrid turns may be classified by comparison with their αα counterparts. The available crystallographic information on hydrogen-bonded hybrid turns is surveyed in this review. Several recent examples demonstrate that individual ω-amino acid residues and hybrid dipeptide segments may be incorporated into the regular structures of α-peptides. Examples of both peptide helices and hairpins are presented. The present review explores the relationships between folded conformations in hybrid sequences and their counterparts in all α-residue sequences. The use of stereochemically constrained ω-residues promises to expand the range of peptide design strategies to include ω-amino acids. This approach is exemplified by well-folded structures like the C12(αγ) and C14(γγ) helices formed in short peptides containing multiply substituted γ-residues. The achiral γ-residue gabapentin is a readily accessible building block in the design of peptides containing γ-amino acids. The construction of globular polypeptide structures using diverse hybrid sequences appears to be a realistic possibility.
The Croonian lecture 2006 Structure of the living cell
Authors: Campbell Iain D
Published: January 2007

The smallest viable unit of life is a single cell. To understand life, we need to visualize the structure of the cell as well as all cellular components and their complexes. This is a formidable task that requires sophisticated tools. These have developed from the rudimentary early microscopes of 350 years ago to a toolbox that includes electron microscopes, synchrotrons, high magnetic fields and vast computing power. This lecture briefly reviews the development of biophysical tools and illustrates how they begin to unravel the ‘molecular logic of the living state’.
Cognitive adaptations of social bonding in birds
Authors: Emery Nathan J , Seed Amanda M , von Bayern Auguste M.P , Clayton Nicola S
Published: January 2007

The ‘social intelligence hypothesis’ was originally conceived to explain how primates may have evolved their superior intellect and large brains when compared with other animals. Although some birds such as corvids may be intellectually comparable to apes, the same relationship between sociality and brain size seen in primates has not been found for birds, possibly suggesting a role for other non-social factors. But bird sociality is different from primate sociality. Most monkeys and apes form stable groups, whereas most birds are monogamous, and only form large flocks outside of the breeding season. Some birds form lifelong pair bonds and these species tend to have the largest brains relative to body size. Some of these species are known for their intellectual abilities (e.g. corvids and parrots), while others are not (e.g. geese and albatrosses). Although socio-ecological factors may explain some of the differences in brain size and intelligence between corvids/parrots and geese/albatrosses, we predict that the type and quality of the bonded relationship is also critical. Indeed, we present empirical evidence that rook and jackdaw partnerships resemble primate and dolphin alliances. Although social interactions within a pair may seem simple on the surface, we argue that cognition may play an important role in the maintenance of long-term relationships, something we name as ‘relationship intelligence’.
Social brains, simple minds: does social complexity really require cognitive complexity?
Authors: Barrett Louise , Henzi Peter , Rendall Drew
Published: January 2007

The social brain hypothesis is a well-accepted and well-supported evolutionary theory of enlarged brain size in the non-human primates. Nevertheless, it tends to emphasize an anthropocentric view of social life and cognition. This often leads to confusion between ultimate and proximate mechanisms, and an over-reliance on a Cartesian, narratively structured view of the mind and social life, which in turn lead to views of social complexity that are congenial to our views of ourselves, rather than necessarily representative of primate social worlds. In this paper, we argue for greater attention to embodied and distributed theories of cognition, which get us away from current fixations on ‘theory of mind’ and other high-level anthropocentric constructions, and allow for the generation of testable hypotheses that combine neurobiology, psychology and behaviour in a mutually reinforcing manner.
The social brain?
Authors: Frith Chris D
Published: January 2007

The notion that there is a ‘social brain’ in humans specialized for social interactions has received considerable support from brain imaging and, to a lesser extent, from lesion studies. Specific roles for the various components of the social brain are beginning to emerge. For example, the amygdala attaches emotional value to faces, enabling us to recognize expressions such as fear and trustworthiness, while the posterior superior temporal sulcus predicts the end point of the complex trajectories created when agents act upon the world. It has proved more difficult to assign a role to medial prefrontal cortex, which is consistently activated when people think about mental states. I suggest that this region may have a special role in the second-order representations needed for communicative acts when we have to represent someone else's representation of our own mental state. These cognitive processes are not specifically social, since they can be applied in other domains. However, these cognitive processes have been driven to ever higher levels of sophistication by the complexities of social interaction.
Social intelligence, human intelligence and niche construction
Authors: Sterelny Kim
Published: January 2007

This paper is about the evolution of hominin intelligence. I agree with defenders of the social intelligence hypothesis in thinking that externalist models of hominin intelligence are not plausible: such models cannot explain the unique cognition and cooperation explosion in our lineage, for changes in the external environment (e.g. increasing environmental unpredictability) affect many lineages. Both the social intelligence hypothesis and the social intelligence–ecological complexity hybrid I outline here are niche construction models. Hominin evolution is hominin response to selective environments that earlier hominins have made. In contrast to social intelligence models, I argue that hominins have both created and responded to a unique foraging mode; a mode that is both social in itself and which has further effects on hominin social environments. In contrast to some social intelligence models, on this view, hominin encounters with their ecological environments continue to have profound selective effects. However, though the ecological environment selects, it does not select on its own. Accidents and their consequences, differential success and failure, result from the combination of the ecological environment an agent faces and the social features that enhance some opportunities and suppress others and that exacerbate some dangers and lessen others. Individuals do not face the ecological filters on their environment alone, but with others, and with the technology, information and misinformation that their social world provides.
Allelic variation and heterosis in maize: How do two halves make more than a whole?
Authors: Springer Nathan M. , Stupar Robert M.
Published: January 2007

In this review, we discuss the recent research on allelic variation in maize and possible implications of this work toward our understanding of heterosis. Heterosis, or hybrid vigor, is the increased performance of a hybrid relative to the parents, and is a result of the variation that is present within a species. Intraspecific comparisons of sequence and expression levels in maize have documented a surprisingly high level of allelic variation, which includes variation for the content of genic fragments, variation in repetitive elements surrounding genes, and variation in gene expression levels. There is evidence that transposons and repetitive DNA play a major role in the generation of this allelic diversity. The combination of allelic variants provides a more comprehensive suite of alleles in the hybrid that may be involved in novel allelic interactions. A major unresolved question is how the combined allelic variation and interactions in a hybrid give rise to heterotic phenotypes. An understanding of allelic variation present in maize provides an opportunity to speculate on mechanisms that might lead to heterosis. Variation for the presence of genes, the presence of novel beneficial alleles, and modified levels of gene expression in hybrids may all contribute to the heterotic phenotypes.
MEGAN analysis of metagenomic data
Authors: Huson Daniel H. , Auch Alexander F. , Qi Ji , Schuster Stephan C.
Published: January 2007

Metagenomics is the study of the genomic content of a sample of organisms obtained from a common habitat using targeted or random sequencing. Goals include understanding the extent and role of microbial diversity. The taxonomical content of such a sample is usually estimated by comparison against sequence databases of known sequences. Most published studies use the analysis of paired-end reads, complete sequences of environmental fosmid and BAC clones, or environmental assemblies. Emerging sequencing-by-synthesis technologies with very high throughput are paving the way to low-cost random “shotgun” approaches. This paper introduces MEGAN, a new computer program that allows laptop analysis of large metagenomic data sets. In a preprocessing step, the set of DNA sequences is compared against databases of known sequences using BLAST or another comparison tool. MEGAN is then used to compute and explore the taxonomical content of the data set, employing the NCBI taxonomy to summarize and order the results. A simple lowest common ancestor algorithm assigns reads to taxa such that the taxonomical level of the assigned taxon reflects the level of conservation of the sequence. The software allows large data sets to be dissected without the need for assembly or the targeting of specific phylogenetic markers. It provides graphical and statistical output for comparing different data sets. The approach is applied to several data sets, including the Sargasso Sea data set, a recently published metagenomic data set sampled from a mammoth bone, and several complete microbial genomes. Also, simulations that evaluate the performance of the approach for different read lengths are presented.
Nonpharmacologic Treatment of Atrial Fibrillation in Elderly Persons
Authors: Willems Rik , Heidbüchel Hein
Published: January 2007

In recent years, new nonpharmacologic possibilities have emerged for the treatment of atrial fibrillation. The roles of surgery, radiofrequency catheter ablation, pacing, and atrial defibrillation in the treatment of atrial fibrillation are discussed. This text focuses on the interaction between different treatment modalities and the pathophysiologic mechanisms of atrial fibrillation and on the available data about the effectiveness in elderly persons.
Quality of Life in Older Patients With Atrial Fibrillation
Authors: Schron Eleanor B. , Jenkins Louise S.
Published: January 2007

This review summarizes what is known about quality of life (QOL) in older patients with atrial fibrillation (AF). The studies reviewed in this paper represent an increasingly broad repertoire of therapies for the treatment of AF and suggest that QOL in older patients does improve with treatment. The most dramatic improvements in QOL are noted in patients who are highly symptomatic and have poorer QOL at baseline. The data from studies where ablation and pacing therapy is used for treatment in patients with refractory AF vividly demonstrate this statement. There is also evidence of improvement in QOL in those with less severe symptoms, though it is extremely challenging to measure improvements in older patients who are asymptomatic (e.g., silent AF) or mildly symptomatic. Recommendations about new knowledge needed to optimize outcomes, particularly QOL, in patients with AF are based on these findings and the gaps in existing knowledge.
Treatment of Stable Angina: Medical and Invasive Therapy—Implications for the Elderly
Authors: Scheidt Stephen
Published: January 2007

Currently available therapies for chronic stable angina are reviewed. Revascularization, i.e., coronary artery bypass surgery and percutaneous transluminal coronary angioplasty, is summarized briefly, with short‐ and long‐term results summarized from several large registries and review articles. Advancing age is a risk factor for both coronary artery bypass surgery and percutaneous transluminal coronary angioplasty, but risks of coronary events are also higher without interventions in the elderly. In‐hospital mortality for coronary artery bypass surgery is about 8% for patients over age 80 in one large national registry and not much different in elective coronary artery bypass surgery in highly‐selected patients over age 90 in one institution. The few randomized trials of invasive vs. noninvasive therapy for stable coronary artery disease are described. Although patient numbers in available studies are too small to be conclusive as to which type of therapy is generally better, data appear to suggest that higher‐risk patients have better outcomes with revascularization. Methods of risk stratification are discussed. Finally, unusual therapies for angina are briefly noted, including transmyocardial revascularization, external counterpulsation, and gene therapy.
Ambulatory Hemodynamics in Patients With Chronic Heart Failure: Implications for Volume Management in Elderly Patients
Authors: Adamson Philip B.
Published: January 2007

Invasive hemodynamic assessment of patients with chronic heart failure is helpful in managing severe congestive symptoms associated with acute volume exacerbations that lead to hospitalizations. Information useful in guiding medication changes targeting control of left ventricular filling pressures can be obtained from measurements in the right ventricle. With the advent of implantable devices designed to treat heart failure, the logical next development is an implanted device that incorporates sophisticated monitoring systems capable of continuous acquisition of hemodynamic information over a long‐term period. An implantable hemodynamic monitoring system (Chronicle; Medtronic, Inc., Minneapolis, MN) is safe to implant and has a pressure sensor with proven long‐term reliability. Using transtelephonic data transmission and Internet‐based information systems, ambulatory hemodynamic monitoring may reduce the need for hospitalizations and overall health care utilization in patients with symptomatic heart failure. This approach may be especially helpful for elderly patients with chronic heart failure in whom overdiuresis or volume contraction may lead to gait instability and falls. Additionally, elderly patients with heart failure from primary diastolic dysfunction may have a very narrow therapeutic window of optimal volume that is difficult to assess by daily weights and physical examination alone. This hypothesis is currently being tested in a prospective randomized clinical trial.
Endovascular Therapies for Noncoronary Atherosclerosis in the Elderly: Supra‐Aortic Vessels and Thoracoabdominal Aorta Lesions
Authors: Rigatelli Gianluca , Zanchetta Mario
Published: January 2007

Due to the aging of the population and the fact that people are living longer, there are increasing numbers of older patients with noncoronary atherosclerosis. Carotid and subclavian arteries are often the first involved vessels in atherosclerosis, and thoracoabdominal aortic involvement is becoming even more frequent. New techniques, such as intra‐arterial thrombolysis, protection and thromboaspiration devices, and new stent graft designs are becoming available for percutaneous treatment of atherosclerosis in such vessels. In this review, the authors offer geriatric cardiologists an overview and an update of the most recent advances in techniques and results in the field of interventional treatments of atherosclerosis of supra‐aortic vessels and thoracoabdominal aorta in the elderly.
Choice of Pacemakers in Patients Aged 75 Years and Older: Ventricular Pacing Mode vs. Dual‐Chamber Pacing Mode
Authors: Vlietstra Ronald E. , Jahangir Arshad , Shen Win K.
Published: January 2007

Half of all pacemakers implanted in the United States are for patients aged 75 years and older. The expectations and needs of an older group are different from patients who are younger, yet it is only recently that different pacing mode benefits for elderly persons have been tested in clinical trials. Some of the results have been surprising and suggest new algorithms for management. Other issues are still on the threshold of investigation. These include pacing for heart failure in elderly patients and pacing combined with cardioverter‐defibrillator implantation.
JNC 7 Category and Risk of Cardiovascular Death in Men: Are There Differences by Age?
Authors: Bowman Thomas S. , Sesso Howard D. , Glynn Robert J. , Gaziano J. Michael
Published: January 2007

The authors evaluated the seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) blood pressure classification scheme on the risk of cardiovascular disease death and whether the association varies by age. In a prospective cohort study, 53,163 apparently healthy participants aged 39–85 years were followed for 5.7 years. The authors calculated relative risks and 95% confidence intervals for cardiovascular disease death, adjusting for major risk factors, then stratified by age (39–49, 50–59, 60–69, and 70–84 years) and performed a test of heterogeneity. Compared with men with normal blood pressure, those with prehypertension had a multivariate‐adjusted relative risk of 1.02 (95% confidence interval, 0.73–1.42) and those with hypertension had a relative risk of 1.54 (95% confidence interval, 1.08–2.19). There was no strong age‐related effect (Pinteraction, 0.22). In this large cohort, the JNC 7 categorization of prehypertension was not associated with a significantly increased risk of cardiovascular disease death, and there was no significant effect modification by age.
Heart Failure in the Oldest Patients: The Impact of Comorbid Conditions
Authors: Rich Michael W.
Published: January 2007

Heart failure (HF) is the leading cause of hospitalization in older adults; it is also an important cause of death and chronic disability. HF in the elderly differs in many respects from HF occurring during middle age; in particular, the diagnosis and treatment of HF in the elderly are often complicated by the presence of multiple cardiac and noncardiac comorbid conditions, many of which have important implications for the care of the older HF patient. This article reviews the effects of common noncardiac comorbidities on the management of HF in older adults and discusses the impact of noncardiac comorbid conditions on clinical outcomes in the geriatric HF patient.
Health‐Related Quality of Life Predicts Mortality in Older but Not Younger Patients Following Cardiac Surgery
Authors: Ho P. Michael , Masoudi Frederick A. , Peterson Pamela N. , Shroyer A. Laurie , McCarthy Martin , Grover Frederick L. , Hammermeister Karl E. , Rumsfeld John S.
Published: January 2007

The investigators assessed preoperative health‐related quality of life as a predictor of 6‐month mortality after cardiac surgery in older (65 years of age and older) vs. younger patients. Multivariable regression, stratified by age groups, was used to compare the association between preoperative Physical Component Summary and Mental Component Summary scores from the Short Form‐36 health status survey and mortality. In multivariable analyses of older patients, lower preoperative Physical Component Summary (odds ratio, 1.54; 95% confidence interval, 1.19–2.00; p=0.01) and Mental Component Summary (odds ratio, 1.26; 95% confidence interval, 1.06–1.49; p=0.03) scores were independently associated with mortality. In contrast, neither Physical Component Summary (p=0.82) nor Mental Component Summary (p=0.79) scores were associated with mortality in the younger subgroup. This study demonstrated that preoperative health status is an independent predictor of mortality following cardiac surgery in older but not younger patients. Preoperative patient self‐report of health status may be particularly useful in refining risk stratification and informing decision‐making before and following cardiac surgery in older patients.
New Diagnosis of Left Atrial Myxoma in a 93‐Year‐Old Woman
Authors: Kang Gurjaipal , Bhullar Parampal , Kang Manjot
Published: January 2007

A 93‐year‐old woman with a history of hypertension was noted to have a mass in the left atrium prolapsing partially through the mitral valve on a routine surface echocardiogram in 2002. A transesophageal echocardiogram was then performed revealing an irregular mass with an appearance of protruding fronds of tissue. The echogenicity of the mass was inhomogeneous with some areas of punctate calcification, and the mass was attached to the interatrial septum. The echocardiographic appearance of the mass was almost pathognomic of atrial myxoma, and this is the oldest patient yet to have been diagnosed with a probable myxoma. The patient did not want surgical removal of the mass. She is still asymptomatic at the age of 95 years.
Does Increased Arterial Stiffness Increase the Risk for Postural Hypotension?
Authors: Sengstock David , Vaitkevicius Peter V. , Supiano Mark A.
Published: January 2007

This study tests the hypothesis that increased arterial stiffness is associated with postural hypotension in older adults. Aortic pulse wave velocity and postural blood pressure (BP) response were assessed in 49 nondiabetic community‐dwelling normotensive (n=27) and hypertensive (n=22) older adults (mean age ± SD, 71 ±6.7 years) who were not receiving vasoactive medications. During the 5‐minute period of upright posture, 13 subjects had no change or a postural increase in systolic BP (SBP)( +10.6±14.6 mm Hg), 27 had a postural decrease of <20 mm Hg (−9.3±4.2 mm Hg), and nine had a postural decrease of >20 mm Hg (−29.1 ±8.1 mm Hg). Contrary to the proposed hypothesis, pulse wave velocity was significantly greater in subjects with a postural increase in SBP than in those with a postural decrease in SBP <20 mm Hg (10.2 ±0.68 m/sec vs. 8.3 ±0.37 m/sec; p=0.03) and tended to be greater than in those with a postural decrease in SBP >20 mm Hg (10.2 ±0.68 m/s vs. 8.5±0.73 m/sec; p=0.11). Higher pulse wave velocity was associated with a more positive postural SBP response at 1 minute (r=0.42; p=0.024), 3 minutes (r=0.38; p=0.007), and 5 minutes (r=0.45; p=0.001). This study does not support a relationship between arterial stiffness and a postural decrease in BP among healthy older adults; other age‐related factors regulating BP homeostasis likely play a greater role.
Titration of Carvedilol in Elderly Heart Failure Patients
Authors: Lawless Christine E. , Tamlyn Thomas , Shah Rajesh , Karim Fouzia Muhammed , Khan Erum , Creech Steve
Published: January 2007

Physicians may withhold β blockers from elderly heart failure patients based on perceptions of poor tolerability in this group. This study analyzed the success and tolerability of carvedilol titration in elderly (70 years and older) and younger (younger than 70) heart failure patients (n=360). The mean duration of titration was similar in both groups. The target carvedilol dosage (50 mg/d) was achieved by 55.3% and 62.0%, and a partial dose was achieved by 44.7% and 35.5% (p=0.028) of elderly and younger patients, respectively. The mean achieved dosage was lower in elderly patients than in younger patients (42.4±27.2 mg/d vs. 55.1 ±30.1 mg/d; p<0.0001), possibly due to significant between‐group differences in baseline characteristics or rates of target dose achieved. When adjusted for body weight, the mean achieved dose was similar in elderly (0.58±0.32 mg/kg/d) and younger (0.64±0.30 mg/kg/d) patients (p=nonsignificant). Adverse events were more frequent in the elderly but did not appear to significantly impact titration duration or carvedilol dose achieved when corrected for body weight. In conclusion, carvedilol should not be withheld from elderly heart failure patients based on perceptions of poor potential tolerability.
What Does the Medicare Prescription Drug Legislation Mean for the American Cardiologist?
Authors: Schwartz Janice B. , Redberg Rita F.
Published: January 2007

The Medicare Modernization Act of 2003 authorized the most sweeping changes to the Medicare and Medicaid programs since their inception in 1965. One key feature, a prescription drug benefit, will begin enrolling seniors in November 2005, and the benefit will begin in January 2006. This benefit will have complex and largely unknown effects on medication adherence in the elderly. It has a complex system of copayments and deductibles and subsidy eligibility requirements, as well as a “donut hole.” Drug coverage for people dually eligible for Medicare and Medicaid will change greatly. Medicare beneficiaries will have to choose from a large, bewildering choice of prescription plans and many will turn to their physicians for advice. This article details the background, benefits, and expected impact of all of these aspects of the new Medicare Part D prescription drug benefit.
The Implications of the Medicare Modernization Act for Dual Eligibles
Authors: Deshpande Monica
Published: January 2007

Medicare beneficiaries with incomes at or near the poverty level are also eligible for benefits provided by state Medicaid programs. The Medicare Modernization Act of 2003 details special provisions for these “dually eligible” individuals compared with other Medicare beneficiaries. Issues related to enrollment, benefits, and patient compliance are discussed, as well as challenges physicians face in caring for this vulnerable population.