bluuebunny/crossref_metadata_2025 huggingface dataset:
Spinal dorsal horn neuronal responses to myelinated versus unmyelinated heat nociceptors and their modulation by activation of the periaqueductal grey in the rat
Authors: McMullan Simon , Lumb Bridget M.
Published: August 2006

The aim of this study was to further understand the central processing of inputs arising from unmyelinated and myelinated nociceptors by (i) determining the response characteristics of Class 2 dorsal horn neurones to preferential activation of C‐ and A‐fibre heat nociceptors, and (ii) investigating the control exerted by the dorsolateral/lateral region of the midbrain periaqueductal grey (DL/L‐PAG) on C‐ and A‐fibre‐evoked responses of these neurones. The use of different rates of skin heating to preferentially activate unmyelinated (C‐fibre; 2.5°C s−1) versus myelinated (A‐fibre; 7.5°C s−1) heat nociceptors revealed that, in response to C‐nociceptor activation, Class 2 neurones encode well only over the first 5°C above threshold, and that at higher temperatures responses decline. In contrast, responses to A‐nociceptor activation are linear and encode skin temperature over more than 10°C, and almost certainly into the tissue‐damaging range. PAG stimulation raised thresholds and decreased significantly the magnitude of responses to A‐ and C‐nociceptor activation. However, differences were revealed in the effects of descending control on the relationships between skin temperature and neuronal firing rate; the linear relationship that occurred over the first 5°C of slow rates of skin heating was no longer evident, whereas that to fast rates of skin heating was maintained over the entire range, albeit shifted to the right. These data indicate that the sensori‐discriminative information conveyed in A‐fibre nociceptors is maintained and that the information from C‐nociceptors is lost in the presence of descending control from the DL/L‐PAG. The data are discussed in relation to the role of the DL/L‐PAG in mediating active coping strategies.
PirB Restricts Ocular-Dominance Plasticity in Visual Cortex
Authors: Syken Josh , GrandPre Tadzia , Kanold Patrick O. , Shatz Carla J.
Published: August 2006

Experience can alter synaptic connectivity throughout life, but the degree of plasticity present at each age is regulated by mechanisms that remain largely unknown. Here, we demonstrate that Paired-immunoglobulin–like receptor B (PirB), a major histocompatibility complex class I (MHCI) receptor, is expressed in subsets of neurons throughout the brain. Neuronal PirB protein is associated with synapses and forms complexes with the phosphatases Shp-1 and Shp-2. Soluble PirB fusion protein binds to cortical neurons in an MHCI-dependent manner. In mutant mice lacking functional PirB, cortical ocular-dominance plasticity is more robust at all ages. Thus, an MHCI receptor is expressed in central nervous system neurons and functions to limit the extent of experience-dependent plasticity in the visual cortex throughout life. PirB is also expressed in many other regions of the central nervous system, suggesting that it may function broadly to stabilize neural circuits.
Dok-7 Mutations Underlie a Neuromuscular Junction Synaptopathy
Authors: Beeson David , Higuchi Osamu , Palace Jackie , Cossins Judy , Spearman Hayley , Maxwell Susan , Newsom-Davis John , Burke Georgina , Fawcett Peter , Motomura Masakatsu , Müller Juliane S. , Lochmüller Hanns , Slater Clarke , Vincent Angela , Yamanashi Yuji
Published: August 2006

Congenital myasthenic syndromes (CMSs) are a group of inherited disorders of neuromuscular transmission characterized by fatigable muscle weakness. One major subgroup of patients shows a characteristic “limb girdle” pattern of muscle weakness, in which the muscles have small, simplified neuromuscular junctions but normal acetylcholine receptor and acetylcholinesterase function. We showed that recessive inheritance of mutations in Dok-7, which result in a defective structure of the neuromuscular junction, is a cause of CMS with proximal muscle weakness.
Anomalous Increase in Carbon Capacitance at Pore Sizes Less Than 1 Nanometer
Authors: Chmiola J. , Yushin G. , Gogotsi Y. , Portet C. , Simon P. , Taberna P. L.
Published: August 2006

Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. Studying the effect of the pore size on capacitance could potentially improve performance by maximizing the electrode surface area accessible to electrolyte ions, but until recently, no studies had addressed the lower size limit of accessible pores. Using carbide-derived carbon, we generated pores with average sizes from 0.6 to 2.25 nanometer and studied double-layer capacitance in an organic electrolyte. The results challenge the long-held axiom that pores smaller than the size of solvated electrolyte ions are incapable of contributing to charge storage.
Comparison of annexin II, p63 and α-methylacyl-CoA racemase immunoreactivity in prostatic tissue: a tissue microarray study
Authors: Stewart Jocelyn , Fleshner Neil , Cole Heather , Sweet Joan
Published: August 2006

Background:Current ancillary markers for diagnosis in prostate biopsies include p63 and α-methylacyl-CoA racemase (AMACR). Annexin II (ANXII), a calcium and phospholipid binding protein, is lost in prostate cancer.

Aims:To investigate ANXII expression in order to assess its utility as a novel diagnostic marker in comparison to p63 and AMACR.

Methods:Using immunohistochemistry on six tissue microarrays, ANXII, p63, and AMACR expression was analysed from 210 radical prostatectomy cases. Staining was evaluated in benign and atrophic glands, high-grade prostatic intraepithelial neoplasia (HGPIN), and prostatic adenocarcinoma. Separate scores were given for ANXII, AMACR and p63 expression.

Results:Diffuse cytoplasmic expression of ANXII correlated with p63 reactivity in basal cells. Benign glands were positive for ANXII in 286/292 cores (98%) and negative for AMACR in all 292 cores. HGPIN showed heterogeneous expression of AMACR and ANXII. A significantly larger proportion of HGPIN glands were correctly identified as ANXII negative than as positive for AMACR. ANXII loss in prostate cancer was found in 282/320 cores (88%) and correlated with positive AMACR expression (272/320 cores, 85%), which was not statistically significant. There was no statistically significant correlation between ANXII scores and the clinical parameters examined.

Conclusions:Immunohistochemical staining for ANXII is a consistent and reliable marker of prostatic neoplasia. The findings of this study suggest the potential utility of ANXII as a diagnostic aid in prostate cancer histopathology.
SUPERSYMMETRY, HOMOLOGY WITH TWISTED COEFFICIENTS AND n-DIMENSIONAL KNOTS
Authors: OGASA EIJI
Published: August 2006

In this paper, we study and construct a set of Witten indexes for K, where K is any n-dimensional knot in Sn+2 and n is any natural number. We form a supersymmetric quantum system for K by, first, constructing a set of functional spaces (spaces of fermionic (resp. bosonic) states) and a set of operators (supersymmetric infinitesimal transformations) in an explicit way. Our Witten indexes are topological invariant and they are nonzero in general. These indexes are zero if K is equivalent to a trivial knot. Besides, our Witten indexes restrict to the Alexander polynomials of n-knots, and one of the Alexander polynomials of K is nontrivial if any of the Witten indexes is nonzero. Our indexes are related to homology with twisted coefficients. Roughly speaking, these indexes posseses path-integral representation in the usual manner of supersymmetric theory.
NO INTERACTIONS FOR A COLLECTION OF WEYL GRAVITONS INTERMEDIATED BY A SCALAR FIELD
Authors: BIZDADEA C. , CIOROIANU E. M. , LUNGU A. C.
Published: August 2006

The cross-couplings among several Weyl gravitons (described in the free limit by a sum of linearized Weyl actions) in the presence of a scalar field are studied with the help of the deformation theory based on local BRST cohomology. Under the hypotheses of locality, smoothness of the interactions in the coupling constant, Poincaré invariance, (background) Lorentz invariance, and the preservation of the number of derivatives on each field, together with the supplementary assumption that the internal metric defined by the sum of Weyl Lagrangians is positively defined, we prove that there are no consistent cross-interactions among different Weyl gravitons in the presence of a scalar field. The couplings of a single Weyl graviton to a scalar field are also discussed.
ON THE ANOMALIES AND SCHWINGER TERMS IN NONCOMMUTATIVE GAUGE THEORIES
Authors: ARDALAN F. , ARFAEI H. , SADOOGHI N.
Published: August 2006

Invariant (nonplanar) anomaly of noncommutative QED is reexamined in this paper. It is found that just as in ordinary gauge theory UV regularization is needed to discover anomalies, in noncommutative case, in addition, an IR regularization is also required to exhibit the existence of invariant anomaly. Thus resolving the controversy in the value of invariant anomaly, an expression for the unintegrated anomaly is found. Schwinger terms of the current algebra of the theory are derived.
ACCELERATING UNIVERSE FROM EXTRA SPATIAL DIMENSION
Authors: CHATTERJEE S. , BANERJEE A. , ZHANG Y. Z.
Published: August 2006

We present a simple higher dimensional FRW-type of model where the acceleration is apparently caused by the presence of the extra dimensions. Assuming an ansatz in the form of the deceleration parameter, we get a class of solutions some of which shows the desirable feature of dimensional reduction as well as reasonably good physical properties of matter. Interestingly we do not have to invoke an extraneous scalar field or a cosmological constant to account for this acceleration. One argues that the terms containing the higher dimensional metric coefficients produces an extra negative pressure that apparently drives the inflation of the 4D space with an accelerating phase. It is further found that in line with the physical requirements our model admits of a decelerating phase in the early era along with an accelerating phase at present. Further the models asymptotically mimic a steady-state-type of universe although it starts from a big-bang-type of singularity. Correspondence to Wesson's induced matter theory is also briefly discussed and, in line with it, it is argued that the terms containing the higher dimensional metric coefficients apparently creates a negative pressure which drives the inflation of the 3-space with an accelerating phase.
EDUCING THE VOLUME OUT OF THE PHASE-SPACE BOUNDARY
Authors: COBAS MANUEL A. , OSORIO M. A. R. , SUÁREZ MARÍA
Published: August 2006

We explicitly show that, in a system with T-duality symmetry, the configuration space volume degrees of freedom may hide on the surface boundary of the region of accessible states with energy lower than a fixed value. This means that, when taking the decompactification limit (big volume limit), a number of accessible states proportional to the volume is recovered even if no volume dependence appears when energy is high enough. All this behavior is contained in the exact way of computing sums by making integrals. We will also show how the decompactification limit for the gas of strings can be defined from a microcanonical description at finite volume.
MIRROR MATTER ADMIXTURES IN KS→γγ
Authors: SÁNCHEZ-COLÓN G. , GARCÍA A.
Published: August 2006

The latest measurement of the KS→γγ branching ratio clearly shows an enhancement over the current theoretical prediction. As in other K and B meson decays, this invites to consider the possibility of the contribution of new physics. We study a particular form of the latter, which may be refered to as manifest mirror symmetry. The experimental data are described using previously determined values for the mixing angles of the admixtures of mirror matter in ordinary hadrons and by assuming that for π0, η, η′ → γγ, the mirror decay amplitudes have the same magnitudes as their ordinary counterparts.
THE STOYANOVSKY–RIBAULT–TESCHNER MAP AND STRING SCATTERING AMPLITUDES
Authors: GIRIBET GASTON , NAKAYAMA YU
Published: August 2006

Recently, Ribault and Teschner pointed out the existence of a one-to-one correspondence between N-point correlation functions for the SL (2,ℂ)k/ SU (2) WZNW model on the sphere and certain set of 2N-2-point correlation functions in Liouville field theory. This result is based on a seminal work by Stoyanovsky. Here, we discuss the implications of this correspondence focusing on its application to string theory on curved backgrounds. For instance, we analyze how the divergences corresponding to worldsheet instantons in AdS3 can be understood as arising from the insertion of the dual screening operator in the Liouville theory side. We also study the pole structure of N-point functions in the 2D Euclidean black hole and its holographic meaning in terms of the Little String Theory. This enables us to interpret the correspondence between CFT's as encoding a LSZ-type reduction procedure. Furthermore, we discuss the scattering amplitudes violating the winding number conservation in those backgrounds and provide a formula connecting such amplitudes with observables in Liouville field theory. Finally, we study the WZNW correlation functions in the limit k → 0 and show that, at the point k = 0, the Stoyanovsky–Ribault–Teschner dictionary turns out to be in agreement with the FZZ conjecture at a particular point of the space of parameters where the Liouville central charge becomes cL = -2. This result makes contact with recent studies on the dynamical tachyon condensation in closed string theory.
EXTENSION OF THE SHIRAFUJI MODEL FOR MASSIVE PARTICLES WITH SPIN
Authors: FEDORUK SERGEY , FRYDRYSZAK ANDRZEJ , LUKIERSKI JERZY , MIQUEL-ESPANYA CÈSAR
Published: August 2006

We extend the Shirafuji model for massless particles with primary space–time coordinates and composite four-momenta to a model for massive particles with spin and electric charge. The primary variables in the model are the space–time four-vector, four scalars describing spin and charge degrees of freedom as well as a pair of Weyl spinors. The geometric description proposed in this paper provides an intermediate step between the free purely twistorial model in two-twistor space in which both space–time and four-momenta vectors are composite, and the standard particle model, where both space–time and four-momenta vectors are elementary. We quantize the model and find explicitly the first-quantized wave functions describing relativistic particles with mass, spin and electric charge. The space–time coordinates in the model are not commutative; this leads to a wave function that depends only on one covariant projection of the space–time four-vector (covariantized time coordinate) defining plane wave solutions.
J/ψ, ψ′ AND ϒ PRODUCTION AT HADRON COLLIDERS: A REVIEW
Authors: LANSBERG JEAN-PHILIPPE
Published: August 2006

We give an overview of the present status of knowledge of the production of J/ψ, ψ′ and ϒ in high-energy hadron collisions. We first present two early models, namely the Color-Singlet Model (CSM) and the Color-Evaporation Model (CEM). The first is the natural application of pQCD to quarkonium production and has been shown to fail dramatically to describe experimental data, the second is its phenomenological counterpart and was introduced in the spirit of the quark–hadron duality in the late 1970's. Then, we expose the most recent experimental measurements of J/ψ, ψ′ and ϒ prompt and direct production at nonzero pTfrom two high-energy hadron colliders, the Tevatron and RHIC. In a third part, we review six contemporary models describing J/ψ, ψ′ and ϒ production at nonzero pT.
CONSTRAINING NEW MODELS WITH PRECISION ELECTROWEAK DATA
Authors: CHEN MU-CHUN , DAWSON SALLY , KRUPOVNICKAS TADAS
Published: August 2006

Electroweak precision data have been extensively used to constrain models containing physics beyond that of the Standard Model (SM). When the model contains Higgs scalars in representations other than singlets or doublets, and hence ρ≠1 at tree-level, a correct renormalization scheme requires more inputs than the three commonly used for the SM case. In such cases, the one-loop electroweak results cannot be split into a SM contribution plus a piece which vanishes as the scale of new physics becomes much larger than MW. We illustrate our results by presenting the dependence of MW on the top-quark mass in a model with a Higgs triplet and in the SU (2)L × SU (2)R left–right symmetric model. In these models, the allowed range for the lightest neutral Higgs mass can be as large as a few TeV.
EINSTEIN'S FLUCTUATION FORMULA: A HISTORICAL OVERVIEW
Authors: VARRÓ SÁNDOR
Published: August 2006

A historical overview is given on the basic results which appeared by the year 1926 concerning Einstein's fluctuation formula of black-body radiation, in the context of light-quanta and wave-particle duality. On the basis of the original publications – from Planck's derivation of the black-body spectrum and Einstein's introduction of the photons up to the results of Born, Heisenberg and Jordan on the quantization of a continuum – a comparative study is presented on the first lines of thoughts that led to the concept of quanta. The nature of the particle-like fluctuations and the wave-like fluctuations are analysed by using several approaches. With the help of classical probability theory, it is shown that the infinite divisibility of the Bose distribution leads to the new concept of classical "poissonian photo-multiplets" or to the "binary photo-multiplets" of fermionic character. As an application, Einstein's fluctuation formula is derived as a sum of fermion type fluctuations of the binary photo-multiplets.
ELECTRON TRANSFER RATE UNIFORMLY VALID FROM NONADIABATIC TO ADIABATIC REGIME BASED ON THE ZHU–NAKAMURA THEORY
Authors: ZHAO YI , NAKAMURA HIROKI
Published: August 2006

On the basis of the generalized nonadiabatic transition state theory recently introduced to remedy the crucial deficiencies of the conventional transition state theory, we have presented a new formula for electron transfer rate, which can cover the whole range from adiabatic to nonadiabatic regime in the absence of solvent dynamics control. The rate is expressed as a product of the well-known Marcus theory and a new coefficient that represents the effects of nonadiabatic transition at the crossing seam surface. The numerical comparisons are performed with different approaches and the present approach shows an excellent agreement with the quantum mechanical numerical solutions from weak to strong electronic coupling. The explanation of the experimental data of Nelsen et al. manifests the potential applicability of the present theory.
THE PARTIAL POTENTIAL ENERGY SURFACE AND SCATTERING RESONANCE STATE OF THE STATE-TO-STATE REACTION Br + HBr(v) → BrH(v′) + Br
Authors: WANG HUAYANG , SUN XIAOMIN , FENG DACHENG , CAI ZHENGTING
Published: August 2006

In this paper, the partial potential energy surface (PPESs) of the Br + HBr and Br - + HBr systems including the minimum energy path and the vibrational potential curves were constructed at MP2/6-311++G** level, based on the conception and constructing approach of the PPESs previously proposed. These results obtained from the PPESs were compared with those from the high resolved threshold photodetachment spectrum of the BrHBr - anion measured by Neumark et al., J Phys Chem94, 1377–1388, 1990. On the basis of the PPESs, the scattering resonance states of the Br + HBr (v) → BrH (v′) + Br state-to-state reaction were studied and the satisfactory results were obtained. Subsequently, we calculated the width and lifetime of the resonance states in this reaction by the one-dimensional square potential well model, and obtained some results consistent to the experiments.
COOPERATIVE MOLECULAR CHIRALITY
Authors: SHAO JIUSHU
Published: August 2006

The cooperative chirality for an ensemble of molecules is analyzed with the Dicke model in which the chiral molecules are described by the two-state systems and their interactions are simply characterized by the couplings to external fields due to their collective motion. It is shown that when the temperature is sufficiently low, a phase transition from the achiral state to the chiral one is possible, which is concomitant with emergence of the superradiance. Some physical properties such as the chiralization are calculated in the thermodynamic limit. The results are used to clarify the localization of pyramidal molecules.
ABEEM/MM-BASED PAIR POTENTIAL FOR MOLECULAR DYNAMICS SIMULATION OF Fe2+(aq) AND Fe3+(aq)
Authors: LI XIN , YANG ZHONG-ZHI
Published: August 2006

On the basis of atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM), we have constructed the effective Fe 2+ and Fe 3+ ion-water potential by fitting to ab initio structures and binding energies for ionic clusters, where Fe 2+ and Fe 3+ ions are in their high spin state. We then apply the ion-water interaction potential in combination with the ABEEM-7P water model to molecular dynamic simulations of single-ion Fe 2+( aq ) and Fe 3+( aq ) solutions, managing to reproduce many experimental, structural and dynamical properties of the solutions. The effects of ionic charges on structural and dynamical properties of water molecules in the hydration shells are discussed.
NEW FORMULATION FOR NON-EQUILIBRIUM SOLVATION: SPECTRAL SHIFTS AND CAVITY RADII OF 6-PROPANOYL-2-(N,N-DIMETHYLAMINO) NAPHTHALENE AND 4-(N,N-DIMETHYLAMINO) BENZONITRILE
Authors: HUANG YAO , LI XIANG-YUAN , FU KE-XIANG , ZHU QUAN
Published: August 2006

In the present work, the new formulations describing spectral shifts by the authors have been introduced and employed to investigate two dye molecules, 6-propanoyl-2-(N,N-dimethylamino) naphthalene and 4-(N,N-dimethylamino) benzonitrile. From the viewpoints of the authors, the cavity radii were overestimated owing to the errors existing in the traditional models. Slightly differing from the results by other authors in the past, this work fits the cavity radii to the values of ~4.5 Å for 6-propanoyl-2-(N,N-dimethylamino) naphthalene and ~3.2 Å for 4-(N,N-dimethylamino) benzonitrile. In the fittings, both point dipole approximation and multipole expansion methods are employed. The calculations of the excited states are performed by means of the time-dependent density functional theory. Comparing the fitted cavity radii from the experimental spectra with those estimated from the molecular volumes by some well-known procedures such as COSMO and PCM, we find that the new formulations give fairly satisfactory results. By taking an atomic ion as an example, the authors argue that the Onsager radii recommended by some popular procedures are greatly exaggerated. The cavity radius derived simply from the volume encompassed by the solvent-accessible surface, without any addition of other parts, is suggested for application.
ELECTRONIC EXCITATIONS OF GREEN FLUORESCENT PROTEINS: MODELING SOLVATOCHROMATIC SHIFTS OF CHROMOPHORE MODEL COMPOUNDS IN SOLUTIONS
Authors: ZHANG LIDONG , XIE DAIQIAN , ZENG JUN
Published: August 2006

Green fluorescent protein (GFP) is a spontaneously fluorescent protein due to its p-hydroxylbenzylideneimidazolidinone chromophore. In this work, we have investigated the electronic structures, liquid structures, and solvent shifts of the GFP chromophore model compounds 4′-hydroxylbenzylidene-2,3-dimethylimidazolin-5-one (HBDI) and 4′-hydroxylbenzylidene-2-methyl-imidazoin-5-one-3-acetate (HBMIA) in NaOH /aqueous solutions, in which both compounds are protonated at anionic state. The electronic structure calculations predict that both model compounds could adopt both cis and trans conformations in solutions. Moreover, liquid simulations elucidate an extensive well-defined hydrogen-bonding network between the solvent and the solute in the ground state. Furthermore, solvent shifts calculations indicate that contributions from the specific solute-solvent hydrogen-bonding interactions are negligible for the solvatochromatic shifts observed in the absorption spectrum of the model compounds in solutions; rather, the solvent shifts are dominated by the dipolar solvation in which both permanent charge–charge interactions and many-body polarizations contribute significantly. Self-Consistent Reaction-Field (SCRF) approach could be the efficient method for studying the unusual optical properties of the GFP chromophore in solutions and proteins.
THEORETICAL DESIGN OF LIGHT-EMITTING POLYMERS — SUBSTITUTION EFFECTS OF EXCITED STATE ORDERING OF POLYDIACETYLENE AND POLYACETYLENE
Authors: CHEN LIPING , HOU XINJUAN , ZHU LINGYUN , YIN SHIWEI , SHUAI Z.
Published: August 2006

The excited states structure, essential in determining the light-emitting properties, in a correlated electron system behaves differently from the one-electron system. Previous investigations show that upon proper chemical substitution, the non-emissive polyacetylene (PA) can be designed to be strongly light-emitting materials. On the basis of the correlated quantum chemical calculations within the INDO/EOM-CCSD approach, we systematically studied both the pristine and substituted polydiacetylene (PDA) about the low-lying excited states orderings. PDA possesses high mobility, but it is non-emissive. We predict that it is impossible to cause PDA to be light-emitting. From these numerical results, we propose a simple and practical rule to design conjugated light-emitting polymers, which require only a molecular orbital calculation instead of sophisticated correlated calculations. This rule is derived from physical pictures of correlated electron model, and is found to be in agreement with the existing experiments for various substituted PA and poly(p-phenylenebutadiynylene) (PPPB).
EFFECT OF SUBSTITUTION ON THE STRUCTURES AND OPTOELECTRONIC PROPERTIES OF MERCURY-CONTAINING DIETHYNYLFLUORENE
Authors: LIAO YI , SHI LI-LI , FENG JI-KANG , YANG LI , REN AI-MIN
Published: August 2006

We report on a quantum-chemical study of the electronic and optical properties of Mercury(II) complexes HgTFT (1) and its electron-withdrawing substitutent HgTFOT (2), HgTFCNT (3) [where TFT = diethynylfluorenyl, TFOT = diethynylfluorenone and TFCNT = diethynyl-(9-(dicyanomethylene)fluorene)]. Our theoretical calculations indicate that the substitution of - CO , - C ( CN )2 for - CH in HgTFT significantly decreases the bond length alternation and increases the electron affinity, which would qualify HgTFOT 2 and HgTFCNT 3, especially 3, as candidates for n-type electrical conductors. The vertical transition energy associated with the low-lying excited state has been examined within the time-dependent DFT formalism for mercury diethynylfluorenyl derivatives. It is found that the electron-withdrawing substitutions lead to remarkable red shift in transition energy and alter the corresponding charge transfer manner.
COMPUTATION OF LARGE SYSTEMS WITH AN ECONOMIC BASIS SET: AB INITIO CALCULATIONS OF BIOLOGICAL NUCLEIC ACID BASE PAIRS
Authors: FAN WENJIE , ZHANG RUIQIN
Published: August 2006

We show that an economic basis set, in which the polarization functions are considered only for oxygen and nitrogen atoms of strong electronegativity, can be used to determine reliable structures of nucleic acid base pairs. Mulliken charge analysis and the HOMO-LUMO gap in single-point energy calculations using standard basis sets on the geometric structures optimized with the economic basis set found reasonable agreements with the ones of standard calculations. This study is expected to provide a general guideline for basis set selection in the computation of large biological systems being performed with considerable high accuracy, using a low cost computation resource.
TOWARD A BLUEPRINT FOR β-PRIMEVEROSIDASE FROM TEA LEAVES STRUCTURE/FUNCTION PROPERTIES: HOMOLOGY MODELING STUDY
Authors: HAN WEI-WEI , LI ZE-SHENG , ZHENG QING-CHUAN , SUN CHIA-CHUNG
Published: August 2006

By means of the Homology modeling and the known structure of cyannogenic β-glycosidase from white clover (1CBG, EC 3.2.1.21), we construct a 3D model of the β-primeverosidase (EC 3.2.1.149) and search for the binding site of substrate. The 3D model is then refined by using molecular mechanics (optimization and molecular dynamics) simulation. Finally, the refined model is further assessed by Profile-3D and PROCHECK, and the results showed that the final model is reliable. Furthermore, the docking of the substrates into the active site of the protein indicates that β-primeverosidase is able to hydrolyze β-primeverosides, but not act on 2-phenylethyl β-D-glucopyranoside. These results suggest that β-primeverosidase shows broad substrate specificity with respect to the disaccharide glycon moiety (subsite -2). This is consistent with the experimental observation. Thr271 and Thr415 play important roles in subsite -2 of β-primeverosidase. Our results may be helpful for further experimental investigations.
THEORETICAL STUDY TOWARD UNDERSTANDING THE CATALYTIC MECHANISM OF PYRUVATE DEHYDROGENASE MULTIENZYME COMPLEX E1 COMPONENT
Authors: WANG JIANYI , LI SHUHUA
Published: August 2006

Density functional calculations are employed to investigate the mechanisms of all elementary reaction steps involved in the catalytic reaction of pyruvate dehydrogenase multienzyme complex E1 (PDHc E1). We have obtained the free energy profiles for all reaction steps, and have demonstrated the importance of some key residues (Glu571, Glu522, His640 and a water molecule) near the active center in each individual step. Glu571 plays an essential role in the ylide formation, the addition of pyruvate, and the release of acetaldehyde. Glu522 helps to orientate the carboxyl of pyruvate in favor of the addition reaction of pyruvate. The protonation of the enamine is found to proceed through a concerted double proton transfer transition state involving His640 and a water molecule. All reaction steps are calculated to be thermodynamically favorable, except for the release of acetaldehyde which is slightly endothermic. The protonation of the enamine is a rate-limiting step with a barrier of 24.5 kcal/mol in the protein environment. Comparing the energetics of the catalytic reaction in PDHc E1 with that in PDC, we find that the relative orientation of some conserved residues and the conformation of the cofactor ThDP have a significant impact on the reaction rates of individual steps.
CHARACTERIZATIONS OF NOVEL BINUCLEAR ALKALINE-EARTH METAL COMPOUNDS: M2(ηn-N5)2 (M=Be AND Mg, n = 1, 2; M=Ca, n = 2, 5)
Authors: ZHANG XIU HUI , LI SE , LI QIAN SHU
Published: August 2006

The first structural characterization for the twelve binuclear alkaline-earth metal compounds M 2(ηn- N 5)2 ( M=Be , Mg ; n = 1, 2) and Ca 2(ηn- N 5)2(n = 2, 5) have been optimized with local energy minimum by density functional theory (DFT). The most energetically favored structures in M 2(ηn- N 5)2( M=Be , Mg , Ca ) are of D2d symmetry Be 2(η1- N 5)2, Mg 2(η2- N 5)2 and Ca 2(η2- N 5)2 and the metal–metal distances are 2.03 Å for Be-Be , 2.77 Å for Mg-Mg and 3.72 Å for Ca-Ca , which are significantly shorter than the experiment values of weakly bound bare diatomic Be 2, Mg 2 and Ca 2.1,2 Ca 2(η5- N 5)2 (D5d or D5h) is the only stable specie with sandwiched structure, bearing an even shorter Ca-Ca distance of 3.66 Å, and lying 24 kcal/mol higher in energy than the D2d structure. The dissociation enthalpies of the twelve M 2(ηn- N 5)2( M=Be , Mg , Ca ) to two M (ηn- N 5) fragments are predicted to be 72.6–73.1, 41.2–43.8, and 27.4–29.7 kcal/mol, respectively, implying a substantial metal–metal bonding. Natural bond orbital (NBO) analysis suggests that metal–metal bonds are of σ-bond. The natural charge of the alkali earth metal atom in the twelve M 2(ηn- N 5)2 species is larger than +0.88, which is consistent with the +1 oxidation state of the metal atoms. Nucleus-independent chemical shift (NICS) values confirm that the planar [Formula: see text] exhibits characteristics of aromaticity for these M 2(ηn- N 5)2 species.
DENSITY FUNCTIONAL THEORY STUDY OF THE INTERACTIONS BETWEEN AN IRON ATOM AND A DINITROGEN MOLECULE I: THE END-ON LINEAR AND BENT STRUCTURES
Authors: WANG CHAO-JIE , XU XIN
Published: August 2006

Density functional theory calculations at the level of B3LYP have been performed to systematically study the linear and bent structures of the end-on FeN 2. The linear structure was found to be more stable than the bent one and the lowest bonding state was concluded to be a linear 13Σ-. The geometric structure and vibrational frequency for each electronic state were reported. The bonding properties were analyzed in terms of natural electronic configurations, natural charges, and spin densities, etc. The results revealed that the interaction between N 2 and the ground state Fe atom is a weak van der Waals interaction; covalently bonded FeN 2 may be formed by using the excited states of Fe atom where the N 2 unit remains almost intact.
CHARGE AND SPIN ORDERING IN Na0.5CoO2 FROM THE HYBRID DENSITY FUNCTIONAL STUDY
Authors: CHEN ZHAOYING , XIANG HONGJUN , LI ZHENYU , YANG JINLONG
Published: August 2006

The electronic and magnetic properties of Na 0.5 CoO 2 are studied within the hybrid density functional methods. A charge-ordered antiferromagnetic insulating state is unambiguously identified as the ground state of Na 0.5 CoO 2. The electronic structures of the ground state are very similar to our previous GGA + U (U = 4 eV ) results, except for the large band gap discrepancy. Our results suggest that the hybrid density functional methods capture the main physics of the strong correlation in Na x CoO 2 system.
The Supernova–Gamma-Ray Burst Connection
Authors: Woosley S.E. , Bloom J.S.
Published: August 2006

Observations show that at least some gamma-ray bursts (GRBs) happen simultaneously with core-collapse supernovae (SNe), thus linking by a common thread nature's two grandest explosions. We review here the growing evidence for and theoretical implications of this association, and conclude that most long-duration soft-spectrum GRBs are accompanied by massive stellar explosions (GRB-SNe). The kinetic energy and luminosity of well-studied GRB-SNe appear to be greater than those of ordinary SNe, but evidence exists, even in a limited sample, for considerable diversity. The existing sample also suggests that most of the energy in the explosion is contained in nonrelativistic ejecta (producing the supernova) rather than in the relativistic jets responsible for making the burst and its afterglow. Neither all SNe, nor even all SNe of Type Ibc produce GRBs. The degree of differential rotation in the collapsing iron core of massive stars when they die may be what makes the difference.
Absolute Magnitude Calibrations of Population I and II Cepheids and Other Pulsating Variables in the Instability Strip of the Hertzsprung-Russell Diagram
Authors: Sandage Allan , Tammann Gustav A.
Published: August 2006

The status of the absolute magnitude calibrations is reviewed for the long period Cepheids of population I and II, RR Lyrae stars, evolved “above horizontal branch” (AHB1) variables (periods 0.8 to 3 days), dwarf Cepheids of both populations (the Delta Scuti and SX Phoenicus variables), and the anomalous Cepheids (AC). Evidence shows that the period-color and period-luminosity (P-L) relations for population I Cepheids in the Galaxy and in the Large and Small Magellanic Clouds have different slopes and zero points. This greatly complicates use of Cepheids for the extragalactic distance scale. Strategies are discussed to patch the problem. A consensus exists for the long distance scale for RR Lyrae stars whose calibrations favor 〈MV(RR)〉 = 0.52 at [Fe/H] = −1.5. Exceptions exist for “second parameter” clusters where the variation of the morphology of the horizontal branch with metallicity is anomalous, the most blatant being NGC 6388 and NGC 6441. The status and calibrations of ABH1 and AC show that different evolutionary paths and masses explain the difference P-L relations for them. AC appear predominantly in the dwarf spheroidal galaxies, but are almost absent in Galactic globular clusters. AHB1 stars are absent in dwarf spheroidals but are present in globular clusters. The difference may be used to study the formation of the remote Galactic halo if it is partially made by tidal disruption of companion dwarf spheroidals.
Stellar Population Diagnostics of Elliptical Galaxy Formation
Authors: Renzini Alvio
Published: August 2006

Major progress has been achieved in recent years in mapping the properties of passively-evolving, early-type galaxies (ETG) from the local universe all the way to redshift ∼2. Here, age and metallicity estimates for local cluster and field ETGs are reviewed as based on color-magnitude, color-σ, and fundamental plane relations, as well as on spectral-line indices diagnostics. The results of applying the same tools at high redshifts are then discussed, and their consistency with the low-redshift results is assessed. Most low- as well as high-redshift (z ∼ 1) observations consistently indicate (a) a formation redshift z ≳ 3 for the bulk of stars in cluster ETGs, with their counterparts in low-density environments being on average ∼1–2 Gyr younger, i.e., formed at z ≳ 1.5–2; (b) the duration of the major star-formation phase anticorrelates with galaxy mass, and the oldest stellar populations are found in the most massive galaxies. With increasing redshift there is evidence for a decrease in the number density of ETGs, especially of the less massive ones, whereas existing data appear to suggest that most of the most-massive ETGs were already fully assembled at z ∼ 1. Beyond this redshift, the space density of ETGs starts dropping significantly, and as ETGs disappear, a population of massive, strongly clustered, starburst galaxies progressively becomes more and more prominent, which makes them the likely progenitors to ETGs.
Observational Constraints on Cosmic Reionization
Authors: Fan Xiaohui , Carilli C.L. , Keating B.
Published: August 2006

Observations have set the first constraints on the epoch of reionization (EoR), corresponding to the formation epoch of the first luminous objects. Studies of Gunn-Peterson (GP) absorption indicate a rapid increase in the neutral fraction of the intergalactic medium (IGM) from xHI< 10−4at z ≤ 5.5, to xHI> 10−3, perhaps up to 0.1, at z∼6, while the large scale polarization of the cosmic microwave background (CMB) implies a significant ionization fraction extending to higher redshifts, z∼11 ± 3. These results, as well as observations of galaxy populations, suggest that reionization is a process that begins as early as z∼14, and ends with the “percolation” phase at z∼6 to 8. Low luminosity star-forming galaxies are likely the dominant sources of reionizing photons. Future low-frequency radio telescopes will make direct measurements of HI 21-cm emission from the neutral IGM during the EoR, and measurements of secondary CMB temperature anisotropy will provide details of the dynamics of the reionized IGM.
Populations of X-Ray Sources in Galaxies
Authors: Fabbiano G.
Published: August 2006

Today's sensitive X-ray observations allow the study of populations of X-ray binaries in galaxies as distant as 20–30 Mpc. Photometric diagrams and luminosity functions applied to these populations provide a direct probe of the evolved binary component of different stellar populations. The study of the X-ray populations of E and S0 galaxies has revamped the debate on the formation and evolution of low-mass X-ray binaries (LMXBs) and on the role of globular clusters in these processes. Though overall stellar mass drives the amount of X-ray binaries in old stellar populations, the amount of sources in star-forming galaxies is related to the star-formation rate. Short-lived, luminous, high-mass X-ray binaries (HMXBs) dominate these young X-ray populations. The most luminous sources in these systems are the debated ultraluminous X-ray sources (ULXs). Observations of the deep X-ray sky, and comparison with deep optical surveys, are providing the first evidence of the X-ray evolution of galaxies.
The Evolution and Structure of Pulsar Wind Nebulae
Authors: Gaensler Bryan M. , Slane Patrick O.
Published: August 2006

Pulsars steadily dissipate their rotational energy via relativistic winds. Confinement of these outflows generates luminous pulsar wind nebulae, seen across the electromagnetic spectrum in synchrotron and inverse Compton emission and in optical emission lines when they shock the surrounding medium. These sources act as important probes of relativistic shocks, particle acceleration, and interstellar gas. We review the many recent advances in the study of pulsar wind nebulae, with particular focus on the evolutionary stages through which these objects progress as they expand into their surroundings, and on morphological structures within these nebulae that directly trace the physical processes of particle acceleration and outflow. We conclude by considering some exciting new probes of pulsar wind nebulae, including the study of TeV gamma-ray emission from these sources, and observations of pulsar winds in close binary systems.
Acute Effects of Estrogen on Neuronal Physiology
Authors: Woolley Catherine S.
Published: August 2006

It has been known for more than 30 years that estrogen can alter the intrinsic and synaptic physiology of neurons within minutes. The physiological significance of these acute effects has been unclear, however, because some effects require higher concentrations of estrogen than are detected in plasma, and because estrogen secreted by the ovary rises and falls over a time course of days, not minutes. These concerns may be answered by new research demonstrating that estrogen is produced at high levels within the brain itself, and that production of estrogen in the brain may be regulated by neuronal activity. Additionally, recent studies indicate that classical estrogen receptor proteins are found not only in the nucleus where they regulate gene expression but also at extranuclear sites, including at synapses. These findings, together with evidence for new types of extranuclear estrogen receptors, suggest that estrogen might act directly at synapses to activate second messenger signaling, thereby rapidly altering neuronal excitability, synaptic transmission, and/or synaptic plasticity.
Aldosterone impairs baroreflex sensitivity in healthy adults
Authors: Monahan Kevin D. , Leuenberger Urs A. , Ray Chester A.
Published: August 2006

Animal studies suggest that acute and chronic aldosterone administration impairs baroreceptor/baroreflex responses. We tested the hypothesis that aldosterone impairs baroreflex control of cardiac period [cardiovagal baroreflex sensitivity (BRS)] and muscle sympathetic nerve activity (MSNA, sympathetic BRS) in humans. Twenty-six young (25 ± 1 yr old, mean ± SE) adults were examined in this study. BRS was determined by using the modified Oxford technique (bolus infusion of nitroprusside, followed 60 s later by bolus infusion of phenylephrine) in triplicate before (Pre) and 30-min after (Post) beginning aldosterone (experimental, 12 pmol·kg−1·min−1; n = 10 subjects) or saline infusion (control; n = 10). BRS was quantified from the R-R interval-systolic blood pressure (BP) (cardiovagal BRS) and MSNA-diastolic BP (sympathetic BRS) relations. Aldosterone infusion increased serum aldosterone levels approximately fourfold ( P < 0.05) and decreased ( P < 0.05) cardiovagal (19.0 ± 2.3 vs. 15.6 ± 1.7 ms/mmHg Pre and Post, respectively) and sympathetic BRS [−4.4 ± 0.4 vs. −3.0 ± 0.4 arbitrary units (AU)·beat−1·mmHg−1]. In contrast, neither cardiovagal (19.3 ± 3.3 vs. 20.2 ± 3.3 ms/mmHg) nor sympathetic BRS (−3.8 ± 0.5 vs. −3.6 ± 0.5 AU·beat−1·mmHg−1) were altered (Pre vs. Post) in the control group. BP, heart rate, and MSNA at rest were similar in experimental and control subjects before and after the intervention. Additionally, neural and cardiovascular responses to a cold pressor test and isometric handgrip to fatigue were unaffected by aldosterone infusion ( n = 6 subjects). These data provide direct experimental support for the concept that aldosterone impairs baroreflex function (cardiovagal and sympathetic BRS) in humans. Therefore, aldosterone may be an important determinant/modulator of baroreflex function in humans.
Effects of sex and estrogen on myosin COOH-terminal isoforms and contractility in rat aorta
Authors: Paul Richard J. , Bowman Peggy Sue , Johnson Jason , Martin Anne F.
Published: August 2006

We reported that estrogen treatment of ovariectomized rats increased uterine smooth muscle contractility and the ratio of the COOH-terminal myosin heavy chain isoform SM1 (204 kDa) and SM2 [200 kDa; Hewett TE, Martin AF, Paul RJ. J Physiol (Lond) 460: 351–364, 1993]. We extended this model to study sex and estrogen effects on vascular contractility. Experimental groups included 10- to 14-wk-old male (M), female (F), ovariectomized female (OF), and OF treated with estrogen (OF&E) for 7 days with a subcutaneous pellet delivery system, resulting in 17β-estradiol of 85 (OF&E) vs. 5 (OF or M) pg/ml. The SM1-to-SM2 ratio increased from 1.8 to 2.6 in thoracic aorta, similar to uterine muscle. Isometric force was measured in 5-mm segments of intact and endothelium-denuded (−endo) aorta. With KCl, the maximum forces were in the order OF ≈ M > OF&E, and ED50OF&E > OF ≈ M. Differences in ED50with estrogen persisted after endothelial denudation. The decreased force in −endo OF aorta was not seen in OF&E, suggesting that estrogen altered an endothelium-dependent effect. No differences in maximum forces were noted with norepinephrine: ED50OF > OF&E > M. Estrogen treatment, in contrast to KCl, increased sensitivity. Endothelial denudation increased sensitivity but reduced the differences between groups. With ACh relaxation, males were more sensitive than females, and estrogen had no effect. In the abdominal aorta, there were no changes in SM1/SM2 with 17β-estradiol, and differences in contractility were blunted. In summary, estrogen treatment decreased responses to KCl but increased sensitivity to norepinephrine; male rats always demonstrated the highest contractility. An increase in the COOH-terminal myosin heavy chain isoform SM1-to-SM2 ratio with 17β-estradiol treatment may underlie the changes observed in contractility.
Testosterone contributes to marked elevations in mean arterial pressure in adult male intrauterine growth restricted offspring
Authors: Ojeda Norma B. , Grigore Daniela , Yanes Licy L. , Iliescu Radu , Robertson Elliot B. , Zhang Huimin , Alexander Barbara T.
Published: August 2006

Our laboratory uses a model of intrauterine growth restriction (IUGR) induced by placental insufficiency in the rat to examine the developmental origins of adult disease. In this model only male IUGR offspring remain hypertensive in adulthood, revealing sex-specific differences. The purpose of this study was to determine whether testosterone with participation of the renin-angiotensin system (RAS) contributes to hypertension in adult male IUGR offspring. At 16 wk of age a significant increase in testosterone (346 ± 34 vs. 189 ± 12 ng/dl, P < 0.05) was associated with a significant increase in mean arterial pressure (MAP) measured by telemetry in IUGR offspring (147 ± 1 vs. 125 ± 1 mmHg, P < 0.05, IUGR vs. control, respectively). Gonadectomy (CTX) at 10 wk of age significantly reduced MAP by 16 wk of age in IUGR offspring (124 ± 2 mmHg, P < 0.05 vs. intact IUGR) but had no effect in control (125 ± 2 mmHg). A significant decrease in MAP in intact IUGR (111 ± 3 mmHg, P < 0.05 vs. untreated intact IUGR) and castrated IUGR (110 ± 4 mmHg, P < 0.05 vs. untreated CTX IUGR) after treatment with enalapril for 2 wk suggests a role for RAS involvement. However, the decrease in blood pressure in response to enalapril was greater in intact IUGR (Δ36 ± 1 mmHg, P < 0.05) compared with CTX IUGR (Δ15 ± 2 mmHg), indicating an enhanced response to RAS blockade in the presence of testosterone. Thus these results suggest that testosterone plays a role in modulating hypertension in adult male IUGR offspring with participation of the RAS.