bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the
Mycobacterium tuberculosis
Sigma Factor SigM by Assessment of Virulence and Identification of SigM-Dependent Genes
Authors: Agarwal Nisheeth , Woolwine Samuel C. , Tyagi Sandeep , Bishai William R.
Published: December 2006

Alternate sigma factors have been implicated in the survival of mycobacteria in response to specific stresses. To characterize the role of SigM in
Mycobacterium tuberculosis
, a
sigM
deletion mutant was generated by allelic exchange in the virulent CDC1551 strain. Comparing the wild-type and Δ
sigM
strains by complete genomic microarray, we observed a low level of baseline expression of
sigM
in wild-type
M. tuberculosis
and no significant differences in the gene expression patterns between these two strains. Alternatively, a SigM-overexpressing
M. tuberculosis
strain was constructed and microarray profiling revealed SigM-dependent expression of a relatively small group of genes, which included four
esat-6
homologues:
esxE
,
esxF
,
esxT
, and
esxU
. An assessment of SigM-dependent promoters from the microarray analysis revealed a putative consensus sequence for
M. tuberculosis
SigM of −35 GGAAC and −10 CGTCR. In vitro expression studies showed that
M. tuberculosis sigM
transcripts accumulate slightly in stationary phase and following heat shock. To understand the role of SigM in pathogenesis, the
M. tuberculosis sigM
deletion strain was compared with the isogenic wild-type strain and the complemented mutant strain for survival in murine macrophages and in the mouse model. The mutant was found to have similar abilities to survive in both the resting and activated J774A.1 macrophages. Mouse organ bacterial burdens indicated that the mutant proliferated and persisted at the same level as that of the wild-type and complemented strains in lung and spleen tissues. In time-to-death experiments in the mouse model, the Δ
sigM
mutant exhibited lethality times comparable to those observed for the wild-type and complemented strains. These data indicate that
M. tuberculosis
SigM governs the expression of a small set of genes, including four
esat-6
homologues, and that the loss of
sigM
does not confer a detectable virulence defect in the macrophages and mouse models of infection.
Capsule Enhances Pneumococcal Colonization by Limiting Mucus-Mediated Clearance
Authors: Nelson Aaron L. , Roche Aoife M. , Gould Jane M. , Chim Kannie , Ratner Adam J. , Weiser Jeffrey N.
Published: December 2006

Expression of a polysaccharide capsule is required for the full pathogenicity of many mucosal pathogens such asStreptococcus pneumoniae. Although capsule allows for evasion of opsonization and subsequent phagocytosis during invasive infection, its role during mucosal colonization, the organism's commensal state, remains unknown. Using a mouse model, we demonstrate that unencapsulated mutants remain capable of nasal colonization but at a reduced density and duration compared to those of their encapsulated parent strains. This deficit in colonization was not due to increased susceptibility to opsonophagocytic clearance involving complement, antibody, or the influx of Ly-6G-positive cells, including neutrophils seen during carriage. Rather, unencapsulated mutants remain agglutinated within lumenal mucus and, thus, are less likely to transit to the epithelial surface where stable colonization occurs. Studies of in vitro binding to immobilized human airway mucus confirmed the inhibitory effect of encapsulation. Likewise, pneumococcal variants expressing larger amounts of negatively charged capsule per cell were less likely to adhere to surfaces coated with human mucus and more likely to evade initial clearance in vivo. Removal of negatively charged sialic acid residues by pretreatment of mucus with neuraminidase diminished the antiadhesive effect of encapsulation. This suggests that the inhibitory effect of encapsulation on mucus binding may be mediated by electrostatic repulsion and offers an explanation for the predominance of anionic polysaccharides among the diverse array of unique capsule types. In conclusion, our findings demonstrate that capsule confers an advantage to mucosal pathogens distinct from its role in inhibition of opsonophagocytosis—escape from entrapment in lumenal mucus.
CHARACTERIZATION OF ATMOSPHERIC PARTICULATE DURING THE RICE STRAW BURNING PERIOD IN A MIDSIZE CITY IN NORTHERN JAPAN
Authors: SAITOH KATSUMI , SERA KOICHIRO , HIRANO KOICHIRO , IWATA YOSHIHIRO
Published: December 2006

Total suspended particulate (TSP) samples were collected from three areas (commercial, residential and agricultural) in and near Akita City in northern Japan, October 1996 (rice straw burning period), over three days with a one-hour sampling interval for each area. The elemental composition and particle shape of TSP samples were determined and/or observed by PIXE and a Scanning Electron Microscope (SEM) combined with Energy Dispersive X-ray (EDX) analysis. In the hourly TSP samples collected during the rice straw burning period, values of 24 elements were determined for each area, and Na , Mg , Al , Si , S , K , Ca and Fe were the major components. Comparing the arithmetic means of elemental concentrations in TSP for the rice straw burning and non-snow-clad period (May – June 1996), in the residential and agricultural areas the Si concentration in the rice straw burning period was approximately two times that in the non-snow-clad period, and K and Ca concentrations in the rice straw burning period were a little higher than those in the non-snow-clad period. In the residential and agricultural areas, change in SPM concentration and change in Si , K and Ca concentrations were in relative agreement during the hours that smoke from rice straw burning was present in the atmospheric space. With the aid of SEM- EDX analysis, many cubic particles were observed for almost all hourly TSP samples. The cubic particles were of the silicon-rich type, and their morphology was rice straw fragments or aggregation of fragments.
AN IMPROVED PARALLEL PREFIX ALGORITHM ON OTIS-MESH
Authors: JANA PRASANTA K. , SINHA BHABANI P.
Published: December 2006

Wang and Sahni [4] reported two parallel algorithms for N-point prefix computation on an N-processor OTIS-Mesh optoelectronic computer. The overall time complexity for both SIMS and MIMD models of their first algorithm was shown to be (8 N1/4- 1) electronic moves and 2 OTIS moves. This was further reduced to (7 N1/4- 1) electronic moves and 2 OTIS moves in their second algorithm. We present here an improved parallel algorithm for N-point prefix computation on an N-processor OTIS-Mesh, which needs (5.5 N1/4+ 3) electronic moves and 2 OTIS moves. Our algorithm is based on the general theme of parallel prefix algorithm proposed in [4] but following the data distribution and local prefix computation similar to that of [1].
SYMMETRIES ABOUT BIG RIP IN SO(1, 1) PHANTOM UNIVERSE
Authors: WEI YI-HUAN
Published: December 2006

We study the SO(1, 1) dark energy model with the inverse power law potential, V = V0Φ-n, and find for n<2 the model has the late-time phantom property and the universe will evolve to the future Big Rip. The inverse linear potential is a special case, for which the field and the scalar factor are respectively T-invariant and CT-invariant about the Big Rip.
EXTENDING THE STUECKELBERG MODEL FOR SPACETIME SYMMETRIES: COSMOLOGICAL IMPLICATIONS
Authors: ALDAYA V. , CALIXTO M. , SÁNCHEZ-SASTRE E.
Published: December 2006

The so-called Stueckelberg transformation is introduced as a prescription of minimal coupling following the procedure of the Utiyama theory, for both internal and spacetime symmetry Lie groups. As a natural example, the theory is applied to the Weyl group and the corresponding gauge gravitational theory is developed. This context appears to be a natural source to account for some sort of dark matter intrinsically related to the gauge-group parameter associated with scale transformations.
POSSIBLE NEW RESONANCE AT THE $D^*\bar D^*$ THRESHOLD IN e+e- ANNIHILATION
Authors: DUBYNSKIY S. , VOLOSHIN M. B.
Published: December 2006

We argue that the recent CLEO-c data on e+e- annihilation into pairs of charmed mesons at c.m. energy around 4.0 GeV are not well described by a single resonance ψ(4040), but can be better understood if there is an additional narrow resonance with mass within few MeV from the [Formula: see text] threshold.
MINIMAL DEGREE SEQUENCE FOR TORUS KNOTS OF TYPE (p,2p-1)
Authors: MADETI PRABHAKAR , MISHRA RAMA
Published: December 2006

In this paper, we explore the issue of minimizing the degree sequence for torus knots. We find the minimal degree sequence for torus knots of type (p, 2p-1) for any integer p ≥2. We use some results from algebraic geometry to prove our main result.
CLASPER-MOVES AMONG RIBBON 2-KNOTS CHARACTERIZING THEIR FINITE TYPE INVARIANTS
Authors: WATANABE TADAYUKI
Published: December 2006

Habiro found in his thesis a topological interpretation of finite type invariants of knots in terms of local moves called Habiro's Ck-moves. Ck-moves are defined by using his claspers. In this paper we define "oriented" claspers and RCk-moves among ribbon 2-knots as modifications of Habiro's notions to give a similar interpretation of Habiro–Kanenobu–Shima's finite type invariants of ribbon 2-knots. It works also for ribbon 1-knots. Furthermore, by using oriented claspers for ribbon 1-knots, we can prove Habiro–Shima's conjecture in the case of ℚ-valued invariants, saying that ℚ-valued Habiro–Kanenobu–Shima finite type invariant and ℚ-valued Vassiliev–Goussarov finite type invariant are the same thing.
GENE ONTOLOGY SIMILARITY MEASURES BASED ON LINEAR ORDER STATISTICS
Authors: KELLER JAMES M. , BEZDEK JAMES C. , POPESCU MIHAIL , PAL NIKHIL R. , MITCHELL JOYCE A. , HUBAND JACALYN M.
Published: December 2006

The standard method for comparing gene products (proteins or RNA) is to compare their DNA or amino acid sequences. Additional information about some gene products may come from multiple sources, including the set of Gene Ontology (GO) annotations and the set of journal abstracts related to each gene product. Gene product similarity measures can be based on evaluating sets of descriptor terms found in the GO taxonomy, and/or the index term sets of the related documents (MeSH annotations). While our techniques can be applied to term sets from any taxonomy, we restrict our examples in this article to GO annotations. We investigate the use of linear order statistics (LOS) to build similarity relations on pairs of terms that are used in the GO as linguistic descriptors of genes and gene products. One of our objectives is to investigate the construction and utility of visual assessments of relational data (in this case, dissimilarity matrices) for discovering tendencies of groups of gene products to "cluster together". We use gene product data derived from a group of 194 gene products representing three protein families extracted from ENSEMBL. Our examples suggest that LOS similarity measures are more effective than traditional sequence-based similarity measures at capturing relationships between pairs of gene products in ENSEMBL families when annotation information is available. We show examples of how these similarity measures can assist in knowledge discovery and gene product family validation.
CAUTIOUS ANALYSIS OF PROJECT RISKS BY INTERVAL-VALUED INITIAL DATA
Authors: UTKIN LEV V.
Published: December 2006

One of the most common performance measures in selection and management of projects is the Net Present Value (NPV). In the paper, we study a case when initial data about the NPV parameters (cash flows and the discount rate) are represented in the form of intervals supplied by experts. A method for computing the NPV based on using random set theory is proposed and three conditions of independence of the parameters are taken into account. Moreover, the imprecise Dirichlet model for obtaining more cautious bounds for the NPV is considered. Numerical examples illustrate the proposed approach for computing the NPV.
A NOTE ON THE MINIMAL VARIABILITY OWA OPERATOR WEIGHTS
Authors: HONG DUG HUN
Published: December 2006

One important issue in the theory of ordered weighted averaging (OWA) operators is the determination of the associated weighting vector. Recently, Fullér and Majlender2 derived the minimal variability weighting vector for any level of orness using the Kuhn-Tucker second-order sufficiency conditions for optimality. In this note, we give a new proof of the problem.
GROWTH CARBON NANOTUBES DIRECTLY ON PRISTINE SILICON SUBSTRATES
Authors: ZHANG ZHENGJUN , ZHOU YA , YUE YANG
Published: December 2006

It is believed that carbon nanotubes were not able to grow on silicon substrates by chemical vapor deposition from a mixture of ferrocene and xylene. This is because iron particles (formed by the decomposition of ferrocene) reacted quickly with silicon to form a discontinuous layer (> 100 nm ) of FeSi 2 and Fe 2 SiO 4 particles. We report, in this letter, that by controlling the growth kinetics, aligned carbon nanotubes could be grown on pristine silicon substrates. The reason is that appropriate growth conditions could slow down and suppress the reaction within the very surface region to form an almost continuous thin layer (< 10 nm ) of Fe 2 SiO 4 particles; thus preventing further reaction and leaving a number of iron particles still active to catalyze the growth of carbon nanotubes. The structure and field emission properties of the nanotubes were also investigated.
SILICON NANOWIRES FORMATION IN CMOS COMPATIBLE MANNER
Authors: AGARWAL AJAY , BALASUBRAMANIAN N. , RANGANATHAN N. , KUMAR R.
Published: December 2006

We present CMOS compatible fabrication technique for silicon nanowire ( SiNW ) on bulk silicon wafers. Our method uses saw-tooth etch-profiles of fins followed by self-limiting oxidation to form vertically self-aligned horizontal SiNW down to 5 nm diameter. The concept of modifying the cross-section shape of SiNW from triangular to circular and the ability to achieve desired nanowire diameter are unique in this work. Nanowires formed by such technique can be utilized to realize several nanoelectronics devices like gate-all-around transistor, single-electron-transistor, etc.; NEMS and bio-medical sensors; all in a CMOS friendly manner. The physical and electrical characterization of the SiNW is also presented in this paper.
FABRICATION OF SELF-ORGANIZED METAL NANOWIRE ARRAY USING POROUS ALUMINA TEMPLATE FOR OFF-CHIP INTERCONNECTS
Authors: BALAKRISHNAN S. , KRIPESH V. , CHONG SER CHOONG
Published: December 2006

Porous anodic alumina formation on silicon substrate is an example of a nanostructured porous array that is well-suited as a template for growing metallic nanowires. Commercial silicon wafer deposited with aluminum is used as substrate. Prior to anodization, the aluminum film is cleaned with mixture of acids solution to remove its native oxide growth. Anodization of aluminum film on silicon wafer is performed in oxalic acid solution to generate uniform and self-organized nanoporous alumina film. The pores are in the range of 60 nm diameter and pore density is about 9 × 109/ cm 2. The nanoporous alumina template is filled with nickel nanowires by wet electrodeposition process. After nanowire is grown on silicon wafer, the alumina template is etched and the as grown nickel nanowire forest is patterned using laser pruning method. The crystallinity pattern of the as grown nickel naowire forest is characterized using X-ray diffraction technique.
IRON-CONTAINING NANOCOMPOSITES BASED ON ZSM-5 ZEOLITE
Authors: ELISEEV A. A. , VYACHESLAVOV A. S. , LUKASHIN A. V. , TRETYAKOV Yu. D. , SUZDALEV I. P. , MAXIMOV Yu. V. , GOERNERT P.
Published: December 2006

Here we report synthesis and investigation of Fe /ZSM-5 magnetic nanocomposites. Intercalation of iron was performed by ion-exchange procedure and by impregnation of ZSM-5 zeolite in H + form by Fe ( CO )5. Magnetic nanocomposites were prepared by thermal treatment of impregnated samples in hydrogen flow at different temperatures. Chemical composition, structure and physical properties of the samples were characterized by chemical analysis, TGA, XRD, TEM, Mössbauer spectroscopy and SQUID magnetization measurements. Nanocomposites prepared by reduction of cation-exchanged zeolite indicate paramagnetic behavior even at 4 K. Repeatable ion-exchange/reduction procedure used to enrich ZSM-5 matrix with iron led to formation of bulk iron. Fe /ZSM-5 nanocomposites prepared by thermal decomposition of Fe ( CO )5 in the channels of ZSM matrix reveal their ferromagnetic behavior even at room temperature. The coercivity at 300 K for annealed samples attain 670 Oe for the crystallization temperature of 450°C. According XRD, TEM and Mössbauer data iron nanoparticles were formed in the cavities of zeolite.
FABRICATION OF GERMANIUM NANOWIRES BY OBLIQUE ANGLE DEPOSITION
Authors: CHEW H. G. , CHOI W. K. , CHIM W. K. , FITZGERALD E. A.
Published: December 2006

In this work, the effects of flux angle, substrate temperature and deposition rate on obliquely deposited germanium ( Ge ) films have been investigated. We observed that the porosity of the film increased as the flux angle became more oblique. It was also possible to obtain polycrystalline Ge films at a substrate temperature of 200°C when deposition was performed using an oblique angle of 87° as compared to normal incident deposition. Raman spectroscopy results indicated that a higher substrate temperature during deposition led to an increase in crystallinity of the film. Agglomeration of the Ge film was reduced at a lower deposition rate and it was possible to obtain isolated polycrystalline Ge nanowires when the deposition was carried out with the vapor flux inclined at 87° to the substrate normal for substrate temperatures between 250°C to 300°C and with a deposition rate of 0.2–1.5 Å/s. Subsequent rapid thermal annealing of such nanowires resulted in the formation of facetted crystallites.
SYNTHESIS AND CHARACTERIZATION OF TITANIUM DIOXIDE NANOPARTICLES COATED ON FLY ASH
Authors: WETCHAKUN N. , PHANICHPHANT S.
Published: December 2006

Titanium dioxide ( TiO 2) nanoparticles in the anatase phase were coated on fly ash by using a sol–gel method. The TiO 2 nanoparticles coated on fly ash were produced from titanium tetraisopropoxide ( Ti ( OPr i )4 3.3 M ) in absolute ethanol, and the fly ash was added into this alcoholic solution. The ratio of TiO 2 nanoparticles to fly ash in the coating process was 1:10 by weight. The ethanolic solution was loaded into a pouch type cellophane membrane and placed for 1 h in a clear solution which containing 1:1 (v/v) ratio of absolute ethanol and distilled water with 0.5–1% concentrated (25%) ammonia solution. After the dialysis process was completed, the mixture was then allowed to dry in an oven at 100–110°C and was calcined in a furnace over the temperatures range of 400–800°C. TiO 2 nanoparticles were then analyzed and characterized by using the techniques of XRD, SEM, EDS, TEM, and BET. The crystalline sizes of anatase form were found to be in the range of 15–20 nm. The characteristics of TiO 2 nanoparticles coated on fly ash were further investigated by utilizing SEM and EDS methodologies. The correlations among crystalline phase, particle size, morphology, and specific surface area were investigated.
HYDROTHERMAL SYNTHESIS OF POTASSIUM BISMUTH TITANATE NANOPARTICLES
Authors: ZHU GANGQIANG , MIAO HONGYAN , TAN GUOQIANG , LIU YUN , XIA AO
Published: December 2006

Potassium bismuth titanate nanoparticles were prepared by the hydrothermal method using Ti ( C 4 H 9 O )4 and Bi ( NO 3)3·5 H 2 O as raw materials in alkaline solution at temperatures of 160–200°C. The crystal phase, particle size, morphology and dispersion of the particles were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the particles with sizes of about 50–100 nm in diameter are well-dispersed K 0.5 Bi 0.5 TiO 3 (KBT) crystals of tetragonal structure, and the alkaline concentration and the temperature of solutions have great effects on the phase composition and morphology of the resultant particles. We could gain the KBT phase of high purity when the concentration of KOH is about 8–12 M and the reaction temperature is about 170–180°C.
The Dynamics of Detonation in Explosive Systems
Authors: Bdzil John B. , Stewart D. Scott
Published: December 2006

This article reviews advances in modeling condensed-phase explosive detonation waves and their interaction with inerts for precision applications. We describe how constitutive data are obtained for a basic, predictive hydrodynamic model for explosives that subsequently can be studied numerically and analytically. Theory for multidimensional, time-dependent detonation dynamics is reviewed with a focus on freely propagating detonation and the asymptotic theory for quasi-one-dimensional, quasi-steady, detonation shock evolution (detonation shock dynamics). We discuss verification of these theories by direct numerical simulation (DNS) and validation by experiment. We describe a subscale model of detonation that uses an evolution equation to predict detonation dynamics and front states in complex engineering geometries that otherwise could not be computed by DNS. Four areas for future research are identified.
Hydrodynamics of Coral Reefs
Authors: Monismith Stephen G.
Published: December 2006

The geometric complexity of coral reefs leads to interesting fluid mechanics problems at scales ranging from those of coral colonies or even branches a few millimeters in diameter up to whole reefs that can be kilometers in horizontal extent. In many cases, both at the colony and reef scale, unsteady flows, usually due to surface waves, behave very differently than do steady flows for which the coral structures may appear to have quite high resistance to any flow through their interior. Allowing for this difference, engineering formulae for mass transfer describe well the uptake of nutrients by corals, although a priori determination of hydrodynamic roughness of corals and coral reefs is not yet possible. Surface wave-driven flows are a common feature of many coral reefs and appear to follow predictions of theories based on radiation stress gradients. However, comparisons to observations have been relatively limited, and there is some question as to the role played by Stokes drift in these flows. Like other near-shore environments, internal waves and flows driven by horizontal buoyancy gradients can also be important.
Intrinsic Flame Instabilities in Premixed and Nonpremixed Combustion
Authors: Matalon Moshe
Published: December 2006

The focus of this article is on intrinsic combustion instabilities in both premixed and nonpremixed systems, identifying, in particular, the roles of differential and preferential diffusion, thermal expansion, and heat losses. For premixed flames, the hydrodynamic instability resulting from thermal expansion plays a central role and is particularly dominant in large-scale flames. It is responsible for the formation of sharp folds and creases in the flame front and for the wrinkling observed over the surface of expanding flames. In contrast, instabilities in diffusion flames, which give rise to cellular and oscillating flames, are mainly driven by diffusive-thermal effects, with thermal expansion playing a secondary role. The discussion also includes instabilities of edge-flames in unmixed reactants, which possess stability characteristics of both premixed and diffusion flames, but with a distinct mode of instability.
The Biomechanics of Arterial Aneurysms
Authors: Lasheras Juan C.
Published: December 2006

The formation of an arterial aneurysm is believed to be a multifactorial and predominantly degenerative process, resulting from a complex interplay between biological processes in the arterial wall and the hemodynamic stimuli on the vessel's wall. Once an aneurysm forms, the repetitive pressure and shear stresses exerted by the blood flow on the weakened arterial wall generally, but not always, cause a gradual expansion. As the wall geometry, composition, and strength progressively degrade through the enlargement process, the aneurysm ruptures when the wall of the distended artery fails to support the stresses resulting from the internal blood flow. This review surveys recent progress in this area and provides a critical assessment of the contribution made by hemodynamics studies to the current understanding of the pathogenesis of the disease and to its clinical management.
A Linear Systems Approach to Flow Control
Authors: Kim John , Bewley Thomas R.
Published: December 2006

The objective of this paper is to introduce the essential ingredients of linear systems and control theory to the fluid mechanics community, to discuss the relevance of this theory to important open problems in the optimization, control, and forecasting of practical flow systems of engineering interest, and to outline some of the key ideas that have been put forward to make this connection tractable. Although many significant advances have already been made, many new challenges lie ahead before the full potential of this synthesis of disciplines can be realized.
Internal Tide Generation in the Deep Ocean
Authors: Garrett Chris , Kunze Eric
Published: December 2006

Internal tides are internal gravity waves generated in stratified waters by the interaction of barotropic tidal currents with variable bottom topography. They play a role in dissipating tidal energy and lead to mixing in the deep ocean. Key dimensionless parameters governing their generation include the tidal excursion compared with the scale of the topography, the bottom slope compared with the angle at which rays of internal waves of tidal frequency propagate, and the height of the topography compared with the depth of the ocean. Recent theoretical developments for parts of this parameter space particularly relevant to the deep ocean show that most of the energy flux is associated with low modes that propagate away from the generation region. For isolated features this energy flux is not strongly dependent on the bottom slope. Intense beams of internal tidal energy are expected near “critical slopes," bottom slopes equal to the ray slope, and lead to local mixing.
Micro- and Nanoparticles via Capillary Flows
Authors: Barrero Antonio , Loscertales Ignacio G.
Published: December 2006

This review surveys some capillary flows capable of stretching fluid interfaces down to the micrometric dimension and below. These types of flows have become the basis for attractive techniques to produce monodisperse micro- and nanoparticles with either simple or core-shell structure (micro- and nanocapsules, coaxial nanofibers, and hollow nanofibers). These techniques enable precise control on the particle mean size. We also review the basic physics of the flow and the dimensionless parameters that govern these capillary flows. Some examples of the types of particles produced by a few devices are also presented.
Estrogen potentiates adrenocortical responses to stress in female rats
Authors: Figueiredo Helmer F. , Ulrich-Lai Yvonne M. , Choi Dennis C. , Herman James P.
Published: December 2006

It is well established that estrogens markedly enhance the glucocorticoid response to acute stress in females. However, the precise mechanism responsible for this regulation is poorly understood. Here, we tested whether estrogens enhance the activation of the paraventricular nucleus (PVN) of the hypothalamus by measuring stress-induced c- fos mRNA expression in the PVN of restraint-stressed ovariectomized (OVX) rats treated with physiologically relevant doses of estradiol (E2), the major female estrogen. As expected, E2 enhanced plasma corticosterone responses to restraint in OVX females. However, E2 markedly attenuated the stress-induced c- fos gene expression in the PVN and inhibited plasma ACTH responses in these animals. Furthermore, E2-inhibitory effects were mimicked by progesterone (P) alone or in combination with E2. Interestingly, the suppressive central effects of both E2 and P were apparently independent of basal paraventricular corticotropin-releasing hormone (CRH) transcription, since these ovarian steroids did not significantly affect PVN CRH mRNA expression in unstressed rats. These unexpected findings suggested that E2 promotes glucocorticoid hypersecretion in females by additional peripheral (i.e., adrenal) mechanisms. Indeed, E2 markedly enhanced plasma corticosterone responses and adrenal corticosterone content in dexamethasone-blocked OVX rats challenged with varying doses of exogenous ACTH. These results suggest that enhanced adrenal sensitive to ACTH is an important physiological mechanism mediating E2-related glucocorticoid hypersecretion in stressed females.
Glucose intolerance and reduced islet blood flow in transgenic mice expressing the FRK tyrosine kinase under the control of the rat insulin promoter
Authors: Annerén Cecilia , Welsh Michael , Jansson Leif
Published: December 2006

The FRK tyrosine kinase has previously been shown to transduce β-cell cytotoxic signals in response to cytokines and streptozotocin and to promote β-cell proliferation and an increased β-cell mass. We therefore aimed to further evaluate the effects of overexpression of FRK tyrosine kinase in β-cells. A transgenic mouse expressing kinase-active FRK under control of the insulin promoter (RIP-FRK) was studied with regard to islet endocrine function and vascular morphology. Mild glucose intolerance develops in RIP-FRK male mice of at least 4 mo of age. This effect is accompanied by reduced glucose-stimulated insulin secretion in vivo and reduced second-phase insulin secretion in response to glucose and arginine upon pancreas perfusion. Islets isolated from the FRK transgenic mice display a glucose-induced insulin secretory response in vitro similar to that of control islets. However, islet blood flow per islet volume is decreased in the FRK transgenic mice. These mice also exhibit a reduced islet capillary lumen diameter as shown by electron microscopy. Total body weight and pancreas weight are not significantly affected, but the β-cell mass is increased. The data suggest that long-term expression of active FRK in β-cells causes an in vivo insulin-secretory defect, which may be the consequence of islet vascular abnormalities that yield a decreased islet blood flow.
Prior exercise increases phosphorylation of Akt substrate of 160 kDa (AS160) in rat skeletal muscle
Authors: Arias Edward B. , Kim Junghoon , Funai Katsuhiko , Cartee Gregory D.
Published: December 2006

The main purpose of this study was to determine whether the increased glucose transport (GT) found immediately postexercise (IPEX) or 4 h postexercise (4hPEX) is accompanied by increased phosphorylation of Akt substrate of 160 kDa (AS160, a protein regulator of GLUT4 translocation). Paired epitrochlearis muscles were dissected from rats (sedentary or IPEX, 2-h swim) and used to measure protein phosphorylation and insulin-independent GT. IPEX values exceeded sedentary values for GT and phosphorylations of AS160, AMP-activated protein kinase (pAMPK) and acetyl-CoA carboxylase (pACC) but not for AS160 abundance or phosphorylation of Akt serine (pSerAkt), Akt threonine (pThrAkt), or glycogen synthase kinase-3 (pGSK3). AS160 phosphorylation was significantly correlated with GT ( R = 0.801, P < 0.01) and pAMPK ( R = 0.655, P < 0.05). Muscles from other rats were studied 4hPEX along with sedentary controls. One muscle per rat was incubated without insulin, and the contralateral muscle was incubated with insulin. 4hPEX values exceeded sedentary values for insulin-stimulated GT. The elevated pAMPK and pACC found IPEX had reversed by 4hPEX. Insulin caused a significant increase in pSerAkt, pThrAkt, pGSK3, and AS160 phosphorylation with or without exercise. Exercise significantly increased AS160 phosphorylation, regardless of insulin, with unchanged AS160 abundance. Among the signaling proteins studied, insulin-stimulated GT was significantly correlated only with insulin-stimulated pThrAkt ( R = 0.720, P < 0.0005). The results are consistent with a role for increased AS160 phosphorylation in the increased insulin-independent GT IPEX, and the exercise effects on AS160 phosphorylation and/or pThrAkt at 4hPEX are potentially relevant to the increased insulin-stimulated glucose transport at this time.
Theoretical Modeling of the N-H and N-D Stretching Bands of Hydrogen-Bonded 1-Methylthymine Crystal and Its Deuterated Form
Authors: Boczar Marek , Boda Łukasz , Wójcik Marek J.
Published: December 2006

Theoretical model for vibrational interactions in the hydrogen bonds in molecular crystals with four molecules forming two centrosymmetric dimers in the unit cell is presented. The model takes into account anharmonic-type couplings between the high-frequency N-H(D) and the low-frequency N•••O stretching vibrations in each hydrogen bond, resonance interactions (Davydov coupling) between equivalent hydrogen bonds in each dimer, resonance interdimer interactions within an unit cell and Fermi resonance between the N-H(D) stretching fundamental and the first overtone of the N-H(D) in-plane bending vibrations. The vibrational Hamiltonian, selection rules, and expressions for the integral properties of an absorption spectrum are derived. The model is used for theoretical simulation of the νs stretching bands of 1-methylthymine and its ND derivative at 300 K. The effect of deuteration is successfully reproduced by our model.
Theoretical Design of Optical Switches Using the Spin Transition Phenomenon
Authors: Henriksson Johan , Nyrell Susanna , Norman Patrick
Published: December 2006

The spin characteristics of octahedrically coordinated Fe(II) compounds are determined from first-principles quantum chemical calculations. Four novel Fe(II) spin transition materials are suggested for use in optical switching applications.
Invited Paper
Authors: Kang Sunwoo , Yan Shihai , Lee Jin Yong
Published: December 2006

Supramolecular chemistry now has become a central part of the research activities. Basically, it mostly concerns molecular recognition and self aggregation by non-covalent weak intermolecular interactions, such as hydrogen bonding, .π-π. stacking, and van der Waals interactions. The computational applications on such large systems are limited for their structural complexity. Several examples of the computational approaches to understand molecular recognition and self-aggregation are discussed. Firstly, bifunctional (fluorescence and visible light absorption) anion sensing mechanism is supported by the DFT calculations. Secondly, an experimentally observed selective recognition of Cu2+ by an azobenzeneappended receptor, which can exhibit Cu2+ selectivity by color change, is discussed based on computational approach. Finally, the intermolecular interaction, which is useful for predicting the self-assembled structures, can be understood by replicating the monomer unit and manipulating the translation and rotation.
B-spline Method for Solving General Singularly Perturbed Boundary Value Problems Using Fitted Mesh
Authors: Kadalbajoo M.K. , Aggarwal Vivek K.
Published: December 2006

In this paper we develop B-spline method for solving a class of Singularly Perturbed two point boundary value problems given as

We use the Fitted mesh technique to generate piecewise uniform mesh, and use B-spline method which leads to a tridiagonal linear system. In case of non-linear problems we first linearize the equation using Quasilinearization technique and the resulting problem is solved by B-spline. The convergence analysis is given and the method is shown to have uniform convergence. Numerical illustrations are given in the end to demonstrate the efficiency of our method.
Evaluation of Radar Multiple-Scattering Effects from a GPM Perspective. Part I: Model Description and Validation
Authors: Battaglia A. , Ajewole M. O. , Simmer C.
Published: January 2007

A numerical model based on the Monte Carlo solution of the vector radiative transfer equation has been adopted to simulate radar signals. The model accounts for general radar configurations such as airborne/spaceborne/ground based and monostatic/bistatic and includes the polarization and the antenna pattern as particularly relevant features. Except for contributions from the backscattering enhancement, the model is particularly suitable for evaluating multiple-scattering effects. It has been validated against some analytical methods that provide solutions for the first and second order of scattering of the copolar intensity for pencil-beam/Gaussian antennas in the transmitting/receiving segment. The model has been applied to evaluate the multiple scattering when penetrating inside a uniform hydrometeor layer. In particular, the impact of the phase function, the range-dependent scattering optical thickness, and the effects of the antenna footprint are considered.
The Role of Forcing in Cell Morphology and Evolution within Midlatitude Squall Lines
Authors: Jewett Brian F. , Wilhelmson Robert B.
Published: December 2006

This study assesses the role of mesoscale forcing on cell morphology and early evolution of midlatitude squall lines. The forcing chosen was a cold front, simulated to frontal collapse to produce a specific set of thermodynamic profiles at the leading edge of the front. Use of a realistic, balanced, and persistent forced state allowed a unique evaluation of its importance in thunderstorm evolution compared with a traditional homogeneous environment without forcing. Three-dimensional squall lines were modeled with and without the front present, in low and high bulk Richardson number environments. The forced convection evolved in significantly different ways than their isolated, unforced counterparts. In low-shear conditions, the line of isolated convective cells split, with the adjacent split cells interfering destructively with neighboring cells in the line. With forcing present, differences in anticyclonic cell intensity and propagation prevented this interaction from occurring, leading to longer-lived cyclonic convection despite a near-normal orientation between cloud-bearing shear and the convective line. The split-cell interaction also failed to occur under higher-shear conditions due to anticyclonic cell decay given the greater cyclonic hodograph curvature. In both low- and higher-shear environments, a strong bias toward cyclonic storms was noted with forcing present, due to shallower anticyclonic cells with the front present and to preexisting vorticity in the environment; updraft–vorticity correlations were skewed accordingly. Forcing also reduced the sensitivity of the evolving convection to detailed aspects of the initialization.
Discrete Propagation in Numerically Simulated Nocturnal Squall Lines
Authors: Fovell Robert G. , Mullendore Gretchen L. , Kim Seung-Hee
Published: December 2006

Simulations of a typical midlatitude squall line were used to investigate a mechanism for discrete propagation, defined as convective initiation ahead of an existing squall line leading to a faster propagation speed for the storm complex. Radar imagery often shows new cells appearing in advance of squall lines, suggesting a causal relationship and prompting the search for an “action-at-a-distance” mechanism to explain the phenomenon. In the simulations presented, the identified mechanism involves gravity waves of both low and high frequency generated in response to the latent heating, which subsequently propagate out ahead of the storm. The net result of the low-frequency response, combined with surface fluxes and radiative processes, was a cooler and more moist lower troposphere, establishing a shallow cloud deck extending ahead of the storm. High-frequency gravity waves, excited in response to fluctuations in convective activity in the main storm, were subsequently ducted by the storm’s own upper-tropospheric forward anvil outflow. These waves helped positively buoyant cumulus clouds to occasionally form in the deck. A fraction of these clouds persisted long enough to merge with the main line, invigorating the parent storm. Discrete propagation occurred when clouds developed into deep convection prior to merger, weakening the parent storm. The ducting conditions, as diagnosed with the Scorer parameter, are shown to be sensitive to vertical wind shear and radiation, but not to the microphysical parameterization or simulation geometry.
Supercell Tornadogenesis over Complex Terrain: The Great Barrington, Massachusetts, Tornado on 29 May 1995
Authors: Bosart Lance F. , Seimon Anton , LaPenta Kenneth D. , Dickinson Michael J.
Published: December 2006

The process of tornadogenesis in complex terrain environments has received relatively little research attention to date. Here, an analysis is presented of a long-lived supercell that became tornadic over complex terrain in association with the Great Barrington, Massachusetts (GBR), F3 tornado of 29 May 1995. The GBR tornado left an almost continuous 50–1000-m-wide damage path that stretched for ∼50 km. The apparent rarity of significant tornadogenesis in rough terrain from a supercell well documented in operational Doppler radar motivated this case study. Doppler radar observations showed that the GBR supercell possessed a midlevel mesocyclone well prior to tornadogenesis and that the mesocyclone intensified as it crossed the eastern edge of New York’s Catskill Mountains and entered the Hudson Valley. Tornadogenesis occurred as the GBR mesocyclone crossed the Hudson Valley and ascended the highlands to the east. Subsequently, the mesocyclone weakened as it approached the Taconic Range in western Massachusetts before it intensified again as it moved downslope into the Housatonic Valley where it was associated with the GBR tornado. Because of a dearth of significant mesoscale surface and upper-air observations, the conclusions and inferences presented in this paper must be necessarily limited and speculative. What data were available suggested that on a day when the mesoscale environment was supportive of supercell thunderstorm development, according to conventional indicators of wind shear and atmospheric stability, topographic configurations and the associated channeling of ambient low-level flows conspired to create local orographic enhancements to tornadogenesis potential. Numerical experimentation is needed to address these inferences, speculative points, and related issues raised by the GBR case study.
A Preliminary Survey of Rear-Flank Descending Reflectivity Cores in Supercell Storms
Authors: Rasmussen Erik N. , Straka Jerry M. , Gilmore Matthew S. , Davies-Jones Robert
Published: December 2006

This paper develops a definition of a supercell reflectivity feature called the descending reflectivity core (DRC). This is a reflectivity maximum pendant from the rear side of an echo overhang above a supercell weak-echo region. Examples of supercells with and without DRCs are presented from two days during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX), as well as one day with tornadic high-precipitation supercell storms in central Kansas. It was found that in all cases, tornado formation was preceded by the descent of a DRC. However, the sample reported herein is much too small to allow conclusions regarding the overall frequency of DRC occurrence in supercells, or the frequency with which DRCs precede tornado formation. Although further research needs to be done to establish climatological frequencies, the apparent relationship observed between DRCs and impending tornado formation in several supercells is important enough to warrant publication of preliminary findings.
Using Wind Anomalies to Forecast East Coast Winter Storms
Authors: Stuart Neil A. , Grumm Richard H.
Published: December 2006

Forecasting major winter storms is a critical function for all weather services. Conventional model-derived fields from numerical weather prediction models most frequently utilized by operational forecasters, such as pressure level geopotential height, temperature fields, quantitative precipitation forecasts, and model output statistics, are often insufficient to determine whether a winter storm represents a large departure from normal, or has the potential to produce significant snowfall. This paper presents a method, using normalized departures from climatology, to assist forecasters in identifying long-duration and potentially significant winter storms. The focus of this paper is on anomalous low- and upper-level wind anomalies associated with winter storms along the U.S. east coast.

Observed and forecast low-level (850 hPa) and upper-level (300 and 250 hPa) easterly wind anomalies are compared with a 30-yr (1961–90) reanalysis climatology. Anomalous easterly low-level winds are correlated with enhanced low-level forcing and frontogenesis. Strong low-level winds can also contribute to enhanced precipitation rates. Upper-level winds that are anomalously below normal, represented as easterly wind anomalies, are also correlated with systems that are cut off from the main belt of westerlies, which may result in slower movement of the system, leading to long-duration events. The proposed method of evaluating easterly wind anomalies is shown to assist in identifying potentially slow-moving storms with extended periods of enhanced precipitation.

To illustrate this method, winter storms on 25–26 December 2002 and 2–4 January 2003 will be compared with past historical winter storms. The results suggest that the low- and upper-level wind anomalies in the two recent snowstorms share common characteristics with several record snowstorms over the past 52 yr. Many of these storms were associated with easterly wind anomalies that departed significantly (2 or more standard deviations) from normal. The examination of climatic anomalies from model forecasts may assist forecasters in identifying significant winter storms in the short range (2–3 days) and potentially out to ranges as long as 7 days when ensemble forecast guidance is utilized.
Dry Sliding Wear of a Powder Metallurgy Copper-based Metal Matrix Composite Reinforced with Iron Aluminide Intermetallic Particles
Authors: Venkateswaran K. , Kamaraj M. , Prasad Rao K.
Published: December 2006

In the present study, dry sliding wear behavior of a powder metallurgy copper alloy matrix composite containing iron aluminide (Fe3Al) intermetallic particles was investigated using a pin-on-disk machine. A sintered copper alloy (Cu—90%, Sn—10%) was used as matrix. Reinforcement Fe3Al particles were prepared by mechanical alloying (42 h) and used as reinforcement (10 and 20 vol%) in the matrix. The processing of the composites included mixing and cold compaction followed by sintering at 850 °C. The influence of Fe3Al additions on the dry sliding wear behavior was studied at loads of 20 and 40 N at sliding distances of 2160, 3240, 4320, and 6480 m. The study showed that the composite exhibited lower wear rate than that of the matrix and the wear rate was influenced by the volume percentage of Fe3Al particles. It is understood that iron aluminide particle reinforcement has a beneficial effect on the wear properties by providing better support to the matrix. The wear mechanisms could be interpreted with scanning electron microscopy (SEM) examination of the worn surfaces.
Compliant Mechanical Amplifier Design using Multiple Optimally Placed Actuators
Authors: Bharti Smita , Frecker Mary
Published: December 2006

This article discusses a methodology for designing compliant mechanisms with piezoelectric actuation to obtain maximum deflection and force at the output point. The focus is on design of compliant mechanisms with multiple piezoelectric actuators. The number, size, and position of the actuators within the compliant mechanism are optimized for the maximum output deflection. Predicted results demonstrate that compliant mechanisms with multiple, optimally placed actuators outperform those with a single actuator placed at a predetermined location.