bluuebunny/crossref_metadata_2025 huggingface dataset:
Examination of Type IV Pilus Expression and Pilus-Associated Phenotypes in
Kingella kingae
Clinical Isolates
Authors: Kehl-Fie Thomas E. , Porsch Eric A. , Yagupsky Pablo , Grass Elizabeth A. , Obert Caroline , Benjamin Daniel K. , St. Geme Joseph W.
Published: February 2010

Kingella kingae
is a gram-negative bacterium that is being recognized increasingly as a cause of septic arthritis and osteomyelitis in young children. Previous work established that
K. kingae
expresses type IV pili that mediate adherence to respiratory epithelial and synovial cells. PilA1 is the major pilus subunit in
K. kingae
type IV pili and is essential for pilus assembly. To develop a better understanding of the role of
K. kingae
type IV pili during colonization and invasive disease, we examined a collection of clinical isolates for pilus expression and
in vitro
adherence. In addition, in a subset of isolates we performed nucleotide sequencing to assess the level of conservation of PilA1. The majority of respiratory and nonendocarditis blood isolates were piliated, while the majority of joint fluid, bone, and endocarditis blood isolates were nonpiliated. The piliated isolates formed either spreading/corroding or nonspreading/noncorroding colonies and were uniformly adherent, while the nonpiliated isolates formed domed colonies and were nonadherent. PilA1 sequence varied significantly from strain to strain, resulting in substantial variability in antibody reactivity. These results suggest that type IV pili may confer a selective advantage on
K. kingae
early in infection and a selective disadvantage on
K. kingae
at later stages in the pathogenic process. We speculate that PilA1 is immunogenic during natural infection and undergoes antigenic variation to escape the immune response.
UpaH Is a Newly Identified Autotransporter Protein That Contributes to Biofilm Formation and Bladder Colonization by Uropathogenic
Escherichia coli
CFT073
Authors: Allsopp Luke P. , Totsika Makrina , Tree Jai J. , Ulett Glen C. , Mabbett Amanda N. , Wells Timothy J. , Kobe Bostjan , Beatson Scott A. , Schembri Mark A.
Published: February 2010

Escherichia coli
is the primary cause of urinary tract infection (UTI) in the developed world. The major factors associated with virulence of uropathogenic
E. coli
(UPEC) are fimbrial adhesins, which mediate specific attachment to host receptors and trigger innate host responses. Another group of adhesins is represented by the autotransporter (AT) subgroup of proteins. In this study, we identified a new AT-encoding gene, termed
upaH
, present in a 6.5-kb unannotated intergenic region in the genome of the prototypic UPEC strain CFT073. Cloning and sequencing of the
upaH
gene from CFT073 revealed an intact 8.535-kb coding region, contrary to the published genome sequence. The
upaH
gene was widely distributed among a large collection of UPEC isolates as well as the
E. coli
Reference (ECOR) strain collection. Bioinformatic analyses suggest β-helix as the predominant structure in the large N-terminal passenger (α) domain and a 12-strand β-barrel for the C-terminal β-domain of UpaH. We demonstrated that UpaH is expressed at the cell surface of CFT073 and promotes biofilm formation. In the mouse UTI model, deletion of the
upaH
gene in CFT073 and in two other UPEC strains did not significantly affect colonization of the bladder in single-challenge experiments. However, in competitive colonization experiments, CFT073 significantly outcompeted its
upaH
isogenic mutant strain in urine and the bladder.
Concomitant Infection Decreases the Malaria Burden but Escalates Relapsing Fever Borreliosis
Authors: Lundqvist Jenny , Larsson Christer , Nelson Maria , Andersson Marie , Bergström Sven , Persson Cathrine
Published: February 2010

About 500 million cases of malaria occur annually. However, a substantial number of patients who actually have relapsing fever (RF)
Borrelia
infection can be misdiagnosed with malaria due to similar manifestations and geographic distributions of the two diseases. More alarmingly, a high prevalence of concomitant infections with malaria and RF
Borrelia
has been reported. Therefore, we used a mouse model to study the effects of such mixed infection. We observed a 21-fold increase in spirochete titers, whereas the numbers of parasitized erythrocytes were reduced 15-fold. This may be explained by polarization of the host immune response toward the intracellular malaria parasite, resulting in unaffected extracellular spirochetes and hosts that succumb to sepsis. Mixed infection also resulted in severe malaria anemia with low hemoglobin levels, even though the parasite counts were low. Overall, coinfected animals had a higher fatality rate and shorter time to death than those with either malaria or RF single infection. Furthermore, secondary malaria infection reactivated a quiescent RF brain infection, which is the first evidence of a clinically and biologically relevant cue for reactivation of RF
Borrelia
infection. Our study highlights the importance of investigating concomitant infections
in vivo
to elucidate the immune responses that are involved in the clinical outcome.
Extracellular Vesicles from
Cryptococcus neoformans
Modulate Macrophage Functions
Authors: Oliveira Débora L. , Freire-de-Lima Célio G. , Nosanchuk Joshua D. , Casadevall Arturo , Rodrigues Marcio L. , Nimrichter Leonardo
Published: February 2010

Cryptococcus neoformans
and distantly related fungal species release extracellular vesicles that traverse the cell wall and contain a varied assortment of components, some of which have been associated with virulence. Previous studies have suggested that these extracellular vesicles are produced
in vitro
and during animal infection, but the role of vesicular secretion during the interaction of fungi with host cells remains unknown. In this report, we demonstrate by fluorescence microscopy that mammalian macrophages can incorporate extracellular vesicles produced by
C. neoformans
. Incubation of cryptococcal vesicles with murine macrophages resulted in increased levels of extracellular tumor necrosis factor alpha (TNF-α), interleukin-10 (IL-10), and transforming growth factor β (TGF-β). Vesicle preparations also resulted in a dose-dependent stimulation of nitric oxide production by phagocytes, suggesting that vesicle components stimulate macrophages to produce antimicrobial compounds. Treated macrophages were more effective at killing
C. neoformans
yeast. Our results indicate that the extracellular vesicles of
C. neoformans
can stimulate macrophage function, apparently activating these phagocytic cells to enhance their antimicrobial activity. These results establish that cryptococcal vesicles are biologically active.
Radical addition to ynol ethers — A convenient procedure for the stereoselective preparation of α-iodo enol ethers in neutral conditions
Authors: Longpré Fanny , Rusu Natalia , Larouche Maxime , Hanna Rana , Daoust Benoit
Published: February 2010

α-Iodo enol ethers, precursors of acyl anion equivalents, are not easily prepared. Herein we report that addition of activated iodoalkanes to ynol ethers under mild and neutral radical reaction conditions leads to α-iodo enol ethers in moderate to excellent yields with high stereoselectivity. The reaction can be carried out in various solvents at different temperatures. The methodology allows the preparation of β-alkylated and β,β-dialkylated α-iodo enol ethers. Reduction of the carbon-iodine bond of these species leads to the corresponding enol ethers with good yields.Key words: ynol ethers, enol ethers, radical addition, stereoselective.
Comparison of chelating ion exchange resins in sorption of copper(II) and zinc(II) complexes with ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA)
Authors: Kołodyńska Dorota , Hubicki Zbigniew
Published: February 2010

This paper investigates the macroporous chelating ion exchangers with different functional groups for their sorption properties towards the copper(II) and zinc(II) ions. The investigations by the dynamic and static methods were carried out in the presence of traditional complexing agents. The differences in affinity of Cu(II) and Zn(II) complexes with these complexones result from the kind of functional groups of the chelating ion exchangers, such as thiourea, aminomethylphosphonate, iminodiacetate, and polyamine groups as well as from the pH value. The quantitative removal of studied heavy metal complexes using chelating ion exchangers is achieved in the case when resins compete successfully for the heavy metal ions against these chelators.Key words: chelating resins, heavy metals, EDTA, NTA.
Synthesis of dipyrrins bearing chirality adjacent to the conjugated skeleton — Electron-poor pyrroles exhibit dramatically reduced nucleophilicity
Authors: Beshara Cory S , Pearce Beth M , Thompson Alison
Published: February 2010

With the aim of furthering our investigations into the asymmetric complexation of dipyrrinato ligands, a dipyrrin bearing a stereogenic centre directly adjacent to the conjugated skeleton was synthesized. The electron-withdrawing nature of the chiral 4-(2,2,2-trifluoro-1-hydroxyethyl)- substituent significantly reduced the nucleophilicity of corresponding pyrroles, such that 2,2′-symmetrically substituted bis(dipyrrin)s bearing this motif were inaccessible. Furthermore, solutions of mononuclear dipyrrinato complexes were found to be less stable to acid-catalyzed decomplexation than the corresponding dinuclear complexes.Key words: dipyrrin, dipyrromethene, complexation, electron-poor pyrrole, chirality.
Vibrational spectroscopic characterization of some environmentally important organoarsenicals — A guide for understanding the nature of their surface complexes
Authors: Cowen Scott , Duggal Megha , Hoang Tuan , Al-Abadleh Hind A
Published: February 2010

Organoarsenicals are found in the environment from the biomethylation of inorganic arsenic compounds and from anthropogenic sources. It is clear that organoarsenicals pose a health and an environmental risk due to their potential cycling to the most toxic forms of arsenic as a result of redox activity in soils and natural waters. The environmental fate of arsenic compounds depends to a large extent on the surface interactions with geosorbents, mainly minerals and organic matter. Hence, elucidating the nature of surface complexes is important in understanding binding mechanisms and thermodynamics. In this paper, we report the vibrational spectra of a number of organoarsenicals in the aqueous and solid phases using attenuated total internal reflectance Fourier transform infrared (ATR-FTIR), transmission FTIR, and Raman spectroscopies. Analysis of the aqueous phase spectra revealed that for completely deprotonated anions, increasing the organic substituents on the AsOx moiety results in increasing the frequency of v(AsOx), whereas the opposite trend is observed for completely protonated molecules. Analysis of solid phase spectra showed that incorporation of water molecules in the crystalline structure and extensive hydrogen bonding with neighboring molecules significantly affect As–O bond lengths and hence frequencies of v(AsOx). Results are discussed in the context of identifying geometry of organoarsenicals surface complexes in situ using the ATR-FTIR technique.Key words: ATR-FTIR, organoarsenicals; oxyanion adsorption, arsenate, in situ spectroscopy.
Inside the black box — Perspectives on transformations in catalysis
Authors: Fogg Deryn E
Published: February 2010

Tandem catalysis and olefin metathesis are powerful tools in the development of sustainable synthetic practices. This Award Lecture describes our advances in designing new tandem metathesis-hydrogenation methodologies for the synthesis of “designer materials” and Ru-pseudohalide metathesis catalysts that amplify opportunities for tuning catalyst activity, selectivity, and lifetime. Also discussed is the operation of a previously unrecognized oligomerization-backbiting pathway in ring-closing metathesis of conformationally flexible α,ω-dienes, which has important implications for the sustainable synthesis of medium and large rings.Key words: tandem catalysis, green chemistry, olefin metathesis, ring-closing metathesis, mechanism.
Synthesis and properties of end-capped bis(oligothienyl) sulfides
Authors: Myles Daniel J. T , Chahma M’hamed , Hicks Robin G
Published: February 2010

The synthesis, and the optical and electrochemical properties, of a series of mesitylthio (MesS-) end-capped bis(oligothienyl) sulfides are presented. The target compounds were synthesized principally by convergent protocols, whereby a series of short thiophene oligomers bearing one terminal mesitylthio (MesS-) substituent were first assembled by metal-catalyzed cross-coupling reactions and then coupled via divalent sulfur through reactions with bis(phenylsulfonyl) sulfide. The spectroscopic and electrochemical features of the bis(oligothienyl) sulfides are qualitatively similar to those of the related mesitylthio-capped fully conjugated oligothiophenes, suggesting that the degree of electronic communication between the two oligothiophene chromophores in the bis(oligothienyl) sulfides is low. Cyclic voltammetry studies on the bis(oligothienyl) sulfides reveal that these species can be reversibly oxidized to radical cations, but the reversibility of subsequent oxidations depends on oligothienyl chain length and the presence and position of more electron-rich ethylenedioxythiophene (EDOT) groups. In general, the bis(oligothienyl) sulfides possess fewer than the expected number of reversible oxidations based on comparisons with their corresponding mesitylthio-capped fully conjugated oligothiophenes; excessive charge accumulation at or near the central linking sulfur atom is believed to be responsible for the irreversible behavior. Analysis of the irreversible voltammetric response of one of the bis(oligothienyl) sulfides leads to the suggestion of a decomposition mechanism for the cationic species involving carbon-sulfur bond cleavage and subsequent coupling of thiophene fragments — a finding with potential implications for the poor environmental stability of doped poly(p-phenylene sulfide), one of the prototypical conducting polymers.Key words: conjugated materials, conducting polymers, oligothiophenes, electronic communication.
FTIR spectroscopic investigation of pyruvate electroreduction on copper in alkaline medium — On the mechanistic aspects
Authors: Martin Cédric , Hahn Françoise , Servat Karine , Huser Hervé , Tito Duarte , Kalaji Maher , Kokoh K Boniface
Published: February 2010

In this work some important aspects related to the electrocatalytic reduction of pyruvate on copper cathode were investigated in alkaline medium (0.5 mol/L NaOH). In situ IR reflectance spectroscopy (SPAIRS and SNIFTIRS techniques) was used to investigate the adsorbed intermediates and reaction products from the reduction of pyruvate. The results revealed that hydrogenation of the substrate to lactate occurred at the copper surface involving weakly adsorbed species. The identification of the different electroreactive species allowed to postulate a reaction mechanism for the transformation of pyruvate into lactate on copper.Key words: copper, electroreduction, pyruvate, lactate, in situ infrared reflectance spectroscopy, reaction mechanism.
THE SELF-DUAL CHERN–SIMONS HIGGS EQUATION ON A COMPACT RIEMANN SURFACE WITH BOUNDARY
Authors: WANG MENG
Published: February 2010

We study the self-dual Chern–Simons Higgs equation on a compact Riemann surface with Neumann boundary condition. We show that the Chern–Simons Higgs equation with parameter λ > 0 has at least two solutions [Formula: see text] for λ sufficiently large, such that [Formula: see text] almost everywhere as λ → + ∞, and that [Formula: see text] almost everywhere as λ → ∞, where u0 is a (negative) Green function on M.
BERGMAN KERNELS AND EQUILIBRIUM MEASURES FOR POLARIZED PSEUDO-CONCAVE DOMAINS
Authors: BERMAN ROBERT J.
Published: February 2010

Let X be a domain in a closed polarized complex manifold (Y,L), where L is a (semi-) positive line bundle over Y. Any given Hermitian metric on L induces by restriction to X a Hilbert space structure on the space of global holomorphic sections on Y with values in the k-th tensor power of L (also using a volume form ωn on X. In this paper the leading large k asymptotics for the corresponding Bergman kernels and metrics are obtained in the case when X is a pseudo-concave domain with smooth boundary (under a certain compatibility assumption). The asymptotics are expressed in terms of the curvature of L and the boundary of X. The convergence of the Bergman metrics is obtained in a more general setting where (X,ωn) is replaced by any measure satisfying a Bernstein–Markov property. As an application the (generalized) equilibrium measure of the polarized pseudo-concave domain X is computed explicitly. Applications to the zero and mass distribution of random holomorphic sections and the eigenvalue distribution of Toeplitz operators will be described elsewhere.
NONSTABILITY OF THE IDEALS OF THE CORONA ALGEBRA OF A SEPARABLE STABLE PRIME C*-ALGEBRA
Authors: NG PING WONG
Published: February 2010

Let [Formula: see text] be a separable stable and prime C*-algebra. We show that every proper nontrivial ideal in [Formula: see text] (and hence every proper ideal in [Formula: see text] which properly contains [Formula: see text]) is not stable.

Some consequences are counterexamples naturally occuring, in the non-σ-unital case, to Zhang's Dichotomy as well as the Hjelmborg–Rørdam theory of stability.
VACUUM STRUCTURE AND QCD SUM RULES: INTRODUCTION
Authors: SHIFMAN M.
Published: February 2010

This note was written as an introduction to the volume Vacuum Structure and QCD Sum Rules (North-Holland, 1992). It has never been published.
PANDORA'S BOX AND NON-SELFDUAL TOPOLOGICAL EXCITATIONS
Authors: ÜNSAL MITHAT
Published: February 2010

In the last few years, we have realized the existence of a new class of topological excitations, which are rather distinct from the platonic world of monopoles, monopole-instantons and instantons. All of the latter arise as solutions of the Prasad-Sommerfield type first order differential (self-duality) equations and have been extensively discussed in the context of confinement and chiral symmetry breaking for the last 30 years. However, new calculable deformations of asymptotically free chiral and vector-like gauge theories give us a new picture of these physical phenomena. Most often, the excitations which lead to confinement are not solutions to PS-type equations, they are non-selfdual and they are often bizarre. They are referred to as magnetic bions, triplets, and quintets, due to their composite nature. Bizarre as they are, combined with large-N volume independence, these novel non-self-dual excitations may also provide hope that at least some non-abelian gauge theories may be solvable.
M2-BRANES AND AdS/CFT
Authors: KLEBANOV IGOR R.
Published: February 2010

We provide a brief introduction to the ABJM theory, the level kU(N) × U(N) superconformal Chern-Simons matter theory which has been conjectured to describe N coincident M2 -branes. We discuss its dual formulation in terms of M -theory on AdS4 × S7/ℤk and review some of the evidence in favor of the conjecture. We end with a brief discussion of the important role played by the monopole operators.
CONFORMALITY LOST
Authors: KAPLAN D. B. , LEE J.-W. , SON D. T. , STEPHANOV M. A.
Published: February 2010

We consider zero-temperature transitions from conformal to non-conformal phases in quantum theories. We argue that there are three generic mechanisms for the loss of conformality: (i) fixed point goes to zero coupling, (ii) fixed point runs off to infinite coupling, or (iii) an IR fixed point annihilates with a UV fixed point and they both disappear into the complex plane. We give examples of the last case and show that the critical behavior of the mass gap is similar to that of the inverse correlation length in the finite temperature Berezinskii-Kosterlitz-Thouless (BKT) phase transition, ξ ~ exp (c/|T-Tc|1/2). We speculate that the chiral phase transition in QCD at large number of fermion flavors belongs to this universality class, and attempt to identify the UV fixed point that annihilates with the Banks-Zaks fixed point at the lower end of the conformal window.
CHIRAL SYMMETRY BREAKING IN A SOFT-WALL MODEL OF AdS/QCD
Authors: KAPUSTA JOSEPH I. , KELLEY THOMAS M. , GHERGHETTA TONY
Published: February 2010

We incorporate chiral symmetry breaking in a soft-wall version of the AdS/QCD model by using a modified dilaton profile and a quartic term in the bulk scalar potential. This allows one to separate the dependence on spontaneous and explicit chiral symmetry breaking. The resulting mass spectra in the scalar, vector and axial-vector sectors compares favorably with the respective QCD resonances.
DARK MATTER AXIONS
Authors: SIKIVIE P.
Published: February 2010

The hypothesis of an 'invisible' axion was made by Misha Shifman and others, approximately thirty years ago. It has turned out to be an unusually fruitful idea, crossing boundaries between particle physics, astrophysics and cosmology. An axion with mass of order 10-5 eV (with large uncertainties) is one of the leading candidates for the dark matter of the universe. It was found recently that dark matter axions thermalize and form a Bose-Einstein condensate (BEC). Because they form a BEC, axions differ from ordinary cold dark matter (CDM) in the non-linear regime of structure formation and upon entering the horizon. Axion BEC provides a mechanism for the production of net overall rotation in dark matter halos, and for the alignment of cosmic microwave anisotropy multipoles. Because there is evidence for these phenomena, unexplained with ordinary CDM, an argument can be made that the dark matter is axions.
SEARCHING FOR AXIONS AND OTHER EXOTICS WITH DARK MATTER DETECTORS
Authors: POSPELOV MAXIM
Published: February 2010

I consider models of light super-weakly interacting cold dark matter, with [Formula: see text] mass, focusing on bosonic candidates such as pseudoscalars and vectors. I analyze the cosmological abundance, the γ-background created by particle decays, the impact on stellar processes due to cooling, and the direct detection capabilities in order to identify classes of models that pass all the constraints. In certain models, variants of photoelectric (or axioelectric) absorption of dark matter in direct-detection experiments can provide a sensitivity to the superweak couplings to the Standard Model which is superior to all existing indirect constraints. In all models studied, the annual modulation of the direct-detection signal is at the currently unobservable level of O(10-5).
SYMMETRIES IN THE GROSS-NEVEU PHASE DIAGRAM
Authors: DUNNE GERALD V.
Published: February 2010

The existence of crystalline condensates in the temperature and chemical potential phase diagram of the Gross-Neveu models can be traced to intricate symmetries of the associated inhomogeneous gap equation. The gap equation based on the Ginzburg-Landau expansion is precisely the mKdV or AKNS hierarchy of integrable nonlinear equations for the Gross-Neveu model with discrete or continuous chiral symmetry, respectively. The former model also has a dense-dilute symmetry that is due to the energy-reflection duality of the underlying quasi-exactly soluble spectral operators.
STRONGLY COUPLED CONDENSATE OF HIGH DENSITY MATTER
Authors: GABADADZE GREGORY
Published: February 2010

Arguments are summarized, that neutral matter made of helium, carbon, etc., should form a quantum liquid at the above-atomic but below-nuclear densities for which the charged spin-0 nuclei can condense. The resulting substance has distinctive features, such as a mass gap in the bosonic sector and a gap-less spectrum of quasifermions, which determine its thermodynamic properties. I discuss an effective field theory description of this substance, and as an example, consider its application to calculation of a static potential between heavy charged impurities. The potential exhibits a long-range oscillatory behavior in which both the fermionic and bosonic low-energy degree of freedom contribute. Observational consequences of the condensate for cooling of helium-core white dwarf stars are briefly discussed.
DOUBLE WELL POTENTIAL: PERTURBATION THEORY, TUNNELING, WKB (BEYOND INSTANTONS)
Authors: TURBINER ALEXANDER V.
Published: February 2010

A simple approximate solution for the quantum-mechanical quartic oscillator V = m2x2 + gx4 in the double-well regime m2 < 0 at arbitrary g ≥ 0 is presented. It is based on a combining of perturbation theory near true minima of the potential, semi-classical approximation at large distances and a description of tunneling under the barrier. It provides 9-10 significant digits in energies and gives for wavefunctions the relative deviation in real x-space less than ≲ 10-3.
MELTING BEHAVIOR AND THE GRÜNEISEN PARAMETER OFNaClAT HIGH PRESSURE: A MOLECULAR DYNAMICAL STUDY
Authors: CUI SHOUXIN , CAI LINGCANG , HU HAIQUAN , GONG ZIZHENG , ZHAO JIJUN
Published: February 2010

The improved Tosi–Fumi pair potential has been employed to simulate the melting behavior and Grüneisen parameters of sodium chloride ( NaCl ) using molecular dynamics (MD) method at constant volume. The melting curve of NaCl is compared with the experimental data and other calculations in a pressure range from 0 to 144 GPa. The simulated results validate the amount of 20% superheating of the NaCl solid and yield an approximate power law dependence of the Grüneisen parameter (γ) on compression γ = γ0(V/V0)q, with q ≈ 1.078, in the temperature range from 298 to 1073 K and pressure range from 0 to 60 GPa.
MECHANOCHEMICAL SYNTHESIS OF SINGLE PHASE NANOCRYSTALLINE FORSTERITE POWDER
Authors: TAVANGARIAN F. , EMADI R.
Published: February 2010

Pure nanocrystalline forsterite ( Mg 2 SiO 4) powder was successfully synthesized by mechanochemical route and subsequent annealing. The starting materials were talc ( Mg 3 Si 4 O 10( OH )2) and magnesium carbonate ( MgCO 3) powders. To produce forsterite powder, first talc and magnesium carbonate powders were calcined at 1200°C for 1 h and 700°C for 2 h, respectively. After that the mixture of obtained powders was milled by a planetary ball mill, and then annealed at 1000°C and 1200°C for 1 h. Thermogravimetric (TG) analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques were utilized to characterize the initial and prepared powders. The results showed that a single phase nanocrystalline forsterite powder with a crystallite size of 49 nm was obtained after 40 h milling and subsequent annealing at 1000°C for 1 h.
DO QUANTUM EFFECTS HOLD TOGETHER DNA CONDENSATES?
Authors: IORIO ALFREDO , SEN SAMIK , SEN SIDDHARTHA
Published: February 2010

We model DNA-cation complexes as infinite, one-dimensional, charged wires to single-out the interaction due to quantum fluctuations of the electric field from counterion-induced and water-related interactions. We obtain a frustration-free Casimir-like (codimension 2) interaction that extensive numerical analysis show to be a good candidate to explain the formation and stability of DNA aggregates.
PHOTOINDUCED MAGNETISM IN THE FERROMAGNETIC SEMICONDUCTORS
Authors: MISHRA SUBODHA , SATPATHY SASHI
Published: February 2010

We study the enhancement of the magnetic transition temperature Tc due to incident light in ferromagnetic semiconductors such as EuS. The photoexcited carriers mediate an extra ferromagnetic interaction due to the coupling with the localized magnetic moments increasing the Tc. The Hamiltonian consists of a Heisenberg model for the localized moments and an interaction term between the photoexcited carriers and the localized moments. The model predicts a small enhancement of the transition temperature, about a fraction of a degree K, in semi-quantitative agreement with the experiments.
MODELING HEAT-INDUCED CHEMICAL REACTION IN NANOTHERMITES EXCITED BY PULSE LASER: A HOT SPOT MODEL
Authors: PENG YAJING , WANG YINGHUI , PALPANT BRUNO , HE XING , ZHENG XIANXU , YANG YANQIANG
Published: February 2010

A hot spot model, involving interaction of pulse laser with nanoparticles where heat diffusion and exothermic chemical reaction are considered and spread out of heat and chemical reaction, is developed to model the thermal reaction dynamic process of Al/NC (nitrocellulose) nanothermites excited by pulse laser for the purpose of verifying the experimental ablation criterion proposed recently and providing a microscopic insight into different physical pathways leading to ablation. In this model, the spatial position and conversion of matters taking place in chemical reactions are regarded as the functions of time, space, and temperature. An exact expression of power density absorbed by nanoparticles in matrix is incorporated to calculate the diameters of chemical reaction region. Calculation results justify experimental ablation criterion, and show that thermal decomposition mechanism predominates the nanosecond pulse-excited process before ablation but it is not suitable for the 100 ps regime which is qualitatively attributed to shock pressure. The effects of pulse duration and nanoparticle size on ablation threshold are examined.
STRUCTURES AND MECHANICAL PROPERTIES OF MODULATED ZrB2/W AND ZrB2/WNx NANOMULTILAYERS
Authors: TAN M. , LI D. J. , LIU G. Q. , DONG L. , DENG X. Y. , LIU H. , SUN X.
Published: February 2010

ZrB 2, W , WN x coatings and ZrB 2/ W , ZrB 2/ WN x multilayered coatings have been synthesized by ion beam assisted deposition at room temperature. X-ray diffraction (XRD), XP-2 surface profiler, scanning electron microscopy (SEM) and nano indenter were employed to investigate the influence of modulation periods and N + beam bombardment on microstructure and mechanical properties of the coatings. The low-angle XRD patterns and cross-sectional SEM indicate a well-defined composition modulation and layer structure of the multilayers. The multilayers with modulation periods ranging from 9 to 16 nm without N + bombardment possessed higher hardness and elastic modulus than the rule-of-mixtures value of monolithic ZrB 2 and W coatings. The highest hardness was 24 GPa. N + bombardment to growing multilayers gave a significant contribution to mechanical property enhancement. When modulation period is 9.6 nm, ZrB 2/ WN x multilayer with 200 eV N + bombardment reveals the highest hardness (30.2 GPa) and elastic modulus. This hardest multilayer also showed the improved residual stress and fracture resistance.
EFFECT OF DEPOSITION PARAMETERS ON STRUCTURE AND MECHANICAL PROPERTIES OF TiB2/Si3N4 NANO MULTILAYERS
Authors: DONG L. , LIU G. Q. , SUN Y. D. , LIU M. Y. , LI D. J.
Published: February 2010

TiB 2/ Si 3 N 4 nano multilayers have been synthesized under different deposition parameters related to substrate by ion beam assisted deposition (IBAD). XRD, Nano indenter, profiler, and multi-functional tester for material surface properties were used to characterize the microstructure and mechanical properties of the multilayers. The results indicated a well-defined composition modulation and layer structure of the multilayers. To the multilayers with constant modulation ratio of 15.4:1 and modulation period of 11.8 nm, the multilayer deposited on Al 2 O 3(111) substrate with 38 nm-thick Ti buffer layer at deposition temperature of 225°C revealed the highest hardness (37.4 GPa) and elastic modulus. This hardest multilayer also showed the improved residual stress, friction coefficient, and fracture resistance.
EFFECT OF CALCIUM SULPHATE NANOPARTICLES ON FUSION, MECHANICAL AND THERMAL BEHAVIOUR POLYVINYL CHLORIDE (PVC)
Authors: PATIL C. B. , SHISODE P. S. , KAPADI U. R. , HUNDIWALE D. G. , MAHULIKAR P. P.
Published: February 2010

Calcium Sulphate [ CaSO 4] was synthesized by in-situ deposition technique and its nano size (60 to 100 nm) was confirmed by Transmission Electron Microscopy (TEM). Composites of the filler CaSO 4 (micro and nano) and the matrix poly (vinyl chloride) ( PVC ) were prepared with different filler loading (0-5 wt. %) by melt mixing. The Brabender torque rheometer equipped with an internal mixer was used for preparation and evaluation of fusion behaviour of composites of different formulations. The effect of nano and micro- CaSO 4 content on the structure and properties of composites was studied. The nanostructures and dispersion were studied by wide angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). The mechanical and thermal properties of PVC / micro and nano- CaSO 4 composites were characterized using Universal Testing Machine (UTM) and Thermo Gravimetric Analyzer (TGA). From the results of WAXD and SEM the flocculation of CaSO 4 nanoparticles were observed on the surfaces of PVC matrix. The thermal analysis results showed that the first thermal degradation onset (T onset) of PVC /nano- CaSO 4 composites for 1 wt. % of filler were higher as compared with corresponding microcomposites and pristine PVC . However, the tensile strength was decreasing with increasing filler content while, it shows increment in magnitude at 1 and 2 wt. % of nano- CaSO 4 as compared with corresponding micro- CaSO 4 as well as pristine PVC .
MECHANICAL AND TRIBOLOGICAL BEHAVIOR OF NANOSTRUCTURED TIB2 COATING ON HIGH SPEED STEEL
Authors: PANICH NUROT , WANGYAO PANYAWAT , VISUTTIPITUKUL PATAMA , TUNGASMITA SUKKANESTE , TAN YONG KWANG , SUN YONG
Published: February 2010

Attempts have been made to fabricate the superhard coatings with the purpose to reduce the wear and to improve the tribological performance of the coatings for industrial applications. Several coatings have been produced by the use of direct current and radio frequency magnetron sputtering technique using titanium and TiB 2 as material targets and high speed steel as substrate. The resultant TiB 2 coatings were characterised by a variety of experimental techniques. Scanning electron microscopy (SEM) was employed for coating failure behaviour investigation. Nanoindentation and Micro-scratch were used to extract the intrinsic hardness and elastic modulus evaluation and critical load to the coating failure, respectively. Ball-on-disc sliding test under unlubricated sliding was employed for tribological measurement, for instance, friction coefficient and coating wear-life. The experimental results showed that under unlubricated sliding against an alumina ball, the TiB 2 coatings produced under various deposition conditions obviously increase the wear resistance of high speed steel by more than three times but extremely excellent wear resistance with encountering steel ball.
FINITE DEFORMATION BEHAVIOR OF A SOFT POLYMER COATING ADHERING TO TITANIUM ALLOY (TI6AL4V)
Authors: PUNANTAPONG BOONYONG
Published: February 2010

This article presents the experimental methodology which elucidates the stress-state dependency of the deformation behavior of a soft polymer coating adhering to titanium alloy ( Ti 6 Al 4 V ). The methodology included in situ observations of the evolution of the deformation behavior of elastic film and a rigid substrate under a micro-indenter. The tip of indenter is driven to the polymer film coating at constant displacement rate until interfacial fracture is observed. However, the stress and strain fields which develop in the coating during penetration have been calculated using finite element analysis. For the experimental results, the interfacial stresses are affected by the constraint of the rigid substrate. When the crack was constant, the region in which the stress field increased with time. In addition, the maximum shear stress and the initiation of the interfacial crack were in this region. Furthermore, the high interfacial shear stresses are distributed over a large radial distance, which lead to the fracture initiation in the region of interface.
MICROMECHANICAL CHARACTERIZATION OF HYDROGEL-BASED CONTACT LENS
Authors: LI CHUAN , AHEARNE MARK , LIU KUO-KANG
Published: February 2010

A new micro-shaft-poking (MSP) apparatus has been applied for characterizing the mechanical properties of hydrogel-based contact lens. The instrument allows measurement of the force-displacement curve of the contact lens under a wide range of strain and strain rate. The materials display hysteresis and stress relaxation (50-60%) manifested in the experimental compliance curves. In parallel, a Finite Element Analysis (FEA) modeling incorporated with nonlinear elasticity has been performed for simulating the contact lens under large deformation. Through comparison between the simulated results and experimental data, the mechanical properties, e.g., stiffness, of the lens can be quantitatively determined. The viscoelastic characteristic of the lens has also been parametric fitted based on a five-parameter quasi-viscoelastic model.
PREPARATION AND CHARACTERIZATION OF BIOACTIVE COMPOSITES OF PCL/BIOACTIVE FILLERS
Authors: LI YING , CHEAH CHI MUN , CHANG HENGKY , LOH LEONARD , KUM ADELINE
Published: February 2010

A variety of bioactive composites have been invested over the last two decades as substitute materials for diseased or damaged tissues in the human body. In this paper, bioactive composites were prepared using polycaprolactone ( PCL ) and hydroxyapatite ( HA ). The influence of micro-sized and nano-sized HA on composite properties was investigated. The nano- HA was prepared by wet chemical co-precipitation reaction method. Studies of biocomposite specimen morphology were performed by Field-emission scanning electron microscopy (SEM). XRD (X-Ray Diffraction) and DSC (Differential scanning calorimetry) were used to assess the crystal structure of HA and thermal properties of the composites, respectively. The synthesized nano- HA is found to be of high purity HA structure. The relationship between composition, structure and properties was studied. Different methods to prepare uniform composites were tried, and the outcome of this work suggests that by proper manipulation of biodegradable polymers and bioactive ceramics through material design, bioactive composites with controlled properties might be achievable.
PREPARATION, MORPHOLOGY AND MECHANICAL PROPERTIES OF EPOXY NANOCOMPOSITES WITH ALUMINA FILLERS
Authors: LIM SHEAU HOOI , ZENG KAIYANG , HE CHAOBIN
Published: February 2010

This paper presents recent studies on the processing and characterization of epoxy-alumina nanocomposites. Nano-sized alumina particles are incorporated into epoxy resin via solvent-assisted method, so that the particles are dispersed homogeneously in the epoxy matrix. The morphologies, mechanical and thermomechanical properties of the resulting nanocomposites are studied using transmission electron microscope (TEM), conventional tensile testing and thermomechanical testing methods. TEM results show that the alumina nano-particles with a higher specific surface area tend to agglomerate. Furthermore platelet shape particles shows a better dispersion homogeneity as well as better improvement in the mechanical properties of the composites compared to the rod shape particles.
THE APPLICATION OF TAPANULI CLAY AS NANOFILLER IN NANOCOMPOSITES: SYNTHESIS AND THEIR CHARACTERIZATION
Authors: JUWONO ARIADNE L. , SIHOMBING RIWANDI , KRISNANDI YUNI K. , SUTARNO  , SUBAWI HANDOKO , CHITRANINGRUM NIDYA
Published: February 2010

Organo layered silicates (OLS) were successfully synthesized from Tapanuli clay through an intercalated ultrasonic method using hexadecyltrimethylamonium bromide ( HDTMABr ) as a cation exchange agent. Tapanuli clay–epoxy nanocomposites were also successfully synthesized with an in-situ polymerization. X-Ray Diffraction and Transmission Electron Microscope (TEM) results demonstrated a pattern of clay morphology typically found in nanocomposite systems. Although the nanocomposites' diffractogram showed an exfoliation structure, the TEM findings confirmed that the OLS d -spacing is between 2.58 nm (the minimum value) up to 14.74 nm (the maximum value); which indicates the nanocomposites posses a mixed structure between intercalated and exfoliated structures. It was found that the presence of 1wt% Tapanuli organo clay in the epoxy systems provides higher stiffness and higher Heat Deflection Temperature by 30 % and 7 % respectively.
INTERFACE FRACTURE TOUGHNESS ASSESSMENT OF SOLDER JOINTS USING DOUBLE CANTILEVER BEAM TEST
Authors: LOO SHANE ZHI YUAN , LEE PUAY CHENG , LIM ZAN XUAN , YANTARA NATALIA , TEE TONG YAN , TAN CHER MING , CHEN ZHONG
Published: February 2010

In the current work, a test scheme to evaluate solder joint interface fracture toughness using double cantilever beam (DCB) test has been successfully demonstrated. The obtained results, in terms of critical energy release rate, predict the joint failure based on the principle of fracture mechanics. The results can be used as a materials property in the reliability design of various types of solder-ball joined packages. DCB specimens made of 99.9 wt% copper were selected in the current work. Eutectic Sn -37 Pb and lead-free Sn -3.5 Ag -0.5 Cu solders were used to join two pieces of the copper beams with controlled solder thickness. The test record showed steady propagation of the crack along the solder / copper interface, which verifies the viability of such a testing scheme. Interface fracture toughness for as-joined, extensively-reflowed and thermally aged samples has been measured. Both the reflow treatment and the thermal aging lead to degradation of the solder joint fracture resistance. Reflow treatment was more damaging as it induces much faster interface reaction. Fractographic analysis established that the fracture has a mixed micromechanism of dimple and cleavage. The dimples are formed as a result of the separation between the hard intermetallic compound (IMC) particles and the soft solder material, while the cleavage is formed by the brittle split of the IMCs. When the IMC thickness is increased due to extended interface reaction, the proportion of IMC cleavage failure increases, and this was reflected in the decrease of the critical energy release rate.
FAILURE ANALYSIS OF A SEMICONDUCTOR PACKAGING LEADFRAME USING THE SIGNAL PROCESSING APPROACH
Authors: ABDULLAH SHAHRUM , ARIFFIN AHMAD KAMAL , NIZWAN CHE KU EDDY , ABDULLAH MOHAMAD FAIZAL , JALAR AZMAN , MOD YUNOH MOHD FARIDZ
Published: February 2010

This paper presents a durability analysis of two types of copper leadframe, i.e. the un-oxidised leadframe and the oxidised leadframe. Both leadframe types were used in the fabrication process of a Quad Flat No-Lead (QFN) package, which can be said as a recent type of the 3D stacked die semiconductor package. This study involved the durability test and analysis on QFN packages when these packages were subjected under constant cyclic loadings. In order to perform the cyclic test, the procedure of the three-point cyclic bending test has been employed on the packages. In addition, a strain gauge which was connected to the dynamic data acquisition system was used for each tested QFN package for determining the response of the captured cyclic strain signal. It has been found that the variable amplitude pattern of signal response has been obtained during the constant cyclic test. The obtained response signals for both type of leadframe were then analysed using the approaches of signal processing technique, which is relatively new in this field. The collected response signal were analysed using the normal statistical methods, the Power Spectrum Density (PSD) calculation and also the time-frequency localization analysis. From the detail signal analysis, it has been found that the un-oxidised leadframe showed a lower range of strain response compared to the oxidised leadframe, indicating higher lifetime. As a result, this finding lead to the durability conclusion, for which the un-oxidised leadframe has more durability effects and it also has higher lifetime compared to the oxidised leadframe. Finally, a micro-crack phenomenon at the epoxy interface between the die and the leadframe was also observed for the QFN package with the oxidised leadframe.
EFFECTS OF PRECURSOR ROOTED CONTAMINATION IN THE SINTERING AND DENSIFICATION BEHAVIOR OF THERMO-CHEMICALLY MANUFACTURED W-CU NANOCOMPOSITES
Authors: HASHEMPOUR MAZDAK , RAZAVIZADEH HEKMAT , REZAIE HAMID REZA , HEIDARI DORNA
Published: February 2010

Tungsten and copper, two metals of complete mutual immiscibility, show a variety of densification behaviors due to the processing condition in the sintering stage. In this regard, the presence of different impurities during the densification process, have different influences on the consolidation of the primary powder. In this work, the effects of impurities introduced to the powder by the precursor salt in a novel thermo-chemical homogeneous co-precipitation method were investigated. Addition of sodium tungstate to the aqueous solution of copper nitrate saturated in aqueous ammonia solution, will result in precipitation of CuWO 4·2 H 2 O which will float in a mass of wandering Na + ions in the solution. Removal of these sticking ions by multi stage washing has a certain effect on the final density of the sintered powder. The density of the sintered product was evaluated both with and without the removal of the Na and the mechanism by which this impurity deteriorates the densification was discussed in this work.
INDENTATION SIZE EFFECT ON THE CREEP BEHAVIOR OF A SnAgCu SOLDER
Authors: HAN Y. D. , JING H. Y. , NAI S. M. L. , XU L. Y. , TAN C. M. , WEI J.
Published: February 2010

In the present study, nanoindentation studies of the 95.8 Sn -3.5 Ag -0.7 Cu lead-free solder were conducted over a range of maximum loads from 20 mN to 100 mN, under a constant ramp rate of 0.05 s-1. The indentation scale dependence of creep behavior was investigated. The results revealed that the creep rate, creep strain rate and indentation stress are all dependent on the indentation depth. As the maximum load increased, an increasing trend in the creep rate was observed, while a decreasing trend in creep strain rate and indentation stress were observed. On the contrary, for the case of stress exponent value, no trend was observed and the values were found to range from 6.16 to 7.38. Furthermore, the experimental results also showed that the creep mechanism of the lead-free solder is dominated by dislocation climb.
COMPUTATIONAL STUDY OF TENSILE DEFORMATION OF A CONSTRAINED NANOSCALE METALLIC GLASS
Authors: PANG JIANJUN , TAN MING-JEN , LIEW KIM-MEOW
Published: February 2010

In this study a nanometer-sized metallic glass (nano-MG) Ti 50 Cu 50 was generated with constrained atoms at both ends and was extended until fracture under a tensile load by molecular dynamics simulation using the general embedded-atom model (GEAM) potential. Totally different mechanical behavior was observed in the nano-MG, such as strain hardening and necking, both of which have been discovered in a few real and simulated MGs and can be related to the generation of shear transformation zones (STZs). A dramatic drop in Young's modulus was found due to the surface effect. Such effect results from the large fraction of surface atoms which have a different surrounding configuration from bulk atoms. At fracture the nano-MG breaks by atomic separation as reported in metal nanowires. The fracture strain is as large as about 120%, indicating that nano-MGs are intrinsically ductile.
NONCLASSICAL SCALAR FIELD IN THE FRW UNIVERSE
Authors: VENKATARATNAM K. K. , SURESH P. K.
Published: February 2010

Nonclassical representation of a minimally coupled scalar field in the open and closed FRW universe, is studied in the semiclassical theory of gravity. Particle production of a nonclassical scalar field in the coherent and squeezed state formalisms in the open FRW universe is examined. Numerical solutions to the semiclassical Friedmann equations are obtained for both the closed and open models in the coherent and squeezed state formalisms. Mandel's Q parameter of the quantum optics is studied in the cosmological context with associated cosmological parameters, in the semiclassical theory of gravity.