bluuebunny/crossref_metadata_2025 huggingface dataset:
Terahertz electromagnetic interactions with biological matter and their applications
Authors: Son Joo-Hiuk
Published: May 2009

The characteristics of electromagnetic interactions with biological matter in the terahertz region are reviewed. The recent development of terahertz technology has made possible the study of the scientifically rich spectral region where molecular rotational and vibrational modes exist. The technology is reviewed in terms of sources, detectors, and related techniques for spectroscopy and imaging. The spectroscopic technique has been utilized for the investigation of various biological molecules including DNAs, RNAs, nucleobases, proteins, polypeptides, and biological liquids to reveal intermolecular and intramolecular dynamics. Terahertz imaging has also proven to be a potential modality of medical diagnosis using the results of preliminary researches of skin and breast cancers.
A membrane basis for bacterial identification and discrimination using laser-induced breakdown spectroscopy
Authors: Rehse Steven J. , Jeyasingham Narmatha , Diedrich Jonathan , Palchaudhuri Sunil
Published: May 2009

Nanosecond single-pulse laser-induced breakdown spectroscopy (LIBS) has been used to discriminate between two different genera of Gram-negative bacteria and between several strains of the Escherichia coli bacterium based on the relative concentration of trace inorganic elements in the bacteria. Of particular importance in all such studies to date has been the role of divalent cations, specifically Ca2+ and Mg2+, which are present in the membranes of Gram-negative bacteria and act to aggregate the highly polar lipopolysaccharide molecules. We have demonstrated that the source of emission from Ca and Mg atoms observed in LIBS plasmas from bacteria is at least partially located at the outer membrane by intentionally altering membrane biochemistry and correlating these changes with the observed changes in the LIBS spectra. The definitive assignment of some fraction of the LIBS emission to the outer membrane composition establishes a potential serological, or surface-antigen, basis for the laser-based identification. E. coli and Pseudomonas aeruginosa were cultured in three nutrient media: trypticase soy agar as a control, a MacConkey agar with a 0.01% concentration of bile salts including sodium deoxycholate, and a trypticase soy agar with a 0.4% deoxycholate concentration. The higher concentration of deoxycholate is known to disrupt bacterial outer membrane integrity and was expected to induce changes in the observed LIBS spectra. Altered LIBS emission was observed for bacteria cultured in this 0.4% medium and laser ablated in an all-argon environment. These spectra evidenced a reduced calcium emission and in the case of one species, a reduced magnesium emission. Culturing on the lower (0.01%) concentration of bile salts altered the LIBS spectra for both the P. aeruginosa and two strains of E. coli in a highly reproducible way, although not nearly as significantly as culturing in the higher concentration of deoxycholate did. This was possibly due to the accumulation of divalent cations around the bacteria by the formation of an extracellular polysaccharide capsule. Lastly, a discriminant function analysis demonstrated that in spite of alterations in the LIBS spectrum induced by growth in the three different media, the analysis could correctly identify all samples better than 90% of the time. This encouraging result illustrates the potential utility of LIBS as a rapid bacteriological identification technology.
Biophysical mechanisms of modification of skin optical properties in the UV wavelength range with nanoparticles
Authors: Popov A. P. , Priezzhev A. V. , Lademann J. , Myllylä R.
Published: May 2009

In this paper, by means of the Mie theory and Monte Carlo simulations we investigate modification of optical properties of the superficial layer of human skin (stratum corneum) for 310- and 400-nm ultraviolet (UV) radiation by embedding of 35–200-nm-sized particles of titanium dioxide (TiO2) and silicon (Si). Problem of skin protection against UV light is of major importance due to increased frequency of skin cancer provoked by excessive doses of accepted UV radiation. For 310-nm light, the optimal sizes of the TiO2 and Si particles are found to be 62 and 55 nm, respectively, and for 400-nm radiation, 122 and 70 nm, respectively.
Laser interference microscopy in erythrocyte study
Authors: Yusipovich A. I. , Parshina E. Yu. , Brysgalova N. Yu. , Brazhe A. R. , Brazhe N. A. , Lomakin A. G. , Levin G. G. , Maksimov G. V.
Published: May 2009

With the laser interference microscopy (LIM) technique, one can measure phase height of cells—a variable proportional to the cell thickness and the difference in the refractive indices of the cell and the surrounding medium. This makes functional optical cell imaging possible, and estimation of shape, thickness, and area of erythrocytes feasible. In this paper, we studied changes in erythrocyte shape and volume with osmolarity and pH. Obtained from the LIM technique, erythrocyte phase heights and area values, as well as the hematocrit-measured erythrocyte volume, were used to estimate changes in the refractive index with osmolarity and pH. A comparison between the estimated refractive index with the refractive index, calculated in the assumption that it can only depend on the hemoglobin concentration in the cell, indicates that these two estimates are identical in the range of osmolarity (250–1000 mOsm) and pH (4.5–10.0) values. Thus, refractive index changes result exclusively from the changes in hemoglobin concentration with the changes in erythrocyte volume. Under these conditions, it is possible to estimate the amount of hemoglobin in an erythrocyte from its phase height and area, obtained from LIM.
Possibility for a full optical determination of photodynamic therapy outcome
Authors: Vollet-Filho J. D. , Menezes P. F. C. , Moriyama L. T. , Grecco C. , Sibata C. , Allison R. R. , Castro e Silva O. , Bagnato V. S.
Published: May 2009

The efficacy of photodynamic therapy (PDT) depends on a variety of parameters: concentration of the photosensitizer at the time of treatment, light wavelength, fluence, fluence rate, availability of oxygen within the illuminated volume, and light distribution in the tissue. Dosimetry in PDT requires the congregation of adequate amounts of light, drug, and tissue oxygen. The adequate dosimetry should be able to predict the extension of the tissue damage. Photosensitizer photobleaching rate depends on the availability of molecular oxygen in the tissue. Based on photosensitizers photobleaching models, high photobleaching has to be associated with high production of singlet oxygen and therefore with higher photodynamic action, resulting in a greater depth of necrosis. The purpose of this work is to show a possible correlation between depth of necrosis and the in vivo photosensitizer (in this case, Photogem®) photodegradation during PDT. Such correlation allows possibilities for the development of a real time evaluation of the photodynamic action during PDT application. Experiments were performed in a range of fluence (0–450 J/cm2) at a constant fluence rate of 250 mW/cm2 and applying different illumination times (0–1800 s) to achieve the desired fluence. A quantity was defined (ψ) as the product of fluorescence ratio (related to the photosensitizer degradation at the surface) and the observed depth of necrosis. The correlation between depth of necrosis and surface fluorescence signal is expressed in ψ and could allow, in principle, a noninvasive monitoring of PDT effects during treatment. High degree of correlation is observed and a simple mathematical model to justify the results is presented.
Controlled localization and enhanced gathering of particles on microfabricated concentrators assisted by ac-electro-osmosis
Authors: Tanguy Laurent , Nicu Liviu
Published: May 2009

ac-electro-osmosis is used to concentrate particles on circular gold electrodes. Localization of the concentration of particles is predicted and experimentally observed by slight modifications of the electrical parameters (frequency, voltage intensity). Efficiency evaluations of the concentrators are proposed and applied to our system and compared with the predictions. Experimental concentration on dedicated test devices is 200 times faster than classical diffusion. An optimization of the collection rate is obtained by switching the frequency signal between two determined values. This optimization allows doubling the arrival rate of particles.
Does the deoxyribonucleic acid shape dictate its conductivity?
Authors: Romano P. , Polcari A. , Granata V. , Sabatino L. , Colantuoni V.
Published: May 2009

We present the evolution of current-voltage characteristics measured on linear fragments of deoxyribonucleic acid (DNA) molecules as a function of their length. The nonlinear behavior systematically observed at room temperature and also reported on circular plasmids suggests that the more molecules are involved in the conduction process, the higher are the current values measured. At the same time, a characteristic steplike feature superimposed to an overall increasing background appears more pronounced. We interpret this behavior in terms of simultaneous coherent and incoherent transport processes, the former taking place inside the DNA molecule, the latter through the network of molecules. Following our previous analysis on circular molecules, a phenomenological model is developed, in which a tunneling current with an energy dependent transmission coefficient is superimposed to a hopping current. The model provides a semiquantitative evidence that the steplike feature represents the signature of charge transmission inside the molecule. Our results are consistent with many of the conductivity data present in the literature.
Device considerations for development of conductance-based biosensors
Authors: Lee Kangho , Nair Pradeep R. , Scott Adina , Alam Muhammad A. , Janes David B.
Published: May 2009

Design and fabrication of electronic biosensors based on field-effect-transistor (FET) devices require understanding of interactions between semiconductor surfaces and organic biomolecules. From this perspective, we review practical considerations for electronic biosensors with emphasis on molecular passivation effects on FET device characteristics upon immobilization of organic molecules and an electrostatic model for FET-based biosensors.
Emerging technologies for diagnosis of dental caries: The road so far
Authors: Amaechi Bennett T.
Published: May 2009

It is now universally recognized that the development of new technologies for early detection and quantitative monitoring of dental decay at an early stage of formation could provide health and economic benefits ranging from timely preventive interventions to reduction in the time required for clinical trials of anticaries agents. The use of technologies as adjunct to clinical visual examination for caries diagnosis will facilitate preventive care in dentistry to lower treatment cost as well as reduce the cost and time for testing potential anticaries agents. This article describes the various technologies available to aid the dental practitioners in detecting dental caries at the earliest stage of its formation, assessing the activities of the detected carious lesion, and quantitatively or qualitatively monitoring of the lesion over time. The need and the importance of these technologies were also discussed. The data discussed are primarily based on published scientific studies and reviews from case reports, clinical trials, and in vitro and in vivo studies. References have been traced manually by MEDLINE® or through manufacturer’s websites. While some of the devices are fully developed and commercially available, others are still under development. The devices vary in their modes of action as well as their capability as caries diagnostic aids. It is clear that the differences in caries presentations and behavior in different anatomical sites make it unlikely that any one diagnostic modality will have adequate sensitivity and specificity of detection of carious lesions for all sites; a combination of diagnostic tools will help us diagnose lesions earlier and detect failing restorations sooner, all to avoid more costly, destructive dental procedures and truly take dentistry into the preventive rather than the reactive mode.
Low dielectric loss and non-Debye relaxation of gamma-Y2Si2O7 ceramic at elevated temperature in X-band
Authors: Cao Mao-Sheng , Hou Zhi-Ling , Yuan Jie , Xiong Lan-Tian , Shi Xiao-Ling
Published: May 2009

Bulk single-phase gamma-Y2Si2O7 ceramic has been synthesized from a mixture of Y2O3 powder and SiO2 nanopowder at 1400 °C. The dielectric properties are reported at the temperature ranging from room temperature to 1400 °C in X-band. The results show that gamma-Y2Si2O7 exhibits low dielectric loss and non–Debye relaxation behavior different from that of SiO2. The peculiar relaxation peak is attributed to the structural relaxation polarization caused by thermal-excitation structural defects, which implies that no ionic conductance exists in this material. Such low dielectric loss will draw much attention for potential dielectric applications at high temperature.
Ultraflat monocrystalline Pt (111) electrodes
Authors: Trassin M. , Viart N. , Ulhaq-Bouillet C. , Versini G. , Barre S. , Leuvrey C. , Pourroy G.
Published: May 2009

We report here the growth of Pt electrodes presenting at the same time an ultraflat surface (rms=0.3 nm) and a perfect (111) monocrystalline orientation. These electrodes were grown by pulsed laser deposition on yttrium-stabilized zirconia (111), using a few nanometers thick titanium adhesion layer. Such high crystalline quality electrodes allow the growth of subsequent layers with a very reduced number of variants. They therefore open perspectives for the anisotropic characterization of multiferroic or magnetoelectric materials. The optimized growth of the magnetoelectric GaFeO3 on such a Pt(111) electrode is shown as an example.
A first-principles study of the effects of Hf doping on the dielectric response in ZrO2
Authors: Dutta Gargi
Published: May 2009

The electronic structure and dielectric response of 25% and 50% Hf substituted zirconia (ZrO2) are determined, using first-principles density functional theory calculations based on pseudopotentials and a plane wave basis. It is found that Zr0.75Hf0.25O2 is more promising with higher dielectric response compared to pure ZrO2, the dielectric constant increases further upon introduction of oxygen vacancies. In contrast, Zr0.5Hf0.5O2 shows a decrease in the response compared to pure ZrO2. The IR-active phonon modes cause enhanced response in 25% Hf substituted ZrO2 and the material remains insulating making it promising for applications such as a gate oxide material.
Spin-glasslike behavior in rhombohedral (Ge,Mn)Te–(Sn,Mn)Te mixed crystal
Authors: Kilanski L. , Arciszewska M. , Dobrowolski W. , Domukhovski V. , Slynko V. E. , Slynko E. I.
Published: May 2009

We present studies of magnetic and transport properties of Ge1−x−ySnxMnyTe mixed crystals with chemical compositions 0.083≤x≤0.142 and 0.012≤y≤0.119. The transport characterization measurements were performed at temperatures 4.2<T<300 K. The results showed feature characteristic for narrow gap semiconductors, e.g., metallic conductivity with ρxx≈10−4 Ω cm and hole concentrations p>1021 cm−3. It was found that the transport properties strongly depend on the chemical composition of the alloy. The magnetic investigations included measurements of linear χ1 and harmonic χ2,3 ac susceptibilities as a function of temperature and of the applied magnetic field amplitude and frequency. Qualitative analysis of our experimental data showed that in the studied system, in the investigated composition range, the spin glass order exists at temperatures up to 50 K.
High-resolution spectroscopy of weak and short-lived bands of the S1 B13u←S A1g transition of naphthalene
Authors: Yoshida Kazuto , Semba Yosuke , Kasahara Shunji , Yamanaka Takaya , Baba Masaaki
Published: May 2009

Rotationally resolved high-resolution spectra and fluorescence decay curves have been observed for weak and short-lived vibronic bands of the S1 B13u←S0 A1g transition of naphthalene. Fluorescence lifetime of the vibronic band with an excess energy of 1390 cm−1 (000+1390 cm−1 band) is remarkably shorter than that of other bands. Zeeman splitting of rotational lines is very small, so that the main radiationless process is not intersystem crossing to the triplet state but internal conversion to the ground state. The lifetime is thought to be governed by the strength of vibronic coupling between vibrational levels of the S0 and S1 states. As for the 000+2570 cm−1 band, energy shifts were found in only a few rotational levels although the excess energy was higher than the threshold of intramolecular vibrational redistribution. We conclude that all of the rotational levels are mixed with other vibrational levels. The 000+3068 cm−1 band spectrum is fairly complicated with numerous rotational lines, which is attributed to strong vibronic coupling with the S2 B12u state.
Faster strain fluctuation methods through partial volume updates
Authors: Pronk Sander , Geissler Phillip L.
Published: May 2009

Elastic systems that are spatially heterogeneous in their mechanical response pose special challenges for molecular simulations. Standard methods for sampling thermal fluctuations of a system’s size and shape proceed through a series of homogeneous deformations, whose magnitudes can be severely restricted by its stiffest parts. Here we present a Monte Carlo algorithm designed to circumvent this difficulty, which can be prohibitive in many systems of modern interest. By deforming randomly selected subvolumes alone, it naturally distributes the amplitude of spontaneous elastic fluctuations according to intrinsic heterogeneity. We describe in detail implementations of such “slice moves” that are consistent with detailed balance. Their practical application is illustrated for crystals of two-dimensional hard disks and random networks of cross-linked polymers.
Pre-edges in oxygen (1s) x-ray absorption spectra: A spectral indicator for electron hole depletion and transport blocking in iron perovskites
Authors: Braun Artur , Bayraktar Defne , Erat Selma , Harvey Ashley S. , Beckel Daniel , Purton John A. , Holtappels Peter , Gauckler Ludwig J. , Graule Thomas
Published: May 2009

The eg↑/(t2g↓+eg↓) band ratio in cation-substituted La–Fe oxides is identified in O (1s) x-ray absorption spectra as a linear spectral indicator for conducting electron holes. The t2g↓ and eg↓ bands act as a conductivity inhibitor by ferromagnetic double exchange coupling on the eg↑ electron. Disorder induced by substitution appears to modulate the hole conduction such that an exponential relation is found between the conductivity and the eg↑/(t2g↓+eg↓) ratio and hole concentration. The quantitative correlation of conductivity and x-ray absorption spectra from heterovalent-substituted LaFeO3 lets substitution-driven metal insulator transitions appear in a new light.
Chemically mediated diffusion of d-metals and B through Si and agglomeration at Si-on-Mo interfaces
Authors: Tsarfati Tim , Zoethout Erwin , van de Kruijs Robbert , Bijkerk Fred
Published: May 2009

Chemical diffusion and interlayer formation in thin layers and at interfaces is of increasing influence in nanoscopic devices, such as nanoelectronics and reflective multilayer optics. Chemical diffusion and agglomeration at interfaces of thin Ru, Mo, Si, and B4C layers have been studied with x-ray photoelectron spectroscopy, cross section electron energy loss spectroscopy, high-angle annular dark field scanning transmission electron microscopy, and energy dispersive x-ray in relation to observations in Ru-on-B4C capped Mo/Si multilayers. Rather than in the midst of the Si layer, silicides and borides are formed at the Si-on-Mo interface front, notably RuSix and MoBx. The interface apparently acts as a precursor for further chemical diffusion and agglomeration of B, Ru, and also other investigated d-metals. Reversed “substrate-on-adlayer” interfaces can yield entirely suppressed reactivity and diffusion, stressing the influence of surface free energy and the supply of atoms to the interface via segregation during thin layer growth.
On the collective network of ionic liquid/water mixtures. III. Structural analysis of ionic liquids on the basis of Voronoi decomposition
Authors: Schröder C. , Neumayr G. , Steinhauser O.
Published: May 2009

Three different mixtures of 1-butyl-3-methyl-imidazolium tetrafluoroborate with water have been studied by means of molecular dynamics simulations. Based on the classical Lopes–Padua force field trajectories of approximately 60 ns were computed. This is the third part of a series concerning the collective network of 1-butyl-3-methyl-imidazolium tetrafluoroborate/water mixtures. The first part [C. Schröder et al., J. Chem. Phys. 127, 234503 (2007)] dealt with the orientational structure and static dielectric constants. The second part [C. Schröder et al., J. Chem. Phys. 129, 184501 (2008)] was focused on the decomposition of the dielectric spectrum of these mixtures. In this work the focus lies on the characterization of the neighborhood of ionic liquids by means of the Voronoi decomposition. The Voronoi algorithm is a rational tool to uniquely decompose the space around a reference molecule without using any empirical parameters. Thus, neighborhood relations, direct and indirect ones, can be extracted and were used in combination with g-coefficients. These coefficients represent the generalization of the traditional radial distribution function in order to include the mutual positioning and orientation of anisotropic molecules. Furthermore, the Voronoi method provides, as a by-product, the mutual coordination numbers of molecular species.
On a class of solutions of the Einstein–Maxwell field equations in scalar-tensor theories of gravity
Authors: Sobreira A. A. R. , Marques Geusa de A. , Fonseca-Neto J. B. , Bezerra V. B.
Published: May 2009

In this paper we obtain a class of static cylindrically symmetric solutions of the Einstein–Maxwell field equations in the framework of scalar-tensor theories of gravity. In this context, in which both a Maxwell field and a dilaton field are sources of the stress energy, the solutions were obtained by using the Rainich conditions of general relativity, appropriately modified to take into account the presence of the scalar field.
A new thermodynamic framework for second-grade Korteweg-type viscous fluids
Authors: Cimmelli V. A. , Sellitto A. , Triani V.
Published: May 2009

A model of viscous fluid of Korteweg type, with first-order nonlocal constitutive equations, is developed. The restrictions placed by the dissipation principle are investigated by applying a generalized Liu procedure. Some remarkable nonlocal properties of the entropy function are carried out.
A wide-band-gap p-type thermoelectric material based on quaternary chalcogenides of Cu2ZnSnQ4 (Q=S,Se)
Authors: Liu Min-Ling , Huang Fu-Qiang , Chen Li-Dong , Chen I-Wei
Published: May 2009

Chalcopyritelike quaternary chalcogenides, Cu2ZnSnQ4 (Q=S,Se), were investigated as an alternative class of wide-band-gap p-type thermoelectric materials. Their distorted diamondlike structure and quaternary compositions are beneficial to lowering lattice thermal conductivities. Meanwhile, partial substitution of Cu for Zn creates more charge carriers and conducting pathways via the CuQ4 network, enhancing electrical conductivity. The power factor and the figure of merit (ZT) increase with the temperature, making these materials suitable for high temperature applications. For Cu2.1Zn0.9SnQ4, ZT reaches about 0.4 at 700 K, rising to 0.9 at 860 K.
Band structures built by the elongation method
Authors: Pomogaeva Anna , Springborg Michael , Kirtman Bernard , Gu Feng Long , Aoki Yuriko
Published: May 2009

A recently proposed approach for extracting band structures from finite-cluster calculations is improved so that (avoided) band crossings can be handled and the problems related to so-called doublings and holes are reduced. In particular, we demonstrate how the method can be combined with the elongation method for the finite-system calculations and apply it to extracting band structures for polymers from oligomer calculations. As illustrations of the approach we discuss a chain of water molecules, polyacetylene, polyethylene, and a BN nanotube without and with an impurity.
Three dimensional quantum geometry and deformed symmetry
Authors: Joung E. , Mourad J. , Noui K.
Published: May 2009

We study a three dimensional noncommutative space emerging in the context of three dimensional Euclidean quantum gravity. Our starting point is the assumption that the isometry group is deformed to the Drinfeld double D(SU(2)). We generalize to the deformed case the construction of E3 as the quotient of its isometry group ISU(2) by SU(2). We show that the algebra of functions on E3 becomes the noncommutative algebra of SU(2) distributions, C(SU(2))∗, endowed with the convolution product. This construction gives the action of ISU(2) on the algebra and allows the determination of plane waves and coordinate functions. In particular, we show the following: (i) plane waves have bounded momenta; (ii) to a given momentum are associated several SU(2) elements leading to an effective description of ϕ∊C(SU(2))∗ in terms of several physical scalar fields on E3; (iii) their product leads to a deformed addition rule of momenta consistent with the bound on the spectrum. We generalize to the noncommutative setting the “local” action for a scalar field. Finally, we obtain, using harmonic analysis, another useful description of the algebra as the direct sum of the algebra of matrices. The algebra of matrices inherits the action of ISU(2): rotations leave the order of the matrices invariant, whereas translations change the order in a way we explicitly determine.
Connectivity in the potential energy landscape for binary Lennard-Jones systems
Authors: de Souza Vanessa K. , Wales David J.
Published: May 2009

Connectivity in the potential energy landscape of a binary Lennard-Jones system can be characterized at the level of cage-breaking. We calculate the number of cage-breaking routes from a given local minimum and determine the branching probabilities at different temperatures, along with correlation factors that represent the repeated reversals of cage-breaking events. The number of reversals increases at lower temperatures and for more fragile systems, while the number of accessible connections decreases. We therefore associate changes in connectivity with super-Arrhenius behavior. Reversals in minimum-to-minimum transitions are common, but often correspond to “non-cage-breaking” processes. We demonstrate that the average waiting time within a minimum shows simple exponential behavior with decreasing temperature. To describe the long-term behavior of the system, we consider reversals and connectivity in terms of the “cage-breaking” processes that are pertinent to diffusion [V. K. de Souza and D. J. Wales, J. Chem. Phys. 129, 164507 (2008)]. These cage-breaking events can be modeled by a correlated random walk. Thus, a full correlation factor can be calculated using short simulations that extend up to two cage-breaking events.
Phase equilibrium of colloidal suspensions with particle size dispersity: A Monte Carlo study
Authors: Yiannourakou Marianna , Economou Ioannis G. , Bitsanis Ioannis A.
Published: May 2009

We have studied the crystalline-amorphous coexistence for systems of polydisperse soft spheres that interact via a purely repulsive power law potential. Potential softness quantified by the exponent of the potential was a primary input in our simulations. Simulations were performed in the isobaric semigrand statistical ensemble, i.e., the composition of the parent distribution was not fixed in our systems. Gibbs–Duhem integration was used to trace the coexistence pressure as a function of potential softness for monodisperse systems. A second Gibbs–Duhem integration, initiated from the monodisperse coexistence curve, was employed to determine coexistence pressure versus imposed variance of the activity distribution. Amorphous-crystalline coexistence densities and volume fractions were determined to be monotonically increasing functions of the breadth of particle size dispersity. Semigrand ensemble simulations testified to the existence of a terminal diameter dispersity, i.e., a dispersity above which no amorphous-crystalline phase coexistence was observed. At the terminus size dispersity increases from 5.8% to 6.1% to 6.4% and to 6.7% and 6.5% for the crystalline phase as the steepness parameter n, takes on smaller values: from 100 to 50 to 12 to 10 and 8, respectively. In sharp contrast to the crystalline phases’ enhanced, by potential softness, allowable size dispersity the amorphous phase exhibits an opposite trend, as potential interactions soften. Furthermore, amorphous phases accommodate, on average, smaller particles than those of the ordered (fcc) phase. Contrary to widely accepted intuition crystalline phases composed of size-disperse particulates exhibit a higher degree of local order than their monodisperse counterparts, admittedly at differing thermodynamic conditions.
Surface and core magnetic anisotropy in maghemite nanoparticles determined by pressure experiments
Authors: Komorida Y. , Mito M. , Deguchi H. , Takagi S. , Millán A. , Silva N. J. O. , Palacio F.
Published: May 2009

In magnetic nanoparticles, anisotropy energy has extra contributions compared to that of the bulk counterparts, being the most relevant surface anisotropy. Here we use pressure to separate core from surface anisotropy in one system of maghemite nanoparticles dispersed in a polymer. The core anisotropy is Kcore=7.7×105 erg/cm3 while the surface anisotropy is KS=4.2×10−2 erg/cm2. This in-one-sample separation is possible due to changes in structurally ordered and disordered ratio, which induce changes in the average magnetic anisotropy energy.
Theoretical study of Ban+–RG (RG=rare gas) complexes and transport of Ban+ through RG (n=1,2; RG=He–Rn)
Authors: McGuirk Maureen F. , Viehland Larry A. , Lee Edmond P. F. , Breckenridge W. H. , Withers Carolyn D. , Gardner Adrian M. , Plowright Richard J. , Wright Timothy G.
Published: May 2009

We present high-level ab initio potential energy curves for barium cations and dications interacting with RG atoms (RG=rare gas). These potentials are employed to derive spectroscopic parameters for the Ba+–RG and Ba2+–RG complexes, and also to derive the transport coefficients for Ba+ and Ba2+ moving through a bath of the rare gas. The results are compared to the limited experimental data, which generally show reasonable agreement. We identify a large change in binding energy going from Ba+–He and Ba+–Ne to Ba+–Ar, which is not present in Ba2+–RG, and show that this is due to significant dispersion interactions in Ba+–RG.
Nonlinear dust-acoustic waves in a strongly coupled dusty plasma with vortexlike ion distribution
Authors: Anowar M. G. M. , Rahman M. S. , Mamun A. A.
Published: May 2009

The nonlinear features of dust-acoustic (DA) waves in a strongly coupled unmagnetized dusty plasma (containing electrons following Boltzmann distribution, ions obeying vortexlike distribution, and negatively charged mobile dust) are investigated by using reductive perturbation method. It is observed that the nonlinear propagation of the DA waves gives rise to solitary structures when the strong correlation is absent and gives rise to shock structures when the strong correlation among the dust grains is present. The condition for the formation of oscillatory and monotonic shock structures is also found. The implications of our result in space and laboratory dusty plasmas are discussed.
A method of reduction of order for discrete systems
Authors: Gordoa P. R. , Pickering A.
Published: May 2009

We show how, by establishing a suitable Bäcklund correspondence, a reduction in order can be effected for discrete systems having a certain structure. In this way we succeed in extending to discrete systems ideas previously developed within the context of ordinary differential equations. It is also worth emphasizing that our approach represents an application of properties characteristic of completely integrable systems outside of that context, that is, to systems of discrete equations, integrable or otherwise.
A test of implicit solvent models on the folding simulation of the GB1 peptide
Authors: Shao Qiang , Yang Lijiang , Gao Yi Qin
Published: May 2009

To quantify the effects of implicit solvent model on the folding of protein, thermodynamics calculation was performed for the folding of C-terminal hairpin from B1 domain of protein G using AMBER ff96 force field and different implicit solvent models (GBOBC and GBn). In the multiple AMBER force fields, ff96 strongly favors the hairpin conformations whereas the other force fields (e.g., ff94 and ff99) favor the helical conformations. In recent studies ff96 was found to be better balanced for various secondary structures than other force fields. The two implicit solvent models mentioned above were shown to be the most appropriate for β-hairpin folding [M. S. Shell et al., J. Phys. Chem. B 112, 6878 (2008)]. The free energy landscape as a function of several different reaction coordinates was studied for both solvent models. The comparison of the results from these implicit models shows that the combination of AMBER ff96 with the GBOBC model yields stable structures that are in better agreement with experiments and results calculated using the explicit solvent model.
Effects of varying magnetosheath flow and dissipation on the two-dimensional reconnection structure at the magnetopause
Authors: Westerberg Lars G. , Åkerstedt Hans O. , Taavola J. Henric
Published: May 2009

The stationary Riemann problem including dissipation in form of resistivity and viscosity for the reconnection structure at the dayside magnetopause is considered. Including tangential velocity shear and gradients across the complete reconnection structure from the magnetosheath side into the magnetosphere, it is shown how dissipation affects the thickness of the intermediate shock wave in the vicinity of a reconnection site. We present how plasma flow structure undergoes a significant change for a nonzero uniform plasma velocity and velocity gradient. It is also shown how the reconnection rate changes and leads to a cutoff when the velocity becomes Alfvénic.
Electron scale structures in collisionless magnetic reconnection
Authors: Jain Neeraj , Sharma A. Surjalal
Published: May 2009

The early time-dependent phase of collisionless reconnection, which is dominated by electron dynamics, is investigated using electron-magnetohydrodynamic simulations. Simulations initialized with multi-wavelength perturbations lead to reconnection at multiple sites and the interaction of electron flows generated at the neighboring sites leads to secondary instabilities. These electron-scale processes limit the size of the current sheet and lead to an out-of-plane magnetic field with nested quadrupoles. These structures have important implications for multi-spacecraft missions exploring Earth’s magnetotail.
Theory of antibunching of photon emission II
Authors: Seki Kazuhiko , Tachiya M.
Published: May 2009

Recently single photon emission has been observed for systems in which multiple excitons are generated by pulsed excitation. When fast pair annihilation of excitons takes place, finally a single exciton remains and single photon can be emitted. Its efficiency depends on the competition among pair annihilation, unimolecular nonradiative, and radiative processes. The efficiency of single photon emission is usually studied by measuring the correlation of emitted photons after pulsed excitation by the Hanbury-Brown and Twiss method. The photon correlation measured in this method is different from that calculated by taking into account all pairs of emitted photons, which was presented in a previous paper. We calculate the former rigorously for the first time in the case of multiple excitations and compare it with the latter. We also calculate correlation of arrival times of two photons by the Hanbury-Brown and Twiss method. These results should be useful for the analysis of the antibunching measurement by the Hanbury-Brown and Twiss method.
A generalized model for conic flexure hinges
Authors: Chen Guimin , Liu Xiaoyuan , Gao Hongwei , Jia Jianyuan
Published: May 2009

Flexure hinges have been used to produce frictionless and backlashless transmission in a variety of precision instruments. Many kinds of flexure profile were proposed during the past decade. The present work brings elliptical arc, parabolic, and hyperbolic profiles together by proposing a generalized conic flexure hinge model. By utilizing the generalized equation for conic curves in polar coordinates, all the elements in the compliance and precision matrices for conic flexure hinges are deduced. These equations were verified by finite element analysis and experimentation. The analytical results are within 11% error compared to the finite element results and within 6% error compared to the experimental results.
Magnetoelectric effect of polymer electrolyte composites with Terfenol-D and lead zirconate titanate inclusions
Authors: Chau K. H. , Wong Y. W. , Shin F. G.
Published: May 2009

The magnetoelectric effects of three-phase composites in 0-0-3 connectivity were investigated. The composites consist of particulate Terfenol-D and lead zirconate titanate blended in different polymer matrices. The magnetoelectric coefficient αq, which is the charge density change in response to a change in the applied magnetic field, of the samples was measured under short circuit condition. The results show that the αq of the samples with an electrolytic polymer matrix is larger than that of the samples with an insulating matrix, while samples with an ion-doped electrolytic polymer matrix exhibit the largest αq. These results conform with the expectation that higher matrix conductivity has an effect of enhancing the magnetoelectric signals.
Antiphase and in-phase synchronization of nonlinear oscillators: The Huygens’s clocks system
Authors: Dilão Rui
Published: May 2009

We introduce an interaction mechanism between oscillators leading to exact antiphase and in-phase synchronization. This mechanism is applied to the coupling between two nonlinear oscillators with a limit cycle in phase space, leading to a simple justification of the antiphase synchronization as observed in Huygens’s pendulum clocks experiment. If the two coupled nonlinear oscillators reach the antiphase or the in-phase synchronized oscillatory state, the period of oscillation is different from the eigenperiods of the uncoupled oscillators.
Single-mode operation of a high-brightness narrow-band single-photon source
Authors: Scholz M. , Koch L. , Ullmann R. , Benson O.
Published: May 2009

We demonstrate a narrow-band single-photon source based on cavity-enhanced parametric downconversion for efficient coupling to atomic quantum memories. Selecting a single longitudinal cavity mode by spectral filtering, we achieve a spectral brightness of ∼330 biphotons/(s mW MHz) and an overall bandwidth of 2.7 MHz, which suits the width of naturally broadened transitions in alkali gases like rubidium or cesium.
Urban mockingbirds quickly learn to identify individual humans
Authors: Levey Douglas J. , Londoño Gustavo A. , Ungvari-Martin Judit , Hiersoux Monique R. , Jankowski Jill E. , Poulsen John R. , Stracey Christine M. , Robinson Scott K.
Published: May 2009

Practically all animals are affected by humans, especially in urban areas. Although most species respond negatively to urbanization, some thrive in human-dominated settings. A central question in urban ecology is why some species adapt well to the presence of humans and others do not. We show that Northern Mockingbirds (
Mimus polyglottos
) nesting on the campus of a large university rapidly learn to assess the level of threat posed by different humans, and to respond accordingly. In a controlled experiment, we found that as the same human approached and threatened a nest on 4 successive days, mockingbirds flushed from their nest at increasingly greater distances from that human. A different human approaching and threatening the nest identically on the fifth day elicited the same response as the first human on the first day. Likewise, alarm calls and attack flights increased from days 1–4 with the first human, and decreased on day 5 with the second human. These results demonstrate a remarkable ability of a passerine bird to distinguish one human from thousands of others. Also, mockingbirds learned to identify individual humans extraordinarily quickly: after only 2 30-s exposures of the human at the nest. More generally, the varying responses of mockingbirds to intruders suggests behavioral flexibility and a keen awareness of different levels of threat posed by individuals of another species: traits that may predispose mockingbirds and other species of urban wildlife to successful exploitation of human-dominated environments.
Transcriptional signatures of ancient floral developmental genetics in avocado (
Persea americana
; Lauraceae)
Authors: Chanderbali André S. , Albert Victor A. , Leebens-Mack Jim , Altman Naomi S. , Soltis Douglas E. , Soltis Pamela S.
Published: May 2009

The debate on the origin and evolution of flowers has recently entered the field of developmental genetics, with focus on the design of the ancestral floral regulatory program. Flowers can differ dramatically among angiosperm lineages, but in general, male and female reproductive organs surrounded by a sterile perianth of sepals and petals constitute the basic floral structure. However, the basal angiosperm lineages exhibit spectacular diversity in the number, arrangement, and structure of floral organs, whereas the evolutionarily derived monocot and eudicot lineages share a far more uniform floral ground plan. Here we show that broadly overlapping transcriptional programs characterize the floral transcriptome of the basal angiosperm
Persea americana
(avocado), whereas floral gene expression domains are considerably more organ specific in the model eudicot
Arabidopsis thaliana
. Our findings therefore support the “fading borders” model for organ identity determination in basal angiosperm flowers and extend it from the action of regulatory genes to downstream transcriptional programs. Furthermore, the declining expression of components of the staminal transcriptome in central and peripheral regions of
Persea
flowers concurs with elements of a previous hypothesis for developmental regulation in a gymnosperm “floral progenitor.” Accordingly, in contrast to the canalized organ-specific regulatory apparatus of
Arabidopsis
, floral development may have been originally regulated by overlapping transcriptional cascades with fading gradients of influence from focal to bordering organs.
Baby schema modulates the brain reward system in nulliparous women
Authors: Glocker Melanie L. , Langleben Daniel D. , Ruparel Kosha , Loughead James W. , Valdez Jeffrey N. , Griffin Mark D. , Sachser Norbert , Gur Ruben C.
Published: May 2009

Ethologist Konrad Lorenz defined the baby schema (“Kindchenschema”) as a set of infantile physical features, such as round face and big eyes, that is perceived as cute and motivates caretaking behavior in the human, with the evolutionary function of enhancing offspring survival. The neural basis of this fundamental altruistic instinct is not well understood. Prior studies reported a pattern of brain response to pictures of children, but did not dissociate the brain response to baby schema from the response to children. Using functional magnetic resonance imaging and controlled manipulation of the baby schema in infant faces, we found that baby schema activates the nucleus accumbens, a key structure of the mesocorticolimbic system mediating reward processing and appetitive motivation, in nulliparous women. Our findings suggest that engagement of the mesocorticolimbic system is the neurophysiologic mechanism by which baby schema promotes human caregiving, regardless of kinship.
The main green tea polyphenol epigallocatechin-3-gallate counteracts semen-mediated enhancement of HIV infection
Authors: Hauber Ilona , Hohenberg Heinrich , Holstermann Barbara , Hunstein Werner , Hauber Joachim
Published: May 2009

Peptide fragments, derived from prostatic acidic phosphatase, are secreted in large amounts into human semen and form amyloid fibrils. These fibrillar structures, termed semen-derived enhancer of virus infection (SEVI), capture HIV virions and direct them to target cells. Thus, SEVI appears to be an important infectivity factor of HIV during sexual transmission. Here, we are able to demonstrate that epigallocatechin-3-gallate (EGCG), the major active constituent of geen tea, targets SEVI for degradation. Furthermore, it is shown that EGCG inhibits SEVI activity and abrogates semen-mediated enhancement of HIV-1 infection in the absence of cellular toxicity. Therefore, EGCG appears to be a promising supplement to antiretroviral microbicides to reduce sexual transmission of HIV-1.
Peripheral tumors induce depressive-like behaviors and cytokine production and alter hypothalamic-pituitary-adrenal axis regulation
Authors: Pyter Leah M. , Pineros Vanessa , Galang Jerome A. , McClintock Martha K. , Prendergast Brian J.
Published: May 2009

A strong and positive correlation exists between chronic disease and affective disorders, but the biological mechanisms underlying this relationship are not known. Here we show that rats with mammary cancer exhibit depression- and anxiety-like behaviors in the absence of overt sickness behaviors. The production of proinflammatory cytokines, known to induce depressive-like behaviors, was elevated in the periphery and in the hippocampus of rats with tumors compared with controls. In tumor-bearing rats, circulating corticosterone, which inhibits cytokine signaling, was suppressed following a stressor, and gene expression of hippocampal glucocorticoid receptors was elevated. The results establish that tumors alone are sufficient to trigger changes in emotional behaviors. Dampened glucocorticoid responses to stressors may exacerbate the deleterious effects of tumor-induced cytokines on affective states.