bluuebunny/crossref_metadata_2025 huggingface dataset:
Vorticity structure and evolution in a transverse jet
Authors: MARZOUK YOUSSEF M. , GHONIEM AHMED F.
Published: March 2007

Transverse jets arise in many applications, including propulsion, effluent dispersion, oil field flows, and V/STOL aerodynamics. This study seeks a fundamental, mechanistic understanding of the structure and evolution of vorticity in the transverse jet. We develop a high-resolution three-dimensional vortex simulation of the transverse jet at large Reynolds number and consider jet-to-crossflow velocity ratiosrranging from 5 to 10. A new formulation of vorticity-flux boundary conditions accounts for the interaction of channel wall vorticity with the jet flow immediately around the orifice. We demonstrate that the nascent jet shear layer contains not only azimuthal vorticity generated in the jet pipe, but wall-normal and azimuthal perturbations resulting from the jet–crossflow interaction. This formulation also yields analytical expressions for vortex lines in the near field as a function ofr.

Transformation of the cylindrical shear layer emanating from the orifice begins with axial elongation of its lee side to form sections of counter-rotating vorticity aligned with the jet trajectory. Periodic roll-up of the shear layer accompanies this deformation, creating complementary vortex arcs on the lee and windward sides of the jet. Counter-rotating vorticity then drives lee-side roll-ups in the windward direction, along the normal to the jet trajectory. Azimuthal vortex arcs of alternating sign thus approach each other on the windward boundary of the jet. Accordingly, initially planar material rings on the shear layer fold completely and assume an interlocking structure that persists for several diameters above the jet exit. Though the near field of the jet is dominated by deformation and periodic roll-up of the shear layer, the resulting counter-rotating vorticity is a pronounced feature of the mean field; in turn, the mean counter-rotation exerts a substantial influence on the deformation of the shear layer. Following the pronounced bending of the trajectory into the crossflow, we observe a sudden breakdown of near-field vortical structures into a dense distribution of smaller scales. Spatial filtering of this region reveals the persistence of counter-rotating streamwise vorticity initiated in the near field.
Experimental investigation of the instability of a sedimenting suspension of fibres
Authors: METZGER BLOEN , BUTLER JASON E. , GUAZZELLI ÉLISABETH
Published: March 2007

Observations of the flow structures formed by rigid fibres of high aspect ratio sedimenting within a viscous fluid at a Reynolds number of approximately 10−4 confirm the existence of an instability as reported in previous theories, experiments, and numerical simulations. Using data generated from particle image velocimetry measurements, we quantify the sedimentation structures over a wide range of parameters, which include the height of fluid, cross-section of the sedimentation cell, fibre dimensions, fluid properties, and volume fractions ranging from dilute to semi-dilute. Alternating structures of streamers and backflow regions which span the height of the sedimentation cell form at short times and transition from large wavelengths to smaller wavelength as the sedimentation proceeds. No simple dependence of the horizontal wavelength on the length scales and concentration was observed in the experiments, suggesting the need for additional analysis. We also report the mean velocities and velocity fluctuations; the strength of the velocity fluctuations strongly correlates with the size of the vertical component of the sedimentation structure. Measurements of the orientation distribution, using an efficient and newly employed technique, agree with previously published results. A movie is available with the online version of the paper.
Local implications for self-similar turbulent plume models
Authors: SCASE M. M. , CAULFIELD C. P. , LINDEN P. F. , DALZIEL S. B.
Published: March 2007

The local implications of the well-known flux conservation equations of Morton et al. (Proc. R. Soc. Lond. A, vol. 234, 1956, p.1) for plumes and jets are considered. Given the vertical velocity distributions of a model plume or jet, the divergence-free radial velocity distributions are calculated. It is shown that in general the velocity of the plume boundary is not described by the local total fluid velocity in this way. A two-fluid model tracking the evolution of both ‘plume’ and ‘ambient’ fluid is proposed which resolves this apparent inconsistency and also provides a way of explicitly describing the mixing process within a model plume. The plume boundary acts as a phase boundary across which ambient fluid is entrained, and the plume boundary moves at the velocity of the plume fluid. The difference between the plume-fluid radial velocity and the total fluid velocity quantifies in a natural way the purely horizontal entrainment flux of ambient fluid into the plume across the phase boundary at the plume edge.
Sensory processing in the brain related to the control of food intake
Authors: Rolls Edmund T.
Published: March 2007

Complementary neurophysiological recordings in rhesus macaques (Macaca mulatta) and functional neuroimaging in human subjects show that the primary taste cortex in the rostral insula and adjoining frontal operculum provides separate and combined representations of the taste, temperature and texture (including viscosity and fat texture) of food in the mouth independently of hunger and thus of reward value and pleasantness. One synapse on, in the orbitofrontal cortex, these sensory inputs are for some neurons combined by learning with olfactory and visual inputs. Different neurons respond to different combinations, providing a rich representation of the sensory properties of food. In the orbitofrontal cortex feeding to satiety with one food decreases the responses of these neurons to that food, but not to other foods, showing that sensory-specific satiety is computed in the primate (including the human) orbitofrontal cortex. Consistently, activation of parts of the human orbitofrontal cortex correlates with subjective ratings of the pleasantness of the taste and smell of food. Cognitive factors, such as a word label presented with an odour, influence the pleasantness of the odour, and the activation produced by the odour in the orbitofrontal cortex. Food intake is thus controlled by building a multimodal representation of the sensory properties of food in the orbitofrontal cortex and gating this representation by satiety signals to produce a representation of the pleasantness or reward value of food that drives food intake. Factors that lead this system to become unbalanced and contribute to overeating and obesity are described.
Authentic materials and authenticity in foreign language learning
Authors: Gilmore Alex
Published: March 2007

This article reviews some of the wide-ranging issues and research surrounding authentic materials and authenticity in foreign language learning. After a brief historical overview and a discussion of some of the definitional ambiguities associated with authenticity, the paper goes on to discuss four important areas of concern: i) the gap between authentic and textbook discourse; ii) the English-as-a-world-language debate; iii) authenticity and motivation; iv) text difficulty and task design and their effects on language acquisition. The article concludes by examining some of the reasons behind resistance to change in curriculum and materials design and possible future directions.
Optical spectroscopy and confocal fluorescence imaging of upconverting Er3+-doped CaF2 nanocrystals
Authors: Kumar G. A. , Chen C. W. , Riman R. E.
Published: March 2007

Up-conversion emission and confocal fluorescence imaging of Er3+-doped CaF2 nanocrystals were investigated using infrared excitation. At Er3+ concentrations less than 2.8mol%, green emission was dominant while red prevailed at higher concentrations. The simultaneous green and red emission and change in relative intensities is explained with a mechanism utilizing concepts of TPA, ESA, ET, and CR processes.
On pointed Hopf algebras associated with unmixed conjugacy classes in Sm
Authors: Andruskiewitsch Nicolás , Fantino Fernando
Published: March 2007

Let π∊Sm be a product of disjoint cycles of the same length, C the conjugacy class of π, and ρ an irreducible representation of the centralizer of π. We prove that either the Nichols algebra B(C,ρ) is infinite dimensional or the braiding of the Yetter-Drinfeld module is negative.
Parallel implementation of a direct method for calculating electrostatic potentials
Authors: Jusélius Jonas , Sundholm Dage
Published: March 2007

The authors present a method for calculating the electrostatic potential directly in a straightforward manner. While traditional methods for calculating the electrostatic potential usually involve solving the Poisson equation iteratively, the authors obtain the electrostatic interaction potential by performing direct numerical integration of the Coulomb-law expression using finite-element functions defined on a grid. The singularity of the Coulomb operator is circumvented by an integral transformation and the resulting auxiliary integral is obtained using Gaussian quadrature. The three-dimensional finite-element basis is constructed as a tensor (outer) product of one-dimensional functions, yielding a partial factorization of the expressions. The resulting algorithm has, without using any prescreening or other computational tricks, a formal computational scaling of O(N4∕3), where N is the size of the grid. The authors show here how to implement the method for efficiently running on parallel computers. The matrix multiplications of the innermost loops are completely independent, yielding a parallel algorithm with the computational costs scaling practically linearly with the number of processors.
Omnidirectional light emission via surface plasmon polaritons
Authors: Liu John S. Q. , Brongersma Mark L.
Published: March 2007

The simulations and experiments on light emitters within a planar, metal/insulator/metal cavity demonstrate an omnidirectional resonance. This is a resonance for which the maximum decay rate enhancement in the cavity occurs at a well-defined wavelength independent of emission angle. It is shown numerically that the resonance occurs when the cavity thickness is a quarter of the surface plasmon wavelength. Experiments on a gold/blue-emitting polymer/gold cavity support this. Further simulations show that low loss omnidirectional cavities have an emission intensity that is largely independent of angle, which may find application for solid state light sources that require a broad emission cone.
The impact of small-scale turbulence on laminar magnetic reconnection
Authors: Watson P. G. , Oughton S. , Craig I. J. D.
Published: March 2007

Initial states in incompressible two-dimensional magnetohydrodynamics that are known to lead to strong current sheets and (laminar) magnetic reconnection are modified by the addition of small-scale turbulent perturbations of various energies. The evolution of these states is computed with the aim of ascertaining the influence of the turbulence on the underlying laminar solution. Two main questions are addressed here: (1) What effect does small-scale turbulence have on the energy dissipation rate of the underlying solution? (2) What is the threshold turbulent perturbation level above which the original laminar reconnective dynamics is no longer recognizable. The simulations show that while the laminar dynamics persist the dissipation rates are largely unaffected by the turbulence, other than modest increases attributable to the additional small length scales present in the new initial condition. The solutions themselves are also remarkably insensitive to small-scale turbulent perturbations unless the perturbations are large enough to undermine the integrity of the underlying cellular flow pattern. Indeed, even initial states that lead to the evolution of small-scale microscopic sheets can survive the addition of modest turbulence. The role of a large-scale organizing background magnetic field is also addressed.
Ultraviolet electroluminescence from ZnO∕p-Si heterojunctions
Authors: Chen Peiliang , Ma Xiangyang , Yang Deren
Published: March 2007

Nominally undoped ZnO films were deposited by reactive sputtering on the lightly boron-doped (p−) and heavily boron-doped (p+) silicon substrates. The sputtered ZnO films were identified to be highly ⟨002⟩ oriented in crystallinity and n type in electrical conductivity. The current-voltage (I-V) characteristics revealed that the ZnO∕p−-Si heterojunction exhibited well-defined rectifying behavior while the ZnO∕p+-Si heterojunction did not possess rectifying function. As for the ZnO∕p+-Si heterojunction, it was electroluminescent to a certain extent in the visible region under sufficient forward bias with the positive voltage on the silicon substrate, while it emitted ultraviolet light characteristics of near-band-edge emission of ZnO under the reverse bias, which significantly dominated the visible emission. In contrast to the ZnO∕p+-Si heterojunction, the ZnO∕p−-Si heterojunction did not exhibit detectable electroluminescence (EL) under either forward or reverse bias. The I-V characteristics and EL mechanism of the above-mentioned heterojunctions have been tentatively explained in terms of the energy-band structures of the heterojunctions.
Mesoscopic simulations of the diffusivity of ethane in beds of NaX zeolite crystals: Comparison with pulsed field gradient NMR measurements
Authors: Papadopoulos George K. , Theodorou Doros N. , Vasenkov Sergey , Kärger Jörg
Published: March 2007

Mesoscopic kinetic Monte Carlo simulations and pulsed field gradient nuclear magnetic resonance (PFG NMR) measurements are compared in order to investigate the transport of ethane in a bed of NaX crystals. A novel molecular mechanics particle-based reconstruction method is employed for the digital representation of the bed, enabling for the first time a parallel study of the real system and of a computer model tailored to reproduce the void fraction, particle shape and average size of the real system. Simulation of the long-range diffusion of ethane in the bed over the Knudsen, transient, and molecular diffusion regimes is consistent with the PFG NMR measurements in yielding tortuosity factors which depend upon the regime of diffusion; more specifically, tortuosity factors defined in the conventional way are higher in the Knudsen than in the molecular diffusion regime. Detailed statistical analysis of the computed molecular trajectories reveals that this difference arises in a nonexponential distribution of the lengths and in a correlation between the directions of path segments traversed between collisions with the solid in the Knudsen regime. When the Knudsen tortuosity is corrected to account for these features, a single, regime-independent value is obtained within the error of the calculations.
Increased real contact in thermal interfaces: A carbon nanotube/foil material
Authors: Cola Baratunde A. , Xu Xianfan , Fisher Timothy S.
Published: March 2007

The thermal performance of an interface material comprised of a metal foil with dense, vertically oriented carbon nanotube (CNT) arrays synthesized on both of its surfaces is characterized for rough and smooth interfaces. The CNT/foil deforms in the interfaces by two mechanisms, CNT deformation and foil deformation, that may significantly increase the number of CNT contact spots on both sides of the foil. As a result, thermal interface resistances less than 10mm2K∕W are achieved at moderate pressures and compare very favorably to alternative interface materials and structures.
On the kinetic stability of magnetic structures in electron drift turbulence
Authors: Jucker Martin , Pavlenko Vladimir P.
Published: March 2007

The generation of large-scale magnetic fields in magnetic electron drift mode turbulence is investigated. The mechanism of magnetic Reynolds stress is elucidated with the help of kinetic theory, and a sufficient criterion in the form of Nyquist’s criterion for the generation of zonal magnetic fields is developed. This criterion is then applied to a narrow wave packet, where an amplitude threshold due to finite width of the wave spectrum in k space is found.
Mach probe interpretation in the presence of suprathermal electrons
Authors: Gunn J. P. , Fuchs V.
Published: March 2007

The collisionless theory of Mach probes assuming isothermal, Maxwellian electrons is extended to include an isotropic, two-temperature electron distribution function. The kinetic equations for ion and electron motion in the probe wake are solved using a quasineutral particle-in-cell method, which compares qualitatively well with the results of a simple fluid model. The measured Mach number decreases slightly with increasing hot electron concentration, but the main effect is on the measured electron temperature. Due to the fact that the probe is sensitive to even a tiny population of hot electrons, the resulting ion sound speed can be overestimated by up to a factor of 2, leading to measurements of absolute flow speed that are too large.
Quantitative investigation of a terahertz artificial magnetic resonance using oblique angle spectroscopy
Authors: Driscoll T. , Andreev G. O. , Basov D. N. , Palit S. , Ren Tong , Mock Jack , Cho Sang-Yeon , Jokerst Nan Marie , Smith D. R.
Published: March 2007

The authors present a spectroscopic analysis of a planar split-ring-resonator (SRR) medium at terahertz frequencies, quantitatively characterizing the associated magnetic resonance. Experimental quantification at terahertz and infrared frequencies of metamaterial optical constants has been primarily absent, largely due to the difficulty of collecting phase information at these frequencies. In this letter, the authors circumvent the need for phase information in the characterization by acquiring the power transmitted through the metamaterial at a series of oblique angles, and relating the multiangle data set to the effective permittivity and permeability through the Fresnel expressions. The resulting measurements reveal the expected resonant permeability of the SRR which exhibits a range of negative values, the minimum value being μ=−0.8 at 1.1THz.
Impedance spectroscopy of an electrolytic cell limited by ohmic electrodes
Authors: Barbero G. , Batalioto F. , Neto A. M. Figueiredo
Published: March 2007

We investigate the influence of the ohmic character of the electrodes on the impedance spectroscopy of a cell of a dielectric liquid containing ions. According to our calculations, the finite conductivity of the electrodes is responsible for an increasing of the real part of the electrical impedance in the low frequency range. It follows that the anomalous increasing of the resistance of the cell, experimentally observed by several groups, could be related also to the exchange of charge at the electrodes. Our analysis is based on a generalization of the Butler-Wolmer equation, for small values of the external voltage.
Study of the electronic and vibrational properties of poly(ethylene terephthalate) and poly(ethylene naphthalate) films
Authors: Laskarakis A. , Logothetidis S.
Published: March 2007

We investigate the optical properties of biaxially stretched poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) polymer films by spectroscopic ellipsometry (SE) in a wide spectral region, from the infrared (IR) (900−3500 cm−1) to the vis-far UV (vis-fUV) (1.5−6.5 eV), in terms of their optical, electronic, and vibrational response. The stretching procedure during the fabrication of the films leads to the rearrangement of the macromolecular chains parallel to the stretching direction (or machine direction), resulting in an optical anisotropy of the films. For the deduction of valuable and accurate information about the films’ electronic and vibrational response, the analysis of the measured SE spectra has been realized by approximating the PET and PEN films as uniaxial materials with their optic axes parallel to the surface. In the vis-fUV spectral region, the characteristic features corresponding to the n→π* electronic transitions of the carbonyl −C=O and the A1g1→B1u1 electronic transition due to the π→π* excitation of the π-electron structures were identified and analyzed. Also, based on the assumption of the optical behavior of a uniaxial material, we have determined the principal components ε||(ω) and ε⊥(ω) of the dielectric function, parallel and perpendicular to the stretching direction of the polymer films. Furthermore, the study of the Fourier transform infrared (IR) SE spectra allowed the assignment of the characteristic features of the measured dielectric function ε(ω) to the vibrational modes of the different chemical bonds of the PET and PEN monomer units. Finally, the above analysis resulted in a detailed calculation of the bulk dielectric function of the PET and PEN polymer films in an extended spectral region from the IR to the vis-fUV.
XPS studies on aluminum ions modified polyimide with the PIII technique
Authors: Han Zhao Jun , Tay Beng Kang , Ha Peter C.T. , Sze Jia Yin , Chua Daniel H.C.
Published: March 2007

Polyimide samples modified by aluminum (Al) ions produced by filtered cathodic vacuum arc (FCVA) with plasma immersion ion implantation (PIII) technique, under ambient argon and oxygen gases (flow rate Ar:O2=2:1) were investigated by x-ray photoelectron spectroscopy (XPS). The working pressure was about 8×10−4 Torr and the plasma density was estimated to be 109 ions∕cm3. The applied bias voltages were varied from 5 to 12.5 kV but with fixed frequency at 900 Hz and duty time of 15μs. For 1 min process time, C 1s and O 1s spectra for modified samples clearly indicated that the carbonyl group (C=O) was largely destroyed by incident Al ions while Al 2p spectra suggested Al atoms remain inside polyimide matrices in the form of C-O-Al complexes. For a 5 min process time, when the ion fluence became large, both C 1s and O 1s spectra suggested a structure of “aluminum oxide-mixed layer-polyimide” and Al 2p spectra confirmed that most Al atoms were bonded to oxygen atoms on the top surface. These XPS results revealed the chemical bonds between implanted and deposited Al ions and polyimide matrix by using the PIII technique. The structural information can also be suggested. Furthermore in this paper, some discussions with the theoretical [the stopping and range of ions in matter (SRIM)] simulation were also mentioned in order to explore the effectiveness of Al ions irradiation on polyimide.
Effective medium properties and photonic crystal superstructures of metallic nanoparticle arrays
Authors: Lidorikis Elefterios , Egusa Shunji , Joannopoulos J. D.
Published: March 2007

Using the finite-difference time-domain method we extract the effective optical constants of metallic nanoparticle arrays. We explore their behavior in the full range of filling fractions and find excellent agreement with the Maxwell-Garnett [Philos. Trans. R. Soc. London 203, 385 (1904)] effective medium theory for the effective dielectric constant. We also find that the resonance response of such systems exhibits an effective magnetic component, typically overlooked in standard effective medium theories. We verify that the description of these nanoarrays as an effective bulk medium is exact within numerical precision, at least in one-dimensional arrangements, by comparing with full simulations of more complex superlayer configurations. Finally, using the effective constants we study photonic crystal superstructures consisting of these arrays, demonstrating an interesting optical response where resonant absorption and reflection bands are separated by extremely sharp edges of almost 100% relative change per nanometer wavelength.
Ferroelectric rods with adjustable dielectric tunability
Authors: Zheng Yue , Woo C. H. , Wang Biao , Zhu Z. Y.
Published: March 2007

The polarization, dielectric constant, and tunability of a radial-loaded ferroelectric rod inside a highly pressurized polyethylene tube are calculated for both macro- and nanodimensions within a thermodynamic model. All studied properties, including the Curie temperature, are found to vary substantially by the applied load. The authors’ results indicate that many properties of the ferroelectric rod, including its tunability, can be optimized in this design by adjusting the applied pressure.
Full-color electroluminescence from ZnO-based heterojunction diodes
Authors: Nakamura A. , Ohashi T. , Yamamoto K. , Ishihara J. , Aoki T. , Temmyo J. , Gotoh H.
Published: March 2007

Red, green, and blue electroluminescence have been observed from ZnO-based heterojunction diodes consisting of n-ZnO∕n-MgyZn1−yO∕Zn1−xCdxO∕p-SiC layers. The heterostructures were grown by remote-plasma-enhanced metal-organic chemical vapor deposition. The rectifying I-V characteristics at room temperature reveal the red, green, and blue wavelengths near 720, 520, and 480nm, respectively, when the diodes are forward biased. It is observed that the emission color can be controlled by changing the cadmium content in the emission layer.
Photovoltaic properties and exciplex emission of polyphenylenevinylene-based blend solar cells
Authors: Yin Chunhong , Kietzke Thomas , Neher Dieter , Hörhold Hans-Heinrich
Published: March 2007

By studying the photoluminescence emission and photovoltaic properties of blends of polyphenylenevinylene (PPV)-based electron donating and accepting polymers, the authors observed a strict anticorrelation between relative exciplex emission in the solid state and photovoltaic efficiency of corresponding blend devices. Comparative studies on defined bilayer geometries showed that the overall shape of the current-voltage characteristics under illumination is independent of device geometry and layer thickness. Consequently, they conclude that the photocurrent in PPV-based blends is mainly determined by the efficiency to form free carriers rather than by free carrier recombination.
Image storage through gray-scale encoding of second harmonic signals in azo-dye copolymers
Authors: Gindre Denis , Ka Ibrahima , Boeglin Alex , Fort Alain , Dorkenoo Kokou D.
Published: March 2007

The authors investigated the optical data and image storage in polymeric materials functionalized with azo-dye molecules. Thin films are initially poled to generate a spatially homogeneous second harmonic signal. The information is locally inscribed through the disorientation of the azo chromophores by successive isomerization cycles induced through the two-photon absorption processes. The resulting micron-scale controlled decrease in second harmonic signal can be exploited to perform optical storage. As a demonstration of the proposed method, they store a picture with an 8bit gray-scale encoding. This image can only be retrieved through second harmonic detection and not by linear optical imaging techniques.
Submicron-diameter semiconductor pillar microcavities with very high quality factors
Authors: Lecamp G. , Hugonin J. P. , Lalanne P. , Braive R. , Varoutsis S. , Laurent S. , Lemaître A. , Sagnes I. , Patriarche G. , Robert-Philip I. , Abram I.
Published: March 2007

Pillar microcavities are subject to two common fabrication artifacts: Bragg mirror corrugation and oxide deposit cladding. In this letter the authors investigate the impact of these features on the quality factor. A quasiperiodic variation of the quality factor as a function of the pillar diameter is experimentally observed and well described by theory. Moreover, observation of quality factors in excess of 1500, close to the theoretical limit, is reported for 600-nm-diameter GaAs micropillars bounded by AlGaAs∕GaAs Bragg mirrors.
Mapping local strain in thin film/substrate systems using x-ray microdiffraction topography
Authors: Yan Hanfei , Murray Conal E. , Noyan I. C.
Published: March 2007

The authors report experimental data and modeling results for reflection microbeam x-ray topographs from a Si substrate strained by an overlying pseudomorphic SiGe film edge. The diffracted x-ray intensity from the Si substrate is strongly asymmetric as a function of distance from the film edge. A model of the diffracted intensity based on the classical Ewald–von Laue dynamical diffraction theory for an antisymmetric strain distribution indicates that the asymmetry in the diffracted beam profile is only due to the scattering process; individual intensity maxima in the intensity profile cannot be uniquely ascribed to individual features in the local strain distribution.
Strong green-yellow electroluminescence from oxidized amorphous silicon nitride light-emitting devices
Authors: Huang Rui , Chen Kunji , Han Peigao , Dong Hengping , Wang Xiang , Chen Deyuan , Li Wei , Xu Jun , Ma Zhongyuan , Huang Xinfan
Published: March 2007

High efficiency luminescent amorphous silicon nitride films grown at room temperature with subsequent plasma oxidation were used as the active layers in the electroluminescent devices. A strong uniform green-yellow light emission from the devices was realized under forward biased conditions. It was found that the turn-on voltage could be reduced to as low as 6V while the electroluminescence (EL) intensity is significantly enhanced by two to four times by using p-type Si anode instead of indium tin oxide substrate under the same forward voltage. Furthermore, the EL peak position is blueshifted from 560to540nm, which is more close to that of the corresponding photoluminescence peak. The origin of light emission is suggested to be the same kind of luminescent centers related to the Si–O bonds.
Phase separation of acetonitrile-water mixtures and minimizing of ice crystallites from there in confinement of MCM-41
Authors: Kittaka Shigeharu , Kuranishi Miki , Ishimaru Shinji , Umahara Osamu
Published: March 2007

The effect of confinement of an acetonitrile-water mixture, whose correlation length was comparable to the pore size of the mesopores of MCM-41 (d=2.4–3.6nm), on the phase changes was studied. Used techniques were low temperature differential scanning calorimetry and Fourier transform infrared spectroscopy, where the phase separation, lowering of the freezing and melting temperatures, and phase transitions of the acetonitrile were detected. The latter occurred in the mesopores at temperatures similar to that of the pure liquid, while the melting temperature of the water in the mesopores <3.1nm decreased markedly at higher acetonitrile contents, suggesting a marked lowering of ice crystallite size.
Size Matters: Saccades during Scene Perception
Authors: von Wartburg Roman , Wurtz Pascal , Pflugshaupt Tobias , Nyffeler Thomas , Lüthi Mathias , Müri René M
Published: March 2007

We investigated the effect of image size on saccade amplitudes. First, in a meta-analysis, relevant results from previous scene perception studies are summarised, suggesting the possibility of a linear relationship between mean saccade amplitude and image size. Forty-eight observers viewed 96 colour scene images scaled to four different sizes, while their eye movements were recorded. Mean and median saccade amplitudes were found to be directly proportional to image size, while the mode of the distribution lay in the range of very short saccades. However, saccade amplitudes expressed as percentages of image size were not constant over the different image sizes; on smaller stimulus images, the relative saccades were found to be larger, and vice versa. In sum, and as far as mean and median saccade amplitudes are concerned, the size of stimulus images is the dominant factor. Other factors, such as image properties, viewing task, or measurement equipment, are only of subordinate importance. Thus, the role of stimulus size has to be reconsidered, in theoretical as well as methodological terms.
A female-biased expressed elongase involved in long-chain hydrocarbon biosynthesis and courtship behavior inDrosophila melanogaster
Authors: Chertemps Thomas , Duportets Line , Labeur Carole , Ueda Ryu , Takahashi Kuniaki , Saigo Kaoru , Wicker-Thomas Claude
Published: March 2007

Drosophila melanogasterproduces sexually dimorphic cuticular pheromones that are a key component of the courtship behavior leading to copulation. These molecules are hydrocarbons, with lengths of 23 and 25 carbons in males (mainly with one double bond) and 27 and 29 carbons in females (mainly with two double bonds). Here, we describe an elongase gene,eloF, with female-biased expression. The 771-bp ORF encodes a 257-aa protein that shows the highest sequence identity with mouse SSC1 elongase (33%). The activity of the cDNA expressed in yeast was elongation of saturated and unsaturated fatty acids up to C30. RNAi knockdown inDrosophilaled to a dramatic modification of female hydrocarbons, with decreased C29 dienes and increased C25 dienes accompanied by a modification of several courtship parameters: an increase in copulation latency and a decrease in both copulation attempts and copulation. Feminization of the hydrocarbon profile in males by using targeted expression of thetransformergene resulted in high expression levels ofeloF, suggesting that the gene is under the control of the sex-determination hierarchy. There is no expression ofeloFinDrosophila simulans, which synthesize only C23 and C25 hydrocarbons. These results strongly support the hypothesis thateloFis a crucial enzyme for female pheromone biosynthesis and courtship behavior inD. melanogaster.
Experimental constraints on mate preferences inDrosophila pseudoobscuradecrease offspring viability and fitness of mated pairs
Authors: Anderson Wyatt W. , Kim Yong-Kyu , Gowaty Patricia Adair
Published: March 2007

UsingDrosophila pseudoobscura, we tested the hypothesis that social constraints on the free expression of mate preferences, by both females and males, decrease offspring viability and reproductive success of mating pairs. Mate preference arenas eliminated intrasexual combat and intersexual coercion. The time female and male choosers spent in arena tests near either of two opposite-sex individuals measured the preferences of choosers. We placed choosers in breeding trials with their preferred or nonpreferred discriminatee when they met the minimum criteria for showing the same preference in two consecutive tests. There was no statistically significant difference in the frequency of female and male choosers meeting minimal preference criteria. There was a significant difference between female and male choosers for offspring viability, with female choice having the greater effect, but there was not a significant difference in the overall reproductive success of male and female choosers. There were significant differences in fitness between matings to preferred and nonpreferred partners. Female and male choosers paired with their nonpreferred discriminatees had offspring of significantly lower viability, as predicted by the constraints hypothesis. Reproductive success, our measure of overall fitness, was greater when males or females mated with the partner they preferred rather than the one they did not prefer.
Needle-free delivery of macromolecules across the skin by nanoliter-volume pulsed microjets
Authors: Arora Anubhav , Hakim Itzhak , Baxter Joy , Rathnasingham Ruben , Srinivasan Ravi , Fletcher Daniel A. , Mitragotri Samir
Published: March 2007

Needle-free liquid jet injectors were invented >50 years ago for the delivery of proteins and vaccines. Despite their long history, needle-free liquid jet injectors are not commonly used as a result of frequent pain and bruising. We hypothesized that pain and bruising originate from the deep penetration of the jets and can potentially be addressed by minimizing the penetration depth of jets into the skin. However, current jet injectors are not designed to maintain shallow dermal penetration depths. Using a new strategy of jet injection, pulsed microjets, we report on delivery of protein drugs into the skin without deep penetration. The high velocity (
v
>100 m/s) of microjets allows their entry into the skin, whereas the small jet diameters (50–100 μm) and extremely small volumes (2–15 nanoliters) limit the penetration depth (≈200 μm).
In vitro
experiments confirmed quantitative delivery of molecules into human skin and
in vivo
experiments with rats confirmed the ability of pulsed microjets to deliver therapeutic doses of insulin across the skin. Pulsed microjet injectors could be used to deliver drugs for local as well as systemic applications without using needles.
Comparative annotation of viral genomes with non-conserved gene structure
Authors: de Groot Saskia , Mailund Thomas , Hein Jotun
Published: March 2007

Motivation: Detecting genes in viral genomes is a complex task. Due to the biological necessity of them being constrained in length, RNA viruses in particular tend to code in overlapping reading frames. Since one amino acid is encoded by a triplet of nucleic acids, up to three genes may be coded for simultaneously in one direction. Conventional hidden Markov model (HMM)-based gene-finding algorithms may typically find it difficult to identify multiple coding regions, since in general their topologies do not allow for the presence of overlapping or nested genes. Comparative methods have therefore been restricted to likelihood ratio tests on potential regions as to being double or single coding, using the fact that the constrictions forced upon multiple-coding nucleotides will result in atypical sequence evolution. Exploiting these same constraints, we present an HMM based gene-finding program, which allows for coding in unidirectional nested and overlapping reading frames, to annotate two homologous aligned viral genomes. Our method does not insist on conserved gene structure between the two sequences, thus making it applicable for the pairwise comparison of more distantly related sequences.

Results: We apply our method to 15 pairwise alignments of six different HIV2 genomes. Given sufficient evolutionary distance between the two sequences, we achieve sensitivity of ∼84–89% and specificity of ∼97–99.9%. We additionally annotate three pairwise alignments of the more distantly related HIV1 and HIV2, as well as of two different hepatitis viruses, attaining results of ∼87% sensitivity and ∼98.5% specificity. We subsequently incorporate prior knowledge by ‘knowing’ the gene structure of one sequence and annotating the other conditional on it. Boosting accuracy close to perfect we demonstrate that conservation of gene structure on top of nucleotide sequence is a valuable source of information, especially in distantly related genomes.

Availability: The Java code is available from the authors.

Contact:  degroot@stats.ox.ac.uk
Strength in numbers: preventing rereplication via multiple mechanisms in eukaryotic cells
Authors: Arias Emily E. , Walter Johannes C.
Published: March 2007

In eukaryotic cells, prereplication complexes (pre-RCs) are assembled on chromatin in the G1 phase, rendering origins of DNA replication competent to initiate DNA synthesis. When DNA replication commences in S phase, pre-RCs are disassembled, and multiple initiations from the same origin do not occur because new rounds of pre-RC assembly are inhibited. In most experimental organisms, multiple mechanisms that prevent pre-RC assembly have now been identified, and rereplication within the same cell cycle can be induced through defined perturbations of these mechanisms. This review summarizes the diverse array of inhibitory pathways used by different organisms to prevent pre-RC assembly, and focuses on the challenge of understanding how in any one cell type, various mechanisms cooperate to strictly enforce once per cell cycle regulation of DNA replication.
New insights into Acinetobacter baumannii pathogenesis revealed by high-density pyrosequencing and transposon mutagenesis
Authors: Smith Michael G. , Gianoulis Tara A. , Pukatzki Stefan , Mekalanos John J. , Ornston L. Nicholas , Gerstein Mark , Snyder Michael
Published: March 2007

Acinetobacter baumannii has emerged as an important and problematic human pathogen as it is the causative agent of several types of infections including pneumonia, meningitis, septicemia, and urinary tract infections. We explored the pathogenic content of this harmful pathogen using a combination of DNA sequencing and insertional mutagenesis. The genome of this organism was sequenced using a strategy involving high-density pyrosequencing, a novel, rapid method of high-throughput sequencing. Excluding the rDNA repeats, the assembled genome is 3,976,746 base pairs (bp) and has 3830 ORFs. A significant fraction of ORFs (17.2%) are located in 28 putative alien islands, indicating that the genome has acquired a large amount of foreign DNA. Consistent with its role in pathogenesis, a remarkable number of the islands (16) contain genes implicated in virulence, indicating the organism devotes a considerable portion of its genes to pathogenesis. The largest island contains elements homologous to the Legionella/Coxiella Type IV secretion apparatus. Type IV secretion systems have been demonstrated to be important for virulence in other organisms and thus are likely to help mediate pathogenesis of A. baumannii. Insertional mutagenesis generated avirulent isolates of A. baumannii and verified that six of the islands contain virulence genes, including two novel islands containing genes that lacked homology with others in the databases. The DNA sequencing approach described in this study allows the rapid elucidation of the DNA sequence of any microbe and, when combined with genetic screens, can identify many novel genes important for microbial pathogenesis.
ELISA system for detection of immune responses to FVIII: a study of 246 samples and correlation with the Bethesda assay
Authors: SAHUD M. A. , PRATT K. P. , ZHUKOV O. , QU K. , THOMPSON A. R.
Published: March 2007

Summary.  Inhibitors of FVIII are usually IgG polyclonal antibodies that develop as alloimmune responses in patients with congenital haemophilia A or as autoimmune responses resulting in acquired haemophilia. Their recognition can be difficult, especially when the titre is low. Furthermore, results from a Bethesda assay often require several days as samples are referred to a specialty laboratory. The aim of this study is to assess the utility of an ELISA system for detecting immune responses to FVIII. A total of 246 plasma samples submitted from 176 individuals with immune responses to FVIII, as verified with the Bethesda assay, and samples from 50 control subjects were tested for the presence of FVIII‐specific IgG using an ELISA‐based assay. Paired sera from 18 of the patients were also tested by the ELISA. Of the 246 samples that were positive for a FVIII inhibitor by the Bethesda assay, 235 (95.5%) were also positive by ELISA. The regression coefficient, using Log BU was r = 0.82. The correlation data were strengthened when 27 inhibitor samples were diluted further. There was a strong correlation between ELISA results for the 18‐paired serum and plasma samples (r = 0.99). There is a strong correlation between the ELISA and Bethesda methods in detecting immune responses to FVIII. The ELISA provides rapid screening that could be available well in advance of confirmation by the Bethesda assay.
Self‐harm and the words that bind: a critique of common perspectives
Authors: ALLEN S.
Published: March 2007

The issue of self‐harm is not only a widespread phenomenon but also a challenging one. Nurses in particular are faced with this challenge, as they tend to be the primary professional group when working with people who self‐harm within health service provision. The purpose of this paper is to offer a critical appraisal of common perspectives as reported in the existing literature. Having highlighted these areas, the paper will attempt to address the challenges faced by nurses and other healthcare professionals through the proposal of strategies, including the suggestion that self‐harm may be considered from a position of social constructionism to achieve a more informed and effective response when working with someone who self‐harms.
Investigation on the association between atopic dermatitis and the development of mycosis fungoides in dogs: a retrospective case‐control study
Authors: Santoro D. , Marsella R. , Hernandez J.
Published: March 2007

In human medicine, the relationship between the immunodysregulation observed in atopic dermatitis (AD) and the development of mycosis fungoides (MF) has triggered considerable interest due to the increasing number of patients with MF who have a previous history of AD. The purpose of this retrospective case‐control study was to investigate whether dogs diagnosed with MF were more likely to have AD. The records of 96 000 canine patients at the University of Florida were searched. Inclusion criteria were a clinical and histological diagnosis of MF. Dogs admitted to the University of Florida, Veterinary Medical Center during the same time period (1991–2004) without a diagnosis of MF were included as controls. Four controls for each study dog were randomly selected (matched by year of admission). Frequency of AD and other exposure variables were compared among case and control dogs by using conditional logistic regression. Records of 19 dogs with a diagnosis of MF were identified. Five of them (5/19, 26.3%) had previous diagnosis of AD. The odds of having MF was 12 times (OR = 12.54; 95% CI = 1.95–80.39; P < 0.01) higher in dogs with AD than in dogs without AD. In conclusion, this study suggests an association between AD and MF in dogs. Future studies are necessary to confirm this finding and to investigate the pathogenic mechanisms involved in this association.
High prevalence of atopy, but not of asthma, among children in an industrialized area in North Italy: The role of familial and environmental factors – a population‐based study
Authors: Duse Marzia , Donato Francesco , Porteri Vera , Pirali Francesco , Spinoni Vania , Tosoni Cinzia , Vettore Manuela , Lombardi Carlo
Published: March 2007

The prevalence of atopy and asthma, and their association with familial and environmental factors were investigated among 13‐ to 14‐yr‐old children living in Brescia, an industrialized town in North Italy. All the 1450 children attending primary school in the town were invited to participate, and 967 of them (66.7%, 493 males) provided a valid questionnaire filled in by their parents at home. We used a modified version of the questionnaire adopted in the Italian Study of Respiratory Disorders in Childhood and Environment, which is an extended version of the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. Six hundred and twenty‐eight subjects underwent skin prick test (SPT), and 308 of them (49%) were positive for at least one of the 12 allergen extracts commonly employed. Ninety‐nine children (10.2%) had a physician's diagnosis of asthma – 12.4% of the males and 8.0% of the females (p = 0.03). The prevalence of wheezing in the past 12 months was 6.2%. Atopy was found in 76.8% of the subjects with, and in 45.6% of those without physician's diagnosis of asthma (p < 0.001). Analysis by multiple logistic regression showed an inverse association between physician‐diagnosed asthma and female sex (odds ratio, OR = 0.5); presence of relatives in the bedroom in initial years of life (OR = 0.6); attending day care (OR = 0.4) and infant school (OR = 0.4); a positive association with parental history of wheezing (OR = 2.5) and asthma (OR = 3.8); and the child's history of asthmatic bronchitis (OR = 31.9) and atopic eczema (OR = 3.8) in the first 2 yr of life. The strength of the associations did not change when restricting the analysis to atopic asthma. In conclusion, atopy and clinical asthma among 13‐ to 14‐yr‐old adolescents are significantly associated with some familial and environmental factors, providing further support for the hygiene hypothesis. Prevalence of atopy, but not of asthma, is high in this industrialized area. The strong association found between atopy and clinical asthma suggests that atopy may play a role in causing asthma in genetically predisposed children only.