bluuebunny/crossref_metadata_2025 huggingface dataset:
Secondary organic aerosol yields from cloud‐processing of isoprene oxidation products
Authors: Ervens Barbara , Carlton Annmarie G. , Turpin Barbara J. , Altieri Katye E. , Kreidenweis Sonia M. , Feingold Graham
Published: January 2008

While there is a growing understanding from laboratory studies of aqueous phase chemical processes that lead to secondary organic aerosol (SOA) formation in cloud droplets (SOAdrop), the contribution of aqueous phase chemistry to atmospheric SOA burden is yet unknown. Using a parcel model including a multiphase chemical mechanism, we show that SOAdrop carbon yields (Yc) from isoprene (1) depend strongly on the initial volatile organic carbon (VOC)/NOx ratio resulting in 42% > Yc > 0.4% over the atmospherically‐relevant range of 0.25 < VOC/NOx < 100; (2) increase with increasing cloud‐contact time; (3) are less affected by cloud liquid water content, pH, and droplet number. (4) The uncertainty associated with gas/particle‐partitioning of semivolatile organics introduces a relative error of −50% ≤ ΔYc < +100 %. The reported yields can be applied to air quality and climate models as is done with SOA formed on/in concentrated aerosol particles (SOAaer).
Stokes waves modulation by internal waves
Authors: Lee Kwi‐Joo , Hwung Hwung‐Hweng , Yang Ray‐Yeng , Shugan Igor V.
Published: January 2008

The effect of subsurface currents induced by internal waves on nonlinear surface waves is theoretically analyzed. An analytical and numerical solution of the modulation equations are found under the conditions close to the group velocity resonance. It is shown that smoothing of the down current surface waves is accompanied by a relatively high‐frequency modulation while the profile of the opposing current is reproduced by the surface wave's envelope. Long surface waves can form the wave modulation forerunner ahead of the internal wave, while the relatively short surface waves create the trace of the internal wave.
A study of the electromagnetic proton cyclotron instability as a generation mechanism for EMIC waves in the Earth's magnetosphere using SCATHA data
Authors: Nguyen Son T. , Perez J. D. , Fennell Joseph F.
Published: January 2008

Using 59 days of magnetic field data from SCATHA, a study of the electromagnetic proton cyclotron instability as a generation mechanism for EMIC waves in the Earth's magnetosphere has been conducted. From 1181 events found, we selected 373 events that were not influenced by the presence of He+ and O+ ions, i.e., events with frequency above the local He+ cyclotron frequency and that had all the required accompanying data. These events occurred in all magnetic local times (MLT) sectors, with L ranging from 5.6 to 8.1 and magnetic latitudes (MLAT) from −13.7° to 15.6°. Assuming a pure proton plasma, the proton temperature anisotropy, Ap, is determined from the maximum normalized frequency at which power is emitted. Using measured parameters and estimated total number density, the convective growth rate, S, of Electromagnetic Ion Cyclotron (EMIC) waves as a function of frequency depends only on the parallel proton temperature, T∥. Matching the observed peak in the frequency spectrum and the calculated peak in S allows the determination of T∥ and the proton perpendicular temperature, T⊥, for each event. Analysis of the results yields a new empirical expression for Ap as a function of the hot proton parallel beta, β∥h, and the maximum value of the wave temporal growth rate. The relationship between Ap and β∥h is consistent with theoretical predictions. The dependence of Ap on T∥ is consistent with the expectation that the free energy source of EMIC waves is energetic protons with T⊥ > T∥.
Inversion solutions of the elliptic cone model for disk frontside full halo coronal mass ejections
Authors: Zhao X. P.
Published: February 2008

A new algorithm is developed for inverting six unknown elliptic cone model parameters from five observed CME halo parameters. It is shown that the halo parameter α includes the information on the coronal mass ejection (CME) propagation direction denoted by two model parameters. On the basis of the given halo parameter α, two approaches are presented to find out the CME propagation direction. The two‐point approach uses two values of α observed simultaneously by COR1 and COR2 on board STEREO A and B. The one‐point approach combines the value of α with such simultaneous observation as the location of CME‐associated flare, which includes the information associated with CME propagation direction. Model validation experiments show that the CME propagation direction can be accurately determined using the two‐point approach, and the other four model parameters can also be well inverted, especially when the projection angle is greater than 60°. The propagation direction and other four model parameters obtained using the one‐point approach for six disk frontside full halo CMEs appear to be acceptable, though the final conclusion on its validation should be made after STEREO data are available.
Stable carbon isotopic ratios and ionic composition of the high‐Arctic aerosols: An increase in δ13C values from winter to spring
Authors: Narukawa M. , Kawamura K. , Li S.‐M. , Bottenheim J. W.
Published: January 2008

Atmospheric particles were collected in the high Arctic at Alert during winter (February) and spring (April–May) and were subjected to stable carbon isotopic (δ13C) measurements to better understand the source of carbonaceous aerosols. The mean δ13C values of aerosol total carbon (TC) were observed to increase from winter (−25.7 ± 0.7‰) to spring (−23.7 ± 0.8‰). A strong correlation (r2 = 0.92, p < 0.001) was found between the δ13C values and Na+/TC ratios. The increased δ13C values were most likely explained by an enhanced sea‐to‐air emission of marine organic matter to the high Arctic and also by a decreased atmospheric transport of anthropogenic carbon from the midlatitudes. The backward trajectory analysis together with inorganic ion analysis indicated that spring aerosols were more affected by the Arctic Ocean than winter aerosols that were mainly derived from the primary pollutants emitted in the midlatitudes. On the basis of the δ13C values and Na+/TC ratios, contribution of marine organic matter to aerosol TC was estimated to be 45% in late spring. The enhanced sea‐to‐air emission of marine organic carbon is probably linked with a melting of sea ice, expansion of leads, and increased biological activity in the Arctic Ocean after the polar sunrise in spring.
Micro-scale observations of the structure of aerobic microbial granules used for the treatment of nutrient-rich industrial wastewater
Authors: Lemaire Romain , Webb Richard I , Yuan Zhiguo
Published: February 2008

The structure and function of aerobic microbial granules from a lab-scale sequencing batch reactor treating nutrient-rich abattoir wastewater were investigated. These wastewater-fed granules were examined using a wide range of micro-scale techniques including light microscopy, scanning and transmission electron microscopy, fluorescent in situ hybridisation (FISH) combined with confocal laser scanning microscopy and oxygen and pH microsensors, in conjunction with a range of measurements in the bulk liquid phase. Interesting structural features were observed in these granules that have not been reported in synthetic-fed granules. The complex nature of abattoir wastewater was suggested to be responsible for accelerating the breaking process of large mature granules due to a rapid clogging of the granules pores and channels and for the very diverse microbial community observed displaying specific spatial distribution throughout the granules. More importantly, the dissolution at lower pH of mineral complexes associated to the granule matrix of extracellular polymeric substances might have caused the structural damages observed on the granules even though some pH buffer capacity was observed inside these granules. Ciliate protozoa were found to be very abundant on the surface of these wastewater-fed granules, which could potentially assist with reducing the high levels of suspended solids usually present in the aerobic granular sludge effluent. All these observations provide support to future studies on aerobic granular sludge treating real wastewater especially with regard to the granule structure and the mechanisms involved in their formation.
Apoptotic gene expression in neuropathic pain
Authors: Siniscalco Dario , Giordano Catia , Fuccio Carlo , Luongo Livio , Migliozzi Annalucia , Rossi Francesco , Maione Sabatino
Published: January 2008

Pain initiated or caused by a primary lesion or dysfunction in the nervous system is defined as neuropathic pain. It results from direct injury to nerves in the peripheral or central nervous system and is associated with several clinical symptoms. Neuropathic pain treatment is extremely difficult, as it is a very complex disease, involving several molecular pathways. Excitatory or inhibitory pathways controlling neuropathic pain development show altered gene expression, caused by peripheral nerve injury.This study used several experimental pain models to demonstrate the occurrence of programmed cell death in the centers controlling pain induction and maintenance, such as spinal cord and pre-frontal cortex. We combined behavioural, molecular and morphological approaches to assess the involvement of bcl-2 gene family and caspases in neuropathic pain. Chronic constriction injury (CCI) and spared nerve injury (SNI) of rodent sciatic nerve induced the appearance of pain-like behaviours, such as hyperalgesia and allodynia. An early (2-3 days post-CCI) apoptosis appeared in the spinal cord neurons as the pro-apoptotic bax gene increased (320±19%). The incidence of apoptosis appeared to be limited to the first few days following nerve injury. Subsequently, increased expression of anti-apoptotic bcl-2 family genes may inhibit further neuron loss. SNI triggered apoptotic pathway and caspases activation in pre-frontal cortex 7, 14, and 21 days post-injury. Among the time-points analyzed, RT-PCR analysis showed increased expression of the bax/bcl-2 ratio (40±2%), bid (16±2%), caspase-1 (84±3%), caspase-8 (53±6%), caspase-9 (25±6%), caspase-12 (58±2%), TNF (32±2%) genes in the cortex by 7 days post-injury. Western blot analysis showed increased active Caspase-3 protein levels in the cortex at 3, 7, 14, and 21 post-surgery. This study shows that apoptotic genes could be an useful pharmacological target in neuropathic pain controlling.
Neuroprotective effects of prior limb use in 6‐hydroxydopamine‐treated rats: possible role of GDNF
Authors: Cohen Ann D. , Tillerson Jennifer L. , Smith Amanda D. , Schallert Timothy , Zigmond Michael J.
Published: February 2008

Unilateral administration of 6‐hydroxydopamine (6‐OHDA) into the medial forebrain bundle (MFB) causes a loss of dopamine (DA) in the ipsilateral striatum and contralateral motor deficits. However, if a cast is placed on the ipsilateral limb during the first 7 days following 6‐OHDA infusion, forcing the animal to use its contralateral limb, both the behavioral and neurochemical deficits are reduced. Here, we examine the effect of forced reliance on a forelimb during the 7 days prior to ipsilateral infusion of 6‐OHDA on the deficits characteristic of this lesion model. Casted animals displayed no behavioral asymmetries as measured 14–28 days postlesion and a marked attenuation in the loss of striatal DA and its metabolites at 30 days. In addition, animals receiving a unilateral cast alone had an increase in glial cell‐line derived neurotrophic factor (GDNF) protein in the striatum corresponding to the overused limb. GDNF increased within 1 day after the onset of casting, peaked at 3 days, and returned to baseline within 7 days. These results suggest that preinjury forced limb‐use can prevent the behavioral and neurochemical deficits to the subsequent administration of 6‐OHDA and that this may be due in part to neuroprotective effects of GDNF.
Pivotal roles of α‐melanocyte‐stimulating hormone and the melanocortin 4 receptor in leptin stimulation of prolactin secretion in rats
Authors: Watanobe Hajime , Schiöth Helgi B. , Izumi Junkichi
Published: February 2008

Leptin, the obese gene product, was reported to stimulate prolactin (PRL) secretion, but the neuroendocrine mechanism underlying this hormonal response is largely unknown. Thus, in this study we examined the involvement of several important PRL regulators in the leptin‐induced PRL secretion in male rats. Compared with the values in normally fed rats, food deprivation for 3 days significantly decreased both PRL and leptin levels in the plasma. These changes were reverted to normal by a 3‐day constant infusion of 75 μg/kg/day of leptin to the fasted rats, while 225 μg/kg/day of leptin further elevated both PRL and leptin levels. These four groups of animals were used for the following experiments. Results of dopamine and serotonin turnover studies in the brain and the pituitary indicated that neither of these biogenic amines plays a primary role in mediating leptin's effects on PRL. Repeated intracerebroventricular injections over 72 h of neutralizing antibodies against vasoactive intestinal peptide, PRL‐releasing peptide, or β‐endorphin, did not significantly suppress the leptin actions. However, both the blockade of the melanocortin (MC) 4 receptor (R) and the immunoquenching of brain α‐melanocyte‐stimulating hormone (α‐MSH) completely abolished the leptin‐induced PRL release, and the stimulation of the MC4‐R, but not the MC3‐R, significantly elevated PRL levels in the fasted rats. These results suggest that α‐MSH, a cleaved peptide from pro‐opiomelanocortin of which synthesis is stimulated by leptin, may be the pivotal neuropeptide in the brain mediating the leptin's stimulatory influence on PRL secretion. It was also suggested that the MC4‐R may be the primary subtype of the MC‐Rs mediating this action of α‐MSH.
Laser-based volumetric flow visualization by digital color imaging of a spectrally coded volume
Authors: McGregor T. J. , Spence D. J. , Coutts D. W.
Published: January 2008

We present the framework for volumetric laser-based flow visualization instrumentation using a spectrally coded volume to achieve three-component three-dimensional particle velocimetry. By delivering light from a frequency doubled Nd:YAG laser with an optical fiber, we exploit stimulated Raman scattering within the fiber to generate a continuum spanning the visible spectrum from 500to850nm. We shape and disperse the continuum light to illuminate a measurement volume of 20×10×4mm3, in which light sheets of differing spectral properties overlap to form an unambiguous color variation along the depth direction. Using a digital color camera we obtain images of particle fields in this volume. We extract the full spatial distribution of particles with depth inferred from particle color. This paper provides a proof of principle of this instrument, examining the spatial distribution of a static field and a spray field of water droplets ejected by the nozzle of an airbrush.
The critical adsorption point of self-avoiding walks: A finite-size scaling approach
Authors: Luo Meng-Bo
Published: January 2008

The critical adsorption of self-avoiding polymer chain in a simple cubic lattice onto a flat surface is studied with Monte Carlo simulations. The dependence of number of surface contacts M on chain length N and polymer-surface interaction ϵ is investigated by a finite-size scaling approach. We estimate the critical adsorption point ϵc=0.291±0.002 and the exponent ϕ=0.54±0.01. The asymptotic behaviors M∝N for ϵ⪢ϵc and M∝N0 for ϵ⪡ϵc are also obtained from the finite-size scaling relation. We have also estimated the critical adsorption point by using Binder’s cumulant method as well as configurational properties.
2-methylterrylene in hexadecane: Do we see single rotational quantum jumps of methyl groups?
Authors: Sigl A. , Scharnagl Chr. , Friedrich J. , Gourdon A. , Orrit M.
Published: January 2008

We performed comparative low temperature (2–30K) hole-burning and single molecule experiments with 2-methylterrylene with the goal to detect single rotational tunneling jumps of methyl groups. The hole-burned spectrum with its sharply structured side features which are perfectly symmetrically arranged with respect to the central hole supports the assignment to rotational tunneling transitions. However, instead of one, three clearly distinguishable methyl groups show up in the spectrum. Based on molecular mechanics simulations we attribute them to different, nearly degenerate orientations of guest molecules in one specific site of the hexadecane lattice. The frequency distribution of spontaneous jumps of single molecules reflects the features of the hole-burned spectra, although the distribution in the single molecule experiments is significantly broader. The photoinduced frequency transformation of single molecules (“single molecule photobleaching experiments”) fits to the features of the hole-burned spectra, except that, surprisingly, no significant number of spectral jumps could be generated in the frequency range where the prominent narrow antiholes are observed in the hole-burned spectra.
An algorithm for mass matrix calculation of internally constrained molecular geometries
Authors: Aryanpour Masoud , Dhanda Abhishek , Pitsch Heinz
Published: January 2008

Dynamic models for molecular systems require the determination of corresponding mass matrix. For constrained geometries, these computations are often not trivial but need special considerations. Here, assembling the mass matrix of internally constrained molecular structures is formulated as an optimization problem. Analytical expressions are derived for the solution of the different possible cases depending on the rank of the constraint matrix. Geometrical interpretations are further used to enhance the solution concept. As an application, we evaluate the mass matrix for a constrained molecule undergoing an electron-transfer reaction. The preexponential factor for this reaction is computed based on the harmonic model.
Dispersion relation and growth in a two-stream free electron laser with helical wiggler and ion channel guiding
Authors: Mehdian Hassan , Abbasi Negar
Published: January 2008

A linear theory of two-stream free electron laser (FEL) with helical wiggler and ion channel guiding is presented. The dispersion relation is obtained with the help of fluid theory and the growth rate is analyzed through the numerical solutions. The considerable enhancement of the growth rate is demonstrated due to the two-stream instability and continuous tuning of peak growth rate ratio, two-stream FEL compared to single-stream FEL, in terms of varying the ion channel frequency is illustrated.
Improving upon CCSD(T): ΛCCSD(T). II. Stationary formulation and derivatives
Authors: Taube Andrew G. , Bartlett Rodney J.
Published: January 2008

Analytical derivatives are formulated and implemented for the ΛCCSD(T) method. As the historically first size-extensive and orbitally invariant extension of coupled-cluster (CC) theory to exploit the left-hand ground state eigenvector, it offers a vastly better treatment of bond breaking than does CCSD(T), and points the way toward further generalizations of single-reference CC theory that enhance its accuracy away from equilibrium geometries. Application to diatomic force curves and transition states of several well-characterized reactions are made. Surprisingly, despite ΛCCSD(T) describing bond breaking much better than CCSD(T), for transition states both methods are extremely close in both structures and activation barriers. Force curves, however, demonstrate the overall superiority of ΛCCSD(T).
Hot-pressed Sm2Fe17Nx∕Fe–Co composites: Factors controlling densification and in situ nitrogenization of Sm2Fe17 phase
Authors: Gabay A. M. , Akdogan N. G. , Hadjipanayis G. C. , Marinescu M. , Liu J. F. , Ali A.
Published: January 2008

The effects of powder preparation and conditions of hot pressing on the structure and density of consolidated Sm2Fe17Nx and Sm2Fe17Nx∕Fe–Co magnets have been studied. Densities achieved in the case of Sm2Fe17Nx powders prepared through a low-energy milling were higher than after a high-energy milling. The difference is mostly caused by the different particle size, and it can be eliminated by an additional low-energy milling of the coarse high-energy milled powder. The presence of a ductile soft magnetic phase greatly facilitates densification, leading to considerably higher absolute and relative densities in hot-pressed Sm2Fe17Nx∕Fe0.65Co0.35 composites. We have found that during hot pressing, nitrogenization of the Sm2Fe17 phase may occur in situ if pressed together with Fe–Co–N powders. Because Fe–Co–N releases nitrogen below the decomposition temperature of Sm2Fe17Nx, we were able to fabricate the Sm2Fe17Nx∕Fe0.65Co0.35 composite with the density up to 7.6g∕cm3 by hot-pressing mixtures of Sm2Fe17 and (Fe0.65Co0.35)89N11 powders.
Improvement of stress-induced magnetization reversal process of DyFeCo thin films
Authors: Saito Naoya , Yamada Michiya , Nakagawa Shigeki
Published: January 2008

DyFeCo films sputter deposited at relatively low Ar gas pressure condition exhibited the change of easy axis of magnetization by applying relatively low mechanical stress. In order to attain magnetization reversal at lower magnetic field and low applied mechanical stress, a critical mechanical stress, which means the minimum mechanical stress to cause the change of magnetic anisotropy from perpendicular to in plane, should be as low as possible. The saturation field of the magnetization characteristics of the film at the critical field should be as low as possible.
Quantum and surface states of charge carriers in the optical spectra of nanoclusters in a low-permittivity matrix
Authors: Bondar N. V. , Brodyn M. S.
Published: February 2008

The optical spectra of quantum dots of CdS and ZnSe grown in borosilicate glass by the sol–gel method are obtained and analyzed. It is found that at concentrations of the two semiconductors x<0.06% the emission spectra are due to annihilation of free (internal) excitons in quantum states. The mean size of the quantum dots (QDs) for a given concentration of ZnSe and CdS is calculated and found to be in good agreement with the x-ray data, and the exciton binding energy is calculated with allowance for the dielectric mismatch between the semiconductor and matrix. It is proposed that this mismatch may be the cause giving rise to the exciton percolation level that is observed in QD arrays for both systems at x>0.06%. The emission from the surface level of CdS QDs in the region ∼2.7eV, formed by the outer atoms with dangling bonds, is observed for the first time, as is the emission band from surface localized states. The relation between the position of the maximum of this band and the energy of the 1S state of the free exciton is established. It is shown that the properties of surface localized states are largely similar to the analogous properties of localized states of 3D (amorphous semiconductors, substitutional solid solutions of substitution) and 2D (quantum wells and superlattices) structures.
Controlled domain wall nucleation and resulting magnetoresistance in Ni81Fe19 nanoconstrictions
Authors: Hickey M. C. , Atkinson D. , Marrows C. H. , Hickey B. J.
Published: February 2008

We have developed magnetic nanostructures which comprise two thin film Ni81Fe19 pads of differing coercive field connected by a nanoscale constriction. In the region of field between the two coercive fields, a domain wall nucleates in the constriction and the resistivity associated with this wall is determined by comparing electrical measurements with micron scale magneto-optic measurements. There is an excellent correspondence between the field region where the wall nucleates and the change in magnetoresistance, which is dominated by anisotropic magnetoresistance. Shape optimization of the pads gives a larger field range over which the domain wall is stable.
Cavitation in anisotropic fluids
Authors: Seddon James R. T. , Mullin Tom
Published: February 2008

Sustained cavitation in the lubrication layer between a rotating heavy sphere and a nearby wall in a Newtonian fluid is an essential aspect of the motion. Here we extend these findings to the case of anisotropic materials using both shear-thinning and viscoelastic fluids. As in the case of Newtonian fluids, cavitation is observed but new interesting features emerge. These include the formation of long fingers that can either be steady or dynamic with apparent irregular interactions.
Radiation relations for electromagnetic excitation of a layered chiral medium by an interior dipole
Authors: Athanasiadis Christodoulos , Tsitsas Nikolaos L.
Published: January 2008

In this paper we establish certain fundamental radiation integral relations, refereed also as radiation theorems or principles, which connect the fields and far-field patterns due to the spherical wave excitation of a layered chiral obstacle by a dipole in its interior. The investigation of problems involving such types of excitations is motivated by significant applications including, for example, radiation from thin wires embedded in layered chiral media as well as from chiral in chiral composites. Reciprocity and general radiation theorems are established, relating the total, primary, and secondary Beltrami fields with the respective far-field patterns. As a consequence of the general radiation theorem, we obtain the optical theorem expressing the extinction cross section by means of the secondary Beltrami field at the dipole’s location. For an obstacle excited by a plane and a spherical wave mixed radiation-scattering theorems are derived. The theorems recover as special cases the respective known results for chiral and achiral media.
On the magnetohydrodynamic load and the magnetohydrodynamic metage
Authors: Chakraborty Sagar , Guha Partha
Published: January 2008

In analogy with the load and the metage in hydrodynamics, this paper defines magnetohydrodynamic load and magnetohydrodynamic metage in the case of magnetofluids. They can be used to write the magnetic field in MHD in Clebsch’s form. It has been shown herein how these two concepts can be utilized to derive the magnetic analog of the Ertel’s theorem and also, how in the presence of nontrivial topology of the magnetic field in the magnetofluid one may associate the linking number of the magnetic field lines with the invariant MHD loads. The paper illustrates that the symmetry translation of the MHD metage in the corresponding label space generates the conservation of cross helicity.
The microstructure and electrical transport properties of immiscible copper-niobium alloy thin films
Authors: Banerjee Rajarshi , Bose Sangita , Genc Arda , Ayyub Pushan
Published: February 2008

Mutually immiscible in the solid state, copper and niobium exhibit a relatively strong clustering (phase separating) tendency in the liquid state and can therefore only be alloyed in a highly metastable form: for example, by vapor quenching. We have deposited metastable Cu–Nb alloy thin films with nominal compositions ranging from 5 to 90 at. % Nb by magnetron cosputtering. The microstructure of these films depends strongly on the composition and ranges from coarse-grained solid solutions for Cu-rich and Nb-rich compositions to phase-separated amorphous mixtures when the two elements are in comparable amounts. The crystalline Cu- or Nb-rich compositions exhibit positive temperature coefficients of resistivity (TCR) with the Cu–90 at. % Nb film exhibiting a superconducting transition with (TC)onset∼4.5 K. The amorphous films show high room temperature resistivity, a negative TCR, and composition dependent superconducting transitions. We investigate the relation between the microstructure, phase stability, and the electrical transport properties.
Monte Carlo investigation of terahertz plasma oscillations in ultrathin layers of n-type In0.53Ga0.47As
Authors: Millithaler J.-F. , Reggiani L. , Pousset J. , Varani L. , Palermo C. , Knap W. , Mateos J. , González T. , Perez S. , Pardo D.
Published: January 2008

By numerical simulations we investigate the dispersion of the plasma frequency in a n-type In0.53Ga0.47As layer of thickness W and submicron length at T=300K. For W=100nm and carrier concentrations of 1016–1018cm−3 the results are in good agreement with the standard three-dimensional (3D) expression of the plasma frequency. For W⩽10nm the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency values are in good agreement with the two-dimensional (2D) expression of the plasma frequency obtained for a ballistic regime within the in-plane approximation for the electric field. A region of cross over between the 2D and 3D behaviors of the plasma frequency is evidenced for W>10nm.
Strain development in nanoporous metallic foils formed by dealloying
Authors: Schofield Eleanor J. , Ingham Bridget , Turnbull Alan , Toney Michael F. , Ryan Mary P.
Published: January 2008

Nanoporous Au foils were formed by dealloying a Ag–Au alloy in concentrated HNO3. The resultant foils, which have a “spongelike” morphology with interconnecting ligaments, were studied using synchrotron-based diffraction. A three-dimensional visualization of the nanostructure is generated from small angle experiments and the lattice parameter is derived from diffraction. The data show the development of two interspersed nanoscale strained regions within the material: one in significant tension and one in compression. We interpret this by considering regions of high positive and negative curvatures in the material; this curvature decreases with increasing pore size resulting in a relaxation in lattice strain.
Electrical properties of GaN (Fe) buffers for AlGaN∕GaN high electron mobility transistor structures
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Yugova T. G. , Markov A. V. , Dabiran A. M. , Wowchak A. M. , Cui B. , Xie J. , Osinsky A. V. , Chow P. P. , Pearton S. J.
Published: January 2008

The electrical properties of AlGaN∕GaN high electron mobility transistor structures grown on composite GaN(Fe)∕GaN buffers by molecular beam epitaxy were reported. The concentration of Fe in the GaN(Fe) layer ranged from 8×1016to3×1017cm−3 as established by secondary ion mass spectrometry. The thickness of the undoped GaN layer of the buffer was varied from 2.2to4.1μm. For thinner buffers and higher Fe concentration, the buffer was semi-insulating, with the Fermi level pinned near Ec-0.57eV. For thicker buffers and lower Fe concentration, the top part of the buffer was conducting. Admittance spectra measured in conducting buffers also showed a prominent contribution from Ec-(055–0.6)eV electron traps. Despite the universal prominence of these traps in all our films, the behavior of their concentration with Fe doping and with increased distance from the GaN (Fe)∕GaN boundary is not compatible with the assumption that they are due to substitutional Fe acceptors. Possible compensation mechanisms in the studied structures were discussed.
One-step grown suspended n-type semiconducting single wall carbon nanotube field effect transistors with carbon nanotube electrodes
Authors: Lee Yun-Hi , Lee Jong-Hee , Noh Ji-Young
Published: January 2008

The authors report on the in situ formation of n-type ferromagnetic single wall carbon nanotube field effect transistors for the first time using a rapid heating process with a continuous flow of H2 gas under a vacuum of millitorr and their electromagnetic transport properties. The suspended n-type single wall carbon nanotube (SWNT) bridge including nanosized Fe catalyst impurities also shows gate controlled magnetic field dependent field effect behavior. The interesting features of these devices can be understood qualitatively based on the influence of the nonoxidant interface and nano Fe residing at the growth site of the SWNT bridge.
Nanophotoswitches with a high on/off ratio based on a structure of indium tin oxide/organic insulator/metal
Authors: Xu Xinjun , Li Lidong , Yu Gui , Di Chong-An , Wei Dacheng , Ye Shanghui , Liu Yunqi
Published: January 2008

Highly photosensitive nanoswitches with a structure of indium tin oxide/organic insulator/metal have been fabricated. Electric current in the photoswitches is sensitive to ultraviolet (UV) radiation, and can be inhibited and recovered by exposing the photoswitch to, or shielding it from, UV radiation, respectively. Photoswitches with a very high on/off ratio exceeding 106, which is the highest ratio recorded for all reported organic photoswitches, have been demonstrated under UV radiation even with a low power density (∼10−5W∕cm2).
Controlling the alignment of neutral iodine molecules in the elliptical channels of AlPO4-11 crystals
Authors: Zhai J. P. , Li I. L. , Ruan S. C. , Lee H. F. , Tang Z. K.
Published: January 2008

Al P O 4 - 11 (AEL) single crystal provides well-aligned one-dimensional elliptical nanochannels, wherein neutral iodine molecules can be trapped and aligned. Since the iodine molecules are well accommodated in the matrix of the AEL single crystal, it offers us a good example for studying polarized Raman spectra in a controllable way. Polarization dependence of Raman intensity of the iodine molecular vibration modes indicates that the iodine molecules are strictly oriented in two directions, either along the long axis of the elliptical channel or along the AEL channel direction.
The chemical and electronic structures of YOxNy on Si(100)
Authors: Wang X. J. , Zhang L. D. , He G. , Zhang J. P. , Liu M. , Zhu L. Q.
Published: January 2008

Effects of nitrogen incorporation on interfacial property, band gap, and band alignments of high-k Y2O3 gate dielectrics have been investigated. It was found that the incorporation of nitrogen into Y2O3 films can effectively suppress the growth of the interfacial layer between Y2O3 and Si substrate. The incorporation of nitrogen into Y2O3 films leads to the reduction of band gap and valence band offset, but not the conduction offset of Y2O3 films. High temperature annealing will help to increase the band gap and valence band offset of YOxNy film due to the release of the interstitial N atoms.
Efficient, visible organic light-emitting diodes utilizing a single polymer layer doped with quantum dots
Authors: Campbell I. H. , Crone B. K.
Published: January 2008

We demonstrate organic light-emitting diodes (OLEDs) using a single active layer consisting of CdSe∕ZnS quantum dots (QDs) dispersed in poly (9,9-dioctylfluorene) (PFO). The diodes have an external quantum efficiency of ∼0.5% and reach 0.1A∕cm2 at 6.5V. These results are comparable to complex, multilayer QD OLEDs. Built-in potential measurements show that the QD valence levels are shifted to lower binding energy when compared to quantum confinement based estimates, and are close to PFO valence levels. Devices using red and green QDs emit predominantly from the QDs but the spectrum of blue QDs is perturbed by interactions with PFO.
Control of homoepitaxial Si nanostructures by locally modified surface reactivity
Authors: Portavoce A. , Hull R. , Reuter M. C. , Copel M. , Ross F. M.
Published: February 2008

We describe a technique for the homoepitaxial growth of epitaxial, faceted Si islands on Si(001), consisting of predeposition of Ga surfactant followed by ultrahigh vacuum chemical vapor deposition (CVD) of Si. Ga-mediated Si CVD leads to the formation of Si islands exhibiting {113} and {102} facets. Surfactant-mediated CVD is shown to provide a new degree of freedom for the production of nanoscale structures without lithography.
Ganglioside GM2/GM3 complex affixed on silica nanospheres strongly inhibits cell motility through CD82/cMet-mediated pathway
Authors: Todeschini Adriane Regina , Dos Santos Jose Nilson , Handa Kazuko , Hakomori Sen-itiroh
Published: February 2008

Ganglioside GM2 complexed with tetraspanin CD82 in glycosynaptic microdomain of HCV29 and other epithelial cells inhibits hepatocyte growth factor-induced cMet tyrosine kinase. In addition, adhesion of HCV29 cells to extracellular matrix proteins also activates cMet kinase through “cross-talk” of integrins with cMet, leading to inhibition of cell motility and growth. Present studies indicate that cell motility and growth are greatly influenced by expression of GM2, GM3, or GM2/GM3 complexes, which affect cMet kinase activity of various types of cells, based on the following series of observations: (
i
) Cells expressing CD82, cultured with GM2 and GM3 cocoated on silica nanospheres, displayed stronger and more consistent motility inhibition than those cultured with GM2 or GM3 alone or with other glycosphingolipids. (
ii
) GM2-GM3, in the presence of Ca
2+
form a heterodimer, as evidenced by electrospray ionization (ESI) mass spectrometry and by specific reactivity with mAb 8E11, directed to GM2/GM3 dimer structure. (
iii
) Cells expressing cMet and CD82 were characterized by enhanced motility associated with HGF-induced cMet activation. Both cMet and motility were strongly inhibited by culturing cells with GM2/GM3 dimer coated on nanospheres. (
iv
) Adhesion of HCV29 or YTS-1/CD82 cells to laminin-5-coated plate activated cMet kinase in the absence of HGF, whereas GM2/GM3 dimer inhibited adhesion-induced cMet kinase activity and inhibited cell motility. (
v
) Inhibited cell motility as in
i
,
iii
, and
iv
was restored to normal level by addition of mAb 8E11, which blocks interaction of GM2/GM3 dimer with CD82. Signaling through Src and MAP kinases is activated or inhibited in close association with cMet kinase, in response to GM2/GM3 dimer interaction with CD82. Thus, a previously uncharacterized GM2/GM3 heterodimer complexed with CD82 inhibits cell motility through CD82-cMet or integrin-cMet pathway.
A guardian of grasses: Specific origin and conservation of a unique disease-resistance gene in the grass lineage
Authors: Sindhu Anoop , Chintamanani Satya , Brandt Amanda S. , Zanis Michael , Scofield Steven R. , Johal Gurmukh S.
Published: January 2008

The maize
Hm1
gene provides protection against a lethal leaf blight and ear mold disease caused by
Cochliobolus carbonum
race 1 (CCR1). Although it was the first disease-resistance (DR) gene to be cloned, it remains a novelty because, instead of participating in the plant recognition and response system as most DR genes do,
Hm1
disarms the pathogen directly. It does so by encoding an NADPH-dependent reductase, whose function is to inactivate
Helminthosporium carbonum
(HC) toxin, an epoxide-containing cyclic tetrapeptide, which the pathogen produces as a key virulence factor to colonize maize. Although CCR1 is strictly a pathogen of maize, orthologs of
Hm1
and the HC-toxin reductase activity are present in the grass family, suggesting an ancient and evolutionarily conserved role of this DR trait in plants. Here, we provide proof for such a role by demonstrating its involvement in nonhost resistance of barley to CCR1. Barley leaves in which expression of the
Hm1
homologue was silenced became susceptible to infection by CCR1, but only if the pathogen was able to produce HC toxin. Phylogenetic analysis indicated that
Hm1
evolved exclusively and early in the grass lineage. Given the devastating ability of CCR1 to kill maize, these findings imply that the evolution and/or geographical distribution of grasses may have been constrained if
Hm1
did not emerge.
The effect of acculturation on depressive moods: Immigrant boys and girls during their transition from late adolescence to early adulthood
Authors: Turjeman Hagit , Mesch Gustavo , Fishman Gideon
Published: January 2008

Using data (N = 773) from a longitudinal study of former Soviet Union immigrants to Israel, this study aimed to identify the psychosocial correlates of depressive mood among immigrant adolescents and differences by age and gender. OLS regression results suggest acculturative and social factors as useful variables in predicting depression. Adolescents with a high probability of assimilating (simultaneous strengthening of Israeli identity and weakening of Russian identity) proved more likely to report low levels of depression. Consistent with the literature, girls were more depressed than boys and age was positively related to depressive moods. As expected, different factors explain the psychological well‐being of adolescents of different age groups and sex: in boys, depression was found mainly related to acculturation difficulties; in girls it was related more to their social support. As for age, more independent variables were statistically significant in accounting for depression in the older than in the younger group, which suggests that depression is age‐related. The study results should be understood in connection with socialization processes to sex roles and the impact immigration has on this process.
Fudging the Numbers: Distributing Chocolate Influences Student Evaluations of an Undergraduate Course
Authors: Youmans Robert J. , Jee Benjamin D.
Published: February 2008

Student evaluations provide important information about teaching effectiveness. Research has shown that student evaluations can be mediated by unintended aspects of a course. In this study, we examined whether an event unrelated to a course would increase student evaluations. Six discussion sections completed course evaluations administered by an independent experimenter. The experimenter offered chocolate to 3 sections before they completed the evaluations. Overall, students offered chocolate gave more positive evaluations than students not offered chocolate. This result highlights the need to standardize evaluation procedures to control for the influence of external factors on student evaluations.
A Novel Role for PA28γ-Proteasome in Nuclear Speckle Organization and SR Protein Trafficking
Authors: Baldin Véronique , Militello Muriel , Thomas Yann , Doucet Christine , Fic Weronika , Boireau Stephanie , Jariel-Encontre Isabelle , Piechaczyk Marc , Bertrand Edouard , Tazi Jamal , Coux Olivier
Published: February 2008

In eukaryotic cells, proteasomes play an essential role in intracellular proteolysis and are involved in the control of most biological processes through regulated degradation of key proteins. Analysis of 20S proteasome localization in human cell lines, using ectopic expression of its CFP-tagged α7 subunit, revealed the presence in nuclear foci of a specific and proteolytically active complex made by association of the 20S proteasome with its PA28γ regulator. Identification of these foci as the nuclear speckles (NS), which are dynamic subnuclear structures enriched in splicing factors (including the SR protein family), prompted us to analyze the role(s) of proteasome-PA28γ complexes in the NS. Here, we show that knockdown of these complexes by small interfering RNAs directed against PA28γ strongly impacts the organization of the NS. Further analysis of PA28γ-depleted cells demonstrated an alteration of intranuclear trafficking of SR proteins. Thus, our data identify proteasome-PA28γ complexes as a novel regulator of NS organization and function, acting most likely through selective proteolysis. These results constitute the first demonstration of a role of a specific proteasome complex in a defined subnuclear compartment and suggest that proteolysis plays important functions in the precise control of splicing factors trafficking within the nucleus.
Recent Fungal Diseases of Crop Plants: Is Lateral Gene Transfer a Common Theme?
Authors: Oliver Richard P. , Solomon Peter S.
Published: February 2008

A cursory glance at old textbooks of plant pathology reveals that the diseases which are the current scourge of agriculture in many parts of the world are a different set from those that were prominent 50 or 100 years ago. Why have these new diseases arisen? The traditional explanations subscribe to the “nature abhors a vacuum” principle—that control of one disease creates the condition for the emergence of a replacement—but does little to explain why the new pathogen succeeds. The emergence of a new disease requires a series of conditions and steps, including the enhanced fecundity of the new pathogen, enhanced survival from season to season, and spread around the world. Recently, evidence was obtained that wheat tan spot emerged through a lateral gene transfer event some time prior to 1941. Although there have been sporadic and persistent reports of lateral gene transfer between and into fungal plant pathogens, most examples have been dismissed through incomplete evidence. The completion of whole genome sequences of an increasing number of fungal pathogens no longer allows such proposed cases of lateral gene transfer to be dismissed so easily. How frequent are lateral gene transfers involving fungal plant pathogens, and can this process explain the emergence of many of the new diseases of the recent past? Many of the apparently new diseases are dependant on the expression of host-specific toxins. These are enigmatic molecules whose action requires the presence of plant genes with products that specifically encode sensitivity to the toxin and susceptibility to the disease. It is also notable that many new diseases belong to the fungal taxon dothideomycetes. This review explores the coincidence of new diseases, interspecific gene transfer, host-specific toxins, and the dothideomycete class.
Conditions for Development of Powdery Mildew of Tomato Caused by Oidium neolycopersici
Authors: Jacob D. , David D. Rav , Sztjenberg A. , Elad Y.
Published: February 2008

Oidium neolycopersici causes severe powdery mildew on all aerial parts of tomato, excluding the fruit. The objective of the present work was to examine factors that influence the development of O. neolycopersici on tomato and to identify potential methods for managing tomato powdery mildew. Under controlled conditions, the highest rates of conidial germination were observed at 25°C, 99% relative humidity (RH) and minimal light, and the lowest on leaves adjacent to fruits. Optimal conditions for appressoria formation were 25°C, RH ranging from 33 to 99%, and 1,750 lux light intensity. More conidia were formed at 20°C, 70 to 85% RH, and 5,150 lux light intensity than at 16 and 26°C, 99% RH, and 480 to 1,750 lux, respectively. Conidia survived and remained capable of germination for over four months when initially incubated at lower temperatures and higher RH, as compared with their fast decline under more extreme summer shade conditions. In growth chamber experiments, disease did not develop at 28°C. Within the range of 70 to 99% RH, disease was less severe under the higher RH than the drier conditions. Disease was also less severe at lower light intensities. Data collected in three commercial-like greenhouse experiments involving various climate regimes were used to draw correlations regarding the effects of temperature and RH on the development of epidemics. Severity of powdery mildew was positively correlated with the duration of the range 15 to 25°C, 1 to 4 weeks before disease evaluation (BDE), RH levels of 60 to 90% at 2 to 4 weeks BDE, and RH of 50 to 60% during the week BDE. Conversely, disease was negatively correlated with the duration of temperatures in the low and high ranges (5 to 15°C and 35 to 40°C) at 1 to 4 weeks BDE, with the duration of RH levels of 40% and below at 1 to 4 weeks BDE, and with 50 to 60% RH during the third week BDE. High (90 to 100%) RH was also negatively correlated with disease severity. These results suggest that the combination of high temperatures and low RH may help reduce O. neolycopersici powdery mildew severity in greenhouse tomatoes.