bluuebunny/crossref_metadata_2025 huggingface dataset:
First meiosis of early dictyate nuclei from primordial oocytes in mature and activated mouse oocytes
Authors: Czolowska Renata , Tarkowski Andrzej K.
Published: September 2008

Nuclei of diplotene (dictyate) primordial oocytes (PO) were transferred to metaphase II oocytes and to activated mouse oocytes using cell fusion techniques. In a metaphase II oocyte, the PO nucleus condenses within 2–3 h to bivalents which become arranged on the first meiotic spindle. After oocyte activation, homologous chromosomes segregate between the oocyte and the first polar body, and a diploid pronucleus-like nucleus reforms from the one set of dyads. This nucleus condenses in the first embryonic mitosis into 40 ‘somatic’ chromosomes which coexist in the common metaphase plate with 20 somatic chromosomes originating from the female pronucleus. Shortening of the time between fusion and activation to about 1 h prevents bivalent differentiation. The PO nucleus condenses only partially and reforms, after oocyte activation, a pronucleus-like nucleus. This nucleus gives rise at the first embryonic mitosis to 20 bivalents which coexist with 20 somatic chromosomes originating from the female pronucleus. A PO nucleus introduced into an activated egg completes the first cell cycle as an intact interphase nucleus. It never condenses in the first embryonic mitosis into bivalents, and undergoes only initial condensation (preceding bivalent differentiation). These results indicate that: (1) condensation into bivalents, meiotic spindle formation and first meiotic division can be greatly accelerated by the introduction of an early diplotene (dictyate) oocyte nucleus into a metaphase II oocyte, and (2) depending on whether the diplotene nucleus enters the first embryonic (mitotic) cell cycle after just initiating or after completing the first meiosis, it gives rise at the first cleavage division to meiotic (bivalents) or ‘somatic’ chromosomes respectively.
Isolation of viable sperm cells from tobacco (Nicotiana tabacum)
Authors: Cao Yajuan , Reece Adonis , Russell Scott D.
Published: September 2008

Viable sperm cells of Nicotiana tabacum were isolated by the semi-vivo technique. After pollination, excised styles were floated, cut end immersed, in a solution of 15% sucrose with 0.01% boric and 0.03% Ca(NO3)2 at 27°C in a growth chamber until pollen tubes emerged. After sperm cells were formed (at least 8 h after pollination) tubes were immersed in a 9% mannitol solution. In this solution, sperm cells are nearly ellipsoidal and retain viability for over 6 h.
Mouse oocytes penetrated by sperm at GV or GVBD stage lose the ablity to fuse with additional spermatozoa
Authors: Pyrzyńska Beata , Maleszewski M. , Maluchnik D.
Published: September 2008

Mouse oocytes penetrated by spermatozoa during germinal vesicle (GV) breakdown undergo maturation and are arrested at metaphase of the second meiotic division despite the presence of sperm nuclei within the ooplasm. When these oocytes were re-inseminated, none was penetrated by newly added spermatozoa. When GV oocytes were inseminated and cultured in the presence of dibutyryl cAMP, the oocytes remained at GV stage, yet they did not permit entry of additional spermatozoa. These observations suggest that the plasma membrane of maturing oocytes is modified by precociously penetrating spermatozoa independently from cortical granule exocytosis. Sperm components incorporated into the oocytes seem to be responsible for the modification of the oocyte's plasma membrane.
Centrosomes with striated rootlets in rabbit zygotes
Authors: Szöllösi M.S. , Adenot P. , Szöllösi D.
Published: September 2008

An electron microscopic study of the rabbit zygote has shown the presence of numerous paracrystalline structures (PSs) around the pronuclei. The majority of these structures are situated in the narrow space between pronuclei. The PSs during interphase are associated with small dense knobs, and filamentous material;some of them, namely those situated in the internuclear space, are also associated with striated rootlets. The PS and its appendages form a complex which nucleates microtubules during interphase and phase M. The structure of these complexes changes with the cell cycle. Striated rootlets disappear at G2/M. Dense Knobs and filamentous material separate from the PS, become loose and associate with numerous microtubules at the poles of the first mitotic spindle. PSs and their associated structures are considered to be a newly discovered morphological form of the centrosome.
Structure and function of asterosaps, sperm-activating peptides from the jelly coat of starfish eggs
Authors: Nishigaki Takuya , Chiba Kazuyoshi , Miki Wataru , Hoshi Motonori
Published: September 2008

Jelly coat of starfish eggs has the capacity to activate homologous spermatozoa and induce the acrosome reaction. We have isolated 12 sperm-activating peptides (SAPs) from the egg jelly of the starfish,Asterias amurensis. Eleven SAPs were structurally identified by sequence analysis and electro-spray ionisation mass spectrometry. All of them are glutamine-rich tetratriacontapeptides with an intramolecular disulphide linkage between Cys8and Cys32. They are much larger than sea urchin SAPs and do not show any significant sequence similarities to known proteins. Thus we have collectively named them asterosaps. The amino terminal region, where structural diversity of asterosaps is observed, is not important for their activity, whereas the disulphide linkage is essential. Asterosaps do not induce the acrosome reaction by themselves, but are able to induce the acrosome reaction in combination with an egg jelly glycoconjugate named ARIS. Furthermore, anti-asterosap rabbit antibody significantly decreased the acrosome reaction-inducing activity of the jelly solution and the activity was restored by addition of excess asterosap. These results support our hypothesis that the main physiological role of SAPs is the induction of the acrosome reaction in cooperation with two other jelly components, ARIS and Co-ARIS.
Gonadotropin suppression of apoptosis in follicle somatic cells
Authors: Galeati G. , Forni M. , Spinaci M.
Published: September 2008

In each oestrous cycle only a limited number of follicles are selected for ovulation whereas the remaining majority undergo atresia. The earliest and most prominent feature of atresia is the death of granulosa cells. Recent biochemical evidence has demonstrated that granulosa cell death during follicular atresia in swine (Tillyet al., 1992), bovine (Jollyet al., 1994) and rodent (Tillyet al., 1991) ovaries occurs by apoptosis, a process whereby cells die in a controlled manner. A biochemical event considered to be characteristic of apoptotic cell death is the intranucleosomal cleavage of genomic DNA into fragments 180–200 bp in size, which separate into a distinctive ladder-like pattern on agarose gel electrophoresis. Detection of this pattern of oligonucleosomes in DNA provides a marker of apoptotic cell death.
Folloicular dominance and oocyte maturation
Authors: Campbell B.K. , McNeilly A.S.
Published: September 2008

The ovulatory follicle has the dual role of releasing a viable oocyte capable of fertilisation and the production of key endocrine signals that result in mating behaviour, the induction of the preovulatory LH surge and ovulation. Further, following ovulation the ovulatory follicle must be capable of forming a viable corpus luteum if pregnancy is to be maintained. Follicle growth is therefore a developmental process during which the follicle progressively acquires a number of properties, each of which is an essential prerequisite for further development. Failure to acquire these properties at the correct time and in an exact sequence will lead to failure of the developmental process and to the deterioration of the follicle through atresia and degeneration of the oocyte.
Beneficial effect of medium with high concentration serum for direct sperm injection into mouse oocytes using a conventional pipette
Authors: Suzuki Kazuo , Yanagimachi R.
Published: September 2008

Although the piezo-electrically driven pipette is much more effective than a conventional pipette for direct sperm injection into mouse oocytes, the piezo-pipette driving unit is expensive and may not be readily accessible to most basic laboratories. We reprot here that the inefficiency of the conventional pipette can be improved by performing the operation in a medium with high serum concentration.
Laser blastocyst biopsy for preimplantation diagnosis in the human
Authors: Veiga A. , Sandalinas M. , Benkhalifa M. , Boada M. , Carrera M. , Santaló J. , Barri P.N. , Ménézo Y.
Published: September 2008

A new methodology for blastocyst biopsy that uses a 1.48μm in diode laser is described. Trophectoderm cells are biopsied after laster zona drilling and culture, fixed and processed for fluorescent in situ hybridisation (FISH) analysis. Preliminary results on the efficiency of the procedure and blastocyst recovery rate are promising. Blastocyst laser biopsy is a useful tool in preimplantation genetic diagnosis (PGD) as it allows a more reliable diagnosis and widens the diagnostic possibilities on account of the higher number of cells obtained in the biopsy.
Seeking Anderson's faulting in seismicity: A centennial celebration
Authors: Célérier Bernard
Published: September 2008

The reactivation of faults with near‐optimal orientations is commonly considered to control the state of stress in the crust. Near the surface, where a principal stress direction is vertical, the attitude of such faults is explained by Anderson's theory. This raises the questions of how prevalent this type of faulting actually is in current seismicity, down to what depth it frequently occurs, and what range of friction angles explains it best. The Global Centroid Moment Tensor catalog is analyzed to address these questions. Dip‐slip and strike‐slip mechanisms are dominant, and oblique slips are relatively rare for well‐constrained events with depths shallower than 30 km. Preferred Andersonian faulting is the simplest, but not the unique, explanation for this dominance. Isolating reverse, strike‐slip, and normal events reveals an asymmetry in the distribution of nodal plane dips and plunges of the P, B, and T axes between reverse and normal faulting. Assuming that the most frequent events correspond to reactivation near optimal orientations yields 40–60° and 0–20° friction angles for reverse and normal faults, respectively. This indicates that reverse and normal faulting mechanics are not symmetrical with respect to stress configuration as predicted by Anderson's theory.
Electron properties of high‐speed solar wind from polar coronal holes obtained by Ulysses thermal noise spectroscopy: Not so dense, not so hot
Authors: Issautier K. , Le Chat G. , Meyer‐Vernet N. , Moncuquet M. , Hoang S. , MacDowall R. J. , McComas D. J.
Published: September 2008

We present radio observations of Ulysses' third fast latitude scan near the 2007 solar activity minimum of cycle 23. We deduce in situ measurements of the electron density and temperature using the method of quasi‐thermal noise spectroscopy. We study the large‐scale properties of the fast solar wind coming from polar coronal holes and compare our results to those obtained during Ulysses' first fast scan in 1994–1995 near the minimum of cycle 22. The fast solar wind in both hemispheres is less dense and cooler by about 19% and 13% respectively, as compared to the last solar minimum.
Shear wave splitting in the southern margin of the Ordos Block, north China
Authors: Huang Zhouchuan , Xu Mingjie , Wang Liangshu , Mi Ning , Yu Dayong , Li Hua
Published: September 2008

The southern margin of the Ordos Block in North China marks the transition from a stable cratonic block to active transextensional deformation in the Weihe Graben, driven by the northeastward expansion of the Tibet Plateau. We deployed 29 portable digital stations across this boundary and studied the upper mantle anisotropy using SKS splitting. The anisotropy is weak (δt < 0.5 s) at stations within the Ordos Block and in the North Weihe Graben, but strong (δt = 1.23 ± 0.39 s) in the South Weihe Graben and Qinling Orogen further south. The directions of the fast S‐wave are 98 ± 7°, subparallel to the orientations of surface structures and the GPS site velocities relative to stable Asian continent. We suggest that this E‐W oriented anisotropy is the result of both the collision between the North and South China Blocks in the Mesozoic, and the eastward upper mantle flow driven by the Indo‐Asian collision.
Midlatitude nighttime enhancement in F region electron density from global COSMIC measurements under solar minimum winter condition
Authors: Luan Xiaoli , Wang Wenbin , Burns Alan , Solomon Stanley C. , Lei Jiuhou
Published: September 2008

Ionospheric electron density profiles retrieved from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites measurements from 6 November 2006 to 5 February 2007 are used to study the ionospheric nighttime electron density enhancements under winter, solar minimum, and geomagnetically quiet conditions. In this work, the peak electron densities of F2 layer (NmF2) derived from COSMIC measurements are found to be in reasonably good agreement with ionosonde observations during the night. Therefore the morphology of nighttime enhancements is investigated at geomagnetic midlatitudes (MLAT 20–60°) in the northern hemisphere using COSMIC observations. The enhancements of electron density are evident near the F2 layer peak at most latitudes and longitudes; however, significant variations in the latitudinal dependence of the occurrence time and net magnitudes of the enhancements are found in different regions. The characteristics of enhancements in the North Atlantic Ocean sector are distinctly different from those in the eastern part of the North American sector and also from those at longitudes from Europe to Asia, in the Pacific Ocean, and in the western part of the North American sectors. The longitudinal variations of the morphology of the electron density enhancements during nighttime are possibly caused by different downward plasma flux, meridional winds, and electric field drifts under the effect of the geomagnetic field.
Magnetospheric amplification and emission triggering by ELF/VLF waves injected by the 3.6 MW HAARP ionospheric heater
Authors: Gołkowski M. , Inan U. S. , Gibby A. R. , Cohen M. B.
Published: September 2008

The HF dipole array of the High Frequency Active Auroral Research Program (HAARP) in Gakona, Alaska, was recently upgraded to 180 elements, facilitating operations at a total radiated power level of 3.6 MW and an effective radiated power of ∼575 MW. In the first experiments at the new power level, the HAARP array is used for magnetospheric wave injection. Modulated heating of auroral electrojet currents in the ionosphere yields radiation in the ELF/VLF frequency range. The HAARP‐generated signals are injected into the magnetosphere, where they propagate in the whistler mode in field‐aligned “ducts,” allowing them to be observed at the conjugate point on a ship‐borne receiver and on autonomous buoy platforms. The observation of the 1‐hop signals is accompanied by the observation of associated 2‐hop components in the northern hemisphere, which have reflected from the ionospheric boundary in the southern hemisphere. The observed signals are accompanied by triggered emissions and exhibit temporal amplification of 15–25 dB/s and bandwidth broadening to ∼50 Hz. Amplification occurs at injected signal frequencies selected in near real time on the basis of observations of natural emission activity, and only certain components of the frequency‐time formats transmitted are amplified. Observations at multiple sites and dispersion analysis show that the signals are injected into the magnetosphere directly above the HF heater. The duration of echo observation and the prevalence of 1‐hop observations are consistent with statistics from 1986 Siple Station experiments. The particle‐trapping wave amplitude near the magnetic equator is estimated in the range 0.1–0.4 pT and gyroresonance with 10 keV–100 keV electrons.
Metabolic Predictors of Inflammation, Adhesion, and Coagulability in Healthy Younger‐aged Adults
Authors: Mills Paul J. , Shapiro David , Goldstein Iris B. , Ottaviani Cristina , Pung Meredith A. , Khandrika Srikrishna , von Känel Roland , Rutledge Thomas R.
Published: September 2008

Elevated levels of inflammatory biomarkers are associated with the pathophysiology of cardiovascular diseases and are predictors of cardiovascular events. The objective of this study was to determine the unique contributions of metabolic factors as predictors of inflammation (C‐reactive protein (CRP) and interleukin‐6 (IL‐6)), adhesion (soluble intercellular adhesion molecule‐1 (sICAM‐1)), and coagulation (D‐dimer) in healthy younger‐aged adults. Participants were 83 women and 92 men (mean age 30.04 years, s.d. ± 4.8, range 22–39) of normal weight to moderate obese weight (mean BMI 24.4 kg/m2, s.d. ± 3.35, range 17–32). The primary data analytical approaches included Pearson correlation and multiple linear regression. Circulating levels of CRP, IL‐6, sICAM‐1, and D‐dimer were determined in plasma. Higher levels of CRP were independently associated with higher BMI, a greater waist‐to‐hip ratio, female gender, and higher triglycerides (P < 0.001). Higher IL‐6 levels were independently associated with a greater waist‐to‐hip ratio (P < 0.01). Higher levels of sICAM‐1 were independently associated with higher BMI, higher triglycerides, and lower insulin resistance (P < 0.001). Higher D‐dimer levels were independently associated with higher BMI and being female (P < 0.001). Having a higher BMI was most consistently associated with elevated biomarkers of inflammation, adhesion, and coagulation in this sample of healthy younger‐aged adults, although female gender, insulin resistance, and lipid levels were also related to the biomarkers. The findings provide insight into the adverse cardiovascular risk associated with elevated body weight in younger adults.
Enhanced backscattering by multiple nanocylinders illuminated by TE plane wave
Authors: She Hao-Yuan , Li Le-Wei , Chua Soo Jin , Ewe Wei-Bin , Martin Olivier J. F. , Mosig Juan R.
Published: September 2008

In this paper, we study the multiple scattering by electrically small (the radius of the cylinder is much smaller than the wavelength) plasmonic nanocylinders near surface plasmon resonance. The cylinders are assumed to be identical in dimension and composition. The incident plane wave is assumed to be TE polarized so that the plasmon resonance of two-dimensional cylindrical structures (for both individual and group of cylinders) can be excited. It is found that multiple plasmonic cylinders enhance the near-field magnetic field intensity due to mutual coupling. When the electrical dimension q of the cylinders (q=k0R, where k0 is the wave number of the free space and R is the radius of the cylinder) is fixed, the magnitude of the field distribution primarily depends on the positions of the cylinders at normal incidence.
Coherent control of molecular alignment of homonuclear diatomic molecules by analytically designed laser pulses
Authors: Zou Shiyang , Sanz Cristina , Balint-Kurti Gabriel G.
Published: September 2008

We present an analytic scheme for designing laser pulses to manipulate the field-free molecular alignment of a homonuclear diatomic molecule. The scheme is based on the use of a generalized pulse-area theorem and makes use of pulses constructed around two-photon resonant frequencies. In the proposed scheme, the populations and relative phases of the rovibrational states of the molecule are independently controlled utilizing changes in the laser intensity and in the carrier-envelope phase difference, respectively. This allows us to create the correct coherent superposition of rovibrational states needed to achieve optimal molecular alignment. The validity and efficiency of the scheme are demonstrated by explicit application to the H2 molecule. The analytically designed laser pulses are tested by exact numerical solutions of the time-dependent Schrödinger equation including laser-molecule interactions to all orders of the field strength. The design of a sequence of pulses to further enhance molecular alignment is also discussed and tested. It is found that the rotating wave approximation used in the analytic design of the laser pulses leads to small errors in the prediction of the relative phase of the rotational states. It is further shown how these errors may be easily corrected.
Reaction mechanism of the direct gas phase synthesis of H2O2 catalyzed by Au3
Authors: Njegic Bosiljka , Gordon Mark S.
Published: September 2008

The gas phase reaction of molecular oxygen and hydrogen catalyzed by a Au3 cluster to yield H2O2 was investigated theoretically using second order Z-averaged perturbation theory, with the final energies obtained with the fully size extensive completely renormalized CR-CC(2,3) coupled cluster theory. The proposed reaction mechanism is initiated by adsorption and activation of O2 on the Au3 cluster. Molecular hydrogen then binds to the Au3O2 global minimum without an energy barrier. The reaction between the activated oxygen and hydrogen molecules proceeds through formation of hydroperoxide (HO2) and a hydrogen atom, which subsequently react to form the product hydrogen peroxide. All reactants, intermediates, and product remain bound to the gold cluster throughout the course of the reaction. The steps in the proposed reaction mechanism have low activation energy barriers below 15kcal∕mol. The overall reaction is highly exothermic by ∼30kcal∕mol.
Electrical, structural, and chemical properties of HfO2 films formed by electron beam evaporation
Authors: Cherkaoui K. , Monaghan S. , Negara M. A. , Modreanu M. , Hurley P. K. , O’Connell D. , McDonnell S. , Hughes G. , Wright S. , Barklie R. C. , Bailey P. , Noakes T. C. Q.
Published: September 2008

High dielectric constant hafnium oxide films were formed by electron beam (e-beam) evaporation on HF last terminated silicon (100) wafers. We report on the influence of low energy argon plasma (∼70 eV) and oxygen flow rate on the electrical, chemical, and structural properties of metal-insulator-silicon structures incorporating these e-beam deposited HfO2 films. The use of the film-densifying low energy argon plasma during the deposition results in an increase in the equivalent oxide thickness (EOT) values. We employ high resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and medium energy ion scattering experiments to investigate and understand the mechanisms leading to the EOT increase. We demonstrate very good agreement between the interfacial silicon oxide thicknesses derived independently from XPS and HRTEM measurements. We find that the e-beam evaporation technique enabled us to control the SiOx interfacial layer thickness down to ∼6 Å. Very low leakage current density (<10−4 A/cm2) is measured at flatband voltage +1 V into accumulation for an estimated EOT of 10.9±0.1 Å. Based on a combined HRTEM and capacitance-voltage (CV) analysis, employing a quantum-mechanical CV fitting procedure, we determine the dielectric constant (k) of HfO2 films, and associated interfacial SiOx layers, formed under various processing conditions. The k values are found to be 21.2 for HfO2 and 6.3 for the thinnest (∼6 Å) SiOx interfacial layer. The cross-wafer variations in the physical and electrical properties of the HfO2 films are presented.
The relationship between ionic structure and viscosity in room-temperature ionic liquids
Authors: Li Hualin , Ibrahim Murvat , Agberemi Ismail , Kobrak Mark N.
Published: September 2008

We investigate the relationship between ionic structure and viscosity in room-temperature ionic liquids. We build on an earlier theoretical work and derive an ionic property we call the charge lever moment (CLM) that provides insight on ionic liquid dynamics. We use electronic structure calculations to determine the CLM for ions in typical ionic liquids and demonstrate a correlation between this property and the experimental viscosities of ionic liquids. The relationship provides insight into the role of librational motion in ionic liquids in general, and the interpretation of Kerr effect experiments is discussed.
Roles of ion and electron dynamics in the onset of magnetic reconnection due to current sheet instabilities
Authors: Moritaka Toseo , Horiuchi Ritoku
Published: September 2008

Roles of ion and electron kinetic effects in the trigger mechanism of magnetic reconnection due to current sheet instabilities are investigated by means of (2+1∕2)D explicit particle simulation. The simulation is performed for the Harris equilibrium without guide fields in the plane perpendicular to the antiparallel magnetic fields. The instabilities excited in the vicinity of the neutral sheet are classified into two modes, i.e., one is a longer wavelength kink mode and the other is a shorter wavelength kink mode. The growth of the longer kink mode depends only on the ion mass, while the growth of the shorter one depends only on the electron mass. Before the growth of these kink modes, the lower hybrid drift instability leads to two types of plasma diffusion: diffusion at the periphery controlled by ions and diffusion in the vicinity of the neutral sheet controlled by electrons. The diffusion at the periphery affects the ion distribution function at the neutral sheet through the ion meandering motion, and the ion-ion kink mode is destabilized as the electron-independent longer kink mode. The generation of the reconnection electric field at the neutral sheet due to the longer wavelength kink mode is characterized only by the ion dynamics and can take place commonly in ion-scale current sheets observed in the magnetosphere and laboratories.
Photoluminescence properties of ZnO nanoneedles grown by metal organic chemical vapor deposition
Authors: Lin Shisheng , Ye Zhizhen , He Haiping , Zhao Binghui , Zhu Liping , Huang Jingyun
Published: September 2008

The authors report on growth of ZnO nanoneedles (NNs) by metal organic chemical vapor deposition (MOCVD). Photoluminescence spectra of the NNs at 20 K are dominated by a surface excitonic (SX) emission at 3.367 eV. Temperature-dependent PL reveals the activation energies for the quenching of SX (∼11.2 meV) and donor bound excition (∼21 meV) are close to their localization energies. From 20 K to room temperature, no obvious green emission is observed. These characteristics demonstrate that the surface of NNs grown by MOCVD are not necessarily subjected to nonradiative or deep-level defects on the surface of ZnO nanorods grown by vapor transport method. Furthermore, using three different expressions, we fit the data of temperature dependent A free exciton energy (FXA) transition energy and the results are described and compared. The Debye and Einstein temperatures are found to be 660 and 238 K, respectively. The dependence of the full width at half maximum of the FXA peak as a function of temperature is investigated. The broadening of FXA band is mainly attributed to the scattering by the acoustic phonons in the NNs.
Monolithic Mach–Zehnder-type quantum cascade laser
Authors: Hoffmann L. K. , Austerer M. , Mujagić E. , Andrews A. M. , Klang P. , Schrenk W. , Strasser G.
Published: September 2008

A midinfrared quantum cascade laser with Mach–Zehnder cavity and split contacts is investigated with respect to interference effects. By increasing the temperature in one of the two coupled active waveguides, the value of the effective refractive index is varied and the modal phase is shifted. As a result, destructive interference is observed within the resonator, which manifests itself in a minimum of the modulated output power. The dissipated heat is controlled by locally adding a continuous current to the drive current pulses. In the first step, thermal properties, threshold values, and far fields are analyzed and compared to a Fabry–Pérot resonator to gain insight into the physical principles of the monolithic interferometer. Based on these findings, the temperature distribution is calculated in a two-dimensional heat transfer simulation, which leads to a match between the thermal change of the effective refractive index and the condition for destructive interference; a phase shift of π between the two interfering beams is confirmed. By modulating the effective refractive index using evanescent fields instead of temperature variations, a monolithic midinfrared interferometric sensing device becomes feasible.
Oxygen adsorption-induced nanostructures and island formation on Cu{100}: Bridging the gap between the formation of surface confined oxygen chemisorption layer and oxide formation
Authors: Lahtonen K. , Hirsimäki M. , Lampimäki M. , Valden M.
Published: September 2008

Surface oxidation of Cu(100) has been investigated by variable temperature scanning tunneling microscopy and quantitative x-ray photoelectron spectroscopy as a function of O2 pressure (8.0×10−7 and 3.7×10−2mbar) at 373K. Three distinct phases in the initial oxidation of Cu(100) have been observed: (1) the formation of the mixed oxygen chemisorption layer consisting of Cu(100)-c(2×2)-O and Cu(100)-(22×2)R45°-O domains, (2) the growth of well-ordered (22×2)R45°-O islands, and (3) the onset of subsurface oxide formation leading to the growth of disordered Cu2O. We demonstrate that the (22×2)R45°-O reconstruction is relatively inert in the low pressure regime. The nucleation and growth of well-ordered two-dimensional Cu–O islands between two (22×2)R45°-O domains is revealed by time-resolved scanning tunneling microscopy experiments up to 0.5 ML of oxygen. The formation of these islands and their nanostructure appear to be critical to the onset of further migration of oxygen atoms deeper into copper and subsequent Cu2O formation in the high pressure regime. The reactivity of each phase is correlated with the surface morphology and the role of the various island structures in the oxide growth is discussed.
Phase induced current in presence of nonequilibrium bath: A quantum approach
Authors: Bhattacharya Satyabrata , Chaudhury Pinaki , Chattopadhyay Sudip , Chaudhuri Jyotipratim Ray
Published: September 2008

Based on a system-reservoir nonlinear coupling model, where the associated bath is externally driven by a fluctuating force, we present a microscopic approach to quantum state-dependent diffusion and multiplicative noises in terms of a quantum (Markovian) Langevin equation in overdamped limit when the associated bath is in nonequilibrium state. We then explore the possibility of observing a quantum current when the bath is modulated by white noise, the phenomena which is absent in the classical regime.
Theory of simple biochemical “shape recognition” via diffusion from activator coated nanoshapes
Authors: Daniels D. R.
Published: September 2008

Inspired by recent experiments, we model the shape sensitivity, via a typical threshold initiation response, of an underlying complex biochemical reaction network to activator coated nanoshapes. Our theory re-emphasizes that shape effects can be vitally important for the onset of functional behavior in nanopatches and nanoparticles. For certain critical or particular shapes, activator coated nanoshapes do not evoke a threshold response in a complex biochemical network setting, while for different critical or specific shapes, the threshold response is rapidly achieved. The model thus provides a general theoretical understanding for how activator coated nanoshapes can enable a chemical system to perform simple “shape recognition,” with an associated “all or nothing” response. The novel and interesting cases of the chemical response due to a nanoshape that shrinks with time is additionally considered, as well as activator coated nanospheres. Possible important applications of this work include the initiation of blood clotting by nanoshapes, nanoshape effects in nanocatalysis, physiological toxicity to nanoparticles, as well as nanoshapes in nanomedicine, drug delivery, and T cell immunological response. The aim of the theory presented here is that it inspires further experimentation on simple biochemical shape recognition via diffusion from activator coated nanoshapes.
Plasmonic absorption in textured silver back reflectors of thin film solar cells
Authors: Haug F.-J. , Söderström T. , Cubero O. , Terrazzoni-Daudrix V. , Ballif C.
Published: September 2008

We study the influence of different textures and dielectric environments on the excitation of surface plasmon resonances on silver because textured metallic films often serve as back contacts of silicon thin film solar cells. For coupling between light and the surface plasmon excitation we use a periodic sinusoidal structure that enables us to sample the dispersion relation at well defined conditions with a simple spectral reflection measurement. We use three layer samples of amorphous silicon/ZnO/silver to mimic the behavior of the back contact in a thin film silicon solar cell; the measurements suggest that losses due to plasmon excitation can very well extend in the spectral region where optimum reflectance is desired. An appropriate thickness of ZnO is able to reduce absorption losses. Our findings on periodic structures are also found useful to explain the behavior of surface plasmon excitation on randomly textured ZnO/Ag reflector layers.
Simulation on binding efficiency of immunoassay for a biosensor with applying electrothermal effect
Authors: Huang Kuan-Rong , Chang Jeng-Shian , Chao Sheng D. , Wu Kuang-Chong , Yang Chih-Kai , Lai Cheng-Yu , Chen Shyh-Haur
Published: September 2008

The working principle of immunoassays is based on the specific binding reaction of an analyte-ligand protein pair in physiological environments. However, for a diffusion-limited protein, the diffusion boundary layer of the analyte on the reaction surface of a biosensor would hinder the binding reaction from association and dissociation. The formation of such association and dissociation layers thus limits the response time and the overall performance of a biosensor. In this work we have performed a two-dimensional full time scale finite element simulation on the binding reaction kinetics of two commonly used proteins, C-reactive protein (CRP) and immunoglobulin G (IgG). By applying a nonuniform ac electric field to the flow microchannel of the biosensor, the electrothermal force can be generated to induce a pair of vortices to stir the flow field. With the aid of the vortices and a suitable choice of the location of the biosensor, the fluids flowing over the reacting surface can be accelerated fast enough to depress efficiently the growth of the diffusion boundary layer on the reaction surface, and enhance the association or dissociation of analyte-ligand complex. The interference patterns of the flow field due to the existence of the sensor at different locations of the microchannel could cause different degrees of enhancement to the association and the dissociation. By changing the location of the sensor the largest enhancement is found at the position near the negative electrode. For the configuration of the microchannel we studied, the initial slope of the curve of the analyte-ligand complex versus time can be raised up to 5.17 for CRP and 1.93 for IgG in association, and 3.74 for CRP and 1.28 for IgG in dissociation, respectively, under the applied ac field 15 Vrms peak-to-peak and operating frequency 100 kHz. At this optimal sensor location, we also studied the effect of various settings of temperature boundary conditions on the top and bottom walls, including the two limiting cases, namely, constant temperature and thermal insulation on both walls. We show that varying the temperature boundary conditions can cause an essential effect on the enhancement of the binding reaction and can be employed to find an optimal binding enhancement. Utilizing these simulation results, an improved design incorporating a pair of electrodes and a neck region near the reaction surface is demonstrated. The sensor is fixed to locate at the middle of the bottom side. With the existence of the stirring flow field, the association rate of the 30 μm neck is 2.73 times faster than that of the original channel with no neck.
Variation of the enhancement mechanism in the critical current density of Cu-doped MgB2 samples sintered at different temperatures
Authors: Ma Zongqing , Liu Yongchang , Han Yajing , Zhao Qian , Gao Zhiming
Published: September 2008

MgB 2 samples with 3 at. % Cu addition were synthesized by means of in situ sintering at different temperatures (525, 575, and 850 °C). Based on thermal analysis, phase identification, and microstructural observation, it is first found that the Cu addition mainly concentrates at the edge of the void in the form of Mg2Cu and thus does not degrade the grain coupling of MgB2 phase in the low-temperature sintered sample. As sintering temperature rises to 850 °C, the MgB2 grains grow larger and some Cu addition may form MgCu2 nanoinclusions distributing in the MgB2 grains through the reaction, 2Mg2Cu(L)+6B=3MgB2+MgCu2. As a result, the mechanism of enhancement in the Jc of the Cu-doped MgB2 samples varies distinctly from the grain-boundary pinning to the possible MgCu2 nanoinclusions pinning as the sintering temperature increases from low temperature to high-temperature.
Numerical analysis of microelectrodes for cell electrokinetic applications
Authors: Martínez G. , Sanchis A. , Sancho M.
Published: September 2008

Manipulation of cells using nonuniform electric fields is an area of growing interest for biological and medical applications. The article presents a numerical analysis of fields and dielectrophoretic forces in typical electrode configurations, overcoming some limitations of previous approaches. An accurate version of the boundary element method is employed to compute the field distributions very precisely. Parallel bar, sawtooth, and castellated electrode shapes are analyzed. The effect of a dielectric coating is discussed.
Numerical solution of the nonlinear Poisson equation for semiconductor devices by application of a diffusion-equation finite difference scheme
Authors: Jóźwikowska Alina
Published: September 2008

An effective iterative finite difference method for solving a nonlinear Poisson equation for semiconductor device theory is presented. The nonlinear Poisson equation is replaced by an equivalent diffusion equation. As a result, a stable and fully controlled iterative method was found to solve this equation, regardless of the level of heterostructure complexity and the type of electrical contacts, passivating dielectric layers or environment. Selected numerical results obtained using this method for a gated HgCdTe photodiode with metal contacts are reported.
Competing magnetic interactions in nickel ferrite nanoparticle clusters: Role of magnetic interactions
Authors: Malik Rakesh , Annapoorni S. , Lamba Subhalakshmi , Sharma Parmanand , Inoue Akihisa
Published: September 2008

The magnetic behavior of nickel ferrite nanoparticles of different sizes was studied by annealing nickel ferrite powders at temperatures ranging from 300 to 900 °C. Transmission electron microscopy studies show that the average particle sizes change from ∼8 to ∼120 nm with increasing annealing temperatures. The x-ray diffraction patterns of the annealed samples reveal that a single phase is retained. Hysteresis measurements performed up to a field of 10 kOe show a tendency toward saturation. The saturation magnetization is found to increase with annealing temperature (particle size) with the magnetization tending toward the bulk value for powders annealed at 900 °C. Zero field cooled–field cooled measurements performed at 0.5 kOe indicate the presence of a superparamagnetic phase up to an annealing temperature of 700 °C with blocking temperatures in the range of 150–330 K. Numerical simulations are carried out using an interacting model of an array of single domain magnetic particles to explain the change in the magnetic behavior of the samples with annealing temperature and to estimate the anisotropy of the system. Our studies indicate that the observed magnetic behavior can be explained by the changes in the anisotropy of the system and the dominance of the short range interparticle exchange interactions over the long range dipolar interactions with increasing particle sizes. This change in the interaction profile is further confirmed by the Henkel plots for the particles annealed at different temperatures.
Polarization of a permanent magnet to yield specific magnetic field distribution
Authors: Kim Woochul , Kim Mintae , Kim Yoon Young
Published: September 2008

The objective of this research is to develop a method of finding the polarization distribution of a permanent magnet to produce a desired magnetic field on a target plane located at some distance away from the magnet. Even if the distance between a magnet and the plane is small, magnetic flux fringe effects make it difficult to configure the exact magnet polarization. To solve the problem of magnetic polarization distribution, an iterative numerical topology optimization is formulated. As specific applications, the permanent magnet polarization in the actuators of some optical disk drives is considered. The physics related to the magnetic field obtained by the identified polarization is also examined.
Scanning tunneling microscopy study of nitrogen incorporated HfO2
Authors: Ong Y. C. , Ang D. S. , O’Shea S. J. , Pey K. L. , Wang S. J. , Tung C. H. , Li X.
Published: September 2008

The impact of nitrogen incorporation on the physical and electrical characteristics of the HfO2 is examined. X-ray photoelectron spectroscopy shows that nitrogen can be incorporated into the HfO2 via a two-step thermal anneal—first in ultrahigh vacuum (UHV) and subsequently in N2. Following the N2 anneal, scanning tunneling microscopy in UHV reveals a marked reduction in the low-voltage leakage current under gate injection biasing. From band theory and existing first-principles simulation results, one may consistently attribute this improvement to the passivation of oxygen vacancies in the HfO2 by nitrogen. Improvement in the breakdown strength of the HfO2 subjected to ramp-voltage stress (substrate injection) is also observed after the N2 anneal. The local current-voltage curves acquired concurrently during the ramp-voltage stress exhibit “space-charge limited conduction,” which implies that the observed improvement in breakdown strength may be related to a limitation of the current flow through the gate stack in the high stress voltage regime.
Effects of internal structure on equilibrium of field-reversed configuration plasma sustained by rotating magnetic field
Authors: Yambe Kiyoyuki , Inomoto Michiaki , Okada Shigefumi , Kobayashi Yuka , Asai Tomohiko
Published: September 2008

The effects of an internal structure on the equilibrium of a field-reversed configuration (FRC) plasma sustained by rotating magnetic field is investigated by using detailed electrostatic probe measurements in the FRC Injection Experiment apparatus [S. Okada, et al., Nucl. Fusion. 45, 1094 (2005)]. An internal structure installed axially on the geometrical axis, which simulates Ohmic transformer or external toroidal field coils on the FRC device, brings about substantial changes in plasma density profile. The internal structure generates steep density-gradients not only on the inner side but on the outer side of the torus. The radial electric field is observed to sustain the ion thermal pressure-gradient in the FRC without the internal structure; however, the radial electric field is not sufficient to sustain the increased ion thermal pressure-gradient in the FRC with the internal structure. Spontaneously driven azimuthal ion flow will be accountable for the imbalance of the radial pressure which is modified by the internal structure.
The influence of gravity on the steady propagation of a semi-infinite bubble into a flexible channel
Authors: Hazel Andrew L. , Heil Matthias
Published: September 2008

Motivated by discrepancies between recent bench-top experiments [A. Juel and A. Heap, J. Fluid Mech. 572, 287 (2007)] and numerical simulations [A. L. Hazel and M. Heil, ASME J. Biomech. Eng. 128, 573 (2006)] we employ computational methods to examine the effects of transverse gravity on the steady propagation of a semi-infinite, inviscid air finger into a two-dimensional elastic channel filled with a Newtonian fluid. The special case of propagation in a rigid channel is also discussed in Appendix B. The coupled free-surface, fluid-structure-interaction problem is solved numerically using the object-oriented multiphysics finite-element library OOMPH-LIB. In the absence of gravity the relationship between the applied pressure and the propagation speed of the finger is nonmonotonic, with a turning point at small values of the propagation speed. We demonstrate that the turning point disappears when a modest gravitational force is applied and conjecture that it is this effect of gravity rather than any instability of the zero-gravity solution, as postulated in previous studies, that explains why the turning point has never been observed in experiments. At large propagation speeds, the presence of transverse gravity is shown to increase the pressure required to drive the air finger at a given speed, which is consistent with the observed discrepancies between previous zero-gravity simulations and the experimental results. Finally, we briefly discuss the possible implications of our results for the physiological problem of pulmonary airway reopening.
Probing of nonlinear evolution of laser wakefield by Raman scattering of laser light
Authors: Zhou Weimin , Mima Kunioki , Nakamura Tatsufumi , Nagatomo Hideo
Published: September 2008

When a weak probe laser pulse is injected into a wakefield excited by a short high-intensity pump laser pulse, the probe pulse will be Raman scattered by the wakefield. It is possible to determine the density profile from the spectrum of this forward Raman scattered probe laser [R. E. Slusher and C. M. Surko, Phys. Fluids 23, 472 (1980)]. In this paper, an analytical solution for the multiple sidebands of the forward Raman scattering of the probe laser pulse is presented. These multiple sidebands are connected with the steepening of density perturbation of the wakefield. More detailed information of the laser wakefield can be obtained from these multiple sidebands. The propagation of the probe pulse in wakefields is studied with one-dimensional particle-in-cell (PIC) simulations. The analytical solution and the results of PIC simulations are consistent with each other and other experiments.
Veering the motion of a magnetic chemical locomotive in a liquid
Authors: Dey Krishna Kanti , Sharma Deepika , Basu Saurabh , Chattopadhyay Arun
Published: September 2008

The motion of micron-sized catalytic polymer beads coated with thin film or nanoparticle form of Ni in aqueous H2O2 is reported herein. In the absence of any magnetic field, the beads moved vertically upward in the medium, owing to sufficient bubbles deposited on them following catalytic decomposition of H2O2 by Ni. However, in the presence of an external magnetic field (perpendicular to the direction of motion), angular deviation in the motion is observed, with the deviations increasing with the strength of the field. The results are explained based on a model involving interaction of the beads with the external magnetic field.