bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro fertilization in inbred BALB/c mice I: isotonic osmolarity and increased calcium-enhanced sperm penetration through the zona pellucida and male pronuclear formation
Authors: Kito Seiji , Ohta Yuki
Published: June 2008

To optimize IVF conditions for BALB/c mice, which are known to have poor in vitro fertilizability, the requirements for sperm–ova interaction were studied by use of modified simplex optimization medium (mKSOM) as a basic medium. Modified human tubal fluid (mHTF) was used for sperm preincubation and acted as a positive control. When the two media were compared, neither capacitation nor fertilization was supported in mKSOM. Increasing the calcium concentration in mKSOM to 5 mM or more during sperm: ova coincubation improved zona penetration but not male pronuclear (MPN) formation to the same level as those cells incubated in mHTF. When medium osmolarity was varied from 230–305 mOsmol by NaCl at 5 mM CaCl2, MPN formation improved at 280 mOsmol or higher osmolarity to the same level as that found when using mHTF. When NaCl equivalent to 25–75 mOsmol was substituted with trehalose, no significant reduction in fertilization was observed. Substitution of NaCl equivalent to 75 mOsmol with other osmotic reagents (sucrose, choline chloride and sorbitol) resulted in similar levels of fertilization as found with mHTF, except for sorbitol, which reduced fertilization significantly caused by its detrimental effect on sperm viability. At isotonic osmolarity (305 mOsmol), maximum fertilization was observed at 5 mM CaCl2; lower or higher concentrations of CaCl2 resulted in reduced fertilization. Calcium and osmolarity, therefore, are important for sperm : ova interaction in BALB/c mice and the increases in calcium to 5 mM and osmolarity to 305 mOsmol are optimal for BALB/c sperm to penetrate through the zona and to form MPN.
Effect of volume of oocyte cytoplasm on embryo development after parthenogenetic activation, intracytoplasmic sperm injection, or somatic cell nuclear transfer
Authors: Sayaka Wakayama , Satoshi Kishigami , Van Thuan Nguyen , Hiroshi Ohta , Takafusa Hikichi , Eiji Mizutani , Thuy Bui Hong , Masashi Miyake , Teruhiko Wakayama
Published: June 2008

Animal cloning methods are now well described and are becoming routine. Yet, the frequency at which live cloned offspring are produced remains below 5%, irrespective of the nuclear donor species or cell type. One possible explanation is that the reprogramming factor(s) of each oocyte is insufficient or not properly adapted for the receipt of a somatic cell nucleus, because it is naturally prepared only for the receipt of a gamete. Here, we have increased the oocyte volume by oocyte fusion and examined its subsequent development. We constructed oocytes with volumes two to nine times greater than the normal volume by the electrofusion or mechanical fusion of intact and enucleated oocytes. We examined their in vitro and in vivo developmental potential after parthenogenetic activation, intracytoplasmic sperm injection (ICSI) and somatic cell nuclear transfer (SCNT). When the fused oocytes were activated parthenogenetically, most developed to morulae or blastocysts, regardless of their original size. Diploid fused oocytes were fertilized by ICSI and developed normally and after embryo transfer, we obtained 12 (4–15%) healthy and fertile offspring. However, enucleated fused oocytes could not support the development of mice cloned by SCNT. These results suggest that double fused oocytes have normal potential for development after fertilization, but oocytes with extra cytoplasm do not have enhanced reprogramming potential.
Presence and distribution of E-cadherin in the 4-cell golden hamster embryo. Effect of maternal age and parity
Authors: Trejo A. , Ambriz D. , Navarro-Maldonado M. C. , Mercado E. , Rosado A.
Published: June 2008

Maternal age dependency of gestation time in hamster and in other mammals is a well demonstrated fact. We have recently shown that adult nulliparous and multiparous hamster females show significant asynchrony and retard on early embryo development (from two blastomeres to morula stages) when compared with nulliparous young females. The number of cell–cell adhesions between blastomeres in early embryo development has been reported to be a good indication of the ability of embryos to cleave and develop. In this work we studied, by indirect immunofluorescence, the presence and distribution of E-cadherin in 4-cell embryos obtained from nulliparous young (NYF), nulliparous adult (NAF) and multiparous adult (MAF) hamster females. Distribution and intensity of fluorescence was observed and registered using confocal microscopy. Staining intensities for E-cadherin were quantified by computed densitometry in the free membrane regions, in the cytoplasm region and in the cell–cell adhesion zones of each embryo. E-Cadherin in all the studied zones was significantly higher (p< 0.01) in NYF. Cadherin concentration in the intercellular membranes was always statistically higher (p< 0.05) than in the free membrane regions. An appreciable concentration of E-cadherin was found in the cytoplasm of the 4-cell embryos obtained from the three groups of females, but was significantly higher in NYF. No statistical differences were observed in any of the parameters studied between NAF and MAF. Our results seem to indicate that changes in the reproductive behavior related to age and/or multiparity may be correlated with changes in the processes related to intercellular adhesions during early cleavage.
Early oocyte penetration can predict the efficiency of bovine embryo production in vitro
Authors: Machatkova M. , Horakova J. , Hulinska P. , Reckova Z. , Hanzalova K.
Published: June 2008

The aim of this work was to characterize oocyte fertilization and embryo cleavage in nine AI bulls to find parameters suitable for prediction of in vitro fertility. According to the d8 blastocysts rate, they were categorized as high, medium and low productive (HP, MP and LP, mean: 25.4, 21.0 and 13.6% respectively) bulls. For these categories, oocyte penetration and fertilization efficiency were assessed at 6 and 18 hours post insemination (hpi), respectively. Some presumptive zygotes were cultured and cleaved and fast-cleaved embryo rates were checked at 44 hpi. The penetration rate was significantly higher for HP bulls than for MP and LP bulls (67.9 versus 50.3 and 33.1%; p < 0.01). The syngamy rate was significantly higher for HP bulls than for MP and LP bulls (21.4 versus 10.2 and 5.7%; p < 0.05). Conversely, no significant differences in fertilization rates were found among HP, MP and LP bulls. The cleavage rate was significantly higher for HP than LP bulls (82.4 versus 74.4%; p < 0.01). The fast cleavage rate was significantly higher for both HP and MP bulls, as compared with LP bulls (82.1 and 84.7 versus 73.5%; p < 0.01). A strong correlation was found between blastocyst production and penetration (r = 0.803), syngamy (r = 0.826), cleavage (r = 0.635) and fast cleavage (r = 0.709). In conclusion, all the evaluated parameters showed a predictive value, the most significant being early penetration and syngamy.
THE NEW LATIN NATION
Authors: Portes Alejandro
Published: June 2008

This article presents an overview of the Hispanic population of the United States, focusing on the sources of its growth, its internal composition, its connections with the countries of origin, its role in the U.S. economy, and the emerging second generation. Intergenerational differences in outlooks and self-identities and the forces leading to the emergence of a “thick” Hispanic identity in the second generation are examined. The obstacles to successful integration faced by this youthful population and evidence of both “upward” and “downward” assimilation among its members are analyzed. Implications for the field of race and ethnic relations and for public policy toward immigrants and their offspring are discussed.
MEXICAN ASSIMILATION
Authors: Jiménez Tomás R. , Fitzgerald David
Published: June 2008

One of the principal theoretical and policy questions in the sociology of international migration is the extent to which post-1965 immigrants are either assimilating in the United States or remain stuck in an ethnic “underclass.” This paper aims to recast conventional approaches to assimilation through a temporal and spatial reorientation, with special attention to the Mexican-origin case. Attending to the effects of the replenishment of the Mexican-origin population through a constant stream of new immigrants shows significant assimilation taking place temporally between a given immigrant cohort and subsequent generations. Thinking outside the national box, through comparing the growing differences between Mexican migrants and their descendants, on the one hand, and Mexicans who stay in Mexico, on the other, reveals, spatially, a dramatic upward mobility and a process of “homeland dissimilation” that conventional accounts miss. We demonstrate the analytic utility of these two perspectives through an empirical comparison with more orthodox approaches to educational stratification.
FROM COOLIE TO MODEL MINORITY
Authors: Junn Jane
Published: June 2008

I examine how and why the social construction of Asian Americans has changed from coolie to model minority over the last century. I examine the role of the U.S. government in creating policies that systematically select particular types of entrants to the United States. Federal immigration policy privileges high-skilled workers, and a disproportionately large number of Asian immigrants are granted the status of lawful permanent resident by the federal government on the basis of employment preferences. U.S. immigration policy thus creates a selection bias, favoring Asian immigrants with high levels of formal education and social standing. I also consider the consequences of this selection bias for the construction of racial tropes and Asian American identity, and argue that the normative content of the dominant tropes of racial identity is critical in establishing the incentives and costs of identifying with racial and ethnic groups. Immigration policy, and the selection biases it may engender, is an important factor in how those tropes are constructed and experienced. Racial identity should, and does, vary as a function of the unique histories of migration, labor market demands, and shared experiences for people classified by race.
ARE MEXICANS IN THE UNITED STATES A THREAT TO THE AMERICAN WAY OF LIFE?
Authors: Saenz Rogelio , Filoteo Janie , Murga Aurelia Lorena
Published: June 2008

The Latino population has grown significantly over the last few decades in the United States and population projections suggest that the number of Latinos will increase disproportionately, relative to other immigrant groups, in the coming decades. These trends have resulted in great concern among some who fear that Latinos, especially Mexicans, are not acculturating and assimilating into mainstream, White America. Fears of the “browning of America” and of Latinos' presumed threat to the American way of life have led some to call for measures to ensure the preservation of America's national identity. Samuel Huntington is the latest public figure to make such claims. This paper provides an overview of Huntington's claims as well as the responses that his work has drawn from supporters and critics. Using data from the 2000 5% Public Use Microdata Sample, we assess the validity of Huntington's claims by examining the extent to which Mexicans, the largest Latino subgroup, have integrated into the United States, basing our assessment on a variety of selected demographic, social, and economic indicators. The results suggest that Mexicans have integrated in various dimensions, with the level of integration increasing with length of residence in the United States. We conclude with a discussion of the historical and contemporary context in which Mexicans have been racialized in the United States.
IMMIGRANTS, IMMIGRATION, BROADER CONTEXTS, AND PUBLIC POLICY DISCONNECTS
Authors: García John A.
Published: June 2008

This essay attempts to broaden the context of public and policy discourses about the nature and complexities associated with migration to the United States. Several dimensions are examined: (1) global and U.S. migration trends; (2) the effects of migration on both the communities of origin and destination; (3) issues related to the rights and standing of migrants; (4) the gendered dimensions related to migration; (5) patterns of migrants' integration into their host society; (6) the impact of human-capital investment and its consequences; and (7) the limitations of the current policy discussions and initiatives. In the case of the latter, the need to move away from polarizing and simplistic perspectives and to integrate the many socioeconomic and political complexities associated with international migration is discussed. A more comprehensive understanding of migration recognizes that it is not exclusively the result of individual behaviors and motivations. Structural relationships, both domestically and internationally, as well as public policies have also had an effect on migration flows and patterns.
Asparagus, a Love Story
Authors: Laney Cara , Morris Erin K. , Bernstein Daniel M. , Wakefield Briana M. , Loftus Elizabeth F.
Published: June 2008

In two experiments, involving 231 subjects, we planted the suggestion that subjects loved to eat asparagus as children. Relative to controls, subjects receiving the suggestion became more confident that they had loved asparagus the first time they tried it. These new (false) beliefs had consequences for those who formed them, including increased general liking of asparagus, greater desire to eat asparagus in a restaurant setting, and a willingness to pay more for asparagus in the grocery store. Ratings of photographs made after the suggestion reveal that the altered nutritional choices may relate to the fact that the sight of asparagus simply looks more appetizing and appealing. These results demonstrate that adults can be led to believe that they had a positive food-related experience as children, and that these false beliefs can have healthy consequences.
A Comparison of Bilateral Versus Unilateral Target and Distractor Presentation in the Remote Distractor Paradigm
Authors: Benson Valerie
Published: June 2008

The remote distractor effect (RDE) is a robust finding of an increase in saccade onset latencies (20–40 ms) when a distractor is presented simultaneously with a target, compared to when a target is presented on its own ( Walker, Deubel, Schneider, & Findlay, 1997 ). Distractors presented at fixation produce the largest RDE and the effect decreases as distractors are moved into the periphery. Data from two experiments that contrast with these standard findings are reported. Under bilateral target presentation, larger RDE magnitudes occurred for peripheral than for central distractors, whereas under unilateral presentation, the pattern reversed. The findings are discussed with reference to discrimination processes, attentional factors and current models of oculomotor control. It is suggested that in bilateral target presentation the competition between the distractor and the target results in the programming of a saccade to the distractor, as well as a saccade to the target. Time taken to cancel the saccade to the distractor produces the increased saccade latency for peripheral distractors in that condition.
Occurrence of reconnection jets at the dayside magnetopause: Double Star observations
Authors: Trenchi L. , Marcucci M. F. , Pallocchia G. , Consolini G. , Bavassano Cattaneo M. B. , Di Lellis A. M. , Rème H. , Kistler L. , Carr C. M. , Cao J. B.
Published: June 2008

We present a statistical study on reconnection occurrence at the dayside magnetopause performed using the Double Star TC1 plasma and magnetic field data. We examined the magnetopause crossings that occurred during the first year of the mission in the 0600–1800 LT interval and we identified plasma flows, at the magnetopause or in the boundary layer, with a different velocity with respect to the adjacent magnetosheath. We used the Walén relation to test which of these flows could be generated by magnetic reconnection. For some event we observed opposite‐directed reconnection jets, which could be associated with the passage of the X‐line near the satellite. We analyzed the occurrence of the reconnection jets and reconnection jet reversals in relation to the magnetosheath parameters, in particular the local Alfvèn Mach number, the plasma β, and the magnetic shear angle. We also studied the positions and velocities of the reconnection jets and jet reversals in relation to the magnetosheath magnetic field clock angle. We found that the observations indicate the presence of a reconnection line hinged near the subsolar point and tilted according to the observed magnetosheath clock angle, consistently with the component merging model.
Particle and field characteristics of broadband electrons observed by the FAST satellite during geomagnetic storms: A multievent study
Authors: Nakajima A. , Shiokawa K. , Seki K. , McFadden J. P. , Carlson C. W. , Strangeway R. J. , Yumoto K.
Published: June 2008

During geomagnetic storms, remarkable electron‐flux enhancements (>1012 eV cm−2 s−1) over a broadband energy range (∼0.05–10 keV) are sometimes observed near the equatorward edge of the auroral oval. We call such electron flux enhancements broadband electrons (BBEs). In this paper, we identified 12 BBE events from the electron‐energy spectra obtained by the Fast Auroral Snapshot (FAST) satellite during 81 large geomagnetic storms (minimum Dst index <−90 nT) between September 1996 and March 2004. Ground‐based magnetic field data show that the BBEs are observed ∼6–28 min after the onset of substorms during the main phase of large storms. During these events, the pitch angle distributions of electrons show isotropic features at a higher energy range above ∼1 keV, except for an upward loss cone. At a lower energy range below ∼1 keV, field‐aligned downward electron fluxes are most intense, and perpendicular fluxes are weakest. These results imply that a higher‐energy part of BBEs originates from higher altitudes in the inner magnetosphere and that a lower‐energy part is accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields and enhanced lower‐frequency (0.1 Hz to 16 kHz) waves are observed during the BBEs. These characteristics are common for all BBE events. We compared lower‐energy (<1 keV) electron fluxes with field‐aligned Poynting fluxes of the waves at 0.06–4 Hz during the BBEs. The Poynting fluxes are systematically downward with intensity comparable to that of the lower‐energy electron fluxes, suggesting downward acceleration of lower‐energy electrons by the observed low‐frequency waves.
Relation between the wind stress curl in the North Atlantic and the Atlantic inflow to the Nordic Seas
Authors: Sandø A. B. , Furevik T.
Published: June 2008

In this study an isopycnic coordinate ocean model has been used to investigate the relationships between the North Atlantic wind stress curl (WSC) and the inflow of Atlantic water to the Nordic Seas. For the period 1995–2001, there is a maximum in the correlation between the zonally averaged WSC at 55°N and the inflow with a 15‐month time lag, capturing a relation already found in observational data. In the model this relation is linked to the mixing along the western flank of the Rockall Bank (56°N, 15°W). For the period 1995–2001 the atmospheric forcing in the northeastern North Atlantic is relatively weak, and the depth of the mixed layer is shallower than the sill depths of the Greenland‐Scotland Ridge (GSR). Slowly moving, baroclinic disturbances caused by anomalies in the wind forcing will then be transmitted into the Nordic Seas where they are recorded as anomalous volume transports in the Norwegian Atlantic Current. In contrast, for the pentad prior to this period the atmospheric forcing is much more intense, and generates mixing well below sill depths of the GSR for all winters. Baroclinic disturbances forced by variations in the atmospheric forcing will then tend to follow f/H contours that do not enter the Nordic Seas, and the 15‐month lagged relations between the wind and the volume transports will vanish. Recent observational data support this view.
Chemically segregated optical and microphysical properties of ambient aerosols measured in a single‐particle mass spectrometer
Authors: Moffet Ryan C. , Qin Xueying , Rebotier Thomas , Furutani Hiroshi , Prather Kimberly A.
Published: June 2008

This paper describes results from the first direct measurements of the size‐resolved optical properties as a function of chemical mixing states for atmospheric particle types sampled in Mexico City and Riverside, California. The coupled size, chemistry, and optical measurements were used to derive refractive indices and effective densities for chemically distinct particle mixing states. On the basis of the measured dependence of scattering intensity as a function of relative humidity and size, the Riverside particles contained detectable amounts of liquid water, whereas the Mexico City particles were relatively dry. Aerosol particles in Mexico City were observed to exhibit a wide range of densities (1.1–3.4 g/cm3), suggesting a dynamic, externally mixed aerosol population. Daily variations were observed as the particles in Mexico City underwent photochemical aging processes leading to a diurnal variation in particle morphology. In contrast, the optical properties of the Riverside aerosol, sampled during the fall season, were strongly impacted by the condensation of water and ammonium nitrate during periods of intense pollution buildup, resulting in microphysical properties that were similar across mixing states for a specific relative humidity.
Incident spectral irradiance in the Arctic Basin during the summer and fall
Authors: Grenfell Thomas C. , Perovich Donald K.
Published: June 2008

Calibrated values of incident spectral irradiance are reported from the Healy Oden Transarctic Experiment during August and September 2005. Spectra were obtained for a wide range of solar zenith angles, cloud conditions, and surface types to provide basic data for regional shortwave radiative energy balance calculations as well as climate model parameterization and validation. Supervised principal component analysis on the spectral continuum showed that three principal components explain over 99% of the variance resulting from darkening across the solar spectrum with increasing cloud cover by volume scattering, from stronger attenuation in the solar infrared relative to visible wavelengths by H2O, and from Rayleigh scattering. Comparison of the observations with the atmospheric radiation model SBDART showed that good agreement was obtained varying only the cloud optical depth. Applying the model, we showed how the surface albedo affects incident spectral irradiance under clear as well as cloudy skies, and we obtained a quantitative estimate of the visual effects of “water sky” and “ice blink.” We also determined the spectral albedo of the atmosphere for a dense arctic stratus cloud deck decoupled from the influence of the underlying surface. Incident spectral irradiances were integrated numerically and compared with calibrated pyranometer observations. Agreement was within 5% for cases where the cloud transparency and incident irradiance did not fluctuate strongly over the 10‐min pyranometer recording intervals. A new set of values for total albedo for clear versus cloudy conditions at high and low Sun angles is presented for six prominent arctic surface types.
Laser‐probe 40Ar/39Ar dating of strain fringes: Mid‐Cretaceous synconvergent orogen‐parallel extension in the interior of the Sevier orogen
Authors: Wells Michael L. , Spell Terry L. , Hoisch Thomas D. , Arriola Tonia , Zanetti Kathleen A.
Published: June 2008

UV and CO2 laser‐probe 40Ar/39Ar in situ analyses of phlogopite and muscovite in fibrous strain fringes from greenschist‐facies metamorphic rocks document mica growth ages at temperatures lower than their closure temperatures, and therefore directly date deformation. The new dates resolve the age of the earliest ductile fabric recorded in the Raft River–Albion–Grouse Creek metamorphic core complex of Utah and Idaho. Phlogopite was dated in quartz‐calcite‐phlogopite strain fringes around pyrite in Pennsylvanian‐Permian rocks from the Grouse Creek Mountains (Utah) using both the UV and CO2 laser probe; muscovite was dated in quartz‐muscovite strain fringes around pyrite in deformed Jurassic sills from the Black Pine Mountains (Idaho) using the CO2 laser probe. Phlogopite 40Ar/39Ar ages for individual strain fringes (Grouse Creek Mountains) range from 92 Ma to 110 Ma, with the most reliable ages ranging from 101 Ma to 110 Ma (mean age, 105.0 ± 5.8 Ma). Muscovite 40Ar/39Ar ages for individual strain fringes (Black Pine Mountains) range from 97 Ma to 112 Ma (mean age, 104.7 ± 5.8 Ma). Strain fringes are associated with a subhorizontal foliation and a generally N‐trending elongation lineation exhibiting components of top‐to‐the‐north simple shear and coaxial strain accommodating N‐S extension and subvertical shortening. Midcrustal northward flow at 105 (±6) Ma within the interior of the Sevier orogen, coeval with east‐directed shortening in the foreland and with plate convergence, records orogen‐parallel synconvergent extension. We favor gravitational relaxation of structural culminations resulting from focused crustal shortening as a driving mechanism for orogen‐parallel flow.
Near‐surface soil moisture assimilation for quantifying effective soil hydraulic properties using genetic algorithm: 1. Conceptual modeling
Authors: Ines Amor V. M. , Mohanty Binayak P.
Published: June 2008

We used a genetic algorithm (GA) to identify soil water retention θ(h) and hydraulic conductivity K(h) functions by inverting a soil‐water‐atmosphere‐plant (SWAP) model using observed near‐surface soil moisture (0‐5 cm) as search criterion. Uncertainties of parameter estimates were estimated using multipopulations in GA and considering data and modeling errors. Three hydrologic cases were considered: (1) homogenous free‐draining soil column, (2) homogenous soil column with shallow water table, and (3) heterogeneous soil column under free‐drainage condition, considering three different rainfall patterns in northern Texas. Results (cases 1 and 2) showed the identifiability of soil hydraulic parameters improving at coarse and fine scales of the soil textural class. Medium‐textured soils posed identifiability problems when the soil is dry. Nonlinearity in θ(h) and K(h) is greater at drier conditions, and some parameters are less sensitive for estimation. Flow regimes controlled by upward fluxes were found less successful, as the information content of observed near‐surface data may no longer influence the hydrologic processes in the subsurface. The identifiability of soil hydraulic parameters was found better when the soil profile is predominantly draining. In case 3, top soil layer hydraulic properties were defined using near‐surface data alone as criterion. Adding evapotranspiration (ET) improved identification of the second soil layer, although not all parameters were identifiable. Under uncertainties, θ(h) was found to be well defined while K(h) is more uncertain. Finally, we applied the method to a validation site in Little Washita watershed, Oklahoma, where derived effective soil hydraulic properties closely matched the measured ones at the field site.
Genomic patterns of recombination, clonal divergence and environment in marine microbial populations
Authors: Konstantinidis Konstantinos T , DeLong Edward F
Published: June 2008

Microorganisms represent the largest reservoir of biodiversity on Earth, both in numbers and total genetic diversity, but it remains unclear whether this biodiversity is organized in discrete units that correspond to ecologically coherent species. To further explore this question, we examined patterns of genomic diversity in sympatric microbial populations. Analyses of a total of ∼200 Mb of microbial community genomic DNA sequence recovered from 4000 m depth in the Pacific Ocean revealed discrete sequence-defined populations of Bacteria and Archaea, with intrapopulation genomic sequence divergence ranging from ∼1% to ∼6%. The populations appeared to be maintained, at least in part, by intrapopulation genetic exchange (homologous recombination), although the frequency of recombination was estimated to be about three times lower than that observed previously in thermoacidophilic archaeal biofilm populations. Furthermore, the genotypes of a given population were clearly distinguishable from their closest co-occurring relatives based on their relative abundance in situ. The genetic distinctiveness and the matching sympatric abundances imply that these genotypes share similar ecophysiological properties, and therefore may represent fundamental units of microbial diversity in the deep sea. Comparisons to surface-dwelling relatives of the Sargasso Sea revealed that distinct sequence-based clusters were not always detectable, presumably due to environmental variations, further underscoring the important relationship between environmental contexts and genetic mechanisms, which together shape and sustain microbial population structure.
Time- and frequency-resolved coherent anti-Stokes Raman scattering spectroscopy with sub-25fs laser pulses
Authors: Lausten Rune , Smirnova Olga , Sussman Benjamin J. , Gräfe Stefanie , Mouritzen Anders S. , Stolow Albert
Published: June 2008

In general, many different diagrams can contribute to the signal measured in broadband four-wave mixing experiments. Care must therefore be taken when designing an experiment to be sensitive to only the desired diagram by taking advantage of phase matching, pulse timing, sequence, and the wavelengths employed. We use sub-25fs pulses to create and monitor vibrational wavepackets in gaseous iodine, bromine, and iodine bromide through time- and frequency-resolved femtosecond coherent anti-Stokes Raman scattering (CARS) spectroscopy. We experimentally illustrate this using iodine, where the broad bandwidths of our pulses, and Boltzmann population in the lower three vibrational levels conspire to make a single diagram dominant in one spectral region of the signal spectrum. In another spectral region, however, the signal is the sum of two almost equally contributing diagrams, making it difficult to directly extract information about the molecular dynamics. We derive simple analytical expressions for the time- and frequency-resolved CARS signal to study the interplay of different diagrams. Expressions are given for all five diagrams which can contribute to the CARS signal in our case.
Theory of current-free double layers in plasmas
Authors: Goswami K. S. , Saharia K. , Schamel H.
Published: June 2008

The existence of current-free double layers in unmagnetized plasma is studied by means of the quasipotential method applied to the Vlasov–Poisson system. Crucial for its existence are trapped particle populations that are characterized by notches (dips) in the velocity distribution functions at resonant velocity becoming flat at large amplitude limit. The potential drop across the double layer, or its amplitude ψ, can be arbitrarily strong covering the whole range 0<ψ<∞. Both the small and large amplitude limit are worked out explicitly, inclusively effective kinetic temperatures and pressures. It is, hence, the effective electron (ion) temperature increase (decrease) with increasing potential, caused by the trapped particles, which is responsible for the existence of this two-parameter family of solutions.
Energetic collimated ion bunch generation from an ultraintense laser interacting with thin concave targets
Authors: Liu Ming-Ping , Wu Hai-Cheng , Xie Bai-Song , Liu Jie , Wang Hong-Yu , Yu M. Y.
Published: June 2008

The interaction of an ultraintense laser pulse with parabolic concave target is studied using two-dimensional particle-in-cell simulation. It is found that ions at the back of the concave target can be accelerated more effectively than that with a plane target because of a large electrostatic field on the propagation axis induced by focusing of the laser expelled electrons. A highly collimated ion bunch with high particle and current densities appears. The dependence of the quality of ion acceleration and bunching on the width of the concave cavity is examined. It is found that the maximum ion energy is greatly enhanced when the width of the cavity attains a threshold, and an optimum width for generating a high-quality ion bunch exists. The results should be useful in the design of targets used in producing highly collimated energetic ions in high-energy-density physics.
Viscous flow over outflow slits covered by an anisotropic Brinkman medium: A model of flow above interendothelial cell clefts
Authors: Vincent P. E. , Sherwin S. J. , Weinberg P. D.
Published: June 2008

An analytic series solution is presented for the shear driven flow of a viscous fluid over an infinite series of outflow slits covered by a Brinkman medium with an anisotropic Darcy permeability. The solution is used to model the cellular scale flow of water over and within the endothelial glycocalyx, when the transmural water flux through the vascular endothelium is only allowed to pass via interendothelial cell clefts. Results are presented illustrating the effect of both the glycocalyx properties and the applied shearing rate (imposed by vascular scale fluid dynamics) on several relevant measures of the velocity field, including the wall normal velocity and the shear rate evaluated at the luminal surface of the glycocalyx.
Substrate design or reconstruction from free surface data for thin film flows
Authors: Sellier Mathieu
Published: June 2008

This paper addresses two inverse problems relevant to the flow of thin liquid films on uneven surfaces. The first one consists in controlling the free surface profile by a suitable design of the substrate and the second involves the reconstruction of the substrate topography from a known free surface profile. These problems are treated in the classical lubrication approximation framework and admit, for planar flows, a surprisingly simple close-form solution, which is successfully tested on a range of problems.
Model system-bath Hamiltonian and nonadiabatic rate constants for proton-coupled electron transfer at electrode-solution interfaces
Authors: Navrotskaya Irina , Soudackov Alexander V. , Hammes-Schiffer Sharon
Published: June 2008

An extension of the Anderson–Newns–Schmickler model for electrochemical proton-coupled electron transfer (PCET) is presented. This model describes reactions in which electron transfer between a solute complex in solution and an electrode is coupled to proton transfer within the solute complex. The model Hamiltonian is derived in a basis of electron-proton vibronic states defined within a double adiabatic approximation for the electrons, transferring proton, and bath modes. The interaction term responsible for electronic transitions between the solute complex and the electrode depends on the proton donor-acceptor vibrational mode within the solute complex. This model Hamiltonian is used to derive the anodic and cathodic rate constants for nonadiabatic electrochemical PCET. The derivation is based on the master equations for the reduced density matrix of the electron-proton subsystem, which includes the electrons of the solute complex and the electrode, as well as the transferring proton. The rate constant expressions differ from analogous expressions for electrochemical electron transfer because of the summation over electron-proton vibronic states and the dependence of the couplings on the proton donor-acceptor vibrational motion. These differences lead to additional contributions to the total reorganization energy, an additional exponential temperature-dependent prefactor, and a temperature-dependent term in the effective activation energy that has different signs for the anodic and cathodic processes. This model can be generalized to describe both nonadiabatic and adiabatic electrochemical PCET reactions and provides the framework for the inclusion of additional effects, such as the breaking and forming of other chemical bonds.
A detailed experimental and theoretical study of the femtosecond A-band photodissociation of CH3I
Authors: de Nalda Rebeca , Durá Judith , García-Vela Alberto , Izquierdo Jesús G. , González-Vázquez Jesús , Bañares Luis
Published: June 2008

The real time photodissociation dynamics of CH3I from the A band has been studied experimentally and theoretically. Femtosecond pump-probe experiments in combination with velocity map imaging have been carried out to measure the reaction times (clocking) of the different (nonadiabatic) channels of this photodissociation reaction yielding ground and spin-orbit excited states of the I fragment and vibrationless and vibrationally excited (symmetric stretch and umbrella modes) CH3 fragments. The measured reaction times have been rationalized by means of a wave packet calculation on the available ab initio potential energy surfaces for the system using a reduced dimensionality model. A 40fs delay time has been found experimentally between the channels yielding vibrationless CH3(ν=0) and I(P3∕22) and I*(P1∕22) that is well reproduced by the calculations. However, the observed reduction in delay time between the I and I* channels when the CH3 fragment appears with one or two quanta of vibrational excitation in the umbrella mode is not well accounted for by the theoretical model.
Effect of γ precipitates on martensitic transformation and magnetic properties in aged Mn–Ni–Ga alloys
Authors: Cai W. , Zhang J. , Gao Z. Y. , Sui J. H.
Published: June 2008

Multiple martensitic transformation peaks were observed from differential scanning calorimetry curves in aged Mn50Ni25Ga25 alloys in which transformation temperature varied with aging temperature. The magnetization and coercivity were enhanced as a result of aging above magnetic transition temperature. A maximum magnetization up to 54emu∕g and a magnetization difference between two phases of 28emu∕g was achieved in the alloy aged at 873K. However, coercivity as large as 1.2kOe was obtained in 573K aged alloy, with a high saturation field, which can be understood in terms of domain wall pinning.
Tuning the torsional properties of carbon nanotube systems with axial prestress
Authors: Jeong Byeong-Woo , Lim Jang-Keun , Sinnott Susan B.
Published: June 2008

The effects of tensile or compressive prestress on the torsional responses of carbon nanotubes are examined using classical molecular dynamics simulations. Prestressing the nanotubes is predicted to significantly change their critical torsional moment and stiffness. This is therefore an approach by which the torsional mechanical properties and oscillation frequencies of carbon nanotubes may be tuned. Importantly, the predicted changes in torsional stiffness are unique relative to conventional linear elastic materials and are indicative of nonlinear oscillations due to nonlinear mechanical effects.
Energy-dependent carrier relaxation in self-assembled InAs quantum dots
Authors: Ling H. S. , Lee C. P. , Lo M. C.
Published: June 2008

Selective excitation photoluminescence spectroscopy was employed to study InAs/GaAs self-assembled quantum dots (QDs). Under different excitation energies, different groups of QDs are selected and then emit light. The excited carriers relax to the ground state through different mechanisms when excited at different energies. Three distinct regions with different mechanisms in carrier excitation and relaxation are identified in the emission spectra. These three regions can be categorized from high energy to low energy, as continuum absorption, electronic state excitation, and multiphonon resonance. The special joint density of state tail of the QD that extends from the wetting layer band edge facilitates carrier relaxation and is posited to explain these spectral results.
Enhanced emission efficiency of GaN∕InGaN multiple quantum well light-emitting diode with an embedded photonic crystal
Authors: Kwon Min-Ki , Kim Ja-Yeon , Park Il-Kyu , Kim Ki Seok , Jung Gun-Young , Park Seong-Ju , Kim Je Won , Kim Yong Chun
Published: June 2008

A photonic crystal (PC) structure of periodic SiO2 pillar cubic array is embedded in n-GaN layer of InGaN∕GaN multiple quantum well (MQW) blue (480nm) light-emitting diode (LED). The diameter, period, and depth of SiO2 pillar are 124±6, 230±10, and 130±10nm, respectively. The increments of 70% for external quantum efficiency, 17% for internal quantum efficiency, and 45% for light extraction efficiency from photoluminescence measurement, and 33% for optical output power at 20mA are observed for LEDs with an embedded PC layer. This improvement can be attributed to the increased extraction efficiency by PC effect as well as increased internal quantum efficiency due to the decrease of dislocation density in n-GaN layer because of an epitaxial lateral over-growth process.
Three gratings coupling during the holographic grating recording process in azobenzene-functionalized polymer
Authors: Sobolewska Anna , Bartkiewicz Stanislaw
Published: June 2008

The authors present a mechanism explaining complex diffraction efficiency dynamics of the holographic grating recording process in azobenzene-functionalized polymer. The mechanism assumes simultaneous formation of three coupling phase gratings with different recording time constants and constant, equal to 0 or π, phase shifts between them. Two of gratings originate from the refractive index changes in the bulk of material and the third one from the surface relief modulation. Diffraction efficiency dynamics curves calculated using the proposed model are in a very good agreement with the experimental results.
Tamm plasmon polaritons: Slow and spatially compact light
Authors: Sasin M. E. , Seisyan R. P. , Kalitteevski M. A. , Brand S. , Abram R. A. , Chamberlain J. M. , Egorov A. Yu. , Vasil’ev A. P. , Mikhrin V. S. , Kavokin A. V.
Published: June 2008

We report on the first experimental observation of Tamm plasmon polaritons (TPPs) formed at the interface between a metal and a dielectric Bragg reflector (DBR). In contrast to conventional surface plasmons, TPPs have an in-plane wavevector less than the wavevector of light in vacuum, which allows for their direct optical excitation. The angular resolved reflectivity and transmission spectra of a GaAs∕AlAs DBR covered by Au films of various thicknesses show the resonances associated with the TPP at low temperatures and room temperature. The in-plane dispersion of TTPs is parabolic with an effective mass of 4×10−5 of the free electron mass.
Does a Spin–Orbit Coupling Between the Sun and the Jovian Planets Govern the Solar Cycle?
Authors: Wilson I. R. G. , Carter B. D. , Waite I. A.
Published: June 2008

We present evidence to show that changes in the Sun's equatorial rotation rate are synchronized with changes in its orbital motion about the barycentre of the Solar System. We propose that this synchronization is indicative of a spin–orbit coupling mechanism operating between the Jovian planets and the Sun. However, we are unable to suggest a plausible underlying physical cause for the coupling. Some researchers have proposed that it is the period of the meridional flow in the convective zone of the Sun that controls both the duration and strength of the Solar cycle. We postulate that the overall period of the meridional flow is set by the level of disruption to the flow that is caused by changes in Sun's equatorial rotation speed. Based on our claim that changes in the Sun's equatorial rotation rate are synchronized with changes in the Sun's orbital motion about the barycentre, we propose that the mean period for the Sun's meridional flow is set by a Synodic resonance between the flow period (∼22.3 yr), the overall 178.7-yr repetition period for the solar orbital motion, and the 19.86-yr synodic period of Jupiter and Saturn.
Mammalian-like features of sleep structure in zebra finches
Authors: Low Philip Steven , Shank Sylvan S. , Sejnowski Terrence J. , Margoliash Daniel
Published: June 2008

A suite of complex electroencephalographic patterns of sleep occurs in mammals. In sleeping zebra finches, we observed slow wave sleep (SWS), rapid eye movement (REM) sleep, an intermediate sleep (IS) stage commonly occurring in, but not limited to, transitions between other stages, and high amplitude transients reminiscent of K-complexes. SWS density decreased whereas REM density increased throughout the night, with late-night characterized by substantially more REM than SWS, and relatively long bouts of REM. Birds share many features of sleep in common with mammals, but this collective suite of characteristics had not been known in any one species outside of mammals. We hypothesize that shared, ancestral characteristics of sleep in amniotes evolved under selective pressures common to songbirds and mammals, resulting in convergent characteristics of sleep.
Seminaphthofluorones are a family of water-soluble, low molecular weight, NIR-emitting fluorophores
Authors: Yang Youjun , Lowry Mark , Xu Xiangyang , Escobedo Jorge O. , Sibrian-Vazquez Martha , Wong Lisa , Schowalter Corin M. , Jensen Timothy J. , Fronczek Frank R. , Warner Isiah M. , Strongin Robert M.
Published: June 2008

A readily accessible new class of near infrared (NIR) molecular probes has been synthesized and evaluated. Specific fluorophores in this unique xanthene based regioisomeric seminaphthofluorone dye series exhibit a combination of desirable characteristics including (
i
) low molecular weight (339 amu), (
ii
) aqueous solubility, and (
iii
) dual excitation and emission from their fluorescent neutral and anionic forms. Importantly, systematic changes in the regiochemistry of benzannulation and the ionizable moieties afford (
iv
) tunable deep-red to NIR emission from anionic species and (
v
) enhanced Stokes shifts. Anionic SNAFR-6, exhibiting an unusually large Stokes shift of ≈200 nm (5,014 cm
−1
) in aqueous buffer, embodies an unprecedented fluorophore that emits NIR fluorescence when excited in the blue/green wavelength region. The successful use of SNAFR-6 in cellular imaging studies demonstrates proof-of-concept that this class of dyes possesses photophysical characteristics that allow their use in practical applications. Notably, each of the new fluorophores described is a minimal template structure for evaluation of their basic spectral properties, which may be further functionalized and optimized yielding concomitant improvements in their photophysical properties.
Helical twist controls the thickness of F-actin bundles
Authors: Claessens M. M. A. E. , Semmrich C. , Ramos L. , Bausch A. R.
Published: June 2008

In the presence of condensing agents such as nonadsorbing polymer, multivalent counter ions, and specific bundling proteins, chiral biopolymers typically form bundles with a finite thickness, rather than phase-separating into a polymer-rich phase. Although short-range repulsive interactions or geometrical frustrations are thought to force the equilibrium bundle size to be limited, the precise mechanism is yet to be resolved. The importance of the tight control of biopolymer bundle size is illustrated by the ubiquitous cytoskeletal actin filament bundles that are crucial for the proper functioning of cells. Using an
in vitro
model system, we show that size control relies on a mismatch between the helical structure of individual actin filaments and the geometric packing constraints within bundles. Small rigid actin-binding proteins change the twist of filamentous actin (F-actin) in a concentration-dependent manner, resulting in small, well defined bundle thickness up to ≈20 filaments, comparable to those found in filopodia. Other F-actin cross-linking proteins can subsequently link these small, well organized bundles into larger structures of several hundred filaments, comparable to those found in, for example,
Drosophila
bristles. The energetic tradeoff between filament twisting and cross-linker binding within a bundle is suggested as a fundamental mechanism by which cells can precisely adjust bundle size and strength.