bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal niche segregation in two rodent assemblages of subtropical Mexico
Authors: Castro-Arellano Ivan , Lacher Thomas E.
Published: October 2009

Temporal niche partitioning can be a viable mechanism for coexistence, but has received less attention than other niche axes. We characterized and compared patterns of activity, and overlap of temporal activity among the five common rodent species from a tropical semideciduous forest (TSF) and between the two common rodent species from cloud forest (CF) at El Cielo Biosphere Reserve in Mexico. Capture frequencies over 2-h intervals, obtained via live trapping (6850 trap-nights) in chosen months over 3 y formed the empirical basis for analyses. Trap transects were set from 19h00 to 07h00 and checked every 2 h. Analyses of 484 captures evinced two distinct assemblages. The TSF assemblage was diverse and with non-random temporal niche segregation, whereas the CF assemblage was depauperate with its two dominant species evincing the same activity pattern. Predator avoidance between open- and closed-microhabitat species, as well as niche complementarity may explain temporal segregation at TSF. This is the first documentation of assemblage-wide non-random temporal segregation of neotropical rodents. Time of activity may be a largely under-appreciated mechanism in other species-rich tropical rodent assemblages as well as in other species-rich biotas.
Community structure of pre-dispersal seed predatory insects on elevenShorea(Dipterocarpaceae) species
Authors: Hosaka Tetsuro , Yumoto Takakazu , Kojima Hiroaki , Komai Furumi , Noor Nur Supardi Md.
Published: October 2009

The Dipterocarpaceae in South-East Asia are known for their strict mast fruiting. During fruiting, pre-dispersal seed predation by insects contributes to mortality of dipterocarp seeds. We documented the community structure of insect seed predators on 11Shoreaspecies in Peninsular Malaysia. Fruits were sampled sequentially throughout seed development, and 2144 and 1655 individuals of seed predator weevils and moths were collected in two mast-fruiting events. Four weevils:Nanophyes shoreae, nanophyid sp. 1,Alcidodes dipterocarpiandAlcidodes humeralis, and one mothAndrioplecta shoreaewere abundant in seeds of theShoreaspecies. The proportion ofN. shoreaeto the total predators became larger in the latter fruiting event than the former while that ofAlcidodesspp. became smaller. The predator species composition changed during seed development; nanophyid spp. emerged from immature fruits whileAlcidodesspp. emerged from mature fruits.Andrioplecta shoreaeemerged from both immature and mature fruits. The level of host specificity measured by Kullback–Leibler distance was low for most predator species in both events. Predator species composition of manyShoreawas similar to each other due to the dominance ofN. shoreaethough it might gradually differ with the phylogenetic distance between hosts. In conclusion, predator species composition ofShoreavaried during seed development within a host rather than among hosts. Intermittent synchronized fruiting by congenericShoreatrees would be advantageous to avoid pre-dispersal insect seed predators, and contribute to their reproduction.
Vicissitudes of leaves in a tropical rain forest in Madagascar
Authors: Heatwole Harold , Unsicker Sybille , Andriamiarisoa Lala Roger , Lowman Margaret D.
Published: October 2009

A sample of 1834 leaves from 83 plants in 26 families was collected in tropical rain forest in Madagascar from three vertical strata: top of emergent trees (up to 37 m), top of trees in upper canopy (about 22 m), and shrubs and saplings at ground level. These leaves were examined for damage by seven different agents: fungi, epiphyllae, mechanical injury, galls, leaf miners, grazing insects and skeletonizing insects. Fungi affected more than 60% of the leaves and grazing insects 45–65%, with other agents each affecting 3–30%; fewer than 4% of the leaves escaped unscathed by any agent. Individual leaves were attacked by up to five agents. There was a sharp decline in proportion of leaves affected by fungi, leaf miners, epiphyllae and mechanical breakage with increasing category of severity. Grazing insects, mechanical injury, and perhaps galls, had greater impact at ground level than in the canopy, with fungi and skeletonizing insects showing the opposite pattern. Leaf miners had lower incidence in the canopy than elsewhere. The observed vertical stratification means that a tree not only needs to balance its defences to meet multiple threats in any stratum, but must adapt to a different suite of challenges during its lifetime. Attack by grazing insects and fungi are major challenges for saplings at ground level, but with increasing height above the ground fungal attack on leaves becomes more prevalent, but attack by grazing insects less so.
Serovars ofLeptospiraisolated from dogs and rodents
Authors: SUEPAUL S. M. , CARRINGTON C. V. F. , CAMPBELL M. , BORDE G. , ADESIYUN A. A.
Published: October 2009

We determined the frequency of isolation ofLeptospirafrom dogs and rodents, the serovars ofLeptospira, and the clinical, gross and histological manifestations in dogs with leptospirosis in Trinidad. From dogs, samples of urine, blood and kidney were collected while only kidney and blood samples of trapped rodents were used. Isolates were cultured and serotyped using a panel of 23 international serovars and monoclonal antibodies. The risk factors for leptospirosis were also determined in owned dogs using a standard questionnaire. Of a total of 468 animals investigated forLeptospira, 70 (15·0%) were positive, comprising nine (18·0%) of 50 suspected canine leptospirosis cases, seven (3·4%) of 207 stray dogs and 54 (25·6%) of 211 rodents. The observation that rodents have a statistically (P<0·05, χ2) higher frequency of isolation emphasizes the importance of rodents as reservoirs of leptospirosis in the country. Copenhageni was the predominant serovar found in 100·0% (7/7), 33·3% (2/6) and 68·5% (37/54) of isolates from suspected canine leptospirosis cases, stray dogs and rodents, respectively. Serovars Icterohaemorrhagiae and Canicola, the two serovars present in the commercial vaccines used locally, were detected in one (1·5%) and zero (0·0%) isolates respectively of the 67 tested. Data provided suggest that the apparent vaccine failure may be a consequence of the fact that the predominant serovar (Copenhageni) detected in sick, apparently healthy dogs and in rodents is not contained in the vaccines used locally to protect dogs against canine leptospirosis.
Ultrastructural Observations Reveal the Presence of Channels between Cork Cells
Authors: Teixeira Rita Teresa , Pereira Helena
Published: October 2009

The ultrastructure of phellem cells ofQuercus suberL. (cork oak) andCalotropis procera(Ait) R. Br. were analyzed using electron transmission microscopy to determine the presence or absence of plasmodesmata (PD). Different types ofQ. subercork samples were studied: one year shoots; virgin cork (first periderm), reproduction cork (traumatic periderm), and wet cork. The channel structures of PD were found in all the samples crossing adjacent cell walls through the suberin layer of the secondary wall.Calotropisphellem also showed PD crossing the cell walls of adjacent cells but in fewer numbers compared toQ. suber. In one year stems of cork oak, it was possible to follow the physiologically active PD with ribosomic accumulation next to the aperture of the channel seen in the phellogen cells to the completely obstructed channels in the dead cells that characterize the phellem tissue.
Gravity wave ducting in the upper mesosphere and lower thermosphere duct system
Authors: Walterscheid R. L. , Hickey M. P.
Published: October 2009

We report on a numerical study of gravity wave propagation in a pair of ducts located in a region where dramatic changes in the airglow most likely associated with ducted wave trains are observed. We examine ducting in an upper mesosphere inversion (INV) and an always present lower thermosphere stable layer (LTD) for a range of phase speeds and horizontal wavelengths characteristic of ducting events. We analyze the propagation and modal structure of ducted waves for backgrounds with increasing realism, starting with a climatological temperature profile where only the LTD is present. In succession, we add the INV based on the work of Smith et al. (2003), climatological winds, and winds in the upper mesosphere based on the work of Smith et al. (2003). We examine ducting for phase speeds between 40 and 100 m s−1 and horizontal wavelengths between 20 and 60 km. We find that without winds, only the LTD supports ducting of waves forced from below. When observed winds and temperatures are included, strong ducting is evident in both regions. For waves forced from below, the strongest ducted modes are those with slower phase speeds, and of these the third gravest agree reasonably well with the observed phase speeds and wavelengths, indicating that the observations are consistent with linear ducted waves. For waves forced in the INV, we find an intense and strongly dominant fundamental mode. This is a fast mode having phase speeds ∼100 m s−1 for a horizontal wavelength of 30 km in the INV and much faster in the LTD. That the fundamental is not seen in Smith et al.'s (2003) observations indicates that the waves were forced from below and that the lowest mode was blocked by an evanescent barrier below the INV. Our results show that the two ducts communicate: the upward extensions of waves ducted in the INV are seen in the LTD. This is particularly significant in the case of in situ forcing, where the fundamentals combine to give amplification exceeding a factor of 10 in the LTD.
Elemental carbon distribution in Svalbard snow
Authors: Forsström S. , Ström J. , Pedersen C. A. , Isaksson E. , Gerland S.
Published: October 2009

The concentration of apparent elemental carbon (ECa, based on a thermal‐optical method) in the snow was investigated in Svalbard (European Arctic) during spring 2007. The median ECa concentration of 81 samples was 4.1 μg l−1 and the values ranged from 0 to 80.8 μg l−1 of melt water. The median concentration is nearly an order of magnitude lower than the previously published data of equivalent black carbon (BCe, based on an optical method), obtained from Svalbard snow in the 1980s. A systematic regional difference was evident: ECa concentrations were higher in east Svalbard compared to west Svalbard. The observations of snow ECa cover spatial scales up to several hundred kilometers, which is comparable to the resolution of many climate models. Measurements of atmospheric carbonaceous aerosol (2002–2008) at Zeppelin station in Ny‐Ålesund, Svalbard, were divided to air mass sectors based on calculated back trajectories. The results show that air originating from the eastern sector contains more than two and half times higher levels of soot than air arriving from south to west. The observed east–west gradient of ECa concentrations in snow may be because of a combination of the atmospheric concentration gradient, the orographic effect of the archipelago, and the efficient scavenging of the carbonaceous particles through precipitation.
A quantitative assessment of human impacts on decrease in sediment flux from major Chinese rivers entering the western Pacific Ocean
Authors: Chu Z. X. , Zhai S. K. , Lu X. X. , Liu J. P. , Xu J. X. , Xu K. H.
Published: October 2009

Major rivers with high sediment or water discharge act as natural integrators of surficial processes, including human activities within their drainage basins, and they are also the primary sources of terrestrial materials entering the ocean. The river‐derived materials flux entering the coastal oceans, however, has been strongly affected by anthropogenic activities. Recent studies related to human impacts on river sediment flux have mainly focused on qualitative descriptions. Here we present a quantitative assessment of human impacts on decrease in sediment flux from nine major Chinese rivers entering the western Pacific Ocean, including Changjiang (Yangtze), Huanghe (Yellow), Zhujiang (Pearl), Songhuajiang, Liaohe, Haihe, Huaihe, Qiantangjiang, and Minjiang. During 1959–2007, dams and reservoirs, soil and water conservation programs, water consumption, as well as sand mining decreased the amount of sediment delivered to the ocean by 28, 11.5, 7.5 and 3 gigatons (Gt), respectively. If combined (50 Gt for the period 1959–2007), this reduction was close to the total decreased sediment flux (43 Gt) measured from these nine major rivers over the same period. Besides, the temporal variations in water and sediment fluxes into the ocean from these rivers generally during 1953–2007 were presented. These results are useful for further studies on Chinese and even global river‐derived material flux to the ocean and associated ecological risks.
Fram Strait sea ice volume export estimated between 2003 and 2008 from satellite data
Authors: Spreen Gunnar , Kern Stefan , Stammer Detlef , Hansen Edmond
Published: October 2009

Satellite‐based estimates of monthly sea ice volume exports through Fram Strait for the years 2003 to 2008 are presented. These are obtained from individual satellite observations of sea ice thickness, area, and drift. First, sea ice freeboard is inferred from ICESat laser altimeter observations and then converted to ice thickness estimates. Sea ice area and drift are derived from AMSR‐E 89 GHz data. Retrieved sea ice thickness estimates compare within 0.5 m with the few ULS data available in the Fram Strait. The mean, minimum, and maximum observed monthly Fram Strait sea ice volume export amounts to 217, 92, and 420 km3/month, respectively. In comparison to former Fram Strait sea ice volume export estimates obtained during the 1990s our estimates are slightly smaller (−33 km3/month) but are within the natural variability and no significant change of the total amount of Fram Strait sea ice export can be observed.
Barents Sea multidecadal variability
Authors: Levitus S. , Matishov G. , Seidov D. , Smolyar I.
Published: October 2009

We present area‐averaged time series of temperature for the 100–150 m depth layer of the Barents Sea from 1900 through 2006. This record is dominated by multidecadal variability on the order of 4°C which is correlated with the Atlantic Multidecadal Oscillation Index.
First results of the limb imaging of 630.0 nm airglow using FORMOSAT‐2/Imager of Sprites and Upper Atmospheric Lightnings
Authors: Rajesh P. K. , Liu J. Y. , Chiang C. Y. , Chen A. B. , Chen W. S. , Su H. T. , Hsu R. R. , Lin C. H. , Hsu M.‐L. , Yee J. H. , Nee J. B.
Published: October 2009

This is the first report of the most comprehensive 630.0 nm airglow limb images taken using Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) onboard FORMOSAT‐2. The limb scans reveal two distinct airglow layers: the upper one corresponds to the thermospheric O(1D) emission and the lower one corresponds to the OH (9–3) emissions. Sequences of such observations are combined to generate altitude‐latitude maps of the emissions, which reveal intensity enhancements of both the layers at certain locations where they often appear to be linked/joined vertically. A detailed analysis of the location and occurrence of the enhancements in the entire observations, together with simulations of the emissions suiting the ISUAL limb geometry are carried out to understand the causes and related processes.
An improved photon path length probability density function–based radiative transfer model for space‐based observation of greenhouse gases
Authors: Oshchepkov Sergey , Bril Andrey , Yokota Tatsuya
Published: October 2009

We present an improved model to describe the photon path length probability density function (PPDF) that effectively accounts for both aerosol and thin cloud effects for rapid retrieval of greenhouse gas data from space‐based high spectral resolution measurements. The reasonably simple PPDF and effective transmittance parameterization permit vertical inhomogeneity of gas absorption and three plane‐parallel arbitrarily located layers to account for light‐scattering effects due to aerosol and clouds. The basic assumption to construct the PPDF model refers mainly to the presentation of PPDF in terms of weakly correlated aerosol and cloud path length components. The model was validated using Monte Carlo simulations of photon trajectories and tested for a representative set of atmospheric conditions in which both aerosol and clouds modified the path length significantly. This study also focused on the connection of PPDF parameters to atmospheric optical characteristics commonly utilized in the solution of radiative transfer equations. These characteristics were converted into PPDF parameters by PPDF retrieval from a very limited spectral range of simulated radiance including at least one gas absorption line. The results demonstrate that this method can be used effectively for rapid radiative transfer spectral calculations over a rather wide spectral range of radiance at given atmospheric optical characteristics. Another important application of such conversion is to account for a priori knowledge of atmospheric optical characteristics when retrieving amounts of gases within PPDF‐based or other methods, such as full physics algorithms that utilize the solutions of radiative transfer equations.
Role of Eurasian snow cover in wintertime circulation: Decadal simulations forced with satellite observations
Authors: Orsolini Yvan J. , Kvamstø Nils G.
Published: October 2009

We investigate the impact of the Eurasian snow cover extent on the Northern Hemisphere winter circulation by performing a suite of ensemble simulations with the Météo‐France “Arpege Climat” atmospheric general circulation model, spanning 2 decades (1979–2000). Observed snow cover derived from satellite infrared and visible imagery has been forced weekly into the model. Variability in autumn‐early winter snow cover extent over eastern Eurasia is linked to circulation anomalies over the North Pacific that are influencing the North Atlantic sector in late winter through the development of the Aleutian‐Icelandic Low Seesaw teleconnection. The forcing of realistic snow cover in the model augments potential predictability over eastern Eurasia and the North Pacific and improves the hindcast skill score of the Aleutian‐Icelandic Low Seesaw teleconnection. Enhanced eastern Eurasia snow cover is associated with an anomalous upper‐tropospheric wave train across Eurasia, anomalously high upward wave activity flux, and a displaced stratospheric polar vortex.
On the role of groundwater and soil texture in the regional water balance: An investigation of the Nebraska Sand Hills, USA
Authors: Wang Tiejun , Istanbulluoglu Erkan , Lenters John , Scott Durelle
Published: October 2009

Partitioning of precipitation between evapotranspiration and runoff at the basin scale is primarily controlled by climate and basin characteristics. Here we use the Budyko hypothesis to investigate the impacts of soil texture and groundwater (e.g., baseflow) on annual and long‐term mean annual water balances of basins in a semiarid region located in and around the Sand Hills region of Nebraska, USA. Native grasslands are dominant across the study area with soil textures dramatically different for the Nebraska Sand Hills (primarily sand deposits) and the adjacent regions (mainly less permeable silt loam). For each basin, long‐term hydrologic and meteorological data are obtained, and a baseflow index is calculated using daily streamflow data to quantify the groundwater contribution to streamflow. We found sound field evidence that suggests the control of soil texture on mean annual water balance and the impact of groundwater storage on interannual variability of water balance at catchment scales, which is usually seen at plot scales and in theoretical models. Our results show that compared to the basins located in the adjacent regions, the Nebraska Sand Hills basins experience much higher long‐term mean annual surface runoff ratios (/) and thus lower ratios of ( − )/, where is the long‐term mean annual precipitation. The high baseflow index and its positive correlation with the ratio of / in the Sand Hills basins illustrate the role of lower (higher) evapotranspiration (recharge) rates. On annual time scales, the baseflow‐dominated basins exhibit a negative relationship between annual (P − R) / P and annual aridity index (i.e., the ratio of annual potential evapotranspiration to annual precipitation), which deviates from the original Budyko hypothesis. Moreover, with decreasing baseflow index, this negative relationship gradually transits into a positive relationship that follows Budyko's curves. Our results suggest that soil textural differences may strongly modify the impact of climate on regional water balance. These findings may have important implications for managing water resources under a fluctuating climate.
Elevated Systemic Hepcidin and Iron Depletion in Obese Premenopausal Females
Authors: Tussing‐Humphreys Lisa M. , Nemeth Elizabeta , Fantuzzi Giamila , Freels Sally , Guzman Grace , Holterman Ai‐Xuan L. , Braunschweig Carol
Published: October 2009

Hepcidin, the body's main regulator of systemic iron homeostasis, is upregulated in response to inflammation and is thought to play a role in the manifestation of iron deficiency (ID) observed in obese populations. We determined systemic hepcidin levels and its association with body mass, inflammation, erythropoiesis, and iron status in premenopausal obese and nonobese women (n = 20/group) matched for hemoglobin (Hb). The obese participants also had liver and abdominal visceral and subcutaneous adipose tissue assessed for tissue iron accumulation and hepcidin mRNA expression. Despite similar Hb levels, the obese women had significantly higher serum hepcidin (88.02 vs. 9.70 ng/ml; P < 0.0001) and serum transferrin receptor (sTfR) (P = 0.001) compared to nonobese. In the obese women hepcidin was not correlated with serum iron (r = −0.02), transferrin saturation (Tsat) (r = 0.17) or sTfR (r = −0.12); in the nonobese it was significantly positively correlated with Tsat (r = 0.70) and serum iron (r = 0.58), and inversely with sTfR (r = −0.63). Detectable iron accumulation in the liver and abdominal adipose tissue of the obese women was minimal. Liver hepcidin mRNA expression was ∼700 times greater than adipose tissue production and highly correlated with circulating hepcidin levels (r = 0.61). Serum hepcidin is elevated in obese women despite iron depletion, suggesting that it is responding to inflammation rather than iron status. The source of excess hepcidin appears to be the liver and not adipose tissue. The ID of obesity is predominantly a condition of a true body iron deficit rather than maldistribution of iron due to inflammation. However, these findings suggest inflammation may perpetuate this condition by hepcidin‐mediated inhibition of dietary iron absorption.
Cholesterol-dependent phase separation in cell-derived giant plasma-membrane vesicles
Authors: Levental Ilya , Byfield Fitzroy J. , Chowdhury Pramit , Gai Feng , Baumgart Tobias , Janmey Paul A.
Published: October 2009

Cell-derived GPMVs (giant plasma-membrane vesicles) enable investigation of lipid phase separation in a system with appropriate biological complexity under physiological conditions, and in the present study were used to investigate the cholesterol-dependence of domain formation and stability. The cholesterol level is directly related to the abundance of the liquid-ordered phase fraction, which is the majority phase in vesicles from untreated cells. Miscibility transition temperature depends on cholesterol and correlates strongly with the presence of detergent-insoluble membrane in cell lysates. Fluorescence correlation spectroscopy reveals two distinct diffusing populations in phase-separated cell membrane-derived vesicles whose diffusivities correspond well to diffusivities in both model systems and live cells. The results of the present study extend previous observations in purified lipid systems to the complex environment of the plasma membrane and provide insight into the effect of cholesterol on lipid phase separation and abundance.
Clopidogrel, independent of the vascular P2Y12 receptor, improves arterial function in small mesenteric arteries from AngII-hypertensive rats
Authors: Giachini Fernanda R. C. , Osmond David A. , Zhang Shali , Carneiro Fernando S. , Lima Victor V. , Inscho Edward W. , Webb R. Clinton , Tostes Rita C.
Published: October 2009

The P2Y12 receptor antagonist clopidogrel blocks platelet aggregation, improves systemic endothelial nitric oxide bioavailability and has anti-inflammatory effects. Since P2Y12 receptors have been identified in the vasculature, we hypothesized that clopidogrel ameliorates AngII (angiotensin II)-induced vascular functional changes by blockade of P2Y12 receptors in the vasculature. Male Sprague–Dawley rats were infused with AngII (60 ng/min) or vehicle for 14 days. The animals were treated with clopidogrel (10 mg·kg−1 of body weight·day−1) or vehicle. Vascular reactivity was evaluated in second-order mesenteric arteries. Clopidogrel treatment did not change systolic blood pressure [(mmHg) control-vehicle, 117±7.1 versus control-clopidogrel, 125±4.2; AngII–vehicle, 197±10.7 versus AngII–clopidogrel, 198±5.2], but it normalized increased phenylephrine-induced vascular contractions [(%KCl) vehicle-treated, 182.2±18% versus clopidogrel, 133±14%), as well as impaired vasodilation to acetylcholine [(%) vehicle-treated, 71.7±2.2 versus clopidogrel, 85.3±2.8) in AngII-treated animals. Vascular expression of P2Y12 receptor was determined by Western blot. Pharmacological characterization of vascular P2Y12 was performed with the P2Y12 agonist 2-MeS-ADP [2-(methylthio) adenosine 5′-trihydrogen diphosphate trisodium]. Although 2-MeS-ADP induced endothelium-dependent relaxation [(Emax %)=71±12%) as well as contractile vascular responses (Emax %=83±12%), these actions are not mediated by P2Y12 receptor activation. 2-MeS-ADP produced similar vascular responses in control and AngII rats. These results indicate potential effects of clopidogrel, such as improvement of hypertension-related vascular functional changes that are not associated with direct actions of clopidogrel in the vasculature, supporting the concept that activated platelets contribute to endothelial dysfunction, possibly via impaired nitric oxide bioavailability.
Nonlinear stability of boundary layer solution to the Boltzmann equation with diffusive effect at the boundary
Authors: Tian Qianzhu , Sun Jie
Published: October 2009

In this paper, the stability of boundary layer solutions to the Boltzmann equation with diffusive effect at the boundary for hard sphere model is considered. When the Mach number of the far field is less than −1, the exponential decay in time is proven for linearized operator first. At last, based on this property, nonlinear stability of the boundary layers is obtained by bootstrap argument.
Absolute and convective instabilities of an inviscid compressible mixing layer: Theory and applications
Authors: Caillol P.
Published: October 2009

This study aims to examine the effect of compressibility on unbounded and parallel shear flow linear instabilities. This analysis is of interest for industrial, geophysical, and astrophysical flows. We focus on the stability of a wavepacket as opposed to previous single-mode stability studies. We consider the notions of absolute and convective instabilities first used to describe plasma instabilities. The compressible-flow modal theory predicts instability whatever the Mach number. Spatial and temporal growth rates and Reynolds stresses nevertheless become strongly reduced at high Mach numbers. The evolution of disturbances is driven by Kelvin–Helmholtz instability that weakens in supersonic flows. We wish to examine the occurrence of absolute instability, necessary for the appearance of turbulent motions in an inviscid and compressible two-dimensional mixing layer at an arbitrary Mach number subject to a three-dimensional disturbance. The mixing layer is defined by a parametric family of mean-velocity and temperature profiles. The eigenvalue problem is solved with the help of a spectral method. We ascertain the effects of the distribution of temperature and velocity in the mixing layer on the transition between convective and absolute instabilities. It appears that, in most cases, absolute instability is always possible at high Mach numbers provided that the ratio of slow-stream temperature over fast-stream temperature may be less than a critical maximal value but the temporal growth rate present in the absolutely unstable zone remains small and tends to zero at high Mach numbers. The transition toward a supersonic turbulent regime is therefore unlikely to be possible in the linear theory. Absolute instability can be also present among low-Mach-number coflowing mixing layers provided that this same temperature ratio may be small, but nevertheless, higher than a critical minimal value. Temperature distribution within the mixing layer also has an effect on the growth rate, this diminishes when the slow stream is heated. These results are applied to the dynamics of mixing layers in the interstellar medium and to the dynamics of the heliopause, frontier between the interstellar medium, and the solar wind.
A microfluidic oscillating tube densitometer
Authors: Coléou Chloé Marion , Dryden Philip , Harrison Christopher
Published: October 2009

This article discusses a microfluidic oscillating tube densitometer with an internal volume of approximately 20 μl. Accuracy better than +/−0.5% in density is demonstrated over a range of temperatures (50 °C–150 °C) and pressures (150–15 000 psi) by prior calibration with air and water. The flexibility of the tubing facilitates use of a novel actuation and detection system that greatly simplifies the fabrication. Two simple and automated calibration methods are discussed using measurements performed with an evacuated and a water-filled tube. Measurements show that the effective spring constant of the tube is strongly affected by temperature and is largely insensitive to pressure. The tube volume, on the other hand, is strongly affected by pressure.
Discrete power spectrum of line width roughness
Authors: Hiraiwa A. , Nishida A.
Published: October 2009

The variation of device characteristics is a challenge to present and future large-scale integrations. One of the origins of the variation is line width roughness (LWR). To facilitate the efforts to cope with LWR, we developed a method to accurately characterize LWR basing on the analysis of power spectral densities (PSDs). Because experimental PSDs are intrinsically discrete, we derive simple analytic formulas of the discrete PSDs by assuming that the autocorrelation function (ACF) exponentially decays with distance. The PSDs calculated by using the formulas agree excellently with experimentally obtained PSDs of photoresist LWR. From the result we find that the photoresist LWR of this study has a standard deviation of 2.5 nm and an exponentially-decaying autocorrelation function with a correlation length of 35 nm. Although the experimental PSDs inevitably contain a component produced by scanning-electron-microscope (SEM)-image noise, the two components of LWR and noise are separately determined by the method of this study. Due to this feature, the resultant variance of LWR is independent of the noise intensity. However, it is still important to reduce the noise component in order to maintain the accuracy of analysis especially in the case of LWR that has an unknown functional form of PSD. This is because even the PSDs that have different functional forms sometimes look alike in the presence of large noise. To reduce the noise effect, it is effective to average the SEM images perpendicularly to fine lines before edge detections. The procedure does not reduce the variance unlike averaging along the lines. The method of this study is applicable not only to LWR but also to other cases as far as the ACF exponentially decays with distance, or equivalently the spectral line shape is Lorentzian. Accordingly, it forms the basis for spectral analysis of most experimental results.
Influence of strain and grain boundary variations on magnetism of Cr-doped AlN films
Authors: Fan B. , Zeng F. , Chen C. , Yang Y. C. , Yang P. Y. , Pan F.
Published: October 2009

Cr-doped AlN films are prepared by reactive dc magnetron cosputtering under a negative substrate bias ranging from 50 to 110 V. The bias induces variation of the texture from (002) to (110) orientation, enhances the stress and reduces the grain size in the films. All of the samples are ferromagnetic. The atomic magnetic moment (AMM) of Cr increases with the bias from 50 to 90 V and reaches the maximum of 0.18μB/Cr at a bias of 90 V. As the bias increases further to 110 V, the AMM decreases. The dielectric constant also changes in the same trend with the bias, as well as the AMM does. The variations in these two properties are determined by the collective effects of the lattice deformations induced by the changing stress, the amount of boundary defects and the grain size in the films.
Strain-induced variations of electronic energy band edges of embedded semiconductor quantum dots in half-space substrates
Authors: Pan Ernie , Zou Yu , Chung Peter W. , Albrecht John D.
Published: October 2009

The strain-induced local electronic band edge states in semiconductor quantum dots (QDs) are studied using a k⋅p description of the electronic eigenstates coupled with the induced lattice strain as calculated using the continuum mechanics (CM) description. In the CM method, the misfit-lattice induced strain can be reduced to an analytical expression that is straightforward to evaluate numerically. Different from most previous analyses for QDs in infinite spaces, we address cubic and pyramidal QDs located in half-space substrates with different lattice orientations, which more realistically describe experimental situations in most instances. The band edges within the cubic and pyramidal InAs QDs embedded in GaAs substrates are predicted within the six-band k⋅p basis via both a published approximation and the presented exact approach. Comparison of the strain-induced local band edge shows that the approximate method adopted previously in literature could result in a substantial error near the interface region of the QD. The strain-induced band edges along the bottom center line of the QD can differ by a factor of 2 between the two approaches. Furthermore, the effect of the free surface on the strain-induced band edges is studied by varying the depth of the buried QD. When the QD is moved away from the surface, the band edges converge in a consistent way to the infinite-space solution. Comparison with available experimental results validates our exact model within the half-space substrate and shows the importance of treating the surface in a theoretically rigorous way.
Enhancement in the coercivity in Nd2Fe14B/α-Fe nanocomposite alloys by Ti doping
Authors: Zhang P. Y. , Hiergeist R. , Albrecht M. , Braun K.-F. , Sievers S. , Lüdke J. , Ge H. L.
Published: October 2009

Nanocomposite α-Fe/Nd2Fe14B alloys with high coercivity were prepared by melt spinning. The influence of Ti addition on the microstructure and magnetic properties of these nanocomposite alloys were investigated. Ti addition has proved to result in relevant improvements in the microstructure and magnetic properties, especially in the coercivity Hc. It is shown that the magnetic properties of α-Fe/Nd2Fe14B nanocomposite are improved by an additional 5 at. % Ti, in particular, Hc from 595 up to 1006 kA/m, and (BH)max from 126.7 up to 135.3 kJ/m3. The coercivity mechanism of the α-Fe/Nd2Fe14B nanocomposite magnets was analyzed by studying the behavior of Hc(T)/Ms(T) versus HNmin(T)/Ms(T) (Kronmüller plot) and the dependence of Mirrev(H)/2Mr on the reverse field H. The results of this analysis show that nucleation is the dominating mechanism for the magnetization reversal in these nanocomposites. The Kronmüller plot gives evidence for a reduction in the exchange coupling resulting in an increase in the coercivity.
Ultrafast all-optical switching in AlGaAs photonic crystal waveguide interferometers
Authors: Szymanski D. M. , Jones B. D. , Skolnick M. S. , Fox A. M. , O’Brien D. , Krauss T. F. , Roberts J. S.
Published: October 2009

We have demonstrated ultrafast all-optical switching with photonic crystals integrated into AlGaAs Mach–Zehnder interferometers. The nonlinearity is induced by optical excitation of carriers into one arm of the interferometer, and switching times as short as 3 ps are achieved by surface recombination at the air holes in the photonic crystal. The fast recombination times and high nonlinearities of the AlGaAs material make this design suitable for high speed all-optical switching applications.
Metallic wire structures under an intense electromagnetic field
Authors: Chui S. T. , Zhang Weiyi
Published: October 2009

We discuss the limitation of metallic wire structures as absorbers of high intensity electromagnetic radiation due to the large local electrical fields developed at junctions and free ends of the wires. We find that at resonance the breakdown external electric field applied to the body of the wire structure is smaller by several orders of magnitude than the dielectric breakdown field induced at the ends of the wire. We consider the double split ring structure and find that it can offer an enhancement of the Ohmic power absorbed by an order of magnitude over those of single component systems. For multiple connected wire structures we find classes of resonant modes with zero local fields at the junctions but the fields at the free wire ends remain finite.
Analytical model for the 1∕f noise in the tunneling current through metal-oxide-semiconductor structures
Authors: Crupi F. , Giusi G. , Iannaccone G. , Magnone P. , Pace C. , Simoen E. , Claeys C.
Published: October 2009

In this paper we propose an analytical model for the 1∕f noise in the tunneling current through metal-oxide-semiconductor structures. The 1∕f noise is ascribed to the superimposition of random telegraph signals due to elastic electron tunneling from the inversion layer to oxide traps and vice versa. The model is based on the observation that an electron trapped in the dielectric locally increases the potential barrier thus reducing the current density. The local reduction in the current density is described in terms of an effective blocking area where the current density is null when the electron is trapped. The radius of the blocking area depends smoothly on the trap spatial position and on the applied voltage, and it is roughly equal to half of the oxide thickness. Detrapping to the gate is not considered. Numerical simulations show that it is important only in a thin intermediate region inside the oxide and that the corresponding power contribution is negligible respect to that generated by traps closer to the substrate interface. The model allows us to extract an effective trap density inside the dielectric as a function of the Fermi energy from current 1∕f noise measurements for different bias voltages. Trap densities in the order of 1020cm−3eV−1 are obtained from 1∕f noise measurements carried on SiO2/polysilicon gate n-metal-oxide-semiconductor-field-effect-transistors (nMOSFETs) which are in agreement with values already reported by previous works. Experiments have confirmed the area, frequency, and bias dependence of the gate current noise predicted by the proposed model.
Microscopic mechanism of leakage currents in silica junctions
Authors: Luo Xin , Wang Biao , Zheng Yue
Published: October 2009

Combining the nonequilibrium Green’s functions with the density-functional theory, we investigated the structural and electronic properties of silica junctions sandwiched between Al electrodes. The results show that the oxygen vacancies and tensile strain field play an important role in the electron transport properties of these two-probe systems. Sizable changes in leakage current across the barrier are found for the oxygen deficient system. It is found that Si dangling bonds formed by the introduction of oxygen vacancies are the main building blocks of the conduction channel in silica thin film. The midband gap states generated by the Si dangling bonds contribute to the leakage current. Detail analysis shows that four conduction channels are generated in silica junction after the presence of oxygen vacancies, resulting in a large enhancement of the electron transmission coefficient at the Fermi level. This leakage current mechanism provides useful information in the microelectronic designs.
Pitch-angle diffusion of ions via nonresonant interaction with Alfvénic turbulence
Authors: Yoon P. H. , Wang C. B. , Wu C. S.
Published: October 2009

The present discussion revisits the problem of nonresonant heating of ions by Alfvénic turbulence. It is shown that in the limit of weak Alfvénic turbulence it is appropriate to describe the nonresonant heating of protons as perpendicular pseudoheating. However, in a more general situation it is demonstrated that the more appropriate view of the nonresonant heating process is the pitch-angle scattering in the wave frame. The purpose of this paper is to generalize the earlier theory to the case in which the energy density of the turbulent Alfvén waves is not necessarily very low. For weakly turbulent situation the present analysis confirms the earlier finding by Wu and Yoon [Phys. Rev. Lett. 99, 075001 (2007)], according to whom the nonresonant Alfvén wave heating is described as leading to perpendicular pseudoheating of the protons. However, for more general situation the present paper demonstrates that pitch-angle scattering plays the principal role in the Alfvén wave pseudoheating process, and thereby shows that the perpendicular heating discussed by Wu and Yoon is kinetic in nature, not attributable to fluid motion.
Influence of quantum-interference on the fringing-field magnetoresistance of hybrid ferromagnetic/semiconductor devices
Authors: Lin T.-Y. , Bae J.-U. , Bohra G. , Lim K. , Reno J. L. , Bird J. P.
Published: October 2009

We investigate magnetotransport in hybrid ferromagnetic devices, comprised of laterally confined semiconductor channels that are bridged by nanomagnets that generate magnetic barriers. We identify a regime of low-temperature behavior in these devices, in which the magnetoresistance generated by the nanomagnets is suppressed with decrease of temperature. This result is shown to be correlated with the onset of quantum-interference effects (weak localization) in the semiconductor channel.
Imaging transient species in the femtosecond A-band photodissociation of CH3I
Authors: Durá J. , de Nalda R. , Amaral G. A. , Bañares L.
Published: October 2009

A nonresonant femtosecond laser pulse centered at 802 nm is used to probe the real time photodissociation dynamics of CH3I in the A-band at 267 nm. Using multiphoton ionization with this probe laser pulse and velocity map ion imaging of CH3+, we have followed the time evolution of the translational energy and spatial anisotropy of the CH3 fragment, which in turn has permitted to image the C–I bond breaking from the initial Franck–Condon region up to the final products along the reaction coordinate. Given the temporal width of our pump and probe laser pulses (∼80 fs), a mechanism is proposed by which transient species are probed by simultaneous absorption of pump and probe laser pulses through intermediate Rydberg and ionic states of CH3I while the pump and probe pulses overlap in time. This study shows how the combination of femtosecond multiphoton ionization and ion imaging techniques provides an ideal tool to resolve in time the different stages of the bond breaking event in a polyatomic molecule.
Dependence of long term stability on the initial radius of small inverted domains formed on congruent single-crystal LiTaO3
Authors: Odagawa Nozomi , Cho Yasuo
Published: October 2009

The dependence of the initial radius on the long term stability of small inverted domain dots was investigated by heat treatment of an 80-nm-thick congruent LiTaO3 plate with inverted domain dots with radii of 20–200 nm at 250 °C for 20 h. A linear relationship between the dot area after heat treatment and the initial dot area was determined, and the initial radius dependency on the long term stability of small inverted domains was formulated.
Magnetostriction-driven cantilevers for dynamic atomic force microscopy
Authors: Penedo M. , Fernández-Martínez I. , Costa-Krämer J. L. , Luna M. , Briones F.
Published: October 2009

An actuation mode is presented to drive the mechanical oscillation of cantilevers for dynamic atomic force microscopy. The method is based on direct mechanical excitation of the cantilevers coated with amorphous Fe–B–N thin films, by means of the film magnetostriction, i.e., the dimensional change in the film when magnetized. These amorphous magnetostrictive Fe–B–N thin films exhibit soft magnetic properties, excellent corrosion resistance in liquid environments, nearly zero accumulated stress when properly deposited, and good chemical stability. We present low noise and high resolution topographic images acquired in liquid environment to demonstrate the method capability.
Nonlinear evolution equations admitting multilinear variable separable solutions
Authors: Qu Changzheng , Shen Shoufeng
Published: October 2009

Based on the Hirota’s bilinear transformation method, it is shown that a family of nonlinear partial differential equations admit multilinear variable separation solutions. This extends the class of nonlinear partial differential equations which admit the multilinear variable separation solutions.
The response of carbon nanotube ensembles to fluid flow: Applications to mechanical property measurement and diagnostics
Authors: Deck C. P. , Ni C. , Vecchio K. S. , Bandaru P. R.
Published: October 2009

We demonstrate an experimental method to understand the mechanical response of carbon nanotube (CNT) ensembles to fluid flow through the measurement of the flexural rigidity EI, where E is the elastic modulus and I is the moment of inertia. A flexural rigidity (EI) of ∼7.5×10−16 N m2 was determined for the samples examined, by monitoring the transmitted light intensity for the CNTs subject to flow induced deflections. The robustness of the measurements was revealed through the digital response of CNTs to fluid flow and their use in gas flow diagnostics.
Controlling single cluster dynamics at the nanoscale
Authors: Paolicelli G. , Rovatti M. , Vanossi A. , Valeri S.
Published: October 2009

Gold nanoclusters deposited on highly oriented pyrolitic graphite are selectively detached and moved as a function of their size using the atomic force microscope. Control is obtained working in amplitude modulation and by tuning the interaction strength between oscillating tip and clusters. We show that fundamental controlling parameter is the energy dissipation that can be adjusted varying the tip amplitude oscillation and monitoring the phase shift signal. We characterize the energy detachment threshold of nanoclusters with sizes of 24 and 42 nm of diameter, then we precisely induce and control the movement of clusters with diameter below 40 nm within a mixed deposition.
A magneto-optic probe for magnetic fluctuation measurements
Authors: Przybysz W. S. , Ellis J. , Thakur S. Chakraborty , Hansen A. , Hardin R. A. , Sears S. , Scime E. E.
Published: October 2009

Results from a proof-of-principle experiment are presented that demonstrate it is possible to construct a completely optical, robust, and compact probe capable of spatially resolved measurements of magnetic field fluctuations smaller than 1 G over a frequency range of 1 Hz–8 MHz in a plasma. In contrast to conventional coil probes, the signal strength is independent of fluctuation frequency and the measurement technique is immune to electrostatic pickup. The probe consists of a high Verdet constant crystal, two polarizers, optical fibers, and a photodetector.