bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen and phosphorus as limiting factors for growth and primary production in a flooded savanna in the Venezuelan Llanos
Authors: Sarmiento Guillermo , da Silva Marta Pereira , Naranjo Maria Elena , Pinillos Marcela
Published: February 2006

The effects of N, P, NP and NPKS application on plant growth, above-ground primary production and N and P accumulation in the above-ground biomass of a flooded savanna were assessed over two growth cycles. Application of N or P did not improve plant growth and primary production, addition of NP had a noticeable effect, whereas NPKS fertilization led to a three-fold increase in plant production. The four most important grasses in the analysed ecosystem responded to nutrient application with increasing growth, indicating that they all are constrained by nutrient availability, but each species exhibited a different seasonal growth pattern suggesting a temporal division of nutrient resources. N accumulated in the harvested biomass during the growth season was 50% above that of control plants when NP was applied and showed a four-fold increase when NPKS was added. With NP addition, in 2 mo plants accumulated three times more P in the harvested biomass than the control plants. The maximum N accumulated during the growth season in the NPKS treatment represented half the fertilizer N, and probably all the N added (15 g m−2) may have been used if the whole biomass had been considered. With the rather small amounts of P added to the soil in the P treatment (2 g m−2), the maximum amount of P accumulated after 2 mo scarcely represented 13% of the added P, suggesting that most of the fertilizer P became rapidly immobilized or sorbed, not being available to plants in the short term. However, the increasing growth rates of grasses during the following 7 mo indicate that some P fluxed from these pools to the soil solution and to plants.
The evolution of human fatness and susceptibility to obesity: an ethological approach
Authors: Wells Jonathan C. K.
Published: February 2006

Human susceptibility to obesity is an unusual phenomenon amongst animals. An evolutionary analysis, identifying factors favouring the capacity for fat deposition, may aid in the development of preventive public health strategies. This article considers the proximate causes, ontogeny, fitness value and evolutionary history of human fat deposition. Proximate causes include diet composition, physical activity level, feeding behaviour, endocrine and genetic factors, psychological traits, and exposure to broader environmental factors. Fat deposition peaks during late gestation and early infancy, and again during adolescence in females. As in other species, human fat stores not only buffer malnutrition, but also regulate reproduction and immune function, and are subject to sexual selection. Nevertheless, our characteristic ontogenetic pattern of fat deposition, along with relatively high fatness in adulthood, contrasts with the phenotype of other mammals occupying the tropical savannah environment in which hominids evolved. The increased value of energy stores in our species can be attributed to factors increasing either uncertainty in energy availability, or vulnerability to that uncertainty. Early hominid evolution was characterised by adaptation to a more seasonal environment, when selection would have favoured general thriftiness. The evolution of the large expensive brain in the genus Homo then favoured increased energy stores in the reproducing female, and in the offspring in early life. More recently, the introduction of agriculture has had three significant effects: exposure to regular famine; adaptation to a variety of local niches favouring population‐specific adaptations; and the development of social hierarchies which predispose to differential exposure to environmental pressures. Thus, humans have persistently encountered greater energy stress than that experienced by their closest living relatives during recent evolution. The capacity to accumulate fat has therefore been a major adaptive feature of our species, but is now increasingly maladaptive in the modern environment where fluctuations in energy supply have been minimised, and productivity is dependent on mechanisation rather than physical effort. Alterations to the obesogenic environment are predicted to play a key role in reducing the prevalence of obesity.
Qualitative and quantitative changes in marine biofilms as a function of temperature and salinity in summer and winter
Authors: Chiu J. M. Y. , Thiyagarajan V. , Tsoi M. M. Y. , Qian P. Y.
Published: February 2006

This study examined quantitative (dry weight, chlorophyll a content and C : N ratio) and qualitative (community compositions of bacteria and diatoms) changes in marine biofilms as a function of season (summer 2003 and winter 2004), temperature (16, 23 and 30°C) and salinity (20‰, 27‰ and 34‰) under laboratory conditions. Biofilms were allowed to develop for 20 days in the laboratory, using natural sea water collected from Port Shelter, Hong Kong. The following results were obtained: (1) biofilm dry weight was greater in summer than in winter, and greater at 34‰ than at 20‰; (2) biofilm chlorophyll a content was affected by all three factors (season, temperature and salinity), with significant interactive effects among the three factors; and (3) C : N ratio was affected by season (winter > summer) and temperature (30°C>16°C in summer), but not by salinity. Bacterial community composition was analyzed by terminal restriction-fragment length polymorphism of polymerase chain reaction-amplified 16 S rRNA genes. In summer, community compositions of both bacteria and diatoms were strongly affected by salinity. In addition, natural summer biofilms that developed at three field sites, where different salinities were found, harbored appreciably different bacterial and diatom community compositions. In contrast, in winter, temperature exerted a major influence on community compositions. The present study adds to the growing evidence that environmental factors are important determinants of both the quality and quantity of marine biofilms.
Modeling the summertime evolution of sea‐ice melt ponds
Authors: Lüthje M. , Feltham D. L. , Taylor P. D. , Worster M. G.
Published: February 2006

We present a mathematical model describing the summer melting of sea ice. We simulate the evolution of melt ponds and determine area coverage and total surface ablation. The model predictions are tested for sensitivity to the melt rate of unponded ice, enhanced melt rate beneath the melt ponds, vertical seepage, and horizontal permeability. The model is initialized with surface topographies derived from laser altimetry corresponding to first‐year sea ice and multiyear sea ice. We predict that there are large differences in the depth of melt ponds and the area of coverage between the two types of ice. We also find that the vertical seepage rate and the melt rate of unponded ice are important in determining the total surface ablation and area covered by melt ponds.
Aerosol indirect effect studies at Southern Great Plains during the May 2003 Intensive Operations Period
Authors: Feingold Graham , Furrer Reinhard , Pilewskie Peter , Remer Lorraine A. , Min Qilong , Jonsson Haflidi
Published: February 2006

During May 2003 the Department of Energy's Atmospheric Radiation Measurement Program conducted an Intensive Operations Period (IOP) to measure the radiative effects of aerosol and clouds. A suite of both in situ and remote sensing measurements were available to measure aerosol and cloud parameters. This paper has three main goals: First, it focuses on comparison between in situ retrievals of the radiatively important drop effective radius re and various satellite, airborne, and surface remote sensing retrievals of the same parameter. On 17 May 2003, there was a fortuitous, near‐simultaneous sampling of a stratus cloud by five different methods. The retrievals of re agree with one another to within ∼20%, which is approximately the error estimate for most methods. Second, a methodology for deriving a best estimate of re from these different instruments, with their different physical properties and sampling volumes, is proposed and applied to the 17 May event. Third, the paper examines the response of re to changes in aerosol on 3 days during the experiment and examines the consistency of remote sensing and in situ measurements of the effect of aerosol on re. It is shown that in spite of the generally good agreement in derived re, the magnitude of the response of re to changes in aerosol is quite sensitive to the method of retrieving re and to the aerosol proxy for cloud condensation nuclei. Nonphysical responses are sometimes noted, and it is suggested that further work needs to be done to refine these techniques.
Magnitude and variance of near‐bottom horizontal heat flux at the Main Endeavour hydrothermal vent field
Authors: Veirs Scott R. , McDuff Russell E. , Stahr Frederick R.
Published: February 2006

We characterize hydrothermal plumes and hydrography within the axial valley of the Endeavour segment (Juan de Fuca ridge, northeast Pacific) using data from an autonomous underwater vehicle, a lowered CTD, and two current meter moorings. Our survey of the Main Endeavour hydrothermal vent field (MEF) shows hydrographic variability on scales as short as ∼20 m and ∼10 min. Within the ∼100 m deep axial valley, the mean flow is 1–5 cm/s to the north, and tidal oscillations have ∼5 cm/s amplitude. Combining the mean flow with an estimate of the difference in average temperature observed north and south of MEF, we find that the net along‐axis horizontal heat flux has a mean magnitude of ∼8–42 MW. An advection/diffusion model forced by local current records explains the observed temporal hydrographic variability and shows that mean horizontal flux variance is correspondingly high (standard deviation ∼63 MW). A steady state MEF heat budget, constrained by the observed horizontal flux and measurements of vertical fluxes from other studies, has two implications: the MEF heat flux is partitioned about equally between diffuse and focused vents, and about 85% of the flux from diffuse plumes is entrained by focused plumes.
Metal‐silicate segregation in deforming dunitic rocks
Authors: Hustoft Justin W. , Kohlstedt David L.
Published: February 2006

We report the results of an investigation of the microstructural evolution of rocks composed of a silicate plus a molten metal sulfide phase deformed plastically in simple shear. Deformation experiments on samples of San Carlos olivine (Fo90) + 3, 5, or 9 vol% iron sulfide reveal the segregation of iron sulfide melt from the solid polycrystalline olivine matrix into regions enriched in metallic melt separated by regions depleted in the metallic melt. Previously published experimental studies on core‐composition metals in silicate rocks, performed under hydrostatic pressure conditions, suggested that metallic melts could not segregate from silicates by porous flow below a critical melt fraction of ∼0.05. In contrast, we demonstrate that metallic melts can segregate from solid silicates by grain boundary percolation assisted by deformation, down to a pinch‐off melt fraction of ∼0.01. The segregated metallic melt can accumulate into bands containing melt fractions exceeding 0.3. Using a model network of melt‐rich sheets with melt fractions of 0.3, calculated Earth‐scale permeabilities are as high as 10−9m2. Segregation velocities for these sulfide melts can be up to 150 km/yr, fast enough for formation of Earth's core to proceed by deformation‐induced segregation well within the geochemically determined timescale of 30 million years. Therefore plastic deformation can facilitate removal of large enough quantities of metallic liquid from a solid silicate mantle to satisfy the geochemical constraints of the inefficient core formation theory without invoking the presence of a magma ocean.
ODP Site 1224: A missing link in the investigation of seafloor weathering
Authors: Paul Heather J. , Gillis Kathryn M. , Coggon Rosalind M. , Teagle Damon A. H.
Published: February 2006

A section of Eocene (46 Ma) upper oceanic crust was recovered at Ocean Drilling Program (ODP) Site 1224 in the northeast Pacific basin. The secondary mineralogy and geochemistry of altered basalts and isotopic composition of Ca‐carbonate were studied to determine the extent and nature of alteration at this site. Most basalts are <5% altered to secondary mineral assemblages of Fe‐oxyhydroxides, celadonite, saponite, Ca‐carbonate, trace pyrite, and rare phillipsite and quartz. Alteration is concentrated within brown and dark gray haloes, which formed adjacent to veins and fractures. Haloes comprise 10% of the core (9% dark gray; 1% brown); veins comprise <1% of the core, with an average of 18 veins per meter of recovered cores. Calculated chemical fluxes, which account for groundmass alteration and the composition and abundance of secondary minerals associated with veins, vesicles, and haloes, indicate significant additions of Si, FeT, Mg, Ca, and CO2 and minor additions of Al, Mn, and Na to the crust. The magnitude of these fluxes is low relative to other drilled volcanic sections such as Sites 504, 896, 417, and 418. 87Sr/86Sr ratios (0.70776 to 0.70824) and trace element ratios (Mg/Ca) of calcite imply that Ca‐carbonate formed within 20 Ma of crustal formation from relatively unaltered seawater. Oxygen isotope data yield Ca‐carbonate formation temperatures of 4 to 11°C. The relative freshness of the Site 1224 lavas is attributed to the capping of the volcanic section by massive flows.
Atmospheric iron fluxes over the last deglaciation: Climatic implications
Authors: Gaspari Vania , Barbante Carlo , Cozzi Giulio , Cescon Paolo , Boutron Claude F. , Gabrielli Paolo , Capodaglio Gabriele , Ferrari Christophe , Petit Jean Robert , Delmonte Barbara
Published: February 2006

A decrease in the micronutrient iron supply to the Southern Ocean is widely believed to be involved in the atmospheric CO2 increase during the last deglaciation. Here we report the first record of atmospheric iron fluxes as determined in 166 samples of the Dome C ice core and covering the last glacial‐interglacial transition (22–9 kyr B.P.). It reveals a decrease in fallout flux from 24 × 10−2 mg Fe m−2 yr−1 during the Last Glacial Maximum to 0.7 × 10−2 mg Fe m−2 yr−1 at the onset of the Holocene. The acid leachable fraction of iron determined in our samples was the 60% of the total iron mass in glacial samples, about twice the value found for Holocene samples. This emerging difference in iron solubility over different climatic stages provides a new insight for evaluating the iron hypothesis over glacial/interglacial periods.
Upper mantle thermal variations beneath the Transantarctic Mountains inferred from teleseismic S‐wave attenuation
Authors: Lawrence Jesse F. , Wiens Douglas A. , Nyblade Andrew A. , Anandakrishan Sridhar , Shore Patrick J. , Voigt Donald
Published: February 2006

This study examines teleseismic S‐wave attenuation variations between the Ross Sea in West Antarctica and Vostok Subglacial Highlands in East Antarctica. These analyses indicate that δt* is ∼1 second greater beneath the Ross Sea than East Antarctica, with the transition occurring beneath the Transantarctic Mountains. While the structure is non‐unique, low attenuation beneath East Antarctica is consistent with thick subcontinental lithosphere (≥250 km) and negligible asthenosphere. In contrast, the Ross Sea possesses a thin lithosphere underlain by thick, highly anelastic asthenosphere. Independent temperature estimates from velocity and quality factor indicate that the mantle is 200–400°C colder beneath East Antarctica than the Ross Sea between 80 and 220 km depth. The temperature variation beneath the Transantarctic Mountains may have assisted in the asymmetric uplift of the mountains. Attenuation and velocity anomalies within East Antarctica may delineate regions of elevated temperature, representing recently modified sections between older lithospheric blocks.
Neutral atom emission in the direction of the high‐latitude magnetopause for northward IMF: Simultaneous observations from IMAGE spacecraft and SuperDARN radar
Authors: Taguchi S. , Hosokawa K. , Nakao A. , Collier M. R. , Moore T. E. , Yamazaki A. , Sato N. , Yukimatu A. S.
Published: February 2006

During a northward interplanetary magnetic field on 27 March 2001, the Low Energy Neutral Atom (LENA) imager on the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) spacecraft in the magnetosphere observed an enhanced emission in the direction of the very high‐latitude magnetopause. Simultaneous observations from IMAGE/LENA and SuperDARN radar show that the LENA emission appears concurrently with the enhancement of the sunward flow of the reverse convection in the ionosphere. The field line mapping from the magnetosphere to the ionosphere suggests that the source ions for the LENA emission are in the sunward flow region. Although the direction of the emission is relatively stable, its direction changes slightly so that the emission may shift poleward or equatorward. From these observations, we suggest that LENA can monitor the ion entry caused by cusp reconnection and that the reconnection site moves on a timescale of several minutes.
Field measurements of sintering after fracture of snowpack weak layers
Authors: Birkeland Karl W. , Kronholm Kalle , Logan Spencer , Schweizer Jürg
Published: February 2006

This research documents two cases where field workers unintentionally fractured a snowpack weak layer, but no avalanche released. Measurements from before and after the fractures provide unique data sets on the temporal change of snow stability. Shear strength decreased immediately after fracture on both slopes. Subsequent strengthening occurred in both cases, though the rates differed presumably due to the characteristics of the weak layers. Our results have two important implications. First, they suggest the sub‐critical weak layer fractures assumed as a prerequisite in some snow slab avalanche release models are transient features, and future modeling efforts must take this into account. Second, they provide insights into interpreting snow stability tests and assessing the stability of slopes with fractured weak layers.
Upwelling around Cabo Frio, Brazil: The importance of wind stress curl
Authors: Castelao Renato M. , Barth John A.
Published: February 2006

Data from the SeaWinds scatterometer on the QuikSCAT satellite are used to estimate upwelling around Cabo Frio, Brazil, due to Ekman transport and Ekman pumping. The region close to shore (up to 200 km from the coast) is characterized by negative wind stress curl (upwelling favorable) year‐round, with maximum values during summer, and minimum values during fall. Integrated values from São Sebastião Island to Vitória reveal that during summer, Ekman pumping and Ekman transport are of the same magnitude in the region. Estimates of Ekman transport are relatively uniform along the coast during summer. Ekman pumping, on the other hand, is strongly enhanced between São Sebastião Island and Vitória, the region where the coldest water on satellite images is frequently found. This suggests that wind stress curl‐driven upwelling is a major contributor to the coldest surface water being found near Cabo Frio.
Spatial and temporal evolution of the subducting Pacific plate structure along the western Pacific margin
Authors: Miller M. S. , Kennett B. L. N. , Toy V. G.
Published: February 2006

Tomographic images of the subducting Pacific plate beneath the Izu‐Bonin‐Mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc. Recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western Pacific island arcs, but reasons for the variation in geometry and morphology are still poorly understood. By comparing high‐resolution tomographic images of the western Pacific and updated paleogeographic reconstructions, we are able to link the spatiotemporal evolution of the subducting Pacific plate back to the mid‐Miocene. We have reconstructed tectonic motions along the Kurile‐Japan‐Izu‐Bonin‐Mariana arc system and the Ryukyu arc to provide an independent, additional interpretation of the subducting Pacific plate using the most current plate motion data. We then investigate the plausibility of our model and three other proposed models based on the interpreted slab structure from tomographic images. The new reconstruction agrees with the basic characteristics of former trench retreat models but illustrates the importance of the collision of the Ogasawara Plateau with the trench in the mid‐Miocene and its subsequent effect on the slab structure at depth and the impact of other aseismic ridge collisions along the plate boundary. The combination of evidence in changed physical properties imaged with tomography and the current interpreted slab morphology can be analyzed with the past plate motions to understand subduction zone processes.
Estimating forest carbon fluxes in a disturbed southeastern landscape: Integration of remote sensing, forest inventory, and biogeochemical modeling
Authors: Masek Jeffrey G. , Collatz G. James
Published: February 2006

Quantifying carbon fluxes between the atmosphere and land surface requires detailed knowledge of the disturbance regime as well as the photosynthetic response of vegetation to climate. In this study, we use a combination of satellite remote sensing, forest inventory data, and biogeochemical modeling to assess forest carbon fluxes from central Virginia, a landscape pervasively disturbed by harvest. Using historical Landsat imagery, we have reconstructed the disturbance history and age structure of forest stands at a resolution of 90 m, from 1973–1999. Forest inventory data provide breakdowns of forest type and age structure for older stands. These data, together with climate and vegetation greenness from advanced very high resolution radiometer (AVHRR), are used as inputs to a version of the Carnegie‐Stanford‐Ames (CASA) biogeochemical model, which simulates the uptake, allocation, and respiration of carbon and associated effects of disturbance. Modeling results indicate that forests in the study region have an average net ecosystem productivity (NEP) of ∼80 gC m−2 yr−1, reflecting the young age structure of rapid‐rotation forests. Variability in annual forest carbon fluxes due to variations in clearing rate and climate are also examined. We find that observed variations in clearing rate may account for NEP variability of ∼30 gC m−2 yr−1, while observed variations in climate may account for NEP variability of 80–130 gC m−2 yr−1. Increased temperatures tend to drive both increased photosynthesis and increased heterotrophic respiration, buffering the system from larger swings in NEP. However, this response depends strongly on stand age.
Depth distribution of magnetofossils in near‐surface sediments from the Blake/Bahama Outer Ridge, western North Atlantic Ocean, determined by low‐temperature magnetism
Authors: Housen Bernard A. , Moskowitz Bruce M.
Published: February 2006

Fe‐oxide and Fe‐sulfide trace minerals in sediments and sedimentary rocks provide proxy records of biogeochemical processes, record past variations in the geomagnetic field, and can serve as proxies for climatic variations. An important class of these Fe‐oxides is produced by bacteria. Magnetic particles produced by magnetotactic bacteria have been proposed as a primary recorder of the geomagnetic field in many terrestrial marine sediments, and have also been suggested to represent fossil evidence of life on the planet Mars. To better understand their distribution and preservation in the sediment column, and their relationship to other biochemical processes, we present rock‐magnetic data that document the occurrence and abundance of fossil biogenic magnetite (magnetofossils) in marine sediments from the Blake/Bahama Outer Ridge. Magnetic hysteresis and low‐temperature magnetism both indicate that the occurrence of magnetofossils is closely linked to the depth of the modern Fe‐redox boundary within the sediment column, and that a fraction of the magnetic minerals in the sediment column above the Fe‐redox boundary are in the form of intact and relatively unaltered chains of nanophase magnetite crystals. Below the Fe‐redox boundary the abundance of these magnetofossils is markedly decreased. The important conclusions of this work are to demonstrate that nondestructive rock‐magnetic methods can be used to successfully document the occurrence and relative abundance of magnetofossils in geologic materials.
Transcription in four dimensions: nuclear receptor‐directed initiation of gene expression
Authors: Métivier Raphaël , Reid George , Gannon Frank
Published: February 2006

Regulated gene expression, achieved through the coordinated assembly of transcription factors, co‐regulators and the basal transcription machinery on promoters, is an initial step in accomplishing cell specificity and homeostasis. Traditional models of transcriptional regulation tend to be static, although gene expression profiles change with time to adapt to developmental and environmental cues. Furthermore, biochemical and structural studies have determined that initiation of transcription progresses through a series of ordered events. By integrating time into the analysis of transcription, chromatin immunoprecipitation assays and live‐cell imaging techniques have revealed the dynamic, cooperative, functionally redundant and cyclical nature of gene expression. In this review, we present a dynamic model of gene transcription that integrates data obtained by these two techniques.
CH
stretch/internal rotor dynamics in ethyl radical: High-resolution spectroscopy in the CH3-stretch manifold
Authors: Häber Thomas , Blair Andrew C. , Nesbitt David J. , Schuder Michael D.
Published: February 2006

High-resolution IR absorption spectra of supersonically cooled ethyl radicals (Trot≈20K) have been obtained in a slit supersonic jet discharge expansion, revealing first rotationally resolved data for CH-stretch excitation of the methyl group. Three different vibrational bands are observed, one parallel (k=0←0) and two perpendicular (∣k∣=1←0), which for a nearly decoupled methyl rotor framework would correspond to symmetric and (nearly degenerate) asymmetric CH-stretch excitations. However, the splitting between the two asymmetric CH-stretch excitations is anomalously large (≈125cm−1), signaling the presence of interactions between the CH2 radical moiety and the opposing CH bond on the methyl group. This suggests an improved zeroth-order vibrational description as an isolated CH stretch, strongly redshifted by hyperconjugation, with localized vibrations in the remaining CH bonds split into symmetric and asymmetric stretches. Such a dynamical picture highlights a remarkably strong coupling between methyl CH-stretch vibrations and C–C torsional geometry and begins to elucidate discrepancies with previous matrix observations.
Crystallographic and morphological characterization of thin pentacene films on polycrystalline copper surfaces
Authors: Oehzelt M. , Resel R. , Suess C. , Friedlein R. , Salaneck W. R.
Published: February 2006

The degree of crystallinity, the structure and orientation of crystallites, and the morphology of thin pentacene films grown by vapor deposition in an ultrahigh vacuum environment on polycrystalline copper substrates have been investigated by x-ray diffraction and tapping-mode scanning force microscopy (TM-SFM). Depending on the substrate temperature during deposition, very different results are obtained: While at 77K a long-range order is missing, the films become crystalline at elevated temperatures. From a high-resolution x-ray-diffraction profile analysis, the volume-weighted size of the crystallites perpendicular to the film surface could be determined. This size of the crystallites increases strongly upon changing temperature between room temperature and 333K, at which point the size of individual crystallites typically exceeds 100nm. In this temperature region, three different polymorphs are identified. The vast majority of crystallites have a fiber texture with the (001) net planes parallel to the substrate. In this geometry, the molecules are oriented standing up on the substrate (end-on arrangement). This alignment is remarkably different from that on single-crystalline metal surfaces, indicating that the growth is not epitaxial. Additionally, TM-SFM images show needlelike structures which suggest the presence of at least one additional orientation of crystallites (flat-on or edge-on). These results indicate that properties of thin crystalline pentacene films prepared on technologically relevant polycrystalline metal substrates for fast electronic applications may be compromised by the simultaneous presence of different local molecular aggregation states at all temperatures.
Permanent electric dipole moments of four tryptamine conformers in the gas phase: A new diagnostic of structure and dynamics
Authors: Nguyen Tri V. , Pratt David W.
Published: February 2006

Rotationally resolved electronic spectroscopy in the gas phase, in the absence and presence of an applied electric field, has been used to determine the charge distribution of a cross section of the energy landscape of tryptamine (TRA). We report the magnitude and direction of the permanent electric dipole moments of the four TRA conformers GPyout, GPyup, GPhup, and Antiup in their S0 and S1 electronic states. Each dipole moment is unique, providing a powerful new tool for the conformational analysis of biomolecules in the gas phase. A comparison of the results for the different conformers of TRA reveals that the position and orientation of the ethylamine side chain play a major role in determining both the permanent and induced electric dipole moments of the different species in both electronic states.
IR laser manipulation of cis↔trans isomerization of 2-naphthol and its hydrogen-bonded clusters
Authors: Kouyama Kyouko , Miyazaki Mitsuhiko , Mikami Naohiko , Ebata Takayuki
Published: February 2006

The cis↔trans isomerization reaction has been carried out for 2-naphthol and its hydrogen (H) bonded clusters by infrared (IR) laser in the electronic excited state (S1) in supersonic jets. A specific isomer in the jet was pumped to the X–H stretching vibration in the S1 state, where X refers to C, O, or N atom, by using a stepwise UV-IR excitation, and the dispersed emission spectra of the excited species or generated fragments were observed. It was found that the isomerization occurs only in the H-bonded clusters but a bare molecule does not exhibit the isomerization in the examined energy region of Ev⩽3610cm−1, indicating a reduction of the isomerization barrier height upon the H bonding. The relative yield of the isomerization was observed as a function of internal energy. The isomerization yield was found to be very high at the low IR frequency excitation, and was rapidly reduced with the IR frequency due to the competition of the dissociation of the H bond within the isomer. Density-functional theory (DFT) and time-dependent DFT calculations were performed for estimating the barrier height of the isomerization for bare 2-naphthol and its cluster for electronic ground and excited states. The calculation showed that the isomerization barrier height is highly dependent on the electronic states. However, the reduction of the height upon the hydrogen bonding was not suggested at the level of our calculation.
Study of elastic constant ratios in nematic liquid crystals
Authors: Strömer J. F. , Raynes E. P. , Brown C. V.
Published: February 2006

A technique has recently been proposed for determining the elastic constant ratio K22∕K11 in nematic liquid crystals [E. P. Raynes, C. V. Brown, and J. F. Strömer, Appl. Phys. Lett. 82, 13 (2003)]. This technique has been applied to five nematic materials that cover a range of K33∕K11 elastic constant ratio values. An unusually high value of K22∕K11 is found in one material. High values of the ratio K22∕K11 tended to occur in materials that also have high values of the ratio K33∕K11. The results are validated with independent measurements of K22 from cholesteric helix unwinding.
Inner-shell ionizations and satellites studied by the open-shell reference symmetry-adapted cluster/symmetry-adapted cluster configuration-interaction method
Authors: Ohtsuka Yuhki , Nakatsuji Hiroshi
Published: February 2006

Open-shell reference version of the symmetry-adapted cluster (SAC) and SAC-configuration-interaction (CI) methods, termed open-shell reference (OR)-SAC and OR-SAC-CI methods, are developed and applied to inner-shell ionizations of CH4,NH3,H2O, and HF. The inner-shell ionization potentials and spectra calculated by the OR-SAC and OR-SAC-CI methods are in excellent agreement with the experimental data. Including both of the electron correlation and orbital relaxation is important for quantitative agreements. Timing comparisons with the SAC-CI general-R calculations that give similar high accuracies show an efficiency of the present OR-SAC and OR-SAC-CI methods.
An effective pair potential for thermodynamics and structural properties of liquid mercury
Authors: Bomont Jean-Marc , Bretonnet Jean-Louis
Published: February 2006

The properties of liquid mercury are investigated by using an empirical effective pair potential. Its parameters are determined with the aid of Monte Carlo simulation along the liquid branch of the liquid-vapor coexistence curve. The complexity of the electronic structure of dense metal mercury supposes a state dependence of the interatomic interactions, while no more state dependence is found in the metal-nonmetal transition region. It is shown that the use of this effective potential leads to an accurate description of the structural and thermodynamic properties of the expanded liquid mercury. Then, the melting and freezing phenomena are investigated with that potential. Sharp melting and freezing temperatures are observed at 234 and 169K, respectively. This large hysteresis loop between freezing and melting is consistent with the experiments for the bulk mercury.
Critical behavior of the aqueous electrolytic system 3-methylpyridine+D2O+NaBr
Authors: Madhavan Unni P. K.
Published: February 2006

The system 3-methylpyridine(3MP)+water(H2O)+NaBr has been the subject of an intense scientific debate since the work of Jacob et al. [Phys. Rev. E. 58, 2188 (1988)] and Anisimov et al. [Phys. Rev. Lett. 85, 2336 (2000)]. The crossover critical behavior of this system seemed to show remarkable sensitivity to the weight fraction (X) of the ionic impurity NaBr. In the range X⩽0.10 the system displayed Ising behavior and a pronounced crossover to mean-field behavior in the range 0.10⩽X⩽0.16. A complete mean-field behavior was observed at X=0.17, a result that was later attributed to the existence of long-living nonequilibrium states in this system [Kostko et al., Phys. Rev. E. 70, 026118 (2004)]. In this paper, we report the near-critical behavior of osmotic susceptibility in the isotopically related ternary system, 3MP+heavywater(D2O)+NaBr. Detailed light-scattering experiments performed at exactly the same NaBr concentrations as investigated by Jacob et al. reveal that the system 3MP+D2O+NaBr shows a simple Ising-type critical behavior with γ≃1.24 and ν≃0.63 over the entire NaBr concentration range 0⩽X⩽0.1900. The crossover behavior is predominantly nonmonotonic and is completed well outside the critical domain. An analysis in terms of the effective susceptibility exponent (γeff) reveals that the crossover behavior is nonmonotonic for 0⩽X⩽0.1793 and tends to become monotonic for X>0.1793. The correlation length amplitude ξo, has a value of ≃2Å for 0.0250⩽X⩽0.1900, whereas for X=0, ξo≃3.179Å. Since isotopic H→D substitution is not expected to change the critical behavior of the system, our results support the recent results obtained by Kostko et al. [Phys. Rev. E. 70, 026118 (2004)] that 3MP+H2O+NaBr exhibits universal Ising-type critical behavior typical for other aqueous solutions.
Single electron tunneling transistor with tunable barriers using silicon nanowire metal-oxide-semiconductor field-effect transistor
Authors: Fujiwara Akira , Inokawa Hiroshi , Yamazaki Kenji , Namatsu Hideo , Takahashi Yasuo , Zimmerman Neil M. , Martin Stuart B.
Published: February 2006

We have achieved the operation of single-electron tunneling (SET) transistors with gate-induced electrostatic barriers using silicon nanowire metal-oxide-semiconductor field-effect transistor (MOSFET) structures. The conductance of tunnel barriers is tunable by more than three orders of magnitude. By using the flexible control of the tunable barriers, the systematic evolution from a single charge island to double islands was clearly observed. We obtained excellent reproducibility in the gate capacitances: values on the order of 10 aF, with the variation smaller than 1 aF. This flexibility and controllability both demonstrate that the device is highly designable to build a variety of SET devices based on complementary metal-oxide-semiconductor technology.
Observation of thermally activated domain wall transformations
Authors: Laufenberg M. , Backes D. , Bührer W. , Bedau D. , Kläui M. , Rüdiger U. , Vaz C. A. F. , Bland J. A. C. , Heyderman L. J. , Nolting F. , Cherifi S. , Locatelli A. , Belkhou R. , Heun S. , Bauer E.
Published: February 2006

The spin structure of head-to-head domain walls in Ni80Fe20 structures is studied using high-resolution photoemission electron microscopy. The quantitative phase diagram is extracted from these measurements and found to exhibit two phase boundaries between vortex and transverse domain walls. The results are compared with available theoretical predictions and micromagnetic simulations and differences to the experiment are explained, taking into account thermal excitations. Temperature-dependent measurements show a thermally activated transformation of transverse to vortex domain walls in 7 nm thick and 730 nm wide structures at a transition temperature between 260 °C and 310 °C, which corresponds to a nucleation barrier height for a vortex wall between 6.7×10−21J and 8.0×10−21J.
Electrical noise in gold nanocluster sensors
Authors: Kruppa W. , Ancona M. G. , Rendell R. W. , Snow A. W. , Foos E. E. , Bass R.
Published: February 2006

Motivated by applications to chemiresistive vapor sensing, the electrical noise properties of large-area gold nanocluster films are investigated experimentally. Measurements show thermal noise to dominate at low voltages and high frequencies, with a 1∕f noise component becoming more important at a higher voltage and a lower frequency. The latter contribution obeys the Hooge formula in its frequency, voltage, and size dependences, and with a Hooge parameter whose relatively large size is attributed to constraints imposed by Coulomb blockade and disorder. Based on these results, a detection limit for nanocluster-based chemiresistors can be projected to approach one part per billion by volume.
Thermal donor formation processes in silicon and the catalytic role of hydrogen
Authors: Tsetseris L. , Wang Sanwu , Pantelides S. T.
Published: February 2006

We report the results of first-principles calculations on the interactions of hydrogen with oxygen clusters in silicon and other processes that relate to the formation of thermal donors (TD). We find that pre-existing small O clusters transform to thermal donors with a low activation energy of 1.15 eV. Clusters formed due to O–H codiffusion bind H strongly in TD precursor configurations and H release requires high temperatures to overcome a 1.9 eV barrier, a value in agreement with experiments on the dissociation of TD-H complexes. Repeated trapping and release from such clusters establish a catalytic role for H in TD formation.
Nanometer-scale strain measurements in semiconductors: An innovative approach using the plasmon peak in electron energy loss spectra
Authors: Sanchez A. M. , Beanland R. , Papworth A. J. , Goodhew P. J. , Gass M. H.
Published: February 2006

We present an innovative technique for quantitative measurement of strain in semiconductor materials with high spatial resolution. The plasmon loss peak, seen in electron energy-loss spectra, has been considered following the Drude-Lorentz model, and we find that plasmon energy is extremely sensitive to lattice parameter. We have tested this model using a heterostructure of In0.2Ga0.8As and AlAs layers in GaAs. The experimental data are in excellent agreement with the model. We estimate that strains smaller than 0.036% can be detected, corresponding to a change of x=0.005 in InxGa1−xAs, at a spatial resolution better than 2.8 nm.
Enhanced spin injection polarization in Co∕Cu∕Co nonlocal lateral spin valves
Authors: Ji Y. , Hoffmann A. , Pearson J. E. , Bader S. D.
Published: February 2006

Nonlocal spin injection is demonstrated in Co∕Cu∕Co lateral spin valves. Measurement of a series of structures with varying Cu length between the Co electrodes permits a direct determination of both the Cu spin diffusion length λs and the spin injection polarization P at the Co∕Cu interface. The value of λs is 200±20nm at 10K and ⩾110nm at 300K, which is shorter than previously reported, due to the possible presence of impurities in the Cu. However, the value of P is >7%, which is improved compared with previous reports of 2%, which is attributed to a higher interfacial quality.
Exclusive-OR gate with a single carbon nanotube
Authors: Sordan R. , Balasubramanian K. , Burghard M. , Kern K.
Published: February 2006

Carbon nanotubes (CNTs) are now well-established as efficient channels for field-effect transistors (FETs). Logic circuitry based on CNTs have until now been demonstrated by replacing the silicon channel of a conventional metal-oxide-semiconducutor FET by a CNT. We propose a circuit design utilizing the ambipolarity of the Schottky-barrier-type CNT-FET to realize an exclusive-OR (XOR) gate using a single CNT. The merits and limitations of such a CNT-XOR gate with respect to conventional XOR gates are discussed.
Contact resistance modulation in carbon nanotube devices investigated by four-probe experiments
Authors: Kanbara Takayoshi , Takenobu Taishi , Takahashi Tetsuo , Iwasa Yoshihiro , Tsukagoshi Kazuhito , Aoyagi Yoshinobu , Kataura Hiromichi
Published: February 2006

The contact resistance (Rcont) between nanotube and metal electrodes was directly measured in a four-terminal configuration of field-effect transistors for individual single-walled carbon nanotube (SWNT) bundles and a multiwalled carbon nanotube (MWNT). Both Rcont and the nanotube resistance (RNT) in a semiconducting SWNT device drastically changed with gate voltage, while Rcont, being more than one-order smaller than Rcont in metallic SWNTs and MWNTs, was almost constant against the gate voltage. Carriers introduced either by gate voltage or chemical doping induced a rapid decrease in Rcont compared with the resistance of semiconducting SWNTs.
Acoustic mixing at low Reynold’s numbers
Authors: Sritharan K. , Strobl C. J. , Schneider M. F. , Wixforth A. , Guttenberg Z.
Published: February 2006

In microfluidic devices, hydrodynamic flow is usually governed by very low Reynold’s numbers. Under these conditions, only laminar flow is possible. Hence, mixing in microfluidics occurs by diffusion only. Interaction of small fluid volumes and acoustic waves in a solid leads to pronounced streaming effects in the fluid inducing mixing and stirring even at low Reynold’s numbers. We demonstrate the applicability of such acoustically induced mixing in a variety of different microfluidic geometries, including planar and conventional three-dimensional microfluidic devices.
Long wavelength emission of InGaAsN∕GaAsSb type II “W” quantum wells
Authors: Yeh J.-Y. , Mawst L. J. , Khandekar A. A. , Kuech T. F. , Vurgaftman I. , Meyer J. R. , Tansu N.
Published: February 2006

Low temperature (30K) long wavelength photoluminescence emission (λ=1400–1600nm) from metalorganic chemical vapor deposition grown InGaAsN–GaAsSb type II “W” quantum wells (QWs), on GaAs substrates has been demonstrated. Thin layers (2–3nm) and high antimony-content (30%) GaAsSb were utilized in this study for realizing satisfactory wave function overlap and long wavelength emission. Tensile strained GaAsP barriers effectively improve the material structural and luminescence properties of the compressive strained active region. Room temperature photoluminescence data show that the type-II QW design is a promising candidate for realizing long wavelength GaAs-based diode lasers beyond 1500nm.
Ordered-mesoporous-silica-thin-film-based chemical gas sensors with integrated optical polarimetric interferometry
Authors: Qi Zhi-mei , Honma Itaru , Zhou Haoshen
Published: February 2006

A technology to make integrated optical chemical gas sensors using sol-gel surfactant-templated mesoporous thin films was demonstrated. The sensor was prepared by dip coating of an ordered mesoporous silica thin film onto a tapered thin TiO2 layer sputtered on top of a tin-diffused glass waveguide. The sensor employs single-beam polarimetric interferometry to detect molecular adsorption in the mesoporous silica film because the adsorption can lead to a change of the phase difference (Δϕ) between the fundamental transverse electric (TE0) and magnetic (TM0) modes propagating in the waveguide. The sensor is sensitive to humidity and NH3 gas at room temperature (RT). The sensitivity of Δϕ>180° was detected for 40min exposure of the sensor to 2ppm of NH3 in dry air. The sensor was recoverable from the HN3 exposure but its recovery was too slow to cause a detectable Δϕ per unit time. The slow response and recovery of the sensor were ascribed to slow diffusion of gaseous molecules in the laterally oriented tube-like pores of the silica film.
Domain pinning in GaAs∕AlGaAs quantum well infrared photodetectors
Authors: Schneider H. , Schönbein C. , Rehm R. , Walther M. , Koidl P.
Published: February 2006

We have analyzed the spatial distribution of electric field domains induced by negative differential photoconductivity in n-type GaAs∕AlGaAs quantum well infrared photodetectors. We find strong evidence of two different domain configurations, with the high-field domain and the low-field domain, respectively, adjacent to the emitter contact. A distinctive signature of these domain configurations is provided by the observed total current, which is observed to be close to either the valley current or the peak current. We also discuss the emergence of the two configurations.
Micromagnetic properties of MnAs(0001)∕GaAs(111) epitaxial films
Authors: Engel-Herbert R. , Hesjedal T. , Schaadt D. M. , Däweritz L. , Ploog K. H.
Published: February 2006

The micromagnetic properties of MnAs thin films grown on the (111)B-oriented GaAs surface have been investigated. Compared to films grown on (001) surfaces, these films exhibit completely different domain patterns, as the c axis of the hexagonal unit cell is oriented normal to the surface. In the course of the first order phase transition, ferromagnetic α-MnAs forms a network of quasihexagonal areas separated by β-MnAs. We present an analysis of the micromagnetic properties based on imaging and simulations. We observe closure domains that either appear as a vortex-like state or a stripe structure.
Magnetic field dependence of voltage-current characteristics of Fe3O4 thin films at room temperature
Authors: Zhao Kun , Feng Jiafeng , Huang Yanhong , Zhao Jian-gao , Lu Huibin , Han Xiufeng , Zhan Wenshan
Published: February 2006

Fe 3 O 4 thin films have been fabricated on glass substrate by the facing-target sputtering technique and their field-modulated voltage-current behavior was investigated. The nonlinear dependence of voltage on current density displays a switching from high-resistivity to low-resistivity states above a threshold current density. The low-resistivity state is very sensitive to the applied magnetic field, and a large negative magnetoresistance of ∼−27% is observed at 300 Oe under a high current density of 100Acm−2 at room temperature. Furthermore, the dependence of the magnetoresistance on the magnetic field reveals a good linear relationship. The observed results seem to favor a picture of spin-polarized intergrain tunneling through the grain boundaries.