bluuebunny/crossref_metadata_2025 huggingface dataset:
Duplex ultrasound investigation of the veins in chronic venous disease of the lower limbs-UIP consensus document. Part II. Anatomy
Authors: Cavezzi  , Labropoulos  , Partsch  , Ricci  , Caggiati  , Myers  , Nicolaides  , Smith
Published: February 2007

Background: Duplex ultrasound investigation has become the reference standard in assessing the morphology and haemodynamics of the lower limb veins. The project described in this paper was an initiative of the Union Internationale de Phlébologie (UIP). The aim was to obtain a consensus of international experts on the methodology to be used for assessment of anatomy of superficial and perforating veins in the lower limb by ultrasound imaging. Methods: The authors performed a systematic review of the published literature on duplex anatomy of the superficial and perforating veins of the lower limbs; afterwards they invited a group of experts from a wide range of countries to participate in this project. Electronic submissions from the authors and the experts (text and images) were made available to all participants via the UIP website. The authors prepared a draft document for discussion at the UIP Chapter meeting held in San Diego, USA in August 2003. Following this meeting a revised manuscript was circulated to all participants and further comments were received by the authors and included in subsequent versions of the manuscript. Eventually, all participants agreed the final version of the paper. Results: The experts have made detailed recommendations concerning the methods to be used for duplex ultrasound examination as well as the interpretation of images and measurements obtained. This document provides a detailed methodology for complete ultrasound assessment of the anatomy of the superficial and perforating veins in the lower limbs. Conclusions: The authors and a large group of experts have agreed a methodology for the investigation of the lower limbs venous system by duplex ultrasonography, with specific reference to the anatomy of the main superficial veins and perforators of the lower limbs in healthy and varicose subjects.
Using the material‐point method to model sea ice dynamics
Authors: Sulsky Deborah , Schreyer Howard , Peterson Kara , Kwok Ron , Coon Max
Published: February 2007

The material‐point method (MPM) is a numerical method for continuum mechanics that combines the best aspects of Lagrangian and Eulerian discretizations. The material points provide a Lagrangian description of the ice that models convection naturally. Thus properties such as ice thickness and compactness are computed in a Lagrangian frame and do not suffer from errors associated with Eulerian advection schemes, such as artificial diffusion, dispersion, or oscillations near discontinuities. This desirable property is illustrated by solving transport of ice in uniform, rotational and convergent velocity fields. Moreover, the ice geometry is represented by unconnected material points rather than a grid. This representation facilitates modeling the large deformations observed in the Arctic, as well as localized deformation along leads, and admits a sharp representation of the ice edge. MPM also easily allows the use of any ice constitutive model. The versatility of MPM is demonstrated by using two constitutive models for simulations of wind‐driven ice. The first model is a standard viscous‐plastic model with two thickness categories. The MPM solution to the viscous‐plastic model agrees with previously published results using finite elements. The second model is a new elastic‐decohesive model that explicitly represents leads. The model includes a mechanism to initiate leads, and to predict their orientation and width. The elastic‐decohesion model can provide similar overall deformation as the viscous‐plastic model; however, explicit regions of opening and shear are predicted. Furthermore, the efficiency of MPM with the elastic‐decohesive model is competitive with the current best methods for sea ice dynamics.
Hierarchy of models for meandering rivers and related morphodynamic processes
Authors: Camporeale C. , Perona P. , Porporato A. , Ridolfi L.
Published: February 2007

We review the importance of the physical mechanisms involved in river meandering by comparing some existing linear models and extensions thereof. Such models are hierarchically derived from a common and general mathematical framework and then analyzed with a detailed discussion of the physical processes and relevant hypotheses that are involved. Experiments and field data are also used to discuss the related morphodynamic processes. The analysis of the models shows the importance of the closure of secondary currents especially in the modeling of eddy viscosity. This aspect confirms the usefulness of using simplified models for some practical applications, provided the secondary currents are modeled in detail. On the other hand, the free response of the sediments, the phase lag of secondary currents, and the momentum redistribution due to the coupling between the main and the transverse flow are shown to be less relevant. Hence the second‐order models, which neglect the effect of superelevation induced by the topography‐driven lateral flow on the longitudinal flow, can reasonably be considered a good approximation for both predictive analysis and the computation of the resonant conditions. Finally, the analysis of higher harmonics suggests that the multilobed pattern can intrinsically be present in both second‐ and fourth‐order models.
Reach‐averaged sediment routing model of a canyon river
Authors: Wiele S. M. , Wilcock P. R. , Grams P. E.
Published: February 2007

Spatial complexity in channel geometry indicates that accurate prediction of sediment transport requires modeling in at least two dimensions. However, a one‐dimensional model may be the only practical or possible alternative, especially for longer river reaches of practical concern in river management or landscape modeling. We have developed a one‐dimensional model of the Colorado River through upper Grand Canyon that addresses this problem by reach averaging the channel properties and predicting changes in sand storage using separate source and sink functions coupled to the sand routing model. The model incorporates results from the application of a two‐dimensional model of flow, sand transport, and bed evolution, and a new algorithm for setting the near‐bed sand boundary condition for sand transported over an exposed bouldery bed. Model predictions were compared to measurements of sand discharge during intermittent tributary inputs and varying discharges controlled by dam releases. The model predictions generally agree well with the timing and magnitude of measured sand discharges but tend to overpredict sand discharge during the early stages of a high release designed to redistribute sand to higher‐elevation deposits.
East African soil erosion recorded in a 300 year old coral colony from Kenya
Authors: Fleitmann Dominik , Dunbar Robert B. , McCulloch Malcolm , Mudelsee Manfred , Vuille Mathias , McClanahan Tim R. , Cole Julia E. , Eggins Stephen
Published: February 2007

Soil erosion is a key socio‐economic and environmental problem in Kenya, which has been poorly documented due to the lack of long, continuous records. Here we present Ba/Ca records from Porites corals from the Malindi coral reef documenting the flux of suspended sediment from the Sabaki River with a sub‐weekly resolution for the last 300 years. While sediment flux from the Sabaki River is almost constant between 1700 and 1900, a continuous rise in sediment flux is observed since 1900, first due to British settlements and afterwards due to steadily increasing demographic pressure on land use. The peak in suspended sediment load and hence soil erosion occurred between 1974 and 1980 when there is a five to tenfold increase relative to natural levels. This is attributed to the combined effects of dramatically increasing population, unregulated land use, deforestation and severe droughts in the early 1970's. We conclude that despite laudable attempts to instigate soil conservation measures, it is unlikely that there will be a sustainable reduction in soil erosion without a significant improvement in socio‐economic conditions.
Zonally symmetric oscillations in the Northern Hemisphere stratosphere during the winter of 2003–2004
Authors: Pancheva Dora V. , Mukhtarov Plamen J. , Andonov Borislav A.
Published: February 2007

The paper presents clear evidence of zonally symmetric planetary waves with very large amplitudes present in the UK Met Office zonal wind data of the Northern Hemisphere stratosphere in the winter of 2003–2004. The spectral analysis reveals that three prevailing periods of ∼23, 17 and 11 days contribute to the observed zonally symmetric oscillations. These waves are extracted from the data and their amplitudes and phases are studied in detail depending on height and latitude. The wave amplitudes ‐ particularly those of the 11‐ and the 17‐day zonally symmetric waves ‐ clearly indicate the presence of two latitudinal branches of amplifications centred at 50–60°N and 20–30°N. The phase analysis shows that these waves are vertically upward propagating waves and that the waves from the high‐latitude and tropical branches are almost out of phase. A possible forcing mechanism is suggested. The zonally symmetric waves play an important role in coupling the dynamical regimes of the high‐ and low‐latitude stratosphere particularly during the major stratwarm event in the Arctic winter of 2003–2004.
On the El Niño‐Indian monsoon predictive relationships
Authors: Rajeevan M. , Pai D. S.
Published: February 2007

Most of the severe droughts over India are associated with El Niño. However, only less than half of El Niño events are associated with deficient rainfall over India. In other El Niño years, Indian summer monsoon rainfall (ISMR) was either normal or excess. A recent study suggested that the El Niño events with the warmest SST anomalies in the central Pacific are more effective in focusing drought producing subsidence over India than events with the warmest SST anomalies in the eastern equatorial Pacific. They have further suggested that the incorporation of additional information on the spatial distribution of SST anomalies over the equatorial Pacific Ocean in the statistical models should improve monsoon forecast skill. The present study explores this hypothesis on the skill of monsoon forecasts by analyzing SST data for the period 1880–2004. The present study reveals that incorporation of information on the spatial pattern of SST anomalies (by incorporating the Trans Niño Index) does not improve the association between El Niño and Indian monsoon rainfall. Simply using the SST index over the central Pacific (Niño‐3.4) may be a better indicator for the association than the Combined Niño Index derived from Niño‐3 and Trans Niño Index (TNI).
Modeling the mechanisms that control in‐stream dissolved organic carbon dynamics in upland and forested catchments
Authors: Futter M. N. , Butterfield D. , Cosby B. J. , Dillon P. J. , Wade A. J. , Whitehead P. G.
Published: February 2007

We present a new, process‐based model of soil and stream water dissolved organic carbon (DOC): the Integrated Catchments Model for Carbon (INCA‐C). INCA‐C is the first model of DOC cycling to explicitly include effects of different land cover types, hydrological flow paths, in‐soil carbon biogeochemistry, and surface water processes on in‐stream DOC concentrations. It can be calibrated using only routinely available monitoring data. INCA‐C simulates daily DOC concentrations over a period of years to decades. Sources, sinks, and transformation of solid and dissolved organic carbon in peat and forest soils, wetlands, and streams as well as organic carbon mineralization in stream waters are modeled. INCA‐C is designed to be applied to natural and seminatural forested and peat‐dominated catchments in boreal and temperate regions. Simulations at two forested catchments showed that seasonal and interannual patterns of DOC concentration could be modeled using climate‐related parameters alone. A sensitivity analysis showed that model predictions were dependent on the mass of organic carbon in the soil and that in‐soil process rates were dependent on soil moisture status. Sensitive rate coefficients in the model included those for organic carbon sorption and desorption and DOC mineralization in the soil. The model was also sensitive to the amount of litter fall. Our results show the importance of climate variability in controlling surface water DOC concentrations and suggest the need for further research on the mechanisms controlling production and consumption of DOC in soils.
Deleterious Effects of Dihydrotestosterone on Cerebral Ischemic Injury
Authors: Cheng Jian , Alkayed Nabil J , Hurn Patricia D
Published: February 2007

Outcome from cerebral ischemia is sexually dimorphic in many experimental models. Male animals display greater sensitivity to ischemic injury than do their female counterparts; however, the underlying mechanism is unclear. The present study determined if the potent and nonaromatizable androgen, dihydrotestosterone (DHT), exacerbates ischemic damage in the male rat and alters postischemic gene expression after middle cerebral artery occlusion. At 22 h reperfusion, removal of androgens by castration provided protection from ischemic injury in both cortex and striatum (2,3,5-triphenyltetrazolium chloride (TTC) histology), whereas DHT replacement (50 mg subcutaneous implant) restored infarction volume to that of the intact male; testosterone (50 mg) had similar but less potent effects. We utilized microarray and real-time quantitative polymerase chain reaction (PCR) to identify genes differentially expressed at 6 h reperfusion in periinfarct cortex from castrated rats with or without DHT replacement. We identify, for the first time, a number of gene candidates that are induced by DHT with or without ischemia, many of which could account for cell death through enhanced inflammation, dysregulation of blood–brain barrier and the extracellular matrix, apoptosis, and ionic imbalance. Our data suggest that androgens are important mediators of ischemic damage in male brain and that transcriptional mechanisms should be considered as we seek to understand innate male sensitivity to cerebral ischemia.
Aging Effects on Cerebral Blood and Cerebrospinal Fluid Flows
Authors: Stoquart-ElSankari Souraya , Balédent Olivier , Gondry-Jouet Catherine , Makki Malek , Godefroy Olivier , Meyer Marc-Etienne
Published: February 2007

Phase-contrast magnetic resonance imaging (PC-MRI) is a noninvasive reliable technique, which enables quantification of cerebrospinal fluid (CSF) and total cerebral blood flows (tCBF). Although it is used to study hydrodynamic cerebral disorders in the elderly group (hydrocephalus), there is no published evaluation of aging effects on both tCBF and CSF flows, and on their mechanical coupling. Nineteen young (mean age 27 ± 4 years) and 12 elderly (71 ± 9 years) healthy volunteers underwent cerebral MRI using 1.5 T scanner. Phase-contrast magnetic resonance imaging pulse sequence was performed at the aqueductal and cervical levels. Cerebrospinal fluid and blood flow curves were then calculated over the cardiac cycle, to extract the characteristic parameters: mean and peak flows, their latencies, and stroke volumes for CSF (cervical and aqueductal) and vascular flows. Total cerebral blood flow was ( P < 0.01) decreased significantly in the elderly group when compared with the young subjects with a linear correlation with age observed only in the elderly group ( R2 = 0.7; P = 0.05). Arteriovenous delay was preserved with aging. The CSF stroke volumes were significantly reduced in the elderly, at both aqueductal ( P < 0.01) and cervical ( P < 0.05) levels, whereas aqueduct/cervical proportion ( P = 0.9) was preserved. This is the first work to study aging effects on both CSF and vascular cerebral flows. Data showed (1) tCBF decrease, (2) proportional aqueductal and cervical CSF pulsations reduction as a result of arterial loss of pulsatility, and (3) preserved intracerebral compliance with aging. These results should be used as reference values, to help understand the pathophysiology of degenerative dementia and cerebral hydrodynamic disorders as hydrocephalus.
Normobaric Hyperoxia Delays Perfusion/Diffusion Mismatch Evolution, Reduces Infarct Volume, and Differentially Affects Neuronal Cell Death Pathways after Suture Middle Cerebral Artery Occlusion in Rats
Authors: Henninger Nils , Bouley James , Nelligan Julia M , Sicard Kenneth M , Fisher Marc
Published: February 2007

Normobaric hyperoxia (NBO) has been shown to extend the reperfusion window after focal cerebral ischemia. Employing diffusion (DWI)- and perfusion (PWI)-weighted magnetic resonance imaging (MRI), the effect of NBO (100% started at 30 mins after middle cerebral artery occlusion (MCAO)) on the spatiotemporal evolution of ischemia during and after permanent (pMCAO) and transient suture middle cerebral artery occlusion (tMCAO) was investigated (experiment 3). In two additional experiments, time window (experiment 1) and cell death pathways (experiment 2) were investigated in the pMCAO model. In experiment 1, NBO treatment reduced infarct volume at 24 h after pMCAO by 10% when administered for 3 h ( P > 0.05) and by 44% when administered for 6 h ( P < 0.05). In experiment 2, NBO acutely (390 mins, P < 0.05) reduced in situ end labeling (ISEL) positivity in the ipsilesional penumbra but increased contralesional necrotic as well as caspase-3-mediated apoptotic cell death. In experiment 3, CBF characteristics and CBF-derived lesion volumes did not differ between treated and untreated animals, whereas the apparent diffusion coefficient (ADC)-derived lesion volume essentially stopped progressing during NBO treatment, resulting in a persistent PWI/DWI mismatch that could be salvaged by delayed (3 h) reperfusion. In conclusion, NBO (1) acutely preserved the perfusion/diffusion mismatch without altering CBF, (2) significantly extended the time window for reperfusion, (3) induced lasting neuroprotection in permanent ischemia, and (4) although capable of reducing cell death in hypoperfused tissue it also induced cell death in otherwise unaffected areas. Our data suggest that NBO may represent a promising strategy for acute stroke treatment.
Crossed Cerebellar Diaschisis in Acute Ischemic Stroke: A Study with Serial SPECT and MRI
Authors: Liu Yawu , Karonen Jari O , Nuutinen Juho , Vanninen Esko , Kuikka Jyrki T , Vanninen Ritva L
Published: February 2007

This study evaluated the relationship between crossed cerebellar diaschisis (CCD) and (1) lesion volume and location in the acute phase and 1 week after stroke onset and (2) clinical outcome. Twenty-two patients with cerebral ischemic stroke underwent single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI) within 48 h and on day 8 from onset. Interhemispheric asymmetric indices (AI) on SPECT were calculated for medial, intermediate, and lateral zones of the cerebellum. Lesion volumes and locations were obtained from diffusion-weighted MRI. Neurological status and 3-month clinical outcome were evaluated. Within 48 h, lesion locations in the temporal association cortex and pyramidal tract of the corona radiata were independent determinants for the AI of the medial zone ( R2 = 0.439). Lesion locations in the primary, premotor, and supplementary motor cortices, primary somatosensory cortex, and anterior part of the posterior limb of the internal capsule were determinants for the AI of the intermediate zone ( R2 = 0.785). Lesions in the primary motor cortex, premotor, and supplementary motor cortices and in the genu of the internal capsule were determinants for the AI of the lateral zone ( R2 = 0.746). On day 8, the associations were decreased. The AIs of the intermediate and lateral zones and lesion location in the parietal association cortex were independently associated with the 3-month clinical outcome ( R2 > 0.555). Acute CCD is a result of functional deafference, while in the subacute phase, transneuronal degeneration might contribute to CCD. CCD in the intermediate and later zones is a better indicator than that in the medial zone.
Optical anisotropy in [hkil]-oriented wurtzite semiconductor quantum wells
Authors: Chen Chun-Nan , Chang Sheng-Hsiung , Hung Meei-Ling , Chiang Jih-Chen , Lo Ikai , Wang Wan-Tsang , Gau Ming-Hong , Kao Hsiu-Fen , Lee Meng-En
Published: February 2007

An 8×8 band edge potential matrix of the [hkil]-oriented wurtzite Hamiltonian is developed and applied to explore optical anisotropy in [hkil]-oriented wurtzite semiconductor quantum wells. The wave-vector-dependent optical matrix elements are expressed entirely in terms of Hamiltonian matrix elements, thus avoiding the requirement to introduce any additional optical parameters. To accommodate the noncubic symmetry of the wurtzite lattice, spinor rotation is taken into account when performing the calculations for different crystal orientations. The optical matrix elements are formulated and calculated for both the real finite-barrier-height case and the approximate infinite-barrier-height case. It is found that giant anisotropy of the optical matrix elements appears in the [101¯0]- and [101¯2]-oriented well planes.
Shear-driven release of a bud from a multicomponent vesicle
Authors: Smith Kurt A. , Uspal William E.
Published: February 2007

The authors study the response of a multicomponent budded vesicle to an imposed shear flow using dissipative particle dynamics. Under certain circumstances, phase separation in the vesicle membrane leads to the formation of a minority domain which deforms into a nearly spherical bud in order to reduce its interfacial energy. The authors show that an imposed shear force has a varying effect on the vesicle, tending either to separate the bud from the vesicle or to stretch the bud open, depending on the vesicle orientation. The authors examine the interplay of membrane bending rigidity, line tension, and shear in determining the behavior of the vesicle. With the appropriate design, vesicles can be made to release buds in a controlled manner in response to shear. The authors outline a regime in which bud release is favorable.
Fragmentation dynamics of methane by few-cycle femtosecond laser pulses
Authors: Wu Zhifeng , Wu Chengyin , Liang Qingqing , Wang Sufan , Liu Min , Deng Yongkai , Gong Qihuang
Published: February 2007

The fragmentation pattern of CH4 was experimentally studied at an intensity of approximately 1014W∕cm2 with laser durations varying from 8to110fs. When the laser duration was 8fs, only the primarily fragmental CH3+ ion was observed in addition to the parent CH4+ ion. When the laser duration was 30fs, small fragmental CH2+ and H+ ions appeared. When the laser duration was 110fs, some doubly charged ions were also observed in addition to the abundant singly charged ions. The large mass spectra difference demonstrated that the pulse duration had a strong effect on the fragmentation of the parent ion produced in the single ionization. The effect of laser intensity on the fragmentation of CH4+ was also studied for few-cycle femtosecond laser pulses. The results demonstrated that the first-return recollision between the rescattered electron and the parent ion played a significant role in the fragmentation dynamics of the parent ion. Depending on the ion-electron impact energy, the recollision excited the parent ion to a dissociated state or doubly charged state. The experimentally observed singly charged fragmental ions resulted from the recollision-induced dissociation of CH4+ or the Coulomb explosion of CH42+.
Complete band gaps and deaf bands of triangular and honeycomb water-steel phononic crystals
Authors: Hsiao Fu-Li , Khelif Abdelkrim , Moubchir Hanane , Choujaa Abdelkrim , Chen Chii-Chang , Laude Vincent
Published: February 2007

Phononic crystals with triangular and honeycomb lattices are investigated experimentally and theoretically. They are composed of arrays of steel cylinders immersed in water. The measured transmission spectra reveal the existence of complete band gaps but also of deaf bands. Band gaps and deaf bands are identified by comparing band structure computations, obtained by a periodic-boundary finite element method, with transmission simulations, obtained using the finite difference time domain method. The appearance of flat bands and the polarization of the associated eigenmodes is also discussed. Triangular and honeycomb phononic crystals with equal cylinder diameter and smallest spacing are compared. As previously obtained with air-solid phononic crystals, it is found that the first complete band gap opens for the honeycomb lattice but not for the triangular lattice, thanks to symmetry reduction.
Combined molecular and supramolecular bottom-up nanoengineering for enhanced nonlinear optical response: Experiments, modeling, and approaching the fundamental limit
Authors: Pérez-Moreno Javier , Asselberghs Inge , Song Kai , Clays Koen , Zhao Yuxia , Nakanishi Hachiro , Okada Shuji , Nogi Kyoko , Kim Oh-Kil , Je Jongtae , Mátrai Janka , Maeyer Marc De , Kuzyk Mark G.
Published: February 2007

The authors study the combination of two independent strategies that enhance the hyperpolarizability of ionic organic chromophores. The first molecular-level strategy is the extension of the conjugation path in the active chromophore. The second supramolecular-level strategy is the bottom-up nanoengineering of an inclusion complex of the chromophore in an amylose helix by self-assembly. The authors study a series of five (dimethylamino)stilbazolium-type chromophores with increasing conjugation length between the (dimethylamino)phenyl donor ring and the pyridinium acceptor ring in conjunction with four amylose helices of differing molecular weights. The first hyperpolarizabilities of the self-assembled inclusion complexes, as determined with frequency-resolved femtosecond hyper-Rayleigh scattering at 800 and 1300nm, are compared with experimental values for the free chromophores in solution and with theoretical values. While the experimental values for the hyperpolarizability in solution are lower than the theoretically predicted values, an enhancement upon inclusion is observed, with the longest chromophore in the best amylose helix showing an enhancement by one order of magnitude. Molecular modeling of the inclusion of the chromophore suggests that the coplanarity of the two rings is more important than all-trans configuration in the conjugation path. The fundamental limit analysis indicates that the inclusion inside the amylose helix results in an optimal excited-level energy spacing that is responsible for breaching the apparent limit.
Interfacial electronic structure of magnesium deposited on Ag-covered tris(8-hydroxyquinolato) aluminum film: A synchrotron radiation photoemission study
Authors: Pi Tun-Wen , Lee Hsin-Han , Lin Hsiao-Hsuan , Hwang J.
Published: February 2007

The deposition of magnesium on tris(8-hydroxyquinolato) aluminum (Alq3) precovered with thin silver was investigated with high resolution synchrotron radiation photoemission. The noble-metal deposit first occupies the vicinity of the pyridyl ring. The appearance of a Fermi level suggests that the incorporated Ag behaves as a metallic cluster, consistent with the results of the Ag 3d cores, which show a nonzero Doniach-Sunjic singularity index of 0.061. Upon Mg adsorption on the Ag∕Alq3 surface, a MgAg mixture begins to develop such that the Ag 4d valence band becomes narrowed and its centroid shifts towards higher binding energy. A phase transformation is thus observed at the interface, from a Ag-rich phase to a Mg-rich phase. The product of the MgAg mixture prevents subsequent Mg atoms from penetrating into the Alq3 film, which grows as a metal on top of the MgAg∕Alq3 interface.
Low resistance Ti∕Al∕Ti–W∕Au Ohmic contact to n-GaN for high temperature applications
Authors: Fernández S. , Peña R. , Rodrigo M. T. , Plaza J. , Verdú M. , Sánchez F. J. , Montojo M. T.
Published: February 2007

Metallization schemes consisting of titanium/aluminum/titanium-tungsten/gold (Ti∕Al∕Ti–W∕Au) were developed to Ohmic contact formation to n-GaN. The effect of Ti–W as a diffusion barrier layer on electrical and microstructural contact behaviors was evaluated. Regarding the electrical properties, excellent Ohmic contact resistances were obtained at the relatively low annealing temperature of 750°C, showing values as low as 0.29±0.01Ωmm. Intermetallic reactions formed during Ohmic contact annealing were investigated by energy dispersion spectroscopy. “Donutlike” features appeared on the surface showing a dependence of the size/density with the Ti–W layer thickness and the alloying conditions.
Accurate ab initio based multisheeted double many-body expansion potential energy surface for the three lowest electronic singlet states of H3+
Authors: Viegas Luís P. , Alijah Alexander , Varandas António J. C.
Published: February 2007

The authors present diabatic and adiabatic potential energy surfaces for the three lowest electronic singlet states of H3+. The modeling of the surfaces is based on the multi-sheeted double many-body expansion method which consists of dressing the various matrix elements of the diatomics-in-molecules potential matrix with three-body terms. The avoided crossing between the two lowest states and the conical intersection between the second and the third state are accurately represented by construction.
Development of structural order during supercooling of a fragile oxide melt
Authors: Hennet L. , Pozdnyakova I. , Bytchkov A. , Price D. L. , Greaves G. N. , Wilding M. , Fearn S. , Martin C. M. , Thiaudière D. , Bérar J.-F. , Boudet N. , Saboungi M.-L.
Published: February 2007

The authors have studied the structural evolution of the fragile glass-forming liquid CaAl2O4 during supercooling from the stable liquid phase to the cold glass below Tg. The evolution is characterized by a sharpening of the first diffraction peak and a shortening of the average nearest-neighbor bond length around 1.25Tg, indicating an increase in the degree of both intermediate-range and short-range orders occurring close to the dynamical crossover temperature. The cooling curve developed a kink at this temperature, indicating a simultaneous change in thermodynamic properties.
Structures, stabilities, and electronic and optical properties of C52 fullerene, ions, and metallofullerenes
Authors: Chen De-Li , Tian Wei Quan , Feng Ji-Kang , Sun Chia-Chung
Published: February 2007

The 437 classical isomers of fullerene C52 have been studied by PM3, HCTH/3-21G, and B3LYP∕6-31G(d). C2:029 with the least number of adjacent pentagons is predicted to be the most stable isomer. The investigations show that both the number of adjacent pentagons and the degree of aromaticity play important roles in the relative stabilities of fullerene isomers. To clarify the relative stabilities of the C52 isomers in a wide range of temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP∕6-31G(d) level. C2:029 prevails in a wide temperature range. In addition, the electronic spectra and second-order hyperpolarizabilities are determined by means of ZINDO and sum-over-states model. The static second-order hyperpolarizability of C2:029 is 51% larger than that of C60. Furthermore, intensity-dependent refractive index γ (−ω;ω,ω,−ω) (ω=1.1653eV) of C2:029 is 13 times larger than that of C60. The encapsulation of Ca atom in C52 fullerene is exothermic and the metallofullerene Ca-C52 is described as Ca2+-C522−.
Fabrication of TiO2 nanocrystallized glass
Authors: Masai Hirokazu , Fujiwara Takumi , Mori Hiroshi , Komatsu Takayuki
Published: February 2007

Nanocrystallization of rutile and anatase was observed in a CaO–B2O3–Bi2O3–Al2O3–TiO2 crystallized glass. The color of the present crystallized glass was changed by the heat-treatment temperature, and x-ray diffraction (XRD) patterns of the crystallized glass show that the apparent color change is correlated with the formation of titania nanocrystallites. The particle size of crystallites observed in the transmission electron microscope image is comparable to that measured by XRD pattern. In addition, a large change of refractive index between the rutile particles and glass matrix, 0.8 or larger, was obtained. The present titania crystallized glass will be not only a photocatalytic material but also a promising candidate for random lasing devices.
Ultrafast carrier dynamics of Si quantum dots embedded in SiN matrix
Authors: Van Dao Lap , Davis Jeff , Hannaford Peter , Cho Young-Hyun , Green Martin A. , Cho Eun-Chel
Published: February 2007

Femtosecond spectrally resolved two-color three-pulse nonlinear spectroscopy is used to study the dynamics and coherence properties of excited carriers in Si quantum dot structures embedded in silicon nitride. A very short dephasing time of <180fs at room temperature is observed. Ultrashort population relaxation times of ∼400fs and 6–10ps are measured and discussed in the context of the different contributions from transverse optical and transverse acoustic phonon-assisted transitions.
Three-stage transition during silicon carbide nanowire growth
Authors: Shim Hyun Woo , Huang Hanchen
Published: February 2007

This letter reports the fabrication of silicon carbide (SiC) nanowires using vapor deposition and their characterizations using electron microscopy. The study reveal a spontaneous transition process, during growth, among three distinctly different structures or morphologies. At the first stage, SiC nanowires are in the form of periodically twinned crystals. At the second stage, they are in the form of core-shells, with the core being crystalline and modulating diameter, and the shell being amorphous. At the third stage, SiC nanowires are also in the form of core-shells, except that the core is of uniform diameter.
Extraction of small-diameter beams from single-component plasmas
Authors: Danielson J. R. , Weber T. R. , Surko C. M.
Published: February 2007

A nondestructive technique is described to extract small-diameter beams from single-component plasmas confined in a Penning-Malmberg trap following radial compression using a rotating electric field. Pulsed beams with Gaussian radial profiles and diameters as small as 50μm are extracted from electron plasmas initially 2mm in diameter. A simple theory for the beam diameter predicts 4λD (full width to 1∕e), where λD is the Debye length, in good agreement with experimental measurements on electron plasmas. Applications and extensions of this technique to create bright, finely focused beams of positrons and other scarce particles are discussed.
Chip-scale atomic magnetometer with improved sensitivity by use of the Mx technique
Authors: Schwindt Peter D. D. , Lindseth Brad , Knappe Svenja , Shah Vishal , Kitching John , Liew Li-Anne
Published: February 2007

The fabrication and performance of a miniature optically pumped atomic magnetometer constructed with microfabricated components are discussed. This device measures the spin precession frequency of Rb87 atoms to determine the magnetic field by use of the Mx technique. It has a demonstrated sensitivity to magnetic fields of 5pT∕Hz1∕2 for a bandwidth from 1to100Hz, nearly an order of magnitude improvement over our previous chip-scale magnetometer. The 3dB bandwidth has also been increased to 1kHz by reconfiguring the miniature vapor cell heater.
Nanoampere pumping of Cooper pairs
Authors: Vartiainen Juha J. , Möttönen Mikko , Pekola Jukka P. , Kemppinen Antti
Published: February 2007

The authors have employed a tunable Cooper-pair transistor, the sluice, with radio frequency control to pump current over a resistive circuit. They find that the charge transferred per pumping cycle can be controlled with the resolution of a single Cooper pair up to hundreds of pairs. The achieved nanoampere current features more than an order of magnitude improvement over the previously reported results and it is close to the theoretical maximum value for the measured sample.
First-principles prediction of high Curie temperature for ferromagnetic bcc-Co and bcc-FeCo alloys and its relevance to tunneling magnetoresistance
Authors: Ležaić M. , Mavropoulos Ph. , Blügel S.
Published: February 2007

The authors determine from first principles the Curie temperature TC for bulk Co in the hcp, fcc, bcc, and body-centered-tetragonal (bct) phases, for FeCo alloys, and for bcc and bct Fe. For bcc Co, TC=1420K is predicted. This would be the highest Curie temperature among the Co phases, suggesting that bcc-Co∕MgO∕bcc-Co tunnel junctions offer high magnetoresistance ratios even at room temperature. The Curie temperatures are calculated by mapping ab initio results to a Heisenberg model, which is solved by a Monte Carlo method.
Does an Estimate of Environmental Size Precede Size Scaling on a Form-Comparison Task?
Authors: Bennett David J
Published: February 2007

In a number of studies reaction time has been found to increase with increases in size ratio on a same – different form-comparison task. Bennett and Warren (2002, Perception & Psychophysics64 462–477) teased apart environmental and retinal size ratios by showing the forms along a (simulated) texture hallway, viewed monocularly, on a simultaneous form-comparison task; roughly equal effects of environmental and retinal size ratios were found. The current study enhanced scene-size information by showing the forms in simulated stereo and by adding texture to the forms themselves; special care was also taken to perceptually isolate the stimuli. In two experiments, with different kinds of forms, strong effects of environmental size ratio were found; no effect of retinal size ratio (same trials) was observed in either experiment. The results support the hypothesis that the (same-trial) form-size codings reflect ‘all told’ estimates of environmental size, and place constraints on modeling the functional architecture of the visual system.
An ancient chordin-like gene in organizer formation of
Hydra
Authors: Rentzsch Fabian , Guder Corina , Vocke Dirk , Hobmayer Bert , Holstein Thomas W.
Published: February 2007

Signaling centers or organizers play a key role in axial patterning processes in animal embryogenesis. The function of most vertebrate organizers involves the activity of secreted antagonists of bone morphogenetic proteins (BMPs) such as Chordin or Noggin. Although BMP homologs have been isolated from many phyla, the evolutionary origin of the antagonistic BMP/Chordin system in organizer signaling is presently unknown. Here we describe a Chordin-like molecule (HyChdl) from
Hydra
that inhibits BMP activity in zebrafish embryos and acts in
Hydra
axis formation when new head organizers are formed during budding and regeneration.
hychdl
transcripts are also up-regulated in the head regeneration-deficient mutant strain reg-16. Accordingly, HyChdl has a function in organizer formation, but not in head differentiation. Our data indicate that the BMP/Chordin antagonism is a basic property of metazoan signaling centers that was invented in early metazoan evolution to set up axial polarity.
An estimate of anthropogenic CO
2
inventory from decadal changes in oceanic carbon content
Authors: Tanhua Toste , Körtzinger Arne , Friis Karsten , Waugh Darryn W. , Wallace Douglas W. R.
Published: February 2007

Increased knowledge of the present global carbon cycle is important for our ability to understand and to predict the future carbon cycle and global climate. Approximately half of the anthropogenic carbon released to the atmosphere from fossil fuel burning is stored in the ocean, although distribution and regional fluxes of the ocean sink are debated. Estimates of anthropogenic carbon (
C
ant
) in the oceans remain prone to error arising from (
i
) a need to estimate preindustrial reference concentrations of carbon for different oceanic regions, and (
ii
) differing behavior of transient ocean tracers used to infer
C
ant
. We introduce an empirical approach to estimate
C
ant
that circumvents both problems by using measurement of the decadal change of ocean carbon concentrations and the exponential nature of the atmospheric
C
ant
increase. In contrast to prior approaches, the results are independent of tracer data but are shown to be qualitatively and quantitatively consistent with tracer-derived estimates. The approach reveals more
C
ant
in the deep ocean than prior studies; with possible implications for future carbon uptake and deep ocean carbonate dissolution. Our results suggest that this approachs applied on the unprecedented global data archive provides a means of estimating the
C
ant
for large parts of the world's ocean.
Differential contribution of frugivores to complex seed dispersal patterns
Authors: Jordano P. , García C. , Godoy J. A. , García-Castaño J. L.
Published: February 2007

Frugivores are highly variable in their contribution to fruit removal in plant populations. However, data are lacking on species-specific variation in two central aspects of seed dispersal, distance of dispersal and probability of dispersal among populations through long-distance transport. We used DNA-based genotyping techniques onPrunus mahalebseeds dispersed by birds (small- and medium-sized passerines) and carnivorous mammals to infer each seed's source tree, dispersal distance, and the probability of having originated from outside the study population. Small passerines dispersed most seeds short distances (50% dispersed <51 m from source trees) and into covered microhabitats. Mammals and medium-sized birds dispersed seeds long distances (50% of mammals dispersed seeds >495 m, and 50% of medium-sized birds dispersed seeds to >110 m) and mostly into open microhabitats. Thus, dispersal distance and microhabitat of seed deposition were linked through the contrasting behaviors of different frugivores. When the quantitative contribution to fruit removal was accounted for, mammals were responsible for introducing two-thirds of the immigrant seeds into the population, whereas birds accounted for one-third. Our results demonstrate that frugivores differ widely in their effects on seed-mediated gene flow. Despite highly diverse coteries of mutualistic frugivores dispersing seeds, critical long-distance dispersal events might rely on a small subset of large species. Population declines of these key frugivore species may seriously impair seed-mediated gene flow in fragmented landscapes by truncating the long-distance events and collapsing seed arrival to a restricted subset of available microsites.
4,300-Year-old chimpanzee sites and the origins of percussive stone technology
Authors: Mercader Julio , Barton Huw , Gillespie Jason , Harris Jack , Kuhn Steven , Tyler Robert , Boesch Christophe
Published: February 2007

Archaeological research in the African rainforest reveals unexpected results in the search for the origins of hominoid technology. The ancient Panin sites from Côte d'Ivoire constitute the only evidence of prehistoric ape behavior known to date anywhere in the world. Recent archaeological work has yielded behaviorally modified stones, dated by chronometric means to 4,300 years of age, lodging starch residue suggestive of prehistoric dietary practices by ancient chimpanzees. The “Chimpanzee Stone Age” pre-dates the advent of settled farming villages in this part of the African rainforest and suggests that percussive material culture could have been inherited from an common human–chimpanzee clade, rather than invented by hominins, or have arisen by imitation, or resulted from independent technological convergence.
Targeted deletion of titin N2B region leads to diastolic dysfunction and cardiac atrophy
Authors: Radke Michael H. , Peng Jun , Wu Yiming , McNabb Mark , Nelson O. Lynne , Granzier Henk , Gotthardt Michael
Published: February 2007

Titin is a giant protein that is in charge of the assembly and passive mechanical properties of the sarcomere. Cardiac titin contains a unique N2B region, which has been proposed to modulate elasticity of the titin filament and to be important for hypertrophy signaling and the ischemic stress response through its binding proteins FHL2 and αB-crystallin, respectively. To study the role of the titin N2B region in systole and diastole of the heart, we generated a knockout (KO) mouse deleting only the N2B exon 49 and leaving the remainder of the titin gene intact. The resulting mice survived to adulthood and were fertile. Although KO hearts were small, they produced normal ejection volumes because of an increased ejection fraction. FHL2 protein levels were significantly reduced in the KO mice, a finding consistent with the reduced size of KO hearts. Ultrastructural analysis revealed an increased extension of the remaining spring elements of titin (tandem Ig segments and the PEVK region), which, together with the reduced sarcomere length and increased passive tension derived from skinned cardiomyocyte experiments, translates to diastolic dysfunction as documented by echocardiography. We conclude from our work that the titin N2B region is dispensable for cardiac development and systolic properties but is important to integrate trophic and elastic functions of the heart. The N2B-KO mouse is the first titin-based model of diastolic dysfunction and, considering the high prevalence of diastolic heart failure, it could provide future mechanistic insights into the disease process.
Structural basis and evolutionary origin of actin filament capping by twinfilin
Authors: Paavilainen Ville O. , Hellman Maarit , Helfer Emmanuèle , Bovellan Miia , Annila Arto , Carlier Marie-France , Permi Perttu , Lappalainen Pekka
Published: February 2007

Dynamic reorganization of the actin cytoskeleton is essential for motile and morphological processes in all eukaryotic cells. One highly conserved protein that regulates actin dynamics is twinfilin, which both sequesters actin monomers and caps actin filament barbed ends. Twinfilin is composed of two ADF/cofilin-like domains, Twf-N and Twf-C. Here, we reveal by systematic domain-swapping/inactivation analysis that the two functional ADF-H domains of twinfilin are required for barbed-end capping and that Twf-C plays a critical role in this process. However, these domains are not functionally equivalent. NMR-structure and mutagenesis analyses, together with biochemical and motility assays showed that Twf-C, in addition to its binding to G-actin, interacts with the sides of actin filaments like ADF/cofilins, whereas Twf-N binds only G-actin. Our results indicate that during filament barbed-end capping, Twf-N interacts with the terminal actin subunit, whereas Twf-C binds between two adjacent subunits at the side of the filament. Thus, the domain requirement for actin filament capping by twinfilin is remarkably similar to that of gelsolin family proteins, suggesting the existence of a general barbed-end capping mechanism. Furthermore, we demonstrate that a synthetic protein consisting of duplicated ADF/cofilin domains caps actin filament barbed ends, providing evidence that the barbed-end capping activity of twinfilin arose through a duplication of an ancient ADF/cofilin-like domain.