bluuebunny/crossref_metadata_2025 huggingface dataset:
Convective initiation on 19 June 2002 during IHOP: High‐resolution simulations and analysis of the mesoscale structures and convection initiation
Authors: Wang Qi‐Wei , Xue Ming
Published: May 2012

The 19 June 2002 convective initiation (CI) case from the International H2O Project (IHOP) is simulated using the ARPS at 1 km grid spacing. It involves three distinct CI groups, CI‐A, CI‐B, and CI‐C, associated with a cold front‐dryline system. Initial condition at 1800 UTC, 19 June 2002 was created using the ARPS 3DVAR, including standard as well as special observations. The simulation captured the three groups of CIs rather well, with small timing and spatial errors. CI‐A is most typical of dryline initiation. Vertical cross sections through the initiation locations show typical dryline structures with an upward moisture bulge forced by lifting along the dryline convergence. For CI‐B, the model‐predicted mesoscale structures agree with special IHOP aircraft dropsonde observations closely. Strong low‐level convergence from opposing cold front and dryline circulations produces deep symmetric upwelling of moist air, and the convection is initiated at the crest of the moisture bulge. CI‐C is more typical of frontal convection where deep convection is first initiated at the front edge of the cold air. For CI‐B and CI‐C, north‐south moisture bands that have dryline characteristics (and can be considered multiple drylines) and contain enhanced vertical motion and upward moisture bulges intercept the dryline and cold front, respectively, providing the most favored locations on the dryline or cold front for initiation. Furthermore, the air parcels feeding the initial cells at CI‐B and CI‐C have trajectories along the moisture bands and have already experienced uplifting when they reach the dryline and cold front locations.
Diversity of active aerobic methanotrophs along depth profiles of arctic and subarctic lake water column and sediments
Authors: He Ruo , Wooller Matthew J , Pohlman John W , Quensen John , Tiedje James M , Leigh Mary Beth
Published: May 2012

Methane (CH4) emitted from high-latitude lakes accounts for 2–6% of the global atmospheric CH4 budget. Methanotrophs in lake sediments and water columns mitigate the amount of CH4 that enters the atmosphere, yet their identity and activity in arctic and subarctic lakes are poorly understood. We used stable isotope probing (SIP), quantitative PCR (Q-PCR), pyrosequencing and enrichment cultures to determine the identity and diversity of active aerobic methanotrophs in the water columns and sediments (0–25 cm) from an arctic tundra lake (Lake Qalluuraq) on the north slope of Alaska and a subarctic taiga lake (Lake Killarney) in Alaska’s interior. The water column CH4 oxidation potential for these shallow (∼2 m deep) lakes was greatest in hypoxic bottom water from the subarctic lake. The type II methanotroph, Methylocystis, was prevalent in enrichment cultures of planktonic methanotrophs from the water columns. In the sediments, type I methanotrophs (Methylobacter, Methylosoma and Methylomonas) at the sediment-water interface (0–1 cm) were most active in assimilating CH4, whereas the type I methanotroph Methylobacter and/or type II methanotroph Methylocystis contributed substantially to carbon acquisition in the deeper (15–20 cm) sediments. In addition to methanotrophs, an unexpectedly high abundance of methylotrophs also actively utilized CH4-derived carbon. This study provides new insight into the identity and activity of methanotrophs in the sediments and water from high-latitude lakes.
Macrofauna regulate heterotrophic bacterial carbon and nitrogen incorporation in low-oxygen sediments
Authors: Hunter William R , Veuger Bart , Witte Ursula
Published: May 2012

Oxygen minimum zones (OMZs) currently impinge upon >1 million km2 of sea floor and are predicted to expand with climate change. We investigated how changes in oxygen availability, macrofaunal biomass and retention of labile organic matter (OM) regulate heterotrophic bacterial C and N incorporation in the sediments of the OMZ-impacted Indian continental margin (540–1100 m; [O2]=0.35–15 μmol l−1). In situ pulse-chase experiments traced 13C:15N-labelled phytodetritus into bulk sediment OM and hydrolysable amino acids, including the bacterial biomarker d-alanine. Where oxygen availability was lowest ([O2]=0.35 μmol l−1), metazoan macrofauna were absent and bacteria assimilated 30–90% of the labelled phytodetritus within the sediment. At higher oxygen levels ([O2]=2–15 μmol l−1) the macrofaunal presence and lower phytodetritus retention with the sediment occur concomitantly, and bacterial phytodetrital incorporation was reduced and retarded. Bacterial C and N incorporation exhibited a significant negative relationship with macrofaunal biomass across the OMZ. We hypothesise that fauna–bacterial interactions significantly influence OM recycling in low-oxygen sediments and need to be considered when assessing the consequences of global change on biogeochemical cycles.
Superstation in New Mexico would unite fragmented US electrical grid
Authors: Matthews Jermey N. A.
Published: May 2012

High-T c superconductor cables would provide interregional access to renewable energy.
The three-dimensional flow organization past a micro-ramp in a supersonic boundary layer
Authors: Sun Z. , Schrijer F. F. J. , Scarano F. , van Oudheusden B. W.
Published: May 2012

The three-dimensional instantaneous flow organization in the near wake of a micro-ramp interacting with a Mach 2.0 supersonic turbulent boundary layer is studied using tomographic particle image velocimetry. The mean flow reveals a wake with approximately circular cross section dominated by a pair of counter-rotating streamwise vortices generating a focused upwash motion at the symmetry plane. In the instantaneous flow organization a flow instability of Kelvin-Helmholtz (K-H) type is observed in the shear layer between the wake and outer flow. Intermittent arc-shaped vortices are visualized that locally accelerate the outer fluid and further decelerate the inner region. The streamwise vortex pair displays an undulating behavior. Their interaction with the K-H vortices considerably increases the overall complexity of the wake. It appears that the streamwise vortex filaments under the K-H vortex train approach each other due to the focused ejection activity resulting from the K-H vortex. The statistical properties of turbulent fluctuations yield maximum activity at the core of the streamwise vortex and within the upwash region, and the Reynolds stresses peak within the shear layer. The topological organization of the wake vortices is formulated through a conditional average over the vorticity field.
Comparison between bulk and nanoscale copper-silicide: Experimental studies on the crystallography, chemical, and oxidation of copper-silicide nanowires on Si(001)
Authors: Ng P. K. , Fisher B. , Low K. B. , Joshi-Imre A. , Bode M. , Lilley C. M.
Published: May 2012

Self-assembled copper-silicide (Cu-Si) nanowires were prepared by the evaporation of Cu onto Si(001) under high vacuum conditions. The Cu-Si nanowires were studied in situ by scanning electron microscopy. Crystallographic, structural, and chemical properties of the nanowires were investigated by transmission electron microscopy at cross-sections of these nanowires fabricated by focused ion beam. In addition, chemical of nanowires were also studied by scanning transmission electron microscopy. The morphology of Cu-Si nanowires due to oxidation at ambient conditions was investigated as well. Experimental results obtained from the Cu-Si nanowires were compared to bulk data reported previously by other authors.
Effect of discrete time observations on synchronization in Chua model and applications to data assimilation
Authors: Nurujjaman Md. , Shivamurthy Sumanth , Apte Amit , Singla Tanu , Parmananda P.
Published: May 2012

Data assimilation is a tool, which incorporates observations in the model to improve the forecast, and it can be thought of as a synchronization of the model with observations. This paper discusses results of numerical identical twin experiments, with observations acting as master system coupled unidirectionally to the slave system at discrete time instances. We study the effects of varying the coupling constant, the observational frequency, and the observational noise intensity on synchronization and prediction in a low dimensional chaotic system, namely, the Chua circuit model. We observe synchrony in a finite range of coupling constant when coupling the x and y variables of the Chua model, but not when coupling the z variable. This range of coupling constant decreases with increasing levels of noise in the observations. The Chua system does not show synchrony when the time gap between observations is greater than about one-seventh of the Lyapunov time. Finally, we also note that the prediction errors are much larger when noisy observations are used than when using observations without noise.
Materials for phase-change memory with elevated temperature stability
Authors: Kao Kin-Fu , Chu Yung-Ching , Tsai Ming-Jinn , Chin Tsung-Shune
Published: May 2012

Thermal stability is one of the key issues in phase-change memory. We try to tackle it by developing new compositions based on Ga-Te-Sb system. Thermal stability is exemplified using Ga18Te12Sb70 which shows crystallization-temperature (Tx) 248 °C and activation energy of non-isothermal crystallization 5.9 eV. Films were isothermally soaked at 5 ∼ 30 °C below Tx to estimate the failure-time when electrical resistance dropped to a half of the original. Arrhenius plot attained using logarithm failure-time versus reciprocal temperature were extrapolated to the temperature corresponding to 10-year failure (T10y) as 183 °C. Pre-crystallization structure upon heating to 2 ∼ 5 °C below Tx reflects stable amorphous phase of the alloy up to at least 240 °C. Memory-cells made of Ga18Te12Sb70 can be set-reset at 20 ∼ 500 ns with electrical currents around 66% those of our Ge2Sb2Te5 cells. We suggest that compositions Ga18–25Te8–12Sb67–70 are optimal to ensure Tx > 240 °C, T10y > 180 °C and with low operation-currents.
Nonlinear theory for a terahertz gyrotron with a special cross-section interaction cavity
Authors: Yuan XueSong , Lan Ying , Han Yu , Yan Yang
Published: May 2012

The fully numerical nonlinear theory for a gyrotron with a special cross-section interaction cavity has been developed in this paper. In this theory, the analytical solution to different modes in the special cross-section interaction cavity is replaced by the numerical solution based on electromagnetic simulation results. A 0.4 THz third harmonic gyrotron with an azimuthally corrugated interaction cavity has been investigated by using this theory and simulation results show that this approach has a significant advantage of developing high harmonic terahertz gyrotrons.
Effects of fast monoenergetic electrons on the generalized Bohm criterion for electronegative dusty plasma
Authors: Chekour S. , Tahraoui A. , Zaham B.
Published: May 2012

In this work, we have generalized the computation of Bohm criterion for electronegative complex plasma in the presence of fast monoenergetic electrons coming from a plane electrode. For this, we have established a 1D, collisionless, stationary, and unmagnetized electronegative plasma sheath model. The electrons and negative ions are considered in thermodynamic equilibrium; however, the positive ions, the dust grains, and the fast monoenergetic electrons are described by cold fluid equations. The generalized Bohm criterion has been calculated by using Sagdeev’s pseudo potential method and the dust grain charge equation. The self-consistent relation between the dust grain surface potential at the edge and dust grains density is also derived. The numerical results reveal that the presence of the fast monoenergetic electrons increases the positive ion Mach number. On the other hand, the raise of electronegativity decreases this positive Mach number. The evolution of dust grain surface potential at the sheath edge is also illustrated and discussed.
A monoclinic-tetragonal ferroelectric phase transition in lead-free (K0.5Na0.5)NbO3-x%LiNbO3 solid solution
Authors: Ge Wenwei , Ren Yang , Zhang Jialiang , Devreugd Christopher P. , Li Jiefang , Viehland D.
Published: May 2012

A monoclinic ferroelectric phase with space group Pm has been discovered in lead-free (K0.5Na0.5)NbO3-5%LiNbO3 solid solution ceramics by high energy synchrotron x-ray powder diffraction measurements. At ambient temperature, the lattice parameters of this monoclinic structure were (am, bm, cm; β) = (4.015 Å, 3.944 Å, 3.987 Å; 90.34°). This monoclinic phase transformed to a tetragonal (P4mm) one on heating between 340 K and 360 K. The results demonstrate the presence of structurally bridging low symmetry monoclinic phase in (K0.5Na0.5)NbO3-x%LiNbO3 solid solution system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering.
Application of abelian holonomy formalism to the elementary theory of numbers
Authors: Abe Yasuhiro
Published: May 2012

We consider an abelian holonomy operator in two-dimensional conformal field theory with zero-mode contributions. The analysis is made possible by use of a geometric-quantization scheme for abelian Chern-Simons theory on S1 × S1 × R. We find that a purely zero-mode part of the holonomy operator can be expressed in terms of Riemann's zeta function. We also show that a generalization of linking numbers can be obtained in terms of the vacuum expectation values of the zero-mode holonomy operators. Inspired by mathematical analogies between linking numbers and Legendre symbols, we then apply these results to a space of Fp = Z/pZ, where p is an odd prime number. This enables us to calculate “scattering amplitudes” of identical odd primes in the holonomy formalism. In this framework, the Riemann hypothesis can be interpreted by means of a physically obvious fact, i.e., there is no notion of “scattering” for a single-particle system. Abelian gauge theories described by the zero-mode holonomy operators will be useful for studies on quantum aspects of topology and number theory.
Effect of oxygen ambient during phosphorous diffusion on silicon solar cell
Authors: Kumar Dinesh , Saravanan S. , Suratkar Prakash
Published: May 2012

Phosphorous (P) diffusion is the most important and crucial process in the fabrication of silicon (Si) solar cells from p-type Si substrates. P-diffusion using phosphorous-oxycholoride (POCl3) as a precursor in a tube furnace had shown the best cell performance over the belt diffusion because of uniform dopant concentration all over the Si surface and gettering of metallic impurities present in the substrate. The emitter formation by using POCl3 is a complex and advanced process which provides the gettering and forming the unwanted dead layer on the front surface due to inactive phosphorous. Along with temperature, the ambient conditions during the diffusion process, such as gas flow rates and their composition, flow kinetics also have an impact on the emitter properties. In the present paper, the impact of oxygen (O2) flow during the diffusion process on the emitter formation and the solar cell performance were studied. It has been found that, the presence of oxygen during the diffusion process influences the concentration of inactive phosphorous over the surface and the gettering process as well. The optimized oxygen flow shows an improvement in the effective minority carrier lifetime of ∼24 μs after diffusion and an absolute efficiency gain of 0.2% at pilot production.
Air supply control for maximum efficiency point tracking in fuel cell systems
Authors: Lu Jun , Zahedi Ahmad
Published: May 2012

The efficiency of the fuel cell system nonlinearly depends on operating conditions and the air flow supplied to the fuel cell system is one of the most significant factors in determining the efficiency. The conventional method of controlling the air flow is to stabilize the oxygen supply at a predetermined constant rate for the optimal efficiency. However, in practice, the optimal point can deviate from the pre-set value due to the varying operating conditions, such as the uncontrollable load. Therefore, the maximum efficiency point tracking (MEPT) controller is necessary to maintain the optimal efficiency over a broad range of operating conditions. In this paper, the MEPT controller is designed based on the extremum seeking control algorithm for searching the optimal oxygen excess ratio in real time to maximize the efficiency of the fuel cell system. Simulation was conducted in the matlab/simulink environment and the results demonstrate that the proposed control method is able to track the maximum efficiency point when variations in operating conditions occur.
Differential membrane-based nanocalorimeter for high-resolution measurements of low-temperature specific heat
Authors: Tagliati S. , Krasnov V. M. , Rydh A.
Published: May 2012

A differential, membrane-based nanocalorimeter for general specific heat studies of very small samples, ranging from 0.5 mg to sub-μg in mass, is described. The calorimeter operates over the temperature range from above room temperature down to 0.5 K. It consists of a pair of cells, each of which is a stack of heaters and thermometer in the center of a silicon nitride membrane, in total giving a background heat capacity less than 100 nJ/K at 300 K, decreasing to 10 pJ/K at 1 K. The device has several distinctive features: (i) The resistive thermometer, made of a Ge1 − xAux alloy, displays a high dimensionless sensitivity |dlnR/dlnT| ≳ 1 over the entire temperature range. (ii) The sample is placed in direct contact with the thermometer, which is allowed to self-heat. The thermometer can thus be operated at high dc current to increase the resolution. (iii) Data are acquired with a set of eight synchronized lock-in amplifiers measuring dc, 1st and 2nd harmonic signals of heaters and thermometer. This gives high resolution and allows continuous output adjustments without additional noise. (iv) Absolute accuracy is achieved via a variable-frequency-fixed-phase technique in which the measurement frequency is automatically adjusted during the measurements to account for the temperature variation of the sample heat capacity and the device thermal conductance. The performance of the calorimeter is illustrated by studying the heat capacity of a small Au sample and the specific heat of a 2.6 μg piece of superconducting Pb in various magnetic fields.
Phononic bandgaps in graphene-based materials
Authors: Sigalas Michael M. , Koukaras Emmanuel N.
Published: May 2012

The phonon density of states of graphene based materials have been studied using density functional theory. Substitution of the carbon atoms with carbon isotopes may result in the appearance of gaps in the phonon density of states. Wider gaps are introduced when selected carbon atoms are replaced with germanium atoms. The effect of the percentage of germanium atoms substituting carbon atoms in graphene has also been studied. The results presented here may find application in the design of efficient thermoelectric materials.
Spatial linear disturbances in a plane wall jet
Authors: Schrader Lars-Uve , Mavriplis Catherine , Brandt Luca
Published: May 2012

A two-dimensional direct numerical simulation study of the linear instability in a laminar plane wall jet is presented. The evolution of the wall jet disturbances is in reasonable agreement with predictions by spatial linear stability theory only with regard to the wavelength and the amplitude shape of the disturbance, whereas significant differences in the linear growth rate are noticed. As a consequence, the “stable island” on the instability map based on linear stability theory turns out to be connected with the outer stable region in the simulations, thus taking the form of a “stable peninsula”. The failure of the theory is attributed to the rapid streamwise spread and decay of the wall jet, which is incompatible with the assumption of parallel flow. We also assess the maximum possible transient linear amplification of two-dimensional disturbances in the plane wall jet, using the concept of optimal initial disturbances. The transient energy growth relies on the Orr mechanism, and the upper bound of the disturbance energy increases linearly in time for the present flow configuration. The optimal disturbances exhibit local maxima near the edge of the jet and close to the wall, where sites of effective receptivity are hence expected. We find that the outer region of the plane wall jet is more receptive to time periodic forcing than the inner region.
Observation of a Coulomb blockade in strontium titanate thin films
Authors: Grosse V. , Schmidl F. , Seidel P.
Published: May 2012

We report on the study of the low temperature electronic transport in strontium titanate thin films having a thickness of 25–30 nm. I-V characteristics measured below 4.2 K show unique structures which are evidence for the occurrence of a Coulomb blockade. Simulations of the measured characteristics suggest that this behavior is closely related to the formation of nanoscopic metallic islands within an insulating matrix which arrange in a network connected via tunneling currents.
Visualization of the flow profile inside a thinning filament during capillary breakup of a polymer solution via particle image velocimetry and particle tracking velocimetry
Authors: Gier S. , Wagner C.
Published: May 2012

We investigated the flow profile of a polymer solution in a thinning capillary bridge. Fluorescent tracer particles with a diameter of 3 μm were used to visualize the flow. The cylindrical shape of the filament introduced strong optical abberations that could be corrected for, and we were able to characterize the flow in filaments with a thickness ranging from 150 to 30 μm. In the first regime when the filament was still sufficiently large, we used a PIV algorithm to deduce the flow field. At later stages when the number of particles in the observation plane decreased a PTV algorithm was used. The main two results of our measurements are as follows. First, the flow profile at the formation of the cylindrical filament is highly inhomogeneous and there is only flow in the outer parts of the filament. Second, we find that in most parts of the regime, where the temporal radius of the thinning filament can be fitted with an exponential law the flow indeed is purely extensional.
Density-dependent separation of encapsulated cells in a microfluidic channel by using a standing surface acoustic wave
Authors: Nam Jeonghun , Lim Hyunjung , Kim Choong , Yoon Kang Ji , Shin Sehyun
Published: May 2012

This study presents a method for density-based separation of monodisperse encapsulated cells using a standing surface acoustic wave (SSAW) in a microchannel. Even though monodisperse polymer beads can be generated by the state-of-the-art technology in microfluidics, the quantity of encapsulated cells cannot be controlled precisely. In the present study, mono-disperse alginate beads in a laminar flow can be separated based on their density using acoustophoresis. A mixture of beads of equal sizes but dissimilar densities was hydrodynamically focused at the entrance and then actively driven toward the sidewalls by a SSAW. The lateral displacement of a bead is proportional to the density of the bead, i.e., the number of encapsulated cells in an alginate bead. Under optimized conditions, the recovery rate of a target bead group (large-cell-quantity alginate beads) reached up to 97% at a rate of 2300 beads per minute. A cell viability test also confirmed that the encapsulated cells were hardly damaged by the acoustic force. Moreover, cell-encapsulating beads that were cultured for 1 day were separated in a similar manner. In conclusion, this study demonstrated that a SSAW can successfully separate monodisperse particles by their density. With the present technique for separating cell-encapsulating beads, the current cell engineering technology can be significantly advanced.
Complementary resistive switching in tantalum oxide-based resistive memory devices
Authors: Yang Yuchao , Sheridan Patrick , Lu Wei
Published: May 2012

Complementary resistive switches (CRS) are considered as a potential solution for the sneak path problem in large-scale integration of passive crossbar resistive memory arrays. A typical CRS is composed of two bipolar memory cells that are connected anti-serially. Here, we report a tantalum-oxide based resistive memory that achieves the complementary switching functionality within a single memory cell. The complementary switching effect is accompanied by switching polarity reversal in different voltage bias regimes. These effects were explained by the redistribution of oxygen vacancies inside the tantalum-oxide layers. The effects of symmetry breaking on bipolar switching and complementary switching were also discussed.
Photothermal cantilever deflection spectroscopy of a photosensitive polymer
Authors: Yun Minhyuk , Kim Seonghwan , Lee Dongkyu , Jung Namchul , Chae Inseok , Jeon Sangmin , Thundat Thomas
Published: May 2012

The mechanical and chemical information of a poly(methyl methacrylate) (PMMA) film on a microcantilever were simultaneously acquired by photothermal cantilever deflection spectroscopy as a function of ultraviolet (UV) irradiation time. Nanomechanical infrared (IR) spectra from the PMMA-coated microcantilever agreed well with the Fourier transform infrared spectroscopy (FTIR) spectra of PMMA on gold-coated silicon wafer. The decreasing intensities of nanomechanical IR peaks represent chemical as well as mechanical information of UV radiation-induced photodegradation processes in the PMMA which cannot be obtained by a conventional FTIR technique. The observed decrease in the resonance frequency of the microcantilever is related to the change in the Young’s modulus of the PMMA under UV exposure.
Trapped nobeliumions yield first direct measurements of transuranic masses
Authors: Schwarzschild Bertram
Published: May 2012

In the search for the island of stability expected to lie not far beyond the heaviest known elements, it will help to have good measurements of nuclear binding energies along the way.
Is transpiration efficiency a viable plant trait in breeding for crop improvement?
Authors: Sinclair Thomas R.
Published: May 2012

Increased transpiration efficiency – commonly the ratio of mass accumulation to transpiration – is often suggested as a critical opportunity for genetic improvement for increased crop yields in water-limited environments. However, close inspection of transpiration efficiency (TE) shows that it is a complex term that is explicitly dependent upon both physiological and environmental variables. Physiological variables include leaf photosynthetic capacity, biochemical composition of the plant productions and possible hydraulic limitation on water flow in the plant. Environmental variables include atmospheric CO2 concentration and atmospheric vapour pressure deficit. To complicate the resolution of transpiration efficiency, a weighted integration over the daily cycle and over the dates of interest needs to be resolved. Consequently, it is concluded that transpiration efficiency is not a variable easily resolved for use in many breeding programs. Instead, component traits contributing to TE need to be studied to increase the effective use of available water through the growing season to ultimately maximise growth and yield of the crop.
Root traits and δ13C and δ18O of durum wheat under different water regimes
Authors: Elazab Abdelhalim , Molero Gemma , Serret Maria Dolores , Araus José Luis
Published: May 2012

Plant growth, root characteristics and the stable carbon (δ13C) and oxygen (δ18O) composition were studied in durum wheat. Four recombinant inbred lines with good agronomic adaptation were grown under well watered (WW) and water stress (WS) conditions until mid-grain filling in lysimeters. Gas exchange was measured in the flag leaf just before harvest and then the aerial dry matter (Aerial DM), root weight density (RWD) and root length density (RLD) and the specific root length (SRL) were evaluated and the δ13C and δ18O of the roots, the flag leaf blade and the spike were analysed. Water stress decreased stomatal conductance, plant accumulated transpiration and Aerial DM, whereas δ13C and δ18O increased. Genotypic differences were found for all gas-exchange and root traits and isotope signatures. Aerial DM was positively correlated with RLD, regardless of the water regime, whereas it was negatively correlated with δ13C and δ18O, but only under WW conditions. Moreover, RWD and RLD were negatively related to both δ13C and δ18O under the WW regime, but no clear pattern existed under WS. Our study supports the use of δ13C and δ18O as proxies for selecting root traits associated with higher growth in the absence of water stress.
Alternative methods for scaling leaf hydraulic conductance offer new insights into the structure - function relationships of sun and shade leaves
Authors: Nardini Andrea , Pedá Giulia , Salleo Sebastiano
Published: May 2012

Hydraulic conductance (Kleaf) and morpho-anatomical parameters were measured in sun and shade Quercus ilex L. (holm oak) leaves. Sun leaves had lower surface area (Aleaf) and volume (Vleaf) and higher specific mass (leaf mass per area, LMA) than shade leaves. Transpiration rate and Kleaf scaled by Aleaf (Kleaf_area) were 2-fold higher in sun than in shade leaves. Kleaf_area was not correlated with vein density or stomatal density, which were found to be similar in the two leaf types. Values of Kleaf scaled by Vleaf or leaf dry weight (Kleaf_dw) were only 40% higher in sun than in shade leaves, suggesting that structural changes of Holm oak leaves acclimating to different light intensities enhance water transport to the unit evaporating leaf surface area, while maintaining more constant hydraulic supply to mesophyll cells and carbon costs of the water transport system. Sun leaves had higher Kleaf_dw and LMA than shade ones, indicating that high LMA resulted from resource allocation involved in both water transport and structural rigidity. Future studies of the intra- and inter-specific variability of mass-based hydraulic efficiency might provide important insights into leaf hydraulics and carbon economy. Kleaf_dw might prove to be an important driver of plant acclimation and adaptation to the environment.
Sexual selection and the differential effect of polyandry
Authors: Collet Julie , Richardson David S. , Worley Kirsty , Pizzari Tommaso
Published: May 2012

In principle, widespread polyandry (female promiscuity) creates potential for sexual selection in males both before and after copulation. However, the way polyandry affects pre- and postcopulatory episodes of sexual selection remains little understood. Resolving this fundamental question has been difficult because it requires extensive information on mating behavior as well as paternity for the whole male population. Here we show that in replicate seminatural groups of red junglefowl,
Gallus gallus
, polyandry eroded variance in male mating success, which simultaneously weakened the overall intensity of sexual selection but increased the relative strength of postcopulatory episodes. We further illustrate the differential effect of polyandry on pre- and postcopulatory sexual selection by considering the case of male social status, a key determinant of male reproductive success in this species. In low-polyandry groups, however, status was strongly sexually selected before copulation because dominants mated with more females. In high-polyandry groups, sexual selection for status was weakened and largely restricted after copulation because dominants defended paternity by mating repeatedly with the same female. These results reveal polyandry as a potent and dynamic modulator of sexual selection episodes.
Crust-mantle mechanical coupling in Eastern Mediterranean and Eastern Turkey
Authors: Sinan Özeren M.
Published: May 2012

Present-day crust-mantle coupling in the Eastern Mediterranean and eastern Turkey is studied using the Global Positioning System (GPS) and seismic anisotropy data. The general trend of the shear wave fast-splitting directions in NE Turkey and Lesser Caucaus align well with the geodetic velocities in an absolute plate motion frame of reference pointing to an effective coupling in this part of the region of weak surface deformation. Farther south, underneath the Bitlis Suture, however, there are significant Pn delays with E-W anisotropy axes indicating significant lateral escape. Meanwhile, the GPS reveals very little surface deformation. This mismatch possibly suggests a decoupling along the suture. In the Aegean, the shear wave anisotropy and the Pn anisotropy directions agree with the extensional component of the right-lateral shear strains except under the Crete Basin and other parts of the southern Aegean Sea. This extensional direction matches perfectly also with the southward pulling force vectors across the Hellenic trench; however, the maximum right-lateral shear directions obtained from the GPS data in the Aegean do not match either of these anisotropies. Seismic anisotropy from Rayleigh waves sampled at 15 s, corresponding to the lower crust, match the maximum right-lateral maximum shear directions from the GPS indicating decoupling between the crust and the mantle. This decoupling most likely results from the lateral variations of the gravitational potential energies and the slab-pull forces.
Multiscale diffusion in the mitotic
Drosophila melanogaster
syncytial blastoderm
Authors: Daniels Brian R. , Rikhy Richa , Renz Malte , Dobrowsky Terrence M. , Lippincott-Schwartz Jennifer
Published: May 2012

Despite the fundamental importance of diffusion for embryonic morphogen gradient formation in the early
Drosophila melanogaster
embryo, there remains controversy regarding both the extent and the rate of diffusion of well-characterized morphogens. Furthermore, the recent observation of diffusional “compartmentalization” has suggested that diffusion may in fact be nonideal and mediated by an as-yet-unidentified mechanism. Here, we characterize the effects of the geometry of the early syncytial
Drosophila
embryo on the effective diffusivity of cytoplasmic proteins. Our results demonstrate that the presence of transient mitotic membrane furrows results in a multiscale diffusion effect that has a significant impact on effective diffusion rates across the embryo. Using a combination of live-cell experiments and computational modeling, we characterize these effects and relate effective bulk diffusion rates to instantaneous diffusion coefficients throughout the syncytial blastoderm nuclear cycle phase of the early embryo. This multiscale effect may be related to the effect of interphase nuclei on effective diffusion, and thus we propose that an as-yet-unidentified role of syncytial membrane furrows is to temporally regulate bulk embryonic diffusion rates to balance the multiscale effect of interphase nuclei, which ultimately stabilizes the shapes of various morphogen gradients.
Canonical autophagy dependent on the class III phosphoinositide-3 kinase Vps34 is required for naive T-cell homeostasis
Authors: Willinger Tim , Flavell Richard A.
Published: May 2012

The homeostasis of naive T cells is essential for protective immunity against infection, but the cell-intrinsic molecular mechanisms that control naïve T-cell homeostasis are poorly understood. Genetic ablation in lower organisms has revealed a critical role for Vps34, an evolutionary conserved class III phosphoinositide-3 kinase (PI3K), in regulating endocytosis and autophagy; however, the physiological function of Vps34 in the immune system, especially in T cells, is unclear. Here we report that Vps34 is required for the maintenance of naïve T cells, acting in a cell-intrinsic manner. T-cell–specific deletion of the gene encoding Vps34 resulted in reduced stability of Vps15 and Beclin-1, components of the class III PI3K complex, and impaired autophagy in T cells. Vps34 was dispensable for T-cell development but important for the survival of naïve T cells. Vps34-deficient T cells showed increased mitochondrial mass and accumulation of reactive oxygen species, consistent with deficient removal of damaged mitochondria. Thus, Vps34-dependent canonical autophagy plays a critical role in maintaining T-cell homeostasis by promoting T-cell survival through quality control of mitochondria.
Image restoration: Total variation, wavelet frames, and beyond
Authors: Cai Jian-Feng , Dong Bin , Osher Stanley , Shen Zuowei
Published: May 2012

The variational techniques (e.g. the total variation based method) are well established and effective for image restoration, as well as many other applications, while the wavelet frame based approach is relatively new and came from a different school. This paper is designed to establish a connection between these two major approaches for image restoration. The main result of this paper shows that when spline wavelet frames of are used, a special model of a wavelet frame method, called the analysis based approach, can be viewed as a discrete approximation at a given resolution to variational methods. A convergence analysis as image resolution increases is given in terms of objective functionals and their approximate minimizers. This analysis goes beyond the establishment of the connections between these two approaches, since it leads to new understandings for both approaches. First, it provides geometric interpretations to the wavelet frame based approach as well as its solutions. On the other hand, for any given variational model, wavelet frame based approaches provide various and flexible discretizations which immediately lead to fast numerical algorithms for both wavelet frame based approaches and the corresponding variational model. Furthermore, the built-in multiresolution structure of wavelet frames can be utilized to adaptively choose proper differential operators in different regions of a given image according to the order of the singularity of the underlying solutions. This is important when multiple orders of differential operators are used in various models that generalize the total variation based method. These observations will enable us to design new methods according to the problems at hand, hence, lead to wider applications of both the variational and wavelet frame based approaches. Links of wavelet frame based approaches to some more general variational methods developed recently will also be discussed.
RTEL1 contributes to DNA replication and repair and telomere maintenance
Authors: Uringa Evert-Jan , Lisaingo Kathleen , Pickett Hilda A. , Brind'Amour Julie , Rohde Jan-Hendrik , Zelensky Alex , Essers Jeroen , Lansdorp Peter M.
Published: May 2012

Telomere maintenance and DNA repair are important processes that protect the genome against instability. mRtel1, an essential helicase, is a dominant factor setting telomere length in mice. In addition, mRtel1 is involved in DNA double-strand break repair. The role of mRtel1 in telomere maintenance and genome stability is poorly understood. Therefore we used mRtel1-deficient mouse embryonic stem cells to examine the function of mRtel1 in replication, DNA repair, recombination, and telomere maintenance. mRtel1-deficient mouse embryonic stem cells showed sensitivity to a range of DNA-damaging agents, highlighting its role in replication and genome maintenance. Deletion of mRtel1 increased the frequency of sister chromatid exchange events and suppressed gene replacement, demonstrating the involvement of the protein in homologous recombination. mRtel1 localized transiently at telomeres and is needed for efficient telomere replication. Of interest, in the absence of mRtel1, telomeres in embryonic stem cells appeared relatively stable in length, suggesting that mRtel1 is required to allow extension by telomerase. We propose that mRtel1 is a key protein for DNA replication, recombination, and repair and efficient elongation of telomeres by telomerase.
Common Problems of the Menopause
Authors: Rigg Carolyn
Published: May 2012

Menopausal symptoms and their management are a common presenting complaint. Hormone replacement therapy (HRT) is effective in the relief of menopausal symptoms; however, its use remains controversial. There are alternative treatment options available for women who cannot or do not wish to take HRT. This article aims to provide an overview of some common menopausal symptoms experienced by women and an approach to their management.
Significant Reduction in Central Venous Catheter–related Bloodstream Infections in Children on HPN After Starting Treatment With Taurolidine Line Lock
Authors: Chu Hui‐Ping , Brind Joanne , Tomar Rajeev , Hill Susan
Published: May 2012

Objective:

The aim of this study was to review the incidence and type of central venous catheter–related bloodstream infection in children on treatment with home parenteral nutrition (PN) before and after the introduction of taurolidine. Taurolidine is a catheter lock solution that prevents biofilm formation and has broad‐spectrum bactericidal and antifungal action. Its use in pediatric patients on PN has only been reported in case studies.

Methods:

A total of 19 children were reviewed, with the diagnoses of enteropathy (8 cases), short bowel syndrome (7 cases), and gastrointestinal dysmotility (4 cases). Incidence and type of sepsis were reviewed for 8 to 12 months pre‐ (when heparin was used) and 2 to 33 months postintroduction of the taurolidine catheter lock.

Results:

There were 8.6 episodes of catheter‐related bloodstream infections per 1000 catheter days with heparin and 1.1 episodes per 1000 catheter days with taurolidine (P = 0.002). A total of 14 of the 19 patients (74%) had no infections for up to 33 months after changing to taurolidine. No reports of multiresistant organisms or adverse effects with taurolidine were found.

Conclusions:

Taurolidine line lock was associated with a decreased incidence of catheter‐related bloodstream infections. This finding supports its use in patients with a history of septicemia on treatment with cyclical PN.
Three-dimensional structure of the Epstein–Barr virus capsid
Authors: Germi Raphaele , Effantin Gregory , Grossi Laurence , Ruigrok Rob W. H. , Morand Patrice , Schoehn Guy
Published: May 2012

Epstein–Barr virus (EBV), a gammaherpesvirus, infects >90 % of the world’s population. Primary infection by EBV can lead to infectious mononucleosis, and EBV persistence is associated with several malignancies. Despite its importance for human health, little structural information is available on EBV. Here we report the purification of the EBV capsid by CsCl- or sucrose density-gradient centrifugation. Cryo-electron microscopy and image analysis resulted in two slightly different three-dimensional structures at about 20 Å resolution. These structures were compared with that of human herpesvirus 8, another gammaherpesvirus. CsCl-gradient purification leads to the removal of part of the triplex complex around the fivefold axes, whereas the complexes between hexons remained in place. This may be due to local differences in stability resulting from variation in quasi-equivalent interactions between pentons and hexons compared with those between hexons only.
An Investigation of the Basic Physics of Irrigation in Urology and the Role of Automated Pump Irrigation in Cystoscopy
Authors: Chang Dwayne , Manecksha Rustom P. , Syrrakos Konstantinos , Lawrentschuk Nathan
Published: May 2012

Objective. To investigate the effects of height, external pressure, and bladder fullness on the flow rate in continuous, non-continuous cystoscopy and the automated irrigation fluid pumping system (AIFPS).Materials. Each experiment had two 2-litre 0.9% saline bags connected to a continuous, non-continuous cystoscope or AIFPS via irrigation tubing. Other equipment included height-adjustable drip poles, uroflowmetry devices, and model bladders.Methods. In Experiment 1, saline bags were elevated to measure the increment in flow rate. In Experiment 2, saline bags were placed under external pressures to evaluate the effect on flow rate. In Experiment 3, flow rate changes in response to variable bladder fullness were measured.Results. Elevating saline bags caused an increase in flow rates, however the increment slowed down beyond a height of 80 cm. Increase in external pressure on saline bags elevated flow rates, but inconsistently. A fuller bladder led to a decrease in flow rates. In all experiments, the AIFPS posted consistent flow rates.Conclusions. Traditional irrigation systems were susceptible to changes in height of irrigation solution, external pressure application, and bladder fullness thus creating inconsistent flow rates. The AIFPS produced consistent flow rates and was not affected by any of the factors investigated in the study.
Qualitative Evaluation of the Project P.A.T.H.S.: An Integration of Findings Based on Program Implementers
Authors: Shek Daniel T. L.
Published: May 2012

An integration of the qualitative evaluation findings collected from program implementers conducting the Project P.A.T.H.S. (Positive Adolescent Training through Holistic Social Programmes) in different years (n=177participants in 36 focus groups) was carried out. General qualitative data analyses utilizing intra and interrater reliability techniques were performed. Results showed that the descriptors used to describe the program and the metaphors named by the informants that could stand for the program were generally positive in nature. Program participants also perceived the program to be beneficial to the development of the students in different psychosocial domains. The present study further supports the effectiveness of the Tier 1 Program of the Project P.A.T.H.S. in Hong Kong based on the perspective of the program implementers.
Therapeutic Angiogenesis Using Basic Fibroblast Growth Factor in Combination with a Collagen Matrix in Chronic Hindlimb Ischemia
Authors: Zhou Jianyin , Zhao Yilin , Wang Jinling , Zhang Sheng , Liu Zhengjin , Zhen Maochuan , Liu Yun , Liu Pingguo , Yin Zhenyu , Wang Xiaomin
Published: May 2012

Although therapeutic angiogenesis by angiogenic cytokines is a feasible strategy to improve regional blood flow in ischemic regions, the optimal delivery mode needs to be established. Here we designed a complex of collagen matrix (CM) and basic fibroblast growth factor (bFGF) and evaluated its proangiogenic effect in ischemic hindlimbs. The bFGF-CM was prepared using lyophilization. The morphology, porosity and toxicity of CM were examined. The bFGF releasing profile and bioactivity of released bFGF were assessed. bFGF-CM was intramuscularly implanted into the rabbit ischemic hindlimb model. Oxygen saturation parameters (OSP) of ischemic hindlimbs was measured to evaluate the extremity perfusion at intervals. Histological examination was performed to evaluate the level of angiogenesis. The CM and bFGF-CM were of identical multiporous structure lacking cytotoxicity. The releasing profile lasted 10 days and the released bFGF remained bioactive. OSP in bFGF-CM group was significantly higher than that in CM, bFGF and ischemic groups at 2 and 4 weeks. The number of capillaries and mature vessels in bFGF-CM group were significantly greater than that in untreated control, CM and bFGF groups. Therefore, bFGF-CM enables the safe and effective long-term release of bFGF with improved angiogenesis in ischemic hindlimbs compared with CM devoid of bFGF.