bluuebunny/crossref_metadata_2025 huggingface dataset:
High giant magnetoresistance in electrodeposited Cu/Co nano‐multilayers
Authors: Gupta Priyanka , Pandya Dinesh K. , Kashyap Subhash C. , Chaudhary Sujeet
Published: May 2007

Nano‐multilayers of Cu(6 nm)/Co(∼22 nm) have been electrodeposited in potentiostatic pulse mode on ITO coated glass substrates. Cyclic voltammetry and chronoamperometric studies were performed to determine the potential and duration for the deposition of individual layers. A 50‐bilayer stack exhibited a room temperature GMR of 12.5%, at 8 kOe. Even at low fields of ∼3 kOe, this multilayer exhibited ∼10% GMR, thereby demonstrating the potential application of electrodeposition (ED) process in achieving appreciable value of GMR at room temperature and at lower field values. The observed high value of GMR at room temperature may be attributed to the antiferromagnetically (AF) aligned magnetic layers in the absence of magnetic field. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Integration of enhancement and depletion‐mode AlGaN/GaN MIS‐HFETs by fluoride‐based plasma treatment
Authors: Wang Ruonan , Cai Yong , Tang Wilson C. W. , Lau Kei May , Chen Kevin J.
Published: May 2007

Enhancement‐mode AlGaN/GaN metal–insulator–semiconductor HFETs (MIS‐HFETs) are demonstrated by combining CF4 plasma treatment technique and a two‐step Si3N4 deposition process. The threshold voltage has been shifted from –4 to 2 V using this technique. A 15 nm Si3N4 layer is inserted under the gate to provide additional isolation between the gate metal and AlGaN surface, which can lead to higher gate turn‐on voltage. The two‐step Si3N4 deposition process is developed to reduce the gate coupling capacitances in the source and drain access regions, while assuring the plasma‐treated gate region being fully covered by the gate electrode. The forward gate turn‐on voltage can be as large as 6.8 V. By tuning the plasma treatment parameters, the threshold voltage of the enhancement‐mode MIS‐HFETs can be raised to as high as 4.3 V. By integrating with depletion‐mode MIS‐HFETs, a direct‐coupled FET logic inverter has been fabricated, with logic low and high noise margins of 2.1 and 2 V. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of millimeter‐wave GaN HFET technology
Authors: Higashiwaki M. , Mimura T. , Matsui T.
Published: May 2007

This paper describes approaches that we have used to improve the high‐frequency device characteristics of GaN‐based heterostructure field‐effect transistors (HFETs). We developed three novel techniques to suppress short‐channel effects: high‐Al‐composition and thin barrier layers, SiN passivation by catalytic chemical vapor deposition, and sub‐100‐nm Ti‐based gates. These techniques were used to enhance the high‐frequency device characteristics of Al0.4Ga0.6N/GaN HFETs, which had a record current‐gain cutoff frequency of 181 GHz. In addition, high‐performance depletion‐ and enhancement‐mode AlN/GaN HFETs, which had DC and RF device characteristics fully comparable with those of state‐of‐the‐art AlGaN/GaN HFETs, were also fabricated with these techniques. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐fmax GaN HEMT with high breakdown voltage over 100 V for millimeter‐wave applications
Authors: Makiyama Kozo , Ohki Toshihiro , Kanamura Masahito , Imanishi Kenji , Hara Naoki , Kikkawa Toshihide
Published: May 2007

This paper discusses the technology of state‐of‐the‐art GaN high electron mobility transistors (GaN‐HEMTs) used for millimeter‐wave amplifiers. A high maximum frequency of oscillation (fmax) device with high breakdown voltage (BVgd) was focused on to improve the gain and efficiency of a millimeter‐wave amplifier. In this study, we demonstrated a high fmax of 210 GHz with a BVgd of over 100 V using a novel Y‐shaped Schottky‐gate and GaN‐cap structure, for the first time. The effect of the AlGaN layer and the device dimensions were investigated to obtain a highly reliable millimeter‐wave power amplifier. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
AlGaN/GaN high electron mobility transistor sensor sensitive to ammonium ions
Authors: Alifragis Y. , Volosirakis A. , Chaniotakis N. A. , Konstantinidis G. , Iliopoulos E. , Georgakilas A.
Published: May 2007

Chemically modified Field Effect Transistor (ChemFET) sensor for ammonium (NH$ ^+_4 $) ions was developed from AlGaN/GaN High Electron Mobility Transistor (HEMT) structures (NH$ ^+_4 $‐ChemHEMT). The sensor consists of a HEMT device with non‐metallized gate, which was coated with a polyvinyl chloride (PVC) membrane enriched with ammonium ionophore (Nonactin). The AlGaN/GaN NH$ ^+_4 $‐ChemHEMT with gate width of 100 μm and gate length of 100 μm exhibited a constant sensitivity of 55.5 mV/pNH$ ^+_4 $ for NH$ ^+_4 $ concentration in the range from 10–5 M to 10–2 M. The NH$ ^+_4 $ concentration detection limit was 5.4 × 10–6 M, which is approximately one order of magnitude lower compared to Si based insulator gate ChemFETs. The sensor exhibited also sufficiently long storage lifetime, indicating the strong adhesion of the PVC membrane to the GaN(0001) surface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental demonstration of enhancement mode GaN MOSFETs
Authors: Huang W. , Chow T. P. , Khan T.
Published: May 2007

We report on the demonstration of enhancement‐mode n‐channel GaN high‐voltage metal–oxide field‐effect transistor (MOSFET) realized on both p‐ and n‐GaN epilayer on sapphire substrates. These MOSFETs, with different gate geometries, shows good DC characteristics with world‐best field‐effect mobility of 167 cm2/V s and maximum blocking voltage of 940 V. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theory of quantum transport in carbon nanotubes: Perfect conductance, dynamical conductivity, and inter‐wall interaction
Authors: Ando Tsuneya , Asada Yoichi , Uryu Seiji
Published: May 2007

A brief review is given on transport properties of carbon nanotubes mainly from a theoretical point of view. The topics include an effective‐mass description of electronic states, the absence of backward scattering except for scatterers with a potential range smaller than the lattice constant, the presence of a perfectly conducting channel, and effects of symmetry breaking perturbations. The dynamical conductivity in the presence of a perfect channel and inter‐wall interactions in double‐wall nanotubes are also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Light‐induced cytotoxicity of 16 polycyclic aromatic hydrocarbons on the US EPA priority pollutant list in human skin HaCaT keratinocytes: Relationship between phototoxicity and excited state properties
Authors: Wang Shuguang , Sheng Yinghong , Feng Manliang , Leszczynski Jerzy , Wang Lei , Tachikawa Hiroyasu , Yu Hongtao
Published: May 2007

The photocytotoxicity of 16 polycyclic aromatic hydrocarbons (PAHs) on the priority pollutant list of the United States Environmental Protection Agency (US EPA) were tested in human skin HaCaT keratinocytes. A selected PAH was mixed with HaCaT cells and irradiated with a solar simulator lamp for a dose equivalent to 5 min of outdoor sunlight and the cell viability was determined immediately and also after 24 h of incubation. For the cells without incubation after the treatments, it is found that all PAHs with three rings or less, except anthracene, are not photocytotoxic, while the four or five‐ring PAHs (except chrysene), benz[a]anthracene, dibenzo[a,h]anthracene, benzo[ghi]perylene, benzo[a]pyrene, indeno[1,2,3‐cd]pyrene, benzo[b]fluorenthene, fluorenthene, and pyrene, are photocytotoxic to the human skin HaCaT keratinocytes. If the cells were incubated for 24 h after the treatments, the photocytotoxic effect of the PAHs was greatly amplified in comparison to the nonincubated cells. For the 24 h incubated cells, all PAHs except naphthalene exhibit photocytotoxicity to some extent. Exposure to 5 μM of the 4‐ and 5‐ring PAHs (except chrysene) and 3‐ring anthracene more than 80% of the cells lose viability. The photocytotoxicity of the PAHs correlates well with several of their excited state properties: light absorption, excited singlet‐state energy, excited triplet‐state energy, and HOMO‐LUMO energy gap. All the photocytotoxic PAHs absorb light at >300 nm, in the solar UVB and UVA region. There is a threshold for each of the three excited state descriptors of a photocytotoxic PAH: singlet energy <355 kJ/mol (corresponding to 337 nm light), triplet energy <230 kJ/mol (corresponding to 520 nm light), HOMO‐LUMO gap <3.6 eV (corresponding to 344 nm light) obtained at the Density Functional Theory B3LYP/6‐31G(d) level. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 318–327, 2007.
First report of microcystin‐LR in the cyanobacterium Gloeotrichia echinulata
Authors: Carey Cayelan C. , Haney James F. , Cottingham Kathryn L.
Published: May 2007

Gloeotrichia echinulata is a bloom‐forming cyanobacterium that is common in eutrophic lakes, and less prevalent but increasing in oligotrophic lakes. We used an enzyme‐linked immunosorbent assay analysis to test for the presence of the hepatotoxin microcystin‐LR (MC‐LR) in G. echinulata collected from an oligotrophic lake in central New Hampshire, USA. We found that G. echinulata contained MC‐LR at mean concentrations of 97.07 ± 7.78 (1 s.e.) ng MC‐LR g−1 dry wt colonies. This suggests that recent outbreaks of G. echinulata in oligotrophic lakes used as water sources throughout New England (USA) may pose a health concern. The toxicity of G. echinulata reported here suggests the need for future monitoring of microcystins in oligotrophic lakes. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 337–339, 2007.
Application of high‐intensity focused ultrasound for umbilical artery occlusion in a rabbit model
Authors: Ichizuka K. , Ando S. , Ichihara M. , Ishikawa T. , Uchiyama N. , Sasaki K. , Umemura S. , Matsuoka R. , Sekizawa A. , Okai T. , Akabane T. , Kushima M.
Published: May 2007

Objectives

To investigate the application of high‐intensity focused ultrasound (HIFU) for fetal umbilical artery blood flow occlusion in a rabbit model.

Methods

A prototype HIFU transducer in combination with an imaging probe with Doppler capability was constructed. Using this transducer, HIFU was applied at 1.4, 2.75 or 5.5 kW/cm2 through the maternal abdominal skin to the fetal intra‐abdominal umbilical arteries of four time‐mated Japanese White rabbits (11 fetuses) on gestational day 25. Courses of 5‐s HIFU exposure were performed until cessation of umbilical blood flow and cardiac arrest were confirmed by Doppler ultrasonography. Fetal necropsy was performed and exposed lesions were assessed by microscopic histological analysis.

Results

The mean diameter of the fetal umbilical artery was 0.6 ± 0.2 mm and the mean peak systolic velocity of arterial blood flow was 44.7 ± 18.5 cm/s. When HIFU was applied at 5.5 kW/cm2, blood flow was completely occluded within 15 courses. HIFU exposure brought about vacuolar degeneration and destruction of elastic fibers in the tunica media of the artery.

Conclusions

HIFU can be used to occlude umbilical artery blood flow in fetal rabbits. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.
Where two oceans meet: distribution and offshore interactions of great-winged petrels Pterodroma macroptera and Leach’s storm petrels Oceanodroma leucorhoa off southern Africa
Authors: Camphuysen Kees C. J.
Published: May 2007

During seabird surveys off southern Africa, great-winged petrel Pterodroma macroptera and Leach’s storm petrel Oceanodroma leucorhoa were widespread and relatively common. Similar aerial displays, frequent (social) interactions, a tendency to “huddle” in tight (mixed) gatherings and interactions during foraging inspired a study of their behaviour and distribution. Both species peaked at >2,000-m-deep ocean waters, with lower densities over the shelf and with Leach’s storm petrels (ca. 0.5 km−2) twice as abundant as great-winged petrels (ca. 0.25 km−2). The results suggest half a million great-winged petrels and well over a million Leach’s storm petrels occurring over deep waters off southern Africa. Active fishing vessels elevated background densities of petrels in some areas, indicating the utilisation of discarded material, but in most areas hardly any fisheries were encountered and on the shelf with no discernable effect on petrel densities. Both species showed an association with meso-scale hydrographic features in the Agulhas current retroflection region. High densities of Leach’s storm petrels occurred in offshore areas with steep salinity and sea surface temperature gradients. No such tendency was found in great-winged petrels. Great-winged petrels spent relatively little time feeding during daylight (10.3% of birds observed) in comparison to Leach’s storm petrels (66.2%), but were frequently seen to join feeding Leach’s storm petrels where they profited from the searching skills of Leach’s. Both species performed displays as individuals, in pairs, in larger groups and in mixed-species groups. Tight gatherings of petrels swimming at sea (huddling) occurred, consisting either of one species or both. When disturbed, such flocks would disperse after take off and often engage in aerial displays. It is speculated that the formation of these flocks is part of the anti-predator strategy of petrels against attacks from under water.
Growing Up and Living with Neurofibromatosis1 (NF1): A British Bangladeshi Case‐study
Authors: Rozario Santi
Published: May 2007

In this article, I analyse a narrative by Rohima1, a Bangladeshi woman now living in the UK who was diagnosed in adulthood as having NF1 (neurofibromatosis). While some themes in her narrative account resemble those of persons with NF1 in the general European and American population, other themes relate specifically to Bangladeshi cultural issues and practices. These particularly concern gender, sexual identity and marriage. As a young woman, Rohima's dark skin coloration and the tumors or lumps associated with her condition led her parents and relatives to regard her as unmarriageable and in effect, despite her evident intelligence and competence, to deny that she was a woman. Bangladeshi men and women alike found her appearance a bar to any social acceptability. Even after her marriage (to a non‐Bangladeshi man), her family have been unwilling to accept her and her children fully into their kinship network. The article explores the consequences of genetic disorders such as NF1 in cultures where social identity and concepts of personhood, particularly for women, are inextricably related to appearance and to judgements regarding marriageability.
Indian Ocean Studies and the ‘new thalassology’
Authors: Vink Markus P. M.
Published: May 2007

This article explores the past, present, and possible future directions of the ‘‘new thalassology’’ [from the ancient Greek thalassa, ‘‘sea’’] and Indian Ocean studies from its humble beginnings in the 1950s and 1960s, and the cross-fertilization between the ‘Annales’ school and world-systems analysis in the 1980s, to its – admittedly incomplete – institutionalization in the early twenty-first century. In addition, it defines the numerous, often flexible and permeable, spatial and temporal boundaries or ‘frontiers’ of the Indian Ocean world(s). A final section surveys some of the potentialities and pitfalls of Indian Ocean studies and the new thalassology, with the strengths outweighing the weaknesses. The new thalassology undoubtedly presents some daunting challenges. It is to be hoped, however, that charting some of the ‘hundred frontiers’ of the globalized, inter-regional Indian Ocean seascape provides some sense of direction for this exciting field of scholarship and helps shape the future contours of maritime-based studies
Thermophysical properties of the Isidis basin, Mars
Authors: Murphy Nathaniel W. , Jakosky Bruce M. , Rafkin Scot C. , Larsen Kristopher W. , Putzig Nathaniel E. , Mellon Michael T.
Published: May 2007

We investigated the thermal properties of the Isidis basin in order to understand the high values (>450 J m−2 K−1 s−1/2) located in the southern region of the basin. Thermal inertia data were compared to a variety of complementary data sets, including radar, visible, and results from mesoscale atmospheric simulations. We considered four mechanisms for creating the high thermal inertia, including (1) the thinning of a dust mantle, (2) the presence of unconsolidated, coarse‐grained material, (3) high rock abundance, and (4) a high degree of induration. Induration is the scenario most consistent with the data, although we cannot rule out unconsolidated materials and it is likely that rocks contribute to values of thermal inertia to a lesser degree. We also investigated three mechanisms for controlling the geographical distribution of the high thermal inertia values, including (1) the influence of topography, (2) the role of surface morphology, and (3) present aeolian processes. Topography plays a significant role along the southern boundary of the basin but not within the basin itself. THEMIS data show a complex relationship between the thermal inertia and morphology. The wind patterns modeled by the Mars Regional Atmospheric Modeling System (MRAMS) are not fully consistent with the wind directions implied by streaks in the thermal data but are consistent with a second group of streaks observed in the visible data. This suggests that small‐scale (tens of kilometers) streaks observed in the thermal data did not form under present‐day, nominal winds.
Contribution of the polarizability anisotropy to Rayleigh scattering
Authors: Sharma Ramesh D.
Published: May 2007

A calculation from first principles of the differential cross section for Rayleigh scattering shows that the contribution of polarizability anisotropy found in the literature is valid only in the high rotational quantum number limit of the vector coupling coefficients, that is, in the high‐temperature or classical limit. The additional term in the total Rayleigh scattering cross section arising from the polarizability anisotropy is about four times smaller than what is called the King factor in the literature. These errors, resulting from ignoring the constraints imposed by the conservation of angular momentum, can lead to significant corrections in estimating populations from stratospheric and mesospheric measurements.
Neogene evolution of Atlantic thermohaline circulation: Perspective from Walvis Ridge, southeastern Atlantic Ocean
Authors: Thomas Deborah J. , Via Rachael K.
Published: May 2007

We present new Nd isotope records from Walvis Ridge Ocean Drilling Program (ODP) sites 1262–1264 (southeastern Atlantic) spanning the past 24 Ma to investigate the Neogene evolution of Atlantic thermohaline circulation. The new data indicate that deepwater ɛNd(t) values from ODP Site 1262 decrease from −11.0 at 10.6 Ma to −12.5 by 7.3 Ma. This decrease parallels the Nd isotope trends contained in Fe‐Mn crust records from the northwestern Atlantic; however, the shift at ODP Site 1262 (4755 m water depth) occurred up to ∼6 Ma earlier than the corresponding changes in crust records from the Atlantic and earlier than any Atlantic site shallower than 2700 m paleowater depth. Recent interpretations of the rapid decrease in Fe‐Mn crust Nd ɛNd(t)ssvalues invoke changes in weathering inputs to the Labrador Sea region rather than a fundamental change in deepwater convection in the Labrador Sea. However, the new evidence for significant depth stratification of the Nd isotope signal in the southeastern Atlantic between 10.6 and 7.3 Ma suggests that the onset of deepwater convection in the Labrador Sea may have played a role in the deepwater decrease in Nd isotopic composition. Climatic conditions during the middle to late Miocene likely favored an increase in the importance of glacially induced mechanical weathering, while at the same time promoting deep convection in the Labrador Sea.
Testing regional vertical total electron content maps over Europe during the 17–21 January 2005 sudden space weather event
Authors: Orus R. , Cander L. R. , Hernandez‐Pajares M.
Published: May 2007

The intense level of solar activity recorded from 16 to 23 January 2005 led to a series of events with different signatures at the Earth's ionospheric distances. Measurements of the critical frequency of the F2 layer foF2 and the vertical total electron content (VTEC) are used to describe the temporal and spatial electron density distributions during this space weather event, which gives an excellent opportunity to test regional VTEC maps over Europe under such disturbed solar‐terrestrial conditions. In this context, the tests used to validate the International GNSS Service (IGS) VTEC maps have been applied to assess the accuracy of the European Rutherford Appleton Laboratory (RAL) VTEC maps. Thus the self‐consistency test and the Jason altimeter test have been used to compare such performances with the IGS and Universitat Politecnica de Catalunya global ionospheric maps. The results show discrepancies between the RAL maps and the IGS ones, which leads to significant RMS and bias values of several total electron content units. Moreover, in this work a kriging technique to improve the accuracy of any regional VTEC map is also considered, with relative improvements of the RAL VTEC maps up to more than 20% at the peak of the storm.
Estimation of spin transfer torque effect and thermal activation effect on magnetization reversal in CoFeB∕MgO∕CoFeB magnetoresistive tunneling junctions
Authors: Yoshikawa Masatoshi , Ueda Tomomasa , Aikawa Hisanori , Shimomura Naoharu , Kitagawa Eiji , Nakayama Masahiko , Kai Tadashi , Nishiyama Katsuya , Nagase Toshihiko , Kishi Tatsuya , Ikegawa Sumio , Yoda Hiroaki
Published: May 2007

In the CoFeB∕MgO∕CoFeB magnetoresistive tunneling junctions, the bias-dependent magnetic switching curves are investigated and the spin transfer torque effect and the thermal activation effect on the magnetic switching are estimated. The different switching behaviors at the positive and negative biases were observed, which are the asymmetric changes of the coercive force and the shift field. In order to investigate the asymmetric reduction of the coercive force according to the bias direction, the magnetic excitation effect due to the hot electron was introduced. Consequently, from the analysis by using the current versus magnetic field phase diagram, the asymmetric reduction of the coercive force at the positive and negative biases was explained quantitatively by the relationship between the thermal activation effect due to the Joule heating and the magnetic excitation effect due to the hot electron.
Chemical reaction modeling for hypervelocity collisions between O and HCl
Authors: Ozawa T. , Levin D. A. , Wysong I. J.
Published: May 2007

The sensitivity of a rarefied-to-transitional flow to the fidelity of the chemical reaction model is investigated for a new molecular dynamics/quasiclassical trajectory (MD/QCT)-derived model and compared with the widely used total collision energy (TCE) model of Bird. For hypervelocity collisions that occur in the space environment, it is not clear, a priori, that the TCE model will provide reasonable results for the required high energy range and, particularly, if strong favoring of the reaction among different forms of reactant energy occurs. In fact, in previous work, the TCE model, using available Arrhenius parameters, has been found, for these flow conditions, to give unphysical probabilities. A chemical reaction model, suitable for use in the direct simulation Monte Carlo (DSMC) method, is developed to simulate the hypervelocity collisions of O(P3)+HCl(Σ+1)→OH(Π2)+Cl(P2), an example of an important reaction in high-altitude atmospheric-jet interactions. The model utilizes the MD/QCT method with a new benchmark triplet A″ surface. Since the modeling of chemical reactions in DSMC simulations requires the use of a reaction probability, the adequacy of the overall collision cross section, usually modeled by the variable hard sphere (VHS) model, is also considered. To obtain an accurate collision cross section, the approach of Tokumasu and Matsumoto was used in the MD/QCT method with the aforementioned potential energy surface. Energy transfer between the target HCl translational and internal energy modes was investigated and it was found that the variation of the inelastic cross section has a negligible effect on the transport cross section. Therefore, a MD/QCT VHS equivalent collision cross section was obtained and along with the MD/QCT reaction cross sections were utilized in the full DSMC calculation of the flow field. It was found that for a low enthalpy reaction, in hypervelocity collisions, the TCE model with accurate Arrhenius rates appears to agree well with the rigorous MD/QCT calculations which shows that the reaction does not exhibit strong favoring.
High frequency tunable band stop filters using antiferromagnetic films
Authors: Veerakumar V. , Camley R. E.
Published: May 2007

We study the performance of a high frequency band stop filter which can work in both the microwave and infrared regions using an antiferromagnet film as the active material. We find that the band stop frequencies can be adjusted by changing the applied magnetic field or by changing the temperature. Also, the attenuation of the wave at a band stop frequency can be controlled by varying the physical parameters such as the thickness of the antiferromagnetic film or the thickness of the dielectric spacer. In addition, the attenuation is strongly dependent on the anisotropy field in the antiferromagnet. Further, the band stop filter using antiferromagnet does not have the constraints due to skin depth and conductivity losses as many of the antiferromagnets are insulators.
Fluorescence lifetime fluctuations of single molecules probe the local environment of oligomers around the glass transition temperature
Authors: Vallée R. A. L. , Baruah M. , Hofkens J. , De Schryver F. C. , Boens N. , Van der Auweraer M. , Beljonne D.
Published: May 2007

Single molecule fluorescence experiments have been performed on a BODIPY-based dye embedded in oligo(styrene) matrices to probe the density fluctuations and the relaxation dynamics of chain segments surrounding the dye molecules. The time-dependent fluorescence lifetime of the BODIPY probe was recorded as an observable for the local density fluctuations. At room temperature, the mean fraction of holes surrounding the probes is shown to be unaffected by the molecular weight in the glassy state. In contrast, the free volume increases significantly in the supercooled regime. These observations are discussed in the framework of the entropic theories of the glass transition.
Weakly dispersive hydraulic flows in a contraction: Parametric solutions and linear stability
Authors: Ee Bernard K. , Clarke Simon R.
Published: May 2007

We consider the propagation of stratified fluid through a contraction near resonance, for which the governing asymptotic equation is the forced Korteweg–de Vries equation. Steady solutions of this equation are sought that have constant but differing amplitudes upstream and downstream of the contraction, and for which leading-order dispersive effects are retained. A numerical algorithm is outlined to obtain such solutions, yielding a parametric relationship between the normalized velocity perturbation and the normalized width perturbation. Matrix methods are then used to investigate the linear stability of these solutions.
Ab initio investigation of ammonia-borane complexes for hydrogen storage
Authors: Miranda Caetano R. , Ceder Gerbrand
Published: May 2007

The structural, electronic, and thermodynamic properties of ammonia-borane complexes with varying amounts of hydrogen have been characterized by first principles calculations within density functional theory. The calculated structural parameters and thermodynamic functions (free energy, enthalpy and entropy) were found to be in good agreement with experimental and quantum chemistry data for the crystals, dimers, and molecules. The authors find that zero-point energies change several H2 release reactions from endothermic to exothermic. Both the ammonia-borane polymeric and borazine-cyclotriborazane cycles show a strong exothermic decomposition character (approximately −10kcal∕mol), implying that rehydrogenation may be difficult to moderate H2 pressures. Hydrogen bonding in these systems has been characterized and they find the N–H bond to be more covalent than the more ionic B–H bond.
Characterization of flow behavior in an enclosed cylinder with a partially rotating end wall
Authors: Yu P. , Lee T. S. , Zeng Y. , Low H. T.
Published: May 2007

The vortex breakdown phenomena in an enclosed cylindrical chamber with a rotating disk whose radius is smaller than that of the chamber were investigated by a numerical model based on the steady, axisymmetric Navier-Stokes equations. The flow behaviors were investigated over a wide range of parameters. The main recirculation region remains unchanged if the cylinder-to-disk ratio, the ratio of the chamber radius to the disk radius, is beyond the recirculation-invariance ratio. The recirculation-invariance ratio displays a generally linear relationship with the vertical ratio, the ratio of the chamber height to disk radius. The trends of the vortex breakdown boundary curves at different cylinder-to-disk ratios suggest that three regions, namely the quasi whole end-wall rotating region, the vortex-breakdown boundary invariance region, and the mixed region, can be used to characterize the occurrence of vortex breakdown. Depending on the specific conditions, the presence of the stationary end wall either serves to precipitate or delay the onset of vortex breakdown. The stationary end wall has the effect of reducing the physical aspect ratio but it also dissipates the fluid’s angular momentum along its surface. These two opposite effects lead to different trends of the vortex-breakdown boundary curves in different regions, depending on which effect is dominant.
Reply to “Comment on ‘Melting dynamics of superheated argon: Nucleation and growth’” [J. Chem. Phys. 126, 034505 (2007)]
Authors: Luo Sheng-Nian , Zheng Lianqing , Strachan Alejandro , Swift Damian C.
Published: May 2007

The critical size of melt nuclei in homogeneous nucleation was claimed to be exactly the number of atoms around a single vacancy in the preceding Comment. However, this number only represents a lower limit of the critical size. The melt nuclei in homogeneous nucleation form and grow or shrink via fluctuations. The critical size of a nucleus is inevitably tied to the characteristics of its fluctuations and is about 100 atoms (as opposed to about ten atoms) for argon as shown in our recent work, which lends firm support to phenomenological classical nucleation and growth theories.
Spin-orbit relaxation of Cl(P1∕22) and F(P1∕22) in a gas of H2
Authors: Abrahamsson Erik , Groenenboom Gerrit C. , Krems Roman V.
Published: May 2007

The authors present quantum scattering calculations of rate coefficients for the spin-orbit relaxation of F(P1∕22) atoms in a gas of H2 molecules and Cl(P1∕22) atoms in a gas of H2 and D2 molecules. Their calculation of the thermally averaged rate coefficient for the electronic relaxation of chlorine in H2 agrees very well with an experimental measurement at room temperature. It is found that the spin-orbit relaxation of chlorine atoms in collisions with hydrogen molecules in the rotationally excited state j=2 is dominated by the near-resonant electronic-to-rotational energy transfer accompanied by rotational excitation of the molecules. The rate of the spin-orbit relaxation in collisions with D2 molecules increases to a great extent with the rotational excitation of the molecules. They have found that the H2∕D2 isotope effect in the relaxation of Cl(P1∕22) is very sensitive to temperature due to the significant role of molecular rotations in the nonadiabatic transitions. Their calculation yields a rate ratio of 10 for the electronic relaxation in H2 and D2 at room temperature, in qualitative agreement with the experimental measurement of the isotope ratio of about 5. The isotope effect becomes less significant at higher temperatures.
Surface effects on photopolymerization induced anisotropic phase separation in liquid crystal and polymer composites
Authors: Jin Min Young , Lee Tae-Hee , Jung Jong-Wook , Kim Jae-Hoon
Published: May 2007

The surface effects on the anisotropic phase separation in photopolymerization induced phase separation of liquid crystal and polymer composites have been studied. It was found that the surface interaction between the substrate and the prepolymer and/or liquid crystal plays a crucial role in anisotropic phase separation. A theoretical model is suggested to describe the surface effects by adapting a phenomenological free energy approach. The formation of polymer layer in the presence of surface effects can be understood as competition between entropic flow and surface directed flow of polymer and liquid crystal.
Roughing titanium quantum wire on patterned monohydride diamond (001) surface
Authors: Tan X. , Ouyang G. , Yang G. W.
Published: May 2007

The authors have performed the roughing of titanium (Ti) quantum wires forming on a hydrogen-terminated diamond (001)-2×1 surface patterned with an ordered bare strip array and demonstrated that well-ordered Ti quantum wires are achieved only if the growth conditions (temperature and flux) have optimal values via kinetic Monte Carlo simulations. Considering that a scanning tunneling microscope is capable of selectively desorbing H from diamond (001)-2×1-H surface, they proposed a viable and easy approach to fabricate “ideal quantum wires” on the patterned hydrogen-terminated diamond (001) surface. The physical origin of the Ti quantum wire formation was pursued.
Experimental and ab initio study of the mechanical properties of hydroxyapatite
Authors: Snyders R. , Music D. , Sigumonrong D. , Schelnberger B. , Jensen J. , Schneider J. M.
Published: May 2007

The authors have studied the elastic properties of radio frequency sputtered phase pure, stoichiometric, and dense hydroxyapatite films by nanoindentation. The measured elastic modulus values have been compared to ab initio calculated data. The calculation technique was based on the determination of all elastic constants. The calculated and measured elastic modulus values differ by ∼10%. The good agreement indicates that the elasticity of hydroxyapatite can be described using ab initio calculations, establishing the elastic modulus thereof.
Effect of water supply on leaf area development, stomatal activity, transpiration, and dry matter production and distribution in young olive trees
Authors: Gómez-del-Campo María
Published: May 2007

Two-year-old olive trees cv. Cornicabra, trained in a central leader form for hedgerow planting, were grown outdoors in 45-L weighing lysimeters to evaluate the effect of water supply on growth and development. Four treatments were established and maintained for 155 days during spring–autumn. Treatment T100 was irrigated to maintain the potting medium close to water-holding capacity by progressive replenishment of consumption that was measured at weekly intervals by weighing and recording drainage. Treatments T80, T60, and T40 received 80, 60, and 40%, respectively, of the water applied to T100. For these treatments, transpiration and leaf area were measured every fortnight. Dry matter in roots, stems, and leaves was measured at the beginning and end of the experiment. Leaf conductance was measured at 09 : 00 and 12 : 00 solar time every fortnight and at c. 2-hourly intervals throughout one day each month. Over the experimental period, T100 produced 0.42 ± 0.01 m2 leaf area, 319.6 ± 60.4 g dry biomass, and transpired 77.5 ± 1.1 L water. Water stress significantly reduced leaf area development and dry matter production (P < 0.05) in T60 and T40, but not in T80. There was no effect on dry matter partitioning to the various organs of the trees or the roots/aerial part ratio. Leaf conductance was more sensitive to water stress than vegetative growth, with significant differences (P < 0.05) established among treatments 3 weeks before differences were observed in transpiration. In autumn, transpiration and leaf conductance increased in all treatments independently of soil water status. Over the experiment, transpiration efficiency (TE, g/L) increased with reduced water supply, with a significant difference (P < 0.10) between T100 and both T60 and T40. The study has established that maximum growth of young olive plants can be achieved, without effect on the distribution of biomass between organs, at water supply less than that required to support maximum transpiration.
A Single Complementary-Sense Transcript of a Geminiviral DNA β Satellite Is Determinant of Pathogenicity
Authors: Saeed Muhammad , Behjatnia S. A. Akbar , Mansoor Shahid , Zafar Yusuf , Hasnain Shahida , Rezaian M. Ali
Published: May 2007

Small circular single-stranded DNA satellites, termed DNAβ, have recently been found associated with some geminivirus infections. The DNA β associated with Cotton leaf curl virus is responsible for symptom expression of a devastating disease in Pakistan. Mutagenesis of DNA β revealed that the complementary-sense open reading frame (ORF) βC1 is required for inducing disease symptoms in Nicotiana tabacum. An ORF present on the virion-sense strand βV1 appeared to have no role in pathogenesis. Tobacco plants transformed with a βC1 ORF under the control of the Cauliflower mosaic virus 35S promoter or with a dimeric DNA β exhibited severe disease-like phenotypes, while plants transformed with a mutated version of βC1 appeared normal. Northern blot analysis of RNA from the transgenic plants, using strand-specific probes, identified a single complementary-sense transcript. The transcript carries the full βC1 ORF encoding a 118-amino acid product. It maps to the DNA β at nucleotide position 186 to 563 and contains a polyadenylation signal 18 nt upstream of the stop codon. A TATA box is located 43 nt upstream of the start codon. Our results indicate that βC1 protein is responsible for DNA β-induced disease symptoms.
Transcript Profiles of Blumeria graminis Development During Infection Reveal a Cluster of Genes That Are Potential Virulence Determinants
Authors: Both Maike , Eckert Sabine E. , Csukai Michael , Müller Elisabeth , Dimopoulos George , Spanu Pietro D.
Published: May 2007

High-density cDNA microarrays (2,027 unigenes) were used to analyze transcript profiles of the plant-pathogenic fungus Blumeria graminis f. sp. hordei throughout its asexual life cycle and development of infection. RNA was obtained from four stages preceding penetration and four stages after penetration of the host cells. The microarray data was validated by comparing the expression of a plasma membrane H+-ATPase and fructose-1,6-bis phosphatase with the data obtained from a quantitative polymerase chain reaction (PCR) assay. The results showed that there was a global switch in expression between the pre- and postpenetrative stages. This was largely due to accumulation of RNA encoding protein biosynthesis genes in the late stages. Other functional clusters, such as virulence-related genes and sterol metabolism genes, are up-regulated in pre- and postpenetration stages, respectively. A group of RNAs whose abundance correlated with the expression of cap20, a gene known to be required for virulence in Colletotrichum gloeosporioides, identified genes that are strong candidates for pathogenicity factors in B. graminis.
Differences in Intensity and Specificity of Hypersensitive Response Induction in Nicotiana spp. by INF1, INF2A, and INF2B of Phytophthora infestans
Authors: Huitema Edgar , Vleeshouwers Vivianne G. A. A. , Cakir Cahit , Kamoun Sophien , Govers Francine
Published: May 2007

Elicitins form a family of structurally related proteins that induce the hypersensitive response (HR) in plants, particularly Nicotiana spp. The elicitin family is composed of several classes. Most species of the plant-pathogenic oomycete genus Phytophthor produce the well-characterized 10-kDa canonical elicitins (class I), such as INF1 of the potato and tomato pathogen Phytophthora infestans. Two genes, inf2A and inf2B, encoding a distinct class (class III) of elicitinlike proteins, also occur in P. infestans. Unlike secreted class I elicitins, class III elicitins are thought to be cell-surface- anchored polypeptides. Molecular characterization of the inf2 genes indicated that they are widespread in Phytophthora spp. and occur as a small gene family. In addition, Southern blot and Northern blot hybridizations using gene-specific probes showed that inf2A and inf2B genes and transcripts can be detected in 17 different P. infestans isolates. Functional secreted expression in plant cells of the elicitin domain of the inf1 and inf2 genes was conducted using a binary Potato virus X (PVX) vector (agroinfection) and Agrobacterium tumefaciens transient transformation assays (agroinfiltration), and resulted in HR-like necrotic symptoms and induction of defense response genes in tobacco. However, comparative analyses of elicitor activity of INF1, INF2A, and INF2B revealed significant differences in intensity, specificity, and consistency of HR induction. Whereas INF1 induced the HR in Nicotiana benthamiana, INF2A induced weak symptoms and INF2B induced no symptoms on this plant. Nonetheless, similar to INF1, HR induction by INF2A in N. benthamiana required the ubiquitin ligase-associated protein SGT1. Overall, these results suggest that variation in the resistance of Nicotiana spp. to P. infestans is shadowed by variation in the response to INF elicitins. The ability of tobacco, but not N. benthamiana, to respond to INF2B could explain differences in resistance to P. infestans observed for these two species.
Evidence That RNA Silencing-Mediated Resistance to Beet necrotic yellow vein virus Is Less Effective in Roots Than in Leaves
Authors: Andika Ida Bagus , Kondo Hideki , Tamada Tetsuo
Published: May 2007

In plants, RNA silencing is part of a defense mechanism against virus infection but there is little information as to whether RNA silencing-mediated resistance functions similarly in roots and leaves. We have obtained transgenic Nicotiana benthamiana plants encoding the coat protein readthrough domain open reading frame (54 kDa) of Beet necrotic yellow vein virus (BNYVV), which either showed a highly resistant or a recovery phenotype following foliar rub-inoculation with BNYVV. These phenotypes were associated with an RNA silencing mechanism. Roots of the resistant plants that were immune to foliar rub-inoculation with BNYVV could be infected by viruliferous zoospores of the vector fungus Polymyxa betae, although virus multiplication was greatly limited. In addition, virus titer was reduced in symptomless leaves of the plants showing the recovery phenotype, but it was high in roots of the same plants. Compared with leaves of silenced plants, higher levels of transgene mRNAs and lower levels of transgene-derived small interfering RNAs (siRNAs) accumulated in roots. Similarly, in nontransgenic plants inoculated with BNYVV, accumulation level of viral RNA-derived siRNAs in roots was lower than in leaves. These results indicate that the RNA silencing-mediated resistance to BNYVV is less effective in roots than in leaves.
The T-DNA Oncogene A4-orf8 from Agrobacterium rhizogenes A4 Induces Abnormal Growth in Tobacco
Authors: Umber Marie , Clément Bernadette , Otten Léon
Published: May 2007

The related orf8 and iaaM T-DNA genes from Agrobacterium are each composed of two distinct parts. The 5′ parts (called Norf8 or NiaaM) encode a 200-amino-acid (aa) sequence with homology to various T-DNA oncoproteins such as RolB, RolC, and 6b. The 3′ parts (Corf8 or CiaaM) encode a 550-aa sequence with homology to IaaM proteins from Pseudomonas and Pantoea spp. Whereas iaaM genes encode flavin adenine dinucleotide (FAD)-dependent tryptophan 2-monooxygenases that catalyze the synthesis of indole-3-acetamide (IAM), A4-orf8 from Agrobacterium rhizogenes A4 does not. Plants expressing a 2x35S-A4-Norf8 construct accumulate soluble sugars and starch. We now have regenerated plants that express the full-size 2x35S-A4-orf8 and the truncated 2x35S-A4-Corf8 gene. 2x35S-A4-Corf8 plants accumulate starch and show reduced growth like 2x35SA4-Norf8 plants but, in addition, display a novel set of characteristic growth modifications. These consist of leaf hypertrophy and hyperplasia (blisters); thick, dark-green leaves; thick stems; and swollen midveins. Mutations in the putative FAD-binding site of A4-Orf8 did not affect the blister syndrome. Plants expressing 2x35S-A4-Corf8 had a normal phenotype but contained less starch and soluble sugars than did wild-type plants. When 2x35S-A4-Corf8 plants were crossed to starch-accumulating 2x35S-A4-Norf8 plants with reduced growth, A4-Corf8 partially restored growth and reduced starch accumulation. A4-Corf8xA4-Norf8 crosses did not lead to the blister syndrome, suggesting that this requires physical linkage of the A4-NOrf8 and A4-COrf8 sequences.
Novel Quorum-Sensing-Controlled Genes in Erwinia carotovora subsp. carotovora: Identification of a Fungal Elicitor Homologue in a Soft-Rotting Bacterium
Authors: Pemberton C. L. , Whitehead N. A. , Sebaihia M. , Bell K. S. , Hyman L. J. , Harris S. J. , Matlin A. J. , Robson N. D. , Birch P. R. J. , Carr J. P. , Toth I. K. , Salmond G. P. C.
Published: May 2007

Seven new genes controlled by the quorum-sensing signal molecule N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) have been identified in Erwinia carotovora subsp. carotovora. Using TnphoA as a mutagen, we enriched for mutants defective in proteins that could play a role in the interaction between E. carotovora subsp. carotovora and its plant hosts, and identified NipEcc and its counterpart in E. carotovora subsp. atroseptica. These are members of a growing family of proteins related to Nep1 from Fusarium oxysporum which can induce necrotic responses in a variety of dicotyledonous plants. NipEcc produced necrosis in tobacco, NipEca affected potato stem rot, and both affected virulence in potato tubers. In E. carotovora subsp. carotovora, nip was shown to be subject to weak repression by the LuxR family regulator, EccR, and may be regulated by the negative global regulator RsmA.
Salicylic Acid-Induced Resistance to Cucumber mosaic virus in Squash and Arabidopsis thaliana: Contrasting Mechanisms of Induction and Antiviral Action
Authors: Mayers Carl N. , Lee Kian-Chung , Moore Catherine A. , Wong Sek-Man , Carr John P.
Published: May 2007

Salicylic acid (SA)-induced resistance to Cucumber mosaic virus (CMV) in tobacco (Nicotiana tabacum) results from inhibition of systemic virus movement and is induced via a signal transduction pathway that also can be triggered by antimycin A, an inducer of the mitochondrial enzyme alternative oxidase (AOX). In Arabidopsis thaliana, inhibition of CMV systemic movement also is induced by SA and antimycin A. These results indicate that the mechanisms underlying induced resistance to CMV in tobacco and A. thaliana are very similar. In contrast to the situation in tobacco and A. thaliana, in squash (Cucurbita pepo), SA-induced resistance to CMV results from inhibited virus accumulation in directly inoculated tissue, most likely through inhibition of cell-to-cell movement. Furthermore, neither of the AOX inducers antimycin A or KCN induced resistance to CMV in squash. Additionally, AOX inhibitors that compromise SAinduced resistance to CMV in tobacco did not inhibit SAinduced resistance to the virus in squash. The results show that different host species may use significantly different approaches to resist infection by the same virus. These findings also imply that caution is required when attempting to apply findings on plant-virus interactions from model systems to a wider range of host species.