bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of the total lightning structure in a leading‐line, trailing‐stratiform mesoscale convective system over Houston, Texas
Authors: Ely Brandon L. , Orville Richard E. , Carey Lawrence D. , Hodapp Charles L.
Published: April 2008

Line‐normal, vertical cross sections of Houston Lightning Detection and Ranging (LDAR) VHF radiation sources and radar reflectivity provide new insights into the three‐dimensional total lightning structure and evolution of a leading‐line, trailing‐stratiform (LLTS) mesoscale convective system (MCS) over Houston, Texas, on 31 October 2005. Previous research examining only the mature stage of an MCS showed that the overwhelming majority of VHF lightning sources occurred in the convective region with a lightning pathway extending rearward and descending in altitude into the stratiform region. This descending pathway was most likely associated with small, charged ice particles advected from the convective line. Unlike previous research, the lightning pathway observed during the evolution of the MCS on 31 October 2005 initially extended rearward 40 km at a nearly constant height of 9–10 km. In less than an hour, the lightning pathway evolved into a sloped pathway, similar to that found by previous research, with a horizontal extent between 50 to 60 km and downward descent of 4 to 5 km. During the lightning pathway evolution, radar analysis showed an increase of reflectivity in the midlevels of the stratiform region, consistent with increased depositional and aggregational growth above the melting layer. Broadening (increased range of values) of radar reflectivity above the melting layer was most likely an indication of a strengthening mesoscale updraft in the stratiform region. This strengthening updraft may have contributed to an increase in the growth of the small, charge carrying ice crystals giving them a greater fall speed. In addition, the mesoscale updraft may have promoted an environment conducive to local stratiform region charge generation in the mixed phase region just above the melting layer.
Validation of Ozone Monitoring Instrument level 1b data products
Authors: Dobber M. , Kleipool Q. , Dirksen R. , Levelt P. , Jaross G. , Taylor S. , Kelly T. , Flynn L. , Leppelmeier G. , Rozemeijer N.
Published: April 2008

The validation of the collection 2 level 1b radiance and irradiance data measured with the Ozone Monitoring Instrument (OMI) on NASA's Earth Observing System (EOS) Aura satellite is investigated and described. A number of improvements from collection 2 data to collection 3 data are identified and presented. It is shown that with these improvements in the calibration and in the data processing the accuracy of the geophysically calibrated level 1b radiance and irradiance is improved in the collection 3 data. It is shown that the OMI level 1b irradiance product can be reproduced from a high‐resolution solar reference spectrum convolved with the OMI spectral slit functions within 3% for the Fraunhofer structure and within 0.5% for the offset. The agreement of the OMI level 1b irradiance data product with other available literature irradiance spectra is within 4%. The viewing angle dependence of the irradiance and the irradiance goniometry are discussed, and improvements in the collection 3 data are described. The in‐orbit radiometric degradation since launch is shown to be smaller than 0.5% above 310 nm and increases to about 1.2% at 270 nm. It is shown how the viewing angle dependence of the radiance is improved in the collection 3 data. The calculation of the surface albedo from OMI measurement data is discussed, and first results are presented. The OMI surface albedo values are compared to literature values from the Total Ozone Mapping Spectrometer (TOMS) and the Global Ozone Monitoring Experiment (GOME). Finally, improvements in the spectral and spatial stray light corrections from collection 2 data to collection 3 data are presented and discussed.
THEMIS observations of a hot flow anomaly: Solar wind, magnetosheath, and ground‐based measurements
Authors: Eastwood J. P. , Sibeck D. G. , Angelopoulos V. , Phan T. D. , Bale S. D. , McFadden J. P. , Cully C. M. , Mende S. B. , Larson D. , Frey S. , Carlson C. W. , Glassmeier K.‐H. , Auster H. U. , Roux A. , Le Contel O.
Published: April 2008

The THEMIS spacecraft encountered a Hot Flow Anomaly (HFA) on the dusk flank of the Earth’s bow shock on 4 July 2007, observing it on both sides of the shock. Meanwhile, the THEMIS ground magnetometers traced the progress of the associated Magnetic Impulse Event along the dawn flank of the magnetosphere, providing a unique opportunity to study the transmission of the HFA through the shock and the subsequent downstream response. THEMIS‐A, in the solar wind, observed classic HFA signatures. Isotropic electron distributions inside the upstream HFA are attributed to the action of the electron firehose instability. THEMIS‐E, just downstream, observed a much more complex disturbance with the pressure perturbation decoupled from the underlying discontinuity. Simple calculations show that the pressure perturbation would be capable of significantly changing the magnetopause location, which is confirmed by the ground‐based observations.
Phase equilibria trigger for explosive volcanic eruptions
Authors: Fowler Sarah J. , Spera Frank J.
Published: April 2008

A mechanism for explosive volcanic eruptions based on multicomponent phase equilibria modelling of four explosive volcanic systems is proposed. In each system, either isochoric or isobaric crystallization, where either crystals or crystals and exsolved fluid are chemically fractionated from melt, leads inevitably to near‐solidus dynamical instability culminating in violent explosive eruption. Driving this instability is a dramatic increase in the volume fraction of fluid bubbles in the magma exceeding the limit for magma fragmentation. This phenomenon is independent of magma decompression. Country rock may be weak, allowing magma to remain in lithostatic equilibrium with its host rock, or strong, leading to divergence of magma and lithostatic pressure. Bubbles may be retained or expelled during crystallization. Instability is the inevitable outcome of crystallization at shallow levels in the crust for all four systems, regardless of the mechanical state of host country rock. We speculate that this phase equilibria mechanism driving explosive eruptions has general significance.
Snow Cover in South Dakota: Statistical analysis of spatiotemporal diversity
Authors: Shmagin Boris , Johnston Carol
Published: April 2008

Snow distribution and accumulation influence many human activities and the dynamic sustainability of ecological systems. Snow cover distribution analysis is a second research step towards creating a Atlas of Climate and Water Resources for SD (temperature analysis was presented last year). We analyzed the regional diversity of monthly total snowfall based on long-term data obtained from the High Plains Regional Climate Center for South Dakota. Multidimensional statistical methods were used, and the results presented for the State of South Dakota.The sets of initial matrixes were compiled with snow observations for the state. The first type of initial matrix of time series {Xt*n}, where t = number of years (67) and n = number of meteorological stations (25), contains 25 stations with mutual observational interval (1931-1998) of 67 winters. The second type of initial matrix {Xt*m}, where t = number of years (67) and m = number of months in a year, included seven initial matrixes.Statistical analysis allowed us to differentiate weather stations by temporal trends and spatial distribution for the time intervals 1931-1998. The average annual sum of total monthly snowfall (October-May) ranged from 25.5 to 53.5 inches for 25 stations trough this time interval. The most variable stations (Bowman Court House, Alexandria, Colony, Gordon, Clark, hot Springs and Eureka) were determined; their seasonality was described (the most variable months and correlation among months during period of snowfall) and their seasonal regime determined.
MUSIC - Multisimulation Coordinator: Request For Comments
Authors: Ekeberg Örjan , Djurfeldt Mikael
Published: April 2008

MUSIC is an API allowing large scale neuron simulators using MPI internally to exchange data during runtime. MUSIC provides mechanisms to transfer massive amounts of event information and continuous values from one parallel application to another. Special care has been taken to ensure that existing simulators can be adapted to MUSIC. In particular, MUSIC handles data transfer between applications that use different time steps and different data allocation strategies. This RFC - Request For Comments - document invites comments on the proposed design and prototype specifications.
Classroom-Based Language Goals and Intervention for Children Who Use AAC: Back to Basics
Authors: Binger Cathy
Published: April 2008

When working with a preschool or school-aged child who uses aided AAC, much of the speech-language pathologist's (SLP's) focus is commonly on the AAC tools that the child is using. SLPs will often talk with educators and parents about the technology itself, and sometimes, many of the child's IEP goals center around use of the AAC technologies. Many educators (and sometimes even SLPs), however, are often reluctant to use technologies with which they are not comfortable. In the midst of all of the complications that come with technology use, it can be helpful to remember that AAC technologies are simply tools that provide the child with access to language. Most children who use AAC experience language deficits (e.g., Binger & Light, in press), and the purpose of AAC is to provide the child with a means of overcoming these language deficits. Given these facts, the goals, objectives, and intervention techniques that SLPs use with children who use AAC should not, in many cases, be very different from the goals and techniques for children who primarily rely on speech to communicate. In other words, it is important to put the language back into speech-language pathology, when working with children who use AAC. To illustrate these points, three cases of children who use AAC and who have very different profiles are presented below, with example language goals and intervention techniques that may be used with each child.
AAC in the Schools: Current Issues and Future Directions
Authors: Fallon Karen A.
Published: April 2008

For students with complex communication needs, positive educational outcomes are heavily dependent on support services that facilitate access to AAC technologies, the acquisition of literacy skills, and access to the academic curriculum within supportive classroom communities. Although the AAC research literature documents continuous progress in the quality and effectiveness of school-based services, by many indicators the field has a distance to go in pursuit of excellence in AAC service delivery. In reflecting upon the current state of school-based practice, several important factors emerge as critical to the success of students who require AAC, including the expertise of practicing professionals, effective collaborations of service-delivery teams, and the availability of empirical studies to guide practitioners. This article examines key issues affecting AAC service delivery in the schools and discusses critical clinical and research needs in the areas of personnel preparation, collaborative team building, and the provision of quality AAC services. Suggestions for the development and refinement of best practices are also explored in a discussion of future directions for school-based AAC services.
The Changing “Face” of Aphasia Therapy
Authors: Lee Jaime B. , Cherney Leora R.
Published: April 2008

Purpose:
Clinicians and researchers are searching for cost effective ways to deliver intensive aphasia treatment. The purpose of this article is to describe one method of providing less costly but intensive treatment via a computer software program called AphasiaScripts
TM
.

Method:
First, we describe the unique, interactive computer software program developed for individuals with aphasia to practice conversations that have been individually scripted for them. In AphasiaScripts
TM
, an avatar serves as the virtual therapist or conversational partner. The simplicity of the user interface allows the person with aphasia to quickly learn how to use the program and to manage the level of supportive cueing needed. Second, we clarify the role of the speech-language pathologist in the light of new technology that allows the person with aphasia to practice these conversations intensively and independently.

Conclusions:
AphasiaScripts
TM
serves as an example of a software program that makes use of advanced computer technology, yet still requires the clinical expertise of the speech-language pathologist.
Think Tank Deliberates Future Directions for the Social Approach to Aphasia
Authors: Simmons-Mackie Nina , Conklin Jamie , Kagan Aura
Published: April 2008

Purpose
: This article describes the rationale and outcome of an international meeting held to explore evidence related to social approaches to aphasia intervention.

Method
: A think tank and conference took place in Toronto, Canada, in September 2007 with the purpose of mobilizing a process of collaboration to document and collect evidence related to social approaches to aphasia. Using a framework called “Living with Aphasia: Framework for Outcome Measurement” (A-FROM), meeting participants worked to identify evidence available in the literature related to social approaches, identify gaps in evidence, and establish a plan to move forward in the process of establishing a comprehensive evidence base.

Results
: A preliminary summary of evidence was defined according to A-FROM domains, and weaknesses and gaps were identified. Concrete directions for the future were set forth as action plans.

Conclusions:
This report on the outcomes of the international think tank serves as an invitation to those interested in furthering the evidence for social approaches to aphasia to become involved in a collaborative process of evaluating and collecting evidence.
A molecular simulation study of an organosilane self-assembled monolayer/SiO2 substrate interface
Authors: Yamamoto Hideaki , Watanabe Takanobu , Ohdomari Iwao
Published: April 2008

The bonding network of an alkylsilane self-assembled monolayer (SAM)∕SiO2 substrate interface is investigated by means of canonical Monte Carlo (MC) simulations. SAM∕SiO2 systems with different interfacial bonding topologies are sampled by the Metropolis MC method, and the AMBER potential with a newly developed organosilicon parameters are used to obtain an optimized structure with a given bonding topology. The underlying substrates are modeled as hydroxy-terminated (100) or (111) cristobalites. The SAM∕SiO2 interface is characterized by a polysiloxane bonding network which comprises anchoring bonds and cross-linking bonds, namely, molecule-substrate and molecule-molecule Si–O–Si bonds, respectively. We show that at thermal equilibrium, the ratio of the number of anchoring bonds to cross-linking bonds decreases as a total Si–O–Si bond density increases, and that nevertheless, number of anchoring bonds always dominate over that of cross-linking bonds. Moreover we show that the total Si–O–Si bond density strongly affects the lateral ordering of the alkylsilane molecules, and that increase in the Si–O–Si bond density disorders the molecular packing. Our results imply that a lab-to-lab variation in the experimentally prepared SAMs can be attributed to different Si–O–Si bond densities at the SAM∕SiO2 interface.
Experimental study on the velocity limits of magnetized rotating plasmas
Authors: Teodorescu C. , Clary R. , Ellis R. F. , Hassam A. B. , Lunsford R. , Uzun-Kaymak I. , Young W. C.
Published: April 2008

An experimental study on the physical limits of the rotation velocity of magnetized plasmas is presented. Experiments are performed in the Maryland Centrifugal Experiment (MCX) [R. F. Ellis et al., Phys. Plasmas 12, 055704 (2005)], a mirror magnetic field plasma rotating azimuthally. The externally applied parameters that control the plasma characteristics—applied voltage, external magnetic field, and fill pressure—are scanned across the entire available range of values. It is found that the plasma rotation velocity does not exceed the Alfvén velocity, in agreement with the equilibrium requirements of magnetically confined plasmas. Measured rotation velocities are also lower than the critical ionization velocity in hydrogen, but a strict limit was not observable within MCX parametric capabilities.
Self-consistent polarization neglect of diatomic differential overlap: Application to water clusters
Authors: Chang Daniel T. , Schenter Gregory K. , Garrett Bruce C.
Published: April 2008

Semiempirical self-consistent field (SCF) methods based on the neglect of diatomic differential overlap (NDDO) formalism have the ability to treat the formation and breaking of chemical bonds but have been found to poorly describe hydrogen bonding and weak electrostatic complexes. In contrast, most empirical potentials are not able to describe bond breaking and formation but have the ability to add missing elements of hydrogen bonding by using classical electrostatic interactions. We present a new method which combines aspects of both NDDO-based SCF techniques and classical descriptions of polarization to describe the diffuse nature of the electronic wavefunction in a self-consistent manner. We develop the “self-consistent polarization neglect of diatomic differential overlap” (SCP-NDDO) theory with the additional description of molecular dispersion developed as a second-order perturbation theory expression. The current study seeks to model water-water interactions as a test case. To this end, we have parametrized the method to accurate ab initio complete basis set limit estimates of small water cluster binding energies of Xantheas and co-workers [J. Chem. Phys. 116, 1493 (2002); 120, 823 (2004)]. Overall agreement with the ab initio binding energies (n=2–6, and 8) is achieved with a rms error of 0.19kcal∕mol. We achieve noticeable improvements in the structure, vibrational frequencies, and energetic predictions of water clusters (n⩽21) relative to standard NDDO-based methods.
On slip velocity boundary conditions for electroosmotic flow near sharp corners
Authors: Craven Thomas J. , Rees Julia M. , Zimmerman William B.
Published: April 2008

The Helmholtz–Smoluchowski (HS) slip velocity boundary condition is often used in computational models of microchannel flows because it allows the motion of the electric double layer (EDL) to be approximated without resolving the charge density profiles close to the walls while dramatically reducing the computational effort required to solve the flow model. The approximation works well for straight channel flows but breaks down in areas of high wall curvature such as sharp corners, where large nonphysical velocities are generated. Many microfluidic applications such as the on-chip focusing and separation of biomolecules rely on the interaction of electroosmosis and electrophoresis in complex channel geometries. In order for these effects to be properly treated using the slip velocity boundary condition, the errors introduced into the solution at corners must be understood. In this article, a complete model for the ion concentrations, electric field, and fluid flow in complex microchannel geometries is presented and is used to compute a pure electroosmotic flow in a two-dimensional microchannel cross slot. The full model solution near the corner at the edge of the EDL is compared to the approximate solution computed by using the HS boundary condition, and it is shown that the accuracy of the approximate solution may be greatly increased by “patching” the full solution as a boundary condition for the approximate solution at the edge of the double layer region. Finally, an empirically derived modified slip velocity boundary condition for electroosmotic flow is proposed. It is shown to improve the accuracy of the flow solution at sharp corners by about 60% when compared to the original boundary condition while also delivering a modest improvement in computational performance because of the elimination of a singularity in the velocity field.
Effect of the induced-dipole force on charging rates of aerosol particles
Authors: Robertson Scott , Sternovsky Zoltan
Published: April 2008

Natanson’s model {Zh. Tekh. Fiz., 30, 573 (1960) [English translation: Sov. Phys. Tech. Phys. 5, 538 (1960)]} for the collection of ions by aerosol particles is modified so that both the Coulomb force and the induced-dipole force are included for the case of attractive aerosol particles. Natanson included the induced-dipole force and the Coulomb force together only for the Coulomb force being repelling. The induced-dipole force increases ion collection rates by about a factor of 2 for the smallest aerosol particles. The results are applicable to the collection of both ions and electrons by noctilucent cloud particles and meteoritic dust in the mesosphere.
Structure and assembly of dense solutions and melts of single tethered nanoparticles
Authors: Jayaraman Arthi , Schweizer Kenneth S.
Published: April 2008

The microscopic polymer reference interaction site model theory is generalized and applied to study intermolecular pair correlation functions and collective structure factors of dense solutions and melts of spherical nanoparticles carrying a single tethered chain. The complex interplay of entropy (translational, conformational, and packing) and enthalpy (particle-particle attraction) leads to different structural arrangements with distinctive small and wide angle scattering signatures. Strong concentration fluctuations, indicative of aggregate formation and/or a tendency for microphase separation, occur as the total packing fraction and/or particle-particle attraction strength increase. In analogy with block copolymers, the microphase spinodal curve is estimated by extrapolation of the inverse of the amplitude of the small angle scattering peak. For nanoparticles that are twice the diameter of monomers, the microphase separation boundary spinodal occurs at higher particle-particle attraction strength (or lower temperature) as compared to the macrophase demixing curve for nanoparticles with no tethers when the packing fraction is below 0.45, while the opposite trend is observed above 0.45. Increasing nanoparticle diameter results in a reduction in the microphase spinodal temperature and a qualitative change in its packing fraction dependence.
Self-assembled ordered polymer nanocomposites directed by attractive particles
Authors: Knorowski C. D. , Anderson J. A. , Travesset A.
Published: April 2008

We theoretically investigate general conditions under which an inorganic phase can direct the self-assembly of an ordered polymer nanocomposite. For this purpose, we consider a solution of triblock copolymers forming a hexagonal phase of micelles and investigate the effect of adding attractive particles. We show that if the triblock is functionalized at its ends by attaching groups with specific affinity for the particles, thus effectively becoming a pentablock, the particles direct the self-assembly of the system into phases where both the polymers and the particles exhibit mesoscopic order. Different lamellar and gyroid phases (both with Ia3¯d and I4132 space symmetries) are presented in detail. Our results show that functionalization is a very powerful route for directing self-assembly of polymer nanocomposites. We briefly discuss the connections with recent theoretical and experimental results in diblock melts with nanoparticles as well as for problems where polymers are used to template the growth of an inorganic phase in solution.
S
-matrix calculation of radiation characteristics from dipole oscillation in two-dimensional photonic crystal slabs
Authors: Taniyama Hideaki , Notomi Masaya
Published: April 2008

The effects of the photonic band structure on the radiation from a dipole moment placed within photonic crystal (PC) slabs are investigated. Radiation above the slab surface and coupling with the slab’s propagating mode are calculated for frequencies above and below the light line of air cladding. The strongly enhanced emission from the surface and coupling with propagating modes and its polarization vector dependence are explained in terms of the photonic band of the PC slab structures. The emitted electromagnetic field is mainly extracted through coupling with the leaky modes of PC slabs.
Characterization of polycrystalline 3C-SiC films deposited from the precursors 1,3-disilabutane and dichlorosilane
Authors: Roper Christopher S. , Radmilovic Velimir , Howe Roger T. , Maboudian Roya
Published: April 2008

Polycrystalline 3C-SiC thin films are deposited via low pressure chemical vapor deposition from the precursors 1,3-disilabutane (DSB) and dichlorosilane (DCS). Elemental composition, microstructure, surface morphology, and residual stress are characterized as functions of DCS flow rate fraction. Elemental composition varies linearly with DCS fraction, while microstructure changes drastically with slight changes in DCS fraction. Residual stress varies from 1.2GPa tensile to 240MPa tensile, and the causes of which are traced to variations in elemental composition and grain size. A model of residual stress accounting for the effects of elemental composition and grain size on intrinsic stress is developed and found to be in reasonable agreement with experimental data.
A novel method to construct stationary solutions of the Vlasov–Maxwell system
Authors: Suzuki Akihiro , Shigeyama Toshikazu
Published: April 2008

A novel method to derive stationary solutions of the Vlasov–Maxwell system is established. This method is based on the assumption that the deviation of the velocity distribution from the Maxwell–Boltzmann distribution can be expanded by the Hermite polynomials. By applying our method, a new two-dimensional equilibrium is derived, which may provide an initial setup for investigations of three-dimensional collisionless reconnection of magnetic fields.
Current conduction mechanisms in atomic-layer-deposited HfO2/nitrided SiO2 stacked gate on 4H silicon carbide
Authors: Cheong Kuan Yew , Moon Jeong Hyun , Kim Hyeong Joon , Bahng Wook , Kim Nam-Kyun
Published: April 2008

In this paper, current conduction mechanisms of an atomic-layer-deposited HfO2 gate stacked on different thicknesses of thermally nitrided SiO2 based on n-type 4H SiC have been investigated and analyzed. Current-voltage and high-frequency capacitance-voltage measurements conducted at various temperatures (25−140 °C) were performed in metal-oxide-semiconductor test structures with 13 nm thick HfO2 stacked on 0-, 2-, 4-, or 6 nm thick nitrided SiO2. Various conduction mechanisms, such as Schottky emission, Fowler-Nordheim tunneling, Poole-Frenkel emission, and space-charge-limited conduction, have been systematically evaluated. The mechanisms of the current conducted through the oxides were affected by the thickness of the nitrided oxide and the electric field applied. Finally, current conduction mechanisms that contributed to hard and soft dielectric breakdown have been proposed.
Formation mechanisms of ZnO amorphous layers due to thermal treatment of ZnO thin films grown on p-InP (100) substrates
Authors: Yuk J. M. , Lee J. Y. , No Y. S. , Kim T. W. , Choi W. K.
Published: April 2008

High-resolution transmission electron microscopy (HRTEM) images, selected-area electron diffraction (SAED) patterns, and energy dispersive x-ray spectroscopy (EDS) profiles showed that P atoms accumulated due to thermal treatment on the top sides and in the heterointerface layers of ZnO thin films grown on p-InP (100) substrates, resulting in the formation of amorphous ZnO layers in the ZnO thin films. The formation mechanisms of the ZnO amorphous layers due to thermal treatment are described on the basis of the HRTEM, the SAED, and the EDS measurements.
Electrical and photoelectrical characterization of undoped and S-doped nanocrystalline diamond films
Authors: Kulkarni P. , Porter L. M. , Koeck F. A. M. , Tang Y.-J. , Nemanich R. J.
Published: April 2008

Nanocrystalline diamond (NCD) films are being intensively researched for a variety of potential applications, such as optical windows, electrochemical electrodes, and electron emitting surfaces for field emission displays. In this study Zr, Ti, Cu, and Pt on intrinsic and lightly sulfur-doped (n-type) NCD films were electrically and photoelectrically characterized. Intrinsic and sulfur-doped NCD films were synthesized on 1in. diameter quartz and silicon substrates by microwave plasma assisted chemical vapor deposition. All metals showed linear (Ohmic) current-voltage characteristics in the as-deposited state. The Schottky barrier heights (ΦB) at the metal-film interface were investigated using x-ray and ultraviolet photoelectron spectroscopies. The undoped NCD films exhibited a negative electron affinity and a band gap of 5.0±0.4eV. The ΦB were calculated based on this band gap measurement and the consistent indication from Hall measurements that the films are n-type. The ΦB values were calculated from shifts in the core-level (C1s) peaks immediately obtained before and after in situ, successive metal depositions. The ΦB values for Zr, Ti, and Pt on undoped films were calculated to be 3.3, 3.2, and 3.7eV, respectively. The S-doped films also showed increasing ΦB with metal work functions: 3.0, 3.1, and 3.4eV for Zr, Ti, and Pt, respectively. In general accordance with the barrier height trends, the specific contact resistivity (ρc) values increased with the metal work functions for both undoped and S-doped films. For the undoped films ρc increased from 3×10−5Ωcm2 for Zr to 6.4×10−3Ωcm2 for Pt. The ρc values for the S-doped films were approximately two orders of magnitude lower than those for the undoped films: 3.5×10−7–4.5×10−5Ωcm2 for Zr and Pt, respectively. The Hall-effect measurements indicated that the average sheet resistivity and carrier concentration values were 0.16 and 3.5×1018cm−3 for the undoped films and 0.15Ωcm and 4.9×1019cm−3 for the S-doped films.
Ferroelectric transitions by Ca substitution in Pb0.7Nd0.2TiO3
Authors: Wang John , Sim Chow Hong , Lao Zijun , Soon Hwee Ping
Published: April 2008

Ferroelectric Pb0.7(1−y)Ca0.7yNd0.2TiO3 (PCNT-y) compositions with y ranging from 0 to 0.60, were synthesized via a mechanical activation route. The tetragonality (c/a) of PCNT-y at room temperature decreases from 1.0125 to 1.0000 upon substitution of Pb2+ with smaller sized Ca2+. The composition with Ca-doping y=0.60 demonstrates a unit-cell volume shrinkage of 4.063% as compared to that of Pb0.7Nd0.2TiO3, while the Raman spectra are of the characteristic features of PbTiO3. As the Ca content (y) increases from 0 to 0.60, there is a crossover from a displacive phase transition (y=0 and 0.10) to a diffusive one (0.20≤y≤0.40), accompanied by a decrease in transition temperature (TC or Tmax) at a linear rate of ∼8.2 K/at. %. The compositions with y<0.10 demonstrated the Curie–Weiss behavior in dielectric behavior, while those compositions of 0.20≤y≤0.40 could well be fitted to the Uchino equation with the diffusivity, in agreement with a relaxor ferroelectric behavior. At y≥0.50, ε′ was much reduced and became less sensitive to temperature. Neither εmax′ nor frequency dispersion was detected in PCNT-0.50 and -0.60 in the ε′-T plot, down to 80 K.
Excess Mg addition MgB2/Fe wires with enhanced critical current density
Authors: Zeng R. , Lu L. , Li W. X. , Wang J. L. , Shi D. Q. , Horvat J. , Dou S. X. , Bhatia M. , Sumption M. , Collings E. W. , Yoo J. M. , Tomsic M. , Rindfleisch M.
Published: April 2008

MgB 2 / Fe wires with 10 at. % excess Mg produced by in situ powder-in-tube processing were compared to normal stoichiometric MgB2/Fe wires prepared by the same method. It was found that the critical current density (Jc) and the irreversibility field (Hirr) were significantly enhanced for MgB2/Fe wires with excess Mg. The transport Jc for 10 at. % Mg excess samples sintered at 800 °C, measured at a field of up to 14 T, increased by a factor of 2 compared to that for the normal MgB2 wires. The best Jc results for the 10 at. % Mg excess sample were obtained by heating the sample at 600 °C for 1 h; the Jc at a field of 8 T and at temperature of 10 K reached 3×104 A/cm2. The detailed analysis of the effect of excess Mg on the microstructures, the Jc, and the Hirr, of MgB2/Fe wires are presented in this paper.
Investigation of the structure of GexAsySe1−x−y glasses by x-ray photoelectron spectroscopy
Authors: Wang R. P. , Rode A. V. , Choi D. Y. , Luther-Davies B.
Published: April 2008

We have measured and analyzed x-ray photoelectron spectra of a series of GexAsySe1−x−y glasses. The valence band spectra show that a number of Se-rich structures exist in the samples. After decomposing Ge, As, and Se3d spectra into several doublets and assigning them to the different local bond structures, it was found that, while GeSe4/2 tetrahedral, AsSe3/2 pyramidal, and Se trimers decrease in their integrated areas, most defect bonds increase with increasing mean coordination number. Moreover, while the appearance of Se trimers is reasonable in Se-rich samples, they never vanish, even in Se-poor samples. A possible mechanism to form Se trimers in Se-poor samples is discussed.
Suppression of boron deactivation and diffusion in preamorphized silicon after nonmelt laser annealing by carbon co-implantation
Authors: Poon Chyiu Hyia , See Alex , Tan Yunling , Zhou Meisheng , Gui Dong
Published: April 2008

For preamorphized boron-implanted samples subjected to nonmelt laser spike annealing (LSA), increasing the LSA temperature at temperatures below 1250 °C results in negligible sheet resistance changes due to the formation of inactive boron-interstitial clusters (BICs). These clusters, which are evidenced as a kink in the boron profile beyond the amorphous/crystalline interface, result chiefly from the inadequate removal of end-of-range (EOR) defects. When the LSA temperature is elevated beyond 1250 °C, sheet resistance improvement takes place due to the increase in active boron dose from the dissolution of the BIC at higher temperatures. Cluster dissolution also gives rise to a supersaturation of silicon interstitials that deepen the junctions as a result of transient enhanced diffusion (TED). With an additional post-LSA treatment, severe deactivation, especially at lower LSA temperatures, and further TED is observed. Two concurrent mechanisms, namely, boron clustering (which gives rise to deactivation and sheet resistance degradation) and dissolution of the BIC (which gives rise to TED) formed during the LSA step, are believed to take place during the post-LSA thermal budget. As the LSA temperature increases, TED from the as-LSA profile upon rapid thermal annealing (RTA) is significantly reduced as a result of the improved effectiveness of the EOR defect dissolution during the higher temperature LSA step. When carbon co-implantation is performed, deactivation and TED is successfully suppressed with the reduction in free silicon interstitial concentration due to the formation of complexes of carbon and silicon interstitials. The amount of deactivation upon RTA becomes independent of LSA temperature for the carbon-implanted samples, largely because boron clustering becomes limited by the small concentration of free silicon interstitials present instead of the LSA temperatures used.
Controlling intrinsic electrostatic resonances of negative permittivity artificial multilayers
Authors: Mejdoubi Abdelilah , Brosseau Christian
Published: April 2008

We report a numerical study of the electrostatic resonances (ERs) in arrays of elliptical particles with a core-shell structure embedded in a surrounding host. The core medium is supposed to have a complex permittivity with a negative real part, while the shell and the host have real and positive permittivity. These simulations are valid within the quasistatic approximation, when that all length scales must be much smaller compared to both the wavelength of the wave in the medium and the skin depth. The ER features can be tuned by properly selecting the core and shell material parameters, i.e., by tuning the shell thickness, the core loss, and the aspect ratio of the elliptical particle. In addition, very large enhancements of the local field of the order of a few hundreds can be achieved at the resonance. Since the enhanced fields are localized at the perimeter of the core-shell structures, they can serve as a local probe of the dielectric environment in small parts of the particle perimeter. Apart from its fundamental value, this analysis suggests also several factors which help to understand the systematics observed for the optical response of arrays of coated noble-metal nanoparticles.
Synthesis of Dianionic and Trianionic Chiral, Chelating Ligands Based on Amino Acids
Authors: Schultz Madeleine , Kulis Jakov , Murison Julie , Andrews Genevieve W.
Published: April 2008

The synthesis of two new families of amino acid-containing chiral ligands, based on methyliminodiacetic acid and nitrilotriacetic acid cores, has been accomplished using a simple protection, solution-phase amide coupling, and deprotection strategy. The amino acids glycine, leucine, aspartic acid, and phenylalanine were used to demonstrate the versatility of the synthetic route, and that no epimerization occurs. The tridentate ligands bear C3 symmetry, whereas the bidentate ligands have C1 symmetry.
Templating Linear Alignment of Fullerene C60 Molecules Involving a Curved Macrocycle
Authors: Norret Marck , Makha Mohamed , Sobolev Alexandre N. , Raston Colin L.
Published: April 2008

A nickel macrocycle bearing 15-crown-5 ether pendant moieties forms a 1:1 complex with fullerene C60, with the macrocycle templating the formation of linear arrays of the fullerenes, and the inter-fullerene contacts being associated with parallel six-membered rings, with the fullerene…fullerene centroid distances remarkably short at 9.757 Å. Three crystalline solids involving this macrocycle were isolated and studied by X-ray structure analysis and the complex reveals a self-inclusion mode of packing in its guest-free form, while acting as a host in its inclusion compounds with C60 and C60/toluene.
The Bro1-related protein HD-PTP/PTPN23 is required for endosomal cargo sorting and multivesicular body morphogenesis
Authors: Doyotte Aurelie , Mironov Aleksandr , McKenzie Edward , Woodman Philip
Published: April 2008

The
Saccharomyces cerevisiae
protein Bro1p is required for sorting endocytic cargo to the lumen of multivesicular bodies (MVBs). The mammalian ortholog of Bro1p is not known; although Alix, a structurally related protein, supports the topologically similar process of virus budding, functional studies have so far failed to identify a role for Alix in MVB formation. To establish whether Alix or similar protein(s) participate in endosomal sorting, we attached a retroviral peptide that binds Alix to a reporter receptor. This chimera was sorted efficiently away from the early endosome to the lumen of late endocytic compartments. Surprisingly, sorting was not prevented by depleting Alix but instead required the Alix-related protein His domain phosphotyrosine phosphatase (HD-PTP)/His-Domain/Type N23 protein tyrosine phosphatase (PTPN23). Depletion of HD-PTP also reduced transfer of fluid-phase markers and EGF receptor to lysosomes, caused the accumulation of ubiquitinated proteins on endosomal compartments and disrupted the morphogenesis of MVBs. Rescue experiments using an RNAi-resistant version of HD-PTP and HD-PTP mutants demonstrated an essential role for the HD-PTP Bro1 domain, with ESCRT-III binding correlating with full biological activity.
Loss of microRNA cluster miR-29a/b-1 in sporadic Alzheimer's disease correlates with increased BACE1/β-secretase expression
Authors: Hébert Sébastien S. , Horré Katrien , Nicolaï Laura , Papadopoulou Aikaterini S. , Mandemakers Wim , Silahtaroglu Asli N. , Kauppinen Sakari , Delacourte André , De Strooper Bart
Published: April 2008

Although the role of
APP
and
PSEN
genes in genetic Alzheimer's disease (AD) cases is well established, fairly little is known about the molecular mechanisms affecting Aβ generation in sporadic AD. Deficiency in Aβ clearance is certainly a possibility, but increased expression of proteins like APP or BACE1/β-secretase may also be associated with the disease. We therefore investigated changes in microRNA (miRNA) expression profiles of sporadic AD patients and found that several miRNAs potentially involved in the regulation of APP and BACE1 expression appeared to be decreased in diseased brain. We show here that miR-29a, -29b-1, and -9 can regulate BACE1 expression
in vitro
. The miR-29a/b-1 cluster was significantly (and AD-dementia-specific) decreased in AD patients displaying abnormally high BACE1 protein. Similar correlations between expression of this cluster and BACE1 were found during brain development and in primary neuronal cultures. Finally, we provide evidence for a potential causal relationship between miR-29a/b-1 expression and Aβ generation in a cell culture model. We propose that loss of specific miRNAs can contribute to increased BACE1 and Aβ levels in sporadic AD.
Ancient associations of aquatic beetles and tank bromeliads in the Neotropical forest canopy
Authors: Balke Michael , Gómez-Zurita Jesús , Ribera Ignacio , Viloria Angel , Zillikens Anne , Steiner Josephina , García Mauricio , Hendrich Lars , Vogler Alfried P.
Published: April 2008

Water reservoirs formed by the leaf axils of bromeliads are a highly derived system for nutrient and water capture that also house a diverse fauna of invertebrate specialists. Here we investigate the origin and specificity of bromeliad-associated insects using Copelatinae diving beetles (Dytiscidae). This group is widely distributed in small water bodies throughout tropical forests, but a subset of species encountered in bromeliad tanks is strictly specialized to this habitat. An extensive molecular phylogenetic analysis of Neotropical Copelatinae places these bromeliadicolous species in at least three clades nested within other
Copelatus
. One lineage is morphologically distinct, and its origin was estimated to reach back to 12–23 million years ago, comparable to the age of the tank habitat itself. Species of this clade in the Atlantic rainforest of southern Brazil and mountain ranges of northern Venezuela and Trinidad show marked phylogeographical structure with up to 8% mtDNA divergence, possibly indicating allopatric speciation. The other two invasions of bromeliad water tanks are more recent, and haplotype distributions within species are best explained by recent expansion into newly formed habitat. Hence, bromeliad tanks create a second stratum of aquatic freshwater habitat independent of that on the ground but affected by parallel processes of species and population diversification at various temporal scales, possibly reflecting the paleoclimatic history of neotropical forests.
Unusually rapid evolution of Neuroligin-4 in mice
Authors: Bolliger Marc F. , Pei Jimin , Maxeiner Stephan , Boucard Antony A. , Grishin Nick V. , Südhof Thomas C.
Published: April 2008

Neuroligins (NLs) are postsynaptic cell-adhesion molecules that are implicated in humans in autism spectrum disorders because the genes encoding NL3 and NL4 are mutated in rare cases of familial autism. NLs are highly conserved evolutionarily, except that no
NL4
was detected in the currently available mouse genome sequence assemblies. We now demonstrate that mice express a distant NL4 variant that rapidly evolved from other mammalian
NL4
genes and that exhibits sequence variations even between different mouse strains. Despite its divergence, mouse NL4 binds neurexins and is transported into dendritic spines, suggesting that the core properties of NLs are retained in this divergent NL isoform. The selectively rapid evolution of NL4 in mice suggests that its function in the brain is under less stringent control than that of other NLs, shedding light on why its mutation in autism spectrum disorder patients is not lethal, but instead leads to a discrete developmental brain disorder.
Structural diversity in the RGS domain and its interaction with heterotrimeric G protein α-subunits
Authors: Soundararajan Meera , Willard Francis S. , Kimple Adam J. , Turnbull Andrew P. , Ball Linda J. , Schoch Guillaume A. , Gileadi Carina , Fedorov Oleg Y. , Dowler Elizabeth F. , Higman Victoria A. , Hutsell Stephanie Q. , Sundström Michael , Doyle Declan A. , Siderovski David P.
Published: April 2008

Regulator of G protein signaling (RGS) proteins accelerate GTP hydrolysis by Gα subunits and thus facilitate termination of signaling initiated by G protein-coupled receptors (GPCRs). RGS proteins hold great promise as disease intervention points, given their signature role as negative regulators of GPCRs—receptors to which the largest fraction of approved medications are currently directed. RGS proteins share a hallmark RGS domain that interacts most avidly with Gα when in its transition state for GTP hydrolysis; by binding and stabilizing switch regions I and II of Gα, RGS domain binding consequently accelerates Gα-mediated GTP hydrolysis. The human genome encodes more than three dozen RGS domain-containing proteins with varied Gα substrate specificities. To facilitate their exploitation as drug-discovery targets, we have taken a systematic structural biology approach toward cataloging the structural diversity present among RGS domains and identifying molecular determinants of their differential Gα selectivities. Here, we determined 14 structures derived from NMR and x-ray crystallography of members of the R4, R7, R12, and RZ subfamilies of RGS proteins, including 10 uncomplexed RGS domains and 4 RGS domain/Gα complexes. Heterogeneity observed in the structural architecture of the RGS domain, as well as in engagement of switch III and the all-helical domain of the Gα substrate, suggests that unique structural determinants specific to particular RGS protein/Gα pairings exist and could be used to achieve selective inhibition by small molecules.
DNA synthesis from unbalanced nucleotide pools causes limited DNA damage that triggers ATR-CHK1-dependent p53 activation
Authors: Hastak Kedar , Paul Rajib K. , Agarwal Mukesh K. , Thakur Vijay S. , Amin A. R. M. Ruhul , Agrawal Sudesh , Sramkoski R. Michael , Jacobberger James W. , Jackson Mark W. , Stark George R. , Agarwal Munna L.
Published: April 2008

p53-dependent G
1
and G
2
cell cycle checkpoints are activated in response DNA damage that help to maintain genomic stability. p53 also helps to protect cells from damage that occurs during S phase, for example, when the cells are starved for DNA precursors or irradiated with a low dose of UV. p53 is activated in normal cells starved for pyrimidine nucleotides by treatment with
N
-(phosphonacetyl)-
l
-aspartate (PALA). The treated cells progress through a first S phase with kinetics similar to those of untreated cells. However, the DNA of the treated cells begins to become damaged rapidly, within 12 h, as revealed by a comet assay, which detects broken DNA, and by staining for phosphorylated histone H2AX, which accumulates at sites of DNA damage. Because the cells survive, the damage must be reversible, suggesting single-strand breaks or gaps as the most likely possibility. The transiently damaged DNA stimulates activation of ATR and CHK1, which in turn catalyze the phosphorylation and accumulation of p53. Although PALA-induced DNA damage occurs only in dividing cells, the p53 that is activated is only competent to transcribe genes such as p21 and macrophage inhibitory cytokine 1 (whose products regulate G
2
and G
1
or S phase checkpoints, respectively) after the cells have exited the S phase during which damage occurs. We propose that p53 is activated by stimulation of mismatch repair in response to the misincorporation of deoxynucleotides into newly synthesized DNA, long before the lack of pyrimidine nucleoside triphosphates causes the rate of DNA synthesis to slow appreciably.