bluuebunny/crossref_metadata_2025 huggingface dataset:
QUANTIFIED LOGIC OF AWARENESS AND IMPOSSIBLE POSSIBLE WORLDS
Authors: SILLARI GIACOMO
Published: March 2009

Among the many possible approaches to dealing with logical omniscience, I consider here awareness and impossible worlds structures. The former approach, pioneered by Fagin and Halpern, distinguishes between implicit and explicit knowledge, and avoids logical omniscience with respect to explicit knowledge. The latter, developed by Rantala and by Hintikka, allows for the existence of logically impossible worlds to which the agents are taken to have “epistemological” access; since such worlds need not behave consistently, the agents’ knowledge is fallible relative to logical omniscience. The two approaches are known to be equally expressive in propositional systems interpreted over Kripke semantics. In this paper I show that the two approaches are equally expressive in propositional systems interpreted over Montague-Scott (neighborhood) semantics. Furthermore, I provide predicate systems of both awareness and impossible worlds structures interpreted on neighborhood semantics and prove the two systems to be equally expressive.
INTRANSITIVITY AND VAGUENESS
Authors: HALPERN JOSEPH Y.
Published: March 2009

There are many examples in the literature that suggest that indistinguishability is intransitive, despite the fact that the indistinguishability relation is typically taken to be an equivalence relation (and thus transitive). It is shown that if the uncertainty perception and the question of when an agentreportsthat two things are indistinguishable are both carefully modeled, the problems disappear, and indistinguishability can indeed be taken to be an equivalence relation. Moreover, this model also suggests a logic ofvaguenessthat seems to solve many of the problems related to vagueness discussed in the philosophical literature. In particular, it is shown here how the logic can handle thesorites paradox.
Compositions of dikes and lavas from the Pito Deep Rift: Implications for crustal accretion at superfast spreading centers
Authors: Pollock Meagen A. , Klein Emily M. , Karson Jeffrey A. , Coleman Drew S.
Published: March 2009

The northwest trending walls of the Pito Deep Rift (PDR), a tectonic window in the southeast Pacific, expose in situ oceanic crust generated ∼3 Ma at the superfast spreading southern East Pacific Rise (SEPR). Whole rock analyses were performed on over 200 samples of dikes and lavas recovered from two ∼8 km2 study areas. Most of the PDR samples are incompatible‐element‐depleted normal mid‐ocean ridge basalts (NMORB; (La/Sm)N < 1.0) that show typical tholeiitic fractionation trends. Correlated variations in Pb isotope ratios, rare earth element patterns, and ratios of incompatible elements (e.g., (Ce/Yb)N) are best explained by mixing curves between two enriched and one depleted mantle sources. Pb isotope compositions of most PDR NMORB are offset from SEPR data toward higher values of 207Pb/204Pb, suggesting that an enriched component of the mantle was present in this region in the past ∼3 Ma but is not evident today. Overall, the PDR crust is highly variable in composition over long and short spatial scales, demonstrating that chemically distinct lavas and dikes can be emplaced within the same segment over short timescales. However, the limited spatial distribution of high 206Pb/204Pb samples and the occurrence of relatively homogeneous MgO compositions (ranging <2.5 wt %) within a few of the individual dive transects (over distances of ∼1 km) suggests that the mantle source composition evolved and magmatic temperatures persisted over timescales of tens of thousands of years. The high degree of chemical variability between pairs of adjacent dikes is interpreted as evidence for along‐axis transport of magma from chemically distinct portions of the melt lens. Our findings suggest that lateral dike propagation occurs to a significant degree at superfast spreading centers.
Land clearing, climate variability, and water resources increase in semiarid southwest Niger: A review
Authors: Favreau G. , Cappelaere B. , Massuel S. , Leblanc M. , Boucher M. , Boulain N. , Leduc C.
Published: March 2009

The water table in southwestern Niger has been rising continuously for the past decades (4 m rise from 1963 to 2007), despite a ∼23% deficit in monsoonal rainfall from 1970 to 1998. This paradoxical phenomenon has been linked with a change in land use from natural savannah to millet crops that have expanded in area sixfold since 1950 and have caused soil crusting on slopes that has, in turn, enhanced Hortonian runoff. Runoff concentrates in closed ponds and then recharges the aquifer; therefore, higher runoff increases aquifer recharge. At the local scale (2 km2), a physically based, distributed hydrological model showed that land clearing increased runoff threefold, whereas the rainfall deficit decreased runoff by a factor of 2. At a larger scale (500 km2, 1950–1992 period), historical aerial photographs showed a 2.5‐fold increase in the density of gullies, in response to an 80% decrease in perennial vegetation. At the scale of the entire study area (5000 km2), analytical modeling of groundwater radioisotope data (3H and 14C) showed that the recharge rate prior to land clearing (1950s) was about 2 mm a−1; postclearing recharge, estimated from groundwater level fluctuations and constrained by subsurface geophysical surveys, was estimated to be 25 ± 7 mm a−1. This order of magnitude increase in groundwater fluxes has also impacted groundwater quality near ponds, as shown by a rising trend in groundwater nitrate concentrations of natural origin (75% of δ15N values in the range +4 to +8‰). In this well‐documented region of semiarid Africa, the indirect impacts of land use change on water quantity and quality are much greater than the direct influence of climate variability.
Parallel electric fields in mixing hot and cold plasmas in the auroral downward current region: Double layers and ambipolar fields
Authors: Singh Nagendra , Arcot Kalyan , Wells B. E.
Published: March 2009

Using a 2.5‐D parallel particle‐in‐cell simulation of a plasma of long length parallel to an ambient magnetic field Bo, we study the processes involved in determining the distribution of an applied electric potential drop parallel to Bo. The simulated plasma consists of both hot and cold plasmas of the magnetospheric and ionospheric origins, respectively. The former plasma is at a higher positive potential with respect to the latter, and thus the simulation results are relevant to the auroral downward current regions. The parallel processing enables us to simulate a long system with the magnetic field‐aligned dimension Lz ∼ 8192 λdo, where λdo is the plasma Debye length. We find that when the initially empty simulation box accumulates sufficient plasma supplied from hot plasma from the top and cold plasma from the bottom, a density cavity forms at the interface between the hot and cold plasmas. A part of the applied potential drop occurs in the cavity as a double layer (DL), while the rest of it as ambipolar fields supported by the density gradient in the hot plasma density on the high‐potential side (HPS) of the DL. The DL propagates upward. The HPS of the DL is rich in large‐amplitude electron holes. At later times in the evolution of plasma and fields as the DL reaches the top boundary, we find that a major part of the applied potential is distributed over long distances giving only a weak ambipolar type of parallel electric fields. Then again the distributed potential evolves into localized potential drops like in a stack of multiple double layers. The double layers and associated cavities emerge from low‐frequency and long‐wavelength oscillations in the presence of very hot ions. Parallel currents in the plasma seem to be the only source of free energy for driving the oscillations. We report the evolution of the electron velocity distribution functions as the potential distribution evolves.
More efficient optimization of long‐term water supply portfolios
Authors: Kirsch Brian R. , Characklis Gregory W. , Dillard Karen E. M. , Kelley C. T.
Published: March 2009

The use of temporary transfers, such as options and leases, has grown as utilities attempt to meet increases in demand while reducing dependence on the expansion of costly infrastructure capacity (e.g., reservoirs). Earlier work has been done to construct optimal portfolios comprising firm capacity and transfers, using decision rules that determine the timing and volume of transfers. However, such work has only focused on the short‐term (e.g., 1‐year scenarios), which limits the utility of these planning efforts. Developing multiyear portfolios can lead to the exploration of a wider range of alternatives but also increases the computational burden. This work utilizes a coupled hydrologic‐economic model to simulate the long‐term performance of a city's water supply portfolio. This stochastic model is linked with an optimization search algorithm that is designed to handle the high‐frequency, low‐amplitude noise inherent in many simulations, particularly those involving expected values. This noise is detrimental to the accuracy and precision of the optimized solution and has traditionally been controlled by investing greater computational effort in the simulation. However, the increased computational effort can be substantial. This work describes the integration of a variance reduction technique (control variate method) within the simulation/optimization as a means of more efficiently identifying minimum cost portfolios. Random variation in model output (i.e., noise) is moderated using knowledge of random variations in stochastic input variables (e.g., reservoir inflows, demand), thereby reducing the computing time by 50% or more. Using these efficiency gains, water supply portfolios are evaluated over a 10‐year period in order to assess their ability to reduce costs and adapt to demand growth, while still meeting reliability goals. As a part of the evaluation, several multiyear option contract structures are explored and compared.
Correction for the Effect of Rising Plasma Glucose Levels on Quantification of MRglc with FDG-PET
Authors: Dunn Joel T , Anthony Karen , Amiel Stephanie A , Marsden Paul K
Published: March 2009

Positron emission tomography (PET) using the tracer [18F]-fluorodeoxyglucose (FDG) is commonly used for measuring metabolic rate of glucose ( MRglc) in the human brain. Conventional PET methods (e.g., the Patlak method) for quantifying MRglc assume the tissue transport and phosphorylation mechanisms to be in steady state during FDG uptake. As FDG and glucose use the same transporters and phosphorylation enzymes, changing blood glucose levels can change the rates of FDG transport and phosphorylation. Compartmental models were used to simulate the effect of rising arterial glucose, from normal to hyperglycemic levels on FDG uptake for a typical PET protocol. The subsequent errors on the values of MRglc calculated using the Patlak method were investigated, and a correction scheme based on measured arterial glucose concentration ( Gp) was evaluated. Typically, with a 40% rise in Gp over the duration of the PET study, the true MRglc varied by only 1%; however, the Patlak method overestimated MRglc by 15%. The application of the correction reduced this error to −2%. In general, the application of the correction resulted in values of MRglc consistently significantly closer to the true steady state calculation of MRglc independently of changes to the parameters defining the model.
Early Metabolic Characteristics of Lesion and Nonlesion Tissue after Head Injury
Authors: Coles Jonathan P , Cunningham Alison S , Salvador Raymond , Chatfield Doris A , Carpenter Adrian , Pickard John D , Menon David K
Published: March 2009

We defined lesion and structurally normal regions using magnetic resonance imaging at follow-up in patients recovering from head injury. Early metabolic characteristics in these regions of interest (ROIs) were compared with physiology in healthy volunteers. Fourteen patients with severe head injury had positron emission tomography within 72 h, and magnetic resonance imaging at 3 to 18 months after injury. Cerebral blood flow (CBF), oxygen utilization (CMRO2), and oxygen extraction fraction (OEF) were all lower in lesion ROIs, compared with nonlesion and control ROIs ( P < 0.001); however, there was substantial overlap in physiology. Control ROIs showed close coupling among CBF, blood volume (CBV), and CMRO2, whereas relationships within lesion and nonlesion ROIs were abnormal. The relationship between CBF and CMRO2 generally remained coupled but the slope was reduced; that for CBF and OEF was variable; whereas that between CBF and CBV was highly variable. There was considerable heterogeneity between and within patients. Although irreversibly damaged tissue is characterized by marked derangements in physiology, a more detailed analysis shows acute changes in physiology and physiologic relationships within regions of the brain that appear structurally normal at follow-up. Such pathophysiological derangements may result in selective neuronal loss and impact on functional outcome.
Critical Closing Pressure: Comparison of Three Methods
Authors: López-Magañna Jorge A , Richards Hugh K , Radolovich Danila K , Kim Dong-Joo , Smielewski Peter , Kirkpatrick Peter J , Pickard John D , Czosnyka Marek
Published: March 2009

Critical closing pressure (CCP) is an arterial pressure threshold below which small arterial vessels collapse. Our aim was to compare different methods to estimate CCP in the cerebrovascular circulation using the relationships between transcranial Doppler flow velocity (FV), laser-Doppler flux (LDF), and arterial blood pressure (ABP). A total of 116 experiments in rabbits were analyzed retrospectively. At the end of each recording, cardiac arrest (CA) was induced. Arterial blood pressure in femoral artery, basilar artery FV, cortical blood LDF, intracranial pressure (ICP) was recorded. Critical closing pressure was estimated using linear regression between decreasing mean ABP values, FV, and LDF during CA. In addition, CCP was calculated from FV waveform just before CA. The correlation between CCP evaluated using LDF and FV during CA was 0.98 ( P < 0.0001). The correlation between CCP measured during CA and CCP estimated from the transcranial Doppler ultrasonography (TCD) waveform was weaker ( R=0.39; P <0.001), with CCP calculated from waveform being significantly greater than CCP from CA (median difference 9 mm Hg; P < 0.003). Critical closing pressures obtained from FV waveform and CA correlated with mean ICP before CA ( R = 0.40; P = 0.001). In conclusion strong correlation exists between CCP values obtained by means of FV and LDF during cardiac arrest. However, predictions of CCP using TCD waveform analysis show substantial differences from values of CCP recorded during cardiac arrest.
The Importance of Latency in the Focality of Perfusion and Oxygenation Changes Associated with Triggered after Discharges in Human Cortex
Authors: Ma Hongtao , Geneslaw Andrew , Zhao Mingrui , Suh Minah , Perry Challon , Schwartz Theodore H
Published: March 2009

The spatiotemporal dynamics of neurovascular coupling during epilepsy are not well understood, and there are little data from studies of the human brain. We investigated changes in total hemoglobin (Hbt) and hemoglobin oxygenation in patients undergoing epilepsy surgery with intraoperative intrinsic optical spectroscopy (IOS) during triggered afterdischarges (ADs). We found an early (~0.5 secs) focal dip in hemoglobin oxygenation, arising precisely in the stimulated gyrus that lasted for 11.5 ± 10.0 secs, approximately the length of the AD (10.4 ± 4.4 secs). A later oxygen overshoot and increase in blood volume occurred in the adjacent surrounding gyri. After a significant delay (~20 to 30 secs), the overshoot and blood volume signal became extremely focal to the area of the onset of the AD. A smaller very late undershoot, the last phase of the ‘triphasic’ response, was also identified, although localization was inconsistent. In this study, we show that a ‘late focal overshoot’ and late Hbt signal may be extremely useful, in addition to the early dip, for the localization of seizure onset. It is likely that a separate mechanism underlies the persistent focal increase in cerebral blood volume after a long-duration cortical stimulation, compared with the nonspecific mechanism that causes the initial increase in cerebral blood flow.
The Neural Control Mechanisms Underlying Memory-Guided Attention
Authors: Gould Ian , Stokes Mark , Atherton Kathryn , Nobre Anna
Published: March 2009

The control mechanisms that guide selective attention are typically examined in response to explicit attentional cues. In everyday life, however, the focus of attention is more typically guided according to past experiences than direct instruction. We therefore developed a novel behavioural paradigm to examine the neural substrate of memory-guided attentional orienting. Participants first learn the location of target stimuli hidden within naturalistic scenes. After the target locations have been learned, participants then perform an attention-orienting task. Each experimental trial begins with a cue stimulus, consisting of the memory scene presented without the target stimulus. A test scene is then presented, with a 50% probability of a target stimulus being present at the remembered location. Participants are instructed to use their memories to guide the focus of attention. In a previous fMRI study (Summerfield et al., 2006, Neuron), trials involving memory-guided attention were shown to engage activity in the same dorsal frontoparietal network that is typically associated with explicitly cued shifts of spatial attention, and in the hippocampus. However, it was not possible to isolate target-related processes from cue-related processes. In the present study, we tested and verified the roles of dorsal frontoparietal cortex and hippocampus activity in the neural control of memory-guided attention, by dissociating mnemonic cue-related activity from target-related activity. These results provide additional insights into the functional neural architecture of memory-guided attention, broadening the neuroscientific foundations for a more generalised account of attentional control during real-world behaviour.
Transient cooling response of smart vascular materials for self-cooling
Authors: Lee J. , Lorente S. , Bejan A.
Published: March 2009

Here we report the transient cooling performance of a body vascularized with tree-shaped channels supplied with coolant, which flows from one side of the body to the other. The vasculature consists of trees that alternate with upside down trees. Heat is generated volumetrically through the body at t=0. A time delay td separates the start of the flow of coolant from the start of heating. Three-dimensional simulations of conduction and convection in the solid-fluid composite show the formation and evolution of hot spots in the material. If the delay is not short enough, the maximum temperature of the body overshoots the maximum allowable level. The paper shows how to design the cooling delay time such that the hot-spot temperature does not exceed the safe level represented by the maximum temperature in the limit of steady state operation. The critical delay time is determined as a function of the applied pressure difference and the complexity of the dendritic flow architecture.
Effect of Ga doping on charge transport mechanism of La0.85Zr0.15Mn1−xGaxO3
Authors: Ling D. C. , Cheng J. H. , Lee C. L. , Chien F. Z.
Published: March 2009

Structural properties, temperature-dependent resistivity ρ(T) and thermoelectric power S(T) of La0.85Zr0.15Mn1−xGaxO3 (LZMGO) manganites with 0.0≤x≤0.06 have been extensively investigated. It is found that the Mn–O–Mn bond angle decreases and the Mn–O bond length increases with increasing Ga content, indicative of a significant distortion of MnO6 octahedra in LZMGO. The local lattice distortion and suppression of double exchange ferromagnetism induced by the Ga doping shift both Curie temperature (TC) and metal-insulator transition temperature (TMI) toward lower temperatures. Followed by the metal-insulator transition, ρ(T) exhibits an insulatinglike behavior accompanied by a relatively small value of S(T) below T∗ at low temperatures. An anomalous peak observed in S(T) is attributed to an enhancement of electron-magnon interaction caused by the Ga doping and a decrease in magnetic entropy near TMI. Three different charge transport mechanisms were identified in three temperature regions based on detailed analyses of ρ(T) and S(T) data. The small-polaron hopping mechanism governs the charge transport in the high-temperature paramagnetic region (T>TMI). The polaron binding energy determined from the ρ(T) and S(T) data increases with increasing Ga content, suggesting that polaron in La0.85Zr0.15MnO3 has a magnetic nature. In addition, the electron-magnon scattering dominates the charge transport in the intermediate-temperature metallic region (T∗<T<TMI), whereas the transport behavior in the low-temperature insulating region (T<T∗) can be described by the three-dimensional variable-range-hopping model.
The magnetoresistance origin of FeCo nanocontacts with current-perpendicular-to-plane spin-valve structure (invited)
Authors: Takagishi M. , Fuke H. N. , Hashimoto S. , Iwasaki H. , Kawasaki S. , Shiozaki R. , Sahashi M.
Published: March 2009

We have developed the FeCo nanocontact magnetoresistance (NCMR) with spin-valve structure [H. N. Fuke et al., IEEE Trans. Magn. 43, 2848 (2007)] which exhibits up to a MR ratio of 11%–12% at a resistance area (RA) of 0.3–0.55 Ω μm2. The nanocontact configurations were estimated at about 2 nm in in-plane diameter, 1.2 nm in thickness, and 0.55% in density for a RA∼0.5 Ω μm2 film based on in-plane current distribution by conductive atomic-force microscopy cross sectional transmission electron microscope images of the NCMR. The origin of the NCMR was discussed by comparing magnetic field dependence of resistance, with micromagnetics simulation based on the diffusive MR theory. It is found that our NCMR cannot be explained by diffusive domain wall theory or bulk scattering in free and pinned layers. It is likely that a theory on the basis of a ballistic MR consideration is needed to interpret our MR origin.
Thermoelectric and structural characterization of Ba2Ho(Cu3−xCox)O6+y
Authors: Wong-Ng W. , Yang Z. , Hu Y. F. , Huang Q. , Lowhorn N. , Otani M. , Kaduk J. A. , Li Q.
Published: March 2009

The search for thermoelectric materials for power generation and for solid-state cooling has led to increased interest of layered cobalt-containing oxides because of their thermal stability at high temperature and their desirable thermoelectric properties. This paper examines the effect of substitution of Co in the layered pervoskite Ba2Ho(Cu3−xCox)O6+y (x=0.3, 0.4, 0.5, 0.6, and 1.0). Structural analysis using the neutron Rietveld refinement technique reveals that when x≤0.4, Co substitutes mainly for Cu in the “chain sites” of the Ba2Ho(Cu3−xCox)O6+y structure. As x>0.4, Co also enters in the Cu-O “plane sites” as well. The thermoelectric properties of polycrystalline Ba2Ho(Cu3−xCox)O6+y samples were studied in the temperature range of 10–390 K. In general, as the cobalt content x increases, the resistivity and Seebeck coefficient of these samples increase while the thermal conductivity decreases. Among the five Ba2Ho(Cu3−xCox)O6+y compositions, the x=0.4 member gives the highest figure of merit ZT of ≈0.02 at approximately 270 K.
Direct observation of lifetime killing defects in 4H SiC epitaxial layers through spin dependent recombination in bipolar junction transistors
Authors: Cochrane C. J. , Lenahan P. M. , Lelis A. J.
Published: March 2009

We have identified a magnetic resonance spectrum associated with minority carrier lifetime killing defects in device quality 4H SiC through magnetic resonance measurements in bipolar junction transistors using spin dependent recombination (SDR). The SDR spectrum has nine distinguishable lines; it is, within experimental error, essentially isotropic with four distinguishable pairs of side peaks symmetric about the strong center line. The line shape is, within experimental error, independent of bias voltage and recombination current. The large amplitude and spacing of the inner pair of side peaks and three more widely separated pairs of side peaks are not consistent with either a simple silicon or carbon vacancy or a carbon or silicon antisite. This indicates that the lifetime killing defect is not a simple defect but a defect aggregate. The spectrum is consistent with a multidefect cluster with an electron spin S=12. (The observed spectrum has not been reported previously in the magnetic resonance literature on SiC.) A fairly strong argument can be made in terms of a first order model linking the SDR spectrum to a divacancy or possibly a vacancy/antisite pair. The SDR amplitude versus gate voltage is semiquantitatively consistent with a very simple model in which the defect is uniformly distributed within the depletion region of the base/collector junction and is also the dominating recombination center. The large relative amplitude of the SDR response is more nearly consistent with a Kaplan–Solomon–Mott-like model for spin dependent recombination than the Lepine model.
A proposal for dust-ion-acoustic soliton excitation in a discharge plasma
Authors: Abbasi H. , Pajouh H. Hakimi
Published: March 2009

Nonlinear dynamics of disintegration process of a localized perturbation into dust-ion-acoustic (DIA) solitons is studied. The present paper is a theoretical attempt to propose and model the experimental DIA soliton excitation [Y. Nakamura and A. Sarma, Phys. Plasmas 8, 3921 (2001)] in the presence of both superthermal and trapped electrons. The proposal is designed for low-pressure electrical gas discharges that are in nonequilibrium state. In the discharge plasmas, the electron temperature is usually much greater than ion temperature. Thus, the electron distribution function (DF) that in low-pressure discharges is generally non-Maxwellian has to be modeled. For this purpose, the generalized Lorentzian (κ)-DF is used to simulate the electron DF. The formalism is derived near the ion-plasma frequency. In this range of frequency, the ion dynamics is considerable and the DIA solitons are the outcome of the disintegration process. Electron trapping is included in the model as the result of positive polarity of the initial potential. A Gaussian initial perturbation is used to model the localized perturbation. It is shown that a slowly varying dynamics of the order of ion motions causes an initial Gaussian perturbation to be, adiabatically, disintegrated to a number of DIA solitons. The disintegration attributes and influence of both trapped and superthermal electrons on this process, are studied.
The Rayleigh–Taylor instability in quantum magnetized plasma with para- and ferromagnetic properties
Authors: Modestov Mikhail , Bychkov Vitaly , Marklund Mattias
Published: March 2009

We investigate influence of magnetic field on the Rayleigh–Taylor instability in quantum plasmas with para- and ferromagnetic properties. Magnetization of quantum plasma happens due to the collective electron spin behavior at low temperature and high plasma density. In the classical case, without magnetization, magnetic field tends to stabilize plasma perturbations with wave numbers parallel to the field and with sufficiently short wavelengths. Paramagnetic effects in quantum plasma make this stabilization weaker. The stabilization disappears completely for short wavelength perturbations in the ferromagnetic limit, when the magnetic field is produced by intrinsic plasma magnetization only. Still, for perturbations of long and moderate wavelength, certain stabilization always takes place due to the nonlinear character of quantum plasma magnetization.
A velocity map imaging detector with an integrated gas injection system
Authors: Ghafur O. , Siu W. , Johnsson P. , Kling M. F. , Drescher M. , Vrakking M. J. J.
Published: March 2009

We present the design of a velocity map imaging spectrometer where the target gas is injected from a capillary that is integrated in the repeller plate of the ion optics assembly that drives electrons/ions formed by ionization or dissociation to a two-dimensional detector. The geometry of this design allows the use of gas densities in the interaction region that are two to three orders of magnitude higher than the densities that are used in standard velocity map imaging spectrometers, making the detector suitable for working with weak light sources such as newly developed attosecond pulse sources, or (quasi-)cw sources such as synchrotrons. In a test where monoenergetic photoelectrons were generated by six-photon ionization of Xe (utilizing the second harmonic of a neodymium doped Nd:YAG), the kinetic energy resolution of the spectrometer was found to be ΔE/E=1.8%. This number was found to be in good agreement with Monte Carlo simulations.
Constraints in nonequilibrium thermodynamics: General framework and application to multicomponent diffusion
Authors: Öttinger Hans Christian
Published: March 2009

We elaborate how holonomic constraints can be incorporated into the general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) framework of nonequilibrium thermodynamics. Dirac’s ideas for constructing constrained Poisson brackets are extended to dissipative brackets. The construction is presented such that it can be put into practice most readily. We illustrate the procedure by developing a symmetric thermodynamic description of diffusion in multicomponent systems and, as a further example, we impose an incompressibility constraint. As a consequence of its more elaborate and restrictive structure, GENERIC removes the ambiguities occurring in the classical thermodynamics of irreversible processes when one works with redundant variables.
Application of grazing incidence x-ray fluorescence technique to discriminate and quantify implanted solar wind
Authors: Kitts K. , Choi Y. , Eng P. J. , Ghose S. K. , Sutton S. R. , Rout B.
Published: March 2009

NASA launched the Genesis return mission to obtain pristine solar wind samples in order to better understand solar wind mechanics, solar physics, and solar system evolution. Unfortunately, the probe crash-landed shattering the collector plates necessitating the application of a grazing incidence x-ray fluorescence technique. This nondestructive methodology differentiates the terrestrial contamination from the low concentration implanted solar wind. Using this technique, the elemental depth distribution is obtained resulting in the determination of absolute solar wind elemental abundance. We describe this application and present the solar wind Fe concentration determination as an example.
Investigation of the electronic properties of nitrogen vacancies in AlGaN
Authors: Cao X. A. , Syed A. A. , Piao H.
Published: March 2009

The effects of premetallization annealing on the electrical characteristics of GaN and AlxGa1−xN (x=0.25 and 0.5) Schottky diodes have been studied. Annealing above 800 °C in an Ar ambient led to a significant preferential N loss, and annealing at 1000 °C caused localized surface decomposition. The Pt/Au Schottky contacts on the annealed GaN became leakier, whereas those on the thermally damaged AlGaN exhibited more rectifying characteristics. Prolonged annealing produced more conductive AlGaN surfaces deficient in both N and Al, as revealed by x-ray photoelectron spectroscopy. These findings suggest that, as opposed to donorlike vacancies in GaN, N vacancies in AlGaN with an Al mole fraction ≥25% behave as deep-level states, compensating the near-surface region. Care must therefore be taken to prevent the loss of N during thermal processing of high-Al content AlGaN.
Dynamical arrest in low density dipolar colloidal gels
Authors: Miller Mark A. , Blaak Ronald , Lumb Craig N. , Hansen Jean-Pierre
Published: March 2009

We report the results of extensive molecular dynamics simulations of a simple, but experimentally achievable model of dipolar colloids. It is shown that a modest elongation of the particles and dipoles to make dipolar dumbbells favors branching of the dipolar strings that are routinely observed for point dipolar spheres (e.g., ferrofluids). This branching triggers the formation of a percolating transient network when the effective temperature is lowered along low packing fraction isochores (ϕ<0.1). Well below the percolation temperature the evolution of various dynamical correlation functions becomes arrested over a rapidly increasing period of time, indicating that a gel has formed. The onset of arrest is closely linked to ongoing structural and topological changes, which we monitor using a variety of diagnostics, including the Euler characteristic. The present system, dominated by long-range interactions between particles, shows similarities to, but also some significant differences from the behavior of previously studied model systems involving short-range attractive interactions between colloids. In particular, we discuss the relation of gel formation to fluid–fluid phase separation and spinodal decomposition in the light of current knowledge of dipolar fluid phase diagrams.
On the flow of associative polymers past a sphere: Evaluation of negative wake criteria
Authors: Mendoza-Fuentes A. J. , Montiel R. , Zenit R. , Manero O.
Published: March 2009

A study on falling spheres descending in associative polymers with sphere-container ratios of 0.05–0.15 for various polymer concentrations and Weissenberg numbers is presented. The fluid exhibits constant viscosity over a wide range of small to moderate shear rates, and shear thinning for large shear rates. The simple shear rheology and linear viscoelasticity of these polymers are modeled with the BMP equation of state [F. Bautista, J. M. de Santos, J. E. Puig, and O. Manero, J. Non-Newtonian Fluid Mech. 80, 93 (1999); O. Manero, F. Bautista, J. F. A. Soltero, and J. E. Puig, J. Non-Newtonian Fluid Mech. 106, 1 (2002)], which enables the prediction of the extensional viscosity as a function of the strain rate. The particle image velocimetry technique allows the measurement of the velocity field in the rear of the sphere. The container wall affects the formation of the negative wake at a critical Weissenberg number, which closely corresponds to the region around the peak of extension thickening of the Trouton ratio in the solution. A characteristic strain rate is estimated from the distance of the sphere surface to the stagnant point where the velocity changes direction. Using these data, various criteria for the appearance of the negative wake are discussed. Conclusions reached by Dou and Phan-Thien [Rheol. Acta 43, 203 (2004)] on the physical mechanisms for negative wake generation, are in agreement with the results exposed in this work.
Band-gap shift and defect-induced annihilation in prestressed elastic structures
Authors: Gei M. , Movchan A. B. , Bigoni D.
Published: March 2009

Design of filters for electromagnetic, acoustic, and elastic waves involves structures possessing photonic/phononic band gaps for certain ranges of frequencies. Controlling the filtering properties implies the control over the position and the width of the band gaps in question. With reference to piecewise homogeneous elastic beams on elastic foundation, these are shown to be strongly affected by prestress (usually neglected in these analyses) that (i) “shifts” band gaps toward higher (lower) frequencies for tensile (compressive) prestress and (ii) may “annihilate” certain band gaps in structures with defects. The mechanism in which frequency is controlled by prestress is revealed by employing a Green’s-function-based analysis of localized vibration of a concentrated mass, located at a generic position along the beam axis. For a mass perturbing the system, our analysis addresses the important issue of the so-called effective negative mass effect for frequencies within the stop bands of the unperturbed structure. We propose a constructive algorithm of controlling the stop bands and hence filtering properties and resonance modes for a class of elastic periodic structures via prestress incorporated into the model through the coefficients in the corresponding governing equations.
An experimental setup to study the expansion dynamics of laser blow-off plasma plume in variable transverse magnetic field
Authors: Kumar Ajai , Chaudhari Vishnu , Patel Kiran , George Sony , Sunil S. , Singh R. K. , Singh Ranjeet
Published: March 2009

In the present work we report generation of uniform and variable pulsed magnetic field in synchronization with pulsed plasma for the study of the expansion dynamics of laser blow-off (LBO) plasma plume. The experimental procedure for optimizing various parameters of the setup, e.g., the production of pulsed field and its synchronization with pulsed plasma and diagnostics system, is also reported. Until now the effect of magnetic field was studied using fixed field. The present setup, however, provides variable and uniform field in synchronization with the setup. A low cost time sequencing control module has been developed for the above purpose. Although the main emphasis is on the technical aspect of the setup, salient features of the effect of transverse magnetic field on the evolution features of the neutral and ionic species are also reported briefly. It is observed that LBO generated plume have a stronger correlation with the magnetic field in comparison to the conventional laser produced plasma experiments as reported earlier.
Thermal-wave radar: A novel subsurface imaging modality with extended depth-resolution dynamic range
Authors: Tabatabaei Nima , Mandelis Andreas
Published: March 2009

Combining the ideas behind linear frequency modulated continuous wave radars and frequency domain photothermal radiometry (PTR), a novel PTR method is introduced. Analytical solutions to the heat diffusion problem for both opaque and transparent solids are provided. Simulations and experimental results suggest a significant improvement in the dynamic range when using the thermal-wave radar (TWR) instead of conventional PTR. A practical TWR image resolution augmentation method is proposed.
High magnetoresistance tunnel junctions with Mg–B–O barriers and Ni–Fe–B free electrodes
Authors: Read J. C. , Cha Judy J. , Egelhoff William F. , Tseng H. W. , Huang P. Y. , Li Y. , Muller David A. , Buhrman R. A.
Published: March 2009

The use of boron-alloyed electrodes with the radio frequency (rf) sputter deposition of MgO yields magnetic tunnel junctions (MTJs) with Mg–B–O tunnel barriers. After annealing, such MTJs can exhibit very high tunneling magnetoresistance (TMR) in the thin (∼1.0 nm) barrier regime. Scanning tunneling spectroscopy of Mg–B–O layers reveals a better defined, but smaller band gap in comparison to that of thin MgO. We produced Fe60Co20B20/Mg–B–O/Ni65Fe15B20 MTJs where after a 350 °C annealing the Ni–Fe–B free electrode crystallizes into a highly textured (001)-normal body centered cubic (bcc) crystal structure and the MTJs achieve 155% TMR.
In situ measurements of the solubilities of salt–water systems by a fiber sensor
Authors: Tan Chun Hua , Huang Xu Guang , Shi Yu Ping
Published: March 2009

A novel fiber sensor for measuring solid solubilities of salt-water systems in situ is described. The sensor consists of a diode laser as light source, three couplers, two sensing fiber ends with protective cladding, and two photodetectors. The measurement principle is based on relative Fresnel reﬂective intensity. This method enabled us to observe in situ transitional process of the equilibration of a solid-liquid system with a small quantity of specimens. By the relatively simple technique, fast determination of the solid solubility is possible. We applied this method to measure a temperature dependence of the solubility of potassium chloride in water in situ and compared with the previous data obtained by other techniques. The measured result has the long-term standard deviation of the concentration of 0.1%, and agrees with the data obtained by the classical method within the error of ±1%. This method is precise and sample saving and is suitable to measure the solubilities of rare and expensive materials.
Anisotropic propagation and confinement of high frequency phonons in nanocomposites
Authors: Sato A. , Knoll W. , Pennec Y. , Djafari-Rouhani B. , Fytas G. , Steinhart M.
Published: March 2009

We show that self-ordered anodic aluminum oxide containing hexagonal arrays of cylindrical nanopores with submicron periodicity is a versatile model system for the exploration of rich phononic phenomena at gigahertz frequencies, which are intimately linked to fluids located in the nanopores and their interactions with the pore walls. Using high-resolution Brillouin spectroscopy we report the first realization of directional flow of elastic energy parallel and perpendicular to the pore axes, phonon localization, and tunability of the phononic band structure.
Electrochemically intercalated indium-tin-oxide/poly(3-hexylthiophene): A solid-state heterojunction solar cell
Authors: Mane Rajaram S. , Lee Wonjoo , Min Sun-Ki , Lee Soo-Hyoung , Joo Oh-Shim , Lokhande C. D. , Shaikh Arif V. , Han Sung-Hwan
Published: March 2009

A heterojunction solar cell design composed of poly(3-hexylthiophene) (P3HT) and intercalated indium-tin-oxide (ITO) donor-acceptor system is explored for the first time. Substantial change in band edge of ITO is noticed after intercalation. Structural and surface morphological studies are reported. Due to tuned band gap of ITO, an increase in short circuit current from 0.0012 to 0.46 mA/cm2, fill factor from 0.39 to 0.51, and power conversion efficiency from 0.000 367 to 0.3% is obtained for heterojunction solar cell when compared to P3HT alone. This novel, room temperature design approach would be of great scientific interest in current solid-state solar cell scenario.
Large tunability of Néel temperature by growth-rate-induced cation inversion in Mn-ferrite nanoparticles
Authors: Yang Aria , Chinnasamy C. N. , Greneche J. M. , Chen Yajie , Yoon Soack D. , Hsu Kailin , Vittoria C. , Harris V. G.
Published: March 2009

The tuning of Néel temperature by greater than 100 K in nanoparticle Mn-ferrite was demonstrated by a growth-rate-induced cation inversion. Mn-ferrite nanoparticles, having diameters from 4 to 50 nm, were synthesized via coprecipitation synthesis. The Néel temperature (TN) increased inversely to the cation inversion parameter, δ (i.e., defined as (Mn1−δFeδ)tet[MnδFe2−δ]octO4). Concomitantly, TN increased with increased particle growth rate and particle size. These results unambiguously establish cation inversion as the dominant mechanism in modifying the superexchange leading to enhanced TN. The ability to tailor TN enables greater flexibility in applying nanoparticle ferrites in emerging technologies.
Metamaterial nanotips
Authors: Rockstuhl C. , Simovski C. R. , Tretyakov S. A. , Lederer F.
Published: March 2009

Nanostructured metamaterials, especially arrays of metallic nanoparticles, which sustain the excitation of localized plasmon polaritons, provide excellent opportunities to mold the flow of light in the linear regime. We suggest a metamaterial structure whose properties are determined not only by its inner geometry but also by its entire shape. We call this structure a metamaterial nanotip. We evaluate the potential of this nanotip to control the size and the location of the field enhancement. Two-dimensional implementations of this metamaterial nanotip were comprehensively numerically simulated and confirm the expected, physically distinct regimes of operation.
Slow light in quantum dot photonic crystal waveguides
Authors: Nielsen Torben Roland , Lavrinenko Andrei , Mørk Jesper
Published: March 2009

A theoretical analysis of pulse propagation in a semiconductor quantum dot photonic crystal waveguide in the regime of electromagnetically induced transparency is presented. The slow light mechanism considered here is based on both material and waveguide dispersion. The group index ng for the combined system is significantly enhanced relative to slow light based on purely material or waveguide dispersion.
Heat-shock dependent oligomeric status alters the function of a plant-specific thioredoxin-like protein, AtTDX
Authors: Lee Jung Ro , Lee Seung Sik , Jang Ho Hee , Lee Young Mee , Park Jin Ho , Park Seong-Cheol , Moon Jeong Chan , Park Soo Kwon , Kim Sun Young , Lee Sun Yong , Chae Ho Byoung , Jung Young Jun , Kim Woe Yeon , Shin Mi Rim , Cheong Gang-Won , Kim Min Gab , Kang Kee Ryeon , Lee Kyun Oh , Yun Dae-Jin , Lee Sang Yeol
Published: March 2009

We found thatArabidopsisAtTDX, a heat-stable and plant-specific thioredoxin (Trx)-like protein, exhibits multiple functions, acting as a disulfide reductase, foldase chaperone, and holdase chaperone. The activity of AtTDX, which contains 3 tetratricopeptide repeat (TPR) domains and a Trx motif, depends on its oligomeric status. The disulfide reductase and foldase chaperone functions predominate when AtTDX occurs in the low molecular weight (LMW) form, whereas the holdase chaperone function predominates in the high molecular weight (HMW) complexes. Because deletion of the TPR domains results in a significant enhancement of AtTDX disulfide reductase activity and complete loss of the holdase chaperone function, our data suggest that the TPR domains of AtTDX block the active site of Trx and play a critical role in promoting the holdase chaperone function. The oligomerization status of AtTDX is reversibly regulated by heat shock, which causes a transition from LMW to HMW complexes with concomitant functional switching from a disulfide reductase and foldase chaperone to a holdase chaperone. Overexpression of AtTDX inArabidopsisconferred enhanced heat shock resistance to plants, primarily via its holdase chaperone activity.
Critical role of promoter IV-driven BDNF transcription in GABAergic transmission and synaptic plasticity in the prefrontal cortex
Authors: Sakata Kazuko , Woo Newton H. , Martinowich Keri , Greene Joshua S. , Schloesser Robert J. , Shen Liya , Lu Bai
Published: March 2009

Transcription of
Bdnf
is controlled by multiple promoters, which drive expression of multiple transcripts encoding for the same protein. Promoter IV contributes significantly to activity-dependent brain-derived neurotrophic factor (BDNF) transcription. We have generated promoter IV mutant mice (BDNF-KIV) by inserting a GFP-STOP cassette within the
Bdnf
exon IV locus. This genetic manipulation results in disruption of promoter IV-mediated
Bdnf
expression. BDNF-KIV animals exhibited significant deficits in GABAergic interneurons in the prefrontal cortex (PFC), particularly those expressing parvalbumin, a subtype implicated in executive function and schizophrenia. Moreover, disruption of promoter IV-driven
Bdnf
transcription impaired inhibitory but not excitatory synaptic transmission recorded from layer V pyramidal neurons in the PFC. The attenuation of GABAergic inputs resulted in an aberrant appearance of spike-timing-dependent synaptic potentiation (STDP) in PFC slices derived from BDNF-KIV, but not wild-type littermates. These results demonstrate the importance of promoter IV-dependent
Bdnf
transcription in GABAergic function and reveal an unexpected regulation of STDP in the PFC by BDNF.