cssi/SciSciGPT-SciSciNet huggingface dataset:
Sparse estimation for structural variability

Proteins are dynamic molecules that exhibit a wide range of motions; often these conformational changes are important for protein function. Determining biologically relevant conformational changes, or true variability, efficiently is challenging due to the noise present in structure data. In this paper we present a novel approach to elucidate conformational variability in structures solved using X-ray crystallography. We first infer an ensemble to represent the experimental data and then formulate the identification of truly variable members of the ensemble (as opposed to those that vary only due to noise) as a sparse estimation problem. Our results indicate that the algorithm is able to accurately distinguish genuine conformational changes from variability due to noise. We validate our predictions for structures in the Protein Data Bank by comparing with NMR experiments, as well as on synthetic data. In addition to improved performance over existing methods, the algorithm is robust to the levels of noise present in real data. In the case of Human Ubiquitin-conjugating enzyme Ubc9, variability identified by the algorithm corresponds to functionally important residues implicated by mutagenesis experiments. Our algorithm is also general enough to be integrated into state-of-the-art software tools for structure-inference.
Enumeration of totally positive Grassmann cells

Postnikov (Webs in totally positive Grassmann cells, in preparation) has given a combinatorially explicit cell decomposition of the totally nonnegative part of a Grassmannian, denoted Grk,n+, and showed that this set of cells is isomorphic as a graded poset to many other interesting graded posets. The main result of our work is an explicit generating function which enumerates the cells in Grk,n+ according to their dimension. As a corollary, we give a new proof that the Euler characteristic of Grk,n+ is 1. Additionally, we use our result to produce a new q-analog of the Eulerian numbers, which interpolates between the Eulerian numbers, the Narayana numbers, and the binomial coefficients.
Transcranial low-level laser therapy enhances learning, memory, and neuroprogenitor cells after traumatic brain injury in mice

The use of transcranial low-level laser (light) therapy (tLLLT) to treat stroke and traumatic brain injury (TBI) is attracting increasing attention. We previously showed that LLLT using an 810-nm laser 4 h after controlled cortical impact (CCI)-TBI in mice could significantly improve the neurological severity score, decrease lesion volume, and reduce Fluoro-Jade staining for degenerating neurons. We obtained some evidence for neurogenesis in the region of the lesion. We now tested the hypothesis that tLLLT can improve performance on the Morris water maze (MWM, learning, and memory) and increase neurogenesis in the hippocampus and subventricular zone (SVZ) after CCI-TBI in mice. One and (to a greater extent) three daily laser treatments commencing 4-h post-TBI improved neurological performance as measured by wire grip and motion test especially at 3 and 4 weeks post-TBI. Improvements in visible and hidden platform latency and probe tests in MWM were seen at 4 weeks. Caspase-3 expression was lower in the lesion region at 4 days post-TBI. Double-stained BrdU-NeuN (neuroprogenitor cells) was increased in the dentate gyrus and SVZ. Increases in double-cortin (DCX) and TUJ-1 were also seen. Our study results suggest that tLLLT may improve TBI both by reducing cell death in the lesion and by stimulating neurogenesis.
Cooper pair formation dynamics in Bi2Sr2CaCu 2O8+δ

We utilize ultrafast terahertz pulses to monitor the carrier dynamics in the high-TC superconductor Bi2Sr2CaCu2O8+δ. The temperature, density and time dependence distinctly exposes a bimolecular recombination process of quasiparticles which underlies formation of Cooper pairs.
Crystal structure and bonding in BaAu5Ga2 and AeAu4+xGa3-x (Ae = Ba and Eu): hexagonal diamond-type Au frameworks and remarkable cation/anion partitioning in the Ae-Au-Ga systems.

Five new polar intermetallic compounds in the Ae–Ga–Au system (Ae = Ba, Eu), BaAu5Ga2 (I), BaAu4.3Ga2.7 (II), Ba1.0Au4.5Ga2.4 (III), EuAu4.8Ga2.2 (IV), and Eu1.1Au4.4Ga2.2 (V), have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. I crystallizes in the orthorhombic crystal system with a large unit cell [Pearson symbol oP64; Pnma, Z = 8, a = 8.8350(5) A, b = 7.1888(3)A, c = 20.3880(7) A], whereas all other compounds are hexagonal [hP24; P62m, Z = 3, a = 8.54–8.77(1) A, c = 7.19–7.24(1) A]. Both structures contain mutually orthogonal layers of Au6 hexagons in chair and boat conformations, resulting in a hexagonal diamond-like network. Ae atoms and additional (Au/Ga)3 groups are formally encapsulated by (Au6)2 distorted hexagonal prisms formed of three edge-sharing hexagons in the boat conformation or, alternatively, lie between two Au6 hexagons in the chair conformation. The (Au/Ga)3 groups can be substituted by Ae atoms in some of the hexagonal structures with ...
Probing the Large-Scale Plasma Structure of the Solar Corona with Faraday Rotation Measurements

Faraday rotation measurements of the solar corona made with the VLA at frequencies of 1465 and 1665 MHz are reported. The measurements were made along 20 lines of sight to 19 extragalactic radio sources in 2005 March and April. The closest heliocentric distances of the lines of sight ranged from 5.6 to 9.7 R☉. Measured rotation measures range from -25 to +6 rad m-2, and perhaps as high as +61 rad m-2. The purpose of these observations is to probe the three-dimensional structure of the coronal plasma in the heliocentric distance range 5-10 R☉, and particularly the strength and structure of the coronal magnetic field. The measured rotation measures are compared with two types of models for the coronal plasma structure. For the majority of the lines of sight, the observed rotation measures are reasonably well represented by the predictions from either type of model. However, 3 or 4 of the 20 lines of sight have large observed-model residuals. These anomalous sources do not seem to be affected by coronal mass ejections (which did occur during the program), but there may be an association between anomalous rotation measures and the presence of streamers along the line of sight. The magnitude of the coronal field necessary to reproduce the majority of the observations is in the range of 46-120 mG at a fiducial heliocentric distance of 5 R☉, with a smaller, preferred range of 46-52 mG.
Achieving computer literacy

"Computer literacy", or "computer competency", has become a widely used term, usually applied to students and their abilities to use computers for often vague purposes. Computer literacy has come to mean a milestone in the educational program, for example, a requirement for graduation from high school or college, or the result of finishing a certain course of study.
α-Siloxyamides from a carbamoylsilane and carbonyl compounds

Abstract The reaction of a carbamoylsilane with aldehydes or ketones affords α-siloxyamides. The addition reaction is catalyzed by fluoride ion (TBAT, 25–50°C), but proceeds in the absence of catalyst at higher temperatures (50–100°C).
A Blowup Criterion for Ideal Viscoelastic Flow

We establish an analog of the Beale–Kato–Majda criterion for singularities of smooth solutions of the system of PDE arising in the Oldroyd model for ideal viscoelastic flow.
Chrysanthemum stunt: a viroid disease.

Abstract Infectious material in crude extracts from chrysanthemum stunt-affected cineraria or chrysanthemum leaves sediments heterogeneously, some pelleting during low-speed centrifugation, some during high-speed centrifugation. High-speed supernatants, however, always contain appreciable amounts of infectious material. Treatment of crude extracts with chloroform-butanol, phenol, or ethanol does not reduce infectivity. The infectious agent is sensitive to treatment with ribonuclease, but not to treatment with deoxyribonuclease. The agent can be concentrated by ethanol precipitation and resuspension in a smaller buffer volume. Partial purification of the infectious agent by methods developed for the purification of potato spindle tuber viroid (PSTV), followed by analysis in linear-log sucrose density gradients and by electrophoresis in 20% polyacrylamide gels demonstrated that the stunt agent is a low molecular weight RNA. Its electrophoretic mobility is somewhat greater than that of PSTV. Thus, the causative agent of the chrysanthemum stunt disease is a viroid similar to, but distinct from, PSTV.
Liouville lost, Liouville regained: central charge in a dynamical background

Abstract Several recent approaches to black hole entropy obtain the density of states from the central charge of a Liouville theory. If Liouville theory is coupled to a dynamical spacetime background, however, the classical central charge vanishes. I show that the central charge can be restored by introducing appropriate constraints, which may be interpreted as fall-off conditions at a boundary such as a black hole horizon.
Algorithm for optimal mode scheduling in switched systems

This paper considers the problem of computing the schedule of modes in an autonomous switched dynamical system, that minimizes a cost functional defined on the trajectory of the system's continuous state variable. It proposes an algorithm that modifies a finite but unbounded number of modes at each iteration, whose computational workload at the various iterations appears to be independent on the number of modes being changed. The algorithm is based on descent directions defined by Gaâteaux differentials of the performance function with respect to variations in mode-sequences, and its convergence to (local) minima is established in the framework of optimality functions and minimizing sequences, devised by Polak for infinite-dimensional optimization problems.
A micro pitch and roll motion sensor

Abstract Characterization of pitch and roll motions of the slider in the hard disk gimbal system is important to achieve higher aerial recording densities. This paper describes a novel piezoresistive-type microsensor that could be directly mounted on the existing slider/gimbal system of a hard disk drive to simultaneously measure the pitch and roll angles of the slider. The size of the fabricated microsensor is designed as 1 mm ×1 mm ×0.1 mm for picoslider applications and the sensor is fabricated by a silicon micromachining process for mass production. The dynamic behavior of the system is slightly altered as expected in a simulation after the sensor is mounted on the slider and the fundamental frequency shift of pitch and roll motion is calculated to be less than 5% of the original system but it is believed that this sensor could provide the best in situ measurement than other currently existing methods. Experimentally, the prototype sensor is capable of detecting pitch and roll angles within ± 3° and the performance is compared with interferometric measurement data and the mismatch is nominally within 14% in average.
Mitsunobu reactions of glycals with phenoxide nucleophiles are SN2′-selective

The C3-hydoxyl group of l-rhamnal (4) and d-glucal 7 underwent SN2′-selective Mitsunobu displacements with substituted phenoxide nucleophiles. These reactions provide access to the corresponding α-arylglycoside.
All-solution-processed CIS solar cells based on electrodeposited ZnO nanopillars

One-dimensional (1D)-nanostructured CuInS 2 (CIS) solar cells based on electrodeposited ZnO nanopillar arrays have been prepared by an all-solution process. The electrodeposition of ZnO is performed galvanostatically from Zn(NO 3 ) 2 aqueous solution. CIS is deposited on the ZnO by dip-coating a molecular-based organic solution and subsequent heating in an Ar atmosphere. This in-situ CIS synthesis method offers good penetration behavior into the gap between ZnO nanopillars and the formation of compact CIS nanocrystal layers without dissolution of ZnO. Characterization of the CIS layer is carried out with an X-ray diffractometer, field-emission scanning electron microscope, and UV-vis-NIR absorption spectrophotometer. To improve the photovoltaic performance, the introduction of a buffer layer and/or an electron blocking layer into the ZnO/CIS interface and the CIS surface, respectively, is also studied by using solution processes.
Equilibrium and kinetic analysis of the interaction of mercury(II) with cadmium(II) metallothionein

The reaction of Cd-metallothionein (MT) with mercury(II) has been studied. The Cd/sub 7/-MT was titrated with from 1 to 14 equiv of HgCl/sub 2/, following which the cadmium(II) and mercury(II) contents, the partition coefficient on a size-exclusion HPLC column, and the uv spectra were measured. The results showed that mercury(II) quantitatively displaces cadmium(II) from the protein. An analysis of the uv spectral data by the method of singular value decomposition (SVD) was used to determine the number of spectrally distinct components and their fractional abundance throughout the titration. A minimum of three spectrally distinct components were found by this method; they corresponded to tetrahedral Cd-S, tetrahedral Hg-S, and linear Hg-S coordination geometries. Initially the mercury(II) occupies tetrahedral sites; however, above a Hg/MT stoichiometry of 4, there is a shift to linear coordination. The size-exclusion data indicate a shift to a more compact structure upon addition of mercury(II) to the metallothionein. Finally, the analysis of a uv spectrum of a mixture of the all-cadmium(II) and the all-mercury(II) metallothioneins indicates that the two forms undergo facile interprotein metal ion exchanges. The analysis of the kinetics of this reaction is best fit by second-order kinetics, which would be consistent with a mechanism wherebymore » there was a direct interaction between the two MTs. 57 references, 7 figures, 1 table.« less
The coding theorem and ordinary least-squares models in economics

This paper considers ordinary least-squares (OLS) models of competitive markets wherein the independent variable represents trader information which should be a predictor of the market clearing price. The market context of the OLS model draws a parallel with an additive noise channel having noiseless feedback. The feedback link represents the information gained by the trader from observing present prices and using this information to modify his next round of market activity. Several models from the economic literature are shown to fit this prescribed information channel format and information theory constructs are used to interpret their economic results.
Introduction and Tribute to H. W. Menard 1920–1986

Henry William Menard, professor of geology at the Scripps Institution of Oceanography, was one of the pioneers and leaders of the great period of exploration of the ocean floor that began after World War II. He led or participated in 25 deep-sea expeditions, mainly in the North Pacific and South Pacific oceans. On the first of these, the Midpac Expedition in 1950, he and his colleagues at the Scripps Institution and the U.S. Navy Electronics Laboratory, Ed Hamilton and Bob Dietz, discovered the Mid-Pacific Mountains, a 4000-m-high mountain range under the sea, which extends for nearly 4000 km from the Hawaiian Island chain to Wake Island. During Midpac, Russell Raitt collected 16 refraction stations showing, for the first time, the uniformity of the ocean crust and Art Maxwell and Roger Revelle discovered that oceanic heat flow was nearly the same as that measured on continents.
Enhanced reactivity in radical cyclizations of hydrazones using the silicon-tethered 1-bromovinyl group

Abstract A silicon-tethered 1-bromovinyl group was shown to function as a radical precursor for tin-mediated vinyl additions to chiral α- or β-hydroxyhydrazone. In contrast to related thiyl-mediated methods, these vinyl bromides were not limited to the 5- exo cyclization mode. A series of Si-tethered 5- exo and 6- exo cyclizations formed the corresponding five- and six-membered exo -methylene-substituted oxasilacycles. Treatment with fluoride cleaved the Si–C and Si–O bonds to afford the corresponding allylic hydrazines. Diastereoselectivities ranged from 2:1 to 25:1 ( anti : syn ) for the 5- exo cyclizations, depending on the size of the exocyclic substituent, but 6- exo cyclization was not diastereoselective. A variant involving Tamao oxidation of the exo -methylene oxasilacyclopentane intermediate afforded a methyl ketone, a net process corresponding to addition of a radical acyl anion equivalent.
An empirical correlation for E(J,T) of a melt-cast-processed BSCCO-2212 superconductor under self field

An empirical correlation is developed for the electrical field strength E(J, T) of a melt-cast processed BSCCO-2212 superconductor. The empirical correlation is based, in part, on the theory of magnetic relaxation and on experimental data at 77 and 87 K. It is developed for temperatures in the range between 77 and 92 K, which is the range of interest for practical devices such as the superconducting fault current limiters. The general form of the correlation may be applicable to other high-T/sub c/ superconductors.
Synthesis and reactions of 2‐amino‐7, 8‐dimethoxy‐1h‐3‐benzazepines. Competitive formation of 2‐amino‐1h‐3‐benzazepines vs. 2‐benzylimidazoles

A short synthesis of 2-amino-7, 8-dimethoxy-1H-3-benzazepine (1a) from 3, 4-dimethoxyphenylacetonitrile (8a) is reported. The synthesis of several other 2-amino-1H-3-benzazepines 1 is also discussed. Conditions which favor the formation of 1 versus the formation of the isomeric 2-benzylimidazoles 11 are evaluated. Several reactions of 1a are also described.
Numerical analysis of the vertex models for simulating grain boundary networks

Polycrystalline materials undergoing coarsening can be represented as evolving networks of grain boundaries, whose statistical characteristics describe macroscopic properties. The formation of various statistical distributions is extremely complex and is strongly influenced by topological changes in the network. This work is an attempt to elucidate the role of these changes by conducting a thorough numerical investigation of one of the simplest types of grain growth simulation models, the vertex model. While having obvious limitations in terms of its ability to represent realistic systems, the vertex model enables full control over topological transitions and retains essential geometric features of the network. We formulate a self-consistent vertex model and investigate the role of microscopic parameters on mesoscale network behavior. This study sheds light on several important questions, such as how statistics are affected by the choice of temporal and spatial resolution and rules governing topological c...
Faraday-Rotation Measurements of Megagauss Magnetic Fields in Laser-Produced Plasmas

Magnetic fields in the megagauss range have been observed in the laser-produced plasma near the focus of a high-power laser pulse. Faraday-rotation measurements utilizing the light of a probing beam and the specularly reflected laser light both show the presence of these large fields.
A new input-output selection system for the Florida Automatic Computer (FLAC)

The ultimate goal of the original FLAC designers was to produce a fully coordinated instrumentation system and data reduction system with a common data language. Their foresight has resulted in a coordinated data gathering and data processing system, capable of many evolutionary changes as the "state of the art" progresses.
THE CHEMOPREVENTION OF CANCER BY DIETARY CAROTENOIDS : STUDIES IN MOUSE AND HUMAN CELLS

In many epidemiologic studies a decreased risk of cancer has been associated with the consumption of diets rich in fruits and in green and yellow vegetables. Of the many components of such a diet the content of carotenoids, particularly β-carotene, has been most consistently linked to decreased risk. The biological mechanism for such protection is at present unclear; multiple possibilities exist: carotenoids are potent antioxidants and oxidative stress is known to contribute to carcinogenesis; many carotenoids can be converted to retinoids, known cancer preventive agents at several anatomic sites; finally carotenoids may possess additional actions in mammalian cells. Experimental studies have been inhibited by difficulties in delivering these molecules to target cells. A novel delivery system, using THE as solvent, has been developed and the activity of several carotenoids tested in mouse 10T1/2 cells. Carotenoids have been shown to: (a) inhibit plasma membrane lipid-oxidation; (b) inhibit carcinogen-induced neoplastic transformation; (c) cause up-regulated expression at the message and protein level of connexin43, a gene coding for the structural unit of a gap junction. This latter activity was statistically correlated with the ability to inhibit neoplastic transformation. While protection from carcinogen-induced neoplastic transformation cannot be directly studied in human cells, Cx43 expression is also up-regulated in human fibroblasts, suggesting that carotenoids have chemopreventive action in humans. We have proposed that increased junctional communication is mechanistically linked to inhibition of transformation. In this model, the gap junction serves as a conduit for growth regulatory signals from normal to carcinogen-initiated cells, thereby suppressing their transformation.
Deuteron-Model Calculation of the High-Energy Nuclear Photoeffect

The high-energy nuclear photoeffect has been calculated according to the "deuteron model" of Levinger. In this model, the photoprocess occurs when a neutron and a proton which are scattering one another inside the nucleus absorb the energy of the incident photon and escape from the nuclear potential well into the laboratory. The nuclear photoeffect cross section is then obtained by averaging the cross section for the above process over all possible neutron-proton pairs in the nucleus, assuming a nucleon momentum distribution. The electric dipole and quadrupole interactions of the radiation field with the neutron and proton are included, and the magnetic terms are neglected. The averaging over all neutron-proton pairs is performed by means of a random flight formulation of the problem. The analytical work involved may conveniently be done using either a zero-temperature Fermi ground-state nucleon momentum distribution or a Gaussian distribution. Numerical results for the energy and angle distributions of photoneutrons and photoprotons are presented in the case of the Gaussian distribution, for four photon energies between 50 and 125 Mev.
Keck Measurement of the XTE J2123-058 Radial Velocity Curve

We measured the radial velocity curve of the companion of the neutron star X-ray transient XTE J2123-058. Its semiamplitude (K2) of 298.5 ? 6.9 km s-1 is the highest value that has been measured for any neutron star low-mass X-ray binary. The high value for K2 is, in part, due to the high binary inclination of the system but may also indicate a high neutron star mass. The mass function (f2) of 0.684 ? 0.047 M?, along with our constraints on the companion's spectral type (K5 V-K9 V) and previous constraints on the inclination, gives a likely range of neutron star masses from 1.2 to 1.8 M?. We also derive a source distance of 8.5 ? 2.5 kpc, indicating that XTE J2123-058 is unusually far, 5.0 ? 1.5 kpc, from the Galactic plane. Our measurement of the systemic radial velocity is -94.5 ? 5.5 km s-1, which is significantly different from what would be observed if this object corotated with the disk of the Galaxy.
Government growth and private contributions to charity

We exploit the time-series properties of charitable giving to provide additional insights into the relationship between charitable contributions and government spending. Cointegration tests reveal a significant long-run relationship between several categories of charitable giving and government spending. Granger causality tests provide evidence on the short-run giving and spending relationship. Evidence suggests that charitable contributions to education respond quite differently to state and local government education expenditures versus federal government expenditures. We argue that the government spending and charitable giving relationship depends on the source of government revenue, how this revenue is used, and the rational ignorance of private donors.
Distinct biological impact of dephosphorylation vs. downregulation of p210Bcr-Abl: implications for imatinib mesylate response and resistance.

Imatinib mesylate suppresses phosphorylation of its kinase target, Bcr-Abl. We hypothesized that loss of p210Bcr-Abl (the kinase target) may lead to imatinib mesylate resistance. We studied K562 cells [chronic myelogenous leukemia (CML) blast crisis line] and MO7E/MBA-1 cells (with MBA-1 cells representing MO7E cells stably transfected with BCR-ABL). Imatinib mesylate resistance developed when p210Bcr-Abl expression was abolished. Furthermore, K562 cells were significantly more growth suppressed after imatinib mesylate exposure than after downregulation of Bcr-Abl expression. Signaling pathways which were functional in the absence of Bcr-Abl expression (NF-κB and mitogen-activated protein kinase activation or the growth factor pathway) were disrupted when p210Bcr-Abl was present but dephosphorylated, suggesting that an intact, but enzymatically inactive Bcr-Abl, may interfere with critical growth/signaling pathways. Downregulation of p210Bcr-Abl may be a mechanism by which imatinib mesylate resistance eme...
An analysis of hearing aid fittings in adults using cochlear implants and contralateral hearing aids

Objectives/Hypothesis: The objective of this study was to assess the appropriateness of hearing aid fittings within a sample of adult cochlear implant recipients who use a hearing aid in the contralateral ear (i.e., bimodal stimulation). Methods: The hearing aid gain was measured using real ear testing for 14 postlingually deaf English-speaking adults who use a cochlear implant in the contralateral ear. Unaided and aided audiometric testing assessed the degree of functional gain derived from hearing aid use. Results: On average, the target to actual output level difference was within 10 dB only at frequencies of 750 Hz and 1,000 Hz. Only 1 of the 14 study participants had a hearing aid for which the majority of the tested frequencies were within 10 dB of the target gain. In addition, a greater amount of functional gain (i.e., the increase in unaided behavioral thresholds after amplification) was provided for lower frequencies than higher frequencies. Conclusions: Hearing aid settings in our sample were suboptimal and may be regarded as a contributing factor to the variability in bimodal benefit. Refining hearing aid fitting strategies tailored to the needs of the concurrent cochlear implant and hearing aid user is recommended.
Weak Coupling Casimir Energies for Finite Plate Configurations

We derive and use an extremely simplified formula for the interaction Casimir energy for two separate bodies in the weak coupling regime for massless scalar fields. We derive closed form solutions for a general arrangement of two δ-function plates finite in one direction and infinite in another. We examine the situation of two parallel plates finite in both transverse directions.
The economic value of biochar in crop production and carbon sequestration

Abstract This paper estimates the economic value of biochar application on agricultural cropland for carbon sequestration and its soil amendment properties. In particular, we consider the carbon emissions avoided when biochar is applied to agricultural soil, instead of agricultural lime, the amount of carbon sequestered, and the value of carbon offsets, assuming there is an established carbon trading mechanism for biochar soil application. We use winter wheat production in Eastern Whitman County, Washington as a case study, and consider different carbon offset price scenarios and different prices of biochar to estimate a farm profit. Our findings suggest that it may be profitable to apply biochar as a soil amendment under some conditions if the biochar market price is low enough and/or a carbon offset market exists.
Spin Glass Computations and Ruelle’s Probability Cascades

We study the Parisi functional, appearing in the Parisi formula for the pressure of the SK model, as a functional on Ruelle's Probability Cascades (RPC). Computation techniques for the RPC formulation of the functional are developed. They are used to derive continuity and monotonicity properties of the functional retrieving a theorem of Guerra. We also detail the connection between the Aizenman-Sims-Starr variational principle and the Parisi formula. As a final application of the techniques, we rederive the Almeida-Thouless line in the spirit of Toninelli but relying on the RPC structure.
Tungsten oxide nanowire growth by chemically induced strain

We have investigated the formation of tungsten oxide nanowires under different chemical vapor deposition (CVD) conditions. We find that exposure of oxidized tungsten films to hydrogen and methane at 900 °C leads to the formation of a dense array of typically 10 nm diameter nanowires. Structural and chemical analysis shows that the wires are crystalline WO3. We propose a chemically driven whisker growth mechanism in which interfacial strain associated with the formation of tungsten carbide stimulates nanowire growth. This might be a general concept, applicable also to other nanowire systems.
Initial Value Problems of the Sine-Gordon Equation and Geometric Solutions

Recent results using inverse scattering techniques interpret every solution φ(x, y) of the sine-Gordon equation as a nonlinear superposition of solutions along the axes x=0 and y=0. This has a well-known geometric interpretation, namely that every weakly regular surface of Gauss curvature K=−1, in arc length asymptotic line parametrization, is uniquely determined by the values φ(x, 0) and φ(0, y) of its coordinate angle along the axes. We introduce a generalized Weierstrass representation of pseudospherical surfaces that depends only on these values, and we explicitely construct the associated family of pseudospherical immersions corresponding to it.
Modular Statically Typed Multimethods

Multimethods offer several well-known advantages over the single dispatching of conventional object-oriented languages, including a simple solution to the binary method problem, a natural implementation of the strategy design pattern, and a form of open objects that enables easy addition of new operations to existing classes. However, previous work on statically typed multimethods whose arguments are treated symmetrically has required the whole program to be available in order to perform typechecking. We describe Dubious, a simple core language including first-class generic functions with symmetric multimethods, a classless object model, and modules that can be separately typechecked. We identify two sets of restrictions that ensure modular type safety for Dubious as well as an interesting intermediate point between these two. We have proved each of these modular type systems sound.
Fixed Costs and Long-Lived Investments

Abstract Fixed costs models are difficult to analyze because they feature non-degenerate, time-varying distributions of capital across firms. If investments are sufficiently long-lived however then the cross-sectional distribution of capital holdings has virtually no bearing on the equilibrium and the aggregate behavior of fixed-cost models is essentially identical to neoclassical models. The findings are due to a near infinite elasticity of investment timing for long-lived investments – a feature shared by fixed-cost models and neoclassical models. “Irrelevance results” found in numerical studies of fixed-cost models are not parametric special cases but instead are fundamental properties of models with long-lived investment goods.
Optimal Power Management in Wireless Control Systems

This paper considers the control of a linear plant when plant state information is being transmitted from a sensor to the controller over a wireless fading channel. The power allocated to these transmissions determines the probability of successful packet reception and is allowed to adapt online to both channel conditions and plant state. The goal is to design plant input and transmit power policies that minimize an infinite horizon cost combining power expenses and the conventional linear quadratic regulator control cost. Since plant inputs and transmit powers are in general coupled, a restricted information structure is imposed allowing them to be designed separately. Under this information structure the standard LQR controller becomes the optimal plant input policy, while the optimal communication policy follows a Markov decision process minimizing transmit power at the sensor and state estimation error at the controller. The optimal power adaptation to channel and plant states is examined qualitatively for general forward error correcting codes. In the particular case of capacity achieving codes event-triggered policies are recovered, where the sensor decides whether to transmit or not based on plant and channel conditions. Approximate dynamic programming is employed to derive a family of tractable suboptimal communication policies exhibiting the same qualitative features as the optimal one. The performance of our suboptimal policies is shown in simulations and is contrasted to other simple transmission policies.
On D3-brane Potentials in Compactifications with Fluxes and Wrapped D-branes

We study the potential governing D3-brane motion in a warped throat region of a string compactification with internal fluxes and wrapped D-branes. If the Kahler moduli of the compact space are stabilized by nonperturbative effects, a D3-brane experiences a force due to its interaction with D-branes wrapping certain four-cycles. We compute this interaction, as a correction to the warped four-cycle volume, using explicit throat backgrounds in supergravity. This amounts to a closed-string channel computation of the loop corrections to the nonperturbative superpotential that stabilizes the volume. We demonstrate that for warped conical spaces the superpotential correction is given by the embedding equation specifying the wrapped four-cycle, in agreement with the general form proposed by Ganor. We verify that the corrected gauge coupling on wrapped D7-branes is holomorphic. Finally, our results have applications to cosmological inflation models in which the inflaton corresponds to a D3-brane moving in a warped throat.
Simulation of Positronium: Toward More Realistic Models of Void Spaces in Materials

Abstract An exact treatment of a positron and electron in a two-chain, Path Integral Monte Carlo (PIMC) simulation is used to calculate both self-annihilation and pick-off rates of Ps at finite temperature. We find the effect of the linear dielectric response of a homogeneous material on the annihilation rate of positrons and Ps in spherical voids. In addition, we find lifetimes and structural information for Ps in cylindrical channels, both with and without adsorbed fluid atoms.
Supergravity couplings of noncommutative D-branes

Abstract We discuss the supergravity couplings of noncommutative D-branes by considering the disk amplitudes with one closed string insertion. The result confirms a recent proposal for the general form of the noncommutative Yang–Mills operators coupling to the massless closed string modes. The construction involves smearing Yang–Mills field variables along an open Wilson line. For multiple D-branes interacting with background supergravity fields, this prescription reduces, in the B =0 limit, to the “symmetrized trace” prescription, and the supergravity fields are seen to be functionals of the nonabelian scalar fields on the branes.
The preparation of 2-arylmethylidene-8-methyl-8-azabicyclo[3.2.1]octan-3-ones

Abstract An efficient and versatile two‐step synthesis of 2‐arylmethylidene‐8‐methyl‐8‐azabicyclo[3.2.1]octane‐3‐ones, via mono aldol condensation of tropinone with a variety of aryl aldehydes followed by pTsOH‐catalyzed dehydration, is described.
Noncontact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites

A 13 mJ NdYAG 1064 nm, 4 ns, laser pulse was employed to produce ultrasonic plate waves in 20 percent porous SiC/SiC composite tensile specimens of three different architectures. An air coupled 0.5 MHz transducer was used to detect and collect the waveforms which contained first antisymmetric plate wave pulses for determining the shear wave velocity (VS). These results were compared to VS values determined on the same specimens with 0.5 MHz ultrasonic transducers with contact coupling. Averages of four noncontact determinations on each of 18 specimens were compared to averages of four contact values. The noncontact VS's fall in the same range as the contact. The standard deviations for the noncontact VS's averaged 2.8 percent. The standard deviations for the contact measurements averaged 2.3 percent, indicating similar reproducibility. Repeated laser pulsing at the same location always lead to deterioration of the ulu-"nic signal. The signal would recover in about 24 hr in air however, indicating that no permanent damage was produced.
Quantum criticality and incipient phase separation in the thermodynamic properties of the Hubbard model

Transport measurements on the cuprates suggest the presence of a quantum critical point (QCP) hiding underneath the superconducting dome near optimal hole doping. We provide numerical evidence in support of this scenario via a dynamical cluster quantum Monte Carlo study of the extended two-dimensional Hubbard model. Single-particle quantities, such as the spectral function, the quasi-particle weight and the entropy, display a crossover between two distinct ground states: a Fermi liquid at low filling and a non-Fermi liquid with a pseudo-gap at high filling. Both states are found to cross over to a marginal Fermi-liquid state at higher temperatures. For finite next-nearest-neighbour hopping t', we find a classical critical point at temperature T(c). This classical critical point is found to be associated with a phase-separation transition between a compressible Mott gas and an incompressible Mott liquid corresponding to the Fermi liquid and the pseudo-gap state, respectively. Since the critical temperature T(c) extrapolates to zero as t' vanishes, we conclude that a QCP connects the Fermi liquid to the pseudo-gap region, and that the marginal Fermi-liquid behaviour in its vicinity is the analogue of the supercritical region in the liquid-gas transition.
Deployment algorithms for a power‐constrained mobile sensor network

This paper presents distributed coverage algorithms for mobile sensor networks in which agents have limited power to move. Rather than making use of a constrained optimization technique, our approach accounts for power constraints by assigning non-homogeneously time-varying regions to each robot. This leads to novel partitions of the environment into limited-range, generalized Voronoi regions. The motion control algorithms are then designed to ascend the gradient of several types of locational optimization functions. In particular, the objective functions reflect the global energy available to the group and different coverage criteria. As we discuss in the paper, this has an effect on limiting each agent's velocity to save energy and balance its expenditure across the network. Copyright © 2009 John Wiley & Sons, Ltd.
Massive string states as extreme black holes

We consider the Schwarz-Sen spectrum of elementary electrically charged massive N R = 1/2 states of the four-dimensional heterotic string and show the maximum spin 1 supermultiplets to correspond to extreme black hole solutions. The N L= 1 states and N L > 1 states (with vanishing left-moving internal momentum) admit a single scalar-Maxwell description with parameters \(\sqrt {3}\) or a = 1, respectively. The corresponding solitonic magnetically charged spectrum conjectured by Schwarz and Sen on the basis ofS-duality is also described by extreme black holes.
Synthesis of ceramic superconductors under low oxygen pressure

We have developed a process for synthesizing orthorhombic YBa2Cu3O x (123) superconducting powders by calcination of the precursor powder under reduced total oxygen pressure. Because a single calcination at 800°C for 4 h in flowing oxygen at a pressure of 2 mm Hg results in essentially phase-pure material, total calcination times have been drastically reduced. At liquid nitrogen temperature, sintered pellets made from this powder have critical current densities of ∼1000 A/cm2 in zero applied magnetic field.
The freedom to contract and the free-rider problem

We present an economic argument for restraining certain voluntary agreements. We identify a class of situations where single individuals or parties may use the freedom to contract to subtly manipulate large groups of individuals by offering them contracts that promote free-riding behavior. We provide three examples where placing restrictions on the freedom to contract may prove beneficial. The first example provides a rationale for the prohibition of exclusionary contracts. We point to the role most favored nation clauses may play in facilitating such inefficient exclusionary practices. The second example provides justification for prohibiting employers from proposing to compensate workers for committing not to join a labor union. The third example provides a rationale for the ban against vote trading.
Evaluating Gas Production Performances in Marcellus Using Data Mining Technologies

Abstract Shale gas development – enabled by the advent of advanced horizontal drilling and hydraulic fracturing technology - has become, over the past several years, a very important energy resource. The estimated ultimate recovery of natural gas from the Marcellus Shale in West Virginia alone has been estimated to be between 98 and 150 trillion cubic feet (Tcf). In 2008, 25 billion cubic feet (Bcf) of natural gas was produced from 41 horizontal wells in West Virginia. By 2012, that gas production reached 301.7 Bcf from 631 horizontal wells. However, the hydraulic fracture stimulation of horizontal wells with multiple stages mechanism, by which that natural gas is produced from shale, is complex. Significant uncertainty about production performance in these unconventional reservoirs represents significant risk for whether resource development will lead to favorable technical and economic performance. The objective of this paper is to use post-hoc analysis techniques to identify correlations between gas production performance of a well and attributes of its completion and geological setting, and to identify those factors most important to predicting gas recovery performance. To accomplish this, the geological attributes of Marcellus Shale in West Virginia were characterized through literature review. Then, the set of 631 wells was down selected to a representative subset of 187 wells for which complete data are available, including well location, completion data, hydraulic fracture treatment data and production data. The wells were classified into four groups based on geological setting. For each geological group, engineering and statistical analyses were applied to study the correlation between well performance and well completion attributes through traditional regression methods. Important factors considered to affect gas production include number of hydraulic fracture stages, lateral length, vertical depth, proppant volume, and fracture fluid volume and treatment rate. The numbers of hydraulic fracture stages and lateral length have relative large influence on well performance. With these analysis results, it was possible to estimate well-scale ultimate natural gas production performance as a function of known geological conditions and completion parameters. The results lead to a better understanding of the trends in Marcellus Formation well performance. These approaches could, in the future, help to optimize stimulation treatments and well completions and improve resource recovery in the Marcellus, and other unconventional hydrocarbon formations.
Somatic generation of immune diversity

One day in the fall of 1970, I received an airmail letter from Renato Dulbecco who was traveling in Europe. At that time I was a postdoctoral fellow in his laboratory at the Salk Institute. The letter, written on stationery of the Hotel Hassler in Rome, said:
Nature and strength of defect interactions in cubic stabilized zirconia

The intrinsic ordering tendencies that limit ionic conduction in doped zirconia electrolytes are fully elucidated using first-principles calculations. A detailed analysis of nearly 300 yttria- and scandia-stabilized cubic-zirconia-ordered vacancy compounds reveals a delicate balance between competing elastic and electrostatic interactions. These results explain several outstanding experimental observations and provide substantial insight needed for improving ionic conduction and enabling low-temperature operation of zirconia-based electrolytes. We show that the surprising $〈111〉$ vacancy ordering in dilute solid solutions is a consequence of repulsive electrostatic and attractive elastic interactions that balance at third-neighbor vacancy separations. In contrast, repulsive elastic vacancy-dopant interactions prevail over electrostatic attraction at all probed defect separations in YSZ and lead to very weak ordering preferences in ScSZ. The total electronic contribution to the defect interactions is shown to be strongly dominated by simple point-charge electrostatics, leaving speciation of defect ordering for a given class of aliovalent dopants to the elastic term. Thus, ion size becomes a critical parameter in controlling the ionic conductivity of doped oxide electrolytes.
Angular Momentum Transport in Particle and Fluid Disks

We examine the angular momentum transport properties of disks composed of macroscopic particles whose velocity dispersions are externally enhanced ("stirred"). Our simple Boltzmann equation model serves as an analogy for unmagnetized fluid disks in which turbulence may be driven by thermal convection. We show that interparticle collisions in particle disks play the same role as fluctuating pressure forces and viscous dissipation in turbulent disks: both transfer energy in random motions associated with one direction to those associated with another and convert kinetic energy into heat. The direction of angular momentum transport in stirred particle and fluid disks is determined by the direction of external stirring and by the properties of the collision term in the Boltzmann equation (or its analog in the fluid problem). In particular, our model problem yields inward transport for vertically or radially stirred disks, provided collisions are suitably inelastic; the transport is outward in the elastic limit. Numerical simulations of hydrodynamic turbulence driven by thermal convection find inward transport; this requires that fluctuating pressure forces do little to no work and is analogous to an externally stirred particle disk in which collisions are highly inelastic.