cssi/SciSciGPT-SciSciNet huggingface dataset:
THE BIMODAL METALLICITY DISTRIBUTION OF THE COOL CIRCUMGALACTIC MEDIUM AT z ∼< 1

We assess the metal content of the cool (~104?K) circumgalactic medium (CGM) about galaxies at z 1 using an H I-selected sample of 28 Lyman limit systems (LLS; defined here as absorbers with 16.2 log N H I 18.5) observed in absorption against background QSOs by the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The N H I selection avoids metallicity biases inherent in many previous studies of the low-redshift CGM. We compare the column densities of weakly ionized metal species (e.g., O II, Si II, Mg II) to N H I in the strongest H I component of each absorber. We find that the metallicity distribution of the LLS (and hence the cool CGM) is bimodal with metal-poor and metal-rich branches peaking at [X/H] ?1.6 and ?0.3 (or about 2.5% and 50% solar metallicities). The cool CGM probed by these LLS is predominantly ionized. The metal-rich branch of the population likely traces winds, recycled outflows, and tidally stripped gas; the metal-poor branch has properties consistent with cold accretion streams thought to be a major source of fresh gas for star forming galaxies. Both branches have a nearly equal number of absorbers. Our results thus demonstrate there is a significant mass of previously undiscovered cold metal-poor gas and confirm the presence of metal enriched gas in the CGM of z 1 galaxies.
Lensing and Supernovae: Quantifying the Bias on the Dark Energy Equation of State

The gravitational magnification and demagnification of Type Ia supernovae (SNe) modify their positions on the Hubble diagram, shifting the distance estimates from the underlying luminosity-distance relation. This can introduce a systematic uncertainty in the dark energy equation of state (EOS) estimated from SNe, although this systematic is expected to average away for sufficiently large data sets. Using mock SN samples over the redshift range 0 < z ≤ 1.7, we quantify the lensing bias. We find that the bias on the dark energy EOS is less than half a percent for large data sets (2000 SNe). However, if highly magnified events (SNe deviating by more than 2.5 σ) are systematically removed from the analysis, the bias increases to ~0.8%. Given that the EOS parameters measured from such a sample have a 1 σ uncertainty of 10%, the systematic bias related to lensing in SN data out to z ~ 1.7 can be safely ignored in future cosmological measurements.
Brane box realization of chiral gauge theories in two dimensions

Abstract We study type IIA configurations of D4-branes and three kinds of NS5-branes. The D4-brane world-volume has finite extent in three directions, giving rise to a two-dimensional low-energy field theory. The models have generically (0, 2) supersymmetry. We determine the rules to read off the spectrum and interactions of the field theory from the brane box configuration data. We discuss the construction of theories with enhanced (0, 4), (0, 6) and (0, 8) supersymmetry. Using T-duality along the directions in which the D4-branes are finite, the configuration can be mapped to D1-branes at C 4 /Γ singularities, with Γ an abelian subgroup of SU(4). This provides a rederivation of the rules in the brane box model. The enhancement of supersymmetry has a nice geometrical interpretation in the singularity picture in terms of the holonomy group of the four-fold singularity.
Free vibration of generally layered composite beams using symbolic computations

A first order shear deformation theory is used to analyze the free vibrations of generally layered composite beams. The model used in this study accounts for both inplane and rotary inertias. The Poisson effect, width effect, boundary conditions, layups, effect of anisotropy on cross-ply and angle-ply laminates, and the effect of couplng, are investigated. The equations of motion are integrated to an arbitrary degree of accuracy by using symbolic computation, and results obtained are validated by comparison with previously published experimental and numerical results. Comparison with results from classical laminate theory is also included.
Buckling and postbuckling of laminated composite plates with ply dropoffs

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1986.
Cosmic ray astronomy

Cosmic ray astronomy attempts to identify and study the sources of ultrahigh energy cosmic rays. It is unique in its reliance on charged particles as the information carriers. While no discrete source of ultrahigh energy cosmic rays has been identified so far, a new generation of detectors is acquiring the huge exposure that is needed at the highest energies, where deflection by magnetic fields is minimized and the background from distant sources is eliminated by pion photoproduction. In this paper, we summarize the status of cosmic ray astronomy, describing the detectors and the analysis techniques.
Effective Temperatures of Late L Dwarfs and the Onset of Methane Signatures

We present a spectral analysis of a sample of late L dwarfs. We use our latest model atmospheres and synthetic spectra and optical and K-band spectra to determine effective temperatures. We derive effective temperatures of 1400-1700 K for L8-L6 dwarfs. The analysis demonstrates that our recent models that rain out the formed dust completely are applicable to optical spectra of late L dwarfs and that more consistent models are needed for intermediate L dwarfs and for infrared spectra. We compare the results for the effective temperatures with the temperatures of the onset of methane formation. Our models predict methane absorption at 3.3 μm to occur at temperatures about 400 K higher than methane absorption at 2.2 μm. This is consistent with our data and previous observations, which show methane absorption at 3.3 μm, but not at 2.2 μm, in late L dwarfs.
Postseismic rebound due to creep of the lower lithosphere and asthenosphere

Postseismic surface deformations are attributed to the inelastic flow of the subcrustal regions of the Earth following an earthquake. A multilayer representation of the Earth's rheological properties is used in conjunction with a finite element computational scheme to calculate time dependent displacements and strains subsequent to a strike slip earthquake. The deviatoric stress strain relations for the uppermost layer is assumed elastic. Lower layers are assumed to be, in order of increasing depth, a standard, linear, three element, viscoelastic solid; a linear viscoelastic fluid; and another elastic solid. Physically these layers correspond to the upper lithosphere, lower lithosphere, asthenosphere, and lower mantle, respectively. Elastic dilatational properties are assumed throughout. Appreciable postseismic displacements, possibly approaching meters, for large earthquakes, arise from viscoelastic relaxation following sudden coseismic slip. Furthermore, compared to the simpler case of an elastic lithosphere over a viscoelastic asthenosphere and the near fault postseismic shear, strain is increased, by a factor of two or more in some cases, by the presence of a viscoelastic lower lithosphere. Also, the duration of postseismic straining is increased by the relatively slow relaxation of this layer.
Experimental demonstration of LDPC coded free-space, space-division-multiplexed systems using Orbital Angular Momentum modes

The performance of LDPC coded four-mode multiplexed Orbital Angular Momentum (OAM) data link using QPSK signal with net data rate of 320Gbit/s is experimentally investigated. The experiment results show that crosstalk effect can be efficiently mitigated and the LDPC codes with soft decoding can provide >7 dB coding depending on OAM crosstalk.
The Cause and Pathogenesis of the Eosinophilia-Myalgia Syndrome

Abstract ▪Objective:To review recent advances in the understanding of the cause and pathogenesis of the eosinophilia-myalgia syndrome associated with ingestion of L-tryptophan. ▪Data Sources:Studie...
In Vitro Assessment of Laser Sintered Bioactive Glass Scaffolds with Different Pore Geometries

Purpose – The purpose of this paper is to utilize the selective laser sintering (SLS) process to fabricate scaffolds with complex pore shapes and investigate the effects of pore geometry in vitro. The pore geometry of scaffolds intended for use in bone repair is one of the most important parameters used to determine the rate of bone regeneration. Design/methodology/approach – Scaffolds with five different architectures, having approximately 50 per cent porosity, were fabricated with silicate (13–93) and borate (13–93B3)-based bioactive glasses using the SLS process. An established late-osteoblasts/early-osteocytes cell line was used to perform cell proliferation tests on the scaffolds. The cell-seeded scaffolds were incubated for two, four and six days followed by MTT assay to quantify the metabolically active cells. Findings – The results indicated that the cells proliferate significantly more on the scaffolds which mimic the trabecular bone architecture compared to traditional lattice structures. The su...
NMR studies of high temperature superconductors

Abstract Results of NMR experiments mostly in YBa 2 Cu 4 O 7−δ are reviewed. The normal state data revealed two important aspects of the magnetic properties, namely, the temperature dependent antiferromagnetic Cu spin correlations and the spin gap behavior, the latter being observed in the reduced oxygen material. These features appear to be the general properties of many high T c cuprates. The Cu nuclear relaxation behavior in the superconducting state show some anomalous feature which remains to be explained.
On Filamentations and Virtual Knots

In this paper, we discuss filamentations on oriented chord diagrams. When a filamentation cannot be realized on an oriented chord diagram, then the corresponding flat virtual knot is non-trivial. If a flat knot diagram is non-trivial, then any virtual diagram whose shadow is the flat diagram must also be non-trivial. We introduce a class of flat diagrams for which no filamentations exist. This class gives the first example of an infinite set of virtual knots for which the Jones polynomial and the fundamental group both evaluate trivially. The related generalized Alexander polynomials for the virtual knots in this class turn out to be distinct, proving that the class is indeed infinite.
NEXAFS investigations of transition metal oxides, nitrides, carbides, sulfides and other interstitial compounds

Abstract Owing to their unique physical and chemical properties, transition metal compounds, especially transition metal oxides, nitrides, carbides and sulfides, have been the subject of many surface science investigations. In this article we will review applications of the near-edge X-ray absorption fine structure (NEXAFS) technique in the investigations of electronic and structural properties of transition metal compounds. This review covers NEXAFS studies of compounds in various physical forms, including bulk single crystals, well-characterized overlayers on surfaces of corresponding parent metals, and amorphous powder materials. In addition to transition metal oxides, nitrides, carbides and sulfides, we will also briefly discuss NEXAFS studies of interstitial compounds containing other 2p and 3p non-metal components, namely boron, fluorine, silicon, phosphorus and chlorine. We will discuss the correlation between experimental NEXAFS spectra and the local bonding environment of these compounds, such as the number of d-electrons, spin configurations, ligand-field splitting, coordination numbers, local symmetries, and crystal structures. In addition, NEXAFS investigations of the adsorption and reaction of probing molecules will also be discussed to reveal the underlying chemical reactivities of these materials. We will use many examples to demonstrate the importance of NEXAFS studies in the overall understanding of the physical and chemical properties of transition metal compounds. Finally, we will conclude this review by summarizing the current applications, as well as potential research opportunities, of NEXAFS in several technologically important research areas, including materials science, catalysis, biological science, earth science and environmental science.
Spatial coordination of a two-arm robot system subjected to kinematical and geometrical constraints

Abstract The spatial coordination of a two-arm robot is achieved by imposing on the robotic system model the proper geometrical and kinematical constraints. The closed loop formation is considered when both end-effectors of the two arms have one point in common or hold the same object from each side. Specified motions resulting from torque generated at the joint links are also considered. The collision avoidance between the two arms in space is illustrated through the use of a minimum distance to be maintained between two different points of the two arms. The governing equations of motion are derived using Kane's equations, and the constraint equations are handled through the generation of orthogonal complement arrays using the Pseudo-Uptriangular Decomposition method (PUTD). The algorithms developed are presented in a computer automated form suitable for computer-aided-desing and dynamic simulation.
Applications of a Counterflow Drag Reduction Technique in High-Speed Systems

Potential applications of a counterflow drag-reduction technique were investigated to assess performance improvements on aerospace vehicles. The motivation for this study was the 30-50% drag reduction achieved by counterflow blowing experiments on hemispherical cylinders at Mach 4 and higher. Exploratory studies indicate that drag improvements by counterflow drag reduction on hemispherical bodies cannot match those of aerodynamically shaped sharp-nosed bodies. Hence, the approach taken in the present study is that for hypersonic Mach numbers: if the nose shape is required to be blunt for considerations other than drag, counterflow blowing can be effective in improving the performance of the system. Although for generic body shapes counterflow blowing is most effective for blunt-nosed bodies, when applied to actual systems, many other factors need to be considered, such as available internal volume and extreme compressed carriage requirements. Depending on the vehicle speed and nose shape, estimated drag reductions of 15-30% were applied to predict the overall performance gains on Space Operations Vehicle, Gun-Launched Rocket, and Pegasus XL configurations. Potential savings in propellant and improvements in burnout velocity and range are reported. For launch systems with high fuel fraction, the payoff with counterflow drag reduction is marginal as the overall effects of aerodynamic drag on performance are small in the upper atmosphere. For the lower fuel fraction vehicle, the Gun Launched Rocket, a range improvement of 7% was achieved for a drag reduction of 30% with 0.3 blunting of nose flying above Mach 3; with greater blunting, however, the volume of fuel cannot compensate for the increase in drag.
Bayesian structure learning in graphical models

We consider the problem of estimating a sparse precision matrix of a multivariate Gaussian distribution, where the dimension p may be large. Gaussian graphical models provide an important tool in describing conditional independence through presence or absence of edges in the underlying graph. A popular non-Bayesian method of estimating a graphical structure is given by the graphical lasso. In this paper, we consider a Bayesian approach to the problem. We use priors which put a mixture of a point mass at zero and certain absolutely continuous distribution on off-diagonal elements of the precision matrix. Hence the resulting posterior distribution can be used for graphical structure learning. The posterior convergence rate of the precision matrix is obtained and is shown to match the oracle rate. The posterior distribution on the model space is extremely cumbersome to compute using the commonly used reversible jump Markov chain Monte Carlo methods. However, the posterior mode in each graph can be easily identified as the graphical lasso restricted to each model. We propose a fast computational method for approximating the posterior probabilities of various graphs using the Laplace approximation approach by expanding the posterior density around the posterior mode. We also provide estimates of the accuracy in the approximation.
In the Name of the Practical: Unearthing the Hegemony of Pragmatics in the Discourse of Environmental Management*

abstract A prominent feature of the rapidly growing ﬁeld of EnvironmentalManagement (EM) is its strong emphasis on pragmatic considerations. Much of EM’slegitimacy stems from its own identity as having practical relevance in resolvingcontemporary environmental problems. With the help of Critical Discourse Analysis,our paper engages closely with the language of practicality in EnvironmentalManagement. We show how the message of practicality emerged through three coremessages in the discourse, viz. economic utilitarianism, compromise and inter-organizational collaboration. We further contend that in the actual material contextof the complex biospheric environment, these messages may have less than pragmaticimplications. We conclude with a discussion of ecological rationality in redeﬁning thediscourse of pragmatics in Environmental Management. INTRODUCTION Practical men, who believe themselves to be quite exempt from any intellectualinﬂuences, are usually the slaves of some defunct economist. ( John MaynardKeynes,
Synthesis of Dihydropyridines and Pyridines from Imines and Alkynes via C−H Activation

A convenient one-pot C−H alkenylation/electrocyclization/aromatization sequence has been developed for the synthesis of highly substituted pyridine derivatives from alkynes and α,β-unsaturated N-benzyl aldimines and ketimines that proceeds through dihydropyridine intermediates. A new class of ligands for C−H activation was developed, providing broader scope for the alkenylation step than could be achieved with previously reported ligands. Substantial information was obtained about the mechanism of the reaction. This included the isolation of a C−H activated complex and its structure determination by X-ray analysis; in addition, kinetic simulations using the Copasi software were employed to determine rate constants for this transformation, implicating facile C−H oxidative addition and slow reductive elimination steps.
On relativistic corrections to microlensing effects: applications to the Galactic black hole

The standard treatment of gravitational lensing by a point mass lens M is based on a weak-field deflection angle α = 2/x 0 , where x 0 = r 0 c 2 /2GM with r 0 being the distance of closest approach to the mass of a lensed light ray. It was shown that for a point mass lens, the total magnification and image centroid shift of a point source remain unchanged by relativistic corrections of second order in 1/x 0 . This paper considers these issues analytically, taking into account the relativistic images, under three assumptions A1-A3, for a Schwarzschild black hole lens with a background point and extended sources having arbitrary surface brightness profiles. The assumptions are A1, the source is close to the line of sight and lies in the asymptotically flat region outside the black hole lens; A2, the observer--lens and lens-source distances are significantly greater than the impact parameters of the lensed light rays; and A3, the distance of closest approach of any light ray that does not wind around the black hole on its travel from the source to the observer, lies in the weak-field regime outside the black hole. We apply our results to the Galactic black hole for lensing scenarios where A1-A3 hold. We show that a single factor characterizes the full relativistic correction to the weak-field image centroid and magnification. As the lens-source distance increases, the relativistic correction factor strictly decreases. In particular, we find that for point and extended sources approximately 10 pc behind the black hole, which is a distance significantly outside the tidal disruption radius of a Sun-like source, the relativistic correction factor is minuscule, of the order of 10 - 1 4 . Therefore, for standard lensing configurations, any detectable relativistic corrections to microlensing by the Galactic black hole will most likely have to come from sources significantly closer to the black hole.
A Prism into the PPP Puzzles: The Micro‐Foundations of Big Mac Real Exchange Rates*

We match Big Mac prices with prices of its ingredients as a unique prism to study real exchange rates (RERs). This approach has several advantages. First, the levels of the Big Mac RER can be measured meaningfully. Second, as the exact composition of a Big Mac is known, the contributions of its tradable and non-tradable components can be estimated relatively precisely. Third, the dynamics of the RER can be studied in a setting free of several biases inherent in CPI-based RERs. Finally, a large cross-country dimension allows us to overturn the Engel result on what drives RERs. In most economies, the exchange rate is the single most important relative price, one that potentially feeds back into a large range of transactions. Obstfeld and Rogoff (2000)
The convergence between for-profit and nonprofit hospitals in the United States

This paper proposes a novel model of the hospital industry in the United States in which firms in effect choose their ownership type and the regulatory and tax regimes under which they must function. Accordingly, I develop a model in which firms have identical objectives but differ in their ability to benefit from a given ownership form. Changes in the economic environment alter firms’ incentives to maintain a given ownership type. This in turn induces firms to modify their capacity and encourages some firms to switch ownership type. One implication of this model is that changes in the economic environment that have occurred since 1960 imply that the optimal size of those firms which choose to be for profit should more closely approximate the optimal size of firms which choose to be nonprofit. Hospital level data indicate that this size convergence has indeed occurred. In 1960, U.S. nonprofit hospitals maintained on average more than three times as many beds per hospital as their for-profit counterparts; following a monotonic decline in relative size, by 2000, the average nonprofit hospital was only 32% larger than the typical for-profit hospital. Declining roles of government hospitals, population growth, suburbanization, and increasing government intervention in the healthcare market help explain the convergence in size. Analysis of data at the state and Metropolitan Statistical Area (MSA) levels is consistent with the principal theoretical predictions.
Efficient and accurate simulation of dynamic dielectric objects

Electrostatic interactions between dielectric objects are complex and of a many-body nature, owing to induced surface bound charge. We present a collection of techniques to simulate dynamical dielectric objects. We calculate the surface bound charge from a matrix equation using the Generalized Minimal Residue method (GMRES). Empirically, we find that GMRES converges very quickly. Indeed, our detailed analysis suggests that the relevant matrix has a very compact spectrum for all non-degenerate dielectric geometries. Each GMRES iteration can be evaluated using a fast Ewald solver with cost that scales linearly or near-linearly in the number of surface charge elements. We analyze several previously proposed methods for calculating the bound charge, and show that our approach compares favorably.
Semiclassical suppression of black hole production in particle collisions

Abstract It is argued that the cross section for production of large black holes, for which a semiclassical description is applicable, cannot be given by the geometric area of the black hole horizon, as claimed recently in the literature. Rather the production cross section in a few-particle collision is suppressed by at least a factor exp(− I E ) with I E being the Gibbons–Hawking (Euclidean) action for the black hole. Thus only essentially non-classical small black holes with mass of the order of the Planck mass can possibly be produced in few-particle collisions at trans-Planckian energies.
Geometric reasoning in sketch-based volumetric decomposition framework for hexahedral meshing

This paper presents a sketch-based volumetric decomposition framework using geometric reasoning to assist in hex meshing. The sketch-based user interface makes the framework user-friendly and intuitive; and the geometric reasoning engine makes the framework smarter and improves the usability. The system first creates a data structure containing B-Rep and 3D medial to capture the exterior and interior of the input model, respectively. The four-step geometric reasoning process consists of (1) Determining sweeping direction and two types of sweepable regions, (2) Providing visual aids on sweeping direction and sweepable region for decomposition, (3) Understanding user’s intent by using prioritized B-Rep and medial entities, and (4) smart decomposition operation. Imprint and merge operations are then performed on the decomposed model before passing it to the sweeping algorithm to create hex meshes. The sketch-based framework has been tested on industrial models.
The theory and phenomenology of jets in nuclear collisions

We report selected results from a recent in-depth study of jet shapes and jet cross sections in ultra-relativistic reactions with heavy nuclei at the LHC. We demonstrate that at the highest collider energies these observables become feasible as a new, differential and accurate test of the underlying QCD theory. Our approach allows for detailed simulations of the experimental acceptance/cuts that help isolate jets emerging from a dense QGP. We show for the first time that the pattern of stimulated gluon emission can be correlated with a variable quenching of the jet rates and provide an approximately model-independent approach to determining the characteristics of the medium-induced bremsstrahlung spectrum. The connection between such cross section attenuation and the in-medium jet shapes is elucidated.
Increased incidence of sighs (augmented inspiratory efforts) during synchronized intermittent mandatory ventilation (SIMV) in preterm neonates

A reflex resulting in a deep, sigh-like inspiratory effort (augmented breath) is frequently triggered during synchronized mechanical ventilation in preterm infants. We studied the incidence of augmented inspiratory efforts and their effect on ventilation and lung compliance during conventional IMV and synchronized IMV (SIMV) in 15 preterm neonates (GA 26.7 +/- 1.5 wks (mean +/- SD), BW 925 +/- 222 g, age 1-8 days). Augmentation of spontaneous inspiratory effort was defined as an esophageal pressure deflection occurring coincident with a synchronized mechanical breath and exceeding the previous unassisted spontaneous effort by more than 50%. The incidence of augmented breaths was higher during SIMV (11.1 +/- 7.7%; P < 0.01) than during conventional IMV (5.1 +/- 6.1%). However, when the synchronized breaths were triggered late (200-300 msec) after the onset of inspiration, augmented breaths occurred no more frequently than during conventional IMV (6.0 +/- 4.7%). The incidence of augmented breaths correlated inversely with dynamic lung compliance (P = 0.014), but was not significantly influenced by a change in PEEP. Although inspiratory effort increased nearly three times during the augmented breaths, tidal volume increased only 12%. The change in tidal volume was limited because the augmented effort reached its maximal negativity only approximately 500 ms after the beginning of the synchronized, mechanical breath and at a time when the mechanical breath had already ended. For this reason the augmented effort did not contribute significantly to minute ventilation, but only prolonged inspiration. Dynamic lung compliance did not change significantly after an augmented breath. The results indicate that augmented inspiratory efforts are more common in preterm neonates ventilated with SIMV than with conventional IMV, but do not contribute significantly to ventilation.
Spatial and temporal models for texture-based video coding

In this paper, we investigate spatial and temporal models for texture analysis and synthesis. The goal is to use these models to increase the coding efficiency for video sequences containing textures. The models are used to segment texture regions in a frame at the encoder and synthesize the textures at the decoder. These methods can be incorporated into a conventional video coder (e.g. H.264) where the regions to be modeled by the textures are not coded in a usual manner but texture model parameters are sent to the decoder as side information. We showed that this approach can reduce the data rate by as much as 15%.
The minimal supersymmetric leptogenesis

We reanalyze the supersymmetric leptogenesis model by one of the authors (H.M.) and Yanagida based on = Hu flat direction in detail. We point out that the appropriate amount of baryon asymmetry can be generated in this model with the neutrino mass matrix consistent with the atmospheric neutrino oscillation and solutions to the solar neutrino problem, preferably the small angle MSW solution. The reheating temperature can be low enough to avoid the cosmological gravitino problem. This model is the minimal one because it does not rely on any new physics beyond supersymmetry and Majorana neutrino masses.
Sampling from large matrices: An approach through geometric functional analysis

We study random submatrices of a large matrix A. We show how to approximately compute A from its random submatrix of the smallest possible size O(rlog r) with a small error in the spectral norm, where r = VAV2F/VAV22 is the numerical rank of A. The numerical rank is always bounded by, and is a stable relaxation of, the rank of A. This yields an asymptotically optimal guarantee in an algorithm for computing low-rank approximations of A. We also prove asymptotically optimal estimates on the spectral norm and the cut-norm of random submatrices of A. The result for the cut-norm yields a slight improvement on the best-known sample complexity for an approximation algorithm for MAX-2CSP problems. We use methods of Probability in Banach spaces, in particular the law of large numbers for operator-valued random variables.
THE FIRST COMPLETE CRYSTAL STRUCTURE OF A STANNATRANE. TRIMERIC METHYL(2,2′,2″-NITRILOTRIETHOXY)STANNANE HEXAHYDRATE

Abstract An X-ray analysis of the 1-methylstannatrane hexahydrate [MeSn(OCH2CH2)3N]3 . 6H2O (4) revealed a trimeric formulation. It crystallizes in the monoclinic space group C2/c (Z = 4) with a = 9.206 (3) A, b = 13.774 (5) A, c = 26.581 (4) A, and β = 93.33 (2)°. The structure refined to R = 0.074 and R w = 0.086. The trimeric unit is disordered about a twofold axis, which passes through the central Sn atom. The geometry around this central atom closely approximates a pentagonal bipyramid. The two crystallographically equivalent end tin atoms have distorted-octahedral geometries. Strong association of the three monomeric methylstannatrane units formally leading to the trimer is suggested by the short Sn[sbnd]O bond lengths involved. These have values of 2.11 (1) and 2.21 (1) A, as compared to corresponding values within the monomers of 2.17 (1) and 2.23 (1) A, respectively. The solid-state structure agrees with solution NMR data suggesting its retention in solution. The trimeric unit is indicated in sol...
Simulated Fuel Economy and Emissions Performance during City and Interstate Driving for a Heavy-Duty Hybrid Truck

We compare simulated fuel economy and emissions for both conventional and hybrid class 8 heavy-duty diesel trucks operating over multiple urban and highway driving cycles. Both light and heavy freight loads were considered, and all simulations included full aftertreatment for NOx and particulate emissions controls. The aftertreatment components included a diesel oxidation catalyst (DOC), urea-selective catalytic NOx reduction (SCR), and a catalyzed diesel particulate filter (DPF). Our simulated hybrid powertrain was configured with a pre-transmission parallel drive, with a single electric motor between the clutch and gearbox. A conventional HD truck with equivalent diesel engine and aftertreatment was also simulated for comparison. Our results indicate that hybridization can significantly increase HD fuel economy and improve emissions control in city driving. However, there is less potential hybridization benefit for HD highway driving. A major factor behind the reduced hybridization benefit for highway driving is that there are fewer opportunities to utilize regenerative breaking. Our aftertreatment simulations indicate that opportunities for passive DPF regeneration are much greater for both hybrid and conventional trucks during highway driving due to higher sustained exhaust temperatures. When passive DPF regeneration is extensively utilized, the fuel penalty for particulate control is virtually eliminated, except for the 0.4%-0.9%more » fuel penalty associated with the slightly higher exhaust backpressure.« less
Decision Support for Crisis Incidents

Crisis incidents occur in both business and public domains. This article focuses on non-routine incidents and explores uses of technologies for supporting crisis management tasks. A Crisis Incident Spiral of Decision Support helps identify useful decision support and information technologies. Additionally, a Crisis Incident Process/Decision Support Matrix categorizes processes of crisis planning, response and management with decision support technologies. Ideally, the matrix helps organize and stimulate thinking about novel DSS applications. Not all crises are of equal magnitude and different computerized decision support is needed in different types of crisis incidents.
The odd Littlewood–Richardson rule

In previous work with Mikhail Khovanov and Aaron Lauda we introduced two odd analogues of the Schur functions: one via the combinatorics of Young tableaux (odd Kostka numbers) and one via an odd symmetrization operator. In this paper we introduce a third analogue, the plactic Schur functions. We show they coincide with both previously defined types of Schur function, confirming a conjecture. Using the plactic definition, we establish an odd Littlewood–Richardson rule. We also re-cast this rule in the language of polytopes, via the Knutson–Tao hive model.
Meritocracy in America: Wages Within and Across Occupations

In The Bell Curve, Herrnstein and Murray argue that the U.S. economy is a meritocracy in which differences in wages (including differences across race and gender) are explained by differences in cognitive ability. In this article we test their claim for wages conditional on occupation using a simultaneous model of occupation choice and wage determination. Our results contradict Herrnstein and Murray's claim that the U.S. labor market operates only on meritocratic principles.
Quantized symplectic actions and W -algebras

With a nilpotent element in a semisimple Lie algebra g one associates a finitely generated associative algebra W called a W-algebra of finite type. This algebra is obtained from the universal enveloping algebra U(g) by a certain Hamiltonian reduction. We observe that W is the invariant algebra for an action of a reductive group G with Lie algebra g on a quantized symplectic affine variety and use this observation to study W. Our results include an alternative definition of W, a relation between the sets of prime ideals of W and of the corresponding universal enveloping algebra, the existence of a one-dimensional representation of W in the case of classical g and the separation of elements of W by finite dimensional representations.
Low cost satellite land mobile service for nationwide applications

A satellite land mobile system using mobile radios in the UHF band, and Ku-band "Communications Routing Terminals: (earth stations) for a nationwide connection from any mobile location to any fixed or mobile location, and from any fixed location to any mobile location is proposed. The proposed nationwide satellite land mobile service provides: telephone network quality (1 out of 100 blockage) service, complete privacy for all the users, operation similar to the telephone network, alternatives for data services up to 32 Kbps data rates, and a cost effective and practical mobile radio compatible with system sizes ranging from 104to about 4 × 106users. Seven satellite alternatives (ranging from 30' diameter dual beam antenna to 210' diameter 77 beam antenna) along with mobile radios having a senitivity figure of merit (G/T) of -15dB/°K are considered. Optimized mobile radio user costs (including mobile radios, earth terminals, satellite terrestrial tails, service and maintenance, and operating costs) are presented as a function of the number of users with the satellite and mobile radio alternatives as system parameters. The configuration of the mobile radios' "Communications Routing Terminals" along with the appropriate networking and signaling arrangements are included.
Limits on a Light Leptophobic Gauge Boson

Abstract We consider the phenomenology of a naturally leptophobic Z -prime boson in the 1 to 10 GeV mass range. The Z -prime's couplings to leptons arise only via a radiatively-generated kinetic mixing with the Z and photon, and hence are suppressed. We map out the allowed regions of the mass-coupling plane and show that such a Z -prime that couples to quarks with electromagnetic strength is not excluded by the current data. We then discuss possible signatures at bottom and charm factories.
Relativized Worlds without Worst-Case to Average-Case Reductions for NP

We prove that, relative to an oracle, there is no worst-case to average-case reduction for NP. We also handle classes that are somewhat larger than NP, as well as worst-case to errorless-average-case reductions. In fact, we prove that relative to an oracle, there is no worst-case to errorless-average-case reduction from NP to BPPpNP. We also handle reductions from NP to the polynomial-time hierarchy and beyond, under strong restrictions on the number of queries the reductions can make.
Spontaneous Cerebrospinal Fluid Leak through the Posterior Aspect of the Petrous Bone

Spontaneous cerebrospinal fluid (CSF) leak through the posterior fossa (PF) aspect of the petrous bone is exceedingly rare. A case series allows analysis of etiologies and how they may differ from the more common middle fossa (MF) route of leakage. The design was a retrospective case series. The setting was a tertiary care institution. A series of three patients with PF spontaneous CSF leaks was identified. High-resolution imaging (CT and MRI) and intraoperative observations were evaluated. Both in this series and in previously reported cases, patients share the demographics typically found in the MF leak population. In our series, two patterns of PF CSF leak were identified: (1) large unilateral with cerebellar encephalocele and (2) small punctate defects just lateral to the endolymphatic sac. Two presented with simultaneous MF and PF leaks suggesting a shared etiology, at least in some cases, with a role for increased intracranial pressure. In spontaneous CSF leaks, it is important to evaluate the posterior petrous bone along with the tegmen. The concomitant appearance of MF with PF leaks points out the risk that repair via MF craniotomy could fail to identify a leakage site in the vicinity of the endolymphatic sac.
Estimating dark matter distributions

Thanks to instrumental advances, new, very large kinematic data sets for nearby dwarf spheroidal (dSph) galaxies are on the horizon. A key aim of these data sets is to help determine the distribution of dark matter in these galaxies. Past analyses have generally relied on specific dynamical models or highly restrictive dynamical assumptions. We describe a new, nonparametric analysis of the kinematics of nearby dSph galaxies designed to take full advantage of the future large data sets. The method takes as input the projected positions and radial velocities of stars known to be members of the galaxies but does not use any parametric dynamical model or the assumption that the mass distribution follows that of the visible matter. The problem of estimating the radial mass distribution M(r) (the mass within the true radius r) is converted into a problem of estimating a regression function nonparametrically. From the Jeans equation we show that the unknown regression function is subject to fundamental shape restrictions, which we exploit in our analysis using statistical techniques borrowed from isotonic estimation and spline smoothing. Simulations indicate that M(r) can be estimated to within a factor of 2 or better with samples as small as 1000 stars over almost the entire radial range sampled by the kinematic data. The technique is applied to a sample of 181 stars in the Fornax dSph galaxy. We show that the galaxy contains a significant, extended dark halo some 10 times more massive than its baryonic component. Although applied here to dSph kinematics, this approach can be used in the analysis of any kinematically hot stellar system in which the radial velocity field is discretely sampled.
Advances in Labyrinth Seal Aeroelastic Instability Prediction and Prevention

Fatigue cracking of an aircraft engine labyrinth seal occurred during pre-flight factory testing. Testing in a static rig revealed that the seal could be aeroelastically excited by the labyrinth leakage air flow. An earlier analytical model used for stability analysis was extended to account for the effect of acoustic natural frequency on the aeroelastic stability. The new model predicted that the ratio of acoustic and mechanical natural frequencies was of vital importance in determining if the nature of the pressure fluctuations within the labyrinth seal teeth provided either positive or negative aerodynamic damping to the seal. The analytical results were verified by further rig testing and also by correlation with test results for several other seals tested as part of a labyrinth seal technology program. A mechanical friction damper sleeve was designed to suppress the aeroelastic instability. The damper sleeve was tested in a rotating rig to evaluate its damping characteristics. The aircraft engine was qualified with the newly designed damper which has demonstrated its effectiveness for eight years of service and half a million hours of operation without incident.
Pre-eclampsia with the nephrotic syndrome

Heavy proteinuria and/or the nephrotic syndrome rarely occur late in pregnancy. We report the clinical and renal biopsy findings on 11 patients with the nephrotic syndrome occurring during pregnancy in whom light and electron microscopic findings were characteristic of pre-eclampsia. Immunofluorescent microscopy revealed deposits of IgG, IgM, IgA, beta 1C globulin, and fibrinogen, predominantly in the subendothelial position. Only two patients were primigravid; three were in their second or third pregnancy; in six, pre-eclampsia first occurred in the fourth to eighth pregnancy. Clinical abnormalities appeared first between the 23rd and 39th week of gestation. All patients had marked elevation of blood pressure and of serum uric acid levels. Of the 12 infants, eight were alive and well, including one set of twins; four were stillborn. Following delivery, clinical resolution was similar to that in less severe pre-eclampsia. The findings suggest the possible importance of the role of intravascular coagulation in the genesis of pre-eclampsia.
Special Lagrangian cones

We study special Lagrangian cones in [inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01i" /] with isolated singularities especially the case n = 3. Our main result constructs an infinite family of special Lagrangian cones in [inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="02i" /] each of which has a toroidal link. We obtain a detailed geometric description of these tori. We prove a regularity result for special Lagrangian cones in [inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="03i" /] with a spherical link—any such cone must be a plane. We also construct a one-parameter family of asymptotically conical special Lagrangian submanifolds from any special Lagrangian cone.
Exchange rate sensitivity of US bilateral trade flows

Abstract The traditional way of assessing the impact of currency depreciation on the trade balance has been to estimate the elasticity of trade volume to relative prices. To this end, most previous studies used aggregate trade data. To avoid aggregation biases potentially hidden in aggregate data, recent studies have relied on bilateral trade data. Since import and export price data is not available on bilateral level, this study proposes an alternative way of assessing the impact of currency depreciation on bilateral trade flows. The models are applied between the US and her 19 industrial trading partners using recent advances in time-series modeling.
Poverty orderings: A graphical illustration

This note graphically illustrates the power of various poverty ordering conditions. Using the Kolm three-person simplex, we are able to show that (1) for a fixed poverty line the power may be increased as higher degrees of stochastic dominance are considered, (2) for a single but variable poverty line the power is reduced as the line increases, and (3) for a range of poverty lines the power of the third degree ordering condition may be reduced to that of the second degree if the lower bound poverty line is arbitrarily close to zero.
Flag flutter in inviscid channel flow

Using nonlinear vortex-sheet simulations, we determine the region in parameter space in which a straight flag in a channel-bounded inviscid flow is unstable to flapping motions. We find that for heavier flags, greater confinement increases the size of the region of instability. For lighter flags, confinement has little influence. We then compute the stability boundaries analytically for an infinite flag and find similar results. For the finite flag, we also consider the effect of channel walls on the large-amplitude periodic flapping dynamics. We find that multiple flapping states are possible but rare at a given set of parameters, when periodic flapping occurs. As the channel walls approach the flag, its flapping amplitude decreases roughly in proportion to the near-wall distance, for both symmetric and asymmetric channels. Meanwhile, its dominant flapping frequency and mean number of deflection extrema (or “wavenumber”) increase in a nearly stepwise fashion. That is, they remain nearly unchanged over a wide range of channel spacing, but when the channel spacing is decreased below a certain value, they undergo sharp increases corresponding to a higher flapping mode.
Life table rates and person month ratios as summary statistics for contraceptive trials.

Abstract Person month statistics consist of ratios of events divided by months of exposure to the risk of such events. They are required as part of the procedure for computing life table rates. If person month statistics are presented for relatively short intervals of contraceptive use, such as the first three months, the second three months, etc. the pitfalls in their use are averted and they constitute a simple and useful statistical methodology. For those who are interested in converting them to life table rates, they can easily do so from published person year data.