cssi/SciSciGPT-SciSciNet huggingface dataset:
X-Ray Observations of the Compact Central Object in Supernova Remnant G347.3-0.5

We present Chandra, XMM-Newton, and Rossi X-Ray Timing Explorer observations of 1WGA J1713.4-3949, a compact source at the center of the Galactic supernova remnant (SNR) G347.3-0.5. The X-ray spectrum of the source is well fitted by the sum of a blackbody component with a temperature of ~0.4 keV plus a power-law component with a photon index of ~4. We found no pulsations down to 4% in the 0.01-0.16 Hz range nor down to 25% in the 0.01-128 Hz range. This source resembles other compact central objects in SNRs, and we suggest that 1WGA J1713.4-3949 is the associated neutron star for G347.3-0.5. We also measured the properties of the adjacent radio pulsar PSR J1713-3945 with a 392 ms period, and we show that it is not associated with 1WGA J1713.4-3949 nor, most probably, is it associated with SNR G347.3-0.5.
Finding optimal hyperpaths in large transit networks with realistic headway distributions

Abstract This paper implements and tests a label-setting algorithm for finding optimal hyperpaths in large transit networks with realistic headway distributions. It has been commonly assumed in the literature that headway is exponentially distributed. To validate this assumption, the empirical headway data archived by Chicago Transit Agency are fitted into various probabilistic distributions. The results suggest that the headway data fit much better with Loglogistic, Gamma and Erlang distributions than with the exponential distribution. Accordingly, we propose to model headway using the Erlang distribution in the proposed algorithm, because it best balances realism and tractability. When headway is not exponentially distributed, finding optimal hyperpaths may require enumerating all possible line combinations at each transfer stop, which is tractable only for a small number of alternative lines. To overcome this difficulty, a greedy method is implemented as a heuristic and compared to the brute-force enumeration method. The proposed algorithm is tested on a large scale CTA bus network that has over 10,000 stops. The results show that (1) the assumption of exponentially distributed headway may lead to sub-optimal route choices and (2) the heuristic greedy method provides near optimal solutions in all tested cases.
1,2-boryl migration empowers regiodivergent synthesis of borylated furans

A regioselective transition metal-catalyzed cycloisomerization reaction of boron-containing alkynyl epoxides toward C2- and C3-borylated furans has been developed. It was found that the copper catalyst as well as the gold catalyst with more basic triflate counterion favor boryl migration toward C3-borylated furans, whereas employment of the cationic gold hexafluoroantimonate affords C2-borylated furan via a formal 1,2-hydrogen shift.
The Effect of Solid Particle Erosion on the Mechanical Properties and Fatigue Life of Fiber-reinforced Composites

The effect of solid particle erosion on the strength and fatigue properties of E-glass/epoxy composite is investigated. Solid particle erosion with SiC particles of 400–500 μm in diameter is simulated on 12-ply [45°/–45°/0°/45°/–45°/0°]S E-glass/epoxy composites with a constant particle velocity of 42.5 m/s and a solid particle to air volume ratio of 6 kg/m3 at impact angles of 90, 60, and 30° for 30, 60, 90, and 120 s. Damaged and undamaged specimens are subjected to tensile tests while monitoring their acoustic emission (AE) activity. An erosion damage parameter is defined as a function of the particle impact angle and the erosion duration to determine the residual tensile strength of the composite. Scanning electron microscope (SEM) images of the erosion-damaged specimens reveal that the same damage mechanism occurs at different impact angles. The AE stress delay parameter is used to predict the residual tensile strength of erosion-damaged composites. Tension–tension fatigue tests are performed on virg...
Metal Enrichment of the Intergalactic Medium and Production of Massive Black Holes

A model for the chemical evolution of the intergalactic medium (IGM) is presented using theoretical yields of very massive stars (VMSs; M_(VMS) > 100 M_☉) and Type II supernovae (SNe II). It is shown that if [Si/C] is indeed as high as ~0.7 in the IGM, then VMSs (M_(VMS) ≈ 140-260 M_☉) associated with pair-instability supernovae (PI-SNe) in low-mass (~10^5 M_☉) halos at high redshift must produce at least 50% of the Si. The remainder is from later galactic outflows of SN II debris, which also provide most of the C and O. Both sources are required to account for the metal inventory in the IGM. The early VMS production must continue until redshift z ~ 15 so that the efficiency of VMS formation per low-mass halo is significantly below unity. Contributions from the later galactic outflows mainly occur at z ~ 4-6. Using a Salpeter initial mass function, we infer that the number of VMSs (M_(VMS) ≈ 260-2000 M_☉) producing massive black holes (MBHs) with an average mass 〈M_(MBH)〉 ~ 270-550 M_☉ is ≈0.72 times the number of VMSs associated with PI-SNe. The amount of metals (particularly Si) in the IGM that is attributable to PI-SNe is thus closely coupled with the total mass of MBHs produced in epochs prior to galaxy formation. Production of ~50% of the Si in the IGM by PI-SNe corresponds to an early inventory of MBHs that constitutes a fraction ~(4-8) × 10^(-5) of the total baryonic mass in the universe. This is comparable to the global mass budget of the central supermassive black holes (SMBHs) in present-day galaxies. The corresponding occurrence rates in each halo of ~10^5 M_☉ during the epoch of VMS formation at z ≳ 15 are ~0.9 Gyr^(-1) for VMSs associated with PI-SNe and ~0.6 Gyr^(-1) for the concomitant more massive stars producing MBHs. These rates may be of use to studies of H_2 dissociation and reionization and to models of SMBH formation.
A tale of three kernels

We study three canonical kernels on domains in ℂ and ℂ n . We exposit both the history and the substance of these concepts, and we also present some new calculations and ideas adherent thereto.
Non-trivial saddle points and band structure of bound states of the two-dimensional O( N) vector model

Abstract We discuss O( N ) invariant scalar field theories in 0 + 1 space-time dimensions (quantum mechanics) and in 1 + 1 space-time dimensions (field theory). Combining ordinary “Large N ” saddle point techniques and simple properties of the diagonal resolvent of one-dimensional Schrodinger operators we find non-trivial (non-constant) solutions to the saddle point equations of these models in addition to the saddle point describing the ground state of the theory. In the “Large N ” limit these saddle points are exact for the quantum mechanical case, but only approximate in the two-dimensional theory. In the latter case they are the leading contributions to the time evolution kernel at short times, or equivalently, the leading contribution to the high temperature expansion of partition function stemming from space dependent static configurations in case of the Euclidean theory. We interpret these novel saddle points as collective O( N ) singlet excitations of the field theory, each embracing a host of finer quantum states arranged in O( N ) multiplets, in an analogous manner to the band structure of molecular spectra.
FOS observations of four NLS1s

Abstract Ultraviolet through optical spectroscopy of four NLS1s shows strong absorption features in the high-ionization UV resonance lines such as C IV, N V, and Si IV. Mg II is not absorbed. The absorption could originate in the warm absorber.
Cloak and Swagger: Understanding Data Sensitivity through the Lens of User Anonymity

Most of what we understand about data sensitivity is through user self-report (e.g., surveys), this paper is the first to use behavioral data to determine content sensitivity, via the clues that users give as to what information they consider private or sensitive through their use of privacy enhancing product features. We perform a large-scale analysis of user anonymity choices during their activity on Quora, a popular question-and-answer site. We identify categories of questions for which users are more likely to exercise anonymity and explore several machine learning approaches towards predicting whether a particular answer will be written anonymously. Our findings validate the viability of the proposed approach towards an automatic assessment of data sensitivity, show that data sensitivity is a nuanced measure that should be viewed on a continuum rather than as a binary concept, and advance the idea that machine learning over behavioral data can be effectively used in order to develop product features that can help keep users safe.
LEQA: latency estimation for a quantum algorithm mapped to a quantum circuit fabric

This paper presents LEQA, a fast latency estimation tool for evaluating the performance of a quantum algorithm mapped to a quantum fabric. The actual quantum algorithm latency can be computed by performing detailed scheduling, placement and routing of the quantum instructions and qubits in a quantum operation dependency graph on a quantum circuit fabric. This is, however, a very expensive proposition that requires large amounts of processing time. Instead, LEQA, which is based on computing the neighborhood population counts of qubits, can produce estimates of the circuit latency with good accuracy (i.e., an average of less than 3% error) with up to two orders of magnitude speedup for mid-size benchmarks. This speedup is expected to increase superlinearly as a function of circuit size (operation count).
Using atomic diffraction of Na from material gratings to measure atom-surface interactions

In atom optics a material structure is commonly regarded as an amplitude mask for atom waves. However, atomic diffraction patterns formed using material gratings indicate that material structures also operate as phase masks. In this study a well collimated beam of sodium atoms is used to illuminate a silicon nitride grating with a period of 100 nm. During passage through the grating slots atoms acquire a phase shift due to the van der Waals (vdW) interaction with the grating walls. As a result the relative intensities of the matter-wave diffraction peaks deviate from those expected for a purely absorbing grating. Thus a complex transmission function is required to explain the observed diffraction envelopes. An optics perspective to the theory of atomic diffraction from material gratings is put forth in the hopes of providing a more intuitive picture concerning the influence of the vdW potential. The van der Waals coefficient ${C}_{3}=2.7\ifmmode\pm\else\textpm\fi{}0.8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.3em}{0ex}}{\mathrm{nm}}^{3}$ is determined by fitting a modified Fresnel optical theory to the experimental data. This value of ${C}_{3}$ is consistent with a van der Waals interaction between atomic sodium and a silicon nitride surface.
Dimerized phase and transitions in a spatially anisotropic square lattice antiferromagnet

We investigate the spatially anisotropic square lattice quantum antiferromagnet. The model describes isotropic spin-$1/2$ Heisenberg chains (exchange constant $J$) coupled antiferromagnetically in the transverse (${J}_{\ensuremath{\perp}}$) and diagonal (${J}_{\ifmmode\times\else\texttimes\fi{}}$), with respect to the chain, directions. Classically, the model admits two ordered ground states--with antiferromagnetic and ferromagnetic interchain spin correlations--separated by a first-order phase transition at ${J}_{\ensuremath{\perp}}=2{J}_{\ifmmode\times\else\texttimes\fi{}}$. We show that in the quantum model this transition splits into two, revealing an intermediate quantum-disordered columnar dimer phase, both in two dimensions and in a simpler two-leg ladder version. We describe quantum-critical points separating this spontaneously dimerized phase from classical ones.
LIGHT SUPERCONDUCTING STRINGS IN THE GALAXY

Observations of the Milky Way by the SPI/INTEGRAL satellite have confirmed the presence of a strong 511 keV gamma ray line emission from the bulge, which requires an intense source of positrons in the galactic center. These observations are hard to account for by conventional astrophysical scenarios, whereas other proposals, such as light DM, face stringent constraints from the diffuse gamma ray background. Here we suggest that light superconducting strings could be the source of the observed 511 keV emission. The associated particle physics, at the ~ 1 TeV scale, is within the reach of planned accelerator experiments, while the distinguishing spatial distribution, proportional to the galactic magnetic field, could be mapped by SPI or by future, more sensitive satellite missions.
Approaching the ultimate limits of communication efficiency with a photon-counting detector

Coherent states achieve the Holevo capacity of a pure-loss channel when paired with an optimal measurement, but a physical realization of this measurement is as of yet unknown, and it is also likely to be of high complexity. In this paper, we focus on the photon-counting measurement and study the photon and dimensional efficiencies attainable with modulations over classical- and nonclassical-state alphabets. We first review the state-of-the-art coherent on-off-keying (OOK) with a photon-counting measurement, illustrating its asymptotic inefficiency relative to the Holevo limit. We show that a commonly made Poisson approximation in thermal noise leads to unbounded photon information efficiencies, violating the conjectured Holevo limit. We analyze two binary-modulation architectures that improve upon the dimensional versus photon efficiency tradeoff achievable with conventional OOK. We show that at high photon efficiency these architectures achieve an efficiency tradeoff that differs from the best possible tradeoff—determined by the Holevo capacity—by only a constant factor. The first architecture we analyze is a coherent-state transmitter that relies on feedback from the receiver to control the transmitted energy. The second architecture uses a single-photon number-state source.
Total synthesis of didemnimide A and B

The total synthesis of didemnimide A and didemnimide B, novel predator-deterrent alkaloids from the Caribbean mangrove ascidian Didemnum conchyliatum, is described.
ACCELERATED MONTE CARLO FOR PARTICLE DISPERSION

We discuss adaptive importance sampling for Markov chains. Such chains arise in many simulation problems, such as related to airborne particle dispersion. Through use of experimental design for simulation runs and regression analysis of the output, importance sampling transition kernels are defined which substantially improve convergence times.
Crystal structure of Zn3.77V1.54Mo1.46O12 containing ZnO6 trigonal prisms

Abstract Single crystals of Zn3.77V1.54Mo1.46O12 were grown in a ZnO/V2O5/MoO3 melt. The colorless needles were determined to be orthorhombic, space group P212121 (No. 19), a=5.048 (4) A , b=10.400 (2) A , c=17.560 (7) A , V=921.9(6) A 3 , and Z=4. One type of zinc cation in the structure exhibits trigonal prismatic coordination, and relatively large distortions of the ZnO bond lengths in the trigonal prisms reduce the symmetry from Pnma (centrosymmetric) to P212121 (acentric).
One-Electron Oxidation of DNA: Reaction at Thymine

The feature article is a review of the reaction of thymine in the one-electron oxidation of duplex DNA. Oxidation of DNA causes chemical reactions that result in remote damage (mutation) to a nucleobase. Normally this reaction occurs at guanine, but in oligonucleotides that lack guanines, or when the DNA contains a thymine–thymine mispair, reaction occurs primarily at thymine notwithstanding its high oxidation potential. Selective substitution of uracil for thymine in TT sequences indicates the operation of a tandem reaction mechanism at adjacent thymines. Analysis of the reaction products suggests that proton-coupled electron transfer generates the 5-thymidyl methyl radical, which is trapped by molecular oxygen to give eventually 5-formyl-2′-deoxyuridine and 5-(hydroxymethyl)-2′-deoxyuridine. In a second process, water adds to the 5,6-double bond of the oxidized thymine giving eventually the cis- and trans-diastereomers of 5,6-dihydroxy-5,6-dihydrothymidine.
Detailed Atmosphere Model Fits to Disk-dominated ULX Spectra

We have chosen six ultraluminous X-ray sources from the XMM-Newton archive whose spectra have high signal-to-noise ratio (S/N) and can be fitted solely with a disk model without requiring any power-law component. To estimate systematic errors in the inferred parameters, we fit every spectrum to two different disk models, one based on local blackbody emission (KERRBB) and one based on detailed atmosphere modeling (BHSPEC). Both incorporate full general relativistic treatment of the disk surface brightness profile, photon Doppler shifts, and photon trajectories. We found in every case that they give almost identical fits and similar acceptable parameters. The best-fit value of the most interesting parameter, the mass of the central object, is between 23 and 73 M☉ in five of the six examples. In every case, the best-fit inclination angle and mass are correlated, in the sense that large mass corresponds to high inclination. Even after allowing for this degeneracy, we find that, with 99.9% formal statistical confidence, three of the six objects have mass 25 M☉; for the other three, these data are consistent with a wide range of masses. A mass greater than several hundred M☉ is unlikely for the three best-constrained objects. These fits also suggest comparatively rapid black hole spin in the three objects whose masses are relatively well determined, but our estimate of the spin is subject to significant systematic error having to do with uncertainty in the underlying surface brightness profile.
Tunneled TLS for multi-factor authentication

When logging onto a remote server, s, from a distrusted terminal, c, one can leak secrets such as passwords and account data to malware. To address this problem, we rely on a trusted personal device, p, as the interface available to users for entering their login credentials. In our proposal, p would send the credentials to s using a tunneled TLS session routed via c. The tunneling would be done within an existing TLS session established between c and s. Upon validating the credentials, s would enable c to access the user account. Consequently, c would never see in plain-text user's credentials. As a powerful application, we show that p could use our protocol to execute a credit-card-like payment at a point-of-sale terminal, c, using an account managed by the card-issuing bank, s.
Impact of Platinum Loading and Catalyst Layer Structure on PEMFC Performance

For a hydrogen-powered fuel cell vehicle to be cost competitive, Pt loading must be reduced to lower than 0.15 gPt kW. Therefore, fuel cell researchers are exploring the limits of Pt loading with established catalyst structures in parallel with advanced catalyst research. It is observed that reducing the cathode Pt loading results in significant voltage loss, which can be partly explained by the Pt-oxide coverage dependent oxygen reduction reaction (ORR) kinetics. For ionomer coated catalysts, an additional transport resistance from the electrode pore to the Pt surface (i.e. local resistance) has been reported that is much higher than oxygen permeability through bulk ionomer.
A Possible Connection between Fast Radio Bursts and Gamma-Ray Bursts

The physical nature of fast radio bursts (FRBs), a new type of cosmological transient discovered recently, is not known. It has been suggested that FRBs can be produced when a spinning supra-massive neutron star loses centrifugal support and collapses to a black hole. Here, we suggest that such implosions can happen in supra-massive neutron stars shortly (hundreds to thousands of seconds) after their births, and an observational signature of such implosions may have been observed in the X-ray afterglows of some long and short gamma-ray bursts (GRBs). Within this picture, a small fraction of FRBs would be physically connected to GRBs. We discuss possible multi-wavelength electromagnetic signals and gravitational wave signals that might be associated with FRBs, and propose an observational campaign to unveil the physical nature of FRBs. In particular, we strongly encourage a rapid radio follow-up observation of GRBs starting from 100 s after a GRB trigger.
Theoretical wavelength dependence of polarization in early-type stars

We have examined the theoretical wavelength dependence of linear polarization produced by electron scattering and modified by an absorptive opacity in the extended, distorted atmospheres of Be and Wolf-Rayet stars. A model atmosphere representing a Wolf-Rayet star recently calculated by Cassinelli and Hartmann was used. This model takes into consideration the subsonic portions of a radial, steady-state flow together with the requirement of radiative equilibrium. The model was then scaled down in temperature to approximate the cooler Be stars, again assuming radiative equilibrium. There were four models altogether, one WR star, and three Be models. All the atmospheres are quite extended by radiation pressure.
Computational complexity analysis for multiple hypothesis tracking

This paper presents a detailed analysis of computational complexity of Multiple Hypothesis Tracking (MHT). The result proves that the computational complexity of MHT is dominated by the number of hypotheses. Effects of track merging and pruning are analyzed also. Certain common design parameters of MHT, such as thresholds, are also discussed in detail. The results of this paper provide a guidance for selecting parameters in an MHT tracker and predicting its performance. Among the design parameters discussed in this paper, track merging appears to be the most important way for controlling the computational complexity of MHT. Thresholds for track deletion are also critical. If not all measurements are allowed to initiate new tracks, the number of new tracks can also be used for tuning the computation requirement of MHT, but it is not as significant as thresholds.
Grade inflation under the threat of students’ nuisance: Theory and evidence

Abstract This study examines a channel, students’ nuisance, to explain grade inflation. “Students’ nuisance” is defined by “students’ pestering the professors for better grades.” This paper contains two parts: the game theoretic model and the empirical tests. The model shows that the potential threat of students’ nuisance can induce the professors to inflate grades. Ceteris paribus, a student is more likely to study little and to pester the professor for a better grade if: (1) the professor is lenient; (2) the studying cost is high; (3) the reward from pestering is high; (4) the cost of pestering is low. My original survey data show that 70%+ of professors think that students’ nuisance is “annoying” and “costly in terms of time, effort, and energy.” Regression results indicate that the more the student values the grade, the higher the studying cost, and the more likely the student is to pester the professor. 1
A data variance technique for automated despiking of magnetotelluric data with a remote reference

ABSTRACT The magnetotelluric method employs co‐located surface measurements of electric and magnetic fields to infer the local electrical structure of the earth. The frequency dependent ‘apparent resistivity’ curves can be inaccurate at long periods if input data are contaminated – even when robust remote reference techniques are employed. Data despiking prior to processing can result in significantly more reliable estimates of long period apparent resistivities. This paper outlines a two‐step method of automatic identification and replacement for spike‐like contamination of magnetotelluric data; based on the simultaneity of natural electric and magnetic field variations at distant sites. This simultaneity is exploited both to identify windows in time when the array data are compromised as well as to generate synthetic data that replace observed transient noise spikes. In the first step windows in data time series that contain spikes are identified according to an intersite comparison of channel ‘activity’– such as the variance of differenced data within each window. In the second step, plausible data for replacement of flagged windows are calculated by Wiener filtering coincident data in clean channels. The Wiener filters – which express the time‐domain relationship between various array channels – are computed using an uncontaminated segment of array training data. Examples are shown where the algorithm is applied to artificially contaminated data and to real field data. In both cases all spikes are successfully identified. In the case of implanted artificial noise, the synthetic replacement time series are very similar to the original recording. In all cases, apparent resistivity and phase curves obtained by processing the despiked data are much improved over curves obtained from raw data.
An intelligent controller for process automation

This paper presents a novel supervisory controller that incorporates both a procedural and rule-based language and is capable of responding to asynchronous real-time sensor interrupts. This supervisory controller has been used for automating the manual operations in GaAs crystal growth in a liquid encapsulated Czochralski (LEC) process-based puller from Cambridge Instruments (CI-358). Although commerical crystal-growth controllers provide some degree of automation to help in relieving the burden on an operator, it is essentially the skill and experience of an operator that determines the quality of the crystals grown. Thus, reproducibility of the process is limited, thereby limiting the quality of crystals grown. This controller, referred to as theMeta-Controller (MC), executes ‘plans’ to sequence the operations of crystal growth. Plans are structured English-like representations of scripts that operators follow to grow crystals. Plans are then executed by the Meta-Controller, which responds to asynchronous sensor data interrupts in real time, and issues actuator commands to a real-time controller module. The notion of time is explicitly incorporated into the syntax of the language. Software structures referred to aslogical sensors and logical actuators perform the translation from numeric to symbolic values and vice-versa. The Meta-Controller has been successfully demonstrated on an LEC puller and has automated three phases of crystal growth, including the ‘seed-on’ phase which is currently the most manual-intensive operation in GaAs crystal growth. The other two phases are ‘synthesis’ and ‘meltback’. More plans are currently being written to automate the entire process of crystal growth.
The lasting effects of crime: The relationship of discovered methamphetamine laboratories and home values

Abstract This study estimates a household's willingness to pay to avoid the stigma of crime while minimizing concerns of omitted variable bias. By assuming methamphetamine producers locate approximately at random within a narrowly defined neighborhood, this study is able to use hedonic estimation methods to estimate the impact of the discovery of a methamphetamine laboratory on the home values near that location. Specifically, the analysis designates those closest to the site as the treated, while those slightly farther away act as the comparison group. The discovery of a methamphetamine laboratory has a significant effect on the property values of those homes close to the location that peaks from 6 to 12 months after each lab's discovery. The estimates found in this study range from a decrease in sale prices of 10% to 19% in the year following a laboratory's discovery compared to the prices for homes that are farther away but still in the same neighborhood.
A Review of Accelerated Test Models

Engineers in the manufacturing industries have used accelerated test (AT) experiments for many decades. The purpose of AT experiments is to acquire reliability information quickly. Test units of a material, component, subsystem, or entire systems are subjected to higher-than-usual levels of one or more accelerating variables such as temperature or stress. Then the AT results are used to predict life of the units at use conditions. The extrapolation is typically justified (correctly or incorrectly) on the basis of physically motivated models or a combination of empirical model fitting with a sufficient amount of previous experience in testing similar units. The need to extrapolate in both time and the accelerating variables generally necessitates the use of fully parametric models. Statisticians have made important contributions in the development of appropriate stochastic models for AT data (typically a distribution for the response and regression relationships between the parameters of this distribution and the accelerating variable(s)), statistical methods for AT planning (choice of accelerating variable levels and allocation of available test units to those levels), and methods of estimation of suitable reliability metrics. This paper provides a review of many of the AT models that have been use successfully in this area.
Reduction methods for nonlinear steady‐state thermal analysis

Hybrid analysis techniques and a problem adaptive computational algorithm are presented for predicting the nonlinear steady state temperature distribution in structures and solids. In the proposed techniques, the structure is discretized by using the finite element method. The vector of nodal temperatures is then expressed as a linear combination of a small number of global temperature modes (or basis vectors), and the Bubnov Galerkin technique is used to compute the amplitudes of the global modes. The global temperature modes (or basis vectors) are chosen to include the various order derivatives of the nodal temperature vector with respect to preselected path parameter(s). The potential of the proposed reduction methods for solution of large scale, nonlinear thermal problems is discussed and the effectiveness of the methods is demonstrated by means of numerical examples, including steady state conduction, convection, and radiation modes of heat transfer.
Multigrid solution of compressible turbulent flow on unstructured meshes using a two‐equation model

The system of equations consisting of the full Navier-Stokes equations and two turbulence equations was solved for in the steady state using a multigrid strategy on unstructured meshes. The flow equations and turbulence equations are solved in a loosely coupled manner. The flow equations are advanced in time using a multistage Runge-Kutta time stepping scheme with a stability bound local time step, while the turbulence equations are advanced in a point-implicit scheme with a time step which guarantees stability and positively. Low Reynolds number modifications to the original two equation model are incorporated in a manner which results in well behaved equations for arbitrarily small wall distances. A variety of aerodynamic flows are solved for, initializing all quantities with uniform freestream values, and resulting in rapid and uniform convergence rates for the flow and turbulence equations.
Design of the Extreme Ultraviolet Explorer long-wavelength grazing incidence telescope optics

Designing optics for photometry in the long-wavelength portion of the EUV spectrum (400-900) A) poses different problems from those arising for optics, operating shortward of 400 A. The available filter materials which transmit radiation longward of 400 A are also highly transparent at wavelengths shortward of 100 A. Conventional EUV optics, with grazing engles of less than about 10 deg, have very high throughput in the EUV, which persists to wavelengths shortward of 100 A. Use of such optics with the longer-wavelength EUV filters thus results in an unacceptably large soft X-ray leak. This problem is overcome by developing a mirror design with larger graze angles of not less than 20 deg, which has high throughput at wavelengths longer than 400 A but at the same time very little throughput shortward of 100 A.
Kinetic studies, mechanism, and substrate specificity of amadoriase I from Aspergillus sp.

Amadoriase is a flavoenzyme that catalyzes the oxidative deglycation of Amadori products (fructosyl amino acids or aliphatic amines) to yield free amine, glucosone, and hydrogen peroxide. The mechanism of action of amadoriase I from Aspergillus sp. has been investigated by stopped-flow kinetic studies using fructosyl propylamine and O2 as substrates in 10 mM Tris HCl, pH 7.9, 4 °C. Using both substrate analogues and fast kinetic techniques, the active configuration of the substrate was found to be the β-pyranose form. Stopped-flow studies showed that the reductive half-reaction is triphasic and generates intermediates that absorb at long wavelengths and is consistent either with (i) the reaction of the substrate with the flavin followed by iminium deprotonation or hydrolysis and then product release or with (ii) the formation of flavin reduction intermediates (carbanion equivalents or adducts), followed by product release. The rate of product release after flavin reduction is lower than the aerobic turnov...
Direct Electrophilic Silylation of Terminal Alkynes

A variety of alkynylsilanes were efficiently prepared via direct silylation of terminal alkynes with aminosilanes in the presence of zinc halides. Base- and nucleophile-sensitive functionalities were perfectly tolerated under the above reaction conditions. Initial mechanistic studies support the electrophilic character of this transformation.
Human performance in monitoring and controlling hierarchical large-scale systems

Human performance in monitoring and controlling activities in a hierarchical large-scale network, such as a communications system is considered. A scenario is described that is used in an experiment to examine three factors affecting humans functioning as network supervisors: cluster size (number of elements per display page), number of levels of pages in the hierarchy and failure rate per elements. The results indicate that increasing cluster size improves performance, increasing number of levels degrades performance, and failure rate affects only subjects' strategies.
PG 2131+066: A Test of Pre-White Dwarf Asteroseismology

PG 2131+066 is a composite-spectrum binary with a hot pulsating PG 1159-type pre-white dwarf and an early M-type main-sequence star. Analysis of Whole Earth Telescope observations of the pulsating pre-white dwarf component provided an asteroseismological determination of its mass, luminosity, and effective temperature. These determinations allowed Kawaler et al. to determine the distance to this star. In this paper, we refine the asteroseismological distance determination and confirm the distance by an independent measurement to the system via the spectroscopic parallax of the M star. PG 2131+066 was observed by the HST using the original Planetary Camera in 1993 September. Exposures with filters F785LP and F555W both showed the companion at a distance of 03. Photometry of the images provides an apparent magnitude for the main sequence companion of mv = 18.97 ± 0.15, from which we find a distance of 560 pc. We also recalculated the asteroseismological distance to the pre-white dwarf using updated models and new spectroscopic constraints from UV spectra. The new seismological distance is 668 pc, in satisfactory agreement with the distance of the secondary star. These results suggest that this is indeed a physical binary and that the seismological distance determination technique may be the best way to determine the distance to the pulsating hot pre-white dwarf stars.
Synthetic studies and mechanistic observations in nickel-catalyzed polycyclizations

A series of polyunsaturated enones were investigated in Ni(COD)2 / organozinc - mediated cyclizations. One substrate class underwent an efficient [2+2+2] cycloaddition reaction to generate a tricyclic ring system from a linear precursor. A discussion of probable mechanisms is provided.
A Case for Using MPI's Derived Datatypes to Improve I/O Performance

MPI-IO, the I/O part of the MPI-2 standard, is a promising new interface for parallel I/O. A key feature of MPI-IO is that it allows users to access several noncontiguous pieces of data from a file with a single I/O function call by defining file views with derived datatypes. We explain how critical this feature is for high performance, why users must create and use derived datatypes whenever possible, and how it enables implementations to perform optimizations. In particular, we describe two optimizations our MPI-IO implementation, ROMIO, performs: data sieving and collective I/O. We demonstrate the performance and portability of the approach with performance results on five different parallel machines: HP Exemplar, IBM SP, Intel Paragon, NEC SX-4, and SGI Origin2000.
Radiation From Flux Flow In Josephson Junction Structures

We derive the radiation power from a single Josephson junction (JJ) and from layered superconductors in the flux-flow regime. For JJ case, we formulate the boundary conditions for the electric and magnetic fields at the edges of the superconducting leads using the Maxwell equations in the dielectric media and find dynamic boundary conditions for the phase difference in JJ which account for the radiation. We derive the fraction of the power fed into JJ transformed into the radiation. In a finite-length JJ this fraction is determined by the dissipation inside JJ and it tends to unity as dissipation vanishes independently of mismatch of the junction and dielectric media impedances. We formulate also the dynamic boundary conditions for the phase difference in intrinsic JJs in highly anisotropic layered superconductors of the Bi2Sr2CaCu2O8 type at the boundary with free space. Using these boundary conditions, we solve equations for the phase difference in the linear regime of Josephson oscillations for rectangular and triangular lattices of Josephson vortices. In the case of rectangular lattice for crystals with the thickness along the c-axis much larger than the radiation wavelength, we estimate the radiation power per unit length in the direction of magnetic field at the frequency 1 THz as ∼N μW/cm for Tl2Ba2CaCu2O8 and ∼0.04 N μW/cm for Bi2Sr2CaCu2O8. For crystals with thickness smaller than the radiation wavelength, we found that the radiation power in the resonance is independent on number of layers and can be estimated at 1 THz as 0.5 W/cm (Tl2Ba2CaCu2O8) and 24 mW/cm (Bi2Sr2CaCu2O8). For rectangular lattice, due to superradiation regime, up to half of power fed into the crystal may be converted into the radiation. In the case of triangular or random lattice in the direction perpendicular to the layers, the fraction of power converted into the radiation depends on the dissipation rate and is much lower than for rectangular lattice in the case of high-temperature superconductors with nodes in the gap.
Peptidomimetics via copper-catalyzed azide–alkyne cycloadditions

This critical review concerns the impact of copper-mediated alkyne–azide cycloadditions on peptidomimetic studies. It discusses how this reaction has been used to insert triazoles into peptide chains, to link peptides to other functionalities (e.g. carbohydrates, polymers, and labels), and as a basis for evolution of less peptidic compounds as pharmaceutical leads. It will be of interest to those studying this click reaction, peptidomimetic secondary structure and function, and to medicinal chemists.
Advancements in Gas Turbine Fuels From 1943 to 2005

The first provisional jet fuel specifications were published in 1943 in England (RDE/F/ KER/210) and 1944 in the U.S. (AN-F-32a). Jet fuel has undergone many changes in subsequent years, with current specifications for JP-5 and JP-8 for the military in the U.S. and Jet A/Jet A-1 for commercial use worldwide. Jet fuel specifications are subject to constant tension between performance requirements and availability/cost considerations. In this paper we will discuss how jet fuels have evolved over the years from the first engines to current gas turbine engines. Jet fuels derived from nonpetroleum sources will also be discussed.
TurfCast: A Service for Controlling Information Dissemination in Wireless Networks

Recent years have witnessed mass proliferation of mobile devices with rich wireless communication capabilities as well as emerging mobile device-based information dissemination applications that leverage these capabilities. This paper proposes TurfCast, a novel information dissemination service that selectively broadcasts information in particular "turfs,a abstract logical spaces in which receivers are situated. Such turfs can be temporal or spatial based on receivers' lingering time or physical areas, respectively. TurfCast has many applications such as electronic proximity advertising and mobile social networking. To enable TurfCast, we propose two supporting technologies: TurfCode and TurfBurst. TurfCode is a nested 0-1 fountain code that enables the broadcaster to transmit either all information or none at all to receivers. TurfBurst exploits the Shannon bound to differentiate among receivers: those who cannot receive information fast enough receive none at all, even if they linger near the broadcaster. We implement TurfCast on real-world devices and conduct experiments in both indoor and outdoor environments. Our experimental results illustrate TurfCast's potential for controlling information dissemination in wireless networks.
Performance Indicator for MIMO MMSE Receivers in the Presence of Channel Estimation Error

We present the derivation of post-processing SNR for minimum mean-squared error (MMSE) receivers with imperfect channel estimates, and show that it is an accurate indicator of the error rate performance of MIMO systems in the presence of channel estimation error. Simulation results show the tightness of the analysis.
Composition dependence of the enthalpies of formation of NiAl

Abstract The enthalpy of formation of NixAl1−x as a function of composition has been determined by high temperature reaction calorimetry over the range 0.44≤x≤0.58. The value for the Ni0.5Al0.5 composition is −61.8±1.1 kJ/mol. The present results are compared with previously published results on the enthalpy of formation of NixAl1−x. In several cases the experiments were performed at two different calorimeter temperatures and the difference in heat content values is compared with the heat capacity of NiAl.
Shear Waves and Giant-Flare Oscillations from Soft Gamma-Ray Repeaters

Recent observations of giant flares from soft gamma-ray repeaters have exhibited multiple ~25-150 Hz oscillations. Frequencies in this range are expected for toroidal shear waves in a neutron star (NS) crust, lending support to Duncan's proposal that such modes may be excited in these events. This motivates a reassessment of how these waves reflect the NS structure and what role the magnetic field plays in setting their frequencies. We calculate the eigenfrequencies and eigenfunctions of toroidal oscillations for a realistic NS crust, including a vertical magnetic field at magnetar strengths (B ~ 1014-1015 G). The lowest radial-order mode has a redshifted frequency of ≈28 Hz[l(l + 1)/6]1/2, with the prefactor depending on the NS's mass and radius and its crust's depth and composition. This mode is independent of the magnetic field for B 4 × 1015 G, a limit much greater than the inferred dipole magnetic fields for these objects. Although this is a good fit to the observed oscillations, only rather loose constraints can be made for the NSs' properties because all that can be fit is this prefactor (a single parameter). Modes with shorter radial wavelengths are more sensitive to the magnetic field starting at B ~ 2 × 1014 G and have higher frequencies (~600-2000 Hz). The discovery of these modes, coupled with the oscillations observed thus far, would provide a powerful probe to the NS crustal structure.
Some Upper Bounds on the Number of Resonances for Manifolds with Infinite Cylindrical Ends

We prove some sharp upper bounds on the number of resonances associated with the Laplacian, or Laplacian plus potential, on a manifold with infinite cylindrical ends.
The Organization of Computer Resources into a Packet Radio Network

Packet radio communications provides an effective way to interconnect fixed and mobile computer resources. The ALOHA System at the University of Hawaii first introduced this capability in the context of a single-hop system using off-the-shelf RF equipment with all terminals within line of sight of the central station. The packet radio network described in this paper is 1) an extension of the basic Hawaii work to a geographically distributed system involving the use of repeaters to achieve area coverage beyond line of sight, and 2) provides added capabilities for authentication, antijam protection, and coexistence with other possibly different systems in the same band. An overview of the packet radio system concept is given in this paper.
Proving time bounds for randomized distributed algorithms

A method of analyzing time bounds for randomized distributed algorithms is presented, in the context of a new and general framework for describing and reasoning about randomized algorithms. The method consists of proving auxiliary statements of the form U (t)->(p) U', which means that whenever the algorithm begins in a state in set U, with probability p, it will reach a state in set U' within time t. The power of the method is illustrated by its use in proving a constant upper bound on the expected time for some process to reach its critical region, in Lehmann and Rabin's Dining Philosophers algorithm.
Hybrid tree reconstruction methods

A major computational problem in biology is the reconstruction of evolutionary trees for species sets, and accuracy is measured by comparing the topologies of the reconstructed tree and the model tree. One of the major debates in the field is whether large evolutionary trees can be even approximately accurately reconstructed from biomolecular sequences of realistically bounded lengths (up to about 2000 nucleotides) using standard techniques (polynomial-time distance methods, and heuristics for NP-hard optimization problems). Using both analytical and experimental techniques, we show that on large trees, the two most popular methods in systematic biology, Neighbor-Joining and Maximum Parsimony heuristics, as well as two promising methods introduced by theoretical computer scientists, are all likely to have significant errors in the topology reconstruction of the model tree. We also present a new general technique for combining outputs of different methods (thus producing hybrid methods), and show experimentally how one such hybrid method has better performance than its constituent parts.