cssi/SciSciGPT-SciSciNet huggingface dataset:
Measurements of materials shielding properties with 1 GeV/nuc 56Fe

Abstract The design of future spacecraft such as the Crew Exploration Vehicle must take into account the radiation shielding properties of both the structural components as well as dedicated shielding materials. Since modest depths of shielding stop the vast majority of Solar Energetic Particles (SEP), the greater challenge is posed by the need to shield the crew from the Galactic Cosmic Rays (GCR), which include highly-charged and highly-energetic particles. Here, we report on results from tests performed with beams of 1 GeV/nuc 56 Fe at the Brookhaven National Laboratory. A wide variety of targets, both elemental and composite, was placed in the particle beams, and the spectra of particles emerging from the targets were measured using a stack of silicon detectors. Results are presented primarily in terms of dose reduction per g cm −2 of target material, and support the conclusions of an earlier calculation by Wilson et al. showing that performance improves as the shield’s mass number decreases, with hydrogen being by far the most effective shielding material. The data also show that, as depth increases, the incremental benefit of adding shielding decreases.
Room-Temperature Stille Cross-Couplings of Alkenyltin Reagents and Functionalized Alkyl Bromides that Possess β Hydrogens

This communication describes a significant expansion in the scope of Stille reactions of Csp3-X electrophiles, specifically, that Pd/P(t-Bu)2Me catalyzes the room-temperature cross-coupling of a variety of functionalized, beta-hydrogen-containing alkyl bromides with an array of alkenyltin reagents. The structure of the phosphine (P(t-Bu)2Me) is well suited for facilitating oxidative addition and avoiding beta-hydride elimination, while the fluoride serves to activate the tin reagent for efficient transmetalation.
On the kinematics and kinetics of mechanical seals, rotors, and wobbling bodies

Abstract Mechanical seals, rotors, and wobbling bodies whirl about a point and are characterized by a kinematical constraint that prevents them from having integral motion with respect to the axis of whirl. A valid kinematical model is a prerequisite to subsequent dynamic analyses. Three previous works have suggested distinctly different kinematical models for the same problem. The analysis herein presents yet another kinematical model that preserves (actually enforces) the proper kinematical constraint. Interestingly, it is found that although no integral rotation is allowed about the axis of whirl, the wobbling body possesses a sustained nonzero angular velocity about that axis. The derivation is done for any finite nutation angle and only final results are being degenerated to small tilt angles. The outcome reaffirms the results of a previous work. For this time-invariant problem the notion of virtual velocity and virtual power emerges, and the equations of motion are derived using Lagrange’s equations to complement results obtained previously by Newton–Euler mechanics.
Linear-programming-based techniques for synthesis of network-on-chip architectures

Application-specific system-on-chip (SoC) design offers the opportunity for incorporating custom network-on-chip (NoC) architectures that are more suitable for a particular application, and do not necessarily conform to regular topologies. This paper presents novel mixed integer linear programming (MILP) formulations for synthesis of custom NoC architectures. The optimization objective of the techniques is to minimize the power consumption subject to the performance constraints. We present a two-stage approach for solving the custom NoC synthesis problem. The power consumption of the NoC architecture is determined by both the physical links and routers. The power consumption of a physical link is dependent upon the length of the link, which in turn, is governed by the layout of the SoC. Therefore, in the first stage, we address the floorplanning problem that determines the locations of the various cores and the routers. In the second stage, we utilize the floorplan from the first stage to generate topology of the NoC and the routes for the various traffic traces. We also present a clustering-based heuristic technique for the second stage to reduce the run times of the MILP formulation. We analyze the quality of the results and solution times of the proposed techniques by extensive experimentation with realistic benchmarks and comparisons with regular mesh-based NoC architectures.
Thresholded covering algorithms for robust and max---min optimization

In a two-stage robust covering problem, one of several possible scenarios will appear tomorrow and require to be covered, but costs are higher tomorrow than today. What should you anticipatorily buy today, so that the worst-case cost (summed over both days) is minimized? We consider the $$k$$ k -robust model where the possible scenarios tomorrow are given by all demand-subsets of size $$k$$ k . In this paper, we give the following simple and intuitive template for $$k$$ k -robust covering problems: having built some anticipatory solution, if there exists a single demand whose augmentation cost is larger than some threshold, augment the anticipatory solution to cover this demand as well, and repeat. We show that this template gives good approximation algorithms for $$k$$ k -robust versions of many standard covering problems: set cover, Steiner tree, Steiner forest, minimum-cut and multicut. Our $$k$$ k -robust approximation ratios nearly match the best bounds known for their deterministic counterparts. The main technical contribution lies in proving certain net-type properties for these covering problems, which are based on dual-rounding and primal---dual ideas; these properties might be of some independent interest. As a by-product of our techniques, we also get algorithms for max---min problems of the form: "given a covering problem instance, which $$k$$ k of the elements are costliest to cover?" For the problems mentioned above, we show that their $$k$$ k -max---min versions have performance guarantees similar to those for the $$k$$ k -robust problems.
Theory of spin fluctuations in striped phases of doped antiferromagnetic cuprates

We study the properties of generalized striped phases of doped cuprate planar quantum antiferromagnets. We invoke an effective, spatially anisotropic, nonlinear sigma model in two space dimensions. Our theoretical predictions are inquantitative agreement with recent experiments in La{2-x}SrxCuO4 with 0≤ x ≤ 0.018. We focus on (i) the magnetic correlation length, (ii) the staggered magnetization at T= 0, and (iii) the Neel temperature, as functions of doping, using parameters determined previously and independently for this system. These results support the proposal that the low doping (antiferromagnetic) phase of the cuprates has a striped configuration.
High-energy physics with polarized electrons and muons

Abstract In this paper I will review the topic of high-energy physics with polarized electrons and muons. The two main topics will be the spin-dependent structure functions of the nucleon and parityviolating electroweak interference observed in the scattering of polarized electrons. Both topics now relate to particle physics and to nuclear physics.
A rigorous formation damage skin factor and reservoir inflow model for a horizontal well

In this paper, we present a new analytical model for formation damage skin factor and the resulting reservoir inflow, including the effect of reservoir anisotropy and damage heterogeneity. The shape of the damaged region perpendicular to the well is based on the pressure equation for an anisotropic medium and, thus, is circular near the well and elliptical far from the well. The new model can be used for various distributions of damage along the well, depending on the time of exposure during drilling and completion. The inflow equation for a damaged, parallel-piped-shape reservoir illustrates the importance of the ratio of the reservoir thickness to the drainage length perpendicular to the well on the influence of formation damage for horizontal well productivity. Our model gives a simple, analytical expression for determining this effect.
Electronic consequences of the mutual presence of thermal and structural disorder

We investigate the simultaneous presence of topological and thermal disorder in amorphous silicon. We find that localized electronic states are very sensitive to moderate amounts of thermal disorder: for a given gap or band tail electronic eigenstate, both the fraction of the total charge on a given site as well as the energy eigenvalue can vary greatly with small (thermally accessible) changes to the positions of the atoms. This observation, which is almost certainly relevant to any disordered insulator including glasses, has important implications to the microscopic theory of transport, optical properties, and doping, as well as existing models of defect kinetics.
On generically stable types in dependent theories

We develop the theory of generically stable types, independence relation based on nonforking and stable weight in the context of dependent theories.
Ignition regime for fusion in a degenerate plasma

We identify relevant parameter regimes in which aneutronic fuels can undergo fusion ignition in hot-ion degenerate plasma. Because of relativistic effects and partial degeneracy, the self-sustained burning regime is considerably larger than previously calculated. Inverse bremsstrahlung plays a major role in containing the reactor energy. We solve the radiation transfer equation and obtain the contribution to the heat conductivity from inverse bremsstrahlung.
Streaking images that appear only in the plane of diffraction in undoped GaAs single crystals: Diffraction imaging (topography) by monochromatic synchrotron radiation

Streaking images restricted to the direction of the diffraction (scattering) vector have been observed on transmission through undoped GaAs. These disruption images (caused by the reduction of diffraction in the direction of observation) appear both in the forward and in Bragg diffracted directions in monochromatic synchrontron radiation diffraction imaging. This previously unobserved phenomenon can be explained in terms of planar defects (interfaces) or platelets which affects the absorption coefficient in anomalous transmission. Such regions of the crystal look perfect despite the presence of imperfections when the scattering vector is not perpendicular to the normal of the platelets. The observed crystallographic orientation of these interfaces strongly indicates that they are antiphase boundaries.
Abundance Analysis of Planetary Host Stars. I. Differential Iron Abundances

We present atmospheric parameters and iron abundances derived from high-resolution spectra for three samples of dwarf stars: stars that are known to host close-in giant planets (CGP), stars for which radial velocity data exclude the presence of a close-in giant planetary companion (no-CGP), as well as a random sample of dwarfs with a spectral type and magnitude distribution similar to that of the planetary host stars (control). All stars have been observed with the same instrument and have been analyzed using the same model atmospheres, atomic data, and equivalent width modeling program. Abundances have been derived differentially to the Sun, using a solar spectrum obtained with Callisto as the reflector with the same instrumentation. We find that the iron abundances of CGP dwarfs are on average 0.22 dex greater than that of no-CGP dwarfs. The iron abundance distributions of both the CGP and no-CGP dwarfs are different than that of the control dwarfs, while the combined iron abundances have a distribution that is very similar to that of the control dwarfs. All four samples (CGP, no-CGP, combined, and control) have different effective temperature distributions. We show that metal enrichment occurs only for CGP dwarfs with temperatures just below solar and ≈300 K higher than solar, whereas the abundance difference is insignificant at Teff around 6000 K.
Comparison of video shot boundary detection techniques

Many algorithms have been proposed for detecting video shot boundaries and classifying shot and shot transition types. Few published studies compare available algorithms, and those that do have looked at limited range of test material. This paper presents a comparison of several shot boundary detection and classification techniques and their variations including histograms, discrete cosine transform, motion vector, and block matching methods. The perfor- mance and ease of selecting good thresholds for these algorithms are evaluated based on a wide variety of video sequences with a good mix of transition types. Threshold selection requires a trade-off between recall and precision that must be guided by the target application. © 1996 SPIE and IS&T.
Wine flavor: chemistry in a glass

Although hundreds of chemical compounds have been identified in grapes and wines, only a few compounds actually contribute to sensory perception of wine flavor. This critical review focuses on volatile compounds that contribute to wine aroma and provides an overview of recent developments in analytical techniques for volatiles analysis, including methods used to identify the compounds that make the greatest contributions to the overall aroma. Knowledge of volatile composition alone is not enough to completely understand the overall wine aroma, however, due to complex interactions of odorants with each other and with other nonvolatile matrix components. These interactions and their impact on aroma volatility are the focus of much current research and are also reviewed here. Finally, the sequencing of the grapevine and yeast genomes in the past ∼10 years provides the opportunity for exciting multidisciplinary studies aimed at understanding the influences of multiple genetic and environmental factors on grape and wine flavor biochemistry and metabolism (147 references).
Secondary Flow, Separation and Losses in the NACA 48-Inch Centrifugal Impeller at Design and Off-Design Conditions

An elliptic flow calculation procedure has been used to model 3-D flow in the NACA 48–inch centrifugal impeller. The results demonstrate that fully elliptic steady flow calculations can be performed at design and off-design conditions. The calculations reproduce the measured overall performance and most of the features of the loss distributions observed in the NACA flow study. They give further insight into the complex 3-D flow with leading-edge separation and tip leakage.The calculated secondary flow patterns are presented and used to explain the convection of vortices in a more recent laser anemometry study of a centrifugal compressor impeller.Copyright © 1988 by ASME
Characterizing Solution Surface Loop Conformational Flexibility of the GM2 Activator Protein

GM2AP has a β-cup topology with numerous X-ray structures showing multiple conformations for some of the surface loops, revealing conformational flexibility that may be related to function, where function is defined as either membrane binding associated with ligand binding and extraction or interaction with other proteins. Here, site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy and molecular dynamic (MD) simulations are used to characterize the mobility and conformational flexibility of various structural regions of GM2AP. A series of 10 single cysteine amino acid substitutions were generated, and the constructs were chemically modified with the methanethiosulfonate spin label. Continuous wave (CW) EPR line shapes were obtained and subsequently simulated using the microscopic order macroscopic disorder (MOMD) program. Line shapes for sites that have multiple conformations in the X-ray structures required two spectral components, whereas spectra of the remaining sites we...
Motivations and measurements in an agile case study

With the recent emergence of agile software development technologies, the software community is awaiting sound, empirical investigation of the impacts of agile practices in a live setting. One means of conducting such research is through industrial case studies. There are a number of influencing factors that contribute to the success of such a case study. In this paper, we describe a case study performed at Sabre Airline SolutionsTM evaluating the effects of adopting Extreme Programming (XP) practices with a team that had characteristically plan-driven risk factors. We compare the team's business-related results (productivity and quality) to two published sources of industry averages. Our case study found that the Sabre team yielded above-average post-release quality and average to above-average productivity. We discuss our experience in conducting this case study, including specifics of how data was collected, the rationale behind our process of data collection, and what obstacles were encountered during the case study. We identify four factors that potentially impact the outcome of industrial case studies: availability of data, tool support, cooperative personnel and project status. Recognizing and planning for these factors is essential to conducting industrial case studies.
A deconvolution approach for the mapping of acoustic sources (DAMAS) determined from phased microphone arrays

Current processing of acoustic array data is burdened with considerable uncertainty. This study reports an original methodology that serves to demystify array results, reduce misinterpretation, and accurately quantify position and strength of acoustic sources. Traditional array results represent noise sources that are convolved with array beamform response functions, which depend on array geometry, size (with respect to source position and distributions), and frequency. The Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) method removes beamforming characteristics from output presentations. A unique linear system of equations accounts for reciprocal influence at different locations over the array survey region. It makes no assumption beyond the traditional processing assumption of statistically independent noise sources. A new robust iterative method seamlessly introduces a positivity constraint (due to source independence) that makes the equation system sufficiently deterministic. DAMAS is quantitatively validated using archival data from a variety of prior high-lift airframe component noise studies, including flap edge/cove, trailing edge, leading edge, slat, and calibration sources. Presentations are explicit and straightforward, as the noise radiated from a region of interest is determined by simply summing the mean-squared values over that region. DAMAS can fully replace existing array processing and presentations methodology in most applications. It appears to dramatically increase the value of arrays to the field of experimental acoustics.
WHARTON FRAGMENTATIONS OF CYCLIC 1, 3-DIOL DERIVATIVES. A REVIEW

(1988). WHARTON FRAGMENTATIONS OF CYCLIC 1, 3-DIOL DERIVATIVES. A REVIEW. Organic Preparations and Procedures International: Vol. 20, No. 1, pp. 1-51.
Cathodic fabrication of platinum microparticles via anodic dissolution of a platinum counter-electrode : electrocatalytic probing and surface analysis of dispersed platinum

Abstract In three-electrode cells without separation of the working and counter electrodes, the application of a sufficiently negative potential at the working electrode is accompanied by the development of a rather positive potential at the counter-electrode. If a platinum-flag counter-electrode is employed in acidic aqueous electrolyte, it undergoes anodic corrosion, to produce dissolved metal, perhaps as a Pt(IV) oxospecies. It serves in turn, as a source of platinum for cathodic electrodeposition at the negative working electrode. Scanning electron micrographs showed that controlled potential electrolysis at − 1.2 V vs. SCE for 6 h (in stirred 1 M H 2 SO 4 ) consistently produced dispersed platinum particles on a carbon working electrode. They were approximately spherical, had diameters of 20–40 nm, and were separated by distances of less than 30–50 nm. The platinum was not deposited when a carbon counter-electrode was employed. Simultaneous codeposition of platinum and polyoxometallates is feasible. Auger electron spectrometry, energy-dispersive X-ray fluorescence and secondary ion mass spectrometry were used to verify the presence of platinum. Shorter electrolysis times (e.g. 30–60 min) produced very low platinum loadings, which were difficult to determine with common surface analytical techniques. The As(III) electrocatalytic oxidation provided a good probe for the detection of traces of platinum, and permitted estimation of the platinum coverage on a carbon substrate.
Is the 2,3-carbon-carbon bond of indole really inert to oxidative cleavage by Oxone?--synthesis of isatoic anhydrides from indoles.

A recent report has indicated that the oxidizing agent Oxone does not possess the ability to cleave the 2,3-carbon–carbon bond of indole. Work in our laboratory shows that this is not the case. Indole and a variety of aryl ring substituted derivatives readily react to form synthetically important isatoic anhydrides.
On the accuracy of modelling the dynamics of large space structures

Proposed space missions will require large scale, light weight, space based structural systems. Large space structure technology (LSST) systems will have to accommodate (among others): ocean data systems; electronic mail systems; large multibeam antenna systems; and, space based solar power systems. The structures are to be delivered into orbit by the Space Shuttle. Because of their inherent size, modelling techniques and scaling algorithms must be developed so that system performance can be predicted accurately prior to launch and assembly. When the size and weight-to-area ratio of proposed LSST systems dictate that the entire system be considered flexible, there are two basic modelling methods which can be used. The first is a continuum approach, a mathematical formulation for predicting the motion of a general orbiting flexible body, in which elastic deformations are considered small compared with characteristic body dimensions. This approach is based on an a priori knowledge of the frequencies and shape functions of all modes included within the system model. Alternatively, finite element techniques can be used to model the entire structure as a system of lumped masses connected by a series of (restoring) springs and possibly dampers. In addition, a computational algorithm was developed to evaluate the coefficients of the various coupling terms in the equations of motion as applied to the finite element model of the Hoop/Column.
Leading radical change in transition economies

New managers in central and east European companies were faced with daunting challenges to manage their companies through the transition from central planning to competition and to change their companies radically so that their firms would be capable of competing effectively. Based on the analysis of six longitudinal company cases from the Czech Republic, I identify the key skills that new managers had to have and where they were able to obtain those skills. The seeds of current managerial expertise could often be found in experiences under central planning, despite the fact that central planning more generally rewarded behaviors that were counterproductive in market‐based competition. Results are discussed in the context of leading radical organizational change.
Hyper-X Stage Separation Wind-Tunnel Test Program

NASA's Hyper-X research program was developed primarily to flight demonstrate a supersonic combustion ramjet engine, fully integrated with a forebody designed to tailor inlet flow conditions and a free expansion nozzle/afterbody to produce positive thrust at design flight conditions. With a point-designed propulsion system the vehicle must depend on some other means for boost to its design flight condition. Clean separation from this initial propulsion system stage within less than a second is critical to the success of the flight. This paper discusses the early planning activity, background, and chronology that developed the series of wind-tunnel tests to support multi-degree-of-freedom simulation of the separation process. Representative results from each series of tests are presented, and issues and concerns during the process and current status are highlighted.
Unsteady Flow Sensing and Estimation via the Gappy Proper Orthogonal Decomposition

Abstract The proper orthogonal decomposition (POD) has been widely used in fluid dynamic applications for extracting dominant flow features. The “gappy” POD is an extension to this method that allows the consideration of incomplete data sets. In this paper, the gappy POD is extended to handle unsteady flow reconstruction problems, such as those encountered when limited flow measurement data is available. In addition, a systematic approach for effective sensor placement is formulated within the gappy framework using a condition number criterion. This criterion allows for accurate flow reconstruction results and yields sensor configurations that are robust to sensor noise. Two applications are considered. The first aims to reconstruct the unsteady flow field using a small number of surface pressure measurements for a subsonic airfoil undergoing plunging motion. The second considers estimation of POD modal content of a cylinder wake flow for active control purposes. In both cases, using the dominant POD basis vectors and a small number of sensor signals, the gappy approach is found to yield accurate flow reconstruction results.
The color of law: an economic theory of legal boundaries

This paper presents an economic theory of property, tort, and contract law based on the goal of efficiently governing economic exchange relationships. In the theory, legal boundaries emerge endogenously in response to exogenous differences in the nature of the underlying transaction concerning the possible existence of unforeseen or non-contractible contingencies, and/or the desire of one of the parties to make non-salvageable investments prior to trade. The analysis asks whether, in this context, the transaction is best governed by property, tort, or contract principles. The conclusions are illustrated by a discussion of several cases that occupy the “boundaries” between the various areas.
Thin Windows for Gaseous and Liquid Targets: An Optimization Procedure

Many particle and nuclear physics experiments require cryogenic liquid, cryogenic high-pressure gas, or simply high-pressure gas targets with thin windows. Typically materials such as Havar,† Mylar,‡ Kapton,§ stainless steels, and various alloys of aluminum have been used. The most frequently used materials are Mylar and Kapton, which have relatively high tensile strengths and relatively low densities and atomic numbers. A comparison of the various materials on the basis of their performance as a target window, however, has not been available. In order that window design may be based on a complete understanding of the relationship between pressure and deflection an experimental program was carried out in two phases.
Viscoacoustic modeling and imaging using low-rank approximation

ABSTRACTA constant-Q wave equation involving fractional Laplacians was recently introduced for viscoacoustic modeling and imaging. This fractional wave equation has a convenient mixed-domain space-wavenumber formulation, which involves the fractional-Laplacian operators with a spatially varying power. We have applied the low-rank approximation to the mixed-domain symbol, which enables a space-variable attenuation specified by the variable fractional power of the Laplacians. Using the proposed approximation scheme, we formulated the framework of the Q-compensated reverse time migration (Q-RTM) for attenuation compensation. Numerical examples using synthetic data demonstrated the improved accuracy of using low-rank wave extrapolation with a constant-Q fractional-Laplacian wave equation for seismic modeling and migration in attenuating media. Low-rank Q-RTM applied to viscoacoustic data is capable of producing images comparable in quality with those produced by conventional RTM from acoustic data.
Applications of BioMEMS in Cell-Related Research

Microelectromechanical systems have been used in biology and medicine for a number of years now. However, in the last decade, biological cell research has been an area where tremendous growth in their applications has been observed. The reason for this growth lies in the flourishing of the life sciences, which coincided with the maturation of the MEMS field. A large number of applications of BioMEMS in disciplines such as neuroscience, oncology, or (particularly) cell biology have been identified. In this talk, Prof. Tatic-Lucic will survey several different ways to exploit BioMEMS in cell biology, including cell manipulation, sorting, trapping and culturing. In addition, she will give examples of the work in this area done at Lehigh University. Specifically, she will address patterned growth of biological cells with application in cell-based sensors, and design, fabrication and characterization of BioMEMS devices for measuring mechanical compliance of cultured cells.
The Prospects for eGovernment and eGovernance in Sub-Saharan Africa: A Case Study of Zambia

EGovernance and eGovernment are critical tools for Good governance and economic development, and are therefore critical for Highly Indebted Poor Countries, a majority of which are in Sub-Saharan Africa. This article reviews literature in order to discuss the prospects of eGovernance and eGovernment in Sub Saharan Countries, and chooses the nation of Zambia as an in-depth case study. Issues of investment climate, market structure, infrastructural capacity, social contexts and political and cultural resistance factors are identified as impediments but also key components if well understood and tackled for effective initiation and implementation of eGovernance and eGovernment projects.
Measuring Stochastic Technology: The Case of Tulare Milk Production

The flexible moment-based approach to production analysis is used to measure the stochastic structure of large-scale dairy production in Tulare County, California. This approach is flexible because it does not impose restrictions on the relationships between decision variables and the moments of the probability distribution of output. The parameter estimates support the hypothesis that second and third moments are functions of inputs and indicate that capital-intensive dairies are riskier. The implied behavior of a risk-averse dairy manager changed markedly when the effects of inputs on the skewness of the output distribution were included in a decision model.
Gaussian Channel With Noisy Feedback and Peak Energy Constraint

Optimal coding over the additive white Gaussian noise channel under the peak energy constraint is studied when there is noisy feedback over an orthogonal additive white Gaussian noise channel. As shown by Pinsker, under the peak energy constraint, the best error exponent for communicating an M-ary message, M ≥ 3, with noise-free feedback is strictly larger than the one without feedback. This paper extends Pinsker's result and shows that if the noise power in the feedback link is sufficiently small, the best error exponent for communicating an M-ary message can be strictly larger than the one without feedback. The proof involves two feedback coding schemes. One is motivated by a two-stage noisy feedback coding scheme of Burnashev and Yamamoto for binary symmetric channels, while the other is a linear noisy feedback coding scheme that extends Pinsker's noise-free feedback coding scheme. When the feedback noise power α is sufficiently small, the linear coding scheme outperforms the two-stage (nonlinear) coding scheme, and is asymptotically optimal as α tends to zero. By contrast, when α is relatively larger, the two-stage coding scheme performs better.
Second Thoughts on Reliability

A nonmathematical discourse on inconsistencies in the present approach to the problem of achieving reliability in electronics for aerospace applications.
Asymmetric Synthesis of Highly Functionalized 8-Oxabicyclo[3.2.1]octene Derivatives

Rhodium(II) carboxylate catalyzed decomposition of vinyldiazomethanes in the presence of furans results in a general synthesis of oxabicyclo[3.2.1]octa-2,6-diene derivatives. These oxabicyclic products are versatile intermediates in organic synthesis. The mechanism of the [3 + 4] annulation is considered to be a tandem cyclopropanation/Cope rearrangement. Such a mechanism is consistent with the excellent regio- and stereocontrol that is observed in these [3 + 4] annulations. Asymmetric synthesis of the oxabicyclic products is possible through utilization of rhodium(II) (S)-N-(tert-butylbenzene)sulfonylprolinate as catalyst or by using (S)-lactate or (R)-pantolactone as chiral auxiliaries on the carbenoid. The highest yields (69−95%) and asymmetric induction (82−95% de) were obtained using 3-siloxy-2-diazo-3-butenoate derivatives as the vinylcarbenoid precursors.
Analysis and performance of a picosecond dye laser amplifier chain

A mathematical analysis is presented for dye laser amplifier chains used to amplify cw mode‐locked dye laser pulses up to the gigawatt regime. The model permits a discussion of the important aspects of the problem such as gain saturation, pulse shaping, and the optimization of pumping efficiencies. Experimentally, an amplifier chain has been demonstrated which is simple in design and operation without sacrificing high performance. A frequency doubled Q‐switched Nd:YAG oscillator alone is used to longitudinally pump three identical Brewster cells with the same flowing dye solution in each. The amplifier boosts the output of a synchronously mode‐locked dye laser to obtain ∼0.5 mJ≲1 psec pulses over a ∼400 A bandwidth. These pulses are suitable for efficient Raman shifting, frequency mixing, and continuum generation to vastly extend the spectral range of the system. Some experimental results are presented to support the mathematical model.
PARKER/BUOYANCY INSTABILITIES WITH ANISOTROPIC THERMAL CONDUCTION, COSMIC RAYS, AND ARBITRARY MAGNETIC FIELD STRENGTH

We report the results of local stability analysis for magnetized, gravitationally stratified plasma-containing cosmic rays. We account for cosmic-ray diffusion and thermal conduction parallel to the magnetic field and allow β = 8πp/B 2 to take any value, where p is the plasma pressure and B is the magnetic field strength. We take the gravitational acceleration to be in the –z-direction and the equilibrium magnetic field to be in the y-direction, and derive the dispersion relation for small-amplitude instabilities and waves in the large-|kx | limit. We use the Routh-Hurwitz criterion to show analytically that the necessary and sufficient criterion for stability in this limit is nkBdT/dz + dp cr/dz + (1/8π) dB 2/dz > 0, where T is the temperature, n is the number density of thermal particles, and p cr is the cosmic-ray pressure. We present approximate analytical solutions for the normal modes in the low- and high-diffusivity limits, show that they are consistent with the derived stability criterion, and compare them to numerical results obtained from the full, unapproximated, dispersion relation. Our results extend earlier analyses of buoyancy instabilities in galaxy-cluster plasmas to the β 1 regime. Our results also extend earlier analyses of the Parker instability to account for anisotropic thermal conduction, and show that the interstellar medium is more unstable to the Parker instability than was predicted by previous studies in which the thermal plasma was treated as adiabatic.
On the Lack of Evolution in Galaxy Star Formation Efficiency

Using reconstructed galaxy star formation histories, we calculate the instantaneous efficiency of galaxy star formation (i.e., the star formation rate divided by the baryon accretion rate) from z = 8 to the present day. This efficiency exhibits a clear peak near a characteristic halo mass of 1011.7 M ☉, which coincides with longstanding theoretical predictions for the mass scale relevant to virial shock heating of accreted gas. Above the characteristic halo mass, the efficiency falls off as the mass to the minus four-thirds power; below the characteristic mass, the efficiency falls off at an average scaling of mass to the two-thirds power. By comparison, the shape and normalization of the efficiency change very little since z = 4. We show that a time-independent star formation efficiency simply explains the shape of the cosmic star formation rate since z = 4 in terms of dark matter accretion rates. The rise in the cosmic star formation from early times until z = 2 is especially sensitive to galaxy formation efficiency. The mass dependence of the efficiency strongly limits where most star formation occurs, with the result that two-thirds of all star formation has occurred inside halos within a factor of three of the characteristic mass, a range that includes the mass of the Milky Way.
Infrared thermal models for Saturn's ring

Infrared (10 and 20 microns) thermal emission data for Saturn's rings are discussed in terms of simple isothermal radiative transfer models of finite optical thickness. Recent brightness temperature measurements, corresponding to essentially maximum ring tilt, indicate that optical single scattering albedos less than 0.75 are required to provide sufficient heating of the ring material. Reconciliation with analyses of the optical scattering properties of the ring requires the backscattering efficiency to be even higher than for a macroscopic sphere. Historical brightness temperature measurements are used to show that no unique isothermal ring model exists. Instead, a temperature gradient perpendicular to the ring plane appears to be present.
Ground- and Excited-State Reactions of Norbornene and Isomers: A CASSCF Study and Comparison with Femtosecond Experiments

The ground-state and ^1(ππ^*)-state potential energy surfaces of norbornene and isomeric C_7H_(10) species were mapped using CASSCF theory and the 6-31G^* basis set and compared with the results of femtosecond experiments on norbornene retro Diels−Alder reactions. Computations explored stepwise and concerted retro Diels−Alder pathways, [1,3]-sigmatropic shifts, and [1,2]-sigmatropic shifts originating from the ^1(ππ^*)-state or ground-state surfaces. Extremely efficient decay occurs from the excited state to the ground state via two different conical intersections (surface crossings). The first of these crossing points is accessed by one-bond cleavage of C1−C6 (or C4−C5). Several possible subsequent ground-state reaction paths have been identified: (a) ring-closure to form norbornene; (b) ring-closure to form bicyclo[3.2.0]hept-2-ene ([1,3]-sigmatropic shift); (c) formation of a metastable 1,3-biradical which closes to form tricyclo[3.2.1.0^(3,7)]heptane ([1,2]-sigmatropic shift); and (d) collapse of a gauche-in biradical to a vibrationally excited cyclopentadiene and ethylene, or norbornene. Excited-state one-bond cleavage of C4−C7 (or C1−C7) leads to the second conical intersection. Possible ground-state reaction pathways from this structure lead to the formation of bicyclo[4.1.0]hept-2-ene ([1,3]-sigmatropic shift product) or to a second 1,3-biradical leading to tricyclo[3.2.1.0^(3,7)]heptane ([1,2]-sigmatropic shift product). The vibrationally excited cyclopentadiene is the 220 fs lifetime species of mass 66 amu, consistent with the retro Diels−Alder reaction observed in the femtosecond laser experiments. It is proposed that biradicaloids formed after decay through the conical intersections are the 94 amu species, with an average lifetime of about 160 fs.
Thermal instabilities in melt spinning of viscoelastic fibers

Abstract Nonisothermal melt spinning of viscoelastic fibers for which the viscosity varies in a step-like manner with respect to temperature is studied in this work. A set of one-dimensional equations based on the slender-jet approximation and the upper convected Maxwell model is used to describe the melt spinning process. The process is characterized by the force required to pull the fiber, the strength of external heating, and the draw ratio, the square of the ratio of the fiber diameter at the spinneret to that at the take-up roller. For low levels of elasticity and sufficiently strong external heating, there can be three pulling forces consistent with the same draw ratio, similar to the Newtonian case studied by Wylie et al. [31] . For higher levels of elasticity, the process exhibits a draw ratio plateau where the draw ratio hardly changes with the pulling force, reflecting a competition between thermal and elastic effects. As in the Newtonian case, external heating introduces a new instability – termed thermal instability – that is absent in isothermal systems. Linear stability analysis reveals that external heating improves stability for low levels of elasticity, but can worsen stability for higher levels of elasticity, which is again a consequence of the interplay between thermal and elastic effects. Nonlinear simulations indicate that the predictions of linear stability analysis carry over to the nonlinear regime, and show that unstable systems exhibit limit-cycle behavior. The results of the present work demonstrate a possible mechanism through which external heating can stabilize the melt spinning of viscoelastic fibers.
Leading coefficients of Kazhdan---Lusztig polynomials and fully commutative elements

Let W be a Coxeter group of type $\widetilde{A}_{n-1}$ . We show that the leading coefficient, μ(x,w), of the Kazhdan---Lusztig polynomial P x,w is always equal to 0 or 1 if x is fully commutative (and w is arbitrary).
Hurwitz ball quotients

We consider the analogue of Hurwitz curves, smooth projective curves $$C$$ of genus $$g \ge 2$$ that realize equality in the Hurwitz bound $$|{{\mathrm{Aut}}}(C)| \le 84 (g - 1)$$ , to smooth compact quotients $$S$$ of the unit ball in $$\mathbb C^2$$ . When $$S$$ is arithmetic, we show that $$|{{\mathrm{Aut}}}(S)| \le 288 e(S)$$ , where $$e(S)$$ is the (topological) Euler characteristic, and in the case of equality show that $$S$$ is a regular cover of a particular Deligne–Mostow orbifold. We conjecture that this inequality holds independent of arithmeticity, and note that work of Xiao makes progress on this conjecture and implies the best-known lower bound for the volume of a complex hyperbolic $$2$$ -orbifold.
A remark on serial correlation in maximum likelihood

Abstract Maximum likelihood estimation can be consistent and asymptotically normal despite serial correlation in the residuals. The usual estimator of the asymptotic covariance of the parameter estimator is inconsistent, but an alternative consistent estimator is derived.
Ionic Conduction and Applications

Solid state ionic conductors are crucial to a number of major technological developments, notably in the domains of energy storage and conversion and in environmental monitoring (such as battery, fuel cell and sensor technologies). Solid state ionic membranes based on fast ion conductors potentially provide important advantages over liquid electrolytes, including the elimination of sealing problems improved stability and the ability to miniaturize electrochemical devices using thin films. This chapter reviews methods of optimizing ionic conduction in solids and controlling the ratio of ionic to electronic conductivity in mixed conductors. Materials are distinguished based on whether they are characterized by intrinsic versus extrinsic disorder, amorphous versus crystalline structure, bulk versus interfacial control, cation versus anion conduction and ionic versus mixed ionic–electronic conduction. Data for representative conductors are tabulated.
Existence, uniqueness, and quenching properties of solutions for degenerate semilinear parabolic problems with second boundary conditions

Let q⩾0, p⩾0, T⩽∞, D=(0,a), D¯=[0,a], Ω=D×(0,T), and Lu=xqut−uxx. This article considers the following degenerate semilinear parabolic initial-boundary value problem, Lu=xpf(u)in Ω, u(x,0)=0on D¯, ux(0,t)=0=ux(a,t)for t>0, where f(0)>0, f′>0, f″⩾0, and limu→c−f(u)=∞ for some positive constant c. Existence of a unique classical solution is proved. It is shown that if p>q, then quenching occurs only at the boundary point x=a while if p<q, then the only quenching point is x=0. If p=q, then the quenching set is D¯.
Two-dimensional packing problems using genetic algorithms

This paper presents a technique for applying genetic algorithms for the two-dimensional packing problem. The approach is applicable to not only convex shaped objects, but can also accommodate any type of concave and complex shaped objects including objects with holes. In this approach, a new concept of a two-dimensional genetic chromosome is introduced. The total layout space is divided into a finite number of cells for mapping it into this 2D genetic algorithm chromosome. The mutation and crossover operators have been modified and are applied in conjunction with connectivity analysis for the objects to reduce the creation of faulty generations. A new feature has been added to the Genetic Algorithm (GA) in the form of a new operator called compaction. Several examples of GA-based layout are presented.
Sticky Places in Slippery Space: A Typology of Industrial Districts*

AbstractAs advances in transportation and information obliterate distance, cities and regions face a tougher time anchoring income-generating activities. In probing the conditions under which some manage to remain “sticky” places in “slippery” space, this paper rejects the “new industrial district,” in either its Marshallian or more recent Italianate form, as the dominant paradigmatic solution. I identify three additional types of industrial districts, with quite disparate firm configurations, internal versus external orientations, and governance structures: a hub-and-spoke industrial district, revolving around one or more dominant, externally oriented firms; a satellite platform, an assemblage of unconnected branch plants embedded in external organization links; and the state-anchored district, focused on one or more public-sector institutions. The strengths and weaknesses of each are reviewed. The hub-and-spoke and satellite platform variants are argued to be more prominent in the United States than the...
A modified magnitude system that produces well-behaved magnitudes, colors, and errors even for low signal-to-noise ratio measurements

We describe a modification of the usual definition of astronomical magnitudes, replacing the usual logarithm with an inverse hyperbolic sine function; we call these modified magnitudes asinh magnitudes. For objects detected at signal-to-noise ratios of greater than about 5, our modified definition is essentially identical to the traditional one; for fainter objects (including those with a formally negative flux), our definition is well behaved, tending to a definite value with finite errors as the flux goes to zero. This new definition is especially useful when considering the colors of faint objects, as the difference of two asinh magnitudes measures the usual flux ratio for bright objects, while avoiding the problems caused by dividing two very uncertain values for faint objects. The Sloan Digital Sky Survey data products will use this scheme to express all magnitudes in their catalogs.