cssi/SciSciGPT-SciSciNet huggingface dataset:
Rate-limited EAFRP-a new improved model for high-speed network traffic

The Extended Alternating Fractal Renewal Process (EAFRP) model has recently been proposed for modeling the self-similar and impulsive traffic of high-speed networks. For mathematical simplicity, it assumes that the available transmission bandwidth in the network is infinite. In reality, the network has a limit R on the total traffic rate through it, and in addition, the ith user's traffic rate is often limited to special value L/sub i/, which is assigned by the bandwidth sharing protocol. We propose a model for single-user traffic, which, by taking into account the aforementioned rate limit L/sub i/ and R, and in the absence of congestion, provides insight on the distinctive two slope behavior of the loglog survival function of multiuser traffic. For small to medium number of users, such as in local area networks (LANs), the model results in non-Gaussian traffic, whereas as the number of users increases, the resulting traffic is Gaussian, both of which are consistent with real network measurements. We discuss model parameter estimation, provide queuing analysis of the multiple-user traffic model, and, based on real data, show that it achieves a closer approximation of the observed reality than existing models.
Spectroscopic determination of the s-wave scattering length of lithium.

Two-photon photoassociation of colliding ultracold ${}^{7}$Li atoms is used to probe the $^{3}\ensuremath{\Sigma}_{u}^{+}(a)$ ground state of ${}^{7}$L${\mathrm{i}}_{2}$. The binding energy of the least-bound state of this triplet potential, $\ensuremath{\upsilon}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}10$, is found to be $12.47\ifmmode\pm\else\textpm\fi{}0.04$ GHz. This spectroscopic information establishes that the $s$-wave scattering length for ${}^{7}$Li atoms in the $F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$, ${m}_{F}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$ state is $(\ensuremath{-}27.3\ifmmode\pm\else\textpm\fi{}0.8){a}_{0}$. The negative sign of the scattering length has important implications as to whether atoms at this doubly spin-polarized state can undergo a Bose-Einstein condensation.
Kuiper Belt Object Sizes and Distances from Occultation Observations

There are several observational campaigns underway to detect kilometer-sized foreground Kuiper belt objects (KBOs) through their occultation of background stars. The interpretation of an occultation light curve, unfortunately, is affected by a geometric degeneracy such that one is unable to determine the KBO size independently of its distance. This degeneracy can be broken through a precise measurement of the relative velocity obtained from simultaneous observations of individual events. While an array of telescopes spread over an area of few square kilometers can be employed, it is unlikely that the relative velocity can be measured to the required accuracy to help break this geometric degeneracy. The presence of diffraction fringes in KBO occultation light curves, when projected sizes of occulted stars are smaller than the Fresnel scale, improves determination of size and distance significantly. In this regard, we discuss the potential role of a dedicated satellite mission for KBO occultation observations. If dwarf stars at the V-band magnitudes of 14 and fainter can be monitored at time intervals of 0.1 s with normalized flux errors at the level of 1%, the occultation observations will allow individual KBO sizes and distances to be determined at the level of a few percent or better.
Synthesis and confirmation of the absolute stereochemistry of the (-)-aflastatin A C9-C27 degradation polyol.

The C8−C18 ethyl ketone and C19−C28 aldehyde aflastatin A fragments were synthesized and coupled using a diastereoselective anti aldol reaction. This adduct was successfully converted into the C9−C27 polyol degradation product of (−)-aflastatin A to confirm the relative and absolute stereochemistry of this region of the natural product.
What Happens When Firms Patent? New Evidence from U.S. Economic Census Data

Abstract We build a new concordance between the NBER Patent Data and U.S. Census microdata and use it to examine what happens when firms patent. We find strong evidence that increases in patent stock are associated with increases in firm size, scope, and skill and capital intensity. We find somewhat weaker evidence that changes in patenting are positively correlated with changes in total factor productivity. We also analyze first-time patentees and find similar effects following initial patent application. Together, these results suggest that patenting is indeed associated with real changes within firms, in particular with growth through increases in scope.
A pseudo-algorithmic separation of lines from pseudo-lines

S = fxij : i < jg be the set of the x-coordinates of the vertices i \ j of the collection. L induces a decomposition of the plane into regions bounded by edges and vertices. This decomposition, A(L), is called the arrangement of the pseudo-lines. It is known that pseudo-line arrangements have a richer combinatorial structure than arrangements of lines: the number of combinatorially di erent pseudo-line arrangements is much larger than the number of line arrangements, as shown by Goodman and Pollack [6].
Wave motion and vortex breakdown.

Vortex breakdown in rotating fluids associated with wave motion along axis of rotation, considering effects of nonzero wave amplitude
Enantioselective ProPhenol-Catalyzed Addition of 1,3-Diynes to Aldehydes to Generate Synthetically Versatile Building Blocks and Diyne Natural Products

A highly enantioselective method for the catalytic addition of terminal 1,3-diynes to aldehydes was developed using our dinuclear zinc ProPhenol (1) system. Furthermore, triphenylphosphine oxide was found to interact synergistically with the catalyst to substantially enhance the chiral recognition. The generality of this catalytic transformation was demonstrated with aryl, α,β-unsaturated and saturated aldehydes, of which the latter were previously limited in alkynyl zinc additions. The chiral diynol products are also versatile building blocks that can be readily elaborated; this was illustrated through highly selective trans-hydrosilylations, which enabled the synthesis of a β-hydroxyketone and enyne. Additionally, the development of this method allowed for the rapid total syntheses of several biologically important diynol-containing natural products.
Actin Capping Protein Is Required for Dendritic Spine Development and Synapse Formation

Dendritic spines serve as the postsynaptic platform for most excitatory synapses in the mammalian brain, and their shape and size are tightly correlated with synaptic strength. The actin cytoskeleton plays a crucial role in the spine structure and its modifications during synapse development and plasticity, but the underlying regulatory mechanisms remain to be elucidated. Here, we report that actin capping protein (CP), a regulator of actin filament growth, plays an essential role for spine development and synapse formation. We found that CP expression in rat hippocampus is elevated at and after the stage of substantial synapse formation. CP knockdown in hippocampal cultures resulted in a marked decline in spine density accompanied by increased filopodia-like protrusions. Moreover, the spines of CP knockdown neurons exhibited an altered morphology, highlighted by multiple thin filopodia-like protrusions emerging from the spine head. Finally, the number of functional synapses was reduced by CP knockdown as evidenced by a reduction in the density of paired presynaptic and postsynaptic markers and in the frequency of miniature EPSCs. These findings indicate that capping of actin filaments by CP represents an essential step for the remodeling of the actin architecture underlying spine morphogenesis and synaptic formation during development.
Traveltime calculation and prestack depth migration in tilted transversely isotropic media

The principal objective of our work is to develop a technique for prestack depth migration in tilted transversely isotropic (TTI) media in which the axis of symmetry is not vertical and may be spatially varying. Such models are required to image seismic data in geologically complex regions such as the Canadian Foothills. We have developed a 2D Kirchhoff integral-based migration algorithm in which the traveltime computation comprises the major task. Among the existing traveltime computation algorithms such as ray tracing with interpolation, ray bending, and eikonal solvers, a direct or a brute force approach of traveltime computation is generally highly robust. We have modified a direct method of first-arrival P-wave traveltime computation in 2D media that accounts for TTI. The algorithm requires that the group velocity be computed at each gridpoint, using either an analytic solution or by an approximate Fourier series expansion. The P-wave traveltime contours computed for complex geologic models show the pronounced effects from TTI media. Our results, using laboratory P-wave data collected over a physical model of an anisotropic thrust sheet, reveal that a 2D Kirchhoff migration based on our traveltime algorithm (TTI model) images the structure beneath the thrust sheet very well. The vertical transversely isotropic (assuming a vertical axis of symmetry) or isotropic imaging introduces false anticlinal structures. We compare our results with those obtained by a recursive-extrapolation method and find that our approach images the underside of one of the thrust sheets better.
Total synthesis of the germacranolide (±)-aristolactone via [2,3] wittig ring contraction

Abstract The total synthesis of (±)-aristolactone (15) is described wherein the key cyclodecenynol precursor 10 is prepared in over 90% yield via a highly regio and stereoselective [2,3] Wittig rearrangement of the 13-membered propargylic ether 9 .
The design and combustion performance of practical swirlers for integral rocket/ramjets

A method was devised for the design and fabrication of swirl inlet hardware with practical application to the integral rocket/ramjet dump combustor. A total of seven swirl inserts were tested to determine the effects of different swirl profiles on combustor performance. Combustor length-to-diameter ratio (LC/D) was varied between 1.5 and 3, and the ratio of the nozzle throat to combustor area (A*/A3) between 40 and 60%. Combustor wall static distributions were measured in all configurations in which LC/D = 3. Airflow immediately downstream of the swirler was probed in cold flow to determine actual swirl angles to compare with prediction. Combustion instability data was recorded for subsequent spectral analysis by fast Fourier transform.
CRIPPLED CAPITALISTS: THE INSCRIPTION OF ECONOMIC DEPENDENCE AND THE CHALLENGE OF FEMALE ENTREPRENEURSHIP IN NINETEENTH-CENTURY AMERICA

Abstract This article examines how women's efforts at capital accumulation and wealth production in late nineteenth-century United States were shaped and channeled by gender stereotypes. These stereotypes influenced the public attitudes held by both men and women that called into question women's financial capabilities, their relationship to money and the financial markets, and their capacity to translate their wealth into political power. Popular American ideals about an individual's ability to make and remake himself or herself competed with equally significant essentialist ideas about what constitutes a man and a woman. While women achieved gains, they did so despite huge challenges that limited their ability to exercise the power Americans commonly associate with financial success.
Planned Obsolescence and the R&D Decision

By investing in RD i.e., the R&D choice that maximizes current profitability does not maximize overall profitability. The result is that if output is sold rather than rented, then in its R&D decision the monopolist has an incentive to practice a type of planned obsolescence that lowers its own profitability.
Commuting self-adjoint extensions of symmetric operators defined from the partial derivatives

We consider the problem of finding commuting self-adjoint extensions of the partial derivatives {(1/i)(∂/∂xj):j=1,…,d} with domain Cc∞(Ω) where the self-adjointness is defined relative to L2(Ω), and Ω is a given open subset of Rd. The measure on Ω is Lebesgue measure on Rd restricted to Ω. The problem originates with Segal and Fuglede, and is difficult in general. In this paper, we provide a representation-theoretic answer in the special case when Ω=I×Ω2 and I is an open interval. We then apply the results to the case when Ω is a d cube, Id, and we describe possible subsets Λ⊂Rd such that {eλ|Id:λ∈Λ} is an orthonormal basis in L2(Id).
Superconductivity of Bi Confined in an Opal Host

Superconductivity is observed in a composite of rhombohedral crystalline bismuth nanoparticles imbedded in an insulating porous opal host via electrical transport and AC magnetic susceptibility. The onset of superconductivity in this system occurs in two steps, with upper transition temperature T c,U =4.1 K and lower transition temperature of T c,L =0.7 K, which we attribute to the granular nature of the composite. The transition at T c,U is observed to split into two transitions with the application of a magnetic field, and these have upper critical fields extrapolated to T=0 K of H c2,1(0)=0.7 T and H c2,2(0)=1.0 T, corresponding to coherence lengths of ξ 1(0)=21 nm and ξ 2(0)=18 nm, respectively. We suggest that because of the lack of bulk-like states in the Bi nanoparticles due to confinement effects, superconductivity originates from surface states arising from Rashba spin-orbit scattering at the interface.
Facile Stereoselective Syntheses of Four of the Six 1, 2, 3, 4-Cyclohexanetetrols: Increasing the Accessibility of Cyclitols for Probing the Molecular Recognition of Saccharides

Abstract New and stereoselective syntheses of (1,2,3/4)-, (1,2/3,4)-, (1,4/2,3)-, and (1,2,4/3)-cyclohexanetetrols (1, 2, 3, and 4 respectively) are described. The known syn and anti 1,4-cyclohex-2-enediols 9 and 10 were used as starting materials. Diols 9 and 10 were allow to react with OsO4 to directly form 3 and 1 respectively. Diols 9 and 10 were epoxidized with MCPBA, which yielded 4 and 2 after acid catalyzed epoxide opening.
Anomalous temperature dependence of the lattice parameters in HoPO4 and HoVO4: rare earth quadrupolar effects

Abstract The temperature dependencies of the lattice parameters in tetragonal HoPO 4 and HoVO 4 were measured using neutron powder diffraction techniques. Below about 100 K, the lattice parameter a of HoPO 4 increases with decreasing temperature while c decreases. In HoVO 4 , the above behaviour is reversed, that is a decreases with decreasing temperature while c increases. Similar measurements on non-magnetic LuPO 4 and LuVO 4 do not show any anomaly. This observation indicates that the unusual temperature dependence of the lattice constants is magnetic in origin. The observed effect can be explained in terms of an Ho 3+ quadrupole interaction with the crystalline lattice. In particular, the calculated electronically generated quadrupole moment of Ho 3+ in HoPO 4 and HoVO 4 exhibits a temperature dependence similar to that observed for the lattice parameters.
The Formation of Islam: Religion and Society in the Near East, 600-1800

Jonathan Berkey's 2003 book surveys the religious history of the peoples of the Near East from roughly 600 to 1800 CE. The opening chapter examines the religious scene in the Near East in late antiquity, and the religious traditions which preceded Islam. Subsequent chapters investigate Islam's first century and the beginnings of its own traditions, the 'classical' period from the accession of the Abbasids to the rise of the Buyid amirs, and thereafter the emergence of new forms of Islam in the middle period. Throughout, close attention is paid to the experiences of Jews and Christians, as well as Muslims. The book stresses that Islam did not appear all at once, but emerged slowly, as part of a prolonged process whereby it was differentiated from other religious traditions and, indeed, that much that we take as characteristic of Islam is in fact the product of the medieval period.
Thermal dilepton radiation at intermediate masses at the CERN - SPS

We investigate the significance of thermal dilepton radiation in the intermediate-mass region in heavy-ion reactions at CERN-SpS energies. Within a thermal fireball model for the space-time evolution, the radiation from hot matter is found to dominate over hard 'background' processes (Drell–Yan and open charm) up to invariant masses of about 2 GeV, with a moderate fraction emerging from early stages with temperatures T≃175–200 MeV associated with deconfined matter. Further including a schematic acceptance for the NA50 experiment we find good agreement with the observed enhancement in the region 1.5 GeV <Mμμ< 3 GeV. In particular, there is no need to invoke any anomalous open charm enhancement.
Differential Equations for Dyson Processes

We call a Dyson process any process on ensembles of matrices in which the entries undergo diffusion. We are interested in the distribution of the eigenvalues (or singular values) of such matrices. In the original Dyson process it was the ensemble of n×n Hermitian matrices, and the eigenvalues describe n curves. Given sets X1,...,X m the probability that for each k no curve passes through X k at time τ k is given by the Fredholm determinant of a certain matrix kernel, the extended Hermite kernel. For this reason we call this Dyson process the Hermite process. Similarly, when the entries of a complex matrix undergo diffusion we call the evolution of its singular values the Laguerre process, for which there is a corresponding extended Laguerre kernel. Scaling the Hermite process at the edge leads to the Airy process (which was introduced by Prahofer and Spohn as the limiting stationary process for a polynuclear growth model) and in the bulk to the sine process; scaling the Laguerre process at the edge leads to the Bessel process. In earlier work the authors found a system of ordinary differential equations with independent variable ξ whose solution determined the probabilities where τ→A(τ) denotes the top curve of the Airy process. Our first result is a generalization and strengthening of this. We assume that each X k is a finite union of intervals and find a system of partial differential equations, with the end-points of the intervals of the X k as independent variables, whose solution determines the probability that for each k no curve passes through X k at time τ k . Then we find the analogous systems for the Hermite process (which is more complicated) and also for the sine process. Finally we find an analogous system of PDEs for the Bessel process, which is the most difficult.
The distribution of Voronoi cells generated by Southern California earthquake epicenters

Author(s): Frederic Paik Schoenberg; Christopher Barr; Jungju Seo | Abstract: Fractional factorial designs are widely used in practice and typically chosen according to the minimum aberration criterion. A sequential algorithm is developed for constructing efficient fractional factorial designs. A construction procedure is proposed that only allows a design to be constructed from its minimum aberration pro jection in the sequential build-up process. To efficiently identify nonisomorphic designs, designs are divided into different categories according to their moment pro jection patterns. A fast isomorphism check procedure is developed by matching the factors using their delete-one-factor pro jections. A method is proposed for constructing minimum aberration designs using only a partial catalog of some good designs. Minimum aberration designs are constructed for 128 runs up to 64 factors, 256 runs up to 28 factors, and 512, 1024, 2048, and 4096 runs up to 23 or 24 factors. Furthermore, this algorithm is used to completely enumerate all 128-run designs of resolution 4 up to 30 factors, all 256-run designs of resolution 4 up to 17 factors, all 512-run designs of resolution 5, all 1024-run designs of resolution 6, and all 2048- and 4096-run designs of resolution 7.
A Note on Jacobians, Tutte Polynomials, and Two-Variable Zeta Functions of Graphs

We address questions posed by Lorenzini about relations between Jacobians, Tutte polynomials, and the Brill–Noether theory of finite graphs, as encoded in his two-variable zeta functions. In particular, we give examples showing that none of these invariants is determined by the other two.
Bayesian analysis of many-pole fits of hadron propagators in lattice QCD

Abstract We use Bayes' probability theorem to analyze many-pole fits of hadron propagators. An alternative method of estimating values and uncertainties of the fit parameters is offered, which has certain advantages over the conventional methods. The probability distribution of the parameters of a fit is calculated. The relative probability of various models is calculated.
Initial Investigation of the Acoustics of a Counter-Rotating Open Rotor Model with Historical Baseline Blades in a Low-Speed Wind Tunnel

A counter-rotating open rotor scale model was tested in the NASA Glenn Research Center 9- by 15-Foot Low-Speed Wind Tunnel (LSWT). This model used a historical baseline blade set with which modern blade designs will be compared against on an acoustic and aerodynamic performance basis. Different blade pitch angles simulating approach and takeoff conditions were tested, along with angle-of-attack configurations. A configuration was also tested in order to determine the acoustic effects of a pylon. The shaft speed was varied for each configuration in order to get data over a range of operability. The freestream Mach number was also varied for some configurations. Sideline acoustic data were taken for each of these test configurations.
Very Slow Cooling Dynamics of Photoexcited Carriers in Graphene Observed by Optical-Pump Terahertz-Probe Spectroscopy

Using optical-pump terahertz-probe spectroscopy, we study the relaxation dynamics of photoexcited carriers in graphene at different substrate temperatures. We find that at lower temperatures the tail of the relaxation transients measured by the differential probe transmission become slower, extending beyond several hundred picoseconds below 50 K. We interpret the observed relaxation transients as resulting from the cooling of the photoexcited carriers via phonon emission. The slow cooling of the photoexcited carriers at low temperatures is attributed to the bulk of the electron and hole energy distributions moving close enough to the Dirac point that both intraband and interband scattering of carriers via optical phonon emission become inefficient for removing heat from the carriers. Our model, which includes intraband carrier scattering and interband carrier recombination and generation, agrees very well with the experimental observations.
Business Ethics-Intuition or Logic?

Business has come under increasing pressure to set standards for ethical behavior. As a result many companies have set up rules for what is ethi cal or unethical. This article points out that the ethical crisis we face can only be solved by studying ethics from an historical and cultural perspec tive. With a firm philosophical basis in ethics, businessmen will be able to communicate their position on controversial issues more effectively.
Stability theory as a guide to the evaluation of transition data.

Dimensional analysis indicates that, in addition to the usual factors affecting transition, important additional parameters are a dimensionless frequency pv/U or wavelength U\/v and an orientation (0), which are characteristic of the initial disturbance spectrum. It is shown that the dependence on dimensionless wavelength can account for what has so far been regarded as a "unit Reynolds number" effect. Further, it is shown how these parameters can help in the orderly sorting out of transition results from different ground test facilities. The relation of these parameters to the predictability of transition in free flight is discussed.
Internal versus external economies in European industry

Abstract This paper presents estimates of indexes of internal returns to scale and external economies for two-digit manufacturing industries in the four European countries for which the requisite data are available in adequate length: West Germany, France, the U.K., and Belgium. Overall, we find very little evidence of internal increasing returns to scale: of the thirteen two-digit industries, only Rubber and Plastic Products, Agricultural and Industrial Machinery, and Mineral Products exhibit any significant internal increasing returns to scale, and for none of the three is internal increasing returns present in more than two of the four countries. Evidence of external economies, on the other hand, exists for all four countries, the effects of which are especially strong in France and Belgium.
Thiazole-diamides as potent γ-secretase inhibitors

Abstract The thiazole-diamide series (1) has been identified as highly potent γ-secretase inhibitors. Several representative compounds showed IC50 values of
1,3-Dioxolan-2-ylium cations from acylfurans: Conversion of furyl ketones to esters under nonoxidative conditions

Acylfurans 3 furnished tosylated glycol monoesters 5 when treated with 1,2-diols in the presence of an equivalent of TsOH. This process likely occurs via protiodefuranation of the intermediate furyl ketals to form 1,3-dioxolan-2-ylium cations 8. Subsequent ring-opening via SN2 nucleophilic displacement by p-toluenesulfonate then provides esters 5. When a 1,3-diol was employed, furan-containing ester 9 was formed instead of the standard product through an apparent aldol dimerization/fragmentation pathway.
Study of equilibrium air total radiation.

Equilibrium air total radiation mechanism, vacuum UV radiation and relation to hypervelocity entry studied, using shock tube blunt model test flow
Practical Issues in Estimating Achievement Gaps From Coarsened Data

In an earlier paper, we presented methods for estimating achievement gaps when test scores are coarsened into a small number of ordered categories, preventing fine-grained distinctions between individual scores. We demonstrated that gaps can nonetheless be estimated with minimal bias across a broad range of simulated and real coarsened data scenarios. In this article, we extend this previous work to obtain practical estimates of the imprecision imparted by the coarsening process and of the bias imparted by measurement error. In the first part of this article, we derive standard error estimates and demonstrate that coarsening leads to only very modest increases in standard errors under a wide range of conditions. In the second part of this article, we describe and evaluate a practical method for disattenuating gap estimates to account for bias due to measurement error.
The physical significance of singularities in the Chern-Simons Fermi liquid description of a partially filled Landau level

We analyze the linear response of a half-filled Landau level to long wavelength and low-frequency driving forces, using Fermi liquid theory for composite fermions. This response is determined by the composite fermions quasi-particle effective mass quasi-particle effective m* and quasi-particle Landau interaction function f(θ − θ′). Analyzing infrared divergences of perturbation theory, we obtain an exact expression for m*, and conjecture the form of f(θ − θ′). We then conclude that in the limit of infinite cyclotron frequency, and small q,ω, the composite fermion excitation spectrum is continuous for ΩHHx, with γ an unknown number. For fractional quantum Hall states near a half-filled Landau level, we derive an exact expression for the energy gap.
Acceptor substrate-based selective inhibition of galactosyltransferases

Abstract This paper describes the discovery of glycosyl acceptor analogs as potent and selective inhibitors of α-1,3- and β-1,4-galactosyltransferases. Incorporation of an appropriate aromatic group to the aglycon position of the enzyme's acceptors results in a strong inhibition, representing the first and most potent small uncharged molecules as selective inhibitors of these two enzymes and thus providing a new strategy for the development of selective glycosyltransferase inhibitors.
Effects of Counterflow on the Aeroacoustic Properties of a Supersonic Jet

The influence of counterflow on the mixing and acoustic characteristics of a Mach 1.4 rectangular jet operated at on- and off-design conditions were studied experimentally for different levels of counterflow. The results show that counterflow significantly enhances shear-layer mixing and reduces the jet potential core length under all operating conditions. Significant changes in both shock-cell spacing and strength were ohserved when counterflow was applied to nonideally expanded jets. Consequently, screech tones were either reduced or totally eliminated, and broadband shock-associated noise was shifted to higher frequencies. In the underexpanded mode, a Mach disk was formed at certain levels of counterflow, which substantially weakened the subsequent periodic shock-cell structure and reduced the broadband shock-associated noise and the overall sound pressure level (OASPL) by as much as 3 dB. Interestingly, it was also discovered that a jet operating at overexpanded conditions could be decelerated nearly isentropically by applying the proper amount of counterflow. This modification led to a 4 dB reduction in OASPL. Based on the present study, it is suggested that counterflow warrants further investigation as a potential noise reduction technique.
Bäcklund transformations for Darboux integrable differential systems

The purpose of this paper is to present a novel group-theoretic method for constructing Backlund transformations between systems of differential equations. Our approach is based upon the definition of Backlund transformations as integrable extensions of exterior differential systems. The construction of these transformations is obtained using the general theory of symmetry reduction of differential systems. Our method is then applied to differential systems which are integrable by the method of Darboux, and a detailed understanding of the Backlund transformations for these systems is obtained.
Ion-induced damage and amorphization in Si

Abstract Ion-induced damage growth in high-energy, self-ion irradiated Si was studied using electron microscopy and Rutherford backscattering spectrometry. The results show that there is a marked variation in the rate of damage growth, as well as the damage morphology, along the path of the ion. Near the ion end-of-range (eor), damage increases monotonically with ion fluence until a buried amorphous layer is formed, while damage growth saturates at a low level in the region ahead. Damage growth remains saturated ahead of the eor until expansion of the buried amorphous layer encroaches into the region. The morphology of the damage in the saturated region is shown to consist predominantly of simple defect clusters such as the divacancy. A homogeneous nucleation and growth model, presented to account for damage saturation, is shown to also predict the dose-rate dependence of the saturation level. Mechanisms are identified which contribute to the unconstrained damage growth observed near the eor prior to amorphization, and subsequently at the interface of the buried amorphous layer. The effects of an imbalance in the generation rates of interstitials and vacancies on damage growth in the eor region are discussed. This imbalance is shown to arise either as a result of added atoms during implantation or spatial separation of the Frenkel defect pairs created during ion impact. A local, uniaxial strain field in the interfacial region of the amorphous layer is identified, and the possibility of its contribution to growth at that location is discussed.
Stability of Standing Accretion Shocks, with an Eye toward Core-Collapse Supernovae

We examine the stability of standing, spherical accretion shocks. Accretion shocks arise in core-collapse supernovae (the focus of this paper), star formation, and accreting white dwarfs and neutron stars. We present a simple analytic model and use time-dependent hydrodynamics simulations to show that this solution is stable to radial perturbations. In two dimensions we show that small perturbations to a spherical shock front can lead to rapid growth of turbulence behind the shock, driven by the injection of vorticity from the now nonspherical shock. We discuss the ramifications this instability may have for the supernova mechanism.
An image processing approach to computer graphics

Abstract Computer graphics was conceived as, and remains for the most part, a line-drawing phenomenon. The cautious management of display lists or of in-line vector generators has captured most of the attention of researchers in computer graphics. Cathode ray tubes with randomly positionable beams have served as the primary medium for this research and development. The underlying position of this paper is that the future of computer graphics does not lie in ‘vectored’ displays but in raster scan television, conceivably as we know it in our homes. This posture is motivated by arguments of cost and compatibility, but the most salient motivation comes in view of the ubiquitous nature of raster scan display technologies. This paper explains a way to implement an image processing approach to computer graphics, one that is conceptually straightforward and, in terms of hardware, fairly easy to design. A device is being built that encompases as much as is known about raster scan, multi-bit per point displays. The work described is conducted, principally, to produce a multi-bit per point graphics output device that dynamically shares its image storage with the memory space of an expanded mini-computer.
The abstruse meets the applicable: Some aspects of time-frequency analysis

The area of Fourier analysis connected to signal processing theory has undergone a rapid development in the last two decades. The aspect of this development that has received the most publicity is the theory of wavelets and their relatives, which involves expansions in terms of sets of functions generated from a single function by translations and dilations. However, there has also been much progress in the related area known astime-frequency analysis orGabor analysis, which involves expansions in terms of sets of functions generated from a single function by translations and modulations. In this area there are some questions of a concrete and practical nature whose study reveals connections with aspects of harmonic and functional analysis that were previously considered quite pure and perhaps rather exotic. In this expository paper, I give a survey of some of these interactions between the abstruse and the applicable. It is based on the thematic lectures which I gave at the Ninth Discussion Meeting on Harmonic Analysis at the Harish-Chandra Research Institute in Allahabad in October 2005.
Synthesis and characterization of dinucleoside phosphorodithioates

Abstract Dinucleoside phosphoramidites, H 2 S, and tetrazole react to form dinucleoside H-phosphonothioates. Oxidation with sulfur yields phosphorodithioates. Iodine oxidation in the presence of amines, alcohols, or water yields phosphorothioamidates, thiotriesters or thiodiesters.
Aerogel keystones: Extraction of complete hypervelocity impact events from aerogel collectors

In January 2006, the Stardust mission will return the first samples from a solid solar system body beyond the Moon and the first samples of contemporary interstellar dust ever collected. Although sophisticated laboratory instruments exist for the analysis of Stardust samples, techniques for the recovery of particles and particle residues from aerogel collectors remain primitive. Here, we describe our recent progress in developing techniques for extracting small volumes of aerogel, which we have called "keystones," which completely contain particle impacts but minimize the damage to the surrounding aerogel collector. These keystones can be fixed to custom-designed micromachined silicon fixtures (so called "microforklifts"). In this configuration, the samples are self-supporting, which can be advantageous in situations where interference from a supporting substrate is undesirable. The keystones may also be extracted and placed onto a substrate without a fixture. We have also demonstrated the capability of homologously crushing these unmounted keystones for analysis techniques that demand flat samples.
Enumeration schemes for vincular patterns

We extend the notion of an enumeration scheme developed by Zeilberger and Vatter to the case of vincular patterns (also called ''generalized patterns'' or ''dashed patterns''). In particular we provide an algorithm which takes in as input a set B of vincular patterns and search parameters and returns a recurrence (called a ''scheme'') to compute the number of permutations of length n avoiding B or confirmation that no such scheme exists within the search parameters. We also prove that if B contains only consecutive patterns and patterns of the form @s"[email protected]"[email protected]"t"-"[email protected]"t, then such a scheme must exist and provide the relevant search parameters. The algorithms are implemented in Maple and we provide empirical data on the number of small pattern sets admitting schemes. We make several conjectures on Wilf-classification based on this data. We also outline how to refine schemes to compute the number of B-avoiding permutations of length n with k inversions.
Interest-group politics under majority rule

Abstract We develop a model of interest-group politics in which the groups and coalitions that arise, and the form of redistributive policies sought, are jointly determined. The model generates three key results. First, programs intended to reduce income inequality are more likely to involve direct payments than are programs that redistribute wealth across groups with similar incomes. Second, nonequalizing redistribution is unlikely unless the various participants in the political process face significantly different political and economic costs of obtaining transfers. Third, many policies that induce asymmetries among interest groups also impose significant deadweight costs. Stable nonequalizing redistribution will therefore tend to involve indirect and economically inefficient methods of transferring income.
Trading Tasks: A Simple Theory of Offshoring

The nature of international trade is changing. For centuries, trade mostly entailed an exchange of goods . Now it increasingly involves bits of value being added in many different locations, or what might be called trade in tasks . Revolutionary advances in transportation and communications technology have weakened the link between labor specialization and geographic concentration, making it increasingly viable to separate tasks in time and space. When instructions can be delivered instantaneously, components and unfinished goods can be moved quickly and cheaply, and the output of many tasks can be conveyed electronically, firms can take advantage of factor cost disparities in different countries without sacrificing the gains from specialization. The result has been a boom in “offshoring” of both manufacturing tasks and other business functions. 1 In this paper, we develop a simple and tractable model of offshoring based on the trade able tasks. We conceptualize production in terms of the many tasks that must be performed by each factor of production. A firm can perform each of the continuum of tasks required for the realization of its product either in close proximity to its headquarters or at an offshore location. Offshoring may be attractive, if some factors can be hired more cheaply abroad than at home, but it also is costly, because remote performance of a task limits the opportunities for monitoring and coordinating workers. 2 To capture this aspect of reality, our model features heterogeneous offshoring costs for the various tasks. In each industry, firms choose the geographic organization
Velocity structure of self-similar spherically collapsed halos

Using a generalized self-similar secondary infall model, which accounts for tidal torques acting on the halo, we analyze the velocity profiles of halos in order to gain intuition for N-body simulation results. We analytically calculate the asymptotic behavior of the internal radial and tangential kinetic energy profiles in different radial regimes. We then numerically compute the velocity anisotropy and pseudo--phase-space density profiles and compare them to recent N-body simulations. For cosmological initial conditions, we find both numerically and analytically that the anisotropy profile asymptotes at small radii to a constant set by model parameters. It rises on intermediate scales as the velocity dispersion becomes more radially dominated and then drops off at radii larger than the virial radius where the radial velocity dispersion vanishes in our model. The pseudo--phase-space density is universal on intermediate and large scales. However, its asymptotic slope on small scales depends on the halo mass and on how mass shells are torqued after turnaround. The results largely confirm N-body simulations but show some differences that are likely due to our assumption of a one-dimensional phase space manifold.
Comparative electronic band structure study of the intrachain ferromagnetic versus antiferromagnetic coupling in the magnetic oxides Ca3Co2O6 and Ca3FeRhO6.

In the (MM‘O6)∞ chains of the transition-metal magnetic oxides Ca3MM‘O6 the MO6 trigonal prisms alternate with the M‘O6 octahedra by sharing their triangular faces. In the (Co2O6)∞ chains of Ca3Co2...
Transition from columnar to point pinning in coated conductors: critical currents that are independent of magnetic field direction

We identify a sharp crossover in the vortex pinning of a high-temperature superconductor with nanocolumnar stacks of precipitates as strong vortex pinning centers. Above a particular, temperature-dependent field BX(T) the vortex response is no longer determined by the nanocolumns, and is instead determined by point-like pinning. This crossover is evident as a change in the dependence of the critical current density on the angle between the applied magnetic field and the nanocolumns. It also leads to the field-orientation-independent power law index n of the E–J curves. Below the transition, there is a strong maximum in JC when the field is aligned parallel to the columns and n depends on field direction. Above the transition, n is independent of the field direction and there is a JC minimum for H parallel to the columns. We discuss a possible mechanism for such behavior change, as well as testing and confirming a prediction that the crossover must become very broad at high temperatures and low fields.
Molecular simulation study of phospholipid bilayers and insights of the interactions with disaccharides.

Molecular simulations of hydrated dipalmitoylphosphatidylcholine lipid bilayers have been performed for temperatures in the range of 250–450 K. The area per headgroup increases with temperature from 58 to 77 A2. Other properties such as hydration number, alkyl tail order parameter, diffusion coefficients, and radial distribution functions exhibit a clear dependence on temperature. Simulations of bilayers have also been performed in the presence of two disaccharides, namely trehalose and sucrose, at concentrations of up to 18 wt % (lipid-free basis). The simulated area per headgroup of the bilayer is not affected by the presence of the disaccharides, suggesting that the overall structure of the bilayer remains undisturbed. The results of simulations reveal that the interaction of disaccharide molecules with the bilayer occurs at the surface of the bilayer, and it is governed by the formation of multiple hydrogen bonds to specific groups of the lipid. Disaccharide molecules are observed to adopt specific conformations to fit onto the surface topology of the bilayer, often interacting with up to three different lipids simultaneously. At high disaccharide concentrations, the results of simulations indicate that disaccharides can serve as an effective replacement for water under anhydrous conditions, which helps explain their effectiveness as lyophilization agents for liposomes and cells.
Quantum chromodynamics with advanced computing

We survey results in lattice quantum chromodynamics from groups in the USQCD Collaboration. The main focus is on physics, but many aspects of the discussion are aimed at an audience of computational physicists.
Constraining the central engine of radio-loud AGNs

Abstract We present an X-ray spectral survey of radio-loud (RL) AGNs using ASCA and RXTE . The goal was to study the structure of their central engines and compare it to that of their radio-quiet (RQ) counterparts. We find systematic differences in the X-ray properties of the two AGN classes. Specifically, RL AGNs exhibit weaker Fe lines and reflection components than RQ AGNs, indicating smaller solid angles subtended by the re-processing medium to the X-ray source. The circumnuclear environs of RL and RQ AGNs also differ: large amounts of cold gas are detected in Broad Line Radio Galaxies and Quasars, contrary to what is found in Seyfert galaxies of similar X-ray luminosity. We also discuss ASCA observations of Weak Line Radio Galaxies, a distinct subset of radio galaxies which may harbor a low-luminosity AGN powered by an advection-dominated accretion flow.
Diagnosis and management of serious urinary complications after major operative laparoscopy.

Objective To evaluate the incidence, diagnosis, and management of serious urinary complications after major operative laparoscopy. Methods For this retrospective study of 953 consecutive cases of major operative laparoscopy from January 1, 1990, to December 31, 1994, we reviewed incidence, method of diagnosis, and management of complications. Urinary complications included bladder injuries, urinary fistulas, and ureteral injuries. Major operative laparoscopic procedures included hysterectomy, adnexectomy, treatment of tubal pregnancy, ovarian cystectomy, and ablation-fulguration of severe endometriosis (stage IV). Results Serious urinary complications were found during or after operative laparoscopy in 15 of 953 patients (1.6%, 95% confidence interval [CI] 0.8–2.4). Four ureteral injuries, three bladder fistulas, and eight bladder perforations were documented in this series. Eight cases of urinary complications were recognized during the original surgery (one ureteral injury and seven bladder injuries) and repaired at that time. Laparotomy or additional major surgery was performed in seven patients (three ureteral injuries, two bladder fistulas, and two bladder perforations). Conclusion Serious urinary complications after major operative laparoscopy were discovered in 1.6% of patients. This incidence compares favorably to serious urinary complications after standard gynecologic surgery. Intraoperative recognition of these complications will likely avoid additional surgery.