cssi/SciSciGPT-SciSciNet huggingface dataset:
The magnetic shielding function of molecules and pi-electron delocalization.

A review. The following topics are discussed: interaction of mols. with magnetic field (shielding function); special NMR properties of arom. mols.; magnetically induced current densities and related models; induced magnetic fields of mols.; electron delocalization and magnetic response for some mols. [on SciFinder (R)]
Spin-diffusion lengths in metals and alloys, and spin-flipping at metal/metal interfaces: an experimentalist's critical review

In magnetoresistance (MR) studies of magnetic multilayers composed of combinations of ferromagnetic (F) and non-magnetic (N) metals, the magnetic moment (or related ‘spin’) of each conduction electron plays a crucial role, supplementary to that of its charge. While initial analyses of MR in such multilayers assumed that the direction of the spin of each electron stayed fixed as the electron transited the multilayer, we now know that this is true only in a certain limit. Generally, the spins ‘flip’ in a distance characteristic of the metal, its purity, and the temperature. They can also flip at F/N or N1/N2 interfaces. In this review we describe how to measure the lengths over which electron moments flip in pure metals and alloys, and the probability of spin-flipping at metallic interfaces. Spin-flipping within metals is described by a spindiffusion length, l M sf , where the metal M = F or N. Spin-diffusion lengths are the characteristic lengths in the current-perpendicular-to-plane (CPP) and lateral non-local (LNL) geometries that we focus upon in this review. In certain simple cases, l N sf sets the distance over which the CPP-MR and LNL-MR decrease as the N-layer thickness (CPP-MR) or N-film length (LNL) increases, and l F does the same for increase of the CPP-MR with increasing F-layer thickness. Spinflipping at M1/M2 interfaces can be described by a parameter, δM1/M2 ,w hich determines the spin-flipping probability, P = 1 − exp(−δ). Increasing δM1/M2 usually decreases the MR. We list measured values of these parameters and discuss the limitations on their determinations.
Double-sided tin nanowire arrays for advanced thermal interface materials

This investigation examines a fundamentally new type of thermal interface material (TIM) based on a double-sided array of tin nanowires (NWs) prepared using a hot-pressing approach with the assistance of anodic aluminum oxide templates. The metal based TIM effectively reduces the contact resistance, while the flexible nanowires show excellent mechanical compliance to increase the actual contact area with the mating rough surfaces. The results indicate that the overall thermal contact resistance of the two rough copper surfaces assisted by the tin NW array can reduce the overall resistance to 29 mm2KW-1 at 0.25 MPa and 20 mm2KW-1 at 1.0 MPa.
Expectations for evolution of cluster scaling relations

Cluster observations with Chandra and XMM-Newton are beginning to reveal how the X-ray luminosity–temperature relation evolves with redshift. Some studies find that this evolution is consistent with the predictions of self-similar cluster models while others do not. While self-similar evolution may be plausible at low redshifts, it cannot continue to arbitrarily high redshifts because radiative cooling and the feedback from galaxy formation become increasingly more important at high redshifts. Likewise, the intracluster baryon fraction is likely to decline at high redshifts, owing to cooling and feedback processes. This article examines the predictions of self-similar models for clusters, which come in several different flavors, proposes some alternative scaling laws that account for radiative cooling and feedback in very a simplistic way, and compares those laws with the existing data.
Data-Efficient Quickest Change Detection with On–Off Observation Control

Abstract In this article we extend Shiryaev's quickest change detection formulation by also accounting for the cost of observations used before the change point. The observation cost is captured through the average number of observations used in the detection process before the change occurs. The objective is to select an on–off observation control policy that decides whether or not to take a given observation, along with the stopping time at which the change is declared, to minimize the average detection delay, subject to constraints on both the probability of false alarm and the observation cost. By considering a Lagrangian relaxation of the constraint problem and using dynamic programming arguments, we obtain an a posteriori probability-based two-threshold algorithm that is a generalized version of the classical Shiryaev algorithm. We provide an asymptotic analysis of the two-threshold algorithm and show that the algorithm is asymptotically optimal—that is, the performance of the two-threshold algorith...
Assembly configurations of planar multi-loop mechanisms with kinematic limitations

This paper examines the problem of identifying the assembly configurations (ACs), also called circuits, of planar multi-loop mechanisms with kinematic limitations, such as joint limits, link interference, collision with stationary obstacles, and constraint regions. First, a technique is given to describe numerically the satisfaction or violation of these kinematic limitations, and then it is applied to find the ACs of mechanisms with kinematic limitations. The method is valid for planar mechanisms with one or two degrees of freedom, and is illustrated with two examples.
Prescribed-Curvature-Distribution Airfoils for the Preliminary Geometric Design of Axial-Turbomachinery Cascades

Blade surfaces with continuous curvature and continuous slope of curvature minimize the possibility of flow separation, lead to improved blade designs, and reduce the direct and inverse blade-design iterations for the seection of isolated airfoils and gas-turbine-blade cascades. A method for generating two-dimensional blade shapes is presented. The geometry near the trailing edge is specified by an analytic polynomial, the main portion of the blade surface is mapped using as input a prescribed surface-curvature distribution, and the leading edge is specified as a thickness distribution added to a construction line. This procedure is similar for the suction and pressure surfaces, and by specification it constructs continuous slope-of-curvature surfaces that result in smooth surface-Mach-number and surface-pressure distributions
Computers challenge engineering education

When quantum theory was newly stirring the world of physics, an older professor was reported to have said to his graduate students studying this subject, "I don't believe you young fellows understand this stuff any better than I do, but you all stick together and say the same thing." You computer enthusiasts say a great deal, some of which I understand. Your computers differ in detail and complexity, yet have much in common in concept and capabilities and in the fantastic rate with which new models appear. They have their limitations, but nobody underestimates their potentialities. Nor are the glamorous, rosy dreams of coming applications as far beyond the horizon as we might think. You know better than I the magnitude and momentum of the development effort and the tremendous interest which has been generated in all areas of technology and business.
The rotational relaxation time of aspartate aminotransferase

Abstract Two independent methods, sucrose density centrifugation and polarization of fluorescence, were used to study the molecular state of the enzyme aspartate amino-transferase at concentrations approaching those used in the enzymatic assays. 1. 1. The sucrose density centrifugation experiments indicated that the sedimentation coefficient of the enzyme (5.5 S) is not appreciably affected by the simple dilution process. 2. 2. The polarization of fluorescence results, conducted at a protein concentration of 0.01 mg/ml, revealed that the enzyme aspartate aminotransferase is characterized by two rotational relaxation times. The longest relaxation time ( ρ h = 130 nsec) corresponds to a rigid macromolecule unit of a mol. wt. of approx. 90 000. The shortest relaxation time ( ρ s = 9 nsec) reflects the Brownian motion of a short segment of the enzyme.
Stochastic aggregation: scaling properties

We study the scaling properties of stochastic aggregation processes in one dimension. Numerical simulations for both diffusive and ballistic transport show that the mass distribution is characterized by two independent non-trivial exponents corresponding to the survival probability of particles and monomers. The overall behaviour agrees qualitatively with the mean-field theory. This theory also provides a useful approximation for the decay exponents, as well as the limiting mass distribution.
Feedback linearization using neural networks

Abstract For a class of single-input single-output continuous-time nonlinear systems, a multilayer neural network-based controller that feedback-linearizes the system is presented. Control action is used to achieve tracking performance for a state-feedback linearizable but unknown nonlinear system. The control structure consists of a feedback linearization portion provided by two neural networks, plus a robustifying portion that keeps the control magniture bounded. A stability proof is given in the sense of Lyapunov. It is shown that all the signals in the closed-loop system are uniformly ultimately bounded. No off-line learning phase is needed; initialization of the network weights is straightforward.
Spontaneously Evolved Social Order versus Positive Legislation in English Constitutional History

Medieval institutions contain an important strain of spontaneous order, especially from the pre-Christian period. A series of irregular successions after the Norman conquest made royal charters increasingly important in establishing the sovereign's legitimacy. Henry I's coronation charter (1100) formed the basis of Henry II's aggressive program of reform legislation, as well as for Magna Carta (1215). Henry II aimed at restoring the legal and political institutions of his grandfather Henry I after a period of civil strife and social degeneration. The fact that almost all later charters grew out of Henry I's charter, combined with the fact that later charters expanded and refined legal and political institutions, establishes the evolution of spontaneous order in the English charters. This evolution continued throughout the middle ages as subsequent kings confirmed Magna Carta.
Earnings inequality narrows for young workers despite a widening wage structure

Abstract Inequality of wage rates has widened in the United States. But inequality of earnings also depends on the distribution of hour's worked. If the distribution of hours contracts sufficiently, earnings inequality may narrow despite a widening wage structure. The present study examines recent trends in inequality for young workers and, consistent with the preceding scenario, finds that rising inequality of wage rates has been overwhelmed by declining inequality of hours worked. As a consequence, earnings inequality of young workers declined during the 1980s.
On the Distribution of X-Ray Surface Brightness from Diffuse Gas

Hot intergalactic gas in clusters, groups, and filaments emanates a continuous background of 0.5-2.0 keV X-rays that ought to be detectable with the new generation of X-ray observatories. Here we present selected results from a program to simulate the surface brightness distribution of this background with an adaptive mesh cosmological hydrodynamics code. We show that the bright end of this distribution is well approximated by combining the cluster temperature function with a β-model for surface brightness and appropriate luminosity-temperature and core radius-luminosity relations. Our simulations verify that the X-ray background from hot gas vastly exceeds observational limits if nongravitational processes do not modify the intergalactic entropy distribution. An entropy floor ~100 keV cm2, which could be established by either heating or cooling, appears necessary to reconcile the simulated background with observations. Because the X-ray background distribution is so sensitive to the effects of nongravitational processes, it offers a way to constrain the thermal history of the intergalactic medium that is independent of the uncertainties associated with surveys of clusters and groups.
Finitely additive stochastic games with Borel measurable payoffs

We prove that a two-person, zero-sum stochastic game with arbitrary state and action spaces, a finitely additive law of motion and a bounded Borel measurable payoff has a value.
Counting descent pairs with prescribed tops and bottoms

Given sets X and Y of positive integers and a permutation @s=@s"1@s"2...@s"n@?S"n, an (X,Y)-descent of @s is a descent pair @s"i>@s"i"+"1 whose ''top''@s"i is in X and whose ''bottom''@s"i"+"1 is in Y. We give two formulas for the number P"n","s^X^,^Y of @s@?S"n with s(X,Y)-descents. P"n","s^X^,^Y is also shown to be a hit number of a certain Ferrers board. This work generalizes results of Kitaev and Remmel [S. Kitaev, J. Remmel, Classifying descents according to parity, math.CO/0508570; S. Kitaev, J. Remmel, Classifying descents according to equivalence modk, math.CO/0604455] on counting descent pairs whose top (or bottom) is equal to 0modk.
Systematic search, belated information, and the gittins' index

Abstract This paper uses multi-armed bandit methods to characterize the optimal solution of a rather complicated search problem. The job search is conducted systematically and there is belated information, that is, some aspect of the job is discerned only after the job has been tested for one period.
Unsteady transonic flow calculations for interfering lifting surface configurations

Unsteady transonic flow calculations are presented for aerodynamically interfering lifting surface configurations. Calculations are performed by extending the XTRAN3S (Version 1.5) unsteady transonic small-disturbance code to allow the treatment of an additional lifting surface. The research was conducted as a first-step toward developing the capability to treat a complete flight vehicle. Grid generation procedures for swept tapered interfering lifting surface applications of XTRAN3S are described. Transonic calculations are presented for wing-tail and canard-wing configurations for several values of mean angle of attack. The effects of aerodynamic interference on transonic steady pressure distributions and steady and oscillatory spanwise lift distributions are demonstrated. Results due to wing, tail, or canard pitching motions are presented and discussed in detail.
Convex optimization of nonlinear feedback controllers via occupation measures

The construction of feedback control laws for underactuated nonlinear robotic systems with input saturation limits is crucial for dynamic robotic tasks such as walking, running, or flying. Existing techniques for feedback control design are either restricted to linear systems, rely on discretizations of the state space, or require solving a nonconvex optimization problem that requires feasible initialization. This paper presents a method for designing feedback controllers for polynomial systems that maximize the size of the time-limited backwards reachable set (BRS). In contrast to traditional approaches based on Lyapunov's criteria for stability, we rely on the notion of occupation measures to pose this problem as an infinite-dimensional linear program which can then be approximated in finite dimension via semidefinite programs (SDPs). The solution to each SDP yields a polynomial control policy and an outer approximation of the largest achievable BRS which is well suited for use in a trajectory library or feedback motion planning algorithm. We demonstrate the efficacy and scalability of our approach on six nonlinear systems. Comparisons to an infinite-horizon linear quadratic regulator approach and an approach relying on Lyapunov's criteria for stability are also included in order to illustrate the improved performance of the presented technique.
Buckybowls: Polynuclear Aromatic Hydrocarbons Related to the Buckminsterfullerene Surface

The synthesis, chemistry, and properties of curved-surface, polynuclear aromatics would be of great interest even if buckminsterfullerene had never been discovered. The presence of both convex and concave surfaces provides the potential for exceptional stereo-selectivities, as well as attractive opportunities for some very interesting metal complexation. However, the fullerenes have been discovered, and there can be no denying that this relationship adds an additional level of excitement to what is already an intriguing new class of aromatic compounds. 46 refs., 3 figs., 1 tab.
Patchiness: A New Diagnostic for Lagrangian Trajectory Analysis in Time-Dependent Fluid Flows

In 2-D time-dependent fluid flows, a patch represents a localized region in space that has a significantly different average velocity compared to its surroundings. We show that one can obtain important information about the Lagrangian particle motion in such flows by studying the nature, long-term evolution, and statistical characteristics of the patchiness behavior. For example, the dispersion of passive tracers at any time is directly related to the distribution of patches in the flow. We thoroughly investigate the transport properties of the Lagrangian trajectories associated with a cellular flow previously used as a model for time-dependent Rayleigh–Benard convection, and a kinematic model of a meandering jet (originally due to Bower [1991]). In both cases, we examine the statistical attributes of the patchiness, their relationship with the geometric features of the stable and unstable manifolds, and the effect of noise on the structure of patchiness. We uncover some interesting features associated with the origin of these patches and their influence on Lagrangian transport.
Mean Field Theory of the Mott-Anderson Transition

We present a theory for disordered interacting electrons that can describe both the Mott and Anderson transitions in the respective limits of zero disorder and zero interaction. We use it to investigate the $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ Mott-Anderson transition at a fixed electron density, as the disorder strength is increased. Surprisingly, we find two critical values of disorder ${W}_{\mathrm{nfl}}$ and ${W}_{c}$. For $Wg{W}_{\mathrm{nfl}}$, the system enters a ``Griffiths'' phase, displaying metallic non-Fermi liquid behavior. At even stronger disorder, ${W\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}W}_{c}g{W}_{\mathrm{nfl}}$ the system undergoes a metal-insulator transition, characterized by the linear vanishing of both the typical density of states and the typical quasiparticle weight.
Angular correlations of the MeV cosmic gamma ray background

The measured cosmic gamma-ray background (CGB) spectrum at MeV energies is in reasonable agreement with the predicted contribution from Type Ia supernovae (SNe Ia). However, the characteristic features in the SN Ia gamma-ray spectrum, weakened by integration over source redshifts, are difficult to measure, and the contributions from other sources in the MeV range are uncertain, so that the SN Ia origin of the MeV CGB remains unproven. Since different CGB sources have different clustering properties and redshift distributions, by combining the CGB spectrum and angular correlation measurements the contributions to the CGB could be identified and separated. The SN Ia CGB large-scale structure follows that of galaxies. Its rms fluctuation at degree scales has a characteristic energy dependence ranging from ~1% to on the order of unity and can be measured to several percent precision by proposed future satellites such as the Advanced Compton Telescope. With the identification of the SN Ia contribution, the SN Ia rate could be measured unambiguously as a function of redshift up to z ~ 1 by combining the spectrum and angular correlation measurements, yielding new constraints on the star formation rate to even higher redshifts. Finally, we show that the gamma-ray and neutrino backgrounds from supernovae should be closely connected, allowing an important consistency test from the measured data. Identification of the astrophysical contributions to the CGB would allow much greater sensitivity to an isotropic high-redshift CGB contribution arising in extra dimension or dark matter models.
Some new maximum VC classes

Set systems of finite VC dimension are frequently used in applications relating to machine learning theory and statistics. Two simple types of VC classes which have been widely studied are the maximum classes (those which are extremal with respect to Sauer's lemma) and so-called Dudley classes, which arise as sets of positivity for linearly parameterized functions. These two types of VC class were related by Floyd, who gave sufficient conditions for when a Dudley class is maximum. It is widely known that Floyd's condition applies to positive Euclidean half-spaces and certain other classes, such as sets of positivity for univariate polynomials.In this paper we show that Floyd's lemma applies to a wider class of linearly parameterized functions than has been formally recognized to date. In particular we show that, modulo some minor technicalities, the sets of positivity for any linear combination of real analytic functions is maximum on points in general position. This includes sets of positivity for multivariate polynomials as a special case. New maximum VC classes arising from parameterized inequalities are shown to exist.The new classes of interest arise from linear combinations of real analytic functions.These include multivariate polynomials with coefficient parameters as a special case.
Particle Acceleration Zones above Pulsar Polar Caps: Electron and Positron Pair Formation Fronts

We investigate self-consistent particle acceleration near a pulsar polar cap (PC) by the electrostatic field due to the effect of inertial frame dragging. Test particles gain energy from the electric field parallel to the open magnetic field lines and lose energy by both curvature radiation (CR) and resonant and nonresonant inverse Compton scattering (ICS) with soft thermal X-rays from the neutron star (NS) surface. Gamma rays radiated by electrons accelerated from the stellar surface produce pairs in the strong magnetic field, which screen the electric field beyond a pair formation front (PFF). Some of the created positrons can be accelerated back toward the surface and produce γ-rays and pairs that create another PFF above the surface. We find that ICS photons control PFF formation near the surface, but because of the different angles at which the electron and positron scatter the soft photons, positron-initiated cascades develop above the surface and may screen the accelerating electric field. Stable acceleration from the NS surface is therefore not possible in the presence of dominant ICS energy losses. However, we find that stable acceleration zones may occur at some distance above the surface, where CR dominates the electron and positron energy losses and there is up-down symmetry between the electron and positron PFFs. We examine the dependence of CR-controlled acceleration zone voltage, width, and height above the surface on parameters of the pulsar and its soft X-ray emission. For most pulsars, we find that acceleration will start at a height of 0.5-1 stellar radii above the NS surface.
Patterns as a paradigm for theory in community-based learning

Learning about information technology is typically not a first-order goal for community-based volunteer organizations. Nonetheless, information technology is vital to such groups for member recruiting and management, communication and visibility to the community, and for primary group activities. During the past 12 years, we have worked with community groups in Centre County, Pennsylvania, and Montgomery County, Virginia. We have built partnerships with these groups to better understand and address their learning challenges with respect to information technology. In this paper, we suggest that patterns, standard solution schemata for recurring problems (as used in architecture and software engineering, among other design domains), can be a paradigm for codifying and developing an understanding of learning in and by community organizations. Patterns are middle-level abstractions; they capture regularities of practices in ways that are potentially intelligible, verifiable, and perhaps useful to the practitioners themselves. We present two example patterns and discuss issues and directions for developing patterns as a theoretical foundation for community-based learning.
Stripes, carriers, pseudogap, and superconductivity in the cuprates

The electronic structure of the high-Tc cuprates is studied on the basis of both "large-U" and "small-U" orbitals. A striped structure is obtained, and three types of carriers: polaron-like "stripons" carrying charge, "quasielectrons" carrying charge and spin, and "svivons" carrying spin and lattice distortion. Anomalous properties of the cuprates and specifically their transport properties are derived. Pairing is found to result from transitions between pair states of quasielectrons and stripons through the exchange of svivons. The pairing results in superconductivity when the stripons conduction is coherent, and in a pseudogap phase when it is not.
The Orbital Structure of Dark Matter Halos with Gas

With the success of the Chandra and XMM missions and the maturation of gravitational lensing techniques, powerful constraints on the orbital structure of cluster dark matter halos are possible. I show that the X-ray emissivity and mass of a galaxy cluster uniquely specify the anisotropy and velocity dispersion profiles of its dark matter halo. I consider hydrostatic as well as cooling flow scenarios and apply the formalism to the lensing cluster Cl 0024+16 and the cooling flow cluster Abell 2199. In both cases, the model predicts a parameter-free velocity dispersion profile that is consistent with independent optical redshift surveys of the clusters.
How “Local” are Local Office Markets?

This paper describes empirical investigations of the geographical extent of office markets in the United States during the 1980s. A mixed temporal autoregressive model was estimated for pooled downtown office markets and pooled suburban markets. Results indicate that while the temporal autoregressive effect is stronger for office market vacancies than is the effect of the national trend, their linkages to national trends are significant. However, a mixed spatial autoregression analysis of the data pooled over time indicates that the regional office vacancy effect is stronger than the national office vacancy effect in both downtown and suburban office markets.
Biological monitoring and genetic screening in the industrial workplace: a synopsis and analysis.

Can new medical technologies decrease the incidence of occupational disease? Do they work to the detriment of other worker interests? Do they shift the burden of maintaining a healthy workplace from employers to employees, by keeping sensitive individuals from jobs that they are otherwise qualified to perform? These are among the central issues presented by the emerging occupational use of biological monitoring and genetic screening, as highlighted at the conference on Biological Monitoring and Genetic Screening in the Industrial Workplace, held in Washington, D.C., on May 12-13, 1983. The meeting was sponsored by the American Society of Law & Medicine and the Boston University Schools of Law, Medicine, and Public Health.
TRANSIENT LUNAR PHENOMENA: REGULARITY AND REALITY

Transient lunar phenomena (TLPs) have been reported for centuries, but their nature is largely unsettled, and even their existence as a coherent phenomenon is controversial. Nonetheless, TLP data show regularities in the observations; a key question is whether this structure is imposed by processes tied to the lunar surface, or by terrestrial atmospheric or human observer effects. I interrogate an extensive catalog of TLPs to gauge how human factors determine the distribution of TLP reports. The sample is grouped according to variables which should produce differing results if determining factors involve humans, and not reflecting phenomena tied to the lunar surface. Features dependent on human factors can then be excluded. Regardless of how the sample is split, the results are similar: ~50% of reports originate from near Aristarchus, ~16% from Plato, ~6% from recent, major impacts (Copernicus, Kepler, Tycho, and Aristarchus), plus several at Grimaldi. Mare Crisium produces a robust signal in some cases (however, Crisium is too large for a feature as defined). TLP count consistency for these features indicates that ~80% of these may be real. Some commonly reported sites disappear from the robust averages, including Alphonsus, Ross D, and Gassendi. These reports begin almost exclusively after 1955, when TLPs became widely known and many more (and inexperienced) observers searched for TLPs. In a companion paper, we compare the spatial distribution of robust TLP sites to transient outgassing (seen by Apollo and Lunar Prospector instruments). To a high confidence, robust TLP sites and those of lunar outgassing correlate strongly, further arguing for the reality of TLPs.
Re-designing Equalization Transfers: An Application to South Africa's Provincial Equitable Share

In this paper we examine the design of transfer systems, focusing on the Provincial Equitable Share (PES) in the Republic of South Africa. Provinces in South Africa have been assigned a wide range of responsibilities. Because provinces are almost completely reliant on transfers from the central government, the design of the PES is of critical importance, especially in its ability to achieve the goal of “equalization” across provinces. Our specific conclusion is that the PES largely fails in its efforts to equalize across provinces. Our more general conclusion that follows from this is that the PES attempts to achieve too many conflicting goals, and so it necessarily fails to achieve all goals equally or well, especially its ability to equalize. We conclude with suggestions for ways to reform the PES to better achieve the goal of equalization, lesson that also apply to other countries.
Transition stages of Rayleigh{Taylor instability between miscible fluids

Direct numerical simulations (DNS) are presented of three-dimensional, Rayleigh–Taylor instability (RTI) between two incompressible, miscible fluids, with a 3:1 density ratio. Periodic boundary conditions are imposed in the horizontal directions of a rectangular domain, with no-slip top and bottom walls. Solutions are obtained for the Navier–Stokes equations, augmented by a species transport-diffusion equation, with various initial perturbations. The DNS achieved outer-scale Reynolds numbers, based on mixing-zone height and its rate of growth, in excess of 3000. Initial growth is diffusive and independent of the initial perturbations. The onset of nonlinear growth is not predicted by available linear-stability theory. Following the diffusive-growth stage, growth rates are found to depend on the initial perturbations, up to the end of the simulations. Mixing is found to be even more sensitive to initial conditions than growth rates. Taylor microscales and Reynolds numbers are anisotropic throughout the simulations. Improved collapse of many statistics is achieved if the height of the mixing zone, rather than time, is used as the scaling or progress variable. Mixing has dynamical consequences for this flow, since it is driven by the action of the imposed acceleration field on local density differences.
Error and attack tolerance of complex networks

Many complex systems display a surprising degree of tolerance against errors. For example, relatively simple organisms grow, persist and reproduce despite drastic pharmaceutical or environmental interventions, an error tolerance attributed to the robustness of the underlying metabolic network1. Complex communication networks2 display a surprising degree of robustness: although key components regularly malfunction, local failures rarely lead to the loss of the global information-carrying ability of the network. The stability of these and other complex systems is often attributed to the redundant wiring of the functional web defined by the systems' components. Here we demonstrate that error tolerance is not shared by all redundant systems: it is displayed only by a class of inhomogeneously wired networks, called scale-free networks, which include the World-Wide Web3,4,5, the Internet6, social networks7 and cells8. We find that such networks display an unexpected degree of robustness, the ability of their nodes to communicate being unaffected even by unrealistically high failure rates. However, error tolerance comes at a high price in that these networks are extremely vulnerable to attacks (that is, to the selection and removal of a few nodes that play a vital role in maintaining the network's connectivity). Such error tolerance and attack vulnerability are generic properties of communication networks.
Hydrogen evolution catalyzed by cobaloximes.

Natural photosynthesis uses sunlight to drive the conversion of energy-poor molecules (H2O, CO2) to energy-rich ones (O2, (CH2O)n). Scientists are working hard to develop efficient artificial photosynthetic systems toward the “Holy Grail” of solar-driven water splitting. High on the list of challenges is the discovery of molecules that efficiently catalyze the reduction of protons to H2. In this Account, we report on one promising class of molecules: cobalt complexes with diglyoxime ligands (cobaloximes). Chemical, electrochemical, and photochemical methods all have been utilized to explore proton reduction catalysis by cobaloxime complexes. Reduction of a CoII-diglyoxime generates a CoI species that reacts with a proton source to produce a CoIII-hydride. Then, in a homolytic pathway, two CoIII-hydrides react in a bimolecular step to eliminate H2. Alternatively, in a heterolytic pathway, protonation of the CoIII-hydride produces H2 and CoIII. A thermodynamic analysis of H2 evolution pathways sheds new lig...
“Conformationally restricted β-amino acid isosteres prepared through regioselectively controlled aza-annulation.”

Abstract A variety of electron withdrawing substituents were used to enhance the aza-annulation of enamines with acryloyl chloride, to direct the regioselectivity of alkene formation, and to facilitate hydrogenation of the unsaturated annulation product. The resulting δ-lactam products were β-amino acid analogs with structural features similar to those of established peptide isosteres.
Helicobacter cinaedi Induced Typhlocolitis in Rag-2-Deficient Mice

Inflammatory bowel diseases (IBD), classified as ulcerative colitis (UC) and Crohn’s disease, affect millions of people worldwide and is characterized by chronic, uncontrolled inflammation of the intestinal mucosa. Epidemiological evidence indicates that humans with IBD have an increased risk of developing colon cancer [1]. The pathogenesis of IBD involves complex interactions including the genetic background of the host, the immunological responses of the host to intestinal microbiota, and environmental factors leading to dysbiosis of the intestinal microflora. Importantly, data from experimental models highlight that enteric flora play a crucial role in initiating and sustaining the inflammatory process [2]. Helicobacter species are microaerobic, gram-negative spiral bacteria that have been associated with gastric cancer in humans, as well as hepatitis, hepatocellular carcinoma, IBD, and colonic adenocarcinoma in mouse models [3–6], H. cinaedi (initially named Campylobacter cinaedi) is an enterohepatic Helicobacter species (EHS) first isolated from homosexual men suffering from enteritis, proctitis, or proctocolitis [7]. Helicobacter cinaedi was subsequently isolated from immunocompromised patients afflicted with meningitis, bacteremia, cellulitis, septic arthritis, and enteritis [8], as well as from immunocompetent patients with metabolic disease [9]. Recently, it has been associated with nosocomial transmission and systemic disease in hospitalized patients [10,11]. In our previous study, we reported that H. cinaedi induced typhlocolitis in IL-10 deficient mice; the disease was characterized by an elevated TH1 immune response. We also determined that cytolethal distending toxin plays a role in H. cinaedi induced intestinal inflammatory responses [12]. To further analyze the immune mechanisms of H. cinaedi induced IBD, we used recombinase-activating gene (Rag)-2-deficient mice in the current study. In the Rag-deficient mouse model, which lack functional T and B lymphocytes, Helicobacter hepaticus-infected mice rapidly developed colitis and large bowel carcinoma, establishing the important relationship of microbial driven innate induced chronic inflammation and colon cancer development [5,6,13]. We investigated whether H. cinaedi, a human pathogen, colonized and induced pathological changes in the Rag2−/− mouse model in a manner similar to H. hepaticus-induced colon adenocarcinoma [13,14].
Accretion onto Intermediate-Mass Black Holes in Dense Protogalactic Clouds

We present the first results from two-dimensional simulations of radiatively-efficient accretion of metal-free gas onto intermediate-mass black holes. We fix the shape of the spectral energy distribution of the radiation produced near the event horizon and study the structure of the irradiated low-angular-momentum accretion flow over three orders of magnitude in radius from the black hole, 10^{14}-10^{17} cm for a 100 M_sun black hole. The luminosity of the central source is made to be proportional to the rate at which gas accretes across the inner boundary, which we set just inside the sonic radius. We find that photoionization heating and radiation pressure modify the structure of the flow. When the ambient gas density is 10^7 cm^{-3}, accretion is intermittent and on average reduced to 32% of the Eddington-limited rate, two orders of magnitude below the "Bondi" rate evaluated ignoring radiation, in agreement with simplified theoretical models. Even if the vicinity of the black hole is supplied with high density gas, accretion is rendered inefficient through heating and radiation pressure.
Lower hybrid to whistler mode conversion on a density striation

[1] When a wave packet composed of short wavelength lower hybrid modes traveling in an homogeneous plasma region encounters an inhomogeneity, it can resonantly excite long wavelength whistler waves via a linear mechanism known as mode conversion. An enhancement of lower hybrid/whistler activity has been often observed by sounding rockets and satellites in the presence of density depletions (striations) in the upper ionosphere. We address here the process of linear mode conversion of lower hybrid to whistler waves, mediated by a density striation, using a scalar-field formalism (in the limit of cold plasma linear theory) which we solve numerically. We show that the mode conversion can effectively transfer a large amount of energy from the short to the long wavelength modes. We also study how the efficiency scales by changing the properties (width and amplitude) of the density striation. We present a general criterion for the width of the striation that, if fulfilled, maximizes the conversion efficiency. Such a criterion could provide an interpretation of recent laboratory experiments carried out on the Large Plasma Device at UCLA.
Signs of death as considered by Dr. B.M. Vance in a lecture fifty years ago.

This work is based on the lecture given by Dr. Bernard M. Vance, then Assistant Chief Medical Examiner of New York, to the Homicide Squad Detectives of New York City on November 2, 1933, at the New York Police Academy. He entitled his presentation "Death, simulation of death and suspicion of death." Dr. Vance was an outstanding member of the New York Office's Forensic Pathology Group and was known for his colorful renditions of the scene and autopsy findings in medicolegal cases.
Meiosis I: when chromosomes undergo extreme makeover

The ultimate success of cell division relies on the accurate partitioning of the genetic material. Errors in this process occur in nearly all tumors and are the leading cause of miscarriages and congenital birth defects in humans. Two cell divisions, mitosis and meiosis, use common as well as unique mechanisms to ensure faithful chromosome segregation. In mitosis, alternating rounds of DNA replication and chromosome segregation preserve the chromosome complement of the progenitor cell. In contrast, during meiosis two consecutive rounds of nuclear division, meiosis I and meiosis II, follow a single round of DNA replication to reduce the chromosome complement by half. Meiosis likely evolved through changes to the mitotic cell division program. This review will focus on the recent findings describing the modifications that transform mitosis into meiosis.
MULTISPECTRAL IMAGE PROCESSING: THE NATURE FACTOR

The images processed by our brain represent our window into the world. For some animals this window is derived from a single eye, for others, including humans, two eyes provide stereo imagery, for others like the black widow spider several eyes are used (8 eyes), and some insects like the common housefly utilize thousands of eyes (ommatidia). Still other animals like the bat and dolphin have eyes for regular vision, but employ acoustic sonar vision for seeing when their regular eyes do not work such as in pitch black caves or turbid water. Of course, other animals have adapted to dark environments by bringing along their own lighting such as the firefly and several creatures from the depths of the ocean floor. Animal vision is truly varied and has developed over millennia in many remarkable ways. We have learned a lot about vision processes by studying these animal systems and can still learn even more.
Cadherin-7 function in zebrafish development

Cadherin cell adhesion molecules play crucial roles in vertebrate development. Most studies have focused on examining the functions of classical type I cadherins (e.g., cadherin-2) in the development of vertebrates. Little information is available concerning the function of classical type II cadherins (e.g., cadherin-7) in vertebrate development. We have previously shown that cadherin-7 mRNA exhibits a dynamic expression pattern in the central nervous system and notochord in embryonic zebrafish. To gain insight into the role of cadherin-7 in the formation of these structures, we analyzed their formation in zebrafish embryos injected with cadherin-7-specific antisense morpholino oligonucleotides (MO). Notochord development was severely disrupted in MO-injected embryos, whereas gross defects in the development of the central nervous system were not detected in MO-injected embryos. Our results thus demonstrate that cadherin-7 plays an important role in the normal development of the zebrafish notochord.
Conflicts of Interest and Accountability in Managed Care: The Aging of Medical Ethics

This article explores how medical accountability has evolved, shifting from being a matter for individual physicians to being governed by professional norms and finally to organizations, payers and the state. It traces how the role of medical ethics has changed in this process.
The Elliptic Solution of the Secondary Flow Problem

This paper presents the elliptic solution of the inviscid incompressible secondary flow in curved passages. The three-dimensional flow field is synthesized between 3 sets of orthogonal nonstream surfaces. The two-dimensional flow field on each set of surfaces is considered to be resulting from a source/sink distribution. The distribution and strength of these sources are dependent on the variation in the flow properties normal to the surfaces. The dependent variables in this formulation are the velocity components, the total pressure, and the main flow vorticity component. The governing equations in terms of these dependent variables are solved on each family of surfaces using the stream-like function formulation. A new mechanism is implemented to exchange information between the solutions on the 3 family surfaces, resulting into a unique solution. In addition, the boundary conditions for the resulting systems of equations are carefully chosen to insure the existence and uniqueness of the solution. The numerical results obtained for the rotational inviscid flow in a curved duct are discussed and compared with the available experimental data.Copyright © 1982 by ASME
Compact packings of the plane with two sizes of discs

We consider packings of the plane using discs of radius 1 and r. A packing is compact if every disc D is tangent to a sequence of discs D1, D2, ..., Dn such that Di is tangent to Di+1. We prove that there are only nine values of r with r < 1 for which such packings are possible. For each of the nine values we describe the possible compact packings.
A Schrödinger singular perturbation problem

Abstract Consider the equation −e2Δue + q(x)ue = f(ue) in R 3 , ∣u(∞)∣ 0. Under what assumptions on q(x) and f(u) can one prove that the solution ue exists and lime→0ue = u(x), where u(x) solves the limiting problem q(x)u = f(u)? These are the questions discussed in the paper.
Family symmetries and proton decay

The proton decay modes p {yields} K{sup 0}e{sup +} and p {yields} K{sup 0}{mu}{sup +} may be visible in certain supersymmetric theories, and if seen would provide evidence for new flavor physics at extremely short distances. These decay modes can arise from the dimension five operator (Q{sub 1}Q{sub 1}Q{sub 2}L{sub 1,2}), where Q{sub i} and L{sub i} are i{sup th} generation quark and lepton superfields respectively. Such an operator is not generated at observable levels due to gauge or Higgs boson exchange in a minimal GUT. However in theories that explain the fermion mass hierarchy, it may be generated at the Planck scale with a strength such that the decays p {yields} K{sup 0}{ell}{sup +} are both compatible with the proton lifetime and visible at Super-Kamiokande. Observable proton decay can even occur in theories without unification.
The generative power of feature geometry

This paper presents a formalization of the common structure underlying different proposals concerning the geometry of phonological features. Using the concepts and tools of elementary set theory, lattice theory, and the theory of independent Boolean algebras, ametatheory of autosegmental feature structure is developed. This metatheory enables us to compare contemporary autosegmental phonology to the now abandoned “standard” phonology and to the historically important Pānini-type phonology as well, and to investigate the restrictions on the use of features in phonological theory.
Linear Ill-Posed Problems and Dynamical Systems☆

A new approach to solving linear ill-posed problems is proposed. The approach consists of solving a Cauchy problem for a linear operator equation and proving that this problem has a global solution whose limit at infinity solves the original linear equation.
New Strategies for Protecting Group Chemistry : Synthesis, Reactivity, and Indirect Oxidative Cleavage of para-Siletanylbenzyl Ethers

Reported herein is a new entry in the growing arsenal of arylmethyl ether protecting groups. The para-siletanylbenzyl (PSB) ether is electronically similar to the benzyl ether. Cleavage of the PSB ether is accomplished under mild conditions—involving alkaline hydrogen peroxide—that are unique among cleavage protocols for arylmethyl ethers. Furthermore, the PSB group affords the user new flexibility in the implementation of protecting group strategies that revolve around multiple arylmethyl ether protecting groups. In addition to hydrogen peroxide-based cleavage protocols, conversion of a PSB ether into a para-methoxybenzyl (PMB) ether and assembly of a PSB ether from a pre-existing para-bromobenzyl (PBB) ether are described. Finally, a new reagent for installing PSB ethers under neutral “mix and heat” conditions is reported.