cssi/SciSciGPT-SciSciNet huggingface dataset:
Dust molecules, strings, and crystals

Summary form only given. In discharges, dust normally resides at the edge of the sheath, where it is subject to ion streaming at velocity c/sub s/. The dust grains interact via a dynamically shielded potential O(r) that takes the form of a wake-field downstream. The dust grains may be strongly coupled to each other, but ions and electrons are only weakly coupled to the grains. However, this system differs from ordinary strongly coupled systems in that the potential O(r) is not symmetric upstream and downstream. Consequently, Newton's third law does not hold and neither energy nor momentum is conserved. We have used both analytic theory and simulation in a systematic exploration of this N-body system. Longer strings can exist only if there is a vertical confining force. As a model for this, we consider equally-spaced grains arranged in a vertical string in a periodic system . If there is also a horizontal confining potential, there are multiple 3-D equilibria occur which are connected by hysteretic processes that resemble phase transitions. In this non-conserving system, there is no general way to distinguish the ground state. However, the problem of two grains in a harmonic well can be reduced to a "quasi-Hamiltonian single-particle" form, permitting solution for ground and excited states. Crystals can be regarded as ordered collections of strings. Crystal structure is determined by the competition between the vertical forces that keep the strings aligned, the repulsive forces between strings, and the vertical and horizontal external confining forces. The phonon instabilities of dust crystals, which lead to melting below a critical pressure, are closely related to the hose instabilities of the strings. Thresholds and growth rates for these instabilities can be calculated using the analytically computed wakefield potentials.
Mineralogical applications of crystal field theory

The second edition of this classic book provides an updated look at crystal field theory - one of the simplest models of chemical bonding - and its applications. Crystal field theory provides a link between the visible region spectra and thermodynamic properties of numerous rock-forming minerals and gems that contain the elements iron, titanium, vanadium, chromium, manganese, cobalt, nickel or copper. These elements are major constituents of terrestrial planets and significantly influence their geochemical and geophysical properties. A unique perspective of the second edition is that it highlights the properties of minerals that make them compounds of interest to solid-state chemists and physicists as well as to all earth and planetary scientists. This book will be useful as a textbook for advanced students as well as a valuable reference work for all research workers interested in this subject.
Why healthy behavior is the hard choice.

Science informs us that nutritious dietary patterns and physical activity improve prospects for health and well-being. Yet pursuing a healthy lifestyle is incredibly difficult in a society designed to incentivize the opposite set of behaviors. For example, individuals may know the value of physical activity, but there may be few parks, playgrounds, fields, and walking paths for exercising their bodies. In inner-city neighborhoods with hazardous, unlit physical environments, for example, parents, fearful of the dangers of firearms and illicit drugs, may not want to send their children out to play. When it comes to our diet, we are constantly pushed toward unhealthy eating. Food manufacturers aggressively market hyperprocessed foods laden with saturated fat, salt, sugar, and refined carbohydrates. These companies put these unhealthy ingredients even in basic “healthy” foods, such as bread, granola, and yogurt. Advertisements for sugar-filled cereals and sodas are targeted to children. Fast-food chains collude with Hollywood and entertainment venues to give away toys in “meals” marketed for kids. It is little better for their parents. Consumers seeking whole, nutritious foods often find them inaccessible or unaffordable, driving many to buy convenient and cheap options. Even the most informed consumer faces a confusing shell game—“low-fat” foods often contain high amounts of sugar and salt, while “low-sugar” foods often are filled with high amounts of saturated fats and calories. Serving sizes are not uniform, stymieing even the most mathematically gifted consumer when comparing products. How can we structure society to make health the easier choice? Four simple ideas could make healthy behaviors the “default” choice for most consumers. To be sure, the evidence for these interventions is mixed, mainly because they are rarely enacted, let alone rigorously evaluated. Although evidence for a given intervention is important, tobacco control has taught us that a suite of measures, working in combination over time, has the best chance of success.
Interval + Communications = Walsh: For signal multiplexing under interval uncertainty, Walsh functions are optimal

In communications, often, statistical characteristics of the noise vary so much that, in essence, we can only have interval estimates for this noise. We show that under this interval uncertainty, the optimal multiplexing technique consists of using Walsh functions. This result provides a new theoretical explanation for the success of Walsh-based multiplexing techniques which are actively used in cellular phones and in other types of wireless communication.
Sequoia 2000: a next-generation information system for the study of global change

Better data management is crucial to the success of scientific investigations of global change. New modes of research about the Earth, especially the synergistic interactions between observations and models, require massive amounts of diverse data to be stored, organized, accessed, distributed, visualized, and analyzed. To address technical issues of better data management, participants in Sequoia 2000, a collaborative effort between computer scientists and Earth scientists at several campuses of the University of California and at Digital Equipment Corporation (DEC), apply refinements in computing to specific applications. The software architecture includes layers for a common device interface, the file system, the database management system (DBMS), applications, and the network. Early prototype applications of this software include a global-change data schema, integration of a general circulation model (GCM), remote sensing, and a data system for climate studies. Longer range efforts include transfer protocols for moving elements of the database, controllers for secondary and tertiary storage, distributed file system, and a distributed DBMS. >
Anhydrobiosis: an unsolved problem

The reversible cessation of metabolism and growth is a unique biological state. There are two types of organisms which are normally capable of of entering this state (cryptobiosis): (1) propagules of certain organisms and (2) certain rotifers, tardigrades, and nematodes. The latter group of organisms offer a unique opportunity to study the discontinuity of life processes, uncomplicated by simultaneous developmental processes and complex endogenous factors such as those responsible for the maintenance of dormancy. Working hypotheses and lines of research are pointed out in the areas of (1) metabolism during anhydrobiosis, (2) biochemical adaptations to desiccation, (3) morphological adaptations to desiccation.
Catastrophe Risk Management : Using Alternative Risk Financing and Insurance Pooling Mechanisms

Residual stochastic risks from catastrophic natural events can be addressed through insurance pooling and risk transfer mechanisms that provide the basis for financial protection and instill strong incentives for reducing vulnerability. To reduce the economic stress after disasters, the author shows, World Bank instruments could be used to support initiaitves to help correct market imperfections in catastrophe insurance. He takes a step-by-step approach to showing how both risk pooling structures and alternative catastrophe coverage mechanisms (long-maturity risk financing facilities, weather-indexed contracts, and capital market instruments) can achieve better risk protection and financing terms--enough to allow the expansion of insurance coverage of public assets and private property. The author examines the insurable assets (private and public) in eight countries in the easternmost part of the Caribbean and, by quantifying the portion of the premium and risk used to fund catastrophe losses, shows that through pooling and the use of credit-type instruments for catastrophe coverage, governments and uninsured property owners or enterprises (with insurable assets) could expect to improve their terms of coverage. Neither local insurers nor reinsurers would suffer in profitability. The risk management options the author examines could lead to real benefits for all participants (buyers and sellers) in insurance markets. But four factors are essential for ensuring the integrity of any participatory insurance scheme for providing risk management in disaster-prone areas such as the Caribbean: 1) stronger regulatory requirements and supervision in the insurance sector; 2) Broad-based, pooled catastrophe funding structures with efficient risk transfer tools; 3) Public insurance policies linked to programs for loss reduction in uninsured sectors; and 4) Stronger risk assessment and enforcement of such structural measures as zoning and compliance with building codes.
Defining explanation in probabilistic systems

As probabilistic systems gain popularity and are coming into wider use, the need for a mechanism that explains the system's findings and recommendations becomes more critical. The system will also need a mechanism for ordering competing explanations. We examine two representative approaches to explanation in the literature-- one due to Gardenfors and one due to Pearl--and show that both suffer from significant problems. We propose an approach to defining a notion of "better explanation" that combines some of the features of both together with more recent work by Pearl and others on causality.
Thermal Stereomutations of Cyclopropanes and Vinylcyclopropanes

1 Introduction 2 Historical Synopsis 3 Experimental Studies 4 Correlations of Reaction Rate Constants 5 Theoretical Models and Calculational Results 6 Disparate Kinetic Results 7 Conclusions 8 Acknowledgements Keywords: thermal stereomutations of cyclopropanes and vinyl cyclopropanes; reaction rate constants; theoretical models and calculational results; disparate kinetic results; substituted cyclopropane; radical stabilization energy parameters
An interpolation theorem related to the a.e. convergence of integral operators

We show that for integral operators of general form the norm bounds in Lorentz spaces imply certain norm bounds for the maximal function. As a consequence, the a.e. convergence for the integral operators on Lorentz spaces follows from the appropriate norm estimates.
Elemental Abundances in the Solar Corona

Elemental abundances in the solar corona and solar wind vary by over an order of magnitude. Two general trends are observed. First, there is an enhancement of elements whose neutral atoms have ionization potentials below about 10 eV (low-FIP) compared with those whose neutral atoms have higher ionization potentials (high-FIP). Second, there is a general depletion of heavier elements relative to hydrogen. This paper summarizes recent observational and theoretical abundance studies.
Generalized Two-Temperature Model for Coupled Phonon-Magnon Diffusion

We generalize the two-temperature model [Sanders and Walton, Phys. Rev. B 15, 1489 (1977)] for coupled phonon-magnon diffusion to include the effect of the concurrent magnetization flow, with a particular emphasis on the thermal consequence of the magnon flow driven by a nonuniform magnetic field. Working within the framework of the Boltzmann transport equation, we derive the constitutive equations for coupled phonon-magnon transport driven by gradients of both temperature and external magnetic fields, and the corresponding conservation laws. Our equations reduce to the original Sanders-Walton two-temperature model under a uniform external field, but predict a new magnon cooling effect driven by a nonuniform magnetic field in a homogeneous single-domain ferromagnet. We estimate the magnitude of the cooling effect in an yttrium iron garnet, and show it is within current experimental reach. With properly optimized materials, the predicted cooling effect can potentially supplement the conventional magnetocaloric effect in cryogenic applications in the future.
Integro‐Differential Equations

This article discusses a variety of methods and approximations used to solve and calculate integrodifferential equations, with emphasis, is on the utilitarian rather than the theoritical. Integrodifferential equations can describe linear and nonlinear systems that have memory, or are not in equilibrium. The appearance of both derivatives and integrals in an equation (e.g., expressing some type of balance with respect to time) means that instantaneous rates (e.g., velocity) and accumulated history (e.g., metal fatigue) determine the state of the system at the present moment. It is this aspect of integrodifferential equations that gives them their intellectual appeal, wide applicability, and challenging nature. Keywords: approximation; integral; iteration; nonlinear; solving
Higher order Bose-Einstein correlations for systems with large halo

Abstract A generalization of the core/halo model to the Bose-Einstein correlation function of any number of particles is presented. In particular, a simple prediction is obtained for the intercept parameter of the n -particle Bose-Einstein correlation functions for arbitrary large values of n .
Implementation of REDD+ Mechanisms in Tanzania

This paper explains the major issues and lessons derived from the national forest management program and REDD+ initiatives in Tanzania. It finds that addressing the most important drivers of forest degradation and deforestation, in particular the country energy needs and landownership, is essential for success in reducing emissions regardless of the type of program implemented. It also finds that, through the national program, forest users have learned to maximize profit from the sustainable use of the forest; however, the program reports great variability in the success of forest conservation. REDD+ may complement the national program by adding funding and other resources to start projects at the local level while giving additional payments for the permanence of carbon stocks may help to improve the social outcomes of those villages practicing sustainable forest management. However, a careful characterization of the national projects is necessary to generalize how REDD+ can be effectively implemented so that additional economic and environmental benefits are generated over what the national program is already achieving. Addressing this issue is key for identifying the conditions under which REDD+ achieves environmental additionality in Tanzania.
Fast Range Searching with Delaunay Triangulations

This paper studies the idea of answering range searching queries using simple data structures. The only data structure we need is the Delaunay Triangulation of the input points. The idea is to first locate a vertex of the (arbitrary) query polygon {\cal q} and walk along the boundary of the polygon in the Delaunay Triangulation and report all the points enclosed by the query polygon. For a set of uniformly distributed random points in 2-D and a query polygon the expected query time of this algorithm is O(n^{1/3} + Q + {\bf E}K + L_{r}n^{1/2}), where Q is the size of the query polygon {\cal q}, {\bf E}K = O(n\bcdot area({\cal q})) is the expected number of output points, L_{r} is a parameter related to the shape of the query polygon {\cal q} and n, and L_{r} is always bounded by the sum of the edge lengths of {\cal q}. Theoretically, when L_{r} = O(1/n^{1/6}) the expected query time is O(n^{1/3} + Q + {\bf E}K), which improves the best known average query time for general range searching. Besides the theoretical meaning, the good property of this algorithm is that once the Delaunay Triangulation is given, no additional preprocessing is needed. In order to obtain empirical results, we design a new algorithm for generating random simple polygons within a given domain. Our empirical results show that the constant coefficient of the algorithm is small, at least for the special (practical) cases when the query polygon is either a triangle (simplex range searching) or an axis-parallel box (orthogonal range searching) and for the general case when the query polygons are generated by our new polygon-generating algorithms and their sizes are relatively small.
Ground‐level detection of auroral kilometric radiation

[1] The Earth's auroral electrons radiate up to ∼1% of their energy in radio waves, called Auroral Kilometric Radiation (AKR). The emission mechanism, called the electron cyclotron maser (ECM), produces similar emissions at other planets, in the solar atmosphere, and possibly in astrophysical systems such as pulsars and blazars. ECM theory applied to AKR predicts radiation beamed outward that cannot penetrate near the Earth. Nevertheless, over the past several decades there have been occasional reports of AKR-like signals detected at low altitudes. Here we show the first evidence that AKR does indeed penetrate to low altitudes. For three examples of AKR-like emissions detected at South Pole Station, Antarctica, we examined data from the Geotail satellite plasma wave receiver, which had a field of view that included the auroral field lines above the station. The AKR-like emissions detected at ground-level have the same frequency-time structure as simultaneous AKR emissions detected on Geotail 115,000–190,000 km away from the Earth. These first coincident detections of AKR in space and on the ground require the existence of a mechanism to produce the ground-level emissions, suggest that previous AKR-like emissions observed at low altitudes may indeed be AKR, and require revision of the widely-held textbook view that AKR is only detectable from space.
Jitter-free signal-averaging picosecond X-ray streak camera

Summary form only given. Commercially available X-ray streak cameras have a temporal resolution of the order of a few picoseconds, but have an internal jitter more than a few tens of picoseconds. On the other hand, it has been shown that with the use of a high-voltage photoconductive switch, which provides the sweep voltage for an optical streak camera-a jitter of /spl plusmn/2 ps is achievable. In this paper we report on the use of a DC-biased semi-insulating (SI) GaAs photoconductive switch as a generator of a high-voltage ramp with a sweep speed of up to 8 ps/mm; shot-to-shot jitter is less /spl plusmn/1 ps for the X-ray streak camera.
Cysteine cathepsins are essential in lysosomal degradation of α-synuclein

A cellular feature of Parkinson’s disease is cytosolic accumulation and amyloid formation of α-synuclein (α-syn), implicating a misregulation or impairment of protein degradation pathways involving the proteasome and lysosome. Within lysosomes, cathepsin D (CtsD), an aspartyl protease, is suggested to be the main protease for α-syn clearance; however, the protease alone only generates amyloidogenic C terminal-truncated species (e.g., 1–94, 5–94), implying that other proteases and/or environmental factors are needed to facilitate degradation and to avoid α-syn aggregation in vivo. Using liquid chromatography–mass spectrometry, to our knowledge, we report the first peptide cleavage map of the lysosomal degradation process of α-syn. Studies of purified mouse brain and liver lysosomal extracts and individual human cathepsins demonstrate a direct involvement of cysteine cathepsin B (CtsB) and L (CtsL). Both CtsB and CtsL cleave α-syn within its amyloid region and circumvent fibril formation. For CtsD, only in the presence of anionic phospholipids can this protease cleave throughout the α-syn sequence, suggesting that phospholipids are crucial for its activity. Taken together, an interplay exists between α-syn conformation and cathepsin activity with CtsL as the most efficient under the conditions examined. Notably, we discovered that CtsL efficiently degrades α-syn amyloid fibrils, which by definition are resistant to broad spectrum proteases. This work implicates CtsB and CtsL as essential in α-syn lysosomal degradation, establishing groundwork to explore mechanisms to enhance their cellular activity and levels as a potential strategy for clearance of α-syn.
Infrastructure and trade preferences for the livestock sector : empirical evidence from the beef industry in Africa

Trade preferences are expected to facilitate global market integration and offer the potential for rapid economic growth and poverty reduction for developing countries. But those preferences do not always guarantee sustainable external competitiveness to beneficiary countries and may risk discouraging their efforts to improve underlying productivity. This paper examines the EU beef import market where several African countries have been granted preferential treatment. The estimation results suggest that profitability improvement achieved by countries under the Cotonou protocol compares unfavorably with the returns to nonbeneficiary countries in recent years. Rather, it shows that public infrastructure, such as paved roads, has an important role in lowering production costs and thus increasing external competitiveness and market shares.
STIS IMAGING OF THE HR 4796A CIRCUMSTELLAR DEBRIS RING

We have obtained high spatial resolution imaging observations of the HR 4796A circumstellar debris dust ring using the broad optical response of the Hubble Space Telescope Imaging Spectrograph (STIS) in coronagraphic mode. We use our visual wavelength observations to improve upon the earlier measured geometrical parameters of the ring-like disk. Two significant flux density asymmetries are noted: (1) preferential forward scattering by the disk grains and (2) an azimuthal surface brightness anisotropy about the morphological minor axis of the disk with corresponding differential ansal brightness. We find the debris ring offset from the location of the star by ~1.4 AU, a shift insufficient to explain the differing brightnesses of the northeast and southwest ansae simply by the 1/r 2 dimmunition of starlight. The STIS data also better quantify the radial confinement of the starlight-scattering circumstellar debris, to a characteristic region less than 14 AU in photometric half-width, with a significantly steeper inner truncation than outward falloff in radial surface brightness. The inferred spatial distribution of the disk grains is consistent with the possibility of one or more unseen co-orbital planetary-mass perturbers, and the colors of the disk grains are consistent with a collisionally evolved population of debris, possibly including ices reddened by radiation exposure to the central star.
Variation in Estimates of Urinary Incontinence Prevalence in the Community: Effects of Differences in Definition, Population Characteristics, and Study Type

OBJECTIVES: Prevalence estimates for urinary incontinence among community-dwelling adults vary from 2 to 55%. A review of the literature was undertaken to investigate the degree to which differences in definitions of incontinence, age, and gender of the populations studied, response rates, measurement techniques, or location could explain differences in reported prevalences. DESIGN: A literature search was conducted to locate all studies published in English reporting the prevalence of urinary incontinence in a population-based sample of adults. MEASUREMENT: Information was abstracted for study size, response rate, type of survey, definition of urinary incontinence, and prevalence of incontinence by age group and gender. Prevalence by type of incontinence was also abstracted where available. Stratification was used to obtain prevalence estimates specific for age, gender, and frequency of incontinence. Data were examined for associations between prevalence and survey type, response rate, year, and location of survey. RESULTS: A total of 21 studies met inclusion criteria. Stratification of reported prevalence by frequency, gender, and age substantially reduced the variation in prevalence estimates. For older women, the estimated prevalence of urinary incontinence ranged from 17 to 55% (median = 35%, pooled mean = 34%), and for daily incontinence it ranged from 3 to 17% (median = 14%, pooled mean = 12%). For older men, incontinence prevalence was estimated to be 11 to 34% (median = 17%, pooled mean = 22%), and 2 to 11% reported daily incontinence (median = 4%, pooled mean = 5%). Within studies, the prevalence of any incontinence was 1.3 to 2.0 times greater for older women than for older men. Among middle-aged and younger adults, prevalence of incontinence ranged from 12 to 42% (median = 28%, pooled mean = 25%) for women and from 3 to 5% (median = 4%, pooled mean = 5%) for men. The ratio of prevalence of any incontinence for women to men in this age group ranged from 4.1 to 4.5. Stress incontinence predominated in younger women, whereas urge and mixed incontinence predominated in older women. There was a tendency for studies using in-person interviews to report higher prevalences. CONCLUSIONS: An accurate estimate of the prevalence of urinary incontinence depends on specifying the definition of incontinence and the age and gender groups of interest.
Summary of magnet development in the past two years

Excepting Co-Sm, which may be considered a mature technology, recent permanent magnet research has proceeded along four lines, (a) improvement of the properties of Fe-Nd-B by alloying additions and processing, (b) the exploration of other alloy systems that feature the tetragonal compound of the Fe14Nd2B type, such as Fe-Pr-B and the carbides, (c) the systematic study of new magnetic compounds, such as those based on the Mn12Th structure, and (d) the characterization, sometimes elusive, of phases that are present in the known systems and contribute to coercivity.
The economics of indeterminacy in overlapping generations models

Abstract Recent research indicates that there are robust examples of overlapping generations economies in which there are indeterminate equilibria without fiat money and equilibria with more than one dimension of indeterminacy. This paper presents simple examples of a stationary, pure exchange overlapping generations economy with one good in each period and a representative consumer, who lives for three periods, in each generation. These examples exhibit every possible form of indeterminacy and instability. Furthermore, the parameters of the principal example agree with empirical evidence. We use our examples as case studies for analyzing the problems involved in computing the equilibria of such economies.
High effectiveness liquid droplet/gas heat exchanger for space power applications

A high-effectiveness liquid droplet/gas heat exchanger (LDHX) concept for thermal management in space is described. Heat is transferred by direct contact between fine droplets (approx. 100 to 300 micron diameter) of a suitable low vapor pressure liquid and an inert working gas. Complete separation of the droplet and gas media in the zero-g environment is accomplished by configuring the LDHX as a vortex chamber. The large heat transfer area presented by the small droplets permits heat exchanger effectiveness of 0.9 to 0.95 in a compact, lightweight geometry which avoids many of the limitations of conventional plate and fin or tube and shell heat exchangers, such as their tendency toward single point failure. The application of the LDHX in a high temperature Bryaton cycle is discussed to illustrate the performance and operational characteristics of this heat exchanger concept.
Electro-Optical Thin Films For Data Storage And Display

Thin film evaporation and sputtering methods in conjunction with photolithographic fabrication techniques provide a simple means for producing useful electro-optical devices. Multilayer Cd 1-xZnxS (CZS) compound photoconductive film deposited with rf sputtering exhibits a spectral response which can be varied between 360 nm to 530 nm. The CZS films exhibit a rise time of 1 pt sec, have good optical transmission characteristics, exhibit a photoconductive gain of approximately 10, respond to 400 mw laser pulses in a 1 mm spot and provide film breakdown strength of 30 x 104 volt/cm. Multilayer CZS films exhibit less photoconductive gain and higher breakdown strength than single layer films. Sn doped indium oxide (ITO) films are produced with magnetron rf sputtering. The conductivity and transmissivity of the ITO films are critically influenced by the amount of free oxygen present during the sputtering deposition. An 02 partial pressure of 4 x 105 results in greater than 80% transmissivity at 600 nm with a bulk conductivity of 100 mhos/cm. The film transmissivity can be substantially increased in the visible spectrum by post heat treatment in an air oven at 300 C for 20 minutes. A scanning cursor device for graphical data extraction was fabricated using various thin film techniques.
Calculating the Isgur-Wise function on the lattice

We calculate the Isgur-Wise function by measuring the heavy-heavy meson transition matrix element on the lattice. The standard Wilson action is used for both the heavy and light quarks. Our first numerical results are presented.
Topological Complexity of the Relative Closure of a Semi-Pfaffian Couple

Gabrielov introduced the notion of relative closure of a Pfaffian couple as an alternative construction of the o-minimal structure generated by Khovanskii’s Pfaffian functions. In this paper, we use the notion of format (or complexity) of a Pfaffian couple to derive explicit upper bounds for the homology of its relative closure. We consider both the singular and the Borel–Moore homology theories.
POLYAK–VIRO FORMULAS FOR COEFFICIENTS OF THE CONWAY POLYNOMIAL

We describe the Polyak–Viro arrow diagram formulas for the coefficients of the Conway polynomial. As a consequence, we obtain the Conway polynomial as a state sum over some subsets of the crossings of the knot diagram. It turns out to be a simplification of a special case of Jaeger's state model for the HOMFLY polynomial.
Wildly ramified covers with large genus

Abstract We study wildly ramified G-Galois covers ϕ : Y → X branched at B (defined over an algebraically closed field of characteristic p). We show that curves Y of arbitrarily high genus occur for such covers even when G, X, B and the inertia groups are fixed. The proof relies on a Galois action on covers of germs of curves and formal patching. As a corollary, we prove that for any nontrivial quasi-p group G and for any sufficiently large integer σ with p ∤ σ , there exists a G-Galois etale cover of the affine line with conductor σ above the point ∞.
Clues to Nuclear Star Cluster Formation from Edge-on Spirals

We find nine nuclear cluster candidates in a sample of 14 edge-on, late-type galaxies observed with the Hubble Space Telescope Advanced Camera for Surveys. These clusters have magnitudes (MI ~ -11) and sizes (reff ~ 3 pc) similar to those found in previous studies of face-on, late-type spirals and dE galaxies. However, three of the nuclear clusters are significantly flattened and show evidence for multiple, coincident structural components. The elongations of these three clusters are aligned to within ~10° of the galaxies' major axes. Structurally, the flattened clusters are well fit by a combination of a spheroid and a disk or ring, with the disk preferred in two of three cases. The nuclear cluster disks/rings have F606W - F814W (~V - I) colors 0.3-0.6 mag bluer than the spheroid components, suggesting that the stars in these components have ages <1 Gyr. In NGC 4244, the nearest of the nuclear clusters, we further constrain the stellar populations via spectroscopy and multiband photometry. This nuclear cluster is equally well fit by single stellar populations with ages of either ~70 Myr or ~0.8 Gyr and with masses of ~3 × 106 M⊙. However, significantly better fits to the spectroscopy and photometry are obtained by combining two or more stellar populations. Exploiting emission lines that appear to originate ~1'' from the NGC 4244 nucleus, we determine a lower limit on the dynamical mass of 2.5 × 106 M⊙ within 19 pc, typical of values found for other nuclear clusters. We also present tentative evidence that another of the nuclear clusters (in NGC 4206) may also host a supermassive black hole. Based on our observational results we propose an in situ formation mechanism for nuclear clusters in which stars form episodically in compact nuclear disks and then lose angular momentum or heat vertically to form an older spheroidal structure. We estimate the period between star formation episodes to be ~0.5 Gyr and discuss possible mechanisms for transforming the disklike components into spheroids. We also note the connection between our objects and massive globular clusters (e.g., ω Cen), ultracompact dwarfs, and supermassive black holes.
The Role of Cell-Cell Adhesion in Wound Healing

We present a stochastic model which describes fronts of cells invading a wound. In the model cells can move, proliferate, and experience cell-cell adhesion. We find several qualitatively different regimes of front motion and analyze the transitions between them. Above a critical value of adhesion and for small proliferation large isolated clusters are formed ahead of the front. This is mapped onto the well-known ferromagnetic phase transition in the Ising model. For large adhesion, and larger proliferation the clusters become connected (at some fixed time). For adhesion below the critical value the results are similar to our previous work which neglected adhesion. The results are compared with experiments, and possible directions of future work are proposed.
Automatic program synthesis: from CAD to CAM

The technology gap between design and manufacturing has stimulated a number of research projects whose common objective is to bring design specification into some form of procedure that specifies the manufacturing sequence and tool path. Most notably, there are two related areas of study---sculptured surfaces and process planning. The former is concerned with representing non-analytic surfaces in parametric forms so that points on a surface can be generated from the parametric equations as cutting tool locations. The latter is concerned with grouping conventional machine parts and describing the part in special programming languages or representing them in codes to arrive at operation sequences, choice of machine tools, cutting data, and other information.
Extensional and compressional instabilities in icy satellite lithospheres

A simple mechanical model of planetary lithospheres and asthenospheres is combined with the most recent experimental results concerning the brittle and ductile deformation of ice I_h to determine the plausibility of forming the grooved terrains on Ganymede, Enceladus, and Miranda by means of lithospheric instabilities. The model assumes a lithosphere of uniform strength atop a substrate whose strength decreases exponentially with depth. The thickness of the lithosphere is defined by the intersection of a near-surface Byerlee's law relationship for brittle failure with a standard exponential ductile flow law at depth. For Ganymede we find that the relatively high surface gravity warm temperatures render virtually unachievable an instability strong enough to account for the observed topographic relief. However, a sufficiently strong instability, capable of producing features with the proper spacing, could develop on a smaller, colder body such as Enceladus or Miranda. The requirements in this case would be a strain rate greater than about 10^(−14) sec^(−1) and a near-surface thermal gradient of a few tens of degrees Kelvin per kilometer. The most reasonable way to accomplish these requirements is by the intrusive emplacement of a thick layer of warm ice beneath a preexisting lithosphere of about a kilometer or so in thickness, accompanied almost contemporaneously by a strain event lasting on the order of 10^5 years for extension or 10^3 years for compression. However, observed properties of grooved terrains on Enceladus and Miranda, such as nonuniform feature spacing and low crater counts, force us to conclude that unstable deformation must be more complicated than this simple model would suggest if it is to explain these features.
Palladium‐Catalyzed SN1 Reactions of Secondary Benzylic Alcohols: Etherification, Amination, and Thioetherification

The reaction of various secondary benzylic alcohols in the presence of PdII catalysts provides ethers in good to high yields. Unsymmetric ethers could also be obtained with good selectivity by coupling two different alcohols. Direct amination is observed with electron-deficient anilines, and thioethers are prepared conveniently in high yields by the direct action of thiols on sec-phenylethyl alcohol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Diagnostic Imaging for Pediatric Scrotal Disorders

Classification of pediatric scrotal disorders into three typical clinical manifestations--acute scrotal disorders, scrotal masses, and cryptorchidism--provides a practical basis for evaluation with the most commonly used modalities--sonography, scintigraphy, and magnetic resonance (MR) imaging. Acute scrotal disorders of children include acute epididymitis, torsion of an appendix testis or appendix epididymis, and torsion of the spermatic cord. Either scintigraphy or sonography may be used as the first imaging study, and both can aid in distinguishing among the disorders to different degrees. However, sonography is becoming the preferred modality, primarily because of the superior anatomic detail provided. Scrotal masses are also best depicted with sonography, although MR imaging can occasionally be a useful adjunctive modality. In cases of suspected cryptorchidism with equivocal clinical findings, both sonography and MR imaging may be useful, although sonography is usually the initial study. Knowledge of characteristic imaging appearances, as well as benefits and limitations of the available modalities, enables appropriate, expeditious radiologic evaluation of pediatric scrotal disorders.
Ring expansion via olefin metathesis.

Various macrocycles were prepared in one step by a novel ring-expansion method using olefin metathesis.
Density-correlator signatures of the vulcanization transition

Certain density correlators, measurable via various experimental techniques, are studied in the context of the vulcanization transition. It is shown that these correlators contain essential information about both the vulcanization transition and the emergent amorphous solid state. Contact is made with various physical ingredients that have featured in experimental studies of amorphous colloidal and gel systems and in theoretical studies of the glassy state.
Dissipation in high temperature superconductors in a magnetic field

The absence of a Lorentz-force dependence on dissipation in the highly anisotropic high-temperature superconductor Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/ has been measured over a wide range of current densities in broadened resistive transitions, current-voltage characteristics, magnetoresistances, and critical current densities, J/sub c/. The magnetoresistances are very useful for determining the correct temperature and field dependences of the activation energy. As an alternative to flux motion, the authors consider a Josephson-coupling model which is consistent with the broadened resistive transitions and the lack of Lorentz-force dependence. It is found that the Josephson-coupling model agrees with the temperature dependences of the activation energy and J/sub c/ and is better matched to the weak-field dependence of J/sub c/ than the flux creep model. Possible origins of Josephson junctions in high-quality films and single crystals are discussed.
Generalized particle flow for nonlinear filters

We generalize the theory of particle flow to stabilize the nonlinear filter. We have invented a new nonlinear filter that is vastly superior to the classic particle filter and the extended Kalman filter (EKF). In particular, the computational complexity of the new filter is many orders of magnitude less than the classic particle filter with optimal estimation accuracy for problems with dimension greater than 4. Our accuracy is typically several orders of magnitude better than the EKF for nonlinear problems. We do not resample, and we do not use any proposal density from an EKF or UKF or other filter. Moreover, our new algorithm is deterministic, and we do not use any MCMC methods; this is a radical departure from other particle filters. The new filter implements Bayes' rule using particle flow rather than with a pointwise multiplication of two functions; this avoids one of the fundamental and well known problems in particle filters, namely "particle degeneracy." In addition, we explicitly stabilize our particle filter using negative feedback, unlike standard particle filters, which are generally very inaccurate for plants with slow mixing or unstable dynamics. This stabilization improves performance by several orders of magnitude for difficult problems.
Effectiveness of prescribed fire as a fuel treatment in Californian coniferous forests

Effective fire suppression and land use practices over the last century have altered forest structure and increased fuel loads in many forests in the United States, increasing the occurrence of catastrophic wildland fires. The most effective methods to change potential fire behavior are to reduce surface fuels, increase the canopy base height and reduce canopy bulk density. This multi-tiered approach breaks up the continuity of surface, ladder and crown fuels. Effectiveness of fuel treatments is often shown indirectly through fire behavior modeling or directly through monitoring wildland fire effects such as tree mortality. The present study investigates how prescribed fire affected fuel loads, forest structure, potential fire behavior, and modeled tree mortality at 90th and 97.5th percentile fire weather conditions on eight National Forests in California. Prescription burning did not significantly change forest structure at most sites. Total fuel loads (litter, duff, 1, 10, 100, and 1000-h) were reduced by 23 to 78% across the sites. The reduction in fuel loads altered potential fire behavior by reducing fireline intensity and increasing torching index and crowning index at most sites. Predicted tree mortality decreased after treatment as an effect of reduced potential fire behavior and fuel loads. To use limited fuel hazard reduction resources efficiently, more effort could be placed on the evaluation of existing fire hazards because several stands in the present study had little potential for adverse fire effects before prescribed fire was applied.
The Trouble with Hubble Types in the Virgo Cluster

Quantitative measures of central light concentration and star formation activity are derived from R and Hα surface photometry of 84 bright S0-Scd Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a good correlation between these two parameters and assigned Hubble types. In the Virgo Cluster, the correlation between central light concentration and star formation activity is significantly weaker. Virgo Cluster spirals have systematically reduced global star formation with respect to isolated spirals, with severe reduction in the outer disk, but normal or enhanced activity in the inner disk. Assigned Hubble types are thus inadequate to describe the range in morphologies of bright Virgo Cluster spirals. In particular, spirals with reduced global star formation activity are often assigned misleading early-type spiral classifications, irrespective of their central light concentrations; 45%±25% of the galaxies classified as Sa in the Virgo Cluster sample have central light concentrations more characteristic of isolated Sb-Sc galaxies. The misleading classification of low-concentration galaxies with low star formation rates as early-type spirals may account for part of the excess of "early-type" spiral galaxies in clusters. Thus, the morphology-density relationship is not all due to a systematic increase in the bulge-to-disk ratio with environmental density.
Key distributions for charmless semileptonic B decay

We present theoretical predictions for a few phenomenologically interesting distributions in the semileptonic b → u decays which are affected by Fermi motion. The perturbative effects are incorporated at the one-loop level and appear to be very moderate. Our treatment of Fermi motion is based directly on QCD, being encoded in the universal distribution function F(x). The decay distributions in the charged lepton energy, invariant mass of hadrons, hadron energy, and q2 are given. We note that typically about 90% of all decay events are expected to have MX < MD; this feature can be exploited in the determination of |Vub|.
WEIGHT SYSTEMS FOR MILNOR INVARIANTS

We use Polyak's skein relation to give a new proof that Milnor's string link invariants μ12⋯n are finite type invariants, and to develop a recursive relation for their associated weight systems. We show that the obstruction to the triviality of these weight systems is the presence of a certain kind of spanning tree in the intersection graph of a chord diagram.
Novel synthetic routes suitable for constructing benzopyrone combinatorial libraries

Abstract A series of O-( t -butylsilyloxy)benzoyl chlorides generated from the corresponding silyl esters were coupled with a range of terminal alkynes to afford the corresponding alkynyl ketones. The alkynyl ketones were converted to enaminoketones and then cyclized to yield the desired benzopyrone ring system. This synthetic protocol utilizes readily available starting materials, mild and high yielding reactions with good functional group tolerance, and is ideal for developing combinatorial libraries centered around the benzopyrone ring system.
Growth and structure of stochastic sequences

We introduce a class of stochastic integer sequences. In these sequences, every element is a sum of two previous elements, at least one of which is chosen randomly. The interplay between randomness and memory underlying these sequences leads to a wide variety of behaviours ranging from stretched exponential to log-normal to algebraic growth. Interestingly, the set of all possible sequence values has an intricate structure.
The SNAP-1 parallel AI prototype

The Semantic Network Array Processor (SNAP) is a parallel architecture for knowledge representation and reasoning that uses the marker-propagation paradigm. The primary application areas of SNAP are natural language understanding and speech processing. A first-generation SNAP-1 system has been designed and constructed using an array of 144 digital signal processors organized as 32 multiprocessing clusters with dedicated communication units, a tiered synchronization scheme, and multiported memory network. Issues in the design, performance, and scalability of a marker-propagation architecture are addressed. >
DLAs AND GALAXY FORMATION

Damped Lyman-α systems (DLAs) are useful probes of star formation and galaxy formation at high-redshift (hereafter high-z). We study the physical properties of DLAs and their relationship to Lyman break galaxies (LBGs) using cosmological hydrodynamic simulations based on the concordance Λ cold dark matter model. Fundamental statistics such as global neutral hydrogen (H I) mass density, H I column density distribution function, DLA rate-of-incidence and mean halo mass of DLAs are reproduced reasonably well by the simulations, but with some deviations that need to be understood better in the future. We discuss the feedback effects by supernovae and galactic winds on the DLA distribution. We also compute the [C II] emission from neutral gas in high-z galaxies, and make predictions for the future observations by the Atacama Large Millimeter Array (ALMA) and Space Infrared Telescope for Cosmology and Astrophysics (SPICA). Agreement and disagreement between simulations and observations are discussed, as well as the future directions of our DLA research.