cssi/SciSciGPT-SciSciNet huggingface dataset:
Interstellar Matter and the Boundary Conditions of the Heliosphere

The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun, and determines the boundary conditions of the heliosphere. Both the Sun and interstellar clouds move through space, so these boundary conditions change with time. Data and theoretical models now support densities in the cloud surrounding the solar system of n(H0) = 0.22 ± 0.06 cm-3, and n(e-) ∼.0.1 cm-3, with larger values allowed for n(H0) by radiative transfer considerations. Ulysses and Extreme Ultraviolet Explorer satellite He0 data yield a cloud temperature of 6400 K. Nearby interstellar gas appears to be structured and inhomogeneous. The interstellar gas in the Local Fluff cloud complex exhibits elemental abundance patterns in which refractory elements are enhanced over the depleted abundances found in cold disk gas. Within a few parsecs of the Sun, inconclusive evidence for factors of 2–5 variation in Mg+ and Fe+ gas phase abundances is found, providing evidence for variable grain destruction. In principle, photoionization calculations for the surrounding cloud can be compared with elemental abundances found in the pickup ion and anomalous cosmic-ray populations to model cloud properties, including ionization, reference abundances, and radiation field. Observations of the hydrogen pile up at the nose of the heliosphere are consistent with a barely subsonic motion of the heliosphere with respect to the surrounding interstellar cloud. Uncertainties on the velocity vector of the cloud that surrounds the solar system indicate that it is uncertain as to whether the Sun and α Cen are or are not immersed in the same interstellar cloud.
Theory of spiral structure.

It is an honor for me to continue the discussion of galactic spirals following Professor Bok, who has contributed to the subject for many years. My experience has been relatively short. My first encounter with the study of galactic spirals occurred in 1961, when I was invited by Professor Bengt Stromgren to attend a conference on interstellar matter at Princeton, N.J. There I first learned about the winding dilemma from Professor Jan Oort. After the conference, Professor Lodewijk Woltjer, who edited the Proceedings, visited me for about a month. Thus, I began slowly to learn about spiral galaxies and to work on the subject. It turned out to be an extremely rewarding experience, for the observational data were already ripe for theoretical analysis, and the hydromagnetic theory of spiral arms was clearly encountering great difficulties. Since I was not educated as an astronomer, I owe my gratitude to Professors Stromgren, Woltjer, and Kevin Prendergast, on whom I depended for correct astronomical facts as I started my work. Without their help, I would not be standing here today. Later on, I was to receive help from many other distinguished astronomers, including Professor Bok from whom you just heard. I am greatly impressed with the community of astronomers as a dedicated group of scientists.
Ab initio study of electron-phonon interaction in phosphorene

The monolayer of black phosphorus, or ``phosphorene,'' has recently emerged as a two-dimensional semiconductor with intriguing highly anisotropic transport properties. Existing calculations of its intrinsic phonon-limited electronic transport properties so far rely on the deformation potential approximation, which is in general not directly applicable to anisotropic materials since the deformation along one specific direction can scatter electrons traveling in all directions. We perform a first-principles calculation of the electron-phonon interaction in phosphorene based on density functional perturbation theory and Wannier interpolation. Our calculation reveals that (1) the high anisotropy provides extra phase space for electron-phonon scattering, and (2) optical phonons have appreciable contributions. Both effects cannot be captured by the deformation potential calculations. Our simulation predicts carrier mobilities $\ensuremath{\sim}170\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}/\mathrm{V}\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ for both electrons and holes at $300\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and a thermoelectric figure of merit $zT$ of up to 0.14 in $p$-type impurity-free phosphorene at $500\phantom{\rule{0.16em}{0ex}}\mathrm{K}$.
AN EMPIRICAL TEST OF PRICING KERNEL MONOTONICITY

A recent literature in finance concerns a curious recurring feature of estimated pricing kernels. Classical theory dictates that the pricing kernel { defined loosely as the ratio of Arrow security prices to an objective probability measure { should be a decreasing function of aggregate resources. Yet a large number of recent empirical studies appear to contradict this prediction. The nonmonotonicity of empirical pricing kernel estimates has become known as the pricing kernel puzzle. In this paper we propose and apply a formal statistical test of pricing kernel monotonicity. The test involves assessing the concavity of the ordinal dominance curve associated with the risk neutral and physical return distributions. We apply the test using thirteen years of data from the market for European put and call options written on the S&P 500 index. Statistically significant violations of pricing kernel monotonicity occur in a substantial proportion of months.
Spacetime Embedding Diagrams for Black Holes

We show that the 1 + 1 dimensional reduction(i.e., the radial plane) of the Kruskal black hole canbe embedded in 2 + 1 Minkowski spacetime and discuss howfeatures of this spacetime can be seen from theembedding diagram. The purpose of this work iseducational: The associated embedding diagrams may beuseful for explaining aspects of black holes to studentswho are familiar with special relativity, but notgeneral relativity.
Health shocks in China : are the poor and uninsured less protected ?

Health shocks have been shown to have important economic consequences in industrial countries. Less is known about how health shocks affect income, consumption, labor market outcomes, and medical expenditures in middle- and low-income countries. The authors explore these issues in China. In addition to providing new evidence on the general impact of health shocks, they also extend previous work by assessing the extent of risk protection afforded by formal health insurance, and by examining differences in the impact of health shocks between the rich and poor. The authors find that health shocks are associated with a substantial and significant reduction in income and labor supply. There are indications that the impact on income is less important for the insured, possibly because health insurance coverage is also associated with limited sickness insurance, but the effect is not significant. They also find evidence that negative health shocks are associated with an increase in unearned income for the poor but not the non-poor. This effect is however not strong enough to offset the impact on overall income. The loss in income is a consequence of a reduction in labor supply for the head of household, and the authors do not find evidence that other household members compensate by increasing their labor supply. Finally, negative health shocks are associated with a significant increase in out-of-pocket health care expenditures. More surprisingly, there is some evidence that the increase is greater for the insured than the uninsured. The findings suggest that households are exposed to considerable health-related shocks to disposable income, both through loss of income and health expenditures, and that health insurance offers very limited protection.
A primer on medical education in the United States through the lens of a current resident physician.

Physician training and standards for medical licensure differ widely across the globe. The medical education process in the United States (US) typically involves a minimum of 11 years of formal training and multiple standardized examinations between graduating from secondary school and becoming an attending physician with full medical licensure. Students in the US traditionally enter a 4-year medical school after completing an undergraduate bachelor’s degree, in contrast to most other countries where medical training begins after graduation from high school. Medical school seniors planning to practice medicine in the US must complete postgraduate clinical training, referred to as residency, within the specialty of their choosing. The duration of residency varies depending on specialty, typically lasting between 3 and 7 years. For subspecialty fields, additional clinical training is often required in the form of a fellowship. Many experts have called for changes in the medical education system to shorten medical training in the US, and reforms are ongoing in some institutions. However, physician education in the US generally remains a progression from undergraduate premedical coursework to 4 years of medical school, followed by residency training with an optional subspecialty fellowship.
The origins of a rich absorption line complex in a quasar at redshift 3.45

We discuss the nature and origin of a rich complex of narrow absorption lines in the quasar J 102325.31 +514251.0 at redshift 3.447. We measure nine C IV(λλ 1548, 1551 ) absorption line systems with velocities from -1400 to -6200 km s -1 , and full widths at half-minimum ranging from 16 to 350 kms -1 . We also detect other absorption lines in these systems, including H C III , N v, O VI and Si IV. Lower ionization lines are not present, indicating a generally high degree of ionization in all nine systems. The total hydrogen column densities range from ≲ 10 17.2 to 10 19.1 cm -2 . The tight grouping of these lines in the quasar spectrum suggests that most or all of the absorbing regions are physically related. We examine several diagnostics to estimate more directly the location and origin of each absorber. Four of the systems can be attributed to a quasar-driven outflow based on line profiles that are smooth and broad compared to thermal linewidths and to the typical absorption lines formed in intergalactic gas or galaxy haloes. Several systems also have other indicators of a quasar outflow origin, including partial covering of the quasar emission source (e.g. in systems with speeds too high for a starburst-driven flow), O vi column densities above 10 15 cm -2 and an apparent line-lock in C IV (in two of the narrow profile systems). A search for line variability yielded null results, although with very poor constraints because the comparison spectra have much lower resolution. Altogether (but not including the tentative line-lock) there is direct evidence for six of the nine systems forming in a quasar outflow. Consistent with a near-quasar origin, eight of the systems have metallicity values or lower limits in the range Z ≥ 1-8 Z ⊙ . The lowest velocity system, which has an ambiguous location based on the diagnostics mentioned above, also has the lowest metallicity, Z ≤ 0.3Z ⊙ , and might form in a non-outflow environment farther from the quasar. Overall, however, this complex of narrow absorption lines can be identified with a highly structured, multicomponent outflow from the quasar. The high metallicities are similar to those derived for other quasars at similar redshifts and luminosities, and are consistent with evolution scenarios wherein quasars appear after the main episodes of star formation and metal enrichment in the host galaxies.
Polyhedrization of discrete convex volumes

In recent years the problem of obtaining a reversible discrete surface polyhedrization (DSP) is attracting an increasing interest within the discrete geometry community. In this paper we propose the first algorithm for obtaining a reversible polyhedrization with a guaranteed performance, i.e., together with a bound on the ratio of the number of facets of the obtained polyhedron and one with a minimal number of facets. The algorithm applies to the case of a convex DSP when a discrete surface M is determined by a convex body in ℝ3. The performance estimation is based on a new lower bound (in terms of the diameter of M) on the number of 2-facets of an optimal polyhedrization. That bound easily extends to an arbitrary dimension n. We also discuss on approaches for solving the general 3D DSP.
Role of Complement and Complement Membrane Attack Complex in Laser-Induced Choroidal Neovascularization

Choroidal neovascularization (CNV), or choroidal angiogenesis, is the hallmark of age-related macular degeneration and a leading cause of visual loss after age 55. The pathogenesis of new choroidal vessel formation is poorly understood. Although inflammation has been implicated in the development of CNV, the role of complement in CNV has not been explored experimentally. A reliable way to produce CNV in animals is to rupture Bruch's membrane with laser photocoagulation. A murine model of laser-induced CNV in C57BL/6 mice revealed the deposition of C3 and membrane attack complex (MAC) in the neovascular complex. CNV was inhibited by complement depletion using cobra venom factor and did not develop in C3(-/-) mice. Anti-murine C6 Abs in C57BL/6 mice inhibited MAC formation and also resulted in the inhibition of CNV. Vascular endothelial growth factor, TGF-beta2, and beta-fibroblast growth factor were elevated in C57BL/6 mice after laser-induced CNV; complement depletion resulted in a marked reduction in the level of these angiogenic factors. Thus, activation of complement, specifically the formation of MAC, is essential for the development of laser- induced choroidal angiogenesis in mice. It is possible that a similar mechanism may be involved in the pathophysiology of other angiogenesis essential diseases.
Economic Growth and Financial Depth : Is the Relationship Extinct Already?

Although the financeâ€“growth nexus has become firmly entrenched in the empirical literature, studies that question the strength of the empirical results have appeared and seem to have become more frequent as well. In this paper we re-examine the core cou
The effect of set management on just-in-time manufacturing

The authors describe the implementation of the set management concept at IBM in Hopewell Junction in 1990. Set management is designed to release a package of layers, which have been combined at the substock crib, into a substrate part number, significantly lowering material handling and inventory levels resulting in improved test yields. In the revolutionized set management approach, layer job release was triggered by a new software system which balanced sets. When completed each layer job was placed directly into the magazine from which it would be released into stocking, eliminating handling steps and kitting. Inventory reduction was immediately visible with inventory levels going from 30-40 days to less than 10 days. Implementation of set management led to a 7% improvement in yield, a 6* reduction in layer inventory, a 3* reduction in crib storage time, and multiple handling and inspection reductions. The savings to IBM amounted to over $12 million. Process change results are now seen on a real-time basis. Software was instituted to do daily inventory checks and ensure that the line is loaded with the correct mix of part numbers to meet the highest measure of serviceability possible. >
Online scheduling to minimize the maximum delay factor

In this paper two scheduling models are addressed. First is the standard model (unicast) where requests (or jobs) are independent. The other is the broadcast model where broadcasting a page can satisfy multiple outstanding requests for that page. We consider online scheduling of requests when they have deadlines. Unlike previous models, which mainly consider the objective of maximizing throughput while respecting deadlines, here we focus on scheduling all the given requests with the goal of minimizing the maximum delay factor. The delay factor of a schedule is defined to be the minimum α ≥ 1 such that each request i is completed by time ai + α(di - ai) where ai is the arrival time of request i and di is its deadline. Delay factor generalizes the previously defined measure of maximum stretch which is based only the processing times of requests [9, 11].We prove strong lower bounds on the achievable competitive ratios for delay factor scheduling even with unit-time requests. Motivated by this, we consider resource augmentation analysis [24] and prove the following positive results. For the unicast model we give algorithms that are (1 + e)-speed O(1/e)-competitive in both the single machine and multiple machine settings. In the broadcast model we give an algorithm for same-sized pages that is (2 + e)-speed O(1/e2)-competitive. For arbitrary page sizes we give an algorithm that is (4 + e)-speed O(1/e2)-competitive.
Computer graphics-as seen on TV

Two multimedia integrated circuits, the TMC22090 and TMC22190 digital video encoders, are described. It is shown that they cost-effectively bring high levels of performance to computer-based video image generation. Systems and personal computer application boards built around these chips and the upcoming companion TMC22070 genlocking video digitizer will endow the professional and consumer computer user with multimedia and video processing capabilities such as text and graphics overlay, picture-in-picture, and special effects generation. >
In-Situ Electron Microscopy Studies of Palladium Supported on Al2O3 SiO2, and ZrO2 in Oxygen

Abstract Controlled atmosphere electron microscopy (CAEM) has been used to observe and compare directly the behavior of palladium particles supported on γ-alumina, silica and zirconia, when heated in the presence of oxygen. Palladium is converted to PdO on all three supports at temperatures in excess of 325°C and undergoes a wetting and spreading action to form thin flat crystallites. At temperatures above 750°C a significant fraction of the PdO disproportionates to form metallic Pd, which subsequently undergoes a rapid interaction with both alumina and silica at 800°C to form compounds that probably consist of mixtures of the respective oxides; however, the precise composition of these species cannot be determined. It is suggested that this phenomenon is responsible for deactivation of these catalyst systems at high temperatures. This type of interaction was not observed when zirconia-supported palladium specimens were treated under the same conditions. In this case, the support appeared to stabilize the formation of PdO up to 900°C. It is significant that on all supports a fraction of the palladium remains in the form of PdO up to the highest temperatures even though bulk thermodynamics predict that it should all be in the metallic state.
Synthesis and properties of the negative thermal expansion material cubic ZrMo2O8

A new phase, cubic ZrMo2O8, has been prepared by the low-temperature dehydration of ZrMo2O7(OH)2·2H2O. This material displays isotropic negative linear thermal expansion (α = −5.0 × 10-6 K-1) over a large temperature range. Unlike the previously reported cubic ZrW2O8, it does not undergo any phase transformations on heating at atmospheric pressure, and it does not display any pressure-induced phase transformations below 0.6 GPa at room temperature.
Short-term contracts and long-term agency relationships

Abstract Long-term contracts are valuable only if optimal contracting requires commitment to a plan today that would not otherwise be adopted tomorrow. We show that commitments are unnecessary, and hence short-term contracts are sufficient if (1) all public information can be used in contracting, (2) the agent can acess a bank on equal terms with the principal, (3) recontracting takes place with common knowledge about technology and preferences and (4) the frontier of expected utility payoffs generated by the set of incentive-compatible contracts is downward sloping at all times.
A FIRST LOOK AT ROTATION IN INACTIVE LATE-TYPE M DWARFS

We have examined the relationship between rotation and activity in 14 late-type (M6−M7) M dwarfs, using high-resolution spectra taken at the W. M. Keck Observatory and flux-calibrated spectra from the Sloan Digital Sky Survey. Most were selected to be inactive at a spectral type where strong Hα emission is quite common. We used the cross-correlation technique to quantify the rotational broadening; six of the stars in our sample have v sin i 3. 5k m s −1 . Our most significant and perplexing result is that three of these stars do not exhibit Hα emission, despite rotating at velocities where previous work has observed strong levels of magnetic field and stellar activity. Our results suggest that rotation and activity in late-type M dwarfs may not always be linked, and open several additional possibilities, including a rotationally dependent activity threshold, or a possible dependence on stellar parameters of the Rossby number at which magnetic/activity “saturation” takes place in fully convective stars.
Classical open string integrability

We present a simple procedure to construct non-local conserved charges for classical open strings on coset spaces. This is done by including suitable reflection matrices on the classical transfer matrix. The reflection matrices must obey certain conditions for the charges to be conserved and in involution. We then study bosonic open strings on AdS5 × S5. We consider boundary conditions corresponding to Giant Gravitons on S5, AdS4 × S2 D5-branes and AdS5 × S3 D7-branes. We find that we can construct the conserved charges for the full bosonic string on a Maximal Giant Graviton or a D7-brane. For the D5-brane, we find that this is possible only in a SU(2) sub-sector of the open string. Moreover, the charges can not be constructed at all for non-maximal Giant Gravitons. We discuss the interpretation of these results in terms of the dual gauge theory spin chains.
The extended phase space formulation of the Vinti problem

The Vinti problem, motion about an oblate spheroid, is formulated using the extended phase space method. The new independent variable, similar to the true anomaly, decouples the radius and latitude equations into two perturbed harmonic oscillators whose solutions toO(J 2 4 ) are obtained using Lindstedt's method. From these solutions and the solution to the Hamilton-Jacobi equation suitable angle variables, their canonical conjugates and the new Hamiltonian are obtained. The new Hamiltonian, accurate toO(J 2 4 ) is function of only the momenta.
GASCAN—An Interactive Code for Thermal Analysis of Gas Turbine Systems

A general, dimensionless formulation of the thermodynamic, heat transfer, and fluid-dynamic processes in a cooled gas turbine is used to construct a compact, flexible, interactive system-analysis program. A variety of multishaft systems using surface or evaporative intercoolers, surface recuperators, or rotary regenerators, and incorporating gas turbine reheat combustors, can be analyzed. Different types of turbine cooling methods at various levels of technology parameters, including thermal barrier coatings, may be represented. The system configuration is flexible, allowing the number of turbine stages, shaft/spool arrangement, number and selection of coolant bleed points, and coolant routing scheme to be varied at will. Interactive iterations between system thermodynamic performance and simplified quasi-three-dimensional models of the turbine stages allow exploration of realistic turbine-design opportunities within the system/thermodynamic parameter space. The code performs exergy-balance analysis to break down and trace system inefficiencies to their source components and source processes within the components, thereby providing insight into the interactions between the components and the system optimization tradeoffs.
Two-Dimensional Analysis of a Flat-Plate Solar Collector

The main objective of this study was to develop a two-dimensional theoretical model of a flat-plate solar collector which later could be used for optimizing the configuration parameters based on least cost per unit of energy absorbed. A rational and systematic two-dimensional analysis of a flat-plate solar collector is presented. By means of this model, for any given set of operating conditions, the instantaneous collector performance can be evaluated without having to assume average plate temperature. The results of this model vary significantly from those of the traditional lumped models, which as one should expect, give higher efficiencies in certain flow regimes. This may prove important in choosing physical dimensions of the collector for many applications.
Discriminants and nonnegative polynomials

For a semialgebraic set K in R^n, let P"d(K)={[email protected]?R[x]"@?"d:f(u)>[email protected][email protected]?K} be the cone of polynomials in [email protected]?R^n of degrees at most d that are nonnegative on K. This paper studies the geometry of its boundary @?P"d(K). We show that when K=R^n and d is even, its boundary @?P"d(K) lies on the irreducible hypersurface defined by the discriminant @D(f) of f. We show that when K={[email protected]?R^n:g"1(x)=...=g"m(x)=0} is a real algebraic variety, @?P"d(K) lies on the hypersurface defined by the discriminant @D(f,g"1,...,g"m) of f,g"1,...,g"m. We show that when K is a general semialgebraic set, @?P"d(K) lies on a union of hypersurfaces defined by the discriminantal equations. Explicit formulae for the degrees of these hypersurfaces and discriminants are given. We also prove that typically P"d(K) does not have a barrier of type [email protected](f) when @f(f) is required to be a polynomial, but such a barrier exists if @f(f) is allowed to be semialgebraic. Some illustrating examples are shown.
Synthesis and Biochemical Activity of Hydrophilic Carborane-Containing Pyrimidine Nucleosides as Potential Agents for DNA Incorporation and BNCT

Abstract A novel type of hydrophilic 5-tethered carborane-containing 2′-deoxyuridine derivative, SUB-7-DIOL, has been developed. This compound is a potential agent for DNA incorporation and BNCT, because it showed satisfactory aqueous solubility and demonstrated an excellent rate of phosphorylation by human thymidine kinase. This study also demonstrated the importance of tethering a flexible hydrocarbon chain between the carborane cage and the 5-position of the nucleoside, and the effectiveness of a water-solubilizing moiety attached to the carbon atom of the lipophilic carborane cage.
Modules-at-Infinity for Quantum Vertex Algebras

This is a sequel to [Li4] and [Li5] in a series to study vertex algebra-like structures arising from various algebras such as quantum affine algebras and Yangians. In this paper, we study two versions of the double Yangian \({DY_{\hbar}(sl_{2})}\) , denoted by DYq(sl2) and \({DY_{q}^{\infty}(sl_{2})}\) with q a nonzero complex number. For each nonzero complex number q, we construct a quantum vertex algebra Vq and prove that every DYq(sl2)-module is naturally a Vq-module. We also show that \({DY_{q}^{\infty}(sl_{2})}\) -modules are what we call Vq-modules-at-infinity. To achieve this goal, we study what we call \({\mathcal{S}}\) -local subsets and quasi-local subsets of \({Hom (W,W((x^{-1})))}\) for any vector space W, and we prove that any \({\mathcal{S}}\) -local subset generates a (weak) quantum vertex algebra and that any quasi-local subset generates a vertex algebra with W as a (left) quasi module-at-infinity. Using this result we associate the Lie algebra of pseudo-differential operators on the circle with vertex algebras in terms of quasi modules-at-infinity.
Sorbitol dehydrogenase inhibitors (SDIs): a new potent, enantiomeric SDI, 4-[2-1R-hydroxy-ethyl)-pyrimidin-4-yl]piperazine-1-sulfonic acid dimethylamide.

We report here on our medicinal chemistry and pharmacology efforts to provide a potent sorbitol dehydrogenase inhibitor (SDI) as a tool to probe a recently disclosed hypothesis centered on the role of sorbitol dehydrogenase (SDH) in the second step of the polyol pathway, under conditions of high glucose flux. Starting from a weak literature lead, 2, and through newly developed structure−activity relationships, we have designed and executed an unambiguous synthesis of enantiomeric SDI, 6, which is at least 10× more potent than 2. Also, 6 potently inhibits SDH in streptozotocin-diabetic rat sciatic nerve. We have described an expedient synthesis of a key building template, 33, for future research in the SDI area that may facilitate the discovery of even more potent SDIs with longer duration of action in vivo.
VARC consensus report: the FDA perspective

The Food and Drug Administration (FDA) is responsible for protecting and promoting the public health of US citizens. In keeping with this mission, FDA's Center for Devices and Radiological Health (CDRH) is tasked with assuring the safety, effectiveness, and quality of medical devices, assuring the safety of radiation-emitting products, fostering innovation, and providing the public with accurate, science-based information about the products we oversee, throughout the total product life cycle.1 In order to enhance our ability to fulfil our mission, CDRH developed a strategic plan to identify priority areas for 2010. One of our goals is to proactively help facilitate medical device innovation and address unmet public health needs.2 To accomplish this objective, CDRH believes it is critical to leverage our regulatory authority and unique understanding of the …
Gravitational waves: just plane symmetry

In four spacetime dimensions gravitational plane waves (a special case of the plane-fronted waves with parallel rays) admit a 5 parameter isometry group. We generalize this group to n-dimensions and explore some special features of spacetimes admitting this isometry group. In particular, it is shown that every generally covariant rank-2 symmetric tensor field constructed from a metric with plane wave symmetry will vanish except multiples of the metric and Ricci tensors. We show that, in four spacetime dimensions, a particular enlargement of the plane wave symmetry group is enough to force the group-invariant metrics to satisfy all generally covariant vacuum equations. We comment on the construction of a “mini-superspace” description of spacetimes admitting plane wave symmetry.
Recent radial turbine research at the NASA Lewis Research Center.

The major results obtained in several recent experimental programs on small radial inflow turbines for space applications are presented and discussed. Specifically, experimental and analytical work associated with these systems that has included examination of blade-shroud clearance, blade loading, and exit diffuser design, is considered. Results indicate high efficiency over a wide range of specific speed, and also insensitivity to clearance and blade loading in the radial part of the rotor. The exit diffuser investigation indicated that a conventional conical outer wall may not provide the velocity variation consistent with minimum overall diffuser loss.
ASSOCIATIVE RECALL BASED ON ABSTRACT OBJECT DESCRIPTIONS LEARNED FROM OBSERVATION: THE CBM NEURAL NET MODEL

The associative recall problem is approached here by means of a new neural net model. The model uses internal representations of objects automatically developed from observation. A feedback loop consisting of a Coulomb network is introduced to a classifier network. The classifier learns descriptions of various object types from observation of typical instances. The internal representations of the classifier are used by the Coulomb network to dynamically transform an incomplete or noisy input. Since the recall is based on abstract object descriptions the output is not limited to an a priori specified collection of memories (objects).
A Differential X-Ray Gunn-Peterson Test Using a Giant Cluster Filament

Using CCD detectors on board the forthcoming Chandra X-Ray Observatory and X-Ray Multimirror Mission, it is possible to devise a measurement of the absolute density of heavy elements in the hypothetical warm gas that is filling intercluster space. This gas may be the largest reservoir of baryonic matter in the universe, but even its existence has not been proved observationally at low redshifts. The proposed measurement would make use of a unique filament of galaxy clusters spanning over 700 h Mpc (0.1 z 0.2) along the line of sight in a small area of the sky in Aquarius. The surface density of Abell clusters there is more than 6 times the sky average. It is likely that the intercluster matter column density is enhanced by a similar factor, making its detection feasible under certain optimistic assumptions about its density and elemental abundances. One can compare photoabsorption depth, mostly in the partially ionized oxygen edges, in the spectra of clusters at different distances along the filament, looking for a systematic increase of depth with the distance. The absorption can be measured by the same detector and through the same Galactic column, hence the differential test. A CCD moderate-energy resolution (?E ~ 100 eV) is adequate for detecting an absorption edge at a known redshift.
A data-fitting procedure for chaotic time series

In this paper we introduce data characterizations for fitting chaotic data to linear combinations of one-dimensional maps (say, of the unit interval) for use in subgrid-scale turbulence models. We test the efficacy of these characterizations on data generated by a chaotically-forced Burgers' equation and demonstrate very satisfactory results in terms of modeled time series, power spectra and delay maps.
Challenges of laser-cooling molecular ions

The direct laser cooling of neutral diatomic molecules in molecular beams suggests that trapped molecular ions can also be laser cooled. The long storage time and spatial localization of trapped molecular ions provides an opportunity for multi-step cooling strategies, but also requires careful consideration of rare molecular transitions. We briefly summarize the requirements that a diatomic molecule must meet for laser cooling, and we identify a few potential molecular ion candidates. We then carry out a detailed computational study of the candidates BH+ and AlH+, including improved ab initio calculations of the electronic state potential energy surfaces and transition rates for rare dissociation events. On the basis of an analysis of the population dynamics, we determine which transitions must be addressed for laser cooling, and compare experimental schemes using continuous-wave and pulsed lasers.
Adaptive gridding strategies for Free-Lagrangian calculations of low speed flows

Abstract Free-Lagrangian methods have been employed in two-dimensional simulations of the long-term evolution of fluid instabilities for low speed flows. For example, calculations of the Rayleigh-Taylor instability have proceeded through the inversion and mixing of two fluid layers and simulations of droplet deformations have continued well beyond droplet shattering. The freedom to choose grid connections permits several important benefits for these calculations. 1. 1. Mass conservation is enforced for all individual fluid elements. 2. 2. Vertex movement is always Lagrangian. 3. 3. Grid adjustments can be made automatically, with no user intervention. 4. 4. Grid connections may be selected to ensure accuracy in the difference equations. 5. 5. Adaptive gridding schemes are local, adding and deleting vertices as dictated by local accuracy estimators. 6. 6. Any geometric configuration may be easily gridded, for any vertex distribution on the boundaries or in the interior of the fluids. This paper will review some two-dimensional results, with the emphasis on the adaptive gridding algorithms and the accuracy of the resultant difference templates for the mathematical operators. The relation of the triangular mesh to the Voronoi mesh will be explored, particularly for the case when they are dual meshes. Three-dimensional algorithms for adaptive gridding will be presented which are exact analogues to the two-dimensional case. Gridding efficiencies will be discussed for several schemes.
Similarity analysis of compressor tip clearance flow structure

A new approach is presented for analyzing compressor tip clearance flow. The basic idea is that the clearance velocity field can be (approximately) decomposed into independent throughflow and crossflow, since chordwise pressure gradients are much smaller than normal pressure gradients in the clearance region. As in the slender body approximation in external aerodynamics, this description implies that the three-dimensional steady clearance flow can be viewed as a two-dimensional, unsteady flow. Using this approach, a similarity scaling for the crossflow in the clearance region is developed and a generalized description of the clearance vortex is derived. Calculations based on the similarity scaling agree well with a wide range of experimental data in regard to flow features such as crossflow velocity field, static pressure field, and tip clearance vortex trajectory.
SEIBERG–WITTEN EQUATIONS ON SURFACES OF LOGARITHMIC GENERAL TYPE

We study the Seiberg–Witten (SW) equations on surfaces of logarithmic general type. First, we show how to construct irreducible solutions of the SW equations for any metric which is "asymptotic" to a Poincare type metric at infinity. Then we compute a lower bound for the L2-norm of scalar curvature on these spaces and give non-existence results for Einstein metrics on blow-ups.
INTELSAT V spacecraft design

Abstract This paper describes the newest and largest of the INTELSAT series of communications satellites being produced by Ford Aerospace and Communications Corporation. Multinational contributions to the proposed program are identified. Key aspects of the communications sub system discussed include antenna coverage areas; dual, circular polarization, multiple shaped beam antennas; communications transponder configuration; graphite-epoxy microwave filters; microwave integrated circuits; and contiguous band multiplexers. Other subystems, including the body-stabilized attitude control subsystem, are also reviewed.
INDETERMINACY IN A ONE-SECTOR MODEL REVISITED: DEMAND VERSUS SUPPLY-SIDE INDETERMINACY

This paper explains how indeterminacy in a one-sector model may arise due to externalities in the disutility of labor supply, which is termed as demand-side indeterminacy. This contrasts supply-side indeterminacy that is driven by externalities in the production function as exemplified by Benhabib and Farmer (Journal of Economic Theory, 1994). For the one-sector models considered, I find that indeterminacy arises more easily from the demand than from the supply side. In addition, demand and supply-side indeterminacy generate different cyclical patterns of wages, a feature that is useful for identifying episodes of self-fulfilling prophecies within the two types of indeterminacy.
Algorithms for unipolar and generalized split graphs

A graph G = ( V , E ) is a unipolar graph if there exists a partition V = V 1 ? V 2 such that V 1 is a clique and V 2 induces the disjoint union of cliques. The complement-closed class of generalized split graphs contains those graphs G such that either G or the complement of G is unipolar. Generalized split graphs are a large subclass of perfect graphs. In fact, it has been shown that almost all C 5 -free (and hence, almost all perfect graphs) are generalized split graphs. In this paper, we present a recognition algorithm for unipolar graphs that utilizes a minimal triangulation of the given graph, and produces a partition when one exists. Our algorithm has running time O ( n m + n m F ) , where m F is the number of edges added in a minimal triangulation of the given graph. Generalized split graphs can be recognized via this algorithm in O ( n 3 ) time. We give algorithms on unipolar graphs for finding a maximum independent set and a minimum clique cover in O ( n + m ) time, and for finding a maximum clique and a minimum proper coloring in O ( n 2.5 / log n ) time, when a unipolar partition is given. These algorithms yield algorithms for the four optimization problems on generalized split graphs that have the same worst-case time bounds. We also report that the perfect code problem is NP-complete for chordal unipolar graphs.
Fault-tolerant and deadlock-free routing in 2-D meshes using rectilinear-monotone polygonal fault blocks

We propose a deterministic fault-tolerant and deadlock-free routing protocol in 2-dimensional (2-D) meshes based on Wu's fault-tolerant odd–even turn model and Wang's rectilinear-monotone polygonal fault block model. The fault-tolerant odd–even turn protocol, also called extended X–Y routing, was originally proposed to achieve fault-tolerant and deadlock-free routing among traditional, rectangular fault blocks. It uses no virtual channels. The number of faults to be tolerated is unbounded as long as nodes outside fault blocks are connected in the mesh network. The recently proposed rectilinear-monotone polygonal fault blocks (also called minimal-connected-components or MCCs) are of the polygonal shapes, and are a refinement of rectangular fault blocks. The formation of MCCs depends on the relative locations of source and destination, and MCCs include far fewer healthy nodes in resultant fault blocks. In this paper, we show that with a simple modification, the extended X–Y routing can also be applied to 2-...
Transformations of the picrotoxanes: The synthesis of corianin and structural analogues from picrotoxinin

Abstract The neurochemically active picrotoxane sesquiterpene corianin and several structural analogues have been prepared from inexpensive, commercially available picrotoxin.
Shock Speed, Cosmic Ray Pressure, and Gas Temperature in the Cygnus Loop

Upper limits on the shock speeds in supernova remnants can be combined with post-shock temperatures to obtain upper limits on the ratio of cosmic ray to gas pressure (P CR/PG ) behind the shocks. We constrain shock speeds from proper motions and distance estimates, and we derive temperatures from X-ray spectra. The shock waves are observed as faint Hα filaments stretching around the Cygnus Loop supernova remnant in two epochs of the Palomar Observatory Sky Survey (POSS) separated by 39.1 years. We measured proper motions of 18 nonradiative filaments and derived shock velocity limits based on a limit to the Cygnus Loop distance of 576 ± 61 pc given by Blair et al. for a background star. The Position Sensitive Proportional Counter (PSPC) instrument on-board ROSAT observed the X-ray emission of the post-shock gas along the perimeter of the Cygnus Loop, and we measure post-shock electron temperature from spectral fits. Proper motions range from 27 to 54 over the POSS epochs and post-shock temperatures range from kT ~ 100-200 eV. Our analysis suggests a cosmic ray to post-shock gas pressure consistent with zero, and in some positions P CR is formally smaller than zero. We conclude that the distance to the Cygnus Loop is close to the upper limit given by the distance to the background star and that either the electron temperatures are lower than those measured from ROSAT PSPC X-ray spectral fits or an additional heat input for the electrons, possibly due to thermal conduction, is required.
Efficient arithmetic coding for wavelet image compression

We address efficient context modeling in arithmetic coding for wavelet image compression. Quantized highpass wavelet coefficients are first mapped into a binary source, followed by high order context modeling in arithmetic coding. A blending technique is used to combine results of context modeling of different orders into a single probability estimate. Experiments show that an arithmetic coder with efficient context modeling is capable of achieving a 10% bitrate saving (or 0.5 dB gain in PSNR) over a zeroth order adaptive arithmetic coder in high performance wavelet image coders.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
The Post-Common Envelope and Pre-Cataclysmic Binary PG 1224+309

We have made extensive spectroscopic and photometric observations of PG 1224+309, a close binary containing a DA white dwarf primary and an M4+ secondary. The Hα line is in emission due to irradiation of the M star by the hot white dwarf and is seen to vary around the orbit. From the radial velocities of the Hα line we derive a period of P = 0.258689 ± 0.000004 days and a semiamplitude of KHα = 160 ± 8 km s-1. We estimate a correction ΔK = 21 ± 2 km s-1, where KM = KHα + ΔK. Radial velocity variations of the white dwarf reveal a semiamplitude of KWD = 112 ± 14 km s-1. The blue spectrum of the white dwarf is well fitted by a synthetic spectrum having Teff = 29,300 K and log g = 7.38. The white dwarf contributes 97% of the light at 4500 A and virtually all of the light blueward of 3800 A. No eclipses are observed. The mass inferred for the white dwarf depends on the assumed mass of the thin residual hydrogen envelope: 0.40 M⊙ ≤ MWD ≤ 0.45 M⊙ for hydrogen envelope masses of 0 M⊙ ≤ MH ≤ 4 × 10-4 M⊙. We argue that the mass of the white dwarf is closer to 0.45 M⊙; hence, it appears that the white dwarf has a relatively large residual hydrogen envelope. The mass of the M star is then MM = 0.28 ± 0.05 M⊙, and the inclination is i = 77° ± 7°. We discuss briefly how PG 1224+309 may be used to constrain theories of close binary star evolution and the past and future histories of PG 1224+309 itself. The star is both a "post–common envelope" star and a "pre–cataclysmic binary" star. Mass transfer by Roche lobe overflow should commence in about 1010 yr.
A Pauson-Khand approach to the hamigerans.

An intramolecular Pauson−Khand reaction has been used in the construction of the tricyclic core common to the hamigeran terpenes. For effective cyclization, it was necessary to tether the olefin-containing moiety to the aromatic framework to reduce its conformation mobility; this was accomplished using a silylene protecting group. Efficient construction of the aryl enyne from a salicylic acid derivative was accomplished via ortho lithiation and Sonogashira cross-coupling chemistry.
The two-loop infrared structure of amplitudes with mixed gauge groups

The infrared structure of (multi-loop) scattering amplitudes is determined entirely by the identities of the external particles participating in the scattering. The two-loop infrared structure of pure QCD amplitudes has been known for some time. By computing the two-loop amplitudes for $\overline{f}f\longrightarrow X$ and $\overline{f}f\longrightarrow V_{1}V_{2}$ scattering in an SU(N)×SU(M)×U(1) gauge theory, I determine the anomalous dimensions which govern the infrared structure for any massless two-loop amplitude.
Radiative Regimes in Gamma-Ray Bursts and Afterglows

We present numerical simulations of gamma-ray bursts arising from external shocks in the impulsive and wind models, including a weak or a strong coupling between electrons and protons plus magnetic fields, and analyze the burst features in each scenario. We follow the dynamics of the ejecta and external medium into the late stages of deceleration in order to study the hydrodynamics of the remnant and the temporal and spectral evolution of the afterglow. A brief comparison with the optical and radio afterglows of GRB 970228 and GRB 970508 is made.
Sonogashira Couplings of Aryl Bromides: Room Temperature, Water Only, No Copper

Cross-coupling reactions between lipophilic terminal alkynes and aryl bromides can be catalyzed by ligated Pd, in the absence of copper, in pure water at ambient temperatures. Small amounts of the nonionic amphiphile PTS assist by virtue of nanometer micelles formed spontaneously in an aqueous medium.