cssi/SciSciGPT-SciSciNet huggingface dataset:
Phase and amplitude control of the radio frequency wave in the two-beam accelerator

Abstract The sensitivity of the radiofrequency (rf) wave generated by the free electron laser portion of a two-beam accelerator (TBA) is analyzed, both analytically and numerically in a “resonant particle” approximation. It is shown that the phase of the rf wave is strongly dependent upon errors in the wiggler strength and wavelength and upon the electron beam characteristics of energy and current. The resulting phase error is shown to be unacceptable for a TBA, given reasonable errors in various components. A feedback system is proposed which will keep the rf wave phase within acceptable bounds. However, the feedback system is, at best, cumbersome and a simpler system would be desirable.
On the sputter alteration of regoliths of outer solar system bodies

Abstract This paper discussed several processes that are expected to occur when the porous regoliths on bodies without atmospheres in the outer Solar System are subjected to energetic ion bombardment. The conclusions reached in many of the papers involving sputtering published in the planetary literature are qualitatively or quantitatively incorrect because effects of soil porosity have been neglected. It is shown theoretically and experimentally that porosity reduces the effective sputtering yield of a soil by more than an order of magnitude. Between 90 and 97% of the sputtered atoms are trapped within the regolith, where they are fractionated by differential desorption. Experiments indicate that more volatile species have higher desorption probabilities. This process is the most important way in which alteration of chemical and optical properties occurs when a regolith is sputtered. When a basic silicate soil is irridiated these effects lead to sputter-deposited films enriched in metallic iron, while O, Na, and K are preferentially lost. The Na and K are present in the atmosphere above the sputtered silicate in quantities much greater than their abundances in the regolith. Icy regoliths of SO 2 should be enriched in elemental S and/or S 2 O. This prediction is supported by the probable identification of S 2 O and polysulfur oxide bands in the IR spectra of H-sputtered SO 2 reported by M. Moore (1984, Icarus 59 , 114–128) . When porous mixtures of water, ammonia, and methane frosts are sputtered, the loss of H and surface reactions of C, N, and O in the deposits should produce complex hydrocarbons and carbohydrates, some of which may be quite dark. Such reactions may have played a role in the formation of the matrix material of carbonaceous chondrites prior to agglomeration.
Effect of Feedback Control on the Power Consumption of Induced-Strain Actuators:

In this paper we study the closed loop power flow characteristics between a controlled piezoelectric actuator and a current controlled drive amplifier for two different structural control laws. We determine the real and reactive power flow through the structure and actuator into the amplifier when the structure is excited with a sinusoidal disturbance force under both control laws. The dependence of the real and reactive components of the power on the material properties of the actuator, structure and the configuration of the controller is presented. These real and reactive power estimates are useful for sizing the drive amplifier for the actuator.
On the Transfer of Resonant-Line Radiation in Mesh Simulations

The last decade has seen applications of adaptive mesh refinement (AMR) methods for a wide range of problems from space physics to cosmology. With the advent of these methods, in which space is discretized into a mesh of many individual cubic elements, the contemporary analog of the extensively studied line radiative transfer (RT) in a semi-infinite slab is that of RT in a cube. In this study we provide an approximate solution of the RT equation, as well as analytic expressions for the probability distribution functions (PDFs) of the properties of photons emerging from a cube, and compare them with the corresponding slab problem. These PDFs can be used to perform fast resonant-line RT in optically thick AMR cells where, otherwise, it could take unrealistically long times to transfer even a handful of photons.
Fully persistent lists with catenation

This paper considers the problem of representing stacks with catenation so that any stack, old or new, is available for access or update operations. This problem arises in the implementation of list-based and functional programming languages. A solution is proposed requiring constant time and space for each stack operation except catenation, which requires O(log log k) time and space. Here k is the number of stack operations done before the catenation. All the resource bounds are amortized over the sequence of operations.
Analysis of cursor movements with a mouse

Abstract With a mouse input device, 32 experienced computer users moved a cursor from a starting position to a target, both of which were displayed simultaneously on the computer’s screen. Cursor movements occurred under conditions of variations in the angle of approach to the target, the target size and shape, the distance to the target, and the nature of the task, drag-drop or point-click. In a fully crossed within-subjects design, all variables studied significantly affected movement time. Fitts’ law accounted for 44% or 97% of the variance in movement time, depending on the method of analysis. Fitts’ law was not equally effective under all combinations of the variables studied. An analysis of residuals showed that residuals were smaller for a point-click task in comparison to a drag-drop task, and residuals were lowest for the largest target displayed at the shortest distance from the starting position. The application of Fitts’ law to cursor movements with a mouse should be qualified by noting the conditions under which the movements were observed.
A Standard Kinetic Energy Reservoir in Gamma-Ray Burst Afterglows

We present a comprehensive sample of X-ray observations of 41 γ-ray burst (GRB) afterglows, as well as jet opening angles, θj, for a subset with measured jet breaks. We show that there is a significant dispersion in the X-ray fluxes, and hence isotropic X-ray luminosities (LX,iso), normalized to t = 10 hr. However, there is a strong correlation between LX,iso and the beaming fractions, fb ≡ [1 - cos(θj)]. As a result, the true X-ray luminosity of GRB afterglows, LX = fbLX,iso, is approximately constant, with a dispersion of only a factor of 2. Since eEb ∝ LX, the strong clustering of LX directly implies that the adiabatic blast wave kinetic energy in the afterglow phase, Eb, is tightly clustered. The narrow distribution of LX also suggests that p ≈ 2, that inverse Compton emission does not in general dominate the observed X-ray luminosity, and that radiative losses at t < 10 hr are relatively small. Thus, despite the large diversity in the observed properties of GRBs and their afterglows, the energy imparted by the GRB central engine to the relativistic ejecta is approximately constant.
Logical-operator tradeoff for local quantum codes

We study the structure of logical operators in local D-dimensional quantum codes, considering both subsystem codes with geometrically local gauge generators and codes defined by geometrically local commuting projectors. We show that if the code distance is d, then any logical operator can be supported on a set of specified geometry containing ˜d qubits, where ˜dd^(1/(D−1)) = O(n) and n is the code length. Our results place limitations on partially self-correcting quantum memories, in which at least some logical operators are protected by energy barriers that grow with system size. We also show that for any two-dimensional local commuting projector code there is a nontrivial logical “string” operator supported on a narrow strip, where the operator is only slightly entangling across any cut through the strip.
LOCAL ENERGY ESTIMATES FOR THE FINITE ELEMENT METHOD ON SHARPLY VARYING GRIDS

Local energy error estimates for the nite element method for el- liptic problems were originally proved in 1974 by Nitsche and Schatz. These estimates show that the local energy error may be bounded by a local ap- proximation term, plus a global \pollution" term that measures the inuence of solution quality from outside the domain of interest and is heuristically of higher order. However, the original analysis of Nitsche and Schatz is restricted to quasi-uniform grids. We present local a priori energy estimates that are valid on shape regular grids, an assumption which allows for highly graded meshes and which much more closely matches the typical practical situation. Our chief technical innovation is an improved superapproximation result.
Permafrost Beneath the Beaufort Sea: Near Prudhoe Bay, Alaska

Nine holes were drilled and 27 sites were probed with a cone penetrometer. The deepest drill hole was 65.I m below the seabed, while a depth of 14.1 m was reached with the cone penetrometer. Engineering and chemical properties were determined from core samples and point penetration resistance data were obtained with the penetrometer. Thermal profiles were acquired at both the drill and probe sites. Temperatures below 0/sup 0/C were observed in all the drill and penetrometer holes logged, although frozen sediments were encountered only occasionally. Seasonally frozen sediments were observed near the seabed at each site. The degree of ice bonding, or strength, could be related to seabed temperature and was greatest in shallow water (<2 m). The penetrometer resistance and thermal data indicated that deeper ice-bonded sediments occur, for example approximately 12.7 m below the seabed in 2 m of water off the Sagavanirktok delta. Of eight holes drilled offshore, it appeared that four encountered bonded permafrost. In general, the position of the ice-bonded permafrost interface was extremely irregular. The depth below the seabed to this interface at various distances from shore along the line studied was 28.8 m at 1 km, 65.1 m at 3.5 km, 44.1more » m at 6.8 km, and 29.5 m at 17.2 km. Shallow, overconsolidated marine sediments were found in the upper fine-grained section at all of the drill sites investigated; the degree of overconsolidation varied considerably among the sites. This fine-grained section was up to 10 m thick and covered sands and coarse gravels.« less
Multipesticide residue method for fruits and vegetables: California Department of Food and Agriculture

This procedure describes the CDFA method for multipesticide residue analysis of fresh fruits and vegetables. An aliquot of chopped sample is blended with acetonitrile. The resulting aqueous acetonitrile extract is filtered and cleaned up via reverse phase solid phase extraction apparatus. The pH of the filtrate is adjusted to neutral using phosphate buffer and the acetonitrile layer is separated from the aqueous layer by a “salting out” process. An aliquot of the acetonitrile layer is concentrated with a K-D evaporator by forming an azeotrope with n-hexane. The prepared sample is assayed for pesticide residues using GLC and HPLC. The performance of this method was evaluated by fortifying 6 representative fruits and vegetables with 7 chlorinated hydrocarbons, 7 organophosphate and 7 N-methylcarbamate pesticides at 0.1–0.2 ppm. No matrix interference was observed and the recovery of residues varied among different samples as well as different pesticides. Chlorothalonil results varied widely with irreproducible recoveries. In general, the method appears to be fast, rugged, and able to detect routinely at the 0.01 ppm level.
The triggering and subsequent development of a solar flare.

High temporal and spatial resolution solar X-ray pictures of a flare at 1827 UT on 5 September 1973 were taken with the S-056 telescope on the Apollo telescope mount. Photographs taken at 9 sec intervals allow detailed information to be obtained about the site of the energy release, as well as about the evolution of the flare itself. Observations suggest that the flare occurred in an entire arcade of loops rather than in any single loop. Sequential brightening of different X-ray features indicates that some excitation moved perpendicular to the magnetic field of the arcade at velocities of 180 to 280 km/sec. The most intense X-ray features were located in places where the magnetic field composing the arcade had a small radius of curvature with horizontal field gradients higher than the surroundings region and where the axis of the arcade changed direction. It was felt that the arcade geometry strongly influenced the propagation of the triggering disturbance, as well as the storage and site of the subsequent deposition of energy. A magnetosonic wave is suggested as the propagating mechanism triggering instabilities that may have existed in the preflare structure.
PROCEED: A Pareto Optimization-Based Circuit-Level Evaluator for Emerging Devices

Evaluation of novel devices in the context of circuits is crucial to identifying and maximizing their value. We propose a new framework, Pareto optimization-based circuit-level evaluator for emerging device (PROCEED), that uses comprehensive performance, power, and area metrics for accurate device-circuit coevaluation through optimization of digital circuit benchmarks. The PROCEED assesses technology suitability over a wide operating region (megahertz to gigahertz) by leveraging available circuit knobs (threshold voltage assignment, power management, sizing, and so on). It improves the benchmark accuracy by $3\times $ to $115\times $ compared with the existing methods while offering orders of magnitude improvements in runtime over full physical design implementation flows. To illustrate the PROCEED's capabilities, we deploy it to assess emerging technologies, including novel tunneling field-effect transistors, compared with conventional silicon CMOS. As a further illustration, we extend PROCEED to evaluate future heterogeneous integration of varied devices onto the same silicon substrate.
Dual formulation of classical W -algebras

By extending the concept of Maurer-Cartan equations, a dual formulation of (classical) nonlinear extensions of the Virasoro algebra is introduced. This dual formulation is closely related to three-dimensional actions which are analogous to a Chern-Simons action. An explicit construction in terms of superfields of theN = 2 superW4-algebra is presented.
Method of Continuous Variations: Applications of Job Plots to the Study of Molecular Associations in Organometallic Chemistry[**]

Applications of the method of continuous variations (MCV or the Method of Job) to problems of interest to organometallic chemists are described. MCV provides qualitative and quantitative insights into the stoichiometries underlying association of m molecules of A and n molecules of B to form AmBn . Applications to complex ensembles probe associations that form metal clusters and aggregates. Job plots in which reaction rates are monitored provide relative stoichiometries in rate-limiting transition structures. In a specialized variant, ligand- or solvent-dependent reaction rates are dissected into contributions in both the ground states and transition states, which affords insights into the full reaction coordinate from a single Job plot. Gaps in the literature are identified and critiqued.
Two-Mirror Apodization for High-Contrast Imaging

Direct detection of extrasolar planets will require imaging systems capable of unprecedented contrast. Apodized pupils provide an attractive way to achieve such contrast, but they are difficult, perhaps impossible, to manufacture to the required tolerance, and they absorb about 90% of the light in order to create the apodization, which of course lengthens the exposure times needed for planet detection. A recently proposed alternative is to use two mirrors to accomplish the apodization. With such a system, no light is lost. In this paper, we provide a careful mathematical analysis, using one-dimensional mirrors, of the on-axis and off-axis performance of such a two-mirror apodization system. There appear to be advantages and disadvantages to this approach. In addition to not losing any light, we show that the nonuniformity of the apodization implies an extra magnification of off-axis sources and thereby makes it possible to build a real system with about half the aperture that one would otherwise require or, equivalently, resolve planets at about half the angular separation as one can achieve with standard apodization. More specifically, ignoring pointing error and stellar disk size, a planet at 1.7?/D ought to be at the edge of detectability. However, we show that the nonzero size of a stellar disk pushes the threshold for high contrast so that a planet must be at least 2.5?/D from its star to be detectable. The off-axis analysis of two-dimensional mirrors is left for future study.
Electromagnetic cascades in pulsars

The development of pair photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters and follows the curvature radiation emitted by the primary, the conversion of this radiation e(+) - e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma ray spectrum above 25 MeV, and that the final gamma ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction.
Ion transport in ionic liquid-swollen ionic polymer transducers

In this work a model of ion transport in ionic liquid-based ionic polymer-metal composites (IPMC's) is formulated using Nernst-Planck/Poisson (NPP) theory and numerical simulations are performed using the finite element method. IPMC's are smart materials which act as both sensors and actuators, and the use of an ionic liquid has been shown to dramatically increase transducer lifetime in free-air use while also allowing for higher applied voltages without chemical decomposition. We consider both the cation and anion of the ionic liquid to be mobile in addition to the mobile countercation of the transducer. The results show a nonlinear dynamic response which gives insight into transduction mechanisms which are unique to ionic liquid IPMC's as compared to their water-based counterparts.
Compressive measurement designs for estimating structured signals in structured clutter: A Bayesian Experimental Design approach

This work considers an estimation task in compressive sensing, where the goal is to estimate an unknown signal from compressive measurements that are corrupted by additive pre-measurement noise (interference, or “clutter”) as well as post-measurement noise, in the specific setting where some (perhaps limited) prior knowledge on the signal, interference, and noise is available. The specific aim here is to devise a strategy for incorporating this prior information into the design of an appropriate compressive measurement strategy. Here, the prior information is interpreted as statistics of a prior distribution on the relevant quantities, and an approach based on Bayesian Experimental Design is proposed. Experimental results on synthetic data demonstrate that the proposed approach outperforms traditional random compressive measurement designs, which are agnostic to the prior information, as well as several other knowledge-enhanced sensing matrix designs based on more heuristic notions.
Types of single particle symmetry breaking in transition metal oxides due to electron correlation

Very accurate wave functions are calculated for small transition metal oxide molecules. These wave functions are decomposed using reduced density matrices to study the underlying correlation of electrons. The correlation is primarily of left-right type between the transition metals and the oxygen atoms, which is mediated by excitations from the nominal single Slater ground state into antibonding and d-type orbitals. In a localized representation, this correlation manifests itself in a 2-electron hopping term that is off-diagonal. This term is of similar magnitude to the commonly considered Hubbard-type on-site interaction.
Synthesis of phosphatidyl-2-O-alkylinositols as potential inhibitors for PI specific PLC

Abstract (±)-Racemic phosphatidyl-2-O-methylinositol and phosphatidyl-2-O-heptylinositol were synthesized and tested as mechanism-based inhibitors of bacterial PI-PLC activity.
Metal–organic frameworks for artificial photosynthesis and photocatalysis

Solar energy is an alternative, sustainable energy source for mankind. Finding a convenient way to convert sunlight energy into chemical energy is a key step towards realizing large-scale solar energy utilization. Owing to their structural regularity and synthetic tunability, metal–organic frameworks (MOFs) provide an interesting platform to hierarchically organize light-harvesting antennae and catalytic centers to achieve solar energy conversion. Such photo-driven catalytic processes not only play a critical role in the solar to chemical energy conversion scheme, but also provide a novel methodology for the synthesis of fine chemicals. In this review, we summarize the fundamental principles of energy transfer and photocatalysis and provide an overview of the latest progress in energy transfer, light-harvesting, photocatalytic proton and CO2 reduction, and water oxidation using MOFs. The applications of MOFs in organic photocatalysis and degradation of model organic pollutants are also discussed.
Two-photon decay of 2 1 S 0 and 2 3 S 1 states of heliumlike ions

Systematic calculations of two-photon decay rates of metastable $2{}^{1}{S}_{0}$ and $2{}^{3}{S}_{1}$ states are presented for heliumlike ions with nuclear charges in the range $Z=2--100$. These calculations include retardation and are carried out using relativistic configuration-interaction wave functions that account for the Breit interaction. Photon energy distributions and total rates are given. The relativistic $2{}^{1}{S}_{0}$ decay rates agree, to within two standard deviations, with precise measurements for heliumlike Ar, Ni, Br, Kr, and Nb. The calculated $2{}^{1}{S}_{0}$ rates are 30% smaller than the corresponding nonrelativistic rates at high $Z$. The $2{}^{3}{S}_{1}$ two-photon decay rates remain a factor of about ${10}^{\ensuremath{-}4}$ of the corresponding $M1$ rates throughout the helium isoelectronic sequence.
Genetic algorithm for control design of biped locomotion

Dynamic biped walking is a difficult control problem. The design involves that of the controller as well as the gait. A typical design procedure involves tedious analysis, careful planning, and testing. The procedure is time consuming and the analysis is often based on some linearized model. Selection of control parameters and nominal trajectory determines the quality of control and in typical designs, some or all of the parameters are selected intuitively. The result is often not the best. If some special goal (such as to walk as fast as possible) is desirable, the design may become even harder. While the analytical approach is not easy, one possible alternative is to obtain the optimal or near-optimal design through parameter search. This study explores this approach. The design of the biped controller and gait is formulated as a parameter search problem, and a genetic algorithm is applied to help obtain the optimal design. Designs to achieve different goals, such as being able to walk on an inclined surface, walk at a high speed, or walk with a specified step size have been evolved with the use of the genetic algorithm. Simulation results show that the genetic algorithm (GA) is capable of finding good solutions. © 1997 John Wiley & Sons, Inc.
Total Synthesis of (+)-Sinefungin.

Sinefungin (1) a nucleoside antibiotic isolated from Streptomyces has been synthesized from d-ribose. Both the C-6 and C-9 stereogenic centers were constructed by efficient asymmetric syntheses. The C-6 amine stereochemistry was set by a highly diastereoselective allylation (>99% de) of a (1S,2R)-1-amino-2-indanol-derived oxazolidinone 9 followed by a Curtius rearrangement of 11 to 12. The C-9 amino acid stereochemistry of sinefungin (1) was established by a rhodium chiral bisphosphine-catalyzed asymmetric hydrogenation of an α-(acylamino)acrylate derivative. The anomeric adenosylation of the mixture of anomeric acetates 20 in the presence of C-6 urethane NH was found to be extremely difficult. Conversion of the C-6 urethane NH as its N-benzyl derivative 21 was necessary prior to the adenosylation reaction. Successful adenosylation was effectively carried out by Vorbruggen's protocol utilizing persilylated N6-benzoyladenine and trimethylsilyl triflate.
Conjugate Addition of Lithiated Methyl Pyridines to Enones

Preparatively useful conjugate addition of lithiated methyl pyridines to cyclic and acyclic enones is reported. Addition of 2-picoline to 3-penten-2-one led to a concise synthesis of the alkaloids (±)-senepodine G and (±)-cermizine C.
Human microsomal prostaglandin E synthase-1 (mPGES-1) binding with inhibitors and the quantitative structure-activity correlation.

The detailed structures of microsomal prostaglandin E synthase-1 (mPGES-1) binding with inhibitors have been studied, for the first time, by using a newly developed computational three-dimensional (3D) structural model of mPGES-1 along with a 3D-quantitative structure−activity relationship (3D-QSAR) analysis. The obtained satisfactory binding structures and 3D-QSAR models strongly suggest that the 3D structural model of mPGES-1 is reasonable for study of mPGES-1 binding with inhibitors and for future design of novel mPGES-1 inhibitors.
On conifolds and D3-branes

Abstract We search for Ricci flat, Kahler geometries which are asymptotic to the cone whose base is the space T 11 by working out covariantly constant spinor equations. The metrics we find are singular in the interior and introducing parallel D3-branes does not form regular event horizons cloaking the naked singularities. We also work out a supersymmetric ansatz involving only the metric and the 5-form field corresponding to D3-branes wrapping over the nontrivial 2-cycle of T 11 . We find a system of first-order equations and argue that the solution has an event horizon and the ADM mass per unit volume diverges logarithmically.
Nickel-catalyzed preparation of stereodefined allylic alcohols using silicon-tethered ynals

Abstract The nickel-catalyzed cyclization of silicon-tethered ynals is reported. The silicon heterocycles obtained may be converted into allylic alcohols that possess a stereodefined alkene unit via a cleavage process that involves stereospecific protodesilylation of the vinyl silane functionality.
VLF and HF plasma waves associated with spread-F plasma depletions observed on the C/NOFS satellite

The C/NOFS spacecraft frequently encounters structured plasma depletions associated with equatorial spread-F along its trajectory that varies between 401 km perigee and 867 km apogee in the low latitude ionosphere. We report two classes of plasma waves detected with the Vector Electric Field Investigation (VEFI) that appear when the plasma frequency is less than the electron gyro frequency, as is common in spread-F depletions where the plasma number density typically decreases below 104/cm3. In these conditions, both broadband VLF waves with a clear cutoff at the lower hybrid frequency and broadband HF waves with a clear cutoff at the plasma frequency are observed. We interpret these waves as “hiss-type” emissions possibly associated with the flow of suprathermal electrons within the inter-hemispherical magnetic flux tubes. We also report evidence of enhanced wave “transients” sometimes embedded in the broader band emissions that are associated with lightning sferics detected within the depleted plasma regions that appear in both the VLF and HF data. Theoretical implications of these observations are discussed.
Fractal Dimensions in Elastic-Plastic Beam Dynamics

Calculations of two types of fractal dimension are reported, regarding the elastic-plastic response of a two-degree-of-freedom beam model to short pulse loading. The first is Mandelbrot’s (1982) self-similarity dimension, expressing independence of scale of a figure showing the final displacement as function of the force in the pulse loading; these calculations were made with light damping. These results are equivalent to a microscopic examination in which the magnification is increased by factors of 102 ; 104 ; and 106 . It is found that the proportion and distribution of negative final displacements remain nearly constant, independent of magnification. This illustrates the essentially unlimited sensitivity to the load parameter, and implies that the final displacement in this range of parameters is unpredictable . The second fractal number is the correlation dimension of Grassberger and Procaccia (1983), derived from plots of Poincare intersection points of solution trajectories computed for the undamped model. This fractional number for strongly chaotic cases underlies the random and discontinuous selection by the solution trajectory of the potential well leading to the final rest state, in the case of the lightly damped model.
Reactions of some sulfur(II)- and iodine(III)-containing electrophiles with endo-tricyclo[6.2.1.02,7]undeca-4,9-diene-3,6-dione

Abstract Reaction of ArSCl (Ar = phenyl or ortho-nitrophenyl) withendo-tricyclo[6.2.1.02,7]- undeca-4,9-diene-3,6-dione (1) results in anti addition across the norbornene carbon-carbon double bond with concomitant aromatization of the cyclohexenedione ring, thereby affording 4 (87%) and 5 (63%), respectively. The corresponding reaction of PHSCl with 1 in the presence of added Ag(I) proceeds via polar addition across the norbornene carbon-carbon double bond with concomitant intramolecular nucleophilic trapping of an intermediate episulfonium ion by a distant CO group, thereby affording 6 (57% yield). The reaction of PhICl2 with 1, when carried out in the presence of SbCl5 or AgBF4, proceeds with concomitant Wagner-Meerwein rearrangement and aromatization to afford adducts 7a and 8, respectively.
Optimal Communication Algorithms for Heterogeneous Computing over ATM Networks

We present efficient algorithms for designing optimal collective communication primitives for cluster-based heterogeneous computing across Asynchronous Transfer Mode (ATM) networks. The virtual path (VP) concept is known to be a powerful transport mechanism for ATM networks. In many parallel processing applications, the potential communication pattern is known in advance. We then seek to find an optimal set of virtual paths to realize the communication pattern, such that the communication overhead of the parallel processing application is minimized, and at the same time, the extent to which the other data traffic in the network is affected by the data traffic generated by the parallel processing application is also minimized.We consider the following four collective communication problems that occur frequently in parallel computation:one-to-all broadcast,all-to-all broadcast,one-to-all scatter, andall-to-all scatter. We formulate these problems as combinatorial optimization problems of finding a system of virtual path routes in networks, with the objectives of minimizing the path length, the link congestion, and the node copy load. We consider two cases of data sources, namely homogeneous and heterogeneous. For the case ofhomogeneous sources, we presentpolynomial-timealgorithms for the problems of one-to-all broadcast, all-to-all broadcast, and one-to-all scatter, by converting these problems to the maximum-flow problems. For the case ofheterogeneous sources, we show that the problems of all-to-all broadcast, one-to-all scatter, and all-to-all scatter are allNP-complete. Finally, we present novelrandomizedalgorithms for these problems, and show that with high probability these algorithms yield good solutions in the sense that the objective functions yield values close to the optimums. The randomized algorithms can also be used to design near-optimummulticastcommunication primitives. These randomized algorithms make use of linear programming and are easy to implement, which makes them a potential candidate for practical implementations, even for very large networks.
ENSEMBLE SIMULATIONS OF PROTON HEATING IN THE SOLAR WIND VIA TURBULENCE AND ION CYCLOTRON RESONANCE

Protons in the solar corona and heliosphere exhibit anisotropic velocity distributions, violation of magnetic moment conservation, and a general lack of thermal equilibrium with the other particle species. There is no agreement about the identity of the physical processes that energize non-Maxwellian protons in the solar wind, but a traditional favorite has been the dissipation of ion cyclotron resonant Alfven waves. This paper presents kinetic models of how ion cyclotron waves heat protons on their journey from the corona to interplanetary space. It also derives a wide range of new solutions for the relevant dispersion relations, marginal stability boundaries, and nonresonant velocity-space diffusion rates. A phenomenological model containing both cyclotron damping and turbulent cascade is constructed to explain the suppression of proton heating at low alpha-proton differential flow speeds. These effects are implemented in a large-scale model of proton thermal evolution from the corona to 1 AU. A Monte Carlo ensemble of realistic wind speeds, densities, magnetic field strengths, and heating rates produces a filled region of parameter space (in a plane described by the parallel plasma beta and the proton temperature anisotropy ratio) similar to what is measured. The high-beta edges of this filled region are governed by plasma instabilities and strong heating rates. The low-beta edges correspond to weaker proton heating and a range of relative contributions from cyclotron resonance. On balance, the models are consistent with other studies that find only a small fraction of the turbulent power spectrum needs to consist of ion cyclotron waves.
ISOTROPICALLY DRIVEN VERSUS OUTFLOW DRIVEN TURBULENCE: OBSERVATIONAL CONSEQUENCES FOR MOLECULAR CLOUDS

Feedback from protostellar outflows can influence the nature of turbulence in star-forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star-forming regions, we previously (Carroll et al.) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here, we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scales effectively reducing the formation of large-scale turbulent density structures. These effects are qualitatively independent of resolution. We have also carried out Principal Component Analysis (PCA) for synthetic data from our simulations. We find that PCA as a tool for identifying the driving scale of turbulence has a misleading bias toward low amplitude large-scale velocity structures even when they are not necessarily the dominant energy containing scales. This bias is absent for isotropically forced turbulence but manifests strongly for collimated outflow driven turbulence.
Predicting Ambulance Demand: a Spatio-Temporal Kernel Approach

Predicting ambulance demand accurately at fine time and location scales is critical for ambulance fleet management and dynamic deployment. Large-scale datasets in this setting typically exhibit complex spatio-temporal dynamics and sparsity at high resolutions. We propose a predictive method using spatio-temporal kernel density estimation (stKDE) to address these challenges, and provide spatial density predictions for ambulance demand in Toronto, Canada as it varies over hourly intervals. Specifically, we weight the spatial kernel of each historical observation by its informativeness to the current predictive task. We construct spatio-temporal weight functions to incorporate various temporal and spatial patterns in ambulance demand, including location-specific seasonalities and short-term serial dependence. This allows us to draw out the most helpful historical data, and exploit spatio-temporal patterns in the data for accurate and fast predictions. We further provide efficient estimation and customizable prediction procedures. stKDE is easy to use and interpret by non-specialized personnel from the emergency medical service industry. It also has significantly higher statistical accuracy than the current industry practice, with a comparable amount of computational expense.
Spin Glass Behavior of Isolated, Geometrically Frustrated Tetrahedra of Iron Atoms in the Intermetallic La21Fe8Sn7C12

Metal flux synthesis in a low-melting eutectic mixture of lanthanum and nickel has produced a family of complex intermetallic carbide phases. La(21)Fe(8)M(7)C(12) (M = Sn, Bi, Sb, Te, Ge) has a new cubic structure featuring tetrahedra of iron atoms capped with carbon on each edge. These tetrahedra are surrounded by a La/M framework and are therefore isolated from each other. The antiferromagnetic coupling of the iron atoms is frustrated by their ideal tetrahedral arrangement; this is evidenced by magnetic susceptibility measurements on the La(21)Fe(8)Sn(7)C(12) analogue. Deviations from Curie-Weiss behavior begin at 100 K; variation in field-cooled vs zero-field-cooled behavior is seen at 5 K indicative of magnetic ordering. AC susceptibility data indicate that the temperature of this transition is frequency-dependent, behavior characteristic of spin glass systems.
Development of ultrahigh-resolution inelastic x-ray scattering optics

One of the major goals of the National Synchrotron Light Source II project is to achieve ultrahigh energy resolution up to 0.1 meV for medium-energy inelastic X-ray scattering spectroscopy based on the angular dispersion optics employing extremely asymmetric backscattering geometry. In this papaer, we describe the complete monochromatization mechanisms underlying the new optics. We have also designed and tested a CDW-CDW prototype under ambient condition, with which we have successfully demonstrated the important angular dispersion effect, the Borrman enhanced transmission effect, and other optical principles involved in every step of the entire diffraction process, and found good agreement with the theoretical expectations. These studies indicate that the new optics are feasible in principle but face some technical challenges that need to be solved by our future systematic research and development activities before their practical applications.
An improved approximation algorithm for uncapacitated facility location problem with penalties

In this paper, we consider an interesting variant of the classical facility location problem called uncapacitated facility location problem with penalties (UFLWP for short) in which each client is either assigned to an opened facility or rejected by paying a penalty. The UFLWP problem has been effectively used to model the facility location problem with outliers. Three constant approximation algorithms have been obtained (Charikar et al. in Proceedings of the Symposium on Discrete Algorithms, pp. 642–651, 2001; Jain et al. in J. ACM 50(6):795–824, 2003; Xu and Xu in Inf. Process. Lett. 94(3):119–123, 2005), and the best known performance ratio is 2. The only known hardness result is a 1.463-inapproximability result inherited from the uncapacitated facility location problem (Guha and Khuller in J. Algorithms 31(1):228–248, 1999). In this paper, We present a 1.8526-approximation algorithm for the UFLWP problem. Our algorithm significantly reduces the gap between known performance ratio and the inapproximability result. Our algorithm first enhances the primal-dual method for the UFLWP problem (Charikar et al. in Proceedings of the Symposium on Discrete Algorithms, pp. 642–651, 2001) so that outliers can be recognized more efficiently, and then applies a local search heuristic (Charikar and Guha in Proceedings of the 39th IEEE Symposium on Foundations of Computer Science, pp. 378–388, 1999) to further reduce the cost for serving those non-rejected clients. Our algorithm is simple and can be easily implemented.
REGRESSIONS, SHORT AND LONG

We study the problem of identification of the long regression E(y|x,z) when the short conditional distributions P(y|x) and P(z|x) are known but the long conditional distribution P(y|x,z) is not known. This problem often arises when a researcher utilizes data from two separate data sets. (A leading example is the ecological inference problem of political science, where voting behavior across electoral districts is observed from administrative records, the demographic composition of voters within a district is observed from census data, and the researcher wants to infer voting behavior conditional on district and demographic attributes.) We isolate an identification region containing feasible values of the long regression, and show that this region forms a sharp bound on the long regression. The identification region can be calculated precisely when y has finite support. When y has infinite support we characterize two sets, one that contains the identification region, and one that is contained by it. Following this completely nonparametric analysis, we examine the identifying power yielded by exclusion restrictions across distinct covariate values. Such restrictions cause the identification region to shrink, in many cases to a single point. To illustrate the theory, we pose and address this hypothetical question: What would be the outcome if the 1996 U.S. presidential election were re-enacted in a population of different demographic composition, ceteris paribus?
Nonwhite migration, welfare, and politics: a re-examination

Professor Jones-Hendrickson (hereafter J-H) raises a very important point regarding the specification of my model. I shall first directly address the basic J-H comment and then I shall correct my model accordingly. I. The J-H criticism Essentially J-H is arguing that in the final analysis my two- equation system is not properly identified. I have two observations to make. First from a technical viewpoint each equation must have at least two exogenous variables and at least one exogenous variable not found in the other equation. Clearly equation (1) has the exogenous variables U(i) and I(i) whereas equation (2) has the exogenous variables U(i) and I(i). Thus since I(i) and Y(i) are not identical the system is in fact appropriately identified - the computer can run the model by TSLS. Second J-H is in a very real theoretical sense correct in his charge because I(i) and Y(i) are so highly (and positively) correlated. In other words the results of my estimates may be biased due to the existence of collinearity between Y(i) and I(i). As a result the hypothesis requires re-examination for my original estimates lack dependability. (excerpt)
A comparative study of the parabolized Navier-Stokes code using various grid-generation techniques

The parabolized Navier-Stokes (PNS) equations are used to calculate the flow-field characteristics about the hypersonic research aircraft X-24C. A comparison of the results obtained using elliptic, hyperbolic, and algebraic grid generators is presented. The outer bow shock is treated as a sharp discontinuity, and the discontinuities within the shock layer are captured. Surface pressures and heat-transfer results at angles of attack of 6 deg and 20 deg, obtained using the three grid generators, are compared. The PNS equations are marched downstream over the body in both Cartesian and cylindrical base coordinate systems, and the results are compared. A robust marching procedure is demonstrated by successfully using large marching step sizes with the implicit shock fitting procedure. A correlation is found between the marching step size, Reynolds number, and the angle of attack at fixed values of smoothing and stability coefficients for the marching scheme.
Identifying Young Brown Dwarfs Using Gravity-Sensitive Spectral Features

We report the initial results of the Brown Dwarf Spectroscopic Survey Gravity Project to study gravity sensitive features as indicators of youth in brown dwarfs. Low-resolution (R ~ 2000) J-band and optical (R ~ 1000) observations using NIRSPEC and LRIS at the W. M. Keck Observatory reveal transitions of TiO, VO, K I, Na I, Cs I, Rb I, CaH, and FeH. By comparing these features in late-type giants and in old field dwarfs, we show that they are sensitive to the gravity (g = GM/R2) of the object. Using low-gravity spectral signatures as age indicators, we observed and analyzed J-band and optical spectra of two young brown dwarfs, G196-3B (20-300 Myr) and KPNO Tau 4 (1-2 Myr) and two possible low-mass brown dwarfs in the σ Orionis cluster (3-7 Myr). We report the identification of the bands of TiO near 1.24 μm and the A-X band of VO near 1.18 μm together with extremely weak J-band lines of K I in KPNO Tau 4. This is the first detection of TiO and VO in the J band in a substellar-mass object. The optical spectrum of KPNO Tau 4 exhibits weak K I and Na I lines, weak absorption by CaH, and strong VO bands, also signatures of a lower gravity atmosphere. G196-3B shows absorption features in both wavelength regions, like those of KPNO Tau 4, suggesting that its age and mass are at the lower end of published estimates. Whereas σ Ori 51 appears to be consistent with a young substellar object, σ Ori 47 shows signatures of high gravity most closely resembling an old L1.5/L0 and cannot be a member of the σ Orionis cluster.
Asset price volatility in a nonconvex general equilibrium model

Asset prices and returns are known to vary significantly more than␣output or aggregate consumption growth, and an order of magnitude in excess of what is justified by innovations to fundamentals. We study excess price volatility in a lifecycle economy with two assets (claims on capital and␣a public debt bubble), heterogeneous agents, and increasing returns to financial intermediation. We show that a relatively modest nonconvexity generates a set valued equilibrium correspondence in asset prices, with two␣stable branches. Price volatility is the outcome of an equilibrium selection mechanism, which mixes adaptive learning with “noise”, and alternates stochastically between the two stable branches of the price correspondence.
Intertemporal choice and the magnitude effect

A robust finding in experiments on time preference is the magnitude effect: subjects tend to be more patient towards larger rewards. Using a calibration theorem, we argue against standard curvature-based explanations for the finding. We axiomatize a model of preferences over dated rewards that generalizes the standard exponential discounting model by permitting the discount factor to depend on the reward being discounted. The model is shown to behaviorally subsume the hyperbolic discounting model as a special case. When embedded in a sequential bargaining game the model gives rise to multiple stationary subgame perfect equilibria. There may exist equilibria in which the first mover gets a smaller share despite also being the more patient player.