cssi/SciSciGPT-SciSciNet huggingface dataset:
TRIGGERING COLLAPSE OF THE PRESOLAR DENSE CLOUD CORE AND INJECTING SHORT-LIVED RADIOISOTOPES WITH A SHOCK WAVE. I. VARIED SHOCK SPEEDS

The discovery of decay products of a short-lived radioisotope (SLRI) in the Allende meteorite led to the hypothesis that a supernova shock wave transported freshly synthesized SLRI to the presolar dense cloud core, triggered its self-gravitational collapse, and injected the SLRI into the core. Previous multidimensional numerical calculations of the shock-cloud collision process showed that this hypothesis is plausible when the shock wave and dense cloud core are assumed to remain isothermal at ~10 K, but not when compressional heating to ~1000 K is assumed. Our two-dimensional models with the FLASH2.5 adaptive mesh refinement hydrodynamics code have shown that a 20 km s?1 shock front can simultaneously trigger collapse of a 1 M ? core and inject shock wave material, provided that cooling by molecular species such as H2O, CO, and H2 is included. Here, we present the results for similar calculations with shock speeds ranging from 1?km?s?1 to 100?km?s?1. We find that shock speeds in the range from 5?km?s?1 to 70?km?s?1 are able to trigger the collapse of a 2.2 M ? cloud while simultaneously injecting shock wave material: lower speed shocks do not achieve injection, while higher speed shocks do not trigger sustained collapse. The calculations continue to support the shock-wave trigger hypothesis for the formation of the solar system, though the injection efficiencies in the present models are lower than desired.
Online algorithms for the multi-armed bandit problem with Markovian rewards

We consider the classical multi-armed bandit problem with Markovian rewards. When played an arm changes its state in a Markovian fashion while it remains frozen when not played. The player receives a state-dependent reward each time it plays an arm. The number of states and the state transition probabilities of an arm are unknown to the player. The player's objective is to maximize its long-term total reward by learning the best arm over time. We show that under certain conditions on the state transition probabilities of the arms, a sample mean based index policy achieves logarithmic regret uniformly over the total number of trials. The result shows that sample mean based index policies can be applied to learning problems under the rested Markovian bandit model without loss of optimality in the order. Moreover, comparision between Anantharam's index policy and UCB shows that by choosing a small exploration parameter UCB can have a smaller regret than Anantharam's index policy.
Experience with a radio frequency gun on the SSRL Injector Linac

A-SSRL/Varian-Associates-built, one-and-a-half cavity, microwave, thermionic-cathode gun has operated on the SSRL Injector Linac reliably without changing the cathode for over 10,000 hours, with no significant decrease in emission. Thus, for a pulsed electron beam, with a maximum of 0.5 A peak at 2 to 3 MeV from a 3.5 MW peak rf pulse of 2 /spl mu/s pulse width at 10 pps, the apparent but small amount of back bombardment of the cathode has been tolerable. Use of a bunch-compression alpha magnet and a stripline chopper after the gun produces the required S-band 3 to 5 microbunches of electrons for injection into a standard 10-m-long linac and on into a booster synchrotron, which in turn is used to fill SPEAR. Component limitations and operating characteristics of the gun and the linac's rf system are discussed. >
Effects of thermal gradients on total internal reflection corner cubes

Uncoated corner cube retroreflectors (CCRs) operating via total internal reflection (TIR) are less susceptible to internal heating than their metal-coated analogs, lacking an absorber on the rear surface. Even so, environments that induce differential heating within the CCR will result in thermal lensing of the incident wavefront, introducing aberrations that will generally reduce the central irradiance of the polarization-sensitive far-field diffraction pattern (FFDP). In this paper, we characterize the sensitivity of TIR CCRs to axial and radial thermal gradients. We present simulated FFDPs for key input polarizations and incidence angles and provide a generalized analytic model that approximates the behavior of the central irradiance as temperature differences are introduced.
Cognitive and psychological computation with neural models

Biological support exists for the idea that large-scale models of the brain should be parallel, distributed, and associative. Some of this neurobiology is reviewed. It is then assumed that state vectors, large patterns of activity of groups of individual somewhat selective neurons, are the appropriate elementary entities to use for cognitive computation. Simple neural models using this approach are presented that will associate and will respond to prototypes of sets of related inputs. Some experimental evidence supporting the latter model is discussed. A model for categorization is then discussed. Educating the resulting systems and the use of error correcting techniques are discussed, and an example is presented to the behavior of the system when diffuse damage occurs to the memory, with and without compensatory learning. Finally, a simulation is presented which can learn partial information, integrate it with other material, and use that information to reconstruct missing information.
Optimal polarizations for radar detection and recognition of targets in clutter

The authors investigate the detection and recognition of stationary ground targets in high-resolution, fully polarimetric synthetic aperture radar (SAR) imagery. Using 1-ft*1-ft SAR imagery of targets and clutter gathered by a 33-GHz sensor, several techniques for improving target detection performance through optimal processing of the fully polarimetric SAR data. >
Could Pantheon Fossae be the result of the Apollodorus crater-forming impact within the Caloris basin, Mercury?

Abstract The ~ 40-km-diameter Apollodorus impact crater lies near the center of Pantheon Fossae, a complex of radiating linear troughs itself at the approximate center of the 1500-km-diameter Caloris basin on Mercury. Here we use a series of finite element models to explore the idea that the Apollodorus crater-forming impact induced the formation of radially oriented graben by altering a pre-existing extensional stress state. Graben in the outer portions of the Caloris basin, which display predominantly circumferential orientations, have been taken as evidence that the basin interior was in a state of horizontal extensional stress as a result of uplift. If the Apollodorus crater formed at the time of such a stress state, impact-induced damage to basin fill material would have caused basin material to move radially outward, leading to a decrease in the radial extensional stress and an increase in the circumferential stress. If this change in differential stress was sufficient to induce failure, the predicted style of faulting would be radial graben extending outward from the exterior crater rim. The ~ 230-km radial extent of Pantheon Fossae implies, by this scenario, that the Apollodorus impact generated a large damage zone, extending to perhaps three crater radii (~ 60 km) or more. The calculations also suggest, under this scenario, that the Caloris basin fill had greater strength than the surrounding crust and that the basin uplift and extensional stress field prior to the Apollodorus impact were close to azimuthally symmetric. The location of Pantheon Fossae very near the center of the Caloris basin appears to be coincidental; any crater similar in size to Apollodorus and located within ~ 300 km of the basin center could have produced a radiating set of graben by the mechanism explored here.
Tradeoff of horizontal decomposition versus vertical stacking in rearrangeable nonblocking networks

A class of rearrangeable nonblocking networks is presented. The proposed networks are fault-tolerant, self-routing, and intended for a very-high-speed environment. Self-routing networks have one major problem when applied to switching: they are blocking networks. To solve this problem, two methods have been used to create self-routing rearrangeable nonblocking networks: horizontal cascading (HC) and vertical stacking (VS). The authors unify the two approaches and propose a novel class of switching networks. The proposed design principle allows the best tradeoffs among design parameters such as fault tolerance, hardware cost, and the frequency of rearrangement activities. A study of the frequency of rearrangement activities is also presented. >
Bone Loss at the Femoral Neck in Premenopausal White Women: Effects of Weight Change and Sex-Hormone Levels

To investigate whether bone loss occurs in the premenopause, we measured the bone mineral content (BMC), bone mineral density (BMD), and bone area in the spine (L2-L4), femoral neck, and total hip, as well as the sex hormone levels of 130 healthy premenopausal white women (age, 31-50 yr) at least three times over 1-9 yr. We found an increase in all three bone measurements at the spine but no change in volumetric density. Neither could we detect any age-related changes in any of the three measurements in the total hip. In contrast, we detected a significant decrease in femoral neck BMD over time, due to a decrease in BMC and increase in bone area. Greater loss in femoral neck BMD was associated independently with weight loss and lower levels of estrone sulfate or E2. Separating the women into those with FSH spikes (>20 IU/liter) and women with consistently low FSH, we found the latter group had smaller decrease in BMD and that the decrease was due less to a decline in BMC and more to an increase in bone area. In summary, femoral neck BMD decreases in premenopausal women, particularly those with lower levels of estrogens resulting from slowing ovarian function despite regular menses. This decrease can be offset by more rapid weight gain.
An "NLC-Style" short bunch length compressor in the SLAC linac

Experimental tests of a "second bunch length compressor" in a linac is important for the next generation of linear colliders and for other future accelerators. These future accelerators need bunches with lengths of order 0.06-0.2 mm. At these lengths, new accelerator dynamics will be encountered. We have studied the possibility of constructing a second compressor with the present SLAC linac and have found a reasonable design. The core of this project is to reconfigure an old beamline (BL-90) at the 1000 m location in the linac to: (1) extract a 10 GeV bunch, (2) pass it through a new 96 m long transport line in which length compression is done, and (3) reinject the beam into the main linac in an available drift section. Using the resulting compressed bunch, accelerator physics tests would be performed in the remaining downstream linac with the resulting very high charge density. The bunch compression in this transport line results from the TRANSPORT element R/sub 56/ as determined from the optics of the transport line. /spl Delta/z=R/sub 56/ /spl Delta/E/E. For example, if /spl Delta/z=-0.5 mm, /spl Delta/E/E=0.5%, R/sub 56/=-0.1 m, a bunch of 5/spl times/10/sup 10/ particles would have a final length (/spl sigmasub 7/) of about 0.08 mm with a peak current of 9600 A. >
Online Engineering Education: Learning Anywhere, Anytime

The emergence of worldwide communications networks and powerful computer technologies has redefined the concept of distance learning and the delivery of engineering education content. This article discusses the Sloan Consortium’s quest for quality, scale, and breadth in online learning, the impact on both continuing education of graduate engineers as well as degree-seeking engineering students, and the future of engineering colleges and schools as worldwide providers of engineering education.
Strategic contributions of game rooms to knowledge management: some prelimenary insights

Academics and practitioners have stressed the significance of managing knowledge in today's competitive environment. This has resulted in many efforts to increase knowledge exchange between organizational members. Much work so far has focused on the use of information technology as either a solution or enabler of knowledge management. While information technology enables easy exchange of explicit knowledge, its contributions to sharing tacit knowledge is restricted to connecting individuals via tools, such as e-mail and groupware. This research adds to the literature by reporting on a people-centered perspective for facilitating tacit knowledge exchange. The article describes an in-depth case study carried out to determine the role played by game rooms in the exchange of tacit knowledge.
Modeling Progressive Failure of Bonded Joints Using a Single Joint Finite Element

Enhanced finite elements are elements with an embedded analytical solution that can capture detailed local fields, enabling more efficient, mesh-independent finite element analysis. In the present study, an enhanced finite element, referred to as a bonded joint element, that is capable of modeling an array of joint types is developed. The joint field equations are derived using the principle of minimum potential energy, and the resulting solutions for the displacement fields are used to generate shape functions and a stiffness matrix for a single joint finite element. This single finite element thus captures the detailed stress and strain fields within the bonded joint, but it can function within a broader structural finite element model. The costs associated with a fine mesh of the joint can thus be avoided,whilestillobtainingadetailedsolutionforthejoint.Additionally,thecapabilitytomodelnonlinearadhesive constitutivebehaviorhasbeenincludedwithinthemethod,andprogressivefailureoftheadhesivecanbemodeledby using a strain-based failure criteria and resizing the joint as the adhesive fails. Results of the model compare favorably with available experimental and finite element results.
If You Provide It, Will They Read It? The Effect of Information on Choices

This paper investigates the effect of information on respondent's choices in an internet survey for measuring the value of water quality improvements in Deckers Creek (DC) watershed in Monongalia and Peterson Counties of West Virginia, USA. A multiattribute, choice experiment and multinomial logit (MNL) models are used in estimating the marginal utilities of restoring the three attributes of DC: aquatic life, swimming safety, and scenic quality. Response times serve as proxy variables regarding whether respondents read or did not read all the information provided in the survey. Response times fell quickly, but then tapered off as they progressed through the various sections of the survey. Results show that the estimated coefficients of subsamples, read and did not read all the information, were statistically different from each other. Based on log likelihood tests of MNL models, two subsamples of the survey population (read and did not read all information) were found to be from different populations. Estimates of marginal utilities reveal that respondents value aquatic life restoration the highest, followed by scenic quality restoration. Average compensating variation estimates for full restoration of the aquatic life and scenic quality attributes are $9 and $ 6 per month per household, respectively, when the subsamples are pooled. However, the individual subsamples resulted in $5 per month for aquatic life and $3 per month for scenic quality for respondents that read the information, while respondents that did not read the information resulted in statistically higher estimates of $16 and $12, respectively. While respondents' motives for not reading the resource information provided is uncertain, results show their values for watershed restoration are substantially higher than respondents that read the information.
Logic synthesis techniques for reduced area implementation of multilevel circuits with concurrent error detection

This paper presents new logic synthesis techniques for generating multilevel circuits with concurrent error detection based on a parity-check code scheme that can detect all errors caused by single stuck-at faults. These synthesis techniques fully automate the design process and allow for a better quality result than previous methods thereby reducing the cost of concurrent error detection. An algorithm is described for selecting a good parity-check code for encoding the outputs of a circuit. Once the code has been chosen, a new procedure called structure-constrained logic optimization is used to minimize the area of the circuit as much as possible while still using a circuit structure that ensures that single stuck-at faults cannot produce undetected errors. The implementation that is generated is path fault secure and when augmented by a checker forms a self-checking circuit. Results indicate that self-checking multilevel circuits can be generated which require significantly less area than using duplication.
The Political Origins of Transparency

Transparency has been hailed as the key to better governance, yet political actors have many reasons to resist transparency. This article studies one prominent transparency policy, Freedom of Information (FOI) laws, which have been passed by over 80 countries. By institutionalizing transparency, FOI laws increase the costs for political actors to use public office—and public information—for private gain. Why have so many states passed FOI laws despite this? I argue that, in competitive political environments, FOI laws can create benefits for political actors as well as costs. Uncertainty over future control creates incentives for incumbents to pass FOI laws in order to ensure their own future access to government information and to credibly commit to future transparency. Event-history-model results show that FOI law passage is more likely when opposition parties pose more credible challenges to incumbents and when recent turnover in executive office has been frequent.
Path-based, randomized, oblivious, minimal routing

Path-based, Randomized, Oblivious, Minimal routing (PROM) is a family of oblivious, minimal, path-diverse routing algorithms especially suitable for Network-on-Chip applications with n x n mesh geometry. Rather than choosing among all possible paths at the source node, PROM algorithms achieve the same effect progressively through efficient, local randomized decisions at each hop. Routing is deadlock-free in all PROM algorithms when the routers have at least two virtual channels.While the approach we present can be viewed as a generalization of both ROMM and O1TURN routing, it combines the low-hardware cost of O1TURN with the routing diversity offered by the most complex n-phase ROMM schemes. As all PROM algorithms employ the same hardware, a wide range of routing behaviors, from O1TURN-equivalent to uniformly path-diverse, can be effected by adjusting just one parameter, even while the network is live and continues to forward packets. Detailed simulation on a set of benchmarks indicates that, on equivalent hardware, the performance of PROM algorithms compares favorably to existing oblivious routing algorithms, including dimension-ordered routing, two-phase ROMM, and O1TURN.
From Local to Global Stability in Stochastic Processing Networks Through Quadratic Lyapunov Functions

We construct a generic, simple, and efficient scheduling policy for stochastic processing networks, and provide a general framework to establish its stability. Our policy is randomized and prioritized: with high probability it prioritizes jobs that have been least routed through the network. We show that the network is globally stable under this policy if there exists an appropriate quadratic local Lyapunov function that provides a negative drift with respect to nominal loads at servers. Applying this generic framework, we obtain stability results for our policy in many important examples of stochastic processing networks: open multiclass queueing networks, parallel server networks, networks of input-queued switches, and a variety of wireless network models with interference constraints. Our main novelty is the construction of an appropriate global Lyapunov function from quadratic local Lyapunov functions, which we believe to be of broader interest.
Molecular Recognition of Organic Compounds by Imprinted Silica

Specific interactions between silica and organic molecules play an important role in molecular imprinting, molecular recognition, and enzyme activity. To understand the specific interactions, six pairs of organic compounds were chosen and investigated for their molecular imprinting capabilities on silica. Silica adsorbents imprinted by methyl red or ρ-methyl red, methyl orange or ethyl orange, and histidine-alanine or histidine-leucine can recognize their imprinting molecules. Silica samples “imprinted” with methyl red or ethyl red, 4,9-diaminoflourenone or 3,3′-diaminodiphenylmethane, and l-histidine or d,l-histidine do not recognize their “imprinting” molecules. The molecular recognition is related to the structure of the imprinting molecules. The following lessons were learnt: 1) Three or more strong interaction sites on the imprinting molecules are necessary to endow silica with recognition capability; 2) Position of functional groups is more important than their size to achieve the molecular recognition; 3) Chiral recognition needs stronger interaction and/or more interaction sites
Chiral Amine Thiourea‐Promoted Enantioselective Domino Michael‐Aldol Reactions between 2‐Mercaptobenzaldehydes and Maleimides

An organocatalytic, enantioselective domino Michael-aldol reaction of 2-mercaptobenz-aldehydes with maleimides has been developed. The process, catalyzed by a bifunctional chiral amine thiourea via a hydrogen-bonding mediated activation mechanism using as low as 1 mol % catalyst loading, affords versatile succinimide-containing benzothiopyrans with the generation of 3 stereogenic centers in one single operation.
Counting Combinatorial Choice Rules

I count the number of combinatorial choice rules that satisfy certain properties: Kelso–Crawford substitutability, and independence of irrelevant alternatives. The results are important for two-sided matching theory, where agents are modeled by combinatorial choice rules with these properties. The rules are a small, and asymptotically vanishing, fraction of all choice rules. But they are still exponentially more than the preference relations over individual agents—which has positive implications for the Gale–Shapley algorithm of matching theory.
Impact of Data Quality on Real-Time Locational Marginal Price

The problem of characterizing impacts of data quality on real-time locational marginal price (LMP) is considered. Because the real-time LMP is computed from the estimated network topology and system state, bad data that cause errors in topology processing and state estimation affect real-time LMP. It is shown that the power system state space is partitioned into price regions of convex polytopes. Under different bad data models, the worst case impacts of bad data on real-time LMP are analyzed. Numerical simulations are used to illustrate worst case performance for IEEE-14 and IEEE-118 networks.
Dynamic Adjustment in U.S. Agriculture under Climate Uncertainty

We construct a stochastic dual model to investigate the structural adjustment of three aggregate input and two aggregate output categories in U.S. agriculture under climatic change uncertainty. A century of national annual data (1910-2011) is used in the empirical analysis. Independent and instantaneous adjustment is rejected for each output and input, but strict fixity cannot be rejected for livestock and capital. It takes about four years for crops, and three years for fertilizer to adjust towards their optimal levels. Labor adjustment reaches the equilibrium within one year.
Error Scaling Laws for Linear Optimal Estimation From Relative Measurements

In this paper, we study the problem of estimating vector-valued variables from noisy ldquorelativerdquo measurements, which arises in sensor network applications. The problem can be posed in terms of a graph, whose nodes correspond to variables and edges to noisy measurements of the difference between two variables. The optimal (minimum variance) linear unbiased estimate of the node variables, with an arbitrary variable as the reference, is considered. This paper investigates how the variance of the estimation error of a node variable grows with the distance of the node to the reference node. A classification of graphs, namely, dense or sparse in Rd, 1 les d les 3 , is established that determines this growth rate. In particular, if a graph is dense in 1-D, 2-D, or 3-D, a node variable's estimation error is upper bounded by a linear, logarithmic, or bounded function of distance from the reference. Corresponding lower bounds are obtained if the graph is sparse in 1-D, 2-D, and 3-D. These results show that naive measures of graph density, such as node degree, are inadequate predictors of the estimation error. Being true for the optimal linear unbiased estimate, these scaling laws determine algorithm-independent limits on the estimation accuracy achievable in large graphs.
Multiple Resolution Bayesian Segmentation of Ultrasound Images

We propose a novel method for obtaining the maximum a posteriori (MAP) probabilistic segmentation of speckle-laden ultrasound images. Our technique is multiple-resolution based, and relies on the conversion of speckle images with Rayleigh statistics to subsampled images with Gaussian statistics. This conversion reduces computation time, as well as allowing accurate parameter estimation for a probabilistic segmentation algorithm. Results appear to provide improvements over previous techniques in terms of low-contrast detail and accuracy.
Strategic Ignorance and the Robustness of Social Preferences

Participants in dictator games frequently avoid learning whether their choice to maximize their own earnings will help or hurt the recipient and then choose selfishly, exploiting the "moral wiggle room" provided by their ignorance. However, this is found in an environment in which the dictator must actively learn the true payoffs, so inaction means ignorance. Does this effect persist when one must actively choose either to be ignorant or to be informed or when one must actively choose to remain ignorant? In fact, whereas 45% of dictators remain ignorant when one must click to become informed, this drops to 25% when one must click in either case and to 3% when one must click to remain ignorant. Although the exploitation of moral wiggle room is not merely an artifact, it is, much like social behavior itself, subject to environmental and psychological factors that may reinforce or undermine its impact. Data, as supplemental material, are available at http://dx.doi.org/10.1287/mnsc.2014.1989 . This paper was accepted by Uri Gneezy, behavioral economics.
Experimental Evaluation of Marangoni Shear in the Contact Line Region of an Evaporating 99+% Pure Octane Meniscus

Image analyzing interferometry was used to study the spreading characteristics of an evaporating octane meniscus (purity: 99+ %) on a quartz surface. The thickness, slope, and curvature profiles in the contact line region of the meniscus were obtained using a microscopic data analysis procedure. The results obtained for the octane were compared to that of pure pentane (purity: >99.8%) under similar operating conditions. Isothermal experimental conditions of the menisci were used for the in situ estimation of the retarded dispersion constant. The experimental results for the pure pentane demonstrate that the disjoining pressure (the intermolecular interactions) in the thin-film region controls the fluid flow. Also, an imbalance between the disjoining pressure in the thin-film region and the capillary pressure in the thicker meniscus region resulted in a creeping evaporating pentane meniscus, which spreads over the solid (quartz) surface. On the contrary, for less pure octane, the intermolecular interactions between octane and quartz had a significantly different contribution for fluid flow, and hence, the octane meniscus of lower purity did not creep over the quartz surface. As a result, we had a stationary, evaporating octane meniscus. Using the experimental data and a simple model for the velocity distribution, we evaluated the Marangoni shear in a portion of the stationary, evaporating octane meniscus. An extremely small change in the concentration due to distillation had a significant effect on fluid flow and microscale heat transfer Also, it was found that nonidealities in small interfacial systems, i.e., the presence of impurities in the working fluid, can have a significant effect on the thickness of the adsorbed film, the heat flux, the spreading characteristics of an almost pure fluid, and, therefore, the assumptions in modeling.
Making Refugees: A Historical Discourse Analysis of the Construction of the ‘Refugee’ in US Social Work, 1900–1957

SummaryThis paper traces the discursive constructions through which refugees were produced as particular kinds of subjects in US social work discourse in the first half of the twentieth century. Prior to the onset of the Second World War, the refugee ideal was valorized in social work discourse to both exhort and contest immigration restrictions. In the war years, actual refugees became framed, instead, as the most troublesome immigrants. The many anti-restrictionists among social work's leaders persistently and prolifically opposed problematized constructions of refugees. But through its uncritical uses of the same unstable measures of fitness through which the problematized identities were constructed, the liberal, anti-restrictionist discourse of social work re-inscribed the discourses it sought to counter. As a study of the disciplinary construction of a particularly vulnerable identity, and a methodological exemplar for examining key constructs, this analysis has broad implication for study of the many categories of identity (e.g. child, client, etc.) upon which social work builds its practice models and explanatory theories.
Conversion of Alcohols to Protected Guanidines Using the Mitsunobu Protocol

Abstract An efficient method for the direct conversion of alcohols to guanidines is presented. A variety of alcohols react with 1 and 2 under Mitsunobu conditions to give the corresponding guanidines in high yield .
Privacy preserving keyword searches on remote encrypted data

We consider the following problem: a user $\mathcal{U}$ wants to store his files in an encrypted form on a remote file server $\mathcal{S}$. Later the user $\mathcal{U}$ wants to efficiently retrieve some of the encrypted files containing (or indexed by) specific keywords, keeping the keywords themselves secret and not jeopardizing the security of the remotely stored files. For example, a user may want to store old e-mail messages encrypted on a server managed by Yahoo or another large vendor, and later retrieve certain messages while travelling with a mobile device. In this paper, we offer solutions for this problem under well-defined security requirements. Our schemes are efficient in the sense that no public-key cryptosystem is involved. Indeed, our approach is independent of the encryption method chosen for the remote files. They are also incremental, in that $\mathcal{U}$ can submit new files which are secure against previous queries but still searchable against future queries.
A Stereospecific Elimination to Form Dehydroamino Acids: Synthesis of the Phomopsin Tripeptide Side Chain

An increasing interest in R,â-dehydroamino acids has developed in recent years based both on their importance as commodity chemicals and their presence in biologically active natural products. Efficient methods for the asymmetric hydrogenation of R,â-dehydroamino acids allow access to a wide variety of unnatural amino acids.1 Dehydroamino acids are also found in many natural products including the antrimycins, tentoxin, and the phosphatase inhibitors microcystin and nodularin.2 Unsaturated amino acids introduce elements of conformational rigidity as well as changes in reactivity due to the presence of an alkene.3 In this report, we describe an efficient and stereoselective method for the synthesis of R,â-dehydroamino acids from readily available â-hydroxyamino acids. These findings grew out of research directed toward the total synthesis of phomopsin A, which is a fungal metabolite that binds to microtubules (Chart 1).4 Our synthetic approach required a
Cheap talk and credibility: The consequences of confidence and accuracy on advisor credibility and persuasiveness

Is it possible to increase one’s influence simply by behaving more confidently? Prior research presents two competing hypotheses: (1) the confidence heuristic holds that more confidence increases credibility, and (2) the calibration hypothesis asserts that overconfidence will backfire when others find out. Study 1 reveals that, consistent with the calibration hypothesis, while accurate advisors benefit from displaying confidence, confident but inaccurate advisors receive low credibility ratings. However, Study 2 shows that when feedback on advisor accuracy is unavailable or costly, confident advisors hold sway regardless of accuracy. People also made less effort to determine the accuracy of confident advisors; interest in buying advisor performance data decreased as the advisor’s confidence went up. These results add to our understanding of how advisor confidence, accuracy, and calibration influence others.
A Survey for Transient Astronomical Radio Emission at 611 MHz

We have constructed and operated the Survey for Transient Astronomical Radio Emission (STARE) to detect transient astronomical radio emission at 611 MHz originating from the sky over the northeastern United States. The system is sensitive to transient events on timescales of 0.125 s to a few minutes, with a typical zenith flux density detection threshold of approximately 27 kJy. During 18 months of around-the-clock observing with three geographically separated instruments, we detected a total of 4,318,486 radio bursts. Of these events, 99.9% were rejected as locally generated interference, determined by requiring the simultaneous observation of an event at all three sites for it to be identified as having an astronomical origin. The remaining 3898 events have been found to be associated with 99 solar radio bursts. These results demonstrate the remarkably effective radio frequency interference rejection achieved by a coincidence technique using precision timing (such as GPS clocks) at geographically separated sites. The nondetection of extrasolar bursting or flaring radio sources has improved the flux density sensitivity and timescale sensitivity limits set by several similar experiments in the 1970s. We discuss the consequences of these limits for the immediate solar neighborhood and the discovery of previously unknown classes of sources. We also discuss other possible uses for the large collection of 611 MHz monitoring data assembled by STARE.
Graph-Based Decoding in the Presence of ISI

We propose a new graph representation for ISI channels that can be used for combined equalization and decoding by linear programming (LP) or iterative message-passing (IMP) decoding algorithms. We derive this graph representation by linearizing the ML detection metric, which transforms the equalization problem into a classical decoding problem. We observe that the performance of LP and IMP decoding on this model are very similar in the uncoded case, while IMP decoding significantly outperforms LP decoding when low-density parity-check (LDPC) codes are used. In particular, in the absence of coding, for certain classes of channels, both LP and IMP algorithms always find the exact ML solution using the proposed graph representation, without complexity that is exponential in the size of the channel memory. This applies even to certain two-dimensional ISI channels. However, for some other channel impulse responses, both decoders have nondiminishing probability of failure as SNR increases. We provide analytical explanations for many of these observations. In addition, we study the error events of LP decoding in the uncoded case, and derive a measure that can be used to classify ISI channels in terms of the performance of the proposed detection scheme.
The Future of Central Banking: A Lesson from United States History

Bennett T. McCallum Carnegie Mellon University Preliminary May 20, 2010 This paper is being prepared for the 17th international conference of the Institute for Monetary and Economic Studies of the Bank of Japan, “The Future of Central Banking Under Globalization,” to be held May 26-27, 2010, in Tokyo. I am grateful to Marvin Goodfriend for helpful discussions.
Robust stability of a class of polynomials with coefficients depending multilinearly on perturbations

Necessary and sufficient conditions are given for robust stability of a family of polynomials. Each polynomial is obtained by a multilinearity perturbation structure. Restrictions on the multilinearity are involved, but, in contrast to existing literature, these restrictions are derived from physical considerations stemming from analysis of a closed-loop interval feedback system. The main result indicates that all polynomials in the family of polynomials have their zeros in the strict left half-plane if and only if two requirements are satisfied at each frequency. The first requirement is the zero exclusion condition involving four Kharitonov rectangles. The second requirement is that a specially constructed theta 0-parameterized set of 16 intervals must cover the positive reals for each theta epsilon (0,2 pi ). >
New chemistry of diazoesters from thermal rearrangement of n-alkyl-n-nitrosoamides

Abstract New chemistry is observed in the thermal rearrangement of N-alkyl-N-nitrosoamides 1 under highly nucleophilic, dissociating conditions. An apparent change in the mechanism of the rate-determining step is noted. In DMSO containing N-methylmorpholine-N-oxide, oxidative deamination of 10 via 11 and 12 (Eqn 3) to aldehydes occurs in good yield.
Jamming of frictional spheres and random loose packing

The role of the friction coefficient, μ, on the jamming properties of disordered, particle packings is studied using computer simulations. Compressed, soft-sphere packings are brought towards the jamming transition—the point where a packing loses mechanical stability—by decreasing the packing fraction. The values of the packing fraction at the jamming transition, ϕμc, gradually decrease from the random close packing point for zero friction, to a value coincident with random loose packing as the friction coefficient is increased over several orders of magnitude. This is accompanied by a decrease in the coordination number at the jamming transition, zμc, which varies from approximately six to four with increasing friction. Universal power law scaling is observed in the pressure and coordination number as a function of distance from the generalised, friction-dependent jamming point. Various power laws are also reported between the ϕμc, zμc, and μ. Dependence on preparation history of the packings is also investigated.
Blazar counterparts for 3EG sources at -40° < decl. < 0°: Pushing south through the bulge

Supplementing existing survey data with Very Large Array (VLA) observations, we have extended γ-ray counterpart identifications down to decl. = -40° using our "figure-of-merit" approach. We find blazar counterparts for ~70% of EGRET sources above decl. = -40° away from the Galaxy. Spectroscopic confirmation is in progress, and spectra for ~24 sources are presented here. We find evidence that increased exposure in the bulge region allowed EGRET to detect relatively faint blazars; a clear excess of nonblazar objects in this region, however, argues for an additional (new) source class.
Monomer Abundance Distribution Patterns as a Universal Biosignature: Examples from Terrestrial and Digital Life

Organisms leave a distinctive chemical signature in their environment because they synthesize those molecules that maximize their fitness. As a result, the relative concentrations of related chemical monomers in life-bearing environmental samples reflect, in part, those compounds’ adaptive utility. In contrast, rates of molecular synthesis in a lifeless environment are dictated by reaction kinetics and thermodynamics, so concentrations of related monomers in abiotic samples tend to exhibit specific patterns dominated by small, easily formed, low-formation-energy molecules. We contend that this distinction can serve as a universal biosignature: the measurement of chemical concentration ratios that belie formation kinetics or equilibrium thermodynamics indicates the likely presence of life. We explore the features of this biosignature as observed in amino acids and carboxylic acids, using published data from numerous studies of terrestrial sediments, abiotic (spark, UV, and high-energy proton) synthesis experiments, and meteorite bodies. We then compare these data to the results of experimental studies of an evolving digital life system. We observe the robust and repeatable evolution of an analogous biosignature in a digital lifeform, suggesting that evolutionary selection necessarily constrains organism composition and that the monomer abundance biosignature phenomenon is universal to evolved biosystems.
Reactions to job characteristics: Moderating effects of the organization.

Canonical analysis established a significant relationship between task design and affective response measures for 784 middle-level executives. Functional specialty moderated the relationship. It wa...
Entry and Patenting in the Software Industry

To what extent are firms kept out of a market by patents covering related technologies? Do patents held by potential entrants make it easier to enter markets? We estimate the empirical relationship between market entry and patents for 27 narrowly defined categories of software products during the period 1990--2004. Controlling for demand, market structure, average patent quality, and other factors, we find that a 10% increase in the number of patents relevant to market reduces the rate of entry by 3%--8%, and this relationship intensified following expansions in the patentability of software in the mid-1990s. However, potential entrants with patent applications relevant to a market are more likely to enter it. Finally, patents appear to substitute for complementary assets in the entry process, because patents have both greater entry-deterring and entry-promoting effects for firms without prior experience in other markets. This paper was accepted by Bruno Cassiman, business strategy.
Efficient particle filtering for road-constrained target tracking

The variable-structure multiple-model particle filtering approach for state estimation of road-constrained targets is addressed. The multiple models are designed to account for target maneuvers including "move-stop-move" and motion ambiguity at an intersection; the time-varying active model sets are adaptively selected based on target state and local terrain condition. The hybrid state space is partitioned into the mode subspace and the target subspace. The mode state is estimated based on random sampling; the target state as well as the relevant likelihood function associated with a mode sample sequence is approximated as Gaussian distribution, of which the conditional mean and covariance are deterministically computed using a nonlinear Kalman filter which accounts for road constraints in its update. The importance function for the sampling of the mode state approximates the optimal importance function under the same Gaussian assumption of the target state.
A copper-catalyzed arylation of tryptamines for the direct synthesis of aryl pyrroloindolines

An operationally simple, copper-catalyzed arylation of N-tosyltryptamines provides direct access to C3-aryl pyrroloindolines. A range of electron-donating and electron-withdrawing substituents is tolerated on both the indole backbone and the aryl electrophile. These reactions occur under ambient temperatures and with equimolar quantities of the coupling partners.
Distributed video coding with progressive significance map

A distributed video coding (DVC) system based on wavelet transform and set partition coding (SPC) is presented in this paper. Conventionally the significance map (sig-map) of SPC is not conducive to Slepian-Wolf (SW) coding, because of the difficulty of generating a side information sig-map and the sensitivity to decoding errors. The proposed DVC system utilizes a higher structured significance map, named progressive significance map (prog-sig-map), which structures the significance information into two parts: a high-level summation significance map (sum-sig-map) and a low-level complementary significance map (comp-sig-map). This prog-sig-map alleviates the above difficulties and thus makes part of the prog-sig-map (specifically, the fixed-length-coded comp-sig-map) suitable for SW coding. Simulation results are provided showing the improved rate-distortion performance of the DVC system even with a simple system configuration.
Flow Properties of Submerged Heated Effluents in a Waterway

An experimental and theoretical investigation has been undertaken to study the trajectory and growth of thermal effluents having a range of discharge velocities and temperatures. The discharge of an effluent into a waterway was mathematically modeled as a submerged jet injection process by using an integral method which accounts for natural fluid mechanisms such as turbulence, entrainment, buoyancy, and heat transfer. The effects of these mechanisms on the jet properties are examined along with the effects of nonuniformity in the free-stream velocity and temperature fields. The results are supported by experimental data and demonstrate the usefulness of the theory for estimating the location, size, and temperature of the thermal plume.
Michaelis–Menten relations for complex enzymatic networks

Most biological processes are controlled by complex systems of enzymatic chemical reactions. Although the majority of enzymatic networks have very elaborate structures, there are many experimental observations indicating that some turnover rates still follow a simple Michaelis–Menten relation with a hyperbolic dependence on a substrate concentration. The original Michaelis–Menten mechanism has been derived as a steady-state approximation for a single-pathway enzymatic chain. The validity of this mechanism for many complex enzymatic systems is surprising. To determine general conditions when this relation might be observed in experiments, enzymatic networks consisting of coupled parallel pathways are investigated theoretically. It is found that the Michaelis–Menten equation is satisfied for specific relations between chemical rates, and it also corresponds to a situation with no fluxes between parallel pathways. Our results are illustrated for a simple model. The importance of the Michaelis–Menten relationship and derived criteria for single-molecule experimental studies of enzymatic processes are discussed.