cssi/SciSciGPT-SciSciNet huggingface dataset:
Prescribing curvatures on three dimensional Riemannian manifolds with boundaries

Let (M, g) be a complete three dimensional Riemannian manifold with boundary ∂M. Given smooth functions K(x) > 0 and c(x) defined on M and ∂M, respectively, it is natural to ask whether there exist metrics conformal to g so that under these new metrics, K is the scalar curvature and c is the boundary mean curvature. All such metrics can be described by a prescribing curvature equation with a boundary condition. With suitable assumptions on K,c and (M, g) we show that all the solutions of the equation can only blow up at finite points over each compact subset of M; some of them may appear on 8M. We describe the asymptotic behavior of the blow-up solutions around each blow-up point and derive an energy estimate as a consequence.
STAR FORMATION FROM DLA GAS IN THE OUTSKIRTS OF LYMAN BREAK GALAXIES AT z ∼ 3

We present evidence for spatially extended low surface brightness emission around Lyman break galaxies (LBGs) in the V-band image of the Hubble Ultra Deep Field, corresponding to the z {approx} 3 rest-frame far-UV (FUV) light, which is a sensitive measure of star formation rates (SFRs). We find that the covering fraction of molecular gas at z {approx} 3 is not adequate to explain the emission in the outskirts of LBGs, while the covering fraction of neutral atomic-dominated hydrogen gas at high redshift is sufficient. We develop a theoretical framework to connect this emission around LBGs to the expected emission from neutral H I gas, i.e., damped Ly{alpha} systems (DLAs), using the Kennicutt-Schmidt (KS) relation. Working under the hypothesis that the observed FUV emission in the outskirts of LBGs is from in situ star formation in atomic-dominated hydrogen gas, the results suggest that the SFR efficiency in such gas at z {approx} 3 is between factors of 10 and 50 lower than predictions based on the local KS relation. The total SFR density in atomic-dominated gas at z {approx} 3 is constrained to be {approx}10% of that observed from the inner regions of LBGs. In addition, the metals produced by inmore » situ star formation in the outskirts of LBGs yield metallicities comparable to those of DLAs, which is a possible solution to the 'Missing Metals' problem for DLAs. Finally, the atomic-dominated gas in the outskirts of galaxies at both high and low redshifts has similar reduced SFR efficiencies and is consistent with the same power law.« less
Geometric phase, rotational transforms, and adiabatic invariants in toroidal magnetic fields

The rotational transform associated with the magnetic surfaces of a toroidal magnetic field with a nonplanar axis is an example of the angle anholonomy which recently has been much discussed in quantum and classical dynamics (the Berry phase and Hannay angle). The same anholonomic angle appears in the phase of a charged particle spiraling around its guiding center in a strong magnetic field. This accounts for a contribution to the longitudinal invariant, associated with the guiding‐center motion, which is different for guiding‐center orbits that circulate in opposite directions and is absent for orbits that are reflected between mirrors.
Phase transitions in the quadratic contact process on complex networks.

The quadratic contact process (QCP) is a natural extension of the well-studied linear contact process where infected (1) individuals infect susceptible (0) neighbors at rate $\ensuremath{\lambda}$ and infected individuals recover ($10$) at rate 1. In the QCP, a combination of two 1's is required to effect a $01$ change. We extend the study of the QCP, which so far has been limited to lattices, to complex networks. We define two versions of the QCP: vertex-centered (VQCP) and edge-centered (EQCP) with birth events $1\ensuremath{-}0\ensuremath{-}11\ensuremath{-}1\ensuremath{-}1$ and $1\ensuremath{-}1\ensuremath{-}01\ensuremath{-}1\ensuremath{-}1$, respectively, where ``$\ensuremath{-}$'' represents an edge. We investigate the effects of network topology by considering the QCP on random regular, Erd\ifmmode \mbox{\H{o}}\else \H{o}\fi{}s-R\'enyi, and power-law random graphs. We perform mean-field calculations as well as simulations to find the steady-state fraction of occupied vertices as a function of the birth rate. We find that on the random regular and Erd\ifmmode \mbox{\H{o}}\else \H{o}\fi{}s-R\'enyi graphs, there is a discontinuous phase transition with a region of bistability, whereas on the heavy-tailed power-law graph, the transition is continuous. The critical birth rate is found to be positive in the former but zero in the latter.
THE BLACK HOLE MASS-STELLAR VELOCITY DISPERSION RELATIONSHIP FOR QUASARS IN THE SLOAN DIGITAL SKY SURVEY DATA RELEASE 7

We assess evolution in the M BH-σ* relationship for quasars in the Sloan Digital Sky Survey Data Release 7 for the redshift range 0.1 109.0 M ☉) and lowest-mass (M BH < 107.5 M ☉) black holes appears to evolve significantly; however, most or all of this apparent evolution can be accounted for by various observational biases due to intrinsic scatter in the relationship and to uncertainties in observed quantities. The M BH-σ* relationship for black holes in the middle mass range (107.5 < M BH < 109.0 M ☉) shows minimal change with redshift. The overall results suggest a limit of ±0.2 dex on any evolution in the M BH-σ* relationship for quasars out to z ≈ 1 compared with the relationship observed in the local universe. Intrinsic scatter may also provide a plausible way to reconcile the wide range of results of several different studies of the black hole-galaxy relationships.
An empirical method for computing leeside centerline heating on the Space Shuttle Orbiter

An empirical method is presented for computing top centerline heating on the Space Shuttle Orbiter at simulated reentry conditions. It is shown that the Shuttle's top centerline can be thought of as being under the influence of a swept cylinder flow field. The effective geometry of the flow field, as well as top centerline heating, are directly related to oil-flow patterns on the upper surface of the fuselage. An empirical turbulent swept cylinder heating method was developed based on these considerations. The method takes into account the effects of the vortex-dominated leeside flow field without actually having to compute the detailed properties of such a complex flow. The heating method closely predicts experimental heat-transfer values on the top centerline of a Shuttle model at Mach numbers of 6 and 10 over a wide range in Reynolds number and angle of attack.
Measurement of the core diameter of graded-index optical fibers: an interlaboratory comparison.

An interlaboratory measurement comparison of optical fiber-core diameter was conducted by the National Bureau of Standards (NBS) in cooperation with the Electronic Industries Association. Participants include NBS and three fiber manufacturers. Six graded-index fibers were measured by all participants using the transmitted near-field method. As a group, the transmitted near-field measurements were consistent and exhibited an average standard deviation of 0.5 μm for 50-μm core fibers. These results were also compared to diameters determined by refracted near-field and transverse interference measurements contributed by other laboratories. For smooth-index profiles, all three methods agree within ~1 μm; substantial differences between the transmitted near-field and the other two methods can exist for fibers having step structure near the core–cladding boundary.
Modeling the Formation of Globular Cluster Systems in the Virgo Cluster

The mass distribution and chemical composition of globular cluster (GC) systems preserve fossil record of the early stages of galaxy formation. The observed distribution of GC colors within massive early-type galaxies in the ACS Virgo Cluster Survey (ACSVCS) reveals a multi-modal shape, which likely corresponds to a multi-modal metallicity distribution. We present a simple model for the formation and disruption of GCs that aims to match the ACSVCS data. This model tests the hypothesis that GCs are formed during major mergers of gas-rich galaxies and inherit the metallicity of their hosts. To trace merger events, we use halo merger trees extracted from a large cosmological N-body simulation. We select 20 halos in the mass range of 2 × 1012 to 7 × 1013 M ☉ and match them to 19 Virgo galaxies with K-band luminosity between 3 × 1010 and 3 × 1011 L ☉. To set the [Fe/H] abundances, we use an empirical galaxy mass-metallicity relation. We find that a minimal merger ratio of 1:3 best matches the observed cluster metallicity distribution. A characteristic bimodal shape appears because metal-rich GCs are produced by late mergers between massive halos, while metal-poor GCs are produced by collective merger activities of less massive hosts at early times. The model outcome is robust to alternative prescriptions for cluster formation rate throughout cosmic time, but a gradual evolution of the mass-metallicity relation with redshift appears to be necessary to match the observed cluster metallicities. We also affirm the age-metallicity relation, predicted by an earlier model, in which metal-rich clusters are systematically several billion younger than their metal-poor counterparts.
4-Homopyrazofurin and an acyclic analogue

Abstract The synthesis of 4-hydroxymethyl-3(5)-(β- d -ribofuranosyl)pyrazole-5(3)-carboxamide ( 2 , 4-homopyrazofurin) is described via a pathway that commences with the dipolar cycloaddition reaction of 2,5-anhydro-3,4,6-tri- O -benzyl-1-deoxy-1-diazo- d -allitol ( 4 ) and methyl 4-benzyloxy-2-butynoate ( 5 ). Preparation of 3(5)-[(2-hydrox,-ethoxy)methyl]-4-(hydroxymethyl)pyrazole-5(3)-carboxamide ( 3 ) as a derivative of 2 possessing the truncated acyclic side chain of acyclovir has been accomplished in a similar manner beginning with the reaction of 5 with 1-diazo-2-[(2-benzyloxy)ethoxy]ethane ( 13 ). Neither compound 2 nor 3 showed any in vitro antiviral activity against human immunodeficiency virus (HIV-1), sandfly fever, Punta Toro, Japanese encephalitis, yellow fever, Venezuelan equine encephalomyelitis, and vaccinia viruses. Both compounds were also nontoxic. These results suggest that direct bonding of the hydroxyl group to the pyrazole ring is important for pyrazofurin based agents to demonstrate biological activity.
Disk-locking and the presence of slow rotators among solar-type stars in young star clusters

The simultaneous presence of both the so-called ultrafast rotators and slowly rotating stars among the solar-type stars (~0.6-1.2 M☉) in the same young star clusters has been a puzzle in the field of stellar rotation. No model to date has been able to explain both by a single mechanism intrinsic to the star, and questions about the appropriate initial conditions for models often complicate the problem. In this paper, using the same starting conditions for the models that we used in examining the origin of the ultrafast rotators in young star clusters, we show that the slowest rotators demand an extrinsic mechanism. Assuming that this mechanism is a disk-star interaction, we determine that a disk-locking timescale of a few Myr must operate for this type of star. If, instead of allowing (radial) differential rotation, we enforce solid-body rotation, the models require timescales about 2-3 times as long.
Cyclic (alkyl)(amino)carbenes (CAACs): stable carbenes on the rise.

ConspectusCarbenes are compounds that feature a divalent carbon atom with only six electrons in its valence shell. In the singlet state, they possess a lone pair of electrons and a vacant orbital and therefore exhibit Lewis acidic and Lewis basic properties, which explains their very high reactivity. Following the preparation by our group in 1988 of the first representative, a variety of stable carbenes are now available, the most popular being the cyclic diaminocarbenes.In this Account, we discuss another class of stable cyclic carbenes, namely, cyclic (alkyl)(amino)carbenes (CAACs), in which one of the electronegative and π-donor amino substituents of diaminocarbenes is replaced by a σ-donating but not π-donating alkyl group. As a consequence, CAACs are more nucleophilic (σ-donating) but also more electrophilic (π-accepting) than diaminocarbenes. Additionally, the presence of a quaternary carbon in the position α to the carbene center provides steric environments that differentiate CAACs dramatically fr...
The Astronomer's Telegram: A Web-based Short-Notice Publication System for the Professional Astronomical Community

The Astronomer's Telegram (ATEL) is a web‐based short‐notice (<4000 characters) publication system for reporting and commenting on new astronomical observations, offering for the first time in astronomy effectively instantaneous distribution of time‐critical information for the entire professional community. It is designed to take advantage of the World Wide Web's simple user interface and the ability of computer programs to provide nearly all the necessary functions. This makes ATEL fast, efficient, and free. In practice, one may post a Telegram, which is instantly (<1 s) available at the web site and is distributed by e‐mail within 24 hours through the Daily Email Digest, which is tailored to the subject selections of each reader. In addition, authors reporting new outbursts of transients or coordinates of new objects (for example, gamma‐ray bursts or microlensing events) may request distribution by Instant Email Notices, which instantly (~minutes) distributes their new Telegram by e‐mail to self‐identified workers interested in the same topic. This speed in distribution is obtained because no editing or reviewing is performed after posting—the last person to review the text before distribution is the author. Telegrams are enumerated chronologically, permanently archived, and referenceable. While ATEL will be of particular use to observers of transient objects (such as gamma‐ray bursts, microlenses, supernovae, novae, or X‐ray transients) or in fields that are rapidly evolving observationally, there are no restrictions on subject matter.
Atomic Scale Foundation of Covalent and Acid–Base Catalysis in Reaction Selectivity and Turnover Rate

Modern industrial catalysts are highly engineered multi-component materials, which are optimized to be highly efficient for the given reaction. The key components of every catalyst are: (1) the active metal and (2) the support. The former is active through the formation of covalent bonds with surface species, activating the bonds in the targeted molecule. In many systems the support is a metal oxide, which can promote charged intermediates in acid–base type catalytic chemistry. When the covalent chemistry of the metal catalyst and the acid–base chemistry of the support work together, the overall catalytic productivity can be much greater than the sum of the parts. This synergic interaction also works in favor of changes in the selectivity of complex reactions. This intent of this article is to analyze covalent metal catalysis both alone and in tandem with acid–base heterogeneous catalysis.
Interpolation of Random Hyperplanes

Let $\{(Z_i,W_i):i=1,\dots,n\}$ be uniformly distributed in $[0,1]^d \times \mathbb{G}(k,d)$, where $\mathbb{G}(k,d)$ denotes the space of $k$-dimensional linear subspaces of $\mathbb{R}^d$. For a differentiable function $f: [0,1]^k \rightarrow [0,1]^d$, we say that $f$ interpolates $(z,w) \in [0,1]^d \times \mathbb{G}(k,d)$ if there exists $x \in [0,1]^k$ such that $f(x) = z$ and $\vec{f}(x) = w$, where $\vec{f}(x)$ denotes the tangent space at $x$ defined by $f$. For a smoothness class ${\cal F}$ of Holder type, we obtain probability bounds on the maximum number of points a function $f \in {\cal F}$ interpolates.
Formation of Electrostatic Potential Drops in the Auroral Zone

In order to examine the self-consistent formation of large-scale quasi-static parallel electric fields in the auroral zone on a micro/meso scale, a particle in cell simulation has been developed. The code resolves electron Debye length scales so that electron micro-processes are included and a variable grid scheme is used such that the overall length scale of the simulation is of the order of an Earth radii along the magnetic field. The simulation is electrostatic and includes the magnetic mirror force, as well as two types of plasmas, a cold dense ionospheric plasma and a warm tenuous magnetospheric plasma. In order to study the formation of parallel electric fields in the auroral zone, different magnetospheric ion and electron inflow boundary conditions are used to drive the system. It has been found that for conditions in the primary (upward) current region an upward directed quasi-static electric field can form across the system due to magnetic mirroring of the magnetospheric ions and electrons at different altitudes. For conditions in the return (downward) current region it is shown that a quasi-static parallel electric field in the opposite sense of that in the primary current region is formed, i.e., the parallel electric field is directed earthward. The conditions for how these different electric fields can be formed are discussed using satellite observations and numerical simulations.
Graph Sparsification by Effective Resistances

We present a nearly linear time algorithm that produces high-quality spectral sparsifiers of weighted graphs. Given as input a weighted graph $G=(V,E,w)$ and a parameter $\epsilon>0$, we produce a weighted subgraph $H=(V,\tilde{E},\tilde{w})$ of $G$ such that $|\tilde{E}|=O(n\log n/\epsilon^2)$ and all $x\in\mathbb{R}^V$ satisfy $(1-\epsilon)\sum_{uv\in E}\,(x(u)-x(v))^2w_{uv}\leq\sum_{uv\in\tilde{E}}\,(x(u)-x(v))^2\tilde{w}_{uv}\leq(1+\epsilon)\sum_{uv\in E}\,(x(u)-x(v))^2w_{uv}$. This improves upon the spectral sparsifiers constructed by Spielman and Teng, which had $O(n\log^{c}n)$ edges for some large constant $c$, and upon the cut sparsifiers of Benczur and Karger, which only satisfied these inequalities for $x\in\{0,1\}^V$. A key ingredient in our algorithm is a subroutine of independent interest: a nearly linear time algorithm that builds a data structure from which we can query the approximate effective resistance between any two vertices in a graph in $O(\log n)$ time.
H2O Masers and Supersonic Turbulence

We use unpublished and published VLBI results to investigate the geometry and the statistical properties of the velocity field traced by H2O masers in five galactic regions of star formation: Sgr B2(M), W49N, W51(MAIN), W51N, and W3(OH). In all sources the angular distribution of the H2O hot spots demonstrates approximate self-similarity (fractality) over almost 4 orders of magnitude in scale, with the calculated fractal dimension d between � 0.2 and 1.0. In all sources, the lower order structure functions for the line-ofsight component of the velocity field are satisfactorily approximated by power laws, with the exponents near their classic Kolmogorov values for high Reynolds number incompressible turbulence. These two facts, as well as the observed significant excess of large deviations of the two-point velocity increments from their mean values, strongly suggest that the H2O masers in regions of star formation trace turbulence. We propose a new conceptual model of these masers in which maser hot spots originate at the sites of ultimate dissipation of highly supersonic turbulence produced in the ambient gas by the intensive gas outflow from a newly born star. Because of the high brightness and small angular sizes of masing hot spots and the possibility of measuring their positions and velocities with high precision, they become a unique probe of supersonic turbulence. Subject headings: ISM: jets and outflows — masers — turbulence
Clock Drawing as a Screen for Impaired Driving in Aging and Dementia: Is It Worth the Time?

Clock drawing is recommended by medical and transportation authorities as a screening test for unsafe drivers. The objective of the present study was to assess the usefulness of different clock drawing systems as screening measures of driving performance in 122 healthy and cognitively impaired older drivers. Clock drawing was measured using four different scoring systems. Driving outcomes included global ratings of safety and the error rate on a standardized on-road test. Findings revealed that clock drawing was significantly correlated with the driving score on the road test for each of the scoring systems. However, receiver operator curve analyses showed limited clinical utility for clock drawing as a screening instrument for impaired on-road driving performance with the area under the curve ranging from 0.53 to 0.61. Results from this study indicate that clock drawing has limited utility as a solitary screening measure of on-road driving, even when considering a variety of scoring approaches.
Carbonyl-initiated cyclization of tetraalkylstannanes

Abstract Trimethylstannyl alkanal and alkanone compounds undergo a five- or six-membered carbocyclization or an internal redox process upon activation with select Lewis acids.
On the stability of test particles in extrasolar multiple planet systems

We have studied the dynamical evolution of test particles in the planetary systems of v Andromedae, GJ 876, 47 UMa and 55 Cnc. Using recent radial velocity data of these stars and also utilizing a relatively new radial velocity fitting routine, we have obtained the orbital parameters of the giant planets of these systems, and studied the possibility of their harbouring of terrestrial-class planets and smaller objects. Our results indicate that, unlike the stable orbit of the newly discovered Earth-like planet of GJ 876, the orbit of the recently announced planet of 55 Cnc is unstable. Our simulations also show that the outer planet of 47 UMa may contain Trojan-type asteroids. We present the results of our detailed study of the orbital stability and dynamical behaviour of test particles throughout these systems, and investigate the possibility of stable orbits in their habitable zones. Within the context of the latter, it seems that the two systems of 47 UMa and 55 Cnc are still the only ones with the capability of harbouring habitable planets, although the new influence zones of their giant planets have caused their habitable regions to be different from the ones reported in the literature.
Bounding the tau neutrino magnetic moment from single photon searches at LEP

Abstract We show that single photon searches at LEP constrain the tau neutrino magnetic moment to be less than O (10 −6 ) μ B . This bound is competitive with low energy ( √s ⋍ 30 GeV ) single photon searches.
The Chemical Versatility of Natural-Product Assembly Lines

Microbial natural products of both polyketide and nonribosomal peptide origin have been and continue to be important therapeutic agents as antibiotics, immunosupressants, and antitumor drugs. Because the biosynthetic genes for these metabolites are clustered for coordinate regulation, the sequencing of bacterial genomes continues to reveal unanticipated biosynthetic capacity for novel natural products. The re-engineering of pathways for such secondary metabolites to make novel molecular variants will be enabled by understanding of the chemical logic and protein machinery in the producer microbes. This Account analyzes the chemical principles and molecular logic that allows simple primary metabolite building blocks to be converted to complex architectural scaffolds of polyketides (PK), nonribosomal peptides (NRP), and NRP-PK hybrids. The first guiding principle is that PK and NRP chains are assembled as thioseters tethered to phosphopantetheinyl arms of carrier proteins that serve as thiotemplates for chain elongation. The second principle is that gate keeper protein domains select distinct monomers to be activated and incorporated with positional specificity into the growing natural product chains. Chain growth is via thioclaisen condensations for PK and via amide bond formation for elongating NRP chains. Release of the full length acyl/peptidyl chains is mediated by thioesterases, some of which catalyze hydrolysis while others catalyze regiospecific macrocyclization to build in conformational constraints. Tailoring of PK and NRP chains, by acylation, alkylation, glycosylation, and oxidoreduction, occurs both during tethered chain growth and after thioesterase-mediated release. Analysis of the types of protein domains that carry out chain initiation, elongation, tailoring, and termination steps gives insight into how NRP and PK biosynthetic assembly lines can be redirected to make novel molecules.
Residential property valuations near transit stations with transit-oriented development

Access to train stations is highly valued and this is reflected in the premium price of residential property near train stations. Transit-oriented development (TOD) and the amenities provided by mixed-use development may also provide value to consumers. The analysis presented here evaluates the median property valuations surrounding eight transit stations with TOD using residential property valuation data provided by Zillow™, an on-line real estate listing firm. A hedonic regression analysis was used to evaluate the association between median block-group-level residential property valuations and the distance to the station with TOD and other stations with direct, non-stop access to New York City, while controlling for demographic and housing variables. Spatial econometric software and techniques are used to control for spatial autocorrelation. Results suggest that while the mixed-use development typically found with TOD is likely valued, proximity to stations with direct access to New York City leads to higher relative property valuations.
Magnetic-Field Generation in Kolmogorov Turbulence

We analyze the initial, kinematic stage of magnetic field evolution in an isotropic and homogeneous turbulent conducting fluid with a rough velocity field, $v(l)\ensuremath{\sim}{l}^{\ensuremath{\alpha}}$, $\ensuremath{\alpha}l1$. This regime is relevant to the problem of magnetic field generation in fluids with small magnetic Prandtl number, i.e., with Ohmic resistivity much larger than viscosity. We propose that the smaller the roughness exponent $\ensuremath{\alpha}$, the larger the magnetic Reynolds number that is needed to excite magnetic fluctuations. This implies that numerical or experimental investigations of magnetohydrodynamic turbulence with small Prandtl numbers need to achieve extremely high resolution in order to describe magnetic phenomena adequately.
Incorporating Automated Vehicle Identification Data into Origin-Destination Estimation

A methodology for the incorporation of automated vehicle identification (AVI) data into origin-destination (O-D) estimation and prediction is presented. AVI technologies facilitate the collection of useful data, such as point-to-point travel times and subpath flows. A framework for the incorporation of AVI data into the well-established O-D estimation and prediction process is presented. Improvements are proposed for both the formulation and the inputs to the O-D estimation and prediction model. Furthermore, as the O-D estimation and prediction process is often used in the traffic estimation and prediction context, approaches to the incorporation of AVI data into other areas of the dynamic traffic assignment framework are outlined. Performance and computational issues are also considered, and the results of a case study are presented to demonstrate the approach.
Corticosterone impairs dendritic cell maturation and function.

Dendritic cells (DC) play a critical role in initiating and directing adaptive immune responses against pathogens and tumours. Immature DC are thought to act as sentinels in peripheral tissues where their main function is to capture antigen at sites of infection, whereas mature DC are highly efficient at priming T-cell-mediated immune responses against infectious pathogens. The DC maturation process is thought to be an important step in the efficient generation of cytotoxic T lymphocytes (CTL). It is well established that many aspects of immune function, including CTL-mediated antiviral immunity, are modulated by neuroendocrine-derived products. Corticosterone (CORT), an adrenal hormone produced at increased concentrations during a stress response, has been shown to play a role in impaired CTL responses in stressed animals, leading to high mortality in mice normally resistant to viral infection. While direct effects of neuroendocrine mediators on CTL have been studied, little is known about their effects on DC that are critical for CTL priming. Here, we found that physiologically relevant concentrations of CORT, acting via the glucocorticoid receptor, functionally compromise DC maturation. DC exposed to CORT remained phenotypically and functionally immature after stimulation with lipopolysaccharide and were impaired for the production of interleukin (IL)-6, IL-12, and tumour necrosis factor-α. These effects were biologically significant, as CORT treatment resulted in a marked reduction in the ability of DC to prime naive CD8+ T cells in vivo. These findings offer a potential mechanism underlying stress-associated immunosuppression.
Purification of sodium and potassium hydrides; preparation of trialkylborohydrides with exceptionally large steric requirements

Abstract Commercially available sodium and potassium hydrides, freed of protective mineral oil and otherwise used as received, show essentially no reactivity toward trialkylboranes with large steric requirements. In contrast, washing with THF solutions of lithium aluminum hydride produces materials which react rapidly and exothermically to afford quantitative yields of highly hindered trialkylborohydrides.
Aeroacoustics of Three-Stream High-Speed Jets from Coaxial and Asymmetric Nozzles

The development of three-stream variable cycle turbofan engines provides an opportunity for noise reduction by optimizing the exhaust conditions of the secondary and tertiary streams. This includes adjustment of the velocity ratios and, more importantly, reshaping of the nozzle. The paper reviews an experimental study of subscale three-stream nozzles, rapid-prototyped with high accuracy and operating at high specific thrust. Far-field noise surveys were collected using a 24-microphone array. For low-bypass configurations, applicable to supersonic aircraft, a coaxial configuration offers no significant noise benefit compared to the single-stream exhaust. Configurations with offset secondary or tertiary streams offer significant noise reduction in the direction of the thicker flow. For bypass ratio around 0.5, reductions of 5.1 dB in overall sound pressure level and 4.2 dB in effective perceived noise level were attained.
Mixing stops at the LHC

We study the phenomenology of a light stop NLSP in the presence of large mixing with either the first or the second generation. R-symmetric models provide a prime setting for this scenario, but our discussion also applies to the MSSM when a significant amount of mixing can be accommodated. In our framework the dominant stop decay is through the flavor violating mode into a light jet and the LSP in an extended region of parameter space. There are currently no limits from ATLAS and CMS in this region. We emulate shape-based hadronic SUSY searches for this topology, and find that they have potential sensitivity. If the extension of these analyses to this region is robust, we find that these searches can set strong exclusion limits on light stops. If not, then the flavor violating decay mode is challenging and may represent a blind spot in stop searches even at 13 TeV. Thus, an experimental investigation of this scenario is well motivated.
Modification of the Doppler effect due to the helicity–rotation coupling

Abstract The helicity–rotation coupling and its current empirical basis are examined. The modification of the Doppler effect due to the coupling of photon spin with the rotation of the observer is considered in detail in connection with its applications in the Doppler tracking of spacecraft. Further implications of this coupling and the possibility of searching for it in the intensity response of a rotating detector are briefly discussed.
Perturbations of plane and axisymmetric entropy layers.

X y The vorticity that is introduced into flowfields by strong curved shock waves considerably increases the difficulty of analyzing downstream flows. Even if the flow becomes nearly parallel again, the reflection and re-reflection of waves by entropy variations invalidates the usual approaches such as ordinary linearized theory, shock expansion methods, etc. This paper treats inviscid linearized perturbations of supersonic entropy layers. The flows induced by small angle flaps or flares on blunted plane or axisymmetric bodies are examples of such flows. Stripwise approximations are used to reduce the governing partial differential equations to a set of simultaneous ordinary differential equations. The formulation of "difference," "integral relations," and hybrid approximations is discussed. Analytic results are obtained in the plane case whereas the axisymmetric case requires numerical integration. Direct comparisons of the difference and integral results for varying numbers of strips show that in the present problem the difference approach is somewhat more accurate for a small number of strips. Simple approximate results are obtained for a single strip whereas accuracy comparable to characteristics is obtained for a large number of strips. The methods, which are applicable to many other problems, are easily programmed for computer derivation as well as computer solution.
Characterization of synthetic peptide byproducts from cyclization reactions using on-line HPLC-ion spray and tandem mass spectrometry

The cyclization of a linear dynorphin A (Dyn A) analogue to give the lactam derivative cyclo[d-Asp2, Dap5]Dyn A(1–13)NH2 (where Dap=α,β-diaminopropionic acid) was studied to evaluate the usefulness of different coupling reagents for side chain to side chain lactam formation. This cyclization proved to be difficult and yielded substantial byproducts that varied depending upon the activating reagent used. On-line HPLC-ion spray mass spectrometry was more practical and useful than conventional HPLC alone for characterizing the products of these cyclization reactions. Peptide byproducts could be identified from the series of multiply charged ions observed, even when some of these peptides eluted from the HPLC with similar retention times. In addition to the desired cyclic peptide, the peptide byproducts observed following the cyclization using BOP (benzotriazol-1-yl-oxy-tris(dimethylamino)phosphonium hexafluorophosphate) were the linear peptide, the cyclic dimeric peptide and the linear peptide resulting from aspartimide rearrangement. The peptide byproducts obtained following cyclization using HATU (O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate) and HAPyU (O-(7-azabenzotriazol-1-yl)-1,1,3,3-bis(tetramethylene)uronium hexafluorophosphate) were predominantly linear tetramethylguanidinium (Tmg) and dipyrrolidinylguanidinium (Dpg) derivatives resulting from alkylation of the side chain of Dap by HATU and HAPyU, respectively; in addition to monomeric guanidinium derivatives, dimeric and aspartimide-containing peptides were also produced. Peptide sequencing by ion spray tandem mass spectrometry was performed to confirm the structure of both pure peptides and peptide byproducts in the crude samples. A unique fragmentation for the β,γ-bond of the Dap side chain was demonstrated and could be used to identify linear peptide byproducts. The distinctive fragment ions from this cleavage were also observed for the peptides containing the Tmg and Dpg functionalities on the Dap side chain.
Quantum Squeezing and Late Time Classical Behavior of Massive Fields in Expanding Robertson-Walker Universe

A Schroedinger picture analysis of time dependent quantum oscillators, in a manner of Guth and Pi, clearly identifies two physical mechanisms for possible decoherence of vacuum fluctuations in the early universe: turning of quantum oscillators upside-down, and rapid squeezing of upside-right oscillators so that certain squeezing factor diverges. In inflationary cosmology the former mechanism explains the stochastic evolution of light inflatons and the classical nature of density perturbations in most of the inflationary models, while the later one is responsible for the classical evolution of relatively heavy fields, with masses in a narrow range above the Hubble parameter: . The same method may be applied to the study of the decoherence of quantum fluctuations in any Robertson–Walker cosmology.
Characterizing the distribution of completion shapes with corners using a mixture of random processes

Abstract We derive an analytic expression for the distribution of contours x(t) generated by fluctuations in x (t)=∂ x (t)/∂t due to random impulses of two limiting types. The first type are frequent but weak while the second are infrequent but strong. The result has applications in computational theories of figural completion and illusory contours because it can be used to model the prior probability distribution of short, smooth completion shapes punctuated by occasional discontinuities in orientation (i.e., corners). This work extends our previous work on characterizing the distribution of completion shapes which dealt only with the case of frequently acting weak impulses.
MÖBIUS TRANSFORMATIONS OF POLYGONS AND PARTITIONS OF 3-SPACE

The image of a polygonal knot K under a spherical inversion of ℝ3 ∪ ∞ is a simple closed curve made of arcs of circles, perhaps some line segments, having the same knot type as the mirror image of K. But suppose we reconnect the vertices of the inverted polygon with straight lines, making a new polygon . This may be a different knot type. For example, a certain 7-segment figure-eight knot can be transformed to a figure-eight knot, a trefoil, or an unknot, by selecting different inverting spheres. Which knot types can be obtained from a given original polygon K under this process? We show that for large n, most n-segment knot types cannot be reached from one initial n-segment polygon, using a single inversion or even the whole Mobius group. The number of knot types is bounded by the number of complementary domains of a certain system of round 2-spheres in ℝ3. We show the number of domains is at most polynomial in the number of spheres, and the number of spheres is itself a polynomial function of the number of edges of the original polygon. In the analysis, we obtain an exact formula for the number of complementary domains of any collection of round 2-spheres in ℝ3. On the other hand, the number of knot types that can be represented by n-segment polygons is exponential in n. Our construction can be interpreted as a particular instance of building polygonal knots in non-Euclidean metrics. In particular, start with a list of n vertices in ℝ3 and connect them with arcs of circles instead of line segments: Which knots can be obtained? Our polygonal inversion construction is equivalent to picking one fixed point p ∈ ℝ3 and replacing each edge of K by an arc of the circle determined by p and the endpoints of the edge.
MCNP6 Simulation of Quasi-Monoenergetic 7Li(p,n) Neutron Sources below 150 MeV

Abstract The applicability of MCNP6 to simulate quasi-monoenergetic neutron sources from interactions of proton beams with energies below 150 MeV on thick 7 Li targets has been studied. Neutron spectra at zero degrees from a 2-mm 7 Li layer backed by a 12-mm carbon beam stopper in an Al flange bombarded with protons of 20, 25, 30, 35, and 40 MeV have been calculated with MCNP6 using the recent Los Alamos data library as well as using the Bertini+Dresner and CEM03.03 event generators. A comparison with the experimental neutron spectra shows that the event generators do not provide a good description of such reactions, while MCNP6 using the LANL data library simulates production of neutrons from p + 7 Li in good agreement with the measured data.
L'Chaim: Jewish holidays and stock market returns

Purpose – The purpose of this paper is to investigate the impact of Jewish holidays on US stock market returns.Design/methodology/approach – The authors use event study and regression methodology to determine abnormal returns on Jewish holidays and windowed periods surrounding the day. In order to seclude the results to Jewish holidays, the authors control for several other known events that impact stock market returns. To substantiate claims of abnormal returns, the authors also use the Fama‐French four‐factor model to seek alpha and evidence returns on Jewish holidays.Findings – This study shows, during the 1990‐2009 period, an increase in average daily returns 32 times greater on nine Jewish holidays than on the other trading days of the year. The demeanor of the specific Jewish holidays also influences stock market returns, as the market returns increase (decrease) on the joyous (solemn) Jewish holidays. Also, individual investors, rather than institutional investors, are a greater catalyst for the in...
The Scope and Organization of Production: Firm Dynamics over the Learning Curve

I introduce a Bayesian-learning model of the firm to account for a variety of empirical facts about firms. The many tasks the firm can undertake (the scope of the firm) are informationally related, so that the firm can enjoy some economies of scope from information. The model predicts changes in firm size and its comovement with firm scope that are broadly consistent with the empirical evidence. It also provides an explanation for the limits to the scope of the firm: the firm may lack information, or it may be costly to communicate the information necessary to undertake many tasks.
A compositional wellbore/reservoir simulator to model multiphase flow and temperature distribution

Abstract Production of hydrocarbon often involves gas and liquid (oil/water) concurrent flow in the wellbore. As a multi-phase/multi-component gas–oil mixture flows from the reservoir to the surface, pressure, temperature, composition and liquid holdup distributions are interrelated. However, nearly all two-phase wellbore simulations are currently performed using “black oil” simulators. In this paper, a compositional-wellbore model coupled with a reservoir simulator to compute pressure and temperature distribution is presented. In this work, compositions of liquid and gaseous phases in the wellbore can be determined by two-phase equilibrium flash calculations and by considering the slip between phases. Our simulator has the capability of predicting the temperature profile in the wellbore, which helps to predict multiphase flow physics such as liquid holdup and pressure drop more accurately. As the wellbore model is coupled with a reservoir simulator, it can be used as a tool to calculate fluid-flow compositions between reservoir and wellbore. The simulated results of our compositional model were compared to the equivalent blackoil model for pressure and temperature distribution. Although the input requirements and computing expenses are higher for compositional calculations than for blackoil, our simulations show that in some cases, such as those involving highly-volatile oil and retrograde condensate gas, ignoring compositional effects may lead to errors in pressure profile prediction for the wellbore.
Landau-Ginzburg orbifolds, mirror symmetry and the elliptic genus

Abstract We compute the elliptic genus for arbitrary two-dimensional N = 2 Landau-Ginzburg orbifolds. This is used to search for possible mirror pairs of such models. We show that if two Landau-Ginzburg models are conjugate to each other in a certain sense, then to every orbifold of the first theory corresponds an orbifold of the second theory with the same elliptic genus (up to a sign) and with the roles of the chiral and anti-chiral rings interchanged. These orbifolds thus constitute a possible mirror pair. Furthermore, new pairs of conjugate models may be obtained by taking the product of old ones. We also give a sufficient (and possibly necessary) condition for two models to be conjugate, and show that it is satisfied by the mirror pairs proposed by one of the authors and Hubsch.
Ladders of a magnetically active element in the structure of the novel complex boride Ti9Fe2Ru18B8: synthesis, structure, bonding, and magnetism.

Polycrystalline samples and single crystals of the complex boride Ti 9 Fe 2 Ru 18 B 8 were synthesized by arc-melting the elements and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray analysis. Ti 9 Fe 2 Ru 18 B 8 is a new substitutional variant of the Zn 11 Rh 18 B 8 structure type, space group P4/mbm (No. 127), whose remarkable feature is that it contains one-dimensional chains of dumbbells of magnetically active Fe atoms, which form "ladders" along the c axis. The Fe-Fe distance within a dumbbell is 2.489(2) A, and the Fe 2 -Fe 2 distance between two dumbbells is 2.968(1) A; in contrast, the chains are well-separated from each other by distances of at least 11.217(2) A. According to the results of tight-binding electronic structure calculations, Ru-B and Ti-Ru contacts are responsible for the structural robustness, while Fe-Fe interactions influence the magnetic behavior. According to magnetization measurements, Ti 9 Fe 2 Ru 18 B 8 orders ferromagnetically between 10 and 200 K. A model for ferromagnetism in this ladder-based structure identifies ferromagnetic coupling among neighboring spin-triplet Fe 2 dimers along the c axis as the origin of the magnetic behavior.
Checkpointing and Rollback-Recovery for Distributed Systems

We consider the problem of bringing a distributed system to a consistent state after transient failures. We address the two components of this problem by describing a distributed algorithm to create consistent checkpoints, as well as a rollback-recovery algorithm to recover the system to a consistent state. In contrast to previous algorithms, they tolerate failures that occur during their executions. Furthermore, when a process takes a checkpoint, a minimal number of additional processes are forced to take checkpoints. Similarly, when a process rolls back and restarts after a failure, a minimal number of additional processes are forced to roll back with it. Our algorithms require each process to store at most two checkpoints in stable storage. This storage requirement is shown to be minimal under general assumptions.
Bose-Einstein condensation in a dilute gas: the first 70 years and some recent experiments (Nobel Lecture).

Abstract Bose-Einstein condensates of dilute gases offer a rich field to study fundamental quantum-mechanical processes, manipulation of the speed at which light propogates, observation of atomic pair-formation and superfluidity, or even simulating white dwarf stars. Still more radical applications are on the horizon. However, their initial creation was a masterpiece of experimental physics. After an initial process of laser cooling (which itself won its developers the 1997 Nobel Prize), atoms in a magnetic-optical trap must be safely transferred into a purely magnetic trap, where the condensation process begins at 170 nK and 20 nK a pure condensate of 2000 atoms could be created. More astonishingly, Wieman and Cornell showed these low temperatures could be achieved in "bench scale" equipment rather than the massive pieces normally demanded by cryoscience. For their 1995 discovery of this new state of matter, they were awarded the 2001 Nobel Prize in Physics.