cssi/SciSciGPT-SciSciNet huggingface dataset:
Causal nets or what is a deterministic computation

The network approach to computation is more direct and “physical” than the one based on some specific computing devices (like Turing machines). However, the size of a usual—e.g., Boolean—network does not reflect the complexity of computing the corresponding function, since a small network may be very hard to find even if it exists. A history of the work of a particular computing device can be described as a network satisfying some restrictions. The size of this network reflects the complexity of the problem, but the restrictions are usually somewhat arbitrary and even awkward. Causal nets are restricted only by determinism (causality) and locality of interaction. Their geometrical characteristics do reflect computational complexities. And various imaginary computer devices are easy to express in their terms. The elementarily of this concept may help bringing geometrical and algebraic (and maybe even physical) methods into the theory of computations. This hope is supported by the group-theoretical criterion given in this paper for computability from symmetrical initial configurations.
Dynamic Network Delay Cartography

Path delays in IP networks are important metrics, required by network operators for assessment, planning, and fault diagnosis. Monitoring delays of all source-destination pairs in a large network are, however, challenging and wasteful of resources. This paper advocates a spatio-temporal Kalman filtering approach to construct network-wide delay maps using measurements on only a few paths. The proposed network cartography framework allows efficient tracking and prediction of delays by relying on both topological as well as historical data. Optimal paths for delay measurement are selected in an online fashion by leveraging the notion of submodularity. The resulting predictor is optimal in the class of linear predictors, and outperforms competing alternatives on real-world data sets.
Organocatalytic Asymmetric Mannich Reactions: New Methodology, Catalyst Design, and Synthetic Applications

The direct, asymmetric Mannich reaction catalyzed by small organic molecules offers a facile route to optically active α- or β-amino acid derivatives and 1,2- and γ-amino alcohols. One-pot reactions of unmodified carbonyl donors with preformed or in situ generated imines can be stereochemically controlled with Organic catalysts such as proline, chiral pyrrolidines, chiral Bronsted acids, and Cinchona alkaloids. The generated Mannich adducts can be further functionalized towards a variety of bioactive molecules. In this Microreview, recent contributions are discussed to present the methodology and synthetic advantages achieved so far in the asymmetric Mannich reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Resonance in asymmetric warped geometry

We study the spectrum of an asymmetric warped braneworld model with different AdS curvatures on either side of the brane. In addition to the RS-like modes we find a resonance state. Its mass is proportional to the geometric mean of the two AdS curvature scales, while the difference between them determines the strength of the resonance peak. There is a complementarity between the RS zero-mode and the resonance: making the asymmetry stronger weakens the zero-mode but strengthens the resonance, and vice versa. We calculate numerically the braneworld gravitational potential and discuss the holographic correspondence for the asymmetric model.
Tychonoff expansions with prescribed resolvability properties

Abstract The recent literature offers examples, specific and hand-crafted, of Tychonoff spaces (in ZFC) which respond negatively to these questions, due respectively to Ceder and Pearson (1967) [3] and to Comfort and Garcia-Ferreira (2001) [5] : (1) Is every ω-resolvable space maximally resolvable? (2) Is every maximally resolvable space extraresolvable? Now using the method of KID expansion, the authors show that every suitably restricted Tychonoff topological space ( X , T ) admits a larger Tychonoff topology (that is, an “expansion”) witnessing such failure. Specifically the authors show in ZFC that if ( X , T ) is a maximally resolvable Tychonoff space with S ( X , T ) ⩽ Δ ( X , T ) = κ , then ( X , T ) has Tychonoff expansions U = U i ( 1 ⩽ i ⩽ 5 ), with Δ ( X , U i ) = Δ ( X , T ) and S ( X , U i ) ⩽ Δ ( X , U i ) , such that ( X , U i ) is: ( i = 1 ) ω-resolvable but not maximally resolvable; ( i = 2 ) [if κ ′ is regular, with S ( X , T ) ⩽ κ ′ ⩽ κ ] τ-resolvable for all τ κ ′ , but not κ ′ -resolvable; ( i = 3 ) maximally resolvable, but not extraresolvable; ( i = 4 ) extraresolvable, but not maximally resolvable; ( i = 5 ) maximally resolvable and extraresolvable, but not strongly extraresolvable.
Minimum-Perimeter Intersecting Polygons

Given a set $\mathcal{S}$ of segments in the plane, a polygon P is an intersecting polygon of $\mathcal{S}$ if every segment in $\mathcal{S}$ intersects the interior or the boundary of P. The problem MPIP of computing a minimum-perimeter intersecting polygon of a given set of n segments in the plane was first considered by Rappaport in 1995. This problem is not known to be polynomial, nor it is known to be NP-hard. Rappaport (Int. J. Comput. Geom. Appl. 5:243–265, 1995) gave an exponential-time exact algorithm for MPIP. Hassanzadeh and Rappaport (Proceedings of the 23rd International Workshop on Algorithms and Data Structures, LNCS, vol. 5664, pp. 363–374, 2009) gave a polynomial-time approximation algorithm with ratio $\frac{\pi}{2} \approx 1.57$. In this paper, we present two improved approximation algorithms for MPIP: a 1.28-approximation algorithm by linear programming, and a polynomial-time approximation scheme by discretization and enumeration. Our algorithms can be generalized for computing an approximate minimum-perimeter intersecting polygon of a set of convex polygons in the plane. From the other direction, we show that computing a minimum-perimeter intersecting polygon of a set of (not necessarily convex) simple polygons is NP-hard.
On Pointwise Decay of Linear Waves on a Schwarzschild Black Hole Background

We prove sharp pointwise t −3 decay for scalar linear perturbations of a Schwarzschild black hole without symmetry assumptions on the data. We also consider electromagnetic and gravitational perturbations for which we obtain decay rates t −4, and t −6, respectively. We proceed by decomposition into angular momentum l and summation of the decay estimates on the Regge-Wheeler equation for fixed l. We encounter a dichotomy: the decay law in time is entirely determined by the asymptotic behavior of the Regge-Wheeler potential in the far field, whereas the growth of the constants in l is dictated by the behavior of the Regge-Wheeler potential in a small neighborhood around its maximum. In other words, the tails are controlled by small energies, whereas the number of angular derivatives needed on the data is determined by energies close to the top of the Regge-Wheeler potential. This dichotomy corresponds to the well-known principle that for initial times the decay reflects the presence of complex resonances generated by the potential maximum, whereas for later times the tails are determined by the far field. However, we do not invoke complex resonances at all, but rely instead on semiclassical Sigal-Soffer type propagation estimates based on a Mourre bound near the top energy.
Solid‐State Au/Hg Microelectrode for the Investigation of Fe and Mn Cycling in a Freshwater Wetland: Implications for Methane Production

The solid-state voltammetric gold-amalgam microelectrode was used to measure multiple redox species (O, S, Fe and Mn) in situ at (sub)millimeter vertical resolution to elucidate rhizosphere processes in Jug Bay wetlands. In vegetated soil, a classic diagenetic redox sequence without any dissolved sulfide was observed in summer. However, the rhizosphere can be quite variable which is due to the introduction of O2 to the anoxic sediments by plants. In nonvegetated soil, the vertical concentration–depth profiles were relatively constant. The presence of Fe(II), Mn(II) and soluble Fe(III) in deeper sediments indicates the oxidation of Fe(II) as well as the nonreductive dissolution of Fe(III) and the reductive dissolution of Fe(III) and Mn(III, IV) solids. Mn(III, IV) and Fe(III) redox chemistry is important in organic matter mineralization mediated by bacteria and in suppressing methane formation. In addition, Mn(III, IV) also can oxidize Fe(II) to supply Fe(III) for bacterial Fe(III) reduction. Studying Fe and Mn cycling via voltammetric methods can give insights to methane production and loss as there is no methane sensor for sediment work at present.
Eigenvalues and expansion of regular graphs

The spectral method is the best currently known technique to prove lower bounds on expansion. Ramanujan graphs, which have asymptotically optimal second eigenvalue, are the best-known explicit expanders. The spectral method yielded a lower bound of k/4 on the expansion of linear-sized subsets of k-regular Ramanujan graphs. We improve the lower bound on the expansion of Ramanujan graphs to approximately k/2. Moreover, we construct a family of k-regular graphs with asymptotically optimal second eigenvalue and linear expansion equal to k/2. This shows that k/2 is the best bound one can obtain using the second eigenvalue method. We also show an upper bound of roughly 1 + √k - 1 on the average degree of linear-sized induced subgraphs of Ramanujan graphs. This compares positively with the classical bound 2√k - 1. As a byproduct, we obtain improved results on random walks on expanders and construct selection networks (respectively, extrovert graphs) of smaller size (respectively, degree) than was previously known.
Smoking Exposure Induces Human Lung Endothelial Cell Adaptation to Apoptotic Stress

Prolonged exposure to cigarette smoking is the main risk factor for emphysema, a component of chronic obstructive pulmonary diseases (COPDs) characterized by destruction of alveolar walls. Moreover, smoking is associated with pulmonary artery remodeling and pulmonary hypertension, even in the absence of COPD, through as yet unexplained mechanisms. In murine models, elevations of intra- and paracellular ceramides in response to smoking have been implicated in the induction of lung endothelial cell apoptosis, but the role of ceramides in human cell counterparts is yet unknown. We modeled paracrine increases (outside-in) of palmitoyl ceramide (Cer16) in primary human lung microvascular cells. In naive cells, isolated from nonsmokers, Cer16 significantly reduced cellular proliferation and induced caspase-independent apoptosis via mitochondrial membrane depolarization, apoptosis-inducing factor translocation, and poly(ADP-ribose) polymerase cleavage. In these cells, caspase-3 was inhibited by ceramide-induced Akt phosphorylation, and by the induction of autophagic microtubule-associated protein-1 light-chain 3 lipidation. In contrast, cells isolated from smokers exhibited increased baseline proliferative features associated with lack of p16(INK4a) expression and Akt hyperphosphorylation. These cells were resistant to Cer16-induced apoptosis, despite presence of both endoplasmic reticulum stress response and mitochondrial membrane depolarization. In cells from smokers, the prominent up-regulation of Akt pathways inhibited ceramide-triggered apoptosis, and was associated with elevated sphingosine and high-mobility group box 1, skewing the cell's response toward autophagy and survival. In conclusion, the cell responses to ceramide are modulated by an intricate cross-talk between Akt signaling and sphingolipid metabolites, and profoundly modified by previous cigarette smoke exposure, which selects for an apoptosis-resistant phenotype.
Gas Phase Photochemical Synthesis of II/VI Metal Sulfide Films and in Situ Luminescence Spectroscopic Identification of Photofragments

This paper reports the facile photochemical synthesis of binary and ternary II/VI metal sulfides from single-source diethyl dithiocarbamate zinc and cadmium precursors, M(S{sub 2}-CNEt{sub 2}){sub 2}, M = Zn, Cd. Photoluminescence spectroscopy is used to simultaneously identify gas phase species present during the CVD process. This study demonstrates one of the first uses of light for both deposition and real time characterization of gas phase species in multiphase materials synthesis. It is demonstrated that ternary Zn{sub x}Cd{sub 1-x}S films as well as ZnS and CdS can be prepared photochemically under mild conditions and only in the area irradiated by the laser beam. Luminescence spectra show that the elements composing the films are produced in the gas phase. 20 refs., 2 figs., 1 tab.
Crossing the Yellow Void: Spatially Resolved Spectroscopy of the Post-Red Supergiant IRC +10420 and Its Circumstellar Ejecta*

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post–red supergiant evolution, these massive stars enter a temperature range (6000–9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden region that de Jager and his collaborators have called the "yellow void." We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long-slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double-peaked Hα emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass-loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently, the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a "rain" model, in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass-loss rate, IRC +10420 may be about to shed its opaque wind, cross the yellow void, and emerge as a hotter star.
On Weyl-Titchmarsh theory for singular finite difference Hamiltonian systems

We develop the basic theory of matrix-valued Weyl-Titchmarsh M-functions and the associated Green's matrices for whole-line and half-line self-adjoint Hamiltonian finite difference systems with separated boundary conditions.
Investigations of the 147 nm radiative efficiency of Xe surface wave discharges

The radiative efficiency of the 147 nm resonance radiation of Xe excited in a low pressure, high-frequency surface wave sustained plasma has been investigated. The radiative UV power has been obtained from optical absorption spectroscopic measurements of the Xe resonance level population and from Monte Carlo calculations of the effective decay rate of this level. Precise measurements of the rf power absorbed by the plasma enable the determination of the absolute vacuum ultraviolet discharge efficiency for the Xe surface wave discharge. Results show efficiencies up to more than 80(±11)% .
Metallicities of M Dwarf Planet Hosts from Spectral Synthesis

We present the first spectroscopic metallicities of three M dwarfs with known or candidate planetary mass companions. We have analyzed high-resolution, high signal-to-noise ratio spectra of these stars, which we obtained at McDonald Observatory. Our analysis technique is based on spectral synthesis of atomic and molecular features using recently revised cool-star model atmospheres and spectrum synthesis code. The technique has been shown to yield results consistent with the analyses of solar-type stars and allows measurements of M dwarf [M/H] values to 0.12 dex precision. From our analysis, we find [M/H] = -0.12, -0.32, and -0.33 for GJ 876, GJ 436, and GJ 581, respectively. These three M dwarf planet hosts have subsolar metallicities, a surprising departure from the trend observed in FGK-type stars. This study is the first part of our ongoing work to determine the metallicities of the M dwarfs included in the McDonald Observatory planet search program.
Studies on Microjet Control Effectiveness in High-Temperature Supersonic Impinging Jets

This study examines the influence of jet temperature on the impinging jet flowfield and compares the effectiveness of microjet control for a Mach 1.5 ideally expanded jet. The tests were performed on a 36.2-mm-diam jet of air, heated to stagnation temperatures up to 1200 K. The jet impinged normally onto a traversable ground plane oriented between 1.5 and 12 throat diameters from the nozzle exit. Findings indicate that the impingement tones persist and generally become more prominent at higher temperatures, and the lift loss levels increase. Microjet injection produced substantial reductions of overall noise levels and considerable lift recovery, although the effectiveness is slightly lower for elevated jet temperatures. In the nozzle-to-ground range resulting in the highest pressure fluctuation levels on the lift plate, reductions reached 9 dB for the 1200 K jet and 10 dB for the cold jet. There was consistent behavior regarding the suppression of near-field and far-field overall sound pressure levels, w...
Stylizing 2.5-D video

In recent years considerable interest has been given to non-photorealistic rendering of photographs, video, and 3D models for illustrative or artistic purposes. Conventional 2D inputs such as photographs and video are easy to create and capture, while 3D models allow for a wider variety of stylization techniques, such as cross-hatching. In this paper, we propose using video with depth information (2.5-D video) to combine the advantages of 2D and 3D input. 2.5-D video is becoming increasingly easy to capture, and with the additional depth information, stylization techniques that require shape information can be applied. However, because 2.5-D video contains only limited shape information and 3D correspondence over time is unknown, it is difficult to create temporally coherent stylized animations directly from raw 2.5-D video. In this paper, we present techniques for processing 2.5-D video to overcome these drawbacks, and demonstrate several styles that can be created using these techniques.
La3Ni2O6: a new double T'-type nickelate with infinite Ni1+/2+O2 layers.

New mixed-valent, Ni1+/Ni2+, metastable nickelate, La3Ni2O6, was synthesized by low-temperature reduction of La3Ni2O7 with CaH2. The crystal structure of La3Ni2O6 (space group: I4/mmm, a = 3.9686(1) A and c = 19.3154(6) A) was determined from powder neutron diffraction data by Rietveld analysis. The structure can be described as an intergrowth of LaO2 fluorite and double infinite layer (LaNiO2)2 blocks and represents the n = 2 homologue of the T‘-type series Lan+1NinO2n+2. Such double T‘-type structural arrangement has never been observed before. The 3d9/3d8 electronic configuration of Ni1+/Ni2+ and the presence of NiO2 infinite layers resemble electronic and structural features of the superconducting cuprates. X-ray absorption spectroscopy supports the 1+/2+ oxidation state and planar coordination of Ni in agreement with the structure determination.
A bifunctional anthraquinone synthon

Abstract Commercially available anthrarufin has been converted into a bifunctional reagent which will be useful for the preparation of anthraquinone C-glycosides.
Merging Photoredox Catalysis with Organocatalysis: The Direct Asymmetric Alkylation of Aldehydes

Photoredox catalysis and organocatalysis represent two powerful fields of molecule activation that have found widespread application in the areas of inorganic and organic chemistry, respectively. We merged these two catalysis fields to solve problems in asymmetric chemical synthesis. Specifically, the enantioselective intermolecular α-alkylation of aldehydes has been accomplished using an interwoven activation pathway that combines both the photoredox catalyst Ru(bpy)3Cl2 (where bpy is 2,2′-bipyridine) and an imidazolidinone organocatalyst. This broadly applicable, yet previously elusive, alkylation reaction is now highly enantioselective and operationally trivial.
Analytic Cross Sections for Substructure Lensing

The magnifications of the images in a strong gravitational lens system are sensitive to small mass clumps in the lens potential; this effect has been used to infer the amount of substructure in galaxy dark matter halos. I study the theory of substructure lensing to identify important general features and to compute analytic cross sections that will facilitate further theoretical studies. I show that the problem of a clump anywhere along the line of sight to a lens can be mapped onto an equivalent problem of a clump in a simple convergence and shear field; clumps at arbitrary redshifts are therefore not difficult to handle in calculations. For clumps modeled as singular isothermal spheres (SISs), I derive simple analytic estimates of the cross section for magnification perturbations of a given strength. The results yield two interesting conceptual points: First, lensed images with positive parity are always made brighter by SIS clumps; images with negative parity can be brightened but are much more likely to be dimmed. Second, the clumps need not lie within the lens galaxy; they can be moved in redshift by several tenths and still have a significant lensing effect. Isolated small halos are expected to be common in hierarchical structure formation models, but it is not yet known whether they are abundant enough compared to clumps inside lens galaxies to affect the interpretation of substructure lensing.
EVIDENCE FOR EXTREMELY HIGH DUST POLARIZATION EFFICIENCY IN NGC 3184

Recent studies have found the Type II-plateau supernova (SN) 1999gi to be highly polarized (pmax = 5.8%, where pmax is the highest degree of polarization measured in the optical bandpass) and minimally reddened [E(B-V) = 0.21 ± 0.09 mag]. From multiple lines of evidence, including the convincing fit of a "Serkowski" interstellar polarization (ISP) curve to the continuum polarization shape, we conclude that the bulk of the observed polarization is likely due to dust along the line of sight and is not intrinsic to SN 1999gi. We present new spectropolarimetric observations of four distant Galactic stars close to the line of sight to SN 1999gi (two are within 002) and find that all are null to within 0.2%, effectively eliminating Galactic dust as the cause of the high polarization. The high ISP coupled with the low reddening implies an extraordinarily high polarization efficiency for the dust along this line of sight in NGC 3184: ISP/E(B-V) = 31% mag -1. This is inconsistent with the empirical Galactic limit [ISP/E(B-V) < 9% mag-1] and represents the highest polarization efficiency yet confirmed for a single sight line in either the Milky Way or an external galaxy.
Suppressed Dispersion for a Randomly Kicked Quantum Particle in a Dirac Comb

I study a model for a massive one-dimensional particle in a singular periodic potential that is receiving kicks from a gas. The model is described by a Lindblad equation in which the Hamiltonian is a Schrodinger operator with a periodic δ-potential and the noise has a frictionless form arising in a Brownian limit. I prove that an emergent Markov process in an adiabatic limit governs the momentum distribution in the extended-zone scheme. The main result is a central limit theorem for a time integral of the momentum process, which is closely related to the particle’s position. When normalized by $t^{\frac{5}{4}}$ the integral process converges to a time-changed Brownian motion whose diffusion rate depends on the momentum process. The scaling $t^{\frac{5}{4}}$ contrasts with $t^{\frac{3}{2}}$ , which would be expected for the case of a smooth periodic potential or for a comparable classical process. The difference is a wave effect driven by momentum reflections that occur when the particle’s momentum is kicked near the half-spaced reciprocal lattice of the potential.
Government in transition

Abstract The speed of economic reforms is not the only important determinant of the success of the transition to a market economy: the transition of government from a communist state to an institution supporting a market economy is as critical. Survey evidence shows that Russia lags significantly behind Poland in the transition of its government, which may account for its inferior economic performance despite adopting similar economic reforms. I argue that the lack of turnover of old communist politicians, and the creation of inappropriate electoral and fiscal incentives for these politicians, may account for the poor performance of the Russian government, and suggest some strategies for improving the situation.
Application of high-performance liquid chromatographic peptide purification to protein microsequencing by solid-phase Edman degradation.

Abstract Peptide purification via high-performance liquid chromatography (HPLC) and solid-phase sequencing were integrated to form a system allowing the determination of complete sequence information on a microscale without the use of radiolabels or modified phenylisothiocyanate. Mixtures of peptides (500 pmol to 10 nmol) resulting from proteolytic digestion or chemical cleavage were applied directly to reverse-phase columns. The columns, equilibrated in either 10 m m K P i or 0.05% trifluoroacetic acid, were then developed using acetonitrile gradients. Eluates were monitored nondestructively by direct ultraviolet detection at both 214 and 254 nm. Each peak was collected as a discrete fraction, and purity was assessed by amino acid analysis prior to covalent attachment to a solid support for sequence analysis. Activation of the peptide carboxyl terminus via a water soluble carbonyldiimide was the solid-phase coupling method used 90% of the time. Coupling yields averaged 52% of starting material. Sequence analysis was performed in the range 100 pmol to 4 nmol of coupled peptide. Phenylthiohydantoin-amino acids were identified by reverse-phase HPLC using ultraviolet detection.
A New Indole Synthesis Promoted by Metal Triflates

A new synthesis of 4- and 7-carbon-substituted indoles is described. The overall sequence involves the addition of a nitrile oxide to 1 carboethoxy-2-(or 3-) allylpyrrole, hydrogenation of the intermediate isoxazoline to β-hydroxy ketone and cyclization of the ketol using magnesium or zinc triflate to the substituted indole. This new indole-forming strategy can also accommodate the introduction of oxygen functionality into the indole 6-position. Possible mechanistic aspects of the reaction are detailed.
Isaac Newton as a Probabilist

In 1693, Isaac Newton answered a query from Samuel Pepys about a problem involving dice. Newton’s analysis is discussed and attention is drawn to an error he made.
NCBO Resource Index: Ontology-based search and mining of biomedical resources

The volume of publicly available data in biomedicine is constantly increasing. However, these data are stored in different formats and on different platforms. Integrating these data will enable us to facilitate the pace of medical discoveries by providing scientists with a unified view of this diverse information. Under the auspices of the National Center for Biomedical Ontology (NCBO), we have developed the Resource Index - a growing, large-scale ontology-based index of more than twenty heterogeneous biomedical resources. The resources come from a variety of repositories maintained by organizations from around the world. We use a set of over 200 publicly available ontologies contributed by researchers in various domains to annotate the elements in these resources. We use the semantics that the ontologies encode, such as different properties of classes, the class hierarchies, and the mappings between ontologies, in order to improve the search experience for the Resource Index user. Our user interface enables scientists to search the multiple resources quickly and efficiently using domain terms, without even being aware that there is semantics ''under the hood.''
Efficient cross-coupling reactions of aryl chlorides and bromides with phenyl- or vinyltrimethoxysilane mediated by a palladium/imidazolium chloride system

A combination of palladium acetate and the imidazolium salt IPr.HCl (1, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) has proven to be highly efficient in the cross coupling reactions of aryl bromides and electron-deficient aryl chlorides with phenyltrimethoxysilane or vinyltrimethoxysilane. The catalytic performance of this system was found to be comparable to that of systems using PCy(3) and P(o-tol)(3).
A convergent synthesis of (+)-pancratistatin based on intramolecular electrophilic aromatic substitution

Abstract A convergent formal synthesis of (+)-pancratistatin ( 1 ) is reported. Specifically, an optically active adduct of piperonyl bromide and acetonated conduritol A was converted to a late-stage intermediate from the Danishefsky-Lee synthesis of 1 . The carbon skeleton was established via intramolecular electrophilic aromatic substitution within the piperonylated conduritol. Some competitive cationic rearrangement was observed in this operation, being dependent on the degree to which a 2-substituent in the piperonyl domain favors attack ipso to the piperonyl benzylic carbon.
Rhodium(II)-catalyzed stereoselective synthesis of allylsilanes.

The rhodium-catalyzed decomposition of 2-(triisopropylsilyl)ethyl aryl- and vinyldiazoacetates results in the stereoselective formation of Z-allylsilanes. The transformation is considered to proceed by silyl-directed intramolecular C–H functionalization to form a β-lactone intermediate followed by a silyl-activated extrusion of carbon dioxide.
Design of Frames Against Buckling Using a Rayleigh Quotient Approximation

A Rayleigh quotient approximation is applied to the design of structures while guarding against elastic instability. It approximates buckling eigenvalues by separately estimating the modal strain energy due to the linear and geometric stiffness of the structure. Previously used during structural optimization for the fundamental natural eigenvalue, the Rayleigh quotient approximation is derived for the buckling design problem for the first time. The critical buckling load is found by solving the eigenvalue problem that arises by considering the geometric nonlinearity of the deforming structure. Rayleigh's principle is used to justify the choice of intermediate design variables for approximating terms in the Rayleigh quotient. A truss model illustrates the importance of the design space chosen for approximating the modal strain energy. A beamTcolumn, two plane frames, and a space frame are used to verify the formulation. Special attention is paid to difficult bimodal optima.
Photochemistry of titanacyclobutanes. Evidence for a metal-centered 1,4-biradical intermediate

Metallacycles are key intermediates in organometallic chemistry and catalysis as well as useful reagents for organic synthesis. Despite numerous studies on the preparation and thermal chemistry of these complexes, few photochemical investigations have been reported. In this paper, they report photochemical studies of the bis(cyclopentadienyl)titanacyclobutanes 1. Photochemical activation of 1 results in clean reductive elimination to form cyclopropanes and titanocene which can be trapped by a number of added reagents. Stereochemical studies strongly suggest a stepwise mechanism in which the primary photochemical step involves metal-carbon bond homolysis to produce a metal-centered 1,4-biradical intermediate.
Coloring inductive graphs on-line

In this paper we consider the problem of on-line graph coloring. In an instance of on-line graph coloring, the nodes are presented one at a time. As each node is presented, its edges to previously presented nodes are also given. Each node must be assigned a color, different from the colors of its neighbors, before the next node is given. LetA(G) be the number of colors used by algorithmA on a graphG and letx(G) be the chromatic number ofG. The performance ratio of an on-line graph coloring algorithm for a class of graphsC is maxG ∈C(A(G)/χ(G)). We consider the class ofd-inductive graphs. A graphG isd-inductive if the nodes ofG can be numbered so that each node has at mostd edges to higher-numbered nodes. In particular, planar graphs are 5-inductive, and chordal graphs arex(G)-inductive. First Fit is the algorithm that assigns each node the lowest-numbered color possible. We show that ifG isd-inductive, then First Fit usesO(d logn) colors onG. This yields an upper bound ofo(logn) on the performance ratio of First Fit on chordal and planar graphs. First Fit does as well as any on-line algorithm ford-inductive graphs: we show that, for anyd and any on-line graph coloring algorithmA, there is ad-inductive graph that forcesA to use Ω(d logn) colors to colorG. We also examine on-line graph coloring with lookahead. An algorithm is on-line with lookaheadl, if it must color nodei after examining only the firstl+i nodes. We show that, forl<n/logn, the lower bound ofd logn colors still holds.
On the defining relations for generalized q-Schur algebras

Abstract We show that the defining relations needed to describe a generalized q -Schur algebra as a quotient of a quantized enveloping algebra are determined completely by the defining ideal of a certain finite affine variety, the points of which correspond bijectively to the set of weights. This explains, unifies, and extends previous results.
Tandem Catalysis: The Sequential Mediation of Olefin Metathesis, Hydrogenation, and Hydrogen Transfer with Single-Component Ru Complexes

Organometallic catalysts are traditionally designed and optimized to mediate a single reaction. However, the increasing demand for expedient and efficient synthetic processes requires the development of organometallic reagents that are capable of catalyzing multiple, mechanistically distinct reactions directly or by simple modification. While the Ru complex (PCy_3)_2Cl_2Ru= CHPh (1) has found extensive use in olefin metathesis, it was also recently shown to be an effective precatalyst for mediating radical additions and hydrogenation reactions. We recently demonstrated all three reactions could be performed in tandem to afford well-defined block copolymers. Herein, we report that complex 1, or its more active derivative 2, is also useful in mediating a variety of other catalytic hydrogenation reactions that include regiospecific ketone and olefin reductions, transfer hydrogenations of ketones, and dehydrogenative oxidations of alcohols. In addition, we demonstrate a variety of “one-pot” tandem metathesis-hydrogenation procedures for the rapid construction of small molecules, including (R)-(-)-Muscone.
Composition, Collimation, Contamination: The Jet of Cygnus X-1

We model the observed size and brightness of the VLBA radio core of the jet in Cygnus X-1 to derive an expression for the jet power as a function of basic jet parameters. We apply this expression to recent constraints on the jet power from observations of a large-scale shocked shell around the source by Gallo and coworkers, which leads us to a set of alternative conclusions: either (1) the jet contains large amounts of protons (?2000 protons per radio-emitting electron), (2) it has a very low volume filling factor of f 3 ? 10-5, (3) the steady, radio-emitting VLBA jet is not the source of the kinetic energy powering the ISM shell, or (4) its asymptotic behavior differs fundamentally from a broad set of plausible analytic jet models.
Experiments with network formation

Abstract We examine how groups of agents form trading networks in the presence of idiosyncratic risk and the possibility of contagion. Specifically, four agents play a two-stage finite repeated game. In the first stage, the network structure is endogenously determined through a non-cooperative proposal game. In the second stage, agents play multiple rounds of a coordination game against all of their chosen ‘neighbors’ after the realization of a payoff relevant shock. While parsimonious, our four agent environment is rich enough to capture all of the important interaction structures in the networks literature: bilateral (marriage), local interaction, star, and uniform matching. Consistent with our theory, marriage networks are the most frequent and stable network structures in our experiments. We find that payoff efficiency is around 90 percent of the ex ante, payoff dominant strategies and the distribution of network structures is significantly different from that which would result from random play.
Two-step syntheses of fused quinoxaline-benzodiazepines and bis-benzodiazepines

A two-step solution phase synthesis employing a double UDC (Ugi/Deprotect/Cyclize) strategy has been utilized to obtain fused 6,7,6,6-quinoxalinone-benzodiazepines and 6,7,7,6-bis-benzodiazepines. Optimization of the methodology to produce these tetracyclic scaffolds was enabled by microwave irradiation, incorporation of trifluoroethanol as solvent, and the use of the convertible isocyanide, 4-tert-butyl cyclohexen-1-yl isocyanide.
Estimating the afferent and efferent temporal interval entropy of neuronal discharge for single spike trains

Abstract We define a biological communication system at the level of a single neuron and quantify the temporal variability of afferent and efferent impulse patterns by means of an interval entropy measure. Two signal transmission conditions which bound a physiologically plausible range of transmission possibilities are explored. The number of efferent synapses is predicted by matching estimates of the mean efferent entropy to the total afferent entropy.
Garnets for short wavelength magneto-optic recording

Abstract The bismuth substituted iron garnets have attracted considerable attention as alternative blue wavelength magneto-optic recording media due to their large magneto-optic effects in the short wavelength region of the visible spectrum. However, these materials currently require a high temperature processing step and have not been deposited on inexpensive substrates with adequate carrier to noise ratios. The low CNR is a result of high media noise which is believed to be related to the underlying microstructure of the film. This paper will discuss the magnetic and magneto-optic properties of garnet films suitable for blue wavelength magneto-optic recording; review the techniques by which films of these materials have been deposited; present the current understanding of the crystallization process and methods for controlling the physical microstructure and uniformity of written magnetic domains; and finally review the current status of the performance of these materials as short wavelength magneto-optic media.
Magnetostriction and magnetic Gruneisen parameters in pseudo-binary rare earth-transition metal alloys

A magnetoelastic Gruneisen parameter has been derived from thermodynamic equations of state. It has been found that the magnetoelastic Gruneisen parameter is proportional to the magnetomechanical coupling coefficient, k. This relates directly the energy conversion efficiency to the anharmonicity in the crystal lattice. It therefore provides a way of predicting the field dependence of the energy conversion efficiency in magnetostrictive materials.
Chronic nicotine exposure reduces N-methyl-d-aspartate receptor-mediated damage in the hippocampus without altering calcium accumulation or extrusion: evidence of calbindin-D28K overexpression

Neuronal accumulation of excess Ca2+ has been implicated in cellular death following several forms of physical and chemotoxic insult. Recent studies have suggested that exposure to agonists at brain nicotinic acetylcholine receptors reduces cytotoxic consequences of increased intracellular Ca2+ following some insults. In the present study, the ability of chronic exposure to (-)-nicotine to reduce cytotoxicity and attenuate increases in intracellular Ca2+ caused by exposure to N-methyl-D-aspartate were examined in organotypic cultures of rat hippocampus. Cultures were exposed to nicotine (0.1-10.0 microM) for five days prior to excitotoxic insult with N-methyl-D-aspartate. Exposure to N-methyl-D-aspartate produced concentration-dependent increases in both accumulation of 45Ca and in early and delayed cell death in the CA1, CA3 and dentate gyrus regions of cultures. The CA1 region of the hippocampus displayed the greatest sensitivity to cytotoxic effects of N-methyl-D-aspartate exposure; however, this regional difference was not associated with increased accumulation of 45Ca. Prior exposure to nicotine markedly attenuated N-methyl-D-aspartate-induced early and delayed cell death in each hippocampal region at concentrations as low as 0.1microM. However, nicotine did not alter the initial N-methyl-D-aspartate-stimulated influx of 45Ca or enhance extrusion of accumulated 45Ca measured at several time-points after insult. Five days of exposure to nicotine markedly increased immunoreactivity of the Ca2+ binding protein calbindin-D28K in each region of hippocampal cultures, effects reduced by mecamylamine co-exposure. These findings suggest that the potent protective effects of chronic nicotine exposure against neuronal overexcitation are not likely attributable to attenuations of Ca2+ accumulation, but are likely related to increased buffering of accumulated Ca2+.
Is Africa an Optimum Currency Area? A Comparison of Macroeconomic Costs and Benefits

This article examines the macroeconomic costs and benefits of adopting a common currency for 37 African countries. Economic theory suggests that the main benefit is enhanced price stability, whereas the main cost is higher business-cycle volatility if the member country's output is not sufficiently correlated with Africa's as a whole. Using data from 1960 to 2000, the article finds that the estimated cost and benefit measures exhibit substantial variability across the countries and are sometimes positively correlated: countries (such as Uganda, Ghana and Guinea) that have a lot to gain from a monetary union, also have a lot to lose from it; whereas other economies (such as Morocco, Cote d'Ivoire and Gabon) that have little to lose by adopting a common African currency, have also little to gain by it. The empirical results can also be used to compare net benefits for individual countries, showing, for example, that Nigeria is a more promising candidate for membership in an African monetary union than Kenya, and that Zambia is an unambiguously better candidate than either Benin or Mauritius. Copyright 2007, Oxford University Press.
Trends in catalytic reaction engineering

Abstract Catalytic reactions in multiphase systems are prevalent in production of fuels, bulk and specialty chemicals, pharmaceuticals, materials, food and feed, etc. Making useful products, at economical yields and selectivities, from the diverse chemistries in such a broad range of applications requires the ability to quantify the interplay of transport phenomena and kinetics. This is the domain of catalytic reaction engineering. In this paper the current state of the art of this discipline is briefly reviewed with the emphasis on describing the increased use of fundamentals in multiphase reactor modeling and scale-up. Packed beds, trickle beds, slurry bubble columns, simultaneous reaction and separation via catalytic distillation, membrane reactors and trickling solids adsorbent, as well as nonconventional multiphase reactor operations are discussed.
Stopping suicide attacks: optimal strategies and unintended consequences

Governments fighting terrorists have many tactical options, yet these options often yield unintended and counterproductive consequences. This paper models a terrorist organization, a religious group from which the terrorists recruit suicide bombers, and the society in which the terrotists are imbedded. The model illuminates how the choice of counterterrorist tactics influences the incidence of attacks, paying particular attention to the direct and indirect (unintended) consequences of the government's actions. The ultimate goal of this work is to identify the best way to stop terrorist attacks.
Fretting Stresses in Single Crystal Superalloy Turbine Blade Attachments

Single crystal nickel base superalloy turbine blades are being utilized in rocket engine turbopumps and turbine engines because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal nickel base turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. High Cycle Fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Blade attachment regions are prone to fretting fatigue failures. Single crystal nickel base superalloy turbine blades are especially prone to fretting damage because the subsurface shear stresses induced by fretting action at the attachment regions can result in crystallographic initiation and crack growth along octahedral planes. Furthermore, crystallographic crack growth on octahedral planes under fretting induced mixed mode loading can be an order of magnitude faster than under pure mode I loading. This paper presents contact stress evaluation in the attachment region for single crystal turbine blades used in the NASA alternate Advanced High Pressure Fuel Turbo Pump (HPFTP/AT) for the Space Shuttle Main Engine (SSME). Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Blades and the attachment region are modeled using a large-scale 3D finite element (FE) model capable of accounting for contact friction, material orthotrophy, and variation in primary and secondary crystal orientation. Contact stress analysis in the blade attachment regions is presented as a function of coefficient of friction and primary and secondary crystal orientation, Stress results are used to discuss fretting fatigue failure analysis of SSME blades. Attachment stresses are seen to reach peak values at locations where fretting cracks have been observed. Fretting stresses at the attachment region are seen to vary significantly as a function of crystal orientation. Attempts to adapt techniques used for estimating fatigue life in the airfoil region, for life calculations in the attachment region, are presented. An effective model for predicting crystallographic crack initiation under mixed mode loading is required for life prediction under fretting action.
Factors Influencing the Incidence of Bribery Payouts by Firms: A Cross-Country Analysis

This article explores micro- and macro-level variables that influence the incidence of bribery payouts by firms. A rich data set with information from 55 countries was utilized to achieve this objective. Results of logit regression models indicate that there are a number of micro- and macro-level factors that significantly affect the incidence of bribery payouts. This suggests that it is not only the characteristics of a firm but also the environment of doing business that affect the firm’s bribery decision. The results of this study provides information that may help firms develop strategies to reduce corruption in their respective industries and thereby improve their image of corporate social responsibility. The analysis also points to possible policy directions that governments could undertake in order to reduce the incidence of bribery in their country.
Regioselective Oxidation of Phenols to o-Quinones with o-Iodoxybenzoic Acid (IBX)

An efficient regioselective method for oxidation of phenols to o-quinones is reported. When this procedure is combined with a subsequent reduction, it proves to be useful for the construction of a variety of catechols.