cssi/SciSciGPT-SciSciNet huggingface dataset:
Semiconducting non-molecular nitrogen up to 240 GPa and its low-pressure stability

The triple bond of diatomic nitrogen has among the greatest binding energies of any molecule. At low temperatures and pressures, nitrogen forms a molecular crystal in which these strong bonds co-exist with weak van der Waals interactions between molecules, producing an insulator with a large band gap1. As the pressure is raised on molecular crystals, intermolecular interactions increase and the molecules eventually dissociate to form monoatomic metallic solids, as was first predicted for hydrogen2. Theory predicts that, in a pressure range between 50 and 94 GPa, diatomic nitrogen can be transformed into a non-molecular framework or polymeric structure with potential use as a high-energy-density material3,4,5. Here we show that the non-molecular phase of nitrogen is semiconducting up to at least 240 GPa, at which pressure the energy gap has decreased to 0.4 eV. At 300 K, this transition from insulating to semiconducting behaviour starts at a pressure of approximately 140 GPa, but shifts to much higher pressure with decreasing temperature. The transition also exhibits remarkably large hysteresis with an equilibrium transition estimated to be near 100 GPa. Moreover, we have succeeded in recovering the non-molecular phase of nitrogen at ambient pressure (at temperatures below 100 K), which could be of importance for practical use.
Potent and specific inhibition of human leukocyte elastase, cathepsin G and proteinase 3 by sulfone derivatives employing the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold.

Abstract This paper describes the results of structure–activity relationship studies in a series of heterocyclic mechanism-based inhibitors based on the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold I and capable of interacting with the S n and S n ′ subsites of a serine proteinase. Sulfone derivatives of I were found to be highly effective, time-dependent inhibitors of human leukocyte elastase (HLE), cathepsin G (Cat G) and proteinase 3 (PR 3). The judicious selection of an R 1 group (accommodated at the primary specificity site S 1 ) that is based on the known substrate specificity of a target serine proteinase, was found to yield highly selective inhibitors. The presence of a benzyl group (R 2 =benzyl) at the S 2 subsite was found to lead to a pronounced enhancement in inhibitory potency. Furthermore, the effective use of computer graphics and modeling has led to the design of potent, water-soluble inhibitors. The results of these studies demonstrate that the 1,2,5-thiadiazolidin-3-one 1,1, dioxide platform provides an effective means for appending recognition elements in a well-defined vector relationship, and in fashioning highly-selective and potent inhibitors of serine proteinases.
Numerical simulations of the ionosphere of Mars during a solar flare

[1] Electron densities in planetary ionospheres increase substantially during solar flares in response to the increased solar irradiance at soft X-ray and extreme ultraviolet wavelengths. Here we modify an existing model of the ionosphere of Mars to incorporate time-dependent solar irradiances and use it to simulate ionospheric conditions during the X14.4 and M7.8 solar flares of 15 and 26 April 2001, respectively. Simulations were validated by comparison to Mars Global Surveyor radio occultation measurements of vertical profiles of ionospheric electron density. Adjustments to the model's representation of the neutral atmosphere were required to adequately reproduce the observations before and during these solar flares. An accurate representation of electron-impact ionization, an important process in the lower ionosphere of Mars, is required in order to adequately simulate the doubling of electron densities that can occur in the lower ionosphere of Mars during a solar flare. We used the W-value representation of electron-impact ionization, in which the number of ion-electron pairs created per photon absorbed equals the ratio of the difference between photon energy and the ionization potential of carbon dioxide to the W-value. A range of possible W-values for Mars have been suggested in the literature, and a value of 28 eV led to the best reproduction of flare-affected observations. Simulated enhancements in the electron density are largest and persist the longest in the M1 region. We predict that the peak electron density in the M1 region can exceed that of the M2 region for short periods during intense solar flares.
Big Bang Nucleosynthesis constraints and light element abundance estimates

Abstract To elucidate the significance of the effect of systematic uncertainties in light element abundance estimates on cosmological bounds derivable from Big Bang Nucleosynthesis (BBN) we present tables giving bounds on Ω baryon and Nv as one changes the limits on primordial 4He and 7Li. This allows us to derive new relations between these estimates and constraints on Ω baryon and Nv. For example, only if the helium mass fraction, Yp ⩾.245 does 7Li (or D) presently play a role in placing an upper limit on the baryon density, and only if Yp >/.250 does 4He cease to play a role in bounding η10. All the elements combine together tend to give a stringent upper bound of.16 on Ω baryon . We also find that ϒP must exceed .239 for consistency between theory and observation if D+ 3 He H is less than 10−4. Updated nuclear reaction rates, an updated neutron half life, Monte Carlo techniques, and correlations between the predicted abundances are incorporated in our analysis. We also discuss the handling of systematic uncertainties in the context of statistical analyses of BBN predictions.
Cosmological constraints from the masses and abundances of L* galaxies

We place limits on the mean density of the Universe (Ω m ) and the effective slope of the linear power spectrum around a megaparsec scale (n e f f ) by comparing the universal mass function to the observed luminosity function. Numerical simulations suggest that the dark matter halo mass function at small scales depends only on Ω m (n e f f + 3) independent of the overall power spectrum normalization. Matching the halo abundance to the observed luminosity function requires knowledge of the relation between the virial mass and luminosity (separately for early-and late-type galaxies) and the fraction of galaxies that resides in larger haloes such as groups and clusters, all of which can be extracted from the galaxy-galaxy lensing. We apply the recently derived values from the Sloan Digital Sky Survey and find Ω m (n e f f + 3) = (0.15 ′ 0.05)/(1 -f d h ), where f d h accounts for the possibility that some fraction of haloes may be dark or without a bright central galaxy. A model with Ω m = 0.25 and primordial n = 0.8 or with Ω m = 0.2 and n = 1 agrees well with these constraints even in the absence of dark haloes, although with the current data somewhat higher values for Ω m and n are also acceptable.
Dark Matter Detection with Cryogenic Noble Liquids

Observations on all fronts strongly support the view of a universe composed of >96% invisible matter and energy. The invisible matter is non-baryonic, cold and likely in the form of new particles generically referred to as Weakly Interacting Massive Particles (WIMPs), relics from the early universe. One way to detect WIMPs is to measure the nuclear recoils produced in their rare elastic collisions with ordinary matter. The predicted interaction rate ranges from the best sensitivity of existing experiments of ~1 evts/kg/yr to ~1 evts/1000 kg/yr. Efforts are underway worldwide to realize sensitive direct detection experiments, with large target mass and improved background rejection capabilities. In this talk I will review experiments headed in this direction with the use of cryogenic noble liquids, focusing on those experiments which use the common technique of a dual-phase (liquid/gas) time projection chamber to measure simultaneously the ionization and the scintillation signals produced by radiation in a large volume of liquid xenon or liquid argon. These include experiments such as XENON, ZEPLIN, WARP and ArDM.
How do bacteria tune translation efficiency

Bacterial proteins are translated with precisely determined rates to meet cellular demand. In contrast, efforts to express recombinant proteins in bacteria are often met with large unpredictability in their levels of translation. The disconnect between translation of natural and synthetic mRNA stems from the lack of understanding of the strategy used by bacteria to tune translation efficiency (TE). The development of array-based oligonucleotide synthesis and ribosome profiling provides new approaches to address this issue. Although the major determinant for TE is still unknown, these high-throughput studies point out a statistically significant but mild contribution from the mRNA secondary structure around the start codon. Here I summarize those findings and provide a theoretical framework for measuring TE.
Guanosine Derivatives as Immunostimulants. Discovery of Loxoribine

Abstract 7-Allyl-8-oxoguanosine (loxoribine, 5) was selected from a series of guanosine derivatives for further evaluation as an immunostimulant. Numerous related analogs were also synthesized and evaluated: 2′,3′-ketals of 5 are particularly interesting because they are active, apparently without being cleaved to the free nucleoside.
Chemistry of electron-rich conjugated polyenes III. Synthesis and acid hydrolysis of 2,2-di- and 2,2,5-trimethoxy-5,6-dihydropyrans

Carbonyl compounds, activated by electron-withdrawing groups, add to 1,1-dimethoxybutadiene (Ia), yielding 2,2-dimethoxy-5,6-dihydropyrans (IIa). 1,1,4-Trimethoxybutadiene (Ib) reacts in a similar way with suitably activated ketones, but gives[2 + 2]-cycloadditions with activated aldehydes. The different behaviour is ascribed to steric factors. Acid hydrolysis of the 2,2-dimethoxydihydropyrans yields α,β-unsaturated esters and corresponding lactones, or dienyl esters depending on the reaction conditions used. 1,1-Dimethoxy-3-(trimethylsilyloxy)butadiene (Ic) yields Diels-Alder adducts even with non-activated carbonyl compounds, when zinc chloride is used as a catalyst. The products can be converted into dihydro-γ-pyrones by treatment with protic solvents (e.g. methanol).
Catalytic reduction of dinitrogen to ammonia at well-defined single metal sites

Dinitrogen (N2) is reduced to ammonia at room temperature and 1atm with molybdenum catalysts that contain tetradentate [HIPTN3N]3- triamidoamine ligands {[HIPTN3N]3-=[{3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2}3N]3-, an example being [HIPTN3N]Mo(N2)} in heptane. Slow addition of the proton source ({2,6-lutidinium}{BAr'4}; Ar'=3,5-(CF3)2C6H3) and reductant (decamethyl chromocene) assure a high yield of ammonia (63-65% in four turnovers) versus dihydrogen formation. Numerous X-ray studies, along with isolation and characterization of seven intermediates in the proposed catalytic reaction (under noncatalytic conditions), suggest that N2 is being reduced at a sterically protected, single Mo centre that cycles between states Mo(III), Mo(IV), Mo(V) and Mo(VI).
PNA-directed solution- and surface-assembly of shell crosslinked (SCK) nanoparticle conjugates

The conjugation of complementary peptide nucleic acid (PNA) sequences to well defined shell crosslinked (SCK) nanoparticles is reported as a mechanism by which to direct their self assembly into higher order structures via selective and tunable binding interactions. Base-pairing-driven aggregation of the SCK's occurred for mixtures of SCK's that presented complementary sequences in aqueous sodium chloride solutions and upon mica substrates. The assembly processes were monitored by dynamic light scattering and atomic force microscopy as a function of salt concentration, and by UV-vis spectroscopy as a function of salt concentration and temperature. Moreover, the stoichiometries of the PNA sequences conjugated per SCK nanoparticle and the stoichiometric ratios in the production of mixtures of SCK's bearing complementary PNA sequences were each altered to tune the hierarchical assemblies.
Ignition by excimer laser photolysis of ozone

Abstract We have ignited mixtures of hydrogen, oxygen, and ozone in closed cells with 248 nm radiation from a KrF excimer laser. Ozone, the only significant absorber in this system, absorbs a single photon and produces oxygen atoms which initiate combustion. A discretized, time-dependent Beer's law model is used to demonstrate that the radical concentration immediately after photolysis is a function of laser power, ozone concentration, focal length, and separation between the lens and reaction cell. Spark schlieren photographs are used to visualize the ignition events and identify the ignition sites. The effects of equivalence ratio, pressure, and the initial gas temperature on the minimum ozone concentration needed to produce ignition are presented, and only the initial temperature has a significant effect. Modeling studies of the ignition process aid in the interpretation of the experimental results, and show that the ignition we observe is not due solely to thermal effects, but is strongly dependent on the number and type of radicals present initially after photolysis. Ignition using other hydrocarbons as fuels was also demonstrated.
Sum rules and spectral measures of Schrödinger operators with L^2 potentials

Necessary and sufficient conditions are presented for a positive measure to be the spectral measure of a half-line Schrodinger operator with square integrable potential.
Biocompatibility of atomic layer-deposited alumina thin films

Presented in this paper is a study of the biocompatibility of an atomic layer-deposited (ALD) alumina (Al2O3) thin film and an ALD hydrophobic coating on standard glass cover slips. The pure ALD alumina coating exhibited a water contact angle of 55 degrees +/- 5 degrees attributed, in part, to a high concentration of -OH groups on the surface. In contrast, the hydrophobic coating (tridecafluoro-1,1,2,2-tetrahydro-octyl-methyl-bis(dimethylamino)silane) had a water contact angle of 108 degrees +/- 2 degrees. Observations using differential interference contrast microscopy on human coronary artery smooth muscle cells showed normal cell proliferation on both the ALD alumina and hydrophobic coatings when compared to cells grown on control substrates. These observations suggested good biocompatibility over a period of 7 days in vitro. Using a colorimetric assay technique to assess cell viability, the cellular response between the three substrates can be differentiated to show that the ALD alumina coating is more biocompatible and that the hydrophobic coating is less biocompatible when compared to the control. These results suggest that patterning a substrate with hydrophilic and hydrophobic groups can control cell growth. This patterning can further enhance the known advantages of ALD alumina, such as conformality and excellent dielectric properties for bio-micro electro mechanical systems (Bio-MEMS) in sensors, actuators, and microfluidics devices.
Synthesis of Alkynyl Ethers and Low-Temperature Sigmatropic Rearrangement of Allyl and Benzyl Alkynyl Ethers

Alpha-alkoxy ketones 3 can be transformed into 1-alkynyl ethers 5 by a two-step procedure involving formation of the enol triflate or phosphate and base-induced elimination. Performing the same reaction sequence with allylic alcohols (R2OH, R2 = allyl) furnishes instead gamma,delta-unsaturated carboxylic acid derivatives 6, derived from [3,3]-sigmatropic rearrangement of the intermediate allyl alkynyl ethers at -78 degrees C and trapping of the subsequently formed ketene with nucleophiles (Nu-H). Benzyl alkynyl ether 5 (R2 = benzyl) rearranges to indanone 7 upon heating to 60 degrees C.
Hilbert Scheme of a Pair of Codimension Two Linear Subspaces

We study the component H n of the Hilbert scheme whose general point parameterizes a pair of codimension two linear subspaces in ℙ n for n ≥ 3. We show that H n is smooth and isomorphic to the blow-up of the symmetric square of &#x1d53e;(n − 2, n) along the diagonal. Further H n intersects only one other component in the full Hilbert scheme, transversely. We determine the stable base locus decomposition of its effective cone and give modular interpretations of the corresponding models, hence conclude that H n is a Mori dream space.
Detection of aperiodically embedded synchronization patterns

Synchronization patterns aperiodically embedded in data may result from applications such as transmission of framed data and compression of video. In this letter, a metric for detection of these patterns is derived. It is assumed that the distribution of the synchronization patterns in the symbol stream is known. By taking advantage of this knowledge, improved synchronization can be realized over traditional correlation with correction. Transmission using binary phase shift keying (BPSK) on an additive white Gaussian noise channel is considered first. This derivation is then extended to higher-order modulation schemes, and high-signal-to-noise ratio approximations to the exact metrics are derived. Experimental results for BPSK and quarternary phase shift keying signaling are shown. Finally, the effects of inexact knowledge of the channel and a priori probabilities are examined, and it is shown that the aperiodic metric is not sensitive to small deviations in the estimates of the channel or the synchronization pattern probabilities.
Color onsets and offsets, and luminance changes can cause change blindness.

It has recently been demonstrated that people often fail to detect between-view changes in their visual environment. This phenomenon, called ‘change blindness’ (CB), occurs whenever the perceptual transient that usually accompanies a change is somehow blocked, or made less salient. In the well-known flicker paradigm, the transient is blocked by inserting a blank screen between the original and changed scenes. We tested whether transients that do not involve the appearance or disappearance of visual objects would also produce CB. Therefore we tested whether the appearance or disappearance of color information, and increments or decrements in luminance, could cause CB. In three experiments, subjects searched for changes in natural scenes. We found that both color transients and luminance transients significantly reduced change detection (by ∼30%) relative to a no-transient condition.
Weight-biased leftist trees and modified skip lists

We propose the weight biased leftist tree as an alternative to traditional leftist trees [CRAN72] for the representation of mergeable priority queues. A modified version of skip lists [PUGH90] that uses fixed size nodes is also proposed. Experimental results show our modified skip list structure is faster than the original skip list structure for the representation of dictionaries. Experimental results comparing weight biased leftist trees and competing priority queue structures are presented.
Activity Coefficient Derivatives of Ternary Systems Based on Scatchard’s Neutral Electrolyte Description

Activity coefficient derivatives with respect to molality are presented for the Scatchard Neutral Electrolyte description of a ternary common-ion electrolyte system. These quantities are needed for the calculation of “diffusion Onsager coefficients” and in turn for tests of the Onsager Reciprocal Relations in diffusion. The usually-omitted b23 term is included. The direct SNE binary approximations and a further approximation are discussed. Binary evaluation strategies other than constant ionic strength are considered.
Nonequilibrium phonon effects in midinfrared quantum cascade lasers

We investigate the effects of nonequilibrium phonon dynamics on the operation of a GaAs-based midinfrared quantum cascade laser over a range of temperatures (77–300 K) via a coupled ensemble Monte Carlo simulation of electron and optical-phonon systems. Nonequilibrium phonon effects are shown to be important below 200 K. At low temperatures, nonequilibrium phonons enhance injection selectivity and efficiency by drastically increasing the rate of interstage electron scattering from the lowest injector state to the next-stage upper lasing level via optical-phonon absorption. As a result, the current density and modal gain at a given field are higher and the threshold current density lower and considerably closer to experiment than results obtained with thermal phonons. By amplifying phonon absorption, nonequilibrium phonons also hinder electron energy relaxation and lead to elevated electronic temperatures.
How efficient is BitTorrent

BitTorrent is arguably the most popular media file distribution protocol used in Internet today. Even though empirically BitTorrent seems to be both efficient and scalable, there has been very little research on the detailed dynamics of its built-in control mechanisms, and their effectiveness across a wide variety of network configurations and protocol parameters. The main goal of this paper is to answer the question of how close BitTorrent is to the optimum, and indirectly how much room there is for further performance optimizations. We develop a centrally scheduled file distribution (CSFD) protocol that can provably minimize the total elapsed time of a one-sender-multiple-receiver file distribution task, and perform a comprehensive comparison between BitTorrent with CSFD . In addition, we compare several peer selection algorithms and analyze the applicability of BitTorrent to real-time streaming applications.
Irregular Mass Transfer in the Polars VV Puppis and V393 Pavonis during the Low State

The polars VV Pup and V393 Pav were observed with XMM-Newton during states of low accretion with peak X-ray luminosities of ~1 × 1030 and ~1 × 1031 ergs s-1, respectively. In both polars, accretion onto the white dwarf was extremely irregular, and the accretion rate varied by more than 1 order of magnitude on timescales of ~1 hr. Our observations suggest that this type of irregular accretion is a common phenomenon in polars during the low state. The likely cause of the accretion rate fluctuations is coronal mass ejections or solar flares on the companion star that intermittently increase the mass transfer into the accretion stream. Our findings demonstrate that the companion stars in cataclysmic variables possess highly active atmospheres.
Yield learning and the sources of profitability in semiconductor manufacturing and process development

A numerical model that identifies the high-leverage variables associated with profitability in semiconductor manufacturing is presented. Varying the parameters of the model demonstrates that a rapid yield-learning rate determines profitability more than any other factor does. Factors such as ramping-up early, adding fab capacity, depressing the terminal fault density, and shrinking die size all yield diminishing returns. The model also suggests that developing a rapid problem-solving capability in the early stages of process development enables successful yield learning.
Geochemical signature of land-based activities in Caribbean coral surface samples

Anthropogenic threats, such as increased sedimentation, agrochemical run-off, coastal development, tourism, and overfishing, are of great concern to the Mesoamerican Caribbean Reef System (MACR). Trace metals in corals can be used to quantify and monitor the impact of these land-based activities. Surface coral samples from the MACR were investigated for trace metal signatures resulting from relative differences in water quality. Samples were analyzed at three spatial scales (colony, reef, and regional) as part of a hierarchical multi-scale survey. A primary goal of the paper is to elucidate the extrapolation of information between fine-scale variation at the colony or reef scale and broad-scale patterns at the regional scale. Of the 18 metals measured, five yielded statistical differences at the colony and/or reef scale, suggesting fine-scale spatial heterogeneity not conducive to regional interpretation. Five metals yielded a statistical difference at the regional scale with an absence of a statistical difference at either the colony or reef scale. These metals are barium (Ba), manganese (Mn), chromium (Cr), copper (Cu), and antimony (Sb). The most robust geochemical indicators of land-based activities are coral Ba and Mn concentrations, which are elevated in samples from the southern region of the Gulf of Honduras relative to those from the Turneffe Islands. These findings are consistent with the occurrence of the most significant watersheds in the MACR from southern Belize to Honduras, which contribute sediment-laden freshwater to the coastal zone primarily as a result of human alteration to the landscape (e.g., deforestation and agricultural practices). Elevated levels of Cu and Sb were found in samples from Honduras and may be linked to industrial shipping activities where copper–antimony additives are commonly used in antifouling paints. Results from this study strongly demonstrate the impact of terrestrial runoff and anthropogenic activities on coastal water quality in the MACR.
Firm Location and Corporate Debt

This study examines the influence of a firm’s geographical location on corporate debt and provides evidence that the higher cost of collecting information on firms distant from urban areas has significant implications on a wide array of corporate debt characteristics. We find that rural firms face higher debt yield spreads and attract smaller and less prestigious bank syndicates than urban firms. Rural firms attempt to reduce their informational disadvantage by relying more on relationship banking. Our results on the effect of location on corporate debt are robust to the inclusion of an extensive set of firm and issue characteristics.
Rhenium-Catalyzed Coupling of Propargyl Alcohols and Allyl Silanes

A mild method for the regioselective coupling of propargyl alcohols and allylsilanes is described. The method employs an air- and moisture-tolerant rhenium-oxo complex ((dppm)ReOCl3) as a catalyst for the formation of sp3-carbon−sp3-carbon bonds without the need for prior activation of the propargyl alcohol as a halide or pseudohalide. The stability of the high oxidation state rhenium complex allows for simple reisolation and reuse of the catalyst. A broad range of functional groups is tolerated including aryl halides, olefins, esters, and acid-labile functional groups such as acetals. Furthermore, displacement of the alcohol occurs preferentially even in the presence of other electrophiles such as primary alkyl halides and conjugated esters. The use of enantiopure crotylsilanes as coupling partners allows for the asymmetric construction of two adjacent stereocenters. The potential of this reaction is demonstrated in an asymmetric synthesis of δ-lactone, di-O-methylcalopin.
Amide surrogates of matrix metalloproteinase inhibitors : Urea and sulfonamide mimics

Abstract A new method for the synthesis of succinyl sulfinyl chlorides was applied to the preparation of sulfonamide peptide mimics of MMP inhibitors. Sulfonamide mimics were determined to be active against MMPs and represent promising new leads for further optimization. Urea mimics were also prepared and found to be unstable and prone to hydantoin formation in protic media.
Heterotic string data and theta functions

We use the language of differential cohomology to give an analytic description of the moduli space of classical vacua for heterotic string theory in eight dimensions. The complex structure of this moduli space is then related to the character of the appropriate Kac–Moody algebra.
Photoreactions of o-vinyltriphenylethylenes II. Photochemistry of 1,1-diphenyl-2-(o-vinylphenyl)- and 1,1-diphenyl-2-(o-propenylphenyl)ethylene

Irradiation of 1,1-diphenyl-2-(o-vinylphenyl)ethylene (3) leads stereoselectively to endo-4,5-diphenylbenzobicyclo[3.1.0]hex-2-ene (6). The analogous reaction of the homologous (o-propenylphenyl)ethylene derivative (4) seems to be less stereoselective, as products 10 and 11 could be isolated. In both cases a photodehydrocyclisation product (7 and 12, respectively) is also found. Possible mechanisms for the photocyclisation reactions are discussed, and the photochemical behaviour of 3 and 4 is compared with that of other o-vinylstilbenes, previously investigated.
Thermal Conductivity of Cage-Like Structures

A two dimensional toy model is developed to study thermal transport in cage like structures such a skutterudites and clathrates. The model consists of host atoms on a rectangular lattice with fillers in the center of each rectangle. The thermal conductivity is calculated by using Green-Kubo equilibrium molecular dynamics simulations. It is generally believed that the smaller and the heavier the filler, the lower is the thermal conductivity. We show that the thermal conductivity decreases with atomic displacement parameter while it has local minima versus filler mass. Our study shows that it is very important to include the correct band dispersion to get the right features of the thermal conductivity. We show that by having a double well potential one can further reduce the thermal conductivity.Copyright © 2011 by ASME
An expedient stereoselective and chemoselective synthesis of bicyclic oxazolidinones from quinols and isocyanates

A mild and efficient synthesis of bicyclic oxazolidinones from quinols and isocyanates, under DBU-mediated conditions at room temperature, is described. The aza-Michael addition to substituted cyclohexadienones is stereoselective and chemoselective.
Bounds on supersymmetry from electroweak precision analysis

Abstract The Standard Model global fit to precision data is excellent. The Minimal Supersymmetric Standard Model can also fit the data well, though not as well as the Standard Model. At best, supersymmetric contributions either decouple or only slightly decrease the total χ2, at the expense of decreasing the number of degrees of freedom. In general, regions of parameter space with large supersymmetric corrections from light superpartners are associated with poor fits to the data. We contrast results of a simple (oblique) approximation with full one-loop results, and show that for the most important observables the non-oblique corrections can be larger than the oblique corrections, and must be taken into account. We elucidate the regions of parameter space in both gravity- and gauge-mediated models which are excluded. Significant regions of parameter space are excluded, especially with positive supersymmetric mass parameter μ. We give a complete listing of the bounds on all the superpartner and Higgs boson masses. For either sign of μ, and for all supersymmetric models considered, we set a lower limit on the mass of the lightest CP-even Higgs scalar, mh ⩾ 78 GeV. Also, the first and second generation squark masses are constrained to be above 280 (325) GeV in the supergravity (gauge-mediated) model.
Two linear transformations each tridiagonal with respect to an eigenbasis of the other

Let K denote a field, and let V denote a vector space over K with finite positive dimension. We consider a pair of linear transformations A:V→V and A*:V→V satisfying both conditions below: 1. [(i)] There exists a basis for V with respect to which the matrix representing A is diagonal and the matrix representing A* is irreducible tridiagonal. 2. [(ii)] There exists a basis for V with respect to which the matrix representing A* is diagonal and the matrix representing A is irreducible tridiagonal. We call such a pair a Leonard pair on V. Refining this notion a bit, we introduce the concept of a Leonard system. We give a complete classification of Leonard systems. Integral to our proof is the following result. We show that for any Leonard pair A,A* on V, there exists a sequence of scalars β,γ,γ*,ϱ,ϱ* taken from K such that both 0=[A,A2A*−βAA*A+A*A2−γ(AA*+A*A)−ϱA*], 0=[A*,A*2A−βA*AA*+AA*2−γ*(A*A+AA*)−ϱ*A], where [r,s] means rs−sr. The sequence is uniquely determined by the Leonard pair if the dimension of V is at least 4. We conclude by showing how Leonard systems correspond to q-Racah and related polynomials from the Askey scheme.
The transport properties of oxygen in aqueous borate solutions

Abstract The solubility and diffusivity of oxygen in borate buffer solutions were studied on a Pt μ electrode under diffusion-controlled conditions. The solubility of oxygen in diluted borate solution is unusually high (4.2 × 10−3 M l−1), whereas its diffusion coefficient is lower (5 × 10−6 cm2 s−1) than in other aqueous solutions The decrease in oxygen solubility at higher ionic strengths is due to the salting-out effect. The results are consistent with the formation of “oxygen-borate” complex whereby the stability of BO3 containing polymeric anions is enhanced.
Amine Additives Greatly Expand the Scope of Asymmetric Hydrosilylation of Imines

Slow addition of a primary amine to the reaction mixture greatly increases the scope of the titanium-catalyzed asymmetric reduction of imines 1. An important added feature of this method is that chiral secondary amines 2 can be obtained in much higher optical purity (up to 99 % ee) than would be predicted from the E:Z ratios of the starting imines 1.
Quantifying dose to the reconstructed breast: Can we adequately treat?

Abstract To evaluate how immediate reconstruction (IR) impacts postmastectomy radiotherapy (PMRT) dose distributions to the reconstructed breast (RB), internal mammary nodes (IMN), heart, and lungs using quantifiable dosimetric end points. 3D conformal plans were developed for 20 IR patients, 10 autologous reconstruction (AR), and 10 expander-implant (EI) reconstruction. For each reconstruction type, 5 right- and 5 left-sided reconstructions were selected. Two plans were created for each patient, 1 with RB coverage alone and 1 with RB + IMN coverage. Left-sided EI plans without IMN coverage had higher heart Dmean than left-sided AR plans (2.97 and 0.84 Gy, p = 0.03). Otherwise, results did not vary by reconstruction type and all remaining metrics were evaluated using a combined AR and EI dataset. RB coverage was adequate regardless of laterality or IMN coverage (Dmean 50.61 Gy, D95 45.76 Gy). When included, IMN Dmean and D95 were 49.57 and 40.96 Gy, respectively. Mean heart doses increased with left-sided treatment plans and IMN inclusion. Right-sided treatment plans and IMN inclusion increased mean lung V20. Using standard field arrangements and 3D planning, we observed excellent coverage of the RB and IMN, regardless of laterality or reconstruction type. Our results demonstrate that adequate doses can be delivered to the RB with or without IMN coverage.
A summary of progress toward proving program correctness

Interest in proving the correctness of programs has grown explosively within the last two or three years. There are now over a hundred people pursuing research on this general topic; most of them are relative newcomers to the field. At least three reasons can be cited for this rapid growth:(1) The inability to design and implement software systems which can be guaranteed correct is severely restricting computer applications in many important areas.(2) Debugging and maintaining large computer programs is now well recognized as one of the most serious and costly problems facing the computer industry.(3) A large number of mathematicians, especially logicians, are interested in applications where their talents can be used.
The complexity of controlled selection

We identify a class of problems, called controlled selection problems, and study their complexity. A controlled selection problem involves a random selection of a sample from a large set subject to certain structural constraints. The structural constraints model some desired relationships among the elements of the set, which we want to preserve under random selection. For example, the set may be divided into equivalence classes and we may want to ensure that not too many elements are chosen from the same class, or the set may correspond to vertices of a graph and we may want to ensure that the sample does not induce a cycle. Controlled selection problems arise in many disciplines, including statistics, mathematical programming, combinatorial algorithms, and resource allocation. This is the first attempt to unify them. We develop techniques for determining the complexity of controlled selection problems given the structural constraints. We use these techniques to determine the complexity of many types of controlled selection problems. We show that a controlled selection problem is polynomial-time reducible to the problem of finding a maximum weight sample satisfying the structural constraints. We also show that a general reduction in the opposite direction would imply that one-way functions do not exist. In contrast, we show that most natural controlled selection problems have the same complexity (within polynomial time) as the problem of finding a maximum weight sample satisfying the structural constraints. We also present efficient algorithms for several controlled selection problems.
Total Synthesis of the Annonaceous Acetogenin (+)-Asimicin. Development of a New Bidirectional Strategy

The total synthesis of the Annonaceous acetogenin (+)-asimicin is described. The approach employs the (R)-α-OSEM allylic stannane 7 of >95% ee and the dialdehyde 8 obtained from (S,S)-diethyl tartrate. Addition of 7 to 8 in the presence of InCl3 afforded the bis-adduct 9 in 71% yield. Tosylation and treatment with TBAF led to the core bis-tetrahydrofuran intermediate, diol 11, in 78% yield. Mono tosylation (n-BuLi, TsCl, THF−DMSO) and subsequent hydrogenolysis with LiBEt3H gave alcohol 14. The iodide 15 was coupled with the higher-order vinylcyanocuprate to afford olefin 30. This was converted to diol 31 of high ee by the Sharpless protocol. This diol yielded the epoxide 33 via the mono-trisylate 32. Addition of (R)-lithio-2-(OTBS)-3-butyne in the presence of BF3·OEt2 afforded the alcohol 34. The SEM derivative 35 was treated with TBAF, and the resulting alcohol was converted to the butenolide 38 by a sequence involving treatment with (CF3CO)2O, then Pd(PPh3)4, CO, THF−H2O, and finally AgNO3/silica gel. C...
Shock effects in olivine and implications for Hugoniot data

Deformation produced in single-crystal olivine samples by shock wave stresses ranging between 16 and 75 GPa are documented by microscopy and spectroscopy. No evidence was found for phase transformation throughout the ‘mixed-phase’ region (about 25 to 70 GPa) contrary to expectations based on the current interpretations of Hugoniot data. Samples retrieved from peak pressures above 20 GPa exhibit extensive plastic strain; a distinctive microundulatory extinction (mosaicism) is associated with elevated dislocation densities. Shock effects in olivine are relatively minor compared to those typical of other silicates: only traces of diaplectic glass are found at pressures above about 50 GPa, and there is no evidence of melting, recrystallization, or recovery. Although civilian (reconstructive) phase transformation has been previously inferred from the Hugoniot data for olivine, this textural evidence is inconsistent with such a process. Calculations of transformation rates for olivine similarly indicate that reconstructive phase transformation is very unlikely under experimental shock conditions and that the Hugoniot data represent highly nonequilibrium states. A new, crystallographically based model is presented for the behavior of olivine under shock: it successfully reproduces the Hugoniot data and is in accord with all available observations. According to this model, olivine is compressed into a slighlty randomized, olivinelike structure at shock pressures above about 20–30 GPa and does not undergo a polymorphic transformation or an increase in cation coordination number. Some evidence indicates that many other silicates may behave similarly and remain untransformed in shock experiments. The results of this study suggest that the current interpretations of shock wave data for silicates and their geophysical applications may need reappraisal.
The crystal structure of diopside at pressure to 10 GPa

The crystal structure of diopside has been determined at various pressures to 10.16 GPa. The results to 5 GPa are consistent with Levien and Prewitt (1981). The crystal structures have been analyzed using the geometric pyroxene model of Thompson and Downs (2004), the anion packing algorithm of Thompson and Downs (2001), and a new algorithm that quantifies the distortion of observed pyroxenes from their geometric model equivalents. Diopside is shown to compress via three main mechanisms: isotropic scaling, kinking of the tetrahedral chains, and collapse of the M1 chain toward its axis. The kinking of the chains accounts for most of the anisotropy of compression observed in the a-c plane, and the collapse of the M1 chain explains the anisotropy seen in the b-c plane. Model behavior is shown to reproduce many of the observations of previous workers. Anion-anion interactions are shown to be important in the distortion of observed diopside from its geometric model equivalent.
Anomalously light mesons in a (1+1)-dimensional supersymmetric theory with fundamental matter

Abstract We consider N =1 supersymmetric Yang–Mills theory with fundamental matter in the large-Nc approximation in 1+1 dimensions. We add a Chern–Simons term to give the adjoint partons a mass and solve for the meson bound states. Here mesons are color-singlet states with two partons in the fundamental representation but are not necessarily bosons. We find that this theory has anomalously light meson bound states at intermediate and strong coupling. We also examine the structure functions for these states and find that they prefer to have as many partons as possible at low longitudinal momentum fraction.
Pharmacokinetics (PK) of 2 dosing regimens of palifermin in patients (Pts) with hematologic malignancies (HM) undergoing high-dose chemoradiotherapy and hematopoietic stem cell transplantation (HSCT)

For pts with HM undergoing HSCT, oral mucositis (OM) is a frequent and debilitating complication that negatively impacts treatment outcomes, patient quality of life, and healthcare resources. Palifermin reduces the incidence and duration of severe OM in the HSCT setting. This phase 1 open-label study assessed the PK of 2 palifermin dosing regimens. Methods: Pts were 18 to 76 years old with HM and a Karnofsky performance score ≥70%. Palifermin was administered intravenously once daily as follows: 60 mcg/kg/day [d] for 3 consecutive days on d -11, -10, and -9 before conditioning (total body irradiation [TBI] + etoposide + cyclophosphamide) and following HSCT on d 0, 1 and 2 (part A) and a single dose of 180 mcg/kg (part B) before conditioning on d -11 and after HSCT on d 0. In part A (6 total doses), PK parameters were assessed after the 1st, 3rd, 4th, and 6th doses. In part B (2 total doses), assessments were made after each dose administration (d -11 and d 0). Results: In part A, 13 pts received palifermin; in part B, 12 pts received the single dose on d -11 and 11 pts received the single dose on d 0. For both dosing regimens, palifermin concentrations declined rapidly (≥98% decrease) in the first 30 minutes postdose, followed by a slight increase in mean concentrations between 1 and 4 hours and then a terminal decay phase. Respective mean (SD) PK parameter values for the 2 dosing regimens are shown in Table 1. In part A, mean AUC0-t values were comparable between doses 1 and 3 (within 15%) and 1 and 4 (within 1%). In part B, mean PK parameter values were similar (within 10% of each other) between doses 1 and 2. The mean AUC after the first 180 mcg/kg dose in part B was approximately 4-fold higher than that after the first 60 mcg/kg dose in part A. Mean half-life values ranged between 3.3 to 5.7 hours in part A and the value was 5.4 hours in part B. Conclusion: The PK data in pts receiving HSCT were consistent with approximately dose-linear PK in the dose range of 60 and 180 mcg/kg, with no observed accumulation, based on AUC, after 3 daily doses of 60 mcg/kg in this pt population in the HSCT setting.
Precision Measurements and Fermion Geography in the Randall-Sundrum Model Revisited

We re-examine the implications of allowing fermion fields to propagate in the five-dimensional bulk of the Randall-Sundrum (RS) localized gravity model. We find that the large mixing between the Standard Model top quark and its Kaluza Klein excitations restricts the fundamental RS scale to lie above 100 TeV. To circumvent this difficulty we propose a ''mixed'' scenario which localizes the third generation fermions on the TeV brane and allows the lighter generations to propagate in the full five-dimensional bulk. We show that this construction naturally reproduces the observed m{sub c}/m{sub t} and m{sub s}/m{sub b} hierarchies. We explore the signatures of this scenario in precision measurements and future high energy experiments. We find that the same region of parameter space that addresses the hierarchies of fermion Yukawa couplings also permits a Higgs boson with a mass of 500 GeV, and remains otherwise invisible at the LHC; however, the entire parameter region consistent with the electroweak precision data is testable at future linear colliders. We briefly discuss possible constraints on this scenario arising from flavor changing neutral currents.
Turbulent Linewidths in Protoplanetary Disks: Predictions from Numerical Simulations

Submillimeter observations of protoplanetary disks now approach the acuity needed to measure the turbulent broadening of molecular lines. These measurements constrain disk angular momentum transport, and furnish evidence of the turbulent environment within which planetesimal formation takes place. We use local magnetohydrodynamic (MHD) simulations of the magnetorotational instability (MRI) to predict the distribution of turbulent velocities in low-mass protoplanetary disks, as a function of radius and height above the mid-plane. We model both ideal MHD disks and disks in which Ohmic dissipation results in a dead zone of suppressed turbulence near the mid-plane. Under ideal conditions, the disk mid-plane is characterized by a velocity distribution that peaks near v {approx_equal} 0.1c{sub s} (where c{sub s} is the local sound speed), while supersonic velocities are reached at z > 3H (where H is the vertical pressure scale height). Residual velocities of v Almost-Equal-To 10{sup -2} c{sub s} persist near the mid-plane in dead zones, while the surface layers remain active. Anisotropic variation of the linewidth with disk inclination is modest. We compare our MHD results to hydrodynamic simulations in which large-scale forcing is used to initiate similar turbulent velocities. We show that the qualitative trend of increasing v with height, seenmore » in the MHD case, persists for forced turbulence and is likely a generic property of disk turbulence. Percentage level determinations of v at different heights within the disk, or spatially resolved observations that probe the inner disk containing the dead zone region, are therefore needed to test whether the MRI is responsible for protoplanetary disk turbulence.« less