cssi/SciSciGPT-SciSciNet huggingface dataset:
Small-Scale X-Ray Variability in the Cassiopeia A Supernova Remnant

A comparison of X-ray observations of the Cassiopeia A supernova remnant taken in 2000, 2002, and 2004 with the Chandra ACIS-S3 reveals the presence of several small-scale features (≤10'') that exhibit significant intensity changes over a 4 yr time frame. Here we report on the variability of six features, four of which show count rate increases from ~10% to over 90%, and two of which show decreases of ~30%-40%. While extracted 1-4.5 keV X-ray spectra do not reveal gross changes in emission-line strengths, spectral fits using nonequilibrium-ionization, metal-rich plasma models indicate increased or decreased electron temperatures for features showing increasing or decreasing count rates, respectively. Based on the observed count rate changes and the assumption that the freely expanding ejecta has a velocity of ~5000 km s-1 at the reverse shock front, we estimate the unshocked ejecta to have spatial scale variations of 0.02-0.03 pc, which is consistent with the X-ray-emitting ejecta belonging to a more diffuse component of the supernova ejecta than that seen in the optically emitting ejecta, which have spatial scales of ~10-3 pc.
Managerial hedging ability and firm risk

Modern portfolio theory suggests that undiversified executives would choose to diversify their significant holdings of their firm’s stock if the opportunity was available. Recent work suggests that managerial hedging is more prevalent than in years past as more innovative hedging instruments have become available to executives. Typically, unrestricted shares are used in these hedging transactions whereas restricted shares are not. In this paper, I examine whether a CEO’s composition of firm stockholdings between restricted and unrestricted shares impacts the level of risk undertaken by the firm. I document a negative and statistically significant relationship between firm risk and the proportion of CEO total shareholdings that are unrestricted and this negative relationship holds for alternative measures of firm risk. This result supports the notion that the composition of a CEO’s portfolio of firm stock between restricted and unrestricted shares is a significant determinant of firm risk.
Hyperelliptic jacobians with real multiplication

Abstract Let K be a field of characteristic p ≠ 2 , and let f ( x ) be a sextic polynomial irreducible over K with no repeated roots, whose Galois group is isomorphic to A 5 . If the jacobian J ( C ) of the hyperelliptic curve C : y 2 = f ( x ) admits real multiplication over the ground field from an order of a real quadratic field D , then either its endomorphism algebra is isomorphic to D , or p > 0 and J ( C ) is a supersingular abelian variety. The supersingular outcome cannot occur when p splits in D .
A note on the characterization of bivariate densities by conditional densities

The compatibility of pairs of conditional densities and the uniqueness of the resulting bivariate densities are discussed. Examples ar given involving beta, gamma, and Gaussian conditional densities.
Low-Wear Partially Fluorinated Polyimides

Tribological studies were conducted on five different polyimide solid bodies formulated from the diamine 2,2-bis 4-(4-aminophenoxy)phenyl hexafluoropropane (4-BDAF) and the dianhydrides pyromellitic acid (PMDS) and benzophenonetetracarboxylic acid (BTDA). The following polyimides were evaluated 4-BDAF/PMDA, 4-BDAF/BTDA, 4-BDAF/80 mole percent PMDA, 20 mole percent BTDA, 4-BDAF/60 mole percent BTDA. Friction coefficients, polyimide wear rates, polyimide surface morphology and transfer films were evaluated at sliding speeds of 0.31 to 11.6 m/s and at temperatures of 25 C to 300 C. The results indicate that the tribological properties are highly dependent on the composition of the polyimide and on the experimental conditions. Two polyimides were found which produced very low wear rates but very high friction coefficients (greater than 0.85) under ambient conditions. They offer considerable potential for high traction types of application such as brakes.
The Power Spectrum, Bias Evolution, and the Spatial Three-Point Correlation Function

We calculate perturbatively the normalized spatial skewness, S3, and full three-point correlation function (3PCF), ζ, induced by gravitational instability of Gaussian primordial fluctuations for a biased tracer-mass distribution in flat and open cold dark matter (CDM) models. We take into account the explicit dependence on cosmological parameters, the shape and evolution of the CDM power spectrum, and we allow the bias to be nonlinear and/or evolving in time, using an extension of Fry's bias evolution model. We derive a scale-dependent, leading-order correction to the standard perturbative expression for S3 in the case of nonlinear biasing, as defined for the unsmoothed galaxy and dark-matter fields, and find that this correction becomes large when probing positive effective power-spectrum indices, i.e., scales above 100 h-1 Mpc for reasonable CDM models. This term implies that the inferred nonlinear-bias parameter, as usually defined in terms of the smoothed density fields, might in general depend on the chosen smoothing scale and could allow better constraints on both the linear- and nonlinear-bias parameters on the basis of skewness measurements alone (or at least distinguish between the smoothed and unsmoothed bias pictures), if S3 could be measured over very large scales. In general, we find that the dependence of S3 on the biasing scheme can substantially outweigh that on the adopted cosmology, with linear and nonlinear bias separately giving rise to distinct signatures in the skewness, but degenerate ones in combination. We demonstrate that the normalized 3PCF, Q, is an ill-behaved quantity, and speculate that reported discrepancies between perturbative and N-body predictions for Q may arise in part from systematic errors associated with the poor choice of normalization. To avoid this problem we investigate QV, the variance-normalized 3PCF. The configuration dependence of QV shows similarly strong sensitivities to the bias scheme as S3, but also exhibits significant dependence on the form of the CDM power spectrum. Though the degeneracy of S3 with respect to the cosmological parameters and constant linear- and nonlinear-bias parameters can be broken by the full configuration dependence of QV, neither statistic can distinguish well between evolving and nonevolving bias scenarios, since an evolving bias is found to effectively mimic a smaller but constant bias. We show that this can be resolved, in principle, by considering the redshift dependence of ζ, which can also yield direct constraints on Ω0 and the epoch of galaxy formation.
Mars - Chemical weathering as a massive volatile sink

The amounts of volatiles incorporated in the Martian regolith by photostimulated oxidation weathering of Fe(2+)-bearing minerals are estimated. The process of photostimulated oxidation weathering is described, and it is noted that all the necessary constituents for this process are present on Mars. The rates at which oxygen and hydrogen are irreversibly removed from the Martian atmosphere by the present process are determined, irreversible and reversible water losses are considered, and the loss of CO2 by carbonate formation is shown to be irreversible. The results suggest that photostimulated oxidation weathering has irreversibly consumed 100 to 100,000 g/sq cm of H2O and 10 to 10,000 g/sq cm of CO2, assuming a uniform rate over geologic time. It is concluded that if the amounts of H2O and CO2 actually removed by photostimulated oxidation are close to the upper limits of the present estimates, then that process may have had a major effect in limiting the amount of H2O and CO2 trapped in the regolith and polar caps.
Constitutionality of the Patient Protection and Affordable Care Act Under the Commerce Clause and the Necessary and Proper Clause

On March 23, 2010, President Barack Obama signed into law the Patient Protection and Affordable Care Act (PPACA). 1 The PPACA is a comprehensive statute reforming how health care is paid for in the...
Prosthetic Voice Restoration With the Tracheostomal Valve: A Clinical Experience

Abstract Introduction: Tracheoesophageal puncture (TEP) and use of a voice prosthesis is not a panacea for all laryngectomies. This report presents results of longitudinal treatment of 24 patients with secondary TEP followed longitudinally for 10 years in a private practice setting. Unique to this report is a focus on the use of the entire voice restoration system including both the voice prosthesis and the automatic tracheostomal valve. Methods: All patients referred for secondary TEP between 1982 and 1992 are included. Voice quality and the longevity of vocal restoration were ascertained. Clinical problems and their solutions are reported. Results: Immediate vocal restitution was achieved in 19 of 24 patients. Voicing was produced in two more patients within a few weeks. Four patients were not available for long-term follow-up because of death due to recurrent disease. Overall, 60% of patients were rated excellent and 5% rated fair in communication over a long-term period. Thirty-five percent were rated failure. Discussion: TEP and the use of the voice restoration system enabled both hands to be free during speaking and is achieved by many laryngectomies. Patient evaluation, training, and follow-up with team problem-solving may increase success rates using this approach.
Unified Theory for the Dynamics and Control of Maneuvering Flexible Aircraft

This work represents a new paradigm for the dynamics and control of maneuvering flexible aircraft. Using the system concept, the theory integrates seamlessly all the necessary material from the areas of analytical dynamics, structural dynamics, aerodynamics, and controls. It includes automatically all six rigid-body degrees of freedom and elastic deformations, as well as the gravity, propulsion, aerodynamic, and control forces, in addition to forces of an external nature, such as gusts. The seamless integration is achieved by using the same reference frame and the same variables to describe the aircraft motions and the forces acting on it, including the aerodynamic forces. The formulation is modular in nature, in the the sense that the structural model, the aerodynamic theory, and the controls method can be replaced by any other ones to better suit different types of aircraft, provided certain criteria are satisfied. A perturbation approach permits the separation of the equations of motion into a flight dynamics problem for the maneuvering aircraft rigid-body translations and rotations and an extended perturbation problem for the elastic deformations and perturbations in the rigid-body variables, where the second problem is subject to inputs from the maneuvering aircraft
Quantum-critical superconductivity in underdoped cuprates

We argue that the pseudogap phase may be an attribute of the non-BCS pairing of quantum-critical, diffusive fermions near the antiferromagnetic quantum critical point. We derive and solve a set of three coupled Eliashberg-type equations for spin-mediated pairing and show that in some T range below the pairing instability, there is no feedback from superconductivity on fermionic excitations, and fermions remain diffusive despite of the pairing. We conject that in this regime, fluctuations of the pairing gap destroy the superconducting condensate but preserve the leading edge gap in the fermionic spectral function.
MR Differentiation of Phaeochromocytoma From Other Adrenal Lesions Based on Qualitative Analysis of T2 Relaxation Times

Abstract Aim: To determine the diagnostic accuracy of MR imaging in differentiating phaeochromocytoma from other adrenal lesions. Materials and methods: Sixty-seven adrenal masses (65 patients) including 17 phaeochromocytomas were imaged using T2-weighted pulse sequences on 0.6T and 1.5T GE MR units. The adrenal lesions were qualitatively assessed by three observers and divided into three categories (benign adenomas, malignant lesions and phaeochromocytomas) based on lesion signal intensity relative to liver and cerebrospinal fluid. Results: Eleven phaeochromocytomas (65%) were correctly identified while the remaining six (35%) were misclassified, five as malignant lesions and one as a benign adenoma, because of atypical low signal intensity on T2-weighted MR images. Conversely, six non-phaeochromocytomas (three benign adenomas, two adrenal carcinomas and one metastasis) were wrongly classified as phaeochromocytomas because of very high lesion signal intensity. The sensitivity of MR imaging for diagnosing phaeochromocytoma was 64.7%, specificity 88.0%, positive predictive value 64.7% and negative predictive value 88.0%. Conclusion: There is considerable overlap between the MR appearance of phaeochromocytoma and other adrenal lesions. A phaeochromocytoma cannot be excluded on the basis of a lack of high signal intensity on T2-weighted MR imaging.
T Dwarfs and the Substellar Mass Function. I. Monte Carlo Simulations

MonteCarlosimulationsofthefieldsubstellarmassfunction(MF)arepresented,basedonthelatestbrowndwarf evolutionary models from Burrows et al. and Baraffe et al. Starting from various representations of the MF below 0.1Mand the stellar birthrate, luminosity functions (LFs) andTeff distributions are produced for comparison with observed samples. These distributions exhibit distinctminima in the mid-type L dwarf regime followed by a rise in number density for fainter/cooler brown dwarfs, predicting many more T-type and cooler brown dwarfs in the field even for relatively shallow mass functions. Deuterium-burning brown dwarfs (0:012 M� � M � 0:075 M� ) dominate field objects with 400 KTeA � 2000 K, while nonfusing brown dwarfs make up a substantial pro- portionoffielddwarfswithTeA � 500K.Theshape ofthe substellarLF isfairly consistentfor variousassumptions of the Galactic birthrate, choice of evolutionary model, and adopted age and mass ranges, particularly for field T dwarfs, which as a population provide the best constraints for the field substellar MF. Exceptions include a depletion of objects with 1200 KTeA � 2000 K in ''halo''systems (ages >9 Gyr), and a substantial increase in the number of very cool brown dwarfs for lower minimum formation masses. Unresolved multiple systems tend to enhance features in the observed LF and may contribute significantly to the space density of very cool brown dwarfs. However, these effects are small (<10% for TeA k300 K) for binary fractions typical for brown dwarf systems (10%-20%). An analytic approximation to correct the observed space density for unresolved multiple systemsinamagnitude-limitedsurveyisderived.Asanexercise,surfacedensitiesasafunctionofTeffarecomputed for shallow near-infrared (e.g., 2MASS) and deep red-optical (e.g., UDF) surveys based on the simulated LFs and empirical absolute magnitude-Teff relations. These calculations indicate that a handful of L and T dwarfs, as well as late-type M and L halo subdwarfs, should be present in the UDF field depending on the underlying MF and disk scale height. These simulations and their dependencies on various factors provide a means for extracting the field substellar MF from observed samples, an issue pursued using 2MASS T dwarf discoveries in Paper II. Subject heading gs: Galaxy: stellar content — methods: numerical — stars: low-mass, brown dwarfs — stars: luminosity function, mass function
Golden Binary Gravitational-Wave Sources: Robust Probes of Strong-Field Gravity

Space-borne gravitational-wave interferometers such as LISA will detect the gravitational wave (GW) signal from the inspiral, plunge, and ringdown phases of massive black hole binary mergers at cosmological distances. From the inspiral waves, we will be able to measure the masses of the binaries' members; from the ringdown waves, we will be able to measure the mass of the final merged remnant. A subset of detected events allow the identification of both the inspiral and the ringdown waveforms in a given source and thus allow a measurement of the total mass-energy lost to GWs over the coalescence, MGW. We define "golden" binary mergers to be those with measurement errors likely to be small enough for a physically useful determination of MGW. A detailed sensitivity study, combined with simple black hole population models, suggests that a few golden binary mergers may be detected during a 3 yr LISA mission lifetime. Any such mass deficit measurement would constitute a robust and valuable observational test of strong-field relativistic gravity. An extension of this concept to include spin measurements may allow a direct empirical test of the black hole area theorem.
Search architectures for the automatic design of graphical presentations

This paper presents an approach for automatically creating explanations of changes in the results generated by quantitative modeling systems. These explanations combine both text and graphics, and therefore serve as a vehicle for exploring the interaction between these two modes of presentation. The approach integrates research from three different areas. Relevant content for explanations is determined using extensions of previous work on comparative analysis of financial models. Discourse planning is performed by applying techniques of rhetorical modeling to the analysis of explanatory dialogues. Graphical presentation is accomplished by extending prior work on automatically designing displays for quantitative data. Finally, this paper presents an approach to coordinating textual and graphical presentations.
Catalytic Rosenmund–von Braun reaction in halide-based ionic liquids

Abstract Ionic liquids based on 1- n -butyl-3-methylimidazolium halide salts (bmiX) have been used as an effective reusable reaction media in the Rosenmund–von Braun reaction of aryl halides and NaCN using copper(I) salts as catalysts. Product isolation is achieved by simple extraction using organic solvents. The copper catalysts immobilized in ionic liquid media can be reused continuously.
On mutual information-based control of range sensing robots for mapping applications

In this paper we examine the correlation between the information content and the spatial realization of range measurements taken by a mapping robot. To do so, we consider the task of constructing an occupancy grid map with a binary Bayesian filter. Using a beam-based sensor model (versus an additive white Gaussian noise model), we prove that any controller tasked to maximize a mutual information reward function is eventually attracted to unexplored space. This intuitive behavior is derived solely from the geometric dependencies of the occupancy grid mapping algorithm and the monotonic properties of mutual information. Since it is dependent on both the robot's position and the uncertainty of the surrounding cells, mutual information encodes geometric relationships that are fundamental to robot control, thus yielding geometrically relevant reward surfaces on which the robot can navigate. We also provide an algorithmic implementation for computing mutual information and show that its worst-case time and space complexities are quadratic and linear, respectively, with respect to the map's spatial resolution. Lastly, we present the results of experiments employing an omnidirectional ground robot equipped with a laser range finder. Our experimental results support our theoretical and computational findings.
A Numerical Technique For Computing Effective Thermal Conductivity Of Fluid-Particle Mixtures

Periodic arrays of particles, foams, and other structures impregnated with a static fluid play an important role in heat transfer enhancement. In this article, we develop a numerical method for com...
Seifert forms and concordance

If a knot K has Seifert matrix VK and has a prime power cyclic branched cover that is not a homology sphere, then there is an innite family of non{concordant knots having Seifert matrix VK .
ESTIMATES OF WORLDWIDE GAS HYDRATE RESOURCES

Gas hydrates have been touted as the next generation of energy resources exploitable for commercial gain and anthropogenic use. It would then seem relevant to estimate the potential resources available in order that one has an appreciation of availability. Several such estimates have been made over the years for both onshore and offshore gas hydrates. This paper examines the relative percentages and the ranges of uncertainty for both the onshore and offshore estimates. In addition, the estimated resources are plotted versus the year in which the estimate was made to see if any convergence of results is being achieved with time as more data become available. The main conclusions are that there seems not to be any systematic pattern of convergence of resource estimates with time, nor does there seem to be any narrowing of the uncertainty of the estimates for either onshore or offshore resource estimates as more data have become available over the last twenty years. It would seem that a concerted effort is n...
The Environmental Consequences of Trade: Evidence from Subnational Trade Flows

Abstract The debate over the environmental consequences of free trade is not only quite heated, but also entails significant policy ramifications. Recently, cross-sectional analysis at the country level has made use of exogenous determinants of trade to identify the causal effect of trade on the environment, finding moderate evidence of a beneficial impact of expanded trade on environmental quality. Given the stakes involved, we revisit this finding using subnational data on ‘trade’ flows across US states and several measures of pollution. Not only does the analysis shed further light on the debate at the international level, but also addresses a heretofore unexamined question: does greater inter-regional commerce at the subnational level harm the environment? Our findings are striking, providing further evidence against a negative environmental impact of trade for the majority of measures analyzed. However, several sources of heterogeneity arise that are noteworthy.
The Higgs boson width is adjustable

Abstract We show that it is possible to construct models in which the width of the Higgs boson is arbitrary — either smaller or larger than a standard model Higgs boson of the same mass. There are no new fields into which the Higgs boson decays. Instead, the coupling of the Higgs boson to the gauge bosons is adjusted. We construct and analyze weakly-coupled models with arbitrary-width Higgs bosons to investigate the phenomenology one might find in a strongly interacting model. In any such model new physics must enter at a mass scale which decreases as the Higgs boson width is adjusted away from its standard model value. In particular, if the Higgs boson is wider than the standard model Higgs boson, then interesting new physics must appear in the isospin-two channel.
Spatial interactions among U.S. cities: 1900–1990

Abstract We test implications of economic geography by exploring spatial interactions among U.S. cities. We use a data set consisting of 1900–1990 metro area populations, and spatial measures including distance from the nearest larger city in a higher-tier, adjacency, and location within U.S. regions. We also date cities from their time of settlement. We find that among cities which enter the system, larger cities are more likely to locate near other cities. Moreover, older cities are more likely to have neighbors. Distance from the nearest higher-tier city is not always a significant determinant of size and growth. We find no evidence of persistent non-linear effects on urban growth of either size or distance, although distance is important for city size for some years.
Microchips for DNA sequencing

Genetic information is vital for understanding features and response of an organism. In humans, genetic errors are linked to the development of major diseases such as cancer and diabetes. In order to maximally exploit this information it is necessary to develop miniature sequencing assays that are rapid and inexpensive. In this paper we show how this could be attained with microfluidic chips that contain integrated assays. To date simple silicon/glass chips aimed for sequencing purpose have been realized; but these chips are not yet practical. Some of the solutions that are used to bring these devices closer to commercial applications are discussed.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Damage resistance of coated optics

Successful application of high energy lasers to national needs in strategic defense, inertial confinement fusion and isotope separation is contingent on the development of optical coatings that can withstand very intense radiation. Significant progress has been made in the development of damage resistant coatings over the past 15 years to support the needs of the inertial confinement fusion and isotope separation programs. However, the requirements evolving from the Strategic Defense Initiative (SDI) are much more severe and demand dramatic improvements in the performance of optical coatings beyond the current state of the art. The approach taken at Los Alamos towards solving the problems of optical coatings for SDI is presented.
FBS 0107-082: A Symbiotic Binary in a Rare Prolonged Outburst?

FBS 0107-082 is an emission line object previously classified as a nova-like cataclysmic variable star. New optical spectroscopy shows very strong hydrogen Balmer lines, along with a nebular forbidden line spectrum and absorption features from an early-F photosphere. When combined with other IR and optical data from the literature, these data point to the object being a symbiotic nova seen in a prolonged outburst. Photometry on timescales of minutes, days, and years shows only very weak variability.
Metal-catalyzed intramolecular hydrolysis of phosphate esters

Abstract A tridentate water-soluble phosphotriester ligand has been synthesized. Kinetics studies have shown that divalent metal ions dramatically enhance the rate of hydrolysis of such phosphotriester at 25 °C and pH 8.0 via intramolecular nucleophilic attack by a metal bound hydroxide.
Circles and quadratic maps between spheres

Consider an analytic map of a neighborhood of 0 in a vector space to a Euclidean space. Suppose that this map takes all germs of lines passing through 0 to germs of circles. Such a map is called rounding. We introduce a natural equivalence relation on roundings and prove that any rounding, whose differential at 0 has rank at least 2, is equivalent to a fractional quadratic rounding. A fractional quadratic map is just the ratio of a quadratic map and a quadratic polynomial. We also show that any rounding gives rise to a quadratic map between spheres. The known results on quadratic maps between spheres have some interesting implications concerning roundings.
LOW-MASS X-RAY BINARIES AND GLOBULAR CLUSTERS IN EARLY-TYPE GALAXIES. II. GLOBULAR CLUSTER CANDIDATES AND THEIR MASS-METALLICITY RELATION

We present an astrometry and photometry catalogue of globular cluster (GC) candidates detected with the Hubble Space Telescope Wide Field Planetary Camera 2 in a sample of 19 early-type galaxies, appropriate for comparison with the low-mass X-ray binary populations observed with Chandra. In a companion paper, we present the Chandra data and investigate the relation between these populations. We demonstrate that, although there is little evidence of a color-magnitude correlation for the GCs, after estimating mass and metallicity from the photometry under the assumption of a single-age simple stellar population, there is a significant positive correlation between mass and metallicity. We constrained [Z/H] = (-2.1 ± 0.2) + (0.25 ± 0.04)log10M, with a 1σ intrinsic scatter of 0.62 dex in metallicity. If GCs are bimodal in metallicity, this relation is consistent with recent suggestions of a mass-metallicity relation only for metal-poor clusters. Adopting a new technique to fit the GC luminosity function (GCLF) accounting for incompleteness and the Eddington bias, we compute the V-band local GC specific frequency (SN ) and specific luminosity (SL ) of each galaxy. We show that SL is the more robust measure of the richness of a GC population where a significant fraction is undetected due to source detection incompleteness. We find that the absolute magnitude of the GCLF turnover exhibits intrinsic scatter from galaxy to galaxy of ~0.3 mag (1σ), limiting its accuracy as a standard distance measure.
The scattering of Lyman-series photons in the intergalactic medium

We re-examine scattering of photons near the Lyα resonance in the intergalactic medium (IGM). We first derive a general integral solution for the radiation field around resonance within the usual Fokker–Planck approximation. Our solution shows explicitly that recoil and spin diffusivity source an absorption feature, whose magnitude increases with the relative importance of recoil compared to Doppler broadening. This spectrum depends on the Lyα line profile, but approximating it with the absorption profile appropriate to the Lorentzian wings of natural broadening accurately reproduces the results for a full Voigt profile so long as the IGM temperature is less than ~1000 K. This approximation allows us to obtain simple analytic formulae for the total scattering rate of Lyα photons and the accompanying energy exchange rate. Our power series solutions converge rapidly for photons that redshift into the Lyα resonance as well as for photons injected at line centre. We confirm previous calculations showing that heating through this mechanism is quite slow and probably negligible compared to other sources. We then show that energy exchange during the scattering of higher-order Lyman-series photons can be much more important than naively predicted by recoil arguments. However, the resulting heating is still completely negligible.
Bypass to Turbulence in Hydrodynamic Accretion Disks: An Eigenvalue Approach

Cold accretion disks with temperatures below ~3000 K are likely to be composed of highly neutral gas. The magnetorotational instability may cease to operate in such disks, so it is of interest to consider purely hydrodynamic mechanisms of generating turbulence and angular momentum transport. With this motivation, we investigate the growth of hydrodynamic perturbations in a linear shear flow sandwiched between two parallel walls. The unperturbed flow is similar to plane Couette flow, but with a Coriolis force included. Although there are no exponentially growing eigenmodes in this system, nevertheless, because of the nonnormal nature of the eigenmodes, it is possible to have a large transient growth in the energy of perturbations. For a constant angular momentum disk, we find that the perturbation with maximum growth is axisymmetric with vertical structure. The energy grows by more than a factor of 100 for a Reynolds number R = 300 and more than a factor of 1000 for R = 1000. Turbulence can be easily excited in such a disk, as found in previous numerical simulations. For a Keplerian disk, on the other hand, similar perturbations with vertical structure grow by no more than a factor of 4, explaining why the same simulations did not find turbulence in this system. However, certain other two-dimensional perturbations with no vertical structure do exhibit modest growth. For the optimum two-dimensional perturbation, the energy grows by a factor of ~100 for R ~ 104.5 and by a factor of 1000 for R ~ 106. Such large Reynolds numbers are hard to achieve in numerical simulations, and so the nonlinear development of these kinds of perturbations is only beginning to be investigated. It is conceivable that these nearly two-dimensional disturbances might lead to self-sustained three-dimensional turbulence, although this remains to be demonstrated. The Reynolds numbers of cold astrophysical disks are much larger even than 106; therefore, hydrodynamic turbulence may be possible in disks through transient growth.
A convenient route to azetidine-2,3-diones and cis-3β-amido azetidinones

Abstract The synthesis of 3β-amido azetidinones, 8a and 8b , via azetidine-2,3-diones is described.
Axial Tomography and Three Dimensional Image Reconstruction

A number of existing cameras for Nuclear Medicine imaging of radio-isotope distributions give depth information about the distribution. These devices have in common that they provide tomographic images of the object, that is, that images of a given object plane have that plane in focus and all other object planes contribute an out-of-focus background superimposed on the in-focus image. We present here a method for three dimensional reconstruction of these axial tomographic images which removes the blurred off-plane activity from a number of transverse planes simultaneously. The method is applicable to a number of tomographic cameras, such as the multiple single-pinhole camera, the rotating slanted-hole collimator, the Anger focussing tomographic scanner, and the positron camera. The method can be implemented on a small computer having a disc system.
Imaginary Squashing Mode Spectroscopy of Helium Three B

We have made precision measurements of the frequency of a collective mode of the superfluid 3He–B order parameter, the J=2− imaginary squashing mode. Measurements were performed at multiple pressures using interference of transverse sound in an acoustic cavity. Transverse waves propagate in the vicinity of this order parameter mode owing to off-resonant coupling. At the crossing of the sound mode and the order parameter mode, the sound wave is strongly attenuated. We use both velocity and attenuation measurements to determine precise values of the mode frequency with a resolution between 0.1% and 0.25%.
The Effect Of Periodically Attached Substructures On The Excitation Of Submerged Cylindrical Shells

Abstract The presence of substructures in a cylindrical shell gives rise to dynamic interactions which influence the distribution of vibration along the shell. In this paper, Lagrange's equations are used to develop the equations governing the forced harmonic vibration of a submerged cylindrical shell with periodically attached internal substructures which is subjected to periodically placed loads. Modal expansions are used to describe the response of the shell and the fields in the fluid. First, a shell without substructures but subjected to periodically placed ring loads is considered. The method of this paper gives nearly the same results as a travelling wave method for an infinite shell subjected to a single ring load. Two types of substructures are examined: circular panels with hinge connections and circular ribs with rigid connections. It is shown that the substructures confine the flexural motion to a region near the location of the applied forces. The localization effect decreases when the forcing frequency is close to the substructure's natural frequencies, and becomes more pronounced when, within a periodic segment, the ribs have varying impedance.
Analysis of Microstrip Dipoles on Planar Artificial Periodic Dielectric Structures

Integrated antennas on electromagnetic band-gap structures have found many useful applications. This paper characterizes the properties of microstrip dipoles on a planar artificial periodic structure. A rigorous full-wave double vector-integral-equation method is used to determine the properties of microstrip dipoles including antenna gain, radiation patterns, and input impedance. Two stages of the moment method are required. The Green's function for a planar periodic structure is first found by solving a volume integral equation in conjunction with an analytic array-scanning scheme. This Green's function is implemented into another integral equation to find the current distribution over strip dipoles. The effects of periodic material layer to the antenna input impedance, mutual impedance, and radiation efficiency are investigated within the content of electromagnetic band-gap structures. The method is applicable to general problems of antennas loaded on an otherwise periodic structure.
nSTAT: open-source neural spike train analysis toolbox for Matlab.

Abstract Over the last decade there has been a tremendous advance in the analytical tools available to neuroscientists to understand and model neural function. In particular, the point process – generalized linear model (PP-GLM) framework has been applied successfully to problems ranging from neuro-endocrine physiology to neural decoding. However, the lack of freely distributed software implementations of published PP-GLM algorithms together with problem-specific modifications required for their use, limit wide application of these techniques. In an effort to make existing PP-GLM methods more accessible to the neuroscience community, we have developed nSTAT – an open source neural spike train analysis toolbox for Matlab ® . By adopting an object-oriented programming (OOP) approach, nSTAT allows users to easily manipulate data by performing operations on objects that have an intuitive connection to the experiment (spike trains, covariates, etc.), rather than by dealing with data in vector/matrix form. The algorithms implemented within nSTAT address a number of common problems including computation of peri-stimulus time histograms, quantification of the temporal response properties of neurons, and characterization of neural plasticity within and across trials. nSTAT provides a starting point for exploratory data analysis, allows for simple and systematic building and testing of point process models, and for decoding of stimulus variables based on point process models of neural function. By providing an open-source toolbox, we hope to establish a platform that can be easily used, modified, and extended by the scientific community to address limitations of current techniques and to extend available techniques to more complex problems.