cssi/SciSciGPT-SciSciNet huggingface dataset:
A generalized corresponding states method for predicting the limits of superheat of mixtures: Application to the normal alcohols

The limits of superheat of the normal alcohols from methanol to octanol and of ethanol/n-propanol, n-propanol/n-butanol, and n-butanol/n-pentanol mixture were measured at atmospheric pressure. The results were predicted using a new method based on the generalized corresponding states principle (GCSP) in which properties of two reference substances were used to predict the superheat limits of the fluids studied. Ethanol and n-butanol, and the two components of each mixture studied, were used as reference fluids for predicting the superheat limits of the pure alcohols and mixtures respectively. Results showed that it is possible to predict superheat limits to well within the accuracy of measured values ( < 1%). The method requires only accurate vapor pressure correlations and acentric factors of the reference fluids, and an accurate method for predicting the variation of the true critical mixture temperature with composition. It is shown that the GCSP reduces to an expression for the superheat limit of a mixture which is a mole fraction weighted average of the limits of superheat of the individual components in solution when the mixture and its components satisfies certain conditions. In the general case, both linear and nonlinear variations of mixture superheat limit with mole fraction can be predicted with the proposed method. Considerable simpiflication using the GCSP over the approach based on classical homogeneous nucleation theory is derived from the fact that no mixture surface tension or bubble point pressure data are required.
Frequency-comb-based remote sensing of greenhouse gases over kilometer air paths

Increasing our understanding of regional greenhouse gas transport, sources, and sinks requires accurate, precise, continuous measurements of small gas enhancements over long ranges. We demonstrate a coherent dual frequency-comb spectroscopy technique capable of achieving these goals. Spectra are acquired spanning 5990 to 6260 cm−1 (1600–1670 nm) covering ∼700 absorption features from CO2, CH4, H2O, HDO, and CO213, across a 2 km path. The spectra have sub-1-kHz frequency accuracy, no instrument lineshape, and a 0.0033 cm−1 point spacing. They are fit with different absorption models to yield dry-air mole fractions of greenhouse gases. These results are compared with a point sensor under well-mixed conditions to evaluate the accuracy of models critical to global satellite-based trace gas monitoring. Under heterogeneous conditions, time-resolved data demonstrate tracking of small variations in mole fractions, with a precision <1 ppm for CO2 and <3 ppb for CH4 in 5 min. Portable systems could enable regional monitoring.
FPGA Acceleration of Rigid Molecule Interactions

Modeling of molecule interactions often uses rigid models and correlation techniques, either in early screening passes or as steps within more complex models. Even rigid models are time-consuming when applied to large models at 10 3 - 10 5 different three-axis rotations. This paper presents an FPGA structure for performing the correlations efficiently using a systolic array for 3-D correlation and an addressing technique for low-overhead rotation of a 3-D voxel models around three axes. We find a 200 × speedup in our FPGA implementation compared to the standard transform-based method.
Beginnings of place value: how preschoolers write three-digit numbers.

Place value notation is essential to mathematics learning. This study examined young children's (4- to 6-year-olds, N = 172) understanding of place value prior to explicit schooling by asking them write spoken numbers (e.g., “six hundred and forty-two”). Children's attempts often consisted of “expansions” in which the proper digits were written in order but with 0s or other insertions marking place (e.g., “600402” or “610042”). This partial knowledge increased with age. Gender differences were also observed with older boys more likely than older girls to produce the conventional form (e.g., 642). Potential experiences contributing to expanded number writing and the observed gender differences are discussed.
Understanding hierarchical protein evolution from first principles.

We propose a model that explains the hierarchical organization of proteins in fold families. The model, which is based on the evolutionary selection of proteins by their native state stability, reproduces patterns of amino acids conserved across protein families. Due to its dynamic nature, the model sheds light on the evolutionary time-scales. By studying the relaxation of the correlation function between consecutive mutations at a given position in proteins, we observe separation of the evolutionary time-scales: at short time intervals families of proteins with similar sequences and structures are formed, while at long time intervals the families of structurally similar proteins that have low sequence similarity are formed. We discuss the evolutionary implications of our model. We provide a "profile" solution to our model and find agreement between predicted patterns of conserved amino acids and those actually observed in nature.
OPTIMAL ADAPTIVE ALGORITHMS FOR FINDING THE NEAREST AND FARTHEST POINT ON A PARAMETRIC BLACK-BOX CURVE

We consider a general model for representing and manipulating parametric curves, in which a curve is specified by a black box mapping a parameter value between 0 and 1 to a point in Euclidean d-space. In this model, we consider the nearest-point-on-curve and farthest-point-on-curve problems: given a curve C and a point p, find a point on C nearest to p or farthest from p. In the general black-box model, no algorithm can solve these problems. Assuming a known bound on the speed of the curve (a Lipschitz condition), the answer can be estimated up to an additive error of e using O(1/e) samples, and this bound is tight in the worst case. However, many instances can be solved with substantially fewer samples, and we give algorithms that adapt to the inherent difficulty of the particular instance, up to a logarithmic factor. More precisely, if OPT(C,p,e) is the minimum number of samples of C that every correct algorithm must perform to achieve tolerance e, then our algorithm performs O(OPT(C,p,e) log(e-1/OPT(C,p,e))) samples. Furthermore, any algorithm requires Ω(k log(e-1/k)) samples for some instance C′ with OPT(C′,p,e) = k; except that, for the nearest-point-on-curve problem when the distance between C and p is less than e, OPT is 1 but the upper and lower bounds on the number of samples are both Θ(1/e). When bounds on relative error are desired, we give algorithms that perform O(OPT · log(2+(1+e-1) · m-1/OPT)) samples (where m is the exact minimum or maximum distance from p to C) and prove that Ω(OPT · log(1/e)) samples are necessary on some problem instances.
Planet Parameters in Microlensing Events

A planetary microlensing event occurs when a planet perturbs one of the two images created in a point-mass microlensing event, causing a deviation from the standard Paczynski curve. Determination of the two physical parameters that can be extracted from a planetary microlensing event, the planet/star mass ratio q, and the planet/star separation in units of the stellar Einstein ring, yp, is hampered by several types of degeneracies. There are two distinct and qualitatively different classes of planetary events: major and minor image perturbations. For major image perturbations, there is a potentially crippling continuous degeneracy in q which is of order δ -->−1d, where δd is the maximum fractional deviation of the planetary perturbation. Since the threshold of detection is expected to be δd ~ 5%, this degeneracy in q can be a factor of ~20. For minor image perturbations, the continuous degeneracy in q is considerably less severe, and is typically less than a factor of 4. We show that these degeneracies can be resolved by observations from dedicated telescopes on several continents together with optical/infrared photometry from one of these sites. There also exists a class of discrete degeneracies. These are typically easy to resolve given good temporal coverage of the planetary event. Unambiguous interpretation of planetary microlensing events requires the resolution of both types of degeneracy. We describe the degeneracies in detail and specify the situations in which they are problematic. We also describe how individual planet masses and physical projected separations can be measured.
Application of Random Matrix Theory to Multivariate Statistics

This is an expository account of the edge eigenvalue distributions in random matrix theory and their application in multivariate statistics. The emphasis is on the Painleve representations of these distribution functions.
Mild and selective sodium azide mediated cleavage of p-nitrobenzoic esters.

A mild and selective cleavage of p-nitrobenzoic esters by sodium azide in methanol is reported. This new methodology is mild enough for use with acid- or base-sensitive compounds. No elimination byproducts are formed. Fmoc- and trifluoroacetyl-amino protecting groups, benzyl esters, and ethyl esters remain unaffected. Less reactive compounds are discussed in terms of steric factors, and yields are increased by altering the azide solvation.
The Effect of Auditing Standard No. 5 on Audit Report Lags

SYNOPSIS: Auditing Standard No. 5 (AS5) introduced by the Public Company Accounting Oversight Board (PCAOB) in June 2007 requires a top-down risk-based approach in auditing and is expected to impro...
Ciudades en la economía global: enfoques teóricos y metodológicos

Ante la pregunta: ?Que significa la nueva o explosiva ampliacion del papel de un tipo particular de ciudad en la economia mundial desde principios de los ochenta?, el articulo asume una doble perspectiva. Por una parte analiza el impacto derivado del incremento de la globalizacion de la actividad economica -lo que ha elevado la escala y complejidad de las transacciones economicas- y por otra, indaga el crecimiento de la intensidad de los servicios en la organizacion de la economia. Atendido a que el proceso clave, desde la perspectiva de la economia urbana, es la demanda creciente de servicios por parte de las empresas en todas las industrias, y el hecho de que las ciudades son sitios preferidos de produccion para dichos servicios, sea en los niveles global, nacional o regional, el articulo examina con detalle los componentes principales en la nueva narrativa que ha surgido de la investigacion sobre ciudades mundiales o globales.
Homological Mirror Symmetry and Fourier–Mukai Transform

We interpret symplectic geometry as certain sheaf theory by constructing a sheaf of curved A_\infty algebras which in some sense plays the role of a "structure sheaf" for symplectic manifolds. An interesting feature of this "structure sheaf" is that the symplectic form itself is part of its curvature term. Using this interpretation homological mirror symmetry can be understood by well-known duality theories in mathematics: Koszul duality or Fourier- Mukai transform. In this paper we perform the above constructions over a small open subset inside the smooth locus of a Lagrangian torus fibration. In a subsequent work we shall use the language of derived geometry to obtain a global theory over the whole smooth locus. However we do not know how to extend this construction to the singular locus. As an application of the local theory we prove a version of homological mirror symmetry between a toric symplectic manifold and its Landau-Ginzburg mirror.
Intertemporal asset-pricing relationships in barter and monetary economies An empirical analysis

This paper explores whether liquidity services and nonsuperneutral effects of money are important for and permit improved explanation of asset returns. Euler equations governing asset choices, implied by dynamic barter, cash-in-advance (CIA), and money-in-the-utility function models, are estimated and testing using generalized-method-of-moments techniques and monthly data for the U.S. Observational equivalence between CIA and barter models is shown under specific assumptions about the timing of information and decisions. The findings suggest that only for one CIA model are monetary effects both important for and permit improved explanation of asset returns. Success in this regard is (not) for stock (treasury-bill) returns.
Communication perspectives on social networking and citizen journalism challenges to traditional newspapers

Communication perspectives are presented on the challenges posed to traditional newspapers by social media and citizen journalism, with special reference to the United States. This is an important topic given the critical role investigative reporting, long the domain of newspapers, plays in fostering democratic practices. New Media and social networking technology are evaluated in terms of their impact on the newspaper enterprise. Alternative scenarios for future developments are examined as are the implications for social values and the role of an informed citizenry in democratic society. Strategic management issues are analyzed, and the possibility is considered that social media can fulfil much of the democracy-enhancing role served traditionally by newspapers.
Value added of teachers in high-poverty schools and lower poverty schools

Using student-level microdata from 2000–2001 to 2004–2005 from Florida and North Carolina, we compare the effectiveness of teachers in schools serving primarily students from low-income families (>70% free-and-reduced-price-lunch students) with teachers in schools serving more advantaged students. The results show that the average effectiveness of teachers in high poverty schools is in general less than teachers in other schools and there is significantly greater variation in teacher quality among high poverty schools. These differences are largely driven by less productive teachers at the bottom of the teacher effectiveness distribution in high-poverty schools. The bulk of the quality differential is due to differences in the unmeasured characteristics of teachers. We find that the gain in productivity to more experienced teachers from additional experience is much stronger in lower-poverty schools. The lower return to experience in high-poverty schools does not appear to be a result of differences in the quality of teachers who leave teaching or who switch schools, however. Our findings suggest that measures that induce highly effective teachers to move to high-poverty schools and which promote an environment in which teachers’ skills will improve over time are more likely to be successful.
Investigating the Differential Emission Measure and Energetics of Microflares with Combined SDO/AIA and RHESSI Observations

An important question in solar physics is whether solar microflares, the smallest currently observable flare events in X-rays, possess the same energetic properties as large flares. Recent surveys have suggested that microflares may be less efficient particle accelerators than large flares, and hence contribute less non-thermal energy, which may have implications for coronal heating mechanisms. We therefore explore the energetic properties of microflares by combining EUV and X-ray measurements. We present forward-fitting differential emission measure (DEM) analysis of 10 microflares. The fitting is constrained by combining, for the first time, high-temperature Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations and flux data from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA). Two fitting models are tested for the DEM; a Gaussian distribution and a uniform DEM profile. A Gaussian fit proved unable to explain the observations for any of the studied microflares. However, 8 of 10 events studied were reasonably fit by a uniform DEM profile. Hence microflare plasma can be considered to be significantly multi-thermal, and may not be significantly peaked or contain resolvable fine structure, within the uncertainties of the observational instruments. The thermal and non-thermal energy is estimated for each microflare, comparing the energy budget with an isothermal plasma assumption. From the multi-thermal fits the minimum non-thermal energy content was found to average approximately 30% of the estimated thermal energy. By comparison, under an isothermal model the non-thermal and thermal energy estimates were generally comparable. Hence, multi-thermal plasma is an important consideration for solar microflares that substantially alters their thermal and non-thermal energy content.
Architecture and performance of the PEP-II low-level RF system

Heavy beam loading in the PEP-II B Factory along with large ring circumferences places unique requirements upon the low-level RF (LLRF) system. RF feedback loops must reduce the impedance observed by the beam while ignoring the cavity transients caused by the ion clearing gap. Special attention must be placed on the cavity tuner loops to allow matching the ion clearing gap transients in the high energy ring and the low energy ring. A wideband fiber optic connection to the longitudinal feedback system allows a RF station to operate as a powerful "sub-woofer" to damp residual low order coupled bunch motion. This paper describes the design and performance of the VXI based, EPICS controlled, PEP-II low-level RF system(s). Baseband in-phase and quadrature (IQ) signal processing using both analog and modern digital techniques are used throughout the system. A family of digital down converters provide extremely accurate measurements of many RF signals throughout the system. Each system incorporates a built-in network analyzer and arbitrary RF function generator which interface with Matlab to provide a wide range of functions ranging from automated configuration of each feedback loop to cavity FM processing. EPICS based sequences make the entire system a turn-key operation requiring minimal operator intervention. In the event of a fault, fast history buffers throughout the system write selected RF signals to disk files which can be viewed later to help diagnose problems. Actual data from commissioning runs of PEP-II is presented.
Complex Patterns of Local Adaptation in Teosinte

Populations of widely distributed species encounter and must adapt to local environmental conditions. However, comprehensive characterization of the genetic basis of adaptation is demanding, requiring genome-wide genotype data, multiple sampled populations, and an understanding of population structure and potential selection pressures. Here, we used single-nucleotide polymorphism genotyping and data on numerous environmental variables to describe the genetic basis of local adaptation in 21 populations of teosinte, the wild ancestor of maize. We found complex hierarchical genetic structure created by altitude, dispersal events, and admixture among subspecies, which complicated identification of locally beneficial alleles. Patterns of linkage disequilibrium revealed four large putative inversion polymorphisms showing clinal patterns of frequency. Population differentiation and environmental correlations suggest that both inversions and intergenic polymorphisms are involved in local adaptation.
IS THE NEW IMMIGRATION REALLY SO BAD

This article reviews the recent evidence on US immigration, focusing on two key questions: (1) Does immigration reduce the labour market opportunities of less skilled natives? (2) Have immigrants who arrived after the 1965 Immigration Reform Act been successfully assimilated? Overall, evidence that immigrants have harmed the opportunities of less educated natives is scant. On the question of assimilation, the success of the US-born children of immigrants is a key yardstick. By this metric, post-1965 immigrants are doing reasonably well. Even children of the least educated immigrant origin groups have closed most of the education gap with the children of natives.
Phosphorus-Nitrogen Compounds XXIII: Oncolytic Phosphorylated Imines

Abstract A series of 15 amidine, iminopiperidine, iso(thio)urea, and guanidine derivatives and six 2,5-dihydro-l,3,5,2-triazaphosphorines were synthesized. Most of the compounds were tested for ability to react with L-cysteine and for antitumor activity against sarcoma 180 and P-388 murine tumor systems. Three acyclic phosphorylated imines and one triazaphosphorine showed activity in the former model to indicate that the P(0)N=C grouping serves as an oncolytic moiety. All agents condensed with L-cysteine with the active antitumor compounds displaying a tendency for relatively higher reactivity with this amino acid.
Modeling homophily and stochastic equivalence in symmetric relational data

This article discusses a latent variable model for inference and prediction of symmetric relational data. The model, based on the idea of the eigenvalue decomposition, represents the relationship between two nodes as the weighted inner-product of node-specific vectors of latent characteristics. This "eigenmodel" generalizes other popular latent variable models, such as latent class and distance models: It is shown mathematically that any latent class or distance model has a representation as an eigenmodel, but not vice-versa. The practical implications of this are examined in the context of three real datasets, for which the eigenmodel has as good or better out-of-sample predictive performance than the other two models.
4-Cyano-2-butenyl Group: A New Type of Protecting Group in Oligonucleotide Synthesis via Phosphoramidite Approach

Abstract 4-Cyano-2-butenyl (CB) is a new type of protecting group for the intemucleotidic bonds in the synthesis of oligodeoxyribonucleotides by the phosphoramidite approach. This group is stable to acidic conditions and can be removed under mild conditions by a δ-elimination pathway using aqueous ammonium hydroxide.
Galaxy density profiles and shapes – I. Simulation pipeline for lensing by realistic galaxy models

Studies of strong gravitational lensing in current and upcoming wide and deep photometric surveys, and of stellar kinematics from (integral-field) spectroscopy at increasing redshifts, promise to provide valuable constraints on galaxy density profiles and shapes. However, both methods are affected by various selection and modelling biases, which we aim to investigate in a consistent way. In this first paper in a series, we develop a flexible but efficient pipeline to simulate lensing by realistic galaxy models. These galaxy models have separate stellar and dark matter components, each with a range of density profiles and shapes representative of early-type, central galaxies without significant contributions from other nearby galaxies. We use Fourier methods to calculate the lensing properties of galaxies with arbitrary surface density distributions, and Monte Carlo methods to compute lensing statistics such as point-source lensing cross-sections. Incorporating a variety of magnification bias modes lets us examine different survey limitations in image resolution and flux. We rigorously test the numerical methods for systematic errors and sensitivity to basic assumptions. We also determine the minimum number of viewing angles that must be sampled in order to recover accurate orientation-averaged lensing quantities. We find that for a range of non-isothermal stellar and dark matter density profiles typical of elliptical galaxies, the combined density profile and corresponding lensing properties are surprisingly close to isothermal around the Einstein radius. The converse implication is that constraints from strong lensing and/or stellar kinematics, which are indeed consistent with isothermal models near the Einstein radius, cannot trivially be extrapolated to smaller and larger radii.
Optimization of diarylamines as non-nucleoside inhibitors of HIV-1 reverse transcriptase.

Abstract Following computational analyses, potential non-nucleoside inhibitors of HIV-1 reverse transcriptase have been pursued through synthesis and assaying for anti-viral activity. The general class Het–NH–Ph–U has been considered, where Het is an aromatic heterocycle and U is an unsaturated, hydrophobic group. Results for compounds with Het = 2-thiazoyl and 2-pyrimidinyl are the focus of this report.
Possible explanation of the solar-neutrino puzzle.

A new derivation of the Mikheyev and Smirnov (1985) mechanism for the conversion of electron neutrinos into mu neutrinos when traversing the sun is presented, and various hypotheses set forth. It is assumed that this process is responsible for the detection of fewer solar neutrinos than expected, with neutrinos below a minimum energy, E(m), being undetectable. E(m) is found to be about 6 MeV, and the difference of the squares of the respective neutrino masses is calculated to be 6 X 10 to the - 5th sq eV. A restriction on the neutrino mixing angle is assumed such that the change of density near the crossing point is adiabatic. It is predicted that no resonance conversion of neutrinos will occur in the dense core of supernovae, but conversion of electron neutrinos to mu neutrinos will occur as they escape outward through a density region around 100.
Estimating returns to education when the IV sample is selective

Abstract The literature estimating returns to education has often utilized spousal education and parental education as instrument variables (IV). However, due to usual survey designs, both IVs are available only for the individuals whose spouse or parents are present in the same household. The IV estimates based on these selective sub-samples may be inconsistent, even when the IVs satisfy the standard assumptions. In this paper, we examine the empirical relevance of this issue in the Chinese context. To our surprise, unlike the selection issue in other situations, this kind of selection does not appear particularly worrisome, suggesting that the previous IV results are robust. In particular, using China Household Income Project 1995 and 2002, we find that correcting for this potential issue has only a modest impact on the magnitude of the standard IV estimates using parental education as an IV, but a negligible impact on those using spousal education. By using the specification tests proposed, we find that these impacts are generally not statistically significant. These results are further confirmed by our analysis using U.S. data. We believe that these results are of use to both policymakers and practitioners.
Is Financial Globalization Beneficial

This lecture examines whether financial globalization is beneficial to developing countries by first examining the evidence on financial development and economic growth and concludes that financial development is indeed a key element in promoting economic growth. It then asks why if financial development is so beneficial, it often does not occur. It then goes on to examine whether globalization, particularly of the financial kind, can help encourage financial and economic development and argues that it can. However, financial globalization does not always work to encourage economic development because it often leads to devastating financial crises. The issue is thus not whether financial globalization is inherently good or bad, but whether it can be done right.
On Angles Whose Squared Trigonometric Functions Are Rational

We consider the rational linear relations between real numbers whose squared trigonometric functions have rational values, angles we call ``geodetic.'' We construct a convenient basis for the vector space over Q generated by these angles. Geodetic angles and rational linear combinations of geodetic angles appear naturally in Euclidean geometry; for illustration we apply our results to equidecomposability of polyhedra.
Early Claiming of Social Security Benefits and Labor Supply Behavior of Older Americans

The labor supply incentives provided by the early retirement rules of the United States Social Security Old Age benefits program are of growing importance as the Normal Retirement Age (NRA) increases to 67, and the labor force participation of Older Americans starts to increase. These incentives allow individuals who claim benefits before the NRA but continue to work, or return to the labor force, to increase their future rate of benefit pay by having benefits withheld. Since the adjustment of the benefit rate takes place only after the NRA is reached, benefits received before the NRA can become actuarially unfair for those who continue to work after claiming. Consistent with these incentives, estimates from bivariate models of the monthly labor force exit and claiming hazards using data from the Health and Retirement Study indicate that early claimers who do not withdraw from the labor force around the time they claim are increasingly likely to stay in the labor force.
On measurement bias in causal inference

This paper addresses the problem of measurement errors in causal inference and highlights several algebraic and graphical methods for eliminating systematic bias induced by such errors. In particulars, the paper discusses the control of partially observable confounders in parametric and non parametric models and the computational problem of obtaining bias-free effect estimates in such models.
A new large-number coincidence and a scaling law for the cosmological constant

An ensemble of pure numbers of the order of 10122 is produced naturally from the fundamental parameters of modern cosmology. This new large-number coincidence problem is resolved by demonstrating implicit physical connections that follow from the standard cosmological model. However, the occurrence of the new large-number coincidence combined with the known coincidence among pure numbers of the order of 1040 poses a distinct problem that is resolved with a scaling law for the cosmological constant that was originally proposed by Zel'dovich.
Sulfonyl‐1,2,3‐Triazoles: Convenient Synthones for Heterocyclic Compounds

1-Sulfonyl-1,2,3-triazoles, which are readily available through copper-catalyzed azide-alkyne cycloaddition, are stable precursors to Rh–azavinyl carbenes, as well as carbene complexes of other metals. Among other transformations, these reactive intermediates can be used for the introduction of a nitrogen atom into various heterocycles that are important in both synthetic and medicinal chemistry. Carbenes generated from diazocarbonyl compounds 1 are known to react with carbonyl groups to produce ylides 2, which usually react in subsequent 1,3-dipolar cycloadditions to access complex structures [Eq. (1)]. Herein, we report that Rh–azavinyl carbenes react with aldehydes to give adducts that undergo an intramolecular cyclization instead of a 1,3-dipolar cycloaddition. This transformation results in homochiral 3-sulfonyl-4-oxazolines 4 [Eq. (2), left], which are produced in excellent yield and with high enantioselectivity. These sparsely studied compounds contain an easily installed stereocenter and a synthetically useful electron-rich double bond.
The almost magical world of photonic crystals

An innovative and exciting new class of materials has emerged called photonic band gap materials, or photonic crystals. The specific applications, needed performance, and overall fabrication costs will dictate the gap properties of the photonic crystal. In this regard a very significant and attractive difference between photonic crystals and electronic semiconductor crystals is the former's inherent ability to provide complete tunability to the desired performance specifications. In recent years, work in the field of photonic crystals has focused primarily on designing and fabricating crystals with 2D and 3D omnidirectional band gaps and on studying the properties of defects in these crystals. Given a photonic crystal with a complete band gap, light with a frequency inside the gap is forbidden to exist within the material unless there is a defect (or a break in the periodic dielectric function) in the otherwise perfect photonic crystal. Such a defect will act like an internal surface within which a photon is confined or localized. A point-like defect will act like a cavity, a line-defect will act like a waveguide, and a planar-defect or surface will act like a perfectly reflecting mirror. Moreover, the structural and material properties of these defects (unlike electronic defects in semiconductors) can be completely and continuously tuned to provide whatever photon properties are desired. Using this great flexibility, researchers could design photonic crystal structures to control and mold the properties of light in new and important ways.
Supply Side Structural Change

The interest rate and the rate of economic growth are often regarded as roughly constant as economies grow. Moreover, the share of agriculture in production and the share of rural population typically shrink. We show that an otherwise standard growth model that includes a backward and an advanced sector can account for these regularities. The mechanism works as follows: as the economy accumulates capital, labor flows from the backward sector to the advanced one. This migration prevents the usual diminishing marginal returns of capital. As a result, the interest rate and the growth rate of the economy remain constant during the transition to the steady state.
Adaptive Volterra filters using orthogonal structures

This paper presents an adaptive Volterra filter that employs a recently developed orthogonalization procedure of Gaussian signals for Volterra system identification. The algorithm is capable of handling arbitrary orders of nonlinearity P as well as arbitrary lengths of memory M for the system model. The adaptive filter consists of a linear lattice predictor of order N, a set of Gram-Schmidt orthogonalizers for N vectors of size P+1 elements each, and a joint process estimator in which each coefficient is adapted individually. The complexity of implementing this adaptive filter is comparable to the complexity of the system model when N is much larger than P, a condition that is true in many practical situations. Experimental results demonstrating the capabilities of the algorithm are also presented in the paper.
X‐ray evidence for multiphase hot gas with nearly solar Fe abundances in the brightest groups of galaxies

We analyse the ASCA spectra accumulated within ∼100 kpc radii of 12 of the brightest groups of galaxies. Upon fitting isothermal models (1T) jointly to the ASCA SIS and GIS spectra we obtain fits for most groups that are of poor or at best marginal quality and give very subsolar metallicities similar to previous studies, 〈Z〉=0.29±0.12 Z⊙. Two-temperature models (2T) provide significantly better fits for 11 out of the 12 groups, and in every case have metallicities that are substantially larger than obtained for the 1T models, 〈Z〉=0.75±0.24 Z⊙. Though not very well constrained, for most of the groups absorption in excess of the Galactic value is indicated for the cooler temperature component of the 2T models. A simple multiphase cooling flow model gives results analogous to the 2T models including large metallicities, 〈Z〉=0.65±0.17 Z⊙. The nearly solar Fe abundances and also solar α/Fe ratios indicated by the 2T and cooling flow models are consistent with models of the chemical enrichment of ellipticals, groups, and clusters which assume ratios of Type Ia to Type II supernovae and an initial mass function (IMF) similar to those of the Milky Way. Thus we have shown that the very subsolar Fe abundances and Si/Fe enhancements obtained from most previous studies within r∼100 kpc of galaxy groups are an artefact of fitting isothermal models to the X-ray spectra, which also has been recently demonstrated for the brightest elliptical galaxies. Owing to the importance of these results for interpreting X-ray spectra, in an appendix we use simulated ASCA observations to examine in detail the ‘Fe bias’ and ‘Si bias’ associated with the spectral fitting of ellipticals, groups and clusters of galaxies.
Effects of a liquid layer on thickness-shear vibrations of rectangular AT-cut quartz plates

Thickness-shear vibrations of rectangular AT-cut quartz with one face in contact with a layer of Newtonian (linearly viscous and compressible) fluid are studied. The two-dimensional (2D) governing equations for vibrations of piezoelectric crystal plates given previously are used in the present study. The solutions for 1D shear wave and compressional wave in a liquid layer are obtained, and the stresses at the bottom of the liquid layer are used as approximations to the stresses exerted on the crystal surface in the plate equations. Closed form solutions are obtained for both free and piezoelectrically forced thickness-shear vibrations of a finite, rectangular AT-cut quartz plate in contact with a liquid layer of finite thickness. From the present solutions, a simple and explicit formula is deduced for the resonance frequency of the fundamental thickness-shear mode, which includes the effects of both shear and compressional waves in the liquid layer and the effect of the thickness-to-length ratio of the crystal plate. The formula reduces to the widely used frequency equation obtained by many previous investigators for infinite plates. The resonance frequency of a rectangular AT-cut quartz, computed as a function of the thickness of the adjacent liquid layer, agrees closely with the experimental data measured by Schneider and Martin (Anal. Chem., vol. 67, pp. 3324-3335, 1995).
Time-periodic solutions of the Benjamin-Ono equation

We present a spectrally accurate numerical method for finding non-trivial timeperiodic solutions of non-linear partial differential equations. The method is based on minimizing a functional (of the initial condition and the period) that is positive unless the solution is periodic, in which case it is zero. We solve an adjoint PDE to compute the gradient of this functional with respect to the initial condition. We include additional terms in the functional to specify the free parameters, which, in the case of the Benjamin-Ono equation, are the mean, a spatial phase, a temporal phase and the real part of one of the Fourier modes at t = 0. We use our method to study global paths of non-trivial time-periodic solutions connecting stationary and traveling waves of the Benjamin-Ono equation. As a starting guess for each path, we compute periodic solutions of the linearized problem by solving an infinite dimensional eigenvalue problem in closed form. We then use our numerical method to continue these solutions beyond the realm of linear theory until another traveling wave is reached (or until the solution blows up). By experimentation with data fitting, we identify the analytical form of the solutions on the path connecting the one-hump stationary solution to the two-hump traveling wave. We then derive exact formulas for these solutions by explicitly solving the system of ODE’s governing the evolution of solitons using the ansatz suggested by the numerical simulations.
Raising the Dead: Clues to Type Ia Supernova Physics from the Remnant 0509–67.5

We present Chandra X-ray observations of the young supernova remnant (SNR) 0509-67.5 in the Large Magellanic Cloud (LMC), believed to be the product of a Type Ia supernova (SN Ia). The remnant is very round in shape, with a distinct clumpy, shell-like structure that extends to an average radius of 148 (3.6 pc) in the X-ray band. Our Chandra data reveal the remnant to be rich in silicon, sulfur, and iron. The yields of our fits to the global spectrum confirm that 0509-67.5 is the remnant of an SN Ia and show a clear preference for delayed-detonation explosion models for SNe Ia. The Chandra spectra extracted from radial rings are in general quite similar; the most significant variation with radius is a drop in the equivalent widths of the strong emission lines right at the edge of the remnant. We study the spectrum of the single brightest isolated knot in the remnant and find that it is enhanced in iron by a factor of roughly 2 relative to the global remnant abundances. This feature, along with similar knots seen in Tycho's SNR, argues for the presence of modest small-scale composition inhomogeneities in SNe Ia. The presence of both Si and Fe, with abundance ratios that vary from knot to knot, indicates that these came from the transition region between the Si- and Fe-rich zones in the exploded star, possibly as a result of energy input to the ejecta at late times because of the radioactive decay of 56Ni and 56Co. Two cases for the continuum emission from the global spectrum were modeled: one in which the continuum is dominated by hydrogen thermal bremsstrahlung radiation, the other in which the continuum arises from nonthermal synchrotron radiation. The former case requires a relatively large value for the ambient density (~1 cm-3). Another estimate of the ambient density comes from using the shell structure of the remnant in the context of dynamical models. This requires a much lower value for the density (<0.05 cm-3) that is more consistent with other evidence known about 0509-67.5. We therefore conclude that the bulk of the continuum emission from 0509-67.5 has a nonthermal origin.
Thermophysical properties of germanium for thermal analysis of growth from the melt

The thermal diffusivity of Ge has been measured over a temperature range from 300° C to 1010° C which includes values for the melt. Specific heat has been measured from room temperature to 727° C. Thermal conductivity has been calculated over the same temperature range as the diffusivity measurements. These data are reported along with the best values from the literature for the other parameters which are required to calculate the temperature and convective fields for the growth of germanium by the Bridgman method. These parameters include the specific heat, the viscosity, the emissivity, and the density as a function of temperature.
Synthesis, Glycosidation, and Hydrolytic Stability of Novel Glycosyl Thioimidates

Despite significant progress in the area of synthetic carbohydrate chemistry, the necessity to form a glycosidic bond with complete stereoselectivity remains to be the main reason chemical O‐glycos...
2('),3(')-didehydro-2('),3(')-dideoxynucleosides are degraded to furfuryl alcohol under acidic conditions.

Abstract 2 ′ ,3 ′ -Didehydro-2 ′ ,3 ′ -dideoxynucleosides are clinically relevant antiviral agents. These nucleosides could be degraded under acidic conditions. Acidic stability studies showed the D4N had the following increasing stability order: D4G
Retrocyclopropanation reactions of fullerenes: complete product analyses.

Mono- and bis-pyrene malonates 1 and 2 were synthesized and reacted with C60 to prepare the corresponding Bingel adducts 3 and 4. These compounds were characterized electrochemically and exhibited the well-established retrocyclopropanation reaction when subjected to bulk electrolytic reductions. For the first time, it was possible to perform detailed product analyses after the retrocyclopropanation reactions, and these showed the presence of the original malonates 1 and 2 along with C60, in reasonable yields, around 50%.
Functional databases, functional languages

Database systems today have evolved a great deal from the first storage structures, towards greater data independence, expressive power in manipulation languages, and expressive power in data models. But their facilities are still poor substitutes for analogues in programming languages: data abstraction, structured control constructs and type systems respectively. Most programming languages, on the other hand, deal inadequately (if at all) with the question of long-lived structured data. The problem is compounded when dealing with both a database system and a programming language that are alien to each other (as is common today).
Looking for a bulk point

We consider Lorentzian correlators of local operators. In perturbation theory, singularities occur when we can draw a position-space Landau diagram with null lines. In theories with gravity duals, we can also draw Landau diagrams in the bulk. We argue that certain singularities can arise only from bulk diagrams, not from boundary diagrams. As has been previously observed, these singularities are a clear diagnostic of bulk locality. We analyze some properties of these perturbative singularities and discuss their relation to the OPE and the dimensions of double-trace operators. In the exact nonperturbative theory, we expect no singularity at these locations. We prove this statement in 1+1 dimensions by CFT methods.
Joint Centrality Distinguishes Optimal Leaders in Noisy Networks

We study the performance of a network of agents tasked with tracking an external unknown signal in the presence of stochastic disturbances and under the condition that only a limited subset of agents, known as leaders, can measure the signal directly. We investigate the optimal leader selection problem for a prescribed maximum number of leaders, where the optimal leader set minimizes total system error defined as steady-state variance about the external signal. In contrast to previously established greedy algorithms for optimal leader selection, our results rely on an expression of total system error in terms of properties of the underlying network graph. We demonstrate that the performance of any given set of noise-free leaders depends on their influence as determined by a new graph measure of the centrality of a set. We define the joint centrality of a set of nodes in a network graph such that a noise-free leader set with maximal joint centrality is an optimal leader set. In the case of a single leader, we prove that the optimal leader is the node with maximal information centrality for the noise-corrupted and noise-free leader cases. In the case of multiple leaders, we show that the nodes in the optimal noise-free leader set balance high information centrality with a coverage of the graph. For special cases of graphs, we solve explicitly for optimal leader sets. Examples are used to illustrate.
Sensitivity study of ice crystal optical properties in the 874 GHz submillimeter band

Abstract Testing of an 874 GHz submillimeter radiometer on meteorological satellites is being planned to improve ice water content retrievals. In this paper we study the optical properties of ice cloud particles in the 874 GHz band. The results show that the bulk scattering and absorption coefficients of an ensemble of ice cloud particles are sensitive to the particle shape and effective diameter, whereas the latter is also sensitive to temperature. The co-polar back scattering cross-section is not sensitive to particle shape, temperature, and the effective diameter in the range of 50–200 μm.
Woodward–Hoffmann’s Stereochemistry of Electrocyclic Reactions: From Day 1 to the JACS Receipt Date (May 5, 1964 to November 30, 1964)

The publication in January 1965 of the first Woodward-Hoffmann paper, The Stereochemistry of Electrocyclic Reactions, ushered into organic chemistry both an explanation of the stereochemistry and "allowedness" or "forbiddenness" of concerted reactions and an impetus for untold numbers of research projects. In the current paper, details of the collaboration between R. B. Woodward and R. Hoffmann, from when they first met to discuss the solution to the "no-mechanism problem" to the date their first paper was received in the offices of the Journal of the American Chemical Society, will be discussed and analyzed. The primary focus will be on the historically relevant extant documents from the early 1960s. These include Hoffmann's laboratory notebooks describing his research, including his extended Huckel calculations used to explain and predict the stereochemistry of electrocyclic reactions. Drafts of the Stereochemistry of Electrocyclic Reactions paper and letters and notes by Woodward, Jerome Berson, and others will further illuminate the development of this first Woodward-Hoffmann paper.