cssi/SciSciGPT-SciSciNet huggingface dataset:
Maximizing Conjunctive Views in Deletion Propagation

In deletion propagation, tuples from the database are deleted in order to reflect the deletion of a tuple from the view. Such an operation may result in the (often necessary) deletion of additional tuples from the view, besides the intentionally deleted one. The article studies the complexity of deletion propagation, where the view is defined by a conjunctive query (CQ), and the goal is to maximize the number of tuples that remain in the view. Buneman et al. showed that for some simple CQs, this problem can be solved by a straightforward algorithm, which is called here the unidimensional algorithm. The article identifies additional cases of CQs where the unidimensional algorithm succeeds, and in contrast, shows that for some other CQs the problem is NP-hard to approximate better than some constant ratio. In fact, it is shown here that among the CQs without self joins, the hard CQs are exactly the ones that the unidimensional algorithm fails on. In other words, the following dichotomy result is proved: for every CQ without self joins, deletion propagation is either APX-hard or solvable (in polynomial time) by the unidimensional algorithm.The article then presents approximation algorithms for certain CQs where deletion propagation is APX-hard. Specifically, two constant-ratio (and polynomial-time) approximation algorithms are given for the class of sunflower CQs (i.e., CQs having a sunflower hypergraph) without self joins. The first algorithm, providing the approximation ratio 1 − 1/e, is obtained by formulating the problem at hand as that of maximizing a monotone submodular function subject to a matroid constraint, and then using a known algorithm for such maximization. The second algorithm gives a smaller approximation ratio, 1/2, yet in polynomial time even under combined complexity. Finally, it is shown that self joins can significantly harden approximation in deletion propagation.
Observations on Noncommuting Coordinates and on Fields Depending on Them

The original ideas about noncommuting coordinates are recalled. The connection between U(1) gauge fields defined on noncommuting coordinates and fluid mechanics is explained.
ERRATA: "THz DETECTION BY RESONANT 2-D PLASMONS IN FIELD EFFECT DEVICES"

We demonstrate resonant detection of terahertz radiation by two-dimensional plasma waves in two field effect devices: a commercial field effect transistor (FET) and a double quantum well field effect transistor with a periodic grating gate. In both devices, the standing 2-D plasmon is tuned to the frequency of the THz radiation by varying the gate bias. The double quantum well field effect transistors exhibits a rich photoconductive response corresponding to spatial harmonics of the standing 2-D plasmons under the metal part of the periodic gate.
The Enchanting Alkaloids of Yuzuriha

The oriental plant Yuzuriha (Daphniphyllum macropodum) elaborates a fascinating family of polycyclic, squalene-derived alkaloids that provide a test for state-of-the-art methods of organic synthesis. The intriguing structures of these natural products have inspired us to design and explore two rather different approaches for their laboratory synthesis. This article recounts and contrasts these two different syntheses. The first approach was based on a method of synthetic design that emphasizes efficient construction of the polycyclic skeleton of the molecule (Corey's “network analysis”). A strategic bond was identified and the synthesis planned around the late formation of this bond. The synthesis that was designed by this approach proceeded smoothly until the point where it was necessary to remove functional groups that had been incorporated solely for the purpose of forming the strategic bond. Although the problems were eventually overcome, the resulting synthesis was too long and did not control the configuration of one of the stereocenters. The second approach was based on a possible biosynthesis of one of the alkaloids and provided surprisingly easy access to the simpler members of the family. The success of this synthesis led to a concrete proposal about the biosynthesis of the alkaloids and to the discovery of the astonishing transformation depicted in Scheme 27. In this marvelous reaction, an acyclic squalene derivative is converted by successive treatment with ordinary commodity chemicals into a pentacyclic alkaloid. The transformation involves the formation of four carbon–carbon bonds, two carbon-nitrogen bonds, and one carbon-hydrogen bond!
Can Food Stamps help to reduce Medicare spending on diabetes

Diabetes is rapidly escalating amongst low-income, older adults at great cost to the Medicare program. We use longitudinal survey data from the Health and Retirement Study linked to administrative Medicare records and biomarker data to assess the relationship between Food Stamp receipt and diabetes health outcomes. We find no significant difference in Medicare spending, outpatient utilization, diabetes hospitalizations and blood sugar (HbA1c) levels between recipients and income-eligible non-recipients after controlling for a detailed set of covariates including individual fixed effects and measures of diabetes treatment compliance. As one-third of elderly Food Stamp recipients are currently diabetic, greater coordination between the Food Stamp, Medicare, and Medicaid programs may improve health outcomes for this group.
Tracking Microstructure of Crystalline Materials: A Post-Processing Algorithm for Atomistic Simulations

Atomistic simulations have become a powerful tool in materials research due to the extremely fine spatial and temporal resolution provided by such techniques. To understand the fundamental principles that govern material behavior at the atomic scale and directly connect to experimental works, it is necessary to quantify the microstructure of materials simulated with atomistics. Specifically, quantitative tools for identifying crystallites, their crystallographic orientation, and overall sample texture do not currently exist. Here, we develop a post-processing algorithm capable of characterizing such features, while also documenting their evolution during a simulation. In addition, the data is presented in a way that parallels the visualization methods used in traditional experimental techniques. The utility of this algorithm is illustrated by analyzing several types of simulation cells that are commonly found in the atomistic modeling literature but could also be applied to a variety of other atomistic studies that require precise identification and tracking of microstructure.
Characterizing the Local Primary Dendrite Arm Spacing in Directionally Solidified Dendritic Microstructures

Characterizing the spacing of primary dendrite arms in directionally solidified microstructures is an important step for developing process–structure–property relationships by enabling the quantification of (i) the influence of processing on microstructure and (ii) the influence of microstructure on properties. In this work, we utilized a new Voronoi-based approach for spatial point pattern analysis that was applied to an experimental dendritic microstructure. This technique utilizes a Voronoi tessellation of space surrounding the dendrite cores to determine nearest neighbors and the local primary dendrite arm spacing. In addition, we compared this technique to a recent distance-based technique and a modification to this using Voronoi tessellations. Moreover, a convex hull-based technique was used to include edge effects for such techniques, which can be important for thin specimens. These methods were used to quantify the distribution of local primary dendrite arm spacings, their spatial distribution, and their correlation with interdendritic eutectic particles for an experimental directionally solidified Ni-based superalloy micrograph. This can be an important step for correlating processing and properties in directionally solidified dendritic microstructures.
Possible behaviours of the reflection ordering of stationary sets

If S, T are stationary subsets of a regular uncountable cardinal c, we say that S reflects fully in T, S < T, if for almost all a G T (except a nonstationary set) S n a is stationary in a. This relation is known to be a well-founded partial ordering. We say that a given poset P is realized by the reflection ordering if there is a maximal antichain (Xp; p E P) of stationary subsets of Reg(rc) so that
Euler and Navier-Stokes solutions for supersonic shear flow past a circular cylinder

Euler and Navier-Stokes solutions of the supersonic shear flow past a circular cylinder are obtained. These solutions are used to study the basic flow structure around the cylinder. Both the inviscid and viscous calculations show the formation of a large recirculating flow region around the front stagnation point. The calculations further show that the overall size of the recirculating region is approximately the same for the Euler and Navier-Stokes solutions but the inside structure is quite different. The inviscid flow shows only one vortex whereas the viscous flow shows two vortices inside the recirculating flow region. The inner vortex in the Navier-Stokes solution is formed primarily due to the viscous effects near the body surface and its size depends upon the Reynolds number. It is found that with increasing Reynolds number, the inner vortex diminishes in size and the Navier-Stokes solution asymptotically approaches the Euler solution. These results indicate that the Euler equations may correctly predict certain high Reynolds number separation phenomenon in flows with natural inviscid vorticity source.
Electrodeposited Metallic Nanowires as a Scanning Probe Tip

This paper describes lateral deformations of electrodeposited Ni nanowires as an atomic force microscope (AFM) probe tip. The maximum end deflections for nanowires to break the elasticity, which beam mechanics indicates, were applicable to our observed results.
Is Routine Pathological Evaluation of Pediatric Hernia Sacs Justified

Abstract Background/Purpose: Herniorrhaphy is the most common general surgical procedure performed on children, and hernia sac material is one of the most common tissue specimens microscopically examined in the authors' surgical pathology laboratory. The risk of accidental vas deferens ligation has prompted the recommendation that all hernia sacs be examined pathologically. The authors hypothesized that the incidence of unrecognized vas deferens or epididymis ligation is actually very low and may not warrant routine pathological examination of all pediatric hernia sacs. Methods: Over a 3-year period (1994 to 1996), pathology reports from all hernia repairs at the authors' institution were reviewed. A total of 1,494 inguinal hernia sacs were pathologically evaluated from 1,077 pediatric patients (417 were bilateral). Pathological diagnoses not affecting clinical management (ie, chronic inflammation, irritated hernia sacs, embryonal remnants, adrenal cortical rests) were classified as incidental findings. Identification of true vas deferens was classified as a positive finding. Results: The study population had a mean age of 3.9 ± 0.1 years and 963 (89%) were boys. The incidence of vas deferens injury from herniorraphy was found to be 0.13% (2 of 1,494), and these were recognized by the pediatric surgeon in the operating room. Conclusions: When vas deferens injury is suspected, the sample should always be sent to the pathology department for confirmation. However, no occult carcinoma or other pathology was identified, and the remainder of the histological findings did not change the clinical treatment of any child. Given a fixed cost of pathological analysis, elimination of routine hernia sac examination may result in substantial annual savings. Therefore, in the current era of cost containment, recommendations for routine pathological examination of excised pediatric hernia sacs should be reevaluated.
The effect of visco-elastic core thickness on modal loss factors of a thick three-layer cylinder:

AbstractFree vibrations of damped three-layer sandwich cylinders with thick layers are considered. In particular, the effect of the different thicknesses for the middle layer on the overall natural frequencies and modal damping factors are studied. The constrained-layer damping is accomplished by sandwiching a linear visco-elastic material between two isotropic elastic cylinders with the same properties. The governing equations are derived analytically by applying Newton's second law of motion for a three-dimensional elastic medium, and by employing complex elastic moduli for the sandwiched layer. Dimensionless natural frequencies and modal loss factors for the first three thickness modes associated with wave numbers of n = 0, 1, 2, 3, and 4 are tabulated for a range of thicknesses for the middle visco-elastic layer while keeping the thicknesses of inner and outer layers unchanged.
Enantioselective Alkenylation via Nickel-Catalyzed Cross-Coupling with Organozirconium Reagents

A new family of organometallic compounds, organozirconium reagents, are shown to serve as suitable partners in cross-coupling reactions of (activated) secondary alkyl electrophiles. Thus, the first catalytic method for coupling secondary α-bromoketones with alkenylmetal reagents has been developed, specifically, a mild, versatile, and stereoconvergent carbon−carbon bond-forming process that generates potentially labile β,γ-unsaturated ketones with good enantioselectivity.
Parallel Computational Geometry

We present efficient parallel algorithms for several basic problems in computational geometry: convex hulls, Voronoi diagrams, detecting line segment intersections, triangulating simple polygons, minimizing a circumscribing triangle, and recursive data-structures for three-dimensional queries.
STRUCTURAL ANALYSIS OF FUEL GROWTH IN FUEL PLATES

Abstract Depletion of fissionable fuels is accompanied by a volumetric increase. In order to prevent coolant contamination, this volume increase must be withstood by the fuel plate cladding. If the cladding is too thin large strains and resulting failure may take place. By defining an effective stress-strain curve of the fuel region, data from small irradiation specimens can be analyzed. Results, which can be extended to other plate geometries, can be used for two purposes: to insure cladding integrity and to determine distortion or instability of fuel plates caused by fuel growth. An example of an effective stress-strain curve derived from SM-2 irradiation test specimens is included.
A New Method for Hydrolyzing 2-Aryl-4,4-Dimethyl-2-Oxazolines to Aryl Carboxylic Acids

Abstract A method of hydrolyzing 2-aryl-4,4-dimethyl-2-oxazolines with trifluoromethanesulfonic anhydride is described which works well even for highly hindered systems where alternate methods fail.
Stereospecificity of triiodothyronine transport into brain, liver, and salivary gland: role of carrier- and plasma protein-mediated transport.

The stereospecificity of T3 transport through the walls of the brain capillary, i.e. the blood-brain barrier (BBB), and the salivary gland capillary and through the hepatocyte plasma membrane was studied with a tissue-sampling single injection technique in rats. In the absence of plasma proteins, the ED50 of inhibition of the saturable transport of [125I]L-T3 through the BBB was 1 microM for unlabeled L-T3 and 9 microM for unlabeled D-T3. The brain extraction of [125I]D-T3, 5.9 +/- 0.1% (+/- SE), was about one third that of [125I]L-T3. Conversely, no saturable and no stereospecific T3 transport was observed for the salivary gland capillary, which, unlike the brain capillary, is porous. The hepatic extraction of T3 was minimally stereospecific in the absence of plasma proteins. In the presence of 5 g/dl bovine albumin, the fraction of circulating D- or L-T3 that was available for transport into liver (50-100%) was many-fold greater than the fraction that was free in vitro (approximately 2%); therefore, both D-T3 and L-T3 were available for uptake by liver from the circulating albumin-bound pool. This plasma protein-mediated transport of T3 is believed to represent a process of enhanced dissociation of T3 from the albumin-binding site, since the plasma protein per se is not significantly taken up by liver on a single pass. However, in the presence of 5 g/dl bovine albumin, the extravascular hepatic extraction of [125I]D-T3 (50 +/- 2%) was nearly half that for [125I]T3 (93 +/- 12%), although no significant difference in the in vitro binding of [125I]D-T3 and [125I]L-T3 to 5 g/dl bovine albumin was found with equilibrium dialysis. In addition, the isoelectric point of bovine albumin bound to [125I] L-T3 (5.1) was higher than that of bovine albumin bound to [125I] D-T3 (5.0), as determined by isoelectric focusing, which indicates that the surface of the bovine albumin molecule is slightly more positive when the protein binds L-T3 as opposed to D-T3. The isoelectric focusing and in vivo transport data together suggest that the interaction between the surfaces of the plasma protein and the hepatic microcirculation that is presumed to cause enhanced hormone dissociation from the protein-binding site is electrostatic in nature. These studies (1) show that the BBB thyroid hormone transport system is sharply stereospecific, and this property is probably a major factor underlying the low biological potency of D-T3 in brain.(ABSTRACT TRUNCATED AT 400 WORDS)
Improving Wellbore Seal Integrity in CO2 Injection Wells

Abstract Work on Carbon Sequestration in subterranean formations has renewed interest in investigating the long term effects of CO 2 on Portland cements. Portland cement will react with the injected CO 2 , and while recent research indicates these conventional cements are not a concern, additional work is ongoing to further improve the long term effectiveness of the wellbore sealant. This paper discusses various solutions to the challenges of selecting a proper wellbore sealant for a CO 2 injection well. Additionally, the paper reviews the available sealant technologies, their application, and includes a discussion of stress modelling for these wells. A brief case history review of the design considerations for two high-rate acid gas injection wells in Wyoming is discussed.
Cinchona Alkaloid-Lewis Acid Catalyst Systems for Enantioselective Ketene−Aldehyde Cycloadditions

Asymmetric cinchona alkaloid-catalyzed acid chloride-aldehyde cyclocondensation (AAC) reactions afford enantioenriched 4-substituted and 3,4-disubstituted beta-lactones with near perfect absolute and relative stereocontrol. These reactions are characterized by the operational simplicity derived from using commercially available or easily obtained (one-step) reaction catalysts and in situ ketene generation from acid chlorides. The range of aldehyde substrates that serve as effective AAC substrates include sterically hindered aldehydes such as cyclohexanecarboxaldehyde and pivaldehyde.
The Value of Access to Highways and Light Rail Transit: Evidence for Industrial and Office Firms

This research examines the importance of access to light rail transit and highway systems in estimating office and industrial property rents. The analysis improves our understanding of the role played by transport facilities in locational decisions for the firm. Hedonic price analysis is utilised on longitudinal data for 520 office properties and 500 industrial properties collected from the San Diego metropolitan area over the period from 1986 to 1995. Results indicate that access to highways is a significant factor in estimating office property rents in the San Diego area, while access to light rail systems is not significant for office properties. Industrial firms in the San Diego area are not paying rent premiums to locate near highways or light rail transit.
Ion kinetic energy spectrometry

Abstract The development of ion kinetic energy spectrometry is used to illustrate how a new technique becomes broad ranging as new applications are found for it. Special emphasis is given to a description of the instrumentation and the philosophy underlying modifications made to it. Important sections of the paper discuss performance in terms of energy, mass and angular resolution and show that the requirements cannot always be optimized simultaneously. Useful scanning procedures and methods of ion detection and data acquisition are also assessed. The basic measurement of ion kinetic energy is used to study unimolecular, ion/molecule and ion/surface reactions. Peak shapes are analyzed for distributions of translational energy release and for energy change in collision processes that are not accompanied by fragmentation. The application of ion kinetic energy spectrometry to various problems in analysis are explored and likely future developments of the subject discussed.
Branes and dynamical supersymmetry breaking

We study dynamical supersymmetry breaking in four dimensions using the fivebrane of M theory, in particular for the Izawa-Yanagida-Intriligator-Thomas (IYIT) model, which we realize as the worldvolume theory of a certain M theory fivebrane configuration. From the brane point of view, supersymmetry is broken when a holomorphic configuration with the proper boundary conditions does not exist. We discuss the difference between explicit and spontaneous supersymmetry breaking and between runaway behavior and having a stable vacuum. As a preparation for the study of the IYIT model, we examine a realization of the orientifold four-plane in M theory. We derive known as well as new results on the moduli spaces of N = 2 and N = 1 theories with symplectic gauge groups. These results are based on a hypothesis that a certain intersection of the fivebrane and the Z_2 fixed plane breaks supersymmetry. In the IYIT model, we show that the brane exhibits runaway behavior when the flavor group is gauged. On the other hand, if the flavor group is not gauged, we find that the brane does not run away. We suggest that a stable supersymmetry-breaking vacuum is realized in the region beyond the reach of the supergravity approximation.
A Critical Reexamination of the Electrostatic Aharonov-Bohm Effect

This paper undertakes a critical reexamination of the electrostatic version of the Aharonov-Bohm (“AB”) effect. The conclusions are as follows: 1. Aharonov and Bohm’s 1959 exposition is invalid because it does not consider the wavefunction of the entire system, including the source of electrostatic potential. 2. As originally proposed, the electrostatic AB effect does not exist. Perhaps surprisingly, this conclusion holds despite the relativistic covariance of the electromagnetic four-potential combined with the well-established magnetic AB effect. 3. Although the authors attempted, in a 1961 paper, to demonstrate that consideration of the entire system would not change their result, they inadvertently assumed the desired outcome in their analysis. 4. Claimed observations of the electrostatic AB or an analogue thereof are shown to be mistaken.
An analysis of the basic space-charge-limited emission algorithm in a finite-element electrostatic gun code

Beam currents computed with a general-purpose gun code can exhibit puzzling behavior as the mesh is refined. To understand such behavior, we analyze the convergence, with respect to element size, of the basic space-charge-limited (SCL) emission algorithm in a one-dimensional (1-D) finite-element electrostatic gun model. With the current density fixed at the Child's law value, we find that the relative error of the potential at the first vertex adjacent to the cathode does not converge to zero, but rather increases as the mesh is refined. Convergence of the basic SCL emission algorithm, which depends on said error, is due instead to the increasing sensitivity of the potential to the current density. The current density converges slowly from above to the Child's law value, with a maximum error of 2.7% and ultimately with a sublinear convergence rate of 2/3. Tests on a three-dimensional parallel plate geometry with unstructured meshes of tetrahedral elements demonstrate that insight from the 1-D model applies to a general-purpose code. The behavior is similar to the 1-D model, but with a maximum error of 4.3%. Thus, using an unstructured mesh instead of a smooth structured mesh introduces only a modest additional error to the beam current. Based on the analysis of the 1-D model, we present two scaled SCL emission algorithms. The first exhibits linear convergence from below. The second limits the maximum error to 0.9%. Similar scalings can be employed in general-purpose gun codes to improve the accuracy of the computed beam current.
Effect of rogue particles on the sub-surface damage of fused silica during grinding/polishing

Abstract The distribution and characteristics of surface cracks (i.e., sub-surface damage or scratching) on fused silica formed during grinding/polishing resulting from the addition of rogue particles in the base slurry has been investigated. Fused silica samples (10 cm diameter × 1 cm thick) were: (1) ground by loose abrasive grinding (alumina particles 9–30 μm) on a glass lap with the addition of larger alumina particles at various concentrations with mean sizes ranging from 15 to 30 μm, or (2) polished (using 0.5 μm cerium oxide slurry) on various laps (polyurethane pads or pitch) with the addition of larger rogue particles (diamond (4–45 μm), pitch, dust, or dried Ceria slurry agglomerates) at various concentrations. For the resulting ground samples, the crack distributions of the as-prepared surfaces were determined using a polished taper technique. The crack depth was observed to: (1) increase at small concentrations (>10 −4 fraction) of rogue particles; and (2) increase with rogue particle concentration to crack depths consistent with that observed when grinding with particles the size of the rogue particles alone. For the polished samples, which were subsequently etched in HF:NH 4 F to expose the surface damage, the resulting scratch properties (type, number density, width, and length) were characterized. The number density of scratches increased exponentially with the size of the rogue diamond at a fixed rogue diamond concentration suggesting that larger particles are more likely to lead to scratching. The length of the scratch was found to increase with rogue particle size, increase with lap viscosity, and decrease with applied load. At high diamond concentrations, the type of scratch transitioned from brittle to ductile and the length of the scratches dramatically increased and extended to the edge of the optic. The observed trends can be explained semi-quantitatively in terms of the time needed for a rogue particle to penetrate into a viscoelastic lap. The results of this study provide useful insights and ‘rules-of-thumb’ relating scratch characteristics observed on surfaces during optical glass fabrication to the characteristics of the rogue particles causing them and their possible source.
Clustering Scatter Plots Using Data Depth Measures

Clustering is rapidly becoming a powerful data mining technique, and has been broadly applied to many domains such as bioinformatics and text mining. However, the existing methods can only deal with a data matrix of scalars. In this paper, we introduce a hierarchical clustering procedure that can handle a data matrix of scatter plots. To more accurately reflect the nature of data, we introduce a dissimilarity statistic based on "data depth" to measure the discrepancy between two bivariate distributions without oversimplifying the nature of the underlying pattern. We then combine hypothesis testing with hierarchical clustering to simultaneously cluster the rows and columns of the data matrix of scatter plots. We also propose novel painting metrics and construct heat maps to allow visualization of the clusters. We demonstrate the utility and power of our new clustering method through simulation studies and application to a microbe-host-interaction study.
RE-EXAMINING LARSON'S SCALING RELATIONSHIPS IN GALACTIC MOLECULAR CLOUDS

The properties of Galactic molecular clouds tabulated by Solomon et al. (SRBY) are re-examined using the Boston University-FCRAO Galactic Ring Survey of 13CO J = 1-0 emission. These new data provide a lower opacity tracer of molecular clouds and improved angular and spectral resolution compared with previous surveys of molecular line emission along the Galactic Plane. We calculate giant molecular cloud (GMC) masses within the SRBY cloud boundaries assuming local thermodynamic equilibrium (LTE) conditions throughout the cloud and a constant H2 to 13CO abundance, while accounting for the variation of the 12C/13C with galactocentric radius. The LTE-derived masses are typically five times smaller than the SRBY virial masses. The corresponding median mass surface density of molecular hydrogen for this sample is 42 M ☉ pc–2, which is significantly lower than the value derived by SRBY (median 206 M ☉ pc–2) that has been widely adopted by most models of cloud evolution and star formation. This discrepancy arises from both the extrapolation by SRBY of velocity dispersion, size, and CO luminosity to the 1 K antenna temperature isophote that likely overestimates the GMC masses and our assumption of constant 13CO abundance over the projected area of each cloud. Owing to the uncertainty of molecular abundances in the envelopes of clouds, the mass surface density of GMCs could be larger than the values derived from our 13CO measurements. From velocity dispersions derived from the 13CO data, we find that the coefficient of the cloud structure functions, v ° = σ v /R 1/2, is not constant, as required to satisfy Larson's scaling relationships, but rather systematically varies with the surface density of the cloud as ~Σ0.5 as expected for clouds in self-gravitational equilibrium.
Hausdorff dimension of the set of points on divergent trajectories of a homogeneous flow on a product space

In this paper we compute the Hausdorff dimension of the set $D(\varphi_n)$ of points on divergent trajectories of the homogeneous flow $\varphi_n$ induced by the one-parameter subgroup $\mathop{\rm diag}(e^t,e^{-t})$ acting by left multiplication on the product space $G^n/\Gamma^n$, where $G=\mathop{\rm SL}(2,{\mathbb R})$ and $\Gamma=\mathop{\rm SL}(2,{\mathbb Z})$. We prove that $\dim_H D(\varphi_n)=3n-\frac{1}{2}$ for $n\ge2$.
On the properties of the exchange graph of a cluster algebra

We prove a conjecture about the vertices and edges of the exchange graph of a cluster algebra $\A$ in two cases: when $\A$ is of geometric type and when $\A$ is arbitrary and its exchange matrix is nondegenerate. In the second case we also prove that the exchange graph does not depend on the coefficients of $\A$. Both conjectures were formulated recently by Fomin and Zelevinsky.
Investigations of coronatine biosynthesis. Overexpression and assay of CmaT, a thioesterase involved in coronamic acid biosynthesis

Abstract The protein (CmaT) encoded by the cmaT gene of the coronamic acid biosynthetic gene cluster has been overexpressed in Escherichia coli in soluble and active form fused to the carboxyl terminus of MalE, the maltose-binding protein. CmaT was also overexpressed in E. coli as an N-terminal His-tagged protein. The N-terminal His-tagged form of CmaT was produced in insoluble form, but it could be refolded to obtain CmaT in soluble and highly active form. Both the MalE-CmaT fusion protein and the refolded His-tagged CmaT protein exhibited esterase activity.
Balloon-Artery Interactions During Stent Placement A Finite Element Analysis Approach to Pressure, Compliance, and Stent Design as Contributors to Vascular Injury

Endovascular stents expand the arterial lumen more than balloon angioplasty and reduce rates of restenosis after coronary angioplasty in selected patients. Understanding the factors involved in vascular injury imposed during stent deployment may allow optimization of stent design and stent-placement protocols so as to limit vascular injury and perhaps reduce restenosis. Addressing the hypothesis that a previously undescribed mechanism of vascular injury during stent deployment is balloon-artery interaction, we have used finite element analysis to model how balloon-artery contact stress and area depend on stent-strut geometry, balloon compliance, and inflation pressure. We also examined superficial injury during deployment of stents of varied design in vivo and in a phantom model ex vivo to show that balloon-induced damage can be modulated by altering stent design. Our results show that higher inflation pressures, wider stent-strut openings, and more compliant balloon materials cause markedly larger surface-contact areas and contact stresses between stent struts. Appreciating that the contact stress and contact area are functions of placement pressure, stent geometry, and balloon compliance may help direct development of novel stent designs and stent-deployment protocols so as to minimize vascular injury during stenting and perhaps to optimize long-term outcomes.
Magnetic Helicity Conservation and Astrophysical Dynamos

We construct a magnetic helicity conserving dynamo theory that incorporates a calculated magnetic helicity current. In this model the fluid helicity plays a small role in large-scale magnetic field generation. Instead, the dynamo process is dominated by a new quantity, derived from asymmetries in the second derivative of the velocity correlation function, closely related to the "twist and fold" dynamo model. The turbulent damping term is, as expected, almost unchanged. Numerical simulations with a spatially constant fluid helicity and vanishing resistivity are not expected to generate large-scale fields in equipartition with the turbulent energy density. The prospects for driving a fast dynamo under these circumstances are uncertain, but if it is possible, then the field must be largely force-free. On the other hand, there is an efficient analog to the α-Ω dynamo. Systems whose turbulence is driven by some anisotropic local instability in a shearing flow, like real stars and accretion disks, and some computer simulations may successfully drive the generation of strong large-scale magnetic fields, provided that ∂rΩ∂θvzωθ > 0. We show that this criterion is usually satisfied. Such dynamos will include a persistent, spatially coherent vertical magnetic helicity current with the same sign as -∂rΩ, that is, positive for an accretion disk and negative for the Sun. We comment on the role of random magnetic helicity currents in storing turbulent energy in a disordered magnetic field, which will generate an equipartition, disordered field in a turbulent medium, and also a declining long-wavelength tail to the power spectrum. As a result, calculations of the Galactic "seed" field are largely irrelevant.
Learning Mixtures of Gaussians in High Dimensions

Efficiently learning mixture of Gaussians is a fundamental problem in statistics and learning theory. Given samples coming from a random one out of k Gaussian distributions in Rn, the learning problem asks to estimate the means and the covariance matrices of these Gaussians. This learning problem arises in many areas ranging from the natural sciences to the social sciences, and has also found many ma- chine learning applications. Unfortunately, learning mixture of Gaussians is an information theoretically hard problem: in order to learn the parameters up to a reasonable accuracy, the number of samples required is exponential in the number of Gaussian components in the worst case. In this work, we show that provided we are in high enough dimensions, the class of Gaussian mixtures is learnable in its most general form under a smoothed analysis framework, where the parameters are randomly perturbed from an adversarial starting point. In particular, given samples from a mixture of Gaussians with randomly perturbed parameters, when n ≥ Ω(k2), we give an algorithm that learns the parameters with polynomial running time and using polynomial number of samples.The central algorithmic ideas consist of new ways to de- compose the moment tensor of the Gaussian mixture by exploiting its structural properties. The symmetries of this tensor are derived from the combinatorial structure of higher order moments of Gaussian distributions (sometimes referred to as Isserlis' theorem or Wick's theorem). We also develop new tools for bounding smallest singular values of structured random matrices, which could be useful in other smoothed analysis settings.
The local time dependence of the anisotropic solar cosmic ray flux.

Abstract The distribution of the solar cosmic radiation flux over the earth is not uniform, but the result of complex phenomena involving the interplanetary magnetic field, the geomagnetic field and latitude and longitude of locations on the earth. The latitude effect relates to the geomagnetic shield; the longitude effect relates to local time. For anisotropic solar cosmic ray events the maximum particle flux is always along the interplanetary magnetic field direction sometimes called the Archimedean spiral path from the sun to the earth. During an anisotropic solar cosmic ray event, the locations on the earth viewing “sunward” into the interplanetary magnetic field direction will observe the largest flux (when adjustments are made for the magnetic latitude effect). To relate this phenomena to aircraft routes, for anisotropic solar cosmic ray events that occur during “normal quiescent” conditions, the maximum solar cosmic ray flux (and corresponding solar particle radiation dose) will be observed in the dawn quadrant, ideally at about 06 hours local time.
Rotation numbers and instability sets

Translation and rotation numbers have played an interesting and important role in the qualitative description of various dynamical systems. In this exposition we are especially interested in applications which lead to proofs of periodic motions in various kinds of dynamics on the annulus. The applications include billiards and geodesic flows. Going beyond this simple qualitative invariant in the study of the dynamics of area preserving annulus maps, G.D. Birkhoff was led to the concept of “regions of instability” for twist maps. We discuss the closely related notion of instability sets for a generic area preserving surface diffeomorphism and develop their properties.
N-triflylthiophosphoramide catalyzed enantioselective Mukaiyama aldol reaction of aldehydes with silyl enol ethers of ketones.

The first Bronsted acid catalyzed asymmetric Mukaiyama aldol reaction of aldehydes using silyl enol ethers of ketones as nucleophiles has been reported. A variety of aldehydes and silyl enol ethers of ketones afforded the aldol products in excellent yields and good to excellent enantioselectivities. Mechanistic studies revealed that the actual catalyst may be changed from the silylated Bronsted acid to the Bronsted acid itself depending on the reaction temperature.
The Impact of Advertising Location and User Task on the Emergence of Banner Ad Blindness: An Eye-Tracking Study

The purpose of this study is to explore the emergence of ad banner blindness in the viewing of e-commerce home pages. Building on the literature on inattention blindness and banner blindness, this article assessed the gaze path of users in goal-directed and free-viewing tasks when viewing pages with advertising banners on the right side of the page and on the top of the page above the main navigation menu. The hypotheses are tested using an analysis of variance. Using an eye-tracking methodology, the results identify significant differences in visual attention for banner ad location and for task type. Banner blindness is strongest for advertising banners on the right side of the page and for goal-directed tasks. Neither participants’ ratings of page visual appeal or of page familiarity could explain the findings. The study contributes to the existing literature by resolving some of the cognitive factors that lead to banner blindness and supplementing previous research that focused on relevant perceptual f...
MAIN-BELT COMET P/2008 R1 (GARRADD)*

We present a study of the newly discovered main-belt comet P/2008 R1 (Garradd), an object with the dynamical characteristics of an asteroid and the physical characteristics of a comet. Photometry sets a limit to the effective radius of the nucleus at re < 0.7 km (red geometric albedo 0.05 assumed). The coma shows a secular fading in our data caused by the escape of dust particles from the near-nucleus environment. The optical reflection spectrum is a nearly neutral continuum devoid of gaseous emission lines, from which we derive a limit to the cyanide (CN) radical production rate of Q CN< 1.4 × 1023 s–1 and infer a mass-loss rate <1.5 kg s–1 at the time of our observations. Unlike the first-reported main-belt comets, P/2008 R1 is not dynamically stable. The nearby 8:3 mean-motion resonance with Jupiter induces dynamical instability on timescales 20-30 Myr. Hence, we conclude that P/2008 R1 has recently arrived from a more stable source elsewhere. The high Tisserand parameter of the orbit (in fact, with TJ = 3.216 it is the highest of any comet) points to a source in the asteroid belt itself, instead of in the Kuiper belt (putative source of the Jupiter family comets). We infer that P/2008 R1 is an icy body from the outer asteroid belt in which sublimation has been triggered by rising temperatures resulting from a decreasing perihelion distance.
Two-player envy-free multi-cake division

Abstract We introduce a generalized cake-cutting problem in which we seek to divide multiple cakes so that two players may get their most-preferred piece selections: a choice of one piece from each cake, allowing for the possibility of linked preferences over the cakes. For two players, we show that disjoint envy-free piece selections may not exist for two cakes cut into two pieces each, and they may not exist for three cakes cut into three pieces each. However, there do exist such divisions for two cakes cut into three pieces each, and for three cakes cut into four pieces each. The resulting allocations of pieces to players are Pareto-optimal with respect to the division. We use a generalization of Sperner’s lemma on the polytope of divisions to locate solutions to our generalized cake-cutting problem.
A stochastic calculus model of continuous trading: Complete markets

Abstract A paper by the same authors in the 1981 volume of Stochastic Processes and Their Applications presented a general model, based on martingales and stochastic integrals, for the economic problem of investing in a portfolio of securities. In particular, and using the terminology developed therein, that paper stated that every integrable contingent claim is attainable (i.e., the model is complete) if and only if every martingale can be represented as a stochastic integral with respect to the discounted price process. This paper provides a detailed proof of that result as well as the following: The model is complete if and only if there exists a unique martingale measure.
Zircon zonation patterns as revealed by cathodoluminescence and backscattered electron images: Implications for interpretation of complex crustal histories

Abstract Zircon exhibits an extraordinary memory. Its stability, durability, low solubility and low elemental diffusivities combine to preserve in it a record of most of the important events that have affected it, its host rocks, and the crust of which it is a part. Zonation in zircon grains delineates the boundaries of discrete geochemical packages formed at different times, each effectively a closed system. The elemental and isotopic compositions of these packages reflect the timing and conditions of growth events, and the morphology of the zonation indicates qualitatively the nature of both growth and intervening degradation events. Cathodoluminescence (CL) and backscattered electron (BSE) imaging reveals detailed zonation patterns that are commonly invisible or barely visible with conventional transmitted and reflected light microscopy. Characteristic patterns are visible in almost all zircons that serve to distinguish igneous from metamorphic growth, to distinguish truncation surfaces of different types (e.g., sedimentary fracturing vs. resorption), and possibly to identify ancient metamictization. Zircons from many rocks record multistage histories that reflect two or more events; those from rocks such as peraluminous granites and high-grade paragneisses are especially likely to reveal long and complex histories. Studies of zonation patterns in zircons provide a clear, though qualitative, history of a rock and its heritage. Furthermore, they provide the basis for a quantification of that history. Elemental and isotopic compositions can reveal the environment in which a zone grew. U-Pb analysis of a zone provides an age for its growth. shrimp analyses that are not guided by detailed knowledge of zonation can straddle two (or more) zones and a discordant U-Pb result from such an analysis may falsely suggest Pb loss, and important growth zones may be missed entirely. Thus, the combined use of CL, BSE, electron microprobe and ion probe methods can elucidate complex crustal histories.
Metal complexes of 1,3-dimethylimidazolium-2-dithiocarboxylate

Abstract Complexes containing the soft acid metals Pt, Pd, Ag, and Au, with the ligand 1,3-dimethylimidazolium-2-dithiocarboxylate (L) have been synthesized and characterized by analytical data and infrared and electronic spectroscopy. The data suggest that the ligand acts as a bidentate ligand with Pt and Pd, a monodentate ligand with Ag and a bridging ligand between two Au atoms.
Numerical Study of the Generation of Linear Energy Transfer Spectra for Space Radiation Applications

In analyzing charged particle spectra in space due to galactic cosmic rays (GCR) and solar particle events (SPE), the conversion of particle energy spectra into linear energy transfer (LET) distributions is a convenient guide in assessing biologically significant components of these spectra. The mapping of LET to energy is triple valued and can be defined only on open energy subintervals where the derivative of LET with respect to energy is not zero. Presented here is a well-defined numerical procedure which allows for the generation of LET spectra on the open energy subintervals that are integrable in spite of their singular nature. The efficiency and accuracy of the numerical procedures is demonstrated by providing examples of computed differential and integral LET spectra and their equilibrium components for historically large SPEs and 1977 solar minimum GCR environments. Due to the biological significance of tissue, all simulations are done with tissue as the target material.
A terahertz two-wire waveguide with low bending loss

We experimentally and numerically study the propagation of terahertz radiation on a two-wire waveguide. We find that this structure exhibits much lower bending losses than a single wire waveguide.