cssi/SciSciGPT-SciSciNet huggingface dataset:
Improved Thermoelectric Performance in Yb14Mn1−xZnxSb11 by the Reduction of Spin-Disorder Scattering

Rare-earth transition metal compounds Yb_(14)Mn_(1−x)Zn_xSb_(11), isostructural with Ca_(14)AlSb_(11), have been prepared using a metal flux growth technique for thermoelectric property measurements (with x = 0.0, 0.2, 0.3, 0.4, 0.7, 0.9, and 1.0). Single-crystal X-ray diffraction and electron microprobe analysis data indicate the successful synthesis of a solid-solution for the Yb_(14)Mn_(1−x)Zn_xSb_(11) structure type for 0 0.4. High-temperature (298 K–1275 K) measurements of the Seebeck coefficient, resistivity, and thermal conductivity were performed on hot-pressed, polycrystalline samples. As the concentration of Zn increases in Yb_(14)Mn_(1−x)Zn_xSb_(11), the Seebeck coefficient remains unchanged for 0 ≤ x ≤ 0.7 indicating that the free carrier concentration has remained unchanged. However, as the nonmagnetic Zn^(2+) ions replace the magnetic Mn^(2+) ions, the spin disorder scattering is reduced, lowering the resistivity. Replacing the magnetic Mn^(2+) with non magnetic Zn^(2+) provides an independent means to lower resistivity without deleterious effects to the Seebeck values or thermal conduction. Alloying the Mn site with Zn reduces the lattice thermal conductivity at low temperatures but has negligible impact at high temperatures. The reduction of spin disorder scattering leads to an ∼10% improvement over Yb_(14)MnSb_(11), revealing a maximum thermoelectric figure of merit (zT) of ∼1.1 at 1275 K for Yb_(14)Mn_(0.6)Zn_(0.4)Sb_(11).
Anisotropic functional deconvolution with long-memory noise: the case of a multi-parameter fractional Wiener sheet

ABSTRACTWe look into the minimax results for the anisotropic two-dimensional functional deconvolution model with the two-parameter fractional Gaussian noise. We derive the lower bounds for the Lp-r...
Synthesis of 5-chloro-2-methyl-3-(5-methylthiazol-2-yl)-4(3H)-quinazolinone and related compounds with potential biological activity

Eight new 2-methyl-4(3H)-quinazolinones (8a-8d, 9c, 9d, 10c, 10d) with one or two chlorine atoms in the benzene ring and a 5-methyl-1,3-thiazol-2-yl, 4-methyl-1,3-thiazol-2-yl, and 5-ethyl-1,3,4-thiadiazol-2-yl substituent in position 3 of the heterocyclic ring were synthesized and characterized. The two step procedure (Scheme 1) utilizes chlorosubstituted anthranilic acids (3a-3d) and acetic anhydride as the starting materials, with the respective chlorosubstituted 2-methyl-4H-3,1-benzoxazin-4-ones (4a-4d) as the intermediates. The quinazoline derivatives were characterized by their melting points, elemental analyses and the mass, ultraviolet, infrared, and 1H and 13C nmr spectra. The new compounds are expected to be biologically active.
Synthesis of asymmetric iron–pybox complexes and their application to aziridine forming reactions

Abstract The synthesis of a series of iron–pybox complexes and their employment in the catalytic asymmetric aziridine forming reaction is presented. When AgSbF6 is used as an initiator, the i-pr- and t-bu-pybox complexes produce 47% of the cis-aziridine in moderate ee’s with the bulk of side products consisting of the trans-isomer and β-amino-α,β-unsaturated esters (AUE’s).
Native silica nanoparticle catalyzed anti-Markovnikov addition of thiols to inactivated alkenes and alkynes: a new route to linear and vinyl thioethers

Abstract A new route for the synthesis of linear and vinyl thioethers has been demonstrated using bare silica nanoparticle as catalyst at room temperature under solvent-free conditions. The catalyst can be reused up to six times without loss of catalytic activity.
Methane-Linked Mechanisms of Electron Uptake from Cathodes by Methanosarcina barkeri.

ABSTRACT The Methanosarcinales, a lineage of cytochrome-containing methanogens, have recently been proposed to participate in direct extracellular electron transfer interactions within syntrophic communities. To shed light on this phenomenon, we applied electrochemical techniques to measure electron uptake from cathodes by Methanosarcina barkeri, which is an important model organism that is genetically tractable and utilizes a wide range of substrates for methanogenesis. Here, we confirm the ability of M. barkeri to perform electron uptake from cathodes and show that this cathodic current is linked to quantitative increases in methane production. The underlying mechanisms we identified include, but are not limited to, a recently proposed association between cathodes and methanogen-derived extracellular enzymes (e.g., hydrogenases) that can facilitate current generation through the formation of reduced and diffusible methanogenic substrates (e.g., hydrogen). However, after minimizing the contributions of such extracellular enzymes and using a mutant lacking hydrogenases, we observe a lower-potential hydrogen-independent pathway that facilitates cathodic activity coupled to methane production in M. barkeri. Our electrochemical measurements of wild-type and mutant strains point to a novel and hydrogenase-free mode of electron uptake with a potential near −484 mV versus standard hydrogen electrode (SHE) (over 100 mV more reduced than the observed hydrogenase midpoint potential under these conditions). These results suggest that M. barkeri can perform multiple modes (hydrogenase-mediated and free extracellular enzyme-independent modes) of electrode interactions on cathodes, including a mechanism pointing to a direct interaction, which has significant applied and ecological implications. IMPORTANCE Methanogenic archaea are of fundamental applied and environmental relevance. This is largely due to their activities in a wide range of anaerobic environments, generating gaseous reduced carbon that can be utilized as a fuel source. While the bioenergetics of a wide variety of methanogens have been well studied with respect to soluble substrates, a mechanistic understanding of their interaction with solid-phase redox-active compounds is limited. This work provides insight into solid-phase redox interactions in Methanosarcina spp. using electrochemical methods. We highlight a previously undescribed mode of electron uptake from cathodes that is potentially informative of direct interspecies electron transfer interactions in the Methanosarcinales.
Unusual effects of Be doping in the iron-based superconductor FeSe

Recent superconducting transition temperatures (T c) over 100 K for monolayer FeSe on SrTiO3 have renewed interest in the bulk parent compound. In KCl:AlCl3 flux-transport-grown crystals of FeSe0.94Be0.06, FeSe0.97Be0.03 and, for comparison, FeSe, this work reports doping of FeSe using Be-among the smallest of possible dopants, corresponding to an effective 'chemical pressure'. According to lattice parameter measurements, 6% Be doping shrank the tetragonal FeSe lattice equivalent to a physical pressure of 0.75 GPa. Using this flux-transport method of sample preparation, 6% of Be was the maximum amount of dopant achievable. At this maximal composition of FeSe0.94Be0.06, the lattice unit cell shrinks by 2.4%, T c-measured in the bulk via specific heat-increases by almost 10%, the T c versus pressure behavior shifts its peak [Formula: see text] downwards by ~1 GPa, the high temperature structural transition around T S = 89 K increases by 1.9 K (in contrast to other dopants in FeSe which uniformly depress T S), and the low temperature specific heat γ increases by 10% compared to pure FeSe. Also, upon doping by 6% Be the residual resistivity ratio, ρ(300 K)/ρ(T → 0), increases by almost a factor of four, while ρ(300 K)/ρ([Formula: see text]) increases by 50%.
THE BULK AND SURFACE STRUCTURE OF γ-ALUMINA

Despite its widespread use, the composition and structure of γ-alumina have been the subject of controversy for decades. In this article we review the historical attempts to resolve two principal questions that have each been extensively debated, but in independent communities: (1) What is the distribution of vacancies over the two cation sublattices in the nominal spinel structure, and (2) what is the hydrogen content of γ-alumina, if any? We then review how recent investigations have shown that these two questions are, in fact, related, and have a single resolution. The experimental study of γ-alumina surfaces has long been dominated by IR spectroscopy of the hydroxylated surfaces, and 27AI NMR. Both techniques have produced perplexing results. Here we review the development of these surface studies and parallel computational studies. Finally, we review recent computational results that explain the puzzling experimental findings.
A library approach to the generation of bisubstrate analogue sulfotransferase inhibitors.

A library of potential bisubstrate analogue inhibitors (1) targeting sulfotransferase enzymes was generated by the chemoselective ligation of the PAPS mimic 2 with a panel of 447 aldehydes. Preliminary screening has identified compounds that inhibit estrogen sulfotransferase (EST), an enzyme relevant to breast cancer.
Inter- and intramolecular Horner–Wadsworth–Emmons reactions of 5-(diethoxyphosphoryl)-1-acyl-2-alkyl(aryl)-2,3-dihydro-4-pyridones

Dihydropyridones of the type 1 were converted to their C-5 alkylidene derivatives 2 by a reaction sequence involving phosphorylation, conjugate reduction or addition to provide piperidones 4, and then olefination via a Horner–Wadsworth–Emmons reaction. An intramolecular version of this method was used to prepare trans-bicyclic enone 13.
A facile synthesis of cyclic enecarbamates using Dess–Martin periodinane

Abstract A simple and efficient synthesis of cyclic enecarbamates from ω-hydroxycarbamates via tandem oxidative cyclization–dehydration was achieved in 84% to quantitative yield using Dess–Martin periodinane in methylene chloride.
One-Dimensional Molybdenum Thiochlorides and Their Use in High Surface Area MoSx Chalcogels

New molybdenum thiochlorides, α-MoSCl3 and β-MoSCl3, have been synthesized by chemical vapor transport. A selenium analog, MoSeCl3, could also be prepared in the same way. The crystal structures consist of infinite chains stabilized by weak van der Waals forces. For the α-phase an infinite chain of ∞1[Mo2(S2)Cl4Cl4/2] runs along the crystallographic c axis, while for the β-phase ∞1[Mo2(S2)Cl3Cl6/2] chain passes through the b-axis. MoSeCl3 is isostructural to α-MoSCl3. The formal charge on molybdenum in these thiochlorides have been assigned by X-ray photoelectron spectroscopy (XPS) to be +IV. β-MoSCl3 and already known Mo3S7Cl4 and MoS2Cl3 are weakly paramagnetic. Thermal decomposition of molybdenum thiochlorides leads to MoS2. Red MoS2Cl3 and Mo3S7Cl4 exhibit band gaps of ∼2.07 and ∼2.11 eV, while black α-MoSCl3, β-MoSCl3, and MoSeCl3 exhibit band gaps of ∼1.2, 1.24, and 1.18 eV, respectively. The new thiochlorides can serve as precursors in the synthesis of molybdenum–sulfide gels and aerogels. The MoSx...
Modular Preparation of Diverse Dipyrrolemethanes

A modular synthesis of polyfunctional dipyrrolemethanes is presented. Diverse side chains are introduced to 2-carboxypyrrole building blocks in two to four steps, resulting in a collection of substituted pyrroles that, when condensed in one step, give rise to diverse structural features.
Synthesis and characterization of new 1,1′‐diester, diketone, and dinitrile derivatives of 2,2′‐biimidazole

Substituted 1,1′-diester, diketone and dinitrile derivatives are prepared from 2,2′-biimidazole. The reactions involved include: Michael addition with halogenated olefins; nucleophilic substitution with ketones, nitriles, and esters; and condensation with amines.
Recent applications of gem-dichloroepoxide intermediates in synthesis

This review highlights recent synthetic applications of the Jocic-Reeve, Corey-Link, and Bargellini reactions, all of which proceed through reactive gem-dichloroepoxide intermediates. Research published between 2001-early 2011 involving enhancements to the named reactions, new synthetic methods, target-directed synthesis, and drug discovery and development is emphasized.
Synthesis of functionalized 2-oxindoles by Friedel–Crafts reactions

Abstract A series of acetonyl-substituted 3-hydroxy-2-oxindoles have been prepared and reacted with arenes in superacid promoted Friedel–Crafts reactions. The product aryl-substituted 2-oxindoles are formed in generally good yields. With substituted arenes such as toluene, bromobenzene, or anisole, the Friedel–Crafts reactions occur with excellent regioselectivity. A mechanism is proposed involving carbocationic electrophiles leading to the aromatic substitution chemistry.
E-1-LITHIO-1-ALKENES IN HYDROCARBON SOLVENT

Abstract Trans-alkenyl iodides are treated with tert-butyllithium in hexane at room temperature to provide pure trans-alkenyllithiums in good yield.
Mitogenomic differentiation in spinner (Stenella longirostris) and pantropical spotted dolphins (S. attenuata) from the eastern tropical Pacific Ocean

Endemic subspecies and multiple stocks have been proposed for spinner (Stenella longirostris) and spotted dolphins (Stenella attenuata), two species with historically high mortality due to bycatch in the eastern tropical Pacific yellowfin tuna fishery. However, there has been low statistical power in tests for genetic differentiation among most of these stocks, due to large historical abundances, ongoing gene flow, and recent divergence. We tested for structure at multiple hierarchical levels by collecting whole mitochondrial genome sequences (mtDNA) and nuclear SNPs (nuDNA) from 104 spinner and 76 spotted dolphins using capture array library enrichment and highly paralleled DNA sequencing. MtDNA showed weak but significant differences between subspecies of spotted (FST: 0.0125; P = 0.0402) and spinner dolphins (FST: 0.0133; P = 0.034). NuDNA supported subspecies of spotted but not spinner dolphins. Relatively strong and significant differentiation was detected between whitebelly and eastern spinner stocks using nuDNA (FST: 0.0297; P = 0.0059). Neither mtDNA nor nuDNA supported the division of existing offshore stocks of spotted dolphins or Tres Marias spinner dolphins. This work identifies a genetic basis for biologically meaningful management units of these two species, a critical component in understanding their response in the face of historical and continued fishery interactions.
More Than One Replication Study Is Needed for Unambiguous Tests of Replication

The problem of assessing whether experimental results can be replicated is becoming increasingly important in many areas of science. It is often assumed that assessing replication is straightforwar...
Enantioselective synthesis of 5-substituted α,β-unsaturated δ-lactones: application to the synthesis of styryllactones

Abstract A flexible enantioselective synthesis of highly functionalized 5-substituted α,β-unsaturated δ-lactones has been achieved by applying the Sharpless catalytic asymmetric dihydroxylation to vinylfuran as the key step. The resulting diols are produced in high enantio excess and can be stereoselectively transformed into differentially protected δ-lactones through a short reaction sequence.
Microwave-Mediated Intramolecular Carbanilide Cyclization to Hydantoins Employing Barium Hydroxide Catalysis

The hydantoin moiety imparts a broad range of biological activities with both medicinal1 (cf. anticonvulsant) and agrochemical2 (cf, fungicidal and herbicidal) applications. Given this utility, it is not surprising that a large number of hydantoins adorned with diverse substituents have been synthesized in solution3 and the solid phase.4 In previous studies, we developed novel routes to spirofused5 and polycyclic6 hydantoin derivatives by carbanilide cyclization chemistry. This strategy delivered hydantoin-containing heterocycles with excellent stereoselective control,7 but formation of the hydantoin moiety carbanilide cyclization required long reaction times at relatively high temperature with excess base. Indeed, the forcing conditions required for carbanilide cyclization in these studies resulted in some thermal decomposition of product. Following the pioneering work of Giguere and Gedye,8 microwave (μW) applications in organic chemistry have become more prevalent.9 The principal advantages of μW mediation are reaction acceleration and accompanying minimization of product decomposition.9,10 The current literature reveals a growing number of examples of heterocycle formation mediated by μW irradiation,11 and our recent report12 of μW-mediated carbanilide cyclization13 employing a barium hydroxide catalyst added to this literature. Here, we expand on this previous report and disclose our investigation of numerous carbanilide cyclizations under μW conditions.
Ultrafast Photochemical Intramolecular Charge and Excited State Solvation

Etude de la solvatation de composes aromatiques et des transferts de charge induisant une fluorescence double
Pd(II)-catalyzed conversion of styrene derivatives to acetals: impact of (-)-sparteine on regioselectivity.

Pd[(−)-sparteine]Cl2 catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride.
Sun Navigation Requires Compass Neurons in Drosophila

Despite their small brains, insects can navigate over long distances by orienting using visual landmarks [1], skylight polarization [2, 3, 4, 5, 6, 7, 8, 9], and sun position [3, 4, 6, 10]. Although Drosophila are not generally renowned for their navigational abilities, mark-and-recapture experiments in Death Valley revealed that they can fly nearly 15 km in a single evening [11]. To accomplish such feats on available energy reserves [12], flies would have to maintain relatively straight headings, relying on celestial cues [13]. Cues such as sun position and polarized light are likely integrated throughout the sensory-motor pathway [14], including the highly conserved central complex [4, 15, 16]. Recently, a group of Drosophila central complex cells (E-PG neurons) have been shown to function as an internal compass [17, 18, 19], similar to mammalian head-direction cells [20]. Using an array of genetic tools, we set out to test whether flies can navigate using the sun and to identify the role of E-PG cells in this behavior. Using a flight simulator, we found that Drosophila adopt arbitrary headings with respect to a simulated sun, thus performing menotaxis, and individuals remember their heading preference between successive flights—even over several hours. Imaging experiments performed on flying animals revealed that the E-PG cells track sun stimulus motion. When these neurons are silenced, flies no longer adopt and maintain arbitrary headings relative to the sun stimulus but instead exhibit frontal phototaxis. Thus, without the compass system, flies lose the ability to execute menotaxis and revert to a simpler, reflexive behavior.
Does dispositional mindfulness moderate how individuals engage in their passions? An investigation into video games

ABSTRACTThe Dualistic Model of Passion (DMP) is an emerging framework in social psychology that assesses individuals’ passion for an activity. Although a passion parallels the definition for a seri...
The influence of personality on memory self-report among black and white older adults

Self-reported memory problems are often the first indicator of cognitive decline; however, they are inconsistently associated with objective memory performance and are known to be influenced by individual factors, such as personality. The current study examined the relationships between personality traits and self-reported memory problems in cognitively intact older adults, and whether these associations differ across Black and White older adults. Data were collected annually via in-person comprehensive medical and neuropsychological examinations as part of the Einstein Aging Study. Community-dwelling older adults in an urban, multi-ethnic area of New York City were interviewed. The current study included a total of 425 older adults (Mage = 76.68, SD = 4.72, 62.59% female; 72.00% White). Multilevel modeling tested the associations of neuroticism, conscientiousness, extraversion, openness, and agreeableness with self-reported memory problems. Results showed that neuroticism was positively related to frequency of memory problems and perceived ten-year memory decline only when other personality traits were not accounted for. Extraversion was negatively related to frequency of memory problems and perceived ten-year decline for both White and Black participants. However, conscientiousness was negatively related to perceived ten-year decline for Black participants only. Our findings highlight the importance of examining the association of all five personality traits with self-reported memory problems, as well as examining whether these associations differ for participants from different race/ethnicities.
Off-policy evaluation for slate recommendation

This paper studies the evaluation of policies that recommend an ordered set of items (e.g., a ranking) based on some context---a common scenario in web search, ads, and recommendation. We build on techniques from combinatorial bandits to introduce a new practical estimator that uses logged data to estimate a policy's performance. A thorough empirical evaluation on real-world data reveals that our estimator is accurate in a variety of settings, including as a subroutine in a learning-to-rank task, where it achieves competitive performance. We derive conditions under which our estimator is unbiased---these conditions are weaker than prior heuristics for slate evaluation---and experimentally demonstrate a smaller bias than parametric approaches, even when these conditions are violated. Finally, our theory and experiments also show exponential savings in the amount of required data compared with general unbiased estimators.
A polyhedron comparison theorem for 3-manifolds with positive scalar curvature

The study of comparison theorems in geometry has a rich history. In this paper, we establish a comparison theorem for polyhedra in 3-manifolds with nonnegative scalar curvature, answering affirmatively a dihedral rigidity conjecture by Gromov. For a large collections of polyhedra with interior non-negative scalar curvature and mean convex faces, we prove the dihedral angles along its edges cannot be everywhere less or equal than those of the corresponding Euclidean model, unless it is isometric to a flat polyhedron.
Reconfiguration graphs of shortest paths

Abstract For a graph G and a , b ∈ V ( G ) , the shortest path reconfiguration graph of G with respect to a and b is denoted by S ( G , a , b ) . The vertex set of S ( G , a , b ) is the set of all shortest paths between a and b in G . Two vertices in V ( S ( G , a , b ) ) are adjacent, if their corresponding paths in G differ by exactly one vertex. This paper examines the properties of shortest path graphs. Results include establishing classes of graphs that appear as shortest path graphs, decompositions and sums involving shortest path graphs, and the complete classification of shortest path graphs with girth 5 or greater. We include an infinite family of well structured examples, showing that the shortest path graph of a grid graph is an induced subgraph of a lattice.
Bayesian model averaging using the k -best Bayesian network structures

We study the problem of learning Bayesian network structures from data. We develop an algorithm for finding the k-best Bayesian network structures. We propose to compute the posterior probabilities of hypotheses of interest by Bayesian model averaging over the k-best Bayesian networks. We present empirical results on structural discovery over several real and synthetic data sets and show that the method outperforms the model selection method and the state-of-the-art MCMC methods.
Proper holomorphic self-maps of symmetric powers of balls

We show that each proper holomorphic self map of a symmetric power of the unit ball is an automorphism naturally induced by an automorphism of the unit ball, provided the ball is of dimension at least two.
Connecting discrete and continuum dislocation mechanics: A non-singular spectral framework

Abstract We present an improved framework of the spectral-based Discrete Dislocation Dynamics (DDD) approach introduced in (Bertin et al., 2015; Bertin and Capolungo, 2018), that establishes a direct connection with the continuum Field Dislocation Mechanics (FDM) approach. First, an analytical method to convert a discrete dislocation network to its continuous dislocation density tensor representation is developed. From there, the mechanical fields are evaluated using a FDM-based spectral framework, while submesh resolution elastic interactions are accounted for via the introduction of a rigorous stress splitting procedure that leverages properties of non-singular dislocation theories. The model results in a computationally efficient approach for DDD simulations that enables the use of elastic anisotropy and heterogeneities, while being compatible with recently developed subcycling time-integrators. As examples, the model is used to perform a work-hardening simulation, and potential applications that take advantage of the full-field nature of the method are explored, such as informing FDM models, and efficiently calculating virtual diffraction patterns.
Enumeration of lifts of commuting elements of a group

Abstract Given commuting elements a , b of a group G and a group epimorphism q : G ′ → G with finite kernel, the set of commuting lifts of a , b to G ′ is finite (possibly, empty). The second named author obtained a formula for the number of such lifts in terms of representations of Ker q. We apply this formula to several group epimorphisms q with the same kernel. In particular, we analyze the case where Ker q = Q 8 is the quaternion group. We show that in this case the number in question is equal to 0, 8, 16, 24, 40. We show that all these numbers are realized by some G , G ′ , q , a , b .
New bounds on cap sets

We provide an improvement over Meshulam's bound on cap sets in $F_3^N$. We show that there exist universal $\epsilon>0$ and $C>0$ so that any cap set in $F_3^N$ has size at most $C {3^N \over N^{1+\epsilon}}$. We do this by obtaining quite strong information about the additive combinatorial properties of the large spectrum.
A forest of linear fractional transformations

The Calkin–Wilf tree is a rooted infinite binary tree whose vertices are the positive rational numbers. Each number occurs in the tree exactly once and in the form a/b, where a and b are relatively prime positive integers. For every 2 × 2 matrix with nonnegative integral coordinates and nonzero determinant, it is possible to construct an analogous tree with this root. If the root is the identity matrix, then the tree consists of all matrices with determinant 1, and this tree possesses the basic properties of the Calkin–Wilf tree of positive rational numbers. The set of all matrices with nonnegative integral coordinates and nonzero determinant decomposes into a forest of rooted infinite binary trees.
Aggregation of affine estimators

We consider the problem of aggregating a general collection of affine estimators for fixed design regression. Relevant examples include some commonly used statistical estimators such as least squares, ridge and robust least squares estimators. Dalalyan and Salmon [DS12] have established that, for this problem, exponentially weighted (EW) model selection aggregation leads to sharp oracle inequalities in expectation, but similar bounds in deviation were not previously known. While results [DRZ12] indicate that the same aggregation scheme may not satisfy sharp oracle inequalities with high probability, we prove that a weaker notion of oracle inequality for EW that holds with high probability. Moreover, using a generalization of the newly introduced $Q$-aggregation scheme we also prove sharp oracle inequalities that hold with high probability. Finally, we apply our results to universal aggregation and show that our proposed estimator leads simultaneously to all the best known bounds for aggregation, including $\ell_{q}$-aggregation, $q\in(0,1)$, with high probability.
Partial rigidity of degenerate CR embeddings into spheres

Abstract In this paper, we study degenerate CR embeddings f of a strictly pseudoconvex hypersurface M ⊂ C n + 1 into a sphere S in a higher dimensional complex space C N + 1 . The degeneracy of the mapping f will be characterized in terms of the ranks of the CR second fundamental form and its covariant derivatives. In 2004, the author, together with X. Huang and D. Zaitsev, established a rigidity result for CR embeddings f into spheres in low codimensions. A key step in the proof of this result was to show that degenerate mappings are necessarily contained in a complex plane section of the target sphere (partial rigidity). In the 2004 paper, it was shown that if the total rank d of the second fundamental form and all of its covariant derivatives is n (here, n is the CR dimension of M ), then f ( M ) is contained in a complex plane of dimension n + d + 1 . The converse of this statement is also true, as is easy to see. When the total rank d exceeds n , it is no longer true, in general, that f ( M ) is contained in a complex plane of dimension n + d + 1 , as can be seen by examples. In this paper, we carry out a systematic study of degenerate CR mappings into spheres. We show that when the ranks of the second fundamental form and its covariant derivatives exceed the CR dimension n , then partial rigidity may still persist, but there is a “defect” k that arises from the ranks exceeding n such that f ( M ) is only contained in a complex plane of dimension n + d + k + 1 . Moreover, this defect occurs in general, as is illustrated by examples.
Embedding Constrained Model Predictive Control in a Continuous-Time Dynamic Feedback

This paper introduces a continuous-time constrained control strategy, which mimics the behavior of a traditional model predictive control scheme using dynamic feedback. The approach is based on the idea that the solution of the optimal control problem can be embedded in the internal states of a dynamic control law running in parallel to the system. Using input-to-state stability arguments, it is shown that if the controller dynamics are sufficiently fast with respect to the plant dynamics, the interconnection between the two systems is asymptotically stable. Additionally, it is shown that, by augmenting the proposed scheme with an add-on unit known as an explicit reference governor, it is possible to guarantee recursive feasibility and limit the residual of the optimal control problem, regardless of any changes in the desired set point. Numerical examples featuring aerospace applications demonstrate the effectiveness of the proposed scheme.
Local Maxima in the Likelihood of Gaussian Mixture Models: Structural Results and Algorithmic Consequences

We provide two fundamental results on the population (infinite-sample) likelihood function of Gaussian mixture models with $M \geq 3$ components. Our first main result shows that the population likelihood function has bad local maxima even in the special case of equally-weighted mixtures of well-separated and spherical Gaussians. We prove that the log-likelihood value of these bad local maxima can be arbitrarily worse than that of any global optimum, thereby resolving an open question of Srebro (2007). Our second main result shows that the EM algorithm (or a first-order variant of it) with random initialization will converge to bad critical points with probability at least $1-e^{-\Omega(M)}$. We further establish that a first-order variant of EM will not converge to strict saddle points almost surely, indicating that the poor performance of the first-order method can be attributed to the existence of bad local maxima rather than bad saddle points. Overall, our results highlight the necessity of careful initialization when using the EM algorithm in practice, even when applied in highly favorable settings.
On the optimality equation for average cost Markov decision processes and its validity for inventory control

As is well known, average-cost optimality inequalities imply the existence of stationary optimal policies for Markov decision processes with average costs per unit time, and these inequalities hold under broad natural conditions. This paper provides sufficient conditions for the validity of the average-cost optimality equation for an infinite state problem with weakly continuous transition probabilities and with possibly unbounded one-step costs and noncompact action sets. These conditions also imply the convergence of sequences of discounted relative value functions to average-cost relative value functions and the continuity of average-cost relative value functions. As shown in this paper, the classic periodic-review setup-cost inventory control problem with backorders and convex holding/backlog costs satisfies these conditions. Therefore, the optimality inequality holds in the form of an equality with a continuous average-cost relative value function for this problem. In addition, the K-convexity of discounted relative value functions and their convergence to average-cost relative value functions, when the discount factor increases to 1, imply the K-convexity of average-cost relative value functions. This implies that average-cost optimal (s, S) policies for the inventory control problem can be derived from the average-cost optimality equation.
Computing Approximate PSD Factorizations

We give an algorithm for computing approximate PSD factorizations of nonnegative matrices. The running time of the algorithm is polynomial in the dimensions of the input matrix, but exponential in the PSD rank and the approximation error. The main ingredient is an exact factorization algorithm when the rows and columns of the factors are constrained to lie in a general polyhedron. This strictly generalizes nonnegative matrix factorizations which can be captured by letting this polyhedron to be the nonnegative orthant.
Limit-periodic Verblunsky coefficients for orthogonal polynomials on the unit circle

Abstract Avila recently introduced a new method for the study of the discrete Schrodinger operator with limit-periodic potential. I adapt this method to the context of orthogonal polynomials in the unit circle with limit-periodic Verblunsky coefficients. Specifically, I represent these two-sided Verblunsky coefficients as a continuous sampling of the orbits of a Cantor group by a minimal translation. I then investigate the measures that arise on the unit circle as I vary the sampling function. I show that generically the spectrum is a Cantor set and we have empty point spectrum. Furthermore, there exists a dense set of sampling functions for which the corresponding spectrum is a Cantor set of positive Lebesgue measure, and all corresponding spectral measures are purely absolutely continuous.
Strategies to Design Signals to Spoof Kalman Filter

We study the problem of designing spoofing signals to corrupt and mislead the output of a Kalman filter. Unlike existing works that focus on detection and filtering algorithms for the observer, we study the problem from the attacker's point-of-view. In our model, the attacker can corrupt the measurements by adding spoofing signals. The attacker seeks to create a separation between the estimate of the Kalman filter with and without spoofing signals. We present a number of results on how to generate such spoofing signals, while minimizing the signal magnitude. The resulting algorithms are evaluated through simulations along with theoretical proofs.
Bandit Learning with Positive Externalities

In many platforms, user arrivals exhibit a self-reinforcing behavior: future user arrivals are likely to have preferences similar to users who were satisfied in the past. In other words, arrivals exhibit {\em positive externalities}. We study multiarmed bandit (MAB) problems with positive externalities. We show that the self-reinforcing preferences may lead standard benchmark algorithms such as UCB to exhibit linear regret. We develop a new algorithm, Balanced Exploration (BE), which explores arms carefully to avoid suboptimal convergence of arrivals before sufficient evidence is gathered. We also introduce an adaptive variant of BE which successively eliminates suboptimal arms. We analyze their asymptotic regret, and establish optimality by showing that no algorithm can perform better.
Sherlock: sparse hierarchical embeddings for visually-aware one-class collaborative filtering

Building successful recommender systems requires uncovering the underlying dimensions that describe the properties of items as well as users' preferences toward them. In domains like clothing recommendation, explaining users' preferences requires modeling the visual appearance of the items in question. This makes recommendation especially challenging, due to both the complexity and subtlety of people's 'visual preferences,' as well as the scale and dimensionality of the data and features involved. Ultimately, a successful model should be capable of capturing considerable variance across different categories and styles, while still modeling the commonalities explained by 'global' structures in order to combat the sparsity (e.g. cold-start), variability, and scale of real-world datasets. Here, we address these challenges by building such structures to model the visual dimensions across different product categories. With a novel hierarchical embedding architecture, our method accounts for both high-level (colorfulness, darkness, etc.) and subtle (e.g. casualness) visual characteristics simultaneously.
A Simple Cache Model for Image Recognition

Training large-scale image recognition models is computationally expensive. This raises the question of whether there might be simple ways to improve the test performance of an already trained model without having to re-train or even fine-tune it with new data. Here, we show that, surprisingly, this is indeed possible. The key observation we make is that the layers of a deep network close to the output layer contain independent, easily extractable class-relevant information that is not contained in the output layer itself. We propose to extract this extra class-relevant information using a simple key-value cache memory to improve the classification performance of the model at test time. Our cache memory is directly inspired by a similar cache model previously proposed for language modeling (Grave et al., 2017). This cache component does not require any training or fine-tuning; it can be applied to any pre-trained model and, by properly setting only two hyper-parameters, leads to significant improvements in its classification performance. Improvements are observed across several architectures and datasets. In the cache component, using features extracted from layers close to the output (but not from the output layer itself) as keys leads to the largest improvements. Concatenating features from multiple layers to form keys can further improve performance over using single-layer features as keys. The cache component also has a regularizing effect, a simple consequence of which is that it substantially increases the robustness of models against adversarial attacks.
Capturing the Dynamical Repertoire of Single Neurons with Generalized Linear Models.

A key problem in computational neuroscience is to find simple, tractable models that are nevertheless flexible enough to capture the response properties of real neurons. Here we examine the capabil...
Dynamic Infrared Electro-optic Response of Soluble Organic Semiconductors in Thin Film Transistors

We use a frequency-dependent electro-optic technique to measure the hole mobility in small molecule organic semiconductors, such as 6,13 bis(triisopropylsilylethynyl)-pentacene. Measurements are made on semiconductor films in bottom gate, bottom contact field-effect transistors (FETs.) Because of the buried metal layer effect the maximum response, due to absorption in the charge layer, will be for a dielectric film ∼ 1/4 of a wavelength (in the dielectric) (e.g. ∼ 1 micron thick in the infrared.) Results are presented for FETs prepared with both spin-cast polymer and alumina dielectrics prepared by atomic layer deposition. At low frequencies the results are fit to solutions to a non-linear differential equation describing the spatial dependence of flowing charge in the FET channel, which allows us to study multiple crystals forming across one set of drain-source contacts. FETs prepared on alumina dielectrics show interesting deviations from the model at high frequencies, possibly due to increased contact impedance.
Kepler Planet Occurrence Rates for Mid-type M Dwarfs as a Function of Spectral Type

Previous studies of planet occurrence rates largely relied on photometric stellar characterizations. In this paper, we present planet occurrence rates for mid-type M dwarfs using spectroscopy, parallaxes, and photometry to determine stellar characteristics. Our spectroscopic observations have allowed us to constrain spectral type, temperatures, and, in some cases, metallicities for 337 out of 561 probable mid-type M dwarfs in the primary Kepler field. We use a random forest classifier to assign a spectral type to the remaining 224 stars. Combining our data with Gaia parallaxes, we compute precise (~3%) stellar radii and masses, which we use to update planet parameters and occurrence rates for Keplermid-type M dwarfs. Within the Kepler field, there are seven M3 V to M5 V stars that host 13 confirmed planets between 0.5 and 2.5 Earth radii and at orbital periods between 0.5 and 10 days. For this population, we compute a planet occurrence rate of 1.19^(+0.70)_(−0.49) planets per star. For M3 V, M4 V, and M5 V, we compute planet occurrence rates of 0.86^(+1.32)_(−0.68), 1.36^(+2.30)_(−1.02), and 3.07^(+5.49)_(−2.4) planets per star, respectively.
Fingerprint Match in Box

We open source fingerprint Match in Box, a complete end-to-end fingerprint recognition system embedded within a 4 inch cube. Match in Box stands in contrast to a typical bulky and expensive proprietary fingerprint recognition system which requires sending a fingerprint image to an external host for processing and subsequent spoof detection and matching. In particular, Match in Box is a first of a kind, portable, low-cost, and easy-to-assemble fingerprint reader with an enrollment database embedded within the reader’s memory and fingerprint spoof detector, feature extractor, and matcher all running on the reader’s internal vision processing unit (VPU). An onboard touch screen and rechargeable battery pack make this device extremely portable and ideal for applying both fingerprint authentication (1:1 comparison) and fingerprint identification (1:N search) to applications (vaccination tracking, food and benefit distribution programs, human trafficking prevention) in rural communities, especially in developing countries. We also show that Match in Box is suited for capturing neonate fingerprints due to its high resolution (1900 ppi) cameras.
Lattice surfaces and smallest triangles

We calculate the area of the smallest triangle and the area of the smallest virtual triangle for many known lattice surfaces. We show that our list of the lattice surfaces for which the area of the smallest virtual triangle greater than $$1\over 20$$ is complete. In particular, this means that there are no new lattice surfaces for which the area of the smallest virtual triangle is greater than .05. Our method follows an algorithm described by Smillie and Weiss and improves on it in certain respects.
Enhanced basic procedures for the projection and rescaling algorithm

Using an efficient algorithmic implementation of Caratheodory’s theorem, we propose three enhanced versions of the projection and rescaling algorithm’s basic procedures. Each of these enhanced procedures improves upon the order of complexity of its analogue in Pena and Soheili (Math Program 166(1):87–111, 2017) when the dimension of the subspace is sufficiently smaller than the dimension of its ambient space.
Lifestyle Tradeoffs and the Decline of Societal Well-Being: An Agent-Based Model

This paper presents a semi-quantitative mathematical model of the changes over time in the statis- tical distribution of well-being of individuals in a society. The model predicts that when individuals overvalue the more socially conspicuous aspects of well-being in their lifestyle choices, then the average well-being of the overall population may experience continuous decline. In addition to tradeo cost and overvaluation, we identify statistical variation in individuals' well-being and turnover within the population as key factors driv- ing negative trends. We investigate the influence of the eects of heterogeneity in the population, as well as economic and/or technological progress.
CBMV: A Coalesced Bidirectional Matching Volume for Disparity Estimation

Recently, there has been a paradigm shift in stereo matching with learning-based methods achieving the best results on all popular benchmarks. The success of these methods is due to the availability of training data with ground truth; training learning-based systems on these datasets has allowed them to surpass the accuracy of conventional approaches based on heuristics and assumptions. Many of these assumptions, however, had been validated extensively and hold for the majority of possible inputs. In this paper, we generate a matching volume leveraging both data with ground truth and conventional wisdom. We accomplish this by coalescing diverse evidence from a bidirectional matching process via random forest classifiers. We show that the resulting matching volume estimation method achieves similar accuracy to purely data-driven alternatives on benchmarks and that it generalizes to unseen data much better. In fact, the results we submitted to the KITTI and ETH3D benchmarks were generated using a classifier trained on the Middlebury 2014 dataset.
Power regulation in high performance multicore processors

This paper presents, implements, and evaluates a power-regulation technique for multicore processors, based on an integral controller with adjustable gain. The gain is designed for wide stability margins, and computed in real time as part of the control law. The tracking performance of the control system is robust with respect to modeling uncertainties and computational errors in the loop. The main challenge of designing such a controller is that the power dissipation of program-workloads varies widely and often cannot be measured accurately; hence extant controllers are either ad hoc or based on a-priori modeling characterizations of the processor and workloads. Our approach is different. Leveraging the aforementioned robustness it uses a simple textbook modeling framework, and adjusts its parameters in real time by a system-identification module. In this it trades modeling precision for fast computations in the loop making it suitable for on-line implementation in commodity data-center processors. Consequently, the proposed controller is agnostic in the sense that it does not require apriori system characterizations. We present an implementation of the controller on Intel's fourth-generation microarchitecture, Haswell, and test it on industry benchmark programs which are used in datacenter applications. Results of these experiments are presented in detail exposing some practical challenges of implementing provably-convergent power regulation solutions in commodity multicore processors.
On some quiver determinantal varieties

Abstract We introduce certain quiver analogue of the determinantal variety. We study the Kempf–Lascoux–Weyman complex associated to a line bundle on the variety. In the case of generalized Kronecker quivers, we give a sufficient condition on when the complex resolves a maximal Cohen–Macaulay module supported on the quiver determinantal variety. This allows us to find the set-theoretical defining equations of these varieties. When the variety has codimension one, the only irreducible polynomial function is a relative tensor invariant. As a by-product, we find some vanishing condition for the Kronecker coefficients. In the end, we make a generalization from the quiver setting to the tensor setting.