cssi/SciSciGPT-SciSciNet huggingface dataset:
Specialized coding of sensory, motor and cognitive variables in VTA dopamine neurons

There is increased appreciation that dopamine neurons in the midbrain respond not only to reward1 and reward-predicting cues1,2, but also to other variables such as the distance to reward3, movements4-9 and behavioural choices10,11. An important question is how the responses to these diverse variables are organized across the population of dopamine neurons. Whether individual dopamine neurons multiplex several variables, or whether there are subsets of neurons that are specialized in encoding specific behavioural variables remains unclear. This fundamental question has been difficult to resolve because recordings from large populations of individual dopamine neurons have not been performed in a behavioural task with sufficient complexity to examine these diverse variables simultaneously. Here, to address this gap, we used two-photon calcium imaging through an implanted lens to record the activity of more than 300 dopamine neurons from the ventral tegmental area of the mouse midbrain during a complex decision-making task. As mice navigated in a virtual-reality environment, dopamine neurons encoded an array of sensory, motor and cognitive variables. These responses were functionally clustered, such that subpopulations of neurons transmitted information about a subset of behavioural variables, in addition to encoding reward. These functional clusters were spatially organized, with neighbouring neurons more likely to be part of the same cluster. Together with the topography between dopamine neurons and their projections, this specialization and anatomical organization may aid downstream circuits in correctly interpreting the wide range of signals transmitted by dopamine neurons.
Oxidative-substitution reactions of polycyclic aromatic hydrocarbons with iodine(III) sulfonate reagents

Polycyclic aromatic hydrocarbons (PAH) undergo regioselective oxidative-substitution reactions with iodine(III) sulfonate reagents in dichloromethane to give the corresponding aryl sulfonate esters. The use of [hydroxy(tosyloxy)iodo]benzene in conjunction with trimethylsilyl isothiocyanate leads to thiocyanation of the PAH nucleus.
Efficient synthesis of protected 3′-deoxyadenosine and 3′-deoxyguanosine from adenosine and guanosine

Abstract Highly efficient synthesis of protected 3′-deoxyadenosine and 3′-deoxyguanosine from adenosine and guanosine were described. The 2′,3′-diol of protected adenosine and guanosine were reacted with α-acetoxyisobutyryl bromide to yield 9-(2′- O -acetyl-3′-bromo-5′- O - tert -butyldiphenylsilyl-3′-deoxy-β- d -xylofuranosyl)-6- N -benzoyl adenine and 9-(2′- O -acetyl-3′-bromo-5′- O - tert -butyldiphenylsilyl-3′-deoxy-β- d -xylofuranosyl)-2- N -( N ′, N ′-dimethylaminomethylene) guanine and subsequently heated with tri- n -butyltin hydride in the presence of 2,2′-azobisisobutyronitrile to afford the protected 3′-deoxyadenosine and 3′-deoxyguanosine in 66–73% over all yield.
High-resolution mapping of heteroduplex DNA formed during UV-induced and spontaneous mitotic recombination events in yeast

In yeast, DNA breaks are usually repaired by homologous recombination (HR). An early step for HR pathways is formation of a heteroduplex, in which a single-strand from the broken DNA molecule pairs with a strand derived from an intact DNA molecule. If the two strands of DNA are not identical, there will be mismatches within the heteroduplex DNA (hetDNA). In wild-type strains, these mismatches are repaired by the mismatch repair (MMR) system, producing a gene conversion event. In strains lacking MMR, the mismatches persist. Most previous studies involving hetDNA formed during mitotic recombination were restricted to one locus. Below, we present a global mapping of hetDNA formed in the MMR-defective mlh1 strain. We find that many recombination events are associated with repair of double-stranded DNA gaps and/or involve Mlh1-independent mismatch repair. Many of our events are not explicable by the simplest form of the double-strand break repair model of recombination.
Exploring Thallium Compounds as Thermoelectric Materials: Seventeen New Thallium Chalcogenides

We have begun investigating thallium-containing compounds as candidate thermoelectric materials. Alkali metal chalcogenide systems have produced compounds with promising thermoelectric properties, and the chemistry of the Tl+ cation is similar to that of the alkali metals. However, Tl is less electropositive and heavier than all alkali metals (except Fr). This may lead to compounds with lower electrical resistivity and lower thermal conductivity, both important for thermoelectric performance. Unlike the alkali metals, Tl+ has a lone pair of electrons which can be stereochemically active and can influence coordination geometries. Here we report the results of our initial study of quaternary Tl chalcogenide systems. We present the synthesis and structure of 17 new compounds. Some are isostructural to known alkali metal compounds, and some are new structure types. We discuss the activity of the Tl lone pairs. In addition, we have measured the thermoelectric properties (electrical resistivity, thermal conduct...
Multiphase assembly of mesoporous-macroporous membranes

A novel procedure has been developed for the synthesis of spongelike silica membranes with three-dimensional meso−macrostructures. The process utilizes multiphase media comprised of a mesoscopically ordered block copolymer/silica phase that macroscopically separates from an electrolyte phase. This results in hierarchically organized composite structures whose different characteristic length scales can be independently adjusted.
A facile method for the preparation of functionalized 2-halo-1-olefins.

Highly functionalized 2-halo-1-olefins were prepared by the reaction of functionalized organozinc halides with 2,3-dihalopropene catalyzed by Cu(I) salts. Yields are high to excellent.
Thy1 (CD90) expression is regulated by DNA methylation during adipogenesis

The obesity epidemic is developing into the most costly health problem facing the world. Obesity, characterized by excessive adipogenesis and enlarged adipocytes, promotes morbidities, such as diabetes, cardiovascular disease, and cancer. Regulation of adipogenesis is critical to our understanding of how fat cell formation causes obesity and associated health problems. Thy1 (also called CD90), a widely used stem cell marker, blocks adipogenesis and reduces lipid accumulation. Thy1-knockout mice are prone to diet-induced obesity. Although the importance of Thy1 in adipogenesis and obesity is now evident, how its expression is regulated is not. We hypothesized that DNA methylation has a role in promoting adipogenesis and affects Thy1 expression. Using the methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-dC), we investigated whether DNA methylation alters Thy1 expression during adipogenesis in both mouse 3T3-L1 preadipocytes and mouse mesenchymal stem cells. Thy1 protein and mRNA levels were decreased dramatically during adipogenesis. However, 5-aza-dC treatment prevented that phenomenon. Methylation-sensitive pyrosequencing analysis showed that CpG sites at the Thy1 locus have increased methylation during adipogenesis, as well as increased methylation in adipose tissue from diet-induced obese mice. These new findings highlight the potential role of Thy1 and DNA methylation in adipogenesis and obesity.-Flores, E. M., Woeller, C. F., Falsetta, M. L., Susiarjo, M., Phipps, R. P. Thy1 (CD90) expression is regulated by DNA methylation during adipogenesis.
Studies on the Synthesis of Nargenicin A1: Highly Stereoselective Synthesis of the Complete Carbon Framework via the Transannular Diels−Alder Reaction of an 18-Membered Macrolide

A synthesis of the complete carbon skeleton of the nargenicins, represented by tricyclic lactone 45, is described. The key step of the synthesis of 45 is the Yamaguchi macrolactonization of hydroxy acid 44 which is followed by the facile transannular Diels−Alder reaction of the 18-membered macrolide 22. This sequence provides tricycle 45 in 66% yield, along with a 14% yield of tricycle 46 which is epimeric at C(10). Macrolide 22 was obtained in 38% yield when the macrolactonization was performed at 80 °C. The transannular Diels−Alder reaction of 22 at 80 °C provided tricycle 45 as the exclusive product (85% yield). In contrast, the intramolecular Diels−Alder reaction of seco ester 43 provided a mixture of trans-fused 47 in 56% yield and the desired cis-fused cycloadduct 48 in only 27% yield. Two independent stereochemical control features determine the success of the transannular Diels−Alder reaction of 22: the C(6)−Br steric directing group that dictates that only one of the two faces of the diene is ac...
A framework for genomics-informed ecophysiological modeling in plants

Dynamic process-based plant models capture complex physiological response across time, carrying the potential to extend simulations out to novel environments and lend mechanistic insight to observed phenotypes. Despite the translational opportunities for varietal crop improvement that could be unlocked by linking natural genetic variation to first principles-based modeling, these models are challenging to apply to large populations of related individuals. Here we use a combination of model development, experimental evaluation, and genomic prediction in Brassica rapa L. to set the stage for future large-scale process-based modeling of intraspecific variation. We develop a new canopy growth submodel for B. rapa within the process-based model Terrestrial Regional Ecosystem Exchange Simulator (TREES), test input parameters for feasibility of direct estimation with observed phenotypes across cultivated morphotypes and indirect estimation using genomic prediction on a recombinant inbred line population, and explore model performance on an in silico population under non-stressed and mild water-stressed conditions. We find evidence that the updated whole-plant model has the capacity to distill genotype by environment interaction (G×E) into tractable components. The framework presented offers a means to link genetic variation with environment-modulated plant response and serves as a stepping stone towards large-scale prediction of unphenotyped, genetically related individuals under untested environmental scenarios.
Preparation of allylsilanes via cross-metathesis

Abstract Allylsilanes are prepared by simple metathetical cross-coupling of terminal olefins with allyltrimethylsilane. Allytrimethylsilane coupling with π-substituted terminal olefins (styrenes, 1-phenyl-1,3-butadiene, and acrylonitrile) proceeds in excellent yield and very high selectivity. Lower, but still useful, selectivities are observed for allyltrimethylsilane/alkyl olefin cross-metathesis reactions.
Ligand-centered reactivity of organometallic radicals

Abstract Due to the increasing number of odd-electron organometallic species implicated in catalytic processes, interest in such compounds has risen. Although the prior emphasis in the literature was on metal-centered reactivity, reports of radical reactivity within ligands have recently become more common and a wider variety of reactions have been observed. This review serves as an overview of ligand-centered reactions of organometallic radicals with emphasis on the recent literature.
Synthesis of (±)-licarin B and eupomatenoids-1 and -12: A general approach to 2-aryl-7-alkoxy-benzofuranoid neolignans

Abstract New syntheses of the title compounds are described using Lewis acid-promoted reactions of styrenes with N-phenylsulfonyl-1,4-benzoquinone monoimines to regioselectively form the 2-arylbenzofuranoid ring system followed by conversion of the aromatic N-phenylsulfonyl moiety into a propenyl substituent.
Stereospecific tetracyclization of icosatetraenes via Mn(III) promoted oxidative free-radical cyclization

Abstract A stereospecific oxidative free-radical cyclization of polyene 10a to the D-homi-5α-androstane system 11a containing seven asymmetric centers is reported.
Dimetalation of pyrazines. a one-pot synthesis of multisubstituted pyrazine C-nucleosides.

As a part of our efforts to pursue direct, convergent, and concise methodologies for the synthesis of pyrazine C-nucleosides, we have successfully established a sequential dilithiation−addition method, which allows one to introduce two different functional groups to a pyrazine ring in a one-pot fashion. 2,6-Dichloropyrazine was dilithiated at −100 °C and then allowed to react with an electrophile, such as bromine, iodine, or disulfides, followed by a reaction with a protected ribonolactone to afford C-nucleosides. After reduction and deprotection, tetrasubstituted pyrazine C-nucleosides, including 2,6-dichloro-3-iodo-5-(β-d-ribofuranosyl)pyrazine and 2-bromo-3,5-dichloro-6-(β-d-ribofuranosyl)pyrazine, were obtained. A tandem reaction sequence occurred when disulfides were used, resulting in the formation of 5,6-bis-methylthio-2-chloro-3-(β-d-ribofuranosyl)pyrazine and 6-(β-d-ribofuranosyl)-2,3,5-tris-phenylthiopyrazine.
Orally active, hydrolytically stable, semisynthetic, antimalarial trioxanes in the artemisinin family

In only three chemical operations, natural trioxane lactone artemisinin (1) was converted into a series of C-10 carbon-substituted 10-deoxoartemisinin compounds 4-9. The three steps involved lactone reduction, replacement of the anomeric lactol OH by F using diethylaminosulfur trifluoride, and finally boron trifluoride-promoted substitution of F by aryl, heteroaryl, and acetylide nucleophiles. All of these C-10 nonacetal, chemically robust, enantiomerically pure compounds 4-9 have high antimalarial potencies in vitro against Plasmodium falciparum malaria parasites, and furans 5a and 5b and pyrrole 7a are antimalarially potent also in vivo even when administered to rodents orally.
Synthesis and Characterization of All-Alkyl-Substituted Mono-, Di-, and Trioxosapphyrins

The synthesis and characterization of the following heterosapphyrins is presented: 3,7,18,22-tetraethyl-2,8,12,13,17,23-hexamethyl-27-oxasapphyrin (5), 3,8,12,13,17,22-hexaethyl-2,7,18,23-tetramethyl-15,29-dioxasapphyrin (6), and 3,7,18,22-tetraethyl-2,8,12,13,17,23-hexamethyl-15,27,29-trioxasapphyrin (7). These macrocycles were synthesized from the hitherto unknown precursors methyl 3,4-dimethylfuran-2-carboxylate (11) and methyl 4-ethyl-3-methylfuran-2-carboxylate (12). Single-crystal X-ray diffraction structures of the bis(hydrochloric acid) salt (5a) and the bis(trifluoroacetic acid) salt (5b) of 5 and of the bis(hydrochloric acid) salt (6a) of 6 were obtained. These structures are compared to those of the parent all-aza sapphyrin 4. In this context, we report the first solid-state structural analysis of a trifluoroacetic acid salt of sapphyrin (4b). Crystals of 5a are triclinic, space group P1 in a cell of the dimensions a = 11.9686(13) A, b = 12.790(2) A, c = 16.236(2) A, α = 80.924(10)°, β = 88.8...
Application of chiral lithium amide bases to the thia-Sommelet dearomatization reaction

Thia-Sommelet dearomatization reactions of benzylsulfonium ylides can create highly congested quaternary centers. Chiral bis-lithium amide bases were shown to effect enantiotopic deprotonation of benzylsulfonium ions, leading to thia-Sommelet rearrangement. The chiral trienes were generated in up to 50% ee.
Synthesis, Crystal Structure, and Magnetic Properties of Novel Intermetallic Compounds R2Co2SiC (R = Pr, Nd)

The intermetallic compounds R2Co2SiC (R = Pr, Nd) were prepared from the reaction of silicon and carbon in either Pr/Co or Nd/Co eutectic flux. These phases crystallize with a new stuffed variant of the W2CoB2 structure type in orthorhombic space group Immm with unit cell parameters a = 3.978(4) A, b = 6.094(5) A, c = 8.903(8) A (Z = 2; R1 = 0.0302) for Nd2Co2SiC. Silicon, cobalt, and carbon atoms form two-dimensional flat sheets, which are separated by puckered layers of rare-earth cations. Magnetic susceptibility measurements indicate that the rare earth cations in both analogues order ferromagnetically at low temperature (TC ≈ 12 K for Nd2Co2SiC and TC ≈ 20 K for Pr2Co2SiC). Single-crystal neutron diffraction data for Nd2Co2SiC indicate that Nd moments initially align ferromagnetically along the c axis around ∼12 K, but below 11 K, they tilt slightly away from the c axis, in the ac plane. Electronic structure calculations confirm the lack of spin polarization for Co 3d moments.
Excised linear introns regulate growth in yeast

Spliceosomal introns are ubiquitous non-coding RNAs that are typically destined for rapid debranching and degradation. Here we describe 34 excised introns in Saccharomyces cerevisiae that-despite being rapidly degraded in log-phase growth-accumulate as linear RNAs under either saturated-growth conditions or other stresses that cause prolonged inhibition of TORC1, which is a key integrator of growth signalling. Introns that become stabilized remain associated with components of the spliceosome and differ from other spliceosomal introns in having a short distance between their lariat branch point and 3' splice site, which is necessary and sufficient for their stabilization. Deletion of these unusual introns is disadvantageous in saturated conditions and causes aberrantly high growth rates in yeast that are chronically challenged with the TORC1 inhibitor rapamycin. The reintroduction of native or engineered stable introns suppresses this aberrant rapamycin response. Thus, excised introns function within the TOR growth-signalling network of S. cerevisiae and, more generally, excised spliceosomal introns can have biological functions.
Highly efficient and highly enantioselective asymmetric hydrogenation of ketones with TunesPhos/1,2-diamine-ruthenium(II) complexes.

The TunePhos/diamine−Ru(II) complex combined with t-BuOK in 2-propanol effectively catalyzes enantioselective hydrogenation of a wide range of simple ketones including aromatic, heteroaromatic, α,β-unsaturated, and cyclopropyl ketones, affording high reactivity (up to 1 000 000 TON) and excellent enantioselectivities (>99% ee for 13 examples).
The regioselective mono-deprotection of 1,3-dioxa-2,2-(di-tert-butyl)-2-silacyclohexanes with BF3*SMe2.

The selective mono-deprotection of di-tert-butylsilylene ethers prepared from substituted 1,3-pentanediols and 2,4-hexanediols has been achieved with BF3·SMe2. The reaction conditions are compatible with esters, allyl ethers, and TIPS ethers. The resulting di-tert-butylfluorosilyl ethers are stable to various conditions including low pH aqueous solutions and silica gel chromatography; the di-tert-butylfluorosilyl ethers are readily cleaved with HF−pyridine. Substrate stereochemistry and conformation influences the efficiency of the deprotection, while the deprotection regiochemistry is consistent with coordination of boron to the sterically more accessible oxygen prior to intramolecular delivery of fluoride.
U(VI) uranyl cation-cation interactions in framework germanates.

The isomorphous compounds NH4[(UO6)2(UO2)9(GeO4)(GeO3(OH))] (1), K[(UO6)2(UO2)9(GeO4)(GeO3(OH))] (2), Li3O[(UO6)2(UO2)9(GeO4)(GeO3(OH))] (3), and Ba[(UO6)2(UO2)9(GeO4)2] (4) were synthesized by hyd...
Role of the Properties and Structure of Liquid Water in Colloidal and Interfacial Systems

The interaction between water and solid surfaces is of great interest to geological materials, polymers, biomaterials, cells, microbes, other particles, etc. Yet little is still known about the str...
Potent HIV-1 Protease Inhibitors: Stereoselective Synthesis of a Dipeptide Mimic.

The synthesis of a differentially protected dipeptide mimic 10 in enantiomerically pure form is described. The key step involves the epimerization of the C-2 center of the lactone 4, hydrolysis and protection of the resulting hydroxy acid, followed by Curtius rearrangement to introduce the urethane functionality. The scope and versatility of this isostere has been demonstrated by its conversion to potent HIV-1 protease inhibitors with nanomolar potencies. Also, established through the synthesis of compound 13 and 14, the 3S hydroxyl configuration of the dipeptide isostere 1 is the preferred configuration for its potency. The present synthesis is efficient and provides an access to other dipeptide mimics with a great deal of structural diversity.
Nonquenchable chemical order-disorder phase transition in yttrium oxyfluoride

A chemical order−disorder polymorphic phase transition in yttrium oxyfluoride (YOF) was studied in situ by X-ray and neutron powder diffraction. The high-temperature form of YOF crystallizes with a cubic Fmm fluorite structure in which the O and F atoms are disordered among the tetrahedrally coordinated sites. The low-temperature form of YOF exhibits rhombohedral Rm symmetry and evolves from the high-temperature form by the phase transition associated with the ordering of the O and F atoms. The transition occurs around 560 °C. The superstructure contains layers of [OY4] and [FY4] tetrahedra alternating along the c-axis of the trigonal cell (parallel to the direction of the parent cubic structure). The ordering of the O and F atoms is accompanied by the significant displacements of the Y, O, and F atoms from their ideal positions in the cubic phase. Bond valence sum calculations indicate considerable bond strain for both O and F in the cubic structure; the strain is relieved in the ordered low-temperature phase. The order−disorder transition in YOF is completely reversible and exhibits fast nonquenchable kinetics. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Synthesis of Nonracemic 2-Vinyl-monoprotected 1,3-Diols from the Reactions of Chiral Allylstannanes with Aldehydes

Abstract A new approach for the synthesis of 2-vinyl monoprotected 1,3-diols has been developed. By employing different Lewis acid, either anti-anti or anti-syn stereoisomer can be selectively prepared.
Informational Efficiency in Securitization after Dodd-Frank

We analyze how Dodd-Frank mandated risk retention affects the information investors extract from issuers' retention choices in the CMBS market. We show that the required retention level is both binding and stringent. Although this implies issuers cannot signal using the level of retention, we provide a model showing that signaling can occur by varying retention structure. The model is consistent with spreads being empirically lower in deals with a purely first-loss retention structure. A stated concern of rulemakers was asymmetric information. However, we show that, post-crisis, the level of asymmetric information in this market is quite low.
Is the addition of higher-order interactions in ecological models increasing the understanding of ecological dynamics?

Abstract Recent work has shown that higher-order terms in population dynamics models can increase the stability, promote the diversity, and better explain the dynamics of ecological systems. While it is known that these perceived benefits come from an increasing number of alternative solutions given by the nature of multivariate polynomials, this mathematical advantage has not been formally quantified. Here, we develop a general method to quantify the mathematical advantage of adding higher-order interactions in ecological models based on the number of free-equilibrium points that can emerge in a system (i.e., equilibria that can be feasible or unfeasible as a function of model parameters). We apply this method to calculate the number of free-equilibrium points in Lotka–Volterra dynamics. While it is known that Lotka–Volterra models without higher-order interactions only have one free-equilibrium point regardless of the number of parameters, we find that by adding higher-order terms this number increases exponentially with the dimension of the system. Hence, the number of free-equilibrium points can be used to compare more fairly between ecological models. Our results suggest that while adding higher-order interactions in ecological models may be good for prediction purposes, they cannot provide additional explanatory power of ecological dynamics if model parameters are not ecologically restricted.
Generalized Center Problems with Outliers

We study the ℱ-center problem with outliers: Given a metric space (X,d), a general down-closed family ℱ of subsets of X, and a parameter m, we need to locate a subset S ∈ ℱ of centers such that the maximum distance among the closest m points in X to S is minimized. Our main result is a dichotomy theorem. Colloquially, we prove that there is an efficient 3-approximation for the ℱ-center problem with outliers if and only if we can efficiently optimize a poly-bounded linear function over ℱ subject to a partition constraint. One concrete upshot of our result is a polynomial time 3-approximation for the knapsack center problem with outliers for which no (true) approximation algorithm was known.
Subpolynomial trace reconstruction for random strings \{and arbitrary deletion probability

The insertion-deletion channel takes as input a bit string ${\bf x}\in\{0,1\}^{n}$, and outputs a string where bits have been deleted and inserted independently at random. The trace reconstruction problem is to recover $\bf x$ from many independent outputs (called "traces") of the insertion-deletion channel applied to $\bf x$. We show that if $\bf x$ is chosen uniformly at random, then $\exp(O(\log^{1/3} n))$ traces suffice to reconstruct $\bf x$ with high probability. For the deletion channel with deletion probability $q < 1/2$ the earlier upper bound was $\exp(O(\log^{1/2} n))$. The case of $q\geq 1/2$ or the case where insertions are allowed has not been previously analyzed, and therefore the earlier upper bound was as for worst-case strings, i.e., $\exp(O( n^{1/3}))$. We also show that our reconstruction algorithm runs in $n^{1+o(1)}$ time. A key ingredient in our proof is a delicate two-step alignment procedure where we estimate the location in each trace corresponding to a given bit of $\bf x$. The alignment is done by viewing the strings as random walks and comparing the increments in the walk associated with the input string and the trace, respectively.
The Lingering of Gradients: How to Reuse Gradients Over Time

Classically, the time complexity of a first-order method is estimated by its number of gradient computations. In this paper, we study a more refined complexity by taking into account the ``lingering'' of gradients: once a gradient is computed at $x_k$, the additional time to compute gradients at $x_{k+1},x_{k+2},\dots$ may be reduced. We show how this improves the running time of gradient descent and SVRG. For instance, if the "additional time'' scales linearly with respect to the traveled distance, then the "convergence rate'' of gradient descent can be improved from $1/T$ to $\exp(-T^{1/3})$. On the empirical side, we solve a hypothetical revenue management problem on the Yahoo! Front Page Today Module application with 4.6m users to $10^{-6}$ error (or $10^{-12}$ dual error) using 6 passes of the dataset.
Efficient adaptive compressive sensing using sparse hierarchical learned dictionaries

Recent breakthrough results in compressed sensing (CS) have established that many high dimensional objects can be accurately recovered from a relatively small number of non-adaptive linear projection observations, provided that the objects possess a sparse representation in some basis. Subsequent efforts have shown that the performance of CS can be improved by exploiting the structure in the location of the non-zero signal coefficients (structured sparsity) or using some form of online measurement focusing (adaptivity) in the sensing process. In this paper we examine a powerful hybrid of these two techniques. First, we describe a simple adaptive sensing procedure and show that it is a provably effective method for acquiring sparse signals that exhibit structured sparsity characterized by tree-based coefficient dependencies. Next, employing techniques from sparse hierarchical dictionary learning, we show that representations exhibiting the appropriate form of structured sparsity can be learned from collections of training data. The combination of these techniques results in an effective and efficient adaptive compressive acquisition procedure.
Growth of the Eigensolutions of Laplacians on Riemannian Manifolds I: Construction of Energy Function

In this paper, we consider the eigen-solutions of $-\Delta u+ Vu=\lambda u$, where $\Delta$ is the Laplacian on a non-compact complete Riemannian manifold. We develop Kato's methods on manifold and establish the growth of the eigen-solutions as $r$ goes to infinity based on the asymptotical behaviors of $\Delta r$ and $V(x)$, where $r=r(x)$ is the distance function on the manifold. As applications, we prove several criteria of absence of eigenvalues of Laplacian, including a new proof of the absence of eigenvalues embedded into the essential spectra of free Laplacian if the radial curvature of the manifold satisfies $ K_{\rm rad}(r)= -1+\frac{o(1)}{r}$.
On the total disconnectedness of the quotient Aubry set

In this paper we show that the quotient Aubry set, associated to a sufficiently smooth mechanical or symmetrical Lagrangian, is totally disconnected (i.e. every connected component consists of a single point). This result is optimal, in the sense of the regularity of the Lagrangian, as Mather's counterexamples (J. N. Mather. Examples of Aubry sets. Ergod. Th. & Dynam. Sys. 24(5) (2004), 1667-1723) show. Moreover, we discuss the relation between this problem and a Morse-Sard-type property for (the difference of) critical subsolutions of Hamilton-Jacobi equations.
Quantum Phase Pumping

In this Letter we consider the adiabatic charge transport through a normal mesoscopic sample sandwiched by superconductors without modulation of local chemical potentials. The deformation of coherent quasiparticles in the normal metal in the presence of periodically changing phases in the superconductors leads to a charge transport. Both the magnitude and the phase dependence of the charge transferred per period through the sample strongly depend on temperature.
Graphs and their associated inverse semigroups

Abstract Directed graphs have long been used to gain an understanding of the structure of semigroups, and recently the structure of directed graph semigroups has been investigated resulting in a characterization theorem and an analog of Frucht’s Theorem. We investigate two inverse semigroups defined over undirected graphs constructed from the notions of subgraph and vertex set induced subgraph. We characterize the structure of the semilattice of idempotents and lattice of ideals of these inverse semigroups. We prove a characterization theorem that states that every graph has a unique associated inverse semigroup up to isomorphism allowing for an algebraic restatement of the Edge Reconstruction Conjecture.
From which world is your graph

Discovering statistical structure from links is a fundamental problem in the analysis of social networks. Choosing a misspecified model, or equivalently, an incorrect inference algorithm will result in an invalid analysis or even falsely uncover patterns that are in fact artifacts of the model. This work focuses on unifying two of the most widely used link-formation models: the stochastic block model (SBM) and the small world (or latent space) model (SWM). Integrating techniques from kernel learning, spectral graph theory, and nonlinear dimensionality reduction, we develop the first statistically sound polynomial-time algorithm to discover latent patterns in sparse graphs for both models. When the network comes from an SBM, the algorithm outputs a block structure. When it is from an SWM, the algorithm outputs estimates of each node's latent position.
Kalman Filtering With Intermittent Observations: Weak Convergence to a Stationary Distribution

The paper studies the asymptotic behavior of discrete time Random Riccati Equations (RRE) arising in Kalman filtering when the arrival of the observations is described by a Bernoulli independent and identically distributed (i.i.d.) process. We model the RRE as an order-preserving, strongly sublinear random dynamical system (RDS). Under a sufficient condition, stochastic boundedness, and using a limit-set dichotomy result for order-preserving, strongly sublinear RDS, we establish the asymptotic properties of the RRE: the sequence of random prediction error covariance matrices converges weakly to a unique invariant distribution, whose support exhibits fractal behavior. For stabilizable and detectable systems, stochastic boundedness (and hence weak convergence) holds for any nonzero observation packet arrival probability and, in particular, we can establish weak convergence at operating arrival rates well below the critical probability for mean stability (the resulting invariant measure in that situation does not possess a first moment). We apply the weak-Feller property of the Markov process governing the RRE to characterize the support of the limiting invariant distribution as the topological closure of a countable set of points, which, in general, is not dense in the set of positive semi-definite matrices. We use the explicit characterization of the support of the invariant distribution and the almost sure (a.s.) ergodicity of the sample paths to easily compute statistics of the invariant distribution. A one-dimensional example illustrates that the support is a fractured subset of the non-negative reals with self-similarity properties.
Bilinear Bandits with Low-rank Structure

We introduce the bilinear bandit problem with low-rank structure in which an action takes the form of a pair of arms from two different entity types, and the reward is a bilinear function of the known feature vectors of the arms. The unknown in the problem is a $d_1$ by $d_2$ matrix $\mathbf{\Theta}^*$ that defines the reward, and has low rank $r \ll \min\{d_1,d_2\}$. Determination of $\mathbf{\Theta}^*$ with this low-rank structure poses a significant challenge in finding the right exploration-exploitation tradeoff. In this work, we propose a new two-stage algorithm called "Explore-Subspace-Then-Refine" (ESTR). The first stage is an explicit subspace exploration, while the second stage is a linear bandit algorithm called "almost-low-dimensional OFUL" (LowOFUL) that exploits and further refines the estimated subspace via a regularization technique. We show that the regret of ESTR is $\widetilde{\mathcal{O}}((d_1+d_2)^{3/2} \sqrt{r T})$ where $\widetilde{\mathcal{O}}$ hides logarithmic factors and $T$ is the time horizon, which improves upon the regret of $\widetilde{\mathcal{O}}(d_1d_2\sqrt{T})$ attained for a naive linear bandit reduction. We conjecture that the regret bound of ESTR is unimprovable up to polylogarithmic factors, and our preliminary experiment shows that ESTR outperforms a naive linear bandit reduction.
Strategic Classification from Revealed Preferences

We study an online linear classification problem in which the data is generated by strategic agents who manipulate their features in an effort to change the classification outcome. In rounds, the learner deploys a classifier, then an adversarially chosen agent arrives and possibly manipulates her features to optimally respond to the learner's choice of classifier. The learner has no knowledge of the agents' utility functions or "real" features, which may vary widely across agents. Instead, the learner is only able to observe their "revealed preferences", i.e., the manipulated feature vectors they provide. For a broad family of agent cost functions, we give a computationally efficient learning algorithm that is able to obtain diminishing "Stackelberg regret" --- a form of policy regret that guarantees that the learner is realizing loss nearly as small as that of the best classifier in hindsight, even allowing for the fact that agents would have best-responded differently to the optimal classifier.
Representations of integers by certain 2k-ary quadratic forms

Abstract Suppose k is a positive integer. In this work, we establish formulas for the number of representations of integers by the quadratic forms x 1 2 + ⋯ + x k 2 + m ( x k + 1 2 + ⋯ + x 2 k 2 ) for m ∈ { 2 , 4 } .
Super-stretched and graded countable Cohen–Macaulay type

Abstract We define what it means for a Cohen–Macaulay ring to be super-stretched and show that Cohen–Macaulay rings of graded countable Cohen–Macaulay type are super-stretched. We use this result to show that rings of graded countable Cohen–Macaulay type, and positive dimension, have possible h-vectors (1), ( 1 , n ) , or ( 1 , n , 1 ) . Further, one-dimensional standard graded Gorenstein rings of graded countable type are shown to be hypersurfaces; this result is not known in higher dimensions. In the non-Gorenstein case, rings of graded countable Cohen–Macaulay type of dimension larger than 2 are shown to be of minimal multiplicity.
Mutations of puzzles and equivariant cohomology of two-step flag varieties

We introduce a mutation algorithm for puzzles that is a three-direction analogue of the classical jeu de taquin algorithm for semistandard tableaux. We apply this algorithm to prove our conjectured puzzle formula for the equivariant Schubert structure constants of two-step flag varieties. This formula gives an expression for the structure constants that is positive in the sense of Graham. Thanks to the equivariant version of the ‘quantum equals classical’ result, our formula specializes to a Littlewood-Richardson rule for the equivariant quantum cohomology of Grassmannians.
Large Cardinal Axioms from Tameness in AECs

We show that various tameness assertions about abstract elementary classes imply the existence of large cardinals under mild cardinal arithmetic assumptions.
Deep Belief Networks used on High Resolution Multichannel Electroencephalography Data for Seizure Detection

Ubiquitous bio-sensing for personalized health monitoring is slowly becoming a reality with the increasing availability of small, diverse, robust, high fidelity sensors. This oncoming flood of data begs the question of how we will extract useful information from it. In this paper we explore the use of a variety of representations and machine learning algorithms applied to the task of seizure detection in high resolution, multichannel EEG data. We explore classification accuracy, computational complexity and memory requirements with a view toward understanding which approaches are most suitable for such tasks as the number of people involved and the amount of data they produce grows to be quite large. In particular, we show that layered learning approaches such as Deep Belief Networks excel along these dimensions.
A cone theorem for nef curves

Following ideas of V. Batyrev, we prove an analogue of the Cone Theorem for the closed cone of nef curves: an enlargement of the cone of nef curves is the closure of the sum of a K_X-non-negative portion and countably many K_X-negative coextremal rays. An example shows that this enlargement is necessary. We also describe the relationship between K_X-negative faces of this cone and the possible outcomes of the minimal model program.
Decay properties of solutions to a 4-parameter family of wave equations

In this paper, persistence properties of solutions are investigated for a 4-parameter family (k−abc equation) of evolution equations having (k+1)-degree nonlinearities and containing as its integrable members the Camassa–Holm, the Degasperis–Procesi, Novikov and Fokas–Olver–Rosenau–Qiao equations. These properties will imply that strong solutions of the k−abc equation will decay at infinity in the spatial variable provided that the initial data does. Furthermore, it is shown that the equation exhibits unique continuation for appropriate values of the parameters k, a, b, and c.
Numerical Computation of Galois Groups

The Galois/monodromy group of a family of geometric problems or equations is a subtle invariant that encodes the structure of the solutions. We give numerical methods to compute the Galois group and study it when it is not the full symmetric group. One algorithm computes generators, while the other studies its structure as a permutation group. We illustrate these algorithms with examples using a Macaulay2 package we are developing that relies upon Bertini to perform monodromy computations.
Do Cloaked Objects Really Scatter Less

Known metamaterial-based ``invisibility cloaks'' have been observed to work only for narrow ranges of electromagnetic waves, for example, making an object invisible to red light, but highly visible to blue light. With a comprehensive and quantitative theoretical analysis, researchers now provide a concrete understanding of the observations and also propose a design for broadband cloaks using diamagnetic or superconducting thin cloaking layers.
Distributed functional observers for LTI systems

We study the problem of designing distributed functional observers for LTI systems. Specifically, we consider a setting consisting of a state vector that evolves over time according to a dynamical process. A set of nodes distributed over a communication network wish to collaboratively estimate certain functions of the state. We first show that classical existence conditions for the design of centralized functional observers do not directly translate to the distributed setting, due to the coupling that exists between the dynamics of the functions of interest and the diverse measurements at the various nodes. Accordingly, we design transformations that reveal such couplings and identify portions of the corresponding dynamics that are locally detectable at each sensor node. We provide sufficient conditions on the network, along with state estimate update and exchange rules for each node, that guarantee asymptotic reconstruction of the functions at each sensor node.
Compactness of weak solutions to the three-dimensional compressible magnetohydrodynamic equations

Abstract The compactness of weak solutions to the magnetohydrodynamic equations for the viscous, compressible, heat conducting fluids is considered in both the three-dimensional space R 3 and the three-dimensional periodic domains. The viscosities, the heat conductivity as well as the magnetic coefficient are allowed to depend on the density, and may vanish on the vacuum. This paper provides a different idea from [X. Hu, D. Wang, Global solutions to the three-dimensional full compressible magnetohydrodynamic flows, Comm. Math. Phys. (2008), in press] to show the compactness of solutions of viscous, compressible, heat conducting magnetohydrodynamic flows, derives a new entropy identity, and shows that the limit of a sequence of weak solutions is still a weak solution to the compressible magnetohydrodynamic equations.
Attractor sets and Julia sets in low dimensions

If $X$ is the attractor set of a conformal IFS in dimension two or three, we prove that there exists a quasiregular semigroup $G$ with Julia set equal to $X$. We also show that in dimension two, with a further assumption similar to the open set condition, the same result can be achieved with a semigroup generated by one element. Consequently, in this case the attractor set is quasiconformally equivalent to the Julia set of a rational map.
Identifying Unknown Unknowns in the Open World: Representations and Policies for Guided Exploration

Predictive models deployed in the real world may assign incorrect labels to instances with high confidence. Such errors or unknown unknowns are rooted in model incompleteness, and typically arise because of the mismatch between training data and the cases encountered at test time. As the models are blind to such errors, input from an oracle is needed to identify these failures. In this paper, we formulate and address the problem of informed discovery of unknown unknowns of any given predictive model where unknown unknowns occur due to systematic biases in the training data. We propose a modelagnostic methodology which uses feedback from an oracle to both identify unknown unknowns and to intelligently guide the discovery. We employ a two-phase approach which first organizes the data into multiple partitions based on the feature similarity of instances and the confidence scores assigned by the predictive model, and then utilizes an explore-exploit strategy for discovering unknown unknowns across these partitions. We demonstrate the efficacy of our framework by varying the underlying causes of unknown unknowns across various applications. To the best of our knowledge, this paper presents the first algorithmic approach to the problem of discovering unknown unknowns of predictive models.
UbuntuWorld 1.0 LTS — A Platform for Automated Problem Solving & Troubleshooting in the Ubuntu OS

In this paper, we present UbuntuWorld 1.0 LTS - a platform for developing automated technical support agents in the Ubuntu operating system. Specifically, we propose to use the Bash terminal as a simulator of the Ubuntu environment for a learning-based agent and demonstrate the usefulness of adopting reinforcement learning (RL) techniques for basic problem solving and troubleshooting in this environment. We provide a plug-and-play interface to the simulator as a python package where different types of agents can be plugged in and evaluated, and provide pathways for integrating data from online support forums like Ask Ubuntu into an automated agent’s learning process. Finally, we show that the use of this data significantly improves the agent’s learning efficiency. We believe that this platform can be adopted as a real-world test bed for research on automated technical support.
Geometrically-frustrated pseudogap phase of Coulomb liquids

Abstract We study a class of models with long-range repulsive interactions of the generalized Coulomb form V ( r ) ∼ 1 / r α . We show that decreasing the interaction exponent in the regime α d dramatically depresses the charge ordering temperature Tc in any dimension d ≥ 2 , reflecting the strong geometric frustration produced by long-range interactions. A nearly frozen Coulomb liquid then survives in a broad pseudogap phase found at T > T c , which is characterized by an unusual temperature dependence of all quantities. In contrast, the leading critical behavior very close to the charge-ordering temperature remains identical as in models with short-range interactions.
Active Learning with Logged Data

Author(s): Yan, Songbai; Chaudhuri, Kamalika; Javidi, Tara | Abstract: We consider active learning with logged data, where labeled examples are drawn conditioned on a predetermined logging policy, and the goal is to learn a classifier on the entire population, not just conditioned on the logging policy. Prior work addresses this problem either when only logged data is available, or purely in a controlled random experimentation setting where the logged data is ignored. In this work, we combine both approaches to provide an algorithm that uses logged data to bootstrap and inform experimentation, thus achieving the best of both worlds. Our work is inspired by a connection between controlled random experimentation and active learning, and modifies existing disagreement-based active learning algorithms to exploit logged data.
Continuous-time marginal pricing of power trajectories in power systems

In this paper we formulate of the Economic Dispatch (ED) problem in Power Systems in continuous time and include in it ramping constraints to derive an expression of the price that reflects some important inter-temporal constraints of the power units. The motivation for looking at this problem is the scarcity of ramping resources and their increasing importance motivated by the variability of power resources, particularly due to the addition of solar power, which exacerbates the need of fast ramping units in the early morning and early evening hours. We show that the solution for the marginal price can be found through Euler-Lagrange equations and we argue that this price signal better reflects the market value of power in the presence of significant ramps in net-load.