cssi/SciSciGPT-SciSciNet huggingface dataset:
Model reduction techniques for computing approximately optimal solutions for Markov decision processes

We present a method for solving implicit (factored) Markov decision processes (MDPs) with very large state spaces. We introduce a property of state space partitions which we call e-homogeneity. Intuitively, an e-homogeneous partition groups together states that behave approximately the same under all or some subset of policies. Borrowing from recent work on model minimization in computer-aided software verification, we present an algorithm that takes a factored representation of an MDP and an 0 ≤ e ≤ 1 and computes a factored e-homogeneous partition of the state space. This partition defines a family of related MDPs--those MDP's with state space equal to the blocks of the partition, and transition probabilities "approximately" like those of any (original MDP) state in the source block. To formally study such families of MDPs, we introduce the new notion of a "bounded parameter MDP" (BMDP), which is a family of (traditional) MDPs defined by specifying upper and lower bounds on the transition probabilities and rewards. We describe algorithms that operate on BMDPs to find policies that are approximately optimal with respect to the original MDP. In combination, our method for reducing a large implicit MDP to a possibly much smaller BMDP using an e-homogeneous partition, and our methods for selecting actions in BMDP's constitute a new approach for analyzing large implicit MDP's. Among its advantages, this new approach provides insight into existing algorithms to solving implicit MDPs, provides useful connections to work in automata theory and model minimization, and suggests methods, which involve varying e, to trade time and space (specifically in terms of the size of the corresponding state space) for solution quality.
Security Patterns and Secure Systems Design

Analysis and design patterns are well established to build high-quality object-oriented software. Patterns combine experience and good practices to develop basic models that can be used for new designs. Security patterns join the extensive knowledge accumulated about security with the structure provided by patterns to provide guidelines for secure system design and evaluation. They are being adopted by companies such as IBM, Sun, and Microsoft. We show the anatomy of a security pattern, a variety of them, and their use in the construction of secure systems. These patterns include Authentication, Authorization, Role-based Access Control, Firewalls, Web Services Security (SAML, XACML, XML Firewall), and others. We apply these patterns through a secure system development method based on a hierarchical architecture whose layers define the scope of each security mechanism. First, the possible attacks are considered from an analysis of use cases. Then the rights of the users are defined from the use cases using a Role-Based Access Control (RBAC) or other security model. The attacks are used to define the policies that could stop them. The rights are reflected in the conceptual class model. We then define additional security constraints that apply to distribution, interfaces, and components. The patterns are shown using UML models and some examples are taken from my book "Security Patterns" (Wiley 2006).
Enabling academic excellence in middle schools through computer-mediated learning

This presentation discusses Rose-Hulman Institute of Technology's (USA) educational outreach program to increase middle school children's competencies in science, mathematics and pre-engineering by using advanced computer technologies as enablers inside and outside the classroom. This three-year program began in January of 1999 and is funded by a one-million dollar grant from the Eli Lilly Endowment.
Radiowave Propagation Concepts

Although radiowaves also propagate in waveguides, cables, and transmission lines, the term radiowave propagation is used generally, and specifically in this article, for signal travel between a source and a receiver without guidance by such artificial devices. Examples of such systems are radio and television broadcasting, radio point-to-point communication, radar, radio navigation, and remote sensing. Much has been learned about radiowave propagation since Hertz first demonstrated wireless transmission from one room to another. Now radiowave propagation is considered a moderately mature science, yet new understanding continues to emerge. This article presents an overview of radiowave propagation concepts. Keywords: radiowave propagation; wireless communication; remote sensing; radio navigation; radar; broadcasting
Growth and Evolution in China's Agricultural Support Policies

China is perhaps the most prominent example of a developing country that has transitioned from taxing to supporting agriculture. In recent years, Chinese price supports and subsidies have risen at an accelerating pace after they were linked to rising production costs. Per-acre subsidy payments to grain producers now equal 7 to 15 percent of those producers’ gross income, but grain payments appear to have little influence on production decisions. Chinese authorities began raising price supports annually to bolster incentives, and Chinese prices for major farm commodities are rising above world prices, helping to attract a surge of agricultural imports. U.S. agricultural exports to China tripled in value during the period when China’s agricultural support was accelerating. Overall, China’s expansion of support is loosely constrained by World Trade Organization (WTO) commitments, but the country’s price-support programs could exceed WTO limits in coming years. Chinese officials promise to continue increasing domestic policy support for agriculture, but the mix of policies may evolve as the Chinese agricultural sector becomes more commercialized and faces competitive pressures.
Precise creation, characterization, and manipulation of single optical qubits

We present the theoretical basis for and experimental verification of arbitrary single-qubit state generation, using the polarization of photons generated via spontaneous parametric downconversion. Our precision measurement and state reconstruction system has the capability to distinguish over 3 million states, all of which can be reproducibly generated using our state creation apparatus. In order to complete the triumvirate of single qubit control, there must be a way to not only manipulate single qubits after creation and before measurement, but a way to characterize the manipulations themselves. We present a general representation of arbitrary processes, and experimental techniques for generating a variety of single qubit manipulations, including unitary, decohering, and (partially) polarizing operations.
Algorithms for Modular Counting of Roots of Multivariate Polynomials

Given a multivariate polynomial P(X1,…,Xn) over a finite field $\ensuremath {\mathbb {F}_{q}}$, let N(P) denote the number of roots over $\ensuremath {\mathbb {F}_{q}}^{n}$. The modular root counting problem is given a modulus r, to determine Nr(P)=N(P)mod r. We study the complexity of computing Nr(P), when the polynomial is given as a sum of monomials. We give an efficient algorithm to compute Nr(P) when the modulus r is a power of the characteristic of the field. We show that for all other moduli, the problem of computing Nr(P) is ${\rm NP}$-hard. We present some hardness results which imply that our algorithm is essentially optimal for prime fields. We show an equivalence between maximum-likelihood decoding for Reed-Solomon codes and a root-finding problem for symmetric polynomials.
Identification and Estimation of Social Interaction-Based Models: A Changes-in-Changes Approach with an Application to Adolescent Substance Use

This paper outlines a method for detecting and assessing the strength of social interactions through a changes-in-changes design. The proposed approach is based on a linear-in-means model and aims to resolve the "reflection problem", unobserved heterogeneities and endogenous group formation that plague identification of social interactions. Using longitudinal data from Add Health with rarely collected information on peer group's composition, we explore an exogenous variation in peer's drug use induced by a "mover friend" that occurs between Add Health's survey periods. This quasi-experiment shares a similar nature of a policy intervention of removing drug-user friends from a peer group. Such treatment-control group differences together with changes over time form the basis of our changes-in-changes design. Our study confirms a strong endogenous effect, which in turn motivates a "social multiplier", both of which are large enough to be relevant and are well worth attention to policy makers, researchers, health-care providers and educators for better understanding of how to protect young people and secure our future.
Spatial Asset Pricing: A First Step

People choose where to live and how much to invest in housing. Traditionally, the first decision has been the domain of spatial economics, while the second has been analyzed in finance. Spatial asset pricing is an attempt to combine equilibrium concepts from both disciplines. In the finance context, we show how spatial decisions can be framed as an expanded portfolio problem. Within spatial economics, we identify the consequences of hedging motives for location decisions. We characterize a number of observable deviations from standard predictions in finance (e.g. the definition of the relevant market portfolio for the pricing of risk includes homeownership rates) and in spatial economics (e.g. hedging considerations and the pricing of risk affect the geographic allocation of human capital).
Classifying representations by way of Grassmannians

Let A be a finite-dimensional algebra over an algebraically closed field. Criteria are given which characterize existence of a fine or coarse moduli space classifying, up to isomorphism, the representations of A with fixed dimension d and fixed squarefree top T. Next to providing a complete theoretical picture, some of these equivalent conditions are readily checkable from quiver and relations of A. In the case of existence of a moduli space-unexpectedly frequent in light of the stringency of fine classification-this space is always projective and, in fact, arises as a closed subvariety (Brassy of a classical Grassmannian. Even when the full moduli problem fails to be solvable, the variety Grass T d is seen to have distinctive properties recommending it as a substitute for a moduli space. As an application, a characterization of the algebras having only finitely many representations with fixed simple top is obtained; in this case of 'finite local representation type at a given simple T', the radical layering (J l M/J l+1 M) l>0 is shown to be a classifying invariant for the modules with top T. This relies on the following general fact obtained as a byproduct: proper degenerations of a local module M never have the same radical layering as M.
The Implications of Alternative Biofuel Policies on Carbon Leakage

We show carbon leakage depends on the type of biofuel policy (tax credit versus mandate), the domestic and foreign gasoline supply and fuel demand elasticities, and on consumption and production shares of world oil markets for the country introducing the biofuel policy. The components of carbon leakage – market leakage and emissions savings – are counteracting: carbon leakage increases with market leakage but decreases with emissions savings. We also distinguish domestic and international leakage where the latter is always positive, but domestic leakage can be negative with a mandate. The IPCC definition of leakage omits domestic leakage, resulting in biased estimates. Leakage with a tax credit always exceeds that of a mandate, while the combination of a mandate and tax credit generates lower leakage than a tax credit alone. In general, a gallon of ethanol (energy equivalent) is found to replace 35 percent of a gallon of gasoline – not 100 percent as assumed by life-cycle accounting. This means ethanol emits 13 percent more carbon than a gallon of gasoline if indirect land use change (iLUC) is not included in the estimated emissions savings effect and 43 percent more when iLUC is included.
Templated [2+2] Photodimerizations in the Solid State

This chapter describes how principles of supramolecular chemistry based on the use of small-molecule and metal-organic templates can be used to direct intermolecular [2+2] photodimerizations in the organic solid state. The approach provides a general means to gain control of reactivity so as to provide access to molecules difficult to achieve in solution stereospecifically, in quantitative yield, and in gram amounts. Keywords: solid-state reactions; supramolecular chemistry; crystal engineering; [2+2] photodimerization
Lexicographic Shellability for Balanced Complexes

We introduce a notion of lexicographic shellability for pure, balanced boolean cell complexes, modelled after the CL-shellability criterion of Bjorner and Wachs (Adv. in Math. 43 (1982), 87–100) for posets and its generalization by Kozlov (Ann. of Comp. 1(1) (1997), 67–90) called CC-shellability. We give a lexicographic shelling for the quotient of the order complex of a Boolean algebra of rank 2n by the action of the wreath product S2 w Sn of symmetric groups, and we provide a partitioning for the quotient complex Δ(Πn)/Sn. Stanley asked for a description of the symmetric group representation βS on the homology of the rank-selected partition lattice ΠnS in Stanley (J. Combin. Theory Ser. A 32(2) (1982), 132–161), and in particular he asked when the multiplicity bS(n) of the trivial representation in βS is 0. One consequence of the partitioning for Δ(Πn)/Sn is a (fairly complicated) combinatorial interpretation for bS(n)s another is a simple proof of Hanlon's result (European J. Combin. 4(2) (1983), 137–141) that b1,…,i(n) e 0. Using a result of Garsia and Stanton from (Adv. in Math. 51(2) (1984), 107–201), we deduce from our shelling for Δ(B2n)/S2 w Sn that the ring of invariants k[x1,…,x2n]S2 w Sn is Cohen-Macaulay over any field k.
Cusps and D-modules

1.1. V-modules on singular varieties. Let Y denote a variety over a field and let Vy denote the full sheaf of differential operators on Y (in characteristic zero Vy is the familiar sheaf of differential operators, and in characteristic p the sheaf Vy will contain all divided powers of operators d). It is well known that on a general singular variety Y, the ring of differential operators is badly behaved: in particular, it need not be Noetherian nor, if Y is affine, a simple ring (see [BGG]). Following Grothendieck, there is an alternative notion of a sheaf with "infinitesi mal parallel transport" called a (co)stratification (see [Be2], [Be3], [BDI] or Section 2), which agrees with the notion of left (respectively, right) Py-module when Y is smooth but will not agree, in general, when Y is singular. Our first result presents a simple vanishing condition that guarantees that the notions of X>-module and (co)stratification on a singular variety coincide.
The standard model and beyond

A review of the standard models of the strong (Quantum Chromodynamics), weak (Weinberg–Salam Gauge theory) and electromagnetic (Quantum Electromagnetic) forces and their unification in the SU−3 x SU−2 x U−1 group are discussed.
Rent-Seeking in Research Markets

Using a standard model of uncertain innovation, this paper examines research rivalry and rent-seeking rivalry in innovation markets. Previous literature has not considered the implications of rent-seeking in research markets. We find that greater rent-seeking by the rival unambiguously lowers own profit-maximizing research and rent-seeking activity. On the other hand, greater research spending by the rival also lowers own research and rent-seeking, especially when the probability of own innovation is low. Policy implications are discussed.
Examining lists on Twitter to uncover relationships between following, membership and subscription

We report on an exploratory analysis of pairwise relationships between three different forms of information consumption on Twitter viz., following, listing and subscribing. We develop a systematic framework to examine the relationships between these three forms. Using our framework, we conducted an empirical analysis of a dataset from Twitter. Our results show that people not only consume information by explicitly following others, but also by listing and subscribing to lists and that the people they list or subscribe to are not the same as the ones they follow. Our work has implications for understanding information propagation and diffusion via Twitter and for generating recommendations for adding users to lists, subscribing and merging or splitting them.
Autoionizing States in Highly Ionized Oxygen, Fluorine, and Silicon

Excitation processes in atoms or ions usually involve the promotion of one of the least tightly bound outer shell electrons to a higher orbital leading to a state lying below the ionization threshold. It is possible however to form highly excited discrete states that are embedded in the continuum if one or more inner core electrons are raised to outer shells. In the present paper we report on such states in high Z 3-electron ions associated with core excited configurations of the type 1s2snl and 1s2pnl. Such states may autoionize rapidly via the Coulomb interaction unless forbidden to do so by selection rules on this process. These metastable autoionizing states either decay by radiation or autoionize at a slower rate via the weaker magnetic interactions. The lowest lying quartet state in 3-electron ions (1s2s2p)4P 5/2 o is metastable against both autoionization and radiation. Our previously measured lifetimes [1] for this state (in nanoseconds) are: S (1.1), Si (2.1), Ar (0.66), Cl (0.91), F (15), and 0 (25). Radiative decay processes involving core-excited states have also been previously observed. For example, one type of decay is an El transition between two metastable quartet states and another is a similar transition from a core excited state to a singly excited state.
Room temperature electron spin coherence in telecom-wavelength quaternary quantum wells

Time-resolved Kerr rotation spectroscopy is used to monitor the room temperature electron spin dynamics of optical telecommunication wavelength AlInGaAs multiple quantum wells lattice matched to InP. The authors found that electron spin coherence times and effective g factors vary as a function of aluminum concentration. The measured electron spin coherence times of these multiple quantum wells, with wavelengths ranging from 1.26to1.53μm, reach approximately 100ps at room temperature, and the measured electron effective g factors are in the range from −2.3to−1.1.
Can We Get the Bottom B

Understanding the solar dynamics and the origin of active regions depends crucially on our knowledge of the magnetic fields deep within the convection zone. Can we determine magnetic fields there? Some clues are given by dynamo theories and modeling of those instabilities in the convection zone which result in the emergence of magnetic flux. Magnetic field generated by dynamo is predominantly azimuthal and believed to be unstable to the formation of flux tubes. Simulations indicate that the emergence of the magnetic flux tubes strongly depends on the field strength and its longitudinal distribution at the bottom of the convection zone. Tn a unifying approach advocated in this paper the solar magnetic field is split into a mean part generated by the mean-field dynamo and a fluctuating part approximated by an ensemble of flux tubes. Observationally, the identification of the longitudinal distribution of emerging photospheric magnetic fields can give us information about the magnetic field strength at the bottom of the convection zone. Distinguishing between the modes of emerging field requires simultaneous magnetic imaging of both sides of the Sun. Correlation of simultaneous Dopplergrams of the photosphere from earthside and from the farside of the Sun opens an opportunity to detect velocity structures at the base of the convection zone, associated with the dynamo and emerging active regions. This global imaging of the photosphere can also be used for detection of a magnetic field in the solar core.
Why a Ring of Stars at r = 20 kpc?

The recently discovered ring of stars near Galactocentric distance r = 20 kpc is interpreted as baryonic matter accreted onto the second caustic ring of dark matter in our galaxy. Caustic rings of dark matter were predicted in the Galactic plane at radii a n ≃ 40 kpc / n where n = 1,2,3… They can reveal themselves by their gravitational influence on the distribution of baryonic matter. There is additional evidence for caustic rings of dark matter in the Milky Way from a series of sharp rises in the Galactic rotation curve. The positions of the rises are consistent at the 3% level with the above law for the caustic ring radii. Also, a triangular feature in the IRAS map of the galactic plane is consistent with the imprint of the caustic ring of dark matter nearest to us (n = 5) upon dust and gas in the Galactic plane. These observations imply that the dark matter in our neighborhood is dominated by a single flow whose density and velocity vector are estimated.
A Proposed Grading System to Standardize the Description of Renal Papillary Appearance at the Time of Endoscopy in Patients with Nephrolithiasis

Abstract Background and Purpose: The appearance of the renal papillae in patients with nephrolithiasis can be quite variable and can range from entirely healthy to markedly diseased. The implications of such findings remain unknown. One potential reason is the lack of a standardized system to describe such features. We propose a novel grading scale to describe papillary appearance at the time of renal endoscopy. Methods: Comprehensive endoscopic renal assessment and mapping were performed on more than 300 patients with nephrolithiasis. Recurring abnormal papillary characteristics were identified and quantified based on degree of severity. Results: Four unique papillary features were chosen for inclusion in the PPLA scoring system— ductal Plugging, Pitting, Loss of contour, and Amount of Randall's plaque. Unique scores are calculated for individual papillae based on reference examples. Conclusions: The description and study of renal papillary appearance in stone formers have considerable potential as both ...
Privacy-preserving group data access via stateless oblivious RAM simulation

Motivated by cloud computing applications, we study the problem of providing privacy-preserving access to an outsourced honest-but-curious data repository for a group of trusted users. We show how to achieve efficient privacy-preserving data access using a combination of probabilistic encryption, which directly hides data values, and stateless oblivious RAM simulation, which hides the pattern of data accesses. We give a method with O(log n) amortized access overhead for simulating a RAM algorithm that has a memory of size n, using a scheme that is data-oblivious with very high probability. We assume that the simulation has access to a private workspace of size O(nv), for any given fixed constant v > 0, but does not maintain state in between data access requests. Our simulation makes use of pseudorandom hash functions and is based on a novel hierarchy of cuckoo hash tables that all share a common stash. The method outperforms all previous techniques for stateless clients in terms of access overhead. We also provide experimental results from a prototype implementation of our scheme, showing its practicality. In addition, we show that one can eliminate the dependence on pseudorandom hash functions in our simulation while having the overhead rise to be O(log2n).
Total synthesis of the microbial antitumor antibiotics actinobolin and bactobolin

Publisher Summary Actinobolin is found to inhibit growth of both gram-positive and gram-negative bacteria. Additionally, actinobolin has been reported to have weak antineoplastic activity and dental cariostatic activity. It has been found that actinobolin interferes with protein synthesis at a late stage in mammalian cells and this phenomenon may account for the biological activity of the metabolite. Currently, actinobolin is shown to have immunosuppressive activity. The structure and absolute stereochemistry of actinobolin was formulated by application of an elegant combination of chemical degradation and spectroscopic methods. Stereostructure is subsequently fully confirmed by X-ray crystallography. A congener of actinobolin, bactobolin, is isolated from Pseudomonas yoshitomiensis Y-12278. Bactobolin is structurally identical to actinobolin except for the unusual dichloromethyl group at C-3. This metabolite is also found to have significant antibacterial activity. However, bactobolin shows considerably higher potency in antitumor screens than bactobolin. Two closely related bactobolin analogs have been isolated from Pseudomonas and are also found to have good antitumor activity.
Devolution, accountability, and service delivery : some insights from Pakistan

This paper studies the relationship between devolution, accountability, and service delivery in Pakistan. It examines the degree of accessibility of local policy-makers and the level of competition in local elections, the expenditure patterns of local governments to gauge their sector priorities, and the extent to which local governments are focused on patronage or the provision of targeted benefits to a few as opposed to providing public goods. The main findings of the paper are three-fold. First, the accessibility of policy-makers to citizens in Pakistan is unequivocally greater after devolution, and local government elections are, with some notable exceptions, as competitive as national and provincial elections. Second, local government sector priorities are heavily tilted toward the provision of physical infrastructure - specifically, roads, water and sanitation, and rural electrification - at the expense of education and health. Third, this sector prioritization is in part a dutiful response to the relatively greater citizen demands for physical infrastructure; in part a reflection of the local government electoral structure that gives primacy to village and neighborhood-specific issues, and in part a reaction to provincial initiatives in education and health that have taken the political space away from local governments in the social sectors, thereby encouraging them to focus more toward physical infrastructure.
Labor Market Implications of Switching the Currency Peg in a General Equilibrium Model for Lithuania

On February 2, 2002, Lithuania switched its currency anchor from the dollar to the euro. While pegging to the dollar (since April 1994) has proven successful throughout the transition years, the recent decision to peg to the euro was motivated by the increasing trade relations with European economies. Pizzati does not argue which peg is more appropriate, but he analyzes the implications of changing the exchange rate regime for different sectors and labor groups. While pegging to the euro entails more stability for the export sector, Lithuania is still dependent on dollar-based imports of primary goods from the Commonwealth of Independent States, more so than other Baltic countries or Central European economies. The author uses a multisector general equilibrium model to compare the effects of dollar-euro exchange rate movements under these alternative pegs. Overall, simulation results suggest that while a euro-peg will provide more stability to GDP and employment, it will also imply more volatility in prices, suggesting that under the new peg macroeconomic policy should be more concerned with inflationary pressures than before. From a sector-specific perspective, pegging to the euro will provide a more stable demand for unskilled-intensive manufacturing and commercial services. But other sectors, such as agriculture, will still face the same vulnerability to exchange rate movements. This suggests that additional policy measures may be needed to compensate sector-specific divergences.
Migrating swarms of brittle‐failure earthquakes in the lower crust beneath Mammoth Mountain, California

[1] Brittle-failure earthquakes in the lower crust, where high pressures and temperatures would typically promote ductile deformation, are relatively rare but occasionally observed beneath active volcanic centers. Where they occur, these earthquakes provide a rare opportunity to observe volcanic processes in the lower crust, such as fluid injection and migration, which may induce brittle faulting under these conditions. Here, we examine recent short-duration earthquake swarms deep beneath the southwestern margin of Long Valley Caldera, near Mammoth Mountain. We focus in particular on a swarm that occurred September 29–30, 2009. To maximally illuminate the spatial-temporal progression, we supplement catalog events by detecting additional small events with similar waveforms in the continuous data, achieving up to a 10-fold increase in the number of locatable events. We then relocate all events, using cross-correlation and a double-difference algorithm. We find that the 2009 swarm exhibits systematically decelerating upward migration, with hypocenters shallowing from 21 to 19 km depth over approximately 12 hours. This relatively high migration rate, combined with a modest maximum magnitude of 1.4 in this swarm, suggests the trigger might be ascending CO2 released from underlying magma.
Why has energy efficiency not scaled-up in the industrial and commercial sectors in Ukraine ? an empirical analysis

Improvement of energy efficiency is one of the main options to reduce energy demand and to reduce greenhouse gas emissions in Ukraine. However, large-scale deployment of energy efficient technologies has been constrained by several financial, technical, information, behavioral, and institutional barriers. This study assesses these barriers through a survey of 500 industrial and commercial firms throughout Ukraine. The results from the survey were used in a cumulative multi-logit model to understand the importance of the barriers. The analysis shows that financial barriers caused by high upfront costs of energy efficient technologies, higher costs of finance, and higher opportunity costs of energy efficiency investment are key barriers to the adoption of energy efficiency measures in Ukraine. Institutional barriers particularly lack government policies, which also contributes to the slow adoption of energy efficient technologies in the country. The results suggest targeted policy and credit enhancements could help trigger adoption of energy efficient measures. The empirical analysis shows strong inter-linkages among the barriers and finds heterogeneity between industrial and commercial sectors on the realization of the barriers.
Constructing and Employing Tree Alignment Graphs for Phylogenetic Synthesis

Tree alignment graphs TAGs provide an intuitive data structure for storing phylogenetic trees that exhibits the relationships of the individual input trees and can potentially account for nested taxonomic relationships. This paper provides a theoretical foundation for the use of TAGs in phylogenetics. We provide a formal definition of TAG that -- unlike previous definition -- does not depend on the order in which input trees are provided. In the consensus case, when all input trees have the same leaf labels, we describe algorithms for constructing majority-rule and strict consensus trees using the TAG. When the input trees do not have identical sets of leaf labels, we describe how to determine if the input trees are compatible and, if they are compatible, to construct a supertree that contains the input trees.
Tutorial on Oxidative Addition

This tutorial introduces oxidative addition as a reactivity pattern and organizing principle for organometallic chemistry. The history, characteristics, and scope of oxidative addition are briefly surveyed, followed by a detailed examination of the variety of mechanisms found for the oxidative addition of alkyl halides and their relevance to practical applications.
Fast, Exact Bootstrap Principal Component Analysis for p > 1 Million

Many have suggested a bootstrap procedure for estimating the sampling variability of principal component analysis (PCA) results. However, when the number of measurements per subject (p) is much larger than the number of subjects (n), calculating and storing the leading principal components from each bootstrap sample can be computationally infeasible. To address this, we outline methods for fast, exact calculation of bootstrap principal components, eigenvalues, and scores. Our methods leverage the fact that all bootstrap samples occupy the same n-dimensional subspace as the original sample. As a result, all bootstrap principal components are limited to the same n-dimensional subspace and can be efficiently represented by their low dimensional coordinates in that subspace. Several uncertainty metrics can be computed solely based on the bootstrap distribution of these low dimensional coordinates, without calculating or storing the p-dimensional bootstrap components. Fast bootstrap PCA is applied to a dataset of sleep electroencephalogram recordings (p = 900, n = 392), and to a dataset of brain magnetic resonance images (MRIs) (p ≈ 3 million, n = 352). For the MRI dataset, our method allows for standard errors for the first 3 principal components based on 1000 bootstrap samples to be calculated on a standard laptop in 47 minutes, as opposed to approximately 4 days with standard methods.
Stiffness and muscle function with age and reduced muscle use

Changes in passive muscle stiffness with age and disuse were assessed in male Fischer-344 and Brown Norway rats. Three groups of rats were studied: young (approximately 7 months old), old (approximately 33 months old), and old that had undergone 2 weeks of hindlimb unweighting, a model of reduced muscle use. Four hindlimb muscles were examined: the soleus (postural), plantaris (locomotor), extensor digitorum longus (nonpostural), and peroneus longus (nonpostural). Supramaximal stimuli elicited peak tetanic tensions throughout the available range of motion (amount of muscle elongation before the maximal attainable contractile or tetanic tension is obtained) for each muscle, permitting the creation of length-tension curves. Passive tension (amount encountered at each millimeter of change in muscle length) was also recorded throughout the available range of motion and was unchanged with aging and unchanged or reduced with hindlimb unweighting; muscle stiffness remained unchanged under both conditions. Passive tension, however, accounted for a greater proportion of total tension with age and particularly with hindlimb unweighting. A significant loss in muscle range of motion, resulting in a leftward shift in the length-tension curve, occurred with aging in only the plantaris. Hindlimb unweighting resulted in a marked loss in muscle range for all four muscles studied, suggesting that the remaining muscle force was constrained to a very small arc. Significant declines in muscle mass and peak contractile tension, associated with age and hindlimb unweighting, were observed for all four muscles.
Controlled MOCVD growth of Bi2Se3 topological insulator nanoribbons.

Topological insulators are a new class of materials that support topologically protected electronic surface states. Potential applications of the surface states in low dissipation electronic devices have motivated efforts to create nanoscale samples with large surface-to-volume ratios and highly controlled stoichiometry. Se vacancies in Bi2Se3 give rise to bulk conduction, which masks the transport properties of the surface states. We have therefore developed a new route for the synthesis of topological insulator nanostructures using metalorganic chemical vapour deposition (MOCVD). MOCVD allows control of the Se=Bi flux ratio during growth. With the aim of rational growth, we vary the Se=Bi flux ratio, growth time, and substrate temperature, and observe morphological changes which indicate a growth regime in which nanoribbon formation is limited by the Bi precursor mass flow. MOCVD growth of Bi2Se3 nanostructures occurs via a distinct growth mechanism that is nucleated by gold nanoparticles at the base of the nanoribbon. By tuning the reaction conditions, we obtain either single-crystalline ribbons up to 10 m long or thin micron-sized platelets. (Some figures may appear in colour only in the online journal)
Combinatorics of diagrams of permutations

There are numerous combinatorial objects associated to a Grassmannian permutation w λ that index cells of the totally nonnegative Grassmannian. We study several of these objects and their q-analogues in the case of permutations w that are not necessarily Grassmannian. We give two main results: first, we show that certain acyclic orientations, rook placements avoiding a diagram of w, and fillings of a diagram of w are equinumerous for all permutations w. Second, we give a q-analogue of a result of Hultman-Linusson-Shareshian-Sjostrand by showing that under a certain pattern condition the Poincare polynomial for the Bruhat interval of w essentially counts invertible matrices over a finite field avoiding a diagram of w. In addition to our main results, we include at the end a number of open questions.
Hydroxyapatite binding domains in salivary proteins.

One of the functions of proteins in human saliva is to maintain a balance between calcium phosphate remineralization and demineralization. Saliva is normally supersaturated with respect to calcium phosphate phases such as hydroxyapatite (HAP) and octacalcium phosphate (OCP), but it can also be undersaturated, locally, with respect to these phases (Gron, 1973). The proteins believed to be the strongest precipitation inhibitors are statherin and a group of acidic proline-rich phosphoproteins (PRPs), all of which adsorb strongly to HAP (Moreno et al., 1978, 1979). These molecules contain phosphoserine residues and have a significant number of negatively charged residues localized in their N-terminal regions, whereas the C-termini contain mainly uncharged residues (Schlesinger and Hay, 1977; Wong et al., 1979). The charged domains of both statherin and the PRPs have been shown to have high affinities for HAP surfaces and to be efficient inhibitors of HAP crystal growth in supersaturated solution (Schlesinger et al., 1987; Moreno et al., 1981). However, several other proteins containing charged domains may be moderate or weaker contributors to precipitation inhibition. HAP adsorption and crystallization modification in the presence of a protein depends on the manner in which it adsorbs at the surface. In this study, these data are compared for some salivary proteins.
Constraining the geometry of the neutron star RX J1856.5−3754

RX J1856.5-3754 is one of the brightest, nearby isolated neutron stars (NSs), and considerable observational resources have been devoted to its study. In previous work, we found that our latest models of a magnetic, hydrogen atmosphere match well the entire spectrum, from X-rays to optical (with best-fitting NS radius R ≈ 14 km, gravitational redshift Żg ∼ 0.2, and magnetic field B ≈ 4 x 10 12 G). A remaining puzzle is the non-detection of rotational modulation of the X-ray emission, despite extensive searches. The situation changed recently with XMM-Newton observations that uncovered 7-s pulsations at the ≈1 per cent level. By comparing the predictions of our model (which includes simple dipolar-like surface distributions of magnetic field and temperature) with the observed brightness variations, we are able to constrain the geometry of RX J1856.5-3754, with one angle <6° and the other angle ≈20°-5°, though the solutions are not definitive, given the observational and model uncertainties. These angles indicate a close alignment between the rotation and the magnetic axes or between the rotation axis and the observer. We discuss our results in the context of RX J1856.5-3754 being a normal radio pulsar and a candidate for observation by future X-ray polarization missions such as Constellation-X or XEUS.
Judging adaptive management practices of U.S. agencies

All U.S. federal agencies administering environmental laws purport to practice adaptive management (AM), but little is known about how they actually implement this conservation tool. A gap between the theory and practice of AM is revealed in judicial decisions reviewing agency adaptive management plans. We analyzed all U.S. federal court opinions published through 1 January 2015 to identify the agency AM practices courts found most deficient. The shortcomings included lack of clear objectives and processes, monitoring thresholds, and defined actions triggered by thresholds. This trio of agency shortcuts around critical, iterative steps characterizes what we call AM-lite. Passive AM differs from active AM in its relative lack of management interventions through experimental strategies. In contrast, AM-lite is a distinctive form of passive AM that fails to provide for the iterative steps necessary to learn from management. Courts have developed a sophisticated understanding of AM and often offer instructive rather than merely critical opinions. The role of the judiciary is limited by agency discretion under U.S. administrative law. But courts have overturned some agency AM-lite practices and insisted on more rigorous analyses to ensure that the promised benefits of structured learning and fine-tuned management have a reasonable likelihood of occurring. Nonetheless, there remains a mismatch in U.S. administrative law between the flexibility demanded by adaptive management and the legal objectives of transparency, public participation, and finality.
Nephrocalcinosis in Calcium Stone Formers Who Do Not have Systemic Disease

Purpose: Nephrocalcinosis is commonly present in primary hyperparathyroidism, distal renal tubular acidosis and medullary sponge kidney disease. To our knowledge it has not been studied in patients with calcium phosphate stones who do not have systemic disease.Materials and Methods: We studied patients undergoing percutaneous nephrolithotomy who had calcium phosphate or calcium oxalate stones and did not have hyperparathyroidism, distal renal tubular acidosis or medullary sponge kidney disease. On postoperative day 1 all patients underwent noncontrast computerized tomography. If there were no residual calcifications, the patient was categorized as not having nephrocalcinosis. If there were residual calcifications, the patient underwent secondary percutaneous nephrolithotomy. If the calcifications were found to be stones, the patient was categorized as not having nephrocalcinosis. If the calcifications were not stones, the patient was categorized as having nephrocalcinosis. Patients were grouped based on t...
Binary Embedding: Fundamental Limits and Fast Algorithm

Binary embedding is a nonlinear dimension reduction methodology where high dimensional data are embedded into the Hamming cube while preserving the structure of the original space. Specifically, for an arbitrary N distinct points in Sp-1, our goal is to encode each point using m-dimensional binary strings such that we can reconstruct their geodesic distance up to δ uniform distortion. Existing binary embedding algorithms either lack theoretical guarantees or suffer from running time O(mp). We make three contributions: (1) we establish a lower bound that shows any binary embedding oblivious to the set of points requires m = Ω(1/δ2log N) bits and a similar lower bound for non-oblivious embeddings into Hamming distance; (2) we propose a novel fast binary embedding algorithm with provably optimal bit complexity m = Ω(1/δ2log N) and near linear running time O(p log p) whenever log N ≪ δ √p with a slightly worse running time for larger log N; (3) we also provide an analytic result about embedding a general set of points K ⊆ Sp-1 with even infinite size. Our theoretical findings are supported through experiments on both synthetic and real data sets.
(UN)Bundling public-private partnership contracts in the water sector : competition in auctions and economies of scale in operation

In public-private partnership transactions in the water sector, one of the alleged concerns is that there is little market competition at the auction stage. This paper casts light on a tradeoff between the competition effect at the auction level and potential economies of scale in service operation. If the authorities design a large-scale public-private partnership water transaction, it is expected to exploit operational scale economies. But the competition effect may have to be sacrificed. The paper shows a risk that the selection of the contract size could be a very restrictive condition that excludes many prospective bidders. Moreover, the paper quantifies the optimal size of public-private partnership contracts in the sector by estimating a cost function. The analysis shows that economies of scale exist but tend to diminish quickly as production increases. When the amount of water sold exceeds about 40 million m3, the statistical significance of economies of scale disappears. And there is no rationale for auctioning the water operation with annual water delivery of more than 400 million m3 under a single contract.
Seasonal variation in the stable isotopic composition of precipitation in the tropical montane forests of Monteverde, Costa Rica

reveal a seasonal signal that may be used to trace water through the hydrologic cycle. Deuterium excess indicates that water evaporated from land is an important flux to the region during the transitional and dry seasons when winds from the Caribbean slope dominate. Following the shift to convective rainfall at the start of the wet season, when the western equatorial winds influence the Pacific slope of Costa Rica, d excess values become depressed. Yet as the wet season progresses, d excess begins to climb. These data suggest that several months of rain are needed following an acute dry season on the northern Pacific slope before a terrestrial evaporative signal is detected in wet season precipitation. The evaporative flux may result from a wet season expansion of surface water bodies and flooding of seasonal wetlands.
Synthesis of pyrrolizidine bases by highly diastereoselective and regioselective catalytic carbon-hydrogen insertion reactions of chiral pyrrolidinediazoacetamides

Abstract Pyrrolizidines, (1S, 8S)-1-hydroxypyrrolizidin-3-one and (−)-heliotridane, have been prepared in high yield from diazoacetamides of 2-substituted-pyrrolidines by carbon-hydrogen insertion catalyzed by dirhodium(II) tetrakis[methyl 1-acylmidazolidin-2-one-4(S)-carboxylates].
Recent Advances in the Study of the Bioactive Conformation of Taxol

Paclitaxel is one of the most important chemotherapeutic drugs in the fight against cancer. This minireview covers the recent advances in the study of the bioactive conformation of paclitaxel in tubulin/microtubules. The tubulin-bound structure of paclitaxel has been studied by means of photoaffinity labeling, cryo-electron microscopy, solid-state NMR, molecular modeling, MD simulations and the synthesis of conformationally restrained analogues and paclitaxel mimics. The bioactive conformation of paclitaxel is important since it could provide critical information that would allow the design of novel analogues with simpler structures and/or increased potency against cancer.
Beyond natural selection and divine intervention: The Lamarckian implication of Adam Smith's invisible hand

Adam Smith's invisible hand metaphor (IH) is examined in light of two different accounts of the origin of traits: Charles Darwin's theory of evolutionary optimization and William Paley's theory of divine intervention. Smith's stand supersedes both accounts. For Smith, intermediating drives, such as the sexual one, neither arise accidentally and favored according to their fitness a la Darwin nor planted by the Deity a la Paley. For Smith, such drives are adopted in light of their ultimate end. Smith did not provide an account of how the drives are connected to their far-reaching, invisible beneficial ends or why do agents become dimly aware of that causality.