cssi/SciSciGPT-SciSciNet huggingface dataset:
Unconditional lower bounds for learning intersections of halfspaces

We prove new lower bounds for learning intersections of halfspaces, one of the most important concept classes in computational learning theory. Our main result is that any statistical-query algorithm for learning the intersection of $\sqrt{n}$ halfspaces in n dimensions must make $2^{\varOmega (\sqrt{n})}$ queries. This is the first non-trivial lower bound on the statistical query dimension for this concept class (the previous best lower bound was n ?(log?n)). Our lower bound holds even for intersections of low-weight halfspaces. In the latter case, it is nearly tight. We also show that the intersection of two majorities (low-weight halfspaces) cannot be computed by a polynomial threshold function (PTF) with fewer than n ?(log?n/log?log?n) monomials. This is the first super-polynomial lower bound on the PTF length of this concept class, and is nearly optimal. For intersections of k=?(log?n) low-weight halfspaces, we improve our lower bound to $\min\{2^{\varOmega (\sqrt{n})},n^{\varOmega (k/\log k)}\},$ which too is nearly optimal. As a consequence, intersections of even two halfspaces are not computable by polynomial-weight PTFs, the most expressive class of functions known to be efficiently learnable via Jackson's Harmonic Sieve algorithm. Finally, we report our progress on the weak learnability of intersections of halfspaces under the uniform distribution.
Determination and experimental verification of high-temperature SAW orientations on langatate

Langatate (LGT) is a member of the langasite family of crystals appropriate for high-temperature frequency control and sensing applications. This paper identifies multiple LGT SAW orientations for use at high temperature, specifically in the 400°C to 900°C range. Orientations with low sensitivity to temperature are desired for frequency control devices and many sensors, conversely large temperature sensitivity is a benefit for temperature sensors. The LGT SAW temperature behavior has been calculated for orientations sweeping the Euler angles (0°,Θ,ψ), (90°,Θ,ψ), and (Φ,90°,ψ), based on newly identified high-temperature elastic constants and temperature coefficients for this material. The temperature coefficient of delay (TCD) and total frequency change over the temperature range were analyzed from 400°C to 900°C. Multiple SAW orientations were identified with zero-TCD between 400°C and 500°C. Although no orientations that have turn-over temperatures above 500°C were identified, several have low frequency variation with temperature, of the order of -0.8% over the range 400°C to 800°C. Temperature-sensitive orientations with TCD up to 75 ppm/°C at 900°C were identified, with potential for high-temperature sensor applications. The reported predictions are shown to agree with measured behavior of LGT SAW delay lines fabricated along 6 orientations in the (90°,23°,ψ) plane. In addition, this work demonstrates that concurrently operated LGT SAW devices fabricated on the same wafer provide means of temperature sensing. In particular, the measured frequency difference between delay lines oriented along (90°,23°,0°) and (90°, 23°, 48°) has fractional temperature sensitivity that ranges from -172 ppm/°C at 25°C to -205 ppm/°C at 900°C.
Oblivious buy-at-bulk in planar graphs

In the oblivious buy-at-bulk network design problem in a graph, the task is to compute a fixed set of paths for every pair of source-destination in the graph, such that any set of demands can be routed along these paths. The demands could be aggregated at intermediate edges where the fusion-cost is specified by a canonical (non-negative concave) function f. We give a novel algorithm for planar graphs which is oblivious with respect to the demands, and is also oblivious with respect to the fusion function f. The algorithm is deterministic and computes the fixed set of paths in polynomial time, and guarantees a O(log n) approximation ratio for any set of demands and any canonical fusion function f, where n is the number of nodes. The algorithm is asymptotically optimal, since it is known that this problem cannot be approximated with better than Ω(log n) ratio. To our knowledge, this is the first tight analysis for planar graphs, and improves the approximation ratio by a factor of log n with respect to previously known results.
Forced Coexistence and Economic Development: Evidence From Native American Reservations

There are large differences in economic development across Native American reservations today. This paper asks whether these differences can be in part explained by the forced integration of historically autonomous sub-tribal bands in the 19th century. To measure forced integration, I combine anthropological data on intra-tribal political integration in pre-reservation times with historical information on the constituent bands of each reservation. Exploring variation in how politically integrated tribes were before reservations and variation in how politically integrated reservations were at the time of their formation, I find that forced integration lowers per capita incomes today by about 30 percent. To account for potential selection into forced integration, I exploit historical mining rushes as a source of exogenous variation in the government’s incentive to combine bands onto reservations. The IV strategy confirms the baseline results. I also provide quantitative evidence on the channels through which forced integration affects incomes today.
Ambiguity attitudes and social interactions: An experimental investigation

This paper reports the results of experiments testing prevalence of non-neutral ambiguity attitudes and how these attitudes change as a result of interpersonal interactions. To address the first question we conducted experiments involving individual choice between betting on ambiguous and unambiguous events of the subject’s choice. We found that a large majority of subjects display ambiguity neutral attitudes, many others display ambiguity incoherent attitudes, and few subjects display either ambiguity-averse attitudes or ambiguity-seeking attitudes. To address the second question we designed a new experiment with a built-in incentive to persuade. We found that interpersonal interactions without incentives to persuade have no effect on behavior. However, when incentives were introduced, the ambiguity neutral subjects were better able to persuade ambiguity seeking and ambiguity incoherent subjects to adopt ambiguity neutral choice behavior and, to a lesser extent, also ambiguity averse subjects.
Sparse, Active Aperture Imaging

We describe an approach to radar imaging of an isolated, rotating target using coherent, sparse, or highly thinned arrays of transmit/receive elements. The array elements are assumed to be randomly positioned and accurately surveyed after placement. Further, the isolated target is assumed to occupy a limited angular sector such that there is no source of backscatter beyond the sector occupied by the target. Estimates of the resolution and image quality are provided when the array elements are widely separated and operate with coherent, multiple-input multiple-output (MIMO) signaling and inverse synthetic aperture radar (ISAR) processing at each MIMO element pair. The sparse array operation can provide superior resolution when compared to the ISAR processing and accurate estimation of scattering properties with a modest number of sparse array elements. The performance of a model-based estimator to physical optics like scattering with MIMO signaling is described. Several important issues relating to feasibility remain to be investigated. These include establishing coherence and timing among the widely separated array elements, adaptive beamforming and processing requirements and coherence of the scattering phenomena with the widely separated MIMO elements.
Position and Spin Operators, Wigner Rotation and the Origin of Hidden Momentum Forces

Using a position operator obtained for spin 1 particles by the present author and Wigner, we obtain a quantum relativistic result for the hidden momentum force expe- rienced by particles with structure. In particular, our result applies to the hidden magnetic forces manifest in some problems of electromagnetism. We also discuss spin and orbital angular momentum operators, as well as Wigner rotation.
An Anionic Nucleophilic Catalyst System for the Diastereoselective Synthesis of trans-β-Lactams

Trans-disubstituted β-lactams show increasing utility and prominence in numerous pharmaceutical applications, making their asymmetric synthesis an attractive goal for chemists. We introduce an anionic, nucleophilic catalyst system that provides an efficient, diastereoselective route to trans-disubstituted β-lactams, a complement to our previously described catalytic methodology for generating the corresponding cis diastereomers. This catalytic, “switch mechanism” process allows for flexibility in the stereoselective synthesis of β-lactams, producing either cis or trans products as desired from the same substrates.
A simple proof of the sharp weighted estimate for Calderon-Zygmund operators on homogeneous spaces

Here we show that Lerner’s method of local mean oscillation gives a simple proof of the A2 conjecture for spaces of homogeneous type, that is, the linear dependence on the A2 norm for weighted L2 Calderon–Zygmund operator estimates. In the Euclidean case, the result is due to Hytonen, and for geometrically doubling spaces, Nazarov, Reznikov, and Volberg obtained the linear bound.
Analysis of Rural Quality of Life and Health: A Spatial Approach:

This article examines the relationship between quality of life, health, and several socioeconomic variables. It draws on survey data from a random sample of more than 2,000 residents in 21 counties in West Virginia and spatial data generated by geocoding survey respondents' addresses and hospital locations. The empirical results are consistent with the theoretical predictions and indicate, for instance, that quality-of-life satisfaction increases with income and education but decreases with unemployment. Also, the results support the notion that inferences drawn regarding substantive issues often change when spatial dependence is taken into account.
Cognitive dissonance and the overtaking anomaly: Psychology in the principal–agent relationship

Abstract We propose that the concept of cognitive dissonance contributes to the explanation of the regularity that wages grow faster than productivity. Cognitive dissonance is the tendency of a person to engage in self-justification after a decision. We show that a consequence of this tendency is that agents prefer increasing sequences of surplus over their career. This is achieved by paying wages less than productivity early in the career and more than productivity later. We refer to this as the overtaking anomaly. We distinguish the cognitive dissonance explanation from other explanations of the overtaking anomaly by identifying their divergent implications.
Heterogeneity and Network Structure in the Dynamics of Diffusion: Comparing Agent-Based and Differential Equation Models

When is it better to use agent-based (AB) models, and when should differential equation (DE) models be used? Whereas DE models assume homogeneity and perfect mixing within compartments, AB models can capture heterogeneity across individuals and in the network of interactions among them. AB models relax aggregation assumptions, but entail computational and cognitive costs that may limit sensitivity analysis and model scope. Because resources are limited, the costs and benefits of such disaggregation should guide the choice of models for policy analysis. Using contagious disease as an example, we contrast the dynamics of a stochastic AB model with those of the analogous deterministic compartment DE model. We examine the impact of individual heterogeneity and different network topologies, including fully connected, random, Watts-Strogatz small world, scale-free, and lattice networks. Obviously, deterministic models yield a single trajectory for each parameter set, while stochastic models yield a distribution of outcomes. More interestingly, the DE and mean AB dynamics differ for several metrics relevant to public health, including diffusion speed, peak load on health services infrastructure, and total disease burden. The response of the models to policies can also differ even when their base case behavior is similar. In some conditions, however, these differences in means are small compared to variability caused by stochastic events, parameter uncertainty, and model boundary. We discuss implications for the choice among model types, focusing on policy design. The results apply beyond epidemiology: from innovation adoption to financial panics, many important social phenomena involve analogous processes of diffusion and social contagion.
Locally and Nonlocally Reacting Flexible Porous Layers; A Comparison of Acoustical Properties

The acoustical properties of a porous layer backed by a rigid wall are studied with particular attention to the difference between locally and nonlocally reacting layers and the role of flexibility of the material. Propagation constant, impedance, reflection, and absorption coefficients are discussed as functions of frequency and the angle of incidence. Characteristics frequencies and scaling laws are considered and the conditions for maximizing the absorption coefficient are determined in terms of the normalized layer thickness D/λ, where λ is the wavelength. The possibility of using the flexibility of the material for the purpose of creating a low frequency resonance with high absorption without significant loss at high frequencies is explored.
Mars exploration rovers orbit determination system modeling

From June 2003 to January 2004, two spinning spacecraft journeyed from Earth to Mars. A team of navigators at the Jet Propulsion Laboratory (JPL) accurately determined the orbits of both Mars Exploration Rovers, Spirit and Opportunity. For the navigation process to be successful, the team needed to know how nongravitational effects and how measurement system properties affected the trajectory and data modeling. To accomplish this, in addition to the standard gravitational and radiometric modeling of the spacecraft, a calibration was performed on each spacecraft to determine the amount of ΔV that might occur during a turn, a high-fidelity solar-radiation-pressure model was created, the spin signature was removed from the tracking data, the station locations of the Deep Space Network were resurveyed, and a model of interplanetary charged particles was developed. The result of this effort was near-perfect accuracy, surpassing the tight atmospheric-entry requirements for navigation of both spacecraft.
Manifolds homotopy equivalent to P n # P n

We classify, up to homeomorphism, all closed manifolds having the homotopy type of a connected sum of two copies of real projective n-space.
Developing country exports of manufactures: Moving up the ladder to escape the fallacy of composition?

This paper tests for a ‘fallacy of composition’ by analysing the demand for exports of the 18 developing countries that are most specialised in manufactures in the markets of the 10 largest industrial countries. Estimated export equations (both time-series and panel data) suggest that most developing countries compete with other developing country exporters rather than with industrialised country producers. A smaller number of countries that export more high-technology products compete with industrialised country producers and also have higher expenditure elasticities for their exports. Thus, the fallacy of composition applies mainly to the larger group of countries exporting mostly low-technology products.
A Feedback Reduction Technique for MIMO Broadcast Channels

A multiple antenna broadcast channel with perfect channel state information at the receivers is considered. If each receiver quantizes its channel knowledge to a finite number of bits which are fed back to the transmitter, the large capacity benefits of the downlink channel can be realized. However, the required number of feedback bits per mobile must be scaled with both the number of transmit antennas and the system SNR, and thus can be quite large in even moderately sized systems. It is shown that a small number of antennas can be used at each receiver to improve the quality of the channel estimate provided to the transmitter. As a result, the required feedback rate per mobile can be significantly decreased.
Random choice solution of hyperbolic systems

Abstract A random choice method for solving nonlinear hyperbolic systems of conservation laws is presented. The method is rooted in Glimm's constructive proof that such systems have solutions. The solution is advanced in time by a sequence of operations which includes the solution of Riemann problems and a sampling procedure. The method can describe a complex pattern of shock wave and slip line interactions without introducing numerical viscosity and without a special handling of discontinuities. Examples are given of applications to one- and two-dimensional gas flow problems.
Soft Selective Sweeps in Complex Demographic Scenarios

Adaptation from de novo mutation can produce so-called soft selective sweeps, where adaptive alleles of independent mutational origin sweep through the population at the same time. Population genetic theory predicts that such soft sweeps should be likely if the product of the population size and the mutation rate toward the adaptive allele is sufficiently large, such that multiple adaptive mutations can establish before one has reached fixation; however, it remains unclear how demographic processes affect the probability of observing soft sweeps. Here we extend the theory of soft selective sweeps to realistic demographic scenarios that allow for changes in population size over time. We first show that population bottlenecks can lead to the removal of all but one adaptive lineage from an initially soft selective sweep. The parameter regime under which such “hardening” of soft selective sweeps is likely is determined by a simple heuristic condition. We further develop a generalized analytical framework, based on an extension of the coalescent process, for calculating the probability of soft sweeps under arbitrary demographic scenarios. Two important limits emerge within this analytical framework: In the limit where population-size fluctuations are fast compared to the duration of the sweep, the likelihood of soft sweeps is determined by the harmonic mean of the variance effective population size estimated over the duration of the sweep; in the opposing slow fluctuation limit, the likelihood of soft sweeps is determined by the instantaneous variance effective population size at the onset of the sweep. We show that as a consequence of this finding the probability of observing soft sweeps becomes a function of the strength of selection. Specifically, in species with sharply fluctuating population size, strong selection is more likely to produce soft sweeps than weak selection. Our results highlight the importance of accurate demographic estimates over short evolutionary timescales for understanding the population genetics of adaptation from de novo mutation.
Supersymmetry in the shadow of photini

Additional neutral gauge fermions { \photini" { arise in string compactications as su- perpartners of U(1) gauge elds. Unlike their vector counterparts, the photini can acquire weak-scale masses from soft SUSY breaking and lead to observable signatures at the LHC through mass mixing with the bino. In this work we investigate the collider consequences of adding photini to the neutralino sector of the MSSM. Relatively large mixing of one or more photini with the bino can lead to prompt decays of the lightest ordinary supersymmetric particle; these extra cascades transfer most of the en- ergy of SUSY decay chains into Standard Model particles, diminishing the power of missing energy as an experimental handle for signal discrimination. We demonstrate that the missing energy in SUSY events with photini is reduced dramatically for supersymmetric spectra with MSSM neutralinos near the weak scale, and study the eects on limits set by the leading hadronic SUSY searches at ATLAS and CMS. We nd that in the presence of even one light photino the limits on squark masses from hadronic searches can be reduced by 400 GeV, with comparable (though more modest) reduction of gluino mass limits. We also consider potential discovery channels such as dilepton and multilepton searches, which remain sensitive to SUSY spectra with photini and can provide an unexpected route to the discovery of supersymmetry. Although presented in the context of photini, our results apply in general to theories in which additional light neutral fermions mix with MSSM gauginos.
The Staff Ride: An Approach to Qualitative Data Generation and Analysis

The authors present and illustrate the research staff ride—the re-creation of a historical event for the purpose of understanding organizational phenomena through observation, reflection, and discussion. Staff rides make unique contributions to research through the independent analysis of events outside organizations by content experts who collectively and concurrently reflect on retrospective data while experiencing context. Staff rides involve the examination of ordered sequences of contextually bound events and, thus, promote participants' understanding of the dependence between past and future observations. In this article, the authors elaborate on the types of data, data collection procedures, and data analyses for research staff rides. Importantly, they discuss potential strengths and challenges associated with staff rides in qualitative research, along with ways to address these challenges.
Fictitious Fraud: Economics and the Presumption of Reliance

In the popular imagination, legal proceedings and their rules of law are thought of as paths to unalloyed truth. Both practitioners and scholars know this is often not the case because the law is, as are other domains, riddled with fictions. Indeed, the law sometimes borrows fictions from other domains to help it achieve results that would otherwise be unobtainable. One such place is securities law, in which courts in the United States have borrowed the concept of the ‘efficient market’ from economics to make fraud class actions possible. But that concept is—if not wholly—at least in good measure fictional.
On homometric sets in graphs

Abstract For a vertex set S ⊆ V ( G ) in a graph G, the distance multiset is the multiset of pairwise distances of vertices of S in G, denoted by D ( S ) . Two vertex sets S , T ⊆ V ( G ) are called homometric if D ( S ) = D ( T ) . For a graph G, the largest integer h, such that there are two disjoint homometric sets of order h in G, is denoted by h ( G ) . We investigate h ( n ) = min h ( G ) over all graphs on n vertices, as well as over special classes of graphs such as trees.
Randomized Work-Competitive Scheduling for Cooperative Computing on k-partite Task Graphs

A fundamental problem in distributed computing is the problem of cooperatively executing a given set of tasks in a dynamic setting. The challenge is to minimize the total work done and to maintain efficiency in the face of dynamically changing processor connectivity. In this setting, work is defined as the total number of tasks performed (counting multiplicities) by all the processors during the course of the computation. In this scenario, we are given a set of t tasks that must be completed in a distributed setting by a set of p processors where the communication medium is subject to failures. We assume that the t tasks are similar, in that they require the same number of computation steps to finish execution. We further assume that the tasks are idempotent - executing a task multiple times has the same effect as a single execution of the task. The tasks have a dependency relationship defined among them captured by a task dependency graph.
Proton magnetic resonance spectroscopic evidence of glial effects of cumulative lead exposure in the adult human hippocampus.

BackgroundExposure to lead is known to have adverse effects on cognition in several different populations. Little is known about the underlying structural and functional correlates of such exposure...
Finite source effects in strong lensing: implications for the substructure mass scale

Flux ratio ‘anomalies’ in quadruply imaged gravitational lenses can be explained with galactic substructure of the sort predicted by ΛCDM, but the strength and uniqueness of that hypothesis need to be further assessed. A good way to do that is to use the physical scale associated with the size of the source quasar, and its dependence on wavelength. We develop a toy model to study finite source effects in substructure lensing. Treating substructure as a singular isothermal sphere allows us to compute the images of a finite source analytically, and then to explore how the image configurations and magnifications depend on source position and size. Although simplified, our model yields instructive general principles: image positions and magnifications are basically independent of source size until the source is large enough to intersect a substructure caustic; even sources that are much larger than the substructure Einstein radius can be perturbed at a detectable level; and, most importantly, there is a tremendous amount to be learned from comparing image positions and magnifications at wavelengths that correspond to different source sizes. In a separate analysis, we carefully study four observed radio lenses to determine which of the images are anomalous. In B0712+472, the evidence for a radio flux ratio anomaly is marginal, but if the anomaly is real then image C is probably the culprit. In B1422+231, the anomaly is in image A. Interestingly, B2045+265 and B1555+375 both appear to have two anomalous images. Coincidentally, in each system one of the anomalies is in image C, and the other is in either image A or image B (both possibilities lead to acceptable models). It remains to be seen whether ΛCDM predicts enough substructure to explain multiple anomalies in multiple lenses. When we finally join our modelling results and substructure theory, we obtain lower bounds on the masses of the substructures responsible for the observed anomalies. The mass bounds are broadly consistent with expectations for ΛCDM. Perhaps more importantly, we outline various systematic effects in the mass bounds; poor knowledge of whether the substructure lies within the main lens galaxy or elsewhere along the line of sight appears to be the dominant systematic.
Identifying Excessively Rounded or Truncated Data

All data are digitized, and hence are essentially integers rather than true real numbers. Ordinarily this causes no difficulties since the truncation or rounding usually occurs below the noise level. However, in some instances, when the instruments or data delivery and storage systems are designed with less than optimal regard for the data or the subsequent data analysis, the effects of digitization may be comparable to important features contained within the data. In these cases, information has been irrevocably lost in the truncation process. While there exist techniques for dealing with truncated data, we propose a straightforward method that will allow us to detect this problem before the data analysis stage. It is based on an optimal histogram binning algorithm that can identify when the statistical structure of the digitization is on the order of the statistical structure of the data set itself.
Contact State Estimation using Multiple Model Estimation and Hidden Markov Models

This paper presents an approach to estimating the contact state between a robot and its environment during task execution. Contact states are modeled by constraint equations parameterized by time-dependent sensor data and time-independent object properties. At each sampling time, multiple model estimation is used to assess the most likely contact state. The assessment is performed by a Hidden Markov Model, which combines a measure of how well each set of constraint equations fit the sensor data with the probability of specific contact state transitions. The latter is embodied in a task-based contact state network. The approach is illustrated for a three dimensional peg-in-hole insertion using a tabletop manipulator robot. Using only position sensing, the contact state sequence is successfully estimated. Property estimates are obtained for the peg dimensions as well as the hole position and orientation.
Hilbert–Schmidt separability probabilities and noninformativity of priors

The Horodecki family employed the Jaynes maximum-entropy principle, fitting the mean (b1) of the Bell-CHSH observable (B). This model was extended by Rajagopal by incorporating the dispersion � σ 2 1 � of the observable, and by Canosa and Rossignoli, by generalizing the observable (Bα) .W e further extend the Horodecki one-parameter model in both these manners, obtaining a three-parameterb1 ,σ 2 1 ,α � two-qubit model, for which we find a highly interesting/intricate continuum (−∞ <α< ∞) of Hilbert-Schmidt (HS) separability probabilities—in which, the golden ratio is featured. Our model can be contrasted with the three-parameterbq ,σ 2 q ,q � one of Abe and Rajagopal, which employs a q(Tsallis)-parameter rather than α, and has simply q-invariant HS separability probabilities of 1 . Our results emerge in a study initially focused on embedding certain information metrics over the two-level quantum systems into a q-framework. We find evidence, in this regard, that Srednicki's recently-stated biasedness criterion fornoninformative priors yields rankings of priors fully consistent with an information-theoretic test of Clarke, previously applied to quantum systems by Slater.
Teams, Autonomy, and the Financial Performance of Firms

I estimate a structural model of teams, autonomy, and financial performance, using a large cross section of British establishments. My findings suggest that team production does in fact improve financial performance for the typical establishment but that self-managed or autonomous teams do no better than closely supervised or non-autonomous teams. I also find that the magnitude of benefits to establishments that are helped by teams far exceeds the magnitude of costs to establishments that are hurt by teams. Finally, I find two interesting patterns of correlations among the unobserved determinants of teams, autonomy, and financial performance. First, unobserved factors that increase the propensity to engage in teams are positively correlated with unobserved determinants of financial performance. Second, unobserved factors that increase the propensity to grant teams autonomy are negatively correlated with unobserved determinants of financial performance when teams are used.
Development of conductive adhesive materials for via fill applications

As mobile computing and telecommunication electronics are spreading fast, a demand for microelectronics packaging schemes for high density, fine pitch, high performance and low cost becomes even more severe. Specifically, the conventional printed circuit board (PCB) with plated-through-hole (PTH) vias is difficult to justify its manufacturing cost as well as the packaging density requirement. To meet this challenge, several new manufacturing schemes of high density and high performance PCB have been recently introduced such as surface laminar circuit (SLC), any layer inner via hole (ALIVH) and others. This new PCB fabrication process is categorized as sequential build-up (SBU) or build-up multilayer (BUM) using laminate-based substrates, where via holes are filled with a conductive paste material to make reliable vertical or Z-interconnects. In this paper, a new electrically conducting paste material to be used for via filling is introduced. The new conducting material consists of a conducting filler powder coated with a low melting point metal or alloy, a mixture of several thermoset resins, and other minor organic additives. By varying the filler content and resin chemistry, several formulations have been produced to fill via holes with a high aspect ratio. Via fill experiments have been performed to demonstrate void-free microstructure with good electrical continuity. Various bulk properties such as thermal, electrical and mechanical have also been characterized to understand the material behavior during via filling as well as the field service.
Charging and Growth of Fractal Dust Grains

The structure and evolution of aggregate grains formed within a plasma environment are dependent on the charge acquired by the micron-sized dust grains during the coagulation process. The manner in which the charge is arranged on developing irregular structures can affect the fractal dimension of aggregates formed during collisions, which, in turn, influences the coagulation rate and size evolution of the dust within the plasma cloud. This paper presents preliminary models for the charge and size evolution of fractal aggregates immersed in a plasma environment calculated using a modification to the orbital-motion-limited (OML) theory. Primary electron and ion currents that are incident on points on the aggregate surface are determined using a line-of-sight (LOS) approximation: only those electron or ion trajectories that are not blocked by another grain within the aggregate contribute to the charging current. Using a self-consistent iterative approach, the equilibrium charge and dipole moment are calculated for the dust aggregate. The charges are then used to develop a heuristic charging scheme, which can be implemented in coagulation models. While most coagulation theories assume that it is difficult for like-charged grains to coagulate, the OML_LOS approximation indicates that the electric potentials of aggregate structures are often reduced enough to allow significant coagulation to occur.
Impact of primordial ultracompact minihaloes on the intergalactic medium and first structure formation

The effects of dark matter annihilation on the evolution of the intergalactic medium (IGM) in the early Universe will be more important if the dark matter structure is more concentrated. Ultracompact minihaloes (UCMHs), which formed through dark matter accretion on to primordial black holes (PBHs) or an initial dark matter overdensity produced by a primordial density perturbation, provide a new type of compact dark matter structure to ionize and heat the IGM after matter–radiation equality zeq, which is much earlier than the formation of the first cosmological dark halo structure and later the first stars. We show that the dark matter annihilation density contributed by UCMHs can completely dominate over the homogeneous dark matter annihilation background, even for a tiny UCMH fraction fUCMH=ΩUCMH(zeq)/ΩDM≥ 10−15(1 +z)2(mχc2/100 GeV)−2/3 with a standard thermal-relic dark matter annihilation cross-section, and can provide a new gamma-ray background in the early Universe. UCMH annihilation becomes important to IGM evolution for approximately fUCMH > 10−6(mχc2/100 GeV). The IGM ionization fraction xion and gas temperature Tm can be increased from the recombination residual xion∼ 10−4 and adiabatically cooling Tm∝ (1 +z)2 in the absence of energy injection, to a maximum value of xion∼ 0.1 and Tm∼ 5000 K at z≥ 10 for the upper bound on UCMH abundance constrained by the cosmic microwave background optical depth. A small fraction of UCMHs are seeded by PBHs. The X-ray emission from gas accretion on to PBHs may totally dominate over dark matter annihilation, and may become the main cosmic ionization source for a PBH abundance fPBH=ΩPBH/ΩDM≫ 10−11 (10−12) with PBH mass MPBH∼ 10−6 M⊙ (102 M⊙). However, the constraints on gas accretion rate and X-ray absorption by baryon accumulation within UCMHs, together with accretion feedback, show that X-ray emission can only be a promising source much later than UCMH annihilation at z < zm≪ 1000, where zm depends on the PBH masses, their host UCMHs and the dark matter particles. Also, UCMH radiation including both annihilation and X-ray emission can significantly suppress the low-mass first baryonic structure formation. The effects of UCMH radiation on baryonic structure evolution are quite small as regards the gas temperature after virialization, but more significant in enhancing gas chemical quantities such as the ionization fraction and molecular hydrogen abundance in baryonic objects.
Hybrid Forms of Business: The Logic of Gift in the Commercial World *

Benedict XVI in Caritas in Veritate advances a positive view of businesses that are hybrids between several traditional categories. He expects that the “logic of gift” that animates civil society infuses the market and the State with relations typical for it—reciprocity, gratuitousness, and solidarity. His theological rationale offers an answer to two questions that have largely remained open in the literature—why hybridization of business occurs and why it is desirable. A rational reconstruction of hybrid enterprise that goes beyond a simple taxonomy of types benefits from the Pope’s call for an intrinsic integration of institutions and processes traditionally attributed to disparate spheres. The relational model of the Trinity defines the unity in diversity that accounts for the benefits of truly hybrid businesses, and the “logic of gift” serves as the agent of integration.
Banking, Liquidity and Bank Runs in an Infinite-Horizon Economy

We develop a variation of the macroeconomic model of banking in Gertler and Kiyotaki (2011) that allows for liquidity mismatch and bank runs as in Diamond and Dybvig (1983). As in Gertler and Kiyotaki, because bank net worth ‡uctuates with aggregate production, the spread between the expected rates of return on bank assets and deposits ‡uctuates countercyclically. However, because bank assets are less liquid than deposits, bank runs are possible as in Diamond and Dybvig. Whether a bank run equilibrium exists depends on bank balance sheets and an endogenous liquidation price for bank assets. While in normal times a bank run equilibrium may not exist, the
Monte Carlo modeling of neutron and gamma-ray imaging systems

Detailed numerical prototypes are essential to the design of efficient and cost-effective neutron and gamma-ray imaging systems. We have exploited the unique capabilities of an LLNL-developed radiation transport code (COG) to develop code modules capable of simulating the performance of neutron and gamma-ray imaging systems over a wide range of source energies. COG allows us to simulate complex, energy-, angle-, and time-dependent radiation sources, model 3D system geometries with 'real world' complexity, specify detailed elemental and isotopic distributions and predict the responses of various types of imaging detectors with full Monte Carlo accuracy. COG references detailed, evaluated nuclear interaction databases allowing users to account for multiple scattering, energy straggling, and secondary particle production phenomena which may significantly effect the performance of an imaging system but may be difficult or even impossible to estimate using simple analytical models. In this work we will present examples illustrating the use of these routines in the analysis of industrial radiographic systems for thick target inspection, non-intrusive luggage and cargo scanning systems, and international treaty verification.
Does Your Cohort Matter? Measuring Peer Effects in College Achievement

We estimate peer effects in college achievement using a data set in which individuals are exogenously assigned to peer groups of about 30 students with whom they are required to spend the majority of their time interacting. This feature enables us to estimate peer effects that are more comparable to changing the entire cohort of peers. Using this broad peer group, we measure academic peer effects of much larger magnitude than found in previous studies. The effects persist at a diminished rate into follow‐on years, and we find evidence of nonlinearities in the magnitude of the effects across student academic ability.
On Expediency and Convergence in Variable-Structure Automata

A stochastic automaton responds to the penalties from a random environment through a reinforcement scheme by changing its state probability distribution in such a way as to reduce the average penalty received. In this manner the automaton is said to possess a variable structure and the ability to learn. This paper discusses the efficiency of learning for an m-state automaton in terms of expediency and convergence, under two distinct types of reinforcement schemes: one based on penalty probabilities and the other on penalty strengths. The functional relationship between the successive probabilities in the reinforcement scheme may be either linear or nonlinear. The stability of the asymptotic expected values of the state probability is discussed in detail. The conditions for optimal and expedient behavior of the automaton are derived. Reduction of the probability of suboptimal performance by adopting the Beta model of the mathematical learning theory is discussed. Convergence is discussed in the light of variance analysis. The initial learning rate is used as a measure of the overall convergence rate. Learning curves can be obtained by solving nonlinear difference equations relating the successive expected values. An analytic expression concerning the convergence behavior of the linear case is derived. It is shown that by a suitable choice of the reinforcement scheme it is possible to increase the separation of asymptotic state probabilities.
Reduced Basis Technique for Nonlinear Analysis of Structures

A reduced basis technique and a computational' algorithm are presented for predicting the nonlinear static response of structures. A total Lagrangian formulation is used and the structure is discretized by using displacement finite element models. The nodal displacement vector is expressed as a linear combination of a small number of basis vectors and a Rayleigh-Ritz technique is used to approximate the finite element equations by a reduced system of nonlinear equations. The Rayleigh-Ritz approximation functions (basis vectors) are chosen to be those commonly used in the static perturbation technique namely, a nonlinear solution and a number of its path derivatives. A procedure is outlined for automatically selecting the load (or displacement) step size and monitoring the solution accuracy. The high accuracy and effectiveness of the proposed approach is demonstrated by means of numerical examples.
The Credit Rating Crisis

Since June 2007, the creditworthiness of structured finance products has deteriorated rapidly. The number of downgrades in November 2007 alone exceeded 2,000 and many downgrades were severe, with 500 tranches downgraded more than 10 notches. Massive downgrades continued in 2008. More than 11,000 of the downgrades affected securities that were rated AAA. This paper studies the credit rating crisis of 2007-2008 and in particular describes the collapse of the credit ratings of ABS CDOs. Using data on ABS CDOs we provide suggestive evidence that ratings shopping may have played a role in the current crisis. We find that tranches rated solely by one agency, and by S&P in particular, were more likely to be downgraded by January 2008. Further, tranches rated solely by one agency are more likely to suffer more severe downgrades.(This abstract was borrowed from another version of this item.)
Ideal solution of an inverse normal mode problem with finite spectral data

Abstract : The problem of reconstructing the density of a vibrating string given the first N eigenfrequencies for two vibrating configurations admits an infinite number of solutions. Among all such strings compatible with the truncated data set, we define the ideal string to be that string for which a weighted average of the density is minimum. We prove that this ideal string must have a finite number of degrees of freedom and hence, that it is made up by a finite number of concentrated point masses. By specializing the optimality criterion, we can also show that the Krein string is an ideal string. (Author)
In vitro models for liver toxicity testing.

Over the years, various liver-derived in vitro model systems have been developed to enable investigation of the potential adverse effects of chemicals and drugs. Liver tissue slices, isolated microsomes, perfused liver, immortalized cell lines, and primary hepatocytes have been used extensively. Immortalized cell lines and primary isolated liver cells are currently the most widely used in vitro models for liver toxicity testing. Limited throughput, loss of viability, and decreases in liver-specific functionality and gene expression are common shortcomings of these models. Recent developments in the field of in vitro hepatotoxicity include three-dimensional tissue constructs and bioartificial livers, co-cultures of various cell types with hepatocytes, and differentiation of stem cells into hepatic lineage-like cells. In an attempt to provide a more physiological environment for cultured liver cells, some of the novel cell culture systems incorporate fluid flow, micro-circulation, and other forms of organotypic microenvironments. Co-cultures aim to preserve liver-specific morphology and functionality beyond those provided by cultures of pure parenchymal cells. Stem cells, both embryonic- and adult tissue-derived, may provide a limitless supply of hepatocytes from multiple individuals to improve reproducibility and enable testing of the individual-specific toxicity. This review describes various traditional and novel in vitro liver models and provides a perspective on the challenges and opportunities afforded by each individual test system.
Signaling, Investment Opportunities, and Dividend Announcements

This article examines potential explanations for the wealth effects surrounding dividend change announcements. We find that new information concerning managers' investment policies is not revealed at the time of the dividend announcement. We also find that dividend increases (decreases) are associated with subsequent significant increases (decreases) in capital expenditure over the three years following the dividend change, and that dividend change announcements are associated with revisions in analysts' forecasts of current earnings. These results are consistent with the cash flow signalling hypothesis rather than the free cash flow hypothesis as an explanation for the observed stock price reactions to dividend change announcements. Article published by Oxford University Press on behalf of the Society for Financial Studies in its journal, The Review of Financial Studies.
Vertical Contracts as Strategic Commitments: How are They Enforced?

This paper addresses the strategic commitment value of various price and nonprice vertical contracts. Assuming contract offers are sufficiently public to have strategic importance, we focus on commitment as a necessary and separable condition to be met. The analysis has two components. First, considering the relationship between a monopolist manufacturer and his imperfectly competing retailers, enforcement conditions necessary for alternative vertical contracts to have commitment value are identified in the static (reputation-free) context. It is shown that external help (i.e., enforcement by nonsignatories) is necessary for bilateral minimum resale price maintenance (price floors) and exclusive territory contracts to have commitment value, whereas maximum resale price maintenance (price ceilings) do not require such help (i.e., they are internally enforcing). Second, the paper provides an analysis of the U.S. case law and discusses the empirical validity of the “external enforcement” assumption that is shown to underlie recent proposals to make certain vertical restraints illegal.