cssi/SciSciGPT-SciSciNet huggingface dataset:
On the conjectures of Atiyah and Sutcliffe

Motivated by certain questions in physics, Atiyah defined a determinant function which to any set of n distinct points x1, . . . , xn in \({\mathbb R^3}\) assigns a complex number D(x1, . . . , xn). In a joint work, he and Sutcliffe stated three intriguing conjectures about this determinant. They provided compelling numerical evidence for the conjectures and an interesting physical interpretation of the determinant. The first conjecture asserts that the determinant never vanishes, the second states that its absolute value is at least one, and the third says that \({|D(x_1,\ldots, x_n)|^{n-2} \geq \prod_{i=1}^n |D(x_1,\ldots, x_{i-1},x_{i+1},\ldots, x_n)|}\). Despite their simple formulation, these conjectures appear to be notoriously difficult. Let Dn denote the Atiyah determinant evaluated at the vertices of a regular n-gon. We prove that \({\lim_{n\to \infty}\frac{\ln D_n}{n^2}=\frac{7\zeta(3)}{2\pi^2}-\frac{\ln 2}{2}=0.07970479\ldots}\) and establish the second conjecture in this case. Furthermore, we prove the second conjecture for vertices of a convex quadrilateral and the third conjecture for vertices of an inscribed quadrilateral.
Bayesian inference applied to the electromagnetic inverse problem.

We present a new approach to the electromagnetic inverse problem that explicitly addresses the ambiguity associated with its ill-posed character. Rather than calculating a single “best” solution according to some criterion, our approach produces a large number of likely solutions that both fit the data and any prior information that is used. Whereas the range of the different likely results is representative of the ambiguity in the inverse problem even with prior information present, features that are common across a large number of the different solutions can be identified and are associated with a high degree of probability. This approach is implemented and quantified within the formalism of Bayesian inference, which combines prior information with that of measurement in a common framework using a single measure. To demonstrate this approach, a general neural activation model is constructed that includes a variable number of extended regions of activation and can incorporate a great deal of prior information on neural current such as information on location, orientation, strength, and spatial smoothness. Taken together, this activation model and the Bayesian inferential approach yield estimates of the probability distributions for the number, location, and extent of active regions. Both simulated MEG data and data from a visual evoked response experiment are used to demonstrate the capabilities of this approach. Hum. Brain Mapping 7:195–212, 1999 Published 1999 Wiley-Liss, Inc. This article is a US government work and, as such, is in the public domain in the United States of America.
Comparing Star Formation on Large Scales in the c2d Legacy Clouds: Bolocam 1.1 mm Dust Continuum Surveys of Serpens, Perseus, and Ophiuchus

We have undertaken an unprecedentedly large 1.1 mm continuum survey of three nearby star-forming clouds using Bolocam at the Caltech Submillimeter Observatory. We mapped the largest areas in each cloud at millimeter or submillimeter wavelengths to date: 7.5 deg2 in Perseus (Enoch and coworkers), 10.8 deg^2 in Ophiuchus (Young and coworkers), and 1.5 deg2 in Serpens with a resolution of 31", detecting 122, 44, and 35 cores, respectively. Here we report on results of the Serpens survey and compare the three clouds. Average measured angular core sizes and their dependence on resolution suggest that many of the observed sources are consistent with power-law density profiles. Tests of the effects of cloud distance reveal that linear resolution strongly affects measured source sizes and densities, but not the shape of the mass distribution. Core mass distribution slopes in Perseus and Ophiuchus (α = 2.1 ± 0.1 and 2.1 ± 0.3) are consistent with recent measurements of the stellar IMF, whereas the Serpens distribution is flatter (α = 1.6 ± 0.2). We also compare the relative mass distribution shapes to predictions from turbulent fragmentation simulations. Dense cores constitute less than 10% of the total cloud mass in all three clouds, consistent with other measurements of low star formation efficiencies. Furthermore, most cores are found at high column densities; more than 75% of 1.1 mm cores are associated with AV ~> 8 mag in Perseus, 15 mag in Serpens, and 20-23 mag in Ophiuchus.
Analytical and Experimental Investigation of Flow-Reversible Heat Exchangers Using Temperature-Entropy Bond Graphs

Modeling of heat exchangers using true bond graphs with temperature and rate of change of entropy as power variables is presented. Techniques used for modeling of irreversabilities and compressible flows are shown. The results of two and three lump models are compared with experimental results, with the agreement between these low order models and the experimental results being good. This paper shows how well a three lump model (6th order) can predict the dynamics of an actual reversal of flow. Heat exchanger response to mass flow rate oscillation is presented.
Determinization of resolution by an algorithm operating on complete assignments

“Determinization” of resolution is usually done by a DPLL-like procedure that operates on partial assignments. We introduce a resolution-based SAT-solver operating on complete assignments and give a theoretical justification for determinizing resolution this way. This justification is based on the notion of a point image of resolution proof. We give experimental results confirming the viability of our approach. The complete version of this paper is given in [2].
Diffuse Light in the Virgo Cluster

We present deep optical imaging of the inner 1.5 x1.5 of the Virgo cluster to search for diffuse intracluster light (ICL). Our image reaches a 1 depth of µv=28.5 mag/arcsec 2 — 1.5 mag/arcsec 2 deeper than previous surveys — and reveals an intricate web of diffuse intracluster light. We see several long (>100 kpc) tidal streamers, as well as a myriad of smaller-scale tidal tails and bridges between galaxies. The diffuse halo of M87 is traced out to nearly 200 kpc, appearing very irregular on these scales, while significant diffuse light is also detected around the M84/M86 pair. Several galaxies in the core are embedded in common envelopes, suggesting they are true physical subgroups. The complex substructure of Virgo’s diffuse ICL reflects the hierarchical nature of cluster assembly, rather than being the product of smooth accretion around a central galaxy. Subject headings:galaxies: clusters: individual (Virgo) — galaxies: interactions
The Effect of Negative-Energy Shells on the Schwarzschild Black Hole

We construct Penrose diagrams for Schwarzschild spacetimes joined by massless shells of matter, in the process correcting minor flaws in the similar diagrams drawn by Dray and ’t Hooft (Commun Math Phys 99:613–625, 1985), and confirming their result that such shells generate a horizon shift. We then consider shells with negative energy density, showing that the horizon shift in this case allows for travel between the heretofore causally separated exterior regions of the Schwarzschild geometry. These drawing techniques are then used to investigate the properties of successive shells, joining multiple Schwarzschild regions. Again, the presence of negative-energy shells leads to a causal connection between the exterior regions, even in (some) cases with two successive shells of equal but opposite total energy.
Favoring the Winner or Loser in Repeated Contests

Should a firm favor a weaker or stronger employee in a contest? Despite a widespread emphasis on rewarding the best employees, managers continue to tolerate and even favor poor performers. Contest theory reveals that evenly matched contests are the most intense, which implies that a contest designer can maximize each player's effort by artificially boosting the underdog's chances. We apply this type of "handicapping" to a two-period repeated contest between employees, in which the only information available about their abilities is their performance in the first period. In this setting, employees are strategic and forward looking, such that they fully anticipate the potential impact of the first-period contest result on the second-period contest and thus adjust their behaviors accordingly. The manager also incorporates these strategic behaviors of employees when determining an optimal handicapping policy. If employees' abilities are sufficiently different, favoring the first-period loser in the second period increases the total effort over both periods. However, if abilities are sufficiently similar, we find the opposite result occurs: total effort increases the most in response to a handicapping strategy of favoring the first-period winner.
Precautionary Wealth Accumulation

This paper provides theoretical foundations for when individual and aggregate wealth accumulation increase as earnings risk increases. Stated in terms of a simple picture, the problem addressed in this paper is to find sufficient conditions such that the pattern in Figure 1 holds. Figure 1 describes a situation in which an individual's expected wealth accumulation profile is weakly greater at each age over the life cycle whenever the individual faces one earnings process that is riskier than another earnings process, other things equal. Two important open questions can be answered by finding sufficient conditions for the pattern in Figure 1 to occur. First, there is the question of when theory predicts that households that face more earnings risk have more expected wealth accumulation at any point in the life cycle than households that face less earnings risk. The development of such a theory would be helpful as there is a sizeable empirical literature related to this question which is surveyed by Browning and Lusardi (1996). Second, there is the question of when theory predicts that aggregate wealth accumulation increases as earnings risk increases. Much of the interest in the precautionary savings literature is based on the possibility that an important part of aggregate wealth is due to uninsured earnings risk. This question can also be answered with Figure 1. The idea is to treat the expected wealth profile of one individual as the realized average wealth profile of a large number of similarly situated individuals. The law of large numbers justifies this when shocks are independent across individuals and, thus, earnings risk is idiosyncratic. Since aggregate wealth holding is a weighted sum of the average wealth holdings of individuals at different ages, an upward shift of the expected wealth profile of all agents then implies that aggregate wealth holding increases with increases in earnings risk, other things equal. This paper provides the first general answer to when the pattern in Figure 1 occurs in the context of a multi-period model with independent earnings shocks. The answer is given at two levels: in terms of properties of the decision rule for savings (i.e. the savings function) and in terms of preferences. A savings function maps an individual's current state (e.g. current wealth and earnings) and age into savings or wealth carried into the next model period, given a specific earnings process. Since economists are familiar with the merits of sufficient conditions stated in terms of preferences, I will try to motivate why sufficient conditions stated in terms of the savings function are interesting. First, they are widely applicable. They apply to theories where savings decisions maximize a utility function or are given by a rule-of-thumb. They also apply to models where there is wage risk and there are both consumption-saving and labour-leisure decisions. Second, in so far as the savings function can be estimated, it is useful for an empirical
Local Causality and Completeness: Bell vs. Jarrett

J.S. Bell believed that his famous theorem entailed a deep and troubling conflict between the empirically verified predictions of quantum theory and the notion of local causality that is motivated by relativity theory. Yet many physicists continue to accept, usually on the reports of textbook writers and other commentators, that Bell’s own view was wrong, and that, in fact, the theorem only brings out a conflict with determinism or the hidden-variables program or realism or some other such principle that (unlike local causality), allegedly, nobody should have believed anyway. Moreover, typically such beliefs arise without the person in question even being aware that the view they are accepting differs so radically from Bell’s own. Here we try to shed some light on the situation by focusing on the concept of local causality that is the heart of Bell’s theorem, and, in particular, by contrasting Bell’s own understanding with the analysis of Jon Jarrett which has been the most influential source, in recent decades, for the kinds of claims mentioned previously. We point out a crucial difference between Jarrett’s and Bell’s own understanding of Bell’s formulation of local causality, which turns out to be the basis for the erroneous claim, made by Jarrett and many others, that Bell misunderstood the implications of his own theorem.
On the density of geometrically finite Kleinian groups

The density conjecture of Bers, Sullivan and Thurston predicts that each complete hyperbolic 3-manifold M with finitely generated fundamental group is an algebraic limit of geometrically finite hyperbolic 3-manifolds. We prove that the conjecture obtains for each complete hyperbolic 3manifold with no cusps and incompressible ends.
Non-heme Fe(IV)-oxo intermediates.

High-valent non-heme iron–oxo intermediates have been proposed for decades as the key intermediates in numerous biological oxidation reactions. In the past three years, the first direct characterization of such intermediates has been provided by studies of several αKG-dependent oxygenases that catalyze either hydroxylation or halogenation of their substrates. In each case, the Fe(IV)–oxo intermediate is implicated in cleavage of the aliphatic C–H bond to initiate hydroxylation or halogenation. The observation of non-heme Fe(IV)–oxo intermediates and Fe(II)-containing product(s) complexes with almost identical spectroscopic parameters in the reactions of two distantly related αKG-dependent hydroxylases suggests that members of this subfamily follow a conserved mechanism for substrate hydroxylation. In contrast, for the αKG-dependent non-heme iron halogenase, CytC3, two distinct Fe(IV) complexes form and decay together, suggesting that they are in rapid equilibrium. The existence of two distinct conformers ...
Two-Dimensional Simulations of Enhanced Heat Transfer in an Intermittently Grooved Channel

Two-dimensional Navier-Stokes simulations of heat and momentum transport in an intermittently grooved passage are performed using the spectral element technique for the Reynolds number range 600≤Re≤1800. The computational domain has seven contiguous transverse grooves cut symmetrically into opposite walls, followed by a flat section with the same length. Periodic inflow/outflow boundary conditions are employed. The development and decay of unsteady flow is observed in the grooved and flat sections, respectively. The axial variation of the unsteady component of velocity is compared to the local heat transfer, shear stress and pressure gradient
Long zero-free sequences in finite cyclic groups

A sequence in the additive group Z"n of integers modulo n is called n-zero-free if it does not contain subsequences with length n and sum zero. The article characterizes the n-zero-free sequences in Z"n of length greater than 3n/2-1. The structure of these sequences is completely determined, which generalizes a number of previously known facts. The characterization cannot be extended in the same form to shorter sequence lengths. Consequences of the main result are best possible lower bounds for the maximum multiplicity of a term in an n-zero-free sequence of any given length greater than 3n/2-1 in Z"n, and also for the combined multiplicity of the two most repeated terms. Yet another application is finding the values in a certain range of a function related to the classic theorem of Erdos, Ginzburg and Ziv.
Robust Kernel Density Estimation by Scaling and Projection in Hilbert Space

While robust parameter estimation has been well studied in parametric density estimation, there has been little investigation into robust density estimation in the nonparametric setting. We present a robust version of the popular kernel density estimator (KDE). As with other estimators, a robust version of the KDE is useful since sample contamination is a common issue with datasets. What "robustness" means for a nonparametric density estimate is not straightforward and is a topic we explore in this paper. To construct a robust KDE we scale the traditional KDE and project it to its nearest weighted KDE in the L2 norm. This yields a scaled and projected KDE (SPKDE). Because the squared L2 norm penalizes point-wise errors superlinearly this causes the weighted KDE to allocate more weight to high density regions. We demonstrate the robustness of the SPKDE with numerical experiments and a consistency result which shows that asymptotically the SPKDE recovers the uncontaminated density under sufficient conditions on the contamination.
A Dynamic Analysis of Educational Attainment, Occupational Choices, and Job Search

This article examines career choices using a dynamic structural model that nests a job search model within a human capital model of occupational and educational choices. Wage growth occurs in the model because workers move between firms and occupations as they search for suitable job matches and because workers endogenously accumulate firm and occupation specific human capital. Simulations performed using the estimated model reveal that both self-selection in occupational choices and mobility between firms account for a much larger share of total earnings and utility than the combined effects of firm and occupation specific human capital.
Firm inventory behavior in east Africa

Firms normally keep certain inventories, including raw materials, work-in-progress, and finished goods, to operate seamlessly and not to miss possible business opportunities. But inventory is costly, and the optimal firm inventory differs depending on various economic conditions, including trade and transport costs. The paper examines firm inventory behavior in East Africa, in which transport connectivity, especially to the ports, is considered as one of the major business constraints. Using firm-level data from Burundi, Kenya, Rwanda, Tanzania, and Uganda, it is shown that transport connectivity significantly affects firm inventory behavior. In particular, road density and transport costs to the port are important to determine the optimal inventory level. With more roads in a city and/or cheaper access to the port, firms would hold smaller inventories.
Assessing the Effectiveness of Juvenile Justice Reforms: A Closer Look at the Criteria and the Impacts on Diverse Stakeholders

Research to date has taken a relatively narrow view of the criteria by which the effectiveness of juvenile justice sentencing policies are to be assessed. This narrowness is particularly striking given the comprehensive “get tough” reforms that recently have been enacted in nearly every state. Drawing on previous research and an analysis of the potential effects of a recent juvenile justice sentencing reform in Texas, this paper argues for greater attention to conceptualizing and empirically assessing effectiveness broadly, including reference to intended and unintended effects, multiple goals and means, and diverse stakeholders. The argument is sustained first by outlining and discussing these key dimensions and then by empirically illustrating the potential importance of one of these dimensions – diverse stakeholders and their respective interests.
Shape-persistent arylene ethynylene macrocycles: syntheses and supramolecular chemistry

This article describes recent developments in the synthesis of macrocycles having rigid, monocyclic skeletons composed of arylene and ethynylene units and the studies on their self-assembling behavior.
A structural analysis of vehicle design responses to Corporate Average Fuel Economy policy

Abstract The US Corporate Average Fuel Economy (CAFE) regulations are intended to influence automaker vehicle design and pricing choices. CAFE policy has been in effect for the past three decades, and new legislation has raised standards significantly. We present a structural analysis of automaker responses to generic CAFE policies. We depart from prior CAFE analyses by focusing on vehicle design responses in long-run oligopolistic equilibrium, and we view vehicles as differentiated products, taking demand as a general function of price and product attributes. We find that under general cost, demand, and performance functions, single-product profit maximizing firm responses to CAFE standards follow a distinct pattern: firms ignore CAFE when the standard is low, treat CAFE as a vehicle design constraint for moderate standards, and violate CAFE when the standard is high. Further, the point and extent of first violation depends upon the penalty for violation, and the corresponding vehicle design is independent of further standard increases. Thus, increasing CAFE standards will eventually have no further impact on vehicle design if the penalty for violation is also not increased. We implement a case study by incorporating vehicle physics simulation, vehicle manufacturing and technology cost models, and a mixed logit demand model to examine equilibrium powertrain design and price decisions for a fixed vehicle body. Results indicate that equilibrium vehicle design is not bound by current CAFE standards, and vehicle design decisions are directly determined by market competition and consumer preferences. We find that with increased fuel economy standards, a higher violation penalty than the current stagnant penalty is needed to cause firms to increase their design fuel economy at equilibrium. However, the maximum attainable improvement can be modest even if the penalty is doubled. We also find that firms’ design responses are more sensitive to variation in fuel prices than to CAFE standards, within the examined ranges.
LexRank: graph-based lexical centrality as salience in text summarization

We introduce a stochastic graph-based method for computing relative importance of textual units for Natural Language Processing. We test the technique on the problem of Text Summarization (TS). Extractive TS relies on the concept of sentence salience to identify the most important sentences in a document or set of documents. Salience is typically defined in terms of the presence of particular important words or in terms of similarity to a centroid pseudo-sentence. We consider a new approach, LexRank, for computing sentence importance based on the concept of eigenvector centrality in a graph representation of sentences. In this model, a connectivity matrix based on intra-sentence cosine similarity is used as the adjacency matrix of the graph representation of sentences. Our system, based on LexRank ranked in first place in more than one task in the recent DUC 2004 evaluation. In this paper we present a detailed analysis of our approach and apply it to a larger data set including data from earlier DUC evaluations. We discuss several methods to compute centrality using the similarity graph. The results show that degree-based methods (including LexRank) outperform both centroid-based methods and other systems participating in DUC in most of the cases. Furthermore, the LexRank with threshold method outperforms the other degree-based techniques including continuous LexRank. We also show that our approach is quite insensitive to the noise in the data that may result from an imperfect topical clustering of documents.
"Santa Evita", historia, ficción y mito: una narrativa "a partir del otro lado"

RESUMENEn Santa Evita , Tomas Eloy Martinez recepciona una variedad amplia de discursos y re-escribe el mito de Evita, renovandolo en una “ficcion verdadera”. En tal proceso imagina-rio revivifica lo que se habia cosificado haciendole re-encontrar su fuerza impulsora denuevos procesos de desarrollo historico. Recuperando la esencia mitica de un personajecentral de la historia argentina, logra negar su musealizacion, su neutralizacion ydespolitizacion. La “verdad” que se pretende establecer queda enmascarada en las “menti-ras” de la ficcion. Palabras claves : Mito, historia, ficcion, paratexto, efecto de realidad, transfiguracion, dis-curso figurativo, ficcion verdadera.ABSTRACTIn Santa Evita , a narrative in which fiction and the pretended truths of historiography arechallenged, Tomas Eloy Martinez uses a wide variety of discourses to re-write and givenew life to the mith of Evita Peron. In this intellectual endeavor that combines imaginationand historical facts (“real fiction”) Martinez breathes new life into and sheds new light onwhat had became a stale myth, a “museum piece” of argentinian history, questioning
A problem of rights arbitration from the Talmud

Abstract A man dies leaving certain amounts of his estate to each of his sons, but the amounts sum to more than the total available. Various solutions are discussed, some based in the theory of games. The method endorsed here regards the problem as one of rights arbitration in which the division is based on interpreting the applicable rules, rather than on weighing the parties' powers and possible benefits.
Growth parameter dependence of gain compression in AlGaN/GaN HFETs

Abstract The dependence of gain compression on the Al-mole fraction and the thickness of the AlGaN barrier layer are reported for typical undoped supply layer AlGaN/GaN HFETs using a physics-based model. The gain compression is calculated using a large signal circuit model. The intrinsic circuit parameters are extracted from a physics-based model that self-consistently solves the Schrodinger and Poisson's equations to determine the 2DEG concentration in the channel including the effects of both spontaneous and piezoelectric polarization present in the AlGaN barrier and the underlying GaN layers. Transport parameters are obtained by ensemble Monte Carlo simulation and device non-linearity is addressed using Volterra series analysis. With AlGaN barrier thickness increasing from 100 to 250 A, the 1 dB gain compression point ranges from 5 to 22 dBm of input power at 300 K for 0.25 × 100 μm Al 0.20 Ga 0.80 N/GaN HEMTs. On the other hand, a similar device with a barrier Al x Ga 1− x N layer thickness of 300 A Al x Ga 1− x N the 1 dB gain compression point at 300 K increases from 6 dBm for x =0.1 to 20 dBm for x =0.3. The improvements in output power handling capability with increasing barrier layer thickness and Al-mole fraction are attributed to an increased device transconductance resulting from an increased sheet carrier density in the channel. A decrease in the gain compression point due to an increase in temperature is also presented.
SUPERLUMINAL CAUSTICS OF CLOSE, RAPIDLY ROTATING BINARY MICROLENSES

The two outer triangular caustics (regions of infinite magnification) of a close binary microlens move much faster than the components of the binary themselves, and can even exceed the speed of light. When 1, where c is the caustic speed, the usual formalism for calculating the lens magnification breaks down. We develop a new formalism that makes use of the gravitational analog of the Lienard-Wiechert potential. We find that as the binary speeds up, the caustics undergo several related changes: First, their position in space drifts. Second, they rotate about their own axes so that they no longer have a cusp facing the binary center of mass. Third, they grow larger and dramatically so for 1. Fourth, they grow weaker roughly in proportion to their increasing size. Superluminal caustic-crossing events are probably not uncommon, but they are difficult to observe.
An architecture for biological information extraction and representation

Motivations: Technological advances in biomedical research are generating a plethora of heterogeneous data at a high rate. There is a critical need for extraction, integration and management tools for information discovery and synthesis from these heterogeneous data. Results: In this paper, we present a general architecture, called ALFA, for information extraction and representation from diverse biological data. The ALFA architecture consists of: (i) a networked, hierarchical, hyper-graph object model for representing information from heterogeneous data sources in a standardized, structured format; and (ii) a suite of integrated, interactive software tools for information extraction and representation from diverse biological data sources. As part of our research efforts to explore this space, we have currently prototyped the ALFA object model and a set of interactive software tools for searching, filtering, and extracting information from scientific text. In particular, we describe BioFerret, a meta-search tool for searching and filtering relevant information from the web, and ALFA Text Viewer, an interactive tool for user-guided extraction, disambiguation, and representation of information from scientific text. We further demonstrate the potential of our tools in integrating the extracted information with experimental data and diagrammatic biological models via the common underlying ALFA representation. Contact: aditya_vailaya@agilent.com
On the optimality of treating interference as noise

It is shown that in the K-user interference channel, if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all values in dB scale), then the simple scheme of using point to point Gaussian codebooks with appropriate power levels at each transmitter and treating interference as noise at every receiver (in short, TIN scheme) achieves all points in the capacity region to within a constant gap. The generalized degrees of freedom (GDoF) region under this condition is a polyhedron, which is shown to be fully achieved by the same scheme, without the need for time-sharing. The results are proved by first deriving a polyhedral relaxation of the GDoF region achieved by TIN, then providing a dual characterization of this polyhedral region via the use of potential functions, and finally proving the optimality of this region in the desired regime.
LDPC-based space-time coded OFDM systems over correlated fading channels: Performance analysis and receiver design

We consider a space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) system with multiple transmitter and receiver antennas over correlated frequency- and time-selective fading channels. It is shown that the product of the time-selectivity order and the frequency-selectivity order is a key parameter to characterize the outage capacity of the correlated fading channel. It is also observed that STCs with large effective lengths and ideal built-in interleavers are more effective in exploiting the natural diversity in multiple-antenna correlated fading channels. We then propose a low-density parity-check (LDPC)-code-based STC-OFDM system. Compared with the conventional space-time trellis code (STTC), the LDPC-based STC can significantly improve the system performance by exploiting both the spatial diversity and the selective-fading diversity in wireless channels. Compared with the previously proposed turbo-code-based STC scheme, LDPC-based STC exhibits lower receiver complexity and more flexible scalability. We also consider receiver design for LDPC-based STC-OFDM systems in unknown fast fading channels and propose a novel turbo receiver employing a maximum a posteriori expectation-maximization (MAP-EM) demodulator and a soft LDPC decoder, which can significantly reduce the error floor in fast fading channels with a modest computational complexity. With such a turbo receiver, the proposed LDPC-based STC-OFDM system is a promising solution to highly efficient data transmission over selective-fading mobile wireless channels.
Shape measurement biases from underfitting and ellipticity gradients

With this study, precision weak gravitational lensing experiments require measurements of galaxy shapes accurate to <1 part in 1000. We investigate measurement biases, noted by Voigt and Bridle (2009) and Melchior et al. (2009), that are common to shape measurement methodologies that rely upon fitting elliptical-isophote galaxy models to observed data. The first bias arises when the true galaxy shapes do not match the models being fit. We show that this "underfitting bias" is due, at root, to these methods' attempts to use information at high spatial frequencies that has been destroyed by the convolution with the point-spread function (PSF) and/or by sampling. We propose a new shape-measurement technique that is explicitly confined to observable regions of k-space. A second bias arises for galaxies whose ellipticity varies with radius. For most shape-measurement methods, such galaxies are subject to "ellipticity gradient bias". We show how to reduce such biases by factors of 20–100 within the new shape-measurement method. The resulting shear estimator has multiplicative errors < 1 part in 103 for high-S/N images, even for highly asymmetric galaxies. Without any training or recalibration, the new method obtains Q = 3000 in the GREAT08 Challenge of blind shear reconstruction on low-noise galaxies, more » several times better than any previous method. « less
A sensitivity tradeoff for plants with time delay

In this paper we show that the sensitivity function of a scalar feedback system must satisfy an integral constraint when the open-loop transfer function is strictly proper and contains a time delay. The integral constraint is identical to the classical Bode sensitivity integral, which holds provided the open-loop gain has greater than a one-pole rolloff. The design implications of the two constraints are somewhat different, however, and this difference is discussed. The relation between open-loop phase and a conflict between bandwidth and sensitivity properties is explored.
Dynamics of desynchronized episodes in intermittent synchronization

Intermittent synchronization is observed in a variety of different experimental settings in physics and beyond and is an established research topic in nonlinear dynamics. When coupled oscillators exhibit relatively weak, intermittent synchrony, the trajectory in the phase space spends a substantial fraction of time away from a vicinity of a synchronized state. Thus to describe and understand the observed dynamics one may consider both synchronized episodes and desynchronized episodes (the episodes when oscillators are not synchronous). This mini-review discusses recent developments in this area. We explain how one can consider variation in synchrony on the very short time-scales, provided that there is some degree of overall synchrony. We show how to implement this approach in the case of intermittent phase locking, review several recent examples of the application of these ideas to experimental data and modeling systems, and discuss when and why these methods may be useful.
The Errors of Individualistic Public Health Interventions: Denial of Treatment to Obese Persons Comment on "Denial of Treatment to Obese Patients-the Wrong Policy on Personal Responsibility for Health".

I agree entirely with Nir Eyal’s perspective that denying treatment to obese patients is morally wrong. However, the reasons for this belief differ in some ways from Eyal’s analysis. In this commentary, I will try to explain the similarities and differences in our perspectives. My primary claim is that the denial of treatment to obese patients is wrong principally because (i) it eschews a whole-population approach to the problem of poor nutrition and is therefore likely to be ineffective; (ii) it is likely to expand obesity-related health inequities; and (iii) it is likely to intensify stigma against already-marginalized social groups. I shall consider each in turn, and explore the extent to which Eyal would be likely to agree with my claims.
The Effect of Medicaid Payment Rates on Access to Dental Care among Children

We examine the effect of payment rates on access to dental care among children on Medicaid and on dentists’ participation in Medicaid. Using data from the Survey of Income and Program Participation combined with data on dental fees from 2001 to 2010 and conditioning on state fixed effects, we find a modest positive relationship between Medicaid payment rates and dental care utilization. We test whether higher fees increase the number of dentists accepting Medicaid patients using data from annual surveys of dentists conducted by the American Dental Association between 1999 and 2009. We find a positive, though small, effect of Medicaid payment rates on whether a dentist treats any publicly insured patients and the percentage of the practice’s patients who have public insurance. The estimates imply that increasing Medicaid payments to the level of private market fees would increase access to care, but at a high cost of inducing additional visits.
Joint inference of groups, events and human roles in aerial videos

With the advent of drones, aerial video analysis becomes increasingly important; yet, it has received scant attention in the literature. This paper addresses a new problem of parsing low-resolution aerial videos of large spatial areas, in terms of 1) grouping, 2) recognizing events and 3) assigning roles to people engaged in events. We propose a novel framework aimed at conducting joint inference of the above tasks, as reasoning about each in isolation typically fails in our setting. Given noisy tracklets of people and detections of large objects and scene surfaces (e.g., building, grass), we use a spatiotemporal AND-OR graph to drive our joint inference, using Markov Chain Monte Carlo and dynamic programming. We also introduce a new formalism of spatiotemporal templates characterizing latent sub-events. For evaluation, we have collected and released a new aerial videos dataset using a hex-rotor flying over picnic areas rich with group events. Our results demonstrate that we successfully address above inference tasks under challenging conditions.
A ‘resource allocator’ for transcription based on a highly fragmented T7 RNA polymerase

Synthetic genetic systems share resources with the host, including machinery for transcription and translation. Phage RNA polymerases (RNAPs) decouple transcription from the host and generate high expression. However, they can exhibit toxicity and lack accessory proteins (r factors and activators) that enable switching between different promoters and modulation of activity. Here, we show that T7 RNAP (883 amino acids) can be divided into four fragments that have to be co-expressed to function. The DNA-binding loop is encoded in a C-terminal 285-aa ‘r fragment’, and fragments with different specificity can direct the remaining 601-aa ‘core fragment’ to different promoters. Using these parts, we have built a resource allocator that sets the core fragment concentration, which is then shared by multiple r fragments. Adjusting the concentration of the core fragment sets the maximum transcriptional capacity available to a synthetic system. Further, positive and negative regulation is implemented using a 67-aa N-terminal ‘a fragment’ and a null (inactivated) r fragment, respectively. The a fragment can be fused to recombinant proteins to make promoters responsive to their levels. These parts provide a toolbox to allocate transcriptional resources via different schemes, which we demonstrate by building a system which adjusts promoter activity to compensate for the difference in copy number of two plasmids.
Bi-deniable public-key encryption

In 1997, Canetti et al. (CRYPTO 1997) put forward the intruiging notion of deniable encryption, which (informally) allows a sender and/or receiver, having already performed some encrypted communication, to produce 'fake' (but legitimate-looking) random coins that open the ciphertext to another message. Deniability is a powerful notion for both practice and theory: apart from its inherent utility for resisting coercion, a deniable scheme is also noncommitting (a useful property in constructing adaptively secure protocols) and secure under selectiveopening attacks on whichever parties can equivocate. To date, however, known constructions have achieved only limited forms of deniability, requiring at least one party to withhold its randomness, and in some cases using an interactive protocol or external parties. In this work we construct bi-deniable public-key cryptosystems, in which both the sender and receiver can simultaneously equivocate; we stress that the schemes are noninteractive and involve no third parties. One of our systems is based generically on "simulatable encryption" as defined by Damgard and Nielsen (CRYPTO 2000), while the other is lattice-based and builds upon the results of Gentry, Peikert and Vaikuntanathan (STOC 2008) with techniques that may be of independent interest. Both schemes work in the so-called "multi-distributional" model, in which the parties run alternative key-generation and encryption algorithms for equivocable communication, but claim under coercion to have run the prescribed algorithms. Although multi-distributional deniability has not attracted much attention, we argue that it is meaningful and useful because it provides credible coercion resistance in certain settings, and suffices for all of the related properties mentioned above.
Synthesis of Silver Colloids: Experiment and Computational Model

We summarize our recent results that model the formation of uniform spherical silver colloids prepared by mixing iso-ascorbic acid and silver-amine complex solutions in the absence of dispersants. We found that the experimental results can be modeled effectively by the two-stage formation mechanism used previously to model the preparation of colloidal gold spheres. The equilibrium concentration of silver atoms and the surface tension of silver precursor nanocrystals are both treated as free parameters, and the experimental reaction time scale is fit by a narrow region of this two-parameter space. The kinetic parameter required to match the final particle size is found to be very close to that used previously in modeling the formation of uniform gold particles, suggesting that similar kinetics governs the aggregation process. The model also reproduces semi quantitatively the effects of temperature and solvent viscosity on particle synthesis.
Effective Dynamics for N-Solitons of the Gross-Pitaevskii Equation

We consider several solitons moving in a slowly varying external field. We present results of numerical computations which indicate that the effective dynamics obtained by restricting the full Hamiltonian to the finite-dimensional manifold of N-solitons (constructed when no external field is present) provides a remarkably good approximation to the actual soliton dynamics. This is quantified as an error of size h 2 where h is the parameter describing the slowly varying nature of the potential. This also indicates that previous mathematical results of Holmer and Zworski (Int. Math. Res. Not. 2008: Art. ID runn026, 2008) for one soliton are optimal. For potentials with unstable equilibria, the Ehrenfest time, log(1/h)/h, appears to be the natural limiting time for these effective dynamics. We also show that the results of Holmer et al. ( arXiv:0912.5122 , 2009) for two mKdV solitons apply numerically to a larger number of interacting solitons. We illustrate the results by applying the method with the external potentials used in the Bose–Einstein soliton train experiments of Strecker et al. (Nature 417:150–153, 2002).
Geometric constraints in dual F-theory and heterotic string compactifications

We systematically analyze a broad class of dual heterotic and F-theory models that give four-dimensional supergravity theories, and compare the geometric constraints on the two sides of the duality. Specically, we give a complete classication of models where the heterotic theory is compactied on a smooth Calabi-Yau threefold that is elliptically �bered with a single section and carries smooth irreducible vector bundles, and the dual F-theory model has a corresponding threefold base that has the form of a P 1 bundle. We formulate simple conditions for the geometry on the F-theory side to support an elliptically �bered Calabi-Yau fourfold. We match these conditions with conditions for the existence of stable vector bundles on the heterotic side, and show that F-theory gives new insight into the conditions under which such bundles can be constructed. In particular, wend that many allowed F-theory models correspond to vector bundles on the heterotic side with exceptional structure groups, and determine a topological condition that is only satised for bundles of this type. We show that in many cases the F-theory geometry imposes a constraint on the extent to which the gauge group can be enhanced, corresponding to limits on the way in which the heterotic bundle can decompose. We explicitly construct all (4962) F-theory threefold bases for dual F-theory/heterotic constructions in the subset of models where the common twofold base surface is toric, and give both toric and non-toric examples of the general results.
GC assertions: using the garbage collector to check heap properties

This paper introduces GC assertions, a system interface that programmers can use to check for errors, such as data structure invariant violations, and to diagnose performance problems, such as memory leaks. GC assertions are checked by the garbage collector, which is in a unique position to gather information and answer questions about the lifetime and connectivity of objects in the heap. By piggybacking on existing garbage collector computations, our system is able to check heap properties with very low overhead -- around 3% of total execution time -- low enough for use in a deployed setting.We introduce several kinds of GC assertions and describe how they are implemented in the collector. We also describe our reporting mechanism, which provides a complete path through the heap to the offending objects. We report results on both the performance of our system and the experience of using our assertions to find and repair errors in real-world programs.
Can macroeconomic policy stimulate private investment in South Africa? New insights from aggregate and manufacturing sector-level evidence

This study explores the determinants of investment using both aggregated industry-level data and disaggretated data on 27 sub-sectors of the manufacturing sector for the period 1970-2001. According to the results in this study, the government has potentially powerful means at its disposal to stimulate private investment. In particular, a domestic demand stimulus and public investment expansion will produce large gains in private investment. While the direct effects of lowering the interest rate appear to be quantitatively small, indirect effects operating notably through domestic demand and cheaper credit are likely to be large. The evidence in this study also indicates that it is important to minimize exchange rate instability to encourage investment.
Energy dependence of proton damage in optical emitters

The energy dependence of proton displacement damage effects is investigated for light-emitting diodes (LEDs) and laser diodes. Injection-enhanced annealing occurs more rapidly when devices are irradiated with protons below 50 MeV compared with annealing from 200-MeV protons. A different interpretation of damage in amphoterically doped LEDs is used to show that the dependence of damage on energy is relatively flat for energies above 50 MeV, in contrast to older results in the literature that show a continued decrease in damage at higher energies.
Quantum cohomology of flag manifolds and Toda lattices

We discuss relations of Vafa's quantum cohomology with Floer's homology theory, introduce equivariant quantum cohomology, formulate some conjectures about its general properties and, on the basis of these conjectures, compute quantum cohomology algebras of the flag manifolds. The answer turns out to coincide with the algebra of regular functions on an invariant lagrangian variety of a Toda lattice.