13,395 research outputs found

    Many-Beam Solution to the Phase Problem in Crystallography

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    Solving crystal structures from electron diffraction patterns rather than X-ray diffraction data is hampered by multiple scattering of the fast electrons within even very thin samples and the difficulty of obtaining diffraction data at a resolution high enough for applying direct phasing methods. This letter presents a method by which the effect of multiple scattering is being used for solving the phase problem, allowing the retrieval of electron structure factors from diffraction patterns recorded with varying angle of incidence without any assumption about the scattering potential itself. In particular, the resolution in the diffraction data does not need to be sufficient to resolve atoms, making this method particularly interesting for electron crystallography of 2-dimensional protein crystals and other beam-sensitive complex structures.Comment: 4 pages, 3 figure

    Privacy as a Public Good

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    Privacy is commonly studied as a private good: my personal data is mine to protect and control, and yours is yours. This conception of privacy misses an important component of the policy problem. An individual who is careless with data exposes not only extensive information about herself, but about others as well. The negative externalities imposed on nonconsenting outsiders by such carelessness can be productively studied in terms of welfare economics. If all relevant individuals maximize private benefit, and expect all other relevant individuals to do the same, neoclassical economic theory predicts that society will achieve a suboptimal level of privacy. This prediction holds even if all individuals cherish privacy with the same intensity. As the theoretical literature would have it, the struggle for privacy is destined to become a tragedy. But according to the experimental public-goods literature, there is hope. Like in real life, people in experiments cooperate in groups at rates well above those predicted by neoclassical theory. Groups can be aided in their struggle to produce public goods by institutions, such as communication, framing, or sanction. With these institutions, communities can manage public goods without heavy-handed government intervention. Legal scholarship has not fully engaged this problem in these terms. In this Article, we explain why privacy has aspects of a public good, and we draw lessons from both the theoretical and the empirical literature on public goods to inform the policy discourse on privacy

    Moment-based analysis of biochemical networks in a heterogeneous population of communicating cells

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    Cells can utilize chemical communication to exchange information and coordinate their behavior in the presence of noise. Communication can reduce noise to shape a collective response, or amplify noise to generate distinct phenotypic subpopulations. Here we discuss a moment-based approach to study how cell-cell communication affects noise in biochemical networks that arises from both intrinsic and extrinsic sources. We derive a system of approximate differential equations that captures lower-order moments of a population of cells, which communicate by secreting and sensing a diffusing molecule. Since the number of obtained equations grows combinatorially with number of considered cells, we employ a previously proposed model reduction technique, which exploits symmetries in the underlying moment dynamics. Importantly, the number of equations obtained in this way is independent of the number of considered cells such that the method scales to arbitrary population sizes. Based on this approach, we study how cell-cell communication affects population variability in several biochemical networks. Moreover, we analyze the accuracy and computational efficiency of the moment-based approximation by comparing it with moments obtained from stochastic simulations.Comment: 6 pages, 5 Figure

    Modelling bonds and credit default swaps using a structural model with contagion

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    This paper develops a two-dimensional structural framework for valuing credit default swaps and corporate bonds in the presence of default contagion. Modelling the values of related firms as correlated geometric Brownian motions with exponential default barriers, analytical formulae are obtained for both credit default swap spreads and corporate bond yields. The credit dependence structure is influenced by both a longer-term correlation structure as well as by the possibility of default contagion. In this way, the model is able to generate a diverse range of shapes for the term structure of credit spreads using realistic values for input parameters

    ON- AND OFF-FARM DIVERSIFICATION

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    The present paper brings together two strands of literature by analysing the interrelationship between on-farm and off-farm diversification econometrically. Estimation results from simultaneous bivariate probit models suggest that on-farm and off-farm diversification decisions are closely related. The degree of diversification is significantly lower for farms where the farm operator works off-the farm. On the other hand, the probability of entering into the off-farm labour market declines with the degree of diversification in farm production.Farm Management,

    Is There a Way for Old Industrial Districts to Become Attractive for Cultural Industry? The Case of Media Businesses in Halle (Saale), Germany

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    manufacturing have collapsed are trying to stimulate entrepreneurial activities of businesses in the cultural industry. The question is whether this strategy could be successful. This article examines the strategy of supporting the sector of Media Industry (´MI´) by policy makers in the region of Halle in East Germany, where a strong de-industrialization has taken place after the German reunification. Stimulated by the policy makers’ support measures, there actually was a remarkable development of MI. However, the number of MI firms and their employees did not further increase in recent years, after having reached a certain level. This illustrates the limits of political measures for turning a city’s path of industrial development voluntarily.media industry, cultural industry, business development, urban development, location factors

    Prime diagnosticity in short-term repetition priming: Is primed evidence discounted, even when it reliably indicates the correct answer?

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    The authors conducted 4 repetition priming experiments that manipulated prime duration and prime diagnosticity in a visual forced-choice perceptual identification task. The strength and direction of prime diagnosticity produced marked effects on identification accuracy, but those effects were resistant to subsequent changes of diagnosticity. Participants learned to associate different diagnosticities with primes of different durations but not with primes presented in different colors. Regardless of prime diagnosticity, preference for a primed alternative covaried negatively with prime duration, suggesting that even for diagnostic primes, evidence discounting remains an important factor. A computational model, with the assumption that adaptation to the statistics of the experiment modulates the level of evidence discounting, accounted for these results

    Electron-magnon scattering in elementary ferromagnets from first principles: lifetime broadening and band anomalies

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    We study the electron-magnon scattering in bulk Fe, Co, and Ni within the framework of many-body perturbation theory implemented in the full-potential linearized augmented-plane-wave method. To this end, a k\mathbf{k}-dependent self-energy (GTGT self-energy) describing the scattering of electrons and magnons is constructed from the solution of a Bethe-Salpeter equation for the two-particle (electron-hole) Green function, in which single-particle Stoner and collective spin-wave excitations (magnons) are treated on the same footing. Partial self-consistency is achieved by the alignment of the chemical potentials. The resulting renormalized electronic band structures exhibit strong spin-dependent lifetime effects close to the Fermi energy, which are strongest in Fe. The renormalization can give rise to a loss of quasiparticle character close to the Fermi energy, which we attribute to electron scattering with spatially extended spin waves. This scattering is also responsible for dispersion anomalies in conduction bands of iron and for the formation of satellite bands in nickel. Furthermore, we find a band anomaly at a binding energy of 1.5~eV in iron, which results from a coupling of the quasihole with single-particle excitations that form a peak in the Stoner continuum. This band anomaly was recently observed in photoemission experiments. On the theory side, we show that the contribution of the Goldstone mode to the GTGT self-energy is expected to (nearly) vanish in the long-wavelength limit. We also present an in-depth discussion about the possible violation of causality when an incomplete subset of self-energy diagrams is chosen
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