The Life-Cycle Permanent-Income Model and Consumer Durables

This paper presents an extension of the life-cycle permanent-income model of consumption to the case of a durable good whose purchase involves lumpy trans- actions costs. Where individual behavior is concerned, the implications of the model are different in some respects from those of standard consumption theory. Specifically, rather than choose an optimal path for the service flow from durables, the optimizing consumer will choose an optimal range and try to keep his service flow inside that range. The dynamics implied by this behavior is different from that of the stock adjustment model. Properties of aggregate durables consumption are derived by explicit aggregation. In particular, it is shown that expenditures on durables display very large short-run elasticity to changes in permanent income. Empirical tests of the sort suggested by Hall (1978) generally produce results that are in line with the predictions of the theory.

Correlation Functions of Coulomb Branch Operators

We consider the correlation functions of Coulomb branch operators in four-dimensional N=2 Superconformal Field Theories (SCFTs) involving exactly one anti-chiral operator. These extremal correlators are the "minimal" non-holomorphic local observables in the theory. We show that they can be expressed in terms of certain determinants of derivatives of the four-sphere partition function of an appropriate deformation of the SCFT. This relation between the extremal correlators and the deformed four-sphere partition function is non-trivial due to the presence of conformal anomalies, which lead to operator mixing on the sphere. Evaluating the deformed four-sphere partition function using supersymmetric localization, we compute the extremal correlators explicitly in many interesting examples. Additionally, the representation of the extremal correlators mentioned above leads to a system of integrable differential equations. We compare our exact results with previous perturbative computations and with the four-dimensional tt^* equations. We also use our results to study some of the asymptotic properties of the perturbative series expansions we obtain in N=2 SQCD.Comment: 47 pages, 6 figures. v2: typos corrected and references adde

Global Stability of a Premixed Reaction Zone (Time-Dependent Liñan’s Problem)

Global stability properties of a premixed, three-dimensional reaction zone are considered. In the nonadiabatic case (i.e., when there is a heat exchange between the reaction zone and the burned gases) there is a unique, spatially one-dimensional steady state that is shown to be unstable (respectively, asymptotically stable) if the reaction zone is cooled (respectively, heated) by the burned mixture. In the adiabatic case, there is a unique (up to spatial translations) steady state that is shown to be stable. In addition, the large-time asymptotic behavior of the solution is analyzed to obtain sufficient conditions on the initial data for stabilization. Previous partial numerical results on linear stability of one-dimensional reaction zones are thereby confirmed and extended

Normal scaling in globally conserved interface-controlled coarsening of fractal clusters

Globally conserved interface-controlled coarsening of fractal clusters exhibits dynamic scale invariance and normal scaling. This is demonstrated by a numerical solution of the Ginzburg-Landau equation with a global conservation law. The sharp-interface limit of this equation is volume preserving motion by mean curvature. The scaled form of the correlation function has a power-law tail accommodating the fractal initial condition. The coarsening length exhibits normal scaling with time. Finally, shrinking of the fractal clusters with time is observed. The difference between global and local conservation is discussed.Comment: 4 pages, 3 eps figure

UK experience of liver transplantation for erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is characterised by excess production of free protoporphyrin from the bone marrow, most commonly due to deficiency of the enzyme ferrochelatase. Excess protoporphyrin gives rise to the cutaneous photosensitivity characteristic of the disease, and in a minority of patients leads to end-stage liver disease necessitating liver transplantation (LT). There is limited information regarding the timing, impact and long-term outcome of LT in such patients, thus we aimed to identify the indications and outcomes of all transplants performed for EPP in the UK using data from the UK Transplant Registry. Between 1987 and 2009, five patients underwent LT for EPP liver disease. Median follow-up was 60 months, and there were two deaths at 44 and 95 months from causes unrelated to liver disease. The remaining recipients are alive at 22.4 years, 61 months and 55 months after transplant. A high rate of postoperative biliary stricturing requiring multiple biliary interventions was observed. Recurrent EPP-liver disease occurred in 4/5 (80%) of patients but graft failure has not been observed. Given the role of biliary obstruction in inducing EPP-mediated liver damage, we suggest that consideration should be given for construction of a Roux loop at the time of transplant. Thus we demonstrate that although EPP liver transplant recipients have a good long-term survival, comparable to patients undergoing LT for other indications, biliary complications and disease recurrence are almost universal, and bone marrow transplantation should be considered where possible

Mechanics and dynamics of X-chromosome pairing at X inactivation

At the onset of X-chromosome inactivation, the vital process whereby female mammalian cells equalize X products with respect to males, the X chromosomes are colocalized along their Xic (X-inactivation center) regions. The mechanism inducing recognition and pairing of the X’s remains, though, elusive. Starting from recent discoveries on the molecular factors and on the DNA sequences (the so-called "pairing sites") involved, we dissect the mechanical basis of Xic colocalization by using a statistical physics model. We show that soluble DNA-specific binding molecules, such as those experimentally identified, can be indeed sufficient to induce the spontaneous colocalization of the homologous chromosomes but only when their concentration, or chemical affinity, rises above a threshold value as a consequence of a thermodynamic phase transition. We derive the likelihood of pairing and its probability distribution. Chromosome dynamics has two stages: an initial independent Brownian diffusion followed, after a characteristic time scale, by recognition and pairing. Finally, we investigate the effects of DNA deletion/insertions in the region of pairing sites and compare model predictions to available experimental data

Game theory of mind

This paper introduces a model of ‘theory of mind’, namely, how we represent the intentions and goals of others to optimise our mutual interactions. We draw on ideas from optimum control and game theory to provide a ‘game theory of mind’. First, we consider the representations of goals in terms of value functions that are prescribed by utility or rewards. Critically, the joint value functions and ensuing behaviour are optimised recursively, under the assumption that I represent your value function, your representation of mine, your representation of my representation of yours, and so on ad infinitum. However, if we assume that the degree of recursion is bounded, then players need to estimate the opponent's degree of recursion (i.e., sophistication) to respond optimally. This induces a problem of inferring the opponent's sophistication, given behavioural exchanges. We show it is possible to deduce whether players make inferences about each other and quantify their sophistication on the basis of choices in sequential games. This rests on comparing generative models of choices with, and without, inference. Model comparison is demonstrated using simulated and real data from a ‘stag-hunt’. Finally, we note that exactly the same sophisticated behaviour can be achieved by optimising the utility function itself (through prosocial utility), producing unsophisticated but apparently altruistic agents. This may be relevant ethologically in hierarchal game theory and coevolution

First step towards the new SPIRAL2 project control system

International audienceThe Spiral2 project at Ganil aims to produce rare ion beams using a Uranium carbide target fission process. The accelerator consists of a RFQ followed by a superconducting cavity linac and is designed to provide high intensity primary beams (deuterons, protons or heavy ions). The accelerator should be commissioned by the end of 2011; then, the first tests aiming to produce exotic beams are planned one year later. The control system will result of the collaboration between several institutes among which the Saclay Dapnia division yet having a good experience and knowledge with Epics. So and also because of its widely used functionalities, Epics has been chosen as the basic framework for the accelerator control and people from the other laboratories belonging to the collaboration are progressively acquiring a first experience with Epics. The paper first explains the organisation of the collaboration then it describes the basic hardware and software choices for the project. Some preliminary implementations are therefore given. As the project is still in its beginning phase, the paper ends by listing some interrogations not yet solved for the control system definition and opened for discussion

Two Notions of Privacy Online

Users of social networking websites tend to disclose much personal information online yet seem to retain some form of an expectation of privacy. Is this expectation of privacy always unreasonable? How do users of online social networks define their expectations of privacy online? These questions were the impetus behind an empirical study, the findings of which are presented in this Article. The project, simultaneously conducted in Canada, at Ryerson University, and in the United States, at the University of Miami, consisted of a survey regarding personal information protection and expectations of privacy on online social networks (OSNs). Approximately 2,500 young adults between the ages of 18 and 24 were surveyed about the personal information they post online, the measures they take to protect such information, and their concerns, if any, regarding their personal information. Respondents also reacted to several hypothetical scenarios in which their privacy was breached on an OSN by measures both within and beyond their control. The theoretical assumption underlying this research project is that two prevalent and competing notions of privacy online exist: one rooted in control and the other in dignity. Of the two, the idea of privacy as control over one\u27s personal information has, to date, been predominant. Legislation, regulation, corporate policy, and technology are often analyzed and evaluated in terms of the measure of control offered to individuals over their personal information. Leading OSNs, such as Facebook and MySpace, propagate a notion of privacy as user control. However, online social networking poses a fundamental challenge to the theory of privacy as control. A high degree of control cannot preclude the possibility that online socializers would post unflattering, defamatory, or personal information about each other, and that this information would in turn be available to a large, if not unrestricted, online audience. Many online socializers post personal information seemingly without much concern over the loss of control, yet it seems that online socializers react with indignation when their personal information is accessed, used, or disclosed by individuals perceived to be outside their social network. The findings presented here indicate indeed that online socializers have developed a new and arguably legitimate notion of privacy online, that if accepted by OSNs, will offer online socializers both control and protection of their dignity and reputation. We call this notion network privacy. According to network privacy, information is considered by online socializers to be private as long as it is not disclosed outside of the network to which they initially disclosed it, if it originates with them, or as long as it does not affect their established online personae, if it originates with others. OSNs, as businesses profiting from socializing online, are best positioned to offer online socializers, often the young and vulnerable, effective protection in accordance with their notion of network privacy above and beyond regular measures of personal information control, and they should be required to do so

GATE : a simulation toolkit for PET and SPECT

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols, and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at the address http://www-lphe.epfl.ch/GATE/