Occupation numbers in strongly polarized Fermi gases and the Luttinger theorem

We study a two-component Fermi gas that is so strongly polarized that it remains normal fluid at zero temperature. We calculate the occupation numbers within the particle-particle random-phase approximation, which is similar to the Nozieres-Schmitt-Rink approach. We show that the Luttinger theorem is fulfilled in this approach. We also study the change of the chemical potentials which allows us to extract, in the limit of extreme polarization, the polaron energy.Comment: 8 pages, 8 figure

Invariant and dual subtraction games resolving the Duch\^e-Rigo conjecture

We prove a recent conjecture of Duch\^ene and Rigo, stating that every complementary pair of homogeneous Beatty sequences represents the solution to an \emph{invariant} impartial game. Here invariance means that each available move in a game can be played anywhere inside the game-board. In fact, we establish such a result for a wider class of pairs of complementary sequences, and in the process generalize the notion of a \emph{subtraction game}. Given a pair of complementary sequences $(a_n)$ and $(b_n)$ of positive integers, we define a game $G$ by setting $\{\{a_n, b_n\}\}$ as invariant moves. We then introduce the invariant game $G^\star$, whose moves are all non-zero $P$-positions of $G$. Provided the set of non-zero $P$-positions of $G^\star$ equals $\{\{a_n,b_n\}\}$, this \emph{is} the desired invariant game. We give sufficient conditions on the initial pair of sequences for this 'duality' to hold.Comment: 11 pages, 2 figure

Variation aware analysis of bridging fault testing

This paper investigates the impact of process variation on test quality with regard to resistive bridging faults. The input logic threshold voltage and gate drive strength parameters are analyzed regarding their process variation induced influence on test quality. The impact of process variation on test quality is studied in terms of test escapes and measured by a robustness metric. It is shown that some bridges are sensitive to process variation in terms of logic behavior, but such variation does not necessarily compromise test quality if the test has high robustness. Experimental results of Monte-Carlo simulation based on recent process variation statistics are presented for ISCAS85 and -89 benchmark circuits, using a 45nm gate library and realistic bridges. The results show that tests generated without consideration of process variation are inadequate in terms of test quality, particularly for small test sets. On the other hand, larger test sets detect more of the logic faults introduced by process variation and have higher test quality

New limits on extragalactic magnetic fields from rotation measures

We take advantage of the wealth of rotation measures data contained in the NRAO VLA Sky Survey catalogue to derive new, statistically robust, upper limits on the strength of extragalactic magnetic fields. We simulate the extragalactic magnetic field contribution to the rotation measures for a given field strength and correlation length, by assuming that the electron density follows the distribution of Lyman-$\alpha$ clouds. Based on the observation that rotation measures from distant radio sources do not exhibit any trend with redshift, while the extragalactic contribution instead grows with distance, we constrain fields with Jeans' length coherence length to be below 1.7~nG at the $2\sigma$ level, and fields coherent across the entire observable Universe below 0.65~nG. These limits do not depend on the particular origin of these cosmological fields.Comment: 5 pages, 3 figures -- v2 to match PRL versio

Non-Intrusive Optical Measurement of Electron Temperature in Near Field Plume of Hall Thruster

Currently there is a large interest in the use of more efficient means of propulsion in long term missions due to the costs and difficulties associated with placing and maintaining the needed fuel for conventional chemical systems in orbit. Mass reduction of upper stages will return large returns due to the great reduction in required lower stage fuel. Due to these factors, alternatives are undergoing active research, though this paper is concerned with the area of electrical propulsion. Electric propulsion is broadly defined as propulsion where the energization of the exhaust occurs via application of electromagnetic fields as opposed to chemical reactions or thermal processes. Frequently plasmas are involved in such processes, and as such, diagnostics related to establishing the characteristics of plasmas are of great value to the field, especially any techniques which do not disrupt the plasma in testing. This study focused on the use of non-intrusive optical techniques to measure electron temperature in the near field of a Hall thruster, a type of electric propulsion. Results indicate that the pursued technique may be of utility to providing a simple to set up and execute diagnostic for determining electron temperatures in the near field of a hall thruster. This will allow for less-expensive rapid turnaround on obtaining of experimental data to test or provide as input for models of plasma behavior, wear in electric propulsion, thruster design, and operation confirmation

Non-Intrusive Optical Measurement of Electron Temperature in Near Field Plume of Hall Thruster

Currently there is a large interest in the use of more efficient means of propulsion in long term missions due to the costs and difficulties associated with placing and maintaining the needed fuel for conventional chemical systems in orbit. Mass reduction of upper stages will return large returns due to the great reduction in required lower stage fuel. Due to these factors, alternatives are undergoing active research, though this paper is concerned with the area of electrical propulsion. Electric propulsion is broadly defined as propulsion where the energization of the exhaust occurs via application of electromagnetic fields as opposed to chemical reactions or thermal processes. Frequently plasmas are involved in such processes, and as such, diagnostics related to establishing the characteristics of plasmas are of great value to the field, especially any techniques which do not disrupt the plasma in testing. This study focused on the use of non-intrusive optical techniques to measure electron temperature in the near field of a Hall thruster, a type of electric propulsion. Results indicate that the pursued technique may be of utility to providing a simple to set up and execute diagnostic for determining electron temperatures in the near field of a hall thruster. This will allow for less-expensive rapid turnaround on obtaining of experimental data to test or provide as input for models of plasma behavior, wear in electric propulsion, thruster design, and operation confirmation

BEC-BCS Crossover and the Liquid-Gas Phase Transition in Hot and Dense Nuclear Matter

The effect of nucleon-nucleon correlations in symmetric nuclear matter at finite temperature is studied beyond BCS theory. Starting from a Hartree-Fock description of nuclear matter with the Gogny effective interaction, we add correlations corresponding to the formation of preformed pairs and scattering states above the superfluid critical temperature within the in-medium T-matrix approach, which is analogous to the Nozieres-Schmitt-Rink theory. We calculate the critical temperature for a BEC superfluid of deuterons, of a BCS superfluid of nucleons, and in the crossover between these limits. The effect of the correlations on thermodynamic properties (equation of state, energy, entropy) and the liquid-gas phase transition is discussed. Our results show that nucleon-nucleon correlations beyond BCS play an important role for the properties of nuclear matter, especially in the low-density region.Comment: 11 pages, 12 figures; v2: minor modifications of the text, references adde

Онтологические основания проблемно-ориентированных исследований

Рассматриваются онтологические основания проблемно-ориентированных исследований. Констатируется, что проблемно-ориентированный процесс научного познания сопровождается двумя взаимообусловленными процессами: "субъективизацией объекта" и "объективизацией субъекта". Данные процессы идут виртуально. Сфера виртуальности выступает в качестве основного онтологического фона осуществления проблемно-ориентированных исследований. Подобное позволяет сохранить за наукой возможность считаться системой объективного знания. В то же время общество сохраняет существенные рычаги воздействия на развитие науки