Critical Currents of Josephson-Coupled Wire Arrays

We calculate the current-voltage characteristics and critical current I_c^{array} of an array of Josephson-coupled superconducting wires. The array has two layers, each consisting of a set of parallel wires, arranged at right angles, such that an overdamped resistively-shunted junction forms wherever two wires cross. A uniform magnetic field equal to f flux quanta per plaquette is applied perpendicular to the layers. If f = p/q, where p and q are mutually prime integers, I_c^{array}(f) is found to have sharp peaks when q is a small integer. To an excellent approximation, it is found in a square array of n^2 plaquettes, that I_c^{array}(f) \propto (n/q)^{1/2} for sufficiently large n. This result is interpreted in terms of the commensurability between the array and the assumed q \times q unit cell of the ground state vortex lattice.Comment: 4 pages, 4 figure

Peracute Infection of Swine With Salmonella

It has recently been experimentally demonstrated that pigs exposed naturally to Salmonella on the floor of abattoir holding pens can become infected between two and six hours after being placed in the pens. In addition we have demonstrated that tonsillar tissue are almost immediately culture positive following such exposure under experimental conditions. The objective of this study was to determine the shortest amount of time necessary for infection of selected tissues and to determine if the tonsil served as a route for Salmonella entry into lymphoid tissues draining the tonsil. Forty-four Salmonella-negative, market age pigs (90 to 110 kg) were fasted overnight and exposed to approximately 2 X 106 Salmonella enterica serotype Typhimurium strain X4232 (nalidixic acid resistant). The bacteria were mixed with a fecal slurry and the slurry spread on the floor of the pens. Pigs were euthanized at 15, 30, 45, 60 and 120 minutes following initial exposure. Tonsil of the soft palate, medial retropharyngeal lymph node, ileocecal lymph node, a five centimeter section of the terminal ileum, cecal contents and 100 ml of blood were cultured for Salmonella. Strain X4232 was isolated from 98 % (43/44) of tonsils. Strain X4232 was isolated from the ileocecal lymph node within 45 minutes (2/9 pigs), terminal ileum within 15 minutes (1/9 pigs), cecal contents within 15 minutes (1/9 pigs), and blood within 45 minutes (1/9 pigs). Strain X4232 was not recovered from the medial retropharyngeal lymph node, indicating that the organism did not move rapidly into this node from the tonsil of the soft palate. Results of this study indicate that Salmonella can be recovered from selected tissues in market age swine in less than the normal two hour abattoir holding time

Gradient mapping of pattern ground characteristics from a photomosaic of the IBP tundra biome site near Barrow, Alaska

An air photographic mosaic covering an area of 44.5×10 5 m 2 was subdivided into 741 rectangular cells (60×100 m). Pattern frequency, center relief, shape, and wedge image clarity were tabulated using three states for each character on a nominal scale. These state variables were converted to an interval scale by the application of a spatial smoothing filter. The new values were subjected to a principal components analysis which indicated that a parsimonious classification of pattern spatial variation could be constructed by equally weighting the first three nominal variables (frequency, relief, shape). The maps derived from this scheme indicate the areas on the tundra surface where polygon evolution may be occurring at the present time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43203/1/11004_2005_Article_BF02082889.pd

Eigenstates of a Small Josephson Junction Coupled to a Resonant Cavity

We carry out a quantum-mechanical analysis of a small Josephson junction coupled to a single-mode resonant cavity. We find that the eigenstates of the combined junction-cavity system are strongly entangled only when the gate voltage applied at one of the superconducting islands is tuned to certain special values. One such value corresponds to the resonant absorption of a single photon by Cooper pairs in the junction. Another special value corresponds to a {\em two-photon} absorption process. Near the single-photon resonant absorption, the system is accurately described by a simplified model in which only the lowest two levels of the Josephson junction are retained in the Hamiltonian matrix. We noticed that this approximation does not work very well as the number of photons in the resonator increases. Our system shows also the phenomenon of ``collapse and revival'' under suitable initial conditions, and our full numerical solution agrees with the two level approximation result.Comment: 7 pages, and 6 figures. To be published in Phys. Rev.

Several small Josephson junctions in a Resonant Cavity: Deviation from the Dicke Model

We have studied quantum-mechanically a system of several small identical Josephson junctions in a lossless single-mode cavity for different initial states, under conditions such that the system is at resonance. This system is analogous to a collection of identical atoms in a cavity, which is described under appropriate conditions by the Dicke model. We find that our system can be well approximated by a reduced Hamiltonian consisting of two levels per junction. The reduced Hamiltonian is similar to the Dicke Hamiltonian, but contains an additional term resembling a dipole-dipole interaction between the junctions. This extra term arises when states outside the degenerate group are included via degenerate second-order (L\"{o}wdin) perturbation theory. As in the Dicke model, we find that, when N junctions are present in the cavity, the oscillation frequency due to the junction-cavity interaction is enhanced by $\sqrt{N}$. The corresponding decrease in the Rabi oscillation period may cause it to be smaller than the decoherence time due to dissipation, making these oscillations observable. Finally, we find that the frequency enhancement survives even if the junctions differ slightly from one another, as expected in a realistic system.Comment: 11 pages. To be published in Phys. Rev.

Resonant-Cavity-Induced Phase Locking and Voltage Steps in a Josephson Array

We describe a simple dynamical model for an underdamped Josephson junction array coupled to a resonant cavity. From numerical solutions of the model in one dimension, we find that (i) current-voltage characteristics of the array have self-induced resonant steps (SIRS), (ii) at fixed disorder and coupling strength, the array locks into a coherent, periodic state above a critical number of active Josephson junctions, and (iii) when $N_a$ active junctions are synchronized on an SIRS, the energy emitted into the resonant cavity is quadratic with $N_a$. All three features are in agreement with a recent experiment [Barbara {\it et al}, Phys. Rev. Lett. {\bf 82}, 1963 (1999)]}.Comment: 4 pages, 3 eps figures included. Submitted to PRB Rapid Com

Benevolent characteristics promote cooperative behaviour among humans

Cooperation is fundamental to the evolution of human society. We regularly observe cooperative behaviour in everyday life and in controlled experiments with anonymous people, even though standard economic models predict that they should deviate from the collective interest and act so as to maximise their own individual payoff. However, there is typically heterogeneity across subjects: some may cooperate, while others may not. Since individual factors promoting cooperation could be used by institutions to indirectly prime cooperation, this heterogeneity raises the important question of who these cooperators are. We have conducted a series of experiments to study whether benevolence, defined as a unilateral act of paying a cost to increase the welfare of someone else beyond one's own, is related to cooperation in a subsequent one-shot anonymous Prisoner's dilemma. Contrary to the predictions of the widely used inequity aversion models, we find that benevolence does exist and a large majority of people behave this way. We also find benevolence to be correlated with cooperative behaviour. Finally, we show a causal link between benevolence and cooperation: priming people to think positively about benevolent behaviour makes them significantly more cooperative than priming them to think malevolently. Thus benevolent people exist and cooperate more