Hamiltonian and physical Hilbert space in polymer quantum mechanics

In this paper, a version of polymer quantum mechanics, which is inspired by loop quantum gravity, is considered and shown to be equivalent, in a precise sense, to the standard, experimentally tested, Schroedinger quantum mechanics. The kinematical cornerstone of our framework is the so called polymer representation of the Heisenberg-Weyl (H-W) algebra, which is the starting point of the construction. The dynamics is constructed as a continuum limit of effective theories characterized by a scale, and requires a renormalization of the inner product. The result is a physical Hilbert space in which the continuum Hamiltonian can be represented and that is unitarily equivalent to the Schroedinger representation of quantum mechanics. As a concrete implementation of our formalism, the simple harmonic oscillator is fully developed.Comment: 19 pages, 2 figures. Comments and references added. Version to be published in CQ

Epidemiology of salmonellosis in sow units of Catalonia (Spain)

A bacteriological study aimed to the detection of sows excreting Salmonella was carried out in 74 sow units. Individual faecal samples were collected and a detailed questionnaire was filled in each farm and the data gathered were used in a bivariate logistic regression analysis to determine risk factors for Salmonella positivity. In 18 farms (24.32 %) Salmonella carriers were detected. Of the total 1480 samples analysed, 50 were positive (3.38 %), accounting for 11 different serotypes. Within positive farms, 13.8 % of sows were positive. Epidemiologic analysis of the results showed three main risk factors: to have open-flushed drainage of slurry, rodent control, and the number of sows in the unit. Our results showed that, in infected farms, the proportion of sows actively excreting Salmonella was considerably high (3.38 %). This fact, and the risk factors detected should be taken into account when designing effective plans for the control of salmonellosis in sows

Comparison of two commercial ELISA for the diagnosis of salmonellosis in swine

Three hundred and sixty-one pig sera collected in farms of Catalonia were randomly selected from a serum bank. Samples were examined by using two commercial ELISA kits. Results were compared with the kappa value using WinEpiscope. Besides, sample/positive ratios (S/P) were calculated. Comparison of results of both ELISA yielded a poor agreement (kappa 0.191), indicating that both ELISA did not measure the same. In addition, when raw optical densities were compared by means of a regression analysis, the results indicated a low correlation (r = 0.54 ). The results of this study clearly indicate that results of both kits are not interchangeable and that normalization of results by using S/P ratios did not serve to improve the agreement between tests. From our results, it is tempting to suggest that Salmotype detects a greater number of IgM positive pigs. The nature of these IgMs (salmonella-specific or not) is not known to us at this moment

Parallelization of an algorithm for the automatic detection of deformable objects

This work presents the parallelization of an algorithm for the detection of deformable objects in digital images. The parallelization has been implemented with the message passing paradigm, using a master-slave model. Two versions have been developed, with synchronous and asynchronous communications

The toxicity and intraspecific variability of Alexandrium andersonii Balech

The toxicity of Alexandrium andersonii Balech is unclear and its intraspecific variability has yet to be studied. To address these gaps in our knowledge, in the present work five strains of A. andersonii from four different localities were characterized. The results showed that despite genetic homogeneity in the 5.8-ITS (internal transcribed spacer) and large subunit (LSU) regions and similar growth rates, strains originating from different locations varied with respect to cell size, the ratios of certain pigments, and their growth patterns. Cultures of the strains grown at 20 8C were analyzed for toxicity using four different methodologies. The two officially established methods, mouse bioassay and high-performance liquid chromatography with fluorescence detection (HPLC-FLD) and post-column reaction analysis of PSP toxins, failed to show the toxicity of any strain. Strains grown at 14 8C were also negative for PSP toxins by HPLC-FLD. However, strains grown at 20 8C exhibited both a response characteristic of the presence of toxin-inhibiting voltage-gated sodium channels, as demonstrated in a neuroblastoma neuro- 2a cell-based assay, as well as hemolytic activity in a sheep red blood cell assay

Reducing vortex density in superconductors using the ratchet effect

A serious obstacle that impedes the application of low and high temperature superconductor (SC) devices is the presence of trapped flux. Flux lines or vortices are induced by fields as small as the Earth's magnetic field. Once present, vortices dissipate energy and generate internal noise, limiting the operation of numerous superconducting devices. Methods used to overcome this difficulty include the pinning of vortices by the incorporation of impurities and defects, the construction of flux dams, slots and holes and magnetic shields which block the penetration of new flux lines in the bulk of the SC or reduce the magnetic field in the immediate vicinity of the superconducting device. Naturally, the most desirable would be to remove the vortices from the bulk of the SC. There is no known phenomenon, however, that could form the basis for such a process. Here we show that the application of an ac current to a SC that is patterned with an asymmetric pinning potential can induce vortex motion whose direction is determined only by the asymmetry of the pattern. The mechanism responsible for this phenomenon is the so called ratchet effect, and its working principle applies to both low and high temperature SCs. As a first step here we demonstrate that with an appropriate choice of the pinning potential the ratchet effect can be used to remove vortices from low temperature SCs in the parameter range required for various applications.Comment: 7 pages, 4 figures, Nature (in press

Voltage rectification by a SQUID ratchet

We argue that the phase across an asymmetric dc SQUID threaded by a magnetic flux can experience an effective ratchet (periodic and asymmetric) potential. Under an external ac current, a rocking ratchet mechanism operates whereby one sign of the time derivative of the phase is favored. We show that there exists a range of parameters in which a fixed sign (and, in a narrower range, even a fixed value) of the average voltage across the ring occurs, regardless of the sign of the external current dc component.Comment: 4 pages, 4 EPS figures, uses psfig.sty. Revised version, to appear in Physical Review Letters (26 August 1996

Optimal conditions for observing Josephson oscillations in a double-well Bose-gas condensate

The Josephson oscillations between condensates in a double-well trap are known theoretically to be strongly effected by the mean field interaction in dilute atomic gases. The most important effect is that the amplitude of oscillation in the relative population of the two wells is greatly suppressed due to the mean field interaction, which can make it difficult to observe the Josephson effect. Starting from the work of Raghavan, Smerzi, Fantoni, and Shenoy, we calculate the maximum amplitude of oscillation in the relative population as a function of various physical parameters, such as the trap aspect ratio, the Gaussian barrier height and width, and the total number of atoms in the condensate. We also compare results for ${}^{23}$Na and ${}^{87}$Rb. Our main new result is that the maximum amplitude of oscillation depends strongly on the aspect ratio of the harmonic trap and can be maximized in a ``pancake'' trap, as used in the experiment of Anderson and Kasevich.Comment: 8 pages with 5 embeded figure

Antimicrobial susceptibility of Salmonella isolated pig carriers

Ninety-six Salmonella isolates from healthy carrier pigs were obtained from a survey in pig farms of Catalonia (Spain). Isolates were serotyped and examined for their antimicrobial susceptibility against a panel of 18 antimicrobial agents. Only isolates having different phenotypic and antimicrobial susceptibility characteristics were considered. With this restriction, we considered to have 62 different strains belonging to 17 serotypes. The most common serotype was Anatum (16.1 %) followed by Rissen (14.5 %), Typhimurium (11.3 %), Derby (9.7 %), Tilburg (8.1 %), Goldcoast (8.1 %) and Typhimurium variant 4,5,12:i:- (6.5 %). Others 10 serotypes were also isolated less than three times each. Antimicrobial susceptibility analysis showed that the highest level of resistance was against tetracycline (68.8 %). Sixty-two percent of the strains showed resistance to three or more antimicrobial agents and 46% were resistant to five or more drugs. The maximum number of compounds to which two strains were resistant was 10 (corresponding to a 4,5,12:i:- strain). None of the strains was resistant to colistin or ceftriaxone and 12 strains were susceptible to all antimicrobial agents tested

Quantum Dynamics of Three Coupled Atomic Bose-Einstein Condensates

The simplest model of three coupled Bose-Einstein Condensates (BEC) is investigated using a group theoretical method. The stationary solutions are determined using the SU(3) group under the mean field approximation. This semiclassical analysis using the system symmetries shows a transition in the dynamics of the system from self trapping to delocalization at a critical value for the coupling between the condensates. The global dynamics are investigated by examination of the stable points and our analysis shows the structure of the stable points depends on the ratio of the condensate coupling to the particle-particle interaction, undergoes bifurcations as this ratio is varied. This semiclassical model is compared to a full quantum treatment, which also displays the dynamical transition. The quantum case has collapse and revival sequences superposed on the semiclassical dynamics reflecting the underlying discreteness of the spectrum. Non-zero circular current states are also demonstrated as one of the higher dimensional effects displayed in this system.Comment: Accepted to PR