Current density inhomogeneity throughout the thickness of superconducting films and its effect on their irreversible magnetic properties

We calculate the distribution of the current density $j$ in superconducting films along the direction of an external field applied perpendicular to the film plane. Our analysis reveals that in the presence of bulk pinning $j$ is inhomogeneous on a length scale of order the inter vortex distance. This inhomogeneity is significantly enhanced in the presence of surface pinning. We introduce new critical state model, which takes into account the current density variations throughout the film thickness, and show how these variations give rise to the experimentally observed thickness dependence of $$ and magnetic relaxation rate.Comment: RevTex, 9 PS figures. To appear in Phys. Rev.

Development of a Knowledge Management System Integrated with Local Communication Channels and Knowledge Management Initiatives for Kenyan Rural Farming Communities

yesThis paper presents an innovative application of wireless, mobile and ubiquitous technologies to support informal and collaborative learning in Kenyan rural farming communities. Such an approach is achieved by the development of a knowledge management system (KMS) integrated with existing local community communication channels, together with experimental knowledge management (KM) initiatives employing the VeSeL (Village e-Science for Life) distributed resource kits (DRKs). The initiatives support illiterate and semi-literate farming community groups, in learning new agriculture practices, and also enable the use of advanced digital technology to improve their agricultural practices and literacy levels. Results of a recent field trip to Kenya are presented and an application sketch is developed. The process of applying wireless and Internet technologies for the education of local farming communities, using irrigation and water management as the application, concludes the paper.EPSR

Catch rate of juveniles Ethamatosa fimbriata, Sardinella maderensis, and Brachydeuterus auritus fishing in Freetown Peninsular

We investigated the incidences of juvenile fishing according to fishing practices in Freetown peninsular. The industrial trawl fishing sector, despite its technology is not fully selective to avoid bycatch of juvenile fish, and artisanal fishing is so less for economic reasons. Ineffective enforcement of fishing regulations is a major cause to the catch of both targeted and non-targeted juvenile fish. We collected data on the quantity of juvenile fish and the daily duration of fishing trips in four landing sites over a two-week period Bernoulli random variables and properties of uniform distribution were used to analyze the data. Catch rates of juveniles Ethamatosa fimbriata, Sardinella maderensis, and Brachydeuterus auritus around the Freetown peninsular were 170.8, 212.4 and 194.60 kg per hour per day, respectively. This rate revealed that the current trend of juvenile fish landings is a threat to the sustainability of fishery capital, revenue, and biodiversity.Key words: High juvenile, landing, national problem, Sierra Leone, by-catch juvenile

Spectrum sensing in cognitive radio using multitaper method based on MIMO-OFDM techniques

The current inefficient utilization of frequency spectrum has alerted regulatory bodies to streamline improvements. Cognitive radio (CR) has recently received considerable attention and is widely perceived as a promising improvement tool in estimating, or equivalently sensing, the frequency spectrum for wireless communication systems. The cognitive cycle in CR systems is capable of recognizing and processing better spectrum estimation (SE) and hence promotes the efficiency of spectrum utilization. Among different SE methods, the multi-taper method (MTM) shows encouraging results. Further performance improvement in the SE for CR can be achieved by applying multiple antennas and combining techniques. This paper proposes a constructive development of SE using MTM, abbreviated as MTSE, and by employing multiple-input multiple-output (MIMO), parsed into separate parallel channels using singular value decomposition (SVD), and maximum ratio combining (MRC) configurations. Deviating from these improvements, however, multicarrier systems such as orthogonal frequency division multiplexing (OFDM) show inferior sensing performances due to the noise multiplicity generated and combined from all subcarrier channels. By means of the quadrature matrix form, the probabilities for such integrated settings of SE have been derived to reach at their approximate asymptotes. Numerical simulations revealed specific better performances stemmed from coupling the fashionable MTSE and MIMO technologies

Irreversible magnetization in thin YBCO films rotated in external magnetic field

The magnetization M of a thin YBaCuO film is measured as a function of the angle $\theta$ between the applied field H and the c-axis. For fields above the first critical field, but below the Bean's field for first penetration H*, M is symmetric with respect to $\theta =\pi$ and the magnetization curves for forward and backward rotation coincide. For H>H* the curves are asymmetric and they do not coincide. These phenomena have a simple explanation in the framework of the Bean critical state model.Comment: 14 pages, 7 PostScript figure

Superconductor strip with transport current: Magneto-optical study of current distribution and its relaxation

The dynamics of magnetic flux distributions across a YBaCuO strip carrying transport current is measured using magneto-optical imaging at 20 K. The current is applied in pulses of 40-5000 ms duration and magnitude close to the critical one, 5.5 A. During the pulse some extra flux usually penetrates the strip, so the local field increases in magnitude. When the strip is initially penetrated by flux, the local field either increases or decreases depending both on the spatial coordinate and the current magnitude. Meanwhile, the current density always tends to redistribute more uniformly. Despite the relaxation, all distributions remain qualitatively similar to the Bean model predictions.Comment: RevTeX, 9 pages, 9 figures, submitted to Supercond. Sci. Technol. Revision: MO image and more refs are adde

Strong Pinning in High Temperature Superconductors

Detailed measurements of the critical current density jc of YBa2Cu3O7 films grown by pulsed laser deposition reveal the increase of jc as function of the filmthickness. Both this thickness dependence and the field dependence of the critical current are consistently described using a generalization of the theory of strong pinning of Ovchinnikov and Ivlev [Phys. Rev. B 43, 8024 (1991)]. From the model, we deduce values of the defect density (10^21 m^-3) and the elementary pinning force, which are in good agreement with the generally accepted values for Y2O3-inclusions. In the absence of clear evidence that the critical current is determined by linear defects or modulations of the film thickness, our model provides an alternative explanation for the rather universal field dependence of the critical current density found in YBa2Cu3O7 films deposited by different methods.Comment: 11 pages; 8 Figures; Published Phys. Rev. B 66, 024523 (2002

Factors influencing consumer wine choice: The case of wine tourism

This research was undertaken to examine the relationship between the wine tourism activities of consumers and their subsequent wine choices. Exploratory research was undertaken giving specific attention to wine tourism, first, as a factor of influence on decision-making, second, on levels of consumer involvement and third on long-term consumer loyalty. A convenience sample of 12 wine consumers in Dublin participated in the study. Semi-structured in-depth interviews were used to gather the qualitative data used. The findings clearly establish links made by consumers between their wine tourism experiences and their subsequent wine purchase preferences. The findings highlight the importance of facilitating the co-creation of memorable wine tourism experiences as a determinant of improved consumer involvement as well as the development of long-term consumer loyalty. Implications for industry practitioners suggest a continued focus on the provision of unique wine tourism experiences; while the findings support the theoretical links between consumers own past experiences and their use as a valuable information source when making purchase decisions

A 160-kilobit molecular electronic memory patterned at 10^(11) bits per square centimetre

The primary metric for gauging progress in the various semiconductor integrated circuit technologies is the spacing, or pitch, between the most closely spaced wires within a dynamic random access memory (DRAM) circuit. Modern DRAM circuits have 140nm pitch wires and a memory cell size of 0.0408 μm^2. Improving integrated circuit technology will require that these dimensions decrease over time. However, at present a large fraction of the patterning and materials requirements that we expect to need for the construction of new integrated circuit technologies in 2013 have ‘no known solution’. Promising ingredients for advances in integrated circuit technology are nanowires, molecular electronics and defect-tolerant architectures, as demonstrated by reports of single devices and small circuits. Methods of extending these approaches to large-scale, high-density circuitry are largely undeveloped. Here we describe a 160,000-bit molecular electronic memory circuit, fabricated at a density of 10^(11) bits cm^(-2) (pitch 33 nm; memory cell size 0.0011 mm^2), that is, roughly analogous to the dimensions of a DRAM circuit projected to be available by 2020. A monolayer of bistable, [2]rotaxane molecules 10 served as the data storage elements. Although the circuit has large numbers of defects, those defects could be readily identified through electronic testing and isolated using software coding. The working bits were then configured to form a fully functional random access memory circuit for storing and retrieving information