The effects of space radiation on thin films of YBa2Cu3O(7-x)

This investigation had two objectives: (1) to determine the effects of space radiation on superconductor parameters that are most important in space applications; and (2) to determine whether this effect can be simulated with Co-60 gamma rays, the standard test method for space materials. Thin films of yttrium barium copper oxide (YBCO) were formed by coevaporation of Y, BaF2, and Cu and post-annealing in wet oxygen at 850 C for 3.5 h. The substrate used was (100) silicon with an evaporated zirconia buffer layer. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were the zero resistance transition temperature T(sub c) and the room temperature resistance. The samples were then exposed to Co-60 gamma-rays in air and in pure nitrogen, and to 780 keV electrons, in air. The parameters were then remeasured. The results are summarized. The results indicate little or no degradation in the parameters measured for samples exposed up to 10 Mrads of gamma-rays in nitrogen. However, complete degradation is preliminarily attributed to the high level of ozone generated in the chamber by the gamma-ray interaction with air. It can be concluded that: (1) the electron component of space radiation does not degrade the critical temperature of the YBCO films described, at least for energies around 800 keV and doses similar to those received by surface materials on spacecraft in typical remote sensing missions; and (2) for qualifying this and other superconducting materials against the space-radiation threat the standard test method used in the aerospace industry, namely, exposure to Co-60 gamma-rays in air, may require some further investigation. As a minimum, the sample must be either in vacuum or in positive nitrogen pressure

The effects of space radiation on thin films of YBa2Cu3O(sub 7-x)

This investigation had two objectives: (1) to determine the effects of space radiation on superconductor parameters that are most important in space applications; and (2) to determine whether this effect can be simulated with Co-60 gamma rays, the standard test method for space materials. Thin films of yttrium barium copper oxide (YBCO) were formed by coevaporation of Y, BaF2, and Cu and post-annealing in wet oxygen at 850 C for 3.5 h. The substrate used was (100) silicon with an evaporated zirconia buffer layer. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were the zero resistance transition temperature (T sub c) and the room temperature resistance. The samples were then exposed to Co-60 gamma-rays in air and in pure nitrogen, and to 780 keV electrons, in air. The parameters were then remeasured. The results are summarized. The results indicate little or no degradation in the parameters measured for samples exposed up to 10 Mrads of gamma-rays in nitrogen. However, complete degradation of samples exposed to 10-Mrad in air was observed. This degradation is preliminarily attributed to the high level of ozone generated in the chamber by the gamma-ray interaction with air. It can be concluded that: (1) the electron component of space radiation does not degrade the critical temperature of the YBCO films described, at least for energies around 800 keV and doses similar to those received by surface materials on spacecraft in typical remote sensing missions; and (2) for qualifying this and other superconducting materials against the space-radiation threat the standard test method in the aerospace industry, namely, exposure to Co-60 gamma-rays in air, may require some further investigation. As a minimum, the sample must be either in vacuum or in positive nitrogen pressure

Probabilistic Guarded P Systems, A New Formal Modelling Framework

Multienvironment P systems constitute a general, formal framework for modelling the dynamics of population biology, which consists of two main approaches: stochastic and probabilistic. The framework has been successfully used to model biologic systems at both micro (e.g. bacteria colony) and macro (e.g. real ecosystems) levels, respectively. In this paper, we extend the general framework in order to include a new case study related to P. Oleracea species. The extension is made by a new variant within the probabilistic approach, called Probabilistic Guarded P systems (in short, PGP systems). We provide a formal definition, a simulation algorithm to capture the dynamics, and a survey of the associated software.Ministerio de Economía y Competitividad TIN2012- 37434Junta de Andalucía P08-TIC-0420

Deterministic and stochastic P systems for modelling cellular processes

This paper presents two approaches based on metabolic and stochastic P systems, together with their associated analysis methods, for modelling biological sys- tems and illustrates their use through two case studies.Kingdom's Engineering and Physical Sciences Research Council EP/ E017215/1Biotechnology and Biological Sciences Research Council/United Kingdom BB/D019613/1Biotechnology and Biological Sciences Research Council/United Kingdom BB/F01855X/

A Multiscale Modeling Framework Based on P Systems

Cellular systems present a highly complex organization at different scales including the molecular, cellular and colony levels. The complexity at each one of these levels is tightly interrelated. Integrative systems biology aims to obtain a deeper understanding of cellular systems by focusing on the systemic and systematic integration of the different levels of organization in cellular systems. The different approaches in cellular modeling within systems biology have been classified into mathematical and computational frameworks. Specifically, the methodology to develop computational models has been recently called executable biology since it produces executable algorithms whose computations resemble the evolution of cellular systems. In this work we present P systems as a multiscale modeling framework within executable biology. P system models explicitly specify the molecular, cellular and colony levels in cellular systems in a relevant and understandable manner. Molecular species and their structure are represented by objects or strings, compartmentalization is described using membrane structures and finally cellular colonies and tissues are modeled as a collection of interacting individual P systems. The interactions between the components of cellular systems are described using rewriting rules. These rules can in turn be grouped together into modules to characterize specific cellular processes. One of our current research lines focuses on the design of cell systems biology models exhibiting a prefixed behavior through the automatic assembly of these cellular modules. Our approach is equally applicable to synthetic as well as systems biology.Kingdom's Engineering and Physical Sciences Research Council EP/ E017215/1Biotechnology and Biological Sciences Research Council/United Kingdom BB/F01855X/1Biotechnology and Biological Sciences Research Council/United Kingdom BB/D019613/

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.

The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

The refrigeration of superconductors in space poses a challenging problem. The problem could be less severe if superconducting materials would not have to be cooled when not in use. Thin films of the YBa2Cu3O(7-x) (YBCO) superconductor were subjected to thermal cycling, which was carried out to simulate a large number of eclipses of a low earth orbit satellite. Electrical measurements were performed to find the effect of the temperature cycling. Thin films of YBCO were formed by coevaporation of Y, BaF2, and Cu and postannealing in wet oxygen at 850 C for 3.5 h. The substrates used were (100) SrTiO3, polycrystalline alumina, and oxidized silicon; the last two have an evaporated zirconia layer. Processing and microstructure studies of these types of films have been published. THe zero resistance transition temperatures of the samples used in this study were 91, 82, and 86 K, respectively. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were: the zero resistance transition temperature, the 10 to 90 percent transition width, and the room temperature resistance, normalized to that measured before temperature cycling. The results for two samples are presented. Each sample had a cumulative exposure. Cycling in atmospheric pressure nitrogen was performed at a rate of about 60 cycles per day, whereas in vacuum the rate was only about 10 cycles per day. The results indicate only little or no changes in the parameters measured. Degradation of superconducting thin films of YBCO has been reported due to storage in nitrogen. It is believed that the relatively good performance of films after temperature cycling is related to the fact that BaF2 was used as an evaporation source. The latest result on extended temperature cycling indicates significant degradation. Further tests of extended cycling will be carried out to provide additional data and to clarify this preliminary finding

Peripheral projections of sensory fascicles in the human superficial radial nerve

The sensory territories of different cutaneous fascicles of the superficial radial nerve were delineated by microneurography at the level of the distal forearm in humans. Three fascicular patterns were found at this level: one supplying the dorsum of the radial aspect of the dorsum of the hand over the first dorsal interosseous space; another supplying the lateral aspect of the first metacarpal extending to the lateral aspect of the thumb; and a third innervating the second interosseous space and the proximal phalanx of the index and middle fingers. The compound fascicular territory is comparable to the classical territory described for the superficial radial nerve. Intraneural microstimulation of individual fascicles did not evoke paraesthesiae or pain beyond their fascicular territory, regardless of the stimulus intensity. We conclude that the superficial radial nerve at the forearm in man is composed of only three fascicles, as shown by the present study and from previous anatomical work. Referred pain seems related to nerve activity in afferent fibres from fascicles supplying deep tissues and muscles, not from cutaneous afferents

Uterine Mast Cells and Immunoglobulin-E Antibody Responses During Clearance of \u3ci\u3eTritrichomonas foetus\u3c/i\u3e

We showed earlier that Tritrichomonas foetus–specific bovine immunoglobulin (Ig)G1 and IgA antibodies in uterine and vaginal secretions are correlated with clearance of this sexually transmitted infection. Eosinophils have been noted in previous studies of bovine trichomoniasis but the role of mast cells and IgE responses have not been reported. The hypothesis that IgE and mast cell degranulation play a role in clearance was tested in 25 virgin heifers inseminated experimentally and infected intravaginally with T. foetus strain D1 at estrus and cultured weekly. Groups were euthanatized at 3, 6, 9, or 12 weeks, when tissues were fixed and secretions were collected for culture and antibody analysis. Immunohistochemistry using a monoclonal antibody to a soluble lipophosphoglycan (LPG)–containing surface antigen (TF1.17) demonstrated antigen uptake by uterine epithelial cells. Lymphoid nodules were detected below antigen-positive epithelium. Little IgG2 antibody was detected but IgG1, IgA, IgM, and IgE T. foetus–specific antibodies increased in uterine secretions at weeks 6 and 9 after infection. This was inversely proportional to subepithelial mast cells numbers and most animals cleared the infection by the sampling time after the lowest mast cell count. Furthermore, soluble antigen was found in uterine epithelium above inductive sites (lymphoid nodules). Cross-linking of IgE on mast cells by antigen and perhaps LPG triggering appears to have resulted in degranulation. Released cytokines may account for production of predominantly Th2 (IgG1 and IgE) and IgA antibody responses, which are related to clearance of the infection

Temperature-dependent double spikes in C-nociceptors of neuropathic pain patients

Five patients with small-fibre neuropathy characterized by temperature-dependent spontaneous pain, hyperalgesia/allodynia and signs of neurogenic inflammation were studied clinically and thermographically, and by microneurography. Thermography revealed hyperthermia confined to painful and hyperalgesic skin of distal extremities, in absence of sympathetic vasomotor denervation. Quantitative sensory testing documented either reduced thresholds or increased suprathreshold magnitude for heat pain. Microneurography identified 13 primary cutaneous C-nociceptors generating abnormal impulses in response to electrical stimuli and, in one patient, nociceptors firing spontaneously. All five patients showed examples of double spikes, in which a single brief electrical stimulus occasionally or regularly evoked two impulses. In one case, a second impulse occurred at one of three different delays. In all five patients, warming of the skin increased the probability of a second impulse occurring. Impulse doubling has previously been reported as occurring rarely in normal subjects and is attributable to unfiltering of multiple orthodromic impulses due to unidirectional conduction failure at branch points. A higher incidence of double firing in neuropathic pain patients is probably due to a reduced safety factor for conduction in the terminal arborizations of their C-nociceptors. These observations show that unidirectional conduction block provides a peripheral mechanism of temperature-dependent nociceptor hyperactivity in small-fibre neuropathy that may contribute to hyperalgesia