Phase-slip flux qubits

In thin superconducting wires, phase-slip by thermal activation near the critical temperature is a well-known effect. It has recently become clear that phase-slip by quantum tunnelling through the energy barrier can also have a significant rate at low temperatures. In this paper it is suggested that quantum phase-slip can be used to realize a superconducting quantum bit without Josephson junctions. A loop containing a nanofabricated very thin wire is biased with an externally applied magnetic flux of half a flux quantum, resulting in two states with opposite circulating current and equal energy. Quantum phase-slip should provide coherent coupling between these two macroscopic states. Numbers are given for a wire of amorphous niobium-silicon that can be fabricated with advanced electron beam lithography.Comment: Submitted to New Journal of Physics, special issue solid state quantum informatio

Absence of a Transcellular Oxalate Transport Mechanism in LLC-PK1 and MDCK Cells Cultured on Porous Supports

Transepithelial oxalate transport across polarized monolayers of LLC-PK1 cells, grown on collagen-coated microporous membranes in Transwell culture chambers, was studied in double-label experiments using [14C]-oxalate together with [3H]-D-mannitol as an extracellular marker. The [14C]-labeled glucose analog α-methyl-glucoside (α-MG) was used as functional marker for active proximal tubular sugar transport. Cellular uptake of oxalate and α-MG at both the apical and basolateral plasma membrane was determined. When added to the upper compartment, α-MG was actively taken up at the apical membrane, directed through the cells to the basolateral membrane and transported to the lower compartment, indicating functional epithelial sugar transport by LLC-PK1 cells. In LLC-PK1 cells, the uptake of α-MG at the apical membrane was approximately 50 times higher than that at the basolateral membrane. In contrast to this active transport of sugar, LLC-PK1 cells did not demonstrate oxalate uptake either at the apical or basolateral plasma membrane. The apical-to-basolateral (A- \u3e B) flux of oxalate in LLC-PK1 cells was identical to the basolateral-to-apical (B- \u3e A) oxalate flux in these cells. Moreover these flux characteristics were similar to those found for D-mannitol, indicating paracellular movement for both compounds. From these data, it is concluded that, under the experimental conditions used, LLC-PK1 cells do not exhibit a specific transcellular transport system for oxalate

Governed by history: Institutional analysis of a contested biofuel innovation system in Tanzania

Initially hailed as a miracle crop for biofuel production, Jatropha has recently attracted criticism for competing with food production, causing adverse biodiversity impacts, and jeopardizing land access by rural populations in tropical countries. This paper analyzes the contested development of Jatropha biofuel sector in Tanzania by anchoring two new concepts of ‘organizational models’ and ‘institutional arrangements’ to the sectoral systems of innovation perspective. The notion of ‘organizational models’ brings into relief the heterogeneity of actors in an innovation system and the ways in which the actors form networks, within and across national borders, to organize innovative activities. The concept of ‘institutional arrangements’ refers to the ensemble of formal and informal institutions assembled during Tanzania’s colonial and post-colonial eras, which directly govern innovative activities in specific organizational models. Based on a location-specific and historically-grounded institutional analysis within the innovation system framework, implications are drawn for the future development of Tanzania’s Jatropha sector including its links with European markets and for the regulation of ‘next-generation’ biofuels

Critical temperature oscillations in magnetically coupled superconducting mesoscopic loops

We study the magnetic interaction between two superconducting concentric mesoscopic Al loops, close to the superconducting/normal phase transition. The phase boundary is measured resistively for the two-loop structure as well as for a reference single loop. In both systems Little-Parks oscillations, periodic in field are observed in the critical temperature Tc versus applied magnetic field H. In the Fourier spectrum of the Tc(H) oscillations, a weak 'low frequency' response shows up, which can be attributed to the inner loop supercurrent magnetic coupling to the flux of the outer loop. The amplitude of this effect can be tuned by varying the applied transport current.Comment: 9 pages, 7 figures, accepted for publication in Phys. Rev.

Clostridium difficile beyond stools : dog nasal discharge as a possible new vector of bacterial transmission

Zoonotic transmission of Clostridium difficile has been largely hypothesised to occur after direct or indirect contact with contaminated animal faeces. Recent studies have reported the presence of the bacterium in the natural environment, including in soils and rivers. If C. difficile spores are scattered in the environment, they can easily enter the respiratory tract of dogs, and therefore, dog nasal discharge could be a direct route of transmission not previously investigated. This study reports for the first time the presence of C. difficile in the respiratory tracts of dogs. The bacterium was isolated from 6 (17.1%) out of 35 nasal samples, with a total of 4 positive dogs (19%). C. difficile was recovered from both proximal and distal nasal cavities. All isolates were toxigenic and belonged to PCR- ribotype 014, which is one of the most predominant types in animals and in community- acquired C. difficile infections in recent years. The findings of this study demonstrate that the nasal cavity of dogs is contaminated with toxigenic C. difficile, and therefore, its secretions could be considered as a new route by which bacteria are spread and transmitted.Peer reviewe

Zeta Potential Measurement and Particle Size Analysis for a Better Understanding of Urinary Inhibitors of Calcium Oxalate Crystallization

To better understand urinary inhibitors of calcium oxalate crystallization, both zeta potential measurement and particle size analysis were chosen to illustrate: (1) the potential therapeutic efficacy of G872, a semi-synthetic sulfated polysaccharide, in stone prevention; and (2) the relative contribution of various urinary fractions {e.g., ultrafiltered urine (UFU), Tamm-Horsfall protein (THP), urinary polyanionsprecipitated with cetylpyridinium chloride (CPC), urinary macromolecular substances with different concentration ratios (UMSl0,50,90 and UMS\u27l0,50,90) and THP-free urine (THPFU)} to total urinary inhibitory activity. The results showed: (1) addition of G872 significantly enhances urinary inhibitory activity and negative zeta potential values; (2) re-addition of the CPC to UFU completely restores urinary inhibitory activity; and (3) artificial urines prepared by mixing UMS\u27 10,50,90 from THPFU with UFU differed in inhibitory activity from that prepared by mixing UMSl0,50,90 from a pooled normal urine with UFU. Based on these experimental results, the following speculations can be made: (1) normal human urines are considered to be a protective colloidal system; (2) urinary inhibitory activity originates mainly from CPC and/or UMS; (3) normal THP is a protective material to maintain urinary inhibitory activity; and (4) mutual interaction between urinary inhibitors may change the total urinary inhibitory activity

Etiology of Experimental Calcium Oxalate Monohydrate Nephrolithiasis in Rats

In a rat-model system, tubular crystal retention as a possible mechanism for the etiology of nephrolithiasis in man, was studied by conventional transmission electron microscopy. The animals were supplied for nine days with a crystal-inducing diet, with ethylene glycol plus NH4Cl in their drinking-water. After this induction period, a two day regime with fresh drinking-water was included, to allow crystals to be removed by spontaneous crystalluria. After aldehyde fixation of the rat kidneys, large crystals were seen inside the tubular lumen. The crystals were attached to cell surfaces and covered by neighboring epithelial cells. Some crystals were overgrown by several epithelial cells and underwent a process of so-called exotubulosis, resulting in free or cell-surrounded crystals in the interstitium, and possibly in crystals in Giant cells. To investigate the fate of the retained crystals, some animals were additionally exposed to a low-oxalate challenge from drinking water containing 0.1 volume per cent of ethylene glycol for 12 or 30 days, respectively. It was assumed that this would interfere with the retained intratubular or interstitial crystals, and allow the crystals to grow into mini-stones. This was not observed. After the oxalate challenge, no crystals were found to be retained in the tubules (free or covered by cells). Interstitial crystals were observed, but it remains to be demonstrated whether such crystals actually grow into mini-stones or that they are removed by the sterile inflammation process observed

Cell type-specific acquired protection from crystal adherence by renal tubule cells in culture

Cell type-specific acquired protection from crystal adherence by renal tubule cells in culture.BackgroundAdherence of crystals to the surface of renal tubule epithelial cells is considered an important step in the development of nephrolithiasis. Previously, we demonstrated that functional monolayers formed by the renal tubule cell line, Madin-Darby canine kidney (MDCK), acquire protection against the adherence of calcium oxalate monohydrate crystals. We now examined whether this property is cell type specific. The susceptibility of the cells to crystal binding was further studied under different culture conditions.MethodsCell-type specificity and the influence of the growth substrate was tested by comparing calcium oxalate monohydrate crystal binding to LLC-PK1 cells and to two MDCK strains cultured on either permeable or impermeable supports. These cell lines are representative for the renal proximal tubule (LLC-PK1) and distal tubule/collecting duct (MDCK) segments of the nephron, in which crystals are expected to be absent and present, respectively.ResultsWhereas relatively large amounts of crystals adhered to subconfluent MDCK cultures, the level of crystal binding to confluent monolayers was reduced for both MDCK strains. On permeable supports, MDCK cells not only obtained a higher level of morphological differentiation, but also acquired a higher degree of protection than on impermeable surfaces. Crystals avidly adhered to LLC-PK1 cells, irrespective of their developmental stage or growth substrate used.ConclusionsThese results show that the prevention of crystal binding is cell type specific and expressed only by differentiated MDCK cells. The anti-adherence properties acquired by MDCK cells may mirror a specific functional characteristic of its in situ equivalent, the renal distal tubule/collecting ducts