Josephson oscillation linewidth of ion-irradiated YBa2_2Cu3_3O7_7 junctions

We report on the noise properties of ion-irradiated YBa$_2$Cu$_3$O$_7$ Josephson junctions. This work aims at investigating the linewidth of the Josephson oscillation with a detector response experiment at $\simeq$132 GHz. Experimental results are compared with a simple analytical model based on the Likharev-Semenov equation and the de Gennes dirty limit approximation. We show that the main source of low-frequency fluctuations in these junctions is the broadband Johnson noise and that the excess ($\frac{1}{f}$) noise contribution does not prevail in the temperature range of interest, as reported in some other types of high-T$_c$ superconducting Josephson junctions. Finally, we discuss the interest of ion-irradiated junctions to implement frequency-tunable oscillators consisting of synchronized arrays of Josephson junctions

Trace formula for dielectric cavities II: Regular, pseudo-integrable, and chaotic examples

Dielectric resonators are open systems particularly interesting due to their wide range of applications in optics and photonics. In a recent paper [PRE, vol. 78, 056202 (2008)] the trace formula for both the smooth and the oscillating parts of the resonance density was proposed and checked for the circular cavity. The present paper deals with numerous shapes which would be integrable (square, rectangle, and ellipse), pseudo-integrable (pentagon) and chaotic (stadium), if the cavities were closed (billiard case). A good agreement is found between the theoretical predictions, the numerical simulations, and experiments based on organic micro-lasers.Comment: 18 pages, 32 figure

Expansion properties of Alginate beads as cell carrier in the fluidized bed bioartificial liver

The homogeneous expansion behaviour of liquid-fluidized beds is exploited in various fields such as minerals engineering and biotechnology. Innovative fluidized bed bioreactor concepts have been also explored for applications as bioartificial organs, particularly the bioartificial liver (1). It has been shown that the fluidized bed bioreactor constituted of alginate beads hosting liver cells is one of the promising solution to a bioartificial liver. Compared to other solutions, fluidization of alginate beads containing the cells does not suffer from the severe limitations to mass transfer between the beads and the perfusion medium. In the present work, appropriate alginate beads were prepared by the alginate drop gelation in calcium chloride. The beads were characterized in terms of size distribution and density. Sauter mean diameter of 813 m and density of 1020 kg/m3 were obtained. The latter shows a value very close to usual perfusion fluid, which required also careful evaluation of the liquid properties. Expansion properties were evaluated for free alginate beads (i.e. without hepatic cells) using saline solutions as fluidization medium. Bed expansions have been conducted in a small-size 1-cm diameter column used for perfusion in in vitro experiments as well as in a bigger 10-cm diameter column close to human size bioreactor. Velocity-voidage plots are reported and elaborated in terms of Richardson-Zaki parameters, showing the effect of walls and the different distributor. ACKNOLEDGEMENTS The financial support of the European Union through the Project FP7-PEOPLE-2012-ITN “Training network for developing innovative bioartificial devices for treatment of kidney and liver disease” is gratefully acknowledged. REFERENCES Gautier A., Carpentier B., Dufresne M., Vu Dinh Q., Paullier P., Legallais C. Impact of alginate type and bead diameter on mass transfers and the metabolic activities of encapsulated C3A cells in bioartificial liver applications. European Cells and Materials 2011, 21:94-106

Large Eddy Simulation of HAWT and VAWT performances in the vicinity of a building

peer reviewedThis work compares the performances of a Horizontal Axis Wind Turbine (HAWT) and a Vertical Axis Wind Turbine (VAWT) using Wall modeled Large Eddy Simulation (WMLES) coupled with an actuator line method. The wind turbines are located in the vicinity of a real size industrial building. Both wind turbines are sized to produce the same power at their respective optimum Tip Speed Ratio for a same incident wind speed. Two relevant incident wind directions (SW and SSW) are investigated, the influence of the building on the performance of the two wind turbines is also analysed. The results obtained show that the HAWT has a better overall performance compared to the VAWT. Overspeeds are observed for both directions analysed, due to the presence of the building which locally increases the flow velocity. However, these overspeeds remain low due to the low height of the building. The change of wind direction only slightly impacts the HAWT production, while the VAWT production remains insensitive. However, the presence of the building improves the global production of both wind turbines. Qualitatively, this change of wind direction induces a deviation in the wake of both turbines, which is greater for a SW direction.7. Affordable and clean energ

Stable Operation of Copper-Protected La(FeMnSi)13Hy Regenerators in a Magnetic Cooling Unit

Magnetic refrigeration leads the current commercialization efforts of ambient caloric cooling technologies, is considered among its peers most promising in terms of anticipated energy efficiency gain, and allows for complete elimination of harmful coolants. By now, functional magnetocaloric components (so-called regenerators) based on Mn-substituted and hydrogenated LaFeSi alloys are commercially available. However, this alloy system exhibits magnetostriction, is susceptible to fracture, oxidation, and does not passivate well, rendering it prone to failure and corrosion, particularly when using water as favorable heat exchange medium. Demonstrating stable and extended operation of LaFeSi-based regenerators under realistic conditions with cost-sensitive measures thus constitutes a key milestone for derisking the materials system, paving a path toward reliable and maintenance-friendly magnetic cooling devices. Building upon a fundamental analysis of materials properties, process, and target specifications, we outline a 2-fold protection strategy, encompassing a highly conformal copper coating working in tandem with a tailored inhibitor system. The former is applied using an optimized electroless plating procedure, allowing us to evenly envelop complex regenerator architectures in a dense, nondefective, homogeneous, and ductile copper film of excellent interfacial quality. The latter addresses the corrosion characteristics of both coating and substrate in the application environment. In-device aging experiments prove the effectiveness of our multifaceted approach in maintaining the chemical, mechanical, and functional integrity of LaFeSi regenerators under continuous use. AB - Magnetic refrigeration leads the current commercialization efforts of ambient caloric cooling technologies, is considered among its peers most promising in terms of anticipated energy efficiency gain, and allows for complete elimination of harmful coolants. By now, functional magnetocaloric components (so-called regenerators) based on Mn-substituted and hydrogenated LaFeSi alloys are commercially available. However, this alloy system exhibits magnetostriction, is susceptible to fracture, oxidation, and does not passivate well, rendering it prone to failure and corrosion, particularly when using water as favorable heat exchange medium. Demonstrating stable and extended operation of LaFeSi-based regenerators under realistic conditions with cost-sensitive measures thus constitutes a key milestone for derisking the materials system, paving a path toward reliable and maintenance-friendly magnetic cooling devices. Building upon a fundamental analysis of materials properties, process, and target specifications, we outline a 2-fold protection strategy, encompassing a highly conformal copper coating working in tandem with a tailored inhibitor system. The former is applied using an optimized electroless plating procedure, allowing us to evenly envelop complex regenerator architectures in a dense, nondefective, homogeneous, and ductile copper film of excellent interfacial quality. The latter addresses the corrosion characteristics of both coating and substrate in the application environment. In-device aging experiments prove the effectiveness of our multifaceted approach in maintaining the chemical, mechanical, and functional integrity of LaFeSi regenerators under continuous use

Merkel Cells as Putative Regulatory Cells in Skin Disorders: An In Vitro Study

Merkel cells (MCs) are involved in mechanoreception, but several lines of evidence suggest that they may also participate in skin disorders through the release of neuropeptides and hormones. In addition, MC hyperplasias have been reported in inflammatory skin diseases. However, neither proliferation nor reactions to the epidermal environment have been demonstrated. We established a culture model enriched in swine MCs to analyze their proliferative capability and to discover MC survival factors and modulators of MC neuroendocrine properties. In culture, MCs reacted to bFGF by extending outgrowths. Conversely, neurotrophins failed to induce cell spreading, suggesting that they do not act as a growth factor for MCs. For the first time, we provide evidence of proliferation in culture through Ki-67 immunoreactivity. We also found that MCs reacted to histamine or activation of the proton gated/osmoreceptor TRPV4 by releasing vasoactive intestinal peptide (VIP). Since VIP is involved in many pathophysiological processes, its release suggests a putative regulatory role for MCs in skin disorders. Moreover, in contrast to mechanotransduction, neuropeptide exocytosis was Ca2+-independent, as inhibition of Ca2+ channels or culture in the absence of Ca2+ failed to decrease the amount of VIP released. We conclude that neuropeptide release and neurotransmitter exocytosis may be two distinct pathways that are differentially regulated

Population Structure of Staphylococcus aureus from Remote African Babongo Pygmies

Staphylococcus aureus is a bacterium that colonizes humans worldwide. The anterior nares are its main ecological niche. Carriers of S. aureus are at a higher risk of developing invasive infections. Few reports indicated a different clonal structure and profile of virulence factors in S. aureus isolates from Sub-Saharan Africa. As there are no data about isolates from remote indigenous African populations, we conducted a cross-sectional survey of S. aureus nasal carriage in Gabonese Babongo Pygmies. The isolates were characterized regarding their susceptibility to antibiotic agents, possession of virulence factors and clonal lineage. While similar carriage rates were found in populations of industrialized countries, isolates that encode the genes for the Panton-Valentine leukocidin (PVL) were clearly more prevalent than in European countries. Of interest, many methicillin-susceptible S. aureus isolates from Babongo Pygmies showed the same genetic background as pandemic methicillin-resistant S. aureus (MRSA) clones. We advocate a surveillance of S. aureus in neglected African populations to control the development of resistance to antibiotic drugs with particular respect to MRSA and to assess the impact of the high prevalence of PVL-positive isolates