1,935 research outputs found
Electrical safety requirements: Implications for the module designer
Commercial photovoltaic array installations, which include residential and intermediate applications, are subject to building and electrical codes and to product safety standards. The National Electrical Code (NEC) Article 690, titled Solar Photovoltaic Systems, contains provisions defining acceptable levels of system safety and emphasizes the system design and its installation. The Underwriters Laboratories, Inc. (UL), document titled: Proposed First Edition of the Standard for Flat Plate Photovoltaic Modules and Panels, UL-1703, identifies module and panel construction requirements that ensure product safety. Together these documents describe requirements intended to minimize hazards such as shock and fire. Although initial focus of these requirements is on single crystal silicon modules, they are generic in nature, and are equally applicable to high voltage ( 30 Vdc), multikilowatt, thin film systems. A major safety concern is insulation breakdown within the module or array wiring system, or discontinuities within the electrical conductors. These failures can result in ground faults, in circuit arcs, or exposure to hazardous electrical parts. Safeguards are discussed
Robustness of force and stress inference in an epithelial tissue
During morphogenesis, the shape of a tissue emerges from collective cellular
behaviors, which are in part regulated by mechanical and biochemical
interactions between cells. Quantification of force and stress is therefore
necessary to analyze the mechanisms controlling tissue morphogenesis. Recently,
a mechanical measurement method based on force inference from cell shapes and
connectivity has been developed. It is non-invasive, and can provide space-time
maps of force and stress within an epithelial tissue, up to prefactors. We
previously performed a comparative study of three force-inference methods,
which differ in their approach of treating indefiniteness in an inverse problem
between cell shapes and forces. In the present study, to further validate and
compare the three force inference methods, we tested their robustness by
measuring temporal fluctuation of estimated forces. Quantitative data of
cell-level dynamics in a developing tissue suggests that variation of forces
and stress will remain small within a short period of time (minutes).
Here, we showed that cell-junction tensions and global stress inferred by the
Bayesian force inference method varied less with time than those inferred by
the method that estimates only tension. In contrast, the amplitude of temporal
fluctuations of estimated cell pressures differs less between different
methods. Altogether, the present study strengthens the validity and robustness
of the Bayesian force-inference method.Comment: 4 pages, 4 figure
Non-Gaussian bubbles in the sky
We point out a possible generation mechanism of non-Gaussian bubbles in the
sky due to bubble nucleation in the early universe. We consider a curvaton
scenario for inflation and assume that the curvaton field phi, whose energy
density is subdominant during inflation but which is responsible for the
curvature perturbation of the universe, is coupled to another field sigma which
undergoes false vacuum decay through quantum tunneling. For this model, we
compute the skewness of the curvaton fluctuations due to its interaction with
sigma during tunneling, that is, on the background of an instanton solution
that describes false vacuum decay. We find that the resulting skewness of the
curvaton can become large in the spacetime region inside the bubble. We then
compute the corresponding skewness in the statistical distribution of the
cosmic microwave background (CMB) temperature fluctuations. We find a
non-vanishing skewness in a bubble-shaped region in the sky. It can be large
enough to be detected in the near future, and if detected it will bring us
invaluable information about the physics in the early universe.Comment: 6 pages, 6 figure
Multi-field open inflation model and multi-field dynamics in tunneling
We consider a multi-field open inflation model, in which one of the fields
dominates quantum tunneling from a false vacuum while the other field governs
slow-roll inflation within the bubble nucleated from false vacuum decay. We
call the former the tunneling field and the latter the inflaton field. In the
limit of a negligible interaction between the two fields, the false vacuum
decay is described by a Coleman-De Luccia instanton. Here we take into account
the coupling between the two fields and construct explicitly a multi-field
instanton for a simple quartic potential model. We also solve the evolution of
the scalar fields within the bubble. We find our model realizes open inflation
successfully. This is the first concrete, viable model of open inflation
realized with a simple potential. We then study the effect of the multi-field
dynamics on the false vacuum decay, specifically on the tunneling rate. We find
the tunneling rate increases in general in comparison with the single field
case, though the increase is small unless the inflaton affects the instanton
solution substantially.Comment: 13 pages, 4 figure
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