3,251 research outputs found
Criteria for evaluation of reflective surface for parabolic dish concentrators
Commercial, second surface glass mirror are emphasized, but aluminum and metallized polymeric films are also included. Criteria for sealing solar mirrors in order to prevent environmental degradation and criteria for bonding sagged or bent mirrors to substrate materials are described. An overview of the technical areas involved in evaluating small mirror samples, sections, and entire large gores is presented. A basis for mirror criteria was established that eventually may become part of inspection and evaluation techniques for three dimensional parabolic reflective surfaces
Low-Cost Experiments with Everyday Objects for Homework Assignments
We describe four classical undergraduate physics experiments that were done
with everyday objects and low-cost sensors: mechanical oscillations,
transmittance of light through a slab of matter, beam deformation under load,
and thermal relaxation due to heat loss. We used these experiments to train
students for experimental homework projects but they could be used and expanded
in a variety of contexts: lecture demonstrations, low cost students' labs,
science projects, distance learning courses...Comment: details on students where added : a section dedicated to the student
difficulties and general feedback on this teaching unit. Minor typos were
fixed. Published in Physics Educatio
Radiation data definitions and compilation for equipment qualification data bank
Dose definitions, physical properties, mechanical properties, electrical properties, and particle definitions are listed for insulators and dielectrics, elastomeric seals and gaskets, lubricants, adhesives, and coatings
On the thermoelastic analysis of solar cell arrays and related material properties
Accurate prediction of failure of solar cell arrays requires accuracy in the computation of thermally induced stresses. This was accomplished by using the finite element technique. Improved procedures for stress calculation were introduced together with failure criteria capable of describing a wide range of ductile and brittle material behavior. The stress distribution and associated failure mechanisms in the N-interconnect junction of two solar cell designs were then studied. In such stress and failure analysis, it is essential to know the thermomechanical properties of the materials involved. Measurements were made of properties of materials suitable for the design of lightweight arrays: microsheet-0211 glass material for the solar cell filter, and Kapton-H, Kapton F, Teflon, Tedlar, and Mica Ply PG-402 for lightweight substrates. The temperature-dependence of the thermal coefficient of expansion for these materials was determined together with other properties such as the elastic moduli, Poisson's ratio, and the stress-strain behavior up to failure
Influence of Disorder on the Hall Effect in BiSrCuO
The in-plane resistivity and Hall coefficient have been measured for the
single-layer compound BiSrCuO for the whole range of
doping states. The deviation of the Hall coefficient, , from a
high-temperature linear behavior and the temperature dependence of the Hall
angle are both only weakly dependent upon doping, contrasting with
BiSrLaCuO and BiSrCaCuO. This
is in contradiction with former proposals that the transverse transport detects
the formation of incoherent Cooper pairs in the pseudogap state. Conversely,
the analysis of the data using a phenomenological angular dependent scattering
rate clearly allows to distinguish between underdoped and overdoped states, and
we propose that the maximum in simply arises due to the combination of
a large isotropic scattering rate and an anisotropic temperature dependent one
Cost/performance of solar reflective surfaces for parabolic dish concentrators
Materials for highly reflective surfaces for use in parabolic dish solar concentrators are discussed. Some important factors concerning performance of the mirrors are summarized, and typical costs are treated briefly. Capital investment cost/performance ratios for various materials are computed specifically for the double curvature parabolic concentrators using a mathematical model. The results are given in terms of initial investment cost for reflective surfaces per thermal kilowatt delivered to the receiver cavity for various operating temperatures from 400 to 1400 C. Although second surface glass mirrors are emphasized, first surface, chemically brightened and anodized aluminum surfaces as well as second surface, metallized polymeric films are treated. Conventional glass mirrors have the lowest cost/performance ratios, followed closely by aluminum reflectors. Ranges in the data due to uncertainties in cost and mirror reflectance factors are given
Status of JPL'S experience with thin 7809 glass for solar energy applications
A shipment of advanced, high transmittance glass for solar thermal power applications is assessed. Results of both mirror and glass inspection are reported. Surface and bulk defects are identified as well as the number broken or chipped during shipment and handling. Of the panels received, the thicker 1.5 mm (0.060 in.) glass exhibited a smaller breakage rate than the thin 1.0 mm (0.040 in.) panels
Glass for low-cost photovoltaic solar arrays
Various aspects of glass encapsulation that are important for the designer of photovoltaic systems are discussed. Candidate glasses and available information defining the state of the art of glass encapsulation materials and processes for automated, high volume production of terrestrial photovoltaic devices and related applications are presented. The criteria for consideration of the glass encapsulation systems were based on the low-cost solar array project goals for arrays: (1) a low degradation rate, (2) high reliability, (3) an efficiency greater than 10 percent, (4) a total array price less than $500/kW, and (5) a production capacity of 500,000 kW/yr. The glass design areas discussed include the types of glass, sources and costs, physical properties, and glass modifications, such as antireflection coatings
Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies
Heat-capacity measurements of a 39 microgramm MgB_2 single crystal in fields
up to 14 T and below 3 K allow the determination of the low-temperature linear
term of the specific heat, its field dependence and its anisotropy. Our results
are compatible with two-band superconductivity, the band carrying the small gap
being isotropic, that carrying the large gap having an anisotropy of ~ 5. Three
different upper critical fields are thus needed to describe the superconducting
state of MgB2.Comment: 4 pages, 4 figures - V2: Bibliography updated and some typo
corrected. One reference added - V3: version accepted for publication in PRL,
changes made in the tex
Current dependent fluctuations in a BiSrCuO thin film
The current dependence of the excess conductivity is measured up to for a BiSrCuO thin film, as a function of doping. It
is found to be anomalously sensitive to the transport current and to behave as
a universal function of in the whole doping range. We discuss these
results in the perspective of a granular superconductor with a gapless-like
behavior
- …