27,277 research outputs found
In an expanding universe, what doesn't expand?
The expansion of the universe is often viewed as a uniform stretching of
space that would affect compact objects, atoms and stars, as well as the
separation of galaxies. One usually hears that bound systems do not take part
in the general expansion, but a much more subtle question is whether bound
systems expand partially. In this paper, a very definitive answer is given for
a very simple system: a classical "atom" bound by electrical attraction. With a
mathemical description appropriate for undergraduate physics majors, we show
that this bound system either completely follows the cosmological expansion, or
-- after initial transients -- completely ignores it. This "all or nothing"
behavior can be understood with techniques of junior-level mechanics. Lastly,
the simple description is shown to be a justifiable approximation of the
relativistically correct formulation of the problem.Comment: 8 pages, 9 eps figure
A guideline for heavy ion radiation testing for Single Event Upset (SEU)
A guideline for heavy ion radiation testing for single event upset was prepared to assist new experimenters in preparing and directing tests. How to estimate parts vulnerability and select an irradiation facility is described. A broad brush description of JPL equipment is given, certain necessary pre-test procedures are outlined and the roles and testing guidelines for on-site test personnel are indicated. Detailed descriptions of equipment needed to interface with JPL test crew and equipment are not provided, nor does it meet the more generalized and broader requirements of a MIL-STD document. A detailed equipment description is available upon request, and a MIL-STD document is in the early stages of preparation
Molecules, ices and astronomy
Molecules in interstellar gas and in interstellar ices play a fundamental role in astronomy. However, the formation of the simplest molecule, molecular hydrogen, is still not fully understood. Similarly, although interstellar ice analogues have received much attention in the laboratory, the evolution of ices in the interstellar medium still requires further study. At UCL we have developed two separate experiments to address these issues and explore the following questions: How is H formed on dust-grain surfaces? What is the budget between internal, kinetic and surface energies in the formation process? What are the astronomical consequences of these results? For ices, we ask: How do molecules desorb from pure and from mixed ices in regions warmed by newly formed stars? What can molecules released from ices tell us about the star-formation process? We put our results in the context of other laboratory work and we describe their application to current problems in astronomy
Piezoelectric copolymer hydrophones for ultrasonic field characterization
Hydrophones to be used in the characterization of medical ultrasonic transducers have
been fabricated using a new polyvinylidene fluoride/trifluoroethylene (VF2/VF3)
copolymer. The copolymer has an advantage over VF2 in that it does not require
prestretching before poling. Thin copolymer films can be cast from solution and then
poled using the corona discharge method. As there is a need for small‐diameter
hydrophones to provide good spatial resolution in measuring highly focused ultrasonic
beams, hydrophones with diameter as small as 0.1 mm have been made. Both
needle‐type and line hydrophones have been tested and their performance reported. In
the case of line hydrophones, the output signal is proportional to the line integral of the
acoustic pressure and a computer tomographic technique has been used to reconstruct the
beam profiles
Cation Exchange Equilibria in Mixed Solvents Sorption Characteristics of Common Metals from Water-Dimethyl Sulfoxide-Hydrochloric Acid Mixed Solvent
The systematic study of sorption of Ca, Cd, Co(II), Cu(II), Fe(III), Hg(II), In(III), La, Mn, Ni(II), Th(IV), Pb, Yb, U(VI), and Zn by Dowex 50 x 8 cation exchange resin from dimethyl sulfoxide-water-hydrochloric acid mixed solvent is presented. The sorption characteristics are much the same as those found for acetone-water-hydrochloric acid mixed solvent. Major differences occur in the case of Fe(III), Ca, Mg, and Pb. Many useful separations involving these elements are indicated
Non-linear resistivity and heat dissipation in monolayer graphene
We have experimentally studied the nonlinear nature of electrical conduction
in monolayer graphene devices on silica substrates. This nonlinearity manifests
itself as a nonmonotonic dependence of the differential resistance on applied
DC voltage bias across the sample. At temperatures below ~70K, the differential
resistance exhibits a peak near zero bias that can be attributed to
self-heating of the charge carriers. We show that the shape of this peak arises
from a combination of different energy dissipation mechanisms of the carriers.
The energy dissipation at higher carrier temperatures depends critically on the
length of the sample. For samples longer than 10um the heat loss is shown to be
determined by optical phonons at the silica-graphene interface.Comment: 4 pages, 4 figure
Efficient decomposition of quantum gates
Optimal implementation of quantum gates is crucial for designing a quantum
computer. We consider the matrix representation of an arbitrary multiqubit
gate. By ordering the basis vectors using the Gray code, we construct the
quantum circuit which is optimal in the sense of fully controlled single-qubit
gates and yet is equivalent with the multiqubit gate. In the second step of the
optimization, superfluous control bits are eliminated, which eventually results
in a smaller total number of the elementary gates. In our scheme the number of
controlled NOT gates is which coincides with the theoretical lower
bound.Comment: 4 pages, 2 figure
ARIA 2016 : Care pathways implementing emerging technologies for predictive medicine in rhinitis and asthma across the life cycle
European Innovation Partnership on Active and Healthy Ageing Reference Site MACVIA-France, EU Structural and Development Fund Languedoc-Roussillon, ARIA.Peer reviewedPublisher PD
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