510 research outputs found
Design and Manufacture of the Superconducting Bus-bars for the LHC Main Magnets
The main magnets of the LHC are series-connected electrically in different powering circuits by means of superconducting bus-bars, carrying a maximum current of 13 kA. These superconducting bus-bars consist of a superconducting cable thermally and electrically coupled to a copper profile all along the length. The function of the copper profile is essentially to provide an alternative path for the current in case the superconducting cable loses its superconducting state and returns to normal state because of a transient disturbance or of a normal zone propagation coming from the neighbouring magnets. When a superconducting bus-bar quenches to normal state its temperature must always stay below a safe values of about 100°C while the copper is conducting. When a resistive transition is detected, the protection systems triggers the ramping down of the current from 13000 A to 0. The ramp rate must not exceed a maximum value to avoid the transition of magnets series-connected in the circuit. This paper concerns the design and the manufacture of the high current superconducting bus-bars needed to interconnect the magnetic elements of the main dipoles, the main quadrupoles of the arcs and of the dispersion suppressors of the LHC
Metal-insulator transition induced by 16O -18O oxygen isotope exchange in colossal negative magnetoresistance manganites
The effect of 16O-18O isotope exchange on the electric resistivity was
studied for (La(1-y)Pr(y))0.7Ca0.3MnO3 ceramic samples. Depending on y, this
mixed perovskite exhibited different types of low-temperature behavior ranging
from ferromagnetic metal (FM) to charge ordered (CO) antiferromagnetic
insulator. It was found that at y=0.75, the substitution of 16O by 18O results
in the reversible transition from a FM to a CO insulator at zero magnetic
field. The applied magnetic field (H >= 2 T) transformed the sample with 18O
again to the metallic state and caused the increase in the FM transition
temperature Tc of the 16O sample. As a result, the isotope shift of Tc at H = 2
T was as high as 63 K. Such unique sensitivity of the system to oxygen isotope
exchange, giving rise even to the metal-insulator transition, is discussed in
terms of the isotope dependence of the effective electron bandwidth which
shifts the balance between the CO and FM phases.Comment: 5 pages (RevTeX), 2 eps figures included, to appear in J. Appl. Phys.
83, (1998
A Method to screen U.S. environmental biomonitoring data for race/ethnicity and income-related disparity
BACKGROUND: Environmental biomonitoring data provide one way to examine race/ethnicity and income-related exposure disparity and identify potential environmental justice concerns. METHODS: We screened U.S. National Health and Nutrition Examination Survey (NHANES) 2001–2008 biomonitoring data for 228 chemicals for race/ethnicity and income-related disparity. We defined six subgroups by race/ethnicity—Mexican American, non-Hispanic black, non-Hispanic white—and income—Low Income: poverty income ratio (PIR) <2, High Income: PIR ≥ 2. We assessed disparity by comparing the central tendency (geometric mean [GM]) of the biomonitoring concentrations of each subgroup to that of the reference subgroup (non-Hispanic white/High Income), adjusting for multiple comparisons using the Holm-Bonferroni procedure. RESULTS: There were sufficient data to estimate at least one geometric mean ratio (GMR) for 108 chemicals; 37 had at least one GMR statistically different from one. There was evidence of potential environmental justice concern (GMR significantly >1) for 12 chemicals: cotinine; antimony; lead; thallium; 2,4- and 2,5-dichlorophenol; p,p’-dichlorodiphenyldichloroethylene; methyl and propyl paraben; and mono-ethyl, mono-isobutyl, and mono-n-butyl phthalate. There was also evidence of GMR significantly <1 for 25 chemicals (of which 17 were polychlorinated biphenyls). CONCLUSIONS: Although many of our results were consistent with the U.S. literature, findings relevant to environmental justice were novel for dichlorophenols and some metals
Non-Perturbative Production of Multi-Boson States and Quantum Bubbles
The amplitude of production of on-mass-shell scalar bosons by a highly
virtual field is considered in a theory with weak
coupling and spontaneously broken symmetry. The amplitude of this
process is known to have an growth when the produced bosons are exactly at
rest. Here it is shown that for the process goes through
`quantum bubbles', i.e. quantized droplets of a different vacuum phase, which
are non-perturbative resonant states of the field . The bubbles provide a
form factor for the production amplitude, which rapidly decreases above the
threshold. As a result the probability of the process may be heavily suppressed
and may decrease with energy as , where the power
depends on the number of space dimensions. Also discussed are the quantized
states of bubbles and the amplitudes of their formation and decay.Comment: 20 pages in LaTeX + 3 figures (fugures not included, hardcopy
available on request), TPI-MINN-93/20-
Semantic features of the phraseological units with the component light within the artistic discourse
Conduct lexical and semantic analysis on the concept light in the artistic discourse of postmodern fictio
Catalyzed decay of false vacuum in four dimensions
The probability of destruction of a metastable vacuum state by the field of a
highly virtual particle with energy is calculated for a (3+1) dimensional
theory in the leading WKB approximation in the thin-wall limit. It is found
that the induced nucleation rate of bubbles, capable of expansion, is
exponentially small at any energy. The negative exponential power in the rate
reaches its maximum at the energy, corresponding to the top of the barrier in
the bubble energy, where it is a finite fraction of the same power in the
probability of the spontaneous decay of the false vacuum, i.e. at .Comment: 9 pages (standard LaTeX)+ 3 figures (one figure in LaTeX, two are
appended in PostScript). TPI-MINN-92/31-
Metal-semiconductor (semimetal) superlattices on a graphite sheet with vacancies
It has been found that periodically closely spaced vacancies on a graphite
sheet cause a significant rearrange-ment of its electronic spectrum: metallic
waveguides with a high density of states near the Fermi level are formed along
the vacancy lines. In the direction perpendicular to these lines, the spectrum
exhibits a semimetal or semiconductor character with a gap where a vacancy
miniband is degenerated into impurity levels.Comment: 4 pages, 3 figure
Development of Hydrometallurgical Process of Non-Ferrous and Rare Metals Recovery from Untraditional Mineral Raw Materials and Natural Brines
In connection with gradual lowering of supplies of tradit- ional ore raw materials involving non-ferrous and rare metals, winch is treated by well-known technologies, invo-lving into the production of untraditional, secondary and technogeneous raw materials appears to be actual task
Superlattices Consisting of "Lines" of Adsorbed Hydrogen Atom Pairs on Graphene
The structures and electron properties of new superlattices formed on
graphene by adsorbed hydrogen molecules are theoretically described. It has
been shown that superlattices of the (n, 0) zigzag type with linearly arranged
pairs of H atoms have band structures similar to the spectra of (n, 0) carbon
nanotubes. At the same time, superlattices of the (n, n) type with a
"staircase" of adsorbed pairs of H atoms are substantially metallic with a high
density of electronic states at the Fermi level and this property distinguishes
their spectra from the spectra of the corresponding (n, n) nanotubes. The
features of the spectra have the Van Hove form, which is characteristic of each
individual superlattice. The possibility of using such planar structures with
nanometer thickness is discussed.Comment: 5 pages, 4 figure
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