517 research outputs found
Built-in bleeder system in laminated plastic structures
Method is described for interplying resin absorbing, glass bleeder cloth with the layup for fabricating laminated nonflammable plastic structures with wrinkle-free surfaces
Operator Transformations Between Exactly Solvable Potentials and Their Lie Group Generators
One may obtain, using operator transformations, algebraic relations between
the Fourier transforms of the causal propagators of different exactly solvable
potentials. These relations are derived for the shape invariant potentials.
Also, potentials related by real transformation functions are shown to have the
same spectrum generating algebra with Hermitian generators related by this
operator transformation.Comment: 13 pages with one Postscript figure, uses LaTeX2e with revte
Unscreened Coulomb repulsion in the one dimensional electron gas
A tight binding model of electrons interacting via bare Coulomb repulsion is
numerically investigated by use of the Density Matrix Renormalization Group
method which we prove applicable also to very long range potentials. From the
analysis of the elementary excitations, of the spin and charge correlation
functions and of the momentum distribution, a picture consistent with the
formation of a one dimensional "Wigner crystal" emerges, in quantitative
agreement with a previous bosonization study. At finite doping, Umklapp
scattering is shown to be ineffective in the presence of long range forces.Comment: RevTex, 5 pages with 8 eps figures. To be published on Phys. Rev.
Point defect structure of La-doped SrTiO3 ceramics with colossal permittivity
Sr1-xLaxTiO3 (SLTO) ceramics with colossal permittivity were fabricated by conventional solid-state reaction method. The point defects of pure STO and SLTO ceramics were analyzed by Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening (CDB). The charge compensation mechanisms and dielectric properties of ceramics were investigated. The results indicated that the intrinsic defects in pure STO ceramics were mainly V00 00 Ti . The charge compensation mechanism of SLTO ceramics was predominantly formation of V00 Sr . With increasing La content, εr of SLTO ceramics increased up to ~70000 at room temperature. The results of first-principle calculations indicated that the colossal permittivity came from a sharp polarization increase caused by dipole structure of defects. tand of SLTO ceramics showed obvious Debye relaxation at high temperatures and the relaxation showed a multiple relaxation times derived from different kinds of polarization mechanism. The main polarization mechanism of SLTO ceramics gradually changed from ion displacement polarization to defect dipole polarization influenced by the concentration of La dopants
Time evolution of the Rabi Hamiltonian from the unexcited vacuum
The Rabi Hamiltonian describes a single mode of electromagnetic radiation
interacting with a two-level atom. Using the coupled cluster method, we
investigate the time evolution of this system from an initially empty field
mode and an unexcited atom. We give results for the atomic inversion and field
occupation, and find that the virtual processes cause the field to be squeezed.
No anti-bunching occurs.Comment: 25 pages, 8 figures, RevTe
Outstanding Thermal Conductivity of Single Atomic Layer Isotope-Modified Boron Nitride
Materials with high thermal conductivities (k) is valuable to solve the
challenge of waste heat dissipation in highly integrated and miniaturized
modern devices. Herein, we report the first synthesis of atomically thin
isotopically pure hexagonal boron nitride (BN) and its one of the highest k
among all semiconductors and electric insulators. Single atomic layer (1L) BN
enriched with 11B has a k up to 1009 W/mK at room temperature. We find that the
isotope engineering mainly suppresses the out-of-plane optical (ZO) phonon
scatterings in BN, which subsequently reduces acoustic-optical scatterings
between ZO and transverse acoustic (TA) and longitudinal acoustic (LA) phonons.
On the other hand, reducing the thickness to single atomic layer diminishes the
interlayer interactions and hence Umklapp scatterings of the out-of-plane
acoustic (ZA) phonons, though this thickness-induced k enhancement is not as
dramatic as that in naturally occurring BN. With many of its unique properties,
atomically thin monoisotopic BN is promising on heat management in van der
Waals (vdW) devices and future flexible electronics. The isotope engineering of
atomically thin BN may also open up other appealing applications and
opportunities in 2D materials yet to be explored
Summing Divergent Perturbative Series in a Strong Coupling Limit. The Gell-Mann - Low Function of the \phi^4 Theory
An algorithm is proposed for determining asymptotics of the sum of a
perturbative series in the strong coupling limit using given values of the
expansion coefficients. Operation of the algorithm is illustrated by test
examples, method for estimating errors is developed, and an optimization
procedure is described. Application of the algorithm to the theory
gives a behavior at large for its Gell-Mann
-- Low function. The fact that the exponent is close to unity can be
interpreted as a manifestation of the logarithmic branching of the type
(with ), which is
confirmed by independent evidence. In any case, the theory is
internally consistent. The procedure of summing perturbartive series with
arbitrary values of expansion parameter is discussed.Comment: 23 pages, PD
Influence of severe plastic deformation on the precipitation hardening of a FeSiTi steel
The combined strengthening effects of grain refinement and high precipitated
volume fraction (~6at.%) on the mechanical properties of FeSiTi alloy subjected
to SPD processing prior to aging treatment were investigated by atom probe
tomography and scanning transmission electron microscopy. It was shown that the
refinement of the microstructure affects the precipitation kinetics and the
spatial distribution of the secondary hardening intermetallic phase, which was
observed to nucleate heterogeneously on dislocations and sub-grain boundaries.
It was revealed that alloys successively subjected to these two strengthening
mechanisms exhibit a lower increase in mechanical strength than a simple
estimation based on the summation of the two individual strengthening
mechanisms
Neutral rare-gas containing charge-transfer molecules in solid matrices : I. HXeCl, HXeBr, HXeI, and HKrCl in Kr and Xe
Ultraviolet-irradiation of hydrogen halide containing rare gas matrices yields the formation of linear centrosymmetric cations of type (XHX)⁺, (X=Ar, Kr, Xe). Annealing of the irradiated doped solids produces, along with thermoluminescence, extremely strong absorptions in the 1700–1000 cm⁻¹ region. Based on isotopic substitution and halogen dependence of these bands, the presence of hydrogen and halogen atom(s) in these species is evident. In the present paper we show the participation of rare gas atom(s) in these new compounds. The evidence is based on studies of the thermally generated species in mixed rare gas matrices. The new species are assigned as neutral charge-transfer molecules HX⁺Y⁻ (Y=halogen), and their vibrational spectra are discussed and compared with those calculated with ab initio methods. This is the first time hydrogen and a rare gas atom has been found to make a chemical bond in a neutral stable compound. The highest level ab initio calculations on the existence of compounds of type HXY corroborate the experimental observations. The mechanism responsible for the formation of these species is also discussed.
PACS: 61.80.Ba, 33.15.Fm, 81.40.Ef, 78.50.-
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