175 research outputs found
Fluctuation Pressure of a Stack of Membranes
We calculate the universal pressure constants of a stack of N membranes
between walls by strong-coupling theory. The results are in very good agreement
with values from Monte-Carlo simulations.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html Latest update of
paper also at http://www.physik.fu-berlin.de/~kleinert/31
Vibrational dynamics of rutile-type GeO2 from micro-Raman spectroscopy experiments and first-principles calculations
The vibrational dynamics of germanium dioxide in the rutile structure has been investigated by using polarized micro-Raman scattering spectroscopy coupled with first-principles calculations. Raman spectra were carried out in backscattering geometry at room temperature from micro-crystalline samples either unoriented or oriented by means of a micromanipulator, which enabled successful detection and identification of all the Raman active modes expected on the basis of the group theory. In particular, the Eg mode, incorrectly assigned or not detected in the literature, has been definitively observed by us and unambiguously identified at 525 cm 12 1 under excitation by certain laser lines, thus revealing an unusual resonance phenomenon. First principles calculations within the framework of the density functional theory allow quantifying both wave number and intensity of the Raman vibrational spectra. The excellent agreement between calculated and experimental data corroborates the reliability of our findings
Vibrational dynamics of rutile-type GeO2 from micro-Raman spectroscopy experiments and first-principles calculations
The vibrational dynamics of germanium dioxide in the rutile structure has been investigated by using polarized micro-Raman scattering spectroscopy coupled with first-principles calculations. Raman spectra were carried out in backscattering geometry at room temperature from micro-crystalline samples either unoriented or oriented by means of a micromanipulator, which enabled successful detection and identification of all the Raman active modes expected on the basis of the group theory. In particular, the Eg mode, incorrectly assigned or not detected in the literature, has been definitively observed by us and unambiguously identified at 525 cm − 1 under excitation by certain laser lines, thus revealing an unusual resonance phenomenon. First principles calculations within the framework of the density functional theory allow quantifying both wave number and intensity of the Raman vibrational spectra. The excellent agreement between calculated and experimental data corroborates the reliability of our findings
Scaling Exponents in the Incommensurate Phase of the Sine-Gordon and U(1) Thirring Models
In this paper we study the critical exponents of the quantum sine-Gordon and
U(1) Thirring models in the incommensurate phase. This phase appears when the
chemical potential exceeds a critical value and is characterized by a
finite density of solitons. The low-energy sector of this phase is critical and
is described by the Gaussian model (Tomonaga-Luttinger liquid) with the
compactification radius dependent on the soliton density and the sine-Gordon
model coupling constant .
For a fixed value of , we find that the Luttinger parameter is
equal to 1/2 at the commensurate-incommensurate transition point and approaches
the asymptotic value away from it. We describe a possible phase
diagram of the model consisting of an array of weakly coupled chains. The
possible phases are Fermi liquid, Spin Density Wave, Spin-Peierls and Wigner
crystal.Comment: 10pages; Improved version; Submitted to Physical Review
Arsenite sorption and co-precipitation with calcite
Sorption of As(III) by calcite was investigated as a function of As(III)
concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log
[As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended
version of the surface precipitation model. At low concentrations, As(OH)3
degrees is adsorbed by complexation to surface Ca surface sites, as previously
described by the X-ray standing wave technique. The inflexion point of the
isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST),
yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this
value, the amount of sorbed arsenic increases linearly with solution
concentration, up to the saturation of arsenic with respect to the
precipitation of CaHAsO3(s). The solid solutions formed in this concentration
range were examined by X-ray and neutron diffraction. The doped calcite lattice
parameters increase with arsenic content while c/a ratio remains constant. Our
results made on bulk calcite on the atomic displacement of As atoms along
[0001] direction extend those published by Cheng et al., (1999) on calcite
surface. This study provides a molecular-level explanation for why As(III) is
trapped by calcite in industrial treatments.Comment: 9 page
Vicinal Surfaces and the Calogero-Sutherland Model
A miscut (vicinal) crystal surface can be regarded as an array of meandering
but non-crossing steps. Interactions between the steps are shown to induce a
faceting transition of the surface between a homogeneous Luttinger liquid state
and a low-temperature regime consisting of local step clusters in coexistence
with ideal facets. This morphological transition is governed by a hitherto
neglected critical line of the well-known Calogero-Sutherland model. Its exact
solution yields expressions for measurable quantities that compare favorably
with recent experiments on Si surfaces.Comment: 4 pages, revtex, 2 figures (.eps
Decay of a Resonance in the Reaction
The narrow (=170 keV) and high spin () resonance in the Mg + Mg reaction at E= 45.7 MeV has been associated with a hyperdeformed molecular state in Cr. Such a description has important consequences for the resonance decay into the favored inelastic channels. Through fragment- coincidence measurements performed ON and OFF resonance using the PRISMA-CLARA array, we have identified the Mg states selectively populated: the and members of the ground state band
Nature and decay of a = resonance in the Mg + Mg reaction
It has been proposed to associate the narrow (\Gamma=170 keV) and high spin (=36^+) resonance in the 24Mg + 24Mg reaction at E_c.m= 45.7 MeV with a hyperdeformed molecular state in 48Cr. Such a description has important consequences for the resonance decay into the favoured inelastic channels. Through fragment- coincidence measurements performed ON and OFF resonance using the PRISMA-CLARA array, we have established that the 24Mg states selectively populated are the 2^+ and 4^+ members of the ground state band
The Structure of Hyperalkaline Aqueous Solutions Containing High Concentrations of Gallium - a Solution X-ray Diffraction and Computational Study
Highly concentrated alkaline NaOH/Ga(OH)3 solutions with 1.18 M Ga(III)T 2.32 M and 2.4 M NaOHT 4.9 M (where the subscript T denotes total or analytical concentrations) have been prepared and investigated by solution X-ray diffraction and also by ab initio quantum chemical calculations. The data obtained are consistent with the presence of only one predominant Ga(III)-bearing species in these solutions, that is the tetrahedral hydroxo complex Ga(OH)4–. This finding is in stark contrast to that found for Al(III)-containing solutions of similar concentrations, in which, besides the monomeric complex, an oxo-bridged dimer was also found to form. From the solution X-ray diffraction measurements, the formation of the dimeric (OH)3Ga–O–Ga(OH)32– could not unambiguously be shown, however, from the comparison of experimental IR, Raman and 71Ga NMR spectra with calculated ones, its formation can be safely excluded. Moreover, higher mononuclear stepwise hydroxo complexes, like Ga(OH)63–, that have been claimed to exist by others in the literature, was not possible to experimentally detect in these solutions with any of the spectroscopic techniques used
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