311 research outputs found
Raman excitation spectroscopy of carbon nanotubes: effects of pressure medium and pressure
Raman excitation and emission spectra for the radial breathing mode (RBM) are
reported, together with a preliminary analysis. From the position of the peaks
on the two-dimensional plot of excitation resonance energy against Raman shift,
the chiral indices (m, n) for each peak are identified. Peaks shift from their
positions in air when different pressure media are added - water, hexane,
sulphuric acid - and when the nanotubes are unbundled in water with surfactant
and sonication. The shift is about 2 - 3 cm-1 in RBM frequency, but
unexpectedly large in resonance energy, being spread over up to 100meV for a
given peak. This contrasts with the effect of pressure. The shift of the peaks
of semiconducting nanotubes in water under pressure is orthogonal to the shift
from air to water. This permits the separation of the effects of the pressure
medium and the pressure, and will enable the true pressure coefficients of the
RBM and the other Raman peaks for each (m, n) to be established unambiguously.Comment: 6 pages, 3 Figures, Proceedings of EHPRG 2011 (Paris
Pressure coefficients of Raman modes of carbon nanotubes resolved by chirality: Environmental effect on graphene sheet
Studies of the mechanical properties of single-walled carbon nanotubes are
hindered by the availability only of ensembles of tubes with a range of
diameters. Tunable Raman excitation spectroscopy picks out identifiable tubes.
Under high pressure, the radial breathing mode shows a strong environmental
effect shown here to be largely independent of the nature of the environment .
For the G-mode, the pressure coefficient varies with diameter consistent with
the thick-wall tube model. However, results show an unexpectedly strong
environmental effect on the pressure coefficients. Reappraisal of data for
graphene and graphite gives the G-mode Grueuneisen parameter gamma = 1.34 and
the shear deformation parameter beta = 1.34.Comment: Submitted to Physical Review
On the Initial Singularity Problem in Two Dimensional Quantum Cosmology
The problem of how to put interactions in two-dimensional quantum gravity in
the strong coupling regime is studied. It shows that the most general
interaction consistent with this symmetry is a Liouville term that contain two
parameters satisfying the algebraic relation in order to assure the closure of the diffeomorphism algebra. The model is
classically soluble and it contains as general solution the temporal
singularity. The theory is quantized and we show that the propagation amplitude
fall tozero in . This result shows that the classical singularities
are smoothed by quantum effects and the bing-bang concept could be considered
as a classical extrapolation instead of a physical concept.Comment: 9pp, Revtex 3.0. New references added. To appear in Phys. Rev.
Hamiltonian quantization of General Relativity with the change of signature
We show in this article how the usual hamiltonian formalism of General
Relativity should be modified in order to allow the inclusion of the Euclidean
classical solutions of Einstein's equations. We study the effect that the
dynamical change of signature has on the superspace and we prove that it
induces a passage of the signature of the supermetric from () to
(). Next, all these features are more particularly studied on the
example of minisuperspaces. Finally, we consider the problem of quantization of
the Euclidean solutions. The consequences of different choices of boundary
conditions are examined.Comment: 32 pages, GCR-93/11/01, To appear in Phys. Rev.
Simultaneous genotyping and species identification using hybridization pattern recognition analysis of generic Mycobacterium DNA arrays
High-density oligonucleotide arrays can be used to rapidly examine large amounts of DNA sequence in a high throughput manner. An array designed to determine the specific nucleotide sequence of 705 bp of the rpoB gene of Mycobacterium tuberculosis accurately detected rifampin resistance associated with mutations of 44 clinical isolates of M. tuberculosis. The nucleotide sequence diversity in 121 Mycobacterial isolates (comprised of 10 species) was examined by both conventional dideoxynucleotide sequencing of the rpoB and 165 genes and by analysis of the rpoB oligonucleotide array hybridization patterns. Species identification for each of the isolates was similar irrespective of whether 16S sequence, rpoB sequence, or the pattern of rpoB hybridization was used. However, for several species, the number of alleles in the 16S and rpoB gene sequences provided discordant estimates of the genetic diversity within a species. In addition to confirming the array's intended utility for sequencing the region of M. tuberculosis that confers rifampin resistance, this work demonstrates that this array can identify the species of nontuberculous Mycobacteria. This demonstrates the general point that DNA microarrays that sequence important genomic regions (such as drug resistance or pathogenicity islands) can simultaneously identify species and provide some insight into the organism's population structure
Implications of invariance of the Hamiltonian under canonical transformations in phase space
We observe that, within the effective generating function formalism for the
implementation of canonical transformations within wave mechanics, non-trivial
canonical transformations which leave invariant the form of the Hamilton
function of the classical analogue of a quantum system manifest themselves in
an integral equation for its stationary state eigenfunctions. We restrict
ourselves to that subclass of these dynamical symmetries for which the
corresponding effective generating functions are necessaarily free of quantum
corrections. We demonstrate that infinite families of such transformations
exist for a variety of familiar conservative systems of one degree of freedom.
We show how the geometry of the canonical transformations and the symmetry of
the effective generating function can be exploited to pin down the precise form
of the integral equations for stationary state eigenfunctions. We recover
several integral equations found in the literature on standard special
functions of mathematical physics. We end with a brief discussion (relevant to
string theory) of the generalization to scalar field theories in 1+1
dimensions.Comment: REVTeX v3.1, 13 page
Quantum equivalence of sigma models related by non Abelian Duality Transformations
Coupling constant renormalization is investigated in 2 dimensional sigma
models related by non Abelian duality transformations. In this respect it is
shown that in the one loop order of perturbation theory the duals of a one
parameter family of models, interpolating between the SU(2) principal model and
the O(3) sigma model, exhibit the same behaviour as the original models. For
the O(3) model also the two loop equivalence is investigated, and is found to
be broken just like in the already known example of the principal model.Comment: As a result of the collaboration of new authors the previously
overlooked gauge contribution is inserted into eq.(43) changing not so much
the formulae as part of the conclusion: for the models considered non Abelian
duality is OK in one loo
An international experience with single-operator cholangiopancreatoscopy in patients with altered anatomy
Background and study aims: The utility of digital single- operator cholangiopancreatoscopy (D-SOCP) in surgically altered anatomy (SAA) is limited. We aimed to evaluate the technical success and safety of D-SOCP in patients SAA.
Patients and methods: Patients with SAA who underwent D-SOCP between February 2015 and June 2020 were retrospectively evaluated. Technical success was defined as completing the intended procedure with the use of D-SOCP.
Results: Thirty-five patients underwent D-SOCP (34 D-SOC, 1 D-SOP). Bilroth II was the most common type of SAA (45.7 %), followed by Whipple reconstruction (31.4 %). Twenty-three patients (65.7 %) patients had prior failed ERCP due to the presence of complex biliary stone (52.2 %). A therapeutic duodenoscope was utilized in the majority of the cases (68.6 %), while a therapeutic gastroscope (22.7 %) or adult colonoscope (8.5 %) were used in the remaining procedures. Choledocholithiasis (61.2 %) and pancreatic duct calculi (3.2 %) were the most common indications for D-SOCP. Technical success was achieved in all 35 patients (100 %) and majority (91.4 %) requiring a single session. Complex interventions included electrohydraulic or laser lithotripsy, biliary or pancreatic stent placement, stricture dilation, and target tissue biopsies. Two mild adverse events occurred (pancreatitis and transient bacteremia).
Conclusions: In SAA, D-SOCP is a safe and effective modality to diagnose and treat complex pancreatobiliary disorders, especially in cases where standard ERCP attempts may fail
Oral health status of 12-year-old school children in Khartoum state, the Sudan; a school-based survey
<p>Abstract</p> <p>Background</p> <p>Few studies have investigated the prevalence of dental caries among school children in the past decades in Sudan rendering it difficult to understand the status and pattern of oral health.</p> <p>Methods</p> <p>A school-based survey was conducted using stratified random cluster sampling in Khartoum state, Sudan. Data was collected through interviews and clinical examination by a single examiner. DMFT was measured according to WHO criteria. Gingival index (GI) of Loe & Silness and Plaque index (PI) of Silness & Loe were used.</p> <p>Results</p> <p>The mean DMFT for 12-year-olds was found to be 0.42 with a significant caries index (SiC) of 1.4. Private school attendees had significantly higher DMFT (0.57) when compared to public school attendees (0.4). The untreated caries prevalence was 30.5%. In multivariate analysis caries experience (DMFT > 0) was found to be significantly and directly associated with socioeconomic status. The mean GI for the six index teeth was found to be 1.05 (CI 1.03 – 1.07) and the mean PI was 1.30 (CI 1.22 – 1.38).</p> <p>Conclusion</p> <p>The prevalence of caries was found to be low. The school children with the higher socioeconomic status formed the high risk group.</p
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