8,281 research outputs found
Low Cost Solar Array Project: Composition Measurements by Analytical Photon Catalysis
The applicability of the photon catalysis technique for effecting composition analysis of silicon samples was assessed. Third quarter activities were devoted to the study of impurities in silicon matrices. The evaporation process was shown to be congruent; thus, the spectral analysis of the vapor yields the composition of the bulk sample. Qualitative analysis of metal impurities in silicon was demonstrated e part per million level. Only one atomic spectral interference was noted; however, it is imperative to maintain a leak tight system due to chemical and spectral interferences caused by the presence of even minute amounts of oxygen in the active nitrogen afterglow
Vertical pairing of identical particles suspended in the plasma sheath
It is shown experimentally that vertical pairing of two identical
microspheres suspended in the sheath of a radio-frequency (rf) discharge at low
gas pressures (a few Pa), appears at a well defined instability threshold of
the rf power. The transition is reversible, but with significant hysteresis on
the second stage. A simple model, which uses measured microsphere resonance
frequencies and takes into account besides Coulomb interaction between
negatively charged microspheres also their interaction with positive ion wake
charges, seems to explain the instability threshold quite well.Comment: 4 pages, 6 figures. to appear in Phys. Rev. Lett. 86, May 14th (2001
Climate, exposed source-rock lithologies, crustal uplift and surface erosion: a theoretical analysis calibrated with data from the Alps/North Alpine Foreland Basin system
Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution
A self-consistent, mean-field model of charge-carrier injection and unipolar
transport in an organic semiconductor diode is developed utilizing the
effective transport energy concept and taking into account a realistic
density-of-states distribution as well as the presence of trap states in an
organic material. The consequences resulting from the model are discussed
exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic
conductor structure. A comparison of the theory to experimental data of a
unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.Comment: 6 pages, 2 figures; to be published in Journal of Applied Physic
Self consistent theory of unipolar charge-carrier injection in metal/insulator/metal systems
A consistent device model to describe current-voltage characteristics of
metal/insulator/metal systems is developed. In this model the insulator and the
metal electrodes are described within the same theoretical framework by using
density of states distributions. This approach leads to differential equations
for the electric field which have to be solved in a self consistent manner by
considering the continuity of the electric displacement and the electrochemical
potential in the complete system. The model is capable of describing the
current-voltage characteristics of the metal/insulator/metal system in forward
and reverse bias for arbitrary values of the metal/ insulator injection
barriers. In the case of high injection barriers, approximations are provided
offering a tool for comparison with experiments. Numerical calculations are
performed exemplary using a simplified model of an organic semiconductor.Comment: 21 pages, 8 figure
Scaling limit of the one-dimensional attractive Hubbard model: The non-half-filled band case
The scaling limit of the less than half filled attractive Hubbard chain is
studied. This is a continuum limit in which the particle number per lattice
site, n, is kept finite (0<n<1) while adjusting the interaction and bandwidth
in a such way that there is a finite mass gap. We construct this limit both for
the spectrum and the secular equations describing the excitations. We find,
that similarly to the half filled case, the limiting model has a massive and a
massless sector. The structure of the massive sector is closely analogous to
that of the half filled band and consequently to the chiral invariant SU(2)
Gross-Neveu (CGN) model. The structure of the massless sector differs from that
of the half filled band case: the excitations are of particle and hole type,
however they are not uniquely defined. The energy and the momentum of this
sector exhibits a tower structure corresponding to a conformal field theory
with c=1 and SU(2)xSU(2) symmetry. The energy-momentum spectrum and the zero
temperature free energy of the states with finite density coincides with that
of the half filled case supporting the identification of the limiting model
with the SU(2) symmetric CGN theory.Comment: Latex, 28 page
Treatment of tuberculosis in a region with high drug resistance: Outcomes, drug resistance amplification and re-infection
Introduction: Emerging antituberculosis drug resistance is a serious threat for tuberculosis (TB) control, especially in Eastern
European countries.
Methods: We combined drug susceptibility results and molecular strain typing data with treatment outcome reports to
assess the influence of drug resistance on TB treatment outcomes in a prospective cohort of patients from Abkhazia
(Georgia). Patients received individualized treatment regimens based on drug susceptibility testing (DST) results. Definitions
for antituberculosis drug resistance and treatment outcomes were in line with current WHO recommendations. First and
second line DST, and molecular typing were performed in a supranational laboratory for Mycobacterium tuberculosis (MTB)
strains from consecutive sputum smear-positive TB patients at baseline and during treatment.
Results: At baseline, MTB strains were fully drug-susceptible in 189/326 (58.0%) of patients. Resistance to at least H or R
(PDR-TB) and multidrug-resistance (MDR-TB) were found in 69/326 (21.2%) and 68/326 (20.9%) of strains, respectively. Three
MDR-TB strains were also extensively resistant (XDR-TB). During treatment, 3/189 (1.6%) fully susceptible patients at baseline
were re-infected with a MDR-TB strain and 2/58 (3.4%) PDR-TB patients became MDR-TB due to resistance amplification. 5/
47 (10.6%) MDR- patients became XDR-TB during treatment. Treatment success was observed in 161/189 (85.2%), 54/69
(78.3%) and 22/68 (32.3%) of patients with fully drug susceptible, PDR- and MDR-TB, respectively. Development of ofloxacin
resistance was significantly associated with a negative treatment outcome.
Conclusion: In Abkhazia, a region with high prevalence of drug resistant TB, the use of individualized MDR-TB treatment
regimens resulted in poor treatment outcomes and XDR-TB amplification. Nosocomial transmission of MDR-TB emphasizes
the importance of infection control in hospitals
SM(2,4k) fermionic characters and restricted jagged partitions
A derivation of the basis of states for the superconformal minimal
models is presented. It relies on a general hypothesis concerning the role of
the null field of dimension . The basis is expressed solely in terms of
modes and it takes the form of simple exclusion conditions (being thus a
quasi-particle-type basis). Its elements are in correspondence with
-restricted jagged partitions. The generating functions of the latter
provide novel fermionic forms for the characters of the irreducible
representations in both Ramond and Neveu-Schwarz sectors.Comment: 12 page
Comparative ergonomic workflow and user experience analysis of MRI versus fluoroscopy-guided vascular interventions:an iliac angioplasty exemplar case study
Purpose A methodological framework is introduced to assess and compare a conventional fluoroscopy protocol for peripheral angioplasty with a new magnetic resonant imaging (MRI)-guided protocol. Different scenarios were considered during interventions on a perfused arterial phantom with regard to time-based and cognitive task analysis, user experience and ergonomics. Methods Three clinicians with different expertise performed a total of 43 simulated common iliac angioplasties (9 fluoroscopic, 34 MRI-guided) in two blocks of sessions. Six different configurations for MRI guidance were tested in the first block. Four of them were evaluated in the second block and compared to the fluoroscopy protocol. Relevant stages’ durations were collected, and interventions were audio-visually recorded from different perspectives. A cued retrospective protocol analysis (CRPA) was undertaken, including personal interviews. In addition, ergonomic constraints in the MRI suite were evaluated. Results Significant differences were found when comparing the performance between MRI configurations versus fluoroscopy. Two configurations [with times of 8.56 (0.64) and 9.48 (1.13) min] led to reduce procedure time for MRI guidance, comparable to fluoroscopy [8.49 (0.75) min]. The CRPA pointed out the main influential factors for clinical procedure performance. The ergonomic analysis quantified musculoskeletal risks for interventional radiologists when utilising MRI. Several alternatives were suggested to prevent potential low-back injuries. Conclusions This work presents a step towards the implementation of efficient operational protocols for MRI-guided procedures based on an integral and multidisciplinary framework, applicable to the assessment of current vascular protocols. The use of first-user perspective raises the possibility of establishing new forms of clinical training and education
New path description for the M(k+1,2k+3) models and the dual Z_k graded parafermions
We present a new path description for the states of the non-unitary
M(k+1,2k+3) models. This description differs from the one induced by the
Forrester-Baxter solution, in terms of configuration sums, of their
restricted-solid-on-solid model. The proposed path representation is actually
very similar to the one underlying the unitary minimal models M(k+1,k+2), with
an analogous Fermi-gas interpretation. This interpretation leads to fermionic
expressions for the finitized M(k+1,2k+3) characters, whose infinite-length
limit represent new fermionic characters for the irreducible modules. The
M(k+1,2k+3) models are also shown to be related to the Z_k graded parafermions
via a (q to 1/q) duality transformation.Comment: 43 pages (minor typo corrected and minor rewording in the
introduction
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