268 research outputs found
Stretching dependence of the vibration modes of a single-molecule Pt-H2-Pt bridge
A conducting bridge of a single hydrogen molecule between Pt electrodes is
formed in a break junction experiment. It has a conductance near the quantum
unit, G_0 = 2e^2/h, carried by a single channel. Using point contact
spectroscopy three vibration modes are observed and their variation upon
stretching and isotope substitution is obtained. The interpretation of the
experiment in terms of a Pt-H_2-Pt bridge is verified by Density Functional
Theory calculations for the stability, vibrational modes, and conductance of
the structure.Comment: 5 pages, 4 figure
The number of transmission channels through a single-molecule junction
We calculate transmission eigenvalue distributions for Pt-benzene-Pt and
Pt-butadiene-Pt junctions using realistic state-of-the-art many-body
techniques. An effective field theory of interacting -electrons is used to
include screening and van der Waals interactions with the metal electrodes. We
find that the number of dominant transmission channels in a molecular junction
is equal to the degeneracy of the molecular orbital closest to the metal Fermi
level.Comment: 9 pages, 8 figure
A self-consistent quantum master equation approach to molecular transport
We propose a self-consistent generalized quantum master equation (GQME) to
describe electron transport through molecular junctions. In a previous study
[M.Esposito and M.Galperin. Phys. Rev. B 79, 205303 (2009)], we derived a
time-nonlocal GQME to cure the lack of broadening effects in Redfield theory.
To do so, the free evolution used in the Born-Markov approximation to close the
Redfield equation was replaced by a standard Redfield evolution. In the present
paper, we propose a backward Redfield evolution leading to a time-local GQME
which allows for a self-consistent procedure of the GQME generator. This
approach is approximate but properly reproduces the nonequilibrium steady state
density matrix and the currents of an exactly solvable model. The approach is
less accurate for higher moments such as the noise.Comment: 9 pages, 4 figure
Disentangling astroglial physiology with a realistic cell model in silico
Electrically non-excitable astroglia take up neurotransmitters, buffer extracellular K+ and generate Ca2+ signals that release molecular regulators of neural circuitry. The underlying machinery remains enigmatic, mainly because the sponge-like astrocyte morphology has been difficult to access experimentally or explore theoretically. Here, we systematically incorporate multi-scale, tri-dimensional astroglial architecture into a realistic multi-compartmental cell model, which we constrain by empirical tests and integrate into the NEURON computational biophysical environment. This approach is implemented as a flexible astrocyte-model builder ASTRO. As a proof-of-concept, we explore an in silico astrocyte to evaluate basic cell physiology features inaccessible experimentally. Our simulations suggest that currents generated by glutamate transporters or K+ channels have negligible distant effects on membrane voltage and that individual astrocytes can successfully handle extracellular K+ hotspots. We show how intracellular Ca2+ buffers affect Ca2+ waves and why the classical Ca2+ sparks-and-puffs mechanism is theoretically compatible with common readouts of astroglial Ca2+ imaging
Effect of Thermoelectric Cooling in Nanoscale Junctions
We propose a thermoelectric cooling device based on an atomic-sized junction.
Using first-principles approaches, we investigate the working conditions and
the coefficient of performance (COP) of an atomic-scale electronic refrigerator
where the effects of phonon's thermal current and local heating are included.
It is observed that the functioning of the thermoelectric nano-refrigerator is
restricted to a narrow range of driving voltages. Compared with the bulk
thermoelectric system with the overwhelmingly irreversible Joule heating, the
4-Al atomic refrigerator has a higher efficiency than a bulk thermoelectric
refrigerator with the same due to suppressed local heating via the
quasi-ballistic electron transport and small driving voltages. Quantum nature
due to the size minimization offered by atomic-level control of properties
facilitates electron cooling beyond the expectation of the conventional
thermoelectric device theory.Comment: 8 figure
Ralstonia pickettii bacteremia in a cardiac surgery patient in Belgrade, Serbia
Ralstonia pickettii is an opportunistic bacterium found in the water environment with an increasing incidence as a nosocomial pathogen. The objectives of this study were to describe R. pickettii bacteremia in a cardiac surgery patient and to evaluate its ability to grow in a saline solution and to form biofilm. The patient in this study underwent mitral and aortic valve replacement surgery with two aortocoronary bypasses. She developed signs of respiratory and renal failure, therefore hemodialysis was started. After 25 days in an intensive care unit, the patient had recurrent episodes of fever with signs of bacteremia. R. pickettii was identified from blood cultures by MALDI-TOF MS. Antimicrobial susceptibility testing was performed using disc diffusion and broth microdilution methods in accordance with EUCAST methodology and results were interpreted following clinical breakpoints for Pseudomonas spp. The isolate was susceptible to all tested antimicrobial agents except aminoglycosides and colistin. Survival of R. pickettii was analyzed in saline solution with four different starting concentrations at 25 degrees C and 37 degrees C for six days. Biofilm capacity was tested using the microtiter plate method. R. pickettii showed substantial growth in saline solution, with starting concentration of 2 CFU ml(-1) reaching 107 CFU ml(-1) after six days. There was no significant difference between growth at 25 degrees C and 37 degrees C. This indicates that storage of contaminated solutions at room temperature can enhance the count of R. pickettii. Our strain did not show the capacity to form biofilm. The patient responded well to adequate treatment with ceftazidime, and after 48 days in ICU she was discharged to convalesce
Spontaneous intraperitoneal hemorrhage as the initial presentation of a gastrointestinal stromal tumor: a case report
Dose-escalation using intensity-modulated radiotherapy for prostate cancer - evaluation of quality of life with and without 18F-choline PET-CT detected simultaneous integrated boost
<p>Abstract</p> <p>Background</p> <p>In comparison to the conventional whole-prostate dose escalation, an integrated boost to the macroscopic malignant lesion might potentially improve tumor control rates without increasing toxicity. Quality of life after radiotherapy (RT) with vs. without <sup>18</sup>F-choline PET-CT detected simultaneous integrated boost (SIB) was prospectively evaluated in this study.</p> <p>Methods</p> <p>Whole body image acquisition in supine patient position followed 1 h after injection of 178-355MBq <sup>18</sup>F-choline. SIB was defined by a tumor-to-background uptake value ratio > 2 (GTV<sub>PET</sub>). A dose of 76Gy was prescribed to the prostate (PTV<sub>prostate</sub>) in 2Gy fractions, with or without SIB up to 80Gy. Patients treated with (n = 46) vs. without (n = 21) SIB were surveyed prospectively before (A), at the last day of RT (B) and a median time of two (C) and 19 month (D) after RT to compare QoL changes applying a validated questionnaire (EPIC - expanded prostate cancer index composite).</p> <p>Results</p> <p>With a median cut-off standard uptake value (SUV) of 3, a median GTV<sub>PET </sub>of 4.0 cm<sup>3 </sup>and PTV<sub>boost </sub>(GTV<sub>PET </sub>with margins) of 17.3 cm<sup>3 </sup>was defined. No significant differences were found for patients treated with vs. without SIB regarding urinary and bowel QoL changes at times B, C and D (mean differences ≤3 points for all comparisons). Significantly decreasing acute urinary and bowel score changes (mean changes > 5 points in comparison to baseline level at time A) were found for patients with and without SIB. However, long-term urinary and bowel QoL (time D) did not differ relative to baseline levels - with mean urinary and bowel function score changes < 3 points in both groups (median changes = 0 points). Only sexual function scores decreased significantly (> 5 points) at time D.</p> <p>Conclusions</p> <p>Treatment planning with <sup>18</sup>F-choline PET-CT allows a dose escalation to a macroscopic intraprostatic lesion without significantly increasing toxicity.</p
Simultaneous measurements of electronic conduction and Raman response in molecular junctions
Electronic conduction through single molecules is affected by the molecular
electronic structure as well as by other information that is extremely
difficult to assess, such as bonding geometry and chemical environment. The
lack of an independent diagnostic technique has long hampered single-molecule
conductance studies. We report simultaneous measurement of the conductance and
the Raman spectra of nanoscale junctions used for single-molecule electronic
experiments. Blinking and spectral diffusion in the Raman response of both
para-mercaptoaniline and a fluorinated oligophenylyne ethynylene correlate in
time with changes in the electronic conductance. Finite difference time domain
calculations confirm that these correlations do not result from the conductance
modifying the Raman enhancement. Therefore, these observations strongly imply
that multimodal sensing of individual molecules is possible in these
mass-producible nanostructures.Comment: 16 pages, 5 figures + supporting material of 15 pages, 10 figure
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