178 research outputs found
Dynamical invariants and nonadiabatic geometric phases in open quantum systems
We introduce an operational framework to analyze non-adiabatic Abelian and
non-Abelian, cyclic and non-cyclic, geometric phases in open quantum systems.
In order to remove the adiabaticity condition, we generalize the theory of
dynamical invariants to the context of open systems evolving under arbitrary
convolutionless master equations. Geometric phases are then defined through the
Jordan canonical form of the dynamical invariant associated with the
super-operator that governs the master equation. As a by-product, we provide a
sufficient condition for the robustness of the phase against a given decohering
process. We illustrate our results by considering a two-level system in a
Markovian interaction with the environment, where we show that the
non-adiabatic geometric phase acquired by the system can be constructed in such
a way that it is robust against both dephasing and spontaneous emission.Comment: 9 pages, 3 figures. v2: minor corrections and subsection IV.D added.
Published versio
Adiabatic compression of terahertz waves using metal flares
We report on the adiabatic free-space coupling of broadband terahertz (THz) radiation through a subwavelength gap using metal flares. Amplitude coupling ratios better than 30% are obtained by optimizing the curvature. This scheme shows a large potential for increasing the sensitivity in THz spectroscopy using high spatial confinement without the need of transmission optics or high precision components. The intrinsic curvature of metal sheets is already sufficient to carry out experiments downsizing the microwave approach.Peer reviewedElectrical and Computer Engineerin
Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor
We report on the layer thickness determination on dielectrically coated metal cylinders using terahertz (THz) time-domain spectroscopy. A considerable sensitivity increase of up to a factor of 150 is obtained for layers down to 2.5 um thickness by introducing an experimental geometry based on a two-cylinder waveguide sensor. The layer attached on one metal cylinder is guided in contact with the second metal cylinder in the THz beam waist. This approach uses concepts of adiabatic THz wave compression and the advantages of THz waveguides. The results are compared to measurements on free-standing layers.Peer reviewedElectrical and Computer Engineerin
Angiotensin II induced inflammation in the kidney and in the heart of double transgenic rats
BACKGROUND: We are investigating a double transgenic rat (dTGR) model, in which rats transgenic for the human angiotensinogen and renin genes are crossed. These rats develop moderately severe hypertension but die of end-organ cardiac and renal damage by week 7. The heart shows necrosis and fibrosis, whereas the kidneys resemble the hemolytic-uremic syndrome vasculopathy. Surface adhesion molecules (ICAM-1 and VCAM-1) are expressed early on the endothelium, while the corresponding ligands are found on circulating leukocytes. Leukocyte infiltration in the vascular wall accompanies PAI-1, MCP-1, iNOS and Tissue Factor expression. Furthermore we show evidence that Ang II causes the upregulation of NF-{kappa}B in our model. METHODS: We started PDTC-treatment on four weeks old dTGR (200 mg/kg sc) and age-matched SD rats. Blood-pressure- and albuminuria- measurements were monitored during the treatment period (four weeks). The seven weeks old animals were killed, hearts and kidneys were isolated and used for immunohistochemical-and electromobility shift assay analysis. RESULTS: Chronic treatment with the antioxidant PDTC decreased blood pressure (162 plus minus 8 vs. 190 plus minus 7 mm Hg, p = 0.02). Cardiac hypertrophy index was significantly reduced (4.90 plus minus 0.1 vs. 5.77 plus minus 0.1 mg/g, p < 0.001) compared to dTGR. PDTC reduced 24 h albuminuria by 85 % (2.7 plus minus 0.5 vs. 18.0 plus minus 3.4 mg/d, p < 0.001) and prevented death significantly. Vascular injury was ameliorated in small renal and cardiac vessels. PDTC inhibited NF-{kappa}B binding activity in heart and kidney. Immunohistochemical analysis shows increased expression of the p65 NF-{kappa}B subunit in the endothelium, smooth muscles cells of damaged small vessels, infiltrated cells, glomeruli, tubuli and collecting ducts of dTGR. PDTC markedly reduced the immunoreactivity of p65. CONCLUSION: Our data show that inhibition of NF-{kappa}B by PDTC markedly reduces inflammation, iNOS expression in the dTGR most likely leading to decreased cytotoxicity, and cell proliferation. Thus, NF-{kappa}B activation plays an important role in ANG II-induced end-organ damage
Adiabatic creation of coherent superposition states via multiple intermediate states
We consider an adiabatic population transfer process that resembles the well
established stimulated Raman adiabatic passage (STIRAP). In our system, the
states have nonzero angular momentums , therefore, the coupling laser fields
induce transitions among the magnetic sublevels of the states. In particular,
we discuss the possibility of creating coherent superposition states in a
system with coupling pattern and . Initially, the system is in the J=0 state. We show that by two delayed,
overlapping laser pulses it is possible to create any final superposition state
of the magnetic sublevels , , . Moreover, we find that
the relative phases of the applied pulses influence not only the phases of the
final superposition state but the probability amplitudes as well. We show that
if we fix the shape and the time-delay between the pulses, the final state
space can be entirely covered by varying the polarizations and relative phases
of the two pulses. Performing numerical simulations we find that our transfer
process is nearly adiabatic for the whole parameter set.Comment: 7 pages, 10 figure
Terahertz two-cylinder waveguide coupler for transverse-magnetic and transverse-electric mode operation
We report the coupling and guiding of broadband terahertz radiation using a two-cylinder waveguide coupler. For the transverse electromagnetic TEM (TM0) geometry, the two opposing metal cylinders exhibit an amplitude transmission comparable to that of the cylindrical silicon lens coupled parallel-plate waveguide, but in the transverse-electric orientation the two-cylinder coupler shows much better amplitude transmission.Peer reviewedElectrical and Computer Engineerin
Adiabatic population transfer via multiple intermediate states
This paper discusses a generalization of stimulated Raman adiabatic passage
(STIRAP) in which the single intermediate state is replaced by intermediate
states. Each of these states is connected to the initial state \state{i} with
a coupling proportional to the pump pulse and to the final state \state{f}
with a coupling proportional to the Stokes pulse, thus forming a parallel
multi- system. It is shown that the dark (trapped) state exists only
when the ratio between each pump coupling and the respective Stokes coupling is
the same for all intermediate states. We derive the conditions for existence of
a more general adiabatic-transfer state which includes transient contributions
from the intermediate states but still transfers the population from state
\state{i} to state \state{f} in the adiabatic limit. We present various
numerical examples for success and failure of multi- STIRAP which
illustrate the analytic predictions. Our results suggest that in the general
case of arbitrary couplings, it is most appropriate to tune the pump and Stokes
lasers either just below or just above all intermediate states.Comment: 14 pages, two-column revtex style, 10 figure
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Plastic fiber design for THz generation through wavelength translation
We report on an all-fiber Terahertz (THz) radiation source by exploiting nonlinear parametric process in a theoretically designed microstructured-core double clad plastic fiber (MC-DCPF). The required phase-matching condition is satisfied through suitable tailoring of the fiber dispersion and nonlinear properties at the pump wavelength of a high power CO2 laser, with a CO laser of much lower power acting as a seed concomitantly. Our simulated results reveal that a THz radiation source at the frequency of ~ 3 THz could be realized with a 3-dB phase-matching band-width of 2.13 GHz in a 65 m long optimized MC-DCPF. Maximum power conversion efficiency >1% is realizable even after including the material loss
A Phase 1 Study of TRC102, An Inhibitor of Base Excision Repair, and Pemetrexed in Patients with Advanced Solid Tumors
Introduction TRC102 potentiates the activity of cancer therapies that induce base excision repair (BER) including antimetabolite and alkylating agents. TRC102 rapidly and covalently binds to apurinic/apyrimidinic (AP) sites generated during BER, and TRC102-bound DNA causes topoisomerase II-dependent irreversible strand breaks and apoptosis. This study assessed the safety, maximum-tolerated dose (MTD), pharmacokinetics and pharmacodynamics of TRC102 alone and in combination with pemetrexed. Purpose Patients with advanced solid tumors received oral TRC102 daily for 4 days. Two weeks later, patients began standard-dose pemetrexed on day 1 in combination with oral TRC102 on days 1 to 4. The pemetrexed-TRC102 combination was repeated every 3 weeks until disease progression. Methods Twenty-eight patients were treated with TRC102 at 15, 30, 60 or 100 mg/m2/d. The MTD was exceeded at 100 mg/m2/d due to grade 3 anemia in 50 % of patients. TRC102 exposure increased in proportion to dose with a mean t1/2 of 28 h. A pharmacodynamic assay confirmed that TRC102 binds to pemetrexed-induced AP sites at all doses studied. Stable disease or better was achieved in 15 of 25 patients evaluable for response (60 %), including one patient with recurrent metastatic oropharyngeal carcinoma that expressed high levels of thymidylate synthase, who achieved a partial response and was progression free for 14 months. Conclusions When administered with pemetrexed, the maximum tolerated dose of oral TRC102 is 60 mg/m2/d for 4 days. Randomized controlled studies are planned to evaluate the clinical benefit of adding TRC102 to pemetrexed and other agents that induce BER. © 2012 Springer Science+Business Media, LLC
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