1,067 research outputs found
Quasi-phase-matching high-harmonic radiation using chirped THz pulses
High-order harmonic generation in the presence of a chirped THz pulse is investigated numerically with
a complete 3D nonadiabatic model. The assisting THz pulse illuminates the high-order harmonic
generation gas cell laterally inducing quasi-phase-matching. We demonstrate that it is possible to
compensate the phase mismatch during propagation and extend the macroscopic cutoff of a propagated
strong IR pulse to the single-dipole cutoff. We obtain 2 orders of magnitude increase in the harmonic
efficiency of cutoff harmonics (170 eV) using a THz pulse of constant wavelength, and a further factor
of 3 enhancement when a chirped THz pulse is use
Velocity Structure Diagnostics of Simulated Galaxy Clusters
Gas motions in the hot intracluster medium of galaxy clusters have an
important effect on the mass determination of the clusters through X-ray
observations. The corresponding dynamical pressure has to be accounted for in
addition to the hydrostatic pressure support to achieve a precise mass
measurement. An analysis of the velocity structure of the ICM for simulated
cluster-size haloes, especially focusing on rotational patterns, has been
performed, demonstrating them to be an intermittent phenomenon, strongly
related to the internal dynamics of substructures. We find that the expected
build-up of rotation due to mass assembly gets easily destroyed by passages of
gas-rich substructures close to the central region. Though, if a typical
rotation pattern is established, the corresponding mass contribution is
estimated to be up to ~17% of the total mass in the innermost region, and one
has to account for it. Extending the analysis to a larger sample of simulated
haloes we statistically observe that (i) the distribution of the rotational
component of the gas velocity in the innermost region has typical values of
~200-300 km/s; (ii) except for few outliers, there is no monotonic increase of
the rotational velocity with decreasing redshift, as we would expect from
approaching a relaxed configuration. Therefore, the hypothesis that the
build-up of rotation is strongly influenced by internal dynamics is confirmed,
and minor events like gas-rich substructures passing close to the equatorial
plane can easily destroy any ordered rotational pattern.Comment: 13 pages, 10 figures; Accepted for publication in MNRA
Cysteine specific bioconjugation with benzyl isothiocyanates
Protein labelling has a wide variety of applications in medicinal chemistry and chemical biology. In addition to covalent inhibition, specific labelling of biomolecules with fluorescent dyes is important in both target discovery, validation and diagnostics. Our research was conducted through the fragment-based development of a new benzyl-isothiocyanate-activated fluorescent dye based on the fluorescein scaffold. This molecule was evaluated against fluorescein isothiocyanate, a prevalent labelling agent. The reactivity and selectivity of phenyl- and benzyl isothiocyanate were compared at different pHs, and their activity was tested on several protein targets. Finally, the clinically approved antibody trastuzumab (and it's Fab fragment) were specifically labelled through reaction with free cysteines reductively liberated from their interchain disulfide bonds. The newly developed benzyl-fluorescein isothiocyanate and its optimized labelling protocol stands to be a valuable addition to the tool kit of chemical biology
The critical window for the classical Ramsey-Tur\'an problem
The first application of Szemer\'edi's powerful regularity method was the
following celebrated Ramsey-Tur\'an result proved by Szemer\'edi in 1972: any
K_4-free graph on N vertices with independence number o(N) has at most (1/8 +
o(1)) N^2 edges. Four years later, Bollob\'as and Erd\H{o}s gave a surprising
geometric construction, utilizing the isoperimetric inequality for the high
dimensional sphere, of a K_4-free graph on N vertices with independence number
o(N) and (1/8 - o(1)) N^2 edges. Starting with Bollob\'as and Erd\H{o}s in
1976, several problems have been asked on estimating the minimum possible
independence number in the critical window, when the number of edges is about
N^2 / 8. These problems have received considerable attention and remained one
of the main open problems in this area. In this paper, we give nearly
best-possible bounds, solving the various open problems concerning this
critical window.Comment: 34 page
Propagation-enhanced generation of intense high-harmonic continua in the 100-eV spectral region
The study of core electron dynamics through nonlinear spectroscopy requires intense isolated attosecond extreme ultraviolet or even X-ray pulses. A robust way to produce these pulses is high-harmonic generation (HHG) in a gas medium. However, the energy upscaling of the process depends on a very demanding next-generation laser technology that provides multi-terawatt (TW) laser pulses with few-optical-cycle duration and controlled electric field. Here, we revisit the HHG process driven by 16-TW sub-two-cycle laser pulses to reach high intensity in the 100-eV spectral region and beyond. We show that the combination of above barrier-suppression intensity with a long generation medium significantly enhances the isolation of attosecond pulses compared to lower intensities and/or shorter media and this way reduces the pulse duration as well as field-stability requirements on the laser driver. This novel regime facilitates the real-time observation of electron dynamics at the attosecond timescale in atoms, molecules, and solids
Demographic patterns and outcomes of patients in level I trauma centers in three international trauma systems
Introduction: Trauma systems were developed to improve the care for the injured. The designation and elements comprising these systems vary across countries. In this study, we have compared the demographic patterns and patient outcomes of Level I trauma centers in three international trauma systems. Methods: International multicenter prospective trauma registry-based study, performed in the University Medical Center Utrecht (UMCU), Utrecht, the Netherlands, John Hunter Hospital (JHH), Newcastle, Australia, and Harborview Medical Center (HMC), Seattle, the United States. Inclusion: patients =18 years, admitted in 2012, registered in the institutional trauma registry. Results: In UMCU, JHH, and HMC, respectively, 955, 1146, and 4049 patients met the inclusion criteria of which 300, 412, and 1375 patients with Injury Severity Score (ISS) > 15. Mean ISS was higher in JHH (13.5; p < 0.001) and HMC (13.4; p < 0.001) compared to UMCU (11.7). Unadjusted mortality: UMCU = 6.5 %, JHH = 3.6 %, and HMC = 4.8 %. Adjusted odds of death: JHH = 0.498 [95 % confidence interval (CI) 0.303-0.818] and HMC = 0.473 (95 % CI 0.325-0.690) compared to UMCU. HMC compared to JHH was 1.002 (95 % CI 0.664-1.514). Odds of death patients ISS > 15: JHH = 0.507 (95 % CI 0.300-0.857) and HMC = 0.451 (95 % CI 0.297-0.683) compared to UMCU. HMC = 0.931 (95 % CI 0.608-1.425) compared to JHH. TRISS analysis: UMCU: Ws = 0.787, Z = 1.31, M = 0.87; JHH, Ws = 3.583, Z = 6.7, M = 0.89; HMC, Ws = 3.902, Z = 14.6, M = 0.84. Conclusion: This study demonstrated substantial differences across centers in patient characteristics and mortality, mainly of neurological cause. Future research must investigate whether the outcome differences remain with nonfatal and long-term outcomes. Furthermore, we must focus on the development of a more valid method to compare systems
Direct Neutron Capture for Magic-Shell Nuclei
In neutron capture for magic--shell nuclei the direct reaction mechanism can
be important and may even dominate. As an example we investigated the reaction
Ca(n,Ca for projectile energies below 250\,keV in a direct
capture model using the folding procedure for optical and bound state
potentials. The obtained theoretical cross sections are in agreement with the
experimental data showing the dominance of the direct reaction mechanism in
this case. The above method was also used to calculate the cross section for
Ca(n,Ca.Comment: REVTeX, 7 pages plus 3 uuencoded figures, the complete uuencoded
postscript file is available at ftp://is1.kph.tuwien.ac.at/pub/ohu/calcium.u
Epidermal Growth Factor–PEG Functionalized PAMAM-Pentaethylenehexamine Dendron for Targeted Gene Delivery Produced by Click Chemistry
Aim of this study was the site-specific conjugation of an epidermal growth factor (EGF)-polyethylene glycol (PEG) chain by click chemistry onto a poly(amido amine) (PAMAM) dendron, as a key step toward defined multifunctional carriers for targeted gene delivery. For this purpose, at first propargyl amine cored PAMAM dendrons with ester ends were synthesized. The chain terminal ester groups were then modified by oligoamines with different secondary amino densities. The oligoamine-modified PAMAM dendrons were well biocompatible, as demonstrated in cytotoxicity assays. Among the different oligoamine-modified dendrons, PAMAM-pentaethylenehexamine (PEHA) dendron polyplexes displayed the best gene transfer ability. Conjugation of PAMAM-PEHA dendron with PEG spacer was conducted via click reaction, which was performed before amidation with PEHA. The resultant PEG-PAMAM-PEHA copolymer was then coupled with EGF ligand. pDNA transfections in HuH-7 hepatocellular carcinoma cells showed a 10-fold higher efficiency with the polyplexes containing conjugated EGF as compared to the ligand-free ones, demonstrating the concept of ligand targeting. Overall gene transfer efficiencies, however, were moderate, suggesting that additional measures for overcoming subsequent intracellular bottlenecks in delivery have to be taken
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