1,875 research outputs found
Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering
Twisted Laguerre-Gaussian lasers, with orbital angular momentum and
characterised by doughnut shaped intensity profiles, provide a transformative
set of tools and research directions in a growing range of fields and
applications, from super-resolution microcopy and ultra-fast optical
communications to quantum computing and astrophysics. The impact of twisted
light is widening as recent numerical calculations provided solutions to
long-standing challenges in plasma-based acceleration by allowing for high
gradient positron acceleration. The production of ultrahigh intensity twisted
laser pulses could then also have a broad influence on relativistic
laser-matter interactions. Here we show theoretically and with ab-initio
three-dimensional particle-in-cell simulations, that stimulated Raman
backscattering can generate and amplify twisted lasers to Petawatt intensities
in plasmas. This work may open new research directions in non-linear optics and
high energy density science, compact plasma based accelerators and light
sources.Comment: 18 pages, 4 figures, 1 tabl
Entanglement versus Quantum Discord in Two Coupled Double Quantum Dots
We study the dynamics of quantum correlations of two coupled double quantum
dots containing two excess electrons. The dissipation is included through the
contact with an oscillator bath. We solve the Redfield master equation in order
to determine the dynamics of the quantum discord and the entanglement of
formation. Based on our results, we find that the quantum discord is more
resistant to dissipation than the entanglement of formation for such a system.
We observe that this characteristic is related to whether the oscillator bath
is common to both qubits or not and to the form of the interaction Hamiltonian.
Moreover, our results show that the quantum discord might be finite even for
higher temperatures in the asymptotic limit.Comment: 14 pages, 8 figures (new version is the final version to appear in
NJP
Using continuous measurement to protect a universal set of quantum gates within a perturbed decoherence-free subspace
We consider a universal set of quantum gates encoded within a perturbed
decoherence-free subspace of four physical qubits. Using second-order
perturbation theory and a measuring device modeled by an infinite set of
harmonic oscillators, simply coupled to the system, we show that continuous
observation of the coupling agent induces inhibition of the decoherence due to
spurious perturbations. We thus advance the idea of protecting or even creating
a decoherence-free subspace for processing quantum information.Comment: 7 pages, 1 figure. To be published in Journal of Physics A:
Mathematical and Genera
Pressure and chemical substitution effects in the local atomic structure of BaFe2As2
The effects of K and Co substitutions and quasi-hydrostatic applied pressure
(P<9 GPa) in the local atomic structure of BaFe2As2, Ba(Fe{0.937}Co{0.063})2As2
and Ba{0.85}K{0.15}Fe2As2 superconductors were investigated by extended x-ray
absorption fine structure (EXAFS) measurements in the As K absorption edge. The
As-Fe bond length is found to be slightly reduced (<~ 0.01 Angstroms) by both
Co and K substitutions, without any observable increment in the corresponding
Debye Waller factor. Also, this bond is shown to be compressible (k =
3.3(3)x10^{-3} GPa^{-1}). The observed contractions of As-Fe bond under
pressure and chemical substitutions are likely related with a reduction of the
local Fe magnetic moments, and should be an important tuning parameter in the
phase diagrams of the Fe-based superconductors.Comment: 7 pages, 6 figure
Quantum Control of a Single Qubit
Measurements in quantum mechanics cannot perfectly distinguish all states and
necessarily disturb the measured system. We present and analyse a proposal to
demonstrate fundamental limits on quantum control of a single qubit arising
from these properties of quantum measurements. We consider a qubit prepared in
one of two non-orthogonal states and subsequently subjected to dephasing noise.
The task is to use measurement and feedback control to attempt to correct the
state of the qubit. We demonstrate that projective measurements are not optimal
for this task, and that there exists a non-projective measurement with an
optimum measurement strength which achieves the best trade-off between gaining
information about the system and disturbing it through measurement back-action.
We study the performance of a quantum control scheme that makes use of this
weak measurement followed by feedback control, and demonstrate that it realises
the optimal recovery from noise for this system. We contrast this approach with
various classically inspired control schemes.Comment: 12 pages, 7 figures, v2 includes new references and minor change
Evaluation of Microencapsulation of The UFV-AREG1 Bacteriophage in Alginate-Ca Microcapsules using Microfluidic Devices
The indiscriminate use of antibiotics and the emergence of resistant
microorganisms have become a major challenge for the food industry. The purpose
of this work was to microencapsulate the bacteriophage UFV-AREG1 in a calcium
alginate matrix using microfluidic devices and to study the viability and
efficiency of retention. The microcapsules were added to gel of propylene
glycol for use as an antimicrobial in the food industry. The technique showed
the number of the phage encapsulation, yielding drops with an average 100-250
m of diameter, 82.1 2% retention efficiency and stability in the gel
matrix for 21 days. The gel added to the microencapsulated phage showed
efficiency (not detectable on the surface) in reducing bacterial contamination
on the surface at a similar level to antimicrobial chemicals (alcohol 70%).
Therefore, it was possible to microencapsulate bacteriophages in alginate-Ca
and apply the microcapsules in gels for use as sanitizers in the food industry.Comment: 8 pages, 5 figure
Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering
Twisted Laguerre–Gaussian lasers, with orbital angular momentum and characterized by doughnut-shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high-gradient positron acceleration. The production of ultra-high-intensity twisted laser pulses could then also have a broad influence on relativistic laser–matter interactions. Here we show theoretically and with ab initio three-dimensional particle-in-cell simulations that stimulated Raman backscattering can generate and amplify twisted lasers to petawatt intensities in plasmas. This work may open new research directions in nonlinear optics and high–energy-density science, compact plasma-based accelerators and light sources
Co-substitution effects on the Fe-valence in the BaFe2As2 superconducting compound: A study of hard x-ray absorption spectroscopy
The Fe K X-ray absorption near edge structure (XANES) of BaFe2-xCoxAs2
superconductors was investigated. No appreciable alteration in shape or energy
position of this edge was observed with Co substitution. This result provides
experimental support to previous ab initio calculations in which the extra Co
electron is concentrated at the substitute site and do not change the
electronic occupation of the Fe ions. Superconductivity may emerge due to
bonding modifications induced by the substitute atom that weakens the
spin-density-wave ground state by reducing the Fe local moments and/or
increasing the elastic energy penalty of the accompanying orthorhombic
distortion.Comment: 4+ pages, 4 figures. Published in Phys. Rev. Let
Genotypic variability and antifungal susceptibility of Candida spp. isolated from hospital surfaces and hands of healthcare professionals
Objectives Candida spp. are responsible for 9095% of hematogenous fungal infections. In Brazil and Latin America, C. albicans is the most common specie, followed by C. parapsilosis and C. tropicalis. Infections caused by Candida spp. may have their origin in exogenous sources, transmitted to patients via contaminated infusions, biomedical devices or even by the hands of the hospital staff members. Molecular biology techniques such as Randomly Amplified Polymorphic DNA (RAPD) can show that the strains found in anatomical sites or abi- otic surfaces have the same pattern genome.Moreover, in the last decades it has been observed increasing the number of yeasts isolated from hospital environment resistant to antifungals. Thus, the aim of this study was to determine the susceptibility to antifungals and intraspecies similarity among isolates of different hospital surfaces and hands of healthcare professionals.
Methods The study was conducted with 25 isolates of Candida spp.: 5 strains of C. albicans and 5 strains of C. parapsilosis isolated from hospital surfaces. 5 strains of C. albicans, 5 strains of C. parapsilosis and 5 strains of C. tropicalis isolated from hands of healthcare professionals. Professionals and surfaces belonged to intensive care units. The minimal inhibitory concentration (MIC) was determined to voriconazole (VOR), fluconazole (FLZ), amphotericin B (AMB) and micafungin (MFG) according to M27-A3 of the Clinical and Labora- tory Standards Institute (CLSI). To determine the intra-species similarity, 3 primers were used: P4 (50 -AAGAGCCCGT-30 ), OPA-18 (50AGCTGACCGT30) and OPE-18 (50GGACTGCAGA 30). RAPD pro- files were analyzed using BioNumerics software version 4.6. The study was approved by the Ethics in research involving human subjects, CAAE 0448.0.093.000-11 protocol.
Results In relation to susceptibility testing (Table 1), it is important to highlight that C. parapsilosis showed 80% of MFG resistance. C. albicans and C. tropicalis showed reduced susceptibility to VOR, and resistence of the AMB was observed for C. albicans (20%). All amplifi- cations revealed distinct polymorphic bands. Genetic distances between each of the isolates were calculated and cluster analysis was used to generate a dendrogram showing relationships between them. The analysis of all primers showed similarity greater than 80% between strains of hands and hospital surfaces for intraspecies. Conclusion Our work shows that, healthy people and hospital surfaces may be colonized by different species yeast. Furthermore, the strains studied had relative resistance to antifungal drugs most frequently used in clinical practice. Finally, there was a high similarity between samples from hands (hospital staff members) and surfaces, providing an infection risk to susceptible individuals. Healthy people working in hospitals can carry yeasts on their hands with the same potential virulence, and which therefore offer the same risk of infection. This information should be considered when preventive measures are established. Attention to the colonization of hands and surfaces should not be restricted to high-risk units such as NICUs, but should also include other sections of hospitals
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