371 research outputs found
Selective photoexcitation of exciton-polariton vortices
We resonantly excite exciton-polariton states confined in cylindrical traps.
Using a homodyne detection setup, we are able to image the phase and amplitude
of the confined polariton states. We evidence the excitation of vortex states,
carrying an integer angular orbital momentum m, analogous to the transverse
TEM01* "donut" mode of cylindrically symmetric optical resonators. Tuning the
excitation conditions allows us to select the charge of the vortex. In this
way, the injection of singly charged (m = 1 & m = -1) and doubly charged (m =
2) polariton vortices is shown. This work demonstrates the potential of
in-plane confinement coupled with selective excitation for the topological
tailoring of polariton wavefunctions
Soliton Instabilities and Vortex Streets Formation in a Polariton Quantum Fluid
Exciton-polaritons have been shown to be an optimal system in order to
investigate the properties of bosonic quantum fluids. We report here on the
observation of dark solitons in the wake of engineered circular obstacles and
their decay into streets of quantized vortices. Our experiments provide a
time-resolved access to the polariton phase and density, which allows for a
quantitative study of instabilities of freely evolving polaritons. The decay of
solitons is quantified and identified as an effect of disorder-induced
transverse perturbations in the dissipative polariton gas
Laser-driven plasma waves in capillary tubes
The excitation of plasma waves over a length of up to 8 centimeters is, for
the first time, demon- strated using laser guiding of intense laser pulses
through hydrogen filled glass capillary tubes. The plasma waves are diagnosed
by spectral analysis of the transmitted laser radiation. The dependence of the
spectral redshift, measured as a function of filling pressure, capillary tube
length and incident laser energy, is in excellent agreement with simulation
results. The longitudinal accelerating field inferred from the simulations is
in the range 1 -10 GV/m
Mixed-State Specific Heat of the Type-II Superconductor Nb0.77Zr0.23 in Magnetic Fields up to B c2
In order to document the behavior of the mean-field mixed-state specific heat of an isotropic. strongly type-II superconductor (i.e., with a large value of the Ginzburg parameterk), and to provide a basis for comparison with high-temperature superconductors, we measured the specific heatC of the alloy Nb0.77Zr0.23 withT c = 10.8K, B c2 (0) = 7.9T, in magnetic fieldsB = 0, 0.2, 1.0, 12, 2.0, 2.4. 3.0, 3.3. 4.0. 4.4, 4.8, 5.2, 6.0. 6.6, 7.2 and 10 T. The values of the upper critical fieldB c2 ( T), thermodynamic critical fieldB c (T), Ginzburg parameterk(T), and coefficient γ(B) = limT0(C(T. B)/T) are derived from the specific heat data and found to be in agreement with the GLAG theory in the dirty limit. The behavior of the mixed-state specific heat is analyzed in terms ofC el /T,∂(C el /T)/∂B, and∂(C el /T)/∂T vs. Tcurves, whereC el is the electronic contribution to the specific hea
Cancellation of probe effects in measurements of spin polarized momentum density by electron positron annihilation
Measurements of the two dimensional angular correlation of the
electron-positron annihilation radiation have been done in the past to detect
the momentum spin density and the Fermi surface. We point out that the momentum
spin density and the Fermi Surface of ferromagnetic metals can be revealed
within great detail owing to the large cancellation of the electron-positron
matrix elements which in paramagnetic multiatomic systems plague the
interpretation of the experiments. We prove our conjecture by calculating the
momentum spin density and the Fermi surface of the half metal CrO2, who has
received large attention due to its possible applications as spintronics
material
Hand soap contamination by Pseudomonas aeruginosa in a tertiary care hospital: no evidence of impact on patients.
BACKGROUND: During an environmental investigation of Pseudomonas aeruginosa in intensive care units, the liquid hand soap was found to be highly contaminated (up to 8 × 10(5)cfu/g) with this pathogen. It had been used over the previous five months and was probably contaminated during manufacturing.
AIM: To evaluate the burden of this contamination on patients by conducting an epidemiological investigation using molecular typing combined with whole genome sequencing (WGS).
METHODS: P. aeruginosa isolates from clinical specimens were analysed by double locus sequence typing (DLST) and compared with isolates recovered from the soap. Medical charts of patients infected with a genotype identical to those found in the soap were reviewed. WGS was performed on soap and patient isolates sharing the same genotype.
FINDINGS: P. aeruginosa isolates (N = 776) were available in 358/382 patients (93.7%). Only three patients (0.8%) were infected with a genotype found in the soap. Epidemiological investigations showed that the first patient was not exposed to the soap, the second could have been exposed, and the third was indeed exposed. WGS showed a high number of core single nucleotide polymorphism differences between patients and soap isolates. No close genetic association was observed between soap and patient isolates, ruling out the hypothesis of transmission.
CONCLUSION: Despite a highly contaminated soap, the combined investigation with DLST and WGS ruled out any impact on patients. Hand hygiene performed with alcohol-based solution for >15 years was probably the main reason. However, such contamination represents a putative reservoir of pathogens that should be avoided in the hospital setting
Hollow microspheres as targets for staged laser-driven proton acceleration
A coated hollow core microsphere is introduced as a novel target in ultra-intense laser-matter interaction experiments. In particular, it facilitates staged laser-driven proton acceleration by combining conventional target normal sheath acceleration (TNSA), power recycling of hot laterally spreading electrons and staging in a very simple and cheap target geometry. During TNSA of protons from one area of the sphere surface, laterally spreading hot electrons form a charge wave. Due to the spherical geometry, this wave refocuses on the opposite side of the sphere, where an opening has been laser micromachined. This leads to a strong transient charge separation field being set up there, which can post-accelerate those TNSA protons passing through the hole at the right time. Experimentally, the feasibility of using such targets is demonstrated. A redistribution is encountered in the experimental proton energy spectra, as predicted by particle-in-cell simulations and attributed to transient fields set up by oscillating currents on the sphere surface
Global bifurcation for asymptotically linear Schr\"odinger equations
We prove global asymptotic bifurcation for a very general class of
asymptotically linear Schr\"odinger equations \begin{equation}\label{1}
\{{array}{lr} \D u + f(x,u)u = \lam u \quad \text{in} \ {\mathbb R}^N, u \in
H^1({\mathbb R}^N)\setmimus\{0\}, \quad N \ge 1. {array}. \end{equation} The
method is topological, based on recent developments of degree theory. We use
the inversion in an appropriate Sobolev space
, and we first obtain bifurcation from the line of
trivial solutions for an auxiliary problem in the variables (\lambda,v) \in
{\mathbb R} \x X. This problem has a lack of compactness and of regularity,
requiring a truncation procedure. Going back to the original problem, we obtain
global branches of positive/negative solutions 'bifurcating from infinity'. We
believe that, for the values of covered by our bifurcation approach,
the existence result we obtain for positive solutions of \eqref{1} is the most
general so fa
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