Surface Oscillations in Overdense Plasmas Irradiated by Ultrashort Laser Pulses

The generation of electron surface oscillations in overdense plasmas irradiated at normal incidence by an intense laser pulse is investigated. Two-dimensional (2D) particle-in-cell simulations show a transition from a planar, electrostatic oscillation at $2\omega$, with $\omega$ the laser frequency, to a 2D electromagnetic oscillation at frequency $\omega$ and wavevector $k>\omega/c$. A new electron parametric instability, involving the decay of a 1D electrostatic oscillation into two surface waves, is introduced to explain the basic features of the 2D oscillations. This effect leads to the rippling of the plasma surface within a few laser cycles, and is likely to have a strong impact on laser interaction with solid targets.Comment: 9 pages (LaTeX, Revtex4), 4 GIF color figures, accepted for publication in Phys. Rev. Let

Dynamics of viscous amphiphilic films supported by elastic solid substrates

The dynamics of amphiphilic films deposited on a solid surface is analyzed for the case when shear oscillations of the solid surface are excited. The two cases of surface- and bulk shear waves are studied with film exposed to gas or to a liquid. By solving the corresponding dispersion equation and the wave equation while maintaining the energy balance we are able to connect the surface density and the shear viscocity of a fluid amphiphilic overlayer with experimentally accessible damping coefficients, phase velocity, dissipation factor and resonant frequency shifts of shear waves.Comment: 19 pages, latex, 3 figures in eps-forma

Spectral shaping of laser generated proton beams

The rapid progress in the field of laser particle acceleration has stimulated a debate about the promising perspectives of laser based ion beam sources. For a long time, the beams produced exhibited quasi-thermal spectra. Recent proof-of-principle experiments demonstrated that ion beams with narrow energy distribution can be generated from special target geometries. However, the achieved spectra were strongly limited in terms of monochromacity and reproducibility. We show that microstructured targets can be used to reliably produce protons with monoenergetic spectra above 2 MeV with less than 10% energy spread. Detailed investigations of the effects of laser ablation on the target resulted in a significant improvement of the reproducibility. Based on statistical analysis, we derive a scaling law between proton peak position and laser energy, underlining the suitability of this method for future applications. Both the quality of the spectra and the scaling law are well reproduced by numerical simulations

Prevalence of antibodies against influenza A and B viruses in children in Germany, 2008 to 2010

The prevalence of influenza A and B virus-specific IgG was determined in sera taken between 2008 and 2010 from 1,665 children aged 0-17 years and 400 blood donors in Germany. ELISA on the basis of whole virus antigens was applied. Nearly all children aged nine years and older had antibodies against influenza A. In contrast, 40% of children aged 0-4 years did not have any influenza A virus-specific IgG antibodies. Eighty-six percent of 0-6 year-olds, 47% of 7-12 year-olds and 20% of 13-17 year-olds were serologically naive to influenza B viruses. By the age of 18 years, influenza B seroprevalence reached approximately 90%. There were obvious regional differences in the seroprevalence of influenza B in Germany. In conclusion, seroprevalences of influenza A and influenza B increase gradually during childhood. The majority of children older than eight years have basal immunity to influenza A, while comparable immunity against influenza B is only acquired at the age of 18 years. Children aged 0-6 years, showing an overall seroprevalence of 67% for influenza A and of 14% for influenza B, are especially at risk for primary infections during influenza B seasons

Mass movement deposits in the 3.6 Ma sediment record of Lake El'gygytgyn, Far East Russian Arctic

This paper focuses on the characterization and genesis of mass movement deposits (MMDs) in the Quater- nary and Pliocene sediments of Lake El’gygytgyn, Far East Russian Arctic. Three partly overlapping holes were drilled into the 320 m long sediment record at International Conti- nental Scientific Drilling Program (ICDP) Site 5011-1 in the lake basin, recovering the Quaternary almost completely, and the Pliocene down to 3.6 Ma with 52 % recovery. Mass move- ment deposits were investigated in all three cores, based on macroscopical core descriptions, radiographic images, high- resolution magnetic susceptibility and gamma-ray density. Five different types of MMDs were identified: turbidites, grain-flow deposits, debrites, slumps and slides. These are formed by transitional mass movement processes, and thus can be co-generic. An initial slope failure is thought to trans- form into a debris flow that deforms frontal sediments, partly disintegrates and dilutes into a turbidity flow. Turbidites are by far the most frequent MMD type in the lake center. They occur throughout the record in all pelagic sedimentary fa- cies, but they are thinner in facies formed during cold cli- mate conditions. All other MMDs, by contrast, incise exclu- sively the pelagic facies deposited during warm climates. In the 123 m thick Quaternary composite sediment record 230 mass movement events are identified, comprising 33% of the sediment length. Turbidites contribute 93 % of the num- ber of Quaternary MMDs, but only 35 % of their thickness. In the Pliocene sediments between 123 and 320 m, 181 ad- ditional mass movement deposits are identified, which con- stitute ⇠ 33 % of the recovered sediments. The mean recur- rence interval for MMDs is 11 and 5 ka in the Quaternary and Pliocene, respectively

Role of surface roughness in hard x-ray emission from femtosecond laser produced copper plasmas

The hard x-ray emission in the energy range of 30-300 keV from copper plasmas produced by 100 fs, 806 nm laser pulses at intensities in the range of 10$^{15}-10^{16}$ W cm$^{-2}$ is investigated. We demonstrate that surface roughness of the targets overrides the role of polarization state in the coupling of light to the plasma. We further show that surface roughness has a significant role in enhancing the x-ray emission in the above mentioned energy range.Comment: 5 pages, 4 figures, to appear in Phys. Rev.

Multijoule scaling of laser-induced condensation in air

Using 100 TW laser pulses, we demonstrate that laser-induced nanometric particle generation in air increases much faster than the beam-averaged incident intensity. This increase is due to a contribution from the photon bath, which adds up with the previously identified one from the filaments and becomes dominant above 550 GW/cm2. It appears related to ozone formation via multiphotondissociation of the oxygen molecules and demonstrates the critical need for further increasing the laser energy in view of macroscopic effects in laser-induced condensation

Factors Associated with the Rapid and Durable Decline in Malaria Incidence in El Salvador, 1980-2017

A decade after the Global Malaria Eradication Program, El Salvador had the highest burden of malaria in Mesoamerica, with approximately 20% due to Plasmodium falciparum. A resurgence of malaria in the 1970s led El Salvador to alter its national malaria control strategy. By 1995, El Salvador recorded its last autochthonous P. falciparum case with fewer than 20 Plasmodium vivax cases annually since 2011. By contrast, its immediate neighbors continue to have the highest incidences of malaria in the region. We reviewed and evaluated the policies and interventions implemented by the Salvadoran National Malaria Program that likely contributed to this progress toward malaria elimination. Decentralization of the malaria program, early regional stratification by risk, and data-driven stratum-specific actions resulted in the timely and targeted allocation of resources for vector control, surveillance, case detection, and treatment. Weekly reporting by health workers and volunteer collaborators-distributed throughout the country by strata and informed via the national surveillance system-enabled local malaria teams to provide rapid, adaptive, and focalized program actions. Sustained investments in surveillance and response have led to a dramatic reduction in local transmission, with most current malaria cases in El Salvador due to importation from neighboring countries. Additional support for systematic elimination efforts in neighboring countries would benefit the region and may be needed for El Salvador to achieve and maintain malaria elimination. El Salvador's experience provides a relevant case study that can guide the application of similar strategies in other countries committed to malaria elimination