Modeling of surface-induced second-harmonic generation from multilayer structures by the transfer matrix method.

We analytically and numerically investigate surface second-harmonic generation (SHG) from a stack of dielectric layers. We develop a theoretical formalism based on the transfer matrix method for the calculation of the surface-driven second-harmonic radiation from multilayer structures and elaborate it for the case of ultrathin dielectric layers using a power series expansion to derive the effective surface nonlinear tensor for the whole stack. We show that for deeply subwavelength thicknesses of the layers the surface responses from all interfaces can efficiently sum up, leading to largely enhanced efficiency of SHG. As a result, such surface-driven nonlinearity can become comparable to the bulk nonlinearity in noncentrosymmetric semiconductors and can yield high performance for nonlinear nanophotonic applications.

Efficient hybrid method for the modal analysis of optical microcavities and nanoresonators.

We propose a novel hybrid method for accurately and efficiently analyzing microcavities and nanoresonators. The method combines the marked spirit of quasinormal mode expansion approaches, e.g., analyticity and physical insight, with the renowned strengths of real-frequency simulations, e.g., accuracy and flexibility. Real- and complex-frequency simulations offer a complementarity between accuracy and computation speed, opening new perspectives for challenging inverse design of nanoresonators.

Experimental Observation of Proton Bunch Modulation in a Plasma at Varying Plasma Densities.

We give direct experimental evidence for the observation of the full transverse self-modulation of a long, relativistic proton bunch propagating through a dense plasma. The bunch exits the plasma with a periodic density modulation resulting from radial wakefield effects. We show that the modulation is seeded by a relativistic ionization front created using an intense laser pulse copropagating with the proton bunch. The modulation extends over the length of the proton bunch following the seed point. By varying the plasma density over one order of magnitude, we show that the modulation frequency scales with the expected dependence on the plasma density, i.e., it is equal to the plasma frequency, as expected from theory.

Experimental Observation of Plasma Wakefield Growth Driven by the Seeded Self-Modulation of a Proton Bunch.

We measure the effects of transverse wakefields driven by a relativistic proton bunch in plasma with densities of 2.1×10^{14} and 7.7×10^{14} electrons/cm^{3}. We show that these wakefields periodically defocus the proton bunch itself, consistently with the development of the seeded self-modulation process. We show that the defocusing increases both along the bunch and along the plasma by using time resolved and time-integrated measurements of the proton bunch transverse distribution. We evaluate the transverse wakefield amplitudes and show that they exceed their seed value (<15 MV/m) and reach over 300 MV/m. All these results confirm the development of the seeded self-modulation process, a necessary condition for external injection of low energy and acceleration of electrons to multi-GeV energy levels.

Proton-driven plasma wakefield acceleration in AWAKE.

In this article, we briefly summarize the experiments performed during the first run of the Advanced Wakefield Experiment, AWAKE, at CERN (European Organization for Nuclear Research). The final goal of AWAKE Run 1 (2013-2018) was to demonstrate that 10-20 MeV electrons can be accelerated to GeV energies in a plasma wakefield driven by a highly relativistic self-modulated proton bunch. We describe the experiment, outline the measurement concept and present first results. Last, we outline our plans for the future. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Quasinormal mode solvers for resonators with dispersive materials.

Optical resonators are widely used in modern photonics. Their spectral response and temporal dynamics are fundamentally driven by their natural resonances, the so-called quasinormal modes (QNMs), with complex frequencies. For optical resonators made of dispersive materials, the QNM computation requires solving a nonlinear eigenvalue problem. This raises a difficulty that is only scarcely documented in the literature. We review our recent efforts for implementing efficient and accurate QNM solvers for computing and normalizing the QNMs of micro- and nanoresonators made of highly dispersive materials. We benchmark several methods for three geometries, a two-dimensional plasmonic crystal, a two-dimensional metal grating, and a three-dimensional nanopatch antenna on a metal substrate, with the perspective to elaborate standards for the computation of resonance modes.

Measuring the electromagnetic chirality of 2D arrays under normal illumination.

We present an electromagnetic chirality measure for 2D arrays of subwavelength periodicities under normal illumination. The calculation of the measure uses only the complex reflection and transmission coefficients from the array. The measure allows the ordering of arrays according to their electromagnetic chirality, which further allows a quantitative comparison of different design strategies. The measure is upper bounded, and the extreme properties of objects with high values of electromagnetic chirality make them useful in both near- and far-field applications. We analyze the consequences that different possible symmetries of the array have on its electromagnetic chirality. We use the measure to study four different arrays. The results indicate the suitability of helices for building arrays of high electromagnetic chirality, and the low effectiveness of a substrate for breaking the transverse mirror symmetry.

The International Association of Student Surgical Societies: A brief history from 2014-2017.

The International Association of Student Surgical Societies (IASSS) was founded in 2011 to link up student surgical societies from around the world. These Societies have been formed by students with an aim to promote interest in surgical education and research amongst undergraduate medical students. Their formation has been fostered by the recent realization that adequate surgical care is a neglected component of global public health.1 The insufficient number of trained surgeons is one of the many barriers to meeting global surgical needs, especially in middle- and low-income countries. This barrier is one the IASSS aims to address.2,3 Since its inauguration, the IASSS has been active in creating opportunities for undergraduate medical students across the world to explore the full spectrum of surgery.

Laboratory realization of relativistic pair-plasma beams.

Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black-hole and neutron-star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with electron-positron pairs. Their role in the dynamics of such environments is in many cases believed to be fundamental, but their behavior differs significantly from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components. So far, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies, which are rather limited. We present the first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN's Super Proton Synchrotron (SPS) accelerator. Monte Carlo simulations agree well with the experimental data and show that the characteristic scales necessary for collective plasma behavior, such as the Debye length and the collisionless skin depth, are exceeded by the measured size of the produced pair beams. Our work opens up the possibility of directly probing the microphysics of pair plasmas beyond quasi-linear evolution into regimes that are challenging to simulate or measure via astronomical observations.

Q-switched laser depigmentation in vitiligo, most effective in active disease.

BACKGROUND: In widespread vitiligo, when repigmentation therapies are no longer feasible, Q-switched lasers can be used to remove the remaining disfiguring pigmentation. However, little literature is available on the long-term effects of Q-switched laser treatment in patients with vitiligo, and the variables influencing the effect of treatment are unknown. OBJECTIVE: To evaluate retrospectively the effectiveness, safety and patient satisfaction of Q-switched ruby (QSR) laser-induced depigmentation in widespread vitiligo. METHODS: We performed a retrospective study on well-documented patients with vitiligo with widespread lesions who received depigmentation therapy with the QSR laser between 2000 and 2012 in our institute. Eligible patients were asked to visit our institute for assessment of depigmentation and to fill in a questionnaire on patient satisfaction and disease variables. RESULTS: After a mean follow-up of 13 months, 48% of the 27 included patients showed > 75% depigmentation. Patients with active disease at the time of treatment had significantly better results than patients with stable disease (P < 0·05). Twenty-three (85%) patients were satisfied after treatment. Eighteen patients (67%) reported temporary side-effects after treatment. None of the patients reported adverse effects, such as scars or infections. CONCLUSION: Q-switched ruby laser therapy is effective in approximately half of patients treated; it is a safe treatment with a high patient satisfaction. Patients with active vitiligo show better results after treatment than patients with stable vitiligo. Therefore, in patients with stable vitiligo resistant to trial treatment, we advise postponing treatment until their vitiligo becomes active.

Biocleaning in operating theatres: validation of cleaning techniques by revealing residual traces of blood.

BACKGROUND: In the operating theatre the biocleaning process is essential after each passage to guarantee the non-transmission of potentially pathogenic microbial agents from patient to patient. AIM: To evaluate the quality of this biocleaning, the Operational Hygiene Team used a very sensitive method to detect residual traces of blood: luminol (3-aminophthalhydrazide) on the basis of methods used by the police. METHODS: Luminol was used after conventional one-step biocleaning with the usual detergent/disinfectant, after bleach disinfection before biocleaning, and after biocleaning with a steam cleaner. FINDINGS: Lunimol revealed extended traces of blood corresponding to the passage of the strip on the floor, in the corners of the room and on certain pieces of furniture which are difficult to clean. However, no luminescence was detected on the surfaces cleaned by a single passage of the steam cleaner. CONCLUSIONS: In all cases, the rooms appeared visually clean and traces of blood only became visible when revealed by luminol. We also showed that usual detergents or disinfectants do not remove blood and instead actually spread it over surfaces that may seem visually clean. These results led us to modify our procedure and also confirmed our wish to generalize the use of the steam cleaning technique for immediate cleaning. Furthermore, our tests show the relevance of luminol as a validation tool for the quality and method of biocleaning.

Motherhood, migration and mortality in Dikgale: modelling life events among women in a rural South African community.

OBJECTIVES: Although particular types of life events in populations are often studied separately, this study investigated the joint effects of three major event types in South African women's lives: motherhood, migration and mortality. STUDY DESIGN: Data were taken from a health and demographic surveillance site (HDSS) over an 11-year period, reflecting the entire population of a defined geographic area as an open cohort, in which individuals participated in regular longitudinal surveillance for health and demographic events. This HDSS is a member of the Indepth Network. METHODS: Multivariate Poisson regression models were built for each of the three life event types, in which individual person-time observed out of the total possible 11-year period was used as a rate multiplier. These models were used to calculate adjusted incidence rate ratios for each factor. RESULTS: In the 21,587 person-years observed for women aged 15-49 years, from 1996 to 2006, adjusted rate ratios for mortality and migration increased substantially over time, while motherhood remained fairly constant. Women who migrated were less likely to bear children; temporary migrants were at greater risk of dying, while permanent in-migrants had higher survival rates. Women who subsequently died were much less likely to bear children or migrate. CONCLUSIONS: The associations between motherhood, migration and mortality among these rural South African women were complex and dynamic. Extremely rapid increases in mortality over the period studied are presumed to reflect the effects of the human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic. Understanding these complex interactions between various life events at population level is crucial for effective public health planning and service delivery.

Far-field polarization signatures of surface optical nonlinearity in noncentrosymmetric semiconductors.

We analyse possibilities to quantitatively evaluate the surface second-order optical nonlinearity in noncentrosymmetric materials based on polarization-resolved analysis of far-field radiation patterns of second-harmonic generation. We analytically demonstrate that for plane-wave illumination the contribution to the second-harmonic signal from the surface of a nonlinear medium exhibits different polarization properties and angular dependencies compared to the contribution from the bulk. In view of this, we optimize the illumination geometry in order to enable the most efficient separation and comparison of both nonlinearities. Furthermore, we consider the illumination of an AlGaAs slab by a tightly-focused linearly-polarized Gaussian beam as an alternative measurement geometry. It is found that the reliable separation of the surface nonlinearity contribution as well as a wide range of detectable values can be achieved with this geometry as well.

Dependencies of micro-pillar cavity quality factors calculated with finite element methods.

We present simulation results for optical modes in micro-pillar cavities that were computed with the finite element method and that show good agreement with experimental data. By means of this viable tool various influences on the quality factor of the fundamental mode were calculated: Firstly, the light confinement depends strongly on the absorption of the semiconductor cavity material. Here we were able to determine absolute maximum quality factors achievable in a GaAs/AlAs Bragg micro-pillar cavity. Furthermore, small pillar diameters as well as the inclination of pillar sidewalls show critical features with respect to light confinement. Additional effects of the top and bottom Bragg stacks in the pillar were calculated as well.

Josephson junction arrays with Bose-Einstein condensates.

We report on the direct observation of an oscillating atomic current in a one-dimensional array of Josephson junctions realized with an atomic Bose-Einstein condensate. The array is created by a laser standing wave, with the condensates trapped in the valleys of the periodic potential and weakly coupled by the interwell barriers. The coherence of multiple tunneling between adjacent wells is continuously probed by atomic interference. The square of the small-amplitude oscillation frequency is proportional to the microscopic tunneling rate of each condensate through the barriers and provides a direct measurement of the Josephson critical current as a function of the intermediate barrier heights. Our superfluid array may allow investigation of phenomena so far inaccessible to superconducting Josephson junctions and lays a bridge between the condensate dynamics and the physics of discrete nonlinear media.

Variability of SCCmec in the Zurich area.

A periodic survey of methicillin-resistant Staphylococcus aureus (MRSA) in Zurich in 2004 and 2006 revealed a consistently low prevalence of MRSA. SCCmec and ccr typing showed fluctuations in the proportions of SCCmec types and in the carriage of mobile virulence determinants. Together with the presence of variant SCCmecs these findings suggest a high clonal diversity and level of SCCmec recombination. The prevalence of a local "drug clone", associated with low-level methicillin resistance and rapid growth, significantly decreased. This clone had spread among intraveneous drug users, steadily increasing from 1994 to 2001 and was dominant in 2001. Apparently, changes in the management of the Zurich drug scene have restricted the spread of this clone.

Cloning and molecular characterization of the orphan carrier protein Slc10a4: expression in cholinergic neurons of the rat central nervous system.

We report on the cloning and molecular characterization of the rat carrier Slc10a4 and its cellular localization in the CNS by immunohistochemistry. Slc10a4 is the rat counterpart of the human orphan carrier SLC10A4, which was recently reported to be highly expressed in brain and placenta. Both carriers belong to the solute carrier family SLC10, formerly named the "sodium/bile acid cotransporter family." So SLC10A4/Slc10a4 has a phylogenetic relationship to the Na+/taurocholate cotransporting polypeptide Ntcp (Slc10a1) and the apical sodium-dependent bile acid transporter Asbt (Slc10a2). The rat Slc10a4 protein consists of 437 amino acids and exhibits a seven transmembrane domain topology with N(exo)/C(cyt)trans-orientation of the N- and C-terminal ends. Expression of the Slc10a4 protein was detected in motor regions of the spinal cord and rhombencephalon, as well as in mesopontine cholinergic neurons, the medial habenula, cholinergic areas of the forebrain, and the gut myenteric plexus. Co-localization studies with the cholinergic marker proteins choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT), and high-affinity choline transporter (CHT1) demonstrated expression of Slc10a4 in cholinergic neurons. Despite its close phylogenetic relationship to Ntcp, Slc10a4 showed no transport activity for the Ntcp substrates taurocholate, estrone-3-sulfate, dehydroepiandrosterone sulfate, and pregnenolone sulfate when expressed in HEK293 cells or Xenopus laevis oocytes. Slc10a4 also did not transport choline, which is a substrate of CHT1. Although the functional properties of Slc10a4 could not be elucidated in this study, Slc10a4 is regarded as a new marker protein for cholinergic neurons in the rat CNS.

Models for guidance in kagome-structured hollow-core photonic crystal fibres.

We demonstrate by numerical simulation that the general features of the loss spectrum of photonic crystal fibres (PCF) with a kagome structure can be explained by simple models consisting of thin concentric hexagons or rings of glass in air. These easily analysed models provide increased understanding of the mechanism of guidance in kagome PCF, and suggest ways in which the high-loss resonances in the loss spectrum may be shifted.

Preliminary crystallographic analysis of salicylate 1,2-dioxygenase from Pseudaminobacter salicylatoxidans.

Salicylate 1,2-dioxygenase, a new ring-fission dioxygenase from the naphthalenesulfonate-degrading strain Pseudaminobacter salicylatoxidans which oxidizes salicylate to 2-oxohepta-3,5-dienedioic acid by a novel ring-fission mechanism, has been crystallized. Diffraction-quality crystals of salicylate 1,2-dioxygenase were obtained using the sitting-drop vapour-diffusion method at 277 K from a solution containing 10%(w/v) ethanol, 6%(w/v) PEG 400, 0.1 M sodium acetate pH 4.6. Crystals belong to the primitive tetragonal space group P4(3)2(1)2 or P4(1)2(1)2, with unit-cell parameters a = 133.3, c = 191.51 A. A complete data set at 100 K extending to a maximum resolution of 2.9 A was collected at a wavelength of 0.8423 A. Molecular replacement using the coordinates of known extradiol dioxygenases structures as a model has so far failed to provide a solution for salicylate 1,2-dioxygenase. Attempts are currently being made to solve the structure of the enzyme by MAD experiments using the anomalous signal of the catalytic Fe(II) ions. The salicylate 1,2-dioxygenase structural model will assist in the elucidation of the catalytic mechanism of this ring-fission dioxygenase from P. salicylatoxidans, which differs markedly from the known gentisate 1,2-dioxygenases or 1-hydroxy-2-naphthoate dioxygenases because of its unique ability to oxidatively cleave salicylate, gentisate and 1-hydroxy-2-naphthoate with high catalytic efficiency.