Turbulent flux and meteorological measurements during ARCTEX-2006 campaign

This dataset present result from the DFG- funded Arctic-Turbulence-Experiment (ARCTEX-2006) performed by the University of Bayreuth on the island of Svalbard, Norway, during the winter/spring transition 2006. From May 5 to May 19, 2006 turbulent flux and meteorological measurements were performed on the monitoring field near Ny-Ålesund, at 78°55'24'' N, 11°55'15'' E Kongsfjord, Svalbard (Spitsbergen), Norway. The ARCTEX-2006 campaign site was located about 200 m southeast of the settlement on flat snow covered tundra, 11 m to 14 m above sea level. The permanent sites used for this study consisted of the 10 m meteorological tower of the Alfred Wegener Institute for Polar- and Marine Research (AWI), the international standardized radiation measurement site of the Baseline Surface Radiation Network (BSRN), the radiosonde launch site and the AWI tethered balloon launch sites. The temporary sites - set up by the University of Bayreuth - were a 6 m meteorological gradient tower, an eddy-flux measurement complex (EF), and a laser-scintillometer section (SLS). A quality assessment and data correction was applied to detect and eliminate specific measurement errors common at a high arctic landscape. In addition, the quality checked sensible heat flux measurements are compared with bulk aerodynamic formulas that are widely used in atmosphere-ocean/land-ice models for polar regions as described in Ebert and Curry (1993, doi:10.1029/93JC00656) and Launiainen and Cheng (1995). These parameterization approaches easily allow estimation of the turbulent surface fluxes from routine meteorological measurements. The data show: - the role of the intermittency of the turbulent atmospheric fluctuation of momentum and scalars, - the existence of a disturbed vertical temperature profile (sharp inversion layer) close to the surface, - the relevance of possible free convection events for the snow or ice melt in the Arctic spring at Svalbard, and - the relevance of meso-scale atmospheric circulation pattern and air-mass advection for the near-surface turbulent heat exchange in the Arctic spring at Svalbard. Recommendations and improvements regarding the interpretation of eddy-flux and laser-scintillometer data as well as the arrangement of the instrumentation under polar distinct exchange conditions and (extreme) weather situations could be derived.

A laboratory-scale experiment and a numerical simulation of unusual spiral plumes in a High-Prandtl-number fluid, links supplementary material

We experimentally and numerically investigated the generation of plumes from a local heat source (LHS) and studied the interaction of these plumes with cellular convective motion (CCM) in a rectangular cavity filled with silicon oil at a Prandtl number (Pr) of approximately two thousand. The LHS is generated using a 0.2-W green laser beam. A roll-type CCM is generated by vertically heating one side of the cavity. The CCM may lead to the formation of an unusual spiral convective plume that resembles a vertical Archimedes spiral. A similar plume is obtained in a direct numerical simulation. We discuss the physical mechanism for the formation of a spiral plume and the application of the results to mantle convection problems. We also estimate the Reynolds (Re) and Rayleigh (Ra) numbers and apply self-similarity theory to convection in the Earth's mantle. Spiral plumes can be used to interpret mantle tomography results over the last decade.

High resolved snow height measurements at Neumayer Station, Antarctica, 2013

Antarctica is a continent with a strong character. High wind speeds, very low temperatures and heavy snow storms. All these parameters are well known due to observations and measurements, but precipitation measurements are still rare because the number of manned stations is very limited in Antarctica. In such a polar snow region many wind driven phenomena associated with snow fall exist like snow drift, blowing snow or sastrugi. Snow drift is defined as a layer of snow formed by the wind during a snowstorm. The horizontal visibility is below eye level. Blowing snow is specified as an ensemble of snow particles raised by the wind to moderate or great heights above the ground; the horizontal visibility at eye level is generally very poor (National Snow And Ice Data Center (NSIDC), 2013). Sastrugi are complex, fragile and sharp ridges or grooves formed on land or over sea ice. They arise from wind erosion, saltation of snow particles and deposition. To get more details about these procedures better instruments than the conventional stake array are required. This small report introduces a new measuring technique and therefore offers a never used dataset of snow heights. It is very common to measure the snow height with a stake array in Antarctica (f.e. Neumayer Station, Kohnen Station) but not with a laser beam. Thus the idea was born to install a new instrument in December 2012 at Neumayer Station.

Symmetry Issues in Directly Irradiated Targets

In direct drive Inertial Confinement Fusion (ICF), the typical laser beam to laser beam angle is around 30o. This fact makes the study of the irradiation symmetry agenuine 3D problem. In this paper we use the three dimensional version of the MULTI hydrocode to assess the symmetry of such ICF implosions. More specifically, we study a shock-ignition proposal for the Laser-M´egajoule facility (LMJ) in which two of the equatorial beam cones are used to implode and pre compress a spherical capsule (the “reference” capsule of HiPER project) made of 0.59 mg of pure Deuterium-Tritium mixture. The symmetry of this scheme is analysed and optimized to get a design inside the operating limits of LMJ. The studied configuration has been found essentially axial-symmetric, so that the use of 2D hydrocodes would be appropriate for this specific situation.

Raman spectrum of group IV nanowires: influence of temperature

Group IV semiconductor nanowires are characterized by Raman spectroscopy. The results are analyzed in terms of the heating induced by the laser beam on the nanowires. By solving the heat transport equation one can simulate the temperature reached by the NWs under the exposure to a laser beam. The results are illustrated with Si and Si1-xGex nanowires. Both bundles of nanowires and individual nanowires are studied. The main experimental conditions contributing to the nanowire heating are discussed

MicroRaman Spectroscopy of Si Nanowires: Influence of Size

Si Nanowires (NWs) were studied by Raman microspectroscopy. The Raman spectrum of the NWs reveals important thermal effects, which broaden and shift the one phonon Raman bands. The low thermal conductivity of the NWs and the low thermal dissipation are responsible for the temperature enhancement in the NW under the excitation with the laser beam. We have modeled, using finite element methods, the interaction between the laser beam and the NWs. The Raman spectrum of Si NWs is interpreted in terms of the temperature induced by the laser beam excitation, in correlation with finite element methods (fem) for studying the interaction between the laser beam and the NWs.

SIMLIDAR Simulation of LiDAR performance in artificially simulate orchards

SIMLIDAR is an application developed in Cþþ that generates an artificial orchard using a Lindenmayer system. The application simulates the lateral interaction between the artificial orchard and a laser scanner or LIDAR (Light Detection and Ranging). To best highlight the unique qualities of the LIDAR simulation, this work focuses on apple trees without leaves, i.e. the woody structure. The objective is to simulate a terrestrial laser sensor (LIDAR) when applied to different artificially created orchards and compare the simulated characteristics of trees with the parameters obtained with the LIDAR. The scanner is mounted on a virtual tractor and measures the distance between the origin of the laser beam and the nearby plant object. This measurement is taken with an angular scan in a plane which is perpendicular to the route of the virtual tractor. SIMLIDAR determines the distance measured in a bi-dimensional matrix N M, where N is the number of angular scans and M is the number of steps in the tractor route. In order to test the data and performance of SIMLIDAR, the simulation has been applied to 42 different artificial orchards. After previously defining and calculating two vegetative parameters (wood area and wood projected area) of the simulated trees, a good correlation (R2 ¼ 0.70e0.80) was found between these characteristics and the wood area detected (impacted) by the laser beam. The designed software can be valuable in horticulture for estimating biomass and optimising the pesticide treatments that are performed in winter.

Terapia por láser de baja potencia: consideraciones óptico-físicas y biológicas determinantes en su aplicación clínica.

Objetivos : Analizar la distribución de energía en un tejido cuando se emplea terapia por láser de baja potencia y estudiar las especificaciones mínimas de equipos de terapia láser para estimar la dosis. Material y métodos: Se ha empleado el método de Monte Carlo para obtener la distribución de energía absorbida por la piel para dos tipos de láser y la teoría de la difusión para estimar la longitud de penetración y el recorrido libre medio. Se ha estudiado la variación de esa distribución en función de la raza (caucásico, asiático, afroamericano) y para dos localizaciones anatómicas distintas. Se ha analizado la información facilitada por diversos fabricantes de equipos comerciales para determinar si es necesario adaptar la dosimetría recomendada. Resultados: La radiación láser infrarroja (810nm) se absorbe mayoritariamente en un espesor de piel de 1,9±0,2mm para caucásicos, entre 1,73±0,08mm (volar del antebrazo) y 1,80±0,11mm (palma) para asiáticos y entre 1,25±0,09mm (volar del antebrazo) y 1,65±0,2mm (palma) para afroamericanos. El recorrido libre medio de la luz siempre es menor que 0,69±0,09mm. Para los equipos comerciales analizados la única característica geométrica del haz láser que se menciona es la superficie que oscila entre 0,08 y 1cm2, pero no se especifica cómo es la distribución de energía, la divergencia del haz, forma de la sección transversal, etc. Conclusiones:Dependiendo del equipo de terapia por láser de baja potencia utilizado, el tipo de paciente y la zona a tratar, el clínico debe adaptar las dosis recomendadas. Abstract: Objectives: To analyze the distribution of energy deposited in a tissue when this is irradiated with a low power laser and to study the minimum characteristics that manufacturers of low power laser therapy equipments should include to estimate the dosage. Material and methods: Monte Carlo simulation was performed to determine the absorption location of the laser energy. The diffusion theory was used to estimate penetration depth and mean free path. Variation of this distribution was studied based on three different skin types (Caucasians, Asians and Afroamericans) and for two different anatomic locations: palm and volar forearm. Information given by several manufactures of low power laser therapy equipments has been analyzed. Results: Infrared (810 nm) laser radiation is mainly absorbed in a skin layer of thickness 1.9±0.2mm for Caucasians, from 1.73±0.08mm (volar forearm) to 1.80±0.11mm (palm) for Asians, and from 1.25±0.09mm (volar forearm) to 1.65±0.2mm (palm) for Afroamericans. The light mean free path is lower than 0.69±0.09mm for all cases. The laser beam characteristics (beam shape, energy distribution on a transversal section, divergence, incidence angle,etc.) are not usually specified by the manufacturers. Only beam size (ranging from 0.08 to 1cm2) is given in some cases. Discussion and conclusions: Depending on the low power laser therapy equipment, on the patient and on the anatomic area to be treated, the staff should adapt the recommended dosage for each individual case.

Effect of substrate-target distance and sputtering pressure in the synthesis of AlN thin films

In this work, we analyze the influence of the processing pressure and the substrate–target distance on the synthesis by reactive sputtering of c-axis oriented polycrystalline aluminum nitride thin films deposited on Si(100) wafers. The crystalline quality of AlN has been characterized by high-resolution X-ray diffraction (HR-XRD). The films exhibited a very high degree of c-axis orientation especially when a low process pressure was used. After growth, residual stress measurements obtained indirectly from radius of curvature measurements of the wafer prior and after deposition are also provided. Two different techniques are used to determine the curvature—an optically levered laser beam and a method based on X-ray diffraction. There is a transition from compressive to tensile stress at a processing pressure around 2 mTorr. The transition occurs at different pressures for thin films of different thickness. The degree of c-axis orientation was not affected by the target–substrate distance as it was varied in between 30 and 70 mm.

Opto-optical modulation in N-(p-methoxybenzylidene)-p-butylaniline

A method of opto-optical modulation in liquid crystals is reported. An Ar+-laser beam is employed to modulate a second He–Ne laser. The highest frequency achieved was 1.5 × 103 pulses per second with input modulating powers smaller than 10 mW. A homeotropic N-(p-methoxybenzylidene)-p-butylaniline liquid-crystal cell was employed as the nonlinear medium.

Experimental measurements of the scattered-light polarization from different liquid flows

An experimental system designed to measure very low optical powers, of the order of a few picowatts, is presented. Its main aid is to detect the polarisation state of scattered light from a fluid flow, in different angular directions with respect to the longitudinal axis of the flow. A laser beam incident linearly polarized crosses the fluid flow orthogonally. The scattered light is detected by means of a photodetector situated behind a lineal polarizer whose orientation can be rotated. The outgoing electrical signal is amplified by means of a Mode-lockin amplifier and is digitally processed.

Symmetry issues in Directly Irradiated Targets

In direct drive Inertial Confinement Fusion (ICF), the typical laser beam to laser beam angle is around 30o. This fact makes the study of the irradiation symmetry agenuine 3D problem. In this paper we use the three dimensional version of the MULTI hydrocode to assess the symmetry of such ICF implosions. More specifically, we study a shock-ignition proposal for the Laser-M´egajoule facility (LMJ) in which two of the equatorial beam cones are used to implode and pre compress a spherical capsule (the “reference” capsule of HiPER project) made of 0.59 mg of pure Deuterium-Tritium mixture. The symmetry of this scheme is analysed and optimized to get a design inside the operating limits of LMJ. The studied configuration has been found essentially axial-symmetric, so that the use of 2D hydrocodes would be appropriate for this specific situation

Raman spectroscopy in Group IV nanowires and nanowire axial heterostructures

The control of the SiGe NW composition is fundamental for the fabrication of high quality heterostructures. Raman spectroscopy has been used to analyse the composition of SiGe alloys. We present a study of the Raman spectrum of SiGe nanowires and SiGe/Si heterostructures. The inhomogeneity of the Ge composition deduced from the Raman spectrum is explained by the existence of a Ge-rich outer shell and by the interaction of the NW with the electromagnetic field associated with the laser beam.

Propiedades de materiales mediante análisis de radiación aleatoria

Las técnicas de speckle tienen un gran interés científico e ingenieril, ya que son métodos de ejecución rápida y no destructiva, con base en el análisis de las fluctuaciones de intensidad de la radiación producida cuando la luz coherente de un haz láser es esparcida por un material dado. En este caso se produce un patrón aleatorio de interferencia y difracción donde la suma de las componentes desfasadas dará lugar a máximos y mínimos de intensidad en distintos puntos del espacio. Éste, pese a tratarse de un ruido nocivo en multitud de áreas tales como la transmisión de señales o la holografía, tiene importantes propiedades físicas que lo caracterizan y lo hacen útil como medio para analizar sistemas reales de muy diversa índole. En el presente estudio, se ha llevado a cabo un análisis polarimétrico de la radiación aleatoria esparcida por una serie de muestras metálicas y dieléctricas con el objetivo de establecer una base comparativa que nos permita poder distinguir unas de otras. Para este fin se han comparado los parámetros de polarización de Stokes, el grado de polarización de la luz, las distribuciones de intensidad y el tamaño medio del speckle registrado en los distintos patrones de intensidad. Además, se analizará la dependencia de la rugosidad en el grado de polarización de la luz para los distintos medios sometidos a estudio. Abstract Speckle techniques have a great scientific and engineering interest as they are methods of rapid and non-destructive execution, based on the analysis of the fluctuations of intensity of the radiation produced when coherent light of a laser beam is scattered by a material given. In this case, a random pattern of interference and diffraction occurs where the sum of phase shifted components will result in maximum or minimum of intensity at different points in space. This, despite being a harmful noise in many areas such as signal transmission or holography, has important physical properties that characterize it and make it useful as a means to analyze real systems of various kinds. In the present study, we have conducted a polarimetric analysis of the random radiation scattered by a series of metal and dielectric samples in order to establish a comparative basis to allow us to distinguish one from another. To this end we have compared, the stokes polarization parameters, the degree of polarization (DOP), the intensity distributions and the average size of the speckle registered in the different intensity patterns. Furthermore, dependence of roughness in the DOP of light for the different means under study will be analyzed.