107 research outputs found
Optical and evaporative cooling of cesium atoms in the gravito-optical surface trap
We report on cooling of an atomic cesium gas closely above an evanescent-wave
atom mirror. At high densitities, optical cooling based on inelastic
reflections is found to be limited by a density-dependent excess temperature
and trap loss due to ultracold collisions involving repulsive molecular states.
Nevertheless, very good starting conditions for subsequent evaporative cooling
are obtained. Our first evaporation experiments show a temperature reduction
from 10muK down to 300nK along with a gain in phase-space density of almost two
orders of magnitude.Comment: 8 pages, 6 figures, submitted to Journal of Modern Optics, special
issue "Fundamentals of Quantum Optics V", edited by F. Ehlotzk
Double- and multi-femtosecond pulses produced by birefringent crystals for the generation of 2D laser-induced structures on a stainless steel surface
Laser-induced textures have been proven to be excellent solutions for modifying wetting, friction, biocompatibility, and optical properties of solids. The possibility to generate 2D-submicron morphologies by laser processing has been demonstrated recently. Employing double-pulse irradiation, it is possible to control the induced structures and to fabricate novel and more complex 2D-textures. Nevertheless, double-pulse irradiation often implies the use of sophisticated setups for modifying the pulse polarization and temporal profile. Here, we show the generation of homogeneous 2D-LIPSS (laser-induced periodic surface structures) over large areas utilizing a simple array of birefringent crystals. Linearly and circularly polarized pulses were applied, and the optimum process window was defined for both. The results are compared to previous studies, which include a delay line, and the reproducibility between the two techniques is validated. As a result of a systematic study of the process parameters, the obtained morphology was found to depend both on the interplay between fluence and inter-pulse delay, as well as on the number of incident pulses. The obtained structures were characterized via SEM (scanning electron microscopy) and atomic force microscopy. We believe that our results represent a novel approach to surface structuring, primed for introduction in an industrial environment
Perancangan Concert Hall di Kota Atambua dengan Pendekatan Mekanisme Akustik
Atambua is the capital of Belu Regency which is located directly adjacent to the State of Timor Leste. In the last two years, Atambua has presented various types of musical activities, especially musical performances, both traditional and modern. The music performance always got enthusiasm from the local community, outside the region and even outside the State of Timor Leste. However, there is still no have a place to accommodate all activities related to organizing technically feasible musical performances, the functions, acoustics and facilities. Concert halls are the best for accommodating all activities related to musical performances. The designing of a concert hall is to purpose design a concert hall for the city of Atambua by paying attention to proper acoustics and comfort for all building users. The application of the analogy architecture of acoustic mechanisms in concert hall design is expected to provide comfortable acoustics, technically feasible, functional, and to present a visually attractive building.Atambua merupakan ibukota Kabupaten Belu yang letaknya berbatasan langsung dengan Negara Timor Leste. Dalam dua tahun terakhir Atambua menghadirkan berbagai jenis kegiatan seni musik khususnya pertunjukan musik baik tradisional maupun modern. Pertunjukan musik yang diadakan mendapat antusias dari masyarakat baik daerah maupun luar daerah bahkan luar Negara (Timor Leste). Meskipun demikian, belum tersedia wadah khusus untuk mewadahi semua kegiatan yang berkaitan dengan penyelenggaraan pertunjukan musik yang layak secara teknis, fungsi, akustika maupun fasilitas. Concert hall merupakan sarana terbaik untuk mewadahi semua kegiatan yang berkaitan dengan pertunjukan musik. Tujuan dari perancangan concert hall di Kota Atambua adalah merancang sebuah concert hall untuk Kota Atambua dengan memperhatikan akustik yang layak dan kenyamanan bagi semua pengguna bangunan. Penerapan tema analogi mekanisme akustik pada perancangan concert hall diharapkan dapat memberikan akustik yang nyaman, layak secara teknis, fungsi, serta mampu menyajikan bangunan yang menarik dari segi visual
Data on 824 fireballs observed by the digital cameras of the European Fireball Network in 2017-2018. I. Description of the network, data reduction procedures, and the catalog
A catalog of 824 fireballs (bright meteors), observed by a dedicated network
of all-sky digital photographic cameras in central Europe in the years
2017-2018 is presented. The status of the European Fireball Network,
established in 1963, is described. The cameras collect digital images of
meteors brighter than an absolute magnitude of about -2 and radiometric light
curves with a high temporal resolution of those brighter than a magnitude ~ -4.
All meteoroids larger than 5 grams, corresponding to sizes of about 2 cm, are
detected regardless of their entry velocity. High-velocity meteoroids are
detected down to masses of about 0.1 gram. The largest observed meteoroid in
the reported period 2017-2018 had a mass of about 100 kg and a size of about 40
cm. The methods of data analysis are explained and all catalog entries are
described in detail. The provided data include the fireball date and time,
atmospheric trajectory and velocity, the radiant in various coordinate systems,
heliocentric orbital elements, maximum brightness, radiated energy, initial and
terminal masses, maximum encountered dynamic pressure, physical classification,
and possible shower membership. Basic information on the fireball spectrum is
available for some bright fireballs (apparent magnitude < -7). A simple
statistical evaluation of the whole sample is provided. The scientific analysis
is presented in an accompanying paper.Comment: accepted in Astronomy and Astrophysic
Cold atom gas at very high densities in an optical surface microtrap
An optical microtrap is realized on a dielectric surface by crossing a
tightly focused laser beam with an horizontal evanescent-wave atom mirror. The
nondissipative trap is loaded with cesium atoms through elastic
collisions from a cold reservoir provided by a large-volume optical surface
trap. With an observed 300-fold local increase of the atomic number density
approaching , unprecedented conditions of cold atoms
close to a surface are realized
Toroidal optical dipole traps for atomic Bose-Einstein condensates using Laguerre-Gaussian beams
We theoretically investigate the use of red-detuned Laguerre-Gaussian (LG)
laser beams of varying azimuthal mode index for producing toroidal optical
dipole traps in two-dimensional atomic Bose-Einstein condensates. Higher-order
LG beams provide deeper potential wells and tighter confinement for a fixed
toroid radius and laser power. Numerical simulations of the loading of the
toroidal trap from a variety of initial conditions is also given.Comment: 12 pages, 5 figures, submitted to Phys. Rev.
Aberration-free ultra-thin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces
The concept of optical phase discontinuities is applied to the design and
demonstration of aberration-free planar lenses and axicons, comprising a phased
array of ultrathin subwavelength spaced optical antennas. The lenses and
axicons consist of radial distributions of V-shaped nanoantennas that generate
respectively spherical wavefronts and non-diffracting Bessel beams at telecom
wavelengths. Simulations are also presented to show that our aberration-free
designs are applicable to high numerical aperture lenses such as flat
microscope objectives
Intensive group training protocol versus guideline physiotherapy for patients with chronic low back pain: a randomised controlled trial
Intensive group training using principles of graded activity has been proven to be effective in occupational care for workers with chronic low back pain. Objective of the study was to compare the effects of an intensive group training protocol aimed at returning to normal daily activities and guideline physiotherapy for primary care patients with non-specific chronic low back pain. The study was designed as pragmatic randomised controlled trial with a setup of 105 primary care physiotherapists in 49 practices and 114 patients with non-specific low back pain of more than 12Â weeks duration participated in the study. In the intensive group training protocol exercise therapy, back school and operant-conditioning behavioural principles are combined. Patients were treated during 10 individual sessions along 20 group sessions. Usual care consisted of physiotherapy according to the Dutch guidelines for Low Back Pain. Main outcome measures were functional disability (Roland Morris disability questionnaire), pain intensity, perceived recovery and sick leave because of low back pain assessed at baseline and after 6, 13, 26 and 52Â weeks. Both an intention-to-treat analysis and a per-protocol analysis were performed. Multilevel analysis did not show significant differences between both treatment groups on any outcome measures during the complete follow-up period, with one exception. After 26Â weeks the protocol group showed more reduction in pain intensity than the guideline group, but this difference was absent after 52Â weeks. We finally conclude that an intensive group training protocol was not more effective than usual physiotherapy for chronic low back pain
Cumulative Low Back Load at Work as a Risk Factor of Low Back Pain: A Prospective Cohort Study
Purpose Much research has been performed on physical exposures during work (e.g. lifting, trunk flexion or body vibrations) as risk factors for low back pain (LBP), however results are inconsistent. Information on the effect of doses (e.g. spinal force or low back moments) on LBP may be more reliable but is lacking yet. The aim of the present study was to investigate the prospective relationship of cumulative low back loads (CLBL) with LBP and to compare the association of this mechanical load measure to exposure measures used previously. Methods The current study was part of the Study on Musculoskeletal disorders, Absenteeism and Health (SMASH) study in which 1,745 workers completed questionnaires. Physical load at the workplace was assessed by video-observations and force measurements. These measures were used to calculate CLBL. Furthermore, a 3-year follow-up was conducted to assess the occurrence of LBP. Logistic regressions were performed to assess associations of CLBL and physical risk factors established earlier (i.e. lifting and working in a flexed posture) with LBP. Furthermore, CLBL and the risk factors combined were assessed as predictors in logistic regression analyses to assess the association with LBP. Results Results showed that CLBL is a significant risk factor for LBP (OR: 2.06 (1.32-3.20)). Furthermore, CLBL had a more consistent association with LBP than two of the three risk factors reported earlier. Conclusions From these results it can be concluded that CLBL is a risk factor for the occurrence of LBP, having a more consistent association with LBP compared to most risk factors reported earlier. © 2012 The Author(s)
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