997 resultados para Polarized laser pulses


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Time-resolved imaging is carried out to study the dynamics of the laser-induced forward transfer of an aqueous solution at different laser fluences. The transfer mechanisms are elucidated, and directly correlated with the material deposited at the analyzed irradiation conditions. It is found that there exists a fluence range in which regular and well-defined droplets are deposited. In this case, laser pulse energy absorption results in the formation of a plasma, which expansion originates a cavitation bubble in the liquid. After the further expansion and collapse of the bubble, a long and uniform jet is developed, which advances at a constant velocity until it reaches the receptor substrate. On the other hand, for lower fluences no material is deposited. In this case, although a jet can be also generated, it recoils before reaching the substrate. For higher fluences, splashing is observed on the receptor substrate due to the bursting of the cavitation bubble. Finally, a discussion of the possible mechanisms which lead to such singular dynamics is also provided.

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Coalescing compact binary systems are important sources of gravitational waves. Here we investigate the detectability of this gravitational radiation by the recently proposed laser interferometers. The spectral density of noise for various practicable configurations of the detector is also reviewed. This includes laser interferometers with delay lines and Fabry-Prot cavities in the arms, both in standard and dual recycling arrangements. The sensitivity of the detector in all those configurations is presented graphically and the signal-to-noise ratio is calculated numerically. For all configurations we find values of the detector's parameters which maximize the detectability of coalescing binaries, the discussion comprising Newtonian- as well as post-Newtonian-order effects. Contour plots of the signal-to-noise ratio are also presented in certain parameter domains which illustrate the interferometer's response to coalescing binary signals.

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Using an original investigative protocol and a data base of 4,127 national delegates from ten Moroccan political organizations, surveyed between 2008 and 2012, this article examines the characteristics of party members in Morocco. Initial results indicate that the field of Moroccan political parties is a small world dominated by city dwellers, mature men, and the most highly educated, wealthiest individuals. However, far from being isolated from ordinary citizens, there are social dynamics at work. While it cannot be reduced to a segmented clientele, it is, nonetheless, shaped by an ideal-typical opposition between parties of notables and parties of activists.

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Polycrystalline Ni-Mn-Ga thin films have been deposited by the pulsed laser deposition (PLD) technique, using slices of a Ni-Mn-Ga single crystal as targets and onto Si (100) substrates at temperatures ranging from 673 K up to 973 K. Off-stoichiometry thin films were deposited at a base pressure of 1×10-6-Torr or in a 5 mTorr Ar atmosphere. Samples deposited in vacuum and temperatures above 823 K are magnetic at room temperature and show the austenitic {220} reflection in their x-ray diffraction patterns. The temperature dependences of both electrical resistance and magnetic susceptibility suggest that these samples exhibit a structural martensitic transition at around 260 K. The magnetoresistance ratio at low temperature can be as high as 1.3%, suggesting the existence of a granular structure in the films

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PURPOSE: Nonvisual light-dependent functions in humans are conveyed mainly by intrinsically photosensitive retinal ganglion cells, which express melanopsin as photopigment. We aimed to identify the effects of circadian phase and sleepiness across 24 hours on various aspects of the pupil response to light stimulation. METHODS: We tested 10 healthy adults hourly in two 12-hour sessions covering a 24-hour period. Pupil responses to narrow bandwidth red (635 ± 18 nm) and blue (463 ± 24 nm) light (duration of 1 and 30 seconds) at equal photon fluxes were recorded, and correlated with salivary melatonin concentrations at the same circadian phases and to subjective sleepiness ratings. The magnitude of pupil constriction was determined from minimal pupil size. The post-stimulus pupil response was assessed from the pupil size at 6 seconds following light offset, the area within the redilation curve, and the exponential rate of redilation. RESULTS: Among the measured parameters, the pupil size 6 seconds after light offset correlated with melatonin concentrations (P < 0.05) and showed a significant modulation over 24 hours with maximal values after the nocturnal peak of melatonin secretion. In contrast, the post-stimulus pupil response following red light stimulation correlated with subjective sleepiness (P < 0.05) without significant changes over 24 hours. CONCLUSIONS: The post-stimulus pupil response to blue light as a marker of intrinsic melanopsin activity demonstrated a circadian modulation. In contrast, the effect of sleepiness was more apparent in the cone contribution to the pupil response. Thus, pupillary responsiveness to light is under influence of the endogenous circadian clock and subjective sleepiness.

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Background: To evaluate outcomes after optimized laser in situ keratomileusis (LASIK) for astigmatism correction with flap created by a mechanical microkeratome or a femtosecond laser. Patients and Methods: In this retrospective study, a total of 102 eyes of 71 consecutive patients were enrolled undergoing optimized LASIK treatments using the Allegretto laser system (WaveLight Laser Technologie AG, Erlangen, Germany). A mechanical microkeratome for flap creation was used (One Use, Moria®) in 46 eyes (31 patients, spherical equivalent [SE] -4.44 D ± 2.4) and a femtosecond laser was used (LDV, Ziemer®) in 56 eyes (40 patients, spherical equivalent [SE] -3.07 D ± 3.3). The two groups were matched for inclusion criteria and were operated under similar conditions by the same surgeon. Results: Overall, the preoperative spherical equivalent was -9.5 diopters (D) to +3.37 D; the preoperative manifest astigmatism was between -1.5 D and -3.5 D. At 6 months postoperatively, the mean postoperative uncorrected distance visual acuity (UDVA) was 0.93 ± 0.17 (range 0.4 to 1.2) in the Moria group and 1.0 ± 0.21 (range 0.6 to 1.6) in the Femto group, which was statistically significant (p = 0.003). Comparing the cylinder power there was a statistical difference between the two groups (p = 0.0015). Conclusions: This study shows that the method of flap creation has a significant impact on postoperative astigmatism with a significantly better postoperative UDVA in the Femto group. These findings suggest that the femtosecond laser provides a better platform for LASIK treatment of astigmatism than the commonly used microkeratome.

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PURPOSE: At 7 Tesla (T), conventional static field (B0 ) projection mapping techniques, e.g., FASTMAP, FASTESTMAP, lead to elevated specific absorption rates (SAR), requiring longer total acquisition times (TA). In this work, the series of adiabatic pulses needed for slab selection in FASTMAP is replaced by a single two-dimensional radiofrequency (2D-RF) pulse to minimize TA while ensuring equal shimming performance. METHODS: Spiral gradients and 2D-RF pulses were designed to excite thin slabs in the small tip angle regime. The corresponding selection profile was characterized in phantoms and in vivo. After optimization of the shimming protocol, the spectral linewidths obtained after 2D localized shimming were compared with conventional techniques and published values from (Emir et al NMR Biomed 2012;25:152-160) in six different brain regions. RESULTS: Results on healthy volunteers show no significant difference (P > 0.5) between the spectroscopic linewidths obtained with the adiabatic (TA = 4 min) and the new low-SAR and time-efficient FASTMAP sequence (TA = 42 s). The SAR can be reduced by three orders of magnitude and TA accelerated six times without impact on the shimming performances or quality of the resulting spectra. CONCLUSION: Multidimensional pulses can be used to minimize the RF energy and time spent for automated shimming using projection mapping at high field. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.

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Terrestrial laser scanning (TLS) is one of the most promising surveying techniques for rockslope characterization and monitoring. Landslide and rockfall movements can be detected by means of comparison of sequential scans. One of the most pressing challenges of natural hazards is combined temporal and spatial prediction of rockfall. An outdoor experiment was performed to ascertain whether the TLS instrumental error is small enough to enable detection of precursory displacements of millimetric magnitude. This consists of a known displacement of three objects relative to a stable surface. Results show that millimetric changes cannot be detected by the analysis of the unprocessed datasets. Displacement measurement are improved considerably by applying Nearest Neighbour (NN) averaging, which reduces the error (1¿) up to a factor of 6. This technique was applied to displacements prior to the April 2007 rockfall event at Castellfollit de la Roca, Spain. The maximum precursory displacement measured was 45 mm, approximately 2.5 times the standard deviation of the model comparison, hampering the distinction between actual displacement and instrumental error using conventional methodologies. Encouragingly, the precursory displacement was clearly detected by applying the NN averaging method. These results show that millimetric displacements prior to failure can be detected using TLS.

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This case study deals with a rock face monitoring in urban areas using a Terrestrial Laser Scanner. The pilot study area is an almost vertical, fifty meter high cliff, on top of which the village of Castellfollit de la Roca is located. Rockfall activity is currently causing a retreat of the rock face, which may endanger the houses located at its edge. TLS datasets consist of high density 3-D point clouds acquired from five stations, nine times in a time span of 22 months (from March 2006 to January 2008). The change detection, i.e. rockfalls, was performed through a sequential comparison of datasets. Two types of mass movement were detected in the monitoring period: (a) detachment of single basaltic columns, with magnitudes below 1.5 m3 and (b) detachment of groups of columns, with magnitudes of 1.5 to 150 m3. Furthermore, the historical record revealed (c) the occurrence of slab failures with magnitudes higher than 150 m3. Displacements of a likely slab failure were measured, suggesting an apparent stationary stage. Even failures are clearly episodic, our results, together with the study of the historical record, enabled us to estimate a mean detachment of material from 46 to 91.5 m3 year¿1. The application of TLS considerably improved our understanding of rockfall phenomena in the study area.

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The determination of line crossing sequences between rollerball pens and laser printers presents difficulties that may not be overcome using traditional techniques. This research aimed to study the potential of digital microscopy and 3-D laser profilometry to determine line crossing sequences between a toner and an aqueous ink line. Different paper types, rollerball pens, and writing pressure were tested. Correct opinions of the sequence were given for all case scenarios, using both techniques. When the toner was printed before the ink, a light reflection was observed in all crossing specimens, while this was never observed in the other sequence types. The 3-D laser profilometry, more time-consuming, presented the main advantage of providing quantitative results. The findings confirm the potential of the 3-D laser profilometry and demonstrate the efficiency of digital microscopy as a new technique for determining the sequence of line crossings involving rollerball pen ink and toner. With the mass marketing of laser printers and the popularity of rollerball pens, the determination of line crossing sequences between such instruments is encountered by forensic document examiners. This type of crossing presents difficulties with optical microscopic line crossing techniques involving ballpoint pens or gel pens and toner (1-4). Indeed, the rollerball's aqueous ink penetrates through the toner and is absorbed by the fibers of the paper, leaving the examiner with the impression that the toner is above the ink even when it is not (5). Novotny and Westwood (3) investigated the possibility of determining aqueous ink and toner crossing sequences by microscopic observation of the intersection before and after toner removal. A major disadvantage of their study resides in destruction of the sample by scraping off the toner line to see what was underneath. The aim of this research was to investigate the ways to overcome these difficulties through digital microscopy and three-dimensional (3-D) laser profilometry. The former was used as a technique for the determination of sequences between gel pen and toner printing strokes, but provided less conclusive results than that of an optical stereomicroscope (4). 3-D laser profilometry, which allows one to observe and measure the topography of a surface, has been the subject of a number of recent studies in this area. Berx and De Kinder (6) and Schirripa Spagnolo (7,8) have tested the application of laser profilometry to determine the sequence of intersections of several lines. The results obtained in these studies overcome disadvantages of other methods applied in this area, such as scanning electron microscope or the atomic force microscope. The main advantages of 3-D laser profilometry include the ease of implementation of the technique and its nondestructive nature, which does not require sample preparation (8-10). Moreover, the technique is reproducible and presents a high degree of freedom in the vertical axes (up to 1000 μm). However, when the paper surface presents a given roughness, if the pen impressions alter the paper with a depth similar to the roughness of medium, the results are not always conclusive (8). It becomes difficult in this case to distinguish which characteristics can be imputed to the pen impressions or the quality of the paper surface. This important limitation is assessed by testing different types of paper of variable quality (of different grammage and finishing) and the writing pressure. The authors will therefore assess the limits of 3-D laser profilometry technique and determine whether the method can overcome such constraints. Second, the authors will investigate the use of digital microscopy because it presents a number of advantages: it is efficient, user-friendly, and provides an objective evaluation and interpretation.

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BACKGROUND and OBJECTIVE: A non-touch laser-induced microdrilling procedure is studied on mouse zona pellucida (ZP). STUDY DESIGN/MATERIALS and METHODS: A 1.48-microns diode laser beam is focused in a 8-microns spot through a 45x objective of an inverted microscope. Mouse zygotes, suspended in a culture medium, are microdrilled by exposing their ZP to a short laser irradiation and allowed to develop in vitro. RESULTS: Various sharp-edged holes can be generated in the ZP with a single laser irradiation. Sizes can be varied by changing irradiation time (3-100 ms) or laser power (22-55 mW). Drilled zygotes present no signs of thermal damage under light and scanning electron microscopy and develop as expected in vitro, except for a distinct eight-shaped hatching behavior. CONCLUSION: The microdrilling procedure can generate standardized holes in mouse ZP, without any visible side effects. The hole formation can be explained by a local photothermolysis of the protein matrix.

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OBJECTIVE: To study a new technic of laser treatment of macular holes. METHODS: 21 eyes with stage II-IV macular hole were treated with Argon-green laser. Pigment epithelium in the area of the hole was whitened with spots of 100-200 microns, 100-300 mW. We expected this treatment to create a cellular proliferation that could close and contract the hole. Follow-up after treatment ranged from 3 to 24 months (mean: 9.3 months). RESULTS: Within one month after treatment, the macular hole was closed in 7 eyes (33%) and partially closed in 5 eyes (24%). The visual acuity increased from 1 to 5 lignes (ETDRS chart) in 9 eyes (43%), it remained the same in 9 eyes (43%) and decreased from 1 to 2 lignes in 3 eyes (14%). CONCLUSION: Laser treatment of macular holes seems to be effective and could be proposed as an alternative to the patients who cannot be operated on by vitrectomy and gas tamponade.

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The Iowa Department of Transportation has been using the Bureau of Public Roads (BPR) Roughometer as part of its detour analysis process for more than 20 years. Advances in technology have made the BPR Roughometer obsolete for ride quality testing. High-speed profilers that can collect the profile of the road at highway speeds are the standard ride instruments for determining ride quality on pavements. The objective of the project was to develop a correlation between the BPR Roughometer and the high-speed laser South Dakota type Profiler (SD Profiler). Nineteen pavement sections were chosen to represent the range of types and conditions for detours. Three computer simulation models were tested on the profiler profiles. The first model is the International Ride Index (IRI) which is considered the standard index for reporting ride quality in the United States. The second model is the Ride Number (RN) developed by the University of Michigan Transportation Research Institute and the third model used is a quarter-car simulation of the BPR Roughometer (ASTM E-1170) which should match the speed and range of roadway features experienced by Iowa's BPR Roughometer Unit. The BPR Roughometer quarter-car model provided the best overall correlation with Iowa's BPR Roughometer.

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La utilización de la tecnología láser en Odontología ha tenido una constante evolución y desarrollo. Con este trabajo se pretende hacer una actualización desde un punto de vista crítico, científico y objetivo de los avances y aplicaciones que se han publicado sobre el láser de baja potencia en el ámbito de cada una de las especialidades odontológicas. Asimismo, se exponen sus características, las normas de seguridad necesarias para su utilización, sus efectos secundarios y sus contraindicaciones.

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El láser de diodo tiene numerosas aplicaciones en la especialidad de Cirugía Bucal siendo utilizado preferentemente para realizar intervenciones quirúrgicas sobre los tejidos blandos siempre que no impliquen un excesivo sangrado. En Endodoncia, Implantología Bucofacial y Periodoncia se emplea por su importante efecto bactericida. También se utiliza en procedimientos de blanqueamiento dentario. Es importante controlar adecuadamente el tiempo de aplicación y la potencia de trabajo para evitar el sobrecalentamiento de los tejidos vecinos, lo que produciría su necrosis. Siempre que se utilice el láser de diodo se debe efectuar la protección ocular recomendada tanto para el profesional, sus ayudantes y personal auxiliar, como para el paciente.