Elliptical Spot Research Articles

A new cleaner species of Elacatinus (Actinopterygii: Gobiidae) from the Southwestern Atlantic

A new species of cleaner goby, Elacatinus phthirophagus sp. n., is described from Fernando de Noronha Archipelago, off northeastern Brazil. It differs from its congeners of the putative “randalli-evelynae” cleaning clade by the following combination of characters: mouth subterminal, pale (bright yellow in life) elliptical spot on dark snout, width of lateral pale (bright yellow in life) stripe almost equal as eye diameter (slightly narrower in live individuals), light purplish sheen (in life) extending laterally from below eye to tail origin, no blue line (in life) from below eye to end of opercular margin, teeth multiserial on the distal portion of both jaws, males with 3 enlarged and recurved teeth on dentary inner row. The new species was recorded at depths ranging from 3 to 18 m and is ubiquitous in the archipelago islets. It tends cleaning stations on coral heads, sponges, and rocky substrata, with up to 15 individuals present in large stations, particularly those on sponges. Elacatinus phthirophagus sp. n. was recorded to clean about 30 species of fish clients, including large carnivores such as the shark Carcharhinus perezi and smaller carnivores such as the grouper Cephalopholis fulva, besides small clients like the planktivorous damselfish Chromis multilineata and the zoobenthivorous butterflyfish Chaetodon ocellatus. The new species increases to three the number of cleaner gobies recorded for Southwestern Atlantic, one from the coast and two from oceanic islands.

Spring constant modulation in a zone plate tweezer using linear polarization

At large NAs a micro-Fresnel zone plate produces a focal spot that is more elliptical than that produced by an objective lens with the same NA. Using this anisotropy we demonstrate a method for modulating the spring constant of an optical trap by rotating the linear input polarization. The focal spot ellipticity is enhanced by the apodization factor of the zone plate and its extremely high NA. By measuring the positions of trapped particles we obtain two-dimensional histograms of particle position. These indicate that the trap spring constant is 2.75 times larger perpendicular to the incident polarization than along it. The elliptical focal spot distribution can be rotated by rotating the incident polarization, allowing the spring constant along a given direction to be modulated.

High energy density and beam induced stress related issues in solid graphite Super-FRS fast extraction targets

AbstractSurvival of the production target in successive experiments (with a repetition rate of 1 Hz) over an extended period of time is one of the key problems encountered in designing the Super-FRS (Superconducting Fragment Separator) at the future Facility forAntiprotons and Ion Research (FAIR). Because of the difficulties involved in construction of a liquid jet metal target, it is highly desirable to employ a solid production target at the Super-FRS. However, with the high beam intensities that will be available at the FAIR, the production target may be destroyed in a single experiment due to high specific energy deposition by the beam in the target material. The level of specific energy deposition can be reduced to an acceptable value by increasing the beam focal spot area. However, the spot size is limited by requirements of achieving good isotope resolution and sufficient transmission of the secondary beam through the system. The resolving power of the fragment separator is inversely proportional to the X-dimension of the focal spot whereas the transmission depends on Y-dimension only. It has been previously shown [Tahir et al., 2005c] that an elliptic focal spot with appropriate dimensions, will fulfill the above two conditions simultaneously and will also have a large enough area to reduce the specific energy deposition to an acceptable level for certain beam intensities of interest. In this paper we present numerical simulations of thermodynamic and hydrodynamic behavior of a solid graphite target that is irradiated by 1 GeV/u uranium beam in the intensity range of 1010 –1011 ions per bunch with a bunch length = 50 ns. These simulations have been carried out using a three-dimensional computer code, PIC3D, that includes elastic-plastic effects. This theoretical work has shown that up to a beam intensity of 1011 ions/bunch, one can employ a solid target while for higher intensities the target will be destroyed due to thermal stresses induced by the beam. It has also been found that a circular focal spot leads to minimum thermal stresses as it generates minimum pressure gradients compared to an elliptic focal spot, for the same specific energy deposition. Moreover, the stress level increases with an increase in the ellipticity of the focal spot. It is therefore recommended that one should use a circular focal spot for lower intensities provided that the criteria for isotope resolution and transmission are fulfilled.

Rosacea treatment using the new‐generation, high‐energy, 595 nm, long pulse‐duration pulsed‐dye laser

Rosacea results from sun-induced hyper-vascularity of exposed facial skin, often accompanied by acneiform papules and pustules. The pulsed-dye laser has an unparalleled safety record and emits an ideal wavelength for treating the abnormal vessels that occur in rosacea patients. In this study we investigate the ability of the long pulse-duration pulsed-dye laser to improve rosacea. Twenty subjects with rosacea were treated with the high-energy, long pulse-duration pulsed-dye laser. An elliptical spot and long pulse-duration was used to spot-treat linear telangiectasias, while a circular spot and short pulse-duration was used to treat the entire face. Improvement was determined by blinded evaluation of photographs and by the treating physician's subjective evaluation, before and 8 weeks following the final treatment. The average rosacea score as estimated by the treating physician decreased from 2.7+/-1.1 to 1.4+ 0.7 (mean+SD) on a 0-6 scale with 0 representing no rosacea and 6 representing the most severe rosacea (P<0.001 level). The average rosacea score as rated by blinded physician observers scoring digital photos was 2.3+/-1.3 before treatment and 1.4+/-0.9 8 weeks following treatment, using a 0 (mild) to 6 (severe) scale. The high-energy, long pulse-duration pulsed-dye laser improves rosacea with a very favorable safety profile, and less purpura than resulted from earlier generation pulsed-dye lasers.

A study of Ni-based WC composite coatings by laser induction hybrid rapid cladding with elliptical spot

Ni-based WC composite coatings by laser induction hybrid rapid cladding (LIHRC) with elliptical spot were investigated. Results indicate that the efficiency using the elliptical spot of 6 mm × 4 mm (the major and minor axis of laser beam are 6 mm and 4 mm, respectively, the major axis is parallel to the direction of laser scanning) is higher than that using the elliptical spot of 4 mm × 6 mm (the major axis is perpendicular to the direction of laser scanning). The precipitated carbides with the blocky and bar-like shape indicate that WC particles suffer from the heat damage of “the disintegration pattern + the growth pattern”, whichever elliptical spot is used at low laser scanning speed. However, at high laser scanning speed, the blocky carbides are only formed if the elliptical spot of 6 mm × 4 mm is adopted, showing that WC particles present the heat damage of “the disintegration pattern”, whereas the fine carbides are precipitated when the elliptical spot of 4 mm × 6 mm is used, showing that WC particles take on the heat damage of “the radiation pattern”. Especially, the efficiency of LIHRC is increased much four times higher than that of the general laser cladding and crack-free ceramic-metal coatings can be obtained.

Bayesian Image Modeling of cDNA Microarray Spots

This letter explores the potential of Bayesian signal processing for improved modeling of microarray images and enhanced estimation of gene expression ratios. Building upon our earlier work, we describe a novel elliptical spot shape model, with a Bayesian model-fitting method. The analysis of gene replicates at the image-modeling level is also briefly discussed. Prior knowledge from neighboring spots is encompassed in the framework of a Markov random field, potentially enhancing the accuracy and reliability of ratio estimates. The techniques may be particularly beneficial for irregular, overlapping, damaged, saturated, or weakly expressed spots.

Modelling the spot shape influence on high-speed transmission lap welding of thermoplastics films

Modelling high-speed laser lap welding of thermoplastic films has been accomplished and the influence of laser beam spot shape, dimensions, and position relative to sample displacement was analysed. Engineering parameters predicted by the model were applied to lap weld of high- and low-density polyethylene transparent samples with thickness between 10 and 100 μm, and experimentally validated. Experimental set-up allowed reaching welding constant linear velocities up to 10 m/s. Theoretical and experimental data show coincidence. Weld strength increases for larger beam spot diameters, and elliptical beam spots increase weld efficiency, allowing higher processing speeds or decreasing required laser power. An angular deviation of elliptical beam spot with regard to the sample's movement direction causes an increase of weld strength and a decrease of welding speed.

Improving the optical profile of electroabsorption modulator using single-sided large optical cavity structure

An electroabsorption modulator with large optical cavity was designed and fabricated successfully. Both the simulated and experimental results show that, the larger optical cavity structure introduced could obviously improve the optical profile of EA modulator, the traditional elliptical near-field spot becomes more rounded, so it will match better with the optical fiber and is beneficial for raising the coupling efficiency.

An overview of the LIDAR observations of asteroid 25143 Itokawa

We present an overview of the laser altimeter(LIDAR) results for asteroid 25143 Itokawa. The trace of a 7 × 12-m elliptical beam spot made it possible to determine the local surface topography with an accuracy of a few meters in altitude, from a home position roughly 7 km above the surface. Sequential detection of the altitude of the spacecraft during two orbital spans of descent for sampling allowed determination of the asteroid mass as 3.58 × 10 10 kg ± 5% and 3.54 × 10 10 kg ± 6%, which are consistent with the most probable mass estimate of 3.51 × 10 10 kg ± 3% given by Fujiwara et al. [Fujiwara, A., Kawaguchi, J., Yeomans, D.K. et al., 2006. The rubble-pile asteroid Itokawa as observed by Hayabusa. Science 312, 1330–1334]. Together with the total volume of the asteroid deduced from a shape model (i.e., 1.84 × 10 7 m 3 ± 3%), this estimate by LIDAR suggests that asteroid Itokawa has a low density of 1.9 g/cm 3 ± 9% and a high bulk porosity of about 40%.

Polar direct drive – Ignition at 1 MJ

Target designs to achieve direct-drive ignition on the NIF using the x-ray-drive beam configuration are examined. This approach, known as polar direct drive (PDD), achieves the required irradiation uniformity by repointing some of the beams toward the target equator, and by increasing the laser intensity at the equator to compensate for the reduced laser coupling from oblique irradiation. Techniques to increase the equatorial intensity can include using phase plates that produce elliptical spot shapes, increasing the power in beams directed toward the equator, and using a ring offset from the equator to redirect rays toward the target normal. The requirements for beam pointing, power balance, single-beam smoothing, and inner-ice-surface roughness are examined. Designs with an incident laser energy of 1.0 MJ are presented. The simulations use the 2-D hydrocode DRACO with 3-D ray trace to model the laser irradiation and Monte Carlo alpha particle transport to model the thermonuclear burn.

Extracellular Space Diffusion in Central Nervous System: Anisotropic Diffusion Measured by Elliptical Surface Photobleaching

Diffusion in the extracellular space (ECS) is crucial for normal central nervous system physiology. The determinants of ECS diffusion include viscous interactions with extracellular matrix/plasma membranes (“viscosity”) and ECS geometry (“tortuosity”). To resolve viscosity versus tortuosity effects, we measured direction-dependent (anisotropic) diffusion in ECS in mouse spinal cord by photobleaching using an elliptical spot produced by a cylindrical lens in the excitation path. Anisotropic diffusion slowed fluorescence recovery when the long axis of the ellipse was parallel versus perpendicular to the direction of faster diffusion. A mathematical model was constructed to deduce diffusion coefficients (Dx, Dy) from fluorescence recovery measured for parallel and perpendicular orientations of the long axis of the ellipse. Elliptical spot photobleaching was validated by photobleaching aqueous-phase fluorophores on a diffraction grating, where diffusion is one-dimensional. Measurement of the diffusion of 70kDa FITC-dextran in spinal cord in living mice indicated that viscosity slows diffusion by ∼1.8-fold compared with its diffusion in solution. ECS geometry hinders diffusion across (but not along) axonal fibers in spinal cord further by approximately fivefold. In cerebral cortex, however, ∼50% of the hindrance to ECS diffusion comes from viscosity and ∼50% from tortuosity. We suggest that the extracellular matrix might have evolved to facilitate rather than hinder diffusion even for large molecules.

The circular and elliptic white-light dark spatial solitons in a photovoltaic self-defocusing nonlinear medium

We observed circular white-light dark spatial solitons in photovoltaic self-defocusing LiNbO3:Fe crystal using an ordinary incandescent lamp as light source (a line source) with the filament of the bulb parallel to the crystalline c axis. Besides the above condition, the formation of the elliptic soliton needs an additive condition that the crystalline c axis is parallel to the minor axis of dark elliptic spot.

On the welding of different materials by diode laser

In technical literature, there are few papers about the use of diode lasers in material processing and particularly in metal welding. In this paper, different materials, according to specific and particular industrial needs and requests, have been tested with a welding process by a diode laser, emitting a 808 nm laser radiation. Beads on plate have been studied. The goal was to evaluate the maximum weldable thickness and define the best process parameters for each material. The experimental evaluation has been carried out considering the following parameters: power level, welding speed (WS), shielding gas, gas nozzle and orientation of the focused elliptical spot as to the welding direction.

光触針式輪郭測定センサの楕円照射化による異常値補正効果

光触針式輪郭測定センサの楕円照射化による異常値補正効果

On the symmetry of cylindrical implosions driven by a rotating beam of fast ions

Cylindrical implosions driven by intense beams of heavy ions are one of the promising ways to create high energy density states in matter. To ensure the needed azimuthal symmetry of the beam energy deposition, it was proposed [Sharkov et al., Nucl. Instrum. Methods Phys. Res. A 464, 1 (2001)] to rotate the ion beam around the target axis. Combining analytical calculations with two-dimensional hydrodynamic simulations, a lower limit is established on the frequency ν of the beam rotation dictated by the target hydrodynamics. This limit is shown to be directly proportional to the desired radial convergence ratio Cr for stepwise beam power profiles, and to Cr1/2 for smooth pulses. With a smooth pulse, 6–10 beam revolutions per pulse should be sufficient to reach Cr≃30, while a stepwise pulse requires ≃100 revolutions. Also, the upper bound on the asymmetry of the elliptical focal spot of a rotating ion beam is calculated.

Dynamics of the plume produced by nanosecond ultraviolet laser ablation of metals

The dynamics of the ablation plume of a partially ionized plasma produced by a nanosecond UV laser with different irradiation spot geometries has been explored. We have used an ensemble of quartz crystal microbalances to make the first systematic and quantitative study of how the shape of the plume varies as the aspect ratio ( b/a) of the elliptical laser spot is varied by about a factor of ten. The flip-over effect can be described by the adiabatic expansion model of Anisimov et al. using a value of the adiabatic constant of about g 51.4. We have also studied the forward peaking of the ablation plume for a large number of metals at the same laser fluence. Contrary to earlier reports, we find that the more refractory metals have the broader angular distributions.

Influence of the equation of state of matter and ion beam characteristics on target heating and compression

The subject of high-energy density (HED) in matter is of considerable interest to many branches of physics. Intense beams of energetic heavy ions are a promising tool for creating large samples of HED matter which can be used to study the equation-of-state properties of such exotic states of matter experimentally. The Gesellschaft fur Schwerionenforschung (GSI), Darmstadt, is a unique laboratory worldwide which has a heavy ion synchrotron facility, SIS18 (with a magnetic rigidity of 18 Tm), that delivers intense heavy ion beams. Using the beams generated at this present facility, interesting experimental work has been carried out in the field of HED matter (D. H. H. Hoffmann et al., Nucl. Instrum. Methods Phys. Res., Sect. B 161-162, 9 (2000)). The GSI is planning to significantly expand its accelerator capabilities with construction of a new synchrotron ring, SIS100, which will have a magnetic rigidity of 100 Tm. This new facility will deliver a uranium beam which will have orders of magnitude higher intensity than the existing facility and will also have the possibility of multibeam acceleration. This paper presents two-dimensional hydrodynamic simulations of different target geo- metries including solid as well as hollow cylinders that are irradiated with beams having different shapes of the focal spot which will be available at the SIS100 facility. These include a circular focal spot, an annular focal spot, and an elliptic focal spot, respectively. The purpose of this study is to determine the region of the physical parameters including density, temperature, and pressure that can be accessed using the SIS100 beam. This information, we hope, will be useful for designing experiments on the studies of thermophysical properties of matter including the designing of appropriate diagnostic tools.

Circularly and linearly polarized bremsstrahlung produced by polarized electrons

Abstract We present an algorithm that enables one to calculate the degree of both the circular and linear polarization of the bremsstrahlung produced by polarized electrons, taking into account beam divergence, off-axis deviation, and elliptical beam spot shape, as well as finite angular acceptances for photons and post-bremsstrahlung electrons. We present conditions for which the contribution of the linearly polarized component is minimal.

Surface treatment with linearly polarized laser beam at oblique incidence

An effective method for surface heat treatment with 10.6 μm linear polarized laser beam at oblique incidence is reported. A circular focused laser spot on the workpiece surface, simultaneously with 2.2–4 times increasing of the absorption are obtained in the 70–80° range of the incidence angle. The main element of the experimental setup is the astigmatic focusing head which focalize the laser beam into an elliptical spot of ellipticity ε>3 at normal incidence. At a proper incidence angle (obtained by the focusing head tilting) the focused laser spot on the work piece surface gets a circular form and p-state of polarization is achieved. We performed laser heat treatment (transformation hardening, surface remelting) of the uncoated surface, as well as the alloying and cladding processes by powder injection. An enhancement of the processing efficiency was obtained; in this way the investment and operation costs for surface treatment with CO 2 laser can be significantly reduced. Several technical advantages concerning the pollution of the focusing optical components, powder jet flowing and reflected radiation by the work piece surface are obtained.

A cylinder-to-sphere Fourier view factor model for azimuthal asymmetry studies in cylindrical hohlraums

This work addresses the analytical calculation of the irradiation coming from a cylindrical surface to a spherical one. This exact solution of the x-ray transport equation allows one to connect the emitted and the received fluxes, expanded as Fourier modes, by coefficients called Fourier view factors. Such a calculation is well suited to a symmetry study in the Laser Megajoule configuration [P.-A. Holstein, M. André, M. Casanova et al., C. R. Acad. Sci. Paris 1, 693 (2000)] where a cylindrical hohlraum and a spherical capsule are irradiated. Indeed, this 60 quad laser system induces an azimuthal asymmetry of the hohlraum lighting depending on the laser focal spot size. Thus, the Fourier view factors allow one to express the modes of the capsule irradiation as functions of the elliptic spot dimensions.