86,797 research outputs found
Vertical-external-cavity semiconductor lasers
No full textSurface-emitting semiconductor lasers can make use of external cavities and optical pumping techniques to achieve a combination of high continuous-wave output power and near-diffraction-limited beam quality that is not matched by any other type of semiconductor source. The ready access to the laser mode that the external cavity provides has been exploited for applications such as intra-cavity frequency doubling and passive mode-locking. The purpose of this Topical Review is to outline the operating principles of these versatile lasers and summarize the capabilities of devices that have been demonstrated so far. Particular attention is paid to the generation of near-transform-limited sub-picosecond pulses in passively mode-locked surface-emitting lasers, which are potentially of interest as compact sources of ultrashort pulses at high average power that can be operated readily at repetition rates of many gigahertz
NEW ASPECTS OF THE INTRACAVITY LASER ABSORPTION SPECTROSCOPY
No full textAuthor Institution: Laboratoire de Spectrom\'{e}trie Physique, Universit\'{e} J. Fourier/CNRS/GrenobleIntracavity laser absorption spectroscopy (ICLAS) is now a well established direct multiplex absorption method with a high sensitivity. This phenomena was discovered about 25 years ago [?, ?]. ICLAS is based on the high sensitivity of a broadband laser to intracavity frequency dependent losses: broadband intracavity losses are compensated by the laser gain whereas for narrow lines, the laser operates like a multipass cell without reflection losses. Equivalent absorption path lengths of several hundred of kilometers may be reached. Since the discovery of this effect, ICLAS has been used with success for the spectroscopy of very weak transitions mainly with dye, color center or ND:glass lasers [?]. The new class of solid state laser is highly promissing for the development of a new type of highly sensitive spectrometer in the infrared or near infrared[?]. We will give an overview about the principle of this technique and about recent applications like spectroscopy with an intracavity supersonic jet, with high resolution... We also will examine the possibilities to use this powerfull technique for measurements of weak concentrations of trace gas with an all solid state ICLAS spectrometer for in-situ detection. [1]L. A. PAKHOMYCHEVA, E.A. SVIRIDENKOV. A.F. SUCHKOV, L.V. TITOVA and S.S. CHURILOV, JETP Lett., 12, 43, (1970). [2]N. C. PETERSON, M.J. KURYLOV, W. BRAUN, A.M. BASS AND R. KELLER. J. Opt. Soc Am. 61, 746, (1971). [3]P. E. TOSCHEK, V. M. BAVE, Losers, spectroscopy and new idears, ed. W.H YEN, M.D. LEVENSON Springer verlag, 1987.[4]A. KACHANOV, A. CHARWAT and F. STOECKEL. J. Opt. Soc. Am. B. 11, 2412, (1995) and 12, 970, (1995.xsxs
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Evaluation of dissolved carbon dioxide to stimulate emergence of red swamp crayfish Procambarus clarkii (Decapoda: Cambaridae) from infested ponds
No full textInvasive crayfish have adverse effects on habitats and native species. Control of invasive crayfish populations is a major challenge facing natural resource managers. This study evaluated the effectiveness and optimal conditions for the control agent carbon dioxide (CO2), which can be diffused into water to facilitate capture of red swamp crayfish (Procambarus clarkii; RSC). The efficacy of CO2 shows promise in its use for a variety of invasive aquatic species. Here, we evaluate CO2’s ability to stimulate movements towards the shoreline and/or induce complete terrestrial emergence from outdoor ponds. Twelve pond trials were conducted using three, 0.02-ha experimental ponds at Auburn University, Alabama, USA. Silt fencing was installed on dry land around the perimeter of each pond with the lower 0.3 m of fencing accordion-folded to provide shelter and a collection point for emerging crayfish. Each pond was stocked with 100 RSC before testing. Experimental treatment ponds were then injected with gaseous CO2 using porous air diffusers, whereas control ponds (C ponds) received no CO2. Multiple water quality parameters were monitored hourly. Three independent treatment scenarios with CO2 diffusion were crayfish captured at the end of trial only (F: final), crayfish captured hourly (H: hourly), and incorporation of continuous inflow of fresh water at a flow rate of 0.2 L/s into the central catch basin to serve as a refuge with crayfish captured hourly (R: refuge). In control ponds, crayfish were captured at the end of trial only. In F ponds, CO2 diffusion for approximately five hours caused a mean of 12% of total crayfish to emerge from the water. However, capture efficiency was increased to a mean of 45% of total crayfish by increasing collection frequency to every hour and netting submerged crayfish near the water edge in addition to capturing terrestrially emerged crayfish. Presence of a freshwater inflow reduced capture efficiency in R ponds relative to H ponds. Odds of capturing crayfish increased with increasing water temperature, CO2 concentration, crayfish mass, and with decreasing pH. Based on results, we provide a set of predictive equations as well as interactive calculators to help natural resource managers explore several environmental and treatment-related scenarios that predict changes in capture probability in small research ponds. Carbon dioxide shows promises as a tool to increase capture rate of RSC. It is not likely to be 100% effective by itself, but could be a useful component of an integrated management strategy
TIME EVOLUTION OF SHORT-LIVED MOLECULAR SPECIES OBSERVED BY INTRACAVITY LASER ABSORPTION SPECTROSCOPY
No full textAuthor Institution: Laboratoire de Spectcometrie Physique Universite Scientifique et Medicale de Grenoble BP68 38042, Saint Martin d'Heres; Department of Chemistry, Davidson College, Davidson; Department of Chemistry, Syracuse University SyracuseWe report the feasibility of using CW intracavity laser absorption spectroscopy (ICLAS) as a probe in detecting transient species generated by pulsed laser photolysis. The method of detection uses a time-generated CW laser beam and time-resolved spectra which are delayed with respect to the photolysis pulse. Variable time delays and a constant generation time have been used to detect the time dependence of the absorbing species at times as short as a few microseconds. We applied the technique to the study of the time evolution of the formation of the free radical HCO generated by photolysis of gas-phase acetaldehyde at pressures down to tens of mtorr. We have also found that the ultimate sensitivity of the ICLAS technique is limited mainly by the mechanical stability of the cavity. M. Chenevier, M. A. Melieres, F. Stoeckel, to be published G. H. Atkinson, A. H. Laufer and M. J. Kurylo, J. Chem. Phys. 59 (1973) 350. G. H. Atkinson, T. M. Heimlich and M. W. Schuyler, J. Chem. Phys. 66 (1977 5005. A. J. Gill and G. H. Atkinson, Chem. Phys. Letters, 64 (1979) 426. R, J. Gill, W. D. Johnson and G. H. Atkinson, Chem. Phys. 58 (1981) 29
A fronto-parietal circuit for tactile object discrimination: an event-related fMRI study.
No full text[Newspaper Clipping: Author Claims Evidence of Second JFK Assassin #1]
No full textNewspaper article titled "Author Claims Evidence of Second JFK Assassin." The article states that author Richard J. Whalen concluded "that there is circumstantial evidence to support the theory of a second assassin in the shooting of President John F. Kennedy.
Also By The Same Author: AKTiveAuthor, a Citation Graph Approach to Name Disambiguation
No full textThe desire for definitive data and the semantic web drive for inference over heterogeneous data sources requires co-reference resolution to be performed on those data. In particular, name disambiguation is required to allow accurate publication lists, citation counts and impact measures to be determined. This paper describes a graph-based approach to author disambiguation on large-scale citation networks. Using self-citation, co-authorship and document source analyses, AKTiveAuthor clusters papers, achieving precision of 0.997 and recall of 0.818 over a test group of eight surname clusters
John F. Kennedy telegram to Roosevelt
No full textJersey Homesteads (later the Borough of Roosevelt) was established in the 1930s as an agro-industrial cooperative community. It was established specifically for urban Jewish garment workers, many of whom had emigrated from Europe. President John F. Kennedy sent a telegram to the citizens of Roosevelt, New Jersey, apologizing for not being able to attend the memorial dedication in honor of former President Franklin Delano Roosevelt. (Jersey Homesteads became Roosevelt in 1945 in honor of the president.) President Kennedy expressed his gratitude to the people of Roosevelt for constructing the memorial, and commented that it will serve as a constant reminder of Roosevelt's good works
Logarithmic variance profiles and the corresponding f-1 spectra of temperature fluctuations in turbulent Rayleigh-Bénard convection
No full textWe report experimental results for the temperature variance 2(z) and the corresponding frequency spectra P(f) in turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratioT= D/L = 1:00 (D = 1:12 m is the diameter and L = 1:12 m the height). The measurements were conducted in the Rayleigh-number range 1011 < Ra < 1:35 1014 and Pr ' 0:8. For Ra = 1:35x1014, 2(z) could be described well by a logarithmic dependence on the vertical position z in a range of z 1 < z < z 2 with z 1 ' 70 and z 2 = 0:1L. Here L=(2Nu) is the thickness of a thin thermal sublayer adjacent to the horizontal plate where the heat flux (denoted by the Nusselt number Nu) is carried mostly by thermal diffusion. In the log layer, we found that the temperature spectra had a significant frequency range over which P(f) f with close to 1. As Ra decreased, increased so that the log layer became thinner. At Ra = 2:05 1011, z 2 < z 1 and therefore there was no range for a log layer. Correspondingly, the temperature spectrum near the horizontal plate did not have the f1 scaling form either
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