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Search Results: 1 - 10 of 187826 matches for " T. W. Hansch "
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An all-optical gray lattice for atoms
H. Stecher,H. Ritsch,P. Zoller,F. Sander,T. Esslinger,T. W. Hansch
Physics , 1996, DOI: 10.1103/PhysRevA.55.545
Abstract: We create a gray optical lattice structure using a blue detuned laser field coupling an atomic ground state of angular momentum J simultaneously to two excited states with angular momenta J and J-1. The atoms are cooled and trapped at locations of purely circular polarization. The cooling process efficiently accumulates almost half of the atomic population in the lowest energy band which is only weakly coupled to the light field. Very low kinetic temperatures are obtained by adiabatically reducing the optical potential. The dynamics of this process is analysed using a full quantum Monte Carlo simulation. The calculations explicitly show the mapping of the band populations on the corresponding momentum intervals of the free atom. In an experiment with subrecoil momentum resolution we measure the band populations and find excellent absolut agreement with the theoretical calculations.
A Frequency Comb calibrated Solar Atlas
P. Molaro,M. Esposito,S. Monai,J. I. Gonzalez Hernandez,T. W. Hansch,R. Holzwarth,A. Manescau,L. Pasquini,R. A. Probst,R. Rebolo,T. Steinmetz,Th. Udem,T. Wilken
Physics , 2013, DOI: 10.1051/0004-6361/201322324
Abstract: The solar spectrum is a primary reference for the study of physical processes in stars and their variation during activity cycles. In Nov 2010 an experiment with a prototype of a Laser Frequency Comb (LFC) calibration system was performed with the HARPS spectrograph of the 3.6m ESO telescope at La Silla during which high signal-to-noise spectra of the Moon were obtained. We exploit those Echelle spectra to study the optical integrated solar spectrum . The DAOSPEC program is used to measure solar line positions through gaussian fitting in an automatic way. We first apply the LFC solar spectrum to characterize the CCDs of the HARPS spectrograph. The comparison of the LFC and Th-Ar calibrated spectra reveals S-type distortions on each order along the whole spectral range with an amplitude of +/-40 m/s. This confirms the pattern found by Wilken et al. (2010) on a single order and extends the detection of the distortions to the whole analyzed region revealing that the precise shape varies with wavelength. A new data reduction is implemented to deal with CCD pixel inequalities to obtain a wavelength corrected solar spectrum. By using this spectrum we provide a new LFC calibrated solar atlas with 400 line positions in the range of 476-530, and 175 lines in the 534-585 nm range. The new LFC atlas improves the accuracy of individual lines by a significant factor reaching a mean value of about 10 m/s. The LFC--based solar line wavelengths are essentially free of major instrumental effects and provide a reference for absolute solar line positions. We suggest that future LFC observations could be used to trace small radial velocity changes of the whole solar photospheric spectrum in connection with the solar cycle and for direct comparison with the predicted line positions of 3D radiative hydrodynamical models of the solar photosphere.
Ramsey type Sub-Recoil Cooling
Frank Sander,Thibaut Devolder,Tilman Esslinger,Theodor W. Hansch
Physics , 1996, DOI: 10.1103/PhysRevLett.78.4023
Abstract: We experimentally study the motion of atoms interacting with a periodically pulsed near resonant standing wave. For discrete pulse frequencies we observe a comb-like momentum distribution. The peaks have widths of 0.3 recoil momenta and a spacing which is an integer multiple of the recoil momentum. The atomic population is trapped in ground states which periodically evolve to dark states each time the standing wave is switched on.
Planar LAAPDs: Temperature Dependence, Performance, and Application in Low Energy X-ray Spectroscopy
L. Ludhova,F. D. Amaro,A. Antognini,F. Biraben,J. M. R. Cardoso,C. A. N. Conde,D. S. Covita,A. Dax,S. Dhawan,L. M. P. Fernandes,T. W. Hansch,V. W. Hughes,O. Huot,P. Indelicato,L. Julien,P. E. Knowles,F. Kottmann,J. A. M. Lopes,Y. -W. Liu,C. M. B. Monteiro,F. Mulhauser,F. Nez,R. Pohl,P. Rabinowitz,J. M. F. dos Santos,L. A. Schaller,D. Taqqu,J. F. C. A. Veloso
Physics , 2004, DOI: 10.1016/j.nima.2004.11.017
Abstract: An experiment measuring the 2S Lamb shift in muonic hydrogen mup is being performed at the Paul Scherrer Institute, Switzerland. It requires small and compact detectors for 1.9 keV x rays (2P-1S transition) with an energy resolution around 25% at 2 keV, a time resolution better than 100 ns, a large solid angle coverage, and insensitivity to a 5 T magnetic field. We have chosen Large Area Avalanche Photodiodes (LAAPDs) from Radiation Monitoring Devices as x-ray detectors, and they were used during the last data taking period in 2003. For x-ray spectroscopy applications, these LAAPDs have to be cooled in order to suppress the dark current noise, hence, a series of tests were performed to choose the optimal operation temperature. Specifically, the temperature dependence of gain, energy resolution, dark current, excess noise factor, and detector response linearity was studied. Finally, details of the LAAPDs application in the muonic hydrogen experiment as well as their response to alpha particles are presented.
Band Population Measurements in a Purely Optical Dark Lattice
Frank Sander,Tilman Esslinger,Theodor W. Hansch,Herwig Stecher,Helmut Ritsch
Physics , 1996,
Abstract: We create a dark optical lattice structure using a blue detuned laser field coupling an atomic ground state of total angular momentum F simultaneously to two excited states with angular momenta F and F-1, or F and F+1. The atoms are trapped at locations of purely circular polarization. The cooling process efficiently accumulates almost half of the atomic population in the lowest energy band which is only weakly coupled to the light field. The populations of the two lowest energy bands reaches 70%. Kinetic energies on the order of the recoil energy are obtained by adiabatically reducing the optical potential. The band populations are directly mapped on free particle momentum intervals by this adiabatic release. In an experiment with subrecoil momentum resolution we measure the band populations and find good absolute agreement with the theoretically calculated steady state band populations.
The Design of Stall-Regulated Wind Turbine Blade for a Maximum Annual Energy Output and Minimum Cost of Energy Based on a Specific Wind Statistic  [PDF]
W. Sridech, T. Chitsomboon
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.26002
Abstract:

The design of a stall-regulated wind turbine to achieve a maximum annual energy output is still a formidable task for engineers. The design could be carried out using an average wind speed together with a standard statistical distribution such as a Weibull with k = 2.0. In this study a more elaborated design will be attempted by also considering the statistical bias as a design criterion. The wind data used in this study were collected from three areas of the Lamtakong weather station in Nakhonratchasima Provice, the Khaokoh weather station in Phetchaboon and the Sirindhorn dam weather station in Ubonratchathani, Thailand. The objective is to design a best aerodynamic configurations for the blade (chord, twist and pitch) using the same airfoil as that of NREL Phase VI wind turbine. Such design is carried out at a design wind speed point. Wind turbine blades were optimized for both maximum annual energy production and minimum cost of energy using a method that take into account aerodynamic and structural considerations. The work will be carried out by the program “SuWiTStat” which was developed by the authors and based on BEM Theory (Blade Element Momentum). Another side issue is the credibility of the Weibull statistic in representing the real wind measurement. This study uses a regression analysis to determine this issue.

Thermal and structural studies of poly (vinyl alcohol) and hydroxypropyl cellulose blends  [PDF]
Osiris W. Guirguis, Manal T. H. Moselhey
Natural Science (NS) , 2012, DOI: 10.4236/ns.2012.41009
Abstract: Polymers and polymeric composites have steadily reflected their importance in our daily life. Blending poly(vinyl alcohol) (PVA) with a potentially useful natural biopolymers such as hydroxypropyl cellulose (HPC) seems to be an interesting way of preparing a polymeric blends. In the present work, blends of PVA/HPC of compositions (100/0, 90/10, 75/25, 50/50, 25/75, and 0/100 wt/wt%) were prepared to be used as bioequivalent materials. Thermal analyses [differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)], and X-ray diffraction (XRD) were employed to characterize and reveal the miscibility map and the structural properties of such blend system. The obtained results of the thermal analyses showed variations in the glass transition temperature (Tg) indicating the miscibility of the blend systems. Moreover, the changes in the melting temperature (Tm), shape and area were attributed to the different degrees of crystallinity and the existence of polymer-polymer interactions between PVA and HPC molecules. The X-ray diffraction (XRD) analysis showed broadening and sharpening of peaks at different HPC concentrations with PVA. This indicated changes in the crystallinity/amorphosity ratio, and also suggested that the miscibility between the amorphous components of homo-polymers PVA and HPC is possible. The results showed that HPC doped in PVA film can improve the thermal stability of the film under investigation, leading to interesting technological applications.
Light Emitting Diodes as a Rapid Visual Display for Use in Psychological Experiments  [PDF]
Clementine Thurgood, T. W. Allan Whitfield
Optics and Photonics Journal (OPJ) , 2013, DOI: 10.4236/opj.2013.31015
Abstract:

In this paper we show how light emitting diodes (LEDs) can be used in conjunction with existing display technologies as a means for achieving ultra-rapid visual stimulus exposure durations. We review existing rapid visual display methods, and show how our apparatus overcomes the limitations inherent with each technique. Our apparatus, the LED tachistoscope, takes advantage of the fast-switching times and high-brightness capabilities of LEDs in order to present stimuli at previously unachievable durations as rapid as 1 ms. The rapid exposure durations are achieved by external LED backlight illumination of images on a liquid crystal display (LCD) after the components of the LCD have stabilized. This ensures that stimulus onset and offset are discrete. Furthermore, the fast-switching of the LEDs enables stimuli to be revealed for very rapid durations. The paper also describes studies in which the LED tachistoscope has already been applied, and offers suggestions for other possible applications. Interestingly, in our studies we show that the human visual system is very adept at extracting information with only very minimal stimulus exposure durations. Such studies have not been possible with existing display equipment. The LED tachistoscope opens up avenues for a variety of psychological and physiological experiments and provides a means for revealing the limits of human visual perception.

Producing Renewable Biodiesel Fuel Using the Transesterification Process  [PDF]
T. W. Chung, Y. J. Chen
World Journal of Engineering and Technology (WJET) , 2015, DOI: 10.4236/wjet.2015.33C016
Abstract:

Biodiesel fuels are considered an alternative to fossil fuels. This is one of the effective means of transferring solar energy to dynamic energy via photosynthesis. It is also being considered in order to reduce the levels of carbon dioxide production worldwide. Biodiesel fuels are a renewable, biodegradable, and clean energy source. Producing enough biofuels to replace fossil fuels will bring the advantages of reduced air pollution and reduced other environmental impacts of fossil fuels. In this study, the response surface methodology (RSM) was used to design the experimental runs and to discuss the manufacturing variables on the transesterification of palm oil into fatty acid methyl ester (i.e. biodiesel fuel). The variation of the degree of effect for each variable in the transesterification process was observed. A second-order model was obtained to predict the yield of biodiesel fuel and the viscosity as a function of the reaction time, the mass fraction of catalyst in methanol and the molar ratio of methanol to plant oil. The experimental data of the yield and the viscosity of biodiesel fuels in different manufacturing variables are discussed in this study. Analysis of variance (ANOVA) was also applied to discuss the main factor and interaction factor effects of the manufacturing variables on the responses of the yield of unrefined biodiesel fuels. The shortage of farmland in Taiwan is a problem that needs to be solved before mass propagation of biofuels can be accomplished. In southeastern Asia, there are many farms and most energy farm products are cultivated (e.g. palm oil or Jatropha oil). In addition to sunflowers and soybeans in Taiwan, those energy farm products are possible choices for production of biodiesel fuel in Taiwan. The cooperation between Indonesia and Taiwan on the plantation of palm or Jatropha trees in Indonesia has conducted and will be one of the possible ways to solve the problem of the shortage of energy farm products in Taiwan.

Método estruturado de design de produtos orientados aos sistemas produto-servi o: proposta e aplica o
Cristiano Roos,Fernanda Hansch Beuren,Samuel Borges Barbosa,Marcelo Gitirana Gomes Ferreira
Iberoamericana de Engenharia Industrial , 2011,
Abstract: O objetivo deste trabalho é propor e aplicar um método de design de produtos que possa contribuir para tornar o Sistema Produto-Servi o mais atraente para o cliente. Esta pesquisa, com base nos objetivos, é classificada em exploratória e, com base nos procedimentos técnicos, é classificada em estudo de caso. Como resultado principal tem-se a proposta de um método estruturado de design de produtos que s o orientados aos Sistemas Produto-Servi o. Como resultados secundários têm-se a aplica o do método em produtos de um Sistema Produto-Servi o, sendo geradas contribui es à organiza o onde a aplica o foi realizada. Contribui es em termos de projetos de produtos mais sustentáveis para a organiza o e que prevêem a utiliza o de inputs e outputs com menor impacto nas variáveis da sustentabilidade. Outra contribui o relevante foi o planejamento do ciclo de vida dos produtos desenvolvidos. Assim, a realiza o deste trabalho proporcionou um maior entendimento acerca da temática proposta, além de mostrar a importancia de um método de design de produtos orientados aos Sistemas Produto-Servi o.
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