Experimental and theoretical analysis of bias ionization by α-particles in a nitrogen laser
NASA Astrophysics Data System (ADS)
Silva, R. R.; Vieira Mendes, L. A.; Tsui, K. H.; De Simone Zanon, R. A.; de Oliveira, A. L.; Fellows, C. E.
2011-09-01
Nitrogen laser performance with TE configuration and wedge electrodes is analyzed with background ionization in the laser discharge channel by α particles at a low exposition rate. With the bias ionization, the laser power presents two peaks as a function of gas pressure, with one at the normal low pressure, without bias ionization, and the other at high pressure generated by bias ionization. A simple theoretical model has been developed in a trial to understand this behavior. This model was first tested in later results for a TE configuration nitrogen laser, with flat electrodes, without and with bias ionization. It has been observed that due to the competition between electrode shielding by positively charged α particles and bulk ionization by impact, the laser energy is suppressed with pressure below 50 Torr and enhanced above it.
Arevalo, E.; Becker, A.
2005-10-15
We study numerically and analytically the role of the combined effect of self-focusing, geometrical focusing, and the plasma defocusing in the formation of the fluorescence signal during the filamentation of a Ti:sapphire laser pulse in nitrogen molecular gas. Results of numerical simulations are used to estimate the number of excited ions in the focal volume, which is proportional to the fluorescence signal. We find good agreement between the theoretical results and the experimental data, showing that such data can be used to get further insight into the effective focal volume during filamentation of femtosecond laser pulses in transparent media.
Theoretical analysis of output performance of GG-IAG fiber laser by multipoint distributed side pump
NASA Astrophysics Data System (ADS)
Zhu, Yonggang; Duan, Kailiang; Shao, Hongmin; Zhao, Baoyin; Zhang, Entao; Zhao, Wei
2012-11-01
Based on a steady-state rate equations (REs) and heat dissipation model considering both convective and radiative heat transfer, the output performance and temperature distribution of Yb3+ doped gain guided and index antiguided (GG-IAG) fiber lasers by multipoint distributed pumping are analyzed by numerically solving REs. The results show that high output power and even temperature distribution can be obtained by increasing pump points and lowering the losses at the points; multipoint side pumping is an optimal method to obtain compact high power GG-IAG fiber lasers. The numerical analysis provides some insights for the construction of high power GG-IAG fiber lasers.
Optical coupling between two lasers on a dielectric surface: experimental and theoretical analysis
NASA Astrophysics Data System (ADS)
Raju, Md Mozammal K.
In order to understand the concept of qubit (or quantum bit) and use it for quantum computation purposes we analyze the phenomenon of "electromagnetically induced transparency" (EIT) from both quantum theoretical and experimental standpoint. The purpose of this work is to couple two lasers through a simultaneous interaction on the surface of a dielectric material. This research led to the use of a capacitor-type configuration for modifying the wavelength of a probe laser field using a voltage across the dielectric, and next, to lock the probe field on the dielectric surface by using a stronger coupling laser. The inclusion of a second stronger coupling laser creates an interference effect, similar as in the case of EIT, with the probe laser of adjusted wavelength due to the capacitor voltage. The Brewster angle method which uses polarized light reflected by surfaces allows us to experimentally observe the EIT feature as a wavy structure embedded in the parabolic shape of the Brewster region. This study can be extended towards many applications such as optical switches, quantum memory, quantum encryption, quantum repeater, fingerprint investigation, to name a few.
Theoretical analysis of dynamic chemical imaging with lasers using high-order harmonic generation
Van-Hoang Le; Anh-Thu Le; Xie Ruihua; Lin, C. D.
2007-07-15
We report theoretical investigations of the tomographic procedure suggested by Itatani et al. [Nature (London) 432, 867 (2004)] for reconstructing highest occupied molecular orbitals (HOMOs) using high-order harmonic generation (HHG). Due to the limited range of harmonics from the plateau region, we found that even under the most favorable assumptions, it is still very difficult to obtain accurate HOMO wave functions using the tomographic procedure, but the symmetry of the HOMOs and the internuclear separation between the atoms can be accurately extracted, especially when lasers of longer wavelengths are used to generate the HHG. Since the tomographic procedure relies on approximating the continuum wave functions in the recombination process by plane waves, the method can no longer be applied upon the improvement of the theory. For future chemical imaging with lasers, we suggest that one may want to focus on how to extract the positions of atoms in molecules instead, by developing an iterative method such that the theoretically calculated macroscopic HHG spectra can best fit the experimental HHG data.
NASA Astrophysics Data System (ADS)
Cho, Jun-Hyung; Heo, Seo Weon; Sung, Hyuk-Kee
2016-05-01
We numerically simulated the performance of an optoelectronic oscillator (OEO) based on a directly modulated (DM) semiconductor laser. The standard coupled rate equations were used to describe the DM-OEO modulation process. A rate-equation-based analysis is a means of analyzing OEO performance that is a variation of the method used to assess standard OEOs that employ external modulators. We modeled an OEO with an open-loop response and calculated the oscillation threshold gain and amplitude of the DM-OEO as functions of the DC bias current. By using this method, we were able to optimize OEO operation conditions for a given laser DC bias level in both gain- and amplitude-limited operating environments.
Theoretical and experimental analysis of injection seeding a Q-switched alexandrite laser
NASA Technical Reports Server (NTRS)
Prasad, C. R.; Lee, H. S.; Glesne, T. R.; Monosmith, B.; Schwemmer, G. K.
1991-01-01
Injection seeding is a method for achieving linewidths of less than 500 MHz in the output of broadband, tunable, solid state lasers. Dye lasers, CW and pulsed diode lasers, and other solid state lasers have been used as injection seeders. By optimizing the fundamental laser parameters of pump energy, Q-switched pulse build-up time, injection seed power and mode matching, one can achieve significant improvements in the spectral purity of the Q-switched output. These parameters are incorporated into a simple model for analyzing spectral purity and pulse build-up processes in a Q-switched, injection-seeded laser. Experiments to optimize the relevant parameters of an alexandrite laser show good agreement.
NASA Astrophysics Data System (ADS)
Mikami, K.; Motokoshi, S.; Somekawa, T.; Jitsuno, T.; Fujita, M.; Tanaka, KA; Azechi, H.
2016-03-01
The temperature dependence of the laser-induced damage threshold on optical coatings was studied in detail for laser pulses from 123 K to 473 K at different temperatures. The laser-induced damage threshold increased with decreasing temperatures when we tested long pulses (200 ps and 4 ns). The temperature dependence, however, was reversed for pulses shorter than a few picoseconds (100 fs testing). We propose a scaling model with a flowchart that includes three separate processes: free-electron generation, electron multiplication, and electron heating. Furthermore, we calculated the temperature dependence of laser-induced damage thresholds at different temperatures. Our calculation results agreed well with the experimental results.
Theoretical and experimental analysis of laser altimeters for barometric measurements over the ocean
NASA Technical Reports Server (NTRS)
Tsai, B. M.; Gardner, C. S.
1984-01-01
The statistical characteristics and the waveforms of ocean-reflected laser pulses are studied. The received signal is found to be corrupted by shot noise and time-resolved speckle. The statistics of time-resolved speckle and its effects on the timing accuracy of the receiver are studied in the general context of laser altimetry. For estimating the differential propagation time, various receiver timing algorithms are proposed and their performances evaluated. The results indicate that, with the parameters of a realistic altimeter, a pressure measurement accuracy of a few millibars is feasible. The data obtained from the first airborne two-color laser altimeter experiment are processed and analyzed. The results are used to verify the pressure measurement concept.
NASA Technical Reports Server (NTRS)
Zhang, Kuanshou; Xie, Changde; Peng, Kunchi
1996-01-01
The dependence of the quantum fluctuation of the output fundamental and second-harmonic waves upon cavity configuration has been numerically calculated for the intracavity frequency-doubled laser. The results might provide a direct reference for the design of squeezing system through the second-harmonic-generation.
Theoretical analysis of exposure times in laser treatment of port wine stains
NASA Astrophysics Data System (ADS)
Carrazana, P.
1987-10-01
Thermal relaxation times of blood vessels associated with port wine stains (PWS), when these vessels are subjected to laser irradiation, are estimated as a function of their diameter. The heat conduction equation with boundary conditions of the first kind is solved exactly, in order to find the temperature distribution inside the vessel. An approximate solution giving data appropriate for clinical applications is found. For the range in diameters of the blood vessels involved, it is found that the relaxation times are, approximately, in the range 0.10-15 ms. In the case of a typical 50 μm diameter vessel, it is found that the cooling process is essentially completed after 3.85 ms.
Theoretical aspects of fibre laser cutting
NASA Astrophysics Data System (ADS)
Mahrle, A.; Beyer, E.
2009-09-01
Fibre lasers offer distinct advantages over established laser systems with respect to power efficiency, beam guidance and beam quality. Consequently, the potential of these new laser beam sources will be increasingly exploited for laser cutting applications that are conventionally carried out with CO2 lasers. However, theoretical estimates of the effective absorptivity at the cut front suggest that the shorter wavelength of the fibre laser in combination with its high focusability seems to be primarily advantageous for thin sheet metal cutting whereas the CO2 laser is probably still capable of cutting thicker materials more efficiently. This surprising result is a consequence of the absorptivity behaviour of metals that shows essential quantitative differences for the corresponding wavelengths of both laser sources as a function of the angle of incidence between the laser beam and the material to be cut. In evaluation of the revealed dependences, solution strategies for an improvement of the efficiency of fibre laser cutting of thicker metal sheets are suggested.
NASA Astrophysics Data System (ADS)
Büsing, Lasse; Bonhoff, Tobias; Behnke, Lars; Stollenwerk, Jochen; Loosen, Peter
2016-02-01
For realising fast and highly dynamical laser-based material processing, scanner systems are already utilised for many different industrial applications. Furthermore, ultra-short pulsed (<1 ps) laser sources provide possibilities of processing most different materials with highest accuracy. Owing to the large spectral bandwidth of ultra-short laser pulses, dispersion in optical components becomes relevant. The dispersion in optical systems for laser scanners may lead to scan angle-depending pulse properties as, for example, pulse front tilt. The investigation of these effects is not state of the art today but absolutely necessary to exploit the full potential of laser scanners for ultra-short pulse applications. By means of an exemplary focusing lens, the simulation and experimental analysis of scan angle-depending pulse front tilt is presented for the first time.
NASA Astrophysics Data System (ADS)
Rastegar, Sohi; Motamedi, Massoud
1990-06-01
Theoretical modeling of the processes oflight and temperature distribution is rapidly developing both as a qualitative as well as a qtiantitative tool for the understanding of laser light interaction with tissue. Many applications oflasers in medicine involve volumetric coagulation of tissue. In these processes laser light incident on tissue is absorbed and scattered by tissue chromophores and subsequently converted to thermal energy resulting in a temperature rise in tissue. It is well known that elevation of temperature can cause tissue coagulation which is, in most tissues, accompanied by a change in optical properties of tissue (Gourgouliatos [1987], Spears et al. [1988]; Jacques and Gaeeni [1989]). The results by Jacques and Gaeeni [1989] provide a quantitative data for absorption and scattering coefficients of dog myocardium as a function of temperature at selected wavelengths. Parametric study of the effect of variation of optical properties on heat generation, temperature distribution, and ablation rate has been done by Motamedi et a! [1989] and Rastegar et al. [1989]. However, these and other analyses ( e.g. Armon and Laufer [1985], McKenzie [1986], Jacques and PraM [1987] )of temperature disiribution in tissue traditionally have not considered the role of dynamic variation of of the optical properties with temperature. This paper presents a method to analyze this effect and explores its potential impact on laser dosimetry prescription for laser applications involving coagulation of tissue.
Lall, A A; Terray, A; Hart, S J
2010-12-20
Laser separation of particles is achieved using forces resulting from the momentum exchange between particles and photons constituting the laser radiation. Particles can experience different optical forces depending on their size and/or optical properties, such as refractive index. Thus, particles can move at different speeds in the presence of an optical force, leading to spatial separations. In this paper, we present a theoretical analysis on laser separation of non-absorbing aerosol particles moving at speeds (1-10 cm/sec) which are several orders of magnitude greater than typical particle speeds used in previous studies in liquid medium. The calculations are presented for particle deflection by a loosely focused Gaussian 1064 nm laser, which simultaneously holds and deflects particles entrained in flow perpendicular to their direction of travel. The gradient force holds the particles against the viscous drag for a short period of time. The scattering force simultaneously pushes the particles, perpendicular to the flow, during this period. Our calculations show particle deflections of over 2500 µm for 15 µm aerosol particles, and a separation of over 1500 µm between 5 µm and 10 µm particles when the laser is operated at 10 W. We show that a separation of about 421 µm can be achieved between two particles of the same size (10 µm) but having a refractive index difference of 0.1. Density based separations are also possible. Two 10 µm particles with a density difference of 600 kg/m3 can be separated by 193 µm. Examples are shown for separation distances between polystyrene, poly(methylmethacrylate), silica and water particles. These large laser guided deflections represent a novel achievement for optical separation in the gas phase. PMID:21196954
Theoretical studies of solar-pumped lasers
NASA Technical Reports Server (NTRS)
Harries, W. L.
1982-01-01
Solar-pumped lasers were investigated by comparing experimental results from pulse experiments with steady state calculations. The time varying behavior of an IBr laser is studied. The analysis is only approximate, but indicates that conditions occurring in a pulsed experiment are quite different from those at steady state. The possibility of steady-state lasing in an IBr laser is determined. The effects of high temperatures on the quenching and recombination rates are examined. Although uncertainties in the values of the rate coefficients make it difficult to draw firm conclusions, it seems steady state running may be possible at high temperatures.
Theoretical studies of solar lasers and converters
NASA Technical Reports Server (NTRS)
Heinbockel, John
1988-01-01
The geometry and setup for the n-C3F7I iodine laser are illustrated. The mathematical modeling of this system is described. The chemical kinetics are summarized. A sensitivity analysis was performed on the parameters occurring in the differential equations describing the chemical kinetics.
Theoretical studies of solar-pumped lasers
NASA Technical Reports Server (NTRS)
Harries, W. L.
1983-01-01
Possible types of lasers were surveyed for solar power conversion. The types considered were (1) liquid dye lasers, (2) vapor dye lasers, and (3) nondissociative molecular lasers. These are discussed.
NASA Astrophysics Data System (ADS)
Qian, Yong; Wang, Yuzhu
2004-04-01
A novel method to generate a collimated hollow-laser-beam (HLB) by only a single axicon is proposed. With some reasonable assumptions, the radial light intensity distribution is calculated in detail by diffraction integral theory. The result of numerical simulation shows that this method is valid. Compared with other methods of generating HLB, this scheme is extraordinarily simple in principle and can be utilized experimentally to construct a light trap in atomic fountain for convenience.
NASA Astrophysics Data System (ADS)
Wang, Feilu; Fujioka, Shinsuke; Nishimura, Hiroaki; Kato, Daiji; Li, Yutong; Zhao, Gang; Zhang, Jie; Takabe, Hideaki
2008-04-01
We composed a time-dependent detailed-configuration-accounting atomic model, which solves rate equations for level population distributions including collisional and radiative atomic processes based on the screened hydrogenic model (R. M. More, Handbook of Plasma Physics, vol. 3, Amsterdam: Elsevier Science Publishers, 1991). This model is used to interpret recent photoionization experiment on the large-scale laser system Gekko-XII (Yamanaka et al., 1981, IEEE, J. Quantum Electron. 17, 1639). In this experiment, the nitrogen gas was bathed in a Planckian radiation field of 80eV and was ionized beyond He-like state (open K-shell). It indicates the ionization parameter is around 10 erg cm/s under near steady-state conditions and the reasonable range of the electron temperature is 20-30eV. The comparison of synthetic and experimental spectra shows reasonable agreement and photoionization plays a significant role in this experiment.
Theoretical studies of solar pumped lasers
NASA Technical Reports Server (NTRS)
Harries, Wynford L.
1990-01-01
One concept for collecting solar energy is to use large solar collectors and then use lasers as energy converters whose output beams act as transmission lines to deliver the energy to a destination. The efficiency of the process would be improved if the conversion could be done directly using solar pumped lasers, and the possibility of making such lasers is studied. There are many applications for such lasers, and these are examined. By including the applications first, the requirements for the lasers will be more evident. They are especially applicable to the Space program, and include cases where no other methods of delivering power seem possible. Using the lasers for conveying information and surveillance is also discussed. Many difficulties confront the designer of an efficient system for power conversion. These involve the nature of the solar spectrum, the method of absorbing the energy, the transfer of power into laser beams, and finally, the far field patterns of the beams. The requirements of the lasers are discussed. Specific laser configurations are discussed. The thrust is into gas laser systems, because for space applications, the laser could be large, and also the medium would be uniform and not subject to thermal stresses. Dye and solid lasers are treated briefly. For gas lasers, a chart of the various possibilities is shown, and the various families of gas lasers divided according to the mechanisms of absorbing solar radiation and of lasing. Several specific models are analyzed and evaluated. Overall conclusions for the program are summarized, and the performances of the lasers related to the requirements of various applications.
Theoretical and Experimental Investigations of Novel Fiber Lasers
NASA Astrophysics Data System (ADS)
Walton, Donnell Thaddeus
Ultrafast science has historically been concerned with the areas of spectroscopy and the study of dynamic processes in the sciences and engineering. With the recent advent of compact, economical sources of ultrashort optical pulses, many potential applications have emerged in the fields of communications, medicine, metrology, and industrial processing. In this thesis, fiber lasers are explored as compact sources of ultra short optical pulses. Several passive modelocking schemes in fiber lasers have been reported. Unfortunately, when implemented in the negative group velocity regime, modelocked fiber lasers are plagued with a multiple-pulsing instability which limits them to low output pulse energy. In this work, a modelocking scheme based on a nonlinear directional coupler is proposed and analyzed. This laser, when embodied as a dual-core fiber, is shown to be immune to the multiple-pulsing instability and produces sub-100-fs pulses in the negative group velocity regime. In the presence of gain saturation, the laser produces 100-fs pulses and can evolve to steady-state from initial noise input when operated under the right conditions. The dual-core fiber laser even produces nanojoule, picosecond when implemented in the regime of positive group velocity dispersion. These pulses are chirped which allows for further compression down to 160 fs. Using a similar model, the first theoretical analysis of passive modelocking in birefringent fiber is performed. The results of the model (45 fs) are in excellent agreement with experimental results (38 fs). Additional wavelengths are also needed if fiber lasers are to be considered viable as compact sources of ultrashort pulses. To this end, a diode-pumped thulium -doped fluorozirconate fiber laser which operates near 800 nm is examined. The upconversion process is shown to be due to avalanche absorption of the pump. By constructing a compact, diode-pumped laser from an unoptimized sample of this fiber, this technique is shown
Theoretical studies of solar lasers and converters
NASA Technical Reports Server (NTRS)
Heinbockel, John H.
1990-01-01
The research described consisted of developing and refining the continuous flow laser model program including the creation of a working model. The mathematical development of a two pass amplifier for an iodine laser is summarized. A computer program for the amplifier's simulation is included with output from the simulation model.
Sturesson, C; Andersson-Engels, S
1996-03-01
A mathematical model for predicting the temperature rise in transurethral laser-induced thermo-therapy for benign prostatic hyperplasia was developed. In the model an optical line source emitting light from an Nd:YAG laser isotropically was placed in the urethra. Water cooling of the urethral epithelium was modelled using a two-tube system. The relationship between the difference in outlet and inlet water temperatures and the highest tissue temperature level reached was theoretically investigated. It was found that the water temperature difference was linearly dependent on the steady-state maximum tissue temperature. The theoretical calculations suggest that the water-cooled applicator can be used to measure the maximum tissue temperature. With temperature control, the prostatic tissue temperature can be prevented from exceeding the boiling point of water, excluding tissue carbonization. The model was also used to evaluate the influence of a number of different parameters on the damaged tissue volume. Increasing the urethral lumen radius by a factor of two by means of inserting different sized tubes was found to augment the tissue volume raised to therapeutic temperatures by up to 50%. The calculations showed that cooling of the urethral epithelium can result in an increase in the damaged volume by 80% as compared to not applying any cooling. The temperature of the cooling water was found to influence the tissue temperature only to a small extent. PMID:8778825
Theoretical studies of solar-pumped lasers
NASA Technical Reports Server (NTRS)
Harries, W. L.
1983-01-01
Metallic vapor lasers of Na2 and Li2 are examined as solar energy converters. The absorbed photons cause transitions to vibrational-rotational levels in an upper electronic state. With broad band absorption the resultant levels can have quantum numbers considerably higher than the upper lasing level. The excited molecule then relaxes to the upper lasing level which is one of the lower vibrational levels in the upper electronic state. The relaxation occurs from collisions, provided the molecule is not quenched into the ground level electronic state. Lasing occurs with a transition to a vibrational level in the lower electronic state. Rough estimates of solar power efficiencies are 1 percent for Na2 and probably a similar figure for Li2. The nondissociative lasers from a family distinct from materials which dissociate to yield an excited atom.
NASA Astrophysics Data System (ADS)
Conde, J. C.; Riveiro, A.; Comesana, R.; Pou, J.
2011-11-01
The properties of orthopaedic/dental implants can be tuned through the laser surface modifications that take place during a laser ablation process. Processing assisted by a laser is adequate to produce macro- and micro-structures on metallic alloys and polymer surfaces in order to improve their biological response. The evaluation of the minimum energy density that causes an optimum ablation process on different kinds of surfaces was theoretically established by numerical simulation of the thermal process and some experiments have been systematically carried out to produce a periodic pattern in the surface. The selection of the laser power has been predicted from numerical analysis solving of the heat conduction differential equation using commercial software, ANSYS (11.0). This analysis has allowed us to predict the extent and the depth of the holes. The theoretical results agree with the experimental measurements that were carried out by profilometry.
Galushkin, M G; Mitin, Konstantin V; Ionin, Andrei A; Kotkov, A A
1998-10-31
Numerical simulation is used as the basis of an analysis of nonlinear optical properties of the active medium in intracavity four-wave mixing of the radiation of a pulsed electron-beam-controlled discharge CO{sub 2} laser on saturated-gain and refractive-index diffraction gratings. The reflection coefficient of the phase-conjugated signal is determined for various cavity Q-factors, specific input energies, and pressures of the laser-active mixture. A comparison is made of the theoretical and experimental results. It is found that the rate of formation of amplitude gratings is governed primarily by the initial population inversion and by the intensities of the interacting waves. It is shown that transient phase gratings make the dominant contribution to the phase-conjugate reflection coefficient at high pressures of the mixture. (nonlinear optical phenomena)
ERIC Educational Resources Information Center
Zare, Richard N.
1984-01-01
Reviews applications of laser methods to analytical problems, selecting examples from multiphoton ionization and fluorescence analysis. Indicates that laser methodologies promise to improve dramatically the detection of trace substances embedded in "real" matrices, giving the analyst a most powerful means for determining the composition of…
Theoretical and experimental studies of optically pumped molecular gas lasers
NASA Astrophysics Data System (ADS)
Ratanavis, Amarin
Optically pumped molecular gas lasers based on vibrational-rotational transitions in the infrared spectral region were studied experimentally and theoretically. A model was developed to predict the performance of such lasers and explore their potentials for energy and power scaling. This rate equation model was applied to explore the performance of a second-overtone (pulsed) and a first-overtone (CW) pumped HBr laser. Experimental improvements concerning temperature spectral tuning and frequency stabilization of a Nd:YAG laser that pumped HBr were accomplished. Lasing at 4 microns was demonstrated from such a system. We identified acetylene and hydrogen cyanide as potential laser gases that can be pumped with lasers emitting in the attractive telecommunication C band region at about 1.5 microns. Estimations and fluorescence measurements suggest the possibility of lasing in the 3 micron region. Lasing was demonstrated for the first time with a 5 ns pump pulse from an optical parametric oscillator using traditional cavities. The first gas filled hollow fiber laser based on population inversion was demonstrated with C2H2 and emission in the 3 micron region was observed. An analytical model indicates the possibility of CW lasing with small Stokes shift in both C2H 2 and HCN.
Augustoni, Arnold L.
2004-10-01
A laser hazard analysis and safety assessment was performed for each various laser diode candidates associated with the High Resolution Pulse Scanner based on the ANSI Standard Z136.1-2000, American National Standard for the Safe Use of Lasers. A theoretical laser hazard analysis model for this system was derived and an Excel{reg_sign} spreadsheet model was developed to answer the 'what if questions' associated with the various modes of operations for the various candidate diode lasers.
NASA Astrophysics Data System (ADS)
Zou, J. L.; He, Y.; Wu, S. K.; Huang, T.; Xiao, R. S.
2015-12-01
The deep penetration-welding threshold (DPWT) is the critical value that describes the welding mode transition from the thermal conduction to the deep penetration. The objective of this research is to clarify the DPWT induced by the lasers with wavelength of 1 μm (1-μm laser), based on experimental observation and theoretical analysis. The experimental results indicated that the DPWT was the ratio between laser power and laser spot diameter (P/d) rather than laser power density (P/S). The evaporation threshold was smaller than the DPWT, while the jump threshold of the evaporated mass flux in the molten pool surface was consistent with the DPWT. Based on the force balance between the evaporation recoil pressure and the surface tension pressure at the gas-liquid interface of the molten pool as well as the temperature field, we developed a self-focusing model, which further confirmed the experimental results.
Theoretical analysis of ARC constriction
Stoenescu, M.L.; Brooks, A.W.; Smith, T.M.
1980-12-01
The physics of the thermionic converter is governed by strong electrode-plasma interactions (emissions surface scattering, charge exchange) and weak interactions (diffusion, radiation) at the maximum interelectrode plasma radius. The physical processes are thus mostly convective in thin sheaths in front of the electrodes and mostly diffusive and radiative in the plasma bulk. The physical boundaries are open boundaries to particle transfer (electrons emitted or absorbed by the electrodes, all particles diffusing through some maximum plasma radius) and to convective, conductive and radiative heat transfer. In a first approximation the thermionic converter may be described by a one-dimensional classical transport theory. The two-dimensional effects may be significant as a result of the sheath sensitivity to radial plasma variations and of the strong sheath-plasma coupling. The current-voltage characteristic of the converter is thus the result of an integrated current density over the collector area for which the boundary conditions at each r determine the regime (ignited/unignited) of the local current density. A current redistribution strongly weighted at small radii (arc constriction) limits the converter performance and opens questions on constriction reduction possibilities. The questions addressed are the followng: (1) what are the main contributors to the loss of current at high voltage in the thermionic converter; and (2) is arc constriction observable theoretically and what are the conditions of its occurrence. The resulting theoretical problem is formulated and results are given. The converter electrical current is estimated directly from the electron and ion particle fluxes based on the spatial distribution of the electron/ion density n, temperatures T/sub e/, T/sub i/, electrical voltage V and on the knowledge of the transport coefficients. (WHK)
NASA Astrophysics Data System (ADS)
Pustovalov, V. K.; Jean, B.
2006-08-01
Theoretical investigations and the results of computer modeling of the optical, thermophysical, and thermochemical processes during laser interaction with ocular tissues are reviewed in this paper. Physical-mathematical models and results of numerical simulation of the processes are presented. The computer modeling was applied for investigations of laser heating and coagulation of ocular tissues for treatment of retina diseases and intraocular tumors, cyclophotocoagulation of the ciliary body for treatment of glaucoma, and laser thermal keratoplasty of the cornea. The influence of radiation parameters on the selectivity of laser coagulation of laminated ocular tissues is considered. The results obtained are of essential interest for laser applications in ophthalmology and can be used for investigation of heating and coagulation of tissues in different fields of laser medicine.
Multicolor laser altimeter for barometric measurements over the ocean - Theoretical
NASA Technical Reports Server (NTRS)
Gardner, C. S.; Tsai, B. M.; Im, K. E.
1983-01-01
It is noted that the optical path length from a satellite to the earth's surface strongly depends on the atmospheric pressure along the propagation path. The theoretical basis of a surface pressure measurement technique, which uses a two-color laser altimeter to observe the change with wavelength in the optical path length from a satellite to the ocean surface, is evaluated. The statistical characteristics of the ocean-reflected pulses and the expected measurement accuracy are analyzed in terms of the altitude parameters. The results show that it is feasible to obtain a pressure accuracy of a few millibars.
Theoretical Modeling of the Discharge-Pumped Xenon - Excimer Laser.
NASA Astrophysics Data System (ADS)
Zhu, Sheng-Bai
The present dissertation is dedicated to a theoretical study of the discharge pumped XeCl excimer laser. For a better description of our system, Two modelings which supplement each other from different angles have been successfully developed. The first one, a comprehensive kinetics model which can be applied to the detailed simulations of the temporal behavior of the discharge characteristics and laser performance, is constructed by a set of coupled first -order differential equations, such as the rate equations, the Boltzmann equation, the external electric circuit equations, the energy balance equation, and the equations of optical resonator. The starting and termination of the discharge are taken into deliberation for the first time, especially for the Blumlein case. Some 70 kinetic processes and 23 chemical species are included. Such a problem can only be numerically solved by means of an elaborate computer code. Another model, on the other hand, pays attention to the quasi-steady-state to facilitate parametric study. A group of rate coefficients for the kinetic processes involving free electrons are approximated by analytic expressions using numerical results compiled from computer code calculations. Explicit expressions of the number densities for all relevant chemical species are obtained. Among them, HCI(O), H, and Cl can never reach steady-state population. Time history of the concentrations for these species are computed instead. With the discussions about the effect of vibrational relaxation and state-to-state transfer in the upper energy level, and the discussions about the rotational structure, collisional broadening, and dissociation of the diatomic ground state, we have extensively investigated the spontaneous emission spectra, the small-signal gain, the non-saturable absorption, the steady-state laser output power, and various efficiencies. Saturation effects in laser oscillators and laser amplifiers are discussed as well. These topics relate to the
Theoretical studies on the mechanisms of laser rust removal
NASA Astrophysics Data System (ADS)
Wang, Yupei; Zhang, Zunyue; Liu, Guigeng; Song, Feng
2016-05-01
Our studies introduce the three-layer model of laser rust removal by rotational mirror scanner and develop dry laser cleaning model Firstly, theoretically simulate the temperature field of the rotational mirror scanner. Use the superposition model of the instantaneous thermal source point from a point to a line, from a line to an area, to simulate the temperature field distribution of rust and iron with thermal source on its surface and how it varies with time. And then take the temperature field distribution of rotational mirror scanner as the thermal load and use ANSYS to solve the thermal conductivity equations with complicated boundary conditions, and calculate the temperature field distribution it can be found that the temperature of the rust surface reaches the melting even the boiling point of the rust, so the rust can be removed by the ablation effect. From the thermal stress distribution of rust and iron in the depth orientation, the thermal stress existed in the rust and iron is large enough to remove the last rust layer in one time. So ablation layer, thermal stress removal layer and substrate consist of the three-layer model of laser rust removal by rotational mirror scanner.
NASA Astrophysics Data System (ADS)
Hanon, M. M.; Akman, E.; Genc Oztoprak, B.; Gunes, M.; Taha, Z. A.; Hajim, K. I.; Kacar, E.; Gundogdu, O.; Demir, A.
2012-06-01
Alumina ceramics have found wide range of applications from semiconductors, communication technologies, medical devices, automotive to aerospace industries. Processing of alumina ceramics is rather difficult due to its high degree of brittleness, hardness, low thermal diffusivity and conductivity. Rapid improvements in laser technologies in recent years make the laser among the most convenient processing tools for difficult-to-machine materials such as hardened metals, ceramics and composites. This is particularly evident as lasers have become an inexpensive and controllable alternative to conventional hole drilling methods. This paper reports theoretical and experimental results of drilling the alumina ceramic with thicknesses of 5 mm and 10.5 mm using milisecond pulsed Nd:YAG laser. Effects of the laser peak power, pulse duration, repetition rate and focal plane position have been determined using optical and Scanning Electron Microscopy (SEM) images taken from cross-sections of the drilled alumina ceramic samples. In addition to dimensional analysis of the samples, microstructural investigations have also been examined. It has been observed that, the depth of the crater can be controlled as a function of the peak power and the pulse duration for a single laser pulse application without any defect. Crater depth can be increased by increasing the number of laser pulses with some defects. In addition to experimental work, conditions have been simulated using ANYS FLUENT package providing results, which are in good agreement with the experimental results.
NASA Technical Reports Server (NTRS)
Brenner, Anita C.; Zwally, H. Jay; Bentley, Charles R.; Csatho, Bea M.; Harding, David J.; Hofton, Michelle A.; Minster, Jean-Bernard; Roberts, LeeAnne; Saba, Jack L.; Thomas, Robert H.; Yi, Donghui
2012-01-01
The primary purpose of the GLAS instrument is to detect ice elevation changes over time which are used to derive changes in ice volume. Other objectives include measuring sea ice freeboard, ocean and land surface elevation, surface roughness, and canopy heights over land. This Algorithm Theoretical Basis Document (ATBD) describes the theory and implementation behind the algorithms used to produce the level 1B products for waveform parameters and global elevation and the level 2 products that are specific to ice sheet, sea ice, land, and ocean elevations respectively. These output products, are defined in detail along with the associated quality, and the constraints, and assumptions used to derive them.
On some theoretical problems of laser wake-field accelerators
NASA Astrophysics Data System (ADS)
Bulanov, S. V.; Esirkepov, T. Zh.; Hayashi, Y.; Kiriyama, H.; Koga, J. K.; Kotaki, H.; Mori, M.; Kando, M.
2016-06-01
> Enhancement of the quality of laser wake-field accelerated (LWFA) electron beams implies the improvement and controllability of the properties of the wake waves generated by ultra-short pulse lasers in underdense plasmas. In this work we present a compendium of useful formulas giving relations between the laser and plasma target parameters allowing one to obtain basic dependences, e.g. the energy scaling of the electrons accelerated by the wake field excited in inhomogeneous media including multi-stage LWFA accelerators. Consideration of the effects of using the chirped laser pulse driver allows us to find the regimes where the chirp enhances the wake field amplitude. We present an analysis of the three-dimensional effects on the electron beam loading and on the unlimited LWFA acceleration in inhomogeneous plasmas. Using the conditions of electron trapping to the wake-field acceleration phase we analyse the multi-equal stage and multiuneven stage LWFA configurations. In the first configuration the energy of fast electrons is a linear function of the number of stages, and in the second case, the accelerated electron energy grows exponentially with the number of stages. The results of the two-dimensional particle-in-cell simulations presented here show the high quality electron acceleration in the triple stage injection-acceleration configuration.
On some theoretical problems of laser wake-field accelerators
NASA Astrophysics Data System (ADS)
Bulanov, S. V.; Esirkepov, T. Zh.; Hayashi, Y.; Kiriyama, H.; Koga, J. K.; Kotaki, H.; Mori, M.; Kando, M.
2016-06-01
Enhancement of the quality of laser wake-field accelerated (LWFA) electron beams implies the improvement and controllability of the properties of the wake waves generated by ultra-short pulse lasers in underdense plasmas. In this work we present a compendium of useful formulas giving relations between the laser and plasma target parameters allowing one to obtain basic dependences, e.g. the energy scaling of the electrons accelerated by the wake field excited in inhomogeneous media including multi-stage LWFA accelerators. Consideration of the effects of using the chirped laser pulse driver allows us to find the regimes where the chirp enhances the wake field amplitude. We present an analysis of the three-dimensional effects on the electron beam loading and on the unlimited LWFA acceleration in inhomogeneous plasmas. Using the conditions of electron trapping to the wake-field acceleration phase we analyse the multi-equal stage and multiuneven stage LWFA configurations. In the first configuration the energy of fast electrons is a linear function of the number of stages, and in the second case, the accelerated electron energy grows exponentially with the number of stages. The results of the two-dimensional particle-in-cell simulations presented here show the high quality electron acceleration in the triple stage injection-acceleration configuration.
Theoretical analysis of multispectral image segmentation criteria.
Kerfoot, I B; Bresler, Y
1999-01-01
Markov random field (MRF) image segmentation algorithms have been extensively studied, and have gained wide acceptance. However, almost all of the work on them has been experimental. This provides a good understanding of the performance of existing algorithms, but not a unified explanation of the significance of each component. To address this issue, we present a theoretical analysis of several MRF image segmentation criteria. Standard methods of signal detection and estimation are used in the theoretical analysis, which quantitatively predicts the performance at realistic noise levels. The analysis is decoupled into the problems of false alarm rate, parameter selection (Neyman-Pearson and receiver operating characteristics), detection threshold, expected a priori boundary roughness, and supervision. Only the performance inherent to a criterion, with perfect global optimization, is considered. The analysis indicates that boundary and region penalties are very useful, while distinct-mean penalties are of questionable merit. Region penalties are far more important for multispectral segmentation than for greyscale. This observation also holds for Gauss-Markov random fields, and for many separable within-class PDFs. To validate the analysis, we present optimization algorithms for several criteria. Theoretical and experimental results agree fairly well. PMID:18267494
Two-dimensional electronic spectroscopy using incoherent light: theoretical analysis.
Turner, Daniel B; Howey, Dylan J; Sutor, Erika J; Hendrickson, Rebecca A; Gealy, M W; Ulness, Darin J
2013-07-25
Electronic energy transfer in photosynthesis occurs over a range of time scales and under a variety of intermolecular coupling conditions. Recent work has shown that electronic coupling between chromophores can lead to coherent oscillations in two-dimensional electronic spectroscopy measurements of pigment-protein complexes measured with femtosecond laser pulses. A persistent issue in the field is to reconcile the results of measurements performed using femtosecond laser pulses with physiological illumination conditions. Noisy-light spectroscopy can begin to address this question. In this work we present the theoretical analysis of incoherent two-dimensional electronic spectroscopy, I((4)) 2D ES. Simulations reveal diagonal peaks, cross peaks, and coherent oscillations similar to those observed in femtosecond two-dimensional electronic spectroscopy experiments. The results also expose fundamental differences between the femtosecond-pulse and noisy-light techniques; the differences lead to new challenges and new opportunities. PMID:23176195
Theoretical Analysis of a Pulse Tube Regenerator
NASA Technical Reports Server (NTRS)
Roach, Pat R.; Kashani, Ali; Lee, J. M.; Cheng, Pearl L. (Technical Monitor)
1995-01-01
A theoretical analysis of the behavior of a typical pulse tube regenerator has been carried out. Assuming simple sinusoidal oscillations, the static and oscillatory pressures, velocities and temperatures have been determined for a model that includes a compressible gas and imperfect thermal contact between the gas and the regenerator matrix. For realistic material parameters, the analysis reveals that the pressure and, velocity oscillations are largely independent of details of the thermal contact between the gas and the solid matrix. Only the temperature oscillations depend on this contact. Suggestions for optimizing the design of a regenerator are given.
Theoretical and experimental investigation of multi-wavelength fiber laser
NASA Astrophysics Data System (ADS)
Wo, Jianghai; Sun, Qizhen
2009-08-01
In this paper, a method for realizing a stable multi-wavelength EDFL at room temperature is analyzed theoretically and obtained experimentally. We have proposed a multi-wavelength fiber ring cavity laser by using EDF as the gain medium. A F-P and a band-pass filter are inserted into the cavity to achieve the selection of multi-wavelength. Meanwhile, by inserting a nonlinear optical loop mirror (NOLM) in the linear cavity, which can suppresses the mode competition owing to the homogeneous broaden line in EDF and eliminates the unstable single wavelength lasing, stable output can be obtained at room temperature. As a result, power-stable, broad bandwidth and uniform multi-wavelength operations with narrow line-width and high side mode suppression ratio are obtained at room temperature. In addition, we also demonstrate a kind of tunable multi-wavelength EDFL based on multi-channel FBG (M-FBG). Four-wavelength output with the flatness and SNR of almost 1dB and more than 50dB is achieved and the output wavelength can be changed by applying stress on the M-FBG.
Theoretical simulation of a 2 micron airborne solid state laser anemometer
NASA Technical Reports Server (NTRS)
Imbert, Beatrice; Cariou, Jean-Pierre
1992-01-01
In the near future, military aircraft will need to know precisely their true airspeed in order to optimize flight conditions. In comparison with classical anemometer probes, an airborne Doppler lidar allows measurement of the air velocity without influence from aircraft aerodynamic disturbance. While several demonstration systems of heterodyne detection using a CO2 laser have been reported, improvements in the technology of solid state lasers have recently opened up the possibility that these devices can be used as an alternative to CO2 laser systems. In particular, a diode pumped Tm:Ho:YAG laser allows a reliable compact airborne system with an eye safe wavelength (lambda = 2.09 microns) to be achieved. The theoretical study of performances of a coherent lidar using a solid state diode pumped Tm:Ho:YAG laser, caled SALSA, for measuring aircraft airspeed relative to atmospheric aerosols is described. A computer simulation was developed in order to modelize the Doppler anemometer in the function of atmospheric propagation and optical design. A clever analysis of the power budget on the detector area allows optical characteristic parameters of the system to be calculated, and then it can be used to predict performances of the Doppler system. Estimating signal to noise ratios (SNR) and heterodyne efficiency provides the available energy of speed measurement as well as a useful measurement of the alignment of the backscattered and reference fields on the detector.
Theoretical Study of the Free-Electron Laser Sideband Instability
NASA Astrophysics Data System (ADS)
Yang, Tser-Yuan Brian
Detailed properties of the sideband instability are investigated for a helical wiggler free-electron laser. The model describes the nonlinear evolution of a right-circularly polarized primary electromagnetic wave. The nonlinear evolution of a free electron laser is investigated within the framework of a macroclump model for the trapped electrons. The macroclump model assumes that the trapped electrons can be treated as tightly bunched macroclumps that interact coherently with the radiation field. The nonlinear evolution of the primary signal is examined when there is no spatial variation of the wave amplitude and phase. The evolution equations are reduced to quadrature, and the maximum excursion of the wave amplitude a_{s,max} is calculated analytically. The nonlinear evolution of the sideband instability is investigated. In the present analysis, the sideband signals are treated as perturbations (not necessarily small) about a constant-amplitude primary electromagnetic wave with slowly varying phase. The coupled orbit and field equations are investigated analytically and numerically over a wide range of system parameters to determine detailed scaling properties of the sideband instability. The results of the present analysis suggest that free electron lasers operating with system parameters corresponding to the strong -pump regime are least vulnerable to the sideband instability. Detailed properties of the sideband instability are investigated for small-amplitude perturbations about a quasi-steady state. A formal dispersion relation is derived for perturbations about a general equilibrium distribution f^{0}(gamma_sp{0 }{'}) which may include both trapped and untrapped electrons. For the case where only trapped electrons are present, the dispersion relation is reduced to a simple analytical form. Detailed properties of the sideband instability are investigated for the case where the trapped electrons uniformly populate the ponderomotive potential up to an energy
A theoretical investigation of laser-sustained plasma thruster
NASA Technical Reports Server (NTRS)
Jeng, San-Mou; Keefer, Dennis
1987-01-01
A numerical code has been successfully developed for the investigation of thruster performance using a laser-sustained hydrogen plasma as the propellant. The plasma was sustained using a 10.6-micron CO2 laser beam focused at different positions within the thruster. The physical model assumed that plasma is in thermodynamical equilibrium (LTE), and geometric ray tracing was adopted to describe the laser beam. The steady-state, axisymmetric, Navier-Stokes equations coupled with the laser power absorption process have been solved numerically. A pressure based Navier-Stokes numerical solver using body-fitted coordinates was used to calculate the laser-supported rocket flow which includes both subsonic and supersonic flow regions. From the limited parametric study, which did not try to optimize the rocket performance, it was found that better performance was obtained when the laser beam was focused closer to the rocket throat.
NASA Technical Reports Server (NTRS)
Jones, W. S.; Forsyth, J. B.; Skratt, J. P.
1979-01-01
The laser rocket systems investigated in this study were for orbital transportation using space-based, ground-based and airborne laser transmitters. The propulsion unit of these systems utilizes a continuous wave (CW) laser beam focused into a thrust chamber which initiates a plasma in the hydrogen propellant, thus heating the propellant and providing thrust through a suitably designed nozzle and expansion skirt. The specific impulse is limited only by the ability to adequately cool the thruster and the amount of laser energy entering the engine. The results of the study showed that, with advanced technology, laser rocket systems with either a space- or ground-based laser transmitter could reduce the national budget allocated to space transportation by 10 to 345 billion dollars over a 10-year life cycle when compared to advanced chemical propulsion systems (LO2-LH2) of equal capability. The variation in savings depends upon the projected mission model.
Akman, E.; Atalay, B.; Candan, L.; Canel, T.; Demir, A.; Demir, P.; Erturk, S.; Genc, B.; Kacar, E.; Kenar, N.; Koymen, E.; Mutlu, M.; Sinmazcelik, T.; Urhan, O.
2007-04-23
Laser Technologies Research and Application Center (LATARUM) was established in 2005 with interdisciplinary cooperation to obtain product based on projects, to train personnel with at highest academic level with knowledge to use latest technology. There are electro-optics, laser material processing and modelling and simulation groups working on projects. Theoretical modeling studies are performed for x-ray laser media. Ne-like nickel and iron and Ni-like tin and molybdenum x-ray laser media for different pumping laser configurations have been modeled using EHYBRID. Theoretical and experimental studies on spectrometer design for wavelength range between X-ray and IR are carried out by electro-optic group. Material processing studies using Nd-YAG laser are performed. Materials of titanium, aluminum and stainless steel have been welded in different laser pulse, power, and repetition rate conditions. Optimum parameters for these welding processes have been obtained.
Analysis of a theoretically optimized transonic airfoil
NASA Technical Reports Server (NTRS)
Lores, M. E.; Burdges, K. P.; Shrewsbury, G. D.
1978-01-01
Numerical optimization was used in conjunction with an inviscid, full potential equation, transonic flow analysis computer code to design an upper surface contour for a conventional airfoil to improve its supercritical performance. The modified airfoil was tested in a compressible flow wind tunnel. The modified airfoil's performance was evaluated by comparison with test data for the baseline airfoil and for an airfoil developed by optimization of leading edge of the baseline airfoil. While the leading edge modification performed as expected, the upper surface re-design did not produce all of the expected performance improvements. Theoretical solutions computed using a full potential, transonic airfoil code corrected for viscosity were compared to experimental data for the baseline airfoil and the upper surface modification. These correlations showed that the theory predicted the aerodynamics of the baseline airfoil fairly well, but failed to accurately compute drag characteristics for the upper surface modification.
A theoretical evaluation of laser-sustained plasma thruster performance
NASA Technical Reports Server (NTRS)
Jeng, San-Mou; Keefer, Dennis
1987-01-01
An extensive numerical experiment has been conducted to evaluate rocket thruster performance using a laser-sustained hydrogen plasma as the propellant. The plasma was sustained using a 30 kW CO2 laser beam operated at 10.6 microns focused inside the thruster. The steady-state Navier-Stokes equations coupled with the laser power absorption process have been solved numerically. A pressure based Navier-Stokes solver using body-fitted coordinate was used to calculate the laser-supported rocket flow which included both recirculating and transonic flow regions. The local thermodynamic equilibrium (LTE) assumption was used for the plasma thermophysical and optical properties. Geometric ray tracing was adopted to describe the laser beam. Several different throat size thrusters operated at 150 and 300 kPa chamber stagnation pressure were studied. It was found that the thruster performance (vacuum specific impulse) was highly dependent on the operating conditions, and a properly designed laser supported thruster can attain a specific impulse around 1500 secs. The heat loading on the thruster wall was also estimated and was in the range of that for a conventional chemical rocket.
An inverse free electron laser accelerator: Experiment and theoretical interpretation
Fang, Jyan-Min
1997-06-01
Experimental and numerical studies of the Inverse Free Electron Laser using a GW-level 10.6 {mu}m CO{sub 2} laser have been carried out at Brookhaven`s Accelerator Test Facility. An energy gain of 2.5 % ({Delta}E/E) on a 40 MeV electron beam has been observed E which compares well with theory. The effects on IFEL acceleration with respect to the variation of the laser electric field, the input electron beam energy, and the wiggler magnetic field strength were studied, and show the importance of matching the resonance condition in the IFEL. The numerical simulations were performed under various conditions and the importance of the electron bunching in the IFEL is shown. The numerical interpretation of our IFEL experimental results was examined. Although good numerical agreement with the experimental results was obtained, there is a discrepancy between the level of the laser power measured in the experiment and used in the simulation, possibly due to the non-Gaussian profile of the input high power laser beam. The electron energy distribution was studied numerically and a smoothing of the energy spectrum by the space charge effect at the location of the spectrometer was found, compared with the spectrum at the exit of the wiggler. The electron bunching by the IFEL and the possibility of using the IFEL as an electron prebuncher for another laser-driven accelerator were studied numerically. We found that bunching of the electrons at 1 meter downstream from the wiggler can be achieved using the existing facility. The simulation shows that there is a fundamental difference between the operating conditions for using the IFEL as a high gradient accelerator, and as a prebuncher for another accelerator.
Theoretical investigation on breaking plant cell wall by laser
NASA Astrophysics Data System (ADS)
Chen, Liang-cai; Wang, Jin-ji; Ma, Peng; Zuo, Du-luo; Wang, Xin-bing; Cheng, Zu-hai
2012-03-01
The experiment collected some spinach leaves which were irradiated by pulsed CO2 laser with energy 5.6J, 8.0J and 9.5J respectively. Each of them was soaked in three kinds of solvents (water, ethanol, the mixture of ethanol and petroleum ether) respectively. The experiment shows that the ethanol solution which contains the irradiated leaves turn dark green than the ethanol solution which contains the intact leaves and the color of solution with the leaves irradiated by CO2 laser with 9.5J changes the most significantly. Further, selective excitation on the molecular level of the cell wall were used to explain the phenomenon.
Theoretical investigation on breaking plant cell wall by laser
NASA Astrophysics Data System (ADS)
Chen, Liang-cai; Wang, Jin-ji; Ma, Peng; Zuo, Du-luo; Wang, Xin-bing; Cheng, Zu-hai
2011-11-01
The experiment collected some spinach leaves which were irradiated by pulsed CO2 laser with energy 5.6J, 8.0J and 9.5J respectively. Each of them was soaked in three kinds of solvents (water, ethanol, the mixture of ethanol and petroleum ether) respectively. The experiment shows that the ethanol solution which contains the irradiated leaves turn dark green than the ethanol solution which contains the intact leaves and the color of solution with the leaves irradiated by CO2 laser with 9.5J changes the most significantly. Further, selective excitation on the molecular level of the cell wall were used to explain the phenomenon.
NASA Technical Reports Server (NTRS)
1988-01-01
Near real-time Lageos laser ranging data are analyzed in terms of range bias, time bias, and internal precision, and estimates for earth orientation parameters X(sub p), Y(sub p), and UT1 are obtained. The results of these analyses are reported in a variety of formats. Copies of monthly summaries from November, 1986 through November, 1987 are included.
An intracavity 16-[mu]m Raman laser: A theoretical investigation
Botha, L.R.; Heerden, S.P. van . Laser Research Dept.)
1994-12-01
A theoretical model describing the dynamics of an intracavity 16-[mu]m laser was developed. This laser consists of a TEA-CO[sub 2] laser with an intracavity Raman cell. The Raman medium could be either hydrogen or deuterium, depending on the required wavelength. Stokes, anti-Stokes, and pump coupling were considered. Output energies as well as pulse shapes were calculated. Optimum output coupling was also determined. The model predicted that the intracavity Raman laser could be a viable alternative to a conventional multipass Raman cell for generating intense 16-[mu]m pulses.
Laser speckle contrast imaging: theoretical and practical limitations.
Briers, David; Duncan, Donald D; Hirst, Evan; Kirkpatrick, Sean J; Larsson, Marcus; Steenbergen, Wiendelt; Stromberg, Tomas; Thompson, Oliver B
2013-06-01
When laser light illuminates a diffuse object, it produces a random interference effect known as a speckle pattern. If there is movement in the object, the speckles fluctuate in intensity. These fluctuations can provide information about the movement. A simple way of accessing this information is to image the speckle pattern with an exposure time longer than the shortest speckle fluctuation time scale-the fluctuations cause a blurring of the speckle, leading to a reduction in the local speckle contrast. Thus, velocity distributions are coded as speckle contrast variations. The same information can be obtained by using the Doppler effect, but producing a two-dimensional Doppler map requires either scanning of the laser beam or imaging with a high-speed camera: laser speckle contrast imaging (LSCI) avoids the need to scan and can be performed with a normal CCD- or CMOS-camera. LSCI is used primarily to map flow systems, especially blood flow. The development of LSCI is reviewed and its limitations and problems are investigated. PMID:23807512
Theoretical analysis of sheet metal formability
NASA Astrophysics Data System (ADS)
Zhu, Xinhai
Sheet metal forming processes are among the most important metal-working operations. These processes account for a sizable proportion of manufactured goods made in industrialized countries each year. Furthermore, to reduce the cost and increase the performance of manufactured products, in addition to the environmental concern, more and more light weight and high strength materials have been used as a substitute to the conventional steel. These materials usually have limited formability, thus, a thorough understanding of the deformation processes and the factors limiting the forming of sound parts is important, not only from a scientific or engineering viewpoint, but also from an economic point of view. An extensive review of previous studies pertaining to theoretical analyses of Forming Limit Diagrams (FLDs) is contained in Chapter I. A numerical model to analyze the neck evolution process is outlined in Chapter II. With the use of strain gradient theory, the effect of initial defect profile on the necking process is analyzed. In the third chapter, the method proposed by Storen and Rice is adopted to analyze the initiation of localized neck and predict the corresponding FLDs. In view of the fact that the width of the localized neck is narrow, the deformation inside the neck region is constrained by the material in the neighboring homogeneous region. The relative rotation effect may then be assumed to be small and is thus neglected. In Chapter IV, Hill's 1948 yield criterion and strain gradient theory are employed to obtain FLDs, for planar anisotropic sheet materials by using bifurcation analysis. The effects of the strain gradient coefficient c and the material anisotropic parameters R's on the orientation of the neck and FLDs are analyzed in a systematic manner and compared with experiments. In Chapter V, Hill's 79 non-quadratic yield criterion with a deformation theory of plasticity is used along with bifurcation analyses to derive a general analytical
Laser Threat Analysis System (LTAS)
NASA Astrophysics Data System (ADS)
Pfaltz, John M.; Richardson, Christina E.; Ruiz, Abel; Barsalou, Norman; Thomas, Robert J.
2002-11-01
LTAS is a totally integrated modeling and simulation environment designed for the purpose of ascertaining the susceptibility of Air Force pilots and air crews to optical radiation threats. Using LTAS, mission planners can assess the operational impact of optically directed energy weapons and countermeasures. Through various scenarios, threat analysts are able to determine the capability of laser threats and their impact on operational missions including the air crew's ability to complete their mission effectively. Additionally, LTAS allows the risk of laser use on training ranges and the requirement for laser protection to be evaluated. LTAS gives mission planners and threat analysts complete control of the threat environment including threat parameter control and placement, terrain mapping (line-of-site), atmospheric conditions, and laser eye protection (LEP) selection. This report summarizes the design of the final version of LTAS, and the modeling methodologies implemented to accomplish analysis.
Physical Violence between Siblings: A Theoretical and Empirical Analysis
ERIC Educational Resources Information Center
Hoffman, Kristi L.; Kiecolt, K. Jill; Edwards, John N.
2005-01-01
This study develops and tests a theoretical model to explain sibling violence based on the feminist, conflict, and social learning theoretical perspectives and research in psychology and sociology. A multivariate analysis of data from 651 young adults generally supports hypotheses from all three theoretical perspectives. Males with brothers have…
Approximate Analysis of Semiconductor Laser Arrays
NASA Technical Reports Server (NTRS)
Marshall, William K.; Katz, Joseph
1987-01-01
Simplified equation yields useful information on gains and output patterns. Theoretical method based on approximate waveguide equation enables prediction of lateral modes of gain-guided planar array of parallel semiconductor lasers. Equation for entire array solved directly using piecewise approximation of index of refraction by simple functions without customary approximation based on coupled waveguid modes of individual lasers. Improved results yield better understanding of laser-array modes and help in development of well-behaved high-power semiconductor laser arrays.
Theoretical and experimental investigations of injection-locked signal extraction of Tm:YAG laser
NASA Astrophysics Data System (ADS)
Wu, Chunting; Chen, Fei; Dai, Tongyu; Ju, Youlun
2015-11-01
Injection-seeded is an effective method to obtain high-power pulsed laser with pure spectrum, which is useful to be the laser source of a coherent Doppler LIDAR or a differential absorption LIDAR. In order to achieve the useful injection-locked signal, mode matching between master laser and slave laser is necessary. In this paper, various factors influencing on the extraction of injection-locked signal are analyzed theoretically. Then, experiments on an injection-seeded Tm:YAG laser are carried on, and injection-locked signal is extracted successfully. Moreover, an injection-seeded Tm:YAG laser is achieved, with pulsed single-frequency at 2013 nm, output energy of 3.16 mJ, and pulse width of 238.7 ns, at a repetition rate of 100 Hz.
Theoretical evaluation of electron-beam-excited vacuum-ultraviolet F2 lasers
NASA Astrophysics Data System (ADS)
Kim, Y.-P.; Obara, M.; Suzuki, T.
1986-03-01
A theoretical kinetic model for an electron-beam-excited F2 laser (157 nm) was successfully developed to evaluate the performance characteristics in terms of electron-beam excitation rate, pumping pulse width, and total operating pressure. As a result, it is made clear that a high excitation rate (above 0.2 MW/cu cm atm) is essential to obtain efficient laser operation. An intrinsic laser efficiency of 4.3 percent is obtainable when a 6.5-atm mixture of He-F2 = 1000/1 is pumped at an excitation rate of 0.5 MW/cu cm atm, giving a laser output of over 4 J/l. It is also found that a higher laser output is obtainable with increasing total operating pressure, while the intrinsic laser efficiency slowly decreases.
Thermoelastic analysis of laser iridectomies.
Srivatsa, L P
1989-07-01
We have attempted to derive the stress-strain-temperature relationships of the iris stroma subject to a restrictive thermal burn from a laser. The corresponding displacement equation embodies the mechanical impulses due to this thermal insult. This thermoelastic analysis of laser iridectomy attempts to describe the mechanism involved in the surgical procedure. It is clear from this study that the flexural behaviour of the iris is principally due to thermal insult and not due to vapour bubbles or redistribution of the aqueous. PMID:2755108
Theoretical analysis of planar pulse microwiggler
Qing-Xiang Liu |; Yong Xu
1995-12-31
The Magnetic field distributions of a planar pulse microwiggler are studied analytically and numerically. Exact solutions of two-dimensional magnetic fields are derived, which show that along the electron axis the fields have a variation close enough to a sine wave. We also investigate wiggler field errors due to machining tolerance and effects of the field errors on trajectories of electron with the help numerical simulations. The results are critical for successful operation of CAEP compact free-electron laser experiment under preparation.
Fast mode-hop-free acousto-optically tuned laser: theoretical and experimental investigations.
Bösel, André; Salewski, Klaus-Dieter
2009-02-10
We developed a theory that describes fast mode-hop-free tuning of an external cavity diode laser in Littrow configuration with two acousto-optic modulators (AOMs) inside the laser cavity. The theory is based on synchronous shifting of the external cavity modes and the Littrow grating selectivity. It allows calculating the driving signals of both AOMs in order to reach a desired temporal variation of the laser frequency, including particularly fast tuning as well as an arbitrary shape of the tuning function. Furthermore, we present a laser setup for which the needed signals for both AOMs are generated by two direct digital synthesizer circuits. Thereby we were able to verify the theoretical predictions experimentally, achieving, e.g., sinusoidal single-mode tuning of the laser frequency over 40 GHz at a repetition rate of 10 kHz and over 12 GHz at 25 kHz. Finally, the limitations of the theory are discussed. PMID:19209191
Nitrogen lasers, optical devices of variable gain coefficient: Theoretical considerations
NASA Astrophysics Data System (ADS)
Sarikhani, S.; Hariri, A.
2010-01-01
Based on our previous measurements on the gain values by employing an oscillator amplifier (OSC-AMP) N2-laser system of variable AMP electrode lengths, a calculation has been made for evaluation of the gain coefficient using rate equations. It is shown both numerically and analytically that small signal gain, g0, is following our experimental observations of g0=m+n/lAMP, where m and n are some constants, and l AMP is the length of the amplifier. For simplifying the calculation in the OCS-AMP circuit, an experimental condition of imposing the OSC-open-circuit operation has been applied, where the voltage waveforms from the relevant sections of the Blumlein circuit have been used for evaluation of the circuit parameters. Due to the fact that during the past years different cross-sections for the electron-impact excitations from the ground to the upper, N2( C), and lower, N2( B), have been introduced, our experimental observations have also been applied to examine the effect of introduced electron impact-excitation cross-sections on the g0(lAMP) behavior.
NASA Astrophysics Data System (ADS)
Zuo, Wanlong; Ben, Shuai; Lv, Hang; Zhao, Lei; Guo, Jing; Liu, Xue-Shen; Xu, Haifeng; Jin, Mingxing; Ding, Dajun
2016-05-01
Nonsequential double ionization (NSDI) of carbon disulfide CS2 in strong 800-nm laser fields is studied experimentally and theoretically. A knee structure is observed in the intensity-dependent double ionization (DI) yield in linearly polarized laser fields, which exhibits a strong dependence on the laser ellipticity. The electron momentum distributions and energy trajectories after DI in both linearly and circularly polarized laser fields are investigated by employing the two-dimensional classical ensemble method. The results clearly show the evidence of NSDI in the strong-field DI of CS2 molecules. It is demonstrated that, similar to that of atoms, NSDI of CS2 molecules is produced via laser-driven electron recollision with the ion core and presents electron-electron correlations in the process. Analysis indicates that both mechanisms in atomic strong-field NSDI, i.e., recollision impact ionization and recollision excitation with subsequent ionization, may also be contributed to NSDI of CS2 in strong laser fields. Further studies are no doubt necessary for a full understanding of the underlying physical mechanism of molecular strong-field NSDI, due to the multicenter character of the molecular structure and the complex molecular excited states that could be involved in the ionization.
Theoretical analysis of the EWEC report
NASA Technical Reports Server (NTRS)
1976-01-01
This analytic investigation shows how the electromagnetic wave energy conversion (EWEC) device, as used for solar-to-electric power conversion, is significantly different from solar cells, with respect to principles of operation. An optimistic estimate of efficiency is about 80% for a full-wave rectifying configuration with solar radiation normally incident. This compares favorably with the theoretical maximum for a CdTe solar cell (23.5%), as well as with the efficiencies of more familiar cells: Si (19.5%), InP (21.5%), and GaAs (23%). Some key technological issues that must be resolved before the EWEC device can be realized are identified. Those issues include: the fabrication of a pn semi-conductor junction with no permittivity resonances in the optical band; and the efficient channeling of the power received by countless microscopic horn antennas through a relatively few number of wires.
Theoretical and experimental research on the ˜980-nm Yb-doped fiber laser
NASA Astrophysics Data System (ADS)
Wang, Yanshan; Ke, Weiwei; Ma, Yi; Sun, Yinhong; Feng, Yujun
2016-07-01
The output properties of the ˜980-nm Yb-doped fiber laser versus pump power and core-cladding ratio of gain fiber, also the amplified spontaneous emission (ASE) at different wavelengths of seed laser, are investigated theoretically. An all-fiber amplifier based on different wavelengths of seed laser at 974.4, 977, and 981.7 nm brings the studies on parasitic oscillation and ASE in the ˜980-nm Yb-doped fiber amplifier. Through the theoretical and experimental research, we found that the controlling of three-level ASE around ˜980-nm is pivotal for obtaining a high-power 980-nm Yb-doped fiber amplifier.
Theoretical Studies on Intense Laser Produced Quasi-Monoenergetic Particle Beams
Sheng, Z. M.; Zhang, J.; Wang, W. M.; Yan, X. Q.; Chen, M.; Chen, J. E.
2009-07-25
A brief review is presented on our recent theoretical studies on the quasi-monoenergetic electron and proton beam generation by intense laser pulses. For the electron beam generation from laser wakefields, the mechanisms of electron injection by a laser pulse in the colliding geometry are investigated. It shows that there exist two mechanisms, which are called collective injection and stochastic injection. The number of injection electrons is studied as a function of the injection pulse intensity, pulse duration, as well as laser polarization. The injection by a transverse intersecting laser pulse is also investigated, which appears relatively easy for experimental setup. The required laser parameters are comparable to the colliding geometry. The proton acceleration by collisionless electrostatic shock waves is investigated and shock wave propagation through the interface of two targets with different ion species is simulated. It is found that ions with a relatively large charge-to-mass ratio can be accelerated successively in two counter-propagating shocks when they are overtaken by shock fronts until their energy is larger than the scalar potential of the shock waves. A scheme of ion acceleration in the new parameter regime called phase stable acceleration is proposed with the use of circularly-polarized laser pulses irradiating on very thin solid targets, which would enable one to obtain quasi-monoenergetic proton beams of multi-100 MeV with 100 TW-class lasers.
Theoretical analysis of HVAC duct hanger systems
NASA Technical Reports Server (NTRS)
Miller, R. D.
1987-01-01
Several methods are presented which, together, may be used in the analysis of duct hanger systems over a wide range of frequencies. The finite element method (FEM) and component mode synthesis (CMS) method are used for low- to mid-frequency range computations and have been shown to yield reasonably close results. The statistical energy analysis (SEA) method yields predictions which agree with the CMS results for the 800 to 1000 Hz range provided that a sufficient number of modes participate. The CMS approach has been shown to yield valuable insight into the mid-frequency range of the analysis. It has been demonstrated that it is possible to conduct an analysis of a duct/hanger system in a cost-effective way for a wide frequency range, using several methods which overlap for several frequency bands.
A theoretical analysis of vertical flow equilibrium
Yortsos, Y.C.
1992-01-01
The assumption of Vertical Flow Equilibrium (VFE) and of parallel flow conditions, in general, is often applied to the modeling of flow and displacement in natural porous media. However, the methodology for the development of the various models is rather intuitive, and no rigorous method is currently available. In this paper, we develop an asymptotic theory using as parameter the variable R{sub L} = (L/H){radical}(k{sub V})/(k{sub H}). It is rigorously shown that present models represent the leading order term of an asymptotic expansion with respect to 1/R{sub L}{sup 2}. Although this was numerically suspected, it is the first time that is is theoretically proved. Based on the general formulation, a series of models are subsequently obtained. In the absence of strong gravity effects, they generalize previous works by Zapata and Lake (1981), Yokoyama and Lake (1981) and Lake and Hirasaki (1981), on immiscible and miscible displacements. In the limit of gravity-segregated flow, we prove conditions for the fluids to be segregated and derive the Dupuit and Dietz (1953) approximations. Finally, we also discuss effects of capillarity and transverse dispersion.
Landscape analysis: Theoretical considerations and practical needs
Godfrey, A.E.; Cleaves, E.T.
1991-01-01
Numerous systems of land classification have been proposed. Most have led directly to or have been driven by an author's philosophy of earth-forming processes. However, the practical need of classifying land for planning and management purposes requires that a system lead to predictions of the results of management activities. We propose a landscape classification system composed of 11 units, from realm (a continental mass) to feature (a splash impression). The classification concerns physical aspects rather than economic or social factors; and aims to merge land inventory with dynamic processes. Landscape units are organized using a hierarchical system so that information may be assembled and communicated at different levels of scale and abstraction. Our classification uses a geomorphic systems approach that emphasizes the geologic-geomorphic attributes of the units. Realm, major division, province, and section are formulated by subdividing large units into smaller ones. For the larger units we have followed Fenneman's delineations, which are well established in the North American literature. Areas and districts are aggregated into regions and regions into sections. Units smaller than areas have, in practice, been subdivided into zones and smaller units if required. We developed the theoretical framework embodied in this classification from practical applications aimed at land use planning and land management in Maryland (eastern Piedmont Province near Baltimore) and Utah (eastern Uinta Mountains). ?? 1991 Springer-Verlag New York Inc.
Landscape analysis: Theoretical considerations and practical needs
NASA Astrophysics Data System (ADS)
Godfrey, Andrew E.; Cleaves, Emery T.
1991-03-01
Numerous systems of land classification have been proposed. Most have led directly to or have been driven by an author's philosophy of earth-forming processes. However, the practical need of classifying land for planning and management purposes requires that a system lead to predictions of the results of management activities. We propose a landscape classification system composed of 11 units, from realm (a continental mass) to feature (a splash impression). The classification concerns physical aspects rather than economic or social factors; and aims to merge land inventory with dynamic processes. Landscape units are organized using a hierarchical system so that information may be assembled and communicated at different levels of scale and abstraction. Our classification uses a geomorphic systems approach that emphasizes the geologic-geomorphic attributes of the units. Realm, major division, province, and section are formulated by subdividing large units into smaller ones. For the larger units we have followed Fenneman's delineations, which are well established in the North American literature. Areas and districts are aggregated into regions and regions into sections. Units smaller than areas have, in practice, been subdivided into zones and smaller units if required. We developed the theoretical framework embodied in this classification from practical applications aimed at land use planning and land management in Maryland (eastern Piedmont Province near Baltimore) and Utah (eastern Uinta Mountains).
Theoretical and experimental analysis of mylar balloons
NASA Astrophysics Data System (ADS)
Romaguera, Antonio; Démery, Vincent; Davidovitch, Benny
2015-03-01
In the present study, we present a theoretical and experimental study of the problem known as the mylar balloon shape. The problem consists of inflating a balloon made of two circular discs of an unstretchable material sewed at the edge. A solution for this problem was given by W. H. Paulsen in 1994 for constrain free. In our analyzes, we fixed the height of the balloon and measure the inflated diameter. As a result, we were able to map the constrained shape in terms of the original mylar balloon's shape. The basic assumption of this problem is that the gravitational, stretching and bending energies are negligible compared with the mechanical energy - pV . Controlling the pressure and the height of the balloon, we are able to find the condition where these assumptions fail, specially in the limit h --> 0 for fixed p. A remarkable feature of this problem is the presence of wrinkles across the equator of the balloon. A precise description for that region must include the large deformation from the flat disc initial condition. We will also present some experimental data on the wrinkle's length and its connection with the pressure and height of the balloon.
Laser power conversion system analysis, volume 2
NASA Technical Reports Server (NTRS)
Jones, W. S.; Morgan, L. L.; Forsyth, J. B.; Skratt, J. P.
1979-01-01
The orbit-to-ground laser power conversion system analysis investigated the feasibility and cost effectiveness of converting solar energy into laser energy in space, and transmitting the laser energy to earth for conversion to electrical energy. The analysis included space laser systems with electrical outputs on the ground ranging from 100 to 10,000 MW. The space laser power system was shown to be feasible and a viable alternate to the microwave solar power satellite. The narrow laser beam provides many options and alternatives not attainable with a microwave beam.
Analysis and studies on the threats to the composite material from laser
NASA Astrophysics Data System (ADS)
Xu, Wei; Yao, Weixing; Wang, Liwei; Wang, Guoliang; Xie, Fang
2015-10-01
It is always an attracting research field for the interaction between laser and matters. The interaction between laser and matters is used not only in the natural science, but also in practical application, for example, laser machine, laser weapon, laser ablations and so on. In this paper, we will give the model for the damage effect of the composite materials caused by the superpower laser weapons. Mechanism of the laser damage on the composite materials have been researched and modeled by the numerical analysis methods. Through the designed model, we analyzed the temperature and the stress fields of the composite material after the superpower lasers attacks with different power densities. By analyzing these modeling results, we achieved some conclusions on the threats to the composite materials from the superpower lasers. From the results, we have obtained the Irradiated threshold from the Laser. This paper will provide the theoretical foundations for the anti-laser design of the composite materials.
Theoretical study on isotope separation of an ytterbium atomic beam by laser deflection
NASA Astrophysics Data System (ADS)
Zhou, Min; Xu, Xin-Ye
2014-01-01
Isotope separation by laser deflecting an atomic beam is analyzed theoretically. Interacting with a tilted one-dimensional optical molasses, an ytterbium atomic beam is split into multi-beams with different isotopes like 172Yb,173Yb, and 174Yb. By using the numerical calculation, the dependences of the splitting angle on the molasses laser intensity and detuning are studied, and the optimal parameters for the isotope separation are also investigated. Furthermore, the isotope separation efficiency and purity are estimated. Finally a new scheme for the efficient isotope separation is proposed. These findings will give a guideline for simply obtaining pure isotopes of various elements.
Medial Cochlear Efferent Function: A Theoretical Analysis
NASA Astrophysics Data System (ADS)
Mountain, David C.
2011-11-01
Since the discovery of the cochlear efferent system, many hypotheses have been put forth for its function. These hypotheses for its function range from protecting the cochlea from over stimulation to improving the detection of sounds in noise. It is known that the medial efferent system innervates the outer hair cells and that stimulation of this system reduces basilar membrane and auditory nerve sensitivity which suggests that this system acts to decrease the gain of the cochlear amplifier. Here I present modeling results as well as analysis of published experimental data that suggest that the function of the medial efferent reflex is to decrease the cochlear amplifier gain by just the right amount so that the nonlinearity in the basilar membrane response lines up perfectly with the inner hair cell nonlinear transduction process to produce a hair cell receptor potential that is proportional to the logarithm of the sound pressure level.
Graph theoretical analysis of climate data
NASA Astrophysics Data System (ADS)
Zerenner, T.; Hense, A.
2012-04-01
Applying methods from graph and network theory to climatological data is a quite new approach and contains numerous difficulties. The atmosphere is a high dimensional and complex dynamical system which per se does not show a network-like structure. It does not consist of well-defined nodes and edges. Thus considering such a system as a network or graph inevitably involves radical simplifications and ambiguities. Nevertheless network analysis has provided useful results for different kinds of complex systems for example in biology or medical science (neural and gene interaction networks). The application of these methods on climate data provides interesting results as well. If the network construction is based on the correlation matrix of the underlying data, the resulting network structures show many well known patterns and characteristics of the atmospheric circulation (Tsonis et al. 2006, Donges et al. 2009). The interpretation of these network structures is yet questionable. Using Pearson Correlation for network construction does not allow to differ between direct and indirect dependencies. An edge does not necessarily represent a causal connection. An interpretation of these structures for instance concerning the stability of the climate system is therefore doubtful. Gene interaction networks for example are often constructed using partial correlations (Wu et al. 2003), which makes it possible to distinguish between direct and indirect dependencies. Although a high value of partial correlation does not guarantee causality it is a step in the direction of measuring causal dependencies. This approach is known as Gaussian Graphical Models, GGMs. For high dimensional datasets such as climate data partial correlations can be obtained by calculating the precision matrix, the inverse covariance matrix. Since the maximum likelihood estimates of covariance matrices of climate datasets are singular the precision matrices can only be estimated for example by using the
Unusual Inorganic Biradicals: A Theoretical Analysis
Miliordos, Evangelos; Ruedenberg, Klaus; Xantheas, Sotiris S.
2013-05-27
Triatomic ions in the series FX_{2}^{+}, where X = O, S, Se, Te and Po are the terminal atoms, exhibit unusually high biradical characters (0.76 < β < 0.92), as measured from the analysis of Multi-Reference Configuration Interaction (MRCI) wavefunctions. Candidates in this series have the largest biradical character among the homologous, 18 valence electron CX_{2}^{2-}, NX_{2}^{-}, X_{3} and OX_{2} (X = O, S, Se, Te and Po) systems. In the same scale the biradical character of ozone (O_{3}) is just 0.19, whereas that of trimethylenemethane [C(CH_{2})_{3}] is 0.97 (β=1 for an "ideal" biradical). For the 24 electron XO_{2} series, consisting of molecules with two oxygen atoms and a moiety X that is isoelectronic to oxygen, i.e. X= CH_{2}, NH, O, F^{+}, the singlet (S) state is lower than the triplet (T) one and the S-T splitting as well the barrier between their "open" and "ring" configurations was found to depend linearly with the inverse of the biradical character.
Cryogenic Laser Calorimetry for Impurity Analysis
NASA Technical Reports Server (NTRS)
Swimm, R. T.
1985-01-01
The results of a one-year effort to determine the applicability of laser-calorimetric spectroscopy to the study of deep-level impurities in silicon are presented. Critical considerations for impurity analysis by laser-calorimetric spectroscopy are discussed, the design and performance of a cryogenic laser calorimeter is described, and measurements of background absorption in high-purity silicon are presented.
Theoretical and experimental study for shortening laser pulse width by pinhole plasma shutter
NASA Astrophysics Data System (ADS)
Jaafari, Ebrahim; Kavosh Tehrani, Masoud; Mohammad, Mohammad Malek; Saghafifar, Hossian
2015-05-01
In this article, a theoretical model is presented to calculate the laser clipped pulse temporal width by the pinhole plasma shutter, and then the model results are compared with the experimental results of CO2 laser clipped pulses by aluminum and copper pinhole plasma shutters. In this model, it is assumed that the laser clipped pulse width is approximately equal to the sum of the plasma formation time and the plasma propagation time in order to reach from pinhole edges to the pinhole center. Furthermore, we assume that the plasma formation time is approximately equal to the time for the surface temperature of pinhole metal plate to reach the boiling point by absorbing the laser pulse energy. Heat conduction equation is used to calculate the time of plasma formation, and Taylor-Sedov's model is used to calculate the plasma propagation time to reach the pinhole center. By these assumptions, a relationship has been established between the laser clipped pulse width on the one hand, and thermo-dynamical and optical parameters of plasma shutter and the involved laser optical parameters on the other. Results of this model are in good agreement with experimental results.
NASA Astrophysics Data System (ADS)
Murata, Setsuko; Nakada, Hiroshi; Abe, Tetsuo
1993-03-01
Because heat transferred between closely spaced elements in a compact laser diode array shortens array lifetime and affects the elements’ operating characteristics, we theoretically and experimentally evaluated the effect of a heat-bypass structure by calculating and measuring the thermal resistance of array elements. Three-dimensional boundary element analysis showed that the heat bypass reduces the thermal resistance by an amount that is independent of cavity length. Measured junction voltages and wavelengths for a 50-μm-spaced 8-beam laser diode array with 600-μm-long cavities showed that the bypass structure reduces the thermal resistance resulting from simultaneous operation of all eight elements by more than 40%. And that the reduction is greatest for elements whose thermal resistance is highest. The resultant reduction in the junction temperature of array elements operating at 100 mW should increase array lifetime at least threefold.
Theoretical analysis on flow characteristics of melt gear pump
NASA Astrophysics Data System (ADS)
Zhao, R. J.; Wang, J. Q.; Kong, F. Y.
2016-05-01
The relationship between Geometric parameters and theoretical flow of melt gear pump is revealed, providing a theoretical basis to melt gear pump design. The paper has an analysis of meshing movement of melt gear pump on the condition of four different tooth numbers, stack movement law and flow ripple. The regulation of flow pulsation coefficient is researched by MATLAB software. The modulus formula of melt gear pump is proposed, consistent with actual situation.
NASA Astrophysics Data System (ADS)
Yan, R.; Yu, X.; Li, X.; Chen, D.; Yu, J.
2012-09-01
A theoretical model on actively Q-switched Nd3+-doped quasi-three-level laser including the energy transfer upconversion and the ground state reabsorption is developed. The analytical expressions of the fractional thermal loading and the average output power are obtained, and the influence of ETU effects on laser performance for different repetition rate is analyzed. The average output power and the thermal focal length of the Q-switched 946 nm laser are acquired in experiment. The good agreement between the experimental data and theoretical results demonstrates the reliability of the theoretical model.
Laser cooling of MgCl and MgBr in theoretical approach
Wan, Mingjie; Shao, Juxiang; Huang, Duohui; Yang, Junsheng; Cao, Qilong; Jin, Chengguo; Wang, Fanhou; Gao, Yufeng
2015-07-14
Ab initio calculations for three low-lying electronic states (X{sup 2}Σ{sup +}, A{sup 2}Π, and 2{sup 2}Π) of MgCl and MgBr molecules, including spin-orbit coupling, are performed using multi-reference configuration interaction plus Davidson correction method. The calculations involve all-electronic basis sets and Douglas–Kroll scalar relativistic correction. Spectroscopic parameters well agree with available theoretical and experimental data. Highly diagonally distributed Franck-Condon factors f{sub 00} for A{sup 2}Π{sub 3/2,1/2} (υ′ = 0) → X{sup 2}Σ{sup +}{sub 1/2} (υ″ = 0) are determined for both MgCl and MgBr molecules. Suitable radiative lifetimes τ of A{sup 2}Π{sub 3/2,1/2} (υ′ = 0) states for rapid laser cooling are also obtained. The proposed laser drives A{sup 2}Π{sub 3/2} (υ′ = 0) → X{sup 2}Σ{sup +}{sub 1/2} (υ″ = 0) transition by using three wavelengths (main pump laser λ{sub 00}; two repumping lasers λ{sub 10} and λ{sub 21}). These results indicate the probability of laser cooling MgCl and MgBr molecules.
The Theoretical Foundation of Sensitivity Analysis for GPS
NASA Astrophysics Data System (ADS)
Shikoska, U.; Davchev, D.; Shikoski, J.
2008-10-01
In this paper the equations of sensitivity analysis are derived and established theoretical underpinnings for the analyses. Paper propounds a land-vehicle navigation concepts and definition for sensitivity analysis. Equations of sensitivity analysis are presented for a linear Kalman filter and case study is given to illustrate the use of sensitivity analysis to the reader. At the end of the paper, extensions that are required for this research are made to the basic equations of sensitivity analysis specifically; the equations of sensitivity analysis are re-derived for a linearized Kalman filter.
Experimental and theoretical evaluation of the laser-assisted machining of silicon nitride
NASA Astrophysics Data System (ADS)
Rozzi, Jay Christopher
This study focused on the experimental and theoretical evaluation of the laser assisted machining (LAM) of silicon nitride ceramics. A laser assisted machining facility was constructed whose main components consist of a COsb2 laser and a CNC lathe. Surface temperature histories were first measured and compared to a transient, three-dimensional numerical simulation for a rotating silicon nitride workpiece heated by a translating laser for ranges of the workpiece rotational and laser-translation speeds, as well as the laser beam diameter and power. Excellent agreement was obtained between the experimental and predicted temperature histories. Laser assisted machining experiments on silicon nitride ceramic workpieces were completed for a wide range of operating conditions. Data for cutting forces and surface temperature histories illustrated that the lower bound for the avoidance of cutting tool and/or workpiece fracture for LAM is defined by the YSiAlON glass transition temperature (920-970sp°C). As temperatures near the cutting tool increase to values above the glass transition temperature range, the glassy phase softened, facilitating plastic deformation and, correspondingly, the production of semi-continuous or continuous chips. The silicon nitride machined workpiece surface roughness (Rsb{a}=0.39\\ mum) for LAM at the nominal operating condition was nearly equivalent to a value associated with the grinding of silicon nitride using a diamond wheel (Rsb{a}=0.2\\ mum). By examining the machined surfaces and chips, it was shown that LAM does not produce detectable sub-surface cracking or significant silicon nitride microstructure alteration, respectively. A transient, three-dimensional numerical heat transfer model of laser assisted machining was constructed, which includes a preheat phase and material removal, with the associated changes in the workplace geometry. Excellent agreement was obtained between the measured and predicted temperature histories. The strong
Sideband analysis and seismic detection in a large ring laser
NASA Astrophysics Data System (ADS)
Stedman, G. E.; Li, Z.; Bilger, H. R.
1995-08-01
A ring laser unlocked by the Earth's Sagnac effect has attained a frequency resolution of 1 part in 3 \\times 1021 and a rotational resolution of 300 prad. We discuss both theoretically and experimentally the sideband structure of the Earth rotation-induced spectral line induced in the microhertz-hertz region by frequency modulation associated with extra mechanical motion, such as seismic events. The relative sideband height is an absolute measure of the rotational amplitude of that Fourier component. An initial analysis is given of the ring laser record from the Arthur's Pass-Coleridge seismic event of 18 June 1994.
Singh, Kamal P.; Ropars, Guy; Brunel, Marc; Le Floch, Albert
2006-03-15
We investigate the two-dimensional optical rotor of a weakly modulated vectorial bistable laser submitted to a single or multiple stochastic perturbations. In the Langevin-type equation of the rotor the role of an even or odd input forcing function on the system dynamics is isolated. Through these two inputs of optical and magnetic natures we verify that the stochastic resonance exists only when the periodic modulation acts on the even parity optical input. When two mutually correlated noises are simultaneously submitted to the input functions of opposite parities, we find a critical regime of the noise interplay whereby one stable state becomes noise-free. In this case, the residence time of the light vector in the noise-free state diverges which leads to a collapse of the output signal-to-noise ratio. But, in this critical regime also obtained when one noise drives both the even and odd functions, if the system symmetry is broken through an independent lever control, we can recover the switching cycle due to a new response mechanism, namely, the dual stochastic response, with a specific output signal-to-noise ratio expression. Both the theoretical analysis and the experiment show that the signal-to-noise ratio now displays a robust behavior for a large range of the input noise amplitude, and a plateau with respect to the input signal amplitude. Furthermore, we isolate an original signature of this synchronization mechanism in the residence-time distribution leading to a broadband forcing frequency range. These noise interplay effects in a double well potential are of generic nature and could be found in other nonlinear systems.
Applications analysis of high energy lasers
NASA Technical Reports Server (NTRS)
Arno, R. D.; Mackay, J. S.; Nishioka, K.
1972-01-01
An analysis and comparison of laser technology with competing technologies were made to determine possible laser applications. The analysis was undertaken as follows: (1) possible applications were listed and categorized; (2) required components were enumerated and the characteristics of these components were extrapolated; (3) complete system characteristics were calculated parametrically for selected applications using the postulated component characteristics; and (4) where possible and appropriate, comparisons were made with competing systems. It was found that any large scale replacement of existing systems and methods by lasers requires many technological advances in laser and associated systems. However, several applications appear feasible, such as low orbit drag make-up, orbit changing, communications, and illumination applications.
Mode Deactivation Therapy (MDT) Family Therapy: A Theoretical Case Analysis
ERIC Educational Resources Information Center
Apsche, J. A.; Ward Bailey, S. R.
2004-01-01
This case study presents a theoretical analysis of implementing mode deactivation therapy (MDT) (Apsche & Ward Bailey, 2003) family therapy with a 13 year old Caucasian male. MDT is a form of cognitive behavioral therapy (CBT) that combines the balance of dialectical behavior therapy (DBT) (Linehan, 1993), the importance of perception from…
Theoretical Notes on the Sociological Analysis of School Reform Networks
ERIC Educational Resources Information Center
Ladwig, James G.
2014-01-01
Nearly two decades ago, Ladwig outlined the theoretical and methodological implications of Bourdieu's concept of the social field for sociological analyses of educational policy and school reform. The current analysis extends this work to consider the sociological import of one of the most ubiquitous forms of educational reform found around…
NASA Technical Reports Server (NTRS)
Davidson, Frederic M.; Field, Christopher T.; Sun, Xiaoli
1996-01-01
We report here the design and the performance measurements of the breadboard receiver of the Geoscience Laser Altimeter System (GLAS). The measured ranging accuracy was better than 2 cm and 10 cm for 5 ns and 30 ns wide received laser pulses under the expected received signal level, which agreed well with the theoretical analysis. The measured receiver sensitivity or the link margin was also consistent with the theory. The effects of the waveform digitizer sample rate and resolution were also measured.
Analysis of Laser Breakdown Data
NASA Astrophysics Data System (ADS)
Becker, Roger
2009-03-01
Experiments on laser breakdown for ns pulses of 532 nm or 1064 nm light in water and dozens of simple hydrocarbon liquids are analyzed and compared to widely-used models and other laser breakdown experiments reported in the literature. Particular attention is given to the curve for the probability of breakdown as a function of the laser fluence at the beam focus. Criticism is made of the na"ive forms of both ``avalanche'' breakdown and multi-photon breakdown. It appears that the process is complex and is intimately tied to the chemical group of the material. Difficulties with developing an accurate model of laser breakdown in liquids are outlined.
Game theoretic analysis of physical protection system design
Canion, B.; Schneider, E.; Bickel, E.; Hadlock, C.; Morton, D.
2013-07-01
The physical protection system (PPS) of a fictional small modular reactor (SMR) facility have been modeled as a platform for a game theoretic approach to security decision analysis. To demonstrate the game theoretic approach, a rational adversary with complete knowledge of the facility has been modeled attempting a sabotage attack. The adversary adjusts his decisions in response to investments made by the defender to enhance the security measures. This can lead to a conservative physical protection system design. Since defender upgrades were limited by a budget, cost benefit analysis may be conducted upon security upgrades. One approach to cost benefit analysis is the efficient frontier, which depicts the reduction in expected consequence per incremental increase in the security budget.
Theoretical analysis of the light interaction with coagulated tissue
NASA Astrophysics Data System (ADS)
Jerath, Maya R.; Welch, Ashley J.
1992-08-01
During laser treatment, coagulation affects the optical properties of the tissue. In particular, the formation of a white lesion increases the scattering coefficient significantly. This change in the optical properties in turn affects the laser light distribution in the tissue. For example, what is the effect of the white lesion formed during photocoagulation of the retina upon reflection and fluence rate? This problem was simulated on a model medium consisting of a thin absorbing black paint layer covered with a 1 cm thick layer of fresh egg white. The egg white layer was subdivided into coagulated (white) and uncoagulated (clear) layers. The optical properties of coagulated and uncoagulated egg white were determined. These values were used to model light distribution in the medium for varying thicknesses of the coagulated egg white layer using the one dimensional Adding Doubling method. Our results show that the fluence reaching the paint layer increase until the coagulated layer reaches 100 micrometers , after which it falls off exponentially. It was also found that the total reflected light increases almost linearly at first as the coagulated layer thickens, and then begins to level off to an R(infinity ) at a coagulation thickness of 2 mm. Experimental measurements of reflection from a lesion with a CCD camera confirm the computed trends. These results provide a theoretical foundation for control of lesion thickness using reflectance images.
Laser power conversion system analysis
NASA Technical Reports Server (NTRS)
1982-01-01
Orbit to orbit and orbit to ground laser power conversion systems and power transfer are discussed. A system overview is presented. Pilot program parameters are considered: SLPS assumptions are listed, a laser SPS overview is presented, specifications are listed, and SLPS coats are considered.
NASA Technical Reports Server (NTRS)
Phipps, Claude R.
1996-01-01
We show that laser-target interaction physics demands the shortest laser pulse of which hardware is capable (but not less than 100 ps) in the ORION ground-based laser concept. We compare two leading ways to achieve such pulses - SRS/SBS cascade compression and grating compression - with the standard MOPA approach, and conclude that the first of these is most robust. However, the state of the art in laser devices will require a year or two to implement these ideas. We present a pulse format and beam footprint protocol which will solve the conflict between relativistic lookahead and beam tilt and should permit all-laser active acquisition and tracking in ORION.
Theoretical and experimental study of elliptical Gaussian-mode size dynamics in ring lasers
Bretenaker, F.; Le Floch, A.; Tache, J.P. )
1990-04-01
In the framework of the {ital ABCD} ray matrix formalism, a theoretical model is proposed to describe the fundamental TEM{sub 00} elliptical Gaussian-mode size variations due to frequency-dependent lenslike effects in ring lasers. Two different mode size dynamics are predicted in the sagittal and tangential planes of the planar ring cavity, leading to the existence of different critical geometries in each plane, i.e., geometries for which the tangential or sagittal mode size at a given point becomes independent of the focal length. The frequency-dependent diffraction losses associated with these mode size variations predict rather complex asymmetries in the output power profiles in usual ring lasers, even in the case of a single-isotope gas mixture. Moreover, a fully critical geometry'' is predicted for which sagittal and tangential critical geometries occur simultaneously, making the two mode sizes independent of the lenses. A first type of experiment confirms the existence of the sagittal and tangential double dynamics and the role played by resonant diffraction thanks to the diffracted-light-spectroscopy technique. A second type of experiment proves the existence of the fully critical geometry. The theoretical predictions are in very good agreement with the experimental results.
Ebata, Takayuki; Kusaka, Ryoji; Xantheas, Sotiris S.
2015-02-01
Extensive laser spectroscopic and theoretical studies have been recently carried out with the aim to reveal the structure and dynamics of encapsulation complexes in the gas phase. The characteristics of the encapsulation complexes are governed by the fact that (i) most of the host molecules are flexible and (ii) the complexes form high dimensional structures by using weak non-covalent interactions. These characteristics result in the possibility of the coexistence of many conformers in close energetic proximity. The combination of supersonic jet/laser spectroscopy and high level quantum chemical calculations is essential in tackling these challenging problems. In this report we describe our recent studies on the structures and dynamics of the encapsulation complexes formed by calix[4]arene (C4A), dibenzo-18-crown-6-ether (DB18C6), and benzo-18-crown-6-ether (B18C6) "hosts" interacting with N2, acetylene, water, and ammonia "guest" molecules. The gaseous host-guest complexes are generated under jet-cooled conditions. We apply various laser spectroscopic methods to obtain the conformer- and isomer-specified electronic and IR spectra. The experimental results are complemented with quantum chemical calculations ranging from density functional theory to high level first principles calculations at the MP2 and CCSD(T) levels of theory. We discuss the possible conformations of the bare host molecules, the structural changes they undergo upon complexation, and the key interactions that are responsible in stabilizing the specific complexes
NASA Astrophysics Data System (ADS)
Bakry, A.; Abdulrhmann, S.; Ahmed, M.
2016-06-01
We theoretically model the dynamics of semiconductor lasers subject to the double-reflector feedback. The proposed model is a new modification of the time-delay rate equations of semiconductor lasers under the optical feedback to account for this type of the double-reflector feedback. We examine the influence of adding the second reflector to dynamical states induced by the single-reflector feedback: periodic oscillations, period doubling, and chaos. Regimes of both short and long external cavities are considered. The present analyses are done using the bifurcation diagram, temporal trajectory, phase portrait, and fast Fourier transform of the laser intensity. We show that adding the second reflector attracts the periodic and perioddoubling oscillations, and chaos induced by the first reflector to a route-to-continuous-wave operation. During this operation, the periodic-oscillation frequency increases with strengthening the optical feedback. We show that the chaos induced by the double-reflector feedback is more irregular than that induced by the single-reflector feedback. The power spectrum of this chaos state does not reflect information on the geometry of the optical system, which then has potential for use in chaotic (secure) optical data encryption.
Ebata, Takayuki; Kusaka, Ryoji; Xantheas, Sotiris S.
2015-01-22
Extensive laser spectroscopic and theoretical studies have been recently carried out with the aim to reveal the structure and dynamics of encapsulation complexes in the gas phase. The characteristics of the encapsulation complexes are governed by the fact that (i) most of the host molecules are flexible and (ii) the complexes form high dimensional structures by using weak non-covalent interactions. These characteristics result in the possibility of the coexistence of many conformers in close energetic proximity. The combination of supersonic jet/laser spectroscopy and high level quantum chemical calculations is essential in tackling these challenging problems. In this report we describe our recent studies on the structures and dynamics of the encapsulation complexes formed by calix[4]arene (C4A), dibenzo-18-crown-6-ether (DB18C6), and benzo-18-crown-6-ether (B18C6) 'hosts' interacting with N{sub 2}, acetylene, water, and ammonia 'guest' molecules. The gaseous host-guest complexes are generated under jet-cooled conditions. We apply various laser spectroscopic methods to obtain the conformer- and isomer-specified electronic and IR spectra. The experimental results are complemented with quantum chemical calculations ranging from density functional theory to high level first principles calculations at the MP2 and CCSD(T) levels of theory. We discuss the possible conformations of the bare host molecules, the structural changes they undergo upon complexation, and the key interactions that are responsible in stabilizing the specific complexes.
Image inpainting: theoretical analysis and comparison of algorithms
NASA Astrophysics Data System (ADS)
King, Emily J.; Kutyniok, Gitta; Lim, Wang-Q.
2013-09-01
An issue in data analysis is that of incomplete data, for example a photograph with scratches or seismic data collected with fewer than necessary sensors. There exists a unified approach to solving this problem and that of data separation: namely, minimizing the norm of the analysis (rather than synthesis) coefficients with respect to particular frame(s).There have been a number of successful applications of this method recently. Analyzing this method using the concept of clustered sparsity leads to theoretical bounds and results, which will be presented. Furthermore, necessary conditions for the frames to lead to sufficiently good solutions will be shown, and this theoretical framework will be use to show that shearlets are able to inpaint larger gaps than wavelets. Finally, the results of numerical experiments comparing this approach to inpainting to numerous others will be presented.
Architectural stability analysis of the rotary-laser scanning technique
NASA Astrophysics Data System (ADS)
Xue, Bin; Yang, Xiaoxia; Zhu, Jigui
2016-03-01
The rotary-laser scanning technique is an important method in scale measurements due to its high accuracy and large measurement range. This paper first introduces a newly designed measurement station which is able to provide two-dimensional measurement information including the azimuth and elevation by using the rotary-laser scanning technique, then presents the architectural stability analysis of this technique by detailed theoretical derivations. Based on the designed station, a validation using both experiment and simulation is presented in order to verify the analytic conclusion. The results show that the architectural stability of the rotary-laser scanning technique is only affected by the two scanning angles' difference. And the difference which brings the best architectural stability can be calculated by using pre-calibrated parameters of the two laser planes. This research gives us an insight into the rotary-laser scanning technique. Moreover, the measurement accuracy of the rotary-laser scanning technique can be further improved based on the results of the study.
Analysis of phased-array diode lasers
Hardy, A.; Streifer, W.
1985-07-01
An improved, more accurate analysis of phased-array diode lasers is presented, which yields results that differ both qualitatively and quantitatively from those previously employed. A numerical example indicating decreased splitting in array mode gains is included.
Analysis of the Laser Lightcraft Vehicle
NASA Technical Reports Server (NTRS)
Feikema, Douglas A.
1999-01-01
Advanced propulsion research and technology concepts require launch and space flight technologies, which can drastically reduce mission costs. Laser propulsion is a concept in which energy of a thrust producing reaction mass is supplied via beamed energy from an off-board power source. A variety of laser beamed energy concepts were theoretically and experimentally investigated since the early 1970's. During the 1980's the Strategic Defense Initiative (SDIO) research lead to the invention of the Laser Lightcraft concept. Based upon the Laser Lightcraft concept, the propulsion research center, TD 40, within the Space Transportation Directorate of NASA MSFC has set out to develop technologies required for launching small payloads into Earth Orbit for a cost of $1.0M or $1000/lb to $100/lb. The near term objectives are to demonstrate technologies and capabilities essential for a future earth to orbit launch capability. Laser propulsion offers the advantages of both high thrust and good specific impulse, I(sp) in excess of 1000 s(exp -1). Other advantages are the simplicity and reliability of the engine because of few moving parts; simplistic propellant feed system, and low specific fuel consumption as a result of high specific impulse. Major limitations of this approach are the laser power available, absorption and distortion of the pulsed laser beam through the atmosphere, and coupling laser power into thrust throughout the flight envelope. This summer's effort focused on performance of the laser engine, which included 1) optical ray tracing and 2), a time dependent calculation of the optically induced blast wave.
Noise analysis in laser speckle contrast imaging
NASA Astrophysics Data System (ADS)
Yuan, Shuai; Chen, Yu; Dunn, Andrew K.; Boas, David A.
2010-02-01
Laser speckle contrast imaging (LSCI) is becoming an established method for full-field imaging of blood flow dynamics in animal models. A reliable quantitative model with comprehensive noise analysis is necessary to fully utilize this technique in biomedical applications and clinical trials. In this study, we investigated several major noise sources in LSCI: periodic physiology noise, shot noise and statistical noise. (1) We observed periodic physiology noise in our experiments and found that its sources consist principally of motions induced by heart beats and/or ventilation. (2) We found that shot noise caused an offset of speckle contrast (SC) values, and this offset is directly related to the incident light intensity. (3) A mathematical model of statistical noise was also developed. The model indicated that statistical noise in speckle contrast imaging is related to the SC values and the total number of pixels used in the SC calculation. Our experimental results are consistent with theoretical predications, as well as with other published works.
NASA Astrophysics Data System (ADS)
Meng, Qinglong; Zhang, Bin; Zhong, Sencheng; Zhu, Liguo
2016-06-01
The damage threshold of lithium niobate crystal under single and multiple femtosecond laser pulses has been studied theoretically and experimentally. Firstly, the model for the damage threshold prediction of crystal materials based on the improved rate equation has been proposed. Then, the experimental measure method of the damage threshold of crystal materials has been given in detail. On the basis, the variation of the damage threshold of lithium niobate crystal with the pulse duration has also been analyzed quantitatively. Finally, the damage threshold of lithium niobate crystal under multiple laser pulses has been measured and compared to the theoretical results. The results show that the transmittance of lithium niobate crystal is almost a constant when the laser pulse fluence is relative low, whereas it decreases linearly with the increase in the laser pulse fluence below the damage threshold. The damage threshold of lithium niobate crystal increases with the increase in the duration of the femtosecond laser pulse. And the damage threshold of lithium niobate crystal under multiple laser pulses is obviously lower than that irradiated by a single laser pulse. The theoretical data fall in good agreement with the experimental results.
Python for Information Theoretic Analysis of Neural Data
Ince, Robin A. A.; Petersen, Rasmus S.; Swan, Daniel C.; Panzeri, Stefano
2008-01-01
Information theory, the mathematical theory of communication in the presence of noise, is playing an increasingly important role in modern quantitative neuroscience. It makes it possible to treat neural systems as stochastic communication channels and gain valuable, quantitative insights into their sensory coding function. These techniques provide results on how neurons encode stimuli in a way which is independent of any specific assumptions on which part of the neuronal response is signal and which is noise, and they can be usefully applied even to highly non-linear systems where traditional techniques fail. In this article, we describe our work and experiences using Python for information theoretic analysis. We outline some of the algorithmic, statistical and numerical challenges in the computation of information theoretic quantities from neural data. In particular, we consider the problems arising from limited sampling bias and from calculation of maximum entropy distributions in the presence of constraints representing the effects of different orders of interaction in the system. We explain how and why using Python has allowed us to significantly improve the speed and domain of applicability of the information theoretic algorithms, allowing analysis of data sets characterized by larger numbers of variables. We also discuss how our use of Python is facilitating integration with collaborative databases and centralised computational resources. PMID:19242557
Laser irradiation of ferrous particles for hyperthermia as cancer therapy, a theoretical study.
Patel, Jigar M; Evrensel, Cahit A; Fuchs, Alan; Sutrisno, Joko
2015-01-01
Our recent in vivo animal studies showed the feasibility of using micron sized iron particles to induce physical damage to breast cancer tumors and thereby triggering a localized immune response to help fight the cancer. Combining a hyperthermic treatment with this ongoing study may enhance the immune response. As a result, a novel treatment of inducing hyperthermia using iron particles excited by a continuous wave near-infrared laser was analyzed. In this theoretical study, Mie scattering calculations were first conducted to determine the absorption and scattering efficiencies of the suspended drug coated particles. The resulting heat transfer between the particles and the surrounding tumor and the healthy tissue was modeled using Pennes' Bioheat equation. Predicted temperature changes were satisfactory for inducing hyperthermia (42(∘)C), thermally triggering drug release, and even thermal ablation (55(∘)C). PMID:25082264
Simulation based analysis of laser beam brazing
NASA Astrophysics Data System (ADS)
Dobler, Michael; Wiethop, Philipp; Schmid, Daniel; Schmidt, Michael
2016-03-01
Laser beam brazing is a well-established joining technology in car body manufacturing with main applications in the joining of divided tailgates and the joining of roof and side panels. A key advantage of laser brazed joints is the seam's visual quality which satisfies highest requirements. However, the laser beam brazing process is very complex and process dynamics are only partially understood. In order to gain deeper knowledge of the laser beam brazing process, to determine optimal process parameters and to test process variants, a transient three-dimensional simulation model of laser beam brazing is developed. This model takes into account energy input, heat transfer as well as fluid and wetting dynamics that lead to the formation of the brazing seam. A validation of the simulation model is performed by metallographic analysis and thermocouple measurements for different parameter sets of the brazing process. These results show that the multi-physical simulation model not only can be used to gain insight into the laser brazing process but also offers the possibility of process optimization in industrial applications. The model's capabilities in determining optimal process parameters are exemplarily shown for the laser power. Small deviations in the energy input can affect the brazing results significantly. Therefore, the simulation model is used to analyze the effect of the lateral laser beam position on the energy input and the resulting brazing seam.
Active polarimeter optical system laser hazard analysis.
Augustoni, Arnold L.
2005-07-01
A laser hazard analysis was performed for the SNL Active Polarimeter Optical System based on the ANSI Standard Z136.1-2000, American National Standard for Safe Use of Lasers and the ANSI Standard Z136.6-2000, American National Standard for Safe Use of Lasers Outdoors. The Active Polarimeter Optical System (APOS) uses a pulsed, near-infrared, chromium doped lithium strontium aluminum fluoride (Cr:LiSAF) crystal laser in conjunction with a holographic diffuser and lens to illuminate a scene of interest. The APOS is intended for outdoor operations. The system is mounted on a height adjustable platform (6 feet to 40 feet) and sits atop a tripod that points the beam downward. The beam can be pointed from nadir to as much as 60 degrees off of nadir producing an illuminating spot geometry that can vary from circular (at nadir) to elliptical in shape (off of nadir). The JP Innovations crystal Cr:LiSAF laser parameters are presented in section II. The illuminating laser spot size is variable and can be adjusted by adjusting the separation distance between the lens and the holographic diffuser. The system is adjusted while platform is at the lowest level. The laser spot is adjusted for a particular spot size at a particular distance (elevation) from the laser by adjusting the separation distance (d{sub diffuser}) to predetermined values. The downward pointing angle is also adjusted before the platform is raised to the selected operation elevation.
NASA Astrophysics Data System (ADS)
Wang, Cheng-Liang; Yang, Zhen-Gang; Liu, Jin-Song; Wang, Sheng-Lie; Wang, Ke-Jia
2015-08-01
Generation of intense broadband terahertz (THz) waves from gas plasma induced by tri-color ultrashort (fundamental (ω), second harmonic (2ω), and third harmonic (3ω)) laser pulses is theoretically investigated. Simulation results show that the 3ω laser pulse can greatly enhance or suppress the generation of THz wave at different values of relative phase (θ 3) between the 3ω and ω fields. Moreover, the polarities of the generated THz waves can be controlled by changing θ 3, with the relative phase θ 2 (between the 2ω and ω fields) fixed to be a certain value. All of our results show that θ 3 plays a key role in the generation process, which promises to control the intensity as well as the polarity of gas plasma-induced THz radiation. Project supported by the Wuhan Applied Basic Research Project, China (Grant No. 20140101010009), the National Natural Science Foundation of China (Grant Nos. 61177095, 61475054, and 61405063), the Natural Science Foundation of Hubei Province, China (Grant Nos. 2012FFA074 and 2013BAA002), the Fundamental Research Funds for the Central Universities, China (Grant Nos. 2013KXYQ004, 2014ZZGH021, and 2014QN023), and the Technology Innovation Foundation from Innovation Institute of Huazhong University of Science and Technology, China (Grant No. CXY13Q015).
Theoretical study of the photodissociation of Li2+ in one-color intense laser fields
NASA Astrophysics Data System (ADS)
Li, Yuanjun; Jiang, Wanyi; Khait, Yuriy G.; Hoffmann, Mark R.
2011-05-01
A theoretical treatment of the photodissociation of the molecular ion Li2+ in one-color intense laser fields, using the time-dependent wave packet approach in a Floquet Born-Oppenheimer representation, is presented. Six electronic states 1,2 2Σg+, 1,2 2Σu+, 1 2Πg, and 1 2Πu are of relevance in this simulation and have been included. The dependences of the fragmental dissociation probabilities and kinetic energy release (KER) spectra on pulse width, peak intensity, polarization angle, wavelength, and initial vibrational level are analyzed to interpret the influence of control parameters of the external field. Three main dissociation channels, 1 2Σg+ (m = -1), 2 2Σg+ (m = -2), and 2 2Σu+ (m = -3), are seen to dominate the dissociation processes under a wide variety of laser conditions and give rise to well separated groups of KER features. Different dissociation mechanisms for the involved Floquet channels are discussed.
NASA Astrophysics Data System (ADS)
Yuan, Ling; Sun, Kaihua; Shen, Zhonghua; Ni, Xiaowu; Lu, Jian
2015-06-01
The laser ultrasound technique has great potential for clinical diagnosis of teeth because of its many advantages. To study laser surface acoustic wave (LSAW) propagation in human teeth, two theoretical methods, the finite element method (FEM) and Laguerre polynomial extension method (LPEM), are presented. The full field temperature values and SAW displacements in an incisor can be obtained by the FEM. The SAW phase velocity in a healthy incisor and dental caries is obtained by the LPEM. The methods and results of this work can provide a theoretical basis for nondestructive evaluation of human teeth with LSAWs.
Analysis of the Laser Propelled Lightcraft Vehicle
NASA Technical Reports Server (NTRS)
Feikema, Douglas
2000-01-01
Advanced propulsion research and technology require launch and space flight technologies, which can drastically reduce mission costs. Laser propulsion is a concept in which energy of a thrust producing reaction mass is supplied via beamed energy from an off-board power source. A variety of laser/beamed energy concepts were theoretically and experimentally investigated since the early 1970's. During the 1980's the Strategic Defense Initiative (SDI) research lead to the invention of the Laser Lightcraft concept. Based upon the Laser Lightcraft concept, the U.S. Air Force and NASA have jointly set out to develop technologies required for launching small payloads into Low Earth Orbit (LEO) for a cost of $1.0M or $1000/lb to $ 100/lb. The near term objectives are to demonstrate technologies and capabilities essential for a future earth to orbit launch capability. Laser propulsion offers the advantages of both high thrust and good specific impulse, I(sub sp), in excess of 1000 s. Other advantages are the simplicity and reliability of the engine because of few moving parts, simpler propellant feed system, and high specific impulse. Major limitations of this approach are the laser power available, absorption and distortion of the pulsed laser beam through the atmosphere, and coupling laser power into thrust throughout the flight envelope, The objective of this paper is to assist efforts towards optimizing the performance of the laser engine. In order to accomplish this goal (1) defocusing of the primary optic was investigated using optical ray tracing and (2), time dependent calculations were conducted of the optically induced blast wave to predict pressure and temperature in the vicinity of the cowl. Defocusing of the primary parabolic reflector causes blurring and reduction in the intensity of the laser ignition site on the cowl. However, because of the caustic effect of ray-tracing optics the laser radiation still forms a well-defined ignition line on the cowl. The
Theoretical analysis of quantum ghost imaging through turbulence
Chan, Kam Wai Clifford; Simon, D. S.; Sergienko, A. V.; Hardy, Nicholas D.; Shapiro, Jeffrey H.; Dixon, P. Ben; Howland, Gregory A.; Howell, John C.; Eberly, Joseph H.; O'Sullivan, Malcolm N.; Rodenburg, Brandon; Boyd, Robert W.
2011-10-15
Atmospheric turbulence generally affects the resolution and visibility of an image in long-distance imaging. In a recent quantum ghost imaging experiment [P. B. Dixon et al., Phys. Rev. A 83, 051803 (2011)], it was found that the effect of the turbulence can nevertheless be mitigated under certain conditions. This paper gives a detailed theoretical analysis to the setup and results reported in the experiment. Entangled photons with a finite correlation area and a turbulence model beyond the phase screen approximation are considered.
NASA Astrophysics Data System (ADS)
Auzinsh, M.; Berzins, A.; Ferber, R.; Gahbauer, F.; Kalnins, U.
2016-03-01
We show that it is possible to model accurately optical phenomena in intense laser fields by taking into account the intensity distribution over the laser beam. We present an extension of an earlier theoretical model that divides an intense laser beam into concentric regions, each with a Rabi frequency that corresponds to the intensity in that region, and solve a set of coupled optical Bloch equations for the density matrix in each region. Experimentally obtained magneto-optical resonance curves for the Fg=2 ⟶Fe=1 transition of the D1 line of 87Rb agree very well with the theoretical model up to a laser intensity of around 200 mW/cm2 for a transition whose saturation intensity is around 4.5 mW/cm2. We examine the spatial dependence of the fluorescence intensity in an intense laser beam experimentally and theoretically. We present and discuss the results of an experiment in which a broad, intense pump laser excites the Fg=4 ⟶Fe=4 transition of the D2 line of cesium while a narrow probe beam scans the atoms within the pump beam and excites the D1 line of cesium, whose fluorescence is recorded as a function of probe beam position. Experimentally obtained spatial profiles of the fluorescence intensity agree qualitatively with the predictions of the model.
Analysis and Design of Vertical Cavity Surface Emitting Lasers
NASA Astrophysics Data System (ADS)
Yu, S. F.
2003-08-01
A practical, hands-on guidebook for the efficient modeling of VCSELs Vertical Cavity Surface Emitting Lasers (VCSELs) are a unique type of semiconductor laser whose optical output is vertically emitted from the surface as opposed to conventional edge-emitting semiconductor lasers. Complex in design and expensive to produce, VCSELs nevertheless represent an already widely used laser technology that promises to have even more significant applications in the future. Although the research has accelerated, there have been relatively few books written on this important topic. Analysis and Design of Vertical Cavity Surface Emitting Lasers seeks to encapsulate this growing body of knowledge into a single, comprehensive reference that will be of equal value for both professionals and academics in the field. The author, a recognized expert in the field of VCSELs, attempts to clarify often conflicting assumptions in order to help readers achieve the simplest and most efficient VCSEL models for any given problem. Highlights of the text include: * A clear and comprehensive theoretical treatment of VCSELs * Detailed derivations for understanding the operational principles of VCSELs * Mathematical models for the investigation of electrical, optical, and thermal properties of VCSELs * Case studies on the mathematical modeling of VCSELs and the implementation of simulation programs
Skinner, M G; Iizuka, M N; Kolios, M C; Sherar, M D
1998-12-01
A number of heating sources are available for minimally invasive thermal therapy of tumours. The purpose of this work was to compare, theoretically, the heating characteristics of interstitial microwave, laser and ultrasound sources in three tissue sites: breast, brain and liver. Using a numerical method, the heating patterns, temperature profiles and expected volumes of thermal damage were calculated during standard treatment times with the condition that tissue temperatures were not permitted to rise above 100 degrees C (to ensure tissue vaporization did not occur). Ideal spherical and cylindrical applicators (200 microm and 800 microm radii respectively) were modelled for each energy source to demonstrate the relative importance of geometry and energy attenuation in determining heating and thermal damage profiles. The theoretical model included the effects of the collapse of perfusion due to heating. Heating patterns were less dependent on the energy source when small spherical applicators were modelled than for larger cylindrical applicators due to the very rapid geometrical decrease in energy with distance for the spherical applicators. For larger cylindrical applicators, the energy source was of greater importance. In this case, the energy source with the lowest attenuation coefficient was predicted to produce the largest volume of thermally coagulated tissue, in each tissue site. PMID:9869030
Laser power conversion system analysis, volume 1
NASA Technical Reports Server (NTRS)
Jones, W. S.; Morgan, L. L.; Forsyth, J. B.; Skratt, J. P.
1979-01-01
The orbit-to-orbit laser energy conversion system analysis established a mission model of satellites with various orbital parameters and average electrical power requirements ranging from 1 to 300 kW. The system analysis evaluated various conversion techniques, power system deployment parameters, power system electrical supplies and other critical supplies and other critical subsystems relative to various combinations of the mission model. The analysis show that the laser power system would not be competitive with current satellite power systems from weight, cost and development risk standpoints.
Theoretical analysis of the performance of a foam fractionation column
Tobin, S. T.; Weaire, D.; Hutzler, S.
2014-01-01
A model system for theory and experiment which is relevant to foam fractionation consists of a column of foam moving through an inverted U-tube between two pools of surfactant solution. The foam drainage equation is used for a detailed theoretical analysis of this process. In a previous paper, we focused on the case where the lengths of the two legs are large. In this work, we examine the approach to the limiting case (i.e. the effects of finite leg lengths) and how it affects the performance of the fractionation column. We also briefly discuss some alternative set-ups that are of interest in industry and experiment, with numerical and analytical results to support them. Our analysis is shown to be generally applicable to a range of fractionation columns. PMID:24808752
Theoretical analysis of dynamic processes for interacting molecular motors
NASA Astrophysics Data System (ADS)
Teimouri, Hamid; Kolomeisky, Anatoly B.; Mehrabiani, Kareem
2015-02-01
Biological transport is supported by the collective dynamics of enzymatic molecules that are called motor proteins or molecular motors. Experiments suggest that motor proteins interact locally via short-range potentials. We investigate the fundamental role of these interactions by carrying out an analysis of a new class of totally asymmetric exclusion processes, in which interactions are accounted for in a thermodynamically consistent fashion. This allows us to explicitly connect microscopic features of motor proteins with their collective dynamic properties. A theoretical analysis that combines various mean-field calculations and computer simulations suggests that the dynamic properties of molecular motors strongly depend on the interactions, and that the correlations are stronger for interacting motor proteins. Surprisingly, it is found that there is an optimal strength of interactions (weak repulsion) that leads to a maximal particle flux. It is also argued that molecular motor transport is more sensitive to attractive interactions. Applications of these results for kinesin motor proteins are discussed.
Laser Safety and Hazardous Analysis for the ARES (Big Sky) Laser System
AUGUSTONI, ARNOLD L.
2003-01-01
A laser safety and hazard analysis was performed for the ARES laser system based on the 2000 version of the American National Standards Institute's (ANSI) Standard Z136.1,for Safe Use of Lasers and the 2000 version of the ANSI Standard Z136.6, for Safe Use of Lasers Outdoors. The ARES laser system is a Van/Truck based mobile platform, which is used to perform laser interaction experiments and tests at various national test sites.
Laser Photothermal Analysis of Magnetoelectric Materials
NASA Astrophysics Data System (ADS)
Penchev, S.; Pencheva, V.; Nedkov, I.; Kutzarova, T.; Naboko, V.
2010-01-01
Modulated optical reflectance (MOR) technique of laser photothermal analysis is implemented to magnetoresistive La0,7Sr0,3MnO3 (LSMO) thin film. The sensor signal is based on the measurement of the variations of optical reflectivity of the sample subjected to periodic photothermal modulation. Assuming Drude model, it is proportional to the variations of the charge carrier concentration. The optical setup is mounted as a flexible laser microscope, based on elements of integral and fibre optics. The noncontact, nondestructive measurement scheme is prospective for applications to structural analysis and characterization of new magnetic and magnetoelectric materials for the next generation electronic devices.
Analysis of Surface Roughness at Overlapping Laser Shock Peening
NASA Astrophysics Data System (ADS)
Dai, F. Z.; Zhang, Z. D.; Zhou, J. Z.; Lu, J. Z.; Zhang, Y. K.
2016-02-01
The overlapping effects on surface roughness are studied when samples are treated by laser shock peening (LSP). Surface roughness of overlapped circular laser spot is calculated by ISO 25178 height parameters. The usually used overlapping styles namely isosceles-right-triangle-style (AAP) and equilateral-triangle-style (AAA) are carefully investigated when the overlapping degree in x-axis (ηx) is below 50%. Surface roughness of isosceles-right-triangle-style attains its minimum value at ηx of 29.3%, and attains its maximum value at ηx of 43.6%. Surface roughness of equilateral-triangle-style attains its minimum value at ηx of 42.3%, and attains its maximum value at ηx of 32%. Experimental results are well consistent with theoretical analysis.
Theoretical analysis of hot electron dynamics in nanorods
Kumarasinghe, Chathurangi S.; Premaratne, Malin; Agrawal, Govind P.
2015-01-01
Localised surface plasmons create a non-equilibrium high-energy electron gas in nanostructures that can be injected into other media in energy harvesting applications. Here, we derive the rate of this localised-surface-plasmon mediated generation of hot electrons in nanorods and the rate of injecting them into other media by considering quantum mechanical motion of the electron gas. Specifically, we use the single-electron wave function of a particle in a cylindrical potential well and the electric field enhancement factor of an elongated ellipsoid to derive the energy distribution of electrons after plasmon excitation. We compare the performance of nanorods with equivolume nanoparticles of other shapes such as nanospheres and nanopallets and report that nanorods exhibit significantly better performance over a broad spectrum. We present a comprehensive theoretical analysis of how different parameters contribute to efficiency of hot-electron harvesting in nanorods and reveal that increasing the aspect ratio can increase the hot-electron generation and injection, but the volume shows an inverse dependency when efficiency per unit volume is considered. Further, the electron thermalisation time shows much less influence on the injection rate. Our derivations and results provide the much needed theoretical insight for optimization of hot-electron harvesting process in highly adaptable metallic nanorods. PMID:26202823
Theoretical analysis of hot electron dynamics in nanorods.
Kumarasinghe, Chathurangi S; Premaratne, Malin; Bao, Qiaoliang; Agrawal, Govind P
2015-01-01
Localised surface plasmons create a non-equilibrium high-energy electron gas in nanostructures that can be injected into other media in energy harvesting applications. Here, we derive the rate of this localised-surface-plasmon mediated generation of hot electrons in nanorods and the rate of injecting them into other media by considering quantum mechanical motion of the electron gas. Specifically, we use the single-electron wave function of a particle in a cylindrical potential well and the electric field enhancement factor of an elongated ellipsoid to derive the energy distribution of electrons after plasmon excitation. We compare the performance of nanorods with equivolume nanoparticles of other shapes such as nanospheres and nanopallets and report that nanorods exhibit significantly better performance over a broad spectrum. We present a comprehensive theoretical analysis of how different parameters contribute to efficiency of hot-electron harvesting in nanorods and reveal that increasing the aspect ratio can increase the hot-electron generation and injection, but the volume shows an inverse dependency when efficiency per unit volume is considered. Further, the electron thermalisation time shows much less influence on the injection rate. Our derivations and results provide the much needed theoretical insight for optimization of hot-electron harvesting process in highly adaptable metallic nanorods. PMID:26202823
Analysis of the theoretical bias in dark matter direct detection
Catena, Riccardo
2014-09-01
Fitting the model ''A'' to dark matter direct detection data, when the model that underlies the data is ''B'', introduces a theoretical bias in the fit. We perform a quantitative study of the theoretical bias in dark matter direct detection, with a focus on assumptions regarding the dark matter interactions, and velocity distribution. We address this problem within the effective theory of isoscalar dark matter-nucleon interactions mediated by a heavy spin-1 or spin-0 particle. We analyze 24 benchmark points in the parameter space of the theory, using frequentist and Bayesian statistical methods. First, we simulate the data of future direct detection experiments assuming a momentum/velocity dependent dark matter-nucleon interaction, and an anisotropic dark matter velocity distribution. Then, we fit a constant scattering cross section, and an isotropic Maxwell-Boltzmann velocity distribution to the simulated data, thereby introducing a bias in the analysis. The best fit values of the dark matter particle mass differ from their benchmark values up to 2 standard deviations. The best fit values of the dark matter-nucleon coupling constant differ from their benchmark values up to several standard deviations. We conclude that common assumptions in dark matter direct detection are a source of potentially significant bias.
Fornaini, Carlo; Passaretti, Francesca; Villa, Elena; Rocca, Jean-Paul; Merigo, Elisabetta; Vescovi, Paolo; Meleti, Marco; Manfredi, Maddalena; Nammour, Samir
2011-07-01
The Nd:YAG laser has been used since 1970 in dental laboratories to weld metals on dental prostheses. Recently in several clinical cases, we have suggested that the Nd:YAG laser device commonly utilized in the dental office could be used to repair broken fixed, removable and orthodontic prostheses and to weld metals directly in the mouth. The aim of this work was to evaluate, using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and dynamic mechanical analysis (DMA), the quality of the weld and its mechanical strength, comparing a device normally used in dental laboratory and a device normally used in the dental office for oral surgery, the same as that described for intraoral welding. Metal plates of a Co-Cr-Mo dental alloy and steel orthodontic wires were subjected to four welding procedures: welding without filler metal using the laboratory laser, welding with filler metal using the laboratory laser, welding without filler metal using the office laser, and welding with filler metal using the office laser. The welded materials were then analysed by SEM, EDS and DMA. SEM analysis did not show significant differences between the samples although the plates welded using the office laser without filler metal showed a greater number of fissures than the other samples. EDS microanalysis of the welding zone showed a homogeneous composition of the metals. Mechanical tests showed similar elastic behaviours of the samples, with minimal differences between the samples welded with the two devices. No wire broke even under the maximum force applied by the analyser. This study seems to demonstrate that the welds produced using the office Nd:YAG laser device and the laboratory Nd:YAG laser device, as analysed by SEM, EDS and DMA, showed minimal and nonsignificant differences, although these findings need to be confirmed using a greater number of samples. PMID:20437262
A theoretical analysis of vacuum arc thruster performance
NASA Technical Reports Server (NTRS)
Polk, James E.; Sekerak, Mike; Ziemer, John K.; Schein, Jochen; Qi, Niansheng; Binder, Robert; Anders, Andre
2001-01-01
In vacuum arc discharges the current is conducted through vapor evaporated from the cathode surface. In these devices very dense, highly ionized plasmas can be created from any metallic or conducting solid used as the cathode. This paper describes theoretical models of performance for several thruster configurations which use vacuum arc plasma sources. This analysis suggests that thrusters using vacuum arc sources can be operated efficiently with a range of propellant options that gives great flexibility in specific impulse. In addition, the efficiency of plasma production in these devices appears to be largely independent of scale because the metal vapor is ionized within a few microns of the cathode electron emission sites, so this approach is well-suited for micropropulsion.
Theoretical analysis of sound transmission loss through graphene sheets
Natsuki, Toshiaki; Ni, Qing-Qing
2014-11-17
We examine the potential of using graphene sheets (GSs) as sound insulating materials that can be used for nano-devices because of their small size, super electronic, and mechanical properties. In this study, a theoretical analysis is proposed to predict the sound transmission loss through multi-layered GSs, which are formed by stacks of GS and bound together by van der Waals (vdW) forces between individual layers. The result shows that the resonant frequencies of the sound transmission loss occur in the multi-layered GSs and the values are very high. Based on the present analytical solution, we predict the acoustic insulation property for various layers of sheets under both normal incident wave and acoustic field of random incidence source. The scheme could be useful in vibration absorption application of nano devices and materials.
[Theoretical analysis of recompression-based therapies of decompression illness].
Nikolaev, V P; Sokolov, G M; Komarevtsev, V N
2011-01-01
Theoretical analysis is concerned with the benefits of oxygen, air and nitrogen-helium-oxygen recompression schedules used to treat decompression illness in divers. Mathematical modeling of tissue bubbles dynamics during diving shows that one-hour oxygen recompression to 200 kPa does not diminish essentially the size of bubble enclosed in a layer that reduces tenfold the intensity of gas diffusion from bubbles. However, these bubbles dissolve fully in all the body tissues equally after 2-hr. air compression to 800 kPa and ensuing 2-d decompression by the Russian navy tables, and 1.5-hr. N-He-O2 compression to this pressure followed by 5-day decompression. The overriding advantage of the gas mixture recompression is that it obviates the narcotic action of nitrogen at the peak of chamber pressure and does not create dangerous tissue supersaturation and conditions for emergence of large bubbles at the end of decompression. PMID:21970044
Peyghambarian, N.; Koch, S.W.
1987-01-01
The coherent interaction of femtosecond laser pulses and a thin CdSe sample is investigated both experimentally and theoretically. Observation of coherent phenomena in semiconductors is very rare because the incoherent processes occur in the femtosecond time domain in these materials. One example of such a phenomena is the so called optical Stark effect of exciton where a blue shift of the exciton resonance occurs as a result of pumping below the bandgap. The coherent effects involving band-to-band and also exciton transitions. Using femtosecond transmission measurements clear evidence was observed for coherent interference effects of the light field and the driven material polarization. These interferences manifest themselves as oscillatory structures in the differential transmission spectra. The oscillatory features are explained by comparison with a semiclassical theory. Examples of the computed results are presented for different time delays between probe and pump. To analyze the situation where the transmission spectra are measured in the vicinity of the exciton, the exciton is a single homogeneously broadened transition.
Geometric analysis of satellite laser ranging data
NASA Technical Reports Server (NTRS)
Conklin, Brion; Bucey, Steven; Husson, Van S.; Decker, Winfield M.; Degnan, John J.
1993-01-01
The analysis of simultaneous laser data is investigated using the method of trilateration. Analysis of data from 1987 to 1992 is presented with selected baseline rates and station positions. The use of simultaneous Etalon data is simulated to demonstrate the additional global coverage these satellites provide. Trilateration has a great potential for regional deformation studies with monthly LAGEOS American solutions between 3-12 millimeters.
Consistency analysis on laser signal in laser guided weapon simulation
NASA Astrophysics Data System (ADS)
Yin, Ruiguang; Zhang, Wenpan; Guo, Hao; Gan, Lin
2015-10-01
The hardware-in-the-loop simulation is widely used in laser semi-active guidance weapon experiments, the authenticity of the laser guidance signal is the key problem of reliability. In order to evaluate the consistency of the laser guidance signal, this paper analyzes the angle of sight, laser energy density, laser spot size, atmospheric back scattering, sun radiation and SNR by comparing the different working state between actual condition and hardware-in-the-loop simulation. Based on measured data, mathematical simulation and optical simulation result, laser guidance signal effects on laser seeker are determined. By using Monte Carlo method, the laser guided weapon trajectory and impact point distribution are obtained, the influence of the systematic error are analyzed. In conclusion it is pointed out that the difference between simulation system and actual system has little influence in normal guidance, has great effect on laser jamming. The research is helpful to design and evaluation of laser guided weapon simulation.
Theoretical analysis of the state of balance in bipedal walking.
Firmani, Flavio; Park, Edward J
2013-04-01
This paper presents a theoretical analysis based on classic mechanical principles of balance of forces in bipedal walking. Theories on the state of balance have been proposed in the area of humanoid robotics and although the laws of classical mechanics are equivalent to both humans and humanoid robots, the resulting motion obtained with these theories is unnatural when compared to normal human gait. Humanoid robots are commonly controlled using the zero moment point (ZMP) with the condition that the ZMP cannot exit the foot-support area. This condition is derived from a physical model in which the biped must always walk under dynamically balanced conditions, making the centre of pressure (CoP) and the ZMP always coincident. On the contrary, humans follow a different strategy characterized by a 'controlled fall' at the end of the swing phase. In this paper, we present a thorough theoretical analysis of the state of balance and show that the ZMP can exit the support area, and its location is representative of the imbalance state characterized by the separation between the ZMP and the CoP. Since humans exhibit this behavior, we also present proof-of-concept results of a single subject walking on an instrumented treadmill at different speeds (from slow 0.7 m/s to fast 2.0 m/s walking with increments of 0.1 m/s) with the motion recorded using an optical motion tracking system. In order to evaluate the experimental results of this model, the coefficient of determination (R2) is used to correlate the measured ground reaction forces and the resultant of inertial and gravitational forces (anteroposterior R² = 0.93, mediolateral R² = 0.89, and vertical R² = 0.86) indicating that there is a high correlation between the measurements. The results suggest that the subject exhibits a complete dynamically balanced gait during slow speeds while experiencing a controlled fall (end of swing phase) with faster speeds. This is quantified with the root-mean-square deviation (RMSD
Theoretical Analysis of the Electron Spiral Toroid Concept
NASA Technical Reports Server (NTRS)
Cambier, Jean-Luc; Micheletti, David A.; Bushnell, Dennis M. (Technical Monitor)
2000-01-01
This report describes the analysis of the Electron Spiral Toroid (EST) concept being promoted by Electron Power Systems Inc. (EPS). The EST is described as a toroidal plasma structure composed Of ion and electron shells. It is claimed that the EST requires little or no external confinement, despite the extraordinarily large energy densities resulting from the self-generating magnetic fields. The present analysis is based upon documentation made available by EPS, a previous description of the model by the Massachusetts Institute of Technology (MIT), and direct discussions with EPS and MIT. It is found that claims of absolute stability and large energy storage capacities of the EST concept have not been substantiated. Notably, it can be demonstrated that the ion fluid is fundamentally unstable. Although various scenarios for ion confinement were subsequently suggested by EPS and MIT, none were found to be plausible. Although the experimental data does not prove the existence of EST configurations, there is undeniable experimental evidence that some type of plasma structures whose characteristics remain to be determined are observed. However, more realistic theoretical models must first be developed to explain their existence and properties before applications of interest to NASA can he assessed and developed.
Avramopoulos, H.; French, P.M.W.; Williams, J.A.R.; New, G.H.C.; Taylor, J.R. )
1988-09-01
The optimization of any femtosecond laser requires the various sources of frequency chirp to be taken into account. In particular, for a passively mode-locked CPM ring dye laser, the effects of group velocity dispersion and self-phase modulation arising from time-dependent absorption saturation and the optical Kerr effect must be considered. In this paper a detailed experimental and theoretical study has been made of the role of these parameters in a Rhodamine 110 CPM dye laser. Periodic pulse evolutions are observed, when both positive and negative frequency chirp are present, which are reminiscent of those governed by the nonlinear Schrodinger equation but which are, in fact, distinctly different. Similar results have been obtained with the standard Rhodamine 6G system and it is believed that the theoretical model is generally applicable to any passively mode-locked femtosecond dye laser. An important consequence of this work is that is permits the absolute value of the net group velocity dispersion in the laser cavity to be estimated.
NASA Astrophysics Data System (ADS)
Zhang, Baofu; He, Guangyuan; Jiao, Zhongxing; Wang, Biao
2016-03-01
We demonstrate an effective and simplified theoretical model of the in-band-pumped gain-switched thulium-doped fiber laser in which the effective pump power and effective population density are defined as the approximation of spatial variables. The numerical simulation results based on the model are in good agreement with the experimental data. The parameters of the pump source and the cavity configuration are considered in our numerical model for the optimization of the laser system. The pump condition in which the pulse distortion can be avoided is presented.
GRETNA: a graph theoretical network analysis toolbox for imaging connectomics
Wang, Jinhui; Wang, Xindi; Xia, Mingrui; Liao, Xuhong; Evans, Alan; He, Yong
2015-01-01
Recent studies have suggested that the brain’s structural and functional networks (i.e., connectomics) can be constructed by various imaging technologies (e.g., EEG/MEG; structural, diffusion and functional MRI) and further characterized by graph theory. Given the huge complexity of network construction, analysis and statistics, toolboxes incorporating these functions are largely lacking. Here, we developed the GRaph thEoreTical Network Analysis (GRETNA) toolbox for imaging connectomics. The GRETNA contains several key features as follows: (i) an open-source, Matlab-based, cross-platform (Windows and UNIX OS) package with a graphical user interface (GUI); (ii) allowing topological analyses of global and local network properties with parallel computing ability, independent of imaging modality and species; (iii) providing flexible manipulations in several key steps during network construction and analysis, which include network node definition, network connectivity processing, network type selection and choice of thresholding procedure; (iv) allowing statistical comparisons of global, nodal and connectional network metrics and assessments of relationship between these network metrics and clinical or behavioral variables of interest; and (v) including functionality in image preprocessing and network construction based on resting-state functional MRI (R-fMRI) data. After applying the GRETNA to a publicly released R-fMRI dataset of 54 healthy young adults, we demonstrated that human brain functional networks exhibit efficient small-world, assortative, hierarchical and modular organizations and possess highly connected hubs and that these findings are robust against different analytical strategies. With these efforts, we anticipate that GRETNA will accelerate imaging connectomics in an easy, quick and flexible manner. GRETNA is freely available on the NITRC website.1 PMID:26175682
Comparative analysis of planetary laser ranging concepts
NASA Astrophysics Data System (ADS)
Dirkx, D.; Bauer, S.; Noomen, R.; Vermeersen, B. L. A.; Visser, P. N.
2014-12-01
missions for various combinations of clock and state arc length. Thereby, we quantify the relative capabilities of the one- and two-way laser range systems. In addition, we study the optimal data analysis strategies for these missions, which we apply for LRO orbit determination. Finally, we compare the performance of the laser ranging systems with typical DSN tracking.
Advanced Orion Optimized Laser System Analysis
NASA Technical Reports Server (NTRS)
1996-01-01
Contractor shall perform a complete analysis of the potential of the solid state laser in the very long pulse mode (100 ns pulse width, 10-30 hz rep-rate) and in the very short pulse mode (100 ps pulse width 10-30 hz rep rate) concentrating on the operation of the device in the 'hot-rod' mode, where no active cooling the laser operation is attempted. Contractor's calculations shall be made of the phase aberrations which develop during the repped-pulse train, and the results shall feed into the adaptive optics analyses. The contractor shall devise solutions to work around ORION track issues. A final report shall be furnished to the MSFC COTR including all calculations and analysis of estimates of bulk phase and intensity aberration distribution in the laser output beam as a function of time during the repped-pulse train for both wave forms (high-energy/long-pulse, as well as low-energy/short-pulse). Recommendations shall be made for mitigating the aberrations by laser re-design and/or changes in operating parameters of optical pump sources and/or designs.
Jiao, L S; Ng, E Y K; Zheng, H Y; Zhang, Y L
2015-02-23
Maxwell's wave equation was solved for fs laser drilling of silicon. The pre-formed hole wall's influence on the propagation behavior of subsequent laser pulses was investigated. The laser intensity at hole bottom shows distinct profile as compared with that at hole entrance. The multi-peaks and ring structure of the laser intensity were found at hole bottom. The position of maximum laser intensity (MLI) in relation to the wall taper angle was studied. It was found that the position of the MLI point would be closer to the hole entrance with increasing taper angle. This observation provides valuable information in predicting the position of plasma plume which is a key factor influencing laser drilling process. The elliptical entrance hole shape and zonal structure at the hole bottom reported in the literatures have been reasonably explained using the laser intensity distribution obtained in the present model. PMID:25836527
Theoretical and experimental analysis of the physics of water rockets
NASA Astrophysics Data System (ADS)
Barrio-Perotti, R.; Blanco-Marigorta, E.; Fernández-Francos, J.; Galdo-Vega, M.
2010-09-01
A simple rocket can be made using a plastic bottle filled with a volume of water and pressurized air. When opened, the air pressure pushes the water out of the bottle. This causes an increase in the bottle momentum so that it can be propelled to fairly long distances or heights. Water rockets are widely used as an educational activity, and several mathematical models have been proposed to investigate and predict their physics. However, the real equations that describe the physics of the rockets are so complicated that certain assumptions are usually made to obtain models that are easier to use. These models provide relatively good predictions but fail in describing the complex physics of the flow. This paper presents a detailed theoretical analysis of the physics of water rockets that concludes with the proposal of a physical model. The validity of the model is checked by a series of field tests. The tests showed maximum differences with predictions of about 6%. The proposed model is finally used to investigate the temporal evolution of some significant variables during the propulsion and flight of the rocket. The experience and procedure described in this paper can be proposed to graduate students and also at undergraduate level if certain simplifications are assumed in the general equations.
Theoretical and Numerical Assessment of Strain Pattern Analysis
NASA Astrophysics Data System (ADS)
Milne, R. D.; Simpson, A.
1996-04-01
The Strain Pattern Analysis (SPA) method was conceived at the RAE in the 1970s as a means of estimating the displacement shape of a helicopter rotor blade by using only strain gauge data, but no attempt was made to provide theoretical justification for the procedure. In this paper, the SPA method is placed on a firm mathematical basis by the use of vector space theory. It is shown that the natural normwhich underlies the SPA projection is the strain energy functionalof the structure under consideration. The natural norm is a weightedversion of the original SPA norm. Numerical experiments on simple flexure and coupled flexure-torsion systems indicate that the use of the natural norm yields structural deflection estimates of significantly greater accuracy than those obtained from the original SPA procedure and that measurement error tolerance is also enhanced. Extensive numerical results are presented for an emulation of the SPA method as applied to existing mathematical models of the main rotor of the DRA Lynx ZD559 helicopter. The efficacy of SPA is demonstrated by using a quasi-linear rotor model in the frequency domain and a fully non-linear, kinematically exact model in the time domain: the procedure based on the natural (or weighted) norm is again found to be superior to that based on the original SPA method, both in respect of displacement estimates and measurement error tolerance.
GraTeLPy: graph-theoretic linear stability analysis
2014-01-01
Background A biochemical mechanism with mass action kinetics can be represented as a directed bipartite graph (bipartite digraph), and modeled by a system of differential equations. If the differential equations (DE) model can give rise to some instability such as multistability or Turing instability, then the bipartite digraph contains a structure referred to as a critical fragment. In some cases the existence of a critical fragment indicates that the DE model can display oscillations for some parameter values. We have implemented a graph-theoretic method that identifies the critical fragments of the bipartite digraph of a biochemical mechanism. Results GraTeLPy lists all critical fragments of the bipartite digraph of a given biochemical mechanism, thus enabling a preliminary analysis on the potential of a biochemical mechanism for some instability based on its topological structure. The correctness of the implementation is supported by multiple examples. The code is implemented in Python, relies on open software, and is available under the GNU General Public License. Conclusions GraTeLPy can be used by researchers to test large biochemical mechanisms with mass action kinetics for their capacity for multistability, oscillations and Turing instability. PMID:24572152
A novel theoretical approach to the analysis of dendritic transients.
Agmon-Snir, H
1995-01-01
A novel theoretical framework for analyzing dendritic transients is introduced. This approach, called the method of moments, is an extension of Rall's cable theory for dendrites. It provides analytic investigation of voltage attenuation, signal delay, and synchronization problems in passive dendritic trees. In this method, the various moments of a transient signal are used to characterize the properties of the transient. The strength of the signal is measured by the time integral of the signal, its characteristic time is determined by its centroid ("center of gravity"), and the width of the signal is determined by a measure similar to the standard deviation in probability theory. Using these signal properties, the method of moments provides theorems, expressions, and efficient algorithms for analyzing the voltage response in arbitrary passive trees. The method yields new insights into spatiotemporal integration, coincidence detection mechanisms, and the properties of local interactions between synaptic inputs in dendritic trees. The method can also be used for matching dendritic neuron models to experimental data and for the analysis of synaptic inputs recorded experimentally. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 10 PMID:8580308
Experimental and theoretical analysis results for high temperature air combustion
Tanigawa, Tadashi; Morita, Mitsunobu
1998-07-01
With Japan's preparation of its Action program to prevent global warming in 1990 and the holding of the United National Conference on Environment and Development (the Earth Summit) in 1992 as a backdrop, reflecting the global effort to protect the environment, a high performance industrial furnace development project was launched in 1993 by the New Energy and Industrial Technology Development Organization (NEDO). This project focuses on the development of a combustion technology which uses air that is preheated to extremely high temperatures (above 1,000 C), heretofore considered impossible. Not only can this technology reduce carbon dioxide emission, thought to cause the greenhouse effect, by over 30%, but it can also reduce nitrogen oxide emission by nearly half. This new technology makes use of the recently-developed high-cycle regenerative heat exchanger, for preheating the furnace air supply. This exchanger preheats air to above 1,000 C, much higher than for conventional furnaces, and then this air is injected with fuel. R and D data have shown that CO{sub 2} and NO{sub x} emissions can be reduced markedly. However, the theoretical analysis is yet to be made, thereby hampering efforts to have this advanced technology become widely adopted. This project accumulated new data related to uniform temperature distribution, high energy heat transfer and low NO{sub x} as common characteristics of high temperature air combustion.
Theoretical and experimental analysis of a soluble enzyme membrane reactor.
Greco, G; Alfani, F; Iorio, G; Cantarella, M; Formisano, A; Gianfreda, L; Palescandolo, R; Scardi, V
1979-08-01
Recently enzyme immobilization techniques have been proposed that are mainly founded on the formation of an enzyme-gel layer onto the active surface of an ultrafiltration membrane within an unstirred ultrafiltration cell. If the membrane molecular-weight cutoff is less than the enzyme molecular weight and hence such as to completely prevent enzyme permeation (once the enzyme solution has been charged into the test cell and pressure applied to the system), a time progressive increase in enzyme concentration takes place at the upstream membrane surface that can eventually lead to gelation and hence to enzyme immobilization. However, depending on the total enzyme amount fed, the maximum enzyme concentration achieved in the unsteady state could be less than the gelation level. In this situation, no immobilization occurs and the enzyme still remains in the soluble form although it is practically confined within a limited region immediately upstream the membrane and at fairly high concentrations. In this paper, the experimental conditions that allow gelling to occur are discussed together with a theoretical analysis of the soluble enzyme membrane reactor which is obtained when no gelling takes place. Such a system could be usefully employed in performing kinetic analyses at high enzyme concentration levels that are still in the soluble form. PMID:454808
Theoretical analysis of magnetic field interactions with aortic blood flow
Kinouchi, Y.; Yamaguchi, H.; Tenforde, T.S.
1996-04-01
The flow of blood in the presence of a magnetic field gives rise to induced voltages in the major arteries of the central circulatory system. Under certain simplifying conditions, such as the assumption that the length of major arteries (e.g., the aorta) is infinite and that the vessel walls are not electrically conductive, the distribution of induced voltages and currents within these blood vessels can be calculated with reasonable precision. However, the propagation of magnetically induced voltages and currents from the aorta into neighboring tissue structures such as the sinuatrial node of the heart has not been previously determined by any experimental or theoretical technique. In the analysis presented in this paper, a solution of the complete Navier-Stokes equation was obtained by the finite element technique for blood flow through the ascending and descending aortic vessels in the presence of a uniform static magnetic field. Spatial distributions of the magnetically induced voltage and current were obtained for the aortic vessel and surrounding tissues under the assumption that the wall of the aorta is electrically conductive. Results are presented for the calculated values of magnetically induced voltages and current densities in the aorta and surrounding tissue structures, including the sinuatrial node, and for their field-strength dependence. In addition, an analysis is presented of magnetohydrodynamic interactions that lead to a small reduction of blood volume flow at high field levels above approximately 10 tesla (T). Quantitative results are presented on the offsetting effects of oppositely directed blood flows in the ascending and descending aortic segments, and a quantitative estimate is made of the effects of assuming an infinite vs. a finite length of the aortic vessel in calculating the magnetically induced voltage and current density distribution in tissue.
Laser safety and hazard analysis for the temperature stabilized BSLT ARES laser system.
Augustoni, Arnold L.
2003-08-01
A laser safety and hazard analysis was performed for the temperature stabilized Big Sky Laser Technology (BSLT) laser central to the ARES system based on the 2000 version of the American National Standards Institute's (ANSI) Standard Z136.1, for Safe Use of Lasers and the 2000 version of the ANSI Standard Z136.6, for Safe Use of Lasers Outdoors. As a result of temperature stabilization of the BSLT laser the operating parameters of the laser had changed requiring a hazard analysis based on the new operating conditions. The ARES laser system is a Van/Truck based mobile platform, which is used to perform laser interaction experiments and tests at various national test sites.
Yaroshchyk, Pavel; Morrison, Richard J S; Body, Doug; Chadwick, Bruce L
2004-11-01
Optimal conditions are determined for laser-induced breakdown spectroscopy in liquid jets by investigating laser de-focusing and laser energy variation in aqueous liquid jets containing dilute levels of calcium chloride. It has been found that the atomic emission shows a strong correlation with both laser pulse energy and focal position. The data cannot be rationalized on the basis of electron density or ionization temperature changes alone, but rather it requires the additional consideration of the volume of the liquid sample interacting with the laser and that portion of the volume which is above the threshold energy for plasma formation. A moving breakdown model has been applied to the plasma formation in the jet to calculate the amount of sample ablated with sufficient energy for plasma formation, which models well the observed results and allows prediction of optimal focusing conditions for a given laser energy. PMID:18070410
Theoretical And Experimental Investigations On The Plasma Of A CO2 High Power Laser
NASA Astrophysics Data System (ADS)
Abel, W.; Wallter, B.
1984-03-01
The CO2 high power laser is increasingly used in material processing. This application of the laser has to meet some requirements: at one hand the laser is a tool free of wastage, but at the other hand is to guarantee that the properties of that tool are constant in time. Therefore power, geometry and mode of the beam have to be stable over long intervalls, even if the laser is used in rough industrial environment. Otherwise laser material processing would not be competitive. The beam quality is affected by all components of the laser - by the CO2 plasma and its IR - amplification, by the resonator which at last generates the beam by optical feedback, and also by the electric power supply whose effects on the plasma may be measured at the laser beam. A transversal flow laser has been developed at the Technical University of Vienna in cooperation with VOest-Alpine AG, Linz (Austria). This laser produces 1 kW of beam power with unfolded resonator. It was subject to investigations presented in this paper.
A theoretical analysis of optimum consumer population and its control.
Jiang, Z; Mao, Z; Wang, H
1994-01-01
Material production is related to population consumption in every society. Consumption also constantly transforms materials, energy, and information. In this sense, consumption provides both impetus for material production and a self-adapting mechanism for population development and control. Population structure variables affecting economic production can be divided according to non-adults, working-age work force and the elderly, social status, and urban-rural structure. The consumptive structures among people of different social status reflect different needs for social and economic development. The theoretical calculation of the consumer population in the national economy demonstrates that the national income in a certain year of a given national economy equals consumption fund plus accumulation fund where consumption fund includes social consumption fund and residential consumption fund. Social consumption fund is spent mostly on public utilities, administrative management, national defense, education, public health and urban construction, as well as on environment management and disaster relief. The residential consumption fund can be divided into basic expenditure such as clothing, food, shelter and transportation, and self-improvement expenditure such as recreation, education, and travel. As a result of economic development, not only the percentage of the expenditure on food will decrease and the percentage of the expenditure on clothing, shelter, transportation, and other daily necessities will increase, but expenses on recreation and education also will grow. Residential consumption is divided into subsistence consumption (Type I consumption) and self-improvement (recreation and education) consumption (Type II consumption) in order to determine consumer population and the degree of urbanization and its impact upon social and economic development. A moderate consumer population model of urban and rural areas was established by using the urban and rural
A theoretical analysis of basin-scale groundwater temperature distribution
NASA Astrophysics Data System (ADS)
An, Ran; Jiang, Xiao-Wei; Wang, Jun-Zhi; Wan, Li; Wang, Xu-Sheng; Li, Hailong
2015-03-01
The theory of regional groundwater flow is critical for explaining heat transport by moving groundwater in basins. Domenico and Palciauskas's (1973) pioneering study on convective heat transport in a simple basin assumed that convection has a small influence on redistributing groundwater temperature. Moreover, there has been no research focused on the temperature distribution around stagnation zones among flow systems. In this paper, the temperature distribution in the simple basin is reexamined and that in a complex basin with nested flow systems is explored. In both basins, compared to the temperature distribution due to conduction, convection leads to a lower temperature in most parts of the basin except for a small part near the discharge area. There is a high-temperature anomaly around the basin-bottom stagnation point where two flow systems converge due to a low degree of convection and a long travel distance, but there is no anomaly around the basin-bottom stagnation point where two flow systems diverge. In the complex basin, there are also high-temperature anomalies around internal stagnation points. Temperature around internal stagnation points could be very high when they are close to the basin bottom, for example, due to the small permeability anisotropy ratio. The temperature distribution revealed in this study could be valuable when using heat as a tracer to identify the pattern of groundwater flow in large-scale basins. Domenico PA, Palciauskas VV (1973) Theoretical analysis of forced convective heat transfer in regional groundwater flow. Geological Society of America Bulletin 84:3803-3814
Category Theoretic Analysis of Hierarchical Protein Materials and Social Networks
Spivak, David I.; Giesa, Tristan; Wood, Elizabeth; Buehler, Markus J.
2011-01-01
Materials in biology span all the scales from Angstroms to meters and typically consist of complex hierarchical assemblies of simple building blocks. Here we describe an application of category theory to describe structural and resulting functional properties of biological protein materials by developing so-called ologs. An olog is like a “concept web” or “semantic network” except that it follows a rigorous mathematical formulation based on category theory. This key difference ensures that an olog is unambiguous, highly adaptable to evolution and change, and suitable for sharing concepts with other olog. We consider simple cases of beta-helical and amyloid-like protein filaments subjected to axial extension and develop an olog representation of their structural and resulting mechanical properties. We also construct a representation of a social network in which people send text-messages to their nearest neighbors and act as a team to perform a task. We show that the olog for the protein and the olog for the social network feature identical category-theoretic representations, and we proceed to precisely explicate the analogy or isomorphism between them. The examples presented here demonstrate that the intrinsic nature of a complex system, which in particular includes a precise relationship between structure and function at different hierarchical levels, can be effectively represented by an olog. This, in turn, allows for comparative studies between disparate materials or fields of application, and results in novel approaches to derive functionality in the design of de novo hierarchical systems. We discuss opportunities and challenges associated with the description of complex biological materials by using ologs as a powerful tool for analysis and design in the context of materiomics, and we present the potential impact of this approach for engineering, life sciences, and medicine. PMID:21931622
Laser speckle analysis synchronised with cardiac cycle
NASA Astrophysics Data System (ADS)
Zakharov, Pavel; Scheffold, Frank; Weber, Bruno
2015-07-01
We present an improved Laser speckle imaging approach to investigate the cerebral blood flow response following function stimulation of a single vibrissa. By synchronising speckle analysis with the cardiac cycle we are able to obtain robust averaging of the correlation signals while at the same time removing the contributions due to the pulsation of blood flow and associated tissue adaptation. With our inter-pulse correlation analysis we can follow second-scale dynamics of the cortical vascular system in response to functional brain activation. We find evidence for two temporally separated processes in the blood flow pattern following stimulation we tentatively attribute to vasodilation and vasoconstriction phases, respectively.
ARTICLES: Laser spectrochromatographic analysis of petroleum components
NASA Astrophysics Data System (ADS)
Korobeĭnik, G. S.; Letokhov, V. S.; Montanari, S. G.; Tumanova, L. M.
1985-01-01
A system combining a gas chromatograph and a laser optoacoustic spectrometer (with a CO2 laser and means for fast frequency scanning) was used to investigate model hydrocarbon mixtures, as well as some real objects in the form of benzine fractions of petroleum oil. The fast scanning regime was used to record optoacoustic spectra of hydrocarbons (in the range 9.2-10.8μ) during the travel time (1-10 sec) of the individual components of a mixture through an optoacoustic cell in the course of chromatrographic separation of these components. The spectra were used to carry out a group hydrocarbon analysis of benzine fractions of petroleum oil from various locations. The proposed method was relatively fast and was characterized by a good ability for identification of various components, compared with the usually employed method such as gas-liquid capillary chromatography.
Emission spectroscopy analysis during Nopal cladodes dethorning by laser ablation
NASA Astrophysics Data System (ADS)
Peña-Díaz, M.; Ponce, L.; Arronte, M.; Flores, T.
2007-04-01
Optical emission spectroscopy of the pulsed laser ablation of spines and glochids from Opuntia (Nopal) cladodes was performed. Nopal cladodes were irradiated with Nd:YAG free-running laser pulses on their body, glochids and spines. Emission spectroscopy analyses in the 350-1000 nm region of the laser induced plasma were made. Plasma plume evolution characterization, theoretical calculations of plasma plume temperature and experiments varying the processing atmosphere showed that the process is dominated by a thermally activated combustion reaction which increases the dethorning process efficiency. Therefore, appropriate laser pulse energy for minimal damage of cladodes body and in the area beneath glochids and spines can be obtained.
Theoretical analysis and experimental verification on optical rotational Doppler effect.
Zhou, Hailong; Fu, Dongzhi; Dong, Jianji; Zhang, Pei; Zhang, Xinliang
2016-05-01
We present a theoretical model to sufficiently investigate the optical rotational Doppler effect based on modal expansion method. We find that the frequency shift content is only determined by the surface of spinning object and the reduced Doppler shift is linear to the difference of mode index between input and output orbital angular momentum (OAM) light, and linear to the rotating speed of spinning object as well. An experiment is carried out to verify the theoretical model. We explicitly suggest that the spatial spiral phase distribution of spinning object determines the frequency content. The theoretical model makes us better understand the physical processes of rotational Doppler effect, and thus has many related application fields, such as detection of rotating bodies, imaging of surface and measurement of OAM light. PMID:27137615
Theoretical analysis and experimental verification on optical rotational Doppler effect
NASA Astrophysics Data System (ADS)
Zhou, Hailong; Fu, Dongzhi; Dong, Jianji; Zhang, Pei; Zhang, Xinliang
2016-05-01
We present a theoretical model to sufficiently investigate the optical rotational Doppler effect based on modal expansion method. We find that the frequency shift content is only determined by the surface of spinning object and the reduced Doppler shift is linear to the difference of mode index between input and output orbital angular momentum (OAM) light, and linear to the rotating speed of spinning object as well. An experiment is carried out to verify the theoretical model. We explicitly suggest that the spatial spiral phase distribution of spinning object determines the frequency content. The theoretical model makes us better understand the physical processes of rotational Doppler effect, and thus has many related application fields, such as detection of rotating bodies, imaging of surface and measurement of OAM light.
Theoretical foundations of detection of terahertz radiation in laser-plasma interactions
Frolov, A. A.
2013-02-15
A theory is developed enabling one to calculate the temporal profile and spectrum of a terahertz wave packet from the energy of the second harmonic of optical radiation generated during the nonlinear interaction between terahertz and circularly polarized laser pulses in the skin layer of an overdense plasma. It is shown that the spectral and temporal characteristics of the envelope of the second harmonic of optical radiation coincide with those of the terahertz pulse only at small durations of the detecting laser radiation. For long laser pulses, the temporal profile and spectrum of the second harmonic are mainly determined by the characteristics of optical radiation at the carrier frequency.
Relocation of the Aged: A Review and Theoretical Analysis
ERIC Educational Resources Information Center
Schulz, Richard; Brenner, Gail
1977-01-01
Literature on relocation of the aged is examined and findings are presented within a framework of three types of moves--institution to institution, home to institution, and home to home--with each type having a voluntary and involuntary component. A theoretical model is proposed to explain contradictory results reported. (Author)
Geophysical parameters from the analysis of laser ranging to Starlette
NASA Technical Reports Server (NTRS)
Schutz, B. E.; Shum, C. K.; Tapley, B. D.
1991-01-01
The University of Texas Center for Space Research (UT/CSR) research efforts covering the time period from August 1, 1990 through January 31, 1991 have concentrated on the following areas: (1) Laser Data Processing (more than 15 years of Starlette data (1975-90) have been processed and cataloged); (2) Seasonal Variation of Zonal Tides (observed Starlette time series has been compared with meteorological data-derived time series); (3) Ocean Tide Solutions . (error analysis has been performed using Starlette and other tide solutions); and (4) Lunar Deceleration (formulation to compute theoretical lunar deceleration has been verified and applied to several tidal solutions). Concise descriptions of research achievement for each of the above areas are given. Copies of abstracts for some of the publications and conference presentations are included in the appendices.
Spectroscopic analysis of femtosecond laser plasma filament in air
NASA Astrophysics Data System (ADS)
Bernhardt, J.; Liu, W.; Théberge, F.; Xu, H. L.; Daigle, J. F.; Châteauneuf, M.; Dubois, J.; Chin, S. L.
2008-03-01
We report a spectroscopic analysis of a filament generated by a femtosecond laser pulse in air. In the filament spectra, the characteristic Stark broadened atomic oxygen triplet centered at 777.4 nm has been observed. The measured electron impact Stark broadening parameter of the triplet is larger than the theoretical value by Griem [H.R. Griem, Plasma Spectroscopy, McGraw Hill, New York, 1964] by a factor 6.7 . Using the experimental value 0.0166nm , the plasma densities derived from Stark broadening agree well with those most recently obtained from Théberge et al.'s measurement of the nitrogen fluorescence calibrated by longitudinal diffraction [F. Théberge, W. Liu, P.T. Simard, A. Becker, S. L. Chin, Phys. Rev. E 74 (2006) 036406]. However, the Stark broadening approach is much simpler and can be used to non-invasively measure the filament plasma density distribution in air under different propagation conditions.
Theoretical study and simulation for a nanometer laser based on Gauss-Hermite source expansion
NASA Astrophysics Data System (ADS)
Gu, Xiaowei
2013-07-01
Recently there has been worldwide interest in constructing a new generation of continuously tunable nanometer lasers for a wide range of scientific applications, including femtosecond science, biological molecules, nanoscience research fields, etc. The high brightness electron beam required by a short wavelength self-amplified spontaneous emission FEL can be reached only with accurate control of the beam dynamics in the facility. Numerical simulation codes are basic tools for designing new nanometer laser devices. We have developed a MATLAB quasi-one-dimensional code based on a reduced model for the FEL. The model uses an envelope description of the transverse dynamics of the laser beam and full longitudinal particle motion. We have optimized the LCLS facility parameters, then given the characteristics of the nanometer laser.
Theoretical research on period microstructure induced by femtosecond laser in transparent dielectric
NASA Astrophysics Data System (ADS)
Fan, Shuwei; Zhang, Yan
2014-11-01
In this paper, we do some research on the interior period microstructure of transparent materials induced by a femtosecond laser of 800-nm wavelength. By adopting a nonlinear propagation physical model of femtosecond laser pulses and considering the spherical aberration effect(SA), we analyze the influence of nonlinear effects such an self-focusing, GDV, MPA, plasma defocusing and interface aberration on femtosecond laser propagation in transparent materials. Meantime, in the case with nonlinear effects and interface aberration, we research the influence of fs laser power, pulse width, numerical aperture and focusing depth on period microvoid. Simultaneously, compared with simulating results in different focusing lens numerical aperture, we find that big numerical aperature and deep focusing more easily produced period voids.
Laser Atmospheric Wind Sounder (LAWS) performance analysis
NASA Technical Reports Server (NTRS)
Kenyon, D.; Petheram, J.
1991-01-01
The science objectives of the NASA's Laser Atmospheric Sounder (LAWS) are discussed, and results of the performance analysis of the LAWS system are presented together with the instrument configuration used for these performance analyses. The results of analyses show that the science requirements for the wind-velocity accuracies of m/sec in the lower troposphere and 5 m/sec in the upper troposphere will be met by the present design of the LAWS system. The paper presents the performance estimates of the LAWS in terms of the global coverage, spatial resolution, signal-to-noise ratio, line-of-sight velocity error, and horizontal inversion accuracy.
NASA Technical Reports Server (NTRS)
Stallcop, J. R.
1974-01-01
The theory for calculating the absorption of laser radiation by hydrogen is outlined for the temperatures and pressures of common laboratory plasmas. Nonhydrogenic corrections for determining the absorption by helium are also included. The coefficients for the absorption of He-Ne laser radiation at the wavelengths of 0.633, 1.15, and 3.39 microns in a H plasma is presented for temperatures in the range from 10,000 to 40,000 K and electron number densities in the range from 10 to the 15th power to 10 to the 18th power per cu cm. The total absorption of a H-He plasma calculated from this theory is compared with the measured absorption. The theoretical composition of the H-He absorption is analyzed with respect to the significant absorption processes, inverse bremsstrahlung, photoionization, resonance excitation, and photodetachment.
Theoretical analysis of protein organization in lipid membranes.
Gil, T; Ipsen, J H; Mouritsen, O G; Sabra, M C; Sperotto, M M; Zuckermann, M J
1998-11-10
The fundamental physical principles of the lateral organization of trans-membrane proteins and peptides as well as peripheral membrane proteins and enzymes are considered from the point of view of the lipid-bilayer membrane, its structure, dynamics, and cooperative phenomena. Based on a variety of theoretical considerations and model calculations, the nature of lipid-protein interactions is considered both for a single protein and an assembly of proteins that can lead to aggregation and protein crystallization in the plane of the membrane. Phenomena discussed include lipid sorting and selectivity at protein surfaces, protein-lipid phase equilibria, lipid-mediated protein-protein interactions, wetting and capillary condensation as means of protein organization, mechanisms of two-dimensional protein crystallization, as well as non-equilibrium organization of active proteins in membranes. The theoretical findings are compared with a variety of experimental data. PMID:9804966
Remodeling of the bone material containing microcracks: A theoretical analysis
NASA Astrophysics Data System (ADS)
Ramtani, S.; Zidi, M.
1999-12-01
The question is, what happens when the bone loses its ability for load-driven adaptation, when damage is no longer repaired as it seems to be the case for bone loss associated with age, medication or disease? In this study, we tempt to show how damage can influence the remodeling process. A thermodynamic theoretical framework is therefore provided as a basis for a consistent formulation of bone remodeling involving a chemical reaction and mass transfer between two constituents in presence of microcracks.
Theoretical analysis of microtubule dynamics at all times.
Li, Xin; Kolomeisky, Anatoly B
2014-12-01
Microtubules are biopolymers consisting of tubulin dimer subunits. As a major component of cytoskeleton they are essential for supporting most important cellular processes such as cell division, signaling, intracellular transport and cell locomotion. The hydrolysis of guanosine triphosphate (GTP) molecules attached to each tubulin subunit supports the nonequilibrium nature of microtubule dynamics. One of the most spectacular properties of microtubules is their dynamic instability when their growth from continuous attachment of tubulin dimers stochastically alternates with periods of shrinking. Despite the critical importance of this process to all cellular activities, its mechanism remains not fully understood. We investigated theoretically microtubule dynamics at all times by analyzing explicitly temporal evolution of various length clusters of unhydrolyzed subunits. It is found that the dynamic behavior of microtubules depends strongly on initial conditions. Our theoretical findings provide a microscopic explanation for recent experiments which found that the frequency of catastrophes increases with the lifetime of microtubules. It is argued that most growing microtubule configurations cannot transit in one step into a shrinking state, leading to a complex overall temporal behavior. Theoretical calculations combined with Monte Carlo computer simulations are also directly compared with experimental observations, and good agreement is found. PMID:25390471
Analysis of laser jamming to satellite-based detector
NASA Astrophysics Data System (ADS)
Wang, Si-wen; Guo, Li-hong; Guo, Ru-hai
2009-07-01
The reconnaissance satellite, communication satellite and navigation satellite used in the military applications have played more and more important role in the advanced technique wars and already become the significant support and aid system for military actions. With the development of all kinds of satellites, anti-satellite laser weapons emerge as the times require. The experiments and analyses of laser disturbing CCD (charge coupled detector) in near ground have been studied by many research groups, but their results are not suitable to the case that using laser disturbs the satellite-based detector. Because the distance between the satellite-based detector and the ground is very large, it is difficult to damage it directly. However the optical receive system of satellite detector has large optical gain, so laser disturbing satellite detector is possible. In order to determine its feasibility, the theoretical analyses and experimental study are carried out in the paper. Firstly, the influence factors of laser disturbing satellite detector are analyzed in detail, which including laser power density on the surface of the detector after long distance transmission, and laser power density threshold for disturbing etc. These factors are not only induced by the satellite orbit, but dependence on the following parameters: laser average power in the ground, laser beam quality, tracing and aiming precision and atmospheric transmission. A calculation model is developed by considering all factors which then the power density entering into the detector can be calculated. Secondly, the laser disturbing experiment is performed by using LD (laser diode) with the wavelength 808 nm disturbing CCD 5 kilometer away, which the disturbing threshold value is obtained as 3.55×10-4mW/cm2 that coincides with other researcher's results. Finally, using the theoretical model, the energy density of laser on the photosensitive surface of MSTI-3 satellite detector is estimated as about 100m
NASA Astrophysics Data System (ADS)
Shelton, John D.
1995-10-01
Expressions for the variance and the power spectral density of turbulence-induced log-amplitude fluctuations are derived for Gaussian-beam waves in the regime of weak scattering. This formulation includes effects that are due to turbulence strength variations along the propagation path, offset of the observation point from the beam axis, and sensitivity to focus and beam diameter. Comparison of theoretical results with observed scintillation during experiments with a laser-illuminated satellite reveals good agreement. Copyright (c) 1995 Optical Society of America
Thomas, John
2012-05-01
Systems Theoretic Process Analysis (STPA) is a powerful new hazard analysis method designed to go beyond traditional safety techniques - such as Fault Tree Analysis (FTA) - that overlook important causes of accidents like flawed requirements, dysfunctional component interactions, and software errors. While proving to be very effective on real systems, no formal structure has been defined for STPA and its application has been ad-hoc with no rigorous procedures or model-based design tools. This report defines a formal mathematical structure underlying STPA and describes a procedure for systematically performing an STPA analysis based on that structure. A method for using the results of the hazard analysis to generate formal safety-critical, model-based system and software requirements is also presented. Techniques to automate both the analysis and the requirements generation are introduced, as well as a method to detect conflicts between the safety and other functional model-based requirements during early development of the system.
Egorov, Alexander A
2011-07-31
We consider theoretical, experimental and numerical methods which make it possible to analyse the key characteristics of laser radiation scattered in the integrated-optical waveguide with three-dimensional irregularities. The main aspects of the three-dimensional vector electrodynamic problem of waveguide scattering are studied. The waveguide light scattering method is presented and its main advantages over the methods of single scattering of laser radiation are discussed. The experimental setup and results of measurements are described. Theoretical and experimental results confirming the validity of the vector theory of three-dimensional waveguide scattering of laser radiation developed by the author are compared for the first time. (fiber and integrated optics)
NASA Technical Reports Server (NTRS)
Shutz, Bob E.; Urban, Timothy J.
2014-01-01
This ATBD summarizes (and links with other ATBDs) the elements used to obtain the geolocated GLAS laser spot location, with respect to the Earth Center of Mass. Because of the approach used, the reference frame used to express the geolocation is linked to the reference frame used for POD and PAD, which are related to the ITRF. The geolocated spot coordinates (which includes the elevation or height, with respect to an adopted reference ellipsoid) is the inferred position of the laser spot, since the spot location is not directly measured. This document also summarizes the GLAS operation time periods.
Theoretical research on damage mechanism of ultrafast laser ablation crystal silicon
NASA Astrophysics Data System (ADS)
Shao, Junfeng; Guo, Jin; Wang, Tingfeng
2013-09-01
High peak power picosecond laser ablation of silicon draws great attention in solar cell manufacture,laser optoelectric countermeasure applications, eta. This paper reports the damage process of ultrafast lasers interaction with silicon,which is based on Two-Temperature Model(TTM) and 1-on-1 damage threshold test method. Pulsed laser caused damage manifests in several ways, such as heat damage, mechanical effect and even eletrical effect. In this paper, a modified Two Temperature Model is applied in ultrashort laser interaction with silicon.The traditional Two-Temperature Model methods is proposed by Anismov in 1970s to calculate the interaction between ultrafast laser with metals, which is composed of free electrons and lattice. Beyond the carrier and lattice temperture model, an additional excited term and Auger recombination term of carriers is taken into account in this modified Two-Temperature Model model to reflect the characteristics in semicondutors. Under the same pulse-duration condition, the damage threshold is found to be 161 mJ/cm2 and a characteritic double-peak shape shows up. As the pulse energy density rises from 50mJ/cm2 to 161 mJ/cm2, the difference between carrier and lattice temperature steps down proportionally.Also,a detailed interaction process between photon-electron and electron-phonon is discussed. Electron and lattice temperature evolutes distinctly different, while the former is much higher than the latter until heat tranfer finished at 200 picoseconds. Two-peak feature of electron temperature is also identified. As the pulse duration increases from 20 picosecond to 60 picosecond, the he difference between carrier and lattice temperature steps down significantly. The calculated damage threshold does not change fundamentally, remaining approximately 0.16J/cm2. Also, the damage mechanism is found to be thermal heating with the pulse width between 20 and 60 picoseconds at threshold fluences which is identical to experiment test result
Role of temperature in the theoretical analysis of holmium pnictides
NASA Astrophysics Data System (ADS)
Bhardwaj, Purvee; Singh, Sadhna
2016-01-01
The high-pressure structural phase transition and associated properties of holmium pnictides (HoX; X = P, As, Sb and Bi) have been investigated in the present work. The Realistic Interaction Potential Approach (RIPA) including the effect of temperature has been applied. The occurrence of first order phase transition is evidenced from a sudden collapse in volume. These compounds transform from B1 to B2 structure under high pressure. The high temperature and pressure behaviour of elastic constants and bulk modulus are also reported. Our results are in general in good agreement with experimental and other theoretical results where available, and provide predictions where they are unavailable.
NASA Astrophysics Data System (ADS)
Qi, Huan
Direct metal deposition (DMD), a laser-cladding based solid freeform fabrication technique, is capable of depositing multiple materials at desired composition which makes this technique a flexible method to fabricate heterogeneous components or functionally-graded structures. The inherently rapid cooling rate associated with the laser cladding process enables extended solid solubility in nonequilibrium phases, offering the possibility of tailoring new materials with advanced properties. This technical advantage opens the area of synthesizing a new class of materials designed by topology optimization method which have performance-based material properties. For better understanding of the fundamental phenomena occurring in multi-material laser cladding with coaxial powder injection, a self-consistent 3-D transient model was developed. Physical phenomena including laser-powder interaction, heat transfer, melting, solidification, mass addition, liquid metal flow, and species transportation were modeled and solved with a controlled-volume finite difference method. Level-set method was used to track the evolution of liquid free surface. The distribution of species concentration in cladding layer was obtained using a nonequilibrium partition coefficient model. Simulation results were compared with experimental observations and found to be reasonably matched. Multi-phase material microstructures which have negative coefficients of thermal expansion were studied for their DMD manufacturability. The pixel-based topology-optimal designs are boundary-smoothed by Bezier functions to facilitate toolpath design. It is found that the inevitable diffusion interface between different material-phases degrades the negative thermal expansion property of the whole microstructure. A new design method is proposed for DMD manufacturing. Experimental approaches include identification of laser beam characteristics during different laser-powder-substrate interaction conditions, an
Theoretical and software considerations for nonlinear dynamic analysis
NASA Technical Reports Server (NTRS)
Schmidt, R. J.; Dodds, R. H., Jr.
1983-01-01
In the finite element method for structural analysis, it is generally necessary to discretize the structural model into a very large number of elements to accurately evaluate displacements, strains, and stresses. As the complexity of the model increases, the number of degrees of freedom can easily exceed the capacity of present-day software system. Improvements of structural analysis software including more efficient use of existing hardware and improved structural modeling techniques are discussed. One modeling technique that is used successfully in static linear and nonlinear analysis is multilevel substructuring. This research extends the use of multilevel substructure modeling to include dynamic analysis and defines the requirements for a general purpose software system capable of efficient nonlinear dynamic analysis. The multilevel substructuring technique is presented, the analytical formulations and computational procedures for dynamic analysis and nonlinear mechanics are reviewed, and an approach to the design and implementation of a general purpose structural software system is presented.
Theoretical analysis of crosstalk in near-infrared topography
NASA Astrophysics Data System (ADS)
Okada, E.; Okui, N.
2006-09-01
Crosstalk between changes in concentration of oxy-and deoxy-haemoglobin calculated by modified Lambert-Beer law in near-infrared topography is theoretically investigated. The change in intensity detected with source-detector pairs on the scalp caused by global or focal ahsorption change in the brain is predicted by Monte Carlo simulation. The topographic images of changes in oxy- and deoxy-haemoglobin are obtained from the changes in intensity detected with source-detector pairs on the scalp. The crosstalk depends on the relative position of the focal absorption change to source-detector pairs. The crosstalk is minimised when the focal absorption change is located below a measurement point that is the midpoint between a source and a detector.
Mass media and environmental issues: a theoretical analysis
Parlour, J.W.
1980-01-01
A critique of the weak empirical and theoretical foundations of commentaries on the mass media in the environmental literature argues that they stem from the incidental rather than fundamental concern for the social dimensions of environmental problems. The contributions of information theory, cybernetics, sociology, and political science to micro and macro theories of mass communications are reviewed. Information from empirical analyses of the mass media's portrayal of social issues, including the environment, is related to Hall's dominant ideology thesis of the mass media and the elitist-conflict model of society. It is argued that the media's portrayal of environmental issues is structured by dominant power-holding groups in society with the result that the media effectively function to maintain and reinforce the status quo to the advantage of these dominant groups. 78 references.
Analysis of Boling's laser-damage morphology
Sparks, M.S.
1980-08-15
Boling observed that his total-internal-reflection laser-damage sites in glass closely resembled the scattering cross section for small (ka << 1), perfectly conducting sphere and suggested that a very small plasma formed and grew to a larger size, still with ka << 1 satisfied. Even with ka = 1, for which the cross section is different from that observed, the scattered field still is too small to explain the damage in terms of constructive interference between the incident- and scattered fields. Furthermore, the characteristic shape of the scattering cross section that matches the damage patterns is for circular polarization or unpolarized light, in contrast to the experimental plane polarizations. Extending the ideas to include effects of the scattered field outside the glass, such as plasma formation, and to include the correct field (with interesting polarization, including longitudinal circuler polarization at certain distances from the surface) incident on the sphere may explain the experiments. Additional experiments and analysis would be useful to determine if the extended model is valid and to investigate related materials improvement, nondestructive testing, and the relation between laser damage, plasma initiation, and failure under stress, all initiated at small isolated spots.
Laser capture microdissection for gene expression analysis.
Bidarimath, Mallikarjun; Edwards, Andrew K; Tayade, Chandrakant
2015-01-01
Laser capture microdissection (LCM) is an excellent and perhaps the only platform to isolate homogeneous cell populations from specific microscopic regions of heterogeneous tissue section, under direct microscopic visualization. The basic operations of the LCM system are based on (a) microscopic visualization of phenotypically identified cells of interest, (b) selective adherence of cells to a melting thermolabile film/membrane using a low-energy infrared laser (IR system) or photovolatization of cells within a selected region (UV system), (c) capturing or catapulting of structurally intact cells from a stained tissue section. RNA/DNA or protein can be extracted from the cell or tissue fragments for downstream applications to quantitatively study gene expression. This method can be applied to many downstream analyses including but not limited to quantitative real-time polymerase chain reaction (PCR), microarray, DNA genotyping, RNA transcript profiling, generation of cDNA library, mass spectrometry analysis, and proteomic discovery.The application of LCM is described here to specifically and reliably obtain a homogeneous cell population in order to extract RNA to study microRNA expression by quantitative real-time PCR. PMID:25308266
Multispectral laser imaging for advanced food analysis
NASA Astrophysics Data System (ADS)
Senni, L.; Burrascano, P.; Ricci, M.
2016-07-01
A hardware-software apparatus for food inspection capable of realizing multispectral NIR laser imaging at four different wavelengths is herein discussed. The system was designed to operate in a through-transmission configuration to detect the presence of unwanted foreign bodies inside samples, whether packed or unpacked. A modified Lock-In technique was employed to counterbalance the significant signal intensity attenuation due to transmission across the sample and to extract the multispectral information more efficiently. The NIR laser wavelengths used to acquire the multispectral images can be varied to deal with different materials and to focus on specific aspects. In the present work the wavelengths were selected after a preliminary analysis to enhance the image contrast between foreign bodies and food in the sample, thus identifying the location and nature of the defects. Experimental results obtained from several specimens, with and without packaging, are presented and the multispectral image processing as well as the achievable spatial resolution of the system are discussed.
Diode Lasers and Practical Trace Analysis.
ERIC Educational Resources Information Center
Imasaka, Totaro; Nobuhiko, Ishibashi
1990-01-01
Applications of lasers to molecular absorption spectrometry, molecular fluorescence spectrometry, visible semiconductor fluorometry, atomic absorption spectrometry, and atomic fluorescence spectrometry are discussed. Details of the use of the frequency-doubled diode laser are provided. (CW)
A theoretical analysis of time-dependent fragment momenta in indirect photofragmentation.
Henriksen, Niels E
2010-06-21
We study theoretically diatomic molecules which are prepared in a superposition of quasibound resonance states by a femtosecond laser pulse. An analytical (Landau-Zener-like) result is derived for the momentum distribution of the atomic fragments in the asymptotic force-free region after a single passage of a curve crossing. Furthermore, at later times, simple analytical expressions show how the emerging structures in the momentum distribution are related to the energies of the resonance states. PMID:20572709
Theoretical investigation of a semiconductor ring laser driven by Chua's oscillator
NASA Astrophysics Data System (ADS)
Takougang Kingni, Sifeu; Woafo, Paul
2013-06-01
The modeling and numerical investigation of the dynamical behavior of a semiconductor ring laser (SRL) driven by Chua's oscillator are reported. By increasing the coupling strength between the SRL and Chua's oscillator at a fixed bias current, the SRL exhibits an intermittency route to anti-phase chaos. However, for a fixed value of the coupling strength, we report a period-doubling route to out-of-phase and anti-phase chaos when varying one of the parameters of the Chua's oscillator are reported. We also demonstrate that a SRL driven by the chaotic output of Chua's oscillator generates a more complex chaos compared to the one found in a SRL subject to a sinusoidally modulated current. This new way of modulation of semiconductor lasers would not only bring a general benefit in the physical equipment and reduce their cost but could have an impact for some relevant engineering applications.
Optical diagnosis and theoretical simulation of laser induced lead plasma spectrum
Hong Bofu; Chuan Songchen; Bao Yuanman; Xiao Song; Dong Liu
2012-01-15
Plasmas generated during incipient laser ablation of lead in air were studied using emission spectroscopy and fast photography by an intensified charge coupled device (ICCD) camera. An improved plasma emission model was introduced, invoking one-dimensional radiative transfer, to describe the observed emission spectra, while taking into account Gaussian intensity distribution of the laser used to form plasma. The effects of different parameters to the fitting results are discussed. The plasma temperature got by Saha-Boltzmann plot method and the electron number density got by line broadening method were compared with the fitting results. We also found that the distribution of plasma temperature is more uniform than that of the electron number density in the radial direction.
Kusaka, Ryoji; Inokuchi, Yoshiya; Xantheas, Sotiris S.; Ebata, Takayuki
2010-04-01
We report laser spectroscopic studies of host/guest hydration interactions between functional molecules (hosts) and water (guest) in supersonic jets. The examined hosts include dibenzo-18-crown-6-ether (DB18C6), benzo-18-crown-6-ether (B18C6) and calix[4]arene (C4A). The gaseous complexes between the functional molecular hosts and water are generated under jet-cooled conditions. Various laser spectroscopic methods are applied for these species: the electronic spectra are observed by laser-induced fluorescence (LIF) , massselected resonance enhanced multiphoton ionization (REMPI) and ultraviolet-ultraviolet holeburning (UV-UV HB) spectroscopy, whereas the vibrational spectra for each individual species are observed by infrared-ultraviolet double resonance (IR-UV DR) spectroscopy. The obained results are analyzed by first principles electronic structure calculations. We discuss the conformations of the host molecules, the various structures of the complexes and the key interactions that result in the complexation as well as the effect of the host conformation in the resulting complexation mechanism.
Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study
Michael, Stephan; Chow, Weng; Schneider, Hans
2016-05-13
In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. We study the influence of two important quantum-dot material parameters, here, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density canmore » compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. By minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.« less
Multipoint laser vibrometer for modal analysis.
MacPherson, William N; Reeves, Mark; Towers, David P; Moore, Andrew J; Jones, Julian D C; Dale, Martin; Edwards, Craig
2007-06-01
Experimental modal analysis of multifrequency vibration requires a measurement system with appropriate temporal and spatial resolution to recover the mode shapes. To fully understand the vibration it is necessary to be able to measure not only the vibration amplitude but also the vibration phase. We describe a multipoint laser vibrometer that is capable of high spatial and temporal resolution with simultaneous measurement of 256 points along a line at up to 80 kHz. The multipoint vibrometer is demonstrated by recovering modal vibration data from a simple test object subject to transient excitation. A practical application is presented in which the vibrometer is used to measure vibration on a squealing rotating disk brake. PMID:17514265
Theoretical analysis of single molecule spectroscopy lineshapes of conjugated polymers
NASA Astrophysics Data System (ADS)
Devi, Murali
Conjugated Polymers(CPs) exhibit a wide range of highly tunable optical properties. Quantitative and detailed understanding of the nature of excitons responsible for such a rich optical behavior has significant implications for better utilization of CPs for more efficient plastic solar cells and other novel optoelectronic devices. In general, samples of CPs are plagued with substantial inhomogeneous broadening due to various sources of disorder. Single molecule emission spectroscopy (SMES) offers a unique opportunity to investigate the energetics and dynamics of excitons and their interactions with phonon modes. The major subject of the present thesis is to analyze and understand room temperature SMES lineshapes for a particular CP, called poly(2,5-di-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (DEH-PPV). A minimal quantum mechanical model of a two-level system coupled to a Brownian oscillator bath is utilized. The main objective is to identify the set of model parameters best fitting a SMES lineshape for each of about 200 samples of DEH-PPV, from which new insight into the nature of exciton-bath coupling can be gained. This project also entails developing a reliable computational methodology for quantum mechanical modeling of spectral lineshapes in general. Well-known optimization techniques such as gradient descent, genetic algorithms, and heuristic searches have been tested, employing an L2 measure between theoretical and experimental lineshapes for guiding the optimization. However, all of these tend to result in theoretical lineshapes qualitatively different from experimental ones. This is attributed to the ruggedness of the parameter space and inadequateness of the L2 measure. On the other hand, when the dynamic reduction of the original parameter space to a 2-parameter space through feature searching and visualization of the search space paths using directed acyclic graphs(DAGs), the qualitative nature of the fitting improved significantly. For a more
Anderson, D.Z.; Chow, W.W.; Scully, M.O.; Sanders, V.E.
1980-10-01
We describe a four-mode ring laser that exhibits none of the mode-locking characteristics that plague laser gyros. This laser is characterized by a bias that changes sign with a change in the direction of rotation and prevents the counterpropagating modes from locking. A theoretical analysis explaining the experimental results is outlined.
A computational and theoretical analysis of falling frequency VLF emissions
NASA Astrophysics Data System (ADS)
Nunn, David; Omura, Yoshiharu
2012-08-01
Recently much progress has been made in the simulation and theoretical understanding of rising frequency triggered emissions and rising chorus. Both PIC and Vlasov VHS codes produce risers in the region downstream from the equator toward which the VLF waves are traveling. The VHS code only produces fallers or downward hooks with difficulty due to the coherent nature of wave particle interaction across the equator. With the VHS code we now confine the interaction region to be the region upstream from the equator, where inhomogeneity factor S is positive. This suppresses correlated wave particle interaction effects across the equator and the tendency of the code to trigger risers, and permits the formation of a proper falling tone generation region. The VHS code now easily and reproducibly triggers falling tones. The evolution of resonant particle current JE in space and time shows a generation point at -5224 km and the wavefield undergoes amplification of some 25 dB in traversing the nonlinear generation region. The current component parallel to wave magnetic field (JB) is positive, whereas it is negative for risers. The resonant particle trap shows an enhanced distribution function or `hill', whereas risers have a `hole'. According to recent theory (Omura et al., 2008, 2009) sweeping frequency is due primarily to the advective term. The nonlinear frequency shift term is now negative (˜-12 Hz) and the sweep rate of -800 Hz/s is approximately nonlinear frequency shift divided by TN, the transition time, of the order of a trapping time.
Theoretical analysis and applications in inverse T-shape structure.
Li, Boxun; Li, Hongjian; Zeng, Lili; Zhan, Shiping; He, Zhihui; Chen, Zhiquan; Xu, Hui
2016-05-01
An inverse T-shape structure, consisting of a bus waveguide coupled with two perpendicular rectangular cavities, has been investigated numerically and theoretically. The position of the transparency window can be manipulated by adjusting the lateral displacement between the two perpendicular cavities. The effects of changing different structural parameters on the transmission features are investigated in detail. The results indicate that the length of two cavities play important roles in optimizing optical response. Finally, two simple applications based on the inverse T-shape structure are briefly discussed. The findings demonstrate that the first- and second-order modes can be separated without interference, and the sensitivity of the inverse T-shape is as high as 1750 nm per refractive index unit (RIU); the corresponding figure of merit (FOM) reaches up to 77.1 RIU^{-1}, which is higher than in previous reports. The plasmonic configuration possesses the advantages of easy fabrication, compactness, and higher sensitivity as well as higher FOM, which will greatly benefit the compact plasmonic filter and high-sensitivity nanosensor in highly integrated optical devices. PMID:27140878
Genome mapping by random anchoring: A discrete theoretical analysis
NASA Astrophysics Data System (ADS)
Zhang, M. Q.; Marr, T. G.
1993-11-01
As a part of the international human genome project, large-scale genomic maps of human and other model organisms are being generated. More recently, mapping using various anchoring (as opposed to the traditional "fingerprinting") strategies have been proposed based largely on mathematical models. In all of the theoretical work dealing with anchoring, an anchor has been idealized as a point on a continuous, infinite-length genome. In general, it is not desirable to make these assumptions, since in practice they may be violated under a variety of actual biological situations. Here we analyze a discrete model that can be used to predict the expected progress made when mapping by random anchoring. By virtue of keeping all three length scales (genome length, clone length, and probe length) finite, our results for the random anchoring strategy are derived in full generality, which contain previous results as special cases and hence can have broad application for planning mapping experiments or assessing the accuracy of the continuum models. Finally, we pose a challenging nonrandom anchoring model corresponding to a more efficient mapping scheme.
A Logical Analysis of Majorana's Papers on Theoretical Physics
NASA Astrophysics Data System (ADS)
Drago, A.; Esposito, S.
2006-05-01
We study two celebrated Majorana's papers through a method of investigation which relies upon the recently recognized distinction between classical logic and several kinds of non-classical logics, i.e. the failure of the double negation law. This law fails when a double negated sentence is not equivalent to the corresponding positive sentence, owing to the lack of scientific evidence of the latter one. All recognized double negated sentences inside the text of each paper are listed; the mere sequence of such sentences giving the logical thread of Majorana's arguing. This one is recognized to be of the Lagrangian kind, which mixes logical arguing and mathematical calculation; i.e. the author puts a fundamental problem which is solved by anticipating the mathematical hypothesis able to solve it, and then by drawing from this hypothesis the mathematical consequences in order to reach to desired result. Furthermore the rethoric of presentation used by Majorana results to be a juridical one, owing to his style of presenting the laws to which an ideal theoretical physicist has to conform his mind in order to solve the problem at issue.
Theoretical analysis of the electronic properties of N3 derivatives.
Rekhis, Maamar; Labat, Frédéric; Ouamerali, Ourida; Ciofini, Ilaria; Adamo, Carlo
2007-12-20
The structural and electronic properties of nine derivatives of the N3 complex (cis-[Ru(4,4'-COOH-2,2'-bpy)2(NCS)2]) have been studied, using density functional theory (DFT) at a hybrid (PBE0) level, with the aim of finding a systematic way to improve their spectral absorption in the visible region for photoelectrochemical applications. To this end, by means of time dependent-DFT (TD-DFT) calculations, excited states were investigated in solution to simulate UV-vis spectra. Several effects have been taken into account: the effect of the presence and deprotonation of the carboxylic groups as well as the variation of the chalcogen within the NCX ligand (X=S, Se, or Te). Besides the excellent agreement between theoretical and available experimental data, with regards to potential future experimental applications of the investigated complexes, from the calculations, the cis-Ru(dcbpyH2)(NCSe)2 may appear as a good candidate to enhance the response of the N3 dye to light, even if only slightly. PMID:18004827
Theoretical Analysis of Membrane Tension in Moving Cells
Schweitzer, Yonatan; Lieber, Arnon D.; Keren, Kinneret; Kozlov, Michael M.
2014-01-01
Lateral tension in cell plasma membranes plays an essential role in regulation of a number of membrane-related intracellular processes and cell motion. Understanding the physical factors generating the lateral tension and quantitative determination of the tension distribution along the cell membrane is an emerging topic of cell biophysics. Although experimental data are accumulating on membrane tension values in several cell types, the tension distribution along the membranes of moving cells remains largely unexplored. Here we suggest and analyze a theoretical model predicting the tension distribution along the membrane of a cell crawling on a flat substrate. We consider the tension to be generated by the force of actin network polymerization against the membrane at the cell leading edge. The three major factors determining the tension distribution are the membrane interaction with anchors connecting the actin network to the lipid bilayer, the membrane interaction with cell adhesions, and the force developing at the rear boundary due to the detachment of the remaining cell adhesion from the substrate in the course of cell crawling. Our model recovers the experimentally measured values of the tension in fish keratocytes and their dependence on the number of adhesions. The model predicts, quantitatively, the tension distribution between the leading and rear membrane edges as a function of the area fractions of the anchors and the adhesions. PMID:24411240
A game theoretic analysis of research data sharing
Wiersma, Paulien H.; van Weerden, Anne; Schieving, Feike
2015-01-01
While reusing research data has evident benefits for the scientific community as a whole, decisions to archive and share these data are primarily made by individual researchers. In this paper we analyse, within a game theoretical framework, how sharing and reuse of research data affect individuals who share or do not share their datasets. We construct a model in which there is a cost associated with sharing datasets whereas reusing such sets implies a benefit. In our calculations, conflicting interests appear for researchers. Individual researchers are always better off not sharing and omitting the sharing cost, at the same time both sharing and not sharing researchers are better off if (almost) all researchers share. Namely, the more researchers share, the more benefit can be gained by the reuse of those datasets. We simulated several policy measures to increase benefits for researchers sharing or reusing datasets. Results point out that, although policies should be able to increase the rate of sharing researchers, and increased discoverability and dataset quality could partly compensate for costs, a better measure would be to directly lower the cost for sharing, or even turn it into a (citation-) benefit. Making data available would in that case become the most profitable, and therefore stable, strategy. This means researchers would willingly make their datasets available, and arguably in the best possible way to enable reuse. PMID:26401453
Tuan, P H; Wen, C P; Yu, Y T; Liang, H C; Huang, K F; Chen, Y F
2014-02-01
Experimentally resonant modes are commonly presumed to correspond to eigenmodes in the same bounded domain. However, the one-to-one correspondence between theoretical eigenmodes and experimental observations is never reached. Theoretically, eigenmodes in numerous classical and quantum systems are the solutions of the homogeneous Helmholtz equation, whereas resonant modes should be solved from the inhomogeneous Helmholtz equation. In the present paper we employ the eigenmode expansion method to derive the wave functions for manifesting the distinction between eigenmodes and resonant modes. The derived wave functions are successfully used to reconstruct a variety of experimental results including Chladni figures generated from the vibrating plate, resonant patterns excited from microwave cavities, and lasing modes emitted from the vertical cavity. PMID:25353549
Graph theoretical analysis of resting magnetoencephalographic functional connectivity networks
Rutter, Lindsay; Nadar, Sreenivasan R.; Holroyd, Tom; Carver, Frederick W.; Apud, Jose; Weinberger, Daniel R.; Coppola, Richard
2013-01-01
Complex networks have been observed to comprise small-world properties, believed to represent an optimal organization of local specialization and global integration of information processing at reduced wiring cost. Here, we applied magnitude squared coherence to resting magnetoencephalographic time series in reconstructed source space, acquired from controls and patients with schizophrenia, and generated frequency-dependent adjacency matrices modeling functional connectivity between virtual channels. After configuring undirected binary and weighted graphs, we found that all human networks demonstrated highly localized clustering and short characteristic path lengths. The most conservatively thresholded networks showed efficient wiring, with topographical distance between connected vertices amounting to one-third as observed in surrogate randomized topologies. Nodal degrees of the human networks conformed to a heavy-tailed exponentially truncated power-law, compatible with the existence of hubs, which included theta and alpha bilateral cerebellar tonsil, beta and gamma bilateral posterior cingulate, and bilateral thalamus across all frequencies. We conclude that all networks showed small-worldness, minimal physical connection distance, and skewed degree distributions characteristic of physically-embedded networks, and that these calculations derived from graph theoretical mathematics did not quantifiably distinguish between subject populations, independent of bandwidth. However, post-hoc measurements of edge computations at the scale of the individual vertex revealed trends of reduced gamma connectivity across the posterior medial parietal cortex in patients, an observation consistent with our prior resting activation study that found significant reduction of synthetic aperture magnetometry gamma power across similar regions. The basis of these small differences remains unclear. PMID:23874288
Theoretical performance analysis for CMOS based high resolution detectors.
Jain, Amit; Bednarek, Daniel R; Rudin, Stephen
2013-03-01
High resolution imaging capabilities are essential for accurately guiding successful endovascular interventional procedures. Present x-ray imaging detectors are not always adequate due to their inherent limitations. The newly-developed high-resolution micro-angiographic fluoroscope (MAF-CCD) detector has demonstrated excellent clinical image quality; however, further improvement in performance and physical design may be possible using CMOS sensors. We have thus calculated the theoretical performance of two proposed CMOS detectors which may be used as a successor to the MAF. The proposed detectors have a 300 μm thick HL-type CsI phosphor, a 50 μm-pixel CMOS sensor with and without a variable gain light image intensifier (LII), and are designated MAF-CMOS-LII and MAF-CMOS, respectively. For the performance evaluation, linear cascade modeling was used. The detector imaging chains were divided into individual stages characterized by one of the basic processes (quantum gain, binomial selection, stochastic and deterministic blurring, additive noise). Ranges of readout noise and exposure were used to calculate the detectors' MTF and DQE. The MAF-CMOS showed slightly better MTF than the MAF-CMOS-LII, but the MAF-CMOS-LII showed far better DQE, especially for lower exposures. The proposed detectors can have improved MTF and DQE compared with the present high resolution MAF detector. The performance of the MAF-CMOS is excellent for the angiography exposure range; however it is limited at fluoroscopic levels due to additive instrumentation noise. The MAF-CMOS-LII, having the advantage of the variable LII gain, can overcome the noise limitation and hence may perform exceptionally for the full range of required exposures; however, it is more complex and hence more expensive. PMID:24353390
Accuracy Analysis of a Box-wing Theoretical SRP Model
NASA Astrophysics Data System (ADS)
Wang, Xiaoya; Hu, Xiaogong; Zhao, Qunhe; Guo, Rui
2016-07-01
For Beidou satellite navigation system (BDS) a high accuracy SRP model is necessary for high precise applications especially with Global BDS establishment in future. The BDS accuracy for broadcast ephemeris need be improved. So, a box-wing theoretical SRP model with fine structure and adding conical shadow factor of earth and moon were established. We verified this SRP model by the GPS Block IIF satellites. The calculation was done with the data of PRN 1, 24, 25, 27 satellites. The results show that the physical SRP model for POD and forecast for GPS IIF satellite has higher accuracy with respect to Bern empirical model. The 3D-RMS of orbit is about 20 centimeters. The POD accuracy for both models is similar but the prediction accuracy with the physical SRP model is more than doubled. We tested 1-day 3-day and 7-day orbit prediction. The longer is the prediction arc length, the more significant is the improvement. The orbit prediction accuracy with the physical SRP model for 1-day, 3-day and 7-day arc length are 0.4m, 2.0m, 10.0m respectively. But they are 0.9m, 5.5m and 30m with Bern empirical model respectively. We apply this means to the BDS and give out a SRP model for Beidou satellites. Then we test and verify the model with Beidou data of one month only for test. Initial results show the model is good but needs more data for verification and improvement. The orbit residual RMS is similar to that with our empirical force model which only estimate the force for along track, across track direction and y-bias. But the orbit overlap and SLR observation evaluation show some improvement. The remaining empirical force is reduced significantly for present Beidou constellation.
A theoretical analysis of sliding of rough surfaces
NASA Astrophysics Data System (ADS)
Walsh, J. B.
2003-08-01
I used a model proposed by [1966], who analyzed closure between a rough surface and a smooth surface under normal stress, to analyze the growth of slip under increasing shear stress, normal stress remaining constant. The two bodies are elastic half-spaces, one rough and one smooth, and Coulomb friction resists slip at sliding contacts. The elastic and dissipative components of the constitutive relation in shear depend upon statistical parameters which describe the topography of the rough surface. I made a parametric study of the effect of topography on the constitutive relations in shear by comparing a model in which the progress of slip at a contact is continuous with one in which the contact goes discontinuously from "stuck" to sliding. The effect of topography was also studied by assuming that the probability density distribution of the heights of asperities is Gaussian or, alternatively, a negative exponential. These variations in topography produced only minor differences in the constitutive behavior. This insensitivity of the constitutive behavior to differences in the statistical description of the topography arises in part because, only relatively, a small range of asperity heights is active in typical experiments. Work done against friction introduces a dissipative component into the constitutive behavior which I evaluated analytically; I show that the components have a simple graphical construction on plots of shear stress versus displacement developed from experimental observations. Sliding in the reverse sense which occurs when the applied shear stress is relaxed is analyzed, resulting in expressions which describe the shape of hysteresis loops formed when shear stress is cycled. Introducing measurements made on surfaces of specimens of granite and quartzite into the theoretical relations, I found reasonable agreement with experimental data.
Analysis of Theoretical Metaphors with Illustrations from Family Systems Theory.
ERIC Educational Resources Information Center
Rosenblatt, Paul C.
Metaphoric analysis of family systems theory illustrates how metaphors and alternatives to those metaphors identify what a psychological theory has highlighted and obscured about the phenomena at its focus and how it has structured that phenomena. The most commonly used metaphors in family systems theory are the metaphors of system (system…
Theoretical Consideration of Forcible Rape: A Critical Analysis.
ERIC Educational Resources Information Center
Clagett, Arthur F.
1988-01-01
Examined differences in hypothetical apperceptive fantasies of committing forcible rape, which are held by male subjects, as compared with the hypothetical apperceptive fantasies of being forcibly raped, held by the female subjects. Developed a critical analysis of social and cross-cultural variables affecting rape. (Author/ABL)
An Optimality-Theoretic Analysis of Codas in Brazilian Portuguese
ERIC Educational Resources Information Center
Goodin-Mayeda, C. Elizabeth
2015-01-01
Brazilian Portuguese allows only /s, N, l, r/ syllable finally, and of these, only /s/ is realized faithfully (as well as /r/ for some speakers). In order to avoid unacceptable codas, dialects of Brazilian Portuguese employ such strategies as epenthesis, nasal absorption, debucalization, and gliding. The current analysis argues that codas in…
Laser cooling of the AlCl molecule with a three-electronic-level theoretical model
NASA Astrophysics Data System (ADS)
Wan, Mingjie; Yuan, Di; Jin, Chengguo; Wang, Fanhou; Yang, Yujie; Yu, You; Shao, Juxiang
2016-07-01
Feasibility of laser-cooling AlCl molecule is investigated using ab initio quantum chemistry. Potential energy curves, permanent dipole moments, and transition dipole moments for the X1Σ+, a3Π, and A1Π states are studied based on multi-reference configuration interaction plus Davidson corrections (MRCI+Q) method with ACVQZ basis set, spin-orbit coupling effects are considered at the MRCI+Q level. Highly diagonally distributed Franck-Condon factors (f00 = 0.9988 and f11 = 0.9970) and branching ratios (R00 = 0.9965, R01 = 2.85 × 10-3, R02 = 6.35 × 10-4, and R03 = 2.05 × 10-6) for the A 1 Π 1 ( ν ' = 0 ) → X 1 Σ0 + + ( ν ″ = 0 ) transition are determined. A sufficiently radiative lifetime τ (A1Π1) = 4.99 ns is predicted for rapid laser cooling. The proposed cooling wavelength is deep in the ultraviolet region at λ00 = 261.75 nm. Total emission rates for the a 3 Π 0 + → X 1 Σ0 + + , a 3 Π 1 → X 1 Σ0 + + , A1Π1 → a3Π0+, and A1Π1 → a3Π1 transitions are particularly small (˜10 s-1-650 s-1). The calculated vibrational branching loss ratio to the intermediate a3Π0+ and a3Π1 states can be negligible. The results imply the probability of laser cooling AlCl molecule with three-electronic-level.
Theoretical Calculation for the Ionization of Molecules by Short Strong Laser Pulses
Nagy, L.; Borbely, S.
2011-10-03
We have developed several calculation methods for the ionization of atoms and molecules by strong and ultrashort laser pulses, based on the numerical solution of the time dependent Schroedinger equation (TDSE) in the momentum space. We have performed calculations within the strong field approximation (Volkov) and using iterative and direct methods for solving the TDSE. The investigated molecules are H{sub 2}{sup +} and H{sub 2}O. In case of the ionization of diatomic molecules the interference effects in the ejected electron spectra due to the coherent addition of the waves associated to the electrons ejected from the vicinity of different nuclei were also analysed.
NASA Astrophysics Data System (ADS)
Raghunathan, Ravi
In recent years, passively mode-locked quantum dot lasers have shown great promise as compact, efficient and reliable pulsed sources of light for a range of precision and high performance applications, such as high bit-rate optical communications, diverse waveform generation, metrology, and clock distribution in high-performance computing (HPC) processors. For such applications, stable optical pulses with short picosecond pulse durations and multi-gigahertz repetition rates are required. In addition, a low pulse-to-pulse timing jitter is also necessary to prevent errors arising from the ambiguity between neighboring pulses. In order to optimize pulse quality in terms of optical characteristics such as pulse shape and pulse train behavior, as well as RF characteristics such as phase noise and timing jitter, understanding the nonlinear output dynamics of such devices is of critical importance, not only to get a sense of the regimes of operation where device output might be stable or unstable, but also to gain insight into the parameters that influence the output characteristics the most, and how they can be accessed and exploited to optimize design and performance for next generation applications. In this dissertation, theoretical and experimental studies have been combined to investigate the dynamical trends of two-section passively mode-locked quantum dot lasers. On the theoretical side, a novel numerical modeling scheme is presented as a powerful and versatile framework to study the nonlinear dynamics specific to a device, with device-specific parameters extracted over a range of operating conditions. The practical utility of this scheme is then demonstrated, first, in an analytical capability to interpret and explain dynamical trends observed in experiment, and subsequently, as a predictive tool to guide experiment to operate in a desired dynamical regime. Modeling results are compared to experimental findings where possible. Finally, optical feedback from an
NASA Technical Reports Server (NTRS)
Javan, A.; Guerra, M.
1981-01-01
The possibility of obtaining CW laser oscillation by optical pumping in the infrared at an elevated gas pressure is reviewed. A specific example utilizing a mixture of CO and NO gases is included. The gas pressures considered are in excess of several atmospheres. Laser frequency tuning over a broad region becomes possible at such elevated gas pressures due to collisional broadening of the amplifying transitions. The prior-rate and surprisal analysis are applied to obtain detailed VV and VT rates for CO and NO molecules and the transfer rates in a CO-NO gas mixture. The analysis is capable of giving temperature dependence of the rate constants. Computer estimates of the rates are presented for vibrational levels up to v = 50. The results show that in the high-lying vibrational states the VV transfer rates with Delta nu = 2 become appreciable.
In vitro analysis of laser meniscectomy.
Vangsness, C T; Akl, Y; Nelson, S J; Liaw, L H; Smith, C F; Marshall, G J
1995-01-01
Partial meniscectomies were performed on 32 fresh human meniscal autopsy specimens. The following laser systems were tested: carbon dioxide (CO2), neodymium:yttrium aluminum garnet (Nd:YAG), potassium titanyl phosphate (KTP), holmium:YAG (Ho:YAG), and excimer. Meniscectomies with these lasers were compared with scalpel, mechanical, and electrocautery meniscectomies. Lasers were applied to specimens in and out of normal saline. Routine hematoxylin and eosin and sirius red sections were prepared for each specimen, and the depths of thermal changes were analyzed. Scanning electron microscopy was used to visualize the meniscectomy interface. Among these specimens, the scalpel and mechanical meniscectomies showed the least extension of cellular changes (range, 10-15 nm). The excimer laser caused the least tissue changes of the lasers tested. Tissue changes were less extensive with the pulsed CO2 laser than with the holmium:YAG, neodymium:YAG, and KTP lasers. Scanning electron microscopy showed that use of the scalpel meniscectomy resulted in the smoothest meniscectomy edge, followed by use of the excimer, CO2, holmium:YAG, neodymium:YAG, and KTP lasers. The most surface disruption occurred with electrocautery. Meniscectomies under saline required more energy and took longer in each case, with the holmium:YAG, neodymium:YAG, and CO2 laser cutting the best. Saline meniscectomies showed less thermal change. The CO2 and KTP lasers cut best in air. PMID:7641441
Theoretical analysis of wake-induced parachute collapse
Spahr, H.R.; Wolf, D.F.
1981-01-01
During recent drop tests of a prototype weapon system, the parachute collapsed soon after it became fully inflated. The magnitude and duration of the collapses were severe enough to degrade parachute performance drastically. A computer-assisted analysis is presented which models parachute inflation, forebody and parachute wake generation, and interaction between the wake and the inflating or collapsing parachute. Comparison of the analysis results with full-scale drop test results shows good agreement for two parachute sizes; both parachutes were tested with and without permanent reefing. Computer-generated graphics (black and white drawings, color slides, and color movies) show the forebody and inflating parachute, the wake, and the wake and parachute interaction.
Sequential Phenomena in Psychophysical Judgments: A Theoretical Analysis
NASA Technical Reports Server (NTRS)
Atkinson, R. C.; Carterette, E. C.; Kinchla, R. A.
1962-01-01
This paper deals with an analysis of psychophysical detection experiments designed to assess the limit of a human observer's level of sensitivity. A mathematical theory or the detection process is introduced that, in contrast to previous theories, provides an analysis of the sequential effects observed in psychophysical data. Two variations of the detection task are considered: information feedback and no-information feedback. In the feedback situation the subject is given information concerning the correctness of his responses, whereas in the no-feedback situation he is not. Data from a visual detection experiment with no-information feedback, and from an auditory detection experiment with information feedback are analyzed in terms of the theory. Finally, some general results are derived concerning the relationship between performance in the feedback situation and the no-feedback situation.
Woodruff, Steven D.; Mcintyre, Dustin L.
2016-03-29
A device for Laser based Analysis using a Passively Q-Switched Laser comprising an optical pumping source optically connected to a laser media. The laser media and a Q-switch are positioned between and optically connected to a high reflectivity mirror (HR) and an output coupler (OC) along an optical axis. The output coupler (OC) is optically connected to the output lens along the optical axis. A means for detecting atomic optical emission comprises a filter and a light detector. The optical filter is optically connected to the laser media and the optical detector. A control system is connected to the optical detector and the analysis electronics. The analysis electronics are optically connected to the output lens. The detection of the large scale laser output production triggers the control system to initiate the precise timing and data collection from the detector and analysis.
NASA Astrophysics Data System (ADS)
Fortin, Pierre-Yves
2008-06-01
Vectorial laser beams propagating beyond the paraxial limit exhibit an intensity profile at focus that depends upon their field structure and the width of their plane wave spectrum. Under tight focussing conditions, the longitudinal component of the lowest order transverse magnetic laser beam has a field amplitude that becomes comparable to that of the transverse components of the beam; the global intensity profile is then narrower than that produced by a Gaussian beam, thus enabling hyperresolution. With a general polarization eigenmode approach for all propagating directions in anisotropic media, we can show that privileged propagating directions exist, allowing preservation of the transverse magnetic polarization state despite birefringence. Using wave functions satisfying the non-paraxial wave equation, we can also find exact expressions for the field components. During propagation of tightly focussed beams along those privileged directions inside an appropriate anisotropic nonlinear crystal, the longitudinal electric field component may then be used to take advantage of nonlinear tensor terms otherwise ineffective with a paraxial beam. In this work, spectral conversion rate and power conversion efficiency of second-harmonic generation are characterized as a function of effective and undepleted nonlinear pumping in the case of propagation along the anisotropic axis of an uniaxial nonlinear crystal. Even if the phase matching condition is not fully satisfied for propagation along this privileged direction, we show to which extent the nonlinear properties are preserved for a restricted interaction volume.
[Analysis and experimental verification of sensitivity and SNR of laser warning receiver].
Zhang, Ji-Long; Wang, Ming; Tian, Er-Ming; Li, Xiao; Wang, Zhi-Bin; Zhang, Yue
2009-01-01
In order to countermeasure increasingly serious threat from hostile laser in modern war, it is urgent to do research on laser warning technology and system, and the sensitivity and signal to noise ratio (SNR) are two important performance parameters in laser warning system. In the present paper, based on the signal statistical detection theory, a method for calculation of the sensitivity and SNR in coherent detection laser warning receiver (LWR) has been proposed. Firstly, the probabilities of the laser signal and receiver noise were analyzed. Secondly, based on the threshold detection theory and Neyman-Pearson criteria, the signal current equation was established by introducing detection probability factor and false alarm rate factor, then, the mathematical expressions of sensitivity and SNR were deduced. Finally, by using method, the sensitivity and SNR of the sinusoidal grating laser warning receiver developed by our group were analyzed, and the theoretic calculation and experimental results indicate that the SNR analysis method is feasible, and can be used in performance analysis of LWR. PMID:19385197
Ultrasensitive laser spectroscopy for breath analysis
NASA Astrophysics Data System (ADS)
Wojtas, J.; Bielecki, Z.; Stacewicz, T.; Mikołajczyk, J.; Nowakowski, M.
2012-03-01
At present there are many reasons for seeking new methods and technologies that aim to develop new and more perfect sensors for different chemical compounds. However, the main reasons are safety ensuring and health care. In the paper, recent advances in the human breath analysis by the use of different techniques are presented. We have selected non-invasive ones ensuring detection of pathogenic changes at a molecular level. The presence of certain molecules in the human breath is used as an indicator of a specific disease. Thus, the analysis of the human breath is very useful for health monitoring. We have shown some examples of diseases' biomarkers and various methods capable of detecting them. Described methods have been divided into non-optical and optical methods. The former ones are the following: gas chromatography, flame ionization detection, mass spectrometry, ion mobility spectrometry, proton transfer reaction mass spectrometry, selected ion flow tube mass spectrometry. In recent twenty years, the optical methods have become more popular, especially the laser techniques. They have a great potential for detection and monitoring of the components in the gas phase. These methods are characterized by high sensitivity and good selectivity. The spectroscopic sensors provide the opportunity to detect specific gases and to measure their concentration either in a sampling place or a remote one. Multipass spectroscopy, cavity ring-down spectroscopy, and photo-acoustic spectroscopy were characterised in the paper as well.
Analysis of Picosecond Pulsed Laser Melted Graphite
DOE R&D Accomplishments Database
Steinbeck, J.; Braunstein, G.; Speck, J.; Dresselhaus, M. S.; Huang, C. Y.; Malvezzi, A. M.; Bloembergen, N.
1986-12-01
A Raman microprobe and high resolution TEM have been used to analyze the resolidified region of liquid carbon generated by picosecond pulse laser radiation. From the relative intensities of the zone center Raman-allowed mode for graphite at 1582 cm{sup -1} and the disorder-induced mode at 1360 cm{sup -1}, the average graphite crystallite size in the resolidified region is determined as a function of position. By comparison with Rutherford backscattering spectra and Raman spectra from nanosecond pulsed laser melting experiments, the disorder depth for picosecond pulsed laser melted graphite is determined as a function of irradiating energy density. Comparisons of TEM micrographs for nanosecond and picosecond pulsed laser melting experiments show that the structure of the laser disordered regions in graphite are similar and exhibit similar behavior with increasing laser pulse fluence.
NASA Astrophysics Data System (ADS)
Colgan, J.; Barefield, J. E.; Judge, E. J.; Campbell, K.; Johns, H. M.; Kilcrease, D. P.; McInroy, R.; Clegg, S. M.
2016-08-01
We report on a comprehensive study of the emission spectra from laser-induced breakdown spectroscopy (LIBS) measurements on iron oxide. Measurements have been made of the emission from Fe2O3 under atmospheres of air, He, and Ar, and at different atmospheric pressures. The effect of varying the time delay of the measurement is also explored. Theoretical calculations were performed to analyze the plasma conditions and find that a reasonably consistent picture of the change in plasma temperature and density for different atmospheric conditions can be reached. We also investigate the sensitivity of the OI 777 nm emission lines to the plasma conditions, something that has not been explored in detail in the previous work. Finally, we also show that LIBS can be used to differentiate between FeO and Fe2O3 by examining the ratio of the intensities of selected Fe emission to O emission lines.
Graph theoretical analysis of complex networks in the brain
Stam, Cornelis J; Reijneveld, Jaap C
2007-01-01
Since the discovery of small-world and scale-free networks the study of complex systems from a network perspective has taken an enormous flight. In recent years many important properties of complex networks have been delineated. In particular, significant progress has been made in understanding the relationship between the structural properties of networks and the nature of dynamics taking place on these networks. For instance, the 'synchronizability' of complex networks of coupled oscillators can be determined by graph spectral analysis. These developments in the theory of complex networks have inspired new applications in the field of neuroscience. Graph analysis has been used in the study of models of neural networks, anatomical connectivity, and functional connectivity based upon fMRI, EEG and MEG. These studies suggest that the human brain can be modelled as a complex network, and may have a small-world structure both at the level of anatomical as well as functional connectivity. This small-world structure is hypothesized to reflect an optimal situation associated with rapid synchronization and information transfer, minimal wiring costs, as well as a balance between local processing and global integration. The topological structure of functional networks is probably restrained by genetic and anatomical factors, but can be modified during tasks. There is also increasing evidence that various types of brain disease such as Alzheimer's disease, schizophrenia, brain tumours and epilepsy may be associated with deviations of the functional network topology from the optimal small-world pattern. PMID:17908336
Inter-satellite laser link simulation analysis
NASA Astrophysics Data System (ADS)
Tong, Lanjuan; Guan, Hui; Wang, Zhilin
2015-11-01
The characteristic of satellite communication link was firstly described and four application modes were put forward. By comparison, it is suggested that microwave link is used in satellite-to-ground communication and laser link is used in inter-satellite communication. Secondly the condition and composition of laser link establishment was analyzed and laser link model was set up, and the principle and composition of APT system was described. Finally, based on STK and MATLAB platform, the process of inter-satellite laser link establishment was designed, and setting the scene of TDRS capturing and tracking user's satellite as an example, simulation was realized and demonstrated.
Theoretical and experimental analyses of the performance of two-color laser ranging systems
NASA Technical Reports Server (NTRS)
Im, K. E.; Gardner, C. S.
1985-01-01
The statistical properties of the signals reflected from the retroreflector equipped satellites were studied. It is found that coherence interference between pulse reflections from retroreflectors of different ranges on the array platform is the primary cause of signal fluctuations. The performance of a cross-correlation technique to estimate the differential propagation time is analyzed by considering both shot noise and speckle. For the retroreflector arrays, timing performance is dominated by interference induced speckle, and the differential propagation time cannot be resolved to better than the pulse widths of the received signals. The differential timing measurements obtained over a horizontal path are analyzed. The ocean-reflected pulse measurements obtained from the airborne two-color laser altimeter experiment are presented.
Theoretical and experimental comparison of an ultra-high-speed laser data transmission system
NASA Technical Reports Server (NTRS)
Tycz, M.
1973-01-01
The performance of a digital optical data transmission system is specified by the probability that the system erroneously decides a signal has or has not been transmitted. Two factors which induce signal fading and thereby decrease system performance are atmospheric scintillation and transmitter pointing inaccuracy. A channel simulator was developed that is capable of producing the effects of both atmospheric scintillation and the transmitter pointing problem for a neodymium-yag optical data transmission systems. Comparison of data taken from the modulated intensity of a beam having been transmitted through the channel simulator with experimental data from GEOS-B argon laser transmission through the atmosphere to a low earth-orbiting satellite indicates that the modulated signal intensity is log-normal to the degree of measured atmospheric scintillation.
NASA Astrophysics Data System (ADS)
Huang, Jing; Wan, Yuan; Chen, Weibiao
2015-02-01
The influence of temperature and incident pump power on reabsorption loss is theoretically discussed. Temperature characteristic and reabsorption loss rate of a diode-pumped quasi-three-level 946 nm Nd:YAG laser are investigated. Reabsorption effect has a significant impact on laser performance. The results indicate that reabsorption loss increases as the working temperature rises and decreases with the increased incident pump power.
NASA Astrophysics Data System (ADS)
El Amili, Abdelkrim; Kervella, Gaël; Alouini, Mehdi
2013-04-01
A theoretical and experimental investigation of the intensity noise reduction induced by two-photon absorption in a Er,Yb:Glass laser is reported. The time response of the two-photon absorption mechanism is shown to play an important role on the behavior of the intensity noise spectrum of the laser. A model including an additional rate equation for the two-photon-absorption losses is developed and allows the experimental observations to be predicted.
Theoretical analysis of the density within an orbiting molecular shield
NASA Technical Reports Server (NTRS)
Hueser, J. E.; Brock, F. J.
1976-01-01
An analytical model based on the kinetic theory of a drifting Maxwellian gas is used to determine the nonequilibrium molecular density distribution within a hemispherical shell open aft with its axis parallel to its velocity. Separate numerical results are presented for the primary and secondary density distribution components due to the drifting Maxwellian gas for speed ratios between 2.5 and 10. An analysis is also made of the density component due to gas desorbed from the wall of the hemisphere, and numerical results are presented for the density distribution. It is shown that the adsorption process may be completely ignored. The results are applicable to orbital trajectories in any planet-atmosphere system and interplanetary transfer trajectories. Application to the earth's atmosphere is mentioned briefly.
A Theoretical Analysis of Thermal Radiation from Neutron Stars
NASA Technical Reports Server (NTRS)
Applegate, James H.
1993-01-01
As soon as it was realized that the direct URCA process is allowed by many modern nuclear equation of state, an analysis of its effect on the cooling of neutron stars was undertaken. A primary study showed that the occurrence of the direct URCA process makes the surface temperature of a neutron star suddenly drop by almost an order of magnitude when the cold wave from the core reaches the surface when the star is a few years old. The results of this study are published in Page and Applegate. As a work in progress, we are presently extending the above work. Improved expressions for the effect of nucleon pairing on the neutrino emissivity and specific heat are now available, and we have incorporated them in a recalculation of rate of the direct URCA process.
NASA Astrophysics Data System (ADS)
Liu, Wenwen; Niu, Yanxiong; Liu, Haixia; Wang, Caili; Hu, Shuling; Zhang, Chao; Niu, Haisha; Li, Jiyang
2014-02-01
The output window of a high-power laser system is vulnerable to damage, and this is the main limiting factor on the power scaling and structure integrity of the laser system. In endeavoring to obtain higher output powers from the laser system, the impact of the thermal and mechanical effects and the damage mechanism of the output window must be considered. In order to study these issues, a thermal model of the laser window is established based on the heat transfer and thermoelastic theories, and the expressions for the transient thermal and mechanical stress distributions of the output window are deduced in terms of the integral-transform method. Taking the infrared quartz window material as an example, the temperature and mechanical field distributions of a high-power all-solid-state 2-μm laser system window are simulated, and the laser-induced damage mechanism is deeply analyzed. The calculation results show that the laser window-induced damage is mainly caused by melting damage when the temperature exceeds the melting point of the material. The presented theoretical analysis and numerical simulation results are significant for the design and optimization of high-power laser windows.
Analysis and testing of a new method for drop size measurement using laser scatter interferometry
NASA Technical Reports Server (NTRS)
Bachalo, W. D.; Houser, M. J.
1984-01-01
Research was conducted on a laser light scatter detection method for measuring the size and velocity of spherical particles. The method is based upon the measurement of the interference fringe pattern produced by spheres passing through the intersection of two laser beams. A theoretical analysis of the method was carried out using the geometrical optics theory. Experimental verification of the theory was obtained by using monodisperse droplet streams. Several optical configurations were tested to identify all of the parametric effects upon the size measurements. Both off-axis forward and backscatter light detection were utilized. Simulated spray environments and fuel spray nozzles were used in the evaluation of the method. The measurements of the monodisperse drops showed complete agreement with the theoretical predictions. The method was demonstrated to be independent of the beam intensity and extinction resulting from the surrounding drops. Signal processing concepts were considered and a method was selected for development.
NASA Astrophysics Data System (ADS)
Ivanov, D. S.; Lipp, V. P.; Blumenstein, A.; Kleinwort, F.; Veiko, V. P.; Yakovlev, E.; Roddatis, V.; Garcia, M. E.; Rethfeld, B.; Ihlemann, J.; Simon, P.
2015-12-01
The mechanism of surface restructuring by ultrashort laser pulses involves a number of fast, nonequilibrium, and interrelated processes while the solid is in a transient state. As a result, the analysis of the experimental data cannot address all of the mechanisms of nanostructuring. In this paper, we present a direct comparison of a simulation and the experimental results of surface nanomodifications induced by a single laser pulse. The experimental results are obtained by using a mask-projection setup with a laser wavelength of 248 nm and a pulse length of 1.6 ps. Two-beam interference of this short wavelength allows for producing a large-area intensity grating of 40 μ m in diameter on a gold surface with a sinusoidal shape and a period of 500 nm. The formed structures are analyzed at the surface and in a cross section by a scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Then a hybrid atomistic-continuum model capable of capturing the essential mechanisms responsible for the nanostructuring process is used to model the interaction of the laser pulse with a thick gold target. The good agreement between the modeling results and the experimental data justifies the proposed approach as a powerful tool revealing the physics behind the nanostructuring process at a gold surface and providing a microscopic insight into the dynamics of the structuring processes of metals in general. The presented model, therefore, is an important step towards a computational tool for predicting a materials response to an ultrashort laser pulse on the atomic scale. This detailed understanding of the dynamics of the process will pave the way towards predesigned topologies for functionalized surfaces on nanoscales and microscales.
Laney, Jonathan; Adalı, Tülay; McCombe Waller, Sandy; Westlake, Kelly P
2015-01-01
The assessment of neuroplasticity after stroke through functional magnetic resonance imaging (fMRI) analysis is a developing field where the objective is to better understand the neural process of recovery and to better target rehabilitation interventions. The challenge in this population stems from the large amount of individual spatial variability and the need to summarize entire brain maps by generating simple, yet discriminating features to highlight differences in functional connectivity. Independent vector analysis (IVA) has been shown to provide superior performance in preserving subject variability when compared with widely used methods such as group independent component analysis. Hence, in this paper, graph-theoretical (GT) analysis is applied to IVA-generated components to effectively exploit the individual subjects' connectivity to produce discriminative features. The analysis is performed on fMRI data collected from individuals with chronic stroke both before and after a 6-week arm and hand rehabilitation intervention. Resulting GT features are shown to capture connectivity changes that are not evident through direct comparison of the group t-maps. The GT features revealed increased small worldness across components and greater centrality in key motor networks as a result of the intervention, suggesting improved efficiency in neural communication. Clinically, these results bring forth new possibilities as a means to observe the neural processes underlying improvements in motor function. PMID:26106554
Theoretical analysis of a cell's oscillations in an acoustic field
NASA Astrophysics Data System (ADS)
Allen, John S.; Zinin, Pavel
2005-09-01
The analysis and deformation of an individual cell in a high-frequency acoustic field is of fundamental interest for a variety of applications such as ultrasound cell separation and drug delivery. The oscillations of biological cells in a sound field are investigated using a shell model for the cell following an approach developed previously [Zinin, Ultrasonics, 30, 26-34 (1992)]. The model accounts for the three components which comprise the cell's motion: the internal fluid (cytoplasma), the cell membrane, and the surrounding fluid. The cell membrane whose thickness is small compared to the cell radius can be approximated as a thin elastic shell. The elastic properties of this shell together with the viscosities of the internal and external fluids determine the oscillations of the cell. The dipole oscillations of the cell depend on the surface area modulus and the maximum frequency for the relative change in cell area can be determined. Moreover, the higher order oscillations starting with the quadrupole oscillations are governed by the shell's shear modulus. Induced stresses in bacteria cell membranes in the vicinity of an oscillating bubble are investigated and cell rupture with respect to these stresses is analyzed.
Theoretical and numerical analysis of the corneal air puff test
NASA Astrophysics Data System (ADS)
Simonini, Irene; Angelillo, Maurizio; Pandolfi, Anna
2016-08-01
Ocular analyzers are used in the current clinical practice to estimate, by means of a rapid air jet, the intraocular pressure and other eye's parameters. In this study, we model the biomechanical response of the human cornea to the dynamic test with two approaches. In the first approach, the corneal system undergoing the air puff test is regarded as a harmonic oscillator. In the second approach, we use patient-specific geometries and the finite element method to simulate the dynamic test on surgically treated corneas. In spite of the different levels of approximation, the qualitative response of the two models is very similar, and the most meaningful results of both models are not significantly affected by the inclusion of viscosity of the corneal material in the dynamic analysis. Finite element calculations reproduce the observed snap-through of the corneal shell, including two applanate configurations, and compare well with in vivo images provided by ocular analyzers, suggesting that the mechanical response of the cornea to the air puff test is actually driven only by the elasticity of the stromal tissue. These observations agree with the dynamic characteristics of the test, since the frequency of the air puff impulse is several orders of magnitude larger than the reciprocal of any reasonable relaxation time for the material, downplaying the role of viscosity during the fast snap-through phase.
Analysis of the feed-forward method for the referencing of a CW laser to a frequency comb.
Gatti, D; Sala, T; Gambetta, A; Coluccelli, N; Conti, G Nunzi; Galzerano, G; Laporta, P; Marangoni, M
2012-10-22
We report on a comprehensive theoretical and experimental analysis of the feed-forward method for external frequency stabilization of a continuous wave laser against a frequency comb. Application of the method to a distributed feedback diode laser at 1.55 μm allows line narrowing from 800 to 10 kHz, with frequency noise reduction by more than 2 decades up to a Fourier frequency of 100 kHz and a maximum control bandwidth of 0.8 MHz. The results are consistent with a relative phase fluctuation of 1.4 rad rms, as limited by uncompensated high-frequency noise of the slave laser. PMID:23187255
Theoretical analysis of droplet transition from Cassie to Wenzel state
NASA Astrophysics Data System (ADS)
Liu, Tian-Qing; Yan-Jie, Li; Xiang-Qin, Li; Wei, Sun
2015-11-01
Whether droplets transit from the Cassie to the Wenzel state (C-W) on a textured surface is the touchstone that the superhydrophobicity of the surface is still maintained. However, the C-W transition mechanism, especially the spontaneous transition of small droplets, is still not very clear to date. The interface free energy gradient of a small droplet is firstly proposed and derived as the driving force for its C-W evolution in this study based on the energy and gradient analysis. Then the physical and mathematical model of the C-W transition is found after the C-W driving force or transition pressure, the resistance, and the parameters of the meniscus beneath the droplet are formulated. The results show that the micro/nano structural parameters significantly affect the C-W driving force and resistance. The smaller the pillar diameter and pitch, the minor the C-W transition pressure, and the larger the resistance. Consequently, the C-W transition is difficult to be completed for the droplets on nano-textured surfaces. Meanwhile if the posts are too short, the front of the curved liquid-air interface below the droplet will touch the structural substrate easily even though the three phase contact line (TPCL) has not depinned. When the posts are high enough, the TPCL beneath the drop must move firstly before the meniscus can reach the substrate. As a result, the droplet on a textured surface with short pillars is easy to complete its C-W evolution. On the other hand, the smaller the droplet, the easier the C-W shift, since the transition pressure becomes larger, which well explains why an evaporating drop will collapse spontaneously from composite to Wenzel state. Besides, both intrinsic and advancing contact angles affect the C-W transition as well. The greater the two angles, the harder the C-W transition. In the end, the C-W transition parameters and the critical conditions measured in literatures are calculated and compared, and the calculations accord well with
Theoretical modeling of laser-induced plasmas using the ATOMIC code
NASA Astrophysics Data System (ADS)
Colgan, James; Johns, Heather; Kilcrease, David; Judge, Elizabeth; Barefield, James, II; Clegg, Samuel; Hartig, Kyle
2014-10-01
We report on efforts to model the emission spectra generated from laser-induced breakdown spectroscopy (LIBS). LIBS is a popular and powerful method of quickly and accurately characterizing unknown samples in a remote manner. In particular, LIBS is utilized by the ChemCam instrument on the Mars Science Laboratory. We model the LIBS plasma using the Los Alamos suite of atomic physics codes. Since LIBS plasmas generally have temperatures of somewhere between 3000 K and 12000 K, the emission spectra typically result from the neutral and singly ionized stages of the target atoms. We use the Los Alamos atomic structure and collision codes to generate sets of atomic data and use the plasma kinetics code ATOMIC to perform LTE or non-LTE calculations that generate level populations and an emission spectrum for the element of interest. In this presentation we compare the emission spectrum from ATOMIC with an Fe LIBS laboratory-generated plasma as well as spectra from the ChemCam instrument. We also discuss various physics aspects of the modeling of LIBS plasmas that are necessary for accurate characterization of the plasma, such as multi-element target composition effects, radiation transport effects, and accurate line shape treatments. The Los Alamos National Laboratory is operated by Los Alamos National Security, LLC for the National Nuclear Security Administration of the U.S. Department of Energy under Contract No. DE-AC5206NA25396.
NASA Astrophysics Data System (ADS)
Veselovskaya, T. V.; Klochan, E. L.; Lariontsev, E. G.
1990-12-01
A theoretical analysis is made of active mode locking in a solid-state laser with an acoustooptic modulator based on traveling acoustic waves. It is postulated that the acoustooptic modulator is placed in a V-shaped resonator so that diffraction feedback is established in the modulator. It is found that the transmission coefficient of the acoustooptic modulator is a function of time. The mode locking achieved in a V-shaped resonator is equivalent to that observed in lasers with intracavity frequency modulation of the radiation. An investigation is made of the stability of mode locking in a resonator with a traveling-acoustic-wave acoustooptic modulator.
Cold collisions of ground-state calcium atoms in a laser field: A theoretical study
Bussery-Honvault, Beatrice; Launay, Jean-Michel; Moszynski, Robert
2003-09-01
State-of-the-art ab initio techniques have been applied to compute the potential-energy curves for the ground X {sup 1}{sigma}{sub g}{sup +} and excited {sup 1}{pi}{sub g}(4s3d) states of the calcium dimer in the Born-Oppenheimer approximation. The weakly bound ground state was calculated by symmetry-adapted perturbation theory, while the strongly bound excited state was computed using a combination of the linear-response theory within the coupled-cluster singles and doubles framework for the core-valence electronic correlation and of the full configuration interaction for the valence-valence correlation. The ground-state potential has been corrected by considering the relativistic terms resulting from the first-order many-electron Breit theory, and the retardation corrections. The magnetic electronic transition dipole moment governing the {sup 1}{pi}{sub g}(leftarrow){sup 1}{sigma}{sub g}{sup +} transitions has been obtained as the first residue of the polarization propagator computed with the coupled-cluster method restricted to single and double excitations. The computed energies and transition moments have been analytically fitted and used in the dynamical calculations of the rovibrational energy levels, ground-state scattering length, photoassociation intensities at ultralow temperatures, and spontaneous emission coefficients from the {sup 1}{pi}{sub g}(4s3d) to the X {sup 1}{sigma}{sub g}{sup +} state. The spectroscopic constants of the theoretical ground-state potential are in a good agreement with the experimental values derived from the Fourier-transform spectra [O. Allard et al., Eur. Phys. J. D (to be published)]. The theoretical s-wave scattering length for the ground state is a=44 bohrs, suggesting that it should be possible to obtain a stable Bose-Einstein condensate of calcium atoms. Finally, the computed photoassociation intensities and spontaneous emission coefficients suggest that it should be possible to obtain cold calcium molecules by
ERIC Educational Resources Information Center
Zhu, Wenzhong; Liu, Dan
2014-01-01
Based on a review of the literature on ESP and needs analysis, this paper is intended to offer some theoretical supports and inspirations for BE instructors to develop BE curricula for business contexts. It discusses how the theory of need analysis can be used in Business English curriculum design, and proposes some principles of BE curriculum…
Analysis of TOPEX laser retroreflector array characteristics
NASA Technical Reports Server (NTRS)
Varghese, Thomas K.
1993-01-01
The joint U.S./French TOPEX/POSEIDON mission was successfully launched on August 10, 1992 for the study of ocean height variation using microwave altimetry. Accurate determination of the satellite orbit is paramount to the determination of the above phenomenon. To accomplish this, using laser ranging, the satellite is equipped with a laser retroreflector array (LRA) around the altimeter antennae. The goal of laser ranging is to obtain precision orbits with a radial accuracy of 13 cm to the center of mass of the satellite. This requires the laser range correction to the LRA reference be known at the sub-cm level and is quite a challenge considering the geometry of the LRA. Detailed studies were initiated by the TOPEX project office (Christensen) under the auspices of the CDP/DOSE project (Degnan) at Goddard Space Flight Center.
ERIC Educational Resources Information Center
Schewe, Phillip F.
1981-01-01
Examines the nature of laser light. Topics include: (1) production and characteristics of laser light; (2) nine types of lasers; (3) five laser techniques including holography; (4) laser spectroscopy; and (5) laser fusion and other applications. (SK)
Energy level offset analysis of lead atom in laser plasma
NASA Astrophysics Data System (ADS)
Zhou, X. M.; Chen, C. S.; Man, B. Y.; Guo, J.; Wang, J.
2009-08-01
The optical emission spectra of the plasma generated by a 1064 nm laser irradiation of lead target in air were recorded and analyzed. Temporal evolvement trait of spectral lines was investigated. The Stark width and line shift were measured at different delay time and laser energies. The electron densities were determined using Stark-broadening parameters of spectral lines. The atomic energy level offset in plasma surroundings was explored by analyzing the line shift. The experimental data of Stark widths and line shifts were analyzed using the regularity of the Stark parameters’ dependence on effective ionization potential. However an inverse experimental result was found compared with the theoretical calculation. In addition, the change of the Stark widths and line shifts with the delay time and laser energies was discussed.