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Expansion of radiative cooling of the laser induced plasma

Description: To study the expansion and cooling process of the laser induced plasma generated by nanosecond pulsed laser ablation, experiments have been conducted which measure the position of the external shockwaves and the temperature of the vapor plumes. The positions of external shockwaves were determined by a femtosecond laser time-resolved imaging system. Vapor plume temperature was determined from spectroscopic measurements of the plasma emission lines. A model which considers the mass, momentum, and energy conservation of the region affected by the laser energy was developed. It shows good agreement to the experimental data.
Date: May 5, 2006
Creator: Wen, Sy-Bor; Mao, Xianglei; Liu, Chunyi; Greif, Ralph & Russo,Richard
Partner: UNT Libraries Government Documents Department

Radiation from hard objects

Description: The inference of the diameter of hard objects is insensitive to radiation efficiency. Deductions of radiation efficiency from observations are very sensitive - possibly overly so. Inferences of the initial velocity and trajectory vary similarly, and hence are comparably sensitive.
Date: February 1, 1997
Creator: Canavan, G. H.
Partner: UNT Libraries Government Documents Department

On the quasihydrostatic flows of radiatively cooling self-gravitating gas clouds

Description: Two model problems are considered, illustrating the dynamics of quasihydrostatic flows of radiatively cooling, optically thin self-gravitating gas clouds. In the first problem, spherically symmetric flows in an unmagnetized plasma are considered. For a power-law dependence of the radiative loss function on the temperature, a one-parameter family of self-similar solutions is found. The authors concentrate on a constant-mass cloud, one of the cases, when the self-similarity indices are uniquely selected. In this case, the self-similar flow problem can be formally reduced to the classical Lane-Emden equation and therefore solved analytically. The cloud is shown to undergo radiative condensation, if the gas specific heat ratio {gamma} > 4/3. The condensation proceeds either gradually, or in the form of (quasihydrostatic) collapse. For {gamma} < 4/3, the cloud is shown to expand. The second problem addresses a magnetized plasma slab that undergoes quasihydrostatic radiative cooling and condensation. The problem is solved analytically, employing the Lagrangian mass coordinate.
Date: March 1, 1995
Creator: Meerson, B.; Megged, E. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Development of a model to simulate the performance of hydronic radiant cooling ceilings

Description: A significant amount of the electrical energy used to cool non-residential buildings equipped with all-air systems is drawn by the fans that transport the cool air through the thermal distribution system. Hydronic radiant cooling systems have the potential to reduce the amount of air transported through the building by separating the tasks of ventilation and thermal conditioning. Because of the physical properties of water, hydronic radiant cooling systems can transport a given amount of thermal energy using less than 5170 of the otherwise necessary fan energy. This improvement alone significantly reduces the energy consumption and peak power requirement of the air conditioning system. Hydronic radiant cooling systems have been used for more than 30 years in hospital rooms to provide a draft-free, thermally stable environment. The energy savings and peak-load characteristics of these systems have not yet been analyzed systematically. Moreover, adequate guidelines for design and control of these systems do not exist. This has prevented their widespread application to other building types. The evaluation of the theoretical performance of hydronic systems could be made most conveniently by computer models. Energy analysis programs such as DOE-2 do not have the capability to simulate hydronic radiant systems yet. In this paper the development of a model that can simulate accurately the dynamic performance of hydronic radiant cooling systems is described. The model is able to calculate loads, heat extraction rates, room air temperature and room surface temperature distributions, and can be used to evaluate issues such as thermal comfort, controls, system sizing, system configuration and dynamic response. The model was created with the Simulation Problem Analysis and Research Kernel (SPARK) developed at the Lawrence Berkeley Laboratory, which provides a methodology for describing and solving the dynamic, non-linear equations that correspond to complex physical systems.
Date: June 1, 1995
Creator: Stetiu, C. & Feustel, H.E.
Partner: UNT Libraries Government Documents Department


Description: LAUNCHER PERFORMANCE IN THE DIII-D SYSTEM. The thermal performance of three different designs for the steerable mirrors on the ECH launchers installed in the DIII-D tokamak has been evaluated theoretically and experimentally. In each case the disruption forces must be minimized while providing a low loss reflecting surface. One design uses all Glidcop{reg_sign} material, but shaped so that the center is appreciably thicker than the edge. A second design is graphite with a molybdenum surface brazed to the graphite. The latest design is laminated copper/stainless steel construction with a thin copper reflecting surface. All three mirrors employ passive radiative cooling. The mirror temperatures are measured by resistance temperature devices (RTDs) which are attached at the back surfaces of the mirrors. The temperature increases are moderate for the laminated mirror, which has the best overall performance.
Date: July 1, 2003
Partner: UNT Libraries Government Documents Department

X-ray Spectroscopy of Cooling Cluster

Description: We review the X-ray spectra of the cores of clusters of galaxies. Recent high resolution X-ray spectroscopic observations have demonstrated a severe deficit of emission at the lowest X-ray temperatures as compared to that expected from simple radiative cooling models. The same observations have provided compelling evidence that the gas in the cores is cooling below half the maximum temperature. We review these results, discuss physical models of cooling clusters, and describe the X-ray instrumentation and analysis techniques used to make these observations. We discuss several viable mechanisms designed to cancel or distort the expected process of X-ray cluster cooling.
Date: January 17, 2006
Creator: Peterson, J.R.; /SLAC; Fabian, A.C. & /Cambridge U., Inst. of Astron.
Partner: UNT Libraries Government Documents Department

Energy Dependent Morphology in the PWN Candidate HESS J1825-137

Description: Observations with H.E.S.S. revealed a new source of very high-energy (VHE) gamma-rays above 100 GeV - HESS J1825-137 - extending mainly to the south of the energetic pulsar PSRB1823-13. A detailed spectral and morphological analysis of HESS J1825-137 reveals for the first time in VHE gamma-ray astronomy a steepening of the energy spectrum with increasing distance from the pulsar. This behavior can be understood by invoking radiative cooling of the IC-Compton gamma-ray emitting electrons during their propagation. In this scenario the vastly different sizes between the VHE gamma-ray emitting region and the X-ray PWN associated with PSRB1823-13 can be naturally explained by different cooling timescales for the radiating electron populations. If this scenario is correct, HESS J1825-137 can serve as a prototype for a whole class of asymmetric PWN in which the X-rays are extended over a much smaller angular scales than the gamma-rays and can help understanding recent detections of X-ray PWN in systems such as HESS J1640-465 and HESS J1813-178. The future GLAST satellite will probe lower electron energies shedding further light on cooling and diffusion processes in this source.
Date: September 26, 2007
Creator: Funk, S.; /KIPAC, Menlo Park; Hinton, J.A.; U., /Leeds; deJager, O.C. & /North West U., South Africa
Partner: UNT Libraries Government Documents Department

A new method to generate dust with astrophysical properties

Description: In interstellar and interplanetary space, the size distribution and composition of dust grains play an important role. For example, dust grains determine optical and ultraviolet extinction levels in astronomical observations, dominate the cooling rate of our Galaxy, and sets the thermal balance and radiative cooling rates in molecular clouds, which are the birth place of stars. Dust grains are also a source of damage and failure to space hardware and thus present a hazard to space flight. To model the size distribution and composition of dust grains, and their effect in the above scenarios, it is vital to understand the mechanism of dust-shock interaction. We demonstrate a new experiment which employs a laser to subject dust grains to pressure spikes similar to those of colliding astrophysical dust, and which accelerates the grains to astrophysical velocities. The new method generates much larger data sets than earlier methods; we show how large quantities (thousands) of grains are accelerated at once, rather than accelerating individual grains, as is the case of earlier methods using electric fields.
Date: April 21, 2010
Creator: Hansen, J F; van Breugel, W; Bringa, E M; Graham, G A; Remington, B A; Taylor, E A et al.
Partner: UNT Libraries Government Documents Department

Empirical evaluation of the radiative cooling coefficient for krypton gas in the FTU plasma

Description: For future fusion reactors, a careful balance must be achieved between the cooling of the outer plasma via impurity radiation and the deleterious effects of inevitable core penetration by impurity ions. We have injected krypton gas into the Frascati Tokamak Upgrade (FTU) plasma. The measured visible bremsstrahlung and bolometric signals from krypton have been inverted and the resulting radial impurity density profile and power loss profile for krypton gas are extracted. Using the measured electron density and temperature profiles, the radiative cooling coefficient for krypton is derived. The level of intrinsic impurities (Mo, Cr, Mn and Fe) in the plasma during the krypton puffing is monitored with a VUV SPRED spectrometer. Models for krypton emissivity from the literature are compared to our measured results. 7 figs.
Date: November 18, 1997
Creator: Fournier, K.B.; Pacella, D.; Gregory, B.C.; May, M.J.; Mazzitelli, G.; Gabellieri, L. et al.
Partner: UNT Libraries Government Documents Department

Reduction of Tropical Cloudiness by Soot

Description: Measurements and models show that enhanced aerosol concentrations can augment cloud albedo not only by increasing total droplet cross-sectional area, but also by reducing precipitation and thereby increasing cloud water content and cloud coverage. Aerosol pollution is expected to exert a net cooling influence on the global climate through these conventional mechanisms. Here we demonstrate an opposite mechanism through which aerosols can reduce cloud cover and thus significantly offset aerosol-induced radiative cooling at the top of the atmosphere on a regional scale. In model simulations the daytime clearing of trade cumulus is hastened and intensified by solar heating in dark haze (as found over much of the northern Indian Ocean during the northeast monsoon).
Date: May 8, 2000
Creator: Ackerman, A. S.; Toon, O. B.; Stevens, D. E.; Heymsfield, A. J. & Ramanathan, V.
Partner: UNT Libraries Government Documents Department

Evolution of a storm-driven cloudy boundary layer in the Arctic

Description: The cloudy boundary layer under stormy conditions during the summertime Arctic has been studied using observation from the SHEBA experiment and large-eddy simulations (LES). On 29 July 1998, a stable Arctic cloudy boundary layer event was observed after passage of a synoptic low. The local dynamic and thermodynamic structure of the boundary layer was determined from aircraft measurement including analysis of turbulence, cloud microphysics and radiative properties. After the upper cloud layer advected over the existing cloud layer, the turbulent kinetic energy budget indicated that the cloud layer below 200 m was maintained predominantly by shear production. Observations of longwave radiation showed that cloud top cooling at the lower cloud top has been suppressed by radiative effects of the upper cloud layer. Our LES results demonstrate the importance of the combination of shear mixing near the surface and radiative cooling at the cloud top in the storm-driven cloudy boundary layer. Once the low-level cloud reaches a certain height, depending on the amount of cloud-top cooling, the two sources of TKE production begin to separate in space under continuous stormy conditions, suggesting one possible mechanism for the cloud layering. The sensitivity tests suggest that the storm-driven cloudy boundary layer is flexibly switched to the shear-driven system due to the advection of upper clouds or the buoyantly driven system due to the lack of the wind shear. A comparison is made of this storm-driven boundary layer with the buoyantly driven boundary layer previously described in the literature.
Date: October 24, 2003
Creator: Inoue, J; Kosovic, B & Curry, J A
Partner: UNT Libraries Government Documents Department

On the Evolution of and High-Energy Emission from GHz-Peaked-Spectrum Sources

Description: Here we discuss evolution and broad-band emission of compact (&lt; kpc) lobes in young radio sources. We propose a simple dynamical description for these objects, consisting of a relativistic jet propagating into a uniform gaseous medium in the central parts of an elliptical host. In the framework of the proposed model, we follow the evolution of ultrarelativistic electrons injected from a terminal hotspot of a jet to expanding lobes, taking into account their adiabatic energy losses as well as radiative cooling. This allows us to discuss the broad-band lobe emission of young radio sources. In particular, we argue that the observed spectral turnover in the radio synchrotron spectra of these objects cannot originate from the synchrotron self-absorption process but is most likely due to free-free absorption effects connected with neutral clouds of interstellar medium engulfed by the expanding lobes and photoionized by active centers. We also find a relatively strong and complex high-energy emission component produced by inverse-Compton up-scattering of various surrounding photon fields by the lobes electrons. We argue that such high energy radiation is strong enough to account for several observed properties of GHz-peaked-spectrum (GPS) radio galaxies at UV and X-ray frequencies. In addition, this emission is expected to extend up to GeV (or possibly even TeV) photon energies and can thus be probed by several modern {gamma}-ray instruments. In particular, we suggest that GPS radio galaxies should constitute a relatively numerous class of extragalactic sources detected by GLAST.
Date: December 18, 2007
Creator: Stawarz, L.; Ostorero, L.; Begelman, M.C.; Moderski, R.; Kataoka, J. & Wagner, S.
Partner: UNT Libraries Government Documents Department

Site scientific mission plan for the Southern Great Plains CART site: January 1997--June 1997

Description: The Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site is designed to help satisfy the data needs of the Atmospheric Radiation Measurement (ARM) Program Science Team. This document defines the scientific priorities for site activities during the six months beginning on January 1, 1997, and looks forward in lesser detail to subsequent six-month periods. The primary purpose of this Site Scientific Mission Plan is to provide guidance for the development of plans for site operations. It also provides information on current plans to the ARM functional teams (Management Team, Data and Science Integration Team [DSIT], Operations Team, Instrument Team [IT], and Campaign Team) and serves to disseminate the plans more generally within the ARM Program and among the members of the Science Team. This document includes a description of the operational status of the site and the primary site activities envisioned, together with information concerning approved and proposed intensive observation periods (IOPs). The primary users of this document are the site operator, the Site Scientist Team (SST), the Science Team through the ARM Program science director, the ARM Program Experiment Center, and the aforementioned ARM Program functional teams. This plan is a living document that is updated and reissued every six months as the observational facilities are developed, tested, and augmented and as priorities are adjusted in response to developments in scientific planning and understanding.
Date: January 1, 1997
Creator: Peppler, R.A.; Lamb, P.J. & Sisterson, D.L.
Partner: UNT Libraries Government Documents Department

Application of Laboratory and Modeling Capabilities to Extreme Ultraviolet Spectroscopy of Astrophysical Sources

Description: Work funded by the subject LDRD proposal has produced the following results. First, a comprehensive catalog of EUV lines from M-shell iron (Fe IX-XVI) in the 60-140 {angstrom} waveband. Second, a revised estimate of the radiative cooling of high-temperature plasmas by Fe, which dominates the cooling in cosmic-abundance plasmas from 4 x 10{sup 5}K to 1 x 10{sup 7}K. Third, laboratory data to correct theoretical atomic models and develop reliable spectral models of M-shell Fe in the EUV. Fourth, a solution of the origin of the quasi-continuum in EUV spectra of late-type stars, which has been variously ascribed to a high-temperature tail on the emission measure distribution of stellar coronae, reduced metal abundances, resonant scattering (destruction) of emission lines, and incompleteness of atomic models.
Date: February 25, 2000
Creator: Mauche, C.; Liedahl, D.A. & Beiersdorfer, P.
Partner: UNT Libraries Government Documents Department

Stability of a radiative mantle in ITER

Description: We report results of a study to evaluate the efficacy of various impurities for heat dispersal by a radiative mantle and radiative divertor(including SOL). We have derived a stability criterion for the mantle radiation which favors low Z impurities and low ratios of edge to core thermal conductivities. Since on the other hand the relative strength of boundary line radiation to core bremsstrahlung favors high Z impurities, we find that for the ITER physics phase argon is the best gaseous impurity for mantle radiation. For the engineering phase of ITER, more detailed analysis is needed to select between krypton and argon.
Date: December 1, 1996
Creator: Mahdavi, M.A.; Staebler, G.M.; Wood, R.D.; Whyte, D.G. & West, W.P.
Partner: UNT Libraries Government Documents Department

Final Report: Experimental Astrophysics on the Omega Laser

Description: This report summarized results obtained in work supported by this research grant. In hydrodynamic instability experiments related to supernovae, we showed that initial conditions have a controlling effect on material interpenetration, and demonstrated new diagnostic techniques that will provide improved data. In radiative shock experiments, we demonstrated the ability to produce and detect radiative shocks that have collapsed spatially in consequence of radiative cooling.
Date: August 15, 2005
Creator: Drake, R. Paul
Partner: UNT Libraries Government Documents Department

Mesoscale Modeling During Mixed-Phase Arctic Cloud Experiment

Description: Mixed-phase arctic stratus clouds are the predominant cloud type in the Arctic (Curry et al. 2000) and through various feedback mechanisms exert a strong influence on the Arctic climate. Perhaps one of the most intriguing of their features is that they tend to have liquid tops that precipitate ice. Despite the fact that this situation is colloidally unstable, these cloud systems are quite long lived - from a few days to over a couple of weeks. It has been hypothesized that mixed-phase clouds are maintained through a balance between liquid water condensation resulting from the cloud-top radiative cooling and ice removal by precipitation (Pinto 1998; Harrington et al. 1999). In their modeling study Harrington et al. (1999) found that the maintenance of this balance depends strongly on the ambient concentration of ice forming nucleus (IFN). In a follow-up study, Jiang et al. (2002), using only 30% of IFN concentration predicted by Meyers et al. (1992) IFN parameterization were able to obtain results similar to the observations reported by Pinto (1998). The IFN concentration measurements collected during the Mixed-Phase Arctic Cloud Experiment (M-PACE), conducted in October 2004 over the North Slope of Alaska and the Beaufort Sea (Verlinde et al. 2005), also showed much lower values then those predicted (Prenne, pers. comm.) by currently accepted ice nucleation parameterizations (e.g. Meyers et al. 1992). The goal of this study is to use the extensive IFN data taken during M-PACE to examine what effects low IFN concentrations have on mesoscale cloud structure and coastal dynamics.
Date: March 18, 2005
Creator: Avramov, A.; Harringston, J.Y. & Verlinde, J.
Partner: UNT Libraries Government Documents Department

Impact of the ice phase on a mesoscale convective system: Implication of cloud parameterization and cloud radiative properties

Description: This study attempts to provide further understanding of the effect of the ice phase on cloud ensemble features which are useful for improving GCM cumulus parameterization. In addition, cloud model results are used to diagnose the radiative properties of anvils in order to assess cloud/radiation interaction and its feedback on the larger-scale climate for the future work. The heat, moisture and mass budget analyses of a simulated squall line system indicate that, at least for this type of system, the inclusion of the ice phase in the microphysics does not considerably change the net cloud heating and drying effects and the feedback on the large-scale motion. Nonetheless, its impact on the radiative properties of clouds significantly influences not only the squall line system itself, but also the larger-scale circulation due to the favorable stratification for long-lasting anvil clouds. The water budget suggests a simple methodology to parameterize the microphysical effect without considering it as a model physics module. Further application of the water budget might also be used to parameterize the cloud transport of condensates in the anvil cloud region, which allows the GCM columns to interact with each other. The findings of this study suggest that the ice phase could be ignored in the cloud parameterization in order to save significant amounts of computational resources and to simplify the model physics. More scientific effort should, however, be focused on the effect of the ice phase to further explore cloud feedback on the large-scale climate through the radiative process. The cloud/radiation interaction and its feedback on the larger-scale climate will be addressed in a companion study by coupling the radiative transfer model with the cloud model. 19 refs., 13 figs.
Date: August 1, 1991
Creator: Chin, H.N.S.; Bradley, M.M.; Molenkamp, C.R.; Grant, K.E. & Chuang, C.
Partner: UNT Libraries Government Documents Department

Building America Industrialized Housing Partnership (BAIHP)

Description: This final report summarizes the work conducted by the Building America Industrialized Housing Partnership (www.baihp.org) for the period 9/1/99-6/30/06. BAIHP is led by the Florida Solar Energy Center of the University of Central Florida and focuses on factory built housing. In partnership with over 50 factory and site builders, work was performed in two main areas--research and technical assistance. In the research area--through site visits in over 75 problem homes, we discovered the prime causes of moisture problems in some manufactured homes and our industry partners adopted our solutions to nearly eliminate this vexing problem. Through testing conducted in over two dozen housing factories of six factory builders we documented the value of leak free duct design and construction which was embraced by our industry partners and implemented in all the thousands of homes they built. Through laboratory test facilities and measurements in real homes we documented the merits of 'cool roof' technologies and developed an innovative night sky radiative cooling concept currently being tested. We patented an energy efficient condenser fan design, documented energy efficient home retrofit strategies after hurricane damage, developed improved specifications for federal procurement for future temporary housing, compared the Building America benchmark to HERS Index and IECC 2006, developed a toolkit for improving the accuracy and speed of benchmark calculations, monitored the field performance of over a dozen prototype homes and initiated research on the effectiveness of occupancy feedback in reducing household energy use. In the technical assistance area we provided systems engineering analysis, conducted training, testing and commissioning that have resulted in over 128,000 factory built and over 5,000 site built homes which are saving their owners over $17,000,000 annually in energy bills. These include homes built by Palm Harbor Homes, Fleetwood, Southern Energy Homes, Cavalier and the manufacturers participating in the Northwest Energy ...
Date: June 30, 2006
Creator: McIlvaine, Janet; Chandra, Subrato; Barkaszi, Stephen; Beal, David; Chasar, David; Colon, Carlos et al.
Partner: UNT Libraries Government Documents Department

Energy balance and photochemical processes in the inner coma

Description: Energy balance and multifluid flow in the coma are described. Expansion cooling, radiative cooling, photodissociative heating, chemical heating, and relative multifluid flow are the processes determining the energy budget. In the fluid dynamics, fast atomic and molecular hydrogen are considered as separate fluids with larger collision mean free paths than the cold bulk fluid that has a larger mean molecular weight. The transition from fluid flow to free molecular flow is approximated. The model predicts hydrogen and bulk fluid flow velocities in general agreement with observations. The effects of the temperature profile and the fast hydrogen flow on the chemistry in the inner coma are investigated. Results from a model approximating conditions in Halley's comet are presented.
Date: January 1, 1982
Creator: Huebner, W.F. & Keady, J.J.
Partner: UNT Libraries Government Documents Department

Development of a balloon-borne stabilized platform for measuring radiative flux profiles in the atmospheric boundary layer

Description: A stabilized platform has been developed to carry broadband short-wave and long-wave radiometric sensors on the tether line of a small tethered balloon that ascends through atmospheric depths of up to 1.5 km to obtain vertical profiles of radiative flux and flux divergence for evaluating atmospheric radiative transfer models. The Sky Platform was designed to keep the radiometers level despite unpredictable movements of the balloon and tether line occasioned by turbulence and wind shear. The automatic control loop drives motors, gears, and pulleys located on two of the vertices of the triangular frame to climb the harness lines to keep the platform level. Radiometric sensors, an electronic compass, and an on-board data acquisition system make up the remainder of the Sky Platform. Because knowledge of the dynamic response of the tether line-platform system is essential to properly close the automatic control loop on the Sky Platform, a Motion Sensing Platform (MSP) was developed to fly in place of the Sky Platform on the tether line to characterize the Sky Platform`s operating environment. This unstabilized platform uses an array of nine solid-state linear accelerometers to measure the lateral and angular accelerations, velocities, and displacements that the Sky Platform will experience. This paper presents field performance tests of the Sky and Motion Sensing Platforms, as conducted at Richland, Washington, on February 17, 1993. The tests were performed primarily to characterize the stabilization system on the Sky Platform. Test flights were performed on this cold winter day from 1400 to 1800 Pacific Standard Time (PST). During this period, temperature profiles were near the dry adiabatic lapse rate. Flights were made through a jet wind speed profile having peak wind speeds of 7 m/s at a height of 100 m AGL. Wind directions were from the northwest. All flights were performed as continuous ascents, ...
Date: March 1, 1993
Creator: Whiteman, C. D.; Alzheimer, J. M.; Anderson, G. A. & Shaw, W. J.
Partner: UNT Libraries Government Documents Department

An intense source of positrons using a low energy proton beam

Description: An intense source of positrons would make it possible to consider linear collider designs for the flavor factories now being proposed. Such designs might have the advantage of higher luminosity than circular colliders and would also provide an arena for the further development of linear colliders in preparation for the next generation of TeV linear colliders. An intense source of positrons would also make it possible to be more flexible in the design of the next generation of TeV linear colliders. The two conventional sources of positrons now used are electron-beam electroproduction of positrons and reactor-produced {beta}{sup +}-unstable isotopes. Electroproduction sources can be fairly efficient, but suffer from the disadvantages of high capital cost and destruction of the target at higher fluxes. Reactor sources are much more inefficient and have much higher capital costs than electroproduction sources, but might make sense if a reactor already exists at an appropriate site and is principally used for other purposes. In this paper we will show that it should be possible to produce large fluxes of positrons using intense proton beams of modest energy. The basic idea is to use protons from an accelerator rather than neutrons from a reactor to produce {beta}{sup +}-unstable isotopes by the proton capture reaction. Because the targets of a proton beam can be handled more conveniently and much more quickly than insertions in reactors, we are able to consider a larger range of possible targets with shorter decay times than is reasonable for a reactor.
Date: October 1, 1992
Creator: Channell, P. J. & Dreicer, H.
Partner: UNT Libraries Government Documents Department


Description: Infrared radiative cooling is a natural process continually underway in our environment. Thus, this process contributes in an important manner to the heat balance of buildings. An increase in radiative losses during the summer or a reduction of radiative losses during the winter will reduce energy consumption. A quantitative knowledge of the infrared radiative transfer between the atmosphere and a building's surface requires detailed information regarding the angular and spectral distribution of the radiation from the atmosphere. Routine information of this type has apparently never been gathered; most observations are limited to several days in time. The filter spectrometer system described here is intended to provide data records at 30 minute intervals for weeks and months of continuous operation. The spectrometer design incorporates a Barnes Corporation model 12-880 radiometer equipped with an eight-position filter wheel, germanium lens, and pyroelectric detector. Of the eight filter positions, one is an open hole and one is a closed hole used to determine the instrument's zero offset. The remaining 6 filter positions contain infrared interference filters with 'halfpower' cut-on and cut-off points given in microns by (8.1, 13.7), (8.3, 9.1), (9.4, 9.9), (10.0, 11.4), (14.0, 15.8), and (16.6, 21.6). In addition to a stepping mechanism which allows the filter wheel to be positioned automatically, the instrument contains a rotating mirror assembly which allows the instrument's 2{sup o} field of view to be directed into the vertical direction or into a 70 C black body cavity. The entire instrument is under microprocessor control and is accessible to Lawrence Berkeley Laboratory through a MODEM telephone link. The accumulating data is transmitted over this link at intervals of one to three days. Three radiometers are located in the field at the time of this writing. Systems were installed at Tucson, Arizona in August, 1978; at San Antonio, ...
Date: March 1, 1979
Creator: Berdahl, P.
Partner: UNT Libraries Government Documents Department

Electron Energy Distribution in Hotspots of Cygnus A:Filling the Gap with Spitzer Space Telescope

Description: Here we present Spitzer Space Telescope imaging of Cyg A with the Infrared Array Camera at 4.5 {micro}m and 8.0 {micro}m, resulting in the detection of the high-energy tails or cut-offs in the synchrotron spectra for all four hotspots of this archetype radio galaxy. When combined with the other data collected (and re-analyzed) from the literature, our observations allow for detailed modeling of the broad-band (radio-to-X-ray) emission for the brightest spots A and D. We confirm that the X-ray flux detected previously from these features is consistent with the synchrotron self-Compton radiation for the magnetic field intensity B {approx} 170 {micro}G in spot A, and B {approx} 270 {micro}G in spot D. We also find that the energy density of the emitting electrons is most likely larger by a factor of a few than the energy density of the hotspots magnetic field. We construct energy spectra of the radiating ultrarelativistic electrons. We find that for both hotspots A and D these spectra are consistent with a broken power-law extending from at least 100MeV up to {approx} 100GeV, and that the spectral break corresponds almost exactly to the proton rest energy of {approx} 1GeV. We argue that the shape of the electron continuum most likely reflects two different regimes of the electron acceleration process taking place at mildly relativistic shocks, rather than resulting from radiative cooling and/or absorption e.ects. In this picture the protons inertia defines the critical energy for the hotspot electrons above which Fermi-type acceleration processes may play a major role, but below which the operating acceleration mechanism has to be of a different type. At energies {approx}&gt; 100 GeV, the electron spectra cut-off/steepen again, most likely as a result of spectral aging due to radiative loss effects. We discuss several implications of the presented analysis for the physics ...
Date: March 6, 2007
Creator: Stawarz, L.; Cheung, C.C.; Harris, D.E. & Ostrowski, M.
Partner: UNT Libraries Government Documents Department