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Sample records for sobre lo sublime

  1. The Sublime Corpse in Gertrudis Gomez de Avellaneda's Women's Journal "Album Cubano de lo Bueno y lo Bello" (1860)

    ERIC Educational Resources Information Center

    LaGreca, Nancy

    2009-01-01

    This article examines Gertrudis Gomez de Avellaneda's choice to include articles depicting the advanced decay of cadavers, which are simultaneously horrible and awesome, in her women's periodical "Album Cubano de lo Bueno y lo Bello". Background on Avellaneda's biography, women's print culture, and theories of the sublime provide a frame for the…

  2. The Sublime Corpse in Gertrudis Gomez de Avellaneda's Women's Journal "Album Cubano de lo Bueno y lo Bello" (1860)

    ERIC Educational Resources Information Center

    LaGreca, Nancy

    2009-01-01

    This article examines Gertrudis Gomez de Avellaneda's choice to include articles depicting the advanced decay of cadavers, which are simultaneously horrible and awesome, in her women's periodical "Album Cubano de lo Bueno y lo Bello". Background on Avellaneda's biography, women's print culture, and theories of the sublime provide a frame for the…

  3. The Sublime and Education

    ERIC Educational Resources Information Center

    Carson, Jamin

    2006-01-01

    The sublime is a theory of aesthetics that reached its highest popularity in British literature during the Romantic period (c. 1785-1832). This article (1) explicates philosophers' different meanings of the sublime; (2) show how the sublime is relevant to education; and (3) show how the sublime "works" in literature by analyzing William Blake's…

  4. The Sublime and Education

    ERIC Educational Resources Information Center

    Carson, Jamin

    2006-01-01

    The sublime is a theory of aesthetics that reached its highest popularity in British literature during the Romantic period (c. 1785-1832). This article (1) explicates philosophers' different meanings of the sublime; (2) show how the sublime is relevant to education; and (3) show how the sublime "works" in literature by analyzing William Blake's…

  5. Heat rejection sublimator

    NASA Technical Reports Server (NTRS)

    Dingell, Charles W. (Inventor); Quintana, Clemente E. (Inventor); Le, Suy (Inventor); Clark, Michael R. (Inventor); Cloutier, Robert E. (Inventor); Hafermalz, David Scott (Inventor)

    2009-01-01

    A sublimator includes a sublimation plate having a thermal element disposed adjacent to a feed water channel and a control point disposed between at least a portion of the thermal element and a large pore substrate. The control point includes a sintered metal material. A method of dissipating heat using a sublimator includes a sublimation plate having a thermal element and a control point. The thermal element is disposed adjacent to a feed water channel and the control point is disposed between at least a portion of the thermal element and a large pore substrate. The method includes controlling a flow rate of feed water to the large pore substrate at the control point and supplying heated coolant to the thermal element. Sublimation occurs in the large pore substrate and the controlling of the flow rate of feed water is independent of time. A sublimator includes a sublimation plate having a thermal element disposed adjacent to a feed water channel and a control point disposed between at least a portion of the thermal element and a large pore substrate. The control point restricts a flow rate of feed water from the feed water channel to the large pore substrate independent of time.

  6. A sublimation heat engine.

    PubMed

    Wells, Gary G; Ledesma-Aguilar, Rodrigo; McHale, Glen; Sefiane, Khellil

    2015-03-03

    Heat engines are based on the physical realization of a thermodynamic cycle, most famously the liquid-vapour Rankine cycle used for steam engines. Here we present a sublimation heat engine, which can convert temperature differences into mechanical work via the Leidenfrost effect. Through controlled experiments, quantified by a hydrodynamic model, we show that levitating dry-ice blocks rotate on hot turbine-like surfaces at a rate controlled by the turbine geometry, temperature difference and solid material properties. The rotational motion of the dry-ice loads is converted into electric power by coupling to a magnetic coil system. We extend our concept to liquid loads, generalizing the realization of the new engine to both sublimation and the instantaneous vapourization of liquids. Our results support the feasibility of low-friction in situ energy harvesting from both liquids and ices. Our concept is potentially relevant in challenging situations such as deep drilling, outer space exploration or micro-mechanical manipulation.

  7. A sublimation heat engine

    NASA Astrophysics Data System (ADS)

    Wells, Gary G.; Ledesma-Aguilar, Rodrigo; McHale, Glen; Sefiane, Khellil

    2015-03-01

    Heat engines are based on the physical realization of a thermodynamic cycle, most famously the liquid-vapour Rankine cycle used for steam engines. Here we present a sublimation heat engine, which can convert temperature differences into mechanical work via the Leidenfrost effect. Through controlled experiments, quantified by a hydrodynamic model, we show that levitating dry-ice blocks rotate on hot turbine-like surfaces at a rate controlled by the turbine geometry, temperature difference and solid material properties. The rotational motion of the dry-ice loads is converted into electric power by coupling to a magnetic coil system. We extend our concept to liquid loads, generalizing the realization of the new engine to both sublimation and the instantaneous vapourization of liquids. Our results support the feasibility of low-friction in situ energy harvesting from both liquids and ices. Our concept is potentially relevant in challenging situations such as deep drilling, outer space exploration or micro-mechanical manipulation.

  8. A sublimation heat engine

    PubMed Central

    Wells, Gary G.; Ledesma-Aguilar, Rodrigo; McHale, Glen; Sefiane, Khellil

    2015-01-01

    Heat engines are based on the physical realization of a thermodynamic cycle, most famously the liquid–vapour Rankine cycle used for steam engines. Here we present a sublimation heat engine, which can convert temperature differences into mechanical work via the Leidenfrost effect. Through controlled experiments, quantified by a hydrodynamic model, we show that levitating dry-ice blocks rotate on hot turbine-like surfaces at a rate controlled by the turbine geometry, temperature difference and solid material properties. The rotational motion of the dry-ice loads is converted into electric power by coupling to a magnetic coil system. We extend our concept to liquid loads, generalizing the realization of the new engine to both sublimation and the instantaneous vapourization of liquids. Our results support the feasibility of low-friction in situ energy harvesting from both liquids and ices. Our concept is potentially relevant in challenging situations such as deep drilling, outer space exploration or micro-mechanical manipulation. PMID:25731669

  9. Modelling Sublimation of Carbon Dioxide

    ERIC Educational Resources Information Center

    Winkel, Brian

    2012-01-01

    In this article, the author reports results in their efforts to model sublimation of carbon dioxide and the associated kinetics order and parameter estimation issues in their model. They have offered the reader two sets of data and several approaches to determine the rate of sublimation of a piece of solid dry ice. They presented several models…

  10. Modelling Sublimation of Carbon Dioxide

    ERIC Educational Resources Information Center

    Winkel, Brian

    2012-01-01

    In this article, the author reports results in their efforts to model sublimation of carbon dioxide and the associated kinetics order and parameter estimation issues in their model. They have offered the reader two sets of data and several approaches to determine the rate of sublimation of a piece of solid dry ice. They presented several models…

  11. Sublimation systems and associated methods

    DOEpatents

    Turner, Terry D.; McKellar, Michael G.; Wilding, Bruce M.

    2016-02-09

    A system for vaporizing and sublimating a slurry comprising a fluid including solid particles therein. The system includes a first heat exchanger configured to receive the fluid including solid particles and vaporize the fluid and a second heat exchanger configured to receive the vaporized fluid and solid particles and sublimate the solid particles. A method for vaporizing and sublimating a fluid including solid particles therein is also disclosed. The method includes feeding the fluid including solid particles to a first heat exchanger, vaporizing the fluid, feeding the vaporized fluid and solid particles to a second heat exchanger and sublimating the solid particles. In some embodiments the fluid including solid particles is liquid natural gas or methane including solid carbon dioxide particles.

  12. The Sublime and the Vulgar.

    ERIC Educational Resources Information Center

    Swann, Karen

    1990-01-01

    Explores how Edmund Burke's discourse on the sublime helps illuminate attacks on the vulgarization of culture (as typified by Allan Bloom), both for the presumedly "vulgar" reader and for the champions of high culture. (MG)

  13. Enantioenrichment in sublimed amino acid mixtures.

    PubMed

    Viedma, Cristóbal; Ortiz, José E; de Torres, Trinidad; Cintas, Pedro

    2012-04-14

    A real amplification of an initial enantiomeric excess can be detected when two amino acids are sublimed at high temperature, even if one of the components is a racemic compound that does not convert into a conglomerate by sublimation.

  14. Displacement, Substitution, Sublimation: A Bibliography.

    ERIC Educational Resources Information Center

    Pedrini, D. T.; Pedrini, Bonnie C.

    Sigmund Freund worked with the mechanisms of displacement, substitution, and sublimation. These mechanisms have many similarities and have been studied diagnostically and therapeutically. Displacement and substitution seem to fit in well with phobias, hysterias, somatiyations, prejudices, and scapegoating. Phobias, prejudices, and scapegoating…

  15. Eisenhower and the American Sublime

    ERIC Educational Resources Information Center

    O'Gorman, Ned

    2008-01-01

    This essay presents Dwight D. Eisenhower's presidential rhetoric as an iteration of an American synecdochal sublime. Eisenhower's rhetoric sought to re-aim civic sight beyond corporeal objects to the nation's transcendental essence. This rhetoric is intimately connected to prevailing political anxieties and exigencies, especially the problem of…

  16. Eisenhower and the American Sublime

    ERIC Educational Resources Information Center

    O'Gorman, Ned

    2008-01-01

    This essay presents Dwight D. Eisenhower's presidential rhetoric as an iteration of an American synecdochal sublime. Eisenhower's rhetoric sought to re-aim civic sight beyond corporeal objects to the nation's transcendental essence. This rhetoric is intimately connected to prevailing political anxieties and exigencies, especially the problem of…

  17. Membrane evaporator/sublimator investigation

    NASA Technical Reports Server (NTRS)

    Elam, J.; Ruder, J.; Strumpf, H.

    1974-01-01

    Data are presented on a new evaporator/sublimator concept using a hollow fiber membrane unit with a high permeability to liquid water. The aim of the program was to obtain a more reliable, lightweight and simpler Extra Vehicular Life Support System (EVLSS) cooling concept than is currently being used.

  18. APPARATUS FOR CONDENSATION AND SUBLIMATION

    DOEpatents

    Schmidt, R.J.; Fuis, F. Jr.

    1958-10-01

    An apparatus is presented for the sublimation and condensation of uranium compounds in order to obtain an improved crystalline structure of this material. The apparatus comprises a vaporizing chamber and condensing structure connected thereto. There condenser is fitted with a removable liner having a demountable baffle attached to the liner by means of brackets and a removable pin. The baffle is of spiral cross-section and is provided with cooling coils disposed between the surfaces of the baffle for circulation of a temperature controlling liquid within the baffle. The cooling coll provides for controlllng the temperature of the baffle to insure formatlon of a satisfactory condensate, and the removable liner facilitates the removal of condensate formed during tbe sublimation process.

  19. Schopenhauer, Nietzsche, and the Aesthetically Sublime

    ERIC Educational Resources Information Center

    Vandenabeele, Bart

    2003-01-01

    Much has been written on the relationship between Arthur Schopenhauer and Friedrich Nietzsche. Much remains to be said, however, concerning their respective theories of the sublime. In this article, the author first argues against the traditional, dialectical view of Schopenhauer's theory of the sublime that stresses the crucial role the sublime…

  20. Schopenhauer, Nietzsche, and the Aesthetically Sublime

    ERIC Educational Resources Information Center

    Vandenabeele, Bart

    2003-01-01

    Much has been written on the relationship between Arthur Schopenhauer and Friedrich Nietzsche. Much remains to be said, however, concerning their respective theories of the sublime. In this article, the author first argues against the traditional, dialectical view of Schopenhauer's theory of the sublime that stresses the crucial role the sublime…

  1. Canopy Effects on Macroscale Snow Sublimation

    NASA Astrophysics Data System (ADS)

    Svoma, B. M.

    2015-12-01

    Sublimation of snow cover directly affects snow accumulation, impacting ecosystem processes, soil moisture, soil porosity, biogeochemical processes, wildfire, and water resources. Available energy, the exposed surface area of a snow cover, and exposure time with the atmosphere vary greatly in complex terrain (e.g., aspect, elevation, forest cover), with latitude, and with continentality. It is therefore difficult to scale up results from site specific short term studies. Using the 32-km NARR, the 4-km PRISM, with 30-m terrain and forest cover data, meteorological variables are downscaled to simulate sublimation from canopy intercepted snow and from the snowpack over the Salt River Basin in Arizona for a wet and dry year. Simulations indicate that: (1) total sublimation is highly variable in response to variability in both sublimation rate and snow cover duration; (2) total canopy sublimation is similar for both years while ground sublimation is considerably greater during the wet year; (3) sublimation is a relatively greater contribution to the snow water budget during the dry year (28% vs. 20% of total snowfall); (4) at high elevations, ground sublimation is less in open areas than forested areas during the dry year, while the reverse is evident during the wet year as snowpack lasted longer into spring. While a reduction in leaf area index leads to a reduction of total sublimation due to less interception in both years, ground sublimation increases during the dry year, possibly due to less sheltering from solar radiation and wind. This reduction in sheltering results in a large decrease in snowpack duration (i.e., ten days in spring) at mid-elevations for the wet year, leading to a decrease in ground sublimation. This results in a 500 meter difference in the elevation of maximum sublimation reduction upon reduced leaf area index between the two years. Forest cover properties can vary considerably on short and long time scales through natural (wildfire, bark beetle

  2. Experimental Investigation of Transient Sublimator Performance

    NASA Technical Reports Server (NTRS)

    Sheth, Rubik B.; Stephan, Ryan A.; Leimkuehler, Thomas O.

    2012-01-01

    Sublimators have been used as heat rejection devices for a variety of space applications including the Apollo Lunar Module and the Extravehicular Mobility Unit (EMU). Sublimators typically operate with steady-state feedwater utilization at or near 100%. However, sublimators are currently being considered for operations in a cyclical topping mode, which represents a new mode of operation for sublimators. Sublimators can be used as a supplemental heat rejection device during mission phases where the environmental temperature or heat rejection requirement changes rapidly. This scenario may occur during low lunar orbit, low earth orbit, or other planetary orbits. In these mission phases, the need for supplemental heat rejection will vary between zero and some fraction of the overall heat load. In particular, supplemental heat rejection is required for the portion of the orbit where the radiative sink temperature exceeds the system setpoint temperature. This paper will describe the effects of these transient starts and stops on the feedwater utilization during various feedwater timing scenarios. Experimental data from various scenarios is analyzed to investigate feedwater consumption efficiency under the cyclical conditions. Start up utilization tests were conducted to better understand the transient performance. This paper also provides recommendations for future sublimator design and transient operation.

  3. Coating Thermoelectric Devices To Suppress Sublimation

    NASA Technical Reports Server (NTRS)

    Sakamoto, Jeffrey; Caillat, Thierry; Fleurial, Jean-Pierre; Snyder, G. Jeffrey

    2007-01-01

    A technique for suppressing sublimation of key elements from skutterudite compounds in advanced thermoelectric devices has been demonstrated. The essence of the technique is to cover what would otherwise be the exposed skutterudite surface of such a device with a thin, continuous film of a chemically and physically compatible metal. Although similar to other sublimation-suppression techniques, this technique has been specifically tailored for application to skutterudite antimonides. The primary cause of deterioration of most thermoelectric materials is thermal decomposition or sublimation - one or more elements sublime from the hot side of a thermoelectric couple, changing the stoichiometry of the device. Examples of elements that sublime from their respective thermoelectric materials are Ge from SiGe, Te from Pb/Te, and now Sb from skutterudite antimonides. The skutterudite antimonides of primary interest are CoSb3 [electron-donor (n) type] and CeFe(3-x)Co(x)Sb12 [electron-acceptor (p) type]. When these compounds are subjected to typical operating conditions [temperature of 700 C and pressure <10(exp -5) torr (0.0013 Pa)], Sb sublimes from their surfaces, with the result that Sb depletion layers form and advance toward their interiors. As the depletion layer advances in a given device, the change in stoichiometry diminishes the thermal-to-electric conversion efficiency of the device. The problem, then, is to prevent sublimation, or at least reduce it to an acceptably low level. In preparation for an experiment on suppression of sublimation, a specimen of CoSb3 was tightly wrapped in a foil of niobium, which was selected for its chemical stability. In the experiment, the wrapped specimen was heated to a temperature of 700 C in a vacuum of residual pressure <10(exp -5) torr (0.0013 Pa), then cooled and sectioned. Examination of the sectioned specimen revealed that no depletion layer had formed, indicating the niobium foil prevented sublimation of antimony at 700 C

  4. Experimental determination of ice sublimation energies

    NASA Astrophysics Data System (ADS)

    Luna, R.; Canto, J.; Satorre, M. A.; Domingo, M.

    2011-11-01

    In Astrophysics, the study of ices is important due to the wide range of scenarios in which they are present. Their physical and chemical characteristics play an important role in the study of the interstellar medium (ISM). The assessment of the energy of sublimation allows us to improve our understanding of physical and/or chemical processes that take place where ices are present. The energy of sublimation E_sub is defined as the change of energy between solid and gas phase of certain molecule. This value is important to determinate other thermodynamical parameters such as the reticular energy of ionic compounds, the energy of formation in gas phase from the energy of formation in condensed phase, or to estimate the sublimation rate, which is very important in determining the evolution of surfaces of astrophysical objects.

  5. System and method for suppressing sublimation using opacified aerogel

    NASA Technical Reports Server (NTRS)

    Sakamoto, Jeff S. (Inventor); Snyder, G. Jeffrey (Inventor); Calliat, Thierry (Inventor); Fleurial, Jean-Pierre (Inventor); Jones, Steven M. (Inventor); Palk, Jong-Ah (Inventor)

    2008-01-01

    The present invention relates to a castable, aerogel-based, ultra-low thermal conductivity opacified insulation to suppress sublimation. More specifically, the present invention relates to an aerogel opacified with various opacifying or reflecting constituents to suppress sublimation and provide thermal insulation in thermoelectric modules. The opacifying constituent can be graded within the aerogel for increased sublimation suppression, and the density of the aerogel can similarly be graded to achieve optimal thermal insulation and sublimation suppression.

  6. Heat of Sublimation of I-2.

    ERIC Educational Resources Information Center

    Henderson, Giles; Robarts, Ronald A., Jr.

    1978-01-01

    Describes an inexpensive double-beam laser photometry experiment to determine the molar heat of sublimation of I-2. The experiment employs common laboratory materials and components and gives results with a two percent to three percent accuracy. (Author/GA)

  7. No reduction using sublimation of cyanuric acid

    DOEpatents

    Perry, Robert A.

    1990-01-01

    An arrangement for reducing the NO content of a gas stream comprises contacting the gas stream with NHCO into a temperature effective for heat induced decomposition of HNCO and for resultant lowering of the NO content of the gas stream. Preferably, the HNCO is generated by sublimation of cyanuric acid.

  8. NO reduction using sublimation of cyanuric acid

    DOEpatents

    Perry, Robert A.

    1988-01-01

    An arrangement for reducing the NO content of a gas stream comprises contacting the gas stream with HNCO at a temperature effective for heat induced decomposition of HNCO and for resultant lowering of the NO content of the gas stream. Preferably, the HNCO is generated by sublimation of cyanuric acid.

  9. Heat of Sublimation of I-2.

    ERIC Educational Resources Information Center

    Henderson, Giles; Robarts, Ronald A., Jr.

    1978-01-01

    Describes an inexpensive double-beam laser photometry experiment to determine the molar heat of sublimation of I-2. The experiment employs common laboratory materials and components and gives results with a two percent to three percent accuracy. (Author/GA)

  10. Numerical simulation of drifting snow sublimation in the saltation layer

    PubMed Central

    Dai, Xiaoqing; Huang, Ning

    2014-01-01

    Snow sublimation is an important hydrological process and one of the main causes of the temporal and spatial variation of snow distribution. Compared with surface sublimation, drifting snow sublimation is more effective due to the greater surface exposure area of snow particles in the air. Previous studies of drifting snow sublimation have focused on suspended snow, and few have considered saltating snow, which is the main form of drifting snow. In this study, a numerical model is established to simulate the process of drifting snow sublimation in the saltation layer. The simulated results show 1) the average sublimation rate of drifting snow particles increases linearly with the friction velocity; 2) the sublimation rate gradient with the friction velocity increases with increases in the environmental temperature and the undersaturation of air; 3) when the friction velocity is less than 0.525 m/s, the snowdrift sublimation of saltating particles is greater than that of suspended particles; and 4) the snowdrift sublimation in the saltation layer is less than that of the suspended particles only when the friction velocity is greater than 0.625 m/s. Therefore, the drifting snow sublimation in the saltation layer constitutes a significant portion of the total snow sublimation. PMID:25312383

  11. Psychotherapy. Sublimation and the psychodynamics of birding.

    PubMed

    Clemens, Norman A

    2012-07-01

    An adventure in extreme birding prompted the psychoanalyst author to reflect on "why do people do this?" Like myriad human interests, vocations, and avocations, the activity of bird watching is a socially acceptable activity that is the final pathway for multiple motivations that are likely to have a long history in the individual's development. It may have origins in basic survival skills. Various psychological defense mechanisms may be involved, the most mature and successful one being sublimation. Success of a defense-like sublimation may be viewed in terms of freedom from anxiety or from obsessive extremes that interfere with the individual's wellbeing, important relationships, or physical or financial health. The author considers whether the characters in the film The Big Year exemplify such success or the lack of it.

  12. No reduction using sublimation of cyanuric acid

    DOEpatents

    Perry, Robert

    1989-01-01

    An arrangement for reducing the NO content of a gas stream comprises contacting the gas stream with HNCO at a temperature effective for heat induced decomposition of HNCO and for resultant lowering of the NO content of the gas stream. Preferably, the HNCO is generated by sublimation of cyanuric acid and CO or other H-atom generating species is also present or added to the gas stream.

  13. GFEChutes Lo-Fi

    NASA Technical Reports Server (NTRS)

    Gist, Emily; Turner, Gary; Shelton, Robert; Vautier, Mana; Shaikh, Ashraf

    2013-01-01

    NASA needed to provide a software model of a parachute system for a manned re-entry vehicle. NASA has parachute codes, e.g., the Descent Simulation System (DSS), that date back to the Apollo Program. Since the space shuttle did not rely on parachutes as its primary descent control mechanism, DSS has not been maintained or incorporated into modern simulation architectures such as Osiris and Antares, which are used for new mission simulations. GFEChutes Lo-Fi is an object-oriented implementation of conventional parachute codes designed for use in modern simulation environments. The GFE (Government Furnished Equipment), low-fidelity (Lo-Fi) parachute model (GFEChutes Lo-Fi) is a software package capable of modeling the effects of multiple parachutes, deployed concurrently and/or sequentially, on a vehicle during the subsonic phase of reentry into planetary atmosphere. The term "low-fidelity" distinguishes models that represent the parachutes as simple forces acting on the vehicle, as opposed to independent aerodynamic bodies. GFEChutes Lo-Fi was created from these existing models to be clean, modular, certified as NASA Class C software, and portable, or "plug and play." The GFE Lo-Fi Chutes Model provides basic modeling capability of a sequential series of parachute activities. Actions include deploying the parachute, changing the reefing on the parachute, and cutting away the parachute. Multiple chutes can be deployed at any given time, but all chutes in that case are assumed to behave as individually isolated chutes; there is no modeling of any interactions between deployed chutes. Drag characteristics of a deployed chute are based on a coefficient of drag, the face area of the chute, and the local dynamic pressure only. The orientation of the chute is approximately modeled for purposes of obtaining torques on the vehicle, but the dynamic state of the chute as a separate entity is not integrated - the treatment is simply an approximation. The innovation in GFEChutes

  14. Experimental Investigation of Sublimator Performance at Transient Heat Loads

    NASA Technical Reports Server (NTRS)

    Sheth, Rubik B.; Stephen, Ryan A.; Leimkuehler, Thomas O.

    2011-01-01

    Sublimators have been used as heat rejection devices for a variety of space applications including the Apollo Lunar Module and the Extravehicular Mobility Unit (EMU). Sublimators typically operate with steady-state feedwater utilization at or near 100%. However, sublimators are currently being considered to operate in a cyclical topping mode, which represents a new mode of operation for sublimators. Sublimators can be used as a topper during mission phases such as low lunar or low earth orbit. In these mission phases, the sublimator will be repeatedly started and stopped during each orbit to provide supplemental heat rejection for the portion of the orbit where the radiative sink temperature exceeds the system setpoint temperature. This paper will summarize the effort put into understanding sublimator response under a transient heat load. The performance will be assessed by detailing the changes in feedwater utilization due to transient starts and stops during various feedwater timing scenarios. Sublimator start up utilization will be assessed as a possible relationship to transient performance of a sublimator. This paper will also provide recommendations for future sublimator designs and/or feedwater control.

  15. Numerical Implementation of Surface Catalysis, Reaction, and Sublimation

    DTIC Science & Technology

    2007-07-01

    Sublimation RTO-EN-AVT-142 16 - 13 the pores, the vapor molecule decomposes into smaller molecules. This decomposition process absorbs heat and...less than that to the Galileo Probe. There, not only the sublimation but the eactions, Eqs. (15) and (16) could conceivably become important . Surface...RTO-EN-AVT-142 16 - 1 Park, C. (2007) Numerical Implementation of Surface Catalysis, Reaction, and Sublimation . In Experiment, Modeling and

  16. Sublimating grains model of cometary coma.

    NASA Astrophysics Data System (ADS)

    Faggi, S.; Tozzi, G. P.; Brucato, J. R.

    Billion years of space weathering produces a crust of organic matter (see e.g. Kanuchova et al. 2012) that will be released when a comet enter for the first time in the inner Solar System. New comets, coming form the Oort Colud at their first passage close to the Sun, are particularly important because they are not differentiated by the Solar radiation and they are supposed to have a large quantity of ice organic matter close to the surface. When a comet approach to the Sun, its activity is driven by the sublimation of these nucleus ices: if the heliocentric distances, R_H , is greater than 3 AU the sublimation of CO and CO_2 ices is the main source of comet activity, otherwise at shorter distances, the sublimation of water become the most important mechanism of activity. These gases, escaping from the nucleus, drag in the coma grains that can be refractory dust (silicates, carbon), water ice and/or organic ices. Oort comets at their first passage in the inner Solar System, should produce an halo of organic or water icy particles. Our group has been monitoring new, inbound, bright Oort comets (C/2011 F1, C/2012 S1, C/2012 K1, C/2013 V5, C/2012 F3, C/2013 US10, C/2013 X1) to search for these icy grains. The method consists in detecting the cloud of sublimating grains in the inner coma by using the Sigma Af function (Tozzi et al. 2007) directly from images. However this over-population of grains, beside the sublimation, can be also due to short time activity (outburst) or too big grains expanding at very slow velocity, as it has been found in comet 67P/C-G (Tozzi eta al, 2011, A&A, 531, 54). To disentangle between the phenomena it is necessary to monitor the comet both at short timescale, for the outbursts (by repeating the observations after few nights), and at long term (weeks-months). If the cloud does not expand with the decreasing of the heliocentric distance there is high probability that we are in presence of organic and/or water ice grains. We can disentangle

  17. Science Sublime: The Philosophy of the Sublime, Dewey's Aesthetics, and Science Education

    ERIC Educational Resources Information Center

    Cavanaugh, Shane

    2014-01-01

    Feelings of awe, wonder, and appreciation have been largely ignored in the working lives of scientists and, in turn, science education has not accurately portrayed science to students. In an effort to bring the affective qualities of science into the classroom, this work draws on the writings of the sublime by Burke, Kant, Emerson, and Wordsworth…

  18. Science Sublime: The Philosophy of the Sublime, Dewey's Aesthetics, and Science Education

    ERIC Educational Resources Information Center

    Cavanaugh, Shane

    2014-01-01

    Feelings of awe, wonder, and appreciation have been largely ignored in the working lives of scientists and, in turn, science education has not accurately portrayed science to students. In an effort to bring the affective qualities of science into the classroom, this work draws on the writings of the sublime by Burke, Kant, Emerson, and Wordsworth…

  19. Reassessing Aesthetic Appreciation of Nature in the Kantian Sublime

    ERIC Educational Resources Information Center

    Brady, Emily

    2012-01-01

    The sublime has been a relatively neglected topic in recent work in philosophical aesthetics, with existing discussions confined mainly to problems in Kant's theory. Given the revival of interest in his aesthetic theory and the influence of the Kantian sublime compared to other eighteenth-century accounts, this focus is not surprising. Kant's…

  20. Reassessing Aesthetic Appreciation of Nature in the Kantian Sublime

    ERIC Educational Resources Information Center

    Brady, Emily

    2012-01-01

    The sublime has been a relatively neglected topic in recent work in philosophical aesthetics, with existing discussions confined mainly to problems in Kant's theory. Given the revival of interest in his aesthetic theory and the influence of the Kantian sublime compared to other eighteenth-century accounts, this focus is not surprising. Kant's…

  1. In situ transmission electron microscopy of cadmium selenide nanorod sublimation

    SciTech Connect

    Hellebusch, Daniel J.; Manthiram, Karthish; Beberwyck, Brandon J.; Alivisatos, A. Paul

    2015-01-23

    In situ electron microscopy is used to observe the morphological evolution of cadmium selenide nanorods as they sublime under vacuum at a series of elevated temperatures. Mass loss occurs anisotropically along the nanorod’s long axis. At temperatures close to the sublimation threshold, the phase change occurs from both tips of the nanorods and proceeds unevenly with periods of rapid mass loss punctuated by periods of relative stability. At higher temperatures, the nanorods sublime at a faster, more uniform rate, but mass loss occurs from only a single end of the rod. Furthermore, we propose a mechanism that accounts for the observed sublimation behavior based on the terrace–ledge–kink (TLK) model and how the nanorod surface chemical environment influences the kinetic barrier of sublimation.

  2. In situ transmission electron microscopy of cadmium selenide nanorod sublimation

    DOE PAGES

    Hellebusch, Daniel J.; Manthiram, Karthish; Beberwyck, Brandon J.; ...

    2015-01-23

    In situ electron microscopy is used to observe the morphological evolution of cadmium selenide nanorods as they sublime under vacuum at a series of elevated temperatures. Mass loss occurs anisotropically along the nanorod’s long axis. At temperatures close to the sublimation threshold, the phase change occurs from both tips of the nanorods and proceeds unevenly with periods of rapid mass loss punctuated by periods of relative stability. At higher temperatures, the nanorods sublime at a faster, more uniform rate, but mass loss occurs from only a single end of the rod. Furthermore, we propose a mechanism that accounts for themore » observed sublimation behavior based on the terrace–ledge–kink (TLK) model and how the nanorod surface chemical environment influences the kinetic barrier of sublimation.« less

  3. In Situ Transmission Electron Microscopy of Cadmium Selenide Nanorod Sublimation.

    PubMed

    Hellebusch, Daniel J; Manthiram, Karthish; Beberwyck, Brandon J; Alivisatos, A Paul

    2015-02-19

    In situ electron microscopy is used to observe the morphological evolution of cadmium selenide nanorods as they sublime under vacuum at a series of elevated temperatures. Mass loss occurs anisotropically along the nanorod's long axis. At temperatures close to the sublimation threshold, the phase change occurs from both tips of the nanorods and proceeds unevenly with periods of rapid mass loss punctuated by periods of relative stability. At higher temperatures, the nanorods sublime at a faster, more uniform rate, but mass loss occurs from only a single end of the rod. We propose a mechanism that accounts for the observed sublimation behavior based on the terrace-ledge-kink (TLK) model and how the nanorod surface chemical environment influences the kinetic barrier of sublimation.

  4. Sublime science: Teaching for scientific sublime experiences in middle school classrooms

    NASA Astrophysics Data System (ADS)

    Cavanaugh, Shane

    Due to a historical separation of cognition and emotion, the affective aspects of learning are often seen as trivial in comparison to the more 'essential' cognitive qualities - particularly in the domain of science. As a result of this disconnect, feelings of awe, wonder, and astonishment as well as appreciation have been largely ignored in the working lives of scientists. In turn, I believe that science education has not accurately portrayed the world of science to our students. In an effort to bring the affective qualities of science into the science classroom, I have drawn on past research in the field of aesthetic science teaching and learning as well as works by, Burke, Kant, and Dewey to explore a new construct I have called the "scientific sublime". Scientific sublime experiences represent a sophisticated treatment of the cognitive as well as affective qualities of science learning. The scientific sublime represents feelings of awe, wonder, and appreciation that come from a deep understanding. It is only through this understanding of a phenomenon that we can appreciate its true complexity and intricacies, and these understandings when mixed with the emotions of awe and reverence, are sublime. Scientific sublime experiences are an attempt at the re-integration of cognition and feeling. The goal of this research was twofold: to create and teach a curriculum that fosters scientific sublime experiences in middle school science classes, and to better understand how these experiences are manifested in students. In order to create an approach to teaching for scientific sublime experiences, it was first necessary for me to identify key characteristics of such an experience and a then to create a pedagogical approach, both of which are described in detail in the dissertation. This research was conducted as two studies in two different middle schools. My pedagogical approach was used to create and teach two five-week 7 th grade science units---one on weather

  5. The interaction of Io's plumes and sublimation atmosphere

    NASA Astrophysics Data System (ADS)

    McDoniel, William J.; Goldstein, David B.; Varghese, Philip L.; Trafton, Laurence M.

    2017-09-01

    Io's volcanic plumes are the ultimate source of its SO2 atmosphere, but past eruptions have covered the moon in surface frost which sublimates in sunlight. Today, Io's atmosphere is a result of some combination of volcanism and sublimation, but it is unknown exactly how these processes work together to create the observed atmosphere. We use the direct simulation Monte Carlo (DSMC) method to model the interaction of giant plumes with a sublimation atmosphere. Axisymmetric plume/atmosphere simulations demonstrate that the total mass of SO2 above Io's surface is only poorly approximated as the sum of independent volcanic and sublimated components. A simple analytic model is developed to show how variation in the mass of erupting gas above Io's surface can counteract variation in the mass of its hydrostatic atmosphere as surface temperature changes over a Jupiter year. Three-dimensional, unsteady simulations of giant plumes over an Io day are also presented, showing how plume material becomes suspended in the sublimation atmosphere. We find that a plume which produces some total mass above Io's surface at night will cause a net increase in the noon-time atmosphere of only a fraction of the night-time value. However, as much as seven times the night-side mass of the plume will become suspended in the sublimation atmosphere, altering its composition and displacing sublimated material.

  6. The sublime bridge: anatomy and implications in median nerve entrapment.

    PubMed

    Tubbs, R Shane; Marshall, Tyler; Loukas, Marios; Shoja, Mohammadali M; Cohen-Gadol, Aaron A

    2010-07-01

    The sublime bridge is a potential site of entrapment of the median nerve in the forearm. To the authors' knowledge, this structure and its relationship to the median nerve have not been studied. The aim of the present study was to quantitate this structure and elucidate its relationship to the median nerve. Sixty adult cadaveric forearms underwent dissection of the sublime bridge. Relationships of this structure were observed, and measurements of its anatomy were made. The relationship of the median nerve to the sublime bridge was observed with range of motion about the forearm. The sublime bridge was found to be tendinous in the majority (45 [75%]) of specimens and muscular in the remaining forearms (15 [25%]). The maximal mean width of the sublime bridge was 7 cm proximally, and the minimal mean width was 3 cm distally. The mean distance from the medial epicondyle to the apex of the sublime bridge was found to be 8.1 cm. The relation of the median nerve to the bridge was always intimate. On 2 sides (1 left and 1 right) from different male specimens, the median nerve was attached to the deep aspect of the sublime bridge by a strong connective tissue band, thus forming a tunnel on the deep aspect of this structure. With range of motion of the forearm, increased compression of the median nerve by the overlying sublime bridge was seen with extension but no other movement. Based on the authors' study, pronator syndrome is an incorrect term applied to compression of the median nerve at the sublime bridge. This potential site of median nerve compression is distinct and has characteristics that can clinically differentiate it from compression of the median nerve between the heads of the pronator teres. The authors hope that these data will be of use to the surgeon in the evaluation and treatment of patients with proximal median nerve entrapment.

  7. Nietzsche's View of Sublimation in the Educational Process

    ERIC Educational Resources Information Center

    Sharp, Ann Margaret

    1975-01-01

    Article outlined Nietzsche's beliefs on the primary aim of education, the conscious production of the free man through the process of sublimation, the active redirecting of one's life energy in the service of creativity. (Editor/RK)

  8. Scanning electron microscope observations of sublimates from Merapi Volcano, Indonesia

    USGS Publications Warehouse

    Symonds, R.

    1993-01-01

    Sublimates were sampled from high-temperature (up to 800??C) fumaroles at Merapi volcano in January 1984. Sampling is accomplished by inserting silica tubes into high-temperature vents. Volcanic glass flows through the tubes and sublimates precipitate on the inner walls in response to the temperature gradient. With decreasing temperature (800-500??C) in the tubes, there are five sublimate zones. Texturally, the sublimate phases grade from large, well-formed crystals at their highest-temperature occurrence to more numerous, smaller crystals that are less perfect at lower temperatures. These changes imply that the crystal nucleation and growth rates increase and decrease, respectively, as temperature decreases. Overall, the textural data suggest that the gas is saturated or slightly super-saturated with the phases at their hottest occurrence, but that the gas becomes increasingly super-saturated with the phases at lower temperatures. -from Author

  9. Dynamics and Mechanisms of Exfoliated Black Phosphorus Sublimation.

    PubMed

    Fortin-Deschênes, Matthieu; Levesque, Pierre L; Martel, Richard; Moutanabbir, Oussama

    2016-05-05

    We report on real time observations of the sublimation of exfoliated black phosphorus layers throughout annealing using in situ low energy electron microscopy. We found that sublimation manifests itself above 375 ± 20 °C through the nucleation and expansion of asymmetric, faceted holes with the long axis aligned along the [100] direction and sharp tips defined by edges consisting of alternating (10) and (11) steps. This thermally activated process repeats itself via successive sublimation of individual layers. Calculations and simulations using density functional theory and kinetic Monte Carlo allowed to determine the involved atomic pathways. Sublimation is found to occur via detachments of phosphorus dimers rather than single atoms. This behavior and the role of defects is described using an analytical model that captures all essential features. This work establishes an atomistic-level understanding of the thermal stability of exfoliated black phosphorus and defines the temperature window available for material and device processing.

  10. Sublimation as a Landform-Shaping Process on Pluto

    NASA Technical Reports Server (NTRS)

    Moore, J. M.; Howard, A. D.; White, O. L.; Umurhan, O. M.; Schenk, P. M.; Beyer, R. A.; McKinnon, W. B.; Singer, K. N.; Spencer, J. R.; Stern, S. A.; hide

    2016-01-01

    Several icy-world surfaces in the solar system exhibit sublimation-driven landform modification erosion, condensation, and mass wasting [1]. In addition to the obvious role of gravity, mass wasting can work in conjunction with internal disaggregation of a landform's relief-supporting material through the loss (or deteriorating alteration) of its cohesive matrix. To give a conspicuous example, Callisto's landscape exhibits widespread erosion from sublimation erosion of slopes, which results in smooth, undulating, low albedo plains composed of lag deposits, with isolated high albedo pinnacles perched on remnants of crater rims due to the re-precipitation of ice on local cold traps [2, 3, 4]. Sublimation-driven mass wasting was anticipated on Pluto prior to the encounter (see refs in [5]). Here we report on several landscapes on Pluto we interpret to be formed, or at least heavily modified, by sublimation erosion.

  11. Development and Testing of the Contaminant Insensitive Sublimator

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Stephan, Ryan A.; Westheimer, David T.

    2006-01-01

    Sublimators have been used for heat rejection for a variety of space applications including the Apollo Lunar Module and the Extravehicular Mobility Unit (EMU). Some of the attractive features of sublimators are that they are compact, lightweight, and self-regulating. One of the drawbacks of previous designs has been sensitivity to non-volatile contamination in the feedwater, which can clog relatively small pores (approx.3-6 microns) in the porous plates where ice forms and sublimates. A new design that is less sensitive to contaminants is being developed at the Johnson Space Center. This paper describes the design, fabrication, and testing of the Contaminant Insensitive Sublimator (CIS) Engineering Development Unit (EDU).

  12. Development and Testing of the Contaminant Insensitive Sublimator

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Stephan, Ryan A.

    2007-01-01

    Sublimators have been used for heat rejection for a variety of space applications including the Apollo Lunar Module and the Extravehicular Mobility Unit (EMU). Some of the attractive features of sublimators are that they are compact, lightweight, and self-regulating. One of the drawbacks of previous designs has been sensitivity to non-volatile contamination in the feedwater, which can clog relatively small pores (approx. 3-6 micrometers) in the porous plates where ice forms and sublimates. A new design that is less sensitive to contaminants is being developed at the Johnson Space Center (JSC). This paper describes the design, fabrication, and testing of the Contaminant Insensitive Sublimator (CIS) Engineering Development Unit (EDU).

  13. Development and Testing of the Contaminant Insensitive Sublimator

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Stephan, Ryan A.; Westheimer, David T.

    2006-01-01

    Sublimators have been used for heat rejection for a variety of space applications including the Apollo Lunar Module and the Extravehicular Mobility Unit (EMU). Some of the attractive features of sublimators are that they are compact, lightweight, and self-regulating. One of the drawbacks of previous designs has been sensitivity to non-volatile contamination in the feedwater, which can clog relatively small pores (approx.3-6 microns) in the porous plates where ice forms and sublimates. A new design that is less sensitive to contaminants is being developed at the Johnson Space Center. This paper describes the design, fabrication, and testing of the Contaminant Insensitive Sublimator (CIS) Engineering Development Unit (EDU).

  14. Development and Testing of the Contaminant Insensitive Sublimator

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Stephan, Ryan A.

    2007-01-01

    Sublimators have been used for heat rejection for a variety of space applications including the Apollo Lunar Module and the Extravehicular Mobility Unit (EMU). Some of the attractive features of sublimators are that they are compact, lightweight, and self-regulating. One of the drawbacks of previous designs has been sensitivity to non-volatile contamination in the feedwater, which can clog relatively small pores (approx. 3-6 micrometers) in the porous plates where ice forms and sublimates. A new design that is less sensitive to contaminants is being developed at the Johnson Space Center (JSC). This paper describes the design, fabrication, and testing of the Contaminant Insensitive Sublimator (CIS) Engineering Development Unit (EDU).

  15. Sulfur "Concrete" for Lunar Applications - Sublimation Concerns

    NASA Technical Reports Server (NTRS)

    Grugel, Richard N.; Toutanji, Houssam

    2006-01-01

    Melting sulfur and mixing it with an aggregate to form "concrete" is commercially well established and constitutes a material that is particularly well-suited for use in corrosive environments. Discovery of the mineral troilite (FeS) on the moon poses the question of extracting the sulfur for use as a lunar construction material. This would be an attractive alternative to conventional concrete as it does not require water. However, the viability of sulfur concrete in a lunar environment, which is characterized by lack of an atmosphere and extreme temperatures, is not well understood. Here it is assumed that the lunar ore can be mined, refined, and the raw sulfur melded with appropriate lunar regolith to form, for example, bricks. This study evaluates pure sulfur and two sets of small sulfur concrete samples that have been prepared using JSC-1 lunar stimulant and SiO2 powder as aggregate additions. Each set was subjected to extended periods in a vacuum environment to evaluate sublimation issues. Results from these experiments are presented and discussed within the context of the lunar environment.

  16. Sublimation in bright spots on (1) Ceres.

    PubMed

    Nathues, A; Hoffmann, M; Schaefer, M; Le Corre, L; Reddy, V; Platz, T; Cloutis, E A; Christensen, U; Kneissl, T; Li, J-Y; Mengel, K; Schmedemann, N; Schaefer, T; Russell, C T; Applin, D M; Buczkowski, D L; Izawa, M R M; Keller, H U; O'Brien, D P; Pieters, C M; Raymond, C A; Ripken, J; Schenk, P M; Schmidt, B E; Sierks, H; Sykes, M V; Thangjam, G S; Vincent, J-B

    2015-12-10

    The dwarf planet (1) Ceres, the largest object in the main asteroid belt with a mean diameter of about 950 kilometres, is located at a mean distance from the Sun of about 2.8 astronomical units (one astronomical unit is the Earth-Sun distance). Thermal evolution models suggest that it is a differentiated body with potential geological activity. Unlike on the icy satellites of Jupiter and Saturn, where tidal forces are responsible for spewing briny water into space, no tidal forces are acting on Ceres. In the absence of such forces, most objects in the main asteroid belt are expected to be geologically inert. The recent discovery of water vapour absorption near Ceres and previous detection of bound water and OH near and on Ceres (refs 5-7) have raised interest in the possible presence of surface ice. Here we report the presence of localized bright areas on Ceres from an orbiting imager. These unusual areas are consistent with hydrated magnesium sulfates mixed with dark background material, although other compositions are possible. Of particular interest is a bright pit on the floor of crater Occator that exhibits probable sublimation of water ice, producing haze clouds inside the crater that appear and disappear with a diurnal rhythm. Slow-moving condensed-ice or dust particles may explain this haze. We conclude that Ceres must have accreted material from beyond the 'snow line', which is the distance from the Sun at which water molecules condense.

  17. Sulfur "Concrete" for Lunar Applications - Sublimation Concerns

    NASA Technical Reports Server (NTRS)

    Grugel, Richard N.; Toutanji, Houssam

    2006-01-01

    Melting sulfur and mixing it with an aggregate to form "concrete" is commercially well established and constitutes a material that is particularly well-suited for use in corrosive environments. Discovery of the mineral troilite (FeS) on the moon poses the question of extracting the sulfur for use as a lunar construction material. This would be an attractive alternative to conventional concrete as it does not require water. However, the viability of sulfur concrete in a lunar environment, which is characterized by lack of an atmosphere and extreme temperatures, is not well understood. Here it is assumed that the lunar ore can be mined, refined, and the raw sulfur melded with appropriate lunar regolith to form, for example, bricks. This study evaluates pure sulfur and two sets of small sulfur concrete samples that have been prepared using JSC-1 lunar stimulant and SiO2 powder as aggregate additions. Each set was subjected to extended periods in a vacuum environment to evaluate sublimation issues. Results from these experiments are presented and discussed within the context of the lunar environment.

  18. Sublimation in bright spots on (1) Ceres

    NASA Astrophysics Data System (ADS)

    Nathues, A.; Hoffmann, M.; Schaefer, M.; Le Corre, L.; Reddy, V.; Platz, T.; Cloutis, E. A.; Christensen, U.; Kneissl, T.; Li, J.-Y.; Mengel, K.; Schmedemann, N.; Schaefer, T.; Russell, C. T.; Applin, D. M.; Buczkowski, D. L.; Izawa, M. R. M.; Keller, H. U.; O'Brien, D. P.; Pieters, C. M.; Raymond, C. A.; Ripken, J.; Schenk, P. M.; Schmidt, B. E.; Sierks, H.; Sykes, M. V.; Thangjam, G. S.; Vincent, J.-B.

    2015-12-01

    The dwarf planet (1) Ceres, the largest object in the main asteroid belt with a mean diameter of about 950 kilometres, is located at a mean distance from the Sun of about 2.8 astronomical units (one astronomical unit is the Earth-Sun distance). Thermal evolution models suggest that it is a differentiated body with potential geological activity. Unlike on the icy satellites of Jupiter and Saturn, where tidal forces are responsible for spewing briny water into space, no tidal forces are acting on Ceres. In the absence of such forces, most objects in the main asteroid belt are expected to be geologically inert. The recent discovery of water vapour absorption near Ceres and previous detection of bound water and OH near and on Ceres (refs 5, 6, 7) have raised interest in the possible presence of surface ice. Here we report the presence of localized bright areas on Ceres from an orbiting imager. These unusual areas are consistent with hydrated magnesium sulfates mixed with dark background material, although other compositions are possible. Of particular interest is a bright pit on the floor of crater Occator that exhibits probable sublimation of water ice, producing haze clouds inside the crater that appear and disappear with a diurnal rhythm. Slow-moving condensed-ice or dust particles may explain this haze. We conclude that Ceres must have accreted material from beyond the ‘snow line’, which is the distance from the Sun at which water molecules condense.

  19. Are the Sublimation Thermodynamics of Organic Molecules Predictable?

    PubMed

    McDonagh, James L; Palmer, David S; Mourik, Tanja van; Mitchell, John B O

    2016-11-28

    We compare a range of computational methods for the prediction of sublimation thermodynamics (enthalpy, entropy, and free energy of sublimation). These include a model from theoretical chemistry that utilizes crystal lattice energy minimization (with the DMACRYS program) and quantitative structure property relationship (QSPR) models generated by both machine learning (random forest and support vector machines) and regression (partial least squares) methods. Using these methods we investigate the predictability of the enthalpy, entropy and free energy of sublimation, with consideration of whether such a method may be able to improve solubility prediction schemes. Previous work has suggested that the major source of error in solubility prediction schemes involving a thermodynamic cycle via the solid state is in the modeling of the free energy change away from the solid state. Yet contrary to this conclusion other work has found that the inclusion of terms such as the enthalpy of sublimation in QSPR methods does not improve the predictions of solubility. We suggest the use of theoretical chemistry terms, detailed explicitly in the Methods section, as descriptors for the prediction of the enthalpy and free energy of sublimation. A data set of 158 molecules with experimental sublimation thermodynamics values and some CSD refcodes has been collected from the literature and is provided with their original source references.

  20. Sublimation of cometary ices in the presence of organic volatiles

    NASA Astrophysics Data System (ADS)

    Kossacki, Konrad J.; Leliwa-Kopystynski, Jacek; Witek, Piotr; Jasiak, Aleksander; Dubiel, Adrian

    2017-09-01

    Evolution of the surfaces of cometary nuclei is determined by the sublimation of ice. The rate of sublimation is commonly calculated using the simple Hertz-Knudsen formula, which should be corrected by a temperature dependent sublimation coefficient αs (Kossacki et al., 1999; Gundlach et al., 2011; Kossacki and Leliwa-Kopystynski, 2014). In this work influence of C3H6O (acetone), and CH3OH (methanol) present in cometary ice on the sublimation coefficient is investigated. We have found, that the mass fraction of admixtures ≤ 2% in water ice is sufficient for an increase of αs by a factor about 5, depending on the temperature. The sublimation coefficient is sensitive to very small concentrations of admixtures. When the admixture is acetone and the mass fraction f = 0.005 is αs(215 K) ∼ 0.46 instead of ∼ 0.18 for pure water ice. When f = 0.01 is αs(215 K) ∼ 0.74, and when f = 0.02 is αs(215 K) ∼ 0.78. The presence of 0.01 mass fraction of methanol has similar influence on the sublimation coefficient as the presence of 0.01 mass fraction of acetone. At temperatures T > 235 K for all investigated compositions of ice αs ∼ 0.15.

  1. Sublimity and beauty: A view from nursing aesthetics.

    PubMed

    Siles-González, José; Solano-Ruiz, Carmen

    2016-03-01

    Several authors have focused on the aesthetics of nursing care from diverse perspectives; however, there are few studies about the sublime and the beautiful in nursing. To identify beautiful and sublime moments in the context of the aesthetics of nursing care. A theoretical reflection has been contemplated about sublime and beautiful values in the context of the aesthetics of nursing care from the cultural history perspective. For that purpose, a revision of this issue has been completed. The terms 'beautiful' and 'sublime' have been analysed to identify the characteristics of both in the context of nursing care. We have followed all ethical requirements regarding the sources, conducting research and authorship. There is no conflict of interest in this paper. With aesthetic knowledge, the nurse expresses the artistic nature of nursing care by appreciating the act of caring for individuals. The sublime is a complex phenomenon, since apparently contrary feelings are interwoven. Nursing care is an art with an anthropological object-subject on which the 'artist' applies their prior knowledge and skills. Feelings and emotions that develop during the clinical nursing practice - especially at times sublime and beautiful, aesthetic - constitute experiences which are professionally significant. © The Author(s) 2015.

  2. Surface and snowdrift sublimation at Princess Elisabeth station, East Antarctica

    NASA Astrophysics Data System (ADS)

    Thiery, W.; Gorodetskaya, I. V.; Bintanja, R.; Van Lipzig, N. P. M.; Van den Broeke, M. R.; Reijmer, C. H.; Kuipers Munneke, P.

    2012-08-01

    In the near-coastal regions of Antarctica, a significant fraction of the snow precipitating onto the surface is removed again through sublimation - either directly from the surface or from drifting snow particles. Meteorological observations from an Automatic Weather Station (AWS) near the Belgian research station Princess Elisabeth in Dronning Maud Land, East-Antarctica, are used to study surface and snowdrift sublimation and to assess their impacts on both the surface mass balance and the surface energy balance during 2009 and 2010. Comparison to three other AWSs in Dronning Maud Land with 11 to 13 yr of observations shows that sublimation has a significant influence on the surface mass balance at katabatic locations by removing 10-23% of their total precipitation, but at the same time reveals anomalously low surface and snowdrift sublimation rates at Princess Elisabeth (17 mm w.e. yr-1 compared to 42 mm w.e. yr-1 at Svea Cross and 52 mm w.e. yr-1 at Wasa/Aboa). This anomaly is attributed to local topography, which shields the station from strong katabatic influence, and, therefore, on the one hand allows for a strong surface inversion to persist throughout most of the year and on the other hand causes a lower probability of occurrence of intermediately strong winds. This wind speed class turns out to contribute most to the total snowdrift sublimation mass flux, given its ability to lift a high number of particles while still allowing for considerable undersaturation.

  3. Modeling the Variability and Importance of Snow Sublimation in the North-Central Colorado Rocky Mountains

    NASA Astrophysics Data System (ADS)

    Sexstone, G. A.; Clow, D. W.; Fassnacht, S. R.; Liston, G. E.; Hiemstra, C. A.; Knowles, J. F.

    2016-12-01

    In the western United States, where seasonal snowmelt is a critical water resource for ecological and anthropological needs, snow sublimation (sublimation) has been suggested by many studies to be an important component of the snow cover mass balance. However, few studies have evaluated the spatial and temporal variability of sublimation in complex mountainous environments. In this study, we use a process-based snow model (SnowModel) and eddy covariance (EC) measurements to evaluate the variability and importance of sublimation across the north-central Colorado Rocky Mountains for 5 water years (WY 2011 - WY 2015). In-situ EC observations of sublimation compare well with modeled sublimation at sites dominated by surface and canopy components of sublimation, but model verification of blowing sublimation in alpine areas was not feasible because these fluxes often occur when snow is in turbulent suspension, which cannot always be resolved by EC instrumentation. Model simulations showed substantial spatial and temporal variability of sublimation across the study domain. Sublimation rates were found to exhibit differences across landscape characteristics such as elevation and land cover. Land cover type was an important driver of snow sublimation variability, with substantial sublimation occurring in alpine and forested areas, and relatively lower sublimation occurring in open areas below treeline. Sublimation from forested areas accounted for the majority of modeled sublimation losses across the study domain and highlights the importance of sublimation from snow stored in the forest canopy in this region. Additionally, the interannual differences in total sublimation were strongly linked with seasonal snowfall amounts. Results from this study suggest that snow sublimation is a significant component of the winter water balance and have important implications for future water management and decision making.

  4. MALDI Imaging of Lipids after Matrix Sublimation/Deposition

    PubMed Central

    Murphy, Robert C.; Hankin, Joseph A.; Barkley, Robert M.; Zemski Berry, Karin A.

    2011-01-01

    Mass spectrometric techniques have been developed to record mass spectra of biomolecules including lipids as they naturally exist within tissues and thereby permit the generation of images displaying the distribution of specific lipids in tissues, organs, and intact animals. These techniques are based on matrix-assisted laser desorption/ionization (MALDI) that requires matrix application onto the tissue surface prior to analysis. One technique of application that has recently shown significant advantages for lipid analysis is sublimation of matrix followed by vapor deposition directly onto the tissue. Explanations for enhanced sensitivity realized by sublimation/deposition related to sample temperature after a laser pulse and matrix crystal size are presented. Specific examples of sublimation/deposition in lipid imaging of various organs including brain, ocular tissue, and kidney are presented. PMID:21571091

  5. Sublimation rates of explosive materials : method development and initial results.

    SciTech Connect

    Phelan, James M.; Patton, Robert Thomas

    2004-08-01

    Vapor detection of explosives continues to be a technological basis for security applications. This study began experimental work to measure the chemical emanation rates of pure explosive materials as a basis for determining emanation rates of security threats containing explosives. Sublimation rates for TNT were determined with thermo gravimetric analysis using two different techniques. Data were compared with other literature values to provide sublimation rates from 25 to 70 C. The enthalpy of sublimation for the combined data was found to be 115 kJ/mol, which corresponds well with previously reported data from vapor pressure determinations. A simple Gaussian atmospheric dispersion model was used to estimate downrange concentrations based on continuous, steady-state conditions at 20, 45 and 62 C for a nominal exposed block of TNT under low wind conditions. Recommendations are made for extension of the experimental vapor emanation rate determinations and development of turbulent flow computational fluid dynamics based atmospheric dispersion estimates of standoff vapor concentrations.

  6. Formation of filamentary sublimate residues (FSR) from mineral grains

    SciTech Connect

    Storrs, A.D.; Fanale, F.P.; Saunders, R.S.; Stephens, J.B.

    1988-12-01

    The significant interparticle forces observed between solar system dust grains upon desorption or sublimation of excess volatiles in simulated Martian or cometary environments are presently investigated, in order to more precisely define these mechanisms and to simulate the types of deposits thereby formed. Some classes of phyllosilicate mineral grains are noted to bond together to form a highly porous filamentary sublimate residue (FSR) exhibiting an exceptionally high tensile strength for its density; this may be important in its control of erosion and sublimation in Martian and cometary environments. It is concluded that FSR formation from clean mineral grains in water ice may be important in the formation of the Martian polar layered terrain. 41 references.

  7. On the interaction of sublimating gas with cometary bodies

    NASA Astrophysics Data System (ADS)

    Steckloff, Jordan K.

    Sublimation of volatiles is a defining process of comet nuclei, and profoundly affects their dynamics, structure, and appearance. Central to understanding the processes by which comets formed and subsequently evolved is a careful computation of this sublimation pressure as a function of heliocentric distance. Unlike previous efforts, I develop a thermodynamic method to numerically compute the sublimation pressure of any species from limited knowledge of its physical properties. I then describe a novel cometary disruption mechanism in which this sublimation pressure induces differential stresses within the body of the nucleus that exceed its material strength, resulting in structural failure and breakup of the nucleus. I show that this mechanism is consistent with the behavior of Comet ISON (C/2012 S1), and use it to estimate the cohesive strength of ISON's nucleus, a first for a Long-Period Comet. Sublimating volatiles can also generate sublimative torques that alter the rotation state of the nucleus. However, computing these torques requires high-resolution information on the shape and activity of the nucleus, which is available only for the few nuclei visited by spacecraft. To remedy this, I develop a novel framework based on the YORP Effect (the torques asteroids experience by emitting thermal photons from their asymmetric shapes) to study the effects of sublimative torques on populations of cometary bodies. I take advantage of the similar manner in which surfaces emit both thermal photons and sublimating molecules to derive numerical relationships that describe sublimative torques by appropriately scaling the YORP torque equations. I then use this framework to explain the formation of dust striae (long linear features in the tails of Long-Period Comets that align with the Sun), which has remained an enigma for more than a century. I show that the observed ˜10-100 m chunks ejected from comet nuclei experience sublimative torques that spin them up to the point

  8. Micro-computed tomography observation of sublimation interface and image analysis on sublimation process during freeze-drying.

    PubMed

    Xiao, Xin; Tao, Le-Ren; Hua, Tse-Chao

    2007-01-01

    The freeze-drying process is complicated with complex heat and mass transfer during sublimation. The sublimation interface of freeze-drying has become more attractive and meaningful recently. In this study, apple slices undergoing sublimation were scanned by a Micro-CT scanner. The cross-sectional images were reconstructed with those scanning images respectively. The technique of grey value analysis was used to recognize the procedure. The results showed that, from direct scanning images and 2-D reconstructed images, a 3-D moving mode of sublimation interface which contracted to the centre of the sample could be seen, sublimation process proceeded from edge to center gradually. The grey value of ice crystals was determined to be 154 through gauss calculation. By comparing frozen sample with freeze-dried one, the ice crystals regions in the beginning became the porous regions after drying, grey values increased correspondingly. Samples shrunk slightly after drying for 3 to 7 hours, which could be distinguished by the change in grey values.

  9. Canopy effects on snow sublimation from a central Arizona Basin

    NASA Astrophysics Data System (ADS)

    Svoma, Bohumil M.

    2017-01-01

    Guided by 30 m terrain and forest cover data, snow sublimation from the Salt River basin in the Southwest U.S. is simulated for years 2008 (wet year) and 2007 (dry year). Downscaled meteorological input correlates well (r 0.80) with independent observations at AmeriFlux sites. Additionally, model correlation and bias with eddy-covariance vapor flux observations is comparable to previous localized modeling efforts. Upon a 30% reduction in effective leaf area index, canopy sublimation decreases by 1.29 mm (27.0%) and 1.05 mm (23.0%) at the basin scale for the 2008 and 2007 simulations, respectively. Ground sublimation decreases 0.72 mm (4.75%) in 2008 and only 0.17 mm (1.5%) in 2007. Canopy snow-holding capacity and frequent unloading events at lower elevations limit the variability in canopy sublimation from wet year to dry year at the basin scale. The greater decrease in snowpack sublimation in the wet year is partly due to decreased longwave radiation from the canopy reduction over a more extensive snowpack than the dry year. This decrease overcomes the increased solar radiation and wind speed during winter. A second factor is that a greater extent of the snowpack persisted into spring in 2008 than 2007, and the large increase in shortwave flux upon canopy reduction increases melt rates, reducing duration. Only in heavily forested high elevations (>2900 m above sea level) in 2008 does the snowpack persist long enough into spring to result in increased ground sublimation upon canopy reduction. As forest cover change can occur rapidly, these results are critical from water resource and ecosystem function perspectives.

  10. Alumina Paste Sublimation Suppression Barrier for Thermoelectric Device

    NASA Technical Reports Server (NTRS)

    Paik, Jong-Ah (Inventor); Caillat, Thierry (Inventor)

    2014-01-01

    Alumina as a sublimation suppression barrier for a Zintl thermoelectric material in a thermoelectric power generation device operating at high temperature, e.g. at or above 1000K, is disclosed. The Zintl thermoelectric material may comprise Yb.sub.14MnSb.sub.11. The alumina may be applied as an adhesive paste dried and cured on a substantially oxide free surface of the Zintl thermoelectric material and polished to a final thickness. The sublimation suppression barrier may be finalized by baking out the alumina layer on the Zintl thermoelectric material until it becomes substantially clogged with ytterbia.

  11. Drifting snow and its sublimation in turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Li, Guang; Huang, Ning; Wang, Zhengshi

    2017-04-01

    Drifting snow is a special process of mass-energy transport in hydrological cycle especially in alpine region. It can not only change the snow distribution, but also result in phase change of ice crystal into water vapour, which is so called drifting snow sublimation. Thus drifting snow is of glaciological and hydrological importance in cold regions. In this paper, recent research on drifting snow and its sublimation is reviewed, and some new progresses by our research team in Lanzhou University are also introduced.

  12. Enthalpy of sublimation as measured using a silicon oscillator

    NASA Astrophysics Data System (ADS)

    Shakeel, Hamza; Pomeroy, J. M.

    In this study, we report the enthalpy of sublimation of common gases (nitrogen, oxygen, argon, carbon dioxide, neon, krypton, xenon, and water vapor) using a large area silicon oscillator with a sub-ng (~0.027 ng/cm2) mass sensitivity. The double paddle oscillator design enables high frequency stability (17 ppb) at cryogenic temperatures and provides a consistent technique for enthalpy measurements. The enthalpies of sublimation are derived from the rate of mass loss during programmed thermal desorption and are detected as a change in the resonance frequency of the self-tracking oscillator. These measured enthalpy values show excellent agreement with the accepted literature values.

  13. Alumina Paste Layer as a Sublimation Suppression Barrier for Yb14MnSb11

    NASA Technical Reports Server (NTRS)

    Paik, Jong-Ah; Caillat, Thierry

    2010-01-01

    Sublimation is a major cause of degradation of thermoelectric power generation systems. Most thermoelectric materials tend to have peak values at the temperature where sublimation occurs. A sublimation barrier is needed that is stable at operating temperatures, inert against thermoelectric materials, and able to withstand thermal cycling stress. A porous alumina paste layer is suitable as a sublimation barrier for Yb14MnSb11. It can accommodate stress generated by the thermal expansion discrepancy between the suppression layer and thermoelectric materials. Sublimation suppression is achieved by filling pores naturally with YbO2, a natural byproduct of sublimation. YbO2 generated during the sublimation of Yb14MnSb11 fills the porous structure of the alumina paste, causing sublimation to decrease with time as the pores become filled.

  14. Modular Porous Plate Sublimator /MPPS/ requires only water supply for coolant

    NASA Technical Reports Server (NTRS)

    Rathbun, R. J.

    1966-01-01

    Modular porous plate sublimators, provided for each location where heat must be dissipated, conserve the battery power of a space vehicle by eliminating the coolant pump. The sublimator requires only a water supply for coolant.

  15. The Digital Sublime: Lessons from Kelli Connell's "Double Life"

    ERIC Educational Resources Information Center

    Huang, Yi-hui

    2012-01-01

    The digital sublime refers to digital-composite photography that presents "the existence of something unpresentable" and that renders a matchless look a sophisticated fabrication, a perfect and clean composition, a maximum color saturation, a multiple-point perspective, and stunning or newfangled content. Abandoning the traditional one-shot mode…

  16. Modeling the development of martian sublimation thermokarst landforms

    USGS Publications Warehouse

    Dundas, Colin M.; Byrne, Shane; McEwen, Alfred S.

    2015-01-01

    Sublimation-thermokarst landforms result from collapse of the surface when ice is lost from the subsurface. On Mars, scalloped landforms with scales of decameters to kilometers are observed in the mid-latitudes and considered likely thermokarst features. We describe a landscape evolution model that couples diffusive mass movement and subsurface ice loss due to sublimation. Over periods of tens of thousands of Mars years under conditions similar to the present, the model produces scallop-like features similar to those on the Martian surface, starting from much smaller initial disturbances. The model also indicates crater expansion when impacts occur in surfaces underlain by excess ice to some depth, with morphologies similar to observed landforms on the Martian northern plains. In order to produce these landforms by sublimation, substantial quantities of excess ice are required, at least comparable to the vertical extent of the landform, and such ice must remain in adjacent terrain to support the non-deflated surface. We suggest that Martian thermokarst features are consistent with formation by sublimation, without melting, and that significant thicknesses of very clean excess ice (up to many tens of meters, the depth of some scalloped depressions) are locally present in the Martian mid-latitudes. Climate conditions leading to melting at significant depth are not required.

  17. System for NO reduction using sublimation of cyanuric acid

    DOEpatents

    Perry, R.A.

    1989-01-24

    An arrangement for reducing the NO content of a gas stream comprises contacting the gas stream with HNCO at a temperature effective for heat induced decomposition of HNCO and for resultant lowering of the NO content of the gas stream. Preferably, the HNCO is generated by sublimation of cyanuric acid. 1 fig.

  18. Vapor transport and sublimation on Mullins Glacier, Antarctica

    NASA Astrophysics Data System (ADS)

    Lamp, J. L.; Marchant, D. R.

    2017-05-01

    We utilize an environmental chamber capable of recreating the extreme polar conditions of the McMurdo Dry Valleys (MDV) of Antarctica to investigate the sublimation rate of the Mullins Valley debris-covered glacier (hereafter Mullins Glacier), reportedly one of the oldest debris-covered alpine glaciers in the world. We measure ice loss via sublimation beneath sediment thicknesses ranging from 0 to 69 mm; from this, we determine an effective diffusivity for Fickian vapor transport through Mullins till of (5.2 ± 0.3) ×10-6 m2s-1 at -10 °C. We use this value, coupled with micrometeorological data from Mullins Valley (atmospheric temperature, relative humidity, and soil temperature) to model the sublimation rate of buried glacier ice near the terminus of Mullins Glacier, where the overlying till thickness approaches 70 cm. We find that the ice-lowering rate during the modeled year (2011) was 0.066 mm under 70 cm of till, a value which is in line with previous estimates for exceedingly slow rates of ice sublimation. These results provide further evidence supporting the probable antiquity of Mullins Glacier ice and overall landscape stability in upland regions of the MDV.

  19. Sublimation as a landform-shaping process on Pluto

    NASA Astrophysics Data System (ADS)

    Moore, Jeffrey M.; Howard, Alan D.; Umurhan, Orkan M.; White, Oliver L.; Schenk, Paul M.; Beyer, Ross A.; McKinnon, William B.; Spencer, John R.; Grundy, Will M.; Lauer, Tod R.; Nimmo, Francis; Young, Leslie A.; Stern, S. Alan; Weaver, Harold A.; Olkin, Cathy B.; Ennico, Kimberly; New Horizons Science Team

    2017-05-01

    Fields of pits, both large and small, in Tombaugh Regio (Sputnik Planitia, and the Pitted Uplands to the east), and along the scarp of Piri Rupes, are examples of landscapes on Pluto where we conclude that sublimation drives their formation and evolution. Our heuristic modeling closely mimics the form, spacing, and arrangement of a variety of Tombaugh Regio's pits. Pluto's sublimation modified landforms appear to require a significant role for (diffusive) mass wasting as suggested by our modeling. In our models, the temporal evolution of pitted surfaces is such that initially lots of time passes with little happening, then eventually, very rapid development of relief and rapid sublimation. Small pits on Sputnik Planitia are consistent with their formation in N2-dominated materials. As N2-ice readily flows, some other ``stiffer'' volatile ice may play a role in supporting the relief of sublimation degraded landforms that exhibit several hundred meters of relief. A strong candidate is CH4, which is spectroscopically observed to be associated with these features, but the current state of rheological knowledge for CH4 ice at Pluto conditions is insufficient for a firm assessment.

  20. Optimization of Fast Dissolving Etoricoxib Tablets Prepared by Sublimation Technique

    PubMed Central

    Patel, D. M.; Patel, M. M.

    2008-01-01

    The purpose of this investigation was to develop fast dissolving tablets of etoricoxib. Granules containing etoricoxib, menthol, crospovidone, aspartame and mannitol were prepared by wet granulation technique. Menthol was sublimed from the granules by exposing the granules to vacuum. The porous granules were then compressed in to tablets. Alternatively, tablets were first prepared and later exposed to vacuum. The tablets were evaluated for percentage friability and disintegration time. A 32 full factorial design was applied to investigate the combined effect of 2 formulation variables: amount of menthol and crospovidone. The results of multiple regression analysis indicated that for obtaining fast dissolving tablets; optimum amount of menthol and higher percentage of crospovidone should be used. A surface response plots are also presented to graphically represent the effect of the independent variables on the percentage friability and disintegration time. The validity of a generated mathematical model was tested by preparing a checkpoint batch. Sublimation of menthol from tablets resulted in rapid disintegration as compared with the tablets prepared from granules that were exposed to vacuum. The optimized tablet formulation was compared with conventional marketed tablets for percentage drug dissolved in 30 min (Q30) and dissolution efficiency after 30 min (DE30). From the results, it was concluded that fast dissolving tablets with improved etoricoxib dissolution could be prepared by sublimation of tablets containing suitable subliming agent. PMID:20390084

  1. The Digital Sublime: Lessons from Kelli Connell's "Double Life"

    ERIC Educational Resources Information Center

    Huang, Yi-hui

    2012-01-01

    The digital sublime refers to digital-composite photography that presents "the existence of something unpresentable" and that renders a matchless look a sophisticated fabrication, a perfect and clean composition, a maximum color saturation, a multiple-point perspective, and stunning or newfangled content. Abandoning the traditional one-shot mode…

  2. Isotopic Fractionation of Water-Ice from Sublimation

    NASA Astrophysics Data System (ADS)

    Christensen, E.; Boyer, C.; Park, M.; Gormally, J.; Benitez, E.; Dominguez, G.

    2015-12-01

    Elizabeth Christensen, Charisa Boyer, Manesseh Park, Ezra Benitez, Gerardo Dominguez Understanding the multi-isotopic fractionation of water-ice that results from its sublimation may be important for understanding the isotopic composition of cometary ices. Here we describe an experimental setup whose purpose is to understand the effects of various astrophysical processes on the δD and δ18O and δ17O composition of water-ices. Our setup consists of an ultrahigh vacuum (UHV) chamber with oil free pumping, a closed cycle He cryostat to achieve low temperatures (capable of reaching 6K), and a vacuum line connected to the chamber via a UHV feed-through. Water isotopologues H216O, H218O, H217O, and HD16O samples can be measured after sublimation of water-ice with a cavity ring-down spectrometer (Picarro L2120-i) that is connected to the vacuum line. To perform these experiments, ambient water vapor was introduced into, frozen, and purified inside the UHV chamber (T< 150 K). Water-ice samples were sublimated for varying amounts of time to collect various fractions of the original reservoir. We will present the first results on the oxygen and deuterium isotopic fractionation of water-ice sublimation and discuss their implications for interpreting the isotopic compositions of cometary ices.

  3. Literary Study, Measurement, and the Sublime: Disciplinary Assessment

    ERIC Educational Resources Information Center

    Heiland, Donna, Ed.; Rosenthal, Laura J., Ed.

    2011-01-01

    This collection of essays, "Literary Study, Measurement, and the Sublime: Disciplinary Assessment," edited by Donna Heiland and Laura J. Rosenthal, represents an important new venture in the Foundation's communication program. The book is the product of many authors, including the editors, both of whom have written essays for it. But it…

  4. Modeling the development of martian sublimation thermokarst landforms

    NASA Astrophysics Data System (ADS)

    Dundas, Colin M.; Byrne, Shane; McEwen, Alfred S.

    2015-12-01

    Sublimation-thermokarst landforms result from collapse of the surface when ice is lost from the subsurface. On Mars, scalloped landforms with scales of decameters to kilometers are observed in the mid-latitudes and considered likely thermokarst features. We describe a landscape evolution model that couples diffusive mass movement and subsurface ice loss due to sublimation. Over periods of tens of thousands of Mars years under conditions similar to the present, the model produces scallop-like features similar to those on the martian surface, starting from much smaller initial disturbances. The model also indicates crater expansion when impacts occur in surfaces underlain by excess ice to some depth, with morphologies similar to observed landforms on the martian northern plains. In order to produce these landforms by sublimation, substantial quantities of excess ice are required, at least comparable to the vertical extent of the landform, and such ice must remain in adjacent terrain to support the non-deflated surface. We suggest that martian thermokarst features are consistent with formation by sublimation, without melting, and that significant thicknesses of very clean excess ice (up to many tens of meters, the depth of some scalloped depressions) are locally present in the martian mid-latitudes. Climate conditions leading to melting at significant depth are not required.

  5. System for NO reduction using sublimation of cyanuric acid

    DOEpatents

    Perry, Robert A.

    1989-01-01

    An arrangement for reducing the NO content of a gas stream comprises contacting the gas stream with HNCO at a temperature effective for heat induced decomposition of HNCO and for resultant lowering of the NO content of the gas stream. Preferably, the HNCO is generated by sublimation of cyanuric acid.

  6. Differential Sublimation of Terrestrial Permafrost and the Ramifications for Terrain Features on Mars

    NASA Astrophysics Data System (ADS)

    Douglas, T. A.; Mellon, M. T.

    2016-09-01

    Sublimation loss of ice wedge ice in CRREL Permafrost Tunnel in Alaska (2.8 mm) is linear over 386 days, while ice cemented silt sublimation follows a decreasing relationship with time over 51 years with little sublimation over the past 20 years.

  7. Relationship between molecular descriptors and the enthalpies of sublimation of natural amino acids

    NASA Astrophysics Data System (ADS)

    Badelin, V. G.; Tyunina, V. V.; Girichev, G. V.; Tyunina, E. Yu.

    2016-07-01

    A multiparameter correlation between the enthalpies of sublimation and molecular descriptors of natural amino acids is proposed, based on generalized experimental and literature data on the heat effects of sublimation. The contributions from Van der Waals interactions, hydrogen bond formation, and electrostatic effects into enthalpy of sublimation has been evaluated using regression coefficients.

  8. Sublimation of amino acids with enantiomeric excess amplification

    NASA Astrophysics Data System (ADS)

    Guillemin, Jean-Claude; Guillemin, Jean-Claude; Bellec, Aurelien

    The notion of chirality was first reported in 1848 by Pasteur, when he mechanically separated the two enantiomers of tartrate salts.[1] Amino acids are considered as the most important building blocks of life with sugars. On the Earth, the living systems are only composed of L- amino acids and D-sugars. Nowadays, the origin of homochirality on Earth is still unknown, and there are many theories trying to explain this phenomenon. Recently Cooks [2] and Feringa [3] reported that the sublimation of small amounts of L and D amino acid mixtures containing an excess of one of them leads to a huge enantiomeric excess (ee) enhancement of the sublimate. We reinvestigated these experiments to determine the rules leading to this enhancement. Starting from mixtures of L- and DL leucine we observed increasing and decreasing of the ee in function of the starting ratios. By the use of 13C derivatives, the origin of the sublimed enantiomers has been precised. Various parameters (L and D, or L and DL mixtures, dissolution in water before sublimation, . . . ) were studied. We also took into consideration the recently proposed hypothesis of the role played by the eutectic ee in the sublimation. [4] The application of these results to find an explanation of the enantiomeric excess in meteorites or in the Primitive Earth scenarios will be discussed. 1 Pasteur, L. Ann. Phys., 1848, 24, 442. 2 R. H. Perry, C. Wu, M. Nefliu, R. G. Cooks, Chem. Commun., 2007, 1071-1073. 3 S. P. Fletcher, R. B. C. Jagt, B. L. Feringa, Chem. Commun., 2007, 2578-2580. 4 D. G. Blackmond, M. Klussmannb Chem. Commun., 2007, 3990-3996.

  9. Aerosol volatility and enthalpy of sublimation of carboxylic acids.

    PubMed

    Salo, Kent; Jonsson, Asa M; Andersson, Patrik U; Hallquist, Mattias

    2010-04-08

    The enthalpy of sublimation has been determined for nine carboxylic acids, two cyclic (pinonic and pinic acid) and seven straight-chain dicarboxylic acids (C(4) to C(10)). The enthalpy of sublimation was determined from volatility measurements of nano aerosol particles using a volatility tandem differential mobility analyzer (VTDMA) set-up. Compared to the previous use of a VTDMA, this novel method gives enthalpy of sublimation determined over an extended temperature range (DeltaT approximately 40 K). The determined enthalpy of sublimation for the straight-chain dicarboxylic acids ranged from 96 to 161 kJ mol(-1), and the calculated vapor pressures at 298 K are in the range of 10(-6)-10(-3) Pa. These values indicate that dicarboxylic acids can take part in gas-to-particle partitioning at ambient conditions and may contribute to atmospheric nucleation, even though homogeneous nucleation is unlikely. To obtain consistent results, some experimental complications in producing nanosized crystalline aerosol particles were addressed. It was demonstrated that pinonic acid "used as received" needed a further purification step before being suspended as a nanoparticle aerosol. Furthermore, it was noted from distinct differences in thermal properties that aerosols generated from pimelic acid solutions gave two types of particles. These two types were attributed to crystalline and amorphous configurations, and based on measured thermal properties, the enthalpy of vaporization was 127 kJ mol(-1) and that of sublimation was 161 kJ mol(-1). This paper describes a new method that is complementary to other similar methods and provides an extension of existing experimental data on physical properties of atmospherically relevant compounds.

  10. Carbon Dioxide Sublimation on Iapetus: Exploring the Kinetic Possibilities

    NASA Astrophysics Data System (ADS)

    Blackburn, David G.; Rivera-Valentin, E. G.; Ulrich, R.

    2010-10-01

    Although Cassini did not map the northern pole of Iapetus to test the claims of a CO2 polar cap (Palmer and Brown, 2007, Astrophys. Jour., 666, L125-L128), further modeling can determine its likelihood. Recent spectral analysis of the 4.26 micron CO2 absorption feature in the dark material on Iapetus demonstrates that the surface may contain pure, clathrated, or complexed carbon dioxide (Cruikshank et. al., 2010, Icarus, 206, 561-572). We will explore the kinetics behind sublimation from all three possibilities by building upon experimental results of dry ice and CO2 clathrate hydrate sublimation under low temperature and pressure conditions (Leeman et al., 2010, LPSC XLI, 1533; Blackburn et al., 2010, Planet. and Space Sci., 58, 780-791). We will set strict limits on the mass flux of CO2 available from each of these scenarios by applying a new thermal model incorporating albedo from the recent bolometric Bond albedo map that includes coverage of the northern pole from Voyager (Blackburn et al., 2010, Icarus, submitted). While previous sublimation rate estimates have relied on the Langmuir evaporation equation, we contend that this formula sets only the upper limit on the amount of sublimation that can occur. The rate is even further reduced when considering the possibility of CO2 sublimation though an overburden. We will present the implications of this new model on ballistic transport of CO2, stability zones for dry ice, CO2 clathrate hydrate, and complexed CO2, as well as the resident times of a possible CO2 polar cap on Iapetus.

  11. Advances in sublimation studies for particles of explosives

    NASA Astrophysics Data System (ADS)

    Furstenberg, Robert; Nguyen, Viet; Fischer, Thomas; Abrishami, Tara; Papantonakis, Michael; Kendziora, Chris; Mott, David R.; McGill, R. Andrew

    2015-05-01

    When handling explosives, or related surfaces, the hands routinely become contaminated with particles of explosives and related materials. Subsequent contact with a solid surface results in particle crushing and deposition. These particles provide an evidentiary trail which is useful for security applications. As such, the opto-physico-chemical characteristics of these particles are critical to trace explosives detection applications in DOD or DHS arenas. As the persistence of these particles is vital to their forensic exploitation, it is important to understand which factors influence their persistence. The longevity or stability of explosives particles on a substrate is a function of several environmental parameters or particle properties including: Vapor pressure, particle geometry, airflow, particle field size, substrate topography, humidity, reactivity, adlayers, admixtures, particle areal density, and temperature. In this work we deposited particles of 2,4-dinitrotoluene on standard microscopy glass slides by particle sieving and studied their sublimation as a function of airflow velocity, areal particle density and particle field size. Analysis of 2D microscopic images was used to compute and track particle size and geometrical characteristics. The humidity, temperature and substrate type were kept constant for each experiment. A custom airflow cell, using standard microscopy glass slide, allowed in-situ photomicroscopy. Areal particle densities and airflow velocities were selected to provide relevant loadings and flow velocities for a range of potential applications. For a chemical of interest, we define the radial sublimation velocity (RSV) for the equivalent sphere of a particle as the parameter to characterize the sublimation rate. The RSV is a useful parameter because it is independent of particle size. The sublimation rate for an ensemble of particles was found to significantly depend on airflow velocity, the areal density of the particles, and the

  12. Sublimation's impact on temporal change of albedo dichotomy on Iapetus

    NASA Astrophysics Data System (ADS)

    Kimura, Jun; Kawamura, Taichi; Morito, Hisataka; Morota, Tomokatsu; Honda, Chikatoshi; Kuramoto, Kiyoshi; Okada, Tatsuaki

    2011-08-01

    Iapetus, one of the saturnian moons, has an extreme albedo contrast between the leading and trailing hemispheres. The origin of this albedo dichotomy has led to several hypotheses, however it remains controversial. To clarify the origin of the dichotomy, the key approach is to investigate the detailed distribution of the dark material. Recent studies of impact craters and surface temperature from Cassini spacecraft data implied that sublimation of H 2O ice can occur on Iapetus' surface. This ice sublimation can change the albedo distribution on the moon with time. In this study, we evaluate the effect of ice sublimation and simulate the temporal change of surface albedo. We assume the dark material and the bright ice on the surface to be uniformly mixed with a certain volume fraction, and the initial albedo distribution to incorporate the dark material deposits on the surface. That is, the albedo at the apex is lowest and concentrically increases in a sinusoidal pattern. This situation simulates that dark materials existed around the Iapetus' orbit billions of years ago, and the synchronously rotating Iapetus swept the material and then deposited it on its surface. The evolution of the surface albedo during 4.0 Gyr is simulated by estimating the surface temperature from the insolation energy on Iapetus including the effect of Saturn's eccentricity and Iapetus' obliquity precession, and evaluating the sublimation rate of H 2O ice from the Iapetus' surface. As a result, we found that the distribution of the surface albedo changed dramatically after 4.0 Gyr of evolution. The sublimation has three important effects on the resultant surface albedo. First, the albedo in the leading hemisphere has significantly decreased to approach the minimum value. Second, the albedo distribution has been elongated along the equator. Third, the edge of the low albedo region has become clear. Considering the effect of ice sublimation, the current albedo distribution can be reconstructed

  13. Sublimator Driven Coldplate Engineering Development Unit Test Results

    NASA Technical Reports Server (NTRS)

    Sheth, Rubik B.; Stephan, Ryan A.; Leimkuehler, Thomas O.

    2010-01-01

    The Sublimator Driven Coldplate (SDC) is a unique piece of thermal control hardware that has several advantages over a traditional thermal control scheme. The principal advantage is the possible elimination of a pumped fluid loop, potentially increasing reliability and reducing complexity while saving both mass and power. Because the SDC requires a consumable feedwater, it can only be used for short mission durations. Additionally, the SDC is ideal for a vehicle with small transport distances and low heat rejection requirements. An SDC Engineering Development Unit was designed and fabricated. Performance tests were performed in a vacuum chamber to quantify and assess the performance of the SDC. The test data was then used to develop correlated thermal math models. Nonetheless, an Integrated Sublimator Driven Coldplate (ISDC) concept is being developed. The ISDC couples a coolant loop with the previously described SDC hardware. This combination allows the SDC to be used as a traditional coldplate during long mission phases and provides for dissimilar system redundancy

  14. Effects of varying obliquity on Martian sublimation thermokarst landforms

    USGS Publications Warehouse

    Dundas, Colin M.

    2017-01-01

    Scalloped depressions in the Martian mid-latitudes are likely formed by sublimation of ice-rich ground. The stability of subsurface ice changes with the planetary obliquity, generally becoming less stable at lower axial tilt. As a result, the relative rates of sublimation and creep change over time. A landscape evolution model shows that these variations produce internal structure in scalloped depressions, commonly in the form of arcuate ridges, which emerge as depressions resume growth after pausing or slowing. In other scenarios, the formation of internal structure is minimal. Significant uncertainties in past climate and model parameters permit a range of scenarios. Ridges observed in some Martian scalloped depressions could date from obliquity lows or periods of low ice stability occurring <5 Ma, suggesting that the pits are young features and may be actively evolving.

  15. Surface engineering of SiC via sublimation etching

    NASA Astrophysics Data System (ADS)

    Jokubavicius, Valdas; Yazdi, Gholam R.; Ivanov, Ivan G.; Niu, Yuran; Zakharov, Alexei; Iakimov, Tihomir; Syväjärvi, Mikael; Yakimova, Rositsa

    2016-12-01

    We present a technique for etching of SiC which is based on sublimation and can be used to modify the morphology and reconstruction of silicon carbide surface for subsequent epitaxial growth of various materials, for example graphene. The sublimation etching of 6H-, 4H- and 3C-SiC was explored in vacuum (10-5 mbar) and Ar (700 mbar) ambient using two different etching arrangements which can be considered as Si-C and Si-C-Ta chemical systems exhibiting different vapor phase stoichiometry at a given temperature. The surfaces of different polytypes etched under similar conditions are compared and the etching mechanism is discussed with an emphasis on the role of tantalum as a carbon getter. To demonstrate applicability of such etching process graphene nanoribbons were grown on a 4H-SiC surface that was pre-patterned using the thermal etching technique presented in this study.

  16. Preparation of 2:1 urea-succinic acid cocrystals by sublimation

    NASA Astrophysics Data System (ADS)

    Zhang, Tian; Yu, Qiushuo; Li, Xiaorui; Ma, Xiaoxun

    2017-07-01

    The aim of this study is to introduce a sublimation method for preparing cocrystals. The 2:1 urea-succinic acid cocrystals were generated by a simple sublimation apparatus, analyzed by Powder X-ray Diffraction (PXRD), Transmission Fourier Transform Infrared (FTIR) and Differential Scanning Calorimetry (DCS). The role of supersaturations in vapor crystallization was also discussed in detail. This work showed sublimation was a promising method for cocrystallization.

  17. Sublimation measurements and analysis of high temperature thermoelectric materials and devices

    NASA Technical Reports Server (NTRS)

    Shields, V.; Noon, L.

    1983-01-01

    High temperature thermoelectric device sublimation effects are compared for rare earth sulfides, selenides, and state-of-the-art Si-Ge alloys. Although rare earth calcogenides can potentially exhibit superior sublimation characteristics, the state-of-the-art Si-Ge alloy with silicon nitride sublimation-inhibitive coating has been tested to 1000 C. Attention is given to the ceramic electrolyte cells, forming within electrical and thermal insulation, which affect leakage conductance measurements in Si-Ge thermoelectric generators.

  18. The enthalpy of sublimation and thermodynamic functions of fermium

    SciTech Connect

    Haire, R.G.; Gibson, J.K. , Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6375 )

    1989-12-01

    The enthalpy of sublimation of fermium (Fm), element 100, has now been determined directly by measuring the partial pressure of Fm over alloys, for the temperature range of 642 to 905 K. The partial pressures were determined using Knudsen effusion and target collection techniques. Dilute (10{sup {minus}5}--10{sup {minus}7} atom %) solid alloys of Fm and mixtures of Fm and Es in both Sm and Yb solvents were studied. The presence of Es in two of the alloys allowed a direct comparison of the behavior of Fm and Es, where the latter could be used as a reference. It was possible to calculate enthalpies of sublimation and a hypothetical vapor pressure/temperature relationship for pure Fm metal by selecting Yb as the solvent most likely to form a nearly ideal alloy with Fm. From the experimental vapor pressure data, we derived average Second Law values of 33.8{plus minus}3 kcal/mol and 23.5{plus minus}3 cal/mol deg for the enthalpy and entropy of sublimation of Fm at 298 K. Third Law enthalpy values were also calculated using the experimental partial pressure data and entropies estimated from derived free energy functions and heat capacities for the solid and gaseous forms of Fm. The average Third Law values (34.8 kcal/mol and 25.1 cal/mol deg, respectively, at 298 K) are in agreement with those obtained via the Second Law. These results establish that Fm, like Es (element 99), is a divalent metal. The finding that Fm metal is the second divalent actinide element experimentally establishes the trend towards metallic divalency expected in the second half of the actinide series.

  19. Slow ground state molecules from matrix isolation sublimation

    NASA Astrophysics Data System (ADS)

    Oliveira, A. N.; Sacramento, R. L.; Alves, B. X.; Silva, B. A.; Wolff, W.; Cesar, C. L.

    2014-12-01

    We describe the generation and properties of a cryogenic beam of 7Li2 dimers from sublimation of a neon matrix where lithium atoms have been implanted via laser ablation of solid precursors of metallic lithium or lithium hydride (LiH). Different sublimation regimes lead to pulsed molecular beams with different temperatures, densities and forward velocities. With laser absorption spectroscopy these parameters were measured using the molecular 7Li2 (R) transitions A1Σ u+(v\\prime =4,J\\prime =J\\prime\\prime +1) ≤ftarrow X 1Σ g+(v\\prime\\prime =0,J\\prime\\prime =0,1,3). In a typical regime, sublimating a matrix at 16 K, translational temperatures of 6-8 K with a drift velocity of 130 m s-1 in a free expanding pulsed beam with molecular density of 109 cm-3, averaged along the laser axis, were observed. Rotational temperatures around 5-7 K were obtained. In recent experiments we were able to monitor the atomic Li signal—in the D2 line—concomitantly with the molecular signal in order to compare them as a function of the number of ablation pulses. Based on the data and a simple model, we discuss the possibility that a fraction of these molecules are being formed in the matrix, by mating atoms from different ablation pulses, which would open up the way to formation of other more interesting and difficult molecules to be studied at low temperatures. Such a source of cryogenic molecules have possible applications encompassing fundamental physics tests, quantum information studies, cold collisions, chemistry, and trapping.

  20. Sublimation of ices of astrophysical interest: A bibliographic review

    NASA Astrophysics Data System (ADS)

    Fray, N.; Schmitt, B.

    2009-12-01

    The sublimation and condensation of ices play a very important role in the formation of planetary systems, in the evolution of some solar system bodies as well as in the equilibrium and matter exchanges between surface and atmosphere of most planets and satellites. The precise knowledge of vapour pressure of molecular solids at all relevant temperatures is mandatory, but the published sublimation relations are not always accurate enough. All published experimental measurements, and empirical and thermodynamical relations for the vapour pressure of 53 different species in their pure solid phases are reviewed. For several species, we also calculate the vapour pressure with accurate thermodynamic formulae from the triple point down to low temperatures. For 27 species (H 2O, O 2, O 3, CO, CO 2, CH 3OH, HCOOH, CH 4, C 2H 2, C 2H 4, C 2H 6, C 6H 6, HCN, HC 3N, C 2N 2, C 4N 2, N 2, NH 3, NO, N 2O, H 2S, SO 2, AsH 3, Ne, Ar, Kr, and Xe) we are able to propose vapour pressure relations, either empirical or theoretical, valid over a large range of temperatures, representative of astrophysical environments. All these relations are more accurate than those currently used in the astrophysical literature. In particular, most of the relations commonly used in the astrophysical literature are based on the data reported by Lide (2006) in the CRC Handbook of Chemistry and Physics, which are inaccurate for several compounds. The most problematic case is CO ice, for which a sublimation relation extrapolated from the liquid-gas equilibrium ( Fanale and Salvail, 1990) is used in most of the models simulating the activity of comet nuclei.

  1. Adhesive coated electrical apparatus having sublimable protective covering and an assembly method

    DOEpatents

    Wootton, Roy E.

    1982-01-01

    Electrical apparatus including an enclosure, an electrode disposed within the enclosure, and supports for insulatably supporting the electrode within the enclosure has a permanently sticky adhesive material which is disposed on the interior surface of the outer enclosure. A high-vapor-pressure sublimable material is disposed on the permanently sticky adhesive material, with the sublimable material capable of subliming away in the presence of a vacuum. The presence of the sublimable material enables the apparatus to be non-sticky during assembly and handling operations, while being rendered sticky upon commissioning of the apparatus.

  2. Sublimation via virtual melting inside an elastoplastic material

    NASA Astrophysics Data System (ADS)

    Levitas, Valery I.; Altukhova, Nataliya

    2009-06-01

    Thermodynamic, kinetic, and mechanical approaches for sublimation inside elastoplastic material via intermediate (virtual) melting under tensile pressure are developed for a spherical nucleus. Virtual melting represents the appearance of subcritical liquid drop that immediately transforms to gas bubble. The variety of mechanisms and transformation paths are revealed in different pressure ranges. The radius of the critical gas nucleus differs from the classical one because elastic energy of melt is size dependent due to surface tension. Our developed approach can be extended for various structural changes in nanoparticles within a void inside elastoplastic material and two-stage and multistage nucleation processes. Universal mechanical gas bubble instability is revealed.

  3. The IBEX-Lo Sensor

    NASA Astrophysics Data System (ADS)

    Fuselier, S. A.; Bochsler, P.; Chornay, D.; Clark, G.; Crew, G. B.; Dunn, G.; Ellis, S.; Friedmann, T.; Funsten, H. O.; Ghielmetti, A. G.; Googins, J.; Granoff, M. S.; Hamilton, J. W.; Hanley, J.; Heirtzler, D.; Hertzberg, E.; Isaac, D.; King, B.; Knauss, U.; Kucharek, H.; Kudirka, F.; Livi, S.; Lobell, J.; Longworth, S.; Mashburn, K.; McComas, D. J.; Möbius, E.; Moore, A. S.; Moore, T. E.; Nemanich, R. J.; Nolin, J.; O'Neal, M.; Piazza, D.; Peterson, L.; Pope, S. E.; Rosmarynowski, P.; Saul, L. A.; Scherrer, J. R.; Scheer, J. A.; Schlemm, C.; Schwadron, N. A.; Tillier, C.; Turco, S.; Tyler, J.; Vosbury, M.; Wieser, M.; Wurz, P.; Zaffke, S.

    2009-08-01

    The IBEX-Lo sensor covers the low-energy heliospheric neutral atom spectrum from 0.01 to 2 keV. It shares significant energy overlap and an overall design philosophy with the IBEX-Hi sensor. Both sensors are large geometric factor, single pixel cameras that maximize the relatively weak heliospheric neutral signal while effectively eliminating ion, electron, and UV background sources. The IBEX-Lo sensor is divided into four major subsystems. The entrance subsystem includes an annular collimator that collimates neutrals to approximately 7°×7° in three 90° sectors and approximately 3.5°×3.5° in the fourth 90° sector (called the high angular resolution sector). A fraction of the interstellar neutrals and heliospheric neutrals that pass through the collimator are converted to negative ions in the ENA to ion conversion subsystem. The neutrals are converted on a high yield, inert, diamond-like carbon conversion surface. Negative ions from the conversion surface are accelerated into an electrostatic analyzer (ESA), which sets the energy passband for the sensor. Finally, negative ions exit the ESA, are post-accelerated to 16 kV, and then are analyzed in a time-of-flight (TOF) mass spectrometer. This triple-coincidence, TOF subsystem effectively rejects random background while maintaining high detection efficiency for negative ions. Mass analysis distinguishes heliospheric hydrogen from interstellar helium and oxygen. In normal sensor operations, eight energy steps are sampled on a 2-spin per energy step cadence so that the full energy range is covered in 16 spacecraft spins. Each year in the spring and fall, the sensor is operated in a special interstellar oxygen and helium mode during part of the spacecraft spin. In the spring, this mode includes electrostatic shutoff of the low resolution (7°×7°) quadrants of the collimator so that the interstellar neutrals are detected with 3.5°×3.5° angular resolution. These high angular resolution data are combined with

  4. D/H fractionation during the sublimation of water ice

    NASA Astrophysics Data System (ADS)

    Lécuyer, Christophe; Royer, Aurélien; Fourel, François; Seris, Magali; Simon, Laurent; Robert, François

    2017-03-01

    Experiments of sublimation of pure water ice have been performed in the temperature range -105 °C to -30 °C and atmospheric partial pressures ranging from 10-6 to 10-1 mb. Sampling of both vapour and residual ice fractions has been performed with the use of a vacuum line designed for the extraction and purification of gases before the measurement of their D/H ratios. Sublimation was responsible for sizable isotopic fractionation factors in the range 0.969-1.123 for temperatures lying between -105 °C and -30 °C. The fractionation factor exhibits a cross-over at temperatures around -50 °C with the water vapour fraction being D-depleted relative to the residual ice fraction at T < -50 °C (αice-vapour = 0.969-0.995). This cross-over has implications for the understanding of the atmospheric water cycle of some terrestrial planets such as the Earth or Mars. The magnitude of deuterium enrichment or depletion between ice and water vapour cannot explain the differences in the D/H ratios amongst Jupiter comets and long-period comets families nor those that have been documented between Earth's and cometary water.

  5. Dynamic sublimation pressure and the catastrophic breakup of Comet ISON

    NASA Astrophysics Data System (ADS)

    Steckloff, Jordan K.; Johnson, Brandon C.; Bowling, Timothy; Jay Melosh, H.; Minton, David; Lisse, Carey M.; Battams, Karl

    2015-09-01

    Previously proposed mechanisms have difficulty explaining the disruption of Comet C/2012 S1 (ISON) as it approached the Sun. We describe a novel cometary disruption mechanism whereby comet nuclei fragment and disperse through dynamic sublimation pressure, which induces differential stresses within the interior of the nucleus. When these differential stresses exceed its material strength, the nucleus breaks into fragments. We model the sublimation process thermodynamically and propose that it is responsible for the disruption of Comet ISON. We estimate the bulk unconfined crushing strength of Comet ISON's nucleus and the resulting fragments to be 0.5 Pa and 1-9 Pa, respectively, assuming typical Jupiter Family Comet (JFC) albedos. However, if Comet ISON has an albedo similar to Pluto, this strength estimate drops to 0.2 Pa for the intact nucleus and 0.6-4 Pa for its fragments. Regardless of assumed albedo, these are similar to previous strength estimates of JFCs. This suggests that, if Comet ISON is representative of dynamically new comets, then low bulk strength is a primordial property of some comet nuclei, and not due to thermal processing during migration into the Jupiter Family.

  6. The Heat of Sublimation of Solid Ethylene and Acetylene

    NASA Astrophysics Data System (ADS)

    Nelson, R. N.; Allen, J. E., Jr.

    2002-09-01

    The atmospheres of the outer planets and their satellites include trace, but chemically important, amounts of small hydrocarbon molecules. These molecules also appear in solid form in clouds within the atmospheres and as surface layers on the planet or on haze particles in the atmosphere. The modeling of the composition and photochemistry of these atmospheres depends critically on accurate values of the vapor pressure of these hydrocarbons, which in turn requires accurately measured data. It is important to acquire these data over as much of the temperature and pressure range of interest as possible to reduce the need to extrapolate since this can introduce major errors in vapor pressure. In addition to vapor pressures, study of the behavior of solid-vapor equilibrium for small particles, and especially of surface layers, requires information on the heat of sublimation of the solid phases. Ethylene (C2H4) and acetylene (C2H2) are present in the atmospheres of Saturn and Titan, so we previously measured the solid phase vapor pressure of the former from 69 to 97 K (Nelson, Allen, and Harris 1997) and of the latter from 84 to 124 K (Nelson and Allen 1998). We have now refined those data and used them to evaluate the heats of sublimation of these molecules over the same temperature ranges. Nelson, R. N., Allen, J. E., Jr., and Harris, B. C., Jr., 1997, B.A.A.S. 29, 1009 Nelson, R. N. and Allen, J. E., Jr., 1997, B.A.A.S. 30, 1101

  7. Cerium Tetrafluoride: Sublimation, Thermolysis, and Atomic Fluorine Migration.

    PubMed

    Chilingarov, N S; Knot'ko, A V; Shlyapnikov, I M; Mazej, Z; Kristl, M; Sidorov, L N

    2015-08-06

    Saturated vapor pressure p° and enthalpy of sublimation (ΔsH°) of cerium tetrafluoride CeF4 were determined by means of Knudsen effusion mass spectrometry in the range of 750-920 K. It was discovered that sublimation of cerium tetrafluoride from a platinum effusion cell competes with thermal decomposition to CeF3 in the solid phase, but no accompanying release of fluorine to the gas phase occurs. Thus, fluorine atoms migrate within the surface layer of CeF4(s) to the regions of their irreversible drain. We used scanning electron microscopy to study the distribution of the residual CeF3(s) across the inner surface of the effusion cell after complete evaporation of CeF4(s). It was observed that CeF3 accumulates near the edge of the effusion orifice and near the junction of the lid and the body of the cell, that is, in those regions where the fluorine atoms can migrate to a free platinum surface and thus be depleted from the system. Distribution of CeF3(s) solid particles indicates the ways of fluorine atoms migration providing CeF3(s) formation inside the CeF4(s) surface layer.

  8. Determination of surface shear stress with the naphthalene sublimation technique

    NASA Technical Reports Server (NTRS)

    Lee, J. A.; Greeley, Ronald

    1987-01-01

    Aeolian entrainment and transport are functions of surface shear stress and particle characteristics. Measuring surface shear stress is difficult, however, where logarithmic wind profiles are not found, such as regions around large roughness elements. An outline of a method whereby shear stress can be mapped on the surface around an object is presented. The technique involves the sublimation of naphthalene (C10H8) which is a function of surface shear stress and surface temperature. This technique is based on the assumption that the transfer of momentum, heat and mass are analogous (Reynolds analogy). If the Reynolds analogy can be shown to be correct for a given situation, then knowledge of the diffusion of one property allows the determination of the others. The analytical framework and data acquisition for the method are described. The technique was tested in the Planetary Geology Wind Tunnel. Results show that the naphthalene sublimation technique is a reasonably accurate method for determining shear stress, particularly around objects where numerous point values are needed.

  9. Matrix isolation sublimation: An apparatus for producing cryogenic beams of atoms and molecules

    NASA Astrophysics Data System (ADS)

    Sacramento, R. L.; Oliveira, A. N.; Alves, B. X.; Silva, B. A.; Li, M. S.; Wolff, W.; Cesar, C. L.

    2015-07-01

    We describe the apparatus to generate cryogenic beams of atoms and molecules based on matrix isolation sublimation. Isolation matrices of Ne and H2 are hosts for atomic and molecular species which are sublimated into vacuum at cryogenic temperatures. The resulting cryogenic beams are used for high-resolution laser spectroscopy. The technique also aims at loading atomic and molecular traps.

  10. Matrix isolation sublimation: An apparatus for producing cryogenic beams of atoms and molecules

    SciTech Connect

    Sacramento, R. L.; Alves, B. X.; Silva, B. A.; Wolff, W.; Cesar, C. L.; Oliveira, A. N.; Li, M. S.

    2015-07-15

    We describe the apparatus to generate cryogenic beams of atoms and molecules based on matrix isolation sublimation. Isolation matrices of Ne and H{sub 2} are hosts for atomic and molecular species which are sublimated into vacuum at cryogenic temperatures. The resulting cryogenic beams are used for high-resolution laser spectroscopy. The technique also aims at loading atomic and molecular traps.

  11. Thermodynamic investigations of nitroxoline sublimation by simultaneous DSC-FTIR method and isothermal TG analysis.

    PubMed

    Gao, Gau-Yi; Lin, Shan-Yang

    2010-01-01

    To investigate the physicochemical characteristics, thermodynamics, possible sublimation process and kinetics of nitroxoline, differential scanning calorimetry (DSC), isothermal thermogravimetry (TG), and Fourier transform infrared (FTIR) microspectroscopy equipped with a micro hot-stage of DSC microscopy assembly (simultaneous DSC-FTIR method) were used. The DSC result indicates that nitroxoline exhibited a sharp endothermic peak at 182 degrees C with enthalpy of 103.1 J/g due to the melting point of nitroxoline. A sublimation behavior of nitroxoline was found from 129 degrees C by gradual weight loss in TG curve. However, the nonisothermal DSC-FTIR method reveals that the temperature at 95 degrees C was the onset temperature of nitroxoline sublimation. A significant difference between DSC-FTIR method and TG analysis suggests that the simultaneous DSC-FTIR method was more sensitive than that of the TG analysis to detect the beginning temperature of nitroxoline sublimation. The sublimation kinetics of nitroxoline determined by isothermal TG analysis evidenced that the zero-order kinetics was followed over the sublimation time. The sublimation enthalpy correction was also carried out by a group additivity approach for the estimation of heat capacity. The enthalpy of nitroxoline sublimation estimated was 86.14 KJ/mol at 298.15 K.

  12. Matrix isolation sublimation: An apparatus for producing cryogenic beams of atoms and molecules.

    PubMed

    Sacramento, R L; Oliveira, A N; Alves, B X; Silva, B A; Li, M S; Wolff, W; Cesar, C L

    2015-07-01

    We describe the apparatus to generate cryogenic beams of atoms and molecules based on matrix isolation sublimation. Isolation matrices of Ne and H2 are hosts for atomic and molecular species which are sublimated into vacuum at cryogenic temperatures. The resulting cryogenic beams are used for high-resolution laser spectroscopy. The technique also aims at loading atomic and molecular traps.

  13. Direct Isolation of Purines and Pyrimidines from Nucleic Acids Using Sublimation

    NASA Technical Reports Server (NTRS)

    Glavin, Daniel P.; Schubert, Michael; Bada, Jeffrey L.

    2003-01-01

    A sublimation technique was developed to isolate purines and pyrimidines directly from lambda-deoxyribonucleic acid (lambda-DNA) and Escherichia coli cells. The sublimation of adenine, cytosine, guanine, and thymine from lambda-DNA was tested under reduced pressure (approx. 0.5 Torr) at temperatures of >150 C. With the exception of guanine, approximately 60 -75% of each base was sublimed directly from the lambda-DNA and recovered on a coldfinger of the sublimation apparatus after heating to 450 C. Several nucleobases including adenine, cytosine, thymine, and uracil were also recovered from E. coli bacteria after heating the cells to the same temperature, although some thermal decomposition of the bases also occurred. These results demonstrate the feasibility of using sublimation to isolate purines and pyrimidines from native E. coli DNA and RNA without any chemical treatment of the cells.

  14. Direct Isolation of Purines and Pyrimidines from Nucleic Acids Using Sublimation

    NASA Technical Reports Server (NTRS)

    Glavin, Daniel P.; Schubert, Michael; Bada, Jeffrey L.

    2003-01-01

    A sublimation technique was developed to isolate purines and pyrimidines directly from lambda-deoxyribonucleic acid (lambda-DNA) and Escherichia coli cells. The sublimation of adenine, cytosine, guanine, and thymine from lambda-DNA was tested under reduced pressure (approx. 0.5 Torr) at temperatures of >150 C. With the exception of guanine, approximately 60 -75% of each base was sublimed directly from the lambda-DNA and recovered on a coldfinger of the sublimation apparatus after heating to 450 C. Several nucleobases including adenine, cytosine, thymine, and uracil were also recovered from E. coli bacteria after heating the cells to the same temperature, although some thermal decomposition of the bases also occurred. These results demonstrate the feasibility of using sublimation to isolate purines and pyrimidines from native E. coli DNA and RNA without any chemical treatment of the cells.

  15. Mass wasting triggered by seasonal CO2 sublimation under Martian atmospheric conditions: Laboratory experiments

    NASA Astrophysics Data System (ADS)

    Sylvest, Matthew E.; Conway, Susan J.; Patel, Manish R.; Dixon, John C.; Barnes, Adam

    2016-12-01

    Sublimation is a recognized process by which planetary landscapes can be modified. However, interpretation of whether sublimation is involved in downslope movements on Mars and other bodies is restricted by a lack of empirical data to constrain this mechanism of sediment transport and its influence on landform morphology. Here we present the first set of laboratory experiments under Martian atmospheric conditions which demonstrate that the sublimation of CO2 ice from within the sediment body can trigger failure of unconsolidated, regolith slopes and can measurably alter the landscape. Previous theoretical studies required CO2 slab ice for movements, but we find that only frost is required. Hence, sediment transport by CO2 sublimation could be more widely applicable (in space and time) on Mars than previously thought. This supports recent work suggesting CO2 sublimation could be responsible for recent modification in Martian gullies.

  16. Calculational criticality analyses of 10- and 20-MW UF[sub 6] freezer/sublimer vessels

    SciTech Connect

    Jordan, W.C.

    1993-02-01

    Calculational criticality analyses have been performed for 10- and 20-MW UF[sub 6] freezer/sublimer vessels. The freezer/sublimers have been analyzed over a range of conditions that encompass normal operation and abnormal conditions. The effects of HF moderation of the UF[sub 6] in each vessel have been considered for uranium enriched between 2 and 5 wt % [sup 235]U. The results indicate that the nuclearly safe enrichments originally established for the operation of a 10-MW freezer/sublimer, based on a hydrogen-to-uranium moderation ratio of 0.33, are acceptable. If strict moderation control can be demonstrated for hydrogen-to-uranium moderation ratios that are less than 0.33, then the enrichment limits for the 10-MW freezer/sublimer may be increased slightly. The calculations performed also allow safe enrichment limits to be established for a 20-NM freezer/sublimer under moderation control.

  17. The SCITEAS experiment: Optical characterizations of sublimating icy planetary analogues

    NASA Astrophysics Data System (ADS)

    Pommerol, A.; Jost, B.; Poch, O.; El-Maarry, M. R.; Vuitel, B.; Thomas, N.

    2015-05-01

    We have designed and built a laboratory facility to investigate the spectro-photometric and morphologic properties of different types of ice-bearing planetary surface analogs and follow their evolution upon exposure to a low pressure and low temperature environment. The results obtained with this experiment are used to verify and improve our interpretations of current optical remote-sensing datasets. They also provide valuable information for the development and operation of future optical instruments. The Simulation Chamber for Imaging the Temporal Evolution of Analogue Samples (SCITEAS) is a small thermal vacuum chamber equipped with a variety of ports and feedthroughs that permit both in-situ and remote characterizations as well as interacting with the sample. A large quartz window located directly above the sample is used to observe its surface from outside with a set of visible and near-infrared cameras. The sample holder can be easily and quickly inserted and removed from the chamber and is compatible with the other measurement facilities of the Laboratory for Outflow Studies of Sublimating Materials (LOSSy) at the University of Bern. We report here on the results of two of the first experiments performed in the SCITEAS chamber. In the first experiment, fine-grained water ice mixed with dark organic and mineral matter was left to sublime in vacuum and at low temperature, simulating the evolution of the surface of a comet nucleus approaching the Sun. We observed and characterized the formation and evolution of a crust of refractory organic and mineral matter at the surface of the sample and linked the evolution of its structure and texture to its spectro-photometric properties. In the second experiment, a frozen soil was prepared by freezing a mixture of smectite mineral and water. The sample was then left to sublime for 6 h to simulate the loss of volatiles from icy soil at high latitudes on Mars. Colour images were produced using the definitions of the

  18. Uranium hexaflouride freezer/sublimer process simulator/trainer

    SciTech Connect

    Carnal, C.L. ); Belcher, J.D.; Tapp, P.A.; Ruppel, F.R.; Wells, J.C. )

    1991-01-01

    This paper describes a software and hardware simulation of a freezer/sublimer unit used in gaseous diffusion processing of uranium hexafluoride (UF{sub 6}). The objective of the project was to build a plant simulator that reads control signals and produces plant signals to mimic the behavior of an actual plant. The model is based on physical principles and process data. Advanced Continuous Simulation Language (ACSL) was used to develop the model. Once the simulation was validated with actual plant process data, the ACSL model was translated into Advanced Communication and Control Oriented Language (ACCOL). A Bristol Babcock Distributed Process Controller (DPC) Model 3330 was the hardware platform used to host the ACCOL model and process the real world signals. The DPC will be used as a surrogate plant to debug control system hardware/software and to train operators to use the new distributed control system without disturbing the process. 2 refs., 4 figs.

  19. Methods of conveying fluids and methods of sublimating solid particles

    DOEpatents

    Turner, Terry D; Wilding, Bruce M

    2013-10-01

    A heat exchanger and associated methods for sublimating solid particles therein, for conveying fluids therethrough, or both. The heat exchanger includes a chamber and a porous member having a porous wall having pores in communication with the chamber and with an interior of the porous member. A first fluid is conveyed into the porous member while a second fluid is conveyed into the porous member through the porous wall. The second fluid may form a positive flow boundary layer along the porous wall to reduce or eliminate substantial contact between the first fluid and the interior of the porous wall. The combined first and second fluids are conveyed out of the porous member. Additionally, the first fluid and the second fluid may each be conveyed into the porous member at different temperatures and may exit the porous member at substantially the same temperature.

  20. Simulation of Ceres water sublimation and thermal state

    NASA Astrophysics Data System (ADS)

    De Sanctis, M.; Formisano, M.; Capria, M.; Capaccioni, F.; Ammannito, E.; Magni, G.; Bockelee-Morvan, D.; Raymond, C.; Russell, C.

    2014-07-01

    The dwarf planet Ceres is the largest of the minor bodies and is located in the main asteroid belt with a semimajor axis of 2.77 au. The current observational evidence shows that the boundary between rocky bodies and icy bodies is probably within the asteroid belt or a little further, and Ceres is a key object to understand the story of water in the solar system. Ceres represents the key, together with Vesta, to answer some important questions relative to the role of protoplanet sizes and water content in determining their subsequent evolution. Ceres is thought to be differentiated into a silicate core with an icy mantle [1,2,3], and hydrated minerals were found on its surface [4]. Moreover, the presence of water vapour around Ceres has been recently reported by [5] from Herschel observations. Water outgassing was also suggested by a marginal detection of the photodissociation product OH [6]. The recent observations suggest a flux of water vapour from Ceres of at least 10^{26} molecules/s. Moreover, it seems that the flux is originating from localized sources. The variation of the detected activity along the Ceres' orbit could suggest a cometary-like sublimation [5], but cryovolcanism cannot be excluded. Here we applied a ''cometary-like'' sublimation model [7,8] to simulate the thermal properties and the water flux of Ceres in the light of the NASA Dawn mission [9], planned to arrive at Ceres in spring 2015. In the literature, there are several works dedicated to the study of this asteroid [1,3], but they are mainly devoted to simulate the thermal evolution of the body since its formation. The current work, conversely, uses a quasi-3D approach, derived from the thermal evolution models of cometary nuclei, to study the thermal properties of the surface and to investigate the conditions for the observed water activity. The model assumes Ceres to be a spherical body with a fixed radius and made of a homogeneous mixture of dust and ices in different proportions. The

  1. Sublimation Model for Formation of Martian Residual Cap Depressions

    NASA Astrophysics Data System (ADS)

    Byrne, S.; Ingersoll, A. P.

    2000-10-01

    In an effort for explain the formation of the 'Swiss-cheese' terrain visible on the southern residual cap of Mars, we have developed a radiative model to follow the growth/decay of an initial depression due to sublimation/condensation of carbon dioxide. The pits making up this terrain have many distinctive features, they are shallow ( 10m deep), with steep walls and flat floors and contain an interior moat which runs along the bottom of the walls. They have lateral sizes ranging from a few 10's of meters to a kilometer and are quasi-circular. The model accounts for incident sunlight, emitted thermal radiation, and scattered short and long wave radiation. We have investigated many cases involving pure dry-ice with constant albedo, albedo as a function of insolation, and differing albedo for fresh and residual frost (the latter has lower albedo). The last case mentioned shows the most promising results to date. With these conditions it is possible for the depressions to grow and develop flat central portions although they still lack the observed steep walls of the pits. In the other cases mentioned the initial depressions heal themselves and disappear into the surrounding terrain. Other processes or materials could be responsible for the remainder of the observed features. Water ice stored a few meters under a carbon dioxide covering would have dramatic effects on the growth of any depression which encounters it, both due to its low sublimation rate and its ability to store heat. We will extend the current model to include a water ice layer and account for the subsequent heat storage which could possibly follow. For water ice models, a challenge is to reproduce the low brightness temperatures that persist throughout the summer at the residual south polar cap.

  2. Estimating surface sublimation losses from snowpacks in a mountain catchment using eddy covariance and turbulent transfer calculations

    USDA-ARS?s Scientific Manuscript database

    Sublimation is a critical component of the snow cover mass balance. While sublimation can be directly measured using eddy covariance (EC), such measurements are relatively uncommon in complex mountainous environments. EC measurements of surface snowpack sublimation from three consecutive winter sea...

  3. Sublimation characterization and vapor pressure estimation of an HIV nonnucleoside reverse transcriptase inhibitor using thermogravimetric analysis.

    PubMed

    Xie, Minli; Ziemba, Theresa M; Maurin, Michael B

    2003-01-01

    The purpose of this research is to investigate the sublimation process of DPC 963, a second-generation nonnucleoside reverse transcriptase inhibitor for HIV-1 retrovirus, and to better understand the effect of sublimation during active pharmaceutical ingredient (API) manufacture and formulation development, especially the drying processes. Sublimation of DPC 963 at 150 degrees C and above was determined by thermogravimetric analysis-Fourier transform infrared (TGA-FTIR). The rates of sublimation at different temperatures were measured using isothermal TGA. Condensed material was collected and analyzed by differential scanning calorimetry (DSC), x-ray powder diffraction (XRPD), and infrared (IR) spectrometry. Benzoic acid was used as a reference standard to derive a linear logarithmic relationship between sublimation/evaporation rate and vapor pressure specific to the TGA system used in this study. Sublimation and evaporation of DPC 963 were found to follow apparent zero-order kinetics. Using the Eyring equation, the enthalpy and entropy of the sublimation and evaporation processes were obtained. The enthalpies of sublimation and evaporation were found to be 29 and 22 kcal/mol, respectively. The condensed material from the vapor phase was found to exist in 2 physical forms, amorphous and crystalline. Using benzoic acid as a reference standard, vapor pressure of DPC 963 at different temperatures was calculated using the linear logarithmic relationship obtained. DPC 963 undergoes sublimation at appreciable rates at 150 degrees C and above but this is not likely to pose a serious issue during the manufacturing process. Vapor pressure estimation using thermogravimetric analysis provided sufficient accuracy to be used as a fast, simple, and safe alternative to the traditional methods of vapor pressure determination.

  4. Ice sublimation and rheology - Implications for the Martian polar layered deposits

    NASA Technical Reports Server (NTRS)

    Hofstadter, Mark D.; Murray, Bruce C.

    1990-01-01

    If the sublimation and creep of water ice are important processes in the Martian polar layered deposits, ice-rich scenario formation and evolution schemes must invoke a mechanism for the inhibition of sublimation, such as a dust layer derived from the residue of the sublimating deposits. This layer could be of the order of 1 m in thickness. If the deposits are ice-rich, flows of more than 1 km should have occurred. It is noted that the dust particles in question may be cemented by such ice that may be present, but that impurities may also have served to cement dust particles together even in the absence of ice.

  5. Contamination Effects of Getter Ion and Titanium Sublimation Pumped Systems on Optical Surfaces

    NASA Technical Reports Server (NTRS)

    Visentine, James T.; Richmond, Robert G.

    1973-01-01

    Previous studies have indicated that ultraclean vacuum can be produced when titanium sublimation pumps are used in conjunction with getter-ion pumps. Experiments are described in which the degrees of cleanliness of a typical getter-ion, titanium sublimation-pumped system were monitored by measuring the effects of surface contamination on the reflectance of evaporated vacuum ultraviolet mirrors. Results are presented which indicate that severe reflectance losses occurred when startup of a getter-ion pump was initiated at too high a chamber pressure. Significant reflectance losses also occurred as a result of titanium sublimation-pump operation. These data are reviewed and recommendations for improved system performance are presented.

  6. Sublimation rates of carbon monoxide and carbon dioxide from comets at large heliocentric distances

    NASA Technical Reports Server (NTRS)

    Sekanina, Zdenek

    1992-01-01

    Using a simple model for outgassing from a small flat surface area, the sublimation rates of carbon monoxide and carbon dioxide, two species more volatile than water ice that are known to be present in comets, are calculated for a suddenly activated discrete source on the rotating nucleus. The instantaneous sublimation rate depends upon the comet's heliocentric distance and the Sun's zenith angle at the location of the source. The values are derived for the constants of CO and CO2 in an expression that yields the local rotation-averaged sublimation rate as a function of the comet's spin parameters and the source's cometocentric latitude.

  7. Ice sublimation and rheology - Implications for the Martian polar layered deposits

    NASA Technical Reports Server (NTRS)

    Hofstadter, Mark D.; Murray, Bruce C.

    1990-01-01

    If the sublimation and creep of water ice are important processes in the Martian polar layered deposits, ice-rich scenario formation and evolution schemes must invoke a mechanism for the inhibition of sublimation, such as a dust layer derived from the residue of the sublimating deposits. This layer could be of the order of 1 m in thickness. If the deposits are ice-rich, flows of more than 1 km should have occurred. It is noted that the dust particles in question may be cemented by such ice that may be present, but that impurities may also have served to cement dust particles together even in the absence of ice.

  8. Contamination Effects of Getter Ion and Titanium Sublimation Pumped Systems on Optical Surfaces

    NASA Technical Reports Server (NTRS)

    Visentine, James T.; Richmond, Robert G.

    1973-01-01

    Previous studies have indicated that ultraclean vacuum can be produced when titanium sublimation pumps are used in conjunction with getter-ion pumps. Experiments are described in which the degrees of cleanliness of a typical getter-ion, titanium sublimation-pumped system were monitored by measuring the effects of surface contamination on the reflectance of evaporated vacuum ultraviolet mirrors. Results are presented which indicate that severe reflectance losses occurred when startup of a getter-ion pump was initiated at too high a chamber pressure. Significant reflectance losses also occurred as a result of titanium sublimation-pump operation. These data are reviewed and recommendations for improved system performance are presented.

  9. Schiller Goes to the Movies: Locating the Sublime in "Thelma and Louise."

    ERIC Educational Resources Information Center

    Hoyng, Peter

    1997-01-01

    Endeavors to make students aware of similarities between today's movie culture and the theater of the 18th century; parallels between a traditional drama and a movie script; and Schiller's understanding of the sublime. (36 references) (Author/CK)

  10. Imaging the dust sublimation front of a circumbinary disk

    NASA Astrophysics Data System (ADS)

    Hillen, M.; Kluska, J.; Le Bouquin, J.-B.; Van Winckel, H.; Berger, J.-P.; Kamath, D.; Bujarrabal, V.

    2016-04-01

    Aims: We present the first near-IR milli-arcsecond-scale image of a post-AGB binary that is surrounded by hot circumbinary dust. Methods: A very rich interferometric data set in six spectral channels was acquired of IRAS 08544-4431 with the new RAPID camera on the PIONIER beam combiner at the Very Large Telescope Interferometer (VLTI). A broadband image in the H-band was reconstructed by combining the data of all spectral channels using the SPARCO method. Results: We spatially separate all the building blocks of the IRAS 08544-4431 system in our milliarcsecond-resolution image. Our dissection reveals a dust sublimation front that is strikingly similar to that expected in early-stage protoplanetary disks, as well as an unexpected flux signal of ~4% from the secondary star. The energy output from this companion indicates the presence of a compact circum-companion accretion disk, which is likely the origin of the fast outflow detected in Hα. Conclusions: Our image provides the most detailed view into the heart of a dusty circumstellar disk to date. Our results demonstrate that binary evolution processes and circumstellar disk evolution can be studied in detail in space and over time. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 094.D-0865.

  11. Sublimation TiN Coating of RF Power Components

    NASA Astrophysics Data System (ADS)

    Lorkiewicz, J.; Kula, J.; Pszona, S.; Sobczak, J.; Bilinski, A.

    2008-03-01

    Titanium evaporation in a reactive atmosphere of ammonia has been chosen to deposit thin (up to 10 nm) protective surface layers containing titanium nitride and titanium oxinitrides which suppress secondary electron emission. The coating procedure, applied by the author in DESY (Hamburg) for TESLA couplers anti-multipactor protection, has been recently implemented in The Andrzej Soltan Institute for Nuclear Studies (IPJ) where a new coating device is used, equipped with a special titanium sublimation setup in a 100 1 vacuum chamber. Several arrays of cylindrical and coaxial RF coupler windows have been coated so far after optimizing the processing parameters. A check of the obtained surface layers ability to attenuate secondary electron emission has been performed; measurements of the secondary electron yield from TiN layers deposited on alumina samples were done in IPJ on as-delivered coated samples, then after vacuum bake-out and finally after additional electron bombardment of their surfaces. Also chemical composition of the surface layers has been studied using XPS in the Institute of Physical Chemistry (IChF).

  12. Generalized Orbital Projections of a Sublimating Ice Particle

    NASA Technical Reports Server (NTRS)

    Menkin, Evgeny; Bacon, Jack

    2006-01-01

    The issue of orbital debris resulting from human activities in space is a growing concern for the space users' community. Waste generated in Low Earth Orbit (LEO) can stay in orbit for a long time, creating significant hazards for other spacecraft flying at lower intercepting orbits. Many spacecraft, especially crewed vehicles, are required to vent fluids into space. These fluids include propellant, wastewater, excess condensate, and others. It is important to analyze the behavior of particles that result from these activities, since each individual particle is capable of damaging or destroying a spacecraft in a lower, crossing orbit, and such particles are invisible to tracking radar systems on the ground. The deorbit trajectory of an ice particle is complex. It depends on factors including attitude of the vehicle during vent, initial velocities of particles, altitude at which the vent occurred, and numerous evaporation and sublimation factors. These include contamination within the vented water, evolution of bubbles within the clear water, and sun flux factors such as time of the year and current beta angle. The purpose of this study is to examine the influences of these factors on the trajectories of ice particles resulting from condensate water dumps, and to bound the safe trajectories of spacecraft that lie below the venting spacecraft.

  13. Rare earths behaviour during the deposition of volcanic sublimates

    NASA Astrophysics Data System (ADS)

    Censi, P.; Sortino, F.; Zuddas, P.; Saiano, F.; Brusca, L.; Chiavetta, S.; Falcone, E. E.

    2017-02-01

    In this study, the REE distribution between volcanic fluids and related solids in fumaroles with temperatures ranging from approximately 100 to 421 °C was investigated in different geological scenarios. The treatment of geochemical REE data was carried out by calculating the REE enrichment factors (EFREE) relative to the volcanic host rocks in studied sites under the assumption that the REE transport takes place as silicate aerosol in volcanic fluids. Shale-normalised REE concentrations in these fluids have been assessed to investigate whether the REE transport as aqueous complexes in water-saturated volcanic gas is reasonable. The REE behaviour in alkaline condensates according to the above mentioned treatments of geochemical data is very similar, being characterised by positive Ce and Gd anomalies and significant W-type tetrad effects. These evidences suggest that the geochemical behaviour of REE in fumarolic fluids is firstly influenced by the sublimate deposition along the fumarolic conduit or around the vents rather than by the transport mechanism of these elements in volcanic fluids.

  14. Bion and the sublime: the origins of an aesthetic paradigm.

    PubMed

    Civitarese, Giuseppe

    2014-12-01

    In constructing his theory Bion drew on a number of symbolic matrices: psychoanalysis, philosophy, mathematics, literature, aesthetics. The least investigated of these is the last. True, we know that Bion cites many authors of the Romantic period, such as Coleridge, Keats, Blake and Wordsworth, as well as others who were held in high esteem in the Romantic period, such as Milton. However, less is known about the influence exerted on him by the aesthetics of the sublime, which while chronologically preceding Romanticism is in fact one of its components. My working hypothesis is that tracing a number of Bion's concepts back to this secret model can serve several purposes: firstly, it contributes to the study of the sources, and, secondly, it makes these concepts appear much less occasional and idiosyncratic than we might believe, being as they are mostly those less immediately understandable but not less important (O, negative capability, nameless dread, the infinite, the language of achievement, unison etc.). Finally, connecting these notions to a matrix, that is, disclosing the meaning of elements that are not simply juxtaposed but dynamically interrelated, in my view significantly increases not only their theoretical intelligibility but also their usefulness in clinical practice. In conclusion, one could legitimately argue that Bion gradually subsumed all the other paradigms he drew on within the aesthetic paradigm.

  15. Possibility of graphene growth by close space sublimation.

    PubMed

    Sopinskyy, Mykola V; Khomchenko, Viktoriya S; Strelchuk, Viktor V; Nikolenko, Andrii S; Olchovyk, Genadiy P; Vishnyak, Volodymyr V; Stonis, Viktor V

    2014-04-14

    Carbon films on the Si/SiO2 substrate are fabricated using modified method of close space sublimation at atmospheric pressure. The film properties have been characterized by micro-Raman and X-ray photoelectron spectroscopy and monochromatic ellipsometry methods. Ellipsometrical measurements demonstrated an increase of the silicon oxide film thickness in the course of manufacturing process. The XPS survey spectra of the as-prepared samples indicate that the main elements in the near-surface region are carbon, silicon, and oxygen. The narrow-scan spectra of C1s, Si2p, O1s regions indicate that silicon and oxygen are mainly in the SiOx (x ≈ 2) oxide form, whereas the main component of C1s spectrum at 284.4 eV comes from the sp2-hybridized carbon phase. Micro-Raman spectra confirmed the formation of graphene films with the number of layers that depended on the distance between the graphite source and substrate.

  16. Transformation of Polar Ice Sublimate Residue into Martian Circumpolar Sand

    NASA Technical Reports Server (NTRS)

    Saunders, R. S.; Parker, T. J.; Stephens, J. B.; Laue, E. G.; Fanale, F. P.

    1985-01-01

    The experimental demonstration that a credible Martian sand may be formed from dust-bearing ice provides a new set of possible explanations for some of the observed Martian aeolian landforms. It is hypothesized that a light-weight fluffy rind is formed on the polar caps. This could provide material easily entrainable by Martian winds, which generally blow equatorward from the poles. These winds would peel the fluffy rind from the surface of the sublimating summer polar caps and from the equatorward slopes of the polar troughs. These pieces of material would then be rolled into lumps (of high sailarea/mass ratio) by the wind. They would become pigmented as they saltate across the surface, perhaps gathering carbonaceous meteoritic dust or other impurities on their surfaces, or through chemical reactions with the ice-free environment away from their point of origin. Once they became trapped in topographic wind shadows, they would form dune structures because they are hydraulically equivalent to sand particles.

  17. Phase transition and surface sublimation of a mobile Potts model.

    PubMed

    Bailly-Reyre, A; Diep, H T; Kaufman, M

    2015-10-01

    We study in this paper the phase transition in a mobile Potts model by the use of Monte Carlo simulation. The mobile Potts model is related to a diluted Potts model, which is also studied here by a mean-field approximation. We consider a lattice where each site is either vacant or occupied by a q-state Potts spin. The Potts spin can move from one site to a nearby vacant site. In order to study the surface sublimation, we consider a system of Potts spins contained in a recipient with a concentration c defined as the ratio of the number of Potts spins N(s) to the total number of lattice sites N(L)=N(x)×N(y)×N(z). Taking into account the attractive interaction between the nearest-neighboring Potts spins, we study the phase transitions as functions of various physical parameters such as the temperature, the shape of the recipient, and the spin concentration. We show that as the temperature increases, surface spins are detached from the solid phase to form a gas in the empty space. Surface order parameters indicate different behaviors depending on the distance to the surface. At high temperatures, if the concentration is high enough, the interior spins undergo a first-order phase transition to an orientationally disordered phase. The mean-field results are shown as functions of temperature, pressure, and chemical potential, which confirm in particular the first-order character of the transition.

  18. Climatological observations and predicted sublimation rates at Lake Hoare, Antarctica.

    USGS Publications Warehouse

    Clow, G.D.; McKay, C.P.; Simmons, G.M.; Wharton, R.A.

    1988-01-01

    In December 1985, an automated meteorological station was established at Lake Hoare in the dry valley region of Antarctica. Here, we report on the first year-round observations available for any site in Taylor Valley. This dataset augments the year-round data obtained at Lake Vanda (Wright Valley) by winter-over crews during the late 1960s and early 1970s. The mean annual solar flux at Lake Hoare was 92 W m-2 during 1986, the mean air temperature -17.3 degrees C, and the mean 3-m wind speed 3.3 m s-1. The local climate is controlled by the wind regime during the 4-month sunless winter and by seasonal and diurnal variations in the incident solar flux during the remainder of the year. Temperature increases of 20 degrees-30 degrees C are frequently observed during the winter due to strong fo??hn winds descending from the Polar Plateau. A model incorporating nonsteady molecular diffusion into Kolmogorov-scale eddies in the interfacial layer and similarity-theory flux-profiles in the surface sublayer, is used to determine the rate of ice sublimation from the acquired meteorological data. Despite the frequent occurrence of strong winter fo??hns, the bulk of the annual ablation occurs during the summer due to elevated temperatures and persistent moderate winds. The annual ablation from Lake Hoare is estimated to have been 35.0 +/- 6.3 cm for 1986.

  19. Comparison of methods for quantifying surface sublimation over seasonally snow-covered terrain

    USGS Publications Warehouse

    Sexstone, Graham A.; Clow, David W.; Stannard, David I.; Fassnacht, Steven R.

    2016-01-01

    Snow sublimation can be an important component of the snow-cover mass balance, and there is considerable interest in quantifying the role of this process within the water and energy balance of snow-covered regions. In recent years, robust eddy covariance (EC) instrumentation has been used to quantify snow sublimation over snow-covered surfaces in complex mountainous terrain. However, EC can be challenging for monitoring turbulent fluxes in snow-covered environments because of intensive data, power, and fetch requirements, and alternative methods of estimating snow sublimation are often relied upon. To evaluate the relative merits of methods for quantifying surface sublimation, fluxes calculated by the EC, Bowen ratio–energy balance (BR), bulk aerodynamic flux (BF), and aerodynamic profile (AP) methods and their associated uncertainty were compared at two forested openings in the Colorado Rocky Mountains. Biases between methods are evaluated over a range of environmental conditions, and limitations of each method are discussed. Mean surface sublimation rates from both sites ranged from 0.33 to 0.36 mm day−1, 0.14 to 0.37 mm day−1, 0.10 to 0.17 mm day−1, and 0.03 to 0.10 mm day−1 for the EC, BR, BF and AP methods, respectively. The EC and/or BF methods are concluded to be superior for estimating surface sublimation in snow-covered forested openings. The surface sublimation rates quantified in this study are generally smaller in magnitude compared with previously published studies in this region and help to refine sublimation estimates for forested openings in the Colorado Rocky Mountains.

  20. Como Lo Hago Yo: Mielomeningocele En Bolivia

    PubMed Central

    Dabdoub, Carlos F.; Dabdoub, Carlos B.; Villavicencio, Ramiro; Quevedo, Germán

    2014-01-01

    Introducción: Las malformaciones del tubo neural (MTN) representan la segunda causa más frecuente de anomalías congénitas, luego de las cardiopatías. En este grupo se destaca el mielomeningocele (MMC) por su mayor incidencia, y por ser la más incapacitante y la más compleja entre todas las demás malformaciones del sistema nervioso c`entral (SNC). En Bolivia, como en muchos países de Sudamérica, los bajos niveles socio-culturales y la debilidad en el sistema sanitario, hacen que su incidencia y su morbilidad, sean mayores que en las naciones más desarrolladas. Material y Métodos: Se realizó un estudio retrospectivo y descriptivo de 70 casos de MMC, atendidos por un equipo multidisciplinario en el Hospital Universitario Japonés (HUJ) de Santa Cruz de la Sierra, entre 2008-2011. De ellos, 60 fueron intervenidos quirúrgicamente. Resultados: Se realizaron controles prenatales sólo en 27 mujeres (38.6%), diagnosticándose una disrafia espinal en apenas dos casos (7.4%). La edad de ingreso del MMC en su mayoría fue después de las 24 horas (65.6%), predominando su localización en la región lumbosacra (64.3%). De ellos, 67.2% eran abiertos, presentando un 32.9% un daño neurológico motor parcial mientras que 47.1% tenían paraplejia por debajo de la lesión. De los 70 casos, tres (4.3%) no fueron intervenidos, por presentar defectos congénitos severos o estado general grave. Las principales complicaciones posoperatorias inmediatas fueron: dehiscencia de sutura y/o infección de la herida (16.6%), fístula de líquido cefalorraquídeo (LCR) (10%) e infección del SNC (11.7%). La mortalidad general y postoperatoria fue de 7.1% y 3.3%, respectivamente. Al mes de vida presentaban hidrocefalia un 80% de los pacientes operados, colocándose una derivación ventriculoperitoneal (DVP) de presión media. De 9 pacientes que tuvieron un acompanamiento de dos o más años, seis presentaron una médula anclada, que fueron intervenidas quirúrgicamente. Conclusi

  1. Collection-efficient, axisymmetric vacuum sublimation module for the purification of solid materials

    NASA Astrophysics Data System (ADS)

    May, Michael; Paul, Elizabeth; Katovic, Vladimir

    2015-11-01

    A vacuum sublimation module of axisymmetric geometry was developed and employed to purify solid-phase materials. The module provides certain practical advantages and it comprises: a metering valve, glass collector, glass lower body, main seal, threaded bushing, and glass internal cartridge (the latter to contain starting material). A complementary process was developed to de-solvate, sublime, weigh, and collect solid chemical materials exemplified by oxalic acid, ferrocene, pentachlorobenzene, chrysene, and urea. The oxalic acid sublimate was analyzed by titration, melting range, Fourier Transform Infrared (FT-IR) Spectroscopy, cyclic voltammetry, and its (aqueous phase) electrolytically generated gas. The analytical data were consistent with a high-purity, anhydrous oxalic acid sublimate. Cyclic voltammograms of 0.11 mol. % oxalic acid in water displayed a 2.1 V window on glassy carbon electrode beyond which electrolytic decomposition occurs. During module testing, fifteen relatively pure materials were sublimed with (energy efficient) passive cooling and the solid-phase recovery averaged 95 mass %. Key module design features include: compact vertical geometry, low-angle conical collector, uniformly compressed main seal, modest power consumption, transparency, glovebox compatibility, cooling options, and preferential conductive heat transfer. To help evaluate the structural (module) heat transfer, vertical temperature profiles along the dynamically evacuated lower body were measured versus electric heater power: for example, an input of 18.6 W generated a temperature 443-K at the bottom. Experimental results and engineering calculations indicate that during sublimation, solid conduction is the primary mode of heat transfer to the starting material.

  2. Collection-efficient, axisymmetric vacuum sublimation module for the purification of solid materials.

    PubMed

    May, Michael; Paul, Elizabeth; Katovic, Vladimir

    2015-11-01

    A vacuum sublimation module of axisymmetric geometry was developed and employed to purify solid-phase materials. The module provides certain practical advantages and it comprises: a metering valve, glass collector, glass lower body, main seal, threaded bushing, and glass internal cartridge (the latter to contain starting material). A complementary process was developed to de-solvate, sublime, weigh, and collect solid chemical materials exemplified by oxalic acid, ferrocene, pentachlorobenzene, chrysene, and urea. The oxalic acid sublimate was analyzed by titration, melting range, Fourier Transform Infrared (FT-IR) Spectroscopy, cyclic voltammetry, and its (aqueous phase) electrolytically generated gas. The analytical data were consistent with a high-purity, anhydrous oxalic acid sublimate. Cyclic voltammograms of 0.11 mol. % oxalic acid in water displayed a 2.1 V window on glassy carbon electrode beyond which electrolytic decomposition occurs. During module testing, fifteen relatively pure materials were sublimed with (energy efficient) passive cooling and the solid-phase recovery averaged 95 mass %. Key module design features include: compact vertical geometry, low-angle conical collector, uniformly compressed main seal, modest power consumption, transparency, glovebox compatibility, cooling options, and preferential conductive heat transfer. To help evaluate the structural (module) heat transfer, vertical temperature profiles along the dynamically evacuated lower body were measured versus electric heater power: for example, an input of 18.6 W generated a temperature 443-K at the bottom. Experimental results and engineering calculations indicate that during sublimation, solid conduction is the primary mode of heat transfer to the starting material.

  3. LoWMob: Intra-PAN Mobility Support Schemes for 6LoWPAN.

    PubMed

    Bag, Gargi; Raza, Muhammad Taqi; Kim, Ki-Hyung; Yoo, Seung-Wha

    2009-01-01

    Mobility in 6LoWPAN (IPv6 over Low Power Personal Area Networks) is being utilized in realizing many applications where sensor nodes, while moving, sense and transmit the gathered data to a monitoring server. By employing IEEE802.15.4 as a baseline for the link layer technology, 6LoWPAN implies low data rate and low power consumption with periodic sleep and wakeups for sensor nodes, without requiring them to incorporate complex hardware. Also enabling sensor nodes with IPv6 ensures that the sensor data can be accessed anytime and anywhere from the world. Several existing mobility-related schemes like HMIPv6, MIPv6, HAWAII, and Cellular IP require active participation of mobile nodes in the mobility signaling, thus leading to the mobility-related changes in the protocol stack of mobile nodes. In this paper, we present LoWMob, which is a network-based mobility scheme for mobile 6LoWPAN nodes in which the mobility of 6LoWPAN nodes is handled at the network-side. LoWMob ensures multi-hop communication between gateways and mobile nodes with the help of the static nodes within a 6LoWPAN. In order to reduce the signaling overhead of static nodes for supporting mobile nodes, LoWMob proposes a mobility support packet format at the adaptation layer of 6LoWPAN. Also we present a distributed version of LoWMob, named as DLoWMob (or Distributed LoWMob), which employs Mobility Support Points (MSPs) to distribute the traffic concentration at the gateways and to optimize the multi-hop routing path between source and destination nodes in a 6LoWPAN. Moreover, we have also discussed the security considerations for our proposed mobility schemes. The performance of our proposed schemes is evaluated in terms of mobility signaling costs, end-to-end delay, and packet success ratio.

  4. LoWMob: Intra-PAN Mobility Support Schemes for 6LoWPAN

    PubMed Central

    Bag, Gargi; Raza, Muhammad Taqi; Kim, Ki-Hyung; Yoo, Seung-Wha

    2009-01-01

    Mobility in 6LoWPAN (IPv6 over Low Power Personal Area Networks) is being utilized in realizing many applications where sensor nodes, while moving, sense and transmit the gathered data to a monitoring server. By employing IEEE802.15.4 as a baseline for the link layer technology, 6LoWPAN implies low data rate and low power consumption with periodic sleep and wakeups for sensor nodes, without requiring them to incorporate complex hardware. Also enabling sensor nodes with IPv6 ensures that the sensor data can be accessed anytime and anywhere from the world. Several existing mobility-related schemes like HMIPv6, MIPv6, HAWAII, and Cellular IP require active participation of mobile nodes in the mobility signaling, thus leading to the mobility-related changes in the protocol stack of mobile nodes. In this paper, we present LoWMob, which is a network-based mobility scheme for mobile 6LoWPAN nodes in which the mobility of 6LoWPAN nodes is handled at the network-side. LoWMob ensures multi-hop communication between gateways and mobile nodes with the help of the static nodes within a 6LoWPAN. In order to reduce the signaling overhead of static nodes for supporting mobile nodes, LoWMob proposes a mobility support packet format at the adaptation layer of 6LoWPAN. Also we present a distributed version of LoWMob, named as DLoWMob (or Distributed LoWMob), which employs Mobility Support Points (MSPs) to distribute the traffic concentration at the gateways and to optimize the multi-hop routing path between source and destination nodes in a 6LoWPAN. Moreover, we have also discussed the security considerations for our proposed mobility schemes. The performance of our proposed schemes is evaluated in terms of mobility signaling costs, end-to-end delay, and packet success ratio. PMID:22346730

  5. Desorption and sublimation kinetics for fluorinated aluminum nitride surfaces

    SciTech Connect

    King, Sean W. Davis, Robert F.; Nemanich, Robert J.

    2014-09-01

    an additional high temperature peak at 910 °C with E{sub d} = 370 ± 10 kJ/mol that is consistent with both the dehydrogenation of surface AlOH species and H{sub 2} assisted sublimation of AlN. Similarly, N{sub 2} exhibited a similar higher temperature desorption peak with E{sub d} = 535 ± 40 kJ/mol that is consistent with the activation energy for direct sublimation of AlN.

  6. Estimates of the Volume of Snowpack Sublimation in Arizona's Salt River Watershed

    NASA Astrophysics Data System (ADS)

    Svoma, B. M.

    2012-12-01

    The liquid equivalent volumes of snowpack sublimation, melt, and snowfall over the Salt River watershed, a major source of water for the Phoenix metropolitan area, will be estimated using the National Operational Hydrologic Remote Sensing Center's Snow Data Assimilation System (SNODAS) for the nine water years on record (i.e., 2004-2012). SNODAS integrates data from satellites, aircraft, and ground stations with downscaled output from numerical weather prediction models and an energy/mass balance snowpack model. The SNODAS dataset contains daily values of sublimation, snow water equivalent, snowfall, and melt, among other variables, at high (< 1 km2) resolution providing the opportunity to accurately estimate the volumes of snowpack balance variables for regions with complex topography. Snowpack ablation consists of sublimation and melting. Snow particles at sub-freezing temperatures will sublimate rather than melt if surrounded by air that is below the equilibrium water vapor pressure with respect to ice. When sublimation occurs, there is a direct loss of water from the given drainage basin when the vapor is carried away by the prevailing atmospheric flow. Preliminary analyses of water years 2005 (wet El Niño), 2007 (dry El Niño), 2008 (wet La Niña), and 2012 (dry La Niña) suggest that there is a substantial amount of sublimation over the Salt River watershed. From October 1 to April 30, approximately 16 percent of snowfall sublimated during the four years, ranging from approximately 98 million cubic meters (79,884 acre-feet) in water year 2005 to approximately 208 million cubic meters (168,726 acre-feet) in water year 2012. Sublimation is the most prevalent at the highest elevations of the watershed with more than 30 percent of snowfall sublimating at elevations above 2,744 meters above sea level. Of the four years analyzed, the sublimation to snowfall ratio was the highest for the two water years with anomalously high precipitation (i.e, 2005 and 2008). This

  7. Oxidation and sublimation of porous graphite during fiber laser irradiation

    NASA Astrophysics Data System (ADS)

    Phillips, Grady T.; Bauer, William A.; Gonzales, Ashley E.; Herr, Nicholas C.; Perram, Glen P.

    2017-02-01

    Porous graphite plates, cylinders and cones with densities of 1.55-1.82 g/cm3 were irradiated by a 10 kW fiber laser at 0.075 -3.525 kW/cm2 for 120 s to study mass removal and crater formation. Surface temperatures reached steady state values as high as 3767 K. The total decrease in sample mass ranged from 0.06 to 6.29 g, with crater volumes of 0.52 - 838 mm3, and penetration times for 12.7 mm thick plates as short as 38 s. Minor contaminants in the graphite samples produced calcium and iron oxide to be re-deposited on the graphite surface. Significantly increased porosity of the sample is observed even outside of the laser-irradiated region. Total mass removed increases with deposited laser energy at a rate of 4.83 g/MJ for medium extruded graphite with an apparent threshold of 0.15 MJ. Visible emission spectroscopy reveals C2 Swan and CN red, CN violet bands and Li, Na, and K 2P3/2,1/2 - 2S1/2 doublets. The reacting boundary layer is observed using a mid-wave imaging Fourier transform spectrometer (IFTS) at 2 cm-1 spectral resolution, 0.5 mm/pixel spatial resolution, and 0.75 Hz data cube rate. A two-layer radiative transfer model was used to determine plume temperature, CO, and CO2 concentrations from spectral signatures. The new understanding of graphite combustion and sublimation during laser irradiation is vital to the more complex behavior of carbon composites.

  8. LoTi Turns Up the Heat!

    ERIC Educational Resources Information Center

    Moersch, Christopher

    2010-01-01

    When LoTi was first introduced in 1994 as the Levels of Technology Implementation framework, the intent was to create a tool to help district leadership quantify how teachers were using technology in the classroom. After serving the past 15 years as a research framework, self-reporting technology integration survey, and school improvement model,…

  9. The Great Spanish "Le-Lo" Controversy

    ERIC Educational Resources Information Center

    Roldan, Mercedes

    1975-01-01

    The distinction between the clitics "le" and "lo" is different for Peninsular Spanish than for Latin American Spanish but is in both cases systematic. The division in Castilian Spanish is along the line of animate-inanimate. The Latin American division is between accusative and dative case. (TL)

  10. Experimental Study of influence on The Moving of Sublimation Interface by Precooling Rate and Drying Temperature During Freeze-drying

    NASA Astrophysics Data System (ADS)

    Xiao, Xin; Tao, Le-Ren

    2007-06-01

    For complex heat and mass transfer during freeze-drying, the shape and the moving rate of sublimation interface have not been clearly recognized yet. In this paper, Micro-CT scanner was used to follow the moving interface during sublimation. Apple slices cut into 16mm in diameter and 8mm in thickness were used as experimental samples, they were scanned every two hours during sublimation. The scanning images were analyzed and measured, then variation curves of grey value and curves of sublimation rate in two directions were obtained. The moving rates of sublimation interface under various precooling rates and primary drying temperatures were compared. The results show that, heat and mass transfer happens both at the upper and the under surface of the sample. Also it happens at the side surface to some extent. The interface shows as a three-dimensional moving mode, contracts to the geometric centre of the sample and presents an approximately spheral shape. Apple samples frozen at low rate sublimated more quickly than those by high rate. While drying temperature was higher, the sublimation interface moved more quickly. Under slow precooling condition, the sublimation rate rose quickly near the end of sublimation not only in vertical direction, but in horizontal direction.

  11. Mechanism and kinetics for ammonium dinitramide (ADN) sublimation: a first-principles study.

    PubMed

    Zhu, R S; Chen, Hui-Lung; Lin, M C

    2012-11-08

    The mechanism for sublimation of NH(4)N(NO(2))(2) (ADN) has been investigated quantum-mechanically with generalized gradient approximation plane-wave density functional theory calculations; the solid surface is represented by a slab model and the periodic boundary conditions are applied. The calculated lattice constants for the bulk ADN, which were found to consist of NH(4)(+)[ON(O)NNO(2)](-) units, instead of NH(4)(+)[N(NO(2))(2)](-), agree quite well with experimental values. Results show that three steps are involved in the sublimation/decomposition of ADN. The first step is the relaxation of the surface layer with 1.6 kcal/mol energy per NH(4)ON(O)NNO(2) unit; the second step is the sublimation of the surface layer to form a molecular [NH(3)]-[HON(O)NNO(2)] complex with a 29.4 kcal/mol sublimation energy, consistent with the experimental observation of Korobeinichev et al. (10) The last step is the dissociation of the [H(3)N]-[HON(O)NNO(2)] complex to give NH(3) and HON(O)NNO(2) with the dissociation energy of 13.9 kcal/mol. Direct formation of NO(2) (g) from solid ADN costs a much higher energy, 58.3 kcal/mol. Our calculated total sublimation enthalpy for ADN(s) → NH(3)(g) + HON(O)NNO(2)) (g), 44.9 kcal/mol via three steps, is in good agreement with the value, 42.1 kcal/mol predicted for the one-step sublimation process in this work and the value 44.0 kcal/mol computed by Politzer et al. (11) using experimental thermochemical data. The sublimation rate constant for the rate-controlling step 2 can be represented as k(sub) = 2.18 × 10(12) exp (-30.5 kcal/mol/RT) s(-1), which agrees well with available experimental data within the temperature range studied. The high pressure limit decomposition rate constant for the molecular complex H(3)N···HON(O)NNO(2) can be expressed by k(dec) = 3.18 × 10(13) exp (-15.09 kcal/mol/RT) s(-1). In addition, water molecules were found to increase the sublimation enthalpy of ADN, contrary to that found in the ammonium

  12. Sublimation and Irradiation of Glycolaldehyde/Water Ices

    NASA Astrophysics Data System (ADS)

    Burke, Daren; Brown, W. A.; Viti, S.; Woods, P. M.; Slater, B.

    2012-05-01

    There is currently great interest among astronomers and astrobiologists in the inventory of organic molecules in space, in particular in star and planet-forming regions. Observations towards the Galactic Centre have revealed a rich and complex chemistry, from simple organic molecules such as methane (CH4) and methanol (CH3OH) to the recent detection of ethyl formate (C2H5OCHO) and n-propyl cyanide (C3H7CN). Amongst the most important organic species detected in space is glycolaldehyde (CH2OHCHO), an isomer of methyl formate (HCOOCH3) and acetic acid (CH3COOH). Glycolaldehyde is the simplest of the monosaccharide sugars and it reacts with propenal to form ribose, a central constituent of RNA. As a consequence, it is thought that glycolaldehyde may have a role in the origins of life in our universe. We present a detailed investigation of the adsorption and desorption of glycolaldehyde and methyl formate using temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) under ultra-high vacuum. The sublimation of glycolaldehyde/water and methyl formate/water containing ices from a model carbonaceous grain surface (graphite) will be presented, along with kinetic parameters for desorption (such as the binding energy, order of desorption and desorption pre-exponential factor) derived from analysis of TPD. These experimental parameters will be incorporated into astronomical models of star-forming regions. Additional experiments investigating the stability of glycolaldehyde/water containing ices to electron/UV irradiation will also be discussed. Electron irradiation (simulating the effect of cosmic ray ionisation, which produces electrons) and UV irradiation (over a range of wavelengths) is used to examine competing routes for non-thermal desorption, decomposition and formation. RAIRS and TPD will be used to identify any reaction products and to monitor the desorption/decomposition of glycolaldehyde as a function of irradiation time. This

  13. A New Method for Estimating Bacterial Abundances in Natural Samples using Sublimation

    NASA Technical Reports Server (NTRS)

    Glavin, Daniel P.; Cleaves, H. James; Schubert, Michael; Aubrey, Andrew; Bada, Jeffrey L.

    2004-01-01

    We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert were heated to a temperature of 500 C for several seconds under reduced pressure. The sublimate was collected on a cold finger and the amount of adenine released from the samples then determined by high performance liquid chromatography (HPLC) with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from approx. l0(exp 5) to l0(exp 9) E. coli cell equivalents per gram. For most of these samples, the sublimation based cell counts were in agreement with total bacterial counts obtained by traditional DAPI staining. The simplicity and robustness of the sublimation technique compared to the DAPI staining method makes this approach particularly attractive for use by spacecraft instrumentation. NASA is currently planning to send a lander to Mars in 2009 in order to assess whether or not organic compounds, especially those that might be associated with life, are present in Martian surface samples. Based on our analyses of the Atacama Desert soil samples, several million bacterial cells per gam of Martian soil should be detectable using this sublimation technique.

  14. Distributed modelling of climate change impacts on snow sublimation in Northern Mongolia

    NASA Astrophysics Data System (ADS)

    Wimmer, F.; Schlaffer, S.; Aus der Beek, T.; Menzel, L.

    2009-08-01

    Sublimation of snow is an important factor of the hydrological cycle in Mongolia and is likely to increase according to future climate projections. In this study the hydrological model TRAIN was used to assess spatially distributed current and future sublimation rates based on interpolated daily data of precipitation, air temperature, air humidity, wind speed and solar radiation. An automated procedure for the interpolation of the input data is provided. Depending on the meteorological parameter and the data availability for the individual days, the most appropriate interpolation method is chosen automatically from inverse distance weighting, Ordinary Least Squares interpolation, Ordinary or Universal Kriging. Depending on elevation simulated annual sublimation in the period 1986-2006 was 23 to 35 mm, i.e. approximately 80% of total snowfall. Moreover, future climate projections for 2071-2100 of ECHAM5 and HadCM3, based on the A1B emission scenario of the Intergovernmental Panel on Climate Change, were analysed with TRAIN. In the case of ECHAM5 simulated sublimation increases by up to 17% (26...41 mm) while it remains at the same level for HadCM3 (24...34 mm). The differences are mainly due to a distinct increase in winter precipitation for ECHAM5. Simulated changes of the all-season hydrological conditions, e.g. the sublimation-to-precipitation ratio, were ambiguous due to diverse precipitation patterns derived by the global circulation models.

  15. Observations of the northern seasonal polar cap on Mars: I. Spring sublimation activity and processes

    USGS Publications Warehouse

    Hansen, C.J.; Byrne, S.; Portyankina, G.; Bourke, M.; Dundas, C.; McEwen, A.; Mellon, M.; Pommerol, A.; Thomas, N.

    2013-01-01

    Spring sublimation of the seasonal CO2 northern polar cap is a dynamic process in the current Mars climate. Phenomena include dark fans of dune material propelled out onto the seasonal ice layer, polygonal cracks in the seasonal ice, sand flow down slipfaces, and outbreaks of gas and sand around the dune margins. These phenomena are concentrated on the north polar erg that encircles the northern residual polar cap. The Mars Reconnaissance Orbiter has been in orbit for three Mars years, allowing us to observe three northern spring seasons. Activity is consistent with and well described by the Kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere. Three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer: the crest of the dune, the interface of the dune with the interdune substrate, and through polygonal cracks in the ice. Pressurized gas flows through these vents and carries out material entrained from the dune. Furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially-organized channels (“araneiform” terrain), albeit not permanent. Properties of the seasonal CO2 ice layer are derived from timing of seasonal events such as when final sublimation occurs. Modification of dune morphology shows that landscape evolution is occurring on Mars today, driven by seasonal activity associated with sublimation of the seasonal CO2 polar cap.

  16. A neurobiological enquiry into the origins of our experience of the sublime and beautiful

    PubMed Central

    Ishizu, Tomohiro; Zeki, Semir

    2014-01-01

    Philosophies of aesthetics have posited that experience of the sublime—commonly but not exclusively derived from scenes of natural grandeur—is distinct from that of beauty and is a counterpoint to it. We wanted to chart the pattern of brain activity which correlates with the declared intensity of experience of the sublime, and to learn whether it differs from the pattern that correlates with the experience of beauty, reported in our previous studies (e.g., Ishizu and Zeki, 2011). 21 subjects participated in a functional magnetic resonance imaging experiment. Prior to the experiment, they viewed pictures of landscapes, which they rated on a scale of 1–5, with 5 being the most sublime and 1 being the least. This allowed us to select, for each subject, five sets of stimuli—from ones experienced as very sublime to those experienced as not at all sublime—which subjects viewed and re-rated in the scanner while their brain activity was imaged. The results revealed a distinctly different pattern of brain activity from that obtained with the experience of beauty, with none of the areas active with the latter experience also active during experience of the sublime. Sublime and beautiful experiences thus appear to engage separate and distinct brain systems. PMID:25426046

  17. Matrix Sublimation/Recrystallization for Imaging Proteins by Mass Spectrometry at High Spatial Resolution

    PubMed Central

    Yang, Junhai; Caprioli, Richard M.

    2011-01-01

    We have employed matrix deposition by sublimation for protein image analysis on tissue sections using a hydration/recrystallization process that produces high quality MALDI mass spectra and high spatial resolution ion images. We systematically investigated different washing protocols, the effect of tissue section thickness, the amount of sublimated matrix per unit area and different recrystallization conditions. The results show that an organic solvent rinse followed by ethanol/water rinses substantially increased sensitivity for the detection of proteins. Both the thickness of tissue section and amount of sinapinic acid sublimated per unit area have optimal ranges for maximal protein signal intensity. Ion images of mouse and rat brain sections at 50, 20 and 10 µm spatial resolution are presented and are correlated with H&E stained optical images. For targeted analysis, histology directed imaging can be performed using this protocol where MS analysis and H&E staining are performed on the same section. PMID:21639088

  18. The Effect of CO2 Ice Cap Sublimation on Mars Atmosphere

    NASA Technical Reports Server (NTRS)

    Batterson, Courtney

    2016-01-01

    Sublimation of the polar CO2 ice caps on Mars is an ongoing phenomenon that may be contributing to secular climate change on Mars. The transfer of CO2 between the surface and atmosphere via sublimation and deposition may alter atmospheric mass such that net atmospheric mass is increasing despite seasonal variations in CO2 transfer. My study builds on previous studies by Kahre and Haberle that analyze and compare data from the Phoenix and Viking Landers 1 and 2 to determine whether secular climate change is happening on Mars. In this project, I use two years worth of temperature, pressure, and elevation data from the MSL Curiosity rover to create a program that allows for successful comparison of Curiosity pressure data to Viking Lander pressure data so a conclusion can be drawn regarding whether CO2 ice cap sublimation is causing a net increase in atmospheric mass and is thus contributing to secular climate change on Mars.

  19. On the Size Dependences of the Metallic Nanoparticle Evaporation and Sublimation Heats: Thermodynamics and Atomistic Modeling

    NASA Astrophysics Data System (ADS)

    Bembel, A. G.

    2017-02-01

    Size dependences of the nanocrystal sublimation and the evaporation heats of the corresponding nanodrops are investigated using the isothermal molecular dynamics and the tight-binding potential (on examples of Ni and Au nanoparticles). Results of computer simulation demonstrating linear dependences of the evaporation and sublimation heats on the particle reciprocal radius are compared with results of thermodynamic calculations as well as with experimental data for bulk phases of the same metals. It has been found that the size dependences of the evaporation and sublimation heats are directly related with the behavior of the size dependence of the melting heat that in its turn correlates with structural transformations in nanoparticles induced by the change of their size. The conclusion is drawn that there is some characteristic nanoparticle size (of the order of 1 nm) at which its crystal and liquid states become indistinguishable.

  20. Sublimation and reformation of icy grains in the primitive solar nebula

    NASA Technical Reports Server (NTRS)

    Lunine, Jonathan I.; Engel, Steffi; Rizk, Bashar; Horanyi, Mihaly

    1991-01-01

    The quantity of water ice that sublimates during the free fall of grains into the solar nebula from a surrounding interstellar cloud varies from over 90 percent of the grain mass as 30 AU from the nebular center to less than 10 percent at more than 100 AU. Virtually all the water that is sublimated ultimately recondenses, since the cold nebular gas lying beyond 10 AU is unable to hold more than a small portion as vapor. The return of most of the gas to solid phase near the nebular ambient temperature, of about 50 K, may result in at least two grain populations consisting, in one case, of unaltered interstellar grains which did not undergo sublimation, and in the other of water ice which cocondensed with more volatile gases at nebular ambient temperatures to yield volatile-rich amorphous phases.

  1. New method for estimating bacterial cell abundances in natural samples by use of sublimation.

    PubMed

    Glavin, Daniel P; Cleaves, H James; Schubert, Michael; Aubrey, Andrew; Bada, Jeffrey L

    2004-10-01

    We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples, including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert, were heated to a temperature of 500 degrees C for several seconds under reduced pressure. The sublimate was collected on a cold finger, and the amount of adenine released from the samples was then determined by high-performance liquid chromatography with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from approximately 10(5) to 10(9) E. coli cell equivalents per gram. For most of these samples, the sublimation-based cell counts were in agreement with total bacterial counts obtained by traditional DAPI (4,6-diamidino-2-phenylindole) staining.

  2. Conduction type control from n to p type for organic pigment films purified by reactive sublimation

    NASA Astrophysics Data System (ADS)

    Hiramoto, Masahiro; Ihara, Kiyoaki; Fukusumi, Hiroyuki; Yokoyama, Masaaki

    1995-12-01

    The effects of purification by reactive sublimation technique and bromine doping on the Fermi level and the photovoltaic properties of n-type perylene pigment films were investigated. Photovoltage arisen from the Schottky junction between n-type perylene pigment film and Au increased significantly by repeating the train sublimation under methylamine gas atmosphere. This phenomenon was revealed to be due to the negative shift of the Fermi level resulting from the effective removal of unknown but specific impurity acting as an acceptor by reactive sublimation. On the other hand, by bromine doping, Fermi level of the pigment film shifted largely to a positive direction and reached the nearby valence band, while the direction of photocurrent flow arising from the Schottky junction with Au was reversed. This result is a clear demonstration of alternating the type of conduction from n type to p type. This means that the pn control of organic semiconductors is possible.

  3. Sublimation and reformation of icy grains in the primitive solar nebula

    NASA Technical Reports Server (NTRS)

    Lunine, Jonathan I.; Engel, Steffi; Rizk, Bashar; Horanyi, Mihaly

    1991-01-01

    The quantity of water ice that sublimates during the free fall of grains into the solar nebula from a surrounding interstellar cloud varies from over 90 percent of the grain mass as 30 AU from the nebular center to less than 10 percent at more than 100 AU. Virtually all the water that is sublimated ultimately recondenses, since the cold nebular gas lying beyond 10 AU is unable to hold more than a small portion as vapor. The return of most of the gas to solid phase near the nebular ambient temperature, of about 50 K, may result in at least two grain populations consisting, in one case, of unaltered interstellar grains which did not undergo sublimation, and in the other of water ice which cocondensed with more volatile gases at nebular ambient temperatures to yield volatile-rich amorphous phases.

  4. New method for estimating bacterial cell abundances in natural samples by use of sublimation

    NASA Technical Reports Server (NTRS)

    Glavin, Daniel P.; Cleaves, H. James; Schubert, Michael; Aubrey, Andrew; Bada, Jeffrey L.

    2004-01-01

    We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples, including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert, were heated to a temperature of 500 degrees C for several seconds under reduced pressure. The sublimate was collected on a cold finger, and the amount of adenine released from the samples was then determined by high-performance liquid chromatography with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from approximately 10(5) to 10(9) E. coli cell equivalents per gram. For most of these samples, the sublimation-based cell counts were in agreement with total bacterial counts obtained by traditional DAPI (4,6-diamidino-2-phenylindole) staining.

  5. New method for estimating bacterial cell abundances in natural samples by use of sublimation

    NASA Technical Reports Server (NTRS)

    Glavin, Daniel P.; Cleaves, H. James; Schubert, Michael; Aubrey, Andrew; Bada, Jeffrey L.

    2004-01-01

    We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples, including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert, were heated to a temperature of 500 degrees C for several seconds under reduced pressure. The sublimate was collected on a cold finger, and the amount of adenine released from the samples was then determined by high-performance liquid chromatography with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from approximately 10(5) to 10(9) E. coli cell equivalents per gram. For most of these samples, the sublimation-based cell counts were in agreement with total bacterial counts obtained by traditional DAPI (4,6-diamidino-2-phenylindole) staining.

  6. Static sublimation purification process and characterization of LiZnP semiconductor material

    NASA Astrophysics Data System (ADS)

    Montag, Benjamin W.; Reichenberger, Michael A.; Edwards, Nathan; Ugorowski, Philip B.; Sunder, Madhana; Weeks, Joseph; McGregor, Douglas S.

    2015-06-01

    Refinement of the class AIBIICV materials continue as a candidate for solid-state neutron detectors. Such a device would have greater efficiency, in a compact form, than present day gas-filled 3He and 10BF3 detectors. The 6Li(n,t)4He reaction yields a total Q value of 4.78 MeV, larger than 10B, and easily identified above background radiations. Hence, devices composed of either natural Li (nominally 7.5% 6Li) or enriched 6Li (usually 95% 6Li) may provide a semiconductor material for compact high efficiency neutron detectors. A sub-branch of the III-V semiconductors, the filled tetrahedral compounds, AIBIICV, known as Nowotny-Juza compounds, are known for their desirable cubic crystal structure. Starting material was synthesized by combining equimolar portions of Li, Zn, and P sealed under vacuum (10-6 Torr) in quartz ampoules, having boron nitride liners, and subsequently reacted in a compounding furnace (Montag et al., 2015, J. of Cryst. Growth). A static vacuum sublimation in quartz was performed to help purify the synthesized material. The chemical composition of the sublimed material and remaining material was confirmed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Lithium was not detected in the sublimed material, however, approximately stoichiometric concentrations of each constituent element were found in the remaining LiZnP material. X-ray diffraction phase identification scans of the remains material and sublimed material were compared, and further indicated the impurity materials were sublimed away from the synthesized materials. The resulting material from the sublimation process showed characteristics of a higher purity ternary compound.

  7. Crystallization and sublimation of non-racemic mixtures of natural amino acids: a path towards homochirality

    NASA Astrophysics Data System (ADS)

    Tarasevych, Arkadii V.; Guillemin, Jean-Claude

    2012-07-01

    Homochirality of biologically important molecules such as amino acids and sugars is a prerequisite for the origin of life. There are different forces or mechanisms in the Universe to trigger off the primary imbalance in the enantiomeric ratio. Very likely the initial bias of one type of enantiomers over the other on Earth was arisen from the inflow of extraterrestrial matter (carbonaceous meteorites). The phase transitions (crystallization, sublimation) of non-racemic mixtures of enantiomers are ones of the most probable mechanisms for the homochirogenesis[1]. The sublimation, almost uninvestigated subject and forgotten for 30 years, revealed recently a pathway to the enantioenrichment of natural amino acids[2]. Starting from a mixture with a low content of an enantiopure amino acid a partial sublimation gives a considerable enrichment. In our further experiments we combined two first-order phase transitions of amino acid(s) mixtures: crystallization and sublimation. The results show the possibility of the transfer of enantiopurity between different amino acids[3]. Subliming a crystallized mixture of racemic amino acids with an enantiopure one we found that the sublimate is a non-racemic mixture of the same handedness for all components. The significance of the studies can be realized taking into account that just 5 of 22 proteinogenic amino acids are able to homochiral self-organization. The relevance of these studies to the Prebiotic Earth and to the evolution of the single handedness of biological molecules will be discussed. [1] Blackmond, Phil. Trans. R. Soc. B 2011, 366, 2878. [2] Guillemin et al., Chem. Commun. 2010 , 46, 1482. [3] Tarasevych, Guillemin et al., submitted.

  8. PRECISION POINTING OF IBEX-Lo OBSERVATIONS

    SciTech Connect

    Hlond, M.; Bzowski, M.; Moebius, E.; Kucharek, H.; Heirtzler, D.; Schwadron, N. A.; Neill, M. E. O'; Clark, G.; Crew, G. B.; Fuselier, S.; McComas, D. J. E-mail: eberhard.moebius@unh.edu E-mail: stephen.a.fuselier@linco.com E-mail: DMcComas@swri.edu

    2012-02-01

    Post-launch boresight of the IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) is determined based on IBEX-Lo Star Sensor observations. Accurate information on the boresight of the neutral gas camera is essential for precise determination of interstellar gas flow parameters. Utilizing spin-phase information from the spacecraft attitude control system (ACS), positions of stars observed by the Star Sensor during two years of IBEX measurements were analyzed and compared with positions obtained from a star catalog. No statistically significant differences were observed beyond those expected from the pre-launch uncertainty in the Star Sensor mounting. Based on the star observations and their positions in the spacecraft reference system, pointing of the IBEX satellite spin axis was determined and compared with the pointing obtained from the ACS. Again, no statistically significant deviations were observed. We conclude that no systematic correction for boresight geometry is needed in the analysis of IBEX-Lo observations to determine neutral interstellar gas flow properties. A stack-up of uncertainties in attitude knowledge shows that the instantaneous IBEX-Lo pointing is determined to within {approx}0.{sup 0}1 in both spin angle and elevation using either the Star Sensor or the ACS. Further, the Star Sensor can be used to independently determine the spacecraft spin axis. Thus, Star Sensor data can be used reliably to correct the spin phase when the Star Tracker (used by the ACS) is disabled by bright objects in its field of view. The Star Sensor can also determine the spin axis during most orbits and thus provides redundancy for the Star Tracker.

  9. Matrix sublimation method for the formation of high-density amorphous ice

    NASA Astrophysics Data System (ADS)

    Kouchi, A.; Hama, T.; Kimura, Y.; Hidaka, H.; Escribano, R.; Watanabe, N.

    2016-08-01

    A novel method for the formation of amorphous ice involving matrix sublimation has been developed. A CO-rich CO:H2O mixed ice was deposited at 8-10 K under ultra-high vacuum condition, which was then allowed to warm. After the sublimation of matrix CO at 35 K, amorphous ice remained. The amorphous ice formed exhibits a highly porous microscale texture; however, it also rather exhibits a density similar to that of high-density amorphous ice formed under high pressure. Furthermore, unlike conventional vapor-deposited amorphous ice, the amorphous ice is stable up to 140 K, where it transforms directly to cubic ice Ic.

  10. Sublimation of hydrofullerenes C 60H 36 and C 60H 18

    NASA Astrophysics Data System (ADS)

    Dorozhko, P. A.; Lobach, A. S.; Popov, A. A.; Senyavin, V. M.; Korobov, M. V.

    2001-03-01

    Thermal behavior of two hydrofullerenes, C 60H 36 and C 60H 18, was studied by means of Knudsen cell mass-spectrometry and infrared spectroscopy. Vapor pressures and enthalpies of sublimation at T=550-685 K were measured. Sublimation of the hydrofullerenes was accompanied by partial loss of hydrogen. Decomposition of C 60H 36 was confirmed to be a stepwise process with formation of C 60H 18 as an intermediate product. The material of the Knudsen cell strongly affected the partial pressures and mass-spectra of the hydrofullerene vapor species.

  11. Sublimation as a Continuous and Transient Source of Water in Europa's Exosphere

    NASA Astrophysics Data System (ADS)

    Hayne, Paul O.

    2016-10-01

    Europa's crust is composed primarily of water ice, which may be vaporized by sputtering and sublimation when exposed to the jovian radiation environment. Models of H2O in Europa's exosphere have focused primarily on the contribution of sputtering by energetic particles, with globally averaged production rates estimated to be ~1015 H2O m-2 s-1. Although sublimation rates at Europa's average dayside temperature of ~106 K are much lower at ~1010 H2O m-2 s-1, surfaces at low- to mid-latitude experiences temperatures in excess of 130 K, with expected sublimation rates of >1015 H2O m-2 s-1 possible. These production rates would be reduced where the surface ice is mixed with impurities, or through development of a non-ice lag deposit. In addition to the continuous flux due to sublimation, transient outgassing may be caused by exposure of fresh ice to direct sunlight, for example by mass wasting on steep slopes. Here, we revisit the process of sublimation on Europa's surface to quantify possible H2O vapor production on a range of spatial and temporal scales.The model includes solar heating, conduction, and vapor diffusion. Temperatures and sublimation rates are calculated by the instantaneous energy budget within each model layer, and outgassing to the exosphere depends on the surface vapor pressure and molecular thermal velocities. Vapor densities and line-of-sight column abundances can be directly compared to observations. Our results show that for surfaces composed of pure ice, sublimation contributes significant quantities to the dayside exosphere. The production rate declines as a sublimation lag develops, with a characteristic timescale of ~1 - 10 kyr at the equator. Freshly exposed ice may produce localized sources. For example, a fresh exposure of ice at 60° latitude with dimension ~2 km would be expected to produce a line-of-sight column abundance of ~1020 H2O m-2 near the limb. However, expansion of the plume would lead to lower column abundance at higher

  12. Vapor pressures and enthalpies of sublimation of polycyclic aromatic hydrocarbons and their derivatives

    SciTech Connect

    Oja, V.; Suuberg, E.M.

    1998-05-01

    The vapor pressures of a series of polycyclic aromatic hydrocarbons (PAH) and heteroatom-containing PAH have been measured using the Knudsen effusion technique. Aromatic hydrocarbons examined included anthracene, phenanthrene, pyrene, 2,3-benzofluorene, naphthacene, perylene, pentacene, and coronene. Heteroatomic aromatic species examined included phenanthridine, perinaphthenone, 3-hydroxy-1-phenalen-1-one, benz[g]isoquinoline-5,10-dione, 1,2-benzodiphenylene sulfide, 1-hydroxypyrene, and 6,11-dihydroxy-5,12-naphthacenedione. The measurements were all made in the solid sublimation regime, and enthalpies of sublimation were calculated from the Clausius-Clapeyron equation.

  13. On the sublimation of blowing snow and of snow in canopies

    NASA Astrophysics Data System (ADS)

    Taylor, P. A.; Simon, K.; Gordon, M.; Weng, W.

    2003-04-01

    Tests have been made within the Canadian Land Surface Scheme (CLASS) of various parameterizations of sublimation of blowing snow, and tested in the context of data from weather stations (Goose Bay and Resolute) in northern Canada. We will focus on parameterization schemes based on results obtained with the PIEKTUK model of blowing snow. In addition we will present preliminary results concerning the parameterization of sublimation of snow caught in tree canopies, using schemes similar to those for evaporation from wet canopies. This is considered to be a major factor in the water budgets of forested areas in northern Canada.

  14. Recommendations for a Kalman filter to estimate and control freeze and sublime rates of gaseous diffusion plant freezer/sublimer systems

    SciTech Connect

    Ruppel, F.R.

    1992-09-01

    A signal is required to control the flow of UF{sub 6} in gaseous diffusion plant freezer/sublimer systems. The original strategy envisioned for deriving a flow signal was to take the derivative of the freezer/sublimer weigh cell signal. However, the derivative of the digitized weight signal is noisy, preventing good control. In addition, a disturbance is introduced into the weight derivative signal because a refrigerant is circulated through a shell-and-tube heat exchanger inside the freezer/sublimer. The weight of the refrigerant is included in the weight measured by the weigh cell. If the circulation rate of the refrigerant is not steady state, a disturbance exists. Measurements of upstream pressure, vessel pressure, and output to the system control valve are available to the control system. Thus, if the flow through the control valve is characterized properly by these measurements, a Kalman filter can be used in conjunction with these auxiliary inputs and the weigh cell input to overcome the noise and disturbance problem and provide an improved estimate of flow rate. A discussion of the development of a Kalman filter that could be used for this application is given, and recommendations are given for its implementation.

  15. Undergraduate Laboratory Experiment Facilitating Active Learning of Concepts in Transport Phenomena: Experiment with a Subliming Solid

    ERIC Educational Resources Information Center

    Utgikar, Vivek P.

    2015-01-01

    An experiment based on the sublimation of a solid was introduced in the undergraduate Transport Phenomena course. The experiment required the students to devise their own apparatus and measurement techniques. The theoretical basis, assignment of the experiment, experimental results, and student/instructor observations are described in this paper.…

  16. Source of slow lithium atoms from Ne or H2 matrix isolation sublimation

    NASA Astrophysics Data System (ADS)

    Sacramento, R. L.; Alves, B. X.; Almeida, D. T.; Wolff, W.; Li, M. S.; Cesar, C. L.

    2012-04-01

    We have studied, via laser absorption spectroscopy, the velocity distribution of 7Li atoms released from cryogenic matrices of solid neon or molecular hydrogen. The Li atoms are implanted into the Ne or H2 matrices - grown onto a sapphire substrate - by laser ablation of a solid Li or LiH precursor. A heat pulse is then applied to the sapphire substrate sublimating the matrix together with the isolated atoms. With a NiCr film resistor deposited directly onto the sapphire substrate we are able to transfer high instantaneous power to the matrix, thus reaching a fast sublimation regime. In this regime the Li atoms can get entrained in the released matrix gas, and we were also able to achieve matrix sublimation times down to 10 μs for both H2 or Ne matrix, enabling us to proceed with the trapping of the species of our interest such as atomic hydrogen, lithium, and molecules. The sublimation of the H2 matrix, with its large center-of-mass velocity, provides evidence for a new regime of one-dimensional thermalization. The laser ablated Li seems to penetrate the H2 matrix deeper than it does in Ne.

  17. How to Kill a Journalism School: The Digital Sublime in the Discourse of Discontinuance

    ERIC Educational Resources Information Center

    McDevitt, Michael; Sindorf, Shannon

    2012-01-01

    The authors argue that journalism's uncertain identity in academia has made it vulnerable to unreflective instrumentalism in the digital era. They show how instrumentalism intertwined with the digital sublime constitutes a rhetorically resonate rationale for closing a journalism school. Evidence comes from documents and testimony associated with…

  18. Using Mass Transport to Guide the Purification of Small Molecule Organic Semiconductors via Sublimation

    NASA Astrophysics Data System (ADS)

    Morgan, Nathan T.; Zhang, Yi; Grandbois, Matthew L.; Bell, Bruce M.; Holmes, Russell J.; Cussler, E. L.

    2015-03-01

    Organic electronic materials have garnered considerable commercial attention for next generation display and solid-state lighting applications. Widespread adoption of these technologies is slowed by considerable production costs, partially due to an expensive purification step. This work explores the current method of industrial purification, thermal gradient sublimation, in order to isolate the fundamental mechanisms limiting sublimation rate and controlling product deposition. For the archetypical hole transport materials, N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPD) and 4,4',4''-tris(carbazol-9-yl) triphenylamine (TCTA), a combination of viscous flow and physical vapor deposition are shown to be rate-limiting at constant sublimation temperature. Surprisingly, diffusion within the solid feed, reaction at the feed particle surface, and mass transfer within the bed of feed particles are not rate limiting in the case. This mechanism is different from that which is observed in many industrial sublimation systems. These results can be used to guide the design and operation of future large-scale purification systems, which are critical for the widespread adoption of organic optoelectronic devices.

  19. Martian pedestal craters: Marginal sublimation pits implicate a climate-related formation mechanism

    NASA Astrophysics Data System (ADS)

    Kadish, Seth J.; Head, James W.; Barlow, Nadine G.; Marchant, David R.

    2008-08-01

    Pedestal craters on Mars are defined by an outward-facing scarp forming a plateau perched tens of meters above the surrounding terrain. Their origin has been attributed to impact armoring of the surface and subsequent removal of inter-crater terrain by either eolian deflation or sublimation of an ice-rich substrate. We identified 2696 pedestal craters between ~60°N and 60°S latitude; 98% are poleward of 33°N and 40°S. The majority of pedestal crater margins are smoothly sloped, but ~3%, concentrated in Utopia Planitia and Malea Planum, display distinctive marginal pits. These pedestal crater scarps are anomalously tall (usually >80-100 m) and the pits resemble sublimation depressions seen on Earth and elsewhere on Mars, providing evidence for sublimation of volatiles in the scarp, where the armored surface has tapered. The pitted scarps provide insight into the origin of the general pedestal crater population, favoring formation via deposition of a volatile-rich substrate, impact armoring, and sublimation of intervening volatiles. Crater densities and overlapping pedestal craters suggest multiple periods of emplacement and loss of these climate-related, latitude-dependent deposits throughout the Amazonian.

  20. Undergraduate Laboratory Experiment Facilitating Active Learning of Concepts in Transport Phenomena: Experiment with a Subliming Solid

    ERIC Educational Resources Information Center

    Utgikar, Vivek P.

    2015-01-01

    An experiment based on the sublimation of a solid was introduced in the undergraduate Transport Phenomena course. The experiment required the students to devise their own apparatus and measurement techniques. The theoretical basis, assignment of the experiment, experimental results, and student/instructor observations are described in this paper.…

  1. How to Kill a Journalism School: The Digital Sublime in the Discourse of Discontinuance

    ERIC Educational Resources Information Center

    McDevitt, Michael; Sindorf, Shannon

    2012-01-01

    The authors argue that journalism's uncertain identity in academia has made it vulnerable to unreflective instrumentalism in the digital era. They show how instrumentalism intertwined with the digital sublime constitutes a rhetorically resonate rationale for closing a journalism school. Evidence comes from documents and testimony associated with…

  2. New advanced BARC and gap fill materials based on sublimate reduction for 193nm lithography

    NASA Astrophysics Data System (ADS)

    Takei, Satoshi; Shinjo, Tetsuya; Sakaida, Yasushi; Horiguchi, Yusuke; Nakajima, Yasuyuki

    2006-03-01

    Innovative technologies are required by integrated circuit manufacturers to create smaller feature sizes on chips. According to the semiconductor roadmap, feature sizes are slated to be as small as 45nm in 2007, and sizes will be continued to decrease in the following years. Suitable absorbance, Lower etch resistance, straight photoresist profiles, wider D.O.F., thinner film thickness, more effective barrier properties to reduce resist poisoning, and sublimate reduction for defect free coating are the major concerns to be taken into consideration for new BARC and gap fill materials. In this paper, the study of sublimate reduction in the new BARC and gap fill materials was investigated. The effect of sublimate reduction from BARC in bake process is related to decrease defect number. We will introduce new BARC and gap fill material consisted of the polymers with self crosslink-reaction system. In addition of sublimate reduction data, resist profiles and 130 nm via fill performance in via- first dual damascene process presented here would show clearly these materials are ready to be investigated into mass production of 90 nm node IC devices and beyond.

  3. Sublimation-induced orbital perturbations of extrasolar active asteroids and comets: application to white dwarf systems

    NASA Astrophysics Data System (ADS)

    Veras, Dimitri; Eggl, Siegfried; Gänsicke, Boris T.

    2015-09-01

    The metal budgets in some white dwarf (WD) atmospheres reveal that volatile-rich circumstellar bodies must both exist in extrasolar systems and survive the giant branch phases of stellar evolution. The resulting behaviour of these active asteroids or comets which orbit WDs is not well-understood, but may be strongly influenced by sublimation due to stellar radiation. Here we develop a model, generally applicable to any extrasolar system with a main-sequence or WD star, that traces sublimation-induced orbital element changes in approximately km-sized extrasolar minor planets and comets travelling within hundreds of au. We derive evolution equations on orbital time-scales and for arbitrarily steep power-law sublimation dependences on distance, and place our model in a Solar system context. We also demonstrate the importance of coupling sublimation and general relativity, and the orbital consequences of outgassing in arbitrary directions. We prove that non-gravitational accelerations alone cannot result in orbit crossing with the WD disruption radius, but may shrink or expand the orbit by up to several au after a single pericentre passage, potentially affecting subsequent interactions with remnant debris and planets. Our analysis suggests that extant planets must exist in polluted WD systems.

  4. Arrays of widely spaced atomic steps on Si(1 1 1) mesas due to sublimation

    NASA Astrophysics Data System (ADS)

    Chang, Kee-Chul; Blakely, Jack M.

    2005-10-01

    Steps with spacings of microns form on top of mesas fabricated on Si(1 1 1) that is annealed at temperatures where sublimation becomes important. Upon annealing, mesas first develop ridges along their edges, effectively creating craters which then become step-free by a step flow process described in the literature [S. Tanaka, C.C. Umbach, J.M. Blakely, R.M. Tromp, M. Mankos, Appl. Phys. Lett. 69 (9) (1996) 1235; Y. Homma, N. Aizawa, T. Ogino, Jpn. J. Appl. Phys. 35 (2B) (1996) L241]. Due to the miscut of the average surface from (1 1 1), ridge breakdown occurs on one edge of each mesa as sublimation proceeds. The breakdown point then acts as a source of steps which spread out over the mesa surface. The distribution of steps in the resulting step train depends on the sublimation rate, direct step-step interaction and the diffusive exchange of atoms among the steps. Insight into the role of these processes on the self-organization of the wide terrace distributions is provided by computer simulations using BCF (Burton, Cabrera and Frank) theory. This shows that step spacing can be controlled by varying the annealing temperature and the deposition flux. Comparison of the experimental and predicted step distributions suggest that the dynamics of the widely spaced steps are sublimation limited.

  5. Sublimation of ice-tholins mixtures: A morphological and spectro-photometric study

    NASA Astrophysics Data System (ADS)

    Poch, Olivier; Pommerol, Antoine; Jost, Bernhard; Carrasco, Nathalie; Szopa, Cyril; Thomas, Nicolas

    2016-03-01

    Sublimation, the direct transition from solid to gas phase, is a process responsible for shaping and changing the reflectance properties of many Solar System surfaces. In this study, we have characterized the evolution of the structure/texture and of the visible and near-infrared (VIS-NIR) spectral reflectance of surfaces made of water ice mixed with analogues of complex extraterrestrial organic matter, named tholins, under low temperature (<-70 °C) and pressure (10-5 mbar) conditions. The experiments were carried out in the SCITEAS simulation setup recently built as part of the Laboratory for Outflow Studies of Sublimating Materials (LOSSy) at the University of Bern (Pommerol, A. et al. [2015a]. Planet. Space Sci. 109-110, 106-122). As the water ice sublimated, we observed in situ the formation of a sublimation lag deposit made of a water-free porous (>90% porosity) network of organic filaments on top of the ice. The temporal evolution of the tholins and water ice spectral features (reflectance at the absorption bands wavelengths, red slope, from 0.40 to 1.90 μm) are analyzed throughout the sublimation of the samples. We studied how different mixtures of tholins with water (0.1 wt.% tholins as coating or inclusions within the water particles), and different ice particle sizes (4.5 ± 2.5 or 67 ± 31 μm) influence the morphological and spectral evolutions of the samples. The sublimation of the ice below the mantle produces a gas flow responsible for the ejection of mm to cm-sized fragments of the deposit in outbursts-like events. The results show remarkable differences between these samples in term of mantle structure, speed of mantle building, rates and surface area of mantle ejections. These data provide useful references for interpreting remote-sensing observations of icy Solar System surfaces, in particular the activity of comet nuclei where sublimation of organic-rich ices and deposition of organic-dust particles likely play a major role. Consequently, the

  6. Sublimation of natural amino acids and induction of asymmetry by meteoritic amino acids

    NASA Astrophysics Data System (ADS)

    Tarasevych, Arkadii V.; Guillemin, Jean-Claude

    It is believed that the homochirality of building blocks of life like amino acids (AAs) and sugars is a prerequisite requirement for the origin and evolution of life. Among different mechanisms that might have triggered the initial disparity in the enantiomeric ratio on the primitive Earth, the key roles were assigned to: (i) local chiral symmetry breaking and (ii) the inflow of extraterrestrial matter (eg the carbonaceous meteorites containing non-racemic AAs). Recently it has been revealed that sublimation, a subject almost completely neglected for a long time, gives a pathway to enantioenrichment of natural AAs (1,2 and references herein). Sublimation is however one of the key physical processes that occur on comets. Starting from a mixture with a low content of an enantiopure AA, a partial sublimation gives an important enrichment of the sublimate (1,2). The resulted disparity in the ratio between enantiomers of a partial sublimate is determined by the crystalline nature of the starting mixture: we observed a drastic difference in the behavior of (i) mixtures based on true racemic compounds and (ii) mechanical mixtures of two enantiopure solid phases. On the other hand, combination of crystallization and sublimation can lead to segregation of enantioenriched fractions starting from racemic composition of sublimable aliphatic AAs (Ala, Leu, Pro, Val) in mixtures with non-volatile enantiopure ones (Asn, Asp, Glu, Ser, Thr) (3). The resulted sense of chirality correlates with the handedness of the non-volatile AAs: the observed changes in enantiomeric ratios clearly demonstrate the preferential homochiral interactions and a tendency of natural amino acids to homochiral self-organization. It is noteworthy that just these 5 (Asn, Asp, Glu, Ser, Thr) out of 22 proteinogenic amino acids are able to local symmetry breaking. On the other hand, recent data on the enantiomeric composition of the Tagish Lake, a C2-type carbonaceous meteorite, revealed a large L

  7. The Evolution of Starspots on LO Pegasi

    NASA Astrophysics Data System (ADS)

    Harmon, Robert O.; Cochran, Mallory; Shank, Derek; Sweeney, Nicholas; Vesa, Oana

    2017-01-01

    LO Pegasi is an ultrarotator (P = 10.1538 hr) and young solar analog that exibits large starspots on its surface. Starspots are regions of strong magnetic field analogous to sunspots that inhibit convective transport of energy from deeper layers, causing the spots to be cooler and thus darker than the surrounding photosphere. The star's brightness varies as the spots are carried into and out of view of Earth by the star's rotation, so that photometry can provide insight into their characteristics. The amount of rotational modulation depends on the sizes, shapes, and locations of the spots, along with the inclination of the rotation axis to the line of sight, the brightness contrast between the spots and the rest of the surface, and the amount of limb darkening. The brightness contrast and limb darkening differ amond different photometric filter passbands, such that multi-filter observations provide additional information about spot latitudes compared to single-filter observations. We present surface images of LO Pegasi based on an indirect light-curve inversion algorithm applied to BVRI photometry obtained at Perkins Observatory in Delaware, OH from 2006-2016, which include variations in the size of a polar spot deduced from year-to-year variations in the star's average brightness.

  8. Lo Gnomone Clementino Astronomia Meridiana in Basilica

    NASA Astrophysics Data System (ADS)

    Sigismondi, Costantino

    2014-05-01

    Costruito per chiara volontà del papa 70 anni dopo il caso Galileo, lo Gnomone Clementino è un grande telescopio solare che non fa uso di lenti a 92 anni dall’invenzione del cannocchiale. Queste due caratteristiche basterebbero da sole a giustificare l’interesse verso questo strumento. L’astronomia meridiana è alla base dell’astrometria e dell’astrofisica moderna. Lo Gnomone Clementino sta oggi all’astronomia, come il veliero “Amerigo Vespucci” sta alla Marina Italiana. E’ possibile svolgere ogni genere di osservazione e studio su questo strumento, e dal 2002 vi tengo lezioni teorico-pratiche del corso di Storia dell’Astronomia e La Terra nel Sistema Solare della Sapienza, Università di Roma, Facoltà di Lettere e Filosofia. Questo testo aggiunge alcuni tasselli alla ricerca storica sulla meridiana, appoggiandosi, com’è naturale, sulle spalle di giganti che mi hanno preceduto in questi studi. In particolare la misura dell’azimut della meridiana, ed il suo inquadramento tra gli strumenti simili ed alcuni studi di astrometria sui dati del 1701-1703 di Bianchini, che sono apparsi fin’ora soltanto su riviste specializzate ed in Inglese vengono qui proposti in Italiano e semplificati, per valorizzare sempre più questa straordinaria opera d’arte e di scienza.

  9. Static sublimation purification process and characterization of LiZnAs semiconductor material

    NASA Astrophysics Data System (ADS)

    Montag, Benjamin W.; Reichenberger, Michael A.; Edwards, Nathaniel S.; Ugorowski, Philip B.; Sunder, Madhana; Weeks, Joseph; McGregor, Douglas S.

    2016-03-01

    Refinement of the class AIBIICV materials continue as a candidate for solid-state neutron detectors. Such a device would have greater efficiency, in a compact form, than present day gas-filled 3He and 10BF3 detectors. The 6Li(n,t)4He reaction yields a total Q value of 4.78 MeV, larger than 10B, and easily identified above background radiations. Hence, devices composed of either natural Li (nominally 7.5% 6Li) or enriched 6Li (usually 95% 6Li) may provide a semiconductor material for compact high efficiency neutron detectors. A sub-branch of the III-V semiconductors, the filled tetrahedral compounds, AIBIICV, known as Nowotny-Juza compounds, are known for their desirable cubic crystal structure. Starting material was synthesized by equimolar portions of Li, Zn, and As sealed under vacuum (10-6 Torr) in quartz ampoules with a boron nitride lining, and reacted in a compounding furnace [1]. The synthesized material showed signs of high impurity levels from material and electrical property characterization. In the present work, a static vacuum sublimation of synthesized LiZnAs loaded in a quartz vessel was performed to help purify the synthesized material. The chemical composition of the sublimed material and remains material was confirmed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Lithium was not detected in the sublimed material, however, near stoichiometric amounts of each constituent element were found in the remains material for LiZnAs. X-ray diffraction phase identification scans of the remains material and sublimed material were compared, and further indicated the impurity materials were removed from the synthesized materials. The remaining powder post the sublimation process showed characteristics of a higher purity ternary compound.

  10. Preparation of highly porous gastroretentive metformin tablets using a sublimation method.

    PubMed

    Oh, Tack-Oon; Kim, Ju-Young; Ha, Jung-Myung; Chi, Sang-Cheol; Rhee, Yun-Seok; Park, Chun-Woong; Park, Eun-Seok

    2013-04-01

    The present investigation is aimed to formulate floating gastroretentive tablets containing metformin using a sublimation material. In this study, the release of the drug from a matrix tablet was highly dependent on the polymer concentrations. In all formulations, initial rapid drug release was observed, possibly due to the properties of the drug and polymer. The effect of the amount of PEO on swelling and eroding of the tablets was determined. The water-uptake and erosion behavior of the gastroretentive (GR) tablets were highly dependent on the amount of PEO. The water-uptake increased with increasing PEO concentration in the tablet matrix. The weight loss from tablets decreased with increasing amounts of PEO. Camphor was used as the sublimation material to prepare GR tablets that are low-density and easily floatable. Camphor was changed to pores in the tablet during the sublimation process. SEM revealed that the GR tablets have a highly porous morphology. Floating properties of tablets and tablet density were affected by the sublimation of camphor. Prepared floating gastroretentive tablets floated for over 24 h and had no floating lag time. However, as the amount of camphor in the tablet matrix increased, the crushing strength of the tablet decreased after sublimation. Release profiles of the drug from the GR tablets were not affected by tablet density or porosity. In pharmacokinetic studies, the mean plasma concentration of the GR tablets after oral administration was greater than the concentration of glucophase XR. Also, the mean AUC(0-∞) values for the GR tablets were significantly greater than the plasma concentrations of glucophase XR.

  11. Starspots on LO Pegasi, 2006-2014

    NASA Astrophysics Data System (ADS)

    Harmon, Robert O.; Berry, Dominique; Chalmers, Mark; Denison, Josh; Stevens, Don; Yuhas, Kaylee

    2015-01-01

    BVRI light curves of LO Pegasi obtained at Perkins Observatory (Ohio Wesleyan University) from 2006-2014 were used to study the evolution of starspots on its surface over that interval. We present surface maps obtained via a constrained non-linear inversion algorithm that uses variations in limb darkening as seen through different filters to improve the latitude resolution of the reconstructions. In addition, a detailed period analysis of the entire data set using the ANOVA method was performed to search for variations associated with differential rotation. No evidence of period change was found, as the periods for each year were equal to within their uncertainties. For the data set as a whole, the period of rotation was determined to be 10.1538 ± 0.0009 hr, in agreement with previously published results.

  12. Starspots on LO Pegasi, 2006-2015

    NASA Astrophysics Data System (ADS)

    Harmon, Robert O.; Chalmers, Mark; Geda, Robel; Henry, Brandi; Sliupas, Viesulas

    2016-01-01

    LO Pegasi is a rapidly rotating (P = 10.154 hr) young solar analog (spectral class K5-7V) variable star of BY Dra type that exhibits dark starspots on its surface that modulate its brightness as they are carried into and out of view by the star's rotation. Surface maps of the spot distribution were produced based on BVRI photometry obtained at Perkins Observatory from 2006-2015. The maps were generated from the light curves via a non-linear inversion algorithm that uses the differences in the limb darkening through different filter passbands to improve the latitude resolution of the maps. We present an analysis of variations in the size of a polar spot suggested by changes in the average brightness and the amplitude of the rotational modulation from year to year.

  13. "Back-fire to lust": G. Stanley Hall, sex-segregated schooling, and the engine of sublimation.

    PubMed

    Graebner, William

    2006-08-01

    G. Stanley Hall was an advocate of sex-segregated schooling long after most Americans had accepted coeducation. His position was based in part on personal experience: observations of his father and mother, a repressed and guilt-ridden boyhood sexuality, and his conviction that his own career success was a product of sublimated sexual desire, of erotic energy converted into mental energy. Hall theorized that coeducation put sublimation at risk, and that sex-segregated schools, by contributing to proper gendered development and by prolonging and sublimating the sexual tensions of adolescence, would produce social progress.

  14. Adamantane derivatives of sulfonamides: sublimation, solubility, solvation and transfer processes in biologically relevant solvents.

    PubMed

    Perlovich, G L; Volkova, T V; Sharapova, A V; Kazachenko, V P; Strakhova, N N; Proshin, A N

    2016-04-07

    Eight adamantane derivatives of sulfonamides were synthesized and characterized. Temperature dependencies of saturation vapor pressure were obtained using the transpiration method and thermodynamic functions of the sublimation processes were calculated. Solubility values of the selected compounds in buffer (pH 7.4), 1-octanol and 1-hexane were determined at different temperatures using the isothermal saturation method. Thermophysical characteristics of fusion processes (melting points and fusion enthalpies) of the substances were studied using the DSC method. Transfer processes from buffer to 1-octanol, from buffer to 1-hexane and 1-hexane to 1-octanol were analyzed. The impact of the molecules' structural modification on sublimation, solubility and solvation/hydration processes in the solvents was studied. Correlation equations connecting the thermodynamic functions with physicochemical descriptors were obtained.

  15. THE EFFECTS ON BIOLOGICAL MATERIALS OF FREEZING AND DRYING BY VACUUM SUBLIMATION

    PubMed Central

    Greiff, Donald; Pinkerton, Henry

    1954-01-01

    A vacuum sublimation apparatus is described which will permit, (a) the removal of water from virus suspensions at temperatures ranging down to –80°C., (b) continuous operation with a minimum of attention from the investigator, (c) sealing off of samples at operating pressures (10–5 mm. Hg), (d) simultaneous lyophilization of aliquot samples at different temperatures, (e) isolation of a portion of the apparatus without disturbing the remainder of the system, and (f) determination of the end-point of sublimation without disturbing the samples. The time required for drying 0.1 ml. of influenza virus suspension was shown to increase markedly with decrease of temperature, 8 days being required for dehydration at –80°C. in contrast to 2 days at –30°C. and 1 day at 0°C. PMID:13163340

  16. Dehydration polycondensation of dicarboxylic acids and diols using sublimating strong brønsted acids.

    PubMed

    Moyori, Takaya; Tang, Tang; Takasu, Akinori

    2012-05-14

    We investigated catalytic activities of strong brønsted acids for dehydration polycondensations of dicarboxylic acids and diols, which were carried out at low temperature (<100 °C) under reduced pressure (0.3-3 mmHg). Strong Brønsted acids, bis(perfluoroalkanesulfonyl)imide and perfluoroalkanesulfonic acid, showed higher activity than p-toluenesulfonic acid or rare-earth catalysts at 60 °C. In particular, bis(nonafluorobutanesulfonyl)imide (Nf(2)NH) showed the highest activity to synthesize not only aliphatic polyester (M(n) > 19000) but also aromatic polyester (M(n) > 7000). The used Nf(2)NH was sublimated from the reaction flask during polycondensation, and the sublimate, Nf(2)NH, was extra pure so that we can reuse the catalyst without loss of the activity in the dehydration polycondensations.

  17. Practical sublimation source for large-scale chromium gettering in fusion devices

    SciTech Connect

    Simpkins, J.E.; Emerson, L.C.; Mioduszewski, P.K.

    1983-01-01

    This paper describes the technique of chromium gettering with a large-scale sublimation source which resembles in its design the VARIAN Ti-Ball. It consists of a hollow chromium sphere with a diameter of approximately 3 cm and an incandescent filament for radiation heating from inside the ball. While the fabrication of the source is described in a companion paper, we discuss here the gettering technique. The experimental arrangement consists of an UHV system instrumented for total- and partial-pressure measurements, a film-thickness monitor, thermocouples, an optical pyrometer, and appropriate instrumentation to measure the heating power. The results show the temperature and corresponding sublimation rate of the Cr-Ball as function of input power. In addition, an example of the total pumping speed of a gettered surface is shown.

  18. Controlling Gaussian and mean curvatures at microscale by sublimation and condensation of smectic liquid crystals

    NASA Astrophysics Data System (ADS)

    Kim, Dae Seok; Cha, Yun Jeong; Kim, Mun Ho; Lavrentovich, Oleg D.; Yoon, Dong Ki

    2016-01-01

    Soft materials with layered structure such as membranes, block copolymers and smectics exhibit intriguing morphologies with nontrivial curvatures. Here, we report restructuring the Gaussian and mean curvatures of smectic A films with free surface in the process of sintering, that is, reshaping at elevated temperatures. The pattern of alternating patches of negative, zero and positive mean curvature of the air-smectic interface has a profound effect on the rate of sublimation. As a result of sublimation, condensation and restructuring, initially equilibrium smectic films with negative and zero Gaussian curvature are transformed into structures with pronounced positive Gaussian curvature of layers packing, which are rare in the samples obtained by cooling from the isotropic melt. The observed relationship between the curvatures, bulk elastic behaviour and interfacial geometries in sintering of smectic liquid crystals might pave the way for new approaches to control soft morphologies at micron and submicron scales.

  19. Water Drops Dancing on Ice: How Sublimation Leads to Drop Rebound

    NASA Astrophysics Data System (ADS)

    Antonini, C.; Bernagozzi, I.; Jung, S.; Poulikakos, D.; Marengo, M.

    2013-07-01

    Drop rebound is a spectacular event that appears after impact on hydrophobic or superhydrophobic surfaces but can also be induced through the so-called Leidenfrost effect. Here we demonstrate that drop rebound can also originate from another physical phenomenon, the solid substrate sublimation. Through drop impact experiments on a superhydrophobic surfaces, a hot plate, and solid carbon dioxide (commonly known as dry ice), we compare drop rebound based on three different physical mechanisms, which apparently share nothing in common (superhydrophobicity, evaporation, and sublimation), but lead to the same rebound phenomenon in an extremely wide temperature range, from 300°C down to even below -79°C. The formation and unprecedented visualization of an air vortex ring around an impacting drop are also reported.

  20. Darwin's sublime: the contest between reason and imagination in On the Origin of Species.

    PubMed

    Bradley, Benjamin Sylvester

    2011-01-01

    Recent Darwin scholarship has provided grounds for recognising the Origin as a literary as well as a scientific achievement. While Darwin was an acute observer, a gifted experimentalist and indefatigable theorist, this essay argues that it was also crucial to his impact that the Origin transcended the putative divide between the scientific and the literary. Analysis of Darwin's development as a writer between his journal-keeping on HMS Beagle and his construction of the Origin argues the latter draws on the pattern of the Romantic or Kantian sublime. The Origin repeatedly uses strategies which challenge the natural-theological appeal to the imagination in conceiving nature. Darwin's sublime coaches the Origin's readers into a position from which to envision nature that reduces and contains its otherwise overwhelming complexity. As such, it was Darwin's literary achievement that enabled him to fashion a new 'habit of looking at things in a given way' that is the centrepiece of the scientific revolution bearing his name.

  1. Three-dimensional textures and defects of soft material layering revealed by thermal sublimation

    PubMed Central

    Yoon, Dong Ki; Kim, Yun Ho; Kim, Dae Seok; Oh, Seong Dae; Smalyukh, Ivan I.; Clark, Noel A.; Jung, Hee-Tae

    2013-01-01

    Layering is found and exploited in a variety of soft material systems, ranging from complex macromolecular self-assemblies to block copolymer and small-molecule liquid crystals. Because the control of layer structure is required for applications and characterization, and because defects reveal key features of the symmetries of layered phases, a variety of techniques have been developed for the study of soft-layer structure and defects, including X-ray diffraction and visualization using optical transmission and fluorescence confocal polarizing microscopy, atomic force microscopy, and SEM and transmission electron microscopy, including freeze-fracture transmission electron microscopy. Here, it is shown that thermal sublimation can be usefully combined with such techniques to enable visualization of the 3D structure of soft materials. Sequential sublimation removes material in a stepwise fashion, leaving a remnant layer structure largely unchanged and viewable using SEM, as demonstrated here using a lamellar smectic liquid crystal. PMID:24218602

  2. Fast crystalline ice formation at extremely low temperature through water/neon matrix sublimation.

    PubMed

    Hama, Tetsuya; Ishizuka, Shinnosuke; Yamazaki, Tomoya; Kimura, Yuki; Kouchi, Akira; Watanabe, Naoki; Sugimoto, Toshiki; Pirronello, Valerio

    2017-07-21

    Crystalline ice formation requires water molecules to be sufficiently mobile to find and settle on the thermodynamically most stable site. Upon cooling, however, diffusion and rearrangement become increasingly kinetically difficult. Water ice grown by the condensation of water vapor in laboratory is thus generally assumed to be in a metastable amorphous form below 100 K. Here, we demonstrate the possibility of crystalline ice formation at extremely low temperature using a water/neon matrix (1/1000, 30 000 monolayers) prepared at 6 K, which is subsequently warmed to 11-12 K. In situ infrared spectroscopy revealed the assembly of the dispersed water molecules, forming crystalline ice I during the sublimation of the neon matrix for 40-250 seconds. This finding indicates that the high mobility of the water molecules during matrix sublimation can overcome the kinetic barrier to form crystals even at extremely low temperature.

  3. Controlling Gaussian and mean curvatures at microscale by sublimation and condensation of smectic liquid crystals

    PubMed Central

    Kim, Dae Seok; Cha, Yun Jeong; Kim, Mun Ho; Lavrentovich, Oleg D.; Yoon, Dong Ki

    2016-01-01

    Soft materials with layered structure such as membranes, block copolymers and smectics exhibit intriguing morphologies with nontrivial curvatures. Here, we report restructuring the Gaussian and mean curvatures of smectic A films with free surface in the process of sintering, that is, reshaping at elevated temperatures. The pattern of alternating patches of negative, zero and positive mean curvature of the air–smectic interface has a profound effect on the rate of sublimation. As a result of sublimation, condensation and restructuring, initially equilibrium smectic films with negative and zero Gaussian curvature are transformed into structures with pronounced positive Gaussian curvature of layers packing, which are rare in the samples obtained by cooling from the isotropic melt. The observed relationship between the curvatures, bulk elastic behaviour and interfacial geometries in sintering of smectic liquid crystals might pave the way for new approaches to control soft morphologies at micron and submicron scales. PMID:26725975

  4. Water drops dancing on ice: how sublimation leads to drop rebound.

    PubMed

    Antonini, C; Bernagozzi, I; Jung, S; Poulikakos, D; Marengo, M

    2013-07-05

    Drop rebound is a spectacular event that appears after impact on hydrophobic or superhydrophobic surfaces but can also be induced through the so-called Leidenfrost effect. Here we demonstrate that drop rebound can also originate from another physical phenomenon, the solid substrate sublimation. Through drop impact experiments on a superhydrophobic surface, a hot plate, and solid carbon dioxide (commonly known as dry ice), we compare drop rebound based on three different physical mechanisms, which apparently share nothing in common (superhydrophobicity, evaporation, and sublimation), but lead to the same rebound phenomenon in an extremely wide temperature range, from 300 °C down to even below -79 °C. The formation and unprecedented visualization of an air vortex ring around an impacting drop are also reported.

  5. Spectroscopy of lithium atoms sublimated from isolation matrix of solid Ne

    NASA Astrophysics Data System (ADS)

    Sacramento, R. L.; Scudeller, L. A.; Lambo, R.; Crivelli, P.; Cesar, C. L.

    2011-10-01

    We have studied, via laser absorption spectroscopy, the velocity distribution of 7Li atoms released from a solid neon matrix at cryogenic temperatures. The Li atoms are implanted into the Ne matrix by laser ablation of a solid Li precursor. A heat pulse is then applied to the sapphire substrate sublimating the matrix together with the isolated atoms at around 12 K. We find interesting differences in the velocity distribution of the released Li atoms from the model developed for our previous experiment with Cr [R. Lambo, C. C. Rodegheri, D. M. Silveira, and C. L. Cesar, Phys. Rev. A 76, 061401-R (2007)], 10.1103/PhysRevA.76.061401. This may be due to the sublimation regime, which is at much lower flux for the Li experiment than for the Cr experiment, as well as to the different collisional cross sections between those species to the Ne gas. We find a drift velocity compatible with Li being thermally sublimated at 11-13 K, while the velocity dispersion around this drift velocity is low, around 5-7 K. With a slow sublimation of the matrix we can determine the penetration depth of the laser ablated Li atoms into the Ne matrix, an important information that is not usually available in most matrix isolation spectroscopy setups. The present results with Li, together with the previous results with Cr suggest this to be a general technique for obtaining cryogenic atoms, for spectroscopic studies, as well as for trap loading. The release of the isolated atoms is also a useful tool to study and confirm details of the matrix isolated atoms which are masked or poorly understood in the solid.

  6. Spectroscopy of lithium atoms sublimated from isolation matrix of solid Ne.

    PubMed

    Sacramento, R L; Scudeller, L A; Lambo, R; Crivelli, P; Cesar, C L

    2011-10-07

    We have studied, via laser absorption spectroscopy, the velocity distribution of (7)Li atoms released from a solid neon matrix at cryogenic temperatures. The Li atoms are implanted into the Ne matrix by laser ablation of a solid Li precursor. A heat pulse is then applied to the sapphire substrate sublimating the matrix together with the isolated atoms at around 12 K. We find interesting differences in the velocity distribution of the released Li atoms from the model developed for our previous experiment with Cr [R. Lambo, C. C. Rodegheri, D. M. Silveira, and C. L. Cesar, Phys. Rev. A 76, 061401(R) (2007)]. This may be due to the sublimation regime, which is at much lower flux for the Li experiment than for the Cr experiment, as well as to the different collisional cross sections between those species to the Ne gas. We find a drift velocity compatible with Li being thermally sublimated at 11-13 K, while the velocity dispersion around this drift velocity is low, around 5-7 K. With a slow sublimation of the matrix we can determine the penetration depth of the laser ablated Li atoms into the Ne matrix, an important information that is not usually available in most matrix isolation spectroscopy setups. The present results with Li, together with the previous results with Cr suggest this to be a general technique for obtaining cryogenic atoms, for spectroscopic studies, as well as for trap loading. The release of the isolated atoms is also a useful tool to study and confirm details of the matrix isolated atoms which are masked or poorly understood in the solid.

  7. Conditions determining the partitioning of ablation between melt and sublimation on East African glaciers

    NASA Astrophysics Data System (ADS)

    Nicholson, L. I.; Prinz, R.; Moelg, T.; Kaser, G.

    2010-12-01

    A new automatic weather station on Lewis Glacier on Mount Kenya (0°09’ S; 37°18’ E) allows comparison of the surface energy balance there with that of Kersten glacier on Kibo, Kilimanjaro (3°04’ S; 37°21’ E), which is ca. 320 km to the south. Lewis Glacier, at about 4800m is ca. 1000m lower than Kersten Glacier and annual mean temperature is accordingly higher. Consequently, while sublimation dominates in the cold dry setting of Kersten Glacier, melt dominates ablation in the relatively warm, humid atmosphere of Lewis Glacier. Here we use a point mass and surface energy balance model, driven by a year of simultaneous automatic weather station data from the two sites to identify the conditions under which the partitioning of ablation process changes i.e. identifying times and conditions when sublimation occurs on Lewis Glacier and those under which melt occurs on Kersten Glacier, from which we determine a set of limiting meteorological condition for the two ablation processes. Whether ablation occurs by melt or sublimation has implications for the efficiency of ice ablation due to the differing energy consumption of the two processes, and partitioning snow and ice ablation into melt and sublimation determines whether the water equivalent volume is transferred into the hydrological system or the atmosphere. The energy balance of the two sites is compared to identify similarities and differences in (a) the expression of synoptic climate patterns on the two peaks and (b) the sensitivity of snow and ice ablation to variations in key meteorological variables at the two sites.

  8. APPARATUS FOR CHARGING A RECEPTACLE WITH A DENSE SUBLIMATE FORM OF URANIUM CHLORIDE

    DOEpatents

    Davidson, P.H.

    1959-08-18

    An apparatus for filling a tubular storage receptacle with a dense massive form of uranium chloride is described. The apparatus includes an evacuated housing divided into a vaporizing chamber and a portion adapted to receive the receptacle. A nozzle conducts vaporized uranium chloride from the chamber to the interior of the receptacle. The nozzle is withdrawable to progressively deposit the uranium chloride under controlled conditions to produce a dense sublimate which fills the receptacle.

  9. Sublimating icy planetesimals as the source of nucleation seeds for grain condensation in classical novae

    NASA Technical Reports Server (NTRS)

    Matese, John J.; Whitmire, D. P.; Reynolds, R. T.

    1989-01-01

    The problem of grain nucleation during novae outbursts is a major obstacle to our understanding of dust formation in these systems. How nucleation seeds can form in the hostile post-outburst environment remains an unresolved matter. It is suggested that the material for seeding the condensation of ejecta outflow is stored in a primordial disk of icy planetesimals surrounding the system. Evidence is presented that the requisite number of nucleation seeds can be released by sublimation of the planetesimals during outbursts.

  10. Advances in LO2 Propellant Conditioning

    NASA Technical Reports Server (NTRS)

    Mehta, Gopal; Orth, Michael; Stone, William; Perry, Gretchen; Holt, Kimberly; Suter, John

    1994-01-01

    This paper describes the cryogenic testing and analysis that has recently been completed as part of a multi-year effort to develop a new, more robust and operable LO2 propellant conditioning system. Phase 1 of the program consisted of feasibility demonstrations ot four novel propellant conditioning concepts. A no-bleed, passive propellant conditioning option was shown for the first time to successfully provide desired propellant inlet conditions. The benefits of passive conditioning are reduced operations costs, decreased hardware costs, enhanced operability and increased reliability on future expendable launch vehicles In Phase 2 of the test program, effects of major design parameters were studied and design correlation for future vehicle design were developed. Simultaneously, analytical models were developed and validated. Over 100 tests were conducted with a full-scale feedline using LN2 as the test fluid. A circulation pump provided a range of pressure and flow conditions. The test results showed that the passive propellant conditioning system is insensitive to variations in many of the parameters. The test program provides the validation necessary to incorporate the passive conditioning system into the baseline of future vehicles. Modeling of these systems using computational fluid dynamics seems highly promising.

  11. Properties of Filamentary Sublimation Residues from Dispersions of Clay in Ice

    NASA Technical Reports Server (NTRS)

    Stephens, J. B.; Parker, T. J.; Saunders, R. S.; Laue, E. G.; Fanale, F. P.

    1985-01-01

    The properties of sublimate residues are of considerable interest in studies of the thermal modeling of Martian and cometary ice surfaces. The study of the formation of sand grains from this mantle on Martian polar ice is also supported by these experiments. To understand these properties, a series of low temperature vacuum experiments were run during which dirty ices that might be expected to be found in Martian polar caps and in comet nuclei were made and then freeze dried. In addition to using particulate material of appropriate grain size and minerology, particle nucleated ices were simulated by dispersing the particulates in the ice so that they did not contact one another. This noncontact dispersion was the most difficult requirement to achieve but the most rewarding in that it produced a new filamentary sublimate residue that was not a relic of the frozen dispersion. If the siliceous particles are allowed to touch one another in the ice the structure of the contacting particles in the ice will remain as a relic after the ice is sublimed away.

  12. Application of a Kalman filter to UF sub 6 gaseous diffusion plant freezer/sublimer systems

    SciTech Connect

    Ruppel, F.R.

    1992-03-01

    A signal is required to control the flow of UF{sub 6} in gaseous diffusion plant freezer/sublimer systems. The original strategy envisioned for deriving a flow signal was to take the derivative of the freezer/sublimer weigh cell signal. However, the derivative of the digitized weight signal is noisy, preventing good control. In addition, a bias is introduced into the weight derivative signal because a refrigerant is circulated through a shell-and-tube heat exchanger inside the freezer/sublimer. The weight of the refrigerant is included in the weight measured by the weigh cell. If the circulation rate of the refrigerent is not steady state, a bias exists. Measurements of upstream pressure, vessel pressure, and output to the system control valve are available to the control system. Thus, if the flow through the control valve is characterized properly by the measurements, a Kalman filter can be used in conjunction with these auxiliary inputs and the weigh cell input to overcome the noise and bias problem and provide an improve estimate of flow rate. A discussion of the development and the current status of a Kalman filter used for this application is given. 5 refs.

  13. Formulation Design and Optimization of Orodispersible Tablets of Quetiapine Fumarate by Sublimation Method.

    PubMed

    Kalyankar, P; Panzade, P; Lahoti, S

    2015-01-01

    The objective of present study was to formulate directly compressible orodispersible tablets of quetiapine fumarate by sublimation method with a view to enhance patient compliance. A full 3(2) factorial design was used to investigate the effect of two variables viz., concentration of Indion 414 and camphor. Indion 414 (3-5 % w/w) was used as superdisintegrant and camphor (5-15 % w/w) as subliming agent. The tablets were evaluated for thickness, weight variation, hardness, friability, content uniformity, wetting time, porosity, in vitro disintegration time and in vitro drug release. The formulation containing 5% w/w of Indion 414 and 5% w/w camphor was emerged as promising based on evaluation parameters. The disintegration time for optimized formulation was 18.66 s. The tablet surface was evaluated for presence of pores by scanning electron microscopy before and after sublimation. Differential scanning colorimetric study did not indicate any drug excipient incompatibility, either during mixing or after compression. The effect of independent variables on disintegration time, % drug release and friability is presented graphically by surface response plots. Short-term stability studies on the optimized formulation indicated no significant changes in drug content and in vitro disintegration time. The directly compressible orodispersible tablets of quetiapine fumarate with lower friability, greater drug release and shorter disintegration times were obtained using Indion 414 and camphor at optimum concentrations.

  14. Formation of the dumbbell-like nucleus of a comet by sublimation

    NASA Astrophysics Data System (ADS)

    Vavilov, Dmitrii; Medvedev, Yurii; Zatitskiy, Pavel

    2016-10-01

    The nucleus of the comet 67P/Churyumov-Gerasimenko is an elongated body with a deep groove around the middle. There are also other comets that look like dumbbells (e.g. 103P/Hartley 2, 19P/Borrelly, 1P/Halley). Two most probable interpretations are discussed in the scientific society. The first hypothesis explains the creation of such an object as sticking of two cometesimals during the process of formation. The second one suggests that the sublimation process can change the nucleus shape and make a groove in the middle.In this work we consider the second hypothesis. It was assumed that the spin axis of the nucleus is perpendicular to the plane of the cometary orbit and that initially the nucleus shape is a sphere. Thus, the problem is represented as a differential equation, which describes the change of the cometary nucleus. We solved this equation analytically. It was shown that initially a convex cometary nucleus (e.g. a sphere), consisting of homogeneous material, can not be transformed into a dumbbell-like body by the influence of sublimation. However, assuming that the density in the centre of the nucleus is less than on the surface, a groove can arise on the equator of the cometary nucleus as a result of sublimation.

  15. Formulation Development and Characterization of Meclizine Hydrochloride Sublimated Fast Dissolving Tablets

    PubMed Central

    Vangala, Mohan

    2014-01-01

    The intention of present research is to formulate and develop the meclizine hydrochloride fast dissolving tablets using sublimation method to enhance the dissolution rate. In this study an attempt was made to fasten the drug release from the oral tablets by incorporating the superdisintegrants and camphor as sublimating agent. The prepared fast dissolving tablets were subjected to precompression properties and characterized for hardness, weight variation, friability, wetting time, water absorption ratio, and disintegration time. From in vitro release studies, the formulation F9 exhibited fast release profile of about 98.61% in 30 min, and disintegration time 47 sec when compared with other formulations. The percent drug release in 30 min (Q30) and initial dissolution rate for formulation F9 was 98.61 ± 0.25%, 3.29%/min. These were very much higher compared to marketed tablets (65.43 ± 0.57%, 2.18%/min). The dissolution efficiency was found to be 63.37 and it is increased by 1.4-fold with F9 FDT tablets compared to marketed tablets. Differential scanning calorimetry and Fourier transform infrared spectroscopy studies revealed that there was no possibility of interactions. Thus the development of meclizine hydrochloride fast dissolving tablets by sublimation method is a suitable approach to improve the dissolution rate. PMID:27355021

  16. Enhancement of Sublimation of Single Graphene Layer by Interacting with Gas Molecules in Rarefied Environment

    NASA Astrophysics Data System (ADS)

    Murugesan, Ramki; Park, Jae Hyun

    2014-11-01

    Graphene has excellent mechanical properties. One of them is the resistance to high temperature environment. Since the sublimation temperature of graphene is over 4500 K, it has been used for diverse high temperature applications in order to protect the system. In this study, using extensive molecular dynamics simulations, we show that the sublimation of graphene could be enhanced (occurs at the lower temperature) by interacting with the gas molecules. With increase in temperature, the bonds in graphene becomes so sensitive to interact with the incoming gas molecules. When the temperature is low, the graphene is stable to the impingement of gas molecules: The light H2 gases are stick to the graphene surface and remains being attached while the heavy CO2 and H2O are bounced back from the surface. However, at high temperature H2 gases are absorbed on the graphene and destroy the C -C bonds by forming C -H bonds. The local breakage of bond at the impingement spot spreads the entire graphene soon, causing a complete sublimation. Even though the heavy CO2 and H2O molecules also break the C -C bonds at high temperature,but their impingement effect is localized and the breakage does not propagate over the entire surface. This research was supported by Agency for Defence Development (ADD).

  17. Glaciers of the McMurdo dry valleys: Terrestrial analog for Martian polar sublimation

    NASA Astrophysics Data System (ADS)

    MacClune, Karen Lewis; Fountain, Andrew G.; Kargel, Jeffery S.; MacAyeal, Douglas R.

    2003-04-01

    The surfaces of the Martian north and south polar residual caps are marked by unusual ice features: Dark spiralesque troughs up to 1 km deep, 10 km wide, and 300 km long appear on both ice caps, and circular pits that make up the ``Swiss cheese'' terrain appear on the south polar cap. Both types of features are of interest to researchers as a potential means of understanding ice composition and flow rates. Some glaciers of the McMurdo dry valleys have surface features unknown elsewhere on terrestrial glaciers, including canyons over 6 km long, 100 m wide, and tens of meters deep and basins up to 100 m across. High sublimation, dust accumulation, and very little melting is key to their origin. These processes and ice landforms are suggested as terrestrial analogs for the sublimation behavior of Martian ice caps, where dust accumulation and sublimation are significant but surface melting is absent. We have developed a solar radiation model of canyon formation and have applied it to the Martian polar caps. The modeled processes do well to describe direct and reflected radiation within V grooves, a process that may be significant in the development of the spiral troughs and Swiss cheese terrain. The model fails to reproduce the low observed slopes of the Martian troughs. The grooves are too shallow, with opening angles of ~165° compared with model predictions of ~90°. The reason for the failure may be that we have not included creep closure, which should flatten their slopes.

  18. Properties of Filamentary Sublimation Residues from Dispersions of Clay in Ice

    NASA Technical Reports Server (NTRS)

    Stephens, J. B.; Parker, T. J.; Saunders, R. S.; Laue, E. G.; Fanale, F. P.

    1985-01-01

    The properties of sublimate residues are of considerable interest in studies of the thermal modeling of Martian and cometary ice surfaces. The study of the formation of sand grains from this mantle on Martian polar ice is also supported by these experiments. To understand these properties, a series of low temperature vacuum experiments were run during which dirty ices that might be expected to be found in Martian polar caps and in comet nuclei were made and then freeze dried. In addition to using particulate material of appropriate grain size and minerology, particle nucleated ices were simulated by dispersing the particulates in the ice so that they did not contact one another. This noncontact dispersion was the most difficult requirement to achieve but the most rewarding in that it produced a new filamentary sublimate residue that was not a relic of the frozen dispersion. If the siliceous particles are allowed to touch one another in the ice the structure of the contacting particles in the ice will remain as a relic after the ice is sublimed away.

  19. Formulation Design and Optimization of Orodispersible Tablets of Quetiapine Fumarate by Sublimation Method

    PubMed Central

    Kalyankar, P.; Panzade, P.; Lahoti, S.

    2015-01-01

    The objective of present study was to formulate directly compressible orodispersible tablets of quetiapine fumarate by sublimation method with a view to enhance patient compliance. A full 32 factorial design was used to investigate the effect of two variables viz., concentration of Indion 414 and camphor. Indion 414 (3-5 % w/w) was used as superdisintegrant and camphor (5-15 % w/w) as subliming agent. The tablets were evaluated for thickness, weight variation, hardness, friability, content uniformity, wetting time, porosity, in vitro disintegration time and in vitro drug release. The formulation containing 5% w/w of Indion 414 and 5% w/w camphor was emerged as promising based on evaluation parameters. The disintegration time for optimized formulation was 18.66 s. The tablet surface was evaluated for presence of pores by scanning electron microscopy before and after sublimation. Differential scanning colorimetric study did not indicate any drug excipient incompatibility, either during mixing or after compression. The effect of independent variables on disintegration time, % drug release and friability is presented graphically by surface response plots. Short-term stability studies on the optimized formulation indicated no significant changes in drug content and in vitro disintegration time. The directly compressible orodispersible tablets of quetiapine fumarate with lower friability, greater drug release and shorter disintegration times were obtained using Indion 414 and camphor at optimum concentrations. PMID:26180271

  20. Formulation Development and Characterization of Meclizine Hydrochloride Sublimated Fast Dissolving Tablets.

    PubMed

    Vemula, Sateesh Kumar; Vangala, Mohan

    2014-01-01

    The intention of present research is to formulate and develop the meclizine hydrochloride fast dissolving tablets using sublimation method to enhance the dissolution rate. In this study an attempt was made to fasten the drug release from the oral tablets by incorporating the superdisintegrants and camphor as sublimating agent. The prepared fast dissolving tablets were subjected to precompression properties and characterized for hardness, weight variation, friability, wetting time, water absorption ratio, and disintegration time. From in vitro release studies, the formulation F9 exhibited fast release profile of about 98.61% in 30 min, and disintegration time 47 sec when compared with other formulations. The percent drug release in 30 min (Q 30) and initial dissolution rate for formulation F9 was 98.61 ± 0.25%, 3.29%/min. These were very much higher compared to marketed tablets (65.43 ± 0.57%, 2.18%/min). The dissolution efficiency was found to be 63.37 and it is increased by 1.4-fold with F9 FDT tablets compared to marketed tablets. Differential scanning calorimetry and Fourier transform infrared spectroscopy studies revealed that there was no possibility of interactions. Thus the development of meclizine hydrochloride fast dissolving tablets by sublimation method is a suitable approach to improve the dissolution rate.

  1. Characterization of Sulfur and Nanostructured Sulfur Battery Cathodes in Electron Microscopy Without Sublimation Artifacts.

    PubMed

    Levin, Barnaby D A; Zachman, Michael J; Werner, Jörg G; Sahore, Ritu; Nguyen, Kayla X; Han, Yimo; Xie, Baoquan; Ma, Lin; Archer, Lynden A; Giannelis, Emmanuel P; Wiesner, Ulrich; Kourkoutis, Lena F; Muller, David A

    2017-02-01

    Lithium sulfur (Li-S) batteries have the potential to provide higher energy storage density at lower cost than conventional lithium ion batteries. A key challenge for Li-S batteries is the loss of sulfur to the electrolyte during cycling. This loss can be mitigated by sequestering the sulfur in nanostructured carbon-sulfur composites. The nanoscale characterization of the sulfur distribution within these complex nanostructured electrodes is normally performed by electron microscopy, but sulfur sublimates and redistributes in the high-vacuum conditions of conventional electron microscopes. The resulting sublimation artifacts render characterization of sulfur in conventional electron microscopes problematic and unreliable. Here, we demonstrate two techniques, cryogenic transmission electron microscopy (cryo-TEM) and scanning electron microscopy in air (airSEM), that enable the reliable characterization of sulfur across multiple length scales by suppressing sulfur sublimation. We use cryo-TEM and airSEM to examine carbon-sulfur composites synthesized for use as Li-S battery cathodes, noting several cases where the commonly employed sulfur melt infusion method is highly inefficient at infiltrating sulfur into porous carbon hosts.

  2. Deviations from Ideal Sublimation Vapor Pressure Behavior in Mixtures of Polycyclic Aromatic Compounds with Interacting Heteroatoms.

    PubMed

    Goldfarb, Jillian L; Suuberg, Eric M

    2010-08-01

    Despite the relatively small atomic fraction of a given heteroatom in a binary mixture of polycyclic aromatic compounds (PAC), the inclusion of heteroatomic substituted compounds can significantly impact mixture vapor pressure behavior over a wide range of temperatures. The vapor pressures of several binary PAC mixtures containing various heteroatoms show varying behavior, from practically ideal behavior following Raoult's law to significant deviations from ideality depending on the heteroatom(s) present in the mixture. Mixtures were synthesized using the quench-cool technique with equimolar amounts of two PAC, both containing heteroatoms such as aldehyde, carboxyl, nitrogen, and sulfur substituent groups. For some mixtures, deviation from ideality is inversely related to temperature, though in other cases we see deviations from ideality increasing with temperature, whereas some appear independent of temperature. Most commonly we see lower vapor pressures than predicted by Raoult's law, which indicates that the interacting heteroatoms prefer the solid mixture phase as opposed to the vapor phase. Although negative deviations predominate from Raoult's Law, the varying mixtures investigated show both higher and lower enthalpies and entropies of sublimation than predicted. In each mixture, a higher enthalpy of sublimation leads to higher entropy of sublimation than predicted, and vice versa.

  3. Sublimation kinetics and diffusion coefficients of TNT, PETN, and RDX in air by thermogravimetry.

    PubMed

    Hikal, Walid M; Weeks, Brandon L

    2014-07-01

    The diffusion coefficients of explosives are crucial in their trace detection and lifetime estimation. We report on the experimental values of diffusion coefficients of three of the most important explosives in both military and industry: TNT, PETN, and RDX. Thermogravimetric analysis (TGA) was used to determine the sublimation rates of TNT, PETN, and RDX powders in the form of cylindrical billets. The TGA was calibrated using ferrocene as a standard material of well-characterized sublimation rates and vapor pressures to determine the vapor pressures of TNT, PETN, and RDX. The determined sublimation rates and vapor pressures were used to indirectly determine the diffusion coefficients of TNT, PETN, and RDX for the first time. A linear log-log dependence of the diffusion coefficients on temperature is observed for the three materials. The diffusion coefficients of TNT, PETN, and RDX at 273 K were determined to be 5.76×10(-6)m(2)/sec, 4.94×10(-6)m(2)/s, and 5.89×10(-6)m(2)/s, respectively. Values are in excellent agreement with the theoretical values in literature.

  4. Sublimating grains in the coma of new comets originating from the Oort Cloud

    NASA Astrophysics Data System (ADS)

    Faggi, S.; Tozzi, G.; Brucato, J.; Bruni, I.; Licandro, J.; Mazzotta Epifani, E.; Meech, K.; Mottola, S.

    2014-07-01

    It is expected that a billion of years of space weathering (see, e.g., Kanuchova et al., 2012, Icarus, 221, 12) produces a crust of organic matter that will be released when a comet enters, for the first time, in the inner Solar System. When approaching to the Sun, a comet is at heliocentric distances r_h greater than 3 au, the sublimation of CO and CO_2 is the main source of cometary activity. At shorter distances, the sublimation of water becomes the most important mechanism of activity. The gases escaping from the nucleus cause drag for the coma grains that can be refractory dust (silicates, carbon), water ice, and/or organic ices. Oort comets at their first passage in the inner Solar System, should produce an halo of organic or water ice particles. Recently, our group started to monitor new, inbound, bright Oort comets (C/2011 F1, C/2012 S1, C/2012 K1, C/2013 V5, C/2012 F3) to search for these grains. The method consists of detecting the cloud of sublimating grains in the inner coma by using the ΣAf(ρ) function (Tozzi et al., 2007, A&A, 476, 979). However, this over-population of grains, beside the sublimation, can be also due to short-time activity (outburst) or too large grains expanding at very slow velocity, as it has been found in comet 67P/C-G (Tozzi et al., 2011, A&A, 531, 54). To discriminate between the phenomena, it is necessary to monitor the comet both at short timescales for the outbursts (by repeating the observations after a few nights), and in a longer term (weeks to months). If the cloud does not expand with decreasing heliocentric distance, there is a high probability that organic and/or water-ice grains are present. We can discriminate between organic and water-ice grains by measuring their color and spectra. In this work, we will present the results obtained from the observations of C/2011 F1 (LINEAR) and C/2012 S1 (ISON). The comparison between data and theoretical simulations, obtained with a simple model assuming sublimating grains

  5. Laboratory experiments to explore the sediment transport capacity of carbon dioxide sublimation under martian conditions

    NASA Astrophysics Data System (ADS)

    Sylvest, Matthew; Conway, Susan; Patel, Manish; Dixon, John; Barnes, Adam

    2015-04-01

    Every spring, the solid carbon dioxide deposited over the martian high latitudes sublimates. Several, unusual surface features, including dark spots and flows on sand dunes, as well as recent activity in martian gullies, have been associated with this CO2 sublimation. Water and/or brines have also been proposed as potential agents for these events, but the timing of these phenomena suggest CO2 sublimation is more likely. However, the exact mechanism by which CO2 sublimation moves sediment is not fully understood, and this understanding is required to validate the CO2 hypothesis. Here we present the results of the first ever laboratory simulations of this process under martian conditions, and show that significant quantities of loose sediment can be transported. The centrepiece of the apparatus is a 1m diameter, 2m long Mars simulation chamber, housed at The Open University, UK. JSC Mars-1A regolith simulant was formed into a slope, inside a box, ~30 cm long, 23 cm wide by 12 cm deep. The box is constructed of coiled, copper tubing to allow cooling of the regolith by liquid nitrogen. The experimental procedure consists of four stages: 1) establishment of a dry atmosphere in the chamber, 2) cooling the regolith sufficiently to support condensation of CO2 frost at reduced pressure, 3) introduction of cooled CO2 gas above the regolith to deposit as frost, and 4) video recording the surface evolution under radiant heating (~100 mins). Two High Definition digital video cameras were mounted above the box and image pairs taken from the videos were then used to create digital elevation models (DEMs) in Agisoft Photoscan at regular intervals. In our initial experiments we performed four experimental runs where the slope was set at or near the angle of repose (~30°). In each case we observed mass wasting events triggered by the sublimation of the deposited CO2 over the whole duration of the insolation. The highest levels of activity occurred in the first third of the run

  6. Impact of sublimation losses in the mass balance of glaciers in semi-arid mountain regions

    NASA Astrophysics Data System (ADS)

    Ayala, Alvaro; Pellicciotti, Francesca; Burlando, Paolo; MacDonell, Shelley; McPhee, James

    2016-04-01

    Glaciers in semiarid mountain regions may lose an important part of their winter snow accumulation through sublimation processes that are enhanced by the high-elevation, intense radiation and dry atmosphere of these environments. As glaciers in these regions secure freshwater resources to lower valleys during summer and drought periods, it is important to advance in a detailed quantification of their sublimation losses. However, logistical concerns and complex meteorological features make the measuring and modelling of glacier mass balances a difficult task. In this study, we estimated the spring-summer mass balances of Tapado and Juncal Norte glaciers in the semiarid Andes of north-central Chile by running a distributed energy balance model that accounts for melt, refreezing and sublimation from the surface and blowing snow. Meteorological input data were available from on-glacier Automatic Weather Stations (AWS) that were installed during the ablation season of years 2005-06, 2008-09, 2013-14 and 2014-15. Snow pits, ablation stakes and a time-lapse camera that provided surface albedo were also available. Distributed air temperature and wind speed were dynamically downscaled from NASA MERRA reanalysis using the software WINDSIM and validated against the data from the AWSs. The rest of the meteorological variables were distributed using statistical relations with air temperature derived from the AWSs data. Initial snow conditions were estimated using satellite images and distributed manual snow depth measurements. Preliminary results show that total ablation diminishes with elevation and that, during the early ablation season (October-November), melt is the main ablation component below 4500 m with sublimation dominating the ablation above this elevation. Above 4500 m an important fraction of meltwater refreezes during night. As the ablation season advances (December-February), melt extends to higher elevations, refreezing plays a smaller role and sublimation is

  7. Snowmelt and sublimation: field experiments and modelling in the High Atlas Mountains of Morocco

    NASA Astrophysics Data System (ADS)

    Schulz, O.; de Jong, C.

    Snow in the High Atlas Mountains is a major source for freshwater renewal and for water availability in the semi-arid lowlands of south-eastern Morocco. Snowfall- and snow-ablation monitoring and modelling is important for estimating potential water delivery from the mountain water towers to the forelands. This study is part of GLOWA-IMPETUS, an integrated management project dealing with scarce water resources in West Africa. The Ameskar study area is located to the south of the High Atlas Mountains, in their rain shadow. As a part of the M’Goun river basin within the upper Dr'valley, the study area is characterised by high radiation inputs, low atmospheric humidity and long periods with sub-zero temperatures. Its altitude ranges between 2000 m and 4000 m, with dominant north- and south-facing slopes. Snowfall occurs mainly from November to April but even summit regions can become repeatedly devoid of snow cover. Snow cover maps for the M’Goun basin (1240 km2) are derived from calculations of NDSI (Normalized Difference Snow Index) from MODIS satellite images and snow depth is monitored at four automatic weather stations between 2000-4000 m. Snowfall events are infrequent at lower altitudes. The presence of snow penitentes at altitudes above 3000 m indicates that snow sublimation is an important component of snow ablation. Snow ablation was modelled with the UEB Utah Energy Balance Model (Tarboton and Luce, 1996). This single layer, physically-based, point energy and mass balance model is driven by meteorological variables recorded at the automatic weather stations at Tounza (2960 m) and Tichki (3260 m). Data from snow pillows at Tounza and Tichki are used to validate the model’s physical performance in terms of energy and water balances for a sequence of two snowfall events in the winter of 2003/4. First UEB modelling results show good overall performance and timing of snowmelt and sublimation compared to field investigations. Up to 44% of snow ablation is

  8. Graphite Sublimation Tests for the Muon Collider/Neutrino Factory Target Development Program

    SciTech Connect

    Haines, JR

    2002-02-07

    A passively cooled graphite target was proposed for a 1.5 MW neutrino production research facility because of its simplicity and favorable performance as a target material for neutrino production (Ref. 1). The conceptual design for the target in the Reference 1 study was a graphite rod 15 mm in diameter by 800 mm long. Figure 1 shows the graphite target rod supported by graphite spokes, which are mounted to a water-cooled stainless steel support tube. The target is radiatively cooled to the water-cooled surface of the support tube. Based on nuclear analysis results (Ref. 2), the time-averaged power deposition in the target is 35 kW. If this power is deposited uniformly along the axial length of the target, the volumetric power deposition in the target is about 250 MW/m{sup 3}. The target surface temperature required to radiate the deposited power to a water-cooled tube is estimated to be about 1850 C, and the temperature at the center of the target is about 75 C hotter. The sublimation erosion rate (e), estimated assuming that the graphite is submersed in a perfect vacuum environment, can be derived from kinetic theory and is given by: e = p{sub sat} (m/2{pi} kT){sup 1/2} where p{sub sat} is the saturation pressure, m is the molecular weight, k is the Boltzmann constant, and T is the surface temperature. The saturation pressure given in Ref. 3 can be approximated by: p{sub sat} = exp(-A/T + B) where A = 9.47 x 10{sup 3}, B = 24.2, and the units of p{sub sat} and T are atmospheres and K, respectively. Using these equations, the saturation pressure and sublimation erosion rate are plotted in Fig. 2 as a function of temperature. The surface recession rate shown with units of mm/s in Fig. 2 assumes one-sided erosion. At the average power deposition value of 250 MW/m{sup 3}, the surface temperature is 1850 C resulting in a sublimation erosion rate of only 2.2 mm/day. However, if the actual power deposition were peaked by a factor of two in the axial direction, then the

  9. Carbon deposition characteristics of LO2/HC propellants

    NASA Technical Reports Server (NTRS)

    Hernandez, Rosemary; Mercer, Steve D.

    1987-01-01

    The generation and deposition of carbon have been studied using subscale hardware with LO2/RP-1, LO2/propane, and LO2/methane at low mixture ratio conditions. The deposition of carbon on the turbine simulator tubes was evaluated at mixture ratios of 0.20 to 0.60, and at chamber pressures from 720 to 1650 psia. The carbon-deposition rate is a strong function of mixture ratio and a weak function of chamber pressure. There is a mixture ratio that will minimize deposition for LO2/RP-1; a threshold mixture ratio for LO2/propane; and no deposition for LO2/methane at any mixture ratio tested. The turbine drive operating limits were defined for each fuel tested.

  10. A Bayesian Analysis Shows That a Spruce Beetle Outbreak Reduces Snow Interception and Sublimation in a Subalpine Spruce-Fir Forest

    NASA Astrophysics Data System (ADS)

    Frank, J. M.; Massman, W. J.; Ewers, B. E.; Williams, D. G.

    2016-12-01

    Sublimation is a key component in the water cycle of cold, snow dominated ecosystems. In many high elevation spruce-fir forests of western North America, recent spruce beetle outbreaks have caused widespread tree mortality, opened the canopy, and potentially altered the processes that control sublimation. This study evaluates three hypotheses: in these ecosystems the dominant source for sublimation originates from canopy intercepted snow, the loss of canopy following a beetle disturbance leads to significantly less sublimation, and major sublimation events are driven by the flow of sensible heat into the canopy. Bayesian analysis is used to evaluate a two source energy and canopy mass model that explains seventeen years (2000-2016) of winter eddy-covariance flux data at the GLEES AmeriFlux sites where a spruce beetle outbreak caused 75-85% basal area mortality. The model estimated that the resistance to snow sublimation from the canopy was an order of magnitude less than from the snowpack and that the maximum snow loading in the canopy was reduced to 25-56% of its pre-outbreak capacity. Comparing model results obtained using the observed decrease in leaf area index versus a "no beetle" condition, there has been a significant decrease in ecosystem sublimation since 2011. In the past few years, a 5-11% increase in snowpack sublimation has been offset by 28-32% less sublimation from canopy intercepted snow, with the net being 17-25% less total sublimation. This is equivalent to 3-6% of the total precipitation. Informing the model with information other than the above-canopy fluxes indicates that a near snowpack eddy covariance system decreases the canopy contribution to sublimation, including observed sensible heat fluxes requires a correction to resolve the surface energy imbalance, and stable isotopes of water vapor extend sublimation events. Because tree growth and ecological succession are slow in spruce-fir forests, these results could persist for decades.

  11. Piezoelectric crystal microbalance measurements of enthalpy of sublimation of C2-C9 dicarboxylic acids

    NASA Astrophysics Data System (ADS)

    Dirri, F.; Palomba, E.; Longobardo, A.; Zampetti, E.

    2016-02-01

    We present here a novel experimental set-up that is able to measure the enthalpy of sublimation of a given compound by means of piezoelectric crystal microbalances (PCMs). The PCM sensors have already been used for space measurements, such as for the detection of organic and non-organic volatile species and refractory materials in planetary environments. In Earth atmospherics applications, PCMs can be also used to obtain some physical-chemical processes concerning the volatile organic compounds (VOCs) present in atmospheric environments. The experimental set-up has been developed and tested on dicarboxylic acids. In this work, a temperature-controlled effusion cell was used to sublimate VOC, creating a molecular flux that was collimated onto a cold PCM. The VOC recondensed onto the PCM quartz crystal, allowing the determination of the deposition rate. From the measurements of deposition rates, it has been possible to infer the enthalpy of sublimation of adipic acid, i.e. ΔHsub : 141.6 ± 0.8 kJ mol-1, succinic acid, i.e. 113.3 ± 1.3 kJ mol-1, oxalic acid, i.e. 62.5 ± 3.1 kJ mol-1, and azelaic acid, i.e. 124.2 ± 1.2 kJ mol-1. The results obtained show an accuracy of 1 % for succinic, adipic, and azelaic acid and within 5 % for oxalic acid and are in very good agreement with previous works (within 6 % for adipic, succinic, and oxalic acid and within 11 % or larger for azelaic acid).

  12. Piezoelectric crystal microbalance measurements of enthalpy of sublimation of C2-C9 dicarboxylic acids

    NASA Astrophysics Data System (ADS)

    Dirri, F.; Palomba, E.; Longobardo, A.; Zampetti, E.

    2015-07-01

    We present here a novel experimental setup able to measure the enthalpy of sublimation of a given compound by means of Piezoelectric Crystal Microbalances (PCM). This experiment was performed in the TG-Lab facility in IAPS-INAF, dedicated to the development of TGA sensors for space measurements, such as detection of organic and non-organic volatile species and refractory materials in planetary environments. In order to study physical-chemical processes concerning the Volatile Organic Compounds (VOC) present in atmospheric environments, the setup has been tested on Dicarboxylic acids. Acids with low molecular weight are among the components of organic fraction of particulate matter in the atmosphere, coming from different sources (biogenic and anthropogenic). Considering their relative abundance, it is useful to consider Dicarboxylic acid as "markers" to define the biogenic or anthropogenic origin of the aerosol, thus obtaining some information of the emission sources. In this work, a temperature controlled effusion cell was used to sublimate VOC, creating a molecular flux that was collimated onto a cold PCM. The VOC re-condensed onto the PCM quartz crystal allowing the determination of the deposition rate. From the measurements of deposition rates, it was possible to infer the enthalpy of sublimation of Adipic acid, i.e. Δ Hsub: 141.6 ± 0.8 kJ mol-1, Succinic acid, i.e. 113.3 ± 1.3 kJ mol-1, Oxalic acid, i.e. 62.5 ± 3.1 kJ mol-1 and Azelaic acid, i.e. 124.2 ± 1.2 kJ mol-1 (weight average values). The results obtained are in very good agreement with literature within 10 % for the Adipic, Succinic and Oxalic acid.

  13. Large area and structured epitaxial graphene produced by confinement controlled sublimation of silicon carbide.

    PubMed

    de Heer, Walt A; Berger, Claire; Ruan, Ming; Sprinkle, Mike; Li, Xuebin; Hu, Yike; Zhang, Baiqian; Hankinson, John; Conrad, Edward

    2011-10-11

    After the pioneering investigations into graphene-based electronics at Georgia Tech, great strides have been made developing epitaxial graphene on silicon carbide (EG) as a new electronic material. EG has not only demonstrated its potential for large scale applications, it also has become an important material for fundamental two-dimensional electron gas physics. It was long known that graphene mono and multilayers grow on SiC crystals at high temperatures in ultrahigh vacuum. At these temperatures, silicon sublimes from the surface and the carbon rich surface layer transforms to graphene. However the quality of the graphene produced in ultrahigh vacuum is poor due to the high sublimation rates at relatively low temperatures. The Georgia Tech team developed growth methods involving encapsulating the SiC crystals in graphite enclosures, thereby sequestering the evaporated silicon and bringing growth process closer to equilibrium. In this confinement controlled sublimation (CCS) process, very high-quality graphene is grown on both polar faces of the SiC crystals. Since 2003, over 50 publications used CCS grown graphene, where it is known as the "furnace grown" graphene. Graphene multilayers grown on the carbon-terminated face of SiC, using the CCS method, were shown to consist of decoupled high mobility graphene layers. The CCS method is now applied on structured silicon carbide surfaces to produce high mobility nano-patterned graphene structures thereby demonstrating that EG is a viable contender for next-generation electronics. Here we present for the first time the CCS method that outperforms other epitaxial graphene production methods.

  14. Dynamical screening of van der Waals interactions in nanostructured solids: Sublimation of fullerenes

    SciTech Connect

    Tao, Jianmin; Yang, Jing; Rappe, Andrew M.

    2015-04-28

    Sublimation energy is one of the most important properties of molecular crystals, but it is difficult to study, because the attractive long-range van der Waals (vdW) interaction plays an important role. Here, we apply efficient semilocal density functional theory (DFT), corrected with the dynamically screened vdW interaction (DFT + vdW), the Rutgers-Chalmers nonlocal vdW-DF, and the pairwise-based dispersion-corrected DFT-D2 developed by Grimme and co-workers, to study the sublimation of fullerenes. We find that the short-range part, which accounts for the interaction due to the orbital overlap between fullerenes, is negligibly small. Our calculation shows that there exists a strong screening effect on the vdW interaction arising from the valence electrons of fullerenes. On the other hand, higher-order contributions can be as important as the leading-order term. The reasons are that (i) the surface of fullerene molecules is metallic and thus highly polarizable, (ii) the band gap of fullerene solids is small (less than 2 eV), and (iii) fullerene molecules in the solid phase are so densely packed, yielding the high valence electron density and small equilibrium intermolecular distances (the first nearest neighbor distance is only about 10 Å for C{sub 60}). However, these two effects make opposite contributions, leading to significant error cancellation between these two contributions. We demonstrate that, by considering higher-order contributions and the dynamical screening, the DFT + vdW method can yield sublimation energies of fullerenes in good agreement with reference values, followed by vdW-DF and DFT-D2. The insights from this study are important for a better understanding of the long-range nature of vdW interactions in nanostructured solids.

  15. Novel Strategy to Fabricate Floating Drug Delivery System Based on Sublimation Technique.

    PubMed

    Huanbutta, Kampanart; Limmatvapirat, Sontaya; Sungthongjeen, Srisagul; Sriamornsak, Pornsak

    2016-06-01

    The present study aims to develop floating drug delivery system by sublimation of ammonium carbonate (AMC). The core tablets contain a model drug, hydrochlorothiazide, and various levels (i.e., 0-50% w/w) of AMC. The tablets were then coated with different amounts of the polyacrylate polymers (i.e., Eudragit® RL100, Eudragit® RS100, and the mixture of Eudragit® RL100 and Eudragit® RS100 at 1:1 ratio). The coated tablets were kept at ambient temperature (25°C) or cured at 70°C for 12 h before further investigation. The floating and drug release behaviors of the tablets were performed in simulated gastric fluid USP without pepsin at 37°C. The results showed that high amount of AMC induced the floating of the tablets. The coated tablets containing 40 and 50% AMC floated longer than 8 h with a time-to-float of about 3 min. The sublimation of AMC from the core tablets decreased the density of system, causing floating of the tablets. The tablets coated with Eudragit® RL100 floated at a faster rate than those of Eudragit® RS100. Even the coating level of polymer did not influence the time-to-float and floating time of coated tablets containing the same amount of AMC, the drug release from the tablets coated with higher coating level of polymer showed slower drug release. The results suggested that the sublimation technique using AMC is promising for the development of floating drug delivery system.

  16. Large area and structured epitaxial graphene produced by confinement controlled sublimation of silicon carbide

    PubMed Central

    de Heer, Walt A.; Berger, Claire; Ruan, Ming; Sprinkle, Mike; Li, Xuebin; Hu, Yike; Zhang, Baiqian; Hankinson, John; Conrad, Edward

    2011-01-01

    After the pioneering investigations into graphene-based electronics at Georgia Tech, great strides have been made developing epitaxial graphene on silicon carbide (EG) as a new electronic material. EG has not only demonstrated its potential for large scale applications, it also has become an important material for fundamental two-dimensional electron gas physics. It was long known that graphene mono and multilayers grow on SiC crystals at high temperatures in ultrahigh vacuum. At these temperatures, silicon sublimes from the surface and the carbon rich surface layer transforms to graphene. However the quality of the graphene produced in ultrahigh vacuum is poor due to the high sublimation rates at relatively low temperatures. The Georgia Tech team developed growth methods involving encapsulating the SiC crystals in graphite enclosures, thereby sequestering the evaporated silicon and bringing growth process closer to equilibrium. In this confinement controlled sublimation (CCS) process, very high-quality graphene is grown on both polar faces of the SiC crystals. Since 2003, over 50 publications used CCS grown graphene, where it is known as the “furnace grown” graphene. Graphene multilayers grown on the carbon-terminated face of SiC, using the CCS method, were shown to consist of decoupled high mobility graphene layers. The CCS method is now applied on structured silicon carbide surfaces to produce high mobility nano-patterned graphene structures thereby demonstrating that EG is a viable contender for next-generation electronics. Here we present for the first time the CCS method that outperforms other epitaxial graphene production methods. PMID:21960446

  17. Dynamical screening of van der Waals interactions in nanostructured solids: Sublimation of fullerenes

    NASA Astrophysics Data System (ADS)

    Tao, Jianmin; Yang, Jing; Rappe, Andrew M.

    2015-04-01

    Sublimation energy is one of the most important properties of molecular crystals, but it is difficult to study, because the attractive long-range van der Waals (vdW) interaction plays an important role. Here, we apply efficient semilocal density functional theory (DFT), corrected with the dynamically screened vdW interaction (DFT + vdW), the Rutgers-Chalmers nonlocal vdW-DF, and the pairwise-based dispersion-corrected DFT-D2 developed by Grimme and co-workers, to study the sublimation of fullerenes. We find that the short-range part, which accounts for the interaction due to the orbital overlap between fullerenes, is negligibly small. Our calculation shows that there exists a strong screening effect on the vdW interaction arising from the valence electrons of fullerenes. On the other hand, higher-order contributions can be as important as the leading-order term. The reasons are that (i) the surface of fullerene molecules is metallic and thus highly polarizable, (ii) the band gap of fullerene solids is small (less than 2 eV), and (iii) fullerene molecules in the solid phase are so densely packed, yielding the high valence electron density and small equilibrium intermolecular distances (the first nearest neighbor distance is only about 10 Å for C60). However, these two effects make opposite contributions, leading to significant error cancellation between these two contributions. We demonstrate that, by considering higher-order contributions and the dynamical screening, the DFT + vdW method can yield sublimation energies of fullerenes in good agreement with reference values, followed by vdW-DF and DFT-D2. The insights from this study are important for a better understanding of the long-range nature of vdW interactions in nanostructured solids.

  18. Time Variability of the Dust Sublimation Zones in Pre-Main Sequence Disk Systems

    NASA Technical Reports Server (NTRS)

    Sitko, Michael L.; Carpenter, W. J.; Grady, C. A.; Russel, R. W.; Lynch, D. K.; Rudy, R. J.; Mazuk, S. M.; Venturini, C. C.; Kimes, R. L.; Beerman, L. C.; Ablordeppey, K. E.; Puetter, R. C.; Wisnewski, P.; Brafford, S. M.; Polomski, E. R.; Hammel, H. B.; Perry, R. B.; Wilde, J. L.

    2007-01-01

    The dust sublimation zone (DSZ) is the region of pre-main sequence (PMS) disks where dust grains most easily anneal, sublime, and condense out of the gas. Because of this, it is a location where crystalline material may be enhanced and redistributed throughout the rest of the disk. A decade-long program to monitor the thermal emission of the grains located in this region demonstrates that large changes in emitted flux occur in many systems. Changes in the thermal emission between 3 and 13.5 microns were observed in HD 31648 (MWC 480), HD 163296 (MWC 275), and DG Tau. This emission is consistent with it being produced at the DSZ, where the transition from a disk of gas to one of gas+dust occurs. In the case of DG Tau, the outbursts were accompanied by increased emission on the 10 micron silicate band on one occasion, while on another occasion it went into absorption. This requires lofting of the material above the disk into the line of sight. Such changes will affect the determination of the inner disk structure obtained through interferometry measurements, and this has been confirmed in the case of HD 163296. Cyclic variations in the heating of the DSZ will lead to the annealing of large grains, the sublimation of smaller grains, possibly followed by re-condensation as the zone enters a cooling phase. Lofting of dust above the disk plane, and outward acceleration by stellar winds and radiation pressure, can re-distribute the processed material to cooler regions of the disk, where cometesimals form. This processing is consistent with the detection of the preferential concentration of large crystalline grains in the inner few AU of PMS disks using interferometric spectroscopy with the VLTI.

  19. Measuring Enthalpy of Sublimation of Volatiles by Means of Piezoelectric Crystal Microbalances.

    PubMed

    Dirri, Fabrizio; Palomba, Ernesto; Longobardo, Andrea; Zampetti, Emiliano

    2016-09-15

    Piezoelectric Crystal Microbalances (PCM's) are widely used to study the chemical processes involving volatile compounds in any environment, such as condensation process. Since PCM's are miniaturized sensor, they are very suitable for planetary in situ missions, where can be used to detect and to measure the mass amount of astrobiologically significant compounds, such as water and organics. This work focuses on the realization and testing of a new experimental setup, able to characterize volatiles which can be found in a planetary environment. In particular the enthalpy of sublimation of some dicarboxylic acids has been measured. The importance of dicarboxylic acids in planetology and astrobiology is due to the fact that they have been detected in carbonaceous chondritic material (e.g. Murchinson), among the most pristine material present in our Solar System. In this work, a sample of acid was heated in an effusion cell up to its sublimation. For a set of temperatures (from 30 °C to 75 °C), the deposition rate on the PCM surface has been measured. From these measurements, it has been possible to infer the enthalpy of sublimation of Adipic acid, i.e. ΔH = 141.6 ± 0.8 kJ/mol and Succinic acid, i.e. ΔH = 113.3 ± 1.3 kJ/mol. This technique has so demonstrated to be a good choice to recognise a single compound or a mixture (with an analysis upstream) even if some improvements concerning the thermal stabilization of the system will be implemented in order to enhance the results' accuracy. The experiment has been performed in support of the VISTA (Volatile In Situ Thermogravimetry Analyzer) project, which is included in the scientific payload of the ESA MarcoPolo-R mission study.

  20. Sublimation-driven erosion on Hyperion: Topographic analysis and landform simulation model tests

    NASA Astrophysics Data System (ADS)

    Howard, Alan D.; Moore, Jeffrey M.; Schenk, Paul M.; White, Oliver L.; Spencer, John

    2012-07-01

    The unique appearance of Hyperion can be explained in part by the loss to space of ballistic ejecta during impact events, as was proposed by Thomas et al. (Thomas, P.C. et al. [2007a]. Icarus 190, 573-584). We conclude that such loss is a partial explanation, accounting for the lack of appreciable intercrater plains on a saturation-cratered surface. In order to create the smooth surfaces and the reticulate, honeycomb pattern of narrow divides between old craters, appreciable subsequent modification of crater morphology must occur through mass-wasting processes accompanied by sublimation, probably facilitated by the loss of CO2 as a component of the relief-supporting matrix of the bedrock. During early stages of crater degradation, steep, crenulate bedrock slopes occupy the upper crater walls with abrupt transitions downslope onto smooth slopes near the angle of repose mantled by mass wasting debris, as can be seen within young craters. Long-continued mass wasting eventually results in slopes totally mantled with particulate debris. This mass wasting effectively destroys small craters, at least in part accounting for the paucity of sub-kilometer craters on Hyperion. Surface temperatures measured by Cassini CIRS range from 58 K to 127 K and imply a surface thermal inertia of 11 ± 2 J m-2 K-1 s-1/2 and bolometric albedo ranging from 0.05 to 0.33. Resulting H2O sublimation rates are only tens of cm per billion years for most of the surface, so the evolution of the observed landforms is likely to require sublimation of more volatile species such as CO2.

  1. Dynamical screening of van der Waals interactions in nanostructured solids: Sublimation of fullerenes.

    PubMed

    Tao, Jianmin; Yang, Jing; Rappe, Andrew M

    2015-04-28

    Sublimation energy is one of the most important properties of molecular crystals, but it is difficult to study, because the attractive long-range van der Waals (vdW) interaction plays an important role. Here, we apply efficient semilocal density functional theory (DFT), corrected with the dynamically screened vdW interaction (DFT + vdW), the Rutgers-Chalmers nonlocal vdW-DF, and the pairwise-based dispersion-corrected DFT-D2 developed by Grimme and co-workers, to study the sublimation of fullerenes. We find that the short-range part, which accounts for the interaction due to the orbital overlap between fullerenes, is negligibly small. Our calculation shows that there exists a strong screening effect on the vdW interaction arising from the valence electrons of fullerenes. On the other hand, higher-order contributions can be as important as the leading-order term. The reasons are that (i) the surface of fullerene molecules is metallic and thus highly polarizable, (ii) the band gap of fullerene solids is small (less than 2 eV), and (iii) fullerene molecules in the solid phase are so densely packed, yielding the high valence electron density and small equilibrium intermolecular distances (the first nearest neighbor distance is only about 10 Å for C60). However, these two effects make opposite contributions, leading to significant error cancellation between these two contributions. We demonstrate that, by considering higher-order contributions and the dynamical screening, the DFT + vdW method can yield sublimation energies of fullerenes in good agreement with reference values, followed by vdW-DF and DFT-D2. The insights from this study are important for a better understanding of the long-range nature of vdW interactions in nanostructured solids.

  2. Measuring Enthalpy of Sublimation of Volatiles by Means of Piezoelectric Crystal Microbalances

    NASA Astrophysics Data System (ADS)

    Dirri, Fabrizio; Palomba, Ernesto; Longobardo, Andrea; Zampetti, Emiliano

    2016-09-01

    Piezoelectric Crystal Microbalances (PCM's) are widely used to study the chemical processes involving volatile compounds in any environment, such as condensation process. Since PCM's are miniaturized sensor, they are very suitable for planetary in situ missions, where can be used to detect and to measure the mass amount of astrobiologically significant compounds, such as water and organics. This work focuses on the realization and testing of a new experimental setup, able to characterize volatiles which can be found in a planetary environment. In particular the enthalpy of sublimation of some dicarboxylic acids has been measured. The importance of dicarboxylic acids in planetology and astrobiology is due to the fact that they have been detected in carbonaceous chondritic material (e.g. Murchinson), among the most pristine material present in our Solar System. In this work, a sample of acid was heated in an effusion cell up to its sublimation. For a set of temperatures (from 30 °C to 75 °C), the deposition rate on the PCM surface has been measured. From these measurements, it has been possible to infer the enthalpy of sublimation of Adipic acid, i.e. ΔH = 141.6 ± 0.8 kJ/mol and Succinic acid, i.e. ΔH = 113.3 ± 1.3 kJ/mol. This technique has so demonstrated to be a good choice to recognise a single compound or a mixture (with an analysis upstream) even if some improvements concerning the thermal stabilization of the system will be implemented in order to enhance the results' accuracy. The experiment has been performed in support of the VISTA (Volatile In Situ Thermogravimetry Analyzer) project, which is included in the scientific payload of the ESA MarcoPolo-R mission study.

  3. A Novel, Sublimation-Driven YORP-like Effect, and The Formation of Dust Striae in Cometary Tails

    NASA Astrophysics Data System (ADS)

    Steckloff, Jordan; Jacobson, Seth A.

    2014-11-01

    The dust tails of some great comets exhibit linear dust features that align with the Sun (striae). Striae are thought to form from icy chunks of dust ejected from the nucleus that are delayed in time before fragmenting [1]. Models show that striae formation is best fit through a mechanism of continuous fragmentation [2], but the physical mechanism responsible for this delayed fragmentation is unknown. We propose that striae form through a novel rotational fragmentation mechanism driven by the sublimation of volatile ices present in the ejected chunk.We note that sublimating gas molecules scatter off of the surface of a non-specular material similarly to photons (i.e. Lambertian scattering), however gas molecules carry significantly more momentum. By comparing the momentum flux from a sublimating gas with solar radiation pressure, we are able to scale the YORP timescale [3] to derive its sublimation-driven equivalent. We find that this Sublimative YORP-like timescale is significantly shorter than the YORP timescales by 4-5 orders of magnitude for H2O sublimation.We apply this mechanism to Comet West, which exhibited prominent striae in its dust tail. For ejected dust clumps to drift behind the nucleus to form the observed dust striae near 0.4 AU, [1] estimated the β-parameter of the chunks (ratio of solar radiation to solar gravitational forces) to be between 0.6 and 2.4. We equate this to a new parameter βsub (the ratio of dynamic sublimation to solar gravitational forces), which corresponds to icy chunks with radii of 5-20 cm, consistent with chunks ejected from Comet Wild 2 [4]. The sublimation-driven YORP timescales for chunks of this size is 1-3 hours, which allows for a cascade of rotational spin-up and fragmentation of daughter chunks to occur within the ~50-85 hour delay [1] between chunk ejection and striae formation. Thus, Comet West’s dust tail striae are consistent with this novel rotational fragmentation mechanism, which is driven by the sublimation

  4. The formation of striae within cometary dust tails by a sublimation-driven YORP-like effect

    NASA Astrophysics Data System (ADS)

    Steckloff, Jordan K.; Jacobson, Seth A.

    2016-01-01

    Sublimating gas molecules scatter off of the surface of an icy body in the same manner as photons (Lambertian Scattering). This means that for every photon-driven body force, there should be a sublimation-driven analog that affects icy bodies. Thermal photons emitted from the surfaces of asymmetrically shaped bodies in the Solar System generate net torques that change the spin rates of these bodies over time. The long-term averaging of this torque is called the YORP effect. Here we propose a sublimation-driven analog to the YORP effect (Sublimation-YORP or SYORP), in which sublimating gas molecules emitted from the surfaces of icy bodies in the Solar System also generate net torques on the bodies. However, sublimating gas molecules carry ∼104-105 times more momentum away from the body than thermal photons, resulting in much greater body torques. Previous studies of sublimative torques focused on emissions from highly localized sources on the surfaces of Jupiter Family Comet nuclei, and have therefore required extensive empirical observations to predict the resulting behavior of the body. By contrast, SYORP applies to non-localized emissions across the entire body, which likely dominates sublimation-drive torques on small icy chunks and dynamically young comets outside the Jupiter Family, and can therefore be applied without high-resolution spacecraft observations of their surfaces. Instead, we repurpose the well-tested mathematical machinery of the YORP effect to account for sublimation-driven torques. We show how an SYORP-driven mechanism best matches observations of the rarely observed, Sun-oriented linear features (striae) in the tails of comets, whose formation mechanism has remained enigmatic for decades. The SYORP effect naturally explains why striae tend to be observed between near-perihelion and ∼1 AU from the Sun for comets with perihelia less than 0.6 AU, and solves longstanding problems with moving enough material into the cometary tail to form

  5. Modeling of Sublimation-Driven Erosion and Ice Pinnacle Formation on Callisto

    NASA Astrophysics Data System (ADS)

    White, Oliver; Umurhan, Orkan M.; Howard, Alan D.; Moore, Jeffrey M.

    2014-11-01

    Most of the areas observed at high resolution on the Galilean satellite Callisto have a morphology that implies sublimation-driven landform modification and mass wasting is at work [Moore et al., 1999]. These areas comprise rolling dark plains with interspersed bright pinnacles. Howard and Moore [2008], using the MARSSIM landform evolution model, simulated evolution of this landscape as a combination of bedrock volatile sublimation, mass wasting of the dark, non-coherent residue, and redeposition of ice at high-elevation cold traps sheltered from thermal re-radiation to form the pinnacles.The goal of our study is to further investigate the details of pinnacle formation by refining this model, and by constraining values for the variable environmental parameters within the model such that they are consistent with the current understanding of Callisto’s surface environment. We present the results of the updated model and our experimentation with varying key parameters.Our refinement of the model has caused us to revise the result of Howard and Moore [2008] that the pinnacles represent an ice cover of several tens to hundreds of meters. Instead, our results indicate an ice coverage reaching several meters at most, a figure that is consistent with the prediction of Moore et al. [2004]. We have also modified the model such that ice contained within the pinnacles is now subject to sublimation itself.Using Fick’s Law to solve for the diffusive transport rate between a volatile table and an atmosphere [Moore et al., 1996], we have determined that the loss rate of H2O ice from the volatile-refractory bedrock through sublimation is too slow 10-20 kg m-2 s-1) to account for the formation of the ice pinnacles, and that a volatile mixture that contains H2O ice is necessary to facilitate its loss. We find that CO2 hydrate fulfills this role well: loss rates of CO2●6H2O 10-10 kg m-2 s-1) are sufficient to produce deposited ice thicknesses reaching several meters, with the

  6. A process simulator/trainer for the process inventory control system 20-MW freezer/sublimer

    SciTech Connect

    Tapp, P.A.; Carnal, C.L.; Wells, J.C.; Belcher, J.D.; Gibson, F.R.; Ruppel, F.R.

    1991-05-01

    This report describes the development of a process simulator/trainer for the Process Inventory Control System project. The main objective of this work was to build a plant simulator that accepts control signals from the Texas Instruments D/3 distributed control system and produces plant signals to mimic the behavior of a 20-MW freezer/sublimer unit. The simulator/trainer will be used as a surrogate plant to debug control system hardware/software and to train operators to use the new D/3 distributed control system without disturbing the processing of the Paducah Gaseous Diffusion Plant. 4 refs., 28 figs., 8 tabs.

  7. Dust clouds around red giant stars - Evidence of sublimating comet disks?

    NASA Technical Reports Server (NTRS)

    Matese, John J.; Whitmire, Daniel P.; Reynolds, Ray T.

    1989-01-01

    The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.

  8. Induced Recrystallization of CdTe Thin Films Deposited by Close-Spaced Sublimation

    SciTech Connect

    Moutinho, H. R.; Dhere, R. G.; Al-Jassim, M. M.; Levi, D. H.; Kazmerski, L. L.; Mayo, B.

    1998-10-26

    We have deposited CdTe thin films by close-spaced sublimation at two different temperature ranges. The films deposited at the lower temperature partially recrystallized after CdCl2 treatment at 350 C and completely recrystallized after the same treatment at 400 C. The films deposited at higher temperature did not recrystallize at these two temperatures. These results confirmed that the mechanisms responsible for changes in physical properties of CdTe films treated with CdCl2 are recrystallization and grain growth, and provided an alternative method to deposit CSS films using lower temperatures.

  9. The Anomalous Drift of Comet ISON (C/2012 S1) due to Sublimating Volatiles near Perihelion

    NASA Astrophysics Data System (ADS)

    Steckloff, J. K.; Keane, J. V.; Milam, S.; Coulson, I.; Knight, M. M.

    2014-12-01

    Prior to perihelion passage on 28 November 2013, the observed right ascension (RA) and declination (Dec) coordinates of comet C/2012 S1 (ISON) significantly lagged the predicted JPL (# 53) ephemeris. We show that this "braking effect" is due to a dynamic pressure exerted by sublimating gases on the sunward side of the nucleus [1]. Comet ISON was observed November 23 through November 28 using the SCUBA-2 sub-millimeter camera on the James Clerk Maxwell Telescope (JCMT). Imaging is achieved simultaneously at wavelengths of 850 μm and 450 μm, with RA and Dec determined from the central peak in the coma brightness [2]. When comet ISON was first detected at 850 μm, the 1-mm-sized dust particles were tightly bound to the comet nucleus until at least November 23. Three days later, the dust was less tightly bound, elongated and diffuse, spread out over as much as 120 arc seconds (80,000 km) in the anti-solar direction, suggesting a fragmentation event. We compute the average braking velocity of the nucleus of comet ISON by first measuring the distance between the central RA position and the predicted JPL ephemeris. We then calculate the change in this distance between subsequent observations, and divide this value by the elapsed time between the two observations to yield an average drift velocity of the nucleus over this time interval. We assume that comet ISON, like a number of Jupiter Family Comets visited by spacecraft [3], has low thermal inertia. Thus, the sublimating gases are emitted predominantly on the sunward side of the nucleus. Additionally, we assume that water ice dominates the sublimating gases [4]. We then calculate the pressure on the surface of the nucleus due to the emitted gases using the procedure described in [1]. We match the average drift velocity of the nucleus due to this sublimation pressure with the observed average drift velocity from the JCMT observations, which is sensitive to the size of the body, allowing us to estimate the size of the

  10. Search of the Na in the Region of the Sublimation of the Near-Sun Dust

    NASA Astrophysics Data System (ADS)

    Delone, A. B.; Divlekeev, M. I.; Suchanov, E. A.; Gulyaev, R. A.; Yakunina, G. V.; Porfir'eva, G. A.

    An evaluation of the Na number in the sublimation zone of the near-Sun interplanetary dust, based on a comparison with the intensity of the radiation of the Na in the Earth atmosphere, has been obtained. The abundance of the Na in the column along the line of sight is less than 2 x 108atom cm-2. This result is compared with the values, determined on the base of the brightness of the zodiacal light, F-corona and by direct measurements of the dust density with space experiments.

  11. The number of sodium atoms in the region of circumsolar sublimation of interplanetary dust

    NASA Astrophysics Data System (ADS)

    Delone, A. B.; Divlekeev, M. I.; Sukhanov, E. A.; Gulyaev, R. A.; Yakunina, G. V.; Porfir'eva, G. A.

    2008-02-01

    Sodium emission fromthe zone of circumsolar sublimation of interplanetary dust was searched for during the total solar eclipse of March 29, 2006, using a Fabry-Perot interferometer and interference filter transmitting at 590 nm. The upper limit for the column density sodium atoms is 2 × 108 atoms/cm2, is based on the comparison with the atmospheric sodium emission. This result is compared with the brightness of the zodiacal light and F-corona, as well as the dust density directly measured onboard spacecraft.

  12. Chemical transformations of proteinogenic amino acids during their sublimation in the presence of silica

    NASA Astrophysics Data System (ADS)

    Basiuk, Vladimir A.; Gromovoy, Taras Yu; Glukhoy, Alexandr M.; Golovaty, Vitaly G.

    1991-05-01

    Proteinogenic amino acids were sublimed in gram quantities in the presence of silica. High-performance liquid chromatographic and fast-atom-bombardment mass-spectrometric measurements showed that diketopiperazines (DKPs) were the main products of silica catalyzed thermal transformations in the case of aliphatic bifunctional amino acids. Intensive formation of products of decarboxylation, deamination and some other reactions was observed in the cases of trifunctional amino acids and phenylalanine. Possible mechanisms of reactions occured have been discussed. Principal possibility of ‘gas-solid-phase’ DKP synthesis has been demonstrated for bifunctional aliphatic amino acids.

  13. Dust clouds around red giant stars - Evidence of sublimating comet disks?

    NASA Astrophysics Data System (ADS)

    Matese, J. J.; Whitmire, D. P.; Reynolds, R. T.

    1989-09-01

    The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.

  14. Simulation of wind-induced snow transport and sublimation in alpine terrain using a fully coupled snowpack/atmosphere model

    NASA Astrophysics Data System (ADS)

    Vionnet, V.; Martin, E.; Masson, V.; Guyomarc'h, G.; Naaim-Bouvet, F.; Prokop, A.; Durand, Y.; Lac, C.

    2014-03-01

    In alpine regions, wind-induced snow transport strongly influences the spatio-temporal evolution of the snow cover throughout the winter season. To gain understanding on the complex processes that drive the redistribution of snow, a new numerical model is developed. It directly couples the detailed snowpack model Crocus with the atmospheric model Meso-NH. Meso-NH/Crocus simulates snow transport in saltation and in turbulent suspension and includes the sublimation of suspended snow particles. The coupled model is evaluated against data collected around the experimental site of Col du Lac Blanc (2720 m a.s.l., French Alps). First, 1-D simulations show that a detailed representation of the first metres of the atmosphere is required to reproduce strong gradients of blowing snow concentration and compute mass exchange between the snowpack and the atmosphere. Secondly, 3-D simulations of a blowing snow event without concurrent snowfall have been carried out. Results show that the model captures the main structures of atmospheric flow in alpine terrain. However, at 50 m grid spacing, the model reproduces only the patterns of snow erosion and deposition at the ridge scale and misses smaller scale patterns observed by terrestrial laser scanning. When activated, the sublimation of suspended snow particles causes a reduction of deposited snow mass of 5.3% over the calculation domain. Total sublimation (surface + blowing snow) is three times higher than surface sublimation in a simulation neglecting blowing snow sublimation.

  15. Sublime Science

    ERIC Educational Resources Information Center

    Girod, Mark

    2007-01-01

    One of the shortcomings in most efforts to integrate art and science is that many people have a shallow understanding of art, which inevitably leads to shallow connections between art and science. Coloring drawings of planets, building sculptures of volcanoes, and decorating scientific diagrams are fine activities, but they do not link science and…

  16. Sublime Science

    ERIC Educational Resources Information Center

    Girod, Mark

    2007-01-01

    One of the shortcomings in most efforts to integrate art and science is that many people have a shallow understanding of art, which inevitably leads to shallow connections between art and science. Coloring drawings of planets, building sculptures of volcanoes, and decorating scientific diagrams are fine activities, but they do not link science and…

  17. Results for p-shell nuclei at LO, NLO, and N2LO in chiral EFT

    NASA Astrophysics Data System (ADS)

    Maris, Pieter; Vary, James

    2016-09-01

    We present results for p-shell nuclei using interactions derived from chiral effective field theory up to N2LO. The many-body calculations are performed order-by-order in the chiral expansion. We show the dependence of the ground state energies on the chiral order; we also present excitation energies of narrow excited states and other observables such as magnetic and quadrupole moments of selected ground states. We discuss both the theoretical uncertainties due to the truncation of the chiral expansion, as well as the numerical uncertainties associated with the many-body method. Supported by the US DOE Grants DESC0008485 (SciDAC/NUCLEI) and DE-FG02-87ER40371. Computational resources provided by NERSC, supported under US DOE Contract DE-AC02-05CH11231, and by the ALCF, supported under US DOE Contract DE-AC02-06CH11357.

  18. Thermal sublimation: a scalable and controllable thinning method for the fabrication of few-layer black phosphorus

    NASA Astrophysics Data System (ADS)

    Luo, Weijun; Yang, Rui; Liu, Jialun; Zhao, Yunlong; Zhu, Wenjuan; (Maggie Xia, Guangrui

    2017-07-01

    We report uniform layer-by-layer sublimation of black phosphorus under heating below 600 K. The uniformity and crystallinity of BP samples after thermal thinning were confirmed by Raman spectra and Raman mapping. The sublimation rate of BP was around 0.18 nm min-1 at 500 K and 1.15 nm min-1 at 550 K. Both room and high temperature Raman peak intensity ratio \\tfrac{{{Si}}}{{{{A}}}g2} as functions of BP thickness were established for in situ thickness determination and control. Uniform and crystalline 2 to 4-layer BP flakes with areas from 10 to 1000 μm2 were prepared with this method. No micron scale defects were observed. The sublimation thinning method was shown to be a controllable and scalable approach to prepare high-quality few-layer black phosphorus.

  19. [Research on the polycrystalline CdS thin films prepared by close-spaced sublimation].

    PubMed

    Yang, Ding-Yu; Xia, Geng-Pei; Zheng, Jia-Gui; Feng, Liang-Huan; Cai, Ya-Ping

    2009-01-01

    In the present paper, the factors of influence on the deposition rate of CdS films prepared by close-spaced sublimation (CSS) were first studied systematically, and it was found from the experiments that the deposition rate increased with the raised temperature of sublimation source, while decreased with the raised substrate temperature and the deposition pressure. The structure, morphology and light transmittance of the prepared samples were tested subsequently, and the results show: (1) The CdS films deposited under different oxygen partial pressure all present predominating growth lattice orientation (103), and further more the films will be strengthened after annealed under CdCl2 atmosphere. (2) The AFM images of CdS show that the films are compact and uniform in grain diameter, and the grain size becomes larger with the increased substrate temperature. Along with it, the film roughness was also augmented. (3) The transmittance in the shortwave region of visible light through the CdS films would be enhanced when its thickness is reduced, and that will help improve the shortwave spectral response of CdTe solar cells. Finally, the prepared CdS films were employed to fabricate CdTe solar cells, which have achieved a conversion efficiency of 10.29%, and thus the feasibility of CSS process in the manufacture of CdTe solar cells was validated primarily.

  20. TERRESTRIAL PLANET FORMATION THROUGH ACCRETION OF SUBLIMATING ICY PLANETESIMALS IN A COLD NEBULA

    SciTech Connect

    Machida, Ryosuke; Abe, Yutaka

    2010-06-20

    Most of the theories of the solar system formation stand on the assumption that the formation of planetesimals occurs in a transparent (i.e., optically thin) nebula, in which H{sub 2}O ice is unstable at the formation region of the terrestrial planet due to direct stellar irradiation. However, in the astronomical context, it is confirmed by both observations and numerical models that protoplanetary disks are initially opaque (i.e., optically thick) owing to floating small dust particles, and the interior of the disk is colder than the transparent disk. If planetesimals are formed in the opaque cold nebula, they should be mainly composed of H{sub 2}O ice, even at the formation region of terrestrial planets. Abundant icy material would help the formation of planetesimals through enhancement of the dust amount. Icy planetesimals start sublimation when the protoplanetary disk gets transparent through clearance of small dust particles. Here, we investigated the consequence of such icy planetesimal formation through numerical simulations of the competition between the sublimation and accretion of icy planetesimals. It was shown that various types of planets ranging from rocky planets to water-ball planets can be formed inside the location of the snow line of a transparent disk depending on the disk mass and the time evolution of disk transparency. We found size-dependent water content of icy planetesimals, which suggests potential difference in the redox state between meteorites and terrestrial planets at the same distance from the central star.

  1. Sublimator Driven Coldplate Engineering Development Unit Test Results and Development of Second Generation SDC

    NASA Technical Reports Server (NTRS)

    Stephan, Ryan A.; Sheth, Rubik B.

    2009-01-01

    The Sublimator Driven Coldplate (SDC) is a unique piece of thermal control hardware that has several advantages over a traditional thermal control scheme. The principal advantage is the possible elimination of a pumped fluid loop, potentially increasing reliability and reducing complexity while saving both mass and power. Furthermore, the Integrated Sublimator Driven Coldplate (ISDC) concept couples a coolant loop with the previously described SDC hardware. This combination allows the SDC to be used as a traditional coldplate during long mission phases. The previously developed SDC technology cannot be used for long mission phases due to the fact that it requires a consumable feedwater for heat rejection. Adding a coolant loop also provides for dissimilar redundancy on the Altair Lander ascent module thermal control system, which is the target application for this technology. Tests were performed on an Engineering Development Unit at NASA s Johnson Space Center to quantify and assess the performance of the SDC. Correlated thermal math models were developed to help explain the test data. The paper also outlines the preliminary results of an ISDC concept being developed.

  2. Formation of gullies on Mars by debris flows triggered by CO2 sublimation

    NASA Astrophysics Data System (ADS)

    Pilorget, C.; Forget, F.

    2016-01-01

    Martian gully landforms resemble terrestrial debris flows formed by the action of liquid water and have thus been interpreted as evidence for potential habitable environments on Mars within the past few millennia. However, ongoing gully formation has been detected under surface conditions much too cold for liquid water, but at times in the martian year when a thin layer of seasonal CO2 frost is present and defrosting above the regolith. These observations suggest that the CO2 condensation-sublimation cycle could play a role in gully formation. Here we use a thermo-physical numerical model of the martian regolith underlying a CO2 ice layer and atmosphere to show that the pores beneath the ice layer can be filled with CO2 ice and subjected to extreme pressure variations during the defrosting season. The subsequent gas fluxes can destabilize the regolith material and induce gas-lubricated debris flows with geomorphic characteristics similar to martian gullies. Moreover, we find that subsurface CO2 ice condensation, sublimation and pressurization occurs at conditions found at latitudes and slope orientations where gullies are observed. We conclude that martian gullies can result from geologic dry ice processes that have no terrestrial analogues and do not require liquid water. Such dry ice processes may have helped shape the evolution of landforms elsewhere on the martian surface.

  3. How drops bounce and dance on ice: the role of sublimating surfaces

    NASA Astrophysics Data System (ADS)

    Antonini, Carlo; Bernagozzi, Ilaria; Jung, Stefan; Poulikakos, Dimos; Marengo, Marco; Laboratory of Thermodynamics in Emerging Technologies Team; Themal Physics Laboratory Team

    2013-11-01

    Drop rebound is a spectacular event that appears after impact on superhydrophobic surfaces, due to low drop-solid substrate adhesion, and on hot substrates in Leidenfrost conditions, thanks to a vapor layer forming at the liquid-substrate interface, caused by drop evaporation. However, at temperatures below water freezing temperature, i.e. 0C, even superhydrophobicity can get lost. In the present work, we demonstrate that drop rebound can also be originated by another physical phenomenon, i.e. the solid substrate sublimation, at temperatures as low as -79C. To prove this mechanism, drop impact experiments were conducted on solid carbon dioxide, commonly known as dry ice. Drop dynamics and rebound were analyzed, together with the cases of drop impacting on a superhydrophobic surface and on a hot plate, to show how three different physical mechanisms, which apparently share nothing in common, i.e. superhydrophobicity, evaporation and sublimation, can all lead to drop rebound, in an extremely wide temperature range, from 300C down to even below -79C. Additional glycol drop impact tests proved the independence of the observed phenomena from the chosen liquid. Finally, the formation and visualization of an air vortex ring around an impacting drop is also reported. The authors acknowledge funding from Regione Lombardia and European Community (Marie Curie Fellowship).

  4. Computational analysis for dry-ice sublimation assisted CO2 jet impingement flow

    NASA Astrophysics Data System (ADS)

    Kwak, Songmi; Lee, Jaeseon

    2015-11-01

    The flow and heat transfer characteristics of the novel gas-solid two-phase jet impingement are investigated computationally. When the high pressure carbon dioxide (CO2) flow passes through a nozzle or orifice, it experiences the sudden expansion and the rapid temperature drop occurred by Joule-Thomson effect. This temperature drop causes the lower bulk jet fluid temperature than the CO2 sublimation line, so dry-ice becomes formed. By using CO2 gas-solid mixture as a working fluid of jet impingement, it is expected the heat transfer enhancement can be achieved due to the low bulk temperature and the additional phase change latent heat. In this study, 2D CFD model is created to predict the cooling effect of gas-solid CO2 jet. The gas-solid CO2 flow is considered by Euler-Lagrangian approach of mixed phase and the additional heat transfer module is embedded to account for the sublimation phenomena of the solid state CO2. The jet flow and heat transfer performance of gas-solid CO2 jet is investigated by the variance of flow parameter like Reynolds number, solid phase concentration and jet geometries.

  5. Formulation and evaluation of fast dissolving tablets of cinnarizine using superdisintegrant blends and subliming material

    PubMed Central

    Basu, Biswajit; Bagadiya, Abhishek; Makwana, Sagar; Vipul, Vora; Batt, Devraj; Dharamsi, Abhay

    2011-01-01

    The aim of this investigation was to develop fast dissolving tablet of cinnarizine. A combination of super disintegrants, i.e., sodium starch glycolate (SSG) and crosscarmellose sodium (CCS) were used along with camphor as a subliming material. An optimized concentration of camphor was added to aid the porosity of the tablet. A 32 full factorial design was applied to investigate the combined effect of two formulation variables: Amount of SSG and CCS. Infrared (IR) spectroscopy was performed to identify the physicochemical interaction between drug and polymer. IR spectroscopy showed that there is no interaction of drug with polymer. In the present study, direct compression was used to prepare the tablets. The powder mixtures were compressed into tablet using flat face multi punch tablet machine. Camphor was sublimed from the tablet by exposing the tablet to vacuum drier at 60°C for 12 hours. All the formulations were evaluated for their characteristics such as average weight, hardness, wetting time, friability, content uniformity, dispersion time (DT), and dissolution rate. An optimized tablet formulation (F 9) was found to have good hardness of 3.30 ± 0.10 kg/cm2, wetting time of 42.33 ± 4.04 seconds, DT of 34.67 ± 1.53 seconds, and cumulative drug release of not less than 99% in 16 minutes. PMID:22247895

  6. Laboratory experiments to investigate sublimation rates of water ice in nighttime lunar regolith

    NASA Astrophysics Data System (ADS)

    Piquette, Marcus; Horányi, Mihály; Stern, S. Alan

    2017-09-01

    The existence of water ice on the lunar surface has been a long-standing topic with implications for both lunar science and in-situ resource utilization (ISRU). Cold traps on the lunar surface may have conditions necessary to retain water ice, but no laboratory experiments have been conducted to verify modeling results. We present an experiment testing the ability to thermally control bulk samples of lunar regolith simulant mixed with water ice under vacuum in an effort to constrain sublimation rates. The simulant used was JSC-1A lunar regolith simulant developed by NASA's Johnson Space Center. Samples with varying ratios of water ice and JSC-1A regolith simulant, totally about 1 kg, were placed under vacuum and cooled to 100 K to simulate conditions in lunar cold traps. The resulting sublimation of water ice over an approximately five-day period was measured by comparing the mass of the samples before and after the experimental run. Our results indicate that water ice in lunar cold traps is stable on timescales comparable to the lunar night, and should continue to be studied as possible resources for future utilization. This experiment also gauges the efficacy of the synthetic lunar atmosphere mission (SLAM) as a low-cost water resupply mission to lunar outposts.

  7. Vapor pressures and enthalpies of sublimation of D-glucose, D-xylose, cellobiose, and levoglucosan

    SciTech Connect

    Oja, V.; Suuberg, E.M.

    1999-01-01

    The vapor pressures of {alpha}-D-glucose (or dextrose), D-xylose, D-cellobiose (or 4-{beta}-D-glucopyranosyl-D-glucopyranose), and levoglucosan (or 1,6-anhydro-{beta}-D-glucopyranose) have been measured using the Knudsen effusion technique, in the range of temperatures from 344 to 488 K. The measurements were all made in the solid sublimation regime, and enthalpies of sublimation were calculated from the Clausius-Claperon equation. The vapor pressures may be correlated by ln(P/Pa) = A {minus} B/(T/K), where A = 53.16, B = 23.382 ({+-}600) for D-glucose (395--406 K), A = 46.29 and B = 19,006 ({+-} 375) for D-xylose (370--395 K), and A = 70.30 and B = 36,264 ({+-} 5,220) for cellobiose (474--488 K). Levoglucosan displayed a solid phase transition at approximately 386 K, and its vapor pressure was affected accordingly. For this material, A = 38.96 and B = 15,049 ({+-} 123) in the temperature range 344--386 K and A = 31.19 and B = 12,066 ({+-} 709) in the temperature range 386--405 K.

  8. Salicylamide cocrystals: screening, crystal structure, sublimation thermodynamics, dissolution, and solid-state DFT calculations.

    PubMed

    Manin, Alex N; Voronin, Alexander P; Manin, Nikolay G; Vener, Mikhail V; Shishkina, Anastasia V; Lermontov, Anatoly S; Perlovich, German L

    2014-06-19

    A new cocrystal of 2-hydroxybenzamide (A) with 4-acetamidobenzoic acid (B) has been obtained by the DSC screening method. Thermophysical analysis of the aggregate [A:B] has been conducted and a fusion diagram has been plotted. Cocrystal formation from melts was studied by using thermomicroscopy. A cocrystal single-crystal was grown and its crystal structure was determined. The pattern of noncovalent interactions has been quantified using the solid-state DFT computations coupled with the Bader analysis of the periodic electron density. The sublimation processes of A-B cocrystal have been studied and its thermodynamic functions have been calculated. The classical method of substance transfer by inert gas-carrier was chosen to investigate sublimation processes experimentally. The lattice energy is found to be 143 ± 4 kJ/mol. It is lower than the sum of the corresponding values of the cocrystal pure components. The theoretical value of the lattice energy, 156 kJ/mol, is in reasonable agreement with the experimental one. A ternary phase diagram of solubility (A-B-ethanol) has been plotted and the areas with solutions for growing thermodynamically stable cocrystals have been determined.

  9. Sublimator Driven Coldplate Engineering Development Unit Test Results and Development of Second Generation SDC

    NASA Technical Reports Server (NTRS)

    Stephan, Ryan A.; Sheth, Rubik B.

    2009-01-01

    The Sublimator Driven Coldplate (SDC) is a unique piece of thermal control hardware that has several advantages over a traditional thermal control scheme. The principal advantage is the possible elimination of a pumped fluid loop, potentially increasing reliability and reducing complexity while saving both mass and power. Furthermore, the Integrated Sublimator Driven Coldplate (ISDC) concept couples a coolant loop with the previously described SDC hardware. This combination allows the SDC to be used as a traditional coldplate during long mission phases. The previously developed SDC technology cannot be used for long mission phases due to the fact that it requires a consumable feedwater for heat rejection. Adding a coolant loop also provides for dissimilar redundancy on the Altair Lander ascent module thermal control system, which is the target application for this technology. Tests were performed on an Engineering Development Unit at NASA s Johnson Space Center to quantify and assess the performance of the SDC. Correlated thermal math models were developed to help explain the test data. The paper also outlines the preliminary results of an ISDC concept being developed.

  10. Formulation and evaluation of fast dissolving tablets of cinnarizine using superdisintegrant blends and subliming material.

    PubMed

    Basu, Biswajit; Bagadiya, Abhishek; Makwana, Sagar; Vipul, Vora; Batt, Devraj; Dharamsi, Abhay

    2011-10-01

    The aim of this investigation was to develop fast dissolving tablet of cinnarizine. A combination of super disintegrants, i.e., sodium starch glycolate (SSG) and crosscarmellose sodium (CCS) were used along with camphor as a subliming material. An optimized concentration of camphor was added to aid the porosity of the tablet. A 3(2) full factorial design was applied to investigate the combined effect of two formulation variables: Amount of SSG and CCS. Infrared (IR) spectroscopy was performed to identify the physicochemical interaction between drug and polymer. IR spectroscopy showed that there is no interaction of drug with polymer. In the present study, direct compression was used to prepare the tablets. The powder mixtures were compressed into tablet using flat face multi punch tablet machine. Camphor was sublimed from the tablet by exposing the tablet to vacuum drier at 60°C for 12 hours. All the formulations were evaluated for their characteristics such as average weight, hardness, wetting time, friability, content uniformity, dispersion time (DT), and dissolution rate. An optimized tablet formulation (F 9) was found to have good hardness of 3.30 ± 0.10 kg/cm(2), wetting time of 42.33 ± 4.04 seconds, DT of 34.67 ± 1.53 seconds, and cumulative drug release of not less than 99% in 16 minutes.

  11. EVOLUTION OF SIZE DISTRIBUTION OF ICY GRAINS BY SUBLIMATION AND CONDENSATION

    SciTech Connect

    Kuroiwa, Takuto; Sirono, Sin-iti

    2011-09-20

    In the outer part of a protoplanetary disk, dust grains consist of silicate core covered by an ice mantle. A temporal heating event in the disk results in sublimation of the ice mantle. After the end of the heating event, as the temperature decreases, H{sub 2}O molecules recondense on the surface of the dust grain. Ultimately, the dust grain is covered by an ice mantle. Because the equilibrium vapor pressure on the grain surface decreases with the grain size, a large grain grows faster than a small grain. As a result, the size of an icy dust grain changes as a result of the heating event. The change in size also affects the mechanical properties of the dust aggregates formed by the icy grains. In this paper, we investigated the evolution of the size distribution of icy dust grains during sublimation and condensation. We found that the size evolution of icy grains can be divided into two stages. In the first stage, the icy grains grow through condensation of H{sub 2}O molecules. In the second stage, the size of grains changes further as H{sub 2}O molecules are transferred between icy grains while the surrounding gas condenses. The size distribution of the icy dust grains becomes bimodal, with a small number of relatively large grains and many small grains without an icy mantle. Possible effects of the size change on the evolution of icy dust aggregates are discussed.

  12. Statistical theory of noble-gas crystals and the phenomenon of sublimation

    NASA Astrophysics Data System (ADS)

    Bondarev, V. N.

    2005-05-01

    We propose a consistent (without any fitting parameters) statistical theory of classical noble-gas crystals with pair interaction between atoms. Using the equation for the single-particle distribution function of the statistical system, we demonstrate the existence of an infinite number of exact sum rules for the amplitudes of the space-periodic solutions. Even the first sum rule leads to the solution which turns into the exact one at the absolute zero temperature. For the pair distribution function, we obtained the physically correct solution using the well-known exact relation for the compressibility as the self-consistent condition. As a result, we succeeded in recovering the equation of state of the crystal, and starting from the Lennard-Jones potential with the “gaseous” parameters, we calculated the temperature dependencies of the lattice constant and the isothermal compressibility of the crystal at the sublimation line. These calculations (including the form of the sublimation line itself) agree rather well with the corresponding experimental data for the argon-type media in the “classical” temperature region. The question about the bifurcation of the solutions is considered. Ways to further develop the theory are discussed.

  13. Sublimation of water ice mixed with silicates and tholins: Evolution of surface texture and reflectance spectra, with implications for comets

    NASA Astrophysics Data System (ADS)

    Poch, Olivier; Pommerol, Antoine; Jost, Bernhard; Carrasco, Nathalie; Szopa, Cyril; Thomas, Nicolas

    2016-03-01

    The surfaces of many objects in the Solar System comprise substantial quantities of water ice sometimes mixed with minerals and/or organic molecules. The sublimation of the ice changes the structural and optical properties of these objects. We present laboratory data on the evolution of the structure and the visible and near-infrared spectral reflectance of icy surface analogues of cometary ices, made of water ice, complex organic matter (tholins) and silicates, as they undergo sublimation under low temperature (<-70 °C) and pressure (10-5 mbar) conditions inside the SCITEAS simulation chamber. As the water ice sublimated, we observed in situ the formation of a porous sublimation lag deposit, or sublimation mantle, at the top of the ice. This mantle is a network of filaments made of the non-volatile particles. Organics or phyllosilicates grains, able to interact via stronger inter-particulate forces than olivine grains, can form a foam-like structure having internal cohesiveness, holding olivine grains together. As this mantle builds-up, the band depths of the sub-surface water ice are attenuated until complete extinction under only few millimeters of mantle. Optically thick sublimation mantles are mainly featureless in the near infrared. The absorption bands of the minerals present in the mantle are weak, or even totally absent if minerals are mixed with organics which largely dominate the VIS-NIR reflectance spectrum. During sublimation, ejections of large fragments of mantle, triggered by the gas flow, expose ice particles to the surface. The contrast of brightness between mantled and ice-exposed areas depends on the wavelength range and the dust/ice ratio considered. We describe how the chemical nature of the non-volatiles, the size of their particles, the way they are mixed with the ice and the dust/ice mass ratio influence the texture, activity and spectro-photometric properties of the sublimation mantles. These data provide useful references for

  14. LoFASM's FPGA-based Digital Acquisition System

    NASA Astrophysics Data System (ADS)

    Dartez, Louis P.; Jenet, F.; Creighton, T. D.; Ford, A. J.; Hicks, B.; Hinojosa, J.; Kassim, N. E.; Price, R. H.; Stovall, K.; Ray, P. S.; Taylor, G. B.

    2014-01-01

    The Low Frequency All Sky Monitor (LoFASM) is a distributed array of dipole antennas that are sensitive to radio frequencies from 10 to 88 MHz. LoFASM consists of antennas and front end electronics that were originally developed for the Long Wavelength Array (LWA) by the U.S. Naval Research Lab, the University of New Mexico, Virginia Tech, and the Jet Propulsion Laboratory. LoFASM, funded by the U.S. Department of Defense, will initially consist of 4 stations, each consisting of 12 dual-polarization dipole antenna stands. The primary science goals of LoFASM will be the detection and study of low-frequency radio transients, a high priority science goal as deemed by the National Research Council's decadal survey. The data acquisition system for the LoFASM antenna array will be using Field Programmable Gate Array (FPGA) technology to implement a real time full Stokes spectrometer and data recorder. This poster presents an overview of the current design and digital architecture of a single station of the LoFASM array as well as the status of the entire project.

  15. Sublimation of Exposed Snow Queen Surface Water Ice as Observed by the Phoenix Mars Lander

    NASA Astrophysics Data System (ADS)

    Markiewicz, W. J.; Keller, H. U.; Kossacki, K. J.; Mellon, M. T.; Stubbe, H. F.; Bos, B. J.; Woida, R.; Drube, L.; Leer, K.; Madsen, M. B.; Goetz, W.; El Maarry, M. R.; Smith, P.

    2008-12-01

    One of the first images obtained by the Robotic Arm Camera on the Mars Phoenix Lander was that of the surface beneath the spacecraft. This image, taken on sol 4 (Martian day) of the mission, was intended to check the stability of the footpads of the lander and to document the effect the retro-rockets had on the Martian surface. Not completely unexpected the image revealed an oval shaped, relatively bright and apparently smooth object, later named Snow Queen, surrounded by the regolith similar to that already seen throughout the landscape of the landing site. The object was suspected to be the surface of the ice table uncovered by the blast of the retro-rockets during touchdown. High resolution HiRISE images of the landing site from orbit, show a roughly circular dark region of about 40 m diameter with the lander in the center. A plausible explanation for this region being darker than the rest of the visible Martian Northern Planes (here polygonal patterns) is that a thin layer of the material ejected by the retro-rockets covered the original surface. Alternatively the thrusters may have removed the fine surface dust during the last stages of the descent. A simple estimate requires that about 10 cm of the surface material underneath the lander is needed to be ejected and redistributed to create the observed dark circular region. 10 cm is comparable to 4-5 cm predicted depth at which the ice table was expected to be found at the latitude of the Phoenix landing site. The models also predicted that exposed water ice should sublimate at a rate not faster but probably close to 1 mm per sol. Snow Queen was further documented on sols 5, 6 and 21 with no obvious changes detected. The following time it was imaged was on sol 45, 24 sols after the previous observation. This time some clear changes were obvious. Several small cracks, most likely due to thermal cycling and sublimation of water ice appeared. Nevertheless, the bulk of Snow Queen surface remained smooth. The next

  16. THE EFFECTS ON BIOLOGICAL MATERIALS OF FREEZING AND DRYING BY VACUUM SUBLIMATION

    PubMed Central

    Greiff, Donald; Blumenthal, Herman; Chiga, Masahiro; Pinkerton, Henry

    1954-01-01

    The infectivity titre of influenza virus-infected allantoic fluid was determined after a variety of procedures involving cyclic slow freezing and thawing, freezing at various rates with subsequent storage at different temperatures freezing at various rates with subsequent dehydration at various temperatures, and different degrees of dehydration. All these factors were found to influence the survival rate of the virus particles. Five freeze-thaw cycles resulted in a fall in titre from 10–8.6 to 10–0.8 cycles 2, 3, and 4 causing much greater losses than cycles 1 and 5. Rapid cooling to –40°C. or slow cooling to –80 or 190°C. did not cause significant titre loss, but rapid cooling to temperatures above –40° or slow cooling to temperatures above –80°C. caused definite titre loss. Loss of titre on storage occurred only at temperatures above –40deg;C. The effect of lyophilization depends both on the preliminary treatment and on the dehydration temperature. Better conservation of titre was obtained after preliminary cooling to –190 or –80°C. than after preliminary cooling to higher temperatures. The most effective sublimation temperatures were 0 and –80°.; the least effective was +20°C. Titre losses in suspensions sublimated at –10, –30, and –60°C. were in general intermediate. No loss in titre occurred after preliminary cooling to –80 or –190°C. and subsequent dehydration at –80 or 0°C. The degree of dehydration definitely affects the survival of virus on storage at 0°C., but sublimation for 4 hours at 0°C. gave complete protection against titre loss on storage at this temperature. Possible explanations of the observations made are suggested, based on known physiochemical phenomena such as supercooling, vitrification, variations in size and shape of ice crystals with different freezing speeds, differential enzyme inactivation, changes in salt concentration, and changes in energy levels. PMID:13163341

  17. Graphite Sublimation Tests for the Muon Collider/Neutrino Factory Target Development Program

    SciTech Connect

    Haines, JR

    2002-03-25

    A passively cooled graphite target was proposed for a 1.5 MW neutrino production research facility because of its simplicity and favorable performance as a target material for neutrino production. The conceptual design for the target in the Reference 1 study was a graphite rod 15 mm in diameter by 800 mm long. Figure 1 shows the graphite target rod supported by graphite spokes, which are mounted to a water-cooled stainless steel support tube. The target is radiatively cooled to the water-cooled surface of the support tube. Based on nuclear analysis results, the time-averaged power deposition in the target is 35 kW. If this power is deposited uniformly along the axial length of the target, the volumetric power deposition in the target is about 250 MW/m{sup 3}. The target surface temperature required to radiate the deposited power to a water-cooled tube is estimated to be about 1850 C, and the temperature at the center of the target is about 75 C hotter. The sublimation erosion rate (e), estimated assuming that the graphite is submersed in a perfect vacuum environment, can be derived from kinetic theory and is given by: e = p{sub sat}(m/2{pi} kT){sup 1/2} where p{sub sat} is the saturation pressure, m is the molecular weight, k is the Boltzmann constant, and T is the surface temperature. The saturation pressure given in Ref. 3 can be approximated by: p{sub sat} =exp(-A/T + B) where A = 9.47 x 10{sup 3}, B = 24.2, and the units of p{sub sat} and T are atmospheres and K, respectively. Using these equations, the saturation pressure and sublimation erosion rate are plotted in Fig. 2 as a function of temperature. The surface recession rate shown with units of mm/s in Fig. 2 assumes one-sided erosion. At the average power deposition value of 250 MW/m{sup 3}, the surface temperature is 1850 C resulting in a sublimation erosion rate of only 2.2 {micro}m/day. However, if the actual power deposition were peaked by a factor of two in the axial direction, then the surface

  18. Switchover software reliability estimate for Paducah Freezer/Sublimer computer systems

    SciTech Connect

    Flanagan, D.M.; Davis, J.N.

    1993-04-01

    K-25 Engineering Division purchased a series of redundant computer systems and developed software for the purpose of providing continuous process monitoring and control for the Freezer/Sublimer equipment in the gaseous diffusion process at the Paducah Gaseous Diffusion Plant. The application software is loaded on two central processing units (CPU) so that in the event of a failure of the primary unit, the processing can switch to the backup unit and continue processing without error. It is the purpose of this document to demonstrate the reliability of this system with respect to its ability to switch properly between redundant CPU. The total reliability estimation problem -- which considers the computer hardware, the operating system software, and the application software -- has been reduced to one that considers only the application software directly involved in the switchover process. Estimates are provided for software reliability and the testing coverage. Software and hardware reliability models and reliability growth models are considered in addition to Bayesian approaches.

  19. Optimized heat exchange in a CO2 de-sublimation process

    DOEpatents

    Baxter, Larry; Terrien, Paul; Tessier, Pascal; Hoeger, Christopher

    2017-09-19

    The present invention is a process for removing carbon dioxide from a compressed gas stream including cooling the compressed gas in a first heat exchanger, introducing the cooled gas into a de-sublimating heat exchanger, thereby producing a first solid carbon dioxide stream and a first carbon dioxide poor gas stream, expanding the carbon dioxide poor gas stream, thereby producing a second solid carbon dioxide stream and a second carbon dioxide poor gas stream, combining the first solid carbon dioxide stream and the second solid carbon dioxide stream, thereby producing a combined solid carbon dioxide stream, and indirectly exchanging heat between the combined solid carbon dioxide stream and the compressed gas in the first heat exchanger.

  20. Latent fingermark visualisation using reduced-pressure sublimation of copper phthalocyanine.

    PubMed

    Williams, Geraint; ap Llwyd Dafydd, Hefin; Watts, Alun; McMurray, Neil

    2011-01-30

    The sublimation of copper phthalocyanine (CuPc) at a temperature of 400°C under conditions of reduced pressure is shown to be an effective method of developing latent fingermarks on certain types of surface. Preliminary experiments on a limited selection of surfaces including paper, plastic and ceramic tiles were carried out using a simple apparatus consisting of a vacuum desiccator and a resistive heater. CuPc from the gas phase condenses preferentially on fingermark deposits, revealing deep blue patterns with excellent ridge detail clarity on light coloured surfaces. The technique is shown to be most effective on porous surfaces such as paper, but relatively ineffective on non-porous ceramic and plastic surfaces.

  1. Impact of nonintentional Al impurity to carrier lifetime and diffusion in sublimation grown 3C heterostructures

    NASA Astrophysics Data System (ADS)

    Ščajev, P.; Jarašiunas, K.; Kadys, A.; Storasta, J.; Abramov, P. L.; Lebedev, S. P.; Lebedev, A. A.

    2010-11-01

    Using optical techniques, we analyzed an impact of non-intentional Al mpurity and twin boundaries to photoelectrical properties of sublimation-grown 3C heterostructures. Differential transmission techniques revealed Al related contribution to probe beam absorption with cross-section σAl = (1.8±0.5)×10-17 cm2 at 1064 nm, being four times stronger that the free-carrier absorption cross-section at given wavelength. Temperature dependent carrier recombination rates provided trap activation energy of 170 and 210 meV in two samples with different Al concentration. Saturation of probe beam absorption with excitation allowed determination of electrically active Al concentration, not gettered at grain boundaries. Increase of room-temperature mobility with injection in the highly defective layer and the corresponding lifetime decrease pointed out contribution of point and structural defects to carrier scattering.

  2. Enthalpie de sublimation du soufre α : mesure calorimétrique

    NASA Astrophysics Data System (ADS)

    Chastel, R.; Ezzine, M.

    1993-04-01

    An effusion cell-calorimetric method has been used to determine the sublimation enthalpy of α sulfur at 298.15 K. The value 13.05 ± 0. 1 kJ/gram atom, is compared to literature data. L'existence d'une phase vapeur de composition complexe au-dessus de certains éléments rend délicate la définition d'une enthalpie d'évaporation par atome-gramme de l'élément : dans le cas du soufre α, nous avons utilisé une méthode calorimétrique directe qui conduit à : Δ H_{vap(298,15 K)}= 13,05± 0,1 kJ/atome-gramme.

  3. Modeling the Seasonal South Polar Cap Sublimation Rates at Dust Storm Conditions

    NASA Technical Reports Server (NTRS)

    Bonev, B. P.; James, P. B.; Wolff, M. J.; Bjorkman, J. E.; Hansen, G. B.; Benson, J. L.

    2003-01-01

    Carbon dioxide is the principal component of the Martian atmosphere and its interaction with the polar caps forms the CO2 seasonal cycle on the planet. A significant fraction of the atmospheric constituent condenses on the surface during the polar winter and sublimes back during spring. The basic aspects of the CO2 cycle have been outlined by Leighton and Murray and a number of follow-up theoretical models ranging from energy balance to general circulation models have been used to study the physical processes involved in the cycle. This paper presents a modeling study on the seasonal south polar cap subliminiation rate under dust storm conditions. Mars Global Surveyor observations are also presented.

  4. Formation of the molecular crystal structure during the vacuum sublimation of paracetamol

    NASA Astrophysics Data System (ADS)

    Belyaev, A. P.; Rubets, V. P.; Antipov, V. V.; Bordei, N. S.

    2015-04-01

    The results from structural and thermal studies on the formation of molecular crystals during the vacuum sublimation of paracetamol from its vapor phase are given. It is established that the vapor-crystal phase transition proceeds in a complicated way as the superposition of two phase transitions: a first-order phase transition with a change in density, and a second-order phase transition with a change in ordering. It is shown that the latter is a smeared phase transition that proceeds with the formation of a pretransitional phase that is irreversibly dissipated during phase transformation, leading to the formation of crystals of the rhombic syngony. Data from differential scanning calorimetry and X-ray diffraction analysis are presented along with microphotographs.

  5. Testing and Model Correlation of Sublimator Driven Coldplate Coupons and EDU

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.

    2009-01-01

    The Sublimator Driven Coldplate (SDC) is a unique piece of thermal control hardware that has several advantages over a more traditional thermal control system. The principal advantage is the possible elimination of a pumped fluid loop, potentially saving mass, power, and complexity. Because this concept relies on evaporative heat rejection techniques, it is primarily useful for short mission durations. Additionally, the concept requires a conductive path between the heat-generating component and the heat rejection device. Therefore, it is mostly a relevant solution for a vehicle with a relatively low heat rejection requirement and/or short transport distances. Tests were performed on coupons and an Engineering Development Unit (EDU) at NASA s Johnson Space Center to better understand the basic operational principles and to validate the analytical methods being used for the SDC development. This paper outlines the results of the SDC tests, the subsequent thermal model correlation, and a description of the SDC Engineering Development Unit test results.

  6. Sublimation rate of molecular crystals - role of internal degrees of freedom

    SciTech Connect

    Maiti, A; Zepeda-Ruiz, L A; Gee, R H; Burnham, A

    2007-01-19

    It is a common practice to estimate site desorption rate from crystal surfaces with an Arrhenius expression of the form v{sub eff} exp(-{Delta}E/k{sub B}T), where {Delta}E is an activation barrier to desorb and v{sub eff} is an effective vibrational frequency {approx} 10{sup 12} sec{sup -1}. However, such a formula can lead to several to many orders of magnitude underestimation of sublimation rates in molecular crystals due to internal degrees of freedom. We carry out a quantitative comparison of two energetic molecular crystals with crystals of smaller entities like ice and Argon (solid) and uncover the errors involved as a function of molecule size. In the process, we also develop a formal definition of v{sub eff} and an accurate working expression for equilibrium vapor pressure.

  7. The Durability of Various Crucible Materials for Aluminum Nitride Crystal growth by Sublimation

    SciTech Connect

    Liu,B.; Edgar, J.; Gu, Z.; Zhuang, D.; Raghothamachar, B.; Dudley, M.; Sarua, A.; Kuball, M.; Meyer, H.

    2004-01-01

    Producing high purity aluminum nitride crystals by the sublimation-recondensation technique is difficult due to the inherently reactive crystal growth environment, normally at temperature in excess of 2100 C. The durability of the furnace fixture materials (crucibles, retorts, etc.) at such a high temperature remains a critical problem. In the present study, the suitability of several refractory materials for AlN crystal growth is investigated, including tantalum carbide, niobium carbide, tungsten, graphite, and hot-pressed boron nitride. The thermal and chemical properties and performance of these materials in inert gas, as well as under AlN crystal growth conditions are discussed. TaC and NbC are the most stable crucible materials with very low elemental vapor pressures in the crystal growth system. Compared with refractory material coated graphite crucibles, HPBN crucible is better for AlN self-seeded growth, as crystals tend to nucleate in thin colorless platelets with low dislocation density.

  8. HiRISE Images of the Sublimation of the Southern Seasonal Polar Cap of Mars

    NASA Astrophysics Data System (ADS)

    Hansen, C. J.; McEwen, A. S.; Okubo, C.; Byrne, S.; Becker, T.; Kieffer, H.; Mellon, M.; HiRISE Team

    2007-12-01

    The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) has returned images with unprecedented resolution of Mars southern seasonal CO2 polar cap. Several high latitude sites were selected for systematic monitoring throughout the spring as the seasonal cap sublimed away. The capability of MRO to turn off-nadir enabled acquisition of stereo pairs to study the topography. HiRISE color capability distinguishes processes involving dust and frost. Color images show evidence of localized migration of frost as dark spots sublimate. Unique landforms are found in the cryptic terrain[1] region of Mars polar cap. These unusual landforms have narrow channels emanating radially, dubbed spiders[2]. Fans of dust blown by the prevailing wind are hypothesized to come from gas jets of CO2 subliming beneath translucent seasonal ice [3]. HiRISE images show a wide variety of morphologies of narrow channels. In some regions deep narrow channels converge radially, while in others the high channel density is more akin to lace. A smooth evolution of one form to another has been observed. Channels converge dendritically, often uphill, consistent with formation by flowing gas, not liquid. More dust fans are observed in regions of spiders than in lace, suggesting that the sublimating gas under the seasonal ice builds up more pressure and can entrain more dust in spidery areas. These differing terrain types are found within a single 6 x 10 km image, which has presumably homogeneous weather, thus a uniform layer of ice and exposure to atmospheric dust. HiRiSE images show that the dust fans tend to emerge from low spots, where the subsurface is accessed, then are blown up and out onto the surface of the seasonal ice. The fans evolve from a thin diffuse covering to thick blankets filling in the narrow channels. We hypothesize that dust collects in the channels, and that these relatively more permeable dust-filled channels form pathways for the next seasons

  9. Near-equilibrium growth of thick, high quality beta-SiC by sublimation

    NASA Technical Reports Server (NTRS)

    Shields, Virgil B.; Fekade, Konjit; Spencer, Michael G.

    1993-01-01

    A close spaced near-equilibrium growth technique was used to produce thick, high quality epitaxial layers of beta-silicon carbide. The process utilized a sublimation method to grow morphologically smooth layers. The beta silicon carbide growth layers varied from about 200 to 750 microns in thickness. Chemical vapor deposition grown, 2-10 microns, beta silicon carbide films were used as seeds at 1860 and 1910 C growth temperatures. The respective average growth rates were 20 and 30 microns per hour. The layers are p-type with a 3.1 x 10 exp 17/cu cm carrier concentration. Electrical measurements indicate considerable improvement in the breakdown voltage of Schottky barriers on growth samples. Breakdown values ranged from 25 to 60 V. These measurements represent the highest values reported for 3C-SiC.

  10. Sublimation of Ices Containing Organics and/or Minerals and Implications for Icy Bodies Surface Structure and Spectral Properties

    NASA Astrophysics Data System (ADS)

    Poch, O.; Pommerol, A.; Jost, B.; Yoldi, Z.; Carrasco, N.; Szopa, C.; Thomas, N.

    2015-12-01

    The surfaces of many objects in the Solar System comprise substantial quantities of water ice either in pure form or mixed with minerals and/or organic molecules. Sublimation is a process responsible for shaping and changing the reflectance properties of these objects. We present laboratory data on the evolution of the structure and the visible and near-infrared spectral reflectance of icy surfaces made of mixtures of water ice and non-volatile components (complex organic matter and silicates), as they undergo sublimation of the water ice under low temperature and pressure conditions (Poch et al., under review). We prepared icy surfaces which are potential analogues of ices found on comets, icy satellites or trans-neptunian objects (TNOs). The experiments were carried out in the SCITEAS simulation setup recently built as part of the Laboratory for Outflow Studies of Sublimating Materials (LOSSy) at the University of Bern (Pommerol et al., 2015a). As the water ice sublimated, we observed in situ the formation of a sublimation lag deposit, or sublimation mantle, made of the non-volatiles at the top of the samples. The texture (porosity, internal cohesiveness etc.), the activity (outbursts and ejection of mantle fragments) and the spectro-photometric properties of this mantle are found to differ strongly depending on the chemical nature of the non-volatiles, the size of their particles, the way they are mixed with the volatile component and the dust/ice mass ratio. The results also indicate how the band depths of the sub-surface water ice evolve during the build-up of the sublimation mantle. These data provide useful references for interpreting remote-sensing observations of Rosetta (see Pommerol et al., 2015b), and also New Horizons. Poch, O., et al., under review in IcarusPommerol, A., et al., 2015a, Planet. Space Sci. 109-110, 106-122. http://dx.doi.org/10.1016/j.pss.2015.02.004Pommerol, A., et al., 2015b, Astronomy and Astrophysics, in press. http://dx.doi.org/10.1051/0004-6361/201525977

  11. Fe embedded in ice: The impacts of sublimation and energetic particle bombardment

    NASA Astrophysics Data System (ADS)

    Frankland, Victoria L.; Plane, John M. C.

    2015-05-01

    Icy particles containing a variety of Fe compounds are present in the upper atmospheres of planets such as the Earth and Saturn. In order to explore the role of ice sublimation and energetic ion bombardment in releasing Fe species into the gas phase, Fe-dosed ice films were prepared under UHV conditions in the laboratory. Temperature-programmed desorption studies of Fe/H2O films revealed that no Fe atoms or Fe-containing species co-desorbed along with the H2O molecules. This implies that when noctilucent ice cloud particles sublimate in the terrestrial mesosphere, the metallic species embedded in them will coalesce to form residual particles. Sputtering of the Fe-ice films by energetic Ar+ ions was shown to be an efficient mechanism for releasing Fe into the gas phase, with a yield of 0.08 (Ar+ energy=600 eV). Extrapolating with a semi-empirical sputtering model to the conditions of a proton aurora indicates that sputtering by energetic protons (>100 keV) should also be efficient. However, the proton flux in even an intense aurora will be too low for the resulting injection of Fe species into the gas phase to compete with that from meteoric ablation. In contrast, sputtering of the icy particles in the main rings of Saturn by energetic O+ ions may be the source of recently observed Fe+ in the Saturnian magnetosphere. Electron sputtering (9.5 keV) produced no detectable Fe atoms or Fe-containing species. Finally, it was observed that Fe(OH)2 was produced when Fe was dosed onto an ice film at 140 K (but not at 95 K). Electronic structure theory shows that the reaction which forms this hydroxide from adsorbed Fe has a large barrier of about 0.7 eV, from which we conclude that the reaction requires both translationally hot Fe atoms and mobile H2O molecules on the ice surface.

  12. Formulation design and optimization of fast dissolving clonazepam tablets by sublimation method.

    PubMed

    Shirsand, S B; Suresh, Sarasija; Kusumdevi, V; Swamy, P V

    2011-09-01

    Fast dissolving tablets of clonazepam were prepared by sublimation method with a view to enhance patient compliance. A 3(2) full factorial design was applied to investigate the combined effect of two formulation variables: amount of croscarmellose sodium and camphor. Croscarmellose sodium (2-8% w/w) was used as superdisintegrant and camphor (20-40% w/w) was used as subliming agent, to increase the porosity of the tablets, since it helps water to penetrate into the tablets, along with directly compressible mannitol to enhance mouth feel. The tablets were evaluated for hardness, friability, thickness, drug content uniformity, in vitro dispersion time, wetting time and water absorption ratio. Based on in vitro dispersion time (approximately 11 s); the formulation containing 5% w/w croscarmellose sodium and 40% w/w camphor was found to be promising and tested for in vitro drug release pattern (in pH 6.8 phosphate buffer). Short-term stability (at 40°/75% relative humidity for 3 mo) and drug-excipient interaction. Surface response plots are presented to graphically represent the effect of independent variables on the in vitro dispersion time. The validity of the generated mathematical model was tested by preparing two extra-design checkpoints. The optimized tablet formulation was compared with conventional commercial tablet formulation for drug release profiles. This formulation showed nearly nine-fold faster drug release (t(50%) 1.8 min) compared to the conventional commercial tablet formulation (t(50%) 16.4 min). Short-term stability studies on the formulation indicated that there are no significant changes in drug content and in vitro dispersion time (P<0.05).

  13. Erosion and Sublimation Effects On Mercury`s Surface: Past and Present

    NASA Astrophysics Data System (ADS)

    Tehrany, M. G.; Lammer, H.; Hanslmeier, A.; Ribas, I.; Guinan, E. F.; Kolb, C.

    Ground-based observations of heavy constituents like Na, K and O in Mercury`s present exosphere indicate a strong exosphere-surface interaction related to the par- ticle and radiation environment of the close Sun. Recent studies of isotope anomalies in planetary atmospheres and meteorites suggest that our early Sun underwent a highly active phase after its origin that included continuous flare events and had a particle and radiation environment several hundred times stronger than today. Since Mercury is the closest planet to the Sun, its surface was more heavily exposed to the enhanced solar wind particle and radiation fluxes than those of any of the other Solar System bod- ies. To evaluate how such effects may have influenced Mercury`s surface, we study its surface erosion and sublimation during the planet history by using solar analogue G-type stars. The astrophysical parameters of these Sun-like stars were studied within the broader "Sun in Time" program. We use for our study three models for the young Sun: one model with an initial solar mass of 2, where the mass loss rate and luminos- ity decreases exponentially with e-folding times of a few 10E8 years; a second model, which can be compared to solar analogue observations, including large flare events during the first hundred million years; and a third model, which is the standard model. The results of the analysis of these three models are used to estimate and compare the sputter erosion and sublimation rates of Mercury`s surface during its history.

  14. Laboratory studies of the growth, sublimation, and light- scattering properties of single levitated ice particles

    NASA Astrophysics Data System (ADS)

    Bacon, Neil Julian

    2001-12-01

    I describe experiments to investigate the properties of microscopic ice particles. The goal of the work was to measure parameters that are important in cloud processes and radiative transfer, using a novel technique that avoids the use of substrates. The experiments were conducted in two separate electrodynamic balance chambers. Single, charged ice particles were formed from frost particles or from droplets frozen either homogeneously or heteroge neously with a bionucleant. The particles were trapped at temperatures between -38°C and -4°C and grown or sublimated according to the temperature gradient in the cham ber. I describe observations of breakup of sublimating frost particles, measurements of light scattering by hexagonal crystals, and observations of the morphology of ice particles grown from frozen water droplets and frost particles. The breaking strength of frost particles was an order of magnitude less than that of bulk ice. Light scattering features not previously observed were analyzed and related to crystal dimension. Initial results from a computer model failed to reproduce these features. The widths of scattering peaks suggest that surface roughness may play a role in determining the angular distribution of scattered light. Ice particle mass evolution was found to be consistent with diffusion- limited growth. Crystals grown slowly from frozen droplets adopted isometric habits, while faster growth resulted in thin side-planes, although there was not an exact correspondence between growth conditions and particle morphology. From the morphological transition, I infer lower limits for the critical supersaturation for layer nucleation on the prism face of 2.4% at -15°C, 4.4% at -20°C, and 3.1% at -25°C. Analytic expressions for the size dependence of facet stability are developed, indicating a strong dependence of stability on both crystal size and surface kinetics, and compared with data. I discuss the role of complex particle morphologies in

  15. Formulation Design and Optimization of Fast Dissolving Clonazepam Tablets by Sublimation Method

    PubMed Central

    Shirsand, S. B.; Suresh, Sarasija; Kusumdevi, V.; Swamy, P. V.

    2011-01-01

    Fast dissolving tablets of clonazepam were prepared by sublimation method with a view to enhance patient compliance. A 32 full factorial design was applied to investigate the combined effect of two formulation variables: amount of croscarmellose sodium and camphor. Croscarmellose sodium (2-8% w/w) was used as superdisintegrant and camphor (20-40% w/w) was used as subliming agent, to increase the porosity of the tablets, since it helps water to penetrate into the tablets, along with directly compressible mannitol to enhance mouth feel. The tablets were evaluated for hardness, friability, thickness, drug content uniformity, in vitro dispersion time, wetting time and water absorption ratio. Based on in vitro dispersion time (approximately 11 s); the formulation containing 5% w/w croscarmellose sodium and 40% w/w camphor was found to be promising and tested for in vitro drug release pattern (in pH 6.8 phosphate buffer). Short-term stability (at 40°/75% relative humidity for 3 mo) and drug-excipient interaction. Surface response plots are presented to graphically represent the effect of independent variables on the in vitro dispersion time. The validity of the generated mathematical model was tested by preparing two extra-design checkpoints. The optimized tablet formulation was compared with conventional commercial tablet formulation for drug release profiles. This formulation showed nearly nine-fold faster drug release (t50% 1.8 min) compared to the conventional commercial tablet formulation (t50% 16.4 min). Short-term stability studies on the formulation indicated that there are no significant changes in drug content and in vitro dispersion time (P<0.05). PMID:22923860

  16. Estimating snow sublimation using natural chemical and isotopic tracers across a gradient of solar radiation

    NASA Astrophysics Data System (ADS)

    Gustafson, Joseph R.; Brooks, P. D.; Molotch, N. P.; Veatch, W. C.

    2010-12-01

    Changes in both climate and vegetation may dramatically impact the amount of water stored in seasonal snow cover and the timing of spring snowmelt. This study quantifies how spatial variability in solar radiation affects the spatial and temporal patterns in snow water equivalent (SWE), snow chemistry, and snow water isotopes in the Jemez Mountains, New Mexico. Depth, density, stratigraphy, temperature, and snow samples were collected approximately monthly from five locations between January and April 2007 to quantify the effects of solar forcing on snowpack water and chemical balance. Locations varied in solar forcing due to topography and vegetation, while minimizing variability in precipitation, elevation, aspect, interception, and wind redistribution. Snowfall (340 ± 5 mm) was similar across all sites, but peak SWE at maximum accumulation ranged from 187 to 340 mm. Solute concentrations were highest directly under canopies, intermediate in nonshaded forest openings, and lowest in shaded forest openings. Conservative solute concentrations (SO42-, R2 = 0.80), Cl- (R2 = 0.60), and isotope values (δ18O R2 = 0.96) were inversely related to SWE at maximum accumulation. Mass balance estimates of snowpack water balance using solute concentrations and isotopes indicated that sublimation ranged from <2% to ˜20% of winter precipitation, consistent with previous studies at the site. The strong relationships between solar forcing, SWE, and chemistry suggest that snow chemistry at maximum accumulation can be used to estimate overwinter sublimation. Furthermore, variability in solar forcing also can be used to refine spatial estimates of catchment solute and isotope input at melt.

  17. The fate of meteoric metals in ice particles: Effects of sublimation and energetic particle bombardment

    NASA Astrophysics Data System (ADS)

    Mangan, T. P.; Frankland, V. L.; Murray, B. J.; Plane, J. M. C.

    2017-08-01

    The uptake and potential reactivity of metal atoms on water ice can be an important process in planetary atmospheres and on icy bodies in the interplanetary and interstellar medium. For instance, metal atom uptake affects the gas-phase chemistry of the Earth's mesosphere, and has been proposed to influence the agglomeration of matter into planets in protoplanetary disks. In this study the fate of Mg and K atoms incorporated into water-ice films, prepared under ultra-high vacuum conditions at temperatures of 110-140 K, was investigated. Temperature-programmed desorption experiments reveal that Mg- and K-containing species do not co-desorb when the ice sublimates, demonstrating that uptake on ice particles causes irreversible removal of the metals from the gas phase. This implies that uptake on ice particles in terrestrial polar mesospheric clouds accelerates the formation of large meteoric smoke particles (≥1 nm radius above 80 km) following sublimation of the ice. Energetic sputtering of metal-dosed ice layers by 500 eV Ar+ and Kr+ ions shows that whereas K reacts on (or within) the ice surface to form KOH, adsorbed Mg atoms are chemically inert. These experimental results are consistent with electronic structure calculations of the metals bound to an ice surface, where theoretical adsorption energies on ice are calculated to be -68 kJ mol-1 for K, -91 kJ mol-1 for Mg, and -306 kJ mol-1 for Fe. K can also insert into a surface H2O to produce KOH and a dangling H atom, in a reaction that is slightly exothermic.

  18. CURVED WALLS: GRAIN GROWTH, SETTLING, AND COMPOSITION PATTERNS IN T TAURI DISK DUST SUBLIMATION FRONTS

    SciTech Connect

    McClure, M. K.; Calvet, N.; Hartmann, L.; Ingleby, L.; D'Alessio, P.; Espaillat, C.; Sargent, B.; Watson, D. M.; Hernández, J. E-mail: ncalvet@umich.edu E-mail: lingleby@umich.edu E-mail: cespaillat@cfa.harvard.edu E-mail: dmw@pas.rochester.edu

    2013-10-01

    The dust sublimation walls of disks around T Tauri stars represent a directly observable cross-section through the disk atmosphere and midplane. Their emission properties can probe the grain size distribution and composition of the innermost regions of the disk, where terrestrial planets form. Here we calculate the inner dust sublimation wall properties for four classical T Tauri stars with a narrow range of spectral types and inclination angles and a wide range of mass accretion rates to determine the extent to which the walls are radially curved. Best fits to the near- and mid-IR excesses are found for curved, two-layer walls in which the lower layer contains larger, hotter, amorphous pyroxene grains with Mg/(Mg+Fe) = 0.6 and the upper layer contains submicron, cooler, mixed amorphous olivine and forsterite grains. As the mass accretion rates decrease from 10{sup –8} to 10{sup –10} M{sub ☉} yr{sup –1}, the maximum grain size in the lower layer decreases from ∼3 to 0.5 μm. We attribute this to a decrease in fragmentation and turbulent support for micron-sized grains with decreasing viscous heating. The atmosphere of these disks is depleted of dust with dust-gas mass ratios 1 × 10{sup –4} of the interstellar medium (ISM) value, while the midplane is enhanced to eight times the ISM value. For all accretion rates, the wall contributes at least half of the flux in the optically thin 10 μm silicate feature. Finally, we find evidence for an iron gradient in the disk, suggestive of that found in our solar system.

  19. The effect of plasma heating on sublimation-driven flow in Io's atmosphere

    NASA Technical Reports Server (NTRS)

    Wong, Mau C.; Johnson, Robert E.

    1995-01-01

    The atmospheric flow on Io is numerically computed in a flat 2-D axisymmetric geometry for a sublimation atmosphere on the trailing hemisphere subjected to plasma bombardment, UV heating, and IR cooling. Calculations are performed for subsolar vapor pressures of approximately 6.5 x 10(exp -3) Pa (approximately 3 x 10(exp 18) SO2/sq cm) and 6.8 x 10(exp -4) Pa (approximately 4 x 10(exp 17) SO2/sq cm); the latter approximates the vapor pressure of F. P. Fanale et al. (1982). The amount of plasma energy deposited in the atmosphere is 20% of the plasma flow energy due to corotation (J. A. Linker et al., 1988). It is found that plasma heating significantly inflates the upper atmosphere, increasing both the exobase altitude and the amount of surface covered by more than an exospheric column of gas. This in turn controls the supply of the Io plasma torus (M. A. McGrath and R. E. Johnson, 1987). The horizontal flow of mass and energy is also important in determining the exobase altitude; and it is shown that IR cooling can be important, although our use of the equilibrium, cool-to-space approximation for a pure SO2 gas (E. Lellouch et al., 1992) may overestimate this effect. The calculated exobase altitudes are somewhat lower than those suggested by McGrath and Johnson (1987) for supplying the torus, indicating the details of the plasma energy deposition and sputter ejection rate near the exobase, as well as the IR emission from this region need to be examined. In addition, the molecules sublimed (or sputtered) from the surface are transported to the exobase in times short compared to the molecular photodissociation time. Therefore, the exobase is dominated by molecular species and the exobase is supplied by a small region of the surface.

  20. Representing the sublime in the VIMAP and empirical aesthetics: Reviving Edmund Burke's A Philosophical Enquiry into the Origins of Our Ideas of the Sublime and Beautiful. Comment on "Move me, astonish me... delight my eyes and brain: The Vienna Integrated Model of top-down and bottom-up processes in Art Perception (VIMAP) and corresponding affective, evaluative, and neurophysiological correlates" by Matthew Pelowski et al.

    NASA Astrophysics Data System (ADS)

    Hur, Y.-J.; McManus, I. C.

    2017-07-01

    This commentary considers the role of the sublime in the Vienna Integrated Model of Art Perception (VIMAP; Pelowski, Markey, Forster, Gerger, & Leder [17]), and suggest that it is not precisely conceptualised in the model. In part that reflects different views and usages of the sublime in the literature, and here it is recommended that Burke's [2] view of the sublime is used as a primary framework for empirical research on the sublime.

  1. A simple explanation of the enhancement or depletion of the enantiomeric excess in the partial sublimation of enantiomerically enriched amino acids

    NASA Astrophysics Data System (ADS)

    Guillemin, Jean-Claude; Bellec, Aurelien

    Perry et al. [1] and then Flecther et al. [2] have recently reported the partial sublimation of mixtures of enantiomers of an amino acid with an enantiomeric excess (ee). A huge increase of the ee was observed for the sublimed sample. Similar observations had been observed in the partial sublimation of carboxylic acids. Recently Blackmond et al.[3-5] attributed this property to the sublimation of an eutectic mixture, the ee being dependent on the amino acid. The possible role played by such sublimations on the Primitive Earth has been extensively discussed. However, in the lack of a systematic study, this phenomenon has not been elucidated up-to-now. On the basis of these different interpretations, our work focused on the understanding of the behaviour of amino acids during the sublimation process. We have partially sublimed several mixtures of enantiomers of amino acids from the racemate to the pure amino acid and obtained a curve with a plateau. Enantioenrichment but also enantiodepletion have been observed depending on the initial enantiomeric excess starting from (DL + L) or (DL + D) mixtures. On the other hand, we observed a strong decrease of the ee in the sublimation of mixtures of (D + L) amino acids with ee ranging between 10 and 90 We have found a simple explanation for all these results based on the vapour pressure of each components of the starting mixture for several amino acids.[6] On the other hand, in similar experimental conditions, the formation of an eutectic composition for the sublimate can be easily demonstrated for a carboxylic acid like the mandelic acid. [7] Relevance to the origin of homochirality is discussed. [1] Chem. Commun., 2007, 1071. [2] Chem. Commun., 2007, 2578. [3] Nature, 2006, 441:621. [4] Angew. Chem. Int. Ed., 2006, 45:7989. [5] Chem. Comm., 2007, 3990. [6] Chem. Commun. 2010, 46, 1482. [7] J. Fluor. Chem. 2010, in press.

  2. Origin of Sublimation Polygons in the Antarctic Western Dry Valleys: Implications for Patterned Ground Development on Mars

    NASA Astrophysics Data System (ADS)

    Marchant, D. R.; Head, J. W.

    2003-12-01

    Two hypotheses have been developed in order to address the age, origin, and evolution of surface polygons in the western Dry Valleys region of southern Victoria Land. Resolution of this debate has direct relevance and implications for patterned ground in ice-rich terrain on Mars. One hypothesis, the dynamic hypothesis, states that growth of sand-wedges pervasively deforms sediment across polygonal terrain, recycling sediment from troughs to polygon centers and back again over time scales of thousands of years. A second hypothesis, the stability hypothesis, states that deformation associated with sand-wedge polygons, particularly those that form over buried ice, is restricted to polygon troughs; the implication is that polygon centers may contain undisturbed soils >1 million years old. Evidence comes from field data that show that the age, origin, and morphology of polygons that form over buried ice in the western Dry Valleys region is tied collectively to the location and rate of sublimation of underlying ice. In Beacon Valley, sublimation of debris-rich ice produces a dry surface lag that insulates and slows loss of remaining ice. Sub-zero temperature cycling of near-surface ice and soil creates tensile stresses that result in a network of hexagonal cracks, extending upward from buried ice toward the ground surface. Where fines sift downward into open thermal-contraction cracks, a coarse-grained lag deposit forms on top of the ice. Owing to spatial variations in till texture, rates of sublimation vary across the ice surface. High rates occur below coarse-grained lags that cap contraction cracks; low rates are found at polygon centers beneath fine-grained low porosity/permeability debris. Measured concentrations of in-situ produced cosmogenic 3He in two depth profiles through sublimation till show a steady decrease with depth, indicating negligible recycling of surface materials on million-year time scales. These data suggest that once polygon troughs deepen

  3. BabeLO--An Extensible Converter of Programming Exercises Formats

    ERIC Educational Resources Information Center

    Queiros, R.; Leal, J. P.

    2013-01-01

    In the last two decades, there was a proliferation of programming exercise formats that hinders interoperability in automatic assessment. In the lack of a widely accepted standard, a pragmatic solution is to convert content among the existing formats. BabeLO is a programming exercise converter providing services to a network of heterogeneous…

  4. Low energy neutron deuteron scattering to N3LO

    NASA Astrophysics Data System (ADS)

    Margaryan, Arman; Vanasse, Jared; Springer, Roxanne

    2015-10-01

    We calculate the next-to-next-to-next-to-leading order (N3LO) nd scattering amplitude in the framework of nonrelativistic pionless effective field theory (EFTπ/). This theory is only valid when the typical momentum exchange in the scattering is smaller then the mass of the pion. The power counting parameter for EFTπ/ is the ratio Q/Λπ /, where Q is the typical momentum exchange in the scattering and Λπ / is the EFTπ/ breakdown scale, Λπ / LO. At N3LO new 2-body forces appear, which introduce four new EFTπ/ coefficients. These coefficients are fixed by the 3PJ and 1P1 phase shifts of NN scattering. We find that these terms have an important impact. The results of this calculation at N3LO will be important for understanding spin polarization observables in nd scattering, in particular the longstanding Ay puzzle. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Nuclear Physics, under Award Number DE-FG02-05ER41368.

  5. BabeLO--An Extensible Converter of Programming Exercises Formats

    ERIC Educational Resources Information Center

    Queiros, R.; Leal, J. P.

    2013-01-01

    In the last two decades, there was a proliferation of programming exercise formats that hinders interoperability in automatic assessment. In the lack of a widely accepted standard, a pragmatic solution is to convert content among the existing formats. BabeLO is a programming exercise converter providing services to a network of heterogeneous…

  6. Complete Genome Sequence of Burkholderia cepacia Strain LO6

    PubMed Central

    Belcaid, Mahdi; Kang, Yun; Tuanyok, Apichai

    2015-01-01

    Burkholderia cepacia strain LO6 is a betaproteobacterium that was isolated from a cystic fibrosis patient. Here we report the 6.4 Mb draft genome sequence assembled into 2 contigs. This genome sequence will aid the transcriptomic profiling of this bacterium and help us to better understand the mechanisms specific to pulmonary infections. PMID:26067955

  7. Complete Genome Sequence of Burkholderia cepacia Strain LO6.

    PubMed

    Belcaid, Mahdi; Kang, Yun; Tuanyok, Apichai; Hoang, Tung T

    2015-06-11

    Burkholderia cepacia strain LO6 is a betaproteobacterium that was isolated from a cystic fibrosis patient. Here we report the 6.4 Mb draft genome sequence assembled into 2 contigs. This genome sequence will aid the transcriptomic profiling of this bacterium and help us to better understand the mechanisms specific to pulmonary infections.

  8. A comprehensive numerical simulation of Io’s sublimation-driven atmosphere

    NASA Astrophysics Data System (ADS)

    Walker, Andrew C.; Gratiy, Sergey L.; Goldstein, David B.; Moore, Chris H.; Varghese, Philip L.; Trafton, Laurence M.; Levin, Deborah A.; Stewart, Bénédicte

    2010-05-01

    Io's sublimation-driven atmosphere is modeled using the direct simulation Monte Carlo (DSMC) method. These rarefied gas dynamics simulations improve upon earlier models by using a three-dimensional domain encompassing the entire planet computed in parallel. The effects of plasma heating, planetary rotation, inhomogeneous surface frost, molecular residence time of SO 2 on the exposed (non-volatile) rocky surface, and surface temperature distribution are investigated. Circumplanetary flow is predicted to develop from the warm dayside toward the cooler nightside. Io's rotation leads to a highly asymmetric frost surface temperature distribution (due to the frost's high thermal inertia) which results in circumplanetary flow that is not axi-symmetric about the subsolar point. The non-equilibrium thermal structure of the atmosphere, specifically vibrational and rotational temperatures, is also examined. Plasma heating is found to significantly inflate the atmosphere on both the dayside and nightside. The plasma energy flux causes high temperatures at high altitudes but plasma energy depletion through the dense gas column above the warmest frost permits gas temperatures cooler than the surface at low altitudes. A frost map (Douté, S., Schmitt, B., Lopes-Gautier, R., Carlson, R., Soderblom, L., Shirley, J., and the Galileo NIMS Team [2001]. Icarus 149, 107-132) is used to control the sublimated flux of SO 2 which can result in inhomogeneous column densities that vary by nearly a factor of four for the same surface temperature. A short residence time for SO 2 molecules on the "rock" component is found to smooth lateral atmospheric inhomogeneities caused by variations in the surface frost distribution, creating an atmosphere that looks nearly identical to one with uniform frost coverage. A longer residence time is found to agree better with mid-infrared observations (Spencer, J.R., Lellouch, E., Richter, M.J., López-Valverde, M.A., Jessup, K.L, Greathouse, T.K., Flaud, J

  9. Thermal alteration in carbonaceous chondrites and implications for sublimation in rock comets

    NASA Astrophysics Data System (ADS)

    Springmann, Alessondra; Lauretta, Dante S.; Steckloff, Jordan K.

    2015-11-01

    Rock comets are small solar system bodies in Sun-skirting orbits (perihelion q < ~0.15 AU) that form comae rich in mineral sublimation products, but lack typical cometary ice sublimation products (H2O, CO2, etc.). B-class asteroid (3200) Phaethon, considered to be the parent body of the Geminid meteor shower, is the only rock comet currently known to periodically eject dust and form a coma. Thermal fracturing or thermal decomposition of surface materials may be driving Phaethon’s cometary activity (Li & Jewitt, 2013). Phaethon-like asteroids have dynamically unstable orbits, and their perihelia can change rapidly over their ~10 Myr lifetimes (de León et al., 2010), raising the possibility that other asteroids may have been rock comets in the past. Here, we propose using spectroscopic observations of mercury (Hg) as a tracer of an asteroid’s thermal metamorphic history, and therefore as a constraint on its minimum achieved perihelion distance.B-class asteroids such as Phaethon have an initial composition similar to aqueously altered primitive meteorites such as CI- or CM-type meteorites (Clark et al., 2010). Laboratory heating experiments of ~mm sized samples of carbonaceous chondrite meteorites from 300K to 1200K at a rate of 15K/minute show mobilization and volatilization of various labile elements at temperatures that could be reached by Mercury-crossing asteroids. Samples became rapidly depleted in labile elements and, in particular, lost ~75% of their Hg content when heated from ~500-700 K, which corresponds to heliocentric distances of ~0.15-0.3 au, consistent with our thermal models. Mercury has strong emission lines in the UV (~ 185 nm) and thus its presence (or absence) relative to carbonaceous chondrite abundances would indicate if these bodies had perihelia in their dynamical histories inside of 0.15 AU, and therefore may have previously been Phaethon-like rock comets. Future space telescopes or balloon-borne observing platforms equipped with a UV

  10. Precipitation, sublimation, and snow drift in the Antarctic Peninsula region from a regional atmospheric model

    NASA Astrophysics Data System (ADS)

    van Lipzig, N. P. M.; King, J. C.; Lachlan-Cope, T. A.; van den Broeke, M. R.

    2004-12-01

    A regional atmospheric model, with a horizontal grid spacing (Δx) of 14 km, is used to study the surface mass balance components (precipitation, sublimation, and snow drift) in the region of the Antarctic Peninsula (AP). An integration is performed for the 7-year period 1987-1993, using a realistic forcing at the lateral model boundaries and at the sea surface. Output from this integration indicates that the precipitation reaches its maximum value on the northwestern slope of the AP, where the upward motion in the atmosphere is largest. Uplift occurs upstream of the barrier, affecting the precipitation distribution over sea. The effect of the barrier on the precipitation distribution over the Bellingshausen Sea might have important implications for the ocean circulation in this region. The mean precipitation over the grounded ice of the AP (1.20 m water eq yr-1) is 6 times larger than the mean value over all the grounded ice of Antarctica. Our estimates for the surface sublimation and wind transport of snow over the grounding line toward the sea are 9% and 6 ± 1% of the precipitation, respectively. In situ data of the wind distribution at three coastal sites located on the northern, eastern, and western sides of the AP are used to evaluate the modeled wind field, which is important for the snow drift calculations. For two of the three sites considered, the prevailing wind direction and bimodal wind distribution are correctly represented by the model. The calculated distribution of accumulation and ablation due to snow drift shows a complex pattern. The wind removes snow from the spine of the AP, where the near-surface flow field diverges, whereas deposition occurs mainly on the eastern slopes, where the near-surface flow field converges. An intercomparison between two 7-year integrations at different horizontal resolution (Δx = 14 km and Δx = 55 km) shows that the precipitation on the northwestern slope is very sensitive to the model resolution: In the Δx = 14

  11. Time-Dependent SSI Multispectral Properties for Rock, Soil, Ice, and Sublimation Lags at the Phoenix Landing Site on Mars

    NASA Astrophysics Data System (ADS)

    Morris, R. V.; Lemmon, M. T.; Arvidson, R. E.; Blaney, D. L.; Ellehoj, M. D.; Mellon, M. T.; Phoenix, S. T.

    2008-12-01

    The Surface Stereo Imager (SSI) on the Phoenix Lander is a 15 band multispectral imager covering the spectral range from 0.45 to 1.00 micrometers. More than 250 15-filter spectral image cubes have been obtained for surface targets at the Phoenix landing site in the north polar region of Mars. The spectra of surface soils and rocks are dominated by a ferric absorption edge from nanophase ferric oxide, and they are broadly similar to most multispectral data obtained during the Pathfinder and MER missions. Negative spectral slopes between about 0.70 and 1.00 micrometers, indicative of high concentrations of olivine in the El Dorado sand sheet at Gusev crater, were not detected. The albedo (cos(i) corrected) of Phoenix surface spectra is highly dependent on the time of sol (albedo at 0.80 micrometers varies by a factor of 2), consistent with opposition and phase function effects. Subsurface layers bearing water ice were exposed at a depth of about 4 cm by digging with the robotic arm scoop. The SSI spectra of icy materials are highly variable, ranging from typical ice (spectrally neutral and high albedo near 0.7) at the Dodo-Goldilocks trench to low albedo spectra (about 0.3 at 0.80 micrometers) with a ferric absorption edge at the Snow White trench. The differences are attributed, respectively, to low and high concentrations of fine-grained and ferric-rich material dispersed throughout the ice. The spectra of the icy surfaces are dependent on time as the ice sublimes. At Snow White, an optically thick (about 300 micrometers) sublimate lag develops within two sols. At Dodo- Goldilocks, the time scale for development of an optically thick sublimate lag is 5 to greater than 60 sols, depending on location within the trench. The spectra of sublimate lag are equivalent to those for fine-grained soil.

  12. Measuring enthalpy of sublimation of volatiles by means of micro-thermogravimetry: the case of Dicarboxylic acids

    NASA Astrophysics Data System (ADS)

    Dirri, F.; Longobardo, A.; Palomba, E.; Zampetti, E.; Biondi, D.; Boccaccini, A.; Saggin, B.; Bearzotti, A.; Macagnano, A.

    2013-09-01

    VISTA (Volatile In Situ Thermogravimetry Analyser) is a thermogravimeter currently under study for the proposed mission MarcoPolo-R [1,2]. In the framework of this project, we developed a set-up to measure the enthalpy of sublimation ΔH of three dicarboxylic acids, i.e. adipic, succinic and oxalic. The obtained results are in good agreement with literature, and this demonstrates the capability of our device to perform this kind of measurements.

  13. Towards a novel continuous sublimation extraction/laser spectroscopy method for greenhouse gas measurements in the oldest ice

    NASA Astrophysics Data System (ADS)

    Bereiter, Bernhard; Maechler, Lars; Schmitt, Jochen; Walther, Remo; Tuzson, Béla; Scheidegger, Philipp; Emmenegger, Lukas; Fischer, Hubertus

    2017-04-01

    Ice cores are unique archives of ancient air providing the only direct record of past greenhouse gases - key in reconstructing the roles of greenhouse gases in past climate changes. The European Partnership in Ice Core Sciences (EuroPICS) plans to drill an ice core extending over 1.5 Ma, nearly doubling the time span of the existing greenhouse record and covering the time period of the Mid Pleistocene Transition. The ice covering the time interval from 1-1.5 Ma is expected to be close to the bedrock and, due to glacial flow, extremely thinned. A 10,000 yr glacial/interglacial transition can be compressed in 1 m of ice. The targeted 100 yr resolution therefore constrains the sample size to 15-30 g containing only 1-2ml STP air. Within the deepSlice project we aim to unlock such atmospheric archives in extremely thinned ice by developing a novel coupled semi-continuous sublimation extraction/laser spectroscopy system. Vacuum sublimation, with an infrared source, has been chosen as extraction method as it allows 100% gas extraction of all gas species from ice without changing the isotopic composition of CO2. In order to reduce ice waste and accelerate sample throughput, we are building a sublimation extraction system that is able to continuously sublimate an ice-core section and subsequently collect discrete full air samples. For the gas analytics, we develop a custom-made mid-infrared laser spectrometer allowing simultaneous measurement of the CO2, CH4 and N2O concentrations as well as the isotopic composition of CO2 on air samples of only 1-2 ml STP. The two systems will be coupled via cryo-trapping of the sample air in dip tubes, followed by expansion of the sample air into the laser spectrometer. Due to the nondestructive laser technique, the air sample can be recollected and reused for further analytics.

  14. The impacts of moisture transport on drifting snow sublimation in the saltation layer

    NASA Astrophysics Data System (ADS)

    Huang, Ning; Dai, Xiaoqing; Zhang, Jie

    2016-06-01

    Drifting snow sublimation (DSS) is an important physical process related to moisture and heat transfer that happens in the atmospheric boundary layer, which is of glaciological and hydrological importance. It is also essential in order to understand the mass balance of the Antarctic ice sheets and the global climate system. Previous studies mainly focused on the DSS of suspended snow and ignored that in the saltation layer. Here, a drifting snow model combined with balance equations for heat and moisture is established to simulate the physical DSS process in the saltation layer. The simulated results show that DSS can strongly increase humidity and cooling effects, which in turn can significantly reduce DSS in the saltation layer. However, effective moisture transport can dramatically weaken the feedback effects. Due to moisture advection, DSS rate in the saltation layer can be several orders of magnitude greater than that of the suspended particles. Thus, DSS in the saltation layer has an important influence on the distribution and mass-energy balance of snow cover.

  15. Fluctuations and instabilities of steps in the growth and sublimation of crystals

    NASA Astrophysics Data System (ADS)

    Uwaha, Makio; Saito, Yukio; Sato, Masahide

    1995-01-01

    Asymmetry in step kinetics (Schwoebel effect) has drastic effects on the motion of steps, and we study them theoretically and by simulation. With asymmetric step kinetics a step becomes smooth when it melts, whereas it becomes increasingly rough when it grows. When the Mullins-Sekerka type of instability takes place, the step does not form any stable pattern but shows a chaotic behavior although the crystal anisotropy influences the morphology. For a vicinal face consisting of equidistant steps, a similar enhancement of the step fluctuation in growth occurs while the fluctuation of step separation (terrace width) is suppressed because of the interference of the diffusion field. In sublimation, on the other hand, the step width is reduced but the fluctuation of the terrace width is enhanced. This leads to a bunching instability of steps. With one-sided step kinetics, steps always form pairwise bound states which have a hierarchical structure. In general various types of bound states appear, some of which lead to a morphological instability of the vicinal face.

  16. The growth of sublimation crystals and surface hoar on the Antarctic plateau

    NASA Astrophysics Data System (ADS)

    Gallet, J.-C.; Domine, F.; Savarino, J.; Dumont, M.; Brun, E.

    2014-07-01

    On the Antarctic plateau, precipitation quantities are so low that the surface mass budget is for an important part determined by exchanges of water vapor between the snow surface and the atmosphere surface. At Dome C (75° S, 123° E), we have frequently observed the growth of crystals on the snow surface under calm sunny weather. Here we present the time variations of specific surface area (SSA) and density of these crystals. Using the detailed snow model Crocus, we conclude that the formation of these crystals was very likely due to the nighttime formation of surface hoar crystals and to the daytime formation of sublimation crystals. These latter crystals form by processes similar to those involved in the formation of frost flowers on young sea ice. The formation of these crystals impacts the albedo, mass and energy budget of the Antarctic plateau. In particular, the SSA variations of the surface layer can induce an instantaneous forcing at the snow surface up to -10 W m-2 at noon, resulting in a surface temperature drop of 0.45 K. This result confirms that snow SSA is a crucial variable to consider in the energy budget and climate of snow-covered surfaces.

  17. Uptake of Mg and K on ice: Effect of sublimation and energetic particle bombardment

    NASA Astrophysics Data System (ADS)

    Mangan, T.; Frankland, V.; Plane, J. M. C.

    2016-12-01

    Uptake of metals on water ice can occur in polar mesospheric clouds (PMCs) in the mesosphere of Earth, on icy bodies in space and in the interstellar medium (ISM). Uptake of metals on icy particles could have implications for the surface and gas phase chemistry of the mesosphere. While in the ISM, the interactions of metals with water ice could affect processes relating to the agglomeration of matter into planets. In this study we experimentally investigate Mg and K embedded in water ice. Mg and K dosed ice films were prepared under ultra-high vacuum conditions in the laboratory at temperatures ≤ 140 K. Metal dosed ice films were subjected to temperature programmed desorption (TPD) and energetic ion bombardment (Ar+ and Kr+). TPD experiments revealed that negligible Mg and K containing species were co-desorbed with the ice film. This was also previously observed for Fe and suggests that metals contained within sublimating PMC particles in the mesosphere (or Icy particles in the ISM) may not be released into the gas phase. Instead, the metallic species could coalesce leading to the formation of residual particles. Energetic sputtering of metal dosed ice layers by 500 eV energy Ar+ and Kr+ efficiently removed the metals and highlighted significant differences between the two regarding their distribution within the ice layer.

  18. Selective crystallization of indigo B by a modified sublimation method and its redetermined structure

    PubMed Central

    Kettner, Florian; Hüter, Lucie; Schäfer, Johanna; Röder, Konstantin; Purgahn, Uta; Krautscheid, Harald

    2011-01-01

    Good-quality single crystals of the title compound, indigo B [systematic name: 2-(3-oxoindolin-2-yl­idene)indolin-3-one], C16H10N2O2, have been prepared with high selectivity by a sublimation process. The previous structure of indigo B [Süsse & Wolf (1980 ▶). Naturwissenschaften, 67, 453], which showed that the complete mol­ecule is generated by crystallographic inversion symmetry has been confirmed, but the present study reports more realistic geometrical parameters and modern standards of precision (e.g. σ for C—C bonds = 0.002–0.003 Å). Each mol­ecule features two intra­molecular N—H⋯O hydrogen bonds. In the crystal, mol­ecules are linked by strong face-to-face π–π stacking inter­actions involving both the six- and five-membered rings [centroid–centroid separations = 3.6290 (14) and 3.6506 (14) Å] and inter­molecular N—H⋯O hydrogen bonds. PMID:22219907

  19. Selective crystallization of indigo B by a modified sublimation method and its redetermined structure.

    PubMed

    Kettner, Florian; Hüter, Lucie; Schäfer, Johanna; Röder, Konstantin; Purgahn, Uta; Krautscheid, Harald

    2011-11-01

    Good-quality single crystals of the title compound, indigo B [systematic name: 2-(3-oxoindolin-2-yl-idene)indolin-3-one], C(16)H(10)N(2)O(2), have been prepared with high selectivity by a sublimation process. The previous structure of indigo B [Süsse & Wolf (1980 ▶). Naturwissenschaften, 67, 453], which showed that the complete mol-ecule is generated by crystallographic inversion symmetry has been confirmed, but the present study reports more realistic geometrical parameters and modern standards of precision (e.g. σ for C-C bonds = 0.002-0.003 Å). Each mol-ecule features two intra-molecular N-H⋯O hydrogen bonds. In the crystal, mol-ecules are linked by strong face-to-face π-π stacking inter-actions involving both the six- and five-membered rings [centroid-centroid separations = 3.6290 (14) and 3.6506 (14) Å] and inter-molecular N-H⋯O hydrogen bonds.

  20. Sublimation and combustion of coal particles in the erosion laser torch

    SciTech Connect

    Bulat, A.; Shumrikov, V.; Osenny, V.

    2005-07-01

    Rate of coal particles' combustion in low-temperature plasma is of interest both from application and scientific points of view. Necessity of knowing parameters of the process of coal particles' combustion in plasma torch with the temperature of 2500-3000 K is governed by arising a number of state-of-the-art technological tasks related to the problems of finding new methods of power production, generation of high-calorific synthetic gases and using carbon as a high temperature structural material in nuclear power engineering. The present work deals with a rate of combustion of the sorbed coal particles in the erosion laser torch formed by means of interaction of pulse laser radiation (wave length {lambda} = 1,06 {mu}m, power density j = 10{sup 5} - 10{sup 7} Wcm{sup 2} with coals of various grades (in the wide range of carbon concentrations (80-95 %)). Physical and mathematical modeling of the process of coal particles' sublimation and combustion in non-equilibrium plasma flows with weight-average temperature of 2500-3000 K showed a good convergence of results for the particles of 10-100 {mu}m diameter and satisfactory one for the particles of {gt} 250{mu}m diameter.

  1. Modeling Io's Sublimation-Driven Atmosphere: Gas Dynamics and Radiation Emission

    SciTech Connect

    Walker, Andrew C.; Goldstein, David B.; Varghese, Philip L.; Trafton, Laurence M.; Moore, Chris H.; Stewart, Benedicte; Gratiy, Sergey L.; Levin, Deborah A.

    2008-12-31

    Io's sublimation-driven atmosphere is modeled using the direct simulation Monte Carlo method. These rarefied gas dynamics simulations improve upon earlier models by using a three-dimensional domain encompassing the entire planet computed in parallel. The effects of plasma impact heating, planetary rotation, and inhomogeneous surface frost are investigated. Circumplanetary flow is predicted to develop from the warm subsolar region toward the colder night-side. The non-equilibrium thermal structure of the atmosphere, including vibrational and rotational temperatures, is also presented. Io's rotation leads to an asymmetric surface temperature distribution which is found to strengthen circumplanetary flow near the dusk terminator. Plasma heating is found to significantly inflate the atmosphere on both day- and night-sides. The plasma energy flux also causes high temperatures at high altitudes but permits relatively cooler temperatures at low altitudes near the dense subsolar point due to plasma energy depletion. To validate the atmospheric model, a radiative transfer model was developed utilizing the backward Monte Carlo method. The model allows the calculation of the atmospheric radiation from emitting/absorbing and scattering gas using an arbitrary scattering law and an arbitrary surface reflectivity. The model calculates the spectra in the {nu}{sub 2} vibrational band of SO{sub 2} which are then compared to the observational data.

  2. Hexagonal voids and the formation of micropipes during SiC sublimation growth

    NASA Astrophysics Data System (ADS)

    Kuhr, Thomas A.; Sanchez, Edward K.; Skowronski, Marek; Vetter, William M.; Dudley, Michael

    2001-04-01

    Hexagonal voids observed in sublimation grown SiC boules were examined using optical microscopy, atomic force microscopy (AFM), scanning electron microscopy, KOH etching, and synchrotron white-beam x-ray topography. Voids formed at imperfections in the attachment layer between the seed and crucible cap. They are platelet-like in shape with lateral sizes between 50 and 750 μm and thickness along the c axis between 5 and 25 μm. Growth steps were observed on the void facets closest to the seed and evaporation steps were observed on void facets closest to the growth surface, providing evidence for void movement during crystal growth. AFM images revealed that growth steps nucleate at a void sidewall, flow across the bottom of the void, and terminate in a trench-like depression. KOH etching of waters between the void and seed revealed dislocations lining up along the trace of the void path, often with higher densities corresponding to the location of the trench. X-ray topographs showed a random distribution of screw dislocations in the crystal volume above the void, and an absence of screw dislocations in the volume directly below the void. Hollow-core superscrew dislocations, called micropipes, were found at the corners of the void trace. Image forces associated with growth steps and void sidewalls are used to explain the formation of micropipes.

  3. Sublimation studies of NpO sub 2 F sub 2

    SciTech Connect

    Kleinschmidt, P.D. ); Lau, K.H.; Hildenbrand, D.L. )

    1992-08-15

    Using Knudsen effusion mass spectrometry, we have identified the following reaction as the sublimation decomposition mechanism of NpO{sub 2}F{sub 2}({ital s}): 2NpO{sub 2}F{sub 2}({ital s})=NpO{sub 2}({ital s})+O{sub 2}({ital g})+NpF{sub 4}({ital g}). From second-law analysis of the measured pressures of NpF{sub 4}({ital g}) over the temperature range 820--985 K the derived enthalpy change at 298 K is 556.8{plus minus}12.2 kJ/mol and the entropy change is 342.4 {plus minus}13.8 J/K mol. From these values and enthalpies of formation and entropies reported in the literature for the other species we calculate the enthalpy of formation of NpO{sub 2}F{sub 2}({ital s}) to be {minus}1608{plus minus}10 kJ/mol and the entropy to be 147{plus minus}9 J/K mol.

  4. Isolation of Purines and Pyrimidines from the Murchison Meteorite Using Sublimation

    NASA Technical Reports Server (NTRS)

    Glavin, D. P.; Bada, J. L.

    2004-01-01

    The origin of life on Earth, and possibly on other planets such as Mars, would have required the presence of liquid water and a continuous supply of prebiotic organic compounds. The exogenous delivery of organic matter by asteroids, comets, and carbonaceous meteorites could have contributed to the early Earth s prebiotic inventory by seeding the planet with biologically important organic compounds. A wide variety of prebiotic organic compounds have previously been detected in the Murchison CM type carbonaceous chondrite including amino acids, purines and pyrimidines. These compounds dominate terrestrial biochemistry and are integral components of proteins, DNA and RNA. Several purines including adenine, guanine, hypoxanthine, and xanthine, as well as the pyrimidine uracil, have previously been detected in water or formic acid extracts of Murchison using ion-exclusion chromatography and ultraviolet spectroscopy. However, even after purification of these extracts, the accurate identification and quantification of nucleobases is difficult due to interfering UV absorbing compounds. In order to reduce these effects, we have developed an extraction technique using sublimation to isolate purines and pyrimidines from other non-volatile organic compounds in Murchison acid extracts.

  5. Influence of Sublimation and Pyrolysis on Quasi-Steady Deflagrations in Confined Porous Energetic Materials

    SciTech Connect

    Stephen B. Margolis; Alexander M. Telengator

    2001-03-01

    Deflagrations in porous energetic materials under confinement are generally characterized by a relatively rapid increase in the burning rate as the pressure difference, or overpressure, in the burned-gas region relative to that deep within the pores of the unburned solid increases. Specifically, there appears to be a range of overpressures in which the sensitivity, or slope, of the propagation speed as a function of overpressure transitions from relatively small to large values. This effect has been qualitatively attributed to the fact that a sufficient overpressure reverses the gas flow and thus allows the burned gas to permeate, and therefore preheat, the porous material. However, quantitative descriptions of both the process itself and the corresponding burning-rate dependencies have only recently been achieved. The present work reflects a further refinement in this analytical description in that the melt layer, which underlies several previous studies and is likely to exist only at modest overpressures, is replaced by sublimation and pyrolysis at the material surface, followed by an attached gas flame that converts the unburned gaseous reactants to final products. As a result, gaseous reactants as well as products now permeate the porous solid, thereby affecting the propagation speed significantly and modifying both the combustion-wave structure and the transition to convection-enhanced burning.

  6. Deposition of ZnTe thin films by close spaced sublimation: Structural and electrical studies

    SciTech Connect

    Goyal, D.J.; Bilurkar, P.G.; Thorat, S.K.; Mate, N.V.

    1998-12-31

    Zinc telluride has the potential of being a low-cost, environmentally stable, low-resistance and easily manufacturable back contact for CdS/CdTe solar cells. Close Spaced Sublimation (CSS) technique is used to deposit thin films of ZnTe. The results are reported in this study. The effects of substrate temperature and film thickness on the structural properties of the deposited thin films are studied. X-ray diffractograms show that all the films prominently exhibit presence of (111) and (200) orientations. However, the degree of the preferred orientation changes as a function of the film thickness. Increase in film thickness reduces the preferential orientation. The as deposited ZnTe thin films, being that of p-type semiconductor, are highly resistive. In order to effectively use these as contact to CdS/CdTe solar cells, they are made more conductive by doping copper. The doping is effected by dipping the films in alcoholic solution of copper chloride, followed by air annealing at 200 C. The resistivity of all the doped films drops drastically in the initial 10 minutes of annealing. The extent of doping is controlled by varying the dipping time. The effects of substrate temperature, film thickness and doping, on the stoichiometry of the films, are studied using Atomic Absorption Spectroscopy (AAS).

  7. Isolation of Purines and Pyrimidines from the Murchison Meteorite Using Sublimation

    NASA Technical Reports Server (NTRS)

    Glavin, D. P.; Bada, J. L.

    2004-01-01

    The origin of life on Earth, and possibly on other planets such as Mars, would have required the presence of liquid water and a continuous supply of prebiotic organic compounds. The exogenous delivery of organic matter by asteroids, comets, and carbonaceous meteorites could have contributed to the early Earth s prebiotic inventory by seeding the planet with biologically important organic compounds. A wide variety of prebiotic organic compounds have previously been detected in the Murchison CM type carbonaceous chondrite including amino acids, purines and pyrimidines. These compounds dominate terrestrial biochemistry and are integral components of proteins, DNA and RNA. Several purines including adenine, guanine, hypoxanthine, and xanthine, as well as the pyrimidine uracil, have previously been detected in water or formic acid extracts of Murchison using ion-exclusion chromatography and ultraviolet spectroscopy. However, even after purification of these extracts, the accurate identification and quantification of nucleobases is difficult due to interfering UV absorbing compounds. In order to reduce these effects, we have developed an extraction technique using sublimation to isolate purines and pyrimidines from other non-volatile organic compounds in Murchison acid extracts.

  8. Application of a Kalman filter to UF{sub 6} gaseous diffusion plant freezer/sublimer systems

    SciTech Connect

    Ruppel, F.R.

    1992-03-01

    A signal is required to control the flow of UF{sub 6} in gaseous diffusion plant freezer/sublimer systems. The original strategy envisioned for deriving a flow signal was to take the derivative of the freezer/sublimer weigh cell signal. However, the derivative of the digitized weight signal is noisy, preventing good control. In addition, a bias is introduced into the weight derivative signal because a refrigerant is circulated through a shell-and-tube heat exchanger inside the freezer/sublimer. The weight of the refrigerant is included in the weight measured by the weigh cell. If the circulation rate of the refrigerent is not steady state, a bias exists. Measurements of upstream pressure, vessel pressure, and output to the system control valve are available to the control system. Thus, if the flow through the control valve is characterized properly by the measurements, a Kalman filter can be used in conjunction with these auxiliary inputs and the weigh cell input to overcome the noise and bias problem and provide an improve estimate of flow rate. A discussion of the development and the current status of a Kalman filter used for this application is given. 5 refs.

  9. Coupled fluid-thermal analysis of low-pressure sublimation and condensation with application to freeze-drying

    NASA Astrophysics Data System (ADS)

    Ganguly, Arnab

    Freeze-drying is a low-pressure, low-temperature condensation pumping process widely used in the manufacture of bio-pharmaceuticals for removal of solvents by sublimation. The goal of the process is to provide a stable dosage form by removing the solvent in such a way that the sensitive molecular structure of the active substance is least disturbed. The vacuum environment presents unique challenges for understanding and controlling heat and mass transfer in the process. As a result, the design of equipment and associated processes has been largely empirical, slow and inefficient. A comprehensive simulation framework to predict both, process and equipment performance is critical to improve current practice. A part of the dissertation is aimed at performing coupled fluid-thermal analysis of low-pressure sublimation-condensation processes typical of freeze-drying technologies. Both, experimental and computational models are used to first understand the key heat transfer modes during the process. A modeling and computational framework, validated with experiments for analysis of sublimation, water-vapor flow and condensation in application to pharmaceutical freeze-drying is developed. Augmented with computational fluid dynamics modeling, the simulation framework presented here allows to predict for the first time, dynamic product/process conditions taking into consideration specifics of equipment design. Moreover, by applying the modeling framework to process design based on a design-space approach, it has demonstrated that there is a viable alternative to empiricism.

  10. Surface Energy and Surface Stability of Ag Nanocrystals at Elevated Temperatures and Their Dominance in Sublimation-Induced Shape Evolution.

    PubMed

    He, Long-Bing; Zhang, Lei; Tan, Xiao-Dong; Tang, Lu-Ping; Xu, Tao; Zhou, Yi-Long; Ren, Zhan-Yong; Wang, Yun; Teng, Chun-Yu; Sun, Li-Tao; Nie, Jian-Feng

    2017-07-01

    The surface energy and surface stability of Ag nanocrystals (NCs) are under debate because the measurable values of the surface energy are very inconsistent, and the indices of the observed thermally stable surfaces are apparently in conflict. To clarify this issue, a transmission electron microscope is used to investigate these problems in situ with elaborately designed carbon-shell-capsulated Ag NCs. It is demonstrated that the {111} surfaces are still thermally stable at elevated temperatures, and the victory of the formation of {110} surfaces over {111} surfaces on the Ag NCs during sublimation is due to the special crystal geometry. It is found that the Ag NCs behave as quasiliquids during sublimation, and the cubic NCs represent a featured shape evolution, which is codetermined by both the wetting equilibrium at the Ag-C interface and the relaxation of the system surface energy. Small Ag NCs (≈10 nm) no longer maintain the wetting equilibrium observed in larger Ag NCs, and the crystal orientations of ultrafine Ag NCs (≈6 nm) can rotate to achieve further shape relaxation. Using sublimation kinetics, the mean surface energy of Ag NCs at 1073 K is calculated to be 1.1-1.3 J m(-2) . © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Properties of filamentary sublimation residues from dispersions of clay in ice. [on Martian poles, comet nuclei, and icy satellites

    NASA Technical Reports Server (NTRS)

    Saunders, R. S.; Parker, T. J.; Stephens, J. B.; Fanale, F. P.; Sutton, S.

    1986-01-01

    Results are reported from experimental studies of the formation of ice mixed with mineral particles in an effort to simulate similar processes on natural surfaces such as at the Martian poles, on comet nuclei and on icy satellites. The study consisted of low-pressure, low-temperature sublimations of water ice from dilutions of water-clay (montmorillonite and Cabosil) dispersions of various component ratios. Liquid dispersions were sprayed into liquid nitrogen to form droplets at about -50 C. Both clay-water dispersions left a filamentary residue on the bottom of the Dewar after the water ice had sublimated off. The residue was studied with optical and SEM microscopy, the latter method revealing a high electrical conductivity in the residue. The results suggest that the sublimation of the water ice can leave a surface crust, which may be analogous to processes at the Martian poles and on comet nuclei. The process could proceed by the attachment of water molecules to salt crystals during the hottest part of the Martian year. The residue remaining was found to remain stable up to 370 C, be porous, and remain resilient, which could allow it to insulate ice bodies such as comets in space.

  12. International Equations for the Pressure Along the Melting and Along the Sublimation Curve of Ordinary Water Substance

    NASA Astrophysics Data System (ADS)

    Wagner, Wolfgang; Saul, A.; Pruss, A.

    1994-05-01

    In order to define the phase boundary between the solid phase (ice) and the fluid phase (liquid and gas) of ordinary (light) water substance in pressure-temperature coordinates, correlation equations for the pressure along the melting curve of the various modifications of ice as well as for the pressure along the sublimation curve are presented. The five equations for the melting pressure of the ice phases, ice I, ice III, ice V, ice VI, and ice VII, which only contain one to three fitted coefficients, cover the pressure range from the ``normal'' triple point to 20000 MPa. In this entire range the equations represent the selected measurements of the melting pressure within their experimental uncertainty. The 2-coefficient equation for the sublimation pressure covers the temperature range from 190 K to the triple point (273.16 K). The equations correspond to the new International Temperature Scale of 1990 (ITS-90). All these equations form the basis of the revised release on the pressure along the melting and sublimation curves of ordinary water substance. A verbatium copy of this release is presented in the Appendix of this paper. §

  13. Study on the CO2 Solid-Gas Two Phase Flow with Particle Sublimation and Its Basic Applications

    NASA Astrophysics Data System (ADS)

    Zhang, Xin-Rong; Yamaguchi, Hiroshi; Masuda, Minoru

    2008-02-01

    A basic study was carried out on the CO2 solid-gas two phase flow with particle sublimation. The CO2 two phase flow is achieved by liquid CO2 expansion process throughout the CO2 triple point. A cryogenic refrigeration below -56.6 °C is possible from the CO2 solid particle sublimation in the two phase fluid flow. An experiment was conducted in order to investigate some basic points related to the liquid CO2 expanding into the solid-gas fluid flow, which reveals the CO2 particle size and so on. Based on the primary experiment, a new refrigeration method is introduced by using the CO2 solid-gas two phase flow with particle sublimation. A CO2 heat pump, which can achieve a cryogenic refrigeration below -56.6 °C is designed, constructed and tested. In the paper, details of the CO2 heat pump system are presented and the obtained results show that a continuous operation is possible with CO2 solid-gas flow in the closed loop of the heat pump system. Furthermore, the performance of the new CO2 heat pump system is also presented in this paper, which utilize the flow dynamic of liquid CO2 expanding into the solid-gas fluid.

  14. STRUCTURAL CHANGES OF THE SUBLIMATION WALL IN PROTOPLANETARY DISKS DUE TO VARYING ACCRETION ILLUMINATION: A MECHANISM FOR RAPID INFRARED VARIABILITY

    SciTech Connect

    Nagel, E.; Flaherty, K. M.; Muzerolle, J.

    2015-08-01

    We study the changes in the sublimation wall structure due to variable illumination of a stellar hot spot on the dusty surroundings of a young star. The model includes the settling of large grains toward the disk midplane and the effect of the vertical density profile on the shaping of the sublimation wall. From a survey of objects in the young cluster IC 348, we extract three objects (LRLL 32, 40, and 63) that present typical variability in the [3.6] and [4.5] IRAC bands. We use the Spitzer photometry and ground-based 2–5 μm spectra for comparison with the models. Even though there is a correlation between accretion luminosity and dust emission based on the observations, we conclude from the modeling that the systems with lower mass accretion rates (LRLL 32 and 63) cannot be explained simply by a variable hot spot illuminating a sublimation wall. The observed variability amplitude for LRLL 40 (the system with the largest value of the mass accretion rate) can be obtained using the mechanism presented here. When considering a wide range of hot spot sizes and temperatures, the models can reproduce the infrared fluctuations seen in recent surveys, but only with accretion rate fluctuations that are orders of magnitude larger than is typically observed. These results highlight the relevance of accretion as a variability mechanism as well as its limitations in producing the full extent of the observed infrared variability.

  15. Characterization of the Sublimation and Vapor Pressure of 2-(2-Nitrovinyl) Furan (G-0) Using Thermogravimetric Analysis: Effects of Complexation with Cyclodextrins.

    PubMed

    Ruz, Vivian; González, Mirtha Mayra; Winant, Danny; Rodríguez, Zenaida; Van den Mooter, Guy

    2015-08-19

    In the present work, the sublimation of crystalline solid 2-(2-nitrovinyl) furan (G-0) in the temperature range of 35 to 60 °C (below the melting point of the drug) was studied using thermogravimetric analysis (TGA). The sublimated product was characterized using Fourier-transformed-infrared spectroscopy (FT-IR) and thin layer chromatography (TLC). The sublimation rate at each temperature was obtained using the slope of the linear regression model and followed apparent zero-order kinetics. The sublimation enthalpy from 35 to 60 °C was obtained from the Eyring equation. The Gückel method was used to estimate the sublimation rate and vapor pressure at 25 °C. Physical mixtures, kneaded and freeze-dried complexes were prepared with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and sulfobutyl ether-β-cyclodextrin (SBE-β-CD) and analyzed using isothermal TGA at 50 °C. The complexation contributed to reducing the sublimation process. The best results were achieved using freeze-dried complexes with both cyclodextrins.

  16. In-Situ Growth of Yb2O3 Layer for Sublimation Suppression for Yb14MnSb11 Thermoelectric Material for Space Power Applications

    NASA Technical Reports Server (NTRS)

    Nesbitt, James A.; Opila, Elizabeth J.; Nathal, Michael V.

    2012-01-01

    The compound Yb14MnSb11 is a p-type thermoelectric material of interest to the National Aeronautics and Space Administration (NASA) as a candidate replacement for the state-of-the-art Si-Ge used in current radioisotope thermoelectric generators (RTGs). Ideally, the hot end of this leg would operate at 1000 C in the vacuum of space. Although Yb14MnSb11 shows the potential to double the value of the thermoelectric figure of merit (zT) over that of Si-Ge at 1000 C, it suffers from a high sublimation rate at elevated temperatures and would require a coating in order to survive the required RTG lifetime of 14 years. The purpose of the present work is to measure the sublimation rate of Yb14MnSb11 and to investigate sublimation suppression for this material. This paper reports on the sublimation rate of Yb14MnSb11 at 1000 C (approximately 3 x 10(exp -3) grams per square centimeter hour) and efforts to reduce the sublimation rate with an in situ grown Yb2O3 layer. Despite the success in forming thin, dense, continuous, and adherent oxide scales on Yb14MnSb11, the scales did not prove to be sublimation barriers.

  17. Liquid oxygen (LO2) propellant conditioning concept testing

    NASA Technical Reports Server (NTRS)

    Perry, Gretchen L. E.; Orth, Michael S.; Mehta, Gopal K.

    1993-01-01

    Testing of a simplified LO2 propellant conditioning concept for future expendable launch vehicles is discussed. Four different concepts are being investigated: no-bleed, low-bleed, use of a recirculation line, and He bubbling. A full-scale test article, which is a facsimile of a propellant feed duct with an attached section to simulate heat input from an LO2 turbopump, is to be tested at the Cold Flow Facility of the Marshall Space Flight Center West Test Area. Work to date includes: design and fabrication of the test article, design of the test facility and initial fabrication, development of a test matrix and test procedures, initial predictions of test output, and heat leak calibration and heat exchanger tests on the test articles.

  18. Liquid Oxygen (LO2) propellant conditioning concept testing

    NASA Technical Reports Server (NTRS)

    Perry, Gretchen L. E.; Orth, Michael S.; Mehta, Gopal K.

    1993-01-01

    Marshall Space Flight Center (MSFC) and industry contractors have undertaken activities to develop a simplified liquid oxygen (LO2) propellant conditioning concept for future expendable launch vehicles. The objective of these activities is to reduce operations costs and timelines and to improve safety of these vehicles. The approach followed has been to identify novel concepts through system level studies and demonstrate the feasibility of these concepts through small-scale and full-scale testing. Testing will also provide data for design guidelines and validation of analytical models. Four different concepts are being investigated: no-bleed, low-bleed, use of a recirculation line, and helium (He) bubbling. This investigation is being done under a Joint Institutional Research and Development (JIRAD) program currently in effect between MSFC and General Dynamics Space Systems (GDSS). A full-scale test article, which is a facsimile of a propellant feed duct with an attached section to simulate heat input from a LO2 turbopump, will be tested at the Cold Flow Facility at MSFC's West Test Area. Liquid nitrogen (LN2), which has similar properties to LO2, will be used in place of LO2 for safety and budget reasons. Work to date includes design and fabrication of the test article, design of the test facility and initial fabrication, development of a test matrix and test procedures, initial predictions of test output, and heat leak calibration and heat exchanger tests on the test article. The tests for all propellant conditioning concepts will be conducted in the summer of 1993, with the final report completed by October, 1993.

  19. 77 FR 2715 - D'Lo Gas Storage, LLC; Notice of Application

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-01-19

    ... Energy Regulatory Commission D'Lo Gas Storage, LLC; Notice of Application Take notice that on December 29, 2011, D'Lo Gas Storage, LLC (D'Lo), 1002 East St. Mary Blvd., Lafayette, Louisiana 70503, filed in... D'Lo to construct, operate, and maintain a new natural gas storage project to be located in...

  20. Quadrature mixture LO suppression via DSW DAC noise dither

    DOEpatents

    Dubbert, Dale F.; Dudley, Peter A.

    2007-08-21

    A Quadrature Error Corrected Digital Waveform Synthesizer (QECDWS) employs frequency dependent phase error corrections to, in effect, pre-distort the phase characteristic of the chirp to compensate for the frequency dependent phase nonlinearity of the RF and microwave subsystem. In addition, the QECDWS can employ frequency dependent correction vectors to the quadrature amplitude and phase of the synthesized output. The quadrature corrections cancel the radars' quadrature upconverter (mixer) errors to null the unwanted spectral image. A result is the direct generation of an RF waveform, which has a theoretical chirp bandwidth equal to the QECDWS clock frequency (1 to 1.2 GHz) with the high Spurious Free Dynamic Range (SFDR) necessary for high dynamic range radar systems such as SAR. To correct for the problematic upconverter local oscillator (LO) leakage, precision DC offsets can be applied over the chirped pulse using a pseudo-random noise dither. The present dither technique can effectively produce a quadrature DC bias which has the precision required to adequately suppress the LO leakage. A calibration technique can be employed to calculate both the quadrature correction vectors and the LO-nulling DC offsets using the radar built-in test capability.

  1. The ClearfLo project - Understanding London's meteorology and composition

    NASA Astrophysics Data System (ADS)

    Belcher, Stephen; Bohnenstengel, Sylvia

    2014-05-01

    ClearfLo is a large multi-institutional project funded by the UK Natural Environment Research Council (NERC). ClearfLo established integrated measurements of meteorology, gaseous and particulate composition/loading of London's (UK) urban atmosphere in 2011 and 2012 to understand the processes underlying poor air quality. A new and unique long-term measurement infrastructure was established in London at street level, urban background and elevated sites and contrasted against rural locations to determine the urban increment in meteorology and pollution. This approach enables understanding the seasonal variations in the meteorology and composition together with the controlling processes. In addition two intensive observation periods (IOPs) provide more detail in winter 2012 and during the Olympics in summer 2012 focusing upon the vertical structure and evolution of the urban boundary layer, chemical controls on nitrogen dioxide and ozone production, in particular the role of volatile organic compounds, and processes controlling the evolution, size, distribution and composition of particulate matter. In this talk we present early analysis of the meteorology and air quality measurements within ClearfLo. In particular we show measurements that indicate the dominant regimes of London's boundary layer.

  2. Meteorological conditions associated to high sublimation amounts in semiarid high-elevation Andes decrease the performance of empirical melt models

    NASA Astrophysics Data System (ADS)

    Ayala, Alvaro; Pellicciotti, Francesca; MacDonell, Shelley; McPhee, James; Burlando, Paolo

    2015-04-01

    Empirical melt (EM) models are often preferred to surface energy balance (SEB) models to calculate melt amounts of snow and ice in hydrological modelling of high-elevation catchments. The most common reasons to support this decision are that, in comparison to SEB models, EM models require lower levels of meteorological data, complexity and computational costs. However, EM models assume that melt can be characterized by means of a few index variables only, and their results strongly depend on the transferability in space and time of the calibrated empirical parameters. In addition, they are intrinsically limited in accounting for specific process components, the complexity of which cannot be easily reconciled with the empirical nature of the model. As an example of an EM model, in this study we use the Enhanced Temperature Index (ETI) model, which calculates melt amounts using air temperature and the shortwave radiation balance as index variables. We evaluate the performance of the ETI model on dry high-elevation sites where sublimation amounts - that are not explicitly accounted for the EM model - represent a relevant percentage of total ablation (1.1 to 8.7%). We analyse a data set of four Automatic Weather Stations (AWS), which were collected during the ablation season 2013-14, at elevations between 3466 and 4775 m asl, on the glaciers El Tapado, San Francisco, Bello and El Yeso, which are located in the semiarid Andes of central Chile. We complement our analysis using data from past studies in Juncal Norte Glacier (Chile) and Haut Glacier d'Arolla (Switzerland), during the ablation seasons 2008-09 and 2006, respectively. We use the results of a SEB model, applied to each study site, along the entire season, to calibrate the ETI model. The ETI model was not designed to calculate sublimation amounts, however, results show that their ability is low also to simulate melt amounts at sites where sublimation represents larger percentages of total ablation. In fact, we

  3. Formation of dust-rich planetesimals from sublimated pebbles inside of the snow line

    NASA Astrophysics Data System (ADS)

    Ida, S.; Guillot, T.

    2016-11-01

    Context. For up to a few millions of years, pebbles must provide a quasi-steady inflow of solids from the outer parts of protoplanetary disks to their inner regions. Aims: We wish to understand how a significant fraction of the pebbles grows into planetesimals instead of being lost to the host star. Methods: We examined analytically how the inward flow of pebbles is affected by the snow line and under which conditions dust-rich (rocky) planetesimals form. When calculating the inward drift of solids that is due to gas drag, we included the back-reaction of the gas to the motion of the solids. Results: We show that in low-viscosity protoplanetary disks (with a monotonous surface density similar to that of the minimum-mass solar nebula), the flow of pebbles does not usually reach the required surface density to form planetesimals by streaming instability. We show, however, that if the pebble-to-gas-mass flux exceeds a critical value, no steady solution can be found for the solid-to-gas ratio. This is particularly important for low-viscosity disks (α< 10-3) where we show that inside of the snow line, silicate-dust grains ejected from sublimating pebbles can accumulate, eventually leading to the formation of dust-rich planetesimals directly by gravitational instability. Conclusions: This formation of dust-rich planetesimals may occur for extended periods of time, while the snow line sweeps from several au to inside of 1 au. The rock-to-ice ratio may thus be globally significantly higher in planetesimals and planets than in the central star.

  4. Mass removal by oxidation and sublimation of porous graphite during fiber laser irradiation

    NASA Astrophysics Data System (ADS)

    Phillips, Grady T.; Bauer, William A.; Fox, Charles D.; Gonzales, Ashley E.; Herr, Nicholas C.; Gosse, Ryan C.; Perram, Glen P.

    2017-01-01

    The various effects of laser heating of carbon materials are key to assessing laser weapon effectiveness. Porous graphite plates, cylinders, and cones with densities of 1.55 to 1.82 g/cm3 were irradiated by a 10-kW fiber laser at 0.075 to 3.525 kW/cm2 for 120 s to study mass removal and crater formation. Surface temperatures reached steady state values as high as 3767 K. The total decrease in sample mass ranged from 0.06 to 6.29 g, with crater volumes of 0.52 to 838 mm3, and penetration times for 12.7-mm-thick plates as short as 38 s. Minor contaminants in the graphite samples produced calcium and iron oxide to be redeposited on the graphite surface. Dramatic graphite crystalline structures are also produced at higher laser irradiances. Significantly increased porosity of the sample is observed even outside the laser-irradiated region. Total mass removed increases with deposited laser energy at a rate of 4.83 g/MJ for medium extruded graphite with an apparent threshold of 0.15 MJ. At ˜3.5 kW/cm2, the fractions of the mass removed from the cylindrical samples in the crater, surrounding trench, and outer region of decreased porosity are 38%, 47%, and 15%, respectively. Graphite is particularly resistant to damage by high power lasers. The new understanding of graphite combustion and sublimation during laser irradiation is vital to the more complex behavior of carbon composites.

  5. SUBLIMATION-DRIVEN ACTIVITY IN MAIN-BELT COMET 313P/GIBBS

    SciTech Connect

    Hsieh, Henry H.; Hainaut, Olivier; Novaković, Bojan; Bolin, Bryce; Denneau, Larry; Haghighipour, Nader; Kleyna, Jan; Meech, Karen J.; Schunova, Eva; Wainscoat, Richard J.; Fitzsimmons, Alan; Kokotanekova, Rosita; Snodgrass, Colin; Lacerda, Pedro; Micheli, Marco; Moskovitz, Nick; Wasserman, Lawrence; Waszczak, Adam

    2015-02-10

    We present an observational and dynamical study of newly discovered main-belt comet 313P/Gibbs. We find that the object is clearly active both in observations obtained in 2014 and in precovery observations obtained in 2003 by the Sloan Digital Sky Survey, strongly suggesting that its activity is sublimation-driven. This conclusion is supported by a photometric analysis showing an increase in the total brightness of the comet over the 2014 observing period, and dust modeling results showing that the dust emission persists over at least three months during both active periods, where we find start dates for emission no later than 2003 July 24 ± 10 for the 2003 active period and 2014 July 28 ± 10 for the 2014 active period. From serendipitous observations by the Subaru Telescope in 2004 when the object was apparently inactive, we estimate that the nucleus has an absolute R-band magnitude of H{sub R} = 17.1 ± 0.3, corresponding to an effective nucleus radius of r{sub e} ∼ 1.00 ± 0.15 km. The object’s faintness at that time means we cannot rule out the presence of activity, and so this computed radius should be considered an upper limit. We find that 313P’s orbit is intrinsically chaotic, having a Lyapunov time of T{sub l} = 12,000 yr and being located near two three-body mean-motion resonances with Jupiter and Saturn, 11J-1S-5A and 10J+12S-7A, yet appears stable over >50 Myr in an apparent example of stable chaos. We furthermore find that 313P is the second main-belt comet, after P/2012 T1 (PANSTARRS), to belong to the ∼155 Myr old Lixiaohua asteroid family.

  6. Sublimation process and physical properties of vapor grown γ-In2Se3 platelet crystals

    NASA Astrophysics Data System (ADS)

    Ajayakumar, C. J.; Kunjomana, A. G.

    2016-11-01

    Indium selenide (γ-In2Se3) crystals have been grown by the closed tube sublimation process in the absence of seed crystals and chemical transporting agents. The composition, structure and morphology of the samples grown under different vacuum conditions were examined by energy dispersive analysis, X-ray diffraction, and scanning electron microscope. Structural features of the crystals obtained in a vacuum of 10-3 mbar exhibited a few reflections not belonging to γ phase, whereas X-ray diffraction spectra of the crystals deposited under a vacuum of 10-6 mbar revealed evidence of sharp peaks with high intensities of γ-In2Se3 crystalline phase. When growth runs were performed for 72 h, voids were observed on the surface whereas for a duration of 120 h, platelet crystals were obtained. Optical properties of these samples were investigated using the FT-IR and photoluminescence spectroscopy. The average transmittance of the platelets in the visible and near infrared region of solar spectrum was found to be ∼81% and an optical band gap of ∼2.05 eV was computed from the transmission spectrum. Photoluminescence spectra of the grown In2Se3 crystals recorded at room temperature using an excitation laser of wavelength 355 nm showed a peak in the near band edge emission (NBE) corresponding to an energy of 2.01 eV. Under an illumination power of 12 mW/cm2, the photocurrent increased linearly with applied voltage and the dark current was found to be 2.5×10-9 A for 10 V. These results suggest that the as-grown γ-In2Se3 platelets crystallized from vapor deposition, possess superior optoelectronic properties than the other phases for solar cell applications.

  7. CdZnS thin films sublimated by closed space using mechanical mixing: A new approach

    NASA Astrophysics Data System (ADS)

    Mahmood, Waqar; Shah, Nazar Abbas

    2014-06-01

    Cadmium sulfide (CdS) is a prominent material for its tunable band gap used as a window layer in II-VI semiconductor solar cells. The light trapping capability of window layer is one of the powerful tools to enhance the efficiency of the cell. CdS and zinc (Zn) powders were mixed mechanically with different weight percents to make CdZnS (CZS) powder. CZS was deposited onto an ultrasonically cleaned glass substrate using close spaced sublimation (CSS) technique. CZS as-deposited thin films were characterized for structural, surface morphology with energy dispersive X-rays (EDX) and optical properties for the use of window layer in CdS/CdTe based solar cells. The different Zn concentrations in CZS played a vital role on crystallite size in structural analysis and optical properties e.g. transmission, absorption coefficient and energy band gap, etc. The crystallite size of as-deposited CZS thin films were increased as Zn concentration was increased up to certain value. The energy band gap varies from 2.42 eV to 2.57 eV for as-deposited CZS thin films with increasing Zn concentrations and surface morphology changes also. These changes were occurred due to zinc diffusion in CdS thin films. An angle resolved transmission data was taken to check the behavior of CdS and CZS thin film at different angles. A comparative study was carried out between CdS thin films and CZS thin films for the use of good window layer material.

  8. Aluminum Nitride-Silicon Carbide Alloy Crystals Grown on SiC Substrates by Sublimation

    SciTech Connect

    Gu, Z; Du, Li; Edgar, J H; Payzant, E Andrew; Walker, Larry R; Liu, R; Engelhard, M H

    2005-01-01

    AlN-SiC alloy crystals, with a thickness greater than 500μm, were grown on 4H- and 6H-SiC substrates from a mixture of AlN and SiC powders by the sublimation-recondensation method at 1860-1990 C. On-axis SiC substrates produced a rough surface covered with hexagonal grains, while 6H- and 4H- off-axis SiC substrates with different miscut angles (8 or 3.68 ) formed a relatively smooth surface with terraces and steps. The substrate misorientation ensured that the AlNSiC alloy crystals grew two dimensionally as identified by scanning electron microscopy (SEM). Xray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that the AlN-SiC alloys had the wurtzite structure. Electron probe microanalysis (EPMA) and x-ray photoelectron spectroscopy (XPS) demonstrated that the resultant alloy crystals had non-stoichiometric ratios of Al:N and Si:C and a uniform composition throughout the alloy crystal from the interface to the surface. The composition ratio of Al:Si of the alloy crystals changed with the growth temperature, and differed from the original source composition, which was consistent with the results predicted by thermodynamic calculation of the solid-vapor distribution of each element. XPS detected the bonding between Si-C, Si-N, Si-O for the Si 2p spectra. The dislocation density decreased with the growth, which was lower than 10^6cm-2 at the alloy surface, more than two orders of magnitude lower compared to regions close to the crystal/substrate interface, as determined by TEM.

  9. ACCRETION DISKS AROUND MASSIVE STARS: HYDRODYNAMIC STRUCTURE, STABILITY, AND DUST SUBLIMATION

    SciTech Connect

    Vaidya, Bhargav; Fendt, Christian; Beuther, Henrik E-mail: fendt@mpia.de

    2009-09-01

    We investigate the structure of accretion disks around massive protostar applying steady state models of thin disks. The thin disk equations are solved with proper opacities for dust and gas taking into account the huge temperature variation along the disk. We explore a wide parameter range concerning stellar mass, accretion rate, and viscosity parameter {alpha}. The most essential finding is a very high temperature of the inner disk. For e.g., a 10 M{sub sun} protostar with an accretion rate of {approx}10{sup -4} M{sub sun} yr{sup -1}, the disk midplane temperature may reach almost 10{sup 5} K. The disk luminosity in this case is about 10{sup 4} L{sub sun} and, thus, potentially higher than that of a massive protostar. We motivate our disk model with similar hot disks around compact stars. We calculate a dust sublimation radius by turbulent disk self-heating of more than 10 AU, a radius, which is 3 times larger than that caused by stellar irradiation. We discuss implications of this result on the flashlight effect and the consequences for the radiation pressure of the central star. In deference to disks around low-mass protostars, our models suggest rather high values for the disk turbulence parameter {alpha} {<=} 1. However, disk stability to fragmentation due to thermal effects and gravitational instability would require a lower {alpha} value. For {alpha} = 0.1, we find stable disks out to 80 AU. Essentially, our model allows us to compare the outer disk to some of the observed massive protostellar disk sources, and from that, extrapolate the disk structure close to the star which is yet impossible to observe.

  10. Sublimation-Driven Activity in Main-Belt Comet 313p/Gibbs

    NASA Astrophysics Data System (ADS)

    Hsieh, Henry H.; Hainaut, Olivier; Novaković, Bojan; Bolin, Bryce; Denneau, Larry; Fitzsimmons, Alan; Haghighipour, Nader; Kleyna, Jan; Kokotanekova, Rosita; Lacerda, Pedro; Meech, Karen J.; Micheli, Marco; Moskovitz, Nick; Schunova, Eva; Snodgrass, Colin; Wainscoat, Richard J.; Wasserman, Lawrence; Waszczak, Adam

    2015-02-01

    We present an observational and dynamical study of newly discovered main-belt comet 313P/Gibbs. We find that the object is clearly active both in observations obtained in 2014 and in precovery observations obtained in 2003 by the Sloan Digital Sky Survey, strongly suggesting that its activity is sublimation-driven. This conclusion is supported by a photometric analysis showing an increase in the total brightness of the comet over the 2014 observing period, and dust modeling results showing that the dust emission persists over at least three months during both active periods, where we find start dates for emission no later than 2003 July 24 ± 10 for the 2003 active period and 2014 July 28 ± 10 for the 2014 active period. From serendipitous observations by the Subaru Telescope in 2004 when the object was apparently inactive, we estimate that the nucleus has an absolute R-band magnitude of HR = 17.1 ± 0.3, corresponding to an effective nucleus radius of re ∼ 1.00 ± 0.15 km. The object’s faintness at that time means we cannot rule out the presence of activity, and so this computed radius should be considered an upper limit. We find that 313P’s orbit is intrinsically chaotic, having a Lyapunov time of Tl = 12,000 yr and being located near two three-body mean-motion resonances with Jupiter and Saturn, 11J-1S-5A and 10J+12S-7A, yet appears stable over >50 Myr in an apparent example of stable chaos. We furthermore find that 313P is the second main-belt comet, after P/2012 T1 (PANSTARRS), to belong to the ∼155 Myr old Lixiaohua asteroid family.

  11. AdS/QCD, Light-Front Holography, and Sublimated Gluons

    SciTech Connect

    Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U.

    2012-02-16

    The gauge/gravity duality leads to a simple analytical and phenomenologically compelling nonperturbative approximation to the full light-front QCD Hamiltonian - 'Light-Front Holography', which provides a Lorentz-invariant first-approximation to QCD, and successfully describes the spectroscopy of light-quark meson and baryons, their elastic and transition form factors, and other hadronic properties. The bound-state Schroedinger and Dirac equations of the soft-wall AdS/QCD model predict linear Regge trajectories which have the same slope in orbital angular momentum L and radial quantum number n for both mesons and baryons. Light-front holography connects the fifth-dimensional coordinate of AdS space z to an invariant impact separation variable {zeta} in 3+1 space at fixed light-front time. A key feature is the determination of the frame-independent light-front wavefunctions of hadrons - the relativistic analogs of the Schroedinger wavefunctions of atomic physics which allow one to compute form factors, transversity distributions, spin properties of the valence quarks, jet hadronization, and other hadronic observables. One thus obtains a one-parameter color-confining model for hadron physics at the amplitude level. AdS/QCD also predicts the form of the non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q) and its {beta}-function with an infrared fixed point which agrees with the effective coupling a{sub g1} (Q{sup 2}) extracted from measurements of the Bjorken sum rule below Q{sup 2} < 1 GeV{sup 2}. This is consistent with a flux-tube interpretation of QCD where soft gluons with virtualities Q{sup 2} < 1 GeV{sup 2} are sublimated into a color-confining potential for quarks. We discuss a number of phenomenological hadronic properties which support this picture.

  12. Photometry of LO Pegasi in B, V, R colors

    NASA Astrophysics Data System (ADS)

    Csorvási, R.

    2006-09-01

    Variable magnetic activity manifested by starspot distribution is investigated on the single K5-K7 dwarf LO Peg, using one month long photometric observations. We supposed three circular spots for light curve solution. We find variable spot temperature, whose average is 3960 K. The sizes of spots were stable for two spots and one spot showed a significant decrease. Different migration periods on two spots indicate differential rotation, the magnitude of the migration is slow. During the measured 90 stellar rotations (38.5 days) the location of the activity remained on the same hemisphere of the star.

  13. Balmer Absorption Lines in FeLoBALs

    NASA Astrophysics Data System (ADS)

    Aoki, K.; Iwata, I.; Ohta, K.; Tamura, N.; Ando, M.; Akiyama, M.; Kiuchi, G.; Nakanishi, K.

    2007-10-01

    We discovered non-stellar Balmer absorption lines in two many-narrow-trough FeLoBALs (mntBALs) by the near-infrared spectroscopy with Subaru/CISCO. Presence of the non-stellar Balmer absorption lines is known to date only in the Seyfert galaxy NGC 4151; thus our discovery is the first cases for quasars. Since all known active galactic nuclei with Balmer absorption lines share similar characteristics, it is suggested that there is a population of BAL quasars which have unique structures at their nuclei or unique evolutionary phase.

  14. Age and stability of sublimation till over buried glacier ice, inferred from 21Ne measurements, Ong Valley, Antarctica

    NASA Astrophysics Data System (ADS)

    Bibby, T.; Putkonen, J.; Morgan, D. J.; Balco, G.

    2014-12-01

    Ong Valley, in the Central Transantarctic Mountains, contains three distinct glacial drifts deposited by past advances of the Argosy glacier into the valley. Massive ice occurs below two of the till deposits. Potentially, such buried ice under shallow regolith cover could provide access to past climate and biological records more easily than deep ice coring. We measured cosmic-ray produced 21Ne in these tills as a means of constraining the age and stability of the three drifts, as well as the ice below them. We collected samples in vertical profiles from two hand-dug sections through each drift. The pits from two drifts overlying buried ice extended to the buried ice surface. The hypothesis that these are sublimation tills implies that 21Ne concentrations are a function of i) any inheritance from prior exposure; ii) the age since emplacement of the ice and till; iii) the sublimation rate of the ice; and iv) the surface erosion rate of the till. 21Ne concentrations in the youngest drift are ca. 10 M atoms/g and invariant with depth, indicating that they are predominantly due to inheritance, and provide only a weak maximum age constraint of ca. 0.1 Mya. The two older drifts have surface 21Ne concentrations of 200-250 M atoms/ g and depth concentration profiles consistent with a sublimation till origin. Given that 21Ne concentrations in the deepest samples in each of the two older drifts provide an upper limit on the inherited 21Ne concentration, these imply minimum ages of 1 Mya for the middle drift and 1.6 Mya for the oldest. This implies a 1 Mya minimum age for the ice underlying the middle drift.

  15. Fast optically sectioned fluorescence HiLo endomicroscopy

    PubMed Central

    Lim, Daryl; Mertz, Jerome

    2012-01-01

    Abstract. We describe a nonscanning, fiber bundle endomicroscope that performs optically sectioned fluorescence imaging with fast frame rates and real-time processing. Our sectioning technique is based on HiLo imaging, wherein two widefield images are acquired under uniform and structured illumination and numerically processed to reject out-of-focus background. This work is an improvement upon an earlier demonstration of widefield optical sectioning through a flexible fiber bundle. The improved device features lateral and axial resolutions of 2.6 and 17 μm, respectively, a net frame rate of 9.5 Hz obtained by real-time image processing with a graphics processing unit (GPU) and significantly reduced motion artifacts obtained by the use of a double-shutter camera. We demonstrate the performance of our system with optically sectioned images and videos of a fluorescently labeled chorioallantoic membrane (CAM) in the developing G. gallus embryo. HiLo endomicroscopy is a candidate technique for low-cost, high-speed clinical optical biopsies. PMID:22463023

  16. Fast optically sectioned fluorescence HiLo endomicroscopy

    NASA Astrophysics Data System (ADS)

    Ford, Tim N.; Lim, Daryl; Mertz, Jerome

    2012-02-01

    We describe a nonscanning, fiber bundle endomicroscope that performs optically sectioned fluorescence imaging with fast frame rates and real-time processing. Our sectioning technique is based on HiLo imaging, wherein two widefield images are acquired under uniform and structured illumination and numerically processed to reject out-of-focus background. This work is an improvement upon an earlier demonstration of widefield optical sectioning through a flexible fiber bundle. The improved device features lateral and axial resolutions of 2.6 and 17 μm, respectively, a net frame rate of 9.5 Hz obtained by real-time image processing with a graphics processing unit (GPU) and significantly reduced motion artifacts obtained by the use of a double-shutter camera. We demonstrate the performance of our system with optically sectioned images and videos of a fluorescently labeled chorioallantoic membrane (CAM) in the developing G. gallus embryo. HiLo endomicroscopy is a candidate technique for low-cost, high-speed clinical optical biopsies.

  17. Advanced liquid oxygen (LO2) propellant conditioning concept testing

    NASA Technical Reports Server (NTRS)

    Perry, G. L. E.; Suter, J. D.; Turner, S. G.

    1995-01-01

    Advanced methods of liquid oxygen (LO2) propellant conditioning were studied as part of an effort for increasing reliability and operability while reducing cost of future heavy lift launch vehicles. The most promising conditioning concept evaluated was no-bleed (passive recirculation) followed by low-bleed, helium injection, and use of a recirculation line. Full-scale cryogenic testing was performed with a sloped feedline test article to validate models of behavior of LO2 in the feedline and to prove no-bleed feasibility. Test data are also intended to help generate design guidelines for the development of a main propulsion system feed duct. A design-of-experiments matrix of over 100 tests was developed to test all four propellant conditioning concepts and the impact of design parameters on the concepts. Liquid nitrogen was used as the test fluid. The work for this project was conducted from October 1992 through January 1994 at the hydrogen cold flow facility of the west test area of MSFC. Test data have shown that satisfactory temperatures are being obtained for the no-bleed conditioning concept.

  18. Volcanic Activity on lo at the Time of the Ulysses Encounter.

    PubMed

    Spencer, J R; Howell, R R; Clark, B E; Klassen, D R; O'connor, D

    1992-09-11

    The population of heavy ions in lo's torus is ultimately derived from lo volcanism. Groundbased infrared observations of lo between October 1991 and March 1992, contemporaneous with the 8 February 1992 Ulysses observations of the lo torus, show that volcanic thermal emission was at the low end of the normal range at all lo longitudes during this period. In particular, the dominant hot spot Loki was quiescent. Resolved images show that there were at least four hot spots on lo's Jupiter-facing hemisphere, including Loki and a long-lived spot on the leading hemisphere (Kanehekili), of comparable 3.5-micrometer brightness but higher temperature.

  19. An atomic beam of 6Li — 7Li for high resolution spectroscopy from matrix isolation sublimation

    NASA Astrophysics Data System (ADS)

    Oliveira, A. N.; Sacramento, R. L.; Silva, B. A.; Uhlmann, F. O.; Wolff, W.; Cesar, C. L.

    2016-07-01

    We propose the Matrix Isolation Sublimation (MlSu) technique for generating cold lithium atoms for the measurement of the 6Li - 7Li isotope shift in D1 and D2 transitions. The technique is capable of generating cold 6Li and 7Li beams at 4 K with forward velocity of 125 m/s. Using this beam we offer a distinguished source of lithium atoms for transitions measurements, adding a new possibility to make high resolution spectroscopy towards improving the experimental checks of the theory.

  20. Sublimation rates of carbon monoxide and carbon dioxide from comet nuclei at large distances from the Sun

    NASA Technical Reports Server (NTRS)

    Sekanina, Zdenek

    1991-01-01

    One of the more attractive among the plausible scenarios for the major emission event recently observed on Comet Halley at a heliocentric distance of 14.3 AU is activation of a source of ejecta driven by an icy substance much more volatile than water. As prerequisite for the forthcoming detailed analysis of the imaging observations of this event, a simple model is proposed that yields the sublimation rate versus time at any location on the surface of a rotating cometary nucleus for two candidate ices: carbon monoxide and carbon dioxide. The model's variable parameters are the comet's heliocentric distance r and the Sun's instantaneous zenith angle z.

  1. Hg1-xCdxTe vapor deposition on CdZnTe substrates by Closed Space Sublimation technique

    NASA Astrophysics Data System (ADS)

    Rubio, Sandra; Sochinskii, Nikolai V.; Repiso, Eva; Tsybrii, Zinoviia; Sizov, Fiodor; Plaza, Jose Luis; Diéguez, Ernesto

    2017-01-01

    Closed Space Sublimation (CSS) technique has been studied to deposit Hg1-xCdxTe polycrystalline films on CdZnTe substrates at the improved pressure-temperature conditions. The experimental results on film characterization suggest that the CSS optimal conditions are the argon atmospheric pressure (1013 mbar) and the deposition temperature in the range of 500-550 °C. These conditions provide macro-defect free Hg1-xCdxTe films with the uniform size and surface distribution of polycrystals.

  2. Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2010

    NASA Astrophysics Data System (ADS)

    Acree, William; Chickos, James S.

    2010-12-01

    A compendium of phase change enthalpies published within the period 1880-2010 is reported. Phase change enthalpies including fusion, vaporization, and sublimation are included for organic, organometallic, and a few inorganic compounds. This compendium is a combination of three previous series focusing on phase change enthalpies updated to 2009. Sufficient data are presently available for some compounds to permit thermodynamic cycles to be constructed, an important manner of evaluating the reliability of the measurements. Temperature adjustments of phase change enthalpies from the temperature of measurement to the standard reference temperature, T=298.15 K, are briefly discussed and a protocol for doing so is illustrated.

  3. Low-temperature transport properties of multigraphene films grown on the SiC surface by sublimation

    SciTech Connect

    Lebedev, A. A. Agrinskaya, N. V.; Lebedev, S. P.; Mynbaeva, M. G.; Petrov, V. N.; Smirnov, A. N.; Strel'chuk, A. M.; Titkov, A. N.; Shamshur, D. V.

    2011-05-15

    Multigraphene films grown by sublimation on the surface of a semi-insulating 6H-SiC substrate have been studied. It is shown that pregrowth annealing of the substrate in a quasiclosed growth cell improves the structural quality of a multigraphene film. Ohmic contacts to the film have been fabricated, and the Hall effect has been studied at low temperatures. It is found that a 2D electron gas exists in the films. It is concluded that the conductivity of the film is determined by defects existing within the graphene layer or at the interface between the graphene film and a SiC substrate.

  4. Effect of acoustic streaming on the mass transfer from a sublimating sphere

    NASA Astrophysics Data System (ADS)

    Kawahara, N.; Yarin, A. L.; Brenn, G.; Kastner, O.; Durst, F.

    2000-04-01

    particles much smaller than the sound wavelength. Good agreement between experiment and the theory of Yarin et al. is demonstrated. The time-averaged heat and mass transfer rates over a sphere surface are greatest at the sphere's equator and least at its poles in the experiment as predicted by the theory (the ultrasonic standing wave spans the vertical axis passing through the poles). The measured distribution of the mass transfer rate over the sphere surface also agrees with the theoretical predictions, which shows that in strong acoustic fields sublimation (or evaporation) results from the acoustic streaming.

  5. Scaling properties of step bunches induced by sublimation and related mechanisms

    NASA Astrophysics Data System (ADS)

    Krug, J.; Tonchev, V.; Stoyanov, S.; Pimpinelli, A.

    2005-01-01

    This work provides a ground for a quantitative interpretation of experiments on step bunching during sublimation of crystals with a pronounced Ehrlich-Schwoebel (ES) barrier in the regime of weak desorption. A strong step bunching instability takes place when the kinetic length d+=Ds/K+ is larger than the average distance l between the steps on the vicinal surface; here Ds is the surface diffusion coefficient and K+ is the step kinetic coefficient. In the opposite limit d+≪l the instability is weak and step bunching can occur only when the magnitude of step-step repulsion is small. The central result are power law relations of the form Ltilde Hα , lmin˜H-γ between the width L , the height H , and the minimum interstep distance lmin of a bunch. These relations are obtained from a continuum evolution equation for the surface profile, which is derived from the discrete step dynamical equations for the case d+≫l . The analysis of the continuum equation reveals the existence of two types of stationary bunch profiles with different scaling properties. Through comparison with numerical simulations of the discrete step equations, we establish the value γ=2/(n+1) for the scaling exponent of lmin in terms of the exponent n of the repulsive step-step interaction, and provide an exact expression for the prefactor in terms of the energetic and kinetic parameters of the system. For the bunch width L we observe significant deviations from the expected scaling with exponent γ=1-1/α , which are attributed to the pronounced asymmetry between the leading and the trailing edges of the bunch, and the fact that bunches move. Through a mathematical equivalence on the level of the discrete step equations as well as on the continuum level, our results carry over to the problems of step bunching induced by growth with a strong inverse ES effect, and by electromigration in the attachment/detachment limited regime. Thus our work provides support for the existence of universality

  6. Properties and dynamic interaction of step density waves at a crystal surface during electromigration affected sublimation

    NASA Astrophysics Data System (ADS)

    Stoyanov, S.; Tonchev, V.

    1998-07-01

    Electromigration affected sublimation is a complicated phenomenon, involving surface transport coupled to a process of atom exchange between the two-dimensional gas of adatoms and the crystal phase. The case of intensive exchange is theoretically treated and equations of step motion are derived for the case of ``nontransparent'' steps (kinetics with local conservation of adatoms). The numerical integration of these equations manifests step bunching (a formation of step density waves) at step-down direction of the electromigration of adatoms. We studied some properties of the step density waves: the amplitude (the maximum slope of the bunch) and its dependence on the number of steps in the bunch, the kinematic wave velocity and the dynamic interaction of waves of different amplitudes. The central result of this work is the dependence of the minimum interstep distance (in the steady state shape of the bunch) on the model parameters. This dependence, extracted from numerical study, is presented in terms of scaling laws lmin~N-r(A/F)q, where N is the number of steps in the bunch, A is the magnitude of step-step repulsion, and F is the force, inducing electromigration of the adatoms. Both scaling exponents r and q depend on the power n in the step-step repulsion dependence on the interstep distance (U=A/ln) and, therefore, they are a key to the problem of experimental evaluation of n. A striking result of this model is the constant value of lmin in a wide range of values of the average diffusion distance λs. Thus one cannot relate the temperature dependence of lmin to the temperature dependence of λs. Numerical analysis of the dynamics of steps at a crystal surface of small misorientation angle reveals two types of dynamic interaction of bunches of steps: ``bunch size exchange'' and ``effective coalescence.'' The former type of interaction is rather interesting - a smaller (and faster) bunch approaches a larger one and they travel together until the initially larger

  7. Ontogeny of fetal CD8lo4lo thymocytes: expression of CD44, CD25 and early expression of TcR alpha mRNA.

    PubMed

    Andjelić, S; Jain, N; Nikolić-Zugić, J

    1993-09-01

    CD8lo4lo cells are the immediate precursors of immature CD8hi4loTcRlo, CD8lo4hiTcRlo and CD8hi4hiTcRlo double-positive (DP) thymocytes in the adult murine thymus. These cells are the first subset in the adult thymus to express accessory CD8 and CD4 molecules, to rearrange the T cell receptor (TcR) alpha chain genes and to express the TcR alpha beta heterodimer at low levels at the surface. Here, we investigate the fetal ontogeny of CD8lo4lo cells. We detect these cells on day 15 of fetal development. They dominate the thymus on day 15.5, to become progressively less prominent thereafter. An important characteristic of fetal CD8lo4lo cells is the early expression of TcR alpha mRNA (on fetal day 15, 36-48 h earlier than reported previously). Our results also suggest, but do not prove, that the receptor may be expressed on the surface as early as day 15.5. Fetal CD8lo4lo cells, like their adult counterparts, become DP in vitro. However, early fetal CD8lo4lo thymocytes express both CD44 and CD25--unlike the adult subset--and that links them to their putative precursors, fetal CD44+CD25+ double-negative cells. This finding underscores the difference between adult and fetal thymocytes in turnover of membrane molecules and/or the kinetics of progression through phenotypic stages.

  8. Risk assessment of Cumberland unit 2 L-O blades

    SciTech Connect

    Lam, T.C.T.; Puri, A.

    1996-12-31

    Concern about the reliability of the 1,300 mw Cumberland steam turbine units after an unexpected blade tip failure in the fall of 1995 caused TVA to conduct an investigation into the current reliability of the L-O blades. A probabilistic model based on the measured frequencies, damping and material fatigue data was generated. The influence of significant erosion damage on the blade natural frequencies and on the local stresses was estimated. A probabilistic model of the local fatigue limit was generated based on test data. Monte Carlo simulation was employed to estimate the probability of blade failure by comparing the dynamic stress with the fatigue limit. Risk assessment of the blade failure is presented.

  9. Responsivity calibration of the LoWEUS spectrometer

    SciTech Connect

    Lepson, J. K.; Beiersdorfer, P.; Kaita, R.; Majeski, R.; Boyle, D.

    2016-09-02

    We performed an in situ calibration of the relative responsivity function of the Long-Wavelength Extreme Ultraviolet Spectrometer (LoWEUS), while operating on the Lithium Tokamak Experiment (LTX) at Princeton Plasma Physics Laboratory. The calibration was accomplished by measuring oxygen lines, which are typically present in LTX plasmas. The measured spectral line intensities of each oxygen charge state were then compared to the calculated emission strengths given in the CHIANTI atomic database. Normalizing the strongest line in each charge state to the CHIANTI predictions, we obtained the differences between the measured and predicted values for the relative strengths of the other lines of a given charge state. We find that a 3rd degree polynomial function provides a good fit to the data points. Lastly, our measurements show that the responsivity between about 120 and 300 Å varies by factor of ~30.

  10. Responsivity calibration of the LoWEUS spectrometer

    NASA Astrophysics Data System (ADS)

    Lepson, J. K.; Beiersdorfer, P.; Kaita, R.; Majeski, R.; Boyle, D.

    2016-11-01

    We performed an in situ calibration of the relative responsivity function of the Long-Wavelength Extreme Ultraviolet Spectrometer (LoWEUS), while operating on the Lithium Tokamak Experiment (LTX) at Princeton Plasma Physics Laboratory. The calibration was accomplished by measuring oxygen lines, which are typically present in LTX plasmas. The measured spectral line intensities of each oxygen charge state were then compared to the calculated emission strengths given in the CHIANTI atomic database. Normalizing the strongest line in each charge state to the CHIANTI predictions, we obtained the differences between the measured and predicted values for the relative strengths of the other lines of a given charge state. We find that a 3rd degree polynomial function provides a good fit to the data points. Our measurements show that the responsivity between about 120 and 300 Å varies by factor of ˜30.

  11. Responsivity calibration of the LoWEUS spectrometer

    DOE PAGES

    Lepson, J. K.; Beiersdorfer, P.; Kaita, R.; ...

    2016-09-02

    We performed an in situ calibration of the relative responsivity function of the Long-Wavelength Extreme Ultraviolet Spectrometer (LoWEUS), while operating on the Lithium Tokamak Experiment (LTX) at Princeton Plasma Physics Laboratory. The calibration was accomplished by measuring oxygen lines, which are typically present in LTX plasmas. The measured spectral line intensities of each oxygen charge state were then compared to the calculated emission strengths given in the CHIANTI atomic database. Normalizing the strongest line in each charge state to the CHIANTI predictions, we obtained the differences between the measured and predicted values for the relative strengths of the other linesmore » of a given charge state. We find that a 3rd degree polynomial function provides a good fit to the data points. Lastly, our measurements show that the responsivity between about 120 and 300 Å varies by factor of ~30.« less

  12. Responsivity calibration of the LoWEUS spectrometer

    SciTech Connect

    Lepson, J. K.; Beiersdorfer, P.; Kaita, R.; Majeski, R.; Boyle, D.

    2016-09-02

    We performed an in situ calibration of the relative responsivity function of the Long-Wavelength Extreme Ultraviolet Spectrometer (LoWEUS), while operating on the Lithium Tokamak Experiment (LTX) at Princeton Plasma Physics Laboratory. The calibration was accomplished by measuring oxygen lines, which are typically present in LTX plasmas. The measured spectral line intensities of each oxygen charge state were then compared to the calculated emission strengths given in the CHIANTI atomic database. Normalizing the strongest line in each charge state to the CHIANTI predictions, we obtained the differences between the measured and predicted values for the relative strengths of the other lines of a given charge state. We find that a 3rd degree polynomial function provides a good fit to the data points. Lastly, our measurements show that the responsivity between about 120 and 300 Å varies by factor of ~30.

  13. Object-based attention and visual area LO.

    PubMed

    de-Wit, Lee H; Kentridge, Robert W; Milner, A David

    2009-05-01

    We investigated the neural basis of so-called "object-based attention" by examining patient D.F., who has visual form agnosia caused by bilateral damage to the lateral occipital (LO) area of the ventral visual stream. We tested D.F.'s object-based attention in two ways. In the first experiment, we used a spatial cueing procedure to compare the costs associated with shifting attention within versus between two separate outline figures. D.F. did not show the normal advantage of within-object over between-object attention shifts. In the second experiment, we used a complementary paradigm in which two separate stimuli, presented either on the same or on different objects, have to be identified as the same or different, We found no evidence for the normal pattern of superior performance for within versus between figure comparisons. In a third experiment, we checked that D.F. showed normal shift costs for invalid as opposed to valid cueing in a standard Posner spatial attention task. In a final experiment, we compared horizontal versus vertical attention shifting in group of healthy controls without the presence of outline rectangles, and found that their pattern of shift costs was indistinguishable from that seen in D.F. when the rectangles were present (Experiment 1). We conclude that whilst D.F. has a normal spatial orienting system this is completely uninfluenced by object structure. We suggest that area LO may mediate form processing precisely at the stage where visual representations normally influence the spread of attention.

  14. MaTeLo: Automated Testing Suite for Software Validation

    NASA Astrophysics Data System (ADS)

    Guiotto, A.; Acquaroli, B.; Martelli, A.

    It is universally known that testing has a predominant role when developing software: more and more efforts are spent on testing to detect programming faults, to evaluate the code reliability or performance, to ensure that a critical function of a system meets given requirements. The ratio of time spent on testing should not be neglected and this explains why there is a real need to improve the development process, especially as systems are becoming larger and larger. It is necessary to keep under control the schedule and budget of developments, and controlling the testing phase is a real issue, often underestimated in many industrial sectors. The industry is heightened at different stages regarding testing, and the MaTeLo project is committed to promote the use of statistical tools &methods to answer European industry's needs: • have the ability to choose relevant test cases instead of a human- biased selection • know when to stop testing (definition of a stopping criteria) instead of a vague and informal criteria • adopt an identical strategy for different developments • automate the testing process, and thus to make testing not human error prone MaTeLo (Markov Test Logic) study is a study currently under development in the frame of the IST program of the European Community. The aim of the project is to define, implement and validate a new approach for supporting the software testing activities in various industrial fields. One of the major goals is in particular to provide the software teams with a new tool able to automatically produce and execute the Test Cases starting from the software specifications. Further, the tool is conceived to provide metrics that could help technical staff to determine software quality and to evaluate how much expected results are met. The tool is based on Markov chains theory and belongs to statistical testing software tools family [Runeson] [Whittaker].

  15. Controlled growth of vertically aligned MoO{sub 3} nanoflakes by plasma assisted paste sublimation process

    SciTech Connect

    Sharma, Rabindar K.; Reddy, G. B.

    2013-11-14

    In this work, we have successfully developed plasma assisted paste sublimation route to deposit vertically aligned MoO{sub 3} nanoflakes (NFs) on nickel coated glass substrate in oxygen plasma ambience with the assistant of Ni thin layer as a catalyst. In our case, sublimation source (Mo strip surface) is resistively heated by flowing current across it. The structural, morphological, and optical properties of NFs have been investigated systematically using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), High resolution transmission electron microscopy (HRTEM), micro-Raman spectroscopy, and Photoluminescence (PL) spectroscopy. Studies reveal that the presence of oxygen plasma and the nickel thin layer are very essential for the growth of vertically aligned NFs. The observed results divulge that α-MoO{sub 3} NFs are deposited uniformly on large scale with very high aspect (height/thickness) ratio more than 30 and well aligned along [0 k 0] crystallographic direction where k is even (2, 4, 6). Raman spectrum shows a significant size effect on the vibrational property of MoO{sub 3} nanoflakes. The PL spectrum of MoO{sub 3} NFs was recorded at room temperature and four prominent peaks at 365 nm, 395 nm, 452 nm, and 465 nm corresponding to UV-visible region were observed. In this paper, a three step growth strategy for the formation of MoO{sub 3} NFs has been proposed in detail.

  16. Vacuum chamber with distributed titanium sublimation pumping for the G-line wiggler at Cornell High Energy Synchrotron Source

    NASA Astrophysics Data System (ADS)

    Li, Y.; He, Y.; Mistry, N. B.

    2003-07-01

    This article describes a 3-m-long vacuum chamber for the new wiggler magnet at the Cornell Electron Storage Ring (CESR) for the synchrotron light beam line of the Cornell High Energy Synchrotron Source (CHESS). Copper was chosen as the main chamber material for its good electric and thermal conductivities. Proper mechanical design and welding procedure were implemented to meet very tight tolerances to ensure adequate vertical aperture for the stored beams in CESR while allowing the required small wiggler gap. Distributed titanium sublimation pumping is incorporated along the 3 m length of the chamber to provide sufficient pumping speed and capacity for CESR and CHESS operations. The chamber pumping performance was evaluated prior to installation. Linear distributed pumping speeds at the beam line of ~720 l/s/m for N2 and CO and ~4000 l/s/m for H2 were measured. The measured pumping capacities for N2, CO and H2 are ~1.0, ~2.0 and ~77 Torr l, respectively, for each titanium sublimation cycle. Measurements also showed that CO molecules adsorb on the N2 and H2 saturated titanium films with virtually the same initial sticking coefficient as on a fresh titanium film. Analyses indicated very different CO adsorption mechanisms between the N2 and H2 saturated titanium films. While the replacement of surface H2 by CO was observed, little desorption of nitrogen was measured. Operational experience showed excellent vacuum pumping performance over two years after the chamber installation.

  17. Enthalpy of sublimation in the study of the solid state of organic compounds. Application to erythritol and threitol.

    PubMed

    Lopes Jesus, A J; Tomé, Luciana I N; Eusébio, M Ermelinda; Redinha, J S

    2005-09-29

    The enthalpies of sublimation of erythritol and L-threitol have been determined at 298.15 K by calorimetry. The values obtained for the two diastereomers differ from one another by 17 kJ mol(-1). An interpretation of these results is based on the decomposition of this thermodynamic property in a term coming from the intermolecular interactions of the molecules in the crystal (delta(int)H degrees) and another one related with the conformational change of the molecules on going from the crystal lattice to the most stable forms in the gas phase (delta(conf)H degrees). This last term was calculated from the values of the enthalpy of the molecules in the gas state and of the enthalpy of the isolated molecules with the crystal conformation. Both quantities were obtained by density functional theory (DFT) calculations at the B3LYP/6-311G++(d,p) level of theory. The results obtained in this study show that the most important contribution to the differences observed in the enthalpy of sublimation are the differences in the enthalpy of conformational change (13 kJ mol(-1)) rather than different intermolecular forces exhibited in the solid phase. This is explained by the lower enthalpy of threitol in the gas phase relative to erythritol, which is attributed to the higher strength of the intramolecular hydrogen bonds in the former. The comparison of the calculated infrared spectra obtained for the two compounds in the gas phase supports this interpretation.

  18. Redetermination of the crystal structure of boron subphthalocyanine chloride (Cl-BsubPc) enabled by slow train sublimation.

    PubMed

    Virdo, Jessica D; Lough, Alan J; Bender, Timothy P

    2016-04-01

    The crystal structure of boron subphthalocyanine chloride [systematic name: chlorido(subphthalocyaninato)boron], C24H12BClN6, a material of widespread interest in organic electronic device applications, has been redetermined with a higher precision using large single crystals obtained via slow train sublimation. Details are given for the construction and operation of the train sublimation system, which has been designed to reproducibly yield single crystals suitable for diffraction experiments in a manner which approximates the vacuum deposition conditions commonly used to fabricate organic electronic devices. Diffraction experiments were conducted using two crystal samples and four temperatures (90, 123, 147 and 295 K), enabling a discussion of changes in the unit cell and intermolecular interactions with respect to temperature and in comparison to two previously published structures of Cl-BsubPc. The redetermined structure confirms the original structure published 41 years ago [Meller & Ossko (1972). Monatsh. Chem. 103, 150-155], with significantly improved precision for the geometric parameters. Analysis of the crystal structure revealed three intersecting ribbon motifs formed through a combination of π-π and halogen-π (specifically B-Cl...π) interactions. H atoms were refined independently in order to facilitate a thorough discussion of these intermolecular interactions using Hirshfeld surface analysis.

  19. Computational prediction of standard gas, liquid, and solid-phase heats of formation and heats of vaporization and sublimation

    NASA Astrophysics Data System (ADS)

    Politzer, Peter; Ma, Yuguang; Lane, Pat; Concha, Monica C.

    We present a B3PW91/6-31G** computational procedure for predicting standard gas phase heats of formation at 298.15 K by finding ΔH for the process whereby the molecule is produced from its elements and then adding empirical atomic correction terms. Heats of vaporization and sublimation are estimated on the basis of the calculated electrostatic potential on the molecular surface. These results permit prediction of the standard liquid and solid-phase heats of formation. In comparison with experimental data, the average absolute deviations are as follows: for the heats of formation, gas phase, 2.6 kcal/mol; liquid phase, 2.4 kcal/mol; solid phase, 3.8 kcal/mol; for the heats of vaporization, 2.0 kcal/mol; and for the heats of sublimation, 2.8 kcal/mol. Computed values of these properties are given for a number of compounds for which they are not available experimentally.

  20. A centre-triggered magnesium fuelled cathodic arc thruster uses sublimation to deliver a record high specific impulse

    NASA Astrophysics Data System (ADS)

    Neumann, Patrick R. C.; Bilek, Marcela; McKenzie, David R.

    2016-08-01

    The cathodic arc is a high current, low voltage discharge that operates in vacuum and provides a stream of highly ionised plasma from a solid conducting cathode. The high ion velocities, together with the high ionisation fraction and the quasineutrality of the exhaust stream, make the cathodic arc an attractive plasma source for spacecraft propulsion applications. The specific impulse of the cathodic arc thruster is substantially increased when the emission of neutral species is reduced. Here, we demonstrate a reduction of neutral emission by exploiting sublimation in cathode spots and enhanced ionisation of the plasma in short, high-current pulses. This, combined with the enhanced directionality due to the efficient erosion profiles created by centre-triggering, substantially increases the specific impulse. We present experimentally measured specific impulses and jet power efficiencies for titanium and magnesium fuels. Our Mg fuelled source provides the highest reported specific impulse for a gridless ion thruster and is competitive with all flight rated ion thrusters. We present a model based on cathode sublimation and melting at the cathodic arc spot explaining the outstanding performance of the Mg fuelled source. A further significant advantage of an Mg-fuelled thruster is the abundance of Mg in asteroidal material and in space junk, providing an opportunity for utilising these resources in space.

  1. An enhanced model of the contemporary and long-term (200 ka) sublimation of the massive subsurface ice in Beacon Valley, Antarctica

    NASA Astrophysics Data System (ADS)

    Liu, Lu; Sletten, Ronald S.; Hagedorn, Birgit; Hallet, Bernard; McKay, Christopher P.; Stone, John O.

    2015-08-01

    A massive ice body buried under several decimeters of dry regolith in Beacon Valley, Antarctica, is believed to be more than 1 Ma old and perhaps over 8.1 Ma; however, vapor diffusion models suggest that subsurface ice in this region is not stable under current climate conditions. To better understand the controls on sublimation rates and stability of this massive ice, we have modeled vapor diffusion using 12 years of climate and soil temperature data from 1999 to 2011, including field measurements of episodic snow cover and snowmelt events that have not been represented in previous models of ground ice sublimation. The model is then extended to reconstruct the sublimation history over the last 200 ka using paleotemperatures estimated from ice core data from nearby Taylor Dome and a relationship between atmospheric temperature and humidity derived from our meteorological records. The model quantifies the impact of episodic snow events; they account for a nearly 30% reduction in the massive ice loss. The sublimation rate of ground ice averages 0.11 mm a-1 between 1999 and 2011 in Beacon Valley. Parameterized with past environmental conditions and assuming the same regolith thickness, the modeled sublimation rate of ground ice in Beacon Valley averages 0.09 mm a-1 for the last 200 ka, comparable to the long-term average rate estimated independently from various studies based on cosmogenic isotopes. This study provides a realistic estimate of the long-term sublimation history and supports the inference that the buried ice in Beacon Valley is older than 1 Ma.

  2. The not-so-sublime early Earth recorded in Hadean zircons

    NASA Astrophysics Data System (ADS)

    Cavosie, A. J.

    2011-12-01

    oxygen isotope ratios (up to 7.5 %) are evidence that the early formed crust was evolved (granitic), rather than primitive (gabbroic). (4) Variable oxygen and Li isotope ratios in zircon record processes of surface alteration and subsequent magmatic recycling of altered crust, constraining the appearance of low surface temperatures and liquid water oceans by 4.3 to 4.2 Ga. (5) Evidence for the Late Heavy Bombardment has not been identified in Hadean zircons; planar microstructures known to form in shock metamorphosed zircon have not been found in Hadean grains. (6) Other claims, including reports of modern-style plate interactions based on zircon mineral inclusion barometry, and the presence of diamond inclusions in Hadean zircons, remain controversial, and open to interpretation. Many aspects of the Hadean are therefore similar to the Archean; distinguishing the two eons thus remains a challenge. However, the cooling and condensation of liquid surface water and its subsequent effect on magma chemistry, as recorded in Hadean zircons from 4.3 to 4.2 Ga, suggests a global-scale process that created habitats for life, and clearly marked the end of 'hell-like' Hadean surface conditions. As the timescale and processes active on the early Earth become better quantified through careful documentation and measurement of these ancient zircons, the Hadean becomes somewhat less sublime.

  3. Investigations in Martian geology. Part 1: Nature of the mantling deposit in the heavily cratered terrain of northeastern Arabia, Mars. Part 2: Experimental studies of clean and dust-or-sand-covered ice sublimation under Mars-like conditions

    SciTech Connect

    Moore, J.M.

    1990-01-01

    This dissertation consists of two parts. Part 1 describes the geomorphology of a portion of northeastern Arabia, Mars. This surface is covered by an extensive, layered deposit which has been, in places, substantially eroded. Speculative origins for the deposit include formation as a differentially welded pyroclastic tuff, or a differentially compacted, zonally indurated aeolian dust deposit. Part 2 is an experimental study of the sublimation rate of H{sub 2}O ice, both from clean surfaces and from under thin layers of dust or sand, in a Mars-like environment. The major conclusions drawn from the results of this experiment are: (1) even very thin layers of dust greatly lower the sublimation rate of an underlying ice substrate being heated from above, whereas thin layers of sand suppress the sublimation rate of underlying ice being heated from above to a significantly lesser extent; (2) thin layers of dust or sand only mildly suppress the sublimation rate of an underlying ice substrate when sample is wholly isothermal; (3) even a low-flux, desiccated gas flow over the sample surface significantly increases the sublimation rate of any given sample; (4) dry sublimation of ice underlying thin layers of dust or sand may modify the surface texture as a function of particle cohesion and as the ratio of particle layer thickness to the amount by which the surface was lowered; and (5) the actual sublimation rate of clean ice is several factors lower than the sublimation rate predicted by a commonly used formula.

  4. Pan-Observation Results on Snow Sublimation and its Parameterization in Both forested and Open Environment in Taiga of Eastern Siberia

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Suzuki, K.; Kubota, J.; Kadota, T.; Ohata, T.

    2002-12-01

    In the sub-arctic region of Siberia, like the Lena and Bikal basins, the snow cover is a dominant hydrological component to affect the river discharge and regional water resource. Sublimation from snow surface, which can sustained about seven months (later October to earlier May), has been identified as important hydrological process in high altitude and latitude region, which, as result of particularly complex mass and energy exchanges, remain incompletely, understood, though there has been recent progress in process studies. A survey of snow sublimation values from North American and Russian mass balance studies (Mcnay et al., 1988; Barry, 1991;) suggests that in boreal, montane and subalpine forests 25-45 % of the annual snowfall can sublimate from snow (Pomeroy and Gray, 1995). This range has been confirmed for other snowy environments such as maritime Japan (Nakai et al., 1993). From March to May of 2002, intensive observations on snow sublimation using pan method and meteorological condition of near ground surface atmosphere were made in Mogot experimental watershed, which is located in the southern mountain region of eastern Siberia (55.5°N, 124.7°E) approximately 60 km north of Tynda, in the Amur region, Russia. The land surface is predominantly covered by larch forest, but birch forest partly covers the ridge area and higher elevations are covered by pine forest. The observations, including the snow and meteorological elements, were conducted at three sites with different vegetation cover and surface condition: A sparse larch forest covers Site LF; Site OP is grassland and Site ES contains a sparse larch forest of east slope. The transparent plastic pan used for sublimation measurement was in diameter of 22 cm and depth of 20 cm. A natural snow bulk of the same size and shape as the pan was set at the 1 cm higher level than surrounding snow surface. The snow bulk in the pan was renewed according its temperature difference with surrounding snow. But it

  5. A Continuous Flow Diffusion Chamber Study of Sea Salt Particles Acting as Cloud Seeds: Deliquescence, Ice Nucleation and Sublimation

    NASA Astrophysics Data System (ADS)

    Kong, X.; Wolf, M. J.; Garimella, S.; Roesch, M.; Cziczo, D. J.

    2016-12-01

    Sea Salt Aerosols (SSA) are abundant in the atmosphere, and important to the Earth's chemistry and energy budget. However, the roles of sea salts in the context of cloud formation are still poorly understood, which is partially due to the complexity of the water-salt phase diagram. At ambient temperatures, even well below 0°C, SSA deliquesces at sub-water saturated conditions. Since the ratio of the partial pressure over ice versus super-cooled water continuously declines with decreasing temperatures, it is interesting to consider if SSA continues to deliquesce under a super-saturated condition of ice, or if particles act as depositional ice nuclei when a critical supersaturation is reached. Some recent studies suggest hydrated NaCl and simulated sea salt might deliquesce between -35°C to -44°C, and below that deposition freezing becomes possible. Deliquesced droplets can subsequently freeze via the immersion or homogenous freezing mode, depending on if the deliquescence processes is complete. After the droplets or ice particles are formed, it is also interesting to consider how the different processes influence physical properties after evaporation or sublimation. This data is important for climate modeling that includes bromine burst observed in Antarctica, which is hypothesized to be relevant to the sublimation of blowing snow particles. In this study we use a SPectrometer for Ice Nuclei (SPIN; DMT, Inc., Boulder, CO) to perform experiments over a wide range of temperature and RH conditions to quantify deliquescence, droplet formation and ice nucleation. The formation of droplets and ice particles is detected by an advanced Optical Particle Counter (OPC) and the liquid/solid phases are distinguished by a machine learning method based on laser scattering and polarization data. Using an atomizer, four different sea salt samples are generated: pure NaCl and MgCl2 solutions, synthetic seawater, and natural seawater. Downstream of the SPIN chamber, a Pumped

  6. Origin, Evolution, and Preservation of Cold Based Debris Covered Glaciers: Quantifying Sublimation Rates of Ancient Buried Ice in Antarctica

    NASA Astrophysics Data System (ADS)

    Kowalewski, D. E.; Marchant, D. R.

    2007-12-01

    Growing interest in our planet's climate history has placed a premium on acquiring detailed records of past climate change. Of considerable interest are archives of ancient atmosphere trapped within the debris-covered alpine glaciers of the western Dry Valleys region of Antarctica. The Mullins Valley debris-covered glacier (~8 km in length) is sourced from local snowfall at the steep headwall of the valley. The first 1.2 km of this glacier is generally free of overlying debris except for isolated cobbles and boulders. Thereafter, the ice surface is covered with a thin, continuous sheet of dolerite-rich rubble. Factors that influence the origin and modification of this ice include atmospheric temperature and relative humidity, precipitation, incoming solar radiance, surface albedo, till texture, winds, surface roughness, salts, and secondary ice lenses. We applied a diffusion model to track vapor flux within a sublimation till overlying the Mullins Valley debris-covered glacier, purportedly the world's oldest debris-covered alpine glacier. As input, we used meteorological data from HOBO data loggers that captured climate change and till temperatures. Results show that vapor flows into and out of the sublimation till at rates dependent on the non-linear variation of soil temperature with depth. Sublimation rates along the Mullins Glacier varied as a function of till thickness, local climate (using a calculated regional lapse rate of 0.88°C per 100 m), and till texture. Ice loss during the study interval (November 27, 2006 to December 24, 2006) ranged from as high as 2.12 mm for exposed glacier ice in the upper ablation zone, to as low as 0.01 mm for buried ice beneath till >50 cm in thickness. Averaged over the entire ablation zone (6.7 km2), this yields a net ice-surface lowering of 0.32 mm during the study interval. Numerical modeling suggests that a modest ice accumulation rate at the headwall of ~1 cm a-1 appears sufficient to maintain current ice volumes

  7. Material composition assessment and discovering sublimation activity on asteroids 145 Adeona, 704 Interamnia, 779 Nina, and 1474 Beira

    NASA Astrophysics Data System (ADS)

    Busarev, V. V.; Barabanov, S. I.; Puzin, V. B.

    2016-07-01

    Spectrophotometric observations of 145 Adeona, 704 Interamnia, 779 Nina, and 1474 Beira—asteroids of close primitive types—allowed us to detect similar mineralogical absorption bands in their reflectance spectra centered in the range 0.35 to 0.92 μm; the bands are at 0.38, 0.44, and 0.67-0.71 μm. On the same asteroids, the spectral signs of simultaneous sublimation activity were found for the first time. Namely, there are maxima at ˜0.35-0.60 μm in the reflectance spectra of Adeona, Interamnia, and Nina and at ˜0.55-075 μm in the spectra of Beira. We connect this activity with small heliocentric distances of the asteroids and, consequently, with a high insolation at their surfaces. Examination of the samples of probable analogues allowed us to identify Fe3+ and Fe2+ in the material of these asteroids through the mentioned absorption bands. For analogues, we took powdered samples of carbonaceous chondrites Orgueil (CI), Mighei (CM2), Murchison (CM2), and Boriskino (CM2), as well as hydrosilicates of the serpentine group. Laboratory spectral reflectance study of the samples of low-iron Mg serpentines (<2 wt % FeO) showed that the equivalent width of the absorption band centered at 0.44-0.46 μm strongly correlates with the content of Fe3+ in octahedral and tetrahedral coordinations. Our conclusion is that this absorption band can be used as a qualitative indicator of Fe3+ in the surface matter of asteroids and other solid celestial bodies. The comparison of the listed analog samples and the asteroids by parameters of the spectral features suggests that the silicate component of the asteroids' surface material is a mixture of hydrated and oxidized compounds, including oxides and hydroxides of bivalent and trivalent iron and carbonaceous-chondritic material. At the same time, the sublimation activity of Adeona, Interamnia, Nina, and Beira at high surface temperatures points to a substantial content of water ice in their material. This contradicts the

  8. The Role of Sublimation and Condensation in the Dynamics of Aeolian Ice Sedimentation Waves on the North Polar Cap of Mars

    NASA Astrophysics Data System (ADS)

    Herny, C.; Carpy, S.; Bourgeois, O.; Spiga, A.; Rodriguez, S.; Massé, M.; Le Mouélic, S.

    2016-09-01

    We explore the role of sublimation and condensation of water vapor in the development of ice sedimentation waves on the North Polar Cap of Mars. Our observations and simulations are in accordance with the hypothesis that sedimentation waves can migrate upwind or downwind.

  9. Measuring enthalpy of sublimation of volatiles by means of micro-thermogravimetry for the study of water and organic in planetary environments

    NASA Astrophysics Data System (ADS)

    Dirri, F.; Palomba, E.; Longobardo, A.; Zampetti, E.; Biondi, D.; Boccaccini, A.; Pantalei, S.; Zinzi, A.

    In this work, we present a new experimental set up to infer the enthalpy of sublimation for a known specie of dicarboxylic acid, i.e. adipic acid. This type of acids, with various concentrations are present in different environments (e.g. marine, rural, urban). The experiment is performed in the framework of the VISTA (Volatile In Situ Thermogravimetry Analyser) project, an instrument currently under study for the ESA Cosmic Vision proposed mission MarcoPolo-R. The enthalpy of sublimation of adipic acid was measured by means of micro-thermogravimetric analysis (mu -TGA), a widely used technique to investigate condensation/sublimation and absorption/desorption processes of volatile compounds. The measurements were performed with a 10 MHz temperature controlled piezoelectric crystal microbalance (PCM), placed in a vacuum chamber (10-6 mbar). The obtained enthalpy of sublimation is (123±16) kJ× mol-1, a value in good agreement with literature within 10%. This result (connected to the deposition rate curve, from 30 o to 75 oC), demonstrates the capability of our device to perform this kind of measurements.

  10. On the sublimation of ice particles on the surface of Mars; with applications to the 2007/8 Phoenix Scout mission

    NASA Astrophysics Data System (ADS)

    Taylor, Peter A.; Baibakov, Konstantin; Brown, Stephen; Hecht, Michael H.; Hudson, Troy L.; Li, P.-Y.; Lange, Carlos F.; Prieto, Luis; Savelyev, Sergiy

    2006-04-01

    Experimental studies related to the sublimation of ice, in bulk or as small particles, alone or mixed with dust similar to that expected on the surface of Mars, are reported. The experiments, a cloud physics particle sublimation model, and a convection model presented by Ingersoll, all indicate a strong dependence of sublimation rate on temperature, and this appears to be the dominant factor, assuming that the relative humidity of the air is fairly low. In addition the rate of loss of water vapour appears to depend primarily on exposed surface area and less on particle size and the total mass of the sample, or the mass of ice in the sample. The 2007/8 Phoenix Scout mission plans to obtain and analyse samples of sub-surface ice from about 70° N on Mars. A concern is that these samples, in the form of ice chips of size about 1 mm diameter, could be prone to sublimation when exposed for prolonged periods (many hours) to a relatively warm and dry atmosphere. Our laboratory simulations confirm that this could be a problem if particles are simply left lying on the surface, but also indicate that samples kept suitably cold and collected together in confined piles will survive long enough for the collection and delivery (to the analysis instruments) procedure to be completed.

  11. 2D imaging of laser wing effects and of soot sublimation in laser-induced incandescence measurements

    NASA Astrophysics Data System (ADS)

    Delhay, J.; Bouvier, Y.; Therssen, E.; Black, J. D.; Desgroux, P.

    2005-07-01

    The distribution of Laser-Induced Incandescence (LII) signal in sooting flames along the laser beam is imaged using two directions of observation: one counter to the propagation direction of the incident laser (backward LII) and one at right angles. It is shown that the effective probe volume, in which the LII signal is observed, is highly dependent on the laser irradiance profile. At high fluence, the LII from the central part of the beam decreases because of soot sublimation. This decrease can be compensated by an increase in the LII from the wings of the laser beam. This interaction is particularly important in the extraction of quantitative information in the backward LII case, which is the configuration best suited to the practical application of LII for in-situ particle concentration measurements in the exhaust of aero-engines.

  12. Volatilization, transport and sublimation of metallic and non-metallic elements in high temperature gases at Merapi Volcano, Indonesia

    USGS Publications Warehouse

    Symonds, R.B.; Rose, William I.; Reed, M.H.; Lichte, F.E.; Finnegan, David L.

    1987-01-01

    Condensates, silica tube sublimates and incrustations were sampled from 500-800??C fumaroles and lava samples were collected at Merapi Volcano, Indonesia in Jan.-Feb., 1984. With respect to the magma, Merapi gases are enriched by factors greater than 105 in Se, Re, Bi and Cd; 104-105 in Au, Br, In, Pb and W; 103-104 in Mo, Cl, Cs, S, Sn and Ag; 102-103 in As, Zn, F and Rb; and 1-102 in Cu, K, Na, Sb, Ni, Ga, V, Fe, Mn and Li. The fumaroles are transporting more than 106 grams/day ( g d) of S, Cl and F; 104-106 g/d of Al, Br, Zn, Fe, K and Mg; 103-104 g d of Pb, As, Mo, Mn, V, W and Sr; and less than 103 g d of Ni, Cu, Cr, Ga, Sb, Bi, Cd, Li, Co and U. With decreasing temperature (800-500??C) there were five sublimate zones found in silica tubes: 1) cristobalite and magnetite (first deposition of Si, Fe and Al); 2) K-Ca sulfate, acmite, halite, sylvite and pyrite (maximum deposition of Cl, Na, K, Si, S, Fe, Mo, Br, Al, Rb, Cs, Mn, W, P, Ca, Re, Ag, Au and Co); 3) aphthitalite (K-Na sulfate), sphalerite, galena and Cs-K. sulfate (maximum deposition of Zn, Bi, Cd, Se and In; higher deposition of Pb and Sn); 4) Pb-K chloride and Na-K-Fe sulfate (maximum deposition of Pb, Sn and Cu); and 5) Zn, Cu and K-Pb sulfates (maximum deposition of Pb, Sn, Ti, As and Sb). The incrustations surrounding the fumaroles are also chemically zoned. Bi, Cd, Pb, W, Mo, Zn, Cu, K, Na, V, Fe and Mn are concentrated most in or very close to the vent as expected with cooling, atmospheric contamination and dispersion. The highly volatile elements Br, Cl, As and Sb are transported primarily away from high temperature vents. Ba, Si, P, Al, Ca and Cr are derived from wall rock reactions. Incomplete degassing of shallow magma at 915??C is the origin of most of the elements in the Merapi volcanic gas, although it is partly contaminated by particles or wall rock reactions. The metals are transported predominantly as chloride species. As the gas cools in the fumarolic environment, it becomes saturated

  13. Numerical simulation of temperature fields during the sublimation growth of SiC single crystals, using WIAS-HiTNIHS

    NASA Astrophysics Data System (ADS)

    Geiser, Jürgen; Klein, Olaf; Philip, Peter

    2007-05-01

    We present numerical computations of the temperature fields in axisymmetric growth apparatus for sublimation growth of silicon carbide (SiC) bulk single crystals by physical vapor transport (PVT) (modified Lely method). The results are computed using our software WIAS-HiTNIHS, the WIAS High Temperature Numerical Induction Heating Simulator; pronunciation: ˜hit-nice, by solving the energy balance in the entire growth apparatus, taking into account the heat conduction in the solid parts as well as in gas cavities, and also accounting for the radiative heat transfer between the surfaces of the gas cavities. The insulation in a PVT growth apparatus usually consists of graphite felt, where the fibers are aligned in one particular direction, resulting in an anisotropic thermal conductivity. We show that neglecting this anisotropy can overestimate the SiC crystal's temperature by 70 K or underestimate the required heating power by 800 W.

  14. Method of fabricating conducting oxide-silicon solar cells utilizing electron beam sublimation and deposition of the oxide

    DOEpatents

    Feng, Tom; Ghosh, Amal K.

    1979-01-01

    In preparing tin oxide and indium tin oxide-silicon heterojunction solar cells by electron beam sublimation of the oxide and subsequent deposition thereof on the silicon, the engineering efficiency of the resultant cell is enhanced by depositing the oxide at a predetermined favorable angle of incidence. Typically the angle of incidence is between 40.degree. and 70.degree. and preferably between 55.degree. and 65.degree. when the oxide is tin oxide and between 40.degree. and 70.degree. when the oxide deposited is indium tin oxide. gi The Government of the United States of America has rights in this invention pursuant to Department of Energy Contract No. EY-76-C-03-1283.

  15. Volatilization, transport and sublimation of metallic and non-metallic elements in high temperature gases at Merapi Volcano, Indonesia

    NASA Astrophysics Data System (ADS)

    Symonds, Robert B.; Rose, William I.; Reed, Mark H.; Lichte, Frederick E.; Finnegan, David L.

    1987-08-01

    Condensates, silica tube sublimates and incrustations were sampled from 500-800°C fumaroles and lava samples were collected at Merapi Volcano, Indonesia in Jan.-Feb., 1984. With respect to the magma, Merapi gases are enriched by factors greater than 10 5 in Se, Re, Bi and Cd; 10 4-10 5 in Au, Br, In, Pb and W; 10 3-10 4 in Mo, Cl, Cs, S, Sn and Ag; 10 2-10 3 in As, Zn, F and Rb; and 1-10 2 in Cu, K, Na, Sb, Ni, Ga, V, Fe, Mn and Li. The fumaroles are transporting more than 10 6 grams/day ( g/d) of S, Cl and F; 10 4-10 6 g/d of Al, Br, Zn, Fe, K and Mg; 10 3-10 4g/d of Pb, As, Mo, Mn, V, W and Sr; and less than 10 3g/d of Ni, Cu, Cr, Ga, Sb, Bi, Cd, Li, Co and U. With decreasing temperature (800-500°C) there were five sublimate zones found in silica tubes: 1) cristobalite and magnetite (first deposition of Si, Fe and Al); 2) K-Ca sulfate, acmite, halite, sylvite and pyrite (maximum deposition of Cl, Na, K, Si, S, Fe, Mo, Br, Al, Rb, Cs, Mn, W, P, Ca, Re, Ag, Au and Co); 3) aphthitalite (K-Na sulfate), sphalerite, galena and Cs-K. sulfate (maximum deposition of Zn, Bi, Cd, Se and In; higher deposition of Pb and Sn); 4) Pb-K chloride and Na-K-Fe sulfate (maximum deposition of Pb, Sn and Cu); and 5) Zn, Cu and K-Pb sulfates (maximum deposition of Pb, Sn, Ti, As and Sb). The incrustations surrounding the fumaroles are also chemically zoned. Bi, Cd, Pb, W, Mo, Zn, Cu, K, Na, V, Fe and Mn are concentrated most in or very close to the vent as expected with cooling, atmospheric contamination and dispersion. The highly volatile elements Br, Cl, As and Sb are transported primarily away from high temperature vents. Ba, Si, P, Al, Ca and Cr are derived from wall rock reactions. Incomplete degassing of shallow magma at 915°C is the origin of most of the elements in the Merapi volcanic gas, although it is partly contaminated by particles or wall rock reactions. The metals are transported predominantly as chloride species. As the gas cools in the fumarolic environment, it

  16. Influences of CO2 sublimation/condensation processes on the long-term evolution of the Martian atmosphere

    NASA Technical Reports Server (NTRS)

    Kossacki, K.; Leliwa-Kopystynski, J.

    1992-01-01

    The accumulation process of frozen CO2 within the Martian regolith is analyzed. The boundary conditions are taken to be the periodically variable temperature at the Mars surface and the constant heat flux at the bottom of the regolith layers, some hundred meters thick. The mean value of temperature as well as its amplitude are assumed to be dependent on latitude and could be variable with the geological time scale. The flux of gaseous CO2 within the regolith is controlled by the mechanism of gas transport through the porous medium. An appropriate initial geometry of distribution of pores is assumed. The porosity and flux change due to condensation/sublimation processes. The equations of heat and mass transfer are solved numerically for a given latitude. Next, the local (over the parallel of latitude belt) annual balance of CO2 is calculated. The procedure is repeated over the whole Martian surface and next the total annual net flux is calculated.

  17. The role of oxygen in CdS/CdTe solar cells deposited by close-spaced sublimation

    SciTech Connect

    Rose, D.H.; Levi, D.H.; Matson, R.J.

    1996-05-01

    The presence of oxygen during close-spaced sublimation (CSS) of CdTe has been previously reported to be essential for high-efficiency CdS/CdTe solar cells because it increases the acceptor density in the absorber. The authors find that the presence of oxygen during CSS increases the nucleation site density of CdTe, thus decreasing pinhole density and grain size. Photoluminescence showed that oxygen decreases material quality in the bulk of the CdTe film, but positively impacts the critical CdS/CdTe interface. Through device characterization the authors were unable to verify an increase in acceptor density with increased oxygen. These results, along with the achievement of high-efficiency cells (13% AM1.5) without the use of oxygen, led the authors to conclude that the use of oxygen during CSS deposition of CdTe can be useful but is not essential.

  18. A macroscale mixture theory analysis of deposition and sublimation rates during heat and mass transfer in dry snow

    NASA Astrophysics Data System (ADS)

    Hansen, A. C.; Foslien, W. E.

    2015-09-01

    The microstructure of a dry alpine snowpack is a dynamic environment where microstructural evolution is driven by seasonal density profiles and weather conditions. Notably, temperature gradients on the order of 10-20 K m-1, or larger, are known to produce a faceted snow microstructure exhibiting little strength. However, while strong temperature gradients are widely accepted as the primary driver for kinetic growth, they do not fully account for the range of experimental observations. An additional factor influencing snow metamorphism is believed to be the rate of mass transfer at the macroscale. We develop a mixture theory capable of predicting macroscale deposition and/or sublimation in a snow cover under temperature gradient conditions. Temperature gradients and mass exchange are tracked over periods ranging from 1 to 10 days. Interesting heat and mass transfer behavior is observed near the ground, near the surface, as well as immediately above and below dense ice crusts. Information about deposition (condensation) and sublimation rates may help explain snow metamorphism phenomena that cannot be accounted for by temperature gradients alone. The macroscale heat and mass transfer analysis requires accurate representations of the effective thermal conductivity and the effective mass diffusion coefficient for snow. We develop analytical models for these parameters based on first principles at the microscale. The expressions derived contain no empirical adjustments, and further, provide self consistent values for effective thermal conductivity and the effective diffusion coefficient for the limiting cases of air and solid ice. The predicted values for these macroscale material parameters are also in excellent agreement with numerical results based on microscale finite element analyses of representative volume elements generated from X-ray tomography.

  19. Sorbent, Sublimation, and Icing Modeling Methods: Experimental Validation and Application to an Integrated MTSA Subassembly Thermal Model

    NASA Technical Reports Server (NTRS)

    Bower, Chad; Padilla, Sebastian; Iacomini, Christie; Paul, Heather L.

    2010-01-01

    This paper details the validation of modeling methods for the three core components of a Metabolic heat regenerated Temperature Swing Adsorption (MTSA) subassembly, developed for use in a Portable Life Support System (PLSS). The first core component in the subassembly is a sorbent bed, used to capture and reject metabolically produced carbon dioxide (CO2). The sorbent bed performance can be augmented with a temperature swing driven by a liquid CO2 (LCO2) sublimation heat exchanger (SHX) for cooling the sorbent bed, and a condensing, icing heat exchanger (CIHX) for warming the sorbent bed. As part of the overall MTSA effort, scaled design validation test articles for each of these three components have been independently tested in laboratory conditions. Previously described modeling methodologies developed for implementation in Thermal Desktop and SINDA/FLUINT are reviewed and updated, their application in test article models outlined, and the results of those model correlations relayed. Assessment of the applicability of each modeling methodology to the challenge of simulating the response of the test articles and their extensibility to a full scale integrated subassembly model is given. The independent verified and validated modeling methods are applied to the development of a MTSA subassembly prototype model and predictions of the subassembly performance are given. These models and modeling methodologies capture simulation of several challenging and novel physical phenomena in the Thermal Desktop and SINDA/FLUINT software suite. Novel methodologies include CO2 adsorption front tracking and associated thermal response in the sorbent bed, heat transfer associated with sublimation of entrained solid CO2 in the SHX, and water mass transfer in the form of ice as low as 210 K in the CIHX.

  20. Pedestal Craters in Utopia Planitia and Malea Planum: Evidence for a Past Ice-Rich Substrate from Marginal Sublimation Pits.

    NASA Astrophysics Data System (ADS)

    Kadish, S. J.; Head, J. W.; Barlow, N. G.; Marchant, D. R.

    2008-09-01

    Introduction: Pedestal craters (Pd) are a subclass of impact craters unique to Mars [1] characterized by a crater perched near the center of a pedestal (mesa or plateau) that is surrounded by a quasi-circular, outward-facing scarp. The marginal scarp is usually several crater diameters from the crater rim (Figs. 2,4,5), and tens to over 100 meters above the surrounding plains (Fig. 2). Pd have been interpreted to form by armoring of the proximal substrate during the impact event. Hypotheses for the armoring mechanism include an ejecta covering [e.g., 3], increased ejecta mobilization caused by volatile substrates [4], distal glassy/melt-rich veneers [5], and/or an atmospheric blast/thermal effect [6]. Subsequently, a marginal scarp forms by preferential erosion of the substrate surrounding the armored region, most commonly thought to involve eolian removal of fine-grained, non-armored material [e.g., 3]. An understanding of the distribution of Pd, which form predominantly poleward of ~40°N and S latitude [7-9] (Fig. 1), and the role of redistribution of ice and dust during periods of climate change [e.g., 10-11], suggests that the substrate might have been volatile-rich [8-9, 12-14]. As such, some researchers [e.g., 8-9] have proposed a model for Pd formation that involves impact during periods of higher obliquity, when mid- to high-latitude substrates were characterized by thick deposits of snow and ice [e.g., 15]. Subsequent sublimation of the volatile units, except below the armored regions, yielded the perched Pd. Thus, this model predicts that thick deposits of snow/ice should underlie Pd. This is in contrast to the eolian model [3], which calls primarily for deflation of sand and dust. Here, we show the results of our study [8,16] that has documented and characterized 2461 Pd on Mars equatorward of ~65° N and S latitude (Fig. 1) in order to test these hypotheses for the origin of pedestal craters. In particular, we report on the detection of 50 Pd in Utopia

  1. Experimental and theoretical simulation of sublimating dusty water ice with implications for D/H ratios of water ice on Comets and Mars

    NASA Astrophysics Data System (ADS)

    Moores, John E.; Brown, Robert H.; Lauretta, Dante S.; Smith, Peter H.

    2012-12-01

    Sublimation experiments have been carried out to determine the effect of the mineral dust content of porous ices on the isotopic composition of the sublimate gas over medium (days to weeks) timescales. Whenever mineral dust of any kind was present, the D/H ratio of the sublimated gas was seen to decrease with time from the bulk ratio. Fractionations of up to 2.5 were observed for dust mixing ratios of 9 wt% and higher of JSC MARS-1 regolith simulant 1-10 μm crushed and sieved fraction. These favored the presence of the light isotope, H2O, in the gas phase. The more dust was added to the mixture, the more pronounced was this effect. Theoretical modeling of gas migration within the porous samples and adsorption on the excavated dust grains was undertaken to explain the results. Adsorption onto the dust grains is able to explain the low D/H ratios in the sublimate gas if adsorption favors retention of HDO over H2O. This leads to significant isotopic enrichment of HDO on the dust over time and depletion in the amount of HDO escaping the system as sublimate gas. This effect is significant for planetary bodies on which water moves mainly through the gas phase and a significant surface reservoir of dust may be found, such as on Comets and Mars. For each of these, inferences about the bulk water D/H ratio as inferred from gas phase measurements needs to be reassessed in light of the volatile cycling history of each body.

  2. Experimental and theoretical simulation of sublimating dusty water ice with implications for D/H ratios of water ice on Comets and Mars

    NASA Astrophysics Data System (ADS)

    Moores, John E.; Brown, Robert H.; Lauretta, Dante S.; Smith, Peter H.

    2012-04-01

    Sublimation experiments have been carried out to determine the effect of the mineral dust content of porous ices on the isotopic composition of the sublimate gas over medium (days to weeks) timescales. Whenever mineral dust of any kind was present, the D/H ratio of the sublimated gas was seen to decrease with time from the bulk ratio. Fractionations of up to 2.5 were observed for dust mixing ratios of 9 wt% and higher of JSC MARS-1 regolith simulant 1-10 μm crushed and sieved fraction. These favored the presence of the light isotope, H2O, in the gas phase. The more dust was added to the mixture, the more pronounced was this effect. Theoretical modeling of gas migration within the porous samples and adsorption on the excavated dust grains was undertaken to explain the results. Adsorption onto the dust grains is able to explain the low D/H ratios in the sublimate gas if adsorption favors retention of HDO over H2O. This leads to significant isotopic enrichment of HDO on the dust over time and depletion in the amount of HDO escaping the system as sublimate gas. This effect is significant for planetary bodies on which water moves mainly through the gas phase and a significant surface reservoir of dust may be found, such as on Comets and Mars. For each of these, inferences about the bulk water D/H ratio as inferred from gas phase measurements needs to be reassessed in light of the volatile cycling history of each body.

  3. A SCUBA-2 survey of FeLoBAL QSOs. Are FeLoBALs in a `transition phase' between ULIRGs and QSOs?

    NASA Astrophysics Data System (ADS)

    Violino, Giulio; Coppin, Kristen E. K.; Stevens, Jason A.; Farrah, Duncan; Geach, James E.; Alexander, Dave M.; Hickox, Ryan; Smith, Daniel J. B.; Wardlow, Julie L.

    2016-04-01

    It is thought that a class of broad absorption line (BAL) QSOs, characterized by Fe absorption features in their UV spectra (called `FeLoBALs'), could mark a transition stage between the end of an obscured starburst event and a youthful QSO beginning to shed its dust cocoon, where Fe has been injected into the interstellar medium by the starburst. To test this hypothesis, we have undertaken deep Submillimetre Common-User Bolometer Array 2 (SCUBA-2) 850 μm observations of a sample of 17 FeLoBAL QSOs with 0.89 ≤ z ≤ 2.78 and -23.31 ≤ MB ≤ -28.50 to directly detect an excess in the thermal emission of the dust which would probe enhanced star formation activity. We find that FeLoBALs are not luminous sources in the sub-mm, none of them are individually detected at 850 μm, nor as a population through stacking (Fs = 1.14 ± 0.58 mJy). Statistical and survival analyses reveal that FeLoBALs have sub-mm properties consistent with BAL and non-BAL QSOs with matched redshifts and magnitudes. An Spectral Energy Distribution fitting analysis shows that the far-infrared emission is dominated by active galactic nuclei activity, and a starburst component is required only in 6/17 sources of our sample; moreover the integrated total luminosity of 16/17 sources is L ≥ 1012 L⊙, high enough to classify FeLoBALs as infrared luminous. In conclusion, we do not find any evidence in support of FeLoBAL QSOs being a transition population between an ultraluminous infrared galaxy (ULIRG) and an unobscured QSO; in particular, FeLoBALs are not characterized by a cold starburst which would support this hypothesis.

  4. Periodic bedforms generated by sublimation on terrestrial and martian ice sheets under the influence of the turbulent atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    Bordiec, Maï; Carpy, Sabrina; Perret, Laurent; Bourgeois, Olivier; Massé, Marion

    2017-04-01

    The redistribution of surface ice induced the wind flow may lead to the development and migration of periodic bedforms, or "ice ripples", at the surface of ice sheets. In certain cold and dry environments, this redistribution need not involve solid particle transport but may be dominated by sublimation and condensation, inducing mass transfers between the ice surface and the overlying steady boundary layer turbulent flow. These mass transfers diffuse the water vapour sublimated from the ice into the atmosphere and become responsible for the amplification and propagation of ripples in a direction perpendicular to their crests. Such ice ripples, 24 cm in wavelength, have been described in the so-called Blue Ice Areas of Antarctica. In order to understand the mechanisms that generate and develop these periodic bedforms on terrestrial glaciers and to evaluate the plausibility that similar bedforms may develop on Mars, we performed a linear stability analysis applied to a turbulent boundary layer flow perturbed by a wavy ice surface. The model is developed as follow. We first solve the flow dynamics using numerical methods analogous to those used in sand wave models assuming that the airflow is similar in both problems. We then add the transport/diffusion equation of water vapour following the same scheme. We use the Reynolds-averaged description of the equation with a Prandtl-like closure. We insert a damping term in the exponential formula of the Van Driest mixing length, depending on the pressure gradient felt by the flow and related to the thickness of the viscous sublayer at the ice-atmosphere interface. This formulation is an efficient way to properly represent the transitional regime under which the ripples grow. Once the mass flux of water vapour is solved, the phase shift between the ripples crests and the maximum of the flux can be deduced for different environments. The temporal evolution of the ice surface can be expressed from these quantities to infer the

  5. A field study of the geomorphic effects of sublimating CO2 blocks on dune slopes at Coral Pink Dunes, Utah.

    NASA Astrophysics Data System (ADS)

    Bourke, Mary; Nield, Jo; Diniega, Serina; Hansen, Candy; McElwaine, Jim

    2016-04-01

    The seasonal sublimation of CO2 ice is an active driver of present-day surface change on Mars. Diniega et al (2013) proposed that a discrete type of Martian gully, found on southern hemisphere dunes, were formed by the movement of CO2 seasonal ice blocks. These 'Linear Gullies' consist primarily of long (100 m - 2.5 km) grooves with near-uniform width (few-10 m wide), and typical depth of <2 m. They are near-linear throughout most of their length but sometimes contains zones of low-to-high sinuosity. They are commonly bounded by levées. The groove is generally prefaced by a small alcove that originates at the dune brink. We present the results of a set of field experiments that were undertaken at the Coral Pink sand dunes, Utah. These are sister experiments to those undertaken in Arizona (Bourke et al, 2016). The experiments were undertaken on an active barchan dune with a 16 m long lee slope (30.3°). Ambient air temperature was 30°C and relative humidity was 25%; sand surface temperatures were 26.5°C. A CO2 ice block (60x205x210 mm) was placed at the dune brink and with a gentle nudge it moved downslope. The dynamics of the block movement were recorded using a pair of high resolution video cameras. Geomorphological observations were noted and topographic change was quantified using a Leica P20 terrestrial laser scanner with a resolution of 0.8 mm at 10 m, and change detection limits less than 3 mm. The block run was repeated a total of 10 times and launched from the same location at the dune brink. The experiment ran for 45 minutes. The block size was reduced to (45 x 190 x 195 mm) by the end of the run series. The resultant geomorphology shows that the separate block runs occupied different tracks leading to a triangular plan form shape with a maximum width of 3.5 m. This is different from the findings in Arizona where a narrower track span was recorded (1.7m) (Bourke et al, 2016). Similar block dynamics were observed at both sites (as blocks moved straight

  6. 75 FR 61478 - D'Lo Gas Storage, LLC; Notice of Petition

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-05

    ... formation for natural gas storage, all as more fully set forth in the application, which is on file with the... Federal Energy Regulatory Commission D'Lo Gas Storage, LLC; Notice of Petition September 24, 2010. Take notice that on September 21, 2010, D'Lo Gas Storage, LLC (Petitioner), 1002 East St. Mary...

  7. Resonant tunnelling diode oscillator as an alternative LO for SIS receiver applications

    NASA Technical Reports Server (NTRS)

    Blundell, R.; Papa, D. C.; Brown, E. R.; Parker, C. D.

    1993-01-01

    The resonant tunnelling diode (RTD) oscillator has been demonstrated for the first time as a local oscillator (LO) in a heterodyne receiver. Noise measurements made on a sensitive 200 GHz superconductor-insulator-superconductor receiver using both a multiplied Gunn diode and an RTD oscillator as the LO revealed no difference in receiver noise as a function of oscillator type.

  8. Resonant tunnelling diode oscillator as an alternative LO for SIS receiver applications

    NASA Technical Reports Server (NTRS)

    Blundell, R.; Papa, D. C.; Brown, E. R.; Parker, C. D.

    1993-01-01

    The resonant tunnelling diode (RTD) oscillator has been demonstrated for the first time as a local oscillator (LO) in a heterodyne receiver. Noise measurements made on a sensitive 200 GHz superconductor-insulator-superconductor receiver using both a multiplied Gunn diode and an RTD oscillator as the LO revealed no difference in receiver noise as a function of oscillator type.

  9. HMT production and sublimation during thermal process of cometary organic analogs. Implications for its detection with the ROSETTA instruments

    NASA Astrophysics Data System (ADS)

    Briani, Giacomo; Fray, Nicolas; Cottin, Hervé; Benilan, Yves; Gazeau, Marie-Claire; Perrier, Sebastien

    2013-09-01

    One important component of refractory organic residues synthesized from interstellar/cometary ice analogues is hexamethylenetetramine (HMT, C6H12N4). However, HMT has never been observed in any astrophysical or planetary environment so far. We investigated thermal evolution of HMT above ambient temperature. The synthesis of the organic residue (ice deposition, photolysis and warming) as well as its heating to temperatures higher than 300 K are performed by means of the same experimental apparatus. The later also allows in situ continuous monitoring of both the solid organic residue (by FTIR spectrometry) and of the gas species (by mass spectrometry). Two different ice mixtures, composed of H2O:CH3OH:NH3 = 10:1:1 and H2O:CH3OH:NH3:CO2 = 10:1:1:2, were deposited and simultaneously photolyzed at 29 K. Warming these photolyzed ices up to 300 K allows the production of refractory organic residues. At 300 K the organic residues clearly show the presence of HMT, but also some difference, in particular in their oxygenated components. Different evolutions of the organic residues are observed for temperatures >300 K. We characterized the organic residue thermal evolution for temperatures up to 500 K. We observed that HMT is still produced at temperatures higher than 300 K. Production of solid HMT and sublimation are simultaneous. HMT observed in the solid phase could be only a minor fraction of the total HMT production, the major fraction being sublimated. The kinetics of the HMT thermal evolution strongly depends on the organic residue composition at 300 K and seems to depend on the exact nature of the oxygenated fraction of the organic residue. The maximum temperature at which solid HMT is observed is 450 K. As HMT forms only for temperatures greater than 280 K in laboratory conditions, it implies that the detection of solid HMT in extraterrestrial samples will provide a strong indication of their thermal history. Consequently, the search for HMT in both solid cometary

  10. Adsorptive fractionation of HDO on JSC MARS-1 during sublimation with implications for the regolith of Mars

    NASA Astrophysics Data System (ADS)

    Moores, John E.; Smith, Peter H.; Boynton, William V.

    2011-02-01

    A chamber was constructed to simulate the boundary between the ice table, regolith and atmosphere of Mars and to examine fractionation between H 2O and HDO during sublimation under realistic martian conditions of temperature and pressure. Thirteen experimental runs were conducted with regolith overlying the ice. The thickness and characteristic grain size of the regolith layer as well as the temperature of the underlying ice was varied. From these runs, values for the effective diffusivity, taking into account the effects of adsorption, of the regolith were derived. These effective diffusivities ranged from 1.8 × 10 -4 m 2 s -1 to 2.2 × 10 -3 m 2 s -1 for bare ice and from 2.4 × 10 -11 m 2 s -1 to 2.0 × 10 -9 m 2 s -1 with an adsorptive layer present. From these, latent heats of adsorption of 8.6 ± 2.6 kJ mol -1 and 9.3 ± 2.8 kJ mol -1 were derived at ice-surface temperatures above 223 ± 8 K and 96 ± 28 kJ mol -1 and 104 ± 31 kJ mol -1 respectively for H 2O and HDO were derived at colder temperatures. For temperatures below 223 K, the effective diffusivity of HDO was found to be lower than the diffusivity of H 2O by 40% on average, suggesting that the regolith was adsorptively fractionating the sublimating gas with a fractionation factor of 1.96 ± 0.74. Applying these values to Mars predicts that adsorbed water on the regolith is enriched in HDO compared to the atmosphere, particularly where the regolith is colder. Based on current observations, the D/H ratio of the regolith may be as high as 21 ± 8 times VSMOW at 12°S and L S = 357° if the regolith is hydrated primarily by the atmosphere, neglecting any hydration from subsurface ice.

  11. THE NATURE OF LoBAL QSOs. I. SEDs AND MID-INFRARED SPECTRAL PROPERTIES

    SciTech Connect

    Lazarova, Mariana S.; Canalizo, Gabriela; Lacy, Mark; Sajina, Anna E-mail: gabriela.canalizo@ucr.edu E-mail: Anna.Sajina@tufts.edu

    2012-08-10

    We have obtained Spitzer Infrared Spectrograph spectra and MIPS 24, 70, and 160 {mu}m photometry for a volume-limited sample of 22 Sloan Digital Sky Survey selected low-ionization broad absorption line (LoBALs) QSOs at 0.5 < z < 0.6. By comparing their mid-IR spectral properties and far-IR spectral energy distributions (SEDs) with those of a control sample of 35 non-LoBALs matched in M{sub i} , we investigate the differences between the two populations in terms of their infrared emission and star formation (SF) activity. Twenty-five percent of the LoBALs show polycyclic aromatic hydrocarbon features and 45% have weak 9.7 {mu}m silicate dust emission. We model the SEDs and decouple the active galactic nucleus (AGN) and starburst contributions to the far-infrared luminosity in LoBALs and in non-LoBALs. Their median total, starburst, and AGN infrared luminosities are comparable. Twenty percent (but no more than 60%) of the LoBALs and 26% of the non-LoBALs are ultraluminous infrared galaxies (L{sub IR} > 10{sup 12} L{sub Sun }). We estimate star formation rates (SFRs) corrected for the AGN contribution to the FIR flux and find that LoBALs have comparable levels of SF activity to non-LoBALs when considering the entire samples. However, the SFRs of the IR-luminous LoBALs are 80% higher than those of their counterparts in the control sample. The median contribution of SF to the total far-infrared flux in LoBALs and in non-LoBALs is estimated to be 40%-50%, in agreement with previous results for Palomar-Green (PG) QSOs. Overall, our results show that there is no strong evidence from the mid- and far-IR properties that LoBALs are drawn from a different parent population than non-LoBALs.

  12. A ROACH Based Data Acquisition System for the Low Frequency All Sky Monitor (LoFASM)

    NASA Astrophysics Data System (ADS)

    Dartez, Louis P.; Jenet, F.; Cohen, S.; Creighton, T. D.; Ford, A.; Garcia, A.; Hicks, B.; Hinojosa, J.; Kassim, N. E.; Longoria, C.; Lunsford, G.; Mata, A.; Miller, R. B.; Price, R. H.; Quintero, L.; Ray, P. S.; Reser, J.; Rivera, J.; Stovall, K.; Taylor, G. B.

    2013-01-01

    The Low Frequency All Sky Monitor (LoFASM) is a distributed array of dipole antennas that are sensitive to radio frequencies from 5 to 88 MHz. The primary science goals will be the detection and study of low-frequency radio transients. LoFASM consists of antennas and front end electronics that were originally developed for the Long Wavelength Array (LWA) by the U.S. Naval Research Lab, the University of New Mexico, Virginia Tech, and the Jet Propulsion Laboratory. LoFASM, funded by the U.S. Department of Defense, will initially consist of 4 stations, each consisting of 12 dual-polarization dipole antenna stands. The signals received by LoFASM are digitized and processed using Reconfigurable Open Architecture Computing Hardware (ROACH) boards. This poster will describe the LoFASM project with an emphasis on the ROACH data processing pipe-line.

  13. Anticancer activity of baicalein and luteolin studied in colorectal adenocarcinoma LoVo cells and in drug-resistant LoVo/Dx cells.

    PubMed

    Palko-Labuz, Anna; Sroda-Pomianek, Kamila; Uryga, Anna; Kostrzewa-Suslow, Edyta; Michalak, Krystyna

    2017-04-01

    Due to the type-specific diversity of cancer cells, an analysis and elucidation of molecular mechanisms responsible for anticancer properties of biologically active compounds are essential. Plant-derived polyphenolic compounds such as flavonoids may be useful in cancer chemoprevention or treatment because they influence diverse molecular pathways in cancer cells. In these studies anticancer activity of natural occurring flavones, baicalein and luteolin was investigated in colon cancer cells LoVo and in their drug resistant subline LoVo/Dx. Inhibitory activity of these flavones on cells growth and their ability to induce apoptosis were observed. A less pronounced influence of studied flavones on proliferation and apoptosis of LoVo/Dx as compared with LoVo cells well correlated with significantly lower cytotoxicity of these compounds in drug-resistant cells. These effects may be related to overexpression of multidrug transporter P-glycoprotein in drug-resistant LoVo/Dx cells. Our studies indicated that baicalein could be a substrate of this drug transporter. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  14. Plasma assisted growth of MoO{sub 3} films on different substrate locations relative to sublimation source

    SciTech Connect

    Sharma, Rabindar K. Saini, Sujit K.; Kumar, Prabhat; Singh, Megha; Reddy, G. B.

    2016-05-06

    In the present paper, we reported the role of substrate locations relative to source on the growth of MoO{sub 3} films deposited on Ni coated glass substrates using plasma assisted sublimation process (PASP). According to the XRD and SEM results, substrate location is very crucial factor to control the morphology of MoO{sub 3} films and the best nanostructure growth (in terms of alignments and features) is obtained in case of Sample B (in which substrate is placed on source). The structural results point out that all films exhibit only orthorhombic phase of molybdenum oxide (i.e. α-MoO{sub 3})but the most preferential growth is recorded in Sample B due to the presence of intense peaks crossponding to only (0 k 0) family of crystal planes (k = 2, 4,6..). The Raman analysis again confirms the orthorhombic nature of MoO{sub 3} NFs and details of vibrational bondsin Sample B have been given in the present report. The MoO{sub 3} NFs show intense PL emission in wavelength range of 300-700 nm with three peaks located at 415, 490, and 523 nm in accordance to the improved crystallinity in Sample B.

  15. 12% efficient CdTe/CdS thin film solar cells deposited by low-temperature close space sublimation

    NASA Astrophysics Data System (ADS)

    Schaffner, Judith; Motzko, Markus; Tueschen, Alexander; Swirschuk, Andreas; Schimper, Hermann-Josef; Klein, Andreas; Modes, Thomas; Zywitzki, Olaf; Jaegermann, Wolfram

    2011-09-01

    We report 12% efficient CdS/CdTe thin film solar cells prepared by low temperature close space sublimation (CSS). Both semiconductor films, CdS and CdTe, were deposited by high vacuum CSS in superstrate configuration on glass substrates with fluorine doped tin oxide (FTO) front contact. The CdTe deposition was carried out at a substrate temperature (Tsub) of ≤340 ∘C, which is much lower than that used in conventional processes (>500 ∘C). The CdTe films were treated with the usual CdCl2 activation process. Different optimal annealing times and temperatures were found for low-temperature cells (Tsub≤ 340 ∘C) compared to high-temperature cells (Tsub = 520 ∘C). The influence of the activation step on the morphology of high-temperature and low-temperature CdTe is determined by XRD, AFM, SEM top views, and SEM cross-sections. Grain growth, strong recrystallization, and a reduction of planar defects during the activation step are observed, especially for low-temperature CdTe. Further, the influence of CdS deposition parameters on the solar cell performance is investigated by using three different sets of parameters with different deposition rates and substrate temperatures for the CdS preparation. Efficiencies about 10.9% with a copper-free back contact and 12.0% with a copper-containing back contact were achieved using the low temperature CdTe process.

  16. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap

    USGS Publications Warehouse

    Kieffer, H.H.; Christensen, P.R.; Titus, T.N.

    2006-01-01

    The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO 2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth. ?? 2006 Nature Publishing Group.

  17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap.

    PubMed

    Kieffer, Hugh H; Christensen, Philip R; Titus, Timothy N

    2006-08-17

    The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth.

  18. Characterization of CdMnTe films deposited from polycrystalline powder source using closed-space sublimation method

    SciTech Connect

    Lai, Jianming; Wang, Junnan; Wang, Lin; Ji, Huanhuan; Xu, Run; Zhang, Jijun; Huang, Jian; Shen, Yue; Min, Jiahua; Wang, Linjun Xia, Yiben

    2015-09-15

    CdMnTe films were prepared on quartz substrates by closed-space sublimation of polycrystalline Cd{sub 0.74}Mn{sub 0.26}Te powders. This was performed at different substrate temperatures (T{sub s} = 200, 300, 350, and 400 °C). The interfacial adhesion strength between the films and substrates, when fabricated from polycrystalline powders, was greater than that of films grown using a bulk source. X-ray diffraction studies revealed that the as-deposited films had a zinc blende structure with a preferential (111) orientation. Precipitation of Te occurred in the films deposited at T{sub s} = 200 °C, as confirmed using scanning electron microscopy, x-ray diffraction, and Raman spectroscopy. The growth mode and re-evaporation dependence on the value of T{sub s} of the films were investigated. Our results suggested that materials suitable for radiation detection can be grown from a powder source at lower substrate temperatures then when grown from a bulk source.

  19. Solid sulfur in vacuum: Sublimation effects on surface microtexture, color and spectral reflectance, and applications to planetary surfaces

    NASA Technical Reports Server (NTRS)

    Nash, D. B.

    1987-01-01

    A form of sulfur that is white at room temperature and very fluffy in texture has been found in laboratory experiments on the effects of vacuum sublimation (evaporation) on solid sulfur. This work is an outgrowth of proton sputtering experiments on sulfur directed toward understanding Jovian magnetospheric effects on the surface of Io. Fluffy white sulfur is formed on the surface of solid yellow, tan, or brown sulfur melt freezes in vacuum by differential (fractional) evaporation of two or more sulfur molecular species present in the original sulfur; S(8) ring sulfur is thought to be the dominant sublimination phase lost to the vacuum sink, and polymeric chain sulfur S(u) the dominant residual phase that remains in place, forming the residual fluffy surface layer. The reflectance spectrum of the original sulfur surface is greaty modified by formation of the fluffy layer: the blue absorption band-edge and shoulder move 0.05 to 0.06 microns toward shorter wavelengths resulting in a permanent increase in reflectivity near 0.42 to 0.46 microns; the UV reflectivity below 0.40 microns is reduced. This form of sulfur should exist in large quantity on the surface of Io, especially in hotspot regions if there is solid free sulfur there that has solidified from a melt. Its color and spectra will indicate relative crystallization age on a scale of days to months and/or surface temperature distribution history.

  20. In-Space Propulsion Engine Architecture Based on Sublimation of Planetary Resources: From Exploration Robots to NED Mitigation

    NASA Technical Reports Server (NTRS)

    Sibille, Laurent; Mantovani, James G.

    2011-01-01

    Volatile solids occur naturally on most planetary bodies including the Moon, Mars, asteroids and comets. Examples of recent discoveries include water ice, frozen carbon dioxide and hydrocarbons. The ability to utilize readily available resources for in-space propulsion and for powering surface systems during a planetary mission will help minimize the overall cost and extend the op.erational life of a mission. The utilization of volatile solids to achieve these goals is attractive for its simplicity. We have investigated the potential of subliming in situ volatiles and silicate minerals to power propulsion engines for a wide range of in-space applications where environmental conditions are favorable. This paper addresses the' practicality of using planetary solid volatiles as a power source for propulsion and surface systems by presenting results of modeling involving thermodynamic and physical mechanics calculations, and laboratory testing to measure the thrust obtained from ,a volatile solid engine (VSE). Applications of a VSE for planetary exploration are discussed as a means for propulsion and for mechanical actuators and surface mobility platforms.

  1. HiRISE observations of gas sublimation-driven activity in Mars' southern polar regions: III. Models of processes involving translucent ice

    USGS Publications Warehouse

    Portyankina, G.; Markiewicz, W.J.; Thomas, N.; Hansen, C.J.; Milazzo, M.

    2010-01-01

    Enigmatic surface features, known as 'spiders', found at high southern martian latitudes, are probably caused by sublimation-driven erosion under the seasonal carbon dioxide ice cap. The Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) has imaged this terrain in unprecedented details throughout southern spring. It has been postulated [Kieffer, H.H., Titus, T.N., Mullins, K.F., Christensen, P.R., 2000. J. Geophys. Res. 105, 9653-9700] that translucent CO2 slab ice traps gas sublimating at the ice surface boundary. Wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and/or downwind and deposited in a fan shape. Here we model two stages of this scenario: first, the cleaning of CO2 slab ice from dust, and then, the breaking of the slab ice plate under the pressure built below it by subliming ice. Our modeling results and analysis of HiRISE images support the gas jet hypothesis and show that outbursts happen very early in spring. ?? 2009 Elsevier Inc. All rights reserved.

  2. HiRISE observations of gas sublimation-driven activity in Mars’ southern polar regions: III. Models of processes involving translucent ice

    NASA Astrophysics Data System (ADS)

    Portyankina, Ganna; Markiewicz, Wojciech J.; Thomas, Nicolas; Hansen, Candice J.; Milazzo, Moses

    2010-01-01

    Enigmatic surface features, known as 'spiders', found at high southern martian latitudes, are probably caused by sublimation-driven erosion under the seasonal carbon dioxide ice cap. The Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) has imaged this terrain in unprecedented details throughout southern spring. It has been postulated [Kieffer, H.H., Titus, T.N., Mullins, K.F., Christensen, P.R., 2000. J. Geophys. Res. 105, 9653-9700] that translucent CO slab ice traps gas sublimating at the ice surface boundary. Wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and/or downwind and deposited in a fan shape. Here we model two stages of this scenario: first, the cleaning of CO slab ice from dust, and then, the breaking of the slab ice plate under the pressure built below it by subliming ice. Our modeling results and analysis of HiRISE images support the gas jet hypothesis and show that outbursts happen very early in spring.

  3. TriLoNet: Piecing Together Small Networks to Reconstruct Reticulate Evolutionary Histories.

    PubMed

    Oldman, James; Wu, Taoyang; van Iersel, Leo; Moulton, Vincent

    2016-08-01

    Phylogenetic networks are a generalization of evolutionary trees that can be used to represent reticulate processes such as hybridization and recombination. Here, we introduce a new approach called TriLoNet (Trinet Level- one Network algorithm) to construct such networks directly from sequence alignments which works by piecing together smaller phylogenetic networks. More specifically, using a bottom up approach similar to Neighbor-Joining, TriLoNet constructs level-1 networks (networks that are somewhat more general than trees) from smaller level-1 networks on three taxa. In simulations, we show that TriLoNet compares well with Lev1athan, a method for reconstructing level-1 networks from three-leaved trees. In particular, in simulations we find that Lev1athan tends to generate networks that overestimate the number of reticulate events as compared with those generated by TriLoNet. We also illustrate TriLoNet's applicability using simulated and real sequence data involving recombination, demonstrating that it has the potential to reconstruct informative reticulate evolutionary histories. TriLoNet has been implemented in JAVA and is freely available at https://www.uea.ac.uk/computing/TriLoNet. © The Author 2016. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  4. Contrast Invariant Interest Point Detection by Zero-Norm LoG Filter.

    PubMed

    Zhenwei Miao; Xudong Jiang; Kim-Hui Yap

    2016-01-01

    The Laplacian of Gaussian (LoG) filter is widely used in interest point detection. However, low-contrast image structures, though stable and significant, are often submerged by the high-contrast ones in the response image of the LoG filter, and hence are difficult to be detected. To solve this problem, we derive a generalized LoG filter, and propose a zero-norm LoG filter. The response of the zero-norm LoG filter is proportional to the weighted number of bright/dark pixels in a local region, which makes this filter be invariant to the image contrast. Based on the zero-norm LoG filter, we develop an interest point detector to extract local structures from images. Compared with the contrast dependent detectors, such as the popular scale invariant feature transform detector, the proposed detector is robust to illumination changes and abrupt variations of images. Experiments on benchmark databases demonstrate the superior performance of the proposed zero-norm LoG detector in terms of the repeatability and matching score of the detected points as well as the image recognition rate under different conditions.

  5. LoCoH: nonparameteric kernel methods for constructing home ranges and utilization distributions.

    PubMed

    Getz, Wayne M; Fortmann-Roe, Scott; Cross, Paul C; Lyons, Andrew J; Ryan, Sadie J; Wilmers, Christopher C

    2007-02-14

    Parametric kernel methods currently dominate the literature regarding the construction of animal home ranges (HRs) and utilization distributions (UDs). These methods frequently fail to capture the kinds of hard boundaries common to many natural systems. Recently a local convex hull (LoCoH) nonparametric kernel method, which generalizes the minimum convex polygon (MCP) method, was shown to be more appropriate than parametric kernel methods for constructing HRs and UDs, because of its ability to identify hard boundaries (e.g., rivers, cliff edges) and convergence to the true distribution as sample size increases. Here we extend the LoCoH in two ways: "fixed sphere-of-influence," or r-LoCoH (kernels constructed from all points within a fixed radius r of each reference point), and an "adaptive sphere-of-influence," or a-LoCoH (kernels constructed from all points within a radius a such that the distances of all points within the radius to the reference point sum to a value less than or equal to a), and compare them to the original "fixed-number-of-points," or k-LoCoH (all kernels constructed from k-1 nearest neighbors of root points). We also compare these nonparametric LoCoH to parametric kernel methods using manufactured data and data collected from GPS collars on African buffalo in the Kruger National Park, South Africa. Our results demonstrate that LoCoH methods are superior to parametric kernel methods in estimating areas used by animals, excluding unused areas (holes) and, generally, in constructing UDs and HRs arising from the movement of animals influenced by hard boundaries and irregular structures (e.g., rocky outcrops). We also demonstrate that a-LoCoH is generally superior to k- and r-LoCoH (with software for all three methods available at http://locoh.cnr.berkeley.edu).

  6. LoCoH: Non-parameteric kernel methods for constructing home ranges and utilization distributions

    USGS Publications Warehouse

    Getz, Wayne M.; Fortmann-Roe, Scott; Cross, Paul C.; Lyons, Andrew J.; Ryan, Sadie J.; Wilmers, Christopher C.

    2007-01-01

    Parametric kernel methods currently dominate the literature regarding the construction of animal home ranges (HRs) and utilization distributions (UDs). These methods frequently fail to capture the kinds of hard boundaries common to many natural systems. Recently a local convex hull (LoCoH) nonparametric kernel method, which generalizes the minimum convex polygon (MCP) method, was shown to be more appropriate than parametric kernel methods for constructing HRs and UDs, because of its ability to identify hard boundaries (e.g., rivers, cliff edges) and convergence to the true distribution as sample size increases. Here we extend the LoCoH in two ways: ‘‘fixed sphere-of-influence,’’ or r -LoCoH (kernels constructed from all points within a fixed radius r of each reference point), and an ‘‘adaptive sphere-of-influence,’’ or a -LoCoH (kernels constructed from all points within a radius a such that the distances of all points within the radius to the reference point sum to a value less than or equal to a ), and compare them to the original ‘‘fixed-number-of-points,’’ or k -LoCoH (all kernels constructed from k -1 nearest neighbors of root points). We also compare these nonparametric LoCoH to parametric kernel methods using manufactured data and data collected from GPS collars on African buffalo in the Kruger National Park, South Africa. Our results demonstrate that LoCoH methods are superior to parametric kernel methods in estimating areas used by animals, excluding unused areas (holes) and, generally, in constructing UDs and HRs arising from the movement of animals influenced by hard boundaries and irregular structures (e.g., rocky outcrops). We also demonstrate that a -LoCoH is generally superior to k - and r -LoCoH (with software for all three methods available at http://locoh.cnr.berkeley.edu).

  7. LoCoH: Nonparameteric Kernel Methods for Constructing Home Ranges and Utilization Distributions

    PubMed Central

    Getz, Wayne M.; Fortmann-Roe, Scott; Wilmers, Christopher C.

    2007-01-01

    Parametric kernel methods currently dominate the literature regarding the construction of animal home ranges (HRs) and utilization distributions (UDs). These methods frequently fail to capture the kinds of hard boundaries common to many natural systems. Recently a local convex hull (LoCoH) nonparametric kernel method, which generalizes the minimum convex polygon (MCP) method, was shown to be more appropriate than parametric kernel methods for constructing HRs and UDs, because of its ability to identify hard boundaries (e.g., rivers, cliff edges) and convergence to the true distribution as sample size increases. Here we extend the LoCoH in two ways: “fixed sphere-of-influence,” or r-LoCoH (kernels constructed from all points within a fixed radius r of each reference point), and an “adaptive sphere-of-influence,” or a-LoCoH (kernels constructed from all points within a radius a such that the distances of all points within the radius to the reference point sum to a value less than or equal to a), and compare them to the original “fixed-number-of-points,” or k-LoCoH (all kernels constructed from k-1 nearest neighbors of root points). We also compare these nonparametric LoCoH to parametric kernel methods using manufactured data and data collected from GPS collars on African buffalo in the Kruger National Park, South Africa. Our results demonstrate that LoCoH methods are superior to parametric kernel methods in estimating areas used by animals, excluding unused areas (holes) and, generally, in constructing UDs and HRs arising from the movement of animals influenced by hard boundaries and irregular structures (e.g., rocky outcrops). We also demonstrate that a-LoCoH is generally superior to k- and r-LoCoH (with software for all three methods available at http://locoh.cnr.berkeley.edu). PMID:17299587

  8. Higgs boson gluon-fusion production beyond threshold in N3LO QCD

    DOE PAGES

    Anastasiou, Charalampos; Duhr, Claude; Dulat, Falko; ...

    2015-03-18

    In this study, we compute the gluon fusion Higgs boson cross-section at N3LO through the second term in the threshold expansion. This calculation constitutes a major milestone towards the full N3LO cross section. Our result has the best formal accuracy in the threshold expansion currently available, and includes contributions from collinear regions besides subleading corrections from soft and hard regions, as well as certain logarithmically enhanced contributions for general kinematics. We use our results to perform a critical appraisal of the validity of the threshold approximation at N3LO in perturbative QCD.

  9. Holographic wavefront sensor based on Karhunen-Loève decomposition

    NASA Astrophysics Data System (ADS)

    Anzuola, Esdras; Zepp, Andreas; Gladysz, Szymon; Stein, Karin

    2016-09-01

    In this paper we introduce the use of Karhunen-Loève functions as a basis set to decompose atmospheric phase aberrations in a digital holographic wavefront sensor (HWS). We show that the intermodal crosstalk when using Karhunen-Loève functions is reduced in comparison to the Zernike decomposition. Additionally, the sensor's response showed an improved linearity and better robustness to scintillation. Intermodal crosstalk remains a significant problem for this sensor but operation of an adaptive optics system based on HWS is less challenging when using Karhunen-Loève functions instead of Zernike polynomials.

  10. A redetermination of the ice/vapor ratio of Enceladus’ plumes: Implications for sublimation and the lack of a liquid water reservoir

    NASA Astrophysics Data System (ADS)

    Kieffer, Susan W.; Lu, Xinli; McFarquhar, Greg; Wohletz, Kenneth H.

    2009-09-01

    The discovery of plumes of H 2O vapor and ice particles erupting from the south pole of Enceladus, the tiny frigid satellite of Saturn, sparked controversy over whether these plumes are produced by boiling, or by sublimation with subsequent recondensation of the sublimated vapor [Porco, C.C., Helfenstein, P., Thomas, P.C., Ingersoll, A.P., Wisdom, J., West, R., Neukum, G., Denk, T., Wagner, R., Roatsch, T., Kieffer, S., Turtle, E., McEwen, A., Johnson, T.V., Rathbun, J., Veverka, J., Wilson, D., Perry, J., Spitale, J., Brahic, A., Burns, J.A., DelGenio, A.D., Dones, L., Murray, C.D., Squyres, S., 2006. Science 311, 1393-1401]. Porco et al.'s analysis that the masses of ice (I) and vapor (V) in the plume were comparable was taken to argue against the occurrence of sublimation and recondensation, leading to the hypothesis that the reservoir was boiling water, possibly as close as 7 m to the surface. Thus, it has been advocated that Enceladus should be a target for astrobiology exploration. Here we show, with recalculations using the original data and methodologies, as well as with new sensitivity studies, that the mass of ice in the column is significantly less than the mass of water vapor, and that by considering three additional effects, I/V is likely to be <0.2-0.1. This means that the plume is dominated by vapor that the thermodynamics permits to be easily produced by sublimation with recondensation. The low I/V ratio provides no compelling criterion for consideration of a liquid water reservoir. The uncertainties on the I/V ratio have not previously been discussed in the literature. Although the I/V ratio is sensitive to particle sizes and size distributions, the masses of ice (I) and vapor (V) are not comparable in any scenario constrained by available observations. We thus discuss the implications of sublimation from a thermodynamic point of view in a context that has not been presented previously. Constraints on I/V ratio from future spacecraft measurements

  11. RANKL induces heterogeneous DC-STAMP(lo) and DC-STAMP(hi) osteoclast precursors of which the DC-STAMP(lo) precursors are the master fusogens.

    PubMed

    Mensah, Kofi A; Ritchlin, Christopher T; Schwarz, Edward M

    2010-04-01

    Osteoclasts (OC) are multinucleated bone resorbing cells that form via RANKL-induced fusion of heterogeneous mononuclear OC precursors (OCP). Currently, there are no unique surface markers to distinguish these OCP populations, which are diagnostic for erosive and metabolic bone diseases using culture assays. Thus, we investigated expression of DC-STAMP, a surface receptor required for OCP fusion, during osteoclastogenesis in vitro using a novel monoclonal antibody (1A2). Immunoprecipitation-Western blot analysis of OCP membrane proteins detected 106 kDa dimeric and 53 kDa monomeric DC-STAMP in non-denaturing and denaturing conditions, respectively, with greater sensitivity versus rabbit anti-sera (KR104). 1A2 also detected 99.9% of undifferentiated monocytes as a single population by flow cytometry with a MFI 100-fold over background, while KR104 was not useful in this assay. Functionally, 1A2 inhibited OCP fusion in vitro. RANKL stimulation of OCP induced DC-STAMP(lo) and DC-STAMP(hi) cells, which mature into OC and mononuclear cells respectively as determined by fluorescent microscopy and TRAP assays. Addition of DC-STAMP(hi) cells to purified DC-STAMP(lo) cultures produced larger, more nucleated OC vs. pure DC-STAMP(lo) cultures. RT-qPCR analysis of these two populations showed that OC markers (Trap and Oc-stamp) and fusogenic gene expression (Cd9 and Cd47), were significantly increased in DC-STAMP(lo) vs. DC-STAMP(hi) cells. Collectively, these results demonstrate that DC-STAMP is expressed on OCP as a dimer, which is efficiently detected by 1A2 via flow cytometry. RANKL induces osteoclastogenesis by stimulating DC-STAMP internalization in some OCP, and these DC-STAMP(lo) cells display the "master fusogen" phenotype. In contrast, DC-STAMP(hi) OCP can only act as mononuclear donors. J. Cell. Physiol. 223: 76-83, 2010. (c) 2009 Wiley-Liss, Inc.

  12. LINDLEY NURSERY COMPLEX NORTH loOKING SOUTHEAST ACROSS FORMER FIELDS THROUGH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    LINDLEY NURSERY COMPLEX NORTH loOKING SOUTHEAST ACROSS FORMER FIELDS THROUGH MORNING MIST - Overhills, Fort Bragg Military Reservation, Approximately 15 miles NW of Fayetteville, Overhills, Harnett County, NC

  13. Proposal for a New LoD and Multi-Representation Concept for CityGML

    NASA Astrophysics Data System (ADS)

    Löwner, M.-O.; Gröger, G.; Benner, J.; Biljecki, F.; Nagel, C.

    2016-10-01

    The Open Geospatial Consortium (OGC) CityGML standard offers a Level of Detail (LoD) concept that enables the representation of CityGML features from a very detailed to a less detailed description. Due to a rising application variety, the current LoD concept seems to be too inflexible. Here, we present a multi representation concept (MRC) that enables a user-defined definition of LoDs. Because CityGML is an international standard, official profiles of the MRC are proposed. However, encoding of the defined profiles reveals many problems including mapping the conceptual model to the normative encoding, missing technologies and so on. Therefore, we propose to use the MRC as a meta model for the further definition of an LoD concept for CityGML 3.0.

  14. LoPSiL: A Location-Based Policy-Specification Language

    NASA Astrophysics Data System (ADS)

    Ligatti, Jay; Rickey, Billy; Saigal, Nalin

    This paper describes the design of LoPSiL, a language for specifying location-dependent security and privacy policies. Policy- specification languages like LoPSiL are domain-specific programming languages intended to simplify the tasks of specifying and enforcing sound security policies on untrusted (i.e., potentially insecure) software. As far as we are aware, LoPSiL is the first imperative policy-specification language to provide abstractions specifically tailored to location-dependent policies for mobile-device applications. We have implemented a proof-of-concept compiler that inputs a LoPSiL policy P and a mobile-device application program A and outputs a new application program A' equivalent to A, except that A' contains inlined enforcement code that ensures that A' satisfies P at runtime. We report our experiences using this compiler to design and implement several policies for mobile-device applications.

  15. Development of HiLo Microscope and its use in In-Vivo Applications

    NASA Astrophysics Data System (ADS)

    Patel, Shreyas J.

    The functionality of achieving optical sectioning in biomedical research is invaluable as it allows for visualization of a biological sample at different depths while being free of background scattering. Most current microscopy techniques that offer optical sectioning, unfortunately, require complex instrumentation and thus are generally costly. HiLo microscopy, on the other hand, offers the same functionality and advantage at a relatively low cost. Hence, the work described in this thesis involves the design, build, and application of a HiLo microscope. More specifically, a standalone HiLo microscope was built in addition to implementing HiLo microscopy on a standard fluorescence microscope. In HiLo microscopy, optical sectioning is achieved by acquiring two different types of images per focal plane. One image is acquired under uniform illumination and the other is acquired under speckle illumination. These images are processed using an algorithm that extracts in-focus information and removes features and glare that occur as a result of background fluorescence. To show the benefits of the HiLo microscopy, several imaging experiments on various samples were performed under a HiLo microscope and compared against a traditional fluorescence microscope and a confocal microscope, which is considered the gold standard in optical imaging. In-vitro and ex-vivo imaging was performed on a set of pollen grains, and optically cleared mouse brain and heart slices. Each of these experiments showed great reduction in background scattering at different depths under HiLo microscopy. More importantly, HiLo imaging of optically cleared heart slice demonstrated emergence of different vasculature at different depths. Reduction of out-of-focus light increased the spatial resolution and allowed better visualization of capillary vessels. Furthermore, HiLo imaging was tested in an in-vivo model of a rodent dorsal window chamber model. When imaging the same sample under confocal microscope

  16. Cadmium sulfide thin films deposited by close spaced sublimation and cadmium sulfide/cadmium telluride solar cells

    NASA Astrophysics Data System (ADS)

    Marinskiy, Dmitriy Nikolaevich

    1998-12-01

    One of the applications of CdS films is as a window layer in CdTe and Cu(In,Ga)Sesb2 solar cells. The study of the optical and structural properties of CdS films deposited by close spaced sublimation as well as their influence on CdS/CdTe solar cell performance is part of the CdTe solar cell program at the University of South Florida. CdS films have been deposited by the close-spaced sublimation technique. The influence of the main process parameters, the substrate and source temperatures, and the ambient in the deposition chamber has been investigated. As-deposited films have been subjected to heat treatments in Hsb2 ambient, in CdClsb2 atmosphere, and in atmosphere with small amounts of oxygen. A special annealing chamber was built to carry out the annealing experiments in the presence of CdClsb2 vapor and oxygen. Several CSS chambers were assembled to study the influence of various process parameters simultaneously and validate the results. Results of scanning electron microscopy and photoluminescence measurements have been used as the primary characterization techniques. X-ray diffraction, electron microprobe analysis, and transmission measurements have also been carried out. It was found that as deposited CdS films have a hexagonal structure independent of the process parameters used. The presence of a CdO phase was detected in the samples grown with the highest oxygen concentration in the ambient. The resistivity of CdS films is controlled by intergrain barriers. Photoluminescence measurements showed the presence of oxygen-acceptor transition and a wide variation in the intensity of deep emission bands. The variation in the intensities was correlated with the variation in the deposition and annealing conditions. However, no correlation was found between the PL intensities of defect bands and cell performance. CdS/CdTe junctions have been fabricated using standard deposition and postgrowth techniques developed in the USF solar cells laboratory. All cells have

  17. Effect of Propellant Flowrate and Purity on Carbon Deposition in LO2/Methane Gas Generators

    NASA Technical Reports Server (NTRS)

    Bossard, J. A.; Burkhardt, W. M.; Niiya, K. Y.; Braam, F.

    1989-01-01

    The generation and deposition of carbon was studied in the Carbon Deposition Program using subscale hardware with LO2/Liquid Natural Gas (LNG) and LO2/Methane propellants at low mixture ratios. The purpose of the testing was to evaluate the effect of methane purity and full scale injection density on carbon deposition. The LO2/LNG gas generator/preburner testing was performed at mixture ratios between 0.24 and 0.58 and chamber pressures from 5.8 to 9.4 MPa (840 to 1370 psia). A total of seven 200 second duration tests were performed. The LNG testing occurred at low injection densities, similar to the previous LO2/RP-1, LO2/propane, and LO2/methane testing performed on the carbon deposition program. The current LO2/methane test series occurred at an injection density factor of approximately 10 times higher than the previous testing. The high injection density LO2/methane testing was performed at mixture ratios between from 0.23 to 0.81 and chamber pressures from 6.4 to 15.2 MPa (925 to 2210 psia). A total of nine high injection density tests were performed. The testing performed demonstrated that low purity methane (LNG) did not produce any detectable change in carbon deposition when compared to pure methane. In addition, the C* performance and the combustion gas temperatures measured were similar to those obtained for pure methane. Similar results were obtained testing pure methane at higher propellant injection densities with coarse injector elements.

  18. LoFASM: A Low Frequency All Sky Monitor for Radio Transients and Student Training

    DTIC Science & Technology

    2015-09-02

    SECURITY CLASSIFICATION OF: The Low-Frequency All -Sky Monitor (LoFASM) is an innovative new radio astronomy observatory. Designed and built by... All four stations have now started taking data. The observatory has also been a vital recruiting and training tool for physics students from the...Feb-2015 Approved for Public Release; Distribution Unlimited Final Report: LoFASM: A Low Frequency All Sky Monitor for Radio Transients and Student

  19. m-LoCoS UI: A Universal Visible Language for Global Mobile Communication

    NASA Astrophysics Data System (ADS)

    Marcus, Aaron

    The LoCoS universal visible language developed by the graphic/sign designer Yukio Ota in Japan in 1964 may serve as a usable, useful, and appealing basis for a mobile phone application that can provide capabilities for communication and storytelling among people who do not share a spoken language. User-interface design issues including display and input are discussed in conjunction with prototype screens showing the use of LoCoS for a mobile phone.

  20. Investigating the differences of cirrus cloud properties in nucleation, growth and sublimation regions based on airborne water vapor lidar measurements

    NASA Astrophysics Data System (ADS)

    Urbanek, Benedikt; Groß, Silke; Wirth, Martin

    2017-04-01

    Cirrus clouds impose high uncertainties on weather and climate prediction, as knowledge on important processes is still incomplete. For instance it remains unclear how cloud optical, microphysical, and radiative properties change as the cirrus evolves. To gain better understanding of cirrus clouds, their optical and microphysical properties and their changes with cirrus cloud evolution the ML-CIRRUS campaign was conducted in March and April 2014. Measurements with a combined in-situ and remote sensing payload were performed with the German research aircraft HALO based in Oberpfaffenhofen. 16 research flights with altogether 88 flight hours were performed over the North-Atlantic, western and central Europe to probe different cirrus cloud regimes and cirrus clouds at different stages of evolution. One of the key remotes sensing instruments during ML-CIRRUS was the airborne differential absorption and high spectral lidar system WALES. It measures the 2-dimensional distribution of water vapor inside and outside of cirrus clouds as well as the optical properties of the clouds. Bases on these airborne lidar measurements a novel classification scheme to derive the stage of cirrus cloud evolution was developed. It identifies regions of ice nucleation, particle growth by deposition of water vapor, and ice sublimation. This method is used to investigate differences in the distribution and value of optical properties as well as in the distribution of water vapor and relative humidity depending on the stage of evolution of the cloud. We will present the lidar based classification scheme and its application on a wave driven cirrus cloud case, and we will show first results of the dependence of optical cloud properties and relative humidity distributions on the determined stage of evolution.

  1. Recent ice-rich deposits formed at high latitudes on Mars by sublimation of unstable equatorial ice during low obliquity.

    PubMed

    Levrard, Benjamin; Forget, François; Montmessin, Franck; Laskar, Jacques

    2004-10-28

    Observations from the gamma-ray spectrometer instrument suite on the Mars Odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near-surface ice in high latitudes of both martian hemispheres. Ice concentrations are estimated to range from 70 per cent at 60 degrees latitude to 100 per cent near the poles, possibly overlain by a few centimetres of ice-free material in most places. This result is supported by morphological evidence of metres-thick layered deposits that are rich in water-ice and periglacial-like features found only at high latitudes. Diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution, but such a degree of concentration is difficult to accommodate with such processes. Alternatively, there are suggestions that ice-rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity, but these results have been difficult to reproduce with other models. Here we propose instead that, during periods of low obliquity (less than 25 degrees), high-latitude ice deposits form in both hemispheres by direct deposition of ice, as a result of sublimation from an equatorial ice reservoir that formed earlier, during a prolonged high-obliquity excursion. Using the ice accumulation rates estimated from global climate model simulations we show that, over the past ten million years, large variations of Mars' obliquity have allowed the formation of such metres-thick, sedimentary layered deposits in high latitude and polar regions.

  2. Interaction of nitrogen bases with iron-porphyrin nitrito complexes Fe(Por)(ONO) in sublimed solids.

    PubMed

    Kurtikyan, Tigran S; Hovhannisyan, Astghik A; Gulyan, Gurgen M; Ford, Peter C

    2007-08-20

    The reactions of the nitrogen Lewis bases (B) 1-methylimidazole (1-MeIm), pyridine (Py), and NH3 as gases with sublimed layers containing the 5-coordinate nitrito iron(III)-porphyrinato complexes Fe(Por)(eta1-ONO) (1) are described (Por = meso-tetraphenyl-porphyrinato or meso-tetra-p-tolyl-porphyrinato dianions). In situ FTIR and optical spectra are used to characterize the formation of the 6-coordinate nitro complexes formed by the reaction of 1 with B = 1-MeIm, Py, or NH3. These represent the first examples of 6-coordinate amino-nitro complexes with sterically unprotected iron-porphyrins. The interaction of ammonia with Fe(Por)(ONO) at 140 K initially led to the nitrito species Fe(Por)(NH3)(eta1-ONO), and this species isomerized to the nitro complexes Fe(Por)(NH3)(eta1-NO2) upon warming to 180 K. When the latter were warmed to room temperature under intense pumping, the initial nitrito complexes Fe(Por)(eta1-ONO) were restored. Assignments of vibrational frequencies for the coordinated nitro group in 6-coordinate iron-porphyrin complexes are given and confirmed using 15N-labeled nitrogen dioxide to identify characteristic infrared bands. For M(Por)(B)(NO2) complexes (M = Fe or Co), an inverse correlation between the net charge transfer from the axial ligand B to the nitro group and the value of Deltanu = nua(NO2) - nus(NO2) is proposed. These observations are discussed in the context of growing interest in potential physiological roles of nitrite ion reactions with ferro- and ferri-heme proteins.

  3. Deep analysis of Raman spectra of ZnO:Mo and ZnO:In sprayed thin films along with LO and TA+LO bands investigation

    NASA Astrophysics Data System (ADS)

    Souissi, A.; Amlouk, M.; Khemakhem, H.; Guermazi, S.

    2016-04-01

    ZnO and Mo, In doped ZnO thin films with the molar ratios (Mo/Zn) and (In/Zn) were dosed at 1%, 2% and 3%, respectively. These films were deposited on amorphous SiO2 substrate at 460 °C by the spray-pyrolysis process. A useful and concise reminder of the spatial resolutions of Raman spectroscopy was presented. The vibrational responses of these films at high doping exhibited strong fluctuations that were resolved by successive digital processing, choice of the optimal profile of the baseline, suppression of fluorescence and/or photoluminescence, and noise reduction. These treated spectra have allowed to identify possible multi-modes in highly doped studied samples and revealed the presence of LO and TA+LO broad bands, whose second was at cascade and could be explored in optoelectronic and sensitive systems.

  4. Fate of outflow channel effluents in the northern lowlands of Mars: The Vastitas Borealis Formation as a sublimation residue from frozen ponded bodies of water

    NASA Astrophysics Data System (ADS)

    Kreslavsky, Mikhail A.; Head, James W.

    2002-12-01

    We analyze the fate of the Hesperian-aged outflow channel effluents emplaced into the northern lowlands of Mars. We have modeled the evolution of these effluents under the assumption that they were emplaced under a range of atmospheric conditions comparable to those of today and thought to have prevailed in the Hesperian. Under these conditions we find that the evolution of the sediment-loaded water after it left the channels includes three phases. Phase 1: Emplacement and intensive cooling: Violent emplacement of water followed by a short period of intensive evaporation from the surface and near-surface layer, and intensive convection. During this phase the water maintained and redistributed its large suspended sediment load. Water vapor strongly influenced the climate, at least for a geologically short time. When the temperature of the water reached the temperature of the maximum density or the freezing point, boiling and intensive convection ceased and the water deposited the sediments. Phase 2: Freezing solid: Geologically rapid freezing of the water body accompanied by weak convective water movement occurred over a period of the order of ~104 years. Phase 3: Sublimation and loss: This period involved sublimation of the ice and lasted longer than the freezing phase. The rate and latitudinal dependence of the sublimation, as well as the location of water vapor condensation, crucially depend on the planetary obliquity, climate, and sedimentary veneering of the ice. Phase 3 would have been very short geologically (~105-106 years) if an insulating sedimentary layer did not build up rapidly. If such an insulating layer did form rapidly, sublimation could cease and residual ice hundreds of meters thick could remain below the surface today. The northern lowlands of Mars are largely covered by the Late Hesperian-aged Vastitas Borealis Formation (VBF), which has sharp boundaries clearly seen in the map of kilometer-scale roughness, and a distinctive kilometer

  5. THE DUST SUBLIMATION RADIUS AS AN OUTER ENVELOPE TO THE BULK OF THE NARROW Fe Kα LINE EMISSION IN TYPE 1 AGNs

    SciTech Connect

    Gandhi, Poshak; Hönig, Sebastian F.; Kishimoto, Makoto

    2015-10-20

    The Fe Kα emission line is the most ubiquitous feature in the X-ray spectra of active galactic nuclei (AGNs), but the origin of its narrow core remains uncertain. Here, we investigate the connection between the sizes of the Fe Kα core emission regions and the measured sizes of the dusty tori in 13 local Type 1 AGNs. The observed Fe Kα emission radii (R{sub Fe}) are determined from spectrally resolved line widths in X-ray grating spectra, and the dust sublimation radii (R{sub dust}) are measured either from optical/near-infrared (NIR) reverberation time lags or from resolved NIR interferometric data. This direct comparison shows, on an object-by-object basis, that the dust sublimation radius forms an outer envelope to the bulk of the Fe Kα emission. R{sub Fe} matches R{sub dust} well in the AGNs, with the best constrained line widths currently. In a significant fraction of objects without a clear narrow line core, R{sub Fe} is similar to, or smaller than, the radius of the optical broad line region. These facts place important constraints on the torus geometries for our sample. Extended tori in which the solid angle of fluorescing gas peaks at well beyond the dust sublimation radius can be ruled out. We also test for luminosity scalings of R{sub Fe}, finding that the Eddington ratio is not a prime driver in determining the line location in our sample. We also discuss in detail potential caveats of data analysis and instrumental limitations, simplistic line modeling, uncertain black hole masses, and sample selection, showing that none of these is likely to bias our core result. The calorimeter on board Astro-H will soon vastly increase the parameter space over which line measurements can be made, overcoming many of these limitations.

  6. Sublimation of icy aggregates in the coma of comet 67P/Churyumov-Gerasimenko detected with the OSIRIS cameras on board Rosetta

    NASA Astrophysics Data System (ADS)

    Gicquel, A.; Vincent, J.-B.; Agarwal, J.; A'Hearn, M. F.; Bertini, I.; Bodewits, D.; Sierks, H.; Lin, Z.-Y.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; Barucci, M. A.; Bertaux, J.-L.; Besse, S.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; Deller, J.; De Cecco, M.; Frattin, E.; El-Maarry, M. R.; Fornasier, S.; Fulle, M.; Groussin, O.; Gutiérrez, P. J.; Gutiérrez-Marquez, P.; Güttler, C.; Höfner, S.; Hofmann, M.; Hu, X.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Knollenberg, J.; Kovacs, G.; Kramm, J.-R.; Kührt, E.; Küppers, M.; Lara, L. M.; Lazzarin, M.; Moreno, J. J. Lopez; Lowry, S.; Marzari, F.; Masoumzadeh, N.; Massironi, M.; Moreno, F.; Mottola, S.; Naletto, G.; Oklay, N.; Pajola, M.; Pommerol, A.; Preusker, F.; Scholten, F.; Shi, X.; Thomas, N.; Toth, I.; Tubiana, C.

    2016-11-01

    Beginning in 2014 March, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analysed the dust monitoring observations shortly after the southern vernal equinox on 2015 May 30 and 31 with the WAC at the heliocentric distance Rh = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness as a function of the distance of the jet is much steeper than the background coma, which is a first indication of sublimation. We adapted a model of sublimation of icy aggregates and studied the effect as a function of the physical properties of the aggregates (composition and size). The major finding of this paper was that through the sublimation of the aggregates of dirty grains (radius a between 5 and 50 μm) we were able to completely reproduce the radial brightness profile of a jet beyond 4 km from the nucleus. To reproduce the data, we needed to inject a number of aggregates between 8.5 × 1013 and 8.5 × 1010 for a = 5 and 50 μm, respectively, or an initial mass of H2O ice around 22 kg.

  7. Structure-function elucidation of a new α-conotoxin, Lo1a, from Conus longurionis.

    PubMed

    Lebbe, Eline K M; Peigneur, Steve; Maiti, Mohitosh; Devi, Prabha; Ravichandran, Samuthirapandian; Lescrinier, Eveline; Ulens, Chris; Waelkens, Etienne; D'Souza, Lisette; Herdewijn, Piet; Tytgat, Jan

    2014-04-04

    α-Conotoxins are peptide toxins found in the venom of marine cone snails and potent antagonists of various subtypes of nicotinic acetylcholine receptors (nAChRs). nAChRs are cholinergic receptors forming ligand-gated ion channels in the plasma membranes of certain neurons and the neuromuscular junction. Because nAChRs have an important role in regulating transmitter release, cell excitability, and neuronal integration, nAChR dysfunctions have been implicated in a variety of severe pathologies such as epilepsy, myasthenic syndromes, schizophrenia, Parkinson disease, and Alzheimer disease. To expand the knowledge concerning cone snail toxins, we examined the venom of Conus longurionis. We isolated an 18-amino acid peptide named α-conotoxin Lo1a, which is active on nAChRs. To the best of our knowledge, this is the first characterization of a conotoxin from this species. The peptide was characterized by electrophysiological screening against several types of cloned nAChRs expressed in Xenopus laevis oocytes. The three-dimensional solution structure of the α-conotoxin Lo1a was determined by NMR spectroscopy. Lo1a, a member of the α4/7 family, blocks the response to acetylcholine in oocytes expressing α7 nAChRs with an IC50 of 3.24 ± 0.7 μM. Furthermore, Lo1a shows a high selectivity for neuronal versus muscle subtype nAChRs. Because Lo1a has an unusual C terminus, we designed two mutants, Lo1a-ΔD and Lo1a-RRR, to investigate the influence of the C-terminal residue. Lo1a-ΔD has a C-terminal Asp deletion, whereas in Lo1a-RRR, a triple-Arg tail replaces the Asp. They blocked the neuronal nAChR α7 with a lower IC50 value, but remarkably, both adopted affinity for the muscle subtype α1β1δε.

  8. Structure-Function Elucidation of a New α-Conotoxin, Lo1a, from Conus longurionis

    PubMed Central

    Lebbe, Eline K. M.; Peigneur, Steve; Maiti, Mohitosh; Devi, Prabha; Ravichandran, Samuthirapandian; Lescrinier, Eveline; Ulens, Chris; Waelkens, Etienne; D'Souza, Lisette; Herdewijn, Piet; Tytgat, Jan

    2014-01-01

    α-Conotoxins are peptide toxins found in the venom of marine cone snails and potent antagonists of various subtypes of nicotinic acetylcholine receptors (nAChRs). nAChRs are cholinergic receptors forming ligand-gated ion channels in the plasma membranes of certain neurons and the neuromuscular junction. Because nAChRs have an important role in regulating transmitter release, cell excitability, and neuronal integration, nAChR dysfunctions have been implicated in a variety of severe pathologies such as epilepsy, myasthenic syndromes, schizophrenia, Parkinson disease, and Alzheimer disease. To expand the knowledge concerning cone snail toxins, we examined the venom of Conus longurionis. We isolated an 18-amino acid peptide named α-conotoxin Lo1a, which is active on nAChRs. To the best of our knowledge, this is the first characterization of a conotoxin from this species. The peptide was characterized by electrophysiological screening against several types of cloned nAChRs expressed in Xenopus laevis oocytes. The three-dimensional solution structure of the α-conotoxin Lo1a was determined by NMR spectroscopy. Lo1a, a member of the α4/7 family, blocks the response to acetylcholine in oocytes expressing α7 nAChRs with an IC50 of 3.24 ± 0.7 μm. Furthermore, Lo1a shows a high selectivity for neuronal versus muscle subtype nAChRs. Because Lo1a has an unusual C terminus, we designed two mutants, Lo1a-ΔD and Lo1a-RRR, to investigate the influence of the C-terminal residue. Lo1a-ΔD has a C-terminal Asp deletion, whereas in Lo1a-RRR, a triple-Arg tail replaces the Asp. They blocked the neuronal nAChR α7 with a lower IC50 value, but remarkably, both adopted affinity for the muscle subtype α1β1δϵ. PMID:24567324

  9. First-order feasibility analysis of a space suit radiator concept based on estimation of water mass sublimation using Apollo mission data

    NASA Astrophysics Data System (ADS)

    Metts, Jonathan G.; Klaus, David M.

    2012-01-01

    Thermal control of a space suit during extravehicular activity (EVA) is typically accomplished by sublimating water to provide system cooling. Spacecraft, on the other hand, primarily rely on radiators to dissipate heat. Integrating a radiator into a space suit has been proposed as an alternative design that does not require mass consumption for heat transfer. While providing cooling without water loss offers potential benefits for EVA application, it is not currently practical to rely on a directional, fixed-emissivity radiator to maintain thermal equilibrium of a spacesuit where the radiator orientation, environmental temperature, and crew member metabolic heat load fluctuate unpredictably. One approach that might make this feasible, however, is the use of electrochromic devices that are capable of infrared emissivity modulation and can be actively controlled across the entire suit surface to regulate net heat flux for the system. Integrating these devices onto the irregular, compliant space suit material requires that they be fabricated on a flexible substrate, such as Kapton film. An initial assessment of whether or not this candidate technology presents a feasible design option was conducted by first characterizing the mass of water loss from sublimation that could theoretically be saved if an electrochromic suit radiator was employed for thermal control. This is particularly important for lunar surface exploration, where the expense of transporting water from Earth is excessive, but the technology is potentially beneficial for other space missions as well. In order to define a baseline for this analysis by comparison to actual data, historical documents from the Apollo missions were mined for comprehensive, detailed metabolic data from each lunar surface outing, and related data from NASA's more recent "Advanced Lunar Walkback" tests were also analyzed. This metabolic database was then used to validate estimates for sublimator water consumption during surface

  10. Optically sectioned in vivo imaging with speckle illumination HiLo microscopy

    NASA Astrophysics Data System (ADS)

    Lim, Daryl; Ford, Tim N.; Chu, Kengyeh K.; Mertz, Jerome

    2011-01-01

    We present a simple wide-field imaging technique, called HiLo microscopy, that is capable of producing optically sectioned images in real time, comparable in quality to confocal laser scanning microscopy. The technique is based on the fusion of two raw images, one acquired with speckle illumination and another with standard uniform illumination. The fusion can be numerically adjusted, using a single parameter, to produce optically sectioned images of varying thicknesses with the same raw data. Direct comparison between our HiLo microscope and a commercial confocal laser scanning microscope is made on the basis of sectioning strength and imaging performance. Specifically, we show that HiLo and confocal 3-D imaging of a GFP-labeled mouse brain hippocampus are comparable in quality. Moreover, HiLo microscopy is capable of faster, near video rate imaging over larger fields of view than attainable with standard confocal microscopes. The goal of this paper is to advertise the simplicity, robustness, and versatility of HiLo microscopy, which we highlight with in vivo imaging of common model organisms including planaria, C. elegans, and zebrafish.

  11. G-LoSA for Prediction of Protein-Ligand Binding Sites and Structures.

    PubMed

    Lee, Hui Sun; Im, Wonpil

    2017-01-01

    Recent advances in high-throughput structure determination and computational protein structure prediction have significantly enriched the universe of protein structure. However, there is still a large gap between the number of available protein structures and that of proteins with annotated function in high accuracy. Computational structure-based protein function prediction has emerged to reduce this knowledge gap. The identification of a ligand binding site and its structure is critical to the determination of a protein's molecular function. We present a computational methodology for predicting small molecule ligand binding site and ligand structure using G-LoSA, our protein local structure alignment and similarity measurement tool. All the computational procedures described here can be easily implemented using G-LoSA Toolkit, a package of standalone software programs and preprocessed PDB structure libraries. G-LoSA and G-LoSA Toolkit are freely available to academic users at http://compbio.lehigh.edu/GLoSA . We also illustrate a case study to show the potential of our template-based approach harnessing G-LoSA for protein function prediction.

  12. An Orientation Dependent Size Illusion Is Underpinned by Processing in the Extrastriate Visual Area, LO1

    PubMed Central

    Mikellidou, Kyriaki; Gouws, André D.; Clawson, Hannah; Thompson, Peter; Morland, Antony B.

    2016-01-01

    We use the simple, but prominent Helmholtz’s squares illusion in which a vertically striped square appears wider than a horizontally striped square of identical physical dimensions to determine whether functional magnetic resonance imaging (fMRI) BOLD responses in V1 underpin illusions of size. We report that these simple stimuli which differ in only one parameter, orientation, to which V1 neurons are highly selective elicited activity in V1 that followed their physical, not perceived size. To further probe the role of V1 in the illusion and investigate plausible extrastriate visual areas responsible for eliciting the Helmholtz squares illusion, we performed a follow-up transcranial magnetic stimulation (TMS) experiment in which we compared perceptual judgments about the aspect ratio of perceptually identical Helmholtz squares when no TMS was applied against selective stimulation of V1, LO1, or LO2. In agreement with fMRI results, we report that TMS of area V1 does not compromise the strength of the illusion. Only stimulation of area LO1, and not LO2, compromised significantly the strength of the illusion, consistent with previous research that LO1 plays a role in the processing of orientation information. These results demonstrate the involvement of a specific extrastriate area in an illusory percept of size. PMID:27733896

  13. Gas-phase enthalpies of formation and enthalpies of sublimation of amino acids based on isodesmic reaction calculations.

    PubMed

    Dorofeeva, Olga V; Ryzhova, Oxana N

    2014-05-15

    Accurate gas-phase enthalpies of formation (ΔfH298°) of 20 common α-amino acids, seven uncommon amino acids, and three small peptides were calculated by combining G4 theory calculations with an isodesmic reaction approach. The internal consistency over a set of ΔfH298°(g) values was achieved by sequential adjustment of their values through the isodesmic reactions. Four amino acids, alanine, β-alanine, sarcosine, and glycine, with reliable internally self-consistent experimental data, were chosen as the key reference compounds. These amino acids together with about 100 compounds with reliable experimental data (their accuracy was supported by G4 calculations) were used to estimate the enthalpies of formation of remaining amino acids. All of the amino acids with the previously established enthalpies of formation were later used as the reference species in the isodesmic reactions for the other amino acids. A systematic comparison was made of 14 experimentally determined enthalpies of formation with the results of calculations. The experimental enthalpies of formation for 10 amino acids were reproduced with good accuracy, but the experimental and calculated values for 4 compounds differed by 11–21 kJ/mol. For these species, the theoretical ΔfH298°(g) values were suggested as more reliable than the experimental values. On the basis of theoretical results, the recommended values for the gas-phase enthalpies of formation were also provided for amino acids for which the experimental ΔfH298°(g) were not available. The enthalpies of sublimation were evaluated for all compounds by taking into account the literature data on the solid-phase enthalpies of formation and the ΔfH298°(g) values recommended in our work. A special attention was paid to the accurate prediction of enthalpies of formation of amino acids from the atomization reactions. The problems associated with conformational flexibility of these compounds and harmonic treatment of low frequency torsional

  14. A Study of LoRa: Long Range & Low Power Networks for the Internet of Things

    PubMed Central

    Augustin, Aloÿs; Yi, Jiazi; Clausen, Thomas; Townsley, William Mark

    2016-01-01

    LoRa is a long-range, low-power, low-bitrate, wireless telecommunications system, promoted as an infrastructure solution for the Internet of Things: end-devices use LoRa across a single wireless hop to communicate to gateway(s), connected to the Internet and which act as transparent bridges and relay messages between these end-devices and a central network server. This paper provides an overview of LoRa and an in-depth analysis of its functional components. The physical and data link layer performance is evaluated by field tests and simulations. Based on the analysis and evaluations, some possible solutions for performance enhancements are proposed. PMID:27618064

  15. Implementation and Evaluation of the Enhanced Header Compression (IPHC) for 6LoWPAN

    NASA Astrophysics Data System (ADS)

    Ludovici, Alessandro; Calveras, Anna; Catalan, Marisa; Gómez, Carles; Paradells, Josep

    6LoWPAN defines how to carry IPv6 packets over IEEE 802.15.4 low power wireless or sensor networks. Limited bandwidth, memory and energy resources require a careful application of IPv6 in a LoWPAN. The IEEE 802.15.4 standard defines a maximum frame size of 127 bytes that decreases to 102 bytes considering the header overhead. A further reduction is due to the security, network and transport protocols header overhead that, in case of IPv6 and UDP, leave only 33 bytes for application data. A compression algorithm is necessary in order to reduce the overhead and save space in data payload. This paper describes and compares the proposed IPv6 header compression mechanisms for 6LoWPAN environments.

  16. Temperature dependence of the LO phonon sidebands in free exciton emission of GaN

    NASA Astrophysics Data System (ADS)

    Xu, S. J.; Li, G. Q.; Xiong, S.-J.; Che, C. M.

    2006-04-01

    Temperature-dependent radiative recombination of free excitons involving one or two LO phonons in GaN is investigated in detail. It is found that both phonon sidebands possess asymmetric lineshapes and their energy spacings from the zero-phonon line strongly deviate from the characteristic energy of LO phonons as the temperature increases. Furthermore, the deviation rates of one- and two-phonon sidebands are significantly different. Segall-Mahan [Phys. Rev. 171, 935 (1968)] theory, taking the exciton-photon and exciton-phonon interactions into account, is employed to calculate the sidebands of one or two LO phonons for free excitons in a wide temperature range. Excellent agreement between the theory and experiment is achieved by using only one adjustable parameter, which leads to determination of the effective mass of heavy holes (~0.5m0).

  17. Improving high resolution retinal image quality using speckle illumination HiLo imaging

    PubMed Central

    Zhou, Xiaolin; Bedggood, Phillip; Metha, Andrew

    2014-01-01

    Retinal image quality from flood illumination adaptive optics (AO) ophthalmoscopes is adversely affected by out-of-focus light scatter due to the lack of confocality. This effect is more pronounced in small eyes, such as that of rodents, because the requisite high optical power confers a large dioptric thickness to the retina. A recently-developed structured illumination microscopy (SIM) technique called HiLo imaging has been shown to reduce the effect of out-of-focus light scatter in flood illumination microscopes and produce pseudo-confocal images with significantly improved image quality. In this work, we adopted the HiLo technique to a flood AO ophthalmoscope and performed AO imaging in both (physical) model and live rat eyes. The improvement in image quality from HiLo imaging is shown both qualitatively and quantitatively by using spatial spectral analysis. PMID:25136486

  18. A Study of LoRa: Long Range & Low Power Networks for the Internet of Things.

    PubMed

    Augustin, Aloÿs; Yi, Jiazi; Clausen, Thomas; Townsley, William Mark

    2016-09-09

    LoRa is a long-range, low-power, low-bitrate, wireless telecommunications system, promoted as an infrastructure solution for the Internet of Things: end-devices use LoRa across a single wireless hop to communicate to gateway(s), connected to the Internet and which act as transparent bridges and relay messages between these end-devices and a central network server. This paper provides an overview of LoRa and an in-depth analysis of its functional components. The physical and data link layer performance is evaluated by field tests and simulations. Based on the analysis and evaluations, some possible solutions for performance enhancements are proposed.

  19. Finite-Range Separable Pairing Interaction Within New N3LO DFT Approach

    NASA Astrophysics Data System (ADS)

    Veselý, P.; Dobaczewski, J.; Michel, N.; Toivanen, J.

    2011-10-01

    For over four decades, the Skyrme functional within various parametrizations has been used to calculate nuclear properties. In the last few years there was a number of attempts to improve its performance and introduce generalized forms. In particular, the most general phenomenologi-cal quasi-local energy density functional, which contains all combinations of density, spin-density, and their derivatives up to the sixth order (N3LO), was proposed in reference [1]. Since in the phe-nomenological functional approaches the particle-particle (pp) interaction channel is treated independently from the particle-hole (ph) channel, there remains a question of what pairing interaction is suitable to use within the N3LO energy functional. In our study, we use the separable, finite-range, translationally invariant form given in [2], which we generalize to the arbitrary angular momentum channel. We discuss the application of this pairing interaction within the N3LO energy functional.

  20. A close-space sublimation driven pathway for the manipulation of substrate-supported micro- and nanostructures

    NASA Astrophysics Data System (ADS)

    Sundar, Aarthi

    gold beneath the grid selectively attaches to it due to the surface energy gradient which drives gold from the low surface energy oxide surface to the higher surface energy nickel mesh. With this process being confined to areas adjacent to and in contact with the grid surface the film ruptures at well-defined locations to form isolated islands of gold and subsequently, a periodic array of microstructures. The process can be carried out on substrates of different crystallographic orientations leading to nanostructures which are formed epitaxially and have orientations based on underlying substrate orientations. The process can be extended by placing a metallic foil of Pt or Ni over preformed templates, in which case a reduction in the size of the initial structures is observed. Placing a foil on structures with random placement and a wide size distribution results, not only in a size reduction, but also a narrowed size distribution. Additive processes are carried out by using materials which possess high vapor pressures much below the sublimation temperature of the template materials. In this case a germanium substrate was used as a source of germanium adatoms while gold or silver nanostructures were used as heterogeneous nucleation sites. At elevated temperatures the adatoms collect in sufficient quantities to transform each site into a liquid alloy which, upon cooling, phase separates into elemental components sharing a common interface and, hence, resulting in the formation of heterodimers and hollowed metal nanocrescents upon etching away the Ge. A process which combined aspects of the additive and subtractive process was carried out by using a metallic foil with a high vapor pressure and higher surface energy than the substrate surface (in this case Pd foil). This process resulted in the initial preformed gold templates being annihilated and replaced by nanostructures of palladium, thereby altering their chemical composition. The assembly process relies on the

  1. Soft-gluon corrections for t W production at N3LO

    NASA Astrophysics Data System (ADS)

    Kidonakis, Nikolaos

    2017-08-01

    I present approximate results that include third-order soft-gluon corrections for the associated production of a single top quark with a W boson. The calculation uses expressions from soft-gluon resummation at next-to-next-to-leading-logarithm (NNLL) accuracy. From the NNLL resummed cross section, I derive approximate next-to-next-to-next-to-leading-order (a N3LO ) cross sections for the process b g →t W- at LHC and Tevatron energies. The a N3LO top-quark transverse-momentum and rapidity distributions in t W production are also presented.

  2. The Thermodynamic Characteristics of Sublimation of Aluminum and Indium Complexes with Tetraphenylporphin according to the High-Temperature Mass Spectrometry Data

    NASA Astrophysics Data System (ADS)

    Stuzhina, O. V.; Lomova, T. N.; Pelipets, O. V.; Girichev, G. V.

    2008-02-01

    The thermodynamic characteristics of vaporization of meso-tetraphenylporphin complexes (X)MTPP (M = Al, In; X = Cl, OH; TPP is the meso-tetraphenylporphin H2TPP dianion) were studied by the Knudsen effusion method with mass spectrometric control of vapor composition. Chloride complexes sublimed as monomers over the temperature range 480-590 K. The hydroxo complex of aluminotetraphenylporphin was transferred into the gas phase in the form of the μ-oxo dimer. The temperature dependences of saturated vapor pressure were used to determine the enthalpies of sublimation of metalloporphyrins, which were found to be 203 ± 3.5 and 207 ± 6 kJ/mol for the chloride complexes of In and Al, respectively, and 206 ± 8 and 406 ± 40 kJ/mol for the monomer and μ-oxo dimer of (hydroxy)aluminum(III)porphyrin, respectively. The thermodynamic parameters of vaporization and the melting point of (OH)AlTPP were also determined (ΔvapH° = 116 ± 6 kJ/mol, ΔapS° = 72 ± 11 J/(mol K), and Tm = 579 K). Composition-thermodynamic property correlations were analyzed for metalloporphyrins.

  3. Numerical Investigation of LO2 and LCH4 Storage Tanks on the Lunar Surface

    NASA Technical Reports Server (NTRS)

    Moder, Jeff; Barsi, Stephen; Kassemi, Mohammad

    2008-01-01

    Currently NASA is developing technologies to enable human exploration of the lunar surface for duration of up to 210 days. While trade studies are still underway, a cryogenic ascent stage using liquid oxygen (LO2) and liquid methane (LCH4) is being considered for the Altair lunar lander. For a representative Altair cryogenic ascent stage, we present a detailed storage analysis of the LO2 and LCH4 propellant tanks on the lunar surface for durations of up to 210 days. Both the LO2 and LCH4 propellant tanks are assumed to be pressurized with gaseous helium at launch. A two-phase lumped-vapor computational fluid dynamics model has been developed to account for the presence of a noncondensable gas in the ullage. The CFD model is used to simulate the initial pressure response of the propellant tanks while they are subjected to representative heat leak rates on the lunar surface. Once a near stationary state is achieved within the liquid phase, multizone model is used to extrapolate the solution farther in time. For fixed propellant mass and tank size, the long-term pressure response for different helium mass fractions in both the LO2 and LCH4 tanks is examined.

  4. Implementation Of Secure 6LoWPAN Communications For Tactical Wireless Sensor Networks

    DTIC Science & Technology

    2016-09-01

    TERMS Wireless Sensor Networks (WSN), Sensor Nodes, 6LoWPAN, IEEE 802.15.4, energy constrained node, centralized routing, keying mechanism, network...attacks, denial of service (DOS), man-in-the-middle (MITM), spoofing 15. NUMBER OF PAGES 255 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT...45  6.  New Events ...................................................................................46  7.  Check For Energy Use

  5. Structural Validity of the Professional Development Profile of the LoTi Digital-Age Survey

    ERIC Educational Resources Information Center

    Mehta, Vandhana; Hull, Darrell M.

    2013-01-01

    The present study was used to examine the structural construct validity of the Professional Development Profile of the LoTi Digital-Age Survey, a measure of teacher instructional practices with technology in the classroom. Teacher responses ("N" = 2,840) from across the United States were used to assess factor structure of the instrument…

  6. Structural Validity of the Professional Development Profile of the LoTi Digital-Age Survey

    ERIC Educational Resources Information Center

    Mehta, Vandhana; Hull, Darrell M.

    2013-01-01

    The present study was used to examine the structural construct validity of the Professional Development Profile of the LoTi Digital-Age Survey, a measure of teacher instructional practices with technology in the classroom. Teacher responses ("N" = 2,840) from across the United States were used to assess factor structure of the instrument…

  7. The Karhunen-Loève Transform for bioastronomy and SETI

    NASA Astrophysics Data System (ADS)

    Maccone, C.

    2006-02-01

    I present here a short description of the Karhunen-Loève Transform (KLT) used to detect very weak radio signals over narrow-band and wide-band extraterrestrial telecommunications out of the cosmic background noise. It appears that the KLT is more appropriate than the well known Fourier Transform (FT).

  8. A Low-Noise Terahertz SIS Mixer Incorporating a Waveguide Directional Coupler for LO Injection

    NASA Astrophysics Data System (ADS)

    Kojima, Takafumi; Kuroiwa, Kouichi; Uzawa, Yoshinori; Kroug, Matthias; Takeda, Masanori; Fujii, Yasunori; Kaneko, Keiko; Miyachi, Akihira; Wang, Zhen; Ogawa, Hideo

    2010-11-01

    We have developed a low-noise heterodyne waveguide Superconductor-Insulator-Superconductor (SIS) mixer with a novel local oscillator (LO) injection scheme for the Atacama Large Millimeter/submillimeter Array (ALMA) band 10, over the frequency range 0.78-0.95 THz. The SIS mixer uses radio frequency (RF) and LO receiving horns separately and a waveguide 10 dB LO coupler integrated in the mixer block. The insertion loss of the waveguide and coupling factor of the coupler were evaluated at terahertz frequencies at both room and cryogenic temperatures. The double-sideband (DSB) receiver noise temperatures were below 330 K (7.5 hf/ k B) at LO frequencies in the range 0.801-0.945 THz. The minimum temperature was 221 K at 0.873 THz over the intermediate frequency range of 4-12 GHz at an operating temperature of 4 K. This waveguide heterodyne SIS mixer exhibits great potential for practical applications, such as high-frequency receivers of the ALMA.

  9. CC2 oscillator strengths within the local framework for calculating excitation energies (LoFEx)

    NASA Astrophysics Data System (ADS)

    Baudin, Pablo; Kjærgaard, Thomas; Kristensen, Kasper

    2017-04-01

    In a recent work [P. Baudin and K. Kristensen, J. Chem. Phys. 144, 224106 (2016)], we introduced a local framework for calculating excitation energies (LoFEx), based on second-order approximated coupled cluster (CC2) linear-response theory. LoFEx is a black-box method in which a reduced excitation orbital space (XOS) is optimized to provide coupled cluster (CC) excitation energies at a reduced computational cost. In this article, we present an extension of the LoFEx algorithm to the calculation of CC2 oscillator strengths. Two different strategies are suggested, in which the size of the XOS is determined based on the excitation energy or the oscillator strength of the targeted transitions. The two strategies are applied to a set of medium-sized organic molecules in order to assess both the accuracy and the computational cost of the methods. The results show that CC2 excitation energies and oscillator strengths can be calculated at a reduced computational cost, provided that the targeted transitions are local compared to the size of the molecule. To illustrate the potential of LoFEx for large molecules, both strategies have been successfully applied to the lowest transition of the bivalirudin molecule (4255 basis functions) and compared with time-dependent density functional theory.

  10. A Simultaneous Discovery: The Case of Johannes Stark and Antonino Lo Surdo

    NASA Astrophysics Data System (ADS)

    Leone, Matteo; Paoletti, Alessandro; Robotti, Nadia

    2004-09-01

    In 1913 the German physicist Johannes Stark (1874 1957) and the Italian physicist Antonino Lo Surdo (1880 1949)discovered virtually simultaneously and independently that hydrogen spectral lines are split into components by an external electric field. Both of their discoveries ensued from studies on the same phenomenon, the Doppler effect in canal rays, but they arose in different theoretical contexts. Stark had been working within the context of the emerging quantum theory, following a research program aimed at studying the effect of an electric field on spectral lines. Lo Surdo had been working within the context of the classical theory, and his was an accidental discovery. Both discoveries, however, played important roles in the history of physics: Stark’s discovery contributed to the establishment of both the old and the new quantum theories; Lo Surdo’s discovery led Antonio Garbasso (1871 1933)to introduce research on the quantum theory into Italian physics. Ironically, soon after their discoveries, both Stark and Lo Surdo rejected developments in modern physics and allied themselves with the political and racial programs of Hitler and Mussolini.

  11. XYZ-like spectra from Laplace sum rule at N2LO in the chiral limit

    NASA Astrophysics Data System (ADS)

    Albuquerque, R.; Narison, S.; Fanomezana, F.; Rabemananjara, A.; Rabetiarivony, D.; Randriamanatrika, G.

    2016-12-01

    We present new compact integrated expressions of QCD spectral functions of heavy-light molecules and four-quark XY Z-like states at lowest order (LO) of perturbative (PT) QCD and up to d = 8 condensates of the Operator Product Expansion (OPE). Then, by including up to next-to-next leading order (N2LO) PT QCD corrections, which we have estimated by assuming the factorization of the four-quark spectral functions, we improve previous LO results from QCD spectral sum rules (QSSR), on the XY Z-like masses and decay constants which suffer from the ill-defined heavy quark mass. PT N3LO corrections are estimated using a geometric growth of the PT series and are included in the systematic errors. Our optimal results based on stability criteria are summarized in Tables 11-14 and compared, in Sec. 10, with experimental candidates and some LO QSSR results. We conclude that the masses of the XZ observed states are compatible with (almost) pure JPC = 1+±, 0++ molecule or/and four-quark states. The ones of the 1-±, 0-± molecule/four-quark states are about 1.5 GeV above the Yc,b mesons experimental candidates and hadronic thresholds. We also find that the couplings of these exotics to the associated interpolating currents are weaker than that of ordinary D,B mesons (fDD ≈ 10-3f D) and may behave numerically as 1/m¯b3/2 (respectively 1/m¯b) for the 1+, 0+ (respectively 1-, 0-) states which can stimulate further theoretical studies of these decay constants.

  12. Forwarding techniques for IP fragmented packets in a real 6LoWPAN network.

    PubMed

    Ludovici, Alessandro; Calveras, Anna; Casademont, Jordi

    2011-01-01

    Wireless Sensor Networks (WSNs) are attracting more and more interest since they offer a low-cost solution to the problem of providing a means to deploy large sensor networks in a number of application domains. We believe that a crucial aspect to facilitate WSN diffusion is to make them interoperable with external IP networks. This can be achieved by using the 6LoWPAN protocol stack. 6LoWPAN enables the transmission of IPv6 packets over WSNs based on the IEEE 802.15.4 standard. IPv6 packet size is considerably larger than that of IEEE 802.15.4 data frame. To overcome this problem, 6LoWPAN introduces an adaptation layer between the network and data link layers, allowing IPv6 packets to be adapted to the lower layer constraints. This adaptation layer provides fragmentation and header compression of IP packets. Furthermore, it also can be involved in routing decisions. Depending on which layer is responsible for routing decisions, 6LoWPAN divides routing in two categories: mesh under if the layer concerned is the adaptation layer and route over if it is the network layer. In this paper we analyze different routing solutions (route over, mesh under and enhanced route over) focusing on how they forward fragments. We evaluate their performance in terms of latency and energy consumption when transmitting IP fragmented packets. All the tests have been performed in a real 6LoWPAN implementation. After consideration of the main problems in forwarding of mesh frames in WSN, we propose and analyze a new alternative scheme based on mesh under, which we call controlled mesh under.

  13. Forwarding Techniques for IP Fragmented Packets in a Real 6LoWPAN Network

    PubMed Central

    Ludovici, Alessandro; Calveras, Anna; Casademont, Jordi

    2011-01-01

    Wireless Sensor Networks (WSNs) are attracting more and more interest since they offer a low-cost solution to the problem of providing a means to deploy large sensor networks in a number of application domains. We believe that a crucial aspect to facilitate WSN diffusion is to make them interoperable with external IP networks. This can be achieved by using the 6LoWPAN protocol stack. 6LoWPAN enables the transmission of IPv6 packets over WSNs based on the IEEE 802.15.4 standard. IPv6 packet size is considerably larger than that of IEEE 802.15.4 data frame. To overcome this problem, 6LoWPAN introduces an adaptation layer between the network and data link layers, allowing IPv6 packets to be adapted to the lower layer constraints. This adaptation layer provides fragmentation and header compression of IP packets. Furthermore, it also can be involved in routing decisions. Depending on which layer is responsible for routing decisions, 6LoWPAN divides routing in two categories: mesh under if the layer concerned is the adaptation layer and route over if it is the network layer. In this paper we analyze different routing solutions (route over, mesh under and enhanced route over) focusing on how they forward fragments. We evaluate their performance in terms of latency and energy consumption when transmitting IP fragmented packets. All the tests have been performed in a real 6LoWPAN implementation. After consideration of the main problems in forwarding of mesh frames in WSN, we propose and analyze a new alternative scheme based on mesh under, which we call controlled mesh under. PMID:22346615

  14. Otra perspectiva sobre lo que los ninos deben estar aprendiendo (Another Look at What Young Children Should Be Learning). ERIC Digest.

    ERIC Educational Resources Information Center

    Katz, Lilian G.

    This Spanish-language ERIC Digest addresses the question of what young children should be learning that will best serve their development and learning in the long term. Two major dimensions of development--normative and dynamic--are explored, and four categories of learning goals are discussed: (1) knowledge; (2) skills; (3) dispositions; and (4)…

  15. Lo Que los Padres y los Maestros Deberian Saber sobre la...Aceleraction (What Parents and Teachers Should Know about Academic Acceleration).

    ERIC Educational Resources Information Center

    Guenther, Alex

    Designed for Spanish-speaking educators and parents, this pamphlet discusses academic acceleration for gifted children. Major types of academic acceleration and their benefits are described. These include: (1) early admission to kindergarten that saves parents of gifted children the expenses of a year of preschool, allows children to be…

  16. Co-expression of COX-2 and 5-LO in primary glioblastoma is associated with poor prognosis.

    PubMed

    Wang, Xingfu; Chen, Yupeng; Zhang, Sheng; Zhang, Lifeng; Liu, Xueyong; Zhang, Li; Li, Xiaoling; Chen, Dayang

    2015-11-01

    Cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LO) are important factors in tumorigenesis and malignant progression; however, studies of their roles in glioblastoma have produced conflicting results. To define the frequencies of COX-2 and 5-LO expression and their correlation with clinicopathological features and prognosis, tumor tissues from 76 cases of newly diagnosed primary ordinary glioblastoma were examined for COX-2 and 5-LO expression by immunohistochemistry. The expression levels of COX-2 and 5-LO and the relationships between the co-expression of COX-2/5-LO and patient age and gender, edema index (EI), Karnofsky Performance Scale and overall survival (OS) were analyzed. COX-2 and 5-LO were expressed in 73.7 % (56/76) and 92.1 % (70/76) of the samples, respectively. Among the clinicopathological characteristics, only age (>60 years) exhibited a significant association with the high expression of COX-2. No statistically significant correlations were found in the 5-LO cohort. A significant positive correlation was revealed between the COX-2 and 5-LO scores (r = 0.374; p = 0.001). The elevated co-expression of COX-2 and 5-LO was observed primarily in the patients over the age of 60 years. Patients with a high expression of COX-2 had a significantly shorter OS (p < 0.01), whereas the immunoexpression of 5-LO was not associated with the OS of patients with glioblastoma. Survival analysis indicated that simultaneous high levels of COX-2 and 5-LO expression were significantly correlated with poor OS and, conversely, that a low/low expression pattern of these two proteins was significantly associated with better OS (p < 0.05). Moreover, the Cox multivariable proportional hazard model showed that a high expression of COX-2, high co-expression of COX-2 and 5-LO, and a high Ki-67 index were significant predictors of shorter OS in primary glioblastoma, independent of age, gender, EI, 5-LO expression and p53 status. The hazard ratios for OS were 2.347 (95 % CI 1

  17. A simple experimental arrangement for measuring the vapour pressures and sublimation enthalpies by the Knudsen effusion method: Application to DNA and RNA bases

    NASA Astrophysics Data System (ADS)

    de Barros, A. L. F.; Medina, A.; Zappa, F.; Pereira, J. M.; Bessa, E.; Martins, M. H. P.; Coelho, L. F. S.; Wolff, W.; de Castro Faria, N. V.

    2006-05-01

    We measured the vapour pressure of several DNA and RNA bases—uracil, adenine, guanine, thymine and cytosine—in the 300-450 K range. In each case the sample mass loss rate was measured as function of temperature with a simple setup consisting of a commercial film deposition system and a homemade oven. Afterwards vapour pressure values were extracted from these data using the Knudsen effusion method. Sublimation enthalpy values, obtained from vapour pressure data by applying the Clausius-Clapeyron equation, are in very good agreement with literature values. The results suggest that crystal-based film thickness monitors may be useful in on-line cross-section measurements, monitoring the gas target thickness. They also show the viability of using this oven for producing a biomolecular gas target.

  18. Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds and Ionic Liquids. Sublimation, Vaporization, and Fusion Enthalpies from 1880 to 2015. Part 2. C11-C192

    NASA Astrophysics Data System (ADS)

    Acree, William; Chickos, James S.

    2017-03-01

    The second part of this compendium concludes with a collection of phase change enthalpies of organic molecules inclusive of C11-C192 reported over the period 1880-2015. Also included are phase change enthalpies including fusion, vaporization, and sublimation enthalpies for organometallic, ionic liquids, and a few inorganic compounds. Paper I of this compendium, published separately, includes organic compounds from C1 to C10 and describes a group additivity method for evaluating solid, liquid, and gas phase heat capacities as well as temperature adjustments of phase changes. Paper II of this compendium also includes an updated version of a group additivity method for evaluating total phase change entropies which together with the fusion temperature can be useful in estimating total phase change enthalpies. Other uses include application in identifying potential substances that either form liquid or plastic crystals or exhibit additional phase changes such as undetected solid-solid transitions or behave anisotropically in the liquid state.

  19. The effect of substrate temperature on material properties and the device performance of close-spaced sublimation deposited CdTe/CdS devices

    NASA Astrophysics Data System (ADS)

    Li, X.; Albin, D.; Asher, S.; Moutinho, H.; Keyes, B.; Matson, R.; Hasoon, F.; Sheldon, P.

    1996-01-01

    High-efficiency polycrystalline CdS/CdTe solar cells have been fabricated using CdTe absorber layers deposited by close-spaced sublimation (CSS). CSS employs high substrate temperatures (Tsub) during film growth, which can promote the formation of larger grains and higher Voc's yielding better device performance. However, as Tsub increases beyond 610 °C, voids or pinholes begin to form in the CdTe layer. When the back contact is applied, these voids serve as shunt paths that effectively lower Voc. In this fashion, benefits associated with higher substrate temperatures are seriously compromised. Concurrent with voiding is the observation that higher temperatures promote interdiffusion at the CdS/CdTe interface such that the effective thickness of the CdS layer is reduced. Variations in processing that correct for these detrimental effects have led to a total-area device efficiency of 12%.

  20. Enhanced performance of CdS/CdTe thin-film devices through temperature profiling techniques applied to close-spaced sublimation deposition

    SciTech Connect

    Xiaonan Li; Sheldon, P.; Moutinho, H.; Matson, R.

    1996-05-01

    The authors describe a methodology developed and applied to the close-spaced sublimation technique for thin-film CdTe deposition. The developed temperature profiles consisted of three discrete temperature segments, which the authors called the nucleation, plugging, and annealing temperatures. They have demonstrated that these temperature profiles can be used to grow large-grain material, plug pinholes, and improve CdS/CdTe photovoltaic device performance by about 15%. The improved material and device properties have been obtained while maintaining deposition temperatures compatible with commercially available substrates. This temperature profiling technique can be easily applied to a manufacturing environment by adjusting the temperature as a function of substrate position instead of time.

  1. 100-LBF LO2/LCH4 - Reaction Control Engine Technology Development for Future Space Vehicles

    NASA Technical Reports Server (NTRS)

    Robinson, Philip J.; Veith, Eric M.; Hurlbert, Eric A.; Jimenez, Rafael; Smith, Timothy D.

    2008-01-01

    The National Aeronautics and Space Administration (NASA) has identified liquid oxygen (LO2)/liquid methane (LCH4) propulsion systems as promising options for some future space vehicles. NASA issued a contract to Aerojet to develop a 100-lbf (445 N) LO2/LCH4 Reaction Control Engine (RCE) aimed at reducing the risk of utilizing a cryogenic reaction control system (RCS) on a space vehicle. Aerojet utilized innovative design solutions to develop an RCE that can ignite reliably over a broad range of inlet temperatures, perform short minimum impulse bits (MIB) at small electrical pulse widths (EPW), and produce excellent specific impulse (Isp) across a range of engine mixture ratios (MR). These design innovations also provide a start transient with a benign MR, ensuring good thrust chamber compatibility and long life. In addition, this RCE can successfully operate at MRs associated with main engines, enabling the RCE to provide emergency backup propulsion to minimize vehicle propellant load and overall system mass.

  2. Ulysses Radio Occultation Observations of the lo Plasma Torus During the Jupiter Encounter.

    PubMed

    Bird, M K; Asmar, S W; Brenkle, J P; Edenhofer, P; Funke, O; Pätzold, M; Volland, H

    1992-09-11

    Radio signals from Ulysses were used to probe the lo plasma torus (IPT) shortly after the spacecraft's closest approach to Jupiter. The frequencies of the two downlinks at S-band (2.3 gigahertz) and X-band (8.4 gigahertz) were recorded, differenced, and integrated in order to derive the columnar electron density of the IPT. The measurements agree qualitatively with contemporary models of the IPT based on Voyager data, but significant differences are apparent as well. The overall level of the IPT electron density is approximately the same as the prediction, implying that the amount of gas (or plasma) injected from lo is similar to that observed during the Voyager era. On the other hand, the IPT seems to be less extended out of the centrifugal equator, implying a smaller plasma temperature than predicted.

  3. Sedimentation survey of Lago Loíza, Trujillo Alto, Puerto Rico, July 2009

    USGS Publications Warehouse

    Soler-López, Luis R.; Licha-Soler, N.A.

    2014-01-01

    Lago Loíza is a reservoir formed at the confluence of Río Gurabo and Río Grande de Loíza in the municipality of Trujillo Alto in central Puerto Rico, about 10 kilometers (km) north of the town of Caguas, about 9 km northwest of Gurabo, and about 3 km south of Trujillo Alto (fig. 1). The Carraizo Dam is owned and operated by the Puerto Rico Aqueduct and Sewer Authority (PRASA), and was constructed in 1953 as a water-supply reservoir for the San Juan Metropolitan area. The dam is a concrete gravity structure that is located in a shallow valley and has a gently sloping left abutment and steep right abutment. Non-overflow sections flank the spillway section. Waterways include an intake structure for the pumping station and power plant, sluiceways, a trash sluice, and a spillway. The reservoir was built to provide a storage capacity of 26.8 million cubic meters (Mm3) of water at the maximum pool elevation of 41.14 meters (m) above mean sea level (msl) for the Sergio Cuevas Filtration Plant that serves the San Juan metropolitan area. The reservoir has a drainage area of 538 square kilometers (km2) and receives an annual mean rainfall that ranges from 1,600 to 5,000 millimeters per year (mm/yr). The principal streams that drain into Lago Loíza are the Río Grande de Loíza, Río Gurabo, and Río Cañas. Two other rivers, the Río Bairoa and Río Cagüitas, discharge into the Río Grande de Loíza just before it enters the reservoir. The combined mean annual runoff of the Río Grande de Loíza and the Río Gurabo for the 1960–2009 period of record is 323 Mm3. Flow from these streams constitutes about 89 percent of the total mean annual inflow of 364 Mm3 to the reservoir (U.S. Geological Survey, 2009). Detailed information about Lago Loíza reservoir structures, historical sediment accumulation, and a dredge conducted in 1999 are available in Soler-López and Gómez-Gómez (2005). During July 8–15, 2009, the U.S. Geological Survey (USGS) Caribbean Water Science

  4. Neutron matter from chiral two- and three-nucleon calculations up to N3LO

    NASA Astrophysics Data System (ADS)

    Drischler, C.; Carbone, A.; Hebeler, K.; Schwenk, A.

    2016-11-01

    Neutron matter is an ideal laboratory for nuclear interactions derived from chiral effective field theory since all contributions are predicted up to next-to-next-to-next-to-leading order (N3LO ) in the chiral expansion. By making use of recent advances in the partial-wave decomposition of three-nucleon (3 N ) forces, we include for the first time N3LO 3 N interactions in many-body perturbation theory (MBPT) up to third order and in self-consistent Green's function theory (SCGF). Using these two complementary many-body frameworks we provide improved predictions for the equation of state of neutron matter at zero temperature and also analyze systematically the many-body convergence for different chiral EFT interactions. Furthermore, we present an extension of the normal-ordering framework to finite temperatures. These developments open the way to improved calculations of neutron-rich matter including estimates of theoretical uncertainties for astrophysical applications.

  5. Cucurbitane glycosides from unripe fruits of Lo Han Kuo (Siraitia grosvenori).

    PubMed

    Li, Dianpeng; Ikeda, Tsuyoshi; Matsuoka, Nanae; Nohara, Toshihiro; Zhang, Hourui; Sakamoto, Tatsunori; Nonaka, Gen-Ichiro

    2006-10-01

    From the unripe fruits of Lo Han Kuo (Siraitia grosvenori), a Chinese medicinal plant, two new cucurbitane triterpene glycosides, 20-hydroxy-11-oxomogroside IA(1) (1) and 11-oxomogroside IIE (2), were isolated along with five known cucurbitane glycosides, 11-oxomogroside IA(1) (3), mogroside IIE (4), mogroside III (5), mogroside IVA (6), and mogroside V (7), and two flavonoid glycosides, kaempferol 7-O-alpha-L-rhamnopyranoside (8) and kaempferol 3,7-di-O-alpha-L-rhamnopyranoside (9). Their structures were determined on the basis of detailed analyses of 1D, 2D-NMR spectroscopic methods and by comparing with literature values. This paper describes the first investigation of unripe bitter Lo Han Kuo fruits.

  6. LoC-SERS toward clinical application: quantification of antibiotics in human urine samples

    NASA Astrophysics Data System (ADS)

    Hidi, I. J.; Jahn, M.; Weber, K.; Pletz, M. W.; Bocklitz, T. W.; Cialla-May, D.; Popp, J.

    2017-02-01

    The determination of the concentration of xenobiotics in biological matrix followed by the change of the prescribing procedure plays a major role in the transition from general to personalized medicine. For this contribution, human urine samples collected from healthy volunteers and from patients having urinary tract infection were used as biological matrix to assess the potential and limitation of LoC-SERS to detected levofloxacin and nitroxoline. The determination of both antibiotics at clinically relevant concentrations, 1.38 mM +/- 0.68 mM for levofloxacin and 10-40 µM for nitroxoline, will be presented. For quantification purposes the standard addition method is combined with LoC-SERS.

  7. N3LO NN interaction adjusted to light nuclei in ab exitu approach

    DOE PAGES

    Shirokov, A. M.; Shin, I. J.; Kim, Y.; ...

    2016-08-09

    Here, we use phase-equivalent transformations to adjust off-shell properties of similarity renormalization group evolved chiral effective field theory NN interaction (Idaho N3LO) to fit selected binding energies and spectra of light nuclei in an ab exitu approach. Then, we test the transformed interaction on a set of additional observables in light nuclei to verify that it provides reasonable descriptions of these observables with an apparent reduced need for three- and many-nucleon interactions.

  8. Infra red active modes due to coupling of cyclotron excitation and LO phonons in polar semiconductor

    NASA Astrophysics Data System (ADS)

    Agrawal, Ratna; Dubey, Swati; Ghosh, S.

    2013-06-01

    Effects of free carrier concentration, external magnetic field and Callen effective charge on infra red active modes in a polar semiconductor have been analytically investigated using simple harmonic oscillator model. Callen effective charge considerably enhances reflectivity and shifts minima towards lower values of energy. Presence of magnetic field leads towards the coupling of collective cyclotron excitations with LO phonon giving rise to maximum reflectivity whereas cyclotron resonance absorption results into minimum reflectivity.

  9. Combination of Vandetanib, Radiotherapy, and Irinotecan in the LoVo Human Colorectal Cancer Xenograft Model

    SciTech Connect

    Wachsberger, Phyllis; Burd, Randy; Ryan, Anderson; Daskalakis, Constantine; Dicker, Adam P.

    2009-11-01

    Purpose: The tumor growth kinetics of the human LoVo colorectal xenograft model was assessed in response to vandetanib, an orally available receptor tyrosine kinase inhibitor, radiotherapy (RT), or irinotecan (CPT-11), as single therapies and in combination. Methods and Materials: LoVo cells were injected subcutaneously into the right hind limb (5x10{sup 6} cells in 100muL phosphate-buffered saline) of athymic NCR NUM mice and tumors were grown to a volume of 200-300 mm{sup 3} before treatment. Vandetanib was administered at 50 mg/kg daily orally for 14 days starting on Day 1. RT was given as three fractions (3x3 Gy) on Days 1, 2, and 3. CPT-11 was given at 15 mg/kg intraperitoneally on Days 1 and 3. Tumor volumes were measured on a daily basis and calculated by measuring tumor diameters with digital calipers in two orthogonal dimensions. Results: All three single treatments (vandetanib, CPT-11, and radiation) significantly slowed LoVo colorectal tumor growth. Vandetanib significantly increased the antitumor effects of CPT-11 and radiation when given in combination with either of these treatments. These treatment combinations resulted in a slow tumor growth rate during the 2 weeks of vandetanib administration. The triple combination of vandetanib, CPT-11, and radiation produced the most marked improvement in response as observed by measurable shrinkage of tumors during the first week of treatment. Conclusions: The tumor growth delay kinetics observed in this study of the LoVo colorectal model suggest concurrent and sustained post-sequencing of vandetanib with cytotoxic therapy may be beneficial in tumors of this type.

  10. Using deposition rate to increase the thermal and kinetic stability of vapor-deposited hole transport layer glasses via a simple sublimation apparatus.

    PubMed

    Kearns, Kenneth L; Krzyskowski, Paige; Devereaux, Zachary

    2017-05-28

    Deposition rate is known to affect the relative stability of vapor-deposited glasses; slower rates give more stable materials due to enhanced mobility at the free surface of the film. Here we show that the deposition rate can affect both the thermodynamic and kinetic stabilities of N,N(')-bis(3-methylphenyl)-N,N(')-diphenylbenzidine (TPD) and N,N(')-di-[(1-naphthyl)-N,N(')-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPD) glasses used as hole transport layers for organic light emitting diodes (OLEDs). A simple, low-vacuum glass sublimation apparatus and a high vacuum deposition chamber were used to deposit the glass. 50 μm thick films were deposited in the sublimation apparatus and characterized by differential scanning calorimetry while 75 nm thick films were prepared in the high vacuum chamber and studied by hot-stage spectroscopic ellipsometry (SE). The thermodynamic stability from both preparation chambers was consistent and showed that the fictive temperature (Tfictive) was more than 30 K lower than the conventional glass transition temperature (Tg) at the slowest deposition rates. The kinetic stability, measured as the onset temperature (Tonset) where the glass begins to transform into the supercooled liquid, was 16-17 K greater than Tg at the slowest rates. Tonset was systematically lower for the thin films characterized by SE and was attributed to the thickness dependent transformation of the glass into the supercooled liquid. These results show the first calorimetric characterization of the stability of glasses for OLED applications made by vapor deposition and the first direct comparison of deposition apparatuses as a function of the deposition rate. The ease of fabrication will create an opportunity for others to study the effect of deposition conditions on glass stability.

  11. Towards an understanding of the molecular mechanism of solvation of drug molecules: a thermodynamic approach by crystal lattice energy, sublimation, and solubility exemplified by paracetamol, acetanilide, and phenacetin.

    PubMed

    Perlovich, German L; Volkova, Tatyana V; Bauer-Brandl, Annette

    2006-10-01

    Temperature dependencies of saturated vapor pressure for the monoclinic modification of paracetamol (acetaminophen), acetanilide, and phenacetin (acetophenetidin) were measured and thermodynamic functions of sublimation calculated (paracetamol: DeltaGsub298=60.0 kJ/mol; DeltaHsub298=117.9+/-0.7 kJ/mol; DeltaSsub298=190+/-2 J/mol.K; acetanilide: DeltaGsub298=40.5 kJ/mol; DeltaHsub298=99.8+/-0.8 kJ/mol; DeltaSsub298=197+/-2 J/mol.K; phenacetin: DeltaGsub298=52.3 kJ/mol; DeltaHsub298=121.8+/-0.7 kJ/mol; DeltaSsub298=226+/-2 J/mol.K). Analysis of packing energies based on geometry optimization of molecules in the crystal lattices using diffraction data and the program Dmol3 was carried out. Parameters analyzed were: (a) energetic contribution of van der Waals forces and hydrogen bonding to the total packing energy; (b) contributions of fragments of the molecules to the packing energy. The fraction of hydrogen bond energy in the packing energy increases as: phenacetin (17.5%)sublimation and fusion. Activity coefficients of the drugs in n-octanol were calculated from cryoscopic data and by estimation of dilution enthalpy obtained from solubility and calorimetric experiments (for infinite dissolution). Solubility temperature dependencies in n-octanol and n-hexane were measured. The thermodynamic functions of solubility and solvation processes were deduced. Specific and nonspecific solvation terms were distinguished using the transfer from the "inert" n-hexane to the other solvents. The transfer of the molecules from water to n-octanol is enthalpy driven for paracetamol; for acetanilide and phenacetin, entropy driven.

  12. Using deposition rate to increase the thermal and kinetic stability of vapor-deposited hole transport layer glasses via a simple sublimation apparatus

    NASA Astrophysics Data System (ADS)

    Kearns, Kenneth L.; Krzyskowski, Paige; Devereaux, Zachary

    2017-05-01

    Deposition rate is known to affect the relative stability of vapor-deposited glasses; slower rates give more stable materials due to enhanced mobility at the free surface of the film. Here we show that the deposition rate can affect both the thermodynamic and kinetic stabilities of N ,N' -bis(3-methylphenyl)-N ,N' -diphenylbenzidine (TPD) and N ,N' -di-[(1-naphthyl)-N ,N' -diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPD) glasses used as hole transport layers for organic light emitting diodes (OLEDs). A simple, low-vacuum glass sublimation apparatus and a high vacuum deposition chamber were used to deposit the glass. 50 μm thick films were deposited in the sublimation apparatus and characterized by differential scanning calorimetry while 75 nm thick films were prepared in the high vacuum chamber and studied by hot-stage spectroscopic ellipsometry (SE). The thermodynamic stability from both preparation chambers was consistent and showed that the fictive temperature (Tfictive) was more than 30 K lower than the conventional glass transition temperature (Tg) at the slowest deposition rates. The kinetic stability, measured as the onset temperature (Tonset) where the glass begins to transform into the supercooled liquid, was 16-17 K greater than Tg at the slowest rates. Tonset was systematically lower for the thin films characterized by SE and was attributed to the thickness dependent transformation of the glass into the supercooled liquid. These results show the first calorimetric characterization of the stability of glasses for OLED applications made by vapor deposition and the first direct comparison of deposition apparatuses as a function of the deposition rate. The ease of fabrication will create an opportunity for others to study the effect of deposition conditions on glass stability.

  13. A network access control framework for 6LoWPAN networks.

    PubMed

    Oliveira, Luís M L; Rodrigues, Joel J P C; de Sousa, Amaro F; Lloret, Jaime

    2013-01-18

    Low power over wireless personal area networks (LoWPAN), in particular wireless sensor networks, represent an emerging technology with high potential to be employed in critical situations like security surveillance, battlefields, smart-grids, and in e-health applications. The support of security services in LoWPAN is considered a challenge. First, this type of networks is usually deployed in unattended environments, making them vulnerable to security attacks. Second, the constraints inherent to LoWPAN, such as scarce resources and limited battery capacity, impose a careful planning on how and where the security services should be deployed. Besides protecting the network from some well-known threats, it is important that security mechanisms be able to withstand attacks that have not been identified before. One way of reaching this goal is to control, at the network access level, which nodes can be attached to the network and to enforce their security compliance. This paper presents a network access security framework that can be used to control the nodes that have access to the network, based on administrative approval, and to enforce security compliance to the authorized nodes.

  14. A local framework for calculating coupled cluster singles and doubles excitation energies (LoFEx-CCSD)

    DOE PAGES

    Baudin, Pablo; Bykov, Dmytro; Liakh, Dmitry I.; ...

    2017-02-22

    Here, the recently developed Local Framework for calculating Excitation energies (LoFEx) is extended to the coupled cluster singles and doubles (CCSD) model. In the new scheme, a standard CCSD excitation energy calculation is carried out within a reduced excitation orbital space (XOS), which is composed of localised molecular orbitals and natural transition orbitals determined from time-dependent Hartree–Fock theory. The presented algorithm uses a series of reduced second-order approximate coupled cluster singles and doubles (CC2) calculations to optimise the XOS in a black-box manner. This ensures that the requested CCSD excitation energies have been determined to a predefined accuracy compared tomore » a conventional CCSD calculation. We present numerical LoFEx-CCSD results for a set of medium-sized organic molecules, which illustrate the black-box nature of the approach and the computational savings obtained for transitions that are local compared to the size of the molecule. In fact, for such local transitions, the LoFEx-CCSD scheme can be applied to molecular systems where a conventional CCSD implementation is intractable.« less

  15. Fast Calcium Imaging with Optical Sectioning via HiLo Microscopy

    PubMed Central

    Sternberg, Jenna R.; Wyart, Claire; Emiliani, Valentina

    2015-01-01

    Imaging intracellular calcium concentration via reporters that change their fluorescence properties upon binding of calcium, referred to as calcium imaging, has revolutionized our way to probe neuronal activity non-invasively. To reach neurons densely located deep in the tissue, optical sectioning at high rate of acquisition is necessary but difficult to achieve in a cost effective manner. Here we implement an accessible solution relying on HiLo microscopy to provide robust optical sectioning with a high frame rate in vivo. We show that large calcium signals can be recorded from dense neuronal populations at high acquisition rates. We quantify the optical sectioning capabilities and demonstrate the benefits of HiLo microscopy compared to wide-field microscopy for calcium imaging and 3D reconstruction. We apply HiLo microscopy to functional calcium imaging at 100 frames per second deep in biological tissues. This approach enables us to discriminate neuronal activity of motor neurons from different depths in the spinal cord of zebrafish embryos. We observe distinct time courses of calcium signals in somata and axons. We show that our method enables to remove large fluctuations of the background fluorescence. All together our setup can be implemented to provide efficient optical sectioning in vivo at low cost on a wide range of existing microscopes. PMID:26625116

  16. Fast Calcium Imaging with Optical Sectioning via HiLo Microscopy.

    PubMed

    Lauterbach, Marcel A; Ronzitti, Emiliano; Sternberg, Jenna R; Wyart, Claire; Emiliani, Valentina

    2015-01-01

    Imaging intracellular calcium concentration via reporters that change their fluorescence properties upon binding of calcium, referred to as calcium imaging, has revolutionized our way to probe neuronal activity non-invasively. To reach neurons densely located deep in the tissue, optical sectioning at high rate of acquisition is necessary but difficult to achieve in a cost effective manner. Here we implement an accessible solution relying on HiLo microscopy to provide robust optical sectioning with a high frame rate in vivo. We show that large calcium signals can be recorded from dense neuronal populations at high acquisition rates. We quantify the optical sectioning capabilities and demonstrate the benefits of HiLo microscopy compared to wide-field microscopy for calcium imaging and 3D reconstruction. We apply HiLo microscopy to functional calcium imaging at 100 frames per second deep in biological tissues. This approach enables us to discriminate neuronal activity of motor neurons from different depths in the spinal cord of zebrafish embryos. We observe distinct time courses of calcium signals in somata and axons. We show that our method enables to remove large fluctuations of the background fluorescence. All together our setup can be implemented to provide efficient optical sectioning in vivo at low cost on a wide range of existing microscopes.

  17. The First Photometric Study of the Short-period Shallow Contact System LO Comae

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Han, Q. W.; Liu, J. Z.

    2016-12-01

    In this paper, the first complete photometric light curves in the B, V, and R passbands for an eclipsing binary LO Com are presented, and the photometric solution for the LO Com is derived by analyzing these light curves by using the Wilson and Devinney code. From the photometric solution, it is found that the LO Com is a W-type W UMa binary with a mass ratio of q={m}2/{m}1=2.478 and a contact degree of f=(3.2+/- 0.25) % . By combining the two new minimum times with those published earlier in the literature, we have found that the (O - C) curve shows a downward parabolic variation corresponding to a long-term decrease in the orbital period with a rate of {{d}}P/{{d}}t=-1.18× {10}-7 days yr-1. This long-term decrease in its orbital period may be caused by mass transfer from the more massive component to the less massive one.

  18. A Network Access Control Framework for 6LoWPAN Networks

    PubMed Central

    Oliveira, Luís M. L.; Rodrigues, Joel J. P. C.; de Sousa, Amaro F.; Lloret, Jaime

    2013-01-01

    Low power over wireless personal area networks (LoWPAN), in particular wireless sensor networks, represent an emerging technology with high potential to be employed in critical situations like security surveillance, battlefields, smart-grids, and in e-health applications. The support of security services in LoWPAN is considered a challenge. First, this type of networks is usually deployed in unattended environments, making them vulnerable to security attacks. Second, the constraints inherent to LoWPAN, such as scarce resources and limited battery capacity, impose a careful planning on how and where the security services should be deployed. Besides protecting the network from some well-known threats, it is important that security mechanisms be able to withstand attacks that have not been identified before. One way of reaching this goal is to control, at the network access level, which nodes can be attached to the network and to enforce their security compliance. This paper presents a network access security framework that can be used to control the nodes that have access to the network, based on administrative approval, and to enforce security compliance to the authorized nodes. PMID:23334610

  19. Infrared SEDs And Star Formation Rates Of LoBAL QSOs

    NASA Astrophysics Data System (ADS)

    Lazarova, Mariana S.; Canalizo, G.; Lacy, M.

    2010-01-01

    Low-ionization Broad Absorption Line QSOs (LoBALs) are a rare class of objects, accounting only for 1-3% of the general population of QSOs.  Their defining characteristic is the presence of high velocity (>2000 km/s) mass outflows of low- and high-ionization ions, which are evident in the very broad blue-shifted absorption troughs in their rest-UV spectra.  There is some observational evidence that LoBALs at low redshifts might exclusively reside in Ultra Luminous Infrared Galaxies (ULIRGs) with disturbed morphologies and young stellar populations as a result of a recent galaxy merger.  Those studies and the currently sparked interest in AGN feedback as a possible mechanism for regulating galaxy evolution have highlighted the importance of testing previous ideas proposing that BALs represent a short-lived outflow phase early in the life of QSOs.  Herein we present the first results from a multiwavelength, systematic study of a complete sample of 22 LoBALs drawn from the SDSS DR3 within 0.5 < z < 0.6.  We model their infrared SEDs and measure the total IR luminosities from 24, 70, and 160 micron Spitzer/MIPS observations.  Also, we estimate the star formation rates from their IR luminosities and the PAH features in their Spitzer/IRS spectra.

  20. Nature of the X(5568) — A critical Laplace sum rule analysis at N2LO

    NASA Astrophysics Data System (ADS)

    Albuquerque, R.; Narison, S.; Rabemananjara, A.; Rabetiarivony, D.

    2016-06-01

    We scrutinize recent QCD spectral sum rules (QSSR) results to lowest order (LO) predicting the masses of the BK molecule and (su)(bd¯) four-quark states. We improve these results by adding NLO and N2LO corrections to the PT contributions giving a more precise meaning on the b-quark mass definition used in the analysis. We extract our optimal predictions using Laplace sum rule (LSR) within the standard stability criteria versus the changes of the external free parameters (τ-sum rule variable, tc continuum threshold and subtraction constant μ). The smallness of the higher order PT corrections justifies (a posteriori) the LO order results ⊕ the uses of the ambiguous heavy quark mass to that order. However, our predicted spectra in the range (5173 ˜ 5226) MeV, summarized in Table 7, for exotic hadrons built with four different flavors (buds), do not support some previous interpretations of the D0 candidate,1 X(5568), as a pure molecule or a four-quark state. If experimentally confirmed, it could result from their mixing with an angle: sin 2𝜃 ≈ 0.15. One can also scan the region (2327 ˜ 2444) MeV (where the Ds0∗(2317) might be a good candidate) and the one (5173 ˜ 5226) MeV for detecting these (cuds) and (buds) unmixed exotic hadrons (if any) via, eventually, their radiative or π+hadrons decays.