Ordering mechanisms of periodic stripe arrays on boron-doped Si(100)

NASA Astrophysics Data System (ADS)

Ermanoski, Ivan; Kellogg, Gary; Bartelt, Norman

2009-03-01

We have used low energy electron microscopy to determine the factors that control the degree of order in self-assembled periodic stripe arrays on the atomically flat Si(100) with high boron doping. The stripes consist of extremely elongated vacancy islands of single atomic height, formed at ˜900C, confined in micrometer-sized pits. ``Perfect'' arrays of parallel stripes (in pits of up to ˜10um in size) were formed by allowing various defects to heal over relatively long periods of time. Sublimation was compensated for by an external Si doser, allowing observation of stripe evolution over the course of hours, with no net loss or gain of Si from the area of interest. Stripe formation and ordering mechanisms include spontaneous nucleation and growth of new islands, longitudinal splitting, as well as coarsening due to surface diffusion. Stripe periodicity depends on temperature, allowing for control of this property. Stripes are stable in a range of ˜100C, outside of which they assume the familiar shape of elongated islands, shaped by the anisotropy in step energy. Stripe order can be preserved to room temperature by quenching. References: [1] J.-F. Nielsen et al., Appl. Phys. Lett. 79 (2001) 3857

Fire retardancy using applied materials

NASA Technical Reports Server (NTRS)

Feldman, R.

1971-01-01

An example of advanced technology transfer from the Little Joe, Surveyor, Comsat, re-entry and Apollo age to everyday fire protection needs is presented. Utilizing the principle of sublimation cooling for thermostatic temperature control, the material meets a wide range of fire retardancy and heat transmission control requirements. Properties vary from flexible tape for conduits and electrical cables to rigid coatings for column protection, with a broad spectrum of sublimation temperatures available. The material can be applied in the field or in the factory, utilizing mass production techniques, yielding a product that is reliable, effective, widely available and low in cost.

The significance of vertical moisture diffusion on drifting snow sublimation near snow surface

NASA Astrophysics Data System (ADS)

Huang, Ning; Shi, Guanglei

2017-12-01

Sublimation of blowing snow is an important parameter not only for the study of polar ice sheets and glaciers, but also for maintaining the ecology of arid and semi-arid lands. However, sublimation of near-surface blowing snow has often been ignored in previous studies. To study sublimation of near-surface blowing snow, we established a sublimation of blowing snow model containing both a vertical moisture diffusion equation and a heat balance equation. The results showed that although sublimation of near-surface blowing snow was strongly reduced by a negative feedback effect, due to vertical moisture diffusion, the relative humidity near the surface does not reach 100 %. Therefore, the sublimation of near-surface blowing snow does not stop. In addition, the sublimation rate near the surface is 3-4 orders of magnitude higher than that at 10 m above the surface and the mass of snow sublimation near the surface accounts for more than half of the total snow sublimation when the friction wind velocity is less than about 0.55 m s-1. Therefore, the sublimation of near-surface blowing snow should not be neglected.

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

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.

Infiltration of CdTe nano crystals into a ZnO wire vertical matrix by using the isothermal closed space technique

NASA Astrophysics Data System (ADS)

Larramendi, S.; Vaillant Roca, Lidice; Saint-Gregoire, Pierre; Ferraz Dias, Johnny; Behar, Moni

2017-10-01

A ZnO nanorod structure was grown by the hydrothermal method and interpenetrated with CdTe using the isothermal closed space sublimation technique. The obtained structure was studied by using the Rutherford backscattering spectrometry (RBS), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM). The X-ray Diffraction (XRD) technique confirmed the presence of CdTe nanocrystals (NCs) of very small size formed on the surface and in the interspaces between the ZnO nanorods. The RBS observations together with the SEM observations give information on the obtained structure. Finally the photoluminescence studies show a strong energy confinement effect on the grown CdTe NCs.

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…

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.

Possible recent and ancient glacial ice flow in the south polar region of Mars

NASA Technical Reports Server (NTRS)

Kargel, J. S.

1992-01-01

Martian polar science began almost as soon as small telescopes were trained on the planet. The seasonal expansion and contraction of the polar caps and their high albedoes led most astronomers to think that water ice is the dominant constituent. In 1911 Lowell perceived a bluish band around the retreating edge of the polar caps, and interpreted it as water from melting polar ice and seasonal snow. An alternative idea in his time was that the polar caps consist of frozen carbonic acid. Lowell rejected the carbonic acid hypothesis on account of his blue band. He also pointed out that carbonic acid would sublimate rather than melt at confining pressures near and below one bar, hence, carbonic acid could not account for the blue band. In comparing Lowell's theories with today's knowledge, it is recognized that (1) sublimation is mainly responsible for the growth and contraction of Mars' polar caps, (2) carbon dioxide is a major component of the southern polar cap, and (3) Lowell's blue band was probably seasonal dust and/or clouds. Geomorphic evidence that glacial ice and glacial melt waters once flowed over broad areas of the southern polar region. Two aspects of the south polar region suggest possible glacial processes during two distinct eras in Mars' history.

A close-space sublimation driven pathway for the manipulation of substrate-supported micro- and nanostructures

NASA Astrophysics Data System (ADS)

Sundar, Aarthi

The ability to fabricate structures and engineer materials on the nanoscale leads to the development of new devices and the study of exciting phenomena. Nanostructures attached to the surface of a substrate, in a manner that renders them immobile, have numerous potential applications in a diverse number of areas. Substrate-supported nanostructures can be fabricated using numerous modalities; however the easiest and most inexpensive technique to create a large area of randomly distributed particles is by the technique of thermal dewetting. In this process a metastable thin film is deposited at room temperature and heated, causing the film to lower its surface energy by agglomerating into droplet-like nanostructures. The main drawbacks of nanostructure fabrication via this technique are the substantial size distributions realized and the lack of control over nanostructure placement. In this doctoral dissertation, a new pathway for imposing order onto the thermal dewetting process and for manipulating the size, placement, shape and composition of preformed templates is described. It sees the confinement of substrate-supported thin films or nanostructure templates by the free surface of a metal film or a second substrate surface. Confining the templates in this manner and heating them to elevated temperatures leads to changes in the characteristics of the nanostructures formed. Three different modalities are demonstrated which alters the preformed structures by: (i) subtracting atoms from the templates, (ii) adding atoms to the template or (iii) simultaneously adding and subtracting atoms. The ability to carry out such processes depends on the choice of the confining surface and the nanostructured templates used. A subtractive process occurs when an electroformed nickel mesh is placed in conformal contact with a continuous gold film while it dewets, resulting in the formation of a periodic array of gold microstructures on an oxide substrate surface. When heated the 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 concurrent sublimation of palladium and gold which results in the complete transfer of the templated gold from the substrate to the foil, but not before the templates act as heterogeneous nucleation sites for palladium adatoms arriving to the substrate surface. Thus, the process is not only subtractive, but also additive due to the addition of palladium and removal of gold.

Physical and environmental factors affecting the persistence of explosives particles (Conference Presentation)

NASA Astrophysics Data System (ADS)

Papantonakis, Michael R.; Nguyen, Viet K.; Furstenberg, Robert; White, Caitlyn; Shuey, Melissa; Kendziora, Christopher A.; McGill, R. Andrew

2017-05-01

Knowledge of the persistence of trace explosives materials is critical to aid the security community in designing detection methods and equipment. The physical and environmental factors affecting the lifetimes of particles include temperature, airflow, interparticle distance, adlayers, humidity, particle field size and vapor pressure. We are working towards a complete particle persistence model that captures the relative importance of these effects to allow the user, with known environmental conditions, to predict particle lifetimes for explosives or other chemicals. In this work, particles of explosives are sieved onto smooth glass substrates using particle sizes and loadings relevant to those deposited by fingerprint deposition. The coupon is introduced into a custom flow cell and monitored under controlled airflow, humidity and temperature. Photomicroscopy images of the sample taken at fixed time intervals are analyzed to monitor particle sublimation and characterized as a size-independent radial sublimation velocity for each particle in the ensemble. In this paper we build on previous work by comparing the relationship between sublimation of different materials and their vapor pressures. We also describe the influence of a sebum adlayer on particle sublimation, allowing us to better model `real world' samples.

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 infestation, drought) and anthropogenic (land management practices) processes. Therefore, understanding how small scale changes impact snow sublimation at larger spatial scales, and how this varies temporally, is critical from ecosystem function and water resources perspectives.

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.

Simulations of snow distribution and hydrology in a mountain basin

USGS Publications Warehouse

Hartman, Melannie D.; Baron, Jill S.; Lammers, Richard B.; Cline, Donald W.; Band, Larry E.; Liston, Glen E.; Tague, Christina L.

1999-01-01

We applied a version of the Regional Hydro-Ecologic Simulation System (RHESSys) that implements snow redistribution, elevation partitioning, and wind-driven sublimation to Loch Vale Watershed (LVWS), an alpine-subalpine Rocky Mountain catchment where snow accumulation and ablation dominate the hydrologic cycle. We compared simulated discharge to measured discharge and the simulated snow distribution to photogrammetrically rectified aerial (remotely sensed) images. Snow redistribution was governed by a topographic similarity index. We subdivided each hillslope into elevation bands that had homogeneous climate extrapolated from observed climate. We created a distributed wind speed field that was used in conjunction with daily measured wind speeds to estimate sublimation. Modeling snow redistribution was critical to estimating the timing and magnitude of discharge. Incorporating elevation partitioning improved estimated timing of discharge but did not improve patterns of snow cover since wind was the dominant controller of areal snow patterns. Simulating wind-driven sublimation was necessary to predict moisture losses.

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

PubMed

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

2013-11-26

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.

X-38 Advanced Sublimator

NASA Technical Reports Server (NTRS)

Dingell, Chuck; Quintana, Clemente; Le, Suy; Hafemalz, David S.; Clark, Mike; Cloutier, Robert

2009-01-01

A document discusses a heat rejection device for transferring heat from a space vehicle by venting water into space through the use of a novel, two-stage water distribution system. The system consists of two different, porous media that stop water-borne contaminants from clogging the system and causing operational failures. Feedwater passes through a small nozzle, then into a porous disk made of sintered stainless steel, and then finally into large-pore aluminum foam. The smaller pore layer of the steel disk controls the pressure drop of the feedwater. The ice forms in the foam layer, and then sublimates, leaving any contaminants behind. The pore-size of the foam is two orders of magnitude larger than the current porous plate sublimators, allowing for a greater tolerance for contaminants. Using metallic fibers in the foam also negates problems with compression seen in the use of poly(tetrafluoroethylene) felt.

Prediction of Sublimation Pressures of Low Volatility Solids

NASA Astrophysics Data System (ADS)

Drake, Bruce Douglas

Sublimation pressures are required for solid-vapor phase equilibrium models in design of processes such as supercritical fluid extraction, sublimation purification and vapor epitaxy. The objective of this work is to identify and compare alternative methods for predicting sublimation pressures. A bibliography of recent sublimation data is included. Corresponding states methods based on the triple point (rather than critical point) are examined. A modified Trouton's rule is the preferred method for estimating triple point pressure in the absence of any sublimation data. Only boiling and melting temperatures are required. Typical error in log_{10} P _{rm triple} is 0.3. For lower temperature estimates, the slope of the sublimation curve is predicted by a correlation based on molar volume. Typical error is 10% of slope. Molecular dynamics methods for surface modeling are tested as estimators of vapor pressure. The time constants of the vapor and solid phases are too different to allow the vapor to come to thermal equilibrium with the solid. The method shows no advantages in prediction of sublimation pressure but provides insight into appropriate models and experimental methods for sublimation. Density-dependent augmented van der Waals equations of state based on hard-sphere distribution functions are examined. The perturbation term is almost linear and is well fit by a simple quadratic. Use of the equation provides reasonable fitting of sublimation pressures from one data point. Order-of-magnitude estimation is possible from melting temperature and solid molar volume. The inverse -12 fluid is used to develop an additional equation of state. Sublimation pressure results, including quality of pressure predictions, are similar to the hard-sphere results. Three-body (Axilrod -Teller) interactions are used to improve results.

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

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.

An Analysis of Ablation-Shield Requirements for Manned Reentry Vehicles

NASA Technical Reports Server (NTRS)

Roberts, Leonard

1960-01-01

The problem of sublimation of material and accumulation of heat in an ablation shield is analyzed and the results are applied to the reentry of manned vehicles into the earth's atmosphere. The parameters which control the amount of sublimation and the temperature distribution within the ablation shield are determined and presented in a manner useful for engineering calculation. It is shown that the total mass loss from the shield during reentry and the insulation requirements may be given very simply in terms of the maximum deceleration of the vehicle or the total reentry time.

Io meteorology - How atmospheric pressure is controlled locally by volcanos and surface frosts

NASA Technical Reports Server (NTRS)

Ingersoll, Andrew P.

1989-01-01

The present modification of the Ingersoll et al. (1985) hydrodynamic model of the SO2 gas sublimation-driven flow from the day to the night side of Io includes the effects of nonuniform surface properties noted in observational studies. Calculations are conducted for atmospheric pressures, horizontal winds, sublimation rates, and condensation rates for such surface conditions as patchy and continuous frost cover, volcanic venting, surface temperature discontinuities, subsurface cold trapping, and the propagation of insolation into the frost. While pressure is found to follow local vapor pressure away from the plumes, it becomes higher inside them.

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.

Measured and modelled sublimation on the tropical Glaciar Artesonraju, Perú

NASA Astrophysics Data System (ADS)

Winkler, M.; Juen, I.; Mölg, T.; Kaser, G.

2008-09-01

Sublimation plays a decisive role in the surface energy balance of tropical glaciers. During the dry season low specific humidity and high surface roughness favour the direct transition from ice to vapour and drastically reduce the energy available for melting. However, field measurements are scarce and little is known about the performance of sublimation parametrisations in glacier mass balance and runoff models. During 15 days in August 2005 sublimation was measured on the tongue of Glaciar Artesonraju (8°58' S, 77°38' W) in the Cordillera Blanca, Perú, using simple lysimeters. Indicating a strong dependence on surface roughness, daily totals of sublimation range from 1 3 kg m-2 for smooth to 2 5 kg m-2 for rough conditions. Measured sublimation was related to characteristic surface roughness lengths for momentum (zm) and for the scalar quantities of temperature and water vapour (zs), using a process-based mass balance model. Input data were provided by automatic weather stations, situated on the glacier tongue at 4750 m ASL and 4810 m ASL, respectively. Under smooth conditions the combination zm=2.0 mm and zs=1.0 mm appeared to be most appropriate, for rough conditions zm=20.0 mm and zs=10.0 mm fitted best. Extending the sublimation record from April 2004 to December 2005 with the process-based model confirms, that sublimation shows a clear seasonality. 60 90% of the energy available for ablation is consumed by sublimation in the dry season, but only 10 15% in the wet season. The findings are finally used to evaluate the parametrisation of sublimation in the lower-complexity mass balance model ITGG, which has the advantage of requiring precipitation and air temperature as only input data. It turns out that the implementation of mean wind speed is a possible improvement for the representation of sublimation in the ITGG model.

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.

The Mars water cycle at other epochs: History of the polar caps and layered terrain

NASA Technical Reports Server (NTRS)

Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

1992-01-01

The atmospheric water cycle at the present epoch involves summertime sublimation of water from the north polar cap, transport of water through the atmosphere, and condensation on one or both winter CO2 caps. Exchange with the regolith is important seasonally, but the water content of the atmosphere appears to be controlled by the polar caps. The net annual transport through the atmosphere, integrated over long timescales, must be the driving force behind the long-term evolution of the polar caps; clearly, this feeds back into the evolution of the layered terrain. We have investigated the behavior of the seasonal water cycle and the net integrated behavior at the pole for the last 10 exp 7 years. Our model of the water cycle includes the solar input, CO2 condensation and sublimation, and summertime water sublimation through the seasonal cycles, and incorporates the long-term variations in the orbital elements describing the Martian orbit.

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).

Life Testing of Yb14MnSb11 for High Performance Thermoelectric Couples

NASA Technical Reports Server (NTRS)

Paik, Jong-Ah; Brandon, Erik; Caillat, Thierry; Ewell, Richard; Fleurial, Jean-Pierre

2011-01-01

The goal of this study is to verify the long term stability of Yb14MnSb11 for high performance thermoelectric (TE) couples. Three main requirements need to be satisfied to ensure the long term stability of thermoelectric couples: 1) stable thermoelectric properties, 2) stable bonding interfaces, and 3) adequate sublimation suppression. The efficiency of the couple is primarily based on the thermoelectric properties of the materials selected for the couple. Therefore, these TE properties should exhibit minimal degradation during the operating period of the thermoelectric couples. The stability of the bonding is quantified by low contact resistances of the couple interfaces. In order to ensure high efficiency, the contact resistances of the bonding interfaces should be negligible. Sublimation suppression is important because the majority of thermoelectric materials used for power generation have peak figures of merit at temperatures where sublimation rates are high. Controlling sublimation is also essential to preserve the efficiency of the couple. During the course of this research, three different life tests were performed with Yb14MnSb11 coupons. TE properties of Yb14MnSb11 exhibited no degradation after 6 months of aging at 1273K, and the electrical contact resistance between a thin metallization layer and the Yb14MnSb11 remained negligible after 1500hr aging at 1273K. A sublimation suppression layer for Yb14MnSb11 was developed and demonstrated for more than 18 months with coupon testing at 1273K. These life test data indicate that thermoelectric elements based on Yb14MnSb11 are a promising technology for use in future high performance thermoelectric power generating couples.

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.

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.

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.

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.

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).

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.

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.

Measured and modelled sublimation on the tropical Glaciar Artesonraju, Perú

NASA Astrophysics Data System (ADS)

Winkler, M.; Juen, I.; Mölg, T.; Wagnon, P.; Gómez, J.; Kaser, G.

2009-02-01

Sublimation plays a decisive role in the surface energy and mass balance of tropical glaciers. During the dry season (May-September) low specific humidity and high surface roughness favour the direct transition from ice to vapour and drastically reduce the energy available for melting. However, field measurements are scarce and little is known about the performance of sublimation parameterisations in glacier mass balance and runoff models. During 15 days in August 2005 sublimation was measured on the tongue of Glaciar Artesonraju (8°58' S, 77°38' W) in the Cordillera Blanca, Perú, using simple lysimeters. Indicating a strong dependence on surface roughness, daily totals of sublimation range from 1-3 kg m-2 for smooth to 2-5 kg m-2 for rough conditions. (The 15-day means at that time of wind speed and specific humidity were 4.3 m s-1 and 3.8 g kg-1, respectively.) Measured sublimation was related to characteristic surface roughness lengths for momentum (zm) and for the scalar quantities of temperature and water vapour (zs), using a process-based mass balance model. Input data were provided by automatic weather stations, situated on the glacier tongue at 4750 m a.s.l. and 4810 m a.s.l., respectively. Under smooth conditions the combination zm=2.0 mm and zs=1.0 mm appeared to be most appropriate, for rough conditions zm=20.0 mm and zs=10.0 mm fitted best. Extending the sublimation record from April 2004 to December 2005 with the process-based model confirms, that sublimation shows a clear seasonality. 60-90% of the energy available for ablation is consumed by sublimation in the dry season, but only 10-15% in the wet season (October-April). The findings are finally used to evaluate the parameterisation of sublimation in the lower-complexity mass balance model ITGG, which has the advantage of requiring precipitation and air temperature as only input data. It turns out that the implementation of mean wind speed is a possible improvement for the representation of sublimation in the ITGG model.

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.

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.

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…

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. This was a considerable improvement, considering that uncoated CoSb3 had been found to decompose to form the lowest antimonide at the surface at only 600 C. Evidently, because the mean free path of Sb at the given temperature and pressure was of the order of tens of centimeters, any barrier closer than tens of centimeters (as was the niobium foil) would have suppressed transport of Sb vapor, thereby suppressing sublimation of Sb

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…

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.;

Blowing Snow Sublimation and Transport over Antarctica from 11 Years of CALIPSO Observations

NASA Technical Reports Server (NTRS)

Palm, Stephen P.; Kayetha, Vinay; Yang, Yuekui; Pauly, Rebecca

2017-01-01

Blowing snow processes commonly occur over the earth's ice sheets when the 10 mile wind speed exceeds a threshold value. These processes play a key role in the sublimation and redistribution of snow thereby influencing the surface mass balance. Prior field studies and modeling results have shown the importance of blowing snow sublimation and transport on the surface mass budget and hydrological cycle of high-latitude regions. For the first time, we present continent-wide estimates of blowing snow sublimation and transport over Antarctica for the period 2006-2016 based on direct observation of blowing snow events. We use an improved version of the blowing snow detection algorithm developed for previous work that uses atmospheric backscatter measurements obtained from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar aboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite. The blowing snow events identified by CALIPSO and meteorological fields from MERRA-2 are used to compute the blowing snow sublimation and transport rates. Our results show that maximum sublimation occurs along and slightly inland of the coastline. This is contrary to the observed maximum blowing snow frequency which occurs over the interior. The associated temperature and moisture reanalysis fields likely contribute to the spatial distribution of the maximum sublimation values. However, the spatial pattern of the sublimation rate over Antarctica is consistent with modeling studies and precipitation estimates. Overall, our results show that the 2006-2016 Antarctica average integrated blowing snow sublimation is about 393 +/- 196 Gt yr(exp -1), which is considerably larger than previous model-derived estimates. We find maximum blowing snow transport amount of 5 Mt km-1 yr(exp -1) over parts of East Antarctica and estimate that the average snow transport from continent to ocean is about 3.7 Gt yr(exp -1). These continent-wide estimates are the first of their kind and can be used to help model and constrain the surface mass budget over Antarctica.

"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.

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.

Low temperature simulation of subliming boundary layer flow in Jupiter atmosphere

NASA Technical Reports Server (NTRS)

Chen, C. J.

1976-01-01

A low-temperature approximate simulation for the sublimation of a graphite heat shield under Jovian entry conditions is studied. A set of algebraic equations is derived to approximate the governing equation and boundary conditions, based on order-of-magnitude analysis. Characteristic quantities such as the wall temperature and the subliming velocity are predicted. Similarity parameters that are needed to simulate the most dominant phenomena of the Jovian entry flow are also given. An approximate simulation of the sublimation of the graphite heat shield is performed with an air-dry-ice model. The simulation with the air-dry-ice model may be carried out experimentally at a lower temperature of 3000 to 6000 K instead of the entry temperature of 14,000 K. The rate of graphite sublimation predicted by the present algebraic approximation agrees to the order of magnitude with extrapolated data. The limitations of the simulation method and its utility are discussed.

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

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…

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.

Characterization and thermogravimetric analysis of lanthanide hexafluoroacetylacetone chelates

DOE PAGES

Shahbazi, Shayan; Stratz, S. Adam; Auxier, John D.; ...

2016-08-30

This work reports the thermodynamic characterizations of organometallic species as a vehicle for the rapid separation of volatile nuclear fission products via gas chromatography due to differences in adsorption enthalpy. Because adsorption and sublimation thermodynamics are linearly correlated, there is considerable motivation to determine sublimation enthalpies. A method of isothermal thermogravimetric analysis, TGA-MS and melting point analysis are employed on thirteen lanthanide 1,1,1,5,5,5-hexafluoroacetylacetone complexes to determine sublimation enthalpies. An empirical correlation is used to estimate adsorption enthalpies of lanthanide complexes on a quartz column from the sublimation data. Additionally, four chelates are characterized by SC-XRD, elemental analysis, FTIR and NMR.

Assessing the Impact of Sublimation on the Stable Water Isotope Signal of Surface Ice

NASA Astrophysics Data System (ADS)

Dennis, D. P.; Ehrenfeucht, S.; Marchant, D. R.

2017-12-01

Sublimation is often a significant, if not the dominant, mechanism for ablation in polar and high elevation glacial systems. Previous field studies on firn and ice have suggested that sublimation can enrich the stable water isotope (δD and δ18O) signatures of these exposed materials. Several additional studies have attempted to replicate this effect through laboratory experiments. However, neither the magnitude of alteration caused by sublimation nor the maximum depth at which ice is affected are well-constrained. The effect of sublimation-induced alteration on the original meteoric signal relative to other post-depositional processes is additionally unknown. Here, we present the results of an experimental study on the effect of sublimation on stable water isotope ratios in surface ice. Using high-resolution data, we attempt to assess the suitability of δD and δ18O in near-surface and exposed ice for use as paleoclimate proxies. This type of analysis is particularly useful for future studies of ice from hyper-arid polar regions like the Antarctic McMurdo Dry Valleys, and may be extended to icy planetary bodies, including surface ice on Mars.

Experiments On Sublimating Carbon Dioxide Ice And Implications For Contemporary Surface Processes On Mars.

PubMed

Mc Keown, L E; Bourke, M C; McElwaine, J N

2017-10-27

Carbon dioxide is Mars' primary atmospheric constituent and is an active driver of Martian surface evolution. CO 2 ice sublimation mechanisms have been proposed for a host of features that form in the contemporary Martian climate. However, there has been very little experimental work or quantitative modelling to test the validity of these hypotheses. Here we present the results of the first laboratory experiments undertaken to investigate if the interaction between sublimating CO 2 ice blocks and a warm, porous, mobile regolith can generate features similar in morphology to those forming on Martian dunes today. We find that CO 2 sublimation can mobilise grains to form (i) pits and (ii) furrows. We have documented new detached pits at the termini of linear gullies on Martian dunes. Based on their geomorphic similarity to the features observed in our laboratory experiments, and on scaling arguments, we propose a new hypothesis that detached pits are formed by the impact of granular jets generated by sublimating CO 2 . We also study the erosion patterns formed underneath a sublimating block of CO 2 ice and demonstrate that these resemble furrow patterns on Mars, suggesting similar formation mechanisms.

Heat and mass transfer scale-up issues during freeze-drying, I: atypical radiation and the edge vial effect.

PubMed

Rambhatla, Shailaja; Pikal, Michael J

2003-01-01

The aim of this study is to determine whether radiation heat transfer is responsible for the position dependence of heat transfer known as the edge vial effect. Freeze drying was performed on a laboratory-scale freeze dryer using pure water with vials that were fully stoppered but had precision cut metal tubes inserted in them to ensure uniformity in resistance to vapor flow. Sublimation rates were determined gravimetrically. Vials were sputter-coated with gold and placed at selected positions on the shelf. Average sublimation rates were determined for vials located at the front, side, and center of an array of vials. Sublimation rates were also determined with and without the use of aluminum foil as a radiation shield. The effect of the guardrail material and its contribution to the edge vial effect by conduction heat transfer was studied by replacing the stainless steel band with a low-thermal conductivity material (styrofoam). The emissivities (epsilon) of relevant surfaces were measured using an infrared thermometer. Sublimation rate experiments were also conducted with vials suspended off the shelf to study the role of convection heat transfer. It was found that sublimation rates were significantly higher for vials located in the front compared to vials in the center. Additional radiation shields in the form of aluminum foil on the inside door resulted in a decrease in sublimation rates for the front vials and to a lesser extent, the center vials. There was a significant decrease in sublimation rate for gold-coated vials (epsilon approximately 0.4) placed at the front of an array when compared to that of clear vials (epsilon approximately 0.9). In the case of experiments with vials suspended off the shelf, the heat transfer coefficient was found to be independent of chamber pressure, indicating that pure convection plays no significant role in heat transfer. Higher sublimation rates were observed when the steel band was used instead of Styrofoam while the highest sublimation rates were obtained in the absence of the guardrail, indicating that the metal band can act as a thermal shield but also transmits some heat from the shelf via conduction and radiation. Atypical radiation heat transfer is responsible for higher sublimation rates for vials located at the front and side of an array. However, the guardrail contributes a little to heat transfer by conduction.

Homogeneity of Gd-based garnet transparent ceramic scintillators for gamma spectroscopy

NASA Astrophysics Data System (ADS)

Seeley, Z. M.; Cherepy, N. J.; Payne, S. A.

2013-09-01

Transparent polycrystalline ceramic scintillators based on the composition Gd1.49Y1.49Ce0.02Ga2.2Al2.8O12 are being developed for gamma spectroscopy detectors. Scintillator light yield and energy resolution depend on the details of various processing steps, including powder calcination, green body formation, and sintering atmosphere. We have found that gallium sublimation during vacuum sintering creates compositional gradients in the ceramic and can degrade the energy resolution. While sintering in oxygen produces ceramics with uniform composition and little afterglow, light yields are reduced, compared to vacuum sintering. By controlling the atmosphere during the various process steps, we were able to minimize the gallium sublimation, resulting in a more homogeneous composition and improved gamma spectroscopy performance.

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.

Dust ring formation due to sublimation of dust grains drifting radially inward by the Poynting-Robertson drag: An analytical model

NASA Astrophysics Data System (ADS)

Kobayashi, Hiroshi; Watanabe, Sei-ichiro; Kimura, Hiroshi; Yamamoto, Tetsuo

2009-05-01

Dust particles exposed to the stellar radiation and wind drift radially inward by the Poynting-Robertson (P-R) drag and pile up at the zone where they begin to sublime substantially. The reason they pile up or form a ring is that their inward drifts due to the P-R drag are suppressed by stellar radiation pressure when the ratio of radiation pressure to stellar gravity on them increases during their sublimation phases. We present analytic solutions to the orbital and mass evolution of such subliming dust particles, and find their drift velocities at the pileup zone are almost independent of their initial semimajor axes and masses. We derive analytically an enhancement factor of the number density of the particles at the outer edge of the sublimation zone from the solutions. We show that the formula of the enhancement factor reproduces well numerical simulations in the previous studies. The enhancement factor for spherical dust particles of silicate and carbon extends from 3 to more than 20 at stellar luminosities L=0.8-500L, where L is solar luminosity. Although the enhancement factor for fluffy dust particles is smaller than that for spherical particles, sublimating particles inevitably form a dust ring as long as their masses decrease faster than their surface areas during sublimation. The formulation is applicable to dust ring formation for arbitrary shape and material of dust in dust-debris disks as well as in the Solar System.

Latent cooling and microphysics effects in deep convection

NASA Astrophysics Data System (ADS)

Fernández-González, S.; Wang, P. K.; Gascón, E.; Valero, F.; Sánchez, J. L.

2016-11-01

Water phase changes within a storm are responsible for the enhancement of convection and therefore the elongation of its lifespan. Specifically, latent cooling absorbed during evaporation, melting and sublimation is considered the main cause of the intensification of downdrafts. In order to know more accurately the consequences of latent cooling caused by each of these processes (together with microphysical effects that they induce), four simulations were developed with the Wisconsin Dynamical and Microphysical Model (WISCDYMM): one with all the microphysical processes; other without sublimation; melting was suppressed in the third simulation; and evaporation was disabled in the fourth. The results show that sublimation cooling is not essential to maintain the vertical currents of the storm. This is demonstrated by the fact that in the simulation without sublimation, maximum updrafts are in the same range as in the control simulation, and the storm lifespan is similar or even longer. However, melting was of vital importance. The storm in the simulation without melting dissipated prematurely, demonstrating that melting is indispensable to the enhancement of downdrafts below the freezing level and for avoiding the collapse of low level updrafts. Perhaps the most important finding is the crucial influence of evaporative cooling above the freezing level that maintains and enhances mid-level downdrafts in the storm. It is believed that this latent cooling comes from the evaporation of supercooled liquid water connected with the Bergeron-Findeisen process. Therefore, besides its influence at low levels (which was already well known), this evaporative cooling is essential to strengthen mid-level downdrafts and ultimately achieve a quasi-steady state.

Diagnosis of the hydrology of a small Arctic basin at the tundra-taiga transition using a physically based hydrological model

NASA Astrophysics Data System (ADS)

Krogh, Sebastian A.; Pomeroy, John W.; Marsh, Philip

2017-07-01

A better understanding of cold regions hydrological processes and regimes in transitional environments is critical for predicting future Arctic freshwater fluxes under climate and vegetation change. A physically based hydrological model using the Cold Regions Hydrological Model platform was created for a small Arctic basin in the tundra-taiga transition region. The model represents snow redistribution and sublimation by wind and vegetation, snowmelt energy budget, evapotranspiration, subsurface flow through organic terrain, infiltration to frozen soils, freezing and thawing of soils, permafrost and streamflow routing. The model was used to reconstruct the basin water cycle over 28 years to understand and quantify the mass fluxes controlling its hydrological regime. Model structure and parameters were set from the current understanding of Arctic hydrology, remote sensing, field research in the basin and region, and calibration against streamflow observations. Calibration was restricted to subsurface hydraulic and storage parameters. Multi-objective evaluation of the model using observed streamflow, snow accumulation and ground freeze/thaw state showed adequate simulation. Significant spatial variability in the winter mass fluxes was found between tundra, shrubs and forested sites, particularly due to the substantial blowing snow redistribution and sublimation from the wind-swept upper basin, as well as sublimation of canopy intercepted snow from the forest (about 17% of snowfall). At the basin scale, the model showed that evapotranspiration is the largest loss of water (47%), followed by streamflow (39%) and sublimation (14%). The models streamflow performance sensitivity to a set of parameter was analysed, as well as the mean annual mass balance uncertainty associated with these parameters.

Evaporation Behavior and Characterization of Eutectic Solvent and Ibuprofen Eutectic Solution.

PubMed

Phaechamud, Thawatchai; Tuntarawongsa, Sarun; Charoensuksai, Purin

2016-10-01

Liquid eutectic system of menthol and camphor has been reported as solvent and co-solvent for some drug delivery systems. However, surprisingly, the phase diagram of menthol-camphor eutectic has not been reported previously. The evaporation behavior, physicochemical, and thermal properties of this liquid eutectic and ibuprofen eutectic solution were characterized in this study. Differential scanning calorimetry (DSC) analysis indicated that a eutectic point of this system was near to 1:1 menthol/camphor and its eutectic temperature was -1°C. The solubility of ibuprofen in this eutectic was 282.11 ± 6.67 mg mL(-1) and increased the drug aqueous solubility fourfold. The shift of wave number from Fourier transform infrared spectroscopy (FTIR) indicated the hydrogen bonding of each compound in eutectic mixture. The weight loss from thermogravimetric analysis of menthol and camphor related to the evaporation and sublimation, respectively. Menthol demonstrated a lower apparent sublimation rate than camphor, and the evaporation rate of eutectic solvent was lower than the sublimation rate of camphor but higher than the evaporation of menthol. The evaporation rate of the ibuprofen eutectic solution was lower than that of the eutectic solvent because ibuprofen did not sublimate. This eutectic solvent prolonged the ibuprofen release with diffusion control. Thus, the beneficial information for thermal behavior and related properties of eutectic solvent comprising menthol-camphor and ibuprofen eutectic solution was attained successfully. The rather low evaporation of eutectic mixture will be beneficial for investigation and tracking the mechanism of transformation from nanoemulsion into nanosuspension in the further study using eutectic as oil phase.

Heat Transfer Analysis of an Optimized, Flexible Holder System for Freeze-Drying in Dual Chamber Cartridges Using Different State-of-the-Art PAT Tools.

PubMed

Korpus, Christoph; Pikal, Michael; Friess, Wolfgang

2016-11-01

The aim of this study was to determine the heat transfer characteristics of an optimized flexible holder device, using Tunable Diode Laser Absorption Spectroscopy, the Pressure Rise Test, and the gravimetric procedure. Two different controlled nucleation methods were tested, and an improved sublimation process, "preheated plate," was developed. Tunable Diode Laser Absorption Spectroscopy identified an initial sublimation burst phase. Accordingly, steady-state equations were adapted for the gravimetric procedure, to account for this initial non-steady-state period. The heat transfer coefficient, K DCC , describing the transfer from the holder to the DCC, was the only heat transfer coefficient showing a clear pressure dependence with values ranging from 3.81E-04 cal/(g·cm 2 ·K) at 40 mTorr to 7.38E-04 cal/(g·cm 2 ·K) at 200 mTorr. The heat transfer coefficient, K tot , reflecting the overall energy transfer via the holder, increased by around 24% from 40 to 200 mTorr. This resulted in a pressure-independent sublimation rate of around 42 ± 1.06 mg/h over the whole pressure range. Hence, this pressure-dependent increase in energy transfer completely compensated the decrease in driving force of sublimation. The "flexible holder" shows a substantially reduced impact of atypical radiation, improved drying homogeneity, and ultimately a better transferability of the freeze-drying cycle for process optimization. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

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).

Spectroscopic determinations of carbon fluxes, sources, and shielding in the DIII-D divertors

NASA Astrophysics Data System (ADS)

Isler, R. C.; Colchin, R. J.; Brooks, N. H.; Evans, T. E.; West, W. P.; Whyte, D. G.

2001-10-01

The most important mechanisms for eroding plasma-facing components (PFCs) and introducing carbon into tokamak divertors are believed to be physical sputtering, chemical sputtering, sublimation, and radiation enhance sublimation (RES). The relative importance of these processes has been investigated by analyzing the spectral emission rates and the effective temperatures of CI, CD, and C2 under several operating conditions in the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515]. Discrimination of chemical sputtering from physical sputtering is accomplished by quantitatively relating the fraction of CI influxes expected from dissociation of hydrocarbons to the measured CD and C2 influxes. Characteristics of sublimation are studied from carbon test samples heated to surface temperatures exceeding 2000 K. The shielding efficiency of carbon produced at the divertor target is assessed from comparison of fluxes of neutral atoms and ions; approximately 95% of the primary influx appears to be redeposited before being transported far enough upstream to fuel the core plasma.

Spectroscopic determinations of carbon fluxes, sources, and shielding in the DIII-D divertors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isler, R. C.; Colchin, R. J.; Brooks, N. H.

2001-10-01

The most important mechanisms for eroding plasma-facing components (PFCs) and introducing carbon into tokamak divertors are believed to be physical sputtering, chemical sputtering, sublimation, and radiation enhance sublimation (RES). The relative importance of these processes has been investigated by analyzing the spectral emission rates and the effective temperatures of CI, CD, and C{sub 2} under several operating conditions in the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515]. Discriminationmore » of chemical sputtering from physical sputtering is accomplished by quantitatively relating the fraction of CI influxes expected from dissociation of hydrocarbons to the measured CD and C{sub 2} influxes. Characteristics of sublimation are studied from carbon test samples heated to surface temperatures exceeding 2000 K. The shielding efficiency of carbon produced at the divertor target is assessed from comparison of fluxes of neutral atoms and ions; approximately 95% of the primary influx appears to be redeposited before being transported far enough upstream to fuel the core plasma.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sacramento, R. L.; Alves, B. X.; Silva, B. A.

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.

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 interpreting remote-sensing observations of comets and also icy satellites or trans-neptunian objects.

In situ observation of the formation of hollow zinc oxide shells

DOE PAGES

Tringe, J. W.; Levie, H. W.; El-Dasher, B. S.; ...

2011-06-14

Single crystal zinc particles, 1–2 μm1–2 μm in diameter, were observed in situ with transmission electron microscopy during sublimation. The rate of sublimation is strongly dependent on the presence of a surface oxide layer. Near 375°, minimally oxidized Zn surfaces sublime in tens of seconds, consistent with a model in which the particle behaves similarly to an isolated microscale effusion cell. By contrast, zinc particles fully enclosed by oxide sublime less than one-tenth as quickly. Here these results provide new insight into the synthesis mechanisms of hollow ZnO microspheres and related structures formed from metallic zinc at elevated temperatures.

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

NASA Astrophysics Data System (ADS)

Hofstadter, M. D.; Murray, B. C.

1990-04-01

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.

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.

Nitrogen-atom endohedral fullerene synthesis with high efficiency by controlling plasma-ion irradiation energy and C60 internal energy

NASA Astrophysics Data System (ADS)

Cho, Soon Cheon; Kaneko, Toshiro; Ishida, Hiroyasu; Hatakeyama, Rikizo

2015-03-01

The nitrogen-atom endohedral fullerene (N@C60) has been synthesized by controlling the plasma ion irradiation energy (Ei) and fullerene (C60) behavior in the sublimation phase. We examined the relationship between the synthesis purity of N@C60 [molar concentration ratio of N@C60 to pristine fullerene (C60)] and Ei, which was controlled by changing the substrate bias voltages (Vsub) and gas pressure (PN2) during the plasma irradiation process. High-density nitrogen-molecular ions (N2+) with a suitable Ei near 80 eV are confirmed to be the optimum condition of the nitrogen plasma for the synthesis of high-purity N@C60. In addition, high sublimation of C60 contributes to a higher yield due to the high internal energy of C60 and the related cage defects that are present under these conditions. As a result, a purity of 0.83% is realized for the first time, which is almost two orders of magnitude higher than that using other methods.

Survival of Amino Acids in Micrometeorites During Atmospheric Entry

NASA Technical Reports Server (NTRS)

Glavin, Daniel P.; Bada, Jeffrey L.

2003-01-01

The delivery of amino acids by micrometeorites to the early Earth during the period of heavy bombardment could have been a significant source of the Earth's prebiotic amino acid inventory provided that these organic compounds survived atmospheric entry heating. To investigate the sublimation of amino acids from a micrometeorite analog at elevated temperature, grains from the CM-type carbonaceous chondrite Murchison were heated to 550 C inside a glass sublimation apparatus (SA) under reduced pressure. The sublimed residue that had collected on the cold finger of the SA after heating was analyzed for amino acids by HPLC. We found that when the temperature of the meteorite reached approx. 150 C, a large fraction of the amino acid glycine had vaporized from the meteorite, recondensed onto the end of the SA cold finger, and survived as the rest of the grains heated to 550 C. alpha-Aminoisobutryic acid and isovaline, which are two of the most abundant non-protein amino acids in Murchison, did not sublime from the meteorite and were completely destroyed during the heating experiment. Our experimental results suggest that sublimation of glycine present in micrometeorite grains may provide a way for this amino acid to survive atmospheric entry heating at temperatures less than 550 C; all other amino acids apparently are destroyed. Key Words: Amino acids-Exogenous delivery-Micrometeorites-Sublimation.

[The present status and development of thermal control system of spacesuits for extravehicular activity].

PubMed

Zhao, C Y; Sun, J B; Yuan, X G

1999-04-01

With the extension of extravehicular activity (EVA) duration, the need for more effective thermal control of EVA spacesuits is required. The specific schemes investigated in heat sink system for EVA are discussed, including radiator, ice storage, metal hydride heat pump, phase-change storage/radiator and sublimator. The importance and requirements of automatic thermal control for EVA are also discussed. Existed automatic thermal control for EVA are reviewed. Prospects of further developments of thermal control of spacesuits for EVA are proposed.

Spatial Variation of Pressure in the Lyophilization Product Chamber Part 2: Experimental Measurements and Implications for Scale-up and Batch Uniformity.

PubMed

Sane, Pooja; Varma, Nikhil; Ganguly, Arnab; Pikal, Michael; Alexeenko, Alina; Bogner, Robin H

2017-02-01

Product temperature during the primary drying step of freeze-drying is controlled by a set point chamber pressure and shelf temperature. However, recent computational modeling suggests a possible variation in local chamber pressure. The current work presents an experimental verification of the local chamber pressure gradients in a lab-scale freeze-dryer. Pressure differences between the center and the edges of a lab-scale freeze-dryer shelf were measured as a function of sublimation flux and clearance between the sublimation front and the shelf above. A modest 3-mTorr difference in pressure was observed as the sublimation flux was doubled from 0.5 to 1.0 kg·h -1 ·m -2 at a clearance of 2.6 cm. Further, at a constant sublimation flux of 1.0 kg·h -1 ·m -2 , an 8-fold increase in the pressure drop was observed across the shelf as the clearance was decreased from 4 to 1.6 cm. Scale-up of the pressure variation from lab- to a manufacturing-scale freeze-dryer predicted an increased uniformity in drying rates across the batch for two frequently used pharmaceutical excipients (mannitol and sucrose at 5% w/w). However, at an atypical condition of shelf temperature of +10°C and chamber pressure of 50 mTorr, the product temperature in the center vials was calculated to be a degree higher than the edge vial for a low resistance product, thus reversing the typical edge and center vial behavior. Thus, the effect of local pressure variation is more significant at the manufacturing-scale than at a lab-scale and accounting for the contribution of variations in the local chamber pressures can improve success in scale-up.

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.

The Sublimation Rate of CO2 Under Simulated Mars Conditions and the Possible Climatic Implications

NASA Astrophysics Data System (ADS)

Bryson, Kathryn; Chevrier, V.; Roe, L.; White, K.; Blackburn, D.

2008-09-01

In order to understand the behavior of CO2 on Mars, we have studied the sublimation of dry ice under simulated martian conditions. Our experiments resulted in an average sublimation rate for CO2 ice of 1.20 ± 0.27 mm h-1. These results are very close to those observed of the martian polar caps retreat, and suggest a common process for the sublimation mechanism on Mars and in our chamber. Based on these results we created a model where irradiance from the sun is the primary source of heat on the martian polar surface. Our model predicts a 32 cm offset between the amount of CO2 ice sublimated and deposited in the southern polar region. The eccentricity of the martian orbit causes the southern hemisphere to sublimate more then it deposits back during one martian year. We have compared MOC and HiRISE images from approximately the same season (Ls 285.57º and 289.5º, respectively) from three martian years apart. These images indicate an average sublimation rate of 0.43 ± 0.04 m y-1, very close to the 0.32 m y-1 predicted by our model. Due to the length of Mars’ precession cycle, 93,000 martian years, it will take an extensive amount of time for the equinoxes to change. Therefore, we predict that the CO2 of the south polar cap will migrate entirely to the northern polar cap before such changes could occur. If the CO2 ice is only a thin layer above a much thicker water ice layer, this could expose large amounts of water ice, having a drastic climactic affect.

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.

On Sublimation.

PubMed

Civitarese, Giuseppe

2016-10-01

Although it encapsulates the Freudian theory of art, the theory of sublimation has become outmoded. What is more, since its inception there has always been something ill-defined about it. Does it use sexualized or de-sexualized drive energy? Is it a defence or an alternative to defence? Does it serve Eros or Thanatos? Is it useful in clinical work or is it unusable? The only, albeit uncertain, aid to a definition relies on the extrinsic criterion of concrete artistic realization. My aim here to revisit and possibly 'reinvent' sublimation in the light of certain principles of the pre-Romantic aesthetics of the sublime. Both are theories of spiritual elevation, in other words, elevation that moves towards abstract thinking, and of man's 'moral' achievement; and both attempt to explain the mystery of aesthetic experience. On the one hand, the aesthetics of the sublime offers a modern myth that helps us articulate a series of factors occasionally referred to by various authors as constitutive of sublimation but which have not been incorporated into a single organic framework: loss and early mourning work; the earlier existence of a catastrophic factor - to be regarded, depending on the situation, as either traumatic or simply 'negative'; the correspondence with a process of somatopsychic categorization which coincides with subjectivity. On the other hand, it also helps us grasp the experience of negative pleasure empathically, living it 'from the inside'. Copyright © 2016 Institute of Psychoanalysis.

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.

Structure-property relationships in halogenbenzoic acids: Thermodynamics of sublimation, fusion, vaporization and solubility.

PubMed

Zherikova, Kseniya V; Svetlov, Aleksey A; Kuratieva, Natalia V; Verevkin, Sergey P

2016-10-01

Temperature dependences of vapor pressures for 2-, 3-, and 4-bromobenzoic acid, as well as for five isomeric bromo-methylbenzoic acids were studied by the transpiration method. Melting temperatures and enthalpies of fusion for all isomeric bromo-methylbenzoic acids and 4-bromobenzoic acid were measured with a DSC. The molar enthalpies of sublimation and vaporization were derived. These data together with results available in the literature were collected and checked for internal consistency using a group-additivity procedure and results from X-ray structural diffraction studies. Specific (hydrogen bonding) interactions in the liquid and in the crystal phase of halogenbenzoic acids were quantified based on experimental values of vaporization and sublimation enthalpies. Structure-property correlations of solubilities of halogenobenzoic acids with sublimation pressures and sublimation enthalpies were developed and solubilities of bromo-benzoic acids were estimated. These new results resolve much of the ambiguity in the available thermochemical and solubility data on bromobenzoic acids. The approach based on structure property correlations can be applied for the assessment of water solubility of sparingly soluble drugs. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

NASA Astrophysics Data System (ADS)

Puybaret, Renaud; Patriarche, Gilles; Jordan, Matthew B.; Sundaram, Suresh; El Gmili, Youssef; Salvestrini, Jean-Paul; Voss, Paul L.; de Heer, Walt A.; Berger, Claire; Ougazzaden, Abdallah

2016-03-01

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5-8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.

Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puybaret, Renaud; Jordan, Matthew B.; Voss, Paul L.

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5–8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metalmore » organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.« less

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.

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.

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

Atomic steps on an ultraflat Si(111) surface upon sublimation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sitnikov, S. V., E-mail: sitnikov@isp.nsc.ru; Latyshev, A. V.; Kosolobov, S. S.

2016-05-15

The kinetics of atomic steps on an ultraflat Si(111) surface is studied by in situ ultrahigh-vacuum reflection electron microscopy at temperatures of 1050–1350°C. For the first time it is experimentally shown that the rate of displacement of an atomic step during sublimation nonlinearly depends on the width of the adjacent terrace. It is established that the atomic mechanism of mass-transport processes at the surface at temperatures higher than 1200°C is controlled by nucleation and the diffusion of surface vacancies rather than of adsorbed Si atoms. The studies make it possible to estimate the activation energy of the dissolution of vacanciesmore » from the surface into the bulk of Si. The estimated activation energy is (4.3 ± 0.05) eV.« less

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)

An investigation on the mechanism of sublimed DHB matrix on molecular ion yields in SIMS imaging of brain tissue.

PubMed

Dowlatshahi Pour, Masoumeh; Malmberg, Per; Ewing, Andrew

2016-05-01

We have characterized the use of sublimation to deposit matrix-assisted laser desorption/ionization (MALDI) matrices in secondary ion mass spectrometry (SIMS) analysis, i.e. matrix-enhanced SIMS (ME-SIMS), a common surface modification method to enhance sensitivity for larger molecules and to increase the production of intact molecular ions. We use sublimation to apply a thin layer of a conventional MALDI matrix, 2,5-dihydroxybenzoic acid (DHB), onto rat brain cerebellum tissue to show how this technique can be used to enhance molecular yields in SIMS while still retaining a lateral resolution around 2 μm and also to investigate the mechanism of this enhancement. The results here illustrate that cholesterol, which is a dominant lipid species in the brain, is decreased on the tissue surface after deposition of matrix, particularly in white matter. The decrease of cholesterol is followed by an increased ion yield of several other lipid species. Depth profiling of the sublimed rat brain reveals that the lipid species are de facto extracted by the DHB matrix and concentrated in the top most layers of the sublimed matrix. This extraction/concentration of lipids directly leads to an increase of higher mass lipid ion yield. It is also possible that the decrease of cholesterol decreases the potential suppression of ion yield caused by cholesterol migration to the tissue surface. This result provides us with significant insights into the possible mechanisms involved when using sublimation to deposit this matrix in ME-SIMS.

Blowing Snow Sublimation at a High Altitude Alpine Site and Effects on the Surface Boundary Layer

NASA Astrophysics Data System (ADS)

Vionnet, V.; Guyomarc'h, G.; Sicart, J. E.; Deliot, Y.; Naaim-Bouvet, F.; Bellot, H.; Merzisen, H.

2017-12-01

In alpine terrain, wind-induced snow transport strongly influences the spatial and temporal variability of the snow cover. During their transport, blown snow particles undergo sublimation with an intensity depending on atmospheric conditions (air temperature and humidity). The mass loss due to blowing snow sublimation is a source of uncertainty for the mass balance of the alpine snowpack. Additionally, blowing snow sublimation modifies humidity and temperature in the surface boundary layer. To better quantify these effects in alpine terrain, a dedicated measurement setup has been deployed at the experimental site of Col du Lac Blanc (2720 m a.s.l., French Alps, Cryobs-Clim network) since winter 2015/2016. It consists in three vertical masts measuring the near-surface vertical profiles (0.2-5 m) of wind speed, air temperature and humidity and blowing snow fluxes and size distribution. Observations collected during blowing snow events without concurrent snowfall show only a slight increase in relative humidity (10-20%) and near-surface saturation is never observed. Estimation of blowing snow sublimation rates are then obtained from these measurements. They range between 0 and 5 mmSWE day-1 for blowing snow events without snowfall in agreement with previous studies in different environments (North American prairies, Antarctica). Finally, an estimation of the mass loss due to blowing snow sublimation at our experimental site is proposed for two consecutive winters. Future use of the database collected in this study includes the evaluation of blowing snow models in alpine terrain.

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.

Nitrogen-atom endohedral fullerene synthesis with high efficiency by controlling plasma-ion irradiation energy and C{sub 60} internal energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Soon Cheon; Kaneko, Toshiro, E-mail: kaneko@ecei.tohoku.ac.jp; Ishida, Hiroyasu

2015-03-28

The nitrogen-atom endohedral fullerene (N@C{sub 60}) has been synthesized by controlling the plasma ion irradiation energy (E{sub i}) and fullerene (C{sub 60}) behavior in the sublimation phase. We examined the relationship between the synthesis purity of N@C{sub 60} [molar concentration ratio of N@C{sub 60} to pristine fullerene (C{sub 60})] and E{sub i}, which was controlled by changing the substrate bias voltages (V{sub sub}) and gas pressure (P{sub N2}) during the plasma irradiation process. High-density nitrogen-molecular ions (N{sub 2}{sup +}) with a suitable E{sub i} near 80 eV are confirmed to be the optimum condition of the nitrogen plasma for themore » synthesis of high-purity N@C{sub 60}. In addition, high sublimation of C{sub 60} contributes to a higher yield due to the high internal energy of C{sub 60} and the related cage defects that are present under these conditions. As a result, a purity of 0.83% is realized for the first time, which is almost two orders of magnitude higher than that using other methods.« less

Sublimation of icy planetesimals and the delivery of water to the habitable zone around solar type stars

NASA Astrophysics Data System (ADS)

Brunini, Adrián; López, María Cristina

2018-06-01

We present a semi analytic model to evaluate the delivery of water to the habitable zone around a solar type star carried by icy planetesimals born beyond the snow line. The model includes sublimation of ice, gas drag and scattering by an outer giant planet located near the snow line. The sublimation model is general and could be applicable to planetary synthesis models or N-Body simulations of the formation of planetary systems. We perform a short series of simulations to asses the potential relevance of sublimation of volatiles in the process of delivery of water to the inner regions of a planetary system during early stages of its formation. We could anticipate that erosion by sublimation would prevent the arrival of much water to the habitable zone of protoplanetary disks in the form of icy planetesimals. Close encounters with a massive planet orbiting near the outer edge of the snow line could make possible for planetesimals to reach the habitable zone somewhat less eroded. However, only large planetesimals could provide appreciable amounts of water. Massive disks and sharp gas surface density profiles favor icy planetesimals to reach inner regions of a protoplanetary disk.

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 (approximately 50 students participated) and the other on ecology (24 students participated). Both units proved to be a success in terms of the learning that resulted and in the positive experiences of the students and myself as the teacher. In both cases, students were give a pre and post multiple-choice test that covered questions typical of those found on the state's achievement exam and the schools' regular tests covering weather and ecology. Both groups of students showed a significant increase in learning. In an attempt to gain an understanding of student experiences with this type of learning, surveys and interviews were administered. The units appear to have profoundly affected students' ideas of weather and ecology---many reporting to see these concepts in new, richer ways. The goal of teaching for scientific sublime experiences is not only content knowledge, but to transform students' understanding of the world. Based on student comments and observations of classroom discussions, I feel that I largely achieved my goal.

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)

Comment on 'The effect of liquid water on thunderstorm charging' by C.P.R. Saunders et al

NASA Technical Reports Server (NTRS)

Williams, Earle; Zhang, Renyi

1993-01-01

This paper is a comment on the claims made in the paper by Saunders et al. (1991), which reports on a laboratory simulation of ice particle charging in thunderstorms, concerning the microphysical condition of riming ice particles and the conditions for sublimation and negative charging in thunderclouds. It is argued that the interpretation of Saunders is contrary to the findings of Williams et al. (1991), which support the hypothesis that sublimating graupel charge negatively (in collision with smaller ice particles) and graupel in deposition charge positively. Based on microphysical calculations as well as observations in thunderclouds, it is concluded that, while sublimation of the rimer surface and negative charging do not appear to account for the laboratory observations reported by Saunders et al., these authors do not have sufficient evidence for rejecting the sublimation hypothesis presented by Williams et al. (1991) for thunderstorms.

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.

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

The Evolution of the Martian Hydrosphere.

NASA Astrophysics Data System (ADS)

Clifford, S. M.; Parker, T. J.

2001-12-01

The Martian outflow channels provide persuasive evidence that Mars is water-rich. The elevation of the channel source regions (which average several km above the northern plains) also indicates that, at the time the channels formed, much of this inventory of H2O was stored in the subsurface in disequilibrium with the global topography. The preservation of a reservoir of groundwater under disequilibrium conditions can be explained if it is confined beneath a thick layer of frozen ground, a hydraulic barrier whose existence is consistent with the climatic and geothermal conditions that are thought to have characterized the planet at this time ( ~2-3 Ga). However, earlier in the planet's history, a higher geothermal heat flux would have resulted in a considerably thinner cryosphere - precluding confinement and resulting in a distribution of H2O that was essentially in a state of hydrostatic equilibrium. If so, then it suggests that, following the development of the global dichotomy, an ice-covered ocean may have occupied the northern plains, with numerous lakes and seas residing in low-lying elevations elsewhere on the planet. The progressive crustal assimilation of these early surface reservoirs of water appears to have been a natural consequence of the planet's subsequent climatic and geothermal evolution, with the thermodynamic instability of H2O at low-latitudes leading to its sublimation and ultimate cold-trapping at the poles. Eventually, this process would have resulted in polar deposits that were thick enough to undergo basal melting - introducing the water, originally associated with the northern ocean and other low-latitude reservoirs, into the subsurface at both poles. In response to the planet's declining internal heat flow, the progressive cold-trapping of water into the growing cryosphere would have significantly depleted the remaining inventory of groundwater - a process that could well explain the apparent decline in outflow channel activity during the Amazonian. If the initial inventory of groundwater was small, then no remnant may now survive at depth - outside of that transiently produced by the local melting of ground ice by igneous intrusions and other geothermal anomalies. However, if the initial inventory of groundwater was large, then a substantial subpermafrost reservoir may persist to the present day. Given the plausible range (and likely heterogeneity) of crustal properties (as well as regional differences in climatic and geologic evolution) the present distribution and state of subsurface water on Mars is likely to be quite complex. At low-latitudes, the instability of ground ice may have resulted in local depths of desiccation ranging from centimeters to as much as a kilometer, with the potential for significant variations in saturation state beneath the sublimation front. Similarly, in the northern plains, the former presence of a primordial ocean, followed by repeated episodes of eolian deposition, volcanism, impacts, catastrophic flooding and high-obliquity sublimation, is likely to have yielded a complex stratigraphy of segregated ice deposits (ranging up to hundreds of meters thick) sandwiched between layers of varying lithology and pore saturation. The uncertainty regarding the magnitude and nature of these variations effectively prohibits theoretical or geomorphic attempts to make reliable and quantitative predictions of the present 3-D distribution and state of subsurface water. The greatest progress towards this goal will likely be made by geophysical investigations.

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.

Potential Identification of Sublimation-Driven Downslope Mass Movement on Mercury

NASA Astrophysics Data System (ADS)

Malliband, C. C.; Conway, S. J.; Rothery, D. A.; Balme, M. R.

2018-05-01

We have identified a further example of mass movement, in addition to the previously identified example in the pyroclastic vent NE of Rachmaninoff. Both examples show evidence of hollow sublimation being a cause of the mass movements.

Nanowire growth and sublimation: CdTe quantum dots in ZnTe nanowires

NASA Astrophysics Data System (ADS)

Orrù, M.; Robin, E.; Den Hertog, M.; Moratis, K.; Genuist, Y.; André, R.; Ferrand, D.; Cibert, J.; Bellet-Amalric, E.

2018-04-01

The role of the sublimation of the compound and of the evaporation of the constituents from the gold nanoparticle during the growth of semiconductor nanowires is exemplified with CdTe-ZnTe heterostructures. Operating close to the upper temperature limit strongly reduces the amount of Cd present in the gold nanoparticle and the density of adatoms on the nanowire sidewalls. As a result, the growth rate is small and strongly temperature dependent, but a good control of the growth conditions allows the incorporation of quantum dots in nanowires with sharp interfaces and adjustable shape, and it minimizes the radial growth and the subsequent formation of additional CdTe clusters on the nanowire sidewalls, as confirmed by photoluminescence. Uncapped CdTe segments dissolve into the gold nanoparticle when interrupting the flux, giving rise to a bulblike (pendant-droplet) shape attributed to the Kirkendall effect.

Transformations of snow chemistry in the boreal forest: Accumulation and volatilization

USGS Publications Warehouse

Pomeroy, J.W.; Davies, T.D.; Jones, H.G.; Marsh, P.; Peters, N.E.; Tranter, M.

1999-01-01

This paper examines the processes and dynamics of ecologically-important inorganic chemical (primarily NO3-N) accumulation and loss in boreal forest snow during the cold winter period at a northern and southern location in the boreal forest of western Canada. Field observations from Inuvik, Northwest Territories and Waskesiu, Saskatchewan, Canada were used to link chemical transformations and physical processes in boreal forest snow. Data on the disposition and overwinter transformation of snow water equivalent, NO3-, SO42- and other major ions were examined. No evidence of enhanced dry deposition of chemical species to intercepted snow was found at either site except where high atmospheric aerosol concentrations prevailed. At Inuvik, concentrations of SO42- and Cl- were five to six times higher in intercepted snow than in surface snow away from the trees. SO4-S and Cl loads at Inuvik were correspondingly enhanced three-fold within the nearest 0.5 m to individual tree stems. Measurements of snow affected by canopy interception without rapid sublimation provided no evidence of ion volatilization from intercepted snow. Where intercepted snow sublimation rates were significant, ion loads in sub-canopy snow suggested that NO3- volatized with an efficiency of about 62% per snow mass sublimated. Extrapolating this measurement from Waskesiu to sublimation losses observed in other southern boreal environments suggests that 19-25% of snow inputs of NO3- can be lost during intercepted snow sublimation. The amount of N lost during sublimation may be large in high-snowfall, high N load southern boreal forests (Quebec) where 0.42 kg NO3-N ha-1 is estimated as a possible seasonal NO3- volatilization. The sensitivity of the N fluxes to climate and forest canopy variation and implications of the winter N losses for N budgets in the boreal forest are discussed.This paper examines the processes and dynamics of ecologically-important inorganic chemical (primarily NO3-N) accumulation and loss in boreal forest snow during the cold winter period at a northern and southern location in the boreal forest of western Canada. Field observations from Inuvik. Northwest Territories and Waskesiu, Saskatchewan, Canada were used to link chemical transformations and physical processes in boreal forest snow. Data on the disposition and overwinter transformation of snow water equivalent, NO3-, SO42- and other major ions were examined. No evidence of enhanced dry deposition of chemical species to intercepted snow was found at either site except where high atmospheric aerosol concentrations prevailed. At Inuvik, concentrations of SO42- and Cl- were five to six times higher in intercepted snow than in surface snow away from the trees. SO4-S and Cl loads at Inuvik were correspondingly enhanced three-fold within the nearest 0.5 m to individual tree stems. Measurements of snow affected by canopy interception without rapid sublimation provided no evidence of ion volatilization from intercepted snow. Where intercepted snow sublimation rates were significant, ion loads in sub-canopy snow suggested that NO3- volatized with an efficiency of about 62% per snow mass sublimated. Extrapolating this measurement from Waskesiu to sublimation losses observed in other southern boreal environments suggests that 19-25% of snow inputs of NO3- can be lost during intercepted snow sublimation. The amount of N lost during sublimation may be large in high-snowfall, high N load southern boreal forests (Quebec) where 0.42 kg NO3-N ha-1 is estimated as a possible seasonal NO3- volatilization. The sensitivity of the N fluxes to climate and forest canopy variation and implications of the winter N losses for N budgets in the boreal forest are discussed.

Preservation of Groundwater on Mars Depends on Preservation of an Icy Cryosphere.

NASA Astrophysics Data System (ADS)

Grimm, R. E.; Kirchoff, M. R.; Stillman, D. E.

2017-12-01

We seek to understand the constraints and controls on the existence of groundwater on Mars today. Tropical ground ice undergoes long-term sublimation and likely exospheric escape. Using multi-reservoir models for the evolution of D/H ratios, we derive a median estimate of the Hesperian-Amazonian H2O loss of 60 m (interquartile range 30-120 m) Global Equivalent Layer (GEL). These figures are substantially smaller than volumes inferred for geological work and for the holding capacity of the upper crust. This suggests that Mars still has substantial subsurface H2O, but it is unknown whether ground water lies beneath ground ice. Without restriction of sublimation, the cryosphere will eventually breach, leading to massive evaporative loss of any underlying groundwater. Using a multiphase H2O transport model, we find that sublimation is retarded (in order of decreasing priority) by higher obliquity, smaller porosity, higher tortuosity, lower heat flow, and smaller pore radius. Our published results suggested low bulk porosity ( 5%) was necessary to limit sublimation to 60 m GEL, but we now recognize that the dependence of effective tortuosity and pore radius on ice saturation can sharply retard loss due to cold trapping, and thus allow nominal ( 30%) porosities. Separately, we find that single-layer ejecta (SLE) craters—long thought to tap subsurface ice—have formed throughout the Amazonian, without any evidence for a declining rate. This suggests that tropical ground ice has remained at relatively shallow depths, at least where these craters are forming. However, there is a striking spatial mixing in highlands near the equator of layered and normal, radial-ejecta craters. This implies strong spatial heterogeneity in the distribution of tropical ground ice. If the cryospheric ice seal is incomplete due to laterally heterogeneous sublimation of ice, then escape of water vapor through the gaps can lead to nearly total loss of groundwater by evaporation. The D/H-inferred loss indicates either that this has been mitigated, for example if aquifers are laterally compartmented similarly to the overlying cryosphere, or that the global water inventory has always been much smaller than the available pore volume since the early Hesperian. Geophysical sounding is necessary to assess the existence of aquifers on Mars today.

Polymeric compositions and their method of manufacture. [forming filled polymer systems using cryogenics

NASA Technical Reports Server (NTRS)

Moser, B. G.; Landel, R. F. (Inventor)

1972-01-01

Filled polymer compositions are made by dissolving the polymer binder in a suitable sublimable solvent, mixing the filler material with the polymer and its solvent, freezing the resultant mixture, and subliming the frozen solvent from the mixture from which it is then removed. The remaining composition is suitable for conventional processing such as compression molding or extruding. A particular feature of the method of manufacture is pouring the mixed solution slowly in a continuous stream into a cryogenic bath wherein frozen particles of the mixture result. The frozen individual particles are then subjected to the sublimation.

Alumina Paste Sublimation Suppression Barrier for Thermoelectric Device

NASA Technical Reports Server (NTRS)

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

Sublime frequencies:  The construction of sublime listening experiences in the sonification of scientific data.

PubMed

Supper, Alexandra

2014-02-01

In the past two decades, the sonification of scientific data - an auditory equivalent of data visualization in which data are turned into sounds - has become increasingly widespread, particularly as an artistic practice and as a means of popularizing science. Sonification is thus part of the recent trend, discussed in public understanding of science literature, towards increased emphasis on 'interactivity' and 'crossovers' between science and art as a response to the perceived crisis in the relationship between the sciences and their publics. However, sonification can also be understood as the latest iteration in a long tradition of theorizing the relations between nature, science and human experience. This article analyses the recent public fascination with sonification and argues that sonification grips public imaginations through the promise of sublime experiences. I show how the 'auditory sublime' is constructed through varying combinations of technological, musical and rhetorical strategies. Rather than maintain a singular conception of the auditory sublime, practitioners draw on many scientific and artistic repertoires. However, sound is often situated as an immersive and emotional medium in contrast to the supposedly more detached sense of vision. The public sonification discourse leaves intact this dichotomy, reinforcing the idea that sound has no place in specialist science.

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.

Morphology and Evolution of Sublimation Pits on Pluto

NASA Astrophysics Data System (ADS)

Abu-Hashmeh, N.; Conrad, J. W.; Nimmo, F.; Moore, J. M.; Stern, A.; Olkin, C.; Weaver, H. A., Jr.; Ennico Smith, K.; Young, L. A.

2017-12-01

Pluto's Sputnik Planitia region hosts a geologically young surface of nitrogen ice that exhibits striking pitted terrain (Moore et al., Science 351, 2016). These pits are most likely formed by sublimation due to incident sunlight, similar to the southern polar cap of Mars (Byrne and Ingersoll, Science 299, 2003); however, their evolution over time has resulted in unique morphological characteristics. Motivated by this, we used the high-resolution mosaic strips captured by New Horizons' Long Range Reconnaissance Imager (LORRI) to map sublimation pits in the southernmost region of Sputnik Planitia. Statistical data shows pit orientations appearing North-South dominant; their morphology also indicates extensional evolution along the major axis caused by further sublimation and contact-coalescence processes. Qualitative analysis of the region yielded indications of an evolutionary path for individual pits that coalesce into each other and exhibit an elongated end-stage. Additionally, densely-pitted regions generally appear to correlate with regions containing longer pits, implying that coalescence may be an important process for elongation. We also model the evolution geometry through competing effects of diffusion (viscous relaxation) and retreat (sublimation) (Buhler and Ingersoll, LPSC Abstract #1746, 2017). The model demonstrates single-pit and coalescing-pit evolutions that influence overall length, as well as a potential ability for the pit center to move in space while the pit morphology evolves.

Phase 1 engineering and technical data report for the thermal control extravehicular life support system

NASA Technical Reports Server (NTRS)

1975-01-01

A shuttle EVLSS Thermal Control System (TCS) is defined. Thirteen heat rejection subsystems, thirteen water management subsystems, nine humidity control subsystems, three pressure control schemes and five temperature control schemes are evaluated. Sixteen integrated TCS systems are studied, and an optimum system is selected based on quantitative weighting of weight, volume, cost, complexity and other factors. The selected sybsystem contains a sublimator for heat rejection, a bubble expansion tank for water management, and a slurper and rotary separator for humidity control. Design of the selected subsystem prototype hardware is presented.

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)

Snow accumulation under various forest stand densities at Tenderfoot Creek Experimental Forest, Montana, USA

Treesearch

Chadwick A. Moore; Ward W. McCaughey

1997-01-01

Snow accumulation in forested watersheds is controlled by climate, elevation, topographic factors and vegetation structure. Conifers affect snow accumulation principally by intercepting snow with the canopy which may later be sublimated. Various tree, stand, species and canopy densities of a subalpine fir habitat (ALBANASC) in central Montana were studied to determine...

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 particle field size. To compare sublimation studies these parameters must be known.

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.

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.

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…

76 FR 51436 - Post Office Closing

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-18

... POSTAL REGULATORY COMMISSION [Docket No. A2011-45; Order No. 801] Post Office Closing AGENCY... the closing of the Sublime, Texas post office has been filed. It identifies preliminary steps and... Postal Service's determination to close the post office in Sublime, Texas. The petition was filed by...

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.

Numerical modeling and analytical modeling of cryogenic carbon capture in a de-sublimating heat exchanger

NASA Astrophysics Data System (ADS)

Yu, Zhitao; Miller, Franklin; Pfotenhauer, John M.

2017-12-01

Both a numerical and analytical model of the heat and mass transfer processes in a CO2, N2 mixture gas de-sublimating cross-flow finned duct heat exchanger system is developed to predict the heat transferred from a mixture gas to liquid nitrogen and the de-sublimating rate of CO2 in the mixture gas. The mixture gas outlet temperature, liquid nitrogen outlet temperature, CO2 mole fraction, temperature distribution and de-sublimating rate of CO2 through the whole heat exchanger was computed using both the numerical and analytic model. The numerical model is built using EES [1] (engineering equation solver). According to the simulation, a cross-flow finned duct heat exchanger can be designed and fabricated to validate the models. The performance of the heat exchanger is evaluated as functions of dimensionless variables, such as the ratio of the mass flow rate of liquid nitrogen to the mass flow rate of inlet flue gas.

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.

System Level Analysis of a Water PCM HX Integrated into Orion's Thermal Control System

NASA Technical Reports Server (NTRS)

Navarro, Moses; Hansen, Scott; Seth, Rubik; Ungar, Eugene

2015-01-01

In a cyclical heat load environment such as low Lunar orbit, a spacecraft's radiators are not sized to reject the full heat load requirement. Traditionally, a supplemental heat rejection device (SHReD) such as an evaporator or sublimator is used to act as a "topper" to meet the additional heat rejection demands. Utilizing a Phase Change Material (PCM) heat exchanger (HX) as a SHReD provides an attractive alternative to evaporators and sublimators as PCM HXs do not use a consumable, thereby leading to reduced launch mass and volume requirements. In continued pursuit of water PCM HX development an Orion system level analysis was performed using Thermal Desktop for a water PCM HX integrated into Orion's thermal control system in a 100km Lunar orbit. The study verified of the thermal model by using a wax PCM and analyzed 1) placing the PCM on the Internal Thermal Control System (ITCS) versus the External Thermal Control System (ETCS) 2) use of 30/70 PGW verses 50/50 PGW and 3) increasing the radiator area in order to reduce PCM freeze times. The analysis showed that for the assumed operating and boundary conditions utilizing a water PCM HX on Orion is not a viable option for any case. Additionally, it was found that the radiator area would have to be increased by at least 40% in order to support a viable water-based PCM HX.

System Level Analysis of a Water PCM HX Integrated Into Orion's Thermal Control System Abstract

NASA Technical Reports Server (NTRS)

Navarro, Moses; Hansen, Scott; Ungar, Eugene; Sheth, Rubik

2015-01-01

In a cyclical heat load environment such as low Lunar orbit, a spacecraft's radiators are not sized to reject the full heat load requirement. Traditionally, a supplemental heat rejection device (SHReD) such as an evaporator or sublimator is used to act as a "topper" to meet the additional heat rejection demands. Utilizing a Phase Change Material (PCM) heat exchanger (HX) as a SHReD provides an attractive alternative to evaporators and sublimators as PCM HXs do not use a consumable, thereby leading to reduced launch mass and volume requirements. In continued pursuit of water PCM HX development an Orion system level analysis was performed using Thermal Desktop for a water PCM HX integrated into Orion's thermal control system and in a 100km Lunar orbit. The study analyzed 1) placing the PCM on the Internal Thermal Control System (ITCS) versus the External Thermal Control System (ETCS) 2) use of 30/70 PGW verses 50/50 PGW and 3) increasing the radiator area in order to reduce PCM freeze times. The analysis showed that for the assumed operating and boundary conditions utilizing a water PCM HX on Orion is not a viable option. Additionally, it was found that the radiator area would have to be increased over 20% in order to have a viable water-based PCM HX.

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.

A binary main-belt comet.

PubMed

Agarwal, Jessica; Jewitt, David; Mutchler, Max; Weaver, Harold; Larson, Stephen

2017-09-20

Asteroids are primitive Solar System bodies that evolve both collisionally and through disruptions arising from rapid rotation. These processes can lead to the formation of binary asteroids and to the release of dust, both directly and, in some cases, through uncovering frozen volatiles. In a subset of the asteroids called main-belt comets, the sublimation of excavated volatiles causes transient comet-like activity. Torques exerted by sublimation measurably influence the spin rates of active comets and might lead to the splitting of bilobate comet nuclei. The kilometre-sized main-belt asteroid 288P (300163) showed activity for several months around its perihelion 2011 (ref. 11), suspected to be sustained by the sublimation of water ice and supported by rapid rotation, while at least one component rotates slowly with a period of 16 hours (ref. 14). The object 288P is part of a young family of at least 11 asteroids that formed from a precursor about 10 kilometres in diameter during a shattering collision 7.5 million years ago. Here we report that 288P is a binary main-belt comet. It is different from the known asteroid binaries in its combination of wide separation, near-equal component size, high eccentricity and comet-like activity. The observations also provide strong support for sublimation as the driver of activity in 288P and show that sublimation torques may play an important part in binary orbit evolution.

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…

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.

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.

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.

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…

Modeling & processing of ceramic and polymer precursor ceramic matrix composite materials

NASA Astrophysics Data System (ADS)

Wang, Xiaolin

Synthesis and processing of novel materials with various advanced approaches have attracted much attention of engineers and scientists for the past thirty years. Many advanced materials display a number of exceptional properties and can be produced with different novel processing techniques. For example, AlN is a promising candidate for electronic, optical and opto-electronic applications due to its high thermal conductivity, high electrical resistivity, high acoustic wave velocity and large band gap. Large bulk AlN crystal can be produced by sublimation of AlN powder. Novel nonostructured multicomponent refractory metal-based ceramics (carbides, borides and nitrides) show a lot of exceptional mechanical, thermal and chemical properties, and can be easily produced by pyrolysis of suitable preceramic precursors mixed with metal particles. The objective of this work is to study sublimation and synthesis of AlN powder, and synthesis of SiC-based metal ceramics. For AlN sublimation crystal growth, we will focus on modeling the processes in the powder source that affect significantly the sublimation growth as a whole. To understand the powder porosity evolution and vapor transport during powder sublimation, the interplay between vapor transport and powder sublimation will be studied. A physics-based computational model will be developed considering powder sublimation and porosity evolution. Based on the proposed model, the effect of a central hole in the powder on the sublimation rate is studied and the result is compared to the case of powder without a hole. The effect of hole size on the sublimation rate will be studied. The effects of initial porosity, particle size and driving force on the sublimation rate are also studied. Moreover, the optimal growth condition for large diameter crystal quality and high growth rate will be determined. For synthesis of SiC-based metal ceramics, we will focus on developing a multi-scale process model to describe the dynamic behavior of filler particle reaction, microstructure evolution, at the microscale as well as transient fluid flow, heat transfer, and species transport at the macroscale. The model comprises of (i) a microscale model and (ii) a macroscale transport model, and aims to provide optimal conditions for the fabrication process of the ceramics. The porous media macroscale model for SiC-based metal-ceramic materials processing will be developed to understand the thermal polymer pyrolysis, chemical reaction of active fillers and transport phenomena in the porous media. The macroscale model will include heat and mass transfer, curing, pyrolysis, chemical reaction and crystallization in a mixture of preceramic polymers and submicron/nano-sized metal particles of uranium, zirconium, niobium, or hafnium. The effects of heating rate, sample size, size and volume ratio of the metal particles on the reaction rate and product uniformity will be studied. The microscale model will be developed for modeling the synthesis of SiC matrix and metal particles. The macroscale model provides thermal boundary conditions to the microscale model. The microscale model applies to repetitive units in the porous structure and describes mass transport, composition changes and motion of metal particles. The unit-cell is the representation unit of the source material, and it consists of several metal particles, SiC matrix and other components produced from the synthesis process. The reactions between different components, the microstructure evolution of the product will be considered. The effects of heating rate and metal particle size on species uniformity and microstructure are investigated.

A Simple Sonication Improves Protein Signal in Matrix-Assisted Laser Desorption Ionization Imaging

NASA Astrophysics Data System (ADS)

Lin, Li-En; Su, Pin-Rui; Wu, Hsin-Yi; Hsu, Cheng-Chih

2018-02-01

Proper matrix application is crucial in obtaining high quality matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI). Solvent-free sublimation was essentially introduced as an approach of homogeneous coating that gives small crystal size of the organic matrix. However, sublimation has lower extraction efficiency of analytes. Here, we present that a simple sonication step after the hydration in standard sublimation protocol significantly enhances the sensitivity of MALDI MSI. This modified procedure uses a common laboratory ultrasonicator to immobilize the analytes from tissue sections without noticeable delocalization. Improved imaging quality with additional peaks above 10 kDa in the spectra was thus obtained upon sonication treatment. [Figure not available: see fulltext.

Sulfur in vacuum - Sublimation effects on frozen melts, and applications to Io's surface and torus

NASA Technical Reports Server (NTRS)

Nash, Douglas B.

1987-01-01

Vacuum sublimation effects on solid sulfur yield a form of the element that is white at room temperature, is fluffy in texture, and forms on frozen sulfur in vacuum through differential evaporation of molecular species in the solid. This vacuum sulfur should exist in large quantity on Io, if the solid free sulfur there has solidified from a melt; a sulfur volcanism model for Io is accordingly developed on this basis which implies that the color and spectra of different sulfur regions of Io could indicate their relative crystallization ages and cooling histories. The flux of sublimating hotspot sulfur appears consistent with estimated turnover rates of the Io surface.

The Residual South Polar Cap of Mars: Stable or Transitory?

NASA Astrophysics Data System (ADS)

Glenar, David A.; Bonev, B. P.; Hansen, G. B.; James, P. B.; Bjorkman, J. E.

2006-09-01

It remains uncertain whether the CO2 residual south polar cap (RSPC) is a permanent feature of the present Mars climate, or whether it occasionally sublimes completely during years marked by dramatic dust storm activity. While there is no firm evidence for complete disappearance of the cap in the past, observations show that the residual cap lost significant CO2 material in the spring / summer season prior to the Mariner 9 encounter. On the other hand, little interannual change has been observed in the RSPC during the MGS mission [1], despite the massive early-spring dust storm which occurred in 2001. We discuss whether a global dust storm beginning near perihelion could enhance the net CO2 sublimation sufficiently to completely remove the RSPC. We utilize a surface-plus-aerosol radiative transfer model under conditions of both modest and heavy atmospheric dust loading. The sublimination behavior depends critically on the extended (visible to thermal IR) albedo spectrum of the polar CO2 ice, which we have strongly constrained [2] from a combination of HST photometric imaging, ground based near-IR imaging spectroscopy and spectroscopic measurements by the Mars Express PFS. The extension of the cap spectrum to thermal IR wavelengths was accomplished by forward modeling using a semi-infinite grid of scattering grains. Results of this analysis depend on the strength of possible feedback mechanisms (increased surface dust content; exposure of water ice) as well as on the possibility of dust confinement by the polar vortex; but the general conclusion is that it would require multiple, intense dust storms in a given year in order to completely remove the CO2 ice veneer layer. This work has been supported by the NASA Planetary Astronomy and Mars Data Analysis Programs. [1] Benson and James, Icarus 174, 513, 2005; [2] Bonev et al., Planet Space Sci. 2006 (accepted).

Chemical regeneration of emitter surface increases thermionic diode life

NASA Technical Reports Server (NTRS)

Breiteieser, R.

1966-01-01

Chemical regeneration of sublimated emitter electrode increases the operating efficiency and life of thermionic diodes. A gas which forms chemical compounds with the sublimated emitter material is introduced into the space between the emitter and the collector. The compounds migrate to the emitter where they decompose and redeposit the emitter material.

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.

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…

New Perspectives on Blowing Snow Transport, Sublimation, and Layer Thermodynamic Structure over Antarctica

NASA Technical Reports Server (NTRS)

Palm, Steve; Kayetha, Vinay; Yang, Yuekui; Pauly, Rebecca M.

2017-01-01

Blowing snow over Antarctica is a widespread and frequent event. Satellite remote sensing using lidar has shown that blowing snow occurs over 70% of the time over large areas of Antarctica in winter. The transport and sublimation of blowing snow are important terms in the ice sheet mass balance equation and the latter is also an important part of the hydrological cycle. Until now the only way to estimate the magnitude of these processes was through model parameterization. We present a technique that uses direct satellite observations of blowing snow and model (MERRA-2) temperature and humidity fields to compute both transport and sublimation of blowing snow over Antarctica for the period 2006 to 2016. The results show a larger annual continent-wide integrated sublimation than current published estimates and a significant transport of snow from continent to ocean. The talk will also include the lidar backscatter structure of blowing snow layers that often reach heights of 200 to 300 m as well as the first dropsonde measurements of temperature, moisture and wind through blowing snow layers.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levin, Barnaby D. A.; Zachman, Michael J.; Werner, Jörg G.

Abstract 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 demonstratemore » 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.« less

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.

Management of the Post-Shuttle Extravehicular Mobility Unit (EMU) Water Circuits

NASA Technical Reports Server (NTRS)

Steele, John W.; Etter, David; Rector, Tony; Hill, Terry; Wells, Kevin

2011-01-01

The EMU incorporates two separate water circuits for the rejection of metabolic heat from the astronaut and the cooling of electrical components. The first (the Transport Water Loop) circulates in a semi-closed-loop manner and absorbs heat into a Liquid Coolant and Ventilation Garment (LCVG) warn by the astronaut. The second (the Feed Water Loop) provides water to a cooling device (Sublimator) with a porous plate, and that water subsequently sublimates to space vacuum. The cooling effect from the sublimation of this water translates to a cooling of the LCVG water that circulates through the Sublimator. Efforts are underway to streamline the use of a water processing kit (ALCLR) that is being used to periodically clean and disinfect the Transport Loop Water. Those efforts include a fine tuning of the duty cycle based on a review of prior performance data as well as an assessment of a fixed installation of this kit into the EMU backpack or within on-orbit EMU interface hardware. Furthermore, testing is being conducted to ensure compatibility between the International Space Station (ISS) Water Processor Assembly (WPA) effluent and the EMU Sublimator as a prelude to using the WPA effluent as influent to the EMU Feed Water loop. This work is undertaken to reduce the crew-time and logistics burdens for the EMU, while ensuring the long-term health of the EMU water circuits for a post-Shuttle 6-year service life.

Management of the Post-Shuttle Extravehicular Mobility Unit (EMU) Water Circuits

NASA Technical Reports Server (NTRS)

Steele, John W.; Etter, David; Rector, Tony; Hill, Terry; Wells, Kevin

2012-01-01

The EMU incorporates two separate water circuits for the rejection of metabolic heat from the astronaut and the cooling of electrical components. The first (the Transport Water Loop) circulates in a semi-closed-loop manner and absorbs heat into a Liquid Coolant and Ventilation Garment (LCVG) worn by the astronaut. The second (the Feed-water Loop) provides water to a cooling device (Sublimator) with a porous plate, and that water subsequently sublimates to space vacuum. The cooling effect from the sublimation of this water translates to a cooling of the LCVG water that circulates through the Sublimator. Efforts are underway to streamline the use of a water processing kit (ALCLR) that is being used to periodically clean and disinfect the Transport Loop Water. Those efforts include a fine tuning of the duty cycle based on a review of prior performance data as well as an assessment of a fixed installation of this kit into the EMU backpack, within on-orbit EMU interface hardware or as a stand-alone unit. Furthermore, testing is being conducted to ensure compatibility between the International Space Station (ISS) Water Processor Assembly (WPA) effluent and the EMU Sublimator as a prelude to using the WPA effluent as influent to the EMU Feed Water loop. This work is undertaken to reduce the crewtime and logistics burdens for the EMU, while ensuring the long-term health of the EMU water circuits for a 6-year service life.

An examination of the thermodynamics of fusion, vaporization, and sublimation of ibuprofen and naproxen by correlation gas chromatography.

PubMed

Maxwell, Rachel; Chickos, James

2012-02-01

The vaporization enthalpies of (S)-ibuprofen and (S)-naproxen measured by correlation gas chromatography at T = 298.15 K are reported and compared with literature values. Adjustment of the fusion enthalpies of (RS)- and (S)-ibuprofen and (S)-naproxen to T = 298.15 K and combined with the vaporization enthalpy of the (S)-enantiomer of both ibuprofen and naproxen also at T = 298.15 K resulted in the sublimation enthalpies of both (S)-enantiomers. On the assumption that the vaporization enthalpy of the racemic form of ibuprofen is within the experimental uncertainty of the chiral form, the sublimation enthalpy of racemic ibuprofen was also evaluated. The vaporization and sublimation enthalpies compare favorably to the most of the literature values for the racemic form of ibuprofen but differ from the value reported for chiral ibuprofen. The literature values of (S)-naproxen are somewhat smaller than the values measured in this work. The following vaporization enthalpies were measured for (S)-ibuprofen and (S)-naproxen, respectively: ΔH(vap) (298.15 K), 106.0 ± 5.5, 132.2 ± 5.0 kJ·mol(-1) . Sublimation enthalpies of 122.7 ± 5.6 and 155.2 ± 7.1 kJ·mol(-1) were calculated for the (S)-enantiomers of ibuprofen and naproxen and a value of 128.9 ± 5.8 kJ·mol(-1) was estimated for the racemic form of ibuprofen. Copyright © 2011 Wiley Periodicals, Inc.

Equatorial ground ice on Mars: Steady-state stability

NASA Technical Reports Server (NTRS)

Mellon, Michael T.; Jakosky, Bruce M.; Postawko, Susan E.

1993-01-01

Current Martian equatorial surface temperatures are too warm for water ice to exist at the surface for any appreciable length of time before subliming into the atmosphere. Subsurface temperatures are generally warmer still and, despite the presence of a diffusive barrier of porous regolith material, it has been shown by Smoluchowski, Clifford and Hillel, and Fanale et al. that buried ground ice will also sublime and be lost to the atmosphere in a relatively short time. We investigate the behavior of this subliming subsurface ice and show that it is possible for ice to maintain at a steady-state depth, where sublimation and diffusive loss to the atmosphere is balanced by resupply from beneath by diffusion and recondensation of either a deeper buried ice deposits or ground water. We examine the behavior of equatorial ground ice with a numercial time-marching molecular diffusion model. In our model we allow for diffusion of water vapor through a porous regolith, variations in diffusivity and porosity with ice content, and recondensation of sublimed water vapor. A regolith containing considerable amounts of ice can still be very porous, allowing water vapor to diffuse up from deeper within the ice layer where temperatures are warmer due to the geothermal gradient. This vapor can then recondense nearer to the surface where ice had previously sublimed and been lost to the atmosphere. As a result we find that ice deposits migrate to find a steady-state depth, which represents a balance between diffusive loss to the atmosphere through the overlying porous regolith and diffusive resupply through a porous icy regolith below. This depth depends primarily on the long-term mean surface temperature and the nature of the geothermal gradient, and is independent of the ice-free porosity and the regolith diffusivity. Only the rate of loss of ground ice depends on diffusive properties.

Summer energy balance and ablation of high elevation glaciers in the central Chilean Andes

NASA Astrophysics Data System (ADS)

Brock, Benjamin; Rivera, Andres; Burger, Flavia; Bravo, Claudio

2014-05-01

Glaciers of the semi-arid central Chilean Andes are an important freshwater source for the populous Central Valley region of Chile, but have been shrinking in recent decades. The surface energy balance of these glaciers is of high scientific interest as summer ablation occurs through both sublimation and melt. During the 2012-13 Austral Summer a glacio-meteorological monitoring programme was established on Olivares Alfa (3.9 km2, 4130-4800 m elevation) and Beta (8.3 km2, 3620-4850 m elevation) Glaciers and their forelands in the Upper Olivares Valley, 33°00'-33°11' S, 70°05'-70°15' W, approximately 50 km north-east of Santiago. This included complete automatic weather stations (AWSs) with sonic rangers to record surface ablation on the ablation zones of the two glaciers, and one AWS in the proglacial area of Olivares Alfa Glacier including precipitation gauge. To complement these point data, daily images of the glaciers were captured with fixed cameras in order to calculate snow cover and albedo distributions. To calculate the surface energy balance and rates of melt and sublimation, a model was developed which uses direct AWS measurements of the radiative fluxes and calculates the turbulent fluxes of sensible and latent heat using the bulk aerodynamic approach. The model also calculates the subsurface heat flux and includes a simple scheme to estimate refreezing of melt water within surface snow or ice. Meteorological data and model results for the December to May period will be presented in this paper. Model calculations match closely the cumulative ablation curve of the sonic ranger at Olivares Alfa, with a slight overestimation, and overestimate cumulative ablation recorded by the sonic ranger at Olivares Beta, possibly due, at least in part, to uncertain snow density values. Modelled cumulative ablation in the December-April period is 2.2 m water equivalent (w.e.) at Olivares Alfa (0.10 m sublimation, 2.10 m melt) and 2.34 m w.e. at Olivares Beta (0.18 m sublimation, 2.16 m melt). The surface energy balance is dominated by shortwave radiation, which is the only net energy input, apart from a minor contribution from sensible heat, while the main outputs of energy are net longwave radiation, melt and sublimation. Ablation is dominated by melt during the warmer midsummer months at the two AWS sites, with mean rates exceeding 30 mm w.e. per day. However, due to the high latent heat of sublimation, it is only in January and February that the melt energy flux clearly exceeds the sublimation energy flux. Sublimation rates are typically ~1 mm w.e. per day and are 50 to 100 % higher at Olivares Beta as a result of higher wind speed and surface temperature, despite similar air temperatures at the two sites. Melt rates are around twice as high in summer months with mean air temperature > -2° C, compared with cooler months. This implies that future atmospheric warming will accelerate shrinkage of these glaciers as the ablation regime switches increasingly from sublimation to a more efficient melt regime.

Modelling of the sublimation of icy grains in the coma of comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Gicquel, A.; Vincent, J.-B.; Shi, X.; Sierks, H.; Rose, M.; Güttler, C.; Tubiana, C.

2015-10-01

The ESA (European Space Agency) Rosetta spacecraft was launched on 2 March 2004, to reach comet 67P/Churyumov-Gerasimenko in August 2014. Since March 2014, images of the nucleus and the coma (gas and dust) of the comet have been acquired by the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) camera system [1] using both, the wide angle camera (WAC) and the narrow angle camera (NAC). The orbiter will be maintained in the vicinity of the comet until perihelion (Rh=1.3 AU) or even until Rh=1.8 AU post-perihelion (December 2015). Nineteen months of uninterrupted, close-up observations of the gas and dust coma will be obtained and will help to characterize the evolution of comet gas and dust activity during its approach to the Sun. Indeed, for the first time, we will follow the development of a comet's coma from a close distance. Also the study of the dust-gas interaction in the coma will highlight the sublimation of icy grains. Even if the sublimation of icy grains is known, it is not yet integrated in a complete dust-gas model. We are using the Direct Simulation Monte Carlo (DSMC) method to study the gas flow close to the nucleus. The code called PI-DSMC (www.pidsmc. com) can simulate millions of molecules for multiple species.When the gas flow is simulated, we inject the dust particle with a zero velocity and we take into account the 3 forces acting on the grains in a cometary environment (drag force, gravity and radiative pressure). We used the DLL (Dynamic Link Library) model to integrate the sublimation of icy grains in the gas flowand allow studying the effect of the additional gas on the dust particle trajectories. For a quantitative analysis of the sublimation of icy, outflowing grains we will consider an ensemble of grains of various radii with different compositions [2] The evolution of the grains, once they are ejected into the coma, depends on their initial size, their composition and the heliocentric distance (because the temperature of the grain is higher close to the Sun). The grain temperatures will be derived by assuming equilibrium between the energy absorbed from the Sun, the energy re-radiated in the infrared, and the cooling by sublimation. We will use Mie theory [3, 4] to compute the scattering properties of an assumed grain (grain size, shape and composition, including mineralogy and porosity). We follow the evolution of grains until the icy layer sublimates completely. Once ejected in the gas flow, the generated molecules have no preferred direction. First results highlighted that the sublimation has a significant influence on the dust trajectories and generates a gas cloud that moves with the velocity of the icy grains. Our model can produce artificial images for a wide range of parameters, including outgassing rate, surface temperature, dust properties and sublimation of icy grains. The results of this model will be compared to the images obtained with OSIRIS camera and to the published data from other instruments.

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.…

Effects of Atmospheric and Surface Dust on the Sublimation Rates of CO2 on Mars

NASA Technical Reports Server (NTRS)

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

2003-01-01

We present an overview of our modeling work dedicated to study the effects of atmospheric dust on the sublimation of CO2 on Mars. The purpose of this study is to better understand the extent to which dust storm activity can be a root cause for interannual variability in the planetary CO2 seasonal cycle, through modifying the springtime regression rates of the south polar cap. We obtain calculations of the sublimation fluxes for various types of polar surfaces and different amounts of atmospheric dust. These calculations have been compared qualitatively with the regression patterns observed by Mars Global Surveyor (MGS) in both visible and infrared wavelengths, for two years of very different dust histories (1999, and 2001).

Electrical control of charged carriers and excitons in atomically thin materials

NASA Astrophysics Data System (ADS)

Wang, Ke; De Greve, Kristiaan; Jauregui, Luis A.; Sushko, Andrey; High, Alexander; Zhou, You; Scuri, Giovanni; Taniguchi, Takashi; Watanabe, Kenji; Lukin, Mikhail D.; Park, Hongkun; Kim, Philip

2018-02-01

Electrical confinement and manipulation of charge carriers in semiconducting nanostructures are essential for realizing functional quantum electronic devices1-3. The unique band structure4-7 of atomically thin transition metal dichalcogenides (TMDs) offers a new route towards realizing novel 2D quantum electronic devices, such as valleytronic devices and valley-spin qubits8. 2D TMDs also provide a platform for novel quantum optoelectronic devices9-11 due to their large exciton binding energy12,13. However, controlled confinement and manipulation of electronic and excitonic excitations in TMD nanostructures have been technically challenging due to the prevailing disorder in the material, preventing accurate experimental control of local confinement and tunnel couplings14-16. Here we demonstrate a novel method for creating high-quality heterostructures composed of atomically thin materials that allows for efficient electrical control of excitations. Specifically, we demonstrate quantum transport in the gate-defined, quantum-confined region, observing spin-valley locked quantized conductance in quantum point contacts. We also realize gate-controlled Coulomb blockade associated with confinement of electrons and demonstrate electrical control over charged excitons with tunable local confinement potentials and tunnel couplings. Our work provides a basis for novel quantum opto-electronic devices based on manipulation of charged carriers and excitons.

Iapetus Surface Temperatures, and the Influence of Sublimation on the Albedo Dichotomy: Cassini CIRS Constraints

NASA Astrophysics Data System (ADS)

Spencer, J. R.; Pearl, J. C.; Segura, M.; Cassini CIRS Team

2005-08-01

The Composite Infrared Spectrometer (CIRS) on the Cassini orbiter obtained extensive observations of Iapetus' thermal emission during the New Year 2005 flyby, with best 8 - 16 μ m spatial resolution of 35 km per pixel. Observed subsolar temperatures on the dark terrain reach nearly 130 K, much warmer than any other satellite surface in the Saturn system, due to the combination of low albedo and slow rotation. These high temperatures mean that, uniquely in the Saturn system, water ice sublimation rates are significant at low latitudes on Iapetus' dark side, and surface water ice is probably not stable there on geological timescales. This result is consistent with the lack of water ice at low latitudes on the dark terrain inferred from Cassini UVIS UV spectra (Hendrix et al., 2005 LPSC). Thermally-controlled migration of water ice may thus contribute to the curious shape of the light/dark boundary on Iapetus, with bright poles and dark terrain extending round the equator onto the trailing side. Impacts of Saturn-centric or prograde heliocentric material cannot alone explain this shape, as their impact flux depends only on distance from the apex of motion (though the impact distribution of Oort cloud comet dust may be consistent with the observed albedo pattern (Cook and Franklin 1970)). We model the ballistic migration of water ice across the surface of Iapetus, determining temperatures and sublimation rates assuming CIRS-constrained thermal inertia and a simple dependence of albedo on distance from the apex of motion. Water ice is lost rapidly from low latitudes on the dark leading side and accumulates near the poles, and is also lost, though more slowly, in equatorial regions near the sub-Saturn and anti-Saturn points. The resulting water ice distribution pattern matches the distribution of Iapetus' bright terrain remarkably well. Albedo modification by thermal migration can thus help to reconcile Iapetus' albedo patterns with albedo control by Saturn-centric or prograde heliocentric impactors.

THERMAL COOK-OFF EXPERIMENTS OF THE HMX BASED HIGH EXPLOSIVE LX-04 TO CHARACTERIZE VIOLENCE WITH VARYING CONFINEMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garcia, F; Vandersall, K S; Forbes, J W

Thermal cook-off experiments were carried out using LX-04 explosive (85% HMX and 15% Viton by weight) with different levels of confinement to characterize the effect of confinement on the reaction violence. These experiments involved heating a porous LX-04 sample in a stainless steel container with varying container end plate thickness and assembly bolt diameter to control overall confinement. As expected, detonation did not occur and reducing the overall confinement lowered the reaction violence. This is consistent with modeling results that predict that a lower confinement will act to lower the cook-off pressure and thus the overall burn rate which lowersmore » the overall violence. These results suggest that controlling the overall system confinement can modify the relative safety in a given scenario.« less

Partitioning of sublimation and evaporation from Lake Bonney using water vapor isotope and latent heat fluxes

NASA Astrophysics Data System (ADS)

Bellagamba, A. W.; Berkelhammer, M. B.; Winslow, L.; Peter, D.; Myers, K. F.

2017-12-01

The landscapes of the McMurdo Dry Valleys in Antarctica are characterized by a series of frozen lakes. Although the conditions in this region are severe, the lakes share common characteristics with lakes at glacial termini elsewhere. Geochemical and geomorphological evidence suggest these lakes have experienced large historical changes indicative of changes water balances. While part of these shifts in lake volume arise from changes in glacial inflow, they likely also reflect changes in the latent heat flux from the lake surfaces. Here we present a joint analysis of the stable isotopic ratio of surface ice/water and the water vapor flux over Dry Valley frozen lakes to ascertain the processes controlling water losses from the lake surfaces. We compare the isotopic ratio of the latent heat flux with the surface water isotopes to derive a fractionation factor associated with latent flux. This data is then used to provide insight into how much of the water vapor flux is sublimated versus evaporated, as well as how the sublimation and evaporative components of the flux change with synoptic weather. We used a Picarro L2130-I isotopic water analyzer to measure humidity and the isotopic ratio of water vapor at three heights over Lake Bonney in Taylor Valley, Antarctica and used the flux-gradient approach to convert the isotopic ratio of the vapor to an "isoflux". An on-site meteorological station recorded temperature, relative humidity and wind direction/intensity at two different heights above the lake and an infrared radiometer recorded lake skin temperature. These data were used to calculate the sensible and latent heat fluxes. The fractionation factor was close to 0, which indicates that sublimation was the primary component of the flux although evaporation became increasingly prominent following a katabatic wind event. The results suggest this technique could be an effective tool to study the sensitivity of latent heat fluxes to weather here and in other similar environments. The trial run performed at Lake Bonney in November-December 2016 was performed as part of the ongoing LTER (Long Term Ecological Research) project at the McMurdo Dry Valleys and a second experiment will be performed in January 2018.

Increased evaporation following widespread tree mortality limits streamflow response

NASA Astrophysics Data System (ADS)

Biederman, J. A.; Harpold, A. A.; Gochis, D. J.; Ewers, B. E.; Reed, D. E.; Papuga, S. A.; Brooks, P. D.

2014-07-01

A North American epidemic of mountain pine beetle (MPB) has disturbed over 5 million ha of forest containing headwater catchments crucial to water resources. However, there are limited observations of MPB effects on partitioning of precipitation between vapor loss and streamflow, and to our knowledge these fluxes have not been observed simultaneously following disturbance. We combined eddy covariance vapor loss (V), catchment streamflow (Q), and stable isotope indicators of evaporation (E) to quantify hydrologic partitioning over 3 years in MPB-impacted and control sites. Annual control V was conservative, varying only from 573 to 623 mm, while MPB site V varied more widely from 570 to 700 mm. During wet periods, MPB site V was greater than control V in spite of similar above-canopy potential evapotranspiration (PET). During a wet year, annual MPB V was greater and annual Q was lower as compared to an average year, while in a dry year, essentially all water was partitioned to V. Ratios of 2H and 18O in stream and soil water showed no kinetic evaporation at the control site, while MPB isotope ratios fell below the local meteoric water line, indicating greater E and snowpack sublimation (Ss) counteracted reductions in transpiration (T) and sublimation of canopy-intercepted snow (Sc). Increased E was possibly driven by reduced canopy shading of shortwave radiation, which averaged 21 W m-2 during summer under control forest as compared to 66 W m-2 under MPB forest. These results show that abiotic vapor losses may limit widely expected streamflow increases.

Formulation and evaluation of floating tablet of H2-receptor antagonist.

PubMed

Kesarla, Rajesh S; Vora, Pratik Ashwinbhai; Sridhar, B K; Patel, Gunvant; Omri, Abdelwahab

2015-01-01

Conventional sustained dosage form of ranitidine hydrochloride (HCl) does not prevent frequent administration due to its degradation in colonic media and limited absorption in the upper part of GIT. Ranitidine HCl floating tablet was formulated with sublimation method to overcome the stated problem. Compatibility study for screening potential excipients was carried out using Fourier transform infrared spectroscopy (FT-IR) and differential scanning chromatography (DSC). Selected excipients were further evaluated for optimizing the formulation. Preliminary screening of binder, polymer and sublimating material was based on hardness and drug release, drug release with release kinetics and floating lag time with total floatation time, respectively. Selected excipients were subjected to 3(2) factorial design with polymer and sublimating material as independent factors. Matrix tablets were obtained by using 16/32" flat-faced beveled edges punches followed by sublimation. FT-IR and DSC indicated no significant incompatibility with selected excipients. Klucel-LF, POLYOX WSR N 60 K and l-menthol were selected as binder, polymer and sublimating material, respectively, for factorial design batches after preliminary screening. From the factorial design batches, optimum concentration to release the drug within 12 h was found to be 420 mg of POLYOX and 40 mg of l-menthol. Stability studies indicated the formulation as stable. Ranitidine HCl matrix floating tablets were formulated to release 90% of drug in stomach within 12 h. Hence, release of the drug could be sustained within narrow absorption site. Moreover, the dosage form was found to be floating within a fraction of second independent of the pH of media ensuring a robust formulation.

Very high temperature behavior of HTGR core materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soo, P.; Uneberg, G.; Sabatini, R.

1978-01-01

A description is given of experiments to investigate the behavior of HTGR core materials during hypothetical heatup accidents in which the core temperature is assumed to reach values between 2400/sup 0/C and the graphite sublimation range (>3600/sup 0/C). The work includes BISO coated fuel particle failure, simulated fission product migration in core graphite, and graphite sublimation behavior.

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…

Product mass transfer resistance directly determined during freeze-drying cycle runs using tunable diode laser absorption spectroscopy (TDLAS) and pore diffusion model.

PubMed

Kuu, Wei Y; O'Bryan, Kevin R; Hardwick, Lisa M; Paul, Timothy W

2011-08-01

The pore diffusion model is used to express the dry layer mass transfer resistance, [Formula: see text], as a function of the ratio r(e)/?, where r(e) is the effective pore radius and ? is the tortuosity factor of the dry layer. Using this model, the effective pore radius of the dry layer can be estimated from the sublimation rate and product temperature profiles measured during primary drying. Freeze-drying cycle runs were performed using the LyoStar II dryer (FTS Systems), with real-time sublimation rate profiles during freeze drying continuously measured by tunable diode laser absorption spectroscopy (TDLAS). The formulations chosen for demonstration of the proposed approach include 5% mannitol, 5% sucrose, 5% lactose, 3% mannitol plus 2% sucrose, and a parenteral nutrition formulation denoted VitaM12. The three different methods used for determination of the product resistance are: (1) Using both the sublimation rate and product temperature profiles, (2) using the sublimation rate profile alone, and (3) using the product temperate profile alone. Unlike the second and third methods, the computation procedure of first method does not need solution of the complex heat and mass transfer equations.

Kinetics of laser irradiated nanoparticles cloud

NASA Astrophysics Data System (ADS)

Mishra, S. K.; Upadhyay Kahaly, M.; Misra, Shikha

2018-02-01

A comprehensive kinetic model describing the complex kinetics of a laser irradiated nanoparticle ensemble has been developed. The absorbed laser radiation here serves dual purpose, viz., photoenhanced thermionic emission via rise in its temperature and direct photoemission of electrons. On the basis of mean charge theory along with the equations for particle (electron) and energy flux balance over the nanoparticles, the transient processes of charge/temperature evolution over its surface and mass diminution on account of the sublimation (phase change) process have been elucidated. Using this formulation phenomenon of nanoparticle charging, its temperature rise to the sublimation point, mass ablation, and cloud disintegration have been investigated; afterwards, typical timescales of disintegration, sublimation and complete evaporation in reference to a graphite nanoparticle cloud (as an illustrative case) have been parametrically investigated. Based on a numerical analysis, an adequate parameter space describing the nanoparticle operation below the sublimation temperature, in terms of laser intensity, wavelength and nanoparticle material work function, has been identified. The cloud disintegration is found to be sensitive to the nanoparticle charging through photoemission; as a consequence, it illustrates that radiation operating below the photoemission threshold causes disintegration in the phase change state, while above the threshold, it occurs with the onset of surface heating.

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.

Comet 67p/Churyumov-Gerasimenko, possible origin of the depression Hatmehit

NASA Astrophysics Data System (ADS)

Kossacki, Konrad J.; Czechowski, Leszek

2018-05-01

On the nucleus of comet 67P/Churyumov-Gerasimenko numerous pits and depressions of different sizes are identified. In the present work the origin of depression Hatmehit is investigated. We propose a mechanism that includes recession of the surface due to sub-dust sublimation together with formation of cavities. Recession of the surface is calculated taking into account the sub-dust sublimation of water ice with volatile organic components, formation of a strengthened ice-dust crust due to sintering of ice grains and the increase of the gas pressure in pores due to release of gaseous CO. Our simulations indicate, that the formation of a 300 m deep depression due to the sub-dust sublimation of ice can take as little as 50 orbital periods assuming that the heliocentric distance at perihelion is close to its present value (Ip. et al., 2016). When amorphous water ice is present at small depth the release of gaseous CO may cause either compression of low-strength material beneath the strengthened crust, or ejection of the crust. In both cases a cavity is formed and grows due to the sublimation of ice from the wall and the floor.

An examination of the thermodynamics of fusion, vaporization, and sublimation of several parabens by correlation gas chromatography.

PubMed

Umnahanant, Patamaporn; Chickos, James

2011-05-01

The vaporization, fusion, and sublimation enthalpies of methyl, ethyl, propyl, and butyl paraben are reported and compared with literature values. The vaporization enthalpies were measured by correlation gas chromatography and the fusion enthalpies by differential scanning calorimetry. Adjusted to T = 298.15 K, these enthalpies were combined to yield the sublimation enthalpy. The results compare favorably to some of the literature values but do not support the reversal in magnitude of both the vaporization and sublimation enthalpy previously reported for propyl and butyl paraben. The following fusion and vaporization enthalpies were measured for methyl through to butyl paraben, respectively: ΔH(fus) (T(fus) ) 26.3 ± 0.1 (398.6 K), 26.5 ± 0.1 (388.5 K), 27.3 ± 0.1 (368.8), and 25.9 ± 0.3 (340.7 K) kJ·mol(-1); ΔH(vap) (298.15 K) 79.5 ± 0.5, 84.0 ± 0.5, 89.7 ± 0.6, and 95.8 ± 0.6 kJ·mol(-1). The results are believed to be accurate to ± 4 kJ·mol(-1). Copyright © 2011 Wiley-Liss, Inc.

Building solids inside nano-space: from confined amorphous through confined solvate to confined 'metastable' polymorph.

PubMed

Nartowski, K P; Tedder, J; Braun, D E; Fábián, L; Khimyak, Y Z

2015-10-14

The nanocrystallisation of complex molecules inside mesoporous hosts and control over the resulting structure is a significant challenge. To date the largest organic molecule crystallised inside the nano-pores is a known pharmaceutical intermediate - ROY (259.3 g mol(-1)). In this work we demonstrate smart manipulation of the phase of a larger confined pharmaceutical - indomethacin (IMC, 357.8 g mol(-1)), a substance with known conformational flexibility and complex polymorphic behaviour. We show the detailed structural analysis and the control of solid state transformations of encapsulated molecules inside the pores of mesoscopic cellular foam (MCF, pore size ca. 29 nm) and controlled pore glass (CPG, pore size ca. 55 nm). Starting from confined amorphous IMC we drive crystallisation into a confined methanol solvate, which upon vacuum drying leads to the stabilised rare form V of IMC inside the MCF host. In contrast to the pure form, encapsulated form V does not transform into a more stable polymorph upon heating. The size of the constraining pores and the drug concentration within the pores determine whether the amorphous state of the drug is stabilised or it recrystallises into confined nanocrystals. The work presents, in a critical manner, an application of complementary techniques (DSC, PXRD, solid-state NMR, N2 adsorption) to confirm unambiguously the phase transitions under confinement and offers a comprehensive strategy towards the formation and control of nano-crystalline encapsulated organic solids.

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.

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.

An integrated process analytical technology (PAT) approach to monitoring the effect of supercooling on lyophilization product and process parameters of model monoclonal antibody formulations.

PubMed

Awotwe Otoo, David; Agarabi, Cyrus; Khan, Mansoor A

2014-07-01

The aim of the present study was to apply an integrated process analytical technology (PAT) approach to control and monitor the effect of the degree of supercooling on critical process and product parameters of a lyophilization cycle. Two concentrations of a mAb formulation were used as models for lyophilization. ControLyo™ technology was applied to control the onset of ice nucleation, whereas tunable diode laser absorption spectroscopy (TDLAS) was utilized as a noninvasive tool for the inline monitoring of the water vapor concentration and vapor flow velocity in the spool during primary drying. The instantaneous measurements were then used to determine the effect of the degree of supercooling on critical process and product parameters. Controlled nucleation resulted in uniform nucleation at lower degrees of supercooling for both formulations, higher sublimation rates, lower mass transfer resistance, lower product temperatures at the sublimation interface, and shorter primary drying times compared with the conventional shelf-ramped freezing. Controlled nucleation also resulted in lyophilized cakes with more elegant and porous structure with no visible collapse or shrinkage, lower specific surface area, and shorter reconstitution times compared with the uncontrolled nucleation. Uncontrolled nucleation however resulted in lyophilized cakes with relatively lower residual moisture contents compared with controlled nucleation. TDLAS proved to be an efficient tool to determine the endpoint of primary drying. There was good agreement between data obtained from TDLAS-based measurements and SMART™ technology. ControLyo™ technology and TDLAS showed great potential as PAT tools to achieve enhanced process monitoring and control during lyophilization cycles. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

Determination of mass and heat transfer parameters during freeze-drying cycles of pharmaceutical products.

PubMed

Hottot, A; Vessot, S; Andrieu, J

2005-01-01

The principal aim of this study was to evaluate the water vapour mass transfer resistance of the dried layer and the vial heat transfer coefficient values of a pharmaceutical product during the primary drying period. First, overall vial heat transfer coefficient values, Kv, were determined by a gravimetric method based on pure ice sublimation experiments. Thus, it was possible to set up a map of the total heat flux received by each vial throughout the plate surface of our pilot scale freeze-dryer. Important heterogeneities were observed for the vials placed at the plate edges and for the vials placed at the center of the plate. As well, the same gravimetric method was also used to precisely determine the influence of main lyophilization operating parameters (shelf temperature and gas total pressure) or the vial types and sizes on these overall heat transfer coefficient values. A semi-empirical relationship as a function of total gas pressure was proposed. The transient method by pressure rise analysis (PRA method) after interrupting the water vapour flow between the sublimation chamber and the condenser, previously set up and validated in our laboratory, was then extensively used with an amorphous BSA-based formulation to identify the dried layer mass transfer resistance values, Rp, the ice front temperature, and the total heat transfer coefficient values, Kv, with or without annealing treatment. It was proved that this method gave accurate and coherent data only during the first half of the sublimation period when the totality of the vials of the set was still sublimating. Thus, this rapid method allowed estimation of, on line and in situ, the sublimation front temperature and the characterization of the morphology and structure of the freeze-dried layer, all along the first part of the sublimation period. The estimated sublimation temperatures shown by the PRA model were about 2 degrees C lower than the experimental values obtained using thermocouples inserted inside the vial, in accordance with previous data given by this method for similar freeze-drying conditions. As well, by using this method we could confirm the homogenization of the dried layer porous structure by annealing treatment after the freezing step. Furthermore, frozen matrix structure analysis (mean pore diameter) using optical microscopy and mass transfer modelling of water vapour by molecular diffusion (Knudsen regime) allowed, in some cases, to predict the experimental values of this overall mass transfer resistance directly related to the freeze-dried cake permeability.

Lithography process for patterning HgI2 photonic devices

DOEpatents

Mescher, Mark J.; James, Ralph B.; Hermon, Haim

2004-11-23

A photolithographic process forms patterns on HgI.sub.2 surfaces and defines metal sublimation masks and electrodes to substantially improve device performance by increasing the realizable design space. Techniques for smoothing HgI.sub.2 surfaces and for producing trenches in HgI.sub.2 are provided. A sublimation process is described which produces etched-trench devices with enhanced electron-transport-only behavior.

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.

Modeling ground thermal regime of an ancient buried ice body in Beacon Valley, Antarctica using a 1-D heat equation with latent heat effect

NASA Astrophysics Data System (ADS)

Liu, L.; Sletten, R. S.; Hallet, B.; Waddington, E. D.; Wood, S. E.

2013-12-01

An ancient massive ice body buried under several decimeters of debris in Beacon Valley, Antarctica is believed to be over one million years old, making it older than any known glacier or ice cap. It is fundamentally important as a reservoir of water, proxy for climatic information, and an expression of the periglacial landscape. It is also one of Earth's closest analog for widespread, near-surface ice found in Martian soils and ice-cored landforms. We are interested in understanding controls on how long this ice may persist since our physical model of sublimation suggests it should not be stable. In these models, the soil temperatures and the gradient are important because it determines the direction and magnitude of the vapor flux, and thus sublimation rates. To better understand the heat transfer processes and constrain the rates of processes governing ground ice stability, a model of the thermal behavior of the permafrost is applied to Beacon Valley, Antarctica. It calculates soil temperatures based on a 1-D thermal diffusion equation using a fully implicit finite volume method (FVM). This model is constrained by soil physical properties and boundary conditions of in-situ ground surface temperature measurements (with an average of -23.6oC, a maximum of 20.5oC and a minimum of -54.3oC) and ice-core temperature record at ~30 m. Model results are compared to in-situ temperature measurements at depths of 0.10 m, 0.20 m, 0.30 m, and 0.45 m to assess the model's ability to reproduce the temperature profile for given thermal properties of the debris cover and ice. The model's sensitivity to the thermal diffusivity of the permafrost and the overlaying debris is also examined. Furthermore, we incorporate the role of ice condensation/sublimation which is calculated using our vapor diffusion model in the 1-D thermal diffusion model to assess potential latent heat effects that in turn affect ground ice sublimation rates. In general, the model simulates the ground thermal regime well. Detailed temperature comparison suggests that the 1-D thermal diffusion model results closely approximate the measured temperature at all depths with the average square root of the mean squared error (SRMSE) of 0.15oC; a linear correlation between modeled and measured temperatures yields an average R2 value of 0.9997. Prominent seasonal temperature variations diminish with depth, and it equilibrates to mean annual temperature at about 21.5 m depth. The amount of heat generated/consumed by ice condensation/sublimation is insufficient to significantly impact the thermal regime.

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. © 2011 American Institute of Physics

TRIGGERING SUBLIMATION-DRIVEN ACTIVITY OF MAIN BELT COMETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haghighipour, N.; Maindl, T. I.; Dvorak, R.

2016-10-10

It has been suggested that the comet-like activity of main belt comets (MBCs) is due to the sublimation of sub-surface water–ice that has been exposed as a result of their surfaces being impacted by meter-sized bodies. We have examined the viability of this scenario by simulating impacts between meter-sized and kilometer-sized objects using a smooth particle hydrodynamics approach. Simulations have been carried out for different values of the impact velocity and impact angle, as well as different target material and water-mass fractions. Results indicate that for the range of impact velocities corresponding to those in the asteroid belt, the depthmore » of an impact crater is slightly larger than 10 m, suggesting that if the activation of MBCs is due to the sublimation of sub-surface water–ice, this ice has to exist no deeper than a few meters from the surface. Results also show that ice exposure occurs in the bottom and on the interior surface of impact craters, as well as on the surface of the target where some of the ejected icy inclusions are re-accreted. While our results demonstrate that the impact scenario is indeed a viable mechanism to expose ice and trigger the activity of MBCs, they also indicate that the activity of the current MBCs is likely due to ice sublimation from multiple impact sites and/or the water contents of these objects (and other asteroids in the outer asteroid belt) is larger than the 5% that is traditionally considered in models of terrestrial planet formation, providing more ice for sublimation. We present the details of our simulations and discuss their results and implications.« less

Thermophysics of fractures on comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Höfner, S.; Vincent, J.-B.; Blum, J.; Davidsson, B. J. R.; Sierks, H.; El-Maarry, M. R.; Deller, J.; Hofmann, M.; Hu, X.; Pajola, M.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; A'Hearn, M. F.; Auger, A.-T.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Bodewits, D.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; Fornasier, S.; Fulle, M.; Gicquel, A.; Groussin, O.; Gutiérrez, P. J.; Gutiérrez-Marqués, P.; Güttler, C.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Knollenberg, J.; Kovacs, G.; Kramm, J.-R.; Kührt, E.; Küppers, M.; La Forgia, F.; Lazzarin, M.; Lopez-Moreno, J. J.; Marzari, F.; Michalik, H.; Moissl-Fraund, R.; Moreno, F.; Mottola, S.; Naletto, G.; Oklay, N.; Preusker, F.; Scholten, F.; Shi, X.; Thomas, N.; Toth, I.; Tubiana, C.; Zitzmann, S.

2017-12-01

Context. The camera OSIRIS on board Rosetta obtained high-resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Great parts of the nucleus surface are composed of fractured terrain. Aims: Fracture formation, evolution, and their potential relationship to physical processes that drive activity are not yet fully understood. Observed temperatures and gas production rates can be explained or interpreted with the presence of fractures by applying appropriate modelling methods. Methods: We followed a transient thermophysical model approach that includes radiative, conductive, and water-ice sublimation fluxes by considering a variety of heliocentric distances, illumination conditions, and thermophysical properties for a set of characteristic fracture geometries on the nucleus of 67P. We computed diurnal temperatures, heat fluxes, and outgassing behaviour in order to derive and distinguish the influence of the mentioned parameters on fractured terrain. Results: Our analysis confirms that fractures, as already indicated by former studies about concavities, deviate from flat-terrain topographies with equivalent properties, mostly through the effect of self-heating. Compared to flat terrain, illuminated cometary fractures are generally warmer, with smaller diurnal temperature fluctuations. Maximum sublimation rates reach higher peaks, and dust mantle quenching effects on sublimation rates are weaker. Consequently, the rough structure of the fractured terrain leads to significantly higher inferred surface thermal inertia values than for flat areas with identical physical properties, which might explain the range of measured thermal inertia on 67P. Conclusions: At 3.5 AU heliocentric distance, sublimation heat sinks in fractures converge to maximum values >50 W / m2 and trigger dust activity that can be related mainly to H2O. Fractures are likely to grow through the erosive interplay of alternating sublimation and thermal fatigue.

Matrix isolation studies of carbonic acid--the vapor phase above the β-polymorph.

PubMed

Bernard, Jürgen; Huber, Roland G; Liedl, Klaus R; Grothe, Hinrich; Loerting, Thomas

2013-05-22

Twenty years ago two different polymorphs of carbonic acid, α- and β-H2CO3, were isolated as thin, crystalline films. They were characterized by infrared and, of late, by Raman spectroscopy. Determination of the crystal structure of these two polymorphs, using cryopowder and thin film X-ray diffraction techniques, has failed so far. Recently, we succeeded in sublimating α-H2CO3 and trapping the vapor phase in a noble gas matrix, which was analyzed by infrared spectroscopy. In the same way we have now investigated the β-polymorph. Unlike α-H2CO3, β-H2CO3 was regarded to decompose upon sublimation. Still, we have succeeded in isolation of undecomposed carbonic acid in the matrix and recondensation after removal of the matrix here. This possibility of sublimation and recondensation cycles of β-H2CO3 adds a new aspect to the chemistry of carbonic acid in astrophysical environments, especially because there is a direct way of β-H2CO3 formation in space, but none for α-H2CO3. Assignments of the FTIR spectra of the isolated molecules unambiguously reveal two different carbonic acid monomer conformers (C(2v) and C(s)). In contrast to the earlier study on α-H2CO3, we do not find evidence for centrosymmetric (C(2h)) carbonic acid dimers here. This suggests that two monomers are entropically favored at the sublimation temperature of 250 K for β-H2CO3, whereas they are not at the sublimation temperature of 210 K for α-H2CO3.

Mechanical collapse of confined fluid membrane vesicles.

PubMed

Rim, Jee E; Purohit, Prashant K; Klug, William S

2014-11-01

Compact cylindrical and spherical invaginations are common structural motifs found in cellular and developmental biology. To understand the basic physical mechanisms that produce and maintain such structures, we present here a simple model of vesicles in confinement, in which mechanical equilibrium configurations are computed by energy minimization, balancing the effects of curvature elasticity, contact of the membrane with itself and the confining geometry, and adhesion. For cylindrical confinement, the shape equations are solved both analytically and numerically by finite element analysis. For spherical confinement, axisymmetric configurations are obtained numerically. We find that the geometry of invaginations is controlled by a dimensionless ratio of the adhesion strength to the bending energy of an equal area spherical vesicle. Larger adhesion produces more concentrated curvatures, which are mainly localized to the "neck" region where the invagination breaks away from its confining container. Under spherical confinement, axisymmetric invaginations are approximately spherical. For extreme confinement, multiple invaginations may form, bifurcating along multiple equilibrium branches. The results of the model are useful for understanding the physical mechanisms controlling the structure of lipid membranes of cells and their organelles, and developing tissue membranes.

PENTACARBON DIOXIDE (C{sub 5}O{sub 2}) FORMATION AND ITS ROLE AS A TRACER OF SOLAR SYSTEM EVOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Förstel, Marko; Maksyutenko, Pavlo; Kaiser, Ralf I.

2016-02-20

Carbon monoxide is the second most abundant molecule on icy grains in the interstellar medium. These grains are under the influence of ionizing radiation, which induces the chemical reaction within the ice. Here we report the first observation of subliming pentacarbon dioxide (C{sub 5}O{sub 2}) after irradiation of pure carbon monoxide ice with energetic electrons. Our results show that pentacarbon dioxide is a stable reaction product in a carbon monoxide matrix that survives the sublimation in star-forming regions at sublimation temperatures of 175 K. Along with carbon suboxide (C{sub 3}O{sub 2}), this molecule can serve as a powerful tracer ofmore » the temperature history of formerly carbon monoxide rich ices in molecular clouds and star-forming regions.« less

Some observations on value and greatness in drama.

PubMed

Mandelbaum, George

2011-04-01

This paper argues that value in drama partly results from the nature of the resistance in a scene, resistance used in its common, everyday meaning. A playwright's ability to imagine and present such resistance rests on several factors, including his sublimation of the fantasies that underpin his work. Such sublimation is evident in Chekhov's continuing reworking in his plays of a fantasy that found its initial embodiment for him in one of the central scenes in Hamlet. The increasingly higher value of the scenes Chekhov wrote as he repeatedly reworked Shakespeare's scene resulted from his increasing sublimation of the initial fantasy and is reflected in the ever more complex nature of the resistance found in Chekhov's scenes, resistance that, in turn, created an ever more life-like, three-dimensional central character in the scenes. Copyright © 2011 Institute of Psychoanalysis.

Cell confinement controls centrosome positioning and lumen initiation during epithelial morphogenesis

PubMed Central

Rodríguez-Fraticelli, Alejo E.; Auzan, Muriel; Alonso, Miguel A.; Bornens, Michel

2012-01-01

Epithelial organ morphogenesis involves sequential acquisition of apicobasal polarity by epithelial cells and development of a functional lumen. In vivo, cells perceive signals from components of the extracellular matrix (ECM), such as laminin and collagens, as well as sense physical conditions, such as matrix stiffness and cell confinement. Alteration of the mechanical properties of the ECM has been shown to promote cell migration and invasion in cancer cells, but the effects on epithelial morphogenesis have not been characterized. We analyzed the effects of cell confinement on lumen morphogenesis using a novel, micropatterned, three-dimensional (3D) Madin-Darby canine kidney cell culture method. We show that cell confinement, by controlling cell spreading, limits peripheral actin contractility and promotes centrosome positioning and lumen initiation after the first cell division. In addition, peripheral actin contractility is mediated by master kinase Par-4/LKB1 via the RhoA–Rho kinase–myosin II pathway, and inhibition of this pathway restores lumen initiation in minimally confined cells. We conclude that cell confinement controls nuclear–centrosomal orientation and lumen initiation during 3D epithelial morphogenesis. PMID:22965908

Investigation of drying stresses on proteins during lyophilization: differentiation between primary and secondary-drying stresses on lactate dehydrogenase using a humidity controlled mini freeze-dryer.

PubMed

Luthra, Sumit; Obert, Jean-Philippe; Kalonia, Devendra S; Pikal, Michael J

2007-01-01

This article describes the design, performance testing, and application of a controlled humidity mini-freeze-dryer in studying the physical stability of lactate dehydrogenase during lyophilization. Performance evaluation of the mini-freeze-dryer was conducted with tests, namely water sublimation, radiation heat exchange, lowest achievable temperature, and leak testing. Protein stability studies were conducted by comparing protein activity at various stages of lyophilization with the initial activity. The shelf and condenser temperature were stable at <-40 degrees C, wall temperature was within 2 degrees C of the shelf temperature, and the leak rate was small. The chamber pressure was controlled by the ice on the condenser and the product temperature during sublimation was equal to the shelf temperature. Addition of Tween 80 prevented activity loss in solution and after freeze-thaw. No activity loss was observed after primary-drying even in absence of lyoprotectants and with collapse of cake structure. Five percent (w/w) sucrose concentration was required to achieve full stabilization. In conclusion, performance testing established that the mini-freeze-dryer was suitable for mechanistic freeze-drying studies. Secondary-drying was the critical step for protein stability. The concentration of sucrose required to stabilize the protein completely was several orders of magnitude higher than that required to satisfy the direct interaction requirement of the protein. (c) 2006 Wiley-Liss, Inc. and the American Pharmacists Association.

Capturing Gases in Carbon Honeycomb

NASA Astrophysics Data System (ADS)

Krainyukova, Nina V.

2017-04-01

In our recent paper (Krainyukova and Zubarev in Phys Rev Lett 116:055501, 2016. doi: 10.1103/PhysRevLett.116.055501) we reported the observation of an exceptionally stable honeycomb carbon allotrope obtained by deposition of vacuum-sublimated graphite. A family of structures can be built from absolutely dominant {sp}2-bonded carbon atoms, and may be considered as three-dimensional graphene. Such structures demonstrate high absorption capacity for gases and liquids. In this work we show that the formation of honeycomb structures is highly sensitive to the carbon evaporation temperature and deposition rates. Both parameters are controlled by the electric current flowing through thin carbon rods. Two distinctly different regimes were found. At lower electric currents almost pure honeycomb structures form owing to sublimation. At higher currents the surface-to-bulk rod melting is observed. In the latter case densification of the carbon structures and a large contribution of glassy graphite emerge. The experimental diffraction patterns from honeycomb structures filled with absorbed gases and analyzed by the advanced method are consistent with the proposed models for composites which are different for Ar, Kr and Xe atoms in carbon matrices.

High-Speed Boundary-Layer Transition: Study of Stationary Crossflow Using Spectral Analysis

NASA Astrophysics Data System (ADS)

McGuire, Patrick Joseph

Crossflow instability is primary cause of boundary-layer transition on swept wings used in high-speed applications. Delaying the downstream location of transition would drastically reduce the viscous drag over the wing surface, and subsequently improves the overall aircraft efficiency. By studying the development of instability growth rates and how they interact with the surroundings, researchers can control the crossflow transition location. Experiments on the 35° swept-wing model were performed in the NASA Langley 20-Inch Supersonic Wind Tunnel with Mach 2.0 flow conditions and 20 μm tall discrete roughness elements (DRE) with varying spacing placed along the leading edge. Fluorene was used as the sublimating chemical in the surface flow visualization technique to observe the transition front and stationary crossflow vortex patterns in the laminar flow region. Spatial spectral decomposition was completed on high-resolution images of sublimating chemical runs using a newly developed image processing technique. Streamwise evolution of the vortex track wavelengths within the laminar boundary-layer region was observed. The spectral information was averaged to produce dominant modes present throughout the laminar region.

Railgun armature velocity improvement, SBIR phase 2

NASA Astrophysics Data System (ADS)

Thurmond, Leo E.; Bauer, David P.

1992-08-01

Railgun hypervelocity performance has not been repeatably demonstrated at velocities over 6 km/s. A significant performance limiting phenomena is the formation of secondary current paths in parallel with the main projectile accelerating plasma. A confined plasma armature technique was developed to prevent secondary armature formation. Confinement prevents loss of ionized material from the plasma armature and thereby prevents formation of a low rail-to-rail conductance. We controlled pressure in the confined armature via controlled venting through ports in the rails. Railgun tests with the confined armature show that sealing at the rail-confinement vessel interface is critical and difficult to achieve. Our tests show that during low seal leakage operation secondaries are prevented. However, maintaining good seal for the entire launch is very difficult.

The Mars water cycle at other epochs: Recent history of the polar caps and layered terrain

NASA Technical Reports Server (NTRS)

Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

1992-01-01

The Martian polar caps and layered terrain presumably evolves by the deposition and removal of small amounts of water and dust each year, the current cap attributes therefore represent the incremental transport during a single year as integrated over long periods of time. The role was studied of condensation and sublimation of water ice in this process by examining the seasonal water cycle during the last 10(exp 7) yr. In the model, axial obliquity, eccentricity, and L sub s of perihelion vary according to dynamical models. At each epoch, the seasonal variations in temperature are calculated at the two poles, keeping track of the seasonal CO2 cap and the summertime sublimation of water vapor into the atmosphere; net exchange of water between the two caps is calculated based on the difference in the summertime sublimation between the two caps (or on the sublimation from one cap if the other is covered with CO2 frost all year). Results from the model can help to explain (1) the apparent inconsistency between the timescales inferred for layer formation and the much older crater retention age of the cap and (2) the difference in sizes of the two residual caps, with the south being smaller than the north.

A new method for laminar boundary layer transition visualization in flight: Color changes in liquid crystal coatings

NASA Technical Reports Server (NTRS)

Holmes, B. J.; Gall, P. D.; Croom, C. C.; Manuel, G. S.; Kelliher, W. C.

1986-01-01

The visualization of laminar to turbulent boundary layer transition plays an important role in flight and wind-tunnel aerodynamic testing of aircraft wing and body surfaces. Visualization can help provide a more complete understanding of both transition location as well as transition modes; without visualization, the transition process can be very difficult to understand. In the past, the most valuable transition visualization methods for flight applications included sublimating chemicals and oil flows. Each method has advantages and limitations. In particular, sublimating chemicals are impractical to use in subsonic applications much above 20,000 feet because of the greatly reduced rates of sublimation at lower temperatures (less than -4 degrees Farenheit). Both oil flow and sublimating chemicals have the disadvantage of providing only one good data point per flight. Thus, for many important flight conditions, transition visualization has not been readily available. This paper discusses a new method for visualizing transition in flight by the use of liquid crystals. The new method overcomes the limitations of past techniques, and provides transition visualization capability throughout almost the entire altitude and speed ranges of virtually all subsonic aircraft flight envelopes. The method also has wide applicability for supersonic transition visualization in flight and for general use in wind tunnel research over wide subsonic and supersonic speed ranges.

Inner Edges of Compact Debris Disks around Metal-rich White Dwarfs

NASA Astrophysics Data System (ADS)

Rafikov, Roman R.; Garmilla, José A.

2012-12-01

A number of metal-rich white dwarfs (WDs) are known to host compact, dense particle disks, which are thought to be responsible for metal pollution of these stars. In many such systems, the inner radii of disks inferred from their spectra are so close to the WD that particles directly exposed to starlight must be heated above 1500 K and are expected to be unstable against sublimation. To reconcile this expectation with observations, we explore particle sublimation in H-poor debris disks around WDs. We show that because of the high metal vapor pressure the characteristic sublimation temperature in these disks is 300-400 K higher than in their protoplanetary analogs, allowing particles to survive at higher temperatures. We then look at the structure of the inner edges of debris disks and show that they should generically feature superheated inner rims directly exposed to starlight with temperatures reaching 2500-3500 K. Particles migrating through the rim toward the WD (and rapidly sublimating) shield the disk behind them from strong stellar heating, making the survival of solids possible close to the WD. Our model agrees well with observations of WD+disk systems provided that disk particles are composed of Si-rich material such as olivine, and have sizes in the range ~0.03-30 cm.

Noncontact Infrared-Mediated Heat Transfer During Continuous Freeze-Drying of Unit Doses.

PubMed

Van Bockstal, Pieter-Jan; De Meyer, Laurens; Corver, Jos; Vervaet, Chris; De Beer, Thomas

2017-01-01

Recently, an innovative continuous freeze-drying concept for unit doses was proposed, based on spinning the vials during freezing. An efficient heat transfer during drying is essential to continuously process these spin frozen vials. Therefore, the applicability of noncontact infrared (IR) radiation was examined. The impact of several process and formulation variables on the mass of sublimed ice after 15 min of primary drying (i.e., sublimation rate) and the total drying time was examined. Two experimental designs were performed in which electrical power to the IR heaters, distance between the IR heaters and the spin frozen vial, chamber pressure, product layer thickness, and 5 model formulations were included as factors. A near-infrared spectroscopy method was developed to determine the end point of primary and secondary drying. The sublimation rate was mainly influenced by the electrical power to the IR heaters and the distance between the IR heaters and the vial. The layer thickness had the largest effect on total drying time. The chamber pressure and the 5 model formulations had no significant impact on sublimation rate and total drying time, respectively. This study shows that IR radiation is suitable to provide the energy during the continuous processing of spin frozen vials. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

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.

A Low Cost Inflatable CubeSat Drag Brake Utilizing Sublimation

NASA Astrophysics Data System (ADS)

Horn, Adam Charles

The United Nations Inter-Agency Debris Coordination Committee has adopted a 25-year post-mission lifetime requirement for any satellite orbiting below 2000 km in order to mitigate the growing orbital debris threat. Low-cost CubeSats have become important satellite platforms with startling capabilities, but this guideline restricts them to altitudes below 600 km because they remain in orbit too long. In order to enable CubeSat deployments at higher release altitudes, a low-cost, ultra-reliable deorbit device is needed. This thesis reports on efforts to develop a deployable and passively inflatable drag brake that can deorbit from higher orbital altitudes, thereby complying with the 25-year orbital lifetime guideline. On the basis of concepts first implemented during the NASA Echo Satellite Project, this study investigated the design of an inflatable CubeSat drag device that utilizes sublimating benzoic acid powder as the inflation propellant. Testing has focused on demonstrating the functionality of charging a Mylar drag brake bladder with appropriate quantities of benzoic acid powder, and the exposure to a controlled-temperature vacuum chamber causing the bladder to inflate. Although results show a measureable increase in internal pressure when introduced to anticipated orbital temperatures, a significant air-derived expansion prior to sublimation was encountered due to the undetectable volume of ambient residual air in the fabricated membrane bladders. These tests have demonstrated the feasibility of this approach, thereby demonstrating that this concept can create a potentially smaller and less expensive drag device, eliminating inflation gas tanks and valves. In that way, this system can provide a low-cost, miniaturized system that reduces a CubeSat's orbital lifetime to less than 25 years, when placed at higher orbital altitude.

Exploring the effects of overburden on the sublimation and transport of H2O on Iapetus

NASA Astrophysics Data System (ADS)

Rivera-Valentin, Edgard G.; Blackburn, David G.; Ulrich, Richard K.

2012-08-01

It has been shown through both measurements and simulations that there exists a measurable ice-free, porous, overburden overlaying water ice on Cassini Regio. Mass transfer through this porous media in a vacuum would occur in the Knudsen regime, which provides sublimation rates orders of magnitude smaller than Hertz-Langmuir sublimation. The availability of water ice for transport from this region is thus currently controlled by mass transfer through the dark material overburden. Thermal segregation suggests that Iapetus' polar regions have been brightened via ballistic transport of water and its subsequent cold trapping since exogenic deposition models predict dark high latitudes on the leading hemisphere. The limiting effect of the dark material on transport of water ice may thus greatly impact the current mass balance at the poles. The effects of the overburden on the global stability and transport of H2O is addressed in order to gain insight into its influence on the polar albedo distribution and current state of thermal segregation within the dark terrain. Results indicate that thermal segregation is currently an inactive or weak process within Cassini Regio, though it is an ongoing process at the inter-terrain regions. Modeling of polar accumulation suggests that even accounting for the current dark material cover within Cassini Regio there exists sufficient ballistically inbound water to overcome exogenic darkening mechanisms. Topographic effects on local albedo differences are also simulated to provide a more complete water stability study of Iapetus. Results suggest that topographically induced changes in heat flux may be sufficient to create the observed local albedo contrasts and also support ongoing dark exogenic deposition within Cassini Regio to explain the lack of bright slopes deep within the dark terrain.

First Production of C60 Nanoparticle Plasma Jet for Study of Disruption Mitigation for ITER

NASA Astrophysics Data System (ADS)

Bogatu, I. N.; Thompson, J. R.; Galkin, S. A.; Kim, J. S.; Brockington, S.; Case, A.; Messer, S. J.; Witherspoon, F. D.

2012-10-01

Unique fast response and large mass-velocity delivery of nanoparticle plasma jets (NPPJs) provide a novel application for ITER disruption mitigation, runaway electrons diagnostics and deep fueling. NPPJs carry a much larger mass than usual gases. An electromagnetic plasma gun provides a very high injection velocity (many km/s). NPPJ has much higher ram pressure than any standard gas injection method and penetrates the tokamak confining magnetic field. Assimilation is enhanced due to the NP large surface-to-volume ratio. Radially expanding NPPJs help achieving toroidal uniformity of radiation power. FAR-TECH's NPPJ system was successfully tested: a coaxial plasma gun prototype (˜35 cm length, 96 kJ energy) using a solid state TiH2/C60 pulsed power cartridge injector produced a hyper-velocity (>4 km/s), high-density (>10^23 m-3), C60 plasma jet in ˜0.5 ms, with ˜1-2 ms overall response-delivery time. We present the TiH2/C60 cartridge injector output characterization (˜180 mg of sublimated C60 gas) and first production results of a high momentum C60 plasma jet (˜0.6 g.km/s).

Uniquely confining Cu2S nanoparticles in graphitized carbon fibers for enhanced oxygen evolution reaction

NASA Astrophysics Data System (ADS)

Zhao, Xiaoqian; Liu, Li; Zhang, Yan; Zhang, Huijuan; Wang, Yu

2017-08-01

Up to now, the literature on Cu2S with specific morphology applied to oxygen evolution reaction (OER) in the electrocatalytic field has been limited. In this work, unique peapod-like Cu2S/C exhibiting superb electrocatalytic performance toward OER is successfully synthesized, by employing Cu(OH)2 nanorods as the template and nontoxic glucose as the carbon source and then annealing with sublimed sulfur. It can be seen that this work explores a new application area for Cu2S. More precisely, the novel morphology contributes to increasing the electrochemical active surface area effectively and promoting contact between the Cu2S nanoparticles and the electrolyte. During electrochemical measurements, the peapod-like Cu2S/C shows enhanced electrocatalytic activity with a low overpotential of 401 mV at the current density of 10 mA cm-2 and a Tafel slope of 52 mV dec-1. More importantly, our material is able to maintain stability for at least 8 h at constant potential and the current loss is negligible after 2000 cycles. Obviously, these striking properties fully demonstrate that the peapod-like Cu2S/C as an efficient catalyst shows great promise for OER.

Orbital Evolution of Dust Particles in the Sublimation Zone near the Sun

NASA Astrophysics Data System (ADS)

Shestakova, L. I.; Demchenko, B. I.

2018-03-01

We have performed the calculations of the orbital evolution of dust particles from volcanic glass ( p-obsidian), basalt, astrosilicate, olivine, and pyroxene in the sublimation zone near the Sun. The sublimation (evaporation) rate is determined by the temperature of dust particles depending on their radius, material, and distance to the Sun. All practically important parameters that characterize the interaction of spherical dust particles with the radiation are calculated using the Mie theory. The influence of radiation and solar wind pressure, as well as the Poynting-Robertson drag force effects on the dust dynamics, are also taken into account. According to the observations (Shestakova and Demchenko, 2016), the boundary of the dust-free zone is 7.0-7.6 solar radii for standard particles of the zodiacal cloud and 9.1-9.2 solar radii for cometary particles. The closest agreement is obtained for basalt particles and certain kinds of olivine, pyroxene, and volcanic glass.

Trust: the sublime duty in health care leadership.

PubMed

Piper, Llewellyn E

2010-01-01

Trust is the essence of human social existence. From the moment of birth, trust is the basic component in any human relationship and interaction. Trust is the Holy Grail for human confidence in others. From human survival to organizational survival, trust is the primordial bond. No organization is more dependent on trust than health care. This article views trust as the most basic fundamental quality for leadership. Trust is a sublime duty of a leader and the leadership of an organization. Leadership sets the culture of trust. Trust is the one quality that is essential for guiding an organization toward serving others. This article addresses trust from many perspectives. Trust is viewed from our subordinates, our peers, our superiors, and the public we serve. This article postulates how trust in an organization is the sublime duty of leadership that unites all human understanding and without it destroys all human relationships.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Rabindar K., E-mail: rkrksharma6@gmail.com; Reddy, G. B., E-mail: rkrksharma6@gmail.com

In this report, we synthesize vertically aligned molybdenum trioxide (α−MoO{sub 3}) nanoflakes (NFs) with high aspect ratio (height/thickness >15) on the cobalt coated glass substrates by the plasma assisted sublimation process, employing Mo metal strip as a sublimation source. The effect of substrate temperature, nature of substrate as well as the geometry of the sublimation source (Mo-strip) have been investigated on the morphological, structural and optical properties of the grown NFs, keeping plasma parameters as fixed. The surface morphology, crystalline structure and optical properties of MoO{sub 3} NFs have been studied systematically by using scanning electron microscope (SEM), transmission electronmore » microscope (TEM) with selected area electron diffraction (SAED), X-ray diffractometer, and IR- spectroscopy. The experimental observations endorse that the characteristics of MoO{sub 3} NFs are strongly depend on substrate temperature, substrate nature as well as geometry of Mo-strip. All the observed results are well in consonance with each other.« less

Diffusive-convective physical vapor transport of PbTe from a Te-rich solid source

NASA Technical Reports Server (NTRS)

Zoutendyk, J.; Akutagawa, W.

1982-01-01

Crystal growth of PbTe by physical vapor transport (sublimation) in a closed ampoule is governed by the vapor species in thermal equilibrium with the solid compound. Deviations from stoichiometry in the source material cause diffusion limitation of the transport rate, which can be modified by natural (gravity-driven) convection. Mass-transport experiments have been performed using Te-rich material wherein sublimation rates have been measured in order to study the effects of natural convection in diffusion-limited vapor transport. Linear velocities for both crystal growth and evaporation (back sublimation) have been measured for transport in the direction of gravity, horizontally, and opposite to gravity. The experimental results are discussed in terms of both the one-dimensional diffusive-advective model and current, more sophisticated theory which includes natural convection. There is some evidence that convection effects from radial temperature gradients and solutal density gradients have been observed.

Sulfur in vacuum - Sublimation effects on frozen melts, and applications to Io's surface and torus

NASA Astrophysics Data System (ADS)

Nash, D. B.

1987-10-01

The author has found from laboratory experiments that vacuum sublimation has a profound effect on the molecular composition, microtexture, bulk density (porosity), and the UV/visible spectral reflectance of the surface of solid sulfur samples, both when the sulfur is in the form of frozen or quenched melts and as laboratory-grade sulfur powder. These sublimation effects produce a unique surface material, the understanding of which may have important implications for deciphering the many enigmatic optical and textural properties of the surface of Jupiter's satellite Io. This planetary body is thought to have a surface greatly enriched in volcanically produced elemental sulfur and sulfur compounds and to have a surface atmospheric pressure with an upper limit of ≡10-7atm, comparable to a good laboratory vacuum, and surface hotspots at temperatures of about 300K covering about 0.3% of its global surface.

Sublimation, culture, and creativity.

PubMed

Kim, Emily; Zeppenfeld, Veronika; Cohen, Dov

2013-10-01

Combining insights from Freud and Weber, this article explores whether Protestants (vs. Catholics and Jews) are more likely to sublimate their taboo feelings and desires toward productive ends. In the Terman sample (Study 1), Protestant men and women who had sexual problems related to anxieties about taboos and depravity had greater creative accomplishments, as compared to those with sexual problems unrelated to such concerns and to those reporting no sexual problems. Two laboratory experiments (Studies 2 and 3) found that Protestants produced more creative artwork (sculptures, poems, collages, cartoon captions) when they were (a) primed with damnation-related words, (b) induced to feel unacceptable sexual desires, or (c) forced to suppress their anger. Activating anger or sexual attraction was not enough; it was the forbidden or suppressed nature of the emotion that gave the emotion its creative power. The studies provide possibly the first experimental evidence for sublimation and suggest a cultural psychological approach to defense mechanisms.

Transfer of Asymmetry between Proteinogenic Amino Acids under Harsh Conditions

NASA Astrophysics Data System (ADS)

Tarasevych, Arkadii V.; Vives, Thomas; Snytnikov, Valeriy N.; Guillemin, Jean-Claude

2017-09-01

The heating above 400 °C of serine, cysteine, selenocysteine and threonine leads to a complete decomposition of the amino acids and to the formation in low yields of alanine for the three formers and of 2-aminobutyric acid for the latter. At higher temperature, this amino acid is observed only when sublimable α-alkyl-α-amino acids are present, and with an enantiomeric excess dependent on several parameters. Enantiopure or enantioenriched Ser, Cys, Sel or Thr is not able to transmit its enantiomeric excess to the amino acid formed during its decomposition. The presence during the sublimation-decomposition of enantioenriched valine or isoleucine leads to the enantioenrichment of all sublimable amino acids independently of the presence of many decomposition products coming from the unstable derivative. All these studies give information on a potentially prebiotic key-reaction of abiotic transformations between α-amino acids and their evolution to homochirality.

Ceres: predictions for near-surface water ice stability and implications for plume generating processes

USGS Publications Warehouse

Titus, Timothy N.

2015-01-01

This paper will constrain the possible sources and processes for the formation of recently observed H2O vapor plumes above the surface of the dwarf planet Ceres. Two hypotheses have been proposed: (1) cryovolcanism where the water source is the mantle and the heating source is still unknown or (2) comet-like sublimation where near-surface water ice is vaporized by seasonally increasing solar insolation. We test hypothesis #2, comet-like near-surface sublimation, by using a thermal model to examine the stability of water-ice in the near surface. For a reasonable range of physical parameters (thermal inertia, surface roughness, slopes), we find that water ice is only stable at latitudes higher than ~40-60 degrees. These results indicate that either (a) the physical properties of Ceres are unlike our expectations or (b) an alternative to comet-like sublimation, such as the cryovolcanism hypothesis, must be invoked.

Comparative rates of freeze-drying for lactose and sucrose solutions as measured by photographic recording, product temperature, and heat flux transducer.

PubMed

Chen, Rongjun; Slater, Nigel K H; Gatlin, Larry A; Kramer, Tony; Shalaev, Evgenyi Y

2008-01-01

Sublimation from lactose and sucrose solutions has been monitored by temperature measurement, visual observation, heat flux sensing and manometric measurements. Estimates of energy transfer rates to the subliming mass made from visual observations and heat flux measurements are in broad agreement, demonstrating for the first time that heat flux sensors can be used to monitor the progress of lyophilization in individual vials with low sample volumes. Furthermore, it is shown that under identical lyophilization conditions the initial rate of drying for lactose solutions is low with little water sublimation for up to 150 minutes, which contrasts markedly with the much faster initial rate of drying for sucrose solutions. Measurement of the initial heat flux between shelf and vial indicated a lower flux to a 10% lactose solution than to a 10% sucrose solution.

Thermal control extravehicular life support system

NASA Technical Reports Server (NTRS)

1975-01-01

The results of a comprehensive study which defined an Extravehicular Life Support System Thermal Control System (TCS) are presented. The design of the prototype hardware and a detail summary of the prototype TCS fabrication and test effort are given. Several heat rejection subsystems, water management subsystems, humidity control subsystems, pressure control schemes and temperature control schemes were evaluated. Alternative integrated TCS systems were studied, and an optimum system was selected based on quantitative weighing of weight, volume, cost, complexity and other factors. The selected subsystem contains a sublimator for heat rejection, bubble expansion tank for water management, a slurper and rotary separator for humidity control, and a pump, a temperature control valve, a gas separator and a vehicle umbilical connector for water transport. The prototype hardware complied with program objectives.

Control of plasma stored energy for burn control using DIII-D in-vessel coils

DOE PAGES

Hawryluk, Richard J.; Eidietis, Nicholas W.; Grierson, Brian A.; ...

2015-04-09

A new approach has been experimentally demonstrated to control the stored energy by applying a non-axisymmetric magnetic field using the DIII-D in-vessel coils to modify the energy confinement time. In future burning plasma experiments as well as magnetic fusion energy power plants, various concepts have been proposed to control the fusion power. The fusion power in a power plant operating at high gain can be related to the plasma stored energy and hence, is a strong function of the energy confinement time. Thus, an actuator that modifies the confinement time can be used to adjust the fusion power. In relativelymore » low collisionality DIII-D discharges, the application of nonaxisymmetric magnetic fields results in a decrease in confinement time and density pumpout. Furthermore, gas puffing was used to compensate the density pumpout in the pedestal while control of the stored energy was demonstrated by the application of non-axisymmetric fields.« less

Comparison and analysis of theoretical models for diffusion-controlled dissolution.

PubMed

Wang, Yanxing; Abrahamsson, Bertil; Lindfors, Lennart; Brasseur, James G

2012-05-07

Dissolution models require, at their core, an accurate diffusion model. The accuracy of the model for diffusion-dominated dissolution is particularly important with the trend toward micro- and nanoscale drug particles. Often such models are based on the concept of a "diffusion layer." Here a framework is developed for diffusion-dominated dissolution models, and we discuss the inadequacy of classical models that are based on an unphysical constant diffusion layer thickness assumption, or do not correctly modify dissolution rate due to "confinement effects": (1) the increase in bulk concentration from confinement of the dissolution process, (2) the modification of the flux model (the Sherwood number) by confinement. We derive the exact mathematical solution for a spherical particle in a confined fluid with impermeable boundaries. Using this solution, we analyze the accuracy of a time-dependent "infinite domain model" (IDM) and "quasi steady-state model" (QSM), both formally derived for infinite domains but which can be applied in approximate fashion to confined dissolution with proper adjustment of a concentration parameter. We show that dissolution rate is sensitive to the degree of confinement or, equivalently, to the total concentration C(tot). The most practical model, the QSM, is shown to be very accurate for most applications and, consequently, can be used with confidence in design-level dissolution models so long as confinement is accurately treated. The QSM predicts the ratio of diffusion layer thickness to particle radius (the Sherwood number) as a constant plus a correction that depends on the degree of confinement. The QSM also predicts that the time required for complete saturation or dissolution in diffusion-controlled dissolution experiments is singular (i.e., infinite) when total concentration equals the solubility. Using the QSM, we show that measured differences in dissolution rate in a diffusion-controlled dissolution experiment are a result of differences in the degree of confinement on the increase in bulk concentration independent of container geometry and polydisperse vs single particle dissolution. We conclude that the constant diffusion-layer thickness assumption is incorrect in principle and should be replaced by the QSM with accurate treatment of confinement in models of diffusion-controlled dissolution.

Basal sublimation and venting of the north seasonal cap of Mars

NASA Astrophysics Data System (ADS)

Piqueux, S.; Christensen, P. R.

2007-12-01

Spots, fans and dark polygonal patterns form during the spring on the southern seasonal cap of Mars as a consequence of 1) the basal sublimation of the translucent and impermeable slab of carbon dioxide and 2) the venting of the CO2 gas loaded with dust and sand size material scoured from the surface of the polar layered deposits. The dark polygons on the cap have a similar formation process as the spots but the dust and sand erupt from elongated vents rather than point sources. In the summer, spiders and etched polygons remain on the southern polar layered deposits. The spiders are shaped by the scouring action of confined CO2 gas flowing between the cap and the basement and converging toward point sources, whereas the etched polygons result form the forced migration of the CO2 gas over longer distances. Comparable observations during the spring near the north pole on the seasonal cap indicate that similar processes occur in both polar regions and that the venting model developed for the south seasonal cap also operates near the north pole. However, spider and etched polygonal features are extremely uncommon on the north substrate, indicating that the conditions for their formation (e.g. mechanical strength of the slab and the substrate, transparency of the seasonal cap) are not met. The continual erosion and re-sedimentation occurring at the surface of the polar layered deposits by the seasonal degassing is a major geomorphological agent shaping the polar regions. The polar layered deposits have been proposed to contain the stratigraphic record of climatic changes and catastrophic events of very high interest for future missions. Our observations suggest that both polar regions deposits may have been locally disrupted by the seasonal sub-ice gas flow and that the stratigraphic record may have been partially lost. The Phoenix landing site might have been affected in the past and the stratigraphic information associated with the original deposition of the polar material partially disrupted due to this surface reworking.

Evaluation of spin freezing versus conventional freezing as part of a continuous pharmaceutical freeze-drying concept for unit doses.

PubMed

De Meyer, L; Van Bockstal, P-J; Corver, J; Vervaet, C; Remon, J P; De Beer, T

2015-12-30

Spin-freezing as alternative freezing approach was evaluated as part of an innovative continuous pharmaceutical freeze-drying concept for unit doses. The aim of this paper was to compare the sublimation rate of spin-frozen vials versus traditionally frozen vials in a batch freeze-dryer, and its impact on total drying time. Five different formulations, each having a different dry cake resistance, were tested. After freezing, the traditionally frozen vials were placed on the shelves while the spin-frozen vials were placed in aluminum vial holders providing radial energy supply during drying. Different primary drying conditions and chamber pressures were evaluated. After 2h of primary drying, the amount of sublimed ice was determined in each vial. Each formulation was monitored in-line using NIR spectroscopy during drying to determine the sublimation endpoint and the influence of drying conditions upon total drying time. For all tested formulations and applied freeze-drying conditions, there was a significant higher sublimation rate in the spin-frozen vials. This can be explained by the larger product surface and the lower importance of product resistance because of the much thinner product layers in the spin frozen vials. The in-line NIR measurements allowed evaluating the influence of applied drying conditions on the drying trajectories. Copyright © 2015 Elsevier B.V. All rights reserved.

Simulated Martian pressure cycle based on the sublimation and deposition of polar CO2

NASA Astrophysics Data System (ADS)

Kemppinen, Osku; Paton, Mark; Savijärvi, Hannu; Harri, Ari-Matti

2014-05-01

The Martian atmospheric pressure cycle is driven by sublimation and deposition of CO2 at polar caps. In the thin atmosphere of Mars the surface energy balance and thus the phase changes of CO2 are dominated by radiation. Additionally, because the atmosphere is so thin, the annual polar cap cycle can have a large relative effect on the pressure. In this work we utilize radiative transfer models to calculate the amount of radiation incoming to Martian polar latitudes over each sol of the year, as well as the amount of energy lost from the surface due to thermal radiation. The energy budget calculated in this way allows us to estimate the amount of CO2 sublimating and depositing at each hour of the Martian year. Since virtually all of the sublimated CO2 is believed to enter and stay in the atmosphere until depositing, this estimate allows us to calculate the annual pressure cycle, assuming that the CO2 is distributed approximately evenly over the planet. The model is running with physically plausible parameters and producing encouragingly good fits to in situ measured data made by e.g. Viking landers. In the next phase we will validate the simulation runs against polar ice cap thickness measurements as well as compare the calculated CO2 source and sink strengths to the sources and sinks of global atmospheric models.

Apollo experience report: Lunar module environmental control subsystem

NASA Technical Reports Server (NTRS)

Gillen, R. J.; Brady, J. C.; Collier, F.

1972-01-01

A functional description of the environmental control subsystem is presented. Development, tests, checkout, and flight experiences of the subsystem are discussed; and the design fabrication, and operational difficulties associated with the various components and subassemblies are recorded. Detailed information is related concerning design changes made to, and problems encountered with, the various elements of the subsystem, such as the thermal control water sublimator, the carbon dioxide sensing and control units, and the water section. The problems associated with water sterilization, water/glycol formulation, and materials compatibility are discussed. The corrective actions taken are described with the expection that this information may be of value for future subsystems. Although the main experiences described are problem oriented, the subsystem has generally performed satisfactorily in flight.

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.

78 FR 73379 - List of Approved Spent Fuel Storage Casks: HI-STORM 100 Cask System; Amendment No. 9

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-06

..., and criticality control. If there is no loss of confinement, shielding, or criticality control, the... would prevent loss of confinement, shielding, and criticality control. If there is no loss of...;Federal Register / Vol. 78, No. 235 / Friday, December 6, 2013 / Rules and Regulations#0;#0; [[Page 73379...

The sublimation kinetics of GeSe single crystals

NASA Technical Reports Server (NTRS)

Irene, E. A.; Wiedemeier, H.

1975-01-01

The sublimation kinetics of (001) oriented GeSe single crystal platelets was studied by high-temperature mass spectroscopy, quantitative vacuum microbalance techniques, and hot stage optical microscopy. For a mean experimental temperature of 563 K, the activation enthalpy and entropy are found to equal 32.3 kcal/mole and 19.1 eu, respectively. The vaporization coefficient is less than unity for the range of test temperatures, and decreases with increasing temperature. The combined experimental data are correlated by means of a multistep surface adsorption mechanism.

Chemical reactions confined within carbon nanotubes.

PubMed

Miners, Scott A; Rance, Graham A; Khlobystov, Andrei N

2016-08-22

In this critical review, we survey the wide range of chemical reactions that have been confined within carbon nanotubes, particularly emphasising how the pairwise interactions between the catalysts, reactants, transition states and products of a particular molecular transformation with the host nanotube can be used to control the yields and distributions of products of chemical reactions. We demonstrate that nanoscale confinement within carbon nanotubes enables the control of catalyst activity, morphology and stability, influences the local concentration of reactants and products thus affecting equilibria, rates and selectivity, pre-arranges the reactants for desired reactions and alters the relative stability of isomeric products. We critically evaluate the relative advantages and disadvantages of the confinement of chemical reactions inside carbon nanotubes from a chemical perspective and describe how further developments in the controlled synthesis of carbon nanotubes and the incorporation of multifunctionality are essential for the development of this ever-expanding field, ultimately leading to the effective control of the pathways of chemical reactions through the rational design of multi-functional carbon nanoreactors.

Kinetics of electron-beam dispersion of fullerite C60

NASA Astrophysics Data System (ADS)

Razanau, Ihar; Mieno, Tetsu; Kazachenko, Victor

2012-06-01

Electron-beam dispersion of pressed fullerite C60 targets in vacuum leads to the deposition of thin films containing polymeric forms of C60. The aim of the present report is to analyze physical-chemical processes in the fullerite target during its electron-beam dispersion through the analysis of the kinetics of the radiation temperature of the target surface, the coating growth rate and the density of negative current on the substrate. It was shown that the induction stage of the process is determined by the negative charging and radiation-induced modification and heating of the target. The transitional stage is characterized by nonstationary sublimation of the target material through the pores in the modified surface layer and release of the accumulated negative charge. Stabilization of the process parameters owing to the convection cooling of the target by the sublimation products and the decrease in the pressure inside the microcavities beneath the pores leads to a quasi-stationary stage of target sublimation and deposition of a coating containing polymeric forms of C60.

Past, present, and future of sublimation transfer imaging

NASA Astrophysics Data System (ADS)

Akada, Masanori

1990-07-01

SONY's announcement of tlavica system shaked the world in 1981. In the new nonphotographic imaging system, image is acquired with CCD to be converted into electric image-signal, stored in magnetic recording media,displayed on a CR1 and printed on a special sheet. To get a hard copy, Sublimation Transfer technology was developed. That announcement brought about world-wide R&D of competitive color imaging systems: Ink-jet, Wax transfer,. Sublimation Transfer(ST) and Electrophotography. In spite of much effort,most of those were insufficient for getting a good hard copy. Developing sufficient ST recording media, Dai Nippon Printing started ST recording media business in 1986. It was the first manufacturing scale production and sale of ST recording media in the world. Nowadays ST technology is known for its advantages: high image quality, consistency from copy to copy, smooth tone-reproduction from high-light to maximum density, and easiness to use. In the following paper progress of ST recording media and the present situation and future markets of the media will be presented.

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.

Thermogravimetric study of vapor pressure of TATP synthesized without recrystallization.

PubMed

Mbah, Jonathan; Knott, Debra; Steward, Scott

2014-11-01

This study aims at characterizing the vapor pressure signatures generated by triacetone triperoxide (TATP) that was synthesized without recrystallization by thermogravimmetric analysis (TGA) for exploitation by standoff detection technologies of explosive devices. The thermal behavior of the nonrecrystallized sample was compared with reported values. Any phase change, melting point and decomposition identification were studied by differential scanning calorimeter. Vapor pressures were estimated by the Langmuir method of evaporation from an open surface in a vacuum. Vapor pressures of TATP at different temperatures were calculated using the linear logarithmic relationship obtained from benzoic acid reference standard. Sublimation of TATP was found to follow apparent zero-order kinetics and sublimes at steady rates at 298 K and above. While the enthalpy of sublimation found, 71.7 kJ mol(-1), is in agreement with reported values the vapor pressures deviated significantly. The differences in the vapor pressures behavior are attributable to the synthesis pathway chosen in this study. Copyright © 2014 Elsevier B.V. All rights reserved.

Impact of water temperature and stressor controllability on swim stress-induced changes in body temperature, serum corticosterone, and immobility in rats.

PubMed

Drugan, Robert C; Eren, Senem; Hazi, Agnes; Silva, Jennifer; Christianson, John P; Kent, Stephen

2005-10-01

The present study compared the effects of three different water temperatures (20, 25, and 30 degrees C) and stressor controllability on several physiological and behavioral endpoints in an intermittent swim stress paradigm. The escape latency of rats in the 20 and 25 degrees C water was less than that observed for the 30 degrees C group. Both escape and yoked groups at 20 and 25 degrees C exhibited moderate to severe hypothermia following the swim stress session that returned to prestress levels 30-40 min post-stress. At 30 degrees C core body temperature (Tb) only decreased by 1 degree C for either swim group. Following swim, serum corticosterone (CORT) levels were significantly elevated in both escape and yoked groups in comparison to confined and home cage controls. The confined control group showed a significant elevation that was approximately halfway between the home cage control and the swim stress groups. At 30 degrees C, there was still a significant elevation of serum CORT in both swim groups in comparison to confined and home cage controls. Therefore, 30 degrees C appears to be the optimal water temperature to evaluate stress controllability effects in the current paradigm. In a final experiment, swim stressor controllability effects were examined in a 5 min forced swim test (FST) 24 h following the initial stress exposure. Rats exposed to yoked-inescapable swim stress at 30 degrees C exhibited more immobility than their escapable swim stress and confined counterparts, while the escape and confined controls did not differ. These results demonstrate that the behavioral deficits observed in the FST are attributable to the stress of inescapable swim and not swim stress per se.

The Dependence of the Circumnuclear Coma Structure on the Properties of the Nucleus. IV. Structure of the Night-Side Gas Coma of a Strongly Sublimating Nucleus

NASA Astrophysics Data System (ADS)

Crifo, J. F.; Rodionov, A. V.

2000-12-01

The structure of the nightside coma in the vicinity of a strongly active comet nucleus of pure ice is investigated by solving gasdynamic equations for the flow of water vapour sublimated from—or condensed onto—the nucleus surface. To guarantee the physical validity of the solution, both Euler and Navier-Stokes Equations are solved, and the solutions are compared. A spherical nucleus is considered first and then a triaxial ellipsoidal nucleus. The results show that (1) a fluid coma of significant extent and very complicated physical structure is formed; (2) for low heat conduction transfer across the nucleus from the dayside to the nightside surface, a narrow conical weak shock appears near to the antisolar axis; the whole nightside surface acts as a cold trap for the vapor, part of which recondenses onto it; (3) for intermediate heat conduction, part of the nightside surface becomes weakly sublimating, and a different weak shock pattern is formed; and (4) at high heat conduction, the whole nightside surface is weakly sublimating, and the resulting flow pattern becomes similar to that existing in a coma formed by diffusion from the nucleus interior (see Crifo, Rodionov and Bockelée-Morvan, 1999, Icarus138, 83-106). The results are compared to related model results by other authors, and a discussion is made of their relevance to the 1996 observation of the near-nucleus nightside coma of Comet C/1996 B2 Hyakutake.

Spatial Variation of Pressure in the Lyophilization Product Chamber Part 1: Computational Modeling.

PubMed

Ganguly, Arnab; Varma, Nikhil; Sane, Pooja; Bogner, Robin; Pikal, Michael; Alexeenko, Alina

2017-04-01

The flow physics in the product chamber of a freeze dryer involves coupled heat and mass transfer at different length and time scales. The low-pressure environment and the relatively small flow velocities make it difficult to quantify the flow structure experimentally. The current work presents the three-dimensional computational fluid dynamics (CFD) modeling for vapor flow in a laboratory scale freeze dryer validated with experimental data and theory. The model accounts for the presence of a non-condensable gas such as nitrogen or air using a continuum multi-species model. The flow structure at different sublimation rates, chamber pressures, and shelf-gaps are systematically investigated. Emphasis has been placed on accurately predicting the pressure variation across the subliming front. At a chamber set pressure of 115 mtorr and a sublimation rate of 1.3 kg/h/m 2 , the pressure variation reaches about 9 mtorr. The pressure variation increased linearly with sublimation rate in the range of 0.5 to 1.3 kg/h/m 2 . The dependence of pressure variation on the shelf-gap was also studied both computationally and experimentally. The CFD modeling results are found to agree within 10% with the experimental measurements. The computational model was also compared to analytical solution valid for small shelf-gaps. Thus, the current work presents validation study motivating broader use of CFD in optimizing freeze-drying process and equipment design.

An examination of the thermodynamics of fusion, vaporization, and sublimation of (R,S)- and (R)-flurbiprofen by correlation gas chromatography.

PubMed

Umnahanant, Patamaporn; Hasty, Darrell; Chickos, James

2012-06-01

The vaporization, fusion, and sublimation enthalpies of (R,S)- and (R)-flurbiprofen at T = 298.15 K are reported and compared with literature values when available. Correlation gas chromatography experiments were first performed to identify appropriate standards that could be used for materials containing a single fluorine substituent. Subsequent correlations resulted in a vaporization enthalpy for (R,S)-flurbiprofen and (R)-flurbiprofen, ΔH(vap) (298.15 K), of (127.5 ± 5.5) and (127.4 ± 4.7) kJ mol, respectively. Fusion enthalpies, ΔH(fus) (387 K), of (28.2 ± and, ΔH(fus) (381 K), (22.8 ± kJ mol(-1) were also measured by differential scanning calorimetry for the racemic and chiral forms of flurbiprofen. Adjusted to T = 298.15 K and combined with the vaporization enthalpy resulted in sublimation enthalpies, ΔH(sub) (298.15 K), of (155.6 ± 5.8) and (145.1 ± 5.7) kJ mol(-1) for (R,S)- and (R)-flurbiprofen, respectively. The fusion enthalpy measured for the racemic form was in excellent agreement with the literature value, while the sublimation enthalpy varies substantially from previous work. Two weak solid-solid phase transitions were also observed for (R)-flurbiprofen at T = 353.9 K (0.30 ± 0.1) and 363.2 K (0.21 ± 0.03) kJ · mol(-1). Copyright © 2012 Wiley Periodicals, Inc.

Effect of laser peening with glycerol as plasma confinement layer

NASA Astrophysics Data System (ADS)

Tsuyama, Miho; Ehara, Naoya; Yamashita, Kazuma; Heya, Manabu; Nakano, Hitoshi

2018-03-01

The effects of controlling the plasma confinement layer on laser peening were investigated by measuring the hardness and residual stress of laser-peened stainless steels. The plasma confinement layer contributes to increasing the pressure of shock waves by suppressing the expansion of the laser-produced plasma. Most previous studies on laser peening have employed water as the plasma confinement layer. In this study, a glycerol solution is used in the context of a large acoustic impedance. It is found that this glycerol solution is superior to water in its ability to confine plasma and that suitable conditions exist for the glycerol solution to act as a plasma confinement layer to achieve efficient laser peening.

Robotic system for retractable teleoperated arm within enclosed shell with capability of operating within a confined space

DOEpatents

Randolph, John David; Lloyd, Peter Downes; Love, Lonnie Joe; Kwon, Dong Soo; Blank, James Allen; Davis, Hurley Thomas

2001-01-01

An apparatus for performing a task in a confined space having an access port. The apparatus comprise: a confinement box securable to the access port of the confined space; a shell extending from the confinement box; a teleoperated arm movable between a retracted position, in which the teleoperated arm is disposed within the shell, and a deployed position, in which the teleoperated arm extends through the access port and into the confined space to perform the task; and a control system for commanding the teleoperated arm. The arm links and joint connectors of the teleoperated arm assembly are the conduits for the process

Alternative E ammonia feedstock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lentz, M.J.; Wright, R.A.

1999-07-01

Power plants are using more Ammonia for increasing precipitator and baghouse efficiency, for SCR and SNCR processes, and for controlling acid stack plumes and dewpoint corrosion. These simple systems inject ammonia and air into the furnace or the precipitator or baghouse inlet ductwork. The common feedstocks in use today are Anhydrous ammonia [NH{sub 3}] and Aqueous ammonia [NH{sub 4}OH], both defined as poison gases by US authorities and most Western nations. Storage and handling procedures for these products are strictly regulated. Wilhelm Environmental Technologies Inc. is developing use of solid, formed or prilled Urea [CO(NH{sub 2}){sub 2}] as the feedstock.more » When heated in moist air, Urea sublimes to ammonia [NH{sub 3}] and carbon dioxide [CO{sub 2}]. Urea is stored and handled without restrictions or environmental concerns. Urea is a more expensive feedstock than NH{sub 3}, but much less expensive than [NH{sub 4}OH]. The design, and operating results, of a pilot system at Jacksonville Electric St. John's River Plant [Unit 2] are described. The pilot plant successfully sublimed Urea up to 100 pounds/hour. Further testing is planned. Very large ammonia use may favor NH{sub 3}, but smaller quantities can be produced at attractive prices with Urea based ammonia systems. Storage costs are far less. Many fluidized-bed boilers can use pastille or solid urea metered directly into the existing cyclones for NO{sub x} control. This is more economical than aqueous ammonia or aqueous urea based technology.« less

Alaskan Permafrost Analogs of Martian Small Valley Networks, Thermokarst, Terrain Softening, Terraces, and Volcanic Craters

NASA Technical Reports Server (NTRS)

Kargel, Jeffrey S.; Wessels, Rick; Beget, James E.; Eddy, Thomas; Lloyd, Sandra; Macaulay, Don; Proch, Mark; Skinner, Jim; Tanaka, Kenneth L.

2004-01-01

A geomorphic landscape analog in the Bering Land Bridge National Preserve (Alaska) offers a model for Mars where (1) fluvial and alluvial deposition, volcanism, and other processes first produced a layered ice-rich upper crust, and then (2) severe permafrost conditions (mild by today's Martian standards) and heterogeneous heat flow and volcanism have modified this terrain to produce a geomorphic areal mosaic that is alternately dominated by (a) geothermal meltwater and sublimation (bottom-up heat flow) and (b) surface-driven meltwater and sublimation (top-down heat flow).

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.

Solid-phase equilibria on Pluto's surface

NASA Astrophysics Data System (ADS)

Tan, Sugata P.; Kargel, Jeffrey S.

2018-03-01

Pluto's surface is covered by volatile ices that are in equilibrium with the atmosphere. Multicomponent phase equilibria may be calculated using a thermodynamic equation of state and, without additional assumptions, result in methane-rich and nitrogen-rich solid phases. The former is formed at temperature range between the atmospheric pressure-dependent sublimation and condensation points, while the latter is formed at temperatures lower than the sublimation point. The results, calculated for the observed 11 μbar atmospheric pressure and composition, are consistent with recent work derived from observations by New Horizons.

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.

Silent cries, dancing tears: the metapsychology of art revisited/revised.

PubMed

Aragno, Anna

2011-04-01

Against the backdrop of a broad survey of the literature on applied psychoanalysis, a number of concepts underpinning the metapsychology of art are revisited and revised: sublimation; interrelationships between primary and secondary processes; symbolization; "fantasy"; and "cathexis." Concepts embedded in dichotomous or drive/energic contexts are examined and reformulated in terms of a continuum of semiotic processes. Freudian dream structure is viewed as a biological/natural template for nonrepressive artistic forms of sublimation. The synthesis presented proposes a model of continuous rather than discontinuous processes, in a nonenergic, biosemiotic metatheoretical framework.

Determination of molar enthalpy of sublimation in case of orotic acid as obtained from experimental and computational data

NASA Astrophysics Data System (ADS)

Marochkin, Ilya I.; Altova, Ekaterina P.; Chilingarov, Norbert S.; Vilkova, Anna L.; Shishkov, Igor F.

2018-03-01

Saturated vapor pressure, ln(p/Pa) = (-21316 ± 511)/(T/K)+(41.64 ± 0.11), and enthalpy of sublimation of orotic acid, Δsub Hm0 (Tm) = 177 ± 4 kJ/mol, were determined by means of Knudsen effusion mass spectrometry in the temperature range of 423÷493 K. The computational approaches supported the experimental results reported. The theoretical estimation of the gas-phase enthalpy of formation for orotic acid was done with different working reactions used.

Beauty and sublime. 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)

Perlovsky, Leonid

2017-07-01

The VIMAP model presented in this review [1] is an interesting and detailed model of neural mechanisms of aesthetic perception. In this Comment I address one deficiency of this model: it does not address in details the fundamental notions of the VIMAP, beauty and sublime. In this regard VIMAP is similar to other publications on aesthetics.

Volatile molecule PuO 3 observed from subliming plutonium dioxide

NASA Astrophysics Data System (ADS)

Ronchi, C.; Capone, F.; Colle, J. Y.; Hiernaut, J. P.

2000-06-01

Mass spectrometric measurements of effusing vapours over PuO 2 and (U, Pu)O 2 indicate the presence of volatile PuO 3 (g) molecules. The formation of plutonium trioxide vapour is due to a chemical process involving oxygen adsorbed during oxidation of the sample. Although in the examined samples, the fraction of trioxide effusing in vacuo was of the order of 0.02 ppm of the plutonium content, under steady-state oxidation conditions it has been shown that the process can have a relevant effect on the sublimation rate of the dioxide.

Effect of confinement in small space flight size cages on insulin sensitivity of exercise-trained rats

NASA Technical Reports Server (NTRS)

Mondon, C. E.; Dolkas, C. B.; Reaven, G. M.

1983-01-01

The effect of confinement in small cages (simulating the size to be used in future space Shuttle missions) on insulin sensitivity was studied in rats having an increased insulin sensitivity due to exercise training prior to confinement. Oral glucose tolerance tests (OGTT) were given to both control and exercise-trained rats before and after placement in the small cages for 7 days. The insulin resistance was assessed by the product of the area of the insulin and glucose curves of the OGTT (IG index). Results show that the values obtained before confinement were one-half as high in exercise-trained rats as those in control rats, reflecting an increased sensitivity to insulin with exercise training. After 7 days confinement, the IG index was found to be not significantly different from initial values for both control and exercise-trained rats. These findings suggest that increased insulin sensitivity in exercise-trained rats persists 7 days after cessation of running activity. The data also indicate that exercise training, before flight, may be beneficial in minimizing the loss of insulin sensitivity expected with decreased use of gravity dependent muscles during exposure to hypogravity in space flight.

Medicare Home Health Services: A Difficult Program to Control

DTIC Science & Technology

1981-09-25

example, that the individual is to be confined to his or her home but that this does not necessarily mean that the patient is bedridden . At the same...certify in all cases that the beneficiary is confined to his home * An individual [HOWEVER) does not have to be bedridden to be con- sidered as confined

Bimetallic Microswimmers Speed Up in Confining Channels.

PubMed

Liu, Chang; Zhou, Chao; Wang, Wei; Zhang, H P

2016-11-04

Synthetic microswimmers are envisioned to be useful in numerous applications, many of which occur in tightly confined spaces. It is therefore important to understand how confinement influences swimmer dynamics. Here we study the motility of bimetallic microswimmers in linear and curved channels. Our experiments show swimmer velocities increase, up to 5 times, with the degree of confinement, and the relative velocity increase depends weakly on the fuel concentration and ionic strength in solution. Experimental results are reproduced in a numerical model which attributes the swimmer velocity increase to electrostatic and electrohydrodynamic boundary effects. Our work not only helps to elucidate the confinement effect of phoretic swimmers, but also suggests that spatial confinement may be used as an effective control method for them.

Insights into Interactions of Water Ice with Regolith under Simulated Martian Conditions.

NASA Astrophysics Data System (ADS)

Chittenden, Julie; Chevrier, V.; Sears, D. W.; Roe, L. A.; Bryson, K.; Billingsly, L.; Hanley, J.

2006-09-01

In order to understand the diffusion process of water vapor through regolith, we have investigated the sublimation process of subsurface ice under varying depths of JSC Mars-1 soil simulant under martian conditions. Measurements were made at 0oC and 5.25 Torr in a CO2 atmosphere. We corrected for variations in temperature of the ice and the difference in gravity of Mars in relation to the Earth. Our results show that for depths up to 40 mm the process is mainly diffusion controlled and that for thicker regolith layers, desorption becomes the main process. After correction for the effect of desorption, we observed a decrease in sublimation rate from 0.625 ± 0.073 mm.h-1 at 5 mm of soil to 0.187 ± 0.093 mm.h-1 for 200 mm of soil. To characterize the diffusion process, we use the Farmer model (1976), which hypothesizes that the sublimation rate is equal to the diffusion coefficient divided by the soil depth. The derived diffusion coefficient from this data is 2.52 ± 0.55 mm2.h-1, or 7.0 ± 1.5 x 10-10 m2.s-1. Knowing the diffusion coefficient in the regolith, we can calculate the survival time, κ, of a layer of ice under a regolith layer which is given by τ = liceL/D, where lice is the thickness of the ice layer. Using this equation, we find that a 10 cm-thick layer of ice buried under 1 m of regolith would last for more than 4 years at 0oC. Therefore, our study indicates that the transport of water through a regolith layer is a complex multi-faceted process that is readily quantified by laboratory investigations. This is especially important in interpreting previous theoretical models and in understanding in situ observations to be performed by martian landers such as Phoenix. The W.M. Keck Foundation funded this research.

[Relationships between defense mechanisms and coping strategies, facing exam anxiety performance].

PubMed

Grebot, E; Paty, B; Girarddephanix, N

2006-01-01

Defence mechanisms and coping strategies rely on different theoretical backgrounds and describe distinct psychological processes. Cramer has based a distinction on the following dimensions: conscious processes vs. not; intentionality vs. not; hierarchical conception vs. not. On the contrary to these distinctions, the two notions of defense mechanisms and coping strategies are defined as similar in the Diagnostical and Statistical Manual (DSM IV). This assimilation between coping and defenses in the DSM IV is not confirmed by some researches, namely the one by Callahan and Chabrol. It indeed proves a relationship between adaptive coping and mature defenses, as well as between maladaptive coping and immature defenses. Similarly, Plutchik offered theoretical correspondences between eight defense mechanisms and eight coping strategies: (a) Defenses: repression, isolation, introjection and Coping escape; (b) Defense denial and Coping minimalization; (c) Defense undoing and coping substitution; (d) Defenses: regression, acting out and coping social support; (e) Defenses: compensation, identification, fantasy and coping replacement; (f) Defenses: intellectualization, sublimation, annulation, rationalisation and coping: planification; (g) Defense projection and coping blame; (h) Defense: reactional formation and coping inversion. this research aims at testing the relations observed by Callahan and Chabrol and some theoretical correspondences proposed by Plutchik between defences and coping strategies in a population of students similar to the one used by Callahan and Chabrol. It also aims at studying the relationships between coping strategies and conscious derives of defense mechanisms, such as defined by Bond (1995). Defenses were evaluated the first day of the examination week. the population includes 184 women students in human sciences (sociology and psychology). defenses were evaluated with the Defense Style Questionnaire by Bond (DSQ 40). Its French version is made of 40 items and validated by Guelfi et al. It explores 20 defense mechanisms, as well as 3 defense styles: (1) a "mature style", composed by 4 defenses: sublimation, humor, anticipation, repression; (2) a "neurotic style", composed by 4 defenses: annulation, reactional formation, altruism and idealization; (3) an "immature style", composed by 12 defenses. Coping strategies were measured by the French version of the Way of Coping Check-List-Revised, (WCC-R) by Lazarus and Folkman, validated by Graziani et al. It evaluates 10 factors: 1) Problem solving; 2) Evasion; 3) Social support; 4) Self-control; 5) Escape; 6) Responsabilization-Replanification; 7) Resignation; 8)Diplomacy; 9) Confrontation; 10) Personal evolution. Our results confirm partially Callahan and Chabrol's conclusions in favour of existing relationships between adaptive coping strategies and mature defenses, as well as between maladaptive coping strategies and immature defenses. They demonstrate three positive relationships: 1) a relation between Problem solving resolution coping and two mature defenses (Sublimation, Anticipation); 2) a relation between Evasion coping and nevrotic and immature defenses; 3) a relation between Escaping coping and immature defenses. The correspondences between defense mechanisms and coping strategies, such as proposed by Plutchik psycho-evolutionist emotional model are partly validated. Some links were indeed validated in this research, between: a) Defense Undoing and Escaping or Evasion coping; b) Defense Fantasy and Responzabilization coping, c) Defense Sublimation and Problem solving resolution coping; d) Defense Sublimation and Responsabilization coping or Problem solving resolution coping; e) Défense Annulation and Responzabilisation coping.

Facile fabrication of BiVO4 nanofilms with controlled pore size and their photoelectrochemical performances

NASA Astrophysics Data System (ADS)

Feng, Chenchen; Jiao, Zhengbo; Li, Shaopeng; Zhang, Yan; Bi, Yingpu

2015-12-01

We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO4 photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures.We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO4 photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06584d

A sublimate sorbent for stir-bar sorptive extraction of aqueous endocrine disruptor pesticides for gas chromatography-electron capture detection.

PubMed

Huang, Yu-Wen; Lee, Hua Kwang; Shih, Hou-Kuang; Jen, Jen-Fon

2018-06-06

A dumbbell-shaped magnetic stir-bar with sublimate sorbent was prepared for the stir bar sorptive extraction (SBSE) of pesticides in an aqueous sample prior to gas chromatography-micro-electron capture detection (GC-μECD). Cyclododecane (CDD) was coated onto a magnetic stir-bar surface as a sublimate sorbent, and steel balls were placed on both ends to form a dumbbell-shaped magnetic stir-bar for SBSE. Four EDC pesticides including chlorpyrifos, ethion, bromopropylate, and λ-cyhalothrin in aqueous samples were selected as model species to examine the proposed SBSE and the following desorption. The parameters studied were those affecting the extraction efficiencies including the coating (solvent for CDD and thickness), extraction (sample pH, stirring rate, time, and salting out effect), dissolution solvent volume, and the loss of CDD sublimated in air. The maximum extraction efficiency was obtained under the following conditions. The stir bar (with CDD thickness of 5.2 μm) was added into a 10 mL sample solution (at pH 7) for a 20-min extraction at 600 rpm. Then, the stir bar was gently removed from the sample solution, disassembled, and immersed into a 0.2 mL insert tube consisting of 3 μL hexane to dissolve; 1 μL was used for GC-ECD analysis. The linear ranges were 0.005-5 μg L -1 with coefficients of determination ranging from 0.9950 - 0.9994. Detection limits (based on S/N = 3) of the four EDCs were 0.4-4.5 ngL -1 with a relative standard deviation (RSD) of 2.4-6.3%, and quantitation limits (based on S/N = 5) were 1-15 ngL -1 . The relative recoveries of the spiked samples were in the range of 83.2-98.7% with RSDs of 2.1-8.4% in farm field waters. The proposed sublimation sorbent obtained excellent enrichment factors (101-834) and provided a simple, rapid, sensitive, and eco-friendly sample preparation method. Copyright © 2018 Elsevier B.V. All rights reserved.

Mass Wasting and Ground Collapse in Terrains of Volatile-Rich Deposits as a Solar System-Wide Geological Process: The Pre-Galileo View

NASA Technical Reports Server (NTRS)

Moore, Jeffrey M.; Mellon, Michael T.; Zent, Aaron P.

1996-01-01

The polar terrains of Mars are covered in many places with irregular pits and retreating scarps, as are some of the surfaces of the outer-planet satellites. These features are interpreted by us as diagnostic of exogenic degradation due to the loss of a volatile rock-forming matrix or cement. In this study we propose that sublimation degradation is a plausible Solar Systemwide geological process. Candidate examples have been identified on Mars, Io, and Triton, and possibly Europa and Ganymede. We envision this process as having two end-member expressions (pits and scarps), for which we hypothesize two end-member mechanisms (massive localized lenses and areally extensive basal layers). In this study we focus on the role this process may play on the surfaces of the galilean satellites. Our principle modeling results are that for these satellites, H2S, CO2, and NH3 are the only viable candidate volatiles for sublimation degradation of landforms, in light of galilean satellite cosmochemistry. For Io's polar regions only H2S, and then only from slopes that face the Sun and have thin lags, is volatile enough to cause the observed sublimation-induced erosion at those latitudes. SO2 is not a viable candidate as an agent of erosion, especially for these polar landforms. In the case of Europa, only CO2 and H2S are viable candidates (given surface age constraints). Both species could be efficient eroders in nonpolar regions. H2S could generate erosion within the polar regions if the deposition and erosion conditions were essentially identical as those we invoked for Io's polar regions. For Ganymede (and Callisto) NH3 might be an agent of erosion in equatorial terrains of great age. The sublimation of CO2 and H2S is much more robust than NH3. The much slower rate of sublimation degradation from NH3 might be detectable by Galileo and used as a compositional indicator.

Quantum control of quasi-collision states: A protocol for hybrid fusion

NASA Astrophysics Data System (ADS)

Vilela Mendes, R.

2018-04-01

When confined to small regions quantum systems exhibit electronic and structural properties different from their free space behavior. These properties are of interest, for example, for molecular insertion, hydrogen storage and the exploration of new pathways for chemical and nuclear reactions. Here, a confined three-body problem is studied, with emphasis on the study of the “quantum scars” associated to dynamical collisions. For the particular case of nuclear reactions, it is proposed that a molecular cage might simply be used as a confining device with the collision states accessed by quantum control techniques.

Trapping of Methanol, Hydrogen Cyanide, and n-Hexane in Water Ice, above Its Transformation Temperature to the Crystalline Form

NASA Astrophysics Data System (ADS)

Notesco, G.; Bar-Nun, A.

1997-04-01

HCN and n-C 6H 14were found experimentally to be trapped in water ice, when codeposited with water vapor on a cold plate, at 140 K and CH 3OH even at 160 K. At these temperatures at least part of the water ice is cystalline. These three gases have relatively high sublimation temperatures, whereas the gases studied earlier, Ar, Kr, Xe, CO, CH 4, and N 2, which have lower sublimination temperatures, are trapped only in amorphous water ice, up to ˜100 K. It seems that the major factor determining the efficiency of gas trapping by water ice, during codeposition of a gas-water vapor mixture on a cold plate, is the sublimation temperatures of the gases to be trapped. Those with a high sublimation temperature remain, during codeposition, longer in the pores of the water ice which are open to the surface, until they are covered by additional ice layers. Only methanol seems to form a clathrate hydrate, in agreement with the experimental results of D. Blake et al.(1991), Science254, 548-551), which points to the importance of the interaction of the gas molecules with the water molecules in the ice. Consequently, comets and icy satellites that were formed in the Jupiter-Saturn region and their subnebulae could trap CH 3OH, HCN, and heavy hydrocarbons, whereas comets and icy satellites that were formed in the Uranus-Neptune region, at the outskirts of the Saturnian subnebulae (Titan), and beyond the planets in the Kuiper belt could trap also gases having lower sublimation temperatures.

Efforts to Reduce International Space Station Crew Maintenance Time in the Management of the Extravehicular Mobility Unit Transport Loop Water Quality

NASA Technical Reports Server (NTRS)

Etter,David; Rector, Tony; Boyle, robert; Zande, Chris Vande

2012-01-01

The EMU (Extravehicular Mobility Unit) contains a semi-closed-loop re-circulating water circuit (Transport Loop) to absorb heat into a LCVG (Liquid Coolant and Ventilation Garment) worn by the astronaut. A second, single-pass water circuit (Feed-water Loop) provides water to a cooling device (Sublimator) containing porous plates, and that water sublimates through the porous plates to space vacuum. The cooling effect from the sublimation of this water translates to a cooling of the LCVG water that circulates through the Sublimator. The quality of the EMU Transport Loop water is maintained through the use of a water processing kit (ALCLR - Airlock Cooling Loop Remediation) that is used to periodically clean and disinfect the water circuit. Opportunities to reduce crew time associated with ALCLR operations include a detailed review of the historical water quality data for evidence to support an extension to the implementation cycle. Furthermore, an EMU returned after 2-years of use on the ISS (International Space Station) is being used as a test bed to evaluate the results of extended and repeated ALCLR implementation cycles. Finally, design, use and on-orbit location enhancements to the ALCLR kit components are being considered to allow the implementation cycle to occur in parallel with other EMU maintenance and check-out activities, and to extend the life of the ALCLR kit components. These efforts are undertaken to reduce the crew-time and logistics burdens for the EMU, while ensuring the long-term health of the EMU water circuits for a post- Shuttle 6-year service life.

Efforts to Reduce International Space Station Crew Maintenance for the Management of the Extravehicular Mobility Unit Transport Loop Water Quality

NASA Technical Reports Server (NTRS)

Steele, John W.; Etter, David; Rector, Tony; Boyle, Robert; Vandezande, Christopher

2013-01-01

The EMU (Extravehicular Mobility Unit) contains a semi-closed-loop re-circulating water circuit (Transport Loop) to absorb heat into a LCVG (Liquid Coolant and Ventilation Garment) worn by the astronaut. A second, single-pass water circuit (Feed-water Loop) provides water to a cooling device (Sublimator) containing porous plates, and that water sublimates through the porous plates to space vacuum. The cooling effect from the sublimation of this water translates to a cooling of the LCVG water that circulates through the Sublimator. The quality of the EMU Transport Loop water is maintained through the use of a water processing kit (ALCLR Airlock Cooling Loop Remediation) that is used to periodically clean and disinfect the water circuit. Opportunities to reduce crew time associated with on-orbit ALCLR operations include a detailed review of the historical water quality data for evidence to support an extension to the implementation cycle. Furthermore, an EMU returned after 2-years of use on the ISS (International Space Station) is being used as a test bed to evaluate the results of extended and repeated ALCLR implementation cycles. Finally, design, use and on-orbit location enhancements to the ALCLR kit components are being considered to allow the implementation cycle to occur in parallel with other EMU maintenance and check-out activities, and to extend the life of the ALCLR kit components. These efforts are undertaken to reduce the crew-time and logistics burdens for the EMU, while ensuring the long-term health of the EMU water circuits for a post-Shuttle 6-year service life.

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.

Equation of State for Solid Phase I of Carbon Dioxide Valid for Temperatures up to 800 K and Pressures up to 12 GPa

NASA Astrophysics Data System (ADS)

Martin Trusler, J. P.

2011-12-01

The available thermodynamic-property data for solid phase I of carbon dioxide ("dry ice") are reviewed and used to determine the parameters of a new fundamental equation of state constructed in the form of a Helmholtz energy function with temperature and molar volume as the independent variables. The experimental data considered include the pressure, molar volume, and isobaric heat capacity along the sublimation curve, the melting-pressure curve, and molar volume in the compressed solid at temperatures from 295 to 764 K and pressures up to 12 GPa. The equation of state is based on the quasi-harmonic approximation, incorporating a Debye oscillator distribution for the vibrons, two discrete modes for the librons and a further three distinct modes for the internal vibrations of the CO2 molecule. A small anharmonic correction term is included, which is significant mainly in the region of the triple point. The estimated relative uncertainty of molar volume at specified temperature and pressure calculated from the equation of state is 0.02% on the sublimation curve and 1.5% in the compressed solid; for isobaric heat capacity on the sublimation curve, the uncertainty varies from 5.0% to 0.5% between 2 and 195 K. Auxiliary equations for the pressure and molar volume on the sublimation and melting curves are given. The equation of state is valid at temperatures from 0 to 800 K and at pressures from the solid-fluid phase boundary to 12 GPa.

An atomic carbon source for high temperature molecular beam epitaxy of graphene.

PubMed

Albar, J D; Summerfield, A; Cheng, T S; Davies, A; Smith, E F; Khlobystov, A N; Mellor, C J; Taniguchi, T; Watanabe, K; Foxon, C T; Eaves, L; Beton, P H; Novikov, S V

2017-07-26

We report the use of a novel atomic carbon source for the molecular beam epitaxy (MBE) of graphene layers on hBN flakes and on sapphire wafers at substrate growth temperatures of ~1400 °C. The source produces a flux of predominantly atomic carbon, which diffuses through the walls of a Joule-heated tantalum tube filled with graphite powder. We demonstrate deposition of carbon on sapphire with carbon deposition rates up to 12 nm/h. Atomic force microscopy measurements reveal the formation of hexagonal moiré patterns when graphene monolayers are grown on hBN flakes. The Raman spectra of the graphene layers grown on hBN and sapphire with the sublimation carbon source and the atomic carbon source are similar, whilst the nature of the carbon aggregates is different - graphitic with the sublimation carbon source and amorphous with the atomic carbon source. At MBE growth temperatures we observe etching of the sapphire wafer surface by the flux from the atomic carbon source, which we have not observed in the MBE growth of graphene with the sublimation carbon source.

Vacuum Vaporization Technique for Latent Fingerprints Development on Thermal Papers using Lawsone Natural Products

NASA Astrophysics Data System (ADS)

Phungyimnoi, N.; Eksinitkun, G.; Phutdhawong, W.

2017-09-01

The vacuum vaporization technique is widely used to develop of visualized latent fingerprints on substrate surface for forensics investigation. In this study, we reported the first utilization of lawsone in the vacuum vaporization technique. The lawsone was sublimation in vacuum and showed the detected latent fingerprints on thermal papers. The method involves hanging the thermal paper samples 5, 10, 15 cm above a heating source with dispersed lawsone solids in a vacuum chamber. The optimized condition for lawsone sublimation are 50, 100, 150 mg with low-vacuum (0.1 mbar) and vaporizing temperature at 40-60°C. The sample fingerprints were left for 1, 3, 7 and 30 days before examination comparison between lawsone and fingerprint ink pad using an Automated Fingerprint Identification (AFIS). The resulted showed that using 100 mg lawsone sublimation on thermal paper at the range of 10 cm evidenced the clear, detectable minutiae which can be used for visualization and identification of latent prints without the background black staining known. Thus, this study might be interested application for developing latent fingerprints as a solvent free technique and non-hazardous materials.

An Examination of the Phase Transition Thermodynamics of (S)- and (RS)-Naproxen as a Basis for the Design of Enantioselective Crystallization Processes.

PubMed

Buchholz, Hannes; Emel'yanenko, Vladimir N; Lorenz, Heike; Verevkin, Sergey P

2016-05-01

A detailed experimental analysis of the phase transition thermodynamics of (S)-naproxen and (RS)-naproxen is reported. Vapor pressures were determined experimentally via the transpiration method. Sublimation enthalpies were obtained from the vapor pressures and from independent TGA measurements. Thermodynamics of fusion which have been well-studied in the literature were systematically remeasured by DSC. Both sublimation and fusion enthalpies were adjusted to one reference temperature, T = 298 K, using measured heat capacities of the solid and the melt phase by DSC. Average values from the measurements and from literature data were suggested for the sublimation and fusion enthalpies. In order to prove consistency of the proposed values the vaporization enthalpies obtained by combination of both were compared to vaporization enthalpies obtained by the group-additivity method and the correlation-gas chromatography method. The importance of reliable and precise phase transition data for thermochemical calculations such as the prediction of solid/liquid phase behaviour of chiral compounds is highlighted. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Integration of a Micro-Chip Amino Acid Chirality Detector into the MOD Instrument Concept

NASA Technical Reports Server (NTRS)

Bada, Jeffrey L.; Grunthaner, Frank; Mathies, Richard

2004-01-01

The MOD (Mars Organic Detector) instrument concept consists of a sublimation apparatus for organic compound isolation connected to a microfabricated microfluidic analyzer containing a sipper, pumps and a separation channel for organic compound characterization. The target organic compounds are amino acids and polycyclic aromatic hydrocarbons (PAHs). Solid samples are placed within the sublimation apparatus and heated to release organic compounds which sublime onto a cold finger. Half of the cold finger is coated with fluorescamine. which reacts with amino acids and other primary amines to generate an intense fluorescent derivative while the other half is uncoated and is used to directly detect PAH fluorescence, A capillary sipper is then used to dissolve and sample the labeled amino acids and integrated microfabricated pumps transport the labeled amino acids to the chip for analysis. The sample is separated using capillary zone electrophoresis (CZE) together with chiral dextrins to determine amino acid composition and chirality. During the grant period, the following steps have been completed toward the development of a robust instrument and chemistry.

Enhancing Kondo coupling in alkaline-earth-metal atomic gases with confinement-induced resonances in mixed dimensions

NASA Astrophysics Data System (ADS)

Cheng, Yanting; Zhang, Ren; Zhang, Peng; Zhai, Hui

2017-12-01

The Kondo effect describes the spin-exchange interaction between localized impurities and itinerant fermions. The ultracold alkaline-earth atomic gas provides a natural platform for quantum simulation of the Kondo model, utilizing its long-lived clock state and the nuclear-spin exchange interaction between clock state and ground state. One of the key issue now is whether the Kondo temperature can be high enough to be reached in current experiments, for which we have proposed to use transverse confinement to confine atoms into a one-dimensional tube and to use the confinement-induced resonance to enhance Kondo coupling. In this work, we further consider the (1 +0 ) -dimensional scattering problem when the clock state is further confined by an axial harmonic confinement. We show that this axial confinement for the clock-state atoms not only plays a role for localizing them, but can also act as an additional control knob to reach the confinement-induced resonance. We show that, in the presence of both the transverse and the axial confinements, the confinement-induced resonance can be reached in the practical conditions and the Kondo effect can be attainable in this system.

Studies in Support of the Application of Statistical Theory to Design and Evaluation of Operational Tests. Annex D. An Application of Bayesian Statistical Methods in the Determination of Sample Size for Operational Testing in the U.S. Army

DTIC Science & Technology

1977-07-01

SIZE C XNI. C UE2 - UTILITY OF EXPERIMENT OF SIZE C XN2. C ICHECK - VARIABLE USLD TO CHECK FOR C TERMINATION, C~C DIMENSION SUBLIM{20),UPLIM(20),UEI(20...1J=UPLIM(K4-I)-XNI (K+1)+SU8LIt1(K+i*. C CHECK FOR TERMINATION. 944 ICHECK =SUBLIM(K)+2 IFIICHECK.GEUPLiHMK.,OR.K.G1.20’ GO TO 930 GO TO 920 930

Enthalpies of Formation of Hydrazine and Its Derivatives.

PubMed

Dorofeeva, Olga V; Ryzhova, Oxana N; Suchkova, Taisiya A

2017-07-20

Enthalpies of formation, Δ f H 298 ° , in both the gas and condensed phase, and enthalpies of sublimation or vaporization have been estimated for hydrazine, NH 2 NH 2 , and its 36 various derivatives using quantum chemical calculations. The composite G4 method has been used along with isodesmic reaction schemes to derive a set of self-consistent high-accuracy gas-phase enthalpies of formation. To estimate the enthalpies of sublimation and vaporization with reasonable accuracy (5-20 kJ/mol), the method of molecular electrostatic potential (MEP) has been used. The value of Δ f H 298 ° (NH 2 NH 2 ,g) = 97.0 ± 3.0 kJ/mol was determined from 75 isogyric reactions involving about 50 reference species; for most of these species, the accurate Δ f H 298 ° (g) values are available in Active Thermochemical Tables (ATcT). The calculated value is in excellent agreement with the reported results of the most accurate models based on coupled cluster theory (97.3 kJ/mol, the average of six calculations). Thus, the difference between the values predicted by high-level theoretical calculations and the experimental value of Δ f H 298 ° (NH 2 NH 2 ,g) = 95.55 ± 0.19 kJ/mol recommended in the ATcT and other comprehensive reference sources is sufficiently large and requires further investigation. Different hydrazine derivatives have been also considered in this work. For some of them, both the enthalpy of formation in the condensed phase and the enthalpy of sublimation or vaporization are available; for other compounds, experimental data for only one of these properties exist. Evidence of accuracy of experimental data for the first group of compounds was provided by the agreement with theoretical Δ f H 298 ° (g) value. The unknown property for the second group of compounds was predicted using the MEP model. This paper presents a systematic comparison of experimentally determined enthalpies of formation and enthalpies of sublimation or vaporization with the results of calculations. Because of relatively large uncertainty in the estimated enthalpies of sublimation, it was not always possible to evaluate the accuracy of the experimental values; however, this model allowed us to detect large errors in the experimental data, as in the case of 5,5'-hydrazinebistetrazole. The enthalpies of formation and enthalpies of sublimation or vaporization have been predicted for the first time for ten hydrazine derivatives with no experimental data. A recommended set of self-consistent experimental and calculated gas-phase enthalpies of formation of hydrazine derivatives can be used as reference Δ f H 298 ° (g) values to predict the enthalpies of formation of various hydrazines by means of isodesmic reactions.

Study of Polymer Crystallization by Physical Vapor Deposition

NASA Astrophysics Data System (ADS)

Jeong, Hyuncheol

When a polymer is confined under the submicron length scale, confinement size and interfaces can significantly impact the crystallization kinetics and resulting morphology. The ability to tune the morphology of confined polymer systems is of critical importance for the development of high-performance polymer microelectronics. The wisdom from the research on confined crystallization suggests that it would be beneficial to have a processing route in which the crystallization of polymers is driven by interface and temperature effects at a nanometer-scale confinement. In practice, for atomic and small-molecular systems, physical vapor deposition (PVD) has been recognized as the most successful processing route for the precise control of the film structure at surface utilizing confinement effects. While standard PVD technologies are not generally applicable to the deposition of the chemically fragile macromolecules, the development of matrix-assisted pulsed laser evaporation (MAPLE) now enables the non-destructive PVD of high-molecular weight polymers. In this thesis work, we investigated the use of MAPLE for the precise control of the crystallization of polymer films at a molecular level. We also sought to decipher the rules governing the crystallization of confined polymers, by using MAPLE as a tool to form confined polymer systems onto substrates with a controlled temperature. We first explored the early stages of film growth and crystallization of poly(ethylene oxide) (PEO) at the substrate surface formed by MAPLE. The unique mechanism of film formation in MAPLE, the deposition of submicron-sized polymer droplets, allowed for the manifestation of confinement and substrate effects in the crystallization of MAPLE-deposited PEO. Furthermore, we also focused on the property of the amorphous PEO film formed by MAPLE, showing the dependence of polymer crystallization kinetics on the thermal history of the amorphous phase. Lastly, we probed how MAPLE processing affected the semi-crystalline structure in MAPLE-deposited polyethylene (PE) films. Depositing PE at various temperatures remarkably allowed for the tunability of the melting temperature and crystallinity of the PE films, thus manipulating the semi-crystalline structure. By comparing the structure of PE formed by different processing routes, i.e., MAPLE and melt-crystallization, we discussed how processing routes affect the development of semi-crystalline phase in polymer films.

Artificial Bone and Teeth through Controlled Ice Growth in Colloidal Suspensions

NASA Astrophysics Data System (ADS)

Tomsia, Antoni P.; Saiz, Eduardo; Deville, Sylvain

2007-06-01

The formation of regular patterns is a common feature of many solidification processes involving cast materials. We describe here how regular patterns can be obtained in porous alumina and hydroxyapatite (HAP) by controlling the freezing of ceramic slurries followed by subsequent ice sublimation and sintering, leading to multilayered porous ceramic structures with homogeneous and well-defined architecture. These porous materials can be infiltrated with a second phase of choice to yield biomimetic nacre-like composites with improved mechanical properties, which could be used for artificial bone and teeth applications. Proper control of the solidification patterns provides powerful means of control over the final functional properties. We discuss the relationships between the experimental results, ice growth fundamentals, the physics of ice and the interaction between inert particles and the solidification front during directional freezing.

Artificial Bone and Teeth through Controlled Ice Growth in Colloidal Suspensions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomsia, Antoni P.; Saiz, Eduardo; Deville, Sylvain

2007-06-14

The formation of regular patterns is a common feature of many solidification processes involving cast materials. We describe here how regular patterns can be obtained in porous alumina and hydroxyapatite (HAP) by controlling the freezing of ceramic slurries followed by subsequent ice sublimation and sintering, leading to multilayered porous ceramic structures with homogeneous and well-defined architecture. These porous materials can be infiltrated with a second phase of choice to yield biomimetic nacre-like composites with improved mechanical properties, which could be used for artificial bone and teeth applications. Proper control of the solidification patterns provides powerful means of control over themore » final functional properties. We discuss the relationships between the experimental results, ice growth fundamentals, the physics of ice and the interaction between inert particles and the solidification front during directional freezing.« less

Qualification of a sublimation tool applied to the case of metalorganic chemical vapor deposition of In{sub 2}O{sub 3} from In(tmhd){sub 3} as a solid precursor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szkutnik, P. D., E-mail: pierre.szkutnik@cea.fr; Jiménez, C.; Angélidès, L.

2016-02-15

A solid delivery system consisting of a source canister, a gas management, and temperature controlled enclosure designed and manufactured by Air Liquide Electronics Systems was tested in the context of gas-phase delivery of the In(tmhd){sub 3} solid precursor. The precursor stream was delivered to a thermal metalorganic chemical vapor deposition reactor to quantify deposition yield under various conditions of carrier gas flow and sublimation temperature. The data collected allowed the determination of characteristic parameters such as the maximum precursor flow rate (18.2 mg min{sup −1} in specified conditions) and the critical mass (defined as the minimum amount of precursor ablemore » to attain the maximum flow rate) found to be about 2.4 g, as well as an understanding of the influence of powder distribution inside the canister. Furthermore, this qualification enabled the determination of optimal delivery conditions which allowed for stable and reproducible precursor flow rates over long deposition times (equivalent to more than 47 h of experiment). The resulting In{sub 2}O{sub 3} layers was compared with those elaborated via pulsed liquid injection obtained in the same chemical vapor deposition chamber and under the same deposition conditions.« less

Understanding potential exposure sources of perfluorinated carboxylic acids in the workplace.

PubMed

Kaiser, Mary A; Dawson, Barbara J; Barton, Catherine A; Botelho, Miguel A

2010-11-01

This paper integrates perspectives from analytical chemistry, environmental engineering, and industrial hygiene to better understand how workers may be exposed to perfluorinated carboxylic acids when handling them in the workplace in order to identify appropriate exposure controls. Due to the dramatic difference in physical properties of the protonated acid form and the anionic form, this family of chemicals provides unique industrial hygiene challenges. Workplace monitoring, experimental data, and modeling results were used to ascertain the most probable workplace exposure sources and transport mechanisms for perfluorooctanoic acid (PFOA) and its ammonium salt (APFO). PFOA is biopersistent and its measurement in the blood has been used to assess human exposure since it integrates exposure from all routes of entry. Monitoring suggests that inhalation of airborne material may be an important exposure route. Transport studies indicated that, under low pH conditions, PFOA, the undissociated (acid) species, actively partitions from water into air. In addition, solid-phase PFOA and APFO may also sublime into the air. Modeling studies determined that contributions from surface sublimation and loss from low pH aqueous solutions can be significant potential sources of workplace exposure. These findings suggest that keeping surfaces clean, preventing accumulation of material in unventilated areas, removing solids from waste trenches and sumps, and maintaining neutral pH in sumps can lower workplace exposures.

Crossed-field divertor for a plasma device

DOEpatents

Kerst, Donald W.; Strait, Edward J.

1981-01-01

A divertor for removal of unwanted materials from the interior of a magnetic plasma confinement device includes the division of the wall of the device into segments insulated from each other in order to apply an electric field having a component perpendicular to the confining magnetic field. The resulting crossed-field drift causes electrically charged particles to be removed from the outer part of the confinement chamber to a pumping chamber. This method moves the particles quickly past the saddle point in the poloidal magnetic field where they would otherwise tend to stall, and provides external control over the rate of removal by controlling the magnitude of the electric field.

Effects of Institutional Confinement for Delinquency on Levels of Depression and Anxiety among Male Adolescents

PubMed Central

White, Helene R.; Shi, Jing; Hirschfield, Paul; Mun, Eun-Young; Loeber, Rolf

2013-01-01

Youth within the juvenile justice system report higher rates of mental illnesses than their peers. This study tested whether institutional confinement increases levels of depression and anxiety among male adolescents. We examined heterogeneous trajectories of depression and anxiety from ages 11 to 14 for 510 male adolescents. Youths who were first placed in custody at age 15 (treatment group) were matched with control boys (no official arrest or reported confinement during adolescence) within each trajectory group using a propensity score matching procedure. Matches were found for 37 pairs for depression and 34 pairs for anxiety. There were no significant differences between the confined and control groups in levels of depression or anxiety at age 16. More research is needed to identify aspects of the juvenile justice system that may positively or negatively affect youth’s mental health status. PMID:23504068

Spatial confinement governs orientational order in patchy particles

NASA Astrophysics Data System (ADS)

Iwashita, Yasutaka; Kimura, Yasuyuki

2016-06-01

Orientational order in condensed matter plays a key role in determining material properties such as ferromagnetism, viscoelasticity or birefringence. We studied purely orientational ordering in closely-packed one-patch colloidal particles confined between flat substrates, where the particles can only rotate and are ordered via the sticky interaction between the patches. For the first time, we experimentally realized a rich variety of mesoscopic patterns through orientational ordering of colloids by controlling patch size and confinement thickness. The combination of experiment and numerical simulation reveals the decisive role of confinement: An ordered state(s) is selected from the (meta)stable options in bulk when it is commensurate with the system geometry and boundary conditions; otherwise, frustration induces a unique order. Our study offers a new means of systematic control over mesoscopic structures via orientational ordering in patchy particles. The system would also possess unique functionalities through the rotational response of the particles to external stimuli.

Rosetta Images of Comet 67P/CHURYUMOV-GERASIMENKO: Inferences from its Terrain and Structure

NASA Astrophysics Data System (ADS)

Wallis, Max; Wickramasinghe, N. Chandra

The Rosetta mission has given us remarkable images of comet 67P/C-G both from the orbiter, and recently from the Philae lander during its brief days before running out of power. Though its crust is very black, there are several indicators of an underlying icy morphology. Comet 67P displays smooth, planar `seas' (the largest 600 m × 800 m) and flat-bottomed craters, both features seen also on Comet Tempel-1. Comet 67P's surface is peppered with mega-boulders (10-70 km) like Comet Hartley-2, while parallel furrowed terrain appears as a new ice feature. The largest sea (`Cheops' Sea, 600 m × 800 m) curves around one lobe of the 4 km diameter comet, and the crater lakes extending to ~150 m across are re-frozen bodies of water overlain with organic-rich debris (sublimation lag) of order 10 cm. The parallel furrows relate to flexing of the asymmetric and spinning two-lobe body, which generates fractures in an underlying body of ice. The mega-boulders are hypothesised to arise from bolide impacts into ice. In the very low gravity, boulders ejected at a fraction of 1 m/s would readily reach ~100 m from the impact crater and could land perched on elevated surfaces. Where they stand proud, they indicate stronger refrozen terrain or show that the surface they land on (and crush) sublimates more quickly. Outgassing due to ice-sublimation was already evident in September at 3.3 AU, with surface temperature peaks of 220-230 K, which implies impure ice mixtures with less strongly-bound H2O. Increasing rates of sublimation as Rosetta follows comet 67P around its 1.3 AU perihelion will further reveal the nature and prevalence of near-surface ices.

Origin and effective reduction of inversion domains in aluminum nitride grown by a sublimation method

NASA Astrophysics Data System (ADS)

Shigetoh, Keisuke; Horibuchi, Kayo; Nakamura, Daisuke

2017-11-01

Owing to the large differences in the chemical properties between Al and N polarities in aluminum nitride (AlN), the choice of the polar direction for crystal growth strongly affects not only the quality but also the shape (facet formation) of the grown crystal. In particular, N-polar (0 0 0 -1) has been considered to be a more preferable direction than Al-polar (0 0 0 1) for sublimation growth because compared to Al-polar (0 0 0 1), N-polar (0 0 0 -1) exhibits better stability at high growth rate (high supersaturation) conditions and enables easier lateral enlargement of the crystal. However, some critical growth conditions induce polarity inversion and hinder stable N-polar growth. Furthermore, the origin of the polarity inversion in AlN growth by the sublimation method is still unclear. To ensure stable N-polar growth without polarity inversion, the formation mechanism of the inversion domain during AlN sublimation growth must be elucidated. Therefore, herein, we demonstrate homoepitaxial growth on an N-polar seed and carefully investigate the obtained crystal that shows polarity inversion. Annular bright-field scanning transmission electron microscopy reveals that polarity is completely converted to the Al polarity via the formation of a 30 nm thick mixed polar layer (MPL) just above the seed. Moreover, three-dimensional atom probe tomography shows the segregation of the oxygen impurities in the MPL with a high concentration of about 3 atom%. Finally, by avoiding the incorporation of oxygen impurity into the crystal at the initial stage of the growth, we demonstrate an effective reduction (seven orders of magnitude) of the inversion domain boundary formation.

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

2017-12-01

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.

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.;

Thermodynamic and structural aspects of novel 1,2,4-thiadiazoles in solid and biological mediums.

PubMed

Perlovich, German L; Proshin, Alexey N; Volkova, Tatyana V; Bui, Cong Trinh; Bachurin, Sergey O

2011-10-03

Novel 1,2,4-thiadiazoles were synthesized. Crystal structures of these compounds were solved by X-ray diffraction experiments, and comparative analysis of packing architecture and hydrogen bond networks was carried out. Thermodynamic aspects of sublimation processes of the compounds under study were analyzed using temperature dependencies of vapor pressure. Thermophysical characteristics of the molecular crystals were obtained and compared with the sublimation and structural parameters. The melting points correlate with sublimation Gibbs energies. Moreover, an increase of donor-acceptor interactions in crystal structures leads to growth of Gibbs energy values. Relationships between the melting points and the fragmental contributions to the packing energies were established: R(1)-R(4) fragmental interactions are responsible for the fusion processes of this class of compounds. Solubility and solvation processes of 1,2,4-thiadiazoles in buffer, n-hexane and n-octanol were studied within a wide range of temperature intervals, and their thermodynamic functions were calculated. Specific and nonspecific interactions of molecules resolved in crystals and solvents were estimated and compared. It was found that the melting points correlate with sublimation Gibbs energies. Distribution processes of compounds in buffer/n-octanol and buffer/n-hexane systems (describing different types of membranes) were investigated. Transfer processes of the studied molecules from the buffer to n-octanol/n-hexane phases were analyzed by the diagram method with evaluation of the enthalpic and entropic terms. This approach allowed us to design drug molecules with optimal passive transport properties. Calcium-blocking properties of the substances were evaluated. The trend between the ability to inhibit Glu-Ca uptake and the distribution coefficients in buffer/hexane system was observed.

Gate-defined Quantum Confinement in Suspended Bilayer Graphene

NASA Astrophysics Data System (ADS)

Allen, Monica

2013-03-01

Quantum confined devices in carbon-based materials offer unique possibilities for applications ranging from quantum computation to sensing. In particular, nanostructured carbon is a promising candidate for spin-based quantum computation due to the ability to suppress hyperfine coupling to nuclear spins, a dominant source of spin decoherence. Yet graphene lacks an intrinsic bandgap, which poses a serious challenge for the creation of such devices. We present a novel approach to quantum confinement utilizing tunnel barriers defined by local electric fields that break sublattice symmetry in suspended bilayer graphene. This technique electrostatically confines charges via band structure control, thereby eliminating the edge and substrate disorder that hinders on-chip etched nanostructures to date. We report clean single electron tunneling through gate-defined quantum dots in two regimes: at zero magnetic field using the energy gap induced by a perpendicular electric field and at finite magnetic fields using Landau level confinement. The observed Coulomb blockade periodicity agrees with electrostatic simulations based on local top-gate geometry, a direct demonstration of local control over the band structure of graphene. This technology integrates quantum confinement with pristine device quality and access to vibrational modes, enabling wide applications from electromechanical sensors to quantum bits. More broadly, the ability to externally tailor the graphene bandgap over nanometer scales opens a new unexplored avenue for creating quantum devices.

Continuous plasma laser. [method and apparatus for producing intense, coherent, monochromatic light from low temperature plasma

NASA Technical Reports Server (NTRS)

Libby, W. F.; Jensen, C. A.; Wood, L. L. (Inventor)

1977-01-01

The apparatus includes a housing for confining a gas at subatmospheric pressure and including a set of reflectors defining an optical cavity. At least one anode and cathode are positioned within the gas. First control means control the voltage applied to the anode and second control means independently control the temperature of the cathode. The pressure of the gas is controlled by a third control means. An intense monochromatic output is achieved by confining the gas in the housing at a controlled pre-determined reduced pressure, independently controlling the temperature of the electron emitting cathode and applying predetermined controlled low voltage to the anode.

Micro X-ray CT Imaging of Sediments under Confining Pressure

NASA Astrophysics Data System (ADS)

Schindler, M.; Prasad, M.

2016-12-01

We developed a pressure and temperature control system for use inside the micro X-ray CT scanner Xradia 400. We succeeded in building a pressure vessel that can be pressurized to 34.5 MPa (5000 psi) while being transparent to X-rays. The setup can currently be cooled to -5°C and heated to 40°C. We were able to observe grain damage and porosity reduction due to applied confining pressure in clean quartz sand samples and quartz sand and bentonite samples. By comparing micro CT images at atmospheric pressure and 13.8 MPa (2000 psi) confining pressure, we observed compaction of the samples resulting in grain damage and fracturing of sediment grains (Figure 1). When the confining pressure was decreased some grains experienced further fracturing. The grain damage appears irreversible. Further fracturing of grains in pre-compacted sediment was observed upon repeated confining pressure cycling. We are currently working on feed-throughs for fluid lines and electric wiring to use ultrasonic transducers and pressure control in combination. Further we plan to include pore pressure in addition to confining pressure into the system. The pressure control system in combination with ultrasonic transducers will allow us to visually observe pore scale changes in rock samples while simultaneously identifying their influence on ultrasonic velocities. Such pore-scale changes are usually not taken into account by rock physics models and could help to identify why laboratory data diverges from theoretical models. Further, it is possible to compute compressibility from mCT images at different stress states by image correlation

Immune responses in humans after 60 days of confinement

NASA Technical Reports Server (NTRS)

Schmitt, D. A.; Peres, C.; Sonnenfeld, G.; Tkackzuk, J.; Arquier, M.; Mauco, G.; Ohayon, E.

1995-01-01

A confinement experiment in a normobaric diving chamber was undertaken to better understand the effect of confinement and isolation on human psychology and physiology. Pre- and postconfinement blood samples were obtained from four test subjects and control donors to analyze immune responses. No modification in the levels of CD2+, CD3+, CD4+, CD8+, CD19+, and CD56+ cells was observed after confinement. Mitogen-induced T-lymphocyte proliferation and interleukin-2 receptor expression were not altered significantly. Whole blood interferon-alpha and gamma-induction and plasma cortisol levels were also unchanged, as was natural killer cell activity. These data suggest that in humans, no specific components of the immune response are affected by a 2-month isolation and confinement of a small group.

Theory for controlling individual self-propelled micro-swimmers by photon nudging II: confinement.

PubMed

Selmke, Markus; Khadka, Utsab; Bregulla, Andreas P; Cichos, Frank; Yang, Haw

2018-04-18

Photon nudging allows the manipulation and confinement of individual self-propelled micro-swimmers in 2D and 3D environments using feedback controls. Presented in this second part of a two-part contribution are theoretical models that afford the characterization for the positioning distribution associated with active localization. A derivation for the optimal nudging speed and acceptance angle is given for minimal placement uncertainty. The analytical solutions allow for a discussion on the physical underpinning that underlies controllability and optimality.

Method of lift-off patterning thin films in situ employing phase change resists

DOEpatents

Bahlke, Matthias Erhard; Baldo, Marc A; Mendoza, Hiroshi Antonio

2014-09-23

Method for making a patterned thin film of an organic semiconductor. The method includes condensing a resist gas into a solid film onto a substrate cooled to a temperature below the condensation point of the resist gas. The condensed solid film is heated selectively with a patterned stamp to cause local direct sublimation from solid to vapor of selected portions of the solid film thereby creating a patterned resist film. An organic semiconductor film is coated on the patterned resist film and the patterned resist film is heated to cause it to sublime away and to lift off because of the phase change.

Microphysical growth state of ice particles and large-scale electrical structure of clouds

NASA Technical Reports Server (NTRS)

Williams, Earle; Zhang, Renyi; Boccippio, Dennis

1994-01-01

Cloud temperature, liquid water content, and vertical air velocity are all considered in evaluating the microphysical growth state of ice phase precipitation particles in the atmosphere. The large-scale observations taken together with in situ measurements indicated that the most prevalent growth condition for large ice particles in active convection is sublimation during riming, whereas the most prevalent growth condition in stratiform precipitation is vapor deposition. The large-scale electrical observations lend further support to the idea that particles warmed by riming into sublimation charge negatively and particles in vapor deposition charge positively in collisions with small ice particles.

Coagulation of linear carbon molecules into nanoparticles: a molecular dynamics study

NASA Astrophysics Data System (ADS)

Yamaguchi, Yasutaka; Wakabayashi, Tomonari

2004-04-01

Using molecular dynamics (MD) simulations, the coagulation of carbon chain molecules that occurs on the subliming surface of a carbon-containing rare-gas matrix is investigated. Intermolecular connections with dangling bonds enhance the sublimation of the matrix and that results in the emission of a layer of nested carbon chains into vacuum at a velocity about 100 m/s. The following conversion from carbon sp- to more stable sp 2-type bonds heats up the carbon material above 3000 K. During this process, the nested carbon layer self-anneals via a graphitic mono-layer into a conjunct array of particles with a dimension about 10 nm.

Methods for producing Cu-67 radioisotope with use of a ceramic capsule for medical applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ehst, David A.; Willit, James L.

The present invention provides a method for producing Cu67 radioisotope suitable for use in medical applications. The method comprises irradiating a metallic zinc-68 (Zn68) target within a sealed ceramic capsule with a high energy gamma ray beam. After irradiation, the Cu67 is isolated from the Zn68 by any suitable method (e.g. chemical and or physical separation). In a preferred embodiment, the Cu67 is isolated by sublimation of the zinc in a ceramic sublimation tube to afford a copper residue containing Cu67. The Cu67 can be further purified by chemical means.

Technical, analytical and computer support

NASA Technical Reports Server (NTRS)

1972-01-01

The development of a rigorous mathematical model for the design and performance analysis of cylindrical silicon-germanium thermoelectric generators is reported that consists of two parts, a steady-state (static) and a transient (dynamic) part. The material study task involves the definition and implementation of a material study that aims to experimentally characterize the long term behavior of the thermoelectric properties of silicon-germanium alloys as a function of temperature. Analytical and experimental efforts are aimed at the determination of the sublimation characteristics of silicon germanium alloys and the study of sublimation effects on RTG performance. Studies are also performed on a variety of specific topics on thermoelectric energy conversion.

CO2 Jets and Wind Patterns on Mars

NASA Astrophysics Data System (ADS)

Hatcher, Chase; Aye, K.-Michael; Portyankina, Ganna

2017-10-01

In Martian winters, the poles get covered by a layer of transparent CO2 ice. In spring, sunlight causes substrate under the ice to heat up which sublimates CO2 under the ice. The accumulating gas eventually causes the ice above it to rupture and the CO2 and substrate mixture spews out like a geyser and settles back down on the surface. The shape, size, and alignment of the deposits on the surface as viewed by the HiRISE camera are related to physical processes like sublimation, weather, and wind on Mars. The jet deposits are identified by citizen scientists on a website called Planet Four. Users are shown sections of HiRISE images and asked to mark different surface features with different tools. The markings are averaged, filtered, and sorted to ensure that the data accurately represents the images. By analyzing trends in the change of different characteristics of these surface features over time, we conclude that different regions on Mars have different sublimation processes and different wind patterns. We also conclude that wind and weather patterns generally repeat from year to year, and that sediment deposits affect local weather as well.

Experimental and molecular dynamics simulation study of the sublimation energetics of cyclopentadienyltricarbonylmanganese (Cymantrene).

PubMed

Picciochi, Ricardo; Canongia Lopes, José N; Diogo, Hermínio P; Minas da Piedade, Manuel E

2008-10-16

The standard molar enthalpy of sublimation of monoclinic cyclopentadienyltricarbonylmanganese, Mn(eta (5)-C 5H 5)(CO) 3, at 298.15 K, was determined as Delta sub H m (o)[Mn(eta (5)-C 5H 5)(CO) 3] = 75.97 +/- 0.37 kJ x mol (-1) from Knudsen effusion and Calvet-drop microcalorimetry measurements, thus considerably improving the very large inaccuracy (>10 kJ x mol (-1)) of the published data. The obtained value was used to assess the extension of the OPLS-based all-atom force field we previously developed for iron metallocenes to manganese organometallic compounds. The modified force field was able to reproduce the volumetric properties (density and unit-cell volume) of crystalline Mn(eta (5)-C 5H 5)(CO) 3 with a deviation of 0.6% and the experimentally determined enthalpy of sublimation with an accuracy of 1 kJ x mol (-1). The interaction (epsilon) and atomic-diameter (sigma) parameters of the Lennard-Jones (12-6) potential function used to calculate dispersion contributions within the framework of the force field were found to be transferable from iron to manganese.

Measurements of Enthalpy of Sublimation of Ne, N2, O2, Ar, CO2, Kr, Xe, and H2O using a Double Paddle Oscillator.

PubMed

Shakeel, Hamza; Wei, Haoyan; Pomeroy, Joshua M

2018-03-01

We report precise experimental values of the enthalpy of sublimation (Δ H s ) of quenched condensed films of neon (Ne), nitrogen (N 2 ), oxygen (O 2 ), argon (Ar), carbon dioxide (CO 2 ), krypton (Kr), xenon (Xe), and water (H 2 O) vapor using a single consistent measurement platform. The experiments are performed well below the triple point temperature of each gas and fall in the temperature range where existing experimental data is very limited. A 6 cm 2 and 400 µm thick double paddle oscillator (DPO) with high quality factor (Q ≈ 4 × 10 5 at 298K) and high frequency stability (33 parts per billion) is utilized for the measurements. The enthalpies of sublimation are derived by measuring the rate of mass loss during temperature programmed desorption. The mass change is detected due to change in the resonance frequency of the self-tracking oscillator. Our measurements typically remain within 10% of the available literature, theory, and National Institute of Standards and Technology (NIST) Web Thermo Tables ( WTT ) values, but are performed using an internally consistent method across different gases.

Geomorphological Mapping of Sputnik Planum on Pluto: Convection, Glacial Flow, Sublimation and Re-deposition of Nitrogen Ice

NASA Astrophysics Data System (ADS)

White, O. L.; Moore, J. M.; Stern, S. A.; Weaver, H. A., Jr.; Olkin, C.; Ennico Smith, K.; Young, L. A.; Cheng, A. F.

2016-12-01

The New Horizons flyby of Pluto provided extensive high-resolution coverage of its encounter hemisphere. The most prominent surface feature in this hemisphere is the high albedo region informally named Tombaugh Regio, the western portion of which is represented by the expansive nitrogen ice plains informally named Sputnik Planum. A large fraction of Sputnik Planum displays a distinct cellular pattern, with individual cells typically displaying ovoid planforms and shallow pitting on a scale of a few hundred meters. Troughs with medial ridges define the boundaries between cells. Prior studies have argued that this pattern is indicative of solid-state convection occurring within the nitrogen ice. The southern non-cellular plains are either featureless or display dense fields of often elongate and aligned pits typically reaching a few km across, interpreted to have formed via sublimation. The mapping that will be presented at AGU focuses on identifying the different plains units that compose Sputnik Planum and defining the boundaries between them, which aids in assessing their time sequencing and correlation to one another. The cellular plains are divided into bright and dark units, with the bright unit forming a continuous high albedo zone with the bright uplands of east Tombaugh Regio. We interpret the dark plains to represent the main body of convecting N2 ice that forms the cellular plains of Sputnik Planum, with the low albedo caused by a high concentration of entrained dark material (likely tholins). Preferential sublimation of N2 ice from these plains would leave the dark ice exposed, and re-deposition of the N2 ice on the eastern cellular plains and uplands of east Tombaugh Regio would create a thin veneer of pure, bright N2 ice covering these landscapes. The non-cellular plains are universally bright and display evidence for southwards flow of the N2 ice, based on the orientations of fields of elongate sublimation pits as well as the presence of `extinct cells' that appear to have migrated away from the zone of active convection. The larger pits that occur within the non-cellular plains imply that these plains are older than the cellular plains, where resurfacing via convection limits the maximum size attainable by sublimation pits.

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 nucleus (or its fragments) shortly before perihelion. References: [1] Steckloff et al. (2014) Submitted Nature [2] Keane et al. (2014) Submitted Ap. J. [3] Groussin et al. (2013) Icarus 222, 580-594 [4] Combi et al. (2014) Ap. J. 788:L7 (5pp)

Aerogel/Particle Composites for Thermoelectric Devices

NASA Technical Reports Server (NTRS)

Paik, Jong-Ah; Sakamoto, Jeffrey; Jones, Steven

2006-01-01

Optimizing solution chemistry and the addition of titania and fumed silica powder reduces shrinkage. These materials would serve to increase thermal efficiency by providing thermal insulation to suppress lateral heat leaks. They would also serve to prolong operational lifetime by suppressing sublimation of certain constituents of thermoelectric materials (e.g., sublimation of Sb from CoSb3) at typical high operating temperatures. [The use of pure silica aerogels as cast-in-place thermal-insulation and sublimation-suppression materials was described in "Aerogels for Thermal Insulation of Thermoelectric Devices" (NPO-40630), NASA Tech Briefs, Vol. 30, No. 7 (July 2006), page 50.] A silica aerogel is synthesized in a solgel process that includes preparation of a silica sol, gelation of the sol, and drying of the gel in a solvent at a supercritical temperature and pressure. The utility of pure silica aerogel is diminished by a tendency to shrink (and, therefore, also to crack) during the gelation and supercritical-drying stages. Moreover, to increase suppression of sublimation, it is advantageous to make an aerogel having greater density, but shrinkage and cracking tend to increase with density. A composite material of the type under investigation consists mostly of titania oxide powder particles and a small addition of fumed silica powder, which are mixed into the sol along with other ingredients prior to the gelation stage of processing. The silica aerogel and fumed silica act as a binder, gluing the titania particles together. It is believed that the addition of fumed silica stiffens the aerogel network and reduces shrinkage during the supercritical-drying stage. Minimization of shrinkage enables establishment of intimate contact between thermoelectric legs and the composite material, thereby maximizing the effectiveness of the material for thermal insulation and suppression of sublimation. To some extent, the properties of the composite can be tailored via the proportions of titania and other ingredients. In particular (see figure), the addition of a suitably large proportion of titania (e.g., 0.6 g/cu cm) along with a 10-percent increase in the amount of tetraethylorthosilicate [TEOS (an ingredient of the sol)] to an aerogel component having a density 40 mg/cm3makes it possible to cast a high-average-density (>0.1 g/cm3) aerogel/particle composite having low shrinkage (2.3 percent).

Bidirectional reflectance and VIS-NIR spectroscopy of cometary analogues under simulated space conditions

NASA Astrophysics Data System (ADS)

Jost, Bernhard; Pommerol, Antoine; Poch, Olivier; Yoldi, Zuriñe; Fornasier, Sonia; Hasselmann, Pedro Henrique; Feller, Clément; Carrasco, Nathalie; Szopa, Cyril; Thomas, Nicolas

2017-10-01

This work is intended to be the second publication in a series of papers reporting on the spectro-photometric properties of cometary analogues measured in the laboratory. Herein, we provide in-situ hyperspectral imaging data in the 0.40-2.35 μm range from three sublimation experiments under simulated space conditions in thermal vacuum from samples made of water ice, carbonaceous compounds and complex organic molecules. The dataset is complemented by measurements of the bidirectional reflectance in the visible (750 nm) spectral range before and after sublimation. A qualitative characterization of surface evolution processes is provided as well as a description of morphological changes during the simulation experiment. The aim of these experiments is to mimic the spectrum of comet 67P/Churyumov-Gerasimenko (67P) as acquired by the Rosetta mission by applying sublimation experiments on the mixtures of water ice with a complex organic material (tholins) and carbonaceous compounds (carbon black; activated charcoal) studied in our companion publication (Jost et al., submitted). Sublimation experiments are needed to develop the particular texture (high porosity), expected on the nucleus' surface, which might have a strong influence on spectro-photometric properties. The spectrally best matching mixtures of non volatile organic molecules from Jost et al. (submitted) are mixed with fine grained water ice particles and evolved in a thermal vacuum chamber, in order to monitor the influence of the sublimation process on their spectro-photometric properties. We demonstrate that the way the water ice and the non-volatile constituents are mixed, plays a major role in the formation and evolution of a surface residue mantle as well as having influence on the consolidation processes of the underlying ice. Additionally it results in different activity patterns under simulated insolation cycles. Further we show that the phase curves of samples having a porous surface mantle layer display higher coincidence with data of 67P than the phase curves of the samples having a more compact surface layer with smooth texture. The analysis of spectral absorption bands of water ice in the near-infrared (NIR) range, similar to those acquired by the VIRTIS instrument onboard Rosetta, allows to link compositional considerations with surface activity and texture.

Low-level precipitation sublimation on the coasts of East Antarctica

NASA Astrophysics Data System (ADS)

Grazioli, Jacopo; Genthon, Christophe; Madeleine, Jean-Baptiste; Lemonnier, Florentin; Gallée, Hubert; Krinner, Gerhard; Berne, Alexis

2017-04-01

The weather of East Antarctica is affected by the peculiar morphology of this large continent and by its isolation from the surroundings. The high-elevation interior of the continent, very dry in absolute terms, originates winds that can reach the coastal areas with very high speed and persistence in time. The absence of topographic barriers and the near-ground temperature inversion allow these density-driven air movements to fall from the continent towards the coasts without excessive interaction and mixing with the atmosphere aloft. Thus, the air remains dry in absolute terms, and very dry in relative terms because of the higher temperatures near the coast and the adiabatic warming due to the descent. The coasts of Antarctica are less isolated and more exposed to incoming moist air masses than the rest of the continent, and precipitation in the form of snowfall more frequently occurs. Through its descent, however, snowfall encounters the layer of dry air coming from the continent and the deficit in humidity can lead to the partial or complete sublimation of the precipitating flux. This phenomenon is named here LPS (Low-level Precipitation Sublimation) and it has been observed by means of ground-based remote sensing instruments (weather radars) and atmospheric radio-sounding balloons records in the framework of the APRES3 campaign (Antarctic Precipitation: REmote Sensing from Surface and Space) in the coastal base of Dumont d' Urville (Terre Adélie), and then examined at the continental scale thanks to numerical weather models. LPS occurs over most of the coastal locations, where the total sublimated snowfall can be a significant percentage of the total snowfall. For example, in Dumont d' Urville the total yearly snowfall at 341 m height is less than 80% of the snowfall at 941 m height (the height of maximum yearly accumulation), and at shorter time scales complete sublimation (i.e. virga) often occurs. At the scale of individual precipitation events, LPS is overall inversely proportional to the intensity of precipitation, because more developed systems can extend further into the continent and eventually saturate the low levels of the atmosphere. This contribution presents the data, models, and analysis used to characterize LPS over the coastal regions of East Antarctica and discusses the possible implications for predicting climate change in Antarctica.

Curvature-Guided Motility of Microalgae in Geometric Confinement

NASA Astrophysics Data System (ADS)

Ostapenko, Tanya; Schwarzendahl, Fabian Jan; Böddeker, Thomas J.; Kreis, Christian Titus; Cammann, Jan; Mazza, Marco G.; Bäumchen, Oliver

2018-02-01

Microorganisms, such as bacteria and microalgae, often live in habitats consisting of a liquid phase and a plethora of interfaces. The precise ways in which these motile microbes behave in their confined environment remain unclear. Using experiments and Brownian dynamics simulations, we study the motility of a single Chlamydomonas microalga in an isolated microhabitat with controlled geometric properties. We demonstrate how the geometry of the habitat controls the cell's navigation in confinement. The probability of finding the cell swimming near the boundary increases with the wall curvature, as seen for both circular and elliptical chambers. The theory, utilizing an asymmetric dumbbell model of the cell and steric wall interactions, captures this curvature-guided navigation quantitatively with no free parameters.

Process for controlling morphology and improving thermal-mechanical performance of high performance interpenetrating and semi-interpenetrating polymer networks

NASA Technical Reports Server (NTRS)

Pater, Ruth H. (Inventor); Hansen, Marion G. (Inventor)

1997-01-01

In the process of the present invention, a non-polar, aprotic solvent is removed from an oligomer/polymer solution by freeze-drying in order to produce IPNs and semi-IPNs. By thermally quenching the solution to a solid in a short length of time, the size of the minor constituent-rich regions is greatly reduced as they are excluded along with the major constituent from the regions of crystallizing solvent. The use of this process sequence of controlling phase morphology provides IPNs and semi-IPNs with improved fracture toughness, microcracking resistance, and other physical-mechanical properties as compared to IPNs and semi-IPNs formed when the solvent is evaporated rather than sublimed.

Process for controlling morphology and improving thermal mechanical performance of high performance interpenetrating and semiinterpenetrating polymer networks

NASA Technical Reports Server (NTRS)

Pater, Ruth H. (Inventor); Hansen, Marion G. (Inventor)

1998-01-01

In the process of the present invention, a non-polar, aprotic solvent is removed from an oligomer/polymer solution by freeze-drying in order to produce IPNs and semi-IPNs. By thermally quenching the solution to a solid in a short length of time, the size of the minor constituent-rich regions is greatly reduced as they are excluded along with the major constituent from the regions of crystallizing solvent. The use of this process sequence of controlling phase morphology provides IPNs and semi-IPNs with improved fracture toughness, microcracking resistance, and other physical-mechanical properties as compared to IPNs and semi-IPNs formed when the solvent is evaporated rather than sublimed.

North-Polar Martian Cap as Habitat for Elementary Life

NASA Astrophysics Data System (ADS)

Wallis, M. K.; Wickramasinghe, J. T.; Wickramasinghe, N. C.

2008-09-01

North-polar cap over millenia Atmospheric water in Mars tends currently as for the past millenia to distil onto the polar caps and be buried under dust deposits. Diffusive release from ground-ice (and its excavation in meteorite impacts [1]) replenishes atmospheric water, allowing the gradual build up of polar ice-dust deposits. When sunlit, this warmed and sublimating ice-dust mix has interest as a potential habitat for micro-organisms. Modelling shows precipitable vapour at 10-50μm/yr, varying sensitively with small changes in orbitable obliquity around the present 25° [2]. The modelling applies to a globe with regionally uniform albedo, unlike the steep topography and dark layering of the north polar cap whose upper 300m have accumulated over the last 500 kyr [3]. The cliffs and ravines of the north-polar cap are thought to form through south-facing slopes sublimating and gaining a dirt-encrusted surface, while horizontal surfaces brighten through frost deposits. The two-phase surface derives from the dust and frost feedback on surface albedo [4] and the resulting terrain develops over diurnal cycles of frosting and sublimation, and over annual seasonal cycles. The steep south-facing sides of observed ravines when unshadowed would see for a few hours the full intensity of sunlight at near normal incidence, without the atmospheric dimming at similar inclinations on Earth. As exposed ice sublimates at T > 200K (partial pressure exceeds typical martian 0.1 Pa), a crust of dirt develops to maintain quasi-stability. The dirt crust's main function is to buffer the ice against diurnal temperature fluctuations, but it also slows down vapour diffusion - analogous to south polar ice sublimation [5] and the growth of ground-ice [6]. We envisage 1-10 mm/yr as the net sublimation rate, compatible with the 100 kyr life and scales of the north polar ravines. Modelling of icy-dirt crusts in the polar cap Plane-parallel layers have been used to model the changing temperature through the dirt-encrusted ice cliff [7]. Thermal conduction through the dirt crust limits sublimation of underlying ice. This allows use of the thermal wave solution: where the thermal diffusivity α combining conductivity and specific heat is taken constant and τ0 = 1.88 yr is the martian year. As in [6] we adopt a sinusoidal temperature variation and take α = 0.0001 m²/hour. Like the martian ground ice case, the transition from dirt to ice is quite sharp. The surface temperature variation at the polar cap determined from local radiative balance is largely determined by albedo, while sublimation losses from a south-facing cliff are concentrated in the summer months. For fresh frost, the albedo is close to unity but values 0.6-0.8 allow for varying amounts of exposed dirt or dust, as explored in Figure 1. This shows the integrated ice loss over one martian year (687 Earth days) using the thermal wave solution and the Clausius-Clapeyron equation for ice sublimation: for T in degrees Kelvin. The solutions in Fig. 1 indicate a 10-15cm dirt crust develops quite quickly, within a few decades, becoming thick enough to choke back the sublimation rate to under 1mm/yr, compatible with the age of the cliffs. Less steep slopes develop rather thinner crusts. The seasonal thermal wave of Equ.1 applies for depths exceeding ~5cm (two diurnal skin depths). For A of 0.6, Fig. 1 shows a 10 cm thick crust builds up in ~30yr; this thick a crust may plausibly be maintained against weathering processes. If A<0.5, the mean temperature is too high for thermal inertia alone to choke the sublimation; the crust thickens to >10 cm within a few years and the self-sealing (deposition) and flow-retarding (adsorption/desorption) properties become significant in the thicker and hotter crust [5]. For A>0.7, a 5 cm crust cuts the sublimation rate to <0.1 mm/yr - we expect frost deposition to dominate, keeping the surface icy with high albedo for most of the diurnal cycle. The thermal lag due to latent heat needs including for realistic modeling of the dirt-ice crust. Thus our parameterized exploration reveals a regime where sublimation is 10-100 times higher than precipitable water deposition, implying vapour pressures relatively favourable for ice-living microbes. Schorghofer's [2] modelling for horizontal nearpolar surfaces has ~30 cm deep soil that has filled with pore ice over the last 500 kyr. Environments for ice-based life Ice-dwelling micro-organisms found in the antarctic may be viable on Mars [8,9]. Ices generally have mobile water on internal surfaces of crystals and contaminants, which is presumed to facilitate diffusive transport of nutrients, enzymes and waste products, and to be available for cell processes. Species of archaea are found living in low-T ice. Data on methane in the GISP2 ice core and N2O in the Vostok core have been used [10] to infer there is no cut-off at T as low as -40oC and to derive an exp (-A/T) fit to data indicative of metabolic rates. We conceive that the dirt crusts formed on sublimating ice provide a habitat for psychrotrophic microbes. They reactivate metabolically under the midday warming pulse and take advantage of vapour from the underlying ice. On Mars like on comets, cmscale crusts would protect microbes from the harsh surface UV conditions. The extreme cold of the nightside and polar winter presents little problem to microbial spores and resting states. However, the ecological niches are isolated. We envisage that meteorite impacts on Mars mobilise material from these niches and disperse their micro-life around the planet. Meteorite impact cratering rates come from lunar data scaled to Mars, with account for the air decelerating and fragmenting small impacters [11]. This limits the power law to Δ > 10 m and gives a functional fit Ψ = 1.5 x 10-12 Δ-3.1 / km2.yr from Δ = 10 m to 100 m. (3) The volume integral of the excavated mass equates to an average `gardening' rate ~1 cm / Myr, dominated by the smallest craters ~ 0.3m deep. The craters are sparse on a Myr timescale, though secondary craters from excavated material surely contribute to mobilising cm-deep crusts. The formation and fragmentation of crusts that contained micro-organisms would contribute a biological component to martian soils in the polar regions, that could potentially reach the location of the Phoenix probe (at 68°N). One might expect these to be distinguishable via the onboard microscopy. References [1] Wallis M.K. (1995) Adv. Space Res. 15(4), 113-6. [2] Schorghofer N. (2007) Nature 449, 192-195. [3] Milkovich S.M., Head J.W., Neukum G. and the HRSC Co-Investigator Team (2008) Planet. Space Sci. 56, 266-288. [4] Pelletier J.D. (2004) Geology 32, 365-367 & 384. [5] Skorov Yu.V., Markiewicz W.J., Basilevsky A.T. and Keller H.U. (2001) Planet. Space Sci. 49, 59-63. [6] Schorghofer N. and Aharonson O. (2005) J.Geophys. Res., 110, E05003, 1-16. [7] Wallis M.K., Wickramasinghe N.C. and Wickramasinghe J.T. (2005) 5th EANA Workshop on Astrobiology, p.37, Budapest; Wickramasinghe J.T. (2007) The Role of Comets in Panspermia, Ph D. Thesis, Cardiff University [8] McKay C.P. (2003) Third Mars Polar Sci. Conf. 8056. [9] Hoover R.B., et al. (2004) in SPIE 5163, 191-202 (www.astrobiology.cf.ac.uk/SPIE2004.pdf). [10] Tung H.C., Bramhall N.E. & Price P.B. (2005) Proc. Nat. Acad. Sci. 102, 18292-18296. [11] Hartmann W.K. (2005) Icarus 174, 294-320.

APPARATUS FOR MINIMIZING ENERGY LOSSES FROM MAGNETICALLY CONFINED VOLUMES OF HOT PLASMA

DOEpatents

Post, R.F.

1961-10-01

An apparatus is described for controlling electron temperature in plasma confined in a Pyrotron magnetic containment field. Basically the device comprises means for directing low temperature electrons to the plasma in controlled quantities to maintain a predetermined optimum equilibrium electron temperature whereat minimum losses of plasma ions due to ambipolar effects and energy damping of the ions due to dynamical friction with the electrons occur. (AEC)

Freeze-Casting of Porous Biomaterials: Structure, Properties and Opportunities

PubMed Central

Deville, Sylvain

2010-01-01

The freeze-casting of porous materials has received a great deal of attention during the past few years. This simple process, where a material suspension is simply frozen and then sublimated, provides materials with unique porous architectures, where the porosity is almost a direct replica of the frozen solvent crystals. This review focuses on the recent results on the process and the derived porous structures with regards to the biomaterials applications. Of particular interest is the architecture of the materials and the versatility of the process, which can be readily controlled and applied to biomaterials applications. A careful control of the starting formulation and processing conditions is required to control the integrity of the structure and resulting properties. Further in vitro and in vivo investigations are required to validate the potential of this new class of porous materials.

Adsorbed molecules in external fields: Effect of confining potential

NASA Astrophysics Data System (ADS)

Tyagi, Ashish; Silotia, Poonam; Maan, Anjali; Prasad, Vinod

2016-12-01

We study the rotational excitation of a molecule adsorbed on a surface. As is well known the interaction potential between the surface and the molecule can be modeled in number of ways, depending on the molecular structure and the geometry under which the molecule is being adsorbed by the surface. We explore the effect of change of confining potential on the excitation, which is largely controlled by the static electric fields and continuous wave laser fields. We focus on dipolar molecules and hence we restrict ourselves to the first order interaction in field-molecule interaction potential either through permanent dipole moment or/and the molecular polarizability parameter. It is shown that confining potential shapes, strength of the confinement, strongly affect the excitation. We compare our results for different confining potentials.

Confinement-induced Molecular Templating and Controlled Ligation

NASA Astrophysics Data System (ADS)

Berard, Daniel; Shayegan, Marjan; Michaud, François; Henkin, Gil; Scott, Shane; Leith, Jason; Leslie, Sabrina; Leslie Lab Team

Loading and manipulating long DNA molecules within sub-50 nm cross-section nanostructures for genomic and biochemical analyses, while retaining their structural integrity, present key technological challenges to the biotechnology sector, such as device clogging and molecular breakage. We overcome these challenges by using Convex Lens-induced Confinement (CLiC) technology to gently load DNA into nanogrooves from above. Here, we demonstrate single-fluorophore visualization of custom DNA barcodes as well as efficient top-loading of DNA into sub-50 nm nanogrooves of variable topographies. We study confinement-enhanced self-ligation of polymers loaded in circular nanogrooves. Further, we use concentric, circular nanogrooves to eliminate confinement gradient-induced drift of stretched DNA.

The effects of pressure, temperature, and pore water on velocities in Westerly granite. [for seismic wave propagation

NASA Technical Reports Server (NTRS)

Spencer, J. W., Jr.; Nur, A. M.

1976-01-01

A description is presented of an experimental assembly which has been developed to conduct concurrent measurements of compressional and shear wave velocities in rocks at high temperatures and confining pressures and with independent control of the pore pressure. The apparatus was used in studies of the joint effects of temperature, external confining pressure, and internal pore water on sonic velocities in Westerly granite. It was found that at a given temperature, confining pressure has a larger accelerating effect on compressional waves in dry rock, whereas at a given confining pressure, temperature has a larger retarding effect on shear waves.

Photonic engineering of highly linearly polarized quantum dot emission at telecommunication wavelengths

NASA Astrophysics Data System (ADS)

Mrowiński, P.; Emmerling, M.; Schneider, C.; Reithmaier, J. P.; Misiewicz, J.; Höfling, S.; Sek, G.

2018-04-01

In this work, we discuss a method to control the polarization anisotropy of spontaneous emission from neutral excitons confined in quantum-dot-like nanostructures, namely single epitaxial InAs quantum dashes emitting at telecom wavelengths. The nanostructures are embedded inside lithographically defined, in-plane asymmetric photonic mesa structures, which generate polarization-dependent photonic confinement. First, we study the influence of the photonic confinement on the polarization anisotropy of the emission by photoluminescence spectroscopy, and we find evidence of different contributions to a degree of linear polarization (DOLP), i.e., from the quantum dash and the photonic mesa, in total giving rise to DOLP =0.85 . Then, we perform finite-difference time-domain simulations of photonic confinement, and we calculate the DOLP in a dipole approximation showing well-matched results for the established model. Furthermore, by using numerical calculations, we demonstrate several types of photonic confinements where highly linearly polarized emission with DOLP of about 0.9 is possible by controlling the position of a quantum emitter inside the photonic structure. Then, we elaborate on anisotropic quantum emitters allowing for exceeding DOLP =0.95 in an optimized case, and we discuss the ways towards efficient linearly polarized single photon source at telecom bands.

Microorganisms in Confined Habitats: Microbial Monitoring and Control of Intensive Care Units, Operating Rooms, Cleanrooms and the International Space Station

PubMed Central

Mora, Maximilian; Mahnert, Alexander; Koskinen, Kaisa; Pausan, Manuela R.; Oberauner-Wappis, Lisa; Krause, Robert; Perras, Alexandra K.; Gorkiewicz, Gregor; Berg, Gabriele; Moissl-Eichinger, Christine

2016-01-01

Indoor environments, where people spend most of their time, are characterized by a specific microbial community, the indoor microbiome. Most indoor environments are connected to the natural environment by high ventilation, but some habitats are more confined: intensive care units, operating rooms, cleanrooms and the international space station (ISS) are extraordinary living and working areas for humans, with a limited exchange with the environment. The purposes for confinement are different: a patient has to be protected from infections (intensive care unit, operating room), product quality has to be assured (cleanrooms), or confinement is necessary due to extreme, health-threatening outer conditions, as on the ISS. The ISS represents the most secluded man-made habitat, constantly inhabited by humans since November 2000 – and, inevitably, also by microorganisms. All of these man-made confined habitats need to be microbiologically monitored and controlled, by e.g., microbial cleaning and disinfection. However, these measures apply constant selective pressures, which support microbes with resistance capacities against antibiotics or chemical and physical stresses and thus facilitate the rise of survival specialists and multi-resistant strains. In this article, we summarize the available data on the microbiome of aforementioned confined habitats. By comparing the different operating, maintenance and monitoring procedures as well as microbial communities therein, we emphasize the importance to properly understand the effects of confinement on the microbial diversity, the possible risks represented by some of these microorganisms and by the evolution of (antibiotic) resistances in such environments – and the need to reassess the current hygiene standards. PMID:27790191

Microorganisms in Confined Habitats: Microbial Monitoring and Control of Intensive Care Units, Operating Rooms, Cleanrooms and the International Space Station.

PubMed

Mora, Maximilian; Mahnert, Alexander; Koskinen, Kaisa; Pausan, Manuela R; Oberauner-Wappis, Lisa; Krause, Robert; Perras, Alexandra K; Gorkiewicz, Gregor; Berg, Gabriele; Moissl-Eichinger, Christine

2016-01-01

Indoor environments, where people spend most of their time, are characterized by a specific microbial community, the indoor microbiome. Most indoor environments are connected to the natural environment by high ventilation, but some habitats are more confined: intensive care units, operating rooms, cleanrooms and the international space station (ISS) are extraordinary living and working areas for humans, with a limited exchange with the environment. The purposes for confinement are different: a patient has to be protected from infections (intensive care unit, operating room), product quality has to be assured (cleanrooms), or confinement is necessary due to extreme, health-threatening outer conditions, as on the ISS. The ISS represents the most secluded man-made habitat, constantly inhabited by humans since November 2000 - and, inevitably, also by microorganisms. All of these man-made confined habitats need to be microbiologically monitored and controlled, by e.g., microbial cleaning and disinfection. However, these measures apply constant selective pressures, which support microbes with resistance capacities against antibiotics or chemical and physical stresses and thus facilitate the rise of survival specialists and multi-resistant strains. In this article, we summarize the available data on the microbiome of aforementioned confined habitats. By comparing the different operating, maintenance and monitoring procedures as well as microbial communities therein, we emphasize the importance to properly understand the effects of confinement on the microbial diversity, the possible risks represented by some of these microorganisms and by the evolution of (antibiotic) resistances in such environments - and the need to reassess the current hygiene standards.

Slumps and Fog in Valles Marineris

NASA Astrophysics Data System (ADS)

Ojha, L.; Chojnacki, M.; Toigo, A. D.; McDonald, G. D.; Wolff, M. J.; Leung, C. W. S.

2016-12-01

The first spectral evidence for H2O ice clouds on Mars came from the interferometer spectrometer on board the Mariner 9 spacecraft. Water ice clouds on Mars form by freezing of atmospheric water vapor, of which the main surface source is the seasonal sublimation of the polar caps, and have been observed around the Tharsis volcanoes, Olympus Mons, Alba Patera, Valles Marineris (VM) and the southern highlands. Cloud activity in some of these regions display a seasonal trend, where the cloud area increases in warmer seasons, and decreases during colder seasons. The atmospheric hazes in VM are relatively small in areal extent, confined within canyon topography, and are difficult to replicate in models of global or regional vapor transport, indicating that they may be locally sourced. This distinguishes the VM hazes from the global-scale clouds. Spectral data from the Planetary Fourier Spectrometer onboard the Mars Express orbiter have been reported as consistent with water ice in the atmospheric fog, however results from Mars Express favored dust as responsible for low-elevation hazes. Here we report observations and spectroscopic analyses of low elevation haze in Juventae Chasma, which are spatially correlated with locations of seasonal flows thought to be caused by briny liquid water. Furthermore, we report the seasonality of the haze and explore its potential role in the creation of contemporary mass-wasting features on Mars.

Thermal etching of silver: Influence of rolling defects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ollivier, M., E-mail: o.maelig@imperial.ac.uk

2016-08-15

Silver is well known to be thermally etched in an oxygen-rich atmosphere and has been extensively studied in the laboratory to understand thermal etching and to limit its effect when this material is used as a catalyst. Yet, in many industrial applications the surface of rolled silver sheets is used without particular surface preparation. Here, it is shown by combining FIB-tomography, FIB-SIMS and analytical SEM that the kinetics of thermal etch pitting are significantly faster on rolled Ag surfaces than on polished surfaces. This occurs due to range of interacting phenomena including (i) the reaction of subsurface carbon-contamination with dissolvedmore » oxygen to form pores that grow to intersect the surface, (ii) surface reconstruction around corrosion pits and surface scratches, and (iii) sublimation at low pressure and high temperature. A method to identify subsurface pores is developed to show that the pores have (111) and (100) internal facets and may be filled with a gas coming from the chemical reaction of oxygen and carbon contamination. - Highlights: Thermal etching of industrial silver sheets vs. polished silver sheets Effect of annealing atmosphere on the thermal etching of silver: surface and subsurface characterization Link between etch pitting and defects induced by rolling. FIB-tomography coupled with EBSD for determining crystal planes of the facets of subsurface pores. FIB-SIMS characterization to probe the gas confined inside subsurface pores.« less

Regulation and Measurement of the Heat Generated by Automatic Tooth Preparation in a Confined Space.

PubMed

Yuan, Fusong; Zheng, Jianqiao; Sun, Yuchun; Wang, Yong; Lyu, Peijun

2017-06-01

The aim of this study was to assess and regulate heat generation in the dental pulp cavity and circumambient temperature around a tooth during laser ablation with a femtosecond laser in a confined space. The automatic tooth preparing technique is one of the traditional oral clinical technology innovations. In this technique, a robot controlled an ultrashort pulse laser to automatically complete the three-dimensional teeth preparing in a confined space. The temperature control is the main measure for protecting the tooth nerve. Ten tooth specimens were irradiated with a femtosecond laser controlled by a robot in a confined space to generate 10 teeth preparation. During the process, four thermocouple sensors were used to record the pulp cavity and circumambient environment temperatures with or without air cooling. A statistical analysis of the temperatures was performed between the conditions with and without air cooling (p < 0.05). The recordings showed that the temperature with air cooling was lower than that without air cooling and that the heat generated in the pulp cavity was lower than the threshold for dental pulp damage. These results indicate that femtosecond laser ablation with air cooling might be an appropriate method for automatic tooth preparing.

Requirements for modeling airborne microbial contamination in space stations

NASA Astrophysics Data System (ADS)

Van Houdt, Rob; Kokkonen, Eero; Lehtimäki, Matti; Pasanen, Pertti; Leys, Natalie; Kulmala, Ilpo

2018-03-01

Exposure to bioaerosols is one of the facets that affect indoor air quality, especially for people living in densely populated or confined habitats, and is associated to a wide range of health effects. Good indoor air quality is thus vital and a prerequisite for fully confined environments such as space habitats. Bioaerosols and microbial contamination in these confined space stations can have significant health impacts, considering the unique prevailing conditions and constraints of such habitats. Therefore, biocontamination in space stations is strictly monitored and controlled to ensure crew and mission safety. However, efficient bioaerosol control measures rely on solid understanding and knowledge on how these bioaerosols are created and dispersed, and which factors affect the survivability of the associated microorganisms. Here we review the current knowledge gained from relevant studies in this wide and multidisciplinary area of bioaerosol dispersion modeling and biological indoor air quality control, specifically taking into account the specific space conditions.

Control of exciton confinement in quantum dot-organic complexes through energetic alignment of interfacial orbitals.

PubMed

Frederick, Matthew T; Amin, Victor A; Swenson, Nathaniel K; Ho, Andrew Y; Weiss, Emily A

2013-01-09

This paper describes a method to control the quantum confinement, and therefore the energy, of excitonic holes in CdSe QDs through adsorption of the hole-delocalizing ligand phenyldithiocarbamate, PTC, and para substitutions of the phenyl ring of this ligand with electron-donating or -withdrawing groups. These substitutions control hole delocalization in the QDs through the energetic alignment of the highest occupied orbitals of PTC with the highest density-of-states region of the CdSe valence band, to which PTC couples selectively.

State and Local Perspective on Implementation of the Centers for Disease Control and Prevention Dog Confinement Agreement.

PubMed

Zaganjor, I; Sinclair, J R; Coleman, M S

2015-12-01

The Centers for Disease Control and Prevention (CDC) works in conjunction with state, territorial, local and tribal agencies (STLTAs) to prevent the transmission of infectious agents. Issuance of confinement agreements using CDC Form 75.37 'Notice to Owners and Importers of Dogs' to importers of dogs that are not vaccinated or incompletely vaccinated against rabies is part of the agency's regulatory programme to prevent the entry of dogs infected with rabies. Although this is a regulatory programme that depends heavily on partnerships between CDC and STLTAs, CDC had never formally evaluated the acceptability of the confinement agreement process with these partners. Thus, a short survey of nine STLTAs was conducted to evaluate whether these partners have enough personnel and resources to implement the regulation and their general opinions of the confinement agreement process. The results illustrate that CDC partners are dissatisfied to some extent with the process, and there are multiple issues limiting their success in enforcing the regulation. © 2015 Blackwell Verlag GmbH.

Confined Space Evaluation Student Manual, #19613

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chochoms, Michael

Many workplaces contain spaces that are considered to be “confined” because their configuration hinders the activities of employees who must enter into, work in, and exit from them. In general, the permit-required confined spaces (PRCSs) Occupational Safety and Health Administration (OSHA) standard requires that Los Alamos National Laboratory (LANL) evaluate the workplace to determine if any spaces are PRCSs. The standard specifies strict procedures for the evaluation and atmospheric testing of a space before and during an entry by workers. The OSHA PRCS standard provides for alternative (less stringent than full-permit) entry procedures in cases where the only hazard inmore » a space is atmospheric and the hazard can be controlled by forced air. At LANL, all confined spaces or potential confined spaces on LANL-owned or -operated property must be identified and evaluated by a confined space evaluator accompanied by a knowledgeable person. This course provides the information needed by confined space evaluators to make judgements about whether a space is a confined space, and if so, whether the space will require a permit for entry.« less

Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.; Wu, Y.

1988-01-01

A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

Understanding Potential Exposure Sources of Perfluorinated Carboxylic Acids in the Workplace

PubMed Central

Kaiser, Mary A.; Dawson, Barbara J.; Barton, Catherine A.; Botelho, Miguel A.

2010-01-01

This paper integrates perspectives from analytical chemistry, environmental engineering, and industrial hygiene to better understand how workers may be exposed to perfluorinated carboxylic acids when handling them in the workplace in order to identify appropriate exposure controls. Due to the dramatic difference in physical properties of the protonated acid form and the anionic form, this family of chemicals provides unique industrial hygiene challenges. Workplace monitoring, experimental data, and modeling results were used to ascertain the most probable workplace exposure sources and transport mechanisms for perfluorooctanoic acid (PFOA) and its ammonium salt (APFO). PFOA is biopersistent and its measurement in the blood has been used to assess human exposure since it integrates exposure from all routes of entry. Monitoring suggests that inhalation of airborne material may be an important exposure route. Transport studies indicated that, under low pH conditions, PFOA, the undissociated (acid) species, actively partitions from water into air. In addition, solid-phase PFOA and APFO may also sublime into the air. Modeling studies determined that contributions from surface sublimation and loss from low pH aqueous solutions can be significant potential sources of workplace exposure. These findings suggest that keeping surfaces clean, preventing accumulation of material in unventilated areas, removing solids from waste trenches and sumps, and maintaining neutral pH in sumps can lower workplace exposures. PMID:20974675

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.

Oxide nanoelectronics on demand.

PubMed

Cen, Cheng; Thiel, Stefan; Mannhart, Jochen; Levy, Jeremy

2009-02-20

Electronic confinement at nanoscale dimensions remains a central means of science and technology. We demonstrate nanoscale lateral confinement of a quasi-two-dimensional electron gas at a lanthanum aluminate-strontium titanate interface. Control of this confinement using an atomic force microscope lithography technique enabled us to create tunnel junctions and field-effect transistors with characteristic dimensions as small as 2 nanometers. These electronic devices can be modified or erased without the need for complex lithographic procedures. Our on-demand nanoelectronics fabrication platform has the potential for widespread technological application.

Ablative overlays for Space Shuttle leading edge ascent heat protection

NASA Technical Reports Server (NTRS)

Strauss, E. L.

1975-01-01

Ablative overlays were evaluated via a plasma-arc simulation of the ascent pulse on the leading edge of the Space Shuttle Orbiter. Overlay concepts included corkboard, polyisocyanurate foam, low-density Teflon, epoxy, and subliming salts. Their densities ranged from 4.9 to 81 lb per cu ft, and the thicknesses varied from 0.107 to 0.330 in. Swept-leading-edge models were fabricated from 30-lb per cu ft silicone-based ablators. The overlays were bonded to maintain the surface temperature of the base ablator below 500 F during ascent. Foams provided minimum-weight overlays, and subliming salts provided minimum-thickness overlays. Teflon left the most uniform surface after ascent heating.

Improved di-p-xylylene polymer and apparatus and method for making the same

DOEpatents

Jahn, R.K.; Liepins, R.

Solid di-para-xylyene dimer is sublimed in a sublimation furnace at approximately 100 to 200/sup 0/C and subsequently conducted to a pyrolysis furnace where it is pyrolyzed to the diradical p-xylylene monomer while in the vapor state at approximately 600 degrees C. The diradical monomer is then introduced into a deposition chamber for deposition onto a suitable substrate. The deposition chamber includes electrodes for producing a low pressure plasma through which the diradical monomer passes prior to deposition. The interaction of the diradical monomer with the low pressure plasma results in the formation of poly-p-xylyene film which is exceptionally hard and thermally stable.

Observational evidence for an active surface reservoir of solid carbon dioxide on Mars.

PubMed

Malin, M C; Caplinger, M A; Davis, S D

2001-12-07

High-resolution images of the south polar residual cap of Mars acquired in 1999 and 2001 show changes in the configuration of pits, intervening ridges, and isolated mounds. Escarpments have retreated 1 to 3 meters in 1 martian year, changes that are an order of magnitude larger than can be explained by the sublimation of water ice, but close to what is expected for sublimation of carbon dioxide ice. These observations support a 35-year-old conjecture that Mars has a large surface reservoir of solid carbon dioxide. The erosion implies that this reservoir is not in equilibrium with the present environment and that global climate change is occurring on Mars.

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.

Stability of polar frosts in spherical bowl-shaped craters on the moon, Mercury, and Mars

NASA Technical Reports Server (NTRS)

Ingersoll, Andrew P.; Svitek, Tomas; Murray, Bruce C.

1992-01-01

A model of spherical bowl-shaped craters is described and applied to the moon, Mercury, and Mars. The maximum temperature of permanently shadowed areas are calculated using estimates of the depth/diameter ratios of typical lunar bowl-shaped craters and assuming a saturated surface in which the craters are completely overlapping. For Mars, two cases are considered: water frost in radiative equilibrium and subliming CO2 frost in vapor equilibrium. Energy budgets and temperatures are used to determine whether a craterlike depression loses mass faster or slower than a flat horizontal surface. This reveals qualitatively whether the frost surface becomes rougher or smoother as it sublimes.

Investigation on the morphological and optical evolution of bimetallic Pd-Ag nanoparticles on sapphire (0001) by the systematic control of composition, annealing temperature and time.

PubMed

Pandey, Puran; Kunwar, Sundar; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2017-01-01

Multi-metallic alloy nanoparticles (NPs) can offer additional opportunities for modifying the electronic, optical and catalytic properties by the control of composition, configuration and size of individual nanostructures that are consisted of more than single element. In this paper, the fabrication of bimetallic Pd-Ag NPs is systematically demonstrated via the solid state dewetting of bilayer thin films on c-plane sapphire by governing the temperature, time as well as composition. The composition of Pd-Ag bilayer remarkably affects the morphology of alloy nanostructures, in which the higher Ag composition, i.e. Pd0.25Ag0.75, leads to the enhanced dewetting of bilayers whereas the higher Pd composition (Pd0.75Ag0.25) hinders the dewetting. Depending on the annealing temperature, Pd-Ag alloy nanostructures evolve with a series of configurations, i.e. nucleation of voids, porous network, elongated nanoclusters and round alloy NPs. In addition, with the annealing time set, the gradual configuration transformation from the elongated to round alloy NPs as well as size reduction is demonstrated due to the enhanced diffusion and sublimation of Ag atoms. The evolution of various morphology of Pd-Ag nanostructures is described based on the surface diffusion and inter-diffusion of Pd and Ag adatoms along with the Ag sublimation, Rayleigh instability and energy minimization mechanism. The reflectance spectra of bimetallic Pd-Ag nanostructures exhibit various quadrupolar and dipolar resonance peaks, peak shifts and absorption dips owing to the surface plasmon resonance of nanostructures depending on the surface morphology. The intensity of reflectance spectra is gradually decreased along with the surface coverage and NP size evolution. The absorption dips are red-shifted towards the longer wavelength for the larger alloy NPs and vice-versa.

Determining hydrological changes in a small Arctic treeline basin using cold regions hydrological modelling and a pseudo-global warming approach

NASA Astrophysics Data System (ADS)

Krogh, S. A.; Pomeroy, J. W.

2017-12-01

Increasing temperatures are producing higher rainfall ratios, shorter snow-covered periods, permafrost thaw, more shrub coverage, more northerly treelines and greater interaction between groundwater and surface flow in Arctic basins. How these changes will impact the hydrology of the Arctic treeline environment represents a great challenge. To diagnose the future hydrology along the current Arctic treeline, a physically based cold regions model was used to simulate the hydrology of a small basin near Inuvik, Northwest Territories, Canada. The hydrological model includes hydrological processes such as snow redistribution and sublimation by wind, canopy interception of snow/rain and sublimation/evaporation, snowmelt energy balance, active layer freeze/thaw, infiltration into frozen and unfrozen soils, evapotranspiration, horizontal flow through organic terrain and snowpack, subsurface flow and streamflow routing. The model was driven with weather simulated by a high-resolution (4 km) numerical weather prediction model under two scenarios: (1) control run, using ERA-Interim boundary conditions (2001-2013) and (2) future, using a Pseudo-Global Warming (PGW) approach based on the RCP8.5 projections perturbing the control run. Transient changes in vegetation based on recent observations and ecological expectations were then used to re-parameterise the model. Historical hydrological simulations were validated against daily streamflow, snow water equivalent and active layer thickness records, showing the model's suitability in this environment. Strong annual warming ( 6 °C) and more precipitation ( 20%) were simulated by the PGW scenario, with winter precipitation and fall temperature showing the largest seasonal increase. The joint impact of climate and transient vegetation changes on snow accumulation and redistribution, evapotranspiration, active layer development, runoff generation and hydrograph characteristics are analyzed and discussed.

Thermomagnetic burn control for magnetic fusion reactor

DOEpatents

Rawls, J.M.; Peuron, A.U.

1980-07-01

Apparatus is provided for controlling the plasma energy production rate of a magnetic-confinement fusion reactor, by controlling the magnetic field ripple. The apparatus includes a group of shield sectors formed of ferromagnetic material which has a temperature-dependent saturation magnetization, with each shield lying between the plasma and a toroidal field coil. A mechanism for controlling the temperature of the magnetic shields, as by controlling the flow of cooling water therethrough, thereby controls the saturation magnetization of the shields and therefore the amount of ripple in the magnetic field that confines the plasma, to thereby control the amount of heat loss from the plasma. This heat loss in turn determines the plasma state and thus the rate of energy production.

Adsorbed molecules in external fields: Effect of confining potential.

PubMed

Tyagi, Ashish; Silotia, Poonam; Maan, Anjali; Prasad, Vinod

2016-12-05

We study the rotational excitation of a molecule adsorbed on a surface. As is well known the interaction potential between the surface and the molecule can be modeled in number of ways, depending on the molecular structure and the geometry under which the molecule is being adsorbed by the surface. We explore the effect of change of confining potential on the excitation, which is largely controlled by the static electric fields and continuous wave laser fields. We focus on dipolar molecules and hence we restrict ourselves to the first order interaction in field-molecule interaction potential either through permanent dipole moment or/and the molecular polarizability parameter. It is shown that confining potential shapes, strength of the confinement, strongly affect the excitation. We compare our results for different confining potentials. Copyright © 2016 Elsevier B.V. All rights reserved.

Digital Transfer Growth of Patterned 2D Metal Chalcogenides by Confined Nanoparticle Evaporation

DOE PAGES

Mahjouri-Samani, Masoud; Tian, Mengkun; Wang, Kai; ...

2014-10-19

Developing methods for the facile synthesis of two-dimensional (2D) metal chalcogenides and other layered materials is crucial for emerging applications in functional devices. Controlling the stoichiometry, number of the layers, crystallite size, growth location, and areal uniformity is challenging in conventional vapor phase synthesis. Here, we demonstrate a new route to control these parameters in the growth of metal chalcogenide (GaSe) and dichalcogenide (MoSe 2) 2D crystals by precisely defining the mass and location of the source materials in a confined transfer growth system. A uniform and precise amount of stoichiometric nanoparticles are first synthesized and deposited onto a substratemore » by pulsed laser deposition (PLD) at room temperature. This source substrate is then covered with a receiver substrate to form a confined vapor transport growth (VTG) system. By simply heating the source substrate in an inert background gas, a natural temperature gradient is formed that evaporates the confined nanoparticles to grow large, crystalline 2D nanosheets on the cooler receiver substrate, the temperature of which is controlled by the background gas pressure. Large monolayer crystalline domains (~ 100 m lateral sizes) of GaSe and MoSe 2 are demonstrated, as well as continuous monolayer films through the deposition of additional precursor materials. This novel PLD-VTG synthesis and processing method offers a unique approach for the controlled growth of large-area, metal chalcogenides with a controlled number of layers in patterned growth locations for optoelectronics and energy related applications.« less

Feedback controlled, reactor relevant, high-density, high-confinement scenarios at ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Lang, P. T.; Blanken, T. C.; Dunne, M.; McDermott, R. M.; Wolfrum, E.; Bobkov, V.; Felici, F.; Fischer, R.; Janky, F.; Kallenbach, A.; Kardaun, O.; Kudlacek, O.; Mertens, V.; Mlynek, A.; Ploeckl, B.; Stober, J. K.; Treutterer, W.; Zohm, H.; ASDEX Upgrade Team

2018-03-01

One main programme topic at the ASDEX Upgrade all-metal-wall tokamak is development of a high-density regime with central densities at reactor grade level while retaining high-confinement properties. This required development of appropriate control techniques capable of coping with the pellet tool, a powerful means of fuelling but one which presented challenges to the control system for handling of related perturbations. Real-time density profile control was demonstrated, raising the core density well above the Greenwald density while retaining the edge density in order to avoid confinement losses. Recently, a new model-based approach was implemented that allows direct control of the central density. Investigations focussed first on the N-seeding scenario owing to its proven potential to yield confinement enhancements. Combining pellets and N seeding was found to improve the divertor buffering further and enhance the operational range accessible. For core densities up to about the Greenwald density, a clear improvement with respect to the non-seeding reference was achieved; however, at higher densities this benefit is reduced. This behaviour is attributed to recurrence of an outward shift of the edge density profile, resulting in a reduced peeling-ballooning stability. This is similar to the shift seen during strong gas puffing, which is required to prevent impurity influx in ASDEX Upgrade. First tests indicate that highly-shaped plasma configurations like the ITER base-line scenario, respond very well to pellet injection, showing efficient fuelling with no measurable impact on the edge density profile.

Physical confinement signals regulate the organization of stem cells in three dimensions

PubMed Central

Sean, David; Ignacio, Maxime; Godin, Michel; Slater, Gary W.; Pelling, Andrew E.

2016-01-01

During embryogenesis, the spherical inner cell mass (ICM) proliferates in the confined environment of a blastocyst. Embryonic stem cells (ESCs) are derived from the ICM, and mimicking embryogenesis in vitro, mouse ESCs (mESCs) are often cultured in hanging droplets. This promotes the formation of a spheroid as the cells sediment and aggregate owing to increased physical confinement and cell–cell interactions. In contrast, mESCs form two-dimensional monolayers on flat substrates and it remains unclear if the difference in organization is owing to a lack of physical confinement or increased cell–substrate versus cell–cell interactions. Employing microfabricated substrates, we demonstrate that a single geometric degree of physical confinement on a surface can also initiate spherogenesis. Experiment and computation reveal that a balance between cell–cell and cell–substrate interactions finely controls the morphology and organization of mESC aggregates. Physical confinement is thus an important regulatory cue in the three-dimensional organization and morphogenesis of developing cells. PMID:27798278

Facile fabrication of BiVO4 nanofilms with controlled pore size and their photoelectrochemical performances.

PubMed

Feng, Chenchen; Jiao, Zhengbo; Li, Shaopeng; Zhang, Yan; Bi, Yingpu

2015-12-28

We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO(4) photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures.

Use of manometric temperature measurements (MTM) to characterize the freeze-drying behavior of amorphous protein formulations.

PubMed

Johnson, Robert E; Oldroyd, Megan E; Ahmed, Saleem S; Gieseler, Henning; Lewis, Lavinia M

2010-06-01

The freeze-drying behavior and cake morphology of a model protein in an amorphous formulation were studied at varying protein concentrations using conservative (-25 degrees C) and aggressive (+25 degrees C) shelf temperatures at constant chamber pressure during primary drying. The two cycles were characterized by manometric temperature measurements (MTM) in a SMART freeze dryer that estimates the sublimation rate (dm/dt), product temperature at the freeze-drying front (T(p-MTM)) and product resistance (R(p)) during a run. The calculated sublimation rates (dm/dt) were 3-4 times faster in the aggressive cycle compared to the conservative cycle. For conservatively dried cakes R(p) increased with both dry layer thickness and protein concentration. For aggressively dried cakes (where freeze-drying occurs at the edge of microcollapse), R(p) also increased with protein concentration but was independent of the dry layer thickness. The sublimation rate was influenced by R(p), dry layer thickness and T(p-MTM) in the conservative cycle, but was governed mainly by T(p-MTM) in the aggressive cycle, where R(p) is independent of the dry layer thickness. The aggressively dried cakes had a more open and porous structure compared to their conservatively dried counterparts. (c) 2009 Wiley-Liss, Inc. and the American Pharmacists Association

Preparation and optimization of glyceryl behenate-based highly porous pellets containing cilostazol.

PubMed

Hwang, Kyu-Mok; Byun, Woojin; Cho, Cheol-Hee; Park, Eun-Seok

2018-06-01

The aim of this study was to prepare a highly porous multiparticulate dosage form containing cilostazol for gastroretentive drug delivery. The floating pellets were prepared with glyceryl behenate as a matrix former and camphor as a sublimating agent by extrusion/spheronization and sublimation under vacuum. Granules prepared with sublimation at 60 °C displayed a slower dissolution rate and smoother surface morphology than those prepared at lower temperatures. This was unexpected as the reported melting point of glyceryl behenate is higher than 69 °C. The DSC study revealed that melting began at a lower temperature owing to the multicomponent property of glyceryl behenate, which led to a sintering effect. The prepared pellets were spherical with unimodal size distribution. They also had porous structures with increased porosity, which led to immediate buoyancy. As cilostazol is a hydrophobic drug that has an erosion-based release mechanism, drug release profile was highly correlated with the percentage of disintegrated pellets. Various excipients were added to the glyceryl behenate-based formulation to increase the floating duration. When hydroxyethyl cellulose was added to the glyceryl behenate-based pellets, acceptable dissolution rate and buoyancy were acquired. This system could potentially be used for gastroretentive delivery of various hydrophobic drugs, which was generally considered difficult.

Cryostratigraphy and the Sublimation Unconformity in Permafrost from an Ultraxerous Environment, University Valley, McMurdo Dry Valleys of Antarctica

NASA Technical Reports Server (NTRS)

Lapalme, Caitlin M.; Fortier, Daniel; Pollard, Wayne; Lacelle, Denis; Davila, Alfonso; McKay, Christopher P.

2017-01-01

The cryostratigraphy of permafrost in ultraxerous environments is poorly known. In this study, icy permafrost cores from University Valley (McMurdo Dry Valleys, Antarctica) were analyzed for sediment properties, ground-ice content, types and distribution of cryostructures, and presence of unconformities. No active layer exists in the valley, but the ice table, a sublimation unconformity, ranges from 0 to 60 cm depth. The sediments are characterized as a medium sand, which classifies them as low to non-frost susceptible. Computed tomography (CT) scan images of the icy permafrost cores revealed composite cryostructures that included the structureless, porous visible, suspended and crustal types. These cryostructures were observed irrespective of ground-ice origin (vapour deposited and freezing of snow meltwater), suggesting that the type and distribution of cryostructures could not be used as a proxy to infer the mode of emplacement of ground ice. Volumetric ice content derived from the CT scan images underestimated measured volumetric ice content, but approached measured excess ice content. A palaeo-sublimation unconformity could not be detected from a change in cryostructures, but could be inferred from an increase in ice content at the maximum predicted ice table depth. This study highlights some of the unique ground-ice processes and cryostructures in ultraxerous environments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jewitt, David, E-mail: jewitt@ucla.edu; Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1567

Some asteroids eject dust, unexpectedly producing transient, comet-like comae and tails. First ascribed to the sublimation of near-surface water ice, mass-losing asteroids (also called 'main-belt comets') can in fact be driven by a surprising diversity of mechanisms. In this paper, we consider 11 dynamical asteroids losing mass, in nine of which the ejected material is spatially resolved. We address mechanisms for producing mass loss including rotational instability, impact ejection, electrostatic repulsion, radiation pressure sweeping, dehydration stresses, and thermal fracture, in addition to the sublimation of ice. In two objects (133P and 238P) the repetitive nature of the observed activity leavesmore » ice sublimation as the only reasonable explanation, while in a third ((596) Scheila), a recent impact is the cause. Another impact may account for activity in P/2010 A2, but this tiny object can also be explained as having shed mass after reaching rotational instability. Mass loss from (3200) Phaethon is probably due to cracking or dehydration at extreme ({approx}1000 K) perihelion temperatures, perhaps aided by radiation pressure sweeping. For the other bodies, the mass-loss mechanisms remain unidentified, pending the acquisition of more and better data. While the active asteroid sample size remains small, the evidence for an astonishing diversity of mass-loss processes in these bodies is clear.« less

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.

Graphite and ablative material response to CO2 laser, carbon-arc, and xenon-arc radiation

NASA Technical Reports Server (NTRS)

Brewer, W. D.

1976-01-01

The behavior was investigated of graphite and several charring ablators in a variety of high-radiative heat-flux environments. A commercial-grade graphite and nine state-of-the-art charring ablators were subjected to various radiative environments produced by a CO2 laser and a carbon arc. Graphite was also tested in xenon-arc radiation. Heat-flux levels ranged from 10 to 47 MW/sq m. Tests were conducted in air, nitrogen, helium, and a CO2-N2 mixture which simulated the Venus atmosphere. The experimental results were compared with theoretical results obtained with a one-dimensional charring-ablator analysis and a two-dimensional subliming-ablator analysis. Neither the graphite nor the charring ablators showed significant differences in appearance or microstructure after testing in the different radiative environments. The performance of phenolic nylon and graphite was predicted satisfactorily with existing analyses and published material property data. Good agreement between experimental and analytical results was obtained by using sublimation parameters from a chemical nonequilibrium analysis of graphite sublimation. Some charring ablators performed reasonably well and could withstand radiative fluxes of the level encountered in certain planetary entries. Other materials showed excessive surface recession and/or large amounts of cracking and spalling, and appear to be unsuitable for severe radiative environments.

Abnormal gas-liquid-solid phase transition behaviour of water observed with in situ environmental SEM.

PubMed

Chen, Xin; Shu, Jiapei; Chen, Qing

2017-04-24

Gas-liquid-solid phase transition behaviour of water is studied with environmental scanning electron microscopy for the first time. Abnormal phenomena are observed. At a fixed pressure of 450 Pa, with the temperature set to -7 °C, direct desublimation happens, and ice grows continuously along the substrate surface. At 550 Pa, although ice is the stable phase according to the phase diagram, metastable liquid droplets first nucleate and grow to ~100-200 μm sizes. Ice crystals nucleate within the large sized droplets, grow up and fill up the droplets. Later, the ice crystals grow continuously through desublimation. At 600 Pa, the metastable liquid grows quickly, with some ice nuclei floating in it, and the liquid-solid coexistence state exists for a long time. By lowering the vapour pressure and/or increasing the substrate temperature, ice sublimates into vapour phase, and especially, the remaining ice forms a porous structure due to preferential sublimation in the concave regions, which can be explained with surface tension effect. Interestingly, although it should be forbidden for ice to transform into liquid phase when the temperature is well below 0 °C, liquid like droplets form during the ice sublimation process, which is attributed to the surface tension effect and the quasiliquid layers.

New Equations for the Sublimation Pressure and Melting Pressure of H2O Ice Ih

NASA Astrophysics Data System (ADS)

Wagner, Wolfgang; Riethmann, Thomas; Feistel, Rainer; Harvey, Allan H.

2011-12-01

New reference equations, adopted by the International Association for the Properties of Water and Steam (IAPWS), are presented for the sublimation pressure and melting pressure of ice Ih as a function of temperature. These equations are based on input values derived from the phase-equilibrium condition between the IAPWS-95 scientific standard for thermodynamic properties of fluid H2O and the equation of state of H2O ice Ih adopted by IAPWS in 2006, making them thermodynamically consistent with the bulk-phase properties. Compared to the previous IAPWS formulations, which were empirical fits to experimental data, the new equations have significantly less uncertainty. The sublimation-pressure equation covers the temperature range from 50 K to the vapor-liquid-solid triple point at 273.16 K. The ice Ih melting-pressure equation describes the entire melting curve from 273.16 K to the ice Ih-ice III-liquid triple point at 251.165 K. For completeness, we also give the IAPWS melting-pressure equation for ice III, which is slightly adjusted to agree with the ice Ih melting-pressure equation at the corresponding triple point, and the unchanged IAPWS melting-pressure equations for ice V, ice VI, and ice VII.

Experimental and molecular dynamics simulation study of the sublimation and vaporization energetics of iron metalocenes. crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)].

PubMed

Lousada, Claudio M; Pinto, Susana S; Lopes, José N Canongia; da Piedade, M Fatima Minas; Diogo, Hermínio P; da Piedade, Manuel E Minas

2008-04-03

The standard molar enthalpies of sublimation of ferrocene, 1,1'-dimethylferrocene, decamethylferrocene, ferrocenecarboxaldehyde and alpha-methylferrocenemethanol, and the enthalpy of vaporization of N,N-dimethyl(aminomethyl)ferrocene, at 298.15 K, were determined by Calvet-drop microcalorimetry and/or the Knudsen effusion method. The obtained values were used to assess and refine our previously developed force field for metallocenes. The modified force field was able to reproduce the deltasubHdegreesm and deltavapHdegreesm values of the test-set with an accuracy better than 5 kJ.mol-1, except for decamethylferrocene, in which case the deviation between the calculated and experimental deltasubHdegreesm values was 16.1 kJ.mol-1. The origin of the larger error found in the prediction of the sublimation energetics of decamethylferrocene, and which was also observed in the estimation of structural properties (e.g., density and unit cell dimensions), is discussed. Finally, the crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)] at 293 and 150 K, respectively, are reported.

THE DUST SUBLIMATION RADIUS AS AN OUTER ENVELOPE TO THE BULK OF THE NARROW Fe Kα LINE EMISSION IN TYPE 1 AGNs

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 directmore » 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.« less

Latitude dependence of Martian pedestal craters: Evidence for a sublimation-driven formation mechanism

NASA Astrophysics Data System (ADS)

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

2009-10-01

We report on the results of a survey to document and characterize pedestal craters on Mars equatorward of ˜60°N and 65°S latitude. The identification of 2696 pedestal craters reveals a strong latitude dependence, with the vast majority found poleward of 33°N and 40°S. This latitudinal extent is correlated with many climate indicators consistent with the presence of an ice-rich substrate and with climate model predictions of where ice is deposited during periods of higher obliquity in the Amazonian. We have measured key physical attributes of pedestal craters, including the farthest radial extents of the pedestals, pedestal heights, and the circularity of the pedestal margins. In conjunction with the geographic distribution, our measurements strongly support a sublimation-related formation mechanism. This is in contrast to previous hypotheses, which have relied on eolian deflation to produce the elevated plateaus. The identification of marginal pits on the scarps of some pedestal craters, interpreted to be sublimation pits, provide direct evidence for the presence of ice-rich material underlying the armored surface of pedestal craters. On the basis of our findings, we propose a formation mechanism whereby projectiles impact into a volatile-rich dust/snow/ice substrate tens to hundreds of meters thick overlying a dominantly fragmental silicate regolith. The area surrounding the resulting crater becomes armored. Pedestals extend to a distance of multiple crater radii, farther than typical ejecta deposits, necessitating an armoring mechanism that is capable of indurating the surface to a distance greater than the reach of the ejecta. Return to low obliquity causes sublimation of the volatile-rich layer from the intercrater plains, lowering the elevation of the regional terrain. This yields generally circular pedestal craters elevated above the surrounding plains. As a result, the armored surfaces of pedestal craters have preserved a significant record of Amazonian climate history in the form of ice-rich deposits.

Interpretation of spectrophotometric surface properties of comet 67P/Churyumov-Gerasimenko by laboratory simulations of cometary analogs

NASA Astrophysics Data System (ADS)

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

2015-11-01

The OSIRIS imaging system [1] onboard European Space Agency’s Rosetta mission has been orbiting the comet 67P/Churyumov-Gerasimenko (67P) since August 2014. It provides an enormous quantity of high resolution images of the nucleus in the visible spectral range. 67P revealed an unexpected diversity of complex surface structures and spectral properties have also been measured [2].To better interpret this data, a profound knowledge of laboratory analogs of cometary surfaces is essential. For this reason we have set up the LOSSy laboratory (Laboratory for Outflow Studies of Sublimating Materials) to study the spectrophotometric properties of ice-bearing cometary nucleus analogs. The main focus lies on the characterization of the surface evolution under simulated space conditions. The laboratory is equipped with two facilities: the PHIRE-2 radio-goniometer [3], designed to measure the bidirectional visible reflectance of samples under a wide range of geometries and the SCITEAS simulation chamber [4], designed to study the evolution of icy samples subliming under low pressure/temperature conditions by hyperspectral imaging in the VIS-NIR range. Different microscopes complement the two facilities.We present laboratory data of different types of fine grained ice particles mixed with non-volatile components (complex organic matter and minerals). As the ice sublimes, a deposition lag of non-volatile constituents is built-up on top of the ice, possibly mimic a cometary surface. The bidirectional reflectance of the samples have been characterized before and after the sublimation process.A comparison of our laboratory findings with recent OSIRIS data [5] will be presented.[1] Keller, H. U., et al., 2007, Space Sci. Rev., 128, 26[2] Thomas, N. , 2015, Science, 347, Issue 6220, aaa0440[3] Jost, B., submitted, Icarus[4] Pommerol, A., et al., 2015. Planet Space Sci 109:106-122.[5] Fornasier, S., et al., in press. Icarus, arXiv:1505.06888

The Pinnacles of Callisto

NASA Technical Reports Server (NTRS)

Moore, Jeffrey M.; Howard, Alan D.; Schenk, Paul M.

2013-01-01

Many regions of Callisto feature an unusual landscape consisting of rolling dark plains with interspersed bright knobs (pinnacles) and ridges. In earlier work we interpreted the dark plains as dusty, mass-wasted residue from sublimation from volatile-rich bedrock and the bright knobs (often crater rims) as water ice accumulations at locations sheltered from thermal reradiation from the dusty residue. We simulated evolution of Callisto's craters as a combination of bedrock volatile sublimation, mass wasting of the dark, non-coherent residue, and redeposition of ice, and concluded that the ice pinnacles and ridges might be underlain by tens to hundreds of meters of ice. Here we report the initial work of a new study of pinnacles addressing additional questions: 1) Is there an evolutionary sequence starting, e.g., from a cratered initial surface through growth and formation of a dust mantle and pinnacles, to eventual loss of ice to sublimation resulting in just a dark, dusty surface? 2) What determines the areal density and spatial scale of pinnacles - volatile content of bedrock, crater density, surface age, broad-scale topographic setting? 3) Are pinnacles still forming? Several observations address these questions. In a few places scattered high-albedo blocks approx. 25-60 m in diameter occur in the vicinity of large icy pinnacles. We interpret these blocks to be remnants from the collapse of tall pinnacles that were undermined by mass wasting. Some high-relief icy knobs have developed a skeletonized planform due to mass wasting by avalanching, or perhaps to seeding of new sites of ice deposition on mass-wasted ice blocks. Some areas nearly lack fresh craters with well-defined ejecta and ice-free rims. This may imply rapid transformation of fresh craters by sublimation, mass wasting, and ice reprecipitation. In other areas small sharp-rimmed craters occur which lack ice pinnacles, but the craters nonetheless lack visible ejecta sheets. Our preliminary interpretation is that mass wasting is very efficient on Callisto, or alternatively the dust cover is very thick and lacks competent coarse materials.

Protostellar accretion traced with chemistry. High-resolution C18O and continuum observations towards deeply embedded protostars in Perseus

NASA Astrophysics Data System (ADS)

Frimann, Søren; Jørgensen, Jes K.; Dunham, Michael M.; Bourke, Tyler L.; Kristensen, Lars E.; Offner, Stella S. R.; Stephens, Ian W.; Tobin, John J.; Vorobyov, Eduard I.

2017-06-01

Context. Understanding how accretion proceeds is a key question of star formation, with important implications for both the physical and chemical evolution of young stellar objects. In particular, very little is known about the accretion variability in the earliest stages of star formation. Aims: Our aim is to characterise protostellar accretion histories towards individual sources by utilising sublimation and freeze-out chemistry of CO. Methods: A sample of 24 embedded protostars are observed with the Submillimeter Array (SMA) in context of the large program "Mass Assembly of Stellar Systems and their Evolution with the SMA" (MASSES). The size of the C18O-emitting region, where CO has sublimated into the gas-phase, is measured towards each source and compared to the expected size of the region given the current luminosity. The SMA observations also include 1.3 mm continuum data, which are used to investigate whether or not a link can be established between accretion bursts and massive circumstellar disks. Results: Depending on the adopted sublimation temperature of the CO ice, between 20% and 50% of the sources in the sample show extended C18O emission indicating that the gas was warm enough in the past that CO sublimated and is currently in the process of refreezing; something which we attribute to a recent accretion burst. Given the fraction of sources with extended C18O emission, we estimate an average interval between bursts of 20 000-50 000 yr, which is consistent with previous estimates. No clear link can be established between the presence of circumstellar disks and accretion bursts, however the three closest known binaries in the sample (projected separations <20 AU) all show evidence of a past accretion burst, indicating that close binary interactions may also play a role in inducing accretion variability.

Seasonal Nitrogen Cycles on Pluto

NASA Technical Reports Server (NTRS)

Hansen, Candice J.; Paige, David A.

1996-01-01

A thermal model, developed to predict seasonal nitrogen cycles on Triton, has been modified and applied to Pluto. The model was used to calculate the partitioning of nitrogen between surface frost deposits and the atmosphere, as a function of time for various sets of input parameters. Volatile transport was confirmed to have a significant effect on Pluto's climate as nitrogen moved around on a seasonal time scale between hemispheres, and sublimed into and condensed out of the atmosphere. Pluto's high obliquity was found to have a significant effect on the distribution of frost on its surface. Conditions that would lead to permanent polar caps on Triton were found to lead to permanent zonal frost bands on Pluto. In some instances, frost sublimed from the middle of a seasonal cap outward, resulting in a "polar bald spot". Frost which was darker than the substrate did not satisfy observables on Pluto, in contrast to our findings for Triton. Bright frost (brighter than the substrate) came closer to matching observables. Atmospheric pressure varied seasonally. The amplitudes, and to a lesser extent the phase, of the variation depended significantly on frost and substrate properties. Atmospheric pressure was found to be determined both by Pluto's distance from the sun and by the subsolar latitude. In most cases two peaks in atmospheric pressure were observed annually: a greater one associated with the sublimation of the north polar cap just as Pluto receded from perihelion, and a lesser one associated with the sublimation of the south polar cap as Pluto approached perihelion. Our model predicted frost-free dark substrate surface temperatures in the 50 to 60 K range, while frost temperatures typically ranged between 30 to 40 K. Temporal changes in frost coverage illustrated by our results, and changes in the viewing geometry of Pluto from the Earth, may be important for interpretation of ground-based measurements of Pluto's thermal emission.

Trapping of CH4, CO, and CO2 in Amorphous Water Ice

NASA Astrophysics Data System (ADS)

Mastrapa, R. M. E.; Brown, R. H.; Anicich, V. G.; Cohen, B. A.; Dai, W.; Lunine, J. I.

1999-09-01

In this study, CO, CH4, and CO2 were trapped in H2O at temperatures as low as 20 K and pressures between 10-5 and 10-8 Torr. IR spectra were taken of each sample before sublimation to confirm the presence of volatiles. The samples were then heated at rates from 0.25 K/min to 1 K/min and the escape ranges were measured with a mass spectrometer. The volatiles escaped from the ice mixtures in temperature ranges similar to those found in previous work (1, 2, 3), namely 48-52 K, 145-160 K, 170-185 K. H2O is released from 150 K to 185 K. However, the temperature range of escape is strongly dependent on deposition temperature and heating rate. If the deposition temperature is below the point where the solid volatile rapidly sublimates in the ambient environment of our experiment, then the first range of volatile escape is centered around it's sublimation point, and there is little of the volatile remaining from 170-185 K. The location of the third escape range shifts to lower temperatures with slower sublimation rate. It was determined that 0.5 K/min is the ideal sample heating rate to determine these escape ranges. In our data, the infrared spectrum of CO trapped in water ice shows a splitting of the 2145 cm-1 solid CO line into two bands at 2343 cm-1 and 2135 cm-1. These shifts are similar to those seen by Sandford, et al. (4). (1) Bar-Nun, A., G. Herman, D. Laufer, and M. L. Rappaport, (1985), Icarus, 63, 317-332. (2) Bar-Nun, A., J. Dror, E. Kochavi, and D. Laufer, (1987), Physical Review B, 35, no. 5, 2427-2435. (3) Hudson, R. L., and B. Donn, (1991), Icarus, 94, 326-332. (4) Sandford, S. A., L. J. Allamandola, A. G. G. M. Tielens, and G. J. Valero, (1988), Astrophysical Journal, 329, 498-510.

Formation of Authigenic Sulfates in Cold Dry Glaciers: Terrestrial and Planetary Implications of Sublimites

NASA Astrophysics Data System (ADS)

Massé, M.; Rondeau, B.; Ginot, P.; Schmitt, B.; Bourgeois, O.; Mitri, G.

2015-12-01

Salts are common on planetary surfaces, and sulfates have been widely observed on Earth, Mars (Gendrin et al., 2005) and on some of Jupiter's and Saturn's icy moons like Europa (Dalton et al., 2007). These minerals can form under a wide range of conditions, and the determination of sulfate formation processes can provide key elements for deciphering past planetary surface conditions. Most terrestrial sulfates form as evaporites in warm environments with high water/rock ratios, but these conditions are rarely encountered on other planets. Here we describe the formation of cryogenic sulfates in an extreme cold and dry environment: the Guanaco glacier located in the Chilean Andes (Fig.1a, Rabatel et al., 2011). Field analyses reveal that it is a cold-based glacier, its surface temperature remains below 0°C throughout the year, and ablation occurs mostly by sublimation. Ablation creates ice cliffs punctuated of pluricentimetric whitish, tapered crystals embedded in the ice (Fig.1b, c). By Raman and chemistry, they proved to be gypsum, covered by micrometric crystals of jarosite, halotrichite and native sulfur. The euhedral morphology of these soft minerals indicates that they are neoformed and have not been transported in the ice. This is supported by the absence of gypsum crystals in ice cores drilled through the glacier. We infer that the crystallization thus occurred at the glacier surface during ice sublimation and does not involve liquid water. To distinguish this original salt formation process from the more common evaporites, we name these minerals "sublimites". Though this formation process is uncommon and generates minor quantities of sulfates on Earth, it may be dominant on other bodies in the Solar System where sublimation is effective. Examples of planetary sublimites may include gypsum on the North Polar Cap of Mars (Massé et al., 2012), and other sulfates on icy moons where sublimation has been observed (Howard et al., 2008).

Generating equilateral random polygons in confinement

NASA Astrophysics Data System (ADS)

Diao, Y.; Ernst, C.; Montemayor, A.; Ziegler, U.

2011-10-01

One challenging problem in biology is to understand the mechanism of DNA packing in a confined volume such as a cell. It is known that confined circular DNA is often knotted and hence the topology of the extracted (and relaxed) circular DNA can be used as a probe of the DNA packing mechanism. However, in order to properly estimate the topological properties of the confined circular DNA structures using mathematical models, it is necessary to generate large ensembles of simulated closed chains (i.e. polygons) of equal edge lengths that are confined in a volume such as a sphere of certain fixed radius. Finding efficient algorithms that properly sample the space of such confined equilateral random polygons is a difficult problem. In this paper, we propose a method that generates confined equilateral random polygons based on their probability distribution. This method requires the creation of a large database initially. However, once the database has been created, a confined equilateral random polygon of length n can be generated in linear time in terms of n. The errors introduced by the method can be controlled and reduced by the refinement of the database. Furthermore, our numerical simulations indicate that these errors are unbiased and tend to cancel each other in a long polygon.

Confinement regulates complex biochemical networks: initiation of blood clotting by "diffusion acting".

PubMed

Shen, Feng; Pompano, Rebecca R; Kastrup, Christian J; Ismagilov, Rustem F

2009-10-21

This study shows that environmental confinement strongly affects the activation of nonlinear reaction networks, such as blood coagulation (clotting), by small quantities of activators. Blood coagulation is sensitive to the local concentration of soluble activators, initiating only when the activators surpass a threshold concentration, and therefore is regulated by mass transport phenomena such as flow and diffusion. Here, diffusion was limited by decreasing the size of microfluidic chambers, and it was found that microparticles carrying either the classical stimulus, tissue factor, or a bacterial stimulus, Bacillus cereus, initiated coagulation of human platelet-poor plasma only when confined. A simple analytical argument and numerical model were used to describe the mechanism for this phenomenon: confinement causes diffusible activators to accumulate locally and surpass the threshold concentration. To interpret the results, a dimensionless confinement number, Cn, was used to describe whether a stimulus was confined, and a Damköhler number, Da(2), was used to describe whether a subthreshold stimulus could initiate coagulation. In the context of initiation of coagulation by bacteria, this mechanism can be thought of as "diffusion acting", which is distinct from "diffusion sensing". The ability of confinement and diffusion acting to change the outcome of coagulation suggests that confinement should also regulate other biological "on" and "off" processes that are controlled by thresholds.

Quantum confinement of exciton-polaritons in a structured (Al,Ga)As microcavity

NASA Astrophysics Data System (ADS)

Kuznetsov, Alexander S.; Helgers, Paul L. J.; Biermann, Klaus; Santos, Paulo V.

2018-05-01

The realization of quantum functionalities with polaritons in an all-semiconductor platform requires the control of the energy and spatial overlap of the wave functions of single polaritons trapped in potentials with precisely controlled shape and size. In this study we reach the confinement of microcavity polaritons in traps with an effective potential width down to 1 µm, produced by patterning the active region of the (Al,Ga)As microcavity between two molecular beam epitaxy growth runs. We correlate spectroscopic and structural data to show that the smooth surface relief of the patterned traps translates into a graded confinement potential characterized by lateral interfaces with a finite lateral width. We show that the structuring method is suitable for the fabrication of arrays of proximal traps, supporting hybridization between adjacent lattice sites.

How to Recharge a Confined Aquifer: An Exploration of Geologic Controls on Groundwater Storage.

NASA Astrophysics Data System (ADS)

Maples, S.; Fogg, G. E.; Maxwell, R. M.; Liu, Y.

2017-12-01

Decreased snowpack storage and groundwater overdraft in California has increased interest in managed aquifer recharge (MAR) of excess winter runoff to the Central Valley aquifer system, which has unused storage capacity that far exceeds the state's surface reservoirs. Recharge to the productive, confined aquifer system remains a challenge due to the presence of nearly-ubiquitous, multiple silt and clay confining units that limit recharge pathways. However, previous studies have identified interconnected networks of sand and gravel deposits that bypass the confining units and accommodate rapid, high-volume recharge to the confined aquifer system in select locations. We use the variably-saturated, fully-integrated groundwater/surface-water flow code, ParFlow, in combination with a high-resolution, transition probability Markov-chain geostatistical model of the subsurface geologic heterogeneity of the east side of the Sacramento Valley, CA, to characterize recharge potential across a landscape that includes these geologic features. Multiple 180-day MAR simulations show that recharge potential is highly dependent on subsurface geologic structure, with a several order-of-magnitude range of recharge rates and volumes across the landscape. Where there are recharge pathways to the productive confined-aquifer system, pressure propagation in the confined system is widespread and rapid, with multi-kilometer lateral pressure propagation. Although widespread pressure propagation occurs in the confined system, only a small fraction of recharge volume is accommodated there. Instead, the majority of recharge occurs by filling unsaturated pore spaces. Where they outcrop at land surface, high-K recharge pathways fill rapidly, accommodating the majority of recharge during early time. However, these features become saturated quickly, and somewhat counterintuitively, the low-K silt and clay facies accommodate the majority of recharge volume during most of the simulation. These findings (1) highlight the large variability of MAR potential across the landscape, wherein the recharge capacity in select areas far exceeds recharge potential over most of the landscape, and (2) elucidate important physical processes that control MAR potential in alluvial aquifer systems.

Thermomagnetic burn control for magnetic fusion reactor

DOEpatents

Rawls, John M.; Peuron, Unto A.

1982-01-01

Apparatus is provided for controlling the plasma energy production rate of a magnetic-confinement fusion reactor, by controlling the magnetic field ripple. The apparatus includes a group of shield sectors (30a, 30b, etc.) formed of ferromagnetic material which has a temperature-dependent saturation magnetization, with each shield lying between the plasma (12) and a toroidal field coil (18). A mechanism (60) for controlling the temperature of the magnetic shields, as by controlling the flow of cooling water therethrough, thereby controls the saturation magnetization of the shields and therefore the amount of ripple in the magnetic field that confines the plasma, to thereby control the amount of heat loss from the plasma. This heat loss in turn determines the plasma state and thus the rate of energy production.

Combinational concentration gradient confinement through stagnation flow.

PubMed

Alicia, Toh G G; Yang, Chun; Wang, Zhiping; Nguyen, Nam-Trung

2016-01-21

Concentration gradient generation in microfluidics is typically constrained by two conflicting mass transport requirements: short characteristic times (τ) for precise temporal control of concentration gradients but at the expense of high flow rates and hence, high flow shear stresses (σ). To decouple the limitations from these parameters, here we propose the use of stagnation flows to confine concentration gradients within large velocity gradients that surround the stagnation point. We developed a modified cross-slot (MCS) device capable of feeding binary and combinational concentration sources in stagnation flows. We show that across the velocity well, source-sink pairs can form permanent concentration gradients. As source-sink concentration pairs are continuously supplied to the MCS, a permanently stable concentration gradient can be generated. Tuning the flow rates directly controls the velocity gradients, and hence the stagnation point location, allowing the confined concentration gradient to be focused. In addition, the flow rate ratio within the MCS rapidly controls (τ ∼ 50 ms) the location of the stagnation point and the confined combinational concentration gradients at low flow shear (0.2 Pa < σ < 2.9 Pa). The MCS device described in this study establishes the method for using stagnation flows to rapidly generate and position low shear combinational concentration gradients for shear sensitive biological assays.

Controlling Spatial Confinement Effects in La0.3Pr0.4Ca0.3MnO3 Microbridges via Post Ar and Air Annealing

NASA Astrophysics Data System (ADS)

Jeon, Jaechun; Jung, Jan; Chow, Kim H.

2017-08-01

We report the effects of post Ar and air annealing of La0.3Pr0.4Ca0.3MnO3 microbridges which do not initially show spatial confinement effects. The removal or addition of oxygen via the post annealing changes the sizes and distribution of the metallic and insulating phase domains within these films and can create spatial confinement effects such as percolation induced resistance jumps and tunneling magnetoresistance.

Accretor: Generative Materiality in the Work of Driessens and Verstappen.

PubMed

Whitelaw, Mitchell

2015-01-01

Accretor, by the Dutch artists Erwin Driessens and Maria Verstappen, is a generative artwork that adopts and adapts artificial life techniques to produce intricate three-dimensional forms. This article introduces and analyzes Accretor, considering the enigmatic quality of the generated objects and in particular the role of materiality in this highly computational work. Accretor demonstrates a tangled continuity between digital and physical domains, where the constraints and affordances of matter inform both formal processes and aesthetic interpretations. Drawing on Arp's notion of the concrete artwork and McCormack and Dorin's notion of the computational sublime, the article finally argues that Accretor demonstrates what might be called a processual sublime, evoking expansive processes that span both computational and non-computational systems.

Optimized heat exchange in a CO2 de-sublimation process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baxter, Larry; Terrien, Paul; Tessier, Pascal

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 betweenmore » the combined solid carbon dioxide stream and the compressed gas in the first heat exchanger.« less

Di-p-xylylene polymer and method for making the same

DOEpatents

Jahn, Randy K.; Liepins, Raimond

1985-01-01

A method and apparatus for forming an improved poly-p-xylylene film. Solid di-para-xylylene dimer is sublimed in a sublimation furnace at approximately 100.degree. to 200.degree. C. and subsequently conducted to a pyrolysis furnace where it is pyrolyzed to the diradical p-xylylene monomer while in the vapor state at approximately 600 degrees C. The diradical monomer is then introduced into a deposition chamber for deposition onto a suitable substrate. The deposition chamber includes electrodes for producing a low pressure plasma through which the diradical monomer passes prior to deposition. The interaction of the diradical monomer with the low pressure plasma results in the formation of poly-p-xylylene film which is exceptionally hard and thermally stable.

Selective Area Sublimation: A Simple Top-down Route for GaN-Based Nanowire Fabrication.

PubMed

Damilano, B; Vézian, S; Brault, J; Alloing, B; Massies, J

2016-03-09

Post-growth in situ partial SiNx masking of GaN-based epitaxial layers grown in a molecular beam epitaxy reactor is used to get GaN selective area sublimation (SAS) by high temperature annealing. Using this top-down approach, nanowires (NWs) with nanometer scale diameter are obtained from GaN and InxGa1-xN/GaN quantum well epitaxial structures. After GaN regrowth on InxGa1-xN/GaN NWs resulting from SAS, InxGa1-xN quantum disks (QDisks) with nanometer sizes in the three dimensions are formed. Low temperature microphotoluminescence experiments demonstrate QDisk multilines photon emission around 3 eV with individual line widths of 1-2 meV.

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. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.

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.

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.

Isothermal Decomposition of Hydrogen Peroxide Dihydrate

NASA Technical Reports Server (NTRS)

Loeffler, M. J.; Baragiola, R. A.

2011-01-01

We present a new method of growing pure solid hydrogen peroxide in an ultra high vacuum environment and apply it to determine thermal stability of the dihydrate compound that forms when water and hydrogen peroxide are mixed at low temperatures. Using infrared spectroscopy and thermogravimetric analysis, we quantified the isothermal decomposition of the metastable dihydrate at 151.6 K. This decomposition occurs by fractional distillation through the preferential sublimation of water, which leads to the formation of pure hydrogen peroxide. The results imply that in an astronomical environment where condensed mixtures of H2O2 and H2O are shielded from radiolytic decomposition and warmed to temperatures where sublimation is significant, highly concentrated or even pure hydrogen peroxide may form.

Growing instead of confining

NASA Astrophysics Data System (ADS)

Sun, Yang-Kook; Yoon, Chong Seung

2017-10-01

Confining sulfur in high-surface-area carbon is a widely adapted approach in Li-S batteries, but it often results in low sulfur utilization and low energy density. Now, controlled nucleation of discrete Li2S particles on a network of low-surface-area carbon fibres provides a possible solution to the endemic problems of Li-S batteries.

Control of ITBs in Magnetically Confined Burning Plasmas

NASA Astrophysics Data System (ADS)

Panta, S. R.; Newman, D. E.; Terry, P. W.; Sanchez, R.

2017-10-01

In the magnetically confined burning plasma devices (in this case Tokamaks), internal transport barriers (ITBs) are those regimes in which the turbulence is suppressed by the E X B velocity shear, reducing the turbulent transport. This often occurs at a critical gradient in the profiles. The change in the transport then modifies the density and temperature profiles feeding back on the system. These transport barriers have to be controlled both to form them for improved confinement and remove them to both prevent global instabilities and to remove the ash and unnecessary impurities in the device. In this work we focus on pellet injection and modulated RF heating as a way to trigger and control the ITBs. These have an immediate consequence on density and temperature and hence pressure profiles acting as a control knob. For example, depending upon pellet size and its radial position of injection, it either helps to form or strengthen the barrier or to get rid of ITBs in the different transport channels of the burning plasmas. This transport model is then used to investigate the control and dynamics of the transport barriers in burning plasmas using pellets and RF addition to the NBI power and alpha power.

Fine control of nuclear confinement identifies a threshold deformation leading to lamina rupture and induction of specific genes.

PubMed

Le Berre, Maël; Aubertin, Johannes; Piel, Matthieu

2012-11-01

The quest to understand how the mechanical and geometrical environment of cells impacts their behavior and fate has been a major force driving the recent development of new technologies in cell biology research. Despite rapid advances in this field, many challenges remain in order to bridge the gap between the classical and simple cell culture plate and the biological reality of actual tissue. In tissues, cells have their physical space constrained by neighboring cells and the extracellular matrix. Here, we propose a simple and versatile device to precisely and dynamically control this confinement parameter in cultured cells. We show that there is a precise threshold deformation above which the nuclear lamina breaks and reconstructs, whereas nuclear volume changes. We also show that different nuclear deformations correlate with the expression of specific sets of genes, including nuclear factors and classical mechanotransduction pathways. This versatile device thus enables the precise control of cell and nuclear deformation by confinement and the correlative study of the associated molecular events.

Non-cultural methods of human microflora evaluation for the benefit of crew medical control in confined habitat

NASA Astrophysics Data System (ADS)

Viacheslav, Ilyin; Lana, Moukhamedieva; Georgy, Osipov; Aleksey, Batov; Zoya, Soloviova; Robert, Mardanov; Yana, Panina; Anna, Gegenava

2011-05-01

Current control of human microflora is a great problem not only for the space medicine but also for practical health care. Due to many reasons its realization by classical bacteriological method is difficult in practical application or cannot be done. To evaluate non-cultural methods of microbial control of crews in a confined habitat we evaluated two different methods. The first method is based on digital treatment of microbial visual images, appearing after gram staining of microbial material from natural sample. This way the rate between gram-positive and gram-negative microbe could be gained as well as differentiation of rods and cocci could be attained, which is necessary for primary evaluation of human microbial cenosis in remote confined habitats. The other non-culture method of human microflora evaluation is gas chromatomass spectrometry (gcms) analysis of swabs gathered from different body sites. Gc-ms testing of swabs allows one to validate quantitative and special microflora based on specific lipid markers analysis.

Effect of stress during handling, seawater acclimation, confinement, and induced spawning on plasma ion levels and somatolactin-expressing cells in mature female Liza ramada.

PubMed

Khalil, Noha A; Hashem, Amal M; Ibrahim, Amal A E; Mousa, Mostafa A

2012-08-01

The present experiments were designed to determine the effect of different stress factors; handling, seawater acclimation, confinement, and induced spawning on plasma cortisol, hydro mineral balance as well as changes in size, number and integrated intensity of somatolactin (SL)-expressing cells in Liza ramada mature females confined to fresh water ponds. The plasma levels of cortisol, PO(4)(3-), Na(+), and K(+) were higher, while Ca(2+) and Mg(2+) were lower than controls during transportation without anesthesia. By using clove oil (5 mg L(-1)) as an anesthetic during transportation, the plasma cortisol, PO(4) (3-), Na(+), and K(+) were similar to controls, while Ca(2+) and Mg(2+) were higher. During seawater acclimation, the plasma cortisol and minerals were significantly higher except Na(+) which was lower than controls. In addition, during induction of spawning, the plasma levels of cortisol, PO(4)(3-), Na(+), K(+), and Mg(2+) were significantly higher than controls. The SL-producing cells are located in the pars intermedia (PI) bordering the neurohypophysis. The stress affected the number, size, and immunostaining of SL-expressing cells. During seawater acclimation, the size and the integrated intensity of SL immunoreactivity were lower, but the number of these cells was higher than controls. Furthermore, the number, size, and the integrated intensity of SL immunoreactivity were significantly lower than controls during handling and after spawning, which was opposite to confinement. The response of SL-expressing cells in PI in parallel with changes in cortisol and hydro mineral balance induced by stress support the possible role of SL in the adaptive response of fish to stress. © 2012 WILEY PERIODICALS, INC.

Nanobubbles in confined solution: Generation, contact angle, and stability.

PubMed

Wei, Jiachen; Zhang, Xianren; Song, Fan; Shao, Yingfeng

2018-02-14

The formation of gas bubbles presents a frequent challenge to microfluidic operations, for which fluids are geometrically confined to a microscale space. Here, to understand the mechanism of nucleating gas bubbles in microfluidic devices, we investigate the formation and stability of nanobubbles in confined solutions. Our molecular dynamics simulations show that while pinning of the contact line is a prerequisite for the stability of surface nanobubbles in open systems that can exchange gas with surrounding environment, in confined solutions, stable nanobubbles can exist even without pinning. In supersaturated condition, stable bubbles can be found in confined solutions with acute or obtuse contact angle, depending on the substrate hydrophobicity. We also demonstrate that when open to the bulk solution, the stable nanobubbles in closed systems would become unstable unless both supersaturation and pinning of the contact line are satisfied. Our results not only shed light on the design of novel heterogeneous surfaces for generating nanobubbles in confined space with controllable shape and stability but also address the crucial effect of gas exchange with the surroundings in determining the stability of nanobubbles.

Nanobubbles in confined solution: Generation, contact angle, and stability

NASA Astrophysics Data System (ADS)

Wei, Jiachen; Zhang, Xianren; Song, Fan; Shao, Yingfeng

2018-02-01

The formation of gas bubbles presents a frequent challenge to microfluidic operations, for which fluids are geometrically confined to a microscale space. Here, to understand the mechanism of nucleating gas bubbles in microfluidic devices, we investigate the formation and stability of nanobubbles in confined solutions. Our molecular dynamics simulations show that while pinning of the contact line is a prerequisite for the stability of surface nanobubbles in open systems that can exchange gas with surrounding environment, in confined solutions, stable nanobubbles can exist even without pinning. In supersaturated condition, stable bubbles can be found in confined solutions with acute or obtuse contact angle, depending on the substrate hydrophobicity. We also demonstrate that when open to the bulk solution, the stable nanobubbles in closed systems would become unstable unless both supersaturation and pinning of the contact line are satisfied. Our results not only shed light on the design of novel heterogeneous surfaces for generating nanobubbles in confined space with controllable shape and stability but also address the crucial effect of gas exchange with the surroundings in determining the stability of nanobubbles.

UCLA Tokamak Program Close Out Report.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, Robert John

2014-02-04

The results of UCLA experimental fusion program are summarized. Starting with smaller devices like Microtor, Macrotor, CCT and ending the research on the large (5 m) Electric Tokamak. CCT was the most diagnosed device for H-mode like physics and the effects of rotation induced radial fields. ICRF heating was also studied but plasma heating of University Type Tokamaks did not produce useful results due to plasma edge disturbances of the antennae. The Electric Tokamak produced better confinement in the seconds range. However, it presented very good particle confinement due to an "electric particle pinch". This effect prevented us from reachingmore » a quasi steady state. This particle accumulation effect was numerically explained by Shaing's enhanced neoclassical theory. The PI believes that ITER will have a good energy confinement time but deleteriously large particle confinement time and it will disrupt on particle pinching at nominal average densities. The US fusion research program did not study particle transport effects due to its undue focus on the physics of energy confinement time. Energy confinement time is not an issue for energy producing tokamaks. Controlling the ash flow will be very expensive.« less

Tokamak power reactor ignition and time dependent fractional power operation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vold, E.L.; Mau, T.K.; Conn, R.W.

1986-06-01

A flexible time-dependent and zero-dimensional plasma burn code with radial profiles was developed and employed to study the fractional power operation and the thermal burn control options for an INTOR-sized tokamak reactor. The code includes alpha thermalization and a time-dependent transport loss which can be represented by any one of several currently popular scaling laws for energy confinement time. Ignition parameters were found to vary widely in density-temperature (n-T) space for the range of scaling laws examined. Critical ignition issues were found to include the extent of confinement time degradation by alpha heating, the ratio of ion to electron transportmore » power loss, and effect of auxiliary heating on confinement. Feedback control of the auxiliary power and ion fuel sources are shown to provide thermal stability near the ignition curve.« less

Confinement Regulates Complex Biochemical Networks: Initiation of Blood Clotting by “Diffusion Acting”

PubMed Central

Shen, Feng; Pompano, Rebecca R.; Kastrup, Christian J.; Ismagilov, Rustem F.

2009-01-01

Abstract This study shows that environmental confinement strongly affects the activation of nonlinear reaction networks, such as blood coagulation (clotting), by small quantities of activators. Blood coagulation is sensitive to the local concentration of soluble activators, initiating only when the activators surpass a threshold concentration, and therefore is regulated by mass transport phenomena such as flow and diffusion. Here, diffusion was limited by decreasing the size of microfluidic chambers, and it was found that microparticles carrying either the classical stimulus, tissue factor, or a bacterial stimulus, Bacillus cereus, initiated coagulation of human platelet-poor plasma only when confined. A simple analytical argument and numerical model were used to describe the mechanism for this phenomenon: confinement causes diffusible activators to accumulate locally and surpass the threshold concentration. To interpret the results, a dimensionless confinement number, Cn, was used to describe whether a stimulus was confined, and a Damköhler number, Da2, was used to describe whether a subthreshold stimulus could initiate coagulation. In the context of initiation of coagulation by bacteria, this mechanism can be thought of as “diffusion acting”, which is distinct from “diffusion sensing”. The ability of confinement and diffusion acting to change the outcome of coagulation suggests that confinement should also regulate other biological “on” and “off” processes that are controlled by thresholds. PMID:19843446

Formulation and optimization of mouth dissolve tablets containing rofecoxib solid dispersion.

PubMed

Sammour, Omaima A; Hammad, Mohammed A; Megrab, Nagia A; Zidan, Ahmed S

2006-06-16

The purpose of the present investigation was to increase the solubility and dissolution rate of rofecoxib by the preparation of its solid dispersion with polyvinyl pyrrolidone K30 (PVP K30) using solvent evaporation method. Drug-polymer interactions were investigated using differential scanning calorimetry (DSC), x-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). For the preparation of rofecoxib mouth dissolve tablets, its 1:9 solid dispersion with PVP K30 was used with various disintegrants and sublimable materials. In an attempt to construct a statistical model for the prediction of disintegration time and percentage friability, a 3(2) randomized full and reduced factorial design was used to optimize the influence of the amounts of superdisintegrant and subliming agent. The obtained results showed that dispersion of the drug in the polymer considerably enhanced the dissolution rate. The drug-to-carrier ratio was the controlling factor for dissolution improvement. FTIR spectra revealed no chemical incompatibility between the drug and PVP K30. As indicated from XRD and DSC data, rofecoxib was in the amorphous form, which explains the better dissolution rate of the drug from its solid dispersions. Concerning the optimization study, the multiple regression analysis revealed that an optimum concentration of camphor and a higher percentage of crospovidone are required for obtaining rapidly disintegrating tablets. In conclusion, this investigation demonstrated the potential of experimental design in understanding the effect of the formulation variables on the quality of mouth dissolve tablets containing solid dispersion of a hydrophobic drug.

Investigation of Condensing Ice Heat Exchangers for MTSA Technology Development

NASA Technical Reports Server (NTRS)

Padilla, Sebastian; Powers, Aaron; Ball, Tyler; Lacomini, Christie; Paul, Heather L.

2009-01-01

Metabolic heat regenerated Temperature Swing Adsorption (MTSA) technology is being developed for thermal, carbon dioxide (CO2) and humidity control for a Portable Life Support Subsystem (PLSS). Metabolically-produced CO2 present in the ventilation gas of a PLSS is collected using a CO2-selective adsorbent via temperature swing adsorption. The temperature swing is initiated through cooling to well below metabolic temperatures. Cooling is achieved with a sublimation heat exchanger using water or liquid carbon dioxide (L CO2) expanded below sublimation temperature when exposed to low pressure or vacuum. Subsequent super heated vapor, as well as additional coolant, is used to further cool the astronaut. The temperature swing on the adsorbent is then completed by warming the adsorbent with a separate condensing ice heat exchanger (CIHX) using metabolic heat from moist ventilation gas. The condensed humidity in the ventilation gas is recycled at the habitat. The water condensation from the ventilation gas represents a significant source of potential energy for the warming of the adsorbent bed as it represents as much as half of the energy potential in the moist ventilation gas. Designing a heat exchanger to efficiently transfer this energy to the adsorbent bed and allow the collection of the water is a challenge since the CIHX will operate in a temperature range from 210K to 280K. The ventilation gas moisture will first freeze and then thaw, sometimes existing in three phases simultaneously.

Transient Modeling and Analysis of a Metabolic Heat-Regenerated Temperature Swing Adsorption (MTSA) System for a PLSS

NASA Technical Reports Server (NTRS)

Iacomini, Christie; Powers, Aaron; Speight, Garland; Padilla, Sebastian; Paul, Heather L.

2009-01-01

A Metabolic heat-regenerated Temperature Swing Adsorption (MTSA) system is being developed for carbon dioxide, water and thermal control in a lunar and martian portable life support system (PLSS). A previous system analysis was performed to evaluate the impact of MTSA on PLSS design. That effort was Mars specific and assumed liquid carbon dioxide (LCO2) coolant made from martian resources. Transient effects were not considered but rather average conditions were used throughout the analysis. This effort takes into further consideration the transient effects inherent in the cycling MTSA system as well as assesses the use of water as coolant. Standard heat transfer, thermodynamic, and heat exchanger methods are presented to conduct the analysis. Assumptions and model verification are discussed. The tool was used to perform various system studies. Coolant selection was explored and takes into account different operational scenarios as the minimum bed temperature is driven by the sublimation temperature of the coolant (water being significantly higher than LCO2). From this, coolant mass is sized coupled with sorbent bed mass because MTSA adsorption performance decreases with increasing sublimation temperature. Reduction in heat exchanger performance and even removal of certain heat exchangers, like a recuperative one between the two sorbent beds, is also investigated. Finally, the coolant flow rate is varied over the cycle to determine if there is a more optimal means of cooling the bed from a mass perspective. Results of these studies and subsequent recommendations for system design are presented.

Landform Degradation and Slope Processes on Io: The Galileo View

NASA Technical Reports Server (NTRS)

Moore, Jeffrey M.; Sullivan, Robert J.; Chuang, Frank C.; Head, James W., III; McEwen, Alfred S.; Milazzo, Moses P.; Nixon, Brian E.; Pappalardo, Robert T.; Schenk, Paul M.; Turtle, Elizabeth P.;

The distribution of Martian ground ice at other epochs

NASA Technical Reports Server (NTRS)

Mellon, M. T.; Jakosky, B. M.

1993-01-01

The past orbital evolution of Mars is examined in relation to changes in ice stability as well as the condensation, sublimation, and diffusion of atmospheric water in an exchange with the regolith. The Martian obliquity has undergone significant oscillations in its recent past. During periods of high obliquity, the solar energy would have been distributed such that the equatorial and midlatitude regions would have been colder that at present and the polar regions would have been warmer. Warmer polar regions would result in the sublimation of more polar cap water into the atmosphere and thus higher atmospheric water abundances. This combination of effects would have resulted in ground ice being stable globally. During periods of low obliquity the opposite would have occurred. Modeling results of the regolith thermal behavior and the molecular diffusion of water vapor within the regolith and in exchange with the atmosphere have shown significant quantities of ground ice can form at all latitudes within the top 50 cm to 1 m of the regolith during periods of high obliquity. The amount of ice that forms can be as much as the regolith pores can hold. During low obliquity most or all of this ice sublimes and diffuses away. Below this depth a longer-term stability is observed at some latitudes where ice steadily increases in concentration regardless of orbital oscillations that occur.

New candidates for active asteroids: Main-belt (145) Adeona, (704) Interamnia, (779) Nina, (1474) Beira, and near-Earth (162,173) Ryugu

NASA Astrophysics Data System (ADS)

Busarev, Vladimir V.; Makalkin, Andrei B.; Vilas, Faith; Barabanov, Sergey I.; Scherbina, Marina P.

2018-04-01

For the first time, spectral signs of subtle coma activity were observed for four main-belt primitive asteroids (145) Adeona, (704) Interamnia, (779) Nina, and (1474) Beira around their perihelion distances in September 2012, which were interpreted as manifestations of the sublimation of H2O ice in/under the surface matter (Busarev et al., 2015a, 2015b). We confirm the phenomenon for Nina when it approached perihelion in September 2016. At the same time, based on results of spectral observations of near-Earth asteroid (162,173) Ryugu (Vilas, 2008) being a target of Japan's Hayabusa 2 space mission, we suspected a periodic similar transient activity on the Cg-type asteroid. However, unlike the main-belt primitive asteroids demonstrating sublimation of ices close to their perihelion distances, the effect on Ryugu was apparently registered near aphelion. To explain the difference, we calculated the subsolar temperature depending on heliocentric distance of the asteroids, considered qualitative models of internal structure of main-belt and near-Earth primitive asteroids including ice and performed some analytical estimations. Presumed temporal sublimation/degassing activity of Ryugu is a sign of a residual frozen core in its interior. This could be an indication of a relatively recent transition of the asteroid from the main asteroid belt to the near-Earth area.

Space Suit Radiator Performance in Lunar and Mars Environments

NASA Technical Reports Server (NTRS)

Nabity, James; Mason, Georgia; Copeland, Robert; Libberton, Kerry; Stephan, Ryan; Trevino, Luis; Paul, Heather

2005-01-01

During an ExtraVehicular Activity (EVA), both the heat generated by the astronaut's metabolism and that produced by the Portable Life Support System (PLSS) must be rejected to space. The heat sources include the heat of adsorption of metabolic CO2, the heat of condensation of water, the heat removed from the body by the liquid cooling garment and the load from the electrical components. Although the sublimator hardware to reject this load weighs only 1.58 kg (3.48 lbm), an additional 3.6 kg (8 lbm) of water are loaded into the unit, most of which is sublimated and lost to thus become the single largest expendable during an eight hour EVA. We can significantly reduce the amount of expendable water consumed in the sublimator by using a radiator to reject heat from the Astronaut during an EVA. Last year we reported on the design and initial operational assessment tests of our novel radiator designated the Radiator And Freeze Tolerant heat eXchanger (RAFT-X). Herein, we report on tests conducted in the NASA Johnson Space Center Chamber E Thermal Vacuum Test Facility. Up to 260 W (900 Btu/h) of heat were rejected in Lunar and Mars environments with temperatures as cold as -170 C (- 275 F). Further, the RAFT-X endured several freeze / thaw cycles and in fact, the heat exchanger was completely frozen three times without any apparent damage to the unit.

Quantum confinement and magnetic field effects on the electron Landé g factor in GaAs-(Ga,Al)As double quantum wells

NASA Astrophysics Data System (ADS)

Perea, J. Darío; Mejía-Salazar, J. R.; Porras-Montenegro, N.

2011-12-01

Nowadays the spin-related phenomena have attracted great attention for the possible spintronic and optoelectronic applications. The manipulation of the Landé g factor by means of the control of the electron confinement, applied magnetic field and hydrostatic pressure offers the possibility of having a wide range of ways to control single qubit operation and to have pure spin states to guarantee that no losses occur when the electron spins transport information. In this work we have performed a theoretical study of the quantum confinement (geometrical and barrier potential confinements) and growth direction applied magnetic field effects on the conduction-electron effective Landé g factor in GaAs-(Ga,Al)As double quantum wells. Our calculations of the Landé g factor are performed by using the Ogg-McCombe effective Hamiltonian, which includes non-parabolicity and anisotropy effects for the conduction-band electrons. Our theoretical results are given as function of the central barrier widths for different values of the applied magnetic fields. We have found that in this type of heterostructure the geometrical confinement commands the behavior of the electron effective Landé g factor as compared to the effect of the applied magnetic field. Present theoretical reports are in very good agreement with previous experimental and theoretical results.

The shuttle orbiter cabin atmospheric revitalization systems

NASA Technical Reports Server (NTRS)

Ward, C. F.; Owens, W. L.

1975-01-01

The Orbiter Atmospheric Revitalization Subsystem (ARS) and Pressure Control Subsystem (ARPCS) are designed to provide the flight crew and passengers with a pressurized environment that is both life-supporting and within crew comfort limitations. The ARPCS is a two-gas (oxygen-nitrogen) system that obtains oxygen from the Power Reactant Supply and Distribution (PRSD) subsystem and nitrogen from the nitrogen storage tanks. The ARS includes the water coolant loop; cabin CO2, odor, humidity and temperature control; and avionics cooling. Baseline ARPCS and ARS changes since 1973 include removal of the sublimator from the water coolant loop, an increase in flowrates to accommodate increased loads, elimination of the avionics bay isolation from the cabin, a decision to have an inert vehicle during ferry flight, elimination of coldwall tubing around windows and hatches, and deletion of the cabin heater.

A general lithography-free method of microscale/nanoscale fabrication and patterning on Si and Ge surfaces

PubMed Central

2012-01-01

Here, we introduce and give an overview of a general lithography-free method to fabricate silicide and germanide micro-/nanostructures on Si and Ge surfaces through metal-vapor-initiated endoepitaxial growth. Excellent controls on shape and orientation are achieved by adjusting the substrate orientation and growth parameters. Furthermore, micro-/nanoscale pits with controlled morphologies can also be successfully fabricated on Si and Ge surfaces by taking advantage of the sublimation of silicides/germanides. The aim of this brief report is to illustrate the concept of lithography-free synthesis and patterning on surfaces of elemental semiconductors, and the differences and the challenges associated with the Si and the Ge surfaces will be discussed. Our results suggest that this low-cost bottom-up approach is promising for applications in functional nanodevices. PMID:22315969

Experimental setup for the study of resonant inelastic X-ray scattering of organometallic complexes in gas phase

NASA Astrophysics Data System (ADS)

Ismail, I.; Guillemin, R.; Marchenko, T.; Travnikova, O.; Ablett, J. M.; Rueff, J.-P.; Piancastelli, M.-N.; Simon, M.; Journel, L.

2018-06-01

A new setup has been designed and built to study organometallic complexes in gas phase at the third-generation Synchrotron radiation sources. This setup consists of a new homemade computer-controlled gas cell that allows us to sublimate solid samples by accurately controlling the temperature. This cell has been developed to be a part of the high-resolution X-ray emission spectrometer permanently installed at the GALAXIES beamline of the French National Synchrotron Facility SOLEIL. To illustrate the capabilities of the setup, the cell has been successfully used to record high-resolution Kα emission spectra of gas-phase ferrocene F e (C5H5) 2 and to characterize their dependence with the excitation energy. This will allow to extend resonant X-ray emission to different organometallic molecules.

An outbreak of echovirus 11 amongst neonates in a confinement home in Penang, Malaysia.

PubMed

Bina Rai, S; Wan Mansor, H; Vasantha, T; Norizah, I; Chua, K B

2007-08-01

Confinement homes are private institutions that provide full-time care for newborn babies and their respective postpartum mothers up to one month after delivery. An outbreak of fever and diarrhoea amongst newborns occurred in one such confinement home in Penang between the months of September to October 2004. An outbreak investigation was carried out including all babies, their respective mothers and workers in the home to determine the source of the outbreak and to institute control measures. Based on a working case definition of febrile illness with or without diarrhoea, 11 out of the 13 babies in the confinement home met the case definition. One hundred percent had symptoms of fever. 36.4% had symptoms of diarrhea and other respiratory conditions respectively. The attack rate of among babies in the confinement home was 90%. Echovirus 11 was isolated from 3 out of the 11 febrile cases. Echovirus 11 was isolated from the cerebrospinal fluid and stool of another baby at a private hospital that was epidemiologically linked to the first case. In conclusion, the outbreak of febrile illness amongst newborn babies in the affected confinement home was due to echovirus 11. The source was probably health-care associated with efficient transmission within the confinement home. The faecal-oral route was the most likely mode of transmission.

Influence of loading and unloading velocity of confining pressure on strength and permeability characteristics of crystalline sandstone

NASA Astrophysics Data System (ADS)

Zhang, Dong-ming; Yang, Yu-shun; Chu, Ya-pei; Zhang, Xiang; Xue, Yan-guang

2018-06-01

The triaxial compression test of crystalline sandstone under different loading and unloading velocity of confining pressure is carried out by using the self-made "THM coupled with servo-controlled seepage apparatus for containing-gas coal", analyzed the strength, deformation and permeability characteristics of the sample, the results show that: with the increase of confining pressures loading-unloading velocity, Mohr's stress circle center of the specimen shift to the right, and the ultimate intensity, peak strain and residual stress of the specimens increase gradually. With the decrease of unloading velocity of confining pressure, the axial strain, the radial strain and the volumetric strain of the sample decrease first and then increases, but the radial strain decreases more greatly. The loading and unloading of confining pressure has greater influence on axial strain of specimens. The deformation modulus decreases rapidly with the increase of axial strain and the Poisson's ratio decreases gradually at the initial stage of loading. When the confining pressure is loaded, the deformation modulus decrease gradually, and the Poisson's ratio increases gradually. When the confining pressure is unloaded, the deformation modulus increase gradually, and the Poisson's ratio decreases gradually. When the specimen reaches the ultimate intensity, the deformation modulus decreases rapidly, while the Poisson's ratio increases rapidly. The fitting curve of the confining pressure and the deformation modulus and the Poisson's ratio in accordance with the distribution of quadratic polynomial function in the loading-unloading confining pressure. There is a corresponding relationship between the evolution of rock permeability and damage deformation during the process of loading and unloading. In the late stage of yielding, the permeability increases slowly, and the permeability increases sharply after the rock sample is destroyed. Fitting the permeability and confining pressure conform to the variation law of the exponential function.

Calculations of spin-polarized Goos-Hänchen displacement in magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit couplings

NASA Astrophysics Data System (ADS)

Lu, Mao-Wang; Chen, Sai-Yan; Zhang, Gui-Lian; Huang, Xin-Hong

2018-04-01

We theoretically investigate Goos-Hänchen (GH) displacement by modelling the spin transport in an archetypal device structure—a magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit coupling (SOC). Both Rashba and Dresselhaus SOCs are taken into account. The degree of spin-polarized GH displacement can be tuned by Rashba or Dresselhaus SOC, i.e. interfacial confining electric field or strain engineering. Based on such a semiconductor nanostructure, a controllable spatial spin splitter can be proposed for spintronics applications.

Calculations of spin-polarized Goos-Hänchen displacement in magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit couplings.

PubMed

Lu, Mao-Wang; Chen, Sai-Yan; Zhang, Gui-Lian; Huang, Xin-Hong

2018-04-11

We theoretically investigate Goos-Hänchen (GH) displacement by modelling the spin transport in an archetypal device structure-a magnetically confined GaAs/Al x Ga 1-x As nanostructure modulated by spin-orbit coupling (SOC). Both Rashba and Dresselhaus SOCs are taken into account. The degree of spin-polarized GH displacement can be tuned by Rashba or Dresselhaus SOC, i.e. interfacial confining electric field or strain engineering. Based on such a semiconductor nanostructure, a controllable spatial spin splitter can be proposed for spintronics applications.

Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary.

PubMed

Evans, T E; Moyer, R A; Thomas, P R; Watkins, J G; Osborne, T H; Boedo, J A; Doyle, E J; Fenstermacher, M E; Finken, K H; Groebner, R J; Groth, M; Harris, J H; La Haye, R J; Lasnier, C J; Masuzaki, S; Ohyabu, N; Pretty, D G; Rhodes, T L; Reimerdes, H; Rudakov, D L; Schaffer, M J; Wang, G; Zeng, L

2004-06-11

A stochastic magnetic boundary, produced by an applied edge resonant magnetic perturbation, is used to suppress most large edge-localized modes (ELMs) in high confinement (H-mode) plasmas. The resulting H mode displays rapid, small oscillations with a bursty character modulated by a coherent 130 Hz envelope. The H mode transport barrier and core confinement are unaffected by the stochastic boundary, despite a threefold drop in the toroidal rotation. These results demonstrate that stochastic boundaries are compatible with H modes and may be attractive for ELM control in next-step fusion tokamaks.

Frosted Crater

NASA Image and Video Library

2002-08-05

This image from NASA Mars Odyssey spacecraft displays a frosted crater in the Martian northern hemisphere. It was taken during the northern spring, when the CO2 ice cap starts to sublimate and recede.

Gold nanoparticles propulsion from surface fueled by absorption of femtosecond laser pulse at their surface plasmon resonance.

PubMed

Huang, Wenyu; Qian, Wei; El-Sayed, Mostafa A

2006-10-18

Femtosecond laser irradiation of assembled nanoprisms on a quartz substrate at their strong absorbing surface plasmon resonance frequency causes their propulsion from the substrate. SEM and AFM show that the particles fly while keeping their prismatic shape, but they decrease in size by an amount that can be calculated assuming atomic sublimation. Several mechanisms are mentioned, but the sublimation mechanism, which rapidly builds up pressure under the particle and propels it away from substrate, is discussed in detail. From the kinetic energy given to the flying nanoparticle, an initial velocity of approximately 160 m/s ( approximately 360 miles/h) is calculated. The dependence of the observed flying mechanism on the rate of energy deposition (i.e., with nanosecond vs femtosecond laser pulses) is discussed.

Analysis of the thermal reaction products of para polyphenylene by combined gas chromatography-mass spectrometry

NASA Technical Reports Server (NTRS)

Fewell, L. L.

1976-01-01

Analysis of the volatiles and sublimate produced when para-polyphenylene is pyrolyzed to constant weight under vacuum in the temperature range from 380 to 1000 C indicates that the polymer undergoes thermal degradation in two stages. The first stage involved dehydrohalogenation, which is essentially a curing reaction that produces crosslinking between polyphenylene chains resulting from the loss of chlorine from the polymer in the form of hydrogen chloride. The second stage of the thermal degradation is dehydrogenation because hydrogen is the major volatile species. Increasing amounts of polycyclic aromatic hydrocarbons (phenanthrene and 9, 10 benzphenanthrene) in the sublimate, concomitant with increasing C/H ratios of the polymeric residue with pyrolysis temperature, is consistent with the buildup of polynuclear structures in the polymer matrix.

Negative Pressure Vitrification of the Isochorically Confined Liquid in Nanopores.

PubMed

Adrjanowicz, K; Kaminski, K; Koperwas, K; Paluch, M

2015-12-31

Dielectric relaxation studies for model glass-forming liquids confined to nanoporous alumina matrices were examined together with high-pressure results. For confined liquids which show the deviation from bulk dynamics upon approaching the glass transition (the change from the Vogel-Fulcher-Tammann to the Arrhenius law), we have observed a striking agreement between the temperature dependence of the α-relaxation time in the Arrhenius-like region and the isochoric relaxation times extrapolated from the positive range of pressure to the negative pressure domain. Our finding provides strong evidence that glass-forming liquid confined to native nanopores enters the isochoric conditions once the mobility of the interfacial layer becomes frozen in. This results in the negative pressure effects on cooling. We also demonstrate that differences in the sensitivity of various glass-forming liquids to the "confinement effects" can be rationalized by considering the relative importance of thermal energy and density contributions in controlling the α-relaxation dynamics (the E(v)/E(p) ratio).

Physical confinement alters tumor cell adhesion and migration phenotypes

PubMed Central

Balzer, Eric M.; Tong, Ziqiu; Paul, Colin D.; Hung, Wei-Chien; Stroka, Kimberly M.; Boggs, Amanda E.; Martin, Stuart S.; Konstantopoulos, Konstantinos

2012-01-01

Cell migration on planar surfaces is driven by cycles of actin protrusion, integrin-mediated adhesion, and myosin-mediated contraction; however, this mechanism may not accurately describe movement in 3-dimensional (3D) space. By subjecting cells to restrictive 3D environments, we demonstrate that physical confinement constitutes a biophysical stimulus that alters cell morphology and suppresses mesenchymal motility in human breast carcinoma (MDA-MB-231). Dorsoventral polarity, stress fibers, and focal adhesions are markedly attenuated by confinement. Inhibitors of myosin, Rho/ROCK, or β1-integrins do not impair migration through 3-μm-wide channels (confinement), even though these treatments repress motility in 50-μm-wide channels (unconfined migration) by ≥50%. Strikingly, confined migration persists even when F-actin is disrupted, but depends largely on microtubule (MT) dynamics. Interfering with MT polymerization/depolymerization causes confined cells to undergo frequent directional changes, thereby reducing the average net displacement by ≥80% relative to vehicle controls. Live-cell EB1-GFP imaging reveals that confinement redirects MT polymerization toward the leading edge, where MTs continuously impact during advancement of the cell front. These results demonstrate that physical confinement can induce cytoskeletal alterations that reduce the dependence of migrating cells on adhesion-contraction force coupling. This mechanism may explain why integrins can exhibit reduced or altered function during migration in 3D environments.—Balzer, E. M., Tong, Z., Paul, C. D., Hung, W.-C., Stroka, K. M., Boggs, A. E., Martin, S. S., Konstantopoulos, K. Physical confinement alters tumor cell adhesion and migration phenotypes. PMID:22707566

Smooth and Fractured Deposits in Eridania Valleys

NASA Image and Video Library

2017-01-13

The ancient highland channels in this image empty into the Eridania Basin (not visible), a large topographically low enclosure with smooth-appearing terrains that may have once contained a large paleolake or ancient sea. Water in these channels flowed to the east into Ariadnes Basin, a smaller basin located within the confines of Eridiana. Light-toned knobs are exposed in the northern channel, while the other channels are partially filled with smooth appearing lobe-shaped surface flows that are extensively fractured when viewed at high-resolution. Although the origin of these knobs is not known, interpretations include fumarolic mounds, erosional remnants, pingos, mud volcanoes and spring mounds. The movement of the once ice-rich, channel-filling flows over the knobby terrains likely created radial tension stresses producing the cracks that we see on the surface of these deposits. As the material slowly thinned, it eventually led to the formation of an elephant skin-like texture. This texture is different from the surrounding eroding mantling deposit that has become pitted as the ice sublimated causing the overlying surface to collapse. The combination of such knobby terrain and smooth, channel-filling deposits are seen only in a few places on Mars. One such example is the Navua Valles channels northeast of the Hellas Basin that may have also hosted a large, ice-covered lake in the past. Their morphological similarities, particularly in their surface materials, suggest that they formed under similar paleoclimatic conditions. http://photojournal.jpl.nasa.gov/catalog/PIA12968

Fivefold confinement time increase in the Madison Symmetric Torus using inductive poloidal current drive

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoneking, M.R.; Lanier, N.E.; Prager, S.C.

1996-12-01

Current profile control is employed in the Madison Symmetric Torus reversed field pinch to reduce the magnetic fluctuations responsible for anomalous transport. An inductive poloidal electric field pulse is applied in the sense to flatten the parallel current profile, reducing the dynamo fluctuation amplitude required to sustain the equilibrium. This technique demonstrates a substantial reduction in fluctuation amplitude (as much as 50%), and improvement in energy confinement (from 1 ms to 5 ms); a record low fluctuation (0.8%) and record high temperature (615 eV) for this device were observed simultaneously during current drive experiments. Plasma beta increases by 50% andmore » the Ohmic input power is three times lower. Particle confinement improves and plasma impurity contamination is reduced. The results of the transient current drive experiments provide motivation for continuing development of steady-state current profile control strategies for the reversed field pinch.« less

System and method for confining an object to a region of fluid flow having a stagnation point

NASA Technical Reports Server (NTRS)

Schroeder, Charles M. (Inventor); Babcock, Hazen P. (Inventor); Shaqfeh, Eric S. G. (Inventor); Chu, Steven (Inventor)

2006-01-01

A device for confining an object to a region proximate to a fluid flow stagnation point includes one or more inlets for carrying the fluid into the region, one or more outlets for carrying the fluid out of the region, and a controller, in fluidic communication with the inlets and outlets, for adjusting the motion of the fluid to produce a stagnation point in the region, thereby confining the object to the region. Applications include, for example, prolonged observation of the object, manipulation of the object, etc. The device optionally may employ a feedback control mechanism, a sensing apparatus (e.g., for imaging), and a storage medium for storing, and a computer for analyzing and manipulating, data acquired from observing the object. The invention further provides methods of using such a device and system in a number of fields, including biology, chemistry, physics, material science, and medical science.

Overview of C-2W Field-Reversed Configuration Experimental Program

NASA Astrophysics Data System (ADS)

Gota, H.; Binderbauer, M. W.; Tajima, T.; Putvinski, S.; Tuszewski, M.; Dettrick, S.; Korepanov, S.; Romero, J.; Smirnov, A.; Song, Y.; Thompson, M. C.; van Drie, A.; Yang, X.; Ivanov, A. A.; TAE Team

2017-10-01

Tri Alpha Energy's research has been devoted to producing a high temperature, stable, long-lived field-reversed configuration (FRC) plasma state by neutral-beam injection (NBI) and edge biasing/control. C-2U experiments have demonstrated drastic improvements in particle and energy confinement properties of FRC's, and the plasma performance obtained via 10 MW NBI has achieved plasma sustainment of up to 5 ms and plasma (diamagnetism) lifetimes of 10 + ms. The emerging confinement scaling, whereby electron energy confinement time is proportional to a positive power of the electron temperature, is very attractive for higher energy plasma confinement; accordingly, verification of the observed Te scaling law will be a key future research objective. The new experimental device, C-2W (now also called ``Norman''), has the following key subsystem upgrades from C-2U: (i) higher injected power, optimum energies, and extended pulse duration of the NBI system; (ii) installation of inner divertors with upgraded edge-biasing systems; (iii) fast external equilibrium/mirror-coil current ramp-up capability; and (iv) installation of trim/saddle coils for active feedback control of the FRC plasma. This paper will review highlights of the C-2W program.

Confinement and controlling the effective compressive stiffness of carbyne

NASA Astrophysics Data System (ADS)

Kocsis, Ashley J.; Aditya Reddy Yedama, Neta; Cranford, Steven W.

2014-08-01

Carbyne is a one-dimensional chain of carbon atoms, consisting of repeating sp-hybridized groups, thereby representing a minimalist molecular rod or chain. While exhibiting exemplary mechanical properties in tension (a 1D modulus on the order of 313 nN and a strength on the order of 11 nN), its use as a structural component at the molecular scale is limited due to its relative weakness in compression and the immediate onset of buckling under load. To circumvent this effect, here, we probe the effect of confinement to enhance the mechanical behavior of carbyne chains in compression. Through full atomistic molecular dynamics, we characterize the mechanical properties of a free (unconfined chain) and explore the effect of confinement radius (R), free chain length (L) and temperature (T) on the effective compressive stiffness of carbyne chains and demonstrate that the stiffness can be tuned over an order of magnitude (from approximately 0.54 kcal mol-1 Å2 to 46 kcal mol-1 Å2) by geometric control. Confinement may inherently stabilize the chains, potentially providing a platform for the synthesis of extraordinarily long chains (tens of nanometers) with variable compressive response.

Calcium and Titanium Isotope Fractionation in CAIS: Tracers of Condensation and Inheritance in the Early Solar Protoplanetary Disk

NASA Technical Reports Server (NTRS)

Simon, J. I.; Jordan, M. K.; Tappa, M. J.; Kohl, I. E.; Young, E. D.

2016-01-01

The chemical and isotopic compositions of calcium-aluminum-rich inclusions (CAIs) can be used to understand the conditions present in the protoplantary disk where they formed. The isotopic compositions of these early-formed nebular materials are largely controlled by chemical volatility. The isotopic effects of evaporation/sublimation, which are well explained by both theory and experimental work, lead to enrichments of the heavy isotopes that are often exhibited by the moderately refractory elements Mg and Si. Less well understood are the isotopic effects of condensation, which limits our ability to determine whether a CAI is a primary condensate and/or retains any evidence of its primordial formation history.

Thermodynamic Models for Aqueous Alteration Coupled with Volume and Pressure Changes in Asteroids

NASA Technical Reports Server (NTRS)

Mironenko, M. V.; Zolotov, M. Y.

2005-01-01

All major classes of chondrites show signs of alteration on their parent bodies (asteroids). The prevalence of oxidation and hydration in alteration pathways implies that water was the major reactant. Sublimation and melting of water ice, generation of gases, formation of aqueous solutions, alteration of primary minerals and glasses and formation of secondary solids in interior parts of asteroids was likely to be driven by heat from the radioactive decay of short-lived radionuclides. Progress of alteration reactions should have affected masses and volumes of solids, and aqueous and gas phases. In turn, pressure evolution should have been controlled by changes in volumes and temperatures, escape processes, and production/ consumption of gases.

Application of ASTM E-1559 Apparatus to Study H2O Desorption

NASA Technical Reports Server (NTRS)

Woronowicz, Michael; Perry, Radford, III; Meadows, George A.

2015-01-01

The NASA James Webb Space Telescope project identified a need to measure water vapor desorption from cryogenic surfaces in order to validate predictions of spacecraft design performance. A review of available scientific literature indicated no such measurements had been reported below 131 K. Contamination control personnel at NASA Goddard Space Flight Center recognized the possibility they readily possessed the means to collect these measurements at lower temperatures using an existing apparatus commonly employed for making outgassing observations. This presentation will relate how the ASTM E-1559 Molekit apparatus was used without physical modification to measure water vapor sublimation down to 120 K and compare this data to existing equilibrium vapor pressure models.

Optimal remediation of unconfined aquifers: Numerical applications and derivative calculations

NASA Astrophysics Data System (ADS)

Mansfield, Christopher M.; Shoemaker, Christine A.

1999-05-01

This paper extends earlier work on derivative-based optimization for cost-effective remediation to unconfined aquifers, which have more complex, nonlinear flow dynamics than confined aquifers. Most previous derivative-based optimization of contaminant removal has been limited to consideration of confined aquifers; however, contamination is more common in unconfined aquifers. Exact derivative equations are presented, and two computationally efficient approximations, the quasi-confined (QC) and head independent from previous (HIP) unconfined-aquifer finite element equation derivative approximations, are presented and demonstrated to be highly accurate. The derivative approximations can be used with any nonlinear optimization method requiring derivatives for computation of either time-invariant or time-varying pumping rates. The QC and HIP approximations are combined with the nonlinear optimal control algorithm SALQR into the unconfined-aquifer algorithm, which is shown to compute solutions for unconfined aquifers in CPU times that were not significantly longer than those required by the confined-aquifer optimization model. Two of the three example unconfined-aquifer cases considered obtained pumping policies with substantially lower objective function values with the unconfined model than were obtained with the confined-aquifer optimization, even though the mean differences in hydraulic heads predicted by the unconfined- and confined-aquifer models were small (less than 0.1%). We suggest a possible geophysical index based on differences in drawdown predictions between unconfined- and confined-aquifer models to estimate which aquifers require unconfined-aquifer optimization and which can be adequately approximated by the simpler confined-aquifer analysis.

South Polar Autumn

NASA Image and Video Library

2006-04-22

This MOC image shows a portion of the south polar residual cap; darkened edges of the pits and mesas are evidence of the removal, by sublimation, of frozen carbon dioxide during the recent martian summer

Transmission Electron Microscopy of Vacuum Sensitive, Radiation Sensitive, and Structurally Delicate Materials

NASA Astrophysics Data System (ADS)

Levin, Barnaby

The transmission electron microscope (TEM) is a powerful tool for characterizing the nanoscale and atomic structure of materials, offering insights into their fundamental physical properties. However, TEM characterization requires very thin samples of material to be placed in a high vacuum environment, and exposed to electron radiation. The high vacuum will induce some materials to evaporate or sublimate, preventing them from being accurately characterized, radiation may damage the sample, causing mass loss, or altering its structure, and structurally delicate samples may collapse and break apart when they are thinned for TEM imaging. This dissertation discusses three different projects in which each of these three difficulties pose challenges to TEM characterization of samples. Firstly, we outline strategies for minimizing radiation damage when characterizing materials in TEM at atomic resolution. We consider types of radiation damage, such as vacancy enhanced displacement, that are not included in some previous discussions of beam damage, and we consider how to minimize damage when using new imaging techniques such as annular bright-field scanning TEM. Our methodology emphasizes the general principle that variation of both signal strength and damage cross section must be considered when choosing an experimental electron beam voltage to minimize damage. Secondly, we consider samples containing sulfur, which is prone to sublimation in high vacuum. TEM is routinely used to attempt to characterize the sulfur distribution in lithium-sulfur battery electrodes, but sublimation artifacts can give misleading results. We demonstrate that sulfur sublimation can be suppressed by using cryogenic TEM to characterize sulfur at very low temperatures, or by using the recently developed airSEM to characterize sulfur without exposing it to vacuum. Finally, we discuss the characterization of aging cadmium yellow paint from early 20th century art masterpieces. The binding medium holding paint particles together bends and curls as sample thickness is reduced to 100 nm, making high resolution characterization challenging. We acquire lattice resolution images of the pigment particles through the binder using high voltage zero-loss energy filtered TEM, allowing us to measure the pigment particle size and determine the pigment crystal structure, providing insight into why the paint is aging and how it was synthesized.

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 filters foreseen for the CaSSIS imager of the Exomars/TGO mission in order to prepare future science operations.

CFCC: A Covert Flows Confinement Mechanism for Virtual Machine Coalitions

NASA Astrophysics Data System (ADS)

Cheng, Ge; Jin, Hai; Zou, Deqing; Shi, Lei; Ohoussou, Alex K.

Normally, virtualization technology is adopted to construct the infrastructure of cloud computing environment. Resources are managed and organized dynamically through virtual machine (VM) coalitions in accordance with the requirements of applications. Enforcing mandatory access control (MAC) on the VM coalitions will greatly improve the security of VM-based cloud computing. However, the existing MAC models lack the mechanism to confine the covert flows and are hard to eliminate the convert channels. In this paper, we propose a covert flows confinement mechanism for virtual machine coalitions (CFCC), which introduces dynamic conflicts of interest based on the activity history of VMs, each of which is attached with a label. The proposed mechanism can be used to confine the covert flows between VMs in different coalitions. We implement a prototype system, evaluate its performance, and show that our mechanism is practical.

A novel feedback algorithm for simulating controlled dynamics and confinement in the advanced reversed-field pinch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahlin, J.-E.; Scheffel, J.

2005-06-15

In the advanced reversed-field pinch (RFP), the current density profile is externally controlled to diminish tearing instabilities. Thus the scaling of energy confinement time with plasma current and density is improved substantially as compared to the conventional RFP. This may be numerically simulated by introducing an ad hoc electric field, adjusted to generate a tearing mode stable parallel current density profile. In the present work a current profile control algorithm, based on feedback of the fluctuating electric field in Ohm's law, is introduced into the resistive magnetohydrodynamic code DEBSP [D. D. Schnack and D. C. Baxter, J. Comput. Phys. 55,more » 485 (1984); D. D. Schnack, D. C. Barnes, Z. Mikic, D. S. Marneal, E. J. Caramana, and R. A. Nebel, Comput. Phys. Commun. 43, 17 (1986)]. The resulting radial magnetic field is decreased considerably, causing an increase in energy confinement time and poloidal {beta}. It is found that the parallel current density profile spontaneously becomes hollow, and that a formation, being related to persisting resistive g modes, appears close to the reversal surface.« less

Hydrogeology and soil gas at J-Field, Aberdeen Proving Ground, Maryland

USGS Publications Warehouse

Hughes, W.B.

1993-01-01

Disposal of chemical warfare agents, munitions, and industrial chemicals in J-Field, Aberdeen Proving Ground, Maryland, has contaminated soil, groundwater and surface water. Seven exploratory borings and 38 observation wells were drilled to define the hydrogeologic framework at J-Field and to determine the type, extent, and movement of contaminants. The geologic units beneath J-Field consist of Coastal Plain sediments of the Cretaceous Patapsco Formation and Pleistocene Talbot Formation. The Patapsco Formation contains several laterally discontinuous aquifers and confining units. The Pleistocene deposits were divided into 3 hydrogeologic units--a surficial aquifer, a confining unit, and a confined aquifer. Water in the surficial aquifer flows laterally from topographically high areas to discharge areas in marshes and streams, and vertically to the underlying confined aquifer. In offshore areas, water flows from the deeper confined aquifers upward toward discharge areas in the Gunpowder River and Chesapeake Bay. Analyses of soil-gas samples showed high relative-flux values of chlorinated solvents, phthalates, and hydrocarbons at the toxic-materials disposal area, white-phosphorus disposal area, and riot-control-agent disposal area. The highest flux values were located downgradient of the toxic materials and white phosphorus disposal areas, indicating that groundwater contaminants are moving from source areas beneath the disposal pits toward discharge points in the marshes and estuaries. Elevated relative-flux values were measured upgradient and downgradient of the riot-control agent disposal area, and possibly result from soil and (or) groundwater contamination.

Spatially confined synthesis of SiOx nano-rod with size-controlled Si quantum dots in nano-porous anodic aluminum oxide membrane.

PubMed

Pai, Yi-Hao; Lin, Gong-Ru

2011-01-17

By depositing Si-rich SiOx nano-rod in nano-porous anodic aluminum oxide (AAO) membrane using PECVD, the spatially confined synthesis of Si quantum-dots (Si-QDs) with ultra-bright photoluminescence spectra are demonstrated after low-temperature annealing. Spatially confined SiOx nano-rod in nano-porous AAO membrane greatly increases the density of nucleated positions for Si-QD precursors, which essentially impedes the route of thermally diffused Si atoms and confines the degree of atomic self-aggregation. The diffusion controlled growth mechanism is employed to determine the activation energy of 6.284 kJ mole(-1) and diffusion length of 2.84 nm for SiO1.5 nano-rod in nano-porous AAO membrane. HRTEM results verify that the reduced geometric dimension of the SiOx host matrix effectively constrain the buried Si-QD size at even lower annealing temperature. The spatially confined synthesis of Si-QD essentially contributes the intense PL with its spectral linewidth shrinking from 210 to 140 nm and its peak intensity enhancing by two orders of magnitude, corresponding to the reduction on both the average Si-QD size and its standard deviation from 2.6 to 2.0 nm and from 25% to 12.5%, respectively. The red-shifted PL wavelength of the Si-QD reveals an inverse exponential trend with increasing temperature of annealing, which is in good agree with the Si-QD size simulation via the atomic diffusion theory.

Hierarchical self-assembly of actin in micro-confinements using microfluidics

PubMed Central

Deshpande, Siddharth; Pfohl, Thomas

2012-01-01

We present a straightforward microfluidics system to achieve step-by-step reaction sequences in a diffusion-controlled manner in quasi two-dimensional micro-confinements. We demonstrate the hierarchical self-organization of actin (actin monomers—entangled networks of filaments—networks of bundles) in a reversible fashion by tuning the Mg2+ ion concentration in the system. We show that actin can form networks of bundles in the presence of Mg2+ without any cross-linking proteins. The properties of these networks are influenced by the confinement geometry. In square microchambers we predominantly find rectangular networks, whereas triangular meshes are predominantly found in circular chambers. PMID:24032070

Experimental Study of Hollow Formation

NASA Astrophysics Data System (ADS)

Parman, S. W.; Orlando, T. M.; Milliken, R. E.; Head, J. W.; Jones, B. M.; Anzures, B. A.

2018-05-01

Hollows are enigmatic features on the surface of Mercury caused by sublimation and/or space weathering. Here we propose a comprehensive experimental study in which candidate hollows materials are exposed to a range of relevant conditions.

Chemistry Notes.

ERIC Educational Resources Information Center

School Science Review, 1983

1983-01-01

Presents background information, laboratory procedures, classroom materials/activities, and chemistry experiments. Topics include sublimation, electronegativity, electrolysis, experimental aspects of strontianite, halide test, evaluation of present and future computer programs in chemistry, formula building, care of glass/saturated calomel…

Polar Plumage

NASA Image and Video Library

2006-05-08

This Mars MOC image shows dunes in the north polar region of Mars covered by a layer of carbon dioxide frost that accumulated during the winter in 2005. Dark spots indicate areas where frost has begun to sublime away

Pluto Pits

NASA Image and Video Library

2015-11-10

NASA New Horizons cameras have spied swarms of mysterious pits across the informally named Sputnik Planum. Scientists believe the pits may form through a combination of sublimation and ice fracturing. http://photojournal.jpl.nasa.gov/catalog/PIA20151

Exhuming South Polar Crater

NASA Technical Reports Server (NTRS)

2004-01-01

7 February 2004 The large, circular feature in this image is an old meteor impact crater. The crater is larger than the 3 kilometers-wide (1.9 miles-wide) Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, thus only part of the crater is seen. The bright mesas full of pits and holes--in some areas resembling swiss cheese--are composed of frozen carbon dioxide. In this summertime view, the mesa slopes and pit walls are darkened as sunlight causes some of the ice to sublime away. At one time in the past, the crater shown here may have been completely covered with carbon dioxide ice, but, over time, it has been exhumed as the ice sublimes a little bit more each summer. The crater is located near 86.8oS, 111.6oW. Sunlight illuminates this scene from the upper left.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2015. Part 1. C1 - C10

NASA Astrophysics Data System (ADS)

Acree, William; Chickos, James S.

2016-09-01

A compendium of phase change enthalpies published in 2010 is updated to include the period 1880-2015. Phase change enthalpies including fusion, vaporization, and sublimation enthalpies are included for organic, organometallic, and a few inorganic compounds. Part 1 of this compendium includes organic compounds from C1 to C10. Part 2 of this compendium, to be published separately, will include organic and organometallic compounds from C11 to C192. Sufficient data are presently available to permit thermodynamic cycles to be constructed as an independent means of evaluating the reliability of the data. Temperature adjustments of phase change enthalpies from the temperature of measurement to the standard reference temperature, T = 298.15 K, and a protocol for doing so are briefly discussed.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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 functionmore » 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.« less

Thermal desorption study of physical forces at the PTFE surface

NASA Technical Reports Server (NTRS)

Wheeler, D. R.; Pepper, S. V.

1987-01-01

Thermal desorption spectroscopy (TDS) of the polytetrafluoroethylene (PTFE) surface was successfully employed to study the possible role of physical forces in the enhancement of metal-PTFE adhesion by radiation. The thermal desorption spectra were analyzed without assumptions to yield the activation energy for desorption over a range of xenon coverage from less than 0.1 monolayer to more than 100 monolayers. For multilayer coverage, the desorption is zero-order with an activation energy equal to the sublimation energy of xenon. For submonolayer coverages, the order for desorption from the unirradiated PTFE surface is 0.73 and the activation energy for desorption is between 3.32 and 3.36 kcal/mol; less than the xenon sublimation energy. The effect of irradiation is to increase the activation energy for desorption to as high as 4 kcal/mol at low coverage.

Thermal desorption study of physical forces at the PTFE surface

NASA Technical Reports Server (NTRS)

Wheeler, D. R.; Pepper, S. V.

1985-01-01

Thermal desorption spectroscopy (TDS) of the polytetrafluoroethylene (PTFE) surface was successfully employed to study the possibile role of physical forces in the enhancement of metal-PTFE adhesion by radiation. The thermal desorption spectra were analyzed without assumptions to yield the activation energy for desorption over a range of xenon coverage from less than 0.1 monolayer to more than 100 monolayers. For multilayer coverage, the desorption is zero-order with an activation energy equal to the sublimation energy of xenon. For submonolayer coverages, the order for desorption from the unirradiated PTFE surface is 0.73 and the activation energy for desorption is between 3.32 and 3.36 kcal/mol; less than the xenon sublimation energy. The effect of irradiation is to increase the activation energy for desorption to as high as 4 kcal/mol at low coverage.

Micro-Detection System for Determination of the Biotic or Abiotic Origin of Amino Acids

NASA Technical Reports Server (NTRS)

Bada, Jeffrey L.; Betts, Bruce (Technical Monitor)

2002-01-01

The research involved the development of a breadboard version of a spacecraft based system for the detection of amino acid chirality (handedness) on solar system bodies. The design concept has three distinct components: a sublimation chamber for the release of amino acids from an acquired sample; a microchip based capillary electrophoresis (CE) chip for the separation of amino acids and their enantiomers; and a fluorescent based detection system. In addition, we have investigated the use of a microfluidics system for the extraction of amino acids in samples in which sublimation has proven to be problematic. This is a joint project carried out at the Scripps Institution of Oceanography (SIO), University of California at San Diego; the Jet Propulsion Laboratory (JPL), Pasadena; and the Department of Chemistry, University of California, Berkeley.

Katabatic winds diminish precipitation contribution to the Antarctic ice mass balance.

PubMed

Grazioli, Jacopo; Madeleine, Jean-Baptiste; Gallée, Hubert; Forbes, Richard M; Genthon, Christophe; Krinner, Gerhard; Berne, Alexis

2017-10-10

Snowfall in Antarctica is a key term of the ice sheet mass budget that influences the sea level at global scale. Over the continental margins, persistent katabatic winds blow all year long and supply the lower troposphere with unsaturated air. We show that this dry air leads to significant low-level sublimation of snowfall. We found using unprecedented data collected over 1 year on the coast of Adélie Land and simulations from different atmospheric models that low-level sublimation accounts for a 17% reduction of total snowfall over the continent and up to 35% on the margins of East Antarctica, significantly affecting satellite-based estimations close to the ground. Our findings suggest that, as climate warming progresses, this process will be enhanced and will limit expected precipitation increases at the ground level.

Katabatic winds diminish precipitation contribution to the Antarctic ice mass balance

PubMed Central

Grazioli, Jacopo; Madeleine, Jean-Baptiste; Gallée, Hubert; Forbes, Richard M.; Genthon, Christophe; Krinner, Gerhard; Berne, Alexis

2017-01-01

Snowfall in Antarctica is a key term of the ice sheet mass budget that influences the sea level at global scale. Over the continental margins, persistent katabatic winds blow all year long and supply the lower troposphere with unsaturated air. We show that this dry air leads to significant low-level sublimation of snowfall. We found using unprecedented data collected over 1 year on the coast of Adélie Land and simulations from different atmospheric models that low-level sublimation accounts for a 17% reduction of total snowfall over the continent and up to 35% on the margins of East Antarctica, significantly affecting satellite-based estimations close to the ground. Our findings suggest that, as climate warming progresses, this process will be enhanced and will limit expected precipitation increases at the ground level. PMID:28973875

Hybrid sp2+sp3 carbon phases created from carbon nanotubes

NASA Astrophysics Data System (ADS)

Tingaev, M. I.; Belenkov, E. A.

2017-11-01

Using the density functional theory in the gradient approximation (DFT-GGA) methods was calculated the geometrically optimized structure and electronic properties for six new hybrid carbon phases. These hybrid phases consists of atoms in three - and four-coordinated (sp2+sp3-hybridized) states. The initial structure of the carbon phases was constructed by partial cross-linking of (8,0) carbon nanotube bundles. Sublimation energies calculated for hybrid phases above the sublimation energy of cubic diamond, however, fall into the range of values typical for carbon materials, which are stable under normal conditions. The density of electronic states at the Fermi energy for the two phases is non-zero and these phases should have metallic properties. The other hybrid phases should be semiconductors with a band gap from 0.5 to 1.1 eV.

Tubular sublimatory evaporator heat sink

NASA Technical Reports Server (NTRS)

Webbon, B. W. (Inventor)

1977-01-01

An evaporative refrigerator or cooler comprising a bundle of spaced, porous walled tubes closed at one of their ends and vented to a vacuum at the other end is disclosed. The tube bundle is surrounded by a water jacket having a hot water inlet distribution manifold and a cooled water outlet through a plenum chamber. Hot water is pumped into the jacket to circulate around the tubes, and when this water meets the vacuum existing inside the tubes, it evaporates thereby cooling the water in the jacket. If cooling proceeds to the point where water penetrating or surrounding all or part of the tubes freezes, operation continues with local sublimation of the ice on the tubes while the circulating water attempts to melt the ice. Both sublimation and evaporation may take place simultaneously in different regions of the device.

Rapid determination of vial heat transfer parameters using tunable diode laser absorption spectroscopy (TDLAS) in response to step-changes in pressure set-point during freeze-drying.

PubMed

Kuu, Wei Y; Nail, Steven L; Sacha, Gregory

2009-03-01

The purpose of this study was to perform a rapid determination of vial heat transfer parameters, that is, the contact parameter K(cs) and the separation distance l(v), using the sublimation rate profiles measured by tunable diode laser absorption spectroscopy (TDLAS). In this study, each size of vial was filled with pure water followed by a freeze-drying cycle using a LyoStar II dryer (FTS Systems) with step-changes of the chamber pressure set-point at to 25, 50, 100, 200, 300, and 400 mTorr. K(cs) was independently determined by nonlinear parameter estimation using the sublimation rates measured at the pressure set-point of 25 mTorr. After obtaining K(cs), the l(v) value for each vial size was determined by nonlinear parameter estimation using the pooled sublimation rate profiles obtained at 25 to 400 mTorr. The vial heat transfer coefficient K(v), as a function of the chamber pressure, was readily calculated, using the obtained K(cs) and l(v) values. It is interesting to note the significant difference in K(v) of two similar types of 10 mL Schott tubing vials, primary due to the geometry of the vial-bottom, as demonstrated by the images of the contact areas of the vial-bottom. (c) 2008 Wiley-Liss, Inc. and the American Pharmacists Association

Processes that generate and deplete liquid water and snow in thin midlevel mixed-phase clouds

NASA Astrophysics Data System (ADS)

Smith, Adam J.; Larson, Vincent E.; Niu, Jianguo; Kankiewicz, J. Adam; Carey, Lawrence D.

2009-06-01

This paper uses a numerical model to investigate microphysical, radiative, and dynamical processes in mixed-phase altostratocumulus clouds. Three cloud cases are chosen for study, each of which was observed by aircraft during the fifth or ninth Complex Layered Cloud Experiment (CLEX). These three clouds are numerically modeled using large-eddy simulation (LES). The observed and modeled clouds consist of a mixed-phase layer with a quasi-adiabatic profile of liquid, and a virga layer below that consists of snow. A budget of cloud (liquid) water mixing ratio is constructed from the simulations. It shows that large-scale ascent/descent, radiative cooling/heating, turbulent transport, and microphysical processes are all significant. Liquid is depleted indirectly via depositional growth of snow (the Bergeron-Findeisen process). This process is more influential than depletion of liquid via accretional growth of snow. Also constructed is a budget of snow mixing ratio, which turns out to be somewhat simpler. It shows that snow grows by deposition in and below the liquid (mixed-phase) layer, and sublimates in the remainder of the virga region below. The deposition and sublimation are balanced primarily by sedimentation, which transports the snow from the growth region to the sublimation region below. In our three clouds, the vertical extent of the virga layer is influenced more by the profile of saturation ratio below the liquid (mixed-phase) layer than by the mixing ratio of snow at the top of the virga layer.

Literary aesthetics: beauty, the brain, and Mrs. Dalloway.

PubMed

Hogan, Patrick Colm

2013-01-01

Empirical research indicates that beauty is in part a matter of prototype approximation. Some research suggests that unanticipated pattern recognition is important as well. This essay begins by briefly outlining an account of beauty based on these factors. It goes on to consider complications. Minor complications include the partial incompatibility of these accounts and the importance of differentiating judgments of beauty from aesthetic response. More serious issues include the relative neglect of literature in neurologically-based discussions of beauty, which tend to focus on music or visual art. There is also a relative neglect of emotion, beyond the reward system. Finally, there is the almost complete absence of the sublime. After considering these problems broadly, the essay turns to Virginia Woolf's Mrs. Dalloway, examining its treatment of beauty and sublimity. The aim of this section is not merely to illuminate Woolf's novel by reference to neuroscientific research. It is equally, perhaps more fully, to expand our neuroscientifically grounded account of aesthetic response by drawing on Woolf's novel. In Mrs. Dalloway, there are gestures toward prototypes and patterns in beauty. But the key features are clearly emotional. Specifically, the emotions at issue in feelings of beauty and sublimity appear to be primarily attachment, on the one hand, and a profound sense of isolation, on the other. Woolf's novel also points us toward other features of aesthetic experience, crucially including the emotion-sharing that is a key function of the production and circulation of art. © 2013 Elsevier B.V. All rights reserved.

Evidence for geologic processes on comets

NASA Astrophysics Data System (ADS)

Sunshine, Jessica M.; Thomas, Nicolas; El-Maarry, Mohamed Ramy; Farnham, Tony L.

2016-11-01

Spacecraft missions have resolved the nuclei of six periodic comets and revealed a set of geologically intriguing and active small bodies. The shapes of these cometary nuclei are dominantly bilobate reflecting their formation from smaller cometesimals. Cometary surfaces include a diverse set of morphologies formed from a variety of mechanisms. Sublimation of ices, driven by the variable insolation over the time since each nucleus was perturbed into the inner Solar System, is a major process on comets and is likely responsible for quasi-circular depressions and ubiquitous layering. Sublimation from near-vertical walls is also seen to lead to undercutting and mass wasting. Fracturing has only been resolved on one comet but likely exists on all comets. There is also evidence for mass redistribution, where material lifted off the nucleus by subliming gases is deposited onto other surfaces. It is surprising that such sedimentary processes are significant in the microgravity environment of comets. There are many enigmatic features on cometary surfaces including tall spires, kilometer-scale flows, and various forms of depressions and pits. Furthermore, even after accounting for the differences in resolution and coverage, significant diversity in landforms among cometary surfaces clearly exists. Yet why certain landforms occur on some comets and not on others remains poorly understood. The exploration and understanding of geologic processes on comets is only beginning. These fascinating bodies will continue to provide a unique laboratory for examining common geologic processes under the uncommon conditions of very high porosity, very low strength, small particle sizes, and near-zero gravity.

What generates Callisto's atmosphere? - Indications from calculations of ionospheric electron densities and airglow

NASA Astrophysics Data System (ADS)

Hartkorn, O. A.; Saur, J.; Strobel, D. F.

2016-12-01

Callisto's atmosphere has been probed by the Galileo spacecraft and the Hubble Space Telescope (HST) and is expected to be composed of O2 and minor components CO2 and H2O. We use an ionosphere model coupled with a parametrized atmosphere model to calculate ionospheric electron densities and airglow. By varying a prescribed neutral atmosphere and comparing the model results to Galileo radio occultation and HST-Cosmic Origin Spectrograph observations we find that Callisto's atmosphere likely possesses a day/night asymmetry driven by solar illumination. We see two possible explanation for this asymmetry: 1) If sublimation dominates the atmosphere formation, a day/night asymmetry will be generated since the sublimation production rate is naturally much stronger at the day side than at the night side. 2) If surface sputtering dominates the atmosphere formation, a day/night asymmetry is likely generated as well since the sputtering yield increases with increasing surface temperature and, therefore, with decreasing solar zenith angle. The main difference between both processes is given by the fact that surface sputtering, in contrast to sublimation, is also a function of Callisto's orbital position since sputtering projectiles predominately co-rotate with the Jovian magnetosphere. On this basis, we develop a method that can discriminate between both explanations by comparing airglow observations at different orbital positions with airglow predictions. Our predictions are based on our ionosphere model and an orbital position dependent atmosphere model originally developed for the O2 atmosphere of Europa by Plainaki et al. (2013).

Why drive? Psychoanalytic reflections on the film Never let me go.

PubMed

Storck, Timo

2016-02-01

The author presents a psychoanalytic interpretation of Mark Romanek's film Never Let Me Go, which concerns a society in which young adult clones have their internal organs 'harvested' for transplantation. Following some general remarks on the method of psychoanalytic film interpretation, strongly emphasising the aesthetics of form and artistic elements specific to film, the author develops the notion that through its cinematic perspectives and shots, Never Let Me Go dramatizes a specific relationship between the sublime and solitude. The film therefore deals with a particular intrinsic difference between expanse and constraint, as well as the limited and the eternal. This leads the viewer to participate directly in a film-specific way in the inner conflicts at work both in the film's theme and in its protagonists. In terms of aesthetic content, these conflicts are revealed as those of an inescapable thanatological theme that is essentially intertwined with an erotic one. The film shows how love, sexuality, and internal and external images arise from thanatological forces, and it simultaneously provides a way of sublating them (Hegel's Aufhebung) - that is, the film itself represents a benign drive fusion. The film's protagonists, however, struggle with a lack of early parenting and thus with the helplessness of facing individual drive development and the longing for a holding object. Hence, in formal terms, the film deals with the sublime, and, as I will show, it also deals with sublimation at the level of its content. Copyright © 2016 Institute of Psychoanalysis.

Engineering On-Surface Spin Crossover: Spin-State Switching in a Self-Assembled Film of Vacuum-Sublimable Functional Molecule.

PubMed

Kumar, Kuppusamy Senthil; Studniarek, Michał; Heinrich, Benoît; Arabski, Jacek; Schmerber, Guy; Bowen, Martin; Boukari, Samy; Beaurepaire, Eric; Dreiser, Jan; Ruben, Mario

2018-03-01

The realization of spin-crossover (SCO)-based applications requires study of the spin-state switching characteristics of SCO complex molecules within nanostructured environments, especially on surfaces. Except for a very few cases, the SCO of a surface-bound thin molecular film is either quenched or heavily altered due to: (i) molecule-surface interactions and (ii) differing intermolecular interactions in films relative to the bulk. By fabricating SCO complexes on a weakly interacting surface, the interfacial quenching problem is tackled. However, engineering intermolecular interactions in thin SCO active films is rather difficult. Here, a molecular self-assembly strategy is proposed to fabricate thin spin-switchable surface-bound films with programmable intermolecular interactions. Molecular engineering of the parent complex system [Fe(H 2 B(pz) 2 ) 2 (bpy)] (pz = pyrazole, bpy = 2,2'-bipyridine) with a dodecyl (C 12 ) alkyl chain yields a classical amphiphile-like functional and vacuum-sublimable charge-neutral Fe II complex, [Fe(H 2 B(pz) 2 ) 2 (C 12 -bpy)] (C 12 -bpy = dodecyl[2,2'-bipyridine]-5-carboxylate). Both the bulk powder and 10 nm thin films sublimed onto either quartz glass or SiO x surfaces of the complex show comparable spin-state switching characteristics mediated by similar lamellar bilayer like self-assembly/molecular interactions. This unprecedented observation augurs well for the development of SCO-based applications, especially in molecular spintronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

[Diurnal variations of grassland evapotranspiration over different periods in the Pailugou basin in the upper reach of the Heihe River, Northwest China.

PubMed

Wang, Zhong Fu; Zhang, Lan Hui; Wang, Yi Bo; He, Chan Sheng

2016-11-18

Evapotranspiration (ET) is an important component of water cycle, but its measurement in high altitude mountainous region is quite difficult, resulting in the poor understanding of the temporal and spatial variations of actual ET in high altitude mountainous region. In this paper, a weighing lysimeter was used to measure the hourly ET in a grassland in the Pailugou basin in the upper reach of the Heihe River, Northwest China. Based on the measured data, diurnal variations of grassland ET over different periods were analyzed. Results indicated that snow and ice sublimation appeared during the freezing period, with a very different diurnal variation pattern compared with other three periods. During the period without sunshine, the amount of snow and ice sublimation was nearly constant. When the highest global radiation and lowest relative humidity appeared in the same period, the amount of snow and ice sublimation increased a little. The early growth period was a period when snow and ice started to melt, during which snowmelt evaporation and soil evaporation occurred at the same time. The growth period had the highest ET rate. Due to continuous rainfall events, maximum and minimum ET values appeared at the same hour. ET in the late growth period mainly came from soil evaporation, producing 3 peaks in diurnal variation, which was different from only one peak in both the early growth period and the growth period.

A Leidenfrost Engine

NASA Astrophysics Data System (ADS)

Wells, Gary; Ledesma-Aguillar, Ridrigo; McHale, Glen; Sefiane, Khellil

2015-11-01

The Leidenfrost effect, the sustained levitation of evaporating liquid droplets by a cushion of their on vapour on very hot surfaces, has received increased attention over the past few years. On patterned surfaces, rectification of the vapour layer flow can lead to rich dynamics of evaporating drops or sublimating blocks of dry ice, including self-propulsion, orbiting and conjoint rotation. In this paper we show that the Leidenfrost effect can be exploited to drive the rotation of rigid objects, such as solid hydrophilic plates coupled to water droplets and blocks of dry ice, by using turbine-like substrates. Using a hydrodynamic model, we show that drag-based rotation is achieved at low-Reynolds number by a rectification mechanism of the flow in the vapour layer caused by the underlying turbine-like geometry. Our theoretical model determines the maximum weight of Leidenfrost rotors and the net torque driving their motion in terms of operational parameters, showing an excellent agreement with experiments using dry-ice blocks. We generalise the concept of rotation into a new concept for a heat engine capable of harvesting thermal energy using either thin-film boiling or sublimation as a phase-change mechanism. As a proof principle, we implement the new sublimation engine in the lab to create a simple electromagnetic generator. Our results support the feasibility of low-friction in situ energy harvesting from both liquids and ices in challenging situations such as deep drilling, outer space exploration or micro-mechanical manipulation.

Mercury's Crater-Hosted Hollows: Chalcogenide Pryo-Thermokarst, and Permafrost Analogs on Earth, Mars, and Titan

NASA Astrophysics Data System (ADS)

Kargel, Jeffrey

2013-04-01

MESSENGER has acquired stunning images of pitted, light-toned and variegated light/dark terrains located primarily on the floors—probably impact-melt sheets—of many of Mercury's large craters. Termed "hollows", the pitted terrains are geomorphologically similar to some on Mars formed by sublimation of ice-rich permafrost and to lowland thermokarst on Earth formed by permafrost thaw; to "swiss cheese" terrain forming by sublimation of frozen CO2 at the Martian South Pole; and to suspected hydrocarbon thermokarst at Titan's poles. I shall briefly review some analogs on these other worlds. The most plausible explanation for Mercury's hollows is terrain degradation involving melting or sublimation of heterogeneous chalcogenide and sulfosalt mineral assemblages. I refer to these Mercurian features as pyrothermokarst; the etymological redundancy distinguishes the conditions and mineral agents from the ice-related features on Earth and Mars, though some of the physical processes may be similar. Whereas ice and sulfur have long been suspected and ice recently was discovered in permanently shadowed craters of Mercury's polar regions, the hollows occur down to the equator, where neither ice nor sulfur is plausible. The responsible volatiles must be only slightly volatile on the surface and/or in the upper crust of Mercury's low to middle latitudes at 400-800 K, but they must be capable of either melting or sublimating on geologically long time scales. Under prevailing upper crustal and surface temperatures, chalcophile-rich "permafrost" can undergo either desulfidation or melting reactions that could cause migration or volume changes of the permafrost, and hence lead to collapse and pitting. I propose the initial emplacement of crater-hosted chalcogenides, sulfosalts and related chalcophile materials such as pnictides, in impact-melt pools (involving solid-liquid and silicate-sulfide fractionation) and further differentiation by associated dry or humid fumaroles (solid-vapor and liquid-vapor fractionation and recondensation). Key phase transitions can occur in the temperature range of Mercury's surface and upper crust. Vapor-solid, vapor-liquid, and solid-liquid transitions of the heated materials resulted in migration and loss of volatiles and anatectic liquids, causing collapse pits to form. Seasonal heating near perihelion may work together with geothermal flux or early impact heating to drive off volatiles and produce the pits. In some cases, local recondensation of moderately volatile materials may have occurred on the rims of the pits; some volatiles may have been transported to the polar regions or lost by exospheric escape. Impacts by comets may have caused local oxidation and formation of oxygenated salts and other minerals, whose local recondensation from fumarole gases can explain the light-toned layers and light-toned rims of many pits. Plating of native volatile metals and semi-metals may also account for some light-toned deposits. Large contrasts in thermal conductivity as well as local topographic shading and latitude controls may result in large differences in element mobility and mineral assemblages. Pyrothermokarst on Mercury may be more chemically heterogeneous and complex in its development than any other thermokarst in the Solar System. Validation of this model would require a future mission with high-resolution multispectral imaging and neutral/ion detection.

Observations and simulations of snowpack cold content and its relationship to snowmelt timing and rate

NASA Astrophysics Data System (ADS)

Jennings, K. S.; Molotch, N. P.

2017-12-01

Mountain snowpacks serve as a vital water resource for more than 1 billion people across the globe. Two key properties of snowmelt—rate and timing—are controlled by the snowpack energy budget where incoming positive fluxes are balanced by a decrease in the energy deficit of the snowpack and a change in the phase of water from solid to liquid. In this context, the energy deficit, or cold content, regulates snowmelt as runoff does not commence until the deficit approaches zero. There is significant uncertainty surrounding cold content despite its relevance to snowmelt processes, likely due to the inherent difficulties in its observation. Our work has clarified the previously unresolved meteorological and energy balance controls on cold content development in seasonal snowpacks by leveraging two unique datasets from the Niwot Ridge LTER in the Rocky Mountains of Colorado. The first is a long-term snow pit record of snowpack properties from an alpine and subalpine site within the LTER. These data were augmented with a 23-year simulation of the snowpack at both sites using a quality controlled, serially complete, hourly forcing dataset. The observations and simulations both indicated that cold content primarily developed through new snowfall, while a negative energy budget provided a secondary pathway for cold content development, mainly through longwave emission and sublimation. Cold content gains from snowfall outnumbered energy balance gains by 438% in the alpine and 166% in the subalpine. Increased spring precipitation and later peak cold content significantly delayed snowmelt onset and daily melt rates were reduced by 32.2% in the alpine and 36.1% in the subalpine when an energy deficit needed to be satisfied. Furthermore, preliminary climate change simulations indicated warmer air temperatures reduced cold content accumulation, which increased the amount of snow lost to melt throughout the winter as incoming positive fluxes had to overcome smaller energy deficits. Overall, this work shows that meteorological and energy balance processes that increase cold content (e.g., snowfall, longwave emission, and sublimation) delay snowmelt onset and damp snowmelt rate, a relationship that will likely be impacted by climate warming with resultant effects on water resource availability.

Controlled Growth of Rubrene Nanowires by Eutectic Melt Crystallization

NASA Astrophysics Data System (ADS)

Chung, Jeyon; Hyon, Jinho; Park, Kyung-Sun; Cho, Boram; Baek, Jangmi; Kim, Jueun; Lee, Sang Uck; Sung, Myung Mo; Kang, Youngjong

2016-03-01

Organic semiconductors including rubrene, Alq3, copper phthalocyanine and pentacene are crystallized by the eutectic melt crystallization. Those organic semiconductors form good eutectic systems with the various volatile crystallizable additives such as benzoic acid, salicylic acid, naphthalene and 1,3,5-trichlorobenzene. Due to the formation of the eutectic system, organic semiconductors having originally high melting point (Tm > 300 °C) are melted and crystallized at low temperature (Te = 40.8-133 °C). The volatile crystallizable additives are easily removed by sublimation. For a model system using rubrene, single crystalline rubrene nanowires are prepared by the eutectic melt crystallization and the eutectic-melt-assisted nanoimpinting (EMAN) technique. It is demonstrated that crystal structure and the growth direction of rubrene can be controlled by using different volatile crystallizable additives. The field effect mobility of rubrene nanowires prepared using several different crystallizable additives are measured and compared.

Investigation on the morphological and optical evolution of bimetallic Pd-Ag nanoparticles on sapphire (0001) by the systematic control of composition, annealing temperature and time

PubMed Central

Pandey, Puran; Kunwar, Sundar; Sui, Mao; Bastola, Sushil

2017-01-01

Multi-metallic alloy nanoparticles (NPs) can offer additional opportunities for modifying the electronic, optical and catalytic properties by the control of composition, configuration and size of individual nanostructures that are consisted of more than single element. In this paper, the fabrication of bimetallic Pd-Ag NPs is systematically demonstrated via the solid state dewetting of bilayer thin films on c-plane sapphire by governing the temperature, time as well as composition. The composition of Pd-Ag bilayer remarkably affects the morphology of alloy nanostructures, in which the higher Ag composition, i.e. Pd0.25Ag0.75, leads to the enhanced dewetting of bilayers whereas the higher Pd composition (Pd0.75Ag0.25) hinders the dewetting. Depending on the annealing temperature, Pd-Ag alloy nanostructures evolve with a series of configurations, i.e. nucleation of voids, porous network, elongated nanoclusters and round alloy NPs. In addition, with the annealing time set, the gradual configuration transformation from the elongated to round alloy NPs as well as size reduction is demonstrated due to the enhanced diffusion and sublimation of Ag atoms. The evolution of various morphology of Pd-Ag nanostructures is described based on the surface diffusion and inter-diffusion of Pd and Ag adatoms along with the Ag sublimation, Rayleigh instability and energy minimization mechanism. The reflectance spectra of bimetallic Pd-Ag nanostructures exhibit various quadrupolar and dipolar resonance peaks, peak shifts and absorption dips owing to the surface plasmon resonance of nanostructures depending on the surface morphology. The intensity of reflectance spectra is gradually decreased along with the surface coverage and NP size evolution. The absorption dips are red-shifted towards the longer wavelength for the larger alloy NPs and vice-versa. PMID:29253017

The energy confinement response of DIII-D plasmas to Resonant Magnetic Perturbations

DOE PAGES

Cui, L.; Nazikian, Raffi; Grierson, B. A.; ...

2017-07-11

Here, Resonant Magnetic Perturbations (RMPs) are a leading method for edge localized modes (ELMs) Control in fusion plasmas. However they can also cause a rapid degradation in energy confinement. In this paper we show that the energy confinement in low collisionality (v* e < 0.3) DIII-D ITER Similar Shape (ISS) plasmas often recovers after several energy confinement times for RMP amplitudes up to the threshold for ELM suppression. Immediately following the application of the RMP, the plasma stored energy decreases in proportion to the decrease in the line-averaged density during density "pump-out". Later in the discharge confinement recovery is observedmore » in the thermal ion channel and is correlated with the increase in the ion temperature at the top of the H-mode pedestal. A correlation between the inverse scale length of the ion temperature (α/L Ti) and the E x B shearing rate at the top of the pedestal is seen during the confinement recovery phase. Transport analysis reveals that the confinement improvement in the ion channel results from the self-similarity in the ion temperature profiles in the plasma core combined with the observed increase in α/L Ti in the plasma edge following density pump-out. In contrast the electron temperature scale length (α/L Ti) remains essentially unchanged in response to the application of the RMP. At significantly higher RMP levels the edge EXB shearing rate and α/L Ti does not increase and the confinement does not recover following density pump-out.« less

On the buckling of elastic rings by external confinement.

PubMed

Hazel, Andrew L; Mullin, Tom

2017-05-13

We report the results of an experimental and numerical investigation into the buckling of thin elastic rings confined within containers of circular or regular polygonal cross section. The rings float on the surface of water held in the container and controlled removal of the fluid increases the confinement of the ring. The increased compressive forces can cause the ring to buckle into a variety of shapes. For the circular container, finite perturbations are required to induce buckling, whereas in polygonal containers the buckling occurs through a linear instability that is closely related to the canonical Euler column buckling. A model based on Kirchhoff-Love beam theory is developed and solved numerically, showing good agreement with the experiments and revealing that in polygons increasing the number of sides means that buckling occurs at reduced levels of confinement.This article is part of the themed issue 'Patterning through instabilities in complex media: theory and applications.' © 2017 The Author(s).

Gate-defined quantum confinement in suspended bilayer graphene

NASA Astrophysics Data System (ADS)

Allen, M. T.; Martin, J.; Yacoby, A.

2012-07-01

Quantum-confined devices that manipulate single electrons in graphene are emerging as attractive candidates for nanoelectronics applications. Previous experiments have employed etched graphene nanostructures, but edge and substrate disorder severely limit device functionality. Here we present a technique that builds quantum-confined structures in suspended bilayer graphene with tunnel barriers defined by external electric fields that open a bandgap, thereby eliminating both edge and substrate disorder. We report clean quantum dot formation in two regimes: at zero magnetic field B using the energy gap induced by a perpendicular electric field and at B>0 using the quantum Hall ν=0 gap for confinement. Coulomb blockade oscillations exhibit periodicity consistent with electrostatic simulations based on local top-gate geometry, a direct demonstration of local control over the band structure of graphene. This technology integrates single electron transport with high device quality and access to vibrational modes, enabling broad applications from electromechanical sensors to quantum bits.

Suppressed ion-scale turbulence in a hot high-β plasma

NASA Astrophysics Data System (ADS)

Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.

2016-12-01

An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements.

On the buckling of elastic rings by external confinement

PubMed Central

Hazel, Andrew L.

2017-01-01

We report the results of an experimental and numerical investigation into the buckling of thin elastic rings confined within containers of circular or regular polygonal cross section. The rings float on the surface of water held in the container and controlled removal of the fluid increases the confinement of the ring. The increased compressive forces can cause the ring to buckle into a variety of shapes. For the circular container, finite perturbations are required to induce buckling, whereas in polygonal containers the buckling occurs through a linear instability that is closely related to the canonical Euler column buckling. A model based on Kirchhoff–Love beam theory is developed and solved numerically, showing good agreement with the experiments and revealing that in polygons increasing the number of sides means that buckling occurs at reduced levels of confinement. This article is part of the themed issue ‘Patterning through instabilities in complex media: theory and applications.’ PMID:28373386

Suppressed ion-scale turbulence in a hot high-β plasma

PubMed Central

Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.

2016-01-01

An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements. PMID:28000675

Control of a laser inertial confinement fusion-fission power plant

DOEpatents

Moses, Edward I.; Latkowski, Jeffery F.; Kramer, Kevin J.

2015-10-27

A laser inertial-confinement fusion-fission energy power plant is described. The fusion-fission hybrid system uses inertial confinement fusion to produce neutrons from a fusion reaction of deuterium and tritium. The fusion neutrons drive a sub-critical blanket of fissile or fertile fuel. A coolant circulated through the fuel extracts heat from the fuel that is used to generate electricity. The inertial confinement fusion reaction can be implemented using central hot spot or fast ignition fusion, and direct or indirect drive. The fusion neutrons result in ultra-deep burn-up of the fuel in the fission blanket, thus enabling the burning of nuclear waste. Fuels include depleted uranium, natural uranium, enriched uranium, spent nuclear fuel, thorium, and weapons grade plutonium. LIFE engines can meet worldwide electricity needs in a safe and sustainable manner, while drastically shrinking the highly undesirable stockpiles of depleted uranium, spent nuclear fuel and excess weapons materials.

Confinement-Induced Drug-Tolerance in Mycobacteria Mediated by an Efflux Mechanism

PubMed Central

Luthuli, Brilliant B.; Purdy, Georgiana E.; Balagaddé, Frederick K.

2015-01-01

Tuberculosis (TB) is the world’s deadliest curable disease, responsible for an estimated 1.5 million deaths annually. A considerable challenge in controlling this disease is the prolonged multidrug chemotherapy (6 to 9 months) required to overcome drug-tolerant mycobacteria that persist in human tissues, although the same drugs can sterilize genetically identical mycobacteria growing in axenic culture within days. An essential component of TB infection involves intracellular Mycobacterium tuberculosis bacteria that multiply within macrophages and are significantly more tolerant to antibiotics compared to extracellular mycobacteria. To investigate this aspect of human TB, we created a physical cell culture system that mimics confinement of replicating mycobacteria, such as in a macrophage during infection. Using this system, we uncovered an epigenetic drug-tolerance phenotype that appears when mycobacteria are cultured in space-confined bioreactors and disappears in larger volume growth contexts. Efflux mechanisms that are induced in space-confined growth environments contribute to this drug-tolerance phenotype. Therefore, macrophage-induced drug tolerance by mycobacteria may be an effect of confined growth among other macrophage-specific mechanisms. PMID:26295942

Optimization of the freeze-drying cycle: adaptation of the pressure rise analysis model to non-instantaneous isolation valves.

PubMed

Chouvenc, P; Vessot, S; Andrieu, J; Vacus, P

2005-01-01

The principal aim of this study is to extend to a pilot freeze-dryer equipped with a non-instantaneous isolation valve the previously presented pressure rise analysis (PRA) model for monitoring the product temperature and the resistance to mass transfer of the dried layer during primary drying. This method, derived from the original MTM method previously published, consists of interrupting rapidly (a few seconds) the water vapour flow from the sublimation chamber to the condenser and analysing the resulting dynamics of the total chamber pressure increase. The valve effect on the pressure rise profile observed during the isolation valve closing period was corrected by introducing in the initial PRA model a valve characteristic function factor which turned out to be independent of the operating conditions. This new extended PRA model was validated by implementing successively the two types of valves and by analysing the pressure rise kinetics data with the corresponding PRA models in the same operating conditions. The coherence and consistency shown on the identified parameter values (sublimation front temperature, dried layer mass transfer resistance) allowed validation of this extended PRA model with a non-instantaneous isolation valve. These results confirm that the PRA method, with or without an instantaneous isolation valve, is appropriate for on-line monitoring of product characteristics during freeze-drying. The advantages of PRA are that the method is rapid, non-invasive, and global. Consequently, PRA might become a powerful and promising tool not only for the control of pilot freeze-dryers but also for industrial freeze-dryers equipped with external condensers.

Heat and mass transfer scale-up issues during freeze-drying, III: control and characterization of dryer differences via operational qualification tests.

PubMed

Rambhatla, S; Tchessalov, S; Pikal, Michael J

2006-04-21

The objective of this research was to estimate differences in heat and mass transfer between freeze dryers due to inherent design characteristics using data obtained from sublimation tests. This study also aimed to provide guidelines for convenient scale-up of the freeze-drying process. Data obtained from sublimation tests performed on laboratory-scale, pilot, and production freeze dryers were used to evaluate various heat and mass transfer parameters: nonuniformity in shelf surface temperatures, resistance of pipe, refrigeration system, and condenser. Emissivity measurements of relevant surfaces such as the chamber wall and the freeze dryer door were taken to evaluate the impact of atypical radiation heat transfer during scale-up. "Hot" and "cold" spots were identified on the shelf surface of different freeze dryers, and the impact of variation in shelf surface temperatures on the primary drying time and the product temperature during primary drying was studied. Calculations performed using emissivity measurements on different freeze dryers suggest that a front vial in the laboratory lyophilizer received 1.8 times more heat than a front vial in a manufacturing freeze dryer operating at a shelf temperature of -25 degrees C and a chamber pressure of 150 mTorr during primary drying. Therefore, front vials in the laboratory are much more atypical than front vials in manufacturing. Steady-state heat and mass transfer equations were used to study a combination of different scale-up issues pertinent during lyophilization cycles commonly used for the freeze-drying of pharmaceuticals.

The Depersonalization of Sex

ERIC Educational Resources Information Center

Frankl, Viktor E.

1977-01-01

Love is frequently interpreted in a reductionistic way as a mere sublimation of sexual drives and instincts which man shares with all the other animals. Such an interpretation blocks a true understanding of all the various human phenomena. (Author)

Pitting from Sublimation of Underlying Dry-Ice Layer

NASA Image and Video Library

2011-04-21

NASA Mars Reconnaissance Orbiter took these images of an area near Mars south pole where coalescing or elongated pits are interpreted as signs of an underlying deposit of frozen carbon dioxide, or dry ice.

Quantitative trait loci for magnitude of the plasma cortisol response to confinement in rainbow trout.

PubMed

Quillet, E; Krieg, F; Dechamp, N; Hervet, C; Bérard, A; Le Roy, P; Guyomard, R; Prunet, P; Pottinger, T G

2014-04-01

Better understanding of the mechanisms underlying interindividual variation in stress responses and their links with production traits is a key issue for sustainable animal breeding. In this study, we searched for quantitative trait loci (QTL) controlling the magnitude of the plasma cortisol stress response and compared them to body size traits in five F2 full-sib families issued from two rainbow trout lines divergently selected for high or low post-confinement plasma cortisol level. Approximately 1000 F2 individuals were individually tagged and exposed to two successive acute confinement challenges (1 month interval). Post-stress plasma cortisol concentrations were determined for each fish. A medium density genome scan was carried out (268 markers, overall marker spacing less than 10 cM). QTL detection was performed using qtlmap software, based on an interval mapping method (http://www.inra.fr/qtlmap). Overall, QTL of medium individual effects on cortisol responsiveness (<10% of phenotypic variance) were detected on 18 chromosomes, strongly supporting the hypothesis that control of the trait is polygenic. Although a core array of QTL controlled cortisol concentrations at both challenges, several QTL seemed challenge specific, suggesting that responses to the first and to a subsequent exposure to the confinement stressor are distinct traits sharing only part of their genetic control. Chromosomal location of the steroidogenic acute regulatory protein (STAR) makes it a good potential candidate gene for one of the QTL. Finally, comparison of body size traits QTL (weight, length and body conformation) with cortisol-associated QTL did not support evidence for negative genetic relationships between the two types of traits. © 2014 Stichting International Foundation for Animal Genetics.

10 CFR 835.1001 - Design and control.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 10 Energy 4 2014-01-01 2014-01-01 false Design and control. 835.1001 Section 835.1001 Energy DEPARTMENT OF ENERGY OCCUPATIONAL RADIATION PROTECTION Design and Control § 835.1001 Design and control. (a... administrative controls. The primary methods used shall be physical design features (e.g., confinement...

10 CFR 835.1001 - Design and control.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 10 Energy 4 2012-01-01 2012-01-01 false Design and control. 835.1001 Section 835.1001 Energy DEPARTMENT OF ENERGY OCCUPATIONAL RADIATION PROTECTION Design and Control § 835.1001 Design and control. (a... administrative controls. The primary methods used shall be physical design features (e.g., confinement...

10 CFR 835.1001 - Design and control.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 10 Energy 4 2011-01-01 2011-01-01 false Design and control. 835.1001 Section 835.1001 Energy DEPARTMENT OF ENERGY OCCUPATIONAL RADIATION PROTECTION Design and Control § 835.1001 Design and control. (a... administrative controls. The primary methods used shall be physical design features (e.g., confinement...

10 CFR 835.1001 - Design and control.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 10 Energy 4 2013-01-01 2013-01-01 false Design and control. 835.1001 Section 835.1001 Energy DEPARTMENT OF ENERGY OCCUPATIONAL RADIATION PROTECTION Design and Control § 835.1001 Design and control. (a... administrative controls. The primary methods used shall be physical design features (e.g., confinement...

10 CFR 835.1001 - Design and control.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 10 Energy 4 2010-01-01 2010-01-01 false Design and control. 835.1001 Section 835.1001 Energy DEPARTMENT OF ENERGY OCCUPATIONAL RADIATION PROTECTION Design and Control § 835.1001 Design and control. (a... administrative controls. The primary methods used shall be physical design features (e.g., confinement...

Study of the confinement properties in a reversed-field pinch with mode rotation and gas fuelling

NASA Astrophysics Data System (ADS)

Cecconello, M.; Malmberg, J.-A.; Nielsen, P.; Pasqualotto, R.; Drake, J. R.

2002-08-01

An extensive investigation of the global confinement properties in different operating scenarios in the rebuilt EXTRAP T2R reversed-field pinch (RFP) experiment is reported here. In particular, the role of a fast gas puff valve system, used to control plasma density, on confinement is studied. Without gas puffing, the electron density decays below 0.5×1019 m-3. The poloidal beta varies between 5% and 15%, decreasing at large I/N. The energy confinement time ranges from 70 to 225 μs. With gas puffing, the density is sustained at ne≈1.5×1019 m-3. However, a general slight deterioration of the plasma performances is observed for the same values of I/N: the plasma becomes cooler and more radiative. The poloidal beta is comparable to that in the scenarios without puff but the energy confinement time drops ranging from 60 to 130 μs. The fluctuation level and the energy confinement time have been found to scale with the Lundquist number as S-0.05+/-0.07 and S0.5+/-0.1, respectively. Mode rotation is typical for all the discharges and rotation velocity is observed to increase with increasing electron diamagnetic velocity.

Controlling the state of polarization via optical nanoantenna feeding with surface plasmon polaritons

NASA Astrophysics Data System (ADS)

Xie, Yu-Bo; Liu, Zheng-Yang; Wang, Qian-Jin; Sun, Guang-Hou; Zhang, Xue-Jin; Zhu, Yong-Yuan

2016-03-01

Optical nanoantennas, usually referring to metal structures with localized surface plasmon resonance, could efficiently convert confined optical energy to free-space light, and vice versa. But it is difficult to manipulate the confined visible light energy for its nanoscale spatial extent. Here, a simple method is proposed to solve this problem by controlling surface plasmon polaritons to indirectly manipulate the localized plasmons. As a proof of principle, we demonstrate an optical rotation device which is a grating with central circular polarization optical nanoantenna. It realized the arbitrary optical rotation of linear polarized light by controlling the retard of dual surface plasmon polaritons sources from both side grating structures. Furthermore, we use a two-parameter theoretical model to explain the experimental results.

Longitudinal wave function control in single quantum dots with an applied magnetic field

PubMed Central

Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A.; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai

2015-01-01

Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots. PMID:25624018

Longitudinal wave function control in single quantum dots with an applied magnetic field.

PubMed

Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai

2015-01-27

Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.

A new confined high pressure rotary shear apparatus: preliminary results

NASA Astrophysics Data System (ADS)

Faulkner, D.; Coughlan, G.; Bedford, J. D.

2017-12-01

The frictional properties of fault zone materials, and their evolution during slip, are of paramount importance for determining the earthquake mechanics of large tectonic faults. Friction is a parameter that is difficult to determine from seismological methods so much of our understanding comes from experiment. Rotary shear apparatuses have been widely used in experimental studies to elucidate the frictional properties of faults under realistic earthquake slip velocities (0.1-10 m/s) and displacements (>20 m). However one technical limitation of rotary shear experiments at seismic slip rates has been the lack of confinement. This has led to a limit on the normal stress (due to the strength of the forcing blocks) and also a lack of control of measurements of the pore fluid pressure. Here we present the first preliminary results from a rotary shear apparatus that has been developed to attempt to address this issue. The new fully confined ring shear apparatus has a fast-acting servo-hydraulic confining pressure system of up to 200 MPa and a servo-controlled upstream and downstream pore pressure system of up to 200 MPa. Displacement rates of 0.01μ/s to 2 m/s can be achieved. Fault gouge samples can therefore be sheared at earthquake speed whilst being subject to pressures typically associated with the depth of earthquake nucleation.

Human Impairment from Living near Confined Animal (Hog) Feeding Operations

PubMed Central

Kilburn, Kaye H.

2012-01-01

Problem. To determine whether neighbors around manure lagoons and massive hog confinement buildings who complained of offensive odors and symptoms had impaired brain and lung functions. Method. We compared near hog manure neighbors of lagoons to people living beyond 3 kilometers in Ohio and to unexposed people controls in a nearby state for neurophysiological, cognitive, recall and memory functions, and pulmonary performance. Results. The 25 exposed subjects averaged 4.3 neurobehavioral abnormalities, significantly different from 2.5 for local controls and 2.3 for Tennessee controls. Exposed subjects mean forced vital capacity and expiratory volume in 1 sec were reduced significantly compared to local and regional controls. Conclusions. Near neighbors of hog enclosures and manure lagoon gases had impaired neurobehavioral functions and pulmonary functions and these effects extended to nearby people thought to be controls. Hydrogen sulfide must be abated because people living near lagoons cannot avoid rotten egg gas. PMID:22496706

Discovery of stationary operation of quiescent H-mode plasmas with net-zero neutral beam injection torque and high energy confinement on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burrell, K. H.; Chen, X.; Garofalo, A. M.

Recent experiments in DIII-D [J. L. Luxon et al., in Plasma Physics and Controlled Nuclear Fusion Research 1996 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H{sub 98y2} international tokamakmore » energy confinement scaling (H{sub 98y2} = 1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggered in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers E × B rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbulence to increase. In the H-mode edge, a narrow transport barrier usually grows until MHD instability (a peeling ballooning mode) leads to the ELM heat burst. However, the increased turbulence reduces the pressure gradient, allowing the development of a broader and thus higher transport barrier. A 60% increase in pedestal pressure and 40% increase in energy confinement result. An increase in the E × B shearing rate inside of the edge pedestal is a key factor in the confinement increase. Strong double-null plasma shaping raises the threshold for the ELM instability, allowing the plasma to reach a transport-limited state near but below the explosive ELM stability boundary. The resulting plasmas have burning-plasma-relevant β{sub N} = 1.6–1.8 and run without the need for extra torque from 3D magnetic fields. To date, stationary conditions have been produced for 2 s or 12 energy confinement times, limited only by external hardware constraints. Stationary operation with improved pedestal conditions is highly significant for future burning plasma devices, since operation without ELMs at low rotation and good confinement is key for fusion energy production.« less

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 with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures. Devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit. However, sublimation from a high temperature, high velocity carrier gas is not efficient enough to form a large ore deposit. Re, Se, Cd and Bi could be used as supporting evidence for magmatic fluid transport in an ore deposit. ?? 1987.

Distribution and evolution of scalloped terrain in the southern hemisphere, Mars

NASA Astrophysics Data System (ADS)

Zanetti, Michael; Hiesinger, Harald; Reiss, Dennis; Hauber, Ernst; Neukum, Gerhard

2010-04-01

Scalloped depressions are a unique martian surface morphology found in the northern and southern hemisphere latitude-dependent dust and ice-rich surface mantles. These features exhibit a distinct asymmetric north-south slope profile, characterized by steep pole-facing scarps, flat floors and gentle equator-facing slopes. We examined High Resolution Stereo Camera (HRSC) images of the southern hemisphere to determine their longitudinal distribution, which revealed that a majority of scalloped terrain is located in the region of the southern wall of the Hellas Basin and northern Malea Planum. A detailed map of this area was produced where scallops were found to contour the southern wall of the basin, and where the ice-rich mantle was seen to be thickest. Scalloped terrain is concentrated along the topographic highs near the Amphitrites and Peneus Paterae and areal extent and depth decreases with increasing depth into the basin. We also examined existing hypothesis for the formation and evolution of scalloped depressions using High Resolution Imaging Science Experiment (HiRISE) images and data from the Thermal Emission Imaging System-Infrared (THEMIS-IR) and the Thermal Emission Spectrometer (TES). Our approach provides regional context for the development of scalloped terrains within the southern hemisphere, and offers detailed evidence of scallop depressions forming around small cracks, presumably caused by thermal contraction. Morphometric measurements show that scalloped depressions can be as much as 40 m deep, with typical depths of between 10 and 20 m. Our observations of scallop formation and development in the southern hemisphere support a solar-insolation model proposed by previous researchers (e.g. [Morgenstern, A., Hauber, E., Reiss, D., van Gasselt, S., Grosse, G., Schirrmeister, L., 2007. J. Geophys. Res. 112, CiteID E06010; Lefort, A., Russell, P.S., Thomas, N., McEwen, A.S., Dundas, C.M., Kirk, R.L., 2009a. J. Geophys. Res. 114, E04005; Lefort, A., Russell, P.S., Thomas, N., 2009b. Icarus, in press]). Observations made using HiRISE images suggest that scalloped depressions most likely form from small cracks in the mantle, which become larger and deeper through sublimation of interstitial ice from within the mantle. Sublimation is likely enhanced on equator-facing slopes because of increased solar insolation, which accounts for the asymmetric slope profile and hemispherical orientation and is demonstrated by THEMIS-IR images. We suggest that sublimation lag deposits can possibly be removed by dust devils or strong slope winds related to the Hellas Basin, offering an explanation as to why scalloped terrain is so abundant only in this area of the southern hemisphere. Daytime maximum summer temperatures suggest that sublimation in the study area of Malea Planum is possible under current conditions if the sublimation lag is removed. While it cannot be ruled out that scalloped terrain in Malea Planum is presently evolving, we attribute the extensive distribution to geologically recent obliquity excursions when conditions were more conducive to mesoscale modification of the ice-rich mantle.

Predicting Molecular Crystal Properties from First Principles: Finite-Temperature Thermochemistry to NMR Crystallography.

PubMed

Beran, Gregory J O; Hartman, Joshua D; Heit, Yonaton N

2016-11-15

Molecular crystals occur widely in pharmaceuticals, foods, explosives, organic semiconductors, and many other applications. Thanks to substantial progress in electronic structure modeling of molecular crystals, attention is now shifting from basic crystal structure prediction and lattice energy modeling toward the accurate prediction of experimentally observable properties at finite temperatures and pressures. This Account discusses how fragment-based electronic structure methods can be used to model a variety of experimentally relevant molecular crystal properties. First, it describes the coupling of fragment electronic structure models with quasi-harmonic techniques for modeling the thermal expansion of molecular crystals, and what effects this expansion has on thermochemical and mechanical properties. Excellent agreement with experiment is demonstrated for the molar volume, sublimation enthalpy, entropy, and free energy, and the bulk modulus of phase I carbon dioxide when large basis second-order Møller-Plesset perturbation theory (MP2) or coupled cluster theories (CCSD(T)) are used. In addition, physical insight is offered into how neglect of thermal expansion affects these properties. Zero-point vibrational motion leads to an appreciable expansion in the molar volume; in carbon dioxide, it accounts for around 30% of the overall volume expansion between the electronic structure energy minimum and the molar volume at the sublimation point. In addition, because thermal expansion typically weakens the intermolecular interactions, neglecting thermal expansion artificially stabilizes the solid and causes the sublimation enthalpy to be too large at higher temperatures. Thermal expansion also frequently weakens the lower-frequency lattice phonon modes; neglecting thermal expansion causes the entropy of sublimation to be overestimated. Interestingly, the sublimation free energy is less significantly affected by neglecting thermal expansion because the systematic errors in the enthalpy and entropy cancel somewhat. Second, because solid state nuclear magnetic resonance (NMR) plays an increasingly important role in molecular crystal studies, this Account discusses how fragment methods can be used to achieve higher-accuracy chemical shifts in molecular crystals. Whereas widely used plane wave density functional theory models are largely restricted to generalized gradient approximation (GGA) functionals like PBE in practice, fragment methods allow the routine use of hybrid density functionals with only modest increases in computational cost. In extensive molecular crystal benchmarks, hybrid functionals like PBE0 predict chemical shifts with 20-30% higher accuracy than GGAs, particularly for 1 H, 13 C, and 15 N nuclei. Due to their higher sensitivity to polarization effects, 17 O chemical shifts prove slightly harder to predict with fragment methods. Nevertheless, the fragment model results are still competitive with those from GIPAW. The improved accuracy achievable with fragment approaches and hybrid density functionals increases discrimination between different potential assignments of individual shifts or crystal structures, which is critical in NMR crystallography applications. This higher accuracy and greater discrimination are highlighted in application to the solid state NMR of different acetaminophen and testosterone crystal forms.

Tuning and Switching a Plasmonic Quantum Dot "Sandwich" in a Nematic Line Defect.

PubMed

Mundoor, Haridas; Sheetah, Ghadah H; Park, Sungoh; Ackerman, Paul J; Smalyukh, Ivan I; van de Lagemaat, Jao

2018-03-27

We study the quantum-mechanical effects arising in a single semiconductor core/shell quantum dot (QD) controllably sandwiched between two plasmonic nanorods. Control over the position and the "sandwich" confinement structure is achieved by the use of a linear-trap liquid crystal (LC) line defect and laser tweezers that "push" the sandwich together. This arrangement allows for the study of exciton-plasmon interactions in a single structure, unaltered by ensemble effects or the complexity of dielectric interfaces. We demonstrate the effect of plasmonic confinement on the photon antibunching behavior of the QD and its luminescence lifetime. The QD behaves as a single emitter when nanorods are far away from the QD but shows possible multiexciton emission and a significantly decreased lifetime when tightly confined in a plasmonic "sandwich". These findings demonstrate that LC defects, combined with laser tweezers, enable a versatile platform to study plasmonic coupling phenomena in a nanoscale laboratory, where all elements can be arranged almost at will.

Control of morphology and formation of highly geometrically confined magnetic skyrmions

PubMed Central

Jin, Chiming; Li, Zi-An; Kovács, András; Caron, Jan; Zheng, Fengshan; Rybakov, Filipp N.; Kiselev, Nikolai S.; Du, Haifeng; Blügel, Stefan; Tian, Mingliang; Zhang, Yuheng; Farle, Michael; Dunin-Borkowski, Rafal E

2017-01-01

The ability to controllably manipulate magnetic skyrmions, small magnetic whirls with particle-like properties, in nanostructured elements is a prerequisite for incorporating them into spintronic devices. Here, we use state-of-the-art electron holographic imaging to directly visualize the morphology and nucleation of magnetic skyrmions in a wedge-shaped FeGe nanostripe that has a width in the range of 45–150 nm. We find that geometrically-confined skyrmions are able to adopt a wide range of sizes and ellipticities in a nanostripe that are absent in both thin films and bulk materials and can be created from a helical magnetic state with a distorted edge twist in a simple and efficient manner. We perform a theoretical analysis based on a three-dimensional general model of isotropic chiral magnets to confirm our experimental results. The flexibility and ease of formation of geometrically confined magnetic skyrmions may help to optimize the design of skyrmion-based memory devices. PMID:28580935

Tuning and Switching a Plasmonic Quantum Dot “Sandwich” in a Nematic Line Defect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mundoor, Haridas; Sheetah, Ghadah H.; Park, Sungoh

We study the quantum-mechanical effects arising in a single semiconductor core/shell quantum dot (QD) controllably sandwiched between two plasmonic nanorods. Control over the position and the 'sandwich' confinement structure is achieved by the use of a linear-trap liquid crystal (LC) line defect and laser tweezers that 'push' the sandwich together. This arrangement allows for the study of exciton-plasmon interactions in a single structure, unaltered by ensemble effects or the complexity of dielectric interfaces. We demonstrate the effect of plasmonic confinement on the photon antibunching behavior of the QD and its luminescence lifetime. The QD behaves as a single emitter whenmore » nanorods are far away from the QD but shows possible multiexciton emission and a significantly decreased lifetime when tightly confined in a plasmonic 'sandwich'. These findings demonstrate that LC defects, combined with laser tweezers, enable a versatile platform to study plasmonic coupling phenomena in a nanoscale laboratory, where all elements can be arranged almost at will.« less

Tuning and Switching a Plasmonic Quantum Dot “Sandwich” in a Nematic Line Defect

DOE PAGES

Mundoor, Haridas; Sheetah, Ghadah H.; Park, Sungoh; ...

2018-02-28

We study the quantum-mechanical effects arising in a single semiconductor core/shell quantum dot (QD) controllably sandwiched between two plasmonic nanorods. Control over the position and the 'sandwich' confinement structure is achieved by the use of a linear-trap liquid crystal (LC) line defect and laser tweezers that 'push' the sandwich together. This arrangement allows for the study of exciton-plasmon interactions in a single structure, unaltered by ensemble effects or the complexity of dielectric interfaces. We demonstrate the effect of plasmonic confinement on the photon antibunching behavior of the QD and its luminescence lifetime. The QD behaves as a single emitter whenmore » nanorods are far away from the QD but shows possible multiexciton emission and a significantly decreased lifetime when tightly confined in a plasmonic 'sandwich'. These findings demonstrate that LC defects, combined with laser tweezers, enable a versatile platform to study plasmonic coupling phenomena in a nanoscale laboratory, where all elements can be arranged almost at will.« less

John H. Dillon Medal Talk: Polymer Droplets

NASA Astrophysics Data System (ADS)

Dalnoki-Veress, Kari

2008-03-01

The simplicity of a liquid droplet, say a dew drop on spider silk, is both esthetically beautiful and scientifically intriguing. The interplay of surface energies, thermal motion, and confinement of the liquid, especially on small length scales can reveal interesting physics. Droplets are an ideal confining geometry because the length scales can be easily controlled and it is possible to arrange the system such that each droplet acts as an independent experiment. The talk will focus on some recent examples where we have used the droplet geometry to learn about material properties. It will become apparent in the presentation that the deviations from the ``expected'' behaviour in confined systems are far from subtle!

Volume-confined synthesis of ligand-free gold nanoparticles with tailored sizes for enhanced catalytic activity

NASA Astrophysics Data System (ADS)

Shaik, Firdoz; Zhang, Weiqing; Niu, Wenxin; Lu, Xianmao

2014-10-01

Ligand-free Au nanoparticles with controlled sizes are synthesized via a volume-confined method. In this synthesis, mesoporous hollow silica shells (mHSS) are used as nano-containers for the impregnation of HAuCl4 solution before they are separated from the bulk solution. With a simple heating process, the Au precursor confined within the cavity of the isolated hollow shells is converted into ligand-free Au nanoparticles. The size of the Au nanoparticles can be tuned precisely by loading HAuCl4 solution of different concentrations, or by using mHSS with different cavity volumes. The ligand-free Au nanoparticles demonstrate superior catalytic activity than sodium citrate-capped Au nanoparticles.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, L.; Nazikian, Raffi; Grierson, B. A.

Here, Resonant Magnetic Perturbations (RMPs) are a leading method for edge localized modes (ELMs) Control in fusion plasmas. However they can also cause a rapid degradation in energy confinement. In this paper we show that the energy confinement in low collisionality (v* e < 0.3) DIII-D ITER Similar Shape (ISS) plasmas often recovers after several energy confinement times for RMP amplitudes up to the threshold for ELM suppression. Immediately following the application of the RMP, the plasma stored energy decreases in proportion to the decrease in the line-averaged density during density "pump-out". Later in the discharge confinement recovery is observedmore » in the thermal ion channel and is correlated with the increase in the ion temperature at the top of the H-mode pedestal. A correlation between the inverse scale length of the ion temperature (α/L Ti) and the E x B shearing rate at the top of the pedestal is seen during the confinement recovery phase. Transport analysis reveals that the confinement improvement in the ion channel results from the self-similarity in the ion temperature profiles in the plasma core combined with the observed increase in α/L Ti in the plasma edge following density pump-out. In contrast the electron temperature scale length (α/L Ti) remains essentially unchanged in response to the application of the RMP. At significantly higher RMP levels the edge EXB shearing rate and α/L Ti does not increase and the confinement does not recover following density pump-out.« less

Exciton-polariton trapping and potential landscape engineering

NASA Astrophysics Data System (ADS)

Schneider, C.; Winkler, K.; Fraser, M. D.; Kamp, M.; Yamamoto, Y.; Ostrovskaya, E. A.; Höfling, S.

2017-01-01

Exciton-polaritons in semiconductor microcavities have become a model system for the studies of dynamical Bose-Einstein condensation, macroscopic coherence, many-body effects, nonclassical states of light and matter, and possibly quantum phase transitions in a solid state. These low-mass bosonic quasiparticles can condense at comparatively high temperatures up to 300 K, and preserve the fundamental properties of the condensate, such as coherence in space and time domain, even when they are out of equilibrium with the environment. Although the presence of a confining potential is not strictly necessary in order to observe Bose-Einstein condensation, engineering of the polariton confinement is a key to controlling, shaping, and directing the flow of polaritons. Prototype polariton-based optoelectronic devices rely on ultrafast photon-like velocities and strong nonlinearities exhibited by polaritons, as well as on their tailored confinement. Nanotechnology provides several pathways to achieving polariton confinement, and the specific features and advantages of different methods are discussed in this review. Being hybrid exciton-photon quasiparticles, polaritons can be trapped via their excitonic as well as photonic component, which leads to a wide choice of highly complementary trapping techniques. Here, we highlight the almost free choice of the confinement strengths and trapping geometries that provide powerful means for control and manipulation of the polariton systems both in the semi-classical and quantum regimes. Furthermore, the possibilities to observe effects of the polariton blockade, Mott insulator physics, and population of higher-order energy bands in sophisticated lattice potentials are discussed. Observation of such effects could lead to realization of novel polaritonic non-classical light sources and quantum simulators.

Exercise thermoregulation with bed rest, confinement, and immersion deconditioning

NASA Technical Reports Server (NTRS)

Greenleaf, J. E.

1997-01-01

Altered thermoregulation following exposure to prolonged (12-14 days) of bed rest and 6 hr of head-down thermoneutral water immersion in humans, and cage confinement (8 weeks) in male, mongrel dogs resulted in occasional increased core temperature (Tcore) at rest, but consistent "excessive" increase in Tcore during submaximal exercise. This excessive increase in Tcore in nonexercising and exercising subjects was independent of the mode (isometric or isotonic) of exercise training during bed rest, and was associated with the consistent hypovolemia in men but not in women taking estrogen supplementation (1.25 mg premarin/ day) which restored plasma volume during bed rest to ambulatory control levels. Post-bed rest exercise sweating (evaporative heat loss) was unchanged or higher than control levels; however, calculated tissue heat conductance was significantly lower in men, and forearm venoconstriction was greater (venous volume was reduced) in women during exercise after bed rest. Because sweating appeared proportional to the increased level of Tcore, these findings suggest that one major factor for the excessive hyperthermia is decreased core to periphery heat conduction. Exercising dogs respond like humans with excessive increase in both rectal (Tre) and exercising muscle temperatures (Tmu) after confinement and, after eight weeks of exercise training on a treadmill following confinement, they had an attenuated rate of increase of Tre even below ambulatory control levels. Intravenous infusion of glucose also attenuated not only the rise in Tre during exercise in normal dogs, but also the excessive rise in Tre and exercising Tmu after confinement. Oral glucose also appeared to reduce the rate of increase in excessive Tre in men after immersion deconditioning. There was a greater rate of rise in Tcore in two cosmonauts during supine submaximal exercise (65% VO2 max) on the fifth recovery day after the 115-day Mir 18 mission. Thus, the excessive rise in core temperature after deconditioning appears to be caused by decreased peripheral vasodilation in humans. Factors related to glucose metabolism may influence this mechanism.

Fast Ion Transport Studies in DIII-D High βN Steady-State Scenarios

NASA Astrophysics Data System (ADS)

Holcomb, C. T.

2014-10-01

DIII-D research is identifying paths to optimize energetic particle (EP) transport in high βN steady-state tokamak scenarios. Operation with qmin > 2 is predicted to achieve high βN, confinement, and bootstrap fraction. However DIII-D experiments have shown that Alfvén eigenmodes (AE) and correlated EP transport can limit the performance of some qmin > 2 plasmas. Enhanced EP transport occurs in plasmas with qmin = 2-2.5, q95 = 5-7, and relatively long slowing down time. Strong AEs are present, the confinement factor H89 = 1.6-1.8 and βN is limited to ~3 by the available power. These observations are consistent with EP transport models having a critical gradient in βf. However, adjusting the parameters can recover classical EP confinement or improve thermal confinement so that H89 > 2 . One example is a scenario with βP and βN ~ 3 . 2 , qmin > 3 and q95 ~ 11 developed to test control of long pulse, high heat flux operation on devices like EAST. This has an internal transport barrier at ρ ~ 0 . 7 , bootstrap fraction >75%, density limit fraction ~1, and H89 >= 2 . In these cases AE activity and EP transport is very dynamic - it varies between classical and anomalous from shot to shot and within shots. Thus these plasmas are close to a threshold for enhanced EP transport. This may be governed by a combination of a relatively low ∇βfast due to good thermal confinement and lower beam power, short slowing down time, and possibly changes to the q-profile. Another example is scenarios with qmin ~ 1.1. These typically have classical EP confinement and good thermal confinement. Thus by using its flexible parameters and profile control tools DIII-D is comparing a wide range of steady-state scenarios to identify the key physics setting EP transport. Work supported by the US Department of Energy under DE-AC52-07NA27344, SC-G903402, DE-FC02-04ER54698, and DE-AC02-09CH11466.

The embodiment design of the heat rejection system for the portable life support system

NASA Technical Reports Server (NTRS)

Stuckwisch, Sue; Francois, Jason; Laughlin, Julia; Phillips, Lee; Carrion, Carlos A.

1994-01-01

The Portable Life Support System (PLSS) provides a suitable environment for the astronaut in the Extravehicular Mobility Unit (EMU), and the heat rejection system controls the thermal conditions in the space suit. The current PLSS sublimates water to the space environment; therefore, the system loses mass. Since additional supplies of fluid must be available on the Space Shuttle, NASA desires a closed heat rejecting system. This document presents the embodiment design for a radiative plate heat rejection system without mass transfer to the space environment. This project will transform the concept variant into a design complete with material selection, dimensions of the system, layouts of the heat rejection system, suggestions for manufacturing, and financial viability.

A Sublimation Model for the Martian Polar Swiss-Cheese Features. Observational and Modeling Studies of the South Polar Residual Cap

NASA Technical Reports Server (NTRS)

Byrne, Shane; Ingersoll, Andrew P.

2002-01-01

In their pioneering work Leighton and Murray argued that the Mars atmosphere, which is 95 percent CO2 today, is controlled by vapor equilibrium with a much larger polar reservoir of solid CO2. Here we argue that the polar reservoir is small and cannot function as a long-term buffer to the more massive atmosphere. Our work is based on modeling the circular depressions (Swiss-cheese features) in the south polar cap. We argue that a solid CO2 layer approximately 8 meters thick is being etched away to reveal water ice underneath. Preliminary results from the THEMIS (Thermal Emission Imaging System) instrument seem to confirm our model.

Russell Crater Dunes, Defrosted

NASA Image and Video Library

2010-10-27

The Russell Crater dune field is covered seasonally by carbon dioxide frost; this image from NASA Mars Reconnaissance Orbiter shows the dune field after the frost has sublimated. There are just a few patches left of the bright seasonal frost.

Adavanced RTG and thermoelectric materials study

NASA Technical Reports Server (NTRS)

Eggers, P. E.

1971-01-01

A comprehensive, generalized two-dimensional RTG analysis computer program was developed. This program is capable of analyzing any specified RTG design under a wide range of transient as well as steady-state operating conditions. The feasibility of a new concept for the design of segmented (or single-phase) thermoelectric couples was demonstrated. A SiGe-PbTe segmented couple involving pressure contacted junctions at the intermediate- and hot-junction temperatures was successfully encapsulated in a hermetically sealed bellows enclosure. This bellows-encapsulated couple was operated between a hot- and cold-junction temperature of 1200 K and 450 K, respectively, with a measured energy conversion efficiency of 7.6 + or - .5 per cent. An experimental study of selected sublimation barrier schemes revealed that a significant reduction in the sublimation rate of p-type PbTe could be achieved by using multiple layers of SiO2 fibers. A comparison of the barrier effectiveness is given for three different barrier designs.

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.

Rosetta's comet 67P/Churyumov-Gerasimenko sheds its dusty mantle to reveal its icy nature.

PubMed

Fornasier, S; Mottola, S; Keller, H U; Barucci, M A; Davidsson, B; Feller, C; Deshapriya, J D P; Sierks, H; Barbieri, C; Lamy, P L; Rodrigo, R; Koschny, D; Rickman, H; A'Hearn, M; Agarwal, J; Bertaux, J-L; Bertini, I; Besse, S; Cremonese, G; Da Deppo, V; Debei, S; De Cecco, M; Deller, J; El-Maarry, M R; Fulle, M; Groussin, O; Gutierrez, P J; Güttler, C; Hofmann, M; Hviid, S F; Ip, W-H; Jorda, L; Knollenberg, J; Kovacs, G; Kramm, R; Kührt, E; Küppers, M; Lara, M L; Lazzarin, M; Moreno, J J Lopez; Marzari, F; Massironi, M; Naletto, G; Oklay, N; Pajola, M; Pommerol, A; Preusker, F; Scholten, F; Shi, X; Thomas, N; Toth, I; Tubiana, C; Vincent, J-B

2016-12-23

The Rosetta spacecraft has investigated comet 67P/Churyumov-Gerasimenko from large heliocentric distances to its perihelion passage and beyond. We trace the seasonal and diurnal evolution of the colors of the 67P nucleus, finding changes driven by sublimation and recondensation of water ice. The whole nucleus became relatively bluer near perihelion, as increasing activity removed the surface dust, implying that water ice is widespread underneath the surface. We identified large (1500 square meters) ice-rich patches appearing and then vanishing in about 10 days, indicating small-scale heterogeneities on the nucleus. Thin frosts sublimating in a few minutes are observed close to receding shadows, and rapid variations in color are seen on extended areas close to the terminator. These cyclic processes are widespread and lead to continuously, slightly varying surface properties. Copyright © 2016, American Association for the Advancement of Science.

Carbon Dioxide Landforms

NASA Technical Reports Server (NTRS)

2004-01-01

19 March 2004 The martian south polar residual ice cap is mostly made of frozen carbon dioxide. There is no place on Earth that a person can go to see the landforms that would be produced by erosion and sublimation of hundreds or thousands of cubic kilometers of carbon dioxide. Thus, the south polar cap of Mars is as alien as alien can get. This image, acquired in February 2004 by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), shows how the cap appears in summer as carbon dioxide is subliming away, creating a wild pattern of pits, mesas, and buttes. Darker surfaces may be areas where the ice contains impurities, such as dust, or where the surface has been roughened by the removal of ice. This image is located near 86.3oS, 0.8oW. This picture covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the top/upper left.

Beer Law Constants and Vapor Pressures of HgI2 over HgI2(s,l)

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Zhu, Shen; Ramachandran, N.; Burger, A.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

The optical absorption spectra of the vapor phase over HgI2(s,l) were measured for wavelengths between 200 and 600 nm. The spectra show that the sample sublimed congruently into HgI2 with no Hg or I2 absorption spectrum observed. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were determined. From these constants the vapor pressure of H912, P, was established as a function of temperatures for the liquid and the solid Beta-phases. The expressions correspond to the enthalpies of vaporization and sublimation of 15.30 and 20.17 Kcal/mole, respectively, for the liquid and the Beta-phase HgI2. The difference in the enthalpies gives an enthalpy of fusion of 4.87 Kcal/mole and the intersection of the two expressions gives a melting point of 537 K.

Summer South Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

13 April 2004 The martian south polar residual ice cap is composed mainly of frozen carbon dioxide. Each summer, a little bit of this carbon dioxide sublimes away. Pits grow larger, and mesas get smaller, as this process continues from year to year. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a view of a small portion of the south polar cap as it appeared in mid-summer in January 2004. The dark areas may be places where the frozen carbon dioxide contains impurities, such as dust, or places where sublimation of ice has roughened the surface so that it appears darker because of small shadows cast by irregularities in the roughened surface. The image is located near 86.9oS, 7.6oW. The image covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left.

Callisto: A World in its Own Right

NASA Technical Reports Server (NTRS)

Moore, Jeffrey M.; Schenk, Paul M.

2003-01-01

Callisto, once unknown and then disregarded after Voyager, has emerged in the post-Galileo era worthy of the same intense scientific scrutiny that is lavished upon her sisters, playing an essential role in our understanding of the evolution of icy moons, and in a larger sense, the grand tapestry of solar system history. Along with the discovery of Callisto s con- ducting, probably fluid sub-surface layer, major Gulileo discoveries about Callisto include the complete absence of cryo-volcanic resurfacing, the relatively undifferentiated interior, and the presence of massive landform erosion from sublimation processes. Callisto s landscape at decameter scales is unique among the Galilean satellites, and might be most akin to that of cometary nuclei. The process of sublimation degradation, previously underappreciated, is now recognized as a major surface modification process on Callisto. Its role in mass wasting and landslide initiation was elemental in creating the bizarre and astonishing scenery imaged by Galileo.

Tricyanomethane and Its Ketenimine Tautomer: Generation from Different Precursors and Analysis in Solution, Argon Matrix, and as a Single Crystal.

PubMed

Banert, Klaus; Chityala, Madhu; Hagedorn, Manfred; Beckers, Helmut; Stüker, Tony; Riedel, Sebastian; Rüffer, Tobias; Lang, Heinrich

2017-08-01

Solutions of azidomethylidenemalononitrile were photolyzed at low temperatures to produce the corresponding 2H-azirine and tricyanomethane, which were analyzed by low-temperature NMR spectroscopy. The latter product was also observed after short thermolysis of the azide precursor in solution whereas irradiation of the azide isolated in an argon matrix did not lead to tricyanomethane, but to unequivocal detection of the tautomeric ketenimine by IR spectroscopy for the first time. When the long-known "aquoethereal" greenish phase generated from potassium tricyanomethanide, dilute sulfuric acid, and diethyl ether was rapidly evaporated and sublimed, a mixture of hydronium tricyanomethanide and tricyanomethane was formed instead of the previously claimed ketenimine tautomer. Under special conditions of sublimation, single crystals of tricyanomethane could be isolated, which enabled the analysis of the molecular structure by X-ray diffraction. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2015. Part 1. C{sub 1} − C{sub 10}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Acree, William; Chickos, James S.

2016-09-15

A compendium of phase change enthalpies published in 2010 is updated to include the period 1880–2015. Phase change enthalpies including fusion, vaporization, and sublimation enthalpies are included for organic, organometallic, and a few inorganic compounds. Part 1 of this compendium includes organic compounds from C{sub 1} to C{sub 10}. Part 2 of this compendium, to be published separately, will include organic and organometallic compounds from C{sub 11} to C{sub 192}. Sufficient data are presently available to permit thermodynamic cycles to be constructed as an independent means of evaluating the reliability of the data. Temperature adjustments of phase change enthalpies frommore » the temperature of measurement to the standard reference temperature, T = 298.15 K, and a protocol for doing so are briefly discussed.« less

Experimental and computational investigation of the thermochemistry of the six isomers of dichloroaniline.

PubMed

Ribeiro da Silva, Manuel A V; Amaral, Luísa M P F; Gomes, José R B

2006-07-27

The standard (p(o) = 0.1 MPa) molar enthalpies of formation of 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-dichloroanilines were derived from the standard molar energies of combustion, in oxygen, to yield CO(2)(g), N(2)(g) and HCl.600H(2)O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The Calvet high-temperature vacuum sublimation technique was used to measure the enthalpies of sublimation of the six isomers. These two thermodynamic parameters yielded the standard molar enthalpies of formation of the six isomers of dichloroaniline, in the gaseous phase, at T = 298.15 K. The gas-phase enthalpies of formation were also estimated by G3MP2B3 calculations, which were further extended to the computation of gas-phase acidities, proton affinities, and ionization enthalpies.

Macroparticle generation in DC arc discharge from a WC cathode

NASA Astrophysics Data System (ADS)

Zhirkov, Igor; Polcik, Peter; Kolozsvári, Szilard; Rosen, Johanna

2017-03-01

We have studied macroparticle generation from a tungsten carbide cathode used in a dc vacuum arc discharge. Despite a relatively high decomposition/melting point (˜3100 K), there is an intensive generation of visible particles with sizes in the range 20-35 μm. Visual observations during the discharge and scanning electron microscopy of the cathode surface and of collected macroparticles indicate a new mechanism for particle formation and acceleration. Based on the W-C phase diagram, there is an intensive sublimation of carbon from the melt resulting from the cathode spot. The sublimation supports the formation of a sphere, which is accelerated upon an explosion initiated by Joule heating at the critical contact area between the sphere and the cathode body. The explosive nature of the particle acceleration is confirmed by surface features resembling the remains of a splash on the droplet surface.

The physical and infrared spectral properties of CO2 in astrophysical ice analogs

NASA Technical Reports Server (NTRS)

Sandford, S. A.; Allamandola, L. J.

1990-01-01

Results of measurements of the infrared spectroscopic and condensation-vaporization properties of CO2 in pure and mixed ices are presented. Detailed examination of five infrared CO2 bands, 2.20, 2.78, 4.27, 15.2, and 4.39 microns, shows that the peak position, FWHM, and profile of the bands provide important information about the composition, formation, and subsequent thermal history of the ices. Absorption coefficients and their temperature dependence for all five CO2 bands are determined. The temperature dependence variation is found to be less than 15 percent from 10 to 150 K, i.e., the temperature at which H2O ice sublimes. The number of parameters associated with the physical behavior of CO2 in CO2- and H2O-rich ices, including surface binding energies, and condensation and sublimation temperatures, are determined under experimental conditions. The implications of the data obtained for cometary models are considered.

Theoretical studies of volatile processes in the outer solar system

NASA Technical Reports Server (NTRS)

Lunine, Jonathan I.

1991-01-01

Four studies of volatile processes in the outer solar system are discussed. Researchers suggest that the convective and conductive regions of Triton's atmosphere join at the tropopause near 10 km. A model of volatile transport on Triton's surface was constructed that predicts that Triton's surface north of 15 degrees north latitude is experiencing deposition of nitrogen frosts, as are the bright portions of the south polar cap near the equator. Also discussed are numerical models of the evolution of Titan's surface and atmosphere. Results of a study of the rheology of ammonia-water liquids were applied to the icy satellites of the outer solar system. Finally, the researchers examined the frictional heating, sublimation, and re-condensation of grains free-falling into the solar nebula from a surrounding interstellar cloud. The sublimation model includes the effect of various volatile species and accounts for the poor radiating properties of small grains using Mie theory.

Frosty Wind Streaks

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-532, 2 November 2003

As seasonal polar frosts sublime away each spring, winds may re-distribute some of the frost or move sediment exposed from beneath the frost. This action creates ephemeral wind streaks that can be used by scientists seeking to study the local circulation of the martian [missing text] surveyor (MGS) Mars Orbiter Camera (MOC) image shows a suite of wind streaks created in subliming carbon dioxide frost. These dark streaks appear to conform to the shape of the slopes on which they occur, suggesting that slope winds play a dominant role in creating and orienting these streaks. This picture is located near 73.8oS, 305.7oW. The image is illuminated by sunlight from the upper left and covers an area 3 km (1.9 mi) wide. Winds responsible for the streaks generally blew from the bottom/right (south/southeast) toward the top/upper left (north/northwest).

Sublimation behavior of silicon nitride /Si3N4/ coated silicon germanium /SiGe/ unicouples. [for Radioisotope Thermoelectric Generators

NASA Technical Reports Server (NTRS)

Stapfer, G.; Truscello, V. C.

1975-01-01

For the Multi-Hundred Watt (MHW) Radioisotope Thermoelectric Generator (RTG), the silicon germanium unicouples are coated with silicon nitride to minimize degradation mechanisms which are directly attributable to material sublimation effects. A program is under way to determine the effective vapor suppression of this coating as a function of temperature and gas environment. The results of weight loss experiments, using Si3N4 coated hot shoes (SiMo), operating over a temperature range from 900 C to 1200 C, are analyzed and discussed. These experiments were conducted both in high vacuum and at different pressures of carbon monoxide (CO) to determine its effect on the coating. Although the results show a favorable vapor suppression at all operating temperatures, the pressure of the CO and the thickness of the coating have a decided effect on the useful lifetime of the coating.

Phase-controlled synthesis of α-NiS nanoparticles confined in carbon nanorods for High Performance Supercapacitors

NASA Astrophysics Data System (ADS)

Sun, Chencheng; Ma, Mingze; Yang, Jun; Zhang, Yufei; Chen, Peng; Huang, Wei; Dong, Xiaochen

2014-11-01

A facile and phase-controlled synthesis of α-NiS nanoparticles (NPs) embedded in carbon nanorods (CRs) is reported by in-situ sulfurating the preformed Ni/CRs. The nanopore confinement by the carbon matrix is essential for the formation of α-NiS and preventing its transition to β-phase, which is in strong contrast to large aggregated β-NiS particles grown freely without the confinement of CRs. When used as electrochemical electrode, the hybrid electrochemical charge storage of the ultrasmall α-NiS nanoparticels dispersed in CRs is benefit for the high capacitor (1092, 946, 835, 740 F g-1 at current densities of 1, 2, 5, 10 A g-1, respectively.). While the high electrochemical stability (approximately 100% retention of specific capacitance after 2000 charge/discharge cycles) is attributed to the supercapacitor-battery electrode, which makes synergistic effect of capacitor (CRs) and battery (NiS NPs) components rather than a merely additive composite. This work not only suggests a general approach for phase-controlled synthesis of nickel sulfide but also opens the door to the rational design and fabrication of novel nickel-based/carbon hybrid supercapacitor-battery electrode materials.

Phase-controlled synthesis of α-NiS nanoparticles confined in carbon nanorods for high performance supercapacitors.

PubMed

Sun, Chencheng; Ma, Mingze; Yang, Jun; Zhang, Yufei; Chen, Peng; Huang, Wei; Dong, Xiaochen

2014-11-14

A facile and phase-controlled synthesis of α-NiS nanoparticles (NPs) embedded in carbon nanorods (CRs) is reported by in-situ sulfurating the preformed Ni/CRs. The nanopore confinement by the carbon matrix is essential for the formation of α-NiS and preventing its transition to β-phase, which is in strong contrast to large aggregated β-NiS particles grown freely without the confinement of CRs. When used as electrochemical electrode, the hybrid electrochemical charge storage of the ultrasmall α-NiS nanoparticels dispersed in CRs is benefit for the high capacitor (1092, 946, 835, 740 F g(-1) at current densities of 1, 2, 5, 10 A g(-1), respectively.). While the high electrochemical stability (approximately 100% retention of specific capacitance after 2000 charge/discharge cycles) is attributed to the supercapacitor-battery electrode, which makes synergistic effect of capacitor (CRs) and battery (NiS NPs) components rather than a merely additive composite. This work not only suggests a general approach for phase-controlled synthesis of nickel sulfide but also opens the door to the rational design and fabrication of novel nickel-based/carbon hybrid supercapacitor-battery electrode materials.

Phase-controlled synthesis of α-NiS nanoparticles confined in carbon nanorods for High Performance Supercapacitors

PubMed Central

Sun, Chencheng; Ma, Mingze; Yang, Jun; Zhang, Yufei; Chen, Peng; Huang, Wei; Dong, Xiaochen

2014-01-01

A facile and phase-controlled synthesis of α-NiS nanoparticles (NPs) embedded in carbon nanorods (CRs) is reported by in-situ sulfurating the preformed Ni/CRs. The nanopore confinement by the carbon matrix is essential for the formation of α-NiS and preventing its transition to β-phase, which is in strong contrast to large aggregated β-NiS particles grown freely without the confinement of CRs. When used as electrochemical electrode, the hybrid electrochemical charge storage of the ultrasmall α-NiS nanoparticels dispersed in CRs is benefit for the high capacitor (1092, 946, 835, 740 F g−1 at current densities of 1, 2, 5, 10 A g−1, respectively.). While the high electrochemical stability (approximately 100% retention of specific capacitance after 2000 charge/discharge cycles) is attributed to the supercapacitor-battery electrode, which makes synergistic effect of capacitor (CRs) and battery (NiS NPs) components rather than a merely additive composite. This work not only suggests a general approach for phase-controlled synthesis of nickel sulfide but also opens the door to the rational design and fabrication of novel nickel-based/carbon hybrid supercapacitor-battery electrode materials. PMID:25394517

Geometric control of capillary architecture via cell-matrix mechanical interactions.

PubMed

Sun, Jian; Jamilpour, Nima; Wang, Fei-Yue; Wong, Pak Kin

2014-03-01

Capillary morphogenesis is a multistage, multicellular activity that plays a pivotal role in various developmental and pathological situations. In-depth understanding of the regulatory mechanism along with the capability of controlling the morphogenic process will have direct implications on tissue engineering and therapeutic angiogenesis. Extensive research has been devoted to elucidate the biochemical factors that regulate capillary morphogenesis. The roles of geometric confinement and cell-matrix mechanical interactions on the capillary architecture, nevertheless, remain largely unknown. Here, we show geometric control of endothelial network topology by creating physical confinements with microfabricated fences and wells. Decreasing the thickness of the matrix also results in comparable modulation of the network architecture, supporting the boundary effect is mediated mechanically. The regulatory role of cell-matrix mechanical interaction on the network topology is further supported by alternating the matrix stiffness by a cell-inert PEG-dextran hydrogel. Furthermore, reducing the cell traction force with a Rho-associated protein kinase inhibitor diminishes the boundary effect. Computational biomechanical analysis delineates the relationship between geometric confinement and cell-matrix mechanical interaction. Collectively, these results reveal a mechanoregulation scheme of endothelial cells to regulate the capillary network architecture via cell-matrix mechanical interactions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Manipulating Energetic Ion Velocity Space to Control Instabilities and Improve Tokamak Performance

NASA Astrophysics Data System (ADS)

Pace, David C.

2017-10-01

The first-ever demonstration of independent current (I) and voltage (V) control of high power neutral beams in tokamak plasma shots has successfully reduced the prevalence of instabilities and improved energetic ion confinement in experiments at the DIII-D tokamak. Energetic ions drive Alfvén eigenmode (AE) instabilities through a resonant energy exchange that can increase radial diffusion of the ions, thereby reducing beam heating and current drive efficiency. This resonance is incredibly sensitive to the ion velocity and orbit topology, which then allows changes in beam voltage (keeping the injected power constant through compensating changes in current) to remove nearly all instability drive. The implementation of temporal control of beam current and voltage allows for a reduction in the resonant energetic ion velocity space while maintaining the ability to inject maximum power. DIII-D low confinement (L-mode) plasmas demonstrate a nearly complete avoidance of AE activity in plasmas with 55 kV beam injection compared to the many AEs that are observed in plasmas featuring similar total beam power at 70 kV. Across the experimental range of beam settings, resulting increases in beam divergence have been inconsequential. High performance steady-state scenarios featuring equilibria that are conducive to dense arrays of Alfvén waves benefit the most from instability control mechanisms. One such scenario, the so-called high qmin scenario, demonstrates improved confinement and equilibrium evolution when the injected beam voltage begins at lower values (i.e., fewer resonances) and then increases as the plasma reaches its stationary period. These results suggest a future in which plasma confinement and performance is improved through continuous feedback control of auxiliary heating systems such that the energetic ion distribution is constantly adapted to produce an optimal plasma state. Work supported by US DOE under DE-FC02-04ER54698.