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At least 343 records · Page 19Linked to original sources
PubMed2003

MORICE--new technology for mechanical oil recovery in ice infested waters.

Mechanical oil recovery in ice infested waters (MORICE) was initiated in 1995 to develop technology for the recovery of oil spills in ice. It has been a multinational effort involving Norwegian, Canadian, American and German organizations and researchers. Through a stepwise approach with the development organized in six separate phases, laboratory tests and field experiments have been conducted to study various ideas and concepts, and to refine the ideas that were considered to have the best potential for removing oil in ice. Put together in one unit, these concepts included ice processing equipment and two alternative oil recovery units installed on a work platform. In January 2002, the final oil and ice testing with MORICE concepts was conducted at the Ohmsett test facility in Leonardo, New Jersey. The unit has been referred to as a harbor version to indicate the size and operating conditions, but the concepts could be scaled up to increase the capacity of oil and ice processing. For heavier ice conditions it would also be necessary to increase the overall strength.

Accidents↗
PubMed1997

Sea-ice production and transport of pollutants in the Laptev Sea, 1979-1993.

Pollutants such as radionuclides can be incorporated into ice formed in shallow waters of the marginal seas, by suspension freezing, including frazil- and anchor-ice formation. This ice thickens through the winter and can survive the summer melt to eventually be pushed into the perennial ice zone and thus be transported long distances. After a few years, when the ice finally melts, these radionuclides can be re-released in biologically rich waters. We estimate that a mean of 256,000 km2 of sea ice is produced annually in the shallow water area of the Laptev Sea during the October freeze-up and in the flaw lead during winter, accounting for approx. 20% of the total ice area fluxing through the Fram Strait per year.

Arctic Regions↗
PubMed1997

The determination of ice composition with instruments on cometary landers.

The determination of the composition of materials that make up comets is essential in trying to understand the origin of these primitive objects. The ices especially could be made in several different astrophysical settings including the solar nebula, protosatellite nebulae of the giant planets, and giant molecular clouds that predate the formation of the solar system. Each of these environments makes different ices with different composition. In order to understand the origin of comets, one needs to determine the composition of each of the ice phases. For example, it is of interest to know that comets contain carbon monoxide, CO, but it is much more important to know how much of it is a pure solid phase, is trapped in clathrate hydrates, or is adsorbed on amorphous water ice. In addition, knowledge of the isotopic composition of the constituents will help determine the process that formed the compounds. Finally, it is important to understand the bulk elemental composition of the nucleus. When these data are compared with solar abundances, they put strong constraints on the macro-scale processes that formed the comet. A differential scanning calorimeter (DSC) and an evolved gas analyzer (EGA) will make the necessary association between molecular constituents and their host phases. This combination of instruments takes a small (tens of mg) sample of the comet and slowly heats it in a sealed oven. As the temperature is raised, the DSC precisely measures the heat required, and delivers the gases to the EGA. Changes in the heat required to raise the temperature at a controlled rate are used to identify phase transitions, e.g., crystallization of amorphous ice or melting of hexagonal ice, and the EGA correlates the gases released with the phase transition. The EGA consists of two mass spectrometers run in tandem. The first mass spectrometer is a magnetic-sector ion-momentum analyzer (MAG), and the second is an electrostatic time-of-flight analyzer (TOF). The TOF acts as a detector for the MAG and serves to resolve ambiguities between fragments of similar mass such as CO and N2. Because most of the compounds of interest for the volatile ices are simple, a gas chromatograph is not needed and thus more integration time is available to determine isotopic ratios. A gamma-ray spectrometer (GRS) will determine the elemental abundances of the bulk cometary material by determining the flux of gamma rays produced from the interaction of the cometary material with cosmic ray produced neutrons. Because the gamma rays can penetrate a distance of several tens of centimeters a large volume of material is analyzed. The measured composition is, therefore, much more likely to be representative of the bulk comet than a very small sample that might have lost some of its volatiles. Making these measurements on a lander offers substantial advantages over trying to address similar objectives from an orbiter. For example, an orbiter instrument can determine the presence and isotopic composition of CO in the cometary coma, but only a lander can determine the phase(s) in which the CO is located and separately determine the isotopic composition of each reservoir of CO. The bulk composition of the nucleus might be constrained from separate orbiter analyses of dust and gas in the coma, but the result will be very model dependent, as the ratio of gas to dust in the comet will vary and will not necessarily be equal to the bulk value.

Ammonia↗
PubMed2000

The ice test versus the rest test in myasthenia gravis.

OBJECTIVE: To compare the ice test with the rest test in subjects with myasthenic and nonmyasthenic ptosis. DESIGN: Randomized, noninterventional trial. PARTICIPANTS: (1) Ten subjects with ptosis from previously undiagnosed myasthenia gravis. (2) Fifteen subjects with nonmyasthenic ptosis. METHODS: Application of ice compared with rest. MAIN OUTCOME MEASURES: Improvement in eyelid elevation in millimeters after the application of a surgical glove filled with ice or cotton. RESULTS: In myasthenic subjects, the median improvement of ptosis with the rest test was 2 mm and with the ice test was 4.5 mm. The difference between the rest and ice tests is significant (P: < 0.001). There was no improvement in ptosis in nonmyasthenic subjects with either test. CONCLUSION: In myasthenic ptosis, improvement in eyelid elevation after the ice test is in part caused by rest. The ice test significantly improves ptosis more than rest alone does.

Adolescent↗
PubMed2000

Low-dose irradiation as a measure to improve microbial quality of ice cream.

The present study was undertaken to investigate the efficacy of low-dose irradiation to improve the microbial safety of ice cream. Initially three different flavors (vanilla, strawberry and chocolate) of ice cream were exposed, at -72 degrees C, to doses of 1, 2, 5, 10 and 30 kGy to gamma-radiation. Irradiation at 1 kGy resulted in reduction of microbial population by one log cycle, thus meeting the requirement limits prescribed by Bureau of Indian Standards. Pathogens such as Listeria monocytogenes 036, Yersinia enterocoliticta 5692 and Escherichia coli O157:H19, respectively, showed the D10 values 0.38, 0.15 and 0.2 kGy in ice cream at -72 degrees C suggesting the efficacy of low doses (1 kGy) in eliminating them. Sensory evaluation studies of ice cream irradiated at 1, 2, 3 and 5 kGy by a 15 member panel demonstrated that doses higher than 2 kGy irradiation induced off-odour and an aftertaste was evident in vanilla ice cream. A radiation dose of 1 kGy was sufficient to eliminate the natural number of pathogens present in the ice cream. No statistically significant differences were observed in the sensory attributes of all the three flavours of ice cream either unirradiated or exposed to 1 kGy (P < 0.05).

Colony Count, Microbial↗
PubMed1999

The effectiveness of ice as a topical anesthetic for the insertion of intravenous catheters.

In a paired clinical trial, the effectiveness of ice in reducing the pain of intravenous catheter placement was assessed in 28 adult volunteers. An ice pack was placed over one arm for 10 minutes, followed by insertion of an 18-gauge angiocatheter in both arms. Patients recorded their pain assessment after each venipuncture on a previously validated 100-mm visual analog scale (VAS) and identified their preferred method for the procedure (pretreatment with ice or no pretreatment). The mean pain score for catheter placement on arms pretreated with ice was 27.5+/-15.9 mm; the mean pain score for the control arms was 34.2+/-21.6 mm (P = .17). Most patients (61%) preferred no pretreatment (P = .014). Although most men (75%) preferred no pretreatment, 75% of women preferred pretreatment with ice (P = .014). Future studies should examine whether ice is effective at reducing pain from other more painful procedures and whether the response to ice is gender-related.

Administration, Topical↗
PubMed2002

Influence of ice and snow covers on the UV exposure of terrestrial microbial communities: dosimetric studies.

Bacillus subtilis spore biological dosimeters and electronic dosimeters were used to investigate the exposure of terrestrial microbial communities in micro-habitats covered by snow and ice in Antarctica. The melting of snow covers of between 5- and 15-cm thickness, depending on age and heterogeneity, could increase B. subtilis spore inactivation by up to an order of magnitude, a relative increase twice that caused by a 50% ozone depletion. Within the snow-pack at depths of less than approximately 3 cm snow algae could receive two to three times the DNA-weighted irradiance they would receive on bare ground. At the edge of the snow-pack, warming of low albedo soils resulted in the formation of overhangs that provided transient UV protection to thawed and growing microbial communities on the soils underneath. In shallow aquatic habitats, thin layers of heterogeneous ice of a few millimetres thickness were found to reduce DNA-weighted irradiances by up to 55% compared to full-sky values with equivalent DNA-weighted diffuse attenuation coefficients (K(DNA)) of >200 m(-1). A 2-mm snow-encrusted ice cover on a pond was equivalent to 10 cm of ice on a perennially ice covered lake. Ice covers also had the effect of stabilizing the UV exposure, which was often subject to rapid variations of up to 33% of the mean value caused by wind-rippling of the water surface. These data show that changing ice and snow covers cause relative changes in microbial UV exposure at least as great as those caused by changing ozone column abundance.

Antarctic Regions↗
PubMed2001

Mid- and far-infrared spectroscopic studies of the influence of temperature, ultraviolet photolysis and ion irradiation on cosmic-type ices.

Infrared (IR) studies of laboratory ices can provide information on the evolution of cosmic-type ices as a function of different simulated space environments involving thermal, ultraviolet (UV), or ion processing. Laboratory radiation experiments can lead to the formation of complex organic molecules. However, because of our lack of knowledge about UV photon and ion fluxes, and exposure lifetimes, it is not certain how well our simulations represent space conditions. Appropriate laboratory experiments are also limited by the absence of knowledge about the composition, density, and temperature of ices in different regions of space. Our current understanding of expected doses due to UV photons and cosmic rays is summarized here, along with an inventory of condensed-phase molecules identified on outer solar system surfaces, comets and interstellar grains. Far-IR spectra of thermally cycled H2O are discussed since these results reflect the dramatic difference between the amorphous and crystalline phases of H2O ice, the most dominant condensed-phase molecule in cosmic ices. A comparison of mid-IR spectra of products in proton-irradiated and UV-photolyzed ices shows that few differences are observed for these two forms of processing for the simple binary mixtures studied to date. IR identification of radiation products and experiments to determine production rates of new molecules in ices during processing are discussed. A new technique for measuring intrinsic IR band strengths of several unstable molecules is presented. An example of our laboratory results applied to Europa observations is included.

Carbonic Acid↗
PubMed1998

Soil temperatures and stability of ice-cemented ground in the McMurdo Dry Valleys, Antarctica.

Year-round temperature measurements at 1600 m elevation during 1994 in the Asgard Range Antarctica, indicate that the mean annual frost point of the ice-cemented ground, 25 cm below the surface, is -21.7 +/- 0.2 degrees C and the mean annual frost point of the atmosphere is -27.5 +/- 1.0 degrees C. The corresponding mean annual temperatures are -24.9 degrees C and -23.3 degrees C. These results imply that there is a net flux of water vapour from the ice to the atmosphere resulting in a recession of the ice-cemented ground by about 0.4-0.6 mm yr-1. The level of the ice-cemented permafrost is about 12 cm below the level of dry permafrost. The summer air temperatures would have to increase about 7 degrees C for thawing temperatures to just reach the top of the subsurface ice. Either subsurface ice at this location is evaporating over time or there are sporadic processes that recharge the ice and maintain equilibrium over long timescales.

Antarctic Regions↗
PubMed2005

Stability of two-dimensional tessellation ice on the hydroxylated beta-cristobalite (100) surface.

Monolayer adsorbed water on the beta-cristobalite (100) surface is studied via classical molecular dynamics simulations. The ordered two-dimensional (2D) tessellation ice structure (i.e., the four-membered and the eight-membered rings appear alternatively) is justified at low temperatures in the simulations. The stability of this possible new ice phase is further investigated by heating the system from 5 to 300 K. An order-disorder structural transition is observed between 100 and 200 K, featuring the melting process of the tessellation ice. This process is characterized by the water oxygen-oxygen radial distribution function, the coordination number, the distance vector between the center of mass of the oxygen and the hydrogen atoms in water, the mean square displacement of oxygen in water, and the vibrational density of state. The above techniques show consistency on that the order-disorder transition temperature of the 2D tessellation ice is far below 300 K. The 2D tessellation ice structure is also obtained via density functional calculations with different generalized gradient approximations. By comparing the calculated adsorption and the lateral energies between different methods, we find that the melting temperature of the specific 2D ice structure is strongly method dependent. Therefore, further experimental works are urged to justify this possible new ice phase and probe its stability.

Computer Simulation↗
PubMed2000

Thickness of tropical ice and photosynthesis on a snowball Earth.

On a completely ice-covered "snowball" Earth the thickness of ice in the tropical regions would be limited by the sunlight penetrating into the ice cover and by the latent heat flux generated by freezing at the ice bottom--the freezing rate would balance the sublimation rate from the top of the ice cover. Heat transfer models of the perennially ice-covered Antarctic dry valley lakes applied to the snowball Earth indicate that the tropical ice cover would have a thickness of 10 m or less with a corresponding transmissivity of > 0.1%. This light level is adequate for photosynthesis and could explain the survival of the eukaryotic algae.

Antarctic Regions↗
PubMed2000

Ocean circulation off east Antarctica affects ecosystem structure and sea-ice extent.

Sea ice and oceanic boundaries have a dominant effect in structuring Antarctic marine ecosystems. Satellite imagery and historical data have identified the southern boundary of the Antarctic Circumpolar Current as a site of enhanced biological productivity. Meso-scale surveys off the Antarctic peninsula have related the abundances of Antarctic krill (Euphausia superba) and salps (Salpa thompsoni) to inter-annual variations in sea-ice extent. Here we have examined the ecosystem structure and oceanography spanning 3,500 km of the east Antarctic coastline, linking the scales of local surveys and global observations. Between 80 degrees and 150 degrees E there is a threefold variation in the extent of annual sea-ice cover, enabling us to examine the regional effects of sea ice and ocean circulation on biological productivity. Phytoplankton, primary productivity, Antarctic krill, whales and seabirds were concentrated where winter sea-ice extent is maximal, whereas salps were located where the sea-ice extent is minimal. We found enhanced biological activity south of the southern boundary of the Antarctic Circumpolar Current rather than in association with it. We propose that along this coastline ocean circulation determines both the sea-ice conditions and the level of biological productivity at all trophic levels.

Animals↗
PubMed2001

Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice.

Ground ice in the crust and soil may be one of the largest reservoirs of water on Mars. Near-surface ground ice is predicted to be stable at latitudes higher than 40 degrees (ref. 4), where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed. Mid-latitude soils have also been implicated as a water-ice reservoir, the capacity of which is predicted to vary on a 100,000-year timescale owing to orbitally driven variations in climate. It is uncertain, however, whether near-surface ground ice currently exists at these latitudes, and how it is changing with time. Here we report observational evidence for a mid-latitude reservoir of near-surface water ice occupying the pore space of soils. The thickness of the ice-occupied soil reservoir (1-10 m) and its distribution in the 30 degrees to 60 degrees latitude bands indicate a reservoir of (1.5-6.0) x 104 km3, equivalent to a global layer of water 10-40 cm thick. We infer that the reservoir was created during the last phase of high orbital obliquity less than 100,000 years ago, and is now being diminished.

Climate↗
PubMed2003

Recent ice ages on Mars.

A key pacemaker of ice ages on the Earth is climatic forcing due to variations in planetary orbital parameters. Recent Mars exploration has revealed dusty, water-ice-rich mantling deposits that are layered, metres thick and latitude dependent, occurring in both hemispheres from mid-latitudes to the poles. Here we show evidence that these deposits formed during a geologically recent ice age that occurred from about 2.1 to 0.4 Myr ago. The deposits were emplaced symmetrically down to latitudes of approximately 30 degrees--equivalent to Saudi Arabia and the southern United States on the Earth--in response to the changing stability of water ice and dust during variations in obliquity (the angle between Mars' pole of rotation and the ecliptic plane) reaching 30-35 degrees. Mars is at present in an 'interglacial' period, and the ice-rich deposits are undergoing reworking, degradation and retreat in response to the current instability of near-surface ice. Unlike the Earth, martian ice ages are characterized by warmer polar climates and enhanced equatorward transport of atmospheric water and dust to produce widespread smooth deposits down to mid-latitudes.

Climate↗
PubMed2004

Perennial water ice identified in the south polar cap of Mars.

The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2 km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap.

Carbon Dioxide↗
PubMed2005

Isobaric annealing of high-density amorphous ice between 0.3 and 1.9 GPa: in situ density values and structural changes.

We report in situ density values of amorphous ice obtained between 0.3 and 1.9 GPa and 144 to 183 K. Starting from high-density amorphous ice made by pressure-amorphizing hexagonal ice at 77 K, samples were heated at a constant pressure until crystallization to high-pressure ices occurred. Densities of amorphous ice were calculated from those of high-pressure ice mixtures and the volume change on crystallization. In the density versus pressure plot a pronounced change of slope occurs at approximately 0.8 GPa, with a slope of 0.21 g cm(-3) GPa(-1) below 0.8 GPa and a slope of 0.10 g cm(-3) GPa(-1) above 0.8 GPa. Both X-ray diffractograms and Raman spectra of recovered samples show that major structural changes occur up to approximately 0.8 GPa, developing towards those of very high-density amorphous ice reported by (T. Loerting, C. Salzmann, I. Kohl, E. Mayer and A. Hallbrucker, Phys. Chem. Chem. Phys., 2001, 3, 5355) and that further increase of pressure has only a minor effect. In addition, the effect of annealing temperature (T(A)) at a given pressure on the structural changes was studied by Raman spectra of recovered samples in the coupled O-H and decoupled O-D stretching band region: at 0.5 GPa structural changes are observed between approximately 100-116 K, at 1.17 GPa between approximately 121-130 K. Further increase of T(A) or of annealing time has no effect, thus indicating that the samples are fully relaxed. We conclude that mainly irreversible structural changes between 0.3 to approximately 0.8 GPa lead to the pronounced increase in density, whereas above approximately 0.8 GPa the density increase is dominated to a large extent by reversible elastic compression. These results seem consistent with simulation studies by (R. Martonàk, D. Donadio and M. Parrinello, J. Chem. Phys., 2005, 122, 134501) where substantial reconstruction of the topology of the hydrogen bonded network and changes in the ring statistics from e.g. mainly six-membered to mainly nine-membered rings were observed on pressure increase up to 0.9 GPa and further pressure increase had little effect.

Algorithms↗
PubMed2003

Antifreeze protein dimer: when two ice-binding faces are better than one.

A naturally occurring tandem duplication of the 7-kDa type III antifreeze protein from Antarctic eel pout (Lycodichthys dearborni) is twice as active as the monomer in depressing the freezing point of a solution. We have investigated the basis for this enhanced activity by producing recombinant analogues of the linked dimer that assess the effects of protein size and the number and area of the ice-binding site(s). The recombinant dimer connected by a peptide linker had twice the activity of the monomer. When one of the two ice-binding sites was inactivated by site-directed mutagenesis, the linked dimer was only 1.2 times more effective than the monomer. When the two monomers were linked through a C-terminal disulfide bond in such a way that their two ice-binding sites were opposite each other and unable to engage the same ice surface simultaneously, the dimer was again only 1.2 times as active as the monomer. We conclude from these analyses that the enhanced activity of the dimer stems from the two ice-binding sites being able to engage to ice at the same time, effectively doubling the area of the ice-binding site.

Amino Acid Sequence↗
PubMed2006

Clathrate hydrates of oxidants in the ice shell of Europa.

Europa's icy surface is radiolytically modified by high-energy electrons and ions, and photolytically modified by solar ultraviolet photons. Observations from the Galileo Near Infrared Mapping Spectrometer, ground-based telescopes, the International Ultraviolet Explorer, and the Hubble Space Telescope, along with laboratory experiment results, indicate that the production of oxidants, such as H2O2, O2, CO2, and SO2, is a consequence of the surface radiolytic chemistry. Once created, some of the products may be entrained deeper into the ice shell through impact gardening or other resurfacing processes. The temperature and pressure environments of regions within the europan hydrosphere are expected to permit the formation of mixed clathrate compounds. The formation of carbon dioxide and sulfur dioxide clathrates has been examined in some detail. Here we add to this analysis by considering oxidants produced radiolytically on the surface of Europa. Our results indicate that the bulk ice shell could have a approximately 1.7-7.6% by number contamination of oxidants resulting from radiolysis at the surface. Oxidant-hosting clathrates would consequently make up approximately 12-53% of the ice shell by number relative to ice, if oxidants were entrained throughout. We examine, in brief, the consequences of such contamination on bulk ice shell thickness and find that clathrate formation could lead to substantially thinner ice shells on Europa than otherwise expected. Finally, we propose that double occupancy of clathrate cages by O2 molecules could serve as an explanation for the observation of condensed-phase O2 on Europa. Clathrate-sealed, gas-filled bubbles in the near surface ice could also provide an effective trapping mechanism, though they cannot explain the 5771 A (O2)2 absorption.

Ice↗