Mixture Of Water Ice Research Articles

Competitive Entrapment of Hypervolatiles in Interstellar and Cometary Water Ice Analogs

The distribution of chemical species in protoplanetary disks around young stars, especially their division between gas and solid phases, fundamentally shapes the composition of future planets and planetesimals. This distribution is likely affected by entrapment, a mechanism whereby volatile species are mechanically or chemically bound within a less volatile ice. In this study, we investigate the entrapment efficiencies of four hypervolatiles (CH4, CO, N2, and Ar) in multicomponent water ice mixtures deposited at different temperatures and mixture ratios. At low ice deposition temperatures, we observe small differences in entrapment efficiency (CH4>CO>N2∼Ar) up to a factor of two across species. The differences in entrapment between species increase by up to an order of magnitude with increasing deposition temperature. The relative entrapment efficiencies are also impacted by changes in the overall hypervolatile concentration of the ice mixtures. Collectively, these experiments suggest that relative entrapment efficiencies are mainly regulated by small differences in binding energies to the ice matrix, though competition for the best sites also influences entrapment in more concentrated ices. We use these results to better inform interpretations of hypervolatile observations in comets and related objects.

Indene energetic processing in ice mantles in the interstellar medium

Context. Indene, a small PAH, has been detected in the gas phase in the cold dense cloud TMC-1. Due to the low temperature in the cloud, below indene condensation temperature, its presence in the ice mantles of dust grains is likely. Aims. The aim of this work is to study the stability of indene against the energetic processing by VUV photons or cosmic rays in the ice mantles of dense molecular clouds. Methods. Ice layers of pure indene or indene diluted in water ice were grown by vapor deposition on a cold surface held at 10 K, 100 K, or 140 K. The samples were processed with VUV photons (120–180 nm) and 5 keV electrons and the destruction of indene was monitored by following the decay of its absorption bands in the infrared (IR) spectrum. Finally, we recorded the mass spectra of the decomposition products sublimated by thermal programmed desorption of the processed samples. Results. Photolysis and radiolysis cross-sections, along with half-life energy doses for indene in the solid form and diluted in water ice matrices at 10 K were derived. Ketones and alcohols were identified as the main processing products in indene and water–ice mixtures Conclusions. Dilution in water ice enhances the destruction rate of indene under energetic processing. The molecule is expected to survive for more than 107 yr in the ice mantles of grains in the interior of dense clouds, but it will end up getting destroyed within the next few hundred years by the intense VUV field in the diffuse region at the edges of the cloud.

Climate related phase transitions with moving boundaries by virtue of mushy zone investigation in Al–Cu: Experiment and phase‐field modeling

Studying Arctic ice formation stays in the focus of research groups over the past decades in the context of ice cover changes, thermal budget and climate agenda in general. Nevertheless, the phenomenon's underlying mechanisms are still not completely understood and described. The main reason for the lack in understanding is the limited experimental access to the field data when it comes to the processes that occur below the ice floe. Thus, there is a need to build competent analogies between the natural (ocean water–ice) and laboratory (here: binary alloy) conditions of the experiment as a step of data preparation for the verification of the mathematical model. In the current paper, the existing qualitative models describing the process of melting and crystallization were expanded and the experimental method was developed copying the layering of the natural ocean water–ice mixture. The experimental set‐up for studying the solidification within the intermediate zone was designed for Al–Cu alloys being the system with appropriate solidus line for creating a sufficient concentration gradient and by that temperature dependent phase fraction under isothermal conditions. The gained experimental data were used for validating a binary phase‐field model for solidification considering moving boundaries. The model includes the description of the free energy of both phases and their respective diffusion coefficients. It allows modeling a binary system at a mesoscopic spatial level by including the concentration‐driven phase transition and resolidification in the two‐phase region. The novel results will help the quantitative understanding of solidification phenomena and are highly‐evaluated from interdisciplinary point of view, including glaciology and geosciences, being ultimately significant for the understanding the global climate change landscape.

Detecting and characterizing the abundance and form of water-ice in permanently-shadowed regions of the moon using a three-band lidar system

We investigated the ability of a three-band lidar instrument (with wavelengths of 532, 1064, and 1560 nm) to detect and quantify different types of regolith ± water ice mixtures for both mare and highlands regions. A variety of samples were spectrally characterized, focusing on variables such as type of lunar regolith (simulant, lunar meteorite, highland vs mare), grain size (<45 μm, 45–1000 μm, <1 mm), water ice surface coverage and porosity of regolith (discontinuous, continuous, packed), and water ice percentages in intimate mixtures vs areal mixtures. Spectral metrics included absolute reflectance (532, 1064, 1560 nm) and reflectance ratios (1560/532, 1064/532, 1560/1064 nm). The ability to detect water ice in the presence of different types of regolith is critically dependent on the optical properties of end members, the selected wavelength, and the physical nature of the samples, such as grain size and areal vs intimate mixtures. Given the differences in the spectroscopic properties of the end members, both absolute reflectance and reflectance ratios have different predictive powers and both are required for robust analysis. The 1560 nm region is the most sensitive of the three wavelength regions to water ice content, as it falls well within a major water ice absorption band. Spectral contrast affects the ability to detect water ice. It is most sensitive for characterizing water ice + highland materials because the latter are brighter than water ice in this wavelength region. Powdered lunar materials are red-sloped across the 532 to 1064 to 1560 nm regions. By contrast, water ice shows a large downturn in reflectance between 1064 and 1560 nm. Detection limits for water ice in many situations can be as low as 2% and are lower for areal vs intimate mixtures. We found that porosity and angle of incidence with the surface have only minor effects on spectral reflectance properties of regolith. Further confirmation of water ice could be realized by comparing lidar data acquired by transects across permanently-shadowed regions and seeing how absolute reflectance and reflectance ratios vary between sunlit and adjacent shadowed regions. If it is known or assumed that regolith properties do not change as one enters a PSR, with the exception of the presence of surficial water ice, changes in reflectivity and reflectance ratios could provide compelling evidence for the presence of water ice.

High pressure behavior of ethylene and water: From clathrate hydrate to polymerization in solid ice mixtures.

Among the ice mixtures that can be found in our universe, those involving ethylene are poorly studied even though ethylene reportedly exists in the presence of water in several astrochemical domains. Here, we report on the chemistry of ethylene and water mixtures in both pressure (0-15GPa) and temperature (300-370K) ranges relevant to celestial bodies conditions. The behavior of the binary mixture has been tracked, starting from the ethylene clathrate hydrate and following its evolution through two different crystalline phases up to 2.10GPa, where it decomposes into a solid mixture of water ice and crystalline ethylene. The pressure and temperature evolution of this mixture has been studied up to the complete transformation of ethylene into polyethylene and compared with that of the pure hydrocarbon, reporting here for the first time its spectroscopic features upon compression. The spectroscopic analysis of the recovered polymers from the ice mixtures provided hints about the reactivity of the monomer under the environmental stress exerted by the water network. The results of this study are expected to be significant in a variety of fields ranging from astrochemistry to material science and also to fundamental chemistry, particularly regarding the study and modelization of the behavior of complex mixtures.

MOVEMENT OF TWO-PHASE GAS-LIQUID FLOW IN HORIZONTAL AND INCLINED PIPES

"Two-phase flows are found in almost all areas of technology. For example, tubular evaporators, boiling water reactors, boiler blowdown systems, heaters, boilers, gas lift pumps, oil and geothermal wells, oil and gas pipelines, refrigerators, process pipelines, and condensers. Two-phase flows are classified as mixtures. According to the composition of the mixture are divided: (a) for single-component (or one-component) - vapor-liquid flows; (b) multicomponent - gas-liquid flows. One-component mixtures consist of the same substance in different states of aggregation. This can be not only vapor-liquid, but also a mixture of liquid or vapor with a solid phase, a water-ice mixture, or a vapor flow with ice particles, for example, in sublimation installations. Multicomponent mixtures are a combination of substances of different physical nature. These include not only gas-liquid flows, but also, for example, mixtures of air and sand, water and oil. The paper presents the main attention is paid to the movement of two-phase flows in the pipeline."

The development of methods and instruments for thermal conductivity measurement of standard core samples for petrophysical studies

The problem of obtaining qualitative data on the thermal conductivity of standard rock samples for petrophysical studies is considered. It is shown that the existing instruments for thermal conductivity measurement do not allow one to obtain reliable and accurate values of the thermal conductivity of small-sized rock samples. A laboratory installation for thermal conductivity measurement of standard rock samples with a diameter not less than 30 mm has been created. The installation was assembled and tested on small samples. Possible problems in the development, design and exploitation of the laboratory installation were analyzed. A software that allows automated collection and processing of the data has been developed. The key factors, negatively affecting the accuracy and reliability of thermal conductivity measurement results, are identified and excluded. There were unshielded thermocouples, potential changes between the hot and cold junctions (due to uneven melting of the water-ice mixture in the Dewar vessel, where the cold junction is immersed), incorrectly selected dimensions and shape of the object of study and the nonequilibrium ratio of the heat input and dissipation. The installation was tested on samples of pure tin standard and brass LS59 with known thermal conductivity. The thermal conductivity of a small-sized rock sample was measured with an error within 5.6 %.

VIS spectroscopy of NaCl – water ice mixtures irradiated with 1 and 5 keV electrons under Europa's conditions: Formation of colour centres and Na colloids

Recent laboratory efforts and telescopic observations of Europa have shown the relevance of a yellow colouration of sodium chloride (NaCl) caused by crystal defects generated by irradiation. We further investigate this process by irradiating (with energetic electrons) different types of analogues where NaCl is associated in different ways to water ice. We produce two types of icy analogues: compact slabs and granular particles where we investigate two particle sizes (5 and 70 μm). We perform electron irradiation at cryogenic temperatures (100K) and under high vacuum (10−7 mbar) conditions, with energies of 1 and 5 keV. We observe the formation of two different types of colour centres. The so-called F-centres (460 nm) were formed in every sample, but the intensity of the absorption band within the compact slabs surpassed any other icy analogues and was comparable to the intensity of the absorption band within pure NaCl grains. M-centres (720 nm) have not been detected at the surface of Europa so far, and were close to the detection limit during our irradiation of compact slabs. The slabs could be good analogues for Europa's surface as they produce mainly F-centres. Other notable differences have been observed between compact slabs and granular samples, such as the presence of an absorption band at 580 nm attributed to colloids of Na, exclusively within granular samples. Such absorptions have not been reported in previous studies.

Comets, sliding of surface dust II

In this paper we presented the results of laboratory experiments dealing with the sliding of desiccated sand on the inclined surfaces of cometary analogs. The experiments were performed in a vacuum, using porous mixtures of water ice and quartz sand. The inclination angle of the surfaces of the samples was about 10 degrees lower than the repose angle. The sliding was possible when the mobility coefficient defined as the ratio of forces was lower than unity i.e. when the layer of sand as the whole was not fluidized. The observed effect of sliding was due to the rolling, or sliding of grains present on the surface. It is important, that the process of sliding of desiccated sand can be caused by the sublimation of underlying water ice despite its relatively low volatility.

VIS-IR Spectroscopy of Mixtures of Water Ice, Organic Matter, and Opaque Mineral in Support of Small Body Remote Sensing Observations

Visual-to-infrared (VIS-IR) remote sensing observations of different classes of outer solar system objects indicate the presence of water ice and organics. Here, we present laboratory reflectance spectra in the 0.5–4.2 μm spectral range of binary particulate mixtures of water ice, organics analogue (kerite), and an opaque iron sulphide phase (pyrrhotite) to investigate the spectral effects of varying mixing ratios, endmember grain size, and mixing modality. The laboratory spectra are also compared to different implementations of the Hapke reflectance model (Hapke, 2012). We find that minor amounts (≲1 wt%) of kerite (investigated grain sizes of 45–63 μm and &lt;25 μm) can remain undetected when mixed in coarse-grained (67 ± 31 μm) water ice, suggesting that organics similar to meteoritic insoluble organic matter (IOM) might be characterized by larger detectability thresholds. Additionally, our measurements indicate that the VIS absolute reflectance of water ice-containing mixtures is not necessarily monotonically linked to water ice abundance. The latter is better constrained by spectral indicators such as the band depths of water ice VIS-IR diagnostic absorptions and spectral slopes. Simulation of laboratory spectra of intimate mixtures with a semi-empirical formulation of the Hapke model suggests that simplistic assumptions on the endmember grain size distribution and shape may lead to estimated mixing ratios considerably offset from the nominal values. Finally, laboratory spectra of water ice grains with fine-grained pyrrhotite inclusions (intraparticle mixture) have been positively compared with a modified version of the Hapke model from Lucey and Riner (2011).

Compositional Study of Trans-Neptunian Objects at λ &gt; 2.2 μm

Abstract Using data from the Infrared Array Camera on the Spitzer Space Telescope, we present photometric observations of a sample of 100 trans-Neptunian objects (TNOs) beyond 2.2 μm. These observations, collected with two broadband filters centered at 3.6 and 4.5 μm, were done in order to study the surface composition of TNOs, which are too faint to obtain spectroscopic measurements. With this aim, we have developed a method for the identification of different materials that are found on the surfaces of TNOs. In our sample, we detected objects with colors that are consistent with the presence of small amounts of water, and we were able to distinguish between surfaces that are predominantly composed of complex organics and amorphous silicates. We found that 86% of our sample have characteristics that are consistent with a certain amount of water ice, and the most common composition (73% of the objects) is a mixture of water ice, amorphous silicates, and complex organics. Twenty-three percent of our sample may include other ices, such as carbon monoxide, carbon dioxide, methane, or methanol. Additionally, only small objects seem to have surfaces dominated by silicates. This method is a unique tool for the identification of complex organics and to obtain the surface composition of extremely faint objects. Furthermore, this method will be beneficial when using the James Webb Space Telescope for differentiating groups within the trans-Neptunian population.

Experimental Installation at the Water-Ice Phase Transition

The article reviewes the specifics of electricity production in Russia. One of the most effective energy saving methods is the use of heat pump installations. Its main property is the ability to extract heat from the environment: soil, water, reservoirs, the surrounding air, and the sun. Existing heat pumps with a water-ice phase transition are not efficient enough and have a high installation cost due to its complexity. (Research purpose) The research purpose is in determining the parameters and operating modes of the experimental installation at the water-ice phase transition. (Materials and methods) The article presents analogs and a prototype of an experimental installation at the water-ice phase transition. (Results and discussion) The article presents a scheme and an experimental installation for generating energy for the water-ice phase transition, consisting of a tank, pump, refrigerant, evaporator, compressor, condenser, throttle valve, and solar collector. The heat exchanger was manufactured as a flexible corrugated silicone tube with a metal insert, in which antifreeze circulates and ice forms on the surface. It was found that the received energy accumulates inside the silicone tube and is sent to the consumer’s heat exchanger in the form of hot liquid antifreeze. A heater connected to a solar collector was used as a heat source for melting ice. (Conclusions) It has been revealed that the designed installation scheme is made to design heat pumps that consume energy from the water-ice phase transition for heating agricultural, industrial, and infrastructure facilities; at the enterprises of the agro-industrial complex, in systems of thermal accumulators, as well as for obtaining a water-ice mixture for cooling products in agricultural production (milk, for example).

IR absorption spectra of high-pressure polyethylene modified by fish scales

We study polymeric-based composite materials with nanostructured metal filler and bio-filler; they protect the material from environmental influences, including oxidation, and give the required flexibility to the composite, subject to biocompatibility. Composites were obtained from a homogeneous mixture of the powders of the matrix components and the filler using a heated press at a temperature of 420 K and a pressure of 15 MPa. The quenching crystallization mode is the rapid cooling of samples in a water–ice mixture. The results of a study of IR spectra taken with a Fourier spectrometer Varian 640 FT-IR, high-pressure polyethylene composites modified with biological filler, and LDPE [Formula: see text] vol.% FS [Formula: see text] vol.% Fe bio-nanocomposites in the frequency range 4000–400 cm[Formula: see text] were presented. It was revealed that the introduction of modifiers from fish scales (FS) and metallic nanoparticles (Fe) in LDPE in an optimal amount does not contribute to the appearance of new absorption bands, i.e. it practically does not change the shape of their IR spectrum. This means that the modifier of biological origin is technologically compatible with LDPE. The introduction of fish scale filler to LDPE contributes to a noticeable decrease in the intensity of the formation of C–O groups (1720 cm[Formula: see text]), which is a measure of the oxidative degradation of polymer chains. The results show that the introduction of FS into the structures of high-pressure polyethylene contributes to the formation of an optimal and stable structure, which, in turn, interferes with the intensive development of the photooxidative process caused by UV irradiation.

Исследование процесса теплообмена при охлаждении форели с применением диоксида углерода

There is a growing demand for rapid cooling in modern food industry. Traditional methods of fish cooling involve cold air, cold liquid, and ice. These methods have a number of disadvantages. For instance, they may have a negative effect on the appearance of the product, require a longer cooling time, or make fish absorb extra moisture. As a result, the quality of the product and its shelf life decrease, which results in demand contraction. Carbon dioxide is becoming increasingly popular in closed refrigeration systems. It is one of the most promising refrigerants, since traditional refrigeration technologies for fish cooling have a number of serious drawbacks. The paper introduces a utilization method for carbon dioxide obtained at alcohol processing plants. The authors analyzed the prospects of using carbon dioxide in combination with a binary mixture for cooling trout. A series of experiments proved the technological advantages of this technology. The paper features heat transfer in roundfish during cooling with water ice, a mixture of water ice and snow-like carbon dioxide, and snow-like CO2 in pure form. The obtained results show the effect of the concentration of snow-like carbon dioxide in water ice on the intensity of the cooling process. A higher intensity of the cooling process reduced the cooling time and the amount of water ice. The study of quality indicators of trout proved that the environment of water ice and carbon dioxide increased its shelf life by several times. The paper contains temperature graphs and duration curves at different concentrations of CO2.

Experimenting with Mixtures of Water Ice and Dust as Analogues for Icy Planetary Material

Due to its abundance and unique properties, water is a major actor in the formation and evolution of many planetary surfaces as well as a sensitive and reliable tracer of past geologic and climatic processes. Water ice is found in variable abundance at the surfaces of many Solar System objects, from the floor of permanently shadowed craters at the poles of Mercury to large fractions of the surfaces of several trans-Neptunian objects. With few exceptions, water is not found in pure form but associated to contaminants of various nature and concentration. These associations and the nature of the mixing and segregation processes that affect and control them are key for our understanding of some of the most important aspects of planetary evolution processes. The observation and characterization of water ice at the surface of Solar System objects is therefore among the primary scientific objectives of many space missions. The quantitative interpretation of remote sensing data in terms of surface composition and physical properties requires the use of complex physical models that rely on experimental data in two different ways. First, the models require as inputs the fundamental properties of the pure materials, such as the optical or dielectric constant. Second, the models can only be fully tested if their results are confronted to actual measurements performed on samples whose complexity comes close to the one encountered on natural planetary surfaces but which are nevertheless well-enough characterized to serve as reference. Such measurements are challenging as macroscopic ice-rich samples prepared as analogues of icy planetary surfaces tend to be unstable, the ice component being prone to metamorphism and phase change. The questions of the reproducibility of the samples and the relevance of the measurements are therefore critical. The Ice Laboratory at the University of Bern has been set up in 2010 to overcome some of these difficulties. We have developed protocols to prepare, store, handle and characterize various associations of ice with mineral and organics contaminants as analogues of different types of icy Solar System surfaces. The aims of this article are to present the context and background for our investigations, describe these protocols and associated hardware in a comprehensive way, provide quantitative characterization of the samples obtained using these protocols and summarize the main results obtained so far by experimenting with these samples. The current state and possible future evolutions of this project are then discussed in the context of the next generation of space missions to visit icy objects in the Solar System and longer term perspectives on future observations of protoplanetary discs and exoplanetary systems.

Cassini-VIMS observations of Saturn’s main rings: II. A spectrophotometric study by means of Monte Carlo ray-tracing and Hapke’s theory

This work is the second in a series of manuscripts devoted to the investigation of the spectrophotometric properties of Saturn’s rings from Cassini-VIMS (Visible and Infrared Mapping Spectrometer) observations. The dataset used for this analysis is represented by ten radial spectrograms of the rings which have been derived in Filacchione et al. (2014) by radial mosaics produced by VIMS. Spectrograms report the measured radiance factor I/F of the main rings of Saturn as a function of both radial distance (from 73500 to 141375 km) and wavelength (0.35–5.1 µm) for different observation geometries (phase angle ranging in the 2°–132° interval). We take advantage of a Monte Carlo ray-tracing routine (Ciarniello et al., 2014) to characterize the photometric behavior of the rings at each wavelength and derive the spectral Bond albedo of ring particles. This quantity is used to infer the composition of the regolith covering ring particles by applying Hapke’s theory. Four different regions, characterized by different optical depths, and respectively located in the C ring, inner B ring, mid B ring and A ring, have been investigated. Results from photometric modeling indicate that, in the VIS-NIR spectral range, B ring particles are intrinsically brighter than A and C ring particles, with the latter having the lowest albedo, while the single particle phase function of the ring’s particles is compatible with an Europa-like or Callisto-like formulation, depending on the investigated region. Spectral modeling of the inferred Bond albedo indicates that ring spectrum can be reproduced by water ice grains with inclusion of organic materials (tholin) as a UV absorber intimately mixed with variable amounts of other compounds in pure form (carbon, silicates) or embedded in water ice grains (nanophase hydrated iron oxides, carbon, silicates, crystalline hematite, metallic iron, troilite). The abundance of tholin decreases with radial distance from C ring (0.2–0.6%) to A ring (0.06%) for the selected regions. Its distribution is compatible with an intrinsic origin and is possibly related to the different plasma environment of the different ring regions. The identification of the other absorber(s) and its absolute volumetric abundance is uncertain, depending on the adopted grain size and mixing modality (intraparticle or intimate). However, assuming a common composition of the other absorber in the ring plane, we find that its abundance anti-correlates with the optical depth of the investigated regions, being maximum in the thinnest C ring and minimum in the thickest mid B ring. In the case of the C ring, an additional population of low-albedo grains is required to match the positive spectral slope of the continuum in the 0.55–2.2 µm interval, represented by an intraparticle mixture of water ice and a spectrum similar to troilite or metallic iron. The distribution of the darkening compounds is interpreted as the result of a contamination by exogenous material, which is more effective in the less dense regions of the rings because of their lower surface mass density of pure water ice.

A multifunctional setup to record FTIR and UV-vis spectra of organic molecules and their photoproducts in astronomical ices.

This article describes a new, multi-functional, high-vacuum ice setup that allows to record the in situ and real-time spectra of vacuum UV (VUV)-irradiated non-volatile molecules embedded in a low-temperature (10 K) amorphous solid water environment. Three complementary diagnostic tools-UV-visible (UV-vis) and Fourier Transform Infrared (FTIR) spectroscopy and temperature-programmed desorption quadrupole mass spectrometry-can be used to simultaneously study the physical and chemical behavior of the organic molecules in the ice upon VUV irradiation. The setup is equipped with a temperature-controlled sublimation oven that enables the controlled homogeneous deposition of solid species such as amino acids, nucleobases, and polycyclic aromatic hydrocarbons (PAHs) in ice mixtures prepared from precursor gases and/or liquids. The resulting ice is photo-processed with a microwave discharge hydrogen lamp, generating VUV radiation with a spectral energy distribution representative for the interstellar medium. The characteristics, performance, and future potential of the system are discussed by describing three different applications. First, a new method is introduced, which uses broadband interference transmission fringes recorded during ice deposition, to determine the wavelength-dependent refractive index, nλ, of amorphous solid water. This approach is also applicable to other solids, pure and mixed. Second, the UV-vis and FTIR spectroscopy of an VUV-irradiated triphenylene:water ice mixture is discussed, monitoring the ionization efficiency of PAHs in interstellar ice environments. The third and final example investigates the stability of solid glycine upon VUV irradiation by monitoring the formation of dissociation products in real time.

Electrical Properties of Tholins and Derived Constraints on the Huygens Landing Site Composition at the Surface of Titan

AbstractIn 2005, the complex permittivity of the surface of Saturn's moon Titan was measured by the PWA‐MIP/HASI (Permittivity Wave Altimetry‐Mutual Impedance Probe/Huygens Atmospheric Structure Instrument) experiment on board the Huygens probe. The analysis of these measurements was recently refined but could not be interpreted in terms of composition due to the lack of knowledge on the low‐frequency/low‐temperature electrical properties of Titan's organic material, a likely key ingredient of the surface composition. In order to fill that gap, we developed a dedicated measurement bench and investigated the complex permittivity of analogs of Titan's organic aerosols called “tholins.” These laboratory measurements, together with those performed in the microwave domain, are then used to derive constraints on the composition of Titan's first meter below the surface based on both the PWA‐MIP/HASI and the Cassini Radar observations. Assuming a ternary mixture of water ice, tholin‐like dust and pores (filled or not with liquid methane), we find that at least 10% of water ice and 15% of porosity are required to explain observations. On the other hand, there should be at most 50–60% of organic dust. PWA‐MIP/HASI measurements also suggest the presence of a thin conductive superficial layer at the Huygens landing site. Using accurate numerical simulations, we put constraints on the electrical conductivity of this layer as a function of its thickness (e.g., in the range 7–40 nS/m for a 7‐mm thick layer). Potential candidates for the composition of this layer are discussed.

Electric Conductivity and Dielectric Dispersion of Polyvinylchloride–Graphite Composites

The dielectric properties of polyvinylchloride–graphite composites in a wide range of temperatures (20–150°C) and frequencies (25–106 Hz) have been described and analyzed. Polyvinylchloride–graphite composites have been synthesized in accordance with powder technology by hot pressing in a hydraulic press and subsequent rapid cooling in a water–ice mixture (quenching mode). The dielectric permeability and electric conductivity of the polyvinylchloride–graphite composite system obey the power law of the percolation theory. The percolation threshold of these composites is ~6.35 vol % of graphite. At a certain concentration of graphite, polyvinylchloride–graphite composites exhibit high dielectric permeability, significant losses, and high dc and ac electric conductivity. With anincrease in the applied-field frequency, the permeability decreases, while theelectric conductivity, conversely, increases. It has been shown that the main mechanism of electric conductivity in polyvinylchloride–graphite insulators is barrier hopping; according to this mechanism, electrons hop over states localized in the vicinity of the Fermi level. In addition, the temperature and frequency dispersions of e' and tanδ have been discussed; the specific features of the dispersion curves have been revealed.

Sensory and chemical assessment of silver pomfret (Pampus argenteus) treated with Ginkgo biloba leaf extract treatment during storage in ice

This study investigated the physical (L*, a*, b*, texture profile analyses, pH), chemical (TVB-N, K value and TBA), microbiological, amino acid content, and flavor effects that Gingko biloba leaf extract (GBLE) had on silver pomfret (Pampus argenteus) stored at 4 ± 1 °C in ice for 18 days. Fresh pomfret samples were obtained directly from the local fish market and transported to the laboratory with ice immediately. After being gutted, washed, filleted and trimmed in a water-ice mixture, samples were treated with different concentrations of GBLE (0.0 mg/mL, 2.5 mg/mL, 5.0 mg/mL, 10.0 mg/mL) and packaged in Polyethylene bag, then stored in a refrigerator at 4 ± 1 °C with ice. The results show that the shelf-life of untreated (0.0 mg/mL) pomfret samples was 8–9 days compared to 14–15 days for the GBLE1 (2.5 mg/mL) treated group. The assessment results showed that different concentrations of GBLE had variable effects on preserving the texture parameters of acceptability limit, inhibit lipid oxidation, protein degradation, and microorganism growth. 2.5 mg/mL of GBLE was the best for the preservation of pomfret during storage in ice. Therefore, there is potential use for GBLE as a preservative to extend the shelf-life of pomfret during chilled storage in ice.