Meltwater generation in ice stream shear margins: case study in Antarctic ice streams

Liquid water within glacier ice and at the glacier beds exerts a significant control on ice flow and glacier stability through a number of processes, including altering the rheology of the ice and lubricating the bed. Some of this water is generated as melt in regions of rapid deformation, including shear margins, due to heating by viscous dissipation. However, how much meltwater is generated and drained from shear margins remains unclear. Here, we apply a model that describes the evolution of ice temperature, melting, and water transport within deforming ice to estimate the flux of meltwater from shear margins in glaciers. We derive analytical expressions for ice temperature, effective pressure, and porosity in zones of temperate ice, and we apply this model to estimate the flux from three Antarctic glaciers: Bindschadler and MacAyeal Ice Streams, Pine Island Glacier, and Byrd Glacier. We show that the flux of meltwater from shear margins in these regions may be as significant as the meltwater produced by frictional heating at the bed, with average fluxes of ~1000-2000 m^3 yr^ -1. This contribution of shear heating to meltwater flux at the bed may thus affect both the rheology of the ice as well as sliding at the bed, both key controls on fast ice flow.

Overview of 3D-Printed Silica Glass

Not satisfied with the current stage of the extensive research on 3D printing technology for polymers and metals, researchers are searching for more innovative 3D printing technologies for glass fabrication in what has become the latest trend of interest. The traditional glass manufacturing process requires complex high-temperature melting and casting processes, which presents a great challenge to the fabrication of arbitrarily complex glass devices. The emergence of 3D printing technology provides a good solution. This paper reviews the recent advances in glass 3D printing, describes the history and development of related technologies, and lists popular applications of 3D printing for glass preparation. This review compares the advantages and disadvantages of various processing methods, summarizes the problems encountered in the process of technology application, and proposes the corresponding solutions to select the most appropriate preparation method in practical applications. The application of additive manufacturing in glass fabrication is in its infancy but has great potential. Based on this view, the methods for glass preparation with 3D printing technology are expected to achieve both high-speed and high-precision fabrication.

Preferential dissolution of uranium-rich zircon can bias the hafnium isotope compositions of granites

Hafnium (Hf) isotopes in zircon are important tracers of granite petrogenesis and continental crust evolution. However, zircon in granites generally shows large Hf isotope variations, and the reasons for this are debated. We applied U-Pb geochronology, trace-element, and Hf isotope analyses of zircon from the Miocene Himalayan granites to address this issue. Autocrystic zircon had εHf values (at 20 Ma) of –12.0 to –4.3 (median = –9). Inherited zircon yielded εHf values (at 20 Ma) of –34.8 to +0.3 (median = –13); the majority of εHf values were lower than those of autocrystic zircon. The εHf values of inherited zircon with high U concentrations resembled those of autocrystic zircon. Geochemical data indicates that the granites were generated during relatively low-temperature (<800 °C) partial melting of metasedimentary rocks, which, coupled with kinetic hindrance, may have led to the preferential dissolution of high-U zircon that could dissolve more efficiently into anatectic melt due to higher amounts of radiation damage. Consequently, Hf values of autocrystic zircon can be biased toward the values of U-rich zircon in the source. By contrast, literature data indicate that granites generated at high temperatures (<820–850 °C) generally contain autocrystic and inherited zircons with comparable Hf isotope values. During higher-temperature melting, indiscriminate dissolution of source zircon until saturation is reached will result in near-complete inheritance of Hf isotope ratios from the source. Our results impose an extra layer of complexity to interpretation of the zircon Hf isotope archive that is not currently considered.

Improvement of thermostability and catalytic efficiency of glucoamylase from Talaromyces leycettanus JCM12802 via site-directed mutagenesis to enhance industrial saccharification applications

Background Glucoamylase is an important industrial enzyme in the saccharification of starch into glucose. However, its poor thermostability and low catalytic efficiency limit its industrial saccharification applications. Therefore, improving these properties of glucoamylase is of great significance for saccharification in the starch industry. Results In this study, a novel glucoamylase-encoding gene TlGa15B from the thermophilic fungus Talaromyces leycettanus JCM12802 was cloned and expressed in Pichia pastoris. The optimal temperature and pH of recombinant TlGa15B were 65 ℃ and 4.5, respectively. TlGa15B exhibited excellent thermostability at 60 ℃. To further improve thermostability without losing catalytic efficiency, TlGa15B-GA1 and TlGa15B-GA2 were designed by introducing disulfide bonds and optimizing residual charge–charge interactions in a region distant from the catalytic center. Compared with TlGa15B, mutants showed improved optimal temperature, melting temperature, specific activity, and catalytic efficiency. The mechanism underlying these improvements was elucidated through molecular dynamics simulation and dynamics cross-correlation matrices analysis. Besides, the performance of TlGa15B-GA2 was the same as that of the commercial glucoamylase during saccharification. Conclusions We provide an effective strategy to simultaneously improve both thermostability and catalytic efficiency of glucoamylase. The excellent thermostability and high catalytic efficiency of TlGa15B-GA2 make it a good candidate for industrial saccharification applications.

Agar Extraction, Physical Properties, FTIR Analysis and Biochemical Composition of Three Edible Species of Red Seaweeds Gracilaria corticata (J. Agardh), Gracilaria dentata (J. Agardh) and Gracilariopsis longissima (S. G. Gmelin)........

Three species of red algae Gracilaria corticata (J. Agardh), Gracilaria dentata (J. Agardh) and Gracilariopsis longissima (S.G. Gmelin), Steentoft, L. M; Irvine and Farnham (formerly Gracilaria verrucosa (Hudson) were collected from four different sites (Buleji, Hawks Bay, Manora and Paradise Point) of Karachi coast. The G. corticata was the dominant species and the highest yield of agar was compared to other studied species. The physical properties such as gel temperature, melting temperature, density, viscosity and gel strength showed large variations. Interestingly, the gel temperature, melting temperature, density, and gel strength had the highest value in G. corticata samples collected, while gel viscosity recorded the highest value in G. dentata samples. Intensive spectroscopic FTIR analysis was determined in all three species of G. corticata, G. dentata and G. longissima. The bands at 414.7/cm to 3917.2/cm represents stretching and bending vibrations of alcohol O-H, amine N-H, alkane C-H, alkyne C=C, nitriles C=N, carboxyl C=O, nitro aromatic N=O, alkane C-C, nitro methane C-N, aliphatic amines C-N, sulfoxides S=O, alkene C-H alkyl halide C-Cl, C-I groups. The ash content of all studied species (G. corticata, G. dentata and G. longissima) was in the range of 20-30%, while the carbohydrate content was in the range of 22-24%. The results of this study suggested the utilization of our natural resources present in Karachi coast. This could be achieved by determining the quantity and quality of agar in the edible species of Gracilaria/Gracilariopsis.

The improvement of physicomechanical, flame retardant, and thermal properties of lignocellulosic material filled polymer composites

In this study, the effects of alkali and silane coupling agents and coir fiber (CF) loading on the fundamental properties of the CF-filled polypropylene (PP) composites were investigated. Mechanical properties of the PP/CF composites, such as tensile strength, tensile modulus, impact strength, and water absorption were increased by the increase of the CF loading. The inclusion of 3-aminopropyl trimethoxy silane (ATS) and tetramethoxy orthosilicate (TOS) after the alkali pretreatment for the CF increased all the mechanical properties and water desorption of the resulting composites. This trend was more evident with the increase in CF loading. The best results were obtained for PP/TOS composites as compared to other composites. SEM images of fractured samples show improved adhesion between CF and PP matrix after treatment with ATS and TOS. The horizontal rate of combustion is significantly reduced with the inclusion of Mg(OH)2 in PP/ATS and PP/TOS composites. DSC results show improved crystallization temperature, melting temperature, and melting enthalpy as compared with virgin PP. The addition of ATS and TOS after the alkali pretreatment improved the thermal stability of the resultant composites. TOS-modified CF composites showed better resistance than ATS-modified CF composites in water medium.

The Relationship between the Structure and Thermal Properties of Bi2O3-ZnO-B2O3 Glass System

The influence of Bi2O3 and melting temperature on the thermal and structural properties of xBi2O3-(60-x) ZnO-40B2O3 glasses has been investigated in this study. It is expected that these factors can be used to control the degree of reduction of Bi2O3, and the relationship between these factors and the color change of the process for bismuth glass is discussed. Due to high-temperature melting, the bismuth-doped borate glasses have changed into dark/black from original transparent yellow and the light transmittance will decrease, so it is not used in optical applications. The thermal properties of glass are measured by a thermomechanical analyzer (TMA), and the glass structure is analyzed by FTIR and XPS. The results show that the glass is mainly composed of [BiO6] octahedron, [BiO3] triangle, [BO4] tetrahedron, and triangle [BO3] units, and the network of the glass system is mainly bonded by B-O-B, B-O-Zn, B-O-Bi, and Bi-O-Bi. The glass thermal expansion coefficient (CTE) of this glass system increases with the increase of Bi2O3 content, and the O1s nuclear electron binding energy shifts to the lower energy direction with the increase of Bi2O3 addition. In terms of FTIR, as the melting temperature rises, the B-O-B bonding vibration concentration of [BO4] inside the borate glass decreases, and the density of B-O-B bonding vibration of [BO3] increases, Moreover, the increase in melting temperature increases the probability of reducing Bi ions to Bi0, reduces the bonding of Bi-O-B, and increases the bonding of B-O-B, and the CTE also slightly decreases.

Interaction of a Short Peptide with G-Quadruplex-Forming Sequences: An SRCD and CD Study

G-quadruplex (G4) forming DNA sequences were recently found to play a crucial role in the regulation of genomic processes such as replication, transcription and translation, also related to serious diseases. Therefore, systems capable of controlling DNA and RNA G-quadruplex structures would be useful for the modulation of various cellular events. In particular, peptides represent good candidates for targeting G-quadruplex structures, since they are easily tailored to enhance their functionality. In this work, we analyzed, by circular dichroism and synchrotron radiation circular dichroism spectroscopies, the interaction of a 25-residue peptide deriving from RHAU helicases (Rhau25) with three G-quadruplex-forming oligonucleotide sequences, in both sodium- and potassium-containing buffers, the most relevant monovalent cations in physiological conditions. The peptide displayed greater affinity for the G4 sequences adopting a parallel structure. However, it showed the ability to also interact with antiparallel or hybrid G-quadruplex structures, inducing a conformation conversion to the parallel structure. The stability of the oligonucleotide structure alone or in presence of the Rhau25 peptide was studied by temperature melting and UV denaturation experiments, and the data showed that the interaction with the peptide stabilized the conformation of oligonucleotide sequences when subjected to stress conditions.

Coconut Oil Heat Capacity

Heat is energy transferred between a system and its surroundings due to the temperature difference that exists between them. Phase changes of coconut oil can be seen at temperatures between 20°C–100°C. To calculate the incoming heat using the equation Q = m.c.ΔT. Where Q in the experiment is calculated by the equation Q = V.I.t. So to calculate the specific heat of heat (c) = Q/(m.ΔT). The heat capacity is obtained from the equation C = m.c. The method in this practicum is used heater with AC current. The heater used has a voltage of 220 Volts, with a power of 350 Volts. Because the heating voltage is too large, a variable ac (variac) is used to lower the voltage. The voltage used is 20 volts. The material used is coconut oil which is labeled "Barco". The heater directly interacts with the oil. So that the oil can be directly heated homogeneously. Then it is bounded by adiabatic walls. The temperature in this study was controlled, ranging from 150C-500C. the heat of fusion of coconut oil at 28°C. After that, the liquid phase is above 28 °C to 63 °C. This is in accordance with the oil label which states that the melting temperature (melting) is around 26 °C. This difference is due to a leak or air entering the adiabatic wall.