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Shared hydrogen bonds: Water in aluminated faujasite
No full textWater confined in faujasite, a zeolite, with aluminium content, exhibits properties different from those of bulk water as well as water confined in siliceous faujasite. The RDF between oxygen of water (OW) and oxygen of aluminium (OAl) shows a prominent first peak near to 2.9 Ã similar to any oxygen-oxygen RDF seen in bulk water and unlike water confined in siliceous faujasite. Further, HW-OAl shows a peak near 1.9 Ã suggesting hydrogen bonding between hydrogen of water and OAl. The water satisfies the hydrogen bond criteria with both O1Al and O2Al indicating that it is participating in a shared hydrogen bond. The hydrogen bond exchange between such a water forming a shared hydrogen bond to OAl and another water molecule H2Ob is investigated through the changes in the distances and appropriate angles. The O-Al-O angle of the zeolite increases by about 7 degrees on the formation of the shared hydrogen bond. The jump dynamics of the shared hydrogen bond when the two bonds break simultaneously has been obtained and this is reported. This jump reorientation dynamics is different compared to normal hydrogen bonding reported by Laage and Hynes: it has a short lifetime, around 50-100 fs computed from SHB(t). The intermittent and continuous hydrogen bond correlation functions are also reported
A multi-scale deformation analysis for a particulate composite at the rigidity threshold
No full textThe rigidity threshold in a two-phase soft-rigid material is linked to the formation of networks of the rigid phase, which supports a substantial fraction of overall load. Metal filled particulate polymer composites were used to characterize rigidity transition experimentally, as metals and polymers have contrasting mechanical properties enabling easy detection of the rigidity transition. A detailed analysis of the load transferring mechanisms was performed using in-situ synchrotron X-ray diffraction to directly verify the compressive loading of the rigid metal particles at a microscopic scale. Elastic buckling of the force chains was attributed to the non-affine deformation at the rigidity threshold at room temperature, using digital image correlation (DIC) technique at a mesoscopic length scale. However, beyond the glass transition temperature of the polymer, the deformation was homogeneous due to the low viscosity and high compressibility of the polymer and the absence of buckling of force chains. Macroscopically, an increasing Poisson ratio was observed as a function of elastic strains, which is quite unique for these composites. The criteria for having increasing Poisson ratio is discussed based on elastic buckling of force chains and polymer incompressibility, and a link is proposed between deformation at microscopic, mesoscopic and macroscopic scale for the composite
Stability analysis of twin horse-shoe shaped tunnels in rock mass
No full textThis study examines the stability of a single and twin horse-shoe shaped unlined tunnels laid in rock media and loaded with surcharge pressure on ground surface. The tunnels are assumed to be sufficiently long so that the plane strain analysis remains applicable. The failure of rock mass is governed by the generalized Hoek-Brown (GHB) yield criterion. The analysis has been performed by using the lower bound finite elements limit analysis in conjunction with the power cone programming (PCP). No assumption needs to be associated with either the smoothing of the yield surface or fixing the value of the exponent in the GHB criterion. For a given cover to diameter ratio of the tunnels, the maximum permissible value of the surcharge pressure on ground has been computed ensuring the stability of the tunnels. Apart from the different basic material yield parameters (GSI, mi and �ci), the effect of clear spacing (S) between the twin tunnels on the results has also been studied. Failure patterns have also been explored for a number of cases to identify the region of the plastic shear zone. The computations reveal that the optimal spacing (Sopt), beyond which the tunnels behave like isolated ones, remains almost independent with respect to the material parameters and increases continuously with an increase in H/B; the value of Sopt/B increases from 2.5�3.0 for H/B = 1 to 13.0�14.0 for H/B = 6. The computational results have been duly validated and even compared with the different available solutions for square and circular twin tunnels in rock media
Cone snail analogs of the pituitary hormones oxytocin/vasopressin and their carrier protein neurophysin. Proteomic and transcriptomic identification of conopressins and conophysins
No full textTranscriptomic analysis of cone snail venom duct tissue has permitted the identification of diverse conopressin/conophysin precursor sequences from seven distinct Conus species. Multiple precursor isoforms are present in C.monile, C.lividus and C.loroisii. Aqueous extracts of the venom duct tissue from C.monile yield a band, at ~ 15-20 kDa on SDS-PAGE. In-gel trypsin digestion, followed by mass spectrometry establishes the presence of two distinct conopressin/conophysin isoforms that differ at position 8 in the predicted conopressin nonapeptide sequence. Mass spectrometric analysis of aqueous extracts revealed the presence of four conopressin related peptides, whose sequences could be deduced from MS/MS fragmentation patterns. The four sequences determined in this study are CFIRNCPKG*, CFIRNCPEG*, CFIRNCPK* and CFIRNCPE* (� indicates amide), which were further confirmed by comparison with chemically synthesized peptides. A conophysin with a mass of 9419.7 Da was also detected, corresponding to one of the isoforms revealed by the transcriptome data. Complete conservation of fourteen Cys residues and the key residues involved in peptide hormone binding is established by comparison of conophysin sequences, with the crystallographically characterized sequence of bovine neurophysin, in complex with vasopressin. A survey of available sequences for oxytocin/vasopressin peptides in both vertebrates and invertebrates establishes the conopressins as a distinct group in this family. C-terminal amidated, truncated conopressin analogs may arise by alternate post-translational processing
Diffusion barrier with 30-fold improved performance using AlCrTaTiZrN high-entropy alloy
No full textHigh-entropy alloys nitrides (HEA-N) have been proposed as diffusion barriers to prevent metal diffusion. Due to their lack of grain-boundaries and large lattice distortion, HEA-N have lower diffusion than binary nitrides. Despite the interest, very few quantitative studies have been performed to precisely measure metal diffusion in HEA-N. Here we report, for the first time, iron diffusion rates and activation energy in AlCrTaTiZrN HEA-N thin-films, and demonstrate that they are lower than reported values in TiN. AlCrTaTiZrN was deposited on steel from a metal alloy target using reactive radio frequency sputtering under various nitrogen flow rates. X-ray diffraction shows that as the nitrogen flow rate increases, microstructure of the films changes from amorphous to nanocrystalline. Thermal stability studies at 700 -900 degrees C show that AlCrTaTiZrN remains chemically and structurally stable up to 800 degrees C. SIMS shows that the HEA-N films effectively block Fe diffusion up to 800 degrees C. At higher temperatures, the films are mechanically stable but not effective as barrier films, due to recrystallization in AlCrTaTiZrN. The measured diffusion coefficient is 7 x 10(-22) m(2)s(-1) at 700 degrees C, 30 times lower than any polycrystalline nitride barrier reported in literature. The study not only conclusively demonstrates the effectiveness of AlCrTaTiZrN as diffusion barrier, it also provides quantitative data that can be used by engineers to precisely design barrier layers
Low power all optical switching and implementation of universal logic gates using micro-bubbles in semiconductor nanocrystal solutions
No full textWe describe optical switching in solutions of semiconductor nanocrystals illuminated by a 404 nm continuous wave laser source, driven by the formation of a micro-bubble of solvent vapor in the solution. Low boiling solvents such as hexane show an oscillatory modulation of transmitted light intensity (period similar to 4 s) while solvents with intermediate boiling points such as toluene give a stable switching response. An on/off ratio of 83% is observed in the transmitted pump beam. Using this, a pump beam (404 nm, 80 mW continuous wave) was shown to reversibly switch the state of a probe laser (630 nm, 5 mW continuous wave). This switch thus serves as an optical analog of an electronic transistor and demonstrates the potential for all optical switching of low power light beams. Further, all optical universal logic gates, NAND and NOR, were also demonstrated using the micro-bubble switch
Manifestation of intermediate phase in Cu doped Si-Te glasses
No full textAlternating differential scanning calorimetry (ADSC) analysis has been carried out on bulk Si15Te85-xCux(1≤x≤10) glasses to examine the thermal properties of the glassy samples in detail. The investigations on thecompositional dependence ofΔHNR(non- reversing enthalpy) manifests a trough between the composition2≤x≤6 which stands as the basis of the presence of Boolchand's Intermediate phase in that range.Additionally, anomalous behavior has been observed at the compositional dependence of various thermalparameters atx= 9, which stipulates the appearance of chemical threshold at the stated composition. Annealedbulk samples have been exposed to XRD studies to discern the type of formed crystalline phases. The study hasreported the manifestation of Te, Si1Te2,Si2Te3,Cu3Te2 phases
Microwave irradiation assisted rapid growth of ZnO nanorods over metal coated/electrically conducting substrate
No full textIn-spite of intense research in the growth of ZnO over the years, the direct crystallization of ZnO on a metal coated/electrically conducting substrate by a solution growth process has not been carried out. We report one pot, low temperature (�100 °C) and rapid growth (5 min) of ZnO nanorods over an electrically conducting substrate by using microwave irradiation assisted thin film deposition in a liquid medium without the use of any seed layer. High density (2 � 109/cm2), c-axis oriented, uniform and continuous ZnO nanorod films are grown over Cr/Si chromium coated Si(1 0 0) and ITO/glass (indium tin oxide coated glass) substrates whereas aluminium (Al) and gold (Au) coated Si yield non uniform film with mixed texture. Microwave irradiation for 5 min ensures strongly oriented growth of ZnO over Cr/Si and ITO/glass and mixed texture for semiconducting substrates (Si/Ge). The initial nucleation of ZnO nanorods may be due to the formation of thin amorphous oxide (Cr2O3) layer over Cr film, which subsequently changes to hydroxides (CrOH2, CrOH3) in contact with water
Morphology and corrosion properties of FeMn-Graphene oxide composite coatings
No full textMorphology and corrosion properties of electrodeposited iron manganese-graphene oxide (FeMn-GO) composite coatings was investigated as a function of the GO content. The composite coatings exhibited uniform and compact morphology for lower concentrations of GO in the coating. For higher GO concentrations, agglomeration of GO in the electrolyte bath resulted in non-uniform coating morphology with large surface defects. The influence of GO concentration and coating morphology on the corrosion properties of the coatings was studied by Tafel polarization and electrochemical impedance spectroscopic (EIS) techniques. The impermeability of GO to the corrosive media enhanced the corrosion properties of the composite coatings, with respect to pristine FeMn coating, up to the optimum GO concentration, after which the corrosion resistance behaviour of the composite coatings degraded due to defects and micro-pores present on the surface of the coatings
Dual roles of a transparent polymer film containing dispersed N-doped carbon dots: A high-efficiency blue light converter and UV screen
No full textWe report the synthesis of a transparent plastic material with very high performance ultraviolet (UV)-blocking and blue-light (440 nm) emission. Polyvinyl alcohol (PVA) was employed as a transparent plastic matrix that disperses N-doped carbon dots (N-CDs) prepared via hydrothermal treatment of citric acid, ethylene diamine, and HCl solution. Luminescence of these N-CDs is excitation-independent and the quantum yield (QY) is maximal at an excitation wavelength range of 350�370 nm, in the UV-A radiation segment of the solar spectrum. By encapsulating N-CDs in a polyvinyl alcohol (PVA) matrix, the absolute QY achieves 91, which is higher than in aqueous solution. As the particle concentration increases in PVA matrix or in solution, UV absorbance increases and QY decreases. On the other hand, UV absorbance of the film is proportional to thickness with no appreciable deterioration in QY, a quality that is beneficial for UV light absorption as well as conversion into blue light. We propose that this N-CD/PVA composite is an ideal transparent plastic for UV-ray shielding, as well as being useful for blue light emission, composed only of eco-friendly nontoxic elements. The high UV absorption and strong luminescence of N-CDs are beneficial also for other applications that include anti-counterfeiting (secret inks) and greenhouse sheathing that simultaneously blocks UV-rays while generating blue light to promote plant growth