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Unusual Behavior of Donor-Acceptor Stenhouse Adducts in Confined Space of a Water-Soluble Pd-8(II) Molecular Vessel
No full textDonor-acceptor Stenhouse adducts (DASA) are new-generation photochromic compounds discovered recently. DASA exist normally in open form (blue/violet) and readily convert to cyclic (light yellow/colorless) zwitterionic form reversibly in the presence of green light in toluene/dioxane. In aqueous medium, the open form is not stable and converts to the cyclic zwitterionic form irreversibly. We report here a new self assembled Pd8 molecular vessel (MV) that can stabilize and store the open form of DASA even in aqueous medium. Reaction of the 90 acceptor cis-(tmeda)Pd(NO3)(2) (M) tmeda = N,N,N',N'tetramethylethane-1,2-diamine] with a symmetric tetraimidazole donor (L, 3,3',5,5'-tetra(1H-imidazol-1-y1)-1,1'-biphenyl) in a 2:1 molar ratio yielded a water-soluble 8+4] self-assembled M8L4 molecular barrel (MV). This barrel (MV) is found to be a potential molecular vessel to store and stabilize the open forms of DASA in aqueous medium over the more stable zwitterionic cyclic form, while in the absence of the barrel the same DASA exist in cyclic zwitterionic form in aqueous medium. The hydrophobic interaction between the cavity and the open form of DASA molecules benefits reaching an out-of-equilibrium or reverse equilibrium state in aqueous medium. The presence of excess MV could even drive the conversion of the stable cyclic form to the open form in aqueous medium. The host guest complex is stable upon irradiating with green light. To the best of our knowledge, this is the first successful attempt to stabilize the open form of DASA molecules in aqueous medium and the first report on the fate of DASA in a confined space discrete molecular architecture. Furthermore, the molecular vessel has been utilized for catalytic Michael addition reactions of a series of nitrostyrene derivatives with 1,3-indandione in aqueous medium
A proline insertion-deletion in the spike glycoprotein fusion peptide of mouse hepatitis virus strongly alters neuropathology
No full textFusion peptides (FPs) in spike proteins are key players mediating early events in cell-to-cell fusion, vital for intercellular viral spread. A proline residue located at the central FP region has often been suggested to have a distinctive role in this fusion event. The spike glycoprotein from strain RSA59 (PP) of mouse hepatitis virus (MHV) contains two central, consecutive prolines in the FP. Here, we report that deletion of one of these proline residues, resulting in RSA59 (P), significantly affected neural cell syncytia formation and viral titers postinfection in vitro. Transcranial inoculation of C57Bl/6 mice with RSA59 (PP) or RSA59 (P) yielded similar degrees of necrotizing hepatitis and meningitis, but only RSA59 (PP) produced widespread encephalitis that extended deeply into the brain parenchyma. By day 6 postinfection, both virus variants were mostly cleared from the brain. Interestingly, inoculation with the RSA59 (P)-carrying MHV significantly reduced demyelination at the chronic stage. We also found that the presence of two consecutive prolines in FP promotes a more ordered, compact, and rigid structure in the spike protein. These effects on FP structure were due to proline's unique stereochemical properties intrinsic to its secondary amino acid structure, revealed by molecular dynamics and NMR experiments. We therefore propose that the differences in the severity of encephalitis and demyelination between RSA59 (PP) and RSA59 (P) arise from the presence or absence, respectively, of the two consecutive prolines in FP. Our studies define a structural determinant of MHV entry in the brain parenchyma important for altered neuropathogenesis
Stable isotopic composition of rice grain organic matter marking an abrupt shift of hydroclimatic condition during the cultural transformation of Harappan civilization
No full textSeveral hypotheses have been proposed to solve the conundrum of the cause of transition of Harappan civilization to a de-urbanized form in its Late Phase. In view of this, high-resolution off-site palaeoclimatic records along with archaeological findings provide strong evidence of an abrupt climate change similar to 4000 yr BP (before present) that coincides with the civilization's cultural transition. The present study investigates whether this climatic shift recorded in palaeoclimate archives (speleothem, lake and marine sediments) at remote locations can be traced to the human settlements of Harappan civilization. This was accomplished by analyzing the remains of rice cereal-a highly water sensitive crop. The analysis involved measuring carbon and nitrogen isotopic compositions (delta C-13, delta N-15) of well-preserved rice grains recovered from archaeological sites belonging to the Harappan civilization and other contemporary regional cultures, representing the time windows between 4520 and 3400 yr BP. The parameter of intrinsic water use efficiency (WUEi) was used as an index for water availability in the rice crop's growth environment and was ascertained based on delta C-13 values measured in the bulk grain organic matter (OM). The observed WUEi values ranged between 49 and 69 mu mol mol(-1) and captured the variation in water availability. The delta N-15 values ranged from 5 parts per thousand to 6.5 parts per thousand, thereby allowing us to confirm the role of climate in controlling delta C-13 variation in the archaeological grains. The present findings will extend the usage of archaeobotanical cereal remains to deduce environmental changes at human settlements and will further our understanding of the process of Harappan cultural adaptation in response to decline in southwest monsoon at the Middle-Late Holocene boundary
Control of wave propagation response using quasi crystals: A formulation based on spectral finite element
No full textThis paper presents wave propagation studies in quasi crystal structures and quasi crystal reinforced aluminium structures. The analysis is performed using frequency domain spectral finite element formulation. The analysis considers different 2-D decagonal and 3-D icosahedral quasi crystals. First, wave propagation analysis of quasi crystal structure alone is performed and the propagation of phonon and phason modes for different quasi crystals are studied. The study includes the propagation of axial and transverse wave responses in these quasi crystals. The study has found that the amplitude of the phason modes is very small compared to the phonon modes and the increase of the phason mode content (through increase in R) increases the phason mode amplitude, without affecting the phonon mode amplitudes. It is shown that the dominant axial phonon mode is non-dispersive and the dominant flexural phonon mode is dispersive. In the next study, the aluminium beam structure is reinforced with different quasi crystals in different configurations and the wave propagation of axial and transverse responses are studied. For all the combinations of quasi crystal aluminium beam combination, there is substantial suppression of responses both for the axial and the bending responses. Unsymmetrical configuration produces substantial non-dominant phonon modes which propagate dispersively. It is found that for a symmetric bi-morph configuration, the response is reduced significantly, about 68% and 75% for axial loading and 80% and 78% for flexural loading, respectively, for the 2-D decagonal quasi crystal and the 3-D icosahedral quasi crystal
Low Complexity Decoding and Capacity of Index Coding Problems with Symmetric Side-Information
No full textA single unicast index coding problem (SUICP) with symmetric side-information has K messages and K receivers, the kth receiver R-k wants x(k), R-k has some subset of messages as side-information and the side-information is symmetric to its wanted message x(k). Maleki, Cadambe and Jafar studied various symmetric index coding problems because of their importance in topological interference management problems. In our previous work, we constructed binary matrices of size `in x n. for any given arbitrary positive integers m. and n. such that any n, adjacent rows of this matrix are linearly independent. We refer these matrices as Adjacent Independent Row (AIR) matrices. We designed optimal and near-optimal vector linear index codes for various symmetric SUICPs by using AIR matrices. To design the optimal and near -ptimal vector linear index codes, we convert the respective symmetric SUICP into an SUICP with symmetric neighboring and consecutive (SNC) side-information. Then, we use AIR matrix to encode the STACY with SNC side-information. Hence, low-complexity decoding of SUICP with SNC side-information is important for efficient decoding of optimal and near-optimal index codes for various symmetric SUICPs. We analyse some of the combinatorial properties of AIR matrices in this work. By using these properties, we provide a low-complexity decoding for SUICP with SNC side-information. The low-complexity decoding explicitly identifies the set of broadcast symbols required at every receiver to decode its wanted message. By using low complexity decoding, we find the capacity of SUICP with symmetric side-information K-k = {Xk+g,Xk+2g,..x(k+)t(g)}, where g = gcd(K, D) and t = D/g for any positive integer D < K
Strong Single- and Two-Photon Luminescence Enhancement by Nonradiative Energy Transfer across Layered Heterostructure
No full textThe strong light matter interaction in monolayer transition metal dichalcogenides (TMDs) is promising for nanoscale optoelectronics with their direct band gap nature and the ultrafast radiative decay of the strongly bound excitons these materials host. However, the impeded amount of light absorption imposed by the ultrathin nature of the monolayers impairs their viability in photonic applications. Using a layered heterostructure of a monolayer TMD stacked on top of strongly absorbing, nonluminescent, multilayer SnSe2, we show that both single-photon and two-photon luminescence from the TMD monolayer can be enhanced by a factor of 14 and 7.5, respectively. This is enabled through interlayer dipole dipole coupling induced nonradiative Forster resonance energy transfer (FRET) from SnSe2 underneath, which acts as a scavenger of the light unabsorbed by the monolayer TMD. The design strategy exploits the near-resonance between the direct energy gap of SnSe2 and the excitonic gap of monolayer TMD, the smallest possible separation between donor and acceptor facilitated by van der Waals heterojunction, and the in-plane orientation of dipoles in these layered materials. The FRET-driven uniform single- and two-photon luminescence enhancement over the entire junction area is advantageous over the local enhancement in quantum dot or plasmonic structure integrated 2D layers and is promising for improving quantum efficiency in imaging, optoelectronic, and photonic applications
Evolution of oxides and their microstructures at 800 degrees C in a gamma-gamma ` stabilised Co-Ni-Al-Mo-Ta superalloy
No full textThe paper reports mechanism of high temperature oxidation of the new gamma'-strengthened Co-30Ni-10Al-5Mo-2Ta (at%) alloy. The plots of mass gain vs. time show a parabolic growth behaviour at a temperature range of 650-800 degrees C. The cross-sections of the oxidised samples reveal formation of a complex multilayer of oxides. The top layer comprises of Co3O4 followed by a solid solution of (Co1-xNix)O (x varying from 0-0.2). A middle layer evolves with time comprising hexagonal molybdate Co2Mo3O8, metastable TaO and amorphous Al2O3. The gamma' dissolve near the interface exposing the gamma solid solution with growth of amorphous Al2O3 along the grain boundary
Hole Injection and Rectifying Heterojunction Photodiodes through Vacancy Engineering in MoS2
No full textThe lack of techniques for counter doping in two dimensional (2D) semiconductors has hindered the development of p/n junctions, which are the basic building blocks of electronic devices. In this work, low-energy argon ions are used to create sulfur vacancies and are subsequently ``filled'' with oxygen to create p-doped MoS2-xOx. The incorporation of oxygen into the MoS2 lattice and hence band-structure modification reveal the nature of the p-type doping. These changes are validated by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Raman spectroscopy, and photoluminescence measurements combined with density functional theory calculations. Electrical measurements reveal a complete flip in carrier polarity from n-type to p-type, which is further examined using temperature-dependent transport measurements. The enhancement of p-field-effect transistor characteristics is facilitated by employing top-gated transistors and area-selective vacancy engineering only in the contact regions. Finally, on the same flake, an in-plane MoS2 (n)/MoS2-xOx (p) type-I (straddling) heterojunction with rectifying behavior and excellent broadband photoresponse is demonstrated and explained using band diagrams. The spatial/metallurgical abruptness (<100 nm) of the heterojunctions is ascertained using Raman mapping. This process of vacancy engineering, which enables air-stable, area-selective, controlled, CMOS-compatible doping of 2D semiconductors is envisioned to open new vistas in the development of high-performance electronic and optoelectronic devices
Room temperature phosphorescent triarylborane functionalized iridium complexes
No full textWe report a series of room temperature phosphorescent compounds 1-6 composed of triarylborane (TAB) and cyclometallated iridium complexes. The optical characteristics such as energy of transition and luminescence quantum yield of these compounds can be conveniently fine-tuned by judiciously varying the cyclometallating ligand and the spacer between boron and iridium centers. Compounds 1-6 exhibit bright phosphorescence with the emission color ranging from green to red under a N-2 atmosphere. A maximum quantum yield of 0.95 was observed for complex 2. Complexes 1-6 exhibit a rare type of dual emission from singlet and triplet excited states under ambient conditions. The experimental observations are well supported by the theoretical calculations
Time-resolved temperature characterization of a hypersonic shock layer using a single high-speed color camera for aerospace design applications
No full textTwo-color ratio pyrometry (TCRP) using a high-speed color camera has been used for temperature characterization of a hypersonic shock layer. The camera, used as a pyrometer, was calibrated in-house using a monochromator to determine its spectral responsivity and was used to acquire time-resolved images of the flow field over test models at a frame rate of 20 000 fps to understand the evolution of temperature inside the shock region. The optical efficiency of the monochromator and other optical equipment were determined separately and corrected for. Two test models, a flat-faced cylinder of diameter 70 mm and a hemisphere of diameter 80 mm, were used for the experiments to study the effect of geometry on the results. Experiments were performed in a free-piston-driven shock tunnel at a stagnation enthalpy of 5.2 MJ kg(-1). The average steady-state temperature in the stagnation region in the cylinder was about 3650 K +/- 3% (uncertainty in the shock layer due to camera noise), and for the hemisphere it was 3300 K +/- 6%. The resolved temperature was 14% higher than that obtained from a similar, but time-integrated, measurement obtained using a digital single lens reflex (DSLR) camera. Steady 2D numerical simulations were performed to reconstruct the 3D flow assuming azimuthal symmetry, and an algorithm was developed to use the shape of the temperature profile along the line-of-sight (LOS) derived from simulations to predict the actual stagnation-plane temperature from the experimental LOS-integrated TCRP-derived temperature. The actual temperature in the stagnation region on the vertical plane of symmetry (stagnation plane) for the cylinder and the hemisphere were higher by 2.76% and 1.77%, respectively, than the corresponding TCRP-derived LOS-integrated temperature. The results are promising for future use in determining intense temperature gradients and heat flux in the vicinity of space vehicles and for the design of efficient thermal protection systems