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Zinc-Catalysed Hydroboration of Terminal and Internal Alkynes
No full textA regioselective hydroboration of alkynes has been developed by using commercially available zinc triflate as a catalyst, in the presence of catalytic amount of NaBHEt3. The reaction tolerates a wide range of terminal alkynes having several synthetically useful functional groups and proceeds regioselectively to furnish hydroborated products in moderate to excellent yields. This system shows moderate chemoselectivity towards terminal C equivalent to C bond over terminal and internal C=C bond and internal C equivalent to C bond
Structural and electrochemical investigation of binary Na2Fe1-xZnxP2O7 (0 <= x <= 1) pyrophosphate cathodes for sodium-ion batteries
No full textTransition metal pyrophosphate material forms a robust polyanionic cathode family for sodium-ion batteries. Here, binary Na-2(Fe1-yMny)P2O7 (0 <= y <= 1) system has been recently investigated by different groups, as Na2FeP2O7 is reported as a low-cost cathode with promising electrochemical performance and thermal stability. While the isostructural Na2FeP2O7 and Na2MnP2O7 assume triclinic P1 (#2) framework, pyrophosphate system shows structural diversity/polymorphism. Considering this, we have investigated the binary Na-2(Fe1-xZnx)P2O7 (0 <= x <= 1) pyrophosphate family with anisostructural end members Na2FeP2O7 (P1, #2) and Na2ZnP2O7 (P4(2)/n, #86). The current study reports solution combustion as well as solid-state preparation of novel Na-2(Fe1-xZnx)P2O7 (0 <= x <= 1) family of materials, their structural and electrochemical characterizations. The degree of solid-solution formation and effect of Zn on Fe-redox activity in Na-2(Fe1-xZnx)P2O7 (x = 0, 0.25) cathodes has been examined using electrochemical titration techniques such as galvanostatic intermittent titration (GITT) and potentiostatic intermittent titration (PITT) mode
Synapse loss and progress of Alzheimer's disease - A network model
No full textWe present observational evidence from studies on primary cortical cultures from AD transgenic mice, APPSwe/PS1 Delta E9 (APP/PS1) mice, for significant decrease in total spine density at DIV-15 and onward. This indicates reduction in potential healthy synapses and strength of connections among neurons. Based on this, a network model of neurons is developed, that explains the consequent loss of coordinated activity and transmission efficiency among neurons that manifests over time. The critical time when structural connectivity in the brain undergoes a phase-transition, from initial robustness to irreparable breakdown, is estimated from this model. We also show how the global efficiency of signal transmission in the network decreases over time. Moreover, the number of multiple paths of high efficiency decreases rapidly as the disease progresses, indicating loss of structural plasticity and inefficiency in choosing alternate paths or desired paths for any pattern of activity. Thus loss of spines caused by beta-Amyloid (A beta) peptide results in disintegration of the neuronal network over time with consequent cognitive dysfunctions in Alzheimer's Disease (AD)
Influence of Cr3+ doping on multiferroic properties in the morphotropic phase boundary compositions of BiFeO3-PbTiO3 system
No full textIn this paper, we have investigated the effect of Cr3+ substitution on the crystal structure, microstructure, dielectric and magnetic behavior of the morphotropic phase boundary (MPB) composition of the multiferroic ceramic 0.675BiFe((1-x))Cr(x)O(3)-0.325PbTiO(3) (x = 0, 0.02 and 0.05). The average grain size of the specimens increased from similar to 150 nm for x = 0 to 470 nm for x = 0.05. Rietveld refinement analysis of the X-Ray powder diffraction patterns confirmed the coexistence of multiphase i.e. monoclinic Cc and tetragonal P4 mm polymorphs for all the compositions. The system exhibits weak ferromagnetism for x = 0.05. We estimated the magnetoelectric interaction constant (gamma similar to 0.31) for x = 0.05 by Ginzburg-Landau theory. The value of magnetoelectric coupling coefficient is found to be 0.054 mV/cm-Oe, 0.073 mV/cm-Oe, 0.133 mV/cm-Oe for x = 0, 00.02 and 0.05, respectively. High temperature dielectric data also reveals that Curie temperature decreases with increasing Cr3+ concentration
A novel Spatio-Temporal Fuzzy Inference System (SPATFIS) and its stability analysis
No full textModeling an online time series problem is often a challenging task because of the intrinsic dynamical characteristics of the underlying data distribution and the uncertainty stemming from the data. Hence, we propose a novel Spatio-Temporal Fuzzy Inference System (SPATFIS). One of the prime features of SPATFIS lies in the inclusion of memory type neurons which incorporates both spatial and temporal information of the sequences with a dual recurrent structure in its input and defuzzification layers. SPATFIS also proposes a new self-adaptive learning mechanism to add, eliminate and unify its fuzzy rules. This helps it to attain a parsimonious rule base. Furthermore, stability is rigorously inspected and SPATFIS is proved to be stable using Lyapunov's Input to State Stability theorem. The stability analysis encompasses both the structure and the parameter learning phases. To evaluate the efficacy of SPATFIS numerically, it is compared against state-of-the-art self-adaptive neuro-fuzzy systems with benchmark time series problems from the literature. We also evaluate SPATFS' performance under prequential First-Test-Then-Train protocol to show its suitability in handling data stream. The experimental results distinctly indicate SPATFIS to be significantly faster while retaining competitive accuracy and a compact rule base. A thorough statistical analysis is conducted afterwards to further affirm its advantages
Phonon limited anisotropic quantum transport in phosphorene field effect transistors
No full textElectron-phonon coupling limited transport in phosphorene metal oxide semiconductor field effect transistors (MOSFETs) is studied along the armchair (AC) and zigzag (ZZ) directions. In a multiscale approach, the unit cell of phosphorene is first relaxed, and the band structure is calculated using hybrid density functional theory (DFT). The transport equations are then solved quantum mechanically under the nonequilibrium Green's function formalism using DFT-calibrated two-band k.p hamiltonian. The treatment of electron-phonon scattering is done under the self-consistent Born approximation in conjunction with deformation potential theory. It is found that optical phonon modes are largely responsible for degradation of ON-current apart from p-channel AC MOSFET where acoustic phonon modes play a stronger role. It is further observed that electron-phonon scattering is more pronounced in the ZZ direction, whereas the diffusive ON-current of p-MOSFET in a given direction is higher than n-MOSFET. Further study on the complex band structure of phosphorene reveals band wrapping within the bandgap region in the AC direction and multiple crossings in the ZZ direction. This signifies strong phonon-assisted tunneling in the ZZ direction in comparison with the AC direction. For completeness, drain current in the AC tunnel field effect transistor is calculated, and electron-phonon scattering is observed only in the near vicinity of the OFF-current
Evaluation of Polymer Solar Cell Efficiency To Understand the Burn-in Loss
No full textIn this study, the degradation process of a conventional P3HT:PC61BM bulk heterojunction solar cell device due to light-induced aging is evaluated. This structure is chosen so as to reduce the number of interface layers. Continuous light aging is done under AM1.5G light, and devices are analyzed in short periods. The measured electrical properties, such as current-voltage, capacitance-voltage, and capacitance-frequency characteristics, and optical and structural properties suggested the process of device degradation progression. In order to investigate the photodegradation of the device and the trap state formation, various device parameters are determined, such as the density of trap states, trap distribution width, peak trap state position, carrier concentration, and built-in potential. The dual peak nature is observed in the capacitance-voltage spectra of the light-aged device. Formation of defect peaks should be attributed to trap states as well as morphological changes: modification at the donor/acceptor and semiconductor/electrode interface. Additionally, the defect peak intensity increases as the light aging period increases. The calculated carrier concentration and density of trap states are observed to be correlated with the device performance. The detailed analysis of the device properties indicates that interface-induced changes are the initial points of device degradation. The initial point of degradation primarily affects short-circuit current and fill factor (FF). Observed changes in the current density, J(SC), and FF are mainly associated with an increase in the series resistance, R-s. Structural and optical properties of as-prepared and aged devices revealed that there is not much change in the absorbance and crystallinity. These results corroborate that the initial device degradation is mainly due to the electrical part (various resistance) associated with the device. Further, the doublet in the capacitance spectrum under the illuminated condition is discussed. The burn-in loss of the solar cell is connected with an increase in the density of trap states. This work provides direct evidence of the formation of defect states in the device, which is portrayed in the capacitance-voltage spectra of aged samples under the illuminated condition
Double Gaussian distribution of barrier heights and self-powered infrared photoresponse of InN/AlN/Si (111) heterostructure
No full textInN epilayer has been grown by plasma-assisted molecular beam epitaxy on the AlN/n-Si (111) substrate. The self-powered photodetection has been carried out with an infra-red (IR) laser (lambda = 1550 nm, power density similar to 106: 2 mA= cm2), where a photoresponsivity was observed to be 3.36 mu A/W with response times in milliseconds from the InN/AlN/n-Si (111)-based semiconductor-insulator-semiconductor (SIS) interface. Furthermore, to elucidate the vertical electrical transport properties of the SIS interface, low-temperature electrical behavior has been investigated over a range of 100-400 K. Experimental studies revealed an abnormal increase in the barrier height and a decrease in the ideality factor with increasing temperature, suggesting inhomogeneous barrier heights across the heterojunctions. Such inhomogeneity behaviors have been successfully explained on the basis of thermionic emission theory, assuming the existence of a double Gaussian distribution of barrier heights at the heterostructure interface. Moreover, the SIS device structure exhibits mean barrier heights (phi wb0) of 1.11 and 0.63 eV, respectively, in two temperature regimes, indicating the presence of defect states and inhomogeneity at the interface, which is supported by the nonlinear behavior of the photocurrent with the power density
Rapid NMR assignments of intrinsically disordered proteins using two-dimensional C-13-detection based experiments
No full textAn approach for rapid backbone resonance assignments in proteins using only two 2D NMR experiments is presented. The new method involves a combination of high-resolution C-13(alpha)-detected NMR experiments and selective unlabeling of amino acid residues. The C-13 detected 2D hNCA and 2D hNcoCA spectra of a uniformly labeled sample of the protein are analysed in concert with the 2D hNCA spectrum obtained for a selectively unlabeled sample. The combinatorial set of amino acid residues for selective unlabeling is chosen optimally to maximize the assignments. The method is useful for rapid assignment of proteins with low stability such as intrinsically disordered proteins and is applicable to deuterated proteins. This approach helped in assignments of 14.5 kDa human alpha-synuclein during the course of its aggregation
Effects of Stacking Fault Energy on Deformation Mechanisms in Al-Added Medium Mn TWIP Steel
No full textIn this study, the effect of aluminum (Al) addition to a manganese (Mn) steel Fe-12Mn-0.5C in regard to the change in stacking fault energy (SFE) and the consequent evolution of deformation microstructure and texture were investigated during cold rolling. An analysis of the texture and microstructure was performed to understand the deformation micro-mechanisms. Deformation micro-mechanisms were substantiated by the estimation of dislocation density and the arrangement of dislocations in the deformed microstructure by X-ray line profile analysis, which revealed significant changes in the dislocation structure with the addition of Al. Three stages of deformation mechanism were observed in all Al-added compositions. In the early stages of deformation, slip as well as twinning prevailed. In the intermediate stage, twinning took over completely and at large strains, macroscopic shear bands became the dominant deformation mode. An increase in the propensity of nanometer-sized deformation twins was observed with rolling strain. However, the addition of Al decreased the overall twin fraction in the deformed microstructure. The theoretical twinning stress was calculated to explain the crucial role of SFE on the occurrence of deformation twins in these steels. The deformation texture was predominantly of the brass type for all the Al-added compositions; however, appreciable differences were seen with Al content. The < 111 >//ND -fiber, which develops in Al-free Fe-12Mn-0.5C, completely disappeared in 3wtpct Al-containing material