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Probing electronic structures of redox-active ruthenium-quinonoids appended with polycyclic aromatic hydrocarbon (PAH) backbone
No full textThe newly designed electrically neutral complexes [Ru(acac)(2)(Q)] (1-3) involving redox-active polycyclic aromatic hydrocarbon (PAH) derived quinonoids (Q): Q(1)((O,O)) (1) Q(2)((O,NH)) (2) Q(2)((NH,NH)) (3) (acac = acet- ylacetonate) were prepared from the metal precursor [Ru-II(acac)(2)(CH3CN)(2)] and preformed pyrene-4,5-dione (Q(1)) and partially deprotonated pyrene-4,5-diamine (H(4)Q(2)), respectively. The structural characterization of 1-3 established their molecular identities including intermolecular pi-pi stacking interactions between the extended pi-system of pyrene in the adjacent molecules and the hydrogen bonded 1D-polymeric form of 3. The redox sensitive C-O and C-N bond distances of Q in 1, 2 and 3 revealed the dominating ground state electronic forms of [(acac)(2)Ru-III-Q(1)((O,O))(center dot-)] (S = 0), [(acac)(2)Ru-III-Q(2)((O,NH)center dot-)] (S = 0) and [(acac)(2)Ru(II)Q(2)((NH,NH)o)] (S = 0), respectively, where strong antiferromagnetic coupling between Ru-III(t(2g)(5)) and Q(center dot-) resulted in S = 0 state in 1 or 2. Complexes 1-3 exhibited reversible single oxidation and reduction within the potential window of +/- 1.5 V versus SCE in CH3CN, which progressively shifted to the negative potential on moving from 1 to 2 to 3, primarily due to the difference in electronegativity between O and N donors of Q. The collective consideration of experimental (EPR, electronic spectra) and theoretical (DFT, TD-DFT) results of 1(n)-3(n) (n = +1, 0, -1) revealed (i) extensive mixing of metal-ligand orbitals due to the inherent covalency factor and (ii) Q(center dot-) and Ru-II based oxidations of 1/2 and 3, respectively, led to the {Ru-III-Q(o)} electronic form at the metal-ligand interface of the oxidized state (1(-).3(-)), while the reduced state (1(-)-3(-)) could best be described by the resonating form of {Ru-II-Q(center dot-)} {Ru-III-Q(2-)}
Sivers and cos 2 phi asymmetries in semi-inclusive deep inelastic scattering in light-front holographic model
No full textThe spin asymmetries in SIDIS associated with T-odd TMDs are presented in a light-front quark-diquark model of a proton. To incorporate the effects of the final-state interaction, the light front wave functions are modified to have a phase factor which is essential to have Sivers or Boer-Mulders functions. The Sivers and Boer-Mulder asymmetries are compared with HERMES and COMPASS data
Intramolecular Distance Distribution Reveals Mechanisms in Protein Folding and Dynamics
No full textFlexibility and dynamics in polypeptides and proteins give rise to conformational and structural heterogeneity. Quantification of the level of heterogeneity is essential for providing deeper understanding of molecular mechanisms in protein folding. Fluorescence lifetime distribution generated by the maximum entropy method (MEM) provides an unbiased estimate of intramolecular distance distribution. This article discusses several examples where MEM-generated lifetime distribution brings out site-specific conformational and structural heterogeneity in proteins. Use of the information on intamolecular distance distribution in revealing molecular mechanisms of protein folding is also discussed
Competing magnetic and spin-gapless semiconducting behavior in fully compensated ferrimagnetic CrVTiAl: Theory and experiment
No full textWe report the structural, magnetic, and transport properties of the polycrystalline CrVTiAl alloy along with first-principles calculations. The alloy crystallizes in a LiMgPdSn-type structure with a lattice parameter of 6.14 angstrom at room temperature. The absence of the (111) peak along with the presence of a weak (200) peak indicates the antisite disorder of Al with Cr and V atoms, which is different from the pure DO3 type. Magnetization measurements reveal amagnetic transition near 710 K, a coercive field of similar to 100 Oe at 3 K, and a moment of similar to 10(-3) mu(B)/f.u. These observations are indicative of fully compensated ferrimagnetism in the alloy, which is confirmed by theoretical modeling. The temperature coefficient of resistivity is found to be negative, signaling the semiconducting nature. However, the absence of exponential dependence indicates the semiconducting nature with gapless/spin-gapless behavior. Electronic and magnetic properties of CrVTiAl for all three possible crystallographic configurations are studied theoretically. All the configurations are found to be different forms of semiconductors. The ground-state configuration is a fully compensated ferrimagnet with band gaps of 0.58 and 0.30 eV for the spin-up and -down bands, respectively. The next-higher-energy configuration is also fully compensated ferrimagnetic but has a spin-gapless semiconducting nature. The highest-energy configuration corresponds to a nonmagnetic, gapless semiconductor. The energy differences among these configurations are quite small (< 1 mRy/atom), which hints that, at finite temperatures, the alloy exists in a disordered phase, which is a mixture of the three configurations. By taking into account the theoretical and experimental findings, we conclude that CrVTiAl is a fully compensated ferrimagnet with a predominantly spin-gapless semiconducting nature
Impact of modulation bandwidth on multiplexing using principal modes in MMF links
No full textMultimode fibers (MMFs) are widely used for short fiber links. However, the data rates through MMFs is limited owing to modal dispersion. The so-called "principal modes" (PMs) permit transmission and multiplexing through the MMFs without modal dispersion for small modulation bandwidths. For larger modulation bandwidths, however, they lose their dispersion-free nature. In this paper, we model the impact of modulation bandwidth and mode coupling strength on the performance of PMs. We develop a simulator that characterizes the dispersion and cross-talk of the PMs of few-mode and large-core graded-index MMFs with mode-dependent losses (MDL). Simulations reveal that for fibers without MDL, for modulation frequencies beyond 10 GHz diminishes the PMs' frequency response by more than 1 dB for 100 m in large-core MMF links and 10 km few-mode fiber links. With MDL, simulations reveal that for modulation bandwidths beyond 2 GHz diminishes the frequency response by 3 dB for a 1 km few-mode fiber and by more than 4 dB for a 1 km large-core multimode fiber. While multiplexing using PMs in large-core MMFs with MDL, we find that for modulation bandwidths beyond 3 GHz, the cross-talk is 20 dB in 1 km large-core MMF links, thereby limiting system performance. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
Effect of Prior Austenite Grain Size on the Morphology of Nano-Bainitic Steels
No full textThe strength in nanostructured bainitic steels primarily arises from the fine platelets of bainitic ferrite embedded in carbon-enriched austenite. However, the toughness is dictated by the shape and volume fraction of the retained austenite. Therefore, the exact determination of processing-morphology relationships is necessary to design stronger and tougher bainite. In the current study, the morphology of bainitic ferrite in Fe-0.89C-1.59Si-1.65Mn-0.37Mo-1Co-0.56Al-0.19Cr (wt pct) bainitic steel has been investigated as a function of the prior austenite grain size (AGS). Specimens were austenitized at different temperatures ranging from 900 A degrees C to 1150 A degrees C followed by isothermal transformation at 300 A degrees C. Detailed microstructural characterization has been carried out using scanning electron microscopy and X-ray diffraction. The results showed that the bainitic laths transformed in coarse austenite grains are finer resulting in higher hardness, whereas smaller austenite grains lead to the formation of thicker bainitic laths with a large fraction of blocky type retained austenite resulting in lower hardness
3D study of temperature drop behavior of subsonic rarefied gas flow in microchannel
No full text3D Numerical study of temperature variation for subsonic rarefied gas flow in a microchannel is carried out using an in-house MPI-based parallelized DSMC code. The temperature drop in the microchannel decreases with an increase in the aspect ratio whereas it increases with an increase in the pressure ratio, the cross-aspect ratio (CAR), and the Knudsen number. 3D and 2D simulations results are compared and effect of the CAR and Knudsen number are brought out. Finally, a correlation that predicts the temperature drop is formulated along with a list of conditions that ensures a near isothermal flow
Effect of positional isomerism on the spectroelectrochemical response of 3,6-bis(2-pyridyl)-diketopyrrolopyrrolate bridged bis(carbonylhydridoruthenium) compounds
No full textReaction of 3,6-bis(2-pyridyl)-diketopyrrolopyrrole (H-2-BPDPP) with two equivalents of [Ru(H)(CO)(Cl)(PPh3)(3)] in EtOH produced two symmetrical dinuclear isomers, (-BPDPP)[Ru(CO)H(PPh3)(2)](2), green 1 and blue 2, which could be separated chromatographically and characterised spectroscopically (H-1 and P-31 NMR, IR, and UV-VIS). Isomeric forms of 1 and 2 were authenticated using their single crystal X-ray structures. In addition to the essentially planar bis-chelating bridge BPDPP2- and the mutually trans positioned axial PPh3 ligands in both complexes, compound 1 was established with the CO groups trans to the pyrrolate-N atoms, whereas 2 has the acceptors CO and pyridine-N situated trans to each other. While the reduction of 1 and 2 proceeds irreversibly at negative potentials, the reversible oxidations at rather low potentials could be monitored by EPR and UV-VIS-NIR absorption measurements. Together with TD-DFT calculations, these results reveal that the primary electron transfers are largely confined to the BPDPP ligand. Despite the bridge centred processes, small differences between the isomers 1(0/+) and 2(0/+) were found, affecting e.g. the near infrared absorption of the radical cation species
Ballistic impact performance of spaced multilayered and monolithic composite targets: Analytical and experimental studies
No full textBallistic impact performance of spaced multilayered and monolithic composite targets is presented based on propagation of stress wave and energy balance within the target and the impacting projectile. The energy dissipated by the impacting projectile gets absorbed by the composite target through several energy absorbing mechanisms. Specifically, studies are performed on spaced bilayered target separated by air gap and monolithic target having the same total thickness. Energy absorption due to several mechanisms, contact force, projectile velocity, projectile tip displacement, and kinetic energy of the projectile with respect to time are presented. Also, ballistic limit velocity (V-BL) and total energy absorption of the target with respect to target thickness have been evaluated. Spaced bilayered composite targets have higher ballistic limit velocity compared to monolithic composite targets from total target thickness of 16-28mm. Monolithic composite targets have higher ballistic limit velocity compared to spaced bilayered composite targets up to total target thickness of 16mm and beyond target thickness of 28mm. Experimental studies were performed for the validation of analytical results. The analytically predicted value of ballistic limit velocity matches well with the experimental value
An Improved Prediction of Indian Summer Monsoon Onset From State-of-the-Art Dynamic Model Using Physics-Guided Data-Driven Approach
No full textPrediction of Indian Summer Monsoon onset, which marks the beginning of the South Asian monsoon, has significant implications on monsoon characteristics and subsequent nationwide agricultural planning. Here we make the most skillful prediction of monsoon onset with a physics-guided data-driven model integrated with the operational monsoon prediction by Coupled Forecast System version 2. Drivers of the variability of onset, which are well simulated by Coupled Forecast System version 2, viz., tropical Pacific sea surface temperature, reversal of tropospheric temperature gradient and strengthening of westerlies over AS during the early summer are identified as potential predictors. Data-driven method, Least Absolute Shrinkage and Selection Operator, makes the final selection of predictors for the linear regression model of onset. We obtain an improved correlation of 0.6 between simulated and observed onset dates with the proposed integrated statistical dynamical model as compared to 0.44 obtained with the operational dynamic monsoon prediction model