Kinetics and mechanism of olefin methylation reactions on zeolites

Ethylene and propylene methylation rates increased linearly with olefin pressure but did not depend on dimethyl ether (DME) pressures on proton-form FER, MFI, MOR, and BEA zeolites at low conversions (<0.2%) and high DME/olefin ratios (30:1) in accordance with a mechanism that involves the zeolite surface being predominantly covered by DME-derived species reacting with olefins. Higher first-order reaction rate constants for both ethylene and propylene methylation were observed over H-BEA and H-MFI compared with H-FER and H-MOR, indicating that olefin methylation reaction cycles involved in the conversion of methanol-to-gasoline over zeolitic acids are propagated to varying extents by different framework materials. Systematically lower activation barriers and higher rate constants were observed for propylene methylation in comparison with ethylene methylation over all frameworks studied, reflecting the increased stability of reaction intermediates and activated complexes with increasing olefin substitution. A binomial distribution of d₀/d₃/d₆ in unreacted DME upon introduction of equimolar protium- and deuterium-form DME under steady-state reaction conditions of ethylene methylation over H-MFI suggests the presence and facile formation of reactive surface-bound methoxide species and the absence of C–H bond cleavage.     

Study of stress intensity factor on the anisotropic machining behavior of single crystal sapphire

The ductile–brittle transition was investigated based on material crystallography and stress intensity factor on the four distinctive planes of sapphire. Cutting forces were analyzed to explain the anisotropic transition characteristics. The projected stress on the objective plane at the transition point was estimated from the critical stress intensity factor of the corresponding crystal plane. Per cutting direction, the effect of crystal planes on the machinability was discussed, and the estimated stress was compared with measured values. Experimental results showed that the anisotropic machinability can be predicted in terms of crystal orientation and the critical stress intensity factor.     

All-solid-state asymmetric supercapacitors based on VS4 nano-bundles and MXene nanosheets

Transition metal sulfides such as MoS₂ and VS₂ have emerged as promising candidates for energy storage applications in recent years. Among the reported transition metal sulfides, the patronite (VS₄) form of vanadium sulfide is less explored and understanding its charge storage mechanisms is unusual in the literature. Here, we report the pseudocapacitive energy storage performance of patronite (VS₄) nano-bundles synthesized via template-free hydrothermal approach by fabricating a solid-state asymmetric supercapacitor device (SSAD) with MXene (Ti₃C₂T_x) as the negative electrode. The fabricated VS₄//MXene SSAD displayed a remarkable supercapacitive behavior in an expanded working potential window of 1.3 V. The device demonstrated a record high performance with the areal capacitance of 70.9 mF/cm² at the scan rate of 5 mV/s and demonstrated ~ 4.5 and ~ 6 times superior areal capacitance as compared to the bare VS₄ nano-bundles and MXene-based symmetric devices. Further, the device displayed an excellent energy density of 5.65 mW h/cm² with a remarkable power density of 290.9 mW/cm² and good cyclic stability ~ 75% after 3000 cycles in neutral electrolyte. Moreover, we have performed extensive density functional theory simulations to present electronic properties of VS₄ and MXene supporting pseudocapacitive behavior for VS₄ through reversible Faradic redox reactions and pre-dominant electrical double-layer capacitive behavior for MXene due to intercalation/de-intercalation of ions. The diffusion energy barrier for electrolytic ions is lower in VS₄ (only 0.17 eV) satisfying better and rapid transport of charge carriers generated in VS₄ justifying high charge storage performance. Populated electronic states for V 3d orbital in both the valence band and conduction band justify superior redox-type behavior for VS₄ supporting experimental observations.

Graphical abstract

Enhanced energy storage performance of asymmetric supercapacitors based on VS4 and MXene.

     

Deep CNN model for crops’ diseases detection using leaf images

Multidimensional Systems and Signal Processing - The agricultural yield of any country provides the base for the development of that nation. Sustainable growth needs to maintain crop production up...     

Generation of Different Modulation Formats Using Sagnac Fiber Loop With One Electroabsorption Modulator

A simple structure is proposed to generate different modulation formats using a single electroabsorption modulator (EAM). The configuration is based on a Sagnac loop containing two polarization controllers and an EAM which modulates the clockwise and counterclockwise propagating waves inside the Sagnac loop. Measured results demonstrate switchable single-sideband suppression for both reflected and transmitted signals. The second-order harmonic suppression and carrier suppressed modulation are also achieved. A simple analysis explains most of the observed effects.     

Determining the optimal fluoride concentration in drinking water for fluoride endemic regions in South India

Fluoride ion in drinking water is known for both beneficial and detrimental effects on health. The prevalence of fluorosis is mainly due to the intake of large quantities of fluoride through drinking water owing to more than 90% bioavailability. The objective of this study is to predict optimal fluoride level in drinking water for fluoride endemic regions by comprising the levels of fluoride and other water quality parameters in drinking water, prevalence of fluorosis, fluoride intake through water, food and beverages such as tea and coffee and also considering the progressive accumulation of fluoride in animal bones, by comparing with non fluoride endemic areas comprise of the same geological features with the aid of regression analysis. Result of this study shows that increase of fluoride level above 1.33 mg/l in drinking water increases the community fluorosis index (CFI) value more than 0.6, an optimum index value above which fluorosis is considered to be a public health problem. Regression plot between water fluoride and bone fluoride levels indicates that, every increase of 0.5 mg/l unit of water fluoride level increases the bone fluoride level of 52 mg/kg unit within 2 to 3 years. Furthermore, the consumption of drinking water containing more than 0.65 mg/l of fluoride can raise the total fluoride intake per day more than 4 mg, which is the optimum fluoride dose level recommended for adults by the Agency for Toxic Substances and Disease Registry. From the result, the people in fluoride endemic areas in South India are advised to consume drinking water with fluoride level within the limit of 0.5 to 0.65 mg/l to avoid further fluorosis risk.     

Relating Residual Stress and Substructural Evolution During Tensile Deformation of an Aluminum-Manganese Alloy

Interrupted tensile tests were coupled with ex situ measurements of residual stress and microtexture. The residual stress quantification involved measurements of six independent Laue spots and conversion of the interplanar spacings to the residual stress tensor. A clear orientation-dependent residual stress evolution emerged from the experiments and the numerical simulations. For the orientations undergoing negligible changes in ρ _GND (density of geometrically necessary dislocation), the residual stress developments appeared to be governed by the elastic stiffness of the grain clusters. For the others, the evolution of the residual stress and ρ _GND exhibited a clear orientation-dependent scaling.     

Aligned carbon nanotube-polymer hybrid architectures for diverse flexible electronic applications

We present the fabrication and electrical characterization of a flexible hybrid composite structure using aligned multiwall carbon nanotube arrays in a poly(dimethylsiloxane) (PDMS) matrix. Using lithographically patterned nanotube arrays, one can make these structures at any length scale from submicrometer levels to bulk quantities. The PDMS matrix undergoes excellent conformal filling within the dense nanotube network, giving rise to extremely flexible conducting structures with unique electromechanical properties. We demonstrate its robustness against high stress conditions, under which the composite is found to retain its conducting nature. We also demonstrate that these structures can be utilized directly as flexible field-emission devices. Our devices show some of the best field-enhancement factors and turn-on electric fields reported so far.     

Modulation of chewing behavior and reticular pH in nonlactating cows challenged with concentrate-rich diets supplemented with phytogenic compounds and autolyzed yeast

Feeding of concentrate-rich diets impairs chewing behavior and leads to rumen acidosis in cattle. Because of their modulatory effects on ruminal fermentation, phytogenic compounds (PHY) and autolyzed yeast derivatives (AY) may alleviate the negative consequences of high-concentrate diets. Therefore, this research investigated if chewing behavior and the reticular pH dynamics are modulated by AY and PHY supplementation during repeated concentrate-rich challenges used to simulate intermittent rumen acidotic insults. Eight rumen-cannulated, dry, and nonpregnant Holstein cows were assigned to an incomplete double 4 × 3 Latin square design with 3 treatments and 4 experimental runs (n = 8/treatment). Cows were fed concentrates either not supplemented (CON) or supplemented with PHY or AY. Initially, cows were fed a pure forage diet (FD) and switched to a 65% concentrate diet on DM basis for 1 (CONC 1) and 2 (CONC 2) wk. Between CONC 1 and CONC 2, the cows were fed the FD for 1 wk. Chewing activity was measured using noseband sensors and reticular pH by wireless pH sensors. Data showed that cows spent less time ruminating in CONC 1 than in CONC 2. In agreement, reticular pH drop was more pronounced during CONC 1 than during CONC 2. Cows fed with PHY spent 4 h less with reticular pH <6.0 during CONC 1 and 3 h less with pH <6.0 h in CONC 2 as compared with CON cows. Similarly, PHY supplementation extended rumination time with 88 min/d compared with CON cows during CONC 1. The AY supplementation increased DMI by 20% resulting in a longer eating time compared with CON diet during CONC 1. Enhancement of ruminating by PHY and eating time by AY supplementation resulted in longer total chewing time for PHY (474 min/d) and AY (466 min/d) as compared with CON (356 min/d) in CONC 1. In conclusion, cows experiencing 2 intermittent concentrate-rich challenges increased their ruminating behavior during the second challenge, and this effect was associated with higher reticular pH readings. The PHY supplementation enhanced rumination as well as reticular pH during CONC 1. However, the enhanced pH of cows fed with PHY during CONC 2 was not related to greater rumination, suggesting that influencing factors beyond rumination seemed to play a role in modulating reticular pH in PHY cows during CONC 2. The AY supplementation increased DMI without depressing rumination or reticular pH. Effects of both feed additives were more pronounced during CONC 1 challenge when reticular pH was lower.     

Mobile Element Scheduling with Dynamic Deadlines

Wireless networks have historically considered support for mobile elements's an extra overhead. However, recent research has provided the means by which a network can take advantage of mobile elements. Particularly in the case of wireless sensor networks, mobile elements can be deliberately built into the system to improve the lifetime of the network and act as mechanical carriers of data. The mobile element, whose mobility is controlled, visits the nodes to collect their data before their buffers are full. In general, the spatio-temporal dynamics of the sensed phenomenon may require sensor nodes to collect samples at different rates, in which case, some nodes need to be visited more frequently than others. This work formulates the problem of scheduling the mobile element in the network so that there is no data loss due to buffer overflow. The problem is shown to be NP-complete and an integer-linear-programming formulation is given. Finally, some computationally practical algorithms for a single mobile and for the case of multiple mobiles are presented and their performances compared