Nitro Derivatives of 1,3,5-Triazepine as Potential High-Energy Materials

Structure optimization and frequency calculation of six nitro derivatives of 1,3,5-triazepine were performed using a MP2(FULL)/6-311G(d,p) method. In order to obtain reliable energy data, single-point energy and subsequently thermodynamic properties of the species considered were calculated at a fairly high level of theory, CCSD(T)/6-311G(d,p). Solid-phase heats of formation and crystal density were determined using an electrostatic potential (ESP) method utilizing wave function analysis-surface analysis suite (WFA-SAS) code. The result shows that all nitro derivatives possess high positive heats of formation that increase with an increase in the number of nitro groups attached to the ring moiety. The crystal density was found to be in the range of 1.67–1.90 g/cm³. Detonation properties of the compounds were estimated using the Kamlet-Jacobs equation. The results showed that detonation velocity (D) and detonation pressure (P) increased with an increase in the number of nitro groups attached at the ring moiety. It was found that all six nitro derivatives of the title compound had better or comparable performance characteristics than the most widely used commercial explosives, such as TNT, research and development explosives (RDX), and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). The trinitro derivative (1,3,5-trinitro-1,3,5-triazepine, F) yielded detonation pressure (P) and detonation velocity (D) of 45.5 GPa and 9.23 km/s, respectively, at a loading density of 1.90 g/cm³, which are superior to the most powerful available explosive HMX (P = 39.00 GPa and D = 9.11 km/s). The results obtained during the present study show that the title compounds can be used as promising futuristic high-energy-density materials (HEDMs).     

A clocked high-pass-filter-based offset cancellation technique for high-gain biomedical amplifiers

In this article, a simple offset cancellation technique based on a clocked high-pass filter with extremely low output offset is presented. The configuration uses the on-resistance of a complementary metal oxide semiconductor (CMOS) transmission gate (X-gate) and tunes the lower 3-dB cut-off frequency with a matched pair of floating capacitors. The results compare favourably with the more complex auto-zeroing and chopper stabilisation techniques of offset cancellation in terms of power dissipation, component count and bandwidth, while reporting inferior output noise performance. The design is suitable for use in biomedical amplifier systems for applications such as ENG-recording. The system is simulated in Spectre Cadence 5.1.41 using 0.6 μm CMOS technology and the total block gain is ～83.0 dB while the phase error is <5°. The power consumption is 10.2 mW and the output offset obtained for an input monotone signal of 5 μVpp is 1.28 μV. The input-referred root mean square noise voltage between 1 and 5 kHz is 26.32 nV/√Hz.     

DATA ACQUISITION SYSTEM FOR ARC-DRIVEN HF/DF CHEMICAL LASERS

The article focuses on the development of a data acquisition system (DAS) working in a noisy and hostile environment for an arc-operated hydrogen fluoride/deuterium fluoride (HF/DF) chemical laser. PC-based DAS has been configured using Advantech plug and play modules with fiber link connectivity. This article also focuses on implementation of an orifice-based precise gas flow control system. The plasma arc discharge in an arc heater/generator is essentially employed for inducing thermal dissociation of sulfur hexafluoride SF₆ for production of fluorine atoms, and DAS has been used for performance optimization of the composition of the lasing mixture by independently varying the flow rate, pressure, and temperature of its constituents. Since arc load is complex with high voltage transients and electromagnetic noise, an optical fiber link has been implemented for data transmission. This article also discusses digital output interface circuitry for various electro-pneumatic actuators/solenoid valves. The developed DAS has been used for monitoring and performance evaluation of parameters for 50 kW arc tunnel.     

Comparison of biohydrogen production processes

For hydrogen to be a viable energy carrier, it is important to develop hydrogen generation routes that are renewable like biohydrogen. Hydrogen can be produced biologically by biophotolysis (direct and indirect), photo-fermentation and dark-fermentation or by combination of these processes (such as integration of dark- and photo-fermentation (two-stage process), or biocatalyzed electrolysis, etc.). However, production of hydrogen by these methods at commercial level is not reported in the literature and challenges regarding the process scale up remain. In this scenario net energy analysis (NEA) can provide a tool for establishing the viability of different methods before scaling up. The analysis can also be used to set targets for various process and design parameters for bio-hydrogen production.     

Chemically Derived Graphene Oxide: Towards Large‐Area Thin‐Film Electronics and Optoelectronics

Chemically derived graphene oxide (GO) possesses a unique set of properties arising from oxygen functional groups that are introduced during chemical exfoliation of graphite. Large‐area thin‐film deposition of GO, enabled by its solubility in a variety of solvents, offers a route towards GO‐based thin‐film electronics and optoelectronics. The electrical and optical properties of GO are strongly dependent on its chemical and atomic structure and are tunable over a wide range via chemical engineering. In this Review, the fundamental structure and properties of GO‐based thin films are discussed in relation to their potential applications in electronics and optoelectronics.     

Spatial distribution of lead in human primary teeth as a biomarker of pre- and neonatal lead exposure

Lead remains one of the most hazardous toxins in our environment. Because the toxic effects of lead are most prominent during early development, it is important to develop a suitable biomarker for lead exposure during the pre- and neonatal periods. In the present study, the spatial distribution of lead was measured in the enamel and dentine of ten human primary teeth using laser ablation-inductively coupled plasma-mass spectrometry. The neonatal line, visualized using confocal laser scanning microscopy, was used to demarcate the pre- and postnatal regions of the sample teeth. Lead levels in pre- and postnatally formed enamel and dentine were compared to blood-lead levels measured at birth and one year of age for four of these participants. Mean dentine-lead levels ranged from 0.17+/-0.02 to 5.60+/-1.79 microg/g, and mean enamel-lead levels ranged from 0.04+/-0.01 to 1.47+/-0.20 microg/g. The results of this preliminary study showed that the spatial distribution of lead in dentine reflected the blood-lead levels. The present study demonstrates a methodology where the spatial distribution of lead in the dentine of human primary teeth may be used to obtain temporal information of environmental lead exposure during the pre- and neonatal periods.     

Molding of reprocessed thermoplastics with preplastication injection molding

The injection molding of reprocessed plastics with a preplastication plunger injection‐molding machine was investigated with a focus on the processing conditions. The process of the filling of the resin into the mold is much better controlled with preplastication than with processing in a conventional injection‐molding machine. Reprocessing of the resin leads to a reduction in molecular weight due to drastic changes in the resin morphology, thereby causing a reduction in melt viscosity. Direct experimental evidence for reduced viscosity was obtained from measurements of the filling pressure recorded on the machine and also with a melt‐flow indexer. The results of this study provide a practical solution for reducing the resin temperature when reprocessed resin is used in the injection molding of plastics. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1455–1461, 2001     

Image quality assessment based on gradient similarity

In this paper, we propose a new image quality assessment (IQA) scheme, with emphasis on gradient similarity. Gradients convey important visual information and are crucial to scene understanding. Using such information, structural and contrast changes can be effectively captured. Therefore, we use the gradient similarity to measure the change in contrast and structure in images. Apart from the structural/contrast changes, image quality is also affected by luminance changes, which must be also accounted for complete and more robust IQA. Hence, the proposed scheme considers both luminance and contrast-structural changes to effectively assess image quality. Furthermore, the proposed scheme is designed to follow the masking effect and visibility threshold more closely, i.e., the case when both masked and masking signals are small is more effectively tackled by the proposed scheme. Finally, the effects of the changes in luminance and contrast-structure are integrated via an adaptive method to obtain the overall image quality score. Extensive experiments conducted with six publicly available subject-rated databases (comprising of diverse images and distortion types) have confirmed the effectiveness, robustness, and efficiency of the proposed scheme in comparison with the relevant state-of-the-art schemes.     

Rapid growth of angle-confined large-domain graphene bicrystals

In the chemical vapor deposition growth of large-area graphene polycrystalline thin films,the coalescence of randomly oriented graphene domains results in a high density of uncertain grain boundaries (GBs).The structures and properties of various GBs are highly dependent on the misorientation angles between the graphene domains,which can significantly affect the performance of the graphene films and impede their industrial applications.Graphene bicrystals with a specific type of GB can be synthesized via the controllable growth of graphene domains with a predefined lattice orientation.Although the bicrystal has been widely investigated for traditional bulk materials,no successful synthesis strategy has been presented for growing two-dimensional graphene bicrystals.In this study, we demonstrate a simple approach for growing well-aligned large-domain graphene bicrystals with a confined tilt angle of 30° on a facilely recrystallized single-crystal Cu (100) substrate.Control of the density of the GBs with a misorientation angle of 30° was realized via the controllable rapid growth of subcentimeter graphene domains with the assistance of a cooperative catalytic surface-passivation treatment.The large-area production of graphene bicrystals consisting of the sole specific GBs with a tunable density provides a new material platform for fundamental studies and practical applications.