Diatomic dications and dianions

Diatomic dications and dianions are attractive species for quantum chemists and spectroscopists. In comparison with neutral diatomics, these species show a wealth of potential behaviors arising mainly from the presence of residual Coulomb repulsion at the separated ions limit. Due to the stability of dications, numerous reports have been published on their potential curves, vibrational states, stability, and spectroscopic properties. In contrast, there are only a few reports on the stability and potential curves of dianions, since the strong correlation effects in dianions introduce some difficulties in the calculations of their potentials and properties, and perhaps, because they have not been observed in the laboratory due to their short lifetimes. In this review article, interesting subjects related to dications and dianions, the methods used to study their characteristics, and the achievements of these studies are described. Furthermore, the present research topics open on dications and dianions are reviewed. This report would thus serve researchers interested in the examination of quantum dynamical treatment on reactive scattering of ions and the laser–matter interactions and their subsequent phenomena such as vibrational wavepacket evolution, tunneling dissociation, vibronic coupling, and tunneling ionization for which dianions and dications can be regarded as prototypical species.     

User capacity scaling laws for fading multiple-access channels

In this paper, the maximum number of simultaneous active transmitters (i.e. user capacity) is obtained in the many user case for fading multiple-access channels in which a minimum rate must be maintained for all active users. The results are presented in the form of scaling laws as the number of transmitters increases and three commonly used fading models, namely, Rayleigh, Rician and Nakagami are considered. It is shown that in all three cases, the user capacity scales double logarithmically with the number of users and differs only by constants depending on the distributions. We also show that the scheduling policy maximizing the number of simultaneous active transmitters can be implemented in a distributed fashion.     

Assessment of the effect of N-oxide group in a new high-performance energetic tetrazine derivative on its physicochemical and thermodynamic properties,sensitivity, and combustion and detonation performance

Chemistry of Heterocyclic Compounds - This work uses density functional theory and suitable predictive methods to assess the effect of N-oxide group in 1,2-bis(6-nitro-1,2,4,5-tetrazin-3-yl)diazene...     

The Importance of Precursors and Modification Groups of Aerogels in CO2 Capture

The rapid growth of CO₂ emissions in the atmosphere has attracted great attention due to the influence of the greenhouse effect. Aerogels’ application for capturing CO₂ is quite promising owing to their numerous advantages, such as high porosity (~95%); these are predominantly mesoporous (20–50 nm) materials with very high surface area (>800 m²∙g⁻¹). To increase the CO₂ level of aerogels’ uptake capacity and selectivity, active materials have been investigated, such as potassium carbonate, K₂CO₃, amines, and ionic-liquid amino-acid moieties loaded onto the surface of aerogels. The flexibility of the composition and surface chemistry of aerogels can be modified intentionally—indeed, manipulated—for CO₂ capture. Up to now, most research has focused mainly on the synthesis of amine-modified silica aerogels and the evaluation of their CO₂-sorption properties. However, there is no comprehensive study focusing on the effect of different types of aerogels and modification groups on the adsorption of CO₂. In this review, we present, in broad terms, the use of different precursors, as well as modification of synthesis parameters. The present review aims to consider which kind of precursors and modification groups can serve as potentially attractive molecular-design characteristics in promising materials for capturing CO₂.     

Correlation between Shock Sensitivity of Nitramine Energetic Compounds based on Small‐scale Gap Test and Their Electric Spark Sensitivity

Electric spark sensitivity and shock sensitivity based small‐scale gap test for nitramine energetic compounds are two important sensitivity parameters, which are needed for assessment of their safety in working places. A novel method is introduced for reliable prediction of electric spark or shock sensitivity of a desired nitramine energetic compound when reliable data for one of the sensitivity is available. A novel correlation with a high value of correlation coefficient (R² = 0.998) is derived between electric spark and shock sensitivities of 20 cyclic and acyclic nitramines. For these nitramines, the predicted results of electric spark sensitivities of the novel model are compared with two of the best available models. The root‐mean‐square (rms) and maximum deviations of the new model are 0.20 and 0.51 J, respectively, which are much less than two comparative methods. The reliability of the new method for prediction of electric spark sensitivity of further 14 nitramines is also compared with one of the best available methods, where the measured electric spark or shock sensitivities were not available in literature.     

Structural,thermochemical and detonation performance of derivatives of 1,2,4,5-tetrazine and 1,4 <Emphasis Type="Italic">N</Emphasis>-oxide 1,2,4,5-tetrazine as new high-performance and nitrogen-rich energetic materials

In this study, density functional theory calculations are used to estimate enthalpy of sublimation, enthalpy of formation and crystal density of some important derivatives of 1,2,4,5-tetrazine and 1,4 N-oxide 1,2,4,5-tetrazine. These data were used for predicting their detonation properties including heat of detonation, detonation pressure, detonation velocity, detonation temperature, spark sensitivity, deflagration temperature and power of energetic using appropriate methods. The results show that the title compounds exhibit high positive solid-phase enthalpy of formation. It is found that detonation pressure and detonation velocity of these compounds are high because of the large values of crystal density and solid-phase enthalpy of formation. Detonation temperature and spark sensitivity of some derivatives are higher than octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine as one of the high-performance explosives.     

A facile and one pot synthesis of 1,4-disubstituted-1H-1,2,3-triazoles from terminal alkynes and phenacyl azides prepared from styrenes by CAN oxidant and sodium azide

A facile and green synthesis of 1,4-disubstituted-1H-1,2,3-triazoles is reported. The reaction of α-azido ketones and terminal alkynes in the presence of [CuSO₄ (H₂O)₅/sodium ascorbate] in a mixture of H₂O/polyethylene glycol 400 as solvent afforded the corresponding 1,4-disubstituted triazoles at ambient temperature with short reaction times and at high yields. The corresponding α-azido ketones were directly prepared in situ from various substituted styrenes using the oxidant cerium ammonium nitrate and sodium azide in oxygen-saturated methanol.     

p-Type Bismuth Telluride-Based Composite Thermoelectric Materials Produced by Mechanical Alloying and Hot Extrusion

We produced six different composites of p-type bismuth antimony telluride alloys and studied their structure and thermoelectric properties. The components of the composites were obtained in powder form by mechanical alloying. Mixed powders of two different compositions were consolidated by hot extrusion to obtain each bulk composite. The minimum grain size of bulk composites as revealed by scanning electron microscopy shows a 50% reduction compared with the conventional (Bi_0.2Sb_0.8)₂Te₃. X-ray diffraction (XRD) analysis only shows peak broadening with no clear indication of separate phases, and indicates a systematic decrease of crystallite size in the composite materials. Scattering mechanisms of charge carriers were evaluated by Hall-effect measurements. The thermoelectric properties were investigated via the Harman method from 300 K up to 460 K. The composites show no significant degradation of the power factor and high peak ZT values ranging from 0.86 to 1.04. The thermal conductivity of the composites slightly increases with respect to the conventional alloy. This unexpected behavior can be attributed to two factors: (1) the composites do not yet contain a significant number of grains whose sizes are sufficiently small to increase phonon scattering, and (2) each of the combined components of the composites corresponds to a phase with thermal conductivity higher than the minimum value corresponding to the (Bi_0.2Sb_0.8)₂Te₃ alloy.     

Effect of Surface Preparation on Mechanical Properties of Ni Contacts on Polycrystalline (Bi1?x Sb x )2(Te1?y Se y )3 Alloys

We present a comparison of different surface preparation techniques for hot-extruded (Bi_1?x Sb _x )₂(Te_1?y Se _y )₃ alloys prior to Ni plating and their consequences on adhesion. The surface preparation is carried out by a relatively fast and well-controlled electrochemical etching procedure that provides morphologies with homogeneous flat surfaces on a scale of tens of micrometers. This procedure is not optimal for Ni metallization since it does not ensure enough roughness on the surface. Applying wet chemical etching with hypochlorite and nitric acid after the electrochemical etching changes the morphology, and the surface roughness increases, as evidenced by scanning electron microscopy and atomic force microscopy. Tensile tests carried out on n-type and p-type 1-mm-thick specimens, covered with a 12-??m Ni layer followed by Sn-Pb soldered joints, confirm a significant improvement in the ultimate adhesion strength, with fracture occurring within the thermoelectric material. Use of this two-step surface treatment, after slicing and prior to metallization, leads to maximum adhesion strength of around 38?MPa for either type of thermoelectric material. These results are consistent with the morphological changes observed by scanning electron microscopy on the surface after chemical etching.