Noncontact optogalvanic signal detection in DC discharge CO<Subscript>2</Subscript> lasers

A new noncontact method for detecting optogalvanic signals in DC discharge CO₂ lasers is reported. The presented technique is based on the detection of potential difference variations through a capacitor comprised of a discharge plasma column and a coaxial or parallel conductor. The obtained optogalvanic signals exhibit better responsivity and pulse shape in comparison with other conventional techniques; in addition, they are detectable as far as 3 m from a signal source.     

Theoretical 14N and 17O nuclear quadrupole resonance parameters for tirapazamine and related metabolites

Density functional theory (DFT) calculations were performed to realize the effects of the N–O group on the reactivity and electronic properties of 3-amino-1,2,4-benzotriazines. The electric field gradient, EFG, tensors of ¹⁴N and ¹⁷O nuclei and natural bond orbital (NBO) analysis in the tirapazamine (TPZ) and its four derivatives were calculated at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) method in the gas phase. The NBO analysis reveal that the bond strength, proton affinity and position of N–O group in the heterocyclic ring have major influence on the reactivity of considered molecules. Accordingly, we suggest that the TPZ and 4-oxide (d) structures due to having a weaker N–O bond with larger negative charge on the oxygen atom at the 4-position are more active than the other ones. Calculated ¹⁴N and ¹⁷O EFG tensors were used to evaluate nuclear quadrupole coupling tensors, χ, and asymmetry parameters, η _Q . Results showed that oxidation of a nitrogen atom at any position have significant influence on its ¹⁴N nuclear quadrupole resonance (NQR) parameters. Also, the occupancy of nitrogen lone pair plays an important role in determination of the q _zz and χ values of mentioned nuclei. It is found that the η _Q and χ are appropriate parameters to study the contribution of lone pair electrons of nitrogen atom in the formation of chemical bond or conjugation with the aromatic system. Finally, a linear correlation is observed between the χ(¹⁴N) and χ(¹⁷O) values in the N–O bond which may be associated with the reactivity of these compounds.     

An Overview of NO Signaling Pathways in Aging

Nitric Oxide (NO) is a potent signaling molecule involved in the regulation of various cellular mechanisms and pathways under normal and pathological conditions. NO production, its effects, and its efficacy, are extremely sensitive to aging-related changes in the cells. Herein, we review the mechanisms of NO signaling in the cardiovascular system, central nervous system (CNS), reproduction system, as well as its effects on skin, kidneys, thyroid, muscles, and on the immune system during aging. The aging-related decline in NO levels and bioavailability is also discussed in this review. The decreased NO production by endothelial nitric oxide synthase (eNOS) was revealed in the aged cardiovascular system. In the CNS, the decline of the neuronal (n)NOS production of NO was related to the impairment of memory, sleep, and cognition. NO played an important role in the aging of oocytes and aged-induced erectile dysfunction. Aging downregulated NO signaling pathways in endothelial cells resulting in skin, kidney, thyroid, and muscle disorders. Putative therapeutic agents (natural/synthetic) affecting NO signaling mechanisms in the aging process are discussed in the present study. In summary, all of the studies reviewed demonstrate that NO plays a crucial role in the cellular aging processes.     

Comparison of pyrolysis mass spectrometry with high performance liquid chromatography for the analysis of Cremophor EL in drugs and serum

Polyoxyethyleneglycerol triricinoleate 35 (Cremophor EL: CrEL) is a solubilization agent for hydrophobic drugs. Recently, CrEL has shown some side effects in patients. In the present work, we introduce pyrolysis-mass spectrometry (Py-MS) for the determination of CrEL in drugs and blood samples. Mass to charge (m/z) values of 89 and 138 of CrEL and 3-nitroaniline (as internal standard), respectively, were used for quantitative measurements by selected ion monitoring (SIM) method. At a probe pyrolysis temperature range of 350-450 °C the results are highly reproducible. Limit of detection (LOD), linearity and relative standard deviation (R.S.D., n=5) were determined to be 1 ng ml⁻¹, 10 ng ml⁻¹-100 mg ml⁻¹ and 1.3%, respectively. The results of Py-MS are compared with those obtained by high performance liquid chromatography (HPLC) and show that time for analysis, sensitivity and linearity are far better.     

Introducing a novel model for predicting effective thermal conductivity of spacer fabrics based on their structural parameters

Journal of Thermal Analysis and Calorimetry - The knowledge of the thermal properties of textiles is important with regard to their vast applications in most industries. Thermal properties, as one...     

Spectromicroscopic determinations of chemical environments of Ni in MoS2-Ag-Ni ternary systems

Using heterogeneous photocatalysts for harvesting sunlight and converting it for water remediation and splitting are promising to mitigate the possible crisis of environment and energy. Among various composites, the MoS₂-based heterostructures and Ni-based systems exhibit unique electronic, optical properties and redox capabilities, enabling their roles as photocatalysts. Herein, the impacts of chemical environments on the Ni electronic structures within the MoS₂-Ag-Ni ternary systems are studied via X-ray photoemission electron spectroscopy (X-PEEM). Ni nanoparticles with two different sizes of 70 and 200 nm were loaded to MoS₂ flakes with silver buffers as bridges. Heterostructures with a nominal mol percentage of (MoS₂)₇₇Ag_3.7Ni_19.3 were synthesized through an ultrasound-assisted wet method. The oxidation states and various interfacial interactions of Ni with MoS₂ in MoS₂-Ag-Ni ternary composite are spectromicroscopically determined, combining the X-ray absorption spectroscopy near Ni L-edges and the imaging capability of the X-PEEM. Results showed that Ni mainly retrains its chemical states of metal and native oxidizations without observable electronic features subjected to bonding with the sulfur from the MoS₂ flakes. The charge migration channel set up by the Ag buffer thus contributes to electron–hole migrations that facilitate the photocatalytic performance of the ternary system eventually.     

Experimental and Theoretical Study of Enhanced Photocatalytic Activity of Mg‐Doped ZnO NPs and ZnO/rGO Nanocomposites

A systematic experimental and theoretical study of the origin of the enhanced photocatalytic performance of Mg‐doped ZnO nanoparticles (NPs) and Mg‐doped ZnO/reduced graphene oxide (rGO) nanocomposites has been performed. In addition to Mg, Cd was chosen as a doping material for the bandgap engineering of ZnO NPs, and its effects were compared with that of Mg in the photocatalytic performance of ZnO nanostructures. The experimental results revealed that Mg, as a doping material, recognizably ameliorates the photocatalytic performance of ZnO NPs and ZnO/graphene nanocomposites. Transmission electron microscopy (TEM) images showed that the Mg‐doped and Cd‐doped ZnO NPs had the same size. The optical properties of the samples indicated that Cd narrowed the bandgap, whereas Mg widened the bandgap of the ZnO NPs and the oxygen vacancy concentration was similar for both samples. Based on the experimental results, the narrowing of the bandgap, the particle size, and the oxygen vacancy did not enhance the photocatalytic performance. However, Brunauer–Emmett–Teller (BET) and Barret–Joyner–Halenda (BJH) models showed that Mg caused increased textural properties of the samples, whereas rGO played an opposite role. A theoretical study, conducted by using DFT methods, showed that the improvement in the photocatalytic performance of Mg‐doped ZnO NPs was due to a higher electron transfer from the Mg‐doped ZnO NPs to the dye molecules compared with pristine ZnO and Cd‐doped ZnO NPs. Moreover, according to the experimental results, along with Mg, graphene also played an important role in the photocatalytic performance of ZnO.     

Analytical investigation of simultaneous effects of convergent section heating of Laval nozzle,steam inlet condition,and nozzle geometry on condensation shock

Rapid expansion and supercooling of dry vapor in low-pressure steam turbines trigger nucleation phenomenon. Subsequently, following the occurrence of vapor condensation, a vapor–liquid two-phase flow is established. Entropy generation mainly by condensation shock, blade erosion, and ultimately, destruction of equipment and efficiency reduction are among adverse effects of vapor condensation, which should be either attenuated or controlled. In the present research, which is a continuation to the research performed by original authors, a one-dimensional analytical Eulerian–Lagrangian model is used to apply convergent section heating to different supersonic nozzles under various inlet conditions. The results indicate that the flow response to the heating is well dependent on the intensity of condensation shock or inlet conditions. In order to compensate for the mass flow rate resulted from the convergent section heating, effects of simultaneous reduction of inlet stagnation temperature and convergent section heating were investigated. Finally, it was found that, maintaining constant mass flow rate, simultaneous reduction of inlet stagnation temperature and convergent section heating cannot attenuate the condensation shock significantly. Therefore, the best approach to compensate for the reduction in the mass flow rate due to convergent section heating is to simultaneously increase inlet stagnation pressure.     

Protection Group Effects During α,γ‐Diol Lignin Stabilization Promote High‐Selectivity Monomer Production

Protection groups were introduced during biomass pretreatment to stabilize lignin's α,γ‐diol group during its extraction and prevent its condensation. Acetaldehyde and propionaldehyde stabilized the α,γ‐diol without any aromatic ring alkylation, which significantly increased final product selectivity. The subsequent hydrogenolysis catalyzed by Pd/C generated lignin monomers at near‐theoretical yields based on Klason lignin (48 % from birch, 20 % from spruce, 70 % from high‐syringyl transgenic poplar), and with high selectivity to a single 4‐n‐propanolsyringol product (80 %) in the case of the poplar. Unlike direct hydrogenation of native wood, hydrogenolysis of protected lignin with Ni/C also led to high selectivity to this single product (78 %), paving the way to high‐selectivity lignin upgrading with base metal catalysts. The use of extracted lignin facilitated valorization of polysaccharides, leading to high yields of all three major biomass polymers to a single major product.