Studies on the effect of thiuram disulfide on NR vulcanization accelerated by thiazole-based accelerator systems

Thiuram disulfides form synergistic combinations with thiazole and thiazole-based accelerators, namely, N-cyclohexy-2-benzothiazole sulfenamide (CBS), 2-mercaptobenzothiazole(MBT), and 2-mercaptobenzothiazyl disulfide (MBTS). Unfortunately, widely used thiuram disulfides (TD) generate carcinogenic N-nitrosoamine. It is reported that the nitrosamines from N-methylpiperazine and dibenzylamine are free from this menace. So, some investigations were carried out with the binary combinations of each of bis(N-methylpiperazino)thiuram disulfide (MPTD), tetrabenzylthiuram disulnde (TBzTD), and tetramethyl-thiuram disulfide (TMTD) separately with CBS, MBT, and MBTS. It was observed that all the TD are activated by the CBS, MBT, or MBTS in the combinations studied. The intensity of activation is manifested in the enhancement of torque, modulus, tensile strength, cure rate, hardness, and decrease of elongation at break values and is very much dependent upon the ratio of the accelerators used. Considering the torque, modulus, tensile strength, and the elongation at break values, it apears that MPTD and TBzTD are capable of competing with the hitherto unbeaten TMTD as suitable accelerators for the vulcanization of rubber. Some investigations in respect to heat- and age-resistance behavior have also been carried out and the observed differences in the activities of various binary combinations have been explained through a mechanism. The results obtained with filled vulcanizates indicate that the binary systems comprising TD and MBTS provide fruitful results of which the TBzTD–MBTS combination seems to give the best cure and physical data for practical vulcanizates. © 1996 John Wiley & Sons, Inc.     

The effect of bismaleimide resin on curing kinetics of epoxy–amine thermosets

An analysis of the cure kinetics of several formulations composed of diglycidyl ether of bisphenol-A (DGEBPA) and aromatic diamines, methylenedianiline (MDA) and diaminodiphenyl sulfone (DDS), in the absence and presence of 4,4′-bismaleimidodiphenylmethane (BM) was performed. The dynamic differential scanning calorimetry (DSC) thermograms were analyzed with the help of ASTM kinetic software to determine the kinetic parameters of the curing reactions, including the activation energy, preexponential factor, rate constant, and 60 min ½ life temperature. The effects of substitution of one curing agent for another, their concentration, and the absence and presence of BM resin and its concentration on curing behavior, ethalpy, and kinetic parameters are discussed. © 1996 John Wiley & Sons, Inc.     

Permeability characterization. Part 1: A proposed standard reference fabric for permeability

A three-dimensionally woven fabric is proposed as a standard reference material for permeability characterization. The 3-D woven fabric requires care in cutting and handling, although it is more robust than 2-D woven or braided fabrics. If prepared carefully, the permeability of the 3-D woven fabric can be measured reproducibly within 15% in either radial flow or saturated 1-D flow geometries. The material was characterized for permeability in radial, unsaturated and saturated 1-D, and through-thickness flow geometries. The transient results demonstrated the importance of structural heterogeneity on the unsaturated flow behavior, and agree qualitatively with a simplistic model of flow in heterogeneous unsaturated porous media. The effects of heterogeneity were manifested in the proposed SRM by an increasing trend in the “unsaturated permeability.” Experiments were also conducted with a random mat that displayed transient flows dominated by wicking. The effects of wicking on the macroscopic flow behavior were manifested by transients in the “unsaturated permeability” in which a decreasing trend was observed.     

Metazoans and Intrinsic Apoptosis: An Evolutionary Analysis of the Bcl-2 Family

The B-cell lymphoma-2 (Bcl-2) family is a group of genes regulating intrinsic apoptosis, a process controlling events such as development, homeostasis and the innate and adaptive immune responses in metazoans. In higher organisms, Bcl-2 proteins coordinate intrinsic apoptosis through their regulation of the integrity of the mitochondrial outer membrane; this function appears to have originated in the basal metazoans. Bcl-2 genes predate the cnidarian-bilaterian split and have been identified in porifera, placozoans and cnidarians but not ctenophores and some nematodes. The Bcl-2 family is composed of two groups of proteins, one with an α-helical Bcl-2 fold that has been identified in porifera, placozoans, cnidarians, and almost all higher bilaterians. The second group of proteins, the BH3-only group, has little sequence conservation and less well-defined structures and is found in cnidarians and most bilaterians, but not porifera or placozoans. Here we examine the evolutionary relationships between Bcl-2 proteins. We show that the structures of the Bcl-2-fold proteins are highly conserved over evolutionary time. Some metazoans such as the urochordate Oikopleura dioica have lost all Bcl-2 family members. This gene loss indicates that Bcl-2 regulated apoptosis is not an absolute requirement in metazoans, a finding mirrored in recent gene deletion studies in mice. Sequence analysis suggests that at least some Bcl-2 proteins lack the ability to bind BH3-only antagonists and therefore potentially have other non-apoptotic functions. By examining the foundations of the Bcl-2 regulated apoptosis, functional relationships may be clarified that allow us to understand the role of specific Bcl-2 proteins in evolution and disease.     

Biological and health implications of toxic heavy metal and essential trace element interactions

Human civilization and a concomitant increase in industrial activity has gradually redistributed many toxic metals from the earth's crust to the environment and increased the possibility of human exposure. Among the various toxic elements, heavy metals cadmium, lead, and mercury are specially prevalent in nature due to their high industrial use. These metals serve no biological function and their presence in tissues reflects contact of the organism with its environment. They are cumulative poison, and are toxic even at low dose. Studies of metabolism and toxicity of these elements have revealed important interactions between them and some essential dietary elements like calcium, zinc, iron, selenium, copper, chromium, and manganese. In general, a deficiency of these essential elements increases toxicity of heavy metals, whereas an excess appears to be protective. While most of the observations are on laboratory animals, limited human data are in agreement with the results of animal experiments. These suggest that the dietary presence of the essential elements may contribute to the protection of man and animal from the effects of heavy metal exposure, while their deficiency may increase toxicity. Appropriate dietary manipulation thus may be valuable in the prevention and treatment of heavy metal toxicity.     

Interactions of polymers and organic admixtures on portland cement hydration

Interaction of polymers and other organic admixtures on Portland cement hydration is reviewed. This has been compiled in a systematic way. First hydration of Portland cement is described in short. Later, interaction with 4 important components of Portland cement is discussed. Finally interphase effects in polymer modified hydraulic cement are discussed. It is concluded that polymers and organic admixtures interact with the components of Portland cement when they come in contact with water. This interaction is due to ionic binding, causing cross-links which inhibit the film formation property of polymers and influence considerably the crystallisation process during the hardening of concrete. Some low molecular weight organic substances also have a considerable influence on Portland cement during its reaction with water.     

Suppression of fuel and air stream diluted methane–air partially premixed flames in normal and microgravity

The effects of fuel and air stream dilution (ASD) with carbon dioxide on the suppression of normal and microgravity laminar methane–air partially premixed coflow jet flames were experimentally and numerically investigated. Experiments were conducted both in our normal-gravity laboratory and at the NASA Glenn Research Center 2.2 s drop tower. Measurements included flame topology and liftoff heights of diluted flames, critical diluent mole fractions for flame blowout, and the radiant heat loss from flames. The flames were also simulated using an axisymmetric unsteady numerical code that utilizes detailed chemistry and transport models. In addition, counterflow flame simulation results were used to examine similitude between the counterflow and coflow flame suppression, and further characterize the effectiveness of fuel stream versus ASD on flame extinction. A smaller relative fuel stream dilution (FSD) extinguishes partially premixed flames (PPFs) with increasing premixing as compared to dilution of the air stream. Conversely, smaller ASD is required to extinguish PPFs as they become less premixed and approach nonpremixed (NP) behavior. Fuel stream diluted PPFs and air stream diluted NP flames extinguish primarily through a reactant dilution effect while fuel stream diluted NP flames and air stream diluted PPF are extinguished primarily by a thermal cooling effect. Normal gravity flames lift off and blow out with a smaller diluent mole fraction than microgravity flames. The difference between the fuel and ASD effectiveness increases as the gravitational acceleration is reduced. Radiation heat losses are observed to increase with increasing diluent mole fraction and decreasing gravity.     

Modulatory Effects of Biosynthesized Gold Nanoparticles Conjugated with Curcumin and Paclitaxel on Tumorigenesis and Metastatic Pathways—In Vitro and In Vivo Studies

Background: Breast cancer is the most common cancer in women globally, and diagnosing it early and finding potential drug candidates against multi-drug resistant metastatic breast cancers provide the possibilities of better treatment and extending life. Methods: The current study aimed to evaluate the synergistic anti-metastatic activity of Curcumin (Cur) and Paclitaxel (Pacli) individually, the combination of Curcumin–Paclitaxel (CP), and also in conjugation with gold nanoparticles (AuNP–Curcumin (Au-C), AuNP–Paclitaxel (Au-P), and AuNP–Curcumin–Paclitaxel (Au-CP)) in various in vitro and in vivo models. Results: The results from combination treatments of CP and Au-CP demonstrated excellent synergistic cytotoxic effects in triple-negative breast cancer cell lines (MDA MB 231 and 4T1) in in vitro and in vivo mouse models. Detailed mechanistic studies were performed that reveal that the anti-cancer effects were associated with the downregulation of the expression of VEGF, CYCLIN-D1, and STAT-3 genes and upregulation of the apoptotic Caspase-9 gene. The group of mice that received CP combination therapy (with and without gold nanoparticles) showed a significant reduction in the size of tumor when compared to the Pacli alone treatment and control groups. Conclusions: Together, the results suggest that the delivery of gold conjugated Au-CP formulations may help in modulating the outcomes of chemotherapy. The present study is well supported with observations from cell-based assays, molecular and histopathological analyses.     

First and second law analyses of a typical solar air dryer system: a case study

This communication presents an experimental study based on energy and exergy analyses of a typical solar air dryer. On the basis of the experimental results, the first and the second law efficiencies are calculated with respect to the available solar radiation. It is found that the second law efficiency is much less than the first law efficiency irrespective of the mass flow rate of the circulating fluid. It is also found that both efficiencies are an increasing function with respect to the mass flow rate of the working fluid. For a particular day, it is also found that first and second law efficiencies fluctuate according to radiation. The results obtained in this article are found to be consistent with those obtained by earlier authors as given in the literature.     

Thermodynamic analysis and parametric study of an intercooled–reheat closed-cycle gas turbine on the basis of a new isentropic exponent

The thermodynamic analysis and parametric study of an intercooled–reheat closed-cycle gas turbine is presented in this paper, on the basis of a new (harmonic mean) isentropic exponent. An analytical expression is derived for the optimum pressure ratio and maximum non-dimensional net work output. It is found that the optimum pressure ratio and the maximum non-dimensional net work are high when the ratio of extreme temperatures of cycle (i.e. T _max and T _min) and isentropic efficiencies of compressor and turbine (i.e. η_c and η_t) are high. The theoretical results are also compared with the practical conditions of power plant.