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Femtosecond Laser-Induced Recombinative O + O = O-2 Reaction on Single Crystal Pd(100) Surface Requires Thermal Assistance
No full textThe process of recombinative desorption of molecular oxygen (O-adsorbed + O-adsorbed = O-2,O-gas) from the Pd(100) single crystal surface, under femtosecond laser irradiation, has been investigated with the help of pre- and postradiation temperature-programmed desorption (TPD) measurements. This femtosecond optical pulse-induced surface chemistry is found to depend strongly on the initial surface temperature. The threshold temperature is observed to be 400 K, above which this reaction remains active for the absorbed fluence of 2.86 mJ/cm(2). Furthermore, the desorption-yield is observed to be linear with respect to the absorbed fluence. We explain our observations with the help of combined two-temperature model simulation and density functional theory-based computations. A two-step mechanism for the femtosecond optical pulse-induced recombinative desorption of molecular oxygen is evident: the first step involves the hot electron-mediated activation of the oxygen atoms and the second step involves the thermal activation (phonon-mediated) of the oxygen atoms leading to the recombination of oxygen atoms to form molecular oxygen which immediately desorbs from the Pd(100) surface. This is the first report on the femtosecond optical pulse-induced recombinative surface chemistry of adsorbed oxygen atoms on the Pd single crystal surface
Chronic Obstructive Pulmonary Disease and Lung Cancer: Underlying Pathophysiology and New Therapeutic Modalities
No full textChronic obstructive pulmonary disease (COPD) and lung cancer are major lung diseases affecting millions worldwide. Both diseases have links to cigarette smoking and exert a considerable societal burden. People suffering from COPD are at higher risk of developing lung cancer than those without, and are more susceptible to poor outcomes after diagnosis and treatment. Lung cancer and COPD are closely associated, possibly sharing common traits such as an underlying genetic predisposition, epithelial and endothelial cell plasticity, dysfunctional inflammatory mechanisms including the deposition of excessive extracellular matrix, angiogenesis, susceptibility to DNA damage and cellular mutagenesis. In fact, COPD could be the driving factor for lung cancer, providing a conducive environment that propagates its evolution. In the early stages of smoking, body defences provide a combative immune/oxidative response and DNA repair mechanisms are likely to subdue these changes to a certain extent; however, in patients with COPD with lung cancer the consequences could be devastating, potentially contributing to slower postoperative recovery after lung resection and increased resistance to radiotherapy and chemotherapy. Vital to the development of new-targeted therapies is an in-depth understanding of various molecular mechanisms that are associated with both pathologies. In this comprehensive review, we provide a detailed overview of possible underlying factors that link COPD and lung cancer, and current therapeutic advances from both human and preclinical animal models that can effectively mitigate this unholy relationship
Correlation between grafted nanoparticle-matrix polymer interface wettability and slip in polymer nanocomposites
No full textControlling and understanding the flow properties of polymer nanocomposites (PNC) is very important in realising their potential for various applications. In this study we report molecular dynamics simulation studies of slip between a rotating polymer-grafted nanoparticle and the surrounding free linear matrix chains. By varying the interface wettability between the nanoparticle and matrix chains defined by the parameter f, the ratio of the graft to the matrix chain length, or the graft chain density, Sigma, we were able to tune the interface slip, delta, significantly. Both f and Sigma alter the interface wettability by changing the matrix chain penetration depth, lambda, into the graft chain layer. We observed a large value of delta at smaller f or Sigma which reduces with an increasing value of the respective parameters. Since interface slip is also likely to affect other properies of PNCs, like viscosity and the glass transition, we suggest that these parameters could become useful tools to control the flow and mechanical properties of PNCs made with grafted nanoparticles
Response Mode Choice in a Multimodally Duetting Paleotropical Pseudophylline Bushcricket
No full textFemales of the pseudophylline bushcricket species Onomarchus uninotatus respond to a conspecific acoustic call with bouts of tremulation, followed by phonotaxis in some cases. This tremulation sends out a vibratory signal that propagates along the branch of the jackfruit trees where these animals are almost always found, and the male is able to localize the signal and perform vibrotaxis toward the female. Males are unable to localize the signal if it emanates from a branch unconnected to their perch, and therefore, female tremulation might not be a productive response when the nearest male is on an adjacent, disconnected tree. We hypothesized that female behavioral response choice between tremulation and phonotaxis might vary with distance from the caller. A semi-naturalistic experiment indicates that if the male and female are 4 m apart on a connected perch, females tremulate, and never perform phonotaxis while males perform vibrotaxis. However, at a distance of 9 m, 4 out of 10 females begin phonotaxis after a period of tremulation. We then hypothesized that features of the male call that indicate caller distance, such as call sound pressure level (SPL), might be responsible for this distance-dependent variation in the choice between phonotaxis and tremulation However, we found that at all SPLs, the female tremulates in response to male calls before attempting phonotaxis and that the probability of phonotaxis and tremulation both increased with calling song SPL. We conclude that our first hypothesis is upheld and that females do behave differently with respect to distance from the male, but that the cue affecting the distance-dependent increase in the probability of initiation of phonotaxis in female response choice is not the SPL of the male's advertisement call
Divergence in Potential Contact Pheromones and Genital Morphology Among Sympatric Song Types of the Bush Cricket Mecopoda elongata
No full textA well-established route to speciation in animals is via the evolution of divergent male mating signals and female preferences within a species. However, an open question is how common it is for near complete isolation to be achieved through a single signal-receiver system as opposed to multiple aspects of the mate-recognition system diverging simultaneously. The five highly divergent mate-attraction song types of the bush cricket Mecopoda elongata exemplify reproductive isolation in sympatry through long-distance mating signals. Female preference for their own song type has been established as a strong pre-mating reproductive barrier, but the potential existence of additional isolating mechanisms has not been investigated. We quantify divergence in cuticular lipid profiles and external genital structures between song types. These traits show significant variation among species of Orthoptera and are known to be used inmate recognition following contact. We show that divergence among sympatric Mecopoda song types in both cuticular lipid profiles and two external genital structures is sufficiently extensive that either of them can be used to identify individual song type with 90% accuracy. Our findings suggest that multiple isolating mechanisms are likely to evolve simultaneously facilitating a more robust reproductive isolation. Our study indicates a role for sexual selection in the divergence and potential future speciation of these populations and suggests that reproductive isolation may frequently evolve through simultaneous divergence across different aspects of mate recognition systems
INTERACTION OF A SLIDING WEDGE AND A METALLIC SPECIMEN WITH A NEAR-SURFACE INHOMOGENEITY
No full textThe problem of a hard wedge sliding against a metal substrate has been studied extensively for its importance in triboplasticity and deformation processing. Here we explore the effect of introducing a single, near-surface plastic inhomogeneity (termed as a pseudograin) in a metal substrate using Lagrangian finite element (FE) analysis. The pseudograin is allowed to be softer or harder than the surrounding material. The effects of sliding parameters like the size and location of the pseudograin, friction and indenter geometry are also studied. Interestingly, the introduction of the pseudograin can lead to production of surface folds / self-contacts, and acutely-inclined, near-surface, crack like features, which cannot be reproduced by homogeneous specimens. In fact, this tribosystem is phenomenologically very rich, despite differing from classical triboplastic systems of Challen, Oxley and Torrance only by way of the inhomogeneity. Despite its simplicity, the model replicates several experimentally observed features of surface folding, and is a minimal model to obtain folding in sliding. The occurrence of surface folds and concomitant residual surface damage points to the important role played by microstructure-related inhomogeneities in determining surface quality in deformation processing operations (e.g. repeated sliding to generate UFG surfaces) and is also a potentially new mode of sliding wear
From Molecules to Interactions to Crystal Engineering: Mechanical Properties of Organic Solids
No full textCONSPECTUS: Mechanical properties of organic molecular crystals have been noted and studied over the years but the complexity of the subject and its relationship with diverse fields such as mechanochemistry, phase transformations, polymorphism, and chemical, mechanical, and materials engineering have slowed understanding. Any such understanding also needs conceptual advances-sophisticated instrumentation, computational modeling, and chemical insight-lack of such synergy has surely hindered progress in this important field. This Account describes our efforts at focusing down into this interesting subject from the viewpoint of crystal engineering, which is the synthesis and design of functional molecular solids. Mechanical properties of soft molecular crystals imply molecular movement within the solid; the type of property depends on the likelihood of such movement in relation to the applied stress, including the ability of molecules to restore themselves to their original positions when the stress is removed. Therefore, one is interested in properties such as elasticity, plasticity, and brittleness, which are linked to structural anisotropy and the degree to which a structure veers toward isotropic character. However, these matters are still by no means settled and are system dependent. While elasticity and brittleness are probably displayed by all molecular solids, the window of plasticity is perhaps the one that is most amenable to crystal engineering strategies and methods. In all this, one needs to note that mechanical properties have a kinetic component: a crystal that is elastic under slow stress application may become plastic or brittle if the same stress is applied quickly. In this context, nanoindentation studies have shown themselves to be of invaluable importance in understanding structural anisotropy. Several problems in solid state chemistry, including classical ones, such as the melting point alternation in aliphatic straight chain dicarboxylic acids and hardness modulation in solid solutions, have been understood more clearly with this technique. The way may even be open to picoindentation studies and the observation of molecular level movements. As in all types of crystal engineering, an understanding of the intermolecular interactions can lead to property oriented crystal design, and we present examples where complex properties may be deliberately turned on or off in organic crystals: one essentially fine-tunes the degree of isotropy/anisotropy by modulating interactions such as hydrogen bonding, halogen bonding, pi center dot center dot center dot pi interactions, and C-H center dot center dot center dot pi interactions. The field is now wide open as is attested by the activities of several research groups working in the area. It is set to take off into the domains of smart materials, soft crystals, and superelasticity and a full understanding of solid state reactivity
Influence of Nonflow Zone (Back Cavity) Geometry on the Performance of Pumps as Turbines
No full textThe larger objective of this research comes from the fact that optimization studies in ``pumps operated as turbines'' have concentrated only within flow zones without any physical perception regarding the influence of nonflow zones such as back-cavities in standard end-suction pumps. Four pumps of different designs are selected and their back cavities are reduced by inserting solid material, leaving a very small axial clearance. The effects are investigated on an experimental platform, which reveal unique phenomena taking place. The first is associated with the reduction of expected disk friction (hence improvement in shaft torque), while the second is more intricate considering the effect on fluid momentum through reorganization of tangential velocities, based on the mixing zone theory proposed in the paper. The net effect of reducing the volume of nonflow zones (i.e., filling of cavity) is the enhancement of efficiency in the range of 1.3% to 3.6% (+/- 0.4%) in turbine mode. The experimental disk friction coefficient as a function of blade Reynolds number is corroborated with the established theory proposed by different researchers. A significant phenomenon observed was the elimination of vibration and noise at overload operating conditions with the minimal axial clearance
Influence of Layer Thickness and Plasticizers on the Characteristics of Cement-Stabilized Rammed Earth
No full textCement-stabilized rammed earth (CSRE) is used for load-bearing walls. CSRE is a monolithic construction that is constructed by compaction of processed soil in a rigid formwork. The compacted layer thickness varies between 100 and 150 mm. Generally, a dry density in excess of 1,800 kg/m(3) is achieved for CSRE through compaction. Apart from the need for very rigid/stiff formwork, a considerable amount of compaction energy is expended in achieving such high dry densities. The paper (1)examines the influence of layer thickness on characteristics of CSRE; and (2)explores use of superplasticizers for reducing the compaction energy. Considering four different layer thicknesses, the strength and stress-strain characteristics of CSRE were experimentally determined. The compaction energy and characteristics of CSRE were monitored by using different dosages of superplasticizer additive. The major findings of the investigations are (1)optimum compacted layer thickness giving maximum compressive strength for CSRE is 90-100 mm; and (2)the compaction energy reduces by half with the use of 0.65% of superplasticizer with enhanced strength and modulus for CSRE. (C) 2018 American Society of Civil Engineers
Non-affine deformation of free volume during strain dependent diffusion in polymer thin films
No full textWe employ molecular dynamics simulations to understand the influence of non-affine deformation and recovery of free volume on the diffusion behavior of water molecules in polymers, as a function of tensile strain. This study is analogous to strain dependent diffusion of water in polymer thin films which undergo folding in response to water, which is not completely explored. Results reveal that diffusion coefficient of water molecules increases upto 20% strain followed by gradual reduction at higher strain. Non-affine deformation analysis indicates the coupled behavior of relaxation of polymer chains and recovery of free volume. Relaxation process at lower strain coalesces the free volume regions, enhancing the diffusion coefficient. Meanwhile, larger strain dissociates the highly deformed free volume regions. Interestingly, the dissociated regions undergo negligible changes in orientation and shape resulting in reduced diffusion coefficient. The above mechanisms coupled with hydrogen bonds are primarily responsible for shape change in polymer films