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Weak bond effects in adhesively bonded joints between the dissimilar adherends
No full textAdhesively bonded joints provide uniform stress distributions for the width in the bonded region, which is preferred for lightweight assemblages in aircraft structures, but the bonded region is hidden between adherends and suffers due to the existence of weak bonds. Adhesively bonded joints between dissimilar adherends are susceptible to weak bonds due to large differences in the properties and behaviour of adherends. Weak bonds present at the interfaces due to improper curing of adhesive, may go undetected and affect the bond strength. In this paper, an attempt has been made to characterize weak bond effects in adhesive bonded joints between dissimilar adherends. Adhesively bonded single lap joint specimens have been fabricated with CFRP and aluminium using Araldite-2015 adhesive with varied areas of weak bond. PTFE (polytetrafluoroethylene) films used to introduce weak bonds in the bonded region. X-ray radiography and ultrasonic tests have been performed on specimens to verify the presence of weak bond areas. Uniaxial tensile tests have been conducted on specimens to evaluate the mechanical response of adhesive joints in the presence of weak bonds and to obtain failure loads and corresponding failure patterns. Finite element analysis has been carried out to evaluate variations of peel and shear stresses along the bond length. From the studies, it is found that failure occurs at the interface where weak bonds are present irrespective of dimensions of weak bonds and the corresponding failure load decreases with increase in the weak bond area resulting in interface failure
Foil locomotion through non-sinusoidal pitching motion
No full textWe investigate the propulsive characteristics of a neutrally buoyant foil that self propels as it pitches about its quarter chord with a prescribed time periodic waveform. For a fixed pitching frequency and amplitude, we find the foil motion to be strongly dependent on the prescribed waveform. The maximum mean self-propelling speed corresponds to a square shaped waveform for which the foil is held at the two extremes for a significant part of the pitching cycle. In contrast, the cost of transport is minimal, and therefore the energetic efficiency of pitching induced self propulsion a maximum, for a triangle shaped profile in which case the foil's angular speed is largely held constant over the pitching period. Pitching waveform induced variations in the mean self-propelling speed ((u) over bar (p)) are surprisingly well predicted with a simple power-law relationship St(rms)similar to Re-0.37 , where Reynolds number Re is based on (u) over bar (p) and the Strouhal number St(rms) is the ratio of the root mean square foil trailing edge speed and (u) over bar (p). This power-law relationship is shown to arise naturally from a balance between the cycle-averaged inertial thrust generated from prescribed pitching and the enhanced drag owing to the boundary layer thinning. The imposed pitching motion induces a Reynolds number independent out of phase heave motion features of which are remarkably well predicted with a simple inviscid model for the foil's transverse motion. For all the prescribed pitching waveforms, a maximum in the energetic efficiency is always attained over the range 0.3 <= St <= 0.6. The close correspondence between this Strouhal number range for maximum energetic efficiency and the optimal Strouhal number range for swimming and flying animals is indicative of the similarity between self-propelling flapping foil configurations and undulatory biolocomotion. Our results point to the significance of rigid body pitching profile as an important input parameter that can be varied independently to achieve a desired outcome such as maximization of the mean self-propelling speed or energetic efficiency
lncRNA HULC facilitates efficient loading of HCV-core protein onto lipid droplets and subsequent virus-particle release
No full textThe cellular lipid pool plays a central role in hepatitis C virus (HCV) life cycle, from establishing infection to virus propagation. Here, we show that a liver abundant long noncoding RNA, highly upregulated in liver carcinoma (HULC), is upregulated during HCV infection and manipulates the lipid pool to favour virus life cycle. Interestingly, HULC was found to be crucial for the increase in number of lipid droplets in infected cells. This effect was attributed to the role of HULC in lipid biogenesis. Further, we demonstrated that HULC knockdown decreases the association of HCV-core protein with lipid droplets. This exhibited a direct consequence on the release of HCV particles. The role of HULC in HCV-particle release was further substantiated by additional knockdown and mutation experiments. Additionally, we found that increased level of HULC in HCV-infected cells was a result of Retinoid X Receptor Alpha (RXRA)-mediated transcription, which seemed to be aided by HCV-core protein. Taken together, the results identify a distinct role of long noncoding RNA HULC in lipid dynamics during HCV infection, which provides new insights into the complex process of HCV propagation and pathogenesis
New Water-Soluble Oxyamino Chitosans as Biocampatible Vectors for Efficacious Anticancer Therapy via Co-Delivery of Gene and Drug
No full textAmong the many nonviral gene delivery vectors, chitosan, being a polysaccharide of natural origin, has gained special importance. In this report, chitosan (CS) has been solubilized in water by preparing its O-carboxymethyl derivative, CS(CH2COOH), with an optimum degree of carboxymethylation. This has been further derivatized to get the pyridine-substituted product (py)CS(CH2COOH), where the degree of pyridine substitution (47%) was optimized based on zeta potential measurements. The optimized formulation showed a high gene binding ability, forming nanosized positively charged polyelectrolyte complexes with DNA. These polyplexes were stable to DNase and physiological polyanions such as heparin. They also exhibited minimal toxicity in vitro and showed transfection levels comparable to the commercial standard Lipofectamine 2000 and much higher than polyethylenimine (MW, 25 kDa). Additionally, in this study, a hitherto unknown oxyamine derivative of chitosan has been prepared by phthaloyl protection, tosylation, and Gabriel's phthalimide synthesis. Nearly 40% of the primary alcohols were successfully converted to oxyamino functionality, which was used for forming oxime with the anticancer drug doxorubicin. The pH sensitivity of the oxime ether linkage and stability under biologically relevant conditions were then used to establish the compound as a versatile drug delivery vector. Co-delivery of functional gene (p53) and drug (doxorubicin) was accomplished in vitro and in vivo with the chitosan-pyridine imine vector (py)CS(CH2COOH) and the newly synthesized doxorubicin oxime ether CS(Dox). Complete tumor regression with no tumor recurrence and appreciable survivability point to the in vivo effectiveness and biocompatibility of the designed composite formulation. Overall, the pH sensitivity of the oxime linkage aiding slow and steady drug release, together with the sustained gene expression by pyridine-tethered carboxymethyl chitosan, allows us to generate a nanobiocomposite with significantly high anticancer therapeutic potential
Freestyle, a randomized version of ChaCha for resisting offline brute-force and dictionary attacks
No full textThis paper introduces Freestyle, a randomized, and variable round version of the ChaCha cipher. Freestyle demonstrates the concept of hash based halting condition, where a decryption attempt with an incorrect key is likely to take longer time to halt. This makes it resistant to key-guessing attacks i.e. brute-force and dictionary based attacks. Freestyle uses a novel approach for ciphertext randomization by using random number of rounds for each block of message, where the exact number of rounds are unknown to the receiver in advance. Due to its inherent random behavior, Freestyle provides the possibility of generating up to 2(256) different ciphertexts for a given key, nonce, and message; thus resisting key and nonce reuse attacks. This also makes cryptanalysis through known-plaintext, chosen-plaintext, and chosen-ciphertext attacks difficult in practice. Freestyle is highly customizable, making it suitable for both low-powered devices and security-critical applications. It is ideal for: (i) applications that favor ciphertext randomization and resistance to key-guessing and key reuse attacks; and (ii) situations where ciphertext is in full control of an adversary for carrying out an offline key-guessing attack
Spontaneous Light Emission from Molecular Junctions: Theoretical Analysis of Upconversion Signal
No full textSpontaneous light emission from a current-carrying molecular junction is analyzed. There are two leading processes, fluorescence and electroluminescence, as defined using Liouville space diagrams within the perturbative method, that contribute to the light emission from junctions. This allows us to identify a general mechanism that explains the origin of the so-called upconversion electroluminescence (UCEL) signal, which has been observed in a variety of molecular junctions Umera et al. Chem. Phys. Lett. 2007, 448, 232; Dong et al. Nat. Photonics 2010, 4, 50]. Here, we show that a double-peak signal, one at energy less than the applied bias and the other at higher energy (UCEL), is generated due to overlap between two processes: one is electron transfer to create the required excited state, and the other is radiative relaxation of the excited state. The lifetimes induced by the lead interactions play a crucial role in determining the required overlap between these processes. Our analysis shows that, unlike the higher-energy signal, the low-erenergy peak is sensitive to the applied bias and does not correspond to any optical resonance in the junction. The signal at higher energy is enhanced as the temperature is increased. We demonstrate our findings using nonperturbative analytic results for a model system
Shear velocity-based uncertainty quantification for rock joint shear strength
No full textThe shear strength of rock joints is an important property required in order to analyze the stability of rock slopes and tunnels. However, estimation of the shear strength of rock joints for in situ conditions is a complex task due to various influencing factors present in the field. Among these factors, the shear velocity or the shear displacement rate along the rock joints are important parameters which are relatively less studied since their effect is considered to be of second order compared to other factors. However, some recent studies in the literature suggest that shear velocity has a significant influence on the shear strength of rock joints, and hence the shear strength of joints estimated at low shear velocities in laboratories cannot be used under in situ conditions where the possibility of higher shear velocities exist due to the presence of different factors, such as blasting, excavation, and thermal and seismic loads. In this paper, we have addressed these issues in three steps. In the first step, an experimental study on jointed rock specimens is presented to investigate the influence of the displacement rate on the shear strength of rock joints. In the second step, a probabilistic method is developed based on the experimental results and the compiled data from the literature to estimate the in situ shear strength of joints under higher displacement rate conditions, i.e., blasting, excavation, and seismic loads from laboratory-estimated shear strength at the International Society for Rock Mechanics suggested low displacement rates. In the third step, a case study of a Himalayan rock tunnel was used to demonstrate the described approach. It was observed that the shear strength of discontinuities reduced with ncreasing shear velocity and that the rate dependency was higher for low-density rocks and under high confining stress. Further, a considerable effect was observed on the probability of failure of the rock tunnel when the effect of shear velocity was considered in the stability analysis
Injectable Polymer-Nanoparticle Hydrogels for Local Immune Cell Recruitment
No full textThe ability to engineer immune function has transformed modern medicine, highlighted by the success of vaccinations and recent efforts in cancer immunotherapy. Further directions in programming the immune system focus on the design of immunomodulatory biomaterials that can recruit, engage with, and program immune cells locally in vivo. Here, we synthesized shear-thinning and self-healing polymer-nanoparticle (PNP) hydrogels as a tunable and injectable biomaterial platform for local dendritic cell (DC) recruitment. PNP gels were formed from two populations of poly(ethylene glycol)-block-polylactide (PEG-b-PLA) NPs with the same diameter but different PEG brush length (2 or 5 kDa). PEG-b-PLA NPs with the longer PEG brush exhibited improved gel formation following self-assembly and faster recovery after shear-thinning. In all cases, model protein therapeutics were released via Fickian diffusion in vitro, and minor differences in the release rate between the gel formulations were observed. PNP hydrogels were loaded with the DC cytokine CCL21 and injected subcutaneously in a murine model. CCL21-loaded PNP hydrogels recruited DCs preferentially to the site of injection in vivo relative to non-CCL21-loaded hydrogels. Thus, PNP hydrogels comprise a simple and tunable platform biomaterial for in vivo immunomodulation following minimally invasive subcutaneous injection
Influence of the number of calves and lactating adult females in a herd on the adrenocortical activity of free-ranging Asian elephants
No full textContext. Physiological stress has the potential to influence animal population persistence. The endangered Asian elephant (Elephas maximus) is involved in intense conflict with humans in many parts of its range, which likely leads to stress for individuals and groups, with consequences for population survival. Thus, it is important to understand how the elephants' stress levels are influenced by socio-ecological factors when not directly exposed to human-induced threats, and to use this understanding to improve conservation and management strategies. Aims. The present study was designed to provide baseline information on the link between socio-ecological factors and stress levels of undisturbed populations of elephants. The main aim was to determine the influence of a number of factors herd size, season, number of calves and adult females present in a herd and their lactational status and body condition - on the adrenocortical activity of free-ranging adult female Asian elephants living in protected forests (without any direct exposure to human-induced threats), by measuring their faecal glucocorticoid metabolite (fGCM) levels. Methods. A total of 145 fresh faecal samples were collected from 123 identified adult female elephants inhabiting Bandipur andNagaraholeNational Parks of southern India, between the years 2013 and 2015. fGCM levelswere measured by employing a group-specific standardised 11-oxoetiocholanolone enzyme immunoassay (EIA). A generalised linear mixedeffectsmodel (GLMM) was used to assess the influence of socio-ecological factors on fGCMlevels of adult female elephants. Key results. When fGCM levels were analysed with aGLMM, the following patterns were observed: fGCMlevels were negatively correlated with the number of adult females (herd size) and positively correlated with the number of calves in a herd and active lactational status of an adult female. fGCM levels of adult female elephants were higher during the dry season (February to May) than wet season (August to December) and negatively correlated with body condition scores. Conclusions. Adrenocortical activity of female elephants is significantly influenced by the number of calves and adult females present in the herd, seasonality and lactational status. Implications. It is important to consider the influence of multiple ecological and social correlates when assessing and interpreting the adrenocortical activity of Asian elephants. Our findings highlight the importance of maintaining the social structure of elephants in the wild to avoid detrimental effects on their physiological health. Insights from such assessments could be used to evaluate the stress in elephants that are involved in direct conflicts with humans to take appropriate management decisions for mitigating conflicts
Intermolecular Complexes and Molecular Conformations Directed by Hydrogen Bonds: Matrix Isolation and Ab Initio Studies
No full textStudies on hydrogen bonding interaction in various systems, involving phenylacetylene (PhAc), propargyl alcohol (PA), borazine (BNH), propargyl amine (PAm) were performed using matrix isolation infrared spectroscopy and supported by ab initio computations. Weak intermolecular interactions of the above mentioned precursors with water, methanol, ether, acetylene and benzene were studied. These systems manifested O-H center dot center dot center dot pi n-sigma* interactions, such as C-H center dot center dot center dot O, N-H center dot center dot center dot O, O-H center dot center dot center dot O and O-H center dot center dot center dot N. In several cases the complexes were multiply tethered involving two or more of the above mentioned contacts. Many of the weak complexes exhibited a number of isomers, and the relative importance of the multiple non-covalent contacts resulted in a competition between the various isomers for the global minimum. It was found that subtle changes in the structures of the precursors tilted the balance towards one isomer or the other. Our studies also threw up a systematic method of building possible structures for complex systems starting from the known structures of related simple systems. We also studied the homodimers of PA and BNH. The BNH dimer was particularly interesting as one of its isomers was characterized by a bis-dihydrogen bond. We also studied the influence of hydrogen bonding interactions in determining the conformational landscape and preference in amino acids. Here again we were able to draw some generalizations regarding the conformational stability of amino acids. The combination of matrix isolation and ab initio computation is a powerful tool for studies on weak intermolecular interactions and conformations