Time Dependent Gaussian Equivalent Linearization of Duffing Oscillator Using Continuous Wavelet Transform

Evolutionary response analysis of Duffing oscillator using Gaussian equivalent linearization in wavelet based time-frequency frame work is presented here. Cubic （i.e., odd type） non-linearity associated with stiffness and damping is modeled. The goal of this research is to develop the mathematical model of an equivalent linear system which is applicable for different non-stationary input processes （i.e., either summation of amplitude modulated stationary orthogonal processes or digitally simulated non-stationary processes）. The instantaneous parameters of the ELTVS （equivalent linear time varying system） are evaluated by minimizing the error between the displacements of non-linear and equivalent linear systems in wavelet domain. For this purpose, three different basis functions （i.e., Mexican Hat, Morlet and a modified form of Littlewood-Paley） are used. The unknown parameters （i.e., natural frequency and damping） of the ELTVS are optimized in stochastic least square sense. Numerical results are presented for different types of input to show the applicability and accuracy of the proposed wavelet based linearization technique.     

Investigation of HMX‐Based Nanocomposites

Advanced munition systems require explosives which are more insensitive, powerful, and reactive. For this reason, nano‐crystalline explosives present an attractive alternative to conventional energetics. In this study, formulations consisting of 95 % octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) and 5 % polyvinyl alcohol (PVOH) were prepared with mean crystal sizes ranging from 300 nm to 2 μm. The process to create these materials used a combination of mechanical particle size reduction and spray drying, which has the advantages of direct control of crystal size and morphology as well as the elimination of ripening of crystals (which occurs during slurry coating of nanomaterials). The basic physical characteristics of these formulations were determined using a variety of techniques, including scanning electron microscopy and X‐ray diffraction. Compressive stress‐strain tests on pressed pellets revealed that the mechanical properties of the compositions improved with decreasing crystal size, consistent with Hall‐Petch mechanics. The 300 nm HMX/PVOH composition demonstrated a 99 % and 129 % greater strength and stiffness, respectively, than the composition with 2 μm HMX. The formulations were subjected to the Small Scale Gap Test, revealing a significant reduction in shock sensitivity with decreasing crystal size. The formulation containing 300 nm HMX registered a shock initiation pressure 1.6 GPa above that of the formulation with 2 μm HMX, a 44 % improvement in sensitivity. These results serve to highlight the relevance of structure‐property relationships in explosive compositions, and particularly elucidate the substantial benefits of reducing the high explosive crystal size to nano‐scale dimensions.     

Genetically engineered elastin-protein A fusion as a universal platform for homogeneous, phase-separation immunoassay

A simple and universal platform for competitive phase-separation immunoassay is reported based on a fusion protein composed of a temperature-responsive elastin-like polypeptide (ELP) and the antibody-binding staphylococcal protein A (SpA). The basic principle is to take advantage of the ability of SpA to bind a variety of antibodies with high affinity, allowing simple separation of antigen-antibody complex by thermal precipitation. The resulting ELP-SpA fusion was shown to preserve the ability to reversibly precipitate as well as its high affinity toward different IgGs and IgMs. As a model system, a competitive phase-separation immunoassay based on the ELP-SpA format was established for paclitaxel (taxol) with IC(50) (20.18 nM) and the lower detection limit (2.94 nM) very similar to those reported for the ELISA format. Unlike the heterogeneous interaction in ELISA, which decreases the antibody-binding activity, the reported homogeneous immunoassay not only alleviates this problem but also enables the potential for high-throughput automation. We believe that the reported ELP-SpA fusion will find applications not only as a powerful diagnostic tool for diverse analytes but also a potential useful tool for purification and immobilization of antibody.     

PNIPAAM grafted particle monoliths: parameters affecting structure and morphology

Crosslinked polystyrene latex particles generated with surfactant free emulsion polymerization were functionalized with thin layer of ATRP initiator on the surface. The functionalized particles were aggregated as physical networks using high shear techniques. The latex particles as well as the aggregated particles were used to successfully generate thermo-responsive monoliths by grafting PNIPAAM brushes from the surface of the particles by atom transfer radical polymerization and simultaneous crosslinking of these brushes. Different solid fractions and drying conditions were used in the generation of the monoliths and the effect of these variations on the structure and morphology of the monoliths was analyzed. Surprising morphologies consisting of tubes or channels were observed when higher solid fractions were used. This behavior was enhanced when the monoliths were dried at higher temperatures. By using proper solid fractions and drying conditions, homogenous porous monoliths could be achieved.     

Syntheses, characterization and biological activity of diorganotin(IV) derivatives of 2-amino-6-hydroxypurine (guanine)

Novel organotin(IV) derivatives of guanine of the general formula, R₂Sn(HGu)₂ (where, R = Me (1), n-Bu (2) and Ph (3)) have been synthesized by the reaction of R₂SnCl₂ with sodium salt of guanine (H₂Gu or 2-amino-6-hydroxypurine). The IR spectral studies suggest that guanine acts as a monobasic ligand coordinating through N(9) after its deprotonation. The weak bonding through C(6)O may also be evidenced, whereas ¹¹⁹Sn Mössbauer data suggest that the coordination number of tin is superior than four. The polyhedron around tin in R₂Sn(HGu)₂ is distorted trigonal–bipyramidal or pseudo-tetrahedral involving very weak interaction from CO group of neighboring molecule leading to polymerized structure. All the compounds exhibited potent anti-inflammatory activity with no appreciable side effects on blood pressure as evidenced by their very mild cardiovascular activity.     

ELECTROOSMOTIC DEWATERING (EOD) OF CLAYS AND SUSPENSIONS: COMPONENTS OF VOLTAGE IN AN ELECTROOSMOTIC CELL

In the electroosmotic dewatering (EOD) of clays, suspensions and fines, a continuous or interrupted DC voltage, V, is applied between the anode and the cathode. In the previous literature on this subject the components of V have not been completely clarified.

Following a brief outline of the EOD that emphasizes the central role of the electrochemical double layer, we provide an analysis of the components of V, Three case are distinguished

(1)Threshold voltage V-n, for initiating the EOD and its connection to the so-called open-circuit voltage;

(2)EOD at very low voltages viz. around IV;

(3)EOD at very high rates for prolonged times where electrodes such as Al can form barrier oxides and some “caking” is also observed near the a node, This attempt to define the components of V under different conditions of EOD is aimed to identify parameters and processes that arc involved in the effect of V on EOD; RT for example, it is generally not recognized that —pH can form a significant part of V F under some conditions of EOD     

Development of Stretch Flangeable Grade Steels by Inclusion Engineering Approach

The demand for good stretch flangeability in high-strength automotive steels has necessitated due attention on steel cleanliness and processes. The presence of elongated MnS stringers and centerline segregation of nonmetallic inclusions adversely affects the transverse mechanical property. In the present investigation, stretch flangeability of industrially produced steel, with and without Ca treatment, has been compared with Ti-added steel, produced at 40 kg scale without Ca treatment. The study brings out the influence of centerline segregation and modification of nonmetallic inclusions on HER performance. The microstructural analysis of industrial steel revealed that the method of hole formation (punching/drilling) determines crack initiation mechanism. The inclusions, along with the second phase present in the centerline, drive the crack propagation. An addition of Ti in liquid steel promotes formation of Al-Ti-O-based oxide, prior to MnS precipitation, during solidification and acts as nucleation site for MnS inclusion. This obviates the elongated stringer-type MnS inclusions. The centerline segregation-free Ti-modified steel, prepared at the laboratory scale, showed consistent HER property compared with industrial steel. It is also concluded that calcium treatment can be circumvented by modifying the sulfide stringer with the addition of Ti in the steel for further improvement in HER property.