Acoustic response of vortex breakdown modes in a coaxial isothermal unconfined swirling jet

The present experimental work is concerned with the study of amplitude dependent acoustic response of an isothermal coaxial swirling jet. The excitation amplitude is increased in five distinct steps at the burner's Helmholtz resonator mode (i.e., 100 Hz). Two flow states are compared, namely, sub-critical and super-critical vortex breakdown (VB) that occur before and after the critical conical sheet breakdown, respectively. The geometric swirl number is varied in the range 2.14-4.03. Under the influence of external pulsing, global response characteristics are studied based on the topological changes observed in time-averaged 2D flow field. These are obtained from high resolution 2D PIV (particle image velocimetry) in the longitudinal-mid plane. PIV results also illustrate the changes in the normalized vortex core coordinates (r(vcc)/(r(vcc))(0) (Hz), y(vcc)/(y(vcc))(0) (Hz)) of internal recirculation zone (IRZ). A strong forced response is observed at 100 Hz (excitation frequency) in the convectively unstable region which get amplified based on the magnitude of external forcing. The radial extent of this forced response region at a given excitation amplitude is represented by the acoustic response region (b). The topological placement of the responsive convectively unstable region is a function of both the intensity of imparted swirl (characterized by swirl number) and forcing amplitude. It is observed that for sub-critical VB mode, an increase in the excitation amplitude till a critical value shifts the vortex core centre (particularly, the vortex core moves downstream and radially outwards) leading to drastic fanning-out/widening of the IRZ. This is accompanied by similar to 30% reduction in the recirculation velocity of the IRZ. It is also observed that b < R (R: radial distance from central axis to outer shear layer-OSL). At super-critical amplitudes, the sub-critical IRZ topology transits back (the vortex core retracts upstream and radially inwards) and finally undergoes a transverse shrinkage ((r(vcc))/(r(vcc))(0 Hz) decreases by similar to 20%) when b >= R. In contrast, the vortex core of super-critical breakdown mode consistently spreads radially outwards and is displaced further downstream. Finally, the IRZ fans-out at the threshold excitation amplitude. However, the acoustic response region b is still less than R. This is explained based on the characteristic geometric swirl number (S-G) of the flow regimes. The super-critical flow mode with higher S-G (hence, higher radial pressure drop due to rotational effect which scales as Delta P similar to rho u theta(2) and acts inwards towards the center line) compared to sub-critical state imposes a greater resistance to the radial outward spread of b. As a result, the acoustic energy supplied to the super-critical flow mode increases the degree of acoustic response at the pulsing frequency and energizes its harmonics (evident from power spectra). As a disturbance amplifier, the stronger convective instability mode within the flow structure of super-critical VB causes the topology to widen/fan-out severely at threshold excitation amplitude. (C) 2015 AIP Publishing LLC.

Thermal Response on the Microstructure and Texture of ECAP and Cold-Rolled Pure Magnesium

This paper deals with dynamic recrystallization (DRX), static recrystallization, and grain growth phenomena of pure magnesium after equal channel angular pressing (ECAP) by route A and B-C at 523 K (250 A degrees C) followed by 80 pct cold rolling. The ECAP-deformed and the subsequently rolled samples were annealed at 373 K and 773 K (100 A degrees C and 500 A degrees C). The associated changes in the microstructure and texture were studied using electron back-scattered diffraction. ECAP produced an average grain size of 12 to 18 A mu m with B and C-2 fiber textures. Subsequent rolling led to an average grain size 8 to 10 A mu m with basal texture fiber parallel to ND. There was no noticeable increase in the average grain size on annealing at 373 K (100 A degrees C). However, significant increase in the average grain size occurred at 773 K (500 A degrees C). The occurrence of different DRX mechanisms was detected: discontinuous dynamic recrystallization was attributed to basal slip activity and continuous dynamic recovery and recrystallization to prismatic/pyramidal slip systems. Only continuous static recrystallization could be observed on annealing.

Inhibition of protein synthesis leading to unfolded protein response is the major event in abrin-mediated apoptosis

Abrin obtained from the plant Abrus precatorius inhibits protein synthesis and also triggers apoptosis in cells. Previous studies from our laboratory suggested a link between these two events. Using an active site mutant of abrin A-chain which exhibits 225-fold lower protein synthesis inhibitory activity than the wild-type abrin A-chain, we demonstrate in this study that inhibition of protein synthesis induced by abrin is the major factor triggering unfolded protein response leading to apoptosis. Since abrin A-chain requires the B-chain for internalization into cells, the wild-type and mutant recombinant abrin A-chains were conjugated to native ricin B-chain to generate hybrid toxins, and the toxic effects of the two conjugates were compared. The rate of inhibition of protein synthesis mediated by the mutant ricin B-rABRA (R167L) conjugate was slower than that of the wild-type ricin B-rABRA conjugate as expected. The mutant conjugate activated p38MAPK and caspase-3 similar to its wild-type counterpart although at later time points. Overall, these results confirm that inhibition of protein synthesis is the major event contributing to abrin-mediated apoptosis.

BIMODAL NANOINDENTATION RESPONSE OF THE (001) FACE IN CRYSTALLINE SODIUM SACCHARIN DIHYDRATE

The nanoindentation response of the (001) face of sodium saccharin dihydrate is examined. The structure can be demarcated into regular and irregular regions or domains. The regular domains have solid-like and the irregular ones have liquid-like characteristics. Therefore, these domains impart a microstructure to the crystal. The indent face (001) is prominently developed in this crystal and unambiguously presents the regular and irregular regions to nanoindention. Average values of elastic modulus and hardness show a distinct bimodal mechanical response. Such a response has been observed in the case of intergrown polymorphs of aspirin and felodipine. We examine two possible reasons as to why the responses could be for bimodal in this crystal. The first possibility could be that the two domains correspond to regions of the original dihydrate and a lower hydrate that is obtained by the loss of some water. The second possibility could be that these responses correspond to regular and irregular regions in the structure. Nanoindentation is a very useful technique in the characterization of molecular solids, as a complementary technique to X-ray crystallography, because it samples different length scales.

Interferon-Gamma and Nitric Oxide Synthase 2 Mediate the Aggregation of Resident Adherent Peritoneal Exudate Cells: Implications for the Host Response to Pathogens

Interferon-gamma (Ifn gamma), a key macrophage activating cytokine, plays pleiotropic roles in host immunity. In this study, the ability of Ifn gamma to induce the aggregation of resident mouse adherent peritoneal exudate cells (APECs), consisting primarily of macrophages, was investigated. Cell-cell interactions involve adhesion molecules and, upon addition of Ifn gamma, CD11b re-localizes preferentially to the sites of interaction on APECs. A functional role of CD11b in enhancing aggregation is demonstrated using Reopro, a blocking reagent, and siRNA to Cd11b. Studies with NG-methyl-L-arginine (LNMA), an inhibitor of Nitric oxide synthase (Nos), NO donors, e.g., S-nitroso-N-acetyl-DL-penicillamine (SNAP) or Diethylenetriamine/ nitric oxide adduct (DETA/NO), and Nos2(-/-) mice identified Nitric oxide (NO) induced by Ifn gamma as a key regulator of aggregation of APECs. Further studies with Nos2(-/-) APECs revealed that some Ifn. responses are independent of NO: induction of MHC class II and CD80. On the other hand, Nos2 derived NO is important for other functions: motility, phagocytosis, morphology and aggregation. Studies with cytoskeleton depolymerizing agents revealed that Ifn gamma and NO mediate the cortical stabilization of Actin and Tubulin which contribute to aggregation of APECs. The biological relevance of aggregation of APECs was delineated using infection experiments with Salmonella Typhimurium (S. Typhimurium). APECs from orally infected, but not uninfected, mice produce high amounts of NO and aggregate upon ex vivo culture in a Nos2-dependent manner. Importantly, aggregated APECs induced by Ifn gamma contain fewer intracellular S. Typhimurium compared to their single counterparts post infection. Further experiments with LNMA or Reopro revealed that both NO and CD11b are important for aggregation; in addition, NO is bactericidal. Overall, this study elucidates novel roles for Ifn gamma and Nos2 in regulating Actin, Tubulin, CD11b, motility and morphology during the aggregation response of APECs. The implications of aggregation or ``group behavior'' of APECs are discussed in the context of host resistance to infectious organisms.

Tuning the chiro-plasmonic response using high refractive index-dielectric templates

Chiral metamaterials have recently gained attention due to their applicability in developing polarization devices and in the detection of chiral molecules. A common approach towards fabricating plasmonic chiral nanostructures has been decorating metallic nanoparticles on dielectric chiral scaffolds, such as a helix. This resulted in the generation of a large chiro-optical response over a wide range of the electromagnetic spectrum. It has been shown previously that the optical tunability of these chiral metamaterials depends on the geometrical aspects of the overall structure, as well as the nature of the plasmonic constituents. In this study, we have investigated the role of the underlying dielectric scaffold with numerical simulations, and experimentally demonstrated that it is possible to enhance and engineer their chiro-plasmonic response significantly by choosing dielectric scaffolds of appropriate materials.

Dynamic response of a piezoelectric flapping wing

Piezo-composite membranes have advantages over motorized flapping where frequencies are high and certain coupling between bending and twisting is useful to generate lift and forward flight. We draw examples of fruit fly and bumble bee. Wings with Piezo ceramic PZT coating are realized. The passive mechanical response of the wing is characterized experimentally and validated using finite element simulation. Piezoelectric actuation with uniform electrode coating is characterized and optimal frequencies for flapping are identified. The experimental data are used in an empirical model and advanced ratio for a flapping insect like condition for various angular orientations is estimated.

Seismic response of reduced-scale modular block and rigid faced reinforced walls through shaking table tests

This paper focuses on understanding the seismic response of geosynthetic reinforced retaining walls through shaking table tests on models of modular block and rigid faced reinforced retaining walls. Reduced-scale models of retaining walls reinforced with geogrid layers were constructed in a laminar box mounted on a uniaxial shaking table and subjected to various levels of sinusoidal base shaking. Models were instrumented with ultrasonic displacement sensors, earth pressure sensors and accelerometers. Effects of backfill density, number of reinforcement layers and reinforcement type on the performance of rigid faced and modular block walls were studied through different series of model tests. Performances of the walls were assessed in terms of face deformations, crest settlement and acceleration amplification at different elevations and compared. Modular block walls performed better than the rigid faced walls for the same level of base shaking because of the additional support derived by stacking the blocks with an offset. Type and quantity of reinforcement has significant effect on the seismic performance of both the types of walls. Displacements are more sensitive to relative density of the backfill and decrease with increasing relative density, the effect being more pronounced in case of unreinforced walls compared to the reinforced ones. Acceleration amplifications are not affected by the wall facing and inclusion of reinforcement. (C) 2015 Elsevier Ltd. All rights reserved.

Simultaneously targeting inflammatory response and parasite sequestration in brain to treat Experimental Cerebral Malaria

Malaria afflicts around 200 million people annually, with a mortality number close to 600,000. The mortality rate in Human Cerebral Malaria (HCM) is unacceptably high (15-20%), despite the availability of artemisinin-based therapy. An effective adjunct therapy is urgently needed. Experimental Cerebral Malaria (ECM) in mice manifests many of the neurological features of HCM. Migration of T cells and parasite-infected RBCs (pRBCs) into the brain are both necessary to precipitate the disease. We have been able to simultaneously target both these parameters of ECM. Curcumin alone was able to reverse all the parameters investigated in this study that govern inflammatory responses, CD8(+) T cell and pRBC sequestration into the brain and blood brain barrier (BBB) breakdown. But the animals eventually died of anemia due to parasite build-up in blood. However, arteether-curcumin (AC) combination therapy even after the onset of symptoms provided complete cure. AC treatment is a promising therapeutic option for HCM.

Global response sensitivity analysis using probability distance measures and generalization of Sobol's analysis

The study introduces two new alternatives for global response sensitivity analysis based on the application of the L-2-norm and Hellinger's metric for measuring distance between two probabilistic models. Both the procedures are shown to be capable of treating dependent non-Gaussian random variable models for the input variables. The sensitivity indices obtained based on the L2-norm involve second order moments of the response, and, when applied for the case of independent and identically distributed sequence of input random variables, it is shown to be related to the classical Sobol's response sensitivity indices. The analysis based on Hellinger's metric addresses variability across entire range or segments of the response probability density function. The measure is shown to be conceptually a more satisfying alternative to the Kullback-Leibler divergence based analysis which has been reported in the existing literature. Other issues addressed in the study cover Monte Carlo simulation based methods for computing the sensitivity indices and sensitivity analysis with respect to grouped variables. Illustrative examples consist of studies on global sensitivity analysis of natural frequencies of a random multi-degree of freedom system, response of a nonlinear frame, and safety margin associated with a nonlinear performance function. (C) 2015 Elsevier Ltd. All rights reserved.

Mg/BN nanocomposites: Nano-BN addition for enhanced room temperature tensile and compressive response

The present study elucidates the effects of nanoscale boron nitride particles addition on the microstructural and mechanical characteristics of monolithic magnesium. Novel light-weight Mg nanocomposites containing 0.3, 0.6 and 1.2vol% nano-size boron nitride particulates were synthesized using the disintegrated melt deposition method followed by hot extrusion. Microstructural characterization of developed Mg/x-boron nitride composites revealed significant grain refinement due to the uniform distribution of nano-boron nitride particulates. Texture analysis of selected Mg-1.2 boron nitride nanocomposite showed an increase in the intensity of fiber texture alongside enhanced localized recrystallization when compared to monolithic Mg. Mechanical properties evaluation under indentation, tension and compression loading indicated superior response of Mg/x-boron nitride composites in comparison to pure Mg. The uniform distribution of nanoscale boron nitride particles and the modified crystallographic texture achieved due to the nano-boron nitride addition attributes to the superior mechanical characteristics of Mg/boron nitride nanocomposites.

Generalized Partial Response Equalization and Data-Dependent Noise Predictive Signal Detection Over Media Models for TDMR

Two-dimensional magnetic recording (2-D TDMR) is an emerging technology that aims to achieve areal densities as high as 10 Tb/in(2) using sophisticated 2-D signal-processing algorithms. High areal densities are achieved by reducing the size of a bit to the order of the size of magnetic grains, resulting in severe 2-D intersymbol interference (ISI). Jitter noise due to irregular grain positions on the magnetic medium is more pronounced at these areal densities. Therefore, a viable read-channel architecture for TDMR requires 2-D signal-detection algorithms that can mitigate 2-D ISI and combat noise comprising jitter and electronic components. Partial response maximum likelihood (PRML) detection scheme allows controlled ISI as seen by the detector. With the controlled and reduced span of 2-D ISI, the PRML scheme overcomes practical difficulties such as Nyquist rate signaling required for full response 2-D equalization. As in the case of 1-D magnetic recording, jitter noise can be handled using a data-dependent noise-prediction (DDNP) filter bank within a 2-D signal-detection engine. The contributions of this paper are threefold: 1) we empirically study the jitter noise characteristics in TDMR as a function of grain density using a Voronoi-based granular media model; 2) we develop a 2-D DDNP algorithm to handle the media noise seen in TDMR; and 3) we also develop techniques to design 2-D separable and nonseparable targets for generalized partial response equalization for TDMR. This can be used along with a 2-D signal-detection algorithm. The DDNP algorithm is observed to give a 2.5 dB gain in SNR over uncoded data compared with the noise predictive maximum likelihood detection for the same choice of channel model parameters to achieve a channel bit density of 1.3 Tb/in(2) with media grain center-to-center distance of 10 nm. The DDNP algorithm is observed to give similar to 10% gain in areal density near 5 grains/bit. The proposed signal-processing framework can broadly scale to various TDMR realizations and areal density points.

A hybrid method for stochastic response analysis of a vibrating structure

Response analysis of a linear structure with uncertainties in both structural parameters and external excitation is considered here. When such an analysis is carried out using the spectral stochastic finite element method (SSFEM), often the computational cost tends to be prohibitive due to the rapid growth of the number of spectral bases with the number of random variables and the order of expansion. For instance, if the excitation contains a random frequency, or if it is a general random process, then a good approximation of these excitations using polynomial chaos expansion (PCE) involves a large number of terms, which leads to very high cost. To address this issue of high computational cost, a hybrid method is proposed in this work. In this method, first the random eigenvalue problem is solved using the weak formulation of SSFEM, which involves solving a system of deterministic nonlinear algebraic equations to estimate the PCE coefficients of the random eigenvalues and eigenvectors. Then the response is estimated using a Monte Carlo (MC) simulation, where the modal bases are sampled from the PCE of the random eigenvectors estimated in the previous step, followed by a numerical time integration. It is observed through numerical studies that this proposed method successfully reduces the computational burden compared with either a pure SSFEM of a pure MC simulation and more accurate than a perturbation method. The computational gain improves as the problem size in terms of degrees of freedom grows. It also improves as the timespan of interest reduces.

Differential viability response of prokaryotes and eukaryotes to high strength pulsed magnetic stimuli

The present study examines the efficacy of a high strength pulsed magnetic field (PMF) towards bacterial inactivation in vitro, without compromising eukaryotic cell viability. The differential response of prokaryotes Staphylococcus aureus (MESA), Staphylococcus epidermidis, and Escherichia coli], and eukaryotes C2C12 mouse myoblasts and human mesenchymal stem cells, hMSCs] upon exposure to varying PMF stimuli (1-4 T, 30 pulses, 40 ms pulse duration) is investigated. Among the prokaryotes, similar to 60% and similar to 70% reduction was recorded in the survival of staphylococcal species and E. coli, respectively at 4 T PMF as evaluated by colony forming unit (CPU) analysis and flow cytometry. A 2-5 fold increase in intracellular ROS (reactive oxygen species) levels suggests oxidative stress as the key mediator in PMF induced bacterial death/injury. The 4 T PMF treated staphylococci also exhibited longer doubling times. Both TEM and fluorescence microscopy revealed compromised membranes of PMF exposed bacteria. Under similar PMF exposure conditions, no immediate cytotoxicity was recorded in C2C12 mouse myoblasts and hMSCs, which can be attributed to the robust resistance towards oxidative stress. The ion interference of iron containing bacterial proteins is invoked to analytically explain the PMF induced ROS accumulation in prokaryotes. Overall, this study establishes the potential of PMF as a bactericidal method without affecting eukaryotic viability. This non-invasive stimulation protocol coupled with antimicrobial agents can be integrated as a potential methodology for the localized treatment of prosthetic infections. (C) 2015 Elsevier B.V. All rights reserved.

Tailored nitrogen dioxide sensing response of three-dimensional graphene foam

Ultralight and macroporous three-dimensional reduced graphene oxide (rGO) foams are prepared by lyophilization (freeze-drying) technique to avoid a conventional template method. This method allows tailoring the porosity of the foams by varying the weight percentages of graphene oxide dispersions in water. Three different rGO foams of 0.2, 0.5 and 1.0 wt% are used for NO2 sensing. Sensing response from the tailored structure of rGO is found to be directly related to the density. A maximum of 20% sensing response is observed for a higher porosity of the structure, better than the known results so far on graphene foams in the literature. (C) 2015 Elsevier B.V. All rights reserved.