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Effect of bubble distribution on wall drag in turbulent channel flow
No full textSkin-friction drag reduction in (water) turbulent boundary layers using bubble injection has been studied for some time. Ceccio (Annu Rev Fluid Mech 42:183-203, 2010) and Murai (Exp Fluids 55(7):1-28, 2014) have compiled drag reduction data from a number of different studies and facilities, and highlighted the large differences and scatter in the data even at the same bubble void fraction. Motivated by this, in the present work, we experimentally investigate within a single horizontal turbulent channel facility, drag modification using bubbles over a wide range of bubble void fraction (0<alpha<0.15), channel Reynolds number (22,500 <Re< 67,500), and the orientation of bubble injection (top/ bottom wall). In each of the cases, we have simultaneously measured drag modification and visualized the bubble dynamics. The drag modification is obtained from measurement of the mean pressure drop at four different vertical locations within the channel. The results show that even in the same facility, the drag reduction obtained at a fixed void fraction (alpha) can be very different due to changes in bubble dynamics caused by changes in the other flow parameters. The visualizations show a number of bubble dynamics regimes depending on the parameters, with possibilities of both increased and decreased drag compared to the base (no bubble) case. The measurements for the bubble cases show significant vertical variations in the measured pressure drop within the channel, with these vertical variations being also dependent on the bubble distribution/dynamics. Interestingly, in some cases, the pressure drop at a given height even becomes negative, although the integrated pressure drop over the channel height, which is related to the overall drag, remains positive but lower than the base case. In terms of the overall drag, the top-wall injection is observed to give good drag reduction over a wide range of flow Re and alpha, but is seen to saturate beyond a threshold alpha. In contrast, the bottom-wall injection case shows that drag continuously decreases with alpha at high channel Re, while at low channel Re, the drag is found to continually increase with alpha. The present study shows a maximum of about 60% increase and a similar 60% reduction in wall drag over the entire range of conditions investigated. For each of the bubble wall injection orientations (bottom/top/both wall), contour plots of drag modification and gain factor (fractional drag reduction per unit void fraction) are presented in the plane of alpha and Re along with the corresponding bubble dynamics, which helps to delineate the different regimes seen in such bubbly channel flows
Chiral Phase Transition Temperature in (2+1)-Flavor QCD
No full textWe present a lattice-QCD-based determination of the chiral phase transition temperature in QCD with two degenerate, massless quarks and a physical strange quark mass using lattice QCD calculations with the highly improved staggered quarks action. We propose and calculate two novel estimators for the chiral transition temperature for several values of the light quark masses, corresponding to Goldstone pion masses in the range of 58 MeV less than or similar to m(pi) less than or similar to 163 MeV. The chiral phase transition temperature is determined by extrapolating to vanishing pion mass using universal scaling analysis. Finite-volume effects are controlled by extrapolating to the thermodynamic limit using spatial lattice extents in the range of 2.8-4.5 times the inverse of the pion mass. Continuum extrapolations are carried out by using three different values of the lattice cutoff, corresponding to lattices with temporal extents N-tau = 6, 8, and 12. After thermodynamic, continuum, and chiral extrapolations, we find the chiral phase transition temperature T-c(0) = 132(-6)(+3) MeV
A Time-Varying Virtual Resistance Control for Ultracapacitor Based DC-DC Converters
No full textUltracapacitor (UC) based dc-dc power supplies are widely used for addressing surge power demands and to provide energy backup to critical loads. The conventional control techniques, such as unified control strategy, though ensure seamless mode transition, do not offer complete flexibility in charging and discharging controls which is crucial in UC-based backup systems. On the other hand, controls, such as independent switch control, though allow great flexibility in control, do not ensure seamless mode transition without appropriate mode-switch logic. This paper proposes a time-varying virtual resistance based mode transition control for independent switch control which not only ensures smooth, seamless transition between charging and discharging control modes but also ensures complete control over the mode transition durations. The proposed control is found to be robust to error mode identification as compared to introducing dead band between control modes. The proposed control is verified on a proof of concept experimental setup at a power level of P-o = 65W, voltage level of V-g = 26 V with the dc-dc converter switching at f(sw) = 100 kHz. The performance comparison with PWM blocking method is also evaluated where the proposed control is found to work well
Association of variants in HTRA1 and NOTCH3 with MRI-defined extremes of cerebral small vessel disease in older subjects
No full textWe report a composite extreme phenotype design using distribution of white matter hyperintensities and brain infarcts in a population-based cohort of older persons for gene-mapping of cerebral small vessel disease. We demonstrate its application in the 3C-Dijon whole exome sequencing (WES) study (n = 1924, n(WESextremes) = 512), with both single variant and gene-based association tests. We used other population-based cohort studies participating in the CHARGE consortium for replication, using whole exome sequencing (n(WES) = 2,868, n(WESextremes) = 956) and genome-wide genotypes (n(GW) = 9924, n(GWextremes) = 3308). We restricted our study to candidate genes known to harbour mutations for Mendelian small vessel disease: NOTCH3, HTRA1, COL4A1, COL4A2 and TREX1. We identified significant associations of a common intronic variant in HTRA1, rs2293871 using single variant association testing (P-discovery = 8.21 x 10(-5), P-replication = 5.25 x 10(-3), P-combined = 4.72 x 10(-5)) and of NOTCH3 using gene-based tests (P-discovery = 1.61 x 10(-2), P-replication = 3.99 x 10(-2), P-combined = 5.31 x 10(-3)). Follow-up analysis identified significant association of rs2293871 with small vessel ischaemic stroke, and two blood expression quantitative trait loci of HTRA1 in linkage disequilibrium. Additionally, we identified two participants in the 3C-Dijon cohort (0.4%) carrying heterozygote genotypes at known pathogenic variants for familial small vessel disease within NOTCH3 and HTRA1. In conclusion, our proof-of-concept study provides strong evidence that using a novel composite MRI-derived phenotype for extremes of small vessel disease can facilitate the identification of genetic variants underlying small vessel disease, both common variants and those with rare and low frequency. The findings demonstrate shared mechanisms and a continuum between genes underlying Mendelian small vessel disease and those contributing to the common, multifactorial form of the disease
Silicon Nitride based Medium Contrast Gratings for Doubly Resonant Fluorescence Enhancement
No full textWe present the design, fabrication, and experimental characterization of silicon nitride based medium-index contrast gratings on glass substrate for fluorescence enhancement in the yellow to red spectral range with resonances for both incident excitation and fluorescence emission wavelengths under surface normal incidence. A comparison of the design space to realize resonant field enhancement in high-index contrast silicon and medium-index contrast silicon nitride grating structures is presented. The one-dimensional sub-wavelength grating structures studied here are designed with large duty cycle (similar to 80%) to account for the medium refractive index contrast (Delta n similar to 0.5) between silicon nitride and the glass substrate to ensure that the device operates in the two-mode regime. The resonant enhancement of fluorescence is experimentally verified using rhodamine-B isothiocyanate dye as the fluorophore of interest. A resonant enhancement of 10.8 times is demonstrated in this sample when compared to un-patterned film for transverse electric-transverse magnetic (TE-TM) polarization combination. We have also performed simulation study with plane wave excitation and incoherent dipole array emission to model the resonant excitation and emission processes, respectively. The simulations corroborate well with the best observed experimental results for the doubly resonant fluorescence configuration. Silicon nitride based medium contrast gratings are a promising platform to fabricate scalable structures for resonant enhancement of light-matter interaction with potential applications in high-sensitivity biological fluorescence assays and as a platform for polarization selective interrogation of light emission from nanoscale emitters attached to the grating
Defects, conductivity and photoconductivity in Ar+ bombarded KTaO 3
No full textOxygen vacancies play a crucial role in the conductivity of oxides. Here, we report the photoresponse of the electron doped surface of Ar + bombarded oxygen vacant (001) KTaO 3 (KTO) single crystal. The bombardment time defines the amount of oxygen vacancies and hence the electron doping level. The time evolution of photoresponse to daylight illumination remains independent of the carrier density and follows the biexponential function. By contrast, the amplitude of the photoresponse increases with the decreasing charge carrier density. The samples show distinct responses in terms of amplitude as well as response time to the illumination with laser light of wavelengths 633, 532, and 405nm. The defect states distribution within the bandgap is calculated with the photoconductivity relaxation, which involves deep sensitizing hole traps. The combined results of electrical conductivity, photoconductivity, atomic force microscopy, and Kelvin probe force microscopy suggest that the conductivity produced on the KTO surface is not continuous throughout the surface. Rather, Ar + bombardment creates oxygen deficiency patches that are oriented along some preferential crystal orientations and interconnected with each other, thus producing percolating conducting channels on the surface of the sample. Under light illumination, photocarriers are generated in these conducting channels
An investigation into the heat release and emissions from counterflow diffusion flames of methane/dimethyl ether/hydrogen blends in air
No full textIn the present work, the effects of blending dimethyl ether (DME) and hydrogen (H-2) with methane (CH4) have been numerically studied in the context of counterflow diffusion flames. In order to do so, a reaction mechanism consisting of 974 reaction steps among 146 species with updated thermodynamic and transport properties has been developed. This mechanism has been validated against the experimental data on laminar burning velocity, ignition delay time and species profiles in counterflow diffusion flames. The present study suggests that the heat release pattern of the CH4 counter flow diffusion flame shows major changes when DME and H-2 are present in the fuel stream. Furthermore, the results show that the presence of low volume fractions of DME in CH4 increases the formation of benzene (C6H6) in the flame. This fact can be negated by the presence of H-2 together with CH4 and DME in the fuel stream. Moreover, the present study suggests that H-2 mitigates the C6H6 formation in the CH4 diffusion flame with greater effectiveness compared to DME. Contrary to the popular belief, the main reason behind such efficacy of H-2 has been found to be physical rather than chemical. On the other hand, the NO production routes are primarily dominated by the Zeldovich mechanism in the flames involving CH4, DME and H-2 blends. In this regard, the present analysis suggests that the simultaneous presence of DME and H-2 in CH4 effectively prevents the formation of NO in the flame
Modulating non-linear optical absorption through controlled graphitization of carbon nanostructures containing Fe3C-graphite core-shell nanoparticles
No full textCarbonaceous materials containing Fe/Fe3C(core)-graphite(shell) nanoparticles-embedded carbon globules and carbon nanotubes are synthesized using pyrolysis. The thickness of the graphitic shell on the Fe/Fe3C nanoparticles was varied by exposing Fe-acetylacetonate and toluene precursors to different initial temperatures (reaction tube insertion temperatures) T-in. Furthermore, the thickness of the graphitic layer and the degree of graphitization along with the defect concentration in the graphitic layer was controlled by this process. A proposed mechanism for the formation of such carbonaceous nanostructures due to variation of T-in is provided. Non-linear absorption (NLA) experiments were carried out to explore the effect of graphitization and the role of defects on the laser intensity dependent NLA behaviour of these samples. We demonstrate that degree of graphitization and defect concentration in the highly graphitized layers considerably enhances the NLA behaviour of high intensity laser radiation in the material. The enhancement of NLA coefficient is mainly attributed to the excited state absorption (ESA) and free carrier absorption (FCA) processes. Our results emphasize that the reported carbonaceous materials with optimum amount of defects in the graphitized framework are attractive for optical limiting in laser safety applications
Multilocus nuclear markers provide new insights into the origin and evolution of the blackbuck (Antilope cervicapra, Bovidae)
No full textEvolutionary relationships between members of the Antilopina taxon have been much debated in recent years. The `true antelope' Glade is currently comprised of 4 genera viz., Gazella, Nanger, Eudorcas and the monotypic genus Antilope, that includes A. cervicapra. Most studies have focused on the mitochondrial genome or morphological data to study their relationships. However, signals from mitochondrial data can often be misleading when compared with nuclear markers, as has been shown in multiple taxonomic groups. In this study, we revisit the phylogenetic relationships among members of Antilopina, particularly the phylogenetic position of A. cervicapra, using 12 nuclear markers and compare it with the mitochondrial tree. Furthermore, we explore the implications of the results of this study on the taxonomy and biogeography of Indian antelopes. The nuclear phylogenetic trees built using multiple coalescent and concatenated methods all supported a paraphyletic genus Gazella. Antilope was nested within Gazella as opposed to being sister to it, which was suggested by previous studies and our results based on mitochondrial markers. Our fossil-calibrated larger bovid phylogeny, based on nuclear markers, suggested that the Antilope lineage diverged from its sister species more recently in the Pleistocene, rather than in late Miocene as per previous studies. Our biogeographic analyses suggest that the lineage leading to genus Antilope dispersed into India from the Saharo-Arabian realm around 2 mya, post the expansion of grasslands. We speculate that the adaptations of this savanna-grassland specialist did not allow them to extend their range beyond the Indian subcontinent. Whereas, the only other true antelope in India, G. bennetti, extended its range into India more recently, probably after the establishment of the Thar desert in northwest India
Characterization of a glucose tolerant beta-glucosidase from Aspergillus unguis with high potential as a blend-in for biomass hydrolyzing enzyme cocktails
No full textObjectives Characterization of glucose tolerant beta glucosidase (GT-BGL) secreted by Aspergillus unguis NII 08123, determination of the gene and protein sequences of the enzyme and establishing its performance in blends for lignocellulose hydrolysis. Results Supplementation of A. unguis beta glucosidase (BGL) to cellulase released 1.6 times more sugar within 12 h during the hydrolysis of lignocellulosic biomass. The enzyme was determined to be similar to BGL-F from Emericella nidulans by MALDI-TOF analysis, and was found to be a GH3 family protein. Molecular Docking simulation studies showed that the enzyme has lesser affinity for glucose (- 5.7 kcal/mol) compared to its substrate cellobiose (- 7.5 kcal/mol). The residues present in the N-terminal domain are mostly involved in bond formation with both the substrate and the product, while the C-terminal domain contains the catalytic region. In-silico studies showed that its predicted structure is unlike that of previously reported BGLs, which might provide a clue to its exceptional catalytic activity. Conclusion The GT-BGL from A. unguis NII 08123 was proven effective as a blend in for biomass hydrolyzing enzyme cocktails and the possible reasons for its glucose tolerance was determined through studies on its modeled structure