Single Dominant Peak Research Articles

Blockage ratio and Reynolds number effects on flows around a rectangular prism

The combined effects of blockage ratio (BR) and Reynolds number (Re) on the spatiotemporal characteristics of turbulent flow separation around a rectangular prism with depth-to-thickness ratio of 3 were investigated using a time-resolved particle image velocimetry. Four different blockage ratios (BR = 2.5%, 5%, 10%, and 15%) were examined at Reynolds numbers of 3000, 7500, and 15000. Two regimes (unattached and reattached) were identified; however, the boundary between these regimes shows a complex dependency on BR and Re. The mean flow does not reattach onto the prism at low BR and Re but tends to reattach when BR and Re increase. The wake vortices are relatively larger for the unattached test cases. The separation bubbles over and in the wake of the prism are dynamically coupled for prisms in the unattached regime but independent of each other in the reattached regime. Spectral analyses of the velocity fluctuations and coefficient of the first proper orthogonal decomposition mode pair reveal a single dominant peak at the same fundamental shedding frequency for the reattached test cases, whereas multiple competing frequencies are observed for test cases in the unattached regime. The Kelvin–Helmholtz frequency increases with an increase in BR and Re. The vortical structures are more organized for prisms in the reattached regime, and their convective velocities in the wake are comparatively higher.

Europium (II)-Doped CaF2 Nanocrystals in Sol-Gel Derived Glass-Ceramic: Luminescence and EPR Spectroscopy Investigations.

The remarkable properties of Eu2+-activated phosphors, related to the broad and intense luminescence of Eu2+ ions, showed a high potential for a wide range of optical-related applications. Oxy-fluoride glass-ceramic containing Europium (II)-doped CaF2 nanocrystals embedded in silica matrix were produced in two steps: glass-ceramization in air at 800° with Eu3+-doped CaF2 nanocrystals embedded followed by Eu3+ to Eu2+ reduction during annealing in reducing atmosphere. The broad, blue luminescence band at 425 nm and with the long, weak tail in the visible range is assigned to the d → f type transition of the Eu2+ located inside the CaF2 nanocrystals in substitutional and perturbed sites, respectively; the photoluminescence quantum yield was about 0.76. The X-ray photoelectron spectroscopy and Electron paramagnetic spectroscopy confirmed the presence of Eu2+ inside the CaF2 nanocrystals. Thermoluminescence curves recorded after X-ray irradiation of un-doped and Eu2+-doped glass-ceramics showed a single dominant glow peak at 85 °C related to the recombination between F centers and Eu2+ related hole within the CaF2 nanocrystals. The applicability of the procedure can be tested to obtain an oxy-fluoride glass-ceramic doped with other divalent ions such as Sm2+, Yb2+, as nanophosphors for radiation detector or photonics-related applications.

High-transmission narrowband ultraviolet filter based on an aluminum laminated nanostructure on glass.

We present an aluminum (Al) laminated nanostructure stacked on a glass substrate to produce highly transmitted narrowband ultraviolet (UV) filters. The laminated nanostructure was mainly composed of an Al nanohole array, and each Al nanohole had a coaxial Al nanoring at the bottom. This UV filter showed a single dominant peak with a high transmission over 50% and a narrow bandwidth less than 80 nm in the 200-400 nm waveband that was achieved based on the synergy of surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR). The electric field profiles of the laminated nanostructure indicate that SPR selects the transmission wavelength and LSPR contributes to single peak. This narrowband UV filter can be utilized in UV detectors.

Effect of the yaw angle and spanning length on flow characteristics around a near-wall cylindrical structure

Three-dimensional direct numerical simulation is carried out to investigate the effects of the yaw angle and spanning length on the vortex structures and hydrodynamics of flow crossing a near-wall cylindrical structure. Two yaw angles (α = 0°, 45°), and three spanning length ratios (L* = 25, 50, 100) are investigated at Re = 500. Under the normal cylinder condition (α = 0°), a parallel vortex shedding pattern is observed in the wake. The vortex formation lengths are identical for all L*, whereas the spanwise correlation of the vortex shedding declines with the increasing L*, indicating the intensified three-dimensionality. A single dominant peak is found in the lift frequency spectra for each L* case. Under the yawed condition (α = 45°), the flow characteristics are fundamentally changed with negatively-yawed linear vortex shedding tubes being observed in the wake. Different from the normal cases, the vortex formation length for L* = 25 is larger than that of L* = 50 and 100, while the oblique angle of the vortex tube decreases with the increasing L*. It is shown that, at α = 45°, the three-dimensional flow features are fully developed when L* ≥ 50. The lift frequency spectra show multiple peaks while the magnitudes of the secondary peaks are significantly reduced by extending the spanning length. By comparing the results between α = 0° and α = 45°, it is found the Independence Principle (IP) is applicable for predicting the first-order statistics of the hydrodynamic forces and vortex shedding frequency, but fails in predicting the second-order force statistics. The effects of the yaw angle on the pressure and shear stress distributions of the bottom wall are also discussed.

Orchestrating Extracellular Vesicle With Dual Reporters for Imaging and Capturing in Mammalian Cell Culture.

Background: Recent technological advancements have enabled live-cell imaging of intracellular organelles to monitor their biogenesis in mammalian cells. However, applying this method to gain insight into extracellular organelles, such as extracellular vesicles (EVs), presents unique challenges that require special considerations in design and engineering. Results: We have developed a dual-reporter system that combines genetic fusion, fluorescence microcopy and magnetic beads capture of EVs to study the biogenesis of EVs in mammalian cell cultures. First, we genetically produced a series of reporters by fusing a green fluorescent protein (GFP) and an affinity peptide (6xHis), with either the endogenous transmembrane protein, CD63, or EVs targeting vesicular stomatitis viral glycoprotein (VSVG). Transfection of these reporters into human 293T cells resulted in expression and integration of these reporters into pre-exosome compartments, which were subsequently released into the culture medium. Confocal imaging and nano-particle tracking analysis demonstrated that EVs were appropriately labeled and exhibited a single dominant peak in the 80–110 nm size range, indicating that isolated EVs were comprised of micro-vesicles and/or exosome subpopulations. Incubation of isolated EVs with nickel-coated magnetic beads resulted in successful capture of GFP-positive EVs. Finally, addition of EVs into culture medium was able to reveal the cellular uptake of GFP-labeled EVs by recipient cells. Taken together, our dual-reporter system provides a powerful method for both monitoring and capturing of EVs in mammalian cell culture systems. Conclusion: A dual-reporter system provides a robust tool to study the life cycle of EVs in mammalian cells from biogenesis and excretion to cellular uptake.

Understanding the role of the porous electrode microstructure in redox flow battery performance using an experimentally validated 3D pore-scale lattice Boltzmann model

The porous structure of the electrodes in redox flow batteries (RFBs) plays a critical role in their performance. We develop a framework for understanding the coupled transport and reaction processes in electrodes by combining lattice Boltzmann modelling (LBM) with experimental measurement of electrochemical performance and X-ray computed tomography (CT). 3D pore-scale LBM simulations of a non-aqueous RFB are conducted on the detailed 3D microstructure of three different electrodes (Freudenberg paper, SGL paper and carbon cloth) obtained using X-ray CT. The flow of electrolyte and species within the porous structure as well as electrochemical reactions at the interface between the carbon fibers of the electrode and the liquid electrolyte are solved by a lattice Boltzmann approach. The simulated electrochemical performances are compared against the experimental measurements with excellent agreement, indicating the validity of the LBM simulations for predicting the RFB performance. Electrodes featuring one single dominant peak (i.e., Freudenberg paper and carbon cloth) show better electrochemical performance than the electrode with multiple dominant peaks over a wide pore size distribution (i.e., SGL paper), whilst the presence of a small fraction of large pores is beneficial for pressure drop. This framework is useful to design electrodes with optimal microstructures for RFB applications.

Investigations of BaCl2:Eu2+ nanophosphor using electron paramagnetic resonance, structural analysis and thermoluminescence

Structural analysis of the Eu2+-doped BaCl2 nanocrystals and the doping process was monitored and characterized via electron paramagnetic resonance spectroscopy. Structural analysis has shown a slight distortion of the cell which is reflected in the low value of microstrain and the Eu2+-doping effect is limited to the first order chlorine ions neighbors of Ba2+. Electron paramagnetic resonance measurements have indicated the presence of the Eu2+-dopant ions in the BaCl2 host matrix with a solubility limit of about 2%. From the spectra simulation, the isotropic g-value giso = 1.9951(7), the isotropic hyperfine coupling constant Aiso = 42.4 MHz and the high-order zero-field splitting parameters from the crystal field B20 = 21 MHz and B22 = -493 MHz were obtained. During X-ray irradiation, defects are produced and stabilized by the Eu2+ dopant ions. The single dominant thermoluminescence peak at 132 °C (activation energy E = 1.1 eV) was assigned to the recombination of the F(Cl)-center with Eu2+ related hole centers.

Effect of near-wake jet on the lock-in of a freely vibrating square cylinder

We present a numerical study of a freely vibrating square cylinder with steady bleeding at its base side. In particular, we focus on the suppression of vortex-induced vibration (VIV) and the reduction of drag force for the elastically mounted square cylinder at a laminar flow condition via near-wake jet. We examine the base bleeding mechanism in the near-wake region of a square cylinder and its influence over the flow dynamics and the wake characteristics for both stationary (nonlock-in) and freely vibrating (lock-in) conditions. We consider the near-wake jet parameter as a function of the bleed coefficient (Cq), which is the ratio of near-wake jet flow velocity to the freestream velocity and depends on the Reynolds number (Re) based on the diameter of the cylinder. Investigations of the hydrodynamic coefficients and the flow features are carried out for the laminar Re range, namely, Re = 40, 60, 100, and 150. A single dominant frequency peak is observed in the lift coefficient spectrum plot for all the Reynolds numbers considered, but two peaks are observed for Re = 150 at Cq = 0.175 and 0.2. Higher Cq values behave like a splitter plate thereby preventing the interaction of alternating shear layers. The variation of the mean drag is associated with the pressure distribution around the cylinder surface and along the streamwise locations. This leads to a thinner wake width, weaker vortices, and higher vortex shedding frequency as observed earlier in the literature. The sharp spikes of pressure coefficient at the base side of the cylinder are observed for Re ∈ [40, 150] due to the near-wake jet, accounting for the fluctuations of drag force coefficient. We demonstrate the formation of multiple vortices at the wake region due to the near-wake jet from our detailed qualitative analysis. We observe counter-rotating pair of recirculating fluids flanking at the near-wake jet location and examine the recovery of base pressure due to the jet flow. We demonstrate the splitting of big circulation fluid bubble into many smaller counter-rotating fluids due to high-velocity jet flow, resulting into the stabilization of flow profiles in the wake region. We extend this investigation to quantify the effect of the near-wake jet on the two-degree-of-freedom cylinder system at the representative Reynolds number Re = 100 and three mass ratios m* = 1, 2, and 3. We demonstrate the reduction of peak transverse VIV amplitude by 90% in comparison to the plain cylinder counterpart.

Highly selective ultraviolet aluminum plasmonic filters on silicon

We report the use of aluminum patterning to make highly selective UV bandpass filters. We design and fabricate a periodic array of nanoholes in Al thin film on a bare silicon substrate as an analog for potential integration with a Si photodetector. Arrays were designed to operate in the wavelength range of 200-400 nm. Our results show that we can obtain a single dominant peak filter with a linewidth of 30 nm at normal incidence, in contrast to similar structures on glass substrates, where multiple modes influence the UV spectrum. Varying the angle of incidence is shown to split the plasmonic mode and further decrease the linewidth of the maximum wavelength mode down to 10 nm. Our results therefore show high potential for applications in solid-state image sensors for astronomy and planetary studies.

Analysis of gap-free chlorophyll-a data from MODIS in Arabian Sea, reconstructed using DINEOF

ABSTRACTThe chlorophyll-a concentration (chl-a), which is an index of phytoplankton pigment present in the oceans, is considered as a key indicator of health of marine ecosystems that could have direct effect on the human life. In this study, spatial and temporal variability of chl-a in the Arabian Sea (AS) is examined using reconstructed cloud-free ocean colour data for the period 2002–2015. Data Interpolating Empirical Orthogonal Function method is used to reconstruct the missing data. Subsequently, wavelet analysis is applied on the reconstructed data to assess the temporal variability in terms of seasonal, intra-seasonal, and interannual variability of chl-a in the AS. Wavelet analysis clearly depicted the low-frequency, stationary modes or approximation levels inferring the monthly, seasonal, and annual mean of the signal, while the high-frequency, non-stationary modes indicated the local abnormalities. From the analysis of gap-free data, the presence of biennial mode of variability in the northern AS chl-a is observed. The analysis further showed the existence of intra-seasonal oscillations in the northern AS during summer monsoon and single dominant peak during winter monsoon. Chl-a appeared to decline slightly during the entire study period across all the selected regions of the AS. Also, it is observed that chl-a in the northwestern region is highly dynamic than in the other regions of the AS.

Zika virus infection elicits auto-antibodies to C1q

Zika virus (ZIKV) causes mostly asymptomatic infection or mild febrile illness. However, with an increasing number of patients, various clinical features such as microcephaly, Guillain-Barré syndrome and thrombocytopenia have also been reported. To determine which host factors are related to pathogenesis, the E protein of ZIKV was analyzed with the Informational Spectrum Method, which identifies common information encoded by primary structures of the virus and the respective host protein. The data showed that the ZIKV E protein and the complement component C1q cross-spectra are characterized by a single dominant peak at the frequency F = 0.338, suggesting similar biological properties. Indeed, C1q-specific antibodies were detected in sera obtained from mice and monkeys infected with ZIKV. As C1q has been known to be involved not only in immunity, but also in synaptic organization and different autoimmune diseases, a ZIKV-induced anti-C1q antibody response may contribute to the neurological complications. These findings might also be exploited for the design of safe and efficacious vaccines in the future.

Electromagnetic characteristics of geodesic acoustic mode in the COMPASS tokamak

Axisymmetric geodesic acoustic mode (GAM) oscillations of the magnetic field, plasma potential and electron temperature have been identified on the COMPASS tokamak. This work brings an overview of their electromagnetic properties studied by multi-pin reciprocating probes and magnetic diagnostics. The n = 0 fluctuations form a continuous spectrum in limited plasmas but change to a single dominant peak in diverted configuration. At the edge of diverted plasmas the mode exhibits a non-local structure with a constant frequency over a radial extent of at least several centimeters. Nevertheless, the frequency still reacts on temporal changes of plasma temperature caused by an auxiliary NBI heating as well as those induced by periodic sawtooth crashes. Radial wavelength of the mode is found to be about 1–4 cm, with values larger for the plasma potential than for the electron temperature. The mode propagates radially outward and its radial structure induces oscillations of a poloidal E × B velocity, that can locally reach the level of the mean poloidal flow. Bicoherence analysis confirms a non-linear interaction of GAM with a broadband ambient turbulence. The mode exhibits strong axisymmetric magnetic oscillations that are studied both in the poloidal and radial components of the magnetic field. Their poloidal standing-wave structure was confirmed and described for the first time in diverted plasmas. In limited plasmas their amplitude scales with safety factor. Strong suppression of the magnetic GAM component, and possibly of GAM itself, is observed during co-current but not counter-current NBI.

Thermogravimetric and Online Gas Analysis on various Biomass Fuels

Abstract In this work, the biomass property is evaluated based on pyrolysis behavior of biomass fuels by means of TGA and online gas analysis. Wood, sawdust, pine bark, peat, straw, black liquor and microalgae are chosen as the biomass feedstocks for the pyrolysis study. The measurement results show high volatile content for algae and black liquor (around 85%) and low volatile content for pine bark and peat (around 69%). Differently from woody biomass, the DTG curve of straw has a single dominant peak at much lower temperature, which suggests a dominant component of hemicellulose in biomass, while algae and peat have a broader temperature specturm of devolatilization but much lower peak temperature. CO2 is released first and H2 later in the pyrolysis process for all biomass feedstocks, whileas the peak of CO formation follows CO2 formation trend for most feedstocks used, except for peat and pine bark which give a peak later at high temperature. This indicates secondary reactions of tar cracking, steam reforming and char gasification.

Periodic vortex shedding phenomenon for various separation distances between two plane turbulent parallel jets

In the present study, two plane parallel jets with various separation distances between the two jets (d) are numerically simulated using two-dimensional unsteady RANS equations. The Reynolds number based on the jet width w is Re=10,000. The results reveal that when the separation distance between the two jets lies in the range 0.6⩽d/w⩽1.4, the flow field demonstrates a periodic vortex shedding phenomenon close to the nozzle plate similar to what would be expected in the near wake region for flow over a two-dimensional bluff body. On the contrary, for d/w=0.5 and 1.5, the near flow field region remains to be steady with two counter rotating stable vortices in the recirculation zone. Within the range 0.6⩽d/w⩽1.4, the time series of streamwise and transverse velocity signals display a pure sinusoidal oscillation. In this range, for a given d/w, the fast Fourier transform of both the velocity signals exhibits a single dominant frequency peak at a same value of Strouhal number (non-dimensional vortex shedding frequency) that gradually decreases with the progressive increase in the separation distance between the two jets.

In vitro phase I metabolism of cis-zearalenone.

The present study investigates the in vitro phase I metabolism of cis-zearalenone (cis-ZEN) in rat liver microsomes and human liver microsomes. cis-ZEN is an often ignored isomer of the trans-configured Fusarium mycotoxin zearalenone (trans-ZEN). Upon the influence of (UV-) light, trans-ZEN isomerizes to cis-ZEN. Therefore, cis-ZEN is also present in food and feed. The aim of our study was to evaluate the in vitro phase I metabolism of cis-ZEN in comparison to that of trans-ZEN. As a result, an extensive metabolization of cis-ZEN is observed for rat and human liver microsomes as analyzed by HPLC-MS/MS and high-resolution MS. Kinetic investigations based on the substrate depletion approach showed no significant difference in rate constants and half-lives for cis- and trans-ZEN in rat microsomes. In contrast, cis-ZEN was depleted about 1.4-fold faster than trans-ZEN in human microsomes. The metabolite pattern of cis-ZEN revealed a total of 10 phase I metabolites. Its reduction products, α- and β-cis-zearalenol (α- and β-cis-ZEL), were found as metabolites in both species, with α-cis-ZEL being a major metabolite in rat liver microsomes. Both compounds were identified by co-chromatography with synthesized authentic standards. A further major metabolite in rat microsomes was monohydroxylated cis-ZEN. In human microsomes, monohydroxylated cis-ZEN is the single dominant peak of the metabolite profile. Our study discloses three metabolic pathways for cis-ZEN: reduction of the keto-group, monohydroxylation, and a combination of both. Because these routes have been reported for trans-ZEN, we conclude that the phase I metabolism of cis-ZEN is essentially similar to that of its trans isomer. As trans-ZEN is prone to metabolic activation, leading to the formation of more estrogenic metabolites, the novel metabolites of cis-ZEN reported in this study, in particular α-cis-ZEL, might also show higher estrogenicity.

Spectral and coherence signatures of threshold in random lasers

We investigated the spectral and coherence signatures of threshold in random lasers with incoherent feedback consisting of alumina colloidal nanoparticles suspended in rhodamine 6G methanol solution under nanosecond-pulsewidth pumping, based on measurement of temporal and spatial coherence properties and comparison with emission spectra. Feedback in this random laser was provided by multiple scattering from the alumina particles, and the effects of particle concentration and scattering length were studied for the weakly scattering and diffusive scattering regimes. At threshold, in each regime, the visibility of the interference fringes jumped abruptly, coinciding with a substantial increase in peak emission intensity and decrease in the linewidth of a single dominant emission peak.

PUYA HAMATA DEMOGRAPHY AS AN INDICATOR OF RECENT FIRE HISTORY IN THE PÁRAMO OF EL ÁNGEL AND VOLCÁN CHILES, ECUADOR-COLOMBIA

High-altitude paramo grasslands are important for their biodiversity and the ecosystem services that they provide to Andean people, but they are sensitive to disturbances, such as fire. Understanding the ecological impacts of disturbance is critical for the effective management of paramos. Indicator species studies can provide a relatively efficient way to gain such understanding. Puya hamata is a flagship giant rosette plant and has potential as an indicator of recent paramo fire history. To determine population size structure, mortality, recruitment and growth rates of Puya hamata rosettes, all Puya plants in 400 m 2 plots were surveyed in 2008 and again one year later. Sixteen plots were recorded in both years, containing exactly 1000 plants. Mortality was very low during this period (0.6%). Only 27 new plants were recruited. Three different size distribution patterns were observed in the plots: (1) low plant numbers across all size ranges; (2) a single dominant peak in numbers at a particular size; (3) two dominant peaks in numbers at distinct sizes. Estimated life span of Puya hamata was 28 years based on growth rates, and growth rate declined beyond the size at which most rosettes reproduce. To investigate the impact of different fire intensities on Puya hamata mortality, 400 m 2 plots within a mosaic of unburned and burned patches of different fire intensities were surveyed one month after the fire. Fire mortality was low in the medium and high intensity plots, and fires selectively killed smaller plants rather than larger ones. No mortality was observed in the unburned and low intensity fire plots. It is proposed that Puya responds to burning with pulses of seedling recruitment during periods of open vegetation after fires and very little recruitment at other times. Therefore, surveys of Puya plants can reveal past fire events in their population size structure. The combination of sensitivity to fire at recruitment, low fire mortality rates afterwards, and a 28-year lifespan makes Puya hamata an ideal indicator species of recent fire history in paramos.

Vocal Behavior of the Elusive Purple Frog of India (Nasikabatrachus sahyadrensis), a Fossorial Species Endemic to the Western Ghats

Quantitative descriptions of animal vocalizations can inform an understanding of their evolutionary functions, the mechanisms for their production and perception, and their potential utility in taxonomy, population monitoring, and conservation. The goal of this study was to provide the first acoustical and statistical analysis of the advertisement calls of Nasikabatrachus sahyadrensis. Commonly known as the Indian purple frog, N. sahyadrensis is an endangered species endemic to the Western Ghats of India. As the only known species in its family (Nasikabatrachidae), it has ancient evolutionary ties to frogs restricted to the Seychelles archipelago (Sooglossidae). The role of vocalizations in the behavior of this unique species poses interesting questions, as the animal is fossorial and potentially earless and it breeds explosively above the soil for only about two weeks a year. In this study, we quantified 19 acoustic properties of 208 calls recorded from 10 males. Vocalizations were organized into distinct call groups typically composed of two to six short (59 ms), pulsatile calls, each consisting of about five to seven pulses produced at a rate of about 106 pulses/s. The frequency content of the call consisted of a single dominant peak between 1200–1300 Hz and there was no frequency modulation. The patterns of variation within and among individuals were typical of those seen in other frogs. Few of the properties we measured were related to temperature, body size, or condition, though there was little variation in temperature. Field observations and recordings of captive individuals indicated that males engaged in both antiphonal calling and call overlap with nearby calling neighbors. We discuss our findings in relation to previous work on vocal behavior in other fossorial frogs and in sooglossid frogs.

Configuration-Interaction Excitonic Absorption in Small Si/Ge and Ge/Si Core/Shell Nanocrystals

The excitonic properties of Si(core)/Ge(shell) and Ge(core)/Si(shell) nanocrystals (NC’s) with diameters of ∼1.9 nm are investigated using a combination density functional ab initio method to obtain the single particle wave functions and a configuration interaction method to compute the exciton fine structure and absorption coefficient. These core/shell structures exhibit type II confinement, which is more pronounced for the Si/Ge NC as a consequence of strain. The absorption coefficients of these NC’s exhibit a single dominant peak, which has a much larger oscillator strength than the multipeaks found for pure Si and Ge NC’s. The exciton lifetime in Si, Ge, and Ge/Si shows a small temperature dependence in the range 10–300 K, whereas in Si/Ge, the exciton lifetime decreases more than an order of magnitude in the same temperature range.

Frequency-dependent variation in the two-dimensional beam pattern of an echolocating dolphin

Recent recordings of dolphin echolocation using a dense array of hydrophones suggest that the echolocation beam is dynamic and can at times consist of a single dominant peak, while at other times it consists of forward projected primary and secondary peaks with similar energy, partially overlapping in space and frequency bandwidth. The spatial separation of the peaks provides an area in front of the dolphin, where the spectral magnitude slopes drop off quickly for certain frequency bands. This region is potentially used to optimize prey localization by directing the maximum pressure slope of the echolocation beam at the target, rather than the maximum pressure peak. The dolphin was able to steer the beam horizontally to a greater extent than previously described. The complex and dynamic sound field generated by the echolocating dolphin may be due to the use of two sets of phonic lips as sound sources, or an unknown complexity in the sound propagation paths or acoustic properties of the forehead tissues of the dolphin.