Trapping Rate Research Articles

Evaluation of Probodelt cone traps for surveillance of Dacinae in New South Wales, Australia

Early detection of Dacinae (Diptera: Tephritidae) incursions is vital for quick and effective management. A key method for early detection is the implementation of trapping networks in risk areas. Australia relies on the use of extensive trapping networks at, and surrounding, major ports and fruit production areas to identity any fruit fly incursions. Therefore, improvements to the trap efficiency of these networks may result in earlier detection of incursions and hence more rapid response times for management and/or eradication. The current Australian standard, the Lynfield trap, is expensive and does not stack readily for transport. Here, we test the effectiveness of a new trap type, the Probodelt cone trap, compared to the Lynfield trap. We ran three separate trials: an experimental trial in an inland orchard and two field trials using the Sydney trapping network. At the orchard site, Lynfield and Probodelt traps had similar capture rates (within 10%) for Bactrocera tryoni. For the Sydney trapping network, no significant differences were found in the number of species caught or trap rates for B. tryoni, Bactrocera cacuminata, Dacus absonifacies, and Dacus aequalis. Thus, the Probodelt cone trap was at least comparable to the Lynfield trap. Given the economic advantages of the Probodelt cone trap (e.g. reduced shipping and storage costs), the use of the Probodelt trap may be preferred over the Lynfield trap.

Phonon-Suppressed Auger Scattering of Charge Carriers in Defective Two-Dimensional Transition Metal Dichalcogenides.

Two-dimensional transition metal dichalcogenides (TMDs) draw strong interest in materials science, with applications in optoelectronics and many other fields. Good performance requires high carrier concentrations and long lifetimes. However, high concentrations accelerate energy exchange between charged particles by Auger-type processes, especially in TMDs where many-body interactions are strong, thus facilitating carrier trapping. We report time-resolved optical pump-THz probe measurements of carrier lifetimes as a function of carrier density. Surprisingly, the lifetime reduction with increased density is very weak. It decreases only by 20% when we increase the pump fluence 100 times. This unexpected feature of the Auger process is rationalized by our time-domain ab initio simulations. The simulations show that phonon-driven trapping competes successfully with the Auger process. On the one hand, trap states are relatively close to band edges, and phonons accommodate efficiently the electronic energy during the trapping. On the other hand, trap states localize around defects, and the overlap of trapped and free carriers is small, decreasing carrier-carrier interactions. At low carrier densities, phonons provide the main charge trapping mechanism, decreasing carrier lifetimes compared to defect-free samples. At high carrier densities, phonons suppress Auger processes and lower the dependence of the trapping rate on carrier density. Our results provide theoretical insights into the diverse roles played by phonons and Auger processes in TMDs and generate guidelines for defect engineering to improve device performance at high carrier densities.

Occurrence rates of wild rodent hosts and chigger mites and the infection rate ofOrientia tsutsugamushiin the central region of South Korea from 2015 to 2018

AbstractOutbreaks of vector‐borne diseases are dramatically increasing because of climate change, consequently increasing the importance of surveillance of endemic disease vectors. In this study, we surveyed chigger mites, vectors forOrientia tsutsugamushi—the bacteria that causes Tsutsugamushi disease—, and their rodent hosts in Gimcheon, central South Korea, in 2015–2018. A total of 225 rodents were collected, with trap rate and percentage of rodents infected by chigger mites of 9.8 and 72.4%, respectively. Six species of rodents from five genera were collected, the most common rodent beingApodemus agrarius(n = 153, infection rate = 90.8%). The highest number of rodents was collected in spring (trap rate = 10.3), but the rate of infected rodents was higher in fall (81.5%) than in spring (61.3%). Trap rate was highest for bank near waterway (17.9), but the chigger index (CI) was highest in hill (224.1). A total of 20,534 (CI 126.0) chigger mite individuals from 10 species and three genera were found on the collected rodents. The most common species wasLeptotrombidium pallidum(n = 7,982, 83.6%, CI 49.0), followed byL. palpaleandL. scutellare. Chigger mites were most frequent at banks near waterway (n = 11,093, CI 152.0) and hill (n = 2,017, CI 224.1). To detectO. tsutsugamushiin chigger mites, 450 pools of chigger mites (n = 10,991) were analyzed; 24 pools were positive—23 ofA. agrarius, the most frequently collected species in South Korea, 1 ofMicromys minutus—and the minimum positive rate (MPR) was 0.22. The detected strain types included Boryong (dominant in all years, seasons, and habitats), Jecheon, 07–489, and IIOC1202.

Charge carrier injection and transport in QLED layer with dynamic equilibrium of trapping/de-trapping carriers

A theoretical analysis on carrier injection and transport through layers of quantum dot light emitting display (QLED) device was attempted assuming dynamic equilibrium of trapping and detrapping charge carriers. Assuming traps in exponential or Gaussian energy distribution, the effect of parameters on the current-voltage relationship for the device was investigated. The energy level and distribution of charge traps, a Schottky barrier, and the ratio of detrapping rate constant to the trapping rate constant were found to affect the current-voltage relationship significantly in the charge transport layer. The results suggest that the parameters must be modulated simultaneously in order to achieve a charge balance in the quantum dot layer of the QLED device.

Suppressed Blinking under Normal Air Atmosphere in Toxic-Metal-Free, Small Sized, InP-Based Core/Alloy-Shell/Shell Quantum Dots.

Suppressed blinking has been reported in large (diameter ∼14.1 nm) core/shell InP quantum dots (QDs) under reduced air environment. We report here suppressed blinking with approximately four times smaller (diameter ∼3.6 nm) core/alloy-shell/shell InP QDs under ambient air atmosphere. The ⟨ON fraction⟩ has been obtained to be 0.65. Approximately 26% of the single QDs exhibit ON fraction >80%. The smaller ON exponent (1.19) magnitude in comparison to the OFF exponent (1.45) indicates longer ON events are interrupted by smaller OFF events. ON event truncation time is ∼1.5 times that of the OFF event, signifying the detrapping rate is much higher than the trapping rate. Interestingly, the detrapping rate/trapping rate (single-particle level property) could be directly correlated to the photoluminescence quantum yield (ensemble level property). An additional exponential term required to fit the probability density distribution of the ON event duration could be correlated with hole trapping, leading to extended ON times (>60 s).

Increased Absorption with Al Nanoparticle at Front Surface of Thin Film Silicon Solar Cell

This article presents an effective structural design arrangement for light trapping in the front surface of a thin film silicon solar cell (TFSC). Front surface light trapping rate is significantly enhanced here by incorporating the Aluminium (Al) nanoparticle arrays into silicon nitride anti-reflection layer. The light trapping capability of these arrays is extensively analyzed via Finite Difference Time Domain (FDTD) method considering the wavelength ranging from 400 to 1100 nm. The outcome indicates that the structural parameters associated with the aluminium nanoparticle arrays like particle radii and separations between adjacent particles, play vital roles in designing the solar cell to achieve better light trapping efficiency. A detailed comparative analysis has justified the effectiveness of this approach while contrasting the results found with commonly used silver nanoparticle arrays at the front surface of the cell. Because of the surface plasmon excitation, lower light reflectance, and significant near field enhancement, aluminium nanoparticle arrays offer broadband light absorption by the cell.

The use of Easy-Barriers to control soil and water losses in fire-affected land in Quesada, Andalusia, Spain

Soil erosion is enhanced by wildfire, mainly due to the loss of vegetation cover and changes in soil properties. After wildfires, there is a need to control the non-sustainable soil and water losses. Of the strategies commonly applied, the use of contour felled log debris barriers to sediment trapping is widespread, but this is not always successful in Mediterranean Ecosystems. This paper evaluates the effectiveness of a new barrier which can be applied on steep terrains affected by wildfires. The hydrological response and sediment delivery were measured to test a innovative design, which are easy to transport and use. The Easy-Barriers (EB) size is 0.8 × 0.1 × 0.2 m and were designed to restore degraded areas which need a quick, low-cost solution, such as after a wildfire. The experimental design was based on the analysis of a simulated runoff flow of 0.6 l·s-1 circulated on 6 plots of 24 m2 (0.8 × 30 m), on each of which 2 treatments were systematically applied: Control and EB. The EB were set up after the assessment of the runoff generation and the site rainfall characteristics for “extraordinary” events. We measured the rills, the sediments collected on each slope and the topographical changes. The total load and runoff in the outlet of the plots were also quantified using sediment volume and concentration measurements. The EB resulted in a decrease in the peak flow and a delay in the runoff time at the outlet. The sediment trapping rate of the barriers was 42.7%. The soil moisture was higher in the EB plots due to the accumulated sediment. In addition to these features, the EB allow us to save between 30 and 40% of total restoration costs in comparison with traditional barriers, due to the reduction in labour costs. Moreover, all its components are biodegradable.

Electrochemical n-doping of polyfluorenone films

The n-doping electrochemistry of polyfluorenone (PFO) films prepared by electrochemical polymerization of fluoren-9-one in boron trifluoride diethyl etherate (BFEE) has been characterized. Cyclic voltammetry in acetonitrile showed rapid and reversible n-doping. The potential dependence of the capacitance, measured by impedance spectroscopy, shows that PFO behaves primarily as a redox polymer during n-doping, with localized, non-interacting redox sites. However the potential dependence of the resistance suggests that there are long range effects of conjugation. Deactivation due to charge (cation) trapping occurred during repeated cycling through the n-doping wave. The n-doping capacity can be partially restored by p-doping. Use of polyethylene glycol as a stabilizer decreased the rate of charge trapping, and increased the recovery of n-doping capacity. Scanning electron microscopy revealed that charge trapping was associated with notable changes in the morphology of the PFO film that are characteristic of an annealing process.

Annealing Behavior of Vacancy‐Type Defects in Mg‐ and H‐Implanted GaN Studied Using Monoenergetic Positron Beams

Vacancy‐type defects in Mg‐implanted GaN with and without hydrogen (H) implantation are probed by using monoenergetic positron beams. Mg+ and H+ ions are implanted into GaN(000) to obtain 0.1 and 0.7‐µm‐deep box profiles with Mg and H concentrations of 1 × 1019 and 2 × 1020 cm−3, respectively. For the as‐implanted samples, the major defect species is determined to be Ga‐vacancy (VGa) related defects such as VGa, divacancy (VGaVN), and their complexes with impurities. For Mg‐implanted samples, an agglomeration of vacancies starts at 800 °C annealing, leading to the formation of vacancy clusters such as (VGaVN)3. For the samples annealed above 1000 °C, the trapping rate of positrons by vacancies is increased by illumination of a He–Cd laser. This is attributed to the capture of photon‐excited electrons by the defects and their charge transition. For Mg‐ and H‐implanted samples, the hydrogenation of vacancy‐type defects starts after 800 °C annealing. Comparing with the annealing behavior of defects for the samples without H‐implantation, the clustering of vacancy‐type defects is suppressed, which can be attributed to the interaction between Mg, H, and vacancies.

Steady-state flux of diffusing particles to a rough boundary formed by absorbing spikes periodically protruding from a reflecting base.

We study steady-state flux of particles diffusing on a flat surface and trapped by absorbing spikes of arbitrary length periodically protruding from a reflecting base. It is assumed that the particle concentration, far from this comblike boundary, is kept constant. To find the flux, we use a boundary regularization approach that replaces the initial highly rough and heterogeneous boundary by an effective boundary which is smooth and uniform. After such a replacement, the two-dimensional diffusion problem becomes essentially one-dimensional, and the steady-state flux can be readily found. Our main results are simple analytical expressions determining the position of the smooth effective boundary and its uniform trapping rate as functions of the spike length and interspike distance. It is shown that the steady-state flux to the effective boundary is identical to its counterpart to the initial boundary at large distances from this boundary. Our analytical results are corroborated by Brownian dynamics simulations.

Elephant (Elephas maximus) temporal activity, distribution, and habitat use patterns on the tiger's forgotten trails across the seasonally dry, subtropical, hilly Churia forests of Nepal.

Understanding spatial distribution, habitat use, and temporal activity patterns is important for species conservation planning. This information especially is crucial for mega herbivores like elephants as their ranging patterns encompass a myriad of habitats types. Churia habitat is geological fragile yet important for wildlife in Nepal and India. We used camera trapping and sign surveys covering 536 km2 of Churia and surrounding areas within Chitwan National Park. Across 152 trapping locations, we accumulated 2,097 trap nights in a 60-day survey during the winter season of 2010–11. We used a non-parametric kernel density function to analyze winter activity patterns of elephants detected in camera-traps. Additionally, we walked 643 km over 76 grid cells in two surveys (winter and summer) to estimate elephant distribution and intensity of habitat use using an occupancy framework. Multi-season models allowed us to make seasonal (winter versus summer) inferences regarding changes in habitat use based on covariates influencing use and detection. We photographed 25 mammalian species including elephants with calves with a trapping rate of 2.72 elephant photos events per 100 trap nights. Elephant winter activity pattern was found to be mainly nocturnal, with crepuscular peaks. Covariates such as normalized differential vegetation index and terrain ruggedness positively influenced elephant spatial distribution and habitat use patterns within the Churia habitat. We also found lower elephant habitat use () of Churia in winter 0.51 (0.02) than in summer 0.57 (0.02). Elephants heavily used the eastern portion of Churia in both seasons (67–69%). Overall, Churia habitat, which is often ignored, clearly is used by elephants, with increases in summer use in the west and high use year-round in the east, and thus should no longer be neglected or forgotten in species conservation planning.

Vacancy-type defects in GaN self-assembled nanowires probed using monoenergetic positron beam

Vacancy-type defects in GaN nanowires (NWs) and the trapping of electrons by the vacancies were studied by positron annihilation. Undoped, Si-, and Mg-doped GaN NWs were grown on Si substrates by plasma-assisted molecular beam epitaxy. The major species of vacancies in the undoped and Si-doped samples was identified as a complex between a Ga vacancy and impurities such as oxygen and hydrogen. For the Mg-doped samples, the trapping rate of positrons for such defects decreased with the increase in Mg concentration because of the downward shift of Fermi level position and a resultant shift of the vacancy charge states from neutral (negative) to positive. Under the illumination of a 325-nm He-Cd laser, positrons were found to be trapped by vacancy-type defects, which was attributed to the trapping of excited electrons by these defects.

Energy transfer and white light emission of KGdF4 polycrystalline co-doped with Tb3+/Sm3+ ions

KGdF4:Tb3+, KGdF4:Sm3+ and KGdF4:Tb3+,Sm3+ polycrystalline were synthesized under hydrothermal conditions. The XRD and TEM patterns as well as excitation, luminescence spectra and luminescence decay curves of Sm3+, Tb3+ and Gd3+ have been measured at room temperature. For KGdF4:Tb3+(Sm3+), energy transfer processes from Gd3+ ions to Tb3+ (or Sm3+) ions are related to energy migration through Gd3+ ions and energy trapping by Tb3+ (or Sm3+) ions. The energy trapping rate strongly depends on the nature of RE3+ (Tb3+ or Sm3+) ions and it influences to the luminescence efficiency of RE3+ ion. For KGdF4:Tb3+,Sm3+, the characteristic emission bands of Tb3+ ion (blue and green) and Sm3+ ion (orange-red) are obtained simultaneously upon excitation by 375 nm. The chromaticity coordinates and correlated color temperature (CCT) are used to estimate the emission feature of prepared material. The quenching of the luminescence and lifetime of 5D4 (Tb3+) level are relate to the energy transfer process from Tb3+ to Sm3+ ions. It is shown that, by fitting the decay curves of 5D4 (Tb3+) to the Inokuti and Hirayama model, the dominant interaction mechanism between Tb3+ and Sm3+ is dipole-quadrupole interaction. The probability (WET) and the efficiency (ηET) of energy transfer from Tb3+ ions to Sm3+ ions increase with the increase of Sm3+ concentration.

Invader control: factors influencing the attraction of cane toad (Rhinella marina) larvae to adult parotoid exudate

As invasive cane toads (Rhinella marina) spread across Australia, we urgently need effective ways to reduce the impact of toads on native fauna. One potential approach is to target the chemical cues (pheromones) used by the pest species for communication. In particular, the ‘attraction cue’ relies on the strong cannibalistic response of toad tadpoles towards conspecific eggs and hatchlings. Chemicals released into the water by developing embryos can be mimicked using exudate from the parotoid (shoulder) glands of adult cane toads, and this toxin can be used to lure cane toad tadpoles into a trap without attracting native aquatic species. This method works well under controlled conditions in the laboratory, but we know very little about factors that influence the success of tadpole trapping in the field. Our extensive trapping trials showed strong responses to the attraction cue under a wide range of conditions, but with reduced trapping rates at low water temperature (particularly in Western Australian populations), for early-stage tadpoles, and if the bait is frozen prior to use. Efforts to control cane toads using toxin-baited traps should consider these factors when applying trapping protocols in the field.

Formation damage and cleanup in the vicinity of flooding wells: Multi-fluid suspension flow model and calibration on lab data

Injection of water into a rock formation through the flooding wells is a common practice to maintain reservoir pressure and increase ultimate recovery of hydrocarbons. While flowing through the well from surface to the rock formation, injected water typically transports fine particles, which are introduced either externally (untreated water) or internally (e.g., particles detached from the inner surface of a pipeline due to erosion and abrasion as well as mineral particles detached from pore surface). In the framework of the two-fluid approach, we formulate mathematical model for filtration of a particle-laden suspension in the vicinity of flooding wells. Two mechanisms affecting transport of non-colloidal fines are considered: trapping and mobilization. Trapped particles reduce permeability and porosity of the rock, which leads to the injectivity decline of the well. The model contains minimal set of tuning parameters describing particle trapping and mobilization rates. This is achieved by critical overview of existing models. We calibrate suspension filtration model against existing experimental (laboratory) data on fines mobilization and trapping in porous media. A parametric study of different flooding scenarios is carried out numerically. In particular, we investigate the effectiveness of periodic flooding regime, when the periods of injection are followed by flowback in order to wash out trapped fines from the near-wellbore zone and restore well injectivity. Implications to formation damage and cleanup phenomena peculiar to hydraulic fracturing and drilling are discussed. Practical recommendations are given.

Isolation and characterization of CAC antenna proteins and photosystem I supercomplex from the cryptophytic alga Rhodomonas salina.

In the present paper, we report an improved method combining sucrose density gradient with ion-exchange chromatography for the isolation of pure chlorophyll a/c antenna proteins from the model cryptophytic alga Rhodomonas salina. Antennas were used for in vitro quenching experiments in the absence of xanthophylls, showing that protein aggregation is a plausible mechanism behind non-photochemical quenching in R. salina. From sucrose gradient, it was also possible to purify a functional photosystem I supercomplex, which was in turn characterized by steady-state and time-resolved fluorescence spectroscopy. R. salina photosystem I showed a remarkably fast photochemical trapping rate, similar to what recently reported for other red clade algae such as Chromera velia and Phaeodactylum tricornutum. The method reported therefore may also be suitable for other still partially unexplored algae, such as cryptophytes.

Corrections to the Hecht collection efficiency in photoconductive detectors under large signals: non-uniform electric field due to drifting and trapped unipolar carriers

The Hecht collection efficiency η0, and its modified expressions for exponential absorption, have been widely used in time-of-flight type transient photoconductivity experiments as well as in the assessment of the sensitivity of integrating-type radiation detectors. However, the equations apply under small signals in which the internal field remains uniform (unperturbed). We have used Monte Carlo simulation and the numerical solution of the continuity, trapping rate and Poisson equations to calculate the collection efficiency ηr (CE) for various levels of charge injection and deep trapping. The carriers are injected instantaneously very near the radiation receiving electrode and then drift under space charge perturbed conditions. The CE deviation from the ideal Hecht value has been quantified in terms of the injection ratio r and the normalized trapping time τ with respect to the transit time under small signals. The results can be represented by a scaled, compressed exponential with coefficients that depend on τ. A plot is provided for these coefficients. The CE drops significantly below the Hecht value as r increases and the deviation is more pronounced for smaller τ values. The errors in extracting τ from the application of the Hecht equation has been also calculated and mapped as a function of different r and τ values.

Numerical Study of Enhancement of Positive Dielectrophoresis Particle Trapping in Electrode-Multilayered Microfluidic Device.

Enhancement of positive dielectrophoresis (pDEP) particle trapping by a co-occurring fluid flow under an ac electric field in an electrode-multilayered microfluidic device is investigated by three-dimensional particle-fluid flow simulations. The particle motion near one cross section of the microfluidic device is simulated under a zero flow condition by the Eulerian-Lagrangian method incorporating the ac electrothermal effect, thermal buoyancy, and dielectrophoresis. The mean trapping rate under the steady state Rm is evaluated from the simulated number of trapped particles Ntrap for 54 cases with four parameters: electrode excitation pattern, medium conductivity σ, applied voltage ϕe, and the real part of the Clausius-Mossotti factor Re[K(ω)]. The simulated pDEP velocity in the upper part of the flow channel is validated by an experiment using cell suspension and is fitted so that the non-dimensional velocity error is within 15% of a typical velocity of pDEP. The mean trapping rate Rm is greatly increased by the fluid flow only in the high conductivity and high voltage cases. Regardless of the electrode excitation pattern, Rm increased almost proportionally to the inflow rate into the capture region, where the pDEP force is effective. From a fitted equation of the results, the increase of Rm when Re[K(ω)] = 0.1 to 0.5 is found to be about 20% to 30% of the number of particles transported into the capture regions. The results quantify the enhancement of pDEP trapping by the fluid flow occurring under practical conditions in the device.

Photophysical Action Spectra of Emission from Semiconductor Nanocrystals Reveal Violations to the Vavilov Rule Behavior from Hot Carrier Effects

Semiconductor nanocrystals are known to have properties of bulk semiconductors as well as molecules. Two rules that govern molecules are that there is no dual emission (Kasha) and there is no spectrum to the emission quantum yield (Vavilov). We show that the latter rule of molecular spectroscopy is generally violated in semiconductor nanocrystals. Through experiments and theory on CdSe and perovskite nanocrystals, these violations are shown to arise via hot carrier effects. Experiments and simple phenomenology reveal that quantum yield spectra arise because of enhanced hot carrier trapping rates. A semiclassical electron-transfer theory rationalizes a microscopic picture of the carrier kinetics. These effects are especially significant when quantifying syntheses of bright emitters such as perovskite nanocrystals. These effects are also a general approach to simple steady-state measurements of the action of hot carrier kinetics.

Analysis on Influences of Scavenging Ports Width to Scavenging Process Based on Opposed Piston Two Stroke Diesel Engine

In the case of an opposed piston two stroke (OP2S) diesel engine using the “port-port” type scavenging method, the port structure directly affects the effect of the scavenging process, which in turn has a direct impact on the engine performance. In this paper, the influence of ports width on scavenging process under different working conditions was studied. The results show that the intake ports width has little effect on the proportion of each sub-phase of scavenging, the increase of the exhaust ports width increases the proportion of the free exhaust phase and decreases the proportion of the scavenging phase. Under the same ports width, the proportion of the free exhaust phase decreases and the proportion of the scavenging phase increases with the increase of the speed and load. The delivery ratio decreases and the trapping rate increases with the increase in the width of the intake and exhaust ports. Under the same ports width, trapping rate increases while delivery ratio decreases with the increase of engine speed, but load doesn’t produce an obvious effect on the ventilation parameters.