Trap Position Research Articles

Analysis of the buffer trap-induced kink effect in AlGaN/GaN HEMT on SiC substrate

In this study, the mechanism of the kink effect observed during the switching operation in AlGaN/GaN high-electron-mobility transistors is thoroughly analyzed. The I D–V G characteristics show a drop in I D and a positive shift in threshold voltage (V T) when the kink effect occurs. Then, using Silvaco software to simulate the trap position, the negative buffer trap induces the V T to shift positively, dominating the decrease in the I D. By using a long-term DC stress test under bias conditions, where the kink phenomenon occurred, the V T will shift in the negative direction, which shows that the hole generated by impact ionization (II) plays a key role in the kink effect. Furthermore, the I D–V G after kink-effect stress does not respond to red, green or blue light illumination but does to UV light, which means that electron de-trapping cannot restore the V T shift caused by the kink effect. Finally, the complete mechanism of the kink effect is provided. The recombination of hot holes generated by II with the electron trapped in buffer defects is the main mechanism for the kink phenomenon.

Experiment Validation Protocol for Flux Wire Measurements in the Advanced Test Reactor

One of the Advanced Test Reactor’s (ATR’s) functions is to irradiate and qualify nuclear fuels and materials. Due to the large number of experiment or test positions, the cost, and the limited number of vessel penetrations for instrumentation, in-core instrumentation for most experiments is not feasible. In such instances, modeling of experiment conditions using high-fidelity neutron transport codes can quantify such conditions as fission power density and fissile material burnup during irradiation. Validation of fissile material burnup can only be performed during post-irradiation examination, which typically occurs months—or even years—following irradiation. In most experiments, fission power density and fissile material burnup are directly proportional to the thermal neutron flux in the ATR. Additionally, fast neutrons are born from fission in the ATR core, affording a validation of power distribution within the reactor’s experiment locations. During each irradiation cycle, flux wires installed throughout the ATR can be used to validate computational models and determine an adjusted neutron flux for many of the experiment positions. The flux wires are installed as requested by the experiment sponsors in several of the ATR flux traps and consist of cobalt-aluminum alloy and nickel wires. Both kinds of wire enable measurements of the thermal and fast neutron flux in each experiment position. This paper presents the protocol for validating computational models for experiments using flux wires installed in the experiment positions, as well as the results for flux wires placed in the ATR safety rod guide tubes. The best estimate is typically referred to as the adjusted neutron flux. The calculated unadjusted neutron flux is referred to as the a priori neutron flux. The methods presented here provide the adjusted neutron flux, given both the measured and a prior fluxes. The adjusted flux is compared to the a priori flux to provide a bias in the calculated results and the adjusted results. Two model types are evaluated; an eigenvalue case and fixed-source case. Both conditions demonstrate relatively good agreement. The uncertainty for the adjusted flux ranges from 5% to 6% for all three energy ranges. For the eigenvalue case, the bias between the a priori and the adjusted neutron flux is within the statistical uncertainty in all but two wire pairs. For the fixed-source model, four wire pairs are outside of the uncertainty of the adjusted flux. The bias between the a priori and adjusted fast neutron flux is outside of the statistical range for four wires in the eigenvalue case and nine wires in the fixed-source model. As the differences are not contained to one flux trap, it can be assumed that the biases in the calculated models are attributed to localized effects in modeling. An additional evaluation was performed for the ATF-1 experiment in the ATR “I” positions. The differences between the adjusted and a priori are more pronounced in two of the test positions, indicating that additional model evaluation is needed, in particular in the region near the boundary of the ATR model. It is also noted that the eigenvalue model provides slightly better results in the flux trap positions. The fixed-source model is more computationally efficient though produces less accurate results; the differences in some cases are negligible. The work documented in this paper provides a methodology that extends the validation protocol established at the ATR for flux measurements to validate computational models with limited measurement capability during a cycle.

Interception Strategies for Managing Exotic Ambrosia Beetles (Coleoptera: Curculionidae) in Nurseries

Interception Strategies for Managing Exotic Ambrosia Beetles (Coleoptera: Curculionidae) in Nurseries

Generation of ultrahigh-brightness pre-bunched beams from a plasma cathode for X-ray free-electron lasers

The longitudinal coherence of X-ray free-electron lasers (XFELs) in the self-amplified spontaneous emission regime could be substantially improved if the high brightness electron beam could be pre-bunched on the radiated wavelength-scale. Here, we show that it is indeed possible to realize such current modulated electron beam at angstrom scale by exciting a nonlinear wake across a periodically modulated plasma-density downramp/plasma cathode. The density modulation turns on and off the injection of electrons in the wake while downramp provides a unique longitudinal mapping between the electrons’ initial injection positions and their final trapped positions inside the wake. The combined use of a downramp and periodic modulation of micrometers is shown to be able to produces a train of high peak current (17 kA) electron bunches with a modulation wavelength of 10’s of angstroms - orders of magnitude shorter than the plasma density modulation. The peak brightness of the nano-bunched beam can be O(1021A/m2/rad2) orders of magnitude higher than current XFEL beams. Such prebunched, high brightness electron beams hold the promise for compact and lower cost XEFLs that can produce nanometer radiation with hundreds of GW power in a 10s of centimeter long undulator.

Dynamics of cavity soliton driven by chirped optical pulses in Kerr resonators

Recent researches have demonstrated that pulsed driving is an effective method to increase the temporal overlap between cavity soliton (CS) and pump field, thereby increasing the pump-to-comb conversion efficiency. The amplitude-modulated inhomogeneity of the background wave causes the solitons to drift toward edges of the driving pulse. To eliminate the multiple temporal trapping positions, induced by the spontaneous symmetry breaking, we propose the chirped pulse driving for deterministic single soliton generation. We theoretically explain the physical mechanism of the chirp pulse driving, as the combination of amplitude and phase modulation. Our numerical simulations demonstrate the chirp is responsible for the single soliton generation. A detailed investigation for dynamics of CSs sustained by chirped pulses, shows the recovery of spontaneous symmetry breaking. In addition, the desynchronized chirped pulse driving is also considered here. Considering a weak chirp parameter, the desynchronization-dependent trapping position diagram is divided into multiple areas including two CSs, a single CS, two oscillating CSs, and no CS. With a sufficient chirp parameter considered, the trapping position curve becomes a monotonous function of the desynchronized drift velocity, which indicates deterministic single soliton generation.Graphic

Harmonic acoustics for dynamic and selective particle manipulation.

Precise and selective manipulation of colloids and biological cells has long been motivated by applications in materials science, physics and the life sciences. Here we introduce our harmonic acoustics for a non-contact, dynamic, selective (HANDS) particle manipulation platform, which enables the reversible assembly of colloidal crystals or cells via the modulation of acoustic trapping positions with subwavelength resolution. We compose Fourier-synthesized harmonic waves to create soft acoustic lattices and colloidal crystals without using surface treatment or modifying their material properties. We have achieved active control of the lattice constant to dynamically modulate the interparticle distance in a high-throughput (>100 pairs), precise, selective and reversible manner. Furthermore, we apply this HANDS platform to quantify the intercellular adhesion forces among various cancer cell lines. Our biocompatible HANDS platform provides a highly versatile particle manipulation method that can handle soft matter and measure the interaction forces between living cells with high sensitivity.

A hybrid Zeeman slower for lithium.

Zeeman slowers come in two commonly used types: electromagnet-based slowers and permanent-magnet slowers. Both have characteristic advantages and disadvantages. The electric currents required to create strong magnetic fields lead to heat dissipation that limits the achievable fields, while permanent-magnet slowers cause bias magnetic fields at the position of the magneto-optical trap. Here, we combine both approaches and their advantages at our lithium-6 triangular-lattice quantum gas microscope and extend the field of an electromagnet-based Zeeman slower using permanent magnets. We observe nearly doubled loading rates of the magneto-optical trap and no significant stray fields in the trapping region. Our approach allows for a stronger magnetic field in places where geometric constraints prevent the use of coils, and it provides a low-cost upgrade to the loading rate at established experiments.

Evaluation of sex attractants for monitoring ofIlliberis ulmivoraGraeser (Lepidoptera: Zygaenidae: Procridinae): Height, distance, placement, climatic conditions

AbstractThe phytophagous caterpillarIlliberis ulmivorais a serious pest ofUlmus glaucescensFranch (Ulmaceae, Ulmus). In order to test potent sex attractant, field trailsof synthetic candidate attractants were conducted in China. In this study, baits with ternary blends, (2S)‐butyl (7Z)‐dodecenoate, (2S)‐butyl (9Z)‐tetradecenoate, and (2S)‐butyl (5Z)‐decenoate (8:4:1 ratio) resulted in a higher number of male moths capture than the rest of the baits that were offered. Traps positioned at a height of 1.2 m attracted more males than those installed at heights of 2.2 m and 3.2 m. The slope aspect, temperature and humility had a significant effect on the trap catches. More catches occurred in traps placed on semi‐shady and semi‐sunny slopes than those placed on sunny and shady slopes. The number of pheromones in the septa decreased with age. The residual amounts of pheromones in the lures combined with 2,6‐di‐tert ‐ butyl‐p‐cresol (BHT) were higher than those in the control. However, there were no differences in the male captures between components and components combined with BHT during the first 8 d. These findings on monitoring and trap positions can be used to predict the occurrence and population dynamics ofI. ulmivora, to develop ecological management ofI. ulmivora.

Testing trapping protocols for detecting the Citrus Longhorn Beetle, Anoplophora chinensis (Coleoptera: Cerambycidae)

AbstractCitrus Longhorn Beetle (CLB), Anoplophora chinensis (Coleoptera: Cerambycidae) is a highly polyphagous species native to eastern and south‐eastern Asia. In 2000, an outbreak of A. chinensis was detected in Lombardy Region (Italy). In 2017, an extensive trapping experiment was conducted at three infested sites in order to evaluate the effectiveness of three variables: trap model (Econex soft cross‐vane trap, Witasek cross‐vane trap and Witasek multi‐funnel trap), trap position (on a wooden pole in an open space or in the canopy of a host tree) and type of lure (ChemTica, Synergy and Glabriwit pheromones). Each combination of variables was replicated five times at each site, giving a total of 270 traps. At the end of the study, 162 adults had been caught, with catches gradually increasing during the month of June to peak in early July. The two cross‐vane traps outperformed the multi‐funnel traps and the Econex traps captured more females than the Witasek traps, probably due to the structure of the collecting funnel. The three lures had similar catch performance, although the best combination was the Econex trap with Synergy blend, due to the remarkable variability in catches observed with Glabriwit blend. Finally, traps set in the tree canopy outperformed traps set on wooden poles. In conclusion, the best protocol was the use of Econex cross‐vane traps baited with Synergy blend and deployed on the canopy of the host trees.

Investigation and Modeling of Z-Interference in Poly-Si Channel-Based 3-D NAND Flash Memories

In this article, the Z-interference in 3-D charge trap nitride (CTN) NAND flash memory is investigated using technology computer-aided design (TCAD) simulation. In 3-D CTN NAND flash memory, Z-interference is caused by the neighbor word line (WL) programming. When a neighbor WL is programed, nitride layer-induced barrier enhancement (NIBE) and charge spreading effects in the nitride layer cause a threshold voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{t}$ </tex-math></inline-formula>) shift in the victim WL. Also, the victim WL program state dependency of Z-interference caused by the charge spreading effect is investigated. In monocrystalline Si channel, there is a program sequence dependency due to the drain bias-induced barrier lowering (DIBL) effect. However, poly-Si channel has different characteristics because of grain boundaries. Therefore, Z-interference due to poly-Si grain boundary (GB) trap position randomness and GB trap density variation is analyzed. Finally, Z-interference is modeled using Simulation Program with Integrated Circuit Emphasis (SPICE), and the <inline-formula> <tex-math notation="LaTeX">${V}_{t}$ </tex-math></inline-formula> distribution according to the Z-interference is modeled using a Monte Carlo simulation.

Nanotrappy: An open-source versatile package for cold-atom trapping close to nanostructures

Trapping cold neutral atoms in close proximity to nanostructures has raised a large interest in recent years, pushing the frontiers of cavity-QED and boosting the emergence of the waveguide-QED field of research. The design of efficient dipole trapping schemes in evanescent fields is a crucial requirement and a difficult task. Here we present an open-source Python package for calculating optical trapping potentials for neutral atoms, especially in the vicinity of nanostructures. Given field distributions and for a variety of trap configurations, nanotrappy computes the three-dimensional trapping potentials as well as the trap properties, ranging from trap positions to trap frequencies and state-dependent light shifts. We demonstrate the versatility for various seminal structures in the field, e.g., optical nanofiber, alligator slow-mode photonic-crystal waveguide, and microtoroid. This versatile package facilitates the systematic design of structures and provides a full characterization of trapping potentials with applications to the coherent manipulation of atoms and quantum information science.

High-Resolution Optical Tweezers Combined with Multicolor Single-Molecule Microscopy.

We present an instrument that combines high-resolution optical tweezers and multicolor confocal fluorescence spectroscopy. Biological macromolecules exhibit complex conformation and stoichiometry changes in coordination with their motion and activity. To further our understanding of the complex machinery of life, we need methods that can simultaneously probe more than one degree of freedom of single molecules and complexes. Fluorescence optical tweezers, or "fleezers," combine the capabilities of optical tweezers and single-molecule fluorescence microscopy into a single instrument. Here we present the latest generation of a high-resolution fleezers instrument integrated with multicolor fluorescence spectroscopy. The tweezers portion of the instrument can manipulate biological macromolecules with pN scale forces while measuring subnanometer distances. Simultaneous with tweezers measurements, the multicolor fluorescence capability allows the direct observation of multiple molecules or multiple degrees of freedom which allows, for example, the observation of multiple proteins simultaneously within a complex. The instrument incorporates three fluorescence excitation lasers, all sourced from a single-mode optical fiber allowing a reliable alignment scheme, that allows, for example, three independent fluorescent probes or fluorescence resonance energy transfer (FRET) measurements and also increases flexibility in the choice of fluorescent probes. To avoid photobleaching and improve tweezers stability, the instrument implements a timesharing (using a single trap laser to produce a pair of traps via rapid switching between two locations) and interlacing (turning the trapping beam off when the fluorescence excitation beams are on and vice versa) scheme using acousto-optic modulators (AOM) to rapidly and precisely modulate lasers. Our latest "random phase" trap AOM control method obliterates previous residual trap positioning and bead position measurement errors. Here we present the general design principles and detailed construction and testing protocols for the instrument.

Synthesis and characterization of carbon sphere-supported sand-rose like N-GQDs/NiCo2S4 structures with synergetic effect for development of hydrogen storage capacity

Porous carbon spheres (CSs) decorated with sand-rose shaped NiCo2S4/Co9S8/CoS and N- doped graphene quantum dots (N-GQDs) were prepared via one-step free-surfactant hydrothermal route. Ni-Co sulfide based materials (NCS) were created in the presence of Tioglycolic acid (TGA) as both sulfur source and capping agent. Altering of synthesis parameters involving metal salt type, TGA and NaOH amount help to control the sulfide-based materials features. The obtained 3D hierarchical N-GQD/NCS/CS core-double shell spheres were considered in terms of morphology, dimension and porosity. Different formed Ni-Co sulfide structures were evaluated for hydrogen storage capacity. The achieved 3D microspheres could be utilized as a favorable candidate in electrochemical hydrogen storage, incorporating the prominent electro-conductivity of N-GQDs and CSs carbonic materials and high capacity of sand-rose shaped NCS nanostructures. Carbon microspheres formed through rapid sonochemical approach and various linear amines were applied as conductive support. It was discovered that the presenting of N-GQDs prominently improves the discharge efficiency of the core-double shell spheres from 930 to 1244 mAh g−1 because of trap positions formed by both Nitrogen dopants and edge conditions which can adsorb charge transporters to rise the storage proficiency.

Numerical Analysis of Optical Trapping Force Affected by Lens Misalignments

Geometrical optics approximation is a classic method for calculating the optical trapping force on particles whose sizes are larger than the wavelength of the trapping light. In this study, the effect of the lens misalignment on optical force was analyzed in the geometrical optics regime. We used geometrical optics to analyze the influence of off-axis placement and the tilt of the lens on the trapping position and stiffness in an optical trap. Numerical calculation results showed that lens tilting has a greater impact on the optical trap force than the off-axis misalignments, and both misalignments will couple with each other and cause a shift of the equilibrium point and the asymmetry of the optical trap stiffness in different ways. Our research revealed the asymmetry in optical traps caused by lens misalignment and can provide guidance for optimize lens placement in future experiments.

Trapping positions in a dual-beam optical trap

Optical trapping has become an important tool in a wide range of fields. While these traps are most commonly realized using optical tweezers, dual-beam optical traps offer specific advantages for certain experiments. It is commonly assumed that a particle will become trapped midway between the focal points of the two beams. However, this is not always the case. We perform a theoretical and experimental investigation of trapping positions of weakly absorbing, spherical particles in a dual-beam optical trap. We evaluate the effect of offsetting the beams in the direction of propagation and identify four regimes with distinct trapping behavior. The effect of an offset perpendicular to the propagation direction and an imbalance in power between the two beams is also considered. Experiments utilize an aqueous aerosol particle whose size can be readily controlled and monitored over hundreds of nanometers. As such, it serves as an excellent probe of the optical trap. We demonstrate that it is possible to fit the evolution of the particle trapping position in order to determine the position of the particle relative to the focal point of each beam. The results presented here provide key insights into the workings of dual-beam optical traps, elucidating more complex behaviors than previously known.

Fluorescence detection of a trapped ion with a monolithically integrated single-photon-counting avalanche diode

We report on the demonstration of fluorescence detection from a trapped ion using single-photon avalanche photodiodes (SPADs) monolithically integrated with a microfabricated surface ion trap. The SPADs are located below the trapping positions of the ions and designed to detect 370 nm photons emitted from single 174Yb+ and 171Yb+ ions. We achieve an ion/no-ion detection fidelity for 174Yb+ of 0.99 with an average detection window of 7.7(1) ms. We report a dark count rate as low as 1.2 kcps for room temperature operation. The fidelity is limited by laser scatter, dark counts, and heating that prevents holding the ion directly above the SPAD. We measure count rates from each of the contributing sources and fluorescence as a function of ion position. We use the ion as a calibrated light source along with measurements of the active detector area to estimate a SPAD quantum efficiency of 24 ± 1%.

Dynamical power flow and trapping-force properties of two-dimensional Airy-beam superpositions

Abruptly autofocusing beams have attracted more and more attention because of their potential applications in optical manipulation. Here, we not only experimentally and theoretically investigate dynamical propagation properties of two-dimensional (2D) Airy--beam superpositions in free space and disordered media, but also study their stability, dynamical power flow, and trapping force properties from a different point. 2D Airy-beam superpositions have superior stability and can easily control their autofocusing propagations and trapping forces through a changing number of superimposing beams, truncated factor, scale factor, initial position, and the angle between two wings of 2D Airy beams. Based on the analysis of the evolution of power flow and trapping force, it is demonstrated that 2D Airy-beam superpositions repeat many autofocusing propagations, leading to a series of focuses and stable trapping positions to appear in propagation. Compared to traditional autofocusing beams, i.e., circular Airy beams and one-dimensional Airy-beam superpositions, 2D Airy-beam superpositions can show a better optical trapping performance in theory. Moreover, we used 2D Airy-beam superpositions as an optical tweezer to trap particles in the experiment and quantitatively analyzed trapping force properties such as trap stiffness via the power spectra method. The experimental results further demonstrate that 2D Airy-beam superposition can show better optical trapping ability than the circular Airy beam. Our work provides a systematic understanding of the propagation and trapping properties of 2D Airy-beam superpositions in theory and experiment. It is helpful for the further applications of autofocusing beams on the optical tweezer, especially in biomedical research.

Commensal small mammal trapping data in Southern Senegal, 2012–2015: where invasive species meet native ones

Describing patterns and testing hypotheses on processes driving biological invasions represent major issues in ecology. Addressing these questions requires building adequate data sets, i.e., covering areas and spanning periods adapted to the invasion processes studied. Rodents include major invasive species, among which the black rat Rattus rattus and the domestic mouse Mus musculus have nearly colonized the entire world, from their native Asian range. To do so, they have benefitted from their ability to cope with human-modified environments and to live in the immediate vicinity of Man, who served as a vector of their dispersal between regions and continents. In Senegal, both R.rattus and M.musculus, initially introduced by early West European colonizers some centuries ago, are currently expanding thanks to road traffic and infrastructure development and rampant urbanization that concerns even remote regions of the country. As part of projects aimed at studying (1) the role of invasive black rat populations in the emergence of zoonotic diseases in southeastern Senegal, and (2) the evolutionary consequences of parasites in R.rattus and M.musculus invasions in Senegal, we conducted a series of field campaigns throughout the southern half of the country, between May 2012 and September 2015. The objectives were to catch commensal small mammals using standard trapping procedures, identify them using morphological or molecular tools, and take samples from them upon autopsy, to look for zoonotic parasites and pathogens. Along with data on individual specimens, information on microhabitats was gathered at each trap position. This resulted in the constitution of a data set of more than 13,000 trapnights, which allowed the capture of more than 3,100 small mammals, all characterized by a series of associated biological, geographical, and environmental data. The small mammals concerned are mainly rodents (10 species), shrews, and hedgehogs. The two invasive rodent species were the most numerous, exceeding in numbers all the other species pooled. This data set makes it possible to study coarse to fine-scaled distribution of species of this commensal community in southern Senegal, as well as the possible determinants of this distribution in terms of habitat preferences and/or interspecific interactions. This data set can be freely used for non-commercial purposes and is licensed under a Creative Commons Attribution 4.0 International License.

Dual-plane multiple-trapping by tightly focused petal-like circular Airy beam in an aqueous medium

Superposition of two circular Airy vortex beams (CAVB), with opposite sign topological charges (l), produces a new type of petal beam called petal-like circular Airy beam (PCAB) with a transverse field distribution in the form of azimuthally modulated concentric rings that follow Airy function over the radial distance on a transverse plane. In this paper, tight focusing of a truncated PCAB and its application in optical trapping is numerically investigated. It is shown that by adjusting the topological charge, l, and the aperture radius of the focusing objective lens, R, four different trapping configurations can be achieved: a single transverse trap at a single axial position, a multi-trap geometry at a single axial position, two single transverse traps at two positions along the axial direction, and two multi-trap geometries at two different axial positions. It is also shown that the number of trapped particles in the multi-trap configurations is 2l per focal plane, while the number of axial trap positions is determined by the truncation aperture size, R. Moreover, trap stiffnesses and corresponding potential energies for the trapping configurations are presented and discussed. Finally, for a special case of large R and l, it is shown that the focused beam may both guide and traps the particles.

Double-layered silicon-nitride photonic crystal slab guided-mode-resonance high-sensitivity sensor application for refractive index sensing and nanoparticle detection

In this work, the silicon-nitride-based double-layered photonic crystal slab (DPCS) operating on guided-mode resonance (GMR) is demonstrated to realize a high-sensitivity sensor. By applying the three-dimensional finite-difference time-domain (3D-FDTD) analysis method, the relationships between Q -factor and slab thickness, hole radius, and space distance are extensively explored. The highest Q -factor of 7605 has been obtained for the optimized structure. Through detecting the resonant peak shifts when the DPCS sensor is immersed in different liquids, we realize an ultrahigh sensitivity up to 937.64 nm/refractive index unit (RIU). On the other hand, particle detection is simulated by the above-mentioned sensor, and the explanations of different resonant shifts versus different trapped positions are sophisticatedly elucidated. Furthermore, the effect of the vertical alignment deviation (lattice displacement) of the two photonic crystal slabs (PCSs) on the Q -factor and transmittance is discussed in detail. The investigations show that the DPCS sensor allows an alignment deviation of ∼ 40 n m , which exhibits excellent fabrication error robustness.