Trap Configuration Research Articles

Luminescence Dynamics of Silica-Encapsulated Quantum Dots During Optical Trapping

The trade-off between photobrightening and photobleaching controls the emission stability of colloidal quantum dots. This balance is critical in optical trapping configurations, where irradiances that confine and simultaneously excite the nanocrystals in the focal region cannot be indefinitely lowered. In this work, we studied the photobrightening and bleaching behaviors of two types of silica-encapsulated quantum dots excited upon two-photon absorption in an optical trap. The first type consists of alloyed CdSeZnS quantum dots covered with a silica shell. We found that the dynamics of these as-prepared architectures are similar to those previously reported for bare surface-deposited quantum dots, where thousands of times smaller irradiances were used. We then analyzed the same quantum dot systems treated with an extra intermediate sulfur passivating shell for the better understanding of the surface traps influence in the temporal evolution of their emission in the optical trap. We found that these latter...

Optimising sampling methods for small mammal communities in Neotropical rainforests

Abstract Quantifying mammalian biodiversity is a critical yet daunting challenge, particularly in species‐rich ecosystems. Non‐volant small mammals account for >60% of the mammalian diversity and often require several survey methods to estimate their species richness and abundance, because of differences in their size and behaviour. Using 117 studies at 278 sites in a species‐rich biome, the Brazilian Atlantic Forest, we determined the influence of trap configuration, trap type, and sampling effort on measures of species richness and abundance. We used generalised linear mixed‐effects models to determine which methodological approaches influenced estimates of species richness and abundance at the sampling sites. We used estimates of beta (β) to determine which methods improved species richness and abundance estimates, and generated predicted values for the overall species richness as a function of trap configuration (line transect, grid, or both), trap type (pitfall traps, live‐traps or both), and sampling effort (number of trap‐nights). Our results indicated that sites in which pitfall traps alone were used generated higher estimates of the overall small mammal species richness and abundance, and rodent abundance, than sites in which only live‐traps were used. Sites in which pitfall traps alone were used also produced higher estimates of species richness and abundance, and rodent species richness and abundance, than sites in which both trap types were used. Increased sampling effort led to increased estimates of species richness, but sites in which pitfall traps were used alone or together with live‐traps had higher estimates of species richness with less sampling effort than sites in which live‐traps only were used. Using pitfall traps greatly reduced the number of trap‐nights necessary to obtain a good estimate of small mammal species richness in a community. We found no influence of trap configuration (line transects or grids) on estimates of species richness, but the abundance of rodents was estimated to be higher in sites where both line transects and grids were used, than in sites where only one trap configuration was used. Our review shows the importance of using pitfall traps in research, monitoring, and environmental impact studies on species‐rich small mammal communities.

A cylindrically symmetric magnetic trap for compact Bose-Einstein condensate atom interferometer gyroscopes.

We present a variant of the time-orbiting potential trap suitable for Bose-Einstein condensate atom interferometers, which provides weak, cylindrically symmetric confinement as well as support for the atoms against gravity. This trapping configuration is well-suited for the implementation of a compact atom interferometer based gyroscope. The trap is made up of six coils, which were produced using photolithographic techniques and take up a modest volume of approximately 1 cubic inch inside a vacuum chamber. The trapping frequencies and thermal characteristics of the trap are presented, showing cylindrical symmetry and scalability of the trapping frequencies from 1 Hz to 8 Hz in the symmetry plane.

Electric-field induced quantum broadening of the characteristic energy level of traps in semiconductors and oxides

The trap-assisted tunneling (TAT) current in tunnel field-effect transistors (TFETs) is one of the crucial factors degrading the sub-60 mV/dec sub-threshold swing. To correctly predict the TAT currents, an accurate description of the trap is required. Since electric fields in TFETs typically reach beyond 106 V/cm, there is a need to quantify the impact of such high field on the traps. We use a quantum mechanical implementation based on the modified transfer matrix method to obtain the trap energy level. We present the qualitative impact of electric field on different trap configurations, locations, and host materials, including both semiconductors and oxides. We determine that there is an electric-field related trap level shift and level broadening. We find that these electric-field induced quantum effects can enhance the trap emission rates.

Non-Hermitian coupled-mode theory for incoherently pumped exciton-polariton condensates

The generalized Gross-Pitaevskii equation (gGPE) is an effective phenomenological description for the dynamics of incoherently pumped exciton-polariton condensates. However, a brute force numerical simulation of the gGPE provides little physical insight into condensate formation under arbitrary pumping configurations, and is demanding in terms of computational resources. We introduce in this paper a modal description of polariton condensation under incoherent pumping of arbitrary spatial profile, based on eigenmodes of the non-Hermitian generator of the linearized dynamics. A pump-dependent basis is then introduced to formulate a temporal coupled-mode theory that captures condensate dynamics in the presence of all nonlinear interactions. Simulations using a single set of modes for a given pumping and trapping configuration agree very well with a full integration of the gGPE in diverse dynamical regimes, supporting the validity of this modal description, while also providing a speedup in simulation times.

Electron Plasmas Cooled by Cyclotron-Cavity Resonance.

We observe that high-Q electromagnetic cavity resonances increase the cyclotron cooling rate of pure electron plasmas held in a Penning-Malmberg trap when the electron cyclotron frequency, controlled by tuning the magnetic field, matches the frequency of standing wave modes in the cavity. For certain modes and trapping configurations, this can increase the cooling rate by factors of 10 or more. In this Letter, we investigate the variation of the cooling rate and equilibrium plasma temperatures over a wide range of parameters, including the plasma density, plasma position, electron number, and magnetic field.

Comparative Numerical Studies of Ion Traps with Integrated Optical Cavities

We study a range of radio-frequency ion trap geometries and investigate the effect of integrating dielectric cavity mirrors on their trapping potential. We aim to identify ion trap and cavity configurations that are best suited for achieving small cavity volumes and thus large ion-photon coupling as required for scalable quantum information networks. In particular, we investigate the trapping potential distortions caused by the dielectric material of the cavity mirrors for different mirror orientations with respect to the trapping electrodes, as well as for mirror misalignment. We also analyze the effect of the mirror material properties such as dielectric constants and surface conductivity, and study the effect of surface charges on the mirrors. The smallest trapping potential distortions are found if the cavities are aligned along the major symmetry axis of the electrode geometries. These cavity configurations also appear to be the most stable with respect to any mirror misalignment.

Configuration analysis and optimization on multipolar Galatea trap

Multipolar Galatea magnetic trap simulation model was established with the finite element simulation software COMSOL Multiphysics. Analyses about the magnetic section configuration show that better magnetic configuration should make more plasma stay in the weak magnetic field rather than the annular magnetic shell field. Then an optimization model was established with axial electromagnetic force, weak magnetic field area and average magnetic mirror ratio as the optimization goals and with the currents of myxines as design variables. Select appropriate weight coefficients and get optimization results by applying genetic algorithm. Results show that the superiority of the target value of typical application parameters, including the average magnetic mirror can reduce more than 5%, the weak magnetic field area can increase at least 65%, at the same time, axial electromagnetic force acting on the outer myxines can be reduced to less than 50 N. Finally, the results were proved by COMSOL Multiphysics and the results proved the optimized magnetic trap configuration with more plasma in the weak magnetic field can reduce the plasma diffusion velocity and is more conducive for the constraint of plasma.

Light-driven transport of plasmonic nanoparticles on demand.

Laser traps provide contactless manipulation of plasmonic nanoparticles (NPs) boosting the development of numerous applications in science and technology. The known trapping configurations allow immobilizing and moving single NPs or assembling them, but they are not suitable for massive optical transport of NPs along arbitrary trajectories. Here, we address this challenging problem and demonstrate that it can be handled by exploiting phase gradients forces to both confine and propel the NPs. The developed optical manipulation tool allows for programmable transport routing of NPs to around, surround or impact on objects in the host environment. An additional advantage is that the proposed confinement mechanism works for off-resonant but also resonant NPs paving the way for transport with simultaneous heating, which is of interest for targeted drug delivery and nanolithography. These findings are highly relevant to many technological applications including micro/nano-fabrication, micro-robotics and biomedicine.

Optimization of a mirror-based neutron source using differential evolution algorithm

This study is dedicated to the assessment of capabilities of gas-dynamic trap (GDT) and gas-dynamic multiple-mirror trap (GDMT) as potential neutron sources for subcritical hybrids. In mathematical terms the problem of the study has been formulated as determining the global maximum of fusion gain (Qpl), the latter represented as a function of trap parameters. A differential evolution method has been applied to perform the search. Considered in all calculations has been a configuration of the neutron source with 20 m long distance between the mirrors and 100 MW heating power. It is important to mention that the numerical study has also taken into account a number of constraints on plasma characteristics so as to provide physical credibility of searched-for trap configurations. According to the results obtained the traps considered have demonstrated fusion gain up to 0.2, depending on the constraints applied. This enables them to be used either as neutron sources within subcritical reactors for minor actinides incineration or as material-testing facilities.

Realistic Trap Configuration Scheme With Fabrication Processes in Consideration for the Simulations of AlGaN/GaN MIS-HEMT Devices

AlGaN/GaN metal-insulator-semiconductor high-electron mobility transistors (MIS-HEMTs) have become a promising candidate for use in efficient power conversion applications. However, under the practical HEMT device fabrication conditions, additional interfacial trap states generated by the fabrication process will strongly affect the device performance of the MIS-HEMTs. Such influences have so far been considered and modeled only at specific fabrication conditions. At the device design and simulation stage with various different processes, there lacks a simple and versatile scheme for a quick design evaluation. In this paper, we report a scheme of realistic trap configuration with fabrication process taken in consideration. This configuration is able to bring the simulation outcome closer to the actual device performance, which is largely affected by the interfacial trap conditions within various locations. The formation of the proposed configuration scheme started from the raw AlGaN/GaN wafer with transmission-line measurement patterns for 2-D electron gas charge density, followed by benchmarking the normally ON and normally OFF MIS-HEMTs devices made through actual fabrication processes. The relationship between interfacial trap density and fabrication processes was then identified. Finally, a test case on AlGaN/GaN inverter configuration involving both normally ON and normally OFF devices was used to demonstrate the effectiveness of the proposed scheme.

Cotrapping different species in ion traps using multiple radio frequencies

We consider the stability of systems subjected to periodic parametric driving such that their equations of motion are ordinary differential equations with periodic coefficients and carry out a detailed analysis of important aspects of such systems in the context of the confinement of ions by oscillating electric fields. We show how they can be understood in terms of a pseudopotential approximation and resonances arising from the parametric excitation and investigate the properties of a novel linear Paul trap configuration operating with two radio-frequencies to simultaneously confine two species with extremely different charge-to-mass ratios. The theoretical calculations have been verified by molecular dynamics simulations and normal modes analysis.

Design Optimization of Multipole Galatea Trap Coils by Multiple Population Genetic Algorithm

In order to improve the performance of multipole Galatea traps, this paper proposes an optimized method for the design of coil parameters. Based on an accurate magnetic field model, key parameters describing the multipole Galatea magnetic trap configuration were analyzed to establish an optimization model using the axial electromagnetic force, weak magnetic field area, and average magnetic mirror ratio as the optimization goals with the coil current as the design variable. Applying the improved multiple population genetic algorithm (MPGA), which has a strong searching ability and a fast convergence speed, enables production of optimization results following selection of the appropriate weight coefficients. Results confirm that optimization design results from MPGA are consistent with the design goals for different weight coefficients. In addition, the performance of multipole Galatea magnetic traps with optimization coil parameters was improved. Finally, the results from finite-element simulation software proved the validity and feasibility of the proposed method.

All-optical production and transport of a largeLi6quantum gas in a crossed optical dipole trap

We report on an efficient production scheme for a large quantum degenerate sample of fermionic lithium. The approach is based on our previous work on narrow-line $ 2S_{1/2}\rightarrow 3P_{3/2} $ laser cooling resulting in a high phase-space density of up to $3\times10^{-4}$. This allows utilizing a large volume crossed optical dipole trap with a total power of $45\,\textrm{W}$, leading to high loading efficiency and $8\times10^6$ trapped atoms. The same optical trapping configuration is used for rapid adiabatic transport over a distance of $25\,\textrm{cm}$ in $0.9\,\textrm{s}$, and subsequent evaporative cooling. With optimized evaporation we achieve a degenerate Fermi gas with $1.7\times 10^{6}$ atoms at a temperature of $60 \, \textrm{nK}$, corresponding to $T/T_{\text{F}}=0.16\left(2 \right)$. Furthermore, the performance is demonstrated by evaporation near a broad Feshbach resonance creating a molecular Bose-Einstein condensate of $3\times10^5$ lithium dimers.

Enhancing detection sensitivity in gradient liquid chromatography via post-column refocusing and strong-solvent remobilization

We developed earlier the post-column refocusing strategy for isocratic separations, which employs trapping target analytes after an analytical separation and additionally focusing them using a strong remobilization solvent prior to detection, and have now extended it to high-speed gradient LC. A gradient separation of antibiotics and its metabolites, applying a linear aqueous acetonitrile gradient from 2 to 65% (v/v) ACN containing 0.1% FA in 10min, performed on an analytical column was selected as an application. Eluted heart-cut fractions were directed from the analytical silica C18 column to a trap column packed with Hypercarb particles. The remobilization of the target analytes was performed in back-flush mode using solvent mixtures tuned to maximize the solvent strength by mixing isopropanol into the remobilization solvent containing acetonitrile. Additionally, a viscosity-calibration experiment showed that the viscosity difference between trapping and remobilization solvents should be smaller than 0.15mPa·s to prevent viscous fingering. To keep the viscosity difference below this limit, during the gradient separation performed on the analytical column, the composition of the remobilization solvent was changed in time. An empirical equation is provided that allows for the selection of the optimal remobilization-solvent composition. To maximize the signal enhancement, the loading time of target analytes on the trap column should be optimized. Peak dispersion was further minimized by applying a flow rate that corresponded to the optimal van-Deemter flow rate of the trap column (20μL/min). Finally, decreasing the diameter of the trap column from 1mm to 0.3mm led to a significant enhancement of the detection sensitivity with more than one order of magnitude. Using an optimized trap configuration and elution/remobilization conditions, a signal enhancement of a factor of 14 was achieved for sulfaguanidine (early-eluting compound in the gradient separation) and 7.3 for furazolidone (late-eluting compound).

Novel Ion Trap Design for Strong Ion-Cavity Coupling

We present a novel ion trap design which facilitates the integration of an optical fiber cavity into the trap structure. The optical fibers are confined inside hollow electrodes in such a way that tight shielding and free movement of the fibers are simultaneously achievable. The latter enables in situ optimization of the overlap between the trapped ions and the cavity field. Through numerical simulations, we systematically analyze the effects of the electrode geometry on the trapping characteristics such as trap depths, secular frequencies and the optical access angle. Additionally, we simulate the effects of the presence of the fibers and confirm the robustness of the trapping potential. Based on these simulations and other technical considerations, we devise a practical trap configuration that isviable to achieve strong coupling of a single ion.

Identification and Density Estimation of American Martens (Martes americana) Using a Novel Camera-Trap Method

Camera-traps are increasingly used to estimate wildlife abundance, yet few studies exist for small-sized carnivores or comparing efficacy against traditional methods. We developed a camera-trap to identify the unique ventral patches of American martens (Martes americana). Our method was designed to: (1) determine the optimal trap configuration to photograph ventral patches; (2) evaluate the use of temporally clustered photographs to determine independence and improve identification; and (3) determine factors that influence identification probability. We tested our method by comparing camera- and live-trap density estimates using spatial capture–recapture (SCR) models. The ventral patches of radio-collared martens were most visible when traps were placed 15–20 cm above a feeding platform. Radio-collared martens (n = 14) visited camera-traps for long periods (median = 7 min) with long intervals between visits (median = 419 min), and visits by different martens at the same trap <15 min apart was infrequent (n = 3) during both years. Similarly, there was complete agreement among observers that clustered photos of un-collared martens were always of the same individual. Pairwise agreement was high between observers; eight un-collared martens were identifiable by consensus on 90% (54 of 60) of recorded visits. Factors influencing identification probability were directly related to the time martens spent feeding at traps (β = 0.143, P = 0.01) and inversely proportional to the time that elapsed since traps were baited (β = −0.344, P = 0.006). Density estimates were higher and more precise for camera-trapping (0.60, 0.35–1.01 martens/km2) than live-trapping (0.45, 0.16–1.22 martens/km2), providing evidence that SCR density estimates may be biased when capture heterogeneity is present, yet cannot be accounted for due to small sample size. Our camera-trap method provides a minimally invasive and accurate tool for monitoring marten populations.

Reactivity in ion-neutral high density media

The recent development of hybrid traps technology has revolutionized the field of cold chemistry. Recently, new trap configurations have been built in order to explore more involve chemical processes, among them is the three-body recombination involving ions and neutrals. Different ion-neutral-neutral reactions at low collision energies: 0.1 mK - 10 mK, are studied by means of a very recent method for classical trajectory calculations in hyperspherical coordinates for treating three-body collisions [J. Perez-Rios, S. Ragole, J. Wang and C. H. Greene, J. Chem. Phys. 140 , 044307 (2014)]. On the other hand a classically derived threshold law is obtained and numerically confirmed. The derived threshold law predicts molecular ions should dominate over molecular neutrals as the most products formed.

会切磁瓶探析—磁场位形为磁阱的新型磁约束装置

会切磁瓶是由布置在正多面体各顶点的磁体，构成的磁约束装置。其内部的磁场位形，是底部磁感应强度为零的理想磁阱，已达到了阱深定义的极限值。磁感应强度变化曲线显示，在相同容积下，正12面体会切磁瓶的磁感应强度落差，是垒球缝线圈的磁感应强度落差的20多倍，且会切磁瓶还有着极大的可扩展性。会切磁瓶对等离子体的约束原理是依靠磁阱，磁约束理论表明，只有磁阱位形磁场，才能真正做到等离子体的稳定约束。而Tokamak或磁镜，是依靠磁力线对电粒子的粘连，理论和实践都表明，其存在着各种宏观和微观不稳定性。而在会切磁瓶中，这些不稳定性都将不复存在。从会切磁瓶的构成看，无论是材料、运行、扩展性等方面，会切磁瓶都有着传统磁约束装置不可比拟优势。 The cusp magnetic bottle is a magnetic confinement device constituted by magnets on each vertex of the regular polyhedron. The internal magnetic field configuration is an ideal magnetic trap with the bottom magnetic induction intensity of zero, which could reach up to the limit value defined by the trap depth. The changing curve of magnetic induction intensity has indicated that, the magnetic induction intensity difference for cusp magnetic bottle of regular dodecahedron is over 20 times greater than that for softball seal coil of same volume and that the cusp magnetic bottle has a larger space to expand. The constraint theory of plasma by the cusp magnetic bottle is to rely on the magnetic trap and magnetic confinement theory indicates that, only magnetic trap configuration can truly achieve the stable confinement of plasma. Tokamak or magnetic mirror is to rely on the adhesion of particles of electricity on magnetic line of force. However, it has all kinds of macroscopic and microcosmic instabilities from both theoretically and practically. These instabilities would no long exist in the cusp magnetic bottle. From the constitution of cusp magnetic bottle, the materials, operation, structure, flexibility, expansibility and other aspects all indicate that the cusp magnetic bottle is far superior to traditional magnetic confinement devices.

Low-power radio-frequency excitation as a plasma source in a Penning–Malmberg trap: a systematic study

A novel method was experimentally demonstrated to produce a low-density electron plasma in a Penning–Malmberg trap, exploiting the static electric and magnetic confinement fields together with a periodic excitation with amplitudes as low as 0.5–5 V and frequencies in the MHz range. This unusual technique proved to be applicable as a replacement for conventional electron sources in Penning devices and presents interesting aspects both in terms of basic science and technological applications. Nevertheless, the experimental observations demonstrate the high sensitivity of plasma features of interest (charge, mean density and density distribution) to the experimental conditions, namely trap configuration and excitation parameters, and as a consequence clear trends have not been identified so far. We present an experimental campaign of measurements where several parameters were systematically changed leading to a better assessment of the plasma production mechanism and to the identification of common trends.