Carrier Trajectory Research Articles

Numerical analysis of composite preform structure based on flat cross-linked braiding

Composite materials are widely used in aerospace, automotive industry and medical equipment, where most of the structural parts are made of fiber laminates. Rotary braiding is one of the most important methods to prepare composite preforms. The ordinary rotary braided preforms have low porosity and dense yarns, but are single-layer structures after molding, which do not meet the needs of most applications. To solve the problem that traditional laminates are prone to delamination, this paper designs a flat cross-linked braiding process for the preparation of multilayer-interlocking composite panels. The carrier trajectory is analyzed, and the spatial coordinate system of the braided chassis is established by combining the effect of the end traction system on the morphology of the preform yarns. The numerical model of the preform is initially obtained by using cubic B-spline curve fitting, and an algorithm for gathering yarns towards the fabric center is proposed to optimize the numerical model. Experimental samples of flat cross-linked preforms are prepared according to the braiding process, and the reliability of the optimization algorithm is verified by comparing the yarn coordinates of the experimental samples with those of the optimized numerical model.

СИНТЕЗУВАННЯ АПЕРТУРИ АНТЕНИ ЗА СИГНАЛАМИ НАЗЕМНИХ РАДІОЛОКАЦІЙНИХ СТАНЦІЙ З КОСМІЧНОГО НОСІЯ

Today, one of the priority directions of the aerospace industry of Ukraine is the creation of effective aerospace intelligence. Remote sensing of the Earth in the optical range provides the opportunity to obtain images of the Earth's surface for use in the military sphere and the national economy. For this, various sensors are used, which, as a rule, register radiation reflected from the surface of the Earth and objects located on it. Surveying the Earth's surface from space vehicles in the radio range allows solving a wide range of tasks. At the same time, the antenna irradiates the earth's surface with a radio signal with known parameters and receives the signal reflected from the surface over a relatively large area of the carrier's trajectory. When using a side view of the earth's surface to increase the angular separation by the path range, the artificial synthesis of the antenna aperture has become widely used. Artificially synthesizing the antenna aperture is carried out at the stage of coherent or incoherent processing of the reflected signal on a certain section of the carrier's trajectory. At the same time, the parameters of the reference trajectory signal are considered to be known with accuracy to the random phase. In contrast to the classical active methods of antenna aperture synthesis, which require the availability of information about the parameters of the radiated signal, with the passive method of antenna aperture synthesis, the parameters of the received signal are determined by the type of radio radiation source and are a priori unknown. When passively synthesizing the antenna aperture based on ground radar signals, both the maximum possible size of the synthesized aperture and the conditions for determining the azimuthal direction to the source of radio radiation depend on the parameters of the signal emitted by the radar. The paper analyzes the orbit parameters of the spacecraft, which ensure the fulfillment of the condition of the unambiguity of the determination of the azimuthal direction to the source of radio radiation and determine the resolution in terms of the path range during the passive synthesis of the antenna aperture based on the signals of typical radars operating in the pulse mode. Keywords: spacecraft; source of radio emission; resolution; antenna synthesized aperture.

Effects of urban environmental attributes on graduate job preferences in Northeastern China: an application of conjoint analysis and big data methods

A constant supply of novel ideas and contributions from all economic sectors is required to further the sustainable development of cities. Therefore, there is a growing need for well-educated graduates to enter metropolitan job markets. As urban environments and culture have been shown to affect a graduates’ eventual carrier choice and trajectory, governments often seek to change their local environments to attract graduates who can help efficiently allocate and utilize a city’s often-limited environmental budgets. In this study, the conjoint analysis (CA) method was employed to explore the effects of four environmental attributes (water pollution, air pollution, littering, and green area) on graduate employment preferences in northeast China. Water pollution was shown to have the greatest effect on graduate preferences (43.6%), followed by air pollution (34.1%), littering (20.7%), and green area (1.6%). According to this ranking of importance, cities could improve their environmental attributes to maximize the attraction of Northeast graduates. Moreover, this study applied the Baidu index (a big data sharing platform) to improve the attribute selection process of the CA method. The improvement reduced the cost of the CA method and enhanced its objectivity.

Antenna-enhanced high harmonic generation in a wide-bandgap semiconductor ZnO.

High harmonic generation (HHG) in solids has great potential for coherent extreme ultraviolet (EUV) sources, all-optical band-structure reconstruction, and electron dynamics metrology. Solid HHG driven by plasmonic near-fields will open a new paradigm, enabling high repetition-rate HHG with a compact laser, HHG manipulation with meta-surfaces, and precise control over carrier trajectory. In this paper, we demonstrate antenna-enhanced HHG in a wide-bandgap semiconductor ZnO. By exploiting gold nano-antennas resonating at the driver wavelength of 2 μm, we successfully trigger HHG at input intensity of ~0.02 TW/cm2 and observe harmonic radiations up to 9th-order. Orders-of-magnitude enhanced conversion efficiency at the hot-spots brings about ten-fold enhancement in the total yield. The spectral selection rule is found to reflect crystal symmetry, suggesting the possibility of nano-scaled EUV sources and band-structure reconstruction.

Motion of a carrier with a mobile load along a rough inclined plane

The mechanical system consisting of a carrier and a load is considered. The load can move respectively the carrier according to the preset given motion law. The carrier motion from rest caused the load motion is investigated. The carrier can move translationally along rectilinear trajectory along rough inclined plane. The trajectory is the line of the greatest descent. The axis of rectilinear channel along which the load moves is situated in vertical plane containing the carrier trajectory. The Coulomb model is taken to describe the friction forces on sloped plane. Differential equations of motion of carrier with load are obtained. The sufficient condition of the carrier motion without detachment from inclined plane is given. For two special cases of the channel installation angle and the plane inclination angle combination the motion types are described. The computation experiments results are presented: the carrier motions in the special cases are illustrated, the phase portraits for some types of motions are constructed.

Carrier trajectory tracking equations for Simple-band Monte Carlo simulation of avalanche multiplication processes

Avalanche photodiodes (APDs) with steep electric field gradients generally have low excess noise that arises from carrier multiplication within the internal gain of the devices, and the Monte Carlo (MC) method is among popular device simulation tools for such devices. However, there are few articles relating to carrier trajectory modeling in MC models for such devices. In this work, a set of electric-field-gradient-dependent carrier trajectory tracking equations are developed and used to update the positions of carriers along the path during Simple-band Monte Carlo (SMC) simulations of APDs with non-uniform electric fields. The mean gain and excess noise results obtained from the SMC model employing these equations show good agreement with the results reported for a series of silicon diodes, including a p+n diode with steep electric field gradients. These results confirm the validity and demonstrate the feasibility of the trajectory tracking equations applied in SMC models for simulating mean gain and excess noise in APDs with non-uniform electric fields. Also, the simulation results of mean gain, excess noise, and carrier ionization positions obtained from the SMC model of this work agree well with those of the conventional SMC model employing the concept of a uniform electric field within a carrier free-flight. These results demonstrate that the electric field variation within a carrier free-flight has an insignificant effect on the predicted mean gain and excess noise results. Therefore, both the SMC model of this work and the conventional SMC model can be used to predict the mean gain and excess noise in APDs with highly non-uniform electric fields.

Dirac fermion reflector by ballistic graphene sawtooth-shaped npn junctions

We have realized a Dirac fermion reflector in graphene by controlling the ballistic carrier trajectory in a sawtooth-shaped npn junction. When the carrier density in the inner p-region is much larger than that in the outer n-regions, the first straight np interface works as a collimator, and the collimated ballistic carriers can be totally reflected at the second zigzag pn interface. We observed clear resistance enhancement around the np+n regime, which is in good agreement with the numerical simulation. Though the effect observed is mild and needs more validation for future application with better device design, the qualitative tunable reflectance of ballistic carriers could be an elementary and important step for realizing ultrahigh-mobility graphene field effect transistors utilizing Dirac fermion optics in the near future. We also comment on some possible guidelines to improve the quantitative device performance.

Optimization of pre-polishing parameters on a 5-axis milling machine

Pre-polishing and polishing stages are considered as semi-finishing and finishing operations in manufacturing process. Generally, these operations are carried out manually. These stages are health hazards for the operator and may lead to geometrical defects during manufacturing. This paper proposes and optimizes a method to perform these operations on a common 5-axis milling machine. This method uses the flank of a flexible cylindrical tool to link the machine position and the exerted polishing pressure. The toolpath proposed comprises a carrier trajectory on which a loop pattern is repeated. Subsequently, experimental optimization of the pre-polishing cost is proposed, coupled with an estimation of the roughness obtained. Firstly, a screening design of experiments is used to identify the most influential factors of this process. Based on these influential factors, a response surface is used to obtain experimental models to estimate the pre-polishing cost per volume and resulting roughness. These models are used to optimize the pre-polishing factors to reduce the process cost while maintaining specific roughness.

Barrier controlled carrier trapping of extended defects in CdZnTe detector

Transient current techniques using alpha particle source were utilized to study the influence of extended defects on the electron drift time and the detector performance of CdZnTe crystals. Different from the case of trapping through isolated point defect, a barrier controlled trapping model was used to explain the mechanism of carrier trapping at the extended defects. The effect of extended defects on the photoconductance was studied by laser beam induced transient current (LBIC) measurement. The results demonstrate that the Schottky-type depletion space charge region is induced at the vicinity of the extended defects, which further distorts the internal electric field distribution and affects the carrier trajectory in CdZnTe crystals. The relationship between the electron drift time and detector performance has been established.

Improving tool wear and surface covering in polishing via toolpath optimization

Polishing operations are commonly carried out manually, thus inducing variability on the surface quality. The aim of this paper is to automate the polishing of free-form surfaces in order to obtain high quality surfaces. Tool wear and toolpath surface covering have a great impact on surface properties. The current work proposes therefore a toolpath which optimizes both tool wear and surface covering. This toolpath is composed of an optimized elementary pattern repeated along a 5-axis carrier trajectory. Usually, trochoid patterns are used. Non uniform wear of the tool and uneven probability density function of the surface covering are the main inconvenients of such pattern. So, this paper proposes two optimized patterns: Spade and Triangular. Both of them lead to uniform tool wear. Our paper also demonstrates that the second solution provides a uniform probability density function. All presented computations are validated experimentally.

Formula omitted] Structured descriptive experiment design regularization based enhancement of fractional SAR imagery

Feature-enhanced reconstruction of the reflectivity maps (remotely sensed scene images) from the low-resolution fractional SAR imagery is treated for harsh sensing scenarios with uncertainties attributed to possible imperfect sensor calibration, atmospheric turbulence and uncontrolled carrier trajectory deviations. These effects lead to the randomly perturbed signal formation operator resulting in a partial coherence of the system. A low-resolution scene image formed using the conventional matched spatial filtering method serves as a starting point for the enhancement. We commence with the descriptive experiment design regularization (DEDR) approach for solving the image enhancement inverse problem based on the ℓ2 -type squared error norm minimization strategy robust against the problem model uncertainties in the sense of the worst case statistical performance optimization. To exploit structural information on the desired image piecewise smoothness over the scene the ℓ1 structured regularization level is incorporated via aggregating the image total variation (TV) minimization approach with DEDR. In the unified DEDR-TV framework, the image gradient magnitude map sparsity and the overall image texture anisotropy properties are structured by combining the ℓ2 image metric with the ℓ1 image gradient metric in the solution space. The incorporated projections onto convex solution sets guarantee the convergence and speed up the resulting implicit iterative enhancement scheme.

Enhanced Radar Imaging in Uncertain Environment: A Descriptive Experiment Design Regularization Approach

A new robust technique for high‐resolution reconstructive imaging is developed as required for enhanced remote sensing (RS) with imaging array radar or/and synthetic aperture radar (SAR) operating in an uncertain RS environment. The operational scenario uncertainties are associated with the unknown statistics of perturbations of the signal formation operator (SFO) in turbulent medium, imperfect array calibration, finite dimensionality of measurements, uncontrolled antenna vibrations, and random carrier trajectory deviations in the case of SAR. We propose new descriptive experiment design regularization (DEDR) approach to treat the uncertain radar image enhancement/reconstruction problems. The proposed DEDR incorporates into the minimum risk (MR) nonparametric estimation strategy the experiment design‐motivated operational constraints algorithmically coupled with the worst‐case statistical performance (WCSP) optimization‐based regularization. The MR objective functional is constrained by the WCSP information, and the robust DEDR image reconstruction operator applicable to the scenarios with the low‐rank uncertain estimated data correlation matrices is found. We report and discuss some simulation results related to enhancement of the uncertain SAR imagery indicative of the significantly increased performance efficiency gained with the developed approach.

Airborne X-band SAR imaging with 10 cm resolution: technical challenge and preliminary results

The bandwidth of RAMSES, an airborne synthetic aperture radar (SAR) system was recently increased to 1.2 GHz in X- and Ku-bands, yielding (unweighted) 3 dB range resolution of 11 cm. The synthesis of SAR images with matching cross-range resolution requires long integration times, and this disqualifies the temporal-domain back-projection synthesis algorithm as impractically slow. The wider relative bandwidth also disqualifies simplified range/Doppler types of algorithms, as the hypothesis of proportionality between Doppler and squint is no longer valid. Therefore the authors implemented a fast-frequency domain synthesis algorithm (/spl Omega/-k or range-migration algorithm) and designed a new deterministic motion and antenna pattern compensation method for it. As the required accuracy on carrier trajectory exceeded the performance of the differential GPS-hybridised inertial navigation unit, the authors implemented an autofocus based on the phase-tracking of several isotropic point-like echoes.

Traversal times and charge confinement for spatially dependent effective masses within semiconductor heterostructures: the quantum potential approach

The classical traversal time is a well-defined functional of the carrier trajectory and in graded heterostructures acquires significant corrections due to the position-dependent effective mass. The quantum potential corrections for pure states and the corrections to quantum Monte Carlo for mixed states are derived using the Wigner formalism. Application to graded SiGe shows additional transport corrections, including enhanced charge confinement, which are of the same order as the conventional constant mass density gradient corrections.

A Group-Theoretic Construction with Spatiotemporal Wavelets for the Analysis of Rotational Motion

This paper presents a group-theoretic approach for the analysis of rotational motion in image sequences. This method relies on Lie algebras, Lie groups and Lie group representations to provide not only the continuous wavelets but also the related tools of harmonic analysis. This approach can be referred to research works presented in J.S. Byrnes et al. (Wavelets and their Applications, Kluwer Academic Publishers, 1994) who strongly influenced this topic. For the purpose of modeling motion transformations, this paper introduces the concepts of Lie algebras and Lie groups as the actual mathematical foundations of all the observable kinematics embedded in spatio-temporal signals. Rotational motion analysis focuses on the estimation of angular velocity and angular accelerations embedded in image sequences. Rotational motion is usually carried on a trajectory, the complete problem at hand consists in estimating not only the angular velocity and its temporal derivatives but also the position, the translational velocity and its temporal derivatives along the carrier trajectory. The paper starts with the usual affine and Galilei groups and proceeds by successive extensions and sections to the rotational group. The theory of group representations is central to provide families of continuous wavelets, special functions, PDE's, ODE's and integral transforms as new mathematical tools of motion analysis in image sequence to perform optimal and selective detection, estimations, tracking, and reconstructions. This paper defines rotational wavelets and proposes a structured approach to perform estimation and tracking in image sequences which fits to Kalman filters. Simulations on real digital image sequences are also presented with tracking and estimation.

Optical detection of ballistic electrons injected by a scanning-tunneling microscope.

We demonstrate a spectroscopic technique which is based on ballistic injection of minority carriers from the tip of a scanning-tunneling microscope into a semiconductor heterostructure. By analyzing the resulting electroluminescence spectrum as a function of tip-sample bias, both the injection barrier height and the carrier scattering rate in the semiconductor can be determined. This technique is complementary to ballistic electron emission spectroscopy since minority instead of majority carriers are injected, which give the opportunity to study the carrier trajectory after injection.

Charge-carrier transport in nanometer-sized periodic Si/CaF2 structures with participation of traps

A model is proposed for carrier transport in Si/CaF2 nanometer periodic structures with the participation of traps in insulators. Simulation of the current-voltage characteristics of such structures showed that trap participation enhances the total carrier transport by 2–3 orders of magnitude and causes nonmonotonicity of current-voltage characteristics. The carrier transport depends on the energy level corresponding to traps, the number of states in a trap at the carrier trajectory, its deviation from a rectilinear one, insulator thickness, and potential barrier height.

Motion compensation and autofocus of range/Doppler or bidimensional processing for airborne synthetic aperture radar

The airborne use of synthetic aperture radars suffers from difficulties due to the nonlinearities and the lack of accuracy in the measuring of the carrier trajectory. An autofocus technique (of the map-drift type) and a new method for motion compensation allowing the use of two-dimensional processing for image synthesis are introduced. This latter type of processing is known to provide a more elegant and more efficient solution for range migration and range versus Doppler coupling compared to classical range/Doppler processing. Trials with the RAMSES airborne SAR of ONERA confirm the interest of the two methods.

Effect of spontaneous magnetization on the electrical conductivity of ferromagnet-based metallic multilayers

The conductivity of metallic magnetic multilayers (MML) in which the thickness of the ferromagnetic component exceeds the Larmor radius r of charge carrier trajectory in the field of spontaneous magnetic induction B, but is smaller than their mean free path l, is studied theoretically. It is shown that, if the electron scattering at the boundaries is negligible, the MML conductivity σ⊥ at right angles to the field B depends significantly on the probability Q of tunneling of charge carriers from layer to layer, as well as on the ratio of radius r and thickness d of the nonmagnetic metal layers. A considerable decrease in the value of σ⊥ upon a transition from antiferromagnetic to ferromagnetic ordering of spontaneous magnetic moments is predicted if the probability Q≫d/l, r/l. The trajectory effects change the anisotropy of the conducting properties of MML in the plane parallel to the boundary.

Current conduction in quantum well infrared photodetectors under low bias operation

Device operation under low applied bias voltage has been examined for both p-type and n-type quantum well infrared photodetectors. Under low electric fields and at low temperatures, the carrier lifetime in the quantum well bound states is large compared to the intrawell carrier scattering time, allowing the carriers to thermalize in the heavily doped quantum wells. This thermalization process partially or fully decouples the statistical fluctuations in carrier transport through a barrier region from one section to the next. Therefore, the device can be thought of as M statistically independent sections in series, where M is equal to the ratio of active device length over the extended state carrier trajectory. Based on this concept and the additional assumption that the charge transport process is emission limited, the dark current was calculated for four different devices. The excellent agreement between the measured and calculated dark current–voltage characteristics confirms our model assumptions.