Dynamic Splitting Research Articles

All-optical active THz metasurfaces for ultrafast polarization switching and dynamic beam splitting

Miniaturized ultrafast switchable optical components with an extremely compact size and a high-speed response will be the core of next-generation all-optical devices instead of traditional integrated circuits, which are approaching the bottleneck of Moore’s Law. Metasurfaces have emerged as fascinating subwavelength flat optical components and devices for light focusing and holography applications. However, these devices exhibit a severe limitation due to their natural passive response. Here we introduce an active hybrid metasurface integrated with patterned semiconductor inclusions for all-optical active control of terahertz waves. Ultrafast modulation of polarization states and the beam splitting ratio are experimentally demonstrated on a time scale of 667 ps. This scheme of hybrid metasurfaces could also be extended to the design of various free-space all-optical active devices, such as varifocal planar lenses, switchable vector beam generators, and components for holography in ultrafast imaging, display, and high-fidelity terahertz wireless communication systems.

Deterministic proton dose calculation from first principles

The purpose of this paper is to find a deterministic pencil beam algorithm that computes, from first principles, the dose in some region of interest when a known heterogeneous terrain is irradiated by known proton beams.The terrain is discretized into slabs perpendicular to the nominal beam direction. Pencil beams (PBs) are transported through each slab using generalized Fermi–Eyges theory with the correct stopping and scattering powers for each material (no water-like assumption).At transverse heterogeneities PBs are divided into smaller ones using either redefinition (all PBs divided) or dynamic splitting (PBs divided one at a time as needed). Dynamic splitting recurs until the transverse heterogeneity is sufficiently well resolved. After a PB is transported, its dose contribution at the slab exit (if designated as a measuring plane) is added to each point of interest.The calculation depends solely on accurate descriptions of the terrain and of the incident beams. It does not require measurements such as effective source size and position. These follow from the beam line specifications. The calculation ignores nuclear reactions (hard scatters), as do other PB algorithms.Our first comparison with experiment confronts the widely used ‘Hong’ algorithm. The second is a simple study of collimator scatter and the third studies collimator scatter under more extreme conditions. All agree well with the high dose region. The latter two agree substantially with collimator scatter and thickness effects, ignored by conventional algorithms.The algorithm gives a good account of the high dose region, including realistic collimator effects. It is equally amenable to passive beam spreading or pencil beam scanning (PBS). It dispenses with measurements (commissioning) of beam line properties. In PBS it promises to be faster than conventional algorithms since virtual PBs are generated only as needed. These results justify further work towards a full-fledged therapy dose engine.

A Method of Optical Grooming Based on Dynamic Multicast Capable of Adaptive Splitting Under Differential Delay Constraint

Abstract Aiming at the problem of energy efficient transmission for multiple paths under differential delay constraint, we propose a method of optical grooming based on dynamic splitting under differential delay constraint algorithm (OG-DSDA) for optical networks. When a multicast demand cannot be groomed due to the bandwidth fragment, the method constructs two types of logic light-tree sets according to the differential delay constraint between source node and destinations. In order to reduce the network link costs caused by too many split parts, the method gives high priority to the first type logic light-trees with the maximum available bandwidth to meet the requirement. When the bandwidth of first type logic light-tree is insufficient for all sub-requests, the rest of sub-demands is adaptively groomed into a light-tree in second set of light-trees with the lower power consumption. Simulation results show that the proposed method can effectively decrease the network blocking probability and reduce network’s energy consumption.

Effect of strain rate on mechanical properties of the bamboo material under quasi-static and dynamic loading condition

As a kind of fiber-reinforced bio-composite, bamboo material exhibits superior mechanical performance. In present work, quasi-static and dynamic Split Hopkinson Pressure Bar (SHPB) compression experiments at the nominal strain rate range of 500 s−1–2200 s−1 were carried out to investigate the effect of strain rate on mechanical behaviors of the bamboo material. In consideration of the effect of fiber directions on mechanical behaviors, the specimens were crushed with the loading direction parallel to the fiber longitudinal direction and perpendicular to the fiber direction, respectively. The experiments under both loading directions exhibited remarkable strain rate sensitivity. The yield stress for the specimens crushed along the fiber longitudinal direction increased from 38.59 MPa to 94.25 MPa, as the strain rate varied from 1.85 × 10−3 to 2200 s−1, while it increased from 7.18 MPa to 42.04 MPa for the specimens crushed perpendicularly to the fiber direction. Final deformation photographs and scanning electron micrographs of the bamboo microstructures clearly illustrated their damage morphologies and various failure mechanisms, including fiber buckling, fiber fractures, PCs collapse, delamination and crack propagation at different strain rates and loading directions. These results may provide a novel perspective on the mechanical behaviors of bamboo microstructure and design of new bio-inspired structural materials.

Quantum-dot antibody conjugation visualized at the single-molecule scale with high-speed atomic force microscopy.

Conjugates of semiconductor quantum dots (QDs) and antibodies have emerged as a promising bioprobes due to their great combination of QD's efficient fluorescence and the high specificity of antigen-antibody reactions. For further developments in this field, it is essential to understand the molecular conformation of the QD-antibody conjugates at the single-molecule scale. Here, we report on the direct imaging of QD-antibody conjugates at the single-molecule scale by using high-speed atomic force microscopy (HS-AFM). Owing to the high spatiotemporal resolution of HS-AFM, we observed the dynamic splitting of individual antibodies during the conjugation process. QD-antibody conjugates were also clearly visualized at the single-molecule scale details. Several important features were even discovered through dynamic observation of the QD-antibody conjugates. We observed an intermediate state of conjugation, where the antibodies attached and detached to QDs repeatedly. We also revealed that the attached antibodies were not steady but drastically fluctuated in their recognition areas due to the Brownian motion. We also demonstrated that HS-AFM observation is useful for the quantitative analysis of fabricated conjugates.

Improving Efficiency of Passive RFID Tag Anti-Collision Protocol Using Dynamic Frame Adjustment and Optimal Splitting.

Radio frequency identification is a wireless communication technology, which enables data gathering and identifies recognition from any tagged object. The number of collisions produced during wireless communication would lead to a variety of problems including unwanted number of iterations and reader-induced idle slots, computational complexity in terms of estimation as well as recognition of the number of tags. In this work, dynamic frame adjustment and optimal splitting are employed together in the proposed algorithm. In the dynamic frame adjustment method, the length of frames is based on the quantity of tags to yield optimal efficiency. The optimal splitting method is conceived with smaller duration of idle slots using an optimal value for splitting level , where (M > 2), to vary slot sizes to get the minimal identification time for the idle slots. The application of the proposed algorithm offers the advantages of not going for the cumbersome estimation of the quantity of tags incurred and the size (number) of tags has no effect on its performance efficiency. Our experiment results show that using the proposed algorithm, the efficiency curve remains constant as the number of tags varies from 50 to 450, resulting in an overall theoretical gain in the efficiency of 0.032 compared to system efficiency of 0.441 and thus outperforming both dynamic binary tree slotted ALOHA (DBTSA) and binary splitting protocols.

The effect of the dynamic splitting of the conductivity state in homogeneous electric field

The effect of the dynamic splitting of the conductivity state in homogeneous electric field

Impact behavior and microstructure of cement mortar incorporating waste carpet fibers after exposure to high temperatures

Abstract Adding waste carpet fibers to cement mortar as a cleaner production can improve the property of mortar. This study investigated the influence of different parts of industrial carpet waste on impact behavior and microstructure of mortar at elevated temperatures. Mortar containing normal polypropylene fibers, face fibers, backing fibers and hybrid fibers (face fibers and backing fibers) respectively as well as ordinary mortar were prepared and exposed to 20, 300 and 500 °C. The dynamic splitting tensile strength of these specimens was then measured at air pressures of 0.15, 0.2 and 0.25 MPa. In order to obtain the pore distribution and microstructure image, mercury intrusion porosimetry (MIP) and scanning electronic microscopy (SEM) were used. Finally, the fractal analysis was employed to further evaluate the impact of waste carpet fibers on microstructure of mortar. Results of this paper indicated that the incorporation of carpet face fibers is more feasible to improve impact behavior of mortar at elevated temperatures compared with adding ordinary polypropylene fibers. Moreover, the higher impact air pressure, or the higher temperatures, the more significantly reinforcing effects of face fibers is. Backing fibers and hybrid fibers have a negative role on the impact resistance whether heating or not. Pore distribution and microstructure of mortar incorporating face carpet fibers are better than other mortar, which is in agreement with the change of residual strength. Therefore, the addition of carpet face fibers to mortar does not only reduce environment pollution but also enhance the impact behavior of mortar after exposure to high temperatures.

Numerical Simulation on the Dynamic Splitting Tensile Test of reinforced concrete

The research for crack resistance was of RC was based on the split Hopkinson bar and numerical simulate software LS-DYNA3D. In the research, the difference of dynamic splitting failure modes between plane concrete and reinforced concrete were completed, and the change rule of tensile stress distribution with reinforcement ratio was studied; also the effect rule with the strain rate and the crack resistance was also discussed by the radial tensile stress time history curve of RC specimen under different loading speeds. The results shows that the reinforcement in the concrete can impede the crack extension, defer the failure time of concrete, increase the tension intensity of concrete; with strain rate of concrete increased, the crack resistance of RC increased.

Wireless Information and Power Transfer: Rate-Energy Tradeoff for Nonlinear Energy Harvesting

In this paper, we study rate-energy (R-E) tradeoffs for simultaneous wireless information and power transfer (SWIPT). In the existing literature, by invoking a simplistic and ideal assumption of linear energy harvesting, the R-E tradeoff performance was analyzed only for the four SWIPT schemes: the dynamic power splitting, type-I on–off power splitting (OPS), static power splitting, and time switching. Different from such works, in this work, we consider the realistic and practical scenario of nonlinear energy harvesting. Furthermore, to characterize the R-E tradeoff with nonlinear energy harvesting, we propose a new SWIPT scheme, the generalized OPS (GOPS). As a special case of the proposed GOPS, we also investigate an additional SWIPT scheme, the type-II OPS. Through the analysis based on the realistic nonlinear models reported in the literature, we derive new theoretical results on the R-E tradeoff, which are in sharp contrast to those in the existing literature obtained with linear energy harvesting. Furthermore, we provide various useful insights into the SWIPT system with nonlinear energy harvesting.

Dynamic splitting tensile test of hybrid-fiber-reinforced reactive powder concrete

In order to investigate the dynamic splitting tensile strength of reactive powder concrete (RPC) under high strain rates, split Hopkinson pressure bar experiments are conducted on hybrid-fiber-reinforced (2% steel fiber and 0·2% polypropylene fiber) RPC. The results show that the dynamic splitting tensile strength of RPC increases with an increase in nominal strain rate from 100 to 350 s−1. The splitting tensile strength dynamic increasing factor (SDIF) of RPC is lower than that of ordinary concrete with the same compressive strength. This is mainly because the compactness of RPC is higher than that of normal concrete. Further, considering that it is not safe to apply the calculation method of SDIF to RPC in the European code Comité Européen du Béton, empirical relations of SDIF and strain rate for RPC with hybrid fibers are proposed. The proposed SDIF–strain rate relations for RPC can be used to computer programs for evaluating the dynamic response of RPC structures.

A Mach-sensitive implicit–explicit scheme adapted to compressible multi-scale flows

The method presented below focuses on the numerical approximation of the Euler compressible system. It pursues a two-fold objective: being able to accurately follow slow material waves as well as strong shock waves in the context of low Mach number flows. The resulting implicit–explicit(IMEX) fractional step approach leans on a dynamic splitting designed to react to the time fluctuations of the maximal flow Mach number. When the latter rises suddenly, the IMEX scheme, so far driven by a material-wave Courant number, turn into a time-explicit approximate Riemann solver constrained by an acoustic-wave Courant number. It is also possible to enrich the dynamic splitting in order to capture high pressure jumps even when the flow Mach number is low. One-dimensional low Mach number test cases involving single or multiple waves confirm that the present approach is as accurate and efficient as an IMEX Lagrange-Projection method. Besides, numerical results suggest that the stability of the present method holds for any Mach number if the Courant number related to the convective subsystem arising from the splitting is of order unity.

Dynamic Aspects of Chip Formation

A multimass chain model of chip formation in the secondary deformation zone is proposed. The influence of the frictional conditions and cutting conditions on the group motion of the chip elements over the cutter’s front surface is shown. The dynamics of the motion of the chip’s free end has a significant influence on its fracture. In particular, the mass ratio of the last elements involved in the group motion (and positioned on the contact line at the cutter’s front surface) and the free end of the chip gives rise to considerable dynamic splitting forces between the elements. The proposed approach offers broad scope for analysis of the conditions of chip formation, including conditions with intensification of the cutting process by electrical pulses.

Application of particle splitting method for both hydrostatic and hydrodynamic cases in SPH

Smoothed particle hydrodynamics (SPH) method with numerical diffusive terms shows satisfactory stability and accuracy in some violent fluid–solid interaction problems. However, in most simulations, uniform particle distributions are used and the multi-resolution, which can obviously improve the local accuracy and the overall computational efficiency, has seldom been applied. In this paper, a dynamic particle splitting method is applied and it allows for the simulation of both hydrostatic and hydrodynamic problems. The splitting algorithm is that, when a coarse (mother) particle enters the splitting region, it will be split into four daughter particles, which inherit the physical parameters of the mother particle. In the particle splitting process, conservations of mass, momentum and energy are ensured. Based on the error analysis, the splitting technique is designed to allow the optimal accuracy at the interface between the coarse and refined particles and this is particularly important in the simulation of hydrostatic cases. Finally, the scheme is validated by five basic cases, which demonstrate that the present SPH model with a particle splitting technique is of high accuracy and efficiency and is capable for the simulation of a wide range of hydrodynamic problems.

Investigation of mechanical properties of limesand brick under dynamic loading

The results of experimental study of mechanical properties of samples of lime-sand brick under dynamic loading are presented. The tests were carried out using the traditional Kolsky method and its modification - dynamic splitting (the so-called «Brazilian test»). The laws of change in strength, strain, time properties and energy intensity of the investigated material are established in the strain rate range of 5·102-2.5·103 s-1 under compression and in the stress rate range of 2·101-3·102 GPa/s under tension.

Shape evolution and splitting of ferrofluid droplets on a hydrophobic surface in the presence of a magnetic field

We elucidate the phenomena of dynamic wetting, shape evolution and splitting of ferrofluid (FF) droplets on a hydrophobic surface under the influence of a magnetic field. In the case of a FF droplet interacting with a magnetic field, both surface energy and magnetic energy contribute to the total Gibb's free energy and hence the wetting phenomena. The nanoparticles in the FF droplet migrate and get accumulated at the apex of the droplet which enhances the magnetic interaction causing large deformation of the droplet. The FF droplet deformation and subsequent splitting are governed by the interplay between the magnetic Fm and surface tension Fs forces. The ratio of the forces km = (Fm/Fs) was found to be a function of the magnetic Bond number Bom and non-dimensional gap g* as km ∼ (Bom)0.3(g*)-0.86. Splitting of the FF droplets was observed for km > 1 and for km < 1, an equilibrium droplet shape was observed. The wetting behavior of the FF droplets was found to be strongly dependent on the FF concentration c - concentrated (c = 1.2%) FF droplets exhibit contact line (CL) pinning and decrease in contact angle (CA) θ with time throughout, while diluted (c = 0.6%) FF droplets show a mixed mode (CL pinning followed by constant CA). In splitting of FF droplets, the ratio of the volume of the daughter droplet to that of the parent droplet i.e. (Vd/Vp), was found to decrease with an increase in the parent droplet size Vp.

Dynamic Power Splitting Strategy for SWIPT Based Two‐Way Multiplicative AF Relay Networks with Nonlinear Energy Harvesting Model

This paper investigates an energy‐constrained two‐way multiplicative amplify‐and‐forward (AF) relay network, where a practical nonlinear energy harvesting (NLEH) model is equipped at the relay to realize simultaneous wireless information and power transfer (SWIPT). We focus on the design of dynamic power splitting (DPS) strategy, in which the PS ratio is able to adjust itself according to the instantaneous channel state information (CSI). Specifically, we first formulate an optimization problem to maximize the outage throughput, subject to the NLEH. Since this formulated problem is nonconvex and difficult to solve, we further transfer it into an equivalent problem and develop a Dinkelbach iterative method to obtain the corresponding solution. Numerical results are given to verify the quick convergence of the proposed iterative method and show the superior outage throughput of the designed DPS strategy by comparing with two peer strategies designed for the linear energy harvesting (LEH) model.

Joint Power Allocation and Splitting (JoPAS) for SWIPT in Doubly Selective Vehicular Channels

In recent years, the capacity and charging speed of batteries have become the bottleneck of mobile communications systems. With the development of wireless power transfer technologies, simultaneous wireless information and power transfer (SWIPT) emerges as a potential solution for green communications. Due to hardware limitations, the energy harvesting circuit cannot decode the signal directly. Power splitting is a popular and effective solution to this problem. Consequently, the problem of optimal power splitting at the receiver arises in addition to the conventional problem of power allocation in communications systems. SWIPT in vehicular networks is a promising technology that helps extend the lifetime of sensors installed on vehicles and roadside units. However, existing SWIPT schemes fail to consider the doubly selective characteristics of vehicular channels. In this paper, joint power allocation and splitting for SWIPT over such channels is proposed with the objective of maximizing the achievable data rate with constraints on the delivered energy. Simulations show significantly improved performance compared with the existing dynamic power splitting scheme. A suboptimal algorithm, named decoupled power allocation and splitting, is also proposed with significantly reduced computational complexity and simulations demonstrate its near-optimum performance.

Tunable kinoform x-ray beam splitter.

We demonstrate an x-ray beam splitter with high performances for multi-kilo-electron-volt photons. The device is based on diffraction on kinoform structures, which overcome the limitations of binary diffraction gratings. This beam splitter achieves a dynamical splitting ratio in the range 0-99.1% by tilting the optics and is tunable, here shown in a photon energy range of 7.2-19keV. High diffraction efficiency of 62.6%, together with an extinction ratio of 0.6%, is demonstrated at 12.4keV, with angular separation for the split beam of 0.5mrad. This device can find applications in beam monitoring at synchrotrons, at x-ray free electron lasers for online diagnostics and beamline multiplexing and, possibly, as key elements for delay lines or ultrashort x-ray pulses manipulation.

Mesoscale modelling of concrete reinforced with spiral steel fibres under dynamic splitting tension

The addition of discrete steel fibres into concrete has been widely recognised as an effective measure to enhance the ductility, post-cracking resistance and energy absorption of the matrix subjected to impact loads. Despite useful information from experimental studies that investigate the macro-scale performance of steel fibre–reinforced concrete under dynamically applied loadings, results from a series of tests or from tests by different researchers are often found to be scattered. Besides variations in testing conditions, random variations of size, location and orientation of aggregates and fibres in steel fibre–reinforced concrete are deemed the fundamental reason of the scattering test data. High-fidelity modelling of concrete and steel fibre–reinforced concrete in mesoscale has been widely adopted to understand the influence of each component in the composite material. Numerical studies have been published to discuss the behaviour of steel fibre–reinforced concrete under dynamic splitting tension. Different shapes, for example, circles, ovals and polygons, of coarse aggregates were considered in different studies, and different conclusions were drawn. This study investigates the influence of the shape of aggregates on numerical prediction in mesoscale modelling of steel fibre–reinforced concrete materials with spiral fibres under dynamic splitting tension in terms of the strain distribution, cracking pattern and strength. The numerical model is validated by experimental results. It is found that the shape of aggregates in mesoscale modelling of splitting tensile tests has negligible influence. Furthermore, steel fibre–reinforced concrete specimens with different volume fractions of spiral fibres from 0.5% to 3.0% under various loading rates are simulated. Results from parametric simulations indicate the optimal dosage of spiral fibres in steel fibre–reinforced concrete mix with respect to the construction cost and mechanical property control.