Dynamic Splitting Research Articles

Two-photon resonances, ac Stark splittings, and shifts of the resonance peaks in Doppler free absorptive lineshapes of a double-lambda type four level system

Under Doppler free condition and by using semiclassical approach, a double-lambda type four-level system coupled to two electromagnetic fields are investigated. The coupled optical Bloch equations involving the density matrix elements in steady state are solved numerically to investigate the signal lineshapes as the function of signal detuning and pump Rabi-frequencies. The on-resonant pump leads to dynamic Stark splitting. The dent in the absorption lineshape is exhibited for off-resonant pump and is a signature of two-photon resonances. The appearance of extra absorption and emission peaks in the computed lineshapes are attributed by the nonlinear polarizations and hence the spontaneously generated coherences.

Dynamic Multifocus Laser Writing with Acousto‐Optofluidics

AbstractLaser writing of materials is normally performed by the sequential scanning of a single focused beam across a sample. This process is time‐consuming and it can severely limit the throughput of laser systems in key applications such as surgery, microelectronics, or manufacturing. A parallelization strategy based on ultrasound waves in a liquid to diffract light into multiple beamlets is reported. Adjusting amplitude, frequency, or phase of ultrasound allows tunable multifocus distributions with sub‐microsecond control. When combined with sample translation, the dynamic splitting of light leads to high‐throughput laser processing, as demonstrated by locally modifying the morphological and wettability properties of metals, polymers, and ceramics. The results illustrate how acousto‐optofluidic systems are universal tools for fast multifocus generation, with potential impact in fields such as imaging or optical trapping.

Splitting of singly and doubly quantized composite vortices in two-component Bose-Einstein condensates

We study numerically the dynamical instabilities and splitting of singly and doubly quantized composite vortices in two-component Bose-Einstein condensates harmonically confined to quasi two dimensions. In this system, the vortices become pointlike composite defects that can be classified in terms of an integer pair $(\kappa_1,\kappa_2)$ of phase winding numbers. Our simulations based on zero-temperature mean-field theory reveal several vortex splitting behaviors that stem from the multicomponent nature of the system and do not have direct counterparts in single-component condensates. By calculating the Bogoliubov excitations of stationary axisymmetric composite vortices, we find nonreal excitation frequencies (dynamical instabilities) for the singly quantized $(1,1)$ and $(1,-1)$ vortices and for all variants of doubly quantized vortices, which we define by the condition $\max_{j=1,2}|\kappa_j|=2$. While the short-time predictions of the linear Bogoliubov analysis are confirmed by direct time integration of the Gross-Pitaevskii equations of motion, the time integration also reveals intricate long-time decay behavior not captured by the linearized dynamics. First, the $(1,\pm 1)$ vortex is found to be unstable against splitting into a $(1,0)$ vortex and a $(0,\pm 1)$ vortex. Second, the $(2,1)$ vortex exhibits a two-step decay process in which its initial splitting into a $(2,0)$ vortex and a $(0,1)$ vortex is followed by the off-axis splitting of the $(2,0)$ vortex into two $(1,0)$ vortices. Third, the $(2,-2)$ vortex is observed to split into a $(-1,1)$ vortex, three $(1,0)$ vortices, and three $(0,-1)$ vortices. Each of these splitting processes is the dominant decay mechanism of the respective stationary composite vortex for a wide range of intercomponent interaction strengths and relative populations of the two condensate components and should be amenable to experimental detection.

Effect of steel and polypropylene fibers on the quasi-static and dynamic splitting tensile properties of high-strength concrete

The influence of steel-polypropylene hybrid fibers on the tensile properties of high-strength concrete is investigated by quasi-static and dynamic Brazilian disc splitting tests. The failure modes of fiber reinforced concrete specimens and the influence of different fiber mixing ratios on the splitting tensile strength of the specimens are analyzed. The research results indicate that the plain concrete and single-doped polypropylene fiber concrete specimens show straight cracks along the loading line during the experimental process, showing the brittle failure characteristics; while the single-doped steel fiber concrete and hybrid fiber concrete specimens show more bifurcated micro-cracks along the loading line, showing the ductile failure characteristics. The splitting tensile strength of concrete specimens increases with the increase of steel fiber content, and increases first and then decreases with the increase of polypropylene fiber content. The mixed use of steel fiber and polypropylene fiber not only improves the splitting tensile strength of concrete specimens, but also reduces the risk of brittle failure of concrete. Especially when the steel fiber content is S2 (2.5%), the hybrid of steel-polypropylene fibers has a great improvement effect on the splitting properties of concrete specimen. In addition, it is found that the splitting tensile strength of fiber reinforced concrete specimens increases with the increase of force loading rate, showing the enhancing effect of loading rate. Comparing the rate-enhancing effect of specimens with different fiber content, it is found that the change of fiber content has a certain influence on the loading rate-enhancing effect of specimens.

Off-resonant all-optical switching dynamics in a ferromagnetic model system

We present a theoretical study of the effects of optical fields on a ferromagnetic model system of itinerant carriers that includes both magnetism at the level of a time-dependent mean-field and spin-orbit coupling. In the framework of this model, which contains a band gap and is similar to the one introduced by Qaiumzadeh et al. [Phys. Rev. B 88, 064416 (2013)] we investigate the inverse Faraday effect, i.e., how the magnetization of the ferromagnetic bands can be influenced by the helicity of off-resonant optical fields. The magnetization dynamics are calculated self-consistently by including a dynamic ferromagnetic splitting and the corresponding single-particle states. We study the magnetization dynamics for the case of a rapid ramping-up of an optical field that is off-resonant with respect to the gap and find that the magnetization switching occurs due to the interplay of the coherence between the spin-split ferromagnetic bands and incoherent scattering/dephasing processes.

Mechanical properties and behaviour of high-strength plain and hybrid-fiber reinforced geopolymer composites under dynamic splitting tension

Geopolymer materials have been of particular interest to the construction industry due to their environmental benefits. However, their behaviour has rarely been investigated under dynamic loadings, although it is of fundamental concern to assess their vulnerability against higher loading rates. In this study, the dynamic tensile properties of a newly fabricated high-strength ambient cured geopolymer material and fiber reinforced geopolymer composites (FRGC) are presented. Since geopolymers are intrinsically brittle, novel equal-part blend of hooked-end and spiral-shaped steel fibers at two different fiber volume fractions and hybrid steel-polyethylene combination were used to reinforce the geopolymer matrix. The quasi-static splitting tensile tests were performed using a 300 KN displacement controlled Shimadzu test machine, while a modified Ø100-mm split Hopkinson pressure bar (SHPB) apparatus was used to conduct the dynamic splitting-tensile tests. A high-speed camera was used to capture the fracture development processes and crack-opening of different types of FRGC. The test results show that under quasi-static splitting tension, the unreinforced geopolymer exhibited minimal tensile strain capacity. With the addition of steel fibers and hybrid steel-polyethylene fiber reinforcement, the energy absorption capability of FRGC samples was significantly improved. The dynamic tests reveal the strong strain rate dependency and prominent tensile strength enhancements for all composites, although unreinforced geopolymer samples were more sensitive to the strain rate effect within the considered test range. A comparison between the test data and modified CEB guidelines reflect the non-suitability of code formulae to establish the dynamic increase factor (DIFft) relation for geopolymers. Based on the test data, empirical DIFft relationships are proposed for unreinforced and different types of FRGC samples. It is also indicated by image analyses that the excellent bonding of spiral steel fibers with the geopolymer matrix is befittingly complemented by polyethylene fibers to maintain the material integrity.

Experimental Investigation on Rockbolt Performance Under the Tension Load

Rockbolt performance may vary differently under complex geological and stress conditions, especially dynamic disturbance at deep underground mining. Therefore, reinforcement mechanism needs to be further explored to improve the support effect of rockbolt. In this study, static and dynamic Brazilian splitting tests of steel bar reinforced red sandstones were carried out to investigate the rockbolt performance under tension load. The deformation changes on the specimen’s surface and the rockbolt were recorded during the test. The strengths and failure modes of unreinforced and reinforced Brazilian disc samples were investigated. The results show that the stress of bolt increases steadily during elastic deformation process, indicating that the bolt shares the tension loading, and increases sharply when the bear capacity of specimen descends caused by crack propagation, indicating that the load is transferred from sandstone specimen. Furthermore, most of the damaged reinforced samples were still bonded by rockbolt, when the test finished. Therefore, the reinforcement mechanism can be divided into two phases. The first phase is the intact rock stage, during which the bolt shares stress reinforcing the strength. The second phase is crack propagation stage, in which the bolt restricts the crack propagation and almost bears the load. Compared with the results of unreinforced samples, it can be seen that the bolt can reduce failure of rock and the strength of the reinforced samples is enhanced. The results may provide a reference for analysis of reinforced mechanism and design of rockbolts.

Direct imaging of the circular chromosome in a live bacterium

Although the physical properties of chromosomes, including their morphology, mechanics, and dynamics are crucial for their biological function, many basic questions remain unresolved. Here we directly image the circular chromosome in live E. coli with a broadened cell shape. We find that it exhibits a torus topology with, on average, a lower-density origin of replication and an ultrathin flexible string of DNA at the terminus of replication. At the single-cell level, the torus is strikingly heterogeneous, with blob-like Mbp-size domains that undergo major dynamic rearrangements, splitting and merging at a minute timescale. Our data show a domain organization underlying the chromosome structure of E. coli, where MatP proteins induce site-specific persistent domain boundaries at Ori/Ter, while transcription regulators HU and Fis induce weaker transient domain boundaries throughout the genome. These findings provide an architectural basis for the understanding of the dynamic spatial organization of bacterial genomes in live cells.

Dynamical splitting of cubic crystal field levels in rare-earth cage compounds

The Crystalline Electric Field (CEF) influence is usually described by considering an ideally symmetrical rare-earth site. In the case of cage compounds, ample excursions of the rare-earth inside the cage require an adapted CEF description. A corrective, position dependent, CEF term accounts for the deviation from the perfect symmetry. In the paramagnetic range, a CEF level with orbital degeneracy thus acquires a width reflecting the rare-earth spatial distribution. In the case, frequent in cubic systems, of an orbitally degenerate CEF ground state at the center, this width introduces an additional energy scale, influential at low temperature. A spherical simplification allows to identify the major consequences of a cage-split ground multiplet: a Schottky-like anomaly appears in the specific heat with associated reduction of the magnetic entropy and alteration of the magnetic properties. Concomitantly, a centrifugal Jahn-Teller effect develops that expands the distribution of the magnetic ion and softens the rattling phonons. These effects are confronted with anomalous paramagnetic properties of rare-earth cage compounds, notably rare-earth filled skutterudites and hexaborides.

Influence of freeze–thaw cycles on apparent dynamic tensile strength, apparent dynamic fracture toughness and microstructure of concrete under impact loading

The freeze–thaw damage, particularly in cold region, occurs frequently when concrete structures lose their durability. In this study, the dynamic mechanical properties of concrete after 0, 50, 100, 150 cycles of freeze–thaw are investigated. The microstructure of concrete associated with freeze–thaw damage is observed by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) technologies. According to the experimental data, the influences of the freeze–thaw cycles and the loading rate on the dynamic mechanical properties are analysed, respectively. It is shown that the apparent dynamic splitting tensile strength and the apparent dynamic fracture toughness of the specimen both decrease with the increase of the freeze–thaw cycles and the loading rate. On the basis of MIP results, it is found that the porosity, the most probable pore size and the critical diameter of the concrete all increase with the increase of the cycles of freeze–thaw. The micrographs obtained from SEM illustrate that the development of cracks and the production of crystals are dominant performances reflecting the damage of concrete under freeze–thaw cycles. In addition, the freeze–thaw cycles can induce dissolution of the specimen, which benefits the growth of the crystal ettringite.

Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering

Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding.

System Outage Performance for Three-Step Two-Way Energy Harvesting DF Relaying

Wireless energy harvesting (WEH) has been recognized as a promising technique to prolong the lifetime of energy constrained relay nodes in wireless sensor networks. Its application and related performance study in three-step two-way decode-and-forward (DF) relay networks are of high interest but still lack sufficient study. In this paper we propose a dynamic power splitting (PS) scheme to minimize the system outage probability in a three-step two-way energy harvesting DF relay network and derive an analytical expression for the system outage probability with respect to the optimal dynamic PS ratios. In order to further improve the system outage performance, we propose an improved dynamic scheme where both the PS ratios and the power allocation ratio at the relay are dynamically adjusted according to instantaneous channel gains. The corresponding system performance with the improved dynamic scheme is also investigated. Simulation results show that our proposed schemes outperform the existing scheme in terms of the system outage performance and the improved dynamic scheme is superior to the dynamic PS scheme.

Indirect tail states formation by thermal-induced polar fluctuations in halide perovskites

Halide perovskites possess enormous potential for various optoelectronic applications. Presently, a clear understanding of the interplay between the lattice and electronic effects is still elusive. Specifically, the weakly absorbing tail states and dual emission from perovskites are not satisfactorily described by existing theories based on the Urbach tail and reabsorption effect. Herein, through temperature-dependent and time-resolved spectroscopy on metal halide perovskite single crystals with organic or inorganic A-site cations, we confirm the existence of indirect tail states below the direct transition edge to arise from a dynamical Rashba splitting effect, caused by the PbBr6 octahedral thermal polar distortions at elevated temperatures. This dynamic effect is distinct from the static Rashba splitting effect, caused by non-spherical A-site cations or surface induced lattice distortions. Our findings shed fresh perspectives on the electronic-lattice relations paramount for the design and optimization of emergent perovskites, revealing broad implications for light harvesting/photo-detection and light emission/lasing applications.

Tradeoff Between Secrecy Capacity and Harvested Energy for Secure Visible Light Communications With SWIPT

By considering the threefold roles of indoor visible light communications (VLC), i.e., illumination, secure information transmission, and light power transfer, the tradeoff between the secrecy capacity (SC) and the harvested energy (HE) is investigated in this paper. An indoor VLC system consisting of a transmitter, a legitimate receiver, and an eavesdropper is established. The legitimate receiver can perform secure information transmission and light power transfer simultaneously, while the eavesdropper is just an information eavesdropping receiver. Under the non-negativity and the dimmable average optical intensity constraint, a lower bound of the average SC is derived. By employing the dynamic power splitting (DPS) for the legitimate receiver, the closed-form expression of the average HE is obtained. After that, the SC-HE region for the DPS receiver is constructed. As the variants of the DPS receiver, the time switching (TS), static power splitting (SPS) and on–off power splitting (OPS) receivers are provided, and the corresponding SC-HE regions are also obtained. As a benchmark, the performance upper bound of the SC-HE region for any practical receiver is derived. The simulation results show that the performance of the OPS receiver always outperforms that of the other receivers. The DPS and SPS receivers achieve the same performance. The TS receiver is the worst receiver when HE is small, but it is the best receiver when HE is large. Moreover, the impacts of the dimming target, the estimated error, signal processing noise, and the nominal optical intensity on system performance are discussed.

A Low-Rank Algorithm for Weakly Compressible Flow

In this paper, we propose a numerical method for solving weakly compressible fluid flow based on a dynamical low-rank projector splitting. The low-rank splitting scheme is applied to the Boltzmann ...

Optical resonance near the edge of a photonic band gap (PBG): turning the effects of a PBG on/off using a resonant driving field

ABSTRACTWe studied the effects of a coherent monochromatic resonant laser field driving the transition of a two-level atom embedded in a photonic band gap (PBG) material on the emission dynamics of the atom. When the transition frequency of the atom lies outside a PBG and sufficiently far from the band edge that the emission dynamics of the atom is not normally affected by the gap, the dynamic stark splitting of the upper level of the atom into two dressed states by a sufficiently strong resonant driving field can bring the lower dressed state close enough to the band edge or even inside the gap so as to be affected by the gap, providing a switchable means of extending the novel effects of atom–photon interaction near the edge of a PBG for atomic transitions outside the gap and far from the band edge. The net effect is as if a sufficiently strong resonant field driving a transition of an atom embedded in a PBG actively shifts the PBG close enough to the transition so that the gap affects the emission dynamics associated with the transition.

Quasi-static and dynamic splitting of high-strength concretes – tensile stress–strain response and effects of strain rate

Quasi-static and dynamic splitting tensile tests were performed on three high-strength concretes with different compressive strengths – 60 MPa, 80 MPa and 110 MPa, denoted by C60, C80 and C110 respectively – to examine their tensile properties. Quasi-static tests were conducted at a strain rate of ∼2 × 10−6 s−1, using a Shimadzu Universal Testing Machine; and dynamic tests were performed at strain rates of ∼1–10 s−1, using an 80 mm-diameter split Hopkinson pressure bar (SHPB) device. Strain gauging and digital image correlation (DIC) techniques were employed to determine the deformation in specimens. From the force applied and the average tensile strain at the specimen centre, obtained from strain gauge measurements, the uniaxial tensile stress–strain response at that location was derived, by adopting an elastic-plastic analysis, whereby tensile plastic hardening is assumed to be piecewise linear. The effects of strain rate on the tensile response were also examined and analysed. For all three high-strength concretes, significant rate dependence was observed; the yield stress, tensile strength and failure strain all increase with strain rate, and their dynamic values are much higher than their static values. The Dynamic increase factor (DIF), i.e. the ratio between the dynamic and static tensile strengths, was calculated to quantify the rate sensitivity. Similar DIFs were obtained for C60, C80 and C110, and the DIFs determined were compared with predictions based on two empirical formulae, i.e. the CEB-FIP model (2010), and that proposed by Malvar and Ross, which are frequently used for normal-strength concrete. These two formulae appear inadequate in defining the rate dependence of high-strength concrete. Consequently, a bilinear description of the DIF as a function of log10(ɛ˙), with a transition at a strain rate at 1 s−1, was proposed for high-strength concrete, based on the experimental data.

MO2 - How Errors in the Implementation of Background Mortality Leads to Bias in Models

Patients considered in economic models, particularly with long time horizons, often die of ‘competing’ risks, which are generally related to the background risk of death. The implementation of this background risk is often inappropriately defined and based on a population mean, when the risk is not linearly related to age. This research aims to quantify the impact of simplified application of background risk on economic model results. A series of economic models were constructed using simulated disease data. The models incorporated assumed disease-specific mortality according to parametric survival curves, and background mortality (taken from UK Life Tables). The rate of disease-specific mortality and starting age of patients was varied in the models in line with the risks (and age profiles) seen with various common conditions. The outcomes were then compared between background mortality applied using the following (1) based on mean age and gender split at baseline, (2) accounting for the dynamic gender split of patients over time, (3) considering the distribution of patient age at baseline, and (4) at the individual level. The level of bias introduced by simplifications varies, being relatively small when patients are close in age and disease-specific mortality constitutes the majority of risk. Predicted survival can vary dramatically where patients have a wide spread in age, and disease-specific mortality is low, with simplified implementations of background mortality showing considerable bias (up to 6% difference in predicted life years in our example). The implementation of background mortality in economic models is often flawed, which has the potential to meaningfully alter results. While this is not always the case, modellers should be mindful of the risks, particularly where background mortality is the leading cause of death.

Comparative study of tensile tests based on Hopkinson bar for recycled aggregate concrete

To comparatively study the tensile properties and fracture patterns of recycled aggregate concrete with various replacement percentages (i.e. 0%, 25%, 50%, 75%, and 100%) of recycled coarse aggregate, the dynamic direct tensile tests, splitting tests, and spalling tests of recycled aggregate concrete in the strain-rate range of 100–102 s−1 were carried out using large diameter (75 mm) split Hopkinson tensile bar and pressure bar. Test results show that for recycled aggregate concrete, the quasi-static direct tensile strength is more marvelous than its quasi-static splitting strength. When recycled coarse aggregate replacement percentage is 0%–75%, the replacement percentage impact minimally on the quasi-static tensile strength of recycled aggregate concrete. In dynamic tensile tests, there exists apparent difference between the dynamic direct tensile strength and dynamic splitting. The dynamic tensile strength of recycled aggregate concrete increases with the increase of average strain-rate in all three kinds of tests. The average strain-rate affects the damage form of recycled aggregate concrete, which indicates that the recycled aggregate concrete has obvious rate sensitivity. There shows no obvious regularity between the dynamic tensile strength and the recycled coarse aggregate replacement percentage. And the indirect tensile strength calculation method used in this article offers the theoretical basis for the engineering application of recycled aggregate concrete.

A platoon based cooperative eco-driving model for mixed automated and human-driven vehicles at a signalised intersection

The advancements in communication and sensing technologies can be exploited to assist the drivers in making better decisions. In this paper, we consider the design of a real-time cooperative eco-driving strategy for a group of vehicles with mixed automated vehicles (AVs) and human-driven vehicles (HVs). The lead vehicles in the platoon can receive the signal phase and timing information via vehicle-to-infrastructure (V2I) communication and the traffic states of both the preceding vehicle and current platoon via vehicle-to-vehicle (V2V) communication. We propose a receding horizon model predictive control (MPC) method to minimise the fuel consumption for platoons and drive the platoons to pass the intersection on a green phase. The method is then extended to dynamic platoon splitting and merging rules for cooperation among AVs and HVs in response to the high variation in urban traffic flow. Extensive simulation tests are also conducted to demonstrate the performance of the model in various conditions in the mixed traffic flow and different penetration rates of AVs. Our model shows that the cooperation between AVs and HVs can further smooth out the trajectory of the latter and reduce the fuel consumption of the entire traffic system, especially for the low penetration of AVs. It is noteworthy that the proposed model does not compromise the traffic efficiency and the driving comfort while achieving the eco-driving strategy.