Loop Breaking Research Articles

RT Engine: An Efficient Hardware Architecture for Ray Tracing

The reality of the ray tracing technology that leads to its rendering effect is becoming increasingly apparent in computer vision and industrial applications. However, designing efficient ray tracing hardware is challenging due to memory access issues, divergent branches, and daunting computation intensity. This article presents a novel architecture, a RT engine (Ray Tracing engine), that accelerates ray tracing. First, we set up multiple stacks to store information for each ray so that the RT engine can process many rays parallel in the system. The information in these stacks can effectively improve the performance of the system. Second, we choose the three-phase break method during the triangle intersection test, which can make the loop break earlier. Third, the reciprocal unit adopts the approximation method, which combines Parabolic Synthesis and Second-Degree interpolation. Combined with these strategies, we implement our system at RTL level with agile chip development. Simulation and experimental results show that our architecture achieves a performance per area which is 2.4 × greater than the best reported results for ray tracing on dedicated hardware.

Coordinated Vehicle Platooning with Fixed Routes: Adaptive Time Discretization, Strengthened Formulations and Approximation Algorithms

We consider the coordinated vehicle platooning problem over a road network with time constraints and the routes of vehicles are given. The problem is to coordinate the departure time of each vehicle to enable platoon formation hence maximizing the total fuel saving. We first focus on the case that the routes form a tree. In this case, the flexibility time window of each vehicle admits a unified representation, under which the synchronization of departure time is equivalent to the management of time-window overlapping. Based on this observation, a time-window-overlapping induced mixed-integer linear program formulation has been established which is equivalent to the continuous-time formulation established in the previous work. By imposing an adaptive time-discretization procedure, we can further reformulate the time coordination problem using a vehicle-to-time-bucket assignment induced mixed-integer linear program. Compared to the continuous-time formulation, the assignment formulation is free of big-M coefficients, and it is demonstrated by numerical experiments that the assignment formulation is indeed more effective in computational performance. As an independent interest, three approximation algorithms have been derived with provable competitive ratios under a certain regularity assumptions, which is for the first time on this discrete optimization problem. The solution approach has been extended to general cases in which the graph formed by vehicle routes can have loops, by adding a systematic loop breaking scheme. An insightful discovery is that whether there exists an exact equivalent assignment formulation for a general problem instance has a close connection to the pattern of lattice groups.

Dependency Graph-based High-level Synthesis for Maximum Instruction Parallelism

Performance optimization is an important goal for High-level Synthesis (HLS). Existing HLS scheduling algorithms are all based on Control and Data Flow Graph (CDFG) and will schedule basic blocks in sequential order. Our study shows that the sequential scheduling order of basic blocks is a big limiting factor for achievable circuit performance. In this article, we propose a Dependency Graph (DG) with two important properties for scheduling. First, DG is a directed acyclic graph. Thus, no loop breaking heuristic is needed for scheduling. Second, DG can be used to identify the exact instruction parallelism. Our experiment shows that DG can lead to 76% instruction parallelism increase over CDFG. Based on DG, we propose a bottom-up scheduling algorithm to achieve much higher instruction parallelism than existing algorithms. Hierarchical state transition graph with guard conditions is proposed for efficient implementation of such high parallelism scheduling. Our experimental results show that our DG-based HLS algorithm can outperform the CDFG-based LegUp and the state-of-the-art industrial tool Vivado HLS by 2.88× and 1.29× on circuit latency, respectively.

An innovation idea for SBLOCA mitigation strategy: Self-coagulation system in comparison with human hemostatic mechanism

The loss of coolant accident (LOCA), as one of the design basis accidents (DBAs), is a hypothetical accident that is usually considered in the design of nuclear power plant. LOCA is caused by small/large breaks in the reactor primary coolant and pressure boundary and may result in a loss of reactor coolant at a rate in excess of the reactor makeup system capability. Currently, the typical mitigation measures for LOCA are through the vessel high/low pressure coolant injection (HPCI/LPCI), core spray system, or reactor core isolation cooling (RCIC) system, to protect reactor from fuel melting and core degradation. However, is it possible to directly repair the small breaks passively? Inspired by the hemostasis and coagulation mechanism of human blood vessels, the authors are considering to develop a technology which would allow the reactor self-coagulation during the small break loss of coolant accident (SBLOCA). With the assistance of this innovative technology, the speed of losing coolant through reactor primary loop breaks could be significantly reduced or even the loss is stopped. With more and longer existing coolant in the core, the possibility of core degradation will also be significantly reduced. This innovative technology needs to be designed feasible and simple, which can be directly used into the existing nuclear power plants to improve the inherent safety of the cooling system, benefit the economy and safety of the nuclear power plant. In this paper, the authors compare the reactor primary loop of nuclear power plant with the blood circulation system of human beings from comprehensive and multi-angle perspectives, discuss the similarity, feasibility, and economy of nuclear power plant self-coagulation system based on the existing hemostasis and coagulation mechanism of human blood vessels. If possible, this technology will play a revolutionary positive role in alleviating DBAs related to SBLOCA.

Distributed transmission technology of node status in distribution network

With the rapid development of distribution network automation and the construction of DC distribution network and AC / DC hybrid distribution network, the network operation mode is more flexible. If the distribution network wants to realize rapid load transfer, such as the connection of power supply, upstream and downstream fault isolation signals and other node states need to be quickly identified. At present, the node status identification of distribution automation is basically completed by the master station. However, the master station has poor real-time transmission of status information, which is generally in seconds or minutes, and can not meet the demand of real-time load transfer. In this paper, a distributed real-time transmission method of AC and DC distribution network node status is constructed for distribution automation system. Based on IEC61850 goose communication protocol, the real-time transmission of node status is realized in distribution automation terminal. In this method, the positive direction of each tie switch is defined, which is independent of power flow direction, and the tie switch is distinguished along the user-defined positive direction When multiple tie switches have the same upstream node, they are each other’s t nodes. Each tie switch needs to be equipped with a distribution automation terminal with goose communication capability. According to different control strategies, the distribution automation terminal can realize millisecond level node state transmission step by step. Node state can be divided into unconditional transmission state and conditional transmission state. The distributed real-time transmission technology of distribution network node state proposed in this paper has been successfully applied to Tongli integrated energy service The center and Suzhou medium and low voltage DC project lay the foundation for the realization of loop closing, loop breaking control, fast fault isolation and power transfer control strategies.

Heteroclinic Chaotic Threshold in a Nonsmooth System with Jump Discontinuities

In smooth systems, the form of the heteroclinic Melnikov chaotic threshold is similar to that of the homoclinic Melnikov chaotic threshold. However, this conclusion may not be valid in nonsmooth systems with jump discontinuities. In this paper, based on a newly constructed nonsmooth pendulum, a kind of impulsive differential system is introduced, whose unperturbed part possesses a nonsmooth heteroclinic solution with multiple jump discontinuities. Using the recursive method and the perturbation principle, the effects of the nonsmooth factors on the behaviors of the nonsmooth dynamical system are converted to the integral items which can be easily calculated. Furthermore, the extended Melnikov function is employed to obtain the nonsmooth heteroclinic Melnikov chaotic threshold, which implies that the existence of the nonsmooth heteroclinic orbits may be due to the breaking of the nonsmooth heteroclinic loops under the perturbation of damping, external forcing and nonsmooth factors. It is worth pointing out that the form of the nonsmooth heteroclinic Melnikov function is different from the one of the nonsmooth homoclinic Melnikov function, which is quite different from the classical Melnikov theory.

The effect of obstacles in multi-site protein target search with DNA looping

Many fundamental biological processes are regulated by protein-DNA complexes called synaptosomes, which possess multiple interaction sites. Despite the critical importance of synaptosomes, the mechanisms of their formation are not well understood. Because of the multisite nature of participating proteins, it is widely believed that their search for specific sites on DNA involves the formation and breaking of DNA loops and sliding in the looped configurations. In reality, DNA in live cells is densely covered by other biological molecules that might interfere with the formation of synaptosomes. In this work, we developed a theoretical approach to evaluate the role of obstacles in the target search of multisite proteins when the formation of DNA loops and the sliding in looped configurations are possible. Our theoretical method is based on analysis of a discrete-state stochastic model that uses a master equations approach and extensive computer simulations. It is found that the obstacle slows down the search dynamics in the system when DNA loops are long-lived, but the effect is minimal for short-lived DNA loops. In addition, the relative positions of the target and the obstacle strongly influence the target search kinetics. Furthermore, the presence of the obstacle might increase the noise in the system. These observations are discussed using physical-chemical arguments. Our theoretical approach clarifies the molecular mechanisms of formation of protein-DNA complexes with multiple interactions sites.

Analysis and Improvement of Adaptive Coefficient Third Harmonic Voltage Differential Stator Grounding Protection

This paper presents a novel third harmonic voltage differential stator grounding protection (THV-DSGP) method combining the adaptive coefficient and fixed coefficient. It can solve the protection sensitivity degradation problem when the insulation resistance of stator winding to ground is slowly declining. This protection method retains the advantages of the adaptive coefficient, which is to maintain high sensitivity in case of an instantaneous ground fault. Moreover, the fixed coefficient can remember the initial insulation state of the stator winding and prevent relay failure when the stator insulation is slowly declining. In addition, due to zero-sequence voltage disconnection (ZSVD) often leading to malfunctioning of the THV stator ground protection, the existing criterion of the ZSVD was improved according to the electrical characteristics of the generator when ZSVD happens. THV-DSGP with both adaptive coefficient and fixed coefficient was simulated in the Matlab/Simulink. The simulation results show that the proposed protection can be applied to the slow ground fault of the stator winding. Furthermore, the improved criterion of ZSVD can effectively distinguish the stator metal earth fault and the secondary loop break of the zero-sequence voltage.

Numerical Study of Integral Inherently Safe Light Water Reactor in Case of Inadvertent DHR Operation Based on the Multiscale Method

In detailed previous work by the authors, an innovative decay heat removal (DHR) system has been proposed and designed for the Integral Inherently Safe Light Water Reactor (I2S-LWR). The current paper studies the inadvertent actuation of one DHR system train during I2S-LWR normal operation due to a false signal or operator action. The RELAP5 code is used to perform a one-dimensional study, and important thermal-hydraulic characteristics, including primary loop coolant flow rate, pressure, temperature, DHR primary-side flow rate, and coolant temperature, are achieved during this transient. Then, a detailed computational fluid dynamics simulation utilizing STARCCM+ is carried out to investigate the coolant mixing characteristics in the downcomer and lower plenum and obtain the local thermal-hydraulic conditions at the reactor core inlet. It is found that as a consequence of inadvertent DHR actuation, the maximum overcooling at the reactor core inlet is about 3 K, which would not result in significant reactivity insertion. Furthermore, a more severe transient of inadvertent DHR operation with intermediate loop break is studied, and the results show that this would not lead to more significant overcooling to the I2S-LWR core compared with inadvertent DHR operation without intermediate loop break. This work is an indispensable supplement for DHR system comprehensive assessment in the I2S-LWR project.

Optimal Utility Algorithm and Its Application in Library Management

Decision makers build utility functions for decisions based on their information, knowledge, beliefs and risk awareness. This utility function is an important basis for decision makers to make decisions in scientific practice and economic activities. In this paper, a weighted binary relationship is established by comparing the decision-making schemes. The full-order relationship closest to this weight relationship is used as the optimal utility for decision makers. The optimal utility of the loop breaking algorithm is given. Finally, it discusses its application in library management.

Efficient Verification Against Undesired Operating Points for MOS Analog Circuits

Identifying and removing undesired operating points is one of the most important problems in analog circuit design. In this paper, a divide and contraction verification method against undesired operating points in analog circuits is proposed. Unlike traditional methods to find all operating points, this method only targets searching voltage intervals containing undesired operating points. To achieve this, a systematic approach for automatically identifying all positive and negative feedback loops in circuits is introduced. A positive feedback loop breaking method and selection of breaking nodes are discussed to determine whether a monotonic return function can be obtained. Depending on the monotonicity of the return function, two types of divide and contraction algorithms are proposed to efficiently search voltage intervals containing operating points. Simulation results show that this method is effective and efficient in identifying the presence/absence of undesired operating points in a set of commonly used benchmark circuits.

Pcarrier: Individual and family distributions of a susceptibility gene for breast and ovarian cancer based on family history.

e13005 Background: Most of the BRCA1/2 and PALB2 analyses performed in patients with a personal and familial history (FH) of breast/ovarian cancer are negative. In this context, there is no targeted analysis available to identify relatives at high risk (carrier of the causal hypothetical mutated gene). Thus, the recommendations of surveillance to all relatives are based only on the FH of cancer. At the Institut Curie we assess the degree of severity of the FH by calculating the probability of carrying a single autosomal dominant susceptibility gene without taking into account genotyping results but using the LINKAGE software with the parameters of the Claus-Easton model (1993). This reliable but old tool has a slow console interactive interface (roughly 15 min of clinicians time for each assessed family). Methods: We rewrite the model as a Bayesian network combining Mendelian genetics with classical survival analysis. All probabilistic computations are performed through belief propagation (sum-product algorithm) over real numbers or polynomials. The programming language is C++. Results: pCarrier is a modern and efficient implementation of the Claus-Easton model for clinicians with the following features: 1) fast non-interactive command line ( < 1s to process a previously registered family) combined with a graphical user-friendly interface; 2) computations dealing with monozygotic twins or loops without any human intervention (ex: loop breaking); 3) choice between the original discretized model (individual FH into 14 classes) and its continuous version (piecewise constant hazard); 4) marginal individual carrier distribution for all individuals in the pedigree; 5) joint distribution of the number of carriers among any group of individuals (ex: in the entire family, among the living only). Conclusions: pCarrier is experimented since January 2017 in the Institut Curie as a replacement of the existing tool and appears so far to be dramatically faster and easier to use for the clinicians, highly reliable (consistence with the existing tool), and able to provide new useful decision-making probabilities using the distribution of the number of carriers.

Complex astrophysical experiments relating to jets, solar loops, and water ice dusty plasma

Recent results of three astrophysically relevant experiments at Caltech are summarized. In the first experiment magnetohydrodynamically driven plasma jets simulate astrophysical jets that undergo a kink instability. Lateral acceleration of the kinking jet spawns a Rayleigh–Taylor instability, which in turn spawns a magnetic reconnection. Particle heating and a burst of waves are observed in association with the reconnection. The second experiment uses a slightly different setup to produce an expanding arched plasma loop which is similar to a solar corona loop. It is shown that the plasma in this loop results from jets originating from the electrodes. The possibility of a transition from slow to fast expansion as a result of the expanding loop breaking free of an externally imposed strapping magnetic field is investigated. The third and completely different experiment creates a weakly ionized plasma with liquid nitrogen cooled electrodes. Water vapour injected into this plasma forms water ice grains that in general are ellipsoidal and not spheroidal. The water ice grains can become quite long (up to several hundred microns) and self-organize so that they are evenly spaced and vertically aligned.

Studying edge geometry in transiently turbulent shear flows

AbstractIn linearly stable shear flows at moderate Reynolds number, turbulence spontaneously decays despite the existence of a codimension-one manifold, termed the edge, which separates decaying perturbations from those triggering turbulence. We statistically analyse the decay in plane Couette flow, quantify the breaking of self-sustaining feedback loops and demonstrate the existence of a whole continuum of possible decay paths. Drawing parallels with low-dimensional models and monitoring the location of the edge relative to decaying trajectories, we provide evidence that the edge of chaos does not separate state space globally. It is instead wrapped around the turbulence generating structures and not an independent dynamical structure but part of the chaotic saddle. Thereby, decaying trajectories need not cross the edge, but circumnavigate it while unwrapping from the turbulent saddle.

An improved loop test for experimentally approaching the intrinsic strength of alumina nanoscale whiskers

An improved loop test, which consists of twisting a loop in a nanoscale whisker adhered to a transmission electron microscopy (TEM) grid or other flat substrate and pulling the ends until the loop breaks, was developed for experimentally approaching the intrinsic strength of the whisker material. Alumina whiskers with diameters in the 82–320 nm range, as test targets, exhibited an average fracture strength of 39.1 GPa with a maximum of 48.8 ± 1.8 GPa, which is close to the theoretical prediction of ∼46 GPa. In situ TEM fracture analysis demonstrated the brittle fracture of alumina whiskers with thicknesses down to 82 nm. Conventional SEM/TEM imaging induced fracture of the whisker loops that had experienced high strain and a possible mechanism were discussed.

Frustrated colloidal ordering and fully packed loops in arrays of optical traps

We propose that a system of colloidal particles interacting with a honeycomb array of optical traps that each contain three wells can be used to realize a fully packed loop model. One of the phases in this system can be mapped to Baxter's three-coloring problem, offering an easily accessible physical realization of this problem. As a function of temperature and interaction strength, we find a series of phases, including long range ordered loop or stripe states, stripes with sliding symmetries, random packed loop states, and disordered states in which the loops break apart. Our geometry could be constructed using ion trap arrays, BEC vortices in optical traps, or magnetic vortices in nanostructured superconductors.

Defining the Nature of Thermal Intermediate in 3 State Folding Proteins: Apoflavodoxin, a Study Case

The early stages of the thermal unfolding of apoflavodoxin have been determined by using atomistic multi microsecond-scale molecular dynamics (MD) simulations complemented with a variety of experimental techniques. Results strongly suggest that the intermediate is reached very early in the thermal unfolding process and that it has the properties of an “activated” form of the native state, where thermal fluctuations in the loops break loop-loop contacts. The unrestrained loops gain then kinetic energy corrupting short secondary structure elements without corrupting the core of the protein. The MD-derived ensembles agree with experimental observables and draw a picture of the intermediate state inconsistent with a well-defined structure and characteristic of a typical partially disordered protein. Our results allow us to speculate that proteins with a well packed core connected by long loops might behave as partially disordered proteins under native conditions, or alternatively behave as three state folders. Small details in the sequence, easily tunable by evolution, can yield to one or the other type of proteins.

Conformal anomaly of super Wilson loop

Classically supersymmetric Wilson loop on a null polygonal contour possesses all symmetries required to match it onto non-MHV amplitudes in maximally supersymmetric Yang–Mills theory. However, to define it quantum mechanically, one is forced to regularize it since perturbative loop diagrams are not well defined due to presence of ultraviolet divergences stemming from integration in the vicinity of the cusps. A regularization that is adopted by practitioners by allowing one to use spinor helicity formalism, on the one hand, and systematically go to higher orders of perturbation theory is based on a version of dimensional regularization, known as Four-Dimensional Helicity scheme. Recently it was demonstrated that its use for the super Wilson loop at one loop breaks both conformal symmetry and Poincaré supersymmetry. Presently, we exhibit the origin for these effects and demonstrate how one can undo this breaking. The phenomenon is alike the one emerging in renormalization group mixing of conformal operators in conformal theories when one uses dimensional regularization. The rotation matrix to the diagonal basis is found by means of computing the anomaly in the Ward identity for the conformal boost. Presently, we apply this ideology to the super Wilson loop. We compute the one-loop conformal anomaly for the super Wilson loop and find that the anomaly depends on its Grassmann coordinates. By subtracting this anomalous contribution from the super Wilson loop we restore its interpretation as a dual description for reduced non-MHV amplitudes which are expressed in terms of superconformal invariants.

Numerical study of the diffusion-like decay of vortex tangles without mutual friction

The diffusion-like decay of vortex tangles without mutual friction is simulated numerically using the localized induction approximation. This algorithm, previously developed by the authors, is based on an examination of crossing lines, and has been used to study vortex reconnection processes. We have examined the effect of various factors on the decay of inhomogeneous vortex tangles: diffusion (large vortex loops break up into smaller ones which move away from an initial volume), changes in length owing to reconnection processes, the elimination of small vortices below the spatial resolution, and the insertion and removal of points to ensure stability of the numerical algorithm. The simulations show that a vortex tangle initially localized in a small region will spread into the surrounding space. The time evolution of the vortex line density inside the initial region agrees satisfactorily with that obtained by solving a diffusion equation.

Bifurcation search via feedback loop breaking in biochemical signaling pathways with time delay

AbstractWe develop a method to locate bifurcations in time delay systems with a potentially high‐dimensional parameter space. It is based on the feedback loop breaking approach that we developed and applied earlier for bifurcation search in ordinary differential equations. The method is particularly suited for the analysis of biological networks, for example to determine which parameters are relevant for complex dynamical behavior in such networks. To illustrate the benefits that this approach yields for biological network analysis, we apply it to study the effect of parameter variations on oscillations in a model of the MAP kinase cascade with a time delay.Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society