56016 research outputs found
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No full textTraditional collision avoidance algorithms and path planning algorithms, such as A* rapidly-exploring random tree (RRT), or artificial potential field, do not consider the dynamical constraints of the vehicle, so it makes the vehicles sometimes cannot track the generated trajectory or control set-point. Therefore, a geometric avoidance algorithm considering velocity and yaw rate constraints of fixed-wing unmanned areal vehicle (UAV) is studied and constrained geometric avoidance (CGA) algorithm is proposed. It allows the UAVs to avoid neighbor UAVs with keeping distance efficiently. The proposed algorithm is proved by simulation with autopilot system of UAV
Modeling Long-term Spike Frequency Adaptation in SA-I Afferent Neurons Using an Izhikevich-based Biological Neuron Model
No full textTo develop a biomimetic artificial tactile sensing system capable of detecting sustained mechanical touch, we propose a novel biological neuron model (BNM) for slowly adapting type I (SA-I) afferent neurons. The proposed BNM is designed by modifying the Izhikevich model to incorporate long-term spike frequency adaptation. Adjusting the parameters renders the Izhikevich model describing various neuronal firing patterns. We also search for optimal parameter values for the proposed BNM to describe firing patterns of biological SA-I afferent neurons in response to sustained pressure longer than 1-second. We obtain the firing data of SA-I afferent neurons for six different mechanical pressure ranging from 0.1 mN to 300 mN from the ex-vivo experiment on SA-I afferent neurons in rodents. Upon finding the optimal parameters, we generate spike trains using the proposed BNM and compare the resulting spike trains to those of biological SA-I afferent neurons using the spike distance metrics. We verify that the proposed BNM can generate spike trains showing long-term adaptation, which is not achievable by other conventional models. Our new model may offer an essential function to artificial tactile sensing technology to perceive sustained mechanical touch
TRust: A Compilation Framework for In-process Isolation to Protect Safe Rust against Untrusted Code
No full textRust was invented to help developers build highly safe systems. It comes with a variety of programming constructs that put emphasis on safety and control of memory layout. Rust enforces strict discipline about a type system and ownership model to enable compile-time checks of all spatial and temporal safety errors. Despite this advantage in security, the restrictions imposed by Rust???s type system make it difficult or inefficient to express certain designs or computations. To ease or simplify their programming, developers thus often include untrusted code from unsafe Rust or external libraries written in other languages. Sadly, the programming practices embracing such untrusted code for flexibility or efficiency subvert the strong safety guarantees by safe Rust. This paper presents TRUST, a compilation framework which against untrusted code present in the program, provides trustworthy protection of safe Rust via in-process isolation. Its main strategy is allocating objects in an isolated memory region that is accessible to safe Rust but restricted from being written by the untrusted. To enforce this, TRUST employs software fault isolation and x86 protection keys. It can be applied directly to any Rust code without requiring manual changes. Our experiments reveal that TRUST is effective and efficient, incurring runtime overhead of only 7.55% and memory overhead of 13.30% on average when running 11 widely used crates in Rust
Effect of intra-cyclohexane rings in H-shaped reactive molecules on the negative dispersion of optical retardation
No full textArtificial materials which show negative dispersion of retardation are of great importance and interest for applications to geometric phase retarders, compensation films, and augmented reality. Nevertheless, few negative dispersion materials have been reported and the exact correlation between the dispersion and the molecular structure has not been clearly elucidated yet. Here, new H-shaped reactive molecules with different chemical structures were synthesized and an early conversion from positive to negative dispersion of retardation was observed. The effect of the molecular structure on the dispersion of retardation was investigated experimentally as well as theoretically from the view point of molecular orientation and intrinsic molecular refractive index dispersion. The cyclohexane-inserted H-shaped reactive molecule represented a better planar orientation where the central linkage groups are aligned parallel to the surface plane. The relative UV absorption intensity along the long molecular axis was reduced compared to that of the molecule without a cyclohexane ring, while the absorption peak wavelength was not changed. By these two effects, the conversion from positive to negative dispersion could be shown at a lower concentration of the H-shaped molecules
Joint Precoding and Artificial Noise Design for MU-MIMO Wiretap Channels
No full textSecure precoding superimposed with artificial noise (AN) is a promising transmission technique to improve security by harnessing the superposition nature of the wireless medium. However, finding a jointly optimal precoding and AN structure is very challenging in downlink multi-user multiple-input multiple-output wiretap channels with multiple eavesdroppers. The major challenge in maximizing the secrecy rate arises from the non-convexity and non-smoothness of the rate function. Traditionally, an alternating optimization framework that identifies beamforming vectors and AN covariance matrix has been adopted; yet this alternating approach has limitations in maximizing the secrecy rate. In this paper, we put forth a novel secure precoding algorithm that jointly and simultaneously optimizes the beams and AN covariance matrix for maximizing the secrecy rate when a transmitter has either perfect or partial channel knowledge of eavesdroppers. To this end, we first establish an approximate secrecy rate in a smooth function. Then, we derive the first-order optimality condition in the form of the nonlinear eigenvalue problem (NEP). We present a computationally efficient algorithm to identify the principal eigenvector of the NEP as a suboptimal solution for secure precoding. Simulations demonstrate that the proposed methods improve secrecy rate significantly compared to the existing methods
Development of the self-modulation instability of a relativistic proton bunch in plasma
No full textSelf-modulation is a beam-plasma instability that is useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not at all, over a fixed plasma length because the amplitude of the initial wakefields decreases. We show cases for which self-modulation does not develop, and we introduce a simple model discussing the conditions for which it would not occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation instability seeded by a relativistic ionization front, such as the future upgrade of the Advanced WAKefield Experiment
Importance of kink energy in calculating the formation energy of a graphene edge
No full textThe formation energy of an arbitrary graphene edge or that of other 2D materials has been estimated as a summation of the armchair (AC) and zigzag (ZZ) edge sites. Such an estimation assumes that each site is independent from its neighboring sites, which is unlikely due to the overlap of electron densities. Here, we show that to accurately calculate the formation energy of graphene edges with various functional groups the energy of the junction between AC and ZZ sites, the "kink energy," is essential. It is significant that the kink energies of graphene edges with different functional groups are all negative, namely, kink formation stabilizes the chiral graphene edges
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No full textSchool of Business Administration (Management Engineering)clos