Topology-Guided Path Integral Approach for Stochastic Optimal Control in Cluttered Environment

This paper addresses planning and control of robot motion under uncertainty that is formulated as a continuous-time, continuous-space stochastic optimal control problem, by developing a topology-guided path integral control method. The path integral control framework, which forms the backbone of the proposed method, re-writes the Hamilton-Jacobi-Bellman equation as a statistical inference problem; the resulting inference problem is solved by a sampling procedure that computes the distribution of controlled trajectories around the trajectory by the passive dynamics. For motion control of robots in a highly cluttered environment, however, this sampling can easily be trapped in a local minimum unless the sample size is very large, since the global optimality of local minima depends on the degree of uncertainty. Thus, a homology-embedded sampling-based planner that identifies many (potentially) local-minimum trajectories in different homology classes is developed to aid the sampling process. In combination with a receding-horizon fashion of the optimal control the proposed method produces a dynamically feasible and collision-free motion plans without being trapped in a local minimum. Numerical examples on a synthetic toy problem and on quadrotor control in a complex obstacle field demonstrate the validity of the proposed method.Comment: arXiv admin note: text overlap with arXiv:1510.0534

External strengthening of reinforced concrete beams with bamboo fiber–vinyl ester composite plate

A research has been conducted to investigate the potential application of natural fiber composite (NFC) fabricated by bamboo fiber embedded with vinyl ester resin matrix (BFRCP) in external strengthening of reinforced concrete (RC) beams. In this study, bamboo fiber were obtained from the Forest Research Institute Malaysia (FRIM) which had been treated with 10% of sodium hydroxide (NaOH) for 48 hours. The bamboo fiber has a density of 0.890 g/cm3. In terms of the composite behaviour, the composite plates were tested for physical properties, mechanical properties and thermal properties. The experimental works that carried out in this study were Fourier Transform Infrared Spectroscopy (FTIR), Flexural Test (ASTM D790-03), Tensile Test (ASTM D3039) and Thermogravimetric Analysis (TGA). The BFRCPs were fabricated with different fiber volume ratio (0 %, 10 %, 20 %, 30 %, 40 %) to determine the optimum ratio to be used in strengthening of the reinforced concrete beams. From the composite result, both maximum flexural strength and tensile strength were obtained at the fibre volume ratio of 40 %. The fiber content of composite samples from 10 % to 40 % increased the flexural strength from 104.7 % to 140.9 % compared to the unreinforced neat vinyl ester. Same goes to tensile test, the tensile strength increased from 111.7 % up to 702.7 % with the increases of fiber volume ratio from 10 % to 40 %. The result of FTIR certify that the chemical compositions such as cellulose, hemicellulose and lignin were present in the composite plate and its function were to enhance the adhesion between the fiber and the matrix. The TGA test revealed that the exact thermal decomposition temperature of bamboo fiber - vinyl ester composites was at 320°C. For the structural behaviour, four-point loading tests was carried out to study the behaviour of the RC solid beams as well as RC beams with circular openings. The study shows that the strength of the beam strengthened with bamboo fiber - vinyl ester composite plate increased by 2.0 % in RC solid beam and 77.8 % in RC beam with circular opening when compared to the un-strengthened beams. In the case of cracks, the bamboo fiber-vinyl ester composite plate had diverted the cracks to appear on the edge of the plate for RC solid beam and minimal the propagation of diagonal cracks were traced in RC beam with circular openings. Therefore, it is concluded that the bamboo fiber-vinyl ester composite plate is effectively to be used as an external strengthening material for strengthening of RC beams

A new species of Reticulitermes Holmgren, 1913 (Isoptera: Rhinotermitidae) from the southeastern United States

Reticulitermes nelsonae, a new species of subterranean termite (Isoptera, Rhinotermitidae) is described from Sapelo Island, Georgia, United States of America, with specimens also found in North Carolina and Florida. The adult and soldier castes are described and illustrated to distinguish R. nelsonae from the four described Reticulitermes spp. known to occur in the southeastern United States

Anonymous and Adaptively Secure Revocable IBE with Constant Size Public Parameters

In Identity-Based Encryption (IBE) systems, key revocation is non-trivial. This is because a user's identity is itself a public key. Moreover, the private key corresponding to the identity needs to be obtained from a trusted key authority through an authenticated and secrecy protected channel. So far, there exist only a very small number of revocable IBE (RIBE) schemes that support non-interactive key revocation, in the sense that the user is not required to interact with the key authority or some kind of trusted hardware to renew her private key without changing her public key (or identity). These schemes are either proven to be only selectively secure or have public parameters which grow linearly in a given security parameter. In this paper, we present two constructions of non-interactive RIBE that satisfy all the following three attractive properties: (i) proven to be adaptively secure under the Symmetric External Diffie-Hellman (SXDH) and the Decisional Linear (DLIN) assumptions; (ii) have constant-size public parameters; and (iii) preserve the anonymity of ciphertexts---a property that has not yet been achieved in all the current schemes