Non-Hierarchical Architected Materials with Extreme Stiffness and Strength

Stretch-dominated truss and plate microstructures are contenders in the quest for realizing architected materials with extreme stiffness and strength. In the low volume fraction limit, closed-cell isotropic plate microstructures meet theoretical upper bounds on stiffness but have low buckling strength, whereas open-cell truss microstructures have high buckling strength at the cost of significantly reduced stiffness. At finite volume fractions, the picture becomes less clear but both are outperformed by hollow truss lattice and hierarchical microstructures in terms of buckling strength. Despite significant advances in manufacturing methods, hollow and multi-scale hierarchical microstructures are still challenging to build. The question is if there exist realizable microstructures providing stiffness and strength matching or even beating hard-to-realize hollow or hierarchical microstructures? Herein, single-scale non-hierarchical (first order) microstructures that beat the buckling strength of hollow truss lattice structures by a factor of 2.4 and first- and second-order plate microstructures by factors of 5 and 1.4, respectively, are systematically designed, built, and tested. Stiffness of the microstructures is within 40% of theoretical bounds and beats both truss and second order plate microstructures. The microstructures are realized with 3D printing. Experiments validate theoretical predictions and additional insight is provided through numerical modeling of a CT-scanned sample.     

Optimisation de ľefficacité de couplage entre un guide ďonde confiné et une fibre optique monomode par ľintermédiaire ďune lentille boule

Theoretical coupling efficiency between a channel waveguide and a single-mode optical fibre using a ball lens is optimized by varying the parameters of the optical system such as the relative position of the components, the refractive index and the size of the lens. A specific software has been used for the optimization. Numerical calculations have been done under the Gaussian approximation of the fields distributions. The losses due to waveguides misalignments with respect to their ideal position have been evaluated. All these theoretical results are compared with those obtained from buttcoupling.     

Second-Order optical non-linearities of {4-(dimethylamino) stilben z & e 4'-yl} dimesityl borane

Samples of {4-(dimethylamino) stilben Z & E 4'-yl} dimesityl borane (BNS) were synthesised and investigated for their non-linear optical properties. The results show that the quadratic hyperpolarisability of the Z-isomer is smaller than that of the E-isomer, the beta value found for the latter being as high as 60 × 10^?30 esu.     

14C labelling of lignins of normal and bm3 maizes for fermentation studies

[U-¹⁴C] phenylalanine (phe*) and [O¹⁴CH₃] sinapic acid (sin*) were infused into the cut ends of normal and bm3 maizes (anthesis stage) under or above the last node or at mid-internode, with or without the leaf, in light or in darkness. Radioactivity was measured in the organs, and in phenolic constituents of the cell wall and saponified residues of the bases and tops of the apical inter-node. In both maize genotype labelled under the node the radioactivity was distributed more evenly in the organs with sin* than with phe*. Infusion above the node and at mid-internode greatly increased radioactivity in the bases and tops, respectively. Removal of the leaf only slightly increased the radioactivity, mainly in the bases, and no clear-cut effect of darkness was observed. Phe* labelled the phenolic acids and the three lignin units, but the syringyl units of bm3 maize were only slightly labelled. Sin* specifically labelled the syringyl units, which represented the least condensed fraction of lignins. Both the native and labelled lignins were highly alkali soluble. There were differences in lignin biogenesis between the bases and tops, and between normal and bm3 maizes. The newly formed lignins were slightly different from the native lignins but had similar types of heterogeneity, with variations in the internode and between genotypes similar to those in native lignins. Provided due allowance is made for the distinguishing characteristics of newly formed lignins, the [¹⁴C-lignin] cell walls, which are strongly labelled on complementary structures, seem suitable model substrates for fermentation studies.     

Location Management in PCS Networks by Caching Two-Level Forwarding-Pointers

One of the challenging tasks in Personal Communication Services (PCS) is to efficiently maintain the location of PCS subscribers who move from one region to another (hereafter called mobile users). When a mobile user receives a call, the network has to quickly determine its current location. The existing location management scheme suffers from high signaling traffic in locating the mobile users. Two-level forwarding pointer scheme has been proposed from per-user forwarding pointer scheme to reduce the cost of signaling traffic. In this paper, we enhance the two-level forwarding pointer scheme. When a mobile user moves from its current Registered Area (RA), which is served by Mobile Switching Center (MSC), to another RA the local switch that acts as a parent of those two MSCs maintains this movement in its memory (hereafter called cache entry). A cache entry is used to locate rapidly the mobile user instead of querying the Home Location Register (HLR) and waiting for its reply. HLR is centralized in the network and far away from the mobile users so that the signaling traffic crossing it is expensive. Sometimes the cache entry may be failed to reach the mobile user then a two-level forwarding pointers will be created from the corresponding Visitor Location Register (VLR), attached to its MSC, through a correct path to locate the mobile user. Thus, there is a saving in cost of querying the underlying HLR. The analytical results indicate that such proposal efficiently reduces the signaling traffic cost for all values of Call to Mobility Ratio (CMR), this is especially considerable when CMR ≥1, without any increase in the call setup delay. Salah M. Ramadan (samohra@yahoo.com) received the BS and MS degrees from Computers Engineering Department, Al-Azhar University, Cairo, Egypt, in 1995 and 2002, respectively. From 2002, he was a Ph.D. student in Computers Engineering Department at Al-Azhar University and is currently pursuing the Ph.D. degree, where he is a research assistant in the Wireless Networks Branch. His research interests include traffic management in ATM networks, routing protocols, mobility management in PCS networks, and mobile computing. He is currently an instructor in Cisco Academy, Egypt. Ahmed M. El-Sherbini (Sherbini@mcit.gov.eg) received the Ph.D. in Electrical and Communication Engineering, Case Western University, U.S.A. March 1983 and M.Sc. in Communication Engineering, Cairo University, Giza, Egypt, June 1980. (M. Sc. Research Studies at the Ecole Nationale Superieure des Telecommunications (ENST), Paris, France). He is the Director, National Telecommunication Institute – Ministry of Communications and Information Technology, Egypt and Professor of Electrical and Communication Engineering Dept. Faculty of Engineering, Cairo University, Egypt. M. I. Marie received his B.Sc., M.Sc. and Ph.D. in electronic and communication engineering from Cairo University on 1972, 1981, 1985, respectively. Now he is a professor of communications at Computer and System Engineering department Al-Azhar University, Cairo, Egypt. His fields of interest includes digital communication, computer networks and protocols development. M. Zaki (azhar@mailer.scu.eun.eg) is the professor of software engineering, Computer and System Engineering Department, Faculty of Engineering, Al-Azhar University at Cairo. He received his B.Sc. and M.Sc. degrees in electrical engineering from Cairo University in 1968 and 1973 respectively. He received his Ph.D. degrees in computer engineering from Warsaw Technical University, Poland in 1977. His fields of interest include artificial intelligence, soft computing, and distributed system.     

Multihour engineering and traffic routing optimization in hierarchical telephone networks

Classical hierarchical routing in telephone networks is extended to a wider class called out-of-chain routing in such a way that some useful properties of hierarchical routing are retained. This new routing pattern offers more potential paths than the fixed hierarchical one and can be introduced as a dynamic routing where the fixed alternate sequences change at some predetermined instants during the day. The effect of this new routing pattern on the network performances is examined. The main topic of this paper is to present heuristic methods used to optimise such routings in large networks. We show on artificial networks that the throughput of a given network can be significantly improved by suitable routing choices. We demonstrate that the integration of routing changes within a multihour dimensioning process is possible but the lack of realistic data does not permit at this time to quantify the value of routing optimization on real networks.     

Satellite image compression by concurrent representations of wavelet blocks

This paper proposes a complete compression and coding scheme for on-board satellite applications considering the main on-board constraints: low computational power and easy bit rate control. The proposed coding scheme improves the performance of the current Consultative Committee for Space Data Systems (CCSDS) recommendation for a low additional complexity. We consider post-transforms in the wavelet domain, select the best representation for each block of wavelet coefficients, and encode it into an embedded bit stream. After applying a classical wavelet transform of the image, several concurrent representations of blocks of wavelet coefficients are generated. The best representations are then selected according to a rate-distortion criterion. Finally, a specific bit-plane encoder derived from the CCSDS recommendation produces an embedded bit stream ensuring the easy rate control required. In this article, both the post-transforms and the best representation selection have been adapted to the low complexity constraint, and the CCSDS coder has been modified to compress post-transformed representations.     

Hydrogen‐Bonded Organic Semiconductors as Stable Photoelectrocatalysts for Efficient Hydrogen Peroxide Photosynthesis

Research on semiconductor photocatalysts for the conversion of solar energy into chemical fuels has been at the forefront of renewable energy technologies. Water splitting to produce H₂ and CO₂ reduction to hydrocarbons are the two prominent approaches. A lesser‐known process, the conversion of solar energy into the versatile high‐energy product H₂O₂ via reduction of O₂ has been proposed as an alternative concept. Semiconductor photoelectrodes for the direct photosynthesis of H₂O₂ from O₂ have not been applied up to now. Photoelectrocatalytic oxygen reduction to peroxides in aqueous electrolytes by hydrogen‐bonded organic semiconductor is observed photoelectrodes. These materials have been found to be remarkably stable operating in a photoelectrochemical cell converting light into H₂O₂ under constant illumination for at least several days, functioning in a pH range from 1 to 12. This is the first report of a semiconductor photoelectrode for H₂O₂ production, with catalytic performance exceeding prior reports on photocatalysts by one to two orders of magnitude in terms of peroxide yield/catalyst amount/time. The combination of a strongly reducing conduction band energy level with stability in aqueous electrolytes opens new avenues for this widely available materials class in the field of photo(electro) catalysis.