High Clear Bell of Morning by Ann Eriksson

Review of Ann Eriksson\u27s High Clear Bell of Morning

Phenylethynyl Terminated Imide (PETI) Composites Made by High Temperature VARTM

Fabrication of composite structures using vacuum assisted resin transfer molding (VARTM) is generally more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications, a void fraction of <2% is desired. In the current study, two PETI resins, LARC. PETI-330 and LARC. PETI-8 have been used to fabricate test specimens using HT-VARTM. The resins were infused into carbon fiber preforms at 260 C and cured between 316 and 371 C. Photomicrographs of the panels were taken and void contents were determined by acid digestion. Modifications to the thermal cycle used in the laminate fabrication have reduced the void content significantly; typically .3% for carbon fiber biaxially woven fabric and less than 2% for carbon fiber uniaxial fabric. Mechanical properties (short beam shear and flexure) of the panels were determined at both room and elevated temperatures. The results of this work are presented herein. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States

A VLSI synthesis of a Reed-Solomon processor for digital communication systems

The Reed-Solomon codes have been widely used in digital communication systems such as computer networks, satellites, VCRs, mobile communications and high- definition television (HDTV), in order to protect digital data against erasures, random and burst errors during transmission. Since the encoding and decoding algorithms for such codes are computationally intensive, special purpose hardware implementations are often required to meet the real time requirements. -- One motivation for this thesis is to investigate and introduce reconfigurable Galois field arithmetic structures which exploit the symmetric properties of available architectures. Another is to design and implement an RS encoder/decoder ASIC which can support a wide family of RS codes. -- An m-programmable Galois field multiplier which uses the standard basis representation of the elements is first introduced. It is then demonstrated that the exponentiator can be used to implement a fast inverter which outperforms the available inverters in GF(2m). Using these basic structures, an ASIC design and synthesis of a reconfigurable Reed-Solomon encoder/decoder processor which implements a large family of RS codes is proposed. The design is parameterized in terms of the block length n, Galois field symbol size m, and error correction capability t for the various RS codes. The design has been captured using the VHDL hardware description language and mapped onto CMOS standard cells available in the 0.8-µm BiCMOS design kits for Cadence and Synopsys tools. The experimental chip contains 218,206 logic gates and supports values of the Galois field symbol size m = 3,4,5,6,7,8 and error correction capability t = 1,2,3, ..., 16. Thus, the block length n is variable from 7 to 255. Error correction t and Galois field symbol size m are pin-selectable. -- Since low design complexity and high throughput are desired in the VLSI chip, the algebraic decoding technique has been investigated instead of the time or transform domain. The encoder uses a self-reciprocal generator polynomial which structures the codewords in a systematic form. At the beginning of the decoding process, received words are initially stored in the first-in-first-out (FIFO) buffer as they enter the syndrome module. The Berlekemp-Massey algorithm is used to determine both the error locator and error evaluator polynomials. The Chien Search and Forney's algorithms operate sequentially to solve for the error locations and error values respectively. The error values are exclusive or-ed with the buffered messages in order to correct the errors, as the processed data leave the chip

Theoretical foundations of thesaurus construction

The theoretical foundations of recent work on automatic and semiautomatic thesaurus construction are briefly but critically reviewed, and limitations of current methods of automatic construction of thesaurus are pointed out. Need for a deeper study of the theoretical foundations of thesaurus construction is emphasized and a line of approach to it is suggested

Analysis of large disjoint antenna arrays by localised solutions

Thesis (PhD)--Stellenbosch University, 2023.ENGLISH ABSTRACT: The method of moments (MoM) is well suited to the full-wave electromagnetic analysis of antenna arrays. This is especially true for perfect electrically conducting (PEC) antennas, when an electric field integral equation (EFIE) formulation with Rao-Wilton-Glisson (RWG) basis functions is the typical approach. This yields fully populated matrices with the solution cost growing rapidly with array size N, as O(N3) and O(N2) for the runtime and storage respectively, when a standard direct solver is employed. This work is concerned with the efficient an d re liable EF IE RWG MoM an alysis of large antenna arrays consisting of identical disjoint PEC elements. Examples of such arrays are encountered within the international Square Kilometre Array (SKA) project, which motivates this work. The new formulations proposed are based on a MoM domain decomposition technique known as the domain Green’s function method (DGFM), which is a perturbation technique developed for analysing large disjoint antenna arrays. It was originally formulated in the context of printed substrate antennas, but has since been applied more broadly. In its existing form, the DGFM is limited to fairly sparse arrays where mutual coupling effects are less pronounced. Three DGFM-based extensions are proposed, in order for the method to be applicable to dense and very large antenna arrays. The first i s t o i ntroduce l arger l ocal solution domains in combination with an iterative scheme, to enable solutions to a pre-specified accuracy. The second is a physics-based row expansion direct-coupling technique, which is a necessary variation on the standard DGFM approach to far couplings, in order to maintain efficiency wh en de aling wi th mu ltiple si ngle-element ex citations fo r embedded element pattern calculations. Thirdly, a hybrid, single-level adaptive cross approximation (ACA) matrix compression scheme is proposed, which is tailored to the acceleration of the DGFM and is applicable to both new formulations. Results for antenna arrays relevant to the SKA low-frequency band show efficient and reliable performance.AFRIKAANS OPSOMMING: Die moment metode (MoM) is goed geaard vir vol-golf elektromagnetiese analise van antenna samestellings. Dis veral die geval vir perfekte geleier (PG) antennas, in welke geval ’n elektriese veld integraalvergelyking (EVIV) formulering met Rao-Wilton-Glisson (RWG) basis funksies, die tipiese benadering is. Dit lei tot vol matrikse, met oplossingskoste wat vinnig groei met betrekking tot samestellingsgrootte N, as O(N3) en O(N2) vir die looptyd en stoorspasie, onderskeidelik, wanneer ’n standaard direkte oplosser gebruik word. Hierdie werk is gemoeid met die doeltreffende en b etroubare EVIV RWG MoM analise van groot antenna samestellings, wat bestaan uit identiese onverbinde PG elemente. Voorbeelde van sulke samestellings kom voor met die internasionale “Square Kilometre Array (SKA)” projek, wat dien as motivering vir hierdie werk. Die voorgestelde nuwe formulerings is gebaseer op ’n MoM domein-dekomposisie tegniek wat bekendstaan as die domein Green funksie metode (DGFM), wat ’n perturbasie tegniek is, wat ontwikkel is vir die analise van groot onverbinde antenna samestellings. Dit is oorspronklik geformuleer in die gedrukte substraat antenna konteks, maar is latervantyd meer uiteenlopend aangewend. Die DGFM in bestaande vorm, is beperk tot betreklike yl samestellings, waar die invloed van wedersydse koppeling beperk is. Drie DGFM-gebaseerde uitbreidings word voorgestel, om sodoende die metode toepaslik te maak vir digte en baie groot amestellings. Die eerste is om vergrote plaaslike gebiede in te voer, asook uitbreiding na ’n iteratiewe skema, om sodoende plossingsakkuraatheid te kan beheer. Die tweede is ’n fisiese, r y-uitbreiding gebaseerde, direkte-koppelingstegniek, wat ’n vereiste aanpassing tot die standaard DGFM se vêrkoppelingsvoorstelling is, om sodoende doeltreffendheid te handhaaf vir analise van enkelelement aandrywings vir ongewingsgewyse element patroon berekeninge. Derdens word ’n hibriede, enkel-vlak aanpassingsvaardige kruis-benadering (AKB) matriks saampersingskema voorgestel, wat aangepas is tot die versnelling van die DGFM en toepaslik is tot albei nuwe formulerings. Antenna samestelling resultate wat relevant is tot die SKA laefrekwensie band, toon doeltreffende en betroubare werkverrigting.Doctorat

The Conditional Correlation Attack: A Practical Attack on Bluetooth Encryption

Abstract. Motivated by the security of the nonlinear filter generator, the concept of correlation was previously extended to the conditional correlation, that studied the linear correlation of the inputs conditioned on a given (short) output pattern of some specific nonlinear function. Based on the conditional correlations, conditional correlation attacks were shown to be successful and efficient against the nonlinear filter generator. In this paper, we further generalize the concept of conditional correlations by assigning it with a different meaning, i.e. the correlation of the output of an arbitrary function conditioned on the unknown (partial) input which is uniformly distributed. Based on this generalized conditional correlation, a general statistical model is studied for dedicated key-recovery distinguishers. It is shown that the generalized conditional correlation is no smaller than the unconditional correlation. Consequently, our distinguisher improves on the traditional one (in the worst case it degrades into the traditional one). In particular, the distinguisher may be successful even if no ordinary correlation exists. As an application, a conditional correlation attack is developed and optimized against Bluetooth two-level E0. The attack is based on a recently detected flaw in the resynchronization of E0, as well as the investigation of conditional correlations in the Finite State Machine (FSM) governing the keystream output of E0. Our best attack finds the original encryption key for two-level E0 using the first 24 bits of 2 23.8 frames and with 2 38 computations. This is clearly the fastest and only practical known-plaintext attack on Bluetooth encryption compared with all existing attacks. Current experiments confirm our analysis

Faster Correlation Attack on Bluetooth Keystream Generator E0

Abstract. We study both distinguishing and key-recovery attacks against E0, the keystream generator used in Bluetooth by means of correlation. First, a powerful computation method of correlations is formulated by a recursive expression, which makes it easier to calculate correlations of the finite state machine output sequences up to 26 bits for E0 and allows us to verify the two known correlations to be the largest for the first time. Second, we apply the concept of convolution to the analysis of the distinguisher based on all correlations, and propose an efficient distinguisher due to the linear dependency of the largest correlations. Last, we propose a novel maximum likelihood decoding algorithm based on fast Walsh transform to recover the closest codeword for any linear code of dimension L and length n. It requires time O(n + L · 2 L) and memory min(n, 2 L). This can speed up many attacks such as fast correlation attacks. We apply it to E0, and our best key-recovery attack works in 2 39 time given 2 39 consecutive bits after O(2 37) precomputation. This is the best known attack against E0 so far.

Simulated and experimental results of dual resolution sensor based planning for hyper-redundant manipulators

This paper presents a dual-resolution local sensor based planning method for hyper-redundant robot mechanisms. Two classes of sensor feedback control methods, working at different sampling rates and different spatial resolutions, are considered: full shape modification (FSM), and partial shape modification (PSM). FSM and PSM cooperate to utilize a mechanism's hyper-redundancy to enable both local obstacle avoidance and end-effector placement in real-time. These methods have been implemented on a thirty degree of freedom hyper-redundant manipulator which has 11 ultrasonic distance measurement sensors and 20 infrared proximity sensors. The implementation of these algorithms in a dual CPU real-time control computer, an innovative sensor bus architecture, and a novel graphical control interface are described. Experimental results obtained using this test bed show the efficacy of the proposed method