Analysis of composite laminates with transverse cracks

The analysis of the behaviour of composite laminates with general balanced lay-up sequences and containing distributed transverse cracks is discussed and demonstrated in this paper. It is shown that a constitutive model of damage for composites, which has been successfully used to analyse the effects of uniformly distributed transverse cracks in cross-ply laminates, can be readily extended to the analysis of uniformly distributed transverse cracks in more general symmetric laminates. The further extension of the theory to non-uniformly distributed damage can be achieved by finite element analysis. It is shown that the finite element implementation of the theory is particularly simple since the contribution of the damage to the overall behaviour can be incorporated into the force vectors.     

Breaking substitution cyphers using stochastic automata

Let Λ be a finite plaintext alphabet and V be a cypher alphabet with the same cardinality as Λ. In all one-to-one substitution cyphers, there exists the property that each element in V maps onto exactly one element in Λ and vice versa. This mapping of V onto Λ is represented by a function T*, which maps any v∈V onto some λ∈Λ (i.e., T*(v)=λ). The problem of learning the mapping of T* (or its inverse (T *)^-1) by processing a sequence of cypher text is discussed. The fastest reported method to achieve this is a relaxation scheme that utilizes the statistical information contained in the unigrams and trigrams of the plaintext language. A new learning automaton solution to the problem called the cypher learning automaton (CLA) is given. The proposed scheme is fast, and the advantages of the scheme in terms of time and space requirements over the relaxation method have been listed. Simulation results comparing both cypher-breaking techniques are presented     

Scan performance of infinite arrays of microstrip patch elementsloaded with varactor diodes

The analysis and scanning characteristics of an infinite array of rectangular microstrip patches each loaded with a varactor diode is presented. The analysis is based on full-wave moment method theory and uses attachment modes to accurately model the current through the feed and the diode. The effect of the biased varactor diode on the scan performance is presented, and it is shown that the impedance mismatch caused by a scan blindness can be eliminated. Other characteristics are also given such as: the active element gain, the efficiency of each loaded microstrip element, and the level of cross polarization generated by the loading of the patch. The effect of the diode biasing level as well as the position of the diode on each radiating element on these scan characteristics is also considered     

A single-chip 12.7 Mchips/s digital IF BPSK direct sequencespread-spectrum transceiver in 1.2 μm CMOS

This paper describes a fully integrated digital-spread spectrum transceiver chip fabricated through MOSIS in 1.2 μm CMOS. It includes a baseband spread spectrum transmitter and a coherent intermediate frequency (IF) receiver consisting of a Costas loop, an acquisition loop for the pseudo-noise (PN) sequence, and a clock recovery loop with a 406.4 MHz onchip numerically controlled oscillator (NCO). The transceiver is capable of operating at a maximum IF sampling rate of 50.8 MS/s and a maximum chip rate of 12.7 R Mchips/s (Mcps) with selectable data rates of 100, 200, 400, and 800 kbps. At the maximum operating speed of 50.8 R MS/s, it dissipates 1.1 W. In an additive white Gaussian noise channel the IF receiver achieves a receiver output SNR within 1 dB of theory and can acquire code with a wide range of input SNR from -17 dB to over 30 dB. The transceiver chip has been interfaced to an RF up/down converter to demonstrate a wireless voice/data/video link operating in the 902-928 MHz band     

A channel model for characterization of the error data recoveredfrom compact discs

The data recovered from compact discs are contaminated with errors that exhibit a bursty behavior. A channel model is developed to characterize the error bursts and good-data gaps that occur in actual data recovered from compact discs. The probability of having m erroneous symbols in a data block of length n symbols is calculated using the channel model. This probability can be used to evaluate the performance of the error-correction code (ECC) used in the compact disc system     

Influence of the purity of the starting materials on the recording of dynamic holograms in Bi12TiO20 crystals

The parameters of Bi₁₂TiO₂₀ crystals grown with bismuth oxide of different degrees of purity were measured by a holographic recording technique in an external ac electric field and were compared with a crystal specially doped with chromium. Various crystal parameters such as the diffusion length of the photoexcited carriers and the Debye screening length were determined. It was found that the absorption spectrum of the material and the holographic recording efficiency were strongly influenced by light chromium doping and by insufficient purity of the starting mixture. Pis’ma Zh. Tekh. Fiz. 23, 27–32 (March 12, 1997)     

DIVERSITY OF PERCEPTIONS OF MEAT TENDERNESS AND JUICINESS BY CONSUMERS: A TIME-INTENSITY STUDY

Seven judges, untrained in sensory assessment, were trained in the use of Time Intensity (TI) and asked to monitor the tenderness and juiciness of a range of cooked beef and pork samples. The subjects were given no definitions concerning sensory cues to monitor in their assessments, nor did they confer with each other. The shapes of the TI curves they recorded for tenderness and juiciness differed between individuals, although there were similarities in the curve shapes for the 2 attributes for each individual. Correlations between the intensity parameters of the curves (maximum intensity and area under curve) and the chewing time were not significant for the subjects as a group for tenderness, although significant correlations were found for some of the subjects when examined individually. The results indicate that subjects differ in their concepts of sensory tenderness and juiciness, and that perceived tenderness does not correlate with chewing time for all subjects. In more general terms the study supports the use of TI assessments for interpreting individual differences in sensory perceptions.     

NEUTRAL AND ALKALINE MUSCLE PROTEASES OF MARINE FISH AND INVERTEBRATES A REVIEW

Muscle proteases active at neutral and alkaline pH's include calcium-activated neutral proteases, heat-activated thiol proteases, serine proteases, and metallo-proteases. They participate to different extents in postmortem degradation of fish muscle myofibrillar and scaffold proteins. Their activity in fish, the presence of endogenous activators and inhibitors, pH, and temperature. Recent studies indicate that neutral and alkaline proteases have more impact on the postmortem deterioration in quality of fish muscles than the cathepsins active at acid pH. Significant quality losses are caused by enzymatic collagen degradation in raw tissues and by heat-activated enzymes in fish gels.     

Antibacterial activity of sourdough lactic acid bacteria: isolation of a bacteriocin-like inhibitory substance fromLactobacillus sanfranciscoC57

A total of 232 strains from nine species ofLactobacillusisolated from sourdoughs were screened for antagonistic activity against sourdough-related micro-organisms. Seventy-seven strains on agar medium and 52 in culture supernatants, re-adjusted to pH 6.5 and catalase-treated, showed antagonistic activity. The activities were species and strain specific showing different spectra of inhibition against sourdough lactobacilli. All the strains were inhibitory toBacillus subtilisbut not against sourdough yeasts and moulds.Lactobacillus sanfranciscoandLactobacillus plantarumstrains had the largest inhibitory spectrum. All the antimicrobial compounds produced from strains of different species contained a protein moiety and were differently sensitive to different proteinases. A bacteriocin-like inhibitory substance, which was heat-stable (100°C for 20 min), insensitive to lipase and α-amylase, of a protein nature, with an inhibitory spectrum centred about lactic acid bacteria and a bactericidal or bacteriolytic mode of action was isolated fromLb. sanfranciscoC57. The antimicrobial substance also inhibitedListeria monocytogenes, and was mainly produced in the stationary phase of growth and at pH 4.0–5.0.Lb. sanfranciscoC57 variants, which did not contain the nativec. 17 kbp plasmid, maintained their antagonistic activity, therefore, the gene encoding for the bacteriocin-like inhibitory substance fromLb. sanfranciscoC57 is chromosomally located.