Structural search spaces and genetic operators

In a previous paper (Rowe et al., 2002), aspects of the theory of genetic algorithms were generalised to the case where the search space, omega, had an arbitrary group action defined on it. Conditions under which genetic operators respect certain subsets of omega were identified, leading to a generalisation of the term schema. In this paper, search space groups with more detailed structure are examined. We define the class of structural crossover operators that respect certain schemata in these groups, which leads to a generalised schema theorem. Recent results concerning the Fourier (or Walsh) transform are generalised. In particular, it is shown that the matrix group representing omega can be simultaneously diagonalised if and only if omega is Abelian. Some results concerning structural crossover and mutation are given for this case.     

Ultrafast exciton relaxation in the B850 antenna complex of Rhodobacter sphaeroides

Spectral changes were measured with femtosecond resolution following low-intensity, broad-band excitation of the peripheral antenna complex of the purple photosynthetic bacterium Rhodobacter sphaeroides. Absorption anisotropy decays also were measured. We identified a 35-fs relaxation of the absorption and emission spectra of the excited state, as well as a 20-fs anisotropy decay. We interpret these results as interlevel relaxation and dephasing, respectively, of extensively delocalized exciton states of the circular bacteriochlorophyll aggregate.     

Analysis of information leakage from encrypted Skype conversations

Voice over IP (VoIP) has experienced a tremendous growth over the last few years and is now widely used among the population and for business purposes. The security of such VoIP systems is often assumed, creating a false sense of privacy. This paper investigates in detail the leakage of information from Skype, a widely used and protected VoIP application. Experiments have shown that isolated phonemes can be classified and given sentences identified. By using the dynamic time warping (DTW) algorithm, frequently used in speech processing, an accuracy of 60% can be reached. The results can be further improved by choosing specific training data and reach an accuracy of 83% under specific conditions. The initial results being speaker dependent, an approach involving the Kalman filter is proposed to extract the kernel of all training signals.     

Assessment of Mung Bean Quality Through Single Kernel Characterization

With significant interest in incorporating beans, lentils, and pulses as nutrient-rich healthy food sources into our diets, a reliable technique for their rapid and accurate quality evaluation is needed. The method of single kernel characterization to determine the physical properties (i.e., diameter, weight, moisture content, and hardness) of mung beans was assessed in this study. Two mung bean varieties were characterized using the single kernel characterization technique and the results were compared to traditional methods. It was observed that predicted bean weights were accurate to known laboratory measurements (R = 0.98, n = 200). Individual bean characterization was moderately (R = 0.58–0.7, n = 100) correlated in regard to the true diameter of mung beans. An evaluation on moisture content was performed after tempering the two bean varieties to four moisture levels and a good correlation was obtained with the oven drying method (R = 0.92, n = 24). Hardness values obtained by single kernel characterization were moderately correlated to maximum forces measured using an Instron universal testing system. However, a common relationship was observed between mung bean hardness and moisture content when using both methods. Compared to visual inspection, automated characterization of single beans is a superior technique to measure the geometrical and mechanical properties of mung beans in an industrial setup where high throughput is paramount.     

Novel approaches for chemical and microbiological shelf life extension of cereal crops

Abstract

Economic losses due to post-harvest fungal spoilage and mycotoxin contamination of cereal crops is a frequently encountered issue. Typically, chemical preservatives are used to reduce the initial microbial load and the environmental conditions during storage are controlled to prevent microbial growth. However, in recent years the consumers’ desire for more naturally produced foods containing less chemical preservatives has grown increasingly stronger. This article reviews the latest advances in terms of novel approaches for chemical decontamination, namely application cold atmospheric pressure plasma and electrolyzed water, and their suitability for preservation of stored cereal crops. In addition, the alternative use of bio-preservatives, such as starter cultures or purified antimicrobial compounds, to prevent the growth of spoilage organisms or remove in-field accumulated mycotoxins is evaluated. All treatments assessed here show potential for inhibition of microbial spoilage. However, each method encounters draw-backs, making industrial application difficult. Even under optimized processing conditions, it is unlikely that one single treatment can reduce the natural microbial load sufficiently. It is evident that future research needs to examine the combined application of several treatments to exploit their synergistic properties. This would enable sufficient reduction in the microbial load and ensure microbiological safety of cereal crops during long-term storage.     

Mysterious outbreaks of gastrointestinal illness associated with burritos supplied through school lunch programs

From October 1997 through March 1998, three outbreaks of gastrointestinal illness among school children were linked to company A burritos. In September 1998, a similar outbreak occurred in three North Dakota schools following lunches that included company B burritos. We conducted an investigation to determine the source of the North Dakota outbreak, identify other similar outbreaks, characterize the illness, and gather evidence about the cause. The investigation included epidemiologic analyses, environmental investigation, and laboratory analyses. In North Dakota, a case was defined as nausea, headache, abdominal cramps, vomiting, or diarrhea after lunch on 16 September 1998. Case definitions varied in the other states. In North Dakota, 504 students and staff met the case definition; predominant symptoms were nausea (72%), headache (68%), abdominal cramps (54%), vomiting (24%), and diarrhea (16%). The median incubation period was 35 min and median duration of illness was 6 h. Eating burritos was significantly associated with illness (odds ratio, 2.6; 95% confidence interval, 1.6 to 4.2). We identified 16 outbreaks that occurred in seven states from October 1997 through October 1998, affecting more than 1,900 people who ate burritos from two unrelated companies. All tortillas were made with wheat flour, but the fillings differed, suggesting that tortillas contained the etiologic agent. Results of plant inspections, tracebacks, and laboratory investigations were unrevealing. More than two million pounds of burritos were recalled or held from distribution. The short incubation period, symptoms, and laboratory data suggest that these outbreaks were caused by an undetected toxin or an agent not previously associated with this clinical syndrome. Mass psychogenic illness is an unlikely explanation because of the large number of sites where outbreaks occurred over a short period, the similarity of symptoms, the common food item, the lack of publicity, and the link to only two companies. A network of laboratories that can rapidly identify known and screen for unknown agents in food is a critical part of protecting the food supply against natural and intentional contamination.