The Persistence of Human Norovirus Surrogate in Leafy Greens Production System

Since mostly consumed raw, foodborne pathogen contamination of leafy greens has led to a large number of foodborne disease outbreaks and illnesses each year in the United States. Human noroviruses (hNoV) are the most common viral pathogen transmitted by leafy greens. In this dissertation, the persistence of the hNoV surrogate Tulane virus (TV) on pre-harvest lettuce and microgreens was investigated. Lettuces are the most studied leafy green model, while previous hNoV research has mainly focused on the post-harvest stage of production. Here, pre-harvest hydroponically grown lettuce were used to determine TV persistence on leafy greens. After inoculation on leaves at 40 days age, TV reached over 4 log PFU/leaf reductions over the subsequent 4 days of observation. On day 45, TV was still detected on leaves, indicating that the pre-harvest viral contamination may last to post-harvest stages including consumption. Meanwhile, microgreens are a group of novel salad greens whose color, texture, flavor and nutritional values have attracted more consumers in recent years. Currently, the understanding of viral risks in microgreen cultivation systems is limited. This dissertation used sunflower (SF) and pea shoots (PS) as model microgreens to study the virus transmission from two types of soil-free cultivation matrix (SFCM)—biostrate and peat. Without the presence of plants, TV survived over 10 days in SFCM with only 2.08 and 1.76 log PFU/tray reduction in biostrate and peat, respectively. However, when TV were inoculated in SFCM on day 0 before sowing seeds, no virus was detected in harvested microgreen edible tissues on day 10, regardless of the plant variety and SFCM type. Notably, there were significantly lower virus concentrations in the planted SFCM compared to the unplanted control areas. Later, the virus transfer from SFCM to microgreen was further investigated when inoculated with TV at day 7 of plant age. On day 10, there were minor reductions in virus concentrations in SFCM, but in microgreen edible tissue, TV was still not detected. In addition, another study was carried out to characterize virus persistence on microgreen leaves surfaces. A significantly higher virus persistence was observed on PS than SF. From plant age of 7 to 10 days TV reduced on average over 4.5 log PFU/plant (n=2) on SF, while the reduction was only 2.52 on average (n=2) for PS, indicating a plant variety-dependent virus persistence on microgreens. The findings in this dissertation provides insights on virus transmission during pre-harvest production stage of two types of leafy greens—head lettuce and microgreens. This information will help to develop more effective virus prevention and control strategies within leafy green production systems

The characteristics of cycle-nodes-ratio and its application to network classification

Cycles, which can be found in many different kinds of networks, make the problems more intractable, especially when dealing with dynamical processes on networks. On the contrary, tree networks in which no cycle exists, are simplifications and usually allow for analyticity. There lacks a quantity, however, to tell the ratio of cycles which determines the extent of network being close to tree networks. Therefore we introduce the term Cycle Nodes Ratio (CNR) to describe the ratio of number of nodes belonging to cycles to the number of total nodes, and provide an algorithm to calculate CNR. CNR is studied in both network models and real networks. The CNR remains unchanged in different sized Erd\"os R\'enyi (ER) networks with the same average degree, and increases with the average degree, which yields a critical turning point. The approximate analytical solutions of CNR in ER networks are given, which fits the simulations well. Furthermore, the difference between CNR and two-core ratio (TCR) is analyzed. The critical phenomenon is explored by analysing the giant component of networks. We compare the CNR in network models and real networks, and find the latter is generally smaller. Combining the coarse-graining method can distinguish the CNR structure of networks with high average degree. The CNR is also applied to four different kinds of transportation networks and fungal networks, which give rise to different zones of effect. It is interesting to see that CNR is very useful in network recognition of machine learning.Comment: 27 pages,16 figures,3 table

Malentendu et implicite : une nouvelle interprétation du film Balzac et la petite tailleuse chinoise

Le malentendu du public chinois quant au roman de Dai Sijie Balzac et la petite tailleuse chinoise (2000) et à son adaptation filmique homonyme (2002) n’est pas neuf. Dai développe dans le film une série des tensions dans les relations entre les jeunes instruits et le monde rural qui ont pour fonction d’incarner de manière implicite ses points de vue vis-à-vis du monde rural et de l’idéologie du mouvement d’envoi des jeunes instruits à la campagne, où coexistent la critique et la nostalgie. Les relations entre les jeunes instruits et le monde rural seront interprétées selon le « carré sémiotique » d’Algirdas-Julien Greimas, qui constitue une voie d’approche pertinente. Dai Sijie met également l’accent de façon implicite sur la liberté individuelle et les valeurs individuelles à travers la construction du personnage de la petite tailleuse. Cet article est consacré à l’interprétation des implicites mis en jeu dans le film qui rend intelligible cette histoire du passé et propose une vision de la société chinoise de l’époque.The misconception of the Chinese public on the novel by Dai Sijie Balzac and the Little Chinese Seamstress (2000) and its film adaptation (2002) has been around for many years. In the film, Dai plots a series of tensions in the relations between the educated youth and the rural world during the Down to the Countryside Movement to implicitly depict his views on the rural world and on the ideology of the Maoist movement, involving both criticism and nostalgia of this experience. The relations between the educated youth and the rural world will be analyzed by the « Semiotic Square » of Algirdas Julien Greimas, which seems a relevant approach. By the construction of the character of the little seamstress, Dai Sijie reveals implicitly also his emphasis on the individual freedom and individual values. This article is devoted to the interpretation of implicates in the movie which helps us to understand the history and offers us an angle to observe the Chinese society during that period

Cinéma : lieu de la construction de la mémoire collective

Le cinéma est considéré comme un lieu privilégié de la mémoire collective, dont la fonction consiste à transmettre les souvenirs du passé à des contemporains et des générations futures et à permettre l’affirmation d’une identité collective. Cet article sera consacré, en mettant en relation mémoire et identité, à aborder la construction de la mémoire collective de la Révolution culturelle dans le cinéma chinois de la Cinquième Génération des années 1980. La Cinquième Génération désigne un grou..

Dosage compensation on the active X chromosome minimizes transcriptional noise of X-linked genes in mammals

Comparison of gene expression variation in autosomal and X-linked genes reveals that high transcriptional noise is not a necessary consequence of haploid expression