Littérature scientifique sur le sujet « Random polymers »

Using the observation that configurations of N polymers with hard core interactions on a closed random surface correspond to random surfaces with N boundary components, we calculate the free energy of a gas of polymers interacting with fully quantized two-dimensioanal gravity. We derive the equation of state for the polymer gas and find that all the virial coefficients beyond the second one vanish identically.

We discuss some of the problems appearing in the Mean Field Theory of Random Heteropolymers. We show how an hypothesis of replica symmetry maps this problem onto a directed polymer in a random potential, and explain how this hypothesis can be checked through numerical simulations on directed polymers. The approach of Shaknovitch and Gutin is also reviewed in light of these findings.

Sequential regularity control on the n-type conjugated polymers was investigated in this work. The sequentially random polymer produced a near-amorphous structure and a strain-insensitive charge transport performance.

After a brief introduction to the problem of directed polymers in a random medium, several aspects of the problem are addressed in more detail. It is possible to show that, in high enough dimension and above a certain temperature, a phase exists in which the free energy is given by the annealed free energy, with probability one. The proof of this statement is extended to obtain upper and lower bounds on the temperature transition between this phase and a low temperature phase and hence prove the existence of the phase transition. The mean field solution is reviewed and a method of obtaining high dimension expansions around it is presented. The method uses the idea of 'n-tree approximations' as a systematic way of including the correlations present in finite dimensions. Using this approach 1/d expansions are obtained for the free energy, transition temperature, transverse fluctuations and overlaps. The results are consistent with the existence of a finite upper critical dimension above which the behaviour is of a mean field nature. Directed polymers are then considered on disordered hierarchical lattices. On these lattices the problem reduces to the study of the stable laws that occur when one combines random variables in a nonlinear way. Recursion relations for various properties of the system are obtained which are studied using numerical and analytical techniques. It is possible to obtain a perturbative expansion for the free energy, overlaps and non-integer moments of the partition function. Finally, a generalisation of the standard directed polymer problem is considered, in which one allows the walks to contribute positive and negative weights to the partition sum. The solution of the mean field limit of this problem is obtained indirectly, by using the relationship between the mean field directed polymer problem, the random energy model (REM) and the generalised random energy model (GREM). Numerical simultions are presented which give good confirmation of the analytical predictions. It is observed that in solving this generalised polymer problem one has also obtained a formula for the largest Lyapounov exponent of a product of large, sparse random matrices.

Thesis (PhD)--Stellenbosch University, 2002.
ENGLISH ABSTRACT: Most polypropylene copolymers commercially available have ethylene, and to a lesser degree t-butene as comonomers. Commercially available higher a-olefins, mostly even-numbered, are seldom used for the production of pp copolymers, probably due to cost. Sasol's Fischer- Tropsch oil-from-coal process produces many linear and branched a-olefins as by-products that can be isolated and purified by a relatively cheap refinery process, including the odd-numbered 1- pentene olefin. Sasol's gas-phase Novolen pp plant at Secunda, South Africa is ideally suited to the manufacture of high quality pp random copolymers. As such an opportunity was identified to research the use of higher a-olefins, and more specifically 1-pentene, in the gas-phase production of pp random copolymers. Different methods to produce propylene / 1-pentene random copolymers in the slurry phase on bench-scale were investigated. A procedure was subsequently developed to produce propylene / 1-pentene random copolymers in the gas-phase in 10 litre autoclaves. It was found that commercially available fourth generation supported catalysts successfully incorporated the bulky 1-pentene monomer into the propylene backbone, both during slurry and gas-phase polymerisations. Software modelling was employed to determine the dew points of selected gas mixtures typically found during the production of pp random copolymers. The results indicated that typical process conditions could be employed during the gas-phase polymerisation of propylene and 1-pentene without the risk of condensation taking place inside the reactor. Propylene / 1-pentene random copolymers were subsequently successfully produced on the 800 litre BASF pilot plant in Germany followed by the first commercial production of the copolymer on Sasol's 50m3 Novolen gas-phase plant at Secunda. Using commercially available software the impact of introducing 1-pentene as comonomer during the production of random copolymers on the condenser cooling capacity was evaluated. Feasible and safe plant operating conditions were established for the production of propylene / 1-pentene random copolymers. The relationship between operating pressure and powder morphology was investigated to optimise process conditions. Operating at higher pressure in the gas-phase increases the monomer concentration in the reactor and as such improves the space/time/yield ratio of the 50m3 reactors. It was shown that higher operating pressures could be employed through the introduction of 1-pentene as comonomer during the production of PP random copolymer. The dramatic increase in catalyst productivity observed during the 800 litre pilot plant trials, up to a comonomer ratio of about 5%, supported the results obtained from a kinetic study carried out in bench-scale autoclaves. A comprehensive study was undertaken to compare the rheological, thermal, crystallisation, physical and mechanical properties of propylene / 1-pentene random copolymers with those of commercially available pp random copolymers. A series of propylene homo- and random copolymers with 1-pentene and ethylene as comonomers respectively, was prepared. NMR and IR techniques were developed to facilitate the determination of copolymer composition for the new family of 1-pentene random copolymers. The effect of comonomer content, molecular weight and temperature on the properties of the series of polymers was investigated. The propylene / 1-pentene random copolymers show unique rheological behaviour associated with the short propyl branches in the polymer backbone with minimum zero shear viscosity at about 2% 1-pentene content. The effect of molecular structure changes with comonomer content were analysed by the calculation of square average end-toend distance, packing length, tube diameter, molecular mass between entanglements and critical molecular mass. The viscosity of the 1-pentene random copolymers shows higher shear and temperature sensitivity compared to propylene homo- and ethylene random copolymers. The thermodynamic melting point of the propylene / 1-pentene random copolymers showed a significant decrease with increasing comonomer content in the 0 to 5% range. A wider melting range and higher peak melting point depression rate was observed compared to ethylene random copolymers at similar and increasing comonomer content measured on a weight % basis. It was found that the crystal structure of the propylene / 1-pentene random copolymers contains both the Q- and the y-modifications with the ratio of the respective crystal forms a function of both comonomer content and crystallisation temperature. The glass temperature decreased slightly with increasing comonomer (1-pentene) content. It is proposed that the short branch (propyl) "defects" in the polymer backbone are .incorporated into the crystal lattice resulting in increased rate of melting point depression with increasing (wt%) comonomer content compared to other random copolymers while maintaining relative high stiffness. The propylene / 1-pentene random copolymers exhibit the lowest haze values compared to all commercially available pp random copolymers at corresponding levels of comonomer content on a wt% basis. The stiffness to haze ratio of propylene / 1-pentene random copolymers are unique for all the members of the pp family. An inverse relationship between comonomer content and the measured tensile yield strength and modulus is observed. Application studies conducted on the propylene / 1-pentene random copolymers highlighted several interesting characteristics. Films produced from these copolymers exhibited very low haze and xylene soluble values while maintaining mechanical integrity. In the BOPP application the combination of processability and premium film properties presents a unique opportunity for the family of propylene / 1-pentene random copolymers. Blow moulding and injection moulding trials highlighted several advantages of product properties manufactured with propylene / 1-pentene random copolymers if compared to other commercially available random copolymers. The 1-pentene randoms presented lower in-mould as well as total shrinkage than ethylene based random copolymers. Stabilisation and nucleation studies conducted on the propylene / 1-pentene random copolymers showed that a typical combination antioxidant package and nucleating agent, at normal loading levels, could be used. In the larger pp random copolymer family 1-pentene imparts a better balance of properties than other comonomers. The combination of low melting point and xylene solubles with high stiffness and clarity is unique to propylene / 1-pentene random copolymers.
AFRIKAANSE OPSOMMING: Die oorgrote meerderheid van kommersieel beskikbare polipropileen (PP) kopolimere het etileen, en tot 'n mindere mate buteen, as komonomeer. Die relatief hoë koste van kommersieel beskikbare hoër alfa-olefiene is moontlik die rede waarom hulle selde gebruik word vir die vervaardiging van PP kopolimere. Die Sasol Fischer-Tropsch proses, waartydens olie uit steenkool vervaardig word, lewer verskeie liniêre en vertakte alfa-olefiene as neweprodukte wat geïsoleer en gesuiwer kan word in 'n relatiewe goedkoop rafineringsproses. Dit sluit ook die onewe-koolstofgetal 1-penteen-olefien in. Sasol se gasfase Novolen PP aanleg in Secunda, Suid-Afrika, is besonder geskik vir die vervaardiging van hoë standaard PP statistiese kopolimere. Voortvloeiend hieruit is die geleentheid geidentifiseer om die gebruik van hoër alfa-olefiene, en meer spesifiek 1-penteen, na te vors tydens die gasfaseproduksie van PP statistiese kopolimere. Verskeie metodes om propeleen / 1-penteen statistiese kopolimere in 'n koolwaterstofoplosmiddel op laboratoriumskaal te produseer, is ondersoek. 'n Prosedure is daarna ontwikkel om propileen / 1-penteen statistiese kopolimere ook in die gasfase te vervaardig in 10-liter drukvate. Die bevinding was dat kommersieel beskikbare vierde-generasie ondersteunde kataliste die swaarder 1-penteenmonomeer suksesvol geïnkorporeer het in die propileenketting tydens beide die koolwaterstof oplosmiddel- en gasfase polimerisasiereaksies. Rekenaargebaseerde modellering is gebruik om die kondensasiekondisies van tipiese gasmengsels, teenwoordig tydens die produksie van PP statistiese kopolimere, te bepaal. Die resultate het aangedui dat normale proseskondisies tydens die gasfasepolimerisasie van propileen en 1-penteengeen risiko van kondensasie in die reaktor inhou nie. Propileen / 1-penteen statistiese kopolimere is gevolglik met groot sukses vervaardig by die 800-liter BASF loodsaanleg in Duitsland, gevolg deur die eerste kommersiële vervaardiging van die kopolimeer op die Sasol50m3 Novolen gasfase-aanleg in Secunda. Deur gebruik te maak van kommersieel beskikbare sagteware, is die impak van 1-penteen as komonomeer tydens die vervaardiging van statistiese kopolimere op die verkoelingskapasiteit van die kondensator bepaal. Veilige en uitvoerbare aanlegkondisies is uitgestip vir die vervaardiging van propileen /1-penteen statistiese kopolimere. Die verhouding tussen die reaktordruk en poeiermorfologie is ondersoek om die prosestoestande te optimiseer. Vervaardiging van kopolimere in die gasfase by hoër drukke lei tot verhoogde monomeerkonsentrasie in die reaktor en gevolglik hoër produksiedeursette. Daar is bewys dat tydens die produksie van PP statistiese kopolimere, met 1-penteen as komonomeer, hoër reaktordruk ingespan kan word. Die dramatiese toename in katalisproduktiwiteit waargeneem tydens die 800- liter loodsaanleg proefloop, tot en met 'n komonomeer inhoud van ongeveer 5%, word ondersteun deur die resultate van 'n kinetiese studie uitgevoer in laboriumskaal drukvate. 'n Omvattende studie, om die reologiese, termiese, kristallyne, fisiese en meganiese eienskappe van propileen / 1-penteen statistiese kopolimere te vergelyk met kommersieel beskikbare PP statistiese kopolimere, is uitgevoer. 'n Reeks propileen homo- en statistiese kopolimere, met 1-penteen en etileen as komonomere onderskeidelik, is berei. KMR- en IR- tegnieke is ontwikkel om die bepaling van komonomeersamestelling vir die nuwe familie van 1- penteen statistiese kopolimere te fasiliteer. Die invloed van komonomeersamestelling, molekulere gewig en temperatuur op die eienskappe van die reeks polimere is ondersoek. Die propoleen / 1- penteen statistiese kopolimere toon unieke reologiese eienskappe wat geassosieer kan word met die propielsykettings in die polimeerruggraat. Die viskositeit van die propileen / 1-penteen statistiese kopolimere toon 'n hoër wrywings- en temperatuursensitiwiteit in vergelyking met propileen homo- en etileen statistiese kopolimere. 'n Drastiese verlaging in die termodinamiese smeltpunt van die propileen / 1- penteen statistiese kopolimere met 'n toename in komonomeerinhoud is waargeneem tot en met 'n 5% komonomeerinhoud. Die propileen / 1-penteen statistiese kopolimere toon 'n breër smeltgebied en 'n hoër tempo in die piek smeltpuntafname in vergelyking met etileen statistiese kopolimere met soortgelyke komonomeer inhoud, gemeet op 'n massabasis. Daar is bewys dat die kristalstruktuur van die propileen / 1-penteen statistiese kopolimere beide die alfa en gamma modifikasies bevat. Die verhouding van die onderskeie kristalvorms is 'n funksie van komonomeerinhoud en kristalisasietemperatuur. 'n Afname in die glastemperatuur met verhoogde komonomeer inhoud is waargeneem. Die aanname dat die kort propielsykettings in die polimeerruggraat in die kristalstruktuur geïnkorporeer word, is gemaak. Dit verklaar die hoë afname in die tempo van die smeltpunt met toenemende komonomeer inhoud relatief tot ander statistiese kopolimere, met die handhawing van hoë moduluswaardes. Die besondere deursigtigheid van die propileen / 1-penteen statistiese kopolimere tesame met relatief hoë modulus waardes is uniek. 'n Omgekeerde verhouding tussen komonomeer inhoud en treksterkte asook moduluswaardes is waargeneem. 'n Toepassingstudie uitgevoer met die propileen / 1-penteen statistiese kopolimere het verskeie interessante resultate gelewer. Films vervaardig van hierdie kopolimere toon besonderse deursigtigheid en lae waarde van xileenoplosbaarheid, terwyl meganiese integriteit gehandhaaf word. Voordele in die vervaardigingsproses van BOPP-films asook bogemiddelde filmeienskappe hou unieke moontlikhede vir propileen / 1-penteen statistiese kopolimere in. Verskeie voordele tydens blaas- en spuitvormingsprosesse is waargeneem relatief tot ander beskikbare statistiese kopolimere. Die 1-penteen statistiese kopolimere toon 'n laer in-vorm sowel as totale krimping relatief tot etileen- gebaseerde kopolimere. 'n Studie het aangetoon dat tipiese bymiddelpakette by normale toevoegingsvlakke geskik is vir propileen / 1-penteen statistiese kopolimere. Gesien in die groter pp statistiese kopolimeer familie toon 1-penteen 'n beter balans van eienskappe as ander komonomere. Die kombinasie van laer smeltpunt en xileen-oplosbares met hoë moduluswaardes en helderheid is uniek aan propileen /1-penteen statistiese kopolimere.

We grow AB₂ random hyperbranched polymer structures in different ways and using different simulation methods. In particular we use a method of ad hoc construction of the connectivity matrix and the bond fluctuation model on a 3D lattice. We show that hyperbranched polymers split into two universality classes depending on the growth process. For a “slow growth” (SG) process where monomers are added sequentially to an existing molecule which strictly avoids cluster–cluster aggregation the resulting structures share all characteristic features with regular dendrimers. For a “quick growth” (QG) process which allows for cluster–cluster aggregation we obtain structures which can be identified as random fractals. Without excluded volume interactions the SG model displays a logarithmic growth of the radius of gyration with respect to the degree of polymerization while the QG model displays a power law behavior with an exponent of 1/4. By analyzing the spectral properties of the connectivity matrix we confirm the behavior of dendritic structures for the SG model and the corresponding fractal properties in the QG case. A mean field model is developed which explains the extension of the hyperbranched polymers in an athermal solvent for both cases. While the radius of gyration of the QG model shows a power-law behavior with the exponent value close to 4/5, the corresponding result for the SG model is a mixed logarithmic–power-law behavior. These different behaviors are confirmed by simulations using the bond fluctuation model. Our studies indicate that random sequential growth according to our SG model can be an alternative to the synthesis of perfect dendrimers.

We introduce and study four $q$-randomized Robinson--Schensted--Knuth (RSK) insertion tableau dynamics. Each of them is a discrete time Markov dynamics on two-dimensional interlacing particle arrays (these arrays are in a natural bijection with semistandard Young tableaux). For $0Mathematics

We are interested in two probabilistic models of a process interacting with a random environment. Firstly, we consider the model of directed polymers in random environment. In this case, a polymer, represented as the path of a simple random walk on a lattice, interacts with an environment given by a collection of time-dependent random variables associated to the vertices. Under certain conditions, the system undergoes a phase transition from an entropy-dominated regime at high temperatures, to a localised regime at low temperatures. Our main result shows that at high temperatures, even though a central limit theorem holds, we can identify a set of paths constituting a vanishing fraction of all paths that supports the free energy. We compare the situation to a mean-field model defined on a regular tree, where we can also describe the situation at the critical temperature. Secondly, we consider the parabolic Anderson model, which is the Cauchy problem for the heat equation with a random potential. Our setting is continuous in time and discrete in space, and we focus on time-constant, independent and identically distributed potentials with polynomial tails at infinity. We are concerned with the long-term temporal dynamics of this system. Our main result is that the periods, in which the profile of the solutions remains nearly constant, are increasing linearly over time, a phenomenon known as ageing. We describe this phenomenon in the weak sense, by looking at the asymptotic probability of a change in a given time window, and in the strong sense, by identifying the almost sure upper envelope for the process of the time remaining until the next change of profile. We also prove functional scaling limit theorems for profile and growth rate of the solution of the parabolic Anderson model.

Les dispersions colloïdales ont beaucoup d’applications technologiques importantes. A cause du mouvement brownien, les particules ont des collisions fréquentes entre elles. Les forces d’attraction de van der Waals,dérivant de potentiels à longue portés, conduisent à l’agrégation et à la précipitation des particules. Plusieurs méthodes ont été proposées pour diminuer ou contrebalancer l’effet d’attraction de van der Waals et augmenter la stabilité colloïdale. Par exemple, le choix du solvant possédant l’indice de réfraction le plus proche possible de celui des particules peut diminuer les forces de van der Waals. D'autres facteurs influencent la stabilité comme les interactions électrostatiques et les interactions spécifiques liées aux chaînes de polymères. Dans le cas des polymères, les chaînes peuvent être greffées à la surface des particules ou être dissoutes dans le solvant (chaînes libres). Dans ce travail de thèse, nous avons étudié l’effet de la stabilisation par déplétion dans le cas des chaînes de polymères libres (FPI, "free polymer induced interaction"). Des modèles théoriques précédents portent un caractère trop simplifié et utilisent des approximations sans vérification. De plus, l’influence des paramètres de la solution, c’est-à-dire, de la structure de polymères et de son interaction avec la surface de particule, n’a pas été étudiée.Les chaînes polymères libres ont été modélisées comme des marches aléatoires dans un champ moléculaire auto-cohérent qui satisfait à l'équation intégro-différentielle de diffusion. Pour le domaine moléculaire, nous avons utilisé un potentiel chimique qui, pour la solution de polymère semi-dilué, peut être représenté comme une expansion du viriel où nous n’avons pris en considération que les deuxième et troisième coefficients du viriel de la solution de polymère. En variant des paramètres tels que la rigidité du polymère, la longueur du polymère, la concentration en polymère et le régime du solvant (comme le solvant thêta), que ce soit pour une surface colloïdale purement répulsive, pour une surface adsorbée ou pour la surface d'une couche de polymère greffé, nous avons été en mesure d'améliorer la barrière répulsive due aux polymères libres entre les particules et donc nous avons trouvé des conditions de la stabilisation cinétique du système
Stable colloidal dispersions with evenly distributed particles are important for many technological applications. Due to Brownian motion colloidal particles have constant collisions with each other which often lead to their aggregation driven by the long range van der Waals attraction. As a result the colloidal systems often tend to precipitate. A number of methods have been devised to minimize the effect of long-range van der Waals attraction between colloidal particles or to override the influence of the attraction in order to provide the colloidal stability.In the PhD thesis we investigated the colloidal stabilization in solutions of free polymers which is commonly referred to as depletion stabilization. Previous theoretical studies of free-polymer induced (FPI) stabilization were based on oversimplified models involving uncontrolled approximations. Even the most basic features of the depletion stabilization phenomenon were unknown. It was unclear how the PI repulsion depends on the solution parameters, polymer structure and monomer/surface interactions.The free polymer chains were modeled as random walks in a self-consistent molecular field that satisfied to diffusion-like integro-differential equation. As the molecular field we used the chemical potential that for semi-dilute polymer solution can be represented as a virial expansion where we took into account only second and third virial coefficients of the polymer solution. Varying the parameters like polymer stiffness, polymer length, polymer concentration and solvent regime (like theta solvent) whether it is for purely repulsive colloidal surface, adsorbed surface or surface with grafted polymer layer we were able to enhance the repulsive barrier due to the free polymers between the particles and therefore found conditions for kinetic stabilization of the system

This chapter covers the one-dimensional Kardar–Parisi–Zhang equation, weak drive limit, universality, directed polymers in a random medium, replica solutions, statistical mechanics of line ensembles, and its generalization to several components which is used to study equilibrium time correlations of anharmonic chains and of the discrete nonlinear Schrödinger equation.

Polymers, even with attached, non-centrosymmetric, side groups are amorphous due to the random orientation of the chromophores and therefore are not second-harmonic active. They can be made macroscopically non-centrosymmetric by applying strong electric fields (poling) near the glass temperature of the host polymer to align the side groups which normally have large dipole moments.[1] The side groups can be engineered to have large non-resonant nonlinearities so that the poled polymers can have d(2)s of the order of 50-100 pV/m.[1] This has made poled polymers interesting doubling media, especially in channel waveguides which can be easily fabricated using a number of polymer techniques. We have been exploring poled polymers for second harmonic generation (SHG) for operation with 1550 nm inputs for potential application to cascading, WDM frequency shifting, etc.[2,3] Here we report our progress using the modal dispersion phase-matching technique.

The objective of the current work is to conduct a systematic analysis on the effects of manufacturing induced defects such as random distribution of fibers and presence of voids in matrix on the damage initiation in polymeric composites. Upon infusing resin, the initial fiber configuration undergoes perturbation and results in a random distribution with pockets of resin rich areas and fiber clusters. In addition, this could result in micro voids (between the fibers in the bundle) and macro voids (between the fiber bundles). A novel methodology has been put forward to generate random distributions of fibers that would simulate different levels of perturbations in the manufacturing process resulting in different configurations of fiber clusters. An embedded Representative Volume Element (RVE) approach has been adopted in a finite element model to calculate the stress fields without artificial effects of the RVE boundary. Damage initiation is then analyzed using a previously proposed energy based criterion for cavitation in polymers.

One of the emerging technologies is the use of microbial agents for the control of postharvest diseases of fruits and vegetables. A number of antagonistic microorganisms have been discovered which have the potential to effectively control postharvest diseases. Some of this technology has been patented and commercial products such as AspireTM (Ecogen Corporatin, Langhorne, PA, USA), Biosave 10TM and Biosave 11TM (Ecoscience Inc., Worchester, MA, USA) have been registered for commercial use. The principal investigator of this project was involved in developing the yeast-based biofungicide-AspireTM and testing its efficacy under commercial conditions. This research project was initiated to fill the gap between the knowledge available on development and commercial implementation of yeast biocontrol agents and basic understanding of various aspects related to introducing yeast antagonists to fruit surfaces, along with verification of population genetics. The main objectives of this study were: Study ecology, population dynamics and genetic diversity of the yeast antagonists Candida guilliermondii, C. oleophila, and Debaryomyces hansenii, and study the effect of preharvest application of the yeast antagonist C. oleophila naturally occurring epiphytic microbial population and on the development of postharvest diseases of citrus fruit during storage. Our findings, which were detailed in several publications, have shown that an epiphytic yeast population of grapefruit able to grow under high osmotic conditions and a wide range of temperatures was isolated and characterized for its biocontrol activity against green mold decay caused by Penicillium digitatum. Techniques based on random amplified polymorphic DNA (RAPD) and arbitrary primed polymerase chain reaction (ap-PCR), as well as homologies between sequences of the rDNA internal transcribed spacers (ITS) and 5.8S gene, were used to characterize the composition of the yeast population and to determine the genetic relationship among predominant yeast species. Epiphytic yeasts exhibiting the highest biocontrol activity against P. digitatum on grapefruit were identified as Candida guilliermondii, C. oleophila, C. sake, and Debaryomyces hansenii, while C. guilliermondii was the most predominant species. RAPD and ap-PCR analysis of the osmotolerant yeast population showed two different, major groups. The sequences of the ITS regions and the 5.8S gene of the yeast isolates, previously identified as belonging to different species, were found to be identical. Following the need to develop a genetically marked strain of the yeast C. oleophila, to be used in population dynamics studies, a transformation system for the yeast was developed. Histidine auxotrophy of C. oloephila produced using ethyl methanesulfonate were transformed with plasmids containing HIS3, HIS4 and HIS5 genes from Saccharomyces cerevisiae. In one mutant histidin auxotrophy was complemented by the HIS5 gene of S. cerevisiae is functionally homologous to the HIS5 gene in V. oleophila. Southern blot analysis showed that the plasmid containing the S. cerevisiae HIS5 gene was integrated at a different location every C. oleophila HIS+ transformant. There were no detectable physiological differences between C. oleophila strain I-182 and the transformants. The biological control ability of C. oleophila was not affected by the transformation. A genetically marked (with b-glucuronidase gene) transformant of C. oleophila colonized wounds on orange fruits and its population increased under field conditions. Effect of preharvest application of the yeast C. oleophila on population dynamics of epiphytic microbial population on wounded and unwounded grapefruit surface in the orchard and after harvest was also studied. In addition, the effect of preharvest application of the yeast C. oleophila on the development of postharvest decay was evaluated. Population studies conducted in the orchard showed that in control, non-treated fruit, colonization of wounded and unwounded grapefruit surface by naturally occurring filamentous fungi did not vary throughout the incubation period on the tree. On the other hand, colonization of intact and wounded fruit surface by naturally occurring yeasts was different. Yeasts colonized wounded surface rapidly and increased in numbers to about two orders of magnitude as compared to unwounded surface. On fruit treated with the yeast and kept on the tree, a different picture of fungal and yeast population had emerged. The detected fungal population on the yeast-treated intact surface was dramatically reduced and in treated wounds no fungi was detected. Yeast population on intact surface was relatively high immediately after the application of AspireTM and decreased to than 70% of that detected initially. In wounds, yeast population increased from 2.5 x 104 to about 4x106 after 72 hours of incubation at 20oC. Results of tests conducted to evaluate the effect of preharvest application of AspireTM on the development of postharvest decay indicated the validity of the approach.

Frozen, breaded, ready-to-cook chicken products have been implicated in outbreaks of salmonellosis. Some of these outbreaks can be large. For example, one outbreak of Salmonella Enteritidis involved 193 people in nine countries between 2018 and 2020, of which 122 cases were in the UK. These ready-to-cook products have a browned, cooked external appearance, which may be perceived as ready-to-eat, leading to mishandling or undercooking by consumers. Continuing concerns about these products led FSA to initiate a short-term (four month), cross-sectional surveillance study undertaken in 2021 to determine the prevalence of Salmonella spp., Escherichia coli and antimicrobial resistance (AMR) in frozen, breaded or battered chicken products on retail sale in the UK. This study sought to obtain data on AMR levels in Salmonella and E. coli in these products, in line with a number of other FSA instigated studies of the incidence and nature of AMR in the UK food chain, for example, the systematic review (2016). Between the beginning of April and the end of July 2021, 310 samples of frozen, breaded or battered chicken products containing either raw or partly cooked chicken, were collected using representative sampling of retailers in England, Wales, Scotland and Northern Ireland based on market share data. Samples included domestically produced and imported chicken products and were tested for E. coli (including extended-spectrum beta-lactamase (ESBL)-producing, colistin-resistant and carbapenem-resistant E. coli) and Salmonella spp. One isolate of each bacterial type from each contaminated sample was randomly selected for additional AMR testing to determine the minimum inhibitory concentration (MIC) for a range of antimicrobials. More detailed analysis based on Whole Genome Sequencing (WGS) data was used to further characterise Salmonella spp. isolates and allow the identification of potential links with human isolates. Salmonella spp. were detected in 5 (1.6%) of the 310 samples and identified as Salmonella Infantis (in three samples) and S. Java (in two samples). One of the S. Infantis isolates fell into the same genetic cluster as S. Infantis isolates from three recent human cases of infection; the second fell into another cluster containing two recent cases of infection. Countries of origin recorded on the packaging of the five Salmonella contaminated samples were Hungary (n=1), Ireland (n=2) and the UK (n=2). One S. Infantis isolate was multi-drug resistant (i.e. resistant to three different classes of antimicrobials), while the other Salmonella isolates were each resistant to at least one of the classes of antimicrobials tested. E. coli was detected in 113 samples (36.4%), with counts ranging from <3 to >1100 MPN (Most Probable Number)/g. Almost half of the E. coli isolates (44.5%) were susceptible to all antimicrobials tested. Multi-drug resistance was detected in 20.0% of E. coli isolates. E. coli isolates demonstrating the ESBL (but not AmpC) phenotype were detected in 15 of the 310 samples (4.8%) and the AmpC phenotype alone was detected in two of the 310 samples (0.6%) of chicken samples. Polymerase Chain Reaction (PCR) testing showed that five of the 15 (33.3%) ESBL-producing E. coli carried blaCTX-M genes (CTX-M-1, CTX-M-55 or CTX-M-15), which confer resistance to third generation cephalosporin antimicrobials. One E. coli isolate demonstrated resistance to colistin and was found to possess the mcr-1 gene. The five Salmonella-positive samples recovered from this study, and 20 similar Salmonella-positive samples from a previous UKHSA (2020/2021) study (which had been stored frozen), were subjected to the cooking procedures described on the sample product packaging for fan assisted ovens. No Salmonella were detected in any of these 25 samples after cooking. The current survey provides evidence of the presence of Salmonella in frozen, breaded and battered chicken products in the UK food chain, although at a considerably lower incidence than reported in an earlier (2020/2021) study carried out by PHE/UKHSA as part of an outbreak investigation where Salmonella prevalence was found to be 8.8%. The current survey also provides data on the prevalence of specified AMR bacteria found in the tested chicken products on retail sale in the UK. It will contribute to monitoring trends in AMR prevalence over time within the UK, support comparisons with data from other countries, and provide a baseline against which to monitor the impact of future interventions. While AMR activity was observed in some of the E. coli and Salmonella spp. examined in this study, the risk of acquiring AMR bacteria from consumption of these processed chicken products is low if the products are cooked thoroughly and handled hygienically.