Determination of coalescence kernels for high-shear granulation using DEM simulations

Discrete element method (DEM) modeling is used in parallel with a model for coalescence of deformable surface wet granules. This produces a method capable of predicting both collision rates and coalescence efficiencies for use in derivation of an overall coalescence kernel. These coalescence kernels can then be used in computationally efficient meso-scale models such as population balance equation (PBE) models. A soft-sphere DEM model using periodic boundary conditions and a unique boxing scheme was utilized to simulate particle flow inside a high-shear mixer. Analysis of the simulation results provided collision frequency, aggregation frequency, kinetic energy, coalescence efficiency and compaction rates for the granulation process. This information can be used to bridge the gap in multi-scale modeling of granulation processes between the micro-scale DEM/coalescence modeling approach and a meso-scale PBE modeling approach.

Local adaptation and species segregation in two mussel (Mytilus edulis X M. trossulus) hybrid zones

Few marine hybrid zones have been studied extensively, the major exception being the hybrid zone between the mussels Mytilus edulis and M. galloprovincialis in southwestern Europe. Here, we focus on two less studied hybrid zones that also involve Mytilus spp.; M. edulis and M. trossulus are sympatric and hybridize on both western and eastern coasts of the Atlantic Ocean. We review the dynamics of hybridization in these two hybrid zones and evaluate the role of local adaptation for maintaining species boundaries. In Scandinavia, hybridization and gene introgression is so extensive that no individuals with pure M. trossulus genotypes have been found. However, M. trossulus alleles are maintained at high frequencies in the extremely low salinity Baltic Sea for some allozyme genes. A synthesis of reciprocal transplantation experiments between different salinity regimes shows that unlinked Gpi and Pgm alleles change frequency following transplantation, such that post-transplantation allelic composition resembles native populations found in the same salinity. These experiments provide strong evidence for salinity adaptation at Gpi and Pgm (or genes linked to them). In the Canadian Maritimes, pure M. edulis and M. trossulus individuals are abundant, and limited data suggest that M. edulis predominates in low salinity and sheltered conditions, whereas M. trossulus are more abundant on the wave-exposed open coasts. We suggest that these conflicting patterns of species segregation are, in part, caused by local adaptation of Scandinavian M. trossulus to the extremely low salinity Baltic Sea environment.

Cloning and characterization of a gene encoding the major surface protein of the bacterial endosymbiont Wolbachia pipientis

The maternally inherited intracellular symbiont Wolbachia pipientis is well known for inducing a variety of reproductive abnormalities in the diverse arthropod hosts it infects. It has been implicated in causing cytoplasmic incompatibility, parthenogenesis, and the feminization of genetic males in different hosts. The molecular mechanisms by which this fastidious intracellular bacterium causes these reproductive and developmental abnormalities have not yet been determined. In this paper, we report on (i) the purification of one of the most abundantly expressed Wolbachia proteins from infected Drosophila eggs and (ii) the subsequent cloning and characterization of the gene (wsp) that encodes it. The functionality of the wsp promoter region was also successfully tested in Escherichia coli. Comparison of sequences of this gene from different strains of Wolbachia revealed a high level of variability. This sequence variation correlated with the ability of certain Wolbachia strains to induce or rescue the cytoplasmic incompatibility phenotype in infected insects. As such, this gene will be a very useful tool for Wolbachia strain typing and phylogenetic analysis, as well as understanding the molecular basis of the interaction of Wolbachia with its host.

High affinity binding of albicidin phytotoxins by the AlbA protein from Klebsiella oxytoca

Albicidins are a family of phytotoxins and antibiotics which play an important role in the pathogenesis of sugarcane leaf scald disease. The albA gene from Klebsiella oxytoca encodes a protein which inactivates albicidin by heat-reversible binding. Albicidin ligand binding to a recombinant AlbA protein, purified by means of a glutathione S-transferase gene fusion system, is an almost instant and saturable reaction. Kinetic and stoichiometric analysis of the binding reaction indicated the presence of a single high affinity binding site with a dissociation constant of 6.4 x 10(-8) M. The AlbA-albicidin complex is stable from 4 to 40 degrees C, from ph 5 to 9 and in high salt solutions. Treatment with protein denaturants released all bound albicidin. These properties indicate that AlbA may be a useful affinity matrix for selective purification of albicidin antibiotics. AlbA does not bind to p-nitrophenyl butyrate or alpha-naphthyl butyrate, the substrates of the albicidin detoxification enzyme AlbD from Pantoea dispersa. The potential exists to pyramid genes for different mechanisms in transgenic plants to protect plastid DNA replication from inhibition by albicidins.

Role of generalized and episode specific memories in the word frequency effect in recognition

Frequency, recency, and type of prior exposure to very low-and high-frequency words were manipulated in a 3-phase (i.e., familiarization training, study, and test) design. Increasing the frequency with which a definition for a very low-frequency word was provided during familiarization facilitated the word's recognition in both yes-no (Experiment 1) and forced-choice paradigms (Experiment 2). Recognition of very low-frequency words not accompanied by a definition during familiarization first increased, then decreased as familiarization frequency increased (Experiment I). Reasons for these differences were investigated in Experiment 3 using judgments of recency and frequency. Results suggested that prior familiarization of a very low-frequency word with its definition may allow a more adequate episodic representation of the word to be formed during a subsequent study trial. Theoretical implications of these results for current models of memory are discussed.

Calculating current densities and fields due to shielded bi-planar radio-frequency coils

A method for the accurate computation of the current densities produced in a wide-runged bi-planar radio-frequency coil is presented. The device has applications in magnetic resonance imaging. There is a set of opposing primary rungs, symmetrically placed on parallel planes and a similar arrangement of rungs on two parallel planes surrounding the primary serves as a shield. Current densities induced in these primary and shielding rungs are calculated to a high degree of accuracy using an integral-equation approach, combined with the inverse finite Hilbert transform. Once these densities are known, accurate electrical and magnetic fields are then computed without difficulty. Some test results are shown. The method is so rapid that it can be incorporated into optimization software. Some preliminary fields produced from optimized coils are presented.

Sustained gene expression in transplanted skin fibroblasts in rats

Retrovirus-mediated gene transfer into adult skin fibroblasts has provided measurable amounts of therapeutic proteins in animal models. However, the major problem emerging from these experiments was a limited time of vector encoded gene expression once transduced cells were engrafted We hypothesized that sustained transduced gene expression in quiescent fibroblasts in vivo might be obtained by using a fibronectin (Fn) promoter. Fibronectin plays a key role in cell adhesion, migration and wound healing and is up-regulated in quiescent fibroblasts. Retroviral vectors containing human adenosine deaminase (ADA) cDNA linked to rat fibronectin promoter (LNFnA) or viral LTR promoter (LASN) were compared for their ability to express ADA from transduced primary rat skin fibroblasts in vivo. Skin grafts formed from fibroblasts transduced with LNFnA showed strong human ADA enzyme activity from 1 week to 3 months. In contrast, skin grafts containing LASN-transduced fibroblasts tested positive for human ADA for weeks 1 and 2, were faintly positive at week 3 and showed no human ADA expression at 1, 2 and 3 months. Thus, a fibronectin promoter provided sustained transduced gene expression at high levels for at least 3 months in transplanted rat skin fibroblasts, perhaps permitting the targeting of this tissue for human gene therapy.

A rapid selection/amplification procedure for high-level expression of recombinant protein in a metal-amplifiable mammalian expression system

We describe a strategy for the selection and amplification of foreign gene expression in Chinese hamster ovary (CHO) cells employing a metallothionein gene-containing expression vector. This report describes an amplification procedure that results in an enrichment of clones exhibiting high levels of recombinant protein production and reduces the labour required for screening recombinant cell lines.

Association of a glucocorticoid receptor gene marker with human essential hypertension.

Recently, a bi-allelic polymorphism in the glucocorticoid receptor gene (GRL) has been shown to be associated with individuals at high risk of developing hypertension and accumulation of abdominal visceral fat, a known risk factor for cardiovascular disease. The evaluate the role of GRL in essential hypertension and obesity, case-control studies were conducted using 88 hypertensive, 123 normotensive, 150 lean and 94 obese subjects. Genotypes for a highly polymorphic microsatellite marker (D5S207) located within 200 kb of the glucocorticoid receptor gene, were determined by PCR. Allele frequencies between hypertensive and normotensive groups were significantly (P = 0.0005) different whereas no significant differences were observed between lean and obese populations. In conclusion, the results suggest that the glucocorticoid receptor gene or perhaps another gene located in close proximity and in linkage disequilibrium with D5S207, is involved in hypertension development

Gene and genotypic diversity of Phytophthora cinnamomi in South Africa and Australia revealed by DNA polymorphisms

Phytophthora cinnamomi isolates from South Africa and Australia were compared to assess genetic differentiation between the two populations. These two populations were analysed for levels of phenotypic diversity using random amplified polymorphic DNAs (RAPDs) and gene and genotypic diversity using restriction fragment length polymorphisms (RFLPs). Sixteen RAPD markers from four decanucleotide Operon primers and 34 RFLP alleles from 15 putative loci were used. A few isolates from Papua New Guinea known to posses alleles different from Australian isolates were also included for comparative purposes. South African and Australian P. cinnamomi populations were almost identical with an extremely low level of genetic distance between them (D-m = 0.003). Common features for the two populations include shared alleles, low levels of phenotypic/genotypic diversity, high clonality, and low observed and expected levels of heterozygosity. Furthermore, relatively high levels of genetic differentiation between mating type populations (D-m South Africa = 0.020 and D-m Australia = 0.025 respectively), negative fixation indices, and significant deviations from Hardy-Weinberg equilibrium, all provided evidence for the lack of frequent sexual reproduction in both populations. The data strongly suggest that both the South African and Australian P. cinnamomi populations are introduced.

Analysis of the genes flanking xabB: a methyltransferase gene is involved in albicidin biosynthesis in Xanthomonas albilineans

Transposon mutagenesis and complementation studies previously identified a gene (xabB) for a large (526 kDa) polyketide-peptide synthase required for biosynthesis of albicidin antibiotics and phytotoxins in the sugarcane leaf scald pathogen Xanthomonas albilineans. A cistron immediately downstream from xabB encodes a polypeptide of 343 aa containing three conserved motifs characteristic of a family of S-adenosyl-L-methionine (SAM)-dependent O-methyltransferases. Insertional mutagenesis and complementation indicate that the product of this cistron (designated xabC) is essential for albicidin production, and that there is no other required downstream cistron. The xab promoter region is bidirectional, and insertional mutagenesis of the first open reading frame (ORF) in the divergent gene also blocks albicidin biosynthesis. This divergent ORF (designated thp) encodes a protein of 239 aa displaying high similarity to several IS21-like transposition helper proteins. The thp cistron is not located in a recognizable transposon, and is probably a remnant from a past transposition event that may have contributed to the development of the albicidin biosynthetic gene cluster. Failure of 'in trans' complementation of rhp indicates that a downstream cistron transcribed with thp is required for albicidin biosynthesis. (C) 2000 Elsevier Science B.V. All rights reserved.

Promoter studies of a polydnavirus gene from Cotesia rubecula (Hym : Braconidae)

The Cotesia rubecula polydnavirus gene, CrV1, is expressed in a highly transient fashion. Within four hours after egg deposition and virus infection, tissues of the host caterpillar, Pieris rapae, express high levels of the transcript. Twelve hours after infection no transcripts are visible. We have previously shown that the CrV1 secreted protein is mainly produced in host haemocytes. In haemocytes, immune functions such as phagocytosis and cell spreading are abolished by destabilization of the cell cytoskeleton. To test whether the observed down-regulation of CrV1 transcripts is mediated by transcriptional control or by other factors, such as the disruption of cytoskeleton in CrV1-inactivated cells, we cloned the promoter and the 3' untranslated region of the CrV1 gene to study CrV1 expression. The promoter region of the CrV1 gene was cloned into baculovirus expression systems along with the CAT reporter gene. Molecular analyses showed that the CAT gene under the control of CrV1 promoter is expressed as early as 2 h post infection and continues until late phase of infection suggesting that down-regulation of CrV1 expression in host haemocytes is perhaps mediated by post-transcriptional mechanisms.

Progress in high field MRI at the University of Florida

In this article we report on progress in high magnetic field MRI at the University of Florida in support of our new 750MHz wide bore and 11.7T/40cm MR instruments. The primary emphasis is on the associated rf technology required, particularly high frequency volume and phased array coils. Preliminary imaging results at 750MHz are presented. Our results imply that the pursuit of even higher fields seems warranted. (C) 2002 Elsevier Science B.V. All rights reserved.

Perioperative epidural analgesia and outcome after major abdominal surgery in high-risk patients

In a primary analysis of a large recently completed randomized trial in 915 high-risk patients undergoing major abdominal surgery, we found no difference in outcome between patients receiving perioperative epidural analgesia and those receiving IV opioids, apart from the incidence of respiratory failure. Therefore, we performed a selected number of predetermined subgroup analyses to identify specific types of patients who may have derived benefit from epidural analgesia. We found no difference in outcome between epidural and control groups in subgroups at increased risk of respiratory or cardiac complications or undergoing aortic surgery, nor in a subgroup with failed epidural block (all P > 0.05). There was a small reduction in the duration of postoperative ventilation (geometric mean [SD]: control group, 0.3 [6.5] h, versus epidural group, 0.2 [4.8] h, P = 0.048). No differences were found in length of stay in intensive care or in the hospital. There was no relationship between frequency of use of epidural analgesia in routine practice outside the trial and benefit from epidural analgesia in the trial. We found no evidence that perioperative epidural analgesia significantly influences major morbidity or mortality after major abdominal surgery.