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"Ramshaw, John D"
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Brownian Motion in Multiphase Flow
A previous phenomenological theory for Brownian motion of rigid spherical particles in a flowing fluid (Ramshaw, 1979, 1981) is extended to multiphase mixtures and arbitrary flow regimes. It is argued that each phase i possesses its own intrinsic osmotic pressure q ^sub i^ =n ^sub i^ k ^sub B^ T, where n ^sub i^ is the mean number of discrete particles (i.e., inclusions, fragments, blobs, or chunks) of phase i per unit total volume, regardless of their rigidity or their size and shape distributions. The gradient of q ^sub i^ appears as an additional force term in the momentum equation for phase i. The osmotic pressures q ^sub i^ also contribute to the total pressure p of the mixture, so these contributions must be subtracted out before the conventional multiphase pressure forces are computed. The resulting pressure terms in the momentum equation for phase i then become -α ^sub i^ ν(p-q)-νq ^sub i^, where α ^sub i^ is the volume fraction of phase i and q=∑ ^sub i^ q ^sub i^. This formulation provides a single unified description of the flow of both multiphase mixtures and multicomponent gases, and exhibits a smooth transition between these two limiting cases as the particle sizes vary from macroscopic to molecular dimensions. The stability properties of the equations are examined in the incompressible limit, and it is found that the Brownian motion stabilizes and regularizes the system only for microscopically small relative velocities.[PUBLICATION ABSTRACT]
Journal Article
Fugacity and Activity in a Nutshell
A simple unified treatment of fugacity and activity is presented for both gaseous and condensed phases. It is hoped that this treatment will be found useful as a clearer and more general alternative to existing treatments.
Journal Article
General formalism for singly-thermostated Hamiltonian dynamics
A general formalism is developed for constructing modified Hamiltonian dynamical systems which preserve a canonical equilibrium distribution by adding a time evolution equation for a single additional thermostat variable. When such systems are ergodic, canonical ensemble averages can be computed as dynamical time averages over a single trajectory. Systems of this type were unknown until their recent discovery by Hoover and colleagues. The present formalism should facilitate the discovery, construction, and classification of other such systems by encompassing a wide class of them within a single unified framework. This formalism includes both canonical and generalized Hamiltonian systems in a state space of arbitrary dimensionality (either even or odd), and therefore encompasses both few- and many-particle systems. Particular attention is devoted to the physical motivation and interpretation of the formalism, which largely determine its structure. An analogy to stochastic thermostats and fluctuation-dissipation theorems is briefly discussed.
Paper
Controlling the Molecular Structure and Physical Properties of Artificial Honeybee Silk by Heating or by Immersion in Solvents
Honeybee larvae produce silken cocoons that provide mechanical stability to the hive. The silk proteins are small and non-repetitive and therefore can be produced at large scale by fermentation in E. coli. The recombinant proteins can be fabricated into a range of forms; however the resultant material is soluble in water and requires a post production stabilizing treatment. In this study, we describe the structural and mechanical properties of sponges fabricated from artificial honeybee silk proteins that have been stabilized in aqueous methanol baths or by dry heating. Aqueous methanol treatment induces formation of ß-sheets, with the amount of ß-sheet dictated by methanol concentration. Formation of ß-sheets renders sponges insoluble in water and generates a reversibly compressible material. Dry heat treatments at 190°C produce a water insoluble material, that is stiffer than the methanol treated equivalent but without significant secondary structural changes. Honeybee silk proteins are particularly high in Lys, Ser, Thr, Glu and Asp. The properties of the heat treated material are attributed to generation of lysinoalanine, amide (isopeptide) and/or ester covalent cross-links. The unique ability to stabilize material by controlling secondary structure rearrangement and covalent cross-linking allows us to design recombinant silk materials with a wide range of properties.
Journal Article
Identification of Proteins Associated with Adhesive Prints from Holothuria dofleinii Cuvierian Tubules
Cuvierian tubules are expelled as a defence mechanism against predators by various species within the family Holothuridae. When the tubules are expelled, they become sticky almost immediately and ensnare the predator. The mechanism of this rapid adhesion is not clear, but proteins on the surface of the expelled tubules are widely believed to be involved. This study has examined such proteins from
Holothuria dofleinii
, sourced from adhesive prints left on glass after the removal of adhered tubules. Gel electrophoresis showed that seven strongly staining protein bands were consistently present in all samples, with molecular masses ranging from 89 to 17 kDa. N-terminal sequence data was obtained from two bands, while others seemed blocked. Tandem mass spectrometry-based sequencing of tryptic peptides derived from individual protein bands indicated that the proteins were unlikely to be homopolymers. PCR primers designed using the peptide sequences enabled us to amplify, clone and sequence cDNA segments relating to four gel bands; for each, the predicted translation product contained other peptide sequences observed for that band that had not been used in primer design. Database searches using the peptide and cDNA-encoded sequences suggest that two of the seven proteins are novel and one is a C-type lectin, while—surprisingly—at least three of the other four are closely related to enzymes associated with the pentose phosphate cycle and glycolysis. We discuss precedents in which lectins and metabolic enzymes are involved in attachment and adhesion phenomena.
Journal Article
A new class of animal collagen masquerading as an insect silk
Collagen is ubiquitous throughout the animal kingdom, where it comprises some 28 diverse molecules that form the extracellular matrix within organisms. In the 1960s, an extracorporeal animal collagen that forms the cocoon of a small group of hymenopteran insects was postulated. Here we categorically demonstrate that the larvae of a sawfly species produce silk from three small collagen proteins. The native proteins do not contain hydroxyproline, a post translational modification normally considered characteristic of animal collagens. The function of the proteins as silks explains their unusual collagen features. Recombinant proteins could be produced in standard bacterial expression systems and assembled into stable collagen molecules, opening the door to manufacture a new class of artificial collagen materials.
Journal Article
PET Changes Management and Improves Prognostic Stratification in Patients with Recurrent Colorectal Cancer: Results of a Multicenter Prospective Study
The aims of our study were to examine the impact of PET in changing management in patients with proven or suspected colorectal cancer recurrence and to assess the impact of management change on disease-free survival.
Symptomatic patients with a residual structural lesion suggestive of recurrent tumor (group A) or patients with pulmonary or hepatic metastases considered to be potentially resectable (group B) underwent PET scans. Pre-PET management plans were documented by referring clinicians unaware of the PET results, and follow-up to 12 mo was performed to determine actual management and clinical outcomes.
A total of 191 patients (118 men and 73 women; mean age, 66 y) were studied. PET detected additional sites of disease in 48.4% of patients in group A and in 43.9% of patients in group B. A change in planned management was documented in 65.6% of group A and in 49.0% of group B patients. These management plans were implemented in 96% of patients. Follow-up data in group A showed progressive disease in 60.5% of patients with additional lesions detected by PET, compared with conventional imaging, and in 36.2% of patients with no additional lesions detected by PET (P=0.04). In group B, progressive disease was identified in 65.9% of patients with additional lesions detected by PET and in 39.2% of patients with no additional lesions detected by PET (P=0.01). PET also provided valuable prognostic information on patients stratified into curative- or palliative-intent groups.
These data demonstrate the significant impact of PET on management and outcomes in patients with suspected recurrent colorectal cancer.
Journal Article
Comparison of Laparoscopic and Open Ventral Herniorrhaphy
The repair of large and/or recurrent ventral hernias is associated with significant complications and a recurrence rate that can be more than 50 per cent. Laparoscopic ventral herniorrhaphy, a recent development, has been shown to be safe and effective in the repair of ventral hernias. This study retrospectively reviews all ventral hernia repairs over a 3-year period, November 1995 through December 1998, at a community-based teaching hospital. The purpose of the study was to compare open and laparoscopic repairs. A total of 253 ventral hernia repairs were performed during this time, 174 open and 79 laparoscopic. The age, weight, and sex distribution was similar for each group. The hernias in the open group averaged 34.1 cm2 in size, and mesh used averaged 47.3 cm2. In the laparoscopic group, the hernia defect averaged 73.0 cm2, and the mesh size averaged 287.4 cm2. Operative time was longer in the open group, 82.0 versus 58.0 minutes. In the open group, there were 38 (21.8%) minor and 8 (4.6%) major complications, compared with 13 (16.5%) minor and 2 (2.5%) major complications in the laparoscopic group. Hospital stay was shorter for the laparoscopic group, 1.7 versus 2.8 days. At an average follow-up of 21 months (range, 2–40 months), there have been 36 recurrences in the open group (20.7%) compared with 2 recurrences in the laparoscopic group (2.5%). In this series, laparoscopic ventral herniorrhaphy compares favorably to open ventral herniorrhaphy with respect to wound complications, hospital stay, operative time, and recurrence rate.
Journal Article