Search

Objective: To describe a novel surgical technique for management of right dorsal colitis in the horse. Study Design: Clinical report. Animals: 14-year-old Warmblood gelding. Methods: The horse was referred for treatment of a stromal abscess and signs of right dorsal colitis. Plasma chemistry revealed marked hypoproteinemia. Abdominal ultrasonographic examination showed a thickened right dorsal colon (RDC). Medical treatment was unsuccessful. With the horse in left lateral recumbency under general anesthesia, an approach to the right side of the abdomen through a 16th rib resection was made. The thoracic cavity was entered during the approach. Surgical resection of the RDC and side-to-side anastomosis of the diaphragmatic flexure to the small colon (bypass) was performed. The thoracic cavity was closed by attaching the diaphragm to the body wall and air was removed at the completion of surgery. Results: Resection of the RDC and bypass of the resected area was successfully performed. The colic signs and hypoproteinemia resolved. Complications of surgery included a deep surgical site infection with development of a large intrathoracic abscess. The abscess was managed with drainage and long-term antimicrobial treatment. Conclusion: Right dorsal colitis can be treated successfully with resection and bypass of the RDC. In cases where the thoracic cavity is penetrated during the abdominal approach, the diaphragm should be sutured to the body wall at the beginning of surgery to avoid development of an infection within the thoracic cavity. Clinical Relevance: RDC resection and bypass may be an alternative approach for management of horses with right dorsal colitis.

Polyatomic density functional theory was used to model tridecane chains near a hard wall under melt conditions. Polymer reference interaction site model (PRISM) liquid state theory provided the bulk structure input for the density functional. The density profile, the fractional distribution of sites, and the variation of the end‐to‐end separation of the chains as a function of distance from wall contact were calculated, and excellent agreement with the results of full multichain simulation was found.

A study of the variation in the calculated quantities for adatom diffusion with respect to the size of the model crystal is presented. The reported quantities include surface diffusion barrier heights, pre-exponential factors, and dynamical correction factors. Embedded atom method (EAM) potentials were used throughout this effort. Both the layer size and the depth of the crystal were found to influence the values of the Arrhenius factors significantly. In particular, exchange type mechanisms required a significantly larger model than standard hopping mechanisms to determine adatom diffusion barriers of equivalent accuracy. The dynamical events that govern the corrections to transition state theory (TST) did not appear to be as sensitive to crystal depth. Suitable criteria for the convergence of the diffusion parameters with regard to the rate properties are illustrated.

A long range adatom diffusion mechanism has been observed in simulations on the fcc (100) surfaces of embedded atom method (EAM) modeled materials. This mechanism primarily involves the adatom and two atoms in the top substrate layer. After passing through the saddle configuration the adatom is found two rows down and one row over from its original position. The movement of the adatom is like that of a knight on a chess board. The activation barrier of this mechanism is high, and it begins to appear at temperatures about half the melting temperature of the material. Due to the long range nature of this mechanism it could significantly affect the adatom diffusion rate as compared to typical hopping between adjacent minima or diffusion via the exchange mechanism.

To describe a novel surgical technique for management of right dorsal colitis in the horse.Clinical report.14-year-old Warmblood gelding.The horse was referred for treatment of a stromal abscess and signs of right dorsal colitis. Plasma chemistry revealed marked hypoproteinemia. Abdominal ultrasonographic examination showed a thickened right dorsal colon (RDC). Medical treatment was unsuccessful. With the horse in left lateral recumbency under general anesthesia, an approach to the right side of the abdomen through a 16th rib resection was made. The thoracic cavity was entered during the approach. Surgical resection of the RDC and side-to-side anastomosis of the diaphragmatic flexure to the small colon (bypass) was performed. The thoracic cavity was closed by attaching the diaphragm to the body wall and air was removed at the completion of surgery.Resection of the RDC and bypass of the resected area was successfully performed. The colic signs and hypoproteinemia resolved. Complications of surgery included a deep surgical site infection with development of a large intrathoracic abscess. The abscess was managed with drainage and long-term antimicrobial treatment.Right dorsal colitis can be treated successfully with resection and bypass of the RDC. In cases where the thoracic cavity is penetrated during the abdominal approach, the diaphragm should be sutured to the body wall at the beginning of surgery to avoid development of an infection within the thoracic cavity.RDC resection and bypass may be an alternative approach for management of horses with right dorsal colitis.

Objective— To (1) examine the outcome in horses with osteoarthritis or intra-articular soft tissue injuries of the stifle after arthroscopic exploration and debridement and (2) to determine any imaging or surgical findings that may influence prognosis. Design— Case series. Animals— Horses (n=44) with lameness referable to the stifle, diagnosed with osteoarthritis, meniscal tears, or other intra-articular soft tissue injuries based on arthroscopic examination. Methods— Medical records of horses with stifle lameness that had arthroscopic exploration were reviewed. Horses with osteochondrosis lesions, intra-articular fractures, or osseous cyst-like lesions were excluded. Pertinent case information was analyzed and short- and long-term outcome was assessed. Results— There was no association between radiographic score and surgery score. Diagnostic ultrasound had a sensitivity of 79% and a specificity of 56% for identifying meniscal injuries. Follow-up information was available for 35 horses; 23 horses (60%) improved after surgery, 16 (46%) became sound, and 13 (37%) returned to their previous level of function. A negative association was observed between age and degree of preoperative lameness and outcome. More severe changes observed on preoperative radiographs were also negatively associated with prognosis. No horses with grade 3 meniscal tears improved postoperatively and increasing meniscal pathology was negatively associated with return to previous function. A weak association between surgery grade and outcome was also observed. Degree of chondral damage, location of primary pathology, and microfracture techniques had no effect on outcome. Conclusions— Advanced horse age, severe lameness and preoperative radiographic changes, and presence of large meniscal tears are associated with a negative postoperative outcome for horses with stifle lameness. Appearance of the articular surface at surgery appears to be an inconsistent prognostic indicator. Clinical Relevance— Some horses with extensive cartilage damage may return to athletic function after arthroscopic debridement and lavage. A more pessimistic prognosis may be given to older horses, those with more severe preoperative lameness, and those with severe radiographic changes or large meniscal tears.

Minimizing the spatial variation of polarization is critical to tiled AMLCD image quality. With the advent of large tiled AMLCD, low spatial frequency artifacts may become visible. Component birefringence variation of a few nanometers can produce viewer detectable luminance variations. Jones matrix formulation is used to model this effect and compare to experimental measurements.

An expression is presented for computing the classical diffusion constant of a point defect (e.g., an adatom) in an infinite lattice of binding sites at arbitrary temperature. The transition state theory diffusion constant is simply multiplied by a dynamical correction factor that is computed from short‐time classical trajectories initiated at the site boundaries. The time scale limitations of direct molecular dynamics are thus avoided in the low‐ and middle‐temperature regimes. The expression results from taking the time derivative of the particle mean‐square displacement in the lattice‐discretized coordinate system. Applications are presented for surface diffusion on fcc(100) and fcc(111) Lennard‐Jones crystal faces.

Surface self‐diffusion constants have been calculated for the single component Lennard‐Jones fcc(111) system using the dynamical corrections formalism for transition state theory (TST). At high temperatures, these results are found to be in agreement with previous molecular dynamics calculations. Over the extended temperature range in which this method is valid, deviations from Arrhenius behavior are observed. At lower temperatures, a noticeable contribution to the diffusion constant stems from trajectories in which the adatom recrosses the TST boundary, often due to a direction‐reversing collision with the substrate atom on the far side of the binding site. This produces a dip in the dynamical correction factor centered around a reduced temperature of T=0.038. At higher temperatures, the expected multiple‐jump effects are observed.

A method is presented for computing the classically exact, surface or bulk diffusion constant of a point defect at arbitrary temperature. The thermal diffusion constant is expressed using the squared jump length averaged over all possible final states to which the atom can jump. The rate constants that weight this sum are computed using transition state theory and molecular dynamics within a recently developed many‐state dynamical corrections formalism. While these rate constants are valid only in the rare‐event regime (i.e., at low temperature), it is shown that for a periodic lattice of equivalent binding sites, the resulting diffusion contants is valid at any temperature for which the lattice sites remain well defined. It is thus possible to compute classically exact surface or bulk diffusion constant for an arbitrary interatomic potential, without the time scale limitations of direct molecular dynamics.