Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides

The silica-supported transition metal hydrides (=Si-O-Si=)(=Si-O-)2Ta-H and (=Si-O-)xM-H (M, chromium or tungsten) catalyze the metathesis reaction of linear or branched alkanes into the next higher and lower alkanes at moderate temperature (25degrees to 200degreesC). With (=Si-O-Si=)(=Si-O-)2Ta-H, ethane was transformed at room temperature into an equimolar mixture of propane and methane. Higher and lower homologs were obtained from propane, butane, and pentane as well as from branched alkanes such as isobutane and isopentane. The mechanism of the step leading to carbon-carbon bond cleavage and formation likely involves a four-centered transition state between a tantalum-alkyl intermediate and a carbon-carbon final sigma-bond of a second molecule of alkane.     

Spatial Variability of Turbulent Mixing in the Abyssal Ocean

Ocean microstructure data show that turbulent mixing in the deep Brazil Basin of the South Atlantic Ocean is weak at all depths above smooth abyssal plains and the South American Continental Rise. The diapycnal diffusivity there was estimated to be less than or approximately equal to 0.1 x 10(-4) meters squared per second. In contrast, mixing rates are large throughout the water column above the rough Mid-Atlantic Ridge, and the diffusivity deduced for the bottom-most 150 meters exceeds 5 x 10(-4) meters squared per second. Such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry.     

Leucocytoclastic vasculitis associated with Staphylococcus intermedius in the pastern of a horse

A pregnant quarterhorse mare became acutely lame as a result of severe swelling of its right hind leg, thought to have been caused by a fracture or a muscle tear. Diagnostic procedures ruled out a traumatic musculoskeletal cause and a physical examination revealed chronic pastern dermatitis ('scratches'/'grease heel'). Histopathological evaluation of biopsy samples from the right hind leg was consistent with a leucocytoclastic vasculitis, and culture yielded Staphylococcus intermedius. The treatment and infectious causes of pastern dermatitis are discussed.     

Plasma endotoxin concentration in horses: a methods study

Background: Accurate determination of plasma endotoxin concentration is critical for ex vivo and in vitro cellular and molecular studies of endotoxemia in horses. However, reports are conflicting with respect to anticoagulant, handling, and sample preparation.

Objective:

Objective: The purpose of this study was to determine the effect of blood sample fraction and handling time on measurement of endotoxin concentration in horses.

Methods:

Methods: Whole blood, anticoagulated with 3.8% (0.12 M) sodium citrate (9:1), was collected from 5 healthy horses. Whole blood (WB), platelet-rich plasma (PRP), and platelet-poor plasma (PPP) were spiked with endotoxin (2 EU/mL). Endotoxin-spiked WB samples were centrifuged immediately to generate PRP for measurement. Endotoxin concentration was subsequently measured by Limulus amebocyte assay at 0, 15, 30, 45, and 60 minutes. Assays were performed in triplicate and results were analyzed using Student's t -test, with significance set at P < .05.

Results:

Results: Mean endotoxin concentrations in 2 EU/mL-spiked WB were significantly different from those in PPP at all time points tested. Recovery of endotoxin in PRP generated from WB was significantly diminished after just 15 minutes.

Conclusion:

Conclusion: PRP generated from WB is significantly more reliable than PPP in determining endotoxin concentration ex vivo. Measurement of endotoxin in PRP generated from WB was significantly diminished after 15 min, identifying a time frame within which to process blood samples for endotoxin analysis.     

Pneumothorax in dairy cattle: 30 cases (1990-2003)

OBJECTIVE: To evaluate the features, underlying causes, results of diagnostic testing, and treatment of pneumothorax in dairy cattle. DESIGN: Retrospective study. ANIMALS: 30 dairy cattle. PROCEDURE: Medical records of all cattle with a diagnosis of pneumonia were reviewed. For cattle with pneumothorax, information was obtained pertaining to signalment, anamnesis, diagnosis, treatment, and outcome. Survival data were compared between cattle with pneumonia with or without pneumothorax. RESULTS: Pneumothorax was associated with bronchopneumonia in 18 cattle, interstitial pneumonia in 7 cattle, pharyngeal or laryngeal trauma in 3 cattle, and neonatal respiratory distress in 2 calves. Bovine respiratory syncytial virus was the most commonly detected infectious agent. Eighteen of 30 (60%) cattle survived; 8 were euthanatized and 4 died. Survival rate was 81% for cattle with pneumonia without pneumothorax during the same time period. Pneumothorax was a significant risk factor for failure to survive to discharge from the hospital for cattle with underlying chronic bronchopneumonia. CONCLUSIONS AND CLINICAL RELEVANCE: Pneumothorax in dairy cattle appears to occur most commonly in association with chronic bronchopneumonia. Cattle of both sexes and all ages can be affected.