Axial Characteristics of Circular External Skeletal Fixator Single Ring Constructs

OBJECTIVE: Evaluate the effects of varying ring diameter, wire tension, and wire-divergence angle on the axial stiffness characteristics of circular external skeletal fixator single-ring constructs. Study Design-Biomechanical evaluation using circular fixator components and a Delrin cylinder bone model. METHODS: Single ring constructs using two 1.6 mm diameter Kirschner wires to secure a 19 mm Delrin cylinder centered within the ring were examined. Component variables evaluated were ring diameter (50 mm, 66 mm, 84 mm, and 118 mm), wire-divergence angle (30 degrees, 60 degrees, and 90 degrees ), and wire tension (0 kg, 30 kg, 60 kg, and 90 kg). A total of 48 constructs were examined. Rings were rigidly mounted on a universal testing system and the cylinder loaded in axial compression (7.4 N/s) to 220 N. Load/displacement curves were analyzed to determine the following: the displacement (mm) that occurred before the slope of each load/displacement curve became linear, the stiffness (N/mm) of the linear portion of each load/deformation curve, and the total displacement (mm) produced at maximal load. Least-squares linear regression was used to model response variables as linear functions of ring diameter, wire divergence angle, and wire tension. Three-way interactions and 2-way interactions among independent component variables were evaluated first in the modeling process and included in a best model if response variables were found to have statistically significant regression coefficients. The regression coefficients and corresponding standard errors and covariances were used to estimate the maximal effect and standard error attributable to wire divergency angle (change from 30 degrees to 90 degrees ) and wire tension (change from 0 to 90 kg) for each ring diameter. RESULTS: All load/deformation curves had an initial exponential increase in stiffness, with the slope becoming linear at higher loads. The exponential phase was more pronounced in larger-diameter ring constructs and was mitigated by tensioning the wires. Ring diameter had the greatest influence on displacement that occurred before the curve became linear (semipartial r(2) [sp-r2] = .89), stiffness (sp-r2 = .94), and total displacement (sp-r2 = .93). Wire tension exerted a smaller influence on displacement that occurred before the curve became linear (sp-r2 =.06), stiffness (sp-r2 = .03), and total displacement (sp-r2 = .05). Wire divergence angle had a nominal effect on displacement that occurred before the curve became linear (sp-r2 = .0001), on stiffness (sp-r2 = .004), and on total displacement (sp-r2 =.003). CONCLUSIONS: Ring diameter had a profound effect on the axial stiffness characteristic of single ring constructs. Tensioning of the fixation wires can improve the axial stiffness characteristics of these constructs, particularly in larger diameter ring constructs, by mitigating the initial exponential phase of the load/deformation curve. Wire divergence angle had only a nominal differential effect on axial stability. CLINICAL RELEVANCE: Understanding how individual component variables and their interactions influence bone segment stability should help surgeons to optimize interfragmentary strain. Tensioning fixation wires is probably unnecessary in 50 mm diameter ring constructs, but assumes greater importance as ring diameter increases.     

Diagnosis and treatment of equine bacterial endometritis

The diagnosis of equine endometritis should generally begin with a history of reproductive failure followed by demonstration of inflammatory changes in the endometrium. Only then should the results of uterine cultures be considered in establishing an etiological diagnosis.

In therapy, the first consideration should be an attempt to correct the conditions which made the mare susceptible to the disease in the first place. Then advantage should be taken of measures to enhance the mare's natural resistance, perhaps sometimes even allowing her to clear herself of infection without antimicrobial therapy. Finally appropriate antimicrobial therapy should be selected based upon a knowledge of the conditions existing in the uterus and the results of culture and sensitivity.     

The onset of turbulence in pipe flow

Shear flows undergo a sudden transition from laminar to turbulent motion as the velocity increases, and the onset of turbulence radically changes transport efficiency and mixing properties. Even for the well-studied case of pipe flow, it has not been possible to determine at what Reynolds number the motion will be either persistently turbulent or ultimately laminar. We show that in pipes, turbulence that is transient at low Reynolds numbers becomes sustained at a distinct critical point. Through extensive experiments and computer simulations, we were able to identify and characterize the processes ultimately responsible for sustaining turbulence. In contrast to the classical Landau-Ruelle-Takens view that turbulence arises from an increase in the temporal complexity of fluid motion, here, spatial proliferation of chaotic domains is the decisive process and intrinsic to the nature of fluid turbulence.     

Evaluation of transmission of bovine viral diarrhea virus (BVDV) between persistently infected and naive cattle by the horn fly <Emphasis Type="Italic">(Haematobia irritans)</Emphasis>

Identifying reservoirs and transmission routes for bovine viral diarrhea virus (BVDV) are important in developing biosecurity programs. The aim of this study was to evaluate BVDV transmission by the hematophagous horn fly (Haematobia irritans). Flies collected from four persistently infected cattle were placed in fly cages attached to principal (n?=?4) and control (n?=?4) BVDV-naïve calves housed individually in isolation rooms. Flies were able to feed on principal calves, but a barrier prevented fly feeding from control calves. Flies were tested for BVDV by RT-PCR and virus isolation at time of collection from PI cattle and after 48 h of exposure on BVDV-naïve calves. Blood samples were collected from calves and tested for BVDV infection. Virus was isolated from fly homogenates at collection from PI animals and at removal from control and principal calves. All calves remained negative for BVDV by virus isolation and serology throughout the study. Bovine viral diarrhea virus may be detected in horn flies collected from PI cattle, but horn flies do not appear to be an important vector for BVDV transmission.     

Prevalence of fecal-borne parasites detected by centrifugal flotation in feline samples from two shelters in upstate New York

Over a 3.5-year period, fecal samples from 1322 cats from two shelters and affiliated foster homes in upstate New York were processed for parasite detection by both 1.18spg zinc sulfate and 1.3spg sugar double centrifugal flotation. In 50.9% of the samples at least one parasite was detected. Overall, 18 different parasites ranging in prevalence from 0.2% to 21% were recovered. The most prevalent parasites of foster and shelter cats in this study were Cystoisospora species and Toxocara cati (21% prevalence, each). In order of percentage of positive samples, other findings were: Giardia species (8.9%), Aelurostrongylus abstrusus (6.2%), taeniid eggs (3.9%), Cryptosporidium species (3.8%), Aonchotheca species (3.7%), Eucoleus species (2.3%), Ancylostoma species (2.2%), Cheyletiella species (2.0%), Dipylidium caninum (1.1%), Otodectes species, Toxoplasma-like oocysts and Sarcocystis species (0.8% each), Demodex and Spirometra species (0.4% each), and Alaria species and Felicola subrostratus (0.2% each).     

CNS and hypoderm regulatory elements of the Drosophila melanogaster dopa decarboxylase gene

Expression of the dopa decarboxylase gene (Ddc) is regulated in a tissue- and developmental stage-specific manner throughout the life cycle of the fruit fly, Drosophila melanogaster. Essential Ddc regulatory elements lie within 208 base pairs upstream from the RNA start point. Functional elements within this 5' flanking region were mapped by deletion analysis, which assayed expression in vivo after germline integration via P element vectors. One of the elements is essential for expression in both the larval and adult central nervous system, and at least two other elements are necessary for quantitatively normal expression in the hypoderm. Within each of the intervals that have regulatory effects are found sequence elements conserved between the Ddc genes of two distantly related species of flies. On the basis of this correlation, regulatory functions for these sequence elements can be postulated.     

Selective herbicides for establishment of <Emphasis Type="Italic">Eucalyptus benthamii</Emphasis> plantations

Competition control is essential for successful eucalyptus plantation establishment, yet few selective herbicides have been identified. Five herbicides, flumioxazin, imazamox, imazapic, oxyfluorfen, and sulfometuron methyl, were evaluated at either pre- or post-weed emergence timing for selective weed control in the establishment of Eucalyptus benthamii, a frost-tolerant species showing promise for commercial plantations in the southeastern United States and southern Brazil. Herbicides were applied at two or three rates and compared to a non-treated control and to near-complete weed control obtained with repeated glyphosate directed sprays. Herbicides were most efficacious when applied prior to weed emergence, at 2 weeks after planting 16-week-old containerized eucalyptus seedlings. Pre-emergence imazapic treatments resulted in broad-spectrum and persistent weed control, with 77–82% bare-ground at 60 days after treatment, but both pre- and post-emergence applications of imazapic caused excessive eucalyptus injury at the highest rate tested. Imazapic, sulfometuron, and imazamox were most effective for grass control. Both timings of flumioxazin were effective for forb control at the early assessment. All pre-emergence treatments enhanced stem volume compared to the non-treated control, but post-emergence treatments did not, suggesting the need for early weed control to facilitate E. benthamii growth. Pre-emergence applications of medium and high sulfometuron, low imazapic, high imazamox, and high oxyfluorfen rates increased stem volume four-fold to six-fold compared to the non-treated control. Repeated glyphosate directed sprays increased stem volume nearly three-fold compared to the control. These results confirm one early report of flumioxazin effectiveness and identify imazamox and imazapic as new selective herbicides for eucalyptus culture.     

Recording of Visual-Evoked Potentials in Dogs With Scalp Electrodes

Following unsuccessful attempts to record visual-evoked potentials (VEPs) in dogs with scalp electrodes, adoption of a new stimulation technique seems to be beneficial. Previously, flashes of white light administered after dark adaptation induced relatively high amplitude electroretinograms (ERGs) covering any VEP activity over the surface of the skull. ERG amplitude, however, can be significantly reduced using flashes of red light after light adaptation (mostly cone stimulation). Simultaneous ERG and VEP recording allows identification of VEPs composed of three significantly different negative peaks (N1, N2, and N3) measured in dogs anesthetized with chloralose and halothane. No more than two of the three peaks were seen in one recording. Only the N1 and N3 waves were consistently recorded in dogs anesthetized with thiopental and thiopental combined with halothane. In 50% of all recordings, N1 was seen alone. The other VEPs consisted of N1 and N2, or N1 and N3 occurring concurrently. The simultaneous occurrence of N2 and N3 waves, however, was never seen. Among all recordings, N1 was most frequently recorded (85% of measurements), followed by N3 and N2 (38% and 31% of measurements, respectively). Peaks of less than 90 ms are highly reproducible. Anesthesia is necessary to eliminate frequent artifacts obtained in conscious and sedated dogs. Thiopental and/or halothane had no effect on measured latencies compared with chloralose.     

Infection rates in clean surgical procedures: a comparison of ampicillin prophylaxis vs a placebo

A total of 122 dogs and 7 cats were included in a prospective, randomized, blind trial to determine the frequency of wound infection after clean surgical procedures and to compare the infection rates in dogs and cats given ampicillin (group 1) with those given a placebo (group 2). The 2 groups were similar in terms of mean age, sex ratio, duration of hospital stay, and types of surgical procedures. A wound infection developed in one of the dogs given ampicillin; there were no wound infections in the animals given the placebo. The infection rates in the 2 groups were not significantly different.