Wood as a linear orthotropic viscoelastic material

Summary Measurements were made of the principal components of the creep compliance tensor in the radial-longitudinal and the tangential-longitudinal planes of Douglas-fir at 10 percent moisture content. Extensional creep compliance measurements at angles to the grain were also made. The results show that creep parallel to grain occurs at an increase in volume, and that creep at angles to the grain can be predicted from standard transformation equations. It is concluded that wood can be regarded as a linear orthotropic viscoelastic material.     

Quality Assessment of Temperate Zone Deciduous Hardwood Seedlings

Research regarding seedling quality issues has been performed for decades and focused primarily on conifer species, which comprise the greatest proportion of nursery production worldwide. Demand for hardwood seedlings, particularly for conservation purposes, has increased steadily in recent years, emphasizing the need for seedling quality assessment protocols specific to these species. Important differences between conifer (gymnosperm) and hardwood (angiosperm) species require the creation of seedling evaluative programs specific to each group. Variation in phenology and ecological adaptability of hardwood species limits the validity of inferences made between and within genera. Annual cycles of leaf emergence followed by abscission in temperate hardwoods necessitate examination of seasonal variation in indicators of physiological condition that do not require leaf tissue (e.g., mineral nutrition, electrolyte leakage). Also, it is crucial to identify appropriate sampling periods and plant tissues for testing such that test results may be accurately compared. Though certain parameters (e.g., morphological) may be readily used in both conifer and hardwood seedling quality testing programs with little modification, additional refinement is needed to improve predictive capacity for hardwoods across a variety of environments. We review the current state of knowledge regarding seedling quality testing of temperate deciduous hardwood species, discuss limitations in incorporating traditional components of quality testing programs, and set priorities for future study.     

Comparison of lameness outcomes in horses with acute or chronic digital lameness that underwent magnetic resonance imaging

ABSTRACT

Aims: To compare the outcome, in terms of lameness score or return to athletic function, of horses with acute vs. chronic digital lameness that underwent magnetic resonance imaging (MRI) of the distal limb and to compare the proportion of horses that received intra-articular therapy of the distal interphalangeal (DIP) joint and pattern of diagnostic analgesia in these groups.

Methods: This is a retrospective study of horses (n?=?95) with acute (≤12 weeks; n?=?46) or chronic (>12 weeks; n?=?49) digital lameness that underwent MRI of the distal limb from 2009–2016, at two equine referral centres in the USA. Criteria for inclusion in the study were that a majority of lameness localised distal to the fetlock, and that lameness assessments for ≥12 months following MRI could be obtained from the medical record or the owner could be interviewed regarding their horse's athletic function. Outcome was characterised by an improvement score where 2?=?return to work at a previous or higher level or lameness improved by one grade or more, 1?=?return to work at a lower level or lameness improved by less than one grade, and 0?=?did not return to work or lameness grade worsened. Whether horses had received intra-articular therapy of the DIP joint and the pattern of diagnostic analgesia prior to MRI was also obtained from medical records or by interviewing the owner.

Results: There was a difference (p?=?0.004) in the proportion of horses assigned to improvement scores of 0, 1 and 2 between horses with acute or chronic lameness. There was no evidence of a difference in the likelihood of having received intra-articular therapy of the DIP joint prior to MRI between horses with chronic or acute lameness (p = 0.085). Similarly, there was no evidence of a difference in the pattern of diagnostic analgesia prior to MRI between the two groups (p = 0.94). Eighty-two percent of owners of horses with acute and 62% of those with horses with chronic lameness had a positive opinion of the utility of MRI as a diagnostic modality.

Conclusion: In a population of horses with digital lameness undergoing MRI, a difference in the outcome, in terms of lameness score or return to athletic function was identified between horses with acute lameness compared to those with chronic lameness.

Clinical relevance: Horses with digital lameness that undergo MRI when the lameness is acute may have an improved prognosis due to accurate diagnosis and earlier application of appropriate therapy.     

Acquisition and interpretation of radiographs of the equine skull

The complex anatomy of the equine skull creates a radiographic challenge. However, radiographs are a commonly required tool in diagnosing dental and sinonasal disease, as well as other disorders of the equine skull. High quality, complete radiographic studies are essential for adequate evaluation. Radiographic technique and interpretation are reviewed in this paper.     

The effects of medetomidine hydrochloride on the electroretinogram of normal dogs

Purpose  To determine the effects of a standardized intravenous dose of an α-2 agonist (Domitor^®, Orion Pharma, distributed by Pfizer Animal Health, Exton, PA) on the electroretinogram (ERG) response in normal dogs.
Methods  Twenty-five normal dogs were used to collect ERG responses including a- and b-wave implicit times (IT) and amplitudes (AMP) before and after administration of medetomidine. Dogs were dark adapted for 20 min and ERGs were obtained using the HMsERG (RetVetCorp Inc., Columbia, MO). The QuickRetCheck protocol (Narfström) was employed to provide the following flash intensities: 10 mcd s/m², 3 cd s/m², and 10 cd s/m². ERGs were repeated after 375 µg/m² of medetomidine intravenously. Statistical analysis of the difference between the responses before and after medetomidine at all flash intensities was performed using a mixed effects model for anova .
Results  The P value for the effect of medetomidine on each of the ERG responses was < 0.01. The estimates of the effect of medetomidine were (+)1.35 ms, (–)23 µV, (+)3.16 ms, and (–)47 µV for the a-wave IT, a-wave AMP, b-wave IT, and the b-wave AMP, respectively.
Conclusions  Medetomidine significantly prolongs the implicit time and lowers the amplitude response of both the a- and b-waves in normal dogs at all flash intensities examined. Clinically, however, medetomidine only minimally affects the retinal responses and is a viable choice for use in dog ERGs.