Validation of a Laboratory Method for Evaluating Dynamic Properties of Reconstructed Equine Racetrack Surfaces

Background

Racetrack surface is a risk factor for racehorse injuries and fatalities. Current research indicates that race surface mechanical properties may be influenced by material composition, moisture content, temperature, and maintenance. Race surface mechanical testing in a controlled laboratory setting would allow for objective evaluation of dynamic properties of surface and factors that affect surface behavior.

Objective

To develop a method for reconstruction of race surfaces in the laboratory and validate the method by comparison with racetrack measurements of dynamic surface properties.

Methods

Track-testing device (TTD) impact tests were conducted to simulate equine hoof impact on dirt and synthetic race surfaces; tests were performed both in situ (racetrack) and using laboratory reconstructions of harvested surface materials. Clegg Hammer in situ measurements were used to guide surface reconstruction in the laboratory. Dynamic surface properties were compared between in situ and laboratory settings. Relationships between racetrack TTD and Clegg Hammer measurements were analyzed using stepwise multiple linear regression.

Results

Most dynamic surface property setting differences (racetrack-laboratory) were small relative to surface material type differences (dirt-synthetic). Clegg Hammer measurements were more strongly correlated with TTD measurements on the synthetic surface than the dirt surface. On the dirt surface, Clegg Hammer decelerations were negatively correlated with TTD forces.

Conclusions

Laboratory reconstruction of racetrack surfaces guided by Clegg Hammer measurements yielded TTD impact measurements similar to in situ values. The negative correlation between TTD and Clegg Hammer measurements confirms the importance of instrument mass when drawing conclusions from testing results. Lighter impact devices may be less appropriate for assessing dynamic surface properties compared to testing equipment designed to simulate hoof impact (TTD).

Potential Relevance

Dynamic impact properties of race surfaces can be evaluated in a laboratory setting, allowing for further study of factors affecting surface behavior under controlled conditions.     

Variation of physiological and antioxidative responses in tea cultivars subjected to elevated water stress followed by rehydration recovery

Water stress is a major limitation for plant survival and growth. Several physiological and antioxidative mechanisms are involved in the adaptation to water stress by plants. In this experiment, tea cultivars (TV-1, TV-20, TV-29 and TV-30) were subjected to drought stress by withholding water for 20 days followed by rehydration. An experiment was thus performed to test and compare the effect of dehydration and rehydration in growing seedlings of tea cultivars. The effect of drought stress and post stress rehydration was measured by studying the reactive oxygen species (ROS) metabolism in tea. Water stress decreased nonenzymic antioxidants like ascorbate and glutathione contents with differential responses of enzymic antioxidants in selected clones of Camellia sinensis indicating an oxidative stress situation. This was also apparent from increased lipid peroxidation, O₂ ⁻ and H₂O₂ content in water stress imposed plants. But the oxidative damage was not permanent as the plants recovered after rehydration. Comparatively less decrease in antioxidants, higher activities of POX, GR, CAT with higher phenolic contents suggested better drought tolerance of TV-1, which was also visible from the recovery study, where it showed lower ROS level and higher recovery of antioxidant property in response to rehydration, thus proving its better recovery potential. On the other hand, highest H₂O₂ and lipid peroxidation with decrease in phenolic content during stress in TV-29 suggested its sensitivity to drought. The antioxidant efficiency and biochemical tolerance in response to drought stress thus observed in the tested clones of Camellia sinensis can be arranged in the order as TV-30 > TV-1 > TV-29 > TV-20.     

Power-limited contraction dynamics of Vorticella convallaria: an ultrafast biological spring

Vorticella convallaria is one of the fastest and most powerful cellular machines. The cell body is attached to a substrate by a slender stalk containing a polymeric structure—the spasmoneme. Helical coiling of the stalk results from rapid contraction of the spasmoneme, an event mediated by calcium binding to a negatively charged polymeric backbone. We use high speed imaging to measure the contraction velocity as a function of the viscosity of the external environment and find that the maximum velocity scales inversely with the square root of the viscosity. This can be explained if the rate of contraction is ultimately limited by the power delivered by the actively contracting spasmoneme. Microscopically, this scenario would arise if the mechanochemical wave that propagates along the spasmoneme is faster than the rate at which the cell body can respond due to its large hydrodynamic resistance. We corroborate this by using beads as markers on the stalk and find that the contraction starts at the cell body and proceeds down the stalk at a speed that exceeds the velocity of the cell body.     

Responses of Camellia sinensis to Drought and Rehydration

The effects of drought and rehydration on tea seedlings were significant. After five days of drought imposition the contents of chlorophylls, carotenoids, ascorbate and glutathione, and activities of guaiacol peroxidase and glutathione reductase decreased. Simultaneously, contents of proline, H₂O₂ and superoxide anion, lipid peroxidation and activities of catalase and superoxide dismutase increased. These parameters recovered to different degrees during subsequent rehydration.     

Evaluation of denaturing high performance liquid chromatography (DHPLC) for the mutational analysis of the neurofibromatosis type 1 (<Emphasis Type="Italic">NF1</Emphasis>) gene

The identification of mutations in the NF1 gene causing type 1 neurofibromatosis (NF1) has presented a considerable challenge because of the large size of the gene, the lack of significant mutational clustering, the diversity of the underlying pathological lesions and the presence of NF1 pseudogenes. Denaturing high performance liquid chromatography (DHPLC), a high throughput, non-hazardous and largely automated heteroduplex-based technique, is in many ways ideally suited to mutation detection in this condition. DHPLC was therefore optimised for the rapid screening of the 60 exons and splice junctions of the NF1 gene in patients with NF1. The sensitivity of DHPLC was evaluated in a retrospective study of a cohort of 111 unrelated NF1 patients with known germline mutations; 97% of mutations were detected. In a subsequent prospective analysis of 50 unrelated NF1 patients, germline mutations were identified in 34 individuals (68%), 22 of these alterations being novel. This represents the highest rate of mutation detection so far reported for the NF1 gene with a single screening technique and genomic DNA as a target.     

Hopf bifurcation in a stomatal oscillator

Stomata are microscopic openings in leaves of green plants which permit gas exchange. This paper presents a parameter study of a model of a stomatal oscillator first derived by Delwiche and Cooke in 1977. We prove the existence of an unstable limit cycle by using the theory of the Hopf bifurcation. Other bifurcations exhibited by the model are also discussed.     

Identification of main effect and epistatic quantitative trait loci for morphological and yield-related traits in peanut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

An effort was made in the present study to identify the main effect and epistatic quantitative trait locus (QTL) for the morphological and yield-related traits in peanut. A recombinant inbred line (RIL) population derived from TAG 24 × GPBD 4 was phenotyped in seven environments at two locations. QTL analysis with available genetic map identified 62 main-effect QTLs (M-QTLs) for ten morphological and yield-related traits with the phenotypic variance explained (PVE) of 3.84–15.06%. Six major QTLs (PVE >?10%) were detected for PLHT, PPP, YPP, and SLNG. Stable M-QTLs appearing in at least two environments were detected for PLHT, LLN, YPP, YKGH, and HSW. Five M-QTLs governed two traits each, and 16 genomic regions showed co-localization of two to four M-QTLs. Intriguingly, a major QTL reported to be linked to rust resistance showed pleiotropic effect for yield-attributing traits like YPP (15.06%, PVE) and SLNG (13.40%, PVE). Of the 24 epistatic interactions identified across the traits, five interactions involved six M-QTLs. Three interactions were additive × additive and remaining two involved QTL × environment (QE) interactions. Only one major M-QTL governing PLHT showed epistatic interaction. Overall, this study identified the major M-QTLs for the important productivity traits and also described the lack of epistatic interactions for majority of them so that they can be conveniently employed in peanut breeding.     

CYTOPLASMIC INCOMPATIBILITY STUDIES IN THE MYXOMYCETE DIDYMIUM IRIDIS: RECOVERY AND NUCLEAR SURVIVAL IN HETEROKARYONS

At least eleven somatic compatibility loci exist in the myxomycete Didymium iridis. Cell fusion is controlled by at least seven fusion loci (Fus1–Fus7). Cytoplasmic compatibility is controlled by at least four clear-zone loci (Cz1–Cz4). Plasmodia with identical phenotypes at all seven fusion loci, but different phenotypes at the clear-zone loci, will fuse temporarily, but fusion is soon blocked by cytoplasmic reactions which prevent complete mixing. Areas which contain cytoplasm from two incompatible Plasmodia become clearly delineated from healthy cytoplasm. Such areas, termed clear zones, have been isolated and found to recover. If clear zones are sectioned into several small pieces, not all pieces will recover, indicating that toxic cytoplasmic reactions have occurred. Plasmodial fusion studies and F₁ studies of recovered clear zones indicate that the clear-zone loci may also control nuclear survival in heterokaryons.