Shock-formed carbon materials with intergrown sp3- and sp2-bonded nanostructured units.

Studies of dense carbon materials formed by bolide impacts or produced by laboratory compression provide key information on the high-pressure behavior of carbon and for identifying and designing unique structures for technological applications. However, a major obstacle to studying and designing these materials is an incomplete understanding of their fundamental structures. Here, we report the remarkable structural diversity of cubic/hexagonally (c/h) stacked diamond and their association with diamond-graphite nanocomposites containing sp3-/sp2-bonding patterns, i.e., diaphites, from hard carbon materials formed by shock impact of graphite in the Canyon Diablo iron meteorite. We show evidence for a range of intergrowth types and nanostructures containing unusually short (0.31 nm) graphene spacings and demonstrate that previously neglected or misinterpreted Raman bands can be associated with diaphite structures. Our study provides a structural understanding of the material known as lonsdaleite, previously described as hexagonal diamond, and extends this understanding to other natural and synthetic ultrahard carbon phases. The unique three-dimensional carbon architectures encountered in shock-formed samples can place constraints on the pressure-temperature conditions experienced during an impact and provide exceptional opportunities to engineer the properties of carbon nanocomposite materials and phase assemblages.

Diamond-Graphene Composite Nanostructures.

The search for new nanostructural topologies composed of elemental carbon is driven by technological opportunities as well as the need to understand the structure and evolution of carbon materials formed by planetary shock impact events and in laboratory syntheses. We describe two new families of diamond-graphene (diaphite) phases constructed from layered and bonded sp3 and sp2 nanostructural units and provide a framework for classifying the members of this new class of materials. The nanocomposite structures are identified within both natural impact diamonds and laboratory-shocked samples and possess diffraction features that have previously been assigned to lonsdaleite and postgraphite phases. The diaphite nanocomposites represent a new class of high-performance carbon materials that are predicted to combine the superhard qualities of diamond with high fracture toughness and ductility enabled by the graphitic units and the atomically defined interfaces between the sp3- and sp2-bonded nanodomains.

Duration of action of mepivacaine and lidocaine in equine palmar digital perineural blocks in an experimental lameness model.

OBJECTIVE: To establish and compare the onset and duration of action of 2 local anesthetics based on objective lameness and skin sensitivity assessment. STUDY DESIGN: Interventional crossover experimental trial with balanced randomization. ANIMALS: Eight horses. METHODS: Reversible forelimb lameness was induced in 8 horses. A palmar digital nerve block (PDNB) was applied with mepivacaine or lidocaine (both 2%). Quantitative lameness and skin sensitivity data were collected with an inertial sensor system and a force gauge, respectively. The times to lameness resolution/skin desensitization (T1), consistent lameness detection/partial return of skin sensitivity (T2), and complete return of lameness/skin sensitivity (T3) were determined and compared between treatments and assessment methods. RESULTS: Mepivacaine blocks resolved lameness in 8/8 horses, compared to 3/8 horses with lidocaine blocks. Both agents led to skin desensitization in 8/8 horses. Skin desensitization occurred sooner than lameness resolution after mepivacaine (P = .047). Duration of action was longer with mepivacaine than lidocaine (mean T3_lameness mepivacaine 366 minutes, lidocaine 113 minutes (P = .038); T3_skin mepivacaine 195 minutes, lidocaine 63 minutes [P ≤ .001]). Skin sensitivity returned sooner than lameness after lidocaine block at T3 (P = .015). CONCLUSION: The use of lidocaine in PDNBs for the purpose of lameness diagnosis should be reassessed, as it may not resolve lameness despite loss of skin sensation. Mepivacaine is superior, with a reliable onset and longer duration of action. Skin desensitization as an indicator for the onset of action or effectiveness of PDNBs for mepivacaine and lidocaine, or as a measure of the duration of action of lidocaine PDNBs should be interpreted with caution.

An ex vivo biomechanical study comparing strength characteristics of a new technique with the three-loop pulley for equine tenorrhaphy.

OBJECTIVE: To test single cycle to failure tensile strength characteristics of 6 suture material-pattern combinations in equine superficial digital flexor (SDF) tenorrhaphy, specifically to compare a 10-strand modification of the Savage core suture technique with the 3-loop pulley technique. STUDY DESIGN: Ex vivo mechanical experiment comparing 3 different suture patterns with 2 different materials. SAMPLE POPULATION: Forelimb and hindlimb SDF tendons (n=48) harvested from adult Thoroughbred and Standardbred horses of mixed age and gender. METHODS: Six suture material-pattern combinations were evaluated: (1) 10-strand Savage, size 2 polydioxanone (PDS); (2) 10-strand Savage, size 2 polyglactin 910 (PG910); (3) 10-strand Savage, size 2 PDS with Lin-locking epitenon suture, size 2-0 PDS; (4) 10-strand Savage size 2 PG910 with Lin-locking epitenon suture, size 2-0 PDS; (5) 3-loop pulley, size 2 PDS; and (6) 3-loop pulley, size 2 PG910. Maximum load at failure (N), gap at failure (mm), and mode of failure (suture breakage or pull through) were evaluated for each of the 6 suture material-pattern combinations and underwent statistical analysis to determine significance of differences and interactions of the measured data. RESULTS: The 10-strand Savage technique failed at a mean load of 872 (804-939, 95% CI). The 10-strand Savage with Lin-locking failed at a significantly greater mean load of 998 (930-1065, 95% CI). The 3-loop pulley pattern failed with a mean load of 337 (270-405, 95% CI). There were significant interactions between the technique and suture material used. CONCLUSION: The 10-strand Savage technique for repair of transected cadaver SDF tendons has superior strength characteristics with or without the epitenon suture when compared to the 3-loop pulley. Suture material and pattern interactions were observed with PG 910 conferring higher strength for the 10-strand Savage whereas PDS did so for the 3-loop pulley.

Quantifying hexagonal stacking in diamond.

Diamond is a material of immense technological importance and an ancient signifier for wealth and societal status. In geology, diamond forms as part of the deep carbon cycle and typically displays a highly ordered cubic crystal structure. Impact diamonds, however, often exhibit structural disorder in the form of complex combinations of cubic and hexagonal stacking motifs. The structural characterization of such diamonds remains a challenge. Here, impact diamonds from the Popigai crater were characterized with a range of techniques. Using the MCDIFFaX approach for analysing X-ray diffraction data, hexagonality indices up to 40% were found. The effects of increasing amounts of hexagonal stacking on the Raman spectra of diamond were investigated computationally and found to be in excellent agreement with trends in the experimental spectra. Electron microscopy revealed nanoscale twinning within the cubic diamond structure. Our analyses lead us to propose a systematic protocol for assigning specific hexagonality attributes to the mineral designated as lonsdaleite among natural and synthetic samples.

Effects of treatment with omeprazole or ranitidine on gastric squamous ulceration in racing Thoroughbreds.

OBJECTIVE: To compare the effects of oral administration of omeprazole and ranitidine on gastric squamous ulceration in Thoroughbreds in race training. DESIGN: Modified crossover study. ANIMALS: 60 Thoroughbreds in race training with gastric squamous mucosal ulceration. PROCEDURE: Horses were randomly allocated into 3 groups. Group 1 received no treatment for 28 days followed by administration of omeprazole (4 mg/kg [1.8 mg/lb], PO, once daily) for 28 days; group 2 received omeprazole (4 mg/kg, PO, once daily) for 28 days followed by no treatment for 28 days; and group 3 received ranitidine (6.6 mg/kg [3.0 mg/lb], PO, q 8 h) for 28 days followed by administration of omeprazole (4 mg/kg, PO, once daily) for 28 days. Ulceration was assessed endoscopically at days 0, 28, 42, and 56. Lesions were scored from 0 (no ulceration) to 3 (severe ulceration). RESULTS: After the initial 28 days of treatment, the decrease in ulcer severity was significantly greater after omeprazole treatment than after ranitidine treatment. Ulcer severity decreased significantly in group 3 horses after 14 days of treatment with omeprazole. Discontinuation of omeprazole resulted in worsening of ulcer scores; however, ulcer scores at completion of the study were less than at day 0. Horses that received omeprazole after 28 days of ranitidine treatment had a further reduction in ulcer severity. CONCLUSIONS AND CLINICAL RELEVANCE: Omeprazole was more effective than ranitidine in healing gastric squamous ulcers in Thoroughbreds in race training. Improvement was detected by 14 days and persisted in most of the group 2 horses for at least 28 days after omeprazole treatment was discontinued.