Solving the Martian meteorite age conundrum using micro-baddeleyite and launch-generated zircon.

Invaluable records of planetary dynamics and evolution can be recovered from the geochemical systematics of single meteorites. However, the interpreted ages of the ejected igneous crust of Mars differ by up to four billion years, a conundrum due in part to the difficulty of using geochemistry alone to distinguish between the ages of formation and the ages of the impact events that launched debris towards Earth. Here we solve the conundrum by combining in situ electron-beam nanostructural analyses and U-Pb (uranium-lead) isotopic measurements of the resistant micromineral baddeleyite (ZrO2) and host igneous minerals in the highly shock-metamorphosed shergottite Northwest Africa 5298 (ref. 8), which is a basaltic Martian meteorite. We establish that the micro-baddeleyite grains pre-date the launch event because they are shocked, cogenetic with host igneous minerals, and preserve primary igneous growth zoning. The grains least affected by shock disturbance, and which are rich in radiogenic Pb, date the basalt crystallization near the Martian surface to 187 ± 33 million years before present. Primitive, non-radiogenic Pb isotope compositions of the host minerals, common to most shergottites, do not help us to date the meteorite, instead indicating a magma source region that was fractionated more than four billion years ago to form a persistent reservoir so far unique to Mars. Local impact melting during ejection from Mars less than 22 ± 2 million years ago caused the growth of unshocked, launch-generated zircon and the partial disturbance of baddeleyite dates. We can thus confirm the presence of ancient, non-convecting mantle beneath young volcanic Mars, place an upper bound on the interplanetary travel time of the ejected Martian crust, and validate a new approach to the geochronology of the inner Solar System.

Atomic-scale age resolution of planetary events.

Resolving the timing of crustal processes and meteorite impact events is central to understanding the formation, evolution and habitability of planetary bodies. However, identifying multi-stage events from complex planetary materials is highly challenging at the length scales of current isotopic techniques. Here we show that accurate U-Pb isotopic analysis of nanoscale domains of baddeleyite can be achieved by atom probe tomography. Within individual crystals of highly shocked baddeleyite from the Sudbury impact structure, three discrete nanostructural domains have been isolated yielding average 206Pb/238U ages of 2,436±94 Ma (protolith crystallization) from homogenous-Fe domains, 1,852±45 Ma (impact) from clustered-Fe domains and 1,412±56 Ma (tectonic metamorphism) from planar and subgrain boundary structures. Baddeleyite is a common phase in terrestrial, Martian, Lunar and asteroidal materials, meaning this atomic-scale approach holds great potential in establishing a more accurate chronology of the formation and evolution of planetary crusts.

A longitudinal analysis of dentists' attitudes toward advertising their fees and services.

Over the past five years restrictions on advertising by various categories of professionals have gradually been reduced. A study was conducted in 1976 and replicated in 1981 to provide a basis for comparison of the change in attitudes by dentists toward advertising in general, advertising of fees, advertising of services, and the effect of advertising on various public issues. The attitudes of dentists toward advertising changed significantly during this period, generally becoming more positive.

A comparative analysis of the attitudes of dentists toward the advertising of their fees and services.

Restrictions on advertising about services performed by professional groups have recently been questioned by the government and consumers. The purpose of this study was to determine dentists' attitudes about the use of advertising in their profession and to compare the results with responses from physicians, attorneys, and accountants. While a survey of these groups in three metropolitan areas indicates mild support for advertising in general, there was a definite negative reaction to advertising in the respective professions. Participants also reported their attitudes about the effects of advertising on prices and fees, quality of services, and public expectations and governmental regulations.

Medical fee and service advertising: a response from physicians.

Restrictions on advertising about services performed by professional groups have recently been questioned by the government and consumerists. The purpose of this study was to determine physicians' attitudes about the use of advertising in their profession and also to compare these results with responses from dentists, attorneys, and accountants. While a survey of these groups in three metropolitan areas indicate mild support for advertising in general, there was a definite negative reaction to advertising in the respective professions. Participants also reported their attitudes about the effects of advertising on prices and fees, quality of services, and public expectation and governmental regulations. The concepts of social marketing and informative advertising are suggested as approaches that may meet the requirements of both the government and the professions.

A split laryngeal mask as an aid to training in fibreoptic tracheal intubation. A comparison with the Berman II intubating airway.

Thirty patients were randomly allocated to one of two groups in order to compare the use of a split laryngeal mask airway with the Berman II airway as aids to training in fibreoptic laryngoscopy. In both groups anaesthesia was induced with propofol and maintained with isoflurane in N2O/O2 (FIO2 = 0.5). The fibreoptic laryngoscope was guided towards the larynx using the split laryngeal mask airway in group 1 and the Berman airway in group 2. The tracheas of all patients were successfully intubated at the first attempt and no patient's peripheral oxygen saturation decreased below 92%. Two min after intubation mean heart rate was significantly greater in group 1 (101 beat.min-1) than in group 2 (84 beat.min-1) (P < 0.05). The split laryngeal mask is a useful aid to training in fibreoptic intubation and may allow better airway control than the Berman II intubating airway.

The effect of isoflurane or spinal anesthesia on indocyanine green disappearance rate in the elderly.

This study was designed to measure the disappearance rate of indocyanine green (ICG) as an indicator of hepatic blood flow in elderly patients undergoing internal fixation of fractured neck of femur. All patients were aged 60-90 yr and were randomized to receive either spinal (n = 10) or isoflurane (n = 10) anesthesia. In both groups systolic arterial blood pressure was maintained within 15% of resting levels by administration of fluids intravenously without vasoactive drugs. Patients were excluded if they required vasopressors to maintain arterial blood pressure. ICG disappearance rate was calculated using a single bolus technique before induction of anesthesia, and at 30, 60, and 120 min after induction of anesthesia. Sixteen patients completed the study. There were no statistically significant changes in ICG disappearance rate in either group at any time during the study, indicating that hepatic blood flow is not significantly altered by either spinal or isoflurane anesthesia provided that arterial blood pressure is maintained.

Serum mitochondrial aspartate transaminase activity after isoflurane or halothane anaesthesia.

We examined the effect of halothane or isoflurane anaesthesia on hepatic function in 30 ASA I-III patients aged 18-70 yr undergoing lumbar discectomy. Hepatic function was assessed before anaesthesia, at the end of surgery, and at 3, 6, 24 and 48 h after surgery using routine enzyme tests of hepatic function and mitochondrial aspartate transaminase (mAST) activity. Although serum mAST activities increased after surgery in both groups of patients, these increases were statistically significantly greater in the group that received halothane. The groups were similar with regard to other tests of hepatic function. Calculation of the ratio of serum enzyme activities compared to baseline values suggested that mAST is a sensitive marker of anaesthetic-induced hepatic injury.

Serum glutathione S-transferase concentrations and creatinine clearance after sevoflurane anaesthesia.

The effects of sevoflurane and isoflurane on serum glutathione S-transferase concentrations and creatinine clearance were compared in 50 ASA I-III patients aged over 18 years undergoing body surface surgery of 1-3 h predicted duration. Patients randomly received sevoflurane (n = 24) or isoflurane (n = 26) in nitrous oxide and oxygen (FIO2 = 0.4) via a nonrebreathing system. Fluids were standardised and patient's lungs ventilated to normocapnia. Expired concentration of anaesthetic agent was adjusted to maintain systolic arterial pressure between 70 and 100% of baseline. Patients received significantly less (p < 0.05) sevoflurane (1.0 MAC-h) than isoflurane (1.5 MAC-h). Using serum glutathione S-transferase concentrations and creatinine clearance as markers of hepatic and renal function respectively, no statistically significant differences were identified between the groups.