Guadalupe pluton–Mariposa Formation age relationships in the southern Sierran Foothills: Onset of Mesozoic subduction in northern California?

We report a new 153 ± 2 Ma SIMS U-Pb date for zircons from the hypabyssal Guadalupe pluton which crosscuts and contact metamorphoses upper crustal Mariposa slates in the southern Sierra. A ~950 m thick section of dark metashales lies below sandstones from which clastic zircons were analyzed at 152 ± 2 Ma. Assuming a compacted depositional rate of ~120 m/Myr, accumulation of Mariposa volcanogenic sediments, which overlie previously stranded Middle Jurassic and older ophiolite + chert-argillite belts in the Sierran Foothills, began no later than ~160 Ma. Correlative Oxfordian-Kimmeridgian strata of the Galice Formation occupy a similar position in the Klamath Mountains. We speculate that the Late Jurassic was a time of transition from (1) a mid-Paleozoic–Middle Jurassic interval of mainly but not exclusively strike-slip and episodic docking of oceanic terranes; (2) to transpressive plate underflow, producing calcalkaline igneous arc rocks ± outboard blueschists at ~170–150 Ma, whose erosion promoted accumulation of the Mariposa-Galice overlap strata; (3) continued transpressive underflow attending ~200 km left-lateral displacement of the Klamath salient relative to the Sierran arc at ~150–140 Ma and development of the apparent polar wander path cusps for North and South America; and (4) then nearly orthogonal mid and Late Cretaceous convergence commencing at ~125–120 Ma, during reversal in tangential motion of the Pacific plate. After ~120 Ma, nearly head-on subduction involving minor dextral transpression gave rise to voluminous continent-building juvenile and recycled magmas of the Sierran arc, providing the erosional debris to the Great Valley fore arc and Franciscan trench

Canadian Beaufort Sea 2000: The Environmental and Social Setting

The Beaufort Sea Conference 2000 brought together a diverse group of scientists and residents of the Canadian Beaufort Sea region to review the current state of the region's renewable resources and to discuss the future management of those resources. In this paper, we briefly describe the physical environment, the social context, and the resource management processes of the Canadian Beaufort Sea region. The Canadian Beaufort Sea land area extends from the Alaska-Canada border east to Amundsen Gulf and includes the northwest of Victoria Island and Banks Island. The area is defined by its geology, landforms, sources of freshwater, ice and snow cover, and climate. The social context of the Canadian Beaufort Sea region has been set by prehistoric Inuit and Gwich'in, European influence, more recent land-claim agreements, and current management regimes for the renewable resources of the Beaufort Sea.La Conférence de l'an 2000 sur la mer de Beaufort a attiré un groupe hétérogène de scientifiques et de résidents de la région de la mer de Beaufort en vue d'examiner le statut actuel des ressources renouvelables de cette zone et de discuter de leur gestion future. Dans cet article, on décrit brièvement l'environnement physique, le contexte social et les processus de gestion des ressources de la zone canadienne de la mer de Beaufort. La superficie terrestre de la mer de Beaufort au Canada s'étend de la frontière entre ce pays et l'Alaska jusqu'au golfe Amundsen à l'est, et elle englobe le nord-ouest de l'île Victoria et de l'île Banks. Cette zone est définie par sa géologie, son relief, ses sources d'eau douce, son couvert glaciel et nival ainsi que son climat. Le contexte social de la région de la mer de Beaufort canadienne a été établi par les Inuits et Gwich'in préhistoriques, l'influence européenne, les récentes ententes territoriales ainsi que les régimes actuels de gestion des ressources renouvelables de la mer de Beaufort

Search for Spin-Dependent Short-Range Force Using Optically Polarized 3^3He Gas

We propose a new method to detect short-range \textit{P-} and \textit{T-} violating interactions between nucleons, based on measuring the precession frequency shift of polarized $^3$He nuclei in the presence of an unpolarized mass. To maximize the sensitivity, a high-pressure $^3$He cell with thin glass windows (250 $\rm\mu m$) is used to minimize the distance between the mass and $^3$He. The magnetic field fluctuation is suppressed by using the $^3$He gas in a different region of the cell as a magnetometer. Systematic uncertainties from the magnetic properties of the mass are suppressed by flipping both the magnetic field and spin directions. Without any magnetic shielding, our result has already reached the sensitivity of the current best limit. With improvement in uniformity and stability of the field, we can further improve the sensitivity by two orders of magnitude over the force range from $10^{-4}-10^{-2}$ m

Formaldehyde over the central Pacific during PEM-Tropics B

Formaldehyde, CH2O, mixing ratios are reported for the central Pacific troposphere from a series of 41 flights, which took place in March-April 1999 as part of the NASA Pacific Exploratory Mission (PEM) -Tropics B mission. Ambient CH2O was collected in aqueous media and quantified using an enzyme-derivatization fluorescence technique. Primary calibration was performed using aqueous standards and known flow rates. Occasionally, CH2O gas standard additions to ambient air were performed as a secondary calibration. Analytical blanks were determined by replacing ambient air with pure air. The estimated precision was ±30 pptv and the estimated accuracy was the sum of ±30 parts per trillion by volume (pptv) ±15% of the measured value. Approximately 25% of the observations were less than the instrumental detection limit of 50 pptv, and 85% of these occurred above 6 km. CH2O mixing ratios decreased with altitude; for example, near the equator the median value in the lowest 2 km was 275 pptv, decreased to 150 pptv by 6 km and was below 100 pptv above 8 km. Between 130 and 170 W and below 1km, a small variation of CH2O mixing ratio with latitude was noted as near-surface median mixing ratios decreased near the equator (275 pptv) and were greater on either side (375 pptv). A marked decrease in near-surface CH2O (200 pptv) was noted south of 23° S on two flights. Between 3° and 23° S, median CH2O mixing ratios were lower in the eastern tropical Pacific than in the western or central Pacific; nominal differences were >100 pptv near the surface to ∼100 pptv at midaltitude to ∼50 pptv at high altitude. Off the coast of Central America and Mexico, mixing ratios as high as 1200 pptv were observed in plumes that originated to the east over land. CH2O observations were consistently higher than the results from a point model constrained by other photochemical species and meteorological parameters. Regardless of latitude or longitude, agreement was best at altitudes above 4 km where the difference between measured and modeled CH2O medians was less than 50 pptv. Below 2 km the model median was approximately 150 pptv less than the measured median. Copyright 2001 by the American Geophysical Union

Rural parents, teenagers and alcohol: what are parents thinking?

INTRODUCTION: The fundamental role of alcohol in the lives of young Australians is mirrored in the level of drinking by adolescents. In 2001, more than one in four Australian adolescents aged 14-19 years consumed alcohol weekly. Teenagers in rural areas are more likely to consume alcohol than their metropolitan counterparts. Parents are key \u27gatekeepers\u27 of adolescent behaviour and as such are a salient group to consider in relation to adolescent alcohol use. The aim of this study was to explore parents\u27 attitudes, beliefs, concerns and receptiveness to harm minimisation strategies with respect to teenage use of alcohol. METHODS: A convenience sample of parents with adolescent children attended a series of focus groups across the north and north-western area of the State of Victoria, Australia. Schools were approached to advertise the project and invite parents to participate. Snowball sampling was used to enhance recruitment. RESULTS: Parents described patterns of alcohol use such as \u27drinking to get drunk\u27 and the influence of both parents and peers on the consumption of alcohol by adolescents. Few parents were concerned about the long-term risks of alcohol use by teenagers; rather they were more concerned about the short-term harms, for example, road trauma and other accidents and risky behaviours such as binge drinking. Parents indicated that they perceived alcohol to be less harmful than other drugs and many indicated that alcohol was often not perceived to be a drug. A number of strategies were adopted by parents to negotiate teenagers\u27 drinking and to minimise the risks associated with alcohol use. These included transporting teenagers to parties, providing teenagers with a mobile phone, setting clear guidelines about alcohol use and/or providing teenagers with a small amount of alcohol. These were seen by parents as strategies for reducing the risks associated with alcohol consumption. Many parents reported that they do not feel well informed about alcohol use and how and when to use harm reduction strategies. CONCLUSIONS: Rural parents are unsure how to respond to teenagers\u27 alcohol use and drunkenness. While some parental strategies for harm reduction (such as supplying adolescents with a small amount of alcohol) may have good face validity in reducing alcohol consumption among adolescents, these strategies are not supported by previous research findings.<br /

Evolution and chemical consequences of lightning-produced NOx observed in the North Atlantic upper troposphere

Airborne observations of NO during the Subsonics Assessment Ozone and Nitrogen Oxides Experiment (SONEX) reveal episodes of high NOx in the upper troposphere believed to be associated with lightning. Linkage to specific periods of lightning activity is possible through back trajectories and data from the National Lightning Detection Network. Lagrangian model calculations are used to explore the evolution of these high NOx plumes over the 1-2 days between their introduction and subsequent sampling by NASA's DC-8 aircraft. Simulations include expected changes in HNO3, H2O2, CH3OOH, HO2, and OH. Depending on the time of injection and dilution rate, initial NOx concentrations are estimated to range from 1 to 7 ppbv. Similar to many previous studies, simulated HNO3 concentrations tend to be greater than observations. Several possible explanations for this difference are explored. H2O2 observations are shown to be consistent with removal in convective activity. While it is possible that upper tropospheric CH3OOH is enhanced by convection, simulations show such increases in CH3OOH can be short-lived (e.g., &lt; 12 hours) with no perceptible trace remaining at the time of sampling. High NO levels further prevent elevated levels of CH3OOH from propagating into increases in H2O2. HO2 is suppressed through reaction with NO in all cases. Simulated increases in OH exceeded a factor of 2 for some cases, but for the highest NOx levels, loss of OH via OH+NO2 offset production from HO2+NO. Additional increases in OH of 30-60% could result from convection of CH3OOH. A final point of discussion concerns how the chemistry within these plumes, their long-range transport, and their potential importance in sustaining background NOx far from source regions present a challenge to global and regional model simulations. Copyright 2000 by the American Geophysical Union

Intra-Arterial Infusion with Methotrexate in the Rat

The superiority of intra-arterial infusion with methotrexate (MTX) over its systemic use in the treatment of head and neck tumours is still being questioned. A model in the rat, suitable for intra-arterial administration of MTX could be constructed. In this model 3 schedules have been investigated: (1) 7 days continuous intra-arterial infusion with MTX; (2) the same schedule combined with leucovorin (CF) 6-hourly intraperitoneally (i.p.) after Sullivan et al. (1959); (3) intermittent administration of MTX 2 × 24 h intra-arterial infusion on Day 1 and 4, while on Day 2, 3, 5, 6 and 7 the catheter is kept open by the continuous intra-arterial infusion of saline. For all the three schedules intra-arterial MTX proved to be superior to its systemic use