No description available.

No description available.

The technique of transcranial Doppler ultrasound (TCD) was used to assess cerebral blood flow (CBF) in humans. Studies were performed at rest and during dynamic submaximal exercise. In the resting experiments, TCD was combined with the technique of dynamic end-tidal forcing to study the dynamics of the CBF response to step changes in end-tidal (i.e. arterial) PC02 and PO2 In the resting and exercise experiments, the degree of consistency was examined between three indices of CBF that can be extracted from the TCD spectrum. Finally, the ventilatory and the CBF responses to acute isocapnic hypoxia were examined to try to quantify the possible reduction in ventilation that could be attributed to changes in CBF with hypoxia. In the studies performed at rest, during either hypoxia and/or hypercapnia (Chapter 2), the three indices of CBF extracted from the TCD spectrum were all consistent. However, during submaximal exercise (Chapter 5), the indices were less consistent and results suggest that the increase in CBF with exercise that has been reported with TCD needs to be treated with caution. The dynamic studies of the CBF response to step changes in end-tidal PC02 and PO2 in humans revealed that the CBF response to hypercapnia (Chapter 3) is characterised by a significant asymmetry, with a slower on-transient than off-transient, and also by a degree of undershoot following the relief of hypercapnia. The CBF response to hypocapnia (Chapter 4) is also characterised by a significant asymmetry, with a faster on-transient than off-transient. Furthermore, there is a slow progressive adaptation throughout the hypocapnic period. These studies show that the CBF responses to hypercapnia and hypocapnia are much faster than previously been thought. Finally, the work described in Chapter 6 attempts to quantify the possible reduction in ventilation that could be attributed to changes in CBF with hypoxia to determine whether it could be of sufficient magnitude to underlie hypoxic ventilatory decline (HVD). The results suggest that, in awake humans, changes in CBF during acute isocapnic hypoxia are quantitatively insufficient to underlie HVD.

No description available.

No description available.

A model has been developed and run with sufficiently high resolution (~9 km and 45 levels) and a large enough spatial domain to allow for realistic representation of flow through the narrow and shallow straits in the Bering Sea region. This is potentially important for quantification of long-term mean and time-dependent ocean circulation, and water mass and property exchanges between the Pacific and Arctic oceans. The mean modeled circulation in the Bering Sea is found to be in good agreement with the limited observational data. The Bering Sea Basin, Bering Slope Current, and straits on the northern shelf are identified as highly energetic regions based on eddy kinetic energy fields. Some high biological productivity regions of the northern Bering Sea identified in observational studies are coincident with regions of persistently high energy (up to 2600 cm2 s-2 at mid-depth) throughout the annual cycle. Over a twentythree year interval (1979-2001), mean transport through Bering Strait is estimated to be 0.65 Sv. Comparison of model results with published observations indicates that ocean circulation is not only variable at seasonal to interdecadal scales, but it is also responsive to short-term atmospheric forcing. Comparison with observations of nearbottom salinity indicates that the model is reasonably representing the major water mass properties. The long-term model results for the Bering Sea provide important insights into the ocean circulation and fluxes and they are a useful frame of reference for limited observations that are short-term and/or cover only a small geographic region.

The dynamic response of the oceanic mixed-layer to the thermodynamic forcing at the sea surface is analyzed in order to describe the pattern of the oceanic meridional overturning. The technique proposed in this study is based on residual-mean theory, which takes into account the transport of buoyancy and tracers by transient eddies. From the observed air-sea density flux and mixed-layer density distributions, we estimate the two components of the Meridional Overturning Circulation (MOC) corresponding to the adiabatic (along-isopycnal) advection and the diabatic (cross-isopycnal) flux. Calculations are performed for the global ocean and, additionally, for each oceanic basin. The proposed method extends the Walin (1982) mass transformation theory, and permits, for the first time, assessment of the strength of the MOC adiabatic component from the sea surface data. This study offers a statistical description of the atmospheric and oceanic databases and gives some suggestions for the choice of specific datasets. In particular, the two most reliable atmospheric climatology databases (ECMWF and NCEP/NCAR re-analyses) are compared, and the impact of their inaccuracies on the MOC calculations is evaluated.

This study investigates if the descent of odd nitrogen, generated in the thermosphere and the upper mesosphere by energetic particle precipitation (EPP-NOx), has a detectable impact on stratospheric wind and temperature in late winter and spring presumably through the loss of ozone and reduction of absorption of solar UV. In both hemispheres, similar downward propagating geomagnetic signals in the extratropical stratosphere are found in spring for those years when no stratospheric sudden warming occurred in mid-winter. Anomalous easterly winds and warmer polar regions are found when the 4-month averaged winter Ap index (Ap) is high, and the signals become clearer when solar F10.7 is low. In May, significant geomagnetic signals are obtained in the Northern Hemisphere when the data are grouped according to the phase of the stratospheric equatorial QBO. The magnitudes of changes in spring stratospheric wind and temperatures associated with Ap signals are in the range of 10–20 m s−1 and 5–10 K, which are comparable with those of the 11-yr SC signals typically found in late winter. The spring Ap signals show the opposite sign to that expected due to in situ cooling effects caused by catalytic destruction of stratospheric ozone by descending EPP-NOx. Thus it is unlikely that the in situ chemical effect of descending EPP-NOx on stratospheric ozone would have a dominant influence on stratospheric circulation. Instead, we suggest that the detected Ap signals in the extratropical spring stratosphere may be an indirect consequence of geomagnetic and solar activity, dynamically induced by changes in wave ducting conditions.

Les recherches numismatiques systématiques en Albanie ont commencé dans les 1950. L’étude des monnaies de Dyrrachion, la principale cité de la côte orientale de la mer Adriatique pendant l’antiquité (sous l’actuelle ville de Durrës en Albanie centrale), apporte une nouvelle contribution à la numismatique albanaise en dressant le premier corpus monétaire complet établi pour une cité de ce territoire. La période couverte s’étend sur environ trois siècles (IVe av. J -C. Ier av.). Cette étude analyse tout le monnayage d’argent de la ville, qui se répartit en trois séries successives (statères à types corinthiens, à types corcyréens, drachmes à la vache allaitant), comportant sept dénominations différentes. Le catalogue est une étude par coins de 3085 monnaies, provenant des principaux Cabinets Numismatiques du monde et de nombreuses publications. L’étude de la circulation de ces différents numéraires a permis de reconstituer les contacts et le commerce de la cité avec l’étranger et de faire des remarques sur l’économie. En conclusion, l’étude des monnaies a permis de revoir à la lumière des données numismatiques les événements les plus importants qui ont marqué la cité depuis sa fondation. / The systematic numismatic studies in Albania started around 1950. The study of the ancient coins of Dyrrhachium, an important city in the Oriental coast of the Adriatic Sea (the modern town of Durrës in central Albania is located above the ancient site), brings an important contribution to the Albanian numismatic. It also constitutes the first complete monetary corpus of the ancient cities located in the Albanian territory. This study focuses on the silver coinage minted by the city for about three centuries. Three different series have been identified (the staters of Corinthian type, the staters of corcyrean type and the drachmas of cow suckling calf type), including seven denominations. The catalogue is based on a die link study of 3085 coins coming from the most important Coin Cabinets in the world as well as from numerous publications. The study of the circulation of the coins has permitted to make some assumptions about the contacts and exchanges of the city with the foreign world as well as about its economy. Finally, the study of the coins allowed reviewing the important events of the city’s history, from its foundation till the middle of the 1st century B.C., in the prospect of the numismatic data.

Approved for public release; distribution is unlimited. / Large-scale circulations in the 15-25 day period over the western North Pacific during northern summer were determined using the leading modes of a Singular Value Decomposition of 850 hPa winds and outgoing longwave radiation. Composites were constructed to define the wave patterns' structural characteristics. Their evolution is characterized by alternating cyclonic and anticyclonic equatorial anomalies that are linked to anomalous convective activity. Mid-latitude perturbations appear to contribute to the growth of new equatorial disturbances. Variability within the cycle is examined relative to variations in the basic state vertical wind shear and zonal wind convergence or divergence in the region equator-10ðN, 140ðE-160ðE. For the 50 cases in a basic state with easterly vertical wind shear and convergence, westward-moving waves propagate farther northwestward, wavelength contraction is greater, their orientation changes from east-west to southwest-northeast, and waves appear to be coupled with a Southern Hemisphere mid-latitude wave train. For the zonal wind divergence set, wave activity occurs farther eastward, circulations maintain a longer wavelength and more zonal orientation, and linkage with the Southern Hemisphere mid-latitudes is minimal. A statistically-significant relationship exists between the 15-25 day wave phase and tropical cyclone activity. Formation frequency and preferred locations are modulated by the 15-25 day wave. / Lieutenant, United States Navy