31 |
Microwave Remote Sensing of Saharan Ergs and Amazon VegetationStephen, Haroon 17 July 2006 (has links) (PDF)
This dissertation focuses on relating spaceborne microwave data to the geophysical characteristics of the Sahara desert and the Amazon vegetation. Radar and radiometric responses of the Saharan ergs are related to geophysical properties of sand formations and near surface winds. The spatial and temporal variability of the Amazon vegetation is studied using multi-frequency and multi-polarization data. The Sahara desert includes large expanses of sand dunes called ergs that are constantly reshaped by prevailing winds. Radar backscatter measurements observed at various incidence and azimuth angles from the NASA Scatterometer (NSCAT), the ERS scatterometer (ESCAT), the SeaWinds scatterometer aboard QuikScat (QSCAT), and the Precipitation Radar (TRMM-PR) aboard the Tropical Rain Monitoring Mission (TRMM) are used to model the backscatter response from sand dunes. Backscatter incidence and azimuth angle variation depends upon the slopes and orientations of the dune slopes. Sand dunes are modeled as a composite of tilted rough facets, which are characterized by a probability distribution of tilt. The small ripples are modeled as cosinusoidal surface waves that contribute to the return signal at Bragg angles. The backscatter response is high at look angles equal to the mean tilts of the rough facets and is lower elsewhere. The modeled backscatter response is similar to NSCAT and ESCAT observations. Backscatter also varies spatially and reflects the spatial inhomogeneity of the sand surface. A model incorporating the backscatter azimuth modulation and spatial inhomogeneity is proposed. The maxima of the azimuth modulation at 33 degrees incidence angle reflect the orientation of the slip-sides on the sand surface. These slip-side orientations are consistent with the European Centre for Medium-Range Weather Forecasts wind directions spatially and temporally. Radiometric emissions from the ergs have strong dependence on the surface geometry. The radiometric temperature (Tb) of ergs is modeled as the weighted sum of the Tb from all the composite tilted rough facets. The dual polarization Tb measurements at 19 GHz and 37 GHz from the Special Sensor Microwave Imager (SSM/I) aboard the Defense Meteorological Satellite Program and the Tropical Rainfall Measuring Mission Microwave Imager are used to analyze the radiometric response of erg surfaces and compared to the model results. It is found that longitudinal and transverse dune fields are differentiable based on their polarization difference azimuth modulation, which reflects type and orientation of dune facets. Polarization difference at 19 GHz and 37 GHz provide consistent results. In the Amazon, backscatter measurements from Seasat A scatterometer (SASS), ESCAT, NSCAT, QSCAT and TRMM-PR; and Tb measurements from SSM/I are used to study the multi-spectral microwave response of vegetation. Backscatter versus incidence angle signatures of data combined from scatterometers and the precipitation radar depend upon vegetation density. The multi-frequency signatures of backscatter and Tb provide unique responses for different vegetation densities. Backscatter and Tb spatial inhomogeneity is related to spatial geophysical characteristics. Temporal variability of the Amazon basin is studied using C-band ERS data and a Ku-band time series formed by SASS, NSCAT and QSCAT data. Although the central Amazon forest represents an area of very stable radar backscatter measurements, portions of the southern region exhibit backscatter changes over the past two decades.
|
32 |
Reservoir Characterization and Outcrop Analogs to the Navajo Sandstone in the Central Utah Thrust Belt Exploration PlayDalrymple, Ashley 07 July 2007 (has links) (PDF)
Reservoir heterogeneity plays an important role in oil field economics and completion strategies. We herein characterize the reservoir heterogeneity of the Early Jurassic Navajo Sandstone in the Justensen Flat/Devils Canyon area of the San Rafael Swell, Utah. These outcrops are located approximately 60 kilometers (45 mi) east of the recently discovered Covenant oil field which is located in the central Utah thrust belt exploration play. The reservoir for the Covenant field is the Navajo Sandstone. This study can serve as an outcrop analogue for this developing play and other eolian reservoirs worldwide. There are eight facies within the Navajo Sandstone in the Justensen Flat/Devils Canyon area based on differences in primary and secondary sedimentary structures, sedimentary texture, petrology, porosity/permeability, and other macro-scale features of the outcrop. Three facies were deposited by eolian dunes. These serve as the primary reservoir facies of the Navajo in the Justensen Flat/Devils Canyon area, displaying relatively high porosity and permeability (approximately 28 percent porosity and 100 mD of permeability). Five interdune facies display finer grain size, more abundant cement, and relatively lower porosity and permeability (approximately 18 percent porosity and 29 mD of permeability). Four of the five inderdune facies have variable porosity and permeability or are not laterally extensive (tens of meters). These four facies act as baffles to fluid flow within the reservoir. One interdune facies, the Wavy Algal Matted facies (WAM), displays very low porosity (10 percent) and permeability (0.265 mD) based on 4 samples, and is laterally extensive in the field area (greater than 1 km2). There are nine facies in the Wolverine Federal 17-3 core from the Covenant Field, four of which are tidally influenced. This is unique compare to the Justensen Flat/Devils Canyon outcrop. Tidal influence was apparently present in western Utah but did not have a direct influence on sedimentation 60 kilometers (45 mi) to the east. The Large Trough Cross-stratified (LTC) facies, which serves as the primary reservoir of the Navajo Sandstone, was observed in both outcrop and core. The laterally extensive, low permeability WAM facies was also present in both core and outcrop, suggesting the possibility of reservoir partitioning within oil fields having eolian reservoirs similar to the Navajo Sandstone.
|
33 |
The use of Silent Substitution in measuring isolated cone- and rod- Human ERGsKommanapalli, Deepika January 2018 (has links)
After over a decade of its discovery, the Electroretinogram (ERG) still remains
the objective tool that is conventionally used in assessment of retinal function in
health and disease. Although there is ongoing research in developing ERG recording techniques, interpretation and clinical applications, there is still a limited
understanding on how each photoreceptor class contribute to the ERG waveform
and their role and/or susceptibilities in various retinal diseases still remains
unclear. Another limitation with currently used conventional testing protocols in a
clinical setting is the requirement of an adaptation period which is time consuming.
Furthermore, the ERG responses derived in this manner are recorded under different stimulus conditions, thus, making comparison of these signals difficult. To address these issues and develop a new testing method, we employed silent substitution paradigm in obtaining cone- and rod- isolating ERGs
using sine- and square- wave temporal profiles. The ERGs achieved in this
manner were shown to be photoreceptor-selective. Furthermore, these
responses did not only provide the functional index of photoreceptors but their
contributions to their successive postreceptoral pathways. We believe that the
substitution stimuli used in this thesis could be a valuable tool in functional
assessment of individual photoreceptor classes in normal and pathological conditions. Furthermore, we speculate that this method of cone/rod activity isolation could possibly be used in developing faster and efficient photoreceptor-selective testing protocols without the need of adaptation. / Bradford School of Optometry and Vision Sciences scholarship
|
34 |
Incremental and decremental L- and M-cone driven ERG responses: I. Square-wave pulse stimulation.McKeefry, Declan J., Kremers, Jan, Kommanapalli, Deepika, Challa, Naveen K., Murray, I.J., Maguire, John, Parry, Neil R.A. 04 1900 (has links)
No / Electroretinograms (ERGs) elicited by transient, square-wave L- and M-cone isolating stimuli were recorded from human trichromatic (n=19) and dichromatic (n=4) observers. The stimuli were generated on a 4 primary LED stimulator and were equated in terms of cone modulation (cone contrast = 0.11) and retinal illuminance (12,000 trolands). L- and M-cone isolated ERGs had waveforms similar to those observed for luminance responses. However, M-cone ERGs exhibited a phase reversal in their responses to onset and offset stimuli relative to the L-cone responses. This on-off response reversal was observed in trichromats but not dichromats. Simultaneous counter-phase and in-phase combinations of L- and M-cone isolating stimuli generated responses that reflected chromatic and luminance processing, respectively. We conclude that L- and M-cone specific ERGs provide a measure of how photoreceptors contribute to post-receptoral mechanisms.
|
35 |
A key role for peroxynitrite-mediated inhibition of cardiac ERG (Kv11.1) K+ channels in carbon monoxide–induced proarrhythmic early afterdepolarizationsAl-Owais, M.M., Hettiarachchi, N.T., Kirton, H.M., Hardy, Matthew E., Boyle, J.P., Scragg, J.L., Steele, D.S., Peers, C. 25 July 2017 (has links)
Yes / Exposure to CO causes early afterdepolarization arrhythmias. Previous studies in rats have indicated that arrhythmias arose as a result of augmentation of the late Na+ current. The purpose of the present study was to examine the basis for CO-induced arrhythmias in guinea pig myocytes in which action potentials (APs) more closely resemble those of human myocytes. Whole-cell current- and voltage-clamp recordings were made from isolated guinea pig myocytes as well as from human embryonic kidney 293 (HEK293) cells that express wild-type or a C723S mutant form of ether-a-go-go–related gene (ERG; Kv11.1). We also monitored the formation of peroxynitrite (ONOO−) in HEK293 cells fluorimetrically. CO—applied as the CO-releasing molecule, CORM-2—prolonged the APs and induced early afterdepolarizations in guinea pig myocytes. In HEK293 cells, CO inhibited wild-type, but not C723S mutant, Kv11.1 K+ currents. Inhibition was prevented by an antioxidant, mitochondrial inhibitors, or inhibition of NO formation. CO also raised ONOO− levels, an effect that was reversed by the ONOO− scavenger, FeTPPS [5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrinato-iron(III)], which also prevented the CO inhibition of Kv11.1 currents and abolished the effects of CO on Kv11.1 tail currents and APs in guinea pig myocytes. Our data suggest that CO induces arrhythmias in guinea pig cardiac myocytes via the ONOO−-mediated inhibition of Kv11.1 K+ channels. / British Heart Foundation
|
36 |
Die Sauerstoffversorgung der Retina bei KnochenfischenWaser, Wolfgang 14 December 2001 (has links)
Das Vorkommen von über den Umgebungsdruck erhöhten Sauerstoffpartialdrucken in Geweben ist im Tierreich nur von der Schwimmblase und dem Auge von Knochenfischen bekannt. Die physiologischen Mechanismen dieser Sauerstoffkonzentrierung wurden an der Schwimmblase insbesondere des Aals intensiv untersucht, entsprechende Untersuchungen zu den Vorgängen im Auge der Knochenfische fehlen jedoch. In dieser Arbeit wurde daher eine Methode etabliert, mit der die Sauerstoffkonzentrierung im Auge der Knochenfische an isolierten Augen untersucht werden kann. 1. Das Gefäßsystem der Regenbogenforelle (Oncorhynchus mykiss, Walbaum 1792) wurde durch Gefäßausgüsse dargestellt. Das im Auge gelegene choroidale Rete mirabile wird über die Arteria ophthalmica, die gleichzeitig die efferente Pseudobranchienarterie darstellt, versorgt. Die Pseudobranchie selber empfängt das Blut aus der efferenten Arterie des ersten Kiemenbogens. Diese Gefäßtopologie, Versorgung der Pseudobranchie mit bereits im ersten Kiemenbogen oxygeniertem Blut und auschließliche Versorgung des choroidalen Rete mirabile mit Blut aus der Pseudobranchie, weist auf die Bedeutung der Pseudobranchie für die Prozesse im Auge hin. 2. Die Retina der Regenbogenforelle wurde mikroskopisch untersucht. Die einzelnen Schichten der Retina entsprechen denen anderer Wirbeltiere. Die Forellenretina ist mit 407 µm aber wesentlich dicker als z.B. die Retina von Mammaliern. Zusätzlich fehlt der Retina der Forelle die bei vielen Mammaliern vorhandene retinale Blutgefäßversorgung. Mit den der Retina am nächsten gelegenen Gefäßen in der Choroidea bestehen bei der Forelle wesentlich größere Diffusionsstrecken von den Blutgefäßen zum Ort des Sauerstoffverbrauchs in den Zellen der Retina als bei anderen Wirbeltieren. Dies wir durch den erhöhten Sauerstoffpartialdruck in den Choriokapillaren kompensiert. 3. Für die Messung des intraretinalen Sauerstoffpartialdrucks wurden im Rahmen dieser Arbeit Sauerstoffmikroelektroden inklusive der zur Betreibung der Elektroden notwendigen Elektronik entwickelt. Die Elektroden waren vom Recess-Typ: die reaktive Oberfläche schloss nicht mit dem Ende der Glaskapillare ab, sondern war unter Belassung eines Hohlraumes in der Elektrodenspitze (Recess) in das innere der Glaskapillare verlagert. Dadurch waren die Elektroden unempfindlich gegenüber Rühreffekten. Die Mikroelektroden hatten eine Spitzendurchmesser von < 10 µm und eine mittlere Empfindlichkeit von 172 fA Torr-1 O2. Die Linearität der Elektroden über eine Partialdruckbereich von 0 bis 760 Torr O2 war besser als r = 0,9998. 4. Zur Überprüfung des normale Sauerstoffpartialdrucks in der Retina wurden Regenbogenforellen betäubt und künstlich ventiliert. Die systemischen Parameter wie arterieller PO2-Wert, Blutdruck und Herzschlag entsprachen dabei im Mittel mit 99 Torr (arterieller PO2), 28 Torr (Blutdruck) und 1,23 Hz (Herzschlag) den Werten unbetäubter, freischwimmender Forellen. Lediglich der arterielle pH-Wert war mit 8,02 während der künstlichen Ventilation durch eine ungenügende Kompensation einer respiratorischen Alkalose leicht gegenüber dem normalen Wert von 7,9 erhöht. 5. Die Auswirkungen der Präparation des Auges zur Messung des intraretinalen Sauerstoffpartialdrucks auf den Augeninnendruck wurde überprüft. Der Augeninnendruck betrug 4,9 Torr. Die Einbringung der Sauerstoffmikroelektrode hatte keine Auswirkung auf den Augeninnendruck. Erst das Entfernen der Elektrode nach der Messung führte zu einer deutlichen Verringerung des Augeninnendrucks. 6. Zum ersten Mal wurde in der vorliegenden Arbeit die Durchblutungsrate des Auges eines Knochenfisches bestimmt. Aus präparatorischen Gründen wurde die Messung an der afferenten Pseudobranchienarterie durchgeführt. Der mittlere Blutfluss in dem Gefäß betrug 745 µl min-1 kg-1. Durch Verschluss des kontralateralen Gefäßes stieg der Fluss auf 135% des ursprünglichen Wertes, da jetzt durch das ipsilaterale Gefäß und über die zwischen den beiden Gefäßen bestehende Anastomose beide Augen durch das ipsilaterale Gefäß mit Blut versorgt wurden. 7. Die Funktion der Retina während der intraretinalen Sauerstoffmessung wurde durch Ableitung des Elektroretinogramms kontrolliert. Trotz der während der Versuche fortbestehenden Betäubung mit dem Betäubungsmittel MS222, welches sich negativ auf das Elektroretinogramm auswirken soll, konnten normale Elektroretinogramme aufgezeichnet werde. Die invasive Messung des intraretinalen PO2 wirkte sich nicht negativ auf die Funktionalität der Retina aus. 8. Der intraretinale Sauerstoffpartialdruck wurde an betäubten, künstlich ventilierten Forellen überprüft. Der mittlere maximale PO2 im Bereich der Bruch´schen Membran betrug 382 Torr. An der Innenseite der Retina wurde ein PO2 von 10 Torr gemessen. Der Bereich des O2-Partialdruckgradienten in der Retina, gemessen über den Vorschub der Sauerstoffmikroelektrode vom niedrigsten bis zum höchsten PO2, betrug 433 µm, ein Wert der gut mit der mikroskopisch bestimmten Dicke der Retina (407 µm) übereinstimmt. 9. Zur Untersuchung der Einflüsse von Blutparametern auf die Sauerstoffkonzentrierung im Auge der Forelle wurden isolierte Augen künstlich mit verschiedenen Erythrozytensuspensionen perfundiert. Dazu wurde zum einen eine Suspension von Forellenerythrozyten eingesetzt, bei der erst der Root-Effekt in Abhängigkeit vom pH-Wert der Suspension bestimmt wurde. Bei basischem pH-Werten war das Hämoglobin der Erythrozyten vollständig gesättigt. Bei einem pH-Wert von 7,68 war noch eine Sättigung von 90% vorhanden, die bis zu einem pH-Wert von 7,31 auf 50% abnahm. 10% Sättigung wurden bei einem pH-Wert von 6,94 erreicht. Für die Perfusion wurde die Suspension der Forellenerythrozyten mit einem pH-Wert von 7,48 eingesetzt. Bei diesem pH-Wert liegt die Sättigung bei ca. 82% und eine Änderung des pH hat in diesem Bereich eine deutliche Änderung der Sättigung zur Folge, was die Freisetzung von O2 von Hämoglobin erleichtert. Als alternative Perfusionslösung wurde eine Suspension von Humanerythrozyten eingesetzt. Humanhämoglobin weist keinen Root-Effekt auf, es kann also durch die im Auge der Knochenfische vorhandenen Mechanismen kein Sauerstoff freigesetzt werden. 10. Der mittlere intraretinale Sauerstoffpartialdruck isolierter Augen betrug bei Perfusion mit der Suspension von Forellenerythrozyten 99 Torr. Nach dem Wechsel auf die Suspension mit Humanerythrozyten fiel der intraretinale Sauerstoffpartialdruck sofort auf 30 Torr ab. Der Perfusionsdruck änderte sich bei dieser Umstellung nicht. Bei Perfusion mit Ringerlösung fiel der intraretinale PO2 auf 20 Torr, gleichzeitig fiel jetzt auch der Perfusionsdruck ab. 11. Eine Konzentrierung des Sauerstoffs konnte bei der künstlichen Perfusion isolierter Augen nicht nachgewiesen werden. Die Notwendigkeit des Root-Effekts für einen hohen Sauerstoffpartialdruck im Auge wird trotzdem deutlich, da bei Perfusion mit einer Suspension von Humanerythrozyten, die einen höheren Sauerstoffgehalt aufwies als die Suspension der Forellenerythrozyten, der intraretinale Sauerstoffpartialdruck deutlich geringer war. 12. Das Modell des isoliert perfundierten Auges ist zur physiologischen Untersuchung des choroidalen Rete mirabile und Sauerstoffkonzentrierung besser geeignet als in vivo - Experimente, da systemische Einflüsse vermieden und die Auswirkungen der Pseudobranchie auf die Blutchemie ausgeschaltet werden können. / Oxygen partial pressures (Po2) above ambient levels are found only in the swimbladder and the eye of teleost fish species. The mechanisms related to the involved oxygen concentration processes have been investigated to some detail in eel swimbladder, but little attention has been paid to analogous mechanisms of the teleost eye. This thesis has accordingly concentrated on developing a method promoting investigation of oxygen concentrating mechanisms in teleost eyes by application of an isolated perfused eye preparation. 1. The vascular supply of eye and pseudobranch in rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) was depicted by corrosion casts of the vascular system. The choroid rete mirabile is supplied with blood by the ophthalmic artery as the efferent blood vessel of the pseudobranch, with a small anastomosis to the contralateral vessel. The pseudobranch in turn is fed by the efferent artery of the first gill arch. This pattern of serial vascular connection suggests a role for the pseudobranch in the process of providing high oxygen tensions required for the high metabolic demand of the visual perception in the retina. 2. Eyes of various fish species were sectioned after paraffin embedding and examined microscopically. The organisation of teleost fish retinae is characterised by the same features and organisation well known from other vertebrates. However, the total thickness of 407 µm found for the retina of the rainbow is much larger than that observed in other animals such as mammals. The conditions of diffusive oxygen supply of retinal nerve cells is further hampered by the complete lack of intraretinal blood vessels commonly found in mammals. In trout, blood is supplied to only the choroid layer, leaving large diffusion distances to the retinal nerve cells to be spanned by oxygen partial pressures, elevated as compared to the bulk arterial system in the choroid capillaries. 3. Intraretinal oxygen partial pressure was determined in long-term anaesthetised specimens of Oncorhynchus mykiss, using specially developed oxygen microelectrodes and required electronic circuitry. Characteristic features of the electrodes include insensitivity of the signal to stirring, achieved by a recess of the reactive metal surface in a glass capillary, an average tip diameter of less than 10 µm and a characteristic sensitivity to oxygen of 172 fA Torr-1. The response of the electrodes to oxygen was linear over a range of partial pressures from 0 to 760 Torr O2 (r= 0,9998). 4. Normal oxygen partial pressures in trout retina were measured in long-term anaesthetised and artificially ventilated specimens of Oncorhynchus mykiss. In order to conduct the experiments under conditions as close as possible to normal homoiostasis, several systemic valuables were monitored continuously. During experimentation arterial Po2 averaged 99 Torr, mean blood pressure was 28 Torr and heart frequency was on the average 74 bpm, respectively, data in the range of values determined in unanesthetized, freely swimming trout. As the one exception, arterial pH (8,02) was slightly elevated during artificial ventilation as compared to control values (7,89), a shift induced by an inadequately high rate of artificial ventilation. 5. The impact of insertion of electrodes required for intraretinal Po2 measurement into the eye was found to have little effect. The intraocular pressure remained unaffected by opening the eye by puncture with leading cannula and inserted micro-Po2-electrode. The intraocular pressure fell only after removing the electrode after completion of the experiment. 6. Normal function of the retina during experimentation in vivo was checked by repeatedly measuring electroretinograms provoked by light flashes under dark ambient conditions. Although extended anaesthesia with MS222 is expected to affect the electroretinogram in fish, there was no indication of abnormal or reduced electroretinograms during experimentation. Also puncture of the eye with insertion of electrodes did not affect the electroretinogram. 7. Intraretinal Po2 was measured in anaesthetised and artificially ventilated trout. Oxygen profiles were recorded during advancement of the electrode tip though the retina, from the lowest Po2 at the inner surface with about 10 Torr to the highest Po2 in the region of Bruch´s membrane with about 382 Torr, travelling a total distance of 433 µm. This distance closely corresponds to the thickness of the retina measured by microscopic sectioning. 8. Blood flow to the eye as an important parameter for the establishment of an isolated eye preparation was measured in the afferent artery of the pseudobranch. Due to the anatomical situation this represents the closest possible approximation to measurement of flow in the ophthalmic artery. The blood flow was estimated by ultrasonic Doppler techniques with in situ calibration to be 216 µl min-1. Occlusion of the contralateral vessel resulted in an increase of the blood flow in the ipsilateral vessel to 135% of the original as a result of flow through the small anastomosis between the two ophthalmic arteries. This estimate is the first performed for blood flow to the eye of a fish. 9. An isolated eye preparation was used to investigate the influence of specific blood parameters on oxygen concentrating processes in the eye of Oncorhynchus mykiss. Eyes were perfused with suspensions of trout erythrocytes, human erythrocytes and Ringer´s solution. The Root Effect of trout haemoglobin was confirmed in suspension of erythrocytes. The haemoglobin was fully saturated at pH 8.45, still 90% saturated at 7.68, 50% at 7.31 and 10% at pH 6.94. In order to provide optimal starting conditions for the release of oxygen by relatively small changes in pH, pH 7.48 (resulting in 82 % saturation) was chosen for the perfusion of isolated eyes. As a control perfusion, suspensions of human erythrocytes provided a perfusate lacking any Root effect, thus not supporting the oxygen concentrating processes in fish eyes. 10. Perfusion of isolated trout eyes with pH 7.48 trout erythrocyte suspension resulted in an average intraretinal Po2 of 99 Torr, whereas perfusion with human erythrocytes resulted in an immediate decrease of Po2 to (of) 30 Torr, with a further drop to 20 Torr during perfusion with Ringer´s solution. Changes in perfusion between erythrocyte suspensions were performed without any changes in perfusion pressure, but the switch to control perfusion with Ringer´s solution exhibited a drop in perfusion pressure due to the reduced viscosity of the medium. 11. Although perfusion of isolated eyes did not exhibit Po2 above ambient values, the effect of oxygen concentrating processes were clearly indicated by comparison with Root effect-lacking human erythrocyte perfusate (Po2´s of 99 vs. 30 Torr, respectively). 12. It is concluded that studies of oxygen concentrating mechanisms are to be performed preferably on isolated eye preparations. For closer analysis of the involved mechanisms this preparation allows for isolated control of individual parameter of the perfusate. In particular, uncontrolled effects of the pseudobranch on the perfusate can be eliminated.
|
37 |
Chronostratigraphie et distribution spatiale des dépôts éoliens quaternaires du bassin aquitain / Quaternary aeolian deposits of the Aquitain basin (SW France) : chronostratigraphy and spatial distributionSitzia, Luca 03 February 2014 (has links)
La direction des vents nourriciers, obtenue à partir des gradients granulométriques et des morphologies dunaires, semble avoir changé au cours du temps. Celle-ci est orientée O-E au Pléniglaciaire moyen, puis NO-SE au Pléniglaciaire supérieur, tandis qu’au Dryas récent la direction est plutôt SSO-NNE. Dans ce travail, l’hypothèse d’un changement de la saison à laquelle les sables sont remobilisés est privilégiée. Ainsi, par comparaison avec la distribution azimutale actuelle des vents à l’échelle de l’année et en accord avec les reconstitutions pour le LGM, il est suggéré qu’au Pléniglaciaire supérieur la déflation éolienne était décalée vers la saison estivale, c’est-à-dire après la phase de dégel des sols et de fonte de la neige. Au contraire, les orientations établies pour le Pléniglaciaire moyen et le Dyras récent refléteraient une déflation active en période hivernale. / Le Pleniglacial, the north-west during the Upper Pleniglacial, and from south-southwest throughout the Younger Dryas. Here, we connect changing wind directions to seasonal variations in aeolian transport. Comparing annual azimuthal distribution of current wind regimes with wind regime models for LGM suggests that during the Upper Pleniglacial the dominant aeolian transport season shifted towards the summer, i.e. after seasonally frozen ground thawed and snow cover melted. Conversely, Middle Pleniglacial and Younger Dryas wind regimes reflect a general deflation during the winter.
|
38 |
青少年金錢觀:ERG理論之探討 / Money Attitude of Adolescent: Discussing from ERG Theory黃蘭雯, Huang, Lan-Wen Unknown Date (has links)
本研究旨在瞭解青少年的金錢觀、需求滿足與慾望,並以 Alderfer的ERG理論探討需求滿足及慾望對青少年金錢觀的影響。
研究樣本係依校級抽樣臺灣地區八百七十四位十三至十八歲的青少年。以自編之自陳式慾望、需求滿足和金錢觀問卷為研就工具。所得資料以次數分配、變異數分析、徑路分析等統計方法處理。
研究結果發現,在青少年的金錢觀方面,整體而言,大部分青少年均有正確的金錢觀,特別是對金錢在人際互動中的效用以及金錢的獲取方式有正確的看法。此外,不同的樣本指出,女生、國中生、居住在鄉村者以及有儲蓄習慣者對金錢有較正確的看法,反之,零用錢愈多對金錢的看法也較偏差。
其次,以徑路分析解釋需求滿足度和慾望對金錢觀之影響的研究結果指出,慾望是需求滿足影響金錢觀的中介變項。此外,影響青少年金錢觀的主要因素是關係需求和關係慾望,亦即,能夠與重要他人有良好的互動關係以及想要與重要他人建立良好關係的青少年對金錢的看法也較正向。而這二個變項在國中生和高中生樣本中有些許的差異:就國中生而言,關係需求滿足度對金錢觀的影響較關係慾望來得大,在高中生樣本中則恰好相反。
針對以上結果,提出研究討論及後續研究在方法以及變項上的建議,並對青少年之金錢教育提出鼓勵儲蓄、建立支持系統的建議。
|
39 |
Imagerie multi-résolution par tomographie aux rayons X : application à la tomographie locale en science des matériaux / Imagering multi-resolution by the X-ray tomography : application to the local tomography in materials scienceZhang, Tao 22 May 2012 (has links)
L'objectif de cette thèse étudie puis d’implémenter une méthode de reconstruction sur la tomographie aux rayons X qui permette de scanner des gros échantillons avec une bonne résolution qui permettrait de scanner l’intérieur d’un cylindre(tomographie locale) et caractériser des matériaux réels. Notre méthode peut être réalisé pour améliorer la quantitative et la qualitative d'image de fantôme. Dans cette thèse, cet méthode est utilisé sue les matériaux cellulaires. Nous avons réalisé des essais in situ en tomographie aux rayons X sur le mousse ERG et les sphères creuses. Un comparaison entre les résultats d’Élément Finis et des essais réels montre le mécanisme d'endommagement de ces matériaux. / The objective of this thesis studies to implement a method of reconstruction of the X-ray tomography that scanner a large samples with good resolution that would scan inside a cylinder (local tomography) and characterize reals materials. Our method can be done to improve the quantitative and qualitative picture of a ghost. In this thesis, this method is used sue the cellular materials. We conducted tests in situ X-ray tomography on the ERG foam and hollow spheres. A comparison between the results of Finite Element and live testing shows the damage mechanism of these materials.
|
40 |
Localization and function of the endocannabinoid system throughout the retinogeniculate pathway of vervet monkeysJavadi Khomami, Pasha 01 1900 (has links)
Le système endocannabinoïde (eCB) est présent dans le système nerveux central (SNC) de mammifères, incluant la rétine, et est responsable de la régulation de nombreux processus physiologiques. Bien que la présence du récepteur cannabinoïde de type 1 (CB1R) a bien été documenté dans la rétine de rongeurs et primates, il y a encore une controverse quant à la présence du récepteur cannabinoïde de type 2 (CB2R) au niveau du SNC. En utilisant la microscopie confocale, nous sommes les premiers à signaler les patrons d’expression du CB2R dans la rétine de singe. Nos résultats démontrent que le CB2R est exprimé exclusivement dans les cellules de Müller de la rétine du singe. En outre, nous avons comparé les différents patrons d’expression du système eCB dans la rétine de la souris, du toupaye, ainsi que du singe vervet et macaque. Nous rapportons que les distributions de CB1R, FAAH (fatty acid amid hydrolase), MAGL (monoacylglycerol lipase) et DAGLα (diacylglycerol lipase alpha) sont hautement conservées parmi ces espèces alors que CB2R et NAPE-PLD (N-acyl phosphatidylethanolamine phospholipase D) présentent différents profils d'expression. CB2R n'a pas été détecté dans les cellules neuronales de la rétine des primates. L’immunoréactivité de NAPE-PLD est présente dans les couches de la rétine de souris et toupayes, mais a été limitée à la couche des photorécepteurs des singes vervet et macaque.
Pour étudier les corrélats neuronaux et le rôle de la signalisation du système eCB dans la rétine, nous avons établi un protocole standard pour l'électrorétinographie (ERG), puis enregistré la réponse ERG de la rétine après le blocage des récepteurs avec des antagonistes spécifiques pour CB1R (AM251) et CB2R (AM630). Comparé au témoin, dans des conditions photopiques, et à certaines intensités faibles du stimulus, le blocage de CB1R diminue l'amplitude de l'onde-b, alors qu’à des intensités plus élevées, le blocage de CB2R augmente l'amplitude des deux-ondes a et b. De plus, le blocage des récepteurs cannabinoïdes provoque une augmentation de la latence des deux ondes a et b. Dans des conditions d’adaptation à l'obscurité, le blocage de CB1R et CB2R réduit l’amplitudes de l'onde a seulement à des intensités plus élevées et réduit l’onde b à intensités plus faibles. Des augmentations significatives de latence ont été observées dans les deux cas. Ces résultats indiquent que les récepteurs CB1 et CB2 chez les primates non humains sont impliqués dans la fonction rétinienne conditions photopiques.
En outre, nous avons évalué le profil d'expression du CB1R, de FAAH et de NAPE-PLD au-delà de la rétine dans le corps géniculé latéral des singes et nous rapportons pour la première fois que CB1R et FAAH sont exprimés davantage dans les couches magnocellulaires. La NAPE-PLD a été localisée à travers les couches magno- et parvocellulaires. Aucune de ces composantes n’est exprimée dans les couches koniocellulaires.
Ces résultats nous aident à mieux comprendre les effets des cannabinoïdes sur le système visuel qui pourraient nous mener à trouver éventuellement de nouvelles cibles thérapeutiques. / The endocannabinoid (eCB) system is present in the mammalian central nervous system, including the retina, and is responsible for the regulation of many physiological processes. Anatomical and functional data collected in the retina indicate that cannabinoid receptors are important mediators of retinal function. Although the presence of the cannabinoid receptor type 1 (CB1R) has been documented in the rodent and primate retina, there is still some controversy regarding the presence of the CB2 receptor (CB2R) within the central nervous system. By using confocal microscopy, we are the first to report the distribution patterns of CB2R in the monkey retina. Our results show that CB2R is expressed exclusively in the Müller cells of the primate retina. Furthermore, we compared the eCB system distribution patterns in the retinas of mice, tree shrews, and vervet and macaque monkeys. We report that CB1R, FAAH, MAGL, and DAGLα distributions are highly conserved among these 3 species whereas CB2R and NAPE-PLD exhibit different expression patterns. CB2R was not detected in the neuroretinal cells of primates. NAPE-PLD immunoreactivity was present in the retinal layers of mice and tree shrews but was restricted to the photoreceptor layer in both species of primates studied.
To study the neural correlates and the role of eCB signaling in the retina, we first established a standard protocol for electroretinography (ERG) and then recorded the ERG response of the retina after blocking receptors with specific antagonists for CB1R (AM251) and CB2R (AM630). Compare to control, in photopic conditions, at certain low flash intensities, only the blockade of CB1R decreases the amplitude of the a-wave and b-wave, while at some high flash intensities, blockade of CB2R increase the amplitude of both a- and b-waves. Also the blockade of the cannabinoid receptors causes an increase in the latency of both a- and b-waves. In dark-adapted eyes, blockade of the CB1R and CB2R reduces the a-wave only amplitudes in the higher intensities and decrease the b-wave in lower intensities. Some significant increases in latency were observed in both cases. These results indicate that CB1 and CB2 receptors in primates are involved in retinal function under photopic and scotopic conditions.
In addition, we assessed the expression pattern of eCB components CB1R, FAAH, and NAPE-PLD beyond the retina in the dorsal lateral geniculate nucleus (dLGN) of primates and report for the first time that while CB1R and FAAH are more abundantly expressed in the magnocellular layer, NAPE-PLD is distributed throughout both the magno- and parvocellular layers. None of these components are expressed in the koniocellular layer.
These findings augment our understanding of the effects of cannabinoids on the visual system and may lead to novel therapeutics targeted to eCB signaling.
|
Page generated in 0.0658 seconds