Flash floods and their effects on the development in El-Qaá plain area in South Sinai, Egypt

The arid regions are dominated to a much larger degree than humid regions by major catastrophic events. Although most of Egypt lies within the great hot desert belt; it experiences especially in the north some torrential rainfall, which causes flash floods all over Sinai Peninsula. Flash floods in hot deserts are characterized by high velocity and low duration with a sharp discharge peak. Large sediment loads may be carried by floods threatening fields and settlements in the wadis and even people who are living there. The extreme spottiness of rare heavy rainfall, well known to desert people everywhere, precludes any efficient forecasting. Thus, although the limitation of data still reflects pre-satellite methods, chances of developing a warning system for floods in the desert seem remote. The relatively short flood-to-peak interval, a characteristic of desert floods, presents an additional impediment to the efficient use of warning systems. The present thesis contains introduction and five chapters, chapter one points out the physical settings of the study area. There are the geological settings such as outcrop lithology of the study area and the deposits. The alluvial deposits of Wadi Moreikh had been analyzed using OSL dating to know deposits and palaeoclimatic conditions. The chapter points out as well the stratigraphy and the structure geology containing main faults and folds. In addition, it manifests the pesent climate conditions such as temperature, humidity, wind and evaporation. Besides, it presents type of soils and natural vegetation cover of the study area using unsupervised classification for ETM+ images. Chapter two points out the morphometric analysis of the main basins and their drainage network in the study area. It is divided into three parts: The first part manifests the morphometric analysis of the drainage networks which had been extracted from two main sources, topographic maps and DEM images. Basins and drainage networks are considered as major influencing factors on the flash floods; Most of elements were studied which affect the network such as stream order, bifurcation ratio, stream lengths, stream frequency, drainage density, and drainage patterns. The second part of this chapter shows the morphometric analysis of basins such as area, dimensions, shape and surface. Whereas, the third part points the morphometric analysis of alluvial fans which form most of El-Qaá plain. Chapter three manifests the surface runoff through rainfall and losses analysis. The main subject in this chapter is rainfall which has been studied in detail; it is the main reason for runoff. Therefore, all rainfall characteristics are regarded here such as rainfall types, distribution, rainfall intensity, duration, frequency, and the relationship between rainfall and runoff. While the second part of this chapter concerns with water losses estimation by evaporation and infiltration which are together the main losses with direct effect on the high of runoff. Finally, chapter three points out the factors influencing desert runoff and runoff generation mechanism. Chapter four is concerned with assessment of flood hazard, it is important to estimate runoff and tocreate a map of affected areas. Therefore, the chapter consists of four main parts; first part manifests the runoff estimation, the different methods to estimate runoff and its variables such as runoff coefficient lag time, time of concentration, runoff volume, and frequency analysis of flash flood. While the second part points out the extreme event analysis. The third part shows the map of affected areas for every basin and the flash floods degrees. In this point, it has been depending on the DEM to extract the drainage networks and to determine the main streams which are normally more dangerous than others. Finally, part four presets the risk zone map of total study area which is of high inerest for planning activities. Chapter five as the last chapter concerns with flash flood Hazard mitigation. It consists of three main parts. First flood prediction and the method which can be used to predict and forecast the flood. The second part aims to determine the best methods which can be helpful to mitigate flood hazard in the arid zone and especially the study area. Whereas, the third part points out the development perspective for the study area indicating the suitable places in El-Qaá plain for using in economic activities.

Seismic tomographic full-waveform inversion for the Vrancea sinking lithosphere structure using the adjoint method.

The Vrancea region, at the south-eastern bend of the Carpathian Mountains in Romania, represents one of the most puzzling seismically active zones of Europe. Beside some shallow seismicity spread across the whole Romanian territory, Vrancea is the place of an intense seismicity with the presence of a cluster of intermediate-depth foci placed in a narrow nearly vertical volume. Although large-scale mantle seismic tomographic studies have revealed the presence of a narrow, almost vertical, high-velocity body in the upper mantle, the nature and the geodynamic of this deep intra-continental seismicity is still questioned. High-resolution seismic tomography could help to reveal more details in the subcrustal structure of Vrancea. Recent developments in computational seismology as well as the availability of parallel computing now allow to potentially retrieve more information out of seismic waveforms and to reach such high-resolution models. This study was aimed to evaluate the application of a full waveform inversion tomography at regional scale for the Vrancea lithosphere using data from the 1999 six months temporary local network CALIXTO. Starting from a detailed 3D Vp, Vs and density model, built on classical travel-time tomography together with gravity data, I evaluated the improvements obtained with the full waveform inversion approach. The latter proved to be highly problem dependent and highly computational expensive. The model retrieved after the first two iterations does not show large variations with respect to the initial model but remains in agreement with previous tomographic models. It presents a well-defined downgoing slab shape high velocity anomaly, composed of a N-S horizontal anomaly in the depths between 40 and 70km linked to a nearly vertical NE-SW anomaly from 70 to 180km.

An inter-comparison between a VIS/IR and a MW satellite-based methods for cloud detection and classification

This thesis is aimed to assess similarities and mismatches between the outputs from two independent methods for the cloud cover quantification and classification based on quite different physical basis. One of them is the SAFNWC software package designed to process radiance data acquired by the SEVIRI sensor in the VIS/IR. The other is the MWCC algorithm, which uses the brightness temperatures acquired by the AMSU-B and MHS sensors in their channels centered in the MW water vapour absorption band. At a first stage their cloud detection capability has been tested, by comparing the Cloud Masks they produced. These showed a good agreement between two methods, although some critical situations stand out. The MWCC, in effect, fails to reveal clouds which according to SAFNWC are fractional, cirrus, very low and high opaque clouds. In the second stage of the inter-comparison the pixels classified as cloudy according to both softwares have been. The overall observed tendency of the MWCC method, is an overestimation of the lower cloud classes. Viceversa, the more the cloud top height grows up, the more the MWCC not reveal a certain cloud portion, rather detected by means of the SAFNWC tool. This is what also emerges from a series of tests carried out by using the cloud top height information in order to evaluate the height ranges in which each MWCC category is defined. Therefore, although the involved methods intend to provide the same kind of information, in reality they return quite different details on the same atmospheric column. The SAFNWC retrieval being very sensitive to the top temperature of a cloud, brings the actual level reached by this. The MWCC, by exploiting the capability of the microwaves, is able to give an information about the levels that are located more deeply within the atmospheric column.

Effect of substrate surface roughening and cold spray coating on the fatigue life of AA2024 specimens

The effects of cold spray coating and substrate surface preparation on crack initiation under cyclic loading have been studied on Al2024 alloy specimens. Commercially pure (CP) aluminum feedstock powder has been deposited on Al2024-T351 samples using a cold-spray coating technique known as high velocity particle consolidation. Substrate specimens were prepared by surface grit blasting or shot peening prior to coating. The fatigue behavior of both coated and uncoated specimens was then tested under rotating bend conditions at two stress levels, 180 MPa and 210 MPa. Scanning electron microscopy was used to analyze failure surfaces and identify failure mechanisms. The results indicate that the fatigue strength was significantly improved on average, up to 50% at 180 MPa and up to 38% at 210 MPa, by the deposition of the cold-sprayed CP-Al coatings. Coated specimens first prepared by glass bead grit blasting experienced the largest average increase in fatigue life over bare specimens. The results display a strong dependency of the fatigue strength on the surface preparation and cold spray parameters

Consensus Document of the International Union of Angiology (IUA)-2013. Current concept on the management of arterio-venous management

Arterio-venous malformations (AVMs) are congenital vascular malformations (CVMs) that result from birth defects involving the vessels of both arterial and venous origins, resulting in direct communications between the different size vessels or a meshwork of primitive reticular networks of dysplastic minute vessels which have failed to mature to become 'capillary' vessels termed "nidus". These lesions are defined by shunting of high velocity, low resistance flow from the arterial vasculature into the venous system in a variety of fistulous conditions. A systematic classification system developed by various groups of experts (Hamburg classification, ISSVA classification, Schobinger classification, angiographic classification of AVMs,) has resulted in a better understanding of the biology and natural history of these lesions and improved management of CVMs and AVMs. The Hamburg classification, based on the embryological differentiation between extratruncular and truncular type of lesions, allows the determination of the potential of progression and recurrence of these lesions. The majority of all AVMs are extra-truncular lesions with persistent proliferative potential, whereas truncular AVM lesions are exceedingly rare. Regardless of the type, AV shunting may ultimately result in significant anatomical, pathophysiological and hemodynamic consequences. Therefore, despite their relative rarity (10-20% of all CVMs), AVMs remain the most challenging and potentially limb or life-threatening form of vascular anomalies. The initial diagnosis and assessment may be facilitated by non- to minimally invasive investigations such as duplex ultrasound, magnetic resonance imaging (MRI), MR angiography (MRA), computerized tomography (CT) and CT angiography (CTA). Arteriography remains the diagnostic gold standard, and is required for planning subsequent treatment. A multidisciplinary team approach should be utilized to integrate surgical and non-surgical interventions for optimum care. Currently available treatments are associated with significant risk of complications and morbidity. However, an early aggressive approach to elimiate the nidus (if present) may be undertaken if the benefits exceed the risks. Trans-arterial coil embolization or ligation of feeding arteries where the nidus is left intact, are incorrect approaches and may result in proliferation of the lesion. Furthermore, such procedures would prevent future endovascular access to the lesions via the arterial route. Surgically inaccessible, infiltrating, extra-truncular AVMs can be treated with endovascular therapy as an independent modality. Among various embolo-sclerotherapy agents, ethanol sclerotherapy produces the best long term outcomes with minimum recurrence. However, this procedure requires extensive training and sufficient experience to minimize complications and associated morbidity. For the surgically accessible lesions, surgical resection may be the treatment of choice with a chance of optimal control. Preoperative sclerotherapy or embolization may supplement the subsequent surgical excision by reducing the morbidity (e.g. operative bleeding) and defining the lesion borders. Such a combined approach may provide an excellent potential for a curative result. Conclusion. AVMs are high flow congenital vascular malformations that may occur in any part of the body. The clinical presentation depends on the extent and size of the lesion and can range from an asymptomatic birthmark to congestive heart failure. Detailed investigations including duplex ultrasound, MRI/MRA and CT/CTA are required to develop an appropriate treatment plan. Appropriate management is best achieved via a multi-disciplinary approach and interventions should be undertaken by appropriately trained physicians.

Clinical presentation of a traumatic cervical spine disc rupture in alpine sports: a case report

ABSTRACT: Isolated non-skeletal injuries of the cervical spine are rare and frequently missed. Different evaluation algorithms for C-spine injuries, such as the Canadian C-spine Rule have been proposed, however with strong emphasis on excluding osseous lesions. Discoligamentary injuries may be masked by unique clinical situations presenting to the emergency physician. We report on the case of a 28-year-old patient being admitted to our emergency department after a snowboarding accident, with an assumed hyperflexion injury of the cervical spine. During the initial clinical encounter the only clinical finding the patient demonstrated, was a burning sensation in the palms bilaterally. No neck pain could be elicited and the patient was not intoxicated and did not have distracting injuries. Since the patient described a fall prevention attempt with both arms, a peripheral nerve contusion was considered as a differential diagnosis. However, a high level of suspicion and the use of sophisticated imaging (MRI and CT) of the cervical spine, ultimately led to the diagnosis of a traumatic disc rupture at the C5/6 level. The patient was subsequently treated with a ventral microdiscectomy with cage interposition and ventral plate stabilization at the C5/C6 level and could be discharged home with clearly improving symptoms and without further complications.This case underlines how clinical presentation and extent of injury can differ and it furthermore points out, that injuries contracted during alpine snow sports need to be considered high velocity injuries, thus putting the patient at risk for cervical spine trauma. In these patients, especially when presenting with an unclear neurologic pattern, the emergency doctor needs to be alert and may have to interpret rigid guidelines according to the situation. The importance of correctly using CT and MRI according to both - standardized protocols and the patient's clinical presentation - is crucial for exclusion of C-spine trauma.

Tidally Driven Exchange in an Archipelago Strait: Biological and Optical Responses

Measurements in San Bernardino Strait, one of two major connections between the Pacific Ocean and the interior waters of the Philippine Archipelago, captured 2-3 m s(-1) tidal currents that drove vertical mixing and net landward transport. A TRIAXUS towed profiling vehicle equipped with physical and optical sensors was used to repeatedly map subregions within the strait, employing survey patterns designed to resolve tidal variability of physical and optical properties. Strong flow over the sill between Luzon and Capul islands resulted in upward transport and mixing of deeper high-salinity, low-oxygen, high-particle-and-nutrient-concentration water into the upper water column, landward of the sill. During the high-velocity ebb flow, topography influences the vertical distribution of water, but without the diapycnal mixing observed during flood tide. The surveys captured a net landward flux of water through the narrowest part of the strait. The tidally varying velocities contribute to strong vertical transport and diapycnal mixing of the deeper water into the upper layer, contributing to the observed higher phytoplankton biomass within the interior of the strait.

Correction of dephasing oscillations in matter-wave interferometry

Vibrations, electromagnetic oscillations, and temperature drifts are among the main reasons for dephasing in matter-wave interferometry. Sophisticated interferometry experiments, e.g., with ions or heavy molecules, often require integration times of several minutes due to the low source intensity or the high velocity selection. Here we present a scheme to suppress the influence of such dephasing mechanisms—especially in the low-frequency regime—by analyzing temporal and spatial particle correlations available in modern detectors. Such correlations can reveal interference properties that would otherwise be washed out due to dephasing by external oscillating signals. The method is shown experimentally in a biprism electron interferometer where a perturbing oscillation is artificially introduced by a periodically varying magnetic field. We provide a full theoretical description of the particle correlations where the perturbing frequency and amplitude can be revealed from the disturbed interferogram. The original spatial fringe pattern without the perturbation can thereby be restored. The technique can be applied to lower the general noise requirements in matter-wave interferometers. It allows for the optimization of electromagnetic shielding and decreases the efforts for vibrational or temperature stabilization.

Grain size distribution in surface sediments samples of the continental shelf and slope of southeast Greenland

During "Meteor" Cruise 6/1966 in the northwest Atlantic a systematic survey of the bottom topography of the southeast Greenland continental margin was undertaken. Eighty-seven profiles transverse to the shelf edge at distances of 3-4 nautical miles and two longitudinal profiles parallel to the coast were carried out with the ELAC Narrow Beam Echo-Sounder giving a reliable record of even steep slopes. On the basis of the echo soundings the topography and morphology of the continental shelf and slope are evaluated. A detailed bathymetric chart and a serial profile chart were designed as working material for the morphological research. These maps along with the original echograms are morphometrically evaluated. The analysis of the sea bottom features is the basis of a subsequent morphogenetical interpretation, verified and extended by means of interpretation of magnetic data and sediment analysis (grain size, roundness, lithology). The results of the research are expressed in a geomorphological map. The primary findings can be summarized as follows: 1) The southeast Greenland shelf by its bottom topography can be clearly designated as a glacially formed area. The glacial features of the shelf can be classified into two zones nearly parallel to the coast: glacial erosion forms on the inner shelf and glacial accumulation forms on the outer shelf. The inner shelf is characterized by the rugged and hummocky topography of ice scoured plains with clear west/east slope asymmetry. On the outer shelf three types of glacial accumulation forms can be recognized: ice margin deposits with clearly expressed terminal moraines, glacial till plains and glaciomarine outwash fans. Both zones of the shelf can be subdivided into two levels of relief. The ice scoured plains, with average depths of 240 meters (m), are dissected to a maximum depth of 1060 m (Gyldenloves Trough) by trough valleys, which are the prolongations of the Greenland fjords. The banks of the outer shelf, with an average depth of 180 m, surround glacial basins with a maximum depth of 670 meters. 2) The sediments of the continental shelf can be classified as glacial due to their grain size distribution and the degree of roundness of the gravel particles. The ice margin deposits on the outer shelf can be recognized by their high percentage of gravels. On the inner shelf a rock surface is suggested, intermittently covered by glacial deposits. In the shelf troughs fine-grained sediments occur mixed with gravels. 3) Topography and sediments show that the southeast Greenland shelf was covered by an ice sheet resting on the sea floor during the Pleistocene ice-age. The large end moraines along the shelf edge probably indicate the maximum extent of the Wurm shelf ice resting on the sea floor. The breakthroughs of the end moraines in front of the glacial basins suggest that the shelf ice has floated further seaward over the increasing depths. 4) Petrographically the shelf sediments consist of gneisses, granites and basalts. While gneisses and granites occire on the nearby coast, basalt is not known to exist here. Either this material has been drifted by icebergs from the basalt province to the north or exists on the southeast Greenland shelf itself. The last interpretation is supported bythe high portion of basalt contained in the sediment samples taken and the strong magnetic anomalies probably caused by basaltic intrusions. 5) A magnetic profile allows the recognition of two magnetically differing areas which approximately coincide with the glacial erosion and accumulation zones. The inner shelf shows a strong and variable magnetic field because the glacially eroded basement forms the sea floor. The outer shelf is characterized by a weak and homogenous magnetic field, as the magnetized basement lies at greater depthy, buried by a thick cover of glacial sediments. The strong magnetic anomalies of the inner shelf are probably caused by dike swarms, similar to those observed further to the north in the Kangerdlugssuaq Fjord region. This interpretation is supported by the high basalt content of the sediment samples and the rough topography of the ice scoured plains which correlates in general with the magnetic fluctuations. The dike structures of the basement have been differentially eroded by the shelf ice. 6) The continental slope, extending from the shelf break at 313 m to a depth of 1270 m with an average slope of 11°, is characterized by delta-shaped projections in front of the shelf basins, by marginal plateaus, ridges and hills, by canyons and slumping features. The projections could be identified as glaciomarine sediment fans. This conclusion is supported by the strong decrease of magnetic field intensity. The deep sea hills and ridges with their greater magnetic intensities have to be regarded as basement outcrops projecting through the glaciomarine sediment cover. The upper continental rise, sloping seaward at about 2°, is composed of wide sediment fans and slump material. A marginal depression on the continental rise running parallel to the shelf edge has been identified. In this depression bottom currents capable of erosion have been recorded. South of Cape Farvel the depression extends to the accumulation zone of the "Eirik" sedimentary ridge. 7) By means of a study of the recent marine processes, postglacial modification of the ice-formed relief can be postulated. The retention effect of the fjord troughs and the high velocity of the East Greenland stream prevents the glacial features from being buried by sediments. Bottom currents capable of active erosion have only been found in the marginal depression on the continental rise. In addition, at the time of the lowest glacio-eustatic sea level, the shelf bottom was not situated in the zone of wave erosion. Only on the continental slope and rise bottom currents, sediment slumps and turbidity currents have led to significant recent modifications. Considering these results, the geomorphological development of the southeast Greenland continental terrace can be suggested as follows: 1. initial formation of a "peneplain", 2. fluvial incision, 3. submergence, and finally 4. glacial modification.

Age data of ODP Site 181-1124

ODP Site 1124, located 600 km east of the North Island of New Zealand, records post-middle Oligocene variations in the Pacific Deep Western Boundary Current (DWBC) and New Zealand's climatic and tectonic evolution. Sediment parameters, such as terrigenous grain size, flux, magnetic fabric, and non-depositional episodes, are used to interpret DWBC intensity and Antarctic climate. Interpretations of DWBC velocities indicate that the Antarctic Circumpolar Current reached modern intensities at ~23 Ma, as the tectonic seaways expanded, completing the thermal isolation of Antarctica. Periods of more intense bottom water formation are suggested by the presence of hiatuses formed under the DWBC at 22.5-17.6, 16.5-15, and 14-11 Ma. The oldest interval of high current intensity occurs within a climatically warm period during which the intensity of thermohaline circulation around Antarctica increased as a result of recent opening of circum-Antarctic gateways. The younger hiatuses represent glacial periods on Antarctica and major fluctuations in the East Antarctic Ice Sheet, whereas intervals around the hiatuses represent times of relative warmth, but with continued current activity. The period between 11 to 9 Ma is characterized by conditions surrounding a high velocity DWBC around the time of the formation and stabilization of the West Antarctic Ice Sheet. The increased terrigenous input may result from either changing Antarctic conditions or more direct sediment transport from New Zealand. The Pacific DWBC did not exert a major influence on sedimentation at Site 1124 from 9 Ma to the present; the late Miocene to Pleistocene sequence is more influenced by the climatic and tectonic history of New Zealand. Despite the apparent potential for increased sediment supply to this site from changes in sediment channeling, increasing rates of mountain uplift, and volcanic activity, terrigenous fluxes remain low and constant throughout this younger period.

Benthic foraminifera of surface sediments from the continental slope off Sierra Leone, North-West Africa

On "Meteor" cruise 30 (1973) 22 piston-cores were collected off Sierra Leone from water-depths between about 5000 m (Sierra Leone Basin) and 500 m (upper continental slope) with the objective to study the sediment composition and age as well as processes of sedimentation on the continental slope in a tropical humid region. Granulometric analysis and determinations of the carbonate contents of the sediment samples were carried out, as well as qualitative and quantitative analysis of the components of the grain size fractions > 63 µm and of the planktonic and benthonic foraminifera > 160 µm. Presently, the cold Canary Current influences the composition of the planktonic foraminifera within the northwestern area of investigation (profile A), whereas the planktonic fauna of the eastern area (profile C) seems to be truly tropical. In all Quaternary sediments from the continental slope off Sierra Leone, species of Globorotalia are less abundant than in truly pelagic sediments. For that reason, the zonation of the Pleistocene sediments based on the presence or absence of Globorotalia cultrata does not always agree with the climatic changes reflected in the sediments. Concerning past climates better results can be obtained by using the changes in percentage abundances of Globigerina sp. sp. and Globigerinoides sp. sp. as indicators for cool and warm temperatures. The Tertiary sediments contain a pelagic foraminiferal assemblage. In the Holocene sediments the benthonic foraminifera do not only serve as good paleodepth indicators, but their communities are also restricted to defined water masses, which change their positions in accordance with climatic changes. Thus, Cassidulina carinata in the area of investigation is an excellent indicator for sediments deposited during times, which were cooler than today; this is true for all cores from the continental slope off Sierra Leone independent of water-depth although this species presently abounds at water-depths around 600 m. The cores from the continental rise and from the Sierra Leone Basin (M30-261, M30-146, M30-147) were deposited below the calcium carbonate compensation depth. Only small sections of the cores consist of the original carbonate-free sediments, whereas the main part of the sediment column is redeposited material, rich in foraminifera, which normally live on the upper continental slope, or even on the shelf. From these cores only M30-261 can be subdivided into biostratigraphic zones ranging from zone V to zone Y. In all cores from the middle and upper continental slope of the eastern area of investigation (profile C; KL 230, 209-204) and in cores KL 183 and KL 184 from the northwestern area (profile A) we observed an undisturbed succession of sediments from the biostratigraphic zones X (partly), Y and Z. All cores from the central area (M30-181, M30-182, M30-262 to 264) and M30-187 from the upper slope of profile A show variable hiatuses in the sedimentary record. Locally, high velocity bottom currents were probably responsible for erosion, nondeposition or minimal sedimentation rates. These currents might have been initiated partly by the somewhat exposed position of this part of the continental slope, where the shelf edge bends from a northwest towards an eastern direction, and partly by very young tectonic movements. Fracture zones with vertically displaced fault blocs are frequent at Sierra Leone continental margin. According to seismic measurements by McMaster et al. (1975) the sites of the central area are located on an uplifted fault bloc explaining the reduced sediment rates or erosion. Unlike the central area, the eastern area (profile C) is situated on a downfaulted bloc with high sediment rates. The sediments from the cores of profile B as well as the turbiditic deep-sea sediments were deposited under a higher flow regime; therefore they are coarser than the extremely fine-grained sediments of the cores from profile C. Since the sand fraction (> 63 µm) is mainly composed of foraminifera, besides pteropods and light-colored fecal pellets, the carbonate content increases with the increasing percentage of the coarse grain fraction. Higher concentrations of quartz were only observed in core sections with considerable carbonate dissolution (mainly in the X-Zone), and, in general, in all sediments from the eastern area with higher terrigenous input including larger concentration of mica. Especially during times transitional between glacials and interglacials (or interstadials) the bottom currents were intensified. The percentages of coarse fraction and carbonate increase with increasing current velocities. Calcium carbonate dissolution becomes important in water depths > 3500 m. During cooler times the lysokline is depressed. Light-colored fecal pellets were redeposited from Late Neogene sediments (M30-187, M30-181). In the area of investigation they occur in the Holocene and mainly the Pleistocene sediments of the cores from the northwestern and central area because only here Tertiary sediments have been eroded at the uppermost continental slope. In the central area there are at least two periods of non-sedimentation and/or erosion which can be confined as being (1) not older than middle Pliocene and not younger than zone V and (2) younger than zone W. The local character of the erosion is documented by the fact that a complete Late Quaternary section is present in the cores of the northwestern and eastern area, each within less than 100 km from incomplete cores from the central area.

Impact Behavior of Hybrid Glass/Carbon Epoxy Composites

The high velocity impact performance in hybrid woven carbon and S2 and E glass fabric laminates manufactured by resin transfer molding (RTM) was studied. Specimens with different thicknesses and glass-fiber content were tested against 5.5 mm spherical projectiles with impact velocities ranging from 300 to 700 m/s to obtain the ballistic limit. The resulting deformation and fracture micromechanisms were studied. Several impacts were performed on the same specimens to identify the multihit behavior of such laminates. The results of the fracture analysis, in conjunction with those of the impact tests, were used to describe the role played by glass-fiber hybridization on the fracture micromechanisms and on the overall laminate performance under high velocity impact.

Flamelet structures in spray ignition

In typical liquid-fueled burners the fuel is injected as a high-velocity liquid jet that breaks up to form the spray. The initial heating and vaporization of the liquid fuel rely on the relatively large temperatures of the sourrounding gas, which may include hot combustion products and preheated air. The heat exchange between the liquid and the gas phases is enhanced by droplet dispersion arising from the turbulent motion. Chemical reaction takes place once molecular mixing between the fuel vapor and the oxidizer has occurred in mixing layers separating the spray flow from the hot air stream. Since in most applications the injection velocities are much larger than the premixed-flame propagation velocity, combustion stabilization relies on autoignition of the fuel-oxygen mixture, with the combustion stand-off distance being controlled by the interaction of turbulent transport, droplet heating and vaporization, and gas-phase chemical reactions. In this study, conditions are identified under which analyses of laminar flamelets canshed light on aspects of turbulent spray ignition. This study extends earlier fundamental work by Liñan & Crespo (1976) on ignition in gaseous mixing layers to ignition of sprays. Studies of laminar mixing layers have been found to be instrumental in developing un-derstanding of turbulent combustion (Peters 2000), including the ignition of turbulent gaseous diffusion flames (Mastorakos 2009). For the spray problem at hand, the configuration selected, shown in Figure 1, involves a coflow mixing layer formed between a stream of hot air moving at velocity UA and a monodisperse spray moving at velocity USUA. The boundary-layer approximation will be used below to describe the resulting sl ender flow, which exhibits different igniting behaviors depending on the characteristics of t he fuel. In this approximation, consideration of the case U A = U S enables laminar ignition distances to be related to ignition times of unstrained spray flamelets, thereby pro viding quantitative information of direct applicability in regions of low scala r dissipation-rate in turbulent reactive flows (see the discussion in pp. 181–186 of Peters (2000)) . This report is organized as follows. Effects of droplet dispersion dynamics on ignition of sprays in turbulent mixing layers are discussed in Section 2. The formulation f or ignition in laminar mixing layers is outlined in Sections 3 and 4. The results are presented in Section 5. In Section 6, the mixture-fraction field and associated scalar dissipat ion rates for spray ignition are discussed. Finally, some brief conclusions are drawn in Section 7.

Recubrimientos autolubricantes cuasicristalinos tipo composite depositados mediante proyección térmica para aplicaciones espaciales y de alta temperatura

Los recubrimientos lubricantes sólidos son requeridos para reducir la fricción y prevenir el desgaste en componentes que operan a altas temperaturas o en vacío (vehículos espaciales, industria química, motores diésel, turbinas aeronáuticas y de generación de energía…). Los lubricantes líquidos pierden sus características cuando las condiciones de presión, temperatura o ambientales son severas (oxidación, inestabilidad térmica, volatilidad,…), por ejemplo los aceites minerales convencionales se descomponen a temperaturas próximas a 200 ºC. Por tanto, la única manera de poder conseguir una adecuada lubricación a temperaturas extremas es por medio de sólidos, que cada vez más, se aplican en forma de recubrimientos. Estos recubrimientos podrían ser empleados en componentes de vehículos espaciales reutilizables, donde se pueden alcanzar, en la reentrada en la atmósfera, temperaturas de 700 ºC (bisagras, rodamientos, articulaciones y zonas de sellado en las superficies de control, y rodamientos de las turbobombas y las cajas de engranajes). Dichos recubrimientos también deberían ser capaces de proporcionar una lubricación efectiva a bajas temperaturas para las operaciones en tierra, para las operaciones de arranque en frío, incluso en el espacio. El conjunto de requisitos que tendrían que satisfacer las capas tribológicas relacionadas con estas condiciones extremas es muy diverso, lo que hace que el concepto de capas tipo composite (aquéllas constituidas por varios componentes) sea, en principio, muy adecuado para estas aplicaciones. Recubrimientos composite proyectados térmicamente constituidos por una matriz dura y conteniendo lubricantes sólidos pueden ser una buena solución desde el punto de vista tribológico. El “Lewis Research Centre” de la NASA ha estado desarrollando recubrimientos autolubricantes tipo composite, constituidos por la combinación de materiales duros como el carburo de cromo, junto con lubricantes sólidos como plata o la eutéctica de fluoruros de calcio y bario, en una matriz de NiCr, para su uso en aplicaciones terrestres a alta temperatura. Estos recubrimientos han sido aplicados mediante proyección térmica, siendo denominados como series PS100, PS200, PS300 y PS400, reduciendo de forma significativa el coeficiente de fricción y mejorando la resistencia al desgaste en un amplio margen de temperaturas. Otra nueva familia de materiales con comportamiento tribológico prometedor son las aleaciones cuasicristalinas (QC). Presentan características muy atractivas: alta dureza, baja fricción, alto límite elástico de compresión... Son muy frágiles como materiales másicos, por lo que se intentan aplicar en forma de recubrimientos. Se pueden depositar mediante proyección térmica. Algunos de estos materiales cuasicristalinos, como AlCoFeCr, poseen coeficientes de dilatación próximos al de los materiales metálicos, alta estabilidad térmica, baja conductividad térmica y una elevada resistencia a la oxidación y a la corrosión en caliente. En esta tesis se han desarrollado recubrimientos tipo composite conteniendo cuasicristales como componente antidesgaste, NiCr como componente tenaz, y Ag y la eutéctica de BaF2-CaF2, como lubricantes sólidos. Estos recubrimientos han sido depositados con diferentes composiciones (denominadas TH100, TH103, TH200, TH400, TH600…) mediante distintos procesos de proyección térmica: plasma en aire (PS), plasma en baja presión (LPPS) y combustión a alta velocidad (HVOF). Los recubrimientos se han generado sobre el sustrato X-750, una superaleación base níquel, endurecible por precipitación, con muy buena resistencia mecánica y a la oxidación hasta temperaturas de 870 ºC y, además, es empleada en aplicaciones aeroespaciales e industriales. Los recubrimientos han sido caracterizados microestructuralmente en INTA (Instituto Nacional de Técnica Aeroespacial), mediante SEM-EDS (Scanning Electronic Microscopy-Energy Dispersive Spectroscopy) y XRD (X-Ray Diffraction), y tribológicamente mediante medidas de microdureza y ensayos en tribómetro POD (Pin On Disc) para determinar los coeficientes de fricción y de desgaste. Los recubrimientos han sido ensayados tribológicamente a alta temperatura en INTA y en vacío en AMTTARC (Aerospace and Space Materials Technology Testhouse – Austrian Research Centres), en Seibersdorf (Austria). Se ha estudiado la influencia de la carga normal aplicada, la velocidad lineal y el material del pin. De entre las diferentes series de recubrimientos cuasicristalinos tipo composite desarrolladas, dos de ellas, TH100 y TH103 han presentado una excelente calidad microestructural (baja porosidad, distribución uniforme de fases…) y se han mostrado como excelentes recubrimientos antidesgaste. Sin embargo, estas capas presentan un pobre comportamiento como autolubricantes a temperatura ambiente, aunque mejoran mucho a alta temperatura o en vacío. Los resultados del trabajo presentado en esta tesis han proporcionado nuevo conocimiento respecto al comportamiento tribológico de recubrimientos autolubricantes cuasicristalinos tipo composite depositados por proyección térmica. Sin embargo, dichos resultados, aunque son muy prometedores, no han puesto de manifiesto el adecuado comportamiento autolubricante que se pretendía y, además, como ocurre en cualquier trabajo de investigación, durante el desarrollo del mismo siempre aparecen nuevas dudas por resolver. Se proponen nuevas líneas de trabajo futuro que complementen los resultados obtenidos y que puedan encaminar hacia la obtención de un recubrimiento que mejore su comportamiento autolubricante. ABSTRACT Solid lubricant coatings are required to reduce friction and prevent wear in components that operate at high temperatures or under vacuum (space vehicles, chemical industry, diesel engines, power generation turbines and aeronautical turbines, for instance). In these cases neither greases nor liquid lubricants can be employed and the only practicable approach to lubrication in such conditions is by means of solids. These are increasingly applied in the form of coatings which should exhibit low shear strength, whilst maintaining their chemical stability at extremes temperatures and in the space environment. In the space field, these coatings would be employed in re-usable space plane applications, such as elevon hinges, where temperatures of 700 ºC are reached during re-entry into the Earth’s atmosphere. These coatings should also be capable of providing effective lubrication at lower temperatures since “cold start” operation may be necessary, even in the space environment. The diverse and sometimes conflictive requirements in high temperature and space-related tribological coatings make the concept of composite coatings highly suitable for these applications. Thermal-sprayed composites containing solid lubricants in a hard matrix perform well tribologically. NASA‘s Lewis Research Centre had developed self-lubricating composite coatings for terrestrial use, comprising hard materials like chromium carbide as well as solid lubricant additives such as silver and BaF2-CaF2 eutectic on a Ni-Cr matrix. These coatings series, named PS100, PS200, PS300 and PS400, are applied by thermal spray and significantly reduce friction coefficients, improving wear resistance over a wide temperature range. Quasicrystalline alloys (QC) constitute a new family of materials with promising tribological behaviour. Some QC materials exhibit a combination of adequate antifriction properties: low friction coefficient, high hardness and high yield strength under compression, and can be easily produced as coatings on top of metallic and non-metallic materials. Among these QC alloys, AlCoFeCr has high hardness (700 HV0.1), a thermal expansion coefficient close to that of metals, high thermal stability, low thermal conductivity and good oxidation and hot corrosion resistance. However most QC materials have the disadvantage of being very brittle. In order to take advantage of the excellent tribological properties of QCs, thick composite lubricant coatings were prepared containing them as the hard phase for wear resistance, Ag and BaF2-CaF2 eutectic as lubricating materials and NiCr as the tough component. These coatings were deposited in different composition mixtures (named TH100, TH103, TH200, TH400, TH600…) by different thermal spray processes: air plasma spray (PS), low pressure plasma spray (LPPS) and high velocity oxy-fuel (HVOF), on X-750 substrates. X-750 is an age-hardenable nickel-base superalloy with very good strength and a good resistance to oxidising combustion gas environments at temperatures up to about 870 ºC and it is widely used in aerospace and industrial applications. Coatings have been characterized microstructurally, at INTA (National Institute for Aerospace Technology), by means of SEM-EDS (Scanning Electronic Microscopy- Energy Dispersive Spectroscopy) and XRD (X-Ray Diffraction), and tribologically by microhardness measurements and pin-on-disc testing to determine friction coefficients as well as wear resistance. The coatings were tested tribologically at high temperature at INTA and under vacuum at AMTT-ARC (Aerospace and Space Materials Technology Testhouse – Austrian Research Centres), in Seibersdorf (Austria). Different loads, linear speeds and pin materials were studied. TH100 and TH103 QC alloy matrix composite coatings were deposited by HVOF with excellent microstructural quality (low porosity, uniform phase distribution) and showed to be excellent wear resistant coatings. However these QC alloy matrix composite coatings are poor as a self-lubricant at room temperature but much better at high temperature or in vacuum. The results from the work performed within the scope of this thesis have provided new knowledge concerning the tribological behavior of self-lubricating quasicrystalline composite coatings deposited by thermal spraying. Although these results are very promising, they have not shown an adequate self-lubricating behavior as was intended, and also, as in any research, the results have in addition raised new questions. Future work is suggested to complement the results of this thesis in order to improve the selflubricating behaviour of the coatings.

Probing active galactic nuclei with H2O megamasers.

We describe the characteristics of the rapidly rotating molecular disk in the nucleus of the mildly active galaxy NGC4258. The morphology and kinematics of the disk are delineated by the point-like watervapor emission sources at 1.35-cm wavelength. High angular resolution [200 microas where as is arcsec, corresponding to 0.006 parsec (pc) at 6.4 million pc] and high spectral resolution (0.2 km.s-1 or nu/Deltanu = 1.4 x 10(6)) with the Very-Long-Baseline Array allow precise definition of the disk. The disk is very thin, but slightly warped, and is viewed nearly edge-on. The masers show that the disk is in nearly perfect Keplerian rotation within the observable range of radii of 0.13-0.26 pc. The approximately random deviations from the Keplerian rotation curve among the high-velocity masers are approximately 3.5 km.s-1 (rms). These deviations may be due to the masers lying off the midline by about +/-4 degrees or variations in the inclination of the disk by +/-4 degrees. Lack of systematic deviations indicates that the disk has a mass of <4 x 10(6) solar mass (M[symbol: see text]). The gravitational binding mass is 3.5 x 10(7) M[symbol: see text], which must lie within the inner radius of the disk and requires that the mass density be >4 x 10(9) M[symbol: see text].pc-3. If the central mass were in the form of a star cluster with a density distribution such as a Plummer model, then the central mass density would be 4 x 10(12) M[symbol: see text].pc-3. The lifetime of such a cluster would be short with respect to the age of the galaxy [Maoz, E. (1995) Astrophys. J. Lett. 447, L91-L94]. Therefore, the central mass may be a black hole. The disk as traced by the systemic velocity features is unresolved in the vertical direction, indicating that its scale height is <0.0003 pc (hence the ratio of thickness to radius, H/R, is <0.0025). For a disk in hydrostatic equilibrium the quadrature sum of the sound speed and Alfven velocity is <2.5 km.s-1, so that the temperature of the disk must be <1000 K and the toroidal magnetic field component must be <250 mG. If the molecular mass density in the disk is 10(10) cm-3, then the disk mass is approximately 10(4) M[symbol: see text], and the disk is marginally stable as defined by the Toomre stability parameter Q (Q = 6 at the inner edge and 1 at the outer edge). The inward drift velocity is predicted to be <0.007 km.s-1, for a viscosity parameter of 0.1, and the accretion rate is <7 x 10(-5) M[symbol: see text].yr-1. At this value the accretion would be sufficient to power the nuclear x-ray source of 4 x 10(40) ergs-1 (1 erg = 0.1 microJ). The volume of individual maser components may be as large as 10(46) cm3, based on the velocity gradients, which is sufficient to supply the observed luminosity. The pump power undoubtedly comes from the nucleus, perhaps in the form of x-rays. The warp may allow the pump radiation to penetrate the disk obliquely [Neufeld, D. A. & Maloney, P. R. (1995) Astrophys. J. Lett. 447, L17-L19]. A total of 15 H2O megamasers have been identified out of >250 galaxies searched. Galaxy NGC4258 may be the only case where conditions are optimal to reveal a well-defined nuclear disk. Future measurement of proper motions and accelerations for NGC4258 will yield an accurate distance and a more precise definition of the dynamics of the disk