426 research outputs found
Heavy mineral stratigraphy of the Unayzah Formation and Basal Khuff Clastics (Carboniferous to Permian) of Central Saudi Arabia
A study of heavy mineral assemblages in the Unayzah Reservoir sandstones of central Saudi Arabia has
identified successive changes in provenance signature. These define four heavy mineral units that are of
regional extent and largely coincident with the four main depositional units defined by previous authors:
Unayzah C, Unayzah B, Unayzah A and the Basal Khuff Clastics. Sandstone bodies with anomalous mineral
signatures also occur, however, especially within the Unayzah B Member. These are attributed to local
supply of sand from pre-Unayzah Paleozoic sandstones exposed on the Central Arabian Arch and on intrabasinal
highs.
The stratigraphic changes in mineralogy reflect successive developments in the geography and climate of the
region and in the pattern of sand sourcing and transport. The Unayzah C sands and the majority of Unayzah
B sands were derived from the south but whereas the southerly derived Unayzah C sands appear to have
been derived from pre-existing mature sandstones, those of Unayzah B were sourced from a wider range of
rock types including crystalline basement. This contrast is interpreted as indicating that a significant hiatus
may separate the two units. The Unayzah B sands are also characterised by the common presence of apatite,
indicating that the source rocks were relatively unweathered. This observation is compatible with the glacial
origin attributed to many of the Unayzah B sediments.
A further change in provenance signature takes place at the base the newly recognised âun-named middle
Unayzah memberâ, equivalent to the base of Unayzah A of previous authors. This is associated with the onset
of red-bed sedimentation throughout the area. Unayzah A sedimentation was terminated by a fall in sea level
that led to the formation of a widespread unconformity and to the development of deeply incised valleys along
the western basin margin. In most of the study area this unconformity corresponds to the base of the Khuff
Formation, but in the east of the area, where the succession is more complete, it is believed to occur within the
Unayzah Formation, at a level equivalent to the base of the Upper Gharif Member of Oman.
By identifying lateral and vertical changes in sand provenance, heavy mineral analysis provides an important
additional tool in the stratigraphic analysis of the Permian sandstone succession of Saudi Arabia, both at the
regional scale and wand at the scale of individual reservoir sandstone successions
Thermal performance of two heat exchangers for thermoelectric generators
Thermal performance of heat exchanger is important for potential application in integrated solar cell/module and
thermoelectric generator (TEG) system. Usually, thermal performance of a heat exchanger for TEGs is analysed
by using a 1D heat conduction theory which ignores the detailed phenomena associated with thermo-hydraulics.
In this paper, thermal and mass transports in two different exchangers are simulated by means of a steady-state,
3D turbulent flow k -e model with a heat conduction module under various flow rates. In order to simulate an
actual working situation of the heat exchangers, hot block with an electric heater is included in the model. TEG
model is simplified by using a 1D heat conduction theory, so its thermal performance is equivalent to a real TEG.
Natural convection effect on the outside surfaces of the computational model is considered. Computational
models and methods used are validated under transient thermal and electrical experimental conditions of a TEG.
It is turned out that the two heat exchangers designed have a better thermal performance compared with an
existing heat exchanger for TEGs, and more importantly, the fin heat exchanger is more compact and has nearly
half temperature rise compared with the tube heat exchanger
Developing a framework of Quaternary dune accumulation in the northern Rub' al-Khali, Arabia
Located at the crossroads between Africa and Eurasia, Arabia occupies a pivotal position for human migration and dispersal during the Late Pleistocene. Deducing the timing of humid and arid phases is critical to understanding when the Rub' al-Khali desert acted as a barrier to human movement and settlement. Recent geological mapping in the northern part of the Rub' al-Khali has enabled the Quaternary history of the region to be put into a regional stratigraphical framework. In addition to the active dunes, two significant palaeodune sequences have been identified. Dating of key sections has enabled a chronology of dune accretion and stabilisation to be determined. In addition, previously published optically stimulated luminescence (OSL) dates have been put in their proper stratigraphical context, from which a record of Late Pleistocene dune activity can be constructed. The results indicate the record of dune activity in the northern Rub' al-Khali is preservation limited and is synchronous with humid events driven by the incursion of the Indian Ocean monsoon
Probing Multiple Sight Lines through the SN 1006 Remnant by UV Absorption Spectroscopy
Absorption-line spectroscopy is an effective probe for cold ejecta within an
SNR, provided that suitable background UV sources can be identified. For the SN
1006 remnant we have identified four such sources, in addition to the
much-studied Schweitzer-Middleditch (SM) star. We have used STIS on HST to
obtain UV spectra of all four sources, to study "core samples" of the SN 1006
interior. The line of sight closest to the center of the SNR shell, passing
only 2.0 arcmin away, is to a V = 19.5 QSO at z = 1.026. Its spectrum shows
broad Fe II absorption lines, asymmetric with red wings broader than blue. The
similarity of these profiles to those seen in the SM star, which is 2.8 arcmin
from the center in the opposite direction, confirms the existence of a bulge on
the far side of SN 1006. The Fe II equivalent widths in the QSO spectrum are ~
50% greater than in the SM star, suggesting that somewhat more iron may be
present within SN 1006 than studies of the SM star alone have indicated, but
this is still far short of what most SNIa models require. The absorption
spectrum against a brighter z = 0.337 QSO seen at 57% of the shell radius shows
broad silicon absorption lines but no iron other than narrow, probably
interstellar lines. The cold iron expanding in this direction must be confined
within v <~ 5200 km/s, also consistent with a high-velocity bulge on the far
side only. The broad silicon lines indicate that the silicon layer has expanded
beyond this point, and that it has probably been heated by a reverse shock.
Finally, the spectra of two ~ A0V stars near the southern shell rim show no
broad or unusually strong absorption lines, suggesting that the low-ionization
ejecta are confined within 83% of the shell radius, at least at the azimuths of
these background sources.Comment: 26 pages, 8 postscript figure
Pharaonic necrostratigraphy : a review of geological and archaeological studies in the Theban Necropolis, Luxor, West Bank, Egypt
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Terra Nova 21 (2009): 237-256, doi:10.1111/j.1365-3121.2009.00872.x.We present a review of archeological and geological studies on the West Bank as a basis
for discussing the geological setting of the tombs and geologically related problems with a view
to providing archeologists with a framework in which to conduct their investigations on the
restoration, preservation and management of the antique monuments. Whereas the geology of
the Upper Nile Valley appears to be deceptively simple, the lithologic succession is vertically
variable, and we have recognized and defined several new lithologic units within the upper Esna
Shale Formation. We have been able to delineate lithologic (shale/limestone) contacts in several
tombs and observed that the main chambers in some were excavated below the Esna Shale in the
Tarawan Chalk Formation. We have been able to document changing dip in the strata (warping)
in several tombs, and to delineate two major orientations of fractures in the field. Investigations
behind the Temple of Hatshepsut, in the Valley of the Kings and around Deir El Medina, have
revealed four broad regional structures. We confirm that the hills located near the Nile Valley,
such as Sheik Abel Qurna, do not belong to the tabular structure of the Theban Mountain, but
are discrete displaced blocks of the Thebes Limestone and overlying El Miniya, as supported by
Google Earth photographs
Chandra ACIS Survey of M33 (ChASeM33): A First Look
We present an overview of the Chandra ACIS Survey of M33 (ChASeM33): A Deep
Survey of the Nearest Face-on Spiral Galaxy. The 1.4 Ms survey covers the
galaxy out to R \approx 18\arcmin (\approx 4 kpc). These data provide the
most intensive, high spatial resolution assessment of the X-ray source
populations available for the confused inner regions of M33. Mosaic images of
the ChASeM33 observations show several hundred individual X-ray sources as well
as soft diffuse emission from the hot interstellar medium. Bright, extended
emission surrounds the nucleus and is also seen from the giant \hii regions NGC
604 and IC 131. Fainter extended emission and numerous individual sources
appear to trace the inner spiral structure. The initial source catalog, arising
from ~2/3 of the expected survey data, includes 394 sources significant
at the confidence level or greater, down to a limiting luminosity
(absorbed) of 1.6\ergs{35} (0.35 -- 8.0 keV). The hardness ratios of the
sources separate those with soft, thermal spectra such as supernova remnants
from those with hard, non-thermal spectra such as X-ray binaries and background
active galactic nuclei. Emission extended beyond the Chandra point spread
function is evident in 23 of the 394 sources. Cross-correlation of the ChASeM33
sources against previous catalogs of X-ray sources in M33 results in matches
for the vast majority of the brighter sources and shows 28 ChASeM33 sources
within 10\arcsec of supernova remnants identified by prior optical and radio
searches. This brings the total number of such associations to 31 out of 100
known supernova remnants in M33.Comment: accepted for publication ApJS, full resolution images and complete
tables available at http://hea-www.harvard.edu/vlp_m33_public
Loneliness, social support and cardiovascular reactivity to laboratory stress
Self-reported or explicit loneliness and social support have been inconsistently associated with cardiovascular reactivity (CVR) to stress. The present study aimed to adapt an implicit measure of loneliness, and use it alongside the measures of explicit loneliness and social support, to investigate their correlations with CVR to laboratory stress. Twenty-five female volunteers aged between 18 and 39 years completed self-reported measures of loneliness and social support, and an Implicit Association Test (IAT) of loneliness. The systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) reactivity indices were measured in response to psychosocial stress induced in the laboratory. Functional support indices of social support were significantly correlated with CVR reactivity to stress. Interestingly, implicit, but not explicit, loneliness was significantly correlated with DBP reactivity after one of the stressors. No associations were found between structural support and CVR indices. Results are discussed in terms of validity of implicit versus explicit measures and possible factors that affect physiological outcomes
Therapeutic Neonatal Hepatic Gene Therapy in Mucopolysaccharidosis VII Dogs
Dogs with mucopolysaccharidosis VII (MPS VII) were injected intravenously at 2â3 days of age with a retroviral vector (RV) expressing canine ÎČ-glucuronidase (cGUSB). Five animals received RV alone, and two dogs received hepatocyte growth factor (HGF) before RV in an attempt to increase transduction efficiency. Transduced hepatocytes expanded clonally during normal liver growth and secreted enzyme with mannose 6-phosphate. Serum GUSB activity was stable for up to 14 months at normal levels for the RV-treated dogs, and for 17 months at 67-fold normal for the HGF/RV-treated dog. GUSB activity in other organs was 1.5â60% of normal at 6 months for two RV-treated dogs, which was likely because of uptake of enzyme from blood by the mannose 6-phosphate receptor. The body weights of untreated MPS VII dogs are 50% of normal at 6 months. MPS VII dogs cannot walk or stand after 6 months, and progressively develop eye and heart disease. RV- and HGF/RV-treated MPS VII dogs achieved 87% and 84% of normal body weight, respectively. Treated animals could run at all times of evaluation for 6â17 months because of improvements in bone and joint abnormalities, and had little or no corneal clouding and no mitral valve thickening. Despite higher GUSB expression, the clinical improvements in the HGF/RV-treated dog were similar to those in the RV-treated animals. This is the first successful application of gene therapy in preventing the clinical manifestations of a lysosomal storage disease in a large animal
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