1,141 research outputs found
Schlieren Studies of Compressibility Effects on Dynamic Stall of Airfoils in Transient Pitching Motion
Compressibility effects on the flowfield of an airfoil
executing rapid transient pitching motion from 0 - 60 degrees
over a wide range of Mach numbers and pitching
rates were studied using a stroboscopic schlieren flow visualization
technique. The studies have led to the first direct
experiments] documentation of multiple shocks on the
airfoil upper surface flow for certain conditions. Also, at
low Mach numbers, additional coherent vortical structures
were found to be present along with the dynamic stall vortex,
whereas at higher Mach numbers, the flow was dominated
by a single vortex. The delineating Mach number
for significant compressibility effects was 0.3 and the dynamic
stall process was accelerated by increasing the Mach
number above that value. Increasing the pitch rate monotonically
delayed stall to angles of attack as large as 27
degrees.AFOSR-MIPR-87-0029 and 88-0010NAVAIRAR
Structure of Plants across Habitat Types in Amurum Forest Reserve, Plateau State Nigeria
The Amurum Forest Reserve is one of the nature reserves in Plateau State North central Nigeria. Strict Nature reserve is prominent among the methods for in situ conservation of biodiversity in Nigeria and also the world at large. A study was conducted in the Forest across three habitat types in order to measure tree height and diameter at breast height (dbh) of trees. 50m x 50m plots were marked across the habitat types by simple random sampling technique. Trees and shrubs were identified to species level. Measurement were limited to all woody plants with diameter at breast height (dbh) of ≥ 10cm. Data collected was analyzed in excel. A total of 397 woody species were identified during the study period. 87.7 of the plants were shrubs while 12.3% were trees. The gallery forest had the highest diameter class(30-35cm) followed by the savanna(25-30cm) and lastly the rocky outcrop with the diameter class of 20-25cm.The rocky outcrop had the highest number of trees with the lowest dbh (10-15cm) while the gallery forest had more trees in the highest diameter class (30-35) (Figure 2). The highest mean height distribution in the Gallery forest shows that the plant communities in this habitat type has grown over the years without disturbance since the place is a protected site. Therefore, other surrounding bushes should be protected in order to preserve species from local extinction
Consistent Anisotropic Repulsions for Simple Molecules
We extract atom-atom potentials from the effective spherical potentials that
suc cessfully model Hugoniot experiments on molecular fluids, e.g., and
. In the case of the resulting potentials compare very well with the
atom-atom potentials used in studies of solid-state propertie s, while for
they are considerably softer at short distances. Ground state (T=0K) and
room temperatu re calculations performed with the new potential resolve
the previous discrepancy between experimental and theoretical results.Comment: RevTeX, 5 figure
Diffusion of gold nanoclusters on graphite
We present a detailed molecular-dynamics study of the diffusion and
coalescence of large (249-atom) gold clusters on graphite surfaces. The
diffusivity of monoclusters is found to be comparable to that for single
adatoms. Likewise, and even more important, cluster dimers are also found to
diffuse at a rate which is comparable to that for adatoms and monoclusters. As
a consequence, large islands formed by cluster aggregation are also expected to
be mobile. Using kinetic Monte Carlo simulations, and assuming a proper scaling
law for the dependence on size of the diffusivity of large clusters, we find
that islands consisting of as many as 100 monoclusters should exhibit
significant mobility. This result has profound implications for the morphology
of cluster-assembled materials
Reversible Band Gap Engineering in Carbon Nanotubes by Radial Deformation
We present a systematic analysis of the effect of radial deformation on the
atomic and electronic structure of zigzag and armchair single wall carbon
nanotubes using the first principle plane wave method. The nanotubes were
deformed by applying a radial strain, which distorts the circular cross section
to an elliptical one. The atomic structure of the nanotubes under this strain
are fully optimized, and the electronic structure is calculated
self-consistently to determine the response of individual bands to the radial
deformation. The band gap of the insulating tube is closed and eventually an
insulator-metal transition sets in by the radial strain which is in the elastic
range. Using this property a multiple quantum well structure with tunable and
reversible electronic structure is formed on an individual nanotube and its
band-lineup is determined from first-principles. The elastic energy due to the
radial deformation and elastic constants are calculated and compared with
classical theories.Comment: To be appear in Phys. Rev. B, Apr 15, 200
Structure–function relationships explain CTCF zinc finger mutation phenotypes in cancer
CCCTC-binding factor (CTCF) plays fundamental roles in transcriptional regulation and chromatin architecture maintenance. CTCF is also a tumour suppressor frequently mutated in cancer, however, the structural and functional impact of mutations have not been examined. We performed molecular and structural characterisation of five cancer-specific CTCF missense zinc finger (ZF) mutations occurring within key intra- and inter-ZF residues. Functional characterisation of CTCF ZF mutations revealed a complete (L309P, R339W, R377H) or intermediate (R339Q) abrogation as well as an enhancement (G420D) of the anti-proliferative effects of CTCF. DNA binding at select sites was disrupted and transcriptional regulatory activities abrogated. Molecular docking and molecular dynamics confirmed that mutations in residues specifically contacting DNA bases or backbone exhibited loss of DNA binding. However, R339Q and G420D were stabilised by the formation of new primary DNA bonds, contributing to gain-of-function. Our data confirm that a spectrum of loss-, change- and gain-of-function impacts on CTCF zinc fingers are observed in cell growth regulation and gene regulatory activities. Hence, diverse cellular phenotypes of mutant CTCF are clearly explained by examining structure–function relationships
Spatio-temporal genetic tagging of a cosmopolitan planktivorous shark provides insight to gene flow, temporal variation and site-specific re-encounters
Migratory movements in response to seasonal resources often influence population structure and dynamics. Yet in mobile marine predators, population genetic consequences of such repetitious behaviour remain inaccessible without comprehensive sampling strategies. Temporal genetic sampling of seasonally recurring aggregations of planktivorous basking sharks, Cetorhinus maximus, in the Northeast Atlantic (NEA) affords an opportunity to resolve individual re-encounters at key sites with population connectivity and patterns of relatedness. Genetic tagging (19 microsatellites) revealed 18% of re-sampled individuals in the NEA demonstrated inter/multi-annual site-specific re-encounters. High genetic connectivity and migration between aggregation sites indicate the Irish Sea as an important movement corridor, with a contemporary effective population estimate (Ne) of 382 (CI = 241–830). We contrast the prevailing view of high gene flow across oceanic regions with evidence of population structure within the NEA, with early-season sharks off southwest Ireland possibly representing genetically distinct migrants. Finally, we found basking sharks surfacing together in the NEA are on average more related than expected by chance, suggesting a genetic consequence of, or a potential mechanism maintaining, site-specific re-encounters. Long-term temporal genetic monitoring is paramount in determining future viability of cosmopolitan marine species, identifying genetic units for conservation management, and for understanding aggregation structure and dynamics
Lighthouse Schools and Crop Museums in the Philippines
In The Philippines, Lighthouse Schools (LSs) and school-based Crop Museums (CMs) serve as repositories of crop biodiversity. Specifically, LSs are research sites where the integration of school feeding, nutrition education and school gardens, is demonstrated and evidence is established; while CMs are located within the large network of LS and act as seed banks that enable the multiplication and exchange of crop types and varieties across schools. Together they have helped conserve and promote multiple varieties of traditional and indigenous vegetables (IVs)and fruits
What is 3C 324?
We report ground based and HST observations of the z=1.206 radio galaxy 3C
324, a prototypical example of the radio-optical ``alignment effect.'' While
infrared images shows a simple, round object reminiscent of a giant elliptical
galaxy, the HST images reveal a spectacular, linear chain of UV-bright
subcomponents closely aligned with the radio axis. In light of the available
data, we consider various scenarios to explain the properties of 3C 324, as
well as evidence for the presence of dust which may obscure the central active
nucleus and scatter its light to produce the polarized, aligned continuum seen
in the rest-frame UV.Comment: 9 pages, uuencoded gzipped postscript. To appear in ``Galaxies in the
Young Universe,'' ed. H. Hippelein, Springer Verlag. Revised version
(hopefully) corrects postscript error which garbled the last pag
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