23,160 research outputs found
Development and demonstration of a flutter-suppression system using active controls
The application of active control technology to suppress flutter was demonstrated successfully in the transonic dynamics tunnel with a delta-wing model. The model was a simplified version of a proposed supersonic transport wing design. An active flutter suppression method based on an aerodynamic energy criterion was verified by using three different control laws. The first two control laws utilized both leading-edge and trailing-edge active control surfaces, whereas the third control law required only a single trailing-edge active control surface. At a Mach number of 0.9 the experimental results demonstrated increases in the flutter dynamic pressure from 12.5 percent to 30 percent with active controls. Analytical methods were developed to predict both open-loop and closed-loop stability, and the results agreed reasonably well with the experimental results
Silicon isotopic abundance toward evolved stars and its application for presolar grains
Galactic chemical evolution (GCE) is important for understanding the
composition of the present-day interstellar medium (ISM) and of our solar
system. In this paper, we aim to track the GCE by using the 29Si/30Si ratios in
evolved stars and tentatively relate this to presolar grain composition. We
used the APEX telescope to detect thermal SiO isotopologue emission toward four
oxygen-rich M-type stars. Together with the data retrieved from the Herschel
science archive and from the literature, we were able to obtain the 29Si/30Si
ratios for a total of 15 evolved stars inferred from their optically thin 29SiO
and 30SiO emission. These stars cover a range of masses and ages, and because
they do not significantly alter 29Si/30Si during their lifetimes, they provide
excellent probes of the ISM metallicity (or 29Si/30Si ratio) as a function of
time. The 29Si/30Si ratios inferred from the thermal SiO emission tend to be
lower toward low-mass oxygen-rich stars (e.g., down to about unity for W Hya),
and close to an interstellar or solar value of 1.5 for the higher-mass carbon
star IRC+10216 and two red supergiants. There is a tentative correlation
between the 29Si/30Si ratios and the mass-loss rates of evolved stars, where we
take the mass-loss rate as a proxy for the initial stellar mass or current
stellar age. This is consistent with the different abundance ratios found in
presolar grains. We found that older objects (up to possibly 10 Gyr old) in our
sample trace a previous, lower 29Si/30Si value of about 1. Material with this
isotopic ratio is present in two subclasses of presolar grains, providing
independent evidence of the lower ratio. Therefore, the 29Si/30Si ratio derived
from the SiO emission of evolved stars is a useful diagnostic tool for the
study of the GCE and presolar grains.Comment: 7 pages, 4 figure
Infrared Quasi Fixed Points and Mass Predictions in the MSSM II: Large tan(beta) Scenario
We consider the infrared quasi fixed point solutions of the renormalization
group equations for the Yukawa couplings and soft supersymmetry breaking
parameters in the MSSM in the \underline{large } regime. The
existence of IR quasi fixed points together with the values of gauge couplings,
third generation quarks, lepton and Z-boson masses allows one to predict masses
of the Higgs bosons and SUSY particles as functions of the only free parameter,
, or the gluino mass. The lightest Higgs boson mass for TeV is found to be GeV for and
GeV for .Comment: 15 pages, LateX file with 4 eps figures, corrected numbers, new
column in table, last versio
A Note on Doubly Warped Product Contact CR-Submanifolds in trans-Sasakian Manifolds
Warped product CR-submanifolds in Kaehlerian manifolds were intensively
studied only since 2001 after the impulse given by B.Y. Chen. Immediately
after, another line of research, similar to that concerning Sasakian geometry
as the odd dimensional version of Kaehlerian geometry, was developed, namely
warped product contact CR-submanifolds in Sasakian manifolds. In this note we
proved that there exists no proper doubly warped product contact
CR-submanifolds in trans-Sasakian manifolds.Comment: 5 Latex page
Electron-nuclei spin dynamics in II-VI semiconductor quantum dots
We report on the dynamics of optically induced nuclear spin polarization in
individual CdTe/ZnTe quantum dots loaded with one electron by modulation
doping. The fine structure of the hot trion (charged exciton with an
electron in the -shell) is identified in photoluminescence excitation
spectra. A negative polarisation rate of the photoluminescence, optical pumping
of the resident electron and the built-up of dynamic nuclear spin polarisation
(DNSP) are observed in time-resolved optical pumping experiments when the
quantum dot is excited at higher energy than the hot trion triplet state. The
time and magnetic field dependence of the polarisation rate of the
emission allows to probe the dynamics of formation of the DNSP in the optical
pumping regime. We demonstrate using time-resolved measurements that the
creation of a DNSP at B=0T efficiently prevents longitudinal spin relaxation of
the electron caused by fluctuations of the nuclear spin bath. The DNSP is built
in the microsecond range at high excitation intensity. A relaxation time of the
DNSP in about 10 microseconds is observed at and significantly increases
under a magnetic field of a few milli-Tesla. We discuss mechanisms responsible
for the fast initialisation and relaxation of the diluted nuclear spins in this
system
Implementation of biocementation for a partially saturated problematic soil of the UK railway network
This paper refers to biocementation of a problematic soil of the UK railway network as a potential stabilisation technique of this soil using indigenous ureolytic bacteria. The soil is peat, a soft foundation soil also subject to oxidation wastage. As the peat is under existing embankments, electrokinetics (EK) is proposed as a promising technique to implement treatments. In the context of unsaturated soils the paper thus focuses on two particular aspects relevant for the implementation of treatments and the stability of this soil, namely: a) the effect of degree of saturation of the peat on the bio-electrokinetic treatment ; b) the soil water retention curve of the soil affecting flow and transport; these are relevant as we focus on understanding and modelling the implementation of treatments through electrokinetics; moreover for the peat it is of importance to understand moisture exchange in the vadose zone and control groundwater table levels (e.g. during electrokinetics) in order to prevent further oxidation. After isolation and screening of indigenous microorgansisms Bacillus licheniformis was selected for further testing. The results in terms of unconfined compressive strength, CaCO3 content, swelling and compression behaviour and water retention proved the feasibility of biocementation using this indigenous microorganism. Ongoing work is assessing the required treated soil characteristics and related required biocementation degree to solve UK rail's peat foundation problems. Upscaling of the techniques towards in situ implementation is also planned in the next stage of the research
Granulation in K-type Dwarf Stars. II. Hydrodynamic simulations and 3D spectrum synthesis
We construct a 3D radiative-hydrodynamic model atmosphere of parameters Teff
= 4820 K, log g = 4.5, and solar chemical composition. The theoretical line
profiles computed with this model are asymmetric, with their bisectors having a
characteristic C-shape and their core wavelengths shifted with respect to their
laboratory values. The line bisectors span from about 10 to 250 m/s, depending
on line strength, with the stronger features showing larger span. The
corresponding core wavelength shifts range from about -200 m/s for the weak Fe
I lines to almost +100 m/s in the strong Fe I features. Based on observational
results for the Sun, we argue that there should be no core wavelength shift for
Fe I lines of EW > 100 mA. The cores of the strongest lines show contributions
from the uncertain top layers of the model, where non-LTE effects and the
presence of the chromosphere, which are important in real stars, are not
accounted for. The comparison of model predictions to observed Fe I line
bisectors and core wavelength shifts for a reference star, HIP86400, shows
excellent agreement, with the exception of the core wavelength shifts of the
strongest features, for which we suspect inaccurate theoretical values. Since
this limitation does not affect the predicted line equivalent widths
significantly, we consider our 3D model validated for photospheric abundance
work.Comment: A&A, in pres
Pan-Africanism: a contorted delirium or a pseudonationalist paradigm? Revivalist critique
This essaic-article goes against established conventions that there is anything ethno-cultural (and hence national) about the so-called African tribes. Drawing largely from the culture history of precolonial/prepolitical Africans—that is, the Bantu/Cushitic-Ethiopians (Azanians)—the author has demonstrated vividly that far from being distinct ethno-culture national communities, the so-called tribes of African states are better considered subculture groups, whose regional culture practices erstwhile paid tribute to their nation’s main culture center in Karnak. For example, using the culture symbols and practices of some local groups and linking them to the predynastic and dynastic Pharaonic periods, I argued that there is compelling evidence against qualifying Africa’s tribes as distinct ethno-culture national entities. In genuine culture context, I stressed that the Ritual of Resurrection and its twin culture process of the mummification of deceased indigenous Pharaohs tend to suggest that the object of the Bantu/Cushitic-Ethiopians national culture was life (in its eternal manifestation) and then resurrection later, and that there are recurring (culturally sanctioned) ethical examples among the culture custodians of these subculture groups that generally pay tribute to the overarching culture norm. Furthermore, the fact that the Ritual of Resurrection began in the Delta region and ended at the Sources of the Nile, where the spirit of the deceased indigenous Pharaohs was introduced into the spiritual world of their ancestors, contradicts conventional perceptions that ancient Egypt was a distinct national community isolated from precolonial/prepolitical Africa/Azania
Towards the Development of Sustainable Ground Improvement Techniques —Biocementation Study of an Organic Soil
Ongoing research effort is dedicated to the development of innovative, superior and cost-effective ground improvement techniques to mitigate natural and man-made hazards while minimising waste and other environmental impacts. In this context, the nature-based process of biocementation of soils has been proposed as a potentially more sustainable technique than conventional chemical ground improvement practices. This paper focuses on the biocementation of an organic soil of the UK railway network. Having
recently proven the feasibility of biocementing this soil using indigenous ureolytic bacteria, in this paper, the authors perform a parametric study to identify treatments successful in increasing the strength of the soil. Selected treatments are then applied to the soil to assess its volume change during consolidation, secondary compression and shrinkage upon drying. The results show that, depending on the treatments used, biocementation has increased the unconfined compressive strength by up to 81% compared to that of the control
samples. For selected treatments and the range of water contents tested (55–33%), shrinkage upon drying reduced by 16%, while the volumetric strains of the soil upon 1-D compression reduced by 32–47%. This was reflected in the values of the coefficient of volume compressibility and the coefficient of secondary compression (the latter either reduced by up to an order of magnitude or secondary compression was not observed altogether in the testing period). Overall, the results proved that biocementation improved
considerably the mechanical properties of the organic soil, which gives promise for addressing the settlement problems of this soil
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