3,164 research outputs found
Low-speed aerodynamic characteristics of a 0.08-scale YF-17 airplane model at high angles of attack and sideslip
Data were obtained with and without the nose boom and with several strake configurations; also, data were obtained for various control surface deflections. Analysis of the results revealed that selected strake configurations adequately provided low Reynolds number simulation of the high Reynolds number characteristics. The addition of the boom in general tended to reduce the Reynolds number effects
Dynamics of the triple contact line on a non-isothermal heater at partial wetting
The dynamics of the triple gas-liquid-solid contact line is analysed for the
case where the gas is the saturated vapour corresponding to the liquid, like in
the vapour bubble in boiling. It is shown that even small superheating (with
respect to the saturation temperature) causes evaporation of the adsorption
liquid film and the true triple contact is established. It is shown that the
hydrodynamic contact line singularity cannot be relaxed with the Navier slip
condition under such circumstances. Augmented with the second derivative slip
condition is proposed to be applied. For the partial wetting conditions, a
non-stationary contact line problem where the contact line motion is caused by
evaporation or condensation is treated in the lubrication approximation in the
vicinity of the contact line. High heat fluxes in this region require the
transient heat conduction inside the heater to be accounted for. Two 2D
problems, those of drop retraction with no phase change and of drop evaporation
are solved and analysed as illustrations of the proposed approach
Low speed aerodynamic characteristics of an 0.075-scale F-15 airplane model at high angles of attack and sideslip
An 0.075 scale model representative of the F-15 airplane was tested in the Ames 12 foot pressure wind tunnel at a Mach number of 0.16 to determine static longitudinal and lateral directional characteristics at spin attitudes for Reynolds numbers from 1.48 to 16.4 million per meter (0.45 to 5.0 million per foot). Angles of attack ranged from 0 to +90 deg and from -40 deg to -80 deg while angles of sideslip were varied from -20 deg to +30 deg. Data were obtained for nacelle inlet ramp angles of 0 to 11 deg with the left and right stabilators deflected 0, -25 deg, and differentially 5 deg and -5 deg. The normal pointed nose and two alternate nose shapes were also tested along with several configurations of external stores. Analysis of the results indicate that at higher Reynolds numbers there is a slightly greater tendency to spin inverted than at lower Reynolds numbers. Use of a hemispherical nose in place of the normal pointed nose provided an over correction in simulating yawing moment effects at high Reynolds numbers
Anisotropic magneto-Coulomb effect versus spin accumulation in a ferromagnetic single-electron device
We investigate the magneto-transport characteristics of nanospintronics
single-electron devices. The devices consist of single non-magnetic
nano-objects (nanometer size nanoparticles of Al or Cu) connected to Co
ferromagnetic leads. The comparison with simulations allows us attribute the
observed magnetoresistance to either spin accumulation or anisotropic
magneto-Coulomb effect (AMC), two effects with very different origins. The fact
that the two effects are observed in similar samples demonstrates that a
careful analysis of Coulomb blockade and magnetoresistance behaviors is
necessary in order to discriminate them in magnetic single-electron devices. As
a tool for further studies, we propose a simple way to determine if spin
transport or AMC effect dominates from the Coulomb blockade I-V curves of the
spintronics device
Polarization memory in single Quantum Dots
We measured the polarization memory of excitonic and biexcitonic optical
transitions from single quantum dots at either positive, negative or neutral
charge states. Positive, negative and no circular or linear polarization memory
was observed for various spectral lines, under the same quasi-resonant
excitation below the wetting layer band-gap. We developed a model which
explains both qualitatively and quantitatively the experimentally measured
polarization spectrum for all these optical transitions. We consider quite
generally the loss of spin orientation of the photogenerated electron-hole pair
during their relaxation towards the many-carrier ground states. Our analysis
unambiguously demonstrates that while electrons maintain their initial spin
polarization to a large degree, holes completely dephase.Comment: 6 pages, 4 figure
A Mixed-Method Analysis of Remittance Scripts Among Bolivian Immigrants in Spain
The use of mixed methods to deal with the complexity of remittance motivations is still infrequent. This paper uses statistical and qualitative data and provides evidence on the conceptual framework for understanding remittance behaviour proposed by the scholar Jørgen Carling. Carling''s ‘remittance scripts’ understand remittances as multifaceted transactions and enrich the assessment of the relationship between remittances and development at origin. We use quantitative and qualitative data, both extracted from an ethnosurvey conducted in Spain, to shed light on the situation of transnational Bolivian immigrants after the economic crisis of 2008. We argue that the transactions are best represented by the necessity to provide for the recipients'' basic needs
Resolving the decades-long transient FIRST J141918.9+394036: an orphan long gamma-ray burst or a young magnetar nebula?
Ofek (2017) identified FIRST J141918.9+394036 (hereafter FIRST J1419+3940) as
a radio source sharing similar properties and host galaxy type to the compact,
persistent radio source associated with the first known repeating fast radio
burst, FRB 121102. Law et al. (2018) showed that FIRST J1419+3940 is a
transient source decaying in brightness over the last few decades. One possible
interpretation is that FIRST J1419+3940 is a nearby analogue to FRB 121102 and
that the radio emission represents a young magnetar nebula (as several
scenarios assume for FRB 121102). Another interpretation is that FIRST
J1419+3940 is the afterglow of an `orphan' long gamma-ray burst (GRB). The
environment is similar to where most such events are produced. To distinguish
between these hypotheses, we conducted radio observations using the European
VLBI Network at 1.6 GHz to spatially resolve the emission and to search for
millisecond-duration radio bursts. We detect FIRST J1419+3940 as a compact
radio source with a flux density of (on 2018
September 18) and a source size of (i.e. given the angular diameter distance of ).
These results confirm that the radio emission is non-thermal and imply an
average expansion velocity of . Contemporaneous
high-time-resolution observations using the 100-m Effelsberg telescope detected
no millisecond-duration bursts of astrophysical origin. The source properties
and lack of short-duration bursts are consistent with a GRB jet expansion,
whereas they disfavor a magnetar birth nebula.Comment: 8 pages, 4 figures, accepted for publication in ApJ
Two-photon- photoluminescence excitation spectroscopy of single quantum-dots
We present experimental and theoretical study of single semiconductor quantum
dots excited by two non-degenerate, resonantly tuned variably polarized lasers.
The first laser is tuned to excitonic resonances. Depending on its polarization
it photogenerates a coherent single exciton state. The second laser is tuned to
biexciton resonances. By scanning the energy of the second laser for various
polarizations of the two lasers, while monitoring the emission from the
biexciton and exciton spectral lines, we map the biexciton photoluminescence
excitation spectra. The resonances rich spectra of the second photon absorption
are analyzed and fully understood in terms of a many carrier theoretical model
which takes into account the direct and exchange Coulomb interactions between
the quantum confined carriers.Comment: Accepted for publication in PR
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