9,265 research outputs found
Fixture for plating stripped conductors of flat conductor cables /FCC/
Fixture supports flat conductor cables /FCC/ while providing electrical contact to stripped ends of cable during electroplating process. Cable is held in the form of a coil
High resolution study of the solar atmosphere Final report
High resolution study of solar atmosphere of H alpha lin
The Ubiquity of Sidon Sets That Are Not
We prove that every infinite, discrete abelian group admits a pair of
sets whose union is not . In particular, this implies that every such
group contains a Sidon set that is not
Experimental Flow Models for SSME Flowfield Characterization
Full scale flow models with extensive instrumentation were designed and manufactured to provide data necessary for flow field characterization in rocket engines of the Space Shuttle Main Engine (SSME) type. These models include accurate flow path geometries from the pre-burner outlet through the throat of the main combustion chamber. The turbines are simulated with static models designed to provide the correct pressure drop and swirl for specific power levels. The correct turbopump-hot gas manifold interfaces were designed into the flow models to permit parametric/integration studies for new turbine designs. These experimental flow models provide a vehicle for understanding the fluid dynamics associated with specific engine issues and also fill the more general need for establishing a more detailed fluid dynamic base to support development and verification of advanced math models
A quantification of hydrodynamical effects on protoplanetary dust growth
Context. The growth process of dust particles in protoplanetary disks can be
modeled via numerical dust coagulation codes. In this approach, physical
effects that dominate the dust growth process often must be implemented in a
parameterized form. Due to a lack of these parameterizations, existing studies
of dust coagulation have ignored the effects a hydrodynamical gas flow can have
on grain growth, even though it is often argued that the flow could
significantly contribute either positively or negatively to the growth process.
Aims. We intend to provide a quantification of hydrodynamical effects on the
growth of dust particles, such that these effects can be parameterized and
implemented in a dust coagulation code.
Methods. We numerically integrate the trajectories of small dust particles in
the flow of disk gas around a proto-planetesimal, sampling a large parameter
space in proto-planetesimal radii, headwind velocities, and dust stopping
times.
Results. The gas flow deflects most particles away from the
proto-planetesimal, such that its effective collisional cross section, and
therefore the mass accretion rate, is reduced. The gas flow however also
reduces the impact velocity of small dust particles onto a proto-planetesimal.
This can be beneficial for its growth, since large impact velocities are known
to lead to erosion. We also demonstrate why such a gas flow does not return
collisional debris to the surface of a proto-planetesimal.
Conclusions. We predict that a laminar hydrodynamical flow around a
proto-planetesimal will have a significant effect on its growth. However, we
cannot easily predict which result, the reduction of the impact velocity or the
sweep-up cross section, will be more important. Therefore, we provide
parameterizations ready for implementation into a dust coagulation code.Comment: 9 pages, 6 figures; accepted for publication in A&A; v2 matches the
manuscript sent to the publisher (very minor changes
Tools made of ice facilitate forming of soft, sticky materials
Tools made of ice facilitate the forming or shaping of materials that are soft and sticky in the uncured state. The low-temperature of the ice slows the curing of the material, extending the working time available before setup. Handling problems are eliminated because the material does not adhere to the tool, and the melting ice serves as a lubricant
Deflection of Rotating Symmetric Molecules by Inhomogeneous Fields
We consider deflection of rotating symmetric molecules by inhomogeneous
optical and static electric fields, compare results with the case of linear
molecules, and find new singularities in the distribution of the scattering
angle. Scattering of the prolate/oblate molecules is analyzed in detail, and it
is shown that the process can be efficiently controlled by means of short and
strong femtosecond laser pulses. In particular, the angular dispersion of the
deflected molecules may be dramatically reduced by laser-induced molecular
pre-alignment. We first study the problem by using a simple classical model,
and then find similar results by means of more sophisticated methods, including
the formalism of adiabatic invariants and direct numerical simulation of the
Euler-Lagrange equations of motion. The suggested control scheme opens new ways
for many applications involving molecular focusing, guiding, and trapping by
optical and static fields
- …