38,227 research outputs found
Air-cushioning in impact problems
This paper concerns the displacement potential formulation to study the post-impact influence of an aircushioning layer on the two-dimensional impact of a liquid half-space by a rigid body. The liquid and air are both ideal and incompressible and attention is focussed on cases when the density ratio between the air and liquid is small. In particular, the correction to classical Wagner theory is analysed in detail for the impact of circular cylinders and wedges
Time damping of non-adiabatic magnetohydrodynamic waves in a partially ionized prominence plasma: Effect of helium
Prominences are partially ionized, magnetized plasmas embedded in the solar
corona. Damped oscillations and propagating waves are commonly observed. These
oscillations have been interpreted in terms of magnetohydrodynamic (MHD) waves.
Ion-neutral collisions and non-adiabatic effects (radiation losses and thermal
conduction) have been proposed as damping mechanisms. We study the effect of
the presence of helium on the time damping of non-adiabatic MHD waves in a
plasma composed by electrons, protons, neutral hydrogen, neutral helium (He I),
and singly ionized helium (He II) in the single-fluid approximation. The
dispersion relation of linear non-adiabatic MHD waves in a homogeneous,
unbounded, and partially ionized prominence medium is derived. The period and
the damping time of Alfven, slow, fast, and thermal waves are computed. A
parametric study of the ratio of the damping time to the period with respect to
the helium abundance is performed. The efficiency of ion-neutral collisions as
well as thermal conduction is increased by the presence of helium. However, if
realistic abundances of helium in prominences (~10%) are considered, this
effect has a minor influence on the wave damping. The presence of helium can be
safely neglected in studies of MHD waves in partially ionized prominence
plasmas.Comment: Research note submitted in A&
Assessment in mathematics: A multimedia resource for preservice teachers
It is commonly accepted that teachers teach the way they were taught and that innovation is difficult to achieve. In this project, the theoretical framework of situated cognition or situated learning has been used to design an interactive multimedia resource that allows preservice teachers to become aware of different assessment strategies in mathematics education, and how to apply them. The resource enables users to encounter the authentic use of a range of assessment strategies and to view their interpretations from multiple perspectives which include the teacher's decision-making processes, the child's thinking, expert opinion and written documentation
Note on new interesting baryon channels to measure the photon polarization in b -> s gamma
At LHC a large number of b-flavored baryons will be produced. In this note we
propose new baryon modes to determine the photon helicity of the penguin
transition . The decay has the
drawback that the , being neutral and long-lived, will escape
detection most of the time. To overcome this difficulty, transitions of the
type have been proposed, where
denotes an excited state decaying strongly within the detector into the clean
mode . The doublet , that decays weakly, has a number of good
features. The charged baryon will decay into the mode ,
where the ground state hyperon , although it will decay most of the time
outside the detector, can be detected because it is charged. We consider also
the decay of into , where a higher mass state
can decay strongly within the detector. We point out that the initial
transverse polarization of has to be known in all cases. To determine
this parameter through the transition , we distinguish
between different cases, and underline that in some situations one needs {\it
theoretical input} on the asymmetry parameter of the primary
decay. {\it A fortiori} the same considerations apply to the case of the
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