392 research outputs found
Graph models of wind instruments : computing the natural frequencies of some elementary ducts
International audienceA graph-based modelling approach for wind instruments with tone holes has been recently proposed by the author. This preliminary work remained at a rather theoretical level with high degree of generality, focussing nevertheless on musical acoustics applications while laying foundations for concrete applications. The purpose of the present work is to present concrete computation methods and numerical results in order to validate these theoretical results. For this task, elementary resonators are investigated, for which great knowledge has been accumulated for a long time through the impedance, transfer matrix and modal decomposition approaches, which can thus serve for checking. The resonator profiles focussed on belong to a musically useful class : cylinders and stepped cones, as studied by Dalmont and Kergomard 20 years ago. The case of a cylindrical resonator with one tonehole is also presented. One important feature of the approach is that mode matching is automatically satisfied, natural frequencies and eigenmodes being computed at once by the method, even for geometries with discontinuities. Also, perspectives are opened for exhibiting a very wide class of resonators with harmonically related natural frequencies, which is the subject of an another paper
The irish Uillean pipe: a story of lore, hell and hard D
International audienceThe irish Uillean pipe is a bellows-blown bagpipe that resembles other baroque musettes (french musettes de cour) such as the english Northumbrian pipe and french Musette. According to A. Baines, it appeared in Ireland in the late seventeenth century, in a version somewhat simpler than the instrument known in the present days. It is surely among the most evoluated bagpipes nowadays with a rather complex playing. The lowest note of the chanter has the noticeable characteristic, searched after by musicians, of having two different timbres. One of these, known among musicians as the hard D, is strikingly louder and clearer than the other, the soft D. The contrast between them is traditionally a much appreciated quality of an instrument. In this paper, we concentrate on this particular note and propose an explanation for the appearance of these two distinct timbres
BATTERY USAGE IN THE FUTURE FLEET
This research effort examined the current advanced battery requirement (baseline) and projects anticipated battery requirements for the operating force in 2035 and 2045. The research is conducted using a mission engineering perspective to determine the battery requirements. The analysis includes battery chemistry, energy density, charge/discharge rate, safety concerns, and the like, of the battery. In this research the following questions are answered: What is the current advanced battery requirement (baseline)? What is the projection for batteries required by the operating force by 2035? What is the projection for batteries required by the operating force by 2045? Upon completion of the research, the team was able to definitively determine that there will be a role for Li-ion batteries within the fleet of Navy vessels. That role will, however, be limited to running specific subsystems or equipment and will not replace the ship generators. This will remain true until the energy density of battery technology even begins to approach that of petrochemicals, which we believe is many years away if possible.Outstanding ThesisCivilian, Department of the ArmyCivilian, Department of the ArmyCivilian, Department of the ArmyCivilian, Department of the ArmyCivilian, Department of the ArmyApproved for public release. Distribution is unlimited
Quantization on Curves
Deformation quantization on varieties with singularities offers perspectives
that are not found on manifolds. Essential deformations are classified by the
Harrison component of Hochschild cohomology, that vanishes on smooth manifolds
and reflects information about singularities. The Harrison 2-cochains are
symmetric and are interpreted in terms of abelian -products. This paper
begins a study of abelian quantization on plane curves over \Crm, being
algebraic varieties of the form R2/I where I is a polynomial in two variables;
that is, abelian deformations of the coordinate algebra C[x,y]/(I).
To understand the connection between the singularities of a variety and
cohomology we determine the algebraic Hochschild (co-)homology and its
Barr-Gerstenhaber-Schack decomposition. Homology is the same for all plane
curves C[x,y]/(I), but the cohomology depends on the local algebra of the
singularity of I at the origin.Comment: 21 pages, LaTex format. To appear in Letters Mathematical Physic
Discrete exterior calculus (DEC) for the surface Navier-Stokes equation
We consider a numerical approach for the incompressible surface Navier-Stokes
equation. The approach is based on the covariant form and uses discrete
exterior calculus (DEC) in space and a semi-implicit discretization in time.
The discretization is described in detail and related to finite difference
schemes on staggered grids in flat space for which we demonstrate second order
convergence. We compare computational results with a vorticity-stream function
approach for surfaces with genus 0 and demonstrate the interplay between
topology, geometry and flow properties. Our discretization also allows to
handle harmonic vector fields, which we demonstrate on a torus.Comment: 21 pages, 9 figure
Delayed subsidence of the Dead Sea shore due to hydro-meteorological changes
Many studies show the sensitivity of our environment to manmade changes, especially the anthropogenic impact on atmospheric and hydrological processes. The effect on Solid Earth processes such as subsidence is less straightforward. Subsidence is usually slow and relates to the interplay of complex hydro-mechanical processes, thus making relations to atmospheric changes difficult to observe. In the Dead Sea (DS) region, however, climatic forcing is strong and over-use of fresh water is massive. An observation period of 3 years was thus sufficient to link the high evaporation (97 cm/year) and the subsequent drop of the Dead Sea lake level (− 110 cm/year), with high subsidence rates of the Earth’s surface (− 15 cm/year). Applying innovative Global Navigation Satellite System (GNSS) techniques, we are able to resolve this subsidence of the “Solid Earth” even on a monthly basis and show that it behaves synchronous to atmospheric and hydrological changes with a time lag of two months. We show that the amplitude and fluctuation period of ground deformation is related to poro-elastic hydro-mechanical soil response to lake level changes. This provides, to our knowledge, a first direct link between shore subsidence, lake-level drop and evaporation
Turing instabilities in a mathematical model for signaling networks
GTPase molecules are important regulators in cells that continuously run
through an activation/deactivation and membrane-attachment/membrane-detachment
cycle. Activated GTPase is able to localize in parts of the membranes and to
induce cell polarity. As feedback loops contribute to the GTPase cycle and as
the coupling between membrane-bound and cytoplasmic processes introduces
different diffusion coefficients a Turing mechanism is a natural candidate for
this symmetry breaking. We formulate a mathematical model that couples a
reaction-diffusion system in the inner volume to a reaction-diffusion system on
the membrane via a flux condition and an attachment/detachment law at the
membrane. We present a reduction to a simpler non-local reaction-diffusion
model and perform a stability analysis and numerical simulations for this
reduction. Our model in principle does support Turing instabilities but only if
the lateral diffusion of inactivated GTPase is much faster than the diffusion
of activated GTPase.Comment: 23 pages, 5 figures; The final publication is available at
http://www.springerlink.com http://dx.doi.org/10.1007/s00285-011-0495-
Vanishing Twist near Focus-Focus Points
We show that near a focus-focus point in a Liouville integrable Hamiltonian
system with two degrees of freedom lines of locally constant rotation number in
the image of the energy-momentum map are spirals determined by the eigenvalue
of the equilibrium. From this representation of the rotation number we derive
that the twist condition for the isoenergetic KAM condition vanishes on a curve
in the image of the energy-momentum map that is transversal to the line of
constant energy. In contrast to this we also show that the frequency map is
non-degenerate for every point in a neighborhood of a focus-focus point.Comment: 13 page
- …