26,876 research outputs found
Natural and laser-induced cavitation in corn stems: On the mechanisms of acoustic emissions
Water in plant xylem is often superheated, and therefore in a meta-stable
state. Under certain conditions, it may suddenly turn from the liquid to the
vapor state. This cavitation process produces acoustic emissions. We report the
measurement of ultrasonic acoustic emissions (UAE) produced by natural and
induced cavitation in corn stems. We induced cavitation and UAE in vivo, in
well controlled and reproducible experiments, by irradiating the bare stem of
the plants with a continuous-wave laser beam. By tracing the source of UAE, we
were able to detect absorption and frequency filtering of the UAE propagating
through the stem. This technique allows the unique possibility of studying
localized embolism of plant conduits, and thus to test hypotheses on the
hydraulic architecture of plants. Based on our results, we postulate that the
source of UAE is a transient "cavity oscillation" triggered by the disruptive
effect of cavitation inception.Comment: 8 pages, 5 figure
A Jacobian module for disentanglements and applications to Mond's conjecture
Given a germ of holomorphic map from to ,
we define a module whose dimension over is an upper bound
for the -codimension of , with equality if is weighted
homogeneous. We also define a relative version of the module, for
unfoldings of . The main result is that if are nice
dimensions, then the dimension of over is an upper bound of
the image Milnor number of , with equality if and only if the relative
module is Cohen-Macaulay for some stable unfolding . In particular,
if is Cohen-Macaulay, then we have Mond's conjecture for .
Furthermore, if is quasi-homogeneous, then Mond's conjecture for is
equivalent to the fact that is Cohen-Macaulay. Finally, we observe
that to prove Mond's conjecture, it suffices to prove it in a suitable family
of examples.Comment: 19 page
Single-photon exchange interaction in a semiconductor microcavity
We consider the effective coupling of localized spins in a semiconductor
quantum dot embedded in a microcavity. The lowest cavity mode and the quantum
dot exciton are coupled and close in energy, forming a polariton. The fermions
forming the exciton interact with localized spins via exchange. Exact
diagonalization of a Hamiltonian in which photons, spins and excitons are
treated quantum mechanically shows that {\it a single polariton} induces a
sizable indirect exchange interaction between otherwise independent spins. The
origin, symmetry properties and the intensity of that interaction depend both
on the dot-cavity coupling and detuning. In the case of a (Cd,Mn)Te quantum
dot, Mn-Mn ferromagnetic coupling mediated by a single photon survives above 1
K whereas the exciton mediated coupling survives at 15 K.Comment: 4 pages, 3 figure
Mathematical Genesis of the Spatio-Temporal Covariance Functions
Obtaining new and flexible classes of nonseparable spatio-temporal covariances have resulted in a key point of research in the last years within the context of spatiotemporal Geostatistics. Approach: In general, the literature has focused on the problem of full symmetry and the problem of anisotropy has been overcome. Results: By exploring mathematical properties of positive definite functions and their close connection to covariance functions we are able to develop new spatio-temporal covariance models taking into account the problem of spatial anisotropy. Conclusion/Recommendations: The resulting structures are proved to have certain interesting mathematical properties, together with a considerable applicability.Spatial anisotropy, bernstein and complete monotone functions, spatio-temporal geostatistics, positive definite functions, space-time modeling, spatio-temporal data
Spanish Civil War caves of Asturias in archaeology and memory
As the Spanish Civil War drew to a close, retreating Republican troops in the northern region of Asturias took refuge in caves in the mountains from the brutal victor’s justice of the Francoist forces. In this paper we examine three of these caves in the context of the Civil War experiences of the rural municipality of Santo Adriano, based on a combination of archaeological recording and oral history interviews. The paper focuses on the role of the La Ponte-Ecomuseum, a grassroots heritage organisation that has worked to preserve and communicate the tangible and intangible heritage of the district. The Civil War heritage presents cultural, political and practical challenges for the museum: nonetheless it has succeeded in establishing an ongoing programme for its communication and protection
Heavy mesons in the Quark Model
Since the discovery of the , the quark model was very successful in
describing the spectrum and properties of heavy mesons including only
components. However since 2003, with the discovery of the , many
states that can not be accommodated on the naive quark model have been
discovered, and they made unavoidable to include higher Fock components on the
heavy meson states. We will give an overview of the success of the quark model
for heavy mesons and point some of the states that are likely to be more
complicated structures such as meson-meson molecules.Comment: Contribution to the Proceedings of the 15th International Workshop on
Meson Physics - MESON201
A family of complex potentials with real spectrum
We consider a two-parameter non hermitean quantum-mechanical hamiltonian that
is invariant under the combined effects of parity and time reversal
transformation. Numerical investigation shows that for some values of the
potential parameters the hamiltonian operator supports real eigenvalues and
localized eigenfunctions. In contrast with other PT symmetric models, which
require special integration paths in the complex plane, our model is integrable
along a line parallel to the real axis.Comment: Six figures and four table
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