1,858 research outputs found
On the lower bound of the inner radius of nodal domains
We discuss the asymptotic lower bound on the inner radius of nodal domains that arise from Laplacian eigenfunctions \varphi _{\lambda} on a closed Riemannian manifold (M, g) . In the real-analytic case, we present an improvement of the currently best-known bounds, due to Mangoubi (Commun Partial Differ Equ 33:1611–1621, 2008; Can Math Bull 51(2):249–260, 2008). Furthermore, using recent results of Hezari (P Am Math Soc, 2016, https://doi.org/10.1090/proc/13766; Anal PDE 11(4):855–871, 2018), we obtain log-type improvements in the case of negative curvature and improved bounds for (M, g) possessing an ergodic geodesic flow
BVR photometry of the resolved dwarf galaxy Ho IX
We present BVR CCD photometry down to limiting magnitude B=23.5 mag for 232
starlike objects and 11 diffuse objects in a 5.4' x 5.4' field of Ho IX. The
galaxy is a gas-rich irregular dwarf galaxy possibly very close to M 81, which
makes it especially interesting in the context of the evolution of satellite
galaxies and the accretion of dwarf galaxies. Investigations of Ho IX were
hampered by relatively large contradictions in the magnitude scale between
earlier studies. With our new photometry we resolved these discrepancies. The
color magnitude diagram (CMD) of Ho IX is fairly typical of a star-forming
dwarf irregular, consistent with earlier results. Distance estimates from our
new CMD are consistent with Ho IX being very close to M 81 and therefore being
a definite member of the M 81 group, apparently in very close physical
proximity to M 81.Comment: 9 pages, 8 figures, uses aa.cls, A&A in pres
Some remarks on nodal geometry in the smooth setting
We consider a Laplace eigenfunction on a smooth closed Riemannian manifold, that is, satisfying . We introduce several observations about the geometry of its vanishing (nodal) set and corresponding nodal domains. First, we give asymptotic upper and lower bounds on the volume of a tubular neighbourhood around the nodal set of . This extends previous work of Jakobson and Mangoubi in case is real-analytic. A significant ingredient in our discussion are some recent techniques due to Logunov (cf. Ann Math (2) 187(1):241–262, 2018). Second, we exhibit some remarks related to the asymptotic geometry of nodal domains. In particular, we observe an analogue of a result of Cheng in higher dimensions regarding the interior opening angle of a nodal domain at a singular point. Further, for nodal domains on which satisfies exponentially small bounds, we give some quantitative estimates for radii of inscribed balls
Some applications of heat flow to Laplace eigenfunctions
We consider mass concentration properties of Laplace eigenfunctions , that is, smooth functions satisfying the equation , on a smooth closed Riemannian manifold. Using a heat diffusion technique, we first discuss mass concentration/localization properties of eigenfunctions around their nodal sets. Second, we discuss the problem of avoided crossings and (non)existence of nodal domains which continue to be thin over relatively long distances. Further, using the above techniques, we discuss the decay of Laplace eigenfunctions on Euclidean domains which have a central "thick" part and "thin" elongated branches representing tunnels of sub-wavelength opening. Finally, in an Appendix, we record some new observations regarding sub-level sets of the eigenfunctions and interactions of different level sets
Anomalous nucleation far from equilibrium
We present precision Monte Carlo data and analytic arguments for an
asymmetric exclusion process, involving two species of particles driven in
opposite directions on a lattice. We propose a scenario which
resolves a stark discrepancy between earlier simulation data, suggesting the
existence of an ordered phase, and an analytic conjecture according to which
the system should revert to a disordered state in the thermodynamic limit. By
analyzing the finite size effects in detail, we argue that the presence of a
single, seemingly macroscopic, cluster is an intermediate stage of a complex
nucleation process: In smaller systems, this cluster is destabilized while
larger systems allow the formation of multiple clusters. Both limits lead to
exponential cluster size distributions which are, however, controlled by very
different length scales.Comment: 5 pages, 3 figures, one colum
Chemo-dynamical evolution of Globular Cluster Systems
We studied the relation between the ratio of rotational velocity to velocity
dispersion and the metallicity (/\sigma_{v}-metallicity relation) of
globular cluster systems (GCS) of disk galaxies by comparing the relation
predicted from simple chemo-dynamical models for the formation and evolution of
disk galaxies with the observed kinematical and chemical properties of their
GCSs. We conclude that proto disk galaxies underwent a slow initial collapse
that was followed by a rapid contraction and derive that the ratio of the
initial collapse time scale to the active star formation time scale is \sim 6
for our Galaxy and \sim 15 for M31. The fundamental formation process of disk
galaxies was simulated based on simple chemo-dynamical models assuming the
conservation of their angular momentum. We suggest that there is a typical
universal pattern in the /\sigma_{v}-metallicity relation of the GCS
of disk galaxies. This picture is supported by the observed properties of GCSs
in the Galaxy and in M31. This relation would deviate from the universal
pattern, however, if large-scale merging events took major role in
chemo-dynamical evolution of galaxies and will reflect the epoch of such
merging events. We discuss the properties of the GCS of M81 and suggest the
presence of past major merging event.Comment: 25 pages, 8 figures, Accepted for publication in the Astrophysical
Journa
Structural-acoustic properties of flexible rectangular boxes
Rectangular box-like structures are used widely in a large number of engineering applications, e.g. as elements of railway carriages, heavy goods vehicles, buildings, civil engineering constructions, etc. Although flexible rectangular boxes represent one of the geometrically simple types of engineering structures, their structural-acoustic properties cannot be described by closed-form analytical solutions. In the present study, a comprehensive numerical investigation of typical all-flexible rectangular box structures has been carried out to elucidate the physics of structural-acoustic interaction in them and to explore the possibilities of reduction of the associated structure-borne interior noise. Finite element method has been used to compute the resonant frequencies, the mode shapes and the structural-acoustic frequency response functions of different rectangular box models. The obtained results could assist in better understanding of structural-acoustic properties of flexible rectangular boxes as well as of numerous more complex structures using rectangular boxes as their building elements
New approach to investigation of resonant vibrations of noncircular shells based on the theory of coupled waveguides
In the present paper a new simple method of analytical description of resonant vibrations of finite noncircular cylindrical shells is developed. The method is based on the theory of coupled waveguides formed by quasiflat areas of the same noncircular shells having an infinite length (depth). The physical reason for guided wave propagation along quasiflat areas of such shells is the difference between flexural wave velocities in their quasiflat and curved areas, respectively. Using asymptotic expressions for flexural wave velocities in circular shells with different radii of curvature, approximate dispersion equations are derived for waves propagating in such waveguides and their corresponding coupling coefficients. After that, considering shells of finite length, the transition is made from the coupled guided modes to the coupled resonant vibrations of the shell. The obtained resonant frequencies and spatial distributions of the resulting vibration modes are in good agreement with the results of finite element calculations
Finite element study of the effect of structural modifications on structure-borne vehicle interior noise
This paper presents the results of the numerical investigation of structure-borne vehicle interior
noise in a simplified model of vehicle compartment. The aim of the paper is to analyze the effects of different
variations of certain geometrical and material parameters of vehicle structure on structural-acoustic frequency
response functions. It has been found that geometrical modifications have little influence on the structural
natural frequencies. However, they strongly affect the acoustic natural frequencies and normal modes as well
as the resulting sound pressure responses. The increase in thickness of the bottom plate suppresses the sound
pressure responses very efficiently. However, variations of material characteristics of wind- and back-screen
do not have much influence on the interior noise
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