scholarly journals Passive, Nonlinear, Mechanical Structures for Seismic Attenuation

2007 ◽  
Vol 2 (4) ◽  
pp. 290-298 ◽  
Author(s):  
Riccardo DeSalvo
Keyword(s):  
Gravitational Wave ◽  
Nonlinear Response ◽  
Low Frequency ◽  
Space Time ◽  
Seismic Attenuation ◽  
Motion Sensors ◽  
High Quality ◽  
Seismic Motion ◽  
Nonlinear Mechanical ◽  
A Chain

Gravitational wave detectors aim to detect strain perturbations of space-time on the order of 10−21–10−22 at frequencies between 1Hz and a few kHz. This space-time strain, integrated over kilometer scale interferometers, will induce movements of suspended mirrors on the order of 10−18–10−19m. Seismic motion in this frequency band varies between 10−6m and 10−12m. Required seismic attenuation factors, as large as 10−12, by far exceed the performance of motion sensors, and are only obtained by means of a chain of passive attenuators. High quality springs in configurations yielding nonlinear response are used to generate attenuation at low frequency. Similarly, nonlinear mechanisms are used in the horizontal direction. A description of some of these systems and some of the technical challenges that they involve is presented.

scholarly journals Passive, Non-Linear, Mechanical Structures for Seismic Attenuation

2005 ◽  
Author(s):  
Riccardo DeSalvo
Keyword(s):  
Gravitational Wave ◽  
Linear Response ◽  
Low Frequency ◽  
Space Time ◽  
Seismic Attenuation ◽  
Motion Sensors ◽  
High Quality ◽  
Seismic Motion ◽  
Non Linear ◽  
A Chain

Gravitational Wave detectors aim to detect strain perturbations of space-time of the order of 10−21 ~ 10−22 at frequencies between one Hz and a few kHz. This space-time strain, integrated over a few Km long interferometers, will induce movements of suspended mirrors of the order of 10−18 ~ 10−19m. Seismic motion in this frequency band varies between 10−6 and 10−12 m. Required seismic attenuation factors, as large as 10−12, by far exceed the performance of motion sensors, and are only obtained by means of a chain of passive attenuators. High quality springs in configurations yielding non-linear response are used to generate attenuation at low frequency. Similarly non-linear mechanisms are used in the horizontal direction. A description of some of these systems and some of the technical challenges that they involve are presented.

scholarly journals Tunable, synchronized frequency down-conversion in magnetic lattices with defects

2018 ◽  
Vol 376 (2127) ◽  
pp. 20170137 ◽  
Author(s):  
Marc Serra-Garcia ◽  
Miguel Molerón ◽  
Chiara Daraio
Keyword(s):  
Energy Transfer ◽  
Frequency Conversion ◽  
Low Frequency ◽  
Multiple Sources ◽  
Localized Modes ◽  
Nonlinear Energy Transfer ◽  
Nonlinear Mechanical ◽  
Mechanical Analogue ◽  
A Chain

We study frequency conversion in nonlinear mechanical lattices, focusing on a chain of magnets as a model system. We show that, by inserting mass defects at suitable locations, we can introduce localized vibrational modes that nonlinearly couple to extended lattice modes. The nonlinear interaction introduces an energy transfer from the high-frequency localized modes to a low-frequency extended mode. This system is capable of autonomously converting energy between highly tunable input and output frequencies, which need not be related by integer harmonic or subharmonic ratios. It is also capable of obtaining energy from multiple sources at different frequencies with a tunable output phase, due to the defect synchronization provided by the extended mode. Our lattice is a purely mechanical analogue of an opto-mechanical system, where the localized modes play the role of the electromagnetic field and the extended mode plays the role of the mechanical degree of freedom. This article is part of the theme issue ‘Nonlinear energy transfer in dynamical and acoustical systems’.

Very low frequency electromagnetic phenomena: ‘whistlers’ and micropulsations

1977 ◽  
Vol 279 (963) ◽  
pp. 225-238 ◽  
Keyword(s):  
Low Frequency ◽  
Dynamical Behaviour ◽  
Weddell Sea ◽  
Particle Interactions ◽  
Terrestrial Environment ◽  
Wave Amplification ◽  
A Chain ◽  
Magnetic Conjugacy ◽  
Sea Area ◽  
The Antarctic

Observations of natural electromagnetic phenomena, embracing frequencies ranging from millihertz to tens of kilohertz, have made a major contribution to our knowledge of the terrestrial environment extending out to many Earth’s radii. The Antarctic has offered exceptional opportunities in this field for a number of reasons, including: (i) the location of Antarctic bases (including Halley Bay) at key magnetic latitudes, (ii) magnetic conjugacy to Northern Hemisphere thunderstorm sources, (iii) low interference levels. Important aspects of this research are the investigation of the role of wave-particle interactions in the magnetosphere and that of the structure and dynamical behaviour of the plasmapause, using both passive and active techniques. Comparisons of observations made at antarctic stations and their northern geomagnetic conjugates show close similarities in dominant pulsation periods and demonstrate the uniqueness of the Weddell Sea area in relation to magnetospheric wave amplification at the higher frequencies. An extra dimension to this work is being added, during the International Magnetospheric Study (1976-8), through the development of a chain of stations employing the goniometer (direction-finding) technique pioneered at Halley Bay by Sheffield University.

scholarly journals NEW SUPERSTRING ISOMETRIES AND HIDDEN DIMENSIONS

2007 ◽  
Vol 22 (29) ◽  
pp. 5301-5323 ◽  
Author(s):  
DIMITRI POLYAKOV
Keyword(s):  
Extra Dimension ◽  
Isometry Group ◽  
Space Time ◽  
Time Dimension ◽  
Superstring Theory ◽  
Symmetry Transformations ◽  
Noncritical Strings ◽  
A Chain ◽  
Symmetry Generators ◽  
Special Space

We study the hierarchy of hidden space–time symmetries of noncritical strings in RNS formalism, realized nonlinearly. Under these symmetry transformations the variation of the matter part of the RNS action is canceled by that of the ghost part. These symmetries, referred to as the α-symmetries, are induced by special space–time generators, violating the equivalence of ghost pictures. We classify the α-symmetry generators in terms of superconformal ghost cohomologies Hn ~ H-n-2(n≥0) and associate these generators with a chain of hidden space–time dimensions, with each ghost cohomology Hn ~ H-n-2 "contributing" an extra dimension. Namely, we show that each ghost cohomology Hn ~ H-n-2 of noncritical superstring theory in d-dimensions contains d+n+1 α-symmetry generators and the generators from Hk ~ H-k-2, 1≤k ≤n, combined together, extend the space–time isometry group from the naive SO (d, 2) to SO (d+n, 2). In the simplest case of n = 1 the α-generators are identified with the extra symmetries of the 2T-physics formalism, also known to originate from a hidden space–time dimension.

Seismic attenuation, normal moveout stretch, and low-frequency shadows underlying bottom simulating reflector events

2018 ◽  
Vol 66 (5) ◽  
pp. 857-871 ◽  
Author(s):  
José M. Carcione ◽  
Ayman N. Qadrouh ◽  
Hervé Perroud ◽  
Davide Gei ◽  
Jing Ba ◽  
...  
Keyword(s):  
Low Frequency ◽  
Seismic Attenuation ◽  
Bottom Simulating Reflector

scholarly journals Probing the stability and magnetic properties of magnetosome chains in freeze-dried magnetotactic bacteria

2020 ◽  
Vol 2 (3) ◽  
pp. 1115-1121
Author(s):  
Philipp Bender ◽  
Lourdes Marcano ◽  
Iñaki Orue ◽  
Diego Alba Venero ◽  
Dirk Honecker ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Magnetite Nanoparticles ◽  
Magnetotactic Bacteria ◽  
Magnetic Compass ◽  
High Quality ◽  
Magnetospirillum Gryphiswaldense ◽  
Freeze Dried ◽  
A Chain ◽  
The Stability

Magnetospirillum gryphiswaldense biosynthesize high quality magnetite nanoparticles, called magnetosomes, and arrange them into a chain that behaves like a magnetic compass.

Contribution of the Torsional Modes to the Equilibrium Distribution of Vibrational States and to the Specific Heat of a Chain Molecule

1983 ◽  
Vol 38 (12) ◽  
pp. 1285-1292 ◽  
Author(s):  
J. A. Borges da Costa ◽  
C. Scherer ◽  
A. Holz ◽  
J. Naghizadeh
Keyword(s):  
Specific Heat ◽  
Equilibrium Distribution ◽  
Spatial Configuration ◽  
Low Frequency ◽  
Chain Molecule ◽  
Vibrational States ◽  
Polymer Molecules ◽  
The Mean ◽  
A Chain ◽  
Increasing Temperature

Abstract The torsional modes of a chain molecule were studied recently under the assumption that it has a well defined spatial configuration at any time. Here we show how the averages over the possible configurations, for a distribution in thermal equilibrium, should be performed in the calculation of the thermodynamical properties. Our results show that the mean density of torsional states increases in the low frequency region with increasing temperature. The specific heat behaviour shows a considerable difference from the result obtained in the previous paper, where only the lowest energetic configuration was considered. The consequences of this result with respect to the configurational properties of polymer molecules near the θ temperature are discussed.

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