1,280 research outputs found
Relativistic mechanics of Casimir apparatuses in a weak gravitational field
This paper derives a set of general relativistic Cardinal Equations for the
equilibrium of an extended body in a uniform gravitational field. These
equations are essential for a proper understanding of the mechanics of
suspended relativistic systems. As an example, the prototypical case of a
suspended vessel filled with radiation is discussed. The mechanics of Casimir
apparatuses at rest in the gravitational field of the Earth is then considered.
Starting from an expression for the Casimir energy-momentum tensor in a weak
gravitational field recently derived by the authors, it is here shown that, in
the case of a rigid cavity supported by a stiff mount, the weight of the
Casimir energy stored in the cavity corresponds to a gravitational mass
, in agreement with the covariant conservation law of the
regularized energy-momentum tensor. The case of a cavity consisting of two
disconnected plates supported by separate mounts, where the two measured forces
cannot be obtained by straightforward arguments, is also discussed.Comment: 9 pages, improved presentation and new references adde
Casimir energy and the superconducting phase transition
We study the influence of Casimir energy on the critical field of a
superconducting film, and we show that by this means it might be possible to
directly measure, for the first time, the variation of Casimir energy that
accompanies the superconducting transition. It is shown that this novel
approach may also help clarifying the long-standing controversy on the
contribution of TE zero modes to the Casimir energy in real materials.Comment: 12 pages, 5 figures. Talk given at 7th Workshop on Quantum Field
Theory Under the Influence of External Conditions (QFEXT 05), Barcelona,
Catalonia, Spain, 5-9 Sep 200
Nanostructure and phase engineering of manganese oxide thin films grown by pulsed laser deposition: a Raman and XRD study
Manganese, showing stable oxidation states spanning from +2 to +7, gives rise to a variety of oxides (MnOx) whose exploitation in several technological fields, such as energy conversion and storage, catalysis, sensing, environmental and biomedical engineering, is highly promising. Nevertheless, the chemical complexity and the structural richness of MnOx – involving mixed-valence and metastable species – make the correct identification by Raman spectroscopy challenging, further complicated by the laser sensitivity, the poor Raman activity, and the conflicting literature scenario. Moreover, a careful optimization of the material in terms of phase, structure, and morphology is highly desirable in view of the final application, where a precise control over the materials properties is essential. In this work, we discuss the capability of room-temperature pulsed laser deposition (PLD), followed by post-deposition thermal treatments, to successfully grow engineered and pure MnOx thin films, whose phase and morphology at the nanoscale can be totally decoupled and independently optimized. The detailed Raman characterization of these films enabled a clear identification of specific MnOx phases and poses the basis for the rationale of the MnOx Raman spectra. Starting from the same MnO PLD target, we obtained five different MnOx phases (i.e., MnO, Mn3O4, Mn2O3, amorphous MnO2, and α-MnO2) with tailored and tunable degree of porosity and crystallinity, by modulating process parameters like the O2 deposition partial pressure (vacuum – 100 Pa), the type of substrate, and the annealing temperature (300–900 °C) and atmosphere (air/vacuum). The Raman spectroscopy reliability of the MnOx phase assignment was assessed by thoroughly investigating the impact of the exciting laser power, and it was further validated by energy-dispersive X-ray spectroscopy, X-ray photoemission spectroscopy, and X-ray diffraction, providing additional insights into the compositional properties and the crystalline structure
Spectroscopic fingerprints for charge localization in the organic semiconductor (DOEO)4[HgBr4]·TCE
Changes of the electronic structure accompanied by charge localization and a transition to an antiferromagnetic ground state were observed in the organic semiconductor (DOEO)4 [HgBr4 ]·TCE. Localization starts in the temperature region of about 150 K and the antiferromagnetic state occurs below 60 K. The magnetic moment of the crystal contains contributions of inclusions (droplets), and individual paramagnetic centers formed by localized holes and free charge carriers at 2 K. Two types of inclusions of 100–400 nm and 2–5 nm sizes were revealed by transmission electron microscopy. Studying the temperature-and angular dependence of electron spin resonance (ESR) spectra revealed fingerprints of antiferromagnetic contributions as well as paramagnetic resonance spectra of individual localized charge carriers. The results point on coexistence of antiferromagnetic long and short range order as evident from a second ESR line. Photoelectron spectroscopy in the VUV, soft and hard X-ray range shows temperature-dependent effects upon crossing the critical temperatures around 60 K and 150 K. The substantially different probing depths of soft and hard X-ray photoelectron spectroscopy yield nformation on the surface termination. The combined investigation using complementary methods at the same sample eveals the close relation of changes in the transport properties and in the energy distribution of electronic states
Dynamical Casimir Effect with Semi-Transparent Mirrors, and Cosmology
After reviewing some essential features of the Casimir effect and,
specifically, of its regularization by zeta function and Hadamard methods, we
consider the dynamical Casimir effect (or Fulling-Davis theory), where related
regularization problems appear, with a view to an experimental verification of
this theory. We finish with a discussion of the possible contribution of vacuum
fluctuations to dark energy, in a Casimir like fashion, that might involve the
dynamical version.Comment: 11 pages, Talk given in the Workshop ``Quantum Field Theory under the
Influence of External Conditions (QFEXT07)'', Leipzig (Germany), September 17
- 21, 200
Reconstruction of the gravitational wave signal during the Virgo science runs and independent validation with a photon calibrator
The Virgo detector is a kilometer-scale interferometer for gravitational wave
detection located near Pisa (Italy). About 13 months of data were accumulated
during four science runs (VSR1, VSR2, VSR3 and VSR4) between May 2007 and
September 2011, with increasing sensitivity.
In this paper, the method used to reconstruct, in the range 10 Hz-10 kHz, the
gravitational wave strain time series from the detector signals is
described. The standard consistency checks of the reconstruction are discussed
and used to estimate the systematic uncertainties of the signal as a
function of frequency. Finally, an independent setup, the photon calibrator, is
described and used to validate the reconstructed signal and the
associated uncertainties.
The uncertainties of the time series are estimated to be 8% in
amplitude. The uncertainty of the phase of is 50 mrad at 10 Hz with a
frequency dependence following a delay of 8 s at high frequency. A bias
lower than and depending on the sky direction of the GW is
also present.Comment: 35 pages, 16 figures. Accepted by CQ
Local and Global Casimir Energies: Divergences, Renormalization, and the Coupling to Gravity
From the beginning of the subject, calculations of quantum vacuum energies or
Casimir energies have been plagued with two types of divergences: The total
energy, which may be thought of as some sort of regularization of the
zero-point energy, , seems manifestly divergent. And
local energy densities, obtained from the vacuum expectation value of the
energy-momentum tensor, , typically diverge near
boundaries. The energy of interaction between distinct rigid bodies of whatever
type is finite, corresponding to observable forces and torques between the
bodies, which can be unambiguously calculated. The self-energy of a body is
less well-defined, and suffers divergences which may or may not be removable.
Some examples where a unique total self-stress may be evaluated include the
perfectly conducting spherical shell first considered by Boyer, a perfectly
conducting cylindrical shell, and dilute dielectric balls and cylinders. In
these cases the finite part is unique, yet there are divergent contributions
which may be subsumed in some sort of renormalization of physical parameters.
The divergences that occur in the local energy-momentum tensor near surfaces
are distinct from the divergences in the total energy, which are often
associated with energy located exactly on the surfaces. However, the local
energy-momentum tensor couples to gravity, so what is the significance of
infinite quantities here? For the classic situation of parallel plates there
are indications that the divergences in the local energy density are consistent
with divergences in Einstein's equations; correspondingly, it has been shown
that divergences in the total Casimir energy serve to precisely renormalize the
masses of the plates, in accordance with the equivalence principle.Comment: 53 pages, 1 figure, invited review paper to Lecture Notes in Physics
volume in Casimir physics edited by Diego Dalvit, Peter Milonni, David
Roberts, and Felipe da Ros
The variable finesse locking technique
Virgo is a power recycled Michelson interferometer, with 3 km long Fabry-Perot cavities in the arms. The locking of the interferometer has been obtained with an original lock acquisition technique. The main idea is to lock the instrument away from its working point. Lock is obtained by misaligning the power recycling mirror and detuning the Michelson from the dark fringe. In this way, a good fraction of light escapes through the antisymmetric port and the power build-up inside the recycling cavity is extremely low. The benefit is that all the degrees of freedom are controlled when they are almost decoupled, and the linewidth of the recycling cavity is large. The interferometer is then adiabatically brought on to the dark fringe. This technique is referred to as variable finesse, since the recycling cavity is considered as a variable finesse Fabry-Perot. This technique has been widely tested and allows us to reach the dark fringe in few minutes, in an essentially deterministic way
Characterization of the Sos Enattos site for the Einstein Telescope
In this work we report the ongoing characterization of the Sos Enattos former mine (Sardinia, Italy), one of the two candidate sites for the Einstein Telescope (ET), the European third-generation underground interferometric detector of Gravitational Waves. The Sos Enattos site lies on a crystalline basement, made of rocks with good geomechanical properties, characterized by negligible groundwater. In addition, the site has a very low seismic background noise due to the absence of active tectonics involving Sardinia. Finally, the area has a low population density, resulting in a reduced anthropic noise even at the ground level. This location was already studied in 2012-2014 as a promising site for an underground detector. More recently, in March 2019, we deployed a new network of surface and underground seismometers at the site, that is currently monitoring the local seismic noise. Most of the energy carried by the seismic waves is due to the microseisms below 1 Hz, showing a significant correlation with the waves of the west Mediterranean sea. Above 1 Hz the seismic noise in the underground levels of the mine approaches the Peterson's low noise model. Exploiting mine blasting works into the former mine, we were also able to perform active seismic measurements to evaluate the seismic waves propagation across the area. In conclusion we also give a first assessment about the acoustic and magnetic noise in this underground site
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