280 research outputs found
Variation of fluxes of RR Tel emission lines measured in 2000 with respect to 1996
The aim of this work is to make available unpublished non-Fe+ emission line
fluxes from optical spectra of the symbiotic nova RR Tel which were taken in
2000, and to compare them with fluxes of the same lines from spectra taken in
1996. After leaving out blends and misidentifications, as well as the
unreliable far-red and violet lines, we present the log (F2000/F1996) flux
ratios for identified non-Fe+ lines. Mean values of log (F2000/F1996) for
different ionization potential ranges of the ions producing the lines are shown
separately for the permitted and forbidden lines. All means show fading, which
is larger in the lowest range of ionization potential. Provisional
interpretations are suggested. We also measured the values of FWHM in 2000; the
previously known decrease with time of FWHM of lines due to the same ion has
continued.Comment: 16 pages, 5 figure
Polarization measurements and their perspectives: PVLAS Phase II
We sketch the proposal for a "PVLAS-Phase II" experiment. The main physics
goal is to achieve the first direct observation of non-linear effects in
electromagnetism predicted by QED and the measurement of the photon-photon
scattering cross section at low energies (1-2 eV). Physical processes such as
ALP and MCP production in a magnetic field could also be accessible if
sensitive enough operation is reached. The short term experimental strategy is
to compact as much as possible the dimensions of the apparatus in order to
bring noise sources under control and to attain a sufficient sensitivity. We
will also briefly mention future pespectives, such as a scheme to implement the
resonant regeneration principle for the detection of ALPs.Comment: Paper submitted to the proceedings of the "4th Patras Workshop on
Axions, WIMPs and WISPs", DESY, Hamburg Site /Germany, 18-21 June 200
Network constraints on learnability of probabilistic motor sequences
Human learners are adept at grasping the complex relationships underlying
incoming sequential input. In the present work, we formalize complex
relationships as graph structures derived from temporal associations in motor
sequences. Next, we explore the extent to which learners are sensitive to key
variations in the topological properties inherent to those graph structures.
Participants performed a probabilistic motor sequence task in which the order
of button presses was determined by the traversal of graphs with modular,
lattice-like, or random organization. Graph nodes each represented a unique
button press and edges represented a transition between button presses. Results
indicate that learning, indexed here by participants' response times, was
strongly mediated by the graph's meso-scale organization, with modular graphs
being associated with shorter response times than random and lattice graphs.
Moreover, variations in a node's number of connections (degree) and a node's
role in mediating long-distance communication (betweenness centrality) impacted
graph learning, even after accounting for level of practice on that node. These
results demonstrate that the graph architecture underlying temporal sequences
of stimuli fundamentally constrains learning, and moreover that tools from
network science provide a valuable framework for assessing how learners encode
complex, temporally structured information.Comment: 29 pages, 4 figure
Quantum dynamics of a high-finesse optical cavity coupled with a thin semi-transparent membrane
We study the quantum dynamics of the cavity optomechanical system formed by a
Fabry-Perot cavity with a thin vibrating membrane at its center. We first
derive the general multimode Hamiltonian describing the radiation pressure
interaction between the cavity modes and the vibrational modes of the membrane.
We then restrict the analysis to the standard case of a single cavity mode
interacting with a single mechanical resonator and we determine to what extent
optical absorption by the membrane hinder reaching a quantum regime for the
cavity-membrane system. We show that membrane absorption does not pose serious
limitations and that one can simultaneously achieve ground state cooling of a
vibrational mode of the membrane and stationary optomechanical entanglement
with state-of-the-art apparatuses.Comment: 14 pages, 7 figure
Digital holographic interferometry for particle detector diagnostic
In high precision scattering experiments particle tracks must often be reconstructed from a series of hits in successive detector planes. The relative distance between these planes is a critical parameter that must be monitored during operation. To address this problem we have developed a digital holographic interferometer dubbed Holographic Alignment Monitor (HAM) to be used in the MUonE project at CERN. MUonE aims at a precision measurement of the scattering angle between particles after an elastic muon-electron scattering. The HAM is designed to monitor the relative distance between position-sensitive sensor planes inside a MUonE tracking station with a resolution better than the required 10 m. The system uses a 532 nm fiber-coupled laser source both to illuminate a portion of the detector plane (object), and to provide the reference beam. A CMOS image sensor acquires the raw data, and the reconstructed holographic image of the silicon sensor being observed is computed using an algorithm containing a Fourier transform. The relative distance between silicon planes is monitored by superposing successive raw images of the same object on an initial reference one and observing the interference fringes appearing on the reconstructed holographic image. Preliminary tests have yielded a distance resolution of less than 1 m
Radiation pressure sensor
Mechanical elements with dimensions in the nanometer range, at least in one direction, have been successfully employed as sensors in various devices. Their mechanical properties must be known with maximum precision in order to quantify the sensor response to external excitation. This often poses a significant challenge due to the mechanical fragility of the sensor elements. Here we present a measurement of the mechanical response of a 100 nm thick silicon nitride membrane. The external excitation force is provided by a laser beam modulated in amplitude, while the displacement of the membrane is measured by a Michelson interferometer with a homodyne readout
KWISP: an ultra-sensitive force sensor for the Dark Energy sector
An ultra-sensitive opto-mechanical force sensor has been built and tested in
the optics laboratory at INFN Trieste. Its application to experiments in the
Dark Energy sector, such as those for Chameleon-type WISPs, is particularly
attractive, as it enables a search for their direct coupling to matter. We
present here the main characteristics and the absolute force calibration of the
KWISP (Kinetic WISP detection) sensor. It is based on a thin Si3N4
micro-membrane placed inside a Fabry-Perot optical cavity. By monitoring the
cavity characteristic frequencies it is possible to detect the tiny membrane
displacements caused by an applied force. Far from the mechanical resonant
frequency of the membrane, the measured force sensitivity is 5.0e-14
N/sqrt(Hz), corresponding to a displacement sensitivity of 2.5e-15 m/sqrt(Hz),
while near resonance the sensitivity is 1.5e-14 N/sqrt(Hz), reaching the
estimated thermal limit, or, in terms of displacement, 7.5e-16 N/sqrt(Hz).
These displacement sensitivities are comparable to those that can be achieved
by large interferometric gravitational wave detectors.Comment: 9 pages, 8 figures in colo
Detecting solar chameleons through radiation pressure
Light scalar fields can drive the accelerated expansion of the universe.
Hence, they are obvious dark energy candidates. To make such models compatible
with tests of General Relativity in the solar system and "fifth force" searches
on Earth, one needs to screen them. One possibility is the so-called
"chameleon" mechanism, which renders an effective mass depending on the local
matter density. If chameleon particles exist, they can be produced in the sun
and detected on Earth exploiting the equivalent of a radiation pressure. Since
their effective mass scales with the local matter density, chameleons can be
reflected by a dense medium if their effective mass becomes greater than their
total energy. Thus, under appropriate conditions, a flux of solar chameleons
may be sensed by detecting the total instantaneous momentum transferred to a
suitable opto-mechanical force/pressure sensor. We calculate the solar
chameleon spectrum and the reach in the chameleon parameter space of an
experiment using the preliminary results from a force/pressure sensor,
currently under development at INFN Trieste, to be mounted in the focal plane
of one of the X-Ray telescopes of the CAST experiment at CERN. We show, that
such an experiment signifies a pioneering effort probing uncharted chameleon
parameter space.Comment: revised versio
Quantum dynamics of a vibrational mode of a membrane within an optical cavity
Optomechanical systems are a promising candidate for the implementation of
quantum interfaces for storing and redistributing quantum information. Here we
focus on the case of a high-finesse optical cavity with a thin vibrating
semitransparent membrane in the middle. We show that robust and stationary
optomechanical entanglement could be achieved in the system, even in the
presence of nonnegligible optical absorption in the membrane. We also present
some preliminary experimental data showing radiation-pressure induced optical
bistability.Comment: 6 pages, 2 figures. Work presented at the conference QCMC 2010 held
on 19-23 July 2010 at the University of Queensland, Brisbane, Australi
Optomechanically induced transparency in membrane-in-the-middle setup at room temperature
We demonstrate the analogue of electromagnetically induced transparency in a
room temperature cavity optomechanics setup formed by a thin semitransparent
membrane within a Fabry-P\'erot cavity. Due to destructive interference, a weak
probe field is completely reflected by the cavity when the pump beam is
resonant with the motional red sideband of the cavity. Under this condition we
infer a significant slowing down of light of hundreds of microseconds, which is
easily tuned by shifting the membrane along the cavity axis. We also observe
the associated phenomenon of electromagnetically induced amplification which
occurs due to constructive interference when the pump is resonant with the blue
sideband.Comment: 5 pages, 4 figure
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