751 research outputs found
Controlled Heterogeneous Collection: The Role of Occupation Numbers
A controlled heterogeneous collection of identical items is presented. According to their level of wear and tear, they are divided into a finite number of classes and the partition of the collection is allowed to change over time. A suitable exchangeability assumption is made to preserve the property that the items be identical. The role of the occupation numbers is investigated and a filtering problem is set up, where the observation is the cardinality of a particular class. A control on the dynamics of the items is introduced, and the existence of an optimal control is proved. A discrete-time approximation for the separated problem, which is a finite-dimensional one, is performed. As a consequence, an approximation for the value function is given
The end-to-end testbed of the Optical Metrology System on-board LISA Pathfinder
LISA Pathfinder is a technology demonstration mission for the Laser
Interferometer Space Antenna (LISA). The main experiment on-board LISA
Pathfinder is the so-called LISA Technology Package (LTP) which has the aim to
measure the differential acceleration between two free-falling test masses with
an accuracy of 3x10^(-14) ms^(-2)/sqrt[Hz] between 1 mHz and 30 mHz. This
measurement is performed interferometrically by the Optical Metrology System
(OMS) on-board LISA Pathfinder. In this paper we present the development of an
experimental end-to-end testbed of the entire OMS. It includes the
interferometer and its sub-units, the interferometer back-end which is a
phasemeter and the processing of the phasemeter output data. Furthermore,
3-axes piezo actuated mirrors are used instead of the free-falling test masses
for the characterisation of the dynamic behaviour of the system and some parts
of the Drag-free and Attitude Control System (DFACS) which controls the test
masses and the satellite. The end-to-end testbed includes all parts of the LTP
that can reasonably be tested on earth without free-falling test masses. At its
present status it consists mainly of breadboard components. Some of those have
already been replaced by Engineering Models of the LTP experiment. In the next
steps, further Engineering Models and Flight Models will also be inserted in
this testbed and tested against well characterised breadboard components. The
presented testbed is an important reference for the unit tests and can also be
used for validation of the on-board experiment during the mission
A new dataset and empirical relationships between magnitude/intensity and epicentral distance for liquefaction in central-eastern Sicily
Strong earthquakes can trigger several phenomena inducing soil deformation, such as liquefaction, ground fracturing
and landslides, which can often cause more damage than the seismic shaking itself. A research performed
on numerous historical accounts reporting descriptions of seismogeological effects in central-eastern Sicily, allowed
the authors to update the previous liquefaction datasets. 75 liquefaction-induced phenomena observed in
26 sites, triggered by 14 earthquakes, have been used to define relationships between intensity/magnitude values
and epicentral distance from the liquefied sites. The proposed upper bound-curves, at regional scale for central-
eastern Sicily, are realized by using the updating liquefaction dataset and also the new CPTI04 Italian earthquake
parametric catalogue. These relationships can be useful in hazard assessment to evaluate the minimum energy
of an earthquake inducing liquefactions
The Crab pulsar light curve in the soft gamma ray range: FIGARO II results
The FIGARO II experiment (a large area, balloon borne, crystal scintillator detector working from 0.15 to 4.3 MeV) observed the Crab pulsar on 1990 Jul. 9 for about seven hours. The study of the pulse profile confirms some structures detected with a low significance during the shorter observation of 1986, and adds new important elements to the picture. In particular, between the two main peaks, two secondary peaks appear centered at phase values 0.1 and 0.3, in the energy range 0.38 to 0.49 MeV; in the same energy range, a spectral feature at 0.44 MeV, interpreted as a redshifted positron annihilation line, was observed during the same balloon flight in the phase interval including the second main peak and the neighboring secondary peak. If the phase interval considered is extended to include also the other secondary peak, the significance of the spectral line appears to increase
Discrimination of tsunami sources (Earthquake vs. Landslide) on the basis of historical data in Eastern Sicily and southern Calabria
The source mechanisms responsible for large historical tsunamis that
have struck eastern Sicily and southern Calabria are a topic of robust debate. We have
compiled a database of historical coeval descriptions of three large tsunamis: 11 January
1693, 6 February 1783, and 28 December 1908. By using accounts of run-up and
inundation and employing an approach proposed by Okal and Synolakis in 2004, we
can provide discriminants to define the nature of the near-field tsunami sources (fault
dislocation or landslide).
Historical reports for the 1908 event describe affected localities, maximum runups,
and inundation areas. However, for the 1693 and 1783 tsunamis, reports are
limited to inundation and occasional run-up estimates. We calculate run-up values
for these events using available relations between inundation and run-up. We
employed the model of Okal and Synolakis to the obtained profiles of tsunami
run-up along the inundated shorelines. The 1908 run-up data distribution confirms
that the tsunami is compatible with a seismic dislocation source, whereas the
1783 data supports contemporary observations and recent offshore investigations suggesting
that the tsunami was produced by an earthquake-triggered submarine landslide.
Analysis of the 1693 event data suggests that the tsunami was generated
during a tectonic event and thus a seismogenic source should be found offshore
Quality of Life in Glaucoma: A Review of the Literature
The ultimate goal of glaucoma management is the preservation of patients’ visual function and quality of life (QoL). The disease itself as well as the medical or surgical treatment can have an enormous impact on a patient’s QoL. Even the mere diagnosis of a chronic, irreversible, potentially blinding disorder can adversely affect the patient’s sense of well-being and QoL by eliciting significant anxiety. Patients with primary open-angle glaucoma rarely present with visual symptoms, at least early in the course of the disease. A better understanding of patient-reported QoL can improve patient–physician interaction and enhance treatment adherence by customizing treatment options based on individual patient profile, thus optimizing long-term prognosis. These aspects are summarized and critically appraised in this article
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