8,952 research outputs found
Model-Independent Sum Rule Analysis Based on Limited-Range Spectral Data
Partial sum rules are widely used in physics to separate low- and high-energy
degrees of freedom of complex dynamical systems. Their application, though, is
challenged in practice by the always finite spectrometer bandwidth and is often
performed using risky model-dependent extrapolations. We show that, given
spectra of the real and imaginary parts of any causal frequency-dependent
response function (for example, optical conductivity, magnetic susceptibility,
acoustical impedance etc.) in a limited range, the sum-rule integral from zero
to a certain cutoff frequency inside this range can be safely derived using
only the Kramers-Kronig dispersion relations without any extra model
assumptions. This implies that experimental techniques providing both active
and reactive response components independently, such as spectroscopic
ellipsometry in optics, allow an extrapolation-independent determination of
spectral weight 'hidden' below the lowest accessible frequency.Comment: 5 pages, 3 figure
meV resolution in laser-assisted energy-filtered transmission electron microscopy
The electronic, optical, and magnetic properties of quantum solids are
determined by their low-energy (< 100 meV) many-body excitations. Dynamical
characterization and manipulation of such excitations relies on tools that
combine nm-spatial, fs-temporal, and meV-spectral resolution. Currently,
phonons and collective plasmon resonances can be imaged in nanostructures with
sub-nm and 10s meV space/energy resolution using state-of-the-art
energy-filtered transmission electron microscopy (TEM), but only under static
conditions, while fs-resolved measurements are common but lack spatial or
energy resolution. Here, we demonstrate a new method of spectrally resolved
photon-induced near-field electron microscopy (SRPINEM) that allows us to
obtain nm-fs-resolved maps of nanoparticle plasmons with an energy resolution
determined by the laser linewidth (20 meV in this work), and not limited by
electron beam and spectrometer energy spreading. This technique can be extended
to any optically-accessible low-energy mode, thus pushing TEM to a previously
inaccessible spectral domain with an unprecedented combination of space, energy
and temporal resolution.Comment: 19 pages, 7 figure
Early amniotomy after cervical ripening for induction of labor: a systematic review and meta-analysis of randomized controlled trials
OBJECTIVE DATA:
Timing of artificial rupture of membranes (ie, amniotomy) in induction of labor is controversial, because it has been associated not only with shorter labors, but also with fetal nonreassuring testing, at times necessitating cesarean delivery. The aim of this systematic review and metaanalysis of randomized trials was to evaluate the effectiveness of early amniotomy vs late amniotomy or spontaneous rupture of membranes after cervical ripening.
STUDY:
The search was conducted with the use of electronic databases from inception of each database through February 2019. Review of articles included the abstracts of all references that were retrieved from the search.
STUDY APPRAISAL AND SYNTHESIS METHODS:
Selection criteria included randomized clinical trials that compared early amniotomy vs control (ie, late amniotomy or spontaneous rupture of membranes) after cervical ripening with either Foley catheter or prostaglandins at any dose. The primary outcome was the incidence of cesarean delivery. The summary measures were reported as summary relative risk with 95% of confidence interval with the use of the random effects model of DerSimonian and Laird.
RESULTS:
Four trials that included 1273 women who underwent cervical ripening with either Foley catheter or prostaglandins and then were assigned randomly to either early amniotomy, late amniotomy, or spontaneous rupture of membranes (control subjects) were included in the review. Women who were assigned randomly to early amniotomy had a similar risk of cesarean delivery (31.1% vs 30.9%; relative risk, 1.05; 95% confidence interval, 0.71-1.56) compared with control subjects and had a shorter interval from induction to delivery of approximately 5 hours (mean difference, -4.95 hours; 95% confidence interval, -8.12 to -1.78). Spontaneous vaginal delivery was also reduced in the early amniotomy group, but only 1 of the included trials reported this outcome (67.5% vs 69.1%; relative risk, 0.78; 95% confidence interval, 0.66-0.93). No between-group differences were reported in the other obstetrics or perinatal outcomes.
CONCLUSION:
After cervical ripening, routine early amniotomy does not increase the risk of cesarean delivery and reduces the interval from induction to delivery
Experimental tests on operation performance of a LARM leg mechanism with 3-DOF parallel architecture
Abstract. In this paper, a prototype of a LARM leg mechanism is proposed by using a tripod manipulator and its operation performance is investigated through lab experimental tests. In particular, an experimental layout is presented for investigating operational performance. A prescribed motion with an isosceles trapezoid trajectory is used for characterizing the system behavior. Experiment results are analyzed for the purpose of operation evaluation and architecture design characterization of the tripod manipulator and its proposed prototype
A robotic mobile platform for service tasks in cultural heritage
Recently, the preservation and survey of cultural heritage goods is attracting increasing interest from the media. Several famous historical sites seem to require an increased effort to maintain their preservation. Nevertheless, it is very difficult to find sufficient funds and human resources to fulfil these needs. Accordingly, this paper outlines a specific application of service robotics to cultural heritage, with the aim to reduce the required time and costs for surveying and maintaining cultural heritage goods. These applications require careful attention paid to the proper design of a robotic mobile platform with the features necessary to fulfil tasks of architectonic survey and preservation. To this end, specific operation scenarios have been carefully described in order to identify the specific design requirements and constraints that are raised by, for example, the necessity of operation over delicate surfaces, or the presence of unevenness or obstacles. The authors then propose a design solution for a service robot fit for the analysis, survey and conservation of historical sites, as based on the characteristics of the outlined scenarios. A preliminary prototype is also described herewith, in order to show its engineering feasibility in relation to the simulated operation scenarios
From attosecond to zeptosecond coherent control of free-electron wave functions using semi-infinite light fields
Light-electron interaction in empty space is the seminal ingredient for
free-electron lasers and also for controlling electron beams to dynamically
investigate materials and molecules. Pushing the coherent control of free
electrons by light to unexplored timescales, below the attosecond, would enable
unprecedented applications in light-assisted electron quantum circuits and
diagnostics at extremely small timescales, such as those governing
intramolecular electronic motion and nuclear phenomena. We experimentally
demonstrate attosecond coherent manipulation of the electron wave function in a
transmission electron microscope, and show that it can be pushed down to the
zeptosecond regime with existing technology. We make a relativistic pulsed
electron beam interact in free space with an appropriately synthesized
semi-infinite light field generated by two femtosecond laser pulses reflected
at the surface of a mirror and delayed by fractions of the optical cycle. The
amplitude and phase of the resulting coherent oscillations of the electron
states in energymomentum space are mapped via momentum-resolved ultrafast
electron energy-loss spectroscopy. The experimental results are in full
agreement with our theoretical framework for light-electron interaction, which
predicts access to the zeptosecond timescale by combining semi-infinite X-ray
fields with free electrons.Comment: 22 pages, 6 figure
A data sequence aquired at Mt. Etna during the 2002 - 2003 eruption highlights the potential of continuous gravity observations as a tool to monitor and study active volcanoes
A 2.5-month long gravity sequence, encompassing the starting period of the 2002–2003 Etna eruption and coming from a summit
station only 1 km away from the new fractures, is presented and discussed. The sequence comprises some hours-long anomalies that
have a great chance to reflect mass redistributions linked to the ensuing activity. In particular, the start of the eruptive activity on
the northeastern flank was marked by a gravity decrease as strong as about 400 Gal, which reverted soon afterwards. This strong
decrease/increase anomaly is interpreted as the opening, by tectonic forces, of a fracture system along the Northeastern Rift of Mt. Etna, followed by an intrusion of magma from the central conduit to the new fractures. They were used by the intruding magma as
a path to the eruptive vents at lower elevations.
Afterwards, on three occasions, in November and December 2002, 6–12 h-lasting gravity decreases, with amplitude ranging
between 10 and 30 Gal, were observed simultaneously with increases in the amplitude of the volcanic tremor from four seismic
stations. A correlation analysis, between the gravity signal and the overall spectral amplitude of each tremor sequence is performed
over the 7 November–9 December period. A marked anti-correlation is found over each contemporaneous gravity decrease/tremor
increase, while, over the rest of the investigated period, the correlation is negligible. Accordingly, a joint source is inferred to have
acted during the occurrence of the three common anomalies. On the grounds of some volcanological observations spanning the
period covered by our analysis, we propose the temporary accumulation of a gas cloud at some level within the plumbing system
of the volcano to have acted as a joint source.
The present work is a further evidence of the potential of continuous gravity observations as a tool to monitor and study active
volcanoes and encourages their employment in spite of the difficulty of running spring gravimeters in a continuous fashion under
the adverse conditions normally encountered on the summit zone of an active volcano
The MEV project: design and testing of a new high-resolution telescope for Muography of Etna Volcano
The MEV project aims at developing a muon telescope expressly designed for
the muography of Etna Volcano. In particular, one of the active craters in the
summit area of the volcano would be a suitable target for this experiment. A
muon tracking telescope with high imaging resolution was built and tested
during 2017. The telescope is a tracker based on extruded scintillating bars
with WLS fibres and featuring an innovative read-out architecture. It is
composed of three XY planes with a sensitive area of \SI{1}{m^2}; the angular
resolution does not exceeds \SI{0.4}{\milli\steradian} and the total angular
aperture is about \SI{45}{\degree}. A special effort concerned the design
of mechanics and electronics in order to meet the requirements of a detector
capable to work in a hostile environment such as the top of a tall volcano, at
a far distance from any facility. The test phase started in January 2017 and
ended successfully at the end of July 2017. An extinct volcanic crater (the
Monti Rossi, in the village of Nicolosi, about 15km from Catania) is the target
of the measurement. The detector acquired data for about 120 days and the
preliminary results are reported in this work
- …