1,143 research outputs found
Electrostatic force microscopy and potentiometry of realistic nanostructured systems
We investigate the dependency of electrostatic interaction forces on applied
potentials in Electrostatic Force Microscopy (EFM) as well as in related local
potentiometry techniques like Kelvin Probe Microscopy (KPM). The approximated
expression of electrostatic interaction between two conductors, usually
employed in EFM and KPM, may loose its validity when probe-sample distance is
not very small, as often realized when realistic nanostructured systems with
complex topography are investigated. In such conditions, electrostatic
interaction does not depend solely on the potential difference between probe
and sample, but instead it may depend on the bias applied to each conductor.
For instance, electrostatic force can change from repulsive to attractive for
certain ranges of applied potentials and probe-sample distances, and this fact
cannot be accounted for by approximated models. We propose a general
capacitance model, even applicable to more than two conductors, considering
values of potentials applied to each of the conductors to determine the
resulting forces and force gradients, being able to account for the above
phenomenon as well as to describe interactions at larger distances. Results
from numerical simulations and experiments on metal stripe electrodes and
semiconductor nanowires supporting such scenario in typical regimes of EFM
investigations are presented, evidencing the importance of a more rigorous
modelling for EFM data interpretation. Furthermore, physical meaning of Kelvin
potential as used in KPM applications can also be clarified by means of the
reported formalism.Comment: 20 pages, 7 figures, 1 tabl
The Comparative Exploration of the Ice Giant Planets with Twin Spacecraft: Unveiling the History of our Solar System
In the course of the selection of the scientific themes for the second and
third L-class missions of the Cosmic Vision 2015-2025 program of the European
Space Agency, the exploration of the ice giant planets Uranus and Neptune was
defined "a timely milestone, fully appropriate for an L class mission". Among
the proposed scientific themes, we presented the scientific case of exploring
both planets and their satellites in the framework of a single L-class mission
and proposed a mission scenario that could allow to achieve this result. In
this work we present an updated and more complete discussion of the scientific
rationale and of the mission concept for a comparative exploration of the ice
giant planets Uranus and Neptune and of their satellite systems with twin
spacecraft. The first goal of comparatively studying these two similar yet
extremely different systems is to shed new light on the ancient past of the
Solar System and on the processes that shaped its formation and evolution.
This, in turn, would reveal whether the Solar System and the very diverse
extrasolar systems discovered so far all share a common origin or if different
environments and mechanisms were responsible for their formation. A space
mission to the ice giants would also open up the possibility to use Uranus and
Neptune as templates in the study of one of the most abundant type of
extrasolar planets in the galaxy. Finally, such a mission would allow a
detailed study of the interplanetary and gravitational environments at a range
of distances from the Sun poorly covered by direct exploration, improving the
constraints on the fundamental theories of gravitation and on the behaviour of
the solar wind and the interplanetary magnetic field.Comment: 29 pages, 4 figures; accepted for publication on the special issue
"The outer Solar System X" of the journal Planetary and Space Science. This
article presents an updated and expanded discussion of the white paper "The
ODINUS Mission Concept" (arXiv:1402.2472) submitted in response to the ESA
call for ideas for the scientific themes of the future L2 and L3 space
mission
Measurement of the Lifetime Difference Between B_s Mass Eigenstates
We present measurements of the lifetimes and polarization amplitudes for B_s
--> J/psi phi and B_d --> J/psi K*0 decays. Lifetimes of the heavy (H) and
light (L) mass eigenstates in the B_s system are separately measured for the
first time by determining the relative contributions of amplitudes with
definite CP as a function of the decay time. Using 203 +/- 15 B_s decays, we
obtain tau_L = (1.05 +{0.16}/-{0.13} +/- 0.02) ps and tau_H = (2.07
+{0.58}/-{0.46} +/- 0.03) ps. Expressed in terms of the difference DeltaGamma_s
and average Gamma_s, of the decay rates of the two eigenstates, the results are
DeltaGamma_s/Gamma_s = (65 +{25}/-{33} +/- 1)%, and DeltaGamma_s = (0.47
+{0.19}/-{0.24} +/- 0.01) inverse ps.Comment: 8 pages, 3 figures, 2 tables; as published in Physical Review Letters
on 16 March 2005; revisions are for length and typesetting only, no changes
in results or conclusion
Level-2 calorimeter Trigger Upgrade at CDF
The CDF Run II level 2 calorimeter trigger is implemented in hardware and is based on a simple algorithm that was used in Run I. This system has worked well for Run II at low luminosity. As the Tevatron instantaneous luminosity increases, the limitation due to this simple algorithm starts to become clear. As a result, some of the most important jet and MET (missing ET) related triggers have large growth terms in cross section at higher luminosity. In this paper, we present an upgrade of the L2CAL system which makes the full calorimeter trigger tower information directly available to the level 2 decision CPU. This upgrade is based on the Pulsar, a general purpose VME board developed at CDF and already used for upgrading both the level 2 global decision crate and the level 2 silicon vertex tracking. The upgrade system allows more sophisticated algorithms to be implemented in software and both level 2 jets and MET can be made nearly equivalent to offline quality, thus significantly improving the performance and flexibility of the jet and MET related triggers. This is a natural expansion of the already-upgraded level 2 trigger system, and is a big step forward to improve the CDF triggering capability at level 2. This paper describes the design, the hardware and software implementation and the performance of the upgrade system
COVID-19 Vaccination in Pregnancy, Paediatrics, Immunocompromised Patients, and Persons with History of Allergy or Prior SARS-CoV-2 Infection: Overview of Current Recommendations and Pre- and Post-Marketing Evidence for Vaccine Efficacy and Safety
Towards a Muon Collider
A muon collider would enable the big jump ahead in energy reach that is
needed for a fruitful exploration of fundamental interactions. The challenges
of producing muon collisions at high luminosity and 10 TeV centre of mass
energy are being investigated by the recently-formed International Muon
Collider Collaboration. This Review summarises the status and the recent
advances on muon colliders design, physics and detector studies. The aim is to
provide a global perspective of the field and to outline directions for future
work.Comment: 118 pages, 103 figure
Towards a muon collider
A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work
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