38,554 research outputs found
Electron temperature in electrically isolated Si double quantum dots
Charge-based quantum computation can be attained through reliable control of
single electrons in lead-less quantum systems. Single-charge transitions in
electrically-isolated double quantum dots (DQD) realised in phosphorus-doped
silicon can be detected via capacitively coupled single-electron tunnelling
devices. By means of time-resolved measurements of the detector's conductance,
we investigate the dots' occupancy statistics in temperature. We observe a
significant reduction of the effective electron temperature in the DQD as
compared to the temperature in the detector's leads. This sets promises to make
isolated DQDs suitable platforms for long-coherence quantum computation.Comment: 4 pages, 3 figure
On measuring the Galactic dark matter halo with hypervelocity stars
Hypervelocity stars (HVSs) travel from the Galactic Centre across the dark
matter halo of the Milky Way, where they are observed with velocities in excess
of the Galactic escape speed. Because of their quasi-radial trajectories, they
represent a unique probe of the still poorly constrained dark matter component
of the Galactic potential. In this paper, we present a new method to produce
such constraints. Our likelihood is based on the local HVS density obtained by
back-propagating the observed phase space position and quantifies the ejection
probability along the orbit. To showcase our method, we apply it to simulated
Gaia samples of stars in three realistic Galactic potentials with
dark matter components parametrized by spheroidal NFW profiles. We find that
individual HVSs exhibit a degeneracy in the scale mass-scale radius plane
() and are able to measure only the combination .
Likewise, a degeneracy is also present between and the spheroidal
axis-ratio . In the absence of observational errors, we show the whole
sample can nail down both parameters with {\it sub-per cent} precision (about
and for and respectively) with no systematic bias.
This remarkable power to constrain deviations from a symmetric halo is a
consequence of the Galactocentric origin of HVSs. To compare our results with
other probes, we break the degeneracy in the scale parameters and impose a
mass-concentration relation. The result is a competitive precision on the
virial mass of about .Comment: See Fig. 8 for a summar
Building valoristaion strategies for biodiverse products - the approach
The market valorisation of ‘diverse food products’ is crucial to increase diversity in farming systems. It involves multiple actors, from the field to the table, and requires an integrated approach to take into account several dimensions involved
Building Valorisation Strategies for Biodiverse Products - Case Studies
The market valorisation of ‘diverse food products’ is crucial to promote agrobiodiversity. Despite the differences due to the specific contexts, valorisation strategies show relevant common features
Coherent phenomena in semiconductors
A review of coherent phenomena in photoexcited semiconductors is presented.
In particular, two classes of phenomena are considered: On the one hand the
role played by optically-induced phase coherence in the ultrafast spectroscopy
of semiconductors; On the other hand the Coulomb-induced effects on the
coherent optical response of low-dimensional structures.
All the phenomena discussed in the paper are analyzed in terms of a
theoretical framework based on the density-matrix formalism. Due to its
generality, this quantum-kinetic approach allows a realistic description of
coherent as well as incoherent, i.e. phase-breaking, processes, thus providing
quantitative information on the coupled ---coherent vs. incoherent--- carrier
dynamics in photoexcited semiconductors.
The primary goal of the paper is to discuss the concept of quantum-mechanical
phase coherence as well as its relevance and implications on semiconductor
physics and technology. In particular, we will discuss the dominant role played
by optically induced phase coherence on the process of carrier photogeneration
and relaxation in bulk systems. We will then review typical field-induced
coherent phenomena in semiconductor superlattices such as Bloch oscillations
and Wannier-Stark localization. Finally, we will discuss the dominant role
played by Coulomb correlation on the linear and non-linear optical spectra of
realistic quantum-wire structures.Comment: Topical review in Semiconductor Science and Technology (in press)
(Some of the figures are not available in electronic form
Abelian monopole condensation in lattice gauge theories
We investigate the dynamics of lattice gauge theories in an Abelian monopole
background field. By means of the gauge-invariant lattice Schrodinger
functional we study the Abelian monopole condensation in U(1) lattice gauge
theory at zero temperature and in SU(3) lattice gauge theory at finite
temperature.Comment: LATTICE99(Confinement) 3 pages, 3 figure
Gamma-Ray Astronomy around 100 TeV with a large Muon Detector operated at Very High Altitude
Measurements at 100 TeV and above are an important goal for the next
generation of high energy gamma-ray astronomy experiments to solve the still
open problem of the origin of galactic cosmic rays. The most natural
experimental solution to detect very low radiation fluxes is provided by the
Extensive Air Shower (EAS) arrays. They benefit from a close to 90% duty cycle
and a very large field of view (about 2 sr), but the sensitivity is limited by
their angular resolution and their poor cosmic ray background discrimination.
Above 10 TeV the standard technique for rejecting the hadronic background
consists in looking for "muon-poor" showers.
In this paper we discuss the capability of a large muon detector (A=2500 m2)
operated with an EAS array at very high altitude (>4000 m a.s.l.) to detect
gamma-ray fluxes around 100 TeV. Simulation-based estimates of energy ranges
and sensitivities are presented.Comment: 4 pages, proceedings of the 30th ICRC, Merida, Mexico, 200
Transient Rayleigh-Benard-Marangoni Convection due to Evaporation : a Linear Non-normal Stability Analysis
The convective instability in a plane liquid layer with time-dependent
temperature profile is investigated by means of a general method suitable for
linear stability analysis of an unsteady basic flow. The method is based on a
non-normal approach, and predicts the onset of instability, critical wave
number and time. The method is applied to transient Rayleigh-Benard-Marangoni
convection due to cooling by evaporation. Numerical results as well as
theoretical scalings for the critical parameters as function of the Biot number
are presented for the limiting cases of purely buoyancy-driven and purely
surface-tension-driven convection. Critical parameters from calculations are in
good agreement with those from experiments on drying polymer solutions, where
the surface cooling is induced by solvent evaporation.Comment: 31 pages, 8 figure
Charge Detection in Phosphorus-doped Silicon Double Quantum Dots
We report charge detection in degenerately phosphorus-doped silicon double
quantum dots (DQD) electrically connected to an electron reservoir. The sensing
device is a single electron transistor (SET) patterned in close proximity to
the DQD. Measurements performed at 4.2K show step-like behaviour and shifts of
the Coulomb Blockade oscillations in the detector's current as the reservoir's
potential is swept. By means of a classical capacitance model, we demonstrate
that the observed features can be used to detect single-electron tunnelling
from, to and within the DQD, as well as to reveal the DQD charge occupancy.Comment: 4 pages, 3 figure
4He adsorbed inside (10,10) single walled carbon nanotubes
Diffusion Monte Carlo calculations on the adsorption of He in open-ended
single walled (10,10) nanotubes are presented. We have found a first order
phase transition separating a low density liquid phase in which all He
atoms are adsorbed close to the tube wall and a high density arrangement
characterized by two helium concentric layers. The energy correction due to the
presence of neighboring tubes in a bundle has also been calculated, finding it
negligible in the density range considered.Comment: 5 pages, accepted for publication in Phys. Rev.
- …