4,124 research outputs found
Proposal for non-local electron-hole turnstile in the Quantum Hall regime
We present a theory for a mesoscopic turnstile that produces spatially
separated streams of electrons and holes along edge states in the quantum Hall
regime. For a broad range of frequencies in the non-adiabatic regime the
turnstile operation is found to be ideal, producing one electron and one hole
per cycle. The accuracy of the turnstile operation is characterized by the
fluctuations of the transferred charge per cycle. The fluctuations are found to
be negligibly small in the ideal regime.Comment: 4+ pages, 2 figure
Quantum heat fluctuations of single particle sources
Optimal single electron sources emit regular streams of particles, displaying
no low frequency charge current noise. Due to the wavepacket nature of the
emitted particles, the energy is however fluctuating, giving rise to heat
current noise. We investigate theoretically this quantum source of heat noise
for an emitter coupled to an electronic probe in the hot-electron regime. The
distribution of temperature and potential fluctuations induced in the probe is
shown to provide direct information on the single particle wavefunction
properties and display strong non-classical features.Comment: 5 pages, 2 figure
Turbulent mixing of a slightly supercritical Van der Waals fluid at Low-Mach number
Supercritical fluids near the critical point are characterized by liquid-like
densities and gas-like transport properties. These features are purposely
exploited in different contexts ranging from natural products
extraction/fractionation to aerospace propulsion. Large part of studies
concerns this last context, focusing on the dynamics of supercritical fluids at
high Mach number where compressibility and thermodynamics strictly interact.
Despite the widespread use also at low Mach number, the turbulent mixing
properties of slightly supercritical fluids have still not investigated in
detail in this regime. This topic is addressed here by dealing with Direct
Numerical Simulations (DNS) of a coaxial jet of a slightly supercritical Van
der Waals fluid. Since acoustic effects are irrelevant in the Low Mach number
conditions found in many industrial applications, the numerical model is based
on a suitable low-Mach number expansion of the governing equation. According to
experimental observations, the weakly supercritical regime is characterized by
the formation of finger-like structures-- the so-called ligaments --in the
shear layers separating the two streams. The mechanism of ligament formation at
vanishing Mach number is extracted from the simulations and a detailed
statistical characterization is provided. Ligaments always form whenever a high
density contrast occurs, independently of real or perfect gas behaviors. The
difference between real and perfect gas conditions is found in the ligament
small-scale structure. More intense density gradients and thinner interfaces
characterize the near critical fluid in comparison with the smoother behavior
of the perfect gas. A phenomenological interpretation is here provided on the
basis of the real gas thermodynamics properties.Comment: Published on Physics of Fluid
Application of the exact regularized point particle method (ERPP) to particle laden turbulent shear flows in the two-way coupling regime
The Exact Regularized Point Particle method (ERPP), which is a new inter-phase momentum coupling ap- proach, is extensively used for the first time to explore the response of homogeneous shear turbulence in presence of different particle populations. Particle suspensions with different Stokes number and/or mass loading are considered. Particles with Kolmogorov Stokes number of order one suppress turbulent kinetic energy when the mass loading is increased. In contrast, heavier particles leave this observable almost un- changed with respect to the reference uncoupled case. Turbulence modulation is found to be anisotropic, leaving the streamwise velocity fluctuations less affected by unitary Stokes number particles whilst it is increased by heavier particles. The analysis of the energy spectra shows that the turbulence modulation occurs throughout the entire range of resolved scales leading to non-trivial augmentation/depletion of the energy content among the different velocity components at different length-scales. In this regard, the ERPP approach is able to provide convergent statistics up to the smallest dissipative scales of the flow, giving the opportunity to trust the ensuing results. Indeed, a substantial modification of the turbu- lent fluctuations at the smallest-scales, i.e. at the level of the velocity gradients, is observed due to the particle backreaction. Small scale anisotropies are enhanced and fluctuations show a greater level of in- termittency as measured by the probability distribution function of the longitudinal velocity increments and by the corresponding flatness
Experimental verification of reciprocity relations in quantum thermoelectric transport
Symmetry relations are manifestations of fundamental principles and
constitute cornerstones of modern physics. An example are the Onsager relations
between coefficients connecting thermodynamic fluxes and forces, central to
transport theory and experiments. Initially formulated for classical systems,
these reciprocity relations are also fulfilled in quantum conductors.
Surprisingly, novel relations have been predicted specifically for
thermoelectric transport. However, whereas these thermoelectric reciprocity
relations have to date not been verified, they have been predicted to be
sensitive to inelastic scattering, always present at finite temperature. The
question whether the relations exist in practice is important for
thermoelectricity: whereas their existence may simplify the theory of complex
thermoelectric materials, their absence has been shown to enable, in principle,
higher thermoelectric energy conversion efficiency for a given material
quality. Here we experimentally verify the thermoelectric reciprocity relations
in a four-terminal mesoscopic device where each terminal can be electrically
and thermally biased, individually. The linear response thermoelectric
coefficients are found to be symmetric under simultaneous reversal of magnetic
field and exchange of injection and emission contacts. Intriguingly, we also
observe the breakdown of the reciprocity relations as a function of increasing
thermal bias. Our measurements thus clearly establish the existence of the
thermoelectric reciprocity relations, as well as the possibility to control
their breakdown with the potential to enhance thermoelectric performanceComment: 7 pages, 5 figure
The Partial Visibility Representation Extension Problem
For a graph , a function is called a \emph{bar visibility
representation} of when for each vertex , is a
horizontal line segment (\emph{bar}) and iff there is an
unobstructed, vertical, -wide line of sight between and
. Graphs admitting such representations are well understood (via
simple characterizations) and recognizable in linear time. For a directed graph
, a bar visibility representation of , additionally, puts the bar
strictly below the bar for each directed edge of
. We study a generalization of the recognition problem where a function
defined on a subset of is given and the question is whether
there is a bar visibility representation of with for every . We show that for undirected graphs this problem
together with closely related problems are \NP-complete, but for certain cases
involving directed graphs it is solvable in polynomial time.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Spectral distribution and wavefunction of electrons emitted from a single particle source in the quantum Hall regime
We investigate theoretically a scheme for spectroscopy of electrons emitted
by an on-demand single particle source. The total system, with an electron
turnstile source and a single level quantum dot spectrometer, is implemented
with edge states in a conductor in the quantum Hall regime. Employing a Floquet
scattering approach, the source and the spectrometer are analyzed within a
single theoretical framework. The non-equilibrium distribution of the emitted
electrons is analyzed via the direct current at the dot spectrometer. In the
adiabatic and intermediate source frequency regimes, the distribution is found
to be strongly peaked around the active resonant level of the turnstile. At
high frequencies the distribution is split up into a set of fringes, resulting
from the interplay of resonant transport through the turnstile and absorption
or emission of individual Floquet quanta. For ideal source operation, with
exactly one electron emitted per cycle, an expression for the single electron
wavefunction is derived.Comment: 12 pages, 7 figure
Omental well-differentiated liposarcoma: US, CT and MR findings
Liposarcomas are the most common of sarcoma tumours, they are usually located in the lower limbs, retroperitoneum,
or abdominal cavity; up to date, only a few cases of omental liposarcoma with different histotype have been described. We present a case of omental well-differentiated liposarcoma and discuss imaging findings on ultrasound, computed tomography, and magnetic resonance to differentiate omental liposarcomas from other abdominal tumour entities
Energy and Nutrients' Recovery in Anaerobic Digestion of Agricultural Biomass: An Italian Perspective for Future Applications
Anaerobic digestion (AD) is the most adopted biotechnology for the valorization of agricultural biomass into valuable products like biogas and digestate, a renewable fertilizer. This paper illustrates in the first part the actual situation of the anaerobic digestion sector in Italy, including the number of plants, their geographical distribution, the installed power and the typical feedstock used. In the second part, a future perspective, independent of the actual incentive scheme, is presented. It emerged that Italy is the second European country for the number of anaerobic digestion plants with more than 1500 units for a total electricity production of about 1400 MWel. More than 60% of them are in the range of 200 kW-1 MW installed power. Almost 70% of the plants are located in the northern part of the Country where intensive agriculture and husbandry are applied. Most of the plants are now using energy crops in the feedstock. The future perspectives of the biogas sector in Italy will necessarily consider a shift from power generation to biomethane production, and an enlargement of the portfolio of possible feedstocks, the recovery of nutrients from digestate in a concentrated form, and the expansion of the AD sector to southern regions. Power to gas and biobased products will complete the future scenario
Oral malodor in Special Care Patients: current knowledge
Epidemiological studies report that about 50% of the population may have oral malodor
with a strong social and psychological impact in their daily life. When intra-oral causes are
excluded, referral to an appropriate medical specialist is paramount for management and
treatment of extra-oral causes. The intra-oral causes of halitosis are highly common, and the
dentist is the central clinician to diagnose and treat them. Pseudohalitosis or halitophobia
may occur and an early identification of these conditions by the dentist is important in order
to avoid unnecessary dental treatments for patients who need psychological or psychiatric
therapy. The organoleptic technique is still considered the most reliable examination method
to diagnose genuine halitosis. Special needs patients are more prone than others to have
oral malodor because of concurrent systemic or metabolic diseases, and medications.
The present report reviews halitosis, its implications, and the management in special care
dentistry
- …