7,046 research outputs found
Dynamical depinning of chiral domain walls
The domain wall depinning field represents the minimum magnetic field needed
to move a domain wall, typically pinned by samples' disorder or patterned
constrictions. Conventionally, such field is considered independent on the
Gilbert damping since it is assumed to be the field at which the Zeeman energy
equals the pinning energy barrier (both damping independent). Here, we analyse
numerically the domain wall depinning field as function of the Gilbert damping
in a system with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya
interaction. Contrary to expectations, we find that the depinning field depends
on the Gilbert damping and that it strongly decreases for small damping
parameters. We explain this dependence with a simple one-dimensional model and
we show that the reduction of the depinning field is related to the internal
domain wall dynamics, proportional to the Dzyaloshinskii-Moriya interaction,
and the finite size of the pinning barriers
Efficiency of attack strategies on complex model and real-world networks
We investigated the efficiency of attack strategies to network nodes when
targeting several complex model and real-world networks. We tested 5 attack
strategies, 3 of which were introduced in this work for the first time, to
attack 3 model (Erdos and Renyi, Barabasi and Albert preferential attachment
network, and scale-free network configuration models) and 3 real networks
(Gnutella peer-to-peer network, email network of the University of Rovira i
Virgili, and immunoglobulin interaction network). Nodes were removed
sequentially according to the importance criterion defined by the attack
strategy. We used the size of the largest connected component (LCC) as a
measure of network damage. We found that the efficiency of attack strategies
(fraction of nodes to be deleted for a given reduction of LCC size) depends on
the topology of the network, although attacks based on the number of
connections of a node and betweenness centrality were often the most efficient
strategies. Sequential deletion of nodes in decreasing order of betweenness
centrality was the most efficient attack strategy when targeting real-world
networks. In particular for networks with power-law degree distribution, we
observed that most efficient strategy change during the sequential removal of
nodes.Comment: 18 pages, 4 figure
A Hybrid Drift Diffusion Model: Derivation, Weak Steady State Solutions and Simulations
In this paper we derive a new hybrid model for drift di usion equations. This model provides a description of the quantum phenomena in the parts of the device where they are relevant, and degenerates to a semiclassical model where quantum e ects are negligible, so that the system can be considered classically. The study of quantum correction to the equation of state of an electron gas in a semiconductor with the assumption of localized quantum e ects leads to a further condition on the classical-quantum interface. Moreover, we prove the existence of weak solutions for our hybrid model. Finally, we present numerical results for di erent devices, by means of Colsys software
Electro-osmotic flow in coated nanocapillaries: a theoretical investigation
Motivated by recent experiments, we present a theoretical investigation of
how the electro-osmotic flow occurring in a capillary is modified when its
charged surfaces are coated by charged polymers. The theoretical treatment is
based on a three dimensional model consisting of a ternary fluid-mixture,
representing the solvent and two species for the ions, confined between two
parallel charged plates decorated by a fixed array of scatterers representing
the polymer coating. The electro-osmotic flow, generated by a constant electric
field applied in a direction parallel to the plates, is studied numerically by
means of Lattice Boltzmann simulations. In order to gain further understanding
we performed a simple theoretical analysis by extending the Stokes-Smoluchowski
equation to take into account the porosity induced by the polymers in the
region adjacent the walls. We discuss the nature of the velocity profiles by
focusing on the competing effects of the polymer charges and the frictional
forces they exert. We show evidence of the flow reduction and of the flow
inversion phenomenon when the polymer charge is opposite to the surface charge.
By using the density of polymers and the surface charge as control variables,
we propose a phase diagram that discriminates the direct and the reversed flow
regimes and determine its dependence on the ionic concentration.Comment: 15 pages, 6 figures in Physical Chemistry Chemical Physics, 201
Urban imperviousness effects on summer surface temperatures nearby residential buildings in different urban zones of Parma
Rapid and unplanned urban growth is responsible for the continuous conversion of green or generally natural spaces into artificial surfaces. The high degree of imperviousness modifies the urban microclimate and no studies have quantified its influence on the surface temperature (ST) nearby residential building. This topic represents the aim of this study carried out during summer in different urban zones (densely urbanized or park/rural areas) of Parma (Northern Italy). Daytime and nighttime ASTER images, the local urban cartography and the Italian imperviousness databases were used. A reproducible/replicable framework was implemented named "Building Thermal Functional Area" (BTFA) useful to lead building-proxy thermal analyses by using remote sensing data. For each residential building (n = 8898), the BTFA was assessed and the correspondent ASTER-LST value (ST_BTFA) and the imperviousness density were calculated. Both daytime and nighttime ST_BTFA significantly (p < 0.001) increased when high levels of imperviousness density surrounded the residential buildings. These relationships were mostly consistent during daytime and in densely urbanized areas. ST_BTFA differences between urban and park/rural areas were higher during nighttime (above 1 °C) than daytime (about 0.5 °C). These results could help to identify "urban thermal Hot-Spots" that would benefit most from mitigation actions
Hyperspectral monitoring of green roof vegetation health state in sub-mediterranean climate: preliminary results
In urban and industrial environments, the constant increase of impermeable surfaces has
produced drastic changes in the natural hydrological cycle. Decreasing green areas not only produce
negative effects from a hydrological-hydraulic perspective, but also from an energy point of view,
modifying the urban microclimate and generating, as shown in the literature, heat islands in our cities.
In this context, green infrastructures may represent an environmental compensation action that can be
used to re-equilibrate the hydrological and energy balance and reduce the impact of pollutant load on
receiving water bodies. To ensure that a green infrastructure will work properly, vegetated areas have
to be continuously monitored to verify their health state. This paper presents a ground spectroscopy
monitoring survey of a green roof installed at the University of Calabria fulfilled via the acquisition
and analysis of hyperspectral data. This study is part of a larger research project financed by European
Structural funds aimed at understanding the influence of green roofs on rainwater management and
energy consumption for air conditioning in the Mediterranean area. Reflectance values were acquired
with a field-portable spectroradiometer that operates in the range of wavelengths 350–2500 nm.
The survey was carried out during the time period November 2014–June 2015 and data were acquired
weekly. Climatic, thermo-physical, hydrological and hydraulic quantities were acquired as well and
related to spectral data. Broadband and narrowband spectral indices, related to chlorophyll content
and to chlorophyll–carotenoid ratio, were computed. The two narrowband indices NDVI705 and SIPI
turned out to be the most representative indices to detect the plant health status
Triggering Soft Bombs at the LHC
Very high multiplicity, spherically-symmetric distributions of soft
particles, with ~ few hundred MeV, may be a signature of strongly-coupled
hidden valleys that exhibit long, efficient showering windows. With traditional
triggers, such "soft bomb" events closely resemble pile-up and are therefore
only recorded with minimum bias triggers at a very low efficiency. We
demonstrate a proof-of-concept for a high-level triggering strategy that
efficiently separates soft bombs from pile-up by searching for a "belt of
fire": A high density band of hits on the innermost layer of the tracker.
Seeding our proposed high-level trigger with existing jet, missing transverse
energy or lepton hardware-level triggers, we show that net trigger efficiencies
of order 10% are possible for bombs of mass several hundred GeV. We also
consider the special case that soft bombs are the result of an exotic decay of
the 125 GeV Higgs. The fiducial rate for "Higgs bombs" triggered in this manner
is marginally higher than the rate achievable by triggering directly on a hard
muon from associated Higgs production.Comment: 38 pages, 5 tables, 14 figure
Dynamics and interaction of vortex lines in an elongated Bose-Einstein condensate
We study the real-time dynamics of vortex lines in a large elongated
Bose-Einstein condensate (BEC) of sodium atoms using a stroboscopic technique.
Vortices are spontaneously produced via the Kibble-Zurek mechanism in a quench
across the BEC transition and then they slowly precess keeping their
orientation perpendicular to the long axis of the trap as expected for
solitonic vortices in a highly anisotropic condensate. Good agreement with
theoretical predictions is found for the precession period as a function of the
orbit amplitude and the number of condensed atoms. In configurations with two
or more vortex lines, we see signatures of vortex-vortex interaction in the
shape and visibility of the orbits. In addition, when more than two vortices
are present, their decay is faster than the thermal decay observed for one or
two vortices. The possible role of vortex reconnection processes is discussed.Comment: 4 pages, 4 figure
An Inkjet Printed Chipless RFID Sensor for Wireless Humidity Monitoring
A novel chipless RFID humidity sensor based on a finite Artificial Impedance
Surface (AIS) is presented. The unit cell of the AIS is composed of three
concentric loops thus obtaining three deep and high Q nulls in the
electromagnetic response of the tag. The wireless sensor is fabricated using
low-cost inkjet printing technology on a thin sheet of commercial coated paper.
The patterned surface is placed on a metal backed cardboard layer. The relative
humidity information is encoded in the frequency shift of the resonance peaks.
Varying the relative humidity level from 50% to 90%, the frequency shift has
proven to be up to 270MHz. The position of the resonance peaks has been
correlated to the relative humidity level of the environment on the basis of a
high number of measurements performed in a climatic chamber, specifically
designed for RF measurements of the sensor. A very low error probability of the
proposed sensor is demonstrated when the device is used with a 10% RH humidity
level discrimination
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