605 research outputs found
Spin-S Kagome quantum antiferromagnets in a field with tensor networks
Spin- Heisenberg quantum antiferromagnets on the Kagome lattice offer,
when placed in a magnetic field, a fantastic playground to observe exotic
phases of matter with (magnetic analogs of) superfluid, charge, bond or nematic
orders, or a coexistence of several of the latter. In this context, we have
obtained the (zero temperature) phase diagrams up to directly in the
thermodynamic limit thanks to infinite Projected Entangled Pair States (iPEPS),
a tensor network numerical tool. We find incompressible phases characterized by
a magnetization plateau vs field and stabilized by spontaneous breaking of
point group or lattice translation symmetry(ies). The nature of such phases may
be semi-classical, as the plateaus at th, th and
th of the saturated magnetization (the latter followed by a
macroscopic magnetization jump), or fully quantum as the spin-
-plateau exhibiting coexistence of charge and bond orders. Upon
restoration of the spin rotation symmetry a finite compressibility
appears, although lattice symmetry breaking persists. For integer spin values
we also identify spin gapped phases at low enough field, such as the
(topologically trivial) spin liquid with no symmetry breaking, neither spin nor
lattice.Comment: 5 pages, 3 figures, 1 table + supplemental materia
Vertex-Facet Incidences of Unbounded Polyhedra
How much of the combinatorial structure of a pointed polyhedron is contained
in its vertex-facet incidences? Not too much, in general, as we demonstrate by
examples. However, one can tell from the incidence data whether the polyhedron
is bounded. In the case of a polyhedron that is simple and "simplicial," i.e.,
a d-dimensional polyhedron that has d facets through each vertex and d vertices
on each facet, we derive from the structure of the vertex-facet incidence
matrix that the polyhedron is necessarily bounded. In particular, this yields a
characterization of those polyhedra that have circulants as vertex-facet
incidence matrices.Comment: LaTeX2e, 14 pages with 4 figure
Critical rainfall conditions for the initiation of torrential flows: results from the Rebaixader catchment (Central Pyrenees)
Torrential flows like debris flows or debris floods are fast movements formed by a mix of water and different amounts of unsorted solid material. They generally occur in steep torrents and pose high risk in mountainous areas. Rainfall is their most common triggering factor and the analysis of the critical rainfall conditions is a fundamental research task. Due to their wide use in warning systems, rainfall thresholds for the triggering of torrential flows are an important outcome of such analysis and are empirically derived using data from past events.
In 2009, a monitoring system was installed in the Rebaixader catchment, Central Pyrenees (Spain). Since then, rainfall data of 25 torrential flows (âTRIG rainfallsâ) were recorded, with a 5-min sampling frequency. Other 142 rainfalls that did not trigger torrential flows (âNonTRIG rainfallsâ) were also collected and analyzed. The goal of this work was threefold: (i) characterize rainfall episodes in the Rebaixader catchment and compare rainfall data that triggered torrential flows and others that did not; (ii) define and test IntensityâDuration (ID) thresholds using rainfall data measured inside the catchment by with different techniques; (iii) analyze how the criterion used for defining the rainfall duration and the spatial variability of rainfall influences the value obtained for the thresholds.
The statistical analysis of the rainfall characteristics showed that the parameters that discriminate better the TRIG and NonTRIG rainfalls are the rainfall intensities, the mean rainfall and the total rainfall amount. The antecedent rainfall was not significantly different between TRIG and NonTRIG rainfalls, as it can be expected when the source material is very pervious (a sandy glacial soil in the study site). Thresholds were derived from data collected at one rain gauge located inside the catchment. Two different methods were applied to calculate the duration and intensity of rainfall: (i) using total duration, Dtot, and mean intensity, Imean, of the rainfall event, and (ii) using floating durations, D, and intensities, Ifl, based on the maximum values over floating periods of different duration. The resulting thresholds are considerably different (Imean = 6.20 Dtot-0.36 and Ifl_90% = 5.49 D-0.75, respectively) showing a strong dependence on the applied methodology.
On the other hand, the definition of the thresholds is affected by several types of uncertainties. Data from both rain gauges and weather radar were used to analyze the uncertainty associated with the spatial variability of the triggering rainfalls. The analysis indicates that the precipitation recorded by the nearby rain gauges can introduce major uncertainties, especially for convective summer storms. Thus, incorporating radar rainfall can significantly improve the accuracy of the measured triggering rainfall.
Finally, thresholds were also derived according to three different criteria for the definition of the duration of the triggering rainfall: (i) the duration until the peak intensity, (ii) the duration until the end of the rainfall; and, (iii) the duration until the trigger of the torrential flow. An important contribution of this work is the assessment of the threshold relationships obtained using the third definition of duration. Moreover, important differences are observed in the obtained thresholds, showing that ID relationships are significantly dependent on the applied methodology.Peer ReviewedPostprint (author's final draft
Carbon-based materials for humidity sensing: a short review
Humidity sensors are widespread in many industrial applications, ranging from
environmental and meteorological monitoring, soil water content determination in agriculture,
air conditioning systems, food quality monitoring, and medical equipment to many other fields.
Thus, an accurate and reliable measurement of water content in dierent environments and materials
is of paramount importance. Due to their rich surface chemistry and structure designability, carbon
materials have become interesting in humidity sensing. In addition, they can be easily miniaturized
and applied in flexible electronics. Therefore, this short review aims at providing a survey of recent
research dealing with carbonaceous materials used as capacitive and resistive humidity sensors.
This work collects some successful examples of devices based on carbon nanotubes, graphene, carbon
black, carbon fibers, carbon soot, and more recently, biochar produced from agricultural wastes.
The pros and cons of the dierent sensors are also discussed in the present review
The Dust and Molecular Gas in the Brightest Cluster Galaxy in MACS 1931.8-2635
We present new ALMA observations of the molecular gas and far-infrared
continuum around the brightest cluster galaxy (BCG) in the cool-core cluster
MACS 1931.8-2635. Our observations reveal
M of molecular gas, on par with the largest known reservoirs of cold
gas in a cluster core. We detect CO(1-0), CO(3-2), and CO(4-3) emission from
both diffuse and compact molecular gas components that extend from the BCG
center out to kpc to the northwest, tracing the UV knots and H
filaments observed by HST. Due to the lack of morphological symmetry, we
hypothesize that the km s velocity of the CO in the tail is
not due to concurrent uplift by AGN jets, rather we may be observing the
aftermath of a recent AGN outburst. The CO spectral line energy distribution
suggests that molecular gas excitation is influenced by processes related to
both star formation and recent AGN feedback. Continuum emission in Bands 6 and
7 arises from dust and is spatially coincident with young stars and nebular
emission observed in the UV and optical. We constrain the temperature of
several dust clumps to be K, which is too cold to be directly
interacting with the surrounding keV intracluster medium (ICM). The
cold dust population extends beyond the observed CO emission and must either be
protected from interacting with the ICM or be surrounded by local volumes of
ICM that are several keV colder than observed by Chandra.Comment: Accepted for Publication in ApJ, 19 pages, 11 figures. Minor
revisions to the discussion and accompanying figur
Biochar for gas sensors devices
In recent years, biochar applications are present in many fields [1]. It has been studied as substitution for more expensive carbon materials like carbon nanotubes, graphene and others. The evident advantage for biochar is its low cost of production, being an environmentally friendly source of huge carbon content.
On the other hand, nowadays the main application of this material is as field amendment in agriculture [2]. Starting for the peculiarity of biochar, it is possible to modify its features. For instance, after high temperature treatments, its surface area can increase sharply.
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