587 research outputs found
3_D modeling using TLS and GPR techniques to characterize above and below-ground wood distribution in pyroclastic deposits along the Blanco River (Chilean Patagonia)
To date, the study of in-stream wood in rivers has been focused mainly on quantifying wood pieces deposited above
the ground. However, in some particular river systems, the presence of buried dead wood can also represent an
important component of wood recruitment and budgeting dynamics. This is the case of the Blanco River (Southern
Chile) severely affected by the eruption of Chait\ue9n Volcano occurred between 2008 and 2009. The high pyroclastic
sediment deposition and transport affected the channel and the adjacent forest, burying wood logs and standing
trees. The aim of this contribution is to assess the presence and distribution of wood in two study areas (483 m2 and
1989 m2, respectively) located along the lower streambank of the Blanco River, and covered by thick pyroclastic
deposition up to 5 m. The study areas were surveyed using two different devices, a Terrestrial Laser Scanner (TLS)
and a Ground Penetrating Radar (GPR). The first was used to scan the above surface achieving a high point cloud
density ( 48 2000 points m-2) which allowed us to identify and measure the wood volume. The second, was used
to characterize the internal morphology of the volcanic deposits and to detect the presence and spatial distribution
of buried wood up to a depth of 4 m. Preliminary results have demonstrated differences in the numerousness and
volume of above wood between the two study areas. In the first one, there were 43 wood elements, 33 standing
trees and 10 logs, with a total volume of 2.96 m3 (109.47 m3 km-1), whereas the second one was characterized
by the presence of just 7 standing trees and 11 wood pieces, for a total amount of 0.77 m3 (7.73 m3 km-1). The
dimensions of the wood elements vary greatly according to the typology, standing trees show the higher median
values in diameter and length (0.15 m and 2.91 m, respectively), whereas the wood logs were smaller (0.06 m and
1.12 m, respectively). The low dimensions of deposited wood can be probably connected to their origin, suggesting
that these elements were generated by toppling and breaking of surrounding dead trees. Results obtained with the
GPR confirm the ability of this instrument to localize the presence and distribution of buried wood. From the 3-
D analysis it was possible to assess the spatial distribution and to estimate, as first approach, the volume of the
buried wood which represents approximately 0.04% of the entire volcanic deposit. Further analysis will focus on
additional GPR calibration with different wood sizes for a more accurate estimation of the volume. The knowledge
of the overall wood amount stored in a fluvial system that can be remobilized over time, represent an essential
factor to ensure better forest and river management actions
A general method to determine replica symmetry breaking transitions
We introduce a new parameter to investigate replica symmetry breaking
transitions using finite-size scaling methods. Based on exact equalities
initially derived by F. Guerra this parameter is a direct check of the
self-averaging character of the spin-glass order parameter. This new parameter
can be used to study models with time reversal symmetry but its greatest
interest concerns models where this symmetry is absent. We apply the method to
long-range and short-range Ising spin glasses with and without magnetic field
as well as short-range multispin interaction spin glasses.Comment: 5 pages, 4 figures, Revtex fil
Historic Churches and Their Hygrothermal Environment: A Review of Criteria Related to Building Fabric, Artefacts, Artwork and Occupants
Regarded as important cultural heritage, historic churches have been utilised over hundreds of years for worship and community benefit. Simple on/off space heating systems are installed in many churches to increase human comfort. However, the conservation of the important historic artefacts and artwork contained within may not have been fully considered. This review attempts to appraise the standards in place for artefacts and artwork. A consensus of 15–25 °C and 40–65% relative humidity is established as safe from the standards reviewed. Consideration is given to the environment within the church to understand if such exacting conditions can be met. The review finds that the conservation and preservation of artefacts and buildings are aligned goals, although striving to meet specified target ranges for artefact types is not fully compatible with historic churches. The stability of the internal environment is clearly an important factor in conservation and benefits human comfort expectations. Churches may contain microclimates throughout the building, complicating the use of target ranges for artefacts, artwork and comfort. The findings of this study can assist historic churches in managing the change, alteration or installation of heating systems
Critical interfaces of the Ashkin-Teller model at the parafermionic point
We present an extensive study of interfaces defined in the Z_4 spin lattice
representation of the Ashkin-Teller (AT) model. In particular, we numerically
compute the fractal dimensions of boundary and bulk interfaces at the
Fateev-Zamolodchikov point. This point is a special point on the self-dual
critical line of the AT model and it is described in the continuum limit by the
Z_4 parafermionic theory. Extending on previous analytical and numerical
studies [10,12], we point out the existence of three different values of
fractal dimensions which characterize different kind of interfaces. We argue
that this result may be related to the classification of primary operators of
the parafermionic algebra. The scenario emerging from the studies presented
here is expected to unveil general aspects of geometrical objects of critical
AT model, and thus of c=1 critical theories in general.Comment: 15 pages, 3 figure
Encrypted Shared Data Spaces
The deployment of Share Data Spaces in open, possibly hostile, environments arises the need of protecting the confidentiality of the data space content. Existing approaches focus on access control mechanisms that protect the data space from untrusted agents. The basic assumption is that the hosts (and their administrators) where the data space is deployed have to be trusted. Encryption schemes can be used to protect the data space content from malicious hosts. However, these schemes do not allow searching on encrypted data. In this paper we present a novel encryption scheme that allows tuple matching on completely encrypted tuples. Since the data space does not need to decrypt tuples to perform the search, tuple confidentiality can be guaranteed even when the data space is deployed on malicious hosts (or an adversary gains access to the host). Our scheme does not require authorised agents to share keys for inserting and retrieving tuples. Each authorised agent can encrypt, decrypt, and search encrypted tuples without having to know other agents’ keys. This is beneficial inasmuch as it simplifies the task of key management. An implementation of an encrypted data space based on this scheme is described and some preliminary performance results are given
Critical domain walls in the Ashkin-Teller model
We study the fractal properties of interfaces in the 2d Ashkin-Teller model.
The fractal dimension of the symmetric interfaces is calculated along the
critical line of the model in the interval between the Ising and the
four-states Potts models. Using Schramm's formula for crossing probabilities we
show that such interfaces can not be related to the simple SLE, except
for the Ising point. The same calculation on non-symmetric interfaces is
performed at the four-states Potts model: the fractal dimension is compatible
with the result coming from Schramm's formula, and we expect a simple
SLE in this case.Comment: Final version published in JSTAT. 13 pages, 5 figures. Substantial
changes in the data production, analysis and in the conclusions. Added a
section about the crossing probability. Typeset with 'iopart
Living With and Treating Rare Diseases: Experiences of Patients and Professional Health Care Providers
Typical Gibbs configurations for the 1d Random Field Ising Model with long range interaction
We study a one--dimensional Ising spin systems with ferromagnetic,
long--range interaction decaying as n^{-2+\a}, \a \in [0,\frac 12], in the
presence of external random fields. We assume that the random fields are given
by a collection of symmetric, independent, identically distributed real random
variables, gaussian or subgaussian with variance . We show that for
temperature and variance of the randomness small enough, with an overwhelming
probability with respect to the random fields, the typical configurations,
within volumes centered at the origin whose size grow faster than any power of
, % {\bf around the origin} are intervals of spins followed by
intervals of spins whose typical length is \simeq
\th^{-\frac{2}{(1-2\a)}} for 0\le \a<1/2 and
for \a=1/2
4D Spin Glasses in Magnetic Field Have a Mean Field like Phase
By using numerical simulations we show that the 4D Edwards Anderson
spin glass in magnetic field undergoes a mean field like phase transition. We
use a dynamical approach: we simulate large lattices (of volume ) and work
out the behavior of the system in limit where both and go to infinity,
but where the limit is taken first. By showing that the dynamic
overlap converges to a value smaller than the static one we exhibit replica
symmetry breaking. The critical exponents are compatible with the ones obtained
by mean field computations.Comment: Physrev format, 5 ps figures include
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