1,925 research outputs found
Multicriticality of the (2+1)-dimensional gonihedric model: A realization of the (d,m)=(3,2) Lifshitz point
Multicriticality of the gonihedric model in 2+1 dimensions is investigated
numerically. The gonihedric model is a fully frustrated Ising magnet with the
finely tuned plaquette-type (four-body and plaquette-diagonal) interactions,
which cancel out the domain-wall surface tension. Because the
quantum-mechanical fluctuation along the imaginary-time direction is simply
ferromagnetic, the criticality of the (2+1)-dimensional gonihedric model should
be an anisotropic one; that is, the respective critical indices of real-space
(\perp) and imaginary-time (\parallel) sectors do not coincide. Extending the
parameter space to control the domain-wall surface tension, we analyze the
criticality in terms of the crossover (multicritical) scaling theory. By means
of the numerical diagonalization for the clusters with N\le 28 spins, we
obtained the correlation-length critical indices
(\nu_\perp,\nu_\parallel)=(0.45(10),1.04(27)), and the crossover exponent
\phi=0.7(2). Our results are comparable to
(\nu_{\perp},\nu_{\parallel})=(0.482,1.230), and \phi=0.688 obtained by Diehl
and Shpot for the (d,m)=(3,2) Lifshitz point with the \epsilon-expansion method
up to O(\epsilon^2)
Estimation of greenhouse gas emissions from a tracer gas study
This thesis models the emission of three greenhouse gases that exist in nature, CH4, CO2, and N2O, from a hoop structure, using the artificial introduction of a tracer gas, SF6, which exists in nature at levels below detection limit. Hoop structures are facilities used to house pigs before their slaughter. Many other studies of hoop structure emissions measure only one sample of the tracer gas and greenhouse gas at a time. However, the data sets in our study consist of 25 to 45 samples of each gas, taken on fixed grids of points. We will construct models to account for the relation between the greenhouse gases and SF6 as well as spatial relations in the data set. We will use these models along with the known emission rate of SF6 to estimate the relative rate of emission of the greenhouse gases;We fit a Bayesian hierarchical model to the data sets. In this model, we relate the pointwise concentrations of one greenhouse gas and SF6 and then analyze the posterior distribution of a parameter representing the relative rates of emission of the greenhouse gas and SF6. We assume lognormal measurement errors of the greenhouse gas and SF6 around the true concentration of each gas;We also fit geostatistical models to estimate the rates of emission of these gases. We consider block kriging, block co-kriging, and lognormal block kriging to estimate the concentration of each gas. An advantage of geostatistical models over the Bayesian hierarchical model is that we do not assume strict proportionality of the concentrations of the gases. These estimates can be related to the relative rate of emission of the gases. Due to the small size of these data sets, we take into consideration the uncertainty of the variogram parameters and how this uncertainty affects block kriging averages and variances;We use simulations from both geostatistical models and Bayesian hierarchical models to determine superiority of one set of models in terms of coverage probabilities, bias, and length of coverage sets or confidence intervals. We also address the concern of spatial design for the geostatistical models
Some records of wood-inhabiting fungi on Fagus sylvatica in northern Spain
Es presenta una llista d'algunes recol·leccions interessants de macromicets sobre Fagus, fetes en algunes prospeccions a Astúries i Navarra, en novembre de 2005 . Pel cap baix, Antrodiella fissiliformis, Nemania carbonacea y Phellinus cavicola representen les primeres citacions per a l 'estat espanyol. Des del punt de vista de l' interès per a la conservació de la biodiversitat fúngica, les reserves integrals de Lizardoia i Aztaparreta, a Navarra, es consideren d'especial importància per a la conservació dels fongs saproxílics fagícoles del sud-oest d'Europa. Aquest treball vol estimular també l 'estudi continuat dels fongs lignícoles a les fagedes de l 'estat espanyol.A list is given of some interesting records of lignicolous macrofungi found on Fagus during some excursions in Asturias and Navarra in November 2005 . At least Antrodiella fissiliformis, Nemania carbonacea and Phellinus cavicola represent frrst records for the country. In a conservation perspective, the strict forest reserves Lizardoia and Aztaparreta in Navarra are considered to be important for the conservation of saproxylic fungi on beech in south western Europe. It is our hope that the paper will inspire to continued studies of wood-inhabiting fungi in beech forests in Spain.Se presenta una lista de algunos allaazgos interesantes de macromicetes lignícolas sobre Fagus, realizados durante las prospecciones en Asturias y Navarra, en noviembre de 2005. Por lo menos Antrodiella fissiliformis, Nemania carbonacea y Phellinus cavicola representan primeras citas para España. desde una prespectiva de la conservación de la biodiversidad fúngica, las reservas integrales de L izardoia i Aztaparreta, en Navarra, se consideran de especial importancia para la conservación de los hongos saproxílicos fagícolas en el sudoeste de Europa. Este trabajo esta orientado también a fomentar el estudio continuado de los hongos lignícolas en los hayedos de España
Some records of wood-inhabiting fungi on Fagus sylvatica in northern Spain
Es presenta una llista d'algunes recol·leccions interessants de macromicets sobre Fagus, fetes en algunes prospeccions a Astúries i Navarra, en novembre de 2005 . Pel cap baix, Antrodiella fissiliformis, Nemania carbonacea y Phellinus cavicola representen les primeres citacions per a l 'estat espanyol. Des del punt de vista de l' interès per a la conservació de la biodiversitat fúngica, les reserves integrals de Lizardoia i Aztaparreta, a Navarra, es consideren d'especial importància per a la conservació dels fongs saproxílics fagícoles del sud-oest d'Europa. Aquest treball vol estimular també l 'estudi continuat dels fongs lignícoles a les fagedes de l 'estat espanyol.Se presenta una lista de algunos allaazgos interesantes de macromicetes lignícolas sobre Fagus, realizados durante las prospecciones en Asturias y Navarra, en noviembre de 2005. Por lo menos Antrodiella fissiliformis, Nemania carbonacea y Phellinus cavicola representan primeras citas para España. desde una prespectiva de la conservación de la biodiversidad fúngica, las reservas integrales de L izardoia i Aztaparreta, en Navarra, se consideran de especial importancia para la conservación de los hongos saproxílicos fagícolas en el sudoeste de Europa. Este trabajo esta orientado también a fomentar el estudio continuado de los hongos lignícolas en los hayedos de España.A list is given of some interesting records of lignicolous macrofungi found on Fagus during some excursions in Asturias and Navarra in November 2005 . At least Antrodiella fissiliformis, Nemania carbonacea and Phellinus cavicola represent frrst records for the country. In a conservation perspective, the strict forest reserves Lizardoia and Aztaparreta in Navarra are considered to be important for the conservation of saproxylic fungi on beech in south western Europe. It is our hope that the paper will inspire to continued studies of wood-inhabiting fungi in beech forests in Spain
Entropy-driven phase transition in a polydisperse hard-rods lattice system
We study a system of rods on the 2d square lattice, with hard-core exclusion.
Each rod has a length between 2 and N. We show that, when N is sufficiently
large, and for suitable fugacity, there are several distinct Gibbs states, with
orientational long-range order. This is in sharp contrast with the case N=2
(the monomer-dimer model), for which Heilmann and Lieb proved absence of phase
transition at any fugacity. This is the first example of a pure hard-core
system with phases displaying orientational order, but not translational order;
this is a fundamental characteristic feature of liquid crystals
Scalable quantum tomography in a photonic chip
© 2017 IEEE. We formulate a method of quantum tomography that scales linearly with the number of photons and involves only one optical transformation. We demonstrate it experimentally for two-photon entangled states using a special photonic chip
Sublinear-Time Algorithms for Monomer-Dimer Systems on Bounded Degree Graphs
For a graph , let be the partition function of the
monomer-dimer system defined by , where is the
number of matchings of size in . We consider graphs of bounded degree
and develop a sublinear-time algorithm for estimating at an
arbitrary value within additive error with high
probability. The query complexity of our algorithm does not depend on the size
of and is polynomial in , and we also provide a lower bound
quadratic in for this problem. This is the first analysis of a
sublinear-time approximation algorithm for a # P-complete problem. Our
approach is based on the correlation decay of the Gibbs distribution associated
with . We show that our algorithm approximates the probability
for a vertex to be covered by a matching, sampled according to this Gibbs
distribution, in a near-optimal sublinear time. We extend our results to
approximate the average size and the entropy of such a matching within an
additive error with high probability, where again the query complexity is
polynomial in and the lower bound is quadratic in .
Our algorithms are simple to implement and of practical use when dealing with
massive datasets. Our results extend to other systems where the correlation
decay is known to hold as for the independent set problem up to the critical
activity
Soil and Vegetation Drive Sesquiterpene Lactone Content and Profile in Arnica montana L. Flower Heads From Apuseni-Mountains, Romania
Arnica montana L. (AM, Asteraceae) is a perennial, herbaceous vascular plant species of commercial importance. The flower heads’ pharmacological properties are attributed mainly to sesquiterpene lactones (SLs), with phenolic acids and flavonoids also considered of relevance. The botanical drug is still partly collected in different European mountain regions. The SL content can be influenced by genetic factors and environmental conditions (altitude, temperature and rainfall). Surprisingly, the influence of the soil on SL-content have rarely been investigated. However, the soil determines the occurrence, distribution and overall fitness of AM. Equally, environmental factors are crucial determinants for the biosynthesis and fluctuations in plant secondary metabolites. Therefore, different abiotic (pH, C/N ratio, base saturation, cation exchange capacity) and biotic (species richness, vegetation cover) parameters need to be assessed as potential drivers of the variable content of AM’s secondary metabolites. Consequently, we developed an in situ experimental design aiming to cover a wide range of soil pH conditions. We detected and investigated different AM populations growing in grassland on acidic soils, on siliceous as well as calcareous geologies within the same geographical region and altitudinal belt. The total SL content and most single SL contents of the AM flower heads differed significantly between the two geologies. AM flower heads of plants growing on loam on limestone showed a significant higher total SL content than the flower heads of plants growing in siliceous grasslands. Furthermore, the SL contents were significantly correlated with geobotanical species richness and vegetation cover pointing toward an effect of species interactions on the production of SLs. Moreover, the ratios of the main SLs helenalin to dihydrohelenalin esters were significantly correlated to environmental parameters indicating that SL composition might be a function of habitat conditions. The findings of this study shed light upon the often ignored, complex interactions between environmental conditions and plant secondary metabolites. We highlight the importance of both abiotic and biotic habitat parameters for SLs in AM
- …