169,211 research outputs found
A novel approach to CFD analysis of the urban environment
The construction of cities, with their buildings and human activities, not only changes the landscape, but also influences the local climate in a manner that depends on many different factors and parameters: weather conditions, urban thermo-physical and geometrical characteristics, anthropogenic moisture and heat sources. Land-cover and canopy structure play an important role in urban climatology and every environmental assessment and city design face with them.
Inside the previous frame, the objective of this study is both to identify both the key design variables that alter the environment surrounding the buildings, and to quantified the extension area of these phenomena. The tool used for this study is a 2D computational fluid dynamics (CFD) numerical simulation considering different heights for buildings, temperature gaps between undisturbed air and buildingâs walls, velocities of undisturbed air. Results obtained allowed to find a novel approach to study urban canopies, giving a qualitative assessment on the contribution and definition of the total energy of the area surrounding the buildings
On the approach to equilibrium for a polymer with adsorption and repulsion
We consider paths of a one-dimensional simple random walk conditioned to come
back to the origin after L steps (L an even integer). In the 'pinning model'
each path \eta has a weight \lambda^{N(\eta)}, where \lambda>0 and N(\eta) is
the number of zeros in \eta. When the paths are constrained to be non-negative,
the polymer is said to satisfy a hard-wall constraint. Such models are well
known to undergo a localization/delocalization transition as the pinning
strength \lambda is varied. In this paper we study a natural 'spin flip'
dynamics for these models and derive several estimates on its spectral gap and
mixing time. In particular, for the system with the wall we prove that
relaxation to equilibrium is always at least as fast as in the free case
(\lambda=1, no wall), where the gap and the mixing time are known to scale as
L^{-2} and L^2\log L, respectively. This improves considerably over previously
known results. For the system without the wall we show that the equilibrium
phase transition has a clear dynamical manifestation: for \lambda \geq 1 the
relaxation is again at least as fast as the diffusive free case, but in the
strictly delocalized phase (\lambda < 1) the gap is shown to be O(L^{-5/2}), up
to logarithmic corrections. As an application of our bounds, we prove stretched
exponential relaxation of local functions in the localized regime.Comment: 43 pages, 5 figures; v2: corrected typos, added Table
On the probability of staying above a wall for the (2+1)-dimensional SOS model at low temperature
We obtain sharp asymptotics for the probability that the (2+1)-dimensional
discrete SOS interface at low temperature is positive in a large region. For a
square region , both under the infinite volume measure and under the
measure with zero boundary conditions around , this probability turns
out to behave like , with the
surface tension at zero tilt, also called step free energy, and the box
side. This behavior is qualitatively different from the one found for
continuous height massless gradient interface models.Comment: 21 pages, 6 figure
Psychometric properties and validity of an instrument measuring lower secondary studentsâ perceived competence in educational decision-making process
Making decisions about school or career is a very important task for young people since these choices can have long-term consequences. The main purpose of this study is to examine psychometric properties and construct validity of Perceived Competence in Educational Decision-making Process Questionnaire (PCEDPQ). A multi-group confirmatory factor analysis (MCFA) is performed to test the scale theoretical structure and the metric invariance across gender. Results of MCFA are consistent with the hypothesized scale structure and show measurement invariance across gender. The reliability of the scales in terms of internal consistency ranged from .74 to .7
Relations Between Stochastic Orderings and generalized Stochastic Precedence
The concept of "stochastic precedence" between two real-valued random
variables has often emerged in different applied frameworks. In this paper we
consider a slightly more general, and completely natural, concept of stochastic
precedence and analyze its relations with the notions of stochastic ordering.
Such a study leads us to introducing some special classes of bivariate copulas.
Motivations for our study can arise from different fields. In particular we
consider the frame of Target-Based Approach in decisions under risk. This
approach has been mainly developed under the assumption of stochastic
independence between "Prospects" and "Targets". Our analysis concerns the case
of stochastic dependence.Comment: 13 pages, 6 figure
The ecology of social interactions in online and offline environments
The rise in online social networking has brought about a revolution in social
relations. However, its effects on offline interactions and its implications
for collective well-being are still not clear and are under-investigated. We
study the ecology of online and offline interaction in an evolutionary game
framework where individuals can adopt different strategies of socialization.
Our main result is that the spreading of self-protective behaviors to cope with
hostile social environments can lead the economy to non-socially optimal
stationary states
Tensor Multiplets in Six-Dimensional (2,0) Supergravity
We construct the complete coupling of supergravity in six dimensions
to tensor multiplets, extending previous results to all orders in the fermi
fields. The truncation to supergravity coupled to tensor multiplets
exactly reproduces the complete couplings recently obtained.Comment: 13 pages, LATE
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