6,772 research outputs found
Phase diagram of silicon from atomistic simulations
In this letter we present a calculation of the temperature-pressure phase
diagram of Si in a range of pressures covering from -5 to 20 GPa and
temperatures up to the melting point. The phase boundaries and triple points
between the diamond, liquid, -Sn and clathrate phases are
reported. We have employed efficient simulation techniques to calculate free
energies and to numerically integrate the Clausius-Clapeyron equation, combined
with a tight binding model capable of an accuracy comparable to that of
first-principles methods. The resulting phase diagram agrees well with the
available experimental data.Comment: 5 pages, 1 figure, accepted in PR
'Enhancement of the crystallization process of TbxFe1-x thin films upon the formation of alpha-Tb phase'
TbxFe1−x thin films deposited by sputtering on Mo were investigated structurally and magnetically. The microstructure consists of TbFe2 nanoparticles embedded in an amorphous matrix, and the Tb content can be correlated with an increase in the volume of these nanoparticles. Similar microstructure and behavior were found when TbFe2 was deposited on glass and on a Pt buffer layer. Nevertheless, thermal treatments promote a different effect, depending on the mechanical stiffness of the buffer layer. The layers deposited on Mo, a rigid material, show crystalline TbFe2 together with α-Tb phase upon thermal treatment. In contrast, TbFe2 does not crystallize properly on Pt, a material with a lower stiffness than Mo. Intermediate results were observed on the film deposited on glass. Experimental results show the impact of the buffer stiffness on the crystallization process. Moreover, the formation of α-Tb appears to be fundamental to crystallized TbFe2 on layers deposited on rigid buffer
Damage Spreading During Domain Growth
We study damage spreading in models of two-dimensional systems undergoing
first order phase transitions. We consider several models from the same
non-conserved order parameter universality class, and find unexpected
differences between them. An exact solution of the Ohta-Jasnow-Kawasaki model
yields the damage growth law , where in
dimensions. In contrast, time-dependent Ginzburg-Landau simulations and Ising
simulations in using heat-bath dynamics show power-law growth, but with
an exponent of approximately , independent of the system sizes studied.
In marked contrast, Metropolis dynamics shows damage growing via , although the damage difference grows as . PACS: 64.60.-i, 05.50.+qComment: 4 pags of revtex3 + 3 postscript files appended as a compressed and
uuencoded file. UIB940320
Fragility Curves for Thin-Walled Cold-Formed Steel Wall Frames Affected by Ground Settlements Due to Land Subsidence
Land subsidence phenomenon due to ground water withdrawal is a current problem in many places around the world, particularly in the shallows of Mexico. This causes ground differential settlements that affect structures, mainly dwellings and buildings based on reinforced concrete and masonry. Eventually, these structural materials do not exhibit an adequate performance beyond a certain level of angular distortion. This work presents the results about a study regarding the performance of thin-walled cold-formed steel wall frames with different sheathing systems affected by angular distortions simulating ground differential settlements due to land subsidence. The wall frames are composed by vertical (studs) and horizontal elements (tracks), with different sheathing systems: polystyrene, OSB, gypsum and calcium silicate. By means of experimental testing of wall frames subjected to monotonic lateral loads, the rotational stiffness was obtained for the wall frames with polystyrene. Likewise the rotational stiffness of the other wall frame systems was calculated based on the data provided by other author’s publications. On the other hand, by means of numerical simulation, all the wall frame systems were modeled in structural analysis software, calibrating them based on the rotational stiffness. Also, the moment-rotation curves were calculated for the studs and tracks based on the direct strength method. A non-linear static pull down analysis was performed producing several degrees of angular distortion simulating ground settlements for all the wall frames sheathing systems. With the data acquired fragility curves were calculated according three levels of damage for the wall frames with different sheathing system
Excitable media in open and closed chaotic flows
We investigate the response of an excitable medium to a localized
perturbation in the presence of a two-dimensional smooth chaotic flow. Two
distinct types of flows are numerically considered: open and closed. For both
of them three distinct regimes are found, depending on the relative strengths
of the stirring and the rate of the excitable reaction. In order to clarify and
understand the role of the many competing mechanisms present, simplified models
of the process are introduced. They are one-dimensional baker-map models for
the flow and a one-dimensional approximation for the transverse profile of the
filaments.Comment: 14 pages, 16 figure
Exploring the Design Space for Body Transformation Wearables to Support Physical Activity through Sensitizing and Bodystorming
Negative or disturbed body perceptions are often interwoven with people's physical inactivity. While wearables can support body perception changes (body transformation), the design space of body transformation wearables supporting physical activity remains narrow. To expand this design space, we conducted an embodied co-design workshop with users. Using conceptual and tangible sensitizing tools, we explored/reflected on bodily sensations at three moments of movement execution (before/during/after). Conceptual tools were used to evoke/reflect/capture past lived experiences, while tangible tools were used as ideation probes for sensory bodystorming. Two design concepts emerged, reflecting diverging approaches to body transformation wearables: one focused on reminders and movement correction; the other on sensory augmentation and facilitation. We reflect on how each facilitates useful representations of body sensations during movement, and present methodological recommendations for designing technology for sensory augmentation in this area. Finally, we propose a preliminary prototype based on our design concepts and discuss future steps
An intelligent model for road traffic management in the motorway network around barcelona
This paper presents an advanced knowledge-based environment to develop real time traffic management applications called TRYS. The building process supported by the architecture is guided by the progressive definition of knowledge features from the knowledge level to the symbolic level. Firstly, the problem is presented showing the shortcomings perceived in the state of the art of traffic management systems. Secondly, a description of the KSM tool, aimed at supporting the organization of structured models at the knowledge level is commented. Thirdly, the generic model, intended to deal with traffic management, is described using the KSM format. Finally, the domain model of the application developed for Barcelona is described.
Document type: Part of book or chapter of boo
Universality and Scaling for the Structure Factor in Dynamic Order-Disorder Transitions
The universal form for the average scattering intensity from systems
undergoing order-disorder transitions is found by numerical integration of the
Langevin dynamics. The result is nearly identical for simulations involving two
different forms of the local contribution to the free energy, supporting the
idea that the Model A dynamical universality class includes a wide range of
local free-energy forms. An absolute comparison with no adjustable parameters
is made to the forms predicted by the theories of Ohta-Jasnow-Kawasaki and
Mazenko. The numerical results are well described by the former theory, except
in the cross-over region between scattering dominated by domain geometry and
scattering determined by Porod's law.Comment: 10 pages incl. 3 figures, Revtex. Submitted to PR
Mesons with Beauty and Charm: Spectroscopy
Applying knowledge of the interaction between heavy quarks derived from the
study of and bound states, we calculate the
spectrum of mesons. We compute transition rates for the
electromagnetic and hadronic cascades that lead from excited states to the
ground state, and briefly consider the prospects for
experimental observation of the spectrum.Comment: 32 pages + 2 uuencoded PostScript figures Fermilab-Pub-94/032-
Patchiness and Demographic Noise in Three Ecological Examples
Understanding the causes and effects of spatial aggregation is one of the
most fundamental problems in ecology. Aggregation is an emergent phenomenon
arising from the interactions between the individuals of the population, able
to sense only -at most- local densities of their cohorts. Thus, taking into
account the individual-level interactions and fluctuations is essential to
reach a correct description of the population. Classic deterministic equations
are suitable to describe some aspects of the population, but leave out features
related to the stochasticity inherent to the discreteness of the individuals.
Stochastic equations for the population do account for these
fluctuation-generated effects by means of demographic noise terms but, owing to
their complexity, they can be difficult (or, at times, impossible) to deal
with. Even when they can be written in a simple form, they are still difficult
to numerically integrate due to the presence of the "square-root" intrinsic
noise. In this paper, we discuss a simple way to add the effect of demographic
stochasticity to three classic, deterministic ecological examples where
aggregation plays an important role. We study the resulting equations using a
recently-introduced integration scheme especially devised to integrate
numerically stochastic equations with demographic noise. Aimed at scrutinizing
the ability of these stochastic examples to show aggregation, we find that the
three systems not only show patchy configurations, but also undergo a phase
transition belonging to the directed percolation universality class.Comment: 20 pages, 5 figures. To appear in J. Stat. Phy
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