4,125 research outputs found
Efficiency of encounter-controlled reaction between diffusing reactants in a finite lattice: topology and boundary effects
The role of dimensionality (Euclidean versus fractal), spatial extent,
boundary effects and system topology on the efficiency of diffusion-reaction
processes involving two simultaneously-diffusing reactants is analyzed. We
present numerically-exact values for the mean time to reaction, as gauged by
the mean walklength before reactive encounter, obtained via application of the
theory of finite Markov processes, and via Monte Carlo simulation. As a general
rule, we conclude that for sufficiently large systems, the efficiency of
diffusion-reaction processes involving two synchronously diffusing reactants
(two-walker case) relative to processes in which one reactant of a pair is
anchored at some point in the reaction space (one walker plus trap case) is
higher, and is enhanced the lower the dimensionality of the system. This
differential efficiency becomes larger with increasing system size and, for
periodic systems, its asymptotic value may depend on the parity of the lattice.
Imposing confining boundaries on the system enhances the differential
efficiency relative to the periodic case, while decreasing the absolute
efficiencies of both two-walker and one walker plus trap processes. Analytic
arguments are presented to provide a rationale for the results obtained. The
insights afforded by the analysis to the design of heterogeneous catalyst
systems are also discussed.Comment: 15 pages, 8 figures, uses revtex4, accepted for publication in
Physica
Los alfares arandinos
En número dedicado a: La provincia de Burgo
Didactic strategies for comprehension and learning of structural concepts
p. 926-937In previous papers we have established the convenience of formulating educational
strategies at the university level for both disciplines: Civil Engineering and Architecture,
which involves academic topics of mutual interest by means of shared practices. As a
particular matter of this approach, the application of physical experimental models is
considered of special usefulness, in order to understand in better ways the performance of materials and structural systems.
Several strategies of selection and development of such physical models will be discussed in this work, considering as a first step, the establishment of its correspondence with the different levels of structural complexity studied in curriculum plan: statics, strength of materials and structural design, among others.
This task constitutes a part of the work program of the Laboratory of Structural Models,
which is an academic project that develops and applies different didactic prototypes to
structure courses in the Universidad Autónoma Metropolitana, campus Azcapotzalco, in
Mexico City, project we have already presented in recent forums.
Two different modes of application are implemented in classroom sessions and in
structures workshop: the devices for functional demonstration of typical cases of structural work as well as the experimentation with student's own designs of destructible models where certain typologies are tested up to its failure limit.
The first one allows teachers to explain adequately the theoretical principles and formulas
(that usually are expressed on the blackboard) by means of didactic models identified in
accordance to specific cases of the curriculum on variable level of complexity. This kind of practice allows the students of architecture and civil engineering to realize in better ways the possibilities of use and application of the different structural typologies. Such
experimental models are part of more than fifty devices of the Laboratory's catalog.
In the same sense, the possibility of observation of structural work of their own
architectural designs, allows future professionals to achieve a better conception of the
structural solutions that affect positively their designs. Based on specific predefined guides, the students develop their own architectural-structural projects and subject them to diverse loads, observing their behavior under the influence of variable stresses leading up the experiment to its last resistance.
From both experiences a significant learning is obtained for the student's formation and
training, who will be capable in his future professional work to use better tools of
comprehension of the structural concepts applied to architecture as well as of increasing his conscience of the benefits and convenience of multidisciplinary work.Moreno, C.; Abad, A.; Gerdingh, JG.; Garcia M., C.; Gonzalez C., O. (2010). Didactic strategies for comprehension and learning of structural concepts. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/695
Reactive dynamics on fractal sets: anomalous fluctuations and memory effects
We study the effect of fractal initial conditions in closed reactive systems
in the cases of both mobile and immobile reactants. For the reaction , in the absence of diffusion, the mean number of particles is shown to
decay exponentially to a steady state which depends on the details of the
initial conditions. The nature of this dependence is demonstrated both
analytically and numerically. In contrast, when diffusion is incorporated, it
is shown that the mean number of particles decays asymptotically as
, the memory of the initial conditions being now carried by the
dynamical power law exponent. The latter is fully determined by the fractal
dimension of the initial conditions.Comment: 7 pages, 2 figures, uses epl.cl
The Applied Nutrition Project of Eastern Kenya – An Initiative for Reducing Hunger and Malnutrition
Sustainable development is the only kind of development possible for help in the
third world. Due to various historical, political, geographic and climatic conditions the
divergence between those countries providing and those receiving help is so vast that donations
of labor an/or money is simply not enough. Rather, communities have to be
taught to support and develop themselves during the receipt of aid and especially after
the help pulls out. It is our goal in this article to summarize one such »sustainable development
« project. As volunteers for AMREF (African Medical and Research Foundation),
we worked with the remarkable Makueni Applied Nutrition Project in eastern
Kenya in the summer of 2001. Our job was to visit the various locations in this semiarid
and arid environment and to write a report on the situation of the diverse parts of
the project. The Applied Nutrition Project (ANP) started in 1984 and serves as an excellent
example of the significant help that can be provided to needy areas of the world with
a multifaceted approach
The Philippine poor II: Philippine poverty, an annotated bibliography, 1970-1983
There seems to be a consensus on the basic configuration of
the Philippine poor. They are ill-fed, badly-nourished, inadequately.
housed, under-educated, and unorganized. What seems to
be the subject of much debate, however, is how they got to be that
way and how many they are. Let us consider each issue separately
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