1,229 research outputs found
Diffusion-limited deposition with dipolar interactions: fractal dimension and multifractal structure
Computer simulations are used to generate two-dimensional diffusion-limited
deposits of dipoles. The structure of these deposits is analyzed by measuring
some global quantities: the density of the deposit and the lateral correlation
function at a given height, the mean height of the upper surface for a given
number of deposited particles and the interfacial width at a given height.
Evidences are given that the fractal dimension of the deposits remains constant
as the deposition proceeds, independently of the dipolar strength. These same
deposits are used to obtain the growth probability measure through Monte Carlo
techniques. It is found that the distribution of growth probabilities obeys
multifractal scaling, i.e. it can be analyzed in terms of its
multifractal spectrum. For low dipolar strengths, the spectrum is
similar to that of diffusion-limited aggregation. Our results suggest that for
increasing dipolar strength both the minimal local growth exponent
and the information dimension decrease, while the fractal
dimension remains the same.Comment: 10 pages, 7 figure
Diffusion-limited deposition of dipolar particles
Deposits of dipolar particles are investigated by means of extensive Monte
Carlo simulations. We found that the effect of the interactions is described by
an initial, non-universal, scaling regime characterized by orientationally
ordered deposits. In the dipolar regime, the order and geometry of the clusters
depend on the strength of the interactions and the magnetic properties are
tunable by controlling the growth conditions. At later stages, the growth is
dominated by thermal effects and the diffusion-limited universal regime
obtains, at finite temperatures. At low temperatures the crossover size
increases exponentially as T decreases and at T=0 only the dipolar regime is
observed.Comment: 5 pages, 4 figure
Energy loss mechanism for suspended micro- and nanoresonators due to the Casimir force
A so far not considered energy loss mechanism in suspended micro- and
nanoresonators due to noncontact acoustical energy loss is investigated
theoretically. The mechanism consists on the conversion of the mechanical
energy from the vibratory motion of the resonator into acoustic waves on large
nearby structures, such as the substrate, due to the coupling between the
resonator and those structures resulting from the Casimir force acting over the
separation gaps. Analytical expressions for the resulting quality factor Q for
cantilever and bridge micro- and nanoresonators in close proximity to an
underlying substrate are derived and the relevance of the mechanism is
investigated, demonstrating its importance when nanometric gaps are involved
Nonequilibrium wetting transitions with short range forces
We analyze within mean-field theory as well as numerically a KPZ equation
that describes nonequilibrium wetting. Both complete and critical wettitng
transitions were found and characterized in detail. For one-dimensional
substrates the critical wetting temperature is depressed by fluctuations. In
addition, we have investigated a region in the space of parameters (temperature
and chemical potential) where the wet and nonwet phases coexist. Finite-size
scaling analysis of the interfacial detaching times indicates that the finite
coexistence region survives in the thermodynamic limit. Within this region we
have observed (stable or very long-lived) structures related to spatio-temporal
intermittency in other systems. In the interfacial representation these
structures exhibit perfect triangular (pyramidal) patterns in one (two
dimensions), that are characterized by their slope and size distribution.Comment: 11 pages, 5 figures. To appear in Physical Review
Quantum capacitor with discrete charge-anticharge: spectrum and forces
The quantum capacitor with discrete charge is modeled by a Hamiltonian
containing an inductive intrinsic term (tunnel effect between plates). The
spectrum is obtained using a double Hilbert space. Fluctuations in the
charge-anticharge pairs (zero total charge) give rise to an elementary
attraction which is compared to the Casimir force. In this case, the
field-fluctuations force could be also interpreted as charge-fluctuations
force
Virtualization of niebla formation sites (upper miocene) in the Huelva province: valuating the paleontological heritage in differentiate educative settings II
El patrimonio paleontológico del Neógeno de la provincia de Huelva es uno
de los más importantes de España y referente europeo de moluscos de este
período. Sin embargo, no existe un inventario de catalogación básica de los
principales yacimientos ni de los principales grupos fósiles presentes, así como
de su importancia como patrimonio natural. El presente trabajo pretende rellenar
este notable vacío con una proyección tanto hacia materias preuniversitarias
como universitarias, así como hacia posibles instituciones y corporaciones
públicas susceptibles de utilizarlo en sus planes de ordenación. Por otro lado, se
pretende que actúe como mecanismo de interconexión entre titulaciones con bajo
número de alumnos de nuevo ingreso y los centros de Bachillerato, de forma que
incentive una posible elección de estos Grados por los alumnos de las opciones
científico-tecnológicas. También puede ser interesante para captar egresados
hacia Másteres Oficiales en Patrimonio Histórico y Natural. En este sentido, se
ha realizado un DVD documental sobre el patrimonio paleontológico del
Mioceno superior de la provincia de Huelva. Este documental incluye una visión
de conjunto de los principales yacimientos de fósiles marinos de la Fm. Niebla,
desarrollada en un marco transgresivo bajo unas condiciones más húmedas y
cálidas que las actuales. Esta aportación es aplicable al trabajo de campo de
varios Grados y Posgrados universitarios y de fácil uso como material didáctico
en diversas asignaturas de E.S.O. y Bachillerato. Este trabajo se ha realizado en
el marco del proyecto de innovación docente (PID nº 11003) de la Universidad
de Huelva.The paleontological heritage from the Neogene in the province of Huelva is
one of the most important in Spain and it is considered a European reference site
for the mollusk fossil record from this period. However, there are not basic
inventories neither for the main sites nor the major fossil groups. Furthermore,
no inventories exist about their natural heritage importance. This work aims to
fill this significant gap for both pre-university and university levels, as well as to
public institutions and corporations that may use it in their management plans. In
addition, it is intended to act as an linking mechanism between university
degrees with low number of first-year students and high school centres, in order
to encourage a possible choice of these Bachelor’s degrees by scientific and
technological students. It may also be interesting to catch the attention of
graduates for Official Masters in Historical and Natural Heritage. In this sense, a
DVD-documentary has been made about the paleontological heritage from the
Upper Miocene in the province of Huelva. This documental includes an
overview of the main marine fossil sites from the Niebla Formation developed in
a transgressive setting under more humid and warmer conditions than today. This
contribution is useful for the fieldwork at Bachelor and Master Degree level and
it is easy to use as teaching materials in different ESO (Obligatory Secondary
Teaching) and High School subjects. This work has been funded for an
Innovation in Teaching Project (PID No. 10050) of the Huelva University
Renormalisation group determination of the order of the DNA denaturation transition
We report on the nature of the thermal denaturation transition of homogeneous
DNA as determined from a renormalisation group analysis of the
Peyrard-Bishop-Dauxois model. Our approach is based on an analogy with the
phenomenon of critical wetting that goes further than previous qualitative
comparisons, and shows that the transition is continuous for the average
base-pair separation. However, since the range of universal critical behaviour
appears to be very narrow, numerically observed denaturation transitions may
look first-order, as it has been reported in the literature.Comment: 6 pages; no figures; to appear in Europhysics Letter
Orientational order in Deposits of Magnetic Particles
We present preliminary results for the orientational order in deposits of
dipolar particles, on one dimensional substrates. The deposits are generated
using a model where the incoming dipolar particle interacts with the other
particles in the deposit via a dipole-dipole potential. The interdipolar
vectors are restricted to lie on a square lattice although the dipole moments
are free to rotate in three dimensions. The path of the incoming particle is
generated through a Monte Carlo scheme controlled by an effective temperature
T, the case of pure diffusion-limited deposition corresponding to T=infinity$.
We calculate the ferromagnetic and nematic order parameters and the dipolar
orientational probability density of the deposits, at various stages of growth
and two effective temperatures. The dipolar angular correlations along the rows
and columns of the lattice are also investigated. We find that the
orientational order of the deposits depends strongly on the lattice structure,
the stage of growth and the effective temperature.Comment: 18 pages, 6 figure
- …