8,913 research outputs found
Coating thickness and coverage effects on the forces between silica nanoparticles in water
The structure and interactions of coated silica nanoparticles have been
studied in water using molecular dynamics simulations. For 5 nm diameter
amorphous silica nanoparticles we studied the effects of varying the chain
length and grafting density of polyethylene oxide (PEO) on the nanoparticle
coating's shape and on nanoparticle-nanoparticle effective forces. For short
ligands of length and repeat units, the coatings are radially
symmetric while for longer chains () the coatings are highly
anisotropic. This anisotropy appears to be governed primarily by chain length,
with coverage playing a secondary role. For the largest chain lengths
considered, the strongly anisotropic shape makes fitting to a simple radial
force model impossible. For shorter ligands, where the coatings are isotropic,
we found that the force between pairs of nanoparticles is purely repulsive and
can be fit to the form where is the separation
between the center of the nanoparticles, is the radius of the
silica core, and is measured to be between 2.3 and 4.1.Comment: 20 pages, 6 figure
Thermal conductance of pressed aluminum and stainless steel contacts at liquid helium temperatures
The thermal conductance of aluminum and stainless steel 304 sample pairs with surface finishes ranging from 0.1 to 1.6 microns rms roughness was investigated over a temperature range from 1.6 to 6.0 k. The thermal conductance follows a simple power law function of temperature, with the exponent ranging from 0.5 to 2.25, increases asymptotically with increasing applied force, and exhibits an anomaly for surface finishes in the 0.4 micron region
Emotional and Sexual Development in Adolescence: From Puberty to the Formation of Emotional Bonds
The physiological processes, which occur during adolescence and often so abruptly, can threaten the continuity of the previously constructed sense of identity. They do this by questioning the patterns and representations that had previously governed the relations of the teenager with regards to his body and his relational systems. Although puberty is not just about sexual transformations, definitions centered mainly on this aspect can be found in literature. In fact, pubertal development is the acquisition disclosure index of the adult reproductive capacity. The aim of this task is to explore the process of increasing involvement of the adolescent in an emotional and sexual relationship with a partner. Moreover, it will try to understand this process from a relational and ecological perspective, taking into account the mediation of individual and contextual factors that may have an influence. From examinations performed, it is clear that it is important to consider the multitude of issues that come into play in the process of psycho-social adaptation of the adolescent, by interacting with one another over time, by strengthening one another or by eliminating protective or risk factors. In particular, romantic relationships, if they go well, can pose a factor for growth for the teenager and play an important role in the developmental tasks of this stage of life
Soliton ratchets induced by ac forces with harmonic mixing
The ratchet dynamics of a kink (topological soliton) of a dissipative
sine-Gordon equation in the presence of ac forces with harmonic mixing (at
least bi-harmonic) of zero mean is studied. The dependence of the kink mean
velocity on system parameters is investigated numerically and the results are
compared with a perturbation analysis based on a point particle representation
of the soliton. We find that first order perturbative calculations lead to
incomplete descriptions, due to the important role played by the soliton-phonon
interaction in establishing the phenomenon. The role played by the temporal
symmetry of the system in establishing soliton ratchets is also emphasized. In
particular, we show the existence of an asymmetric internal mode on the kink
profile which couples to the kink translational mode through the damping in the
system. Effective soliton transport is achieved when the internal mode and the
external force get phase locked. We find that for kinks driven by bi-harmonic
drivers consisting of the superposition of a fundamental driver with its first
odd harmonic, the transport arises only due to this {\it internal mode}
mechanism, while for bi-harmonic drivers with even harmonic superposition, also
a point-particle contribution to the drift velocity is present. The phenomenon
is robust enough to survive the presence of thermal noise in the system and can
lead to several interesting physical applications.Comment: 9 pages, 13 figure
Influence of the Thermophysical Model on the CFD Analysis of Oil-Cooled Transformer Windings
A disc-type winding of an oil-immersed power transformer is modeled with Computational Fluid Dynamics. Different approaches are implemented to evaluate the feasibility of the Boussinesq approximation: (i) constant fluid properties, (ii) variable viscosity and thermal diffusivity and (iii) temperature-dependent fluid properties. Temperature and flow distributions are reconstructed and put into relation with physical phenomena and model assumptions. Their comparison suggests that numerical results are fairly sensitive to the thermophysical model as long as the buoyancy force is a relevant component of the flow. Nonetheless, all the cases converge to very close predictions of the hot-spot value and location, with possibly positive implications for the use of reference parameters when deriving flow and heat transfer correlations for this topic
Pacemaker-associated cyanosis in an adolescent : the answer hiding behind shadows
Lead thrombosis is a recognized complication of permanent transvenous pacemaker (PM)
implantation. We present the interesting case of an adolescent with a dual-chamber PM presenting
with fatigue and hypoxemia. Due to limitations of various imaging modalities, the diagnosis was
difficult. She was eventually diagnosed with intracardiac PM lead thrombi obstructing tricuspid
valve inflow. The pediatric literature on PM lead thrombosis is also briefly reviewed.peer-reviewe
Correlated Component Analysis for diffuse component separation with error estimation on simulated Planck polarization data
We present a data analysis pipeline for CMB polarization experiments, running
from multi-frequency maps to the power spectra. We focus mainly on component
separation and, for the first time, we work out the covariance matrix
accounting for errors associated to the separation itself. This allows us to
propagate such errors and evaluate their contributions to the uncertainties on
the final products.The pipeline is optimized for intermediate and small scales,
but could be easily extended to lower multipoles. We exploit realistic
simulations of the sky, tailored for the Planck mission. The component
separation is achieved by exploiting the Correlated Component Analysis in the
harmonic domain, that we demonstrate to be superior to the real-space
application (Bonaldi et al. 2006). We present two techniques to estimate the
uncertainties on the spectral parameters of the separated components. The
component separation errors are then propagated by means of Monte Carlo
simulations to obtain the corresponding contributions to uncertainties on the
component maps and on the CMB power spectra. For the Planck polarization case
they are found to be subdominant compared to noise.Comment: 17 pages, accepted in MNRA
Quantum shock waves in the Heisenberg XY model
We show the existence of quantum states of the Heisenberg XY chain which
closely follow the motion of the corresponding semi-classical ones, and whose
evolution resemble the propagation of a shock wave in a fluid. These states are
exact solutions of the Schroedinger equation of the XY model and their
classical counterpart are simply domain walls or soliton-like solutions.Comment: 15 pages,6 figure
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