3,207 research outputs found
Duality in two capacitively coupled layered arrays of ultrasmall Josephson junctions
We consider the problem of two capacitively coupled Josephson junction arrays
made of ultrasmall junctions. Each one of the arrays can be in the
semiclassical or quantum regimes, depending on their physical parameter values.
The former case is dominated by a Cooper-pair superfluid while the quantum one
is dominated by dynamic vortices leading to an insulating behavior. We first
consider the limit when both arrays are in the semiclassical limit, and next
the case when one array is quantum and the other semiclassical. We present WKB
and Mean Field theory results for the critical temperature of each array when
both are in the semiclassical limit. When one array is in the semiclassical
regime and the other one in the quantum fluctuations dominated regimes, we
derive a duality transformation between the charged and vortex dominated arrays
that involve a gauge vector field, which is proportional to the site coupling
capacitance between the arrays. The system considered here has been fabricated
and we make some predictions as to possible experimentally measurable
quantities that could be compared with theory.Comment: 25 pages in Revtex, To appear in J. Stat. Physics In the November
1998 issu
Phase and Charge reentrant phase transitions in two capacitively coupled Josephson arrays with ultra-small junction
We have studied the phase diagram of two capacitively coupled Josephson
junction arrays with charging energy, , and Josephson coupling energy,
. Our results are obtained using a path integral Quantum Monte Carlo
algorithm. The parameter that quantifies the quantum fluctuations in the i-th
array is defined by . Depending on
the value of , each independent array may be in the semiclassical or
in the quantum regime: We find that thermal fluctuations are important when
and the quantum fluctuations dominate when . We have extensively studied the interplay between vortex and charge
dominated individual array phases. The two arrays are coupled via the
capacitance at each site of the lattices. We find a {\it
reentrant transition} in , at low temperatures, when one of
the arrays is in the semiclassical limit (i.e. ) and the
quantum array has , for the values considered for
the interlayer capacitance. In addition, when , and
for all the inter-layer couplings considered above, a {\it novel} reentrant
phase transition occurs in the charge degrees of freedom, i.e. there is a
reentrant insulating-conducting transition at low temperatures. We obtain the
corresponding phase diagrams and found some features that resemble those seen
in experiments with 2D JJA.Comment: 25 Latex pages including 8 encapsulated poscript figures. Accepted
for publication in Phys. Rev B (Nov. 2004 Issue
Comment on "Two Phase Transitions in the Fully frustrated XY Model"
The conclusions of a recent paper by Olsson (Phys. Rev. Lett. 75, 2758
(1995), cond-mat/9506082) about the fully frustrated XY model in two dimensions
are questioned. In particular, the evidence presented for having two separate
chiral and U(1) phase transitions are critically considered.Comment: One page one table, to Appear in Physical Review Letter
Quantum and classical solutions for free particle in wedge billiards
We have studied the quantum and classical solutions of a particle constrained
to move inside a sector circular billiard with angle and its pacman
complement with angle . In these billiards rotational invariance
is broken and angular momentum is no longer a conserved quantum number. The
"fractional" angular momentum quantum solutions are given in terms of Bessel
functions of fractional order, with indices , for the sector and , for the pacman. We derive a ``duality'' relation
between both fractional indices given by and . We find that the
average of the angular momentum is zero but the average of has as eigenvalues and . We also make a
connection of some classical solutions to their quantum wave eigenfunction
counterparts.Comment: 10 pages and two PostScript figure
Life Cycle Assessment of a Multi-Material Car Component
Background, Aims and Scope. In recent years, the automotive industry has been experiencing an increasing concern with environmental requirements. A particular focus is being given to light-weighting of cars, to reducing fuel consumption and to the use of different recycling materials. Consequently, decisions on product design and development must involve economic and technological as well as environmental considerations. In adequate conditions, the LCA methodology enables one to assist an effective integration of the environmental considerations in the decision- making process [1]. In this paper, a multi-material car component which is part of the current automotive brake system, has been modified by its original manufacturer. Such a modification included the use of a new multi-material injection moulding process and the consumption of recyclable materials. The new and the current component were comparatively assessed throughout their life cycles in order to evaluate their respective environmental impacts and, thus, to verify if the new component offers a lower environmental load. The results described in this paper are part of the outcome of a broader research project involving industrial companies, university, technological centres and research institutes based in Portugal, Spain and Germany
Collective cell durotaxis emerges from long-range intercellular force transmission
The ability of cells to follow gradients of extracellular matrix stiffness—durotaxis—has been implicated in development, fibrosis, and cancer. Here, we found multicellular clusters that exhibited durotaxis even if isolated constituent cells did not. This emergent mode of directed collective cell migration applied to a variety of epithelial cell types, required the action of myosin motors, and originated from supracellular transmission of contractile physical forces. To explain the observed phenomenology, we developed a generalized clutch model in which local stick-slip dynamics of cell-matrix adhesions was integrated to the tissue level through cell-cell junctions. Collective durotaxis is far more efficient than single-cell durotaxis; it thus emerges as a robust mechanism to direct cell migration during development, wound healing, and collective cancer cell invasion.Peer ReviewedPostprint (author's final draft
The electrochemical kinetic behaviour of nickel in acid aqueous solutions containing chloride and perchlorate ions
The electrochemical behaviour of polycrystalline nickel in acid solutions containing large excess either of NaCl or NaClO4 has been investigated, at potentials either more positive or negative than the rest potential of the metal. The electrode reactions were studied over a wide range of experimental conditions (pH, nickelous ion activity, temperature), and the influence of each variable on the experimental kinetic parameters has been determinedInstituto de Investigaciones FisicoquÃmicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta
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