28,079 research outputs found
Critical behavior of the Random-Field Ising model at and beyond the Upper Critical Dimension
The disorder-driven phase transition of the RFIM is observed using exact
ground-state computer simulations for hyper cubic lattices in d=5,6,7
dimensions. Finite-size scaling analyses are used to calculate the critical
point and the critical exponents of the specific heat, magnetization,
susceptibility and of the correlation length. For dimensions d=6,7 which are
larger or equal to the assumed upper critical dimension, d_u=6, mean-field
behaviour is found, i.e. alpha=0, beta=1/2, gamma=1, nu=1/2. For the analysis
of the numerical data, it appears to be necessary to include recently proposed
corrections to scaling at and beyond the upper critical dimension.Comment: 8 pages and 13 figures; A consise summary of this work can be found
in the papercore database at http://www.papercore.org/Ahrens201
Application of the discrete Wentzel-Kramers-Brillouin method to spin tunneling
A discrete version of the WKB method is developed and applied to calculate
the tunnel splittings between classically degenerate states of spin
Hamiltonians. The results for particular model problems are in complete accord
with those previously found using instanton methods. The discrete WKB method is
more elementary and also yields wavefunctions.Comment: RevTex, 2ps figures, incorporates errata (typos and omitted
reference) in JMP pape
The Evolution of Intermediary Institutions in Europe: From Corporatism to Governance
This book investigates the consecutive shifts between three types of intermediary institutions in the European context: Corporatist, Neo-corporatist and Governance institutions. It develops a new conceptual framework for understanding the function and position of intermediary institutions in society, as well as a vocabulary capable of explaining the causes and consequences of these shifts for politics, economy and society at large. The book is designed to fill a gap in three rather distinct, yet also overlapping bodies of literature: European Political Economy, European Integration and governance studies, and socio-legal studies in the European context.
Reviews:
- Anne Guisset: Transfer: European Review of Labour and Research, 22, 3, 427-429, 2016.
- Ian Bruff, Capital & Class, 40, 3, 555 – 57, 2016
Direct sampling of complex landscapes at low temperatures: the three-dimensional +/-J Ising spin glass
A method is presented, which allows to sample directly low-temperature
configurations of glassy systems, like spin glasses. The basic idea is to
generate ground states and low lying excited configurations using a heuristic
algorithm. Then, with the help of microcanonical Monte Carlo simulations, more
configurations are found, clusters of configurations are determined and
entropies evaluated. Finally equilibrium configuration are randomly sampled
with proper Gibbs-Boltzmann weights.
The method is applied to three-dimensional Ising spin glasses with +- J
interactions and temperatures T<=0.5. The low-temperature behavior of this
model is characterized by evaluating different overlap quantities, exhibiting a
complex low-energy landscape for T>0, while the T=0 behavior appears to be less
complex.Comment: 9 pages, 7 figures, revtex (one sentence changed compared to v2
Scaling up: A path to effective development
Poverty reduction, Hunger, MDGs, Interventions, Political dynamics, Capacity, Development assistance, Scaling up,
Few-Particle Effects in Semiconductor Quantum Dots: Observation of Multi-Charged-Excitons
We investigate experimentally and theoretically few-particle effects in the
optical spectra of single quantum dots (QDs). Photo-depletion of the QD
together with the slow hopping transport of impurity-bound electrons back to
the QD are employed to efficiently control the number of electrons present in
the QD. By investigating structurally identical QDs, we show that the spectral
evolutions observed can be attributed to intrinsic, multi-particle-related
effects, as opposed to extrinsic QD-impurity environment-related interactions.
From our theoretical calculations we identify the distinct transitions
related to excitons and excitons charged with up to five additional electrons,
as well as neutral and charged biexcitons.Comment: 4 pages, 4 figures, revtex. Accepted for publication in Physical
Review Letter
Molecular Dynamics in grafted layers of poly(dimethylsiloxane) (PDMS)
Dielectric relaxation spectroscopy 10^-1 Hz to 10^6 Hz) is employed to study
the molecular dynamics of poly(dimethylsiloxane) (PDMS, Mw=1.7 10^5 g/mol and
Mw=9.6 10^4 g/mol as grafted films with thicknesses d below and above the
radius of gyration Rg. For d smaller than Rg the molecular dynamics becomes
faster by up to three orders of magnitude with respect to the bulk resulting in
a pronounced decrease of the Vogel temperature T0 and hence the calorimetric
glass transition temperature Tg. For d larger than Rg the molecular dynamics is
comparable to that of the bulk melt. The results are interpreted in terms of a
chain confinement effect and compared with the findings for low molecular eight
glass forming liquids contained in nanoporous glasses and zeolites.
Crystallization effects - well known for PDMS - are observed for films of
thicknesses above and below Rg.Comment: 20 pages, 4 figure
The ground state energy of the Edwards-Anderson spin glass model with a parallel tempering Monte Carlo algorithm
We study the efficiency of parallel tempering Monte Carlo technique for
calculating true ground states of the Edwards-Anderson spin glass model.
Bimodal and Gaussian bond distributions were considered in two and
three-dimensional lattices. By a systematic analysis we find a simple formula
to estimate the values of the parameters needed in the algorithm to find the GS
with a fixed average probability. We also study the performance of the
algorithm for single samples, quantifying the difference between samples where
the GS is hard, or easy, to find. The GS energies we obtain are in good
agreement with the values found in the literature. Our results show that the
performance of the parallel tempering technique is comparable to more powerful
heuristics developed to find the ground state of Ising spin glass systems.Comment: 30 pages, 17 figures. A new section added. Accepted for publication
in Physica
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A Universal Live Cell Barcoding-Platform for Multiplexed Human Single Cell Analysis.
Single-cell barcoding enables the combined processing and acquisition of multiple individual samples as one. This maximizes assay efficiency and eliminates technical variability in both sample preparation and analysis. Remaining challenges are the barcoding of live, unprocessed cells to increase downstream assay performance combined with the flexibility of the approach towards a broad range of cell types. To that end, we developed a novel antibody-based platform that allows the robust barcoding of live human cells for mass cytometry (CyTOF). By targeting both the MHC class I complex (beta-2-microglobulin) and a broadly expressed sodium-potassium ATPase-subunit (CD298) with platinum-conjugated antibodies, human immune cells, stem cells as well as tumor cells could be multiplexed in the same single-cell assay. In addition, we present a novel palladium-based covalent viability reagent compatible with this barcoding strategy. Altogether, this platform enables mass cytometry-based, live-cell barcoding across a multitude of human sample types and provides a scheme for multiplexed barcoding of human single-cell assays in general
No spin-glass transition in the "mobile-bond" model
The recently introduced ``mobile-bond'' model for two-dimensional spin
glasses is studied. The model is characterized by an annealing temperature T_q.
On the basis of Monte Carlo simulations of small systems it has been claimed
that this model exhibits a non-trivial spin-glass transition at finite
temperature for small values of T_q.
Here the model is studied by means of exact ground-state calculations of
large systems up to N=256^2. The scaling of domain-wall energies is
investigated as a function of the system size. For small values T_q<0.95 the
system behaves like a (gauge-transformed) ferromagnet having a small fraction
of frustrated plaquettes. For T_q>=0.95 the system behaves like the standard
two-dimensional +-J spin-glass, i.e. it does NOT exhibit a phase transition at
T>0.Comment: 4 pages, 5 figures, RevTe
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