Polymer simulation by means of tree data-structures and a parsimonious Metropolis algorithm

We show how a Monte Carlo method for generating self-avoiding walks on lattice geometries which employs a binary-tree data structure can be adapted for hard-sphere polymers with continuous degrees of freedom. Data suggests that the time per Monte Carlo move scales logarithmically with polymer size. We combine the method with a variant of the Metropolis algorithm and preserve this scaling for Lennard-Jones polymers with untruncated monomer-monomer interaction. We further show how the replica-exchange method can be adapted for the same purpose.Comment: 10 pages, 10 figure

Advanced multicanonical Monte Carlo methods for efficient simulations of nucleation processes of polymers

The investigation of freezing transitions of single polymers is computationally demanding, since surface effects dominate the nucleation process. In recent studies we have systematically shown that the freezing properties of flexible, elastic polymers depend on the precise chain length. Performing multicanonical Monte Carlo simulations, we faced several computational challenges in connection with liquid-solid and solid-solid transitions. For this reason, we developed novel methods and update strategies to overcome the arising problems. We introduce novel Monte Carlo moves and two extensions to the multicanonical method.Comment: 10 pages, 11 figure

Different Kinds of Protein Folding Identified with a Coarse-Grained Heteropolymer Model

Applying multicanonical simulations we investigated folding properties of off-lattice heteropolymers employing a mesoscopic hydrophobic-polar model. We study for various sequences folding channels in the free-energy landscape by comparing the equilibrium conformations with the folded state in terms of an angular overlap parameter. Although all investigated heteropolymer sequences contain the same content of hydrophobic and polar monomers, our analysis of the folding channels reveals a variety of characteristic folding behaviors known from realistic peptides.Comment: 3 pages, 2 figure

Identification of Characteristic Protein Folding Channels in a Coarse-Grained Hydrophobic-Polar Peptide Model

Folding channels and free-energy landscapes of hydrophobic-polar heteropolymers are discussed on the basis of a minimalistic off-lattice coarse-grained model. We investigate how rearrangements of hydrophobic and polar monomers in a heteropolymer sequence lead to completely different folding behaviors. Studying three exemplified sequences with the same content of hydrophobic and polar residues, we can reproduce within this simple model two-state folding, folding through intermediates, as well as metastability.Comment: 26 pages, 6 figure

High-bandwidth squeezed light at 1550 nm from a compact monolithic PPKTP cavity

We report the generation of squeezed vacuum states of light at 1550 nm with a broadband quantum noise reduction of up to 4.8 dB ranging from 5 MHz to 1.2 GHz sideband frequency. We used a custom-designed 2.6 mm long biconvex periodically-poled potassium titanyl phosphate (PPKTP) crystal. It featured reflectively coated end surfaces, 2.26 GHz of linewidth and generated the squeezing via optical parametric amplification. Two homodyne detectors with different quantum efficiencies and bandwidths were used to characterize the non-classical noise suppression. We measured squeezing values of up to 4.8 dB from 5 to 100 MHz and up to 3 dB from 100 MHz to 1.2 GHz. The squeezed vacuum measurements were limited by detection loss. We propose an improved detection scheme to measure up to 10 dB squeezing over 1 GHz. Our results of GHz bandwidth squeezed light generation provide new prospects for high-speed quantum key distribution.Comment: 8 pages, 4 figure

Collective bargaining structure and its determinants : an empirical analysis with British and German establishment data

"Using two nationally representative establishment data sets, this paper investigates collective bargaining coverage and firms' choice of governance structures for the employment relationship in Britain and in (western and eastern) Germany. Both countries have experienced a substantial decline in collective bargaining coverage in the last decades. While bargaining coverage is generally lower in Britain, single-employer bargaining is relatively more important in Britain, whereas multi-employer collective bargaining clearly dominates in Germany. Econometric analyses show that more or less the same set of variables play a statistically significant role in explaining the structure of collective bargaining in both countries. These include establishment size, establishment age, foreign ownership, public sector affiliation and being a branch plant." (Author's abstract, IAB-Doku) ((en))Tarifverhandlungen - internationaler Vergleich, Tarifautonomie, Tarifpartner, Tarifbindung, Tarifverhandlungen - Determinanten, Betriebsvereinbarung, Flächentarifvertrag, Dezentralisation, IAB-Betriebspanel, Unternehmensgröße, Betriebsgröße, Wirtschaftszweige, Arbeitsbeziehungen, Unternehmenspolitik, Unternehmensführung, Unternehmensalter, öffentlicher Dienst, ausländische Arbeitgeber, regionaler Vergleich, Firmentarifvertrag, Tarifbindung, Bundesrepublik Deutschland, Großbritannien, Ostdeutschland, Westdeutschland

Reforming Social Welfare in Germany: An Applied General Equilibrium Analysis

This paper analyses the effects of a social assistance reform in Germany. In contrast to studies which are based on microsimulation methods we use a computable general equilibrium model which incorporates a discrete choice model of labour supply to simulate a variety of reform scenarios. The main contribution is that we are able to identify general equilibrium effects of a reform on wages and unemployment. The simulation results show that general equilibrium wage reactions tend to mitigate labour supply effects. Moreover, the simulations indicate that substantial employment effects are to be expected only from major cuts in welfare payments. --social assistance,discrete labour supply model,applied general equilibrium

Gaussian entanglement distribution with gigahertz bandwidth

The distribution of entanglement with Gaussian statistic can be used to generate a mathematically-proven secure key for quantum cryptography. The distributed secret key rate is limited by the {entanglement strength, the entanglement bandwidth and the bandwidth of the photo-electric detectors}. The development of a source for strongly, bi-partite entangled light with high bandwidth promises an increased measurement speed and a linear boost in the secure data rate. Here, we present the experimental realization of a Gaussian entanglement source with a bandwidth of more than 1.25\,GHz. The entanglement spectrum was measured with balanced homodyne detectors and was quantified via the inseparability criterion introduced by Duan and coworkers with a critical value of 4 below which entanglement is certified. Our measurements yielded an inseparability value of about 1.8 at a frequency of 300\,MHz to about 2.8 at 1.2\,GHz extending further to about 3.1 at 1.48\,GHz. In the experiment we used two 2.6\,mm long monolithic periodically poled potassium titanyl phosphate (PPKTP) resonators to generate two squeezed fields at the telecommunication wavelength of 1550\,nm. Our result proves the possibility of generating and detecting strong continuous-variable entanglement with high speed.Comment: 5 pages, 3 figures, published in Optics Letter

Elastic Lennard-Jones Polymers Meet Clusters -- Differences and Similarities

We investigate solid-solid and solid-liquid transitions of elastic flexible off-lattice polymers with Lennard-Jones monomer-monomer interaction and anharmonic springs by means of sophisticated variants of multicanonical Monte Carlo methods. We find that the low-temperature behavior depends strongly and non-monotonically on the system size and exhibits broad similarities to unbound atomic clusters. Particular emphasis is dedicated to the classification of icosahedral and non-icosahedral low-energy polymer morphologies.Comment: 9 pages, 17 figure

Two-State Folding, Folding through Intermediates, and Metastability in a Minimalistic Hydrophobic-Polar Model for Proteins

Within the frame of an effective, coarse-grained hydrophobic-polar protein model, we employ multicanonical Monte Carlo simulations to investigate free-energy landscapes and folding channels of exemplified heteropolymer sequences, which are permutations of each other. Despite the simplicity of the model, the knowledge of the free-energy landscape in dependence of a suitable system order parameter enables us to reveal complex folding characteristics known from real bioproteins and synthetic peptides, such as two-state folding, folding through weakly stable intermediates, and glassy metastability.Comment: 10 pages, 1 figur