20,535 research outputs found
Monte Carlo simulations of copolymers at homopolymer interfaces: Interfacial structure as a function of the copolymer density
By means of extensive Monte Carlo simulations of the bond fluctuation model,
we study the effect of adding AB diblock copolymers on the properties of an
interface between demixed homopolymer phases. The parameters are chosen such
that the homopolymers are strongly segregated, and the whole range of copolymer
concentrations in the two phase coexistence region is scanned. We compare the
``mushroom'' regime, in which copolymers are diluted and do not interact with
each other, with the ``wet brush'' regime, where copolymers overlap and
stretch, but are still swollen by the homopolymers. A ``dry brush'' regime is
never entered for our choice of chain lengths. ``Intrinsic'' profiles are
calculated using a block analysis method introduced by us in earlier work. We
discuss density profiles, orientational profiles and contact number profiles.
In general, the features of the profiles are similar at all copolymer
concentrations, however, the profiles in the concentrated regime are much
broader than in the dilute regime. The results compare well with
self-consistent field calculations.Comment: to appear in J. Chem. Phy
Organic Farming Research Support and Research Priorities in the European Union
Support for Organic Farming focused research has increased significantly in successive EU research funding frameworks. This is in line with constantly increasing consumer demand for organic foods over the last 20 years, which has accelerated again over the last 2 years in many European countries, including new member states.
Under the 7th Framework Programme (FP7), the expected new increase of funds for organic farming could significantly decrease, even below the levels made available under the 5th Framework Programme (FP5). Most of the project topics listed focus on the development of methods for economic analyses of Organic Farming and/or follow a very “reductionist” one problem - one potential solution approach.
On the other side, as there is no clear instruments to establish priorities in research programmes at European level. The IFOAM EU Group has developed a consultation process to set organic farming sector priorities, which could be used as a model to set research priorities in the future.
This paper also presents a first assessment of the EU support to organic farming research, reviewing main achievements in organic food production systems research and proposing some changes in the current 7th Framework Programme
Chemical ordering and composition fluctuations at the (001) surface of the Fe-Ni Invar alloy
We report on a study of (001) oriented fcc Fe-Ni alloy surfaces which
combines first-principles calculations and low-temperature STM experiments.
Density functional theory calculations show that Fe-Ni alloy surfaces are
buckled with the Fe atoms slightly shifted outwards and the Ni atoms inwards.
This is consistent with the observation that the atoms in the surface layer can
be chemically distinguished in the STM image: brighter spots (corrugation
maxima with increased apparent height) indicate iron atoms, darker ones nickel
atoms. This chemical contrast reveals a c2x2 chemical order (50% Fe) with
frequent Fe-rich defects on Invar alloy surface. The calculations also indicate
that subsurface composition fluctuations may additionally modulate the apparent
height of the surface atoms. The STM images show that this effect is pronounced
compared to the surfaces of other disordered alloys, which suggests that some
chemical order and corresponding concentration fluctuations exist also in the
subsurface layers of Invar alloy. In addition, detailed electronic structure
calculations allow us to identify the nature of a distinct peak below the Fermi
level observed in the tunneling spectra. This peak corresponds to a surface
resonance band which is particularly pronounced in iron-rich surface regions
and provides a second type of chemical contrast with less spatial resolution
but one that is essentially independent of the subsurface composition.Comment: 7 pages, 5 figure
Consistent SDNs through Network State Fuzzing
The conventional wisdom is that a software-defined network (SDN) operates under the premise that the logically centralized control plane has an accurate representation of the actual data plane state. Nevertheless, bugs, misconfigurations, faults or attacks can introduce inconsistencies that undermine correct operation. Previous work in this area, however, lacks a holistic methodology to tackle this problem and thus, addresses only certain parts of the problem. Yet, the consistency of the overall system is only as good as its least consistent part. Motivated by an analogy of network consistency checking with program testing, we propose to add active probe-based network state fuzzing to our consistency check repertoire. Hereby, our system, PAZZ, combines production traffic with active probes to continuously test if the actual forwarding path and decision elements (on the data plane) correspond to the expected ones (on the control plane). Our insight is that active traffic covers the inconsistency cases beyond the ones identified by passive traffic. PAZZ prototype was built and evaluated on topologies of varying scale and complexity. Our results show that PAZZ requires minimal network resources to detect persistent data plane faults through fuzzing and localize them quickly
Device for in-situ cleaving of hard crystals
Cleaving crystals in a vacuum chamber is a simple method for obtaining
atomically flat and clean surfaces for materials that have a preferential
cleaving plane. Most in-situ cleavers use parallel cutting edges that are
applied from two sides on the sample. We found in ambient experiments that
diagonal cutting pliers, where the cleavage force is introduced in a single
point instead of a line work very well also for hard materials. Here, we
incorporate the diagonal cutting plier principle in a design compatible with
ultra-high vacuum requirements. We show optical microscopy (mm scale) and
atomic force microscopy (atomic scale) images of NiO(001) surfaces cleaved with
this device.Comment: 7 pages, 3 figures Submitted to Review of Scientific Instruments
(2005
The "peace movement" in the Federal Republic of Germany : sociological scope, structure, motivations and problem of control
Thermal Fluctuations in a Lamellar Phase of a Binary Amphiphile-Solvent Mixture: A Molecular Dynamics Study
We investigate thermal fluctuations in a smectic A phase of an
amphiphile-solvent mixture with molecular dynamics simulations. We use an
idealized model system, where solvent particles are represented by simple
beads, and amphiphiles by bead-and-spring tetramers. At a solvent bead fraction
of 20 % and sufficiently low temperature, the amphiphiles self-assemble into a
highly oriented lamellar phase. Our study aims at comparing the structure of
this phase with the predictions of the elastic theory of thermally fluctuating
fluid membrane stacks [Lei et al., J. Phys. II 5, 1155 (1995)]. We suggest a
method which permits to calculate the bending rigidity and compressibility
modulus of the lamellar stack from the simulation data. The simulation results
are in reasonable agreement with the theory
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