788 research outputs found
On the structure of thin4He films on solid hydrogen
We have investigated the adsorption of4He onto a quench-condensed H2 film by means of surface state electrons. Oscillations in the surface state electron conductivity clearly reveal the layerwise character of the adsorption. At temperatures below 2K we have observed an anomaly in the conductivity around the completion of the first monolayer. This new feature is interpreted as an indication of a liquid-to-solid phase transition in the first layer
Donor coordination for effective government policies? Implementation of the new aid effectiveness agenda in health and education in Zambia
There is a growing interest in the debate on aid effectiveness for assessing the impact of aid not only on economic growth and poverty reduction, but also on intermediate outcomes such as health and education. This paper reviews evidence from recent in-depth country work on the impact of government policies and service provision in health and basic education in Zambia, and examines to what extent new aid approaches have contributed to the observed outcomes. It finds that limited coordination and lax adherence to good aid principles undermine the effectiveness of these approaches. The discussion of the findings sheds light on the underlying political economy and incentive structures on both sides of the aid relation that lead to casual adherence to the principles for more effective aid in these new aid approaches. It argues that most of the observed coordination failures can be explained by collective action problems on the part of both donors and recipients. If the international aid effectiveness agenda is to move forward, it will have to devise adequate mechanisms to address these coordination disincentives
Possible correlation effects of surface state electrons on a solid hydrogen film
We have investigated the transport properties of surface state electrons on thin quench-condensed hydrogen films for various electron densities. The surface state electron mobility showed a continuous dependence on the plasma parameter Gamma in the range from 20 to 130, indicating a strong influence of correlation effects within the electron system for all measured values of Gamma
Step roughness on Ag(111) investigated by STM: a systematic study of tip influence
We have investigated monatomic steps on Ag(111) by STM at different temperatures. At room temperature, the rough appearance of these steps is usually attributed to thermal step fluctuations. We have investigated the influence of the tip systematically. Applying a new test, we demonstrate that even subtle influences can lead to wrong results in statistical analysis
A simple, ultrahigh vacuum compatible scanning tunneling microscope for use at variable temperatures
We present the construction of a very compact scanning tunneling microscope (STM) which can be operated at temperatures between 4 and 350 K. The tip and a tiny tip holder are the only movable parts, whereas the sample and the piezoscanner are rigidly attached to the body of the STM. This leads to an excellent mechanical stability. The coarse approach system relies on the slip-stick principle and is operated by the same piezotube which is used for scanning. As an example of the performance of the device, images of a NbSe2 surface with atomic resolution are obtained
Dynamics of fine particles due to quantized vortices on the surface of superfluid He
Peculiar dynamics of a free surface of the superfluid 4He has been observed
experimentally with a newly established technique utilizing a number of
electrically charged fine metal particles trapped electrically at the surface
by Moroshkin et al. They have reported that some portion of the particles
exhibit some irregular motions and suggested the existence of quantized
vortices interacting with the metal particles. We have conducted calculations
with the vortex filament model, which turns out to support the idea of the
vortex-particle interactions. The observed anomalous metal particle motions are
roughly categorized into two types; (1) circular motions with specific
frequencies, and (2) quasi-linear oscillations. The former ones seem to be
explained once we consider a vertical vortex filament whose edges are
terminated at the bottom and at a particle trapped at the surface. Although it
is not yet clear whether all the anomalous motions are due to the quantum
vortices, the vortices seem to play important roles for the motions.Comment: 7 pages, 10 figure
Dynamics of the vortex-particle complexes bound to the free surface of superfluid helium
We present an experimental and theoretical study of the 2D dynamics of
electrically charged nanoparticles trapped under a free surface of superfluid
helium in a static vertical electric field. We focus on the dynamics of
particles driven by the interaction with quantized vortices terminating at the
free surface. We identify two types of particle trajectories and the associated
vortex structures: vertical linear vortices pinned at the bottom of the
container and half-ring vortices travelling along the free surface of the
liquid
On ultrafast magnetic flux dendrite propagation into thin superconducting films
We suggest a new theoretical approach describing the velocity of magnetic
flux dendrite penetration into thin superconducting films. The key assumptions
for this approach are based upon experimental observations. We treat a dendrite
tip motion as a propagating flux jump instability. Two different regimes of
dendrite propagation are found. A fast initial stage is followed by a slow
stage, which sets in as soon as a dendrite enters into the vortex-free region.
We find that the dendrite velocity is inversely proportional to the sample
thickness. The theoretical results and experimental data obtained by a
magneto-optic pump-probe technique are compared and excellent agreement between
the calculations and measurements is found.Comment: 4 pages, 4 figure
Lane reduction in driven 2d-colloidal systems through microchannels
The transport behavior of a system of gravitationally driven colloidal
particles is investigated. The particle interactions are determined by the
superparamagnetic behavior of the particles. They can thus be arranged in a
crystalline order by application of an external magnetic field. Therefore the
motion of the particles through a narrow channel occurs in well-defined lanes.
The arrangement of the particles is perturbed by diffusion and the motion
induced by gravity. Due to these combined influences a density gradient forms
along the direction of motion of the particles. A reconfiguration of the
crystal is observed leading to a reduction of the number of lanes. In the
course of the lane reduction transition a local melting of the
quasi-crystalline phase to a disordered phase and a subsequent crystallization
along the motion of the particles is observed. This transition is characterized
experimentally and using Brownian dynamics (BD) simulations.Comment: 4 pages, 4 figure
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