572 research outputs found
The Mt John University Observatory Search For Earth-mass Planets In The Habitable Zone Of Alpha Centauri
The "holy grail" in planet hunting is the detection of an Earth-analog: a
planet with similar mass as the Earth and an orbit inside the habitable zone.
If we can find such an Earth-analog around one of the stars in the immediate
solar neighborhood, we could potentially even study it in such great detail to
address the question of its potential habitability. Several groups have focused
their planet detection efforts on the nearest stars. Our team is currently
performing an intensive observing campaign on the alpha Centauri system using
the Hercules spectrograph at the 1-m McLellan telescope at Mt John University
Observatory (MJUO) in New Zealand. The goal of our project is to obtain such a
large number of radial velocity measurements with sufficiently high temporal
sampling to become sensitive to signals of Earth-mass planets in the habitable
zones of the two stars in this binary system. Over the past years, we have
collected more than 45,000 spectra for both stars combined. These data are
currently processed by an advanced version of our radial velocity reduction
pipeline, which eliminates the effect of spectral cross-contamination. Here we
present simulations of the expected detection sensitivity to low-mass planets
in the habitable zone by the Hercules program for various noise levels. We also
discuss our expected sensitivity to the purported Earth-mass planet in an
3.24-d orbit announced by Dumusque et al.~(2012).Comment: 16 pages, 7 figures, accepted for publication in the International
Journal of Astrobiolog
Spectral properties of the Dirichlet-to-Neumann operator for exterior Helmholtz problem and its applications to scattering theory
We prove that the Dirichlet-to-Neumann operator (DtN) has no spectrum in the
lower half of the complex plane. We find several application of this fact in
scattering by obstacles with impedance boundary conditions. In particular, we
find an upper bound for the gradient of the scattering amplitude and for the
total cross section. We justify numerical approximations by providing bounds on
difference between theoretical and approximated solutions without using any a
priory unknown constants
Trapped ions in optical lattices for probing oscillator chain models
We show that a chain of trapped ions embedded in microtraps generated by an
optical lattice can be used to study oscillator models related to dry friction
and energy transport. Numerical calculations with realistic experimental
parameters demonstrate that both static and dynamic properties of the ion chain
change significantly as the optical lattice power is varied. Finally, we lay
out an experimental scheme to use the spin degree of freedom to probe the phase
space structure and quantum critical behavior of the ion chain
Timber gridshells: beyond the drawing board
In March 2011, a week-long workshop that invited participation from all architecture and architectural technology students at Sheffield Hallam University, UK was organised with the objective of enhancing students’ thinking and experience by construction thinking. It was aimed at creating a sense of realness to realise a design project collectively. Timber was set as the material of exploration. The students had to make use of bending to design and create a timber gridshell structure. This made use of a quality traditionally felt to be a structural weakness of the material. To do this, students form-found non-mathematically and non-digitally using paper gridmats. This paper describes the aims, activity and outcome of the timber gridshell workshop as a way of preparing architects and technologists of the future and introducing the challenges of architectural design in terms of economics and
construction process, aesthetics, effective communication and structural intuition by working with a given material –
all important aspects in achieving effective architecture
Time-resolved single-particle x-ray scattering reveals electron-density as coherent plasmonic-nanoparticle-oscillation source
Dynamics of optically-excited plasmonic nanoparticles are presently
understood as a series of sequential scattering events, involving
thermalization processes after pulsed optical excitation. One important step is
the initiation of nanoparticle breathing oscillations. According to established
experiments and models, these are caused by the statistical heat transfer from
thermalized electrons to the lattice. An additional contribution by hot
electron pressure has to be included to account for phase mismatches that arise
from the lack of experimental data on the breathing onset. We used optical
transient-absorption spectroscopy and time-resolved single-particle
x-ray-diffractive imaging to access the excited electron system and lattice.
The time-resolved single-particle imaging data provided structural information
directly on the onset of the breathing oscillation and confirmed the need for
an additional excitation mechanism to thermal expansion, while the observed
phase-dependence of the combined structural and optical data contrasted
previous studies. Therefore, we developed a new model that reproduces all our
experimental observations without using fit parameters. We identified
optically-induced electron density gradients as the main driving source.Comment: 32 pages, 5 figures, 1 supporting information document include
Local Detection of Quantum Correlations with a Single Trapped Ion
As one of the most striking features of quantum mechanics, quantum
correlations are at the heart of quantum information science. Detection of
correlations usually requires access to all the correlated subsystems. However,
in many realistic scenarios this is not feasible since only some of the
subsystems can be controlled and measured. Such cases can be treated as open
quantum systems interacting with an inaccessible environment. Initial
system-environment correlations play a fundamental role for the dynamics of
open quantum systems. Following a recent proposal, we exploit the impact of the
correlations on the open-system dynamics to detect system-environment quantum
correlations without accessing the environment. We use two degrees of freedom
of a trapped ion to model an open system and its environment. The present
method does not require any assumptions about the environment, the interaction
or the initial state and therefore provides a versatile tool for the study of
quantum systems.Comment: 6 Pages, 5 Figures + 6 Pages, 1 Figure of Supplementary Materia
Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-Ray Absorption, Emission, and Photoelectron Spectroscopies
Electronic structure of nickel nanoparticles encapsulated in carbon was
characterized by photoelectron, X-ray absorption, and X-ray emission
spectroscopies. Experimental spectra are compared with the density of states
calculated in the frame of the density functional theory. The carbon shell of
Ni nanoparticles has been found to be multilayer graphene with significant
(about 6%) amount of Stone--Wales defects. Results of the experiments evidence
protection of the metallic nanoparticles from the environmental degradation by
providing a barrier against oxidation at least for two years. Exposure in air
for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles
with coverage of functional groups.Comment: 16 pages, 6 figures, accepted in J. Phys. Chem.
DEAR project: Lunar dust surface interactions, risk and removal investigations
The DEAR project (Dusty Environment Application Research) investigates the interaction between lunar regolith and surfaces and components relevant for lunar exploration. Based on the TUBS regolith simulant which is representative in chemistry, size and shape properties to Moon soils to study the regolith transport, adhesion and strategies for cleaning. The regolith simulant will be applied to thermal, structural, optical sensor, sealing and other astronautic systems, providing input for requirements, justification and verification. The key applications are split in human space flight regolith investigations, wrinkled surface with random movement and hardware surfaces, flat material defined movement. The paper provides an overview of the DEAR project including a discussion of the first results, in particular vibration, shock and micro-vibration on regolith bearing surfaces. The investigation shall enable better understand the regolith layers interaction and the release mechanism, as well as potential cross contamination and cleaning strategies. The research is complemented by simulation of the regolith motion as parameter surface plasma interactions. The project is funded and supported by the European Space Agency (ESA). DEAR specifically addresses the development and testing of lunar dust removal strategies on optics, mechanisms and human space flight hardware (e.g., space suits). As the Moons regolith is known to be highly abrasive, electrically chargeable, and potentially chemically reactive, lunar dust might reduce the performance of hardware, such as cameras, thermal control surfaces and solar cells. The dust can cause malfunction on seals for on/off mechanisms or space suits. Of particular interest are risk assessment, avoidance, and cleaning techniques such as the use of electric fields to remove lunar dust from surfaces. Representative dust (e.g., regolith analogues of interesting landing sites) will be used in a dedicated test setup to evaluate risks and effects of lunar dust. We describe designs and methods developed by the DEAR consortium to deal with the regolith-related issues, in particular an electrode design to deflect regolith particles, cleaning of astronautical systems with CO2, design of a robotic arm for the testing within the DEAR chamber, regolith removal via shock, and regolith interaction with cleanroom textile
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