15,716 research outputs found
Influence of clamp-widening on the quality factor of nanomechanical silicon nitride resonators
Nanomechanical resonators based on strained silicon nitride (SiN)
have received a large amount of attention in fields such as sensing and quantum
optomechanics due to their exceptionally high quality factors (s).
Room-temperature s approaching 1 billion are now in reach by means of
phononic crystals (soft-clamping) and strain engineering. Despite great
progress in enhancing s, difficulties in fabrication of soft-clamped samples
limits their implementation into actual devices. An alternative means of
achieving ultra-high s was shown using trampoline resonators with engineered
clamps, which serves to localize the stress to the center of the resonator,
while minimizing stress at the clamping. The effectiveness of this approach has
since come into question from recent studies employing string resonators with
clamp-tapering. Here, we investigate this idea using nanomechanical string
resonators with engineered clampings similar to those presented for
trampolines. Importantly, the effect of orienting the strings diagonally or
perpendicularly with respect to the silicon frame is investigated. It is found
that increasing the clamp width for diagonal strings slightly increases the
s of the fundamental out-of-plane mode at small radii, while perpendicular
strings only deteriorate with increasing clamp width. Measured s agree well
with finite element method simulations even for higher-order resonances. The
small increase cannot account for previously reported s of trampoline
resonators. Instead, we propose the effect to be intrinsic and related to
surface and radiation losses.Comment: 7 pages, 4 figure
Final project report: EEC 2092/91 (ORGANIC) Revision
This report summarises the findings of the project that have been presented in a number of separate reports and publications. In the Chapters 2 to 5 the approach, results and conclusions of the project are summarised, following the structure of the different work packages. Chapter 2 summarises the work on ethical values of organic agriculture. Chapter 3 looks at the differences in the implementation of Regulation (EEC) 2092/91 across Europe and compares the European Regulation with international standards. Chapters 4 and 5 summarise the findings that relate to reducing the dependency on non-organic inputs in the case of feed and seed.
The final Chapter 6 consolidates the recommendations of the whole project arising from the various different work packages in one place. Recommendations are aimed in particular at the second stage of the ongoing revision process of the European Regulation, the transfer of the detailed rules from the Annexes of the Regulation (EEC) 2092/91 that is expected to start after the completion of the project. Further recommendations for standard setting bodies, regulators and research recommendations are also presented.
The overall objective of the project was to provide recommendations for the revision and further development of the Regulation (EEC) 2092/91 and other standards for organic agriculture, broken down into a number of specific objectives that resulted in 12 seperate reports.
The basic ethical values and value differences of organic agriculture in Europe was identified through stakeholder consultation (D 2.1) and through literature as part of developing a procedure for balancing and integrating the basic values in developments of EU regulation (D 2.3).
Organic standards from national and private organisations in Europe were compared with the EU regulation with help of database (www.organicrules.org) and differences were analysed to give recommendations on further harmonisation of the EU regulation (D 3.2).
The knowledge on how to achieve 100 % organic rations in diets for livestock was expanded through a meta-analysis of literature and an overview of the current situation to characterise the availability of protein sources for 100% organic diets for pigs and poultry was produced (D 4.1 part 1 and 2). Criteria for use of organic inputs, evaluation criteria for Annex II C: Feed materials and Annex II D: Dietary supplements of Regulation (EEC) 2092/91 were developed (D. 4.2). A guide for operators was developed (D 4.3).
The knowledge on how to reduce the use of non-organic seed and vegetative propagation materials was improved through reports on seed borne diseases in organic seed and propagation material (D 5.1), on the importance of quality characterising in organic seed and propagation material (D 5.2) and analysis of national derogation regimes (D 5.3).
The project produced 12 reports, 7 scientific publications in peer-reviewed journals, and a project web-page at www.organic-revision.org where all reports and further documents are available. It organised 3 workshops with stakeholders and had ongoing communication with the Unit on Organic Farming in DG Agriculture responsible for the Organic Regulation. Members of the team produced in total more than 250 dissemination items
REDO RSVP: Efficient Signalling for Multimedia in the Internet
Alarming reports of performance and scalability problems associated with per-flow reservations, have led many to lose belief in RSVP and the Integrated Services Architecture that relies on it. Because we are convinced of the need for some form of resource reservation, to support multimedia communications in the Internet, we have set about trying to improve RSVP. By careful study of the protocol, we have identified areas for improvement, and propose REDO RSVP, a reduced overhead version that includes a fast establishment mechanism (FEM). In this paper we describe the rationale for REDO RSVP and present a detailed analysis of its features and operations. We also analyse REDO RSVP by means of simulations, and show that it offers improvements to the performance of RSVP
Mesoscopic magnetoelectric effect in chaotic quantum dots
The magnitude of the inverse Faraday effect (IFE), a static magnetization due
to an ac electric field, can be strongly increased in a mesoscopic sample,
sensitive to time-reversal symmetry (TRS) breaking. Random rectification of ac
voltages leads to a magnetization flux, which can be detected by an asymmetry
of Hall resistances in a multi-terminal setup. In the absence of applied
magnetic field through a chaotic quantum dot the IFE scale, quadratic in
voltage, is found as an analytic function of the ac frequency, screening, and
coupling to the contacts and floating probes, and numerically it does not show
any effect of spin-orbit interaction. Our results qualitatively agree with a
recent experiment on TRS-breaking in a six-terminal Hall cross.Comment: 4+ pages, 2 figures; v2-published version, small change
Giant enhancement of hydrodynamically enforced entropic trapping in thin channels
Using our generalized Fick-Jacobs approach [Martens et al., PRL 110, 010601
(2013); Martens et al., Eur. Phys. J. Spec. Topics 222, 2453-2463 (2013)] and
extensive Brownian dynamics simulations, we study particle transport through
three-dimensional periodic channels of different height. Directed motion is
caused by the interplay of constant bias acting along the channel axis and a
pressure-driven flow. The tremendous change of the flow profile shape in
channel direction with the channel height is reflected in a crucial dependence
of the mean particle velocity and the effective diffusion coefficient on the
channel height. In particular, we observe a giant suppression of the effective
diffusivity in thin channels; four orders of magnitude compared to the bulk
value.Comment: 16 pages, 8 figure
Hydrodynamically enforced entropic trapping of Brownian particles
We study the transport of Brownian particles through a corrugated channel
caused by a force field containing curl-free (scalar potential) and
divergence-free (vector potential) parts. We develop a generalized Fick-Jacobs
approach leading to an effective one-dimensional description involving the
potential of mean force. As an application, the interplay of a pressure-driven
flow and an oppositely oriented constant bias is considered. We show that for
certain parameters, the particle diffusion is significantly suppressed via the
property of hyrodynamically enforced entropic particle trapping.Comment: 5 pages, 4 figures, in press with Physical Review Letter
Negative frequency tuning of a carbon nanotube nano-electromechanical resonator
A suspended, doubly clamped single wall carbon nanotube is characterized as
driven nano-electromechanical resonator at cryogenic temperatures.
Electronically, the carbon nanotube displays small bandgap behaviour with
Coulomb blockade oscillations in electron conduction and transparent contacts
in hole conduction. We observe the driven mechanical resonance in dc-transport,
including multiple higher harmonic responses. The data shows a distinct
negative frequency tuning at finite applied gate voltage, enabling us to
electrostatically decrease the resonance frequency to 75% of its maximum value.
This is consistently explained via electrostatic softening of the mechanical
mode.Comment: 4 pages, 4 figures; submitted for the IWEPNM 2013 conference
proceeding
Cytosol- and clathrin-dependent stimulation of endocytosis in vitro by purified adaptors.
Using stage-specific assays for receptor-mediated endocytosis of transferrin (Tfn) into perforated A431 cells we show that purified adaptors stimulate coated pit assembly and ligand sequestration into deeply invaginated coated pits. Late events in endocytosis involving membrane fission and coated vesicle budding which lead to the internalization of Tfn are unaffected. AP2, plasma membrane adaptors, are active at physiological concentrations, whereas AP1, Golgi adaptors, are inactive. Adaptor-dependent stimulation of Tfn sequestration requires cytosolic clathrin, but is unaffected by clathrin purified from coated vesicles suggesting that soluble and assembled clathrin pools are functionally distinct. In addition to adaptors and cytosolic clathrin other, as yet unidentified, cytosolic factors are also required for efficient coated pit invagination. These results provide new insight into the mechanisms and regulation of coated pit assembly and invagination
Entropic particle transport: higher order corrections to the Fick-Jacobs diffusion equation
Transport of point-size Brownian particles under the influence of a constant
and uniform force field through a three-dimensional channel with smoothly
varying periodic cross-section is investigated. Here, we employ an asymptotic
analysis in the ratio between the difference of the widest and the most narrow
constriction divided through the period length of the channel geometry. We
demonstrate that the leading order term is equivalent to the Fick-Jacobs
approximation. By use of the higher order corrections to the probability
density we derive an expression for the spatially dependent diffusion
coefficient D(x) which substitutes the constant diffusion coefficient present
in the common Fick-Jacobs equation. In addition, we show that in the diffusion
dominated regime the average transport velocity is obtained as the product of
the zeroth-order Fick-Jacobs result and the expectation value of the spatially
dependent diffusion coefficient . The analytic findings are corroborated
with the precise numerical results of a finite element calculation of the
Smoluchowski diffusive particle dynamics occurring in a reflection symmetric
sinusoidal-shaped channel.Comment: 9 pages, 3 figure
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