230 research outputs found
Realization of a monolithic high-reflectivity cavity mirror from a single silicon crystal
We report on the first experimental realization of a high-reflectivity cavity
mirror that solely consists of a single silicon crystal. Since no material was
added to the crystal, the urgent problem of 'coating thermal noise' that
currently limits classical as well as quantum measurements is avoided. Our
mirror is based on a surface nanostructure that creates a resonant surface
waveguide. In full agreement with a rigorous model we realized a reflectivity
of (99.79+/-0.01)% at a wavelength of 1.55 {\mu}m, and achieved a cavity
finesse of 2784. We anticipate that our achievement will open the avenue to
next generation high-precision experiments targeting fundamental questions of
physics.Comment: Phys. Rev. Lett., accepte
The reference frames of Mercury after MESSENGER
We report on recent refinements and the current status for the rotational
state models and the reference frame of the planet Mercury. We summarize the
performed measurements of Mercury rotation based on terrestrial radar
observations as well as data from the Mariner 10 and the MESSENGER missions.
Further, we describe the different available definitions of reference systems
for Mercury, which are realized using data obtained by instruments on board
MESSENGER. In particular, we discuss the dynamical frame, the principal-axes
frame, the ellipsoid frame, as well as the cartographic frame. We also describe
the reference frame adopted by the MESSENGER science team for the release of
their cartographic products and we provide expressions for transformations from
this frame to the other reference frames
Diffractively coupled Fabry-Perot resonator with power-recycling
We demonstrate the optical coupling of two cavities without light
transmission through a substrate. Compared to a conventional coupling
component, that is a partially transmissive mirror, an all-reflective coupler
avoids light absorption in the substrate and therefore associated thermal
problems, and even allows the use of opaque materials with possibly favourable
mechanical and thermal properties. Recently, the all-reflective coupling of two
cavities with a low-efficiency 3-port diffraction grating was theoretically
investigated. Such a grating has an additional (a third) port. However, it was
shown that the additional port does not necessarily decrease the bandwidth of
the coupled cavities. Such an all-reflective scheme for cavity coupling is of
interest in the field of gravitational wave detection. In such detectors light
that is resonantly enhanced inside the so-called power-recycling cavity is
coupled to (kilometre-scale) Fabry-Perot resonators representing the arms of a
Michelson interferometer. In order to achieve a high sensitivity over a broad
spectrum, the Fabry-Perot resonators need to have a high bandwidth for a given
(high) power build-up. We realized such an all-reflective coupling in a
table-top experiment. Our findings are in full agreement with the theoretical
model incorporating the characteristics of the 3-port grating used, and
therefore encourage the application of all-reflective cavity couplers in future
gravitational wave detectors
All-reflective coupling of two optical cavities with 3-port diffraction gratings
The shot-noise limited sensitivity of Michelson-type laser interferometers
with Fabry-Perot arm cavities can be increased by the so-called power-recycling
technique. In such a scheme the power-recycling cavity is optically coupled
with the interferometer's arm cavities. A problem arises because the central
coupling mirror transmits a rather high laser power and may show thermal
lensing, thermo-refractive noise and photo-thermo-refractive noise. Cryogenic
cooling of this mirror is also challenging, and thus thermal noise becomes a
general problem. Here, we theoretically investigate an all-reflective coupling
scheme of two optical cavities based on a 3-port diffraction grating. We show
that power-recycling of a high-finesse arm cavity is possible without
transmitting any laser power through a substrate material. The power splitting
ratio of the three output ports of the grating is, surprisingly, noncritical
Michelson interferometer with diffractively-coupled arm resonators in second-order Littrow configuration
Michelson-type laser-interferometric gravitational-wave (GW) observatories
employ very high light powers as well as transmissively- coupled Fabry-Perot
arm resonators in order to realize high measurement sensitivities. Due to the
absorption in the transmissive optics, high powers lead to thermal lensing and
hence to thermal distortions of the laser beam profile, which sets a limit on
the maximal light power employable in GW observatories. Here, we propose and
realize a Michelson-type laser interferometer with arm resonators whose
coupling components are all-reflective second-order Littrow gratings. In
principle such gratings allow high finesse values of the resonators but avoid
bulk transmission of the laser light and thus the corresponding thermal beam
distortion. The gratings used have three diffraction orders, which leads to the
creation of a second signal port. We theoretically analyze the signal response
of the proposed topology and show that it is equivalent to a conventional
Michelson-type interferometer. In our proof-of-principle experiment we
generated phase-modulation signals inside the arm resonators and detected them
simultaneously at the two signal ports. The sum signal was shown to be
equivalent to a single-output-port Michelson interferometer with
transmissively-coupled arm cavities, taking into account optical loss. The
proposed and demonstrated topology is a possible approach for future
all-reflective GW observatory designs
Berlin V2X: A Machine Learning Dataset from Multiple Vehicles and Radio Access Technologies
The evolution of wireless communications into 6G and beyond is expected to
rely on new machine learning (ML)-based capabilities. These can enable
proactive decisions and actions from wireless-network components to sustain
quality-of-service (QoS) and user experience. Moreover, new use cases in the
area of vehicular and industrial communications will emerge. Specifically in
the area of vehicle communication, vehicle-to-everything (V2X) schemes will
benefit strongly from such advances. With this in mind, we have conducted a
detailed measurement campaign that paves the way to a plethora of diverse
ML-based studies. The resulting datasets offer GPS-located wireless
measurements across diverse urban environments for both cellular (with two
different operators) and sidelink radio access technologies, thus enabling a
variety of different studies towards V2X. The datasets are labeled and sampled
with a high time resolution. Furthermore, we make the data publicly available
with all the necessary information to support the onboarding of new
researchers. We provide an initial analysis of the data showing some of the
challenges that ML needs to overcome and the features that ML can leverage, as
well as some hints at potential research studies.Comment: 5 pages, 6 figures. Accepted for presentation at IEEE conference
VTC2023-Spring. Available dataset at
https://ieee-dataport.org/open-access/berlin-v2
Assessment of radiation damage behaviour in a large collection of empirically optimized datasets highlights the importance of unmeasured complicating effects
A retrospective analysis of radiation damage behaviour in a statistically significant number of real-life datasets is presented, in order to gauge the importance of the complications not yet measured or rigorously evaluated in current experiments, and the challenges that remain before radiation damage can be considered a problem solved in practice
Integrating system and operator perspectives for the evaluation of power-to-gas plants in the future German energy system
In which way, and in which sectors, will renewable energy be integrated in the German Energy System by 2030, 2040, and 2050? How can the resulting energy system be characterised following a −95% greenhouse gas emission reduction scenario? Which role will hydrogen play? To address these research questions, techno-economic energy system modelling was performed. Evaluation of the resulting operation of energy technologies was carried out from a system and a business point of view. Special consideration of gas technologies, such as hydrogen production, transport, and storage, was taken as a large-scale and long-term energy storage option and key enabler for the decarbonisation of the non-electric sectors. The broad set of results gives insight into the entangled interactions of the future energy technology portfolio and its operation within a coupled energy system. Amongst other energy demands, CO2 emissions, hydrogen production, and future power plant capacities are presented. One main conclusion is that integrating the first elements of a large-scale hydrogen infrastructure into the German energy system, already, by 2030 is necessary for ensuring the supply of upscaling demands across all sectors. Within the regulatory regime of 2020, it seems that this decision may come too late, which jeopardises the achievement of transition targets within the horizon 2050
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Genome-wide association study identifies 30 loci associated with bipolar disorder.
Bipolar disorder is a highly heritable psychiatric disorder. We performed a genome-wide association study (GWAS) including 20,352 cases and 31,358 controls of European descent, with follow-up analysis of 822 variants with P < 1 × 10-4 in an additional 9,412 cases and 137,760 controls. Eight of the 19 variants that were genome-wide significant (P < 5 × 10-8) in the discovery GWAS were not genome-wide significant in the combined analysis, consistent with small effect sizes and limited power but also with genetic heterogeneity. In the combined analysis, 30 loci were genome-wide significant, including 20 newly identified loci. The significant loci contain genes encoding ion channels, neurotransmitter transporters and synaptic components. Pathway analysis revealed nine significantly enriched gene sets, including regulation of insulin secretion and endocannabinoid signaling. Bipolar I disorder is strongly genetically correlated with schizophrenia, driven by psychosis, whereas bipolar II disorder is more strongly correlated with major depressive disorder. These findings address key clinical questions and provide potential biological mechanisms for bipolar disorder
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