333 research outputs found
CooperativityâDriven Reactivity of a Dinuclear Copper Dimethylglyoxime Complex
In this report, we present the dinuclear copper(II) dimethylglyoxime (Hdmg) complex [Cu(Hdmg)(Hdmg)(dmg)] (1), which, in contrast to its mononuclear analogue [Cu(Hdmg)] (2), is subject to a cooperativity-driven hydrolysis. The combined Lewis acidity of both copper centers increases the electrophilicity of the carbon atom in the bridging ÎŒ-OâN=C-group of Hdmg and thus, facilitates the nucleophilic attack of H2O. This hydrolysis yields butane-2,3-dione monoxime (3) and NHOH that, depending on the solvent, is then either oxidized or reduced. In ethanol, NHOH is reduced to NH, yielding acetaldehyde as the oxidation product. In contrast, in CHCN, NHOH is oxidized by Cu to form NO and [Cu(CHCN)4]. Herein are presented the combined synthetic, theoretical, spectroscopic and spectrometric methods that indicate and establish the reaction pathway of this solvent-dependent reaction
Landauer vs. Nernst: What is the True Cost of Cooling a Quantum System?
Thermodynamics connects our knowledge of the world to our capability to
manipulate and thus to control it. This crucial role of control is exemplified
by the third law of thermodynamics, Nernst's unattainability principle, stating
that infinite resources are required to cool a system to absolute zero
temperature. But what are these resources and how should they be utilised? And
how does this relate to Landauer's principle that famously connects information
and thermodynamics? We answer these questions by providing a framework for
identifying the resources that enable the creation of pure quantum states. We
show that perfect cooling is possible with Landauer energy cost given infinite
time or control complexity. However, such optimal protocols require complex
unitaries generated by an external work source. Restricting to unitaries that
can be run solely via a heat engine, we derive a novel Carnot-Landauer limit,
along with protocols for its saturation. This generalises Landauer's principle
to a fully thermodynamic setting, leading to a unification with the third law
and emphasising the importance of control in quantum thermodynamics.Comment: 15 pages, 4 figures, 46 pages of appendice
Fast and Not-so-Furious: Case Study of the Fast and Faint Type IIb SN 2021bxu
We present photometric and spectroscopic observations and analysis of
SN~2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova
(SN). SN~2021bxu is unique, showing a large initial decline in brightness
followed by a short plateau phase. With
during the plateau, it is at the lower end of the luminosity distribution of
stripped-envelope supernovae (SE-SNe) and shows a distinct 10 day plateau
not caused by H- or He-recombination. SN~2021bxu shows line velocities which
are at least slower than typical SE-SNe. It is
photometrically and spectroscopically similar to Type IIb SNe during the
photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find
that the bolometric light curve is best described by a composite model of shock
interaction between the ejecta and an envelope of extended material, combined
with a typical SN~IIb powered by the radioactive decay of Ni. The
best-fit parameters for SN~2021bxu include a Ni mass of , an ejecta mass of
, and an ejecta
kinetic energy of . From the fits to the properties of the extended material of
Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing
envelope mass. SN~2021bxu has on the low end compared to
SE-SNe and Ca-rich SNe in the literature, demonstrating that SN~2021bxu-like
events are rare explosions in extreme areas of parameter space. The progenitor
of SN~2021bxu is likely a low mass He star with an extended envelope.Comment: 18 pages, 15 figures, submitted to MNRA
TESS Reveals HD 118203 b to be a Transiting Planet
The exoplanet HD 118203 b, orbiting a bright (V = 8.05) host star, was discovered using the radial velocity method by da Silva et al., but was not previously known to transit. Transiting Exoplanet Survey Satellite (TESS) photometry has revealed that this planet transits its host star. Nine planetary transits were observed by TESS, allowing us to measure the radius of the planet to be 1.136^(+0.029)_(-0.028) R_J, and to calculate the planet mass to be 2.166^(+0.074)_(-0.079) M_J. The host star is slightly evolved with an effective temperature of T_(eff) = 5683^(+84)_(-85) K and a surface gravity of log g = 3.889^(+0.017)_(-0.018). With an orbital period of 6.134985^(+0.000029_(-0.000030) days and an eccentricity of 0.314 ± 0.017, the planet occupies a transitional regime between circularized hot Jupiters and more dynamically active planets at longer orbital periods. The host star is among the 10 brightest known to have transiting giant planets, providing opportunities for both planetary atmospheric and asteroseismic studies
Sicherung von DĂ€mmen, Deichen und Stauanlagen : Handbuch fĂŒr Theorie und Praxis ; Vol. V - 2015
Die UniversitĂ€t Siegen beschĂ€ftigt sich seit ĂŒber 15 Jahren wissenschaftlich und im Bereich der anwendungsorientierten Forschung mit diesem Thema und hat dazu mittlerweile fĂŒnf Symposien durchgefĂŒhrt.
Mit der Veröffentlichung soll die langjĂ€hrige Tradition als etablierte wissenschaftliche Plattform mit einem Wissensaustausch auf europĂ€ischer Ebene fortgesetzt werden. Die Bearbeitung dieser Thematik erfolgt auf der Basis der bewĂ€hrten Kooperation zwischen Geotechnik und Wasserbau an der UniversitĂ€t Siegen. Aktuelle Ereignisse, wie z.B. die aus England oder Australien im Februar des Jahres 2014, machen uns aber auch deutlich, dass ein absoluter Schutz gegen Extremereignisse nicht möglich ist. Sie zeigen aber auch, dass dort wo technischer Hochwasserschutz konsequent umgesetzt wurde SchĂ€den vermieden werden konnten. Wir sind nach den Ereignissen in den vergangenen Jahren aufgefordert wissenschaftlich noch leistungsfĂ€higere und duktilere Systeme zu entwickeln. Weiter ist die Wissenschaft in der Pflicht, die Zivile Sicherheit im Hochwasser-schutz permanent zu bewerten, zu bearbeiten und ganzheitliche-interdisziplinĂ€re und lĂ€nderĂŒbergreifende Lösungen fĂŒr die Zivilgesellschaft einzufordern
The TESS-Keck Survey. III. A Stellar Obliquity Measurement of TOI-1726 c
We report the measurement of a spectroscopic transit of TOI-1726c, one of two planets transiting a G-type star with V = 6.9 in the Ursa Major Moving Group (~400 Myr). With a precise age constraint from cluster membership, TOI-1726 provides a great opportunity to test various obliquity excitation scenarios that operate on different timescales. By modeling the RossiterâMcLaughlin (RM) effect, we derived a sky-projected obliquity of â1^(+35)_(â32)â. This result rules out a polar/retrograde orbit and is consistent with an aligned orbit for planet c. Considering the previously reported, similarly prograde RM measurement of planet b and the transiting nature of both planets, TOI-1726 tentatively conforms to the overall picture that compact multitransiting planetary systems tend to have coplanar, likely aligned orbits. TOI-1726 is also a great atmospheric target for understanding differential atmospheric loss of sub-Neptune planets (planet b 2.2 Râ and c 2.7 Râ both likely underwent photoevaporation). The coplanar geometry points to a dynamically cold history of the system that simplifies any future modeling of atmospheric escape
Searching for eV-scale sterile neutrinos with eight years of atmospheric neutrinos at the IceCube neutrino telescope
We report in detail on searches for eV-scale sterile neutrinos, in the
context of a 3+1 model, using eight years of data from the IceCube neutrino
telescope. By analyzing the reconstructed energies and zenith angles of 305,735
atmospheric and events we construct confidence
intervals in two analysis spaces: vs.
under the conservative assumption ; and
vs. given sufficiently large that
fast oscillation features are unresolvable. Detailed discussions of the event
selection, systematic uncertainties, and fitting procedures are presented. No
strong evidence for sterile neutrinos is found, and the best-fit likelihood is
consistent with the no sterile neutrino hypothesis with a p-value of 8\% in the
first analysis space and 19\% in the second.Comment: This long-form paper is a companion to the letter "An eV-scale
sterile neutrino search using eight years of atmospheric muon neutrino data
from the IceCube Neutrino Observatory". v2: update other experiments contours
on results plo
LeptonInjector and LeptonWeighter: A neutrino event generator and weighter for neutrino observatories
We present a high-energy neutrino event generator, called LeptonInjector,
alongside an event weighter, called LeptonWeighter. Both are designed for
large-volume Cherenkov neutrino telescopes such as IceCube. The neutrino event
generator allows for quick and flexible simulation of neutrino events within
and around the detector volume, and implements the leading Standard Model
neutrino interaction processes relevant for neutrino observatories:
neutrino-nucleon deep-inelastic scattering and neutrino-electron annihilation.
In this paper, we discuss the event generation algorithm, the weighting
algorithm, and the main functions of the publicly available code, with
examples.Comment: 28 pages, 10 figures, 3 table
Measurement of the high-energy all-flavor neutrino-nucleon cross section with IceCube
The flux of high-energy neutrinos passing through the Earth is attenuated due to their interactions with matter. The interaction rate is determined by the neutrino interaction cross section and affects the flux arriving at the IceCube Neutrino Observatory, a cubic-kilometer neutrino detector embedded in the Antarctic ice sheet. We present a measurement of the neutrino cross section between 60 TeV and 10 PeV using the high-energy starting event (HESE) sample from IceCube with 7.5 years of data. The result is binned in neutrino energy and obtained using both Bayesian and frequentist statistics. We find it compatible with predictions from the Standard Model. While the cross section is expected to be flavor independent above 1 TeV, additional constraints on the measurement are included through updated experimental particle identification (PID) classifiers, proxies for the three neutrino flavors. This is the first such measurement to use a ternary PID observable and the first to account for neutrinos from tau decay
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