Electrolyte solutions at curved electrodes. I. Mesoscopic approach

Within the Poisson-Boltzmann (PB) approach electrolytes in contact with planar, spherical, and cylindrical electrodes are analyzed systematically. The dependences of their capacitance $C$ on the surface charge density $\sigma$ and the ionic strength $I$ are examined as function of the wall curvature. The surface charge density has a strong effect on the capacitance for small curvatures whereas for large curvatures the behavior becomes independent of $\sigma$. An expansion for small curvatures gives rise to capacitance coefficients which depend only on a single parameter, allowing for a convenient analysis. The universal behavior at large curvatures can be captured by an analytic expression.Comment: accepted for publication in the Journal of Chemical Physic

Analysis of cool DO-type white dwarfs from the Sloan Digital Sky Survey Data Release 10

We report on the identification of 22 new cool DO-type white dwarfs (WD) detected in Data Release 10 (DR10) of the Sloan Digital Sky Survey (SDSS). Among them, we found one more member of the so-called hot-wind DO WDs, which show ultrahigh excitation absorption lines. Our non-LTE model atmosphere analyses of these objects and two not previously analyzed hot-wind DO WDs, revealed effective temperatures and gravities in the ranges Teff=45-80kK and log g= 7.50-8.75. In eight of the spectra we found traces of C (0.001-0.01, by mass). Two of these are the coolest DO WDs ever discovered that still show a considerable amount of C in their atmospheres. This is in strong contradiction with diffusion calculations, and probably, similar to what is proposed for DB WDs, a weak mass-loss is present in DO WDs. One object is the most massive DO WD discovered so far with a mass of 1.07 M_sun if it is an ONe-WD or 1.09 M_sun if it is a CO-WD. We furthermore present the mass distribution of all known hot non-DA (pre-) WDs and derive the hot DA to non-DA ratio for the SDSS DR7 spectroscopic sample. The mass distribution of DO WDs beyond the wind limit strongly deviates from the mass distribution of the objects before the wind limit. We address this phenomenon by applying different evolutionary input channels. We argue that the DO WD channel may be fed by about 13% by post-extreme-horizontal branch stars and that PG1159 stars and O(He) stars may contribute in a similar extent to the non-DA WD channel.Comment: 13 pages, accepted for publication in A&

Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots

The development of scalable sources of non-classical light is fundamental to unlocking thetechnological potential of quantum photonics. Semiconductor quantum dots are emerging asnear-optimal sources of indistinguishable single photons. However, their performance assources of entangled-photon pairs are still modest compared to parametric down converters.Photons emitted from conventional Stranski–Krastanov InGaAs quantum dots have shownnon-optimal levels of entanglement and indistinguishability. For quantum networks, bothcriteria must be met simultaneously. Here, we show that this is possible with a system thathas received limited attention so far: GaAs quantum dots. They can emit triggered polar-ization-entangled photons with high purity (g(2)(0) = 0.002±0.002), high indistinguish-ability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity(0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dotentanglement sources in future quantum technologie

White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14

White dwarfs carry information on the structure and evolution of the Galaxy, especially through their luminosity function and initial-to-final mass relation. Very cool white dwarfs provide insight into the early ages of each population. Examining the spectra of all stars with $3\sigma$ proper motion in the Sloan Digital Sky Survey Data Release 14, we report the classification for 20 088 spectroscopically confirmed white dwarfs, plus 415 hot subdwarfs, and 311 cataclysmic variables. We obtain Teff, log g and mass for hydrogen atmosphere white dwarf stars (DAs), warm helium atmosphere white dwarfs (DBs), hot subdwarfs (sdBs and sdOs), and estimate photometric Teff for white dwarf stars with continuum spectra (DCs). We find 15793 sdAs and 447 dCs between the white dwarf cooling sequence and the main sequence, especially below Teff= 10000 K; most are likely low-mass metal-poor main sequence stars, but some could be the result of interacting binary evolution.Comment: 18 pages, 13 figure

BINARY CENTRAL STARS OF PLANETARY NEBULAE DISCOVERED THROUGH PHOTOMETRIC VARIABILITY. V. THE CENTRAL STARS OF HaTr 7 AND ESO 330-9

postprin

A far-UV survey of three hot, metal-polluted white dwarf stars: WD0455-282, WD0621-376, and WD2211-495

Using newly obtained high-resolution data ($R\sim{1\times{10}^{5}}$) from the \textit{Hubble Space Telescope}, and archival UV data from the \textit{Far Ultraviolet Spectroscopic Explorer} we have conducted a detailed UV survey of the three hot, metal-polluted white dwarfs WD0455-282, WD0621-376, and WD2211-495. Using bespoke model atmospheres we measured $T_{\mathrm{eff}}$, log $g$, and photospheric abundances for these stars. In conjunction with data from Gaia we measured masses, radii, and gravitational redshift velocities for our sample of objects. We compared the measured photospheric abundances with those predicted by radiative levitation theory, and found that the observed Si abundances in all three white dwarfs, and the observed Fe abundances in WD0621-376 and WD2211-495, were larger than those predicted by an order of magnitude. These findings imply not only an external origin for the metals, but also ongoing accretion, as the metals not supported by radiative levitation would sink on extremely short timescales. We measured the radial velocities of several absorption features along the line of sight to the three objects in our sample, allowing us to determine the velocities of the photospheric and interstellar components along the line of sight for each star. Interestingly, we made detections of circumstellar absorption along the line of sight to WD0455-282 with three velocity components. To our knowledge, this is the first such detection of multi-component circumstellar absorption along the line of sight to a white dwarf.Comment: 19 pages, 23 figures, 8 tables. Accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Wireless wake-up sensor network for structural health monitoring of large-scale highway bridges

To realize in-situ structural health monitoring of critical infrastructure such as bridges, we present a powerful, but also low power and flexible, wireless sensor node utilizing a wake-up transceiver. The sensor node is equipped with several kinds of sensors, such as temperature, pressure and acceleration for in-situ monitoring of critical infrastructure. In addition to these commonly used sensors in wireless sensor networks, some nodes are equipped with global navigation satellite system receivers (GNSS) and others with tilt and acceleration sensors of very high accuracy that were developed by Nothrop Grumman LITEF GmbH. We present a low power wakeup multi-hop routing protocol that is able to transmit data with little overhead by supporting the use of wake-up receivers in combination with long-range communication radios. The wireless sensor nodes and the routing protocol are tested at a large-scale highway bridge in south-west Germany, where a prototype network was installed in June 2015 following a first test installation earlier in June at the same bridge. A gateway node equipped with a Global System for Mobile Communications (GSM) modem transfers the network data to a remote server located at the University of Freiburg