1,283 research outputs found
Multiple Quantum Oscillations in the de Haas van Alphen Spectra of the Underdoped High Temperature Superconductor YBa_2Cu_3O_6.5
By improving the experimental conditions and extensive data accumulation, we
have achieved very high-precision in the measurements of the de Haas-van Alphen
effect in the underdoped high-temperature superconductor
YBaCuO. We find that the main oscillation, so far believed
to be single-frequency, is composed of three closely spaced frequencies. We
attribute this to bilayer splitting and warping of a single quasi-2D Fermi
surface, indicating that \emph{c}-axis coherence is restored at low temperature
in underdoped cuprates. Our results do not support the existence of a larger
frequency of the order of 1650 T reported recently in the same compound [S.E.
Sebastian {\it et al}., Nature {\bf 454}, 200 (2008)]
Tricuspid Valve Endocarditis With Group B Streptococcus After an Elective Abortion: The Need for New Data
Streptococcus agalactiae, commonly known as Group B streptococcus (GBS), was originally discovered as a cause of bovine mastitis. GBS colonizes the genital tract of up to 40% of women and has become a major pathogen in neonatal meningitis. GBS endocarditis is thought to be an uncommon manifestation of this infection and carries a higher mortality compared to other streptococcal pathogens. Studies have shown that endocarditis after abortion has an incidence of about one per million. However, this figure was published prior to routine use of echocardiography for diagnosis. The American Heart Association has recently declared transesophageal echocardiography the gold standard for endocarditis diagnosis. This case report illustrates that, given the potentially devastating consequences of endocarditis, there is a need for updated studies to adequately assess the true incidence of this infection. Pending the outcome of these studies, routine GBS screening and prophylactic antibiotics prior to abortion should be recommended
c-axis electrodynamics of ybco
New measurements of surface impedance in ybco show that the c-axis
penetration depth and conductivity below Tc exhibit behaviour different from
that observed in the planes. The c-axis penetration depth never has the linear
temperature dependence seen in the ab-plane. Instead of the conductivity peak
seen in the planes, the c-axis microwave conductivity falls to low values in
the superconducting state, then rises slightly below 20K. These results show
that c-axis transport remains incoherent below Tc, even though this is one of
the least anisotropic cuprate superconductors.Comment: 4-page
The Ithaca Interpretation of Quantum Mechanics
I list several strong requirements for what I would consider a sensible
interpretation of quantum mechanics and I discuss two simple theorems. One, as
far as I know, is new; the other was only noted a few years ago. Both have
important implications for such a sensible interpretation. My talk will not
clear everything up; indeed, you may conclude that it has not cleared anything
up. But I hope it will provide a different perspective from which to view some
old and vexing puzzles (or, if you believe nothing needs to be cleared up, some
ancient verities.)Comment: 21 pages, plain TEX. Notes for a lecture given at the Golden Jubilee
Workshop on Foundations of Quantum Theory, Tata Institute, Bombay, September
9-12, 199
de Haas-van Alphen oscillations in the underdoped cuprate YBaCuO
The de Haas-van Alphen effect was observed in the underdoped cuprate
YBaCuO via a torque technique in pulsed magnetic fields up to
59 T. Above an irreversibility field of 30 T, the magnetization exhibits
clear quantum oscillations with a single frequency of 540 T and a cyclotron
mass of 1.76 times the free electron mass, in excellent agreement with
previously observed Shubnikov-de Haas oscillations. The oscillations obey the
standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic
observation of quantum oscillations confirms the existence of a well-defined,
close and coherent, Fermi surface in the pseudogap phase of cuprates.Comment: published versio
The Rogue Alpha and Beta Mission: Operations, Infrared Remote Sensing, LEO Data Processing, and Lessons Learned From Three Years on Orbit With Two Laser Communication-Equipped 3U CubeSats
The Aerospace Corporation\u27s Rogue-alpha, beta program was a rapid prototyping demonstration aimed at building and deploying an infrared remote sensing capability into low Earth orbit within 18 months. The two satellites and their data were then used for three years as an experimental testbed for future proliferated low Earth orbit (pLEO) constellations. Their launch took place on November 2, 2019, followed by boost and deployment of two identical spacecraft (Rogue-alpha and beta) by the Cygnus ISS cargo vessel into circular 460-km, 52° inclined orbits on January31, 2020. The primary sensors were 1.4-micron band, InGaAs short wavelength infrared (SWIR) cameras with640x512 pixels and a 28° field-of-view. The IR sensors were accompanied by 10-megapixel visible context cameras with a 37° field-of-view. Star sensors were also tested as nighttime imaging sensors. Three years of spacecraft and sensor operations were achieved, allowing a variety of experiments to be conducted. The first year focused on alignment and checkout of the laser communication systems, sensor calibration, and priority IR remote sensing objectives, including the study of Earth backgrounds, observation of natural gas flares, and detection of rocket launches. The second year of operations added study of environmental remote sensing targets, including severe storms, wildfires, and volcanic eruptions, while continuing to gather Earth backgrounds and rocket launch observations. The final year emphasized advanced data processing and exploitation techniques applied to collected data, using machine learning and artificial intelligence for tasks such as target tracking, frame co-registration, and stereo data exploitation. Mission operations continued in the final year, with an emphasis on collecting additional rocket launch data, and higher frame rate backgrounds data. This report summarizes the Rogue alpha, beta missionâs outcomes and presents processed IR data, including the detection and tracking of rocket launches with dynamic Earth backgrounds, embedded moving targets in background scenes, and the use of pointing-based registration to create fire line videos of severe wildfires and 3D scenes of pyrocumulonimbus clouds. Lessons learned from the experimental ConOps, data exploitation, and database curation are also summarized for application to future pLEO constellation missions
Nernst and Seebeck Coefficients of the Cuprate SuperconductorYBaCuO: A Study of Fermi Surface Reconstruction
The Seebeck and Nernst coefficients and of the cuprate
superconductor YBaCuO (YBCO) were measured in a single crystal with
doping in magnetic fields up to H = 28 T. Down to T=9 K,
becomes independent of field by T, showing that superconducting
fluctuations have become negligible. In this field-induced normal state,
and are both large and negative in the limit, with the
magnitude and sign of consistent with the small electron-like Fermi
surface pocket detected previously by quantum oscillations and the Hall effect.
The change of sign in at K is remarkably similar to that
observed in LaBaCuO, LaNdSrCuO and
LaEuSrCuO, where it is clearly associated with the onset
of stripe order. We propose that a similar density-wave mechanism causes the
Fermi surface reconstruction in YBCO.Comment: Final version accepted for publication in Phys. Rev. Lett. New title,
shorter abstract, minor revision of text and added reference
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