2,740 research outputs found
Non-Primordial Solar Mass Black Holes
We propose a mechanism that can convert a sizeable fraction of neutron stars
into black holes with mass , too light to be produced via
standard stellar evolution. We show that asymmetric fermionic dark matter of
mass TeV, with attractive self-interaction within the range that
alleviates the problems of collisionless cold dark matter, can accumulate in a
neutron star and collapse, forming a seed black hole that converts the rest of
the star to a solar mass black hole. We estimate the fraction of neutron stars
that can become black holes without contradicting existing neutron star
observations. Like neutron stars, such solar mass black holes could be in
binary systems, which may be searched for by existing and forthcoming
gravitational wave detectors. The (non-)observation of binary mergers of solar
mass black holes may thus test the specific nature of the dark matter.Comment: 6 pages, 2 figure
Bench Memoirs: A Review of Five Chiefs by John Paul Stevens
FIVE CHIEFS: A SUPREME COURT MEMOIR. By John Paul Stevens. New York: Little, Brown & Co. 2011. 292 pp. $24-99.
When Justice John Paul Stevens rose from the Supreme Court bench for the final time on June 28, 2010, he had worn the robes of a Justice longer than all but two of his one hundred predecessors: Justice William O. Douglas, who held the seat immediately before him, and the nineteenth-century Justice Stephen Field. As Chief Justice John Roberts noted in saying farewell, Stevens\u27s tenure on the Court accounts for nearly one sixth of its existence
Generic Radar Processing Methods for Monitoring Tasks on Bridge Infrastructure
Kritische Verkehrsinfrastrukturen, wie z. B. BrĂŒcken, können nur dann sicher betrieben werden, wenn ihr Zustand regelmĂ€Ăig bewertet wird. Neben visuellen Inspektionen umfasst die Bewertung auch Messungen des BrĂŒckenverhaltens auf statische oder dynamische Lasten. Diese Messungen werden in der Regel mit einer Vielzahl von Sensoren durchgefĂŒhrt, die direkt an der BrĂŒcke befestigt sind. Zunehmend werden jedoch auch Fernerkundungssensoren eingesetzt, wie z.B. das bodenbasierte interferometrische Radar (engl.: ground-based interferometric radar - GBR). GBR können aus der Ferne Verschiebungen mit einer Genauigkeit im Submillimeterbereich messen, indem sie eine elektromagnetische Welle aussenden, die von Strukturen an der Unterseite der BrĂŒcke reflektiert wird.
Im Vergleich zu direkt befestigten Sensoren wird die Installationszeit verkĂŒrzt und der normale Betrieb der BrĂŒcke wird nicht beeintrĂ€chtigt. Vergleichbare Messunsicherheiten lassen sich jedoch nur erreichen, wenn bei der Prozessierung der Messungen bestimmte Herausforderungen berĂŒcksichtigt werden. Dabei geht es vor allem um die Entfernung externer EinflĂŒsse wie Störungen des Signals oder VerĂ€nderungen atmosphĂ€rischer Parameter. Die Messungen werden auĂerdem durch statischen Clutter und Projektionsfehler beeinflusst, die zu systematischen Abweichungen fĂŒhren. Statischer Clutter wird mit einer angepassten KreisschĂ€tzung bestimmt, wĂ€hrend Projektionsfehler durch die Verwendung mehrerer Sensoren zur SchĂ€tzung separater Verschiebungskomponenten vermindert werden. Mit diesen zusĂ€tzlichen Prozessierungsschritten erreicht GBR eine Ă€hnliche Unsicherheit wie andere Fernerkundungssensoren, was durch Vergleiche mit Referenzsensoren validiert wird. Verbleibende Unterschiede zu diesen Referenzsensoren lassen sich durch Unsicherheiten bei der SchĂ€tzung von Clutter und durch die begrenzte Auflösung einzelner Reflexionen erklĂ€ren.
Die resultierenden Verschiebungsmessungen werden dann zur SchĂ€tzung schadensempfindlicher Merkmale wie Eigenfrequenzen und Eigenformen verwendet. Eigenfrequenzen werden bestimmt, indem ein Modell einer gedĂ€mpften Sinuskurve fĂŒr die Schwingung nach einer FahrzeugĂŒberfahrt geschĂ€tzt wird. Mit diesem Ansatz wird jede FahrzeugĂŒberfahrt separat analysiert, was eine Unterscheidung zwischen verschiedenen Fahrzeugmassen ermöglicht. AuĂerdem erlaubt die groĂe Anzahl von FrequenzschĂ€tzungen eine zuverlĂ€ssigere Bestimmung des Temperatureinflusses auf die Eigenfrequenzen. FĂŒr die Bestimmung der Eigenformen wird ein alternativer Messaufbau erarbeitet. Dieser Aufbau nutzt die flache Unterseite einer BrĂŒcke, um das ausgesendete Signal auf einen Reflektor auf dem Boden zu spiegeln. Eine permanente Installation von Reflektoren an der BrĂŒckenunterseite ist daher nicht erforderlich, wodurch die Anwendung von GBR auf eine groĂe Anzahl von BrĂŒcken erweitert wird. DarĂŒber hinaus kann die Messung nicht durch andere Verschiebungskomponenten beeinflusst werden, was das Auftreten von systematischen Abweichungen verringert. Folglich sind die Eigenformen empfindlicher gegenĂŒber SchĂ€den, da die Unsicherheiten reduziert werden. Das zugrunde liegende Prinzip dieses alternativen Messaufbaus wird wiederum durch Vergleiche mit Referenzsensoren validiert
Candidate Quantum Spin Liquid in the Ce\textsuperscript{3+} Pyrochlore Stannate CeSnO
We report the low temperature magnetic properties of CeSnO, a
rare-earth pyrochlore. Our susceptibility and magnetization measurements show
that due to the thermal isolation of a Kramers doublet ground state,
CeSnO has Ising-like magnetic moments of
. The magnetic moments are confined to the local trigonal axes,
as in a spin ice, but the exchange interactions are antiferromagnetic. Below 1
K the system enters a regime with antiferromagnetic correlations. In contrast
to predictions for classical -Ising spins on the
pyrochlore lattice, there is no sign of long-range ordering down to 0.02 K. Our
results suggest that CeSnO features an antiferromagnetic liquid
ground state with strong quantum fluctuations.Comment: 6 pages, 4 figure
Advancing Ground-Based Radar Processing for Bridge Infrastructure Monitoring
In this study, we further develop the processing of ground-based interferometric radar measurements for the application of bridge monitoring. Applying ground-based radar in such complex setups or long measurement durations requires advanced processing steps to receive accurate measurements. These steps involve removing external influences from the measurement and evaluating the measurement uncertainty during processing. External influences include disturbances caused by objects moving through the signal, static clutter from additional scatterers, and changes in atmospheric properties. After removing these influences, the line-of-sight displacement vectors, measured by multiple ground-based radars, are decomposed into three-dimensional displacement components. The advanced processing steps are applied exemplarily on measurements with two sensors at a prestressed concrete bridge near Coburg (Germany). The external influences are successfully removed, and two components of the three-dimensional displacement vector are determined. A measurement uncertainty of less than 0.1mm is achieved for the discussed application
Determining and Investigating the Variability of Bridgesâ Natural Frequencies with Ground-Based Radar
Assessing the condition of bridge infrastructure requires estimating damage-sensitive features from reliable sensor data. This study proposes to estimate natural frequencies from displacement measurements of a ground-based interferometric radar (GBR). These frequencies are determined from the damped vibration after each vehicle crossing with least squares and compared to a Frequency Domain Decomposition result. We successfully applied the approach in an exemplary measurement campaign at a bridge near Coburg (Germany) with an additional comparison to commonly used strain sensors. Since temperature greatly influences natural frequencies, linear regression is used to correct this influence. A simulation shows that GBR, combined with the least squares approach, achieves the lowest uncertainty and variation in the linear regression, indicating better damage detection results. However, the success of the damage detection highly depends on correctly determining the temperature influence, which might vary throughout the structure. Future work should further investigate the biases and variability of this influence
Prevalence and consequences of patient safety incidents in general practice in the Netherlands: a retrospective medical record review study
BACKGROUND Patient safety can be at stake in both hospital and general practice settings. While severe patient safety incidents have been described, quantitative studies in large samples of patients in general practice are rare. This study aimed to assess patient safety in general practice, and to show areas where potential improvements could be implemented. METHODS We conducted a retrospective review of patient records in Dutch general practice. A random sample of 1,000 patients from 20 general practices was obtained. The number of patient safety incidents that occurred in a one-year period, their perceived underlying causes, and impact on patients' health were recorded. RESULTS We identified 211 patient safety incidents across a period of one year (95% CI: 185 until 241). A variety of types of incidents, perceived causes and consequences were found. A total of 58 patient safety incidents affected patients; seven were associated with hospital admission; none resulted in permanent disability or death. CONCLUSIONS Although this large audit of medical records in general practices identified many patient safety incidents, only a few had a major impact on patients' health. Improving patient safety in this low-risk environment poses specific challenges, given the high numbers of patients and contacts in general practice.The Dutch Ministry of Health, Welfare and Sport (VWS) initiated the project and supported the project financially (without restrictions on the scientific work; grant number 313741)
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