112 research outputs found
Near-source error sensor strategies for active vibration isolation of machines
Due to lightweight construction of vehicles and ships, the reduction of structure borne interior noise problems with passive isolation of engine vibrations might be not sufficient. To improve the isolation, a combination of passive and active isolation techniques can be used (so-called hybrid isolation). This paper focusses on the influence of the sensor positions on the performance of the active isolation. In general two strategies can be distinguished: sensors located in the accommodation with a direct minimization of the sound field and sensors located near the source of vibration. In this paper attention will be paid to an effective weighting of the near-source sensors in such a way that the interior noise in the vehicle is reduced. Also the nearsource strategy of minimization of the injected power is considered. The latter strategy is theoretically very attractive, but is much more difficult to implement in practice. The techniques are explained and compared to each other with the help of numerical models
Charge Form Factor and Cluster Structure of Li Nucleus
The charge form factor of Li nucleus is considered on the basis of its
cluster structure. The charge density of Li is presented as a
superposition of two terms. One of them is a folded density and the second one
is a sum of He and the deuteron densities. Using the available
experimental data for He and deuteron charge form factors, a good
agreement of the calculations within the suggested scheme is obtained with the
experimental data for the charge form factor of Li, including those in
the region of large transferred momenta.Comment: 12 pages 5 figure
Dirac quasinormal modes of the Reissner-Nordstr\"om de Sitter black hole
The quasinormal modes of the Reissner-Nordstr\"om de Sitter black hole for
the massless Dirac fields are studied using the P\"oshl-Teller potential
approximation. We find that the magnitude of the imaginary part of the
quasinormal frequencies decreases as the cosmological constant or the orbital
angular momentum increases, but it increases as the charge or the overtone
number increases. An interesting feature is that the imaginary part is almost
linearly related to the real part as the cosmological constant changes for
fixed charge, and the linearity becomes better as the orbital angular momentum
increases. We also prove exactly that the Dirac quasinormal frequencies are the
same for opposite chirality.Comment: 10 pages, 6 figures, Phys. Rev. D in pres
CDMS, Supersymmetry and Extra Dimensions
The CDMS experiment aims to directly detect massive, cold dark matter
particles originating from the Milky Way halo. Charge and lattice excitations
are detected after a particle scatters in a Ge or Si crystal kept at ~30 mK,
allowing to separate nuclear recoils from the dominating electromagnetic
background. The operation of 12 detectors in the Soudan mine for 75 live days
in 2004 delivered no evidence for a signal, yielding stringent limits on dark
matter candidates from supersymmetry and universal extra dimensions. Thirty Ge
and Si detectors are presently installed in the Soudan cryostat, and operating
at base temperature. The run scheduled to start in 2006 is expected to yield a
one order of magnitude increase in dark matter sensitivity.Comment: To be published in the proceedings of the 7th UCLA symposium on
sources and detection of dark matter and dark energy in the universe, Marina
del Rey, Feb 22-24, 200
Surface Terms as Counterterms in the AdS/CFT Correspondence
We examine the recently proposed technique of adding boundary counterterms to
the gravitational action for spacetimes which are locally asymptotic to anti-de
Sitter. In particular, we explicitly identify higher order counterterms, which
allow us to consider spacetimes of dimensions d<=7. As the counterterms
eliminate the need of ``background subtraction'' in calculating the action, we
apply this technique to study examples where the appropriate background was
ambiguous or unknown: topological black holes, Taub-NUT-AdS and Taub-Bolt-AdS.
We also identify certain cases where the covariant counterterms fail to render
the action finite, and we comment on the dual field theory interpretation of
this result. In some examples, the case of vanishing cosmological constant may
be recovered in a limit, which allows us to check results and resolve
ambiguities in certain asymptotically flat spacetime computations in the
literature.Comment: Revtex, 18 pages. References updated and few typo's fixed. Final
versio
Minutes-duration optical flares with supernova luminosities
In recent years, certain luminous extragalactic optical transients have been observed to last only a few days1. Their short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae), whose timescale is weeks2. Some short-duration transients, most notably AT2018cow (ref. 3), show blue optical colours and bright radio and X-ray emission4. Several AT2018cow-like transients have shown hints of a long-lived embedded energy source5, such as X-ray variability6,7, prolonged ultraviolet emission8, a tentative X-ray quasiperiodic oscillation9,10 and large energies coupled to fast (but subrelativistic) radio-emitting ejecta11,12. Here we report observations of minutes-duration optical flares in the aftermath of an AT2018cow-like transient, AT2022tsd (the ‘Tasmanian Devil’). The flares occur over a period of months, are highly energetic and are probably nonthermal, implying that they arise from a near-relativistic outflow or jet. Our observations confirm that, in some AT2018cow-like transients, the embedded energy source is a compact object, either a magnetar or an accreting black hole
Limits on WIMP–nucleon interactions from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory
More than smell - COVID-19 is associated with severe impairment of smell, taste, and chemesthesis
Recent anecdotal and scientific reports have provided evidence of a link between COVID-19 and chemosensory impairments, such as anosmia. However, these reports have downplayed or failed to distinguish potential effects on taste, ignored chemesthesis, and generally lacked quantitative measurements. Here, we report the development, implementation, and initial results of a multilingual, international questionnaire to assess self-reported quantity and quality of perception in 3 distinct chemosensory modalities (smell, taste, and chemesthesis) before and during COVID-19. In the first 11 days after questionnaire launch, 4039 participants (2913 women, 1118 men, and 8 others, aged 19-79) reported a COVID-19 diagnosis either via laboratory tests or clinical assessment. Importantly, smell, taste, and chemesthetic function were each significantly reduced compared to their status before the disease. Difference scores (maximum possible change ±100) revealed a mean reduction of smell (-79.7 ± 28.7, mean ± standard deviation), taste (-69.0 ± 32.6), and chemesthetic (-37.3 ± 36.2) function during COVID-19. Qualitative changes in olfactory ability (parosmia and phantosmia) were relatively rare and correlated with smell loss. Importantly, perceived nasal obstruction did not account for smell loss. Furthermore, chemosensory impairments were similar between participants in the laboratory test and clinical assessment groups. These results show that COVID-19-associated chemosensory impairment is not limited to smell but also affects taste and chemesthesis. The multimodal impact of COVID-19 and the lack of perceived nasal obstruction suggest that severe acute respiratory syndrome coronavirus strain 2 (SARS-CoV-2) infection may disrupt sensory-neural mechanisms. © 2020 The Author(s) 2020. Published by Oxford University Press. All rights reserved
Thoracoabdominal computed tomography in trauma patients: a cost-consequences analysis
Contains fulltext :
139472.pdf (publisher's version ) (Open Access)BACKGROUND: CT is increasingly used during the initial evaluation of blunt trauma patients. In this era of increasing cost-awareness, the pros and cons of CT have to be assessed. OBJECTIVES: This study was performed to evaluate cost-consequences of different diagnostic algorithms that use thoracoabdominal CT in primary evaluation of adult patients with high-energy blunt trauma. MATERIALS AND METHODS: We compared three different algorithms in which CT was applied as an immediate diagnostic tool (rush CT), a diagnostic tool after limited conventional work-up (routine CT), and a selective tool (selective CT). Probabilities of detecting and missing clinically relevant injuries were retrospectively derived. We collected data on radiation exposure and performed a micro-cost analysis on a reference case-based approach. RESULTS: Both rush and routine CT detected all thoracoabdominal injuries in 99.1% of the patients during primary evaluation (n = 1040). Selective CT missed one or more diagnoses in 11% of the patients in which a change of treatment was necessary in 4.8%. Rush CT algorithm costed euro 2676 (US 3850) and resulted in the same radiation exposure. Selective CT resulted in less radiation dose (23.23 mSv) and costed euro 2771 (US$ 3790). CONCLUSIONS: Rush CT seems to result in the least costs and is comparable in terms of radiation dose exposure and diagnostic certainty with routine CT after a limited conventional work-up. However, selective CT results in less radiation dose exposure but a slightly higher cost and less certainty
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