798 research outputs found
The five-minute oscillations: What's left to be done
Current observational methods for studying these oscillations at large horizontal wavenumbers are discussed in detail and several two dimensional power spectra obtained with a CID camera on the main spectrograph of the McMath telescope at Kitt Peak National Observatory are described. The best-resolved observations of the p-mode obtained at chromospheric elevations are also presented. Recent progress in studies of the p-modes at low wavenumbers with full-disk velocity detection schemes is summarized. These full-disk observations of radial and low-degree non-radial modes were shown to place severe constraints on the theoretical calculation of solar interior structure. Progress in making fully-consistent solar models which fit both the high- and low-wave number observations is described. Finally, the observational and theoretical improvements that are necessary for further progress in solar seismology are summarized
Oscillations in β Ursae Minoris
Aims. From observations of the K4III star β UMi we attempt to determine whether oscillations or any other form of variability is present.
Methods. A high-quality photometric time series of ≈1000 days in length obtained from the SMEI instrument on the Coriolis satellite is analysed. Various statistical tests were performed to determine the significance of features seen in the power density spectrum of the light curve.
Results. Two oscillations with frequencies 2.44 and 2.92 μHz have been identified. We interpret these oscillations as consecutive overtones of an acoustic spectrum, implying a large frequency spacing of 0.48 μHz. Using derived asteroseismic parameters in combination with known astrophysical parameters, we estimate the mass of β UMi to be 1.3 ± 0.3 M. Peaks of the oscillations in the
power density spectrum show width, implying that modes are stochastically excited and damped by convection. The mode lifetime is estimated at 18 ± 9 days
Recommended from our members
Preliminary evaluation of Am/Cm melter feed preparation process upset recovery flowsheets
This document summarizes the results from the development of flowsheets to recover from credible processing errors specified in TTR 99-MNSS/SE-006. The proposed flowsheets were developed in laboratory scale equipment and will be utilized with minor modifications for full scale demonstrations in the Am/Cm Pilot Facility
E-supply chain integration adoption: examination of buyer–supplier relationships
The purpose of this study is to empirically examine the adoption of e-supply chain integration by electrical and electronic industry suppliers. This study has integrated both the transaction cost and resource-dependence models in understanding the influence of buyer–seller relationships on e-supply chain integration. Hypotheses were developed based on the proposed model. Data were collected from 122 electrical and electronic suppliers located in Malaysia. The data was examined using multiple regression analysis. The results showed that Asset Specificity, Product Technological Uncertainty, Transaction frequency, Proportion of sales to e-supply chain integration promoter, and number of customers are able to explain suppliers’ decisions to adopt e-supply chain integrations with their buyers. Buyers that would like to improve the adoptions of e-supply chain integration will be able to formulate and plan strategies from the buyer–seller relationships perspectives
Studies of MCP-PMTs in the miniTimeCube neutrino detector
This report highlights two different types of cross-talk in the
photodetectors of the miniTimeCube neutrino experiment. The miniTimeCube
detector has 24 -anode Photonis MCP-PMTs Planacon XP85012,
totalling 1536 individual pixels viewing the 2-liter cube of plastic
scintillator
Image Quality of the Helioseismic and Magnetic Imager (HMI) Onboard the Solar Dynamics Observatory (SDO)
We describe the imaging quality of the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) as measured during the ground calibration of the instrument. We describe the calibration techniques and report our results for the final configuration of HMI. We present the distortion, modulation transfer function, stray light,image shifts introduced by moving parts of the instrument, best focus, field curvature, and the relative alignment of the two cameras. We investigate the gain and linearity of the cameras, and present the measured flat field
Comparisons of Supergranule Characteristics During the Solar Minima of Cycles 22/23 and 23/24
Supergranulation is a component of solar convection that manifests itself on
the photosphere as a cellular network of around 35 Mm across, with a turnover
lifetime of 1-2 days. It is strongly linked to the structure of the magnetic
field. The horizontal, divergent flows within supergranule cells carry local
field lines to the cell boundaries, while the rotational properties of
supergranule upflows may contribute to the restoration of the poloidal field as
part of the dynamo mechanism that controls the solar cycle. The solar minimum
at the transition from cycle 23 to 24 was notable for its low level of activity
and its extended length. It is of interest to study whether the convective
phenomena that influences the solar magnetic field during this time differed in
character to periods of previous minima. This study investigates three
characteristics (velocity components, sizes and lifetimes) of solar
supergranulation. Comparisons of these characteristics are made between the
minima of cycles 22/23 and 23/24 using MDI Doppler data from 1996 and 2008,
respectively. It is found that whereas the lifetimes are equal during both
epochs (around 18 h), the sizes are larger in 1996 (35.9 +/- 0.3 Mm) than in
2008 (35.0 +/- 0.3 Mm), while the dominant horizontal velocity flows are weaker
(139 +/- 1 m/s in 1996; 141 +/- 1 m/s in 2008). Although numerical differences
are seen, they are not conclusive proof of the most recent minimum being
inherently unusual.Comment: 22 pages, 5 figures. Solar Physics, in pres
- …