4,362 research outputs found
Optimal Masks for Low-Degree Solar Acoustic Modes
We suggest a solution to an important problem of observational
helioseismology of the separation of lines of solar acoustic (p) modes of low
angular degree in oscillation power spectra by constructing optimal masks for
Doppler images of the Sun. Accurate measurements of oscillation frequencies of
low-degree modes are essential for the determination of the structure and
rotation of the solar core. However, these measurements for a particular mode
are often affected by leakage of other p modes arising when the Doppler images
are projected on to spherical-harmonics masks. The leakage results in
overlaping peaks corresponding to different oscillation modes in the power
spectra. In this paper we present a method for calculating optimal masks for a
given (target) mode by minimizing the signals of other modes appearing in its
vicinity. We apply this method to time series of 2 years obtained from
Michelson Doppler Imager (MDI) instrument on board SOHO space mission and
demonstrate its ability to reduce efficiently the mode leakage.Comment: to be published in Astrophys.J. Letter
Emergency escape system uses self-braking mechanism on fixed cable
Slide-wire system with a twist level slide device incorporates automatic descent and braking for the safe and rapid evacuation of personnel from tall structures. This device is used on any tall structure that might require emergency evacuation. It is also used to transfer materials and equipment
Data base management system analysis and performance testing with respect to NASA requirements
Several candidate Data Base Management Systems (DBM's) that could support the NASA End-to-End Data System's Integrated Data Base Management System (IDBMS) Project, later rescoped and renamed the Packet Management System (PMS) were evaluated. The candidate DBMS systems which had to run on the Digital Equipment Corporation VAX 11/780 computer system were ORACLE, SEED and RIM. Oracle and RIM are both based on the relational data base model while SEED employs a CODASYL network approach. A single data base application which managed stratospheric temperature profiles was studied. The primary reasons for using this application were an insufficient volume of available PMS-like data, a mandate to use actual rather than simulated data, and the abundance of available temperature profile data
The variation of floods in the middle reaches of the Yangtze River and its teleconnection with El Niño events
International audienceMiddle reaches of the Yangtze River are the worst flooded segments along the Yangtze River. It is important to understand and study the variations of frequency and magnitude of historical floods in this area and how were they related to or affected by EI Niño in a long historical period. We applied the statistics and time series to study and analyze historical floods (1470-2000) and EI Niño events (1525-1995). The results show that the more floods occurred in the latest 200 years. The power-spectral analysis suggests the main cycle of flood variation is longer than that of EI Niño events. El Nino shows the fluctuations of about 2-year and 3~4 year period while the flood variation is not so significant but can also be identified in the period of 2, 8 and 40 years (it exceeds the level of confidence 0.03). Time series analyses of the fluctuation of flood and El Nino indicate that there is a significant correlation between the two at both high and moderate frequency sections. The result shows that the response of the floods along the middle reaches of the Yangtze River to the effects of El Nino events is not only delayed one or more than one year as suggested by many Chinese scientists, but it also can be somewhat longer delayed up to about 8 years. The result also indicates that the shorter the interval of EI Niño events, the sooner the flood events follows. In other words, flood could be delayed with longer time if the interval time of EI Niño events is longer
On the similarity of Information Energy to Dark Energy
Information energy is shown here to have properties similar to those of dark
energy. The energy associated with each information bit of the universe is
found to be defined identically to the characteristic energy of a cosmological
constant. Two independent methods are used to estimate the universe information
content of ~10^91 bits, a value that provides an information energy total
comparable to that of the dark energy. Information energy is also found to have
a significantly negative equation of state parameter, w < -0.4, and thus exerts
a negative pressure, similar to dark energy.Comment: 5 pages, no figures, no table
Results of data base management system parameterized performance testing related to GSFC scientific applications
The results of a variety of tests designed to demonstrate and evaluate the performance of several commercially available data base management system (DBMS) products compatible with the Digital Equipment Corporation VAX 11/780 computer system are summarized. The tests were performed on the INGRES, ORACLE, and SEED DBMS products employing applications that were similar to scientific applications under development by NASA. The objectives of this testing included determining the strength and weaknesses of the candidate systems, performance trade-offs of various design alternatives and the impact of some installation and environmental (computer related) influences
Detecting solar g-modes with ASTROD
We present an up-to-date estimate for the prospect of using the
Astrodynamical Space Test of Relativity using Optical Devices (ASTROD) for an
unambiguous detection of solar g modes (f < 400 micro Hertz) through their
gravitational signature. There are currently two major efforts to detect
low-frequency gravitational effects, ASTROD and the Laser Interferometer Space
Antenna (LISA). Using the most recent g mode surface amplitude estimates, both
observational and theoretical, it is unclear whether LISA will be capable of
successfully detecting these modes. The ASTROD project may be better suited for
detection as its sensitivity curve is shifted towards lower frequencies with
the best sensitivity occurring in the range 100-300 micro Hertz.Comment: HELAS II international conference "Helioseismology, asteroseismology
and MHD connections", 20-24 August 2007, Goettingen, German
c-axis penetration depth in BiSrCaCuO single crystals measured by ac-susceptibility and cavity perturbation technique
The -axis penetration depth in
BiSrCaCuO (BSCCO) single crystals as a function of
temperature has been determined using two techniques, namely, measurements of
the ac-susceptibility at a frequency of 100 kHz and the surface impedance at
9.4 GHz. Both techniques yield an almost linear function
in the temperature range T<0.5 T_c.
Electrodynamic analysis of the impedance anisotropy has allowed us to estimate
m in BSCCO crystals overdoped with oxygen
( K) and m at the optimal doping
level ( K).Comment: 5 pages, 4 figure
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