1,737 research outputs found
How to control if even experts are not sure: Robust fuzzy control
In real life, the degrees of certainty that correspond to one of the same expert can differ drastically, and fuzzy control algorithms translate these different degrees of uncertainty into different control strategies. In such situations, it is reasonable to choose a fuzzy control methodology that is the least vulnerable to this kind of uncertainty. It is shown that this 'robustness' demand leads to min and max for &- and V-operations, to 1-x for negation, and to centroid as a defuzzification procedure
Exploring the Atmosphere of Neoproterozoic Earth: The Effect of O on Haze Formation and Composition
Previous studies of haze formation in the atmosphere of the Early Earth have
focused on N/CO/CH atmospheres. Here, we experimentally
investigate the effect of O on the formation and composition of aerosols
to improve our understanding of haze formation on the Neoproterozoic Earth. We
obtained in situ size, particle density, and composition measurements of
aerosol particles produced from N/CO/CH/O gas mixtures
subjected to FUV radiation (115-400 nm) for a range of initial
CO/CH/O mixing ratios (O ranging from 2 ppm to 0.2\%).
At the lowest O concentration (2 ppm), the addition increased particle
production for all but one gas mixture. At higher oxygen concentrations (20 ppm
and greater) particles are still produced, but the addition of O
decreases the production rate. Both the particle size and number density
decrease with increasing O, indicating that O affects particle
nucleation and growth. The particle density increases with increasing O.
The addition of CO and O not only increases the amount of oxygen in
the aerosol, but it also increases the degree of nitrogen incorporation. In
particular, the addition of O results in the formation of nitrate bearing
molecules. The fact that the presence of oxygen bearing molecules increases the
efficiency of nitrogen fixation has implications for the role of haze as a
source of molecules required for the origin and evolution of life. The
composition changes also likely affect the absorption and scattering behavior
of these particles but optical properties measurements are required to fully
understand the implications for the effect on the planetary radiative energy
balance and climate.Comment: 15 pages, 3 tables, 8 figures, accepted in Astrophysical Journa
ARES I Upper Stage Subsystems Design and Development
From 2005 through early 2011, NASA conducted concept definition, design, and development of the Ares I launch vehicle. The Ares I was conceived to serve as a crew launch vehicle for beyond-low-Earth-orbit human space exploration missions as part of the Constellation Program Architecture. The vehicle was configured with a single shuttle-derived solid rocket booster first stage and a new liquid oxygen/liquid hydrogen upper stage, propelled by a single, newly developed J-2X engine. The Orion Crew Exploration Vehicle was to be mated to the forward end of the Ares I upper stage through an interface with fairings and a payload adapter. The vehicle design passed a Preliminary Design Review in August 2008, and was nearing the Critical Design Review when efforts were concluded as a result of the Constellation Program s cancellation. At NASA Glenn Research Center, four subsystems were developed for the Ares I upper stage. These were thrust vector control (TVC) for the J-2X, electrical power system (EPS), purge and hazardous gas (P&HG), and development flight instrumentation (DFI). The teams working each of these subsystems achieved 80 percent or greater design completion and extensive development testing. These efforts were extremely successful representing state-of-the-art technology and hardware advances necessary to achieve Ares I reliability, safety, availability, and performance requirements. This paper documents the designs, development test activity, and results
Alternative Employment Arrangements
[Excerpt] Part-time work, temporary work, independent contracting, and self-employment have experienced unprecedented increases in the last several decades. These employment arrangements characterize approximately 25-30 percent of the workforce, and they are growing fast. The rate of growth in part-time workers is 30 percent greater than in the overall work force, the rate of temporary agency workers is more than five times greater, and the growth in self-employment now equals the growth in civilian employment. These changes coincide with the increasing participation of married women in the labor force, the prevalence of dual-earner households, and the restructuring of the traditional employment relationship within many organizations. How have these simultaneous changes in employment arrangements and the demography of the workforce affected families\u27 strategies for managing work and family responsibilities? In this chapter we describe five couple-level employment strategies and examine their relationship to husbands\u27 and wives\u27 demographic and work characteristics, life stage, and objective and subjective measures of work and family success
Detection and Interpretation Of Long-Lived X-Ray Quasi-Periodic Pulsations in the X-Class Solar Flare On 2013 May 14
Quasi-periodic pulsations (QPP) seen in the time derivative of the GOES soft
X-ray light curves are analyzed for the near-limb X3.2 event on 14 May 2013.
The pulsations are apparent for a total of at least two hours from the
impulsive phase to well into the decay phase, with a total of 163 distinct
pulses evident to the naked eye. A wavelet analysis shows that the
characteristic time scale of these pulsations increases systematically from
25 s at 01:10 UT, the time of the GOES peak, to 100 s at 02:00 UT.
A second ridge in the wavelet power spectrum, most likely associated with
flaring emission from a different active region, shows an increase from
40 s at 01:40 UT to 100 s at 03:10 UT. We assume that the QPP that
produced the first ridge result from vertical kink-mode oscillations of the
newly formed loops following magnetic reconnection in the coronal current
sheet. This allows us to estimate the magnetic field strength as a function of
altitude given the density, loop length, and QPP time scale as functions of
time determined from the GOES light curves and RHESSI images. The calculated
magnetic field strength of the newly formed loops ranges from about 500 G
at an altitude of 24 Mm to a low value of 10 G at 60 Mm, in general
agreement with the expected values at these altitudes. Fast sausage mode
oscillations are also discussed and cannot be ruled out as an alternate
mechanism for producing the QPP
Microstructure of nanocrystalline diamond powders studied by powder diffractometry
High resolution x-ray diffraction peaks of diamond nanosize powders of nominal sizes ranging from 5 to 250 nm were analyzed and provided information on grain structure, average size of crystallites, and concentration of dislocations. Selected samples were heat treated at 1670 K at pressures 2.0 and 5.5 GPa or had surface modified by outgassing, heat treatment at vacuum conditions, and by controlled adsorption of gases. The apparent lattice parameter method was applied to characterize the structure of a shell-core model of nanosize particles. The multiple whole profile fitting provided information on crystallite sizes and density of dislocations. Population of dislocations increased with applied pressure, while strain and interplanar distances in the surface layers decreased. Adsorption of foreign gases on the grain surface modified the structure of the surface layers but did not affect dislocations near the center of the grains
The Thermal Properties of Solar Flares Over Three Solar Cycles Using GOES X-ray Observations
Solar flare X-ray emission results from rapidly increasing temperatures and
emission measures in flaring active region loops. To date, observations from
the X-Ray Sensor (XRS) onboard the Geostationary Operational Environmental
Satellite (GOES) have been used to derive these properties, but have been
limited by a number of factors, including the lack of a consistent background
subtraction method capable of being automatically applied to large numbers of
flares. In this paper, we describe an automated temperature and emission
measure-based background subtraction method (TEBBS), which builds on the
methods of Bornmann (1990). Our algorithm ensures that the derived temperature
is always greater than the instrumental limit and the pre-flare background
temperature, and that the temperature and emission measure are increasing
during the flare rise phase. Additionally, TEBBS utilizes the improved
estimates of GOES temperatures and emission measures from White et al. (2005).
TEBBS was successfully applied to over 50,000 solar flares occurring over
nearly three solar cycles (1980-2007), and used to create an extensive catalog
of the solar flare thermal properties. We confirm that the peak emission
measure and total radiative losses scale with background subtracted GOES X-ray
flux as power-laws, while the peak temperature scales logarithmically. As
expected, the peak emission measure shows an increasing trend with peak
temperature, although the total radiative losses do not. While these results
are comparable to previous studies, we find that flares of a given GOES class
have lower peak temperatures and higher peak emission measures than previously
reported. The resulting TEBBS database of thermal flare plasma properties is
publicly available on Solar Monitor (www.solarmonitor.org/TEBBS/) and will be
available on Heliophysics Integrated Observatory (www.helio-vo.eu)
Validating the Commercially Available Garmin Fenix 5x Wrist-Worn Optical Sensor for Aerobic Capacity
Recreational exercisers continue to take a greater interest in monitoring their personal fitness levels. One of the more notable measurements that are monitored and estimated by wrist-worn tracking devices is maximum aerobic capacity (VO2max), which is currently the accepted measure of cardiorespiratory fitness. Traditional methods of obtaining VO2max present expensive barriers, whereas new wearable technology, such as of the Garmin Fenix 5x (GF5) provides a more cost-effective alternative. PURPOSE: To determine the validity of the GF5 VO2max estimation capabilities against the ParvoMedics TrueOne 2400 (PMT) metabolic measurement system in recreational runners. METHODS: Twenty-five recreational runners (17 male and 8 female) ages 18-55 participated in this study. Participants underwent two testing sessions: one consisting of the Bruce Protocol utilizing the PMT, while the other test incorporated the GF5 using the Garmin outdoor protocol. Both testing sessions were conducted within a few days of each other, with a minimum of 24 hours rest between sessions. RESULTS: The mean VO2max values for the PMT trial (49.1 ± 8.4 mL/kg/min) and estimation for the GF5 trial (47 ± 6.0 mL/kg/min) were found to be significantly different (t = 2.21, p = 0.037). CONCLUSION: The average difference between the GF5 estimation and the PMT was 2.16 ml/kg/min. Therefore, the watch is not as accurate compared to a PMT for obtaining VO2max. However, although not statically significant, the proximity of scores to the PMT shows that the GF5 can be an option for a person seeking an affordable and easily available method of determining VO2max.  
The Role of a Hot Gas Environment on the Evolution of Galaxies
Most spiral galaxies are found in galaxy groups with low velocity
dispersions; most E/S0 galaxies are found in galaxy groups with relatively high
velocity dispersions. The mass of the hot gas we can observe in the E/S0 groups
via their thermal X-ray emission is, on average, as much as the baryonic mass
of the galaxies in these groups. By comparison, galaxy clusters have as much or
more hot gas than stellar mass. Hot gas in S-rich groups, however, is of low
enough temperature for its X-ray emission to suffer heavy absorption due to
Galactic HI and related observational effects, and hence is hard to detect. We
postulate that such lower temperature hot gas does exist in low velocity
dispersion, S-rich groups, and explore the consequences of this assumption. For
a wide range of metallicity and density, hot gas in S-rich groups can cool in
far less than a Hubble time. If such gas exists and can cool, especially when
interacting with HI in existing galaxies, then it can help link together a
number of disparate observations, both Galactic and extragalactic, that are
otherwise difficult to understand.Comment: 16 pages with one figure. ApJ Letters, in pres
- …