1,805 research outputs found
The 1.6um Bump as a Photometric Redshift Indicator
I describe the principle of using the 1.6um H- spectral feature as a
photometric redshift indicator and demonstrate that the technique holds promise
by successfully recovering the redshifts of a small sample of z=0-1 galaxies
using only their infrared (JHKL) photometry. I then consider the applicability
of the technique to the 3.6--8um SIRTF filter set and investigate the
systematic errors that could arise in photometric redshifts from random
photometric errors or from a mismatch between target galaxies and fitting
templates in metallicity, star formation history, and amount of interstellar
dust. It appears that SIRTF near-IR data alone should be sufficient to estimate
redshift of most galaxies that are at z>~1.5 and are dominated by stellar
populations older than >~20Myr. Galaxies whose photometric fits indicate them
to be at lower redshifts, z_fit<~1.5, or dominated by very young stellar
populations, age_fit<~20Myr, suffer from severe degeneracies in photometric
redshift, and a reliable photometric determination of their redshifts will have
to include either IR observations at shorter wavelengths (H and K) or optical
data. Overall, it appears that - with care and caveats - the 1.6um bump can
provide a powerful way of estimating redshifts of distant galaxies in deep
infrared imaging surveys that will soon be provided by SIRTF, and, eventually,
by NGST.Comment: AJ in pres
Vibration Monitoring Techniques Applied to Detect Damage in Rotating Disks
Rotor health monitoring and online damage detection are increasingly gaining the interest of the manufacturers of aircraft engines. This is primarily due to the need for improved safety during operation as well as the need for lower maintenance costs. Applied techniques for detecting damage in and monitoring the health of rotors are essential for engine safety, reliability, and life prediction. The goals of engine safety are addressed within the NASA-sponsored Aviation Safety Program (AvSP). AvSP provides research and technology products needed to help the Federal Aviation Administration and the aerospace industry improve aviation safety. The Nondestructive Evaluation Group at the NASA Glenn Research Center is addressing propulsion health management and the development of propulsion-system-specific technologies intended to detect potential failures prior to catastrophe
Ethics, technology, and standard practice in communication centers: Proposing a continuing education credit program based on lessons learned from law, business, and healthcare
Communication centers on university campuses can benefit from an examination of the service and relationship-centered elements of the legal profession, business, and healthcare. Meaningful parallels are presented in three areas: standard practice and education, ethics, and technology. Based on its findings, this article argues centers consider adopting a continuing education credit program. A framework for the program is provided, presenting four categories related to intended outcomes: communication skills, professional development, interpersonal training, and ethics. The program is an intervention concerned with quality and may have the potential to improve a center’s training methods, the tutoring process, and the organization as a whole.
Properties and characterization of ALD grown dielectric oxides for MIS structures
We report on an extensive structural and electrical characterization of
under-gate dielectric oxide insulators Al2O3 and HfO2 grown by Atomic Layer
Deposition (ALD). We elaborate the ALD growth window for these oxides, finding
that the 40-100 nm thick layers of both oxides exhibit fine surface flatness
and required amorphous structure. These layers constitute a base for further
metallic gate evaporation to complete the Metal-Insulator-Semiconductor
structure. Our best devices survive energizing up to ~3 MV/cm at 77 K with the
leakage current staying below the state-of-the-art level of 1 nA. At these
conditions the displaced charge corresponds to a change of the sheet carrier
density of 3 \times 1013 cm-2, what promises an effective modulation of the
micromagnetic properties in diluted ferromagnetic semiconductors.Comment: 8 pages, 5 figures, 14 reference
Exploration of NDE Properties of AMB Supported Rotors for Structural Damage Detection
Recent advancements in actuator technology, power electronics, sensors, and signal processing have created a rapid development of smart machine technologies for rotating machinery. Ranging from machine condition monitoring and diagnostics to full active control of machine behavior, the integration of electrical and computer systems has produced significant advances in machine performance and reliability. Magnetic bearings are a typical mechatronics product. The hardware is composed of mechanical components combined with electronic elements such as sensors and power amplifiers and an information processing part, usually in the form of a microprocessor. In addition, an increasingly important part is software, which specifies the coordination of bearing forces to sensed rotor motion and consequently dictates the dynamic properties of the complete system. The inherent ability for sensing, information processing, and actuation gives the magnetic bearing the potential to become a key element in smart and intelligent machines
System Identification Methods for Dynamic Testing of Fluid-Film Bearings
There are various system identification approaches typically used to extract the rotordynamic coefficients from simultaneously measured dynamic force and motion signals. Since the coefficient values extracted can vary significantly as a function of the system identification approach used, more attention is needed to treat this issue than is typically included in the rotor dynamics literature. This paper describes system identification and data reduction methods used for extracting rotordynamic coefficients of fluid-film journal bearings. Data is used from a test apparatus incorporating a double-spoolshaft spindle which permits independent control over the journal spin speed and the frequency of an adjustable-magnitude circular orbit, for both forward and backward whirling. For example, a least squares linear regression on the force-displacement equations of the experiment provides only one of the rational approaches to extract the anisotropic rotordynamic coefficients (stiffness, damping and fluid inertia effects). Rotordynamic coefficients are also extracted with both first and second order orbital frequency dependencies. To assess the quality of the measured signals, coherence functions are calculated to relate the time-averaged input motion signals and the time-averaged output force signals
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