5,360 research outputs found
Performance of charge-injection-device infrared detector arrays at low and moderate backgrounds
Three 2 x 64 element charge injection device infrared detector arrays were tested at low and moderate background to evaluate their usefulness for space based astronomical observations. Testing was conducted both in the laboratory and in ground based telescope observations. The devices showed an average readout noise level below 200 equivalent electrons, a peak responsivity of 4 A/W, and a noise equivalent power of 3x10 sq root of W/Hz. Array well capacity was measured to be significantly smaller than predicted. The measured sensitivity, which compares well with that of nonintegrating discrete extrinsic silicon photoconductors, shows these arrays to be useful for certain astronomical observations. However, the measured readout efficiency and frequency response represent serious limitations in low background applications
The Relationships Among Student Learning Styles, Course Delivery Method, and Course Outcomes: A Quasi-Experiement Investigating the Case Method of Course Delivery
Infrared Classification of Galactic Objects
Unbiased analysis shows that IRAS data reliably differentiate between the
early and late stages of stellar evolution because objects at these stages
clearly segregate in infrared color-color diagrams. Structure in these diagrams
is primarily controlled by the density distribution of circumstellar dust. The
density profile around older objects is the steepest, declining as ,
while young objects have profiles that vary as and flatter. The
different density profiles reflect the different dynamics that govern the
different environments. Our analysis also shows that high mass star formation
is strongly concentrated within \about 5 kpc around the Galactic center, in
support of other studies.Comment: 11 pages, 3 Postscript figures (included), uses aaspp4.sty. To appear
in Astrophysical Journal Letter
Towards Physical Hybrid Systems
Some hybrid systems models are unsafe for mathematically correct but
physically unrealistic reasons. For example, mathematical models can classify a
system as being unsafe on a set that is too small to have physical importance.
In particular, differences in measure zero sets in models of cyber-physical
systems (CPS) have significant mathematical impact on the mathematical safety
of these models even though differences on measure zero sets have no tangible
physical effect in a real system. We develop the concept of "physical hybrid
systems" (PHS) to help reunite mathematical models with physical reality. We
modify a hybrid systems logic (differential temporal dynamic logic) by adding a
first-class operator to elide distinctions on measure zero sets of time within
CPS models. This approach facilitates modeling since it admits the verification
of a wider class of models, including some physically realistic models that
would otherwise be classified as mathematically unsafe. We also develop a proof
calculus to help with the verification of PHS.Comment: CADE 201
Immunizations for Adults and Children
Vaccines represent the most important medical advance of the twentieth century. The time has passed when large numbers of children and adults suffered serious, life threatening illness from viruses including poliovirus, measles virus, influenza viruses, hepatitis B virus and varicella zoster virus or faced lifelong disability or death from bacterial infections including Hemophilus influenzae, meningococcus and pneumococcus, all infections that can be prevented now by effective vaccines
Dirac Relation and Renormalization Group Equations for Electric and Magnetic Fine Structure Constants
The quantum field theory describing electric and magnetic charges and
revealing a dual symmetry was developed in the Zwanziger formalism. The
renormalization group (RG) equations for both fine structure constants -
electric and magnetic - were obtained. It was shown
that the Dirac relation is valid for the renormalized and at the arbitrary scale, but these RG equations can be considered
perturbatively only in the small region: with given by the Dirac
relation: = 1/4.Comment: 15 pages, 4 figures, made corrections of physics after comments from
Kim Milto
Quantification of Ophthalmic Changes After Long-Duration Spaceflight, and Subsequent Recovery
A subset of crewmembers are subjected to ophthalmic structure changes due to long-duration spaceflight (>6 months). Crewmembers who experience these changes are described as having Spaceflight Associated Neuro-Ocular Syndrome (SANS). Characteristics of SANS include optic disk edema, cotton wool spots, choroidal folds, refractive error, and posterior globe flattening. SANS remains a major obstacle to deep-space and planetary missions, requiring a better understanding of its etiology. Quantification of ocular, structural changes will improve our understanding of SANS pathophysiology. Methods were developed to quantify 3D optic nerve (ON) and ON sheath (ONS) geometries, ON tortuosity, and posterior globe deformation using MR imaging
Effects of Surface Coatings on the Joint Formation During Magnetic Pulse Welding in Tube-to-Cylinder Configuration
Magnetic Pulse Welding (MPW) is a joining technique favorable for the generation of
strong atomic bonded areas between different metals, e.g. aluminum and steel. Brittle
intermetallic phases can be avoided due to the high-speed collision and the absence of
external heat. The demand for the use of this technique in industries like automotive and
plant engineering rises. However, workpieces used in these fields are often coated, e.g. in
order to improve the corrosion resistance. Since the weld quality depends on the materialâs
behavior at the collision zone, surface layers in that region have to be taken into account
as well.
This work investigates the influences of different coating types. Aluminum to steel
welding is used as an example system. On the inner steel part (C45) coatings like zinc,
nickel and chrome are applied, while the aluminum flyer tubes (EN AW-6060) are
anodized, chromated and passivated. Welding tests are performed using two different
welding systems with varying discharging frequencies and four geometrical part setups.
For all combinations, the flyer velocity during the process is measured by Photon Doppler
Velocimetry (PDV). By using the uncoated material combination as a reference, the
removal of surface layers due to jetting is analyzed. Finally, the weld quality is
characterized in peel tests, shear-push tests and by the help of metallographic analysis. It
is found that certain coatings improve the joint formation, while others are obstructive for
the performance of MPW. Some coatings have no influence on the joining process at all
Integrating Systems Health Management with Adaptive Controls for a Utility-Scale Wind Turbine
Increasing turbine up-time and reducing maintenance costs are key technology drivers for wind turbine operators. Components within wind turbines are subject to considerable stresses due to unpredictable environmental conditions resulting from rapidly changing local dynamics. Systems health management has the aim to assess the state-of-health of components within a wind turbine, to estimate remaining life, and to aid in autonomous decision-making to minimize damage. Advanced adaptive controls can provide the mechanism to enable optimized operations that also provide the enabling technology for Systems Health Management goals. The work reported herein explores the integration of condition monitoring of wind turbine blades with contingency management and adaptive controls. Results are demonstrated using a high fidelity simulator of a utility-scale wind turbine
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