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1,585 - 1,597 of
1,597
Very high efficiency photovoltaic cells based on fully organic multiple quantum wells. Quarterly technical progress report, 15 February 1995--15 May 1995
The principal project objective is to demonstrate relatively high solar conversion efficiency using extremely low-cost, thin-film technology based on crystalline organic multiple quantum well (MQW) photovoltaic cells. The authors base their work on recent observations both in the laboratory and elsewhere that have indicated the quantum efficiency of organic photoconductors based on vacuum-deposited thin films can be increased by at least two orders of magnitude (to at least 10%) if the organic films are grown in a highly ordered manner, and if organic multiple quantum wells are used in the absorption region. The authors are investigating the physical origin of this phenomenon, and they are growing thin-film MQW cells that demonstrate relatively high quantum efficiencies to determine the practicality of crystalline organic thin-film cells for solar power applications. The investigations are based on a unique, ultrahigh-vacuum organic molecular beam deposition system in the laboratory.
Date:
March 1, 1997
Creator:
Forrest, S.R.
Object Type:
Report
System:
The UNT Digital Library
VIII. The observational strategy: What are the issues; What must be done?
Throughout its development, the observational strategy of the Earth Observing System (EOS) and its precursor programs has been consistent with that of the Mission to Planet Earth (MTPE) to detect and quantify climate change, document natural climate variability, understand variation and change, determine the causes and impacts of stratospheric ozone depletion, determine the impact of change on ecosystems and mitigate them. Space based observation can contribute significantly to each of these objectives, although its contribution will have to be carefully integrated with aircraft, in situ, international and other contributions and carefully transitioned to long-term operational observations to achieve its maximum potential impact. The interaction between space ad in situ can be in calibration, in interpretation, or in suggesting ways to make important new measurements from space. In atmospheric chemistry is largely involves calibration and global surveys. In ecosystems it involves calibration of EOS and improved sensors. In seasonal to interannual change it involves the testing and calibration of new sensors. In decadal to century change it requires the invention of new sensors. These roles are complementary and reinforcing. Taking full advantage of the synergisms and tradeoffs between space- and ground-based measurements is a potential vehicle for major savings in what …
Date:
March 1, 1997
Creator:
Canavan, G. H.
Object Type:
Report
System:
The UNT Digital Library
The Virtual Robotics Laboratory
The growth of the Internet has provided a unique opportunity to expand research collaborations between industry, universities, and the national laboratories. The Virtual Robotics Laboratory (VRL) is an innovative program at Oak Ridge National Laboratory (ORNL) that is focusing on the issues related to collaborative research through controlled access of laboratory equipment using the World Wide Web. The VRL will provide different levels of access to selected ORNL laboratory equipment to outside universities, industrial researchers, and elementary and secondary education programs. In the past, the ORNL Robotics and Process Systems Division (RPSD) has developed state-of-the-art robotic systems for the Army, NASA, Department of Energy, Department of Defense, as well as many other clients. After proof of concept, many of these systems sit dormant in the laboratories. This is not out of completion of all possible research topics, but from completion of contracts and generation of new programs. In the past, a number of visiting professors have used this equipment for their own research. However, this requires that the professor, and possibly his students, spend extended periods at the laboratory facility. In addition, only a very exclusive group of faculty can gain access to the laboratory and hardware. The VRL is …
Date:
March 1, 1997
Creator:
Kress, R. L. & Love, L. J.
Object Type:
Article
System:
The UNT Digital Library
Visual inspection for CTBT verification
On-site visual inspection will play an essential role in future Comprehensive Test Ban Treaty (CTBT) verification. Although seismic and remote sensing techniques are the best understood and most developed methods for detection of evasive testing of nuclear weapons, visual inspection can greatly augment the certainty and detail of understanding provided by these more traditional methods. Not only can visual inspection offer ``ground truth`` in cases of suspected nuclear testing, but it also can provide accurate source location and testing media properties necessary for detailed analysis of seismic records. For testing in violation of the CTBT, an offending party may attempt to conceal the test, which most likely will be achieved by underground burial. While such concealment may not prevent seismic detection, evidence of test deployment, location, and yield can be disguised. In this light, if a suspicious event is detected by seismic or other remote methods, visual inspection of the event area is necessary to document any evidence that might support a claim of nuclear testing and provide data needed to further interpret seismic records and guide further investigations. However, the methods for visual inspection are not widely known nor appreciated, and experience is presently limited. Visual inspection can be …
Date:
March 1, 1997
Creator:
Hawkins, W. & Wohletz, K.
Object Type:
Report
System:
The UNT Digital Library
Water adsorption in interfacial silane layers by neutron reflection
It is well known that water plays an important role in the degradation of adhesive strength between a wide variety of materials. It is also well established that silane coupling agents can provide excellent bond durability in aqueous environments. However, the detrimental effects of interfacial water are not limited to adhesive failure. The present study was motivated by concerns in the printed circuit board industry regarding the loss of electrical resistance, as well as adhesive failure, which may arise from water at epoxy/silane/E-glass interphases. The commercial silane finish used in this study provides excellent adhesive strength between epoxy and E-glass, and remarkable bond durability even after extensive conditioning in boiling water or a pressure cooker. However, circuit boards with this finish do not perform well in insulation resistance testing following such conditioning. The goal of this work is to develop a detailed understanding of the mechanism by which water interacts with a resin/silane interphase, with a focus on the consequences for both electrical resistance and adhesion. The present report focuses on the measurement of profiles of adsorbed moisture by neutron reflection.
Date:
March 1, 1997
Creator:
Kent, M. S.; McNamara, W. F.; Domeier, L.; Wong, A. P. Y. & Wu, W. L.
Object Type:
Article
System:
The UNT Digital Library
Wheel rolling constraints and slip in mobile robots
It is widely accepted that dead reckoning based on the rolling with no slip condition on wheels is not a reliable method to ascertain the position and orientation of a mobile robot for any reasonable distance. The author establishes that wheel slip is inevitable under the dynamic model of motion using classical results on the accessibility and controllability in nonlinear control theory and an analytical model of rolling of two linearly elastic bodies.
Date:
March 1, 1997
Creator:
Shekhar, S.
Object Type:
Article
System:
The UNT Digital Library
Wheel rolling constraints and slip in mobile robots
It is widely accepted that dead reckoning based on the rolling with no slip condition on wheels is not a reliable method to ascertain the position and orientation of a mobile robot for any reasonable distance. We establish that wheel slip is inevitable under the dynamic model of motion using classical results on the accessibility and controllability in nonlinear control theory and an analytical model of rolling of two linearly elastic bodies.
Date:
March 1, 1997
Creator:
Shekhar, S.
Object Type:
Article
System:
The UNT Digital Library
Why we still don`t know the symmetry of the order parameter in high temperature superconductors
One of the most elusive topics in the study of high temperature superconductors (HTCS) is the orbital symmetry of the superconducting order parameter {Delta}. The low temperature T behavior observed in many experiments suggests that {Delta} might exhibit line nodes, as expected for d{sub x}{sub {minus}y}2 orbital symmetry. However, such behavior also arises from intrinsic proximity coupling and surface states, etc. The paramagnetic Meissner effect, once cited as indirect evidence for a d-wave {Delta}, was recently observed in Nb. Some phase-sensitive Josephson junction experiments gave strong evidence for a substantial isotropic, or s-wave, component to {Delta}, whereas others supported the above d-wave form. However, such experiments are intrinsically unreliable in experimental geometries with sample corners, or with meandering grain boundary junctions and stoichiometry inhomogeneities. Finally, the pseudogap observed recently in underdoped HTCS could arise from a charge-density wave.
Date:
March 1, 1997
Creator:
Klemm, R.A.
Object Type:
Article
System:
The UNT Digital Library
X-ray evidence for capillary pressure driven flow in preserved core from The Geysers
Improved understanding of fluid storage and transport mechanisms relevant to The Geysers reservoir is fundamental to efficient and economic long term production of steam. X-ray computed tomographs of core from research borehole SB-15D made within 72 hours of drilling show characteristic x-ray attenuation profiles that can only be explained by imbibition of drilling fluid at reservoir conditions. The shape of the profile is highly diagnostic. Early time scans, when interpreted taking into account independent measurements of pore size distribution, permeabilities and capillary pressures for the rock matrix sampled by SB-15D, are consistent with strong capillary suctions for the recovered rocks. This indirect indication of imbibition under reservoir conditions, along with detailed analysis of x-ray attenuation in recovered core, suggests that water content was low in much of the preserved core. These measurements are part of a series of laboratory experiments monitored by x-ray methods intended to evaluate movement of various fluids to determine the relative importance capillarity, Darcy flow and vapor phase diffusion.
Date:
March 1, 1997
Creator:
Bonner, B. P.; Roberts, J. J. & Schneberk, D. J.
Object Type:
Article
System:
The UNT Digital Library
An X-ray photoelectron spectroscopic study of the B-N-Ti system
Composite nitrides (such as BN, TiN) are widely used in various industrial applications because of their extreme wear and corrosion resistance, thermal and electrical properties. In order to obtain composite materials with these optimal properties, it is important to elucidate whether any chemical reactions occur at nitride/metal interfaces, e.g., those involving BN-Ti/TiN. Materials of interest include the deposition by PVD of Ti and TiN on BN substrates. Some of these systems were then subjected to varying degrees of physical and thermal alteration. Detailed X-ray photoelectron spectroscopy (XPS) has therefore been rendered of these interfaces using cross-sectional display and sputter etching. Resulting structural and morphological features have been investigated with transmission electron microscopy (TEM) and X-ray diffraction (XRD). Diffusion of the nitridation, oxynitride formation and interfacial growth are of general interest.
Date:
March 1, 1997
Creator:
Seal, S.; Barr, T.L.; Sobczak, N.; Benko, E. & Morgiel, J.
Object Type:
Article
System:
The UNT Digital Library
X-ray radiography of fracture flow and matrix imbibition in Topopah Spring Tuff under a thermal gradient
A method of imaging the flow of liquid in fractures and matrix imbibition in tuff using x-ray radiography has been developed and a formulation for the calculation of saturation in the matrix based on x-ray radiography is presented. Experiments were performed using different thermal gradients and hydrostatic heads. The distance that liquid penetrates the boiling region was found to be dependent on hydrostatic head: during the highest-head experiment, liquid water penetrated the entire fracture and continued to pass through the boiling region. For experiments where flow stopped at the boiling region, x-ray images indicate crystal deposition along the fracture. In some cases, when the sample was cooled, fracture flow resumed, and in other cases the fractures were sealed and flow did not continue.
Date:
March 1, 1997
Creator:
Roberts, J.J., Lin, W.
Object Type:
Article
System:
The UNT Digital Library
XMGR5 users manual
ACE/gr is XY plotting tool for workstations or X-terminals using X. A few of its features are: User defined scaling, tick marks, labels, symbols, line styles, colors. Batch mode for unattended plotting. Read and write parameters used during a session. Polynomial regression, splines, running averages, DFT/FFT, cross/auto-correlation. Hardcopy support for PostScript, HP-GL, and FrameMaker.mif format. While ACE/gr has a convenient point-and-click interface, most parameter settings and operations are available through a command line interface (found in Files/Commands).
Date:
March 1, 1997
Creator:
Jones, K.R. & Fisher, J.E.
Object Type:
Report
System:
The UNT Digital Library
D-Zero run II data management and access
During the Run II data taking period at Fermilab, scheduled to begin in 1999, D0 plans to accumulate at least 200 TB of raw and reconstructed data per year. Data access patterns observed in the Run I experience have been examined in an attempt to establish an efficient data access environment. The needs and models for storing and processing the upcoming data are discussed.
Date:
March 1, 1997
Creator:
Lueking, L.
Object Type:
Article
System:
The UNT Digital Library