218 Matching Results

Search Results

Advanced search parameters have been applied.

Health Technology Case Study Thirty-one: The Contact Lens Industry: Structure, Competition, and Public Policy

Description: A study by the Office of Technology Assessment (OTA) that "presents an analysis of the contact lens industry in the United States, emphasizing the role of economics and public policy in shaping past and future development" (p. 3).
Date: December 1984
Creator: United States. Congress. Office of Technology Assessment.
Partner: UNT Libraries Government Documents Department

Fabrication of MOS capacitor and transitor structure using contact photolithography.

Description: This problem in lieu of thesis report describes a practical photolithographic method to produce micro patterns on metal-oxide-semiconductor or metal-oxide-semiconductor-metal layers for electrical measurements. The desired patterns are then transferred from the photo mask to the photoresist-coated metal film by exposure, followed by wet etching. In the procedure described in this report, it was observed that microstructures as small as 27 mm with an edge roughness of ~ 2 mm can be reproducibly generated with this process. MOS capacitors and transistors structures can be fabricated by using this technique. The method described in this report requires access to only simple facilities so that it is relatively inexpensive, and the overall time required for the whole process is short.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: August 2002
Creator: Su, Danni
Partner: UNT Libraries

Statistical measurements of landing-contact conditions of a heavy bomber

Description: Report presenting statistical measurements of landing-contact conditions for 144 landings of a heavy bomber airplane during routine daytime operations at Carswell Air Force Base. Using measurements obtained by a special photographic method, sinking speeds, bank angles, rolling velocities, and horizontal speeds at the instant before contact were evaluated and analyzed.
Date: June 27, 1955
Creator: Silsby, Norman S. & Harrin, Eziaslav N.
Partner: UNT Libraries Government Documents Department

A Multiple Bridge for Elimination of Contact-Resistance Errors in Resistance Strain-Gauge Measurements

Description: Note presenting a multiple-bridge circuit that eliminates contact-resistance errors of the first order between the arms of the ordinary Wheatstone bridge. The circuit is applied to the elimination of the effects of contact-resistance variations that may occur in resistance strain-gage measurements made through switch contacts or slip rings. The general theory is derived and correct circuits and constructions are described.
Date: March 1946
Creator: Warshawsky, Isidoro
Partner: UNT Libraries Government Documents Department

Wettability of Silicon, Silicon Dioxide, and Organosilicate Glass

Description: Wetting of a substance has been widely investigated since it has many applications to many different fields. Wetting principles can be applied to better select cleans for front end of line (FEOL) and back end of line (BEOL) cleaning processes. These principles can also be used to help determine processes that best repel water from a semiconductor device. It is known that the value of the dielectric constant in an insulator increases when water is absorbed. These contact angle experiments will determine which processes can eliminate water absorption. Wetting is measured by the contact angle between a solid and a liquid. It is known that roughness plays a crucial role on the wetting of a substance. Different surface groups also affect the wetting of a surface. In this work, it was investigated how wetting was affected by different solid surfaces with different chemistries and different roughness. Four different materials were used: silicon; thermally grown silicon dioxide on silicon; chemically vapor deposited (CVD) silicon dioxide on silicon made from tetraethyl orthosilicate (TEOS); and organosilicate glass (OSG) on silicon. The contact angle of each of the samples was measured using a goniometer. The roughness of the samples was measured by atomic force microscopy (AFM). The chemistry of each of the samples were characterized by using X-ray photoelectron spectroscopy (XPS) and grazing angle total attenuated total reflection Fourier transform infrared spectroscopy (FTIR/GATR). Also, the contact angle was measured at the micro scale by using an environmental scanning electron microscope (ESEM).
Date: December 2009
Creator: Martinez, Nelson
Partner: UNT Libraries

Trends of Rolling-Contact Bearings as Applied to Aircraft Gas-Turbine Engines

Description: Note presenting a review of the present and future trends of rolling-contact bearings for aircraft gas-turbine engines, which indicates that while rolling-contact bearings are satisfactory for present production engines, new bearings for future, higher output aircraft engines require more development. These new engines have operating conditions resulting in two primary problems: cage materials and endurance of materials for raceways and rolling elements.
Date: April 1954
Creator: Panel on High-Speed Rolling-Contact Bearings
Partner: UNT Libraries Government Documents Department

FEM of nanoindentation on micro- and nanocrystalline Ni: Analysis of factors affecting hardness and modulus values.

Description: Nanoindentation is a widely used technique to measure the mechanical properties of films with thickness ranging from nanometers to micrometers. A much better understanding of the contact mechanics is obtained mostly through finite element modeling. The experiments were modeled using the software package Nano SP1 that is based on COSMOSM™ (Structural Research & Analysis Corp, www.cosmosm.com), a finite element code. The fundamental material properties affecting pile-up are the ratio of the effective modulus to yield stress Eeff/σ and the work hardening behavior. Two separate cases of work hardening rates were considered; one with no work hardening rate and other with a linear work hardening rate. Specifically, it is observed that pile up is large only when hf/hmax is close to one and degree of work hardening rate is small. It should also be noted that when hf/hmax < 0.7 very little pile-up is observed no matter what the work-hardening behavior of the material. When pile-up occurs the contact area is greater than that predicted by the experimental methods and both the hardness and modulus are overestimated. In this report the amount by which these properties are overestimated are studied and got to be around 22% approx. Bluntness of the tip often leads to the misinterpretation of the load-displacement data. Further analysis was done in order to find out the amount of deviation from the ideal tip due to tip bluntness. Radius of the tips were also calculated for cubecorner (41.35 nm) and conical indenter (986.05 nm).
Date: August 2005
Creator: Pothapragada, Raja Mahesh
Partner: UNT Libraries

Investigation of growth kinetics of self-assembling monolayers by means of contact angle, optical ellipsometry, angle-resolved XPS and IR spectroscopy.

Description: Absorption of octadecanethiol and p-nitrobenzenethiol onto gold surfaces from ethanol solutions has been studied by means of contact angle, optical ellipsometry, angle-resolved XPS (ARXPS), and with grazing angle total reflection FTIR. Growth of the monolayers from dilute solutions has been monitored and Langmuir isotherm adsorption curves were fitted to experimental data. A saturated film is formed within approximately 5h after immersion in solutions of concentrations ranging from 0.0005mM to 0.01mM. We found, that the final density of monolayer depends on the concentration of the solution.
Date: August 2004
Creator: Jakubowicz, Agnieszka
Partner: UNT Libraries

Observed Eye Contact between Selected Students and Teacher in the Music Making Process

Description: High school band members (N=13) and their teacher were observed during six rehearsals of two contrasting band compositions over a six-week period. The contrasting compositions were selected by means of a detailed process between me (the researcher) and the teacher (the conductor). One 60-second excerpt of each composition was selected, during the performance of which, the students were observed. Three video tapings of each composition was done in order to capture occasions when the students would look up from their music. Using a technique adapted from Ekman (1997), the band members and teacher were then interviewed in order to reveal the reasons they recalled for looking up from their music. The results showed that the band members looked up in places where the teacher expected eye contact, that the frequency of eye contact changed little from one rehearsal to the next, and that the frequency of eye contact changed little between the two contrasting compositions. In all cases, the band members were able to recall the reasons for looking up from their music, a fact which led to a detailed analysis about the students' own thoughts while they were engaged in playing as an ensemble. The results are discussed in terms of strategies for teaching practice and implications for future research.
Date: August 2006
Creator: DeLong, D. Phillip
Partner: UNT Libraries

Effect of Substrate Support on Dynamic Graphene/Metal Electrical Contacts

Description: This article investigates the stability of dynamic electrical contacts at a graphene/metal interface using atomic force microscopy (AFM), under static conditions with variable normal loads and under sliding conditions with variable speeds.
Date: March 22, 2018
Creator: Lee, Jihyung; Hu, Xiaoli; Voevodin, Andrey A.; Martini, Ashlie & Berman, Diana
Partner: UNT College of Engineering

[University Academy Contact List]

Description: List of addresses for science and mathematics academies at various universities, including names and information for the presidents of the universities and the academy contacts.
Date: September 1, 1988
Creator: Texas Academy of Mathematics and Science
Partner: Texas Academy of Mathematics and Science

Magnetic Anticrossing of 1D Subbands in Coupled Ballistic Double Quantum Wires

Description: We study the low-temperature in-plane magnetoconductance of vertically coupled double quantum wires. Using a novel flip-chip technique, the wires are defined by two pairs of mutually aligned split gates on opposite sides of a s 1 micron thick AlGaAs/GaAs double quantum well heterostructure. We observe quantized conductance steps due to each quantum well and demonstrate independent control of each ID wire. A broad dip in the magnetoconductance at -6 T is observed when a magnetic field is applied perpendicular to both the current and growth directions. This conductance dip is observed only when 1D subbands are populated in both the top and bottom constrictions. This data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands.
Date: July 13, 2000
Partner: UNT Libraries Government Documents Department

Session 2: Review of the 500 KW Direct Contact Geothermal Plant at East Mesa

Description: The concept of a binary power cycle utilizing direct contact heat exchangers was first proposed by Jacobs and Boehm in 1973 for use with geothermal brines. This concept was proposed primarily to overcome difficulties associated with the fouling and scaling nature of many moderate temperature brines. However, thermodynamic analyses and subsequent economic analyses clearly pointed to possible economic advantages over conventional binary cycles even with non-fouling, non-scaling brines. For a direct contact binary power plant to be economically attractive it is necessary that a small pinch point be obtainable so that a maximum amount of power can be obtained per unit mass flow of geothermal brine. Since the working fluid comes in direct contact with the brine it must be immiscible with the brine, low in cost and, if part of it goes into solution in the brine, easily recoverable. In addition, noncondensible gases from the brine must be controlled to limit their effect on condenser pressure. The 500 kWe DCHX test facility installed at East Mesa was designed to evaluate techniques to provide economical operation. The choice of the East Mesa test site as a first location to evaluate the DCHX system placed additional requirements on the system. The brine at East Mesa was at low pressure, requiring the use of downhole pumps. The selection of isobutane as a working fluid required increasing the pressure of the brine. The high amount of dissolved CO{sub 2} in the brine required that it be preflashed to prevent the carryover of CO{sub 2} gas through the turbine and into the condenser which would adversely affect the system performance. All of these problems have been met by the system designer and operator, Barber-Nichols Engineering. Further, problems with isobutane turbine design, supposed state-of-the-art, were encountered and resolved.
Date: December 1, 1983
Creator: Nichols, Kenneth E.
Partner: UNT Libraries Government Documents Department

Process Knowledge Summary Report for Materials and Fuels Complex Contact-Handled Transuranic Debris Waste

Description: This Process Knowledge Summary Report summarizes the information collected to satisfy the transportation and waste acceptance requirements for the transfer of transuranic (TRU) waste between the Materials and Fuels Complex (MFC) and the Advanced Mixed Waste Treatment Project (AMWTP). The information collected includes documentation that addresses the requirements for AMWTP and the applicable portion of their Resource Conservation and Recovery Act permits for receipt and treatment of TRU debris waste in AMWTP. This report has been prepared for contact-handled TRU debris waste generated by the Idaho National Laboratory at MFC. The TRU debris waste will be shipped to AMWTP for purposes of supercompaction. This Process Knowledge Summary Report includes information regarding, but not limited to, the generation process, the physical form, radiological characteristics, and chemical contaminants of the TRU debris waste, prohibited items, and packaging configuration. This report, along with the referenced supporting documents, will create a defensible and auditable record for waste originating from MFC.
Date: February 1, 2010
Creator: Grant, R. P.; Crane, P. J.; Butler, S. & Henry, M. A.
Partner: UNT Libraries Government Documents Department

Low temperature front surface passivation of interdigitated back contact silicon heterojunction solar cell

Description: The interdigitated back contact silicon heterojunction (IBC-SHJ) solar cell requires a low temperature front surface passivation/anti-reflection structure. Conventional silicon surface passivation using SiO2 or a-SiNx is performed at temperature higher than 400°C, which is not suitable for the IBC-SHJ cell. In this paper, we propose a PECVD a-Si:H/a-SiNx:H/a-SiC:H stack structure to passivate the front surface of crystalline silicon at low temperature. The optical properties and passivation quality of this structure are characterized and solar cells using this structure are fabricated. With 2 nm a-Si:H layer, the stack structure exhibits stable passivation with effective minority carrier lifetime higher than 2 ms, and compatible with IBC-SHJ solar cell processing. A critical advantage of this structure is that the SiC allows it to be HF resistant, thus it can be deposited as the first step in the process. This protects the a-Si/c-Si interface and maintains a low surface recombination velocity.
Date: June 8, 2009
Creator: Shu, Brent; Das, Ujjwal; Jani, Omkar; Hegedus, Steve & Birkmire, Robert
Partner: UNT Libraries Government Documents Department

Multiphase Flow in Complex Fracture Apertures under a Wide Range of Flow Conditions

Description: A better understanding of multiphase flow through fractures requires knowledge of the detailed physics of interfacial flows at the microscopic pore scale. The objective of our project was to develop tools for the simulation of such phenomena. Complementary work was performed by a group led by Dr.~Paul Meakin of the Idaho National Engineering and Environmental Laboratory. Our focus was on the lattice-Boltzmann (LB) method. In particular, we studied both the statics and dynamics of contact lines where two fluids (wetting and non-wetting) meet solid boundaries. Previous work had noted deficiencies in the way LB methods simulate such interfaces. Our work resulted in significant algorithmic improvements that alleviated these deficiencies. As a result, we were able to study in detail the behavior of the dynamic contact angle in flow through capillary tubes. Our simulations revealed that our LB method reproduces the correct scaling of the dynamic contact angle with respect to velocity, viscosity, and surface tension, without specification of an artificial slip length. Further study allowed us to identify the microscopic origin of the dynamic contact angle in LB methods. These results serve to delineate the range of applicability of multiphase LB methods to flows through complex geometries.
Date: December 12, 2006
Creator: Rothman, Daniel H.
Partner: UNT Libraries Government Documents Department

Formation of ohmic contacts to MOCVD grown p-GaN by controlled activation of Mg

Description: We report on the formation of low resistivity ohmic contacts to p-GaN, r{sub c} &lt; 10{sup {minus}4}{Omega}cm{sup 2}, by increasing the concentration of the active Mg in the subcontact zone, via Zr-mediated release of hydrogen. We have investigated the process of evolution of hydrogen from MOCVD grown p-GaN via Zr-based metallization, and determined the optimum processing conditions (temperature and gas ambient) for fabrication of low resistance ohmic contacts. When the process is conducted in N{sub 2} flow, the metallization remains stable at temperatures required to achieve the ohmic behavior, and the morphology of the metal/semiconductor interface is unaltered by such a heat treatment. The processing in O{sub 2}, on the contrary, causes the interdiffusion of metallization constituents and the incorporation of oxygen into the semiconductor subcontact region, which could be responsible for increased resistivity of these contacts.
Date: November 27, 2000
Creator: Kaminska, E.; Piotrowska, A.; Barcz, A.; Bour, D.; Zielinski, M. & Jasinski, J.
Partner: UNT Libraries Government Documents Department

Development and testing of new biologically-based polymers as advanced biocompatible contact lenses

Description: Nature has evolved complex and elegant materials well suited to fulfill a myriad of functions. Lubricants, structural scaffolds and protective sheaths can all be found in nature, and these provide a rich source of inspiration for the rational design of materials for biomedical applications. Many biological materials are based in some fashion on hydrogels, the crosslinked polymers that absorb and hold water. Biological hydrogels contribute to processes as diverse as mineral nucleation during bone growth and protection and hydration of the cell surface. The carbohydrate layer that coats all living cells, often referred to as the glycocalyx, has hydrogel-like properties that keep cell surfaces well hydrated, segregated from neighboring cells, and resistant to non-specific protein deposition. With the molecular details of cell surface carbohydrates now in hand, adaptation of these structural motifs to synthetic materials is an appealing strategy for improving biocompatibility. The goal of this collaborative project between Prof. Bertozzi's research group, the Center for Advanced Materials at Lawrence Berkeley National Laboratory and Sunsoft Corporation was the design, synthesis and characterization of novel hydrogel polymers for improved soft contact lens materials. Our efforts were motivated by the urgent need for improved materials that allow extended wear, and essential feature for those whose occupation requires the use of contact lenses rather than traditional spectacles. Our strategy was to transplant the chemical features of cell surface molecules into contact lens materials so that they more closely resemble the tissue in which they reside. Specifically, we integrated carbohydrate molecules similar to those found on cell surfaces, and sulfoxide materials inspired by the properties of the carbohydrates, into hydrogels composed of biocompatible and manufacturable substrates. The new materials were characterized with respect to surface and bulk hydrophilicity, and n on-specific protein adsorption, properties which are thought to correlate with comfort in the eye. ...
Date: June 1, 2000
Creator: Bertozzi, Carolyn R.
Partner: UNT Libraries Government Documents Department

Direct contact heat exchanger performance

Description: Although the final performance result of a DCHE is the cost of the net electricity produced, the best performance cannot be achieved without optimizing the components of the system as well as the whole system. Thus collection and analysis of data on the internal performance of the column assists in optimizing the operation of the particular column as well as in suggesting ways for improving the operation and design of future columns.
Date: March 12, 1981
Creator: Wahl, E. F.
Partner: UNT Libraries Government Documents Department

Rolling Element Bearing Stiffness Matrix Determination (Presentation)

Description: Current theoretical bearing models differ in their stiffness estimates because of different model assumptions. In this study, a finite element/contact mechanics model is developed for rolling element bearings with the focus of obtaining accurate bearing stiffness for a wide range of bearing types and parameters. A combined surface integral and finite element method is used to solve for the contact mechanics between the rolling elements and races. This model captures the time-dependent characteristics of the bearing contact due to the orbital motion of the rolling elements. A numerical method is developed to determine the full bearing stiffness matrix corresponding to two radial, one axial, and two angular coordinates; the rotation about the shaft axis is free by design. This proposed stiffness determination method is validated against experiments in the literature and compared to existing analytical models and widely used advanced computational methods. The fully-populated stiffness matrix demonstrates the coupling between bearing radial, axial, and tilting bearing deflections.
Date: January 1, 2014
Creator: Guo, Y. & Parker, R.
Partner: UNT Libraries Government Documents Department

Process Knowledge Summary Report for Advanced Test Reactor Complex Contact-Handled Transuranic Waste Drum TRA010029

Description: This Process Knowledge Summary Report summarizes information collected to satisfy the transportation and waste acceptance requirements for the transfer of one drum containing contact-handled transuranic (TRU) actinide standards generated by the Idaho National Laboratory at the Advanced Test Reactor (ATR) Complex to the Advanced Mixed Waste Treatment Project (AMWTP) for storage and subsequent shipment to the Waste Isolation Pilot Plant for final disposal. The drum (i.e., Integrated Waste Tracking System Bar Code Number TRA010029) is currently stored at the Materials and Fuels Complex. The information collected includes documentation that addresses the requirements for AMWTP and applicable sections of their Resource Conservation and Recovery Act permits for receipt and disposal of this TRU waste generated from ATR. This Process Knowledge Summary Report includes information regarding, but not limited to, the generation process, the physical form, radiological characteristics, and chemical contaminants of the TRU waste, prohibited items, and packaging configuration. This report, along with the referenced supporting documents, will create a defensible and auditable record for this TRU waste originating from ATR.
Date: September 1, 2013
Creator: Adams, B. R.; Grant, R. P.; Smith, P. R. & Weisgerber, J. L.
Partner: UNT Libraries Government Documents Department

Light-trapped, interconnected, Silicon-Film{trademark} modules. Final technical status report

Description: AstroPower has continued its development of an advanced thin-silicon-based photovoltaic module product. This module combines the performance advantages of thin light-trapped silicon layers with the capability of integration into a low-cost, monolithically interconnected module. This report summarized work carried out over a 3-year, cost-shared contract. Key results accomplished during this phase include an NREL-verified conversion efficiency of 12.5% on a 0.47-cm{sup 2} device. The device structure used an insulating substrate and an active layer less than 100 {micro}m thick. A new metalization scheme was designed using insulating crossovers. This technology was demonstrated on a 36-segment, 321-cm{sup 2}, interconnected module. That module was tested at NREL with an efficiency of 9.79%. Further advances in metalization have led to an advanced single back-contact design that will offer low cost through ease of processing and higher performance through reduced shading.
Date: April 1, 1998
Creator: Hall, R.B.; Rand, J.A.; Ford, D.H. & Ingram, A.E.
Partner: UNT Libraries Government Documents Department