11,484 Matching Results

Search Results

Adaptive control in optical fibers

Description: Adpative control in combination with ultrafast pulse shaping provides a compelling approach to defeat dispersion, distortion and harness nonlinear phenomena on the femtosecond timescale. Ultrafast pulses propagating in optical fibers generate a number of linear and nonlinear effects which affect the pulse during its travel. The main causes stem from the dependence of the index of refraction on frequency (given that short pulses have a large bandwidth) and from the so-called self-action effects which involve the dependence of the index of refraction on the pulse intensity (which is high given that the pulse energy is confined to a very short amount of time).
Date: January 1, 2002
Creator: Omenetto, F. G. (Fiorenzo G.)
Partner: UNT Libraries Government Documents Department

An investigation of plant fibers for basketry

Description: The problem of investigating the adaptability of plant fibers for basketry was two-fold. The first part was the selection and preparation of the plants. Suitable collection time, drying methods, and processing and soaking procedures were determined through a series of experiments performed during each season of the year. In the second part experimental samples were woven by using the basic basketry techniques to illustrate the usability and versatility of each plant fiber.
Date: August 1977
Creator: Smith, Virginia Sue M.
Partner: UNT Libraries

New perspectives on the fracture of Nicalon fibers

Description: Experimental studies have been conducted to examine the strength and fracture behavior of monofiliment Nicalon{sup 3} SiC fibers ranging in diameter from 8 to 22 {mu}m. The effects of varying fiber diameter, flaw location and flaw population on the tensile behavior of individual fibers were investigated using fractography. Results indicate that variations in fiber diameter influence the apparent fiber fracture toughness K{sub 1c}, with higher K{sub 1c} values observed for decreasing fiber diameters. Observations also suggest that the location of the critical flaw may play a role in the fracture of Nicalon fibers. In addition to surface flaws, three distinct internal flaw populations are seen to cause fracture in Nicalon fibers.
Date: November 1, 1997
Creator: Taylor, S.T.; Lowe, T.C. & Butt, D.P.
Partner: UNT Libraries Government Documents Department

The Nature of Accelerating Modes in PBG Fibers

Description: Transverse magnetic (TM) modes with phase velocities at or just below the speed of light, c, are intended to accelerate relativistic particles in hollow-core, photonic band gap (PBG) fibers. These are so-called 'surface defect modes', being lattice modes perturbed by the defect to have their frequencies shifted into the band gap, and they can have any phase velocity. PBG fibers also support so-called 'core defect modes' which are characterized as having phase velocities always greater than c and never cross the light line. In this paper we explore the nature of these two classes of accelerating modes and compare their properties.
Date: May 19, 2011
Creator: Noble, TRobert J.; /SLAC & ,
Partner: UNT Libraries Government Documents Department


Description: The Federal Bureau of Investigation (FBI) Laboratory currently does not have on site facilities for handling radioactive evidentiary materials and there are no established FBI methods or procedures for decontaminating high explosive (HE) and fire debris (FD) evidence while maintaining evidentiary value. One experimental method for the isolation of HE and FD residue involves using solid phase microextraction or SPME fibers to remove residue of interest. Due to their high affinity for organics, SPME fibers should have little affinity for most metals. However, no studies have measured the affinity of radionuclides for SPME fibers. The focus of this research was to examine the affinity of dissolved radionuclide ({sup 239/240}Pu, {sup 238}U, {sup 237}Np, {sup 85}Sr, {sup 133}Ba, {sup 137}Cs, {sup 60}Co and {sup 226}Ra) and stable radionuclide surrogate metals (Sr, Co, Ir, Re, Ni, Ba, Cs, Nb, Zr, Ru, and Nd) for SPME fibers at the exposure conditions that favor the uptake of HE and FD residues. Our results from radiochemical and mass spectrometric analyses indicate these metals have little measurable affinity for these SPME fibers during conditions that are conducive to HE and FD residue uptake with subsequent analysis by liquid or gas phase chromatography with mass spectrometric detection.
Date: August 28, 2006
Creator: Duff, M; S Crump, S; Robert02 Ray, R; Keisha Martin, K & Donna Beals, D
Partner: UNT Libraries Government Documents Department

Accurate estimation of the elastic properties of porous fibers

Description: A procedure is described to calculate polycrystalline anisotropic fiber elastic properties with cylindrical symmetry and porosity. It uses a preferred orientation model (Tome ellipsoidal self-consistent model) for the determination of anisotropic elastic properties for the case of highly oriented carbon fibers. The model predictions, corrected for porosity, are compared to back-calculated fiber elastic properties of an IM6/3501-6 unidirectional composite whose elastic properties have been determined via resonant ultrasound spectroscopy. The Halpin-Tsai equations used to back-calculated fiber elastic properties are found to be inappropriate for anisotropic composite constituents. Modifications are proposed to the Halpin-Tsai equations to expand their applicability to anisotropic reinforcement materials.
Date: May 1997
Creator: Thissell, W. R.; Zurek, A. K. & Addessio, F.
Partner: UNT Libraries Government Documents Department

Dielectric property measurement of zirconia fibers at high temperatures

Description: Using a self-heating, electronically tunable microwave dielectrometer, the complex dielectric constant of zirconia-based filaments was measured at 915 MHz from 350{degrees} to 1100{degrees}C. This fibrous material cools rapidly to near room temperature within several seconds due to a large surface area to volume ratio. Such rapid sample cooling necessitates the use of a self-heating technique to measure the complex dielectric constant at temperatures up to 1100{degrees}C. Sample temperature was measured with optical fiber thermometry. The effect of sample temperature measurement on data accuracy is discussed.
Date: May 1, 1995
Creator: Vogt, G.J.; Tinga, W.R. & Plovnick, R.H.
Partner: UNT Libraries Government Documents Department

Some new perspective on the strength and fracture of Nicalon fibers

Description: Nicalon{trademark} SiC fibers, processed by melt-spinning, are attractive reinforcing materials for high-temperature structural composites. This paper studies the effects of fiber diameter on fracture and statistical strength distribution of the fibers, by means of fractography on 8-22 {mu}m fibers fractured under tensile load. Flaw population and location effects are also studied.
Date: July 1, 1996
Creator: Taylor, S.T.; Zhu, Y.T.; Butt, D.P.; Stout, M.G.; Blumenthal, W.R. & Lowe, T.C.
Partner: UNT Libraries Government Documents Department

Neutron scintillators using wavelength shifting fibers

Description: A proposed design for an optically-based, one-dimension scintillation detector to replace the gas-filled position-sensitive proportional counter currently used for a wide-angle neutron detector (WAND) at the high-Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) is presented. The scintillator, consisting of a mixture of {sup 6}LiF and ZnS(Ag) powders in an epoxy binder, is coupled to an array of wavelength shifting optical fibers which provide position resolution. The wide-angle neutron detector is designed to cover a 120 degree arc with a 75 cm radius of curvature. The final detector design provides for 600 optical fibers coupled to the scintillator screen with an angular resolution of 0.2 degrees. Each individual pixel of the detector will be capable of operating at count rates exceeding 1 MHz. Results are presented from the measurement of neutron conversion efficiencies for several screen compositions, gamma-ray sensitivity, and spatial resolution of a 16 element one-dimensional array prototype.
Date: June 1, 1995
Creator: Hutchinson, D.P.; Miller, V.C. & Ramsey, J.A.
Partner: UNT Libraries Government Documents Department

Characterization of porous carbon fibers and related materials

Description: This program was geared to support the Fossil Energy Material Sciences Program with respect to several areas of interest in efficient production and utilization of energy. Carbon molecular sieves have great potential for economically purifying gases; i.e. removal of carbon dioxide from natural gas without having to resort to cryogenic techniques. Microporous carbons can be tailored to serve as adsorbents for natural gas in on-board storage in automotive applications, avoiding high pressures and heavy storage tanks. This program is a laboratory study to evaluate production methodologies and activation processes to produce porous carbons for specific applications. The Carbon Materials Technology Group of Oak Ridge National Laboratory (ORNL) is engaged in developmental programs to produce activated carbon fibers (ACF) for applications in fixed beds and/or flowing reactors engineering applications.
Date: July 15, 1996
Creator: Fuller, E. L., Jr.
Partner: UNT Libraries Government Documents Department

Characterization of Porous Carbon Fibers and Related Materials

Description: A one-year subcontract sponsored by the Carbon Materials Technology Group of the Oak Ridge National Laboratory (ORNL) with the Department of Geological Sciences, University Of Tennessee, has been completed. A volumetric sorption system has been upgraded, in cooperation with commercial vendor, to allow the acquisition of data relevant to the program for the production of activated carbon molecular fiber sieves (ACFMS). The equipment and experimental techniques have been developed to determine the pore structure and porosity of reference materials and materials produced at ORNL as part of the development of methods for the activation of carbon fibers by various etching agents. Commercial activated coconut shell charcoal (ACSC) has been studied to verify instrument performance and to develop methodology for deducing cause and effects in the activation processes and to better understand the industrial processes (gas separation, natural gas storage, etc.). Operating personnel have been trained, standard operating procedures have been established, and quality assurance procedures have been developed and put in place. Carbon dioxide and methane sorption have been measured over a temperature range 0 to 200 C for both ACFMS and ACSC and similarities and differences related to the respective structures and mechanisms of interaction with the sorbed components. Nitrogen sorption (at 77 K) has been used to evaluate ''surface area'' and ''porosity'' for comparison with the large data base that exists for other activated carbons and related materials. The preliminary data base reveals that techniques and theories currently used to evaluate activated carbons may be somewhat erroneous and misleading. Alternate thermochemical and structural analyses have been developed that show promise in providing useful information related both to the activation process and to industrial applications of interest in the efficient and economical utilization of fossil fuels in a manner that is friendly to the earth's environment.
Date: January 1, 1993
Creator: Fuller, E.L., Jr.
Partner: UNT Libraries Government Documents Department

Predicted Performance of Neutron Spectrometers Using Scintillating Fibers

Description: One class of neutron spectrometers is devices that provide a measure of the neutron spectrum by using moderating and absorbing materials together with thermal-neutron detectors. Pacific Northwest National Laboratory has developed scintillating fibers that are sensitive to thermal neutrons. Because these fibers are thin, they present an enabling technology for several applications, including highly efficient neutron spectroscopy. The underlying concept is to arrange the fibers in an array of layers separated by materials whose characteristics have been chosen to optimize the instrument function for the application. Monte Carlo experiments have been performed to characterize the conceptual design and to determine the value of the concept as a tool for research and other applications.
Date: February 14, 2000
Creator: Craig, Richard A & Bliss, Mary
Partner: UNT Libraries Government Documents Department

Predicted performance of neutron spectrometers using scintillating fibers

Description: A variety of needs exists for knowing the energy spectral content of a neutron flux. Among these needs are arms-control and national-security applications, which arise because different neutron sources produce different neutron energy spectra. This work is primarily directed at these applications. The concept described herein is a spectrometer in the same sense as a Bonner sphere. The instrument response reflects a statistical average of the energy spectrum. The Bonner sphere is an early rendition of this class. In this, a neutron detector is placed at the center of a moderating (and absorbing) sphere (of varying thickness and composition). Spectral unfolding is required, and the resolution and efficiency are, typically, poor, although the potential bandwidth is very large. A recent variation on the Bonner-sphere approach uses {sup 3}He gas proportional counters with resistive wires to locate the position of the event (Toyokawa et al 1996). The spectrometer concept investigated here has the potential for better resolution and much improved neutron efficiency compared to Bonner spheres and similar devices. These improvements are possible because of the development of neutron-sensitive, scintillating-glass fibers. These fibers can be precisely located in space, which allows a corresponding precision in energy resolution. Also, they can be fabricated into arrays that intercept a large fraction of incident thermal neutrons, providing the improvement in neutron economy.
Date: February 14, 2000
Creator: Craig, RA & Bliss, M
Partner: UNT Libraries Government Documents Department

Strength Test on Optical Fibers to be Used in VLPC

Description: The objective is to determine the strength of the optical fibers to be used in the VLPC cassette. Strength tests were done on optical fibers that are to be used in the VLPC cassette. A number of the fibers will hang vertically and support a suspended copper isotherm. Concern was expressed over whether one fiber could support the entire weight of the isotherm (8 ounces) if uneven shrinkage of the fibers occurs at cryogenic temperatures. The fibers have a polystyrene core and testing done at room temperature showed that one fiber can support the isotherm with a factor of safety of 13.2 before fracture will occur from a uniaxial load. Data in Cryogenic Engineering by Scott shows that the strength of plastics increases (although polystyrene is not listed) as they are cooled. Two tests done to the fibers with liquid nitrogen support this. The safety factor of 13.2 will only increase at cryogenic temperatures. These results were determined through three tests whose summaries are given.
Date: February 9, 1993
Creator: Olis, D. & /Fermilab
Partner: UNT Libraries Government Documents Department

On the statistical strength of nicalon fibers and its characterization

Description: Nicalon fibers are one of the most attractive ceramic fibers for reinforcing high temperature structural composites. Experiment show that the diameter variation (from 8 to 22 {mu}m) in a tow of commercial Nicalon fibers has an effect on statistical strength distribution of Nicalon fibers. Therefore, an appropriate characterization of the statistical distribution of fiber strength, capable of accounting for the effect of diameter variation, is required. The two-parameter single-modal Weibull distribution is found inadequate for characterizing the strength of Nicalon fibers. This work demonstrates that a 3-parameter modified Weibull distribution can successfully characterize the strength of Nicalon fibers; this distribution yields a higher {beta} value, which indicates less scatter in fiber strength than with the 2-parameter single modal Weibull distribution. It more accurately treats the strength variation caused by diameter variation. It is also much easier to use than the 4-parameter bimodal. Moreover, it is seen to more accurately treat the strength variation caused by diameter variation than the single modal 2-parameter analysis.
Date: February 1, 1997
Creator: Zhu, Y.T.; Taylor, S.T.; Stout, M.G.; Butt, D.P.; Blumenthal, W.R. & Lowe, T.C.
Partner: UNT Libraries Government Documents Department

Measurements at 351 nm of temporal dispersion in fibers

Description: 1. Temporal dispersion at 351-nm was measured in the following: a 35-m bundle of 19 each 50-µm-core fibers, a companion 35-m single fiber, a 100-µm-core single fiber (at 4 lengths), and a 50-µm-core single fiber (two samples, 7 lengths). The 50-µm-core fiber was from preform #24; the 100-µm-core fiber was a prototype version having a thick cladding. All of the fibers were developed and manufactured at the Vavilov State Optical Institute, St. Petersburg, Russia. 2. Dispersion measurements were made by propagating a 20-ps 351-nm pulse through the fiber under test and recording the output on an S20 streak camera. The width of the pulse transmitted by the fiber was compared to that of a fraction of the pulse that had propagated over an air path. Values of dispersion were calculated as, D = {radical}(F² - A²) , where F and A are the full widths at half maximum (FWHM) for, respectively, the fiber-path and the air-path streaks. 3. In each of the experiments, the measured dispersion increased with counts in the streak record, which in principle, are proportional to intensity in the fiber. Measured values of dispersion ranged from about 0.6 to 1.0 ps/m for the single fibers. 4. The measured FWHMs of both the fiber-path pulse and the air-path pulse increased with increase in counts in the streak record. The rate of broadening was greatest for the fiber-path pulse, and the broadening of that pulse was the primary cause for the dependence of dispersion on counts in the streak record. Pulse broadening with increase in counts is symptomatic of camera saturation, but it is difficult to understand why saturation should have effected the fiber-path pulses more strongly. 5. There were spatial anomalies in the streak records of the output pulses from some of the fibers. Emission by the bundle ...
Date: November 4, 1998
Creator: Griffith, R; Milam, D; Sell, W & Thompson, C
Partner: UNT Libraries Government Documents Department

Quantum cryptography over underground optical fibers

Description: Quantum cryptography is an emerging technology in which two parties may simultaneously generated shared, secret cryptographic key material using the transmission of quantum states of light whose security is based on the inviolability of the laws of quantum mechanics. An adversary can neither successfully tap the key transmissions, nor evade detection, owing to Heisenberg`s uncertainty principle. In this paper the authors describe the theory of quantum cryptography, and the most recent results from their experimental system with which they are generating key material over 14-km of underground optical fiber. These results show that optical-fiber based quantum cryptography could allow secure, real-time key generation over ``open`` multi-km node-to-node optical fiber communications links between secure ``islands.``
Date: May 1, 1996
Creator: Hughes, R.J.; Luther, G.G.; Morgan, G.L.; Peterson, C.G. & Simmons, C.
Partner: UNT Libraries Government Documents Department

The effect of neutron irradiation on silicon carbide fibers

Description: Nine types of SiC fiber have been exposed to neutron radiation in the Advanced Test Reactor at 250 C for various lengths of time ranging from 83 to 128 days. The effects of these exposures have been initially determined using scanning electron microscopy. The fibers tested were Nicalon{trademark} CG, Tyranno, Hi-Nicalon{trademark}, Dow Corning SiC, Carborundum SiC, Textron SCS-6, polymethysilane (PMS) derived SiC from the University of Michigan, and two types of MER SiC fiber. This covers a range of fibers from widely used commercial fibers to developmental fibers. Consistent with previous radiation experiments, Nicalon fiber was severely degraded by the neutron irradiation. Similarly, Tyranno suffered severe degradation. The more advanced fibers which approach the composition and properties of SiC performed well under irradiation. Of these, the Carborundum SiC fiber appeared to perform the best. The Hi-Nicalon and Dow Corning Fibers exhibited good general stability, but also appear to have some surface roughening. The MER fibers and the Textron SCS-6 fibers both had carbon cores which adversely influenced the overall stability of the fibers.
Date: January 1, 1997
Creator: Newsome, G.A.
Partner: UNT Libraries Government Documents Department

Use of neutron-capture plastic fibers for nondestructive assay

Description: Neutron-capture plastic fibers can be used as a nondestructive assay tool. The detectors consist of an active region assembled from ribbons of boron-({sup 10}B) loaded optical fibers. The mixture of the moderator and thermal neutron absorber in the fiber yields a detector with high efficiency ({var_epsilon}) and a short die-away time ({tau}). The deposited energy of the resultant charged particles is converted to light that is collected by photomultiplier tubes mounted at both ends of the fiber. Thermal neutron coincidence counters (TNCC) made of these fibers can serve to verify fissile materials generated from the nuclear fuel cycle. This type of detector may extend the range of materials now accessible to assay by {sup 3}He detectors. Experiments with single fibers of diameters 0.25, 0.50, and 1.00 mm test their ability to distinguish between the signals generated from neutron interactions and those from gamma rays. These results are compared with those obtained from simulation analyses for the same purpose. Light output and attenuation, neutron detection efficiency, and the signal-to-noise ratios of these fibers have also been investigated. The experimental results for light attenuation and neutron detection efficiency are consistent with the values obtained from simulation studies. A comparison of the performance of various configurations of the plastic scintillating fibers with that of other neutron-capture devices such as {sup 3}He detectors is also discussed.
Date: December 31, 1998
Creator: Heger, A.S.; Grazioso, R.F.; Mayo, D.R.; Ensslin, N.; Miller, M.C.; Huang, H.Y. et al.
Partner: UNT Libraries Government Documents Department

The evaluation of Federal Fabrics-Fibers electrochemical capacitors

Description: The electrochemical capacitor devices described in this report were deliverables from the US Department of Energy-Idaho Operations Office (DOE-ID) as part of the US Department of Energy`s (DOE) High Power Energy Storage Program. The Idaho National Engineering and Environmental Laboratory (INEEL) has the responsibility for technical management, testing, and evaluation of high-power batteries and electrochemical capacitors under this Program. The DOE is currently developing various electrochemical capacitors as candidate power assist devices for the Partnership for a New Generation of Vehicles (PNGV) fast response engine requirement. This contract with Federal Fabrics-Fibers was intended to evaluate the use of their novel Z-axis carbon fiber materials as candidate electrodes for electrochemical capacitors. Deliverables were sent to the INEEL`s Energy Storage Technologies (EST) Laboratory for independent testing and evaluation. This report describes performance testing on four selected devices delivered over a 2-year period. Due to the highly experimental nature of the packages, life cycle testing was not conducted.
Date: September 1, 1997
Creator: Wright, R.B. & Murphy, T.C.
Partner: UNT Libraries Government Documents Department

Development of CVD Mullite Coatings for SiC Fibers

Description: A process for depositing CVD mullite coatings on SiC fibers for enhanced oxidation and corrosion, and/or act as an interfacial protective barrier has been developed. Process optimization via systematic investigation of system parameters yielded uniform crystalline mullite coatings on SiC fibers. Structural characterization has allowed for tailoring of coating structure and therefore properties. High temperature oxidation/corrosion testing of the optimized coatings has shown that the coatings remain adherent and protective for extended periods. However, preliminary tests of coated fibers showed considerable degradation in tensile strength.
Date: March 15, 2000
Creator: Sarin, V. K. & Varadarajan, S.
Partner: UNT Libraries Government Documents Department

Modeling femtosecond pulse propagation in optical fibers.

Description: Femtosecond pulse propagation in optical fibers requires consideration of higher-order nonlinear effects when implementing the non-linear Schroedinger equation. We show excellent agreement of our model with experimental results both for the temporal and phase features of the pulses. Ultrafast pulse propagation in optical fibers presents a number of challenges given the effect of nonlinearities which become important on such a short time scale. The modeling of femtosecond pulse propagation becomes, consequently, a harder task which has to account for all these effects. In this work, we have included higher order corrections in the non-linear Schroedinger equation and compared the numerical simulation results with experimental data. Our work, besides taking into account the temporal evolution of the pulse, keeps into account also the phase behavior of the electric field, which we compare with experimental results obtained with Frequency Resolved Optical Gating [l]. We also account for self-frequency shift of the pulse and obtain excellent agreement with the experimental results on the Raman shift.
Date: January 1, 2001
Creator: Chung, Y. J. (Yeo-Jin); Schaefer, T. B. (Tobias B.); Gabitov, I. R. (Ildar R.); Omenetto, F. G. (Fiorenzo G.) & Taylor, Antoinette J.,
Partner: UNT Libraries Government Documents Department

Remote Synchrotron Light Instrumentation Using Optical Fibers

Description: By coupling the emitted synchrotron light into an optical fiber, it is possible to transmit the signal at substantial distances from the light port, without the need to use expensive beamlines. This would be especially beneficial in all those cases when the synchrotron is situated in areas not easily access because of their location, or due to high radiation levels. Furthermore, the fiber output can be easily switched, or even shared, between different diagnostic instruments. We present the latest results on the coupling and dispersion measurements performed at the Advanced Light Source in Berkeley. In several cases, coupling synchrotron light into optical fibers can substantially facilitate the use of beam diagnostic instrumentation that measures longitudinal beam properties by detecting synchrotron radiation. It has been discussed in with some detail, how fiberoptics can bring the light at relatively large distances from the accelerator, where a variety of devices can be used to measure beam properties and parameters. Light carried on a fiber can be easily switched between instruments so that each one of them has 100% of the photons available, rather than just a fraction, when simultaneous measurements are not indispensable. From a more general point of view, once synchrotron light is coupled into the fiber, the vast array of techniques and optoelectronic devices, developed by the telecommunication industry becomes available. In this paper we present the results of our experiments at the Advanced Light Source, where we tried to assess the challenges and limitations of the coupling process and determine what level of efficiency one can typically expect to achieve.
Date: May 4, 2009
Creator: De Santis, S. & Yin, Y.
Partner: UNT Libraries Government Documents Department

Adaptive control of femtosecond pulse propagation in optical fibers

Description: We present an adaptive control loop that synthesizes fs-pulses that are self-correcting for higher order nonlinear effects when launched in a conventional single-mode fiber, nearly preserving the initial (t{approx}200 fs) pulse duration.
Date: January 1, 2001
Creator: Omenetto, F. G. (Fiorenzo G.); Taylor, Antoinette J.,; Moores, M. D. (Mark D.) & Reitze, David H.
Partner: UNT Libraries Government Documents Department