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Injection-locked composite lasers for mm-wave modulation : LDRD 117819 final report.

Description: This report summarizes a 3-year LDRD program at Sandia National Laboratories exploring mutual injection locking of composite-cavity lasers for enhanced modulation responses. The program focused on developing a fundamental understanding of the frequency enhancement previously demonstrated for optically injection locked lasers. This was then applied to the development of a theoretical description of strongly coupled laser microsystems. This understanding was validated experimentally with a novel 'photonic lab bench on a chip'.
Date: September 1, 2010
Creator: Wendt, Joel Robert; Vawter, Gregory Allen; Raring, James; Tauke-Pedretti, Anna; Alford, Charles Fred (Sandia Staffing Alliance, LLC, Albuquerque, NM); Skogen, Erik J. et al.
Partner: UNT Libraries Government Documents Department

Beam-Profile Measurement of Laser Pulses Using a Spatial Filter to Sample the Hermite Modes of a String of Pulses

Description: Abstract: As a first step in the development of a beam-profile measuring instrument for laser sources that is capable of determining the distribution of low-order (less than 25) Hermitian modes in a series of laser pulses, I designed and evaluated the three key parts of such an instrument. First, there is the telescope system which allows the incident laser beam to be phase, beamwidth, and beam center matched to the optical spatial filter. Second, there is a brief error analysis of the structure of the mismatch function between the beam out of the telescope and that expected by the filter. Finally, there is the detailed analysis and design of the computer-generated spatial filter that will cause the incident-laser beam to be cross correlated with the low-order Hermite modes and will create an array of light spots in the detector (Fourier transform) plane each of which can be uniquely related to a particular Hermite mode of the original laser pulse. The principal conclusion is that the Hermite mode analysis can be done with better than 99 percent separation between modes, provided the phase between modes is uncorrelated from pulse to pulse when the filter has been fabricated with a two-level, gray-scale structure which samples the profile with either 0 percent, or 100 percent transmission.
Date: September 1982
Creator: Johnson, Eric Gunnar, Jr.
Partner: UNT Libraries Government Documents Department

Experimentally determined natural vibration modes of some cantilever-wing flutter models by using an acceleration method

Description: From Summary: "Three-dimensional views are presented of the first three natural vibration mode shapes of ten cantilever-wing models. A table of normalized deflections at six spanwise and five chordwise stations is included for each mode. These mode shapes were measured by a rather unique experimental technique using grains of sand as accelerometers."
Date: April 1957
Creator: Hanson, Perry W. & Tuovila, W. J.
Partner: UNT Libraries Government Documents Department

Christian Roman Dress

Description: The illustration depicts twelve people in Christian Roman dress. The caption beneath is in German and lists the people by role, such as gravedigger, soldier, women, children and men.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: 1864
Creator: Kretschmer, Albert
Partner: UNT College of Visual Arts + Design

Single transverse mode selectively oxidized vertical cavity lasers

Description: Vertical cavity surface emitting lasers (VCSELs) which operate in multiple transverse optical modes have been rapidly adopted into present data communication applications which rely on multi-mode optical fiber. However, operation only in the fundamental mode is required for free space interconnects and numerous other emerging VCSEL applications. Two device design strategies for obtaining single mode lasing in VCSELs based on mode selective loss or mode selective gain are reviewed and compared. Mode discrimination is attained with the use of a thick tapered oxide aperture positioned at a longitudinal field null. Mode selective gain is achieved by defining a gain aperture within the VCSEL active region to preferentially support the fundamental mode. VCSELs which exhibit greater than 3 mW of single mode output power at 850 nm with mode suppression ratio greater than 30 dB are reported.
Date: April 26, 2000
Partner: UNT Libraries Government Documents Department

Enhancement of Mode-converted Electron Bernstein Wave Emission during NSTX H-mode Plasmas

Description: A sudden, threefold increase in emission from fundamental electrostatic electron Bernstein waves (EBW) which mode convert and tunnel to the electromagnetic X-mode has been observed during H-mode [high-confinement mode] transitions on the National Spherical Torus Experiment (NSTX) spherical torus plasma. The mode-converted EBW emission viewed normal to the magnetic field on the plasma midplane increases when the density profile steepens in the vicinity of the mode-conversion layer, which is located in the plasma scrape off. The measured conversion efficiency during the H-mode is consistent with the calculated EBW to X-mode conversion efficiency derived using edge density data. Calculations indicate that there may also be a small residual contribution to the measured X-mode electromagnetic radiation from polarization-scrambled, O-mode emission, converted from EBWs.
Date: August 20, 2001
Creator: Taylor, G.; Efthimion, P.C.; Jones, B.; LeBlanc, B.P. & Maingi, R.
Partner: UNT Libraries Government Documents Department

Characteristics of the First H-mode Discharges in NSTX

Description: We report observations of the first low-to-high (L-H) confinement mode transitions in the National Spherical Torus Experiment (NSTX). The H-mode energy confinement time increased over reference L-mode discharges transiently by 100-300%, as high as {approximately}150 ms. This confinement time is {approximately}1.8-2.3 times higher than predicted by a multi-machine ELM-free H-mode scaling. This achievement extends the H-mode window of fusion devices down to a record low aspect ratio (R/a) {approximately} 1.3, challenging both confinement and L-H power thresholds scalings based on conventional aspect ratio tokamaks.
Date: May 10, 2001
Creator: Maingi, R.; Bell, M.G.; Bell, R.E.; Bush, C.E.; Fredrickson, E.D.; Gates, D.A. et al.
Partner: UNT Libraries Government Documents Department

Simulation of edge-plasma profiles and turbulence related to L-H transitions in tokamaks

Description: Understanding plasma profile evolution and plasma turbulence are two important aspects of developing a predictive model for edge-plasma in tokamaks and other fusion-related devices. Here they describe results relevant to the L-H transition phenomena observed in tokamaks obtained from two simulations codes which emphasize the two aspects of the problem. UEDGE solves for the two-dimensional (2-D) profiles of a multi-species plasma and neutrals given some anomalous cross-field diffusion coefficients, and BOUT solves for the three-dimensional (3-D) turbulence that gives rise to the anomalous diffusion. These two codes are thus complementary in solving different aspects of the edge-plasma transport problem; ultimately, they want to couple the codes so that UEDGE uses BOUT's turbulence transport results, and BOUT uses UEDGE's plasma profiles with a fully automated iteration procedure. This goal is beyond the present paper; here they show how each aspect of the problem, i.e., profiles and turbulent transport, can contribute to L-H type transitions.
Date: September 21, 1999
Creator: Cohen, R H; Rognlien, T D & Xu, X Q
Partner: UNT Libraries Government Documents Department

Recirculation in multiple wave conversions

Description: A one-dimensional multiple wave-conversion model is constructed that allows energy recirculation in ray phase space. Using a modular eikonal approach, the connection coefficients for this model are calculated by ray phase-space methods. Analytical results (confirmed numerically) show that all connection coefficients exhibit interference effects that depend on an interference phase, calculated from the coupling constants and the area enclosed by the intersecting rays. This conceptual model, which focuses on the topology of intersecting rays in phase space, is used to investigate how mode conversion between primary and secondary waves is modified by the presence of a tertiary wave.
Date: July 30, 2008
Creator: Kaufman, A. N.; Brizard, A.J.; Kaufman, A.N. & Tracy, E.R.
Partner: UNT Libraries Government Documents Department

Design, Modeling, and Experiment of a Piezoelectric Pressure Sensor based on a Thickness-Shear Mode Crystal Resonator

Description: This thesis presents the design, modeling, and experiment of a novel pressure sensor using a dual-mode AT-cut quartz crystal resonator with beat frequency analysis based temperature compensation technique. The proposed sensor can measure pressure and temperature simultaneously by a single AT-cut quartz resonator. Apart from AT-cut quartz crystal, a newly developed Langasite (LGS) crystal resonator is also considered in the proposed pressure sensor design, since LGS can operate in a higher temperature environment than AT-cut quartz crystal. The pressure sensor is designed using CAD (computer aided design) software and CAE software - COMSOL Multiphysics. Finite element analysis (FEA) of the pressure sensor is performed to analyze the stress- strain of the sensor's mechanical structure. A 3D printing prototype of the sensor is fabricated and the proposed sensing principle is verified using a force-frequency analysis apparatus. Next to the 3D printing model verification, the pressure sensor with stainless steel housing has been fabricated with inbuilt crystal oscillator circuit. The oscillator circuit is used to excite the piezo crystal resonator at its fundamental vibrational mode and give the frequency as an output signal. Based on the FEA and experimental results, it has been concluded that the maximum pressure that the sensor can measure is 45 (psi). The pressure test results performed on the stainless steel product shows a highly linear relationship between the input (pressure) and the output (frequency).
Date: May 2017
Creator: Pham, Thanh Tuong
Partner: UNT Libraries

Reproduction and Metabolic Responses to Acute and Chronic Hypoxia in Ovoviviparous Blaberid Cockroaches, with a Focus on Blaptica dubia

Description: The major components of the tracheal system of insects are an extension of the exoskeleton, and the size of the exoskeleton is fixed in the adult stage, so any increase in metabolic demand that may accompany reproduction must be met by a relatively unaltered tracheal system that the female set in place at ecdysis, when entering adulthood. Acute hypoxia tends to elicit an increase in ventilation in insects, and here, I observe increased interburst VCO2 release, and a tendency towards a more continuous gas exchange pattern being preferred over discontinuous gas exchange when Blaptica dubia and Eublaberus posticus are exposed to a descending regime of hypoxia. Additionally, higher temperatures appear to increase sensitivity to hypoxia in these species, an expected result because both species, like most ectothermic animals, display a Q10 effect, increasing metabolic rates as temperature increases. The reproductive mode of B. dubia is considered to be lecithotrophic pseudoviviparity (or type A ovoviviparity), and by the time the embryos are born, they have more than doubles in volume from the time of oviposition. This gain is apparent in the wet mass of the embryo, with no change occurring in dry mass. The egg mass that can be attributed to water begins at 39% at oviposition and increased to nearly 82% at hatching. The metabolic rates of females and embryos increase as embryonic development progresses, but bomb calorimetry reveals that energy content of the embryos does not change. It is possible that these embryos gain some nutrition from the mother during embryonic development, but direct evidence remains to be demonstrated. Blaptica dubia and Eublaberus posticusare both blaberid species that display the same reproductive mode, pseudoviviparity, with incubation occurring in a brood sac. Comparisons between the reproductive traits of B. dubia and E. posticus reveal that the two species have similar ...
Date: August 2017
Creator: Mallery, Christopher Sean
Partner: UNT Libraries

A signature analysis method for IC failure analysis

Description: A new method of signature analysis is presented and explained. This method of signature analysis can be based on either experiential knowledge of failure analysis, observed data, or a combination of both. The method can also be used on low numbers of failures or even single failures. It uses the Dempster-Shafer theory to calculate failure mechanism confidence. The model is developed in the paper and an example is given for its use. 9 refs., 5 figs., 9 tabs.
Date: October 1, 1996
Creator: Henderson, C.L. & Soden, J.M.
Partner: UNT Libraries Government Documents Department

The Hydrostatic Mooring System. Quarterly Report for the Period April-June 2000

Description: The following topics are summarized for the 2nd quarter of 2000: (1) We amended the structural design of the buoy, moving the horizontal bulkhead from the bottom to the top of the buoy. (2) We designed the main bearing using Hilman Rollers. We discarded a parallel design using Lubron slide bearings due to concerns about keeping dirt out of the sliding surfaces. (3) We performed a preliminary failure tree risk analysis for the system as required by ABS. (4) We made various drawings of the system and sub-components.
Date: July 15, 2000
Creator: Korsgaard, Jens
Partner: UNT Libraries Government Documents Department

First passage failure: Analysis alternatives

Description: Most mechanical and structural failures can be formulated as first passage problems. The traditional approach to first passage analysis models barrier crossings as Poisson events. The crossing rate is established and used in the Poisson framework to approximate the no-crossing probability. While this approach is accurate in a number of situations, it is desirable to develop analysis alternatives for those situations where traditional analysis is less accurate and situations where it is difficult to estimate parameters of the traditional approach. This paper develops an efficient simulation approach to first passage failure analysis. It is based on simulation of segments of complex random processes with the Karhunen-Loeve expansion, use of these simulations to estimate the parameters of a Markov chain, and use of the Markov chain to estimate the probability of first passage failure. Some numerical examples are presented.
Date: April 17, 2000
Partner: UNT Libraries Government Documents Department

Two-Element Phased Array of Anti-Guided Vertical-Cavity Lasers

Description: We demonstrate for the first time anti-guided coupling of two adjacent vertical-cavity surface-emitting lasers (VCSEL's), obtaining a 1-by-2 phase-locked array at 869 nm. The lateral index modification required for anti-guiding is achieved by a patterned 3-rim etch performed between two epitaxial growths. In contrast with prior evanescently coupled VCSEL's, adjacent anti-guided VCSEL's can emit in-phase and produce a single on-axis lobe in the far field. Greater than 2 mW of in-phase output power is demonstrated with two VCSEL's separated by 8 {micro}m. Moreover, phase locking of two VCSEL's separated by 20 {micro}m is observed, indicating the possibility of a new class of optical circuits based upon VCSEL's that interact horizontally and emit vertically.
Date: September 27, 1999
Partner: UNT Libraries Government Documents Department

On the importance of target materials interfaces during low speed impact

Description: We are conducting a Cooperative Research and Development Project under the sponsorship of the U.S. Department of Energy to determine the applicability of aluminum particulate reinforced alloy laminates to aircraft structures and for containment of aircraft engine turbine blades and debris due to catastrophic engine failure. Within this framework, we are studying the terminal interaction of projectiles impacting targets at speeds of 150- to 500 m/s. Our presentation focuses on a special series of experiments and computational physics analyses of 6061-T6 aluminum alloy targets in single plate and laminate form impacted by steel cylindrical projectiles. Four cases are examined, projectile impact into (1) a single plate, (2) three contiguous plates (frictional interfaces), (3) three contiguous plates separated by Teflon layers (frictionless interfaces), and (4) a spaced array of three plates. We found that the ratio of projectile kinetic energies just at target perforation for the highest to lowest critical projectile speeds over the four targets is 1.75. Considering that target areal density is held constant across the four targets, this is a dramatic result. 2 refs., 7 figs.
Date: July 1996
Creator: Gogolewski, R. P.; Cunningham, B. J.; Riddle, R.; Lesuer, D. & Syn, C.
Partner: UNT Libraries Government Documents Department

Applications of Reductive Analytical Techniques in the Phrygian Settings of the Orgelbüchlein by J.S. Bach

Description: This study aims to two problematic aspects of the Phrygian mode: a. the development of a harmonic pattern at the cadence that differs from that of the other modes and of the major and minor modes as well; b. the observation that the Phrygian scale inverts all of the intervallic properties of the Major scale. The result of these two observations is that when the reductive techniques of Heinrich Schenker are applied in the Phrygian repertory, melodic and harmonic properties are brought into conflict with each other. However, application of alternative models of the Ursatz developed by Lori Burns has certain benefits for demonstrating musical properties in the Phrygian repertory.
Date: May 1995
Creator: Leite, Zilei de Oliveira
Partner: UNT Libraries

English Dress

Description: The illustration contains many examples of English dress from the fourteenth and fifteenth centuries. The legend beneath is written in German.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: 1864
Creator: Kretschmer, Albert
Partner: UNT College of Visual Arts + Design


Description: OAK-B135 Feedback stabilization of the resistive wall mode is usually accomplished by using linear amplifiers. In this paper a study is made of a possibility of controlling resistive wall modes using switches instead of linear amplifiers, i.e., using bang-bang control. The motivation is that bang-bang control systems may be cheaper than conventional feedback systems. A distinct disadvantage of the bang-bang system is complexity due to its inherent nonlinearity. Further studies, particularly of engineering issues, are needed to determine the attractiveness of a bang-bang system.
Date: January 1, 2003
Creator: JENSEN,TH
Partner: UNT Libraries Government Documents Department

Phase-locked arrays of vertical-cavity surface-emitting lasers

Description: Vertical Cavity Surface-Emitting Lasers (VCSELs) are of increasing interest to the photonics community because of their surface-emitting structure, simple fabrication and packaging, wafer-level testability and potential for low cost. Scaling VCSELs to higher power outputs requires increasing the device area, which leads to transverse mode control difficulties if devices become larger than 10-15 microns. One approach to increasing the device size while maintaining a well controlled transverse mode profile is to form coupled or phase-locked, two-dimensional arrays of VCSELs that are individually single-transverse mode. The authors have fabricated and characterized both photopumped and electrically injected two-dimensional VCSEL arrays with apertures over 100 microns wide. Their work has led to an increased understanding of these devices and they have developed new types of devices, including hybrid semiconductor/dielectric mirror VCSEL arrays, VCSEL arrays with etched trench, self-aligned, gold grid contacts and arrays with integrated phase-shifters to correct the far-field pattern.
Date: May 1, 1994
Creator: Warren, M. E.; Hadley, G. R.; Lear, K. L.; Gourley, P. L.; Vawter, G. A.; Zolper, J. C. et al.
Partner: UNT Libraries Government Documents Department