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Experimental ablation cooling

Description: Report presenting the results of an experimental investigation on the ablation of a number of promising materials for heating conditions comparable to those which maybe encountered by unmanned reentry satellite vehicles or heating conditions associated with reentry ballistic missiles. Results regarding exploratory tests, further Teflon tests, and graphite testing are provided.
Date: July 15, 1958
Creator: Bond, Aleck C.; Rashis, Bernard & Levin, L. Ross
Partner: UNT Libraries Government Documents Department

Synthesis and rheological properties of cation-exchanged Laponite suspensions

Description: In this paper we report our new approach to synthesize cation-exchanged Laponite suspensions. General observations of the prepared samples indicated that an aqueous suspension of 1 wt% Laponite retained its free flowing liquid phase characteristics even after aging for several weeks. When bivalent cationic metals (Cu, Co, Ni) were ablated into the suspension, the strong charge of the crystal face was reduced and, on standing, the suspension gelled becoming highly viscous. This sol-gel transition was induced by the formation of a space-filled structure due to both van derWaals and electrostatic bonds between the positively charged rims and negatively charged faces. Rheological properties of such prepared suspensions were measured using a Brookfield DV-H Pro Viscometer with a small sample adapter{SSA18/13RPY). The yield strengths of2.2 N/m2, 3.2 N/m2, and 1.7 N/m2 were measured for Ni-, Co-, and Cu-modified Laponite suspensions, respectively. These yield strengths are sufficiently high for suspending weighting materials such as barite which requires the gel strength of about 0.5 N/m2.
Date: January 1, 2009
Creator: Tran, X.P.; Howard, B. & Chyu, M.K.
Partner: UNT Libraries Government Documents Department

Time Resolved Shadowgraph Images of Silicon during Laser Ablation:Shockwaves and Particle Generation

Description: Time resolved shadowgraph images were recorded of shockwaves and particle ejection from silicon during laser ablation. Particle ejection and expansion were correlated to an internal shockwave resonating between the shockwave front and the target surface. The number of particles ablated increased with laser energy and was related to the crater volume.
Date: May 6, 2006
Creator: Liu, C.Y.; Mao, X.L.; Greif, R. & Russo, R.E.
Partner: UNT Libraries Government Documents Department

Laser Ablated Carbon Nanodots for Light Emission

Description: This article reports the synthesis of fluorescent carbon dots-like nanostructures obtained through the laser ablation of a carbon solid target in liquid environment is reported.
Date: September 22, 2016
Creator: Reyes, Delfino; Camacho, Marco; Camacho, Miguel; Mayorga, Miguel; Weathers, Duncan L.; Salamo, Greg et al.
Partner: UNT College of Arts and Sciences

Qualitative Measurements of the Effective Heats of Ablation of Several Materials in Supersonic Air Jets at Stagnation Temperatures Up to 11,000 Degrees F

Description: Report presenting testing on the effective heats of ablation of a number of materials using supersonic arc jets at stagnation temperatures ranging from 2000 degrees F to 11,000 degrees F. Materials examined included Teflon, nylon, Lucite, polystyrene, ammonium chloride, sodium carbonate, several phenolic resins, and melamine-fiber glass laminate.
Date: July 7, 1958
Creator: Rashis, Bernard; Witte, William G. & Hopko, Russell N.
Partner: UNT Libraries Government Documents Department

AnGa{sub 2}O{sub 4} Thin-Film Phosphors Grown by Pulsed Laser Ablation

Description: The growth and properties of undoped and Mn-doped ZnGa{sub 2}O{sub 4} thin-film phosphors on (100) MgO and glass substrates using pulsed laser ablation were investigated. Blue-white and green emission were observed for as-deposited undoped and Mn-doped films, respectively. Luminescent properties as well as crystallinity were considerably affected by processing conditions and film stoichiometry. Films with enhanced luminescent characteristics were obtained on single crystal substrates without post-annealing.
Date: April 5, 1999
Creator: Lee, Y. E.; Rouleau, C. M.; Park, C. & Norton, D. P.
Partner: UNT Libraries Government Documents Department

Thermo-Chemical Ablation During Reentrant and High Altitude Skipping Flight

Description: Thermo-chemical ablation during reentrant and high altitude skipping flights is treated using a variety of techniques. The solid material response is computed using heat-balance integrals, finite differences, and finite elements. The surface mass loss is computed using curve fits to the standard transport coefficient approach and by a surface kinetic model. Agreement between the approaches, when using the curve fits, is good. All approaches concur that for the skipping trajectory studied there is very little mass loss and surface temperatures remain in a range where the thermal protection system can be reused.
Date: March 28, 2000
Creator: Havstad, M. & Carter, P.
Partner: UNT Libraries Government Documents Department

A Theoretical Study of Stagnation-Point Ablation

Description: "A simplified analysis is made of the shielding mechanism which reduces the stagnation-point heat trasnfer when ablation takes place at the surface. The ablation process considered is that in which the material changes directly from the solid to the gaseous state. The automatic shielding mechanism is discussed and the significant thermal properties of a good ablation material are given. The results of the analysis are given in terms of dimensionless parameters" (p. 1).
Date: September 1958
Creator: Roberts, Leonard
Partner: UNT Libraries Government Documents Department

Momentum Transfer by Laser Ablation of Irregularly Shaped Space Debris

Description: Proposals for ground-based laser remediation of space debris rely on the creation of appropriately directed ablation-driven impulses to either divert the fragment or drive it into an orbit with a perigee allowing atmospheric capture. For a spherical fragment, the ablation impulse is a function of the orbital parameters and the laser engagement angle. If, however, the target is irregularly shaped and arbitrarily oriented, new impulse effects come into play. Here we present an analysis of some of these effects.
Date: February 4, 2010
Creator: Liedahl, D A; Libby, S B & Rubenchik, A
Partner: UNT Libraries Government Documents Department

Design Calculations For NIF Convergent Ablator Experiments

Description: The NIF convergent ablation tuning effort is underway. In the early experiments, we have discovered that the design code simulations over-predict the capsule implosion velocity and shock flash rhor, but under-predict the hohlraum x-ray flux measurements. The apparent inconsistency between the x-ray flux and radiography data implies that there are important unexplained aspects of the hohlraum and/or capsule behavior.
Date: October 25, 2011
Creator: Olson, R E; Hicks, D G; Meezan, N B; Callahan, D A; Landen, O L; Jones, O S et al.
Partner: UNT Libraries Government Documents Department

Synthesis of Mg(OH)2, MgO, and Mg nanoparticles using laser ablation of magnesium in water and solvents

Description: laser ablation of magnesium in deionized water (OW), solutions of OW and sodium dodecyl sulfate (50S) with different concentrations, acetone and 2-propanol has been conducted, The results showed that ablation in acetone and 2-propanol yielded MgO and Mg nanocrystallites as isolated particles and agglomerated chains probably intermixed with organic residues resulting from the alterationj decomposition of the solvents under the high-energy conditions. Brucite-like Mg(OH)2 particles were mainly produced by laser ablation of Mg in either OW or OW~SOS solutions. Ablation in OW yielded particles of fiber-like shapes having a diameter of about 5-lOnm and length as long as 150nm. Materials produced in DW-SOS solutions were composed of various size and shape particles, Some had rough surfaces with irregular shapes. Small particles were about 20-30nm and larger particles were about 120 nm. Particles with rod-like, triangular, and plate-like shapes were also observed.
Date: January 1, 2008
Creator: Tran, P.X.; Howard, B.H.; Martello, D.V.; Soong, Y. & Chyu, M.K.
Partner: UNT Libraries Government Documents Department

Investigating Molecular Structures: Rapidly Examining Molecular Fingerprints Through Fast Passage Broadband Fourier Transform Microwave Spectroscopy

Description: Microwave spectroscopy is a gas phase technique typically geared toward measuring the rotational transitions of Molecules. The information contained in this type of spectroscopy pertains to a molecules structure, both geometric and electronic, which give insight into a molecule's chemistry. Typically this type of spectroscopy is high resolution, but narrowband ≤1 MHz in frequency. This is achieved by tuning a cavity, exciting a molecule with electromagnetic radiation in the microwave region, turning the electromagnetic radiation o, and measuring a signal from the molecular relaxation in the form of a free induction decay (FID). The FID is then Fourier transformed to give a frequency of the transition. "Fast passage" is defined as a sweeping of frequencies through a transition at a time much shorter (≤10 s) than the molecular relaxation (≈100 s). Recent advancements in technology have allowed for the creation of these fast frequency sweeps, known as "chirps", which allow for broadband capabilities. This work presents the design, construction, and implementation of one such novel, high-resolution microwave spectrometer with broadband capabilities. The manuscript also provides the theory, technique, and motivations behind building of such an instrument. In this manuscript it is demonstrated that, although a gas phase technique, solids, liquids, and transient species may be studied with the spectrometer with high sensitivity, making it a viable option for many molecules wanting to be rotationally studied. The spectrometer has a relative correct intensity feature that, when coupled with theory, may ease the difficulty in transition assignment and facilitate dynamic chemical studies of the experiment. Molecules studied on this spectrometer have, in turn, been analyzed and assigned using common rotational spectroscopic analysis. Detailed theory on the analysis of these molecules has been provided. Structural parameters such as rotational constants and centrifugal distortion constants have been determined and reported for most molecules in ...
Date: May 2011
Creator: Grubbs, Garry Smith, II
Partner: UNT Libraries

Final Report for High Precision Short-Pulse Laser Ablation System for Medical Applications

Description: During the three year LDRD funding period, we studied the ablation characteristics of biological tissues using ultrashort pulse lasers (USPL) with pulse widths varying from 100 femtoseconds to tens of picoseconds. During the first year, we performed extensive theoretical studies to develop an improved understanding of the USPL ablation process. Two optical signals were tested for feasibility of use in real-time feedback systems during high repetition rate ablation. In the second year, we devised a real-time, feedback-controlled USPL ablation system, based on luminescence, which may be useful for sensitive micro-spinal surgeries. Effective laser parameters were identified to reduce collateral damage. The final year of the project focused on quantification of the pressure pulse induced by USPL ablation of water surfaces representing biological tissues. Results of these studies were presented in invited talks at domestic and international conferences and numerous journal articles were published (see bibliography). This effort has increased our scientific understanding of physical processes important for the therapeutic biomedical application of ultrashort pulse lasers, and has taken the first steps toward practical realization of such applications.
Date: March 4, 2000
Creator: Kim, B.M.; Feit, M.; Rubenchik, A. & Marion, J.
Partner: UNT Libraries Government Documents Department

Rapid Fabrication of Disposable Micromixing Arrays Using Xurography and Laser Ablation

Description: This article presents a novel split-and-recombine (SAR) array design adapted for interfacing standardized dispensing (handheld micropipette) and sampling (microplate reader) equipment.
Date: February 28, 2017
Creator: Martínez-López, J. Israel; Betancourt, H. A.; García-López, Erika; Rodríguez, Ciro A. & Siller, Héctor R.
Partner: UNT College of Engineering

Expansion of radiative cooling of the laser induced plasma

Description: To study the expansion and cooling process of the laser induced plasma generated by nanosecond pulsed laser ablation, experiments have been conducted which measure the position of the external shockwaves and the temperature of the vapor plumes. The positions of external shockwaves were determined by a femtosecond laser time-resolved imaging system. Vapor plume temperature was determined from spectroscopic measurements of the plasma emission lines. A model which considers the mass, momentum, and energy conservation of the region affected by the laser energy was developed. It shows good agreement to the experimental data.
Date: May 5, 2006
Creator: Wen, Sy-Bor; Mao, Xianglei; Liu, Chunyi; Greif, Ralph & Russo,Richard
Partner: UNT Libraries Government Documents Department

IFE thick liquid wall chamber dynamics: Governing mechanisms andmodeling and experimental capabilities

Description: For thick liquid wall concepts, it is important to understand the different mechanisms affecting the chamber dynamics and the state of the chamber prior to each shot a compared with requirements from the driver and target. These include ablation mechanisms, vapor transport and control, possible aerosol formation, as well as protective jet behavior. This paper was motivated by a town meeting on this subject which helped identify the major issues, assess the latest results, review the capabilities of existing modeling and experimental facilities with respect to addressing remaining issues, and helping guide future analysis and R&D efforts; the paper covers these exact points.
Date: January 24, 2005
Creator: Raffray, A.R.; Meier, W.; Abdel-Khalik, S.; Bonazza, R.; Calderoni, P.; Debonnel, C.S. et al.
Partner: UNT Libraries Government Documents Department

Low-Energy Electron Irradiation of Preheated and Gas-Exposed Single-Wall Carbon Nanotubes

Description: We investigate the conditions under which electron irradiation of single-walled carbon nanotube (SWCNT) bundles with 2 keV electrons produces an increase in the Raman D peak. We find that an increase in the D peak does not occur when SWCNTs are preheated in situ at 600 C for 1 h in ultrahigh vacuum (UHV) before irradiation is performed. Exposing SWCNTs to air or other gases after preheating in UHV and before irradiation results in an increase in the D peak. Small diameter SWCNTs that are not preheated or preheated and exposed to air show a significant increase in the D and G bands after irradiation. X-ray photoelectron spectroscopy shows no chemical shifts in the C1s peak of SWCNTs that have been irradiated versus SWCNTs that have not been irradiated, suggesting that the increase in the D peak is not due to chemisorption of adsorbates on the nanotubes.
Date: December 2016
Creator: Ecton, Philip
Partner: UNT Libraries