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Role of Nucleation and Growth in Two-Phase Microstructure Formation

Description: During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different oscillatory microstructures that depend ...
Date: May 1, 2008
Creator: Shin, Jong Ho
Partner: UNT Libraries Government Documents Department

A Note on Equations for Steady-State Optimal Landscapes

Description: Based on the optimality principle (that the global energy expenditure rate is at its minimum for a given landscape under steady state conditions) and calculus of variations, we have derived a group of partial differential equations for describing steady-state optimal landscapes without explicitly distinguishing between hillslopes and channel networks. Other than building on the well-established Mining's equation, this work does not rely on any empirical relationships (such as those relating hydraulic parameters to local slopes). Using additional constraints, we also theoretically demonstrate that steady-state water depth is a power function of local slope, which is consistent with field data.
Date: June 15, 2010
Creator: Liu, H.H.
Partner: UNT Libraries Government Documents Department

ECN Pressure and Vacuum Vessel Engineering Notes

Description: The following calculations arranged in a spreadsheet format derive the flowrate from both ECN relieving devices. In this case it is assumed that the ECN is full of liquid argon and it is in its steady state cooling mode. One of the other cryostats is assumed to be cooling down while the other is being filled with LAr. Other assumptions in this analysis include: (1) Pressure in the cryostat is 19.75 psig (1.16X(MAWP+FV)). (2) Gaseous Nitrogen is concurrently flowing in the vent piping at a rate of 3477 lb/hr. This is derived from 0.3 gpm required for ECN steady state conditions, 4 gpm required for cooldown (max.), and 5 gpm required for filling with LAr (max.). (3) Mixture mass flows are at their maximum at the junction of the relief device outlets on the ECN (GN2 mass flow actually increases gradually at junctions toward the ECS and there is a short segment of piping between the GAr outlets and the condenser exhaust). (4) The temperature in the vent piping is negligible since a large majority of this piping is insulated. (5) All flows are treated as incompressible (max. Mach No. < 0.3). (6) The temperature of the GN2 prior to mixing in the vent manifold is 84 K, saturated property at 2 atm. (7) Flow equations apply to weight-averaged mixture densities and viscosities.
Date: October 17, 1991
Creator: Wu, J. & Dixon, K.
Partner: UNT Libraries Government Documents Department

Direct Molecular Simulation of Gradient-Driven Diffusion of Large Molecules using Constant Pressure

Description: Dual control volume grand canonical molecular dynamics (DCV-GCMD) is a boundary-driven non-equilibrium molecular dynamics technique for simulating gradient driven diffusion in multi-component systems. Two control volumes are established at opposite ends of the simulation box. Constant temperature and chemical potential of diffusing species are imposed in the control volumes. This results in stable chemical potential gradients and steady-state diffusion fluxes in the region between the control volumes. We present results and detailed analysis for a new constant-pressure variant of the DCV-GCMD method in which one of the diffusing species for which a steady-state diffusion flux exists does not have to be inserted or deIeted. Constant temperature, pressure and chemical potential of all diffusing species except one are imposed in the control volumes. The constant-pressure method can be applied to situations in which insertion and deletion of large molecules would be prohibitively difficult. As an exampIe, we used the method to shnulate diffusion in a biruuy mixture of spherical particles with a 2:1 size ratio. Steady-state diffusion fluxes of both diffbsi.ng species were established. The constant-pressure diffision coefficients agreed closely with the results of the standard constant-volume calculations. In addition, we show how the concentration, chemical potential and flux profiles can be used to calculate kwd binary and Maxwell-Stefim diffusion coefficients. In the case of the 2:1 size ratio mixture, we found that the binary dlffision coefficients were asymmetric and composition dependent, whereas the Maxwell-Stefan diffision coefficients changed very little with composition and were symmetric. This last result verified that the Gibbs-Duhem relation was satisfied locally, thus validating the assumption of local equilibrium.
Date: December 23, 1998
Creator: Heffelfinger, G.S. & Thompson, A.P.
Partner: UNT Libraries Government Documents Department

A comment on Ahmadi and Ma (1990)

Description: A model to predict flow of a particular mixture is described in Ahmadi and Ma (1990) and Ahmadi and Ma (1990); the full model, with closures, appears to result in predictions of unphysical behavior. Specifically, the model with its closure appears to result in spurious creation of energy. In this comment, the predictions of unphysical behavior will first be illustrated; the illustration will be followed by a some discussion of one closure that appears to cause the unphysical behavior in the case discussed.
Date: February 1, 1997
Creator: Liljegren, L.M.
Partner: UNT Libraries Government Documents Department

Modeling the Hall Thruster

Description: The acceleration of the plasma in the Hall thruster to supersonic velocities is examined by the use of a steady state model. Flows that are smooth across the sonic transition plane are found. The possibility of generating flows in which the acceleration across the sonic plane is abrupt, is also studied.
Date: August 1, 1998
Creator: Fisch, N.J. & Fruchtman, A.
Partner: UNT Libraries Government Documents Department

PROOF OF PRINCIPAL TEST TO FEED AND METER GRANULAR COAL INTO 450 PSIG GAS PRESSURE

Description: The objective of this project is to demonstrate proof of principal to feed and meter granular coal into 450 psig gas pressure for use with pressurized fluidized bed combustors. This report summarizes work undertaken in the second quarter of 1999 in support of that objective. Testing has been carried out on a small scale pump, but provided inconsistent data for correlation with performance predictions based on material properties. The problems were due to the inability of the test rig to maintain a steady state condition, compounded by a limitation of the available drive to overcome a gas pressure in excess of 50 psi. In order to obtain sufficient data to enable the requirements for the 450 psi pump to be adequately defined, another series of tests was required on an intermediate pump. This pump was installed and tested in the test rig that will be used for the final high pressure tests,and enabled data to be obtained under steady state conditions up to 175 psi gas pressure. This data has enabled the high pressure pump design to be finalized and implementation of the changes needed is underway. The extra testing carried out has resulted in considerable delays in the project timescale, so a 6 month no-cost extension has been requested. The final high pressure testing is now scheduled to commence in late September 1999.
Date: July 1, 1999
Creator: Aldred, Derek L.
Partner: UNT Libraries Government Documents Department

Extending Molecular Theory to Steady-State Diffusing Systems

Description: Predicting the properties of nonequilibrium systems from molecular simulations is a growing area of interest. One important class of problems involves steady state diffusion. To study these cases, a grand canonical molecular dynamics approach has been developed by Heffelfinger and van Swol [J. Chem. Phys., 101, 5274 (1994)]. With this method, the flux of particles, the chemical potential gradients, and density gradients can all be measured in the simulation. In this paper, we present a complementary approach that couples a nonlocal density functional theory (DFT) with a transport equation describing steady-state flux of the particles. We compare transport-DFT predictions to GCMD results for a variety of ideal (color diffusion), and nonideal (uphill diffusion and convective transport) systems. In all cases excellent agreement between transport-DFT and GCMD calculations is obtained with diffusion coefficients that are invariant with respect to density and external fields.
Date: October 22, 1999
Creator: FRINK,LAURA J. D.; SALINGER,ANDREW G. & THOMPSON,AIDAN P.
Partner: UNT Libraries Government Documents Department

Transient, Real-Time, Particulate Emission Measurements in Diesel Engines

Description: This paper reports our efforts to develop an instrument, TG-1, to measure particulate emissions from diesel engines in real-time. TG-1 while based on laser-induced incandescence allows measurements at 10 Hz on typical engine exhausts. Using such an instrument, measurements were performed in the exhaust of a 1.7L Mercedes Benz engine coupled to a low inertia dynamometer. Comparative measurements performed under engine steady state conditions showed the instrument to agree within {+-}12% of measurements performed with an SMPS. Moreover, the instrument had far better time response and time resolution than a TEOM{reg_sign} 1105. Also, TG-1 appears to surpass the shortcomings of the TEOM instrument, i.e., of yielding negative values under certain engine conditions and, being sensitive to external vibration.
Date: August 24, 2003
Creator: Gupta, S.; Shih, J.; Hillman, G.; Sekar, R.; Graze, R.; Shimpi, S. et al.
Partner: UNT Libraries Government Documents Department

A Third Generation Lower Hybrid Coupler

Description: The Princeton Plasma Physics Laboratory (PPPL) and the Massachusetts Institute of Technology (MIT) are preparing an experiment of current profile control using lower-hybrid waves in order to produce and sustain advanced tokamak regimes in steady-state conditions in Alcator C-Mod. Unlike JET's, ToreSupra's and JT60's couplers, the C-Mod lower-hybrid coupler does not employ the now conventional multijunction design, but will have similar characteristics, compactness, and internal power division while retaining full control of the antenna element phasing. This is achieved by using 3 dB vertical power splitters and a stack of laminated plates with the waveguides milled in them. Construction is simplified and allows easy control and maintenance of all parts. Many precautions are taken to avoid arcing. Special care is also taken to avoid the recycling of reflected power which could affect the coupling and the launched n(subscript ||) spectrum. The results from C-Mod should allow further simplification in the designs of the coupler planned for KSTAR (Korea Superconducting Tokamak Advanced Research) and ITER (International Thermonuclear Experimental Reactor).
Date: December 5, 2001
Creator: Bernabei, S.; Hosea, J.; Kung, C.; Loesser, D.; Rushinski, J.; Wilson, J.R. et al.
Partner: UNT Libraries Government Documents Department

LHe Flow Regime/Pressure Drop for D0 Solenoid at Steady State Conditions

Description: This paper describes in a note taking format what was learned from several sources on two phase liquid helium flow regimes and pressure drops as applied to the D-Zero solenoid upgrade project. Calculations to estimate the steady state conditions for the D-Zero solenoid at 5, 10 and 15 g/s are also presented. For the lower flow rates a stratified type regime can be expected with a pressure drop less than 0.5 psi. For the higher flow rate a more homogeneous flow regime can be expected with a pressure drop between 0.4 to 1.5 psi.
Date: March 3, 1993
Creator: Rucinski, R.
Partner: UNT Libraries Government Documents Department

Development of NOx Sensors for Heavy Vehicle Applications

Description: A DOE CRADA was initiated in February 2000 between Ford Motor Company and the US Department of Energy's Oak Ridge National Laboratory (ORNL). The overall objective of the research agreement was to characterize the performance of emission sensors and identify potential areas of improvement and to develop improved insulating materials with a lower capacitance to minimize radio frequency (RF) interference. A bench-scale device was developed at ORNL to evaluate sensor performance. The test stand was designed to enable control of the gas composition, flow rate, and temperature. An air-actuated three-way valve was used to control the injection of the test gas in order to elucidate the transient behavior of the sensor. The major finding from the studies was that transient test results showed that response time of the sensor to NO was highly dependent on the temperature. The time constant decreased with increasing gas temperature and achieved a constant valve of 610 ms for temperatures greater than or equal to 350 C. The steady-state valves O{sub 2} and NO{sub x} pumping currents were measured under steady-state conditions using a picoammeter. The measured pumping currents were extremely low and required an electrically quiet environment for accurate readings. ORNL developed also modified the existing insulator material to decrease its dielectric constant in order to reduce radio frequency interference from the internal heater. This was accomplished by adding low dielectric constant sintering aids to alumina.
Date: January 18, 2002
Creator: Armstrong, T.R. & Soltis, R.E.
Partner: UNT Libraries Government Documents Department

MODELING THE CATHODIC REGION IN CREVICE CORROSION UNDER A THIN ELECTROLYTE FILM INCLUDING PARTICULATES

Description: Crevice corrosion may be limited by the capacity of the external cathodic region to support anodic dissolution currents within the crevice. The analysis here focuses on behavior of metal surfaces covered by a thin ({approx}microns) layer of the electrolyte film including particulates. The particulates can affect the cathode current capacity (I{sub total}) by increasing the solution resistance (''volume effect'') and by decreasing the electrode area (''surface effect''). In addition, there can be particulate effects on oxygen reduction kinetics and oxygen transport. This work simulates and characterizes the effect of a uniform particulate monolayer on the cathode current capacity for steady state conditions in the presence of a thin electrolyte film. Particulate configurations with varying particle size, shape, arrangement, volume fraction, and electrode area coverage were numerically modeled as a function of the properties of the system. It is observed that the effects of particles can be fully accounted for in terms of two corrections: the volume blockage effect on the electrolyte resistivity can be correlated using Bruggeman's equation, and the electrode coverage effect can be modeled in terms of a simple area correction to the kinetics expression. For the range of parameters analyzed, applying these two correction factors, cathodes covered with thin electrolyte films that contain particles can be represented in terms of equivalent homogeneous electrolytes that can then be analyzed using simpler approaches. Continuing work will examine the effects of greater volume fractions of particles and multiple particle layers.
Date: March 14, 2006
Creator: Agarwal, A.S.; Landau, U.; Shan, X. & Payer, J.H.
Partner: UNT Libraries Government Documents Department

TECHNETIUM SORPTION BY CEMENTITIOUS MATERIALS UNDER REDUCING CONDITIONS

Description: The objective of this study was to measure Tc sorption to cementitious materials under reducing conditions to simulate Saltstone Disposal Facility conditions. Earlier studies were conducted and the experimental conditions were found not to simulate those of the facility. Through a five month subcontract with Clemson University, sorption of {sup 99}Tc to four cementitious materials was examined within an anaerobic glovebag targeting a 0.1% H2(g)/ 99.9% N{sub 2}(g) atmosphere. Early experiments based on Tc sorption and Eh indicated that 0.1% H{sub 2}(g) (a reductant) was necessary to preclude experimental impacts from O{sub 2}(g) diffusion into the glovebag. Preliminary data to date (up to 56 days) indicates that sorption of {sup 99}Tc to cementitious materials increased with increasing slag content for simulated saltstone samples. This is consistent with the conceptual model that redox active sulfide groups within the reducing slag facilitate reduction of Tc(VII) to Tc(IV). These experiments differ from previous experiments where a 2% H{sub 2}(g) atmosphere was maintained (Kaplan et al., 2011 (SRNL-STI-2010-00668)). The impact of the 2% H{sub 2}(g) reducing atmosphere on this data was examined and determined to cause the reduction of Tc in experimental samples without slag. In the present ongoing study, after 56 days, Tc sorption by the 50-year old cement samples (no slag) was undetectable, whereas Tc sorption in the cementitious materials containing slag continues to increase with contact time (measured after 1, 4, 8, 19 and 56 days). Sorption was not consistent with spike concentrations and steady state has not been demonstrated after 56 days. The average conditional K{sub d} value for the Vault 2 cementitious material was 6,362 mL/g (17% slag), for the TR547 Saltstone (45% slag) the conditional K{sub d} was 1258 mL/g, and for TR545 (90% slag) the conditional K{sub d} was 12,112 mL/g. It is anticipated that additional samples ...
Date: January 31, 2012
Creator: Kaplan, D.; Estes, S.; Arai, Y. & Powell, B.
Partner: UNT Libraries Government Documents Department

The Effect of Steady Winds on Radon-222 Entry from soil into houses

Description: Wind affects the radon-222 entry rate from soil into buildings and the resulting indoor concentrations. To investigate this phenomenon, we employ a previously tested three-dimensional numerical model of soil-gas Bow around houses, a commercial computational fluid dynamics code, an established model for determining ventilation rates in the presence of wind, and new wind tunnel results for the ground-surface pressure field caused by wind. These tools and data, applied under steady-state conditions to a prototypical residential building, allow us (1) to determine the complex soil-gas flow patterns that result from the presence of wind-generated ground-surface pressures, (2) to evaluate the effect of these flows on the radon concentration in the soil, and (3) to calculate the effect of wind on the radon entry rate and indoor concentration. For a broad range of soil permeabilities, two wind speeds, and two wind directions, we quantify the"flushing" effect of wind on the radon in the soil surrounding a house, and the consequent sharp decrease in radon entry rates. Experimental measurements of the time-dependent radon concentration in soil gas beneath houses confirm the existence of wind-induced flushing. Comparisons are made to modeling predictions obtained while ignoring the effect of the wind-generated ground-surface pressures. These investigations lead to the conclusion that wind-generated ground-surface pressures play a significant role in determining radon entry rates into residential buildings. [References: 26]
Date: October 1, 1994
Creator: Riley, W.J.; Gadgil, A.J.; Bonnefous, Y.C. & Nazaroff, W.W.
Partner: UNT Libraries Government Documents Department

A quasilinear model for solute transport under unsaturated flow

Description: We developed an analytical solution for solute transport under steady-state, two-dimensional, unsaturated flow and transport conditions for the investigation of high-level radioactive waste disposal. The two-dimensional, unsaturated flow problem is treated using the quasilinear flow method for a system with homogeneous material properties. Dispersion is modeled as isotropic and is proportional to the effective hydraulic conductivity. This leads to a quasilinear form for the transport problem in terms of a scalar potential that is analogous to the Kirchhoff potential for quasilinear flow. The solutions for both flow and transport scalar potentials take the form of Fourier series. The particular solution given here is for two sources of flow, with one source containing a dissolved solute. The solution method may easily be extended, however, for any combination of flow and solute sources under steady-state conditions. The analytical results for multidimensional solute transport problems, which previously could only be solved numerically, also offer an additional way to benchmark numerical solutions. An analytical solution for two-dimensional, steady-state solute transport under unsaturated flow conditions is presented. A specific case with two sources is solved but may be generalized to any combination of sources. The analytical results complement numerical solutions, which were previously required to solve this class of problems.
Date: May 15, 2009
Creator: Houseworth, J.E. & Leem, J.
Partner: UNT Libraries Government Documents Department

Errata Sheet for Post-Closure Inspection and Monitoring Report for Corrective Action Unit 110: Area 3 WMD U-3ax/bl Crater, Nevada Test Site, Nevada

Description: The last sentence of the second paragraph of the Executive Summary on page ix incorrectly states the period for repair. Cracks or areas of settling exceeding the 15 centimeters (6 inches) deep that extend 1.0 meter (3 feet) or more on the cover will be evaluated and repaired within 60 days of detection. The second sentence of the third paragraph of the Executive Summary on page ix incorrectly states the month that cover repair was performed while omitting the discovery of additional settling, which was repaired during the originally-stated repair month. The corrected sentence (with additional sentences added for clarification) reads, 'This area of settling on the cover was repaired in October 2006. Additional cracking was observed during the October 2006 repair that exceeded the action level and was repaired in December 2006.' The last sentence of the fourth bullet of Section 2.2 on page 5 incorrectly states the period for repair. Cracks or areas of settling exceeding the compliance criterion will be evaluated and repaired within 60 days. A repair event was omitted from Section 3.4 on page 13, which should be included as Subsection 3.4.1, 'October 26-30, 2006, Repairs'. The subtext included with this subsection should read, 'During the September 19, 2006, inspection, one area of settling on the southeast portion of the cover exceeded the settling compliance criterion. The area was repaired over the period of October 26-30, 2006. A portable, gas-powered tamper was used to compact the cracks in the cover. The area was backfilled with clean, native soil using wheelbarrows and shovels, and then compacted using the tamper.' Due to the inclusion of the previously-listed omission, Subsection 3.4.1 should be renumbered to Subsection 3.4.2, and the first sentence corrected to read, 'During the October 26-30, 2006, repair, an additional area of settling on the southeast ...
Date: September 13, 2007
Creator: National Security Technologies, LLC
Partner: UNT Libraries Government Documents Department

Q, Break-even and the n{tau{sub E}} Diagram for Transient Fusion Plasmas

Description: Q, break-even and the Lawson diagram are well defined and understood for steady-state fusion plasma conditions. Since many fusion experiments are transient, it is necessary to clarify the definitions for instantaneous Q values and break-even so that the Lawson diagram can be interpreted for transient plasma conditions. This discussion shows that there are two mathematically correct methods to describe the Lawson diagram for a transient plasma: the Lawson/TFTR method and the JET/JT-60 method. These methods are discussed in detail in this paper.
Date: April 1, 1998
Creator: Meade, Dale M.
Partner: UNT Libraries Government Documents Department

Thermostatted delta f

Description: The delta f simulation method is revisited. Statistical coarse-graining is used to rigorously derive the equation for the fluctuation delta f in the particle distribution. It is argued that completely collisionless simulation is incompatible with the achievement of true statistically steady states with nonzero turbulent fluxes because the variance of the particle weights w grows with time. To ensure such steady states, it is shown that for dynamically collisionless situations a generalized thermostat or W-stat may be used in lieu of a full collision operator to absorb the flow of entropy to unresolved fine scales in velocity space. The simplest W-stat can be implemented as a self-consistently determined, time-dependent damping applied to w. A precise kinematic analogy to thermostatted nonequilibrium molecular dynamics (NEMD) is pointed out, and the justification of W-stats for simulations of turbulence is discussed. An extrapolation procedure is proposed such that the long-time, steady-state, collisionless flux can be deduced from several short W-statted runs with large effective collisionality, and a numerical demonstration is given.
Date: January 18, 2000
Creator: Krommes, J.A.
Partner: UNT Libraries Government Documents Department

PROOF OF PRINCIPAL TEST TO FEED AND METER GRANULAR COAL INTO 450 psig GAS PRESSURE

Description: This research program is concerned with the development of a new form of feeder, known as the Stamet Posimetric O High Pressure Solids Feeder, to feed dry granular solids continuously and controllably into gas pressure. The device is a rotary mechanical feeder, which utilizes the interlocking and internal friction of the granular solids to drive the solids through into the outlet pressure in a continuous and controllable way, using a continuous solids material seal on the feeder outlet to control gas leakage. Earlier work sponsored under previous SBIR grants has successfully demonstrated the potential benefits of the Stamet machine over pressurized lock hopper or paste feeder methods. The objective of this project was to demonstrate proof of principal to feed and meter specified granular coal into 450 psig gas pressure for use with next generation pressurized fluidized bed combustors. This report encompasses the development of material transport properties testers, methods to predict feeder performance by calculation, and the modification and testing of Stamet feeders to feed the material supplied into pressure. Testers were made to measure material compressibility, bulk density, both internal and wall friction coefficients, and permeability under typical conditions experienced inside a Stamet high pressure feeder. This data is then used in support of ongoing efforts to develop calculations to predict the performance of Stamet pressure feeders with different materials and conditions. Three Stamet pressure feeders were modified to handle the fine granular or pulverized coal, and were tested under various conditions using different outlet arrangements. The initial testing identified difficulties in handling the fine materials, but through a series of calculations and tests, the issues were overcome and the material was successfully fed into pressure. In all cases the performance calculated based on the measured material properties and feeder geometry agreed well with the test results, confirming ...
Date: July 1, 2000
Creator: Aldred, Derek L.
Partner: UNT Libraries Government Documents Department

Plasma-Catalysis During Temperature Transient Testing

Description: A combination of catalysts is used together with nonthermal plasma in simulated diesel exhaust, while the gas temperature is varied. The catalysts both store and convert pollutants. As a result, pollutant concentrations during temperature ramps are different than those at steady state conditions. The data are presented for plasma followed by BaY, alumina, and Pt catalysts in simulated exhaust. When temperature ramps from high to low, apparent NOx conversion is quite high. However, when temperature is ramped from low to high, lower apparent conversions are seen. In a typical test cycle, average NOx conversion between 100 and 400 C is 60%. Peak conversion during the down ramp is over 90%, and minimum conversion during the up ramp is 30%. The composition of the effluent gas also varies during the temperature cycle. Intermediates such as methyl nitrate and hydrogen cyanide are not present following the combination of catalysts.
Date: August 5, 2001
Creator: Hoard, John
Partner: UNT Libraries Government Documents Department

A Nonlinear Fuel Optimal Reaction Jet Control Law

Description: We derive a nonlinear fuel optimal attitude control system (ACS) that drives the final state to the desired state according to a cost function that weights the final state angular error relative to the angular rate error. Control is achieved by allowing the pulse-width-modulated (PWM) commands to begin and end anywhere within a control cycle, achieving a pulse width pulse time (PWPT) control. We show through a MATLAB{reg_sign} Simulink model that this steady-state condition may be accomplished, in the absence of sensor noise or model uncertainties, with the theoretical minimum number of actuator cycles. The ability to analytically achieve near-zero drift rates is particularly important in applications such as station-keeping and sensor imaging. Consideration is also given to the fact that, for relatively small sensor and model errors, the controller requires significantly fewer actuator cycles to reach the final state error than a traditional proportional-integral-derivative (PID) controller. The optimal PWPT attitude controller may be applicable for a high performance kinetic energy kill vehicle.
Date: June 30, 2002
Creator: Breitfeller, E. & Ng, L.C.
Partner: UNT Libraries Government Documents Department

Meaning of the negative impedance

Description: It is shown that the negative real part of an input impedance does not mean instability of the related circuit. A negative real part of the input impedance means only that the concerned circuit is active.
Date: June 1, 1981
Creator: Conciauro, G. & Puglisi, M.
Partner: UNT Libraries Government Documents Department

Secondary Pollutants from Ozone Reaction with Ventilation Filters and Degradation of Filter Media Additives

Description: Prior research suggests that chemical processes taking place on the surface of particle filters employed in buildings may lead to the formation of harmful secondary byproducts. We investigated ozone reactions with fiberglass, polyester, cotton/polyester and polyolefin filter media, as well as hydrolysis of filter media additives. Studies were carried out on unused media, and on filters that were installed for 3 months in buildings at two different locations in the San Francisco Bay Area. Specimens from each filter media were exposed to {approx}150 ppbv ozone in a flow tube under a constant flow of dry or humidified air (50percent RH). Ozone breakthrough was recorded for each sample over periods of {approx}1000 min; the ozone uptake rate was calculated for an initial transient period and for steady-state conditions. While ozone uptake was observed in all cases, we did not observe significant differences in the uptake rate and capacity for the various types of filter media tested. Most experiments were performed at an airflow rate of 1.3 L/min (face velocity = 0.013 m/s), and a few tests were also run at higher rates (8 to 10 L/min). Formaldehyde and acetaldehyde, two oxidation byproducts, were quantified downstream of each sample. Those aldehydes (m/z 31 and 45) and other volatile byproducts (m/z 57, 59, 61 and 101) were also detected in real-time using Proton-Transfer Reaction - Mass Spectrometry (PTR-MS). Low-ppbv byproduct emissions were consistently higher under humidified air than under dry conditions, and were higher when the filters were loaded with particles, as compared with unused filters. No significant differences were observed when ozone reacted over various types of filter media. Fiberglass filters heavily coated with impaction oil (tackifier) showed higher formaldehyde emissions than other samples. Those emissions were particularly high in the case of used filters, and were observed even in the absence ...
Date: May 1, 2011
Creator: Destaillats, Hugo; Chen, Wenhao; Apte, Michael; Li, Nuan; Spears, Michael; Almosni, Jérémie et al.
Partner: UNT Libraries Government Documents Department