176,798 research outputs found
Determining the size of lightning-induced electron precipitation patches
No full text[1] We analyze Trimpi signatures during 23 and 24 April 1994 at four sites on or near the Antarctic Peninsula (Palmer, Faraday, Rothera, and Halley) on subionospheric VLF signals received from four U. S. naval transmitters (NAA, NSS, NLK, and NPM). Electron precipitation patches are found to be large, i.e., similar to1500 km x 600 km, with the longer axis orientated east-west. Calculations using a three-dimensional Born scattering model, where patch densities are 1.5 electrons cm(-3) above ambient at the center at similar to84 km altitude, provides results that are consistent with this picture. A high proportion (38%) of the Trimpi events were associated with strong lightning flashes in eastern United States. When lightning discharges had currents >65 kA (positive or negative), there was a >80% chance of seeing an associated Trimpi event. The chance of seeing any Trimpi events fell to near zero for discharges of <45 kA. The largest Trimpi perturbations occur when the center of the precipitation patch is 700-800 km from the receivers. This result is consistent with the modeling calculations for large patches. The equatorward edge of the precipitation patch was estimated to be at &SIM;60&DEG;S, close to the magnetic conjugate of the lightning. The close association of the equatorward edge of the precipitation patch with the conjugate location of the causative lightning is consistent with a quasi-ducted whistler-induced precipitation mechanism. Nonducted whistler-induced precipitation mechanisms would predict a 5&DEG;-10&DEG; latitudinal gap between the lightning and the equatorward edge of the patch. However, the lack of observed whistlers at the time of the Trimpi events is consistent with the nonducted whistler mechanism and is not consistent with the quasi-ducted mechanism, although the distances from duct exit point to receiver may have been too large (&SIM;700-1000 km) for the signals to be detectable. Using the significantly larger patch dimensions determined in this study, it is estimated that lightning may well be 10-100 times more effective at depleting the radiation belts than hiss
Energetic electron precipitation during substorm injection events: High-latitude fluxes and an unexpected midlatitude signature
No full textGeosynchronous Los Alamos National Laboratory (LANL-97A) satellite particle data, riometer data, and radio wave data recorded at high geomagnetic latitudes in the region south of Australia and New Zealand are used to perform the first complete modeling study of the effect of substorm electron precipitation fluxes on low-frequency radio wave propagation conditions associated with dispersionless substorm injection events. We find that the precipitated electron energy spectrum is consistent with an e-folding energy of 50 keV for energies <400 keV but also contains higher fluxes of electrons from 400 to 2000 keV. To reproduce the peak subionospheric radio wave absorption signatures seen at Casey (Australian Antarctic Division), and the peak riometer absorption observed at Macquarie Island, requires the precipitation of 50–90% of the peak fluxes observed by LANL-97A. Additionally, there is a concurrent and previously unreported substorm signature at L < 2.8, observed as a substorm-associated phase advance on radio waves propagating between Australia and New Zealand. Two mechanisms are discussed to explain the phase advances. We find that the most likely mechanism is the triggering of wave-induced electron precipitation caused by waves enhanced in the plasmasphere during the substorm and that either plasmaspheric hiss waves or electromagnetic ion cyclotron waves are a potential source capable of precipitating the type of high-energy electron spectrum required. However, the presence of these waves at such low L shells has not been confirmed in this study
Correction to 'Radiation belt electron precipitation into the atmosphere: recovery from a geomagnetic storm'
No full textInternational audienceCorrection to “Radiation belt electron precipitation intothe atmosphere: Recovery from a geomagnetic storm”Craig J. Rodger, Mark A. Clilverd, Neil R. Thomson, Rory J. Gamble, Annika Seppälä,Esa Turunen, Nigel P. Meredith, Michel Parrot, Jean‐André Sauvaud,and Jean‐Jacques BerthelierReceived 17 August 2010; accepted 19 August 2010; published 25 September 2010.Citation: Rodger, C. J., M. A. Clilverd, N. R. Thomson, R. J. Gamble, A. Seppälä, E. Turunen, N. P. Meredith, M. Parrot, J.‐A.Sauvaud, and J.‐J. Berthelier (2010), Correction to “Radiation belt electron precipitation into the atmosphere: Recovery from ageomagnetic storm,” J. Geophys. Res., 115, A09324, doi:10.1029/2010JA016038
Simulation of thermal plant optimization and hydraulic aspects of thermal distribution loops for large campuses
No full textFollowing an introduction, the author describes Texas A&M University and its utilities system. After that, the author presents how to construct simulation models for chilled water and heating hot water distribution systems. The simulation model was used in a $2.3 million Ross Street chilled water pipe replacement project at Texas A&M University. A second project conducted at the University of Texas at San Antonio was used as an example to demonstrate how to identify and design an optimal distribution system by using a simulation model. The author found that the minor losses of these closed loop thermal distribution systems are significantly higher than potable water distribution systems. In the second part of the report, the author presents the latest development of software called the Plant Optimization Program, which can simulate cogeneration plant operation, estimate its operation cost and provide optimized operation suggestions. The author also developed detailed simulation models for a gas turbine and heat recovery steam generator and identified significant potential savings. Finally, the author also used a steam turbine as an example to present a multi-regression method on constructing simulation models by using basic statistics and optimization algorithms. This report presents a survey of the author??s working experience at the Energy Systems Laboratory (ESL) at Texas A&M University during the period of January 2002 through March 2004. The purpose of the above work was to allow the author to become familiar with the practice of engineering. The result is that the author knows how to complete a project from start to finish and understands how both technical and nontechnical aspects of a project need to be considered in order to ensure a quality deliverable and bring a project to successful completion. This report concludes that the objectives of the internship were successfully accomplished and that the requirements for the degree of Degree of Engineering have been satisfied
The Impact of PMSE on VLF Propagation
No full textABSTRACT PMSE or Polar Mesosphere Summer Echoes are a well known phenomenon in the summer northern polar regions, in which anomalous VHF/UHF radar echoes are returned from heights ~85 km. Associated phenomena at these altitudes are noctilucent clouds and electron density biteouts. The latter are electron density depletion layers of up to 90%, which may be several kms thick. Using the NOSC Modefndr code based on Wait's modal theory for subionospheric propagation, we calculate the shifts in received VLF amplitude and phase that occur as a result of electron density biteouts. The code assumes a homogeneous background ionosphere and a homogeneous biteout layer along the Great Circle Path (GCP) corridor, for transmitter receiver path lengths in the range 500-6000 km. For profiles during the 10hrs about midnight and under quiet geomagnetic conditions, where the electron density at 85 km would normally be less than 500 el/cc, it was found that received signal perturbations were significant, of the order of 1-4 dB and 5-40 degrees of phase. Perturbation amplitudes increase roughly as the square root of frequency. At short range perturbations are rather erratic, but more consistent at large ranges, readily interpretable in terms of the shifts in excitation factor, attenuation factor and v/c ratios for Wait's modes. Under these conditions such shifts should be detectable by a well constituted experiment involving multiple paths and multiple frequencies in the north polar region in summer. It is anticipated that VLF propagation could be a valuable diagnostic for biteout/PMSE when electron density at 85 km is under 500 el/cc, under which circumstances PMSE are not directly detectable by VHF/UHF radars. Keywords: 0689 Wave propagation, 2475 Polar ionosphere, 6934 Ionospheric propagation
Intern experience at CH���M Hill, Inc.: an internship report
No full textIncludes author's vita"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirement for the degree of Doctor of Engineering."Includes bibliographical referencesA review of the author's internship experience with CH���M HILL, Inc.
during the period September 1975 through May 1976 is presented. During this nine month
internship the author worked as an Engineer II in the Industrial Processes discipline of this
large consulting engineering firm... The author's prime responsibility was as one of three
lead design engineers on the design of a large wastewater treatment facility for a pulp mill
in Hoquiam, Washington owned by ITT Rayonier Inc. The work generally consisted of the design
of individual treatment units and associated piping and pumping. The purpose of the project
was to provide wastewater treatment capabilities that would satisfy the effluent limitations
(standards) imposed upon the mill by the State of Washington Department of Ecology and the
U.S. Environmental Protection Agency. The author's assignment also entailed necessary
interaction with the project manager and other CH���M HILL design engineers and support staff
members, the client's representatives, and representatives of two other consulting engineering
firms working on the project. Thus, the internship position at CH���M HILL provided considerable
experience coordinating the author's work with the work of other engineers, guiding the design
and administrative efforts of a support staff, and interacting regularly with the client and
other consulting firms. This broad exposure to a variety of engineering and organizational
problems provided a valuable educational experience
Intern experience at the Texas Transportation Institute: an internship report
No full text"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirements for the degree of Doctor of Engineering."Includes vita (leaf 91)Includes bibliographical references (leaf 57)This report discusses the author's engineering experience at the Texas
Transportation Institute (TTI), Texas A&M University from March 1974 through July 1977. A
report of this experience plus twelve additional hours of academic course work were
substituted for an internship according to requirements established by the College of
Engineering. Although the author could not retroactively establish objectives of the type
associated with a typical internship, the work experience gained could be related to the two
general objectives of an intership: 1. To demonstrate an identifiable contribution to the
organization in which the intern served, and 2. To enable the intern to become aware of the
non-technical aspects of working as an engineer in a non-academic environment. While a member
of the Texas Transportation Institute staff, the author worked on a number of projects in the
areas of highway traffic engineering research and the preparation of continuing education
courses for transportation engineering officials. These assignments were contained within the
Urban Transportation Systems Division of TTI. This report delineates the author's contribution
to four particular projects and discusses the technical as well as non-technical experience
gained from each. Having been exposed to more engineering situations than many of the other
Doctor of Engineering students, the author has already formulated some rather specific
milestones for the future. The Doctor of Engineering program is discussed in conjunction with
its potential for helping the author attain these career goals and objectives. Also, some
thoughts are presented regarding the Doctor of Engineering as a viable alternative to the
Ph.D. in preparing for a career in engineering higher education
The long-wavelength view of GG Tau A: rocks in the ring world
No full textWe present the first detection of GG Tau A at centimetre wavelengths, made with the Arcminute Microkelvin Imager Large Array at a frequency of 16 GHz (λ = 1.8 cm). The source is detected at >6 σrms with an integrated flux density of S16GHz = 249 ± 45 µJy. We use these new centimetre-wave data, in conjunction with additional measurements compiled from the literature, to investigate the long-wavelength tail of the dust emission from this unusual protoplanetary system. We use an MCMC-based method to determine maximum likelihood parameters for a simple parametric spectral model and consider the opacity and mass of the dust contributing to the microwave emission. We derive a dust mass of Md ~ 0.1 Msun, constrain the dimensions of the emitting region and find that the opacity index at λ > 7 mm is less than unity, implying a contribution to the dust population from grains exceeding ~4 cm in size. We suggest that this indicates coagulation within the GG Tau A system has proceeded to the point where dust grains have grown to the size of small rocks with dimensions of a few centimetres. Considering the relatively young age of the GG Tau association in combination with the low derived disc mass, we suggest that this system may provide a useful test case for rapid core accretion planet formation models
Intern experience at Honeywell, Inc., Large Information Systems Division: an internship report
No full textIncludes author's vita"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirement for the degree of Doctor of Engineering."Includes bibliographical references (leaves 169-173)This report describes the author's internship assignment at Honeywell
Inc. - Large Information Systems Division from January, 1982 through August, 1982. The purpose
of the assignment was to fulfill the internship requirements of the Doctor of Engineering
Program. During the internship, the author held the position of VLSI design engineer, where he
worked on a predefined project. The project's objective was to evaluate how circuit designs
based on an advanced CMOS process, can be applied to hardware products at LISD. The internship
allowed the author to successfully apply the MOS circuit design training, which ws developed
at Texas A&M, to an industrial project. In addition, involvement in different activities
and exposure to the various problems not encountered in academia, made this internship an
invaluable experience
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