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Preliminary measurements of the aerodynamic yawing derivatives of a triangular, a swept, and an unswept wing performing pure yawing oscillations, with a description of the instrumentation employed

Description: Report presenting an investigation to determine the effect of motion periodicity on the aerodynamic derivatives due to yawing velocity and yawing acceleration for a 60 degree delta wing, a 45 degree sweptback wing, and an unswept wing. Results were obtained from steady-state yawing-flow tests and tests of model performing pure sinusoidal yawing oscillations. Results regarding the static longitudinal characteristics, derivatives due to yawing velocity, and derivatives due to yawing acceleration are provided.
Date: April 2, 1956
Creator: Queijo, M. J.; Fletcher, Herman S.; Marple, C. G. & Hughes, F. M.
Partner: UNT Libraries Government Documents Department

Atomic Scale coexistence of Periodic and quasiperiodic order in a2-fold A1-Ni-Co decagonal quasicrystal surface

Description: Decagonal quasicrystals are made of pairs of atomic planes with pentagonal symmetry periodically stacked along a 10-fold axis. We have investigated the atomic structure of the 2-fold surface of a decagonal Al-Ni-Co quasicrystal using scanning tunneling microscopy (STM). The surface consists of terraces separated by steps of heights 1.9, 4.7, 7.8, and 12.6{angstrom} containing rows of atoms parallel to the 10-fold direction with an internal periodicity of 4{angstrom}. The rows are arranged aperiodically, with separations that follow a Fibonacci sequence and inflation symmetry. The results indicate that the surfaces are preferentially Al-terminated and in general agreement with bulk models.
Date: November 14, 2005
Creator: Park, Jeong Young; Ogletree, D. Frank; Salmeron, Miquel; Ribeiro,R.A.; Canfield, P.C.; Jenks, C.J. et al.
Partner: UNT Libraries Government Documents Department

EXTINCTION OF SPECIES BY PERIODIC COMET SHOWERS

Description: A 26-Myr periodicity has recently been seen in the fossil record of extinction in the geological past. At least two of these extinctions are known to be associated with the impact on the Earth of a comet or asteroid with a diameter of a few kilometres. We propose that the periodic events are triggered by an unseen companion to the Sun, travelling in a moderately eccentric orbit, which at its closest approach (perihelion) passes through the 'Oort cloud' of comets which surrounds the Sun. During each passage this unseen solar companion perturbs the orbits of these comets, sending a large number of them (over 1 x 10{sup 9}) into paths which reach the inner Solar System. Several of these hit the Earth, on average, in the following million years. At present the unseen companion should be approximately at its maximum distance from the Sun, {approx}2.4 light yr, and it will present no danger to the Earth until approximately AD 15,000,000.
Date: January 1, 1984
Creator: Davis, M.; Hut, P. & Muller, R.A.
Partner: UNT Libraries Government Documents Department

Inf-sup estimates for the Stokes problem in a periodic channel

Description: We derive estimates of the Babuska-Brezzi inf-sup constant {beta} for two-dimensional incompressible flow in a periodic channel with one flat boundary and the other given by a periodic, Lipschitz continuous function h. If h is a constant function (so the domain is rectangular), we show that periodicity in one direction but not the other leads to an interesting connection between {beta} and the unitary operator mapping the Fourier sine coefficients of a function to its Fourier cosine coefficients. We exploit this connection to determine the dependence of {beta} on the aspect ratio of the rectangle. We then show how to transfer this result to the case that h is C{sup 1,1} or even C{sup 0,1} by a change of variables. We avoid non-constructive theorems of functional analysis in order to explicitly exhibit the dependence of {beta} on features of the geometry such as the aspect ratio, the maximum slope, and the minimum gap thickness (if h passes near the substrate). We give an example to show that our estimates are optimal in their dependence on the minimum gap thickness in the C{sup 1,1} case, and nearly optimal in the Lipschitz case.
Date: December 10, 2008
Creator: Wilkening, Jon
Partner: UNT Libraries Government Documents Department

An infinite branching hierarchy of time-periodic solutions of the Benjamin-Ono equation

Description: We present a new representation of solutions of the Benjamin-Ono equation that are periodic in space and time. Up to an additive constant and a Galilean transformation, each of these solutions is a previously known, multi-periodic solution; however, the new representation unifies the subset of such solutions with a fixed spatial period and a continuously varying temporal period into a single network of smooth manifolds connected together by an infinite hierarchy of bifurcations. Our representation explicitly describes the evolution of the Fourier modes of the solution as well as the particle trajectories in a meromorphic representation of these solutions; therefore, we have also solved the problem of finding periodic solutions of the ordinary differential equation governing these particles, including a description of a bifurcation mechanism for adding or removing particles without destroying periodicity. We illustrate the types of bifurcation that occur with several examples, including degenerate bifurcations not predicted by linearization about traveling waves.
Date: July 1, 2008
Creator: Wilkening, Jon
Partner: UNT Libraries Government Documents Department

Forces and Stored Energy in Thin Cosine (n0) Accelerator Magnets

Description: We wish to compute Lorentz forces, equilibrium stress and stored energy in thin multipole magnets (Fig.1), that are proportional to cos(n{theta}) and whose strength varies purely as a Fourier sinusoidal series of the longitudinal coordinate z (say proportional to cos (2m-1){pi}z/L where L denotes the half-period and m = 1,2,3...). We shall demonstrate that in cases where the current is situated on such a surface of discontinuity at r = R (i.e. J = f({theta},z)), by computing the Lorentz force and solving the state of equilibrium on that surface, a closed form solution can be obtained for single function magnets as well as for any combination of interacting nested multi function magnets. The results that have been obtained, indicate that the total axial force on the end of a single multipole magnet n is independent (orthogonal) to any other multipole magnet i as long as n {ne} i. The same is true for the stored energy, the total energy of a nested set of multipole magnets is equal to the some of the energy of the individual magnets (of the same period length 2L). Finally we demonstrate our results on a nested set of magnets a dipole (n = 1) and a quadmpole (n=2) that have an identical single periodicity {omega}{sub 1}. We show that in the limiting 2D case (period 2L tends to infinity), the force reduces to the commonly known 2D case.
Date: March 18, 1996
Creator: Caspi, S.
Partner: UNT Libraries Government Documents Department

Inf-sup estimates for the Stokes problem in a periodic channel

Description: We derive estimates of the Babuska-Brezzi inf-sup constant {beta} for two-dimensional incompressible flow in a periodic channel with one flat boundary and the other given by a periodic, Lipschitz continuous function h. If h is a constant function (so the domain is rectangular), we show that periodicity in one direction but not the other leads to an interesting connection between {beta} and the unitary operator mapping the Fourier sine coefficients of a function to its Fourier cosine coefficients. We exploit this connection to determine the dependence of {beta} on the aspect ratio of the rectangle. We then show how to transfer this result to the case that h is C{sup 1,1} or even C{sup 0,1} by a change of variables. We avoid non-constructive theorems of functional analysis in order to explicitly exhibit the dependence of {beta} on features of the geometry such as the aspect ratio, the maximum slope, and the minimum gap thickness (if h passes near the substrate). We give an example to show that our estimates are optimal in their dependence on the minimum gap thickness in the C{sup 1,1} case, and nearly optimal in the Lipschitz case.
Date: June 27, 2007
Creator: Wilkening, Jon
Partner: UNT Libraries Government Documents Department

EUV-multilayers on grating-like topographies

Description: In this study, multilayer morphology near the key anomalies in grating-like structures, namely sharp step-edges and steep walls, are examined. Different deposition schemes are employed. Based on cross section TEM analysis an explanatory model describing the morphology of the successive layers is developed. A further insight into the periodicity and the general performance of the multilayer is obtained by EUV microscopy. The main distortions in multilayer structure and hence EUV performance are found to be restricted to a region within a few hundred nanometers from the anomalies, which is very small compared to the proposed grating period (50-100 {micro}m). These multilayer coated blazed gratings can thus be considered a viable option for spectral purity enhancement of EUV light sources.
Date: March 12, 2010
Creator: van Boogaard, A. J. R.; Louis, E.; Goldberg, K. A.; Mochi, I. & Bijkerk, F.
Partner: UNT Libraries Government Documents Department

Mesoscale Characterization of Coupled Hydromechanical Behavior of a Fractured Porous Slope in Response to Free Water-Surface Movement

Description: To better understand the role of groundwater-level changes on rock-slope deformation and damage, a carbonate rock slope (30 m x 30 m x 15 m) was extensively instrumented for mesoscale hydraulic and mechanical measurements during water-level changes. The slope is naturally drained by a spring that can be artificially closed or opened by a water gate. In this study, a 2-hour slope-dewatering experiment was analyzed. Changes in fluid pressure and deformation were simultaneously monitored, both at discontinuities and in the intact rock, using short-base extensometers and pressure gauges as well as tiltmeters fixed at the slope surface. Field data were analyzed with different coupled hydromechanical (HM) codes (ROCMAS, FLAC{sup 3D}, and UDEC). Field data indicate that in the faults, a 40 kPa pressure fall occurs in 2 minutes and induces a 0.5 to 31 x 10{sup -6} m normal closure. Pressure fall is slower in the bedding-planes, lasting 120 minutes with no normal deformation. No pressure change or deformation is observed in the intact rock. The slope surface displays a complex tilt towards the interior of the slope, with magnitudes ranging from 0.6 to 15 x 10{sup -6} rad. Close agreement with model for both slope surface and internal measurements is obtained when a high variability in slope-element properties is introduced into the models, with normal stiffnesses of k{sub n{_}faults} = 10{sup -3} x k{sub n{_}bedding-planes} and permeabilities of k{sub h{_}faults} = 10{sup 3} x k{sub h{_}bedding-planes}. A nonlinear correlation between hydraulic and mechanical discontinuity properties is proposed and related to discontinuity damage. A parametric study shows that 90% of slope deformation depends on HM effects in a few highly permeable and highly deformable discontinuities located in the basal, saturated part of the slope while the remaining 10% are related to elasto-plastic deformations in the low-permeability discontinuities induced by complex ...
Date: May 15, 2008
Creator: Rutqvist, Jonny; Guglielmi, Y.; Cappa, F.; Rutqvist, J.; Tsang, C.-F. & Thoraval, A.
Partner: UNT Libraries Government Documents Department

In/Si(111): Self-assembled one and two-dimensional electrongases

Description: We present angle-resolved photoemission measurements forultrathin In films on Si(111). Depending on the coverage, this systemself-organizes into a metallic monolayer with either 4x1 or sqrt7 x sqrt3symmetry relative to the substrate. Electronically, they behave likeideal one- and two-dimensional electron gases (1DEG and 2DEG),respectively. The 4x1 system has atomic chains of In whose energy bandsdisperse only parallel to the chains, while for the sqrt7 x sqrt3 system,the dominant reciprocal space features (in both diffraction andbandstructure) resemble a pseudo-square lattice with only weakersecondary features relating to the sqrt7 x sqrt3 periodicity. In bothmaterials the electrons show coupling to the structure. The 1DEG couplesstrongly to phonons of momentum 2kF, leading to an 8x"2" Peierls-likeinsulating ground state. The 2DEG appears to be partially stabilized byelectron gap formation at the sqrt 7 x sqrt3 zone boundary.
Date: January 22, 2001
Creator: Rotenberg, Eli; Yeom, H. W.; Takeda, S.; Matsuda, I.; Horikoshi, K.; Schaefer, J. et al.
Partner: UNT Libraries Government Documents Department

Transit Timing Observations from Kepler: IV. Confirmation of 4 Multiple Planet Systems by Simple Physical Models

Description: Eighty planetary systems of two or more planets are known to orbit stars other than the Sun. For most, the data can be sufficiently explained by non-interacting Keplerian orbits, so the dynamical interactions of these systems have not been observed. Here we present 4 sets of lightcurves from the Kepler spacecraft, which each show multiple planets transiting the same star. Departure of the timing of these transits from strict periodicity indicates the planets are perturbing each other: the observed timing variations match the forcing frequency of the other planet. This confirms that these objects are in the same system. Next we limit their masses to the planetary regime by requiring the system remain stable for astronomical timescales. Finally, we report dynamical fits to the transit times, yielding possible values for the planets masses and eccentricities. As the timespan of timing data increases, dynamical fits may allow detailed constraints on the systems architectures, even in cases for which high-precision Doppler follow-up is impractical.
Date: January 1, 2012
Creator: Fabrycky, Daniel C.; /UC, Santa Cruz; Ford, Eric B.; U., /Florida; Steffen, Jason H.; /Fermilab et al.
Partner: UNT Libraries Government Documents Department

Vector Potential and Stored Energy of a Quadrupole Magnet Array

Description: The vector potential, magnetic field and stored energy of a quadrupole magnet array are derived. Each magnet within the array is a current sheet with a current density proportional to the azimuthal angle 2{theta} and the longitudinal periodicity (2m-1){pi}/L. Individual quadrupoles within the array are oriented in a way that maximizes the field gradient The array does not have to be of equal spacing and can be of a finite size, however when the array is equally spaced and is of infinite size the solution can be simplified. We note that whereas, in a single quadrupole magnet with a current density proportional to cos2{theta} the gradient is pure, such purity is not preserved in a quadrupole array.
Date: March 15, 1999
Creator: Caspi, S.
Partner: UNT Libraries Government Documents Department

Bacillus atrophaeus Outer Spore Coat Assembly and Ultrastructure

Description: Our previous atomic force microscopy (AFM) studies successfully visualized native Bacillus atrophaeus spore coat ultrastructure and surface morphology. We have shown that the outer spore coat surface is formed by a crystalline array of {approx}11 nm thick rodlets, having a periodicity of {approx}8 nm. We present here further AFM ultrastructural investigations of air-dried and fully hydrated spore surface architecture. In the rodlet layer, planar and point defects, as well as domain boundaries, similar to those described for inorganic and macromolecular crystals, were identified. For several Bacillus species, rodlet structure assembly and architectural variation appear to be a consequence of species-specific nucleation and crystallization mechanisms that regulate the formation of the outer spore coat. We propose a unifying mechanism for nucleation and self-assembly of this crystalline layer on the outer spore coat surface.
Date: November 21, 2005
Creator: Plomp, M; Leighton, T J; Wheeler, K E; Pitesky, M E & Malkin, A J
Partner: UNT Libraries Government Documents Department

Color and Variability Characteristics of Point Sources in the Faint Sky Variability Survey

Description: The authors present an analysis of the color and variability characteristics for point sources in the Faint Sky Variability Survey (FSVS). The FSVS cataloged {approx} 23 square degrees in BVI filters from {approx} 16-24 mag to investigate variability in faint sources at moderate to high Galactic latitudes. Point source completeness is found to be >83% for a selected representative sample (V - 17.5-22.0 mag, B-V = 0.0-1.5) containing both photometric B, V detections and 80% of the time-sampled V data available compared to a basic internal source completeness of 99%. Multi-epoch (10-30) observations in V spanning minutes to years modeled by light curve simulations reveal amplitude sensitivities to {approx} 0.015-0.075 mag over a representative V = 18-22 mag range. Periodicity determinations appear viable to time-scales of an order 1 day or less using the most sampled fields ({approx} 30 epochs). The fraction of point sources is found to be generally variable at 5-8% over V = 17.5-22.0 mag. For V brighter than 19 mag, the variable population is dominated by low amplitude (< 0.05 mag) and blue (B-V < 0.35) sources, possibly representing a population of {gamma} Doradus stars. Overall, the dominant population of variable sources are bluer than B-V = 0.65 and have Main Sequence colors, likely reflecting larger populations of RR Lyrae, SX Phe, {gamma} Doradus, and W UMa variables.
Date: March 7, 2005
Creator: Huber, M E; Everett, M E & Howell, S B
Partner: UNT Libraries Government Documents Department

Growth of thick, crystalline material using dc-magnetron sputtering in Mag1 deposition chamber

Description: We demonstrated dense, non-columnar growth of thick Mo films by moving the substrates in and out of the plasma thus allowing the surface reconstruction and by interrupting the growth with Si layers. The multilayers made this way have very smooth surface, about 1.3 nm rms high spatial frequency roughness, while also maintaining the periodicity of a reflective coating. These preliminary results hint that the surface reconstruction is an important physical process that controls the growth mechanisms. Further studies, combined with theoretical modeling, are essential to further our knowledge on how to predict and control desired microstructure for different materials.
Date: November 2, 2005
Creator: Bajt, S; Alameda, J; Baker, S & Taylor, J S
Partner: UNT Libraries Government Documents Department

Investigations of (Delta)14C, (delta)13C, and (delta)15N in vertebrae of white shark (Carcharodon carcharias) from the eastern North Pacific Ocean

Description: The white shark (Carcharodon carcharias) has a complex life history that is characterized by large scale movements and a highly variable diet. Estimates of age and growth for the white shark from the eastern North Pacific Ocean indicate they have a slow growth rate and a relatively high longevity. Age, growth, and longevity estimates useful for stock assessment and fishery models, however, require some form of validation. By counting vertebral growth band pairs, ages can be estimated, but because not all sharks deposit annual growth bands and many are not easily discernable, it is necessary to validate growth band periodicity with an independent method. Radiocarbon ({sup 14}C) age validation uses the discrete {sup 14}C signal produced from thermonuclear testing in the 1950s and 1960s that is retained in skeletal structures as a time-specific marker. Growth band pairs in vertebrae, estimated as annual and spanning the 1930s to 1990s, were analyzed for {Delta}{sup 14}C and stable carbon and nitrogen isotopes ({delta}{sup 13}C and {delta}{sup 15}N). The aim of this study was to evaluate the utility of {sup 14}C age validation for a wide-ranging species with a complex life history and to use stable isotope measurements in vertebrae as a means of resolving complexity introduced into the {sup 14}C chronology by ontogenetic shifts in diet and habitat. Stable isotopes provided useful trophic position information; however, validation of age estimates was confounded by what may have been some combination of the dietary source of carbon to the vertebrae, large-scale movement patterns, and steep {sup 14}C gradients with depth in the eastern North Pacific Ocean.
Date: June 8, 2006
Creator: Kerr, L A; Andrews, A H; Cailliet, G M; Brown, T A & Coale, K H
Partner: UNT Libraries Government Documents Department

Gene Transfer & Hybridization Studies in Hyperthermophilic Species

Description: A. ABSTRACT The importance of lateral gene transfer (LGT) in the evolution of microbial species has become increasingly evident with each completed microbial genome sequence. Most significantly, the genome of Thermotoga maritima MSB8, a hyperthermophilic bacterium isolated by Karl Stetter and workers from Vulcano Italy in 1986, and sequenced at The Institute for Genomic Research (TIGR) in Rockville Maryland in 1999, revealed extensive LGT between % . this bacterium and members of the archaeal domain (in particular Archaeoglobus fulgidus, and Pyracoccus frcriosus species). Based on whole genome comparisons, it was estimated that 24% of the genetic information in this organism was acquired by genetic exchange with archaeal species, Independent analyses including periodicity analysis of the T. maritimu genomic DNA sequence, phylogenetic reconstruction based on genes that appear archaeal-like, and codon and amino acid usage, have provided additional evidence for LGT between T. maritima and the archaea. More recently, DiRuggiero and workers have identified a very recent LGT event between two genera of hyperthermophilic archaea, where a nearly identical DNA fragment of 16 kb in length flanked by insertion sequence (IS) elements, exists. Undoubtedly, additional examples of LGT will be identified as more microbial genomes are completed. For the present moment however, the genome sequence of T. maritima and other hyperthermophiles including P. furiosus, Pyrococcus horikoshii, Pyrococcus abyssi, A. fulgidus, and Aquifex aeolicus, have significantly increased out awareness of evolution being a web of life rather than a tree of life, as suggested by single gene phylogenies. In this proposal, we will aim to determine the extent of LGT across the hyperthemophiles, employing iY maritima as the model organism. A variety of biochemical techniques and phylogenetic reconstructions will allow for a detailed and thorough characterization of the extent of LGT in this species. The complete characterization of LGT in i? maritima ...
Date: October 14, 2005
Creator: Nelson, Karen E.
Partner: UNT Libraries Government Documents Department

Three-fold diffraction symmetry in epitaxial graphene and the SiC substrate

Description: The crystallographic symmetries and spatial distribution of stacking domains in graphene films on 6H-SiC(0001) have been studied by low energy electron diffraction (LEED) and dark field imaging in a low energy electron microscope (LEEM). We find that the graphene diffraction spots from 2 and 3 atomic layers of graphene have 3-fold symmetry consistent with AB (Bernal or rhombohedral) stacking of the layers. On the contrary, graphene diffraction spots from the buffer layer and monolayer graphene have apparent 6-fold symmetry, although the 3-fold nature of the satellite spots indicates a more complex periodicity in the graphene sheets.
Date: December 10, 2009
Creator: Siegel, D A; Zhou, S Y; El Gabaly, F; Schmid, A K; McCarty, K F & Lanzara, A
Partner: UNT Libraries Government Documents Department

The TAOS Project Stellar Variability II. Detection of 15 Variable Stars

Description: The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey data - covering timescales from a fraction of a second to a few hundred days - are a useful source to study stellar variability. A total of 167 star fields, mostly along the ecliptic plane, have been selected for photometric monitoring with the TAOS telescopes. This paper presents our initial analysis of a search for periodic variable stars from the time-series TAOS data on one particular TAOS field, No. 151 (RA = 17{sup h} 30{sup m} 6.67{sup s}, Dec = 27 degrees, 17 minutes, 30 seconds, J2000), which had been observed over 47 epochs in 2005. A total of 81 candidate variables are identified in the 3 square degree field, with magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape of the lightcurves, 32 variables, 18 of which were previously unknown, are classified as RR Lyrae, Cepheid, {delta} Scuti, SX Phonencis, semi-regular and eclipsing binaries.
Date: January 28, 2010
Creator: Mondal, S; Lin, C C; Zhang, Z W; Alcock, C; Axelrod, T; Bianco, F B et al.
Partner: UNT Libraries Government Documents Department

Ideas and concepts for diagnosis of performance and evaluation of data reliability based upon ARSA state-of-health (SOH) data

Description: At the current time, the Pacific Northwest National Laboratory (PNNL) prototype for the Automated Radioxenon Sampler/Analyzer (ARSA) automatically transmits, on a daily basis, a subset of all state-of-health (SOH) data in an e-mail data file to a limited number of recipients. These variables represent what were considered the most critical physical parameters for the ARSA's operation at the beginning of the field demonstration in Freiburg, Germany. Operators at PNNL perform a daily review of the information in the data file for anomalous operational conditions as evidenced by sensor readings. The initial review is easily implemented by plotting the various sensor data versus time and looking for gross deviations in the periodicity of the variables compared to previous sample sensor data. After viewing the 24-hr graphical plots, if necessary, a review is conducted of the tabular data of specific sensor anomalies. In most cases, the experience has been that when there is an ARSA operational problem the data file will have multiple sensor readings that reflect some aspect of the problem.
Date: April 27, 2000
Creator: Abel, KH; Bowyer, TW; Hayes, JC; Heimbigner, TR; Panisko, ME; McIntyre, JI et al.
Partner: UNT Libraries Government Documents Department

COMET SHOWERS ARE NOT INDUCED BY INTERSTELLAR CLOUDS

Description: Encounters with interstellar clouds (IC) have been proposed by Rampino and Stothers as a cause of quasi-periodic intense comet showers leading to earth impacts, in order to explain the periodicity in marine mass extinctions found by Raup and Sepkoski. The model was described further, criticized and defended. The debate has centered on the question of whether the scale height of the clouds is small enough (in comparison to the amplitude of the oscillation of the solar system about the plane of the Galaxy) to produce a modulation in the rate of encounters. We wish to point out another serious, we believe fatal, defect in this model - the tidal fields of ICs are not strong enough to produce intense comet showers leading to earth impacts by bringing comets of the postulated inner Oort cloud into earth crossing orbits, except possibly during very rare encounters with very dense clouds. We will show that encounters with abundant clouds of low density cannot produce comet showers; cloud density N > 10{sup 3} atoms cm{sup -3} is needed to produce an intense comet shower leading to earth impacts. Furthermore, the tidal field of a dense cloud during a distant encounter is too weak to produce such showers. As a consequence, comet showers induced by ICs will be far less frequent than showers caused by passing stars. This conclusion is independent of assumptions about the radial distribution of comets in the inner Oort cloud.
Date: November 1, 1985
Creator: Morris, D.E.
Partner: UNT Libraries Government Documents Department