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Articles 691 - 720 of 969
Full-Text Articles in Physics
Electrical And Spectroscopic Studies Of The Effects Of Dc Electric Fields On Pre-Mixed Propane-Air Flames, S D. Marcum, G D. Gillen, B N. Ganguly
Electrical And Spectroscopic Studies Of The Effects Of Dc Electric Fields On Pre-Mixed Propane-Air Flames, S D. Marcum, G D. Gillen, B N. Ganguly
Physics
The effects of DC electric fields on temperature distributions within pre-mixed propane-air flames have been measured by the technique of thin filament pyrometry (TFP). We have focussed on the dramatic electric-field-induced modifications of the shape and size of the inner cone and the concomitant changes in the temperature profiles of fuel-rich mixtures with equivalence ratios of 1-1.35. Temperature profile measurements show large decreases in the reaction zone volume that is dependent upon the applied voltage polarity, indicating that electron impact excitation is not responsible for the observed effects. Additionally, the observed flame temperature profile modifications are not strongly dependent on …
The Speed And Orientation Of The Parsec-Scale Jet In 3c 279, B. Glenn Piner, Stephen C. Unwind, Ann E. Wehrle, Alma C. Zook, C. Megan Urry, Diane M. Gilmore
The Speed And Orientation Of The Parsec-Scale Jet In 3c 279, B. Glenn Piner, Stephen C. Unwind, Ann E. Wehrle, Alma C. Zook, C. Megan Urry, Diane M. Gilmore
Physics
A high degree of relativistic beaming is inferred for the jets of blazars on the basis of several lines of evidence, but the intrinsic speed and angle of the jet to the line of sight for individual sources are difficult to measure. We have calculated inverse Compton Doppler factors for 3C 279 using the collection of VLBI data (including high-resolution space VLBI data at low frequencies) recently published by us (as Wehrle et al. and Piner et al.) and the collection of multiwavelength spectra recently published by Hartman et al. From the Doppler factor and superluminal apparent speed, we then …
Measurement Of The Index Of Refraction Of A Flat Zinc Germanium Phosphide Wafer In The Infrared, Glen Gillen, Shekhar Guha
Measurement Of The Index Of Refraction Of A Flat Zinc Germanium Phosphide Wafer In The Infrared, Glen Gillen, Shekhar Guha
Physics
We have developed and tested a novel application of interferometry to determine the absolute refractive index of individual infrared materials having flat and parallel surfaces without alteration of the sample in any way, and measured no for ZnGeP2.
Us Nuclear Security Cooperation With Russia And Transparency, David W. Hafemeister
Us Nuclear Security Cooperation With Russia And Transparency, David W. Hafemeister
Physics
This chapter reviews the efforts of Russia and the United States to conclude agreements on the control or reduction of their inventories of nuclear warheads and military fissile materials. While some of the negotiations attempted to codify arms limitation and reduction measures, others were aimed at constraining the spread of fissile materials and technologies to the non-nuclear weapon states (NNWS). A number of the negotiations had elements of both arms control and non-proliferation.
Most of the monitoring provisions contained in nuclear agreements between Russia and the USA are in the category of transparency measures—those that give confidence that a …
Viscoelasticity From A Microscopic Model Of Dislocation Dynamics, M. Christina Marchetti, Karl Saunders
Viscoelasticity From A Microscopic Model Of Dislocation Dynamics, M. Christina Marchetti, Karl Saunders
Physics
It is shown that the dynamics of a viscoelastic medium can be modeled as that of a two-dimensional crystal with a finite concentration of dislocations, as well as vacancy and interstitial defects. At the longest length scales the viscoelasticity is described by the simplest Maxwell model, whose shear and compressional relaxation times are obtained in terms of microscopic quantities, including the density of free dislocations. At short length scales, t bond orientational order effects become important and lead to wave vector dependent corrections to the relaxation times.
Exclusion Limits On The Wimp-Nucleon Cross Section From The Cryogenic Dark Matter Search, D. Abrams, D. S. Akerib, M. S. Armel-Funkhouser, L. Baudis, D. A. Bauer, A. Bolozdynya, P. L. Brink, R. Bunker, B. Cabrera, D. O. Caldwell, J. P. Castle, C. L. Chang, R. M. Clarke, M. B. Crisler, R. Dixon, D. Driscoll, S. Eichblatt, R. J. Gaitskell, S. R. Golwala, E. E. Haller, J. Hellmig, D. Holmgren, M. E. Huber, S. Kamat, A. Lu, V. Mandic, J. M. Martinis, P. Meunier, S. W. Nam, H. Nelson, T. A. Perera, M. C. Perillo Isaac, W. Rau, R. R. Ross, T. Saab, B. Sadoulet, J. Sander, R. W. Schnee, T. Shutt, A. Smith, A. H. Sonnenschein, A. L. Spadafora, G. Wang, S. Yellin, Betty A. Young
Exclusion Limits On The Wimp-Nucleon Cross Section From The Cryogenic Dark Matter Search, D. Abrams, D. S. Akerib, M. S. Armel-Funkhouser, L. Baudis, D. A. Bauer, A. Bolozdynya, P. L. Brink, R. Bunker, B. Cabrera, D. O. Caldwell, J. P. Castle, C. L. Chang, R. M. Clarke, M. B. Crisler, R. Dixon, D. Driscoll, S. Eichblatt, R. J. Gaitskell, S. R. Golwala, E. E. Haller, J. Hellmig, D. Holmgren, M. E. Huber, S. Kamat, A. Lu, V. Mandic, J. M. Martinis, P. Meunier, S. W. Nam, H. Nelson, T. A. Perera, M. C. Perillo Isaac, W. Rau, R. R. Ross, T. Saab, B. Sadoulet, J. Sander, R. W. Schnee, T. Shutt, A. Smith, A. H. Sonnenschein, A. L. Spadafora, G. Wang, S. Yellin, Betty A. Young
Physics
The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.9% efficiency, and surface events are rejected with >95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to ∼10%. Results of …
Two-Dimensional Imaging Of Neutral Alkali Atom Samples Using Surface Ionization, Katharina Gillen-Christandl, Gregory P. Lafyatis, Andrei Modoran, Tung-Hsiu Shih
Two-Dimensional Imaging Of Neutral Alkali Atom Samples Using Surface Ionization, Katharina Gillen-Christandl, Gregory P. Lafyatis, Andrei Modoran, Tung-Hsiu Shih
Physics
We describe the design and characterization of a high resolution, high efficiency detector for two-dimensional imaging of neutral atoms. Incident atoms are surface-ionized by a tungsten-coated hot ribbon and the resulting ions are accelerated into a microchannel plate detector with a phosphor screen output. With this design we can detect individual alkali and other low ionization potential atoms and molecules with a spatial resolution of ∼ 20 μm. We find backgrounds on the order of 30 Hz over an active detection region of 20 mm2, a time response of ⩽ 1/30 s, and a detection efficiency of …
Tuning The Transition Temperature Of Superconducting Ag/Pb Films Via The Proximity Effect, Richard P. Barber Jr., Ben Kain, S. R. Khan
Tuning The Transition Temperature Of Superconducting Ag/Pb Films Via The Proximity Effect, Richard P. Barber Jr., Ben Kain, S. R. Khan
Physics
We report measurements of the transition temperature (TC) of superconducting films composed of various combinations of Ag and Pb layers. For samples with good electrical contact between the layers, the measured TC values show reasonable agreement with the Cooper model of the proximity effect. In poorly coupled samples, the normal layers appear to cause little if any suppression of the TC. We present a simple predictive expression for TC as a function of Ag content.
Discovery Of A Substellar Companion To The K2 Iii Giant Ɩ Draconis, Sabine Frink, David Mitchell, Andreas Quirrenbach, Debra A. Fischer, Geoffrey W. Marcy, R. Paul Butler
Discovery Of A Substellar Companion To The K2 Iii Giant Ɩ Draconis, Sabine Frink, David Mitchell, Andreas Quirrenbach, Debra A. Fischer, Geoffrey W. Marcy, R. Paul Butler
Physics
We report precise radial velocity measurements of the K giant ɩ Dra (HD 137759, HR 5744, HIP 75458), carried out at Lick Observatory, which reveal the presence of a substellar companion orbiting the primary star. A Keplerian fit to the data yields an orbital period of about 536 days and an eccentricity of 0.70. Assuming a mass of 1.05 M8 for ɩ Dra, the mass function implies a minimum companion mass m2 sin i of 8.9 MJ, making it a planet candidate. The corresponding semimajor axis is 1.3 AU. The nondetection of the orbital motion by Hipparcos …
Size And Structure Of The Narrow-Line Region Of Quasars, Nicola Bennert, Heino Falcke, Hartmut Schulz, Andrew S. Wilson, Beverley J. Wills
Size And Structure Of The Narrow-Line Region Of Quasars, Nicola Bennert, Heino Falcke, Hartmut Schulz, Andrew S. Wilson, Beverley J. Wills
Physics
We have observed the narrow-line regions (NLRs) of the seven brightest radio-quiet Palomar-Green (or Bright Quasar Survey) quasars (z < 0.5) with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). Linear-ramp filters were used to image the [O III] λ5007 line emission with 00455-01 pixel resolution. We find that the NLRs are very compact with typical extents of 2''-4''. Two quasars show compact filamentary structures similar to Seyfert NLRs. They may be related to radio outflows. Most interestingly, when including a sample of Seyfert galaxies observed with HST, we tentatively find that the size of the NLR is proportional to the square root …
Asymmetries Between Strange And Antistrange Particle Production In Pion–Proton Interactions, Thomas D. Gutierrez, R. Vogt
Asymmetries Between Strange And Antistrange Particle Production In Pion–Proton Interactions, Thomas D. Gutierrez, R. Vogt
Physics
Recent measurements of the asymmetries between Feynman x distributions of strange and antistrange hadrons in ∏−A interactions show a strong effect as a function of xnF. We calculate strange hadron production in the context of the intrinsic model and make predictions for particle/antiparticle asymmetries in these interactions.
Effect Of Implanted Metal Impurities On Superconducting Tungsten Films, Betty A. Young, T. Saab, Blas Cabrera, A. J. Miller, P. L. Brink, J. P. Castle
Effect Of Implanted Metal Impurities On Superconducting Tungsten Films, Betty A. Young, T. Saab, Blas Cabrera, A. J. Miller, P. L. Brink, J. P. Castle
Physics
The superconducting transition temperature of more than 30 thin-film tungsten samples was measured using a dilution refrigerator. The samples were fabricated using a 99.999% pure tungsten target and a dc magnetron sputtering system. Individual films were then doped with metal impurity ions using an accurate ion implantation technique. The effect of the metal–ion doping on the superconducting transition temperature was measured for samples with superconducting transitions in the range of 40–150 mK. Magnetic dopant species including Ni, Co, and Fe resulted in suppressed values of the tungsten Tc. The suppression was linear with increasing dopant concentration, for concentrations …
Visualizing The Phonon Wave Function, Scott C. Johnson, Thomas D. Gutierrez
Visualizing The Phonon Wave Function, Scott C. Johnson, Thomas D. Gutierrez
Physics
A phonon often is described as ‘‘a quantum of lattice vibration,’’ but this description can be difficult to reconcile with the wave functions explored in a typical undergraduate quantum mechanics class. A phonon wave function is similar to the harmonic oscillator wave functions studied in introductory quantum mechanics, except that it is many-dimensional. We suggest a way to visualize the probability density for this very high-dimensional wave function. The resulting pictures are especially clear and intuitive for a coherent state, which is both a good approximation to a sound wave and a discrete analog to laser light. These pictures can …
Variable Stars In The Field Of Open Cluster Ngc 6819, R. A. Street, Keith Horne, T. A. Lister, A. Penny, Y. Tsapras, A. Quirrenbach, N. Safizadeh, J. Cooke, David Mitchell, A. Collier Cameron
Variable Stars In The Field Of Open Cluster Ngc 6819, R. A. Street, Keith Horne, T. A. Lister, A. Penny, Y. Tsapras, A. Quirrenbach, N. Safizadeh, J. Cooke, David Mitchell, A. Collier Cameron
Physics
We report on the discovery of 25 variable stars plus 13 suspected variables found in the field of the open cluster NGC 6819. The stars were identified from time-series photometric data obtained on the Isaac Newton Telescope, La Palma, during two observing runs covering the 19 nights between 1999 June 22–30 and 1999 July 22–31. The variables found include 12 eclipsing binaries with an additional three suspected, nine BY Draconis systems, plus four variables of other types, including one star believed to be a Cepheid. Three of the 15 eclipsing binaries are believed to be cluster members. Details of a …
A Testing Strategy For The Mass Production Of Cdms Ii Detectors, D. Driacoll, D. S. Akerib, D. Abrams, D. Bauer, P. L. Brink, B. Cabrera, J. P. Castle, C. Chang, M. B. Crisler, R. J. Gaitskell, J. Hellmig, S. Kamat, V. Mandic, P. Meunier, T. A. Perera, M. C. Perillo Isaac, W. Rau, T. Saab, B. Sadoulet, R. W. Schnee, D. N. Seitz, G. Wang, Betty A. Young
A Testing Strategy For The Mass Production Of Cdms Ii Detectors, D. Driacoll, D. S. Akerib, D. Abrams, D. Bauer, P. L. Brink, B. Cabrera, J. P. Castle, C. Chang, M. B. Crisler, R. J. Gaitskell, J. Hellmig, S. Kamat, V. Mandic, P. Meunier, T. A. Perera, M. C. Perillo Isaac, W. Rau, T. Saab, B. Sadoulet, R. W. Schnee, D. N. Seitz, G. Wang, Betty A. Young
Physics
The Cryogenic Dark Matter Search (CDMS) employs detectors which are capable of simultaneously measuring the ionization and phonon energies deposited by a particle collision. These detectors are 1-cm-thick, 7-cm-diameter crystals of either germanium or silicon with a thin film of aluminum and tungsten patterned on the surface. This presentation discusses the testing regimen that a typical CDMS detector undergoes before it gets approval for final installation at the CDMS II deep site in Soudan, MN which will come online in early 2002. Now that our technology is relatively stable, the main focus of our test facilities is to provide quality …
Computer Sound Card Assisted Measurements Of The Acoustic Doppler Effect For Accelerated And Unaccelerated Sound Sources, Thomas J. Bensky, S. E. Frey
Computer Sound Card Assisted Measurements Of The Acoustic Doppler Effect For Accelerated And Unaccelerated Sound Sources, Thomas J. Bensky, S. E. Frey
Physics
An approach to experimentally measuring the speed of a moving object by direct application of the Doppler effect for sound is discussed. The method presented here uses a Windows computer and sound card to record Doppler shifted sound from a moving source. This sound card approach allows for direct acquisition of Doppler shifted sound intensity as a function of time, affording much analytical and pedagogical freedom in undergraduate lab instruction. In addition, the acquisition of such data allows for the experimental study of not only constant velocity sound sources, but of accelerated sound sources as well.
The Cataclysmic Variable Cw 1045+525: A Secondary-Dominated Dwarf Nova?, C. Tappert, J. R. Thorstensen, W. H. Fenton, N. Bennert, L. Schmidtobreick, A. Bianchini
The Cataclysmic Variable Cw 1045+525: A Secondary-Dominated Dwarf Nova?, C. Tappert, J. R. Thorstensen, W. H. Fenton, N. Bennert, L. Schmidtobreick, A. Bianchini
Physics
We present spectroscopic and photometric observations of the cataclysmic variable CW 1045+525. Both the optical spectrum and the photometric lightcurve show a strong contribution of a K5V-M0V secondary. We derive an orbital period d by measuring the radial velocities of the absorption lines of the secondary. The period and spectral type of the secondary suggest a distance of 350-700 pc. There is evidence for additional sources of line- and continuum emission, but no direct evidence of an accretion disc. We discuss several scenarios for the nature of CW 1045+525 on the basis of our results, finding a dwarf nova classification …
Magnetite Morphology And Life On Mars, Peter R. Buseck, Rafal E. Dunin-Borkowski, Bertrand Devouard, Richard B. Frankel, Martha R. Mccartney, Paul A. Midgley, Mihály Pósfai, Mathew Weyland
Magnetite Morphology And Life On Mars, Peter R. Buseck, Rafal E. Dunin-Borkowski, Bertrand Devouard, Richard B. Frankel, Martha R. Mccartney, Paul A. Midgley, Mihály Pósfai, Mathew Weyland
Physics
Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars provide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size resemblance of the crystals from meteorite ALH84001 to crystals formed by certain terrestrial bacteria has been used in support of the biological origin of the extraterrestrial minerals. By using tomographic and holographic methods in a transmission electron microscope, we show that the three-dimensional shapes of such nanocrystals can be defined, that the detailed morphologies of individual crystals from three bacterial strains differ, and that none uniquely match those reported from …
Enhanced Double Ionization With Circularly Polarized Light, Glen D. Gillen, M. A. Walker, L. D. Van Woerkom
Enhanced Double Ionization With Circularly Polarized Light, Glen D. Gillen, M. A. Walker, L. D. Van Woerkom
Physics
Using 120-fs, 800-nm Ti:sapphire laser pulses, ionic yields of singly and doubly charged magnesium ions were measured as a function of intensity and laser field ellipticity. A clear “nonsequential” enhancement of the doubly charged ion is observed for circularly polarized light in addition to linearly polarized light. Over the entire intensity range the double-ionization yield is considerably higher for linear polarization than it is for circular polarization.
Magnetic Microstructure Of Bacterial Magnetite By Electron Holography, Martha R. Mccartney, Ulysses Lins, Marcos Farina, Peter R. Buseck, Richard B. Frankel
Magnetic Microstructure Of Bacterial Magnetite By Electron Holography, Martha R. Mccartney, Ulysses Lins, Marcos Farina, Peter R. Buseck, Richard B. Frankel
Physics
A brackish lagoon at Itaipu, Brazil, contains magnetotactic bacteria with unusually large magnetite magnetosomes (lengths 100–200 nm). The micromagnetic structures of the magnetosomes from two different coccoid organisms from the lagoon have been determined by electron holography. The results are consistent with single-magnetic-domain structure in the elongated magnetosomes from one organism and metastable, single-magnetic-domain structure in the larger, more equi-axed, magnetosomes from the other organism. The results are consistent with theoretical predictions of the transition dimension between stable and metastable single-domain structure in magnetite.
Crystal-Size Distributions And Possible Biogenic Origin Of Fe Sulfides, Mihály Pósfai, Krisztina Cziner, Emö Márton, Péter Márton, Peter R. Buseck, Richard B. Frankel, Dennis A. Bazylinski
Crystal-Size Distributions And Possible Biogenic Origin Of Fe Sulfides, Mihály Pósfai, Krisztina Cziner, Emö Márton, Péter Márton, Peter R. Buseck, Richard B. Frankel, Dennis A. Bazylinski
Physics
Sedimentary greigite (Fe3S4) can form either by ''biologically controlled'' or by ''biologically induced mineralization'' (BCM and BIM, respectively). In order to identify the origin of magnetic Fe sulfides, we studied and compared the sizes and morphologies of greigite crystals produced by a magnetotactic microorganism (previously described and referred to as the ''many-celled magnetotactic prokaryote'', MMP) and Fe sulfides from two specimens of Miocene sedimentary rocks (from Łaka, in the foredeep of the Western Carpathians and from Michalovce, in the Transcarpathian Depression). Greigite grains from the MMP and the Łaka rock show nearly Gaussian crystal-size distributions (CSDs), …
Off-Axis Electron Holography Of Magnetotactic Bacteria: Magnetic Microstructure Of Strains Mv-1 And Ms-1, R. E. Dunin-Borkowski, Martha R. Mccartney, Mihály Pósfai, Richard B. Frankel, Dennis A. Bazylinski, Peter R. Buseck
Off-Axis Electron Holography Of Magnetotactic Bacteria: Magnetic Microstructure Of Strains Mv-1 And Ms-1, R. E. Dunin-Borkowski, Martha R. Mccartney, Mihály Pósfai, Richard B. Frankel, Dennis A. Bazylinski, Peter R. Buseck
Physics
Off-axis electron holography in the transmission electron microscope is used to characterize the magnetic microstructure of magnetotactic bacteria. The practical details of the technique are illustrated through the examination of single cells of strains MV-1 and MS-1, which contain crystals of magnetite (Fe3O4) that are ~50nm in size and are arranged in chains. Electron holography allows the magnetic domain structures within the nanocrystals to be visualized directly at close to the nanometer scale. The crystals are shown to be single magnetic domains. The magnetization directions of small crystals that would be superparamagnetic if they were isolated …
“Soft” Anharmonic Vortex Glass In Ferromagnetic Superconductors, Leo Radzihovsky, A. M. Ettouhami, Karl Saunders, John Toner
“Soft” Anharmonic Vortex Glass In Ferromagnetic Superconductors, Leo Radzihovsky, A. M. Ettouhami, Karl Saunders, John Toner
Physics
Ferromagnetic order in superconductors can induce a spontaneous vortex (SV) state. For external field H = 0, rotational symmetry guarantees a vanishing tilt modulus of the SV solid, leading to drastically different behavior than that of a conventional, external-field-induced vortex solid. We show that quenched disorder and anharmoinc effects lead to elastic moduli that are wave-vector dependent out to arbitrarily long length scales, and non-Hookean elasticity. The latter implies that for weak external fields H, the magnetic induction scales universally like B(H)∼B(0)+cHα, with α≈0.72. For weak disorder, we predict the SV solid is a topologically ordered glass, in …
Instrument For The Measurement Of Hysteresis Loops Of Magnetotactic Bacteria And Other Systems Containing Submicron Magnetic Particles, Hendrik De Waard, James Hilsinger, Richard B. Frankel
Instrument For The Measurement Of Hysteresis Loops Of Magnetotactic Bacteria And Other Systems Containing Submicron Magnetic Particles, Hendrik De Waard, James Hilsinger, Richard B. Frankel
Physics
An electronic control system for the measurement of hysteresis curves of microscopically observed magnetic structures such as chains of magnetosomes in magnetotactic bacteria suspended or swimming in water is described. Using continuous magnetic fields generated by four coils for guidance or orientation of the bacteria or other magnetic structures, and pulsed magnetic fields in two additional coils for changing the degree of magnetization in small steps, hysteresis curves can be traversed. The circuits described can be constructed with readily available components. The guiding- and pulsed-field coils can be fashioned in any standard machine shop. The typical sensitivity of the system …
A Laboratory-Based Nonlinear Dynamics Course For Science And Engineering Students, Nilgun Sungar, John P. Sharpe, Matthew J. Moelter, Neil Fleishon, Kent Morrison, Jean Mcdill, Rod Schoonover
A Laboratory-Based Nonlinear Dynamics Course For Science And Engineering Students, Nilgun Sungar, John P. Sharpe, Matthew J. Moelter, Neil Fleishon, Kent Morrison, Jean Mcdill, Rod Schoonover
Physics
We describe the implementation of a new laboratory-based interdisciplinary undergraduate course on nonlinear dynamical systems. Geometrical methods and data visualization techniques are especially emphasized. A novel feature of the course is a required laboratory where the students analyze the behavior of a number of dynamical systems. Most of the laboratory experiments can be economically implemented using equipment available in many introductory physics microcomputer-based laboratories.
Crossover From Phase Fluctuation To Amplitude-Dominated Superconductivity: A Model System, Richard P. Barber Jr., L. Merchant, J. Ostrick, Robert C. Dynes
Crossover From Phase Fluctuation To Amplitude-Dominated Superconductivity: A Model System, Richard P. Barber Jr., L. Merchant, J. Ostrick, Robert C. Dynes
Physics
We have experimentally studied a model system that demonstrates the crossover from a superconductor that is dominated by phase fluctuations, to one in which the amplitude of the order parameter is the controlling influence on Tc. This model system is comprised of two-dimensional granular Pb with an overlayer of Ag. The system displays many aspects of the phase diagram of the concentration dependence of Tc in the high-Tc superconductors, and this crossover has been applied to explain the phase diagram in that case. We point out the similarities and differences between the model system presented in this paper and the …
Measuring G With A Joystick Pendulum, Thomas J. Bensky
Measuring G With A Joystick Pendulum, Thomas J. Bensky
Physics
A method for experimentally measuring g, the Earth's gravitational acceleration, is presented. This method uses a computer joystick and computer as the primary measuring device. If a computer is available, it costs almost nothing to implement, and can be adapted for use as a high school or undergraduate lab exercise, or as a lecture demonstration.
Orientation And Speed Of The Parsec-Scale Jet In Ngc4261 (3c270), B. Glenn Piner, Dayton L. Jones, Ann E. Wehrle
Orientation And Speed Of The Parsec-Scale Jet In Ngc4261 (3c270), B. Glenn Piner, Dayton L. Jones, Ann E. Wehrle
Physics
NGC 4261 (3C 270) is an elliptical galaxy containing a 300 pc–scale nuclear disk of gas and dust imaged by the Hubble Space Telescope (HST), around a central supermassive black hole. Previous VLBI observations of NGC 4261 revealed a gap in emission in the radio counterjet, presumably due to free-free absorption in the inner parsec of the accretion disk. Here we present three 8 GHz VLBA observations of NGC 4261 that allow us to monitor the location and depth of the gap and check for motions in the jet and counterjet. The separation between the brightest peak and …
In The Shadow Of The Accretion Disk: Higher Resolution Imaging Of The Central Parsec In Ngc 4261, B. Glenn Piner, Dayton L. Jones, Ann E. Wehrle, David L. Meier
In The Shadow Of The Accretion Disk: Higher Resolution Imaging Of The Central Parsec In Ngc 4261, B. Glenn Piner, Dayton L. Jones, Ann E. Wehrle, David L. Meier
Physics
The physical conditions in the inner parsec of accretion disks believed to orbit the central black holes in active galactic nuclei can be probed by imaging the absorption (by ionized gas in the disk) of background emission from a radio counterjet. We report high angular resolution VLBI observations of the nearby (~40 Mpc) radio galaxy NGC 4261 that confirm free-free absorption of radio emission from a counterjet by a geometrically thin, nearly edge-on disk at 1.6, 4.8, and 8.4 GHz. The angular width and depth of the absorption appears to increase with decreasing frequency, as expected. We derive an average …
Above‐Threshold Ionization As A Probe Of Multielectron Physics, L. D. Van Woerkom, M. J. Nando, M. A. Walker, G. D. Gillen, H. G. Muller
Above‐Threshold Ionization As A Probe Of Multielectron Physics, L. D. Van Woerkom, M. J. Nando, M. A. Walker, G. D. Gillen, H. G. Muller
Physics
The study of above-threshold ionization (ATI) is now over 20 years old and much has been learned about the interaction of a single atomic electron with intense laser fields. The development of stable, high repetition rate ultrashort pulse laser systems has allowed experiments to probe intricate details of the ionization process using photoelectron and photoion spectroscopies. To date the overwhelming majority of data show that intense laser fields interact with only a single electron at a time to produce the well known features in electron kinetic energy spectra. We will present an overview of state-of-the-art experiments in ATI and show …