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- Biologically controlled mineralization (2)
- Magnetotactic bacteria (2)
- 3C 270) – galaxies : jets – galaxies : nuclei – radio continuum : galaxies (1)
- 3C 270) – galaxies : jets – galaxies : nuclei – radio continuum (1)
- Accretion (1)
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- Accretion disks – galaxies : active – galaxies : individual (NGC 4261 (1)
- Biologically induced mineralization (1)
- CW 1045+525 (1)
- Cataclysmic variables (1)
- Crystal size distribution (1)
- Fundamental parameters (1)
- Galaxies : active ¬– galaxies : individual (NGC 4261 (1)
- Greigite (1)
- Magnetite nanocrystals (1)
- Off-axis electron holography (1)
- Stars (1)
- Superconductor (1)
Articles 1 - 15 of 15
Full-Text Articles in Physical Sciences and Mathematics
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 …
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.
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 …
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 …
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 …