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Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Analysis Of Doppler-Broadened X-Ray Emission Line Profiles From Hot Stars, David H. Cohen, Roban Hultman Kramer , '03, S. P. Owocki
Analysis Of Doppler-Broadened X-Ray Emission Line Profiles From Hot Stars, David H. Cohen, Roban Hultman Kramer , '03, S. P. Owocki
Physics & Astronomy Faculty Works
We show how X-ray emission arising within an accelerating, expanding medium that also contains a source of continuum absorption generates line profiles of a characteristic shape. A simple, spherical wind model based on this picture provides good fits to the Chandra HETGS spectrum of the prototypical O star, Zeta Pup. We discuss the model, the fitting procedure and the determination of confidence limits on the model parameters, and our initial results for this star. The derived fit parameters are consistent with a generic wind-shock scenario for Zeta Pup, but there are several surprising aspects of the results, including a lower-than-expected …
New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis, N. A. Miller, J. P. Cassinelli, W. L. Waldron, J. J. Macfarlane, David H. Cohen
New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis, N. A. Miller, J. P. Cassinelli, W. L. Waldron, J. J. Macfarlane, David H. Cohen
Physics & Astronomy Faculty Works
The Chandra spectrum of delta Ori A shows emission lines from hydrogen- and helium-like states of Si, Mg, Ne, and O, along with N VII Lyalpha and lines from ions in the range Fe XVII-Fe XXI In contrast to the broad lines seen in zeta Pup and zeta Ori (850 +/- 40 and 1000 +/- 240 km s(-1) half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 +/- 60 km s(-1) HWHM. This is much lower than the measured wind terminal velocity of 2000 km s(-1). The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate …
Experimental Observation Of Energetic Ions Accelerated By Three-Dimensional Magnetic Reconnection In A Laboratory Plasma, Michael R. Brown, C. D. Cothran, Matthew Joseph Landreman , '03, David J. Schlossberg , '01, W. H. Matthaeus
Experimental Observation Of Energetic Ions Accelerated By Three-Dimensional Magnetic Reconnection In A Laboratory Plasma, Michael R. Brown, C. D. Cothran, Matthew Joseph Landreman , '03, David J. Schlossberg , '01, W. H. Matthaeus
Physics & Astronomy Faculty Works
Magnetic reconnection is widely believed responsible for heating the solar corona as well as for generating X-rays and energetic particles in solar flares. On astrophysical scales, reconnection in the intergalactic plasma is a prime candidate for a local source (Mpc) of cosmic rays exceeding the Greisen-Zatsepin-Kuzmin cutoff (∼10(19) eV). In a laboratory astrophysics experiment, we have made the first observation of particles accelerated by magnetic reconnection events to energies significantly above both the thermal and the characteristic magnetohydrodynamic energies. These particles are correlated temporally and spatially with the formation of three-dimensional magnetic structures in the reconnection region.
Energetic Particles From Three-Dimensional Magnetic Reconnection Events In The Swarthmore Spheromak Experiment, Michael R. Brown, C. D. Cothran, Matthew J. Landreman , '03, David J. Schlossberg , '01
Energetic Particles From Three-Dimensional Magnetic Reconnection Events In The Swarthmore Spheromak Experiment, Michael R. Brown, C. D. Cothran, Matthew J. Landreman , '03, David J. Schlossberg , '01
Physics & Astronomy Faculty Works
Measurements are presented from the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] showing a population of superthermal, super-Alfvénic ions with Ē≅90 eV and Emax⩾200 eV accelerated by reconnection activity in three-dimensional magnetic structures. These energetic ions are temporally and spatially correlated with three-dimensional magnetic reconnection events (measured with a 3D probe array) and are accelerated along the X-line normal to the local 2D plane of reconnection. In a typical SSX discharge, the peak reconnection electromotive force ℰ=vBL⩽(105 m/s)(0.05 T)(0.1 m)=500 V consistent with our observations. In addition, test particle simulations using magnetohydrodynamic (MHD) data from …
Radiation Science Using Z-Pinch X-Rays, J. E. Bailey, G. A. Chandler, David H. Cohen, M. E. Cuneo, M. E. Foord, R. F. Heeter, D. Jobe, P. W. Lake, J. J. Macfarlane, T. J. Nash, D. S. Nielson, R. Smelser, J. Torres
Radiation Science Using Z-Pinch X-Rays, J. E. Bailey, G. A. Chandler, David H. Cohen, M. E. Cuneo, M. E. Foord, R. F. Heeter, D. Jobe, P. W. Lake, J. J. Macfarlane, T. J. Nash, D. S. Nielson, R. Smelser, J. Torres
Physics & Astronomy Faculty Works
Present-day Z-pinch experiments generate 200 TW peak power, 5–10 ns duration x-ray bursts that provide new possibilities to advance radiation science. The experiments support both the underlying atomic and plasma physics, as well as inertial confinement fusion and astrophysics applications. A typical configuration consists of a sample located 1–10 cm away from the pinch, where it is heated to 10–100 eV temperatures by the pinch radiation. The spectrally-resolved sample-plasma absorption is measured by aiming x-ray spectrographs through the sample at the pinch. The pinch plasma thus both heats the sample and serves as a backlighter. Opacitymeasurements with this source are …
Effective Index Of Refraction, Optical Rotation, And Circular Dichroism In Isotropic Chiral Liquid Crystals, D. Lacoste, Peter J. Collings, T. C. Lubensky
Effective Index Of Refraction, Optical Rotation, And Circular Dichroism In Isotropic Chiral Liquid Crystals, D. Lacoste, Peter J. Collings, T. C. Lubensky
Physics & Astronomy Faculty Works
This paper concerns optical properties of the isotropic phase above the isotropic-cholesteric transition and of the blue phase BP III. We introduce an effective index, which describes spatial dispersion effects such as optical rotation, circular dichroism, and the modification of the average index due to the fluctuations. We derive the wavelength dependence of these spatial dispersion effects quite generally without relying on an expansion in powers of the chirality and without assuming that the pitch of the cholesteric P is much shorter than the wavelength of the light lambda, an approximation that has been made in previous studies of this …
Renewal Systems, Sharp-Eyed Snakes, And Shifts Of Finite Type, Aimee S. A. Johnson, K. M. Madden
Renewal Systems, Sharp-Eyed Snakes, And Shifts Of Finite Type, Aimee S. A. Johnson, K. M. Madden
Mathematics & Statistics Faculty Works
Johnson and Madden look at collections of bi-infinite strings of symbols that occur in several different areas of mathematics and ask whether these collections are the same in some sense. A dynamical systems property called entropy can be used to show that the shifts of finite type are not all conjugate to uniquely decipherable renewal systems.
C-Cl Bond Fission, Hcl Elimination, And Secondary Radical Decomposition In The 193 Nm Photodissociation Of Allyl Chloride, M. L. Morton, L. J. Butler, Thomas Alex Stephenson, F. Qi
C-Cl Bond Fission, Hcl Elimination, And Secondary Radical Decomposition In The 193 Nm Photodissociation Of Allyl Chloride, M. L. Morton, L. J. Butler, Thomas Alex Stephenson, F. Qi
Chemistry & Biochemistry Faculty Works
The primary photodissociation dynamics of allyl chloride upon excitation at 193 nm is investigated in a crossed laser-molecular beam scattering apparatus. Tunable vacuum ultraviolet (VUV) photoionization of the products provides a unique ability to learn about the secondary reaction products of the nascent photoproducts formed. The data show evidence for four significant primary reaction channels: a previously unidentified low kinetic energy C-Cl bond fission channel producing unstable allyl radicals, an excited state C-Cl bond fission channel producing Cl atoms with high translational energy, an HCl elimination pathway releasing significant energy to product translation to HCl and its momentum-matched mass 40 …
Collision-Induced Electronic Energy Transfer From V=0 Of The E(0+G) Ion-Pair State In I2: Collisions With He And Ar, Christopher J. Fecko , '98, Miriam Arak Freedman , '00, Thomas Alex Stephenson
Collision-Induced Electronic Energy Transfer From V=0 Of The E(0+G) Ion-Pair State In I2: Collisions With He And Ar, Christopher J. Fecko , '98, Miriam Arak Freedman , '00, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
The electronic energy transfer pathways that occur following collisions between I-2 in the E ion-pair electronic state (v = 0, J = 55) and He and Ar atoms have been determined. The nearby D, D', and beta ion-pair states are populated, but with relative branching ratios that vary with the rare gas collision partner. In He/I-2 collisions, the D state is preferentially populated, while Ar/I-2 collisions preferentially populate the beta electronic state. Bimolecular rate constants and effective hard sphere collision cross sections have been determined for each channel; the cross sections range from 7.0 +/- 1.0 Angstrom(2) for populating the …
A Specht Module Analog For The Rook Monoid, Cheryl Grood
A Specht Module Analog For The Rook Monoid, Cheryl Grood
Mathematics & Statistics Faculty Works
The wealth of beautiful combinatorics that arise in the representation theory of the symmetric group is well-known. In this paper, we analyze the representations of a related algebraic structure called the rook monoid from a combinatorial angle. In particular, we give a combinatorial construction of the irreducible representations of the rook monoid. Since the rook monoid contains the symmetric group, it is perhaps not surprising that the construction outlined in this paper is very similar to the classic combinatorial construction of the irreducible Sn-representations: namely, the Specht modules.
Hat Derivatives, Stephen B. Maurer , '67
Hat Derivatives, Stephen B. Maurer , '67
Mathematics & Statistics Faculty Works
No abstract provided.
Mass-Loss And Magnetospheres: X-Rays From Hot Stars And Young Stellar Objects, M. Gagné, David H. Cohen, S. P. Owocki, A. Ud-Doula
Mass-Loss And Magnetospheres: X-Rays From Hot Stars And Young Stellar Objects, M. Gagné, David H. Cohen, S. P. Owocki, A. Ud-Doula
Physics & Astronomy Faculty Works
High-resolution X-ray spectra of high-mass stars and low-mass T-Tauri stars obtained during the first year of the Chandra mission are providing important clues about the mechanisms which produce X-rays on very young stars. For zeta Puppis (O4 If) and zeta Ori (O9.5 I), the broad, blue-shifted line profiles, line ratios, and derived temperature distribution suggest that the X-rays are produced throughout the wind via instability-driven wind shocks. For some less luminous OB stars, like theta^1 Ori C (O7 V) and tau Sco (B0 V), the line profiles are symmetric and narrower. The presence of time-variable emission and very high-temperature lines …
Liquid Crystals: Nature's Delicate Phase Of Matter, Peter J. Collings
Liquid Crystals: Nature's Delicate Phase Of Matter, Peter J. Collings
Physics & Astronomy Faculty Works
No abstract provided.