Physical Sciences and Mathematics Commons^™

On The Strain-Rate Sensitivity Of Columnar Ice, M. E. Manley, E. M. Schulson

Dartmouth Scholarship

A power law relation between stress and strain rate of the form σ ∝ ε̇1/n was used to describe the response to strain rate of S1 ice loaded across the columns at -10°C. The rate exponent, n, decreased with increasing strain from about 4.6 at an observed peak on the load displacement curve to approximately 2.6 at a shortening of 2%. Analysis of these results and of the results of other authors on different forms of ice deformed at the same temperature suggests that the power law exponent, n, is proportional to Fc/Fg. The parameter Fc/Fg is the far-field basal …

A Detailed Comparison Of Hubble Space Telescopefaint Object Spectrograph Andiueultraviolet Spectra Of Selected Seyfert Nuclei, Anuradha Koratkar, Ian Evans, Sharon Pesto, Cynthia Taylor

Dartmouth Scholarship

Despite the contributions of the Hubble Space Telescope Faint Object Spectrograph (FOS) to the archive of UV observations of active galactic nuclei, the vast majority of UV reference data were obtained using the International Ultraviolet Explorer (IUE) satellite. These data remain important since they provide historical information about the intensities of the UV continua and emission lines that is needed to constrain models of the active nucleus. A detailed comparison of the FOS and IUE data is critical to understanding how the measurable quantities depend on the individual instrumental calibrations, and how any conclusions derived from modeling the …

A New Approach To Probing Large-Scale Power With Peculiar Velocities, Hume A. Feldman, Richard Watkins

Dartmouth Scholarship

We propose a new strategy for probing the power spectrum on large scales using galaxy peculiar velocities. We explore the properties of surveys that cover only two small fields in opposing directions on the sky. Surveys of this type have several advantages over those that attempt to cover the entire sky; in particular, by concentrating on galaxies in narrow cones, these surveys are able to achieve the density needed to measure several moments of the velocity field with only a modest number of objects, even for surveys designed to probe scales >∼100h⁻¹Mpc. We construct mock surveys with this …

The Century Survey: A Deeper Slice Of The Universe, Margaret J. Geller, Michael J. Kurtz, Gary Wegner, John R. Thorstensen

Dartmouth Scholarship

The "Century Survey" (CS hereafter) is a complete redshift survey of a 1° wide strip. It covers 0.03 steradians to a limiting m_R = 16.13. The survey is 98.4% complete and contains 1762 galaxies. Large-scale features in the survey are qualitatively similar to those in other surveys: there are large voids surrounded or nearly surrounded by thin dense regions which are sections of structures like (and including) the Great Wall. The survey crosses the classical Corona Borealis supercluster. The galaxy density enhancement associated with this system extends for <˜100h^-1 Mpc^-1 (the Hubble constant is H₀ = 100h …

Task Scheduling In Networks, Cynthia Phillips, Clifford Stein, Joel Wein

Dartmouth Scholarship

Scheduling a set of tasks on a set of machines so as to yield an efficient schedule is a basic problem in computer science and operations research. Most of the research on this problem incorporates the potentially unrealistic assumption that communication between the different machines is instantaneous. In this paper we remove this assumption and study the problem of network scheduling, where each job originates at some node of a network, and in order to be processed at another node must take the time to travel through the network to that node.

Our main contribution is to give approximation algorithms …

The I Band Tully-Fisher Relation For Cluster Galaxies: Data Presentation., Riccardo Giovanelli, Martha P. Haynes, Terry Herter, Nicole P. Vogt, Gary Wegner, John J. Salzer, Luiz N. Da Costa, Wolfram Freudling

Dartmouth Scholarship

Observational parameters which can be used for redshift-independent distance determination using the Tully-Fisher (TF) technique are given for 782 spiral galaxies in the fields of 24 clusters or groups. I band photometry for the full sample was either obtained by us or compiled from published literature. Rotational velocities are derived either from 21 cm spectra or optical emission line long--slit spectra, and converted to a homogeneous scale. In addition to presenting the data, a discussion of the various sources of error on TF parameters is introduced, and the criteria for the assignment of membership to each cluster are given.

Faint Sources In The Euve Survey: Identification Of White Dwarfs, Active Late‐Type Stars, And Galactic Nuclei, Elisha Polomski, Stephane Vennes, John R. Thorstensen, Mihalis Mathioudakis, Emilio E. Falco

Dartmouth Scholarship

We report the classification of 21 new extreme-ultraviolet sources from the recent catalog of Lampton et al. The optical spectra presented identify the objects as 14 active late-type stars (including two double active stars and a possible T Tauri star), three white dwarfs, and six active galactic nuclei (a Seyfert galaxy, the BL Lac object 1ES 1028+511 [=EUVE J1031+508], and four quasi-stellar objects). We have detected Ca II absorption lines in the BL Lac object and measured its redshift. Two of the white dwarfs are unusually massive (M > 1.1 M_☉). Our sample of late-type stars includes five …

Optically Identified Supernova Remnants In The Nearby Spiral Galaxies Ngc 5204, Ngc 5585, Ngc 6946, M81, And M101, David M. Matonick, Robert A. Fesen

Dartmouth Scholarship

We present the results of an optical search for supernova remnants (SNRs) in the spiral galaxies NGC 5204, NGC 5585, NGC 6946, M81, and M101. Using the criterion that emission nebulae with [S II]/Hα ≥ 0.45 are identified as SNRs, we found three SNRs in NGC 5204, five in NGC 5585, 27 in NGC 6946, 41 in M81, and 93 in M101. Including the 35 SNRs recently detected in NGC 2403 by Matonick et al., we have doubled the current number of galaxies that have been well searched for SNRs and increased the number of known extragalactic SNRs by about …

Fast Discrete Polynomial Transforms With Applications To Data Analysis For Distance Transitive Graphs, J. R. Driscoll, D. M. Healy, D. N. Rockmore

Dartmouth Scholarship

Let $\poly = \{P_0,\dots,P_{n-1}\}$ denote a set of polynomials with complex coefficients. Let $\pts = \{z_0,\dots,z_{n-1}\}\subset \cplx$ denote any set of {\it sample points}. For any $f = (f_0,\dots,f_{n-1}) \in \cplx^n$, the {\it discrete polynomial transform} of f (with respect to $\poly$ and $\pts$) is defined as the collection of sums, $\{\fhat(P_0),\dots,\fhat(P_{n-1})\}$, where $\fhat(P_j) = \langle f,P_j \rangle = \sum_{i=0}^{n-1} f_iP_j(z_i)w(i)$ for some associated weight function w. These sorts of transforms find important applications in areas such as medical imaging and signal processing.

In this paper, we present fast algorithms for computing discrete orthogonal polynomial transforms. For a system …

The Self-Organizing Desk, Daniela Rus, Peter De Santis

Dartmouth Scholarship

The self-organizing desk is a system that enhances a physical desk-top with electronic information. It can remember, organize, update, and manipulate the information contained in the documents on a desk. The system consists of a simple robot eye that can survey the desk, a module for smart extraction of information from the images taken by the robot, a module for representing this information in multiple views, and a module that allows a user to interact with this information.

Interpretation Of Ultraviolet Absorption Lines In Sn 1006, A. J. S. Hamilton, R. A. Fesen, C.-C. Wu, D. M. Crenshaw

Dartmouth Scholarship

We present a theoretical interpretation of the broad silicon and iron ultraviolet absorption features observed with the Hubble Space Telescope (HST) in the spectrum of the Schweizer-Middleditch star behind the remnant of SN 1006. These features are caused by supernova ejecta in SN 1006.

We propose that the redshifted Si II 1260 Å feature consists of both unshocked and shocked Si II. The sharp red edge of the line at 7070 km s^-1 indicates the position of the reverse shock, while its Gaussian blue edge reveals shocked Si with a mean velocity of 5050 km s^{-1 …}

Using Fundamental Plane Distances To Estimate The Total Binding Mass In Abell 2626, Joseph J. Mohr, Gary Wegner

Dartmouth Scholarship

We use fundamental plane (FP) distance estimates to the components of the double cluster A2626 (cz ~ 17,500 km/s) to constrain cluster kinematics and estimate total binding mass. We employ deep R band CCD photometry, multi-object spectroscopy, and software designed to account for seeing effects to measure the FP parameters R_e, sigma , and for 24 known early type and S0 cluster members. The FP coefficients from this sample (alpha =1.30+/-0.36 and beta =0.31+/-0.06) are consistent with others reported in the literature. We examine the Mg_b equivalent width distributions within both subclusters and find them to be indistinguishable. Lacking evidence …

Peculiar Velocities Of Clusters In Cold Dark Matter Models, Stefano Borgani, Luiz N. Da Costa, Wolfram Freudling, Riccardo Giovanelli, Martha P. Haynes, John Salzer, Gary Wegner

Dartmouth Scholarship

Recently, peculiar velocity measurements became available for a new sample of galaxy clusters, hereafter the SCI sample. From an accurately calibrated Tully-Fisher relation for spiral galaxies, we compute the rms peculiar velocity, V_rms, and compare it with the linear theory predictions of COBE-normalized low-density and open cold dark matter models (ΛCDM and OCDM, respectively). Confidence levels for model rejection are estimated using a Monte Carlo procedure in order to generate a large ensemble of artificial data sets for each model. Following Zaroubi et al., we express our results in terms of constraints on the (Ω₀, …

Far-Ultraviolet Absorption Lines In The Remnant Of Sn 1006, Chi-Chao Wu, D. Michael Crenshaw, Andrew J. S. Hamilton, Robert A. Fesen

Dartmouth Scholarship

We have obtained a far-ultraviolet spectrum (1150-1600 Å) of a hot subdwarf star behind the remnant of supernova 1006 with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope. The high-quality spectrum is used to test previous identifications of the strong absorption features discovered with the International Ultraviolet Explorer. These features have FWHM = 4000 (±300) km s^-1 and are not at the rest wavelengths of known interstellar lines, as opposed to the broader (~8000 km s^-1 FWHM) Fe II lines from the remnant centered at 0 km s^-1 in near-UV FOS spectra. We …

The Tully-Fisher Relation And H0, Riccardo Giovanelli, Martha P. Haynes, Luiz N. Da Costa, Wolfram Freudling, John Salzer, Gary Wegner

Dartmouth Scholarship

The use of the Tully-Fisher (TF) relation for the determination of H₀ relies on the availability of an adequate template TF relation and of reliable primary distances. Here we use a TF template relation with the best available kinematical zero point, obtained from a sample of 24 clusters of galaxies extending to cz ~ 9000 km s^-1, and the most recent set of Cepheid distances for galaxies fit for TF use. The combination of these two ingredients yields H₀ = 69 ± 5 km s^-1 Mpc^-1. The approach is significantly more accurate than …

The Peculiar Motions Of Early‐Type Galaxies In Two Distant Regions. Iv. The Photometric Fitting Procedure, R. P. Saglia, Edmund Bertschinger, G. Baggley, David Burstein, Matthew Colless, Roger L. Davies, Robert K. Mcmahan Jr., Gary Wegner

Dartmouth Scholarship

The EFAR project is a study of 736 candidate early-type galaxies in 84 clusters lying in two regions toward Hercules-Corona Borealis and Perseus-Cetus at distances cz ≈ 6000-15,000 km s^-1. In this paper we describe a new method of galaxy photometry adopted to derive the photometric parameters of the EFAR galaxies. The algorithm fits the circularized surface brightness profiles as the sum of two seeing-convolved components, an R^1/4 and an exponential law. This approach allows us to fit the large variety of luminosity profiles displayed by the EFAR galaxies homogeneously and to derive (for at least a …

A Mechanical Duffing Oscillator For The Undergraduate Laboratory, J. E. Berger, G. Nunes

Dartmouth Scholarship

The design and construction of a mechanical Duffing oscillator suitable for use in an undergraduate laboratory is described. The oscillator provides a straightforward introduction to nonlinear vibrations and chaotic behavior that is both pedagogically appealing and easily adapted to students at various levels of sophistication. Good agreement is observed between the motion of the oscillator and computer simulations, which provides students with an introduction to the power of mathematical modeling. Period-doubling routes to chaos can be observed both experimentally and numerically.

Pulsations And Accretion Geometry In Yy Draconis: A Study Based On Hubble Space Telescope Observations, Carole A. Haswell, Joseph Patterson, John R. Thorstensen, Coel Hellier

Dartmouth Scholarship

We present 1 Å resolution fast ultraviolet spectroscopy of YY Dra, coordinated U, B, V, R, and I photometry, and Hα spectroscopy. The UV continuum is strongly pulsed: we found 16% semiamplitude pulses with period 264.7(1) s; there was no evidence for power at twice this period. The UBV pulses are in phase with the UV continuum pulsation. A color temperature of 10⁵ K was found for the pulse spectrum, with a corresponding area 0.5% of the white dwarf surface. We refine the white dwarf spin period, obtaining P_spin = 529.31 ± 0.02 s. Optical pulses at …

Transportable Information Agents, Daniela Rus, Robert Gray, David Kotz

Dartmouth Scholarship

Transportable agents are autonomous programs. They can move through a heterogeneous network of computers under their own control, migrating from host to host. They can sense the state of the network, monitor software conditions, and interact with other agents or resources. The network-sensing tools allow our agents to adapt to the network configuration and to navigate under the control of reactive plans. In this paper we describe the design and implementation of the navigation system that gives our agents autonomy. We also discuss the intelligent and adaptive behavior of autonomous agents in distributed information-gathering tasks.

Disk-Directed I/O For Mimd Multiprocessors, David Kotz

Dartmouth Scholarship

Many scientific applications that run on today's multiprocessors, such as weather forecasting and seismic analysis, are bottlenecked by their file-I/O needs. Even if the multiprocessor is configured with sufficient I/O hardware, the file-system software often fails to provide the available bandwidth to the application. Although libraries and enhanced file-system interfaces can make a significant improvement, we believe that fundamental changes are needed in the file-server software. We propose a new technique, disk-directed I/O, to allow the disk servers to determine the flow of data for maximum performance. Our simulations show that tremendous performance gains are possible both for simple reads …

Across-Column Cracks And Axial Splits In S2 Saline Ice Under Compression, E. M. Schulson, S. Qi, J. S. Melton, E. T. Gratz

Dartmouth Scholarship

Experiments on plate-like specimens have established that across-column cracks from within S2 (columnar) salt-water ice when compressed uniaxially along a direction inclined to the long axis of the grains. Wing cracks initiate from the across-column cracks and lengthen into axial splits when the ice is rapidly deformed; correspondingly; the macroscopic behavior changes from ductile to brittle. The across-column cracking is attributed to grain-boundary sliding, and the splitting to the suppression of crack-tip creep.

Matching Numerical Simulations To Continuum Field Theories: A Lattice Renormalization Study, J Borrill, M. Gleiser

Dartmouth Scholarship

The study of nonlinear phenomena in systems with many degrees of freedom often relies on complex numerical simulations. In trying to model realistic situations, these systems may be coupled to an external environment which drives their dynamics. For nonlinear field theories coupled to thermal (or quantum) baths, discrete lattice formulations must be dealt with extreme care if the results of the simulations are to be interpreted in the continuum limit. Using techniques from renormalization theory, a self-consistent method is presented to match lattice results to continuum models. As an application, symmetry restoration in ϕ4 models is investigated.

The Rosat Hri X-Ray Survey Of The Cygnus Loop, N. A. Levenson, J R. Graham, B. Aschenbach, W. P. Blair, W. Brinkmann, J. U. Busser, R. Egger, R. A. Fesen, J. J. Hester, S. M. Kahn, R. I. Klein, C. F. Mckee, R. Petre, R. Pisarski, J. C. Raymond, S. L. Snowden

Dartmouth Scholarship

We describe and report progress on the joint U.S. and German campaign to map the X-ray emission from the entire Cygnus Loop supernova remnant with the ROSAT High Resolution Imager. The Cygnus Loop is the prototype for a supernova remnant that is dominated by interactions with the interstellar medium and supplies fundamental physical information on this basic mechanism for shaping the interstellar medium. The global view that these high-resolution observations provide emphasizes the inhomogeneity of the interstellar medium and the pivotal nature of cloud-blast wave interactions in determining the X-ray morphology of the supernova remnant. While investigating the details of …

Some Applications Of Generalized Ffts, Daniel N. Rockmore

Dartmouth Scholarship

Generalized FFTs are efficient algorithms for computing a Fourier transform of a function defined on finite group, or a bandlimited function defined on a compact group. The development of such algorithms has been accompanied and motivated by a growing number of both potential and realized applications. This paper will attempt to survey some of these applications. Appendices include some more detailed examples.