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Articles 4711 - 4740 of 8860

Full-Text Articles in Astrophysics and Astronomy

Planetary Candidates Observed By Kepler Iv: Planet Sample From Q1-Q8 (22 Months), Christopher J. Burke, Darin Ragozzine Feb 2014

Planetary Candidates Observed By Kepler Iv: Planet Sample From Q1-Q8 (22 Months), Christopher J. Burke, Darin Ragozzine

Aerospace, Physics, and Space Science Faculty Publications

We provide updates to the Kepler planet candidate sample based upon nearly two years of high-precision photometry (i.e., Q1-Q8). From an initial list of nearly 13,400 threshold crossing events, 480 new host stars are identified from their flux time series as consistent with hosting transiting planets. Potential transit signals are subjected to further analysis using the pixel-level data, which allows background eclipsing binaries to be identified through small image position shifts during transit. We also re-evaluate Kepler Objects of Interest (KOIs) 1-1609, which were identified early in the mission, using substantially more data to test for background false positives and …

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Dilute Magnetism And Spin-Orbital Percolation Effects In Sr2Ir1−XRhXO4, J. P. Clancy, A. Lupascu, H. Gretarsson, Z. Islam, Y. F. Hu, D. Casa, C. S. Nelson, S. C. Lamarra, Gang Cao, Young-June Kim Feb 2014

Dilute Magnetism And Spin-Orbital Percolation Effects In Sr2Ir1−XRhXO4, J. P. Clancy, A. Lupascu, H. Gretarsson, Z. Islam, Y. F. Hu, D. Casa, C. S. Nelson, S. C. Lamarra, Gang Cao, Young-June Kim

Physics and Astronomy Faculty Publications

We have used a combination of resonant magnetic x-ray scattering and x-ray absorption spectroscopy to investigate the properties of the doped spin-orbital Mott insulator Sr2Ir1−xRhxO4 (0.07 ≤ x ≤ 0.70). We show that Sr2Ir1−xRhxO4 represents a unique model system for the study of dilute magnetism in the presence of strong spin-orbit coupling, and provide evidence of a doping-induced change in magnetic structure and a suppression of magnetic order at xc ∼ 0.17. We demonstrate that Rh-doping introduces Rh3+/Ir5+ ions which …

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Novel Magnetism Of Ir5+(5D4) Ions In The Double Perovskite Sr2Yiro6, Gang Cao, Tongfei Qi, Li Li, Jsaminka Terzic, Shujuan Yuan, Lance E. De Long, Ganpathy Murthy, Ribhu K. Kaul Feb 2014

Novel Magnetism Of Ir5+(5D4) Ions In The Double Perovskite Sr2Yiro6, Gang Cao, Tongfei Qi, Li Li, Jsaminka Terzic, Shujuan Yuan, Lance E. De Long, Ganpathy Murthy, Ribhu K. Kaul

Physics and Astronomy Faculty Publications

We synthesize and study single crystals of a new double-perovskite Sr2YIrO6. Despite two strongly unfavorable conditions for magnetic order, namely, pentavalent Ir5+(5d4) ions which are anticipated to have Jeff=0 singlet ground states in the strong spin-orbit coupling (SOC) limit and geometric frustration in a face-centered cubic structure formed by the Ir5+ ions, we observe this iridate to undergo a novel magnetic transition at temperatures below 1.3 K. We provide compelling experimental and theoretical evidence that the origin of magnetism is in an unusual interplay between strong noncubic crystal …

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Evidence For A Weak Wind From The Young Sun, Brian E. Wood, Hans-Reinhard Müller, Seth Redfield, Eric Edelman Feb 2014

Evidence For A Weak Wind From The Young Sun, Brian E. Wood, Hans-Reinhard Müller, Seth Redfield, Eric Edelman

Dartmouth Scholarship

The early history of the solar wind has remained largely a mystery due to the difficulty of detecting winds around young stars that can serve as analogs for the young Sun. Here we report on the detection of a wind from the 500 Myr old solar analog π1 UMa (G1.5 V), using spectroscopic observations from the Hubble Space Telescope. We detect H I Lyα absorption from the interaction region between the stellar wind and interstellar medium, i.e., the stellar astrosphere. With the assistance of hydrodynamic models of the π1 UMa astrosphere, we infer a wind only half as strong as …

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Interaction Of Magnetic Reconnection And Kelvin-Helmholtz Modes For Large Magnetic Shear: 2. Reconnection Trigger, Xuanye Ma, Antonius Otto, Peter A. Delamere Feb 2014

Interaction Of Magnetic Reconnection And Kelvin-Helmholtz Modes For Large Magnetic Shear: 2. Reconnection Trigger, Xuanye Ma, Antonius Otto, Peter A. Delamere

Publications

A typical property of magnetopause reconnection is a significant perpendicular shear flow due to the fast streaming magnetosheath plasma. Therefore, the magnetopause represents a large magnetic and flow shear boundary during periods of southward interplanetary magnetic field, which can be unstable to Kelvin‐Helmholtz (KH) modes and to magnetic reconnection. A series of local three‐dimensional MHD and Hall MHD simulations is carried out to investigate the interaction of reconnection and nonlinear KH waves considering magnetic reconnection as the primary process. It is demonstrated that the onset reconnection causes a thinning of the shear flow layer, thereby generating small wavelength KH modes. …

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Searching For Pulsars Using Image Pattern Recognition, W. W. Zhu, Kevin Stovall, Stephanie Cohen, Louis Percy Dartez, Grady Lunsford, Jose Guadalupe Martinez, Alberto Mata, Fredrick A. Jenet Feb 2014

Searching For Pulsars Using Image Pattern Recognition, W. W. Zhu, Kevin Stovall, Stephanie Cohen, Louis Percy Dartez, Grady Lunsford, Jose Guadalupe Martinez, Alberto Mata, Fredrick A. Jenet

Physics & Astronomy Faculty Publications

In the modern era of big data, many fields of astronomy are generating huge volumes of data, the analysis of which can sometimes be the limiting factor in research. Fortunately, computer scientists have developed powerful data-mining techniques that can be applied to various fields. In this paper, we present a novel artificial intelligence (AI) program that identifies pulsars from recent surveys by using image pattern recognition with deep neural nets - the PICS (Pulsar Image-based Classification System) AI. The AI mimics human experts and distinguishes pulsars from noise and interference by looking for patterns from candidate plots. Different from other …

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Arrakis : Atlas Of Resonance Rings As Known In The S4g., S. Comeron, H. Salo, E. Laurikainen, J. H. Knapen, R. J. Buta, M. Herrera-Endoqui, J. Laine, Benne W. Holwerda, K. Sheth, M. W. Regan, J. L. Hinz, J. C. Munoz-Mateos, A. Gil De Paz, K. Menendez-Delmestre, M. Seibert, T. Mizusawa, T. Kim, S. Erroz-Ferrer, D. A. Gadotti, E. Athanassoula, A. Bosma, L. C. Ho Feb 2014

Arrakis : Atlas Of Resonance Rings As Known In The S4g., S. Comeron, H. Salo, E. Laurikainen, J. H. Knapen, R. J. Buta, M. Herrera-Endoqui, J. Laine, Benne W. Holwerda, K. Sheth, M. W. Regan, J. L. Hinz, J. C. Munoz-Mateos, A. Gil De Paz, K. Menendez-Delmestre, M. Seibert, T. Mizusawa, T. Kim, S. Erroz-Ferrer, D. A. Gadotti, E. Athanassoula, A. Bosma, L. C. Ho

Faculty and Staff Scholarship

Context. Resonance rings and pseudorings (here collectively called rings) are thought to be related to the gathering of material near dynamical resonances caused by non-axisymmetries in galaxy discs. This means that they are the result of secular evolution processes that redistribute material and angular momentum in discs. Studying them may give clues on the formation and growth of bars and other disc non-axisymmetries. Aims. Our aims are to produce a catalogue and an atlas of the rings detected in the Spitzer Survey of Stellar Structure in Galaxies (S4G) and to conduct a statistical study of the data in the catalogue. …

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Unveiling The Structure Of Barred Galaxies At 3.6 Μm With The Spitzer Survey Of Stellar Structure In Galaxies (S4g). I. Disk Breaks., Taehyun Kim, Dimitri A. Gadotti, Kartik Sheth, E. Athanassoula, Albert Bosma, Myung Gyoon Lee, Barry F. Madore, Bruce G. Elmegreen, Johan H. Knapen, Dennis Zaritsky, Luis C. Ho, Sebastien Comeron, Benne W. Holwerda, Joannah L. Hinz, Juan Carlos Munoz-Mateos, Mauricio Cisternas, Santiago Erroz-Ferrer, Ron Buta, Eija Laurikainen, Heikki Salo, Jarkko Laine, Karin Menendez-Delmestre, Michael W. Regan, Bonita De Swardt, Armando Gil De Paz, Mark Seibert, Trisha Mizusawa Feb 2014

Unveiling The Structure Of Barred Galaxies At 3.6 Μm With The Spitzer Survey Of Stellar Structure In Galaxies (S4g). I. Disk Breaks., Taehyun Kim, Dimitri A. Gadotti, Kartik Sheth, E. Athanassoula, Albert Bosma, Myung Gyoon Lee, Barry F. Madore, Bruce G. Elmegreen, Johan H. Knapen, Dennis Zaritsky, Luis C. Ho, Sebastien Comeron, Benne W. Holwerda, Joannah L. Hinz, Juan Carlos Munoz-Mateos, Mauricio Cisternas, Santiago Erroz-Ferrer, Ron Buta, Eija Laurikainen, Heikki Salo, Jarkko Laine, Karin Menendez-Delmestre, Michael W. Regan, Bonita De Swardt, Armando Gil De Paz, Mark Seibert, Trisha Mizusawa

Faculty and Staff Scholarship

We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies …

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Determining Optical Constants With An Euv Polarimeter, Fabian Walter, Dr. R. Steven Turley Jan 2014

Determining Optical Constants With An Euv Polarimeter, Fabian Walter, Dr. R. Steven Turley

Journal of Undergraduate Research

Characterizing mirrors is of great importance when designing optical devices. In order to control the reflectivity, these mirrors are made of multilayer structures. The index of refraction n, which allows for the calculation of the reflectivity, depends on the wavelength of the light. In the XUV (extreme ultraviolet) regime, n is not well known and experiments to determine it have to be done under vacuum due to the absorption of XUV light by air. This complicates the performing of experiments with light of that wavelength.

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Characteristics Of An Infrared, Slitless, Spectroscopic, Emission-Line Galaxy Survey, Jacob Peter Fugal, Dr. J. Ward Moody Jan 2014

Characteristics Of An Infrared, Slitless, Spectroscopic, Emission-Line Galaxy Survey, Jacob Peter Fugal, Dr. J. Ward Moody

Journal of Undergraduate Research

Cosmology has always attracted the minds of those who pursue the burning question of how the universe began. Since Edwin Hubble proved not only the existence of galaxies outside the Milky Way but also that the further away they are, the faster they are moving away, more and more research has given support to the “Big Bang” theory of the birth of the universe. This research includes the discovery of the cosmological microwave background radiation and the agreement of modeled and observed ratios of Hydrogen, Deuterium, Helium, and Lithium seen in primitive areas of galaxies.

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The Inner Dynamical Mass Across Galaxy Morphology: A Weak Scaling With Total Stellar Mass, Stacy S. Mcgaugh Jan 2014

The Inner Dynamical Mass Across Galaxy Morphology: A Weak Scaling With Total Stellar Mass, Stacy S. Mcgaugh

Faculty Scholarship

We compile a sample of dispersion-supported and rotation-supported galaxies for which the dynamical mass enclosed at 500 pc can be measured. We find that this dynamical quantity increases only slowly with stellar mass (Mtotal(500 pc) ? M0.16 stars ) over ?9 decades in baryonic mass and ?3 in length scale, with a sudden upturn at the highest masses (Mstars - 1010 M-). This upturn occurs for the earliest types (S0 and Sa) of disk galaxies, and is consistent with the extra mass within 500 pc being predominantly stellar. This sudden change may be indicative of different bulge formation mechanisms between …

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Deposition And Analysis Of Copper Indium Disulfide For Photovoltaic Applications, Frederick Wade Jan 2014

Deposition And Analysis Of Copper Indium Disulfide For Photovoltaic Applications, Frederick Wade

Macalester Journal of Physics and Astronomy

Thin Film semiconductors were created through the methods of electrochemistry to produce a copper, indium and sulfur metal alloy that could be placed on a stainless steel substrate. We observed other properties regarding the relative indium to copper relationships and both the macro and micro structure of the final product. X-­‐ray diffraction, SEM imaging, and atomic absorption spectroscopy data suggest a relatively intact metal alloy, but also an inaccurate ratio of indium to copper.

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Photometric And Spectroscopic Analysis Of Young, Nearby Open Cluster Collinder 70, Clara M. Thomann Jan 2014

Photometric And Spectroscopic Analysis Of Young, Nearby Open Cluster Collinder 70, Clara M. Thomann

Macalester Journal of Physics and Astronomy

We present the results of a wide-field (80’ x 80’) photometric and spectroscopic survey of the young open cluster Collinder 70, which is also known as the ORI OB 1b association, centered on the central star of Orion’s belt, ε Ori (Alnilam). Seventy Coll 70 spectroscopy targets were selected from BVRIc color magnitude diagrams for observation using the CTIO HYDRA multi-object spectrograph; we aimed to identify targets exhibiting H" in emission and a strong lithium 6708Å line in absorption. About a third of our targets (23/70 stars) are consistent with being youthful members of Coll 70. Intermediate resolution (R!20000) HYDRA …

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Monte Carlo Simulation For Silicon On Silane Hwcvd For Thin Film Solar Cells, Annaleigh Smith Jan 2014

Monte Carlo Simulation For Silicon On Silane Hwcvd For Thin Film Solar Cells, Annaleigh Smith

Macalester Journal of Physics and Astronomy

Thin film solar cells offer a viable alternative to crystal silicon solar cells. They are expected to be cheaper to fabricate because they use material more efficiently, and are deposited in a process which can create larger area solar cells [1]. However, a high deposition rate is necessary for economic viability. A Monte Carlo simulation can model the molecular interactions in hot wire chemical vapor deposition and track the position and velocity distribution of molecular species in the gas [2]. Determining the flux on the substrate can help us to increase deposition rate by adjusting control parameters accordingly [3]. As …

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Galaxy Merger Identification In The Goods-South Field, Erin O'Leary Jan 2014

Galaxy Merger Identification In The Goods-South Field, Erin O'Leary

Macalester Journal of Physics and Astronomy

We analyzed a catalog of 7,628 galaxies at 0 < z < 4 from CANDELS1 in the GOODS-South2 field in order to identify a sample of galaxy mergers and interactions. Galaxy mergers are believed to play a fundamental role in galaxy evolution. Developing methods to robustly and efficiently identify mergers becomes vital with our increasing ability to study mergers at higher redshifts and in larger samples. We explored merger identification based on visual morphology classification and preliminary attempts with automated quantitative methods. Using multiple detailed visual morphology classifications for each galaxy conducted by the CANDELS structure and morphology team, we created selection criteria to …

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Shield: Star Formation From Wiyn And Galex Imaging, Samilee J. Moody Jan 2014

Shield: Star Formation From Wiyn And Galex Imaging, Samilee J. Moody

Macalester Journal of Physics and Astronomy

Using images from the GALEX (Galaxy Evolution Explorer) GR6 pipeline (released 2010), as well as the WIYN 3.5m Observatory, we present a survey of the twelve SHIELD galaxies in the far-ultraviolet (FUV, 1500 Å) and near-ultraviolet (NUV, 2200 Å) filters. FUV data were available for eleven of the galaxies, AGC 749237 being the exception. Aperture photometry was performed on each image to determine the AB magnitude in the FUV and NUV filters.These values were then used to calculate flux, luminosity, and star formation rates (SFRs). Similarly, Hα images of each galaxy from WIYN (omitting AGC 749241) were analyzed to determine …

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Numerical Modeling Of The Finite Well With Implications For Observing Quantum Interference Between Coherent Electron Wave, Jacob M. Moen Jan 2014

Numerical Modeling Of The Finite Well With Implications For Observing Quantum Interference Between Coherent Electron Wave, Jacob M. Moen

Macalester Journal of Physics and Astronomy

We use numerical modeling in Fortran to investigate the claims of Wollenhaupt et al. (2006) and Hommelhoff et al. (2002) regarding ultra-­short electron pulses ionized via laser excitation of a tungsten nanotip. We assume that the nanotip acts as a finite one‐dimensional potential well with the depth equal to the work function of tungsten and the width of the order of the radius of curvature of the nanotip. The interactions of propagating Gaussian wave packets are modeled in order to give insight into the temporal and spatial evolution of the generated electron wave packets. Furthermore we hope to demonstrate the …

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Synthesis And Characterization Of Zinc-­‐Oxide/Polystyrene Nanocomposite Thin Films, Christopher Krapu Jan 2014

Synthesis And Characterization Of Zinc-­‐Oxide/Polystyrene Nanocomposite Thin Films, Christopher Krapu

Macalester Journal of Physics and Astronomy

Ultra-thin films containing zinc oxide and polystyrene were prepared by sol-gel mixing and spincoating onto silicon substrate. Photoluminescent measurements were recorded following irradiation at 325 nm. We observed passivation of shallow defect states around 3.1 eV bandgap via confinement. Time-resolved photoluminescence plots suggest a significant time dependence of emission intensity related to photodegradation of the polymer matrix.

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Light-By-Light Scattering Nonlogarithmic Corrections To Hyperfine Splitting In Muonium, Michael I. Eides, Valery A. Shelyuto Jan 2014

Light-By-Light Scattering Nonlogarithmic Corrections To Hyperfine Splitting In Muonium, Michael I. Eides, Valery A. Shelyuto

Physics and Astronomy Faculty Publications

We consider three-loop corrections to hyperfine splitting in muonium generated by the gauge invariant set of diagrams with a virtual light-by-light scattering block. These diagrams produce both recoil and nonrecoil contributions to hyperfine splitting. Recoil corrections are enhanced by large logarithms of the muon-electron mass ratio. Both nonrecoil and logarithmically enhanced radiative-recoil corrections were calculated some time ago. Here we calculate nonlogarithmic radiative-recoil corrections generated by the insertions of the light-by-light scattering block.

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Extensive Study Of Hd 25558, A Long-Period Double-Lined Binary With Two Spb Components, Á. Sódor, Peter De Cat, David J. Wright, Coralie Neiner, Maryline Briquet, Patricia Lampens, Robert J. Dukes, Gregory W. Henry, Michael H. Williamson, Emily Brunsden, Karen R. Pollard, Peter L. Cottrell, Florian Maisonneuve, Pam M. Kilmartin, Jaymie Matthews, Thomas Kallinger, Paul G. Beck, Eiji Kambe, Chris A. Engelbrecht, Robert J. Czanik, Stephenson Yang, Osamu Hashimoto, Satoshi Honda, Jian-Ning Fu, Barbara Castanheira, Holger Lehmann, Zsófia Bognár, Natalie Behara, Simone Scaringi, Hans Van Winckel, Jonathan Menu, Alex Lobel, P. Mathias, Sophie Saesen, Maja Vučković, The Mimes Collaboration Jan 2014

Extensive Study Of Hd 25558, A Long-Period Double-Lined Binary With Two Spb Components, Á. Sódor, Peter De Cat, David J. Wright, Coralie Neiner, Maryline Briquet, Patricia Lampens, Robert J. Dukes, Gregory W. Henry, Michael H. Williamson, Emily Brunsden, Karen R. Pollard, Peter L. Cottrell, Florian Maisonneuve, Pam M. Kilmartin, Jaymie Matthews, Thomas Kallinger, Paul G. Beck, Eiji Kambe, Chris A. Engelbrecht, Robert J. Czanik, Stephenson Yang, Osamu Hashimoto, Satoshi Honda, Jian-Ning Fu, Barbara Castanheira, Holger Lehmann, Zsófia Bognár, Natalie Behara, Simone Scaringi, Hans Van Winckel, Jonathan Menu, Alex Lobel, P. Mathias, Sophie Saesen, Maja Vučković, The Mimes Collaboration

Information Systems and Engineering Management Research Publications

We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The ≈2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves revealed that this object is a double-lined spectroscopic binary with an orbital period of about nine years. The observations do not allow the inference of an orbital solution. We determined the physical parameters of the components, and found that both lie within the SPB instability strip. Accordingly, both show line-profile variations due to stellar pulsations. 11 independent frequencies were identified in the data. All the frequencies were attributed to one …

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Variability In Quasars, Catherine Morris, Dr. Eric Hintz Jan 2014

Variability In Quasars, Catherine Morris, Dr. Eric Hintz

Journal of Undergraduate Research

This project looked for variability in quasars 3C273 and Mark 509. Between May 2003 and July 2003 several nights of data were taken on these quasars. The project was also to see if “good” data on quasars could be obtained using the BYU 16” telescope, since not much research has been done on this topic at BYU. Over the summer data were also taken on various other quasars whose brightness ranged between 12 and 14.

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Constructing The Remote Observatory For Variable Object Research, Jason A. Gilbert, Dr. J. Ward Moody Jan 2014

Constructing The Remote Observatory For Variable Object Research, Jason A. Gilbert, Dr. J. Ward Moody

Journal of Undergraduate Research

Scientists who attempt to unravel the mysteries of the universe have some physical limitations to deal with in their quest. For example, an observer must stay up all night to operate the telescopes that record the data. There are now automated telescopes that allow the scientist to enter a list of objects (stars, asteroids, planets, galaxies, etc.) into the telescope’s computer, and the telescope will move by itself to each one, taking and recording data throughout the course of the night. Some telescopes can even be operated remotely so the scientists can run them from their offices, or even their …

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Growth Kinetics Of Zno By Magnetron Sputtering For Solar Cell Application, Nadia Foo Kune Jan 2014

Growth Kinetics Of Zno By Magnetron Sputtering For Solar Cell Application, Nadia Foo Kune

Macalester Journal of Physics and Astronomy

The goal of this work is study the mechanism of ZnO thin film deposition by rf magnetron sputtering with an argon plasma. This research will help understand the growth kinetics of the ZnO layer in relation to the growth conditions for solar cell application. We study the rate of growth, the electrical properties, the optical transmission and the zinc to oxygen ratio of each sample as a function of growth temperature. We conclude that Zn evaporation competes with incorporation into the film by combining with an arriving O atom.

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Tip-Of-The-Red-Giant-Branch Detection: Estimating The Distance To Resolved Galaxies In Shield, Ian Cave Jan 2014

Tip-Of-The-Red-Giant-Branch Detection: Estimating The Distance To Resolved Galaxies In Shield, Ian Cave

Macalester Journal of Physics and Astronomy

The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) is an ongoing study of twelve galaxies with HI masses between 106 and 107 Solar masses, detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. One of the important characteristics of a galaxy is its distance, since knowing that value allows us to calibrate many other factors and learn more about the galaxy. This research was focused on creating a program to systematically solve for the distance to the galaxies in SHIELD. To perform this calculation, Tip-of-the-Red-Giant-Branch (TRGB) detection was chosen, which is a popular method for galaxies with …

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Electrical Conductivity Of Tellurium Nanowires On Pedot:Pss, Banteaymolu Alebachew Jan 2014

Electrical Conductivity Of Tellurium Nanowires On Pedot:Pss, Banteaymolu Alebachew

Macalester Journal of Physics and Astronomy

The purpose of this project is to understand the electrical conductivity and infrared absorption spectrum of a hybrid material between Tellurium nanowires and a carbon polymer called PEDOT:PSS. This hybrid material shows much higher conductivity than its components and this behavior gives a great promise for thermoelectric effect. The most intriguing property of this material is observed when taking absorption spectrum from far to near infrared. The hybrid material shows a much bigger absorption edge than Te NW. This project attempts to explain this shift using the confinement energy model and Fermi blocking (due to doping). The result from these …

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Sub-Sonic Open-Return Wind-Tunnel And Measurement Apparatus, Michael Adams Jan 2014

Sub-Sonic Open-Return Wind-Tunnel And Measurement Apparatus, Michael Adams

Macalester Journal of Physics and Astronomy

Wind tunnels are an effective tool for understanding relationships between predicted and actual behavior of air foils in laminar flow. In order to improve the ability of Macalester College staff and students to observe and experiment with the effects of laminar air flow on various objects and systems, it was necessary to construct and test a sub-sonic open return wind tunnel. The purpose of the tests was to discover whether or not the air flow through the test section of the tunnel was laminar around the object being tested and also to evaluate the quality of an apparatus constructed to …

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Energy Dependence Of Moments Of Net-Proton Multiplicity Distributions At Rhic, James K. Atkins, Renee H. Fatemi, Wolfgang Korsch, Suvarna Ramachandran, G. Webb, L. Adamczyk, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, C. D. Anson, A. Aparin, D. Arkhipkin, E. C. Aschenauer, G. S. Averichev, J. Balewski, A. Banerjee, Z. Barnovska, D. R. Beavis, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, H. Bichsel, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, W. Borowski Jan 2014

Energy Dependence Of Moments Of Net-Proton Multiplicity Distributions At Rhic, James K. Atkins, Renee H. Fatemi, Wolfgang Korsch, Suvarna Ramachandran, G. Webb, L. Adamczyk, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, C. D. Anson, A. Aparin, D. Arkhipkin, E. C. Aschenauer, G. S. Averichev, J. Balewski, A. Banerjee, Z. Barnovska, D. R. Beavis, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, H. Bichsel, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, W. Borowski

Physics and Astronomy Faculty Publications

We report the beam energy(√8NN = 7.7-200 GeV) and collision centrality dependence of the mean (M), standard deviation (σ), skewness (S), and kurtosis (κ) of the net-proton multiplicity distributions in Au+Au collisions. The measurements are carried out by the STAR experiment at midrapidity (|y|<0.5) and within the transverse momentum range 0.4<ρτ<0.8  GeV/c in the first phase of the Beam Energy Scan program at the Relativistic Heavy Ion Collider. These measurements are important for understanding the quantum chromodynamic phase diagram. The products of the moments, Sσ and κσ2, are sensitive to the correlation length of the hot and dense …

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Interpreting The Ionization Sequence In Agn Emission-Line Spectra, Chris T. Richardson, James T. Allen, Jack A. Baldwin, Paul C. Hewett, Gary J. Ferland Jan 2014

Interpreting The Ionization Sequence In Agn Emission-Line Spectra, Chris T. Richardson, James T. Allen, Jack A. Baldwin, Paul C. Hewett, Gary J. Ferland

Physics and Astronomy Faculty Publications

We investigate the physical cause of the great range in the ionization level seen in the spectra of narrow-lined active galactic nuclei (AGN). We used a recently developed technique called mean field independent component analysis to identify examples of individual Sloan Digital Sky Survey galaxies whose spectra are not dominated by emission due to star formation (SF), which we therefore designate as AGN. We assembled high signal-to-noise ratio (S/N) composite spectra of a sequence of these AGN defined by the ionization level of their narrow-line regions (NLR), and extending down to very low ionization cases. We then used a local …

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Black Hole Variability And The Star Formation-Active Galactic Nucleus Connection: Do All Star-Forming Galaxies Host An Active Galactic Nucleus?, Ryan C. Hickox, James R. Mullaney, David M. Alexander, Chien-Ting J. Chen, Francesca M. Civano, Andy D. Goulding, Kevin N. Hainline Jan 2014

Black Hole Variability And The Star Formation-Active Galactic Nucleus Connection: Do All Star-Forming Galaxies Host An Active Galactic Nucleus?, Ryan C. Hickox, James R. Mullaney, David M. Alexander, Chien-Ting J. Chen, Francesca M. Civano, Andy D. Goulding, Kevin N. Hainline

Dartmouth Scholarship

We investigate the effect of active galactic nucleus (AGN) variability on the observed connection between star formation and black hole accretion in extragalactic surveys. Recent studies have reported relatively weak correlations between observed AGN luminosities and the properties of AGN hosts, which has been interpreted to imply that there is no direct connection between AGN activity and star formation. However, AGNs may be expected to vary significantly on a wide range of timescales (from hours to Myr) that are far shorter than the typical timescale for star formation (100 Myr). This variability can have important consequences for observed correlations. We …

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Self-Heating Model Of Spherical Aluminum Nanoparticle Oxidation, Karen S. Martirosyan, Zamart Ramazanova, Maxim Zyskin Jan 2014

Self-Heating Model Of Spherical Aluminum Nanoparticle Oxidation, Karen S. Martirosyan, Zamart Ramazanova, Maxim Zyskin

Physics & Astronomy Faculty Publications

Aluminum-oxygen reaction is important in highly energetic and high pressure generating systems. Nanoenergetic thermites include mixtures of nanostructured Al and oxidizer particles. The main distinguishing features of these reactive systems are their significant enthalpy release and tunable rate of energy discharge, which gives rise to a wide range of combustion rates, energy release, and ignition sensitivity. In this paper, we consider rapid oxidation of a spherically symmetric aluminum particle. We use the Cabrera Mott oxidation model to describe the kinetics of oxide growth of an aluminum nanoparticle and to predict reaction temperature and oxidation time. We assume that aluminum particle …

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