X-ray Variability and Period Determinations in the Eclipsing Polar DP Leo

An analysis of ROSAT observations for the eclipsing magnetic cataclysmic binary DP Leo provides constraints on the origin, size, temperature, variability and structure of the soft X-ray emission region on the surface of the white dwarf. These data, when combined with prior observations, show a progression of approximately 2 degrees per year in the impact position of the accretion stream onto the white dwarf. One explanation for the observed drift in stream position is that a magnetic activity cycle on the secondary produces orbital period oscillations. These oscillations result in an orbital period which cycles above and below the rotational period of the nearly synchronous white dwarf. The accretion stream and X-ray emission regions are modeled to fit the observational data. A distance to the system is also calculated. [An erroneous value for the cyclotron luminosity, included in an earlier paper version of the preprint, is corrected here.]Comment: uuencoded PostScript file (25 pages) + 8 figures available by anonymous ftp to ftp.astro.psu.edu (in the directory /pub/robinson), to appear in ApJ, PSU preprint 1994-1

Doctor of Philosophy

thesisA new approach has been developed to use, store, and display seismic information as a time-dependent variable in block models. The research illustrates a new technique to model seismic events and combine them into block models, providing the user with the ability to analyze these data as a function of time in a four-dimensional (4-D) model, with the possibility of combining different analysis criteria to display the data, create sections of the information in any direction needed, and cut the data at any elevation to see what has happened through the life and development of the mine. Seismic data, comprising points in three dimensions placed spatially by their location coordinates (x: east, y: north, and z: elevation), are interpolated into a block model to develop solids in three dimensions (3-D) at various energy or magnitude cutoffs. These data are then accumulated in a (4-D) array which can be used to display the evolution of seismicity over a period of time. The data in the blocks can be filtered using the associated location errors, and the number of seismic stations triggered by the seismic events. A model was developed with seismic data collected between the years 1992 and 2012 from a large underground mine, using panel caving techniques. The data comprised approximately 2.1 million seismic events. The seismicity was interpolated using inversedistance interpolations to a block model that consisted of 1,875,000 blocks of 20x20x20 m, with block model extents of 2.5, 3, and 2 km in the east, north, and elevation directions, respectively. The model was developed for the entire mine, using yearly and monthly resolutions for the accumulated parameters. The results from the accumulated energy model were used to analyze the premining seismic conditions of a project that started in 2010 and that it is located between two other projects, one to the north that started in the year 1990 and the other to the south that started in 1998. The seismic history of the mine can be displayed and analyzed using the developed technique, defining areas of progressive deterioration associated to the energy levels released by the seismic events

A search for X-ray pulsations from the galactic center

Data from the SAS-3 satellite were used in a search for X-ray pulsations from the direction of the galactic center. No periodic X-ray behavior was detected in the frequency interval 0.6 Hz to 0.0006 Hz and energy range 2.5 - 35 keV. For periods less than 60 sec, the upper limit to the amplitude of any pulsation in the 2.5 - 10 keV band is approximately .0017 cts/sq cm/s. This corresponds to a pulsed fraction of approximately 1.3 percent of the total GCX flux. Somewhat higher limits apply for longer periods and for energies greater than 10 keV

Plant Growth Research for Food Production: Development and Testing of Expandable Tuber Growth Module

Controlled and reliable growth of a variety of vegetable crops is an important capability for manned deep space exploration systems for providing nutritional supplementation and psychological benefits to crew members. Because current systems have been limited to leafy vegetables that require minimal root space, a major goal for these systems is to increase their ability to grow new types of crops, including tuber plants and root vegetables that require a large root space. An expandable root zone module and housing was developed to integrate this capability into the Vegetable Production System (Veggie). The expandable module uses a waterproof, gas-permeable bag with a structure that allows for root space to increase vertically throughout the growth cycle to accommodate for expanding tuber growth, while minimizing the required media mass. Daikon radishes were chosen as an ideal tuber crop for their subterraneous tuber size and rapid growth cycle, and investigations were done to study expanding superabsorbent hydrogels as a potential growth media. These studies showed improved water retention, but restricted oxygen availability to roots with pure gel media. It was determined that these hydrogels could be integrated in lower proportions into standard soil to achieve media expansion and water retention desired. Using the constructed module prototype and ideal gel and soil media mixture, daikon radishes are being grown in the system to test the capability and success of the system through a full growth cycle

XMM-Newton observes flaring in the polar UZ For during a low state

During an XMM-Newton observation, the eclipsing polar UZ For was found in a peculiar state with an extremely low X-ray luminosity and occasional X-ray and UV flaring. For most of the observation, UZ For was only barely detected in X-rays and about 800 times fainter than during a high state previously observed with ROSAT. A transient event, which lasted about 900 s, was detected simultaneously by the X-ray instruments and, in the UV, by the Optical Monitor. The transient was likely caused by the impact of 10^17-10^18 g of gas on the main accretion region of the white dwarf. The X-ray spectrum of the transient is consistent with 7 keV thermal bremsstrahlung from the shock-heated gas in the accretion column. A soft blackbody component due to reprocessing of X-rays in the white dwarf atmosphere is not seen. The likely origin of the UV emission during the transient is cyclotron radiation from the accretion column. We conclude from our analysis that the unusual flaring during the low state of UZ For was caused by intermittent increases of the mass transfer rate due to stellar activity on the secondary.Comment: To be published in MNRAS, 8 pages, 4 figure

Narrating a Global Crisis from Guayaquil in Real Time: Early Literary Responses to the COVID‐19 Outbreak in Latin America

This article identifies and provides initial insight into the early literary responses to the COVID-19 outbreak in Latin America. It focuses on the case of Guayaquil, the epicentre of the pandemic in Ecuador, to exam- ine how writers responded to the health emergency in real time by using online platforms. I argue that, while the virus was spreading, the death toll was rising, and the lockdown was at its most severe, a body of writing deeply engaged with the crisis was taking shape in digital outlets. Its study enables a uniquely contextual understanding of the global crisis from a Latin American perspective