Graptemys barbouri

Number of Pages: 2Integrative BiologyGeological Science

In-flight damping measurement

A new testing technique is described which can be applied in determining the damping coefficient of the critical vibration modes of an airplane in flight. The damping coefficient can be determined in several different ways from the same data using different features of a modified response curve which implies the possibility of checking one value against the other. The method introduces the effect of sweep rate in the driving system. This effect on the frequency response curve of the critical vibration mode and its various characteristics are used in the determination of damping coefficient. A theoretical examination is made of these characteristics for single degree of freedom systems

Modeling the gravitational potential of a cosmological dark matter halo with stellar streams

Stellar streams result from the tidal disruption of satellites and star clusters as they orbit a host galaxy, and can be very sensitive probes of the gravitational potential of the host system. We select and study narrow stellar streams formed in a Milky-Way-like dark matter halo of the Aquarius suite of cosmological simulations, to determine if these streams can be used to constrain the present day characteristic parameters of the halo's gravitational potential. We find that orbits integrated in static spherical and triaxial NFW potentials both reproduce the locations and kinematics of the various streams reasonably well. To quantify this further, we determine the best-fit potential parameters by maximizing the amount of clustering of the stream stars in the space of their actions. We show that using our set of Aquarius streams, we recover a mass profile that is consistent with the spherically-averaged dark matter profile of the host halo, although we ignored both triaxiality and time evolution in the fit. This gives us confidence that such methods can be applied to the many streams that will be discovered by the Gaia mission to determine the gravitational potential of our Galaxy.Comment: ApJ sub

Using Optically Stimulated Luminescence to Unravel Sedimentary Processes of the Usumacinta and Grijalva Rivers (SE Mexico)

This report provides an optically stimulated luminescence (OSL) chronology for sediment collected through terrace deposits of the Usumacinta and Grijalva rivers in SE Mexico. The Grijalva and Usumacinta rivers are susceptible to flooding during the hurricane season (between May and November), affecting the population of the state of Tabasco, and leaving many households at a flood risk. The present study was initiated to obtain an understanding of the sediment processes, rates and frequency of flood events in the past. The report summaries the initial luminescence profiling, using a SUERC PPSL system, and laboratory analysis, used to characterise the stratigraphy and interpret sedimentary processes in each profile, together with the quantitative quartz SAR dating used to define chronologies in each. Initial luminescence profiling revealed that the stratigraphy in each was complex, reflecting multiple cycles of deposition, with maxima, followed by a tail to lower intensities, possibly indicating deposition during extreme flood events, followed by a period in which the sediment was mixed and the luminescence signals reset. The laboratory profiling reproduced the apparent maxima/trends in the field profiling dataset. In the Grijalva section, the profiling samples encompass the full range of variations in the IRSL net signal intensities, re-affirming the complex stratigraphy. In the Usumacinta section, the profiling samples were positioned on the trend of a normal age-depth progression, which may indicate that the horizons sampled are well suited for quartz SAR dating. Given the nature of the sediment sampled, it is unsurprising that the equivalent dose distributions obtained for each of the dating samples showed considerable scatter, leading to some ambiguity in estimating a stored dose for age calculations. In each, a number of aliquots returned high equivalent dose values, implying residual luminescence signals (leading to higher apparent ages), and others, low values, implying re-setting of the luminescence signals in the modern environment. It is well recognised that fluvial sediment of this sort can enclose mixed-age populations. It has been argued elsewhere (Fuchs and Lang, 2001; Lepper et al., 2000; Olley et al., 1998; Olley et al., 1999) that the lowest population of dose(s) may best represent the burial dose of the youngest depositional component, and that an arbitrary value of say the lowest 5% be used in age calculations. However, if this method was instigated for the Mexican samples, it would include the low equivalent dose values thought to reflect contamination from the surface, by bioturbation or some other weathering process, leading to artificially young ages. Therefore, each sample was evaluated on an individual basis, where low equivalent doses were considered to represent contamination and rejected, along with high equivalent dose outliers and any aliquots which failed SAR acceptance criteria. The weighted mean and weighted standard deviation of the reduced set were used in age calculations. The dating results reported here provide a first chronology to interpret the changing fluvial dynamics of the Usumacinta and Grijalva rivers, and a means to quantify flood events through the historical period. The chronology established for the Grijalva section spans from the 6th century AD to the 12th century AD; and the chronology for the Usumacinta section from the 17th century AD to the 19th century AD

Operator related attenuation effects in radiometric surveys

Radiometric surveys using airborne, vehicular mounted or backpack detector systems are increasingly used to identify and evaluate complex distributions of radioactivity in the environment. The signals detected depend on the energy and spatial distribution of radioactive sources, the material properties of the environment and the specific properties of the detector systems employed. Materials in close vicinity to the detector such as housings, and intermediate materials may have a critical impact on detection efficiency, and must therefore be taken into account in calibration. This study evaluates the effect of shielding by the body of the operator in backpack surveys. Controlled experiments using point sources and absorbers, chosen to represent the form and composition of human tissue, were conducted, and coupled to an analytical radiation transport model to estimate attenuation factors for mapping of 137Cs. In this way generic factors to correct for this effect using portable spectrometers have been determined. The results compare well with observations at sampled calibration sites in Fukushima and the Solway area in Scotland. Reductions of the 137Cs full-energy peak intensity between 20% and 30% may be expected depending on operator stature and the offset position of backpack systems. Similar effects may be present for other radiometric systems carried by a human operator

Action-space clustering of tidal streams to infer the Galactic potential

We present a new method for constraining the Milky Way halo gravitational potential by simultaneously fitting multiple tidal streams. This method requires full three-dimensional positions and velocities for all stars to be fit, but does not require identification of any specific stream or determination of stream membership for any star. We exploit the principle that the action distribution of stream stars is most clustered when the potential used to calculate the actions is closest to the true potential. Clustering is quantified with the Kullback-Leibler Divergence (KLD), which also provides conditional uncertainties for our parameter estimates. We show, for toy Gaia-like data in a spherical isochrone potential, that maximizing the KLD of the action distribution relative to a smoother distribution recovers the true values of the potential parameters. The precision depends on the observational errors and the number of streams in the sample; using KIII giants as tracers, we measure the enclosed mass at the average radius of the sample stars accurate to 3% and precise to 20-40%. Recovery of the scale radius is precise to 25%, and is biased 50% high by the small galactocentric distance range of stars in our mock sample (1-25 kpc, or about three scale radii, with mean 6.5 kpc). About 15 streams, with at least 100 stars per stream, are needed to obtain upper and lower bounds on the enclosed mass and scale radius when observational errors are taken into account; 20-25 streams are required to stabilize the size of the confidence interval. If radial velocities are provided for stars out to 100 kpc (10 scale radii), all parameters can be determined with 10% accuracy and 20% precision (1.3% accuracy in the case of the enclosed mass), underlining the need for ground-based spectroscopic follow-up to complete the radial velocity catalog for faint halo stars observed by Gaia.Comment: Accepted versio

Luminescence Dating of Beach Dunes and Fluvial Sediments, Nayarit, Mexico

The Pacific coast of the state of Nayarit, Mexico, is dominated by extensive sand dune systems and lagoons. 16 samples from three transects through dunes near the town of Santa Cruz were collected to establish ages of the beach dune ridges and establish a robust chronology, to assist in understanding the depositional rates associated with different phases of the evolution of the strand plain. In addition, three samples were collected from a fluvial terrace on the San Pedro River which enters the Pacific near the southernmost of the dune transects. Quartz grains were extracted from the samples, and analysed using an Optically Stimulated Luminescence (OSL) method to determine stored dose and ages. The samples collected nearest the current coast have produced dates of 1500-1900AD, with samples further from the coast being progressively older, spanning a period of over 2000 years with oldest measured date of 400BC. The dates for the upper samples from the San Pedro River is consistent with the ages of the dunes nearest the coast, with the lower sample date closer to the dates of the older dunes further from the coast, indicating that this fluvial deposit was laid down over the same time period as the dune formation

Training to avoid distractions

Introduction: Auditory training has been extensively studied and applied to training software that is currently available for children with attention, hearing, or speech/language difficulties. The extent to which training generalizes, or transfers to an untrained task, is of great theoretical value. To our knowledge, there has not been a study that examines transference to a non-sensory masking task. Methods: 16 adults without ADHD were trained in a contralateral masking task over the course of two days, with 900 trials per day. False alarm rates, thresholds, and reaction times were measured. Pre- and post-tests of contralateral and informational masking were conducted to evaluate improvement on the untrained task following training. Results: Training generalized to the untrained task of informational masking. The results showed that informational and contralateral thresholds significantly improved following training. Discussion: This paper demonstrates transference of learning across two non-sensory masking tasks. This is the beginning of determining the extent of generalization and limiting distractibility in non-sensory masking, and how that may influence the development of auditory training software

The Role of Betrayal in Selected Drama of Tennessee Williams

Much of the critical analysis of Tennessee Williams\u27 drama concerns itself with the inherent conflict between ideals and reality in the universe as perceived by Williams. Such analysis, however, has not considered this conflict as a source of betrayal, or betrayal as a dominant theme in Williams\u27 drama. In at least four of his plays it becomes evident how each of the individual characters in Williams\u27 drama endures the conflict of reality and ideals, and the extent to which their respective approaches to the resolution of this struggle result in betrayal. Four plays--all regarded as among his most successful and most important, and spanning much of his career--were selected for consideration. The plays are The Glass Menagerie, A Streetcar Named Desire, Cat on a Hot Tin Roof, and The Night of the Iguana. In all four plays betrayal has been a primary ingredient of the action. There is also a similarity in the manner in which the betrayals are structured in each play. In each instance at least one betrayal has occurred prior to the action of the drama. The betrayals that occur during the action of the play stem from this initial conflict. In two instances, A Streetcar Named Desire and Cat on a Hot Tin Roof, Williams uses the birth of a child at the end of the play to suggest a setting for future betrayals. Three types of betrayals occur in these plays: self-betrayal, betrayal of ideals, and betrayal of others. Williams indicates through the characters\u27 reactions to the betrayals what they value and what his own views on betrayal are. His view is that betrayal is an inevitable occurrence in life as a result of the conflict between reality and ideals. He therefore is not inclined to pass judgement on the morality of betrayals, but he is offended by the cruelty with which the betrayal of others is often levied. He views self-betrayal resulting from an attempt to retain belief in ideals as tragic in the earlier plays (The Glass Menagerie and A Streetcar Named Desire). In Cat on a Hot Tin Roof there is some progression toward the tentative ability of the protagonist to resolve the conflict and thus avoid ultimate destruction by self-betrayal. In The Night of the Iguana Williams makes a definite positive statement as to the individual\u27s ability to resolve the conflict of ideals and reality and thereby avoid destruction by self-betrayal. If The Night of the Iguana represents Williams\u27 most recent position, then he no longer finds it necessary for his characters to betray others in order to insure their own survival, or to dedicate themselves to ideals which ignore reality and result in self-betrayal. It has become possible for the individual to seek and hope for a reconciliation of ideals and reality

Oats Production in South Dakota

This publication explains oats in rotation, soil fertility, seedbed preparation, time, method, and rate of seeding, as well as seed treatment, weed control, harvesting and storing, and variety selection and recommendations