Suppression of dominant topographic overprints in gravity data by adaptive filtering: southern Wyoming Province

This is the published version, also available here: http://dx.doi.org/10.1029/92JB01200.In areas of the world with a protracted tectonic history, the gravity field may be dominated by anomalies due to individual structural features developed during the latest tectonic event. These individual tectonic features often have a topographic expression. Adaptive filtering techniques can be used to suppress the gravity effects of such features. Iterative space domain techniques are particularly well suited to these types of problems. One such technique, the stochastic gradient algorithm, allows easy updating of filter coefficients at each spatial step through the data. This approach eliminates windowing and spectral estimation problems associated with cross-spectral admittance schemes. In this study, adaptive filtering of Bouguer gravity and topography in the southern Wyoming Province was successful in suppressing gravity signatures of Laramide structural features. The regional gravity trends due to isostatic effects were significantly absent from the residual anomaly map. A large, continuous, positive gravity anomaly stretching from the southern Wind River Range to the northern end of the Laramie Range was another outstanding feature observed in the residual anomaly. This positive anomaly is about the same magnitude, size and shape as anomalies due to greenstone belts observed in other Archean cratonal areas. Scattered occurrences of greenstone lithologies are known throughout the area of the anomaly, but a continuous feature is absent in outcrop. Due to the unusual structural history of the area, it is possible that such a continuous belt does exist, but was buried at shallow crustal levels by Laramide thrusting, or later collapse of a Laramide uplift due to a change in the regional stress field

Ethanol: A Better Preservation Technique For Daphnia

A 4% formalin-40% sucrose solution has been used by limnologists for three decades as the preferred freshwater zooplankton preservative because it kills and fixes cladocera (Branchiopoda) with relatively little distortion. Because of the increasing evidence of health hazards related to formalin, we sought an alternative, safer preservative that satisfies the need for low distortion. Our results suggest the ethanol preservative methods (70% and 95% treatments) are as good or better as using 4% sugar formalin to fix and store samples. Our results indicate the best method is to fix samples in 95% EtOH followed by storage in 70% EtOH. This technique gave us the least frequent distortion, the highest average number of eggs per female, and the fewest embryos lost from the brood chamber. None of the techniques appeared to have positive or negative effects on body length. Using hot water to fix animals before storage is not recommended

Sensory Exploitation And Indicator Models May Explain Red Pelvic Spines In The Brook Stickleback, Culaea Inconstans

Background: Sensory bias models explaining the evolution of sexually selected traits predict that trait preferences evolve as an artifact of a pre-existing preference for certain components of the environment such as specifically coloured prey. Indicator models, in contrast, predict that sexually selected traits indicate mate condition. We investigate the potential for sensory exploitation and condition indication models to explain the evolution of what appears to be a recently evolved sexually selected trait. Question: Did red pelvic spine coloration in male Turnbull National Wildlife Refuge (TNWR) brook stickleback (Culaea inconstans) evolve to exploit a pre-existing sensory bias for red prey, thus helping males draw females to the nest? Or, did it evolve as an intersexual signal indicating male condition to females? Methods: We recorded the frequency of red pelvic spine coloration in males versus females and in breeding versus non-breeding males. We measured the condition factor of males with and without red coloration on their pelvic spines. We presented fish with a paired choice between a red versus an orange, yellow, green, blue, or purple bead, and recorded the proportion of bites at each colour. Results: Red coloration was significantly more common in males than in females and in males during the breeding season than outside the breeding season. Males with strongly red pelvic spines have a significantly higher mean condition factor than those with plain spines. TNWR brook stickleback prefer red to other colours in a predation context. Conclusions: Our results suggest that TNWR brook stickleback red pelvic spine coloration is a secondary sexual character that may exploit a pre-existing sensory bias for red prey while also indicating condition to females

Seismic reflection analysis of the Manson Impact Structure, Iowa

This is the published version, also available here: http://dx.doi.org/10.1029/95JB03117.Our combined interpretation of new, high-resolution seismic reflection data and reprocessed, but previously published, industrial Vibroseis data indicates that the Manson Impact Structure, Iowa, has an apparent crater diameter of 35 km, an annular trough diameter of around 21 km, a shallow floor (0.6–0.7 km), and a central uplift that has a minimum diameter of 7.5 km. The two reflection lines are coincidentally located along an east-west radial transect and are constrained by shallow drill information. Results from the two data sets are correlative; both data sets were instrumental to the final interpretation due to the trade-off between resolution and depth of energy penetration. Based on the combined interpretation, structural uplift of the central peak is estimated to be around 2.8 km. Onlapping seismic sequences are present at the eastern edge of the central uplift. These seismic packages, observed only in the high-resolution line, are interpreted to represent impact breccia or debris material that was shed from the central peak or dynamically transported from outside of the crater

Seismic Reflection Studies in Long Valley Caldera, Califomia

This is the published version, also available here: http://dx.doi.org/10.1029/90JB02401.Seismic reflection studies in Long Valley caldera, California, indicate that seismic methods may be successfully employed to image certain types of features in young silicic caldera environments. However, near-surface geological conditions within these environments severely test the seismic reflection method. Data quality are degraded by static, reverberation, and band-limiting problems due to these near-surface conditions. In Long Valley, seismic reflection and refraction methods were used to image both the shallow and deep geothermal aquifers within the area. The deep geothermal aquifer, the welded Bishop Tuff, was imaged as a fairly continuous reflector across the western moat of the caldera. Near-surface refraction information indicates that there may be a buried paleochannel system or horst and graben system that could control the shallow geothermal flow pattern. High-amplitude events observed in a wide-angle survey were originally interpreted as reflections from a contemporary magma body. However, a migration of the events utilizing the new generalized cellular migration algorithm indicates that these events are probably reflections from the faults of the caldera ring fracture system. The reflections may be caused by the high acoustic impedance contrast associated with the juxtaposition of relatively low-velocity, low-density, caldera fill against the granite plutons and metasediments of the Sierran basement along this fault system

Characterising pandemic severity and transmissibility from data collected during first few hundred studies

Early estimation of the probable impact of a pandemic influenza outbreak can assist public health authorities to ensure that response measures are proportionate to the scale of the threat. Recently, frameworks based on transmissibility and severity have been proposed for initial characterization of pandemic impact. Data requirements to inform this assessment may be provided by "First Few Hundred" (FF100) studies, which involve surveillance-possibly in person, or via telephone-of household members of confirmed cases. This process of enhanced case finding enables detection of cases across the full spectrum of clinical severity, including the date of symptom onset. Such surveillance is continued until data for a few hundred cases, or satisfactory characterization of the pandemic strain, has been achieved. We present a method for analysing these data, at the household level, to provide a posterior distribution for the parameters of a model that can be interpreted in terms of severity and transmissibility of a pandemic strain. We account for imperfect case detection, where individuals are only observed with some probability that can increase after a first case is detected. Furthermore, we test this methodology using simulated data generated by an independent model, developed for a different purpose and incorporating more complex disease and social dynamics. Our method recovers transmissibility and severity parameters to a high degree of accuracy and provides a computationally efficient approach to estimating the impact of an outbreak in its early stages.Andrew J. Black, Nicholas Gear, James M. McCaw, Jodie McVernon, Joshua V. Ros

Effects of soil-moisture content on shallow seismic data

This is the publisher's version, also available electronically from "http://library.seg.org".Repeated shallow‐seismic experiments were conducted at a site on days with different near‐surface moisture conditions in unconsolidated material. Experimental field parameters remained constant to ensure comparability of results. Variations in the seismic data are attributed to the changes in soil‐moisture content of the unconsolidated material. Higher amplitudes of reflections and refractions were obtained under wetter near‐surface conditions. An increase in amplitude of 21 dB in the 100–300 Hz frequency range was observed when the moisture content increased from 18% to 36% in the upper 0.15 m (0.5 ft) of the subsurface. In the time‐domain records, highly saturated soil conditions caused large‐amplitude ringy wavelets that interfered with and degraded the appearance of some of the reflection information in the raw field data. This may indicate that an intermediate near‐surface moisture content is most conducive to the recording of high‐quality shallow‐seismic reflection data at this site. This study illustrates the drastic changes that can occur in shallow‐seismic data due to variations in near‐surface moisture conditions. These conditions may need to be considered to optimize the acquisition timing and parameters prior to collection of data

Inference of epidemiological parameters from household stratified data

We consider a continuous-time Markov chain model of SIR disease dynamics with two levels of mixing. For this so-called stochastic households model, we provide two methods for inferring the model parameters-governing within-household transmission, recovery, and between-household transmission-from data of the day upon which each individual became infectious and the household in which each infection occurred, as might be available from First Few Hundred studies. Each method is a form of Bayesian Markov Chain Monte Carlo that allows us to calculate a joint posterior distribution for all parameters and hence the household reproduction number and the early growth rate of the epidemic. The first method performs exact Bayesian inference using a standard data-augmentation approach; the second performs approximate Bayesian inference based on a likelihood approximation derived from branching processes. These methods are compared for computational efficiency and posteriors from each are compared. The branching process is shown to be a good approximation and remains computationally efficient as the amount of data is increased.James N. Walker, Joshua V. Ross, Andrew J. Blac

The Importance of Taking a Military History

The most important action a provider can take to ensure that a veteran receives optimal health care is perhaps the easiest and, ironically, the most neglected: asking if a patient has served in the military and taking a basic military history. In previously published articles, Jeffrey Brown1 and Ross Boyce,2 physicians with prior military service, reported that their own health care providers had rarely asked about their service. For Dr Brown, in the four decades since his combat service in Vietnam, he noted

Distribution of preferred ice crystal orientation determined from seismic anisotropy: Evidence from Jakobshavn Isbræ and the North Greenland Eemian Ice Drilling facility, Greenland

Preferred crystal orientation fabrics (COFs) within an ice sheet or glacier are typically found from ice cores. We conducted experiments at the North Greenland Eemian Ice Drilling (NEEM) facility ice core location, where COF data were available at Jakobshavn Isbræ west Greenland, to test if COF can be determined seismically. We used observations of anisotropic seismic wave propagation on multioffset gathers and englacial imaging from a 2D reflection profile. Anisotropy analysis of the NEEM data yielded mean c-axes distributed over a conical region of 30° to 32° from vertical. No internal ice seismic reflectors were imaged. Direct COF measurements collected in the ice core agreed with the seismic observations. At Jakobshavn Isbræ, we used a multioffset gather and a 2D reflection profile, but we lacked ice core data. Englacial reflectors allowed the determination of ice column interval properties. Anisotropy analysis found that the upper 1640 m of the ice column consisted of cold (≈−10°C≈−10°C) and mostly isotropic ice with c-axes distributed over a conical region of 80° from vertical. The lower 300 m of the ice column was characterized by warm (>−10°C>−10°C) ice with COF. These observations were consistent with complex ice fabric development and temperature estimations over the same region of Jakobshavn Isbræ. This study demonstrated that the ice sheet and glacier ice anisotropy information can be gained from seismic field observations