Sources In Close Proximity Research Articles

Accurate source location from waves scattered by surface topography

AbstractAccurate source locations of earthquakes and other seismic events are fundamental in seismology. The location accuracy is limited by several factors, including velocity models, which are often poorly known. In contrast, surface topography, the largest velocity contrast in the Earth, is often precisely mapped at the seismic wavelength (>100 m). In this study, we explore the use of P coda waves generated by scattering at surface topography to obtain high‐resolution locations of near‐surface seismic events. The Pacific Northwest region is chosen as an example to provide realistic topography. A grid search algorithm is combined with the 3‐D strain Green's tensor database to improve search efficiency as well as the quality of hypocenter solutions. The strain Green's tensor is calculated using a 3‐D collocated‐grid finite difference method on curvilinear grids. Solutions in the search volume are obtained based on the least squares misfit between the “observed” and predicted P and P coda waves. The 95% confidence interval of the solution is provided as an a posteriori error estimation. For shallow events tested in the study, scattering is mainly due to topography in comparison with stochastic lateral velocity heterogeneity. The incorporation of P coda significantly improves solution accuracy and reduces solution uncertainty. The solution remains robust with wide ranges of random noises in data, unmodeled random velocity heterogeneities, and uncertainties in moment tensors. The method can be extended to locate pairs of sources in close proximity by differential waveforms using source‐receiver reciprocity, further reducing errors caused by unmodeled velocity structures.

Properties of Recycled Aggregate Concrete Reinforced with Polypropylene Fibre

This research work is aimed to investigate how the addition of various proportion of polypropylene fibre affects the mechanical strength and permeability characteristics of recycled aggregate concrete (RAC) which has been produced with treated coarse recycled concrete aggregate (RCA). Further research on RAC properties and their applications is of great importance as the scarcity of virgin aggregate sources in close proximity to major urban centers is becoming a worldwide problem. In this study, the hardened RAC properties at the curing age of 7 and 28 days such as compressive strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption and total porosity were evaluated and compare with control specimens. Experimental result indicates that although the inclusion of the treated coarse RCA can enhance the mechanical strength and permeability properties of RAC, Further modification by addition of polypropylene fibre can optimize the results.

Application of Citizen Science Risk Communication Tools in a Vulnerable Urban Community.

A public participatory geographical information systems (PPGIS) demographic, environmental, socioeconomic, health status portal was developed for the Stambaugh-Elwood (SE) community in Columbus, OH. We hypothesized that soil at SE residences would have metal concentrations above natural background levels. Three aims were developed that allowed testing of this hypothesis. Aim 1 focused on establishing partnerships between academia, state agencies and communities to assist in the development of a community voice. Aim 2 was to design and conduct soil sampling for residents of the SE community. Aim 3 was to utilize our interactive, customized portal as a risk communication tool by allowing residents to educate themselves as to the potential risks from industrial sources in close proximity to their community. Multiple comparisons of means were used to determine differences in soil element concentration by sampling location at p < 0.05. The results demonstrated that eight metals (As, Cd, Cu, Pb, Mo, Se, Tl, Zn) occurred at statistically-significantly greater levels than natural background levels, but most were below risk-based residential soil screening levels. Results were conveyed to residents via an educational, risk-communication informational card. This study demonstrates that community-led coalitions in collaboration with academic teams and state agencies can effectively address environmental concerns.

Evaluation of the rattle noise of a vehicle seat using the coherence analysis technique

The complicated transfer path relationship between the vibrations of a seat and the noise at the locations of the driver’s ears was estimated from the residual spectrum. For accurate quantitative estimation of the rattle noise at the locations of the driver’s ears, in particular the partial coherence function of the pure inputs to the output was modelled by considering the correlation between the inputs and the input–output. Whenever a coherence analysis was performed with the noise sources in close proximity selected as the inputs and the noise at the locations of the driver’s ears modelled as the output, the partially coherent output spectrum as a quantitative contribution of the inputs to the output was determined. In this study, we applied a coherence analysis technique to identify the sources of the rattle noise of a seat by visualizing the noise sources with an acoustic camera while excitation of the seat was carried out using a hydraulic exciter. We were able to generate the rattle noise from the headrest stay, the recliner and the front part of the slide while excitation of the seat was obtained using a hydraulic exciter with white noise. We observed that the noise was generated by utilizing a hydraulic six-axis exciter positioned at the driver’s seat of a middle-sized manual transmission vehicle. We determined that the noise measured at the locations of the driver’s ears had a frequency of 58 Hz using acoustic visualization and a coherence technique. It was selected in particular as the target frequency since the 58 Hz resonant frequency caused by the twisting mode of the seat back was identical with the frequency of the rattle noise. Finally, it was verified through a modal test that the rattle noise at 58 Hz was generated by the vibration characteristics of the seat, which depended on gaps between the headrest stay and the guide.

Space use, foraging success and competitive relationships in Formica cinerea (Hymenoptera Formicidae) on sand dunes in southern Finland

The foraging strategy of a colony of social insects, e.g. ants, is made up of simple individual decisions being influenced by a series of factors like climatic conditions, properties and availability of food and competitive context. We studied the use of space, foraging success and competitive relationships in Formica cinerea around its nests in field conditions in the absence and in the presence of artificial food sources on sand dunes in Finland. Generally, the abundance of foragers was low around colonies. Sources in close proximity were mostly discovered. However, the fact that distant sources were sometimes preferred over discovered close sources during mass exploitation appeared to confer a certain sub-optimality upon the foraging strategy of the species. The use of baits allowed us to analyse the species’ competitive position as well. Generally, rivals could dominate sources far from the nest of F. cinerea, thus a facultative inhibition zone was established around the studied colonies. Although, mostly dominant in contests, F. cinerea could give up food sources to rivals if these were already gathered on the bait. The mixture of submissive and aggressive features, which characterise F. cinerea allows this species to adapt to the current competitive context and the availability of food sources.

Landscape requirements of a primate population in a human-dominated environment

IntroductionAs urban and rural land development become widespread features of the global landscape so an understanding of the landscape requirements of displaced and isolated wildlife species becomes increasingly important for conservation planning. In the Cape Peninsula, South Africa, rapid human population growth, and the associated urban and rural land transformation, threatens the sustainability of the local chacma baboon population. Here we analyse spatial data collected from nine of the 12 extant troops to determine their population-level landscape requirements. We use hurdle models to ascertain the key landscape features influencing baboon occurrence and abundance patterns on two hierarchical spatial scales.ResultsBoth spatial scales produced similar results that were ecologically reliable and interpretable. The models indicated that baboons were more likely to occur, and be more abundant, at low altitudes, on steep slopes and in human-modified habitats. The combination of these landscape variables provides baboons with access to the best quality natural and anthropogenic food sources in close proximity to one another and suitable sleeping sites. Surface water did not emerge as an influential landscape feature presumably as the area is not water stressed.ConclusionsThe model results indicate that land development in the Cape Peninsula has pushed baboons into increasingly marginal natural habitat while simultaneously providing them with predictable and easily accessible food sources in human-modified habitats. The resultant spatial competition between humans and baboons explains the high levels of human-baboon conflict and further erosion of the remaining land fragments is predicted to exacerbate competition. This study demonstrates how the quantification of animal landscape requirements can provide a mechanism for identifying priority conservation areas at the human-wildlife interface.

Carbon nanotube based X-ray sources: Applications in pre-clinical and medical imaging

Field emission offers an alternate method of electron production for Bremsstrahlung based X-ray tubes. Carbon nanotubes (CNTs) serve as very effective field emitters, allowing them to serve as electron sources for X-ray sources, with specific advantages over traditional thermionic tubes. CNT derived X-ray sources can create X-ray pulses of any duration and frequency, gate the X-ray pulse to any source and allow the placement of many sources in close proximity. We have constructed a number of micro-CT systems based on CNT X-ray sources for applications in small animal imaging, specifically focused on the imaging of the heart and lungs. This paper offers a review of the pre-clinical applications of the CNT based micro-CT that we have developed. We also discuss some of the current and potential clinical applications of the CNT X-ray sources.

Homogenized Green's Functions for an Aperiodic Line Source Over Planar Densely Periodic Artificial Impedance Surfaces

The accurate electromagnetic analysis of artificial periodic surfaces formed as planar layers with complicated periodic metallization patterns, having a grid period much smaller than the effective wavelength (densely periodic), is important for the design and analysis of a variety of electromagnetic structures. However, full-wave modeling can be extremely time-consuming and computationally expensive, especially for aperiodic sources in close proximity to periodic surfaces. In this paper, we describe approximate homogenized models for a Green's function that treats planar patterned screens (grids) as quasi-dynamic homogenized impedance surfaces and dielectric layers in a fully dynamic manner. The resulting Green's functions are only slightly more complicated than those for dielectric layers without metallization and can be numerically computed using standard methods for layered media. We restrict attention to line sources and compare numerical results from this method with those from a full-wave array scanning method, which is more complex analytically and much more demanding to evaluate numerically. Very good agreement is found between the two methods except for source and/or field points extremely close to the metallization layer, confirming the accuracy of the homogenized representations of periodic surfaces for near-field sources.

An investigation of community noise in high-rise residential environments

High-rise dwellers in Singapore are often subjected to several community noise sources in close proximity. These include food center, children playground, soccer playground, basketball playground, waste disposal truck, etc. A scientific and reliable approach is required for evaluation of the community noise and its impact on high-rise dwellers. A comprehensive noise survey by a cluster sampling technique, conducted among 522 households in five residential towns in Singapore, showed that community noise was one of the prime sources of noise in a high-rise residential environment. From a subjective noise survey, undertaken concurrent with objective noise measurements, a mean outdoor noise level of 59 dBA was established as an acceptable noise level in the indoor environment. To investigate the level of noise exposure from different community noise sources, software modeling and simulations were carried out. The predicted results were validated with field measured data at five 16 story residential buildings. Analysis of noise exposure data showed that except for waste disposal truck, noise exposure due to other community noise sources (building distance of 15 m) were within the established acceptable noise level. A factor analysis of the survey data identified the key factors related to the disturbance due to community noise sources.

Vertical profile of community noise in high‐rise built environment.

High‐rise public housing apartments in Singapore are often subjected to different types of community noise sources in close proximity. Community noise in housing estates comprises noise sources such as food center noise, children playground noise, soccer court noise, basketball court noise, waste disposal truck noise, etc. It was found as one of the major noise source categories in residential environment. With the enhanced performance quality in many aspects of public housing in recent years, it is imperative that the acoustics performance of the apartments can be enhanced to match overall quality of public housing environment through appropriate characterization of these noise sources. A scientific and reliable approach for characterizing noise propagation from these sources is vital in the implementation of projects. Software modeling and simulation were carried out to study noise propagation characteristics of five types of community noise sources. Five 16‐storey residential buildings were investigate...

Direct observation of two dimensional trace gas distributions with an airborne Imaging DOAS instrument

Abstract. In many investigations of tropospheric chemistry information about the two dimensional distribution of trace gases on a small scale (e.g. tens to hundreds of metres) is highly desirable. An airborne instrument based on imaging Differential Optical Absorption Spectroscopy has been built to map the two dimensional distribution of a series of relevant trace gases including NO2, HCHO, C2H2O2, H2O, O4, SO2, and BrO on a scale of 100 m. Here we report on the first tests of the novel aircraft instrument over the industrialised South African Highveld, where large variations in NO2 column densities in the immediate vicinity of several sources e.g. power plants or steel works, were measured. The observed patterns in the trace gas distribution are interpreted with respect to flux estimates, and it is seen that the fine resolution of the measurements allows separate sources in close proximity to one another to be distinguished.

Cometary cryo-volcanism: Source regions and a model for the UT 2005 June 14 and other mini-outbursts on Comet 9P/Tempel 1

Data on the UT 2005 June 14 mini-outburst of Comet 9P/Tempel 1 taken from different viewpoints have been examined for morphological differences and parallax. The data were taken with the Hubble Space Telescope (HST), from the Deep Impact (DI) spacecraft, and from the Calar Alto Observatory, Spain. The mini-outburst source region was found to be located near 218 ± 6E, 6 ± 5N on the Deep Impact nucleus shape model. The mini-outburst occurred at ∼ 12 pm local solar time. The distribution of light in the mini-outburst is similar to that expected for an ejecta curtain. The method and software used to determine the surface location was checked using position angles of the impact ejecta plume as seen from DI and HST. The general region of impact was recovered and a downrange tilt of the ejecta curtain axis of 10.2 deg from the surface normal was found. We computed tracks of possible source regions for nine other mini-outbursts seen from DI. Five of these tracks converge on the 2005 June 14 event location. Three of the tracks converge at a second location near (60E, 20S), well separated from the first. Multiple mini-outbursts arise at each location either from a single source or from a few sources in close proximity. The mini-outbursts occur both at night and during the day indicating at most weak, if any, control by direct sunlight. The times of outburst are non-random with a preference for early afternoon, dusk and midnight. None of the mini-outbursts occurred near dawn. They occur at low latitudes (between ± 40 deg ) near the points where the principal axis of minimum moment of inertia cuts the surface. These regions are furthest from the center of figure and have the lowest effective surface gravity. We use these results to develop a conceptual model of the mini-outburst process and make comparisons with the theoretical calculations. We find that the tensile strength of the sub-surface material must be very low (e.g., ∼ 10 2 – 10 3 dynes cm −2 ) and, on the basis of features imaged on the western facet of the nucleus, suggest that inflation of the sub-surface may be occurring. Our model makes specific predictions about the kind of surface morphology that should result from mini-outburst activity. We show that one of the isolated rimless depressions and the close-packed depressions found in the Deep Impact images have the properties needed and identify them as possible sites of past and current mini-outburst activity.

A study of near source effects in array-based (SPAC) microtremor surveys

Array-based methods for exploiting ambient seismic noise are receiving increasing attention in the literature, particularly for use in providing shear wave velocity profiles to assist with simulation of site-specific earthquake responses. Many of these microtremor methods—such as the spatial autocorrelation technique (SPAC)—operate under the fundamental assumption of plane wave propagation of surface waves. However, when there are significant microtremor sources in close proximity to an array, wave front curvature becomes significant, and the plane wave assumption becomes a tenuous one. This paper explains the use of a simplified geometry-based approach to examine the effect of source distance on SPAC spectra for hexagonal (six-station) and triangular (three-station) arrays. The results suggest that near source effects are generally minimal provided that most of the sources are located a distance equal to at least two array radii from the centre of the array, although this distance increases when attenuation is considered. Results of a field trial involving the deliberate use of near-sources in proximity to a hexagonal (six-station) array support the findings of the theoretical model. Near source effects generally result in the measured SPAC curve being offset to lower frequencies for wavenumbers less than the first secondary maximum of the SPAC curve (kr < 7.0; λ > 0.86R), resulting in underestimates of shear velocity values in the inverted layered earth model. For the field example, shear velocity was underestimated by up to approximately 17 per cent. Studies of near source effects in a number of theoretical source distributions for hexagonal arrays revealed that cyclic variation in the imaginary SPAC coefficients are indicative of near source effects, although field examples indicate this effect is less significant than the geometric modelling suggests. Modelling of linear microtremor source distributions (intended to represent traffic travelling along a road) resulted in less severe near source effects than full (360°) azimuthal source coverage—a result confirmed by field data. Model and field studies also indicated that in situations of a dominant, close microtremor source of limited azimuthal extent, use of a hexagonal (six-station) array significantly mitigates near source effects compared with a similarly aligned triangular (three-station) array.

Optimising experimental design for MEG beamformer imaging

In recent years, the use of beamformers for source localisation has significantly improved the spatial accuracy of magnetoencephalography. In this paper, we examine techniques by which to optimise experimental design, and ensure that the application of beamformers yields accurate results. We show that variation in the experimental duration, or variation in the bandwidth of a signal of interest, can significantly affect the accuracy of a beamformer reconstruction of source power. Specifically, power will usually be underestimated if covariance windows are made too short, or bandwidths too narrow. The accuracy of spatial localisation may also be reduced. We conclude that for optimum accuracy, experimenters should aim to collect as much data as possible, and use a bandwidth spanning the entire frequency distribution of the signal of interest. This minimises distortion to reconstructed source images, time courses and power estimation. In the case where experimental duration is short, and small covariance windows are therefore used, we show that accurate power estimation can be achieved by matrix regularisation. However, large amounts of regularisation cause a loss in the spatial resolution of the MEG beamformer, hence regularisation should be used carefully, particularly if multiple sources in close proximity are expected.

Impact on drinking water sources in close proximity to the Payatas dumpsite, Philippines

The lack of a source of clean drinking water is a rising public health concern worldwide. Waterborne diseases are a consequence. This study assessed whether the water quality is significantly different between the communities with and without the Payatas dumpsite, and whether the pollution in the dumpsite has a significant health impact on communities, particularly diarrhea. A cross-sectional study design was used. Water quality monitoring and analyses, particularly for the parameters nitrate-nitrogen, total cadmium, total coliform, and sulfate were carried out in 14 drinking water sources of the communities with and without the dumpsite for 6 consecutive months from April to September 2003, covering both dry and wet seasons. A dose–response function model using site-specific morbidity data on diarrhea was obtained from the communities’ health centers and monitored water quality parameters were derived through multiple linear regression analysis. There were no significant differences in the drinking water quality parameters monitored, except for sulfate. The Philippine water quality standards were not exceeded for most parameters, except for total coliform. The regression model confirmed a significant impact on the prevalence of diarrhea by the parameters sulfate and total cadmium. Only the parameter sulfate is significantly different in the drinking water sources of the communities studied. The model derived confirmed a significant impact on the occurrence of diarrhea cases in the communities for the parameters sulfate and total cadmium.

Importance of the personal endotoxin cloud in school-age children with asthma

A number of studies have observed associations between the amount of endotoxin in urban dust and chronic asthma severity, but a direct relationship between personal exposure to household endotoxin and acute asthma worsening has not yet been defined. We sought to investigate the relationship between day-to-day changes in personal endotoxin exposure and asthma severity. In the winter and spring of 1999 through 2000, endotoxin exposures were monitored in asthmatic schoolchildren by using portable, as opposed to stationary, monitors designed to measure inhalable and respirable particulate matter less than or equal to 2.5 and 10 microm in diameter. Children were followed with daily measurements of FEV(1) and asthma symptoms. Over a 24-hour period, median daily personal endotoxin exposures ranged from 0.08 EU/m(3) (measured at a particulate matter size range </=2.5 microm in diameter) to 0.37 EU/m(3) (measured at a particulate matter size range </=10 microm in diameter). Personal exposures were significantly (P < .001) higher than endotoxin measurements from either indoor or outdoor stationary monitors. Moreover, individual exposures did not correlate with stationary measurements, suggesting that exposures derived from sources in close proximity to the children's personal activities might be better correlated with disease severity. Increases in personal endotoxin exposures were associated with decreased FEV(1) values and increased symptoms. These findings demonstrate the importance of using personal monitoring to both measure and correlate endotoxin exposure with asthma severity.

Surface plasmon-polariton mediated light emission through thin metal films

The emission of light by sources in close proximity to a thin metallic film is dominated by surface plasmon-polariton modes supported by that film. We explore the nature of the modes and examine how the energy lost to such modes can be recovered. Both cross-coupled and coupled SPPs are presented as a means of transferring energy across a thin metal film. These modes are then scattered and thereby coupled to light by a wavelength scale grating type microstructure. We show that the photoluminescence emission from a structure containing a microstructured thin metal film that supports coupled SPPs is over 50 times greater than that from a similar planar structure. Similar strong photoluminescence emission is also exhibited by a sample that contains a planar metal film coated with a microstructured dielectric overlayer.

Measurement of brachytherapy sources using MAGIC gel

In this study, we investigated the feasibility of performing measurements of brachytherapy sources in close proximity to the source.

Transperineal interstitial permanent prostate brachytherapy for carcinoma of the prostate

Prostate cancer is the second most frequently diagnosed cancer of men of all ages, in 1997 approximately 18 300 new cases were registered in England and Wales. The ageing of the population means that the number of men with prostate cancer can be expected to increase over the next 10 years. With the increasing use of PSA screening the number of patients diagnosed with organ confined disease has increased significantly. Brachytherapy is the placement of radioactive sources in close proximity to any tumour. It takes advantage of the physical properties of radiation, allowing high radiation dose to tumours with rapid dose decay in normal tissues. It has been an established treatment modality for many tumour sites for a number of years. Like many apparently new developments prostate brachytherapy was first attempted many years ago by Pasteau and Degrais [1], who inserted radium 226 sources using a silver tube through the urethra. Barringer [2], in 1917 reported on the first transperineal application using radium 226. In the early 1970s the technique of open retropubic Iodine-125 seed implantation was developed at the Memorial Hospital, New York, by Whitmore and colleagues [3]. The technique had serious limitations due to inability to accurately place the sources. The poor dose distribution and the inclusion of patient’s with extra capsular disease led to reports of poor outcomes and unacceptable long-term morbidity and the technique was understandably abandoned [4]. The modern era of prostate brachytherapy began in 1983 when Holm et al. [5], described the technique of transrectal ultrasound with template guidance that allowed accurate positioning of needles within the prostate. Blasko and colleagues in Seattle [6] developed and improved the technique with reduced complications and improved outcomes. In North America there has been a dramatic rise in the number of patients undergoing transperineal interstitial permanent prostate brachytherapy (TIPPB) in the last 5 years and a similar expansion is expected in Europe.

High‐Resolution Mid‐Infrared Imaging of G339.88−1.26

G339.88-1.26 is considered to be a good candidate for a massive star with a circumstellar disk. This has been supported by the observations of linearly distributed methanol maser spots believed to delineate this disk and mid-infrared observations that have discovered a source at this location that is elongated at the same position angle as the methanol maser distribution. We used the mid-infrared imager/spectrometer OSCIR at Keck Observatory to make high-resolution images of G339.88-1.26. We resolve the mid-infrared emission into three sources within 15 of the location of the masers. We determine that the methanol masers are most likely not located in a circumstellar disk. Furthermore, we find that the observed radio continuum emission most likely comes from two sources in close proximity to each other. One source is an unobscured massive star with an extended H II region that is responsible for the peak in the radio continuum emission. A second source is embedded and centered on the elongation in the radio continuum emission that is believed to be tracing an outflow in this region.