Gamma-Ray Bursts: Temporal Scales and the Bulk Lorentz Factor

For a sample of Swift and Fermi GRBs, we show that the minimum variability timescale and the spectral lag of the prompt emission is related to the bulk Lorentz factor in a complex manner: For small $\Gamma$'s, the variability timescale exhibits a shallow (plateau) region. For large $\Gamma$'s, the variability timescale declines steeply as a function of $\Gamma$ ($\delta T\propto\Gamma^{-4.05\pm0.64}$). Evidence is also presented for an intriguing correlation between the peak times, t$_p$, of the afterglow emission and the prompt emission variability timescale.Comment: Accepted for publication in Ap

Use of biosolids in enhanced fired clay bricks

The ever growing quantities of waste materials and their management costs, strict regulations declared for landfilling of waste, shortage of landfill spaces, and scarcity of natural earth materials highlight the urgent need to investigate sustainable routes for the recycling and reusing of waste materials. Biosolids are solid and treated organic residual by products from the wastewater treatment process and are available for beneficial use in accordance with relevant regulations. The production of biosolids is increasing annually as a result of increasing water demand and wastewater generation in metropolitan areas throughout the world, which, consequently, presents an urgent need for landfill spaces to dispose of biosolids and other by products. The State of Victoria, Australia, alone produces approximately 95,600 dry tonnes of biosolids annually on top of an approximated 2 million dry tonnes of existing biosolids, which involves a biosolids management cost of approximately A$90 million every year. Therefore, incorporating biosolids into building materials, for instance, fired clay bricks, could be a winwin strategy for the comprehensive recycling of biosolids. Bricks are one of the longest lasting and strongest manufactured building materials, and have been used over a long period of time. Due to their strength, reliability, weather resistance, flexibility in composition, simplicity, and durability, bricks are used extensively throughout the world. Due to a shortage of natural brick soil, brick production has been limited in some countries, such as China, in order to protect the virgin clay quarries. Therefore, innovative approaches to producing fired clay bricks with fewer virgin resources are highly encouraged from the perspective of environmental protection and sustainable development. Attempts have been made to manufacture bricks incorporating various types of waste materials, such as sludge, fly ash, wood sawdust, silica fume, cigarette butts, and polystyrene. The results of these studies showed positive effects from the recycling of waste materials into a ceramic body, such as lightweight bricks with higher thermal insulation properties. This thesis presents and discusses the possible reuse of biosolids in fired clay bricks and the effect of incorporating biosolids on the compressive strength, density, and other physical and mechanical properties of bricks. In this study, biosolids from the stockpiles of the Eastern Treatment Plant (ETP) and Western Treatment Plant (WTP) in Melbourne were used to assess their suitability as a partial replacement material for clay in the formulation of fired clay bricks. The major research outcome in this research is the establishment of a process for manufacturing fired clay bricks incorporating biosolids. Furthermore, the possible levels of environmental impacts, such as the leaching of heavy metals, emissions, and life cycle assessment (LCA) related to the biosolids amended bricks were investigated. In order to achieve the aforementioned objectives, this study was conducted in three stages. In the first stage of the study, extensive laboratory experiments were conducted to investigate the geotechnical properties of different biosolids samples, as the existing knowledge is still limited in this context. The geotechnical properties, such as Atterberg limits, particle size distribution, linear shrinkage, specific gravity, and organic content, were determined. A series of standard Proctor compaction tests were carried out to investigate the variation in the maximum dry density and optimum moisture content of biosolids soil mixtures with different percentages of biosolids. The chemical composition, mineral composition, and thermal analysis of all biosolids samples were also determined. Thereafter, four sets of brick samples were manufactured incorporating 25% of three different ETP biosolids and one WTP biosolids. The physical and mechanical properties of biosolids amended bricks were tested to assess their suitability as a partial replacement material for the brick soil in fabricating clay bricks. Furthermore, all the properties of biosolids amended bricks were compared with conventional bricks. In the second stage of the study, bricks were manufactured incorporating five different percentages (5, 15, 25, 35, and 50%) of selected ETP biosolids, and the physical and mechanical properties of bricks were evaluated. In addition, the effects of the addition of ETP biosolids on the microstructure of the bricks were investigated by means of scanning electron micrographs. A novel method was implemented at the laboratory scale for measuring the energy consumption of bricks during the firing stage. Moreover, the leachate analysis was undertaken for the biosolids amended bricks according to the Australian and US EPA standards. The leaching concentrations of toxic heavy metals were then compared with the respective regulatory limits. In addition, the effect on the physical and mechanical properties, energy consumption, and microstructure of biosolids amended bricks of the organic content present in the brick mixture was investigated. As a final part of stage two, the multivariate statistical analysis was carried out to investigate the effect of organic content on the properties tested, and determine the variations and interdependency of the results. In addition, the effect on the properties of biosolids amended bricks from a change in the heating rates for the firing was investigated. Higher heating rates can significantly reduce the firing time, which, consequently, reduces the energy demand for the firing process. Therefore, investigating the physical and mechanical properties of bricks at different heating rates would provide a better understanding of the use of a precise heating rate without compromising the properties of bricks. Therefore, the effect of incorporating different percentages (5, 10, 15, 20, and 25%) of WTP biosolids and the effect of heating rates (0.7, 1.0, 1.5, and 2.0 °C per min) during the sintering process on the physical and mechanical properties of biosolids amended bricks were investigated. In the third stage of this study, a new technique was developed and used for the measuring of gaseous emissions during the firing of bricks. The emission factors were then developed for CO, CO2, NO, HCN, and SO2 for ETP and WTP biosolids amended bricks. Furthermore, in this stage, a comparative Life Cycle Assessment (LCA) was carried to compare the environmental footprint between biosolids amended bricks and conventional bricks. Potential environmental impacts, such as climate change, ozone depletion, acidification, human toxicity, terrestrial and marine ecotoxicity, urban land occupation, and water depletion, were analysed and compared through the ReCipe midpoint life cycle impact assessment (LCIA) method using SimaPro 8.0.5.13 software. Overall, the experimental results and LCA results found in this study were promising and encouraging for the recycling of biosolids into fired clay bricks. The findings of this study showed that the incorporation of biosolids produced bricks with higher porosity, lower density, better thermal insulation properties, and acceptable compressive strength. Also, it was found that the percentage of organic content present in the brick mixture has a significant effect on the physical and mechanical properties, energy consumption, as well as the microstructure of biosolids amended bricks. The quality of ETP biosolids bricks was found to be relatively better than that of WTP biosolids bricks, which was mainly due to the lower organic content present in the ETP brick mixture than that in the WTP brick mixture. The leachate analysis results showed that the addition of biosolids in a ceramic body immobilised some of the toxic heavy metals present in the biosolids and the organic content present in the brick mixture has an insignificant effect on the leaching concentrations of heavy metals. Interestingly, the leachate test results revealed that the concentrations of toxic heavy metals were well below the Australian and International regulatory limits for industrial solid wastes. The comparative LCA between the biosolids amended bricks and the control bricks showed that the addition of biosolids is beneficial because the biosolids amended bricks had a positive environmental impacts compared to conventional bricks

Incorporation of biosolids in fired clay bricks

In Australia, thousands of tonnes of biosolids are produced and millions of dollars expended for their management annually. Biosolids are derived from wastewater sludge which is the major solid component collected from the wastewater treatment process. This study investigated the incorporation of biosolids into fired clay bricks. Geotechnical characteristics of three biosolids samples produced from Eastern Wastewater Treatment Plant (ETP) in Melbourne were investigated to assess their suitability as a partial replacement material for the clay in fired-clay bricks. Results of classification tests including liquid limit, plastic limit and sieve analysis indicated that the three biosolids samples are silty clayey sand with low to high plasticity. Linear shrinkage of biosolids samples varied from 10% to 15% and organic content from 6% to 14%. Control clay bricks with 0% biosolids and clay-biosolids bricks with 25% by weight biosolids were made and properties including compressive strength, shrinkage, density, initial rate of absorption (IRA), water absorption, thermal conductivity and other properties were determined. The overall results of this preliminary study are promising. Some of the results of this stage of this investigation are presented and discussed in this paper

A Proposal to Localize Fermi GBM GRBs Through Coordinated Scanning of the GBM Error Circle via Optical Telescopes

We investigate the feasibility of implementing a system that will coordinate ground-based optical telescopes to cover the Fermi GBM Error Circle (EC). The aim of the system is to localize GBM detected GRBs and facilitate multi-wavelength follow-up from space and ground. This system will optimize the observing locations in the GBM EC based on individual telescope location, Field of View (FoV) and sensitivity. The proposed system will coordinate GBM EC scanning by professional as well as amateur astronomers around the world. The results of a Monte Carlo simulation to investigate the feasibility of the project are presented.Comment: 2011 Fermi Symposium proceedings - eConf C11050

A New Frequency-Luminosity Relation for Long GRBs?

We have studied power density spectra (PDS) of 206 long Gamma-Ray Bursts (GRBs). We fitted the PDS with a simple power-law and extracted the exponent of the power-law (alpha) and the noise-crossing threshold frequency (f_th). We find that the distribution of the extracted alpha peaks around -1.4 and that of f_th around 1 Hz. In addition, based on a sub-set of 58 bursts with known redshifts, we show that the redshift-corrected threshold frequency is positively correlated with the isotropic peak luminosity. The correlation coefficient is 0.57 +/- 0.03.Comment: 9 pages, 17 figures, 1 table; Accepted for publication in MNRA

Geotechnical and chemical characteristics of ETP and WTP biosolids

Stricter regulations on the quality of wastewater treatment by-products are giving rise to an increasing volume of stockpiled biosolids. The annual production of biosolids in Australia is approximately 300,000 dry tonnes, which involves a biosolids management cost of about A$90 million. Biosolids are the end product and the main solid component collected from the wastewater treatment process. This paper presents some of the geotechnical and chemical properties of two samples of biosolids collected from Melbourne Water's Eastern Wastewater Treatment Plant (ETP) stockpile No. 22 and the Western Wastewater Treatment Plant (WTP) stockpile No. 10. Various geotechnical tests -liquid limit, plastic limit, particle density, particle size distribution, organic content, and linear shrinkage - were undertaken. In addition, chemical tests comprising leachate analysis for heavy metals and chemical composition were conducted on the samples of biosolids. From an environmental perspective, all the samples of biosolids were found to be safe in terms of leaching for use as a landfill application material. The experimental results showed that the ETP biosolids have about 7% of organic content with some of the geotechnical and chemical properties similar to a conventional soil with similar particle size distribution. In addition, empirical relationships were obtained for the compaction behaviour of the ETP biosolids and a comparison soil used in this study. The results obtained in this study can be used as a guide for the use of ETP and WTP biosolids in different civil engineering applications

The First Swift BAT Gamma-Ray Burst Catalog

We present the first Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts (GRBs), which contains bursts detected by the BAT between 2004 December 19 and 2007 June 16. This catalog (hereafter BAT1 catalog) contains burst trigger time, location, 90% error radius, duration, fluence, peak flux, and time averaged spectral parameters for each of 237 GRBs, as measured by the BAT. The BAT-determined position reported here is within 1.75' of the Swift X-ray Telescope (XRT)-determined position for 90% of these GRBs. The BAT T_90 and T_50 durations peak at 80 and 20 seconds, respectively. From the fluence-fluence correlation, we conclude that about 60% of the observed peak energies, Epeak, of BAT GRBs could be less than 100 keV. We confirm that GRB fluence to hardness and GRB peak flux to hardness are correlated for BAT bursts in analogous ways to previous missions' results. The correlation between the photon index in a simple power-law model and Epeak is also confirmed. We also report the current status for the on-orbit BAT calibrations based on observations of the Crab Nebula.Comment: 63 pages, 23 figures, Accepted in ApJS, Corrected for the BAT ground position, the image significance, and the error radius of GRB 051105, Five machine-readable tables are available at http://swift.gsfc.nasa.gov/docs/swift/results/bat1_catalog

Three-dimensional segmentation of three-dimensional ultrasound carotid atherosclerosis using sparse field level sets.

PURPOSE: Three-dimensional ultrasound (3DUS) vessel wall volume (VWV) provides a 3D measurement of carotid artery wall remodeling and atherosclerotic plaque and is sensitive to temporal changes of carotid plaque burden. Unfortunately, although 3DUS VWV provides many advantages compared to measurements of arterial wall thickening or plaque alone, it is still not widely used in research or clinical practice because of the inordinate amount of time required to train observers and to generate 3DUS VWV measurements. In this regard, semiautomated methods for segmentation of the carotid media-adventitia boundary (MAB) and the lumen-intima boundary (LIB) would greatly improve the time to train observers and for them to generate 3DUS VWV measurements with high reproducibility. METHODS: The authors describe a 3D algorithm based on a modified sparse field level set method for segmenting the MAB and LIB of the common carotid artery (CCA) from 3DUS images. To the authors\u27 knowledge, the proposed algorithm is the first direct 3D segmentation method, which has been validated for segmenting both the carotid MAB and the LIB from 3DUS images for the purpose of computing VWV. Initialization of the algorithm requires the observer to choose anchor points on each boundary on a set of transverse slices with a user-specified interslice distance (ISD), in which larger ISD requires fewer user interactions than smaller ISD. To address the challenges of the MAB and LIB segmentations from 3DUS images, the authors integrated regional- and boundary-based image statistics, expert initializations, and anatomically motivated boundary separation into the segmentation. The MAB is segmented by incorporating local region-based image information, image gradients, and the anchor points provided by the observer. Moreover, a local smoothness term is utilized to maintain the smooth surface of the MAB. The LIB is segmented by constraining its evolution using the already segmented surface of the MAB, in addition to the global region-based information and the anchor points. The algorithm-generated surfaces were sliced and evaluated with respect to manual segmentations on a slice-by-slice basis using 21 3DUS images. RESULTS: The authors used ISD of 1, 2, 3, 4, and 10 mm for algorithm initialization to generate segmentation results. The algorithm-generated accuracy and intraobserver variability results are comparable to the previous methods, but with fewer user interactions. For example, for the ISD of 3 mm, the algorithm yielded an average Dice coefficient of 94.4% ± 2.2% and 90.6% ± 5.0% for the MAB and LIB and the coefficient of variation of 6.8% for computing the VWV of the CCA, while requiring only 1.72 min (vs 8.3 min for manual segmentation) for a 3DUS image. CONCLUSIONS: The proposed 3D semiautomated segmentation algorithm yielded high-accuracy and high-repeatability, while reducing the expert interaction required for initializing the algorithm than the previous 2D methods