27 research outputs found
Techno-economic analysis of water management options for unconventional natural gas developments in the Marcellus Shale
Thesis (S.M. in Technology and Policy)-- Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 129-135).The emergence of large-scale hydrocarbon production from shale reservoirs has revolutionized the oil and gas sector, and hydraulic fracturing has been the key enabler of this advancement. As a result, the need for water treatment has increased significantly and became a major cost driver for producers. What to do with the flowback water in light of scarce disposal facilities and substantial handling costs is a major impediment to the development of the natural gas resource, particularly in the Marcellus shale. This thesis explores the technical, economic and regulatory issues associated with water treatment in the shale plays and identifies best practice water management pathways based upon the Marcellus shale characteristics. The key factors that affect the choice of water treatment options and infrastructure investments are identified and investigated in detail. These include, among others, proximity to disposal facilities, transportation costs, potential for wastewater reuse and make-up water requirements. The study is supplemented by an analysis of the flowback water geochemistry and an examination of the chemical components, like barium and strontium hardness ions, that can restrict the potential of flowback water reuse. Important insights that will help inform the policy debate on how to best address both the environmental and operational water issues associated with hydraulic fracturing in the Marcellus region are derived through this study. Better reporting and monitoring of wastewater volumes is one of the main recommendations of this thesis. A wastewater management and reporting system that focuses on the optimization of water reuse among producers and facilitates information sharing could offer significant efficiencies in terms of reducing costs and minimizing negative environmental impacts. Furthermore, desalination technologies are currently cost prohibitive especially for onsite use. A governmental effort to identify and promote the development of desalination technologies that can effectively remove salts without being prohibitively expensive could help develop a sustainable water management solution.by Christina Karapataki.S.M.in Technology and Polic
Hopfield network applied to blood vessel detection in angiograms
A neural network classifier for detecting vascular structures in angiograms is developed. The classifier consists of a Hopfield network applied to a square window in which the centre pixel is classified from binary information within the window. Tests are performed using a binary test image corrupted by inverting a percentage of the image pixels. The resulting noisy images simulate the output of a detector using a simple threshold derived from local image statistics. The factors affecting the size of window and the choice of stored patterns are discussed. The results are compared with those obtained from a multi-layer perceptron using a similar approach. The Hopfield network is found to be effective at rejecting the high levels of noise that would result from low-contrast source imagery. Another important feature is that the processed image retains an accurate representation of blood vessel diameter. A neural network classifier for detecting vascular structures in angiograms is developed. The classifier consists of a Hopfield network applied to a square window in which the centre pixel is classified from binary information within the window. Tests are performed using a binary test image corrupted by inverting a percentage of the image pixels. The resulting noisy images simulate the output of a detector using a simple threshold derived from local image statistics. The factors affecting the size of window and the choice of stored patterns are discussed. The results are compared with those obtained from a multi-layer perceptron using a similar approach. The Hopfield network is found to be effective at rejecting the high levels of noise that would result from low-contrast source imagery. Another important feature is that the processed image retains an accurate representation of blood vessel diameter
Orthodontic extraction of mandibular third molar to avoid nerve injury and promote periodontal healing.
Aim: Impacted mandibular third molar extraction is a common procedure in oral surgery, not without risk of nerve injury and periodontal defects on the distal aspect of the adjacent second molar. The "orthodontic extraction" is proposed as a method to avoid mandibular nerve injury during the extraction of a deeply embedded third molar and to prevent or limit such periodontal problems.
Material and Methods: A 28-year-old man presented a deeply impacted left mandibular third molar that required extraction. Radiographs revealed a very slight quantity of bone at the distal surface of the adjacent second molar. The third molar was extruded according to the "orthodontic extraction" technique. A 3-month retention phase elapsed to ensure adequate bone maturation and the tooth was finally extracted.
Results: No neurological complications occurred. A minimal residual bone defect at the distal surface of the adjacent second molar was detected radiographically both post-operatively and at the 3-year follow-up.
Conclusions: Orthodontic extraction makes third molar removal easier and has no neurological risk. This procedure, followed by a 3-month retention phase, appears to be effective in preventing or limiting the development of periodontal problems on the distal aspect of the adjacent second molar
Orthodontic extraction of mandibular third molar to avoid nerve injury and promote periodontal healing
Effectiveness of a Segmental Approach to Climate Policy
Resistance
to adopting a cap on greenhouse gas emissions internationally,
and across various national contexts, has encouraged alternative climate
change mitigation proposals. These proposals include separately targeting
clean energy uptake and demand-side efficiency in individual end-use
sectors, an approach to climate change mitigation which we characterize
as segmental and technology-centered. A debate has ensued on the detailed
implementation of these policies in particular national contexts,
but less attention has been paid to the general factors determining
the effectiveness of a segmental approach to emissions reduction.
We address this topic by probing the interdependencies of segmental
policies and their collective ability to control emissions. First,
we show for the case of U.S. electricity how the set of suitable energy
technologies depends on demand-side efficiency, and changes with the
stringency of climate targets. Under a high-efficiency scenario, carbon-free
technologies must supply 60–80% of U.S. electricity demand
to meet an emissions reduction target of 80% below 1990 levels by
midcentury. Second, we quantify the enhanced propensity to exceed
any intended emissions target with this approach, even if goals are
set on both the supply and demand side, due to the multiplicative
accumulation of emissions error. For example, a 10% error in complying
with separate policies on the demand and supply side would combine
to result in a 20% error in emissions. Third, we discuss why despite
these risks, the enhanced planning capability of a segmental approach
may help counteract growing infrastructural inertia. The emissions
reduction impediment due to infrastructural inertia is significant
in the electricity sectors of each of the greatest emitters: China,
the U.S., and Europe. Commonly cited climate targets are still within
reach but, as we show, would require more than a 50% reduction in
the carbon intensity of new power plants built in these regions over
the next decade