Multifunctional foams and emulsions for subsurface applications

Foams and emulsions hold immense potential in assisting in the different stages of oil recovery processes such as enhanced oil recovery, drilling, and completion. This work is focused on developing robust, multifunctional foams or emulsions for subsurface applications, which offer unique advantages over conventional methods. The first half of the dissertation is focused on investigating novel foams stabilized using nanoparticles and/or surfactants to improve the gas enhanced oil recovery process. Gas flooding often has poor volumetric sweep efficiency due to viscous fingering, channeling, and gravity override. Foam is a promising tool to improve sweep efficiency in gas floods. It can reduce the mobility of gas by several orders of magnitude by increasing its apparent viscosity while keeping the liquid phase mobility unchanged. For sandstone reservoirs, which are typically water-wet in nature, two different approaches of foam stabilization using nanoparticles were developed. In the first approach, synergistic stabilization of foams with a mixture of hydrophilic nanoparticles and an anionic surfactant was investigated. Foam stability experiments in bulk and porous media tests showed that adding hydrophilic nanoparticles to surfactant formulations increases the foam stability. Microscopy revealed that nanoparticles are trapped in lamellae as well as at the Gibbs-Plateau borders. These nanoparticles act as physical barriers and retard the liquid drainage and the Ostwald ripening process. To fundamentally understand the role of nanoparticles in altering the foam dynamics in porous media, a high-pressure visualization experiment was performed in a 2D layered, heterogeneous porous media. This experiment showed that immiscible foams can result in significant incremental oil recovery of 25% to 34% OOIP (over waterflood). In the second approach, foam stabilized using in-situ surface-activated nanoparticles without any surfactant was explored as an EOR agent. The surface chemistry of the hydrophilic nanoparticles was tailored by adsorption of a small amount of short-chain surface modifiers to obtain surface-modified nanoparticles (SM-NP). Foam stabilization using these SM-NP was compared with that using a conventional surfactant to evaluate the potential of these SM-NP to act as an effective foaming agent. Carbonate reservoirs, which are typically highly heterogeneous and oil-wet in nature, pose additional challenges for an effective foam EOR process. Crude oils are typically detrimental to foam stability. An oil-wet carbonate will have a thin oil film on the surface and thus foam lamellae stabilization is challenging. Therefore, wettability-alteration of rock matrix toward water-wet condition using a surfactant is required to favor the in-situ foam stability. This work demonstrated for the first time a synergistic approach of using foams with wettability-altering capabilities for oil-wet systems. It was shown that optimal surfactant formulations can not only alter the wettability of a carbonate core from oil-wet to water-wet conditions, but also can significantly increase the in-situ foam stability even in presence of crude oil. The second half of the dissertation is focused on developing novel microencapsulation techniques using the concept of water-in-air powders for subsurface applications. A facile, one-step method was reported to encapsulate micro- or nano-sized hydrophilic particles using silica nanoparticles. The encapsulated particles can be released based on an external stimulus, such as a change in pH of the external continuous phase. The use of this novel carrier system was demonstrated for the delayed release of PPG particles for conformance control. The application of this technology was then explored for microencapsulating highly concentrated acids (~10 wt.% HCl) for acid treatment of shales. The advantages of these novel acid-in-air powders over conventional acid-in-oil emulsions (which are typically used for shale acidization processes) were illustrated in terms of the thermal stability, corrosion inhibition efficiency, and shale surface reactivity.Petroleum and Geosystems Engineerin

A comprehensive optimization methodology for strategic environmental sensor station locations

textAdverse weather poses a significant threat to transportation safety. Road weather information systems (RWIS) aim to mitigate the impact of adverse weather by detecting spatiotemporal variations of weather and/or road pavement conditions in real time. Due to the lack of a detailed, unified guideline and diverse weather conditions across the United States, state and city transportation agencies follow different practices for choosing locations for environmental sensor stations (ESS) (the components that collect RWIS weather data). To fill this gap, this study proposes a comprehensive cell-based methodology that is data-driven, using crash records, weather data, and road network information. The contribution of the proposed methodology is that the model optimizes overall benefits derived from RWIS based on weather-sensitive crashes. Both normal and adverse weather crash data are used to derive cell-vulnerability rates in adverse weather. First, a sequential procedure is devised to identify the required number of stations for the region. Then, optimal weather station locations are identified using a genetic algorithm. The proposed approach is especially suited for optimizing region-wide ESS locations involving complex road networks or a large number of road segments. A case study was conducted using data from the Crash Records Information System (CRIS) between 2010 and 2013 in the Austin District, an area especially vulnerable to rain. It was found in the case study that ten ESSs would be a good choice to implement in the region. Their proposed global optimal locations layout would cover 94% of total crashes occurring in the region based on 20 miles of coverage for each station. The RWIS would have spatial coverage of 48% and 92% reliability should one ESS fail.Civil, Architectural, and Environmental Engineerin

Emission Characteristics of the Projectile Fragments at Relativistic Energy

A projectile (84^Kr_36) having kinetic energy around 1 A GeV was used to expose NIKFI BR-2 emulsion target. A total of 700 inelastic events are used in the present studies on projectile fragments. The emission angle of the projectile fragments are strongly affected by charge of the other projectile fragments emitted at same time with different emission angle is observed. The angular distribution studies show symmetrical nature for lighter charge projectile fragments. The symmetrical nature decreased with the charge of projectile fragments. At ~4o of emission angle for double charge projectile fragments, the momentum transfer during interaction is similar for various target species of emulsion were observed. We also observed a small but significant amplitude peaks on both side of the big peak for almost all light charge projectile fragments having different delta angle values. It reflects that there are few percent of projectile fragments that are coming from the decay of heavy projectile fragments or any other process.Comment: 32 pages, 17 Figure

Influence of carbon and nitrogen on electronic structure and hyperfine interactions in fcc iron-based alloys

Carbon and nitrogen austenites, modeled by Fe8N and Fe8C superstructures are studied by full-potential LAPW method. Structure parameters, electronic and magnetic properties as well as hyperfine interaction parameters are obtained. Calculations prove that Fe-C austenite can be successfully modeled by ordered Fe8C superstructure. The results show that chemical Fe-C bond in Fe8C has higher covalent part than in Fe8N. Detailed analysis of electric field gradient formation for both systems is performed. The calculation of electric field gradient allow us to carry out a good interpretation of Moessbauer spectra for Fe-C and Fe-N systems.Comment: 8 pages, 3 figures, IOP-style LaTeX, submitted to J. Phys. Condens. Matte

HH-IPG: Leveraging Inter-Packet Gap Metrics in P4 Hardware for Heavy Hitter Detection

The research community has recently proposed several solutions based on modern programmable switches to detect entirely in the data plane the flows exceeding pre-determined thra eshold in a time window, i.e., Heavy Hitters (HH). This is commonly achieved by dividing the network stream into fixed time slots and identifying each separately without considering the traffic trends from previous intervals. In this work, we show that using specified time windows can lead to high inaccuracies. We make a case for rethinking how switches analyze the incoming packets and propose to leverage per-flow Inter Packet Gap (IPG) analytics instead of using flow counters for HH detection. We propose an algorithm and present a P4 pipeline design using this new metric in mind. We implement our solution on P4 hardware and experimentally evaluate it against real traffic traces. We show that our results are more accurate than related work by up to 20% while reducing the control channel overhead by up to two orders of magnitude. Finally, we showcase a QoS-oriented application of the proposed dataplane-only IPG-based HH detection in a mobile network scenario

Factors controlling tropospheric O3, OH, NOx, and SO2 over the tropical Pacific during PEM-Tropics B

Observations over the tropical Pacific during the Pacific Exploratory Mission (PEM)-Tropics B experiment (March-April 1999) are analyzed. Concentrations of CO and long-lived nonmethane hydrocarbons in the region are significantly enhanced due to transport of pollutants from northern industrial continents. This pollutant import also enhances moderately O3 concentrations but not NOx concentrations. It therefore tends to depress OH concentrations over the tropical Pacific. These effects contrast to the large enhancements of O3 and NOx concentrations and the moderate increase of OH concentrations due to biomass burning outflow during the PEM-Tropics A experiment (September-October 1996). Observed CH3I concentrations, as in PEM-Tropics A, indicate that convective mass outflux in the middle and upper troposphere is largely independent of altitude over the tropical Pacific. Constraining a one-dimensiohal model with CH3I observations yields a 10-day timescale for convective turnover of the free troposphere, a factor of 2 faster than during PEM-Tropics A. Model simulated HO2, CH2O, H2O2, and CH3OOH concentrations are generally in agreement with observations. However, simulated OH concentrations are lower (∼25%) than observations above 6 km. Whereas models tend to overestimate previous field measurements, simulated HNO3 concentrations during PEM-Tropics B are too low (a factor of 2-4 below 6 km) compared to observations. Budget analyses indicate that chemical production of O3 accounts for only 50% of chemical loss; significant transport of O3 into the region appears to take place within the tropics. Convective transport of CH3OOH enhances the production of HOx and O3 in the upper troposphere, but this effect is offset by HOx loss due to the scavenging of H2O2. Convective transport and scavenging of reactive nitrogen species imply a necessary source of 0.4-1 Tg yr-1 of NOx in the free troposphere (above 4 km) over the tropics. A large fraction of the source could be from marine lightning. Oxidation of DMS transported by convection from the boundary layer could explain the observed free tropospheric SO2 concentrations over the tropical Pacific. This source of DMS due to convection, however, would imply in the model free tropospheric concentrations much higher than observed. The model overestimate cannot be reconciled using recent kinetics measurements of the DMS-OH adduct reaction at low pressures and temperatures and may reflect enhanced OH oxidation of DMS during convection. Copyright 2001 by the American Geophysical Union

Fully gapped superconductivity in Ni-pnictide superconductors BaNi2As2 and SrNi2P2

We have performed low-temperature specific heat $C$ and thermal conductivity $\kappa$ measurements on the Ni-pnictide superconductors BaNi$_2$As$_2$ ($T_\mathrm{c}$=0.7 K and SrNi$_2$P$_2$ ($T_\mathrm{c}$=1.4 K). The temperature dependences $C(T)$ and $\kappa(T)$ of the two compounds are similar to the results of a number of s-wave superconductors. Furthermore, the concave field responses of the residual $\kappa$ for BaNi$_2$As$_2$ rules out the presence of nodes on the Fermi surfaces. We postulate that fully gapped superconductivity could be universal for Ni-pnictide superconductors. Specific heat data on Ba$_{0.6}$La$_{0.4}$Ni$_2$As$_2$ shows a mild suppression of $T_\mathrm{c}$ and $H_\mathrm{c2}$ relative to BaNi$_2$As$_2$.Comment: 5 pages, 3 figures, to be published in J. Phys.: Conf. Se

Risk stratification of cardiovascular patients using a novel classification tree induction algorithm with non-symmetric entropy measures

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 95-100).Risk stratification allows clinicians to choose treatments consistent with a patient's risk profile. Risk stratification models that integrate information from several risk attributes can aid clinical decision making. One of the technical challenges in developing risk stratification models from medical data is the class imbalance problem. Typically the number of patients that experience a serious medical event is a small subset of the entire population. The goal of my thesis work is to develop automated tools to build risk stratification models that can handle unbalanced datasets and improve risk stratification. We propose a novel classification tree induction algorithm that uses non-symmetric entropy measures to construct classification trees. We apply our methods to the application of identifying patients at high risk of cardiovascular mortality. We tested our approach on a set of 4200 patients who had recently suffered from a non-ST-elevation acute coronary syndrome. When compared to classification tree models generated using other measures proposed in the literature, the tree models constructed using non-symmetric entropy had higher recall and precision. Our models significantly outperformed models generated using logistic regression - a standard method of developing multivariate risk stratification models in the literature.by Anima Singh.S.M

Controlled synthesis and characterization of templated, magneto-responsive nanoparticle structures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2006.Includes bibliographical references.Magnetic fluids are colloidal dispersions of magnetic nanoparticles that are stable with respect to gravitational and moderate magnetic fields because of their small particle size, and to unbounded aggregation due to their surface coatings. The interaction between individual magnetic nanoparticles in a suspension is negligible even under applied magnetic fields. However, when they are incorporated into composite structures they act in concert to provide the desired magnetic response. The dynamic response of such composite structures can be exploited in a wide range of applications including high energy absorption scenarios. The goal of this thesis was to use magnetic nanoparticles as building blocks to create 3D magneto-responsive nanostructures and manipulate their behavior in the presence of an external magnetic field for various applications. Two approaches were followed to create composite structures. In the first approach, rigid magnetic chains composed of magnetic nanoparticles were synthesized. The layer-by-layer technique was used to coat polystyrene beads with magnetic nanoparticles to create novel core-shell structures. The behavior of these structures under an applied magnetic field was modeled and the results were verified experimentally.(cont.) These magnetic polystyrene beads were then aligned within a microchannel by an external magnetic field and linked together using sol gel chemistry to yield rigid superparamagnetic chains. Linking the magnetically aligned beads with a flexible linker yielded flexible superparamagnetic chains. These permanently-linked magnetic chains can be used as micro-mixers in a microfluidic channel under a rotating magnetic field. The reorientation dynamics of these chains under an external magnetic field was modeled. Microcontact printing was employed to tether the flexible chains in a desired pattern on a glass surface. Tethered flexible magnetic chains have potential applications in microfluidics and separations. Rings and icosahedra shaped electrostatically charged templates were generated from the self-assembly of mixtures of surfactants in an aqueous solution and were investigated for their application in the synthesis of non-spherical magnetic structures. The magnetic response of the magnetic rings was modeled and the results were verified experimentally. "Templateless" aggregation of magnetic nanoparticles using radiation crosslinking was also investigated.(cont.) Aqueous magnetic nanoparticles stabilized with a radiation crosslinkable polymer resulted in magnetic gels at high dosage amount of the ionizing radiation. Magnetic gels can have potential applications in biological areas. Different size monodisperse magnetic nanoparticles were synthesized via an organic synthesis route, and the effect of size on the Nel relaxation behavior of the fixed magnetic nanoparticles was investigated. Theoretical analysis suggested that incorporation of magnetic nanoparticles with high relaxation times in a matrix can be used to absorb energy. The energy penalty associated with the deflection of the magnetic dipole against the field should result in the stiffening of the matrix. This was demonstrated both experimentally and theoretically. Drop ball impact test was performed on foam embedded with infinite Nel relaxation nanoparticles and the deflection profile of the foam was monitored both in the presence and in the absence of a magnetic field. The deflection of the foam by the ball was modeled to calculate the strain profile developed by the foam, which was then converted into the equivalent amount of energy absorbed by the foam and the magnetic nanoparticles.(cont.) A method of electrospinning was used to encapsulate magnetic nanoparticles in a polymeric matrix to create field responsive nanofibers for various applications. The magnetization properties of the nanofibers were also characterized and their behavior under an applied magnetic field was modeled.by Harpreet Singh.Ph.D