Large-scale dynamic hydrofracturing, healing and fracture network characterization

Permeability of a rock is a dynamic property that varies spatially and temporally. Fractures provide the most efficient channels for fluid flow and thus directly contribute to the permeability of the system. Fractures usually form as a result of a combination of tectonic stresses, gravity (i.e. lithostatic pressure) and fluid pressures. High pressure gradients alone can cause fracturing, the process which is termed as hydrofracturing that can determine caprock (seal) stability or reservoir integrity. Fluids also transport mass and heat, and are responsible for the formation of veins by precipitating minerals within open fractures. Veining (healing) thus directly influences the rock’s permeability. Upon deformation these closed factures (veins) can refracture and the cycle starts again. This fracturing-healing-refacturing cycle is a fundamental part in studying the deformation dynamics and permeability evolution of rock systems. This is generally accompanied by fracture network characterization focusing on network topology that determines network connectivity. Fracture characterization allows to acquire quantitative and qualitative data on fractures and forms an important part of reservoir modeling. This thesis highlights the importance of fracture-healing and veins’ mechanical properties on the deformation dynamics. It shows that permeability varies spatially and temporally, and that healed systems (veined rocks) should not be treated as fractured systems (rocks without veins). Field observations also demonstrate the influence of contrasting mechanical properties, in addition to the complexities of vein microstructures that can form in low-porosity and permeability layered sequences. The thesis also presents graph theory as a characterization method to obtain statistical measures on evolving network connectivity. It also proposes what measures a good reservoir should have to exhibit potentially large permeability and robustness against healing. The results presented in the thesis can have applications for hydrocarbon and geothermal reservoir exploration, mining industry, underground waste disposal, CO2 injection or groundwater modeling.

Does residential dissonance impact residential mobility?

This research identifies residential mobility behaviour impacts of residential dissonance in Transit Oriented Developments (TODs) vs. non-TODs in Brisbane, Australia. Based on the characteristics of living environments (density, diversity, connectivity, and accessibility) and the travel preferences of 4545 individuals, respondents in 2009 were classified into one of four categories including: TOD consonants, TOD dissonants, non-TOD dissonants, and non-TOD consonants. Binary logistic regression analyses were employed to identify residential mobility behaviour of groups between 2009 and 2011; controlling for time varying covariates. The findings show that both TOD dissonants and TOD consonants move residences at an equal rate. However, TOD dissonants are more likely to move residences to their preferred non-TOD areas. In contrast, non-TOD dissonants not only moved residences at a lower rate, but their rate of mobility to their preferred TOD neighbourhood is also significantly lower due to costs and other associated factors. The findings suggest that discrete land use policy development is required to integrate non-TOD dissonant and TOD dissonant behaviours to support TOD development in Brisbane.

Networked livecoding at VL/HCC 2013

Network connectivity offers the potential for a group of musicians to play together over the network. This paper describes a trans-Atlantic networked musical livecoding performance between Andrew Sorensen in Germany (at the Schloss Daghstuhl conference on Collaboration and Learning through Live Coding) and Ben Swift in San Jose (at YL/HCC) in September 2013. In this paper we describe the infrastructure developed to enable this performance.

Effect of antimony addition on the thermal and electrical-switching behavior of bulk Se-Te glasses

The thermal properties and electrical-switching behavior of semiconducting chalcogenide SbxSe55-xTe45 (2 <= x <= 9) glasses have been investigated by alternating differential scanning calorimetry and electrical-switching experiments, respectively. The addition of Sb is found to enhance the glass forming tendency and stability as revealed by the decrease in non-reversing enthalpy Delta H-nr. and an increase in the glass-transition width Delta T-g. Further, the glass-transition temperature of SbxSe55-xTe45 glasses, which is a measure of network connectivity, exhibits a subtle increase, suggesting a meager network growth with the addition of Sb. The crystallization temperature is also observed to increase with Sb content. The SbxSe55-xTe45 glasses (2 <= x <= 9) are found to exhibit memory type of electrical switching, which can be attributed to the polymeric nature of network and high devitrifying ability. The metallicity factor has been found to dominate over the network connectivity and rigidity in the compositional dependence of switching voltage. which shows a profound decrease with the addition of Sb.

A composition dependent thermal behavior of GexSe35-xTe65 glasses

Alternating differential scanning calorimetric (ADSC) studies have been performed to understand the thermal behavior of bulk GexSe35-xTe65 glasses (17 <= x <= 25); it is found that the glasses with x <= 20 exhibit two crystallization exotherms (T-c1 & T-c2). On the other hand, those with x >= 20.5, show a single crystallization reaction upon heating. The exothermic reaction at T-c1 has been found to correspond to the partial crystallization of the glass into hexagonal Te and the reaction at T-c2 is associated with the additional crystallization of rhombohedral Ge-Te phase. The glass transition temperature of GexSe35-xTe65 glasses is found to show a linear but not-steep increase, indicating a progressive, but a gradual increase in network connectivity with Ge addition. It is also found that T-c1 of GexSe35-xTe65 glasses with x <= 20, increases progressively with Ge content and eventually merges with T-c2 at x approximate to 20.5 (< r > = 2.41); this behavior has been understood on the basis of the reduction in Te-Te bonds of lower energy and increase in Ge-Te bonds of higher energy, with increasing Ge content. Apart from the interesting composition dependent crystallization, an anomalous melting behavior is also exhibited by the GexSe35-xTe65 glasses.

High field electrical switching behavior of Ge10Se90-xTlx glasses

Electrical Switching Studies on bulk Ge10Se90-xTlx ( 15 <= x <= 34) glasses have been undertaken to examine the type of switching, composition and thickness dependence of switching voltages. Unlike Ge-Se-Tl thin films which exhibit memory switching, the bulk Ge10Se90-xTlx glasses are found to exhibit threshold type switching with fluctuations seen in their current-voltage (I-V) characteristics. Further, it is observed that the switching voltages (V-T) of Ge10Se90-xTlx glasses decrease with the increase in the Tl concentration. An effort has been made to understand the observed composition dependence on the basis of nature of bonding of Tl atoms and a decrease in the chemical disorder with composition. In addition. the network connectivity and metallicity factors also contribute for the observed decrease in the switching voltages of Ge10Se90-xTlx glasses with Tl addition. It is also interesting to note that the composition dependence of switching voltages of Ge10Se90-xTlx glasses exhibit a small Cusp around the composition x = 22. which is understood on the basis of a thermally reversing window in this system in the composition range 22 <= x <= 30. The thickness dependence of switching voltages has been found to provide an insight about the type of switching mechanism involved in these samples. (C) 2009 Elsevier B.V. All rights reserved

Electrical switching behavior of bulk Si15Te85-xSbx chalcogenide glasses - A study of compositional dependence

Studies on the electrical switching behavior of melt quenched bulk Si15Te85-xSbx glasses have been undertaken in the composition range (1 <= x <= 10), in order to understand the effect of Sb addition on the electrical switching behavior of Si15Te85-x base glass. It has been observed that all the Si15Te85-xSbx glasses studied exhibit a smooth memory type switching. Further, the switching voltages are found to decrease almost linearly with Sb content, which indicates that the metallicity of the dopant plays a dominant role in this system compared to network connectivity/rigidity. The thickness dependence of switching voltage (V-th) indicates a clear thermal origin for the switching mechanism. The temperature variation of switching voltages reveals that the Si15Te85-xSbx glasses studied have a moderate thermal stability. (C) 2009 Elsevier B.V. All rights reserved.

Observation of a thermally reversing window in bulk Ge15Te85-xInx glasses

Alternating differential scanning calorimetry measurements have been undertaken on the Ge15Te85-xInx (1 <= x <= 11) series of glasses. It is found that there is a marginal decrease in the glass transition temperature (T-g) in the composition range 1 <= x <= 3. Above x = 3, a monotonic increase is seen in T-g which indicates a continuous build-up in network connectivity and absence of any nanophase separation. The non-reversing heat flow (Delta H-NR) has been found to exhibit a broad trough between the compositions x = 3 and 7, which clearly indicates the presence of a thermally reversing window in Ge15Te85-xInx glasses in the composition range 3 <= x <= 7.

Electrical switching and thermal studies on bulk Ge-Te-Bi glasses

Bulk, melt quenched Ge18Te82-xBix glasses (1 <= x <= 4) have been found to exhibit memory type electrical switching behavior, which is in agreement with the lower thermal diffusivity values of Ge-Te-Bi samples. A linear variation in switching voltages (V-th) has been found in these samples with increase in thickness which is consistent with the memory type electrical switching. Also, the switching voltages have been found to decrease with an increase in temperature which happens due to the decrease in the activation energy for crystallization at higher temperatures. Further. V-th of Ge18Te82-xBix glasses have been found to decrease with the increase in Bi content, indicating that in the Ge-Te-Bi system, the resistivity of the additive has a stronger role to play in the composition dependence of V-th, in comparison with the network connectivity and rigidity factors. In addition, the composition dependence of crystallization activation energy has been found to show a decrease with an increase in Bi content, which is consistent with the observed decrease in the switching voltages. X-ray diffraction studies on thermally crystallized samples reveal the presence of hexagonal Te, GeTe, Bi2Te3 phases, suggesting that bismuth is not taking part in network formation to a greater extent, as reflected in the variation of switching voltages with the addition of Bi. SEM studies on switched and un-switched regions of Ge-Te-Bi samples indicate that there are morphological changes in the switched region, which can be attributed to the formation of the crystalline channel between two electrodes during switching. (C) 2010 Elsevier B.V. All rights reserved.

Electrical switching studies on Ge-Te-Tl chalcogenide glasses: Effect of thallium on the composition dependence of switching voltages

Bulk Ge(17)Te83_,JI glasses (05x.5_13), have been found to exhibit memory type electrical switching. The switching voltages (also known as threshold voltage V-th) of Ge17Te83-xTlx glasses are found to decrease with increasing thallium content. The rate of decrease of Vtry is greater at lower concentrations and \textbackslashid, falls at a slower rate for higher thallium concentrations (x 6). The addition of thallium to the Ge-Te network fragments the covalent network and introduces ionic nature to it; the reduction in network connectivity leads to the decrease in switching voltages with thallium content. The decrease in the glass transition temperatures of Ge17Te83-xTlx glasses with increasing thallium concentration supports the idea of decrease in network connectivity with TI addition. The more metallic nature of TI also contributes to the observed reduction in the switching voltages of Ge17Te83-xTlx glasses with TI content. Further, there is an interesting correlation seen between the threshold voltage V-th and the average bond energy, as a function of TI content. In addition, the switching voltages of Ge17Te83-xTlx glasses have been found to decrease with sample thickness almost linearly. The set-reset studies indicate that the Ge17Te83-xTl2 sample can be switched for more than 10 cycles, whereas other glasses could not be reset beyond two switching cycles. (C) 2010 Elsevier B.V. All rights reserved.

Thermodynamic, kinetic and electrical switching studies on Si(15)Te(85-x)In(x) glasses: Observation of Boolchand intermediate phase

An interesting topic for quite some time is an intermediate phase observed in chalcogenide glasses, which is related to network connectivity and rigidity. This phenomenon is exhibited by Si-Te-In glasses also. It has been addressed here by carrying out detailed thermal investigations by using Alternating Differential Scanning Calorimetry technique. An effort has also been made to determine the stability of these glasses using the data obtained from different thermodynamic quantities and crystallization kinetics of these glasses. Electrical switching behavior by recording I-V characteristics and variation of switching voltages with indium composition have been studied in these glasses for phase change memory applications. (C) 2011 Elsevier Inc. All rights reserved.

The electrical switching and thermal behavior of bulk Ge(15)Te(85-x)Sn(x) and Ge(17)Te(83-x)Sn(x) glasses

Bulk Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses, are found to exhibit memory type electrical switching. The switching voltages (V(t)) and thermal stability of Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses are found to decrease with Sn content. The composition dependence of v, has been understood on the basis of the decrease in the OFF state resistance and thermal stability of these glasses with tin addition. X-ray diffraction studies reveal that no elemental Sn or Sn compounds with Te or Ge are present in thermally crystallized Ge-Te-Sn samples. This indicates that Sn atoms do not interact with the host matrix and form a phase separated network of its own, which remains in the parent glass matrix as an inclusion. Consequently, there is no enhancement of network connectivity and rigidity. The thickness dependence of switching voltages of Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses is found to be linear, in agreement with the memory switching behavior shown by these glasses. (C) 2011 Elsevier B.V. All rights reserved.

Electrical switching and optical studies on amorphous GexSe35-xTe65 thin films

The electrical switching behavior of amorphous GexSe35-xTe65 thin film samples has been studied in sandwich geometry of electrodes. It is found that these samples exhibit memory switching behavior, which is similar to that of bulk Ge-Se-Te glasses. As expected, the switching voltages of GexSe35-xTe65 thin film samples are lower compared to those of bulk samples. In both thin film amorphous and bulk glassy samples, the switching voltages are found to increase with the increase in Ge concentration, which is consistent with the increase in network connectivity with the addition of higher coordinated Ge atoms. A sharp increase is seen in the composition dependence of the switching fields of amorphous GexSe35-xTe65 films above x = 21, which can be associated with the stiffness transition. Further, the optical band gap of a-GexSe35-x Te-65 thin film samples, calculated from the absorption spectra, is found to show an increasing trend with the increase in Ge concentration, which is consistent with the variation of switching fields with composition. The increase in structural cross-linking with progressive addition of 4-fold coordinated Ge atoms is one of the main reasons for the observed increase in switching fields as well as band gaps of GexSe35-xTe65 samples. (C) 2011 Elsevier B.V. All rights reserved.

Electrical switching behavior of amorphous Ge15Te85 Si--x(x) thin films with phase change memory applications

Amorphous Ge15Te85-xSix thin film switching devices (1 <= x <= 6) have been deposited in sandwich geometry, on glass substrates with aluminum electrodes, by flash evaporation technique. These devices exhibit memory type electrical switching, like bulk Ge15Te85-xSix glasses. However, unlike the bulk glasses, a-Ge15Te85-xSix films exhibit a smooth electrical switching behavior. The electrical switching fields of a-Ge15Te85-xSix thin film samples are also comparable with other chalcogenide samples used in memory applications. The switching fields of a-Ge15Te85-xSix films have been found to increase with increasing Si concentration. Also, the optical band gap of a-Ge15Te85-xSix films is found to increase with Si content. The observed results have been understood on the basis of increase in network connectivity and rigidity with Si addition. (C) 2013 Elsevier Ltd. All rights reserved.

Prosocial behavior and gender

This study revisits different experimental data sets that explore social behavior in economic games and uncovers that many treatment effects may be gender-specific. In general, men and women do not differ in "neutral" baselines. However, we find that social framing tends to reinforce prosocial behavior in women but not men, whereas encouraging reflection decreases the prosociality of males but not females. The treatment effects are sometimes statistically different across genders and sometimes not but never go in the opposite direction. These findings suggest that (i) the social behavior of both sexes is malleable but each gender responds to different aspects of the social context; and (ii) gender differences observed in some studies might be the result of particular features of the experimental design. Our results contribute to the literature on prosocial behavior and may improve our understanding of the origins of human prosociality. We discuss the possible link between the observed differential treatment effects across genders and the differing male and female brain network connectivity, documented in recent neural studies.