Tor is a network designed for low-latency anonymous communications. Tor clients form circuits through relays that are listed in a public directory, and then relay their encrypted traffic through these circuits. This indirection makes it difficult for a local adversary to determine with whom a particular Tor user is communicating. Tor may also be used to circumvent regional Internet censorship, since the final hop of a user's connection can be in a different country. In response, some local adversaries restrict access to Tor by blocking each of the publicly listed relays. To deal with such an adversary, Tor uses bridges, which are unlisted relays that can be used as alternative entry points into the Tor network. Unfortunately, issues with Tor's bridge implementation make it easy to discover large numbers of bridges. This makes bridges easy to block. Also, an adversary that hoards this information may use it to determine when each bridge is online over time. If a bridge operator also browses with Tor on the same machine, this information may be sufficient to deanonymize him. We present BridgeSPA as a method to mitigate these issues. A client using BridgeSPA relies on innocuous single packet authorization (SPA) to present a time-limited key to a bridge. Before this authorization takes place, the bridge will not reveal whether it is online. We have implemented BridgeSPA as a working proof-of-concept for GNU/Linux systems. The implementation is available under a free licence. We have integrated our implementation to work in an OpenWRT environment. This enables BridgeSPA support for any client behind a deployed BridgeSPA OpenWRT router, no matter which operating system they are running.

Colloid displacement lithography is proving to be very effective in the designing of nanometer scale electronic devices. Precise control of the structure of matter at the nanometer scale has brought a revolutionary change in science and technology. The use of these nanometer scale devices ranges from the diagnosis of various diseases to cell repair to ultra strong materials. This research focused on optimizing the conditions for gold colloid particle adsorption for colloid displacement lithography, an expansion on gold colloid particle manipulation techniques using a scanned probe microscope. The system consists of a scrupulously cleaned glass surface that is coated with poly(diallyldimethylammonium chloride) (PDDA) and then with 5- or 10- nm gold colloid particles. The optimum conditions include the use of very low molecular weight PDDA (Avg MW <100,000 g/mol) or low molecular weight PDDA (Avg MW 100,000-200,000 g/mol) with an exposure time to the glass substrate of 120 to 150 minutes. This is then followed by a 24-hour exposure to the colloid solution. An atomic force microscope (AFM) is used to pattern the thus prepared colloid coated slides. In this work a variety of salts are used as potential blocking agents to prevent or modify the colloid adsorption. These include potassium iodide, potassium bromide, potassium chloride, sodium fluoride, sodiumsulfate, potassium hydrogen phosphate, potassium hydrogen phthalate, and sodium citrate. In summary, the following were found as a result of this work: The optimum conditions that lead to efficient patterning are: Low molecular weight PDDA with a coating time of 120 to 150 minutes. Exposure to 5-nm gold colloid for 24 hours The most interesting potential blocking agents are the phosphate, sulfate and citrate salts, as they show some potential for modifying the adsorption of the gold colloids on the PDDA. The dispersion of the colloid particles on the PDDA does not change when using the potential blocking agents compared to direct adsorption on the unmodified PDDA layer. The use of the potential blocking agents reduces the force required to pattern by a factor of 100 to 300.

Birefringent fibers have attracted considerable attention in recent years for their potential applications in communication and sensing. In this thesis we selectively infiltrate high-index liquids or liquid crystals (LCs) into specified air holes of the photonic crystal fibers (PCFs) by using a selective blocking technique and the vacuum filling method to form half-filled birefringent PCFs and central-filled liquid crystal PCF (LCPCF). We first measure the bending loss of the half-filled PCF. Smaller bending loss was obtained as the PCF was bent in 0¢X due to the dominat index-guiding. Compared with the full-filled PCF, the half-filled PCF possesses a smaller bending loss for the reduction of liquid-filled air holes. The birefringent properties of the half-filled PCF and the LCPCF were then measured in cooperation with the Sagnac fiber loop. We can obtain the birefringence of the half-filled PCF of 2.39¡Ñ10^-4 at £f = 1411 nm, and the sensitivity to temperature, strain, and torsion can be obtained as -0.614 nm/¢XC, 0.466 pm/£g£`, and -0.316 nm/deg. These large sensitivities make the half-filled PCF useful in sensing applications. We also measured the birefringence of the central-filled LCPCF with variant laser irradiation and temperature. The optical and thermal birefringence variations from 2.8¡Ñ10^-3 to 4.12¡Ñ10^-3 and from 2.3¡Ñ10^-3 to 3.3¡Ñ10^-3 can be oberserved, respectively. The optically and thermally tunable birefringence of the central-filled LCPCF was experimentally demonstrated.

Pico-Cellular architecture fully reuses frequency to increase network capacity. However, it will increase the occurance of Handoff due to the small range of cell. Previous works in channel allocations can reduce blocking probability of handoff call, but it may increase blocking probability of new call. As a result, channel utilization is decreased because they can not adapt to network changes. In this thesis, we present a Dynamic Channel Allocation Mechanism with priority support. All channels and calls are divided into high and low priority. If there is no high_priority channel for high_priority call, high_priority call may downgrade its priority by sacrificing some QoS to utilize low_priority channels. We define two new array for network information status, one is next_cell state, and the other is the transition probability. Next_cell state is used to save prior M Cell_Ids where handoff calls may move to. Transition probability is used to save the probabilities for active calls moving to other neighboring cells. According to next_cell state and transition probability, we can accurately predict the probabilities for mobile hosts moving to other neighboring cells. Therefore, we can dynamically adjust bandwidth reservation requests sending to neighboring cells by the latest transition probability and the number of active calls in this cell. We analyze the proposed mechanism through a mathematical model. In the model, we build a four-dimension Markov Chain and use MATLAB[41] tool to evaluate blocking probability, channel throughput and utilization. We found out that blocking probability of handoff call can be decreased and channel utilization can be increased through the proposed channel allocation mechanisms with high and low priority support.

In order to reduce malaria prevalence worldwide, a better understanding of parasite transmission and the effect of drug resistance is needed. The effect of drug resistance on malaria transmission has been examined for some drugs, but not for mitochondrial inhibitors such as atovaquone and the current basis of malaria therapy, artemisinin. Therefore, the goal of this study was to produce gametocytes, the life cycle stage that transmits from mosquito to human, in several different drug resistant patient isolates as well as to determine the effect of drug resistance on gametocyte development and transmission. Previous studies have shown that the mutation that confers resistance to atovaquone, a common antimalarial, occurs de novo after treatment and transmission of this resistance is not seen in the field. Therefore, to determine whether or not the resistance mutation can be transmitted, mosquito-feeding experiments were conducted using atovaquone resistant parasites and resulting oocyst DNA was analyzed. In addition to these atovaquone studies, artemisinin resistant gametocytes were also grown in vitro and drug pressure was added to determine if resistance mechanisms affect gametocyte development. This study is the first examine gametocyte development in these resistant strains and the first to report that transmission of the atovaquone resistant mutation may be possible. However, data is currently inconclusive on the effect of artemisinin resistance on gametocyte development.

Many gas wells suffer a loss in productivity due to liquid accumulation in the near wellbore region. This problem starts as the flowing bottom hole pressure drops below the dew point in wells producing from gas condensate reservoirs. Chemical stimulation may be used as a remedy, by altering the wettability to non-liquid wetting. Successful treatments decrease liquid trapping, increase fluids mobility, and improve the well’s deliverability. The main focus in this research was to develop an effective chemical treatment to mitigate liquid blocking in gas wells producing from carbonate reservoirs. In the initial stages, screening tests were developed to quickly and effectively identify suitable chemicals from a large pool of compounds. X-ray Photoelectron Spectroscopy (XPS) measurements, drop imbibition tests, and contact angle measurements with water and n-decane were found to be necessary but not sufficient indicators of the effectiveness of the chemicals and were used as screening tools. An integral part of the development of the treatment solution was the selection of a solvent mixture capable of delivering the fluorinated chemical to the rock surface. The treatment solution, mixture of chemical dissolved in solvent, must be stable in the presence of both brine and condensate so that it will not precipitate and will not reduce permeability of the rock. Through phase behavior studies the compatibility of the treatment solution and in-situ brines were investigated to reduce the risk of failure in the coreflood experiments. The measured relative permeability values in Texas Cream Limestone and Silurian Dolomite cores are demonstrate from high-pressure, high-temperature coreflood experiments before and after treatment. Measurements were made using a pseudo-steady-state method with synthetic gas-condensate mixtures. To enhance the durability of the treatment a special amine primer is introduced. / text

Many producing volatile oil reservoirs experience a significant decrease in well deliverability when the bottom-hole pressure of the well falls below the bubble point pressure. This is due to the liberation of a gas phase which resides in the pore space and blocks the flow of the oil phase. This situation is known as "gas blocking". This occurs because the presence of two or three immiscible phases (gas, oil and water) results in a reduction of the oil saturation and a decrease in the oil relative permeability. The main objective of this research was to develop an effective and durable chemical treatment method to improve and/or restore the productivity of volatile oil wells undergoing "gas blocking". The treatment method is based on the use of fluorinated surfactants in tailored solvents to increase the oil relative permeability by changing the wettability of the rock’s surface. High-temperature high-pressure (HTHP) core flood experiments were used to evaluate the uses of fluorinated surfactants under reservoir conditions. Analytical tools such as X-ray photoelectron spectroscopy (XPS), high-performance liquid chromatography (HPLC) and computerized axial tomography (CT Scan) were also used to interpret the experimental results. High-pressure high-temperature (HPHT) coreflood tests showed that the treatments improved the oil and gas relative permeability in both sandstone and limestone cores. This was observed for synthetic volatile oil mixtures with gas-oil ratios (GOR) in the range of 4000 to 13,000 scf/STB at low capillary numbers (Nc) on the order of 1x10-5 to 1x10-6 and for PVT ratios greater than 0.5. The fluorinated chemical treatments were effective in the presence of connate water over the temperature range of 155°F to 275°F. Wettability alteration was measured using contact angle and imbibition rate tests. Results from analytical tools showed that fluorinated surfactants were uniformly adsorbed along the core and the surfactant desorption after treatment was low (10 ppm or less). The gas saturation decreased following treatment and both the oil and gas relative permeability increased. Numerical simulations using the measured relative permeability data were used to estimate the gain in productivity for treated wells. The proposed fluorinated chemical treatments could be used as a preventive treatment or for a damaged well that has already been producing below the bubble point to increase oil production rates and recoverable reserves. / text

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No description available.

When a vehicle enters an intersection with insufficient space to exit on the opposite side the result is often the obstruction of pedestrians and other vehicles, this phenomenon is usually referred to as "blocking the box." The purpose of this study was to determine different characteristics of blocking that might be considered in determining the installment of a "Don't Block the Box" (DBTB) campaign. This study identified potentially problematic intersections in Atlanta, Georgia and collected information, such as the number of vehicles that block the intersection (box junction), the amount of green time with blocking, and the percentages in which approaches were blocked. Based on the results it was found the characteristics of the number of blockers, percentage of green time with blocking, and the percentage of lost capacity are excellent indicators for a possible DBTB campaign. Organizations interested in potentially starting a DBTB should consider these characteristics part of the determination of suitability of DBTB for an intersection. Within this study is was found that the intersections of Peachtree Road & Highland Drive, Peachtree Road & Stratford Road, Peachtree Road & Lenox Mall Entrance, and 10th Street & Williams Street showed to be potential candidates for a DBTB campaign in Atlanta, Georgia. During the study period these intersections had high percentages of lost capacity, high number of blocks, and high percentages of green time with blocking. In conjunction with the DBTB data analysis a "DBTB survey" was developed. The objective of this survey was to help gain a better understanding of the current trends in DBTB campaigns around the United States. The "DBTB Survey" received 75 responses from 415 organizations around the nation, a 18.1% response rate. Six (60%) of the ten participants that currently have a DBTB campaign found a sufficient level of improvement in traffic operations and 46 of the total respondents (60%) proclaimed that if DBTB campaigns were shown to be an economical alternative for traffic management they would consider starting one to help congestion and safety.