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The concept of 3D proteomics is a technique that couples chemical cross-linking with mass spectrometry and has emerged as a tool to study protein conformations and protein-protein interactions. In this thesis I present my work on improving the analytical workflow and developing applications for 3D proteomics in the structural analysis of proteins and protein complexes through four major tasks. I. As part of the technical development of an analytical workflow for 3D proteomics, a cross-linked peptide library was created by cross-linking a mixture of synthetic peptides. Analysis of this library generated a large dataset of cross-linked peptides. Characterizing the general features of cross-linked peptides using this dataset allowed me to optimize the settings for mass spectrometric analysis and to establish a charge based enrichment strategy for cross-linked peptides. In addition to this, 1185 manually validated high resolution fragmentation spectra gave an insight into general fragmentation behaviours of cross-linked peptides and facilitated the development of a cross-linked peptide search algorithm. II. The advanced 3D proteomics workflow was applied to study the architecture of the 670 kDa 15-subunit Pol II-TFIIF complex. This work established 3D proteomics as a structure analysis tool for large multi-protein complexes. The methodology was validated by comparing 3D proteomics analysis results and the X-ray crystallographic data on the 12-subunit Pol II core complex. Cross-links observed from the Pol II–TFIIF complex revealed interactions between the Pol II and TFIIF at the peptide level, which also reflected the dynamic nature of Pol II-TFIIF structure and implied possible Pol II conformational changes induced by TFIIF binding. III. Conformational changes of flexible protein molecules are often associated with specific functions of proteins or protein complexes. To quantitatively measure the differences between protein conformations, I developed a quantitative 3D proteomics strategy which combines isotope labelling and cross-linking with mass spectrometry and database searching. I applied this approach to detect in solution the conformational differences between complement component C3 and its active form C3b in solution. The quantitative cross-link data confirmed the previous observation made by X-ray crystallography. Moreover, this analysis detected the spontaneous hydrolysis of C3 in both C3 and C3b samples. The architecture of hydrolyzed C3-C3(H2O) was proposed based on the quantified cross-links and crystal structure of C3 and C3b, which revealed that C3(H2O) adopted the functional domain arrangement of C3b. This work demonstrated that quantitative 3D proteomics is a valuable tool for conformational analysis of proteins and protein complexes. IV. Encouraged by the achievements in the above applications with relatively large amounts of highly purified material, I explored the application of 3D proteomics on affinity purified tagged endogenous protein complexes. Using an on-beads process which connected cross-linking and an affinity purification step directly, provided increased sensitivity through minimized sample handling. A charge-based enrichment step was carried out to improve the detection of cross-linked peptides. The occurrence of cross-links between complexes was monitored by a SILAC based control. Cross-links observed from low micro-gram amounts of single-step purified endogenous protein complexes provided insights into the structural organization of the S. cerevisiae Mad1-Mad2 complex and revealed a conserved coiled-coil interruption in the S. cerevisiae Ndc80 complex. With this endeavour I have demonstrated that 3D proteomics has become a valuable tool for studying structure of proteins and protein complexes.

This thesis has presented research work carried out searching for an automated measurement technique for the kinetics of chemical reactions in ionic liquids. The aim has been to develop a microchannel reactor system (MCR) to allow reaction kinetics measurement, involving mixing, reaction and sampling, in a single chip rapidly, automatically and accurately. The difficulty of mixing ionic liquids on a microchannel system etched on a chip resulted from two problems; the high viscosity of the liquids together with the low diffusivity of reactant molecules within them, and the small feature size and hence low Reynolds number of flows in microchannels. In order to achieve a mixing time that is negligible compared to the reaction duration, special measures must be taken to accelerate the mixing process. As a result, different mixing schemes were discussed in the thesis, with CFD computations and experimental work. Comparisons were made between different types of mixers involving both their mixing uniformity and pressure drop. The conclusion drawn from the study has been that the folding network mixer was the most effective, and thus it was used in the reaction network of the MCR system. The MCR system (Mark I) has been designed and constructed by selecting and assembling apparatus for the control of pressure, fluid flow, product sampling and analysis. A programme was developed to control the sequence and time scale of each operation, and models are developed for the determination of operating procedure and conditions. Furthermore, measurement techniques were developed for the determination of fluid flow, measurement of species composition and assessment of mixing performance. To assess the system performance, a series of tests have been carried out with a non-reacting solution system, and in addition, kinetics measurement in ionic liquids have been attempted. Drawbacks have been found in the apparatus' behaviour and control technique. Further improvements have then been made on the design and operation of the system. Consequently, the Mark 11 design of the MCR system has been presented, of which a new reaction network was proposed and fabricated, and a set of modified procedures and conditions was presented. With the improved system performance and operating conditions, good repeatability of kinetics measurement has been achieved. The deviation of measurement of reaction kinetics with the MCR system (Mark 11) was estimated to be within 5%.

The places we live, study, and work have major impacts on our health. Except for some diseases that are caused by genetic defects, most of the diseases can be prevented by avoiding exposure to detrimental environments and maintaining a healthy lifestyle, which is highly determined by the built environment in our neighborhood. Thus, measuring the built environment and identifying its health-related elements become important for public health policy and urban planning. Conventional measurement such as questionnaire surveys, however, is time-consuming and not cost-effective. With the state-of-art deep learning and computer vision technology, combined with imagery-based spatial data, we have new opportunities for examining neighborhood health and built environment effectively at a large scale. This dissertation develops and demonstrates the effectiveness of identifying built environment features using deep convolutional neural networks (DCNN). The DCNN-extracted deep features of satellite images and street views show promising performance in modeling the prevalence of obesity at the census tract level. The important deep features that contribute to obesity modeling are identified from the heatmap in the images, including the pavement of roads, decent residential buildings, and amusement parks. The correlation analysis with conventional datasets also suggests that these DCNN-extracted deep features can capture the environment and socioeconomic factors such as PM2.5, employment, poverty, and income. In addition to the public health sector, the research also contributes to the communities of the general public, policymakers, and researchers, by providing a new effective way of analyzing the built environment.

CdZnTe (CZT) detector technology using pixelated anodes is a promising alternative to High-purity Germanium (HPGe) detectors in gamma-ray spectroscopy. Our research group at the University of Michigan has demonstrated that these 3-dimensional positions sensitive (3-D) CZT detectors can achieve close to HPGe energy resolution at room temperatures. Aside from the energy resolution, the detection efficiency is also of great importance. The efficiency characteristics of CZT detector using Integrated Detector Electronics AS (IDEAS) VAS/TAT ASIC system and Brookhaven National Laboratory (BNL)’s analog ASIC have been investigated previously, and the first half of this work focused on the efficiency characteristics of the latest digital ASIC-based CZT detector systems. The intrinsic detection efficiency of a 20mm×20mm×15mm CZT detector from 59 keV to 2614 keV was measured and compared with simulation results. A detailed simulation package modelling the physical processes, digital readout electronics and event reconstruction has been developed to explain the mismatch between measurements and simulations, in order to diagnose the cause of the efficiency deficit. Several efficiency loss mechanisms are revealed. The efficiency loss due to the guard ring and anode side inaccurate reconstruction are the most important factors. Other miscellaneous efficiency loss mechanisms were investigated too. This study presents the most accurate efficiency benchmark experiment on the digital ASIC-based CZT detector. It is the first in-depth study on the efficiency response of 3-D CZT detectors, including near pixel effects. The hardware design of current detectors are based on the concept of “system on board”. The discrete electrical components are integrated on the board-level. The dimension of the assembled systems and the overall power consumption are usually not optimal. With careful engineering, the disadvantages of ”system-on-board” can be minimized, but after all, these hardware are not tailored to the specific application. The room for further improvement and optimization are limited. Similar to how any modern technologies evolve, the constant desire to increase the performance, decrease the physical dimension and reduce the power consumption require higher-level integration. The “system-on-chip” (SoC), where components are integrated on a single silicon die, becomes the most suitable solution for the next-generation radiation detector. A back-end data processing SoC for 3-D CZT detector has been designed at University of Michigan (UM) and named as the DAQ/DSP ASIC. The SoC methodology provides the convenience to combine different circuit and processing functionalities together on a single piece of silicon, therefore provides extra room for power-performance-area (PPA) improvement. The area of the final silicon die is 4.32mm×4.32mm and it is packaged into a 60-pin QFN package. An ASIC design workflow and the script system were built around various design software programs. The workflow covers the full life cycle of the ASIC design and can be used in the future projects. Two hardware platforms and a data acquisition software are developed to test the fabricated DAQ/DSP ASIC. Several problems have been identified during the test. Their causes are understood with the help of simulation and will be corrected in the next design iteration.

As the closest galactic nucleus, the Galactic center provides a unique opportunity for learning about the supermassive black hole at the center of the Milky Way, Sgr A*, and its environment. High-angular-resolution observations in the near-infrared further this advantage. This thesis presents an investigation of the long-term near-infrared accretion properties of Sgr A*, and characterizes the star formation history in this extreme environment. This work utilizes the unique data gathered by the UCLA Galactic Center Group over 25 years to answer fundamental questions about the supermassive black hole and the formation of stars around it. First, we investigate the near-infrared variability of Sgr A* with the longest time baseline yet considered. The recently improved speckle holography technique has led to the capability to detect Sgr A* in the early years of the group's monitoring program. We carry out a new analysis of speckle imaging data (1995 - 2005) obtained from the Keck observatory, enabling new detections of Sgr A* in the near-infrared over a decade that was previously inaccessible at these wavelengths. We report that the near-infrared brightness of Sgr A* and its variability are consistent over 22 years, which addresses variability timescales that are 10 times longer than earlier published studies. The power spectral density of Sgr A* shows a plateau between $\sim$80 days and 7 years, further confirming that it is uncorrelated in time beyond the previously-proposed, single power-law break of $\sim$245 minutes. We also investigate and note that the closest approach of the extended and dusty object G1, experiencing tidal disruption, had no apparent effect on the near-infrared emission from the accretion flow onto Sgr A*. Second, we report the first star-formation history study of the Milky Way's nuclear star cluster (NSC) which includes observational constraints from a large sample of stellar metallicity measurements from Gemini and VLT. Along with stellar photometry and spectroscopically derived stellar temperatures, a Bayesian inference approach is developed to derive the NSC's star formation history. By including metallicity measurements, the low-temperature red giants that were previously difficult to constraint are now accounted for, and the best fit favors a two-component model. The dominant ($\sim$93\% of the mass), metal-rich component has an age of 5$^{+3}_{-2}$ Gyr, which is likely $\sim$3 Gyr younger than earlier studies with fixed (solar) metallicity; this younger age challenges the co-evolution models of the supermassive black hole, the NSC and the bulge. The minor component ($\sim$7\%) is metal-poor and its age is uncertain though likely less than that of the dominant component. We present updated estimates of the number of compact objects at the Galactic center and their rates of mergers in order to inform interpretations of gravitational-wave detections. Of particular note, when metallicity measurements are included, the predictions result in 2 - 4 times fewer neutron stars compared to earlier predictions that assume solar metallicity, introducing a possible new path to understand the so-called ``missing pulsar problem" at the Galactic center.

This dissertation describes and analyzes the syntactic properties of three inter-related structures in both standard and non-standard varieties of Mandarin: yes-no question, unconditional adverbial clauses, and verb echo answers to yes-no questions.All human languages have ways to ask a yes-no question, but cross-linguistically they differ from each other in the exact strategies used. I systematically look at a type of sentence-internal question particle that is only used in forming yes-no questions in Jianghuai Mandarin, providing cross-linguistic evidence for Bhatt & Dayal’s (2020) proposal about the existence of a class of dedicated yes-no question particles in human languages. I further compare three types of yes-no questions formed with a sentence-internal question particle ha/a or/and an A-not-A string in two mutually intelligible varieties of Jianghuai Mandarin spoken in Wuhu and Nanjing. The distributional differences between ha/a and A-not-A string are understandable if they are within two separate functional projections, QuP and PolP respectively. Meanwhile, the parallel behaviors of all three types of yes-no questions are taken as evidence that they all share the same underlying structure that involve both QuP and PolP, and the variation in their surface forms is reduced to the lexicon. Building on Holmberg’s (2016) analysis of yes-no questions, I argue that the syntax of yes-no questions in Jianghuai Mandarin not only involves a PolP headed by an open-valued polarity variable [�Pol], but a QuP headed by a dedicated yes-no question particle must also be present. Furthermore, I discuss another structure where a yes-no question seems to be allowed, unconditional adverbial clauses, which have not attracted much attention in the literature on Mandarin syntax Unlike the traditional assumption, I show that there exist two distinct types of unconditional adverbial clauses in Mandarin: Headed antecedents and bare antecedents consistently differ from each other in both their internal and external syntax. Regarding the internal syntax, bare antecedents involve an impoverished structure: They are TPs without a left periphery; whereas headed antecedents involve a full-fledged CP-domain. I argue that only headed but not bare antecedents involve an embedded interrogative. In terms of the external syntax, bare antecedents are base generated at Spec douP within the consequent and then overtly move to their canonical pre-consequent position, hence they all fall under the category of central adverbial clauses. In contrast, the merger of headed antecedents is independent from dou, and hence they exhibit more flexibility in their attachment sites and varying degrees of integration with the consequent. It is argued that they can realize as any of the three types of adverbial clauses: central adverbial clauses, peripheral adverbial clauses, and overarching speech-act modifiers, each of which show distinct properties in their external syntax (and internal syntax). This provides cross-linguistic evidence for the three-way division in adverbial clauses recently proposed by Frey (2020) and Badan & Haegeman (2022). Neutral yes-no questions are typically answered by repeating the verb in the question (i.e. “verb echo answers” or VEA) in Mandarin, which is the third structure I investigate in this dissertation. Building on existing studies (Liu 2014, Simpson 2015, Holmberg 2016, Wei 2019, a.o.), I provide converging empirical evidence showing that VEAs must not only involve a base-generated verb or a VP, and there must be an underlying sentential structure. I show that Mandarin VEAs do not involve pro-drop and analyses involving pro-drop face two kinds of empirical challenges: Elements that cannot be pro-dropped are nevertheless omitted from VEAs; whereas elements that can be dropped still allow elements extracted from them to surface in VEAs. Meanwhile, I argue that a head movement approach cannot account for (i) variations in VEAs, especially various kinds of phrasal elements occurring in VEAs; and (ii) VEAs to embedded yes-no questions with matrix scope. I instead propose that Mandarin VEAs are derived through (remnant) PolP movement followed by TP ellipsis.

Abstract: Oil and gas production from shale reservoirs has become an indispensable component of the world energy supply. However, the oil recovery rate from shale reservoirs is still relatively low. To achieve efficient exploitation of shale reservoirs, one of the prerequisites is to have a precise capture of the phase behavior of reservoir fluids in shale reservoirs. Compared with conventional oil reservoirs, shale reservoirs contain organic matters within the rock matrix. These organic matters are mainly composed of kerogen, which is in equilibrium with generated hydrocarbons during the expulsion process. Swelling of kerogen by different solvents is a well-known technique to characterize the thermodynamic properties of kerogen and to describe the phase equilibria between different solvents and kerogen. In this thesis, experimental data of kerogen swelling tests from the literature are first collected to validate the efficacy of the Flory-Rehner and regular solution (FRRS) model in describing oil-kerogen two-phase equilibria. The FRRS algorithm can be tuned to well match the measured kerogen swelling test results. The swelling ratios of different types of kerogen are then predicted as a function of solubility parameters and molar volumes of different solvents. The effects of sulfur content and thermal maturity of kerogen on kerogen’s swelling ratio are also studied. Our calculation results show that the swelling ratio of kerogen follows a bell-shaped trend with the change of solubility parameter and molar volume of solvents. Kerogen tends to absorb more aromatics and heavy hydrocarbons than light and saturated hydrocarbons. Compared with normal alkanes, naphthenes induce higher swelling ratios of kerogen. The capacity of kerogen to retain hydrocarbons decreases with an increasing thermal maturity or sulfur content of kerogen.

This thesis is composed of three stand-alone research studies relating to the recent unconventional monetary policy adopted by the Bank of Japan (BOJ). The first study investigates the impact of the BOJ’s policy on stock prices and corporate activities. The empirical results show that the policy has generated heterogenous effects on stock prices. Firms with disproportionately higher BOJ investment experience significantly positive stock returns both in the short term and the long term. Corresponding to the positive price impact, the cost of equity capital reduces and firm value increases. However, further tests fail to find evidence of any real impact. Firms that benefit from a reduction in cost of equity capital do not increase external financing, corporate investment and employment. The concentrated capital structure in Japan and the biased investment scheme adopted may explain this weak policy impact. The second study examines whether and how excess reduction in free float affects stock liquidity. Using the BOJ’s equity purchase program as a natural experiment to tackle endogeneity problems, the results show that firms that experience a larger reduction in free float exhibit a reduction in stock liquidity. The negative effect of free float reduction on stock liquidity survives a battery of robustness tests. Further analyses of the underlying channels show that the number of common shareholders and institutional shareholders in a firm significantly decrease. These findings are consistent with a lack of free floating shares introducing frictions in the process of liquidity provision. The third study examines whether an increase in exchange traded funds (ETF) ownership via indexed investment impedes or improves price efficiency. Utilizing Japan’s ETF purchase program as the identification strategy, empirical tests show that prices of stocks that experience an increase in ETF ownership become less efficient in that they deviate more from a random walk and exhibit longer delays in responding to market information. An increase in ETF ownership is also associated with an increase in post-earnings announcement drift, a decline in analyst coverage, and a reduction in the coefficient of current returns to future earnings. These results together suggest that an excessive increase in ETF ownership curbs information arbitrage activities and results in less informative security prices.

This thesis is devoted to a study of applications of gauged linear sigma models. First, by constructing (0,2) analogues of Hori-Vafa mirrors, we have given and checked proposals for (0,2) mirrors to projective spaces, toric del Pezzo and Hirzebruch surfaces with tangent bundle deformations, checking not only correlation functions but also e.g. that mirrors to del Pezzos are related by blowdowns in the fashion one would expect. Also, we applied the recent proposal for mirrors of non-Abelian (2,2) supersymmetric two-dimensional gauge theories to examples of two-dimensional A-twisted gauge theories with exceptional gauge groups G_2 and E_8. We explicitly computed the proposed mirror Landau-Ginzburg orbifold and derived the Coulomb ring relations (the analogue of quantum cohomology ring relations). We also studied pure gauge theories, and provided evidence (at the level of these topologicalfield-theory-type computations) that each pure gauge theory (with simply-connected gauge group) flows in the IR to a free theory of as many twisted chiral multiplets as the rank of the gauge group. Last, we have constructed hybrid Landau-Ginzburg models that RG flow to a new family of non-compact Calabi-Yau threefolds, constructed as fiber products of genus g curves and noncompact Kahler threefolds. We only considered curves given as branched double covers of P^1. Our construction utilizes nonperturbative constructions of the genus g curves, and so provides a new set of exotic UV theories that should RG flow to sigma models on Calabi-Yau manifolds, in which the Calabi-Yau is not realized simply as the critical locus of a superpotential.

One fundamental question in syntax is how to understand the observed universality and diversity of syntactic structures across different languages. This paper addresses this question by focusing on yes-no question formation in two Chinese dialects spoken in Wuhu and Nanjing. Based on novel data and diagnostics, which involve a systematic comparison of the formal properties of different types of yes-no questions in Wuhu and Nanjing, this paper proposes a uniform analysis to account for both the uniformity and variation of Wuhu and Nanjing yes-no questions. This proposal improves on existing approaches to yes-no question formation by distinguishing between clause-internal question particles and A-not-A strings, and showing that what undergoes movement in Wuhu and Nanjing yes-no questions is the question operator instead of the polarity variable.

Nowadays, social networks services such as Facebook, Twitter, Instagram, etc. have become popular platforms for either celebrities, news media, organizations, governors or general public to express their ideas and opinions. They have created a great opportunity for researchers to explore how information spread through online social networks. Benefited from this, this thesis studies the efficient way of information diffusion on online social networks using the approach of agent-based modeling (ABM). A NetLogo ABM was created to conduct the experiments and analyses, along with the real network dataset retrieved from Twitter. It shows that with the same number of nodes and edges, the network having higher average path length or lower average clustering coefficient tends to have wider information diffusion. In addition, how to locate optimal early adopters in order to satisfy efficient information diffusion mainly depends on the network structure and propagation probabilities among individuals in the network. This thesis aims at contributing to studies of online social networks on information diffusion from the perspective of efficient diffusion with agent-based modeling and simulation. Application of this thesis could benefit those from business or government who want to disseminate advertisement/information in a fast and economic way. Outcomes from this study should also provide hints to the geography likely behind information diffusion in social networks.

This paper studies the effect of public attention, measured by newspaper coverage, on firms’ potential investor base and stock liquidity. Using different model specifications and methodological approaches, I identify a positive causal relationship between a firm’s public attention and the investor base as well as liquidity of its stocks. Firms covered more frequently by the mass media have a larger number of shareholders, and higher stock liquidity. In addition, I find that the effect of attention on stock liquidity is larger in small firms than in large ones. As firm size increases, the improvement in liquidity caused by additional media coverage declines. My findings are robust to different liquidity measures, and industry- and time-fixed effects. Moreover, the non-linearity problem, the reverse causality problem, the firm fixed effect, and endogenous event shocks do not appear to drive my results.

This study explored the phenomenological structure of mystical experience among 139 Chinese Pure Land and Chan Buddhist monks and nuns. Semi-structured interviews, thematic coding, and statistical analyses identified Hood’s Mysticism Scale as a valid tool for studying mysticism across religions and cultures. Stace’s common facets of mysticism as measured by Hood’s scale successfully described Buddhist experience as modified by Buddhist doctrines. Confirmatory factor analysis demonstrated that these facets could be formed into Stace’s three-factor structure. A mystical introvertive unity hypothesized to be separate from an extrovertive unity appeared instead to converge in the Chinese Buddhist context. These results lent strong support to the thesis that the phenomenology of mystical experience reveals a common experiential core that can be discerned across religious and spiritual traditions. These data also demonstrated that this common core can and should be explored using both qualitative and quantitative methodologies.

As silicon CMOS circuit technology is scaled above the GHz range, semiconductor industries face increasingly difficult challenges in implementing high speed metal interconnects. Metal trances are limited in density-speed performance due to the skin effect, electrical conductivity, and cross talk. Optical based interconnects have much higher available bandwidth by virtue of the extremely high carrier frequencies of optical signals (>100 THz). As more and more optical lightwave circuits and intra-chip optical interconnects are fabricated, a compact, low loss optical tapping technology is essential to incorporate optical interconnects into mainstream CMOS processes. In this thesis, a new optical tapping device, which is based on optical refractive index variation induced by ion-implantation, was studied for both applications of intra-chip optical interconnect and optical power monitoring for planar lightwave circuits.Beam propagation simulation was used to study the guided waveguide properties of ion-implanted optical taps. The length and tapping ratio of optical tap was optimized as functions of implanted ion energy and concentration for 1550nm guided light. The behavior of ion-implanted optical taps can be explained by waveguide coupling between ion-implanted waveguides and as-fabricated waveguides. Ion implantation experiments have also been performed on silica-on-silicon planar lightwave circuit devices using hydrogen ions. Ion concentration up to 5×1016 ion/cm3 were used in experiments with implantation energy from 1.2 MeV to 1.35 MeV. Transmission experimental results are qualitatively consistent with the simulation results. Both simulation and experimental results proves the feasibility of ion-implantation to produce effective and CMOS compatible optical tapping devices for wide applications in chip-level optical interconnect and planar lightwave circuits.

Carbon matrix composite (CMC) electrode and surface conducting (SC) electrode have been developed to study the copper-activation and the subsequent xanthate adsorption on insulating sphalerite. Fabricating CMC electrode involves embedding sphalerite particles in carbon to form a carbon matrix composite; and SC electrode is designed by contacting a platinum wire to the sphalerite surface. When these electrodes are activated by heavy metal ions such as copper, a conducting layer is formed on the mineral surfaces that allows dynamic electrochemical studies to be conducted. Voltammetric studies on the copper activated CMC:ZnS electrodes in inert electrolytes show that although the activation product and kinetics may differ with pH, copper-activation occurs at all pH ranges. At acidic pH, a Cu2S-like activation product was formed at open circuit. When activation was conducted at near neutral and alkaline pH at open circuit, the surface products formed were identified to be CuS-like. It was also established that the amount of copper uptaken by sphalerite is strongly dependent on the time of activation and on the electrochemical potential applied during activation. Activation at potentials positive of the rest potential decreases the amount of copper on the surface. Indeed, activation at potentials of 50 to 100 mV more positive of the rest potential in the activating solution completely inhibits copper activation. This result is consistent with the anodic stripping voltammetry that shows copper can be removed from the surface of sphalerite at oxidizing potentials. Activation at potentials mildly negative of the rest potential causes a progressive increase in the amount of copper on the surface, consistent with the diffusion controlled reduction process between ZnS and Cu2+ ions observed in the activating solution. At very low potentials, however, elemental copper is formed, which may worsen the selectivity of the sphalerite flotation. Controlled potential contact angle measurements showed that xanthate adsorption does occur on copper-activated sphalerite at all pH ranges. However, the contact angles and flotation recovery decrease at near neutral pH. This problem is caused by the adsorption of the copper-hydroxy species on the activated sphalerite surface. It was found that addition of small amount of complexing reagent can improve the flotation recovery at the near neutral pH. The results obtained in the present work show that potential control of the activation process can provide a means of controlling copper uptake and, hence, the selectivity and recovery of sphalerite flotation. The development of CMC:ZnS and SC:ZnS electrodes provides a practical and reliable way to quantitatively estimate the amount of copper uptake on sphalerite surface after activation.