科研成果 by Year: 2018

Understanding pore heterogeneity can enable us to obtain a deeper insight into the flow and transport processes in any porous medium. In this study, multifractal analysis was employed to analyze gas adsorption isotherms (CO2 and N2) for pore structure characterization in both a source (Upper-Lower Bakken) and a reservoir rock (Middle Bakken). For this purpose, detected micropores from CO2 adsorption isotherms and meso-macropores from N2 adsorption isotherms were analyzed separately. The results showed that the generalized dimensions derived from CO2 and the N2 adsorption isotherms decrease as q increases, demonstrating a multifractal behavior followed by f(α) curves of all pores exhibiting a very strong asymmetry shape. Samples from the Middle Bakken demonstrated the smallest average H value and largest average α10−-α10+ for micropores while samples from the Upper Bakken depicted the highest average α10−-α10+ for the meso-macropores. This indicated that the Middle Bakken and the Upper Bakken have the largest micropore and meso-macropore heterogeneity, respectively. The impact of rock composition on pore structures showed that organic matter could increase the micropore connectivity and reduce micropore heterogeneity. Also, organic matter will reduce meso-macropore connectivity and increase meso-macropore heterogeneity. We were not able to establish a robust relationship between maturity and pore heterogeneity of the source rock samples from the Bakken.

N2 adsorption is one of the most widely used techniques to assess pore structures of shale samples due to its ability for characterizing pores in nanoscale. Various models have been developed to quantify pore structures based on adsorption isotherms. In this regard, using a suitable model can give us more accurate pore structure information. The Barret, Joyner and Halenda (BJH) model along with density functional theory (DFT), two most frequently used ones for pore structures of shales, employed on Longmaxi shale samples and compared. BJH model can be divided into two sub-models: adsorption (BJHAD) and desorption (BJHDE). First, the multifractal analysis was used to quantify the heterogeneity of pore size distributions derived from these models. Second, partial least regression analysis (PLS) was employed to quantify the correlations between pore structures and rock compositions. The results showed that pore structures (volume and surface area) and pore heterogeneity derived from BJHAD, BJHDE and DFT model would differ. In addition, PLS results indicated that minerals (except dolomite and clay) and organic matter would correlate positively while clay minerals negatively with pore surface area and volume independent of the method that was used. Finally, the comparison of results from these three methods demonstrated that DFT model is superior to BJHAD and BJHDE for pore structure characterization in shale gas formations.

Multiphoton fluorescence microscopy (MPM), using near infrared excitation light, provides increased penetration depth, decreased detection background, and reduced phototoxicity. Using stimulated emission depletion (STED) approach, MPM can bypass the diffraction limitation, but it requires both spatial alignment and temporal synchronization of high power (femtosecond) lasers, which is limited by the inefficiency of the probes. Here, we report that upconversion nanoparticles (UCNPs) can unlock a new mode of near-infrared emission saturation (NIRES) nanoscopy for deep tissue super-resolution imaging with excitation intensity several orders of magnitude lower than that required by conventional MPM dyes. Using a doughnut beam excitation from a 980 nm diode laser and detecting at 800 nm, we achieve a resolution of sub 50 nm, 1/20th of the excitation wavelength, in imaging of single UCNP through 93 mu m thick liver tissue. This method offers a simple solution for deep tissue super resolution imaging and single molecule tracking.

Water is a basic necessity and its allocation and utilization, especially pricing policies, impose various social, economic, and ecological impacts on social groups. Increasing block tariffs (IBTs) has gained popularity because it is expected to incentivize water conservation while protecting poor people benefiting from the redistribution effects because of its nonlinear tariff structure. However, it results in price distortion under certain circumstances. Researchers have also proposed an alternative practical price system and a uniform tariff with rebate (UTR), with the price level set equal to the marginal social cost and a fixed rebate allocated to the poor groups. This study proceeds with a simulation of the two pricing systems, UTR and IBTs, and empirically explores their fundamental merits and limitations. The results confirm the theoretical perspective that a water price system, compared with an optimal tariff system, simultaneously achieves multiple goals to the greatest possible extent.

Stratabound deposits within late Carboniferous carbonate units in the Middle-Lower Yangtze River metallogenic belt are important copper producers in China. Hitherto, the genesis of these deposits has been debated, due to poor constraints regarding the timing and source of the mineralization. Proposed models include a late Carboniferous seafloor exhalative formation (SEDEX), or an Early Cretaceous magmatic-hydrothermal origin. These models imply different metal sources (basinal vs. magmatic fluid, respectively) and would require different exploration strategies. New pyrite Re-Os and trace-element results from the representative Xinqiao Cu-S-Fe-Au deposit favor a Cretaceous (ca. 138 Ma) magmatic-hydrothermal genesis over a SEDEX origin. The distinct initial Os-187/Os-188 compositions (Osi) of different pyrite types (colloform Os-i = 1.35 and euhedral grains Os-i = 0.79), coupled with the pyrite trace-element abundance, indicate that the Os, and by inference other metals (e.g., Cu, Ag, Au), was sourced from a Cretaceous magmatic-hydrothermal system (Os-i = 0.74) and Late Permian metalliferous black shales (Os-i = 7.56 +/- 3.76). In addition, the genesis of Au-bearing stockwork pyrite veins hosted by the Carboniferous sandstone is best explained by the leaching of existing mineralization (e.g., porphyry Au-Mo) by Early Cretaceous magmatic-hydrothermal fluids. This is implied by the lack of common Os, high Re abundances (0.1-3.7 ppm), and highly variable Re-Os model ages (379 and 173 Ma), which are positively correlated with Re and total abundances of Co, Ni, Ag, Au, Tl, and Ba. This study highlights the importance of recycling of multisourced metals (sedimentary and existing mineralization) in the formation of intrusion-related stratabound deposits. Furthermore, it demonstrates the importance of integrating information regarding the source and timing of mineralization within a well-defined geological framework, which can yield information about the ore-forming processes and help to guide mineral exploration.

Understanding the time-dependent mechanical behavior of rocks is important from various aspects and different scales such as predicting reservoir subsidence due to depletion or proppant embedment. Instead of using the conventional creep tests, nano-dynamic mechanical analysis (nano-DMA) was applied in this study to quantify the displacement and mechanical changes in shale samples over its creep time at a very fine scale. The results showed that the minerals with various mechanical properties exhibit different creep behavior. It was found that under the same constant load and time conditions, the creep displacement of hard minerals would be smaller than those that are softer. On the contrary, the changes in mechanical properties (storage modulus, loss modulus, complex modulus and hardness) of hard minerals are larger than soft minerals. The results from curve fitting showed that the changes in creep displacement, storage modulus, complex modulus and hardness over creep time follow a logarithmic function. We further analyzed the mechanical changes in every single phase during the creep time based on the deconvolution method to realize each phase’s response independently. Two distinct mechanical phases can be derived from the deconvolution histograms. As the creep time increases, the volume percentage of the hard mechanical phase decreases, while this shows an increase for soft phases. The results suggest that nano-DMA can be a strong advocate to study the creep behavior of rocks with complex mineralogy.

We review the use of luminescent nanoparticles in super-resolution imaging and single-molecule tracking, and showcase novel approaches to super-resolution imaging that leverage the brightness, stability, and unique optical-switching properties of these nanoparticles. We also discuss the challenges associated with their use in biological systems, including intracellular delivery and molecular targeting. In doing so, we hope to provide practical guidance for biologists and continue to bridge the fields of super-resolution imaging and nanoparticle engineering to support their mutual advancement.

Pores that exist within the organic matter can affect the total pore system of bulk shale samples and, as a result, need to be studied and analyzed carefully. In this study, samples from the Bakken Formation, in conjunction with the kerogen that was isolated from them, were studied and compared through a set of analytical techniques: X-ray diffraction (XRD), Rock-Eval pyrolysis, Fourier Transform infrared spectroscopy (FTIR), and gas adsorption (CO2 and N2). The results can be summarized as follows: 1) quartz and clays are two major minerals in the Bakken samples; 2) the samples have rich organic matter content with TOC greater than 10 wt%; 3) kerogen is marine type II; 4) gas adsorption showed that isolated kerogen compared to the bulk sample has larger micropore volume and surface area, meso- and macropore volume, and Brunauer–Emmett–Teller (BET) surface area; 5) deconvolution of pore size distribution (PSD) curves demonstrated that pores in the isolated kerogen could be separated into five distinct clusters, whereas bulk shale samples exhibited one additional pore cluster with an average pore size of 4 nm hosted in the minerals. The comparison of PSD curves obtained from isolated kerogen and bulk shale samples proved that most of the micropores in the shale are hosted within the organic matter while the mesopores with a size ranging between 2 and 10 nm are mainly hosted by minerals. The overall results demonstrated that organic matter-hosted pores make a significant contribution to the total porosity of the Bakken shale samples.

In this paper, a novel nanoscale-extended correlation is developed to calculate the minimum miscibility pressures (MMPs) for a wide range of dead and live tight oil−gas solvent systems in bulk phase and nanopores. First, experimentally, the slim-tube and coreflood tests as well as the vanishing interfacial tension (VIT) technique are conducted to measure the MMPs of three oil‒gas systems. Second, the newly-developed correlation is proposed as a function of the reservoir temperature, molecular weight of C5+, mole fraction ratios of volatile components to intermediate components in oil and gas samples, and pore radius. Third, theoretically, the new correlation is analyzed on a basis of an oil‒gas MMP database from this study and literature that covers 101 oil‒gas MMP data for fifteen oil and thirteen gas samples at different reservoir temperatures in bulk phase and nanopores. A total of 40 commonly-used existing correlations are analyzed and reviewed. Compared to the seven existing correlations, the new correlation is found to provide the most accurate MMPs with an overall percentage average absolute deviation (AAD%) of 5.72% and maximum absolute deviation (MAD%) of 12.96% for different dead and live oil‒pure CO2 systems in bulk phase. Moreover, for the different oil‒pure and impure gas solvent systems, the new correlation leads to the best calculation accuracy of the MMPs with an overall AAD% of 4.70% and MAD% of 15.81% in comparison with the four existing correlations. More importantly, the new correlation is found to calculate the MMPs of different dead and live oil‒pure and impure gas solvent systems in nanopores in an accurate, efficient, and physical correct manner. The overall AAD% and MAD% in terms of the MMP calculations in nanopores from the new correlation are determined to be 6.91% and 13.66%, respectively.

Many historians consider the 1926/27 PKI Uprisings as important precursors of Indonesia’s nationalist movement, which ultimately led to the country’s independence. When it comes to the actual course of events, however, existing narratives tend to describe the abortive revolts as ill-prepared, poorly organised and easily suppressed – and consequently, of limited impact in shaking the foundation of the Dutch colonial regime. It is also commonly understood that in the aftermath of the rebellions, dutch authorities dealt a crushing blow to the pki and its associated organisations by carrying out large-scale arrests, imprisonments, executions, and banishments. Beyond these facts, however, very little attention has been paid to the deeper meanings that the revolt revealed. as the following sections will demonstrate, the movement created enormous anxiety in the NEI which forced the Dutch colonial government to act with a strong hand. moreover, with frequent exchanges of information and personnel across the Malacca Straits, the NEI uprisings also generated considerable uneasiness in British Malaya.

In this paper, the equilibrium two-phase compositions are predicted and analyzed to elucidate the pressure dependence of the equilibrium interfacial tensions (IFTs) of three different light crude oil–CO2 systems. First, three series of the dynamic IFT tests for a dead light crude oil–pure CO2 system, a live light crude oil–pure CO2 system, and a dead light crude oil–impure CO2 system at different equilibrium pressures from the literature are used. Second, the modified Peng–Robinson equation of state (PR-EOS) is tuned by using measured pressure–volume–temperature (PVT) data to predict the equilibrium two-phase compositions of the three light crude oil–CO2 systems. Such tuned PR-EOS together with the parachor model is applied to predict the equilibrium IFTs, which are compared with and validated by the measured IFT data. Third, the pressure dependence of the equilibrium IFTs, the initial oil and gas composition effects, and the initial gas fraction effect are examined. The density difference between the light crude oil and gas phase is found to be a key factor in the parachor model for the IFT predictions. The equilibrium IFT vs. pressure curve is found to have three different pressure ranges, which correspond well to those for the density difference. Moreover, the initial oil and gas compositions affect the equilibrium two-phase compositions and IFTs to different extents. The live light crude oil–pure CO2 equilibrium IFT is reduced with an increased initial gas fraction. For the dead light crude oil–pure/impure CO2 system, the miscibility with zero IFT can be achieved only if the initial gas phase has more than 0.70 mol fraction. Otherwise, it is the complete gas dissolution into the light crude oil that leads to zero IFT.

As indispensable molecular components, photosensitizers play a crucial role in determining the quantum efficiency of triplet-triplet annihilation upconversion (TTA UC). This emergent technology has attracted great attention in recent years for realizing large anti-Stokes shifts with noncoherent excitation sources. In a typical TTA UC, low-energy photons are first harvested by the photosensitizers, which upon intersystem crossing (ISC) undergo triplet-triplet energy transfer (TTET) to emitters (i.e., annihilators). Following the bimolecular TTA among the emitters, high-energy photons are given off by the singlet excited state of the emitters. Apparently, the efficiencies of photon absorption, ISC, and TTET are all dependent on the sensitizers. With a Dexter-type ET mechanism requiring collisional interactions, a long triplet lifetime of the energy donor (photosensitizer) is evidently favorable for enhancing the efficiency of TTET. This progress report summarizes the recent developments of photosensitizers used for TTA UC, many of which feature a bichromophoric molecular scaffold. Among the various consequences and functions entailed by such bichromophoric designs, the extended triplet lifetime is a particularly advantageous property for TTA UC. Additionally, these new potent photosensitizers with long triplet lifetimes are also useful for other applications such as singlet oxygen sensitization and oxygen sensing.

In recent years, air pollution has become a major concern in China, especially in the capital city of Beijing. Haze events occur in Beijing over all four seasons, exhibiting distinct characteristics. In this study, the typical evolution patterns of atmospheric particulate matter with a diameter of less than 2.5 mu m (PM2.5) in each season were illustrated by episode-based analysis. In addition, a novelmethodwas developed to elucidate the driving species of pollution, which is the largest contributor to the incremental PM2.5 (triangle PM2.5), not PM2.5. This method revealed a temporal variation of the driving species throughout the year: nitrate-driven spring, sulfate-driven summer, nitrate-driven early fall, and organicmatters (OM)-driven late fall and winter. These results suggested that primary organic particles or volatile organic compounds emissions were dominant in the heating season due to residential heating, while NOx and SO2 emissions dominated in the other seasons. Besides, nitrate formation seemed more significant than sulfate formation during severe pollution episodes. It was also found that the pollution formation mechanismin the winter showed some unique features in comparison with the other seasons: aqueous reactions were more important in the winter, while multiple pathways coexisted in the other seasons. Furthermore, this study confirmed that the PM2.5 in Beijing was moderately acidic despite a fully neutralized system. In addition, the acidity variation during pollution episodes displayed different patterns between seasons and was driven by both the variation of aerosol water and chemical compositions. These results provide a new perspective to understand the characteristics and mechanisms of aerosol pollution in Beijing. However, more accurate measurements