Frequency dispersion of the capacitance (C-f) of GaN-based heterostructure are commonly observed at high frequencies. Analytical solutions are derived for frequency dispersion of the heterostructure's capacitance measured on two concentric-circle Schottky contacts, in form of Bessel function, by modeling a distributed network of heterostructure and solving corresponding circular transmission line functions. Solutions reveal C-f is determined by the R-s of 2-D electron gas (2-DEG). So in reverse, the sheet resistance at a certain carrier density can be extracted from the C-f measurement. By fitting experimental C-f data with the model, we obtain a peak mobility of 2044 cm(2)/V.s corresponding to a 2-DEG density of 8.2 x 10(12) cm(-2) and a sheet resistance of 373 Omega/square on an Al0.25Ga0.75N/GaN heterostructure on silicon substrate. The advantage of two Schottky contacts is that they could be implemented by mercury probes with the same geometry, then achieving nondestructive and instant feedback on carrier transport properties and uniformity of as-grown III-V compound semiconductor wafers
Microcredit loans are now common for Inner Mongolian pastoralists and are encouraged by government policy on the basis of their previous success for poverty alleviation. However, the effects of the highly variable weather characteristics of many semiarid rangelands on the efficacy of microcredit have not been fully examined. Pastoralists in our study area are often trapped in a vicious cycle of borrowing more each year to pay for previous debt and the next year’s production. Instead of helping to maintain herds through bad years, microcredit has often led to reduced herds and assets. To understand why, a qualitative, interview-based approach was used to determine the kinds of loans taken out and why they are taken out, as well as to assess household livestock sales, income, and costs in three villages. In poor years, 82% of households used loans to purchase winter forage. However, borrowers sold more livestock because the standard 1-yr loan term, combined with weather and market conditions, often forced sales for repayment. Weather and market variation made annual income and costs difficult to anticipate. Loans became an added household risk, another way that environment can influence the social and economic interactions of a rangeland social-ecological system. Longer-term loans could smooth the uncertainty of weather and market conditions, and supplementary measures such as government subsidies or forage insurance could buffer the inevitable but unpredictable bad years. Globally, study of the impacts of nonequilibrial ecological dynamics on economic and policy institutions would help to understand why many development initiatives have failed in such systems.
In this paper, solubility parameters and minimum miscibility pressures (MMPs) of five tight oil–CO2 systems are calculated in millimeter to nanometer scales. First, the Peng–Robinson equation of state (PR-EOS) is modified to calculate the vapour–liquid equilibrium in nanopores by considering the effects of capillary pressure and shifts of critical temperature and pressure. Second, a thermodynamic formula of the solubility parameter is derived and presented from the modified PR-EOS, which is applied to calculate the solubility parameters in nanopores. Third, the MMPs are estimated from the newly-developed solubility parameter-based method, at which the difference between the solubility parameters of oil and gas phases (Δδ) approximately equals to 3.0(cal/cm3)0.5. The modified PR-EOS is found to be accurate for predicting the oil–CO2 phase behaviour. It is found that Δδ are almost equivalent at low pressures but with the pressure increase, Δδ at a larger pore radius becomes greater. The estimated MMPs are found to agree well with the measured MMPs from the coreflood and slim-tube tests in bulk phase and with the determined MMPs from the diminishing interface method in nanopores, whose average absolute relative deviations (AARD) are within 4.38% except for two abnormal cases. A smaller nanopore is found to contribute to the oil–gas solubility (i.e., a lower Δδ) and the MMP is also decreased with the pore radius. Moreover, the temperature increase and addition of CH4 into the oil and gas phases lead to a larger Δδ, which make the oil and gas phases become more difficult to be soluble so that the corresponding MMPs increase. On the contrary, the oil–gas solubility is beneficial from the addition of C2H6 into gas phase so that the MMP is reduced. Overall, the effects of temperature, initial oil and injection gas compositions on the MMP are found to be weakened in nanopores.
The coating surface temperature of the stealth aircraft increases due to the motion and heating effect, which causes the inhomogeneous temperature distributions between the coating and the metal substrate. In this paper, the millimeter-wave radiation characteristics of the stealth aircraft under motion state are discussed. Firstly, one dimensional heat conduction equation of the stealth aircraft under motion state is established, and we obtain the temperature distributions along the vertical directions. Then, according to the layered coating and th e non-uniformity of diel ectric property caused by temperature variation, the total brightness temperature is calculated by using radiation transfer theory. The calculated results indicate that the temperature distributions of the motional aircraft coating varies with the t ime, and th e millimeter-wave radiation characteristics also have time-varying.
Object matching is critical for updating, maintaining, integrating, and quality assessing spatial data. However, matching data are often obtained from different sources and have problems of positional discrepancy and different levels of detail. To resolve these problems, this article presents a multiscale polygonal object‐matching approach, called the minimum bounding rectangle combinatorial optimization (MBRCO) with spatial district (SD). This method starts with the MBRCO algorithm and its enhancement using the SD to find corresponding MBRs of one‐to‐one, one‐to‐many, and many‐to‐many matching pairs. Then, italigns the MBRs of the matching pairs to identify object matching pairs, which are evaluated using a matching criterion to find geometrically corresponding objects. Our approach was experimentally validated using two topographical datasets at 1:2k and 1:10k. The proposed approach outperforms the common two‐way area overlap method and another method based on the contextual in‐formation and relaxation labeling algorithm. The proposed method achieved accurate aggregation of the many‐to‐many matching pairs under the positional discrepancy scenario.
The allele fraction (AF) distribution, occurrence rate, and evolutionary contribution of postzygotic single-nucleotide mosaicisms (pSNMs) remain largely unknown. In this study, we developed a mathematical model to describe the accumulation and AF drift of pSNMs during the development of multicellular organisms. By applying the model, we quantitatively analyzed two large-scale data sets of pSNMs identified from human genomes. We found that the postzygotic mutation rate per cell division during early embryogenesis, especially during the first cell division, was higher than the average mutation rate in either male or female gametes. We estimated that the stochastic cell death rate per cell cleavage during human embryogenesis was ∼5%, and parental pSNMs occurring during the first three cell divisions contributed to ∼10% of the de novo mutations observed in children. We further demonstrated that the genomic profiles of pSNMs could be used to measure the divergence distance between tissues. Our results highlight the importance of pSNMs in estimating recurrence risk and clarified the quantitative relationship between postzygotic and de novo mutations.
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.
