254 research outputs found
Preprint, 15th Conf. on Numerical Weather Prediction and
No full textthis paper, we report further development of this system, in particular, the addition of two dynamic constraints based on the ARPS equations and the inclusion of the anelastic mass continuity equation as the third constraint. We consider such features very important for the assimilation of data at the convective scales. The inclusion of these equation constraints couple together the analysis variables and make the analysis of variables not directly observed (e.g., temperature and pressure by radar) possible. Corresponding author address: Jidong Gao, CAPS, SEC1110, 100 E. Boyd, Norman, OK 73019 The latter process is often referred to as parameter retrieva
Elastic Wavefield Separation in Anisotropic Media Based on Eigenform Analysis and Its Application in Reverse-Time Migration
No full textSeparating compressional and shear wavefields is an important step in elastic reverse-time migration, which can remove wave-mode crosstalk artefacts and improve imaging quality. In vertical (VTI) and titled (TTI) transversely isotropic media, the state-of-the-art techniques for wavefield separation are based on either non-stationary filter or low-rank approximation. They both require intensive Fourier transforms for models with strong heterogeneity. Based on the eigenform analysis, we develop an efficient pseudo-Helmholtz decomposition method for the VTI and TTI media, which produces vector P and S wavefields with the same amplitudes, phases and physical units as the input elastic wavefields. Starting from the elastic VTI wave equations, we first derive the analytical eigenvalues and eigenvectors, then use the Taylor expansion to approximate the square-root term in the eigenvalues, and finally obtain a zero-order and a first-order pseudo-Helmholtz decomposition operator. Because the zero-order operator is the true solution for the case of ϵ = δ, it produces accurate wavefield separation results for elliptical anisotropic media. The first-order separation operator is more accurate for non-elliptical anisotropy. Since the proposed pseudo-Helmholtz decomposition requires solving an anisotropic Poisson's equation, we propose two fast numerical solvers. One is based on the sparse lower-upper (LU) factorization, which can be repeatedly applied to the input elastic wavefields once computing the lower and upper triangular matrices. The second solver assumes the model parameters are laterally homogeneous within a given migration aperture. This assumption allows us to efficiently solve the anisotropic Poisson's equation in the z k x domain, where k x and z denote the horizontal wavenumber and depth, respectively. Using the coordinate transform, we extend the pseudo-Helmholtz decomposition to the TTI media. The separated vector wavefields are used to produce PP and PS images by applying a dot-product imaging condition. Several numerical examples demonstrate the feasibility and applicability of the proposed methods. © The Author(s) 2019. Published by Oxford University Press on behalf of The Royal Astronomical Society.Natural Sciences and Mathematic
Time-domain least-squares migration using the Gaussian beam summation method
No full textArticle is freely available on publisher's website. Use the Link to ArticleWith a finite recording aperture, a limited source spectrum and unbalanced illumination, traditional imaging methods are insufficient to generate satisfactory depth profiles with high resolution and high amplitude fidelity. This is because traditional migration uses the adjoint operator of the forward modelling rather than the inverse operator.We propose a least-squares migration approach based on the time-domain Gaussian beam summation, which helps to balance subsurface illumination and improve image resolution. Based on the Born approximation for the isotropic acoustic wave equation, we derive a linear time-domain Gaussian beam modelling operator, which significantly reduces computational costs in comparison with the spectral method. Then, we formulate the corresponding adjoint Gaussian beam migration, as the gradient of an L2-norm waveform misfit function. An L1-norm regularization is introduced to the inversion to enhance the robustness of least-squares migration, and an approximated diagonal Hessian is used as a pre-conditioner to speed convergence. Synthetic and field data examples demonstrate that the proposed approach improves imaging resolution and amplitude fidelity in comparison with traditional Gaussian beam migration. © The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society.School of Natural Sciences and Mathematic
Unhealthy diet and lifestyle factors linked to female androgenetic alopecia: a community-based study from Jidong study, China
No full textAbstract Background To explore unhealthy diet and lifestyle factors associated with female androgenetic alopecia (FAGA) in a community-based study. Methods A total of 3,008 participants were recruited from the Jidong community (Tangshan, Hebei, China). FAGA was assessed by the Savin scale. Data collection was conducted through structured questionnaires. Univariate and multivariate logistic regression analyses were employed to identify potential factors. Multivariable models were built by selecting covariates with P 5. The predictive performance was evaluated using the receiver operating characteristic curve. Results The prevalence of FAGA in this study was 6.85% (206/3008). Sleep snoring (adjusted odds ratio [AOR] = 1.398, 95% confidence interval [CI] 1.032–1.894, P = 0.031), frequent consumption of bacon and preserved meat (AOR = 2.205, 95% CI 1.181–4.118, P = 0.013), frequently drinking unboiled water (AOR = 1.984, 95% CI 1.156–3.406, P = 0.013), age (AOR = 1.063, 95% CI 1.050–1.076, P < 0.001) and suboptimal health status score (AOR = 1.033, 95% CI 1.020–1.047, P < 0.001) were identified as independent factors associated with FAGA. Conclusions In conclusion, our data suggest that females who snore during sleep, frequently consume bacon and preserved meats, and regularly drink unboiled water are more susceptible to androgenetic alopecia. Additionally, our analysis revealed that age and suboptimal health status score are significantly correlated with FAGA
Heparin free coating on PLA membranes for enhanced hemocompatibility via iCVD
No full textIn the present work, we report one-step immobilization of nano-heparin coating on PLA membranes via initiated chemical vapor deposition (iCVD) for enhanced hemocompatibility. The nano-coating introduced onto the membrane surface via the crosslinking of P(MAA-EGDA) was confirmed by the FTIR, SEM and weight measurement respectively. The negative carboxyl groups could form the hydration interaction with the protein and platelets and electrostatic interaction with amide groups of thrombin by the mediation of antithrombin, which is similar but different with heparin. The P(MAA-EGDA) coated membranes showed suppressed platelet adhesion and prolonged clotting time (APTTs increased to 59 s, PTs increased to 20.4 s, TTs increased to 17.5 s, and the FIBs declined by 30 mg/dL). Moreover, the complement activation tests demonstrated the formation of C3a and C5a was inhibited. All results demonstrated that the nano-coating of P(MAA-EGDA) via iCVD significantly enhanced the hemocompatibility of PLA membranes, which is also applicable for various membranes. (C) 2017 Elsevier B.V. All rights reserved
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No full textA new efficient dual-resolution (DR) data assimilation algorithm is developed based on the ensemble Kalman filter (EnKF) method and tested using simulated radar radial velocity data for a supercell storm. Radar observations are assimilated on both high-resolution and lower resolution grids using the EnKF algorithm using flow-dependent background error covariances estimated from the lower resolution ensemble. It is shown that the flow-dependent and dynamically evolved background error covariances thus estimated are effective in producing quality analyses on the high-resolution grid. The DR method has the advantage of being able to significantly reduce the computational cost of the EnKF analysis. In the system, the lower resolution ensemble provides the flowdependent background error covariance, while the single high-resolution forecast and analysis provides the benefit of higher resolution which is important for resolving internal structures of thunderstorms. The relative smoothness of the covariance obtained from the lower 4 kmresolution ensemble does not appear to significantly degrade the quality of analysis. This is because the cross-covariance among different variables is of first order importance for ‘retrieving ’ unobserved variables from the radar radial velocity data. For the DR analysis, an ensemble size of 40 appears to be a reasonable choice with the use of a 4 km horizontal resolution in the ensemble and a 1 km resolution in the high-resolution analysis. Several sensitivity tests show that the DR EnKF system is quite robust to different observation errors. A 4 km thinned data resolution is a compromise that is acceptable under the constraint of real time applications. A data density of 8 km leads to a significant degradation to the analysis. i 1
Data_Sheet_1_Seroepidemiology of Chlamydia trachomatis Infection in the General Population of Northern China: The Jidong Community Cohort Study.docx
No full textA longitudinal serological study to investigate the seropositive frequency, incidence, and antibody dynamics of Chlamydia trachomatis infection in the general population of China is urgently needed in order to optimize the strategies for surveillance and precise prevention of C. trachomatis infection. This longitudinal study enrolled 744 subjects aged 18–65 years from Jidong Community of Northern China from 2014 to 2018. Seropositive frequency, incidence, and reinfection of C. trachomatis were determined by detecting antibody against C. trachomatis Pgp3 using “in-house” luciferase immunosorbent assay (LISA). The dynamic of anti-Pgp3 antibody was analyzed using the Generalized Estimating Equation (GEE) model. The overall Pgp3 seropositive frequency among the 18–65-year-old population was 28.1% (95% CI 24.9–31.5), and significantly increased from 12.0% in those aged 18–29 years to 48.6% in the 60–65 years old. The seropositive frequency was slightly higher in women than in men (31.3% vs. 25.4%) without statistical significance. The C. trachomatis incidence and reinfection rate were 11 and 14 per 1,000 person-years, respectively, and showed no significant difference with respect to age, gender, ethnicity, marital status, and education levels. Furthermore, anti-Pgp3 antibody remained detectable in 93.3% (195/209) of the seropositive subjects during the 5 years of follow-up. The overall decay rate for anti-Pgp3 antibody for CT-infected persons was −0.123 Log2 RLU/year, which was dramatically slower than in CT new infection (−3.34 Log2 RLU/year) or reinfection (−1.1 Log2 RLU/year). In conclusion, at least one quarter of the people aged 18–65 years have been infected with C. trachomatis over their lifetime while all age groups are susceptible to C. trachomatis infection in the community of Northern China. Therefore, comprehensive prevention strategies are urgently needed.</p
Possibility of wax control techniques in Indonesian oil fields
No full textWax is one of the common problem which can reduce the oil production, especially for the reservoir with high paraffin content case. When the temperature of crude oil is lower than pour point, wax molecules can begin rapidly precipitated. The impacts of this problem are the clogging of production equipment, sealing off the pores in the reservoir, and decreasing production flow rate. In order to solve the wax problem, several methods have been applied in some oil fields in the world. For example, chemical methods in Jiangsu field (China) and Mumbai High field (India), hot water in Mangala field (India), magnetic method in Daqing field (China), water-dispersible in Bakken basin (US), and microbial in Jidong field (China). In general, the various crude oils present in the Indonesia contain wax content between 10%-39% and pour point of 22oC–49oC. Hot water and chemical method are commonly used to solve wax problems in Indonesian oil fields. However, the primary solution is magnetic method, and the secondary solution is water dispersible
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