A study of monitor functions for two dimensional adaptive mesh generation

This is the published version, also available here: http://dx.doi.org/10.1137/S1064827597327656.In this paper we study the problem of two-dimensional adaptive mesh generation using a variational approach and, specifically, the effect that the monitor function has on the resulting mesh behavior. The basic theoretical tools employed are Green's function for elliptic problems and the eigendecomposition of symmetric positive definite matrices. Based upon this study, a general strategy is suggested for how to choose the monitor function, and numerical results are presented for illustrative purposes.The three-dimensional case is also briefly discussed. It is noted that the strategy used here can be applied to other elliptic mesh generation techniques as well

A Moving Mesh Method Based on the Geometric Conservation Law

This is the published version, also available here: http://dx.doi.org/10.1137/S1064827501384925.A new adaptive mesh movement strategy is presented, which, unlike many existing moving mesh methods, targets the mesh velocities rather than the mesh coordinates. The mesh velocities are determined in a least squares framework by using the geometric conservation law, specifying a form for the Jacobian determinant of the coordinate transformation defining the mesh, and employing a curl condition. By relating the Jacobian to a monitor function, one is able to directly control the mesh concentration. The geometric conservation law, an identity satisfied by any nonsingular coordinate transformation, is an important tool which has been used for many years in the engineering community to develop cell-volume-preserving finite-volume schemes. It is used here to transform the algebraic expression specifying the Jacobian into an equivalent differential relation which is the key formula for the new mesh movement strategy. It is shown that the resulting method bears a close relation with the Lagrangian method. Advantages of the new approach include the ease of controlling the cell volumes (and therefore mesh adaption) and a theoretical guarantee for existence and nonsingularity of the coordinate transformation. It is shown that the method may suffer from the mesh skewness, a consequence resulting from its close relation with the Lagrangian method. Numerical results are presented to demonstrate various features of the new method

Male Clients of Male Sex Workers in China: An Ignored High-Risk Population.

BackgroundThere is a high prevalence of HIV/syphilis among male sex workers, but no formal study has ever been conducted focusing on male clients of male sex workers (MCM). A detailed investigation was thus called for, to determine the burden and sociobehavioral determinants of HIV and syphilis among these MCM in China.MethodsAs part of a multicenter cross-sectional study, using respondent-driven and snowball sampling, 2958 consenting adult men who have sex with men (MSM) were recruited, interviewed, and tested for HIV and syphilis between 2008 and 2009. The distributions of sociodemographic characteristics, risk behaviors, and HIV/syphilis prevalence were determined and compared between MCM and other MSM.ResultsAmong recruited MSM, 5.0% (n = 148) were MCM. HIV prevalences for MCM and other MSM were 7.4% and 7.7%, whereas 18.9% and 14.0% were positive for syphilis, respectively. Condomless anal intercourse (CAI) was reported by 59.5% of MCM and 48.2% of MSM. Multiple logistic regression revealed that compared with other MSM, MCM were more likely to have less education [for ≤ elementary level, adjusted odds ratio (aOR) = 3.13, 95% confidence interval (95% CI): 1.42 to 6.90], higher income (for >500 US Dollars per month, aOR = 2.97, 95% CI: 1.53 to 5.77), more often found partners at parks/restrooms (aOR = 4.01, 95% CI: 2.34 to 6.85), reported CAI (aOR = 1.49, 95% CI: 1.05 to 2.10), reported a larger sexual network (for ≥ 10, aOR = 2.70, 95% CI: 1.44 to 5.07), and higher odds of syphilis (aOR = 1.54, 95% CI: 1.00 to 2.38).ConclusionsThe greater frequency of risk behaviors and high prevalence of HIV and syphilis indicated that HIV/syphilis prevention programs in China need to pay special attention to MCM as a distinct subgroup, which was completely ignored until date

In Vivo screening and discovery of novel candidate thalidomide analogs in the zebrafish embryo and chicken embryo model systems

This study was supported by a Wellcome Trust-NIH PhD Studentship to SB, WDF and NV. Grant number 098252/Z/12/Z. SB, CHC and WDF are supported by the Intramural Research Program, NCI, NIH. NHG and WL are supported by the Intramural Research Program, NIA, NIH.Peer reviewedPublisher PD

Variational Mesh Adaptation Methods for Axisymmetrical Problems

This is the published version, also available here: http://dx.doi.org/10.1137/S0036142902401591.We study variational mesh adaptation for axially symmetric solutions to two-dimensional problems. The study is focused on the relationship between the mesh density distribution and the monitor function and is carried out for a traditional functional that includes several widely used variational methods as special cases and a recently proposed functional that allows for a weighting between mesh isotropy (or regularity) and global equidistribution of the monitor function. The main results are stated in Theorems \ref{thm4.1} and \ref{thm4.2}. For axially symmetric problems, it is natural to choose axially symmetric mesh adaptation. To this end, it is reasonable to use the monitor function in the form G = \lambda_1(r) {\mbox{\boldmath {e}}}_r {\mbox{\boldmath {e}}}_r^T + \lambda_2(r) {\mbox{\boldmath {e}}} _\theta {\mbox{\boldmath {e}}}_\theta^T , where {\mbox{\boldmath {e}}}_r and {\mbox{\boldmath {e}}}_\theta are the radial and angular unit vectors. It is shown that when higher mesh concentration at the origin is desired, a choice of $\lambda_1$ and $\lambda_2$ satisfying $\lambda_1(0) 0$ by choosing $\lambda_1$ and $\lambda_2$. In contrast, numerical results show that the new functional provides better control of the mesh concentration through the monitor function. Two-dimensional numerical results are presented to support the analysis

HBV and HCV test uptake and correlates among men who have sex with men in China: a nationwide cross-sectional online survey.

OBJECTIVES: Hepatitis B virus (HBV) and hepatitis C virus (HCV) cause substantial morbidity and mortality in low-income and middle-income countries, including China. WHO guidelines recommend men who have sex with men (MSM) receive HBV and HCV screening. The purpose of this study was to determine the proportion of MSM in China who have HBV and HCV tested and identify correlates of test uptake. METHODS: We conducted an online cross-sectional survey of young MSM in China. Respondents were asked to report previous HBV and HCV testing, sociodemographic information, sexual risk factors for hepatitis infection, other STI testing and primary care physician (PCP) status. Associations were analysed by logistic regression. RESULTS: 503 eligible MSM completed the survey. 41.0% (206/503) of MSM had HCV tested, and 38.2% (60/157) of MSM with no or uncertain HBV vaccination had HBV tested. In multivariate analysis, HCV testing was correlated with HBV testing (adjusted OR (aOR) 22.98, 95% CI 12.11 to 43.60), HIV testing (aOR 3.64, 95% CI 1.92 to 6.91), HIV-positive status (aOR 1.78, 95% CI 1.07 to 2.98) and having a PCP (aOR 2.40, 95% CI 1.44 to 3.98). Among MSM with no or uncertain HBV vaccination, HBV testing was correlated with HCV testing (aOR 80.85, 95% CI 20.80 to 314.33), HIV testing (aOR 5.26, 95% CI 1.81 to 15.28), HIV-positive status (aOR 3.00, 95% CI 1.22 to 7.37) and having a PCP (aOR 2.69, 95% CI 1.00 to 7.26). CONCLUSIONS: Our data suggest many young MSM in China have not received hepatitis testing. HCV testing rates were lower than those recently reported among MSM in Australia and the USA. The strong correlation between HBV and HCV testing suggests bundled testing interventions may be useful for MSM in China. Men with a PCP were more likely to have received hepatitis testing, consistent with literature demonstrating the importance of primary care in expanding access to testing

Crowdsourcing to Improve HIV and Sexual Health Outcomes: a Scoping Review.

PURPOSE OF REVIEW: This review synthesizes evidence on the use of crowdsourcing to improve HIV/sexual health outcomes. RECENT FINDINGS: We identified 15 studies, including four completed randomized controlled trials (RCTs), one planned RCT, nine completed observational studies, and one planned observational study. Three of the four RCTs suggested that crowdsourcing is an effective, low-cost approach for improving HIV testing and condom use among key populations. Results from the observational studies revealed diverse applications of crowdsourcing to inform policy, research, and intervention development related to HIV/sexual health services. Crowdsourcing can be an effective tool for informing the design and implementation of HIV/sexual health interventions, spurring innovation in sexual health research, and increasing community engagement in sexual health campaigns. More research is needed to examine the feasibility, acceptability, and effectiveness of crowdsourcing interventions, particularly in low- and middle-income countries

Spatiotemporal complexity of a ratio-dependent predator-prey system

In this paper, we investigate the emergence of a ratio-dependent predator-prey system with Michaelis-Menten-type functional response and reaction-diffusion. We derive the conditions for Hopf, Turing and Wave bifurcation on a spatial domain. Furthermore, we present a theoretical analysis of evolutionary processes that involves organisms distribution and their interaction of spatially distributed population with local diffusion. The results of numerical simulations reveal that the typical dynamics of population density variation is the formation of isolated groups, i.e., stripelike or spotted or coexistence of both. Our study shows that the spatially extended model has not only more complex dynamic patterns in the space, but also chaos and spiral waves. It may help us better understand the dynamics of an aquatic community in a real marine environment.Comment: 6pages, revtex

Sex tourism among Chinese men who have sex with men: a cross-sectional observational study.

BACKGROUND: Sex tourism among men who have sex with men (MSM) may exacerbate transmission of HIV and other sexually transmitted infections (STIs). Sex tourism is defined as purchasing sex with gifts or money outside of one's hometown. Our objective was to characterize the frequency, socio-demographic characteristics, and sexual risk behaviors among Chinese MSM sex tourists. METHODS: An online, cross-sectional survey for high-risk MSM throughout China was conducted in November 2015 covering sociodemographic characteristics, sexual risk behaviors, and sex tourism. Univariate and multivariable logistic regressions were performed to identify correlates of sex tourism. The mean MSM HIV prevalence of sex tourism journey origins and destinations were compared. RESULTS: Of 1189 MSM who completed the survey, 62 (5%) men identified as sex tourists; among these sex tourists, twenty (32%) traveled primarily to purchase sex and the remainder purchased sex while traveling for another purpose. There was minimal socio-demographic and behavioral difference between the two groups. In multivariable analyses, adjusting for age and income, sex tourism was correlated with high-risk sexual behaviors, higher income (aOR 4.44, 95%CI 1.77-11.18) and living with HIV (aOR 2.79, 95%CI 1.03-7.55). Sex tourism was more often from locations with lower to higher MSM HIV prevalence (mean = 4.47, SD = 2.01 versus mean = 6.86, SD = 5.24). CONCLUSION: MSM sex tourists were more likely to have risky sexual behaviors and travel to locations with a higher HIV prevalence. MSM sex tourists may be part of core groups that are disproportionately responsible for MSM HIV transmission. Enhanced surveillance and interventions tailored to MSM sex tourists should be considered