Differentiable Physics Simulations with Contacts: Do They Have Correct Gradients w.r.t. Position, Velocity and Control?

In recent years, an increasing amount of work has focused on differentiable physics simulation and has produced a set of open source projects such as Tiny Differentiable Simulator, Nimble Physics, diffTaichi, Brax, Warp, Dojo and DiffCoSim. By making physics simulations end-to-end differentiable, we can perform gradient-based optimization and learning tasks. A majority of differentiable simulators consider collisions and contacts between objects, but they use different contact models for differentiability. In this paper, we overview four kinds of differentiable contact formulations - linear complementarity problems (LCP), convex optimization models, compliant models and position-based dynamics (PBD). We analyze and compare the gradients calculated by these models and show that the gradients are not always correct. We also demonstrate their ability to learn an optimal control strategy by comparing the learned strategies with the optimal strategy in an analytical form. The codebase to reproduce the experiment results is available at https://github.com/DesmondZhong/diff_sim_grads.Comment: 2nd AI4Science Workshop at ICML 202

Childbearing May Increase the Risk of Nondiabetic Cataract in Chinese Women’s Old Age

Backgrounds. Ocular changes may arise during pregnancy and after childbirth, but very few studies have reported the association between childbearing and cataract among older adults. Methods. 14,292 individuals aged 60+ years were recruited in Xiamen, China, in 2013. Physician-diagnosed cataract and diabetes status were assessed by a self-reported questionnaire. Childbearing status was measured by number of children (NOC). Structural equation modeling (SEM) analysis was conducted to examine the relationships among NOC, diabetes, and cataract. Gender-specific logistic models regressing nondiabetic cataract on NOC were performed by adjusting some covariates. Results. 14,119 participants had complete data, of whom 5.01% suffered from cataract, with higher prevalence in women than men (6.41% versus 3.51%). Estimates of SEM models for women suggested that both NOC and diabetes were risk factors for cataract and that no correlation existed between NOC and diabetes. Women who had one or more children faced roughly 2–4 times higher risk of nondiabetic cataract than their childless counterparts (OR [95% CI] = 3.88 [1.24, 17.71], 3.21 [1.04, 14.52], 4.32 [1.42, 19.44], 4.41 [1.46, 19.74], and 3.98 [1.28, 18.10] for having 1, 2, 3, 4-5, and 6 or more children, resp.). Conclusions. Childbearing may increase the risk of nondiabetic cataract in Chinese women’s older age

Evaluation of dietary intake of lactating women in China and its potential impact on the health of mothers and infants

BACKGROUND: Optimal nutrition for lactating mothers is importance for mother and infants’ health and well-being. We determined the nutrient intake and dietary changes during the first 3-month of lactation, and its potential effect on health and disease risk. METHOD: Personal interviews were conducted to collect a 24h diet recall questionnaire from 199 healthy lactating women in the postpartum days 2, 7, 30, 90 and healthy 58 non-pregnant women served as the controls. RESULTS: We found in lactating women (1) the mean daily energy and carbohydrate intake was lower than that of the Chinese Recommended Nutrient Intake (RNI, 2600 Kcal, 357.5 ~ 422.5g) by 11% ~ 17% and 33% ~ 49%, respectively; (2) the fat intake increased from 3% to 13%, which was 9 ~ 77% higher than the RNI (57 ~ 86.7g); (3) the protein intake exceeded the RNI of 85g by 32 ~ 53%; (4) the total calories consumed from carbohydrate (39%-44%), fat (34% ~ 42%) and protein (20%-23%) failed to meet Chinese RNI (5) the intake of vitamin C, B1, folate, zinc, dietary fiber, and calcium was 5% ~ 73% lower than the RNI while vitamin B(2), B(3), E, iron and selenium intake was 20% to 3 times higher than the RNI. Nutrient intake in the control group was lower for all nutrients than the recommended RNI. CONCLUSION: Lactating women on a self-selected diet did not meet the Chinese RNI for many important micronutrients, which may influence the nutritional composition of breast milk and thus impact the potential health of mothers and infants. RNI should consider the regional dietary habits and culture. A single national RNI is not applicable for all of China. Nutritional education into the community is needed

The impact of medical insurance on medical expenses for older Chinese: Evidence from the national baseline survey of CLHLS.

With the deepening population aging process in China, the medical expenses of older adults has become a widespread concerned. Medical insurance is a major source of Chinese medical financing and payment. The study aims to understand the current status of medical expenses for older adults and explore the effect of different types of health insurance on medical expenses in China.The data came from the Chinese Longitudinal Health Longevity Survey (CLHLS) in 2014. The Kruskal-Wallis test and general multivariate linear regression model were applied to analyze the current situation and to explore how medical insurance as the main payment impacts medical expenses.A total of 4376 older participants were included in this study. The median of medical expenses of a total was 1500 Yuan per year. The proportions of participants who had the urban employee-based basic medical insurance (UE-BMI), the urban residents basic medical insurance (UR-BMI), the new rural cooperative medical insurance scheme (NCMS), and the commercial medical insurance were 10.8%, 8.4%, 72.7%, and 0.9%, respectively. 34.8% of older adults paid the health care service via the NCMS and 11.9% paid via the UE-BMI. Participating in the NCMS and UR-BMI are significantly related to the level of the medical fees of older adults. UE-BMI, UR-BMI, and NCMS as main payment eased the pressure of medical expenses.The influence of different types of medical insurances as main payments on the medical expenses of older adults is varied. Implementation of medical insurance should be taken to further relieve the medical expenses of older adults

Genetic Removal of the CH1 Exon Enables the Production of Heavy Chain-Only IgG in Mice

Nano-antibodies possess great potential in many applications. However, they are naturally derived from heavy chain-only antibodies (HcAbs), which lack light chains and the CH1 domain, and are only found in camelids and sharks. In this study, we investigated whether the precise genetic removal of the CH1 exon of the γ1 gene enabled the production of a functional heavy chain-only IgG1 in mice. IgG1 heavy chain dimers lacking associated light chains were detected in the sera of the genetically modified mice. However, the genetic modification led to decreased expression of IgG1 but increased expression of other IgG subclasses. The genetically modified mice showed a weaker immune response to specific antigens compared with wild type mice. Using a phage-display approach, antigen-specific, single domain VH antibodies could be screened from the mice but exhibited much weaker antigen binding affinity than the conventional monoclonal antibodies. Although the strategy was only partially successful, this study confirms the feasibility of producing desirable nano-bodies with appropriate genetic modifications in mice

Reversible Non-Volatile Electronic Switching in a Near Room Temperature van der Waals Ferromagnet

The ability to reversibly toggle between two distinct states in a non-volatile method is important for information storage applications. Such devices have been realized for phase-change materials, which utilizes local heating methods to toggle between a crystalline and an amorphous state with distinct electrical properties. To expand such kind of switching between two topologically distinct phases requires non-volatile switching between two crystalline phases with distinct symmetries. Here we report the observation of reversible and non-volatile switching between two stable and closely-related crystal structures with remarkably distinct electronic structures in the near room temperature van der Waals ferromagnet Fe$_{5-\delta}$GeTe$_2$. From a combination of characterization techniques we show that the switching is enabled by the ordering and disordering of an Fe site vacancy that results in distinct crystalline symmetries of the two phases that can be controlled by a thermal annealing and quenching method. Furthermore, from symmetry analysis as well as first principle calculations, we provide understanding of the key distinction in the observed electronic structures of the two phases: topological nodal lines compatible with the preserved global inversion symmetry in the site-disordered phase, and flat bands resulting from quantum destructive interference on a bipartite crystaline lattice formed by the presence of the site order as well as the lifting of the topological degeneracy due to the broken inversion symmetry in the site-ordered phase. Our work not only reveals a rich variety of quantum phases emergent in the metallic van der Waals ferromagnets due to the presence of site ordering, but also demonstrates the potential of these highly tunable two-dimensional magnets for memory and spintronics applications

Role of regenerating gene IA expression on local invasion and survival in nasopharyngeal carcinoma

Abstract Background Regenerating gene IA (REGIA) plays an important role in tissue regeneration and tumors prognosis of epithelium origin. However, the role of REGIA in nasopharyngeal carcinoma (NPC) is unclear. This study aims to investigate the expression and function of REG1A in NPC. Results We have found that there was 63 patients with REGIA positive expression of 155 patients in this study (40.65%). The positive expression rate of REGIA was 30.50, 44.44 and 47.83% in stage T2, T3 and T4 patients, respectively. The REGIA expression was significantly difference in T2 and T4 stage tumors or T2 and T3–T4 stage. The positive expression rate of REGIA was found to be higher in patients with cervical lymph node persistence than those with cervical lymph node complete regression. Patients with negative REGIA expression had a better overall survival and free survival than those with REGIA positive expression. In addition, according to the univariate and multivariate analysis, the REGIA expression was an independent adverse prognostic factor for NPC patients. Conclusion REGIA expression was a useful biomarker in NPC patients for assessing T stage and survival

The Suppression of WRKY44 by GIGANTEA-miR172 Pathway Is Involved in Drought Response of <i>Arabidopsis thaliana</i>

<div><p>Water availability is an important environmental factor that controls flowering time. Many plants accelerate flowering under drought conditions, a phenomenon called drought escape. Four pathways are involved in controlling flowering time, but which ones participate in drought escape is not yet known. In this study, plants with loss-of-function mutations of <i>GIGANTEA (GI</i>) and <i>CONSTANS</i> (CO) exhibited abnormal drought-escape phenotypes. The peak mRNA levels of <i>GI</i> and FKF1 (Flavin-binding Kelch domain F box protein 1) and the mRNA levels of <i>CO</i> and FT (Flowering locus T) changed under drought stress. The microRNA factor <i>miRNA172E</i> was up-regulated by drought stress, and its up-regulation was dependent on <i>GI</i>, while other <i>miRNA172s</i> were not. Water-loss analyses indicated that <i>gi</i> mutants were more sensitive while <i>miRNA172</i> over-expressing (<i>miRNA</i>172-OX) plants were less so to drought stress than wild-type plants. Digital gene expression and real-time PCR analyses showed that <i>WRKY44</i> was down-regulated by <i>GI</i> and <i>miRNA172</i>. The WRKY44 protein could interact with TOE1 (a target of <i>miRNA</i>172) in a yeast two-hybrid system. We proposed that <i>GI–miRNA172–WRKY44</i> may regulate drought escape and drought tolerance by affecting sugar signaling in <i>Arabidopsis</i>.</p> </div