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Authors: Guo, Zhenhua | Jiang, Song | Xie, Feng

Article Type: Research Article

Abstract: This paper is concerned with the existence of global weak solutions to the 1D compressible Navier–Stokes equations with density-dependent viscosity and initial density that is connected to vacuum with discontinuities. When the viscosity coefficient is proportional to ρθ with 0<θ<max{3−γ, 3/2} where ρ is the density, we prove a global existence theorem, improving thus the result in Meth. Appl. Anal. 12 (2005), 239–252, where 0<θ<1 is required. Moreover, we show that the domain occupied by the fluid expands into vacuum at an algebraic rate as time grows up due to the dispersion effect of the total pressure. It is worth …pointing out that our result covers the interesting case of the Saint-Venant model for shallow water (i.e., θ=1, γ=2). Show more

Keywords: compressible Navier–Stokes equations, vacuum, existence, asymptotic behavior

DOI: 10.3233/ASY-2008-0902

Citation: Asymptotic Analysis, vol. 60, no. 1-2, pp. 101-123, 2008

Authors: Xie, Feng | Han, Maoan | Zhang, Weijiang

Article Type: Research Article

Abstract: In this paper, a class of three-dimensional singularly perturbed systems of ordinary differential equations with two fast variables are considered. Sufficient conditions for the existence of canards are obtained by asymptotic methods.

Keywords: canards, slow manifolds, singular perturbations

Citation: Asymptotic Analysis, vol. 47, no. 1-2, pp. 95-106, 2006

Authors: Michalowsky, Bernhard | Hoffmann, Wolfgang | Xie, Feng

Article Type: Research Article

Abstract: Background: Assessing health-related quality of life in dementia poses challenges due to patients’ cognitive impairment. It is unknown if the newly introduced EQ-5D five-level version (EQ-5D-5L) is superior to the 3-level version (EQ-5D-3L) in this cognitively impaired population group. Objective: To assess the psychometric properties of the EQ-5D-5L in comparison to the EQ-5D-3L in patients living with dementia (PwD). Methods: The EQ-5D-3L and EQ-5D-5L were assessed via interviews with n  = 78 PwD at baseline and three and six months after, resulting in 131 assessments. The EQ-5D-3L and EQ-5D-5L were evaluated in terms of acceptability, agreement, ceiling effects, redistribution properties and …inconsistency, informativity as well as convergent and discriminative validity. Results: Mean index scores were higher for the EQ-5D-5L than the EQ-5D-3L (0.70 versus 0.64). Missing values occurred more frequently in the EQ-5D-5L than the EQ-5D-3L (8%versus 3%). Agreement between both measures was acceptable but poor in PwD with moderate to severe cognitive impairment. The index value’s relative ceiling effect decreased from EQ-5D-3L to EQ-5D-5L by 17%. Inconsistency was moderate to high (13%). Absolute and relative informativity increased in the EQ-5D-5L compared to the 3L. The EQ-5D-5L demonstrated a lower discriminative ability and convergent validity, especially in PwD with moderate to severe cognitive deficits. Conclusion: The EQ-5D-5L was not superior as a self-rating instrument due to a lower acceptability and discriminative ability and a high inconsistency, especially in moderate to severe dementia. The EQ-5D-3L had slightly better psychometric properties and should preferably be used as a self-rating instrument in economic evaluations in dementia. Show more

Keywords: Alzheimer’s diseases, dementia, EQ-5D, patient-reported outcomes, preference-based measures, quality of life, validation

DOI: 10.3233/JAD-210421

Citation: Journal of Alzheimer's Disease, vol. 83, no. 1, pp. 77-87, 2021

Authors: Xie, Feng | Zhou, Honghai | Zhao, Wenju | Huang, Lixin

Article Type: Research Article

Abstract: BACKGROUND: Lumbar disc herniation may result in excruciating pain due to it being one of the most common diseases related to changes of intervertebral disc (IVD). In order to find a better clinical treatment and prevention scheme for relieving the pain caused by spine degeneration, the mechanical behavior analysis of IVD must be studied. OBJECTIVE: A finite element method (FEM) is used in this study to analyze the mechanical behaviors of healthy and herniated IVD. METHOD: In order to compare the responses of IVD under different loading conditions for the annulus fibrosus of IVD, the hyperelastic and elastic constitutive FE …models were used in the FEM. RESULTS: The comparison shows that hyperelastic FE models have a much better capability to describe the mechanical behaviors of the IVD than elastic FE models. It can be found from FE simulation that there was a higher stress concentration at the annulus fibrosus of the herniated disc than the healthy disc. CONCLUSIONS: Higher stress concentration resulted in more damage and ease of bringing out lumbar disc herniation. Numerical examples of FE simulation indicate that the FEM with hyperelastic constitutive model has very good capability for analyzing the mechanical behaviors of IVD. Show more

Keywords: Intervertebral disc, finite element model, hyperelastic, lumbar disc herniation, mechanical behavior

DOI: 10.3233/THC-171320

Citation: Technology and Health Care, vol. 25, no. S1, pp. 177-187, 2017

Authors: Rädke, Anika | Michalowsky, Bernhard | Thyrian, Jochen René | Eichler, Tilly | Xie, Feng | Hoffmann, Wolfgang

Article Type: Research Article

Abstract: Background: Dementia care management (DCM) aims to provide optimal treatment for people with dementia (PwD). Treatment and care needs are dependent on patients’ sociodemographic and clinical characteristics and thus, economic outcomes could depend on such characteristics. Objective: To detect important subgroups that benefit most from DCM and for which a significant effect on cost, QALY, and the individual cost-effectiveness could be achieved. Methods: The analysis was based on 444 participants of the DelpHi-trial. For each subgroup, the probability of DCM being cost-effective was calculated and visualized using cost-effectiveness acceptability curves. The impact of DCM on individual costs and QALYs was …assessed by using multivariate regression models with interaction terms. Results: The probability of DCM being cost-effective at a willingness-to-pay of 40,000€ /QALY was higher in females (96% versus 16% for males), in those living alone (96% versus 26% for those living not alone), in those being moderately to severely cognitively (100% versus 3% for patients without cognitive impairment) and functionally impaired (97% versus 16% for patients without functional impairment), and in PwD having a high comorbidity (96% versus 26% for patients with a low comorbidity). Multivariate analyses revealed that females (b = –10,873; SE = 4,775, p  = 0.023) who received the intervention had significantly lower healthcare cost. DCM significantly improved QALY for PwD with mild and moderate cognitive (b = +0.232, SE = 0.105) and functional deficits (b = +0.200, SE = 0.095). Conclusion: Patients characteristics significantly affect the cost-effectiveness. Females, patients living alone, patients with a high comorbidity, and those being moderately cognitively and functionally impaired benefit most from DCM. For those subgroups, healthcare payers could gain the highest cost savings and the highest effects on QALYs when DCM will be implemented. Show more

Keywords: Alzheimer’s disease, cost-effectiveness acceptability curve, cost-effectiveness analysis, dementia, economic evaluation, health care costs, individual cost-effectiveness ratio, net benefit regression, net monetary benefit

DOI: 10.3233/JAD-190578

Citation: Journal of Alzheimer's Disease, vol. 74, no. 2, pp. 449-462, 2020