Robust stability for stochastic Hopfield neural networks with time delays

This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2006 Elsevier Ltd.In this paper, the asymptotic stability analysis problem is considered for a class of uncertain stochastic neural networks with time delays and parameter uncertainties. The delays are time-invariant, and the uncertainties are norm-bounded that enter into all the network parameters. The aim of this paper is to establish easily verifiable conditions under which the delayed neural network is robustly asymptotically stable in the mean square for all admissible parameter uncertainties. By employing a Lyapunov–Krasovskii functional and conducting the stochastic analysis, a linear matrix inequality (LMI) approach is developed to derive the stability criteria. The proposed criteria can be checked readily by using some standard numerical packages, and no tuning of parameters is required. Examples are provided to demonstrate the effectiveness and applicability of the proposed criteria.This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant GR/S27658/01, the Nuffield Foundation of the UK under Grant NAL/00630/G, and the Alexander von Humboldt Foundation of German

Stochastic stability of uncertain Hopfield neural networks with discrete and distributed delays

This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2006 Elsevier Ltd.This Letter is concerned with the global asymptotic stability analysis problem for a class of uncertain stochastic Hopfield neural networks with discrete and distributed time-delays. By utilizing a Lyapunov–Krasovskii functional, using the well-known S-procedure and conducting stochastic analysis, we show that the addressed neural networks are robustly, globally, asymptotically stable if a convex optimization problem is feasible. Then, the stability criteria are derived in terms of linear matrix inequalities (LMIs), which can be effectively solved by some standard numerical packages. The main results are also extended to the multiple time-delay case. Two numerical examples are given to demonstrate the usefulness of the proposed global stability condition.This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant GR/S27658/01, the Nuffield Foundation of the UK under Grant NAL/00630/G, and the Alexander von Humboldt Foundation of Germany

Design of exponential state estimators for neural networks with mixed time delays

This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2007 Elsevier Ltd.In this Letter, the state estimation problem is dealt with for a class of recurrent neural networks (RNNs) with mixed discrete and distributed delays. The activation functions are assumed to be neither monotonic, nor differentiable, nor bounded. We aim at designing a state estimator to estimate the neuron states, through available output measurements, such that the dynamics of the estimation error is globally exponentially stable in the presence of mixed time delays. By using the Laypunov–Krasovskii functional, a linear matrix inequality (LMI) approach is developed to establish sufficient conditions to guarantee the existence of the state estimators. We show that both the existence conditions and the explicit expression of the desired estimator can be characterized in terms of the solution to an LMI. A simulation example is exploited to show the usefulness of the derived LMI-based stability conditions.This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant GR/S27658/01, the Nuffield Foundation of the UK under Grant NAL/00630/G, the Alexander von Humboldt Foundation of Germany, the Natural Science Foundation of Jiangsu Education Committee of China under Grants 05KJB110154 and BK2006064, and the National Natural Science Foundation of China under Grants 10471119 and 10671172

BONE MINERAL DENSITY AND THYROID-STIMULATING HORMONE ASSOCIATION IN POSTMENOPAUSAL HEALTHY WOMEN

Amaç: Postmenopozal sağlıklı kadınlarda femoral ve lomber kemik mineralyoğunluğunun tiroid stimülan hormon düzeyi ile ilişkisini araştırmak.Gereç ve yöntem: Çalışmaya 152 postmenopozal sağlıklı kadın dahil edilmiştir.Kemik mineral yoğunluğu, DEXA ile anterior-posterior lomber (L1-L4) spine'ler ve femurüzerinden yapıldı ve TSH düzeyi kemilüminesans yöntemi kullanılarak ölçüldü.İstatistiksel analizde Pearson korelasyonu, t - testi, tek yönlü varyans analizi (ANOVA),multiple regresyon analizi kullanıldı p < 0,05 anlamlı kabul edildi.Bulgular: Tiroid stimülan hormon düzeyi ile kemik mineral yoğunluğu arasında anlamlıbir ilişki saptanmadı (toplam lomber spinal (L1-4) T skoru için p = 0,11 ve toplam femurT skoru için p = -0,03). Toplam femur T skoru ile yaş, menopoz yılı, vücut kitle indeksiarasındaki ilişki anlamlı bulundu (p<0,05) Toplam lomber spinal (L1-4) T skoru ile vücutkitle indeksi, menopoz yılı ve hormon replasman tedavisi kullanım süresi arasındakiilişki anlamlı bulundu (p < 0,05). Doğal menopozda, cerrahi menopoza göre toplamfemur T skoru ölçümleri anlamlı olarak daha düşük bulundu (p=0,04). Toplam femur vetoplam lomber spinal (L1-4) T skoru ölçümlerinin her ikisi ile VKI arasında anlamlı birilişki saptandı (p < 0,01) (femur için r2 = 0,15, lomber vertebra spine için r2 =0,12).Sonuç: Postmenopozal sağlıklı kadınlarda kemik mineral yoğunluğu ile iroid stimülanhormon değerleri arasında anlamlı bir korelasyon saptanmadı. Tiroid stimülan hormondeğerinin kemik mineral yoğunluğunu göstermek için iyi bir marker olmadığı düşünüldü.Vücut kitle indeksi ile hem spinal hem de femur T skorları arasında anlamlı bir ilişkiolması ile birlikte vücut kitle indeksinin kemik mineral yoğunluğu için iyi bir göstergeolabileceği görüldü. Benzer çalışmalar menopozal ve premenopozal dönemlerde de yapılarakkemik mineral yoğunluğunun tiroid stimülan hormon düzeyi ve vücut kitle indeksiile ilişkisi daha geniş profilde değerlendirilebilir ve tekrarlayan ölçümlerle bu değişimdaha iyi gösterilebilir.Objective: To investigate the association between bone mineral density (BMD) andserum Thyroid-Stimulating Hormone levels in postmenopausal healthy women.Postmenopozal sağlıklı kadınlarda kemik mineral yoğunluğu-tiroid stimülan 2 hormon ilişkisiMaterial and method: 152 postmenopausal healthy women were included in ourstudy. We measured BMD at the lumbar spine (L1-L4) and femur using dual energy Xrayabsorptiometry and serum TSH concentration using chemiluminisence. Pearson'sCorrelation, t-test, analysis of variance (ANOVA), multiple regression analysis wereused in statistical analysis and p<0.05 was considered statistically significant.Results: There was no significant relation between TSH levels and BMD scores (forlumbar spine p = 0,11 and femur p = -0,03). A significant relation was determinedbetween the total femur T score and age, years since menopause, body mass index(VKI) (p<0.05 ). Also there was a significant relation between total lumbar spine T scoreand VKI, years since menopause, duration for hormone replacement therapy (p<0.05).Total femur T score was lower in natural menopause group than surgical menopausegroup (p=0.04). There was a significant correlation between VKI and both T scores (p <0.01) (for femur r2 = 0.15, for lumber spine r2 =0.12)Conclusion: We did not determine a significant relation between BMD and TSH. TSHvalue seems not a good predictive marker for detecting bone mineral density. Therewas a close relation between VKI and BMD, so we conclude that VKI is a usefulindicator for detecting BMD. Similar studies can be performed in premenopausal andmenopausal women to show the association between TSH, VKI and BMD

Global exponential stability of generalized recurrent neural networks with discrete and distributed delays

This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2006 Elsevier Ltd.This paper is concerned with analysis problem for the global exponential stability of a class of recurrent neural networks (RNNs) with mixed discrete and distributed delays. We first prove the existence and uniqueness of the equilibrium point under mild conditions, assuming neither differentiability nor strict monotonicity for the activation function. Then, by employing a new Lyapunov–Krasovskii functional, a linear matrix inequality (LMI) approach is developed to establish sufficient conditions for the RNNs to be globally exponentially stable. Therefore, the global exponential stability of the delayed RNNs can be easily checked by utilizing the numerically efficient Matlab LMI toolbox, and no tuning of parameters is required. A simulation example is exploited to show the usefulness of the derived LMI-based stability conditions.This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant GR/S27658/01, the Nuffield Foundation of the UK under Grant NAL/00630/G, and the Alexander von Humboldt Foundation of Germany

On global asymptotic stability of neural networks with discrete and distributed delays

This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2005 Elsevier Ltd.In this Letter, the global asymptotic stability analysis problem is investigated for a class of neural networks with discrete and distributed time-delays. The purpose of the problem is to determine the asymptotic stability by employing some easy-to-test conditions. It is shown, via the Lyapunov–Krasovskii stability theory, that the class of neural networks under consideration is globally asymptotically stable if a quadratic matrix inequality involving several parameters is feasible. Furthermore, a linear matrix inequality (LMI) approach is exploited to transform the addressed stability analysis problem into a convex optimization problem, and sufficient conditions for the neural networks to be globally asymptotically stable are then derived in terms of a linear matrix inequality, which can be readily solved by using the Matlab LMI toolbox. Two numerical examples are provided to show the usefulness of the proposed global stability condition.This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant GR/S27658/01, the Nuffield Foundation of the UK under Grant NAL/00630/G, and the Alexander von Humboldt Foundation of Germany

The association of pyschosocial factors with the risk score and the risk factors of coronary heart disease in worklife

Giriş ve Amaç: Koroner kalp hastalığı (KKH) için bilinen biyolojik ve davranışsal risk etmenlerinin yanı sıra psikososyal etmenler önemli bir risk etmeni olarak kabul görmektedir. Bugüne kadar özellikle gelişmiş ülkelerde iş gerilimi ve KKH ilişkisi üzerine yapılmış pek çok araştırma bulunmakla birlikte gelişmekte olan ülkelerde az sayıda araştırma bulunmaktadır. Bu araştırmanın amacı; Balçova İlçesi'ne bağlı olan 5 mahallede yaşayan 30-64 yaş arası toplumda iş gerilimi ve koroner kalp hastalığı (KKH) riski ve metabolik sendrom arasındaki ilişkinin incelenmesidir. Yöntem: Kesitsel ve analitik tipte toplum tabanlı bir araştırmadır. Araştırma örneği, Balçova'nın Kalbi (BAK) projesine katılan 30-64 yaş, çalışan bireyler arasından tabakalı rasgele yöntemi ile seçilmiştir. Anketörler Nisan - Haziran 2010 arasında seçilen örnekteki kişilerin evlerine giderek yüz yüze görüşerek "iş yükü-kontrol-destek" modelini temel alan ölçek aracılığıyla verileri toplamıştır. Çözümlemeler 191 kadın ve 216 erkek çalışan üzerinden yapılmıştır. Bağımlı değişkenler ile bağımsız değişkenler arasındaki ilişkilerin çözümlemesi için t- testi, ki-kare, ANCOVA ve lojistik regresyon analizleri yapılmıştır. Bulgular: Kadınların erkeklere göre daha eğitimli oldukları, daha çok beyaz yakalı işlerde çalıştıkları ve ekonomik durum algılarının daha iyi olduğu saptanmıştır. Erkeklerin %20'si, kadınların ise %18'i yüksek gerilimli işlerde çalışmaktaydı. Hem Framingham Risk Skoru hem de metabolik sendrom ile yapılan çözümlemelerde iş gerilimi ve bileşenleri ile istatistiksel olarak anlamlı bir ilişki saptanmamıştır. Eğitim, yaş, mesleksel durumuna göre yapılan düzeltmeler bulgularda bir değişikliğe neden olmamıştır. Sosyal destek durumu ve iş gerilimi arasındaki etkileşim de istatistiksel olarak anlamlı bulunmamıştır. Ayrıca temel KKH risk etmenleri ile ayrı ayrı yapılan analizlerde de iş gerilimi ve bileşenleri arasında istatisitksel olarak anlamlı ilişki saptanmamıştır. Sonuç: Araştırmada iş gerilimi ile temel KKH risk etmenleri ile hesaplanan Framingham Risk Skoru ve metabolik sendrom arasında istatistiksel olarak anlamlı bir ilişki saptanamamıştır. Psikososyal etmenler KKH için gelişmiş ülkelerde önemli bir risk etmeni olarak görülmekle birlikte, gelişmekte olan ülkelerde benzer sonuçlara dair çok az kanıt bulunmaktadır. Background: Beside the well established biological and behavioral risk factors, psychosocial factors are accepted as important risk factors for coronary heart diseases (CHD). While there is abundant evidence for the association between job strain and CHD in developed countries, there has been inadequate research on this association in developing countries. The aim of this study is to examine the association between job strain and the risk of CHD and metabolic syndrome among the 30-64 year old residents living in 5 neighbourhoods of the Balçova district. Method: This is a population-based cross sectional study. The study sample was derived with stratified random sampling technique from the employed individuals aged between 30 to 64 who participated in "Balçova's Heart Project" . The survey was conducted by means of a face to face interviewbased on the demand-control-support questionnaire applied in participants' houses between April-June 2010. 191 female and 216 male participants were included in the analyses. T-test, chi-square test, ANCOVA and logistic regression models were used in order to assess the association between the dependent and independent variables. Results: Women were found to have higher education levels, have more white-collar jobs, and have better economic status perception than men. 20% of men and 18% of women have been working in high-strained jobs. There was significant association of job strain with neither the Framingham risk score nor metabolic syndrome. The adjustments for education, age, and occupation did not alter the results. The interaction between the social support and job strain was also not signicant. Moreover no significant association was obtained in the separate analyses performed in each major CHD risk factor for job strain and for its each subdomain. Conclusion: In the study it was concluded that job strain did not have an impact on both the Framingham risk score and metabolic syndrome. Although pyschosocial factors are known as important risk factors for CHD in developed countries, the evidence in developing countries is scarce

A Cross - Sectional Analysis of The Association of Job Strain with Metabolic Syndrome and 10-Year Risk of Coronary Heart Disease

Objective: Beside the well-established biological and behavioral risk factors, psychosocial factors have been accepted as important risk factors for coronary heart diseases (CHD). While there is abundant evidence for the association between job strain and CHD in developed countries, more research needed on this association in developing countries. This study aims to examine the association between job strain and the risk of CHD and metabolic syndrome among the 30-64-year-old employed individuals