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A Review on Technologies for the Use of CO2 as a Working Fluid in Refrigeration and Power Cycles

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Energy and Power Engineering 2024年第6期16卷 217-256页

作者： Orelien T. boupda Hyacinthe D. Tessemo Isidore B. Nkounda Fongang Francklin G. Nyami Frederic Lontsi Thomas Djiako Laboratory of Energy Higher National Polytechnic School of Douala University of Douala Douala Cameroon Institut Ucac-Icam Douala Cameroon Department of Energy and Mechanical Engineering ISTA-IUG University of Ngaoundere Ngaoundere Cameroon

The use of carbon dioxide as a working fluid has been the subject of extensive studies in recent years, particularly in the field of refrigeration where it is at the heart of research to replace CFC and HCFC. Its thermodynamic properties make it a fluid of choice in the efficient use of energy at low and medium temperatures in engine cycles. However, the performance of transcritical CO2 cycles weakens under high temperature and pressure conditions, especially in refrigeration systems;On the other hand, this disadvantage becomes rather interesting in engine cycles where CO2 can be used as an alternative to the organic working fluid in small and medium-sized electrical systems for low quality or waste heat sources. In order to improve the performance of systems operating with CO2 in the field of refrigeration and electricity production, research has made it possible to develop several concepts, of which this article deals with a review of the state of the art, followed by analyzes in-depth and critical of the various developments to the most recent modifications in these fields. Detailed discussions on the performance and technical characteristics of the different evolutions are also highlighted as well as the factors affecting the overall performance of the systems studied. Finally, perspectives on the future development of the use of CO2 in these different cycles are presented.

关键词： Refrigeration Cycle Power Cycle System Performance Transcritical CO2 Cycles Working Fluid

Determinants of Sexual Activity among HIV-Infected Adolescents in Cameroon

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Open Journal of Pediatrics 2024年第5期14卷 921-936页

作者： Calixte Ida Penda Rachel Fotso Yogue Nelly Noubi Kamgaing Sena Mouna Penda Loïc boupda Francis Atéba Ndongo Christian Eyoum Ritha Mbono Betoko Grace Dalle Ngondi Patricia Epee Eboumbou Francisca Monebenimp Essome Henri Faculty of Medicine and Pharmaceutical Sciences University of Douala Douala Cameroon General Hospital of Douala Douala Cameroon Faculty of Medicine and Biomedical Sciences University of Yaound 1 Yaound Cameroon University Hospital Centre of Yaound Yaound Cameroon Mokolo Regional Hospital Annex Mokolo Cameroon University of Garoua Garoua Cameroon Mother and Child Centre of the Chantal Biya Foundation in Yaound Yaound Cameroon Douala Laquintinie Hospital Douala Cameroon District Hospital of Bonassama Douala Cameroon

Introduction: Adolescence is a period of transition to adulthood, including for HIV-infected adolescents (HIA), when sexual problems emerge. Few studies have been carried out on the sexuality of HIA. This study aimed to assess the sexual behavior of HIV-infected adolescents in Cameroon. Methodology: A cross-sectional study was conducted in three hospitals in the cities of Yaoundé and Douala, from November 2019 to June 2020. All HIA aged 13 to 19 years followed in the study who knew their HIV status were included in the study after obtaining their assent and their parent’s consent. Socio-demographic and clinical characteristics were collected, as well as sexual practices and the determinants of their sexual activity. A multivariate analysis was performed to explore the relationship between the different variables studied and the sexual activity of these adolescents. Results: Of 204 HIA enrolled in the study, 64 (31.7%) were sexually active, the mean age at first sexual intercourse was 15.6 ± 2.8 years and the sex ratio was 0.94. Of the adolescents in the study, 75.7% of girls and 61.2% of boys had regular sexual activity, while 21.3% of girls and 35.4% of boys had multiple sexual relationships in the six months preceding the study. Nearly 16 (25.0%) of the sexually active HIA had more than 2 sexual encounters per month, 6 (9.3%) of these encounters had been paid for and 9 (27.2%) of the girls had already had at least one pregnancy. More than 7 out of 10 HIA (79.6%) had used a condom the last time they had sex. Age less than 18 years [OR = 11.1 (95% CI: 3.1 - 39.4), p = 0.001], lack of remuneration [OR = 9.8 (95% CI: 2.0 - 47.4), p = 0.001] and self-care were significantly associated with sexual activity in HIA, while school attendance was a protective factor. Self-funded HIAs were 21 times more likely to be sexually active [OR = 21.6 (95% CI: 2.3 - 179), p = 0.004]. Conclusion: More than a third of HIV-infected adolescents were sexually active and risky sexual practi

关键词： HIV Adolescent Sexual Behavior Cameroon

Predictive Factors for Pre-Eclampsia: A Case-Control Study in Two Hospitals in Yaounde

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Open Journal of Obstetrics and Gynecology 2024年第4期14卷 565-574页

作者： Junie Annick Metogo Ntsama Ines Winnie Gouanfo Claude Hector Mbia Wilfried loic Tatsipie Pascal Mpono Madye Ngo Dingom Felix Essiben Claude Cyrille Noa Ndoua Faculty of Medicine and Biomedical Sciences University of Yaound&#233 I Yaound&#233 Cameroon Faculty of Medicine and Pharmaceutical Sciences University of Dschang Dschang Cameroon

Introduction: Pre-eclampsia is a major cause of maternal and prenatal morbidity and mortality, that complicates 2% to 8% of pregnancies worldwide. The aim of this study was to determine the predictive factors for pre-eclampsia in two hospitals in the city of Yaoundé. Methods: A case-control study was conducted at the Gynaecology & Obstetrics department of the Yaoundé Gynaeco-Obstetric and Paediatric Hospital (YGOPH) and the Main Maternity of the Yaoundé Central Hospital (MM-YCH) from February 1 to July 30, 2022. The cases were all pregnant women presenting with pre-eclampsia. The control group included pregnant women without pre-eclampsia. Descriptive statistics followed by logistic regression analyses were conducted with level of significance set at p-value Results: Included in the study were 33 cases and 132 controls, giving a total of 165 participants. The predictive factors for pre-eclampsia after multivariate analysis were: primiparity (aOR = 51.86, 95% CI: 3.01 - 1230.96, p = 0.045), duration of exposure to partner’s sperm Conclusion: The odds of pre-eclampsia increased with primiparity, duration of exposure to partner’s sperm < 3 months, personal history of pre-eclampsia and maternal history of pre-eclampsia. Recognition of these predictor factors would improve the ability to diagnose and monitor women likely to develop pre-eclampsia before the onset of disease for timely interventions.

关键词： Pre-Eclampsia Predictive Factors Yaoundé

The Hidden Side of the Story between the Placenta and Preeclampsia: Preliminary Results of a Prospective Cohort of Pregnant Women in Cameroon

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Open Journal of Obstetrics and Gynecology 2024年第4期14卷 610-620页

作者： Junie Annick Metogo Ntsama Ambroise Merci Engounou Seme Urielle Julie Tchuente Sutchueng Wilfried loic Tatsipie Christian Vagoda Henry-Leonard Chatelin Mol Madye Ngo Dingom Felix Essiben Cyrille Claude Noa Ndoua Yann chris Eng Odile Fernande Zeh Faculty of Medicine and Biomedical Sciences University of Yaound&#233 I Yaound&#233 Cameroon Faculty of Medicine and Pharmaceutical Sciences University of Dschang Dschang Cameroon

Introduction: Pre-eclampsia is a complication of pregnancy that generally occurs in the third trimester. It is associated with a maternal and foetal mortality rate of around 27%. In view of the grim picture painted by this condition for both mother and newborn, studies have been carried out into the early detection of patients at risk of developing pre-eclampsia. These make it possible to introduce pregnancy-specific monitoring and preventive strategies to reduce the incidence of the condition. Objective: To establish the link between placental ultrasound characteristics and the onset of pre-eclampsia. Methodology: A multicentre prospective cohort study was conducted in two hospitals in Yaoundé, namely the Yaoundé Gynaecological Obstetrics and Paediatrics Hospital and the Nkolndongo Health and Social Animation Centre, in the gynaecology and radiology departments over a period of 11 months, from October 2022 to August 2023. It included pregnant women who had undergone obstetric ultrasound between 12 and 18 weeks’ gestation. In addition to routine obstetric ultrasound, we performed obstetric Doppler measurements in these patients. The resistance index of the left and right uterine arteries, the umbilical artery and the placental volume were the characteristics sought. At the end of this examination, two groups were formed: cases (pathological Doppler group) and controls (normal Doppler group). Blood pressure and urine dipstick were taken at each antenatal visit until delivery, then during the immediate postpartum period and finally at 7 days, 21 days and 42 days after delivery. Results: Sixty-seven (67) patients were included. Of these, 35 (47.8%) had pathological Dopplers. Sixteen patients had arterial hypertension associated with proteinuria and were therefore labelled as pre-eclampsia (PE). This gives a prevalence of 23.9%. Fifteen (42.8%) of these patients belonged to the exposed group and one to the unexposed group. The mean IR of the pre-eclampsia patients was s

关键词： Pre-Eclampsia Doppler Ultrasound Placenta

Impact of Therapeutic Education on the Viral Load of HIV Infected Children and Adolescents on Antiretroviral Therapy at the Douala Laquintinie Hospital, Cameroon

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International Journal of Clinical Medicine 2019年第3期10卷 109-121页

作者： Calixte Ida Penda Anne-Cécile Zoung-Kanyi Bissek Serge Clotaire Bilong loic.ardin boupda Cécile Okala Francis Atéba Ndongo Grace Dallé Ngondi Else C. Moukoko Eboumbou Louis Richard Njock Olivier Koki Ndombo Clinical Sciences Department Faculty of Medicine and Pharmaceutical Sciences University of Douala Douala Cameroon Laquintinie Hospital Douala Douala Cameroon Faculty of Biomedical Sciences University of Yaoundé 1 Yaoundé Cameroon Division of Operational Research in Health Ministry of Public Health of Cameroon Yaoundé Cameroon National HIV Drug Resistance Surveillance and Prevention Working Group Yaoundé Cameroon Groupe Technique Central—CNLS Yaoundé Cameroon Biological Sciences Department Faculty of Medicine and Pharmaceutical Sciences University of Douala Douala Cameroon Clinical Biology Laboratory General Hospital Douala Cameroon Chirurgical Department Faculty of Medicine and Pharmaceutical Sciences University of Douala Douala Cameroon Chantal Biya Foundation Mother-Child Centre Yaoundé Cameroon

Introduction: One of the biggest challenges for HIV-infected adolescents on antiretroviral therapy (ART) is the long-term maintenance of viral suppression, which is the third 90% goal of UNAIDS. Therapeutic Education (TE), process of acquiring abilities and skills that help the patient to live optimally with his illness is one of the strategies that contribute to the achievement of viral suppression through the therapeutic adhesion contract and the follow-up of the patient. The aim of this study was to evaluate the impact of TE on the virologic response of children and adolescents aged 8 - 19 under ART and followed up at the Laquintinie Hospital of Douala (LHD). Method: A cross-sectional study was conducted at the Pediatric Unit of the HIV/AIDS Accredited Treatment Center (ATC) at LHD from February to May 2016. Children and adolescents aged 8 to 19 years on ART, followed in ATC/LHD whose parents had agreed to participate in the study, and who had achieved at least one viral load before and after initiation of TE, were recruited consecutively during routine medical follow-up. Data were collected from patients’ medical records and questionnaires administered to study participants. Results: A total of 198 children and adolescents were included in this study with an average age of 14 years (±3). In this study population, 86.1% of children aged 8 - 10 years had acquired knowledge of the importance of taking medications, 95.4% and 97.3% of adolescents aged 11 - 14 years and 15 - 19 years had knowledge of medication schedules respectively. Among children and adolescents with undetectable viral load prior to initiation of TE, 76.5% maintained an undetectable viral load after initiation of TE. In addition, 72.3% of those whose viral load was detectable before initiation of TE had acquired an undetectable or decreasing viral load after initiation of TE. The only exposure factor significantly associated with maintaining undetectable viral load after initiation of TE was

关键词： HIV Children Adolescents Therapeutic Education Cameroon

Ba substitution for enhancement of the thermoelectric properties of LaCoO_(3) ceramics(0≤x≤0.75)

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Journal of Advanced Ceramics 2019年第4期8卷 519-526页

作者： Mohamed Ali BOUSNINA Fabien GIOVANNELLI loic PERRIERE Guillaume GUEGAN Fabian DELORME Université Francois Rabelais de Tours CNRSINSA CVLGREMAN UMR7347IUT de Blois15 rue de la chocolaterieCS2903F-41029 Blois CedexFrance UniversitéParis 13 Sorbonne Paris CiteLaboratoire des Sciences des Procédés et des MatériauxCNRSUPR 340799 avenue J.B.ClémentF-93430 VilletaneuseFrance Institut de Chimie et des Matériaux Paris-Est UMR 7182 CNRS-UPEC2-8 Rue Henri Dunant94320 ThiaisFrance ST Microelectronics 16 Rue Pierre et Marie CurieTours 37100France

In the present work, dense perovskite ceramics were successfully prepared from a series of La1-xBaxCoO3 solid solutions in the range of substitution 0 ≤ x ≤ 0.75 using solid state reaction and conventional sintering. Structural properties of La1-xBaxCoO3 were systematically investigated and thermoelectric properties were measured in the temperature range of 330–1000 K. The results show that the thermoelectric properties of Ba-substituted LaCoO3 depend on x. Indeed, at 330 K, electrical conductivity presents an optimum value for x = 0.25 with a value of σmax ≈ 2.2×105 S·m–1 whereas the Seebeck coefficient decreases when x and/or the temperature increases. The Ba-substituted LaCoO3 samples exhibit p-type semiconducting behaviour. The best power factor value found is 3.4×10–4 W·m–1·K–2 at 330 K for x = 0.075, which is 10% higher than the optimum value measured in La1–xSrxCoO3 for x = 0.05. The thermal diffusivity and thermal conductivity increase with increasing temperature and Ba concentration. La1-xBaxCoO3 shows a maximum figure of merit(ZT = 0.048) for x = 0.05 at 330 K, 25% higher than the best value in La1–xSrxCoO3 compounds.

关键词： perovskite Ba-substituted LaCoO_(3) oxide thermoelectric p-type semiconductor

Formal verification of synchronous data-flow program transformations toward certified compilers

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Frontiers of Computer Science 2013年第5期7卷 598-616页

作者： Van Chan NGO Jean-Pierre TALPIN Thierry GAUTIER Paul Le GUERNIC loic BESNARD INRIA Rennes-Bretagne Atlantique Rennes 35042 France IRISA/CNRS Rennes 35042 France

Translation validation was invented in the 90＇s by Pnueli et al. as a technique to formally verify the correctness of code generators. Rather than certifying the code generator or exhaustively qualifying it, translation validators attempt to verify that program transformations preserve semantics. In this work, we adopt this approach to formally verify that the clock semantics and data dependence are preserved during the compilation of the Signal compiler. Translation valida- tion is implemented for every compilation phase from the initial phase until the latest phase where the executable code is generated, by proving the transformation in each phase of the compiler preserves the semantics. We represent the clock semantics, the data dependence of a program and its trans- formed counterpart as first-order formulas which are called clock models and synchronous dependence graphs （SDGs）, respectively. We then introduce clock refinement and depen- dence refinement relations which express the preservations of clock semantics and dependence, as a relation on clock mod- els and SDGs, respectively. Our validator does not require any instrumentation or modification of the compiler, nor any rewriting of the source program.

关键词： formal verification translation validation certi-fied compiler multi-clocked synchronous programs embed-ded systems.

Polychronous automata and their use for formal validation of AADL models

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Frontiers of Computer Science 2019年第4期13卷 677-697页

作者： Thierry GAUTIER Clement GUY Alexandre HONORAT Paul LE GUERNIC Jean-Pierre TALPIN loic BESNARD Univ. Rennes Inria Rennes-Bretagne-Atlantique Research Centre F-35000 Rennes France Univ. Rennes CNRS IRISA F-35000 Rennes France

This paper investigates how state diagrams can be best represented in the polychronous model of computation (MoC) and proposes to use this model for code validation of behavior specifications in architecture analysis & design language (AADL). In this relational MoC, the basic objects are signals, which are related through dataflow equations. Signals are associated with logical clocks, which provide the capability to describe systems in which components obey multiple clock rates. We propose a model of finite-state automata, called polychronous automata, which is based on clock relationships. A specificity of this model is that an automaton is submitted to clock constraints, which allows one to specify a wide range of control-related configurations, being either reactive or restrictive with respect to their control environment. A semantic model is defined for these polychronous automata, which relies on boolean algebra of clocks. Based on a previously defined modeling method for AADL software architectures using the polychronous MoC, the proposed model is used as a formal model for the AADL behavior annex. This is illustrated with a case study involving an adaptive cruise control system.

关键词： architecture modeling formal semantics finitestate automaton polychronous model synchronous concurrency code generation AADL

Tayloring cell populations for neurodegenerative diseases

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Neural Regeneration Research 2016年第10期11卷 1582-1583页

作者： jeff m.fortin loic p.deleyrolle brent a.reynolds Lillian S.Wells Department of Neurosurgery University of FloridaGainesvilleFLUSA PrestonA.Wells Jr.for Brain Tumor TherapyUniversity of FloridaGainesvilleFLUSA

Neurological disorders are increasing in prevalence world- wide, and interest in stem cell therapies for these amictions has increased over the past two decades. While many neu- rological injuries are too devastating for the repair capabil- ities of endogenous neural stem cells （NSCs） an alternative is to harvest stem cells from a donor and grow them in vitro, to be used later as a donor source for transplantation. Many research groups have already done this, first using animal models and now using clinical trial participants. Despite the regular flow of publications about cell replace- ment therapies for central nervous system （CNS） disorders, there is still a scarcity of clinically-relevant reports of effi- cacy. The capability of donor cells to undergo ample site-di- rected differentiation and functional integration seems to be lacking （Andressen, 2013）. So, while stem cells do have properties that are suited for repair of the injured CNS, a primary remaining question is how these cells can best be grafted to produce long-term functional benefit to the host environment. Moreover, among the challenges in neural cell transplantation is controlling the ultimate characteris- tics of grafted cells, pertaining to their survival, phenotypes and performance.

关键词： cell Tayloring cell populations for neurodegenerative diseases