Autoignition of n-decane Droplets in the Low-, Intermediate-, and High-temperature Regimes from a Mixture Fraction Viewpoint

Detailed numerical simulations of isolated n-decane droplets autoignition are presented for different values of the ambient pressure and temperature. The ignition modes considered included single-stage ignition, twostage ignition and cool-flame ignition. The analysis was conducted from a mixture fraction perspective. Two characteristic chemical time scales were identified for two-stage ignition: one for cool-flame ignition, and another for hot-flame ignition. The appearance and subsequent spatial propagation of a cool flame at lean compositions was found to play an important role in the ignition process, since it created the conditions for activating the hightemperature reactions pathway in regions with locally rich composition. Single-stage ignition was characterized by a single chemical time scale, corresponding to hot-flame ignition. Low-temperature reactions were negligible for this case, and spatial diffusion of heat and chemical species mainly affected the duration of the ignition transient, but not the location in mixture fraction space at which ignition first occurs. Finally, ignition of several cool flames of decreasing strength was observed in the cool-flame ignition case, which eventually lead to a plateau in the maximum gas-phase temperature. The first cool flame ignited in a region where the fuel / air mixture was locally lean, whereas ignition of the remaining cool flames occurred at rich mixture compositions.This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s10494-016-9710-

Direct Numerical Simulations of premixed methane flame initiation by pilot n-heptane spray autoignition

Autoignition of n-heptane sprays in a methane/air mixture and the subsequent methane premixed flame ignition, a constant volume configuration relevant to pilot-ignited dual fuel engines, was investigated by DNS. It was found that reducing the pilot fuel quantity, increases its autoignition time. This is attributed to the faster disappearance of the most reactive mixture fraction (predicted from homogeneous reactor calculations) which is quite rich. Consequently, ignition of the n-heptane occurs at leaner mixtures. The premixed methane flame is eventually ignited due to heating gained by the pressure rise caused by the n-heptane oxidation, and heat and mass transfer of intermediates from the n-heptane autoignition kernels. For large amounts of the pilot fuel, the combustion of the n-heptane results in significant adiabatic compression of the methane–air mixture. Hence the slow methane oxidation is accelerated and is further promoted by the presence of species in the oxidizer stream originating from the already ignited regions. For small amounts of the pilot fuel intermediates reach the oxidizer stream faster due to the very lean mixtures surrounding the n-heptane ignition kernels. Therefore, the premixed methane oxidation is initiated at intermediate temperatures. Depending on the amount of n-heptane, different statistical behaviour of the methane oxidation is observed when this is investigated in a reaction progress variable space. In particular for large amounts of n-heptane the methane oxidation follows roughly an autoignition regime, whereas for small amounts of n-heptane methane oxidation is similar to a canonical premixed flame. The data can be used for validation of various turbulent combustion models for dual-fuel combustion.The computational costs for this work were covered by the EPSRC project ref. no. EP/J021997/1.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.combustflame.2015.09.01

Numerical investigation of kerosene single droplet ignition at high-altitude relight conditions

In this study, the fundamental problem of the ignition of a kerosene single droplet in a quiescent medium at engine high-altitude relight conditions is investigated using numerical simulations. The main objective is to improve the understanding of ignition phenomena with a focus on the effect of droplet evaporation in determining the growth of the ignition kernel and flame establishment. Results show that when the droplet is fully immersed in a high temperature region, ignition occurs when the scalar dissipation rate associated with evaporation decreases enough to allow the initiation of a flame. The ignition time depends on the droplet diameter and the far field temperature, i.e. the position of the droplet with respect to the spark location. As the fuel is consumed, the flame is found to move closer to the droplet surface until the flame cannot sustain itself any more due to increasing scalar dissipation rates. Furthermore, results show that at very low temperatures typical of high-altitude relight conditions no flammable mixture is available around the droplet. Therefore, the success of an ignition event mainly depends on the energy released by the spark and the rate at which this energy is diffused toward the droplet surface to enhance the evaporation rate and create a flammable mixture. The findings are analysed from the perspective of gas turbine applications

Metabolic Perspectives for Non-classical Congenital Adrenal Hyperplasia With Relation to the Classical Form of the Disease

Non-classical congenital adrenal hyperplasia (NC-CAH) represents mild form of CAH with the prevalence of 0. 6 to 9% in women with androgen excess. Clinical and hormonal findings in females with NC-CAH are overlapping with other hyperandrogenic entities such as polycystic ovary syndrome hence causing difficulties in diagnostic approach. Metabolic consequences in subjects with NC-CAH are relatively unknown. We are lacking longitudinal follow of these patients regarding natural course of the disease or the therapeutic effects of the different drug regiments. Patients with NC-CAH similarly to those with classical form are characterized with deteriorated cardiovascular risk factors that are probably translated into cardiometabolic diseases and events. An increased preponderance of obesity and insulin resistance in patients with NC-CAH begin at young age could result in increased rates of metabolic sequelae and cardiovascular disease later during adulthood in both sexes. On the other hand, growth disorder was not proven in patients with NC-CAH in comparison to CAH patients of both gender characterized with reduced final adult height. Similarly, decreased bone mineral density and osteoporosis are not constant findings in patients with NC-CAH and could depend on the sex, and type or dose of corticosteroids applied. It could be concluded that NC-CAH represent a particular form of CAH that is characterized with specificities in clinical presentation, diagnosis, therapeutic approach and metabolic outcomes.This study was funded by the Serbian Ministry of Education, Science and Technological Development (grant numbers 175032 and 41009)

Presence of antiphospholipid antibodies is associated with increased implantation failure following in vitro fertilization technique and embryo transfer: A systematic review and meta-analysis

PURPOSE: A systematic review and meta-analysis was conducted comparing the presence of anti-phospholipid (anti-PL) antibodies between women of reproductive age, without diagnosis of antiphospholipid syndrome, who experienced at least two implantation failures following in vitro fertilization and embryo transfer (IVF-ET), and either women who had a successful implantation after IVF-ET or women with at least one successful spontaneous pregnancy or unselected healthy fertile women with no history of IVF-ET. METHODS: Systematic search of the literature and meta-analysis of the relevant studies studying presence of antiphospholipid antibodies in women experiencing at least two implantation failures in IVF-ET as compared to either women who had a successful implantation after IVF-ET or/and women with at least one successful spontaneous pregnancy or unselected healthy fertile women with no history of IVF-ET. Six hundred ninety-four published reports were retrieved; 17 of them fulfilled the inclusion criteria set. RESULTS: Presence of either any type of anti-phospholipid or anticardiolipin antibodies or lupus-anticoagulant in women experiencing at least two implantation failures in IVF-ET was associated with increased implantation failure compared to women who had a successful implantation after IVF-ET (relative risk, RR: 3.06, 5.06 and 5.81, respectively). Presence of either anticardiolipin or lupus-anticoagulant or anti-beta(2) glycoprotein-I or anti-phosphatidylserine antibodies in women experiencing at least two implantation failures in IVF-EΤ was associated with increased implantation failure compared to unselected healthy fertile women with no history of IVF-ET (RR:13.92, 6.37, 15.04 and 164.58, respectively). CONCLUSION: The prevalence of antiphospholipid antibodies, particularly that of anti-beta(2) glycoprotein-I and anti-phosphatidylserine antibodies, in women experiencing at least two implantation failures in IVF-ET without diagnosis of antiphospholipid syndrome is significantly greater than either in women who had a successful implantation after IVF-ET or women with at least one successful spontaneous pregnancy or unselected healthy fertile women with no history of IVF-ET. TRIAL REGISTRATION NUMBER: PROSPERO ID: CRD4201808145

Morphokinetic parameters of early embryo development via time lapse monitoring and their effect on embryo selection and ICSI outcomes: a prospective cohort study

PURPOSE: To compare the outcomes of embryos selected via time lapse monitoring (TLM) versus those selected with conventional methods of selection in subfertile women undergoing ICSI. METHODS: The study population (239 women) was classified into two groups, based on the monitoring method used: Group 1 (TLM) and Group 2 (conventional monitoring). Groups were compared according to the clinical and ICSI cycle characteristics and reproductive outcomes, while transfers were performed at day 2 or 3. Subgroup analyses were performed, in women of both groups according to age and clinical parameters, and in embryos of Group 1 based on their cellular events. RESULTS: There was a statistically significant difference between the two study groups with regard to the outcome parameters, favoring Group 1 and especially in women >40 years of age. No differences were found in subgroup analyses in participants of both groups, regarding the stimulation protocol used, number of the oocytes retrieved and type of subfertility, while in Group 1 the percentages of "in range" cellular events were higher in certain divisions in ages 35-40, non-smokers, and the GnRH-agonist group, and in embryos that resulted in pregnancy. CONCLUSION: Morphokinetic parameters of early embryo development via TLM are related to the characteristics of subfertile patients and associated with ICSI outcomes

Soot particle size distribution measurements in a turbulent ethylene swirl flame

There is a need to better understand particle size distributions (PSDs) from turbulent flames from a theoretical, practical and even regulatory perspective. Experiments were conducted on a sooting turbulent non-premixed swirled ethylene flame with secondary (dilution) air injection to investigate exhaust and in-burner PSDs measured with a Scanning Mobility Particle Sizer (SMPS) and soot volume fractions (fv) using extinction measurements. The focus was to understand the effect of systematically changing the amount and location of dilution air injection on the PSDs and fv inside the burner and at the exhaust. The PSDs were also compared with planar Laser Induced Incandescence (LII) calibrated against the average fv. LII provides some supplemental information on the relative soot amounts and spatial distribution among the various flow conditions that helps interpret the results. For the flame with no air dilution, fv drops gradually along the centreline of the burner towards the exhaust and the PSD shows a shift from larger particles to smaller. However, with dilution air fv reduces sharply where the dilution jets meet the burner axis. Downstream of the dilution jets fv reduces gradually and the PSDs remain unchanged until the exhaust. At the exhaust, the flame with no air dilution shows significantly more particles with an fv one to two orders of magnitude greater compared to the Cases with dilution. This dataset provides insights into soot spatial and particle size distributions within turbulent flames of relevance to gas turbine combustion with differing dilution parameters and the effect dilution has on the particle size. Additionally, this work measures fv using both ex situ and in situ techniques, and highlights the difficulties associated with comparing results across the two. The results are useful for validating advanced models for turbulent combustion.European Union (EU), Horizon 2020 (H2020), Clean Sky 2 Joint Undertaking, Industrial Leadership (IL) (Project LEAFINNOX, grant number 831804

Association between Brain-Derived Neurotrophic Factor (BDNF) Levels in 2nd Trimester Amniotic Fluid and Fetal Development.

The development of the fetal nervous system mirrors general fetal development, comprising a combination of genetic resources and effects of the intrauterine environment. Our aim was to assess the 2nd trimester amniotic fluid levels of brain-derived neurotrophic factor (BDNF) and to investigate its association with fetal growth. In accordance with our study design, samples of amniotic fluid were collected from women who had undergone amniocentesis early in the 2nd trimester. All pregnancies were followed up until delivery and fetal growth patterns and birth weights were recorded, following which pregnancies were divided into three groups based on fetal weight: (1) AGA (appropriate for gestational age), (2) SGA (small for gestational age), and (3) LGA (large for gestational age). We focused on these three groups representing a reflection of the intrauterine growth spectrum. Our results revealed the presence of notably higher BDNF levels in the amniotic fluid of impaired growth fetuses by comparison with those of normal growth. Both SGA and macrosomic fetuses are characterized by notably higher amniotic fluid levels of BDNF (mean values of 36,300 pg/ml and 35,700 pg/ml, respectively) compared to normal-growth fetuses (mean value of 32,700 pg/ml). Though apparently small, this difference is, nevertheless, statistically significant (p value < 0.05) in SGA fetuses in the extremes of the distribution, i.e., below the 3rd centile. In conclusion, there is clear evidence that severe impairment of fetal growth induces the increased production of fetal brain growth factor as an adaptive mechanism in reaction to a hostile intrauterine environment, thereby accelerating fetal brain development and maturation

Exercise-induced oxidative stress responses in the pediatric population

This is the final version of the article. Available from the publisher via the DOI in this record.Adults demonstrate an upregulation of their pro- and anti-oxidant mechanisms in response to acute exercise while systematic exercise training enhances their antioxidant capacity, thereby leading to a reduced generation of free radicals both at rest and in response to exercise stress. However, less information exists regarding oxidative stress responses and the underlying mechanisms in the pediatric population. Evidence suggests that exercise-induced redox perturbations may be valuable in order to monitor exercise-induced inflammatory responses and as such training overload in children and adolescents as well as monitor optimal growth and development. The purpose of this review was to provide an update on oxidative stress responses to acute and chronic exercise in youth. It has been documented that acute exercise induces age-specific transient alterations in both oxidant and antioxidant markers in children and adolescents. However, these responses seem to be affected by factors such as training phase, training load, fitness level, mode of exercise etc. In relation to chronic adaptation, the role of training on oxidative stress adaptation has not been adequately investigated. The two studies performed so far indicate that children and adolescents exhibit positive adaptations of their antioxidant system, as adults do. More studies are needed in order to shed light on oxidative stress and antioxidant responses, following acute exercise and training adaptations in youth. Available evidence suggests that small amounts of oxidative stress may be necessary for growth whereas the transition to adolescence from childhood may promote maturation of pro- and anti-oxidant mechanisms. Available evidence also suggests that obesity may negatively affect basal and exercise-related antioxidant responses in the peripubertal period during pre- and early-puberty

Metabolic phenotype of male obesity-related secondary hypogonadism pre-replacementand post-replacement therapy with intra-muscular testosterone undecanoate therapy

Aim: To explore the metabolic phenotype of obesity-related Secondary Hypogonadism (SH) in men pre- and post-replacement therapy with long-acting intramuscular (IM) testosterone undecanoate (TU). Methods: A prospective observational pilot study on metabolic effects of TU IM in male obesity-related SH (Hypogonadal [HG] group, n=13), including baseline comparisons with controls (Eugonadal [EG] group, n=15). Half the subjects (n=7 in each group) had Type 2 Diabetes Mellitus (T2D). Baseline metabolic assessment on Human Metabolism Research Unit: fasting blood samples; BodPod (body composition), and; whole-body indirect calorimetry. The HG group was treated with TU IM therapy for 6-29 months (mean 14.8-months [SD 8.7]), and assessment at the Human Metabolism Research Unit repeated. T-test comparisons were performed between baseline and follow-up data (HG group), and between baseline data (HG and EG groups). Data reported as mean (SD). Results: Overall, TU IM therapy resulted in a statistically significant improvement in HbA1C (9mmol/mol, P=0.03), with 52% improvement in HOMA%B. Improvement in glycaemic control was driven by the HG subgroup with T2D, with 18mmol/mol [P=0.02] improvement in HbA1C. Following TU IM therapy, there was a statistically significant reduction in fat mass (3.5Kg, P=0.03) and increase in lean body mass (2.9Kg, P=0.03). Lipid profiles and energy expenditure were unchanged following TU IM therapy. Comparisons between baseline data for HG and EG groups were equivalent apart from differences in testosterone, SHBG and BMR. Conclusion: In men with obesity-related SH (including a subgroup with T2D), TU IM therapy improved glycaemic control, beta cell function and body composition