Optimisation of Low-Thrust and Hybrid Earth-Moon Transfers

This paper presents an optimization procedure to generate fast and low-∆v Earth-Moon transfer trajectories, by exploiting the multi-body dynamics of the Sun-Earth-Moon system. Ideal (first-guess) trajectories are generated at first, using two coupled planar circular restricted three-body problems, one representing the Earth-Moon system, and one representing the Sun-Earth. The trajectories consist of a first ballistic arc in the Sun-Earth system, and a second ballistic arc in the Earth-Moon system. The two are connected at a patching point at one end (with an instantaneous ∆v), and they are bounded at Earth and Moon respectively at the other end. Families of these trajectories are found by means of an evolutionary optimization method. Subsequently, they are used as first-guess for solving an optimal control problem, in which the full three-dimensional 4-body problem is introduced and the patching point is set free. The objective of the optimisation is to reduce the total ∆v, and the time of flight, together with introducing the constraints on the transfer boundary conditions and of the considered propulsion technology. Sets of different optimal trajectories are presented, which represents trade-off options between ∆v and time of flight. These optimal transfers include conventional solar-electric low-thrust and hybrid chemical/solar-electric high/low-thrust, envisaging future spacecraft that can carry both systems. A final comparison is made between the optimal transfers found and only chemical high-thrust optimal solutions retrieved from literature

Preparation and characterisation of whey protein fluid gels:the effects of shear and thermal history

AbstractWith the potential use of fluid gels in structuring fluids, whey protein isolate (WPI) was used as a prerequisite to prepare fluid gels: owing to its high nutritional value and thermal stability on gelling. Fluid gels were prepared via heat-induced gelation of a 10 wt% protein solution under controlled temperature and shear. Physical properties of the resulting gel particles (e.g. size and particle–particle interactions) were found to be dependent on the combination of shear and thermal history. Discrete large aggregates (>120 μm) were obtained at low shear, with aggregate size decreasing (<40 μm) at higher shear. Such microstructural changes in the particles led to the control of the suspension rheology. All suspensions showed a marked shear thinning behaviour associated with particle break-up which was observed to be more apparent for larger aggregates, originally made at low shear. The viscoelastic properties of the particulate systems, once in intimate contact (e.g. high volume fraction) resembled a pseudo solid material. In addition, it was shown that at a given volume fraction, the elasticity of the suspension varied dependant on their original processing conditions, owing to the degree of particle–particle interactions. A qualitative model has therefore been presented for the formation of particles by which the rheology is determined

What are the causes of hypomagnesemia?

The causes of magnesium depletion and hypomagnesemia are decreased gastrointestinal (GI) absorption and increased renal loss. Decreased GI absorption is frequently due to diarrhea, malabsorption, and inadequate dietary intake. Common causes of excessive urinary loss are diuresis due to alcohol, glycosuria, and loop diuretics. Medical conditions putting persons at high risk for hypomagnesemia are alcoholism, congestiveheart failure, diabetes, chronic diarrhea, hypokalemia, hypocalcemia, and malnutrition (strength of recommendation: C, based on expert opinion, physiology, and case series). Evidence suggests that magnesium deficiency is both more common and more clinically significant than generally appreciated

Low-Thrust to Solar-Sail Trajectories: A Homotopic Approach

This paper describes a novel method to compute minimum-time solar-sail trajectories starting from a given low-thrust solution. The method is based on the use homotopy and numerical continuation. Homotopy is used to link the low-thrust with the solar-sail optimal control problem. Numerical continuation is used to compute the optimal solar-sail solution, starting from a given low-thrust planar solution, which is normally easy to find. Planar solar sail trajectories are computed by means of the homotopic approach. These solutions are used to compute, in a single shooting approach, three-dimensional solar-sail trajectories, for transfer scenarios involving a small change of the orbital inclination. The proposed homotopic approach is tested against a conventional approach, based on the use of a genetic algorithm. Numerical test cases are performed both on Earth-Mars and Earth-Apophis rendezvous. The results show that the proposed method is advantageous, in terms of accuracy of the solution and computational time

Preparation and rheological properties of whey protein emulsion fluid gels

The research uses a novel approach to tackle structuring in liquids through shear-gel technology, resulting in advanced material properties.</p

Effects of sex hormones on bronchial reactivity during the menstrual cycle

Background: Many asthmatic women complain of symptom exacerbations in particular periods, i.e. during pregnancy and menstrual cycles (perimenstrual asthma: PMA)". The goal of this study was to study the effect of the luteal and follicular phases of the menstrual cycle on bronchial reactivity (BR) in a group of asthmatic women. Methods: For this purpose, 36 pre-menopausal women were enrolled and underwent testing for resting pulmonary function, measurement of the diffusing capacity of the lung for carbon monoxide (DLCO), and airway responsiveness to methacholine in the follicular and luteal phases of their menstrual cycles. We also measured plasma hormone levels and levels of cyclic adenosine monophosphate (cAMP; a mediator of bronchial smooth muscle contraction) and testosterone in induced sputum samples. Results: Our study showed that about 30% of the asthmatic women had decreased PC20FEV1.0 in the follicular phase of menstrual cycle with a significant correlation between PC20FEV1.0 and serum testosterone levels. Moreover, marked increases in sputum testosterone levels (mean = 2.6-fold increase) together with significant increases in sputum cAMP concentrations (mean = 3.6-fold increases) were observed during the luteal phase of asthmatic patients, suggesting that testosterone contributes to the pathophysiology of PMA. We excluded the possibility that testosterone directly inhibits phosphodiesterase (PDE) activity as incubating PDE with testosterone in vitro did not reduce PDE catalytic activity. Conclusions: In conclusion, our data show that PC20FEV1.0 was decreased in the follicular phase of the menstrual cycle in about 30% of women and was associated with lower cAMP levels in sputum samples, which may contribute to bronchoconstriction. Our results also suggest a link between PMA and testosterone levels. However, whether these findings are of clinical significance in terms of the management of asthma or asthma worsening during the menstrual cycle needs further investigation

Pattern of statin use in southern Italian primary care: Can prescription databases be used for monitoring long-term adherence to the treatment?

Objectives: We sought to evaluate the prescribing pattern of statins according to national and regional health policy interventions and to assess specifically the adherence to the therapy in outpatient setting in Southern Italy. Methods: A population-based study was performed on persons ≥15 years old, living in the catchment area of Caserta (Southern Italy), and registered in Arianna database between 2004 and 2010. Prevalence and incidence of new treatments with statins were calculated for each year and stratified by drug. Adherence to therapy was measured by Medication Possession Ratio. Sub-analyses by individual compound and type of cardiovascular prevention were performed. Results: From 2004 to 2010, the one-year prevalence of statin use increased from 44.9/1,000 inhabitants to 79.8/1,000, respectively, consistently with the incidence of new use from 16.2/1,000 to 19.5/1,000, except a slight decrease after criteria reimbursement revision

Intravenous sildenafil citrate and post-cardiac surgery acute kidney injury: a double-blind, randomised, placebo-controlled trial

Clinical trial registration ISRCTN18386427. open access articleBackground This study assessed whether i.v. sildenafil citrate prevented acute kidney injury in at-risk patients undergoing cardiac surgery with cardiopulmonary bypass. Methods In a double-blind RCT, adults at increased risk of acute kidney injury undergoing cardiac surgery in a single UK tertiary centre were randomised to receive sildenafil citrate 12.5 mg kg−1 i.v. over 150 min or dextrose 5% at the commencement of surgery. The primary outcome was serum creatinine measured at six post-randomisation time points. The primary analysis used a linear mixed-effects model adjusted for the stratification variables, baseline estimated glomerular filtration rate, and surgical procedure. Secondary outcomes considered clinical events and potential disease mechanisms. Effect estimates were expressed as mean differences (MDs) or odds ratios with 95% confidence intervals. Results The analysis population comprised eligible randomised patients that underwent valve surgery or combined coronary artery bypass graft and valve surgery, with cardiopulmonary bypass, between May 2015 and June 2018. There were 60 subjects in the sildenafil group and 69 in the placebo control group. The difference between groups in creatinine concentration was not statistically significant (MD: 0.88 μmol L−1 [–5.82, 7.59]). There was a statistically significant increase in multiple organ dysfunction scores in the sildenafil group (MD: 0.54 [0.02, 1.07]; P=0.044). Secondary outcomes, and biomarkers of kidney injury, endothelial function, and inflammatory cell activation, were not significantly different between the groups. Conclusions These results do not support the use of i.v. sildenafil citrate for kidney protection in adult cardiac surgery