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This study presents a direct trajectory optimization framework for a vertical takeoff and vertical landing (VTVL) reusable rocket with a two-stage structure for a launch mission to simultaneously deliver a payload to the desired orbit and recover the rocket. A two-phase trajectory optimization problem of VTVL reusable rockets is established, with the main features of the flight process. The finite-element collocation approach with Radau collocation is utilized to transcribe the established problem into a nonlinear programming (NLP) problem solved by Interior Point OPTimizer (IPOPT). Novel internal-external-growth initialization strategies are designed to enhance the convergence of solving the NLP problem. The proposed direct trajectory optimization framework is applied to two representative scenarios of VTVL reusable rockets: return to a launch site and return to a drone ship. Simulation results illustrate that the proposed trajectory optimization framework has the adaptability to deal effectively with the complex missions of VTVL reusable rockets. [ABSTRACT FROM AUTHOR]

Background: Unlike influenza viruses, little is known about the prevalence and seasonality of other respiratory viruses because laboratory surveillance for non-influenza respiratory viruses is not well developed or supported in China and other resource-limited countries. We studied the interference between seasonal epidemics of influenza viruses and five other common viruses that cause respiratory illnesses in Hong Kong from 2014 to 2017.Methods: The weekly laboratory-confirmed positive rates of each virus were analyzed from 2014 to 2017 in Hong Kong to describe the epidemiological trends and interference between influenza viruses, respiratory syncytial virus (RSV), parainfluenza virus (PIV), adenovirus, enterovirus and rhinovirus. A sinusoidal model was established to estimate the peak timing of each virus by phase angle parameters.Results: Seasonal features of the influenza viruses, PIV, enterovirus and adenovirus were obvious, whereas annual peaks of RSV and rhinovirus were not observed. The incidence of the influenza viruses usually peaked in February and July, and the summer peaks in July were generally caused by the H3 subtype of influenza A alone. When influenza viruses were active, other viruses tended to have a low level of activity. The peaks of the influenza viruses were not synchronized. An epidemic of rhinovirus tended to shift the subsequent epidemics of the other viruses.Conclusion: The evidence from recent surveillance data in Hong Kong suggests that viral interference during the epidemics of influenza viruses and other common respiratory viruses might affect the timing and duration of subsequent epidemics of a certain or several viruses. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the potential toxicity of the vehicle used for triamcinolone acetonide (TA) to the cornea, lens, ciliary body, and retina of pigmented rabbits. Methods: Forty chinchilla rabbits (40 eyes) were divided into four groups: group A (control group) eyes received an intravitreal injection of 0.1 ml sterile saline solution; group B eyes received 0.1 ml (1.3 mg) TA plus vehicle; group C eyes received 0.1 ml (1.3 mg) TA alone (vehicle eliminated); group D eyes received 0.1 ml vehicle only. Intraocular pressure (IOP) was measured pre-injection and at 1, 7, 14, 30, and 90 days post-injection. Scotopic and photopic electroretinograms (ERG) were examined pre-injection and 7, 30, and 90 days post-injection. Animals were sacrificed 7, 30, and 90 days post-injection. Eyes were enucleated and examined by light microscopy (LM) and electron microscopy (EM). Results: The IOP of groups B and C was higher than that of other groups on days 1, 7, and 14 post-injection (p < 0.05). ERG amplitudes of groups B and D were lower than those of other groups on days 7 and 30 post-injection (p < 0.05). Histopathological sections indicated morphologic changes in the ciliary body, lens, and retina of eyes in groups B and D. Conclusions: Vehicle used for TA is toxic to the lens, ciliary body, and retina of pigmented rabbit eyes after injection of intravitreal TA. [ABSTRACT FROM AUTHOR]

Aims: To investigate the healing mechanism of the rabbit's sclerotomy sites undergoing the Transconjunctival Sutureless Vitrectomy (TSV). Methods: Thirty-two rabbits (Thirty-two eyes) were divided into four groups: The rabbits performed with the core vitrectomy and air tamponade were Group A, performed with the core vitrectomy as Group B, performed with the non-core vitrectomy and air tamponade as Group C, and the non-core vitrectomy as Group D. The sclerotomy sites were observed by the Ultrasound Biomicroscope (UBM model 840, Humphrey Instruments, San Leandro, CA, USA) on days 1, 3, 5, and 9 postoperatively, and the diameter of the internal and the external aperture was estimated on postoperative day 1. The pathological study of the sclerotomy sites on days 3, 5, and 9 postoperatively were investigated under the light microscope. Results: The Ultrasound Biomicroscope and the pathological sections showed that the healing course of the sclerotomy sites lasted nine days. On postoperative day 1, the vitreous incarceration (19/32, 59.4%), the fluid cavity (18/32, 56.3%), and the air cavity under the conjunctiva (7/16, 43.8%) existed in some cases. The diameter of the internal aperture in Group A and Group B was less than Group C and Group D on day 1 postoperatively, P < 0.001. The diameter of the external aperture did not show significant difference in any of the groups. The pathological study verified the healing course was the granulation reaction. Conclusion: The healing mechanism of the rabbit's sclerotomy sites undergoing the (TSV) is the granulation reaction accompanied with the elastic recovery of the sclera. [ABSTRACT FROM AUTHOR]