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The acoustic attenuation spectrum of lipid-coated microbubble suspensions was measured in order to characterize the linear acoustic behavior of ultrasound contrast agents. For that purpose, microbubbles samples were generated with a very narrow size distribution by using microfluidics techniques. A performance as good as optical characterization techniques of single microbubbles was achieved using this method. Compared to polydispersions (i.e., contrast agents used clinically), monodisperse contrast agents have a narrower attenuation spectrum, which presents a maximum peak at a frequency value corresponding to the average single bubble resonance frequency. The low polydispersity index of the samples made the estimation of the lipid viscoelastic properties more accurate since, as previously reported, the shell linear parameters may change with the equilibrium bubble radius. The results showed the great advantage of dealing with monodisperse populations rather than polydisperse populations for the acoustic characterization of ultrasound contrast agents.

The Cox stepwise logistic regression model was applied to analyze 22 factors potentially affecting morbidity and mortality (MM) in a cohort of 104 patients on chronic hemodialysis (CHD). Two groups of predictor variables were considered: patients' characteristics at the start of the study, and treatment-related factors recorded throughout the observation period. End points were either failure (death or admission to a hospital) or success. Patients were followed for 24 months. Thirty-nine patients were hospitalized and seven died in the interval. The two leading causes of failure were cardiovascular and infectious complications. Variables significantly associated with the result were: cardiac status (score greater than 2, beta = 1.16), mean predialysis blood pressure (greater than 115 mm Hg, beta = 0.94), total dialysis dose (greater than 0.90, beta = -0.59) and age (greater than 55 years, beta = 0.51). The probability of failure was 0.13 for patients who presented the four variables in the lowest risk class. This increased to a maximum of 0.60 with one risk factor, to 0.91 with two risk factors, and to 0.99 with three or more risk factors. We conclude that, given the conditions for this study, two treatment-related variables of CHD (mean predialysis blood pressure and total dialysis dose) are MM factors even when simultaneously analyzed with other well-established predictors (cardiac status and age). Mean arterial pressure (MAP) is the most important CHD treatment-related MM predictor.

The Space Technology 7 Disturbance Reduction System (ST7-DRS) is a NASA technology demonstration payload that operated from January 2016 through July of 2017 on the European Space Agency's LISA Pathfinder spacecraft. The joint goal of the NASA and ESA missions was to validate key technologies for a future space-based gravitational wave observatory targeting the source-rich milliHertz band. The two primary components of ST7-DRS are a micropropulsion system based on colloidal micro-Newton thrusters (CMNTs) and a control system that simultaneously controls the attitude and position of the spacecraft and the two free-flying test masses (TMs). This paper presents our main experimental results and summarizes the overall the performance of the CMNTs and control laws. We find that the CMNT performance to be consistent with pre-flight predictions, with a measured system thrust noise on the order of 100 nN/ √ Hz in the 1 mHz ≤ f ≤ 30 mHz band. The control system maintained the TM-spacecraft separation with an RMS error of less than 2 nm and a noise spectral density of less than 3 nm/ √ Hz in the same band. Thruster calibration measurements yield thrust values consistent with the performance model and ground-based thrust-stand measurements, to within a few percent. We also report a differential acceleration noise between the two test masses with a spectral density of roughly 3 fm/s 2 / √ Hz in the 1 mHz ≤ f ≤ 30 mHz band, slightly less than twice as large as the best performance reported with the baseline LISA Pathfinder configuration and below the current requirements for the Laser Interferometer Space Antenna (LISA) mission.

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