PubMed · 11315495
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M Max. 2001. [PEEP].. https://doi.org/10.1007/s001010050990
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We have designed and constructed an atmospheric pressure laser desorption/chemical ionization (AP-LD/CI) source that utilizes a laser pulse to desorb intact neutral molecules, followed by chemical ionization via reagent ions produced by a corona discharge. This source employs a heated capillary atmospheric pressure inlet coupled to a quadrupole ion trap mass spectrometer and allows sampling under normal ambient air conditions. Preliminary results demonstrate that this technique provides approximately 150-fold increase in analyte ions compared to the ion population generated by atmospheric pressure infrared matrix-assisted laser desorption/ionization (AP-IR-MALDI).
The inspiratory flow characteristics in a three-generation lung airway have been numerically investigated using a control volume method to solve the fully three-dimensional laminar Navier-Stokes equations. The three-generation airway is extracted from the fifth to seventh branches of the model of Weibel (Morphometry of the Human Lung, Academic Press, New York, Springer, Berlin, 1963) with in-plane and 90 degrees off-plane configurations. Computations are carried out in the Reynolds number range of 200-1600, corresponding to mouth-air breathing rates ranging from 0.27 to 2.16l/s, or an averaged height of a man breathing from quiet to vigorous state. Particular attention is paid to establishing relations between the Reynolds number and the overall flow characteristics, including flow patterns and pressure drop. The ratio of airflow rate through the medial branch to that of the lateral branch for an in-plane airway increases as Re(0.227). However, the total pressure drop coefficient varies as Re(-0.497) for an in-plane airway and as Re(-0.464) for an off-plane airway. These pressure drop results are in good agreement with the experimentally measured behavior of Re(-0.5) and are more accurate than the numerically determined behavior of Re(-0.61) assuming the airways to be approximated by two-dimensional channels.
The objective of this study was to determine the physical basis of ultrasound (US) reflectivity of echogenic lipid dispersions. These dispersions were made using a process previously described involving sonication of the lipid in water, addition of mannitol, freezing, lyophilization and rehydration. The component lipids were egg phosphatidylcholine, dipalmitoylphosphatidylethanolamine, dipalmitoylphosphatidylglycerol and cholesterol in a molar ratio of 69:8:8:15. Ultrasound reflectivity, as assessed with a 20-MHz intravascular US catheter and analyzed using computer-assisted videodensitometry, was found to be sensitive to variations in ambient pressure; echogenicity was greatly reduced by exposure to 0.5 atm vacuum for 10 s or 1.5 atm pressure for 10 s. Pressure changes of the magnitude that obtain in the arterial circulation had little effect on echogenicity. Vacuum treatment resulted in the release of approximately 100 microL air from a standard preparation of 10 mg lipid in 1 mL. Maximum ultrasonic reflectivity required the presence of 0.1-0.2 mol/L mannitol during the lyophilization step; mere addition of mannitol to the lipid lyophilized in the absence of mannitol produced nonreflective dispersions. Inclusion of sodium phosphate or other electrolytes reduced echogenicity. High echogenicity was associated with the presence of large-volume freeze-dried cakes and fusion of liposomes (which led to a 10 times increase in liposome diameters) during freezing before lyophilization. Lyophilization from water led to liposome fusion, but the cakes were small and US reflectivity was weak. Lyophilization from solutions of cryoprotectants such as trehalose produced large cakes, but little liposome fusion and also led to weak US reflectivity. Filtration through defined pores revealed that approximately 50% of the echogenicity originated from particles smaller than 1 microm and about 2/3 from particles smaller than 3 microm. These results indicate that lyophilization from 0.2 mol/L mannitol solution generates a disrupted array of lipid bilayers that, upon rehydration, fuse and trap small amounts of air distributed among liposome-size particles.