We present a broad-band optimal ventilator waveform (OVW), the concept of which was to create a computer-driven ventilator waveform containing increased energy at specific frequencies (f). Values of f were chosen such that nonlinear harmonic distortion and intermodulation were minimized. The phases at each f were then optimized such that the resulting flow waveform delivered sufficient volume to maintain gas exchange while minimizing peak-to-peak airway opening pressure. Simulations with a linear anatomically consistent branching airway model and a nonlinear viscoelastic model showed that respiratory resistance (Rrs) and elastance (Ers) estimates at 0.1-2 Hz from the OVW are far superior to those from a standard step ventilator waveform (SVW) during healthy and obstructed conditions and that the OVW reduces the influences of harmonic interactions. Using a servo-controlled oscillator, we applied individual sine waves, an OVW containing energy at 0.15625-2.4 Hz, and an SVW to healthy humans and one symptomatic asthmatic subject before and after bronchodilation. The OVW was markedly superior to the SVW and always provided smooth estimates of Rrs and Ers. Before bronchodilation in the asthmatic subject Rrs was highly elevated and Ers was markedly increased with f; after bronchodilation the level of Rrs and the f dependence of Ers decreased. Although based on results from only one asthmatic subject, these data suggest a dominant influence of airway constriction and lung inhomogeneities during asthmatic bronchoconstriction that is alleviated by bronchodilators. These and other results indicate that the OVW approach has high potential for simultaneously probing f and amplitude dependence in the mechanical properties of clinical subjects during physiological breathing conditions and perhaps during dynamic bronchoconstriction.

In this ar ti cle, we an a lyze the prop er ties of ion o spheric elec tron den sity pro fil ing re trieved from FORMOSAT-3/COS MIC ra dio occultation mea sure ments. Two pa ram e ters, namely, the gra di ent and fluc tu a tion of the top side elec tron den sity pro file, serve as in di ca tors to quan ti ta tively de scribe the data qual ity of the re trieved elec tron den sity pro file. On the ba sis of 8 month data (June 2006 -Jan u ary 2007), we find that on av er age 93% of the elec tron den sity pro files have up per elec tron den sity gra di ents and elec tron den sity fluc tu a tions smaller than -0.02 #/m 3 /m and 0.2, re spec tively, which can be treated as good data for fur ther anal y sis. The same re sults are also achieved for the peak height of the elec tron den sity. Af ter re mov ing the ques tion able data, we com pare the gen eral be hav iors of the elec tron den sity be tween FORMOSAT-3 and the IRI model. It is found that the global dis tri bu tions of the peak height and the peak elec tron den sity for the FORMOSAT-3/COS MIC data are gen er ally con sis tent with those for the IRI model. How ever, a sig nif i cant dif fer ence be tween their scale heights of the top side elec tron den sity pro files is found. It sug gests that the shape of the top side elec tron den sity pro file in the IRI model should be revised accordingly such that it more closely resembles the real situation. Ocean. Sci., 20, 193-206, doi: 10.3319/TAO.2007.10.05.01(F3C) IN TRO DUC TIONRa dio occultation tech nique is an old, but very so phis ticated, method for the re trieval ter res trial at mo sphere parameters (Fjeldbo et al. 1971). The core of this tech nique is (under a num ber of as sump tions) to trans form the bend ing an gle of the ra dio ray path to the at mo spheric re frac tive index, which is trans mit ted from a very sta ble source sit u ated on one side of the Earth and re ceived by a re ceiver lo cated on the op po site side of the Earth (Rocken et al. 1997;Hajj et al. 2000). Once the at mo spheric re frac tive in dex is re trieved, the lower at mo spheric tem per a ture, hu mid ity and ion ospheric elec tron den sity at the tan gent point of the ray path pierc ing through the at mo sphere can be es ti mated in ac cordance with the re la tion be tween the re frac tive in dex n and the pa ram e ters given be low:( 1) where P is pres sure (hpa), T is tem per a ture (k), e is wa ter va por pres sure (hpa), f is ra dio wave fre quency (Hz), and n e is elec tron den sity (#/m 3 ). In the ion o sphere (higher than an al ti tude of about 100 km), the con tri bu tion of T, P and e to the at mo spheric re frac tive in dex is neg li gi ble com pared to the elec tron den sity con tri bu tion. As a re sult, n e can be directly es ti mated from n for given f. Ex cept for the at mospheric re frac tive in dex, un der the straight line as sump tion of the ra dio ray path, the height vari a tion of the ion o spheric elec tron den sity can also be re trieved from cal i brated to tal elec tron con tent (TEC) in ac cor...

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