In Fourier-transform ion cyclotron resonance (FT-ICR) mass spectra resulting from the signals. detected with a single pair of detection plates (i.e., real-time-domain signals), the foldback of spectral information about the Nyquist frequency occurs. In heterodyne mode FT-ICR mass spectrometry, using quadrature reference signals, a complex ICR signal consisting of two quadrature reference signals, a complex ICR signal consisting of two quadrature signal components can be acquired easily. By Fourier transform of the signal, the reflection of peaks about the Nyquist frequency in the frequency-domain spectrum can be eliminated. As a result, the available bandwidth of the spectrum is doubled. Validity of this quadrature heterodyne method is confirmed by the experimentally obtained spectrum of Xe" ions.In Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry, when a time-domain signal with a frequency higher than the Nyquist frequency fN is Fourier transformed, the signal is folded back into the frequency range from zero to fN. Usually, this phenomenon, which is referred to as "aligning" or "foldover", can be eliminated by passing a time-domain signal through a low-pass filter. However, since such a filter does not have a perfectly sharp cutoff, it is often difficult to eliminate the reflection near the Nyquist frequency. In particular, when a narrow band is observed in heterodyne mode FT-ICR mass spectrometry, the reflection of peaks above the Nyquist frequency into the frequency range from the reference frequency fief to (fref+fN) becomes important. Besides, such a reflection is more significant for magnitudemode than for absorption-mode spectra.'In FT-nuclear magnetic resonance (NMR) , quadrature detection has been established to resolve the problem of the foldback of information in the frequency spectrum (e.g., Refs 2 and 3). In FT-ICR mass spectrometry, Verdun et u Z .~ have reported quadrature IT-ICR mass spectrometry by detection of signals from two perpendicular pairs of plates. This quadrature detection can be used in both direct and heterodyne modes. However, it is experimentally a little complicated, because one of the two pairs of plates must be used for both excitation and detection.In heterodyne mode FT-ICR mass spectrometry, using two reference signals which are x/2 out of phase with each other, one can acquire two quadrature timedomain signal components from the signal detected with a single pair of detection plates. By treating one of the two components as the real part of a complex timedomain function and the other as the imaginary part, the reflection of peaks about the Nyquist frequency can be eliminated.

In this study, we investigated the use of perforated sheet platforms to improve the attachment of percutaneous devices to surrounding tissues. The model platform was created by a poly(methyl methacrylate) (PMMA) sheet with a matrix of 200-microm diameter perforations covering the groove (width, 3 mm; depth, 0.5 mm) prepared on the PMMA cylinder (diameter, 10 mm; length, 6 mm). Velour cuffs from peritoneal dialysis catheters were used as controls. Specimens were implanted percutaneously in rats, harvested with the surrounding tissues at 4 weeks after surgery, and subjected to mechanical tests and histological observations. The attachment strength of the experimental specimens to tissue was 138.4 +/- 123.6 kPa (n = 5, mean SD); although it was greater than the 67.23 +/- 45.78 kPa (n = 5) of the controls, no statistical significance was found. Histological observations of the experimental specimens revealed the collagen fibers originating from the surrounding tissues, passing through the perforations of the sheet, merging into the collagen fibers running behind the sheet, and thus anchoring the tissues to the device. In contrast, such anchoring of collagen fibers was not evident in the controls. These results suggest that the proposed perforated sheet structures are effective for soft tissue attachment.

Accordion nerve conduit of poly(lactide-co-glycolide-co-ε-caprolactone) with perforations was developed by excimer laser processing. We evaluated its in vivo function for nerve repairing and discussed the influence of pore size and density. It was found that perforations help inner nerve regeneration remarkably, which effect is unrelated to pore size or density, and is not parallel with revascularization increment. Inducing of permeability only to allow substance exchange but not vessel ingrowth could facilitate nerve regeneration too. Perforating micropores with the size of 100 μm and the density of 25/cm provides permeability and vessel ingrowth both, therefore promotes the axon extension the best, larger, and more pores do not advance axon regeneration more.

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