An analytical expression of the lasing threshold for arbi trary photonic crystals was derived, which showed their reduction due to small group velocities of electromagnetic eigenmodes. The lasing threshold was also evaluated numerically for a two-dimensional photonic crystal by examining the divergence of its transmission and reflection coeffcients numerically. A large reduction of lasing threshold caused by a group-velocity anomaly that is peculiar to two- and three- dimensional photonic crystals was found.

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A study was performed on seven traumatic neurologically complete quadriplegic (QP) males and seven age-matched healthy males (control) while they were at rest in the supine position in a climatic chamber (temperature 30 degrees C, relative humidity 60%). Arterial blood pressure waveforms were measured by a continuous noninvasive blood pressure-monitoring system based on arterial tonometry. Furthermore, the spontaneous beat-to-beat systolic blood pressure (SBP) variabilities of subjects were investigated by means of autoregressive power spectral analysis. As shown by earlier studies with an invasive (intra-arterial) blood pressure-monitoring system, in the control group there were two major spectral components: a high-frequency (HF) component [center frequency 0.27 +/- 0.02 (SE) Hz eq, power 0.9 +/- 0.2 mmHg2] and a low-frequency (LF) component (0.10 +/- 0.01 Hz eq, 5.2 +/- 1.4 mmHg2). On the contrary, in the QP group only the HF component was observed (0.28 +/- 0.03 Hz eq, 3.2 +/- 1.4 mmHg2). The results suggest that 1) in the QP subject the disappearance of the LF component in the SBP variability (i.e., the Mayer waves in humans) is presumably caused by the interruption of the spinal pathways linking supraspinal cardiovascular centers with the peripheral sympathetic outflow and 2) the cervical spinal sympathetic pathways may be instrumental in the genesis of the Mayer waves in humans.

The equilibrium and growth morphology of a crystal in a diffusion field are studied by means of a lattice-gas model in a unified way. In a closed system the crystal takes an equilibrium form, and its shape and size in two dimensions agree with those expected from the exact solutions of the corresponding Ising model. In an open system where a crystal is in contact with a gas reservoir, the crystal grows steadily. For a small crystal or at a small chemical potential difference Ap between the gas and the crystal, the growth form is polygonal. Its growth rate and the size are interpreted by a single nucleation and growth mechanism. On increasing Ap or for a large crystal, it becomes dendritic. Further increase of Ap results in a fractal aggregate, which is, however, "compact" in a large scale due to the finiteness of the gas density.

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