Antenatal diagnosis of epignathus with neonatal survival. A case report

Antenatal diagnosis was made of bilobed epignathus arising from the fetal palate. The fetus survived. Antenatal recognition of this malformation allows adequate preparation of the neonatal and surgical teams to ensure optimal fetal survival.

Building Black Holes: Supercomputer Cinema

A new computer code can solve Einstein's equations of general relativity for the dynamical evolution of a relativistic star cluster. The cluster may contain a large number of stars that move in a strong gravitational field at speeds approaching the speed of light. Unstable star clusters undergo catastrophic collapse to black holes. The collapse of an unstable cluster to a supermassive black hole at the center of a galaxy may explain the origin of quasars and active galactic nuclei. By means of a supercomputer simulation and color graphics, the whole process can be viewed in real time on a movie screen.

Streak-camera observations of the pulse emission from a synchronously pumped continuous-wave mode-locked dye laser

Pulse emission from a synchronously pumped cw mode-locked dye laser is investigated with a streak camera. Prominent satellite pulses with nonrepetitive temporal spacing can be detected that are difficult to observe with an autocorrelator.

Ultraviolet phase conjugation

We report the first known demonstration of UV phase conjugation. By use of a 15-psec, 2660-A pulse, 0.1% conjugate reflectivities were obtained through degenerate four-wave mixing in 1-mm samples of CS(2) mixtures. Although pure CS(2) did not exhibit the effect, dilution of CS(2) in several UV-transmitting solvents opened up a concentration- tunable (2450-2850 A) spectral window, allowing the optical Kerr effect to be utilized. Weaker phase conjugation at 2660 A was also observed in other Kerr media and in saturable absorber media.

Picosecond infrared-continuum generation by three-photon parametric amplification in LiNbO3

Picosecond infrared continua are produced by propagating an intense ultrashort 1.064-microm pulse through a LiNbO(3) crystal set near the degenerate point. Under our experimental conditions, gain broadening is identified as the principal mechanism leading to the superbroad spectral output.

Broadly tunable picosecond infrared source

We report a completely grating tuned (1.9-2.4 microm) picosecond traveling-wave infrared generator capable of controlled spectral-bandwidth operation down to the Fourier-transform limit. Subsequent down-conversion in CdSe extends the tuning range to 10-20 microm.

A picosecond pulse train study of exciton dynamics in photosynthetic membranes

The fluorescence decay time of spinach chloroplasts at 77 degrees K was determined at 735 nm (corresponding to the photosystem I emission) using a train of 10-ps laser pulses spaced 10 ns apart. The fluorescence lifetime is constant at congruent to 1.5 ns for up to the fourth pulse, but then decreases with increasing pulse number within the pulse train. This quenching is attributed to triplet excited states, and it is concluded that triplet excitons exhibit a time lag of about 50 ns in diffusing from light harvesting antenna pigments to photosystem I pigments. The diffusion coefficient of triplet excitons is a least 300--400 times slower than the diffusion coefficient of singlet excitons in chloroplast membranes.

Picosecond and steady state, variable intensity and variable temperature emission spectroscopy of bacteriorhodopsin

The bacteriorhodopsin emission lifetime at 77 degrees K has been obtained for different regions of the emission spectrum with single-pulse excitation. The data under all conditions yield a lifetime of 60 +/- 15 ps. Intensity effects on this lifetime have been ruled out by studying the relative emission amplitude as a function of the excitation pulse energy. We relate our lifetime to previously reported values at other temperatures by studying the relative emission quantum efficiency as a function of temperature. These variable temperature studies have indicated that an excited state with an emission maximum at 670 nm begins to contribute to the spectrum as the temperature is lowered. Within our experimental error the picosecond data seem to suggest that this new emission may arise from a minimum of the same electronic state responsible for the 77 degrees K emission at 720 nm. A correlation is noted between a 1.0-ps formation time observed in absorption by Ippen et al. (Ippen, E.P., C.V. Shank, A. Lewis, and M.A. Marcus. 1978. Subpicosecond spectroscopy of bacteriorhodopsin. Science [wash. D.C.]. 200:1279-1281 and a time extrapolated from relative quantum efficiency measurements and the 77 degrees K fluorescence lifetime that we report.

Picosecond and microsecond pulse laser studies of exciton quenching and exciton distribution in spinach chloroplasts at low temperatures

Studies of the fluorescence quantum yield and decay times, determined at the emission maxima of 685 and 735 nm, using picosecond laser pulses for excitation, indicate that the pigments which are responsible for the 735 nm emission derive their energy by transfer of singlet excitons from the light-harvesting pigments and not by direct absorption of photons. Microsecond pulse laser studies of the fluorescence quantum yields at these two fluorescence wavelengths indicate that long lived quenchers (most probably triplet states), which quench singlet excitions, accumulate preferentially within the long wavelength pigment system which gives rise to the 735 nm emission band.

Intensity Dependence of the Fluorescence Lifetime of in vivo Chlorophyll Excited by a Picosecond Light Pulse

New data on intensity-dependent lifetimes indicate that all previous in vivo fluorescence studies of chlorophyll by picosecond techniquies must be reinterpreted. Anomalously short lifetimes result from high-intensity effects due to exciton-excition annihilation processes. Measurements in Chlorella pyrenoidosa with single-pulse, low-intensity excitation indicate a longer "true" lifetime of 650 +/- 150 picoseconds.