M-ary pulse-position modulation and frequency-shift keying with additional polarization/phase modulation for high-sensitivity optical transmission.

We present a new class of optical modulation formats based on the combination of m-ary pulse-position modulation (m-PPM) or m-ary frequency-shift keying (FSK) with additional polarization and/or phase modulation, which is applied on the information carrying pulses in the case of m-PPM or on the information carrying frequency carriers in the case of m-FSK. We describe the principle and implementation of this class of optical modulation formats, and formulate their theoretical receiver sensitivities in optically pre-amplified receivers. Pilot-assisted frequency-domain equalization, similar to that used in coherent optical orthogonal frequency-division multiplexing (CO-OFDM), is used for reliable channel estimation and compensation.

Optical-level shifter and self-linearized optical modulator using a quantum-well self-electro-optic effect device.

We demonstrate an optical-level shifter and a modulator whose transmission varies linearly with drive current, both based on a new, negative-feedback mode of operation of the recently discovered quantum-well self-electro-optic effect device. The system is compatible with both laser diodes and low-power semiconductor electronics and is applicable in both analog and digital optical processing. An extension of the system gives inverted, linear modulation of a coherent beam by an incoherent light source.

Actual modal power distributions in multimode optical fibers and their effect on modal noise.

The modal power distribution, which specifies the amount of power flowing in each mode of a multimode fiber, influences the level of modal noise in optical-fiber systems. Generally, previous work has assumed that power in multimode fibers was distributed uniformly among the fiber modes. By considering the coupling of a semiconductor laser to a lensed fiber, we show that this assumption is grossly incorrect for practical excitations.

Microcomputer stabilization of a Fabry-Perot interferometer.

Fabry-Perot interferometers typically require some form of active stabilization system for long-term operation. A stabilization system based on a microcomputer is described which is able to maintain the finesse of a plane parallel Fabry-Perot interferometer for long periods of time. The microcomputer takes the place of the multichannel analyzer, ramp generator, and stabilizer of a conventionally stabilized system.

Kinetics of genetic recombination in Escheria coli K-12: competition between genetic integration and degradation.

The effect of shifting zygotes from a rich medium into a poor medium (shift-down) on the frequency of recombination has been examined; our results suggest that protein syntheses other than those required for growth may be involved. Experiments with chloramphenicol support this notion, and further suggest that there is a competition between genetic integration and degradation in the recipient cells. By inhibiting protein synthesis one can shift the competition in favor of either integration or segregation, depending on the physiological state of the zygotes.

Genetic mapping in Escherichia coli K-12 by radiation-induced crossing-over.

Conventional methods for chromosomal mapping in Escherichia coli are (i) interruption of matings to obtain minimum marker entry times, (ii) linkage analysis of recombinants, and (iii) cotransduction. Method (i) has a resolution of about 0.5 min (5 x 10(4) nucleotides) and is not useful for distances less than about 1 min; methods (ii) and (iii) are capable of better resolution but are generally not very reproducible and no general theory is available for translating crossing-over and cotransduction frequencies into physical chromosomal distances.

Escherichia coli K-12 mutants resistant to nalidixic acid: genetic mapping and dominance studies.

Escherichia coli K-12 strains tested so far (approximately 20) can be separated into three groups on the basis of their abilities to form colonies on nutrient agar supplemented with nalidixic acid (NAL): (i) Nal(s) or wild type (no growth at 1 to 2 mug/ml); (ii) NalA(r) (growth at 40 mug/ml or higher); and (iii) NalB(r) (growth at 4 mug/ml, but no growth at 10 mug/ml). The NalA(r) group has a spectrum of sensitivity ranging from 60 to over 100 mug/ml. All Hfr strains of the NalA(r) and NalB(r) groups transfer NAL resistance to recipient cells at genetic loci which are at 42.

Conjugation in Escherichia coli K-12 and its modification by irradiation.

The steps of normal bacterial conjugation (union, transfer, integration and segregation) are described in analytical terms. Only two parameters are utilized: nu(mt) (0), the probability of interruption of transfer of the male chromosome per unit chromosomal distance; and nu(r) (0), the probability per unit chromosomal distance of a recombinational event. Experimentally these two parameters have the same value (0.

Effects of temperature, agitation, and donor strain on chromosome transfer in Escherichia coli K-12.

Recombinant production in Escherichia coli K-12 can be described by three parameters: (i) the distance x of a selected male marker from the donor origin; (ii) the gradient constant k (the probability of interruption of the donor chromosome per unit distance during transfer into a recipient cell); and (iii) the extrapolate number A (the probability that a donor cell will produce a recombinant inheriting the donor marker contiguous with the origin). It is usually assumed that chromosomal distances can be measured by marker entry times, i.e.

Genetic recombination in Escherichia coli: clone heterogeneity and the kinetics of segregation.

Several recombinant types may be produced from a single Escherichia coli zygote when the donor parent is Hfr-Hayes and segregation is delayed; usually only one type is produced with Hfr-Cavalli. Statistical experiments confirm well-known pedigree analyses by micromanipulation and suggest that DNA synthesis is required before final genetic integration.