Space-time resolved approach for interacting quantum field theories.

An alternative approach to the usual perturbative S-matrix evaluation of quantum field theories is presented which is nonperturbative and provides full space-time resolution. We study the dynamical development of the force between two fermion wave packets for the Yukawa system. The spatial distribution of the virtual bosons that act as mediators of the force can be analyzed along with the fermionic densities. Using a potential function for the fermion-fermion interaction is a good approximation to the field theoretical calculations when the Fock space is restricted to only one boson, but in the full quantum field theory the fermion-fermion force is enhanced by higher-order multiboson processes. Furthermore, the normally attractive fermion-fermion Yukawa force can, in principle, be manipulated to even be repulsive if the momentum modes available to the virtual bosons are restricted.

Photon-density waves in macroscopic and microscopic plane-parallel scattering samples.

We investigate the validity of the Boltzmann equation to predict the reflection and transmission coefficients for an intensity modulated laser beam passing through a microscopic medium consisting of discrete scatterers. For a one-dimensional model system we demonstrate that the Boltzmann equation works remarkably well for small modulation frequencies, even to describe a medium comprised of only 10 scatterers. Discrepancies can be found only if the modulation wavelength of the laser intensity is commensurate with the spacing between the scatterers and if the medium is sufficiently ordered.

Crying in hospitals: a survey of doctors', nurses' and medical students' experience and attitudes.

OBJECTIVE: To investigate doctors', nurses' and medical students' experiences with, and attitudes of health care personnel towards, crying in hospitals. DESIGN: Descriptive, cross-sectional study, using self-report questionnaires. SETTING AND PARTICIPANTS: The sample comprised 52 doctors (response rate, 33%) and 103 nurses (response rate, 58%) from three Sydney metropolitan general hospitals, and 101 sixth-year medical students (response rate, 99%). RESULTS: Crying was frequent in hospitals; 57% of doctors, 76% of nurses and 31% of medical students had cried at work in the hospital at least once, and women cried significantly more often than men. Being a nurse significantly increased, whereas being a medical student significantly decreased, the likelihood of crying. Medical students reported the highest percentage of negative social consequences of their own crying (e.g., being ridiculed or screamed at). The main reason for all respondents' crying was identification and bonding with suffering and dying patients or their families. The respondents generally viewed crying by patients as a healthy response, and they were empathetic towards the crying patient. About one-third of the respondents were interested in (or would consider) using psychological help to explore their own emotional reactions to crying. CONCLUSION: Despite its limited sample, this study suggests that the topic of "crying" should be included in medical training, and that support be provided for medical staff who are distressed by crying behaviour in hospitals.

Relationship between Cultural Factors and Nematodes on Merion Kentucky Bluegrass.

A 2-year study was conducted on Merion Kentucky bluegrass turf (Poa pratensis) to identify potential relationships among seasonal population dynamics of nematodes, chemical applications, thatch, tillering, dollar spot caused by Sclerotinia homoeocarpa, clipping weight, and other factors. Numbers of Tylenchorhynchus maximus determined during June were inversely related to the wet weight of grass from May. One or more monthly counts of Paratylenchus hamatus, Criconemella rusium, and T. maximus negatively correlated with the numbers of spring tillers. Applications of benomyl, used for dollar spot control, decreased numbers of T. maximus and free-living nematodes, and this chemical was associated with acidification of the thatch. Hoplolaimus galeatus levels were associated with an estimated 8% increase in the severity of dollar spot.

Finite-length line-spread function.

In this paper we derive a formula for calculating the point-spread function (PSF) of a rotationally symmetric imaging system from measurements along a line through the image of an arbitrary separable input object. An important special case of this formula is when the input object is a finite-length slit. The set of measurements in this case is called the finite-length line-spread function (FLSF). The FLSF differs from the infinite-length line-spread function (LSF) only in the assumed finite length of the line that is input into the system. This difference between the FLSF and the LSF becomes important for imaging systems for which the PSF is large in extent and in which the isoplanatic patch is relatively small. The usual LSF-to-PSF conversion formulas cannot be applied accurately to such systems.

Polychlorinated biphenyl dechlorination in aquatic sediments.

The polychlorinated biphenyl (PCB) residues in the aquatic sediments from six PCB spill sites showed changes in PCB isomer and homolog (congener) distribution that indicated the occurrence of reductive dechlorination. The PCB dechlorinations exhibited several distinct congener selection patterns that indicated mediation by several different localized populations of anaerobic microorganisms. The higher (more heavily chlorinated) PCB congeners that were preferentially attacked by the observed dechlorination processes included all those that are either pharmacologically active or persistent in higher animals. All the lower (less heavily chlorinated) PCB congeners formed by the dechlorinations were species that are known to be oxidatively biodegradable by the bacteria of aerobic environments.

Extensive degradation of Aroclors and environmentally transformed polychlorinated biphenyls by Alcaligenes eutrophus H850.

We have isolated and characterized a strain of Alcaligenes eurtrophus, designated H850, that rapidly degrades a broad and unusual spectrum of polychlorinated biphenyls (PCBs) including many tetra- and pentachlorobiphenyls and several hexachlorobiphenyls. This strain, which was isolated from PCB-containing dredge spoils by enrichment on biphenyl, grows well on biphenyl and 2-chlorobiphenyl but poorly on 3- and 4-chlorobiphenyl. Capillary gas-chromatographic analysis showed that biphenyl-grown resting cells of H850 degraded the components of 38 of the 41 largest peaks of Aroclor 1242 and 15 of the 44 largest peaks of Aroclor 1254, resulting in an overall reduction of PCBs by 81% for Aroclor 1242 (10 ppm) and 35% for Aroclor 1254 (10 ppm) in 2 days. Furthermore, H850 metabolized the predominantly ortho-substituted PCB congeners that resulted from the environmental transformation of the more highly chlorinated congeners of Aroclor 1242 by the upper Hudson River anaerobic meta-, para-dechlorination agent system C (J. F. Brown, R. E. Wagner, Jr., D. L. Bedard, M. J. Brennan, J. C. Carnahan, R. J. May, and J. J. Tofflemire, Northeast Environ. Sci. 3:167-179, 1984). The congener selectivity patterns indicate that a two-step process consisting of anaerobic dechlorination followed by oxidation by H850 can effectively degrade all of the congeners in Aroclor 1242 and possibly all those in Aroclor 1254.

Interference effects in optical fiber connections.

Optical interference may occur in fiber connections, and this can have an important effect on transmission loss. A theoretical analysis shows that the effect occurs in both single-mode and multimode fibers and depends on fiber end face separation, the source spectrum, and the modal power distribution in the fiber. Experimental observations of interference in dry multimode fiber connections confirm the analysis for both laser diode and LED sources.

Coupling efficiency of optics in single-mode fiber components.

Many single-mode fiber components include some form of optics, such as lenses or mirrors, for collecting light from a source fiber or laser and concentrating it on a receiving fiber. For such components there is a direct and simple relationship between coupling efficiency and optical aberrations. This paper combines fiber-coupling fundamentals, classical optics, and diffraction theory to provide a compact description of coupling efficiency that includes the effects of aberrations, fiber misalignments, and fiber-mode mismatch.

Electrically controlled optical switch for multimode fiber applications.

An electrically controlled optical switch based on polarization principles is described. It uses a liquid crystal twist cell that rotates polarization by 90 degrees , and it operates on an ac voltage that switches between 0.8 and 2.5 V rms. The switch has a loss of ~0.4 dB, neglecting reflections, in an unpolarized incoherent beam and a cross-talk ratio of ~-20 dB. It operates in collimated light, but it can be applied to multimode fibers using collimating lenses, which are expected to add <0.8 dB to the loss.

Postprocessing of imagery from active optics: some pitfalls.

There may be pitfalls to watch for when recording imagery from active phase compensation devices located in the exit pupil of the system. At least three of these pitfalls are identified, and each is manifested as a degradation in the imagery. Both nearby and high altitude atmospheric disturbances contribute to the degradation. The first pitfall is identified as residual phase errors caused by measurement and hardware limitations. The second pitfall is identified as nonisoplanatism, and it occurs because wavefronts from different source points experience different high altitude disturbances. The third pitfall is identified as amplitude fluctuations in the exit pupil of the system, and it is also caused by the high altitude atmospheric disturbances. The two pitfalls caused by the high altitude disturbances are reduced by applying additional phase compensation in a plane that is the image of the high altitude disturbances. But even this may not be sufficient to eliminate the need for postprocessing of the image ry of extended sources.

A mechanism for initiation of genetic recombination.

A mechanism for the initiation of genetic recombination is proposed. Its key features are the pairing, nicking, and cross-annealing of palindromic loops, i.e., structures formed by DNA with sequences of inverted complementary repeats. This mechanism may provide a simple, yet specific means of producing crossed strand connections between homologous DNA duplexes to form structures which can be intermediates in the process of genetic recombination.

Fabrication of aspherics using a mathematical model for material removal.

A mathematica model has been developed that predicts the aspheric surface that a typical optical surfacing machine will produce. The model, which combines two basic assumptions concerning material wear with the kinematics of the machine, has been verified experimentally for the grinding process. In regions of the surface where the tool extends beyond the edge of the workpiece, pressure becomes nonuniform, and the model must be altered. The established model has been used to synthesize those machine strokes required to produce a desired aspheric surface.

Physical model for predicting grinding rates.

When grinding an optical surface, the material removal rate depends linearly upon pressure and velocity and upon a proportionality constant which accounts for differences in material properties. A physical description of the grinding process has been postulated which results in the linear pressure and velocity relationships and which also allows the value of the proportionality constant to be determined from a knowledge of material properties alone. Previous attempts at predicting material removal rely strictly upon experimental data to determine the proportionality constant. The postulated description incorporates the combined effects of many individual abrasive particles to statistically determine the proportionality constant in terms of abrasive size and the breaking stress of the glass. A simple example indicates that the result is consistent with experiment.