All-optical switching based on inverse Raman scattering in liquid-core optical fibers.

We report on a new platform for all-optical switching based on inverse Raman scattering in liquids. Narrowband switching, which could be suitable for wavelength-division-multiplexed applications, is demonstrated using integrated liquid-core optical fiber infiltrated with both neat liquids (CCl(4) and CS(2)) as well as an organic chromophore (ß-carotene) dissolved in CCl(4). Compared to standard glass optical fibers, these liquids have much larger Raman loss coefficients, which help reduce the pump power by at least an order of magnitude. Further improvements can be expected with the development of highly soluble organic compounds possessing large Raman cross sections.

Demonstration of Zeno switching through inverse Raman scattering in an optical fiber.

We report the observation of Zeno switching through an inverse Raman scattering (IRS) process in an optical fiber. In IRS, light at the anti-Stokes frequency is strongly attenuated in the presence of a pump field, allowing it to be used for all-optical switching and modulation. Our observed level of induced absorption via IRS in the optical fiber is > 20 dB in a time scale of less than 5 ps. The full Raman response spectrum was extracted experimentally and excellent agreement was found between the experimental data and theoretical modeling of IRS.

Design of organic molecules with large two-photon absorption cross sections.

A strategy for the design of molecules with large two-photon absorption cross sections, delta, was developed, on the basis of the concept that symmetric charge transfer, from the ends of a conjugated system to the middle, or vice versa, upon excitation is correlated to enhanced values of delta. Synthesized bis(styryl)benzene derivatives with donor-pi-donor, donor-acceptor-donor, and acceptor-donor-acceptor structural motifs exhibit exceptionally large values of delta, up to about 400 times that of trans-stilbene. Quantum chemical calculations performed on these molecules indicate that substantial symmetric charge redistribution occurs upon excitation and provide delta values in good agreement with experimental values. The combination of large delta and high fluorescence quantum yield or triplet yield exhibited by molecules developed here offers potential for unprecedented brightness in two-photon fluorescent imaging or enhanced photosensitivity in two-photon sensitization, respectively.

Wound infections following spinal fusion with posterior segmental spinal instrumentation.

Twenty-three of 238 patients (9.7%) developed wound infections following segmental spinal instrumentation. When the infected group and a matched control group were compared, the infected group had a significantly higher number of patients with cerebral palsy and myelodysplasia (nonambulatory), patients with wound hematomas, patients with fusions that extended into the sacral region, and patients who were incontinent of urine. A high incidence of infections with gram-negative aerobic bacilli correlated with the extension of the surgery into the sacral region and bowel and/or bladder incontinence. Prophylactic antibiotics with broader coverage for gram-negative bacilli may be warranted for these procedures. Postoperative wound infections were managed by surgical drainage and debridement as well as antibiotics. Removal of the hardware was not necessary to control the infection in these patients who underwent segmental spinal instrumentation.

Two-photon absorption and broadband optical limiting with bis-donor stilbenes.

Large two-photon absorptivities are reported for symmetrical bis-donor stilbene derivatives with dialkylamino or diphenylamino groups. These molecules exhibit strong optical limiting of nanosecond pulses over a broad spectral range in the visible. Relative to bis(di-n-butylamino)stilbene, bis(diphenylamino)stilbene exhibits a 90-nm red shift of its optical limiting band but only a minimal shift of ~13 nm of its lowest one-photon electronic absorption band. Mixtures of these compounds offer an unprecedented combination of broad optical limiting bandwidth and high linear transparency.

Implementation of information security and confidentiality policies, procedures, and standards.

The article describes one approach to developing and implementing a security program in response to the birth and growth of a computer-based patient record in a large teaching hospital. The discussion emphasizes the importance of the collaborative effort between the hospital and school of medicine in establishing one policy and set of standards because information is shared and electronically transferred between both institutions. The hospital's approach is summarized in five major steps: survey and literature search, development of key components or recommendations, institutional approval of the recommendations, feasibility analysis and projected time frame for implementation, and implementation of the recommendations with resolution of impediments to implementation.

A unified description of linear and nonlinear polarization in organic polymethine dyes.

An internal or external electric field F can drive the chemical structure, bond order alternation, and electronic structure of linear polymethine dyes from a neutral, bond-alternated, polyene-like structure, through a cyanine-like structure, and ultimately to a zwitterionic (charge-separated) bond-alternated structure. As the structure evolves under the influence of F, the linear polarizability alpha, the first hyperpolarizability beta, and the second hyperpolarizability gamma are seen to be derivatives, with respect to F, of their next lower order polarization (for alpha) or polarizability (for beta and gamma). These derivative relations provide a unified picture of the dependence of the polarizability and hyperpolarizabilities on the structure in linear polymethine dyes. In addition, they allow for predictions of structure-property relations of higher order hyperpolarizabilities.

Large first hyperpolarizabilities in push-pull polyenes by tuning of the bond length alternation and aromaticity.

Conjugated organic compounds with 3-phenyl-5-isoxazolone or N,N'-diethylthiobarbituric acid acceptors have large first molecular hyperpolarizabilities (beta) in comparison with compounds with 4-nitrophenyl acceptors. For example, julolidinyl-(CH=CH)(3)-CH=N,N'- diethylthiobarbituric acid, which has 12 atoms between the donor and acceptor, has a beta(0) of 911 x 10(-30) electrostatic units, whereas (CH(3))(2)NC(6)H(4),-(CH=CH)(4)-C(6)H(4)NO(2), with 16 atoms between its donor and acceptor, has a beta(0) of 133 x 10(-30) electrostatic units. The design strategies demonstrated here have resulted in chromophores that when incorporated into poled-polymer electrooptic modulators exhibited significant enhancements in electrooptic coefficients relative to polymers containing the commonly used dye Disperse Red-1. Poled polymer devices based on these or related chromophores may ultimately lead to high-speed electrooptic switching elements with low drive-power requirements, suitable for telecommunications applications.

Enhanced reverse saturable absorption and optical limiting in heavy-atom-substituted phthalocyanines.

The reverse saturable absorption and the optical-limiting response of metal phthalocyanines can be enhanced by use of the heavy-atom effect. Phthalocyanines containing heavy-metal atoms, such as In, Sn, and Pb, show a nearly factor-of-2 enhancement in the ratio of effective excited-state to ground-state absorption cross sections compared with those containing lighter atoms, such as Al and Si. In an f/8 optical geometry, homogeneous solutions of heavy-metal phthalocyanines, at 30% linear transmission, limit 8-ns 532-nm laser pulses to

Relation between bond-length alternation and second electronic hyperpolarizability of conjugated organic molecules.

The solvent dependence of the second hyperpolarizability, gamma, of a variety of unsaturated organic compounds has been measured by third harmonic generation at 1907 nanometers. It is seen that the measured gamma is a function of solvent polarity. These solvent-dependent hyperpolarizabilities are associated with changes in molecular geometry from a highly bond-length alternated, polyene-like structure for a formyl-substituted compound in non-polar solvents, to a cyanine-like structure, with little bond-length alternation, for a dicyanovinyl-substituted compound in polar solvents. By tuning bond-length alternation, gamma can be optimized in either a positive or negative sense for polymethine dyes of a given conjugation length.

Synthesis of organic salts with large second-order optical nonlinearities.

A series of organic salts, in which the cation has been designed to have a large molecular hyperpolarizability, has been prepared. Variation of the counterion (anion) in many cases leads to materials with large powder second harmonic generation efficiencies, the highest of which is roughly 1000 times that of a urea reference.

Demonstration of lipopolysaccharide on sheathed flagella of Vibrio cholerae O:1 by protein A-gold immunoelectron microscopy.

Monoclonal antibodies with group and type specificity for lipopolysaccharide antigens were used in combination with protein A-colloidal gold labeling and transmission electron microscopy to demonstrate the presence of lipopolysaccharide antigens on both the sheathed flagellum and the cell surface of Inaba and Ogawa strains of Vibrio cholerae O:1. Labeling was associated with the sheath of the flagellum rather than the core, and flagellar cores were not labeled. Flagellum and cell shared a common set of lipopolysaccharide antigens characteristic of the strain serotype.

Further characterization of the inhibition of casein production in a primary mouse mammary epithelial cell culture by epidermal growth factor. Antagonism by cyclic AMP.

Epidermal growth factor (EGF) inhibited casein production and the accumulation of casein mRNA activity induced by insulin (I), cortisol (F) and prolactin (P) in a primary culture of mammary epithelial cells from pregnant mice. The inhibitory effects of EGF were blocked by 8-bromo cyclic AMP (8-br-cAMP) in a dose-dependent manner. The effect of 8-br-cAMP was observed at a concentration as low as 20 microM and was maximal at 500 microM. Dibutyryl cyclic AMP (db-cAMP), cAMP, and 3-isobutylmethylxanthine (IBMX), an inhibitor of phosphodiesterase, also antagonized the inhibitory effect of EGF on casein production. 8-Br-cAMP had, however, no effect on the mitogenic activity of EGF in this system. These results suggest a possible modulatory role of cAMP in EGF-induced inhibition of casein production in cultured mammary epithelial cells.

The study of differentiative potential of the lactating mouse mammary gland in organ culture.

The organ culture of the mammary gland of lactating mice was used to examine the response of the differentiated gland to lactogenic stimuli, insulin, cortisol, and prolactin. Time course studies showed that casein synthesis in cultured tissue decreased rapidly during the first 2 d despite the presence of the three hormones, but on the 3rd d tissue cultured with either insulin and prolactin or all three hormones regained the ability to synthesize milk proteins, casein, and alpha-lactalbumin: a greater increase occurred in the three hormone system. The delayed addition of prolactin on Day 2 to the culture system containing insulin and cortisol also stimulated casein synthesis. The addition of cytarabine, which inhibited insulin-dependent cell proliferation in cultured explants, did not block the rebound of milk protein synthesis. These results indicate that in the presence of insulin, cortisol, and prolactin mammary epithelial cells in culture first lose and then regain the ability of synthesizing milk protein without requiring the formation of new daughter cells.

The regulatory function of spermidine in hormonal control of the development of mouse mammary gland in culture.

The interplay of insulin, glucocorticoid, and prolactin induces differentiation of mouse mammary gland in culture. Earlier studies indicated that spermidine plays a key role in hormonal control of mammary development by mediating some of the lactogenic actions of glucocorticoid. In this study we examined the effect of progesterone, an inhibitor of lactogenesis, on milk protein synthesis and spermidine accumulation. The maximal degree of inhibition, which was attained at 300 nM, was about 40% for casein synthesis, 90% for alpha-lactalbumin synthesis, and 70% for spermidine accumulation. The increase in the activity of S-adenosyl-L-methionine decarboxylase and spermidine synthetase, two key enzymes in polyamine biosynthesis, was inhibited by 55 and 65%, respectively, by progesterone. The extent of progesterone inhibition of milk protein synthesis was greatest in cultured tissue from virgin mice, which contained a low level of spermidine, whereas mammary explants from lactating mice, which contained a high level of spermidine, were insensitive to progesterone. The inhibitory effect of progesterone can be partially antagonized by cortisol, which causes an enhancement of spermidine accumulation. These results suggest that the synthesis and accumulation of spermidine serve as targets for the inhibitory action of progesterone on lactogenesis.

Comparison of psychophysical and evoked-potential tuning curves in the chinchilla.

Frequency selectivity was examined in normal-hearing chinchillas using psychophysical and evoked-potential tuning curves. The acoustic conditions and masking procedures used for the evoked-potential and psychophysical studies were nearly identical. Frequency selectivities as measured by psychophysical and physiologic techniques were quite similar across different probe frequencies. The results suggest that the relatively efficient evoked-potential procedure may be substituted for the time-consuming psychophysical paradigm. Furthermore, the results are consistent with the view that tuning takes place primarily at the auditory periphery.