Sub-nanoradiant beam pointing monitoring and stabilization system for controlling input beam jitter in gravitational wave interferometers.

In this paper, a simple and effective control system to monitor and suppress the beam jitter noise at the input of an optical system, called a beam pointing control (BPC) system, will be described, showing the theoretical principle and an experimental demonstration for the application of large-scale gravitational wave (GW) interferometers (ITFs), in particular for the Advanced Virgo detector. For this purpose, the requirements for the control accuracy and the sensing noise will be computed by taking into account the Advanced Virgo optical configuration, and the outcomes will be compared with the experimental measurement obtained in the laboratory. The system has shown unprecedented performance in terms of control accuracy and sensing noise. The BPC system has achieved a control accuracy of ~10⁻8 rad for the tilt and ~10⁻7 m for the shift and a sensing noise of less than 1 n rad/√Hz, which is compliant with the Advanced Virgo GW ITF requirements.

Displacement noise from back scattering and specular reflection of input optics in advanced gravitational wave detectors.

The second generation of ground-based interferometric gravitational wave detectors are currently being built and installed. They are designed to be better in strain sensitivity by about a factor 10 with respect to the first generation. Light originating from the laser and following unintended paths, called stray light, has been a major problem during the commissioning of all of the first generation detectors. Indeed, stray light carries information about the phase of the emitting object. Therefore, in the next generation all the optics will be suspended in the vacuum in order to mitigate their associated stray light displacement noise. Despite this additional precaution, the challenging target sensitivity at low frequency which is partially limited by quantum radiation pressure combined with up-conversion effects, requires more detailed investigation. In this paper, we turn our attention to stray light originating from auxiliary optical benches. We use a dedicated formalism to compute the re-coupling of back-reflected and back-scattered light. We show, in particular, how much care should be taken in designing and setting requirements for the input bench optics.

Simulation of the time course of macromolecular separations in an ultracentrifuge. II. Controlling the solute concentrations.

We describe algorithms, based on a simulation described in Part I of this series of papers, for the control of the distribution of one or more solutes in preparative or analytical ultracentrifuges equipped with programmable speed control. All of the methods involve the determination, during numerical integration of the Lamm equation, of protocols for continuously varying the rotor speed. We show one such protocol that has been used for the prevention of cesium chloride crystallization during DNA plasmid purification in the preparative ultracentrifuge. Other protocols that are described involve the in situ controlled mixing of two solutes. Limitations of the method owing to problems with input parameter imprecision, fundamental physical constraints, and mechanical limitations are discussed.

Using caged neurotransmitters.

The development of photolabile caged neurotransmitters has made possible the study of the split-second kinetics of receptor-ligand interactions. An instrument has now been developed for activating the neurotransmitter and measuring the neuron's response.

Pressure effects on the photocycle of purple membrane.

We studied the effects of hydrostatic pressure on the kinetics of the photocycle of purple membrane from Halobacterium halobium. The data were interpreted in terms of a unidirectional and unbranched model. We found that all of the distinct processes of the photocycle are retarded by pressure, with the earlier, fast processes showing less sensitivity to pressure than the later, slow processes. The qualitative similarity of these results with the effects of solvent viscosity on the photocycle kinetics suggests that the primary effects of pressure on the kinetics are via the intrinsic viscosity of the membrane and not via activation volumes. There is a strong quantitative correlation between the pressure effects and the solvent viscosity effects, further supporting this interpretation. We observed a monotonic decrease in the positive absorbance change signal at 640 nm near the end of the photocycle as the pressure is increased. This signal is usually ascribed to the O intermediate, and we interpreted our finding, along with evidence from other experiments, to mean that an ionizable group or groups, such as carboxylic acids, are undissociated and uncharged in O.

Anesthetics and cerebral edema.

Localized edema follows the freezing of a small area of cerebral cortex. Effects of five subsequent hours of anesthesia on this edema were studied in six groups of six dogs each. Six anesthetic techniques were studied. In six additional "awake" dogs, anesthesia (halothane) was discontinued immediately after the lesion was made. Eight control dogs received neither anesthesia nor cryogenic injury. Control white matter contained 67.4 +/- .4 (mean +/- SE) per cent water by weight. Twenty-four hous after the cryogenic injury, water accounted for the following percentages of total weight of white matter adjacent to the lesion: 60 mg/kg pentobarbital, 73.2 +/-.9; 70 per cent N2O/Innovar, 73.6 +/- .9; "awake", 77.9 +/- .9; 1.95 per cent enflurane, 78.2 +/- .9; 1.33 per cent isoflurane, 78.6 +/- .8; 0.86 per cent halothane, 78.2 +/- .6; 1.89 per cent halothane, 79.7 +/- .6. Peak intracranial pressures (ICP) were 15.4 +/- 1.3 torr with pentobarbital, 21.6 +/- 1.8 torr with N2O/Innovar, and 31.1 +/- 2.6 to 38.3 +/- 4.5 torr with the halogenated anesthetics. The water content of white matter and ICP were significantly lower (P less than 0.05) in animals receiving pentobarbital or N2O/Innovar anesthesia than in animals receiving inhalation anesthetics. The authors conclude that pentobarbital and fentanyl-droperidol (Innovar) limit the extent of cerebral edema, but that inhaled anesthetics do not.

Quasielastic light-scattering study on changes in sizes of native white membranes after addition of retinal.

Aqueous suspensions of native white membranes from Halobacterium halobium, strain JW2N, have been studied by quasielastic light scattering. The intensity autocorrelation functions of polarized scattered light from suspensions of white membranes themselves and of white membranes after reconstitution with retinal were measured at various K(2), K being the magnitude of the scattering vector. The first cumulant or the average decay rate of the correlation function was obtained by a cumulant expansion method. The first cumulant for the white membranes increased after retinal was added to the suspension. The first cumulants obtained before and after the addition of retinal were almost independent of pH in the range 7 to 11, and of temperature in the range 15 degrees to 40 degrees C after T/eta scaling, eta being the solvent viscosity. This suggests that photocycling in reconstituted membranes, induced by the probe laser-beam, did not cause any detectable change in spectra, and that the membrane flexibility, if present, was independent of the above conditions, so that the spectral changes after the addition of retinal could be attributed mostly to the changes in the sizes of the membranes. A theoretical formulation for the first cumulant for a rigid disk-like scatterer (Fujime, S. and K. Kubota, 1985, Biophys. Chem., 23:1-13.) was applied to the analysis of the spectra. The results suggest that the radii of the membrane patches decreased by several percent after the addition of retinal.

Thermodynamic properties of purple membrane.

We measured the density, expansivity, specific heat at constant pressure, and sound velocity of suspensions of purple membrane from Halobacterium halobium and their constituent buffers. From these quantities we calculated the apparent values for the density, expansivity, adiabatic compressibility, isothermal compressibility, specific heat at constant pressure, and specific heat at constant volume for the purple membrane. These results are discussed with respect to previously reported measurements on globular proteins and lipids. Our data suggest a simple additive model in which the protein and lipid molecules expand and compress independently of each other. However, this simple model seems to fail to describe the specific heat data. Our compressibility data suggest that bacteriorhodopsin in native purple membrane binds less water than many globular proteins in neutral aqueous solution, a finding consistent with the lipid surround of bacteriorhodopsin in purple membrane.

Inhibitors of nuclear factor kappa B cause apoptosis in cultured macrophages.

The precise role of the transcription factor nuclear factor kappa B (NF- kappaB) in the regulation of cell survival and cell death is still unresolved and may depend on cell type and position in the cell cycle. The aim of this study was to determine if three pharmacologic inhibitors of NF-kappaB, pyrrolidine dithiocarbamate, N-tosyl-L-lysl chloromethyl ketone and calpain I inhibitor, induce apoptosis in a murine macrophage cell line (RAW 264.7) at doses similar to those required for NF-kappaB inhibition. We found that each of the three inhibitors resulted in a dose- and time-dependent increase in morphologic indices of apoptosis in unstimulated, LPS-stimulated and TNF-stimulated cells. Lethal doses were consistent with those required for NF- kappaB inhibition. We conclude that nuclear NF-kappaB activation may represent an important survival mechanism in macrophages.

Trans/13-cis isomerization is essential for both the photocycle and proton pumping of bacteriorhodopsin.

We studied an analogue of bacteriorhodopsin whose chromophore is based on all-trans retinal. A five-membered ring was built around the 13-14 double bond so as to prohibit trans to 13-cis isomerization. No light-induced photochemical changes were seen, other than those due to a small amount (approximately 5%) of unbleached bacteriorhodopsin remaining in the apomembrane used for regeneration. The techniques used included flash photolysis at room and liquid nitrogen temperatures and Fourier-transform infrared difference spectroscopy. When the trans-fixed pigment was incorporated into phospholipid vesicles, no evidence of light-initiated proton pumping could be found. The results indicate that trans to 13-cis isomerization is essential for the photochemical transformation and function of bacteriorhodopsin.

Synthesis, photochemistry, and biological activity of a caged photolabile acetylcholine receptor ligand.

A biologically inert photolabile precursor of carbamoylcholine has been synthesized; it is photolyzed to carbamoylcholine, a well-characterized acetylcholine analogue, with a half-time of 40 microseconds at pH 7.0 and a quantum yield of 0.8. The compound, N-(alpha-carboxy-2-nitrobenzyl)carbamoylcholine, was synthesized from (2-nitrophenyl)glycine. The photolysis rates (of five compounds) and the biological activity (of two compounds) were determined, and both properties were found to depend on the nature of the substituents on the photolabile protecting group. Laser pulse photolysis at wavelengths between 308 and 355 nm was used to investigate the wavelength dependence, quantum yield, and rate of the photolysis reaction. Photolysis products were isolated by high-performance liquid chromatography and identified by chemical and spectroscopic analysis and by their ability to activate the nicotinic acetylcholine receptor. BC3H1 muscle cells containing those receptors and a cell-flow method were used in the biological assays. The approach described may be useful in the preparation and characterization of other photolabile precursors of neurotransmitters that contain amino groups. The importance of these rapidly photolyzed, inert precursors of neurotransmitters is in chemical kinetic investigations of the reactions involving diverse neuronal receptors; such studies have been hampered because the available techniques have an insufficient time resolution.