Multivalent counterions diminish the lubricity of polyelectrolyte brushes.

Polyelectrolyte brushes provide wear protection and lubrication in many technical, medical, physiological, and biological applications. Wear resistance and low friction are attributed to counterion osmotic pressure and the hydration layer surrounding the charged polymer segments. However, the presence of multivalent counterions in solution can strongly affect the interchain interactions and structural properties of brush layers. We evaluated the lubrication properties of polystyrene sulfonate brush layers sliding against each other in aqueous solutions containing increasing concentrations of counterions. The presence of multivalent ions (Y3+, Ca2+, Ba2+), even at minute concentrations, markedly increases the friction forces between brush layers owing to electrostatic bridging and brush collapse. Our results suggest that the lubricating properties of polyelectrolyte brushes in multivalent solution are hindered relative to those in monovalent solution.

Fusion of bolaamphiphile micelles: a method to prepare stable supported biomimetic membranes.

Supported biomimetic membranes (SBMs) on solid substrates have been commonly prepared from vesicle-forming double-tail lipids, such as zwitterionic phospholipids, using the method of vesicle fusion. Here we report on the preparation of SBMs on silica surfaces via a similar process of "micelle fusion" from a cationic single-tail bolaamphiphile GLH-20 that forms spherical and elongated thread-like micelles in solution. We demonstrate that, in contrast to zwitterionic phospholipids, GLH-20 self-assembles into a stable contiguous SBM at both low and high ionic strengths. The cationic charge of GLH-20 promotes the formation of a stable SBM through enhanced double-layer interactions with the negatively charged silica surface. It is also shown that spinach aquaporin PM-28 was successfully incorporated within bolaamphiphile SBM in a manner similar to SBMs prepared by vesicle/proteoliposome fusion; thereby the inherent curvature of the micelle surface does not inhibit protein reconstitution. The results suggest that SBMs based on charged bolaamphiphiles might be an attractive platform for applications such as water purification and biosensors, where the stability and low defect rate of SBMs in diverse conditions are crucial for achieving desired performance.

Doppler and gray-scale sonographic classification of adnexal torsion.

OBJECTIVE: To propose, in cases with coiling of the ovarian vessels, a classification of severity of torsion based on Doppler and gray-scale ultrasound findings and to suggest a treatment strategy for each situation. METHODS: Seventeen patients were examined in a gynecological emergency room between December 1995 and February 2003 due to suspected adnexal torsion. Doppler and gray-scale ultrasound were used to visualize coiling of the ovarian blood vessels. Intraovarian flow was assessed by spectral Doppler and on this basis, along with the patient's clinical condition, the decision was made as to whether surgery was necessary. Findings on surgery were recorded. RESULTS: All 17 patients showed coiling of the ovarian vessels. Nine had arterial and venous blood flow within the ovary and ultrasound and surgical findings usually demonstrated normal sized or mildly enlarged ovaries. Five had only arterial blood flow within the ovary and surgery usually revealed enlarged ovaries with normal color or mild discoloration. Three had neither arterial nor venous blood flow within the ovary, with vessel coiling evident only on gray-scale and not on Doppler examination, and surgical findings included signs of ovarian ischemia or necrosis. CONCLUSION: In cases of coiling of the ovarian vessels, Doppler flow analysis of the ovary can help differentiate between ischemic adnexal torsion and coiling of the ovarian blood vessels without strangulation, aiding in the choice of treatment. According to type of blood flow seen on Doppler examination, we suggest the following classification of severity of adnexal torsion and treatment strategy: Class 1, coiling with arterial and venous ovarian blood flow; a conservative approach may be considered if the clinical condition permits; Class 2, coiling with arterial ovarian flow but no venous flow; surgical intervention is required; and Class 3, true strangulation, with no ovarian blood flow; urgent surgical intervention is required.

Long-term sleep disturbances in adolescents after minor head injury.

It has been demonstrated that patients in the acute phase after minor head injury (MHI) complain of sleep disturbances. The purpose of the present study was to characterize the long-term effects of MHI on sleep in adolescents. Nineteen adolescents who had suffered MHI 3 years before the study and had complained of sleep disturbances completed a sleep questionnaire and were investigated in the sleep laboratory by whole-night polysomnographic recordings and were actigraphically monitored for 5 days at home. Questionnaire results revealed severe complaints regarding sleep behavior. Polysomnographic recordings revealed that in comparison with controls, MHI was associated with lower sleep efficiency (79.8 +/- [9.8]% vs 87.7 +/- [6.8]%; P < 0.005), with more wake time (10.6 +/- [9.0]% vs 3.4 +/- [4.4]%; P < 0.005), and with more awakenings lasting more than 3 minutes (2.1 +/- [1.5] vs 0.6 +/- [0.8]; P < 0.005). These findings were confirmed by actigraphic monitoring that revealed lower sleep efficiency (90 +/- [5]% vs 94 +/- [3]%; P < 0.05), more minutes of wake time (49 +/- [21] min vs 28 +/- [15] min; P < 0.05), and a trend toward more awakenings longer than 5 minutes (1.8 +/- [0.8] vs 1.2 +/- [0.8]; P = 0.063). Our data demonstrated that 3 years after MHI without any discernible clinical sequel, adolescents still complain of sleep disturbances that could be confirmed by both polysomnographic and actigraphic monitoring.

Ionization waves in electron-beam-assisted, shielded capillary discharge

A theory of propagation of cathode-directed ionization waves during the early stages of an electrical breakdown in a shielded, low-pressure capillary is developed. The discharge process occurs due to the ionization of the low-density gas in the capillary by an electron beam that is emanating from a hollow cathode. Due to the strong electric field in the capillary the electrons are in the fast acceleration regime. Consequently, the full momentum equation for the electrons is employed, rather than the electron drift velocity approach. The smallness of the ratio of the capillary radius to the characteristic length of the electric potential variation in the axial direction allows the construction of a quasi-one-dimensional model. The latter retains the important two-dimensional nature of the electron flow as well as the electrodynamic boundary conditions at the capillary wall and the conducting shield and results in a set of one-dimensional, time-dependent partial differential equations for the on-axis distributions of the physical quantities. It is shown that those equations admit self-similar solutions that represent ionization waves propagating with constant velocities. The resulting set of ordinary differential equations is solved numerically for various initial conditions representing a nonperturbed steady state ahead of the ionization front and the resulting features of the ionization waves are investigated and discussed. The obtained solutions describe both ionization growth and virtual anode propagation and represent fast ionization waves in plasma waveguides, for which the maximum value of the mean electron velocity is much higher than the wave velocity. The space-charge distribution associated with the ionization waves is found in the form of plasma oscillations with a continuously increasing frequency and a solitary envelope. The calculated wave velocity increases with the gas pressure and this tendency is in agreement with corresponding experimental observations.

Bilateral focal motor status epilepticus with retained consciousness after stroke.

Bilateral motor seizures with retained consciousness are rare and often mistaken for pseudoseizures. In the few reported cases, the seizures were brief and the underlying lesion usually was a tumor. Here the authors describe a patient with bilateral focal motor status epilepticus with retained consciousness after a stroke. A seizure should be considered as the possible cause of continuous bilateral limb movements with retained consciousness.

Use of sky brightness measurements from ground for remote sensing of particulate polydispersions.

The software code SKYEAD.pack for retrieval of aerosol size distribution and optical thickness from data of direct and diffuse solar radiation is described; measurements are carried out with sky radiometers in the wavelength range 0.369-1.048 µm. The treatment of the radiative transfer problem concerning the optical quantities is mainly based on the IMS (improved multiple and single scattering) method, which uses the delta-M approximation for the truncation of the aerosol phase function and corrects the solution for the first- and second-order scattering. Both linear and nonlinear inversion methods can be used for retrieving the size distribution. Improved calibration methods for both direct and diffuse radiation, the data-analysis procedure, the results from the proposed code, and several connected problems are discussed. The results can be summarized as follows: (a) the SKYRAD.pack code can retrieve the columnar aerosol features with accuracy and efficiency in several environmental situations, provided the input parameters are correctly given; (b) when data of both direct and diffuse solar radiation are used, the detectable radius interval for aerosol particles is approximately from 0.03 to 10 µm; (c) besides the retrieval of the aerosol features, the data-analysis procedure also permits the determination of average values for three input parameters (real and imaginary aerosol refractive index, ground albedo) from the optical data; (d) absolute calibrations for the sky radiometer are not needed, and calibrations for direct and diffuse radiation can be carried out with field data; (e) the nonlinear inversion gives satisfactory results in a larger radius interval, without the unrealistic humps that occur with the linear inversion, but the results strongly depend on the first-guess spectrum; (f) aerosol features retrieved from simulated data showed a better agreement with the given data for the linear inversion than for the nonlinear inversion.

Possible causes of calibration degradation of the Advanced Very High Resolution Radiometer visible and near-infrared channels.

Gradual deterioration of calibration of the Advanced Very High Resolution Radiometer (AVHRR) can be explained by the erosion of the scanning mirror as a result of interaction with interplanetary dust. Other elements of the instrument (optical filters, detector, electronics) were also examined for their behavior in space conditions and were found most likely to be stable and not responsible for the decrease in sensitivity. Calculations show that the erosion of the scanning mirror is of the order of 4.5% per year, although this erosion is very variable because of the variability of the density of interplanetary dust. This erosion can easily explain the 3-5% per year deterioration of theAVHRR sensors on NOAA-7 and NOAA-9.

Urban light pollution: the effect of atmospheric aerosols on astronomical observations at night.

The transfer of diffuse city light from a localized source through a dust-laden atmosphere with optical depth <0.5 has been analyzed in the source-observer plane on the basis of an approximate treatment. The effect on several types of astronomical observation at night has been studied, considering different size distributions and amounts as well as particle shapes of the aerosols. The analysis is made not as a function of the absolute aerosol amount but in terms of the signal-to-noise ratios for a given amount of aerosol. The model is applied to conditions at the Wise Astronomical Observatory in the Negev desert and limiting backgrounds for spectroscopy, photometry, and photography of stars and extended objects have been calculated for a variety of signal-to-noise ratios. Applications to observations with different equipment at various distances from an rban area of any size are possible. Due to the use of signal-to-noise ratios, the conclusions are different for the different experimental techniques used in astronomy.

Contrast reduction by the atmosphere and retrieval of nonuniform surface reflectance.

A radiative transfer model is developed which gives the upward radiance at nadir for any 1-D Lambertian surface reflectance. This model is used to depict the atmospheric effect on the transmittance of contrast for any 1-D surface reflectance. Here by contrast we mean a general variation of the radiation field across the image. With the aid of this model an inversion algorithm is developed for retrieval of true surface reflectance from high resolution satellite data (e.g., Landsat). This inversion technique can be a useful tool for extraction of surface reflectance from satellite data in the case of a surface reflectance variable in one dimension only (e.g., seashore or near borders of big fields). A sensitivity study of the inversion procedure on the knowledge of atmospheric parameters and sensor calibration was performed. It is shown that this inversion technique is stable even in the presence of errors in the sensor calibration and the atmospheric parameters. The method was applied to Landsat data in two wavelengths. The results show reasonable dependence of the derived surface reflectance on the distance from the seashore.

Combined eye-atmosphere visibility model.

The effect of the earth's atmosphere on the visibility in the nadir direction, as determined by the human eye, is presented. The visibility characteristics can be obtained from the combined eye-atmosphere modulation transfer function. This function is applied to the calculation of visibility thresholds of an area of an albedo different from its surroundings. It is shown that the atmospheric effect of diffusing sharp boundaries between adjacent areas has a significant influence on the visibility threshold. A sensitivity study is carried out to investigate the effects of different atmospheric optical conditions on the visibility thresholds. This model emphasizes the use of a combined eye-atmosphere theory to predict visibility conditions from airplanes.

Nonlinear absorption of SF(6) at high infrared intensities and high pressures.

An experimental study of the saturable absorption of SF(6) at high pressure (up to 500 Torr) with high laser irradiance is presented. Experiments carried out at the P(28) line of the CO(2) laser show a decrease of transmittance with increasing laser irradiance before bleaching sets in. This is explained by a theoretical model using a single rate equation. The decrease of transmittance is shown to be due to vibrational excitation, whereas bleaching is caused by rotational hole burning. Previous results on saturation behavior of SF(6) at the P(16) line of CO(2) reported by Armstrong and Gaddy are given a new interpretation using the present model.

Time-resolved molecular excitation and heat effects induced by infrared radiation.

A saturable absorber (SF(6)) is irradiated by a step of radiation from a CO(2) laser, and the step response of the medium is observed. Since the characteristic times of rotational, vibrational, and thermal excitation are different, it is possible to observe each process separately. A set of rate equations is developed for a simplified model of two energy levels. This set includes only one differential equation and qualitatively describes the effects of rotational hole burning and vibrational relaxation. Heat effects are accounted for separately.

Simultaneous heating and temperature measurements by an infrared laser beam.

A method of simultaneous heating and temperature measuring of a gas absorber by means of an ir CO(2) laser is proposed and tested. The proposed method is relatively simple and direct. In this experiment the temperature on the beam axis as a function of the beam intensity, the beam radius, and the absorber mixture is measured. A good agreement is obtained between the experimental results and theoretical predictions based on the level scheme and the physical characteristics of the absorber. The temperature measurement proposed in the present paper is an additional experimental tool in investigating excitation processes in the ir region.

High gain ir laser in passive Q-switching: operating criterion.

A set of rate equations is developed for the operation of an ir laser in passive Q-switching. This set of equations includes the effect of rotational hole burning in the saturable absorber and the high gain and nonuniform losses in the cavity of the laser. Using these equations a set of criteria is developed, which states conditions on the parameters of the laser and the absorber that have to be fulfilled in order that the laser-absorber system should operate in pulses. Experimental verification of the criteria is given. The three phases of the operation of the laser (cw, pulses, and zero output) are depicted on a phase diagram that emphasizes the dependence of the operation on the parameters of the laser and the absorber.

Passive-Q-switching at high intensities and high absorber pressures.

The range of operation of a CO(2) laser in pulses due to passive Q-switching is extended to high pressures of the absorber (200-800 Torr) and high intensities of the irradiation in the absorption cell (1 kW/cm(2) average power). This extension may be applied to igh power CO(2) lasers. The experimental results indicate that thermal saturation is involved in the Q-switching. The theory of passive Q-switching is extended to include this effect and is compared with the experimental results.