Ariel Cohen

LIDAR MULTIPLE SCATTERING FROM CLOUDS

Multiple-scattering LIDAR return calculations obtained by seven different models for the same specified numerical experiment are compared. This work results from an international joint effort stimulated by the workshop group called MUSCLE for MUltiple SCattering Lidar Experiments. The models include approximations to the radiative-transfer theory, Monte-Carlo calculations, a stochastic model of the process of multiple scattering, and an extension of Mie theory for particles illuminated by direct and scattered light. The model solutions are similar in form but differ by up to a factor of 5 in the strength of the multiple-scattering contributions. Various reasons for the observed differences are explored and their practical significance is discussed.

Improved Neuronal Adhesion to the Surface of Electronic Device by Engulfment of Protruding Micro-Nails Fabricated on the Chip Surface

One of the major problems in assembling efficient neuro-electronic hybrids systems is the low electrical coupling between the components. This is mainly due to the low resistance, extracellular cleft formed between the cells plasma membrane and the substrate to which it adhere. This cleft shunts the current generated by the neuron, or the device and thus reduces the signal to noise ratio. To increase the clefts electrical resistance we fabricated gold micronails that protrude from the transistor gate surface. The micronails were functionalized by phagocytosis facilitating peptides. Cultured neurons readily engulf the functionalized micronails forming tight physical contact between the cells and the surface of the device.

Electrically conductive 2D-PAN-containing surfaces as a culturing substrate for neurons

In the present contribution we report on a novel route to synthesize 2D-polyaniline (2DPAN) on sulfonated-poly(styrene) (SPS) templates by allowing first monomer assembly followed by chemical oxidation to achieve polymerization. We show that Aplysia neurons grown on 2D-PAN exhibit an unusual growth pattern and adhesion to this conducting substrate that is manifested by the formation of giant lamellipodia. The lamellipodial domains are characterized by small gap between the plasma membrane and the 2D-PAN substrate (ca. 30 nm) and actin rich skeleton resembling the skeleton of growth cones. This behavior is characteristic to uniform substrates containing only 2DPAN. However, in patterned substrates containing additionally poly(L-lysine) Aplysia neurons prefer to extend new neurites on the poly(L-lysine) domains.

Cloud-droplet-size distribution from lidar multiple-scattering measurements.

A method for calculating droplet-size distribution in atmospheric clouds is presented, based on measurement of laser backscattering and multiple scattering from water clouds. The lidar uses a Nd:YAG laser that emits short pulses at a moderate repetition rate. The backscattering, which is composed mainly of single scattering, is measured with a detector pointing along the laser beam. The multiple scattering, which is mainly double scattering, is measured with a second detector, pointing at a specified angle to the laser beam. The domain of scattering angles that contribute to the doublescattering signal increases monotonically as the pulse penetrates the cloud. The water droplets within the probed volume are assumed to have a constant size distribution. Hence, from the double-scatteringmeasured signal as a function of penetration depth within the cloud, the double-scattering phase function of the scattering volume is derived. Inverting the phase function results in a cloud-droplet-size distribution in the form of a log-normal function.

An Experimental Determination of the Depolarization of Scattered Laser Light by Atmospheric Air

Abstract The previously adopted values of the depolarization factor of clear atmospheric air are checked with the values obtained by lidar facilities, and with those obtained in laboratory measurements, using scattering of a He-Ne gas laser. These values and the importance of the depolarization factor in lidar measurements are discussed.

A feasibility study of multi-site,intracellular recordings from mammalian neurons by extracellular gold mushroom-shaped microelectrodes

The development of multi-electrode array platforms for large scale recording of neurons is at the forefront of neuro-engineering research efforts. Recently we demonstrated, at the proof-of-concept level, a breakthrough neuron-microelectrode interface in which cultured Aplysia neurons tightly engulf gold mushroom-shaped microelectrodes (gMμEs). While maintaining their extracellular position, the gMμEs record synaptic- and action-potentials with characteristic features of intracellular recordings. Here we examined the feasibility of using gMμEs for intracellular recordings from mammalian neurons. To that end we experimentally examined the innate size limits of cultured rat hippocampal neurons to engulf gMμEs and measured the width of the “extracellular” cleft formed between the neurons and the gold surface. Using the experimental results we next analyzed the expected range of gMμEs-neuron electrical coupling coefficients. We estimated that sufficient electrical coupling levels to record attenuated synaptic- and action-potentials can be reached using the gMμE-neuron configuration. The definition of the engulfment limits of the gMμEs caps diameter at ≤2–2.5 μm and the estimated electrical coupling coefficients from the simulations pave the way for rational development and application of the gMμE based concept for in-cell recordings from mammalian neurons.

Lidar Observation of the Atmospheric Boundary Layer in Jerusalem

Abstract The temporal variation of the atmospheric boundary layer (ABL) over Jerusalem is accurately measured by means of a lidar system. The findings are explained and discussed based on the specific synoptic situation of typical summer days in the Middle East. The different behavior of the ABL near the seashore and inland is stressed. The measurement technique is also used to detect the entrainment zone and its development over Jerusalem.

Radiation pressure on randomly oriented infinite cylinders

Expressions are developed for the radiation pressure on infinite dielectric cylinders caused by an oblique incidence as a function of the size parameter alpha = 2pialpha/lambda. It is shown that for nonabsorbing cylinders the radiation pressure is always perpendicular to the axis of the cylinder and thus not along the direction of the incident radiation except for the case of normal incidence. This result applies also for other small nonspherical particles. Consequently, the radiation pressure on a randomly oriented nonspinning group of small nonspherical particles causes the particles to spread away from the direction of propagation of the incident radiation. It is suggested that this conclusion should be taken into account when discussing the effect of the radiation pressure on small particles in space, as compared with other forces such as the dynamic pressure on the solar wind.

Horizontal visibility and the measurement of atmospheric optical depth of lidar

In this paper we describe a generalized treatment of the atmospheric visibility distances for a variety of atmospheric conditions. In the development of the formula for the visibility distance, it is shown how a series of assumptions made in the early work of Koschmieder [Beitr. Phys. Atmos. 12, 33 (1924)] can be reduced to a single assumption covering more atmospheric conditions. Special attention is paid to the cases in which the extinction coefficient is wavelength-dependent. It is shown that neglecting such a dependence may produce errors as large as 20-100%, especially when long visibility distances are considered. The use of a dye-laser radar for the remote sensing of visibility distances is described and discussed.

Lidar measurements of rotational Raman and double scattering

The analysis of unusually strong Raman backscattering signals from clouds shows that such signals cannot be merely related to filter on-line leakage. Theoretical calculations of Raman double scattering in an atmosphere with high optical depth values are presented, and it is shown that the Raman multiple scattering effect is not negligible. The results of the calculations are in good agreement with the experimental data.