Raul Fainchtein

Local determination of hemoglobin concentration and degree of oxygenation in tissue by pulsed photoacoustic spectroscopy

Pulsed-photoacoustic spectroscopy in the near IR portion of the optical spectrum was used as a local technique for quantitative monitoring of tissue hemoglobin concentration and its oxygenation state. A pulsed, tunable optical source coupled to a 1mm-diameter optical fiber cable was used to deliver optical energy to the tissue under study. The fiber was placed either on the exterior surface or inserted into the tissue. An ultrasonic signal was produced in the tissue as a result of the absorbed light pulse energy. Since the rate of conversion of laser light energy to heat was rapid and the laser pulse as much shorter than the tissue thermal- diffusion length, the ultrasonic signal amplitude was proportional to the energy absorbed. Spectra of absorbing compounds were obtained by measuring the variation in the acoustic signal with source wavelength. In contrast with near-IR spectroscopic techniques that measure diffuse light transmission and assume knowledge of the pathlength of light traveling through tissues in order to determine the absorption coefficient, the photoacoustic response is produced directly by light absorption. Light scattering merely modifies the spatial distribution of the absorbed energy. Our studies demonstrate that photoacoustic spectra obtained both in vitro and in vivo allow determination of relative changes in the concentration of oxy- and de- oxyhemoglobin.

Order and low dimensionality in the organic superconductor (BEDT-TTF)2Cu(NCS)2 revealed by STM

Single-crystal samples of [(BEDT-TTF)2]+[Cu(NCS)2]-were synthesized and studied with a scanning tunneling microscope (STM). Real-space images of the anion and cation surfaces with molecular resolution were obtained. The images show no evidence of structural disorder or stacking faults previously suggested. The presence of an additional modulation commensurate with the lattice provides evidence of a lattice distortion. The cause of this modulation is unknown. The presence of a charge density wave in the material would have implications on the dimensionality of the material that may explain the peculiar temperature dependence of the electrical conductivity. This interpretation is consistent with the calculated Fermi surface, which allows nesting of the wave vector.

Scanning tunneling microscopy of quasi‐one‐dimensional organic conductors

We have used a variable temperature ultrahigh vacuum (UHV) scanning tunneling microscope to study the quasi‐one‐dimensional organic conductor, tetrathiafulvalene‐tetracyanoquinodimethane. The experiment has been performed in air and UHV, at temperatures ranging from 10 to 300 K. High resolution images obtained both in air and UHV clearly revealed a one‐dimensional structure. The molecular positions and orientations deduced from the real space images are in good agreement with the lattice parameters obtained from other experimental methods. Below 80 K, a commensurate 2kF charge density wave modulation in real space appeared, and its associated energy gap of about 100 mV was also observed at lower temperatures.

MArs Neutron Energy Spectrometer (MANES): an instrument for the Mars 2003 Lander.

We describe the instrument design and detector development for MANES which has been selected to fly on the Mars 2003 Lander. Section 1 explains the need for the spectrometer in determining the increased risk of carcinogenesis for astronauts. Section 2 presents the instrument design including an outline drawing, a cross-sectional view and a detailed block diagram. Sections 3 and 4 describe the low and high energy detector components of the spectrometer and present responses to monoenergetic neutron beams. Sections 5 and 6 explain the design approaches to charged particle discrimination and instrument transfer function modeling.

Spectral Refractive Index and Extinction Cross-Section of BG Spores

Despite the wide spread need for optical cross-section data on single spore bio-aerosols, available databases are sparse and unreliable. Information reported is based on short path measurements on high concentration media containing particle clusters. This represents an upper bound to the single spore cross-section. Measurements on single spore aerosolized media demand long path lengths and moderate particle concentration. Transmittance measurements need to be in the single scatter limit as well. These requirements are often difficult to meet. We present a procedure that leads to aerosol extinction and backscatter cross-sections in a straightforward manner. Transmittance measurements of thin films of bio-aerosols are used to obtain the bulk refractive index. This result and the measured size distribution can be used in a T-matrix calculation to yield the desired cross-sections. To illustrate this technique, infrared cross-sections are obtained for Bacillus globigii.

Portable real time neutron spectrometry

We describe the early stage of development of an engineering model portable, real-time neutron spectrometer. Several systems of two distinct detector types, a helium 3 gas filled proportional counter and a bulk silicon solid state detector, will be necessary to cover the energy range from thermal to 500 MeV. The advantages and disadvantages of using a moderator were investigated experimentally.

In-situ determination of concentration and degree of oxygenation of hemoglobin in neural tissue by pulsed photoacoustic spectroscopy

Pulsed-photoacoustic spectroscopy (PPAS) is an in-situ technique used for quantitative monitoring of brain-tissue hemoglobin concentration and its oxygenation state. In contrast to most spectroscopic techniques that measure infrared absorption PPAS does not require knowledge of the pathlength of light traveling through tissues in order to determine the absorption coefficient and hence the concentration of absorbing species. The photoacoustic response (PAR) is produced by light absorption. Light scattering modifies the spatial distribution of the absorption. PPAS uses a pulsed, tunable optical source coupled to a 1 mm diameter fiber optic cable to transmit optical energy to the tissue. The fiber can be placed on the exterior surface or inserted into the tissue. An ultrasonic signal is produced by light absorbed in the tissue. Since the rate of conversion of laser light to heat is rapid and the laser pulse much shorter than the tissue thermal-diffusion length, the ultrasonic signal amplitude is proportional to the energy absorbed. Spectra of absorbing compounds can be obtained by measuring the variation in the acoustic signal with source wavelength. Our studies demonstrate that acoustic spectra obtained both in-vitro and in-vivo allows relative changes in the concentration of oxy- and de-oxyhemoglobin to b45e determined.

Scanning tunneling and force microscopies of low-dimensional organic conductors and superconductors

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have been successfully applied to investigate the surface structure and the electron density of states of organic conductors and superconductors. The structural nature of organic conductors and superconductors makes their transport properties susceptible to one-dimensional effects. Low- dimensionality effects in the electrical conductivity of these materials are investigated using scanning tunneling microscopy at room and low temperatures. Effects such as charge density waves and Peierls instabilities are directly observed with the STM. The consequences of low- dimensionality in the electrical conductivity of these materials will be presented.

Scanning Tunneling Microscopy and Spectroscopy of Quasi One-Dimensional Organic Conductors

High resolution images and spectroscopy of different quasi one-dimensional organic conductors and superconductors have been obtained with the scanning tunneling microscope (STM). Single crystals of TTF-TCNQ and related molecular compounds have been studied in air and in ultra high vacuum (UHV) covering a temperature range from 300K to 10K. The images reveal the position and orientation of the molecules that constitute the solid and can be directly related to the structure of the material. The corrugations appearing in the images are in excellent agreement with the crystallographic information. The normalized tunneling conductance of three anion substitutes show similarities in the bands for energies below the Fermi level and differences for energies above the Fermi level. At temperatures below ∼80K images on TTF-TCNQ reveal corrugations with wavelength of double the interchain lattice parameter. This modulation is commensurate with the underlying lattice and can be attributed to a direct observation of the charge density wave (CDW) on this type of material. Low temperature tunneling spectroscopy data show a energy gap between 40–50mV, which confirms the metal-semiconductor transition.