Absence Of Polarization Research Articles

Concentration Polarization in an Ultrafiltering Capillary

Concentration polarization, the accumulation of retained solute next to an ultrafiltering membrane, elevates osmotic pressure above that which would exist in the absence of polarization. For ultrafiltration in a cylindrical tube, use of the radially averaged solute concentration results in an underestimate of osmotic pressure, yielding an effective hydraulic permeability (k) less than the actual membrane hydraulic permeability (k(m)). The extent to which k and k(m) might differ in an ultrafiltering capillary has been examined theoretically by solution of the momentum and species transport equations for idealized capillaries with and without erythrocytes. For diameters, flow velocities, protein concentrations and diffusivities, and ultrafiltration pressures representative of the rat glomerular capillary network, results indicate that the effects of polarization are substantial without erythrocytes (k/k(m) = 0.7) and persist, but to a lesser extent, with erythrocytes (k/k(m) = 0.9), the reduction in polarization in the latter case being due to enhanced plasma mixing. In accord with recent experimental findings in rats, k is found to be relatively insensitive to changes in glomerular plasma flow rate.

The assembly of ribbon-shaped structures in low ionic strength extracts obtained from vertebrate smooth muscle.

In actomyosin extracts from smooth muscle obtained at low ionic strength, an assembly of protein into long ribbon-shaped elements is observed to take place. These ribbons which range up to about 100 nm in width and up to many micrometres in length exhibit a strong repeat period of about 5.6 nm. Optical diffraction analysis shows that they possess a long repeat of 39.1 nm ± 0.4 nm. Tropomyosin purified from vertebrate smooth muscle can be induced to form the same ribbon-shaped elements. On removal of salt from solution the ribbons dissociate into fine filaments of average diameter about 8 nm which show subfilaments of about 2 to 3 nm diameter. In crude preparations the ribbons occur in solution together with myosin. If such preparations are left to stand for several days, ribbons may be found that show a visible 14 nm period which appears to arise from the presence of a regular arrangement of projections. Smooth muscle myosin alone assembles into cylindrical filaments which exhibit a regular arrangement of projections along their entire length, indicating an absence of polarity. These results indicate, as have those recently obtained from section material, that the myosin-containing component of vertebrate smooth muscle contains a protein that forms the core of the filament, which is responsible for its ribbon-like shape and which probably determines the polarity of the attached myosin molecules. It is proposed that this protein is tropomyosin.

On the schlieren texture in nematic and smectic liquid crystals

Observations on schlieren textures of nematic and smectic-C liquid crystals in thin layers are reported. The theory of schlieren textures is discussed and forces between singularities are considered. A singularity can be characterized by a positive or negative number which is proportional to the number of brushes it shows between crossed polarizers. In smectic-C, only singularities with four brushes are observed, nematics may in addition show singularities with two brushes. The latter singularities lead to conclusions on the molecular order and alignment: without the formation of inversion walls they can only occur in the absence of polarity and when the molecules align parallel to the surface. Singularities of opposite sign attract each other, those of equal sign repel each other. The sum of the characteristic numbers of the singularities in an extended layer tends to be zero. Under special assumptions about the elastic constants, it can be shown that the forces between singularities are additive and inversely proportional to the distances and that, for an isolated pair of singularities with the same absolute characteristic number but with opposite sign, the curves of equal molecular alignment are circles through the singularities.

Adsorption and oxidation of formate on palladium in alkaline solution

Anodic and catalytic oxidations of formate ion at an active Pd electrode were studied by the potential-sweep and the galvanostatic methods in connexion with the measurements of the rate of formation of hydrogen on Pd during the catalytic decomposition of formate. A Pd surface oxidized by pre-anodization is reduced with ease by dissolved formate. Formate adsorbed on the cleaned surface decomposes into two fragments such as H ad and CO 2ad − through the reaction HCO 2 − → H ad + CO 2ad −. On standing, CO 2ad − is oxidized further by OH − to CO 3 2− and H ad. In the absence of polarization, the net reaction of the catalytic decomposition is HCO 2 − + OH − → CO 3 2− + 2 H ad. Presence Of H ad on Pd hinders this reaction to some extent, but hydrogen evolution could be observed at high electrolyte concentrations. The net reaction of anodic oxidation of formate is HCO 2 − + 3 OH − → CO 3 2− + 2 H 2O + 2 e, in which reactions such as H ad + OH − → H 2O + e and CO 2ad − + 2 OH − → CO 3 2− + H 2O + e are involved. The nature of the open-circuit voltage in this system is examined by taking these species into consideration.

Radiation-Induced Conductivity in Plastic Films at High Dose Rates

A study has been made of the radiation-induced conductivity (RIC) in poly[ethyleneterephthalate] (Mylar) films, using pulses of electrons of energies up to 30 MeV from a linear accelerator. The absence of polarization indicates that electronic conduction is responsible for the RIC, which has typical values of ∼10−8 Ω−1 cm−1 at 5×109 rad(Mylar)sec−1. The RIC is a bulk effect and shows both a ``prompt'' portion which falls very rapidly at the end of an electron pulse and a ``delayed'' portion which persists for milliseconds. The prompt portion varies as the 0.8 power of the dose rate and is independent of pulse width. The delayed portion varies as a lower power, saturating at dose rates of ∼1010 rad(Mylar)sec−1. The decay of the delayed portion is hyperbolic, and its rate is independent of temperature. The RIC increases monotonically with temperature in the range 100°–300°K. This behavior corresponds to a model in which one sign of carrier is rapidly and permanently trapped, the delayed conductivity being due to the other sign of carrier remaining free until it recombines. The saturation of the delayed conductivity is ascribed to a finite number of such traps.

Non-Coherent Scattering and the Absence of Polarization in Fraunhofer Lines

Non-Coherent Scattering and the Absence of Polarization in Fraunhofer Lines

On the Absence of Polarization in Electron Scattering

In an attempt to explain the discrepancy between Mott's theory and the observational results on the polarization of electrons in the double scattering experiment, we have investigated the depolarizing effect of (1) multiple elastic scattering, (2) inelastic scattering with spin change of the incident electron and (3) exchange scattering in which the exchanged electrons have opposite spins. Although multiple scattering actually takes place in the Au foils used in the experiments, the depolarization caused by such scattering is negligible. For a screened Coulomb field and electrons of 100 kv the depolarization in a 2.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$ cm Au foil is only 2.2 percent whereas a 90-100 percent depolarization is needed to reconcile theory and experiment. The depolarization caused by inelastic scattering is about 100 times smaller than that caused by elastic scattering. The small depolarization in these two cases is due to the fact that while there are many elastic and inelastic collisions, most of these collisions take place with small scattering angle $\ensuremath{\vartheta}$ and for small angles the depolarization per collision is small (of order ${\ensuremath{\vartheta}}^{2}$). The main contribution to the depolarization by inelastic collisions comes then from large scattering angles at which inelastic scattering is relatively infrequent. The exchange scattering contributes practically no depolarization (\ensuremath{\sim}${10}^{\ensuremath{-}12}$). While the depolarization per collision in each exchange process is relatively complete, the number of exchange processes is extremely small due to interference (\ensuremath{\sim}${10}^{\ensuremath{-}14}$ times the number of elastic collisions). Therefore the absence of polarization in electron scattering cannot be explained on the basis of the processes considered here.A discussion of the validity of the first Born approximation is given (Appendix \textsection{}2). It is shown that in the case that the Born expansion parameter $\frac{{e}^{2}Z}{\ensuremath{\hbar}v}$ is of order unity, the first Born approximation gives a result for the scattered intensity which is accurate to within 20 percent or better. The depolarization is given with an accuracy of 18 percent or better.

Absence of polarization in artificial fogs

Absence of polarization in artificial fogs