Blob Density Research Articles

Effects of aging on numbers and sizes of neurons in histochemically defined subregions of monkey striate cortex.

In addition to its horizontal layers, primate striate cortex has a vertical modular organization. Among the vertical modules are histochemically defined areas of high and low cytochrome oxidase labeling in the supragranular layers, referred to, respectively, as blobs and interblobs. Cytochrome c oxidase (CO) blobs and interblobs differ in their inputs from the magnocellular and parvocellular visual pathways, their physiological properties, and many aspects of their neurochemistry. The present study investigated whether aging differentially affects neuron numbers or sizes in the supragranular blobs or interblobs. The right hemisphere from three young adult (5.2-12.4 years) and four old (24.0-26.7 years) rhesus monkeys was used. Tangential sections through the central visual-field representation were stained for CO and counterstained with cresyl violet. Montages were constructed through cortical layers 2 and 3, and neuron counts and size measurements were made in blob and interblob regions using stereological procedures that yield unbiased estimates. Blob density also was calculated. CO blob density was 3.76/mm2 in young adults and 3.95/mm2 in old animals, a difference that was not statistically significant. Neuron soma sizes also did not differ significantly between young adult and old animals or between blob and interblob regions. In addition, neuron density was not significantly different between young adult and old animals. However, independent of age, neuron density was significantly higher in the center of interblobs (394,058 cells/mm3) than in the center of blobs (333,638/mm3). Our results and those of previous studies (Vincent et al. 1989. Anat. Rec. 223:329-341; Peters and Sethares. 1993. Anat. Rec. 236:721-729) suggest that aging has little or no effect on the densities or sizes of the different functional or morphological types of neurons that exist in the different cortical layers or in the different vertical modules marked by CO blobs and interblobs. These findings are consistent with the results of our previous anatomical and physiological studies of the rhesus monkey retina and lateral geniculate nucleus. These results suggest that the retinogenic-ulostriate pathways are relatively unaffected by aging in the rhesus monkey.

Wolf-Rayet star variability and wind inhomogeneities

The wind structure diagnostic possibilities offered by combined study of photo-, spectro-, and polari-metric variability are discussed using data from the Montreal group. These demand the presence in the wind of localised density inhomogeneities and in particular of large ‘blobs’ denser than the ‘mean’ wind and put bounds on the size, mass, and density of individual blobs and their distributions, with implications for theories of blob formation. Blobs responsible for polarimetric variability must be present at the stellar surface rather than forming in the wind, and the relation of this to spectrometric indications that blobs are only detectable at several stellar radii is discussed.

Radiative reprocessing by blobs immersed in the X-ray-emitting regions of AGN

A model is presented that assumes the existence of cold matter immersed as blobs within the central X-ray continuum emitting regions of Seyfert galaxies. Monte Carlo simulations are used to calculate the effect of these blobs on the emergent intermediate (1-100 keV) X-ray spectrum. Model spectra are calculated for a range of blob densities from 10 8 to 10 18 cm −1 and for volume filling fractions from 0 to 1. Various features of these spectra are then analysed in detail. In particular, an iron fluorescence line is produced with an equivalent width up to about 400 eV for semi-opaque blobs and up to about 100 eV for fully opaque blobs. Our results also suggest that, for the reprocessing effect of the blobs to alter significantly the primary power-law spectrum, the individual blob size should be smaller than the size of the continuum region by a factor of at least 100

Track characteristics of low pressure spark chambers

Argon-filled spark chambers (gap sizes 1.9 and 9.5 cm) operated under low gas pressures (80–300 torr) and short pulse lengths (30–120 ns) revealed spark tracks with a distinc structure (blobs) property. The blob density is found to be a function of the gas pressure and particle ionization. Results show that this mode of observation may be utilized with advantage particularly in large area cosmic ray experiments for the measurement of particle ionization.

A new approach for the analysis of shower particles produced in high-energy interactions

The proposed method is based essentially on the characteristics of thept/M distribution of shower particles, which shows clearly resolved peaks for the most copiously produced particles—protons and pions. This distribution is obtained (through the relationpt/M=γβ sin θ) by measuring the values of the emission angle θ and estimating γ from a precise measurement of the blob density. Distribution factors, which give the relative number of different types of particles, are computed for each measured shower particle and thus the distributions of various dynamical quantities are obtained. The method has been applied for the analysis of 22.8 GeV/c p-n interactions and the results have been found to be in very good agreement with those obtained by the usual (g*,pβ) method.

Restricted Energy Loss by Extremely Relativistic Particles

The restricted energy loss of electrons, positrons, protons, and pions passing through nuclear emulsions has been measured by observation of the variation in blob and grain density as a function of $\ensuremath{\gamma}=\frac{1}{{(1\ensuremath{-}{\ensuremath{\beta}}^{2})}^{\frac{1}{2}}}$. All measurements were made in small areas (7 ${\mathrm{cm}}^{2}$) of two Ilford $K\ensuremath{-}5$ emulsion pellicles. A careful examination of the variation of blob density with track depth was made in both pellicles. The results of our measurements on the relativistic rise ($5l\ensuremath{\gamma}l36$) as well as on the Fermi plateau ($\ensuremath{\gamma}g100$) are in agreement with the predictions of the Sternheimer formula using a mean ionization potential $I$ of 434 eV and a cutoff energy ${W}_{0}$ of 6-10 keV. An upper limit of 1% is placed on radiative corrections of the type predicted by Tsytovitch. Correction for the finite number of developable grains traversed by the primary produced a best fit with ${W}_{0}=6$ keV, in excellent agreement with the maximum energy of a $\ensuremath{\delta}$ ray that comes to rest within the working volume of blob counting.

Proton-proton collisions at 19.8 GeV/c

Elastic and inelastic 19.8 GeV/c proton-proton collisions in nuclear emulsion are examined using an external proton beam of the CERN Proton Synchrotron. Multiple scattering, blob density, range and angle measurements give the momentum spectra and angular distributions of secondary protons and pions. The partial cross-sections corresponding to inelastic interactions having two, four, six, eight, ten and twelve charged secondaries are found to be, respectively, (16.3±8.4) mb, (11.5 ± 6.0) mb, (4.3 ± 2.5) mb, (1.9 ± 1.3) mb, (0.5 ± 0.5) mb and (0.5±0.5)mb. The elastic cross-section is estimated to be (4.3±2.5) mb. The mean charged meson multiplicity for inelastic events is 3.7±0.5 and the average degree of inelasticity is 0.35±0.09. Strong forward and backward peaking is observed in the center-of-mass system for both secondary charged pions and protons. Distributions of energy, momentum and transverse momentum for identified charged secondaries are presented and compared with the results of work at other energies and with the results of a statistical theory of proton-proton collisions.

Proton-proton collisions at 3.5 GeV

Ilford G-5 emulsions were exposed to an external, 3.5 GeY proton beam of the Berkeley Bevatron. A total of 1200 nuclear interactions of beam protons was located, of which 128 were identified as protonproton collisions. Multiple scattering, blob density, range and angle measurements were employed to determine the cross-sections for elastic and inelastic interactions as well as the identities and center-of-mass system momenta and scattering angles of secondaries from inelastic proton-proton interactions. This analysis indicates a cross-section of (8.0±2.4) mb for elastic events, (24.1±2.9) mb for two-prong inelasitc events, (7.9±1.4)mb for four-prong events and (0.6±0.3) mb for sixprong events. The mean charged pion multiplicity in inelastic interactions is 1.5±0.2 and corresponds to an average degree of inelasticity of 0.45 ±0.06. Center-of-mass system angular distributions of charged secondaries from inelastic events display a peaking for small scattering angles which is most pronounced for protons and pions from events with low secondary multiplicity. Momentum and transverse momentum distributions of secondary protons and pions from inelastic events are presented and compared with the results at other energies. The angular distribution of elastically scattered protons is found to be in fair agreement with that predicted by a uniform optical model of radius 1.25-10-13 cm and opacity 0.66.

Properties of a stack of thick nuclear emulsions processed without glass backing

The routine for the processing of a stack consisting of 117 K-5 pellicles 15 cm×20 cm×1200 μm in size is described in detail. Measurements of the lateral shrinkage of the processed pellicles indicate absence of irregular deformations. A multiple scattering calibration on K− tracks contained in the stack (715 MeV/c momentum) yields, without corrections, an accuratepβ value in excellent agreement with the knownpβ of the beam. Blob countings on beam tracks show a high degree of uniformity of development throughout the entire depth of the pellicles, a high plateau blob density and good discriminating properties of the emulsion. It is concluded that the qualities of free-processed 1200 μm pellicles are, to all effects, equivalent to those of standard glass-backed emulsions. This enables one to take full advantage, otherwise generally precluded, of the use of such thick pellicles.

On the grain density in ilford G-5 emulsion of singly charged relativistic particles

The grain density in nuclear emulsion has been determined as a function of the value of (γ−1) of the particle producing the track. Values of the parameter (γ−1) between 0.8 and 103 were taken into consideration. The nummer of blobs per unit length has been directly determined. Transformation of blob density into grain density has been carried out. Care has been taken to relate all determinations to each other, a constant scale of reference being found in pions of momentum between 5.2 and 5.7 GeV/c. The results are in agreement with the theory given by Sternheimer. The value (501±8) eV was used for the ionization potential of AgBr in the present work. This value was taken fromBarkas. The cut-off energy consequently determined is 100 keV. It is shown that the results are not very sensitive to this last value.

Fading of minimum tracks in Ilford G-5 and K-5 emulsions

The fading of plateau electron tracks in Ilford G-5 and K-5 emulsions, stored after exposure at temperatures of 20°C, − 1 °C, − 18 °C and − 40 °C, has been compared. It has been found that the same initial grain densities are obtained on tracks in both G-5 and K-5 emulsions with identical development one day after the exposure, while the rate of fading is lower in K-5 than G-5 emulsions. The results also show that the rates of fading in both emulsions are much higher at 68 °F than at the lower temperatures. After four weeks at 20 °C there is a marked effect, the reduction in blob densities being 41% in G-5 and 38% in K-5 emulsions. In emulsions tored at 0 °F, on the other hand, even for 2 1/2 months after the exposure, easily recognizable electron tracks have been obtained with blob densities reduced by only 18% and 13.5% respectively. No significant difference between the rates of fading at − 1 °C, − 18 °C and − 40 °C could be detected. It was also found that fading is much more rapid during the first two weeks after the exposure than during a later period.

Identification of fast heavy nuclei of the cosmic radiation using nuclear emulsion techniques

Various workers disagree in their measured charge spectra of the heavy nuclei of the primary cosmic radiation. This disagreement could be due to unreliable charge identification. Since there is inadequate information on comparison of measurement techniques, we have made measurements of six parameters of tracks of nuclei with 4 ⩽Z ⩽ 9 in a stack of G-5 stripped emulsion flown at 41 ‡N geomagnetic latitude. The θ-ray, blob, and isolated-grain densities, the Fowler-Perkins coefficient, integral gap length, and probability of development have been found for each track. Estimates have been made of the effect of various sources of error in these measurements, including a study of the change in each measured parameter with a 20% change in minimum grain density of the emulsion. From the comparison and analysis of these measurements, recommendations are given on the use of the above techniques in the identification of fast heavy nuclei in nuclear emulsion.

A new measurement technique for use in the region of the blob-density maximum in nuclear emulsions

The blob density (Nb) is insensitive to changes in ionization in the region of its maximum value. However the density (Ns of isolated grains, i.e. blobs which are single grains, has been found to be useful in this region, and thus the combined techniques of measuring Nb and Ns provide a simple and rapid method of track measurement over the complete range of ionization. An approximate theoretical expression for the variation of Ns with the probability of development is presented. This expression is tested by measurements on tracks of relativistic cosmic rays over a wide range of charge, and an application of the technique to cosmic-ray studies described. The variation of Ns with the residual range of protons in two emulsions with plateau grain densities of 8 and 20 grains per 100 μm is compared with the corresponding variation of Nb. Possible sources of error in measured values of Ns are found to be similar to those of Nb.

Fluctuations of Track Parameters in Nuclear Emulsions

The fluctuations in nuclear-emulsion track parameters have been studied in a G5 emulsion of low minimum grain density by measurements of the blob density and integral gap length of long tracks of relativistic heavy nuclei. The intrinsic variations arising from the statistical nature of the process of track formation were found to be in good agreement with those predicted by the Blatt fluctuation theory. Subjective, emulsion and other variations were found in some cases to be comparable to the intrinsic variations. A method of estimating these fluctuation effects in any general experimental measurement is given. Nuclear Research Foundation within the University of Sydney.

The time-dependence of the recording properties of G5 nuclear emulsion

The fading of fast proton and μ-meson tracks in G5 nuclear emulsion has been studied as a function of time and conditions of storage. The storage time for a 50% reduction in the blob density of the tracks is estimated to be 1040 ± 200 days for storage at 5° C and 520 ± 50 days at 25° C. No difference in fading has been found between the emulsions stored in air and those stored in commercial argon. The mechanism responsible for the fading appears to be the thermal ejection of electrons from the latent image. The sensitivity of the emulsion after storage has also been studied. A reduction in blob density of the tracks of fast particles of less than 5% after a storage time of 450 days has been found.

The Characteristics of Tracks in Nuclear Research Emulsions

Formulae are derived giving the dependence of the blob, grain, and gap densities, the total gap length, and the mean gap width in the tracks of charged particles as function of the probability of making a silver halide crystal developable. The growth of the grains during the development process is taken into account. The expressions found are suitable for use in discussions of the effects of changes in emulsion properties, and they show clearly the differences between the various methods of determining the rate of energy loss from the track characteristics. There is good agreement with experiment for both G5 and C2 emulsion.