57 research outputs found
Estimation of the total inelasticity coefficient in interaction of greater than or equal to 20 TeV hadrons with lead
Experimental data on the interaction mean free path of hadrons with energy E 20 TeV in lead obtained with multilayer X-ray emulsion chambers(XEC) are compared with results of simulation of nuclear-electromagnetic cascades in lead chamber. It is shown that, to explain experimental data, the value of the inelasticity coefficients, K .8 should be assumed
Integral functions of electron lateral distribution and their fluctuations in electron-photon cascades
Monte Carlo simulated lateral distribution functions for electrons of EPC developing in lead, at superhigh energies (.1-1 PeV) for depths t or = 60 c.u. delta t=1t. c.u. are presented. The higher moment characteristics, i.e., variation, asymmetry, excess, are presented along with analytical solutions for the same characteristics at fixed observation level calculated to theory approximations A and B by using numerical inversion of the Laplace transformation. The conclusion is made of a complex, usually non-Gaussian shape of the function of the particle number distribution within a circle of given radius at fixed depth
Analytical-numerical methods of calculations of energy and three-dimensional particle distributions in electromagnetic cascades
Analytical and numerical methods of calculation of the energy and three dimensional EPS characteristics are reported. The angular and lateral functions of electrons in EPS have been obtained by the Landau and small angle approximations A and B and compared with earlier data. A numerical method of solution of cascade equations for the EPS distribution function moments has been constructed. Considering the equilibrium rms angle as an example, errors appearing when approximating the elementary process cross sections by their asymptotic expressions are analyzed
Sensitivity of depth of maximum and absorption depth of EAS to hadron production mechanism
Comparison of experimental data on depth of extensive air showers (EAS) development maximum in the atmosphere, T sub M and path of absorption, lambda, in the lower atmosphere of EAS with fixed particle number in the energy region eV with the results of calculation show that these parameters are sensitive mainly to the inelastic interaction cross section and scaling violation in the fragmentation and pionization region. The data are explained in a unified manner within the framework of a model in which scaling is violated slightly in the fragmentation region and strongly in the pionization region at primary cosmic rays composition close to the normal one and a permanent increase of inelastic interaction cross section. It is shown that, while interpreting the experimental data, disregard of two methodical points causes a systematic shift in T sub M: (1) shower selection system; and (2) EAS electron lateral distribution when performing the calculations on basis of which the transfer is made from the Cerenkov pulse FWHM to the depth of shower maximum, T sub M
Electromagnetic showers in a strong magnetic field
We present the results concerning the main shower characteristics in a strong
magnetic field obtained through shower simulation. The processes of magnetic
bremsstrahlung and pair production were taken into account for values of the
parameter . We compare our simulation results with a recently
developed cascade theory in a strong magnetic field.Comment: 11 pages, 9 eps figures, LaTex2e, Iopart.cls, Iopart12.clo,
Iopams.st
Investigating knowledge management factors affecting Chinese ICT firms performance: An integrated KM framework
This is an Author's Accepted Manuscript of an article published in the Journal of Information Systems Management, 28(1), 19 - 29, 2011, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/10580530.2011.536107.This article sets out to investigate the critical factors of Knowledge Management (KM) which are considered to have an impact on the performance of Chinese information and communication technology (ICT) firms. This study confirms that the cultural environment of an enterprise is central to its success in the context of China. It shows that a collaborated, trusted, and learning environment within ICT firms will have a positive impact on their KM performance
Ultra-High Energy Gamma Rays in Geomagnetic Field and Atmosphere
The nature and origin of ultra-high energy (UHE: reffering to > 10^19 eV)
cosmic rays are great mysteries in modern astrophysics. The current theories
for their explanation include the so-called "top-down" decay scenarios whose
main signature is a large ratio of UHE gamma rays to protons. Important step in
determining the primary composition at ultra-high energies is the study of air
shower development. UHE gamma ray induced showers are affected by the
Landau-Pomeranchuk-Migdal (LPM) effect and the geomagnetic cascading process.
In this work extensive simulations have been carried out to study the
characteristics of air showers from UHE gamma rays. At energies above several
times 10^19 eV the shower is affected by geomagnetic cascading rather than by
the LPM effect. The properties of the longitudinal development such as average
depth of the shower maximum or its fluctuations depend strongly on both primary
energy and incident direction. This feature may provide a possible evidence of
the UHE gamma ray presence by fluorescence detectors.Comment: 27 pages, 12 figures, submitted to Phys.Rev.
Anion-Sensitive Regions of L-Type CaV1.2 Calcium Channels Expressed in HEK293 Cells
L-type calcium currents (ICa) are influenced by changes in extracellular chloride, but sites of anion effects have not been identified. Our experiments showed that CaV1.2 currents expressed in HEK293 cells are strongly inhibited by replacing extracellular chloride with gluconate or perchlorate. Variance-mean analysis of ICa and cell-attached patch single channel recordings indicate that gluconate-induced inhibition is due to intracellular anion effects on Ca2+ channel open probability, not conductance. Inhibition of CaV1.2 currents produced by replacing chloride with gluconate was reduced from βΌ75%β80% to βΌ50% by omitting Ξ² subunits but unaffected by omitting Ξ±2Ξ΄ subunits. Similarly, gluconate inhibition was reduced to βΌ50% by deleting an Ξ±1 subunit N-terminal region of 15 residues critical for Ξ² subunit interactions regulating open probability. Omitting Ξ² subunits with this mutant Ξ±1 subunit did not further diminish inhibition. Gluconate inhibition was unchanged with expression of different Ξ² subunits. Truncating the C terminus at AA1665 reduced gluconate inhibition from βΌ75%β80% to βΌ50% whereas truncating it at AA1700 had no effect. Neutralizing arginines at AA1696 and 1697 by replacement with glutamines reduced gluconate inhibition to βΌ60% indicating these residues are particularly important for anion effects. Expressing CaV1.2 channels that lacked both N and C termini reduced gluconate inhibition to βΌ25% consistent with additive interactions between the two tail regions. Our results suggest that modest changes in intracellular anion concentration can produce significant effects on CaV1.2 currents mediated by changes in channel open probability involving Ξ² subunit interactions with the N terminus and a short C terminal region
Effective transvascular delivery of nanoparticles across the blood-brain tumor barrier into malignant glioma cells
<p>Abstract</p> <p>Background</p> <p>Effective transvascular delivery of nanoparticle-based chemotherapeutics across the blood-brain tumor barrier of malignant gliomas remains a challenge. This is due to our limited understanding of nanoparticle properties in relation to the physiologic size of pores within the blood-brain tumor barrier. Polyamidoamine dendrimers are particularly small multigenerational nanoparticles with uniform sizes within each generation. Dendrimer sizes increase by only 1 to 2 nm with each successive generation. Using functionalized polyamidoamine dendrimer generations 1 through 8, we investigated how nanoparticle size influences particle accumulation within malignant glioma cells.</p> <p>Methods</p> <p>Magnetic resonance and fluorescence imaging probes were conjugated to the dendrimer terminal amines. Functionalized dendrimers were administered intravenously to rodents with orthotopically grown malignant gliomas. Transvascular transport and accumulation of the nanoparticles in brain tumor tissue was measured <it>in vivo </it>with dynamic contrast-enhanced magnetic resonance imaging. Localization of the nanoparticles within glioma cells was confirmed <it>ex vivo </it>with fluorescence imaging.</p> <p>Results</p> <p>We found that the intravenously administered functionalized dendrimers less than approximately 11.7 to 11.9 nm in diameter were able to traverse pores of the blood-brain tumor barrier of RG-2 malignant gliomas, while larger ones could not. Of the permeable functionalized dendrimer generations, those that possessed long blood half-lives could accumulate within glioma cells.</p> <p>Conclusion</p> <p>The therapeutically relevant upper limit of blood-brain tumor barrier pore size is approximately 11.7 to 11.9 nm. Therefore, effective transvascular drug delivery into malignant glioma cells can be accomplished by using nanoparticles that are smaller than 11.7 to 11.9 nm in diameter and possess long blood half-lives.</p
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