Function Of Penetration Depth Research Articles

Time Resolved Evanescent Wave Induced Fluorescence Measurements of Surface Adsorbed Bovine Serum Albumin

Despite intensive research, there are still many unresolved questions concerning the exact nature of protein binding at interfaces. One technique of growing interest for probing molecular interactions at surfaces is Time Resolved Evanescent Wave Induced Fluorescence Spectroscopy (TREWIFS), which combines the picosecond time resolution of time-correlated single photon counting, with the depth resolution provided by the use of an evanescent wave as excitation source. Using TREWIFS, the adsorption behavior of extrinsically labeled bovine serum albumin has been investigated as a function of penetration depth and relative surface protein concentration. We have observed changes in the emission kinetics of a protein-bound fluorescence probe upon adsorption at a hydrophilic surface, and find that these kinetics are highly dependent upon relative surface concentration of the labeled protein. Dye/protein complexes adsorbed at a hydrophobic surface exhibit a greater degree of fluorescence quenching than those at a hydrophilic one, due either to a higher surface coverage or to a closer-packed protein structure.

Investigation of the local structure around iron dispersed in vinyl chloride–vinylidene chloride (VC–VdC) copolymer coatings on mild steel using glancing-angle X-ray absorption spectroscopy

The chemistry occurring in vinyl chloride–vinylidene chloride polymer coatings on mild steel has been investigated by probing the local environment around Fe ions using glancing-angle X-ray absorption spectroscopy. Measurements made as a function of penetration depth reveal that close to the air interface the Fe species are present as octahedrally co-ordinated FeIII and have a local structure similar to that observed in disordered γ-FeOOH. Although this structure is found to be independent of the pH of the coating formulation, Fe ion transport from the metal substrate is apparently enhanced at acidic pH formulations. Deeper into the coating the Fe has a structure typical of a mixed tetrahedral–octahedral environment such as Fe3O4.

Two-phase flow analysis of self-similar turbulent mixing by Rayleigh–Taylor instability

The evolution of a randomly perturbed interface between unbounded incompressible fluids undergoing Rayleigh–Taylor instability is analyzed numerically and theoretically. Two-dimensional simulation results, obtained with an interface tracking code, are presented and compared with a theoretical model based on Young’s two-phase flow description of the mixing process. The simplifications implied by self-similarity and by high drag enable simple analytic results to be obtained for the profiles of the average volume fractions and velocities of the two materials as a function of penetration depth. Agreement of the analytic results with the simulation data is demonstrated for a wide range of density ratios.

Redistribution of relativistic electron flux in the region where the strong axial channeling instability occurs

AbstractMeasurements are made of nuclear reaction and hard bremsstrahlung yield for 50‐MeV electron motion along the silicon monocrystal axis. With the obtained data one can determine the electron flux redistribution as a function of penetration depth up to 10 μm. The scale and behaviour of this quantity allow to make a conclusion of the strong instability of particle transverse motion.

Channeling of Antiprotons and Electrons

AbstractBased on the diffusion model, the channeling fraction of antiprotons and electrons as a function of penetration depth is studied numerically. According to the calculations, the dechanneling length of antiprotons is of the same order of magnitude as that of electrons. It is found that, though the dechanneling length of antiprotons is much smaller than that of protons, a definite portion (≈ few %) of axially channeled antiprotons has anomalously large dechanneling length.

Effect of secondary zone dimensions on melt fracture manifestations of high density polyethylene

An experimental study was performed on melt fracture phenomena in extrusion of high density polyethylene. The purpose of the work was to study the sensitivity of melt fracture driven roughness to the size of recirculation zones, viz. secondary zones. The experimental apparatus consists of a right angle die and a hypodermic needle used as a capillary. The position of the needle relative to the die was adjusted using a special fixture. The roughness of the extrudate was studied as a function of penetration depth. A developed procedure provides a comparison between profile lengths of extruded strands. The computed mean, median, and mode values for roughness were presented as a function of capillary position. A qualitative analysis was conducted for the force oscillations during extrusion with a separate set of dies, equipped with the fixed capillaries of identical lengths and different depths of penetration. It was observed that the oscillatory pattern is sensitive to the sizes of the secondary zones. This qualitative observation supports the conclusions from the quantitative analysis that the roughness of the extrudate can be controlled through an adjustment of the secondary zone sizes.

Experimental and calculated effectiveness of a radiochromic dye film to stopping 21 MeV 7Li and 64 MeV 16O ions

Relative radiation effectiveness, RE, of 21 MeV 7Li and 64 MeV 16O ions being completely stopped in a tissue equivalent film dose meter has been measured as a function of penetration depth and energy, and the results have been compared with calculations based on a δ-ray theory for heavy charged particles developed by Katz et al. The experiment was designed to test calculations particularly in the Bragg-peak region of the slowing down particles where significant deviation between theory and experiment was found. Fitting of the characteristic D 37 dose and the size of the radiation sensitive element in the detector, which are important parameters in the theoretical model, does not improve the overall correlation between theory and experiment. It is concluded that disagreement between theoretical and experimental RE-values below 1.5 MeV/amu is partly due to lack of equivalence between the δ-ray spectrum and the slowing down spectrum of electrons from low-LET radiation, and partly from approximations in the calculated distribution of energy deposition of the δ-rays.

Investigations of slow exchange processes at metal and oxide surfaces and interfaces using secondary ion mass spectrometry

Because of its high resolution in the penetration depth the method of ion beam sputtering with secondary ion mass spectrometry is very useful in the investigation of slow reactions occurring at surfaces or interfaces. The measurements yield the ion currents from elements of different masses as functions of penetration depth. In special cases these data allow conclusions to be reached about mechanisms and reaction rates. In many cases the concentrations of different elements have to be calculated as a function of the penetration depth in order to describe the kinetics of the reactions. At present such investigations are restricted to isotope exchange at interfaces. Both types of investigation are described in this paper.

Ion bombardment of alkali halides, V: Particle track effects

Abstract Samples of nominally pure single crystal KCI were irradiated by H, H2, He, C and N positive ions in the energy range 0–2 MeV. The growth of F-type centers was recorded as a function of ion fluence. Depth profiles of damage by H and He ions were constructed, and it was found that the damage profile does not follow the stopping power as a function of penetration depth in the target. Determinations of damage track radii, based on the data, were done, and found to be on the order of 10 A. Comparisons of defect production by H2 with H at the same fluences of nuclei and the same energy per mass showed at low energies more defects by H than by H2, the difference attributable to track overlap.

The lateral spread of MeV helium ions in carbon, aluminum, and copper

A new method, which permits measurements of the lateral spread of fast ions in solids, is described in detail. The width of the lateral-spread distributions of MeV helium ions in C, Al, and Cu has been derived from the energy spectra of the emitted particles in glancing-angle Rutherford backscattering and nuclear-reaction experiments. Measurements of lateral-spread widths (fwhm) are presented as a function of penetration depth and ion energy. The results are compared with theoretical predictions, and good agreement is observed.

Computer code for depth distribution of energy deposition by heavy ion bombardment

For bombardment by a heavy-ion beam, we have written a FORTRAN computer code which yields the distribution of energy deposited into elastic atomic collisions as a function of penetration depth. Our aim has been to develop a simple package, inexpensive to run, that could be operated with little or no previous experience. Our calculation is based on an approximation of Kulcinski et al., refined to include the theory of Lindhard et al. which accounts for cascade energy loss to electronic collisions. Range calculation are obtained from the code of Johnson and Gibbons, which our code incorporates. The results of our code are compared with existing calculations of Brice and of Sigmund et al.

Representation of the Cochlea within the Inferior Colliculus of the Cat: Isofrequency Contours

The three-dimensional pattern of representation of the cochlea within the inferior colliculus has been investigated by determining the “best frequency” of 1846 neurons and 546 neuron clusters studied in 111 penetrations in 20 anesthetized cats. All penetrations were histologically reconstructed. These studies have revealed the following: (1) Auditory responses were encountered in the pericentral nucleus, and a crude tonotopic organization could be demonstrated within it. A reversal or discontinuity in the orderly progression of best frequencies was frequently seen across the boundary of the pericentral and central nucleus, with lowest frequencies encountered along their mutual border. (2) The central nucleus is exquisitely tonotopically organized. Functions relating represented cochlear position to penetration depth derived for penetrations all across the central nucleus were parallel. Reconstruction of rows of penetrations allowed for definition of isofrequency contours and reconstruction of cochlear place representation within the three dimensions of the central nucleus. (3) In penetrations perpendicular to defined isofrequency contours, represented cochlear place was seen to be a near-linear function of penetration depth. These experiments provide the framework for investigation of the functional significance of the highly ordered representation of the cochlear across the three dimensions of the central nucleus of the inferior colliculus. [Supported by NIH Grant NS10414-01.]

Calculations on dechanneling of protons in Si and W

Abstract Dechanneling, i.e. transition of particles from the aligned beam to the random beam, is in a faultless crystal mainly caused by two processes, scattering by thermally vibrating nuclei and by electrons. This leads to an increase in the transverse energy of the channeled particle with penetration depth, while the energy loss of the particle implies a small decrease of the transverse energy. Finally, the transverse energy will reach a certain critical value and the particle will be dechanneled. Starting from Lindhard's(1) description of the scattering of channeled particles, we have calculated the decrease of the channeled fraction as a function of penetration depth for protons in Si and W in the case of incidence parallel with a major axis. Two different expressions for the electronic scattering have been tried. Attempts have been made to take into account the effects of beam divergence, scattering in the surface oxide and the energy dependence of the scattering of the particle during penetration. ...

Statistisches modell einer gas-diffusionselektrode

A model of a statistical electrode has been developed and the apparatus has been used to determine the following data: surface magnitude of the menisci as a function of penetration depth and gas pressure; pressure hysteresis; average depth of gas penetration into the electrode; average length of the three phase boundary gas/electrode/electrolyte; pore volume filled with gas; distribution of the current and of the concentration within the electrode; optimal thickness of electrodes. Methods for experimental testing of the electrode model are discussed.