Variations In Surface Density Research Articles

Preferential diffusion effects on the burning rate of interacting turbulent premixed hydrogen-air flames

The upstream interaction of twin premixed hydrogen-air flames in 2-D turbulence is studied using direct numerical simulations with detailed chemistry. The primary objective is to determine the effect of flame stretch on the overall burning rate during various stages of the interaction. Preferential diffusion effects are accounted for by varying the equivalence ratio from symmetric rich-rich to lean-lean interactions. The results show that the local flame front response to turbulence is consistent with previous understanding of laminar premixed flames, in that rich premixed flames become intensified in regions of negative strain or curvature, while the opposite response is found for lean premixed flames. The overall burning rate history with respect to the surface density variation is found to depend on the mixture condition; the consumption rate enhancement advances (follows) the surface enhancement for the rich-rich (lean-lean) case. For the lean-lean case, a self-turbulization mechanism results in a large positive skewness in the area-weighted mean tangential strain statistics. Because of the statistical dominance of positive stretch on the flame surface, the lean-lean case results in a significantly larger burning enhancement (over a twofold increase) in addition to the surface density production. For the case of rich-rich interaction, the abundance in hydrogen species results in an instantaneous overshoot of the radical pool in the post-flame region, resulting in an additional “burst” in the reactant consumption rate history, suggesting its potential impact on the pollutant formation process.

Microabrasion--a simple method to assess surface degradation of UHMWPE following sterilisation and ageing.

The ageing behaviour of ultra-high molecular weight polyethylene (UHMWPE) has been studied following gamma irradiation (25 or 40 kGy) in air. Accelerated ageing procedures used elevated temperature (70 degrees C) and/or pressurised oxygen (5bar). Shelf-aged UHMWPE was also studied. The variation in surface density and mechanical properties were determined following the various sterilisation and ageing treatments. Microabrasive wear testing was also performed. Wear rates were found to correlate well with stress at break for sterilised and aged UHMWPE but not with elongation to failure. It is proposed that the wear mechanism is fracture dominated and occurs following some disentanglement of the polymer chains. Wear also depends upon embrittlement of the surface layer due to its processing and ageing. Elongation to failure in a tensile test is not a good measure of this embrittlement whereas the microabrasion test provides more surface sensitive information concerning this property.

Nonlinear Propagation of Planet‐generated Tidal Waves

The propagation and evolution of planet-generated density waves in protoplanetary disks is considered. The evolution of waves, leading to shock formation and wake dissipation, is followed in the weakly nonlinear regime. The 2001 local approach of Goodman and Rafikov is extended to include the effects of surface density and temperature variations in the disk as well as the disk cylindrical geometry and nonuniform shear. Wave damping due to shocks is demonstrated to be a nonlocal process spanning a significant fraction of the disk. Torques induced by the planet could be significant drivers of disk evolution on timescales of ~106-107 yr, even in the absence of strong background viscosity. A global prescription for angular momentum deposition is developed that could be incorporated into the study of gap formation in a gaseous disk around the planet.

Novel stationary phase with regulated anion-exchange capacity

A novel stationary phase — phenylaminopropyl (PLA) bonded silica — is proposed for anion-exchange chromatography. Low basicity (p K a about 2.5) attached to silica phenylaminopropyl groups allows a variation of surface density of protonated sites in the pH range from 2 to 5. This enables us to use the same column for the separation of anions having different affinity to anion-exchangers. The effect of mobile phase pH on conditional capacity of PhA-silica was studied. The hypothesis on dependence of ion-exchange selectivity on the column capacity is discussed. Suitability of PhA-silica for ion-chromatographic separation of organic and inorganic anions at different pH values of eluent was demonstrated.

Polar Surface Interactions Vs. Long Range Interactions in the Problem of Nematic Anchoring

A complete theory of surface nematic anchoring was developed earlier, including steric, dielectric, flexoelectric, and notably, surface polarization coupling mechanisms. In the last three cases surface electric field due to the adsorption of surface charges on the substrates is of ultimate importance. The extent of penetration of surface electric field inside a nematic is shorter than believed, due to the important surface screening. This leads to a substantial dehancement of dielectric coupling. Surface polarization, due to the biphilic character of the short-range interaction of asymmetric nematic mesogens with the substrates, can be parallel or antiparallel to the surface electric field. This amounts to a stabilization or a destabilization of the anchoring. Based on the general theory the nonmonotonic behavior of anchoring energy of 5CB on LB films of DPPC with variable surface density is rationalized.

Efficient discrimination between different densities of target antigen by tetracycline-regulatable T bodies.

Engineered T cells expressing chimeric T cell receptors (chTCRs) are of interest for cancer gene therapy but many "cancer antigens" are thought to be unsuitable targets because they are expressed at low levels on normal tissues. We therefore sought to determine whether engineered T cells expressing variable surface densities of a high-affinity chTCR could discriminate different concentrations of the targeted antigen. We plotted the relationship between chTCR density and the concentration of target antigen using Jurkat T cells expressing a hapten-binding chTCR whose expression could be modulated by tetracycline. Our analysis reveals that there is a dynamic equilibrium between cell surface density of the chTCR and the antigen density that optimally triggers T cell activation. At a fixed density of target antigen, optimal T cell activation can be achieved only within a certain range of chTCR densities, while excessive TCR signaling triggers apoptosis of the engineered T cells. Our results show that T cells can be engineered to discriminate different antigen densities and that the T cell response to a fixed concentration of antigen can be optimized by tuning the cell surface density of TCRs.

The two domains in envelope spectrum of ocean ambient noise

Analyzing level fluctuations of the natural ambient underwater noise shows that the spectrum of the envelope usually consists of two frequency domains of different physical nature. The low-frequency domain is governed by variations in wind speed, that is, variations in surface density of the source power. The high-frequency domain is related to rough-surface sound scattering. The boundary between the domains correspond to frequencies of 0.05–0.1 Hz. Experiments have shown that both cross-frequency noise correlation and correlation between the noise and wind speed fluctuations are high if only frequencies lower than 0.1 Hz are retained in the spectrum, these correlations being low for unfiltered noise. Thus, if there is no ship-traffic noise, the frequency correlation coefficient remains to be 0.6–0.8 within 0.1–10 kHz if the high-frequency domain is cut off and it is close to zero in disjoint filtering bands for unfiltered noise. The experimental data are discussed and interpreted with the use of the noise model allowing for space–time parameters of the wind speed.

Measurements of anchoring energy of a nematic liquid crystal, 4-cyano-4′−n-pentylbiphenyl, on Langmuir-Blodgett films of dipalmitoyl phosphatidylcholine

The Langmuir-Blodgett technique was used for deposition of monolayer lipid films of dipalmitoyl phosphatidylcholine (DPPC) on glass with a variable surface density of lipid molecules. In a certain range of surface density these surfaces oriented homeotropically the highly polar nematic liquid crystal of 4-cyano-${4}^{\ensuremath{'}}$-$n$-pentylbiphenyl (5CB). Optical transmission curves of liquid crystal layers sandwiched between orienting lipid monolayers were recorded versus magnetic field with high accuracy. They were further converted into optical retardation and fitted by a complete theory of the transition containing anchoring strength as a parameter. Independent measurements of refractive indices of 5CB were also performed by the prism method. Anchoring energies thus obtained showed a nonmonotonic behavior with increasing packing density of DPPC monolayers and a pronounced minimum around $0.82 {\mathrm{nm}}^{2}$ per molecule. This is explained by a complete theory of surface anchoring including steric, electric, flexoelectric, and notably surface polarization coupling mechanisms. The last one stands for surface polarized layers at the liquid-crystal interfaces interacting with surface electric field due to lipid molecules. The competition of these mechanisms leads to an initial dehancement followed by an enhancement of the anchoring strength at monotonically increasing DPPC packing density. Surface polarization evaluated from the experimental data is in good correspondence with molecular parameters.

A VLA Survey of Rich Clusters of Galaxies

We present a detailed analysis of the results of a two-frequency VLA survey with scaled arrays of 60 flelds near 58 Abell clusters. The sample of sources is complete to a ∞ux density of 2¢ 0 mJy at 1¢ 5 GHz, from which we chose two sub-samples of radio galaxies from clusters that had been surveyed completely out to 0¢ 24, and 0¢ 51 times the Abell radius RA respectively. The following conclusions are drawn from these samples: (i) The sources are strongly concentrated towards their cluster centres, showing a power-law variation of surface density with radius, with an exponent of »i1¢ 6. Each cluster contains an average of two radio galaxies. (ii) The ratios of ∞ux density and surface brightness in the lobes of cluster and background doubles are very similar, as are their spectral indices; the ratios of component area are signiflcantly difierent. (iii) The lobes of cluster doubles have spectra that steepen with radio power, but a less signiflcant relationship is found between spectral index and surface brightness. (iv) Relationships are found between source area and radio power, optical luminosity and r/RA, spectral index and r/RA, and between radio power and optical luminosity. (v) We deflne three polarisation classes on the basis of the presence or absence of observable polarisation at 4¢ 9 and 1¢ 5 GHz; the physical parameters vary systematically across the classes. (vi) Depolarisation in sources that are partially polarised at both frequencies (Class I) is predominantly caused by tangled flelds; sources that are polarised at only the higher frequency (Class II) or at neither frequency (Class III) are depolarised by a combination of tangled flelds and difierential Faraday rotation. The rms dispersion in the scale size of the tangled flelds within the radio plasma is»5 kpc. (vii) Difierential Faraday depolarisation in Classes I and II suggests that thermal electrons are entrained in the radio plasma with densities in the range 1¢ 1{2¢ 3£10 i4 cm i3 . (viii) The magnetic flelds in Class I doubles (with minimum Faraday rotation) favour directions predominantly parallel to the major axis of the double. (ix) The univariate fractional luminosity function suggests that an early-type cluster galaxy with M R•i21¢ 0 has a probability of »0¢ 02 of creating a radio source with P 1¢ 5• 10 24¢ 9 WH z i 1 . (x) The integrated bivariate fractional luminosity function shows that higher luminosity cluster galaxies are more likely to form radio sources, although in each bin of absolute magnitude the fraction of radio sources decreases with increasing radio power. (xi) The average lifetime of a cluster source of »2£10 6 yr is consistent with the travel-time of the plasma at»3000 km s i1 from a once-only acceleration site near the centre of the host galaxy. (xii) The conflnement of the radio lobes can be easily accomplished by the static pressure of the hot intra-cluster gas and/or ram pressure generated by the passage of the galaxy through the gas. (xiii) Radio powers of cluster sources and optical luminosities of their hosts are both independently correlated with cluster X-ray luminosity. This suggests that radio power is maintained by the conflning pressure of the hot gas, but the cause of the ⁄ Paper I, Aust. J. Phys., 1989, 42, 633; Paper II, Aust. J. Phys., 1994, 47, 145; Paper III, Aust. J. Phys., 1996, 49, 977.

Quantitative density measurements from X-ray radiometry

Abstract Qualitative linear X-ray scanning has an established role in the non-destructive imaging of both slabbed and whole core and has been routinely used in visual assessment and quality control of material being subjected to other physical measurements. Since core may be observed in real time, whole core can be oriented to maximum dip prior to slabbing, especially useful where core has been resin-stabilized within an outer liner. Linear scanning is also useful in the observation of heterogeneous lithologies; the features observed are distinguished by their penetrabilities to X-rays. As a result, the linear scanner produces an image which reflects the density variation in the section analysed. A joint project carried out by Robertson Research International Limited and Amerada Hess Limited on 108ft of heterogeneous sediments has shown that the digital X-ray penetrability values (‘luminance’) can be extracted in order to produce a surface density variation log. X-ray luminance values show a linear relationship with the downhole Formation Density Log and may, therefore, provide an accurate tool for the correlation of core density with log density.

Silica-suported polyvinylpyrrolidone filtration membranes

A hybrid ceramic-polymeric membrane was developed by the growth of covalently-bonded polyvinylpyrrolidone (PVP) chains from the surface of a porous silica support membrane via a graft polymerization process. These ceramic-supported polymeric (CSP) membranes can be produced with variable surface density and length of the terminally anchored polymer chains. Hydraulic permeability measurements demonstrated the effect of the grafted chain density and length on the water permeability of the CSP membranes. The potential application of these CSP membranes for the treatment of oil-in-water emulsions, was evaluated in cross-flow filtration experiments. This preliminary evaluation indicated improved performance of a CSP membrane, relative to an unmodified support, since the CSP membrane produced a lower permeate concentration at an equivalent permeability. The improved selectivity and reduced fouling tendency is attributed to the increased hydrophilicity of the membrane surface provided by the grafted PVP chains.

Abnormal signal transduction through CD4 leads to altered tyrosine phosphorylation in T cells derived from MRL-lpr/lpr mice.

CD4+ T cells play a crucial role in the development of lupus in MRL-lpr/lpr mice: incomplete deletion/silencing of self-reactive CD4+ T cells leads to T cell activation, which causes both polyclonal B cell activation and T cell infiltration of multiple organs. Furthermore, anti-CD4 antibody therapy ameliorates disease and prolongs survival. Because CD4 is normally involved in both tolerance induction and T cell activation, we questioned whether signaling through CD4 was normal among T cells in this strain. For this purpose, signal transduction in CD4+ T cells derived from MRL-lpr/lpr and normal mice were compared, using an autoreactive CD4+ T cell clone and freshly isolated CD4+ T cells derived from mice of varying ages. Tyrosine phosphorylation was similar among MRL and normal CD4+ T cells after cross-linking with either anti-TCR antibody or anti-CD3 antibody, and following co-culture with Con A. In constrast, cross-linking of surface CD4 resulted in deficient tyrosine phosphorylation of cellular proteins in MRL T cells. By comparison, lck protein expression in MRL CD4+ T cells was found to be lower than normal. However, following stimulation with Con A, lck enzyme activity, as detected by autophosphorylation of lck, was comparable in MRL and normal T cells. The observed differences were present in the autoreactive T cell clone as well as in T cells isolated from both pre-diseased and diseased mice, and they could not be explained by variation in surface density of CD4. These results raise the possibility that abnormal signaling through CD4 may contribute to impaired tolerance and expansion of autoreactive T cells exhibited in MRL-lpr/lpr mice.

Variation of Mat Surface Density and Its Effect on Permeability Evaluation for RTM Modelling

Continuous fiber strands mats are often used in Resin Transfer Molding (RTM). This paper presents the results of an extensive experimental study where the varia tion of mat surface density was investigated on five commercially available mats. The in- plane permeability for all these mats was also measured and compared with models found in literature. Since none of these models gave a satisfactory prediction for all the mats, a new empirical model is proposed. This model, with a set of specific parameters for each mat, can easily be stored in the data bank of any RTM flow simulation software.

Quantitative analysis of regional variability in the distribution of transverse tubules in rabbit myocardium

The goal of the present investigation was to compare quantitatively the distribution of T-tubules between regions of the myocardium. The volume fraction and surface density of T-tubules in rabbit right atrial free wall, left atrial free wall, right ventricular free wall, left ventricular free wall, right ventricular papillary muscle, and left ventricular papillary muscle were measured using established, electron-microscopic, morphometric techniques. T-tubules were delineated using wheat-germ agglutinin conjugated to horseradish peroxidase as a tracer. No significant differences were found in the morphometric parameters between any two ventricular samples or between atrial samples. Furthermore, little difference between T-tubule volume fraction or surface density was found between individual animals for any given site. Both volume fraction and surface density of ventricular T-tubules were more than ten-times their values in atrial tissue (volume fraction: 3.43% +/- 0.35 vs. 0.20 +/- 0.09; surface density: 2.46 microns 2/microns 3 +/- 0.11 vs 0.10 +/- 0.04). Measurements show that there is greater variation of T-tubule volume fraction and surface density within atrial samples than within ventricular samples. This suggests greater inhomogeneity in T-tubule distribution in atrial myocardium than in ventricular myocardium. Morphometric data also indicate that the mean diameter of atrial T-tubules is greater than that of ventricular T-tubules while qualitative observations show that atrial T-tubules are distributed less regularly and have a larger longitudinal component to their organization than those in the ventricular myocardium.

Bending waves and the structure of Saturn's rings

The surface mass density profiles at four locations within Saturn's rings are calculated using Voyager spacecraft images of spiral bending waves. Bending waves are vertical corrugations in Saturn's rings which are excited at vertical resonances of a moon, e.g., Mimas, whose orbit is inclined with respect to the mean plane of the rings. Bending waves propagate toward Saturn by virtue of the rings' self-gravity; their wavelength depends on the local surface mass density of the rings. Observations of bending waves can thus be used to determine the surface density in regions of Saturn's rings near vertical resonances. The average surface density of the outer B ring near Mimas' 4:2 inner vertical resonance is 54 ± 10 g cm −2. Surface density in this region probably varies by ∼ 30% over radial length scales of tens of kilometers; and irregular radial structure is present on similar length scales in this region. Surface densities ranging from 24 g cm −2 to 45 g cm −2 are found in the A ring. Small scale variations in surface density are not seen in the A ring, consistent with its more uniform optical appearance.

Lipid-protein interaction at solid-water interface. Adsorption of human apo-high density lipoprotein to amphiphilic interfaces.

Hydrophobic glass beads with well characterized physical properties were used as a model system to study at the amphiphilic interface the properties of apolipoproteins A-I and A-II from human serum high density lipoproteins. In this study, spherical glass beads with known diameter were coated covalently with a film of silicone to varying surface density. The decrease in surface tension induced by coating was directly related to the increase in silicone film density and likely to the hydrophobicity of the glass surface. The adsorption of apo-A-I and apo-A-II to the hydrophobic glass bead surface was determined by following the decrease of 1) the radioactivity of preparations of 125I-iodinated proteins from the solution, 2) the UV absorbance of the solution at 206 nm, and 3) the fluorescence emitted by the complex formed between free protein and Fluram II in solution. All of the three measurements gave identical results. Both proteins adsorbed rapidly and reversibly to the hydrophobic glass surface. The adsorption isotherms followed the Langmuir equation with apo-A-II showing a higher surface affinity; delta Gaff = RT ln Kd has a value of -9.1 kcal/mol and -10.5 kcal/mol for apo A-I and apo A-II, respectively. The addition of canine serum high density lipoprotein (HDL) to the above system caused a rapid desorption of apolipoproteins from the beads into the aqueous phase and adsorption onto the HDL surface with no detectable structural changes of this lipoprotein. The results indicate that apo-A-I and apo-A-II can reversibly be adsorbed at a solid hydrophobic surface and that these apoproteins are capable of moving into a HDL particle if added to the system via a solution phase. The data suggest that the rate limiting aspect of the desorption-adsorption processes is the concentration of the apoproteins in solution.

Lipid Bilayers in the “Fluid State: Computer Simulation and Comparison with Model Compounds

Abstract Monte Carlo simulations of mono- and bilayers of alkyl chains at variable surface density have been carried out, whose results are in good agreement with experimental data on model compounds. In particular, the perturbation to the conformation of the alkyl chains in the liquid crystalline environment derived from excluded volume effects is described in detail.

Positron annihilation studies of supercooled liquids. ortho-terphenyl

Positron annihilation measurements are reported on ortho-terphenyl (o-TP) covering the temperature range 230–365 K. The lifetime data were analysed in terms of a three component fit; the two shortest lifetime components correspond to the decay of the free positron and the para-positronium (p-Ps) and the longest lifetime component corresponds to the annihilation of the ortho-positronium (o-Ps). The lifetime plot of the o-Ps against temperature exhibits two changes in slope, the first transition occurring at 240 K and the second at 304 K. The lower temperature is associated with the onset of motion in the glassy phase; the higher temperature is more obscure, but appears to correlate well with the onset of instability as predicted by a weak coupling mean-field treatment of the liquid state. Attempts to correlate the temperature variation of the o-Ps lifetime with the variation of surface tension, density and free-volume indicated that there is no simple explanation for the higher temperature transition feature. Calculations based on the “bubble” model and pick-off rate theory indicate that in the liquid phase and above the higher temperature transition the lifetime and intensity of annihilation of o-Ps correspond closely to those predicted for a simple liquid. In between the two transition temperatures, the variation is inexplicable in terms of a simple “bubble” model and leads to the conclusion that the void size distribution being sampled by the o-Ps is itself a function of the total free-volume available at the temperature of measurement. Comparison of the temperature variation of the self-diffusion coefficient and the o-Ps lifetime data indicate that both properties do not exhibit a simple linear variation with dependence on the free-volume in the supercooled liquid state. However, normalisation of the o-Ps data by the effective free-volume radius leads to an approximately linear correlation between these properties indicating a common basis to the molecular motion being sensed.

Analytic study of azimuthal asymmetries in relativistic hollow e-beams

A study is made of zero-thickness relativistic hollow electron beams propagating in a vacuum guide field. The azimuthal variation in surface density for a beam emitted from an off-centered circular cathode is calculated exactly by solving Laplace’s equation in a region between two eccentric conductors. The cathode problem is used as an initial state for solving the off-centered beam propagation problem in the drift region. The ϑ-bunching effect of the azimuthal asymmetries is estimated and related to specific experiments.

Computation of Eddy Currents on a Surface in $R^3$ by Finite Element Methods

In this paper, we study eddy currents on a thin conductor surface $\Gamma $ in $R^3$. We suppose that these currents result from a periodic alternative time-varying excitation (such as a difference of potential or imposed currents). We shall write the current equations by using the variable surface density of the current which is a tangential complex vector to $\Gamma $. First, we prove that these integro-differential equations admit a unique solution. Then, we introduce an approximate problem on an approximate surface, built by finite elements. We study the error of approximation of this method. Some numerical results have been performed and compared with measure results. (See Nedelec-Verite [to appear].)