Mass Density Values Research Articles

Mass density determination of thin organosilicon films by X-ray reflectometry

The mass density of thin organosilicon films deposited by chemical vapour deposition on silicon (0 0 1) surfaces has been determined by X-ray reflectometry. This method does not give a unique mass density value, but instead a bandwidth of possible values and compositions that are compatible with the experimental data if the layer thickness is not larger than about 350 nm. For thicker films thickness values obtained from ellipsometry data are used. The possible composition ranges are compared with data obtained by X-ray photo electron spectroscopy.

Study of the mechanical properties of tetrahedral amorphous carbon films by nanoindentation and nanowear measurements

Abstract Nanoindentation and nanowear measurements, along with the associated analysis suitable for the mechanical characterization of tetrahedral amorphous carbon (ta-C) films are discussed in this paper. Films of approximately 100-nm thick were deposited on silicon substrates at room temperature in a filtered cathodic vacuum arc evaporation system with an improved S-bend filter that yields films with high values of mass density (3.2 g/cm3) and sp3 content (84–88%) when operating in a broad bias voltage range (−20 V to −350 V). Nanoindentation measurements were carried out on the films with a Berkovich diamond indenter applying loads in the 100 μN–2 mN range, leading to maximum penetration depths between 10 and 60 nm. In this measurement range, the ta-C thin-films present a basically elastic behavior with high hardness (45 GPa) and high Young's modulus (340 GPa) values. Due to the low thickness of the films and the shallow penetration depths involved in the measurement, the substrate influence must be taken into account and the area function of the indenter should be accurately calibrated for determination of both hardness and Young's modulus. Moreover, nanowear measurements were performed on the films with a sharp diamond tip using multiple scans over an area of 3 μm2, producing a progressive wear crater with well-defined depth which shows an increasing linear dependence with the number of scans. The wear resistance at nanometric scale is found to be a function of the film hardness.

CT Densitometry of Lung Mass: The Effect of Reconstruction Algorithm

Purpose: To evaluate the effect of reconstruction algorithms on the CT measurement of mean lung mass density and normal thoracic structures. Materials and Methods: Forty-six patients with a 2 -9 cm-sized lung mass underwent thoracic CT examinations with intravenous contrast enhancement and using a CT HiSpeed Advantage scanner (GE Medical Systems). In each examination, the axial image of the lung mass was reconstructed using soft, standard, detail, and bone algorithms. The mean value and standard deviation of mass density in Hounsfield Units (HU) were measured using ROIs of three different sizes (50 mm2, 200 mm2, and 350 mm2or more), and the same method was used to measure the density of normal lung, muscle, bone, and vessels. In 21 patients, mass density was also measured on unenhanced and delayed enhanced images and the degree of enhancement was calculated. Results: The average maximum difference in mean mass density in the images of the four different algorithms was less than 1 (range, 0.1 -1.9) HU (ROI size, 350 mm 2 or more), 0 -4.2 HU (200 mm 2), and 0.1 -3.6 HU (50mm2). The average maximum difference in the degree of lung mass enhancement was 0.5 -1.2 (range, 0 -1.6 )HU (ROI size, 350 mm2or more). The mean density of the four normal thoracic structures was highest in images reconstructed with the bone algorithm, though there was no significant difference between the four different algorithms (p = 1.000). Conclusion: The measured mean CT density of a lung mass larger than 2 cm does not significantly change ac-cording to the reconstruction algorithm used. When using a small ROI, however, the density difference may increase.

Carbonaceous aerosol (soot) measured in the lower stratosphere during POLARIS and its role in stratospheric photochemistry

This paper describes recent measurements of carbonaceous aerosol made by wire impactors during the Photochemistry Ozone Loss in the Arctic Region in Summer (POLARIS) campaign and assesses their role in stratospheric photochemistry. Ninety‐five percent of the carbonaceous aerosol collected during this campaign was in the form of black carbon aerosol (BCA), or soot. A new method of analyzing impactor samples is described that accounts for particle bounce and models the BCA as fractal aggregates to modify the aerodynamic collection efficiency and determine particle surface area. Results are compared to previously used methods. The new method results in an increase in the measured BCA number density of 4 times, surface area density of ∼15 times, and an increase in mass loading of 6.15 times over one previously used approach. Average values of number, surface area, and mass densities are 0.06 no./cm3,0.03 μm2/ cm3, and 0.64 ng/m3, respectively. BCA number densities are ∼1% of total aerosol number density, and BCA surface area density is ∼10% of the measured sulfuric acid aerosol surface area. Including heterogeneous reactions on BCA in a photochemical model can affect photochemistry leading to renoxification and increased ozone depletion. However, these predicted effects are not supported by the POLARIS observations, in particular, the NOx/NOy ratios. The laboratory data is not conclusive enough to determine to what extent the heterogeneous reaction is catalytic or carbon consuming. Including catalytic reactions on BCA does not statistically improve the agreement between model and measurement in any of the several scenarios considered. Furthermore, if the reactions cause even partial carbon oxidation, the BCA would be consumed at a rate inconsistent with POLARIS observations. These inconsistencies lead us to conclude that the presence of BCA in the stratosphere did not affect stratospheric photochemistry during POLARIS.

Ultrasonics in an aluminum foam

Abstract Open celled foamed aluminum typically consists of an irregular frame of solid struts with typical lengths of the order of millimeters and thicknesses of a fraction of a millimeter. Total aluminum volume fractions are of the order of 10%. Quoted values of static modulus and mass density allow one to infer long wavelength (much greater than strut length) ultrasonic wave speeds. These predictions are compared with the velocities observed in 100 kHz transient signals. At higher frequencies, where wavelengths are comparable with strut lengths, ultrasound can be transported only diffusively. Wave speeds are unmeasurable and of little meaning anyway. We therefore also report on ultrasonic measurements appropriate for the high-frequency regime. These include diffusivity, absorption and modal density. Recent literature has reported measurements of diffusivities and absorption in other materials, particularly in metallic polycrystals. Measurements of modal densities are new.

Experiences with a detailed estimation of the mass density contrasts and of the regional gravity field using geometrical information from seismograms

In this paper a new method of geological stripping (Strykowski, 1997) is illustrated on real data. Complex information about the subsurface (seismograms, borehole data, surface gravity signal) is used. The setup includes many geological layers with varying mass density contrasts in different depths. The mathematical formulation of the problem makes use of all available information in a hierarchic way. The method is based on general considerations about the nature of ambiguity of the solution to the inverse gravimetric problem. The main idea is to avoid that the obtained model of the subsurface reflects implicitly mathematical assumptions. Such assumptions can ensure a unique model, but not necessarily a good approximation to the true physical conditions in the subsurface. Instead, the ambiguity of the modelling problem is exposed in the mathematical formulation. In order to obtain a particular earth's model, the interpreter has to make a conscious choice of how to weight different types of available information relative to each other. The test area is Jutland peninsula (Denmark). The size of the area is 256 km × 206 km. The geology of the area is known to a depth of 10000 m. The model of the subsurface has a horizontal resolution of 2 km × 2 km and a vertical resolution of 500 m. A linear system of equations is set up. The geometrical information about depths to various interfaces in the subsurface (interpolated from seismograms and boreholes) has been transformed to the equivalent surface gravity functions. The unknowns are the absolute mass density values associated with different geological layers in different depths and parameters describing the surface gravity signal generated from large depths (the regional gravity field).

A light-weight CCD camera technique for estimating three-dimensional distribution of foliage density in tree crowns

:A method was developed for non-destructively estimating spatial density of foliage mass and area in crowns of small individual trees. A light-weight CCD camera with a capability for wireless image transmission is mounted on top of a telescoping height measuring pole so that it views the zenith. A daisy flap, a thin 10-cm diameter plastic plate with 12 equally-spaced incisions along its radii, is placed horizontally 20 cm above the camera. Then, images are recorded while the CCD camera is lowered at 10-cm increments from the top of the crown. The number of contacts between the daisy flap and the foliated portions of shoot segments are counted while the CCD camera goes through each 10-cm segment. The number is evaluated (i) by simply counting the contacts regardless of the size of touching shoot or proportion of the daisy flap that makes a contact (referred to as simple CCD method), and (ii) by counting the number of flaplets (12 parts of the daisy flap that are separated by radial incisions) that touch the foliated shoots (weighted CCD method). The methods are repeated five times for the same column of 20 cm × 20 cm base area. Then the foliage density was calculated for each 20-cm cube from regression equations relating the mean contact number among the ten 10-cm segments searched within a 20-cm cube and the foliage density in dry mass or area. The foliage mass estimated by the weighted CCD method was comparable to direct measurement by harvesting, when the method was applied to estimation of total leaf mass of a tree. The calculated value of foliage mass density was also comparable to that estimated by the direct harvesting method of Sainome cutting when 40-cm or larger cubes are used as the unit volume. Advantages and disadvantages of the CCD camera technique are discussed in comparison to other methods available for estimation of foliage distribution in tree crowns and forest canopies.

Can the definition of mechanical stress tensor be applied to a dielectric fluid in an electrostatic or magnetostatic field?

It is proved that, for an uncharged and linear dielectric fluid at rest and in local equilibrium in an electrostatic or magnetostatic field, the definition of stress tensor employed in continuum mechanics is inconsistent with the assumption that the stress tensor depends only on the local values of mass density, temperature, electric- or magnetic-field components and the derivatives of these quantities with respect to space and time.

The position of the fundamental absorption edge and activation energies for thermally activated electrical conductivity in amorphous carbon layers

Amorphous carbon layers (a-C, a-C:H) with a hydrogen content between 3 at.% and 25 at.% were deposited by plasma decomposition processes, sputtering and evaporation. Their mass density values were obtained from a flotation method. The refractive index and absorption coefficient were calculated from spectrophotometric data. Special attention was paid to the Urbach tail and Tauc's plot absorption regions. The electrical conductivity was investigated in the temperature range T = 80–350 K. The conductivity values of all types of layers are discussed in terms of thermally activated conduction processes. In this sense all layers behave like semiconductors. For interpreting the conductivity values of the high gap layers, a Davis-Mott model with broad band tails was applied. However, this model was insufficient for fitting the conductivity data of samples with vanishing gaps. Reproduction of the conductivity values of these layers was possible in terms of a band model considering a structureless band at a position of 10–50 meV above the Fermi level. The conductivity of low gap samples (optical gaps around 0.3 eV) could only be fitted by a superposition of the conductivity laws following from both models. Fortuitously, the superposition of these functions yields a temperature dependence very similar to Mott's T − 1 4 law between 50 K and 300 K, which may be an explanation of this widely observed behaviour.

Biphasic blood volume changes with lower body suction in humans

We recorded blood and plasma mass density and hematocrit of antecubital venous blood in 12 subjects in the supine position before, during, and after 20-40 min of lower body subatmospheric pressure (LBNP) of -35 mmHg. Mass density values decreased during the first minutes of LBNP, indicating a transient 2.8% blood volume gain before they rose as expected. After LBNP, a pronounced further density increase, indicating a further 1.5% hemoconcentration, preceded the return toward control. This pattern suggests reflex-driven transient filtration effects. Computed mass density of fluid exchanged between blood and extravascular space was 1,007.2 +/- 4.4 milligrams (37.0 degrees C); mass density of erythrocytes remained unaltered. We conclude that sudden unloading of central pressure receptors with LBNP causes microvascular fluid gain preceding fluid loss (hemoconcentration) during LBNP, and receptor loading after LBNP additionally causes fluid loss preceding inward filtration (hemodilution) during recovery. These effects can be quantified with high-precision blood and plasma mass densitometry performed by the mechanical oscillator technique.

Stability of self-gravitating systems of fermions

We discuss static equilibrium and infinitesimal radial motion of self-gravitating systems consisting of two kinds of fermions with different masses. Calculations shows that static equilibrium configurations occur in a wide domain of values of central mass density. The domains, in which all equilibrium configurations are stable against radial perturbations, are obtained.

The immunogenicity of soluble haptenated polymers is determined by molecular mass and hapten valence.

T cell-independent Ag are believed to stimulate antibody formation in the relative absence of Ag processing and T cell help. Previous studies on the type 2 T cell independent (TI-2) Ag DNP-polyacrylamide, have shown that when one systematically varies the molecular mass and hapten valence, the immunogenic potential of this type of molecule depends on definable molecular characteristics. It was found that to be immunogenic, these molecules had to exceed a threshold molecular mass of 100,000 Da and a threshold hapten valence of 20. The present study was undertaken to determine whether such findings could be generalized to other molecules belonging to the TI-2 class of Ag. The molecular characteristics of five chemically different fluoresceinated (FL)-polymers were systematically varied, and their ability to stimulate an IgM antihapten immune response was measured. The polymers used as carriers were carefully size-fractionated and consisted of one natural polymer (dextran), one modified natural polymer (carboxymethyl cellulose), and three synthetic polymers (Ficoll, polyvinyl alcohol, and polyacrylamide). The carriers varied in physical structure from the highly cross-linked Ficoll, to the somewhat branched dextran, to the linear polyacrylamide, carboxymethyl cellulose, and polyvinyl alcohol. Polymers were haptenated with FL and size-fractionated so as to yield a panel of molecules with varying molecular mass, hapten valence, and hapten density. Anti-FL IgM response to these haptenated polymers was measured in vivo after i.p. injection of the FL-polymer in saline, and measured in vitro after culture with unfractionated spleen cells from naive mice. In agreement with the previous studies on DNP-polyacrylamide, it was found that to be immunogenic, each of the FL-polymers had to exceed a comparable threshold value of molecular mass and of hapten valence. Optimal immunogenicity occurred when the FL-polymers had values of mass and hapten density lying within a predictable range. Immunogenicity decreased when these optimal parameters were substantially increased or decreased. We conclude that the immunogenicity of soluble haptenated polymers depends on predictable physical molecular characteristics, and is relatively independent of the chemical composition and conformation of the carrier polymer.

Absolute integrated SAXS measurements during the crystallization of linear polyethylene

AbstractAbsolute intensity measurements of a dynamic small‐angle x‐ray scattering from a linear polyethylene were carried out during polymer crystallization from melt in a temperature range of 113.5° to 124.5°C. The mean‐square modulation of the electron density over the irradiated volume was evaluated and the feasibility of dynamic experimentation for crystallization kinetic analysis was established. The results provide an absolute value of mass density of the amorphous phase of a semicrystalline polymer at the crystallization temperature.

BONE DENSITY IN AGEING CAUCASIAN AND AFRICAN POPULATIONS

Fracture surveys in the Johannesburg metropolitan area showed that the rate of femoral-neck fractures rose sharply after the climacteric in Caucasians, whereas the incidence of such fractures in African Negroes of the same age was almost negligible. However, a parallel epidemiological survey of metacarpal bone density in random samples of the same populations showed that absolute values for skeletal mass and bone density were greater in the Caucasians through most of the age-range from 5 to 75 years. Also, although bone density increased more rapidly and reached higher maximum values in young Caucasians than in Africans, it fell more rapidly in the former from the fourth decade onwards. The differences in the pattern of bone density alone are unlikely to account for the large difference in the fracture rates in the two populations. Perhaps quantitative changes in bone mass associated with ageing are accompanied by qualitative changes which may be critical in determining the liability to fracture.

Cyclotron Resonance and the Cohen Nonellipsoidal Nonparabolic Model for Bismuth. III. Experimental Results

Complete measurements of the anisotropy of the central-orbit cyclotron effective masses by Azbel'-Kaner cyclotron resonance have been taken at a frequency of 24.03 GHz and a temperature of 1.15 \ifmmode^\circ\else\textdegree\fi{}K for the magnetic field in the three crystallographic planes of Bi. Deviations of up to 10% from ellipsoidal behavior were observed for the electron-effective-mass anisotropies. Except in one instance, the various effective-mass anisotropies give a good fit to the Cohen nonellipsoidal nonparabolic (NENP) model and the fit is clearly superior to the Lax ellipsoidal nonparabolic model fit. The ratio of the Fermi energy to the $L$-point band-gap energy, $\frac{{E}_{F}}{{E}_{g}}$, was determined from fitting the NENP model and found to be 1.5\ifmmode\pm\else\textpm\fi{}0.4, in good agreement with other measurements. The fit to the NENP model also indicated that $\frac{{m}_{2}}{{m}_{2}}$ is approximately 1, implying that the $L$-point valence and conduction bands have identical parameters. The cyclotron effective masses agree within 3% with the values obtained by Edel'man and Khaikin, and disagree by as much as 30% with the values obtained by Kao. Quantum oscillations of the microwave surface impedance similar in nature to de Haas-Schubnikov oscillations have also been observed, but periods arising from the large cross-sectional areas could not be detected and no conclusions regarding the NENP model could be made. Magnetoplasma oscillations due to standing Alfv\'en waves have also been observed. The mass-density values derived from these measurements agree with the values obtained by other investigators. However, the carrier concentration derived from the Alfv\'en-wave periods differs by nearly 12% with the value derived from the Azbel'-Kaner cyclotron-resonance measurements. This difference may be due to nonellipsoidal effects.

Energy and mass content of high-speed solar-wind streams

The mass and energy flux densities of the solar wind measured by the Vela 3, Vela 4, and Explorer 34 satellites between July 1965 and October 1969 have been examined. Three-hour averages were used to study the properties of large-scale high-speed streams, and 27-day averages were employed in an attempt to identify long-term trends during the rising part of the current 11-year solar cycle. If the cross-sectional area of a stream is estimated by assuming that its extent in heliocentric latitude is the same as its extent in longitude, the total energy (at 1 AU) and mass flux can be calculated by integrating the excess mass and energy flux density above the predisturbance level during corotation of the stream past the observing satellite. The average energy and mass fluxes for dominant high-speed streams are found to be 9 × 1025 erg/sec and 8 × 109 g/sec, respectively. The total mass and energy output of all streams emanating from the sun over a typical 27-day interval, assuming that all last for the entire 27 days, is estimated to be less than 10% (∼7%) of the total solar-wind output from the same range of heliocentric latitudes (generally ±15°). Both large-scale streams and interplanetary shocks are found to contribute relatively little to 27-day average values of either mass or energy flux density. Thus, even though the amount of mass or energy or both per disturbance appeared to increase with increasing solar activity, the solar-wind energy and mass flux density averaged over a solar rotation remained remarkably constant.

Selection of an effective mass-density value for meteoric matter.

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

The anomalous diffusion of the current sheath in a toroidal discharge

The diffusion of the current sheath in ZETA is shown to be incompatible with classical resistive diffusion at high rates of energy input or low pressures. In the anomalous region the diffusion time is approximately proportional to mass density and inversely proportional to the applied electric field. There are considerable asymmetries in the toroidal discharge and complicated convective motions during the diffusion phase, but these appear not to be the primary cause of the enhanced diffusion. Evidence has been obtained that the enhanced diffusion is not due to the presence of a probe in the plasma. It is therefore probable that there must be an enhanced resistivity, depending on the local values of mass density and electric field, which is presumably due to some form of turbulence, but none of the simple models of such turbulence considered account for the results.