Mean Density Measurements Research Articles

Towards Density Measurements In A Supersonic Turbulent Boundary Layer

Quantitative mean density measurements using calibrated schlieren technique are demonstrated in a Mach 2 compressible turbulent boundary layer. A calibration procedure, where schlieren and particle image velocimetry measurements are conducted on a symmetric double wedge model, is utilised. By assuming that the shock and expansion fan generated by the double wedge model can be idealised, the density gradient field is calculated based on the measured velocity field. Thus, based on the calibration data, a linear relation from schlieren intensity to density gradient is constructed. Moreover, to resolve a large range of density gradients expected within the boundary layer, schlieren measurements with five different knife edge positions are performed and the results are stitched together. The combined density gradient and the integrated density profiles showed good agreement with the literature, and therefore the current technique may provide a promising avenue to measure the mean density fields in compressible boundary layer flows.

Constraints on Super-Earth Interiors from Stellar Abundances

Abstract Modeling the interior of exoplanets is essential to go further than the conclusions provided by mean density measurements. In addition to the still limited precision on the planets’ fundamental parameters, models are limited by the existence of degeneracies on their compositions. Here, we present a model of internal structure dedicated to the study of solid planets up to ∼10 Earth masses, i.e., super-Earths. When the measurement is available, the assumption that the bulk Fe/Si ratio of a planet is similar to that of its host star allows us to significantly reduce the existing degeneracy and more precisely constrain the planet’s composition. Based on our model, we provide an update of the mass–radius relationships used to provide a first estimate of a planet’s composition from density measurements. Our model is also applied to the cases of two well-known exoplanets, CoRoT-7b and Kepler-10b, using their recently updated parameters. The core mass fractions of CoRoT-7b and Kepler-10b are found to lie within the 10%–37% and 10%–33% ranges, respectively, allowing both planets to be compatible with an Earth-like composition. We also extend the recent study of Proxima Centauri b and show that its radius may reach 1.94 in the case of a 5 planet, as there is a 96.7% probability that the real mass of Proxima Centauri b is below this value.

Imaging of collagen deposition disorders using optical coherence tomography.

Collagen deposition disorders such as hypertrophic scars, keloids and scleroderma can be associated with significant stigma and embarrassment. These disorders often constitute considerable impairment to quality of life, with treatment posing to be a substantial challenge. Optical coherence tomography (OCT) provides a non-invasive, easily applicable bedside optical imaging method for assessment of the skin. It is hypothesized that OCT imaging may be useful in assessing fibrosis to avoid additional biopsies that could potentially worsen the scarring. Thirty-three patients with ordinary scars, hypertrophic scars, keloid scarring, lichen sclerosus et atrophicus and localized or systemic scleroderma were recruited for this pilot study. Affected tissue and adjacent healthy skin were scanned using OCT and digitally photographed. Density measurements were performed in ImageJ on OCT images from scleroderma patients, both systemic and morphea (10 patients), keloid patients (10 patients) and healthy skin adjacent to keloids (10 patients). OCT images of scarring diseases showed varying degrees of disruption to the skin architecture. OCT characteristics were identified for each lesion type. Hypertrophic scars displayed an increased vascularity and signal-rich bands correlating to excessive collagen deposition. Keloids depicted a disarray of hyper-reflective areas primarily located in the upper dermis. Additionally, the dermis displayed a heterogeneous morphology without indications of any vascular supply or lymphatic network. In contrast to keloids, scleroderma displayed a more cohesive backscattering indicating a difference in density of collagen or other dermal structures. OCT images demonstrated no significant differences between mean density measurements in OCT images of scleroderma, keloid and healthy skin (P=0.07). The OCT imaging appears to identify different scarring mechanisms, and therefore be of potential use in the assessment of outcomes following non-invasive therapy of e.g. early or progressive lesions.

Densitometry and Thermometry of Starburst Galaxies

With a goal toward deriving the physical conditions in external galaxies, we present a survey of formaldehyde (H2CO) and ammonia (NH3) emission and absorption in a sample of starburst galaxies using the Green Bank Telescope. By extending well-established techniques used to derive the spatial density in star formation regions in our own Galaxy, we show how the relative intensity of the 110−111 and 211−212 K-doublet transitions of H2CO can provide an accurate densitometer for the active star formation environments found in starburst galaxies (cf. Mangum et al. 2008). Similarly, we employ the well-established technique of using the relative intensities of the (1,1), (2,2), and (4,4) transitions of NH3 to derive the kinetic temperature in starburst galaxies. Our measurements of the kinetic temperature constrained spatial density in our starburst galaxy sample represent the first mean density measurements made toward starburst galaxies. We note a disparity between kinetic temperature measurements derived assuming direct coupling to dust and those derived from our NH3 measurements which points to the absolute need for direct gas kinetic temperature measurements using an appropriate molecular probe. Finally, our spatial density measurements point to a rough constancy to the spatial density (104.5 to 105.5 cm-3) in our starburst galaxy sample. This implies that the Schmidt-Kennicutt relation between LIR and Mdense: (1) Is a measure of the dense gas mass reservoir available to form stars, and (2) Is not directly dependent upon a higher average density driving the star formation process in the most luminous starburst galaxies.

Polyamorphic transformation induced by electron irradiation ina-SiO2glass

We report a study by electron paramagnetic resonance of amorphous silicon dioxide $(a{\text{-SiO}}_{2})$ irradiated by 2.5 MeV electrons in the dose range from $1.2\ifmmode\times\else\texttimes\fi{}{10}^{3}$ to $5\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{kGy}$. By measuring the change in the splitting of the primary $^{29}\text{S}\text{i}$ hyperfine doublet of the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ centers we evidenced an irradiation induced local (around the defects) densification of $a{\text{-SiO}}_{2}$. Our data show that the local degree of densification of the materials is significantly higher than that obtained by mean density measurements, suggesting that the structural modifications induced by electron irradiation take place prevalently within confined defective regions of the material. The overall results we have found have permitted us to obtain a detailed quantitative description of the electron irradiation-induced densification process of $a{\text{-SiO}}_{2}$ and to point out relevant physical properties which have for many years remained elusive. Among them, we have found strong evidences that the processes of permanent densification induced by irradiation or by high hydrostatic pressure involve quite similar structural modification of the $a{\text{-SiO}}_{2}$ matrix.

A Cdk5 inhibitory peptide reduces tau hyperphosphorylation and apoptosis in neurons

The extracellular aggregation of amyloid beta (Abeta) peptides and the intracellular hyperphosphorylation of tau at specific epitopes are pathological hallmarks of neurodegenerative diseases such as Alzheimer's disease (AD). Cdk5 phosphorylates tau at AD-specific phospho-epitopes when it associates with p25. p25 is a truncated activator, which is produced from the physiological Cdk5 activator p35 upon exposure to Abeta peptides. We show that neuronal infections with Cdk5 inhibitory peptide (CIP) selectively inhibit p25/Cdk5 activity and suppress the aberrant tau phosphorylation in cortical neurons. Furthermore, Abeta(1-42)-induced apoptosis of these cortical neurons was also reduced by coinfection with CIP. Of particular importance is our finding that CIP did not inhibit endogenous or transfected p35/Cdk5 activity, nor did it inhibit the other cyclin-dependent kinases such as Cdc2, Cdk2, Cdk4 and Cdk6. These results, therefore, provide a strategy to address, and possibly ameliorate, the pathology of neurodegenerative diseases that may be a consequence of aberrant p25 activation of Cdk5, without affecting 'normal' Cdk5 activity.

Evolution of the effective nozzle diameter in the buoyancy free development of turbulent jets with variable density

Decay laws in the initial, non buoyant region of round, turbulent, variable density jets can be derived from dimensional similarity considerations. This paper presents the concept of normalized effective diameter. In the case of turbulent jets issuing into a coflow air stream (initial density ratio varying from 0.07 to 1), this quantity is experimentally derived from measurements of mean density and velocity and is found to follow a unique exponential decay. Results are also presented in terms of global force of the nozzle fluid.

Observations of jets in density stratified crossflows

The results are presented of a water tunnel study undertaken to determine the characteristics of a circular jet in a density stratified crossflow. Flow visualization indicates that the salient characteristics include a stable potential core of length L in the vicinity of the jet exit. The length of the stable potential core depends on the velocity ratio α = U J U ∞ and the non-dimensional frequency ND U ∞ . As α is increases the value of L increases; L also increases for increasing values of ND U ∞ < 0.03 . However, L decreases with increasing ND U ∞ for values of ND U ∞ > 0.03 . Knowledge of this variability is necessary for quantifying mixing rates. Further downwind, the jet trajectory evolves to a maximum height of rise z m , and subsequently relaxes to a lower equilibrium level, z e. Values of z m and z e are in agreement with the predictions of scaling arguments. Mean density measurements indicate rapid increase of dilution for small distances from the jet exit; however, for large distances predominantly horizontal mixing processes result in much slower increase of dilution with distance.

Use of automated measurements of mean density as an adjunct to computed tomography.

A system integrated with a first-generation computed tomography (CT) head scanner is described. With the assistance of an additional program and minimal hardware changes, it was possible to examine specific areas on the preinfusion studies and obtain instantaneous printouts of a number of parameters including mean densities. This measurement technique was then applied to the preinfusion scans of "lucent" lesions--abscesses, glioblastomas--as well as "dense" lesions--recent hemorrhages, some uncalcified meningiomas, and some metastatic melanomas. These five lesions had characteristic mean attenuation values that seem to allow classification of each of the five entities. Hardware and software changes are described and practical application of the system is discussed.

The Determination of the Density Distribution of a Gas Flowing in a Pipe from Mean Density Measurements

Information about the density distribution of a gas flowing in a pipe is obtained by measuring the mean densities along straight lines across the pipe. The density distribution is represented by a Fourier series with variable coefficients which satisfy a Volterra type integral equation of the first kind. This equation is solved and a numerical technique for calculating the solution is given.