Density Gradient Measurements Research Articles

Two-dimensional Thomson scattering measurements of misaligned electron density and temperature gradients and associated Biermann battery produced fields

Two-dimensional Thomson scattering measurements of misaligned electron density and temperature gradients and associated Biermann battery produced fields

Neutron phase contrast imaging of PbWO4 crystals for G experiment test masses using a Talbot-Lau neutron interferometer

The use of transparent test/source masses can benefit future measurements of Newton’s gravitational constant G. Such transparent test mass materials can enable nondestructive, quantitative internal density gradient measurements using optical interferometry and allow in-situ optical metrology methods to be realized for the critical distance measurements often needed in a G apparatus. To confirm the sensitivity of such optical interferometry measurements to internal density gradients it is desirable to conduct a check with a totally independent technique. We present an upper bound on possible internal density gradients in lead tungstate (PbWO4) crystals using a Talbot-Lau neutron interferometer on the Cold Neutron Imaging Facility at NIST. We placed an upper bound on a fractional atomic density gradient in two PbWO4 test crystals of cm−1. This value is about two orders of magnitude smaller than required for G measurements. We discuss the implications of this result and of other nondestructive methods for characterization of internal density inhomogeneties which can be applied to test masses in G experiments.

Imaging of PbWO4 crystals for G experiment test masses using a laser interferometer

It is highly desirable for future measurements of Newton’s gravitational constant G to use test/source masses that allow nondestructive, quantitative internal density gradient measurements. High density optically transparent materials are ideally suited for this purpose since their density gradient can be measured with laser interferometry, and they allow in-situ optical metrology methods for the critical distance measurements often needed in a G apparatus. We present an upper bound on possible internal density gradients in lead tungstate (PbWO4) crystals determined using a laser interferometer. We placed an upper bound on the fractional atomic density gradient in two PbWO4 test crystals of cm−1. This value is more than two orders of magnitude smaller than what is required for G measurements. They are also consistent with but more sensitive than a recently reported measurements of the same samples, using neutron interferometry. These results indicate that PbWO4 crystals are well suited to be used as test masses in G experiments. Future measurements of internal density gradients of test masses used for measurements of G can now be conducted non-destructively for a wide range of possible test masses.

Hepatitis E virus persists in the ejaculate of chronically infected men

Hepatitis E virus (HEV) infections are prevalent worldwide. Various viruses have been detected in the ejaculate and can outlast the duration of viremia, indicating replication beyond the blood-testis barrier. HEV replication in diverse organs, however, is still widely misunderstood. We aimed to determine the occurrence, features and morphology of HEV in the ejaculate. The presence of HEV in testis was assessed in 12 experimentally HEV-genotype 3-infected pigs. We further tested ejaculate, urine, stool and blood from 3 chronically HEV genotype 3-infected patients and 6 immunocompetent patients with acute HEV infection by HEV-PCR. Morphology and genomic characterization of HEV particles from various human compartments were determined by HEV-PCR, density gradient measurement, immune-electron microscopy and genomic sequencing. In 2 of the 3 chronically HEV-infected patients, we observed HEV-RNA (genotype 3c) in seminal plasma and semen with viral loads >2 logs higher than in the serum. Genomic sequencing showed significant differences between viral strains in the ejaculate compared to stool. Under ribavirin-treatment, HEV shedding in the ejaculate continued for >9 months following the end of viremia. Density gradient measurement and immune-electron microscopy characterized (enveloped) HEV particles in the ejaculate as intact. The male reproductive system was shown to be a niche of HEV persistence in chronic HEV infection. Surprisingly, sequence analysis revealed distinct genetic HEV variants in the stool and serum, originating from the liver, compared to variants in the ejaculate originating from the male reproductive system. Enveloped HEV particles in the ejaculate did not morphologically differ from serum-derived HEV particles. Enveloped hepatitis E virus particles could be identified by PCR and electron microscopy in the ejaculate of immunosuppressed chronically infected patients, but not in immunocompetent experimentally infected pigs or in patients with acute self-limiting hepatitis E.

Mechanical characterization of powder materials: A general approach detailed for cemented carbides

Material parameter curves in an advanced material model describing compaction of spray dried cemented carbide powder are determined successfully based on a general approach for material characterization of powder materials. Pressing forces from a production machine and equivalent finite element (FE) calculations are used in inverse modelling. A pressing method that includes multiple unloading steps is used. The material model is of Drucker Prager CAP kind and friction between powder and pressing tool is modelled as a function of normal pressure. The results are verified with density gradient measurements using a neutron source. The method is proven to be robust and the results show good agreement between experiment and simulation. Effects that have not been captured numerically previously are captured due to the high accuracy of material characterization. The present approach is detailed for tungsten carbide powders but is valid for other powder materials when properly calibrated for constitutive and frictional effects in the same manner as outlined here.

Sub- and supercritical jet disintegration

Shadowgraph visualization and Planar Laser Induced Fluorescence (PLIF) are applied to single orifice injection in the same facility and same fluid conditions to analyze sub- to supercritical jet disintegration and mixing. The comparison includes jet disintegration and lateral spreading angle. The results indicate that the shadowgraph data are in agreement with previous visualization studies but differ from the PLIF results that provided quantitative measurement of central jet plane density and density gradients. The study further evaluated the effect of thermodynamic conditions on droplet production and quantified droplet size and distribution. The results indicate an increase in the normalized drop diameter and a decrease in the droplet population with increasing chamber temperatures. Droplet size and distribution were found to be independent of chamber pressure.

Erratum to: Combined density gradient and velocity field measurements in transient flows by means of Differential Interferometry and Long-range µPIV

In the present study, Long-range Microparticle Image Velocimetry ( $$\upmu$$ PIV) and Differential Interferometry (DI) are combined in a novel manner to enable both velocity and depth-integrated density gradient field measurements using the same laser pulse for both recordings. In the present work, temperature-driven boundary layer flows could be successfully determined to an accuracy of $$\Updelta T=0.17\,\hbox {K}$$ with a spatial resolution of $$405\,\upmu \hbox {m}$$ for interference and $$101\,\upmu \hbox {m}$$ for $$\upmu$$ PIV measurements. The DI measurements are refraction compensated, and both temperature and velocity fields are compared with results from numerical simulations.

Combined density gradient and velocity field measurements in transient flows by means of Differential Interferometry and Long-range $$\varvec{\upmu }$$ μ PIV

Combined density gradient and velocity field measurements in transient flows by means of Differential Interferometry and Long-range $$\varvec{\upmu }$$ μ PIV

Novel Design of Multi-Purpose Probe for the Measurement of Plasma Density Gradient, Flow and Transport

We have designed, constructed and installed a multi-purpose probe (MPP) for the measurements of plasma density gradient, flow and turbulent transport in edge plasma of IR-T1 tokamak. Moreover, the effects of radial density gradient and parallel flow on turbulent transport have been investigated. The radial gradient density and the parallel flow variation were measured by the electrical part of MPP. The probability distribution function and the expected value between turbulence, density and parallel flow have been computed.

Characterization of Human Thymic Exosomes

Exosomes are nanosized membrane-bound vesicles that are released by various cell types and are capable of carrying proteins, lipids and RNAs which can be delivered to recipient cells. Exosomes play a role in intercellular communication and have been described to mediate immunologic information. In this article we report the first isolation and characterization of exosomes from human thymic tissue. Using electron microscopy, particle size determination, density gradient measurement, flow cytometry, proteomic analysis and microRNA profiling we describe the morphology, size, density, protein composition and microRNA content of human thymic exosomes. The thymic exosomes share characteristics with previously described exosomes such as antigen presentation molecules, but they also exhibit thymus specific features regarding surface markers, protein content and microRNA profile. Interestingly, thymic exosomes carry proteins that have a tissue restricted expression in the periphery which may suggest a role in T cell selection and the induction of central tolerance. We speculate that thymic exosomes may provide the means for intercellular information exchange necessary for negative selection and regulatory T cell formation of the developing thymocytes within the human thymic medulla.

Early Assessment of Defects and Damage in Jet Engines

The jet engine maintenance process is complex, expensive and time-consuming. It often requires engine disassembly or boroscopic examinations. In order to accelerate the process and reduce the down time of an engine we intend to develop a method to locate and characterize defects and damage at an early state, without having to disassemble the engine. The assumption is that various defects in the hot gas path of an engine have a noticeable impact on the spatial density distribution of the exhaust jet of an engine. The resulting differences in the exhaust jet pattern will be measured with the Background Oriented Schlieren method (BOS). We perform numerical simulations (CFD) in order to analyze the effects of various general defect types on the density pattern of the exhaust jet. The defects under investigation include the malfunction of one burner, the increase the turbine blade tip clearance and burned trailing edges of the blades. The changes in the pattern resulting from the defects are compared to the density distribution of the undamaged initial state. It is shown that different exhaust jet patterns can be linked to the investigated hot gas path defects. Furthermore, a BOS set-up is installed in a test cell of a helicopter engine with a two- stage axial turbine to demonstrate the applicability of the BOS method for the measurement of small density gradients resulting from temperature non-uniformities. A cold streak was inserted into the exhaust diffuser to simulate an artificial defect. The completed measurements show that the BOS method is able to detect these small variations. The present paper summarizes the results of different investigations. It presents a combination of BOS measurements of the exhaust jet and CFD simulations of defects within the hot gas path as a promising approach for evaluating the condition of a jet engine.

Merging of high speed argon plasma jets

Formation of an imploding plasma liner for the plasma liner experiment (PLX) requires individual plasma jets to merge into a quasi-spherical shell of plasma converging on the origin. Understanding dynamics of the merging process requires knowledge of the plasma phenomena involved. We present results from the study of the merging of three plasma jets in three dimensional geometry. The experiments were performed using HyperV Technologies Corp. 1 cm Minirailguns with a preionized argon plasma armature. The vacuum chamber partially reproduces the port geometry of the PLX chamber. Diagnostics include fast imaging, spectroscopy, interferometry, fast pressure probes, B-dot probes, and high speed spatially resolved photodiodes, permitting measurements of plasma density, temperature, velocity, stagnation pressure, magnetic field, and density gradients. These experimental results are compared with simulation results from the LSP 3D hybrid PIC code.

应用复Morlet小波变换分析条纹图相位

To reduce the effect of large number of invalid data in fringe patterns on calculation results in the measurement of high dynamic flows using interferometry or Moire deflectometry,an effective phase extraction method was proposed based on the wavelet transform using complex Morlet wavelet.Through choosing proper parameters for the wavelet,the maximum modulus of the wavelet transform of a pattern was proportional to its modulation factor,then it was used as a weighting factor of a phase unwrapping algorithm based on weighted least squares to guarantee reliable phase unwrapping.In the process of wavelet ridge routing,a simple algorithm based on curve fitting was proposed to substantially reduce the routing time and the precision deterioration due to image noise.In simulation experiment,the relative error between calculated phase and actual phase is less than 0.01%.In internal wave measurement experiment,the method is used to analyze the fringe patterns,and the density gradient measurement precision has reached 5×10-6 g/cm4.It shows that the method can reduce the effect of invalid data on analysis precision effectively and can obtain reliable unwrapped phases.

Thermal characteristic identification of an alcohol flame by measuring its density gradient in Shack-Hartmann optical system

Understanding the flame structure for different combustion in industries has drawn the increasing attention around the world. Particularly, for increasing the recent interest of using the hydrogen fuelled vehicles in recent world, structural analysis of flame in combustion chamber has attracted the attention of researchers. However, the high flame temperature and strong flame emissions increase the experimental difficulties, especially, in all kinds of intrusive measurement systems for determining the flame structures and flame temperatures. Therefore, a non-intrusive laser interferometer technique based on Shack-Hartmann optical system has been proposed to measure the thermal characteristic of a flame structure. In the present study, a low-stretched diffusion flame of methanol burner has been used. Shack-Hartmann optical system is a type of wave front sensor. It is commonly used in adaptive optical systems. It consists of an array of lenses to focus the image onto a photon sensor (photo-detector) at the focal plane and measures the wave front tilt. The major objective of the present study is to develop a laser interferometer measurement technique for analyzing the flame structure and its temperature propagation by measuring the density gradient of the flame. Optical interferometer technique is a potential candidate for the non-invasive measurement. In the present paper, a novel method for the measurement of density gradient in flame by using Shack-Hartmann optical system is proposed. A collimated laser beam that has been passed through the flame is tilted due to the density gradient inside the flame. A CCD camera (CCD photo sensor) has been used to observe the wave front tilts at the focal plane.

Measuring the electron density gradients of dense plasmas by deflectometry using short-wavelength probe

A new and simple experimental technique for the measurement of electron density gradients in dense laser-produced plasmas using an electromagnetic wave probe is presented. The main advantage of this method is the low requirements on coherence of the probing beam. The method is based on measuring the deformation of the Talbot pattern of a two-dimensional grating that stems from the distortion of the probe beam wave-front caused by the gradients of the index of refraction. The compromise between spatial resolution and sensitivity for the given wavelength of the probe beam is set by the experimental design. The proposed technique was experimentally verified on plasmas that were created by either a point focus or a line focus of a laser interacting with various solid targets. In the experiments reported here, all plasmas were probed by a Ne-like Zn x-ray laser beam at 21.2 nm, but the technique is applicable for any wavelength of the probe.

Solar modulation in surface atmospheric electricity

The solar wind modulates the flux of galactic cosmic rays impinging on Earth inversely with solar activity. Cosmic ray ionisation is the major source of air's electrical conductivity over the oceans and well above the continents. Differential solar modulation of the cosmic ray energy spectrum modifies the cosmic ray ionisation at different latitudes, varying the total atmospheric columnar conductance. This redistributes current flow in the global atmospheric electrical circuit, including the local vertical current density and the related surface potential gradient. Surface vertical current density and potential gradient measurements made independently at Lerwick Observatory, Shetland, from 1978 to 1985 are compared with modelled changes in cosmic ray ionisation arising from solar activity changes. Both the lower troposphere atmospheric electricity quantities are significantly increased at cosmic ray maximum (solar minimum), with a proportional change greater than that of the cosmic ray change.

X-Ray Tomography of Growing Silica Gel with a Density Gradient

Density gradient laser targets with decreasing density or increasing stepwise density layers were reported in experimental and theoretical papers on astrophysics modeling, equation-of-state (EOS), and shock-wave dynamics studies. The research with targets of smooth density gradient is due. The experiments with gel-catalyst concentration diffusion are discussed for density gradient foam formation. We used multi-image X-ray tomography for measurement of the silica gel layer density gradient in the process of its growth. Gel with a density gradient growing from a flat boundary between a gel-forming solution and a catalyst solution has been investigated through a set of three-dimensional frames of an X-ray computer microtomograph. Laser targets require high (>1 g·cm-3/cm) density gradients of the spatial profile for EOS experiments. The first targets from silica aerogel with a density gradient are demonstrated. Yet these targets perform less density gradient (<0.1 g·cm-3/cm) than is required for pressure multiplication in EOS targets.

Brewster angle reflection measurements of Hg density and laser deflection (Schlieren) measurements of Hg density gradients in an ultra-high pressure arc lamp

A Brewster angle reflection measurement is used to determine the Hg vapor density at the arc tube wall of an ultra-high pressure lamp. The density measurement in combination with the wall temperature yields a pressure of 201 ± 11 bar. This lamp pressure in combination with an arc core temperature measurement yields an arc core Hg vapor density of 1.78 × 1020 cm−3, which agrees with the density from resonance collisional line broadening measurements of the 1014 nm Hg line. These density results are combined with Abel inverted laser deflection or schlieren measurements to determine a density/temperature map of the Hg vapor in the lamp. The laser deflection technique is sensitive in the arc core and mantle, unlike emission techniques which are sensitive only in the arc core.

Stochastic magnetic field driven charge transport and zonal flow during magnetic reconnection

Magnetic fluctuation-induced charge transport, resulting from particle transport that is not intrinsically ambipolar, has been measured in the high-temperature interior of a reversed-field pinch plasma. It is found that global resistive tearing modes and their nonlinear interactions lead to significant charge transport, equivalent to the perpendicular Maxwell stress, in the vicinity of the resonant surface for the dominant core resonant mode during magnetic reconnection. Finite charge transport can result in a zonal flow associated with locally strong radial electric field and electric field shear. In the presence of stochastic magnetic field, radial electric field is expected to be balanced by radial electron pressure gradient. Direct measurement of local density gradient is consistent with the formation of radial electric field and the zonal flow.

Decomposition of acetaldehyde: Experiment and detailed theory

The classic pyrolytic decomposition of acetaldehyde has been examined to the higher temperatures used in combustion and also lower pressures with 85 laser-schlieren, shock-tube measurements of density gradient covering 40–500 torr and 1550–2400 K. This work is supplemented and modeled with a CASPT2 based variable reaction coordinate RRKM prediction of the dissociation kinetics. These RRKM predictions are then incorporated in good two-dimensional master equation fits of the strong falloff seen in the laser-schlieren experiments, and also that shown in some previous shock-tube results using UV absorption of the acetaldehyde as diagnostic. The laser-schlieren data provide not only unambiguous dissociation rates but also solid indications of the secondary chemistry. Modeling of the full density gradient profiles offers good estimates of rates for H-atom abstraction from both the acetaldehyde and the HCO radical, again at high temperatures.