Semi-transparent Regions Research Articles

Soft X-ray radiography for measurements of a dense metal plasma created by intense relativistic electron beam on a tantalum target

A radiographic diagnostic has been developed to quantify the plume of erosion products after the interaction between a target and a relativistic electron beam. The diagnostic is based on a point Z-pinch (PZ-pinch) with a metallic plasma jet. It creates an X-ray source with a typical size of 10 μm, a photon energy of up to 3 keV and a flash duration of 3 ns. The X-ray visualization system is based on a thin scintillator and a CCD camera. The spatial resolution of the diagnostic was evaluated experimentally. The spatial frequency limit was found to be about 1.5 line pairs per millimeter. The diagnostic was tested in an experiment performed using an LIA-5 linear induction accelerator. An electron beam with a current of 400 A, an energy of 3.5 MeV and a pulse duration of 80 ns was focused on a plane tantalum target 1 mm in thickness. The FWHM of the focal spot was ∼ 2 mm. Radiographs of the plume were taken with different delays after different accelerator pulses. According to our data, the plume most commonly propagates toward the beam. After 70 μs its length was about 70 mm, i.e. the plume expansion rate was about 1 km/s. The area density of the semi-transparent regions of the plume was estimated as lying in the range 3 · 10-16–2 · 1017 cm-2.

Alpha Distribution for Alpha Testing

Alpha testing is widely used for rendering surfaces with transparency. While it works well when transparency is a binary function, semi-transparent regions cause problems, as they are classified as either fully transparent or opaque. Unfortunately, semi-transparent texture regions often appear in coarser mipmap levels, causing surfaces to disappear with distance. We introduce the alpha distribution approach for pre-processing the alpha values of a texture such that alpha testing produces expected results with semi-transparency without any modification to render-time operations. We describe two separate algorithms for alpha distribution with similar qualitative behavior. Our results show that alpha distribution can produce high-quality results with low noise. We also explain how alpha distribution can be extended for high-quality rendering with alpha-to-coverage.

Development of Circumventricular Organs in the Mirror of Zebrafish Enhancer-Trap Transgenics.

The circumventricular organs (CVOs) are small structures lining the cavities of brain ventricular system. They are associated with the semitransparent regions of the blood-brain barrier (BBB). Hence it is thought that CVOs mediate biochemical signaling and cell exchange between the brain and systemic blood. Their classification is still controversial and development not fully understood largely due to an absence of tissue-specific molecular markers. In a search for molecular determinants of CVOs we studied the green fluorescent protein (GFP) expression pattern in several zebrafish enhancer trap transgenics including Gateways (ET33-E20) that has been instrumental in defining the development of choroid plexus. In Gateways the GFP is expressed in regions of the developing brain outside the choroid plexus, which remain to be characterized. The neuroanatomical and histological analysis suggested that some previously unassigned domains of GFP expression may correspond to at least six other CVOs–the organum vasculosum laminae terminalis (OVLT), subfornical organ (SFO), paraventricular organ (PVO), pineal (epiphysis), area postrema (AP) and median eminence (ME). Two other CVOs, parapineal and subcommissural organ (SCO) were detected in other enhancer-trap transgenics. Hence enhancer-trap transgenic lines could be instrumental for developmental studies of CVOs in zebrafish and understanding of the molecular mechanism of disease such a hydrocephalus in human. Their future analysis may shed light on general and specific molecular mechanisms that regulate development of CVOs.

The effects of sodium chloride (NaCl) and residues of cellulosic fibres derived from sodium carboxymethylcellulose (NaCMC) synthesis on thermal and mechanical properties of CMC films

The main aim of this work is to provide an accurate determination of the morphological, thermal and mechanical properties of NaCMC films. Indeed, their main applications require good thermal stability and mechanical strength and the literature lacks a good description of these properties. We analyse two types of NaCMC, an analytical (Fluka) and a crude (Niklacell) grade. For both grades, optical micrographs of NaCMC solutions show partially soluble cellulosic fragments. As evidenced by SEM, films prepared with Niklacell display the formation of opaque (CMC-fNo) and semi-transparent (CMC-fNt) regions due to the combined effect of the formation of a NaCl layer and the presence of fragments of cellulosic fibres. After the elimination of NaCl by precipitation of the acid form of the crude grade of CMC, the films (CMC-fNp) are slightly opaque compared to films prepared with analytical NaCMC grade (CMC-fF). This is due to the residues of cellulosic fibres not eliminated during the precipitation and filtration procedures. The TGA curves of the NaCMC films display a three-step degradation. The results of DSC analyses show that NaCl has an impact on the water content of films due to its hygroscopic behaviour. As evidenced by DSC and DMA, NaCl does not influence the Tm (which is determined at ca. 240°C) of NaCMC films. However, NaCl has a considerable impact on the thermal and mechanical properties close to the Tg. CMC-fF (analytical) and CMC-fNp (purified grade) exhibit similar Tg values at ca. 40°C and CMC-fNt and CMC-fNo (crude grade samples) show the highest temperature values for Tg and a remarkable broadening of this transition. NaCl also influences the E' modulus of NaCMC films in the temperature range studied as observed from DMA. The CMC-fF has the highest E' values.

High-temperature infrared properties of forsterite

Polarized emittance measurements were acquired for synthetic forsterite, the pure magnesium end member of the olivines group, on the whole infrared spectral range and up to the melting point by using CO2 laser heating. The experimental data, fitted with a semi-quantum dielectric function model, allowed the retrieval of the temperature dependence of the absorption coefficient of forsterite both in the opaque and semi-transparent regions. The analysis of the phonon parameters indicates that the lattice dynamics evolve drastically with increasing temperature. The normal modes involving motions of the magnesium cations located in site 1 are the more impacted, and some of them vanish around 1,200 K. The results confirm that the enhancement of the lattice anharmonicity and the increasing mobility of the magnesium cations are closely linked and are at the origin of the anomalies observed in the evolution of the thermophysical properties. This complete set of spectroscopic data may be a step toward a more precise evaluation of the impact of thermal radiation heat transfer inside systems involving forsterite and quantification of their heat budget.

Hierarchical super-structure identified by polarized light microscopy, electron microscopy and nanoindentation: Implications for the limits of biological control over the growth mode of abalone sea shells

BackgroundMollusc shells are commonly investigated using high-resolution imaging techniques based on cryo-fixation. Less detailed information is available regarding the light-optical properties. Sea shells of Haliotis pulcherina were embedded for polishing in defined orientations in order to investigate the interface between prismatic calcite and nacreous aragonite by standard materialographic methods. A polished thin section of the interface was prepared with a defined thickness of 60 μm for quantitative birefringence analysis using polarized light and LC-PolScope microscopy. Scanning electron microscopy images were obtained for comparison. In order to study structural-mechanical relationships, nanoindentation experiments were performed.ResultsIncident light microscopy revealed a super-structure in semi-transparent regions of the polished cross-section under a defined angle. This super-structure is not visible in transmitted birefringence analysis due to the blurred polarization of small nacre platelets and numerous organic interfaces. The relative orientation and homogeneity of calcite prisms was directly identified, some of them with their optical axes exactly normal to the imaging plane. Co-oriented "prism colonies" were identified by polarized light analyses. The nacreous super-structure was also visualized by secondary electron imaging under defined angles. The domains of the super-structure were interpreted to consist of crystallographically aligned platelet stacks. Nanoindentation experiments showed that mechanical properties changed with the same periodicity as the domain size.ConclusionsIn this study, we have demonstrated that insights into the growth mechanisms of nacre can be obtained by conventional light-optical methods. For example, we observed super-structures formed by co-oriented nacre platelets as previously identified using X-ray Photo-electron Emission Microscopy (X-PEEM) [Gilbert et al., Journal of the American Chemical Society 2008, 130:17519–17527]. Polarized optical microscopy revealed unprecedented super-structures in the calcitic shell part. This bears, in principle, the potential for in vivo studies, which might be useful for investigating the growth modes of nacre and other shell types.

Normal and Directional Spectral Emittance Measurement of Semi-Transparent Materials Using Two-Substrate Method: Alumina

The normal and directional spectral emittance of alumina is measured using a Fourier transform infrared spectrometer. A new measurement method, called the two-substrate method, is developed to measure infrared optical properties of semi-transparent materials, which comes over the limitations of the substrate heating method. The uncertainty of the emittance is evaluated with the calibration method (black surroundings), phase correction, temperature measurement, background radiation reflection by the sample surface, and the size-of-source effect. The maximum relative combined relative uncertainty (k = 1) is less than 4.3 % at 4 μm, and the minimum value is less than 0.57 % at 10 μm in the case of an alumina sample at 300 °C. The directional spectral emissivity of alumina is successfully measured in semi-transparent and opaque regions, showing a typical behavior of dielectric materials.

Two‐Dimensional Multiangle, Multigroup Neutrino Radiation‐Hydrodynamic Simulations of Postbounce Supernova Cores

We perform axisymmetric (2D) multiangle, multigroup neutrino radiation-hydrodynamic calculations of the postbounce phase of core-collapse supernovae using a genuinely 2D discrete-ordinate (Sn) method. We follow the long-term postbounce evolution of the cores of one nonrotating and one rapidly rotating 20 M☉ stellar model for ~400 milliseconds from 160 to ~550 ms after bounce. We present a multidimensional analysis of the multiangle neutrino radiation fields and compare in detail with counterpart simulations carried out in the 2D multigroup flux-limited diffusion (MGFLD) approximation to neutrino transport. We find that 2D multiangle transport is superior in capturing the global and local radiation-field variations associated with rotation-induced and SASI-induced aspherical hydrodynamic configurations. In the rotating model, multiangle transport predicts much larger asymptotic neutrino flux asymmetries with pole-to-equator ratios of up to ~2.5, while MGFLD tends to sphericize the radiation fields already in the optically semitransparent postshock regions. Along the poles, the multiangle calculation predicts a dramatic enhancement of the neutrino heating by up to a factor of 3, which alters the postbounce evolution and results in greater polar shock radii and an earlier onset of the initially rotationally weakened SASI. In the nonrotating model, differences between multiangle and MGFLD calculations remain small at early times when the postshock region does not depart significantly from spherical symmetry. At later times, however, the growing SASI leads to large-scale asymmetries and the multiangle calculation predicts up to 30% higher average integral neutrino energy deposition rates than MGFLD.

Development of Methods to Determine the Infrared‐Optical Properties of Polymer Films

AbstractSummary: In this paper, two methods for the determination of infrared optical properties of thick polymer films, based on FTIR spectroscopy, were implemented and used. Complex index of refraction data were generated for various ethylene copolymer films. Transmittance and reflectance spectra were measured in the mid infrared range using a gold‐coated 100 mm‐diameter integrating sphere. For the investigated films n and k values ranging from 1.3 to 1.6 and from 10−4 to 0.25 were determined, respectively. Regarding n, a good agreement was obtained for both methods, the transmittance/reflectance procedure (T/R method) used for transparent and semitransparent regions, and Single Substractive Kramers‐Kronig (SSKK) algorithm applied for non‐transparent regions. The highest k values were determined for the CH2 stretching vibration. The k values are dependent on comonomer content and film thickness. The combination of both methods allows for an accurate determination of n and k in the entire IR region relevant for solar application.

Fast transcoding architectures for insertion of non-regular shaped objects in the compressed DCT-domain

This paper addresses the problem concerned with the insertion of non-regular shaped objects, such as logos or subtitles, in compressed video signals. To achieve this objective, a different approach from the usual pixel-domain compositing operation is adopted, in order to avoid the presence of undesired semi-transparent rectangular regions around the inserted objects. The transposition of this technique to the compressed DCT-domain is presented, as well as the integration of the logo insertion module in several architectures of compressed domain video transcoders. A detailed study of the main characteristics of the proposed DCT-domain transcoders, with a special emphasis on the required computational load and on the obtained coding quality (PSNR) of the processed video sequences shows that DCT-domain insertion architectures can offer significant advantages, both in terms of subjective quality and computational cost. Moreover, the distinctive features presented by the proposed architectures provide the means to adapt the insertion scheme to the particular requirements of the target application.

Nuclear effects on bremsstrahlung neutrino rates of astrophysical interest

We calculate in this work the rates for the neutrino pair production by nucleon-nucleon bremsstrahlung taking into account the full contribution from a nuclear one-pion-exchange potential. It is shown that if the temperatures are low enough $(T<~20 \mathrm{MeV}),$ the integration over the nuclear part can be done for the general case, ranging from the completely degenerate (D) to the nondegenerate (ND) regime. We find that the inclusion of the full nuclear contribution enhances the neutrino pair production by $\mathrm{nn}$ and $\mathrm{pp}$ bremsstrahlung by a factor of about 2 in both the D and ND limits when compared with previous calculations. This result may be relevant for the physical conditions of interest in the semitransparent regions near the neutrinosphere in type II supernovae, cooling of neutron stars, and other astrophysical situations.

Thermal radiation properties of molten salts. 2nd Report. Properties of alkaline metal chlorides and conductive-radiative transfer in the salts.

Thermal radiation properties are investigated on three molten alkaline metal chlorides: lithium chloride, sodium chloride and potassium chloride. Reflectance spectra of the salt layers are measured at wavelengths from 0.5 to 13.0μm. The semi-transparent regions of the salts are found to cover the entire wavelength region of the Planckian distribution. The results are analyzed to evaluate the spectra of refractive index and absorption coefficient. Conductive-radiative transfer in the salts is calculated on a simple system to demonstrate the dominant contribution of radiation transfer.

Piezoreflectance as a supplement to photoreflectance for nondestructive characterization of GaAs/AlxGa1−xAs multiple quantum wells

Piezoreflectance is used to identify allowed and forbidden transitions in the spectra of as-grown 100 and 50 Å GaAs/AlxGa1−xAs multiple quantum well samples from which no photoreflectance spectra suitable for characterization could be obtained. Features in the piezoreflectance spectra are shown to result from excitonic transition by direct comparison with the absorbance measurements made on semitransparent regions of these samples. Transition energies are extracted from the piezoreflectance spectra using a form of the Aspnes equation appropriate for the first derivative of a Lorentzian.

Net radiation method for transmission through partially transparent plates

It is shown that the net radiation method for enclosures with opaque surfaces described by Siegel and Howell (1972) can, in an appropriately adapted version, provide a computation procedure suitable for situations with semitransparent regions. This procedure involves simple equations at each interface and can be readily applied to complicated systems such as those consisting of absorbing and nonabsorbing layers, and layers with different reflectivities at each interface. The equations can also be readily incorporated in a computerized design procedure.

On the irradiation of lavrion fluorite

Abstract Fluorite from Lavrion, Attiki, Greece was found to contain transparent and semitransparent regions. The ir spectra of the semitransparent regions of the fluorite showed the presence of water, CO2, and of the anions CO3 2-, NO3 −, SO4 2-and PO4 3-. Solid inclusioris such as galena, sphalerite and chalcopyrite were also found in both regions. The formation temperature of this fluorite is estimated to be lower than 190°C. The optical absorption spectra of the two regions show, after irradiation, the same bands at about 590,400, 320 and 250 nm. The intensity of some of these bands, however, is significantly different between the two regions. The bands at 590 and 320 nm are attributed to colour centres. It is proposed that the band at 400 nm is due to an electronic transition within the ion Y2+(4d1). It is suggested that the existence of blue or green fluorite exhibiting the Smakula spectrum may indicate the presence of radioactive minerals.