Amount Of Phase Change Research Articles

Experimental and numerical investigation of self-pressurization with different methods of insulation for ground and space applications

The necessity of precise estimation and understanding of self-pressurization in a cryogenic storage vessel has increased rapidly over the years because of the influence of self-pressurization phenomena on the design of cryogenic engines. Since propellants are stored at their boiling temperature or subcooled condition, very small heat infiltration itself causes self-pressurization. When heat is transferred to the propellant tank, the liquid near the sidewall is heated up, and a warm stratified layer is developed at the liquid vapor interface, which causes self-pressurization. A numerical model is developed, and experiments are conducted to investigate the self-pressurization effects of cryogenic storage vessels to precisely understand the mechanisms causing it and the effect of methods of insulations, including multi-layer insulations in tanks. The numerical model is developed based on the available correlation to predict the self-pressurization and related parameters of a double wall cryogenic storage tank with different sets of insulations such as air, foam, vacuum, and MLI and different cryogens; hydrogen, nitrogen, and oxygen. A double wall cryogenic storage tank using SS 304 is also developed, conducted self-pressurization studies using liquid nitrogen under different methods of insulation. The experimental results were compared with the numerical model and found in good agreement. Comparing the self-pressurization rate of different cryogens, the value is higher for hydrogen. Since the boiling point of hydrogen is less, the axial heat flux acting will be higher. The low-density fluids will quickly move towards the interface and deposit, causing a warm layer at the liquid-vapour interface. The amount of phase change is also higher for liquid hydrogen, which in turn aid in rapid self-pressurization. Among the insulations used, multi-layer insulation shows the best performance in terms of thermal resistance. The analytical and heat transfer model developed predicts and compared well with the experimental results and can be used for a variety of situations in ground and space for self-pressurization and roll over phenomenon studies and prediction of results in advance.

Revealing of Core Shell Effect on Frequency-Dependent Properties of Bi-based Relaxor/Ferroelectric Ceramic Composites

In this study, electromechanical characteristics of (1-x) Bi0.5Na0.5TiO3–xSrTiO3 (ST26, x = 0.26)/(1-y) Bi0.5Na0.5TiO3–ySrTiO3 (ST10, y = 0.1) (matrix/seed) composites were studied. The ST26 (high relaxor phase) and ST10 (a relaxor ferroelectric (RF), high ferroelectric phase) composite with large (r-ST26-ST10) and small (t-ST26-ST10) grains exhibited frequency-related dielectric properties and large strain response at a low triggering electric field (an incipient piezoelectricity). It is ascribed to a matrix-seed effect originating from the inhomogeneous composition due to the presence of two phases. The r-ST26-ST10 composite sintered at 4 h, prominent material, showed a high normalized dynamic strain (d33*) of ~700 pm/V (large grains) with stable frequency dependence properties at a low field of 40 kV/cm. The properties of the r-ST26-ST10 composite exhibit less decay with frequency-related polarization and strain compared to those of t-ST26-ST10 composite. The increase in soaking time promotes the diffusion and homogenization of the microstructure in composites, leading to changes in the core-shell structure in the solid solution. The polarization and strain of the ST26-ST10 composites with the frequency are linked to the stability of the internal random fields created by non-ergodic relaxor phase of seed and the amount of phase change in the ergodic relaxor matrix.

Experimental realization of Talbot array illumination for a 2-dimensional phase grating

We present the result of a multiple phase level Talbot array illuminator (TAI) based on two dimensional phase grating. The grating was fabricated on glass by a Deep Reactive Ion Etching (DRIE) system with optimized gas combination recipe. The opening ratio of the grating is ∼0.71 with a phase step of 11π. The experimental study on Talbot array illuminations (TAI's) of this fabricated device in near-field region was carried out using a He-Ne laser. The TAI's were observed at the positions 2.81 mm, 8.59 mm, 14.28 mm, and 20.57 mm along the light propagation direction. The computer simulations of wave field distribution in near field region at different fractional Talbot distances have been generated. These simulated results are in reasonably good agreement with our experimental observed results. Our analysis on Talbot array illumination (TAI's) shows that the multiple harmonic phase modulations are transformed into intensity modulations at 1/8, 3/8, 5/8, and 7/8 fractional Talbot position. We have observed three different grating images, viz., attenuated, phase contrast, and diffraction contrast images. We also show the presence of a considerable amount of phase change at the edge of each phase sublevel that enhances the contrast of differential phase contrast imaging. Therefore, the phase contrast signal can be detected at a fractional position using single phase grating without the need of phase stepping.

Static optical cross phase modulation in active multimode interference couplers

The static performance of active multimode interference (MMI) couplers is analyzed in the presence of two different optical signals using a beam propagation method (BPM)-based simulation. To examine the feasibility of a novel all-optical switch based on active MMI; the simulation is mainly used to evaluate the amount of phase change resulting in the output of one optical signal by varying the intensity of the other at different injected carrier density. The simulation code is based on the finite difference (FD)-BPM and is including the distribution of photon density, carrier density, and refractive index.

Fracture orientation determination in sedimentary rocks using multicomponent ground-penetrating radar measurements

The resolution provided by conventional single-component GPR surveys is not always sufficient to determine fracture location and orientation. Multicomponent measurements can help in these determinations through phase and amplitude analysis. The phase of a radar wavelet is altered as it passes through a fracture. The amount of phase change depends upon the relative orientation of the fracture and the direction of the incident electric field. If the phase change is measured for a known orientation of the antennas, then the strike of the fracture can be determined. For our purpose, multicomponent means repeating measurements at the same location for different antenna configurations and orientations.

The tuning of a Zernike phase plate with defocus and variable spherical aberration and its use in HRTEM imaging

With the advent of the double-hexapole aberration corrector in transmission electron microscopy the spherical aberration of the imaging system has become a tunable imaging parameter like the objective lens defocus. Now Zernike phase plates, altering the phase of the diffracted electron wave, can be approximated more perfectly than with the lens defocus alone, and the amount of phase change can be adjusted within wide limits. The tuning of the phase change allows an optimum contrast transfer in high-resolution imaging even for thick crystalline objects, thus surpassing the limits of the well-known Scherzer λ/4 phase plate to the imaging of thin objects. The optimum values for the spherical aberration and the lens defocus are derived, and the limits and imperfections of the approximation explored. A mathematical link to the channelling approximation of high-energy electron diffraction shows how the image contrast of atomic columns can be improved systematically within wide thickness limits. Depending on the specimen thickness different combinations of spherical aberration and defocus are favourable: positive spherical aberration with an underfocus, zero spherical aberration with zero defocus, as well as negative spherical aberration with an overfocus.

Control of resonant wavelength from organic light-emitting materials by use of a Fabry-Perot microcavity structure.

We report the fabrication of Fabry-Perot microcavity structures with the organic light-emitting material tris-(8-hydroxyquinoline) aluminum (Alq3) and derive their optical properties by measuring their photoluminescence (PL) and absorption. Silver and a TiO2-SiO2 multilayer were used as metal and dielectric reflectors, respectively, in a Fabry-Perot microcavity structure. Three types of microcavity were prepared: type A consisted of [air[Ag[Alq3]Ag]glass]; type B, of [air[dielectric[Alq3]dielectric]glass]; and type C, of [air[Ag[Alq2]dielectric]glass]. A bare Alq3 film of [air[Alq3]glass] had its PL peak near 514 nm, and its full width at half-maximum (FWHM) was 80 nm. The broad FWHM of a bare Alq3 film was reduced to 15-27.5, 7-10.5, and 16-16.6 nm for microcavity types A, B, and C, respectively. Also, we could control the PL peak of the microcavity structure by changing the spacer thickness, the amount of phase change on reflection, and the angle of incidence.

Temporal patterns of the responses of auditory-nerve fibers to low-frequency tones

The temporal response patterns of auditory-nerve fibers to low-frequency tones were studied in anesthetized cats using period histograms. ‘Peak-splitting’ was observed mostly in fibers with lower characteristic frequencies (CF < 2 kHz) and with lower-frequency stimulation (⪯ 500 Hz). The occurrence of peak-splitting, the number of peaks, and the time between the peaks were all dependent upon the stimulus frequency. The phases of responses, although complex functions of stimulus frequency, intensity, and the fiber's CF, clearly showed traveling-wave characteristics for all frequencies at or above 100 Hz. The amount of phase change with intensity was generally small for lower-frequency stimuli ( < ∼ 50°), although larger phase changes (e.g., ∼ 180°) were occasionally seen with higher-frequency stimuli. At 50 and 100 Hz, the phase of neural responses in the basal region roughly corresponds to the maximum velocity of the basilar membrane towards scala tympani (as inferred from cochlear microphonic recordings).

Excited states and their relaxation dynamics in trans-polyacetylene.

We investigate excited states in polyacetylene, taking account of electron correlation by transforming the electronic degrees of freedom into a quantum phase variable via boson representation. When the lattice is fixed at the ground-state configuration, there are the following species of excitations: soliton ${S}^{e}$, antisoliton S${\ifmmode\bar\else\textasciimacron\fi{}}^{e}$, the first breather ${B}_{1}^{e}$, and the second breather ${B}_{2}^{e}$. ${S}^{e}$ should not be confused with the usual neutral soliton ${S}^{e\mathrm{\ensuremath{-}}l}$; in the former, the amount of phase change is 2\ensuremath{\pi} and the lattice is in the uniformly dimerized state, while in the latter the amount of phase change is \ensuremath{\pi} and the lattice has a usual soliton structure. ${S}^{e}$, ${B}_{1}^{e}$, and S${\ifmmode\bar\else\textasciimacron\fi{}}^{e}$ are three components of the triplet exciton, and ${B}_{2}^{e}$ is the singlet dipole-forbidden exciton which corresponds to the 2 $^{1}A_{g}$ state in finite polyenes. The electronic structure of ${B}_{2}^{e}$ can be regarded as a bound state of ${S}^{e\mathrm{\ensuremath{-}}l}$'s. We study the dynamics of the lattice relaxation from ${B}_{2}^{e}$ by applying a semiclassical approximation to the boson system. Since the lattice is driven by the electronic structure of ${B}_{2}^{e}$, a neutral soliton pair or their bound state is formed as a relaxation product.

Behaviour and Mechanism of the Allotropic Transformation of Cerium

When cerium is subjected to the thermal cycling between room and liquid air temperatures, the amount of α phase increases after each cycle as the electrical resistance changes accordingly, where the changing manners of both factors are quite similar. However, although terminal temperatures of the thermal cycling are far different from the transformation temperature, the amount of phase change never attains 100%, but a certain equilibrium value. In this paper, the transformation mechanism of cerium was discussed theoretically, while an attempt was made to give a theoretical explanation upon the above mentioned attainment of an equilibrium, utilizing the theory of martensite formation in carbon steel by Cohen, et al, considering the size effect due to the subdivision of crystal grains by the formed martensite leaves. The experimental part of this study was previously reported by the author at Virginia Academy of Science meeting.