Oscillation Wavelength Research Articles

Investigation of Viscor and Methanol Spray Dynamics using Proper Orthogonal Decomposition in Siemens Energy Industrial Atomisers

Abstract The demand to reduce carbon emissions has prompted research into alternative fuels that can replace conventional fuels like diesel in industrial gas turbines. Among different potential biofuels and e-fuels, methanol emerges as a sustainable and high-performance alternative to diesel for gas turbine applications. It is well established that the fuel physical properties, spray dynamics and degree of atomisation are strongly correlated and affect the engine performance. In this study, Proper Orthogonal Decomposition (POD) was applied on spatio-temporally resolved images to characterise Viscor, here used as diesel surrogate, and methanol sprays of pressure-swirl atomisers employed in Siemens Energy industrial gas turbine (SGT-400) combustors. The methanol experimental results were then compared against Viscor results at analogous operating conditions, including density adjusted atomiser pressure drop and ambient pressures. Results confirmed that the methanol spray cone angle is slightly wider than Viscor at corresponding operating conditions. The POD analysis allowed to identify dominant spatial oscillation modes and characterise them in terms of oscillation amplitude, wavelength and onset distance from the atomiser edge for both fuels. Oscillation wavelengths and maximum amplitudes were found to correlate with Weber number, average SMD and axial jet velocities.

Generation of Bessel vortex beams in the subterahertz range using reflecting diffractive optical elements

In this work, we propose a simple method for generating Bessel vortex beams in the subterahertz (subTHz) range with the orbital angular momentum with l = 1 based on reflecting metal diffractive optical elements with a continuous helical microrelief. The elements are fabricated by micromilling in a polished duralumin substrate and by tin casting, and tested using a backward wave oscillator (wavelength λ = 855 µm). When using the micromilled element, Bessel vortex beams are shown to be generated and retain a Bessel intensity profile at a distance of 20–50 mm from the reflecting element, which is in good agreement with the results of numerical simulation. An experimental estimate of the energy efficiency of this element is 63%. When using elements made by tin casting, the vortex beams are generated with a distorted profile due to the presence of residual deformations of tin, which has plasticity. Due to their high conductivity, metallic reflecting elements can be used with high power density sub-THz radiation sources such as free electron lasers and gyrotrons.

Analytical Study of Damped Standing Longitudinal MHD Waves in Flowing Coronal Loops: The Effect of Thermal Conduction

The longitudinal magnetohydrodynamic (MHD) oscillations of coronal loops have been investigated in dissipative flowing loops. Thermal conduction has been considered as the damping mechanism of the wave. We aim to construct the damped longitudinal waves by superposing two propagating waves that propagate in opposite directions. The two propagating components must have the same oscillation frequencies and damping rates, which has been described impossible by some authors, but we have used a technique to overcome this difficulty. The equations of motion are combined to obtain a differential equation for the velocity perturbation. Using the weak damping condition, the perturbation method is used to solve the dispersion relation. In the leading order approximation, the oscillation frequency of the standing waves is determined. In the first-order approximation, we let both the oscillation frequency and wavelength of the propagating waves be perturbed due to the presence of thermal conduction, which enables us to determine the damping rate of the standing waves. Our results show that the plasma flow is an essential parameter in determining the effectiveness of the damping mechanism. Also, the exact solutions of the dispersion relation have been determined without using weak damping assumption. Interestingly the two solutions are the same. Introducing plasma flow to the coronal loop causes the period ratio of the fundamental mode to the first overtone to decrease more.

Asymptotic Series of the Associated Legendre Function with Respect to Seismic Surface Waves

The asymptotic series of the associated Legendre function is investigated for the angular degrees n=2-13 in the context of the amplitude and wavelength of seismic surface waves. The approximate formula for the associated Legendre function is used to determine the wavelength and phase velocity of free oscillations of the Earth and long-period surface waves. The approximate formula is derived from the first term of the asymptotic series and its error increases with decreasing n. In the present study, the effect of higher terms on the approximate formula is studied with respect to the amplitudes of the 1st term (a1), the 2nd term (a2), and the 3rd term (a3). For the colatitude angle θ of π/3≦θ≦2π/3, the amplitude ratios a2/a1 are approximately 3.5％-1.0％ for n=2-11 and are less than 1.0％ for n ≧ 12, while the amplitude ratios a3/a1 are approximately 0.4％ - 0.03％ for n=2-13. The effect of amplitudes of higher terms on the 1st term increases as the colatitude angle approaches the pole or the antipode. The wavelengths of the 1st term (λ1) , the 2nd term (λ2) , and the 3rd term (λ3) are in the sequence λ1 >λ2 >λ3. The wavelength ratiosλ2 /λ1 and λ3 >λ1 for n=2-13 are 0.71%-0.93% and 0.55%-0.87%, respectively. The relationship of the wavelengths between the different angular degrees may be expressed as λ n k =λn-1k+1, where n and k are respectively the angular degree and the ordinal number of the asymptotic series.

Structural, linear/non-linear optical, and optoelectrical properties of PVB/Bi2WO6 nanocomposite for industrial applications

Nanocomposite films composed of polyvinyl butyral (PVB) and Bi2WO6 were produced through solution casting. The goal of this investigation was to examine the effects of different Bi2WO6 concentrations (0%, 2%, and 4% wt.) on the linear/non-linear optical and optoelectrical properties, as well as the structure and dispersion of films of PVB/Bi2WO6 nanocomposite. The direct band gap Eg1 value falls from 5.1 eV to 3.83 eV with the progressive increase in Bi2WO6 content from 0% to 4% wt., while indirect band gap Eg2 decreased from 4.1 eV to 2.89 eV. Conversely, the PVB + 4% Bi2WO6 nanocomposite increased Urbach’s energy (EU) from 1.00 eV for pure PVB to 1.97 eV. Moreover, our research has documented the impact of different concentrations of Bi2WO6 on a range of optical properties, including the refractive index ( n), extinction coefficient ( k), and other pertinent parameters. Utilizing the real and imaginary components of the dielectric constants εr and εi, an investigation was carried out into the dielectrics’ behavior and the optoelectrical parameters’ calculation. Furthermore, investigations were performed on the linear optical susceptibility, the non-linear refractive index, and the third-order non-linear optical susceptibility concerning the concentrations of Bi2WO6. In addition, the results indicated that varying Bi2WO6 concentrations substantially affect the oscillator strength, average oscillator wavelength, and optical conductivity. The nanocomposite films of PVB/Bi2WO6 concentrations exhibited favorable associations between their optoelectrical and non-linear/linear optical parameters, rendering them viable candidates for implementation in flexible electronic devices and radiation shielding.

Demonstration of a violet-distributed feedback laser with fairly small temperature dependence in current-light characteristics

We have developed a GaN-based distributed feedback laser diode (DFB-LD) with the detuning of +5 nm to obtain a smaller temperature dependence of the threshold current. We found that the current-light characteristics almost overlapped up to 300 mW between 25 °C and 80 °C. The estimated characteristic temperature is about 2550 K. These indicate that our DFB-LD is promising for applications that require small temperature dependence in the output power and oscillation wavelength at constant operation current without precise temperature control.

Resonant graviton-photon transitions with cosmological stochastic magnetic field

We explore the possibility of detecting resonant conversions of high frequency gravitational waves to radio-signals. We show how the graviton-photon transitions, from Gertsenshtein effect, can be resonantly amplified in a cosmological stochastic magnetic background. In particular, we found parametric resonances for both the monochromatic and scale invariant power spectrum models of magnetic field fluctuations. Our results substantially departs from those predicted in resonance-less magnetic domain-like models in a large region of magnetic and oscillation wavelength scales. Resonances can be tested by radio telescopes such as ARCADE 2 and EDGES as a probe of high frequency gravitational wave sources and new physics models for magnetogenesis. Analysis are performed with a robust perturbative approach in discrete scheme for including cosmological decoherence in graviton-photon oscillations.

Optical properties of synthesized PVA/Cellulose phosphate composite films doped with Zn2+ ions for optical device applications

In this work, composite films of polyvinyl alcohol/cellulose phosphate doped with Zn2+ (PVA/CP/Zn2+) were prepared through a film casting procedure. The prepared films were analyzed using XRD, FTIR, TGA, and SEM. The XRD revealed a decrease in the semi-crystalline nature as Zn2+ concentrations increased. The TGA showed enhanced thermal stability for the composite films, where the SEM images illustrated the formation of a non-homogeneous surface morphology. The transmittance-absorption spectroscopic measurements showed a noticeable decrease in both the indirect energy gap (Eig) and the direct energy gap (Eg). Eig was decreased from 5.05 to 4.77 eV and Eg decreased from 5.51 eV to 5.12 eV with increasing Zn2+ concentration from zero to 14 wt%. Moreover, the transition strength (Ed), oscillator wavelength (λo), and the excitation energy (Es) were found to increase as Zn2+ content increased. These findings not only shed light on the physicochemical attributes of the prepared films but also emphasize their promising potential utilization in optical components.

Optical and optoelectronic properties of gallium oxide films fabricated by the chemical vapour deposition method

The present work investigated the influence of growth time on the structural, optical, and optoelectronic properties of β-Ga2O3 films produced on Si substrates by the chemical vapour deposition method. The prepared films were characterized by X-ray diffraction, field-emission scanning electron microscope, and UV–Vis spectrophotometer. The films exhibited a mixed phase (β-α)-Ga2O3 crystal structure. The crystallite size ranged between 34.98 and 164.69 nm. The bandgap increased from 4.74 to 4.88 eV. The absorption and extinction coefficients were in the orders of 103 and 10−1, respectively. The refractive index, dispersive energy and single oscillator energy increased from 1.86 to 1.87, 19.24 to 28.64, and 8.36 to 9.54, respectively, with an increase of growth time. The oscillator strength, oscillator wavelength, third-order nonlinear optical susceptibility and dispersion of refractive index were in the orders of 10−4, 10−2, 10−10 and 10−9, respectively. The carrier concentration, optical conductivity, optical mobility, and optical resistivity were also evaluated. The real and imaginary dielectric constants, and plasmon frequency were also determined.

Multi-channel synthetic aperture infrared imaging and experimental research.

The synthetic aperture infrared radio imaging method based on laser local oscillator coherent detection has potential application value for astronomical observations. This paper studies the multi-channel synthetic aperture infrared imaging method and conducts experimental verification using a principle prototype. In the short-wave infrared band, five beam-expanding fiber collimators are used to build an observation structure of five laser local oscillator coherent detection channels at a near-field distance of 5m to carry out physical experiments. The laser local oscillator wavelength is 1.55µm, and the AD sampling rate is 4GHz. For the infrared radiation source signal, the phase relationship of the infrared signals between channels acquired by the prototype principle is stable, and the five-channel synthetic aperture imaging results are consistent with the computer simulated results. The experiment verified the effectiveness of the laser local oscillator comprehensive aperture infrared radio imaging method.

Influence of the content of stacked ZnO on the structural and optical properties of heterostructured ZnO/Ga2O3 films

The rising demand for heterojunction materials stimulated by the great achievements of modern nanotechnology has triggered enormous interests in the investigation of their materials properties. Heterostructured ZnO/Ga2O3 has been deployed for different device applications, but its several optical parameters have rarely been investigated. The present work attempts to investigate the influence of the thickness of stacked ZnO layer on the surface of Ga2O3 film. Optical parameters, such as absorption and extinction coefficient, Urbach energy, refractive index, dielectric constants, optical dispersion energy, single oscillator energy, static refractive index, oscillator strength, and oscillator wavelength of the ZnO/Ga2O3 films were studied. Morphological characterization showed microstructures of various shapes. Cross-section measurements showed that the thickness of the Ga2O3 layer remained approximately the same for all samples, while the thickness of the ZnO layer increased from 0 to 5.14 nm. Structural analysis revealed the coexistence of β-Ga2O3 and wurtzite ZnO crystal phases. UV–Vis absorption spectra demonstrated two distinct absorptions belonging to the β-Ga2O3 and ZnO. The bandgap of the composite ranged between 4.43 and 4.69 eV with an increase in the amount of ZnO at the surface. The absorption and extinction coefficient were in the order of 103 cm−1 and 10−5, respectively. The Urbach energy ranged between 0.688 and 1.125 eV. The refractive index was in the range 2.09–2.85, while the static refractive index ranged between 1.90 and 2.73. Also reported were other optical parameters, such as the real and imaginary dielectric constant, dispersive energy, single oscillator energy, oscillator strength, and oscillator wavelength.

Flame transfer function analysis of hydrogen diffusion swirl flames

This paper investigates the first Flame Transfer Functions (FTFs) of hydrogen diffusion swirl flames, which are crucial for predicting and mitigating thermoacoustic instabilities. Given the need to develop new combustion technologies for hydrogen, it is therefore essential to accurately measure and analyze these FTFs. Employing acoustic and optical methods, we obtained the FTFs over a wide frequency range from 50 to 1000 Hz. Using the acoustic method, the FTFs are deduced from the flame transfer matrices. The FTFs exhibit a low-pass filter behavior with gains decreasing significantly above 150 Hz. Strouhal number normalization effectively collapses the FTFs across various thermal powers, bulk mass flow rates and global equivalence ratios. This result suggests that a generic flame response to acoustic perturbations exists and that the FTF can be interpolated over a range of operating conditions. This study identifies two dominant combustion modes in these hydrogen diffusion swirl flames: a diffusion-mode thin reaction layer near the nozzle and a partially premixed thicker reaction layer downstream. Phase-averaged OH* and OH-PLIF imaging revealed non-uniform transversal oscillations of the reaction zone, offering key insights into the complex swirling flow and the convective wavelength of the coherent heat release rate oscillations along these turbulent hydrogen diffusion swirl flames.

STABILITY OF THE INTERFACE OF LIQUIDS OSCILLATING IN A VERTICAL FLAT CHANNEL

The stability of an oscillating interface between two immiscible low-viscosity fluids of different densities in a vertical flat channel with a harmonic change in the liquid flow rate is studied experimentally. The limiting case of high dimensionless oscillation frequencies when the layer width exceeds the thickness of the Stokes layer is considered. It is found that a standing wave with a length significantly exceeding the gap width develops on the oscillating interface upon reaching a critical amplitude. It is shown that the discovered oscillations are gravity-capillary waves similar to Faraday ripples oscillating with the frequency of the driving force. The wavelength is determined by the interface oscillation frequency and the gravity acceleration and agrees well with the wavelength of gravity-capillary oscillations of the interface. A description of a new phenomenon is given.

Tailoring Optoelectronic Properties of ZnO Nanoparticles via Incorporation of Multiwalled Carbon Nanotube Contents on of ZnO/MWCNT Nanocomposites

The present study demonstrates the tailoring of optoelectronic properties of ZnO nanoparticles (NPs) by adding multi-walled carbon nanotubes (MWCNTs) at different weight ratios. ZnO/MWCNT nanocomposites were successfully prepared using the solution blending method, and the optical spectra of all samples were determined using a UV–vis spectrometer. An increase in the optical absorption coefficient (α) and extinction coefficient (k) was observed with an increase in MWCNT content, resulting in the significant ability to attenuate incident light in ZnO/MWCNT nanocomposites compared to pure ZnO NPs. The optical band gap of pure ZnO NPs decreased from 3.26 eV to 2.58 eV in the ZnO/50 wt% MWCNT nanocomposite. The refractive index values ranged from 1.66 to 1.61 as the wavelength varied between 400 nm and 700 nm. Furthermore, the incorporation of MWCNTs in the ZnO/MWCNT nanocomposite had an impact on various dispersion parameters related to the refractive index. With increasing MWCNT content, the dielectric constant (ε 0) decreased from 2.40 to 1.96, while the mean oscillator wavelength (λ 0) increased from 157.7 nm to 164.2 nm and the oscillator strength (S0) decreased from 5.93 × 10−5 nm−2 to 3.70 × 10−6 nm−2. The localized density of state (N/m*) increased from 7.45 × 1057 to 20.8 × 1057 (m3 Kg) −1, and the long wavelength refractive index (ε ∞) rose from 3.683 to 4.745. Moreover, the plasma frequency (ω p) of the electron exhibited an increase from 2.15 × 1031 to 6.01 × 1031 Hz. These findings highlight the potential of tailoring the optoelectronic properties of ZnO NPs through the incorporation of MWCNTs, paving the way for the development of novel materials with improved optoelectronic characteristics for a wide range of applications.

A Note on the Approximate Formula for the Associated Legendre Function

The approximate formula for the associated Legendre function has been used for the determination of the wavelength and phase velocity of free oscillations of the Earth and long-period surface waves. The approximate formula is defined for several mathematical parameters. One of them is n >>1/ε, where n is the angular degree and εis a parameter related to the colatitude angle θ. In the present study the relationship between n and ε is defined as n0 = [ 1/ε ] +1, where the notation [ ] denotes the Gaussian symbol. If a condition n ≧ n0 (n>1/ε ) is assumed, the approximate formula may be reasonably applied for the angular degrees n ≧2 for π/6≦θ≦5π/6. This condition is in harmony with the practical usage implemented conventionally.

Gamma irradiation-induced changes in structural, linear/nonlinear optical, and optoelectrical properties of PVB/BiVO4 nanocomposite for organic electronic devices

Herein, nanocomposite films based on polyvinyl butyral (PVB) and BiVO4 plates were synthesized through solution casting. The present study aims to investigate the impact of varying doses of gamma irradiation (0, 15, 30, 60, and 90 kGy) on the structural, dispersion, linear/nonlinear optical, and optoelectrical properties of PVB/BiVO4 nanocomposite films. The effects of gamma irradiation on various optical characteristics, such as refractive index (n), extinction coefficient (k), and other related parameters, have been observed. The study of dielectric behavior and the derivation of optoelectrical parameters, including high-frequency dielectric constant (ε∞), plasma frequency (ωP), relaxation time (τ), and optical mobility (µopt.), were conducted using the real and imaginary parts of the dielectric constants εr and εi. In addition, the linear optical susceptibility (χ(1)), the third-order nonlinear optical susceptibility (χ(3)), and the nonlinear refractive index (n2) were studied as a function of gamma irradiation doses. Furthermore, the results demonstrate that the average oscillator wavelength (λ0) values, oscillator strength (S0), and optical conductivity (σopt) vary significantly after gamma radiation treatment. Overall, the strong correlations between the linear/nonlinear optical and optoelectrical parameters of the irradiated PVB/BiVO4 nanocomposite films make them suitable for application in flexible organic electronic devices.

What Are the Balanced and Unbalanced Dynamics of a Tropical Cyclone?

Abstract Recently, Ji and Qiao took into account the unbalanced components and derived an extended Sawyer–Eliassen (SE) equation. This study developed a new derivation of this extended SE equation from the perspective of restoring forces, and gives a physical interpretation for the coefficients that appear in the SE equation. For an unbalanced vortex, we demonstrated that the thermodynamic fields are only determined by the distribution of gradient wind, and thus, the gradient wind and thermodynamic fields always remain in balance as the unbalanced vortex evolves. Consequently, we attributed the gradient wind imbalance to the agradient wind rather than to the thermodynamic fields. Subsequently, we explored the effect of the agradient wind on the secondary circulation, and showed that the agradient wind strengthens the secondary circulation in its vicinity, which can be explained as a consequence of the restoring forces and mass continuity. Furthermore, we speculated that the SE equation, together with the radial velocity equation, could reproduce the primary characteristic of the axisymmetric boundary layer dynamics by prescribing the parameterization of subgrid-scale turbulent mixing. Specifically, the noU_BL and noVa_BL experiments conducted by Fei et al. in an article published in 2021 were reinterpreted, and the oscillation wavelength of the agradient wind in the eyewall was approximated based on this framework. Additionally, a new numerical solution algorithm to overcome the hyperbolicity near the boundary layer was proposed. This study attempts to develop a complete dynamic theory for tropical cyclones in both qualitative and quantitative perspectives.

Experimental study of the injection angle impact on the column Waves: Wavelength, frequency and drop size

An experimental study was performed to investigate the influence of injection angle on further details of breakup of a circular liquid jet injected into an airstream. Wavelength and frequency of axial oscillations caused by column waves, drops size distribution, orientation and aspect ratio of these drops were measured and reported. Injection angles between 30 and 90 degrees were considered. High-speed photography and shadowgraphy techniques were utilized to visualize and record the flow. Experimental data were obtained by processing images with the help of an in-house developed code. We found that gas Weber number and the injection angle are influential on wavelength and frequency of the column waves. The wavelength decreased and the frequency increased with increasing gas Weber number or decreasing the injection angle. Also, momentum ratio, gas Weber number and injection angle were affecting drop's average diameter. By reducing the injection angle, the atomization process was prolonged and the produced drops were larger. Although the injection angle affected the average drop size and number, as long as the regime was not changed, the probability distribution of drop size was independent of the injection angle.We extended theory of Ng et al. [1] to estimate wavelength, frequency of column waves formed on the liquid jet that was injected into an airstream to account for injection angle. A relative gas Weber number was defined by using the relative velocity of the gas to that of the liquid along the flow direction. The introduced relative gas Weber number was found useful in classifying the breakup regimes of the flow. A relation was proposed to estimate these wavelengths with good agreement with our data at different injection angles and other previously published data at normal injection of liquid jets. Two separate correlations for SMD estimation were proposed for before and after bag formation in the flow.

Thickness Dependence on Wavelength Range of Random Laser in Ultrathin ZnO Crystals Grown by Mist-CVD on C-plane Sapphire Substrate

The ultrathin ZnO crystals were grown by mist chemical vapor deposition technique with potentially low-cost and low-environmental impact on commercially available c-plane sapphire substrates. The photoluminescence spectra of the ultrathin ZnO crystals were evaluated, and we observed the random lasing behaviors. In addition, the range of random laser wavelengths of photoluminescence can be shifted with a constant trend by changing the structural parameters of the ultrathin ZnO crystals. Here, the structural parameter was the thickness of the ultrathin ZnO crystals. The results indicate that the oscillation wavelength range of the random laser may be potentially fine-tuned by changing the structural parameters of the random laser medium.

Temperature-independent lasing wavelength of highly stacked InAs quantum dot laser fabricated on InP(311)B substrate with Bi irradiation.

In this study, the effects of bismuth (Bi) irradiation on InAs quantum dot (QD) lasers operating in the telecommunication wavelength band were investigated. Highly stacked InAs QDs were grown on an InP(311)B substrate under Bi irradiation, and a broad-area laser was fabricated. In the lasing operation, the threshold currents were almost the same, regardless of Bi irradiation at room temperature. These QD lasers were operated at temperatures between 20 and 75°C, indicating the possibility of high-temperature operation. In addition, the temperature dependence of the oscillation wavelength changed from 0.531 nm/K to 0.168 nm/K using Bi in the temperature range 20-75°C.