Small Intensity Research Articles

DYNAMIC BEHAVIOR OF TWO ELASTICALLY CONNECTED NANOBEAMS UNDER A WHITE NOISE PROCESS

This paper investigates the almost-sure and moment stability of a double nanobeam system under stochastic compressive axial loading. By means of the Lyapunov exponent and the moment Lyapunov exponent method the stochastic stability of the nano system is analyzed for different system parameters under an axial load modeled as a wideband white noise process. The method of regular perturbation is used to determine the explicit asymptotic expressions for these exponents in the presence of small intensity noises.

Structural, optical, mechanical, and electronic properties of Cr-doped alumina

Cr-doped α-Al2O3 samples (Al2−xCrxO3, 0 ≤ x ≤ 0.25; step 0.05) were synthesized by citrate-precursor autocombustion method. The lattice parameters, bond distortion index, crystallite size, and lattice microstrain of the developed system were investigated using Rietveld profile method. The porous nature of the formed samples was elucidated by a scanning electron microscope. The effect of doping on the vibrational band positions was examined using Fourier-transform infrared technique. The photoluminescence emission showed that a red color was mainly exhibited by all samples, while that with x = 0.05 showed the highest intensity. Other colors appear with a small intensity for higher Cr-doped samples. The electronic, optical, and mechanical stability properties of undoped and doped samples were investigated using density-functional theory calculation.

Subterahertz refractive flat-top beam shaping via 3D printed aspheric lens combination

The viability of 3D printed aspheric lenses for the purpose of frequency-scalable subterahertz Gaussian to flat-top beam shaping is evaluated. A cylindrical one-dimensional Fresnel–Kirchhoff diffraction equation was implemented in Matlab and used to design a pair of aspheric lenses with customized vertex radius of curvature and conic constant. The lenses were printed at maximum possible resolution in acrylonitrile butadiene styrene ( n = 1.6 ) and tested with a 102 GHz continuous-wave subterahertz source. The aspheric lens combination produced a flat-top profile from a low-quality incident Gaussian beam at the minimal cost of 3D printing substrate. The flat-top profile exhibited small ( < 14 % root-mean-square deviation over a flat region) intensity fluctuations and is expected to prove useful in future terahertz applications that require a high degree of beam uniformity.

Evolution of structural and magnetic properties of multifunctional bismuth iron garnets upon Ca and Y doping

A multiscale approach is reported to understand the influence of the Ca and Y co-substitution in Bi-rich iron garnet thin films. Recently, it has been demonstrated that site-selective co-substitution of ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Y}}^{3+}$ in bismuth iron garnet (BIG) leads to either $n$- or $p$-type semiconductor behavior. However, the evolution of the structural and magnetic properties of bismuth iron garnet upon doping is still unknown. In the (Ca,Y):BIG, thin films grown by pulsed laser deposition onto ${\mathrm{Gd}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}$ substrates, structural investigations confirm the epitaxial growth of doped thin films with high crystallinity and a complete strain relaxation from 20 nm above the film/substrate interface. While x-ray diffraction only evidences a single-phase garnet, the presence of secondary phase nanocrystallites, that are absent in pure BIG grown in similar conditions, is observed by aberration-corrected scanning transmission electron microscopy. These nanocrystallites form in between garnet grains as textured and poorly crystallized hematite. Despite the presence of nanoneedles, Ca and Y co-substitution preserves the giant Faraday rotation of pure BIG and maintains the Curie temperature above 590 K. Only minor energy shifts (80 meV) or small intensity changes (10%) of the Faraday rotation are observed upon doping or annealing and are mainly related to band-gap evolution and cell volume change. Furthermore, the easy magnetization axis rotates towards in the out-of-plane direction upon doping which is also promising for potential applications in spintronics.

The role of stony soils in hillslope and catchment runoff formation

Abstract The role of stony soils in runoff response of mountain catchments is rarely studied. We have compared simulated response of stony soils with measured catchment runoff for events caused by rains of small and high intensities in the mountain catchment of the Jalovecký Creek, Slovakia. The soil water response was simulated for three sites with stoniness 10–65% using the Hydrus-2D single porosity model. Soil hydraulic parameters employed in the modelling, i. e. the saturated hydraulic conductivity and parameters of the soil water retention curves, were obtained by two approaches, namely by the Representative Elementary Volume approach (REVa) and by the inverse modelling with Hydrus-1D model (IMa). The soil water outflow hydrographs simulated by Hydrus-2D were compared to catchment runoff hydrographs by analysing their skewness and peak times. Measured catchment runoff hydrographs were similar to simulated soil water outflow hydrographs for about a half of rainfall events. Interestingly, most of them were caused by rainfalls with small intensity (below 2.5 mm/10 min). The REV approach to derive soil hydraulic parameters for soil water outflow modelling provided more realistic shapes of soil water outflow hydrographs and peak times than the IMa approach.

Regimes of thermo-compositional convection and related dynamos in rotating spherical shells

Convection and magnetic field generation in the Earth and planetary interiors are driven by both thermal and compositional gradients. In this work numerical simulations of finite-amplitude double-diffusive convection and dynamo action in rapidly rotating spherical shells full of incompressible two-component electrically-conducting fluid are reported. Four distinct regimes of rotating double-diffusive convection identified in a recent linear analysis (Silva, Mather and Simitev, Geophys. Astrophys. Fluid Dyn. 2019, 113, 377) are found to persist significantly beyond the onset of instability while their regime transitions remain abrupt. In the semi-convecting and the fingering regimes characteristic flow velocities are small compared to those in the thermally- and compositionally-dominated overturning regimes, while zonal flows remain weak in all regimes apart from the thermally-dominated one. Compositionally-dominated overturning convection exhibits significantly narrower azimuthal structures compared to all other regimes while differential rotation becomes the dominant flow component in the thermally-dominated case as driving is increased. Dynamo action occurs in all regimes apart from the regime of fingering convection. While dynamos persist in the semi-convective regime they are very much impaired by small flow intensities and very weak differential rotation in this regime which makes poloidal to toroidal field conversion problematic. The dynamos in the thermally-dominated regime include oscillating dipolar, quadrupolar and multipolar cases similar to the ones known from earlier parameter studies. Dynamos in the compositionally-dominated regime exhibit subdued temporal variation and remain predominantly dipolar due to weak zonal flow in this regime. These results significantly enhance our understanding of the primary drivers of planetary core flows and magnetic fields.

Influences of Low Intensity on Diode Parameters of CdTe Solar Cells.

This study deals with the CdS/CdTe solar cells under low illumination intensity, with cell #1 for the shunt resistance exceeding 100,000 Ω·cm2 and cell #2 for the shunt resistance above 1000 Ω·cm2. The diode parameter variations with the decline of the irradiance intensity are illustrated by dividing 0–100 mW/cm−2 into a number of small intensity ranges for J–V measurements and assuming the diode parameters to be constant within each range, the diode parameters of each range including the series resistance, the shunt resistance, the reverse saturation current density and the ideality factor are then extracted by employing an analytical approach. The mechanism of the cell performance deviations are also investigated by basic theories, reports and experiments. For cell #1 with higher Rsh corresponding to less traps, Rsh shows a upward tendency as the irradiance declines, n and J0 exhibit a rise with the irradiance and keep nearly unchanged at the low irradiance values mainly due to recombination and carrier contributions, Rs shows a slight increase when the irradiance intensity goes down because of the resistance of CdTe absorption layer. For cell #2 with lower Rsh corresponding to more traps, with the decrease of the illumination intensity, Rsh increases sharply only for captured carrier reduction, Rs goes steadily up similarly, n and J0 exhibit a decline with the irradiance due to recombination shift. It should be pointed out that Rs varies much smoother than the traditional approximation of a reciprocal of differential at short circuit, and the distribution of Rsh is diverse, and an average Rsh of for each intensity range can reflect the variation trend.

Investigation of characteristics of bamboo fiber for composite structures

Bamboo fibers have been used for reinforcements in structural composites because of their environmental friendly properties. The purpose of this study was to investigate the characteristics of three types of bamboo, namely Tali bamboo, Gombong bamboo and Haur Hejo bamboo to meet the requirements for a reinforcement in structural composites. The three types of bamboo fibers were alkaline treated by varying the concentrations of NaOH (4% and 6%), and immersion times (1, 2, and 3 hours). The alkaline pre-treatment was conducted at the temperature of 120°C and the pressure of 0.5 MPa using a steam explosion method. The treated bamboo fibers were characterized by FTIR and measured their tensile strengths. The tensile test results showed that the tensile strengths of Tali, Gombong, and Haur Hejo bamboss were 710 MPa, 418 MPa, and 457 MPa respectively. Whereas, the FTIR analysis indicated that there was still a peak of lignin with small intensity marked by aromatic C = C (alkyne) at the wavelength of 1500-2600 cm−1 for all types of bamboo. There was also a peak of cellulose with an increase in the intensity marked by the aromatic group C = H (alkene) at the wavelength of 1900-2400.

Incorporation of turbulence in a nonlinear wake-oscillator model for the prediction of unsteady galloping response

The aeroelastic behavior of certain slender bluff bodies is known to be dominated in smooth flow by the interference of vortex-induced vibration and transverse galloping. In turbulent flow, wind tunnel experiments revealed a more complicated behavior, with some features that have not been fully understood yet. With the aim to explain the oscillation response observed for a sharp-edge rectangular cylinder with a side ratio of 1.5 and to make a step ahead in the simulation of the self-excited behavior of such bodies, a nonlinear wake-oscillator model that provided promising results in smooth flow is considered. The differential equations are randomized to account for the contribution of three-dimensional, partially-correlated, turbulent velocity fluctuations attacking the structure. Given the physical basis of the mathematical model, all the parameters but one are estimated based on wind tunnel tests on a stationary sectional model. In contrast, given the lack of wake measurements, one of the coupling coefficients in the equations is calibrated based on the cylinder response for a given value of the nondimensional mass-damping parameter (Scruton number). Then, the model is used to predict the vibrations recorded for very different values of the Scruton number, showing satisfactory accuracy. This fact highlights the key role played, even in turbulent flow, by vortex shedding and the importance of its nonlinear interaction with oncoming wind velocity fluctuations. The equations are also used to investigate the effect of turbulence intensity and integral length scale. In agreement with the experimental evidence, the response of the cylinder is found to be little sensitive to flow velocity fluctuations with small intensity (say, less than about 4%), but is remarkably affected by strong turbulence. The simulations also disclose a significant influence on the vibration amplitude of the integral length scale of turbulence. Finally, the proposed model might represent a useful engineering tool to estimate the unsteady galloping behavior of a slender structure immersed in a realistic large-scale turbulent flow, which seldom can be correctly reproduced in the wind tunnel.

A new thermo-time domain reflectometry approach to quantify soil ice content at temperatures near the freezing point

Soil ice content (θi) is an important property for many studies associated with cold regions. In situ quantification of θi with thermo-time domain reflectometry (TDR) at temperatures near the freezing point has been difficult. The objective of this study is to propose and test a new thermo-TDR approach to determine θi. First, the liquid water content (θl) of a partially frozen soil is determined from a TDR waveform. Next, a pulse of heat is applied through the thermo-TDR sensor to melt the ice in the partially frozen soil. Then, a second TDR waveform is obtained after melting to determine the θl, which is equivalent to the total water content (θt) of the partially frozen soil. Finally, θi is calculated as the difference between θt and θl. The performance of the new approach was evaluated in sand and loam soils at a variety of θt values. The new approach estimated θt, θl, and θi accurately. The root mean square errors (RMSE) of estimation were 0.013, 0.020, and 0.023 m3 m−3 for sand, and 0.041, 0.026, and 0.031 m3 m−3 for loam. These RMSE values are smaller than those reported in earlier thermo-TDR studies. Repeating the thermo-TDR measurements at the same location on the same soil sample caused decreased accuracy of estimated values, because of radial water transfer away from the heater tube of the thermo-TDR sensor. Further research is needed to determine if it is possible to obtain accurate repeated measurements. The use of a dielectric mixing model to convert the soil apparent dielectric constant to θl improved the accuracy of this approach. In our investigation, application of a small heat intensity until the partially frozen soil temperature became larger than about 1 °C was favorable. The new method was shown to be suitable for estimating ice contents in soil at temperatures between 0 °C and − 2 °C, and it could be combined with the volumetric heat capacity or thermal conductivity thermo-TDR based methods, which measured ice content at colder temperatures. Thus, the thermo-TDR technique could measure θi at all temperatures.

Microphysical Characteristics of Winter Precipitation in Eastern China from 2014 to 2019

To improve solid precipitation monitoring in the hydrology and meteorology field, 1-min precipitation data observed by the PARticle SIze VELocity (PARSIVEL) disdrometer in Nanjing, eastern China, from February 2014 to February 2019 for all days with solid precipitation, were used to study the microphysical characteristics of winter precipitation. In this study, the empirical V-D (velocity–diameter) relationships and observed surface temperature are used for matching precipitation types, and the precipitation data are divided into rain, graupel, wet snow and dry snow. The results show that dry snow and wet snow have maximum Dm (mass-weighted mean diameter) and minimum log10Nw (normalized intercept parameter), while rain shows the opposite. Additionally, the μ-Λ (shape parameter–slope parameter) curve of dry snow and wet snow is very close, and the μ value of dry snow and wet snow is higher than that of graupel and higher than that of rain for the same Λ value. Furthermore, the Ze-S (equivalent reflectivity factor–precipitation intensity) relationships among different types of precipitation are significantly different. If only the Ze-S relationship of rain is used for quantitative precipitation estimation (QPE), then, for small precipitation intensity, solid precipitation will be overestimated, while, for large precipitation intensity, it will be underestimated.

Compatibility of advanced tritium breeders and neutron multipliers

Abstract A new blanket concept of demonstration (DEMO) fusion reactors has been suggested using a mixture of tritium breeders and neutron multipliers. This concept requires long-term stability between tritium breeders and neutron multipliers. To verify the feasibility of the mixing pebble packing concept, compatibility tests of Li-access Li2+xTiO3+y with 20 % Li2ZrO3 (hereinafter referred to as LTZO) and Be12V as an advanced tritium breeder and neutron multiplier, respectively were performed at 973 K, 1073 K, and 1173 K for 100 h, 300 h, and 1000 h, respectively. Cross-sectional scanning electron microscopic observations and X-ray diffraction (XRD) analysis revealed that Be oxides (Li with small intensity) were formed on the surface of Be, however, no reaction layer or a very thin layer was identified. Clarity was received that as the time at each temperature increased, the thickness tended to increase. The thickness of the reaction layer could be described by a parabolic rate law. The conclusion was reached that Be12V in contact with LTZO had a reaction layer whose growth rate was considerably lower by one order of magnitude than that of Be in contact with LTZO.

Asymptotic Accuracy in Estimation of a Fractional Signal in a Small White Noise

The problem of estimating the fractional Ornstein—Uhlenbeck process observed in a linear channel with white noise of small intensity is considered. Exact asymptotic formulas of the error of the filtering and interpolation estimates are obtained. The accuracy analysis is based on approximations of the eigenvalues and eigenfunctions of the signal’s covariance operator.

АСИМПТОТИКА ТОЧНОСТИ ОЦЕНКИ ДРОБНОГО СИГНАЛА В МАЛОМ БЕЛОМ ШУМЕ

This paper revisits the problem of estimating the fractional Ornstein - Uhlenbeck process observed in a linear channel with white noise of small intensity. We drive the exact asymptotic formulas for the mean square errors of the filtering and interpolation estimators. The asymptotic analysis is based on approximations of the eigenvalues and eigenfunctions of the signal's covariance operator.

Colliding solids interactions of earthquake-induced nonlinear structural pounding under stochastic excitation

A simplified analysis model of structural pounding, used in the study of the effects of earthquakes subjected to Gaussian white noise of relatively high intensity, filtered through a Kanai-Tajimi filter is proposed in this investigation. The required distance to avoid pounding is important in structural engineering. As a consequence of frictional contact phenomena, energy is dissipated and the state of a system can change slowly and rapidly, depending on the nature of the contact, continuous or impact condition. Buildings without enough separation often create structural pounding under seismic events. Other effects associated with friction in mechanical systems are the vibration and noise propagation of the system components, nonlinear systems behavior and wear. In this paper, we prove that because of the inherent stochastic nature of the applied earthquake loads or the uncertainty arising from randomness (non-smooth behavior), stochastic p-bifurcations occur at law noise intensities and disappear when increasing noise intensities. Because of the presence of both impact-friction events, p-bifurcations should be observed at weak noise intensities. P-bifurcation occurs and created instability that will increase pounding effects. Some relationship between impact-friction events appears: small noise intensity occurs when the time of friction (continuous) is greater than the impacting events, hence high probability density function (PDF). But if the noise intensity increases, the impact events are great (small friction) with weak PDF. But successive jump effects can create noisy system and great impact. The models stochastic processes of stationary probability density function (PDF) of the earthquake ground motion are set up. The demonstrative application examples which include friction in systems involving contact-impact events are illustrated in Central Africa, a part of Congo Stable Block.

Enhancement of the Multiplexing Capacity and Measurement Accuracy of FBG Sensor System Using IWDM Technique and Deep Learning Algorithm

In this article, we are the first to propose deep learning algorithms for intensity wavelength division multiplexing (IWDM)-based self-healing fiber Bragg grating (FBG) sensor network. A deep learning algorithm is proposed to improve the accuracy of measuring the sensing signal of the sensor system. Furthermore, to increase the total number of FBG sensors multiplexed in the sensor network for multipoint measurements, a multiplexing technique called IWDM is proposed. The proposed IWDM-based ring structure FBG sensor network can also have a self-healing purpose to improve the sensor system's reliability and survivability. However, IWDM has unmeasurable gap or crosstalk problems when the number of FBG sensors increases, which causes high sensing signal measurement errors. To solve this problem, a gated recurrent unit (GRU) deep learning algorithm is proposed and experimentally demonstrated. To prove the sensing signal measurement performance of our proposed algorithm, we test the well-trained GRU model using two cases. The first case is when the spectra of FBGs are overlapped as well as the minimum intensity difference between FBGs is 10%, and the second case is when the spectra of FBGs are overlapped as well as the minimum intensity difference between FBGs is 3% which is a very small intensity difference. From the experimental results, the well-trained GRU algorithm achieves high strain sensing signal measurement performance in both cases compared to other algorithms. Therefore, the proposed IWDM based FBG sensor system using deep learning algorithm enhances the multiplexing capacity and survivability of the sensor system, reduces the computational time, and improves strain sensing signal measurement accuracy of FBGs even when FBGs has very small intensity difference and overlap problem.

Estimate the Primary Parameters of Extreme Earthquake on Banda Sea, Indonesia

Extreme earthquake events always have an impact on human life, when the intensity of events becomes greater than a certain intensity it will cause disaster. The intensity of a small earthquake occurs at any time without significant side effects. Based on statistical analysis it was revealed that earthquakes with greater intensity occur more difficult than small intensities. In the discussion, earthquake data showed that there were fluctuations in earthquake events which indicated a different maximum earthquake. Thus, major disasters occur because a small portion of major events occurs. The Banda Sea Region is an active earthquake area that contains earthquake events above magnitude 5 Richter scale (Rs) each year with a total average of above 815 major earthquake news during 1970-2018. The results of seismic studies in the Banda Sea region show a return period of 7.5 Rs magnitude earthquake quake is around 48 years and a probability of around 0.020%. Magnitude 7.0 Rs earthquake has a repetition interval of around (12-17) years with a probability of around 0.061%. In this study the analysis of earthquake probabilities and earthquake magnitude in the span of 30 years. An earthquake measuring (5.5-6.5) Rs, for example, has a probability of 100%, but if an earthquake measuring 7.7 Rs is chosen, the probability drops to 46%.

Time-Resolved Femtosecond Stimulated Raman Spectra and DFT Anharmonic Vibrational Analysis of an Electronically Excited Rhenium Photosensitizer.

Time-resolved femtosecond stimulated Raman spectra (FSRS) of a prototypical organometallic photosensitizer/photocatalyst ReCl(CO)3(2,2'-bipyridine) were measured in a broad spectral range ∼40-2000 (4000) cm-1 at time delays from 40 fs to 4 ns after 400 nm excitation of the lowest allowed electronic transition. Theoretical ground- and excited-state Raman spectra were obtained by anharmonic vibrational analysis using second-order vibrational perturbation theory on vibrations calculated by harmonic approximation at density functional theory-optimized structures. A good match with anharmonically calculated vibrational frequencies allowed for assigning experimental Raman features to particular vibrations. Observed frequency shifts upon excitation (ν(ReCl) and ν(CC inter-ring) vibrations upward; ν(CC, CN) and ν(Re-C) downward) are consistent with the bonding/antibonding characters of the highest occupied molecular orbital and the lowest unoccupied molecular orbital involved in excitation and support the delocalized formulation of the lowest triplet state as ReCl(CO)3 → bpy charge transfer. FSRS spectra show a mode-specific temporal evolution, providing insights into the intersystem crossing (ISC) mechanism and subsequent relaxation. Most of the Raman features are present at ∼40 fs and exhibit small shifts and intensity changes with time. The 1450-1600 cm-1 group of bands due to CC, CN, and CC(inter-ring) stretching vibrations undergoes extensive restructuring between 40 and ∼150 fs, followed by frequency upshifts and a biexponential (0.38, 21 ps) area growth, indicating progressing charge separation in the course of the formation and relaxation of the lowest triplet state. Early (40-150 fs) restructuring was also observed in the low-frequency range for ν(Re-Cl) and δ(Re-C-O) vibrations that are presumably activated by ISC. FSRS experimental innovations employed to measure low- and high-energy Raman features simultaneously are described and discussed in detail.

Spectral deconvolution in electrophoretic NMR to investigate the migration of neutral molecules in electrolytes.

Electrophoretic nuclear magnetic resonance (eNMR) is a powerful tool in studies of nonaqueous electrolytes, such as ionic liquids. It delivers electrophoretic mobilities of the ionic constituents and thus sheds light on ion correlations. In applications of liquid electrolytes, uncharged additives are often employed, detectable via 1 H NMR. Characterizing their mobility and coordination to charged entities is desirable; however, it is often hampered by small intensities and 1 H signals overlapping with major constituents of the electrolyte. In this work, we evaluate methods of phase analysis of overlapping resonances to yield electrophoretic mobilities even for minor constituents. We use phase-sensitive spectral deconvolution via a set of Lorentz distributions for the investigation of the migration behavior of additives in two different ionic liquid-based lithium salt electrolytes. For vinylene carbonate as an additive, no field-induced drift is observed; thus, its coordination to the Li+ ion does not induce a correlated drift with Li+ . On the other hand, in a solvate ionic liquid with tetraglyme (G4) as an additive, a correlated migration of tetraglyme with lithium as a complex solvate cation is directly proven by eNMR. The phase evaluation procedure of superimposed resonances thus broadens the applicability of eNMR to application-relevant complex electrolyte mixtures containing neutral additives with superimposed resonances.

Delithiated Fe1-xMgxPO4 cathode materials: Structural, magnetic, and Mössbauer studies

Fe1-xMgxPO4 (x = 0.01, 0.05, and 0.1) cathode materials are synthesized by a two-step method, which combines the solid-state reaction method and the chemical lithium deintercalation method. A study was conducted to investigate the structural and the magnetic properties of Fe1-xMgxPO4. The crystalline structure of the samples was analyzed by X-ray diffractometer (XRD) using the Rietveld refinement. The magnetic properties of the samples were determined from vibrating sample magnetometer (VSM) and Mösssbauer spectroscopy, including their magnetic interactions, Fe ion states, and structural ordering. The Néel temperature (TN) of Fe1-xMgxPO4 decreases with the increase of the Mg content due to the weakening of the antiferromagnetic exchange. Furthermore, for Fe1-xMgxPO4, the effective moment value decreases as expected with increasing Mg content. Mössbauer spectroscopy measurements at different temperatures were made. The spectrum at 295 K was fitted with a doublet, which has an isomer shift of δ = 0.32 – 0.43 mm/s (Fe3+). The large value of the electric quadrupole splitting (∆EQ = 0.95 – 1.87 mm/s) is explained by the asymmetric local environment of the Fe ions. Below the TN, the spectra of Fe1-xMgxPO4 in the eight resonance absorption lines (including two relatively small intensities) were analyzed. We can obtain a spin value for Fe ions (S = 5/2) of Fe0.9Mg0.1PO4 from the Brillouin functional analysis.