Dispersion Values Research Articles

Mathematical Physics Analysis of Nozzle Shaping at the Gas Outlet from the Aperture to the Differentially Pumped Chamber in Environmental Scanning Electron Microscopy (ESEM).

A combination of experimental measurement preparations using pressure and temperature sensors in conjunction with the theory of one-dimensional isentropic flow and mathematical physics analyses is presented as a tool for analysis in this paper. Furthermore, the subsequent development of a nozzle for use in environmental electron microscopy between the specimen chamber and the differentially pumped chamber is described. Based on experimental measurements, an analysis of the impact of the nozzle shaping located behind the aperture on the character of the supersonic flow and the resulting dispersion of the electron beam passing through the differential pumped chamber is carried out on the determined pressure ratio using a combination of theory and mathematical physics analyses. The results show that nozzle shapes causing under-expanded gas outflow from the aperture to the nozzle have a worse impact on the dispersion of the primary electron beam. This is due to the flow velocity control. The controlled reduction in the static pressure curve on the primary electron beam path thus causes a significantly higher course of electron dispersion values than variants with shapes causing over-expanded gas outflow.

Dispersity determination of poly(ethylene glycol)s using supercritical fluid chromatography-mass spectrometry and different mass analysers.

Dispersity values are considered critical quality attributes for the quality control of poly(ethylene glycol) formulations due to the direct impact on drug performance. However, when these polymers are analysed using mass spectrometry, the design of the mass analyser can impact the oligomer response and affect the obtained dispersity values, so further understanding is needed. The deconvoluted electrospray ionisation mass spectra of poly(ethylene glycol)s obtained using supercritical fluid chromatography (SFC) hyphenated to different mass analysers were compared, and visualisation diagrams were used to understand the differences in the dispersity value calculations. Five calibration approaches based on a surrogate single oligomer that represents the whole distribution, or the whole distribution itself, for response selection, were used to evaluate ionisation efficiency prior to quantitation. The impact of using an internal standard (ISTD) on the expanded uncertainty was also assessed. Although there were challenges related to the resolution of multiply charged species when low-resolution instruments were used, similar quantitation capabilities were obtained to those when high-resolution mass analysers were used. Evaluation of approaches using a surrogate oligomer or the whole distribution suggested the independence of both approaches and a constant ionisation efficiency across the oligomer chain length. The higher degree of chromatographic resolution of SFC allowed incorporating a monodispersed ISTD to improve the accuracy and precision of the method. The use of low resolution mass analysers was sufficient to provide accurate and precise dispersity values; however, higher resolution instruments were recommended for characterisation due to the improved mass resolution of ions. The introduction of a monodispersed ISTD improved precision without compromising the calculated dispersity value due to the lack of analyte suppression.

Numerical Analysis of Optical Properties Using Octagonal Shaped Ge15As15Se17Te53 Chalcogenide Photonic Crystal Fiber

A novel Ge15As15Se17Te53 chalcogenide-based photonic crystal fiber with an octagonal cladding was designed which exhibits low confinement loss and high nonlinearity. The dispersion properties were investigated over a wide wavelength range of up to 11 µm. Based on preliminary simulation results, three fibers with suitable characteristic quantities are proposed for supercontinuum generation. Among these fibers, fiber #F1 (Ʌ = 3.1 µm, d/Ʌ = 0.3) exhibits all-normal dispersion with a small value of −0.374 ps/[nm.km]. At the same time, the highest nonlinear coefficient of 2876.861 W−1.km−1 at the pump wavelength of 5.45 µm is also found. The #F2 fiber (Ʌ= 4.5 µm, d/Ʌ = 0.3) has anomalous flat dispersion with one zero dispersion wavelength. This fiber has the smallest dispersion and lowest confinement loss values of 0.281 ps/[nm.km] and 1.360×10−9 at 5.7 µm pump wavelength, respectively. With the anomalous dispersion, #F3 fiber (Ʌ = 3.5 µm, d/Ʌ = 0.3) offers a small effective mode area of 20.892 µm2 and a low confinement loss of 4.974×10−8 dB/m at 5.25 µm wavelength. The proposed fibers can be a low peak power, broadband supercontinuum source, suitable for application fields such as optical communication and biomedical sensors.

Characterization of the migration of organic contaminants in laboratory-scale groundwater polluted by underground coal gasification.

Underground coal gasification (UCG) is a promising technology, but the groundwater pollution caused by UCG is a potential risk to the environment. The measured results of the stratum in the combustion cavity resulting from UCG had proven that the combustion cavity would be filled with some UCG residues and caving rocks when UCG was finished. The pollutants in underground water around the combustion cavity include organic pollutants, inorganic pollutants, and ammonia nitrogen, and one of the primary organic pollutants is phenol. The migration and diffusion characteristics of organic pollutants (taking phenol as a representative) in the groundwater of the combustion cavity were investigated by breakthrough experiments and numerical simulations. The results show that the hydraulic conductivity of the coarse UCG residues is much higher than that of fine residues, and the hydraulic conductivity of the UCG residues with the size of - 0.15 mm and 0.15-0.3 mm are 4.68 × 10-6 m/s and 1.91 × 10-4 m/s respectively. The dispersivity λ for the migration of organic pollutants will be influenced significantly by the size of UCG residues in fractures of the combustion cavity, while the distribution coefficient Kd will not. The dispersivity of organic pollutants in the fine UCG residues is more significant than that in the coarse residues, and the λ for the two kinds of residues are 3.868 cm and 1.765 cm, respectively. The shape of the migration path slightly affects the pollutant concentration distribution along the path, but the width of a path has a more pronounced influence on the concentration distribution. In this research, the influence was formulated by a new technical term, MPWIT, which is related to transverse dispersion. Specifically, while the transverse dispersion values account for 20% and 10% of the longitudinal dispersion, respectively, the corresponding MPWIT values are 39.48 mm and 33.96 mm.

Broadband dispersion compensation and high birefringence photonic crystal fiber for CWDM/DWDM networks

In this study, we propose a new design based on photonic crystal fibers (PCFs) for broadband dispersion compensation in telecommunication networks. The proposed design has a hexagonal structure arrangement of air-holes rings of different diameters between the silica core and the cladding. The PCF properties like effective area, nonlinearity, dispersion slope, confinement loss, and birefringence are reported and discussed. For the best performance we present three designs A, B and C. Simulation results show that the three designs cover the six-telecommunication optical bands O-, E-, S-, C-, L- and U- bands (wavelengths ranging from 1260 to 1675 nm). Design A achieves a large negative dispersion value of about − 1716 ps/(nm.km) with relative dispersion slope equals to that of conventional single-mode optical fibers (SMFs) of about 0.0036 nm−1, which makes it very suitable for long-haul DWDM transmission systems. With a little modification in the core, designs B and C achieve much higher confinement ability and achieve a very large birefringence value for polarization mode dispersion and sensing applications. Design C is engineered to have exact opposite dispersion of SMF with zero dispersion at the wavelength 1310 nm, which makes it a promising design in CWDM transmission system. The numerical values have been investigated using the full vector finite element method.

NUMERICAL MODELING OF THE SEPARATION OF LIQUID AND GASEOUS PHASES OF HYDROCARBON MIXTURES IN A VORTEX CHAMBER

Analysis of the separation process in a vortex chamber is based on the assumption of phase equilibrium existence in the system. Dynamic processes occurring while phases moving in a vortex chamber contribute to the separation of the liquid and gaseous phases of hydrocarbon mixtures. Thus, the transition of the fluid to a metastable state in the vortex chamber will occur in less time than using the traditional methods.Based on the developed model of a vortex chamber in ANSYS FLUENT a series of numerical experiments were carried out. The influence of various parameters on the amount of removal of liquid and gaseous phases of hydrocarbon mixtures was determined. Indicators of the properties of the liquid phase have the greatest impact on the dynamics of the removal of liquid with gas, while the characteristics of the gas phase can be neglected due to their statistical insignificance.When studying the design of a vortex chamber, the smallest removal is observedwhen the inlet pipe is installed further from the top of the chamber (more recessed into the flow). The H/D ratio has less influence, but the offset decreases monotonically as the H/D parameter increases. The influence of the flow rate and the ratio of phases formed in the nozzles on the amount of carryover indicates that with an increase in the gas phase in the incoming flow, the removal of liquid increases. The inlet rate has a less influence.Statistical processing and regression analysis of the results of numerical modeling were carried out. Empirical equations for calculating the amount of droplet liquid removal from the vortex chamber are obtained. The dispersion value was calculated and the significance of the regression coefficients was checked. Based on the results of assessing homogeneity, reproducibility, and adequacy, a conclusion was made about the suitability of the developed model for calculations.

Effects of nitrogen addition and leaf age on needle traits and the relationships among traits in Pinus koraiensis

Leaf functional traits are essential for the growth and adaptation of trees to environmental changes. However, how needle traits and trait–trait relationships respond to different nitrogen (N) addition rates and leaf ages remain unclear for evergreen coniferous species. Our study aimed to investigate the effects of N addition and leaf age on needle traits and their bivariate correlations. Understanding resource utilization and distribution strategies during tree growth under the background of increased N deposition is important. We conducted a six-year manipulative field experiment in a Pinus koraiensis plantation in northeastern China with variable N addition levels: control (no N addition, CK); 20 kg N ha−1yr−1 (low-N, LN); 40 kg N ha−1yr−1 (medium-N, MN); and 80 kg N ha−1yr−1 (high-N, HN). The needle trait data were collected in September. The morphological traits, i.e., specific leaf area (SLA) and leaf dry matter content (LDMC); and chemical traits, i.e., leaf nitrogen concentration (LNC), leaf phosphorus concentration (LPC), and leaf nonstructural carbohydrates (NSC) concentrations, were measured to investigate the changes in needle traits and their bivariate correlations. We found that N addition and needle age significantly affected needle traits, and the effect of needle age was much stronger than that of N addition. N addition and needle age had no significant interaction effects on any of the traits except for the LNC. Due to the dispersal trait values of current-year needles, there were almost no significant bivariate correlations between traits under different N addition rates. The SLA–LDMC and LDMC–LNC relationships were found to differ among the various N addition rates, and other traittrait relationships may be relatively stable because of the weak plasticity of older needles. Additionally, needle age significantly affected the slope of the SLA–LDMC relationship and the elevation of the LDMC–LPC and NSC–LNC relationships, indicating differences in the ecological strategies of needles at different ages. In summary, our findings emphasize that trait–trait relationships in current-year and older needles were inconsistent in response to N addition and that the optimal allocation of resources in needles was based on their functional needs during leaf aging.

DETECTING NOISE IN FRACTAL TIME SERIES USING MACHINE LEARNING

This study concentrates on devising a method to evaluate the level of noise in fractal Brownian motion through machine learning methods. A method for classifying trajectories of fractal Brownian motion with varying levels of additive noise using a convolutional neural network has been proposed. Modeled fractal time series with additive noise were utilized as the input dataset. The noise component was generated with different dispersion values, allowing the investigation of the noise level's influence on the system and its environment. The results provide insights into the effectiveness and trustworthiness of employing these machine learning techniques for assessing noise within fractal systems.

Nonlinear compression of mid-infrared supercontinuum generation in dispersion-engineered As2S5 chalcogenide ridge waveguide

We numerically demonstrated nonlinear compression of mid-infrared (mid-IR) supercontinuum (SC) generation in As2S5 chalcogenide glass (ChG) ridge waveguides, achieving a small dispersion value at the pump wavelength of 2.5 µm by adjusting the waveguide width (normal dispersions of -10.547 ps.nm−1.km−1 and the anomalous dispersions of +5.314 ps.nm−1.km−1). These waveguides were designed using the negative slope of the dispersions with the negative third-order dispersion, which are applied to generate the nonlinear compression of SC generation. Using a 50-fs pulse with the peak power of 2000 W, the two waveguides could compress the maximum pulse peak power of 6900 W (> 3.4 octaves) and 6360 W (> 3.1 octaves) and generate the widest SC spectra, spanning from 1.20 µm to 12.96 µm and from 1.25 µm to >13 µm with only short waveguides 0.85 mm and 1 mm long, respectively. The key process behind SC formation in such ChG waveguides is related to self-phase modulation, four-wave mixing, and nonlinear compression. This particular design is effective, and ChG waveguides can generate high peak power and the widest spectra of SC generation. Moreover, the waveguides are also relatively flexible in design, which is concerned with optical design and engineering, and micro-optical devices. As the ultra-wideband mid-IR SC source, high pulse peak power, very short waveguides, and low-energy pulses (<1 pJ) are important for on-chip mid-IR SC sources, the proposed work would offer the greatest benefits in practical application.

The dispersion of the Ep, i–Liso correlation of long gamma-ray bursts is partially due to assembling different sources

Context. Long gamma-ray burst (GRB) prompt emission shows a correlation between the intrinsic peak energy, Ep, i, of the time-average νFν spectrum and the isotropic-equivalent peak gamma-ray luminosity, Lp, iso, as well as the total released energy, Eiso. The same correlation is found within individual bursts, when time-resolved Ep, i and Liso are considered. These correlations are characterised by an intrinsic dispersion, whose origin is still unknown. Discovering the origin of the correlation and of its dispersion would shed light on the still poorly understood prompt emission and would propel GRBs to powerful standard candles. Aims. We studied the dispersion of both isotropic-equivalent and collimation-corrected time-resolved correlations. We also investigated whether the intrinsic dispersion computed within individual GRBs is different from that obtained including different bursts into a unique sample. We then searched for correlations between key features, such as the Lorentz factor and jet opening angle, and intrinsic dispersion, when the latter is treated as one of the characterising properties. Methods. We performed a time-resolved spectral analysis of 20 long type-II or collapsar-candidate GRBs detected by the Fermi Gamma-ray Burst Monitor with a known redshift and estimates of the jet opening angle and/or the Lorentz factor. Time intervals were determined using Bayesian blocks. Then we carried out a statistical analysis starting from distributions of simulated values of the intrinsic dispersion of each burst in the sample. Results. The collimation-corrected correlation appears to be no less dispersed than the isotropic-equivalent one. Also, individual GRBs are significantly less dispersed than the whole sample. We excluded (at a 4.2σ confidence level) the difference in samples’ sizes as the possible reason, thus confirming that individual GRBs are intrinsically less dispersed than the whole sample. No correlation was found between intrinsic dispersion and other key properties for the few GRBs with available information. Conclusions. The contribution to the dispersion by the jet opening angle is not relevant. Moreover, our results prove that the intrinsic dispersion that affects the Ep, i − Liso correlation is partially, though not entirely, due to assembling different GRBs. We therefore conclude that the presence of different GRBs significantly contributes to the observed dispersion of both time-average Ep, i − Lp, iso and Ep, i − Eiso correlations.

Research on chaotic secure optical communication system based on dispersion keying with time delay signatures concealment

In response to the possibility of time delay (TD) signatures (TDSs) leakage becoming a serious problem in chaotic optical communication, from the perspective of improving the security of chaotic optical communication, this paper proposes a chaotic secure optical communication system based on dispersion keying, which generates signals with TDSs concealment characteristics. In this scheme, a common laser is used to drive chaotic synchronization between the transmitter and the receiver. The complex chaotic signal is generated by the combination of all-optical feedback and optical injection, and the TDSs are hidden by using the structure of dual filters and setting the parameters of each device reasonably. The switch is controlled by binary message to connect fiber Bragg gratings (FBGs) with different dispersion coefficients and maps different symbols to different chaotic attractors instead of the traditional way of directly sending messages to the channel. In addition, the generated signal no longer suffered from return map attacks. FBGs can compress and expand signals in the time domain to enhance the complexity of chaotic signals, and the dispersion value is an important key to effectively increasing the key space. Finally, the performance of TDSs concealment, sensitivity of parameter mismatch, and return map attack in this scheme are discussed in detail. The scheme still achieves a bit error rate (BER) of 1.74 × 10−4 when transmitting at a rate of 10Gbit/s under harsh communication environments such as 10 dB signal-to-noise ratio (SNR), which provides a reference for realizing high-speed and secure optical communication at the physical layer.

Non-isothermal kinetics of the organocatalytic ring-opening polymerization of ε-caprolactone with metal-free α‑hydroxy acids: Eco-friendly and facile synthesis process

Metal-free and green α‑hydroxy acids (AHA) such as l-malic (MA), DL-mandelic acid (MDL), and citric acid (CA) were successfully and effectively utilized as an effective initiator for the solvent-free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The performance of AHAs in the polymerization of ε-CL was completely and powerfully investigated via the non-isothermal differential scanning calorimetry (DSC). The proceed of ROP of ε-CL with AHAs could be real-time monitored by the obtained polymerization exotherms at different heating rates. The polymerization exotherms obtained from the ROP of ε-CL with CA occurred at a lower temperature range than MA, and MDA, respectively. From the kinetics study, the average activation energy (Ea) values for the ROP of ε-CL with CA (38.0 ± 1.8 kJ mol−1) were lower than MA (45.2 ± 3.6 kJ mol−1) and MDA (48.8 ± 6.2 kJ mol−1). Using the first-order model fitting, the values of pre-exponential factor (lnA0) for the ROP of ε-CL with CA, MA, and MDA were 7.0 ± 0.3, 8.5 ± 0.2, and 8.9 ± 0.3, respectively. The effectiveness of AHAs in the synthesis of PCL was clarified by conducting a larger-scale (4.0000 g) polymerization using conventional heating and microwave (MW) irradiation methods. From conventional heating, the green AHAs produced PCL with the number average molecular weight (Mn) and dispersity (Đ) values in the range of 5.18 × 103 - 1.43 × 104 g mol−1 and 1.14–2.02, respectively. The irradiation by MW could enhance the synthesis of PCL by reducing the synthesis time. By using the MW power of 450 W and irradiation time of 30 min, the PLC was obtained from the ROP of ε-CL with MA and MDA initiators, and the Mn of the obtained PCL from MW heating was 4.28 × 103 - 8.45 × 103 g mol−1. The mechanism for the ROP of ε-CL with all AHAs was proposed through the activated monomer mechanism.

Highly birefringent photonic crystal fibers with near-zero flattened dispersion for polarization-maintaining terahertz transmission

In this work, we present a novel hexagonal lattice porous-core photonic crystal fiber (PCF) exhibiting high birefringence, low loss, and near-zero flattened dispersion in the terahertz regime. The core design incorporates asymmetric rectangular and triangular air holes to achieve enhanced birefringence performance. The background material, TOPAS, is carefully selected to minimize dispersion and transmission losses. Furthermore, by employing the finite element method, the guiding properties of the proposed PCF are comprehensively investigated. Our simulation results reveal a near-zero flattened dispersion value of ±0.2ps⋅THz−1⋅cm−1 within a broad frequency range of 0.8−1.6THz, accompanied by an impressive birefringence value of 0.072. Additionally, the PCF demonstrates outstanding characteristics in terms of confinement loss, effective material loss, effective mode area, core power fraction, and bending loss. Considering its exceptional attributes, the proposed PCF holds significant promise for polarization-maintaining applications and terahertz communication systems.

Room temperature oxidation of gaseous formaldehyde over silver-doped manganese oxide catalyst

A wide amount of existing building materials and consumables contains formaldehyde (HCHO) that may be released as a gas even after installation. The produced gas may concentrate in housing and offices, leading to a long-term exposure of the occupants. Living in such an environment, even at low concentrations less than 0.5 ppm, may lead to carcinogenic effects and damages of the human central nervous system. As a consequence, the development of methods that oxidize and neutralize the formaldehyde at ambient temperature is welcome. The catalytic oxidation method at ambient temperature is preferred over other available techniques due to its ease of operation and high efficiency. In this work, different weight percentages, ranging from 1 up to 5%, of silver-doped manganese oxides (Ag/MnOx) were synthesized by a co-precipitation process followed by a calcination at 450 °C for 4 h. The XRD and BET analysis results show that the sample at 4% wt of Ag doped in the MnOx matrix exhibit highest crystallinity, surface area and highest dispersion values, very near to theoretical ones. The removal performance of HCHO was tested in a silicon wool bed continuous flow reactor characterized by an inner diameter of 4 mm and a length of 12.5 cm. At ambient temperature a removal efficiency and an amount of produced CO2 of 94% and 66%, respectively.

Impact of the Higher-Order Reactive Nonlinearity on High-Amplitude Dissipative Solitons

In this work, the impact of the higher-order reactive nonlinearity on very high-amplitude solitons of the cubic–quintic complex Ginzburg–Landau equation is investigated. These high amplitude pulses were found in a previous work in the normal and anomalous dispersion regimes, starting from a singularity found by Akhmediev et al. We focus mainly in the normal dispersion regime, where the energy of such pulses is particularly high. In the presence of the higher-order reactive nonlinearity effect, pulse formation are observed for much higher absolute values of dispersion. Under such effect, the amplitude and the energy of the VHA pulses decrease, while their spectral range shrinks. Numerical computations are in good agreement with the predictions based on the method of moments, in the absence of the higher-order reactive nonlinearity effect. However, in the presence of this effect such agreement becomes mainly qualitative. A region of existence of the very high-amplitude pulses was found in the semi-plane defined by the normal dispersion and nonlinear gain.

A simple criterion for the effectiveness of biased estimators

Point estimation is one of the most common forms of statistical inference. This paper touches upon the concepts of unbiasedness and effectiveness of biased estimates. An attractive approximation for the true (quantitative) value of the estimated parameter t whose values belong to a certain numerical set t T is an estimate , for which the sum of the mathematical expectation of the square of the differences between the possible realization of and the estimated parameter t is minimal (least squares estimation). Another approach is to find the value of the parameter t based on the sum of the mathematical expectation of the difference between the possible realisation ϵ = xi and the estimated parameter t, provided that this sum is zero, so that the positive and negative differences are balanced ∑(xi – t) = 0. Implementations of N independent random values have a general distribution that depends on the estimated parameter t. There are other approaches, but at present there is no single convincing definition of the optimality of finding effective estimates. The well-known statistician Box wrote: “All models are wrong, some are useful.” It is not always easy to establish the adequacy of a model, so our choice is defined by its utility! The simple effectiveness criterion of biased estimates given below is too convenient, however this does not mean that the assumption of the effectiveness of biased estimates based on this criterion is true, yet the usefulness of this simple and convenient model is obvious. The Aim of the paper. The paper aims to construct a simple effectiveness criterion of biased estimates and obtain simple effective estimates of dependability indicators for a binomial test plan and a test plan with limited time and recovery using the constructed simple effectiveness criterion of biased estimates. Conclusions. A simple effectiveness criterion of biased estimates was obtained that compensates for the effect of unequal dispersion values and the square of the bias. New effective biased estimates of various dependability indicators were obtained for a binomial test plan and a plan with limited test time and recovery of failed items.

Development of a Solar Powered Seeder for Pea Seeds

One of the most profitable vegetable crops for farmers to plant is peas. Pea seeding by hand is still one of the most tedious techniques farmers use today. Pea seed sowing requires a more significant number of skilled workers. The soil is dug by one person, and the pea seeds is sown there by another. Regarding farmers, the availability of skilled labor is still another issue. Egypt has many small farms; hence, it is necessary to produce small-scale farming machinery. Thus, this research manufactures a solar-powered seeding mechanism exclusively for small farmers at a low cost to overcome the problems of a lack of labor skills, sowing times, labor cost, accurate seeding, and seed losses. Increase profit for farmers who plant vegetable crops. The machine is provided with an accurate system to achieve accurate seed distribution. A complex gear mechanism is replaced with a sensor to make seeding simpler. There is an input LCD screen to sow at various distances between seeds. The distance between rows can be maintained. Also, there is a solar tracking system, which is essential for receiving more direct sunlight. Also, the motors used are 12 volts, so they are compatible with the electricity produced from the solar panel without the need for a voltage converter, which reduces costs. Also, both fuel costs and air pollution do not exist. The study includes two experimental variables: four theoretical hill spacings of 15, 18, 21, and 24 cm and four sowing depths of 2, 3, 4, and 5 cm. The measurements include the plant's longitudinal dispersal, lateral dispersal, emergence percentage, and operating costs. The minimum values of longitudinal and lateral dispersal and the highest value of emergence percentage were obtained at a theoretical hill spacing of 24 cm and a sowing depth of 5 cm. The developed machine can lower the operational cost by 94.96%, as one skilled worker can adequate complete the seeding operation. Therefore, it is suggested to use the solar-powered system for seeding pea seeds in small-scale farming.

Enhancing stability and odor control of water-based foam for pesticide site restoration using xanthan gum

Foam stability plays an important role in the effect of blocking the odorous substances. Based on the characteristic of xanthan gum of enhancing foam stability and preventing foam from water drainage and coarsening, this paper investigated the half-life, foaming volume, viscosity, drainage curve, and bubble microstructure of foam filled with 0.1%, 0.2%, and 0.3% xanthan gum respectively, and further analyzed the correlation between xanthan gum dosage, viscosity of foam solution and foam stability. The effect of different stability foams on para-xylene was tested. The results showed that compared with no xanthan gum, the half-life of foam with 3% xanthan gum was extended from 1 to 61 h, the drainage time increased from 4.5 to 85 h, and the foaming coarsening rate slowed down 3 times. The addition of 0.3% xanthan gum reduced the peak value of the p-xylene dispersion by 83.7% and postponed the peak time by 6 times.

Three-body encounters in black hole discs around a supermassive black hole

Context. Dynamical encounters of stellar-mass black holes (BHs) in a disc of compact objects around a supermassive BH (SMBH) can accelerate the formation and coalescence of BH binaries. It has been proposed that binary–single encounters among BHs in such discs can lead to an excess of highly eccentric BH mergers. However, previous studies have neglected how the disc velocity dispersion and the SMBH’s tidal field affect the three-body dynamics. Aims. We investigate the outcomes of binary–single encounters considering different values of the disc velocity dispersion, and examine the role of the SMBH’s tidal field. We then demonstrate how their inclusion affects the properties of merging BH binaries. Methods. We performed simulations of four-body encounters (i.e. with the SMBH as the fourth particle) using the highly accurate, regularised code TSUNAMI, which includes post-Newtonian corrections up to order 3.5PN. To isolate the effect of the SMBH’s tidal field, we compared these simulations with those of three-body encounters in isolation. Results. The disc velocity dispersion controls how orbits in the disc are aligned and circular, and determines the relative velocity of the binary–single pair before the encounter. As the velocity dispersion decreases, the eccentricity of post-encounter binaries transitions from thermal to superthermal, and binaries experience enhanced hardening. The transition between these two regimes happens at disc eccentricities and inclinations of order e ∼ i ∼ 10−4. These distinct regimes correspond to a disc dominated by random motions (e ∼ i ≳ 10−4) and one dominated by the Keplerian shear (e ∼ i ≲ 10−4). The effect of the SMBH’s tidal field depends on the velocity dispersion of the disc. When the velocity dispersion is low, the resulting binaries are less eccentric compared to isolated encounters. Conversely, binaries become less eccentric compared to isolated encounters at high velocity dispersion. This also affects the number of BH mergers. Conclusions. The inclusion of the SMBH’s tidal field and the disc velocity dispersion can significantly affect the number of GW mergers, and especially the number of highly eccentric inspirals. These can be up to ∼2 times higher at low velocity dispersion, and ∼12 times lower at high velocity dispersions. The spin–orbit alignment is influenced by the tidal field exclusively at high velocity dispersions, effectively inhibiting the formation of anti-aligned binary BHs. Nonetheless, encounters in random-motion-dominated discs around a SMBH are still more effective in producing GW mergers compared to those occurring in spherically symmetric nuclear star clusters without an SMBH.

Local temperature control of magnon frequency and direction of supercurrents in a magnon Bose–Einstein condensate

The creation of temperature variations in magnetization, and hence in the frequencies of the magnon spectrum in laser-heated regions of magnetic films, is an important method for studying Bose–Einstein condensation of magnons, magnon supercurrents, Bogoliubov waves, and similar phenomena. In our study, we demonstrate analytically, numerically, and experimentally that, in addition to the magnetization variations, it is necessary to consider the connected variations of the demagnetizing field. In the case of a heat-induced local minimum of the saturation magnetization, the combination of these two effects results in a local increase in the minimum frequency value of the magnon dispersion at which the Bose–Einstein condensate emerges. As a result, a magnon supercurrent directed away from the hot region is formed.