Obvious Peak Research Articles

Film cooling and aerodynamic loss performance of turbine vanes with fan-shaped and wave-trenched holes

Experimental measurement and numerical simulation were carried out to study the film cooling and aerodynamic loss performances of turbine vanes with cylindrical, fan-shaped, and wave-trenched holes. Tests were performed on a linear cascade. The mainstream inlet Reynolds number based on the vane chord length was 1.03 × 105, and three coolant local blowing ratios were conducted. A single row of film cooling holes was arranged in the acceleration region upstream of the pressure and suction surfaces of the test vanes, respectively. The effects of the hole shape and position of the hole row on the film cooling effectiveness and total pressure loss under various blowing ratios were comprehensively analyzed. Results show that on the pressure surface of the vane, at low blowing ratios, the film cooling effectiveness of wave-trenched holes is higher than that of fan-shaped holes. The wave-trenched hole exhibits obvious double peaks of the film cooling effectiveness. A pair of vortices and a coolant core are observed downstream of the trough wall and crest wall of the wave-trenched hole, respectively. At high blowing ratios, the film cooling effectiveness of them is comparable. On the suction surface of the vane, at low blowing ratios, the film cooling effectiveness of wave-trenched holes is lower than that of fan-shaped holes, and the trend is opposite at high blowing ratios. Two pairs of vortices are observed downstream of the crest wall of the wave-trenched hole. Wave-trenched holes have the highest shear stress rate and total pressure loss, followed by the cylindrical holes and fan-shaped holes at high blowing ratios. To the best of our knowledge, this is one of the few studies available on the systematic analysis of the film cooling and aerodynamic loss performance of turbine vanes with the three shapes of film cooling holes. The conclusions could provide effective guidance for the application of fan-shaped and wave-trenched holes during the elaborate design of film cooling structures on turbine vanes.

The Performance of the Two-Seeded GdBCO Superconductor Bulk with the Buffer by the Modified TSMG Method.

The multiseeding technique is a method to grow large-sized REBa2Cu3O7-δ (REBCO, where RE is a rare earth element) high temperature superconducting bulks. However, due to the existence of grain boundaries between seed crystals, the superconducting properties of bulks are not always better than those of single grain bulks. In order to improve the superconducting properties caused by grain boundaries, we introduced buffer layers with a diameter of 6 mm in the growth of GdBCO bulks. Using the modified top-seeded melt texture growth method (TSMG), that is, YBa2Cu3O7-δ (Y123) as the liquid phase source, two GdBCO superconducting bulks with buffer layers with a diameter of 25 mm and a thickness of 12 mm were successfully prepared. The seed crystal arrangement of two GdBCO bulks with a distance of 12 mm were (100/100) and (110/110), respectively. The trapped field of the GdBCO superconductor bulks exhibited two peaks. The maximum peaks of superconductor bulk SA (100/100) were 0.30 T and 0.23 T, and the maximum peaks of superconductor bulk SB (110/110) were 0.35 T and 0.29 T. The critical transition temperature remained between 94 K and 96 K, with superior superconducting properties. The maximum JC, self-field of SA appeared in specimen b5, which was 4.5 × 104 A/cm2. Compared with SA, the JC value of SB had obvious advantages in a low magnetic field, medium magnetic field and high magnetic field. The maximum JC, self-field value appeared in specimen b2, which was 4.65 × 104 A/cm2. At the same time, it showed an obvious second peak effect, which was attributed to Gd/Ba substitution. Liquid phase source Y123 increased the concentration of the Gd solute dissolved from Gd211 particles, reduced the size of Gd211 particles and optimized JC. For SA and SB under the joint action of the buffer and the Y123 liquid source, except for the contribution of Gd211 particles to be the magnetic flux pinning center with the improvement of JC, the pores also played a positive role in improving the local JC. More residual melts and impurity phases were observed in SA than in SB, which had a negative impact on the superconducting properties. Thus, SB exhibited a better trapped field and JC.

Experimental Study on Titanium Alloy Cutting Property and Wear Mechanism with Circular-arc Milling Cutters

Titanium alloy has been applied in the field of aerospace manufacturing for its high specific strength and hardness. Nonetheless, these properties also cause general problems in the machining, such as processing inefficiency, serious wear, poor workpiece face quality, etc. Aiming at the above problems, this paper carried out a comparative experimental study on titanium alloy milling based on the CAMC and BEMC. The variation law of cutting force and wear morphology of the two tools were obtained, and the wear mechanism and the effect of wear on machining quality were analyzed. The conclusion is that in contrast with BEMC, under the action of cutting thickness thinning mechanism, the force of CAMC was less, and its fluctuation was more stable. The flank wear was uniform and near the cutting edge, and the wear rate was slower. In the early period, the wear mechanism of CAMC was mainly adhesion. Gradually, oxidative wear also occurred with milling. Furthermore, the surface residual height of CAMC was lower. There is no obvious peak and trough accompanied by fewer surface defects.

A novel NAC transcription factor, PpNAP6, is involved in peach ripening by activating ethylene synthesis

Peach (Prunus persica) is a typical climacteric fruit, having an obvious peak of ethylene release during ripening. Transcriptional regulators play key roles in fruit ripening. NAP (NAC-like, activated by AP3/P1) protein is a subfamily of the NAC (NAM, ATAF1/2 and CUC2) transcription factor (TF) family. Here, we discovered the function of peach NAP subfamily NAC TF, PpNAP6, homologous to the tomato ripening-related TF NOR. In the pulp of ‘Zaofengwang’ peach, PpNAP6 is highly expressed, and its transcript level decreased gradually throughout the whole development period, however, it is up-regulated at onset of peach ripening. Transient transformation experiments showed that PpNAP6 over-expression in peach fruit increased ethylene release and accelerated fruit ripening, while PpNAP6 down-expression inhibited ethylene biosynthesis. Dual-luciferase reporter assay (DLR) and electrophoretic mobility shift assay (EMSA) proved that PpNAP6 can directly bind to the promoters of key ethylene biosynthesis genes PpACS1 and PpACO1, and activate their transcription. Moreover, PpNAP6 was heterologously overexpressed in tomato nor mutant, and the transgenic lines showed the overexpression of PpNAP6 could partially recover its ripening-inhibited phenotype. Interestingly, PpNAP6 activates ethylene biosynthesis during peach ripening, whereas its transcription was inhibited treated with ethephon and enhanced with 1-MCP treatment. In summary, our work revealed that PpNAP6 regulates peach fruit ripening through ethylene biosynthesis, and may be involved in the fine regulation of ethylene via a feedback mechanism.

Preparation of CaO–SiO2–Al2O3 inorganic fibers from melting-separated red mud

Abstract To investigate the feasibility of preparing CaO–SiO2–Al2O3 inorganic fibers with melting-separated red mud, the properties of the melting-separated red mud were analyzed by X-ray fluorescence, X-ray diffraction, and differential thermal-thermogravimetric analyses. The composition of the melting-separated red mud satisfied the requirements for the composition of inorganic fibers. During the melting of the melting-separated red mud, tetrahedral skeleton fracture reactions occurred at 1,234°C, anionic group reverse binding occurred at 1,250°C, and there was no other obvious reaction peak during the whole melting process, which lasted for 51 min. The minimum suitable fiber forming temperature of the melting-separated red mud melt was 1,433°C, which was 83°C greater than its crystallization temperature, 1,350°C. Within this temperature range, the activation energy of particle movement in the melt was 1008.65 kJ·mol−1, and the melt exhibited good fluidity. Considering the temperature distribution corresponding to the melting properties of the melting-separated red mud, CaO–SiO2–Al2O3 inorganic fibers could be prepared when the melting-separated red mud was subjected to component reconstruction by increasing the silicon content, reducing the aluminum content, and adding a moderate amount of calcium. Quartz sand and light burnt dolomite were used as modifying agents and inorganic fibers were prepared under laboratory conditions. The fibers prepared from the modified melting-separated red mud by adding different amounts of melting-separated red mud had smooth surfaces and were arranged in a crossed manner at the macroscopic level. Their color was grayish-white, and small quantities of slag balls were doped inside the fibers. With an increase in the amount of melting-separated red mud from 50 to 100%, the average fiber diameter increased from 5.5 to 8.0 μm, and their slag ball content increased from 2.9 to 6.0%. Overall, under laboratory conditions, when the amount of melting-separated red mud added was 50%, dolomite was 22.5% and quartz sand was 27.5%, the performance of the fiber was the best.

The extraction and identification of active components of the sex pheromones of Asian citrus psyllid, Diaphorina citri

In this study, we extracted and identified the active components of the Asian citrus psyllid, Diaphorina citri sex pheromones to provide a basis for further development of sex attractants. Under laboratory conditions, mating activity in D. citri started 3 d after emergence, which peaked at 6–7 d, and mating activity had no obvious peak during the observed period 7:00–21:00 h. Additionally, D. citri males were attracted to the emanations from conspecific females, especially to the n-hexane extracts of the pheromone. A total of 17 compounds were identified from the n-hexane extracts of female and male D. citri by gas chromatography-mass spectrometer (GC–MS). Among them, 13 compounds were identified from the female D. citri n-hexane extracts, of which 7 (dichloromethane, acetic acid, toluene, butyl acetate, ethyl carbamoylacetate, α-pinene, and 1-nonanal) were not found in the male D. citri n-hexane extracts. In addition, a total of 33 compounds were identified from the solid phase microextraction (SPME) volatiles of the male and female D. citri adults. Among these, 17 compounds were identified from the female D. citri volatiles, of which 6 (cycloheptatriene, 5-methyl-2-phenylindole, 1-dodecanol, cis-11-hexadecena, dodecyl aldehyde, and nerylacetone) were not identified in the volatiles of the D. citri males. It was found that males were significantly attracted to 0.1–10 μL/mL acetic acid and 1-nonanal with the selection rates ranging from 62.04%–70.56% and 62.22%–67.22%, respectively. Therefore, the results of this study suggest that acetic acid and 1-nonanal might be the active compounds of the female D. citri sex pheromones.

Changes of dissolved organic matter following salinity invasion in different seasons in a nitrogen rich tidal reach

Dissolved organic matter (DOM) is a heterogeneous mixture of dissolved material found ubiquitously in aquatic systems and dissolved organic nitrogen is one of its most important components. We hypothesised nitrogen species and salinity intrusions affect the DOM changes. Here, using the nitrogen rich Minjiang River as an easily accessible natural laboratory 3 field surveys with 9 sampling sites (S1-S9) were conducted in November 2018, April and August 2019. The excitation emission matrices (EEMs) of DOM were explored with parallel factor (PARAFAC) and cosine-histogram similarity analysis. Four indices including fluorescence index (FI), biological index (BIX), humification index (HIX) and the fluorescent DOM (FDOM) were calculated and the impact of physicochemical properties was assessed. The results suggested that the highest salinities of 6.15, 2.98 and 10.10, during each campaign corresponded to DTN concentrations of 119.29–240.71, 149.12–262.42 and 88.27–155.29 μmol·L−1, respectively. PARAFAC analysis revealed the presence of tyrosine-like proteins (C1), tryptophan-like proteins or a combination of the peak N and tryptophan-like fluorophore (C2) and the humic-like material (C3). The EEMs in the upstream reach (i.e. S1-S3) were complex with larger spectra ranges, higher intensities and similar similarity. Subsequently, the fluorescence intensity of three components decreased significantly with low similarity of EEMs (i.e. S4-S7). At the downstream, the fluorescence levels dispersed significantly and no obvious peaks were seen except in August. In addition, FI and HIX increased, while BIX and FDOM decreased from upstream to downstream. The salinity positively correlated with FI and HIX, and negatively related to BIX and FDOM. Besides, the elevated DTN had a significant effect on the DOM fluorescence indices. Altogether, salinity intrusion and elevated nitrogen are relevant for the distribution of the DOM, which is helpful for the water management tracing the DOM source according to the on-line monitoring of salinity and nitrogen in estuaries.

Statistical behavior of wall-attached motions in open- and closed-channel flows via direct numerical simulation

Direct numerical simulations at two friction Reynolds numbers (550 and 1000) have been performed to explore the statistical behaviors of wall-attached motions (WAMs) in open- and closed-channel flows (OCFs and CCFs). To fully capture the largest energetic WAMs, superlarge domain sizes are employed (24–48 π h along streamwise direction with h being the height of OCFs). Based on the analysis of linear coherence spectrum, both geometric and kinematic characteristics of WAMs are investigated. Results revealed that obvious peaks could be found in spanwise coherence spectra of u (streamwise velocity) and w (spanwise velocity) at a wavelength close to 2h. Both the coherence and energy spectra density value of OCFs are greater than those of CCFs at large wavelengths, indicating that OCFs are more wall-attached. Within y/h = 0.2–0.7, the diagnosed streamwise and spanwise wavelengths of WAMs increase roughly linearly with increasing vertical position y. In the upper region ( y / h > 0.7), the diagnosed wavelengths in OCFs are smaller than those in CCFs. In addition, the inclination angle of u fluctuates around 14° within y / h = 0.4–0.6, and angles of CCFs are slightly larger than those in OCFs when y / h > 0.6. Regarding kinematic behavior, contribution fractions of WAMs to total turbulent intensity in OCFs are always larger than those in CCFs. Additionally, the wall-attached behaviors of u were found to be more sensitive to Reynolds number than w.

A new force-depth model for robotic abrasive belt grinding and confirmation by grinding of the Inconel 718 alloy

• A new force-depth model for robotic abrasive belt grinding is proposed considering the deformation of the contact wheel. • The mapping relationship between the grinding force and the grinding depth is obtained. • When the grinding depress depth is large, the feed force and the normal force appear obvious secondary pressure peaks. • The grinding force ratio of downgrinding (average 0.668) is smaller than that of upgrinding (average 0.724). Robotic abrasive belt grinding has been successfully applied to the grinding and polishing of aerospace parts. However, due to the flexible characteristics of robotic abrasive belt grinding and the time-varying characteristics of the polishing contact force, as well as the plastic and difficult-to-machine material properties of Inconel 718 alloy, it is very difficult to control the actual removal depth and force of the polished surface, which brings great challenges to robot automatic polishing. Therefore, the relationship between the grinding force and the grinding depth in the robotic abrasive belt grinding is analyzed in detail, the robot machining pose error model considering the deformation of the grinding head is established, and the Inconel 718 alloy machining experiment of the robotic abrasive belt grinding is designed. The mapping relationship between the grinding force and the grinding depth is obtained, and the grinding force ratio in the downgrinding and upgrinding mode is discussed. The experimental and theoretical comparisons results show that with the increase of the grinding depress depth, both the grinding depth and the grinding force show an irregular increasing trend, and the increasing trend of the grinding force (increases by about 344.44%–445.45%) is obviously greater than that of the grinding depth (increases by about 52.94%). When the grinding depress depth is large (greater than 3 mm), the feed direction force and the normal force appear obvious secondary pressure peaks at the beginning and end of grinding, which has not been seen in previous studies. In addition, regardless of whether it is downgrinding or upgrinding, the grinding force ratio decreases with the increase of the depress depth, and the grinding force ratio of downgrinding (average 0.668) is smaller than that of upgrinding (average 0.724). This study provides a reference for robotic abrasive belt grinding, and the surface quality of Inconel 718 alloy of robotic abrasive belt grinding can be further improved through the optimization of force and depth.

In Situ X‐Ray and Infrared Measurements of Alkane Absorption and Desorption Processes of Isotactic Poly(4‐Methyl‐1‐Pentene) Film

AbstractSmall molecules are absorbed selectively in the amorphous regions in semicrystalline polymers, except for some specific polymeric systems forming host‐guest cocrystals such as syndiotactic polystyrene. The crystalline density of isotactic poly(4‐methyl‐1‐pentene) (P4MP1) is substantially lower than those of analogs, and it is even slightly lower than the amorphous density. This study is investigated the absorption/desorption behaviors of short alkanes in P4MP1 in situ, and found that the alkanes are mainly absorbed in its amorphous region. Infrared spectroscopy measurements reveal that the P4MP1 film with low crystallinity absorbs higher amount of decane than the high crystallinity film does. Also it is found by small‐angle X‐ray scattering (SAXS) that, when hexane is dropped onto the P4MP1 as‐cast film, a lamellar long‐spacing peak appears at 0.16 nm−1 which disappears with the spontaneous desorption of hexane. Because the pristine P4MP1 films give no obvious SAXS peak due to the close density of crystalline and amorphous regions, the appearance of the SAXS peak indicates that an X‐ray contrast is obtained by the preferential absorption to amorphous region. The disappearance of the peak is thus reasonably understood by the loss of the contrast due to desorption.

Electrochemical activation of oxygen vacancy-rich TiO2@MXene as high-performance electrochemical sensing platform for detecting imidacloprid in fruits and vegetables.

Heterostructured TiO2@MXene rich in oxygen vacancies defects (VO-TiO2@MXene) has beendeveloped to construct anelectrochemical sensing platform for imidacloprid (IMI) determination. For the material design, TiO2 nanoparticles werefirstly in situ grown on MXene and used as a scaffolding to prevent the stack of MXene nanosheets. The obtained TiO2@MXene heterostructure displays excellent layered structure and large specific surface area. After that, electrochemical activation is utilized to treat TiO2@MXene, which greatly increases the concentration of surface oxygen vacancies (VOs), thereby remarkably enhancing the conductivity and adsorption capacity of the composite. Accordingly, the prepared VO-TiO2@MXene displays excellent electrocatalytic activity toward the reduction of IMI. Under optimum conditions, cyclic voltammetry and linear sweep voltammetry techniques were utilized to investigate the electrochemical behavior of IMI at the VO-TiO2@MXene/GCE. The proposed sensor based on VO-TiO2@MXene presents an obvious reduction peak at -1.05 V(vs. Hg|Hg2Cl2) with two linear ranges from 0.07 - 10.0 μM and 10.0 - 70.0 μM with a detection limit of 23.3 nM (S/N= 3). Furthermore, the sensor provides a reliable result for detecting IMI in fruit and vegetable samples with a recovery of 97.9-103% and RSD≤ 4.3%. A sensitive electrochemical sensing platform was reported for imidacloprid (IMI) determination based on heterostructured TiO2@MXene rich in oxygen vacancy defects.

Fe-Single-Atom Nanozyme Catalysts for Sensitive and Selective Detection of Nitrite via Colorimetry and Test Strips

Here, a sensitive and selective strategy for the detection of nitrite via colorimetry and test strips was developed based on Fe-single-atom catalysts (Fe SACs) through the oxidation–reduction and diazotization reactions. Fe SACs possess excellent oxidase-like (OXD) catalytic activity, which can catalyze the oxidation of the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue TMBox with the appearance of an obvious absorbance peak at 652 nm in the presence of oxygen. With the addition of nitrite (NO2–), the oxidation–reduction and diazotization reactions between TMB/TMBox and nitrite can induce the color of the solution to change from blue to green and finally to yellow, with the increase of the peak at 445 nm. Based on this strategy, a dual-signal-ratio colorimetric detection method for nitrite was proposed. Within the concentration range of 1–120 μM, the ratio of A652/A445 has a favorable linear relationship with the logarithm concentration of NO2–, with a detection limit of 0.238 μM. By combining smartphones with the colorimetric method, a more intuitive, visual, and convenient test strip detection platform was developed, which can be utilized for the detection of nitrite within 2–200 μM. The analysis strategy based on the Fe-single-atom nanozyme catalysis integrated with the specific redox/diazotization reaction not only provides a dual-signal ratio sensing with good sensitivity but holds the advantage of good selectivity for the utilization of the specific chemical reaction, which has broad application prospects in food safety supervision and food screening.

Physical and mechanical characterization of microwave and ultrasound-modified zein-corn starch edible films

Edible films and coatings are the biodegradable layers of edible components that are used to coat the food surface or wrap the food in the form of film. In this paper, microwave, and ultrasound technologies, at different processing conditions, separately (US, 70M, 30M) or consecutively in different order (US-70M, 70M-US, US-30M, 30M-US) were applied to the film-forming solutions based on zein and corn starch to increase the compatibility between the biopolymers and to improve some of the edible film characteristics. The physical and mechanical properties and the FTIR spectra of the films were determined. The microwave followed by ultrasound treated edible films (70M-US, 30M-US) were found to be smoother and more homogeneous than the other films. Although all films were found to have hydrophilic character, application of microwave and ultrasound technologies together increased the water contact angle values of the films, providing more hydrophobic film surfaces. 70M-US and 30M-US edible films were found to have the highest tensile strength and elongation % values, respectively. The obvious deeper peaks were observed in the amide-III band of FTIR spectra for microwave followed by ultrasound treated films as an indicator of the enhanced compatibility between zein and corn starch in the film matrix.

Observation of multigap and coherence peak in the noncentrosymmetric superconductor CaPtAs: As75 nuclear quadrupole resonance measurements

We present synthesis and $^{75}$As-nuclear quadrupole resonance (NQR) measurements for the noncentrosymmetric superconductor CaPtAs with a superconducting transition temperature $T_c$ of $\sim 1.5$ K. We discovered two different forms of CaPtAs during synthesis; one is a high-temperature tetragonal form that was previously reported, and the other is a low-temperature form consistent with the orthorhombic structure of CaPtP. According to the $^{75}$As-NQR measurement for superconducting tetragonal CaPtAs, the nuclear spin-lattice relaxation rate $1/T_1$ has an obvious coherence peak below $T_c$ and does not follow a simple exponential variation at low temperatures. These findings indicate that CaPtAs is a multigap superconductor and a large $s$-wave component.

Epidemiological and spatiotemporal analysis of severe fever with thrombocytopenia syndrome in Eastern China, 2011–2021

BackgroundSevere fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease, which is caused by severe fever with thrombocytopenia syndrome virus (SFTSV) with high fatality. Recently, the incidence of SFTS increased obviously in Jiangsu Province. However, the systematic and complete analysis of spatiotemporal patterns and clusters coupled with epidemiological characteristics of SFTS have not been reported so far.MethodsData on SFTS cases were collected during 2011–2021. The changing epidemiological characteristics of SFTS were analyzed by adopting descriptive statistical methods. GeoDa 1.18 was applied for spatial autocorrelation analysis, and SaTScan 10.0 was used to identify spatio-temporal clustering of cases. The results were visualized in ArcMap.ResultsThe annual incidence of SFTS increased in Jiangsu Province from 2011 to 2021. Most cases (72.4%) occurred during May and August with the obvious peak months. Elderly farmers accounted for most cases, among which both males and females were susceptible. The spatial autocorrelation and spatio-temporal clustering analysis indicated that the distribution of SFTS was not random but clustered in space and time. The most likely cluster was observed in the western region of Jiangsu Province and covered one county (Xuyi county) (Relative risk = 8.18, Log likelihood ratio = 122.645, P < 0.001) located in southwestern Jiangsu Province from January 1, 2017 to December 31, 2021. The Secondary cluster also covered one county (Lishui county) (Relative risk = 7.70, Log likelihood ratio = 94.938, P < 0.001) from January 1, 2017 to December 31, 2021.ConclusionsThe annual number of SFTS cases showed an increasing tendency in Jiangsu Province from 2011 to 2021. Our study elucidated regions with SFTS clusters by means of ArcGIS in combination with spatial analysis. The results demonstrated solid evidences for the orientation of limited sanitary resources, surveillance in high-risk regions and early warning of epidemic seasons in future prevention and control of SFTS in Jiangsu Province.

Stability and electronic properties of hydrogenated C3B structure

AbstractExperimental and theoretical studies show that two‐dimensional (2D) materials have great potential applications in the fields of optoelectronics, semiconductors and spintronic devices. Based on the first principles, the stability, band structure, electronic properties and optical properties of hydrogenated C3B, a new graphene like 2D material, are studied in this paper. The results show that: first, with the increase of hydrogenation degree, the sp2 orbital hybridization in C3B structure gradually transits to a more stable sp3 mode, and the valence band energy near the Fermi level decreases. Second, adsorbed H atoms can regulate the bandgap of C3B. When the number of adsorbed H is even, C3B structure behaves as a semiconductor, and meanwhile the bandgap increases. When H atoms is odd, C3B is easy to show metallicity. Finally, the main absorption peak of the optical absorption spectrum decreases first and then increases with the increase of H concentration. The law of the secondary absorption peak is opposite to the main peak. When the ratio of hydrogenation is 50%, an obvious secondary absorption peak appears. This study confirms that hydrogenation is an effective way to regulate the electronic properties of materials, which can expand the application of 2D material C3B in optoelectronic devices.

A Study of Ultrasound on the Rise of Liquid in a Capillary Tube

We study the sonocapillary effect driven by ultrasound by controlling variables. In this experiment, the guideway of the Michelson interferometer is placed vertically, so that the measurable accuracy is reduced to 10μm. And we expand the observation range (0-1000μm), find that the sonocapillary effect has an obvious peak value near 30μm; The sonocapillary effect gradually decreases as the gap increases and finally becomes stable. At the same time, the Fluent software is used to simulate the process. The dynamic mesh is introduced to simulate the ultrasonic action, and the simulation results are verified with the experimental results.

Study on nonlinear dynamic characteristics of propulsion shafting under friction contact of stern bearings

A nonlinear three degree-of-freedom (3-DOF) mode-coupling model considering perturbations of the stochastic rough surface is proposed. The mechanism model is used to simulate the peak value of the friction vibration line spectrum of the real ship, and the calculation results are compared with the test results of the real ship, which verifies the correctness of the mechanism model. A nonlinear dynamic model of propeller-shaft under friction contact of stern bearing is established, which is based on the proposed mechanism model. The stability and response characteristics of the system under different operating parameters of the model are analyzed. The results show that the larger the friction coefficient between shaft and bearing is, the closer the horizontal and vertical stiffness of stern bearing is, and the smaller the modal damping ratio is, the more unstable the system is. When the system produces unstable friction self-excited vibration due to modal coupling, the friction vibration spectrum presents an obvious line spectrum peak, and the peak frequency corresponds to an unstable frequency obtained from the stability analysis, and a continuous harmonics spectrum will be generated. Under the action of friction, the shaft center makes reverse whirl, and the higher the speed is, the greater the amplitude of whirl is. When the system doesn’t have modal coupling instability, under the coupling effect of perturbations of the stochastic rough surface between the shaft and the bearing and the friction excitation of stern bearing, multiple peaks of friction-induced vibration will be generated within the upper limit of the system analysis frequency of 1000 Hz, and the peak frequency corresponds to the natural frequency of the system. Under the coupling action of the unbalanced propeller rotating eccentric force and its stern bearing friction excitation force, the system produces a vibration peak at the shaft frequency, and the frequency of the friction excitation force is equal to the excitation frequency of the unbalanced propeller rotating eccentric force.

Low-Scattering X-Band Planar Phased Vivaldi Array Antenna

A low-scattering X-band planar phased Vivaldi array antenna is proposed in this communication. To reduce the scattering cross section (SCS) of the antenna, two types of Vivaldi elements with the defected ground structures (DGSs) are designed, as well as an embedded absorbing array. Under the normal co-polarized (co-pol) incident waves, the reflections of the two Vivaldi elements are close in magnitude but out of phase. Hence, the scattering of the two elements cancels out in the normal direction. Besides, the problem of obvious bistatic SCS peaks, which always arise when utilizing the phase cancellation method to achieve SCS reduction (SCSR), is solved by the interlacing arrangement of the two elements. Under the cross-polarized (cr-pol) incident waves, the incident power is mostly received and absorbed by the absorbing array, which is composed of the dipole elements in the array center and the slot elements on two edges. According to the measured results, the proposed phased Vivaldi array antenna achieves notable cr-pol SCSR over 6–18 GHz, and the average in-band co-pol SCSR reaches 20 dB simultaneously, without any deterioration on the radiation and scanning performances compared to a referenced one.

A dual-signal fluorometric and colorimetric sensing platform based on gold-platinum bimetallic nanoclusters for the determination of β-galactosidase activity

Herein, a novel dual-signal sensing system for the determination of β-galactosidase (β-Gal) activity was established, which was based on a dual-emission probe assembled from gold-platinum bimetallic nanoclusters (Au–Pt NCs) and rhodamine B. Under the catalysis of β-Gal, 4-nitrophenyl β-D-galactopyranoside (PNPG) was rapidly hydrolyzed to generate p-nitrophenol (PNP), which has an obvious UV absorption peak at 400 nm. The hydrolyzed product PNP can quench the fluorescence of Au–Pt NCs effectively by inner filter effect (IFE), and PNP had no impact on the fluorescence of rhodamine B, which will change the emission intensity ratio of Au–Pt NCs and rhodamine B. Therefore, the ratiometric fluorescent and colorimetric dual-signal sensor based on Au–Pt NCs and rhodamine B was successfully constructed for sensitive detection of β-Gal activity. The linear detection range for the ratiometric fluorescence and colorimetric methods were 2.5–25 U/L and 15–55 U/L with detection limits of 1.2 U/L and 5.2 U/L, respectively. The developed assay method has been used for quantitative detection of β-Gal in spiked serum samples and showed good performance. And the detection platform has high reliability and excellent selectivity, which opens a new avenue for the further application of Au–Pt NCs in chemical sensing and biological analysis.