Decrease In Coefficient Research Articles

Ice Object Exclusion Characteristics of Turboshaft Engine Inlet under Helicopter/Inlet Integration Conditions

In this study, the influence laws of different parameters on the exclusion characteristics of hailstone and ice flake, and on the aerodynamic performance of the inlet are studied by numerical method. The motion of the hailstone and ice flake is simulated using the 6-DOF method. Results show that the inhalation of hailstone in the inlet decreases total pressure distortion by about 20%, and the total pressure recovery coefficient is essentially unchanged. Icing of the upper lip decreases the total pressure distortion of the inlet by about 22%, and the total pressure recovery coefficient decreases by 0.6%. The ice flakes on the inner and outer lip, when shed and brake by collision with the center body, will cause damage to the engine duct. The shedding and breaking of ice flake at an angle of 150° to the lip can result in a large amount of ice flake debris entering the engine duct, threatening the performance and structure of the engine in the rear. The motion characteristics of hailstone and ice flake under helicopter fuselage/rotor/inlet integration conditions are revealed. It also provides a reference on the numerical methods for the numerical study of hailstone/ice flake exclusion characteristics of helicopter fuselage/rotor/inlet integration conditions.

Two-phase numerical simulation of thermal and solutal transport exploration of a non-Newtonian nanomaterial flow past a stretching surface with chemical reaction

Abstract Non-uniform heat sources and sinks are used to control the temperature of the reaction and ensure that it proceeds at the desired rate. It is worldwide in nature and may be found in all engineering applications such as nuclear reactors, electronic devices, chemical reactors, etc. In food processing, heat is used to cook such as microwave ovens, pasteurize infrared heaters, and sterilize food products. Non-uniform heat sources are mainly used in biomedical applications, such as hyperthermia cancer treatment, to target and kill cancer cells. Because of its ubiquitous nature, the idea is taken as our subject of study. Heat and species transfer analysis of a non-Newtonian fluid flow model under magnetic effects past an extensible moving sheet is modelled and examined. Homogeneous chemical reaction inside the fluid medium is also investigated. This natural phenomenon is framed as a set of Prandtl boundary layer equations under the assumed convective surface boundary constraint. Self-similarity transformation is employed to convert framed boundary layer equations to ordinary differential equations. The resultant system is solved using the efficient finite difference utilized Keller box method with the help of MATLAB programming. The influence of various fluid-affecting parameters on fluid momentum, energy, species diffusion and wall drag, heat, and mass transfer coefficients is studied. Accelerating the Weissenberg number decelerates the fluid velocity. The temperature of the fluid rises due to variations in the non-uniform heat source and sink parameters. Ohmic dissipation affects the temperature profile significantly. Species diffusion reduces when thermophoresis parameter and non-uniform heat source and sink parameters vary. The Eckert number enhances the heat and diffusion transfer rate. Increasing the chemical reaction parameter decreases the shear wall stress and energy transmission rate while improving the diffusion rate. The wall drag coefficient and Sherwood number decrease as the thermophoretic parameter increases whereas the Nusselt number increases. We hope that this work will act as a reference for future scholars who will have to deal with urgent problems related to industrial and technical enclosures.

Understanding anti-corrosion mechanisms of the 2,6-dithiopurine (DTP) inhibitor molecule on iron surfaces

Purine derivatives present a high efficiency for anti-corrosion purposes while the nanoscale mechanisms are not yet fully understood. In this work, the inhibition mechanism of the 2,6-dithiopurine (DTP) molecule was investigated using advanced characterizations and atomic simulations. We revealed that the DTP molecule undergoes a multi-layer adsorption mode and is governed by both chemisorption and physisorption processes. An organometallic layer at a thickness of ∼3.8 nm was captured using TEM, comprised of Fe-N and Fe-S bonds strongly anchored to the iron interfaces, as confirmed by the XPS analysis. Our quantum chemical calculations showed that heteroatoms such as N or S in the DTP molecule offer reactive sites that facilitate its chemisorption onto iron surfaces, to form metal-organic bonds (specifically, Fe-N and Fe-S) at the DTP-iron interfaces. We further employed molecular dynamics simulations to investigate the interaction between DTP molecule and various substrates. Our findings suggest that the hydroxyl groups on the lepidocrocite surface can significantly promote bonding between DTP and iron surfaces. Based on large-scale molecular dynamics simulations, we discovered that DTP can exhibit a strong binding affinity for aggressive ions, leading to a considerable decrease in the self-diffusion coefficient of hydronium ions of up to 70 %. This work provides a new understanding of anti-corrosion mechanisms and offers opportunities to design new corrosion inhibitors possessing multiple reactive sites and strong bonding with the substrate.

The effect of inlet profiles on the repeatability in the single-stage compressor

A novel method has been proposed to design inlet gauzes in single-stage low-speed simulation compressor experiments. The aim is to investigate the method for designing inlet profiles and understand how they affect the repeatability of the compressor. Based on the inlet gauzes, the effect of the inlet profile on the compressor repeatability and its flow mechanisms was investigated by the experiments. The experiment results show that, for the single-stage low-speed compressor, as the inlet flow coefficient decreases, the loss and blockage near the rotor casing caused by the tip leakage flow are enhanced, resulting in an increase in the local absolute velocity and the total pressure. Meanwhile, the radial migration of the secondary cross flow in the stator is enhanced, leading to a thinner boundary layer at the stator outlet near casing region. Consequently, the flow capacity near the casing at the compressor outlet is enhanced with a decrease in the inlet flow coefficient. Given that the flow structure and the local loss of the compressor are not sensitive to the inlet profile at the near-choked condition, employing the inlet profile generated based on the compressor outlet profile at the near-stall condition can simulate the repeating stage environment accurately in the single-stage low-speed compressor experiment.

Effects of rotor–rotor interaction for a small tandem rotor operating in a crosswind

This study investigates the effects of rotor–rotor interaction on the wake and thrust characteristics of a small tandem rotor operating in a crosswind. Flow velocity and force measurements were conducted in a wind tunnel with two rotors arranged parallel to a crosswind. The results show that the rotor–rotor interaction significantly influences the wake characteristics and thrust generations of the tandem rotor and its effects vary depending on the crosswind speed and distance between rotor tips. In the tandem rotor configuration, the front rotor wake prevents the crosswind flow from reaching the rear rotor wake, thereby reducing the crosswind influence on it. However, under the strong rotor–rotor interaction, such as that caused by high crosswind speeds and short distances between rotor tips, the wakes of both rotors collide with each other and rapidly break down as they proceed downward. Tip-vortex characteristics are also affected by rotor–rotor interaction, which is investigated in terms of variations in the time-averaged tip-vortex trajectory and dissipation ratio with the strength of rotor–rotor interaction. These wake variations by rotor–rotor interaction lead to a decrease in thrust coefficients of the front and rear rotors, with a more significant reduction observed for the rear rotor. The thrust of the rear rotor is more significantly reduced as the crosswind speed increases and the distance between rotor tips narrows. This is mainly attributed to the increased axially induced velocity near the leading tips on the advancing side, retreating side, and centerline.

Mechanical properties, permeability and microstructural characterisation of rice husk ash sustainable concrete with the addition of carbon nanotubes

This study investigated the effects of incorporating carbon nanotubes (CNTs) into rice husk ash (RHA) sustainable concrete on its mechanical properties, permeability and microstructure characterisation. Mechanical test results suggested that the addition of 0.10 % multiwalled CNTs (MWCNTs) yielded optimal results, with increases in the compressive strength, splitting tensile strength, flexural strength, and elastic modulus of the RHA concrete at 28 days of 7 %, 23.81 %, 17.5 %, and 1.0 %, respectively. However, with further addition of MWCNTs, the mechanical properties ultimately deteriorated. Further, the incorporation of CNTs enhanced the long-term performance of RHA sustainable concrete. The addition of 0.1 % MWCNTs and 15 % RHA yielded a 20 %, 14 %, and 66 % decrease in water absorption, porosity, and chloride diffusion coefficient compared to the mixture solely containing 15 % RHA. Scanning electron microscopy of this mixture revealed the filling and bridging effects of MWCNTs between the hydration products have enhanced the performance of RHA sustainable concrete.

Investigation on the electrical and thermal properties of Cr-doped FeSe2 alloys

FeSe2 is a p-type semiconductor with a narrow band gap, which can be considered a potential thermoelectric material. Herin, the electrical and thermal properties of Cr-doped FeSe2, Fe1-xCrxSe2 (x = 0, 0.03, 0.06, and 0.09), polycrystalline alloys are investigated. All compositions show single-phase marcasite structures of FeSe2 with gradual decreases in lattice parameters with Cr doping x. With increasing x, the electrical conductivity gradually increases from 13 (x = 0) to 46 S/cm (x = 0.09), owing to a large increase in carrier concentration originated from the substitution of Cr2+ and Cr3+ at the Fe site. However, the magnitude of Seebeck coefficient decreases considerably at 300 K, resulting in decrease in power factor. In addition, the density-of-state effective mass decreases significantly from 6.0 m0–1.04 m0. At 700 K, the decrease in Seebeck coefficient is less severe. Although the total and lattice thermal conductivity decrease at all temperatures owing to additional phonon scattering of the extrinsic Cr ions, a thermoelectric figure of merit, zT, generally decreases compared to that of the pristine sample due to power factor decrease at 300 K. Meanwhile, a slight increase of zT to 0.11 is observed for x = 0.06 at 700 K.

Seismic cyclic test of perforated replaceable link for eccentrically braced frames

This study introduces a design comprising a unweakened link and four variants of perforated replaceable links, denoted as specimens RX1 (unweakened link), RX2 and RX3 (with circular holes of 50 mm diameter on the web), RX4 and RX5 specimens (with elliptical holes on the web), and RX6 and RX7 specimens (with weakened flanges and circular holes of 50 mm and 80 mm diameter on the web). Seven link specimens underwent cyclic loading tests. RX1 ultimately failed due to tearing of the weld at the connection between the flange and the end plate, while RX2 to RX7 exhibited deformation concentrated within the energy dissipating region, ceasing loading upon failure of this region, demonstrating enhanced safety and stability. All specimens exhibited relatively full hysteretic curves, with a decrease in the area of hysteretic curves corresponding to an increase in the web perforation ratio. The overstrength coefficient for specimen RX1 ranged from 1.81 to 1.82, while for specimens RX2 to RX7, it ranged from 1.80 to 3.65. Not only were the overstrength coefficients greater than RX1, but also the cumulative energy dissipation was higher than RX1. This indicates that RX2 to RX7 can accommodate larger plastic deformations, effectively utilizing plastic deformation for energy dissipation, thereby exhibiting superior safety. Moreover, an increase in web perforation ratio and weakening of the flanges resulted in a decrease in the overstrength coefficient, load-bearing capacity, and plastic deformation capacity of the specimens. Ductility decreased with increasing web perforation ratio but increased with flange weakening. Additionally, through analysis of link replacement time and residual rotation of links after unloading, it was observed that perforated replaceable links exhibited favorable replaceability.

Dynamic feature-based deep reinforcement learning for flow control of circular cylinder with sparse surface pressure sensing

This study proposes a self-learning algorithm for closed-loop cylinder wake control targeting lower drag and lower lift fluctuations with the additional challenge of sparse sensor information, taking deep reinforcement learning (DRL) as the starting point. The DRL performance is significantly improved by lifting the sensor signals to dynamic features (DFs), which predict future flow states. The resulting DF-based DRL (DF-DRL) automatically learns a feedback control in the plant without a dynamic model. Results show that the drag coefficient of the DF-DRL model is 25 % less than the vanilla model based on direct sensor feedback. More importantly, using only one surface pressure sensor, DF-DRL can reduce the drag coefficient to a state-of-the-art performance of approximately 8 % at Reynolds number $(Re) = 100$ and significantly mitigates lift coefficient fluctuations. Hence, DF-DRL allows the deployment of sparse sensing of the flow without degrading the control performance. This method also exhibits strong robustness in flow control under more complex flow scenarios, reducing the drag coefficient by 32.2 % and 46.55 % at $Re =500$ and 1000, respectively. Additionally, the drag coefficient decreases by 28.6 % in a three-dimensional turbulent flow at $Re =10\,000$ . Since surface pressure information is more straightforward to measure in realistic scenarios than flow velocity information, this study provides a valuable reference for experimentally designing the active flow control of a circular cylinder based on wall pressure signals, which is an essential step toward further developing intelligent control in a realistic multi-input multi-output system.

Assimilation of PSO and SVR into an improved ARIMA model for monthly precipitation forecasting

Precipitation due to its complex nature requires a comprehensive model for forecasting purposes and the efficiency of improved ARIMA (IARIMA) forecasts has been proved relative to the conventional models. This study used two procedures in the structure of IARIMA to obtain accurate monthly precipitation forecasts in four stations located in northern Iran; Bandar Anzali, Rasht, Ramsar, and Babolsar. The first procedure applied support vector regression (SVR) for modeling the statistical characteristics and monthly precipitation of each class, IARIMA-SVR, which improved the evaluation metrics so that the decrease of Theil's coefficient and average relative variance in all stations was 21.14% and 17.06%, respectively. Two approaches are defined in the second procedure which includes a forecast combination (C) scheme, IARIMA-C-particle swarm optimization (PSO), and artificial intelligence technique. Generally, most of the time, IARIMA-C-PSO relative to the other approach, exhibited acceptable results and the accuracy improvement was greater than zero at all stations. Comparing the two procedures, it is found that the capability of IARIMA-C-PSO is higher concerning the IARIMA-SVR, so the decrease in the normalized mean squared error value from IARIMA to IARIMA-SVR and IARIMA-C-PSO is 36.72% and 39.92%, respectively for all stations. The residual predictive deviation (RPD) of IARIMA-C-PSO for all stations is greater than 2, which indicates the high performance of the model. With a comprehensive investigation, the performance of Bandar Anzali station is better than the other stations. By developing an improved ARIMA model, one can achieve a high performance in structure identifying and forecasting of monthly time series which is one of the issues of interest and importance.

Study on the ceiling gas temperature distribution, fire merging, and flame length induced by twin tunnel fires under reduced pressures

A comprehensive understanding of the development characteristics of multiple fires in tunnels holds significant importance in estimating the thermal safe distance required for both people and facilities. In this paper, a series of numerical and experimental works are performed to examine the ceiling gas temperature, fire merging, and flame length of twin fires in a tunnel. Varied thermal hazard scenarios were simulated by altering the ambient pressure, heat release rate, and pool spacing. The findings indicate that as the ambient pressure reduces, the air entrainment coefficient decreases, resulting in a higher ceiling gas temperature. Large pool spacings demonstrate two peak impact points in ceiling gas temperature. However, as the pool spacings decrease further, only one peak impact point appears above the center of two fire sources. As pressure mounts, the low-oxygen zone at the tunnel ceiling contracts progressively, and it primarily appears in the additional region between two fire sources. The temperature processing method is adopted to determine the fire merging and flame length. The fire merging probability is predicted by introducing a piecewise model. Furthermore, a physical model is proposed based on the air entrainment theory to establish the relationship between flame length and the effects of pool spacing, ambient pressure, and heat release rate, which can be applied to both open spaces and tunnels.

Investigation of tribological behavior of coated and untreated rail steels under wet conditions

Rails are exposed to more stresses, especially in the regions of narrow radius curves and switch passages. Therefore, the tribological features of these regions are important. In this study, the effect of boronization on tribological properties was examined. For this purpose, experiments were carried out on samples boronized at 800 °C for 2 h and 8 h and on untreated samples. With these experiments, the friction coefficient, volume loss and surface roughness values of the samples under wet conditions were examined. In addition, the microstructures of the material after boriding were observed by SEM and EDX. The variance and regression method (ANOVA) was used for the statistical analysis of the experimental results. After SEM examinations, a coating layer of ∼22 μm (FeB) and ∼48 μm (FeB+Fe2B) were obtained on the surface of the rail steels boronized for 2 and 8 h, respectively. The microhardness of the rail steels, which was ∼300 HV for the untreated sample, increased to ∼1900 HV and ∼2400 HV with the boronizing process boronized for 2 and 8 h, respectively. According to the ANOVA results, the effects of the boronizing process on the decrease of the friction coefficient and the volume loss were calculated as 42% and 46%, respectively. Finally, according to the corrosion results, the corrosion resistance of the boronized rail steels decreased with the boride layer formed.

Molecular Dynamics Simulation of Methane Adsorption and Diffusion

To study the adsorption and diffusion mechanism of low-rank coal at the microscopic level, samples of Fukang low-rank coal were collected, and the elemental composition, carbon type distribution and functional group type of the Fukang low-rank coal structure were determined by elemental analysis (Ea), Fourier-transform interferometric radiometer (FTIR), X-ray photoelectron spectroscopy (XPS) and 13C nuclear magnetic resonance (13C NMR) experiments to construct a 2D molecular structure of the coal and a 3D macromolecular structure model. The adsorption and diffusion characteristics of methane were researched by giant regular Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The results showed that the excess adsorption amount of methane increased and then decreased with the increase in pressure. The diffusion of methane showed two stages with increasing pressure: a sharp decrease in the diffusion coefficient from 0.5 to 5.0 MPa and a slow decrease in the diffusion coefficient from 5.0 to 15.0 MPa. The lower the pressure, the larger the effective radius of the CH4 and C atoms, and the higher the temperature, the more pronounced the diffusion and the larger the effective radius.

Effect of purity on solidification structure and micro-segregation in a nickel-based single crystal superalloy

The purity of nickel-based single crystal alloys plays an important role in the final service performance of turbine blades as it impacts the solidification structure, elemental segregation, and inclusions of castings. The highest purity of superalloys studied before was of altogether around 10 ppm of contents of N and O produced by the triple purification process (VIM+ESR+VAR). However, the impact mechanism still remains controversial, and meanwhile whether a lower content of N and O still keeps the impacts on castings is not yet clear due to the lack of raw materials. A superhigh purity of second generation of nickel-based single crystal superalloy DD98M with the sum of N and O contents as low as 4 ppm (hitherto the highest purity of the superalloy as published), home-produced by electron beam smelting (EBS), was put on focus in this work. The effect of three levels of purity (N-doped, commercial, and EBS, corresponding to 21, 10, and 4 ppm for the sum of N and O contents, respectively) on the microstructure evolution (including primary dendrite arm spacing (PDAS), eutectic, micropores, and γ′ phase) and the solute segregation behavior at dendritic scale and nano scale (γ/γ′ interfaces) were systematically studied and the influencing mechanisms were elucidated. The results show that the PDAS decreased from 406 μm to 322 μm with the reduction of O and N from 21 ppm to 4 ppm, which was irrelevant to precipitation of the nitride or oxide inclusions. Instead, it was due to the decrease of diffusion coefficient D or the increase of equilibrium coefficient k, or the decrease of the critical nucleation supercooling and the incubation time of dendrites. The micro-segregation, the number and volume fraction of eutectic, and the number and voltage percentage of shrinkage pores and gas pores were all greatly decreased with the increase of purity. These changes were closely related to the reduction of PDAS and the reduction of fluidity of the remained liquid in the interdendrites during solidification. The morphology and the size of the γ′ phase were independent from the purity, while the segregation of alloying elements at the γ/γ′ interface changed remarkably with the variation of the purity.

Carbon emission reduction in public buildings of extreme cold regions: A study on enclosure structure and HVAC system parameter optimization

AbstractThe implementation of strategies aimed at curtailing energy consumption and carbon emissions in buildings is of paramount importance. Priority should be accorded to the reduction of embodied carbon emissions from construction materials and operational carbon emissions during the usage phase. A public building situated in an extremely cold region is chosen as the subject of this study. An initial investigation is conducted into the impact of various enclosure structure materials on embodied carbon. The impact of different heating, ventilation and air conditioning (HVAC) systems on the total carbon emissions of public buildings are studied as well. The findings indicate that the amalgamation of W3 + R + G4 + H4 culminates in the least total carbon emissions. Upon establishing the foundational scheme for the public building, an optimization (nondominated sorting genetic algorithm II [NSGA II] and Criteria Importance Through Intercrieria Correlation [CRITIC]) of the enclosure structure parameters is initiated to examine the optimal parameters of the public building's enclosure structure. The findings reveal that a decrease in the heat transfer coefficient could trigger an increase in total carbon emissions. This is attributed to the fact that the carbon emissions embodied in the production process of these materials could potentially outweigh the reduction observed in operational carbon emissions. Further adjustments were also made to the parameters of the HVAC system in the buildings. The findings indicate that within the context of public buildings, given the presence of optimal parameters and an HVAC system that utilizes solar energy for both heating and cooling in the American Society of Heating, Refrigerating and Air‐Conditioning Engineers, Inc. 6 A climatic zone, the efficiency of the cooling system can exert a significant influence on the operations carbon emissions reduction.

Analysis of operation of heat exchangers of hot water supply system in the scheme of reliable and safe heat supply of residential buildings

The scheme of internal heat supply of residential buildings with independent connection of the heating system to the external heating networks and connection of the heater of the DHW system in a parallel single-stage arrangement, providing reliability of heat supply and the necessary comfort in the premises due to the unrelated regulation of heat supply for heating, ventilation and DHW even in case of fluctuations in water intake, is considered. A mathematical model describing the non-stationary modes of operation of DHW system heaters under the conditions of implementation of this scheme is constructed and investigated. Calculations were carried out using this model, including numerical simulation on a computer using the Monte Carlo method. It is established that in this case, a decrease in the average heat transfer coefficient of the heater of the DHW system due to fluctuations in the flow of mains water following the daily change in water consumption at the DHW can be neglected, since this decrease lies within the usual error of engineering calculation, despite the fact that this coefficient depends on the flow in a nonlinear way, and its growth during the period of increased water intake for DHW does not fully compensate for the decrease during the reduction of water consumption. At the same time, it is proved that with a characteristic number of heat transfer units in a DHW system heater referred to the heated stream, the total amount of heat transferred can decrease quite noticeably, by an amount of 10 to 12 percent; however, with a rational choice of the heater size, such a decrease is within the limits allowed by the applied factors of margin when setting determination of the heat exchange surface.

Adsorption of Diffusing Tracers, Apparent Tortuosity, and Application to Mesoporous Silica.

The apparent tortuosity due to adsorption of diffusing tracers in a porous material is determined by a scaling approach and is used to analyze recent data on LiCl and alkane diffusion in mesoporous silica. The slope of the adsorption isotherm at small loadings is written as β = qA/qG, where qA is the adsorption-desorption ratio and qG = ϵ/(as) - 1 is a geometrical factor depending on the range a of the tracer-wall interaction, the porosity ϵ, and the specific surface area s. The adsorption leads to a decrease of effective diffusion coefficient, which is quantified by multiplying the geometrical tortuosity factor τgeom by an apparent tortuosity factor τapp. In wide pores or when the adsorption barrier is high, τapp = β + 1, as obtained in previous works, but in narrow pores there is an additional contribution from frequent adsorption-desorption transitions. These results are obtained in media with parallel pores of constant cross sections, where the ratio between the effective pore width ϵ/s and the actual width is ≈0.25. Applications to mesoporous silica samples are justified by the small deviations from this ideal ratio. In the analysis of alkane self-diffusion data, the fractions of adsorbed molecules predicted in a recent theoretical work are used to estimate τgeom of the silica samples, which is ≫1 only in the sample with the narrowest pores (nominal 3 nm). The application of the model to Li+ ion diffusion leads to similar values of τgeom and to a difference of energy barriers of desorption and adsorption for those ions of ∼0.06 eV. Comparatively, alkane self-diffusion provides the correct order of magnitude of τgeom, with adsorption playing a less important role, whereas adsorption effects on Li+ diffusion are much more important.

Evaluating the Effects of Metallic Waste on the Structural and Gamma-Ray Shielding Properties of Epoxy Composites.

The objective of the research is to develop novel materials that are both inexpensive and have a low density, while also being able to endure the transportation of γ-photons with low-to-medium energy levels. The outcome consisted of four epoxy resins that were strengthened with different quantities of heavy metallic waste. The density of the formed composites improved from 1.134 ± 0.022 g/cm3 to 1.560 ± 0.0312 g/cm3 when the waste content was raised from 0 to 40 weight percent. The theoretical investigation was determined using Monte Carlo (MCNP) simulation software, and the results of linear attenuation coefficient were justified experimentally in a low and medium energy range of 15-662 keV. The mass attenuation coefficient results in a low gamma energy range (15-122 keV) varied in between 3.175 and 0.159 cm2/g (for E-MW0 composite) and in between 8.212 and 0.164 cm2/g (for E-MW40 composite). The decrease in mass attenuation coefficient was detected in a medium gamma photon energy range (122-662 keV) with 0.123-0.082 cm2/g (for E-MW0 composite) and 0.121-0.080 cm2/g (for E-MW40 composite). The density of the enhanced composites influenced these parameters. As the metallic waste composition increased, the fabricated composites' half-value thickness decreased. At 15 keV, the half-value thickness decreased from 0.19 to 0.05 cm. At 59 keV, it fell from 2.70 to 1.41 cm. At 122 keV, it fell from 3.90 to 2.72 cm. At 662 keV, it fell from 7.45 to 5.56 cm. This decrease occurred as the heavy metal waste concentration increased from 0 to 40 wt.%. The study indicates that as metallic waste concentrations rise, there is a rise in the effective atomic number and a decline in the buildup factors.

Influence of Microwave and Magnetic Fields on the Electrophysical Parameters of a Tunnel Diode

In this paper, we studied the effect of an electromagnetic field of an ultrahigh frequency on the I–V characteristics of tunnel diodes. The influence of thermionic current on the change in the ratio of the values of tunnel currents at depth and the peak formed in the tunnel diode as a result of a strong electromagnetic field and on the change in the ratio of the values of tunnel currents at the highest and lowest points without exposure to a strong electromagnetic field. The I–V characteristics of a tunnel diode under the action of a microwave field is determined based on the theory of Knott and Demassa and the Tsu-Esaki model. The characteristics of the Tsu-Esaki and Karlovsky models used to determine the effect of the tunnel current in the extremely high frequency field (EHF) are shown. Chynoweth's model and Knott and Demassa's theory have shown that in germanium-based tunnel diodes, under an extremely high frequency (EHF) field, the amount of excess current generated in the tunnel diode increases. According to the Tsu-Esaki theory and Knott and Demassa theory is found to decrease the value of the differential resistance of a tunnel diode with a p-n junction under the action of a microwave field, regardless of the type of heterostructure or doping level. According to the Tsu-Esaki theory and Knott and Demassa found decrease in the diffusion capacitance of a tunnel diode with a p-n junction under the action of a microwave field, regardless of the type of heterostructure or doping level. A decrease in the transparency coefficient due to an increase in the internal field at the p-n junction boundary of a Ge-based tunnel diode under the action of a microwave field has been established. A formula is determined for determining the total current of a tunnel diode under the action of both microwave and magnetic fields, taking into account the transparency coefficient of the tunnel diode.

A physical model study on the hydraulic performances of vertical breakwaters with retreated wave walls

This paper describes a 2D physical model study on the hydraulic performances of composite vertical breakwaters with retreated wave walls. The research is an expansion of a previous experimental study by the same Authors: a very large number of experiments, in the order of 2,000, have been carried out by exploring and varying a wide range of wave and geometrical parameters of the structure, to investigate their effect and importance. In order to make feasible the execution of this large number of tests, a small-scale wave flume was used and regular wave conditions were reproduced. The influence of the wave wall retreat has been investigated in terms of wave-induced forces, reflection coefficients and wave overtopping discharges, comparing the hydraulic performances of structures with retreated walls with those of a flushed wall configuration under the same wave conditions. The large number of experiments allowed to formulate a detailed description of the complex phenomena at hand, providing statistical indicators that can be used as guidelines for preliminary design purposes of such structures, quantifying the relevant sources of uncertainty. The analysis confirmed and extended the previous findings and indicates that, on average, the hydraulic performances of structures with retreated crown wall vary significantly from those of flushed wall configurations. Specifically: (I) the forces acting on the wave wall increase of a factor up to 1.5, due to the occurrence of impulsive loads; (II) the forces acting on the caisson trunk decrease of a factor up to 0.91; (III) the global forces can decrease reaching a minimum reduction factor of 0.87, although some dangerous exceptions, in which equal or larger loads, than those occurring for standard flushed wall configuration, have been registered; (IV) the reflection coefficients decrease of a factor up to 0.83; (V) the wave overtopping discharges increase up to 2.55 times those with flushed walls.