Vertical Radiation Research Articles

MHD CONVECTIVE FLOW OF SWCNTS-WATER AND MWCNTS-WATER NANOFLUID OVER A VERTICAL CONE WITH THERMAL RADIATION AND CHEMICAL REACTION

The analysis is carried out to investigate the MHD boundary layer flow, heat, and mass transfer characteristics of two carbon nanotubes, namely single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs), with water as the base fluid by taking thermal radiation and chemical reaction into consideration. Suitable similarity conversions are employed to reduce non-linear partial differential equations into the system of ordinary differential equations, and these equations, together with boundary conditions, are solved numerically using the finite element method. Velocity, temperature, and concentration distributions, as well as skin-friction coefficient, Nusselt number, and Sherwood number for diverse values of influencing parameters, are examined in detail and the results are displayed graphically and in tabular form. It is found that the rate of heat transfer (-Θ'(0)) is remarkably higher in water-based, multi-wall carbon nanotubes than the single-wall carbon nanotubes as the values of nanoparticles volume fraction parameter rises in the boundary layer regime.

Radiation outcoupling from microdisk lasers via dielectric resonant nanoantennas

Microdisk lasers that support whispering gallery modes are very prospective devices in modern nanophotonics due to high Q-factors and low lasing generation thresholds. One of the main fundamental problems of these lasers is the low efficiency of the radiation outcoupling. Moreover, the radiation of the disks propagates mainly in the plane of the disk, whereas in some applications, a vertical radiation outcoupling is required. In this work, we use resonant dielectric nanospheres for the microdisks radiation outcoupling. We have determined the radii at which the radiation outcoupling is most efficient. After transferring a particle to the surface of the disks, we found that the particle shifted the spectral position of the disk’s resonances relative to their original position on the value less than 1 nm and reduced the thresholds of lasing on ≈ 20 %, without broadening the line. Finally, we measured directivities from such disks and observed that nanoantennas results in appearance if the directed emission

Reconfigurable Radiation Angle Continuous Deflection of All-Dielectric Phase-Change V-Shaped Antenna.

All-dielectric optical antenna with multiple Mie modes and lower inherent ohmic loss can achieve high efficiency of light manipulation. However, the silicon-based optical antenna is not reconfigurable for specific scenarios. The refractive index of optical phase-change materials can be reconfigured under stimulus, and this singular behavior makes it a good candidate for making reconfigurable passive optical devices. Here, the optical radiation characteristics of the V-shaped phase-change antenna are investigated theoretically. The results show that with increasing crystallinity, the maximum radiation direction of the V-shaped phase-change antenna can be continuously deflected by 90°. The exact multipole decomposition analysis reveals that the modulus and interference phase difference of the main multipole moments change with the crystallinity, resulting in a continuous deflection of the maximum radiation direction. Thus, the power ratio in the two vertical radiation directions can be monotonically reversed from −12 to 7 dB between 20% and 80% crystallinity. The V-shaped phase-change antenna exhibits the potential to act as the basic structural unit to construct a reconfigurable passive spatial angular power splitter or wavelength multiplexer. The mechanism analysis of radiation directivity involving the modulus and interference phase difference of the multipole moments will provide a reference for the design and optimization of the phase-change antenna.

A Compact Vertically Polarized Fully Metallic Quasi-Yagi Antenna With High Endfire Gain

A compact fully metallic antenna with high endfire gain and vertical polarization is presented for applications that require the antenna to be mounted on large metallic platforms. The proposed structure includes one driven element on a ground plane, in addition to several parasitic directors and reflectors. The antenna behaves like a Yagi array, but with vertical polarization, where multiple directors and reflectors are used to enhance the endfire gain in the plane that contains the ground surface. The driven element is an upside-down U-shaped metallic strip with short vertical sides connected to the ground plane. The radiation is predominantly emitted from these vertical sides giving the antenna its vertical polarization radiation. Directors and reflectors are designed based on the driven element, with directors having the center of the U-shaped strip connected to the ground plane and reflectors without shorting pins in the middle. A prototype is fabricated with a volume of 104 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 55\times $ </tex-math></inline-formula> 6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The measured bandwidth is 18% (5.32–6.38 GHz). The variation of endfire gain is 2 dB around the nominal gain of 10.3 dBi across the bandwidth.

Mathematical modeling of MHD flow and radiative heat transfer past a moving porous rotating disk with Hall effect

PurposeThe present study aims to investigate the effect of radiation on the unsteady magnetohydrodynamic (MHD) flow of a viscous, electrically conducting Newtonian fluid over rotating disk moving upward/downward immersed in a porous medium, considering the Hall effect. The study is motivated by the various applications in the context of solar power technology, electric power generation, Hall accelerators, MHDs generators and other industrial areas when the fluid flow is subjected to the previously mentioned effects such as MHD, Hall effect and thermal radiation.Design/methodology/approachSuitable similarity transformations are employed to reduce the governing nonlinear partial differential equations into the nonlinear ordinary ones. The solutions of the reduced system are numerically obtained using the boundary value problem (BVP) Midrich scheme in Maple. The results are presented graphically for vertical disk movement, magnetic parameter, Hall current, Darcy parameter, thermal radiation and Schmidt number. Skin frictions, mass and heat transfer rates are numerically tabulated.FindingsIt is revealed that the vertical motion of the disk significantly boosts the radial and annular flows. Moreover, the Hall parameter has contrasting effects on velocity profiles for the range of magnetic field but temperature field is oblivious of this behavior. It is observed that heat and mass transfer considerably enhance along vertical disk movement. Also magnetic field, temperature ratio and radiation parameter significantly enhance the temperature field, while reaction rate parameter and Schmidt number decrease the concentration profile. The current model is calibrated in its reduced form to an already published literature with good correlation to ensure the numerical scheme's validity.Originality/valueThis work is original within the best efforts of the authors.

High-Efficiency Grating Couplers for Pixel-Level Flat-Top Beam Generation

We demonstrate a kind of grating coupler that generates a high quality flat-top beam with a small beamwidth from photonic integrated circuits into free-space. The grating coupler is designed on a silicon-on-insulator wafer with a 220-nm-thick silicon layer and consists of a dual-etch grating (DG) and a distributed Bragg reflector (DBR). By adjusting the structural parameters of DG and DBR, a pixel-level (6.6 µm) flat-top beam with a vertical radiation of −0.5 dB and a mode match of 97% at 1550 nm is realized. Furthermore, a series of high-efficiency grating couplers are designed to create a flat-top beam with different scales.

Improvement mechanism of wedged column on the cooling performance of vertical delta radiator

Vertical delta radiators were widely used in dry cooling towers as the key radiator element. But the delta structure was very easy to induce large vortex between its two sides when the air was slantly flow in, which was very commonly under real natural crosswind conditions. To alleviate the adverse effect of large vortex on its adjacent cooling column radiator, one type of wedged cooling column was proposed, which was a columnar cooling tube bundle with a wedged-shaped gap. A three-dimensional (3D) numerical model for natural draft dry cooling tower (NDDCT) with vertical delta radiators was established and validated to study the improvement mechanism of wedged cooling column on the cooling performance of vertical delta radiators. Both aerodynamic field and air temperature field were compared and studied between the vertical delta radiators with wedged columns (VDRWs) and usual vertical delta radiators. It could be found that both the heat transfer temperature difference and air mass flow rate of VDRWs were greater than those usual, which could decrease the exit water temperature by 0.27 and 2.23 °C separately at no crosswind and 7 m/s crosswind. Beside, the equivalent outlet water temperature TA could decrease by 0.493 °C, which suggested that the wedged cooling column could improve the cooling performance of vertical delta radiators to some extent.

Group theory based formation mechanism and evolution of multiple Fano resonances in dielectric nanohole arrays with lattice-perturbed

Based on the electromagnetic properties of all-dielectric optical metamaterial, an all-dielectric metasurface of lattice-perturbed nanohole array is proposed to excite a multiple Fano resonance in the near-infrared region. Combined with the group theory, the formation mechanism and evolution law of multiple Fano resonances in this structure when its unit cell is a square lattice configuration and the square lattice symmetry is broken are explored in depth. The results show that double degenerate mode directly excited by the normal incident plane wave is coupled to vertical free-space radiation continuum to form double Fano resonance when unit cell is symmetrical, while the uncoupled non-degenerate modes excited by the normal incident plane wave is coupled to vertical free-space radiation continuum to form triple Fano resonance with higher &lt;i&gt;Q&lt;/i&gt; factor when the symmetry is broken. Numerical simulation is used to explore the influences of &lt;i&gt;x&lt;/i&gt;-polarized and &lt;i&gt;y&lt;/i&gt;-polarized plane wave on the above Fano resonances, and the results show that the Fano resonance of double degenerate resonance is polarization independent, while the non-degenerate resonance is polarization dependent. The findings in this work can provide an effective theoretical reference for designing other square lattice metasurface to realize the excitation and evolution of multiple Fano resonances.

Thermal environment investigation of asymmetric radiation coupled with convection heating.

The couple of radiation with convection heating owned advantages of less energy utilization, healthier and more comfortable indoor environment. However, local thermal discomfort was often induced by large vertical temperature difference and radiation asymmetry temperature. This work studied indoor thermal environment characteristics under different coupling ways of radiation and convection heating terminals through experiments and CFD simulation. The studied five scenarios were denoted as: (I) lateral air supply + adjacent side wall radiation, (II) lateral air supply + opposite side wall radiation, (III) lateral air supply + floor radiation, (IV) lateral air supply + adjacent side wall radiation + floor radiation, and (V) lateral air supply + opposite side wall radiation + floor radiation. The overall thermal comfort indices (including air diffusion performance index (ADPI), predicted mean vote (PMV), and predicted percent of dissatisfaction (PPD)) and local thermal comfort indices under different scenarios were investigated. For Scenarios I–III, the local dissatisfaction rates caused by vertical air temperature difference were 0.4%, 0.1%, and 0.2%, respectively, which belonged to “A” class according to the ISO-7730 Standard. While the vertical asymmetric radiation temperature of Scenario I/II was about 6.5 °C lower than that of Scenario III/IV/V. The ADPI for Scenarios III–V were about respectively 5.7%, 16.7%, and 21.0% higher than that of Scenarios I–II, indicating that a large radiation area and radiation angle coefficient could reduce the discomfort caused by radiant temperature asymmetry. The coupling mode improved local discomfort by decreasing vertical temperature difference and radiation asymmetry temperature wherefore improving the PMV from −1.6 to −1. The lateral air supply coupled with asymmetric radiation heating could potentially improve the thermal comfort of occupied area, while the comprehensive effect of thermal environmental improvement, energy-saving, and cost-effectiveness needes to be further investigated.

Emission directionality of electronic intraband transitions in stacked quantum dots

We investigate the emission directionality of electronic intraband (intersubband) transitions in stacked coupled quantum dots. Using a well-established eight-band $k \cdot p$ method, we demonstrate that the minor contributions from the valence band mixing into the conduction band govern the polarization and emission directionality of electronic $p$-to-$s$-type intraband transitions. Despite that the contribution from the central-cell part to the momentum matrix element is dominant, we find, the contribution from the matrix elements among the envelope functions cannot be neglected. With the help of an artificial cuboidal quantum dot, we show that the vertical emission from intraband transitions can be tuned via the emitter's vertical aspect ratio. Subsequently, we show that these results can be transferred to more realistic geometries of quantum dots and quantum dot stacks and demonstrate that the vertical emission can be enhanced from $23$ % to $46$ % by increasing the emitter's vertical aspect ratio to the isotropic case with a vertical aspect ratio of 1.0. Therefore, a stacking of a few quantum dots ($\sim$4 for the investigated structures) is already sufficient to improve the vertical radiation significantly. Additionally, we discuss the impact of the number of stacked QDs as well as the effect of the interdot coupling strength on the radiation properties.

Shifting the operating frequency of the piezoceramic electroacoustic transducer langevin type using passive cooling methods

The object of research: the shift of resonant frequency of the piezoceramic electroacoustic transducer Langevin type depending on the shape of the back plate.&#x0D; Investigated problem: the relationship between changes in shape of back plate of the Langevin type transducer with the resonant frequency of the oscillating system. Search quantitative contribution to shift the resonant frequency of each of the modifications: shape, diameter, thickness, weight of back plate.&#x0D; The main scientific results: vibration modes of a transducer with a back plate with horizontal and vertical radiator ribs were obtained. The graphs of the shift resonant frequency depending on the change in the diameter and thickness of the back tail with vertical radiator ribs are presented. It is established, that the change in the thickness and diameter of the back plate of the transducer effects on resonance frequency much less than the change in mass.&#x0D; The area of practical use of the research results: designing piezoceramic electroacoustic transducer with passive cooling method.&#x0D; Innovative technological product: guidelines for choosing the shape changes back plates of the Langevin type transducer for decreasing heating temperature, with keeping resonant frequency.&#x0D; Scope of the innovative technological product: scope of application of the Langevin type transducer: underwater acoustics, ultrasonic technological equipment, ultrasonic engine, piezotransformer, medical equipment, rock drilling devices.

Orientation of Cellulose Nanocrystals Controlled in Perpendicular Directions by Combined Shear Flow and Ultrasound Waves Studied by Small-Angle X-ray Scattering

The combined effect of shear flow and ultrasound (US) waves on the dynamical structural orientations of cellulosic cholesteric liquid crystals was investigated by time-resolved, in situ small-angle X-ray scattering (SAXS). A dedicated channel-type shear flow/ultrasound cell for SAXS characterization was developed to simultaneously generate a shear flow-induced horizontal stress force and a US-induced vertical acoustic radiation force. The control of the alignment of anisometric cellulose nanocrystals (CNCs), with their director parallel to the ultrasonic wave direction of propagation, was revealed at an unprecedented nanometer scale. Concurrently, the application of shear flow induced a horizontal orientation of CNCs with their directors aligned along the velocity direction. By adjusting the level of simultaneously applied shear flow and US intensity to the CNC suspensions, it was possible to tune the direction and the level of orientation of the CNCs during a period of time. For a specific ratio of the applied shear rate to acoustic power, some transient orientation of the CNCs at an intermediate angle between horizontal and vertical directions was evidenced. Relaxation of these orientations’ phenomena upon cessation of flow and/or US was also highlighted.

Study of the influence of the housing on the cooling efficiency of the piezoceramic electroacoustic Langevin-type transducer

The object of research is thermal processes in Langevin-type piezoceramic electroacoustic transducers (PET), taking into account the housing. The piezoceramic electroacoustic transducers heat up during operation. Overheating of the converter leads to negative consequences, accompanied by a change in the parameters, characteristics of the device, as well as the failure of the converter. Or limitation on the duration and mode of operation, output power, current, amplitude and speed of oscillation of the converter. The paper investigates the effect of the housing on the temperature field of a Langevin-type PET by the finite element method, using modeling in SolidWorks. The results of temperature reduction of such cooling methods are shown: – filling the housing cavity with electrical insulating liquid, gas, a mixture of thermal paste; – use of holes in the housing; – changing the shape of the rear cover to have radiator side fins, vertical radiator fins, cylindrical radiator fins; – heat-resistant layer; – use of active air cooling at three different speeds. The most efficient 53 % and a uniform temperature field were found when filling with a mixture of thermal paste, but this solution is accompanied by additional experiments and a preparatory stage with the mixture. The cooling efficiency of 47 % was provided by active cooling – blowing with air, and this method requires additional equipment. Filling with insulating liquid gave a cooling efficiency of 27 % – an optimal result that does not require expensive investments. Slow blowing of the housing or adding only holes resulted in a decrease in the maximum heating temperature from 10 to 20 %, therefore, if the PET design allows the presence of holes, then it is necessary to rationally place them. Changing the shape of the back plate, heat-absorbing element, filling the housing with gas gave an efficiency decrease in the maximum temperature by 6–8 % compared to a closed housing with air. The research results make it possible to choose the optimal option for reducing the heating temperature of the Langevin-type PET to increase its efficiency and long-term trouble-free operation.

Omnidirectional oversized annular lens antenna with high gain for 5G millimeter‐wave channel measurement

AbstractA high gain oversized annular lens antenna for 28‐GHz band channel measurement system is presented. The proposed antenna is composed of an omnidirectional feeding source and an oversized annular lens. The feeding source is a compact multi‐stepped biconical antenna with a wide impedance bandwidth. By rotating a horizontally placed two‐dimensional extended hemispherical lens around the vertical axis, the oversized annular lens is realized, which effectively increases the vertical radiation aperture and maintains high aperture efficiency to enhance the omnidirectional gain. Under the same envelope, the proposed antenna features a higher gain than the biconical antenna and the ordinary annular lens antenna. A prototype is fabricated and measured. The measured results demonstrate that the ‐10‐dB impedance bandwidth is 20.7% (24‐29.6 GHz), with stable vertically polarized (VP) omnidirectional radiation patterns and gain over 10.3 dBi within the entire band of interest.

Modeling Extreme Warm‐Air Advection in the Arctic During Summer: The Effect of Mid‐Latitude Pollution Inflow on Cloud Properties

AbstractUsually the Arctic is relatively free of anthropogenic influence in summer, which means that particles from natural sources can be the most significant nuclei for cloud droplets. However, this is not the case during anomalously warm‐air intrusions when the air origin comes from lower latitudes. In this modeling study, we investigate the effect of mid‐latitude pollution inflow (anthropogenic and biomass burning [BB]) on the aerosol‐cloud‐radiation interactions during an episode of extreme warm‐air advection. This particular episode resulted in anomalously high air temperatures over the East Siberian Sea and has accelerated sea‐ice melting. The impact of different emission sources on aerosol vertical distribution, chemical composition, cloud formation, and radiation budget is examined using the Weather Research and Forecasting model, fully coupled with chemistry. Elevated turbulent clouds that occurred at the beginning of the episode are found to be more sensitive to aerosol variations and their negative feedback on supersaturation, compared to stably stratified fog layers that were dominant during the core period. Omission of either anthropogenic or BB source results in decreased cloud liquid water and cloud droplet concentrations; however, these changes are not substantially large to significantly modify the net surface radiation budget. Significant reduction of the net surface radiation is only observed if both anthropogenic and BB transported pollution reaches the area of interest.

Direct-ARPES and STM Investigation of FeSe Thin Film Growth by Nd:YAG Laser

Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF2 (001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation shows hole-like and electron-like pockets at the Γ and M points of the Fermi surface, consistent with previous observations on cleaved single crystal surfaces. The control achieved in growing quantum materials with volatile elements such as Se by in-situ PLD makes it possible to address the fine analysis of the surfaces by in-situ ARPES and XPS. The study opens wide avenues for the PLD based heterostructures as work-bench for the understanding of proximity-driven effects and for the development of prospective devices based on combinations of quantum materials.

ТЕПЛОТЕХНІЧНІ ОСОБЛИВОСТІ СВІТЛОПРОЗОРИХ ОГОРОДЖУВАЛЬНИХ КОНСТРУКЦІЙ БУДІВЕЛЬ

The use of glass fencing structures - panoramic windows in the residential segment of modern city development is investigated. The peculiarities of the use of panoramic windows in the residential segment of the region are determined. An analysis of scientific publications in magazines with the impact - a factor and the approaches to increasing the energy efficiency of the thermal insulation shell of the building with glass elements of the facade are determined. The advantages and disadvantages of the use of panoramic windows in terms of heat engineering properties of a fencing structure are outlined. It is determined that according to the normative method of calculating the given thermal resistance, there may be a significant difference in calculating the entire facade and design for one room. To confirm the comparative calculation, which resulted in the resulting thermal resistance for a fragment of the facade (where there are two windows) is 3,3 m2 K / W (corresponding to the requirements of the normative value), and when calculating the fragment of this facade of a separate room with a panoramic window with a panoramic window. The result of the given thermal resistance is 2,6 m2 K / W (which is significantly lower than the normative value). The factors influencing the technical state of panoramic windows are outlined and lead to a decrease in the heat-insulating characteristics of the enclosing structures of the building; As well as measures and organizational and technical solutions, which allows the use of panoramic windows in modern housing construction. It is proposed for the heating of premises with panoramic windows of the scheme of placement of heating systems, namely: installation of vertical radiators on the side of the double-glazed windows; Planting a convector-type floor battery; arrangement of the system "Warm floor" and combined systems; internally floor convectors; infrared heaters; Installing slit or plinth convectors in the floor below the window, on the wall or ceiling. Recommended investors of new apartments to pay attention not only to the facade of the facade in the design decisions of external enclosures of buildings with the use of panoramic windows, as well as technical solutions of windows, ventilation and heating systems, which significantly affect the energy efficiency of the future apartment.

CPW-Fed Super-Wideband Antenna With Modified Vertical Bow-Tie-Shaped Patch for Wireless Sensor Networks

In this paper a coplanar waveguide-fed super-wideband antenna is presented for wireless sensor networks. The studied low-profile design is comprised of a modified bow-tie-shaped vertical patch and two asymmetrical ground planes and has been prototyped on a single-sided FR4 microwave substrate. The anticipated antenna has an overall size of $0.25\lambda \times 0.20\lambda $ at 3.035 GHz, the lowest frequency of the operating band. The vertical radiator coupled well with the two coplanar ground planes which enabled the studied antenna to achieve an operating band of 3.035–17.39 GHz (140.56%). The presented antenna demonstrates almost omnidirectional radiation patterns over the entire operating with an average gain of 4.56 dBi and average efficiency of 76.62%. The antenna also features with high fidelity factor, flat group delay, small phase distortion, and good response of transfer function. All these characteristics of the studied antenna make it a robust contender for wireless sensor node applications.

Thoracic flexion provokes circumferential dysesthesia: A symptom of thoracic cord lesions in MS

Thoracic flexion, a rapid forward flexion at the waist, can elicit a circumferential electrical sensation in some patients with multiple sclerosis. The clinical and radiographic features of this phenomenon are described here. This symptom is typically a sensory band around the T6-T7 dermatomes and is usually associated with recent thoracic cord lesions. It is clinically independent of cervical pathology and Lhermitte’s sign. Similar to the vertical radiation of symptoms upon neck flexion due to cervical cord lesions, this sign may help localize MS plaques to the thoracic cord, even when thoracic MRI is negative.

Measurement of natural radioactivity concentrations in walnut collected from different markets in Sulaimanya city-Kurdistan region-Iraq

Walnut is one of the most important and necessary foodstuffs in our daily lives and there are many species in Iraqi Kurdistan from different sources. Therefore, the significant point in this works is gamma rays measuring to estimate various radiation hazards via walnut consumption for different markets. The samples have been collected from different markets and locations in Sulaimanya governorate in Kurdistan region-Iraq.The average specific activities for nuclides found with high probability for the walnut by using a vertical coaxial cylindrical High Purity Germanium Radiation Detector (HPGe). The specific activity for the shell of the walnut were for the three most important radionuclides 232Th, 226Ra and 40K were 14.842 ± 9.450, 7.226 ± 1.805, 107.2 ± 2.563 (Bq/kg) respectively, and for walnut pulp 232Th, 226Ra and 40K were 16.053 ± 8.861, 5.105 ± 1.540, 143.6 ± 2.884 (Bq/kg) respectively. The total average activities were within the average ranges of the accepted values in the world (45, 33 and 420 Bq/kg for 232Th, 226Ra and 40K respectively).