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Speed of sound waves in gases and liquids are governed by the compressibility of the medium. There exists another type of non-dispersive wave where the wave speed depends on stress instead of elasticity of the medium. A well-known example is the Alfven wave, which propagates through plasma permeated by a magnetic field with the speed determined by magnetic tension. An elastic analogue of Alfven waves has been predicted in a flow of dilute polymer solution where the elastic stress of the stretching polymers determines the elastic wave speed. Here we present quantitative evidence of elastic Alfven waves in elastic turbulence of a viscoelastic creeping flow between two obstacles in channel flow. The key finding in the experimental proof is a nonlinear dependence of the elastic wave speed c el on the Weissenberg number Wi, which deviates from predictions based on a model of linear polymer elasticity. An analog of Alfven waves in plasma with velocity set by magnetic tension has been predicted to appear in elastic turbulence. Here the authors observe elastic Alfven waves in elastic turbulence of polymer solution flow between two obstacles where the velocity is defined by elastic stress.

The development of emerging technologies in satellite communications, military applications, scientific research, short-range wireless networks, 5G, and mm-wave machine-to-machine communications always demands ultra-high speed transmission capabilities (high data rates), wide bandwidth, high-gain, and low-latency antennas. To achieve these requirements, a high-gain circular quasi-fractal antenna for advanced 5G communications and mm-waves is analysed, fabricated, and investigated. The super-compact (6127 × 6284 µm2) reduced electrical length patch antenna is fabricated on a low-loss RT Duroid 5880 substrate of thickness 127 μm at U-band 50 GHz frequency. The proposed design utilizes the same concept of a fractal, but it is designed to reduce the electrical length of the antenna patch in reverse-fractal ways. This helps to miniaturize the antenna size to 35.155% and, therefore, the antenna becomes more economical. A two-iteration quasi-fractal is applied to the rectangular patch to minimize the lower current portion from the patch. This results in antenna tuning at 50 GHz, enhancing bandwidth and gain values. The antenna achieves a gain of 7.44 dBi and a wider bandwidth from 42.04 GHz to 57.34 GHz. Therefore, the designed antenna is suitable for wireless personal area networks (WPAN), future LAN, and energy launchers in U-band microstrip to rectangular waveguide transition. A lumped-element electrical equivalent R, L, C circuit of the antenna is generated and validated using the Advanced Design System (ADS) software, and its reflection coefficient (S11) is found in excellent agreement with the S11 of the HFSS-designed antenna.

Electron transport in two-dimensional conducting materials such as graphene, with dominant electron–electron interaction, exhibits unusual vortex flow that leads to a nonlocal current-field relation (negative resistance), distinct from the classical Ohm’s law. The transport behavior of these materials is best described by low Reynolds number hydrodynamics, where the constitutive pressure–speed relation is Stoke’s law. Here we report evidence of such vortices observed in a viscous flow of Newtonian fluid in a microfluidic device consisting of a rectangular cavity—analogous to the electronic system. We extend our experimental observations to elliptic cavities of different eccentricities, and validate them by numerically solving bi-harmonic equation obtained for the viscous flow with no-slip boundary conditions. We verify the existence of a  predicted threshold at which vortices appear. Strikingly, we find that a two-dimensional theoretical model captures the essential features of three-dimensional Stokes flow in experiments. Viscous electron flow in graphene has been shown to exhibit vortices. Here the authors report analogous vortices in viscous fluid flow through a narrow channel making the presented fluidic system an attractive setup for quantative measurements which are otherwise hard to perform with viscous electron flow.

Turbulence generally arises in shear flows if velocities and hence, inertial forces are sufficiently large. In striking contrast, viscoelastic fluids can exhibit disordered motion even at vanishing inertia. Intermediate between these cases, a state of chaotic motion, “elastoinertial turbulence” (EIT), has been observed in a narrow Reynolds number interval. We here determine the origin of EIT in experiments and show that characteristic EIT structures can be detected across an unexpectedly wide range of parameters. Close to onset, a pattern of chevron-shaped streaks emerges in qualitative agreement with linear and weakly nonlinear theory. However, in experiments, the dynamics remain weakly chaotic, and the instability can be traced to far lower Reynolds numbers than permitted by theory. For increasing inertia, the flow undergoes a transformation to a wall mode composed of inclined nearwall streaks and shear layers. This mode persists to what is known as the “maximum drag reduction limit,” and overall EIT is found to dominate viscoelastic flows across more than three orders of magnitude in Reynolds number.

This study introduces a novel antenna based on the binary operation of a modified circular patch in conjunction with the Koch fractal. The antenna is intended for applications in the sub-6 GHz band, partial C-band, and X-band. The low-cost antenna is fabricated on a 1.6-mm-thick FR-4 substrate. A frequency-selective surface (FSS) is used to overcome the decreased values of the gain and bandwidth due to the fractal operations. The introduced split ring resonator (SRR) and the antenna substrate dimension reduction reduce the bandwidth and antenna gain. The air gap between the FSS and the antenna not only enhances the antenna gain but also controls the frequency tuning at the design frequency. The antenna size is miniaturized to 36.67%. A monopole antenna ground loaded with an SRR results in improved closest tuning (3.44 GHz) near the design frequency. The antenna achieves a peak gain of 9.37 dBi in this band. The FSS-based antenna results in a 4.65 dBi improvement in the gain value with the FSS. The measured and simulated plots exhibit an excellent match with each other in all three frequency bands at 2.96–4.72 GHz. These bands cover Wi-MAX (3.5 GHz), sub-6 GHz n77 (3300–3800 MHz), n78 (3300–4200 MHz), and approximately n79 (4400–4990 MHz), in addition to C-band applications.

An antenna for the elimination of in-band application interferences in the sub-6 GHz mid-frequency region is presented. The hybrid patch loaded with a complementary split ring resonator (CSRR) eliminates the in-band interference issue by introducing a notch band from 4.22 GHz to 4.39 GHz, which bisects the wideband into two distinct bands and separates n77/78 bands to interfere with the n79 band. A hybrid patch is obtained on a circular substrate using edge feeding. The hybrid patch comprises a combination of an equilateral triangle and a regular pentagon. The reduced ground length makes the antenna frequency response wideband. This stage has a wideband frequency spectrum and suffers from in-band application interferences between n77 (3.8-4.2 GHz), n78 (3.3-3.8 GHz), and n79 (4.4-5.0 GHz). The CSRR loading eliminates the existing inband application interference. The antenna achieves a gain of 4.72 dBi and 4.54 dBi at 3.39 GHz and 4.46 GHz in the two bands (2.94-4.22 GHz) and (4.39-5.80 GHz), respectively. The HFSS-designed antenna is again designed in the CST software, then fabricated and measured using SVA1075X, and their reflection coefficients and radiation patterns are compared, and these are found in good agreement. The result validates the antenna functionality. This antenna is suitable for Wi-Fi 5 (802.11ac) and Wi-Fi 6 (802.11ax), n77, n78, n79, S-band and C-band satellite, and radar applications. The circular layout antenna is novel in the sense that it occupies less space and becomes compact without its miniaturization exercise concerning traditional antennas designed on the same frequencies.

A series of four A2B corroles (where A = para-nitrophenyl, and B = 2,3,4,5,6-pentafluorophenyl, 2,6-difluoro, 2,6-dichloro and 2,6- dibromophenyl group) have been synthesized and characterized. These four corroles were tested for the sensing ability towards Hg2+ ion. The LOD for these corroles are comparable to reported sensors for Hg2+ ions. All these our A2B corroles exhibit different fluorescence quenching due to the electronic effect of the phenyl group at C10 position, which has a different halogen atom at 2,6 position of the phenyl ring.Graphical abstractA2B free base corroles were synthesized, characterized, and demonstrated as Hg2+ ion sensors. These corroles are highly selective towards the Hg2+ ions and depend on the halogen group substituted on the meso phenyl group.

Purpose This paper aims to present the design development and measurement of two aerodynamic slotted X-bands back-to-back planer substrate-integrated rectangular waveguide (SIRWG/SIW) to Microstrip (MS) line transition for satellite and RADAR applications. It facilitates the realization of nonplanar (waveguide-based) circuits into planar form for easy integration with other planar (microstrip) devices, circuits and systems. This paper describes the design of a SIW to microstrip transition. The transition is broadband covering the frequency range of 8–12 GHz. The design and interconnection of microwave components like filters, power dividers, resonators, satellite dishes, sensors, transmitters and transponders are further aided by these transitions. A common planar interconnect is designed with better reflection coefficient/return loss (RL) (S11/S22 ≤ 10 dB), transmission coefficient/insertion loss (IL) (S12/S21: 0–3.0 dB) and ultra-wideband bandwidth on low profile FR-4 substrate for X-band and Ku-band functioning to interconnect modern era MIC/MMIC circuits, components and devices. Design/methodology/approach Two series of metal via (6 via/row) have been used so that all surface current and electric field vectors are confined within the metallic via-wall in SIW length. Introduced aerodynamic slots in tapered portions achieve excellent impedance matching and tapered junctions with SIW are mitered for fine tuning to achieve minimum reflections and improved transmissions at X-band center frequency. Findings Using this method, the measured IL and RLs are found in concord with simulated results in full X-band (8.22–12.4 GHz). RLC T-equivalent and p-equivalent electrical circuits of the proposed design are presented at the end. Practical implications The measurement of the prototype has been carried out by an available low-cost X-band microwave bench and with a Keysight E4416A power meter in the microwave laboratory. Originality/value The transition is fabricated on FR-4 substrate with compact size 14 mm × 21.35 mm × 1.6 mm and hence economical with IL lie within limits 0.6–1 dB and RL is lower than −10 dB in bandwidth 7.05–17.10 GHz. Because of such outstanding fractional bandwidth (FBW: 100.5%), the transition could also be useful for Ku-band with IL close to 1.6 dB.

Flows through pipes and channels are, in practice, almost always turbulent, and the multiscale eddying motion is responsible for a major part of the encountered friction losses and pumping costs 1 . Conversely, for pulsatile flows, in particular for aortic blood flow, turbulence levels remain low despite relatively large peak velocities. For aortic blood flow, high turbulence levels are intolerable as they would damage the shear-sensitive endothelial cell layer 2 – 5 . Here we show that turbulence in ordinary pipe flow is diminished if the flow is driven in a pulsatile mode that incorporates all the key features of the cardiac waveform. At Reynolds numbers comparable to those of aortic blood flow, turbulence is largely inhibited, whereas at much higher speeds, the turbulent drag is reduced by more than 25%. This specific operation mode is more efficient when compared with steady driving, which is the present situation for virtually all fluid transport processes ranging from heating circuits to water, gas and oil pipelines. Turbulence can be reduced by more than 25% in ordinary pipe flow by unsteady, pulsatile driving specifically mimicking the cardiac cycle and extending this method to large Reynolds numbers.

Pulsating flows through tubular geometries are laminar provided that velocities are moderate. This in particular is also believed to apply to cardiovascular flows where inertial forces are typically too low to sustain turbulence. On the other hand, flow instabilities and fluctuating shear stresses are held responsible for a variety of cardiovascular diseases. Here we report a nonlinear instability mechanism for pulsating pipe flow that gives rise to bursts of turbulence at low flow rates. Geometrical distortions of small, yet finite, amplitude are found to excite a state consisting of helical vortices during flow deceleration. The resulting flow pattern grows rapidly in magnitude, breaks down into turbulence, and eventually returns to laminar when the flow accelerates. This scenario causes shear stress fluctuations and flow reversal during each pulsation cycle. Such unsteady conditions can adversely affect blood vessels and have been shown to promote inflammation and dysfunction of the shear stress-sensitive endothelial cell layer.