Disk Radius Research Articles

A forced convection of water-aluminum oxide nanofluids in a square cavity containing a circular rotating disk of unit speed with high Reynolds number: A Comsol Multiphysics study

This research article concentrates on forced convection with a high Reynolds number of the water-alumina-based nanofluid in the square cavity containing a rotating disk with a unit speed. A very dense mesh is used to obtain the numerical results with the finite element package of COMSOL Multiphysics 5.6. For the research study, we select the parameters, the Reynolds number (106 to 1.005 × 106), a radius of the rotating disk (0.1m–0.2 m), and volume fraction (0.001–0.009 and 0.01–0.05). About 54 simulations are obtained using the Rayleigh numbers 7 × 106 to 1.54 × 106 and keeping the Prandtl number less than 0.7. The outcomes will be validated with correlations from the local Nusselt number literature and the independent mesh study. The results will be displayed with the surface plots and graphs for temperature, average temperature, local and average Nusselt number, mass flow rate, skin friction coefficient, and average values on the surface of the circular rotating disk. A correlation originated between the temperature as an average on the surface of a rotating cylinder and mass flow rate, which describe a negative association between the mass flow rate and the average temperature on the surface of a circular disk. It was concluded that the coefficient of skin friction improves with an upsurge in volume fraction of the nanofluid, whereas it shows a non-functionality with an average Nusselt number when an increment is made in the radius of a circular disk.

The spin of new black hole candidate: MAXI J1803−298 observed by NuSTAR and NICER

ABSTRACT MAXI J1803−298, a newly-discovered Galactic transient, and black hole candidate was first detected by MAXI/GSC on 2021 May 01. In this paper, we present a detailed spectral analysis of MAXI J1803−298. Utilizing the X-ray reflection fitting method, we perform a joint fit to the spectra of MAXI J1803−298, respectively, observed by NuSTAR and NICER/XTI on the same day over the energy range between 0.7–79.0 keV in SIMS state, and the observed inner radius of the accretion disc is demonstrated to have extended to the ISCO radius (Rin =1.08 RISCO). Implementing the relativistic reflection model relxillCp, we found its spin (and the inclination angle i) can be constrained to be close to an extreme value, 0.991 (i ∼ 70 °), at 68 per cent confidence interval. The results suggest that MAXI J1803−298 may be a fast-rotating black hole with a large inclination angle.

ULX pulsar Swift J0243.6+6124 observations with NuSTAR: dominance of reflected emission in the super-Eddington state

ABSTRACT We report the discovery of the bright reflected emission component in the super-Eddington state of the ultraluminous X-ray pulsar Swift J0243.6+6124, based on the NuSTAR observations of the source during its 2017 outburst. The flux of the reflected emission is weakly variable over the pulsar phase while the direct emission shows significantly larger pulsation amplitude. We propose that in this system the neutron star finds itself in the centre of the well formed by the inner edge of the geometrically thick super-Eddington accretion disc truncated by the magnetic field of the pulsar. The aspect ratio of the well is H/R ∼ 1. The inner edge of the truncated disc is continuously illuminated by the emission of the accretion column giving rise to the weakly variable reflected emission. As the neutron star rotates, its emission sweeps through the line of sight, giving rise to the pulsating direct emission. From Doppler broadening of the iron line, we measure the truncation radius of the accretion disc ∼50 Rg. The inferred dipole component of the magnetic field is consistent with previous estimates favouring a not very strong field. The uniqueness of this system is determined by its moderately super-Eddington accretion rate and the moderate magnetic field so that the inner edge of the truncated geometrically thick accretion disc is seen from the neutron star at a large solid angle.

Three-dimensional structure of the central molecular zone

ABSTRACT A detailed comparison of H i and CO line cube data of the Galactic Centre (GC) region from the archives is obtained. The central molecular zone (CMZ) is shown to be embedded in the H i disc (central H i zone, CHZ) of radius ∼320 pc and vertical scale height ∼70 pc. A radio continuum belt is shown to run parallel to molecular Arms I and II. The belt draws a double infinity (∞∞) on the sky, connecting Sgr E (l ∼ −1${_{.}^{\circ}}$2), C, B1, B2, and Sgr D (+1${_{.}^{\circ}}$2), and is interpreted as a warping star-forming ring. The molecular Arms are closely associated with the H i arms on the longitude-velocity diagram (LVD), showing coherent rigid-body ridges. Due to the close relationship between H i and CO, the H i line absorption can be used to determine the Arms’ position relative to Sgr A, B1, B2, and C. Combining the trigonometric data of proper motions of Sgr A* and maser sources of Sgr B2 as well as radial velocities, the 3D velocity vector of Sgr B2 is determined. From these analyses, the molecular Arm I with Sgr B2 is shown to be located in the near side of Sgr A*, and Arm II with Sgr C in the other side, both composing a pair of symmetrical Arms around the GC. We present a possible 3D view of Sgr A through E and Arms I and II along with a parameter list.

High resolution X-ray spectroscopy of V4641 Sgr during its 2020 outburst

ABSTRACT We observed the Galactic black hole X-ray binary V4641 Sgr with the high resolution transmission gratings on Chandra during the source’s 2020 outburst. Over two epochs of Chandra gratings observations, we see numerous highly ionized metal lines, superimposed on a hot, disc-dominated X-ray continuum. The measured inner disc temperatures and luminosities imply an unfeasibly small inner disc radius, such that we suggest that the central engine of V4641 Sgr is obscured, and we are viewing scattered X-rays. We find that the emission lines in the Chandra spectra cannot be constrained by a single photoionized model, instead finding that two separate photoionized model components are required, one to reproduce the iron lines and a second for the other metals. We compare the observed X-ray spectra of V4641 Sgr to optical studies during previous outbursts of the source, suggesting that the lines originate in an accretion disc wind, potentially with a spherical geometry.

Radial solutions for equations of Weingarten type

In this paper we study the linear Weingarten equation defined by the fully non-linear PDEadivDu1+|Du|2+bdetD2u(1+|Du|2)2=ϕ(11+|Du|2) in a domain Ω⊂R2, where ϕ∈C1([−1,1]) and a,b∈R. We approach the existence of radial solutions when Ω is a disk of small radius, giving an affirmative answer when the PDE is of elliptic type. In the hyperbolic case we show that no radial solution exists, while in the parabolic case we find explicitly all the solutions. In the elliptic case we prove uniqueness and symmetry results concerning the Dirichlet problem of such equation.

Growth after the streaming instability: The radial distance dependence of the planetary growth

Streaming instability is hypothesized to be triggered at particular protoplanetary disk locations where the volume density of the solid particles is enriched comparable to that of the gas. A ring of planetesimals thus forms when this condition is fulfilled locally. These planetesimals collide with each other and accrete inward drifting pebbles from the outer disk to further increase masses. We investigate the growth of the planetesimals that form in a ring-belt at various disk radii. Their initial mass distributions are calculated based on the formula summarized from the streaming instability simulations. We simulate the subsequent dynamical evolution of the planetesimals with a protoplanetary disk model based either on the minimum mass solar nebula (MMSN) or on the Toomre stability criterion. For the MMSN model, both pebble accretion and planetesimal accretion are efficient at a close-in orbit of 0.3 AU, resulting in the emergence of several super-Earth mass planets after 1 Myr. For comparison, only the most massive planetesimals undergo substantial mass growth when they are born at r = 3 AU, while the planetesimals at r = 30 AU experience little or no growth. On the other hand, in the denser Toomre disk, the most massive forming planets can reach Earth mass at t = 1 Myr and reach a mass between that of Neptune and that of Saturn within 3 Myr at 30 AU and 100 AU. Both the pebble and planetesimal accretion rate decrease with disk radial distance. Nevertheless, planetesimal accretion is less pronounced than pebble accretion at more distant disk regions. Taken together, the planets acquire higher masses when the disk has a higher gas density, a higher pebble flux, and/or a lower Stokes number of pebbles.

Magnetization reversal and ground states in thin truncated conical nanodisks: Analytical and micromagnetic modelling approach

Simulation of magnetization reversal of soft permalloy thin truncated conical disks is done using micromagnetic modelling. The thickness of the disks are fixed at 20nm. Base radius (R) of the conical disk is varied between 50−100nm while the radius of upper surface (r) is varied such that the ratio σ=r/R lies between 0 to 1. As the conical disks are gradually tapered by reducing r, the remanent states change from vortex state to shifted vortex state to buckled magnetization state. In buckled state, the magnetic moments are essentially parallel except at the corners where they curl away from the applied field direction. The extent of curling away of magnetization in buckled state reduce as base radius R is decreased. Thus at smaller base radius, the buckled states converge to homogeneous magnetization state or so called ferromagnetic state. Analytical expressions for the total energy of these three remanent states are calculated using simple models. Analytical calculations reveal that vortex configuration is the ground state for a wide range of geometrical parameters and shifted vortex state is a metastable state which appears as remanent state in the in-plane magnetization reversal due to a possible existence of energy barrier. Other observations from micromagnetic simulations are well corroborated by the results of analytical calculations.

Formation of Dust Clumps with Sub-Jupiter Mass and Cold Shadowed Region in Gravitationally Unstable Disk around Class 0/I Protostar in L1527 IRS

We have investigated the protostellar disk around a Class 0/I protostar, L1527 IRS, using multiwavelength observations of the dust continuum emission at λ = 0.87, 2.1, 3.3, and 6.8 mm, obtained by the Atacama Large Millimeter/submillimeter Array and the Jansky Very Large Array (VLA). Our observations achieved a spatial resolution of 3–13 au and revealed an edge-on disk structure with a size of ∼80–100 au. The emission at 0.87 and 2.1 mm is found to be optically thick, within a projected disk radius of r proj ≲ 50 au. The emission at 3.3 and 6.8 mm shows that the power-law index of the dust opacity (β) is β ∼ 1.7 around r proj ∼ 50 au, suggesting that grain growth has not yet begun. The dust temperature (T dust) shows a steep decrease with T dust ∝ r proj −2 outside the VLA clumps previously identified at r proj ∼ 20 au. Furthermore, the disk is gravitationally unstable at r proj ∼ 20 au, as indicated by a Toomre Q parameter value of Q ≲ 1.0. These results suggest that the VLA clumps are formed via gravitational instability, which creates a shadow on the outside of the substructure, resulting in the sudden drop in temperature. The derived dust masses for the VLA clumps are ≳0.1 M J. Thus, we suggest that Class 0/I disks can be massive enough to be gravitationally unstable, which may be the origin of gas giant planets in a 20 au radius. Furthermore, the protostellar disks could be cold due to shadowing.

The evolution of protoplanetary disc radii and disc masses in star-forming regions

ABSTRACT Protoplanetary discs are crucial to understanding how planets form and evolve, but these objects are subject to the vagaries of the birth environments of their host stars. In particular, photoionizing radiation from massive stars has been shown to be an effective agent in disrupting protoplanetary discs. External photoevaporation leads to the inward evolution of the radii of discs, whereas the internal viscous evolution of the disc causes the radii to evolve outwards. We couple N-body simulations of star-forming regions with a post-processing analysis of disc evolution to determine how the radius and mass distributions of protoplanetary discs evolve in young star-forming regions. To be consistent with observations, we find that the initial disc radii must be of the order of 100 au, even though these discs are readily destroyed by photoevaporation from massive stars. Furthermore, the observed disc radius distribution in the Orion Nebula Cluster (ONC) is more consistent with moderate initial stellar densities (100 M⊙ pc−3), in tension with dynamical models that posit much higher initial densities for the ONC. Furthermore, we cannot reproduce the observed disc radius distribution in the Lupus star-forming region if its discs are subject to external photoevaporation. A more detailed comparison is not possible due to the well-documented uncertainties in determining the ages of pre-main-sequence (disc-hosting) stars.

Failure Transition and Validity of Brazilian Disc Test under Different Loading Configurations: A Numerical Study

The Brazilian disc test is a popular tensile strength test method for engineering materials. The fracture behavior of specimens in the Brazilian disc test is closely related to the validity of the test results. In this paper, the fracture process of granite discs under different loading configurations is simulated by using a coupled finite–discrete element method. The results show that the maximum tensile stress value is located within 18 mm (0.7 times the disc radius) of the vertical range of the disc center under different loading configurations. In small diameter rods loading, the invalid tensile strength is obtained because the crack initiation and plastic strain is at the end of the disc. The crack initiation points of flat platen loading and curved jaws loading are all within the center of the disc, and the valid tensile strength can be obtained. The tensile strength test results under different loading configurations show that the error of small diameter rods loading is 13%, while the errors of flat platen loading and curved jaws loading are both 1%. The curved jaws loading is the most suitable for measuring the tensile strength of brittle materials such as rock, followed by flat platen loading. The small diameter rods loading is not recommended for the Brazilian test.

Evaluation of Soil Hydraulic Parameters Calculation Methods Using a Tension Infiltrometer

In the present work, a review for the methodologies that have been proposed to calculate the main soil hydraulic properties, hydraulic conductivity (K) and sorptivity (S), at negative pressure heads near to saturation of the soil using a tension infiltrometer is presented. These hydraulic properties can be calculated either from the analysis of steady flow or from early time observations. In particular, the main steady state methods described here are those of Ankeny et al., Reynolds and Elrick, and White and Sully, which are all based on Wooding’s equation. As for the transient flow, the approaches of Haverkamp et al. (complete, two-, three-, four-, five-terms expansions), Zhang and two different linearization methods are examined for the estimation of S and K. Generally, in steady state methods studied, a sequence of pressure heads is applied on the same disc (Ankeny et al., Reynolds and Elrick) or a unique pressure head is applied on a single disc radius (White and Sully), while in transient methods, a unique pressure head is applied on a single disc radius (Zhang and Haverkamp et al.). The conditions of their application and the way of calculating the soil parameters included into each method are critically commented. This gives to the researchers the opportunity to choose the appropriate method and a way to analyze the experimental data.

Redshift and stellar mass dependence of intrinsic shapes of disc-dominated galaxies from COSMOS observations below z = 1.0

ABSTRACT The high abundance of disc galaxies without a large central bulge challenges predictions of current hydrodynamic simulations of galaxy formation. We aim to shed light on the formation of these objects by studying the redshift and mass dependence of their intrinsic 3D shape distributions in the COSMOS galaxy survey below redshift z = 1.0. This distribution is inferred from the observed distribution of 2D shapes, using a reconstruction method which we test using hydrodynamic simulations. Our tests reveal a moderate bias for the inferred average disc circularity and relative thickness, but a large bias on the dispersion of these quantities. Applying the reconstruction method on COSMOS data, we find variations of the average disc circularity and relative thickness with redshift of around ∼1 per cent and ∼10 per cent, respectively, which is comparable to the error estimates on these quantities. The average relative disc thickness shows a significant mass dependence which can be accounted for by the scaling of disc radius with galaxy mass. We conclude that our data provides no evidence for a strong dependence of the average circularity and absolute thickness of disc-dominated galaxies on redshift and mass that is significant with respect to the statistical uncertainties in our analysis. These findings are expected in the absence of disruptive merging or feedback events that would affect galaxy shapes. They hence support a scenario where present-day discs form early ( z > 1.0) and subsequently undergo a tranquil evolution in isolation. However, more data and a better understanding of systematics are needed to reaffirm our results.

Importance of source structure on complex organics emission

Context. The protostellar stage is known to be the richest star formation phase in emission from gaseous complex organic molecules. However, some protostellar systems show little or no millimetre (mm) line emission of such species. This can be interpreted as a low abundance of complex organic molecules. Alternatively, complex species could be present in the system, but are not seen in the gas. Aims. The goal is to investigate the second hypothesis for methanol as the most abundant complex organic molecule in protostellar systems. This work aims to determine how effective dust optical depth is in hiding methanol in the gas, and whether methanol can mainly reside in the ice due to the presence of a disk that lowers the temperatures. Hence, we attempt to answer the question whether the presence of a disk and optically thick dust reduce methanol emission even if methanol and other complex species are abundant in the ices and gas. Methods. Using the radiative transfer code RADMC-3D, we calculated methanol emission lines from an envelope-only model and from an envelope-plus-disk model. We compared the results with each other and with the observations. Methanol gas and ice abundances were parametrised inside and outside of the snow surfaces based on values from observations. Both models included either dust grains with low mm opacity or high mm opacity, and their physical parameters such as envelope mass and disk radius were varied. Results. Methanol emission from the envelope-only model is always stronger than from the envelope-plus-disk model by at least a factor ∼2 as long as the disk radius is larger than ∼30 au (for L = 8 L⊙). In most cases, this is due to lower temperatures (disk shadowing), which causes the smaller amount of warm (≳70 K) methanol inside the snow surface of the envelope-plus-disk model. The intensities drop by more than an order of magnitude for models including high mm opacity dust grains and disk radii of at least ∼50 au (for L = 8 L⊙) due to continuum over-subtraction. Conclusions. The line intensities from the envelope-only models match the observations moderately well when methanol emission is strong, but they overproduce the observations of protostars with lower methanol emission even with large dust optical depth effects. The envelope-plus-disk models can explain the bulk of the observations. However, they can only reproduce the observations of sources with high luminosities and very low methanol emission when the dust optical depth is significant in the envelope and continuum over-subtraction becomes effective in the disk (high mm opacity dust grains are used). Therefore, both the effects of disk and dust optical depth should be considered to explain the observations. In conclusion, it is important to take physical structure into account in future chemical studies of low-mass protostars: absence of gas-phase methanol emission does not imply absence of methanol molecules in either gas or ice.

The disk of FU Orionis viewed with MATISSE/VLTI

Aims. We studied the accretion disk of the archetypal eruptive young star FU Orionis with the use of mid-infrared interferometry, which enabled us to resolve the innermost regions of the disk down to a spatial resolution of 3 milliarcseconds (mas) in the L band, that is, within 1 au of the protostar. Methods. We used the interferometric instrument MATISSE/VLTI to obtain observations of FU Ori’s disk in the L, M, and N bands with multiple baseline configurations. We also obtained contemporaneous photometry in the optical (UBVRIr′i′; SAAO and Konkoly Observatory) and near-infrared (JHKs; NOT). Our results were compared with radiative transfer simulations modeled by RADMC-3D. Results. The disk of FU Orionis is marginally resolved with MATISSE, suggesting that the region emitting in the thermal infrared is rather compact. An upper limit of ~1.3 ± 0.1 mas (in L) can be given for the diameter of the disk region probed in the L band, corresponding to 0.5 au at the adopted Gaia EDR3 distance. This represents the hot, gaseous region of the accretion disk. The N-band data indicate that the dusty passive disk is silicate-rich. Only the innermost region of said dusty disk is found to emit strongly in the N band, and it is resolved at an angular size of ~5 mas, which translates to a diameter of about 2 au. The observations therefore place stringent constraints for the outer radius of the inner accretion disk. Dust radiative transfer simulations with RADMC-3D provide adequate fits to the spectral energy distribution from the optical to the submillimeter and to the interferometric observables when opting for an accretion rate M ~ 2 × 10−5 M⊙ yr−1 and assuming M* = 0.6 M⊙, Most importantly, the hot inner accretion disk’s outer radius can be fixed at 0.3 au. The outer radius of the dusty disk is placed at 100 au, based on constraints from scattered-light images in the literature. The dust mass contained in the disk is 2.4 × 10−4 M⊙, and for a typical gas-to-dust ratio of 100, the total mass in the disk is approximately 0.02 M⊙. We did not find any evidence for a nearby companion in the current interferometric data, and we tentatively explored the case of disk misalignment. For the latter, our modeling results suggest that the disk orientation is similar to that found in previous imaging studies by ALMA. Should there be an asymmetry in the very compact, inner accretion disk, this might be resolved at even smaller spatial scales (≤1 mas).

Dense Gas Formation via Collision-induced Magnetic Reconnection in a Disk Galaxy with a Bisymmetric Spiral Magnetic Field

Recently, a collision-induced magnetic reconnection (CMR) mechanism was proposed to explain a dense filament formation in the Orion A giant molecular cloud. A natural question is whether CMR works elsewhere in the Galaxy. As an initial attempt to answer the question, this paper investigates the triggering of CMR and the production of dense gas in a flat-rotating disk with a modified Bisymmetric spiral (BSS) magnetic field. Cloud−cloud collisions at field reversals in the disk are modeled with the Athena++ code. Under the condition that is representative of the warm neutral medium, the cloud−cloud collision successfully triggers CMR at different disk radii. However, dense gas formation is hindered by the dominating thermal pressure, unless a moderately stronger initial field ≳5 μG is present. The strong-field model, having a larger Lundquist number S L and lower plasma β, activates the plasmoid instability in the collision midplane, which is otherwise suppressed by the disk rotation. We speculate that CMR can be common if more clouds collide along field reversals. However, to witness the CMR process in numerical simulations, we need to significantly resolve the collision midplane with a spatial dynamic range ≳106. If Milky Way spiral arms indeed coincide with field reversals in BSS, it is possible that CMR creates or maintains dense gas in the arms. High-resolution, high-sensitivity Zeeman/Faraday rotation observations are crucial for finding CMR candidates that have helical fields.

No Evidence of the Significant Grain Growth but Tentative Discovery of Disk Substructure in a Disk around the Class I Protostar L1489 IRS

For revealing the first step of planet formation, it is important to understand how and when dust grains become larger in a disk around a protostar. To investigate the grain growth, we analyze dust continuum emission toward a disk around the Class I protostar L1489 IRS at 0.9 and 1.3 mm wavelengths obtained by the Atacama Large Millimeter/submillimeter Array. The dust continuum emission extends to a disk radius (r) of r ∼ 300 au, and the spectral index (α) is derived to be α ∼ 3.6 at a radius of r ∼ 100–300 au, similar to the interstellar dust. Therefore, the grain growth does not occur significantly in the outer disk (r ∼ 100–300 au). Furthermore, we tentatively identify a ring-like substructure at r ∼ 90 au even though the spatial resolution and sensitivity are not enough to determine this structure. If this is the real ring structure, the ring position and small dust in the disk outer part are consistent with the idea of the growth front. These results suggest that the L1489 protostellar disk may be the beginning of planet formation.

The Booth Lemniscate Starlikeness Radius for Janowski Starlike Functions

The function $$G_\alpha (z)=1+ z/(1-\alpha z^2)$$ , $$0\le \alpha <1$$ , maps the open unit disk $$\mathbb {D}$$ onto the interior of a domain known as the Booth lemniscate. Associated with this function $$G_\alpha $$ is the recently introduced class $$\mathcal {BS}(\alpha )$$ consisting of normalized analytic functions f on $$\mathbb {D}$$ satisfying the subordination $$zf'(z)/f(z) \prec G_\alpha (z)$$ . Of interest is its connection with known classes $$\mathcal {M}$$ of functions in the sense $$g(z)=(1/r)f(rz)$$ belongs to $$\mathcal {BS}(\alpha )$$ for some r in (0, 1) and all $$f \in \mathcal {M}$$ . We find the largest radius r for different classes $$\mathcal {M}$$ , particularly when $$\mathcal {M}$$ is the class of starlike functions of order $$\beta $$ , or the Janowski class of starlike functions. As a primary tool for this purpose, we find the radius of the largest disk contained in $$G_\alpha (\mathbb {D})$$ and centered at a certain point $$a \in \mathbb {R}$$ .

A novel method for inward fluid displacement in centrifugal microdevices for highly integrated nucleic acid processing with long-term reagent storage

Rotationally-driven lab-on-a-disc (LoaD) microfluidic systems are among the most promising methods for realizing complex nucleic acid (NA) testing at the point-of-need (PoN). However, despite significant advancements in NA amplification methods, very few sample-to-answer centrifugal microfluidic platforms have been realized due, in part, to a lack of on-disc sample preparation. In many instances, NA extraction (NAE) and/or lysis must be performed off-disc using conventional laboratory equipment and methods, thus tethering the assay to centralized facilities. Omission of in-line cellular lysis and NAE can be partially attributed to the nature of centrifugally-driven fluidics. Since flow is directed radially outward relative to the center of rotation (CoR), the number of possible sequential unit operations is limited by the disc radius. To address this, we report a simple, practical, automatable, and easy-to-implement method for inward fluid displacement (IFD) compatible with downstream nucleic acid amplification tests (NAATs). This approach leverages carbon dioxide (CO2) gas generated from on-board acid-base neutralization to drive liquid from the disc periphery towards the CoR. Large architectural features or highly corrosive chemicals required in other approaches were replaced with safe-to-handle IFD reagents that maintained their reactivity for at least six months of storage on-disc. Further, spatiotemporal control over neutralization initiation and containment of the resultant pneumatic pressure head was reliably achieved using a single diode for both laser-actuated valve opening and channel sealing, which eliminated the need for manual intervention (e.g., taping over vents) required in other IFD methods. Following initial characterization via dye recovery studies, we demonstrated for the first time that CO2-driven displacement does not inhibit downstream NAATs; NAs isolated direct-from-swab on disc were compatible with both ‘gold standard’ polymerase chain reaction (PCR) techniques and loop-mediated isothermal amplification (LAMP). The IFD approach described here stands to significantly ease integration of an increased number of sequential on-board processes, including cellular lysis, nucleic acid extraction, amplification, and detection, to greatly lower barriers towards automatable sample-to-answer LoaDs amenable for use on-site operation by non-technical personnel.

Effect of surface stretching on convective instabilities of Kármán flow of non-Newtonian Carreau fluid

Linear convective instability analysis of non-Newtonian fluids has immense practical applications in the field of aerodynamics and engineering mechanics. The paper deals with linear convective instability analysis of laminar Kármán swirling flow of a non-Newtonian Carreau fluid over a radially stretchable rotating disk of infinite radius when the Coriolis force is significant in the boundary layer. In this paper, the velocity profiles for both shear-thinning and shear-thickening fluids the above-mentioned flow of Carreau model have been determined under stretch boundary condition. By using the Chebyshev collocation method, a study of convective instability has been carried out in order to perform a stability analysis of the flow and determine the neutral stability curves. The stability curves reveal that the bottom disk’s surface stretching has a globally stabilizing effect on the fluid exhibiting shear-thinning flow behaviour and a globally destabilizing effect on shear-thickening flow behaviour. To verify the above physical facts, the flow has been subjected to an energy analysis at the same time.