Summary: study of Au, Ag and Cu- behave as superconductors

 

Density Of State(DOS) is a function of energy, It shows how many states exist for electrons at each possible energy level. In bulk metals, DOS near the Fermi level (the highest occupied energy level at absolute zero) is generally constant.

Quantum confinement is the phenomenon that occurs when the thickness of a metallic film becomes comparable to the wavelength of the electrons in the material. At this ultra-thin scale, the movement of electrons becomes restricted along the thickness of the film, which changes the electronic properties of the material.

Quantum confinement changes the Density Of State. At certain thicknesses, the DOS  increases near the Fermi level, allowing the non-superconducting metals (like gold, silver, and copper) to exhibit superconductivity.

The Eliashberg equation was used in the study.

As per study, The thickness L approaches a critical value close to 5 Å (0.5 nm), there’s increase in electron-phonon coupling parameter λ,  a stronger electron-phonon (phonon-quasiparticle associated with vibration of a crystal lattice) coupling results superconductivity, it promotes the pairing of electrons into Cooper pairs.

Source: https://arxiv.org/abs/2406.16621

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Summary: High temperature effect on Molybdenum disulphide

Scientists measured the displacement cross section of Sulphur atoms in MoS2 at temperatures up to 550◦C using scanning transmission electron microscopy at acceleration voltages of 60 and 90 keV. 

At a temperature of 150◦C, the displacement  cross section of S atoms increased compared to room temperature, which is due to a thermal activation of phonons which increase the maximum transferred energy (highest amount of energy that an electron from the electron beam can transfer to an atom). At higher temperatures the measured cross section decreases significantly. This occurs due to thermal diffusion.

The number of migration steps µ for the defect taken during one image at a given temperature T is 

where Em is the migration energy barrier.

The ratio of the observed and theoretical cross sections which show how the observed defect rate decreases at high temperatures due to the increased migration of vacancies out of the microscope’s field of view.

In study, chemical vapor deposition (CVD) and Scanning Transmission Electron Microscopy were used. Gaussian Distribution was applicable at 60keV. Here CVD is a process used to create very thin, high-quality materials by depositing atoms or molecules layer by layer on a surface.

High temperatures don’t actually reduce or stop the formation of defects caused by the electron beam, they only make the defects difficult to see.

These findings improve understanding of how monolayer MoS₂ responds to electron beams, which is important for its use in electronic devices and for precise material engineering.

Source: https://arxiv.org/html/2411.03200v1

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Overview: Magnetic Field for Jupiter and Neptune Class exoplanets

Dynamo is the process by which a planetary magnetic field is generated through the movement of electrically conductive materials within the planet's interior. The dynamo region is identified based on the magnetic Reynolds number.

At the top of this region, the maximum magnetic field is 

 where 𝑞0 is the reference convective flux, ⟨𝜌⟩ is the average density,

𝐹 is an efficiency factor that accounts for all radially varying features of the dynamo region, and is calculated as 

where 𝐻T(𝑟) is the temperature length scale given by

 𝑃(𝑟) is the pressure, 𝑔(𝑟) the gravitational acceleration, and ∇adv the adiabatic, logarithmic gradient of temperature over pressure.

The convective flux 𝑞c is

𝑣conv the velocity of convective motions, and 𝛿 is the derivative of ln 𝜌 with respect to lnT.

Re mag is a non-dimensional quantity that measures the effects of convection against magnetic diffusion. 

As per study, for Jupiter and Neptune class planets, Magnetic field decay occurs because as planets age, they cool down and their luminosities and their convective flux become gradually weaker. Higher atmospheric envelope fractions cause more material available for convection, which yields stronger magnetic fields and extends the dynamo region.

 The field strength reduces for extremely irradiated planets because they have lower average density. The surface magnetic field decreases past the threshold value as orbital separation (distance between the exoplanet and its host star) further increases.

The magnetic fields could be observable in the radio wavelengths via auroral emission using ground based observations.

Jupiter-class planets have magnetic fields large enough to generate radiation whose peak frequency exceeds the Earth’s ionospheric cutoff. The same occurs for the Neptune-class planets  if they have  𝑀 > 15 𝑀⊕ and 𝑓env> 4%.

For hot jupiter class planets, atmospheric evaporation does not affect magnetic field generation. For hot Neptunes, atmospheric evaporation leads to greater mass loss and causes less material for convection, so they produce weaker magnetic fields. 

Source: https://arxiv.org/html/2411.00674v1

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Summary of Article about Tests of the Hard X-ray Imager

The objective of HXI is to investigate how energy from the sun is released in solar flares.

The relative displacement and rotation were tested from assembly to on-orbit operation and must be maintained under 36 μm and 10 arcsecs.

When HXI reaches a thermal balanced state, further deformation measurements are done and collimator alignment is tested which is essential for accurate imaging.

Deformation of the equipment was mainly influenced by vibration during launch and temperature differences in orbit.

Differential Nonlinearity (DNL) Effect Correction is a calibration technique used to address inaccuracies in data from analog-to-digital converters. It ensures that the energy levels of X-rays from solar flares are accurately represented in the digital data.

The energy calibration is done to calibrate the corresponding energy (keV) for each of the ADC channels of each detector. Mixed calibration sources of Barium and Americium are housed inside every detector module.

Detector response matrix describes how an Hard XRay detector records count flux from incident photon flux. It converts count spectra and images back to photon spectra and images of the X-ray source.

Four-Quadrant Method (FQM) and Least Square Method (LSM)—have been used to determine the position of the Sun’s center in the image. 

source:https://link.springer.com/article/10.1007/s11207-024-02392-x

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Overview : Non newtonian fluid flow rate, viscosity, pressure drop

 

In non-monotonic flow, the graph of flow rate versus shear stress or pressure often forms an S-shaped curve. Initially, the flow rate increases with stress. At a certain threshold, further increases in stress cause the flow rate to drop. fluid can exhibit two different shear rates at the same shear stress, causing a separation or banding in shear rates.

In vorticity banding different regions have distinct shear stresses but the same shear rate. 

Weienberg-Rabinowitsch allows for calculating the shear rate at the tube wall, even when a fluid’s viscosity changes with shear rate.

Wyart and Cates rheological model is used in this study. It explains the behavior of shear-thickening fluids—specifically, how their viscosity increases abruptly under certain conditions. 

ηr​ is the viscosity when all contacts are frictional, ns is for frictionless contacts. Q is flowrate, delta P is pressure drop

At low concentrations the curve is smooth and almost linear, indicate a continuous shear-thickening (CST) behavior. As concentration increases fluid exhibits discontinuous shear thickening (DST), where viscosity increases abruptly. At very high concentrations  the curve forms an S-shape, indicating non-monotonic behavior. Here, the shear rate can decrease with increased shear stress, leading to instabilities like shear banding.

When this type of fluid flows in a tube, streamwise banding occurs, here the pressure gradient can be inhomogeneous, dividing into regions of high viscosity and low viscosity along the tube.

In study, experiment was done at homogeneous and heterogeneous initial conditions. Initially, the flow rate is high. The dispersion of the pressure gradient is a result of the initial distribution of friction and viscosity. With time, the flow rate decreases and the different pressure gradients diverge. Some locations converge to a low gradient, while others converge to a higher pressure gradient.

source:

https://universite-paris-saclay.hal.science/hal-04743748

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Key Points of Article about Measuring gravitational waves by graphene

Current detectors can only capture low-frequency gravitational waves.

By using graphene, higher frequency gravitational waves can be detected and size of detector also reduced. Here relative intensity varies when gravitational waves are measured.

As a gravitational wave propagates through a crystal lattice, it causes directional stretching and compression of the lattice, it causes shifts in the electronic energy band and density of energy states also changes.

Changes occur in graphene under gravitational wave,

Where,  yAB is the overlapping integral of the nearest neighbors, E is Graphene  energy

As per equations, gravitational waves alter the distances between carbon atoms in graphene, changing its lattice structure and causing a slight shift in the electron wave vectors. This affects the electronic transport behavior.

As gravitational wave radiation intensity hGW increases, the relative change in wave vector and wavelength increases.  

When the polarization direction of the gravitational wave is along the z-axis, the

the y-direction lattice of the photonic-like interferometer is stretched while the x-direction lattice is compressed. 

The change in Fermi energy is related to the shift of the energy band and the corresponding change in the density of energy states, which  affects gravitational waves on electrons in k-space. When the Fermi energy increases, the relative changes in the wave vector and wavelength decreases.

The relative intensity change (delta I/I )caused by arm length change in the photonic-like interferometer is about 2782 times larger than that in the laser interferometer because of the shorter electron wavelength.

Gravitational wave detection can be conducted by graphene at extremely low temperatures.

Source: https://arxiv.org/abs/2410.18711

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Equations Used for measuring Exoplanet parameters

In recent article, brightness (flux) of the target star and the reference stars has been measured as analog digital units (ADU). 

The duration of a planetary orbit

𝑅𝑠 is the star radius, 𝑅𝑝 is the planet radius, 𝑀𝑠 is the star mass, 𝑀𝑝 is the planet mass, 𝐺 is the gravitational constant, a is the planetary orbital semi-major axis, e is the planetary orbital eccentricity, i is the planet inclination.

Depth of a planetary transit is the amount by which the light from a star dims when a planet passes in front of it. It is measured as a percentage or fraction of the total light blocked by the planet during the transit. 

L is luminosity, Depth of transit is obtained by 

If the radius of the star is known (from the spectral classification), 𝑅𝑝 can be obtained from Equation

If the orbital period 𝑃 and the mass of the star 𝑀⊙ are also known, the orbital semi-major axis a can be obtained from Kepler’s third law, and therefore the duration of the transit can be obtained.

From above equation latitude of the transit on the star, 𝛿, is calculated.

Traditional radial velocity is measured based on shifts of wavelength at which a star moves toward or away from Earth, which indirectly gives information about an orbiting planet's mass and orbit. But Synthetic radial velocity is  used to calculate mass from the radius using the forecaster model. In this model, Monte Carlo simulation is used to determine radius and mass.

Source: https://arxiv.org/abs/2410.07425

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Overview of Article about Random illumination Microscopy (EDF-RIM)

 

The objective of RIM is to compute the variance (the spread or difference) in the intensity of the images.

Intensity at camera plane depends on ρ sample fluorescence density, h the Point spread function(PSF) of the optical system and S the illumination intensity and distance of the focal plane.

As the light passes through the modulator, it gets scattered in random directions, creating interference, which produces a random, grainy pattern of bright and dark spots known as the speckle pattern. 

Each speckle illumination creates a different intensity pattern on the sample. Electrically tunable lens  made of a shape-changing polymer, is used here.

 Bessel speckle is created by a bessel beam to maintain focus over extended distances which  helps to capture fine details across different depths.

Image reconstruction is done by Wiener filter which enhance high frequencies and remove noise

where h bar is the Fourier transform of the extended depth PSF.

Here, to achieve super-resolved reconstruction, Tikhonov regularization method is used. The equation for Fluorescence density is

  

μ is the Tikhonov regularization parameter.

For simulation, lateral distribution follows the equation  ρ(r,θ) = 1 + cos(40θ), which generates a pattern of higher spatial frequencies towards the center of the patter.

Application: EDF- RIM is used in microscope to image larger, thicker biological samples with super-resolution.

https://www.nature.com/articles/s41377-024-01612-0

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