Summary of article about Transit Simulator for Objects Orbiting Stars


The quadratic limb darkening law was used in study. It is a model that describes the variation in the intensity of a star's photosphere as a function of the viewing angle.

I(μ) is the intensity of the star at u = cos (theta), i.e., the cosine of the angular separation of a point with respect to the center of the star.


As per transit principle the relative change in the observed flux is proportional to the relative area of the blocking object with respect to the area of the star.

They converted the intensity to a cumulative distribution function. 

The orbital phase angle is a phase value corresponding to the location of the planet in its orbit at a certain time. Ω is the orbital velocity and P refers to the orbital period,

the overlapped area was calculated using the Monte Carlo technique.

The asymmetric parameter q is calculated as,

 r0 is the distance between the planet and the star, hf is the second fluid Love number. The second fluid Love number is a parameter that describes the rigidity of a body under the effect of gravity.


Scientists developed a numerical transit simulator which is designed to generate light curves for objects of any arbitrary shape transiting stars.


Source: https://iopscience.iop.org/article/10.3847/1538-3881/ad7d8d

Summary of article: Ultrasonic Atomization for Liquid Metals

 

Ultrasonic atomization is a process that uses ultrasound waves to create tiny droplets from a liquid.

As per study Particle diameter d is

ρ and σ are respectively the density and surface tension of the atomized fluid and

f is a vibration frequency. Particle diameter also depends on Weber, Ohensorge and intensity number.


A liquid film is placed on a smooth surface that vibrates perpendicularly to the surface. The liquid absorbs some of the vibrational energy and creates waves called capillary waves. When the amplitude reaches a critical level, the waves collapse and eject tiny drops of liquid. 


The amplitude of vibrations at 10 um is too small to induce atomization of liquids with parameters similar to water. After a time of 0.0119 [s], the liquid layer does not atomize, it only agglomerates into larger droplets with a thickness of approx(87 μm).


The amplitude necessary for the process of initiating atomization is about 60–70% higher than theoretically predicted. As the frequency increases to 22 kHz, the amplitude necessary to start the atomization process decreases to about 2 μm and then increases linearly to about 3 μm. 


Droplet diameter (in micrometer):  Water(36.3), Al(49.6), Zn(34.8), Steel(52.1) observed in study.

The droplets do not always atomize in the direction perpendicular to the vibrating surface and to the surface of the liquid; their trajectory is changed by the forces of coherence.


Source: https://www.mdpi.com/1996-1944/17/24/6109#:~:text=It%20attempts%20to%20close%20a,surface)%20and%20obtained%20atomization%20results%20(



Summary of Article: melanin as a material for solar light absorbers

 

The infrared transmission spectra, Optical Density spectra, atomic force microscopy is used in study.

As per Lambert-Beer law

d is the melanin film thickness, ln(Ub/Us)  is measured from Optical Density.


The absorption coefficient decreases to ~ 10^4 cm−1 in the visible and near infrared region. So it is reasonable to consider these films as efficient light absorbers of near-ultraviolet radiation.


Melanin conductivity is due to extensive π-conjugation, at which electrons are delocalized across the entire oligomer stack(Oligomer stacks are a result of intermolecular π-π stacking, which is a process that involves the overlap of π-orbitals in the rings of a molecule)


An exponential growth in conductivity with increasing hydration level was observed for melanin film in experiment. 


Fourier Transform Infrared transmission spectrum of eumelanin film has found the presence of OH groups and CHn bonds with both sp3 and sp2 hybridizations. The ratio between the sp2 and sp3 hybridized CHn bonds may play a role in defining the film optical and electrical properties. Higher concentrations of sp2 hybridized bonds may lead to an increase in conductivity.

Source: https://arxiv.org/pdf/2412.07609#:~:text=The%20films%20demonstrate%20indirect%20allowed,in%20photovoltaic%20solar%20energy%20converters.


Overview of article: Study of magnetic field change in Sun


Parker Solar Probe(PSP) has discovered the prevalence of switchbacks (SBs)-switchbacks are sudden reversals in the magnetic field in the solar wind. The researchers used the Adaptively Refined Magnetohydrodynamics Solver (ARMS) method.


Solar wind velocity has a similar behavior characterised by a logarithmic dependence, approximately resembling ln(r)^½.


Mass density, magnetic field decrease as radius increases. Alfvén Velocity (velocity of propagation of Alfvén waves in the direction of the magnetic field) for low plasma beta increases with radius and then decreases. Low plasma beta means that magnetic pressure is dominant over thermal pressure in a plasma.




Magnetic Energy Initially increases, Later decreases with time. The imposed clockwise flow

induces a counter-clockwise twist to the closed magnetic field lines, boosts the total field strength and reduces the pressure. This behaviour explains the magnetic energy’s upward trend and the internal energy’s decline.  Gravitational Energy gradually increases. 

 


Photospheric flow, tangential velocity vb, depends on the gradient of the radial magnetic field, Br, and is given by


Source: https://www.aanda.org/articles/aa/full_html/2024/12/aa52019-24/aa52019-24.html


Key Points of Study of Deformation of the ice front by particle


As the freezing front approaches the droplet, the temperature on one side of the droplet is different than on the other side. That causes a difference in surface tension which occurs as a force, thermal Marangoni force.


As per observation in solidification front of ceramic Zirconia and polystyrene (PS) particle, If the particle is more thermally conductive, heat flows through it, and the ice front bends away and if the particle is less thermally conductive, heat avoids the particle, and the ice front bends toward it. The heat flux chooses the path of least thermal resistance.


As per observation in liquid, at low freezing velocity, the ice front bends toward the droplet.


Marangoni number  indicates the influence of surface tension gradients on fluid flow as a result of the applied thermal gradient.


Application: This study helps in understanding behavior of biology cells, freezing in the casting process, material science.


Source: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.214002


Summary of article: V2O3 metallic property at external V, I

 

Topological defects: These are imperfections in the structure of a material that arise when its internal arrangement (lattice or order parameter) cannot be perfectly aligned.

Resistive switching is a sudden transition between insulating and metallic states triggered by an electric field.

When V2O3 temperature is changed from high to low, the structure changes from rhombohedral shape to less symmetric shape (monoclinic phase) as the material becomes metallic to an insulator.

Researchers used  PhotoEmission Electron Microscopy (PEEM) combined with X-rays. The V2O3​ film is placed between two gold electrodes that apply the electric field. By measuring the current and voltage, they observe that initially, the material resists the current, but once the voltage reaches a certain threshold, the resistance suddenly drops—indicating the formation of conducting pathways.

Source: https://www.nature.com/articles/s41467-024-53726-z

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


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


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


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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