Himalayan Physics

Adsorption of toxic gases by metal-organic frameworks

2023-05-31T12:25:12+00:00

Along with global economic development and population growth, the discharge of highly toxic and corrosive anthropogenic byproducts into the atmosphere or aquatic habitats creates a serious threat to human health. In order to remove such byproducts, more attention should be paid to innovative materials with high uptake capacity and performance. Metal-organic frameworks (MOFs) are crystalline, porous, hybrid materials that are made up of organic ligands as linkers and metal cluster-based nodes. Because of their beneficial features such as their large surface area, tailorable pore sizes, structural diversity, catalytic activity, and wide range of chemical and physical properties, MOFs offer significant potential as adsorbents. As a result, these materials have drawn a significant amount of attention for the capture and/or detoxification of hazardous and toxic chemicals. This review will focus on recent advancements on MOF based experimental and computational studies related to the capture of toxic gases including hydrogen sulfide (H₂S), ammonia (NH₃) sulfur dioxide (SO₂) carbon monoxide (CO), and nitrogen oxides (NO_x).

Cluster modelling of MOF-5 and its application on gas storage

2023-05-31T12:38:04+00:00

MOF-5 exhibits unique characteristics for applications in gas storage particularly in the field of hydrogen storage. MOF-5 is a porous crystalline cubic structure formed by connecting a Zn₄O inorganic moiety to benzene-1, 4-dicarboxylate (BDC), a bidentate ligand where, the Zn₄O-cluster represents the central part of the structure. It can be an alternative to high pressure tanks and multistage compressor used in hydrogen storage. Using the cluster modelling approach, a thorough investigation of MOF-5 is provided. A density functional theory calculation was performed to examine the hydrogen storage potential in MOF-5. The geometry optimizations were carried out using the B3LYP functional together with the LanL2DZ/6-31G basis set. It is observed that the adsorption of hydrogen in MOF-5 cluster is physisorption and the hydrogen molecule is held in the core with the binding energy in the range 26-27 meV.

Electronic and magnetic properties of ternary sulfide Rb2Mn3S4

2023-05-31T12:45:49+00:00

Semiconducting materials, especially with a direct band gap, are helpful for modern photovoltaic and optoelectronic device fabrication. Here, based on density functional theory calculations, we predict the electronic and magnetic properties of Rb₂Mn₃S4 by using the full potential local orbital code. Considering different configurations such as nonmagnetic, ferromagnetic, ferrimagnetic, and antiferromagnetic, the magnetic ground state was found to be ferrimagnetic with the lowest total energy. The calculated effective magnetic moment is 10μ_Bunit cell (two formula units) resulting from the opposite spin interaction between Mn (I) and Mn (II) atoms in Rb₂Mn₃S₄. From our calculations, Rb₂Mn₃S₄ is found to be a semiconductor with a direct energy band gap of 0.75 eV. With the inclusion of the Coulomb interaction (i.e., GGA+U), the band gap is found to rise to 2.34 eV for U = 4 eV.

Dust properties around NGC 7023 nebula in interstellar medium using IRIS, AKARI, and WISE survery

2023-05-31T12:52:15+00:00

We have studied the physical properties of dust around the nebula NGC 7023. The physical properties have been studied at 60 μm and 100 μm in the IRIS survey, 90 μm and 140 μm in the AKARI survey, and 12 μm and 22 μm in the WISE survey at the right ascension (R.A.) (J2000) = 21^h01^m35.60^s, declination (J2000) = + 68^o10^m10.0^s. The nebula is found at a distance of 335.82 pc from us. We found the dust color temperature is in the range between 36.19 K ± 0.03 K to 24.49 K ± 0.03 K with an average dust color temperature of 28.24 K ± 0.03 K in IRIS survey and a range between 38.80 K ± 0.25 K to 21.00 K ± 0.25 K with an average dust color temperature 26.39 K ± 0.25 K in AKARI survey. Similarly, in WISE, the dust color temperature was found in the range between 130.92 K ± 0.01 K to 88.71 K ± 0.01 K with an average of 104.76 K ± 0.25 K. The temperature in WISE is higher than that of the IRIS and AKARI survey. We have also calculated the dust mass, whose average value was found to be 1.18 x 10²⁷ kg (5.93 x 10⁻⁴ M⊙) in IRIS, 1.06 x 10²⁸ kg (5.33 x 10⁻³ M⊙) in AKARI, and 1.06 x 10²⁷ kg (5.33 x 10⁻⁴ M⊙) in the WISE survey. We have also studied the visual extinction parameter due to such dust in infrared bands. This work will contribute to understanding infrared band emission from the dusty region around the nebular structure in the interstellar medium.

Experimental design for tri-state logic

2023-05-31T13:09:31+00:00

Tri-State Logic device effectively connects many devices into the same data line for data transfer. The Tri- State TTL inverter has three output states such as LOW, HIGH, and open or high-impedance (High-Z) states. The High-Z state either electrically isolates the devices from the data transmission line or connects them one at a time to the data transmission line. The measurement of the floating output (opened or disconnected) state is a challenging task. This issue can be resolved by introducing a potential divider into the output of the original Tri-State TTL inverter circuit and making it possible for a lab experiment

Comparison of aerosol optical properties over Lumbini, Pokhara and Langtang-Base Camp

2023-05-31T16:03:56+00:00

The comparative study of aerosol optical properties at different tourist places in Nepal has been performed. Lumbini, Pokhara and Langtang-Base Camp (BC) were the places chosen for observation. Aerosols are made up of a variety of airborne particles both fine and coarse and are most prevalent in urban industrial Areas. The data was collected from AERONET websites between 2017 and 2019 for each of the locations. The ranges of AOD over Pokhara and Langtang-BC were discovered to be lower (0.1 and 0.01) and the maximum and minimum values of AOD (675 nm) in Lumbini occurred predominantly in winter and summer monsoon respectively. The causes of the highest AOD levels were land clearing for crop cultivation and vegetation fires which were then followed by biomass burning for heating purposes and pollution from brick kilns, industry and vehicles. AOD, angstrom exponent (α and β) and Visibility are distinct from typical seasonal variations. The total AE fluctuations show that a combination of fine and coarse mode particles as well as anthropogenic aerosols made up the majority of the aerosol loading during the research period. Visibility was inversely related to the turbidity coefficient (β). Three times as much visibility was discovered over Langtang-BC as compared to Lumbini and Pokhara. Over these three locations, precipitable water peaked in the summer and dropped in the winter. These three sites seasonal changes are found to be distinct for each parameter.

Wavelet coherence analysis foF2 over Boulder station during different geomagnetic activity

2023-05-31T16:22:57+00:00

A geomagnetic storm is a major disturbance of Earth’s magnetosphere that occurs when there is a very efficient exchange of energy from the solar wind into the space environment surrounding Earth. During solar and geomagnetic activities, critical frequency of F2 layer (foF2) varies in a great extent. The focus of the current study is on variations in foF2, the critical frequency of the F2 layer, during the intense geomagnetic storm of solar cycle 24 and quiet storm of solar cycle 25. The foF2 data of mid latitude station BC840 (Boulder) in the American region have been used to study geomagnetic and solar wind properties linked with foF2. Time series analysis and Wavelet Coherence analysis have been used to establish the relationship between those parameters. We have found considerable effect of solar and geomagnetic storm disturbances on foF2 during the geomagnetic storm time. The foF2 is enhanced prior to the storm and depletes during recovery phase with no significant changes observed during weak storm. The enhancement or depletion in foF2 may be used as precursor of geomagnetic storms. With long trend analysis and larger database we can make a catalog which can be used to predict the geomagnetic storm and deepen our understanding in impacts of storms on communication signals due to energy injected in ionosphere.

Complex impedance analysis of soft chemical synthesized NZCF systems

2023-05-31T16:31:45+00:00

The soft chemical method was adopted to prepare of cobalt-substituted nickel-zinc ferrites (Ni_0.95-x Zn_0.05CO_x Fe₂O₄ for x = 0.01, 0.02 and 0.03). We have recently studied their structural, morphological, and magnetic properties, initial permeability, and dielectric constant. They were found to be with cubic ferromagnetic spinel structure, the morphology of which is suitable for high-density recording media. The impedance has a major role in characterizing the electrical and magnetic properties of the sample, which are dependent on their permeability and dielectric constant. So, this study will verify the values obtained before. Next, the energy stored in a capacitor is directly proportional, and its size is inversely proportional to the dielectric constant. Similarly, the resistance offered by a material to the magnetic field to pass through it is related to permeability. This study will focus on the variation of impedance with Co²⁺ concentration. The results were derived with the equivalent circuit model. The impedance analysis is also important in the biological field having a name of Bio-Impedance Analysis (BIA), for determining nutritional status, and many more.

Controlling pests in post-harvested wheat using microwave heating

2023-05-31T16:41:30+00:00

Microwaves refer to electromagnetic waves ranging from 300 MHz to 300 GHz in frequencies. Microwave de-infestation works well without degrading the host material’s quality. In this research, four different samples of wheat grains are taken from each location, which are injected by 20 pests of the same type per sample. Each sample is then put into the microwave oven for the exposure time of 1 minute and 30 seconds, heated at temperatures 60^◦C, 70^◦C, 80^◦C, 90^◦C, and 100^◦C. Finally, the samples are germinated, followed by the analysis of nutrition levels at the laboratory. The statistical analysis of the data shows a significant difference in mortality and germination with temperature changes. The average mortality rate was 95% at 100^◦C for 1 min of exposure time, exposing mortality increases with temperature. The germination decreased with the temperature increment and the exposure time magnitude. Statistical analysis reveals that there is no significant difference in the nutrition levels of wheat with the temperature change. The study concludes that microwave heating is one of the effective tools for controlling pests in post-harvested grains without using pesticides.

Mean value and velocity variation of ions in different magnetic field at constant obliqueness

2023-05-31T16:47:12+00:00

The variation of mean values of different components of velocities concerning the magnetic field has been numerically investigated using a kinetic trajectory simulation model at a constant angle and electric field. At an angle of 30^◦, mean values of different components of velocities at the different magnetic fields have been studied. As the magnetic field changes, the mean values of the three velocity components also change, but as the magnetic field increases from 2.5 mT to 5.5 mT mean value is almost constant.

Comparative study of solar flux using different empirical models at low land urban industrial zone of Biratnagar Nepal

2023-05-31T16:53:47+00:00

Nepal is a developing country where sufficient clean energy is not available in our daily needs for cooking, lighting and other developmental activities. So, it is high time to promote clean and green energy, which is freely available in every corner of the country. In this regard, the present study helps to estimate the global solar radiation at the lowland region Biratnagar (lat. 26^◦28′53′′N, long. 87^◦15′50′′E and Alt. 72 m) using measured global solar radiation (GSR) and sunshine hours on empirical models. This paper uses the regression technique on two different empirical models Angstrom-Prescott(A-P) and Tiwari and Sangeeta, to estimate solar radiation. After analyzing the data on empirical models, the empirical constants 0.25 and 0.23 and 0.13 and 0.24 are found in A-P and Tiwari and Sangeeta models, respectively. The performance of the models was carried out by employing mean bias error (MBE), mean percentage error (MPE), root mean square error (RMSE) and adjusted coefficient of determination (R²). These statistical tools reveal that all these models are statistically significant. Such a study is relevant when reliable data for solar radiation is not adequately available. The findings of empirical coefficients can be utilized for predicting solar radiation and solar energy at similar geographical locations in Nepal.