bluuebunny/crossref_metadata_2025 huggingface dataset:
Modification of activated carbon of rice husk using HDTMA-Br (SMAC) surfactant as nitrite ion (NO2
−) adsorbent
Authors: Arnelli  , Santoso B , Astuti Y
Published: July 2021

Surfactant modified activated carbon (SMAC) is a product resulting from the modification of activated carbon with surfactants to increase the adsorption ability of activated carbon against ions in water. Carbonization using pyrolysis at 300°C, 350°C, and 400°C. Activation of carbon was carried out in two ways, the first activation using H3PO4 activator, followed by heating at 410°C for 1 hour. Second, activation using H3PO4 followed by radiation with microwaves. The resulting activated carbon was modified with HDTMA-Br to form SMAC, then SMAC was applied for adsorption of nitrite (NO2
−) ions. This study aimed to determine the optimum conditions for carbonization temperature, radiation time, radiation power, adsorption time of HDTMA-Br. The adsorption capacity of SMAC on nitrite ions and the adsorption process of HDTMA-Br were studied (thermodynamic data). Characterization was carried out using FTIR, SEM, and GSA. The optimum carbonization temperature was 300°C; the optimum activation was 5 minutes and 400 watts, the optimum time for HDTMA-Br adsorption was 4 hours with the adsorption capacity was 7.304 mg/g. SMAC is effective in adsorbing nitrite ions where the adsorption capacity was 0.741 mg/g, and the adsorption efficiency is 98.833%. The adsorption of HDTMA-Br on activated carbon was physical adsorption, SMAC has an N-(CH3)3 group from HDTMA-Br with a SMAC surface area of 24.173 m2/g.
Sorption of waste lubricant oil spills from seawater using natural hollow fibres
Authors: Sukmawati A , Septiani W , Surkardan M D
Published: July 2021

Waste lubricant oil is mostly produced by its replacement on engines machine, which is frequently discarded into the environment to seawater in particular. Calotropis gigantea and Ceiba pentandra fibres had the potential to be used as a natural oil absorbent material. This study was conducted on these fibres’ oil sorption capacity in artificial seawater, using different variations in the thickness of the oil layer, contact time, mass absorbent, and temperature. The highest sorption capacity was obtained by 65,70 g/g for Calotropis gigantea, 79,71 g/g for Ceiba pentandra on fibre weight of 0.3 g, 9 mm oil film thickness, contact time 60 minutes, at room temperature. This report represents that both fibres are highly effective sorption on waste lubricant oil.
Antimicrobial activity of secondary metabolites of endophytic bacteria F4 of papaya leaf (Carica papaya L)
Authors: Sarjono P R , Silvia D , Mulyani N S , Ismiyarto  , Ngadiwiyana  , Prasetya N B A , Andriani Yosie
Published: July 2021

Papaya leaves have been known to contain secondary metabolite compounds as antimicrobial, so that endophytic bacteria is also suspected of having secondary metabolite compounds as antimicrobial. In previous research, endophytic bacteria have been isolated from papaya leaf and obtained 5 endophytic bacteria which were F1, F2, F3, F4 and F5. Three bacterias that have been known for their antibacterial activity were F1, F3, and F5. This research aims to determine the antimicrobial activity of F4 endophytic bacteria. The results showed that single isolates of endophytic bacteria F4 is a type of Gram-positive bacteria with a basil cell shape (stem). F4 endophytic bacteria has 3 growth phases; they are logarithmic phase occurs at 0-8 hours, stationary phase at 8-34 hours, and phase of death at 34-46 hours. Phytochemical results showed that MS18 contained saponin group compounds, while MS36 contained alkaloids and saponin group compounds. The highest antimicrobial activity was in the death phase, MS36 with minimum inhibitory concentration (KHM) to Escherichia coli, Candida albicans, and Bacillus subtillis were 15.5 mg/mL, respectively; 16.5 mg/mL and 16.5 mg/mL by disc diffusion method, whereas to Aspergillus niger of 0.5 mg/mL by dry weight method.
Effect of chitosan as adsorben to bacto agar quality from Gelidium sp.
Authors: Darmawan M , Siswanti H W , Nurhasni  , Fransiska D
Published: July 2021

Gelidium sp. is a seaweed that produces agar with a high gel strength. Bacto agar must have a high purity, so it needs a right purification method. One of the ways by adsorption process using chitosan. The aim of this research was to determine the influence of chitosan as an adsorbent and the optimum condition of its adsorption process. Bacto agar was extracted with water at 90°C. An alkali and acid pretreatment were added in the extraction process in order to increase thephysico-chemical properties of the agar gels. The agar extract was adsorbed by chitosan with various concentration of chitosan (0.5; 0.75; and 1%) and adsorption time (0, 30, and 60 minutes). The characteristic of bacto agar include moisture content, ash content, acid-insoluble ash content, sulphate content, gel strength, viscosity, syneresis, gelling and melting points, analysis of its molecular structure by FTIR and SEM. Bacto agar resulted in this research were tested as a bacterial culture medium using Total Plate Count (TPC) method. The best chitosan treatment process was obtained in bacto agar at 0,75% and 0 minute of adsorption which is had the physico-chemical properties that met the criteria of commercial bacto agar with 3.50% of bacto agar yield, 14.61% moisture content, 4.02% ash content, 0.93% acid-insoluble ash content, 1.34% sulphate content, 1054.96 g/cm2 gel strength, 60 Cp viscosity, 4.62% syneresis, 65 °C and 20.75 °C of melting and gelling points respectively. The microbial analysis shows that bacto agar can be used as a bacterial culture medium.
Synthesize of self-electrostatic interaction chitosan-carrageenan membrane and its properties
Authors: Ismillayli N , Hadi S , Andayani I G A S , Honiar R , Mariana B , Sanjaya R K , Hermanto D
Published: July 2021

The preparation of polyelectrolyte complex (PEC) based on bio-composite materials often requires crosslinking agents to achieve the desired stability and properties of the material formed. PEC with opposite charges has the advantage in self-crosslinking through electrostatic interactions. Chitosan is a positively charged polysaccharide with -NH3
+ group while κappa-carrageenan is a negatively charged polysaccharide with -OSO3
− group. This work focused on synthesizing chitosan-carrageenan membrane and determining its characteristics. The membrane was prepared by interacting chitosan and carrageenan hydrosols at a pH of 5. The obtained chitosan-carrageenan membrane had better physical-mechanical properties, including tensile strength (load), elongation (strain), and elasticity (modulus young), adsorption, and resistance of water, than the constituent polymers. The FTIR spectra indicated the presence of self interaction in membrane between protonated amine groups of chitosan and sulfate groups of carrageenan. The difference in surface morphology among chitosan-carrageenan membrane and its constituent membranes was confirmed by SEM analysis.
Utilization of bamboo leaf silica as a superhydrophobic coating using trimethylchlorosilane as a surface modification agent
Authors: Silviana S , Dalanta F , Sanyoto G J
Published: July 2021

In recent years, there has been an increasing research interest regarding the development of superhydrophobic coating for various purposes with tetraethyl orthosilicate (TEOS) as the source of silica. Unfortunately, TEOS is hazardous as an alkoxide and need long step as well as time consuming to synthesize it. Typically, previous researches using fluoroalkylsilane (FOK) as the surface modification agent is containing fluoro compound which is not safety to use. This paper is aimed to develop a cost-effective and environmental-friendly superhydrophobic coating by utilizing bamboo leaf silica. This work was particularly conducted to develop the method of purification of bamboo leaf ash as the source of silica to produce superhydrophobic coating material. This method could be an effective and efficient way of preparing a superhydrophobic coating using silica bamboo leaf with eco-friendly solvent exchange agents. This observation used n-hexane, cyclohexane, isooctane as a solvent exchange, and trimethylchlorosilane (TMCS) as a surface modification agent which is not containing fluoro component. The initial bamboo leaf silica and purified silica were examined using XRD, BET, XRF, and SEM EDX Mapping to obtain essential information such as structure, porosity, purity, and surface topography. Also, the coated zinc plat with different solvents was assessed hydrophobicity by contact angle measurement and surface morphology by SEM. The efficient and effective formulation of the superhydrophobic coating was attained by applying n-hexane solvent, 13 %-v/v TMCS, 1.75 %-w/v of bamboo leaf silica was the highest of contact angle.
Synthesis of ferrate using NaOCl and Fe(OH)3 from electrolysis of used iron, and its application for metanil yellow degradation
Authors: Gunawan  , Prasetya N B A , Haris A , Febriliani F
Published: July 2021

Synthesis of ferrate using NaOCl and Fe(OH)3 from electrolysis of used iron, and its application for metanil yellow degradation had been done. The electrolysis was conducted using used iron and zink plates at anode and cathode electrodes, respectively, Na2SO4 electrolyte. The dissolved iron ion from the electrolysis then was made alkaline using NaOH pellet and NaOCl was soaked to the solution to form ferrate (FeO4
2-). The ferrate was used for metanil yellow degradation and it was compared with other oxidators such as permananate, hydrogen peroxide and dichromate. The ferrate solution formed was indicated by a change from brown to dark purple which was indicated the oxidation of Fe(III) to Fe(VI) with a maximum wavelength of 510 nm. The optimum degradation of metanil yellow by ferrate was obtained at pH 8, molar ratio of 2:1, and for 25 min. Ferrate was the most effective oxidator compared with permananate, hydrogen peroxide and dichromate.
Investigation of mango (Mangifera odorate) sap and starch as organic adhesive of bio-briquette
Authors: Rodiah S , Al Jabbar J L , Ramadhan A , Hastati E
Published: July 2021

Rice husk and coconut shell waste is potential biomass found in Palembang that has not been utilized properly. Besides being used for primary purposes, biomass can be used for energy sources like renewable energy. Biomass residues can be obtained from the pyrolysis process with thermal cracking units (UTC) and used as bio-briquettes. Bio-briquette is prepared from a mixture of pyrolysis residues of coconut shell and rice husk with a mass ratio of 2:1 using a combination of adhesive mucilage (mango sap) and paste (starch). The adhesive is prepared by dissolving the starch in water, then mixing it into melted mango sap. The mass ratio of the sap and starch is 1:1 (w/w), while the ratio of the mixture of adhesive and water is 1:10. Based on the ATR-FTIR characterization, it showed that the C = C strain group and the C-H bending group appeared at 2800 cm−1, which was confirmed by its appearance at 800 cm−1 in the fingerprint area. Then, appears peak in the area of 1300 cm−1, indicating the presence of a nitro group, which is assumed to have come from mango sap. Measurements of the briquette physicochemical properties such as moisture content, ash content volatile matter, and fixed carbon were measured using the proximate analysis method. Furthermore, the addition of coconut shells in producing bio briquettes from rice husks increased the calorific value by 7.305 MJ kg−1. So that, bio-briquette is an effective as an alternative energy source to replace fossil fuel for household purposes.
Pure R2 gravity can gravitate about a flat background
Authors: Edery Ariel
Published: July 2021

Pure R2 gravity (R2 gravity by itself with no Einstein-Hilbert term) has attracted attention because it is different from other quadratic gravity theories. In a curved de Sitter (dS) or anti-de Sitter (AdS) background, it is equivalent to Einstein gravity with an additional massless scalar and with a cosmological constant. In contrast to other higher-derivative theories, it is therefore unitary. The equivalence with Einstein gravity is not valid for a flat background. In fact, it has been shown that linearizations of pure R2 gravity about flat spacetime does not produce a graviton. In other words, it does not gravitate about flat space. Pure R2 gravity is invariant under restricted Weyl transformations where the metric is scaled by a conformal factor that obeys a harmonic condition. In this work we consider an action composed of pure R2 gravity, a massless scalar field φ non-minimally coupled to gravity plus other terms. The entire action is invariant under restricted Weyl transformations. We show that when the scalar field φ acquires a non-zero vacuum expectation value (VEV), flat spacetime now becomes a viable gravitating background solution. The restricted Weyl symmetry becomes broken, not explicitly but spontaneously. In other words, when φ acquires a non-zero VEV, the equivalent Einstein action has now the possibility of having a zero cosmological constant and therefore solutions in a Minkowski background. The action can also have, as before, a non-zero cosmological constant, so that solutions in a dS and AdS background are still possible.
Helium as a major portion of the dark matter and the cell structure of the universe
Authors: Ben-Amots Netsivi
Published: July 2021

One of the unsolved problems in physics is called dark matter. It should be called non-shining matter or invisible matter in order to include transparent matter. We will review the discovery of the dark matter and various explanations, some of which state that dark matter consists of baryons. In this article, we will discuss the possibility of 4He as the transparent matter, including claims against and in favor of this idea and various implications, particularly on the evolution of galaxies, galaxy clusters, galaxy superclusters and the large cell structure of the universe. This necessitates a few paradigm shifts regarding the big bang, the black holes, rotation and more. We explain the contradictions in the paradigms accepted at present before deriving the new substitute paradigms suggested in this article. The big-bang theory is replaced with a relativistic expansion of the universe that increases the calculated time since the cosmic microwave background radiation about six times. Quasars and supermassive active galactic nuclei were and are additional factories that produce helium and disperse it in huge jets. Together these phenomena enable the production of helium in sufficient amounts to be the long time sought for transparent matter which is erroneously called dark matter.

As a result, new explanations are obtained for the cell structure of the universe, the structure of galaxies and galaxy clusters, and for their evolution.
Unruh effect and particle decay
Authors: Gaetano Luciano Giuseppe
Published: July 2021

We review the study of the inverse β-decay of uniformly accelerated protons in the context of neutrino flavor mixing. Letting ourselves be guided by some core theoretical principles, such as the general covariance of Quantum Field Theory and the conservation law of the family lepton numbers built into the Standard Model, we infer non-trivial results on the asymptotic nature of neutrinos.
Extended electrodynamics and SHP theory
Authors: Hively L M , Land M
Published: July 2021

This work shows incompleteness and inconsistency in classical electrodynamics (CED) and quantum electrodynamics (QED). Extended electrodynamics (EED) resolves these issues. Stueckelberg-Horwitz-Piron (SHP) theory is equivalent to EED with important implications.
Infrared behavior of Weyl Gravity
Authors: Rachwał Lesław , Giaccari Stefano
Published: July 2021

In this paper, we introduce and motivate the studies of Quantum Weyl Gravity (also known as Conformal Gravity). We discuss some appealing features of this theory both on classical and quantum level. The construction of the quantum theory is described in detail to the one-loop level. To facilitate computations we use only physical degrees of freedom, which are singled out through the York decomposition. At the one-loop level we compute the partition function around a general Einstein space. Next, the functional renormalization group of couplings in Quantum Weyl Gravity is investigated. We reproduce completely previous results obtained on maximally symmetric and Ricci-flat backgrounds. Finally, we comment on further directions and on the issue of conformal anomaly.
Does the Heisenberg uncertainty principle apply along the time dimension?
Authors: Ashmead John
Published: July 2021

Does the Heisenberg uncertainty principle (HUP) apply along the time dimension in the same way it applies along the three space dimensions? Relativity says it should; current practice says no. With recent advances in measurement at the attosecond scale it is now possible to decide this question experimentally.

The most direct test is to measure the time-of-arrival of a quantum particle: if the HUP applies in time, then the dispersion in the time-of-arrival will be measurably increased.

We develop an appropriate metric of time-of-arrival in the standard case; extend this to include the case where there is uncertainty in time; then compare. There is – as expected – increased uncertainty in the time-of-arrival if the HUP applies along the time axis. The results are fully constrained by Lorentz covariance, therefore uniquely defined, therefore falsifiable.

So we have an experimental question on our hands. Any definite resolution would have significant implications with respect to the role of time in quantum mechanics and relativity. A positive result would also have significant practical applications in the areas of quantum communication, attosecond physics (e.g. protein folding), and quantum computing.
Wave-particle duality and the zitterbewegung
Authors: O’Hara Paul
Published: July 2021

In previous work, the Hamilton-Jacobi equation has been associated with the metrics of general relativity and shown to be a generalized Dirac equation for quantum mechanics. This lends itself to a natural definition of wave-particle duality in quantum mechanics. This theory is now further developed to show that a free spinless quantum particle moving with velocity v obeys the standard wave equation of electro-magnetism. We also discuss the implications for the zitterbewegung problem and its relationship to isotropy. Moreover, it is also shown that for the theory to be consistent, the momentum defined by the Hamilton-.!acobi function presupposes the existence of a universal parameter internal to the system. In the case of particles with mass this invariant can be defined by dX = dt/m(t) where t has the units of time and m = m(t) has the units of mass.
Maxwell’s equations from spacetime geometry and the role of Weyl curvature
Authors: Lindgren J , Liukkonen J
Published: July 2021

This research article demonstrates how the field equations of electrodynamics can be shown to be a special case of Einstein field equations of General Relativity. By establishing a special conjecture between the electromagnetic four-potential and the metric of the spacetime, it is first shown how the relativistic wave equation of electrodynamics is a condition for the metric to be Ricci-flat. Moreover, the four-current is identified with a certain four-gradient, which allows one to conjecture that electric charge is related to the covariant divergence of the electromagnetic four-potential. These considerations allow one to understand the Einstein field equations as a nonlinear generalization of Maxwell’s equations. Finally, it is argued that the four-current induces Weyl curvature on the spacetime.
Study of the Radiation Reaction Force for a Step Electric Field and an Electromagnetic Pulse
Authors: Ares de Parga G. , Domínguez-Hernández S. , Salinas-Hernández E. , Ortiz-Domínguez M.
Published: July 2021

The motions of a spin-less point-like charged particle predicted by the Landau-Lifshitz equation and the Hammond method are obtained for a step electric field, a smooth step electric field and an electromagnetic pulse by using analytical and numerical solutions. In addition to Hammond method not presenting the so-called constant force paradox, using step force brings out the apparent physical contradictions of Landau-Lifshitz equation regarding energy conservation. Nevertheless, a smooth step force shows the consistency of the Landau-Lifshitz equation. Unlike other cases, the electromagnetic pulse shows another fundamental difference between the two models. Finally, an analysis of the Hammond method is made.
Influence of surface permeability on gas-dynamic characteristics of high-speed flight
Authors: Alekseeva M M , Kaun Yu V , Chernyshov M V , Yatsenko A A
Published: July 2021

This paper covers the use of gas-permeable materials as the outer surface of a high-speed aircraft. The gas-dynamic structures of supersonic flows are compared in the presence of blowing from the body surface and in its absence. The influence of the blowing speed on the structure of the formed gas-dynamic discontinuities is determined.
On the steady motions control of viscoelastic joined robotic manipulators
Authors: Andreev Aleksandr , Peregudova Olga
Published: July 2021

In this paper, the control problem of the serial multi-link robotic manipulators with rigid and viscoelastic joints is considered. The manipulators structure is such that only the rigid joints are controlled by DC motors. It is shown that such robotic manipulators can make so called stationary motions wherein the part of the generalized coordinates does’t change in time and the others change according to a linear law. The robust output feedback controllers are obtained for the robotic manipulators such that the stationary motion is locally, semi-globally, and globally asymptotically stable.
Oscillations and stability in the coupled mechanical system
Authors: Barabanov I N , Tkhai V N
Published: July 2021

Conservative mechanical systems are considered. Each system is supposed to admit a family of non-degenerate symmetric periodic motions. For the entire set of systems, they form a family of conditionally periodic oscillations, which is assumed to contain a symmetrical periodic motion. Universal couplings for mechanical systems are proposed such that they play the role of controls that ensure the existence, stability, and stabilization of oscillations at the same time for the whole system. Those couplings provide the natural, i.e. without involving any additional controls, stabilization of the oscillation. In addition, mechanical systems perform the synchronization in frequency and phase.
On stability of a collinear libration point in the planar circular restricted photogravitational three-body problem in the cases of first and second order resonances
Authors: Bardin B S , Avdyushkin A N
Published: July 2021

We deal with the planar circular photogravitational three-body problem. That is, we consider the motion of a particle under influence of gravitational and radiation forces acting from two bodies, which move in circular orbits. The stability of collinear point L1
, which located on the line between the bodies, is investigated. By using the method of normal forms and applying theorems of KAM theory we perform a nonlinear stability study for parameter values corresponding to the cases of first and second order resonances. Rigorous conclusions on instability and stability in the sense of Lyapunov have been obtained.
On the equilibriums stability in an approximate problem of the dynamics of a rigid body with a suspension point vibrating along an inclined straight line
Authors: Belichenko Mikhail
Published: July 2021

We consider the heavy rigid body dynamics under the assumption that one of the body points (the suspension point) performs the specified high-frequency vibrations of small amplitude along an inclined straight line, and the body mass centre lies on the principal axis of inertia for the suspension point. In the framework of an approximate autonomous system of canonical equations of motion, the question of existence, number, and stability of the body relative equilibrium positions is solved. It is shown that for all such equilibria, the mass centre radius-vector lies in the vertical plane containing the vibration axis. The number of equilibria is four, six or eight depending on the vibration intensity. Sufficient and necessary conditions for their stability are found. The existence of high-frequency periodic motions of the initial non-autonomous system, which are generated by the investigated equilibria, is justified using Poincare’s method. Conclusions about stability (in linear approximation) of these periodic motions are drawn.
Effect of the heat transfer coefficient on modelling the energy deposition of destructed meteoroid
Authors: Brykina I G , Bragin M D
Published: July 2021

Models of meteoroid destruction into the cloud of fragments moving with a common shock wave are considered: the two-parameter model that takes into account changes of the shape and density of the cloud, and simple models that leave these factors out of account, including those used in the literature. Models differ in equations governing the lateral expansion of the cloud. We numerically simulate the interaction of the Chelyabinsk asteroid with the Earth’s atmosphere by solving the meteor physics equations using fragment cloud models, and study the models abilities to reproduce the observational energy deposition curve. Heat transfer coefficient effect on simulating energy deposition using different models is estimated. For simple fragment cloud models, the optimal coefficient in the cloud lateral expansion equation is proposed as a function of the heat transfer coefficient (ablation parameter) to match the observational altitude of the bolide peak brightness. The optimal value of the uncertainty parameter in the expression for the heat transfer coefficient is found to match also a shape of the observational energy deposition curve. It is shown that the optimal simple and the two-parameter models give results of modelling the energy deposition of the Chelyabinsk asteroid and estimates of its entry mass, which are very close to each other and are consistent with the observational data.
On the uncertainty factor in approximation of the heat transfer coefficient in the problem of modelling the interaction of meteor body with the atmosphere
Authors: Brykina I G , Egorova L A
Published: July 2021

The problem of modelling the interaction of meteor body with the Earth’s atmosphere is considered. The motion, ablation, and energy deposition of the meteoroid and its fragments moving as a single body are modelled by numerically solving the meteor physics equations. For the heat transfer coefficient, which is a governing parameter in these equations, the proposed approximate expression is used, depending on the meteoroid velocity and size and the atmospheric density, as well as a constant value accepted in the literature. An uncertainty parameter is introduced into the formula for the heat transfer coefficient to make allowance for the existing uncertainty in the radiative heat flux computations in the meteoric range of flow parameters. The influence of uncertainty of the heat transfer coefficient on the meteoroid mass loss, velocity, trajectory, and energy deposition is evaluated.
Periodic body motions along a horizontal rough surface by moving two internal masses
Authors: Chekina Evgeniya A
Published: July 2021

The analysis of the translational motion of a body carrying two moving internal masses along a horizontal rough surface is provided. The masses perform harmonic oscillations in the vertical plane, the frequencies of which are equal, and the amplitudes and phases can be arbitrary. It is assumed that the values of the problem parameters are chosen in such a way that the body moves without separation from the surface. Friction between a body and a surface is described by Coulomb’s law. The classification of possible modes of body motion with periodically varying velocity is carried out. In the three-dimensional space of the parameters of the problem, regions in which the periodic motions are of a qualitatively different nature were constructed.
Asymptotically exact value of the distribution function of molecular pairs in a shock-compressed highly dispersed gas mixture
Authors: Demidov I V , Kuznetsov M M , Kuleshova Y D , Tikhonovets A V
Published: July 2021

The aim of this work is to obtain asymptotically strong expressions for the distribution functions of pairs of molecules inside the shock wave front. An asymptotically exact expression is obtained for the distribution function of the pairs of molecules of the heavy component of a binary shock-compressed gas mixture at the beginning of its translational relaxation. This result is extremely important for experimental modeling of the effect of high-speed overshoot in shock tubes.
Heat flux on streamlined body surface after local energy input
Authors: Dobrov Yu V , Renev M E , Lashkov V A , Mashek I Ch , Khoronzhuk R S
Published: July 2021

An experimental and numerical study of interaction between an oblique shock wave and density inhomogeneity is done. The inhomogeneity is created by interelectrode spark discharge in the oncoming flow with a Mach number of 2. As a result of the experiment, we obtained gradient heat flux sensor data and took shadow photography of the process.
3D model of deflection of an asymmetrical needle during motion in soft tissues
Authors: Druzhinin V G , Morozov V A
Published: July 2021

This study describes a mathematical model of deflection of a steel medical injection needle during its motion in the soft tissue phantom (imitation of human tissues). This model is necessary for adjustment of robotically assisted systems during brachytherapy procedures or similar operations where high precision needle tip positioning is prerequisite. Since the needle tip is asymmetrical, the needle will deform when moving in human tissues and consequently deflect from the rectirectilinear motion. Thus, by inserting and rotating the needle around its axis the needle tip can be led along the predetermined path. This study adopts a new approach to describe an external impact on the needle when it moves inside human tissues and also describes 2D and 3D models, a process of selection of coefficients for 3D models, and provides simulation results.
PAINeT: Implementation of neural networks for transport coefficients calculation
Authors: Istomin V , Kustova E
Published: July 2021

In the present study, a possibility of neural networks implementation for evaluation of transport coefficients in atomic gases taking into account electronic excitation and in molecular gases with electronic, vibrational and rotational degrees of freedom is discussed. Atomic nitrogen N and oxygen O, molecular nitrogen N
2 and oxygen O
2, as well as mixtures (N2, N, O2, O) and (N2, N, O2, O, Ar) are considered in the one-temperature approach of the kinetic theory. The results of exact calculations are compared to the neural network-based simulations. It is shown that for single-component gases, the proposed approach yields good accuracy and calculation speedup up to 3 times for atoms and up to 19 times for molecules. The speedup is significant for multi-component mixtures and increases with the mixture complexity, attaining for four- and five-component mixtures from 597 to 1196 times correspondingly. Ways to improve the accuracy of neural-network predictions of multi-component mixtures transport coefficients are discussed.
Multi-mode oscillations of a mechanical system with higher-order singularity
Authors: Kalnitsky V S
Published: July 2021

This article is based on earlier author’s works on the behavior of mechanical systems with a singular configuration space. We obtained exact analytical expressions for the constraints providing multi-mode oscillations of a double mathematical pendulum. It was found that there are infinitely many modes of oscillations determined by the degree of degeneracy at a singular point in the configuration space of the pendulum. The problem of a double pendulum motion with an elliptical constraint, posed by the author earlier, received a complete solution, both theoretical and experimental. For such a constraint, there are exactly two different oscillation modes: symmetric and asymmetric. Each mode can be realized by selecting the system parameters and is completely determined by the smoothness of the trajectory in the configuration space with a singularity. In the study we used only standard tools of classical analytical mechanics.
State-to-state modeling of oxygen relaxation taking into account electron kinetics
Authors: Melnik M , Kustova E
Published: July 2021

Coupled vibrational, chemical and electronic kinetics in oxygen is studied using the detailed state-to-state model. Simulation of zero-dimensional oxygen relaxation in the presence of free electrons in the temperature range 300 – 1000 K is carried out; the master equations for the vibrational state populations and densities of excited species are solved together with the Boltzmann equation for the electron density distribution. Different models for heavy-particle interactions are assessed. It is shown that the forced harmonic oscillator model is suitable in the entire temperature range. The effect of the initial conditions and the presence of free electrons is discussed; it is shown that including electrons modifies the main relaxation mechanisms. Recommendations are given for extending the kinetic scheme to high-temperature regimes.
Study of the hexapod dynamics using equations in redundant coordinates
Authors: Petrova Victoria
Published: July 2021

The dynamics of hexapods (Stewart platforms) has been extensively studied for several decades. In this problem, the equations of motion are usually constructed using the basic theorems of mechanics. Lagrange equations of the second kind are often constructed for the same purpose. In the present paper, a new form of dynamic equations is considered. These equations are a special form of equations of motion of a system of rigid bodies (equations of dynamics in redundant coordinates). This approach is used to obtain the differential equations of motion of a hexapod in redundant coordinates. In this case, the loaded Stewart platform is considered as a rigid body, whose position is determined by setting the radius vector of the center of mass and the unit vectors of the body-axes system. From the vector form of the Lagrange equations of the first kind scalar differential equations of motion of the mechanical system under consideration are obtained. The obtained equations for some standard motions of the hexapod are numerically integrated. It is noted that the stable motion of the mechanical system under consideration can be obtained only with the introduction of feedbacks.
Stability analysis for a class of mechanical systems with piecewise constant coefficients
Authors: Platonov Alexey
Published: July 2021

A nonlinear mechanical system described by a vector equation of the Lienard type is considered. It is assumed that the forces acting on the mechanical system are given by functions that are piecewise constant with respect to time. With the aid of a special variable substitution, the equation is reduced to a system that can be considered as an impulsive switched system with infinite numbers of operating modes. The stability problem for the trivial equilibrium position of the obtained system is studied. The stability analysis is carried out using a specially constructed discontinuous Lyapunov function. This function can be understood as a multiple Lyapunov function, consisting of an infinite number of partial Lyapunov functions, each of which is used for a certain time interval. Differentiating the chosen Lyapunov function with respect to solutions of the given system on the corresponding time intervals and applying the theory of differential inequalities, sufficient conditions of the asymptotic stability of the equilibrium position are established.
Experimental studies of wedge models
Authors: Ruleva L B , Solodovnikov S I
Published: July 2021

The functionality of the more complete validation of the developed CDF is being expanded for “Hypersonic aerodynamic shock tube” laboratory facilities. Models of triple semi-wedge with sharp edge and blunt edges were tested. The regions of the high pressure close to the blunted edge of the model are revealed. In the upper model, the greatest pressure was detected on the front face and in the middle region of the flat channel. The experimental graphs of the pressure distribution on the upper and lower surfaces of the model are compared with numerical simulations at limited distances from the nozzle section.
The collection of mechanisms by P.L. Chebyshev at the department of theoretical and applied mechanics of St. Petersburg university
Authors: Tovstik P E , Yushkov M P , Kuteeva G A , Sinilshchikova G A , Trifonenko B V
Published: July 2021

The paper presents some information and photos dealing with mechanisms by the great Russian mathematician P.L. Chebyshev. These mechanisms are kept at the revived Cabinet of Practical Mechanics of the History of Physics and Mathematics Museum of St. Petersburg State University (SPBU). This revived cabinet is now located at the Mathematics and Mechanics Faculty of SPBU in Peterhof.
Influence of electric charge on surface of a solar sail on dy-namics of the sail which moves along Tsander’s trajectories
Authors: Yakovlev A B
Published: July 2021

The application of a solar sail spacecrafts for a realization of distant flights into a space is actively discussed. However, all bodies in space plasma get electric charge which depends on density and temperature of plasma, a stream of sunlight and electro-physical characteristics of a body. But till now not enough attention has been given a problem of influence of the charging of a solar sail on its dynamics and durability characteristics. The charging of thin films, such as a solar sail has a number of features. Most important of them are: 1) a surface is bilateral and not closed, 2) partial permeability of a film for the charged particles of a space environment. In this work there are the results of calculations of electric charge density on the surface of the solar sail in the space between orbits of the Earth and Jupiter and an estimate of influence of electric charge of a sail on dynamics of solar sail spacecrafts which moves along elliptic Tsander’s a trajectory. The problem about deflection determination is reduced to integration of one-dimensional problem of the motion of a body with variable acceleration. The obtained estimates of the influence of an electric charge induced on the surfaces of the solar sail on the motion of a space vehicle during interplanetary flights along the orbits mentioned above have shown that the influence is small.
Heat-health vulnerabilities in the climate change context—comparing risk profiles between indoor and outdoor workers in developing country settings
Authors: Venugopal Vidhya , Shanmugam Rekha , Perumal Kamalakkannan Latha
Published: July 2021

Occupational heat stress is a crucial risk factor for a range of Heat-Related Illnesses (HRI). Outdoor workers in unorganized work sectors exposed to high ambient temperatures are at increased risk in developing countries. We aim to compare HRI, Productivity Loss (PL), and reduced renal health risk between workers from outdoor unorganized (N = 1053) and indoor organized (N = 1051) work sectors. Using descriptive methods and a large epidemiological cross-sectional study using mixed methods, we compared risk patterns between the two groups. We analyzed the risk of self-reported HRI symptoms, Heat Strain Indicators (HSIs), PL, and reduced kidney function using Multivariate Logistic Regression (MLR) models. Although Wet Bulb Globe Temperature (WBGT) exposures were high in both the outdoor and indoor sectors, significantly more Outdoor Unorganized Workers (OUWs) reported heat stress symptoms (45.2% vs 39.1%) among 2104 workers. OUWs had a significantly higher share of the heavy workload (86.7%) and long years of heat exposures (41.9%), the key drivers of HRIs, than the workers in indoor sectors. MLR models comparing the indoor vs outdoor workers showed significantly increased risk of HRI symptoms (Adjusted Odds Ratio) (AORoutdoor = 2.1; 95% C.I:1.60–2.77), HSI (AORoutdoor = 1.7; 95% C.I:1.00–2.93), PL (AORoutdoor = 11.4; 95% C.I:7.39–17.6), and reduced kidney function (Crude Odds Ratio) (CORoutdoor = 1.4; 95% C.I:1.10–1.84) for the OUWs. Among the heat-exposed workers, OUW had a higher risk of HRI, HSI, and PL even after adjusting for potential confounders. The risk of reduced kidney function was significantly higher among OUWs, particularly for those with heat exposures and heavy workload (AORoutdoor = 1.5; 95% C.I: 0.96–2.44, p = 0.073) compared to the indoor workers. Further, in-depth studies, protective policies, feasible interventions, adaptive strategies, and proactive mitigation efforts are urgently needed to avert health and productivity risks for a few million vulnerable workers in developing nations as climate change proceeds.
Fermion sign problem in path integral Monte Carlo simulations: grand-canonical ensemble
Authors: Dornheim Tobias
Published: July 2021

We present a practical analysis of the fermion sign problem in fermionic path integral Monte Carlo (PIMC) simulations in the grand-canonical ensemble (GCE). As a representative model system, we consider electrons in a 2D harmonic trap. We find that the sign problem in the GCE is even more severe than in the canonical ensemble at the same conditions, which, in general, makes the latter the preferred option. Despite these difficulties, we show that fermionic PIMC simulations in the GCE are still feasible in many cases, which potentially gives access to important quantities like the compressibility or the Matsubara Greens function. This has important implications for contemporary fields of research such as warm dense matter, ultracold atoms, and electrons in quantum dots.
Assessment on shallot farming development in North Padang Lawas Regency, North Sumatra
Authors: Girsang Moral Abadi , Nainggolan Palmarum , Hidayat Shabil , Sitepu Suheri , Ramija Khadijah El
Published: July 2021

The purpose of this study was to obtain information on the existing shallot farming in North Padang Lawas Regency which includes the conditions of agricultural land for shallot, existing technology, and the income of farmers, then provides recommendations for shallot’s farming technology to increase shallot’ production, and to increase farmers’ income. The method used in this research were survey, field observation, and soil sampling. To determine the suitability of land for shallots, the evaluation of land suitability was carried out by comparing the quality/characteristics of the land with the requirements for shallot growth. Analysis of Land evaluation was carried out computerized using the SPKL version 2.01 software. Analysis of shallot farm income was carried out by analyzing the balance between revenue and cost. The results obtained from this study were the technology used by farmers was still simple, land suitability for shallots is dominated by marginal land suitability (S3) so that additional input is needed to increase production, while shallot farming was feasible with an R/C ratio level of 2,19.
K-Nearest Neighbor Algorithm to Identify Cucumber Maturity with Extraction of One-Order Statistical Features and Gray-Level Co-Occurrence
Authors: Syahrorini Syamsudduha , Syamsudin Denny , Saputra Dwi Hadidjaja Rasjid , Ahfas Akhmad
Published: July 2021

Determination of the maturity of cucumber fruit after harvest is subjective. The level of thoroughness of each individual’s cucumber selection is different. The maturity of cucumbers is seen from the age of the fruit, the resemblance of ripe cucumbers or old, raw or young is difficult to distinguish in terms of the texture of the fruit skin. The use of red, green, blue, and grayscale color modes from the cucumber imagery, is then processed using the extraction of the statistical features of the Order-One and Order-Two GLCM methods. Imagery using a 13 megapixels smartphone camera. Texture parameter values are used in the first order: mean, variance, skewness, kurtosis, entropy. Second order: energy, contrast, correlation, inverse different moments, angular second moments, variance 2, and entropy 2. The classification of the texture parameters of both order uses an algorithm from K-Nearest Neighbors as a comparison of test data values and training data. So that the system is made can identify the maturity of cucumbers old and young. The highest accuracy is found in grayscale imagery with a combination of two skewness and kurtosis parameters and euclidean distance calculation in K-Nearest Neighbor classification of 96.05%.
Sugarcane bagasse for environmentally friendly super-absorbent polymer: synthesis methods and potential applications in oil industry
Authors: Riswati Shabrina Sri , Setiati Rini , Kasmungin Sugiatmo , Prakoso Suryo , Fathaddin Muhammad Taufiq
Published: July 2021

Super-absorbent polymer (SAP) is able to absorb water by multiple times more than its own weight. Sugarcane bagasse (SCB) raw material has been excessively produced as a byproduct in sugar factory. The synthesis of SAP from SCB creates a balance between the utilization of industrial by-product and the resulted environmentally friendly material. In oil production water might be a troublesome, thus minimizing water production while extracting oil is essential. Besides, diversion of the flow in heterogeneous reservoir optimizes the oil production. SCB-SAP might have the potential to act as a water absorbing agent and flow diverter by taking the advantage of SAP high swelling ratio characteristic. This study provides the information of SCB-SAP synthesis methods and highlights the current application of SAP in oil industry, including the laboratory studies and field tests.
Petrophysical Analysis to Determine the Initial Oil Reserves in the AHP Field
Authors: Sudi Apolonius Harda Putranta , Sitaresmi Ratnayu , Yulia Prayang Sunny
Published: July 2021

Petrophysic analysis is carried out for the evaluation of petrophysical parameters. The aim of this paper is determine the initial oil in place (OOIP) by Volumetric method in the field that will be conducted research, such as reservoir thickness (h) or net pay, porosity (∅), and also water saturation (Sw). This parameter is used to position the initial oil reserves (OOIP) at two wells that will be examined, namely A1-R wells and A5-R wells. After qualitative analysis of both wells, namely A1-R well and A5-R well, it was seen that A1-R and A5-R, the litilogy well are dominated by limestone and After conducting qualitative analysis conducted quantitative analysis that is to find out the porosity (∅), resistivity, water resistivity, water saturation (Sw) and net pay (h) of the two wells. From the calculation, the porosity value is obtained by 19% in A1-R wells and the average porosity in A5-R wells is 26%, water saturation (Sw) from A1-R wells and A5-R wells are 34% and 28% and net pay (h) values are 2.82 at A1-R wells and 2.83 in A5-R wells. After the volumetric calculation, the OOIP value of A1-R well and A5-R well is 8826315.716 STB and 85308364.22 STB.