Analysis of Spontaneous Ignition of Grass: Chemical Oxidation and Water Vapor Sorption

Self-heating of biomass by chemical oxidation, which can cause spontaneous ignition, is a safety and management concern. This process can be accelerated by aerobic fermentation and water vapor sorption. The chemical oxidation and water vapor sorption of grass were studied in a laboratory oven, measuring the variations in weight and the internal temperature of a sphere with grass within a flexible polymeric network. Both processes were simulated to prove that the proposed mathematical model could fit the experimental data. It was observed that the water vapor sorption capacity of the grass was high, so the experimental increase in the internal temperature of a spherical body was around 47 K, from 73°C to 120°C. This fact can be very important because the chemical oxidation of grass accelerates at high temperatures. For scaling, simulation programs were used to study the sorption and oxidation processes with an increase in internal temperature in spherical bodies and infinite plane slabs. These results can be used to obtain those of other geometric symmetries by interpolation. It was deduced that at 70°C and with vapor sorption, the ignition time can be around 3 days to 5 days, while without vapor sorption, the ignition times can be around 110 days to 140 days. For 35°C the ignition times with vapor sorption can be around 12 days to 18 days, while without vapor sorption the ignition times can be around 3700 days to 4500 days. These results can be of interest for warehouses of similar biomass and for forestry research and management groups of wildfires. Graphical Abstract

Dynamics around Non-Spherical Symmetric Bodies: I. The case of a spherical body with mass anomaly

The space missions designed to visit small bodies of the Solar System boosted the study of the dynamics around non-spherical bodies. In this vein, we study the dynamics around a class of objects classified by us as Non-Spherical Symmetric Bodies, including contact binaries, triaxial ellipsoids, spherical bodies with a mass anomaly, among others. In the current work, we address the results for a body with a mass anomaly. We apply the pendulum model to obtain the width of the spin-orbit resonances raised by non-asymmetric gravitational terms of the central object. The Poincaré surface of section technique is adopted to confront our analytical results and to study the system’s dynamics by varying the parameters of the central object. We verify the existence of two distinct regions around an object with a mass anomaly: a chaotic inner region that extends beyond the corotation radius and a stable outer region. In the latter, we identify structures remarkably similar to those of the classical restrict and planar 3-body problem in the Poincaré surface of sections, including asymmetric periodic orbits associated with 1:1+p resonances. We apply our results to a Chariklo with a mass anomaly, obtaining that Chariklo rings are probably related to first kind periodic orbits and not with 1:3 spin-orbit resonance, as proposed in the literature. We believe that our work presents the first tools for studying mass anomaly systems.

Experimental modeling of the interaction of hard and aeriform body and the onset of a drag crisis with a significant change in velocity

The paper deals with the possibilities and prospects of experimental modeling of the interaction of a solid and a gaseous body. It is assumed that reliable experimental data have already been obtained and published. The problem of approximating the complex aerodynamic characteristics of air flow around a spherical body is posed and solved. The study was carried out using the «Cut-Glue» method for approximating numerical information about blowing experiments. Generally, this information reflects the dependence of the drag coefficient on the Reynolds number. The choice of the Cut-Glue method for the approximation of complex, multiextremal characteristics that can be obtained in physical experiments is substantiated.

The deceleration of small charged bodies in a rarefied plasma

The purpose of this work is to create a method for determining the aerodynamic characteristics of fine particles in a highly rarefied plasma. The created method is based on the theorem on the change in momentum imparted to the body. The “body+surrounding plasma” system was considered to be closed; therefore, the change in the momentum of the body is equal in the impulse of the incident flow and is opposite to it in direction. The change in the pulse flux is calculated using the statistical method. To compare the results and approbation of the calculation method, the deceleration forces of a spherical body in a flow of neutral gas were determined. Next, we calculated the drag coefficient from the side of the charged plasma component. The calculation results are presented in the graphs.

Gravitational Effects on Neutrino Decoherence in the Lense–Thirring Metric

We analyze the effects of gravity on neutrino wave packet decoherence. As a specific example, we consider the gravitational field of a spinning spherical body described by the Lense–Thirring metric. By working in the weak-field limit and employing Gaussian wave packets, we show that the characteristic coherence length of neutrino oscillation processes is nontrivially affected, with the corrections being dependent on the mass and angular velocity of the gravity source. Possible experimental implications are finally discussed.

Fluid mechanics of free subduction on a sphere. Part 1. The axisymmetric case

To understand how a spherical geometry influences the dynamics of gravity-driven subduction of the oceanic lithosphere on Earth, we study a simple model of a thin and dense axisymmetric shell of thickness $h$ and viscosity $\eta _1$ sinking in a spherical body of fluid with radius $R_0$ and a lower viscosity $\eta _0$ . Using scaling analysis based on thin viscous shell theory, we identify a fundamental length scale, the ‘bending length’ $l_b$ , and two key dimensionless parameters that control the dynamics: the ‘flexural stiffness’ $St = (\eta _1/\eta _0)(h/l_b)^3$ and the ‘sphericity number’ $\varSigma = (l_b/R_0)\cot \theta _t$ , where $\theta _t$ is the angular radius of the subduction trench. To validate the scaling analysis, we obtain a suite of instantaneous numerical solutions using a boundary-element method based on new analytical point-force Green functions that satisfy free-slip boundary conditions on the sphere's surface. To isolate the effect of sphericity, we calculate the radial sinking speed $V$ and the hoop stress resultant $T_2$ at the leading end of the subducted part of the shell, both normalised by their ‘flat-Earth’ values (i.e. for $\varSigma = 0$ ). For reasonable terrestrial values of $\eta _1/\eta _0$ ( $\approx$ several hundred), sphericity has a modest effect on $V$ , which is reduced by $< 7\,\%$ for large plates such as the Pacific plate and by up to 34 % for smaller plates such as the Cocos and Philippine Sea plates. However, sphericity has a much greater effect on $T_2$ , increasing it by up to 64 % for large plates and 240 % for small plates. This result has important implications for the growth of longitudinal buckling instabilities in subducting spherical shells.

APLIKASI TEKNOLOGI MIKROBUBBLE PADA PETANI IKAN NILA DI DESA BAYAN

Desa Bayan Kabupaten Lombok Utara memiliki potensi sumberdaya air dengan kuantitas yang cukup memadai. Berdasarkan pemantauaan saat melakukan survey awal pada awal bulan februari 2020, dari segi kualitas, kondisi air yang digunakan untuk kegiatan budidaya ikan belum memenuhi kaidah standart sertifikasi Cara Budidaya Ikan yang Baik (CBIB). Kegiatan pengabdian kepada masyarakat ini bertujuan untuk meningkatkan produktifitas lahan budidaya ikan di Desa Bayan dengan cara melakukan perbaikan kualitas air, yaitu meningkatkan kandungan oksigen terlarut, melalui aplikasi teknologi microbubble. Kegiatan ini dileksanakan melalaui beberapa kegiatan, antara lain dengan melakukan sosialisai tentang sertifikasi Cara Budidaya Ikan yang Baik (CBIB) yang meliputi semua aspek kompleks yang menjadi permasalahan pada kelompok pembudidaya, yaitu manajemen kualitas air, tata kelola letak pembangunan kolam budidaya, SDM pengelola kolam budidaya, pemberian pakan dan obat ikan, panen, transportasi ikan, dll. Pada kelompok tersebut juga diujicobakan teknologi mikrobubble untuk meningkatkan kadar oksigen pada kolam budidaya masyarakat. Micro bubble pada media budidaya ikan dapat dihasilkan dengan beberapa metoda dengan karakteristik yang berbeda-beda. Metoda tersebut antara lain dengan elektrolityc microbubble generator, porous plate (PP), ventury tube type bubble generator, dan spherical body in a flowing water tube. Mikrobubble yang diujicobakan pada kegiatan ini adalah mikrobubble bertipe ventury tube. Aplikasi tekhnologi ini dapat menghasilkan produktifitas ikan yang lebih tinggi dibandingkan dengan pemeliharaan ikan yang tidak menerapkan tekhnologi ini