Equivalent Model of Photovoltaic Power Station Considering Different Generation Units’ Fault Current Contributions

The fault current calculation model of photovoltaic (PV) power stations is usually treated as a capacity weighted equivalent model of a single PV generation unit (PVGU). However, in the same PV power station, different PVGUs have various fault current characteristics. As a result, there are significant differences in fault current characteristics between a PVGU and a PV power station. It means that the existing capacity weighted equivalent model cannot be used for accurately describing the fault current contributions from a practical PV power station. In this paper, the fault behaviors of the PVGUs located at different access points of a PV power station are firstly analyzed. The difference in PVGUs’ fault current contributions is identified and reflected with the activation states of current limiters that are employed for PV inverters. The activation states are represented by a theoretical expression so as to distinguish the PVGUs’ fault contributions. Further, based on the proposed theoretical expression, a novel algorithm is developed for sorting all PVGUs included in a PV power station. The multi-machine calculation model is deduced in order to exactly express the fault current contribution from a PV station. Finally, some simulation tests are conducted. The tested results verify the effectiveness of the proposed calculation model. It can provide support for calculating the protection setting of power grid connected with large-scale PV stations.

Energy-Efficient Trajectory Optimization for UAV-Based Hybrid FSO/RF Communications with Buffer Constraints

This paper focuses on an unmanned aerial vehicle (UAV) assisted hybrid free-space optical (FSO)/radio frequency (RF) communication system. Considering the rate imbalance between the FSO and RF links, a buffer is employed at the UAV. Initially, theoretical models of energy consumption and throughput are obtained for the hybrid system. Based on these models, the theoretical expression of the energy efficiency is derived. Then, a nonconvex trajectory optimization problem is formulated by maximizing the energy efficiency of the hybrid system under the buffer constraint, velocity constraint, acceleration constraint, start–end position constraint, and start–end velocity constraint. By using the sequential convex optimization and first-order Taylor approximation, the nonconvex problem is transformed into a convex one. An iterative algorithm is proposed to solve the problem. Numerical results verify the efficiency of the proposed algorithm and also show the effects of buffer size on a UAV’s trajectory.

Nations must be defended: public health, enmity and immunity in Katherine Mayo’s Mother India

This essay explores repressed hostility and punitive fantasies in the discourse of international health, using Katherine Mayo’s Mother India (1927). Multiple tendencies in interwar thinking converge in Mayo’s book, making it a veritable archive of major, minor and emergent forces, including those shaping the phenomenon of ‘international health’ post-Versailles. Mother India provides a unique opportunity to explore how progressive principles of international public health tend to obscure a ‘minor’ and forgettable yet disturbing truth: the discourse on life and health can ‘safely’ harbour an alternative politics and poetics of enmity. Spotlighting the way international health interventions, centrally shaped by USA, operated across multiple levels of governance, the essay locates the significant detail of Mayo’s representation of India as ‘world-menace’. Propelled by the logic of enmity, her shaming portrait of a dysgenic Hindu India justifying emergency international intervention resonates with a strand of interwar conservatism given theoretical expression in the writings of Mayo’s contemporary, Carl Schmitt. Schmitt’s animosity towards political liberalism helps identify Mother India’s vision of imperial sovereignty as a curious antiliberal, American iteration of the logic of enmity in extra-European space and in the ‘humane’ domain of health. Biologising the discourse of juridical-political maturity at a time when Indian nationalism’s organised challenge to Empire could not be gainsaid, Mother India urges a re-imagination of the political field as a battlefield where ‘the enemy’, construed as a problem of health, will kill. Building a case for continued imperial domination in the name of global health and immunity, the book’s humiliating representation of colonial bodily habits, habitations and contagions aimed to undermine liberal imperialism, internationalism and Indian nationalism, all increasingly vocal after World War I.

Equivalent circuit model of eddy current damping regarding frequency-dependence with test validation

This study proposes an equivalent circuit model to simulate the mechanical behavior and frequency-dependent characteristic of eddy current (EC) damping, with the validations from multi-physics finite element (FE) modeling and dynamic testing. The equivalent circuit model is first presented with a theoretical expression of the EC damping force. Then, the transient analysis with an ANSYS-based FE model of an EC damper is performed. The time-history forces from the FE model are compared with that from the proposed equivalent circuit model. The favorable agreement indicates that the proposed model can simulate the nonlinear behavior of EC damping under different excitation scenarios. A noncontact and friction-free planar EC damper is designed, and its dynamic behavior is measured by employing shake table testing. The experimental observations can be reproduced by the proposed equivalent circuit model with reasonable accuracy and reliability. The proposed equivalent circuit model is compared with the classical viscous model and the higher-order fractional model using a complex EC damper simulated in ANSYS to show the advantages of the proposed model regarding model simplicity and prediction accuracy. A single-degree-of-freedom (SDOF) structure with different EC damping models is further analyzed to illustrate the need for accurate EC damping modeling.

An expression for the angle of repose of dry cohesive granular materials on Earth and in planetary environments

The angle of repose—i.e., the angle θr between the sloping side of a heap of particles and the horizontal—provides one of the most important observables characterizing the packing and flowability of a granular material. However, this angle is determined by still poorly understood particle-scale processes, as the interactions between particles in the heap cause resistance to roll and slide under the action of gravity. A theoretical expression that predicts θr as a function of particle size and gravity would have impact in the engineering, environmental, and planetary sciences. Here we present such an expression, which we have derived from particle-based numerical simulations that account for both sliding and rolling resistance, as well as for nonbonded attractive particle–particle interactions (van der Waals). Our expression is simple and reproduces the angle of repose of experimental conical heaps as a function of particle size, as well as θr obtained from our simulations with gravity from 0.06 to 100 times that of Earth. Furthermore, we find that heaps undergo a transition from conical to irregular shape when the cohesive to gravitational force ratio exceeds a critical value, thus providing a proxy for particle-scale interactions from heap morphology.

Estimation of sulfuric acid concentrations using ambient ion composition and concentration data obtained by ion mass spectrometry measurements (APi-TOF)

Sulfuric acid (H2SO4, SA) is the key compound in atmospheric new particle formation. Therefore, it is crucial to observe its concentration with sensitive instrumentation, such as chemical ionisation inlets coupled to Atmospheric Pressure interface Time-of-Flight mass spectrometers (CI-APi-TOF). However, there are environmental conditions and physical reasons when chemical ionisation cannot be used, for example in certain remote places or flight measurements with limitations regarding chemicals. In these cases, it is important to estimate the SA concentration based on ambient ion composition and concentration measurements that are achieved by APi-TOF alone. Here we derive a theoretical expression to estimate SA concentration and validate it with accurate CI-APi-TOF observations. The developed estimate works very well during daytime and with SA concentrations above 2⋅106 cm-3.

Determination and benchmarking of 27Al(d,α) and 27Al(d,p) reaction cross sections for energies and angles relevant to NRA

The cross-sections of deuteron-induced nuclear reactions suitable for ion beam analysis, measured in different laboratories, are often significantly different. In the present work, differential cross-sections of 27Al(d,p) and 27Al(d,α) reactions were measured, and the cross sections benchmarked with thick target spectra obtained from pure aluminium for the first time in two independent laboratories. The 27Al(d,p) and (d,α) differential cross-sections were measured between 1.4 and 2 MeV at scattering angles of 165°, 150°, and 135° in the VDGT laboratory in Tehran (Iran), and the same measurements for detector angle of 150° were repeated from scratch, including target making, with independent equipment on the SAFIR platform at INSP in Paris (France). The results of these two measurements at 150° are in good agreement, and for the first time a fitted function is proposed to describe the Al-cross sections for which no suitable theoretical expression exists. The obtained differential cross-sections were validated through benchmarking, by fitting with SIMNRA deuteron-induced particle spectra obtained from a high purity bulk Al target at both labs for deuteron incident energies between 1.6 and 2 MeV. The thick target spectra are well-reproduced. The evaluated and benchmarked cross sections have been uploaded to the ion beam analysis nuclear data library database (www-nds.iaea.org/ibandl/).

DESCRIPTION OF THE PARAMETERS OF THE ELLIPSE NEEDLE DISC OF THE SOIL PROCESSING TOOL

Due to the well-known advantages, rotary tillage implements are widely used in the cultivation of many agricultural crops. Structurally, the working units of rotary implements are located (installed) on the frame, as a rule, sequentially one after the other. This reduces the maneuverability of the tillage unit, increases the material consumption of the implement and the energy consumption of the technological operation. In the rotary tillage tool developed at Kazan State Agrarian University for pre-sowing soil cultivation, these disadvantages are eliminated by installing a spiral-screw working unit and a section of active ellipsoidal needle disks on the frame coaxially. The research was carried out in order to determine and substantiate the design parameters of the elliptical needle disk. A theoretical dependence is obtained to substantiate the angle α of inclination of the major axis of the ellipsoid disk to the axis of rotation. It was revealed that its rational value must correspond to the condition: α> 44°…62°. An expression for determining the number of needles on a disk is given. The calculation carried out with a disk diameter D= 0.4 m, an angle α= 65 °, an indicator of a kinematic mode λ= 2, a mulching depth a= 0.04 m, a ridging h= 0.004 m showed that a rational number of needles per disc k= 16. Analytically, a theoretical expression for determining the angle of inclination of the needles to the axis of rotation has been derived. The calculation performed at α= 65 ° revealed that the first needle is inclined to the axis of rotation at a minimum angle jmin= 65 °, the fifth and thirteenth needles are inclined to the axis of rotation at an angle of 90 °, the ninth needle is inclined to the axis of rotation at a maximum angle jmax= 115 °. Also obtained are theoretical dependences for determining the angle of attachment of the needles on the hub and the length of the needles along the entire perimeter of the disk. The calculation showed that each needle is fixed on the disc hub at its calculated angle of inclination, equal to 29.0°...32.6°, and the length of the needles along the perimeter of the hub varies within 0.1372 ... 0.1503 m

27 Al(d,alpha) and 27 Al(d,p) Nuclear Reaction Cross Sections at Ed<2MeV Measured at Three Backward Scattering Angles Related to NRA

The cross-sections of deuteron-induced nuclear reactions suitable for ion beam analysis, measured in different laboratories, are often significantly different. In the present work, differential cross-sections of 27 Al(d,p) and 27 Al(d,α) reactions were measured, and the cross sections benchmarked with thick target spectra obtained from pure aluminium for the first time in two independent laboratories. The 27 Al(d,p) and (d,alpha) differential cross-sections were measured between 1.4 and 2 MeV at scattering angles of 165°, 150°, and 135° in the VDGT laboratory in Tehran (Iran), and the same measurements for detector angle of 150° were repeated from scratch, including target making, with independent equipment on the SAFIR platform at INSP in Paris (France). The results of these two measurements at 150° are in good agreement, and for the first time a fitted function is proposed to describe the Al-cross sections for which no suitable theoretical expression exists. The obtained differential cross-sections were validated through benchmarking, by fitting with SIMNRA deuteron-induced particle spectra obtained from a high purity bulk Al target at both labs for deuteron incident energies between 1.6 and 2 MeV. The thick target spectra are well-reproduced. The evaluated and benchmarked cross sections have been uploaded to the ion beam analysis nuclear data library database (www-nds.iaea.org/ibandl/).