Thermodynamic Properties of Low-Density $${}^{132}\hbox {Xe}$$ Gas in the Temperature Range 165–275 K

The method of static fluctuation approximation was used to calculate selected thermodynamic properties (internal energy, entropy, energy capacity, and pressure) for xenon in a particularly low-temperature range (165–270 K) under different conditions. This integrated microscopic study started from an initial basic assumption as the main input. The basic assumption in this method was to replace the local field operator with its mean value, then numerically solve a closed set of nonlinear equations using an iterative method, considering the Hartree–Fock B2-type dispersion potential as the most appropriate potential for xenon. The results are in very good agreement with those of an ideal gas.     

Miscibility enhancement of poly(vinyl chloride)/polystyrene blend: Application to membrane separation of benzene from benzene/cyclohexane mixture by pervaporation

In order to improve the miscibility of poly(vinyl chloride)/polystyrene (PVC/PS) system and to use the prepared material as a membrane to separate benzene from benzene/cyclohexane mixture by pervaporation technique, two poly(styrene-co-N-vinylpyrrolidone) (PSVP) copolymers containing 6.67 and 13.55 mol% of N-vinylpyrrolidone (N-VP) contents were synthesized through a radical polymerization. A comparative study of the miscibility of the PVC/PSVP blends with different compositions was carried out using differential scanning calorimetry, viscosimetry and Fourier transform infrared spectroscopy methods in which the interaction parameters between the two components were widely investigated. To improve the pervaporative flux of PVC membrane to separate benzene from benzene/cyclohexane mixture, a preliminary test of swelling and sorption was performed on PVC/PSVP7 membranes using an azeotropic benzene/cyclohexane mixture. It was revealed that the PVC/PSVP7 membrane containing 10 wt% of PSVP7 showed the best performance and the diffusion behaviour of this mixture through PVC and PVC/PCVP7 membranes has a Fickian behaviour. The pervaporation parameters of this membrane support those of the swelling and selective sorption data and reveal that this membrane could enhance the total flux without significantly affecting its selectivity to benzene.     

The River Nile and Ethiopia’s Grand Renaissance Dam: challenges to Egypt’s security approach

There are increasing challenges to Egypt’s security approach to the River Nile. The river is under immense pressure. This paper examines the significance of the Nile for Egypt and the factors and problems of diminishing its waters. It reviews Egypt’s long-time policy on the Nile and concludes that this policy is difficult to maintain in the face of the present and future challenges. It recommends a non-security multilateral solution for the benefit of all parties.     

Effect of the primary heat treatment on the bond formation in cold welding of aluminum and steel by cold forging

Cold forging enables the manufacturing of high strength monolithic components. When used as joining technology it can also be extended to an enabler of multi-material product design. The contact conditions at the interface between the components during the cold forging process play a crucial role. The joining of two billets of steel and aluminum is investigated by a finite element analysis with regard to the material distribution and the effect of a primary heat treatment of both materials. These parameters affect the surface enlargement and the contact normal stress which are decisive parameters for the formation of a sound bond between aluminum and the hardly cold weldable steel. The experimental results present the effect of a primary heat treatment on the bond formation. Microscopic analyses of the bond formation allow a deeper insight into the bonding mechanism. Thus, the results lead to process design guidelines for cold welding by cold forging.     

Nonminimal Kane's Equations of Motion for Multibody Dynamical Systems Subject to Nonlinear Nonholonomic Constraints

Nonholonomic constraint equations that are nonlinear in velocities are incorporated with Kane's dynamical equations by utilizing the acceleration form of constraints, resulting in Kane's nonminimal equations of motion, i.e. the equations that involve the full set of generalized accelerations. Together with the kinematical differential equations, these equations form a state-space model that is full-order, separated in the derivatives of the states, and involves no Lagrange multipliers. The method is illustrated by using it to obtain nonminimal equations of motion for the classical Appell–Hamel problem when the constraints are modeled as nonlinear in the velocities. It is shown that this fictitious nonlinearity has a predominant effect on the numerical stability of the dynamical equations, and hence it is possible to use it for improving the accuracy of simulations. Another issue is the dynamics of constraint violations caused by integration errors due to enforcing a differentiated form of the constraint equations. To solve this problem, the acceleration form of the constraint equations is augmented with constraint stabilization terms before using it with the dynamical equations. The procedure is illustrated by stabilizing the constraint equations for a holonomically constrained particle in the gravitational field.     

Asymptotic perturbed feedback linearisation of underactuated Euler's dynamics

A unifying methodology is introduced for smooth asymptotic stabilisation of underactuated rigid body dynamics under one and two degrees of actuation. The methodology is based on the concept of generalised inversion, and it aims to realise a perturbation from the unrealisable feedback linearising transformation. A desired linear dynamics in a norm measure of the angular velocity components about the unactuated axes is evaluated along solution trajectories of Euler's underactuated dynamical equations resulting in a linear relation in the control variables. This relation is used to assess asymptotic stabilisability of underactuated rigid bodies with arbitrary values of inertia parameters, and generalised inversion of the relation produces a control law that consists of particular and auxiliary parts. The generalised inverse in the particular part is scaled by a dynamic factor such that it uniformly converges to the Moore–Penrose inverse, and the null-control vector in the auxiliary part is chosen for asymptotically stable perturbed feedback linearisation of the underactuated system.     

Decentralized Backstepping Control of a Quadrotor with Tilted-rotor under Wind Gusts

International Journal of Control, Automation and Systems - Conventional unmanned aerial vehicles, quadrotor have a plethora of applications for civilian and military purposes. Quadrotors as the...