Bounds on the entanglability of thermal states in liquid-state nuclear magnetic resonance

The role of mixed state entanglement in liquid-state nuclear magnetic resonance (NMR) quantum computation is not yet well-understood. In particular, despite the success of quantum information processing with NMR, recent work has shown that quantum states used in most of those experiments were not entangled. This is because these states, derived by unitary transforms from the thermal equilibrium state, were too close to the maximally mixed state. We are thus motivated to determine whether a given NMR state is entanglable - that is, does there exist a unitary transform that entangles the state? The boundary between entanglable and nonentanglable thermal states is a function of the spin system size $N$ and its temperature $T$. We provide new bounds on the location of this boundary using analytical and numerical methods; our tightest bound scales as $N \sim T$, giving a lower bound requiring at least $N \sim 22,000$ proton spins to realize an entanglable thermal state at typical laboratory NMR magnetic fields. These bounds are tighter than known bounds on the entanglability of effective pure states.Comment: REVTeX4, 15 pages, 4 figures (one large figure: 414 K

Modelling Pulse Magnetic Welding Processes

In recent years pulse magnetic welding technology gained an ever increasing attention. The process was known for over 40 years, yet the poor knowledge of process parameters as well as the difficulties concerning the calculability of the process due to lack of adequate software, performance and appropriate material models hindered the application of the technology. In the past, some simulations treating the process of explosive welding were conducted. There, the assumption was made to define a friction condition to the boundary regions which was reasonable due to similar conditions in the collision region during the process. However, at pulse magnetic welding processes, the contact forces are highly transient and have big gradients over the geometry. In this paper a new empirical approach is presented, which gives the possibility of modelling the welding process by parameter-controlled bonding at the welding interface. The pulse magnetic forming process was simulated by loose coupling of electromagnetic and mechanical FEM software with the commercial code ANSYS. As geometry the joining of a duct with an internally positioned conical bolt was chosen. The material used for both duct and bolt was EN AW 6063. First of all the influences of heat generation were analyzed. Therefore, the additional thermal simulation was coupled with the electromagnetic and the mechanical simulation. The heat generation caused by the plastic deformation was considered. As the resulting temperatures were below the melting temperature of the material, further simulations were carried out without thermal simulation. In order to calibrate the welding model, a set of relevant parameters were defined. It included the cumulative plastic work, the plastic deformation in collision direction, the normal and the tangential components of the collision velocity and the collision angle between the two parts. By comparing the simulation with experiments carried out at the same specific process parameters, it was possible to reduce the set of parameters to the normal collision velocity and plastic deformation. Based on their distribution, the parameter control of the bonding condition could be adjusted. Further experiments gave a high accordance to the simulations carried out with the parameters found for this model

New Impulses in the Forming of Magnesium Sheet Metals

Owing to growing demands by customers for comfort and safety in cars, the weight of the respective individual automobile increases constantly. Hence, the role of construction materials, such as aluminium and magnesium alloys in car body production becomes ever more important. Especially magnesium is highly attractive because of its small density, its positive mechanic-technological properties, and the ready availability as raw material. It is known that magnesium has a reduced formability at room temperature and needs to be heated up to temperatures at around 300°C to be deformable with technologically useful forming rates. So therefore to form sheets made of magnesium alloys, the workpiece has to be heated previously. The idea of combining the processes "inductive heating" and "pulsed magnetic forming" led to the following research work. The aim was to develop a tool that combines both processes to be able to heat up the forming zone at the workpiece to a significant temperature and to form it afterwards without changing the tool. However, in order to manufacture sheet metal components from magnesium innovative manufacturing technologies are necessary. The Institute for Machine Tools and Factory Management (IWF) carries out research and develops solutions in the field of pulsed magnetic forming

Probability distributions consistent with a mixed state

A density matrix $\rho$ may be represented in many different ways as a mixture of pure states, \rho = \sum_i p_i |\psi_i\ra \la \psi_i|. This paper characterizes the class of probability distributions $(p_i)$ that may appear in such a decomposition, for a fixed density matrix $\rho$. Several illustrative applications of this result to quantum mechanics and quantum information theory are given.Comment: 6 pages, submitted to Physical Review

Concurrence of mixed bipartite quantum states in arbitrary dimensions

We derive a lower bound for the concurrence of mixed bipartite quantum states, valid in arbitrary dimensions. As a corollary, a weaker, purely algebraic estimate is found, which detects mixed entangled states with positive partial transpose.Comment: accepted py PR

Process Design for Electromagnetic Forming of Magnesium Alloy AZ31 Using FE Simulation

Magnesium wrought alloys are outstanding lightweight materials due to their low density and high specific strength. The low formability of magnesium wrought alloy AZ31 at room temperature is increased by electromagnetic forming in comparison to quasi-static forming. For a detailed study of electro-magnetic process a coupled FE simulation must be performed. In this paper the process design for electromagnetic forming of magnesium wrought alloy AZ1 using FE simulation is presented. The complexity of an electromagnetic forming process requires the illustration of magnetic, thermal and structural dynamic domains. Moreover, it is also necessary to illustrate the electromagnetic resonant circuit RLC. Short processing time and the strong dependence of the physical domains to each other requires a coupled FE simulation. The illustration of resonant circuit and the resulting formation of magnetic field is carried out in two-dimensional rotationally symmetric model in ANSYS MAPDL using a suitable material model. As a result time-dependent and location-dependent eddy currents and Lorentz forces are estimated. Subsequently, the transmission of the estimated Lorentz forces and joule heat generation rates to ANSYS LS-DYNA is done. Due to the rotational symmetry of 2D ANSYS MAPDL model a transformation of the loads on 3D structures can be realized. The formation of an optimum deformation of a work piece in dependence of a defined die has been carried out. Here, the influence of different coil designs, die materials and geometries and RLC parameters was investigated

Investigation into Energy Efficiency of Outdated Cutting Machine Tools and Identification of Improvement Potentials to Promote Sustainability

AbstractCutting machine tools have a significant impact on manufacturing and sustainability. There exist a large number of outdated cutting machine tools especially in developing and emerging countries which are still taking a considerable share in global value creation. Furthermore, an increasing trend in field of reuse, retrofitting and upgrading can be observed. For Life-Cycle-Assessment and analyses of end-of-life behavior of such machine tools in context of sustainability, reliable values for energy consumption and machining efficiency under realistic machining conditions are indispensable. In the present paper the energy consumption and machining efficiency of an exemplary outdated milling machine have been measured and analyzed under consideration of different influences such as process parameter, machining material and ratio of prim time to secondary time. Additionally a comparison between a newer and the outdated milling machine has been carried out in order to identify and quantify possible improvement potentials of outdated machine tool concerning energy consumption and machining efficiency. Based on obtained results more accurate and realistic decision can be made by enterprises who aim to promote sustainable manufacturing