Density Matrix Renormalization Group in the Heisenberg Picture

In some cases the state of a quantum system with a large number of subsystems can be approximated efficiently by the density matrix renormalization group, which makes use of redundancies in the description of the state. Here we show that the achievable efficiency can be much better when performing density matrix renormalization group calculations in the Heisenberg picture, as only the observable of interest but not the entire state is considered. In some non-trivial cases, this approach can even be exact for finite bond dimensions.Comment: version to appear in PRL, acronyms in title and abstract expanded, new improved numerical example

WASP: a software package for correctly characterizing the topological development of ribbon structures

We introduce the Writhe Application Software Package (WASP) which can be used to characterisze the topology of ribbon structures, the underlying mathematical model of DNA, Biopolymers, superfluid vorticies, elastic ropes and magnetic flux ropes. This characterization is achieved by the general twist–writhe decomposition of both open and closed ribbons, in particular through a quantity termed the polar writhe. We demonstrate how this decomposition is far more natural and straightforward than artificial closure methods commonly utilized in DNA modelling. In particular, we demonstrate how the decomposition of the polar writhe into local and non-local components distinctly characterizes the local helical structure and knotting/linking of the ribbon. This decomposition provides additional information not given by alternative approaches. As example applications, the WASP routines are used to characterise the evolving topology (writhe) of DNA minicircle and open ended plectoneme formation magnetic/optical tweezer simulations, and it is shown that the decomponsition into local and non-local components is particularly important for the detection of plectonemes. Finally it is demonstrated that a number of well known alternative writhe expressions are actually simplifications of the polar writhe measure

Prenatal diagnosis and follow-up of congenital splenic cysts

Los quistes esplénicos congénitos son entidades poco frecuentes, particularmente en la edad pediátrica. En la literatura especializada existen pocos casos publicados con diagnóstico durante el período prenatal. Los autores describen 2 casos clínicos, identificados por ecografía prenatal a las 34 y 30 semanas de gestación, y su evolución posnatal hasta su resolución espontánea a los 5 meses y a los 2 años de vida, respectivamente. Se revisa la etiología, clínica y evolución de esta patología.Congenital splenic cysts are uncommon entities, especially in children. Few cases diagnosed in the prenatal period have been reported in the literature. We describe two cases that were identified by prenatal sonography at 34 and 30 gestational weeks. Their follow- up until spontaneous full regression at 5 months and 2 years, respectively, is discussed. The etiology, clinical findings, and clinical course of this entity are reviewed

Development of a test-rig for exploring optimal conditions of small unmanned aerial vehicle co-axial rotor systems

Due to the recent increase in development and use of co-axial rotor system at the scale of small UAVs a greater understanding of the performance variables that affect the co-axial propulsion system at low Reynolds number operation has become increasingly apparent when optimizing such systems. This paper focuses on and details the development and fabrication of a small UAV co-axial rotor system test-rig, and investigations into the optimal inter-rotor spacing range between contra-rotating rotors. An integrated test-rig has been specifically designed for the testing and analysis of commercial off-the-shelf (COTS) propellers and out-runner motors which are predominantly used in SUAV propulsion systems. The test-rig incorporates linear motion, yaw, force and other performance measurements, to help validate the identified core co-axial rotor system performance attributes. The co-axial test-rig was used to investigate co-axial rotor systems inter-rotor spacing which identified an optimum H/D ratio region of (0.41 – 0.65)