DCA++: A software framework to solve correlated electron problems with modern quantum cluster methods

We present the first open release of the DCA++ project, a high-performance research software framework to solve quantum many-body problems with cutting edge quantum cluster algorithms. DCA++ implements the dynamical cluster approximation (DCA) and its DCA+ extension with a continuous self-energy. The algorithms capture nonlocal correlations in strongly correlated electron systems, thereby giving insight into high-Tc superconductivity. The code’s scalability allows efficient usage of systems at all scales, from workstations to leadership computers. With regard to the increasing heterogeneity of modern computing machines, DCA++ provides portable performance on conventional and emerging new architectures, such as hybrid CPU–GPU, sustaining multiple petaflops on ORNL’s Titan and CSCS’ Piz Daint supercomputers. Moreover, we show how sustainable and scalable development of the code base has been achieved by adopting standard techniques of the software industry. These include employing a distributed version control system, applying test-driven development and following continuous integration

Nettoyage mécanique électrostatique et numérisation simultanée des deux faces de documents historiques sur papier

Cleaning the surfaces of cultural artefacts on paper is a vaguely defined procedure in conservation. In general, however, the term refers to removing from paper surfaces contaminants that are not attached to the paper. A machine-assisted treatment method has been recently developed to remove dust and biological contaminants from paper, photographic materials and textiles. It can be used to clean large stocks efficiently and without mechanical impact on the object surfaces. Contaminant removal is performed by frictionless application of an electrostatic foil. The method is limited to the removal of particles from surfaces and/or from indentations in the surface textures of papers and textiles. However, It is not suitable for removing any discolouration that has penetrated into the depth of the material, contaminants that are caked together with the surface, or in-grown biological contaminants. Hence, improvement of the visual aesthetic appearance of objects will be achieved only to a limited extent. The technology allows removal of dust contaminants from both sides, even from very delicate surfaces, while entirely keeping existing drawing and writing materials or pigment layers intact. Approximately 80 objects per hour can be processed, each having a width of one meter and a length of 1.50 meters. The system is a device which is expandable by modules, and two digitization units have been recently added to its technical equipment, digitizing both sides of each object in one cycle combined with the cleaning process. The advantages and limits of this technology will be shown by means of examples, as will be the methodology of quality management and control of the cleaning process, which has also been newly developed

Nano meets the sheet: adhesive-free application of nanocellulosic suspensions in paper conservation

Abstract Historical papers are often locally damaged by exogenous influences and/or have endogenously degraded paper areas. The stabilization of such papers is very important because further use of the object can cause additional damage. Different types of nanocellulose are interesting as a novel stabilizing materials for paper due to their close structural relation to the paper matrix. Therefore, the present study investigated whether the treatment of historical papers with nanocellulose suspensions is a novel method for paper stabilization. Two different types of nanocelluloses, bacterial cellulose and a mechanically nanofibrillated cellulose based on wood pulp, were tested with regard to their performance in stabilizing fragile papers. Concerning material handling and application in conservation steps, different ways to modify the suspensions were tested. The resulting suspensions were applied to historical papers from several centuries with different extents of damage. The paper-nanocellulose composites were characterized with regard to their optical and microscopic integrity and by physical and chemical analyses. The treatment of mechanical damage and the consolidation of weakened paper areas could be realized by the application of a nanocellulose suspension without an additional adhesive. The results of the treatment depend on the type of nanocellulose, on the paper material, on processing and application techniques. The paper discusses the applicability and stability of the differently prepared nanocellulose suspensions, also with regard to their mode of application and long-term performance. Advantages and limitations are addressed in detail. Graphical abstract Bacterial nanocellulose and nano-fibrillated cellulose from pulp can be used to consolidate damaged historic papers without the application of additional adhesive

Influence of Electronegative Substituents on the Binding Affinity of Catechol-Derived Anchors to Fe₃O₄ Nanoparticles

Successful applications of nanoparticles are often limited by insufficient nanoparticle stability due to low binding affinity of dispersants. However, excellent Fe3O4 nanoparticle stability was reported in a recent study (Nano Lett. 2009, 9,4042-4048) that compared different catechol derivative-anchored low molecular weight dispersants. Here, we investigate mechanistic binding aspects of five different anchors from this study that showed radically different efficiencies as dispersant anchors, namely nitroDOPA, nitrodopamine, DOPA, dopamine, and mimosine, using electron paramagnetic resonance, Fourier transform infrared spectroscopy, and UV-vis spectroscopy. We demonstrate enhanced electron delocalization for nitrocatechols binding to Fe2+ compared to unsubstituted catechols if they are adsorbed on Fe3O4 surfaces. However a too high affinity of mimosine to Fe3+ was shown to lead to gradual dissolution of Fe3O4 nanoparticles through complexation followed by dissociation of the complex. Thus, the binding affinity of anchors should be optimized rather than maximized to achieve nanoparticle stability.</p