Fractional Time Crystals

Time crystals are quantum systems which are able to reveal condensed matter behavior in the time domain. It is known that crystalization in time can be observed in a periodically driven many-body system when interactions between particles force a system to evolve with a period which is an integer multiple of a driving period. This phenomenon is dubbed discrete time crystal formation. Here, we consider ultra-cold atoms bouncing on an oscillating atom mirror and show that the system can spontaneously form a discrete time crystal where the ratio of a period of its motion and a driving period is a rational number. This kind of discrete time crystals requires higher order resonant driving which is analyzed here with the help of an original approach.Comment: version accepted for publication in Phys. Rev.

Anderson Molecules

Atoms can form molecules if they attract each other. Here, we show that atoms are also able to form bound states not due to the attractive interaction but because of destructive interference. If the interaction potential changes in a disordered way with a change of the distance between two atoms, Anderson localization can lead to the formation of exponentially localized bound states. While disordered interaction potentials do not exist in nature, we show that they can be created by means of random modulation in time of the strength of the original interaction potential between atoms and objects that we dub Anderson molecules can be realized in the laboratory.Comment: 13 pages, 5 figures, references added and minor correction

INFLUENCE OF THE PVD PROCESS PARAMETERS ON ZNO: AL THIN FILMS

In recent years a growing interest in searching new material for producing Transparent Conductive Layers (TLC) is observed. ZnO:Al thin films are this type material, interesting due to wide range of potential applications where it can be applied like: transparent electrodes, gas sensors, thin film transistors, sensor devices, electroluminescent diodes and others. The aim of this paper is to discuss influence of the ZnO:Al film deposition parameters of PVD magnetron sputtering method on TCL structure and its chemical composition. It contains description of the ZnO:Al PVD magnetron sputtering deposition method. It discusses results obtained from the analysis of the microstructure of ZnO:Al thin films using a high resolution scanning electron microscope, layers' surface topography determined with atomic force microscope and results of chemical composition analyses

Overcoming the strength-ductility trade-off in additively manufactured AlSi10Mg alloy by ECAP processing

To overcome the trade-off between strength and ductility of the additively manufactured AlSi10Mg alloy used in the automotive and aerospace industries, samples with multilevel structural heterogeneities were produced using single-pass ECAP at 150 degrees C and 200 degrees C. The microstructures of these samples were composed of partially ruptured Al/Si cellular networks and alternatively arranged zones of elongated (pancaked) grains separated by wide zones composed of ultrafine grains. Experimental results demonstrated that AlSi10Mg deformed at 150 degrees C, exhibited a superior ultimate tensile strength (UTS) of ~541 MPa, but limited ductility. The sample deformed at 200 degrees C exhibited both high ultimate tensile strength (UTS ~463 MPa) and excellent elongation at break of ~16.3%. Those results revealed a superior combination of strength and ductility that originated from bimodal grain size distribution, Orowan bowing, mechanical twinning of the hard Si phase, and back-stress hardening. Our results shed new light on the unexploited potential in improving the mechanical properties of additively manufactured alloys.Web of Science918art. no. 16581

CO2 Hydrogenation to Methanol over Ce and Zr Containing UiO-66 and Cu/UiO-66

Direct hydrogenation of CO2 to methanol is an interesting method to recycle CO2 emitted e.g., during combustion of fossil fuels. However, it is a challenging process because both the selectivity to methanol and its production are low. The metal-organic frameworks are relatively new class of materials with a potential to be used as catalysts or catalysts supports, also in the reaction of MeOH production. Among many interesting structures, the UiO-66 draws significant attention owing to its chemical and thermal stability, developed surface area, and the possibility of tuning its properties e.g., by exchanging the zirconium in the nodes to other metal cations. In this work we discuss—for the first time—the performance of Cu supported on UiO-66(Ce/Zr) in CO2 hydrogenation to MeOH. We show the impact of the composition of UiO-66-based catalysts, and the character of Cu-Zr and Cu-Ce interactions on MeOH production and MeOH selectivity during test carried out for 25 h at T = 200 °C and p = 1.8 MPa. Significant increase of selectivity to MeOH was noticed after exchanging half of Zr4+ cations with Ce4+; however, no change in MeOH production occurred. It was found that the Cu-Ce coexistence in the UiO-66-based catalytic system reduced the selectivity to MeOH when compared to Cu/UiO-66(Zr), which was ascribed to lower concentration of Cu0 active sites in Cu/UiO-66(Ce/Zr), and this was caused by oxygen spill-over between Cu0 and Ce4+, and thus, the oxidation of the former. The impact of reaction conditions on the structure stability of tested catalyst was also determined.This work was financed by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wrocław University of Technology and the project 0402/0100/17

The neuropathology of autism: defects of neurogenesis and neuronal migration, and dysplastic changes

Autism is characterized by a broad spectrum of clinical manifestations including qualitative impairments in social interactions and communication, and repetitive and stereotyped patterns of behavior. Abnormal acceleration of brain growth in early childhood, signs of slower growth of neurons, and minicolumn developmental abnormalities suggest multiregional alterations. The aim of this study was to detect the patterns of focal qualitative developmental defects and to identify brain regions that are prone to developmental alterations in autism. Formalin-fixed brain hemispheres of 13 autistic (4–60 years of age) and 14 age-matched control subjects were embedded in celloidin and cut into 200-μm-thick coronal sections, which were stained with cresyl violet and used for neuropathological evaluation. Thickening of the subependymal cell layer in two brains and subependymal nodular dysplasia in one brain is indicative of active neurogenesis in two autistic children. Subcortical, periventricular, hippocampal and cerebellar heterotopias detected in the brains of four autistic subjects (31%) reflect abnormal neuronal migration. Multifocal cerebral dysplasia resulted in local distortion of the cytoarchitecture of the neocortex in four brains (31%), of the entorhinal cortex in two brains (15%), of the cornu Ammonis in four brains and of the dentate gyrus in two brains. Cerebellar flocculonodular dysplasia detected in six subjects (46%), focal dysplasia in the vermis in one case, and hypoplasia in one subject indicate local failure of cerebellar development in 62% of autistic subjects. Detection of flocculonodular dysplasia in only one control subject and of a broad spectrum of focal qualitative neuropathological developmental changes in 12 of 13 examined brains of autistic subjects (92%) reflects multiregional dysregulation of neurogenesis, neuronal migration and maturation in autism, which may contribute to the heterogeneity of the clinical phenotype

Characterisation of Microstructure and Special Grain Boundaries in LPBF AlSi10Mg Alloy Subjected to the KoBo Extrusion Process

Grain boundary engineering (GBE) enhances the properties of metals by incorporating specific grain boundaries, such as twin boundaries (TB). However, applying conventional GBE to parts produced through additive manufacturing (AM) poses challenges, since it necessitates thermomechanical processing, which is not desirable for near-net-shape parts. This study explores an alternative GBE approach for post-processing bulk additively manufactured aluminium samples (KoBo extrusion), which allows thermo-mechanical treatment in a single operation. The present work was conducted to examine the microstructure evolution and grain boundary character in an additively manufactured AlSi10Mg alloy. Microstructural evolution and grain boundary character were investigated using Electron Back Scattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM). The results show that along with grain refinement, the fraction of Coincidence Site Lattice boundaries was also increased in KoBo post-processed samples. The low-Σ twin boundaries were found to be the most common Coincidence Site Lattice boundaries. On the basis of EBSD analysis, it has been proven that the formation of CSL boundaries is directly related to a dynamic recrystallisation process. The findings show prospects for the possibility of engineering the special grain boundary networks in AM Al–Si alloys, via the KoBo extrusion method. Our results provide the groundwork for devising GBE strategies to produce novel high-performance aluminium alloys

Investigation of the Effects of Various Severe Plastic Deformation Techniques on the Microstructure of Laser Powder Bed Fusion AlSi10Mg Alloy

In this paper, we present a complete characterization of the microstructural changes that occur in an LPBF AlSi10Mg alloy subjected to various post-processing methods, including equal-channel angular pressing (ECAP), KoBo extrusion, and multi-axial forging. Kikuchi transmission diffraction and transmission electron microscopy were used to examine the microstructures. Our findings revealed that multi-axis forging produced an extremely fine subgrain structure. KoBo extrusion resulted in a practically dislocation-free microstructure. ECAP processing at temperatures between 100 °C and 200 °C generated moderate grain refinement, with subgrain diameters averaging from 300 nm to 700 nm. The obtained data highlighted the potential of severe plastic deformation as a versatile method for tailoring the microstructure of the AlSi10Mg alloy. The ability to precisely control grain size and dislocation density using specific SPD methods allows for the development of novel materials with ultrafine-grained microstructures that offer the potential for enhanced mechanical and functional properties

On the HKUST-1/GO and HKUST-1/rGO Composites: The Impact of Synthesis Method on Physicochemical Properties

The chemical stability and adsorptive/catalytic properties of the most widely studied metal–organic framework (MOF), which is HKUST-1, can be improved by its combination with graphene oxide (GO) or reduced graphene oxide (rGO). The chemistry of GO or rGO surfaces has a significant impact on their interaction with MOFs. In this work, we demonstrate that GO and rGO interaction with HKUST-1 influences the morphology and textural properties but has no impact on the thermal stability of the final composites. We also show that synthesis environment, e.g., stirring, to some extent influences the formation of HKUST-1/GO and HKUST-1/rGO composites. Homogeneous samples of the sandwich-type composite can be obtained when using reduced graphene oxide decorated with copper (Cu/rGO), which, owing to the presence of Cu sites, allows the direct crystallisation of HKUST-1 and its further growth on the graphene surface. This work is the first part of our research on HKUST-1/GO and HKUST-1/rGO and deals with the influence of the type of graphene material and synthesis parameters on the composites’ physicochemical properties that were determined by using X-ray diffraction, scanning and transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis