Electric quantum walks with individual atoms

We report on the experimental realization of electric quantum walks, which mimic the effect of an electric field on a charged particle in a lattice. Starting from a textbook implementation of discrete-time quantum walks, we introduce an extra operation in each step to implement the effect of the field. The recorded dynamics of such a quantum particle exhibits features closely related to Bloch oscillations and interband tunneling. In particular, we explore the regime of strong fields, demonstrating contrasting quantum behaviors: quantum resonances vs. dynamical localization depending on whether the accumulated Bloch phase is a rational or irrational fraction of 2\pi.Comment: 5 pages, 4 figure

Relating groundwater heat-potential to city-scale heat-demand: A theoretical consideration for urban groundwater resource management

To sustainably plan the use of subsurface resources, a discussion about thermal management is needed, as well as a more coordinated and efficient thermal use of subsurface resources. This contribution outlines a theoretical consideration for how to effectively manage urban subsurface resources. The consideration is made by means of assessing the heat-potential from urban groundwater resources against the background of heat-demand. We illustrate that, in principle, the heat-potential of subsurface resources could be directly ‘mined’ to exploit them and store thermal ‘waste energy’. We show how quantitative flow- and heat-transport modeling approaches can offer a scientific basis for thermal management strategies. In combination with geographic information systems, evaluating heat-potential and heat-demand can become the basis for management concepts as well as for the overall economic and ecological thermal planning of subsurface resource usage. An index which relates groundwater heat-potential to heat-demand is introduced here. This index allows us to quantify the share that thermal ‘waste energy’ from groundwater resources could have to satisfy heat-demand. On the one hand, we demonstrate how the spatial distribution of this index can be derived for the urban area of Basel, Switzerland. On the other hand, we exemplify the temporal evolution of the heat-potential for selected urban areas and discuss the capacity for space heating with a typical annual heat-demand profile

Interlaboratory CEC and exchangeable cation study of bentonite buffer materials : II. alternative methods

Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proven to be one of the most sensitive parameters for detecting changes in mineral properties in bentonite-alteration experiments. An interlaboratory study of CECs and exchangeable cations for three reference bentonite buffer materials that were used in the Alternative Buffer Material test (ABM) project in Äspö, Sweden, was conducted to create a suitable database. The present study focused on CEC accuracy and compared CEC methods where care was taken to prevent dissolution of soluble minerals such as calcite and gypsum. The overall quality of the CEC and exchangeable cation values measured using non-Cu-trien CEC methods were good, with CECs of 74-91±0.5-3.3 meq/100 g and exchangeable cation values of 22-61±1.2-3.9 meq/100 g Na, 7-23±0.8 -1.5 meq/100 g Mg, and 19-39±0.8 -1.6 meq/ 100 g Ca. The precision was comparable to the standard Cu-trien method even for exchangeable Ca , although the laboratories used different solution/solid ratios and reaction-time parameters for Cu-trien which affect carbonate dissolution. The MX80 and Dep. CAN bentonite exchangeable Ca values were more accurate than standard-Cu-trien values. Using the optimized methods of this study, MX80 and Dep.CAN exchangeable Ca values averaged 20.2±1.6 and 38.8±1.4 meq/100 g which amounts to ~70% of the inflated Cu-trien values. A more complex analysis of the CEC data using different methods, anion analyses, and mineralogical analysis is necessary to obtain plausible and accurate CEC values. Even with a more complicated analytical procedure, the CEC and exchangeable cation values were still not accurate enough because of excess anions. Chloride, sulfate, and dolomite might have increased the exchangeable Na, Mg, and Ca values

Interlaboratory CEC and exchangeable cation study of bentonite buffer materials : I. Cu(II)-triethylenetetramine method

Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proved to be one of the most sensitive parameters for detecting changes of mineral properties such as swelling capacity and illitization in alteration experiments. Whether measured differences in CEC values of bentonite buffer samples before and after an experiment are (1) actual differences caused by clay structural changes such as illitization or (2) simply data scatter due to the different methods used by international research teams is an open question. The aim of this study was to measure the CEC of clay samples in five different laboratories using the same method and to evaluate the precision of the values measured. The Cu-trien method and four reference materials of the Alternative Buffer Material (ABM) test project in Aspo, Sweden, were chosen for this interlaboratory study. The precision of the Cu-trien method, which uses visible spectroscopy, was very good with a standard deviation of ±0.7-2.1 meq/100 g for CECs that ranged from 11 to 87 meq/100 g. For the same CEC range, analysis of Cu-trien index cations using inductively coupled plasma (mass spectrometry) and atomic absorption spectroscopy were less precise with a standard deviation of ±2.8-3.9 meq/100 g. Based on the measured precision, greater measured differences in Cu-trien CEC and exchangeable cation values of bentonite buffer samples, before and after an experiment, might be actual differences. Great care must be taken when interpreting measured CEC differences, and analytical characterization of any structural changes may be needed. Compared with results from the 'International Soil-Analytical Exchange' (iSE) program for soils, most absolute concentrations were much larger for the clays studied; however, for the two parameters exchangeable Ca and CEC the range was similar to the iSE ring test and, most importantly, the precision was comparable. Future studies should discuss the accuracy of CEC and exchangeable cation values and compare them to alternative CEC methods in which care is taken to prevent dissolution of soluble minerals, such as calcite and gypsum