Interacting Fermionic Atoms in Optical Lattices Diffuse Symmetrically Upwards and Downwards in a Gravitational Potential

We consider a cloud of fermionic atoms in an optical lattice described by a Hubbard model with an additional linear potential. While homogeneous interacting systems mainly show damped Bloch oscillations and heating, a finite cloud behaves differently: It expands symmetrically such that gains of potential energy at the top are compensated by losses at the bottom. Interactions stabilize the necessary heat currents by inducing gradients of the inverse temperature 1/T, with T<0 at the bottom of the cloud. An analytic solution of hydrodynamic equations shows that the width of the cloud increases with t^(1/3) for long times consistent with results from our Boltzmann simulations.Comment: 4 pages, 4 figures plus supplementary material (2 pages, 1 figure), published versio

Equilibration rates and negative absolute temperatures for ultracold atoms in optical lattices

As highly tunable interacting systems, cold atoms in optical lattices are ideal to realize and observe negative absolute temperatures, T < 0. We show theoretically that by reversing the confining potential, stable superfluid condensates at finite momentum and T < 0 can be created with low entropy production for attractive bosons. They may serve as `smoking gun' signatures of equilibrated T < 0. For fermions, we analyze the time scales needed to equilibrate to T < 0. For moderate interactions, the equilibration time is proportional to the square of the radius of the cloud and grows with increasing interaction strengths as atoms and energy are transported by diffusive processes.Comment: published version, minor change

The Use of Polyurethane Composites with Sensing Polymers as New Coating Materials for Surface Acoustic Wave-Based Chemical Sensors—Part I: Analysis of the Coating Results, Sensing Responses and Adhesion of the Coating Layers of Polyurethane–Polybutylmethacrylate Composites

The sensing layers for surface acoustic wave-based (SAW) sensors are the main factor in defining the selectivity and reproducibility of the responses of the sensor systems. Among the materials used as sensing layers for SAW sensors, polymers present a wide range of advantages, from availability to a large choice of chemical-sensing environments. However, depending on the physical–chemical properties of the polymer, issues about the chemical and mechanical stability of the sensing layer have been reported that can compromise the application of sensor systems in the long-term. The sensor properties are defined basically by the properties of the coating material and the quality of the coating process. The strategy used to improve the properties of polymeric coating layers for SAW technology involved the use of polyurethane (PU) in combination with a second polymer that is responsible for the sensing properties of the resulting layer; this is obtained by a reproducible and robust coating procedure. In this first part of our research, we used polymer composites of different compositions of polybutylmetacrylate (PBMA) as the sensing polymer with polyurethane. The analysis of the coating (ultrasonic parameters), the relative sensor responses and the adhesion results for the PU–PBMA composites were determined. The ultrasonic analysis and the relative sensor responses showed very reproducible and precise results, indicating the reproducibility and robustness of the coating process. Accurate correlations between the results of the ultrasonic parameters due to the coating and the relative sensor responses for the organic analytes analyzed were obtained, showing a precise quantitative relationship between the results and the constitution of the composite coating materials. The composites show practically no significant sensor responses to water. The PU–PBMA composites substantially enhanced adhesion to the surface of the piezoelectric sensor element in comparison to the coating with pure PBMA, without loss of its sensing properties. Other PU–polymer composites will be presented in the future, as well as an analysis of the selectivity for the organic analytes for these types of coating materials

Selective Detection of Aromatic Compounds with a Re-Designed Surface Acoustic Wave Sensor System Using a Short Packed Column

A self-developed and newly re-designed chemical SAW sensor system composed of four polymer-coated and four differently modified nano-diamond-coated SAW sensors was applied to measure aromatic compounds in gasoline in a low-cost, fast, and easy way. An additional short packed column at the system inlet improve the selectivity for various possible fuel applications. The column allows the direct sampling of liquid fuels and pre-separates the different components in groups (aromatic and aliphatic compounds) from a fuel sample. Since the sensors employed show linearity towards concentration, an easy quantification of single fuel components was possible even within the group of aromatic compounds

Long-Term Stability of Polymer-Coated Surface Transverse Wave Sensors for the Detection of Organic Solvent Vapors

Arrays with polymer-coated acoustic sensors, such as surface acoustic wave (SAW) and surface transverse wave (STW) sensors, have successfully been applied for a variety of gas sensing applications. However, the stability of the sensors’ polymer coatings over a longer period of use has hardly been investigated. We used an array of eight STW resonator sensors coated with different polymers. This sensor array was used at semi-annual intervals for a three-year period to detect organic solvent vapors of three different chemical classes: a halogenated hydrocarbon (chloroform), an aliphatic hydrocarbon (octane), and an aromatic hydrocarbon (xylene). The sensor signals were evaluated with regard to absolute signal shifts and normalized signal shifts leading to signal patterns characteristic of the respective solvent vapors. No significant time-related changes of sensor signals or signal patterns were observed, i.e., the polymer coatings kept their performance during the course of the study. Therefore, the polymer-coated STW sensors proved to be robust devices which can be used for detecting organic solvent vapors both qualitatively and quantitatively for several years

Thoughts on opportunities in high-energy nuclear collisions

This document reflects thoughts on opportunities from high-energy nuclear collisions in the 2020s.Comment: 10 pages, pd

RV Kronprins Håkon (cruise no. 2019708) Longyearbyen – Longyearbyen 19.09. – 16.10.2019

The HACON cruise is a major component of the FRINATEK HACON project, which aims at investigating the role of the Gakkel Ridge and Arctic Ocean in biological connectivity amongst ocean basins and global biogeography of chemosynthetic ecosystems. The HACON study area is centered in the Aurora seamount and Aurora vent field