Nodal semimetals in d≥3d\geq3 to sharp pseudo-Landau levels by dimensional reduction

Non-uniform strain applied to graphene's honeycomb lattice can induce pseudo-Landau levels in the single-particle spectrum. Various generalizations have been put forward, including a particular family of hopping models in $d$ space dimensions. Here we show that the key ingredient for sharp pseudo-Landau levels in higher dimensions is dimensional reduction. We consider particles moving on a $d$-dimensional hyper-diamond lattice which displays a semimetallic bandstructure, with a $(d-2)$-dimensional nodal manifold. By applying a suitable strain pattern, the single-particle spectrum evolves into a sequence of relativistic Landau levels. We develop and solve the corresponding field theory: Each nodal point effectively generates a Landau-level problem which is strictly two-dimensional to leading order in the applied strain. While the effective pseudo-vector potential varies across the nodal manifold, the Landau-level spacing does not. Our theory paves the way to strain engineering of single-particle states via dimensional reduction and beyond global minimal coupling.Comment: 5+7 pages, 3+5 figure

Exploring Disordered Quantum Spin Models with a Multi-Layer Multi-Configurational Approach

Numerical simulations of quantum spin models are crucial for a profound understanding of many-body phenomena in a variety of research areas in physics. An outstanding problem is the availability of methods to tackle systems that violate area-laws of entanglement entropy. Such scenarios cover a wide range of compelling physical situations including disordered quantum spin systems among others. In this work, we employ a numerical technique referred to as multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) to evaluate the ground state of several disordered spin models. ML-MCTDH has previously been used to study problems of high-dimensional quantum dynamics in molecular and ultracold physics but is here applied to study spin systems for the first time. We exploit the inherent flexibility of the method to present results in one and two spatial dimensions and treat challenging setups that incorporate long-range interactions as well as disorder. Our results suggest that the hierarchical multi-layering inherent to ML-MCTDH allows to tackle a wide range of quantum many-body problems such as spin dynamics of varying dimensionality.Comment: 13 pages, 5 figure

Spektroskopische Untersuchungen und Speziation von Iod-129 in Umweltproben

Die Kernwaffentests und die Wiederaufarbeitung von Kernbrennstoff sind die do-minierenden Prozesse, durch welche es zu einer kontinuierlichen und dauerhaften Erhöhung der Iod-129 Konzentration in der Umwelt kam und noch immer kommt. Insbesondere in der nördlichen Hemisphäre finden sich in den Umweltkompartimenten Boden, Luft und Wasser stark erhöhte Iod-129/127-Verhältnisse. Während im pränuklearen Zeitalter das Verhältnis bei 10-12 bis 10-11 lag, können heute im Meerwasser aus der Umgebung der Wie-deraufarbeitungsanlagen Sellafield (GBR) und La Hague (FR) Verhältnisse von bis zu 10-5 gemessen werden. Das Ziel dieser Arbeit ist daher, im Rahmen von radioökologischer Untersuchun-gen Informationen über das Verhalten des Iods in der Umwelt mit einem Fokus auf die Speziation des Iods in Meerwasser und im Boden im Hinblick auf dessen Migration zu erhalten. Aus der direkten Umgebung der Wiederaufarbeitungsanlage bei Sellafield an der Westküste Englands wurden Wasserproben entnommen und mit einer gekoppel-ten Technik IC-ICP-MS und AMS untersucht. Die detektierten Iod-129/127-Verhältnisse lagen bei 10-6 bis 10-5. Während Iodat/Iodid-Verhältnisse für Iod-129 zwischen 0,24 und 0,87 bestimmt wurden, zeigten sich für Iod-127 Werte von 0,18 bis 2,4. Die Ergebnisse deuten darauf hin, dass Iod-129 vornehmlich als Iodid vorliegt, was potentielle Reaktionen zu flüchtigen Iodverbindungen ermög-licht. Um die im Boden vorhandene Spezies zu untersuchen, wurden XAS Messungen und sequentielle Extraktionen an Referenzböden (RefeSol) durchgeführt. Dabei wird deutlich, dass bei kurzzeitigem Kontakt (24 h) Iodid schnell sorbiert wird. Mittels EXAFS und sequentieller Extraktion wurde bestätigt, dass organische Io-dverbindungen ausgebildet werden. Iodat hingegen zeigte erst nach 30 d eine Erhöhung der Sorption, was auf einen komplexeren, möglicherweise mehrstufi-gen Bindungsmechanismus hinweist. Im Rahmen der XAS Messungen konnten außer dem applizierten Iodat keine weiteren Spezies identifiziert werden. Durch Migrationsexperimente mit ungestörten Bodensäulen über einen Zeitraum von 386 d konnte die vertikale Bewegung des Iods in der vadosen Zone bestimmt werden. Es zeigte sich innerhalb von 88 d eine Akkumulation im mittleren Bereich der Bodensäule, was dem maximalen Aufstieg des Porenwassers entspricht. Nach Trocknen der Säulen konnte eine weitere Migration bis zur Oberfläche durch die Bildung flüchtiger Iodspezies beobachtet werden

Flexible Time Window Management for Attended Home Deliveries

In the competitive world of online retail, customers can choose from a selection of delivery time windows on a retailer's website. Creating a set of suitable and cost-efficient delivery time windows is challenging, since customers want short time windows, but short time windows can increase delivery costs significantly. Furthermore, the acceptance of a request in a particular short time window can greatly restrict the ability to accommodate future requests. In this paper, we present customer acceptance mechanisms that enable flexible time window management in the booking of time-window based attended home deliveries. We build tentative delivery routes and check which time windows are feasible for each new customer request. We offer the feasible long delivery time windows as a standard and let our approaches decide when to offer short time windows. Our approaches differ in the comprehensiveness of information they consider with regard to customer characteristics as well as detailed characteristics of the evolving route plan. We perform a computational study to investigate the approaches' ability to offer short time windows and still allow for a large number of customers to be served. We consider various demand scenarios, partially derived from real order data from a German online supermarket

Flexible dynamic time window pricing for attended home deliveriesy

In the challenging environment of attended home deliveries, pricing of different delivery options can play a crucial role to ensure profitability and service quality of retailers. To differentiate between standard and premium delivery options, many retailers include time windows of various lengths and fees within their offer sets. Customers want short delivery time windows, but expect low delivery fees. However, longer time windows can help to maintain flexibility and profitability for the retailer. We present flexible dynamic time window pricing policies that measure the impact of short time windows on the underlying route plan during the booking process and set delivery fees accordingly. Our goal is to nudge customers to choose time windows that do not overly restrict the flexibility of route plans. To this end, we introduce three dynamic pricing policies that consider temporal and/or spatial routing and customer characteristics. We consider customer behavior through a nested logit model, which is able to mimic customer choice for time windows of multiple lengths. We perform a computational study considering realistic travel and demand data to investigate the effectiveness of flexible dynamic time window pricing. Our pricing policies are able to outperform static pricing policies that reflect current business practice