Two-fluid hydrodynamic model for semiconductors

The hydrodynamic Drude model (HDM) has been successful in describing the optical properties of metallic nanostructures, but for semiconductors where several different kinds of charge carriers are present, an extended theory is required. We present a two-fluid hydrodynamic model for semiconductors containing electrons and holes (from thermal or external excitation) or light and heavy holes (in $p$-doped materials). The two-fluid model predicts the existence of two longitudinal modes, an acoustic and an optical, whereas only an optical mode is present in the HDM. By extending nonlocal Mie theory to two plasmas, we are able to simulate the optical properties of two-fluid nanospheres and predict that the acoustic mode gives rise to peaks in the extinction spectra that are absent in the HDM.Comment: Accepted in PRB. 17 pages, 9 figures, 1 tabl

Inapproximability Results for Scheduling with Interval and Resource Restrictions

In the restricted assignment problem, the input consists of a set of machines and a set of jobs each with a processing time and a subset of eligible machines. The goal is to find an assignment of the jobs to the machines minimizing the makespan, that is, the maximum summed up processing time any machine receives. Herein, jobs should only be assigned to those machines on which they are eligible. It is well-known that there is no polynomial time approximation algorithm with an approximation guarantee of less than 1.5 for the restricted assignment problem unless P=NP. In this work, we show hardness results for variants of the restricted assignment problem with particular types of restrictions. For the case of interval restrictions - where the machines can be totally ordered such that jobs are eligible on consecutive machines - we show that there is no polynomial time approximation scheme (PTAS) unless P=NP. The question of whether a PTAS for this variant exists was stated as an open problem before, and PTAS results for special cases of this variant are known. Furthermore, we consider a variant with resource restriction where the sets of eligible machines are of the following form: There is a fixed number of (renewable) resources, each machine has a capacity, and each job a demand for each resource. A job is eligible on a machine if its demand is at most as big as the capacity of the machine for each resource. For one resource, this problem has been intensively studied under several different names and is known to admit a PTAS, and for two resources the variant with interval restrictions is contained as a special case. Moreover, the version with multiple resources is closely related to makespan minimization on parallel machines with a low rank processing time matrix. We show that there is no polynomial time approximation algorithm with a rate smaller than 48/47 ? 1.02 or 1.5 for scheduling with resource restrictions with 2 or 4 resources, respectively, unless P=NP. All our results can be extended to the so called Santa Claus variants of the problems where the goal is to maximize the minimal processing time any machine receives

Robustness of the far-field response of nonlocal plasmonic ensembles

Contrary to classical predictions, the optical response of few-nm plasmonic particles depends on particle size due to effects such as nonlocality and electron spill-out. Ensembles of such nanoparticles (NPs) are therefore expected to exhibit a nonclassical inhomogeneous spectral broadening due to size distribution. For a normal distribution of free-electron NPs, and within the simple nonlocal Hydrodynamic Drude Model (HDM), both the nonlocal blueshift and the plasmon linewidth are shown to be considerably affected by ensemble averaging. Size-variance effects tend however to conceal nonlocality to a lesser extent when the homogeneous size-dependent broadening of individual NPs is taken into account, either through a local size-dependent damping (SDD) model or through the Generalized Nonlocal Optical Response (GNOR) theory. The role of ensemble averaging is further explored in realistic distributions of noble-metal NPs, as encountered in experiments, while an analytical expression to evaluate the importance of inhomogeneous broadening through measurable quantities is developed. Our findings are independent of the specific nonclassical theory used, thus providing important insight into a large range of experiments on nanoscale and quantum plasmonics

Size-dependent nonlocal effects in plasmonic semiconductor particles

Localized surface plasmons (LSP) in semiconductor particles are expected to exhibit spatial nonlocal response effects as the geometry enters the nanometer scale. To investigate these nonlocal effects, we apply the hydrodynamic model to nanospheres of two different semiconductor materials: intrinsic InSb and $n$-doped GaAs. Our results show that the semiconductors indeed display nonlocal effects, and that these effects are even more pronounced than in metals. In a $150\mathrm{\,nm}$ InSb particle at $300\mathrm{\,K}$, the LSP frequency is blueshifted 35%, which is orders of magnitude larger than the blueshift in a metal particle of the same size. This property, together with their tunability, makes semiconductors a promising platform for experiments in nonlocal effects.Comment: 7 pages, 3 figures, 1 table, corrected typos in text and figure

Zukunft der Fleischwirtschaft

Die deutsche Fleischindustrie musste in den letzten Jahren rasante Veränderungen verkraften. Internationale Konzentrationsprozesse, EU-Agrarreform, EU-Osterweiterung und Strukturwandel haben weitreichende Folgen für die Branche. Der Kostendruck wächst, die sozialversicherungspflichtige Beschäftigung geht seit Jahren zurück. Schlachthöfe beschäftigen zunehmend Werkvertragarbeitnehmer aus Osteuropa, die häufig aufgrund illegaler Praktiken und schlechter Arbeitsbedingungen in die Schlagzeilen geraten. Darüber hinaus erhöhen gehäuft auftretende Fleischskandale den Druck, Qualität zu produzieren und nachzuweisen.Ziel der Untersuchung ist es, diese Entwicklungen und ihre Auswirkungen auf die Beschäftigungsperspektiven und die Arbeitssituation in der deutschen Fleischwirtschaft zu analysieren. Dafür werden die Veränderungen des weltweiten und europäischen Marktes für Fleisch angesichts der EU-Osterweiterung und der Neuausrichtung der EU-Agrarpolitik ebenso un-tersucht wie der Strukturwandel der deutschen Fleischindustrie unter dem Einfluss wachsender internationaler Konzernstrukturen. Außerdem werden die Entwicklung des Marktes für Fleischprodukte, die Rolle von Handel und Konsum in Deutschland sowie die Entwicklung des Außenhandels vor dem Hintergrund stagnierender Märkte in Europa beleuchtet.Die Publikation basiert auf Primär- und Sekundärdatenanalysen, die durch empirische Erhebungen im Rahmen von Expertengesprächen mit Unternehmen, Verbänden und Institutionen der Branche sowie Vertretern der Politik vertieft wurden

Hydrodynamic acoustic plasmon resonances in semiconductor nanowires and their dimers

The hydrodynamic Drude model known from metal plasmonics also applies to semiconductor structures of sizes in between single-particle quantum confinement and bulk. But contrary to metals, for semiconductors two or more types of plasma may have to be taken into account in order to properly describe their plasmonic properties. In this combined analytical and computational study, we explore predictions of the recently proposed two-fluid hydrodynamic Drude model for the optical properties of plasmonic semiconductor nanowires, in particular for thermally excited InSb nanowires. We focus on the low-frequency acoustic surface and bulk plasmon resonances that are unique fingerprints for this model and are yet to be observed. We identify these resonances in spectra for single nanowires based on analytical calculations, and they are in complete agreement with our numerical implementation of the model. For dimers of nanowires we predict substantial increase of the extinction cross section and field enhancement of the acoustic localized surface plasmon resonance, which makes its observation in dimers more likely.Comment: I would like to inform that Dr.Abbas Zarifi is the corresponding author of this pape

Ökologischer Gemüsebau in Deutschland: Strukturen und Entwicklungen

This paper gives an overview over German organic vegetable production. The aim is to describe the situation and to analyze development perspectives. A general descrip-tion of actual trends is based on an expert survey: The experts emphasize that there is a broad spectrum of farm sizes and production portfolios. Expected general trends are growth in area and the specialization on fewer crops as well as the focus on few distri-bution channels. In this paper, these prognoses are compared with empirical data from a survey of 112 organic vegetable farms

Online Bin Covering with Limited Migration

Semi-online models where decisions may be revoked in a limited way have been studied extensively in the last years. This is motivated by the fact that the pure online model is often too restrictive to model real-world applications, where some changes might be allowed. A well-studied measure of the amount of decisions that can be revoked is the migration factor beta: When an object o of size s(o) arrives, the decisions for objects of total size at most beta * s(o) may be revoked. Usually beta should be a constant. This means that a small object only leads to small changes. This measure has been successfully investigated for different, classical problems such as bin packing or makespan minimization. The dual of makespan minimization - the Santa Claus or machine covering problem - has also been studied, whereas the dual of bin packing - the bin covering problem - has not been looked at from such a perspective. In this work, we extensively study the bin covering problem with migration in different scenarios. We develop algorithms both for the static case - where only insertions are allowed - and for the dynamic case, where items may also depart. We also develop lower bounds for these scenarios both for amortized migration and for worst-case migration showing that our algorithms have nearly optimal migration factor and asymptotic competitive ratio (up to an arbitrary small epsilon). We therefore resolve the competitiveness of the bin covering problem with migration

Die Zukunft des Gastgewerbes - Beschäftigungsperspektiven im deutschen Gastgewerbe

Die vorliegende Studie untersucht die Markt- und Strukturentwicklungen im Gastgewerbe in den letzten zehn Jahren, deren Auswirkungen auf Beschäftigung und Arbeitsbedingungen und gibt einen Ausblick auf die Branchenentwicklung bis ins Jahr 2017. Dafür werden die Entwicklungen in den drei Teilbranchen Beherbergungsgewerbe, Gastronomie und Catering analysiert. Während im Beherbergungsgewerbe und im Catering die Umsätze gewachsen sind, musste - mit Ausnahme der Systemgastronomie - die speisen- und vor allem die getränkegeprägte Gastronomie in den letzten Jahren Umsatzeinbußen hinnehmen. Das führte zu insgesamt sinkenden Umsatzzahlen im gesamten Gastgewerbe. Trotzdem wurde in den letzten Jahren im Gastgewerbe nach den großen Beschäftigungsrückgängen der 1990er Jahre erstmals wieder Beschäftigung aufgebaut. Dieser Beschäftigungsaufbau ist allerdings geprägt durch eine starke Zunahme an Minijobs und Teilzeitbeschäftigten. Das Gastgewerbe zählt bereits heute mit 1,96 Millionen Erwerbstätigen zu den beschäftigungsintensivsten Branchen in Deutschland. Fast jede/r zweite Beschäftigte ist geringfügig beschäftigt. 70 Prozent der seit 2007 im Gastgewerbe hinzugekommenen sozialversicherungspflichtigen Beschäftigten waren Teilzeitbeschäftigte. Damit einher geht die weite Verbreitung von Niedriglöhnen in der Branche. Wenn sich dieser Trend fortsetzt, dann werden in fünf Jahren bereits über zwei Millionen Menschen in Deutschland im Gastgewerbe beschäftigt sein und die Mehrheit dieser Beschäftigten wird ein atypisches Beschäftigungsverhältnis ausüben