Quantum phase-space representation for curved configuration spaces

We extend the Wigner-Weyl-Moyal phase-space formulation of quantum mechanics to general curved configuration spaces. The underlying phase space is based on the chosen coordinates of the manifold and their canonically conjugate momenta. The resulting Wigner function displays the axioms of a quasiprobability distribution, and any Weyl-ordered operator gets associated with the corresponding phase-space function, even in the absence of continuous symmetries. The corresponding quantum Liouville equation reduces to the classical curved space Liouville equation in the semiclassical limit. We demonstrate the formalism for a point particle moving on two-dimensional manifolds, such as a paraboloid or the surface of a sphere. The latter clarifies the treatment of compact coordinate spaces as well as the relation of the presented phase-space representation to symmetry groups of the configuration space.Comment: 14 pages. Corresponds to published versio

Debt Financing of High-growth Startups

We study the business model of venture debt firms, specialized institutions that provide loans to high-growth startups. Venture debt represents an apparent contradiction with traditional debt theory since startups have negative cash flows and lack tangible assets to secure the loan. Yet, we estimate that the U.S. venture debt industry provides at least one venture debt dollar for every seven venture capital dollars invested. We aim to provide the first empirical evidence on the determinants of the lending decision. Building on existing field interviews and case studies, we design a choice experiment of the lending decision and conduct experiments with 55 senior venture lenders. We find support for the hypothesis that backing by venture capital firms substitutes for startups’ cash flow. Furthermore, we illustrate the signaling effect of patents and their role as collateral to facilitate the lending decision.Venture capital; startups; patents

Production strategies and applications of microbial single cell oils

Polyunsaturated fatty acids (PUFAs )of the ω-3 and ω-6 class (e.g. , α-linolenic acid, linoleic acid) are essential for maintaining biofunctions in mammalians like humans. Due to the fact that humans cannot synthesize these essential fatty acids, they must be taken up from different food sources. Classical sources for these fatty acids are porcine liver and fish oil. However, microbial lipids or single cell oils, produced by oleaginous microorganisms such as algae, fungi and bacteria, are a promising source as well. These single cell oils can be used form any valuable chemicals with applications not only for nutrition but also for fuels and are therefore an ideal basis for a bio-based economy. A crucial point for the establishment of microbial lipids utilization is the cost-effective production and purification of fuels or products of higher value. The fermentative production can be realized by submerged (SmF) or solid state fermentation (SSF). The yield and the composition of the obtained microbial lipids depend on the type of fermentation and the particular conditions (e.g., medium, pH-value, temperature, aeration, nitrogensource). From an economical point of view, waste or by-product streams can be used as cheap and renewable carbon and nitrogen sources. Ingeneral, downstream processing costs are one of the major obstacles to be solved for full economic efficiency of microbial lipids. For the extraction of lipids from microbial biomass cell disruption is most important, because efficiency of cell disruption directly influences subsequent downstream operations andoverall extraction efficiencies. A multitude of cell disruption and lipid extraction methods are available, conventional as well as newly emerging methods, which will be described and discussed in terms of large scale applicability, their potential in a modern biorefinery and their influence on product quality. Furthermore, an overview is given about applications of microbial lipids or derived fatty acids with emphasis on food applications

Geoarchaeological evidence of Ostia’s river harbour operating until the fourth century AD

Ancient Ostia at the mouth of the River Tiber into the Tyrrhenian Sea was largely significant for the economic supply of Rome. Ostia itself experienced an extraordinary period of prosperity in the second century AD. Starting in AD 42, a first new harbour at Portus was built by Emperor Claudius close to Ostia. It reached its full functionality under Emperor Trajan in the early second century AD, only. At Ostia itself, previous archaeological and geoarchaeological studies have brought to light a lagoon-type harbour at the western fringe of the city operating between the fourth and the second century BC in an artificially excavated harbour basin. From the second century BC onwards, a considerably smaller and shallower part of this western harbour basin was still in function as a fluvial harbour. So far, it was unclear whether Ostia’s western harbour was still in use when the harbour at Portus was set into function in the first to second century AD, or if the latter partially replaced Ostia’s harbour infrastructure. According to archaeological evidence, Ostia’s navalia-temple-complex, the main building at the eastern fringe of the western river harbour basin, was built in the second quarter of the first century AD. Was this prestigious harbour building erected although the associated harbour seemed to have been already given up before? We conducted detailed geoarchaeological investigations at the immediate western front of the navalia-temple complex. Results were compared with archaeological data obtained from excavations carried out in 2000/2001. A multi-proxy approach was used to reconstruct the history and evolution of the harbour. It was possible to identify subsurface structures and evaluate the local stratigraphy. Vibracoring brought to light a more than 1 m thick section of an opus reticulatum wall with parts of the original opus latericium on top. Such walls originally separated vaulted shipshed chambers of the navalia-temple complex at Ostia, which in turn formed the substructure of a temple complex located above it. Another core revealed the sedimentary infill of a former chamber of the building. Based on radiocarbon dating, the navalia was in use between the first and the fourth centuries AD with a water depth of maximum ca. 1.2 m at the immediate western front. This is in agreement with the date of construction of the navalia-temple complex in the second quarter of the first century AD. The relative sea level at that time was around 0.64 m below the present sea level. The harbour and the navalia were obviously accessible only for flat-keeled lighters and cargo boats. Larger cargo ships were either unloaded along the riverbank to the north of ancient Ostia (Hadler et al. 2019) or moored offshore, their freight being reloaded to smaller lighters. Chronostratigraphic data further show that the navalia-temple complex was in use until the second half of the fourth century AD. It was not before AD 355–363 or shortly afterwards, that the harbour site was abandoned. Ostia’s western river harbour was neither abandoned nor completely silted up before the harbour at Portus was established as previously assumed by other authors. Actually, the western front of the navalia-temple complex was hit by an extreme wave event, leaving a sand layer approx. 0.5 m thick, at or shortly after AD 355–363 which led to the final abandonment of Ostia’s western river harbour. This event is interpreted as a tsunami that may have hit the wider coastal region

Enhancing interoperability and harmonisation of nuclear medicine image data and associated clinical data

Nuclear imaging techniques such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) in combination with computed tomography (CT) are established imaging modalities in clinical practice, particularly for oncological problems. Due to a multitude of manufacturers, different measurement protocols, local demographic or clinical workflow variations as well as various available reconstruction and analysis software, very heterogeneous datasets are generated. This review article examines the current state of interoperability and harmonisation of image data and related clinical data in the field of nuclear medicine. Various approaches and standards to improve data compatibility and integration are discussed. These include, for example, structured clinical history, standardisation of image acquisition and reconstruction as well as standardised preparation of image data for evaluation. Approaches to improve data acquisition, storage and analysis will be presented. Furthermore, approaches are presented to prepare the datasets in such a way that they become usable for projects applying artificial intelligence (AI) (machine learning, deep learning, etc.). This review article concludes with an outlook on future developments and trends related to AI in nuclear medicine, including a brief research of commercial solutions

High performance cluster computing with 3-D nonlinear diffusion filters

This paper deals with parallelisation and implementation aspects of PDE-based image processing models for large cluster environments with distributed memory. As an example we focus on nonlinear diffusion filtering which we discretise by means of an additive operator splitting (AOS). We start by decomposing the algorithm into small modules that shall be parallelised separately. For this purpose image partitioning strategies are discussed and their impact on the communication pattern and volume is analysed. Based on the results we develop an algorithmic implementation with excellent scaling properties on massively connected low latency networks. Test runs on a high-end Myrinet cluster yield almost linear speedup factors up to 209 for 256 processors. This results in typical denoising times of 0.5 seconds for five iterations on a 256 x 256 x 128 data cube