Gold in the investment portfolio

The paper examines the key drivers of gold investment. Since 2000 the gold price has risen drastically, making gold an interesting add-on to a portfolio. As gold futures have negative roll returns, gold pool accounts are characterized by high credit risk and physical possession of gold means high transaction costs, Xetra-Gold might be the most efficient way to enter the market. Xetra-Gold is a product created by the Deutsche Börse in 2007, which is handled like a security but can be exchanged into physical gold any time. In the portfolio context gold has had a positive impact on Euro and USD portfolios between 2000 and 2006 due to considerable returns and low correlation to other assets. However, this has not been true for almost all other periods, the correlation was always low but the returns of gold were almost zero, overriding the positive diversification effect. --Investing in gold,gold in the portfolio,correlation of gold,returns of gold,Xetra-Gold

Tropical parabiotic ants: Highly unusual cuticular substances and low interspecific discrimination

<p>Abstract</p> <p>Background</p> <p>Associations between animal species require that at least one of the species recognizes its partner. Parabioses are associations of two ant species which co-inhabit the same nest. Ants usually possess an elaborate nestmate recognition system, which is based on cuticular hydrocarbons and allows them to distinguish nestmates from non-nestmates through quantitative or qualitative differences in the hydrocarbon composition. Hence, living in a parabiotic association probably necessitates changes of the nestmate recognition system in both species, since heterospecific ants have to be accepted as nestmates.</p> <p>Results</p> <p>In the present study we report highly unusual cuticular profiles in the parabiotic species <it>Crematogaster modiglianii </it>and <it>Camponotus rufifemur </it>from the tropical rainforest of Borneo. The cuticle of both species is covered by a set of steroids, which are highly unusual surface compounds. They also occur in the Dufour gland of <it>Crematogaster modiglianii </it>in high quantities. The composition of these steroids differed between colonies but was highly similar among the two species of a parabiotic nest. In contrast, hydrocarbon composition of <it>Cr. modiglianii </it>and <it>Ca. rufifemur </it>differed strongly and only overlapped in three regularly occurring and three trace compounds. The hydrocarbon profile of <it>Camponotus rufifemur </it>consisted almost exclusively of methyl-branched alkenes of unusually high chain lengths (up to C₄₉). This species occurred in two sympatric, chemically distinct varieties with almost no hydrocarbons in common. <it>Cr. modiglianii </it>discriminated between these two varieties. It only tolerated workers of the <it>Ca. rufifemur </it>variety it was associated with, but attacked the respective others. However, <it>Cr. modiglianii </it>did not distinguish its own <it>Ca. rufifemur </it>partner from allocolonial <it>Ca. rufifemur </it>workers of the same variety.</p> <p>Conclusion</p> <p>We conclude that there is a mutual substance transfer between <it>Cr. modiglianii </it>and <it>Ca. rufifemur</it>. <it>Ca. rufifemur </it>actively or passively acquires cuticular steroids from its <it>Cr. modiglianii </it>partner, while the latter acquires at least two cuticular hydrocarbons from <it>Ca. rufifemur</it>. The cuticular substances of both species are highly unusual regarding both substance classes and chain lengths, which may cause the apparent inability of <it>Cr. modiglianii </it>to discriminate <it>Ca. rufifemur </it>nestmates from allocolonial <it>Ca. rufifemur </it>workers of the same chemical variety.</p

Validity of effective material parameters for optical fishnet metamaterials

Although optical metamaterials that show artificial magnetism are mesoscopic systems, they are frequently described in terms of effective material parameters. But due to intrinsic nonlocal (or spatially dispersive) effects it may be anticipated that this approach is usually only a crude approximation and is physically meaningless. In order to study the limitations regarding the assignment of effective material parameters, we present a technique to retrieve the frequency-dependent elements of the effective permittivity and permeability tensors for arbitrary angles of incidence and apply the method exemplarily to the fishnet metamaterial. It turns out that for the fishnet metamaterial, genuine effective material parameters can only be introduced if quite stringent constraints are imposed on the wavelength/unit cell size ratio. Unfortunately they are only met far away from the resonances that induce a magnetic response required for many envisioned applications of such a fishnet metamaterial. Our work clearly indicates that the mesoscopic nature and the related spatial dispersion of contemporary optical metamaterials that show artificial magnetism prohibits the meaningful introduction of conventional effective material parameters

Augmenting Data with Generative Adversarial Networks to Improve Machine Learning-Based Fraud Detection

While current machine learning methods can detect financial fraud more effectively, they suffer from a common problem: dataset imbalance, i.e. there are substantially more non-fraud than fraud cases. In this paper, we propose the application of generative adversarial networks (GANs) to generate synthetic fraud cases on a dataset of public firms convicted by the United States Securities and Exchange Commission for accounting malpractice. This approach aims to increase the prediction accuracy of a downstream logit, support vector machine (SVM), and eXtreme Gradient Boosting (XGBoost) classifier by training on a more well-balanced dataset. While the results indicate that a state-of-the-art machine learning model like XGBoost can outperform previous fraud detection models on the same data, generating synthetic fraud cases before applying a machine learning model does not improve performance