Fast and exact synthesis of stationary multivariate Gaussian time series using circulant embedding

A fast and exact procedure for the numerical synthesis of stationary multivariate Gaussian time series with a priori prescribed and well controlled auto- and cross-covariance functions is proposed. It is based on extending the circulant embedding technique to the multivariate case and can be viewed as a modification and variation around the Chan and Wood algorithm proposed earlier to solve the same problem. The procedure is shown to yield time series possessing exactly the desired covariance structure, when sufficient conditions are satisfied. Such conditions are discussed theoretically and examined on several examples of multivariate time series models. Issues related to prescribing a priori the spectral structure rather than the covariance one are also discussed. Matlab routines implementing this procedure are publicly available at http://www.hermir.org.     

Verhaltensbasierte Verkettung von Internetsitzungen

Die Analyse der Aktivit?ten eines Internet-Nutzers ist über l?ngere Zeit in der Regel nur mit Kenntnis der bei vielen Internet-Zugangsprovidern mindestens einmal t?glich wechselnden IP-Adressen m?glich. Verwendet der Nutzer zudem einen Anonymisierungsdienst, sollte eine Verkettung der Nutzer-Aktivit?ten auch für den Zugangsprovider unm?glich sein. Der Beitrag zeigt, dass eine verhaltensbasierte Verkettung dennoch m?glich ist und verbreitete Anonymisierungsl?sungen in der Praxis einen deutlich geringeren Schutz vor Beobachtung bieten, als bisher angenommen.     

Electron holography and AFM studies on styrenic block copolymers and a high impact polystyrene

Many of the artifacts of conventional electron microscopy can be avoided if the unstained polymers are studied by electron holography and atomic force microscopy (AFM). Holograms of thin sections (50–70 nm) of organic block copolymers were recorded, and the corresponding phase images were reconstructed. In this way, typical structures such as lamellae and cylinders could be imaged without any staining. In addition, we successfully recorded holograms and performed Lorentz microscopy of an impact‐modified polystyrene (high‐impact polystyrene). The results were compared with the tapping mode AFM phase images. Electron holography and AFM have been demonstrated as suitable tools to image unstained heterogeneous polymers, leading to the understanding of their structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1573–1583, 2005     

Quantitative Imaging of the Magnetic Configuration of Modulated Nanostructures by Electron Holography

By means of off‐axis electron holography the local distribution of the magnetic induction within and around a poly‐crystalline Permalloy (Ni₈₁Fe₁₉) thin film is studied. In addition the stray field above the sample is measured by magnetic force microscopy on a larger area. The film is deposited on a periodically nanostructured (rippled) Si substrate, which was formed by Xe⁺ ion beam erosion. This introduces the periodical ripple shape to the Permalloy film. The created ripple morphology is expected to modify the magnetization distribution within the Permalloy and to induce dipolar stray fields. These stray fields play an important role in spinwave dynamics of periodic nanostructures like magnonic crystals. Micromagnetic simulations estimate those stray fields in the order of only 10 mT. Consequently, their experimental determination at nanometer spatial resolution is highly demanding and requires advanced acquisition and reconstruction techniques such as electron holography. The reconstructed magnetic phase images show the magnetized thin film, in which the magnetization direction follows mainly the given morphology. Furthermore, a closer look to the Permalloy/carbon interface reveals stray fields at the detection limit of the method in the order of 10 mT, which is in qualitative agreement with the micromagnetic simulations.     

African regional innovation systems: bibliometric analysis of research collaboration patterns 2005–2009

Understanding the nature and dynamics of Africa’s collaborative research networks is critical for building and integrating the African innovation system. This paper investigates the collaborative structure of the African research systems, with focus on regions and integration. Drawing on a bibliometric analysis of co-authorship of African research publications in 2005–2009, we propose an empirically derived grouping of African research community into three distinct research regions: Southern–Eastern, Western, and Northern. The three regions are established and defined in terms of active co-authorship clusters within Africa, as well as through co-authorship links with non-African countries and regions. We examine co-authorship links both at the national and city levels in order to provide a robust and nuanced empirical basis for the three African research regions. The collaboration patterns uncovered cast light on the emerging innovation systems in Africa by pointing out the differing national, regional, and global roles of countries and cities within collaborative research networks. Lack of research capabilities is the primary factor arresting the development of African innovation systems, but our analysis also suggests that Africa’s internal research collaboration suffers from structural weaknesses and uneven integration. We also identify that South Africa, and some emerging new research hubs, hold critical networking function for linking African researchers.     

Personality subtypes of young moped drivers, their relationship to risk-taking behavior and involvement in road crashes in an Austrian sample

Objective

This study aimed to identify subtypes of young moped drivers and analyze how these subtypes are involved in risk preferences and road crashes.

Design

A group of Austrian teenage moped drivers (213, 28% girls) completed an online questionnaire about moped usage, injuries, driving style, inattention, impulsivity, and personality according to the Five-Factor Model of Personality and Cloninger's model of personality.

Results

A cluster analysis yielded four types of moped drivers. One type was characterized by a high level of neuroticism, the second type was characterized by a risky personality and a risky driving style, the third type had a more cautious driving style, and the fourth type was characterized by a risky personality and high levels on inattention and impulsivity.

Conclusions

Our conclusions suggest that young moped drivers should not be perceived as a homogenous group, according to measures of injury prevention and intervention.     

Multiple ion isolation applications in FT-ICR MS: exact-mass MSn internal calibration and purification/interrogation of protein-drug complexes

Two new applications using multiple ion isolations in the cell of a Fourier transform-ion cyclotron resonance mass spectrometer equipped with an electrospray ionization source are described. A procedure that uses multiple ion isolations of an analyte and calibrants for internal calibration at each stage in a MSn experiment, under high-resolution exact-mass conditions, for structural characterization/elucidation of angiotensin I and rapamycin is illustrated. Fragment ion mass accuracies < 1.0 ppm are demonstrated and routinely achieved. Purification of a mixture is illustrated by isolating multiple charge states of a protein-drug complex from residual protein for further MSn studies to elucidate the site of covalent drug bonding using IRMPD for a mixture of epidermal growth factor receptor (EGFr) protein and EGFr-drug complex. The procedure developed for multiple ion isolations is referred to as multi-CHEF, multiple correlated harmonic excitation fields, in which tailored waveforms are used to notch out multiple mass regions of a spectrum with minimal off-resonance excitation.