Spatial activity and labour market patterns: A connectivity analysis of commuting flows in Germany

The spatial activity patterns of firms in a multi-regional system are closely connected with the structure and evolution of regional labour markets. Based on an extensive data set (cross-section) on commuting flows in Germany, this paper aims to identify the relationship between entrepreneurial activity and spatial labour markets, by employing in particular the concept of ‘entrepreneurial city’. A network connectivity model is adopted to assess connectivity patterns, using the power-law and exponential law as a statistical test framework, in order to detect the presence of economic activity hubs that may resemble the concept of entrepreneurial cities. Various results are presented and interpreted in the final part of the paper.     

Security protocol for IEEE 802.11 wireless local area network

As Wireless Local Area Networks (WLANs) are rapidly deployed to expand the field of wireless products, the provision of authentication and privacy of the information transfer will be mandatory. These functions need to take into account the inherent limitations of the WLAN medium such as limited bandwidth, noisy wireless channel and limited computational power. Moreover, some of the IEEE 802.11 WLAN characteristics such as the use of a point coordinator and the polling based Point Coordination Function (PCF) have also to be considered in this design. In this paper, we introduce a security protocol for the IEEE 802.11 PCF that provides privacy and authentication, and is designed to reduce security overheads while taking into account the WLAN characteristics. We prove this protocol using the original and modified BAN logic.     

Measurement and modeling of the electron impact-ionization coefficient in silicon up to very high temperatures

In this paper, an experimental investigation on high-temperature electron impact-ionization in silicon is carried out with the aim of improving the qualitative and quantitative understanding of carrier transport under electrostatic discharge (ESD) conditions. Special test devices were designed and manufactured using Infineon's SPT5 technology, namely: a bipolar junction transistor (BJT), a static-induction transistor (SIT) and a vertical DMOS transistor (VDMOS), all of them with a cylindrical geometry. The measurements were carried out using a customized measurement setup that allows very high operating temperatures to be reached. A novel extraction methodology allowing for the determination of the impact-ionization coefficient against electric field and lattice temperature has been used. The experiments, carried out up to 773 K, confirm a previous theoretical investigation on impact-ionization, and widely extend the validity range of the compact model here proposed for implementation in device simulation tools. This is especially useful to predict the failure threshold of ESD-protection and power devices.     

Wicking technique combined with electrical resistance measurements for determination of pore size in ceramic membranes

An easy, fast and inexpensive method to determine the mean pore size of a microfiltration ceramic membrane is offered by the wicking technique combined with electrical resistance measurements. Mean pore size is derived from the measured rates of capillary rise of different liquids of known surface tension through the ceramic membrane, via the Washburn equation. We used low-energy liquids for which the contact angle θ ≈ 0, such as hydrocarbons, and we determined the tortuosity of the membrane pores from electrical resistance measurements so that the mean pore radius was the only unknown in the Washburn equation. The mean pore diameter of the ceramic membrane was also determined from Mercury Intrusion Porosimetry (MIP) for comparison. It was found to be in very good agreement with that afforded by the wicking technique. This revised version was published online in September 2006 with corrections to the Cover Date.     

Meta-Analysis and the Value of Travel Time Savings: A Transatlantic Perspective in Passenger Transport

The value of travel time savings (VTTS) is the monetary value attached to the possibility to save a determined amount of travel time. VTTS is also the most important benefit category aimed at justifying investments in transport infrastructures by public administrations. Hence VTTS played a significant role in various economic studies, both analytical and empirical. The present paper introduces a brief history of meta-analysis and describes the microeconomic formula used in VTTS estimations. It also provides a meta-analytical estimation of a selection of empirical studies, emphasizing the similarities and the differences between European and North-American observations.     

Probability density functions of soft information

It is well known that soft decoding algorithms are based on the use of reliability measures for binary and nonbinary symbols. We consider an analytical estimation of the distributions of reliability measures after soft decoding of block and convolutional codes or intersymbol interference (ISI) channels. This estimation, based on a simple geometric interpretation of reliability measures, allows the observation of different distributions for correct and incorrect symbols, and could be helpful for the analysis of soft decoding algorithms     

Image-based cardiac phase retrieval in intravascular ultrasound sequences

Longitudinal motion during in vivo pullbacks acquisition of intravascular ultrasound (IVUS) sequences is a major artifact for 3-D exploring of coronary arteries. Most current techniques are based on the electrocardiogram (ECG) signal to obtain a gated pullback without longitudinal motion by using specific hardware or the ECG signal itself. We present an image-based approach for cardiac phase retrieval from coronary IVUS sequences without an ECG signal. A signal reflecting cardiac motion is computed by exploring the image intensity local mean evolution. The signal is filtered by a band-pass filter centered at the main cardiac frequency. Phase is retrieved by computing signal extrema. The average frame processing time using our setup is 36 ms. Comparison to manually sampled sequences encourages a deeper study comparing them to ECG signals.     

Novel approach to the statistical analysis of microwave circuits

A method for the statistical prediction of the performance of microwave networks is proposed, founded on the introduction of three types of stochastic cells. The method is suited to Monte Carlo analyses, but it is valuable for finding approximate explicit formulas as well. A formula for the insertion phase is given.