The bordism group of unbounded KK-cycles

We consider Hilsum's notion of bordism as an equivalence relation on unbounded $KK$-cycles and study the equivalence classes. Upon fixing two $C^*$-algebras, and a $*$-subalgebra dense in the first $C^*$-algebra, a $\mathbb{Z}/2\mathbb{Z}$-graded abelian group is obtained; it maps to the Kasparov $KK$-group of the two $C^*$-algebras via the bounded transform. We study properties of this map both in general and in specific examples. In particular, it is an isomorphism if the first $C^*$-algebra is the complex numbers (i.e., for $K$-theory) and is a split surjection if the first $C^*$-algebra is the continuous functions on a compact manifold with boundary when one uses the Lipschitz functions as the dense $*$-subalgebra.Comment: 38 page

Variable Bandwidth Analog Channel Filters for Software Defined Radio

An important aspect of Software Defined Radio is the ability to define the bandwidth of the filter that selects the desired channel. This paper first explains the importance of channel filtering. Then the advantage of analog channel filtering with a variable bandwidth in a Software Defined Radio is demonstrated. This is done by comparing the requirements of the analog-to-digital converter with and without an analog filter with a variable bandwidth. Then, a technique for channel filtering is described, in which two passive filters are combined to obtain a variable bandwidth. Passive filters have the advantage of high linearity, low noise and inherent energy efficiency. Some limitations of the concept are discussed. Finally, conclusions are drawn and our ideas for further research are presented

An Analogue Front-End Architecture for Software Defined Radio

A Software Defined Radio (SDR) is a radio receiver and/or transmitter, whose characteristics can to a large extent be defined by software. Thus, an SDR can receive and/or transmit a wide variety of signals, supporting many different standards. In our research, we currently focus on a demonstrator that is able to receive both Bluetooth and HiperLAN/2. This helps us to identify problems associated with SDR, and will provide a test-bed for possible solutions to these problems. The two standards differ significantly in characteristics like frequency band, signal bandwidth and modulation type. Combining two different standards in one receiver appears to pose new design challenges. For example, in the wide frequency range that we want to receive, many strong signals\ud may exist. This leads to severe linearity requirements for wideband receivers. This paper describes some receiver architectures. One\ud design has been selected. This receiver has been built, and some measurement results are included

Analyzing the Cutting Process of a Heated Flexible Blade in Extruded Polystyrene Foam

For the “Free Form Thick Layered Object Manufacturing” technology that is being developed at the Delft University, it is vital that Extruded Polystyrene Foam (XPS) can be cut accurately with a heated blade. The shape of the blade is actively controlled during the cutting process, which results in double curved cutting surfaces. In order to make this cutting process controllable it must be known how the cutting behavior is under varying conditions, like cutting speed, cutting angle and heating power. The authors executed a range of experiments, analyzed the results and describe a practical model for the cutting process of XPS with a heated blade.Mechanical Engineerin

The effect on annoyance estimation of noise modeling procedures

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A wideband high-linearity RF receiver front-end in CMOS

This paper presents a wideband high-linearity RF receiver-front-end, implemented in standard 0.18 /spl mu/m CMOS technology. The design employs a noise-canceling LNA in combination with two passive mixers, followed by lowpass-filtering and amplification at IF. The achieved bandwidth is >2 GHz, with a noise figure of 6.5 dB, +1 dBm IIP/sub 3/, +34.5 dBm IIP/sub 2/ and <50 kHz 1/f-noise corner frequency

Control and tuning of a suspended Fabry-Perot cavity using digitally-enhanced heterodyne interferometry

We present the first demonstration of real-time closed-loop control and deterministic tuning of an independently suspended Fabry-Perot optical cavity using digitally-enhanced heterodyne interferometry, realising a peak sensitivity of $\sim$10 pm$/\sqrt{\mathrm{Hz}}$ over the 10-1000 Hz frequency band. The methods presented are readily extensible to multiple coupled cavities. As such, we anticipate that refinements of this technique may find application in future interferometric gravitational-wave detectors