Applying formal concepts to learning systems validation

In the problem area of evaluating complex software systems, there are two distinguished areas of research, development, and application identified by the two buzzwords validation and verification, respectively. From the perspective adopted by the authors, verification is usually more formally based and, thus, can be supported by formal reasoning tools like theorem provers, for instance. The scope of verification approaches is limited by the difficulty of finding a sufficiently complete formalization to build upon. In paramount realistic problem domains, validation seems to be more appropriate, although it is less stringent in character and, therefore, validation results are often less definite. The aim of this paper is to exemplify a validation approach based on a clear and thoroughly formal theory. In this way, validation and verification should be brought closer to each other. To allow for precise and sufficiently clear results, the authors have selected the application domain of algorithms and systems for learning formal languages. By means of the validation toolkit TIC, some series of validation experiments have been performed. The results are presented for the sake of illustrating the underlying formal concepts in use. Comparing the validity of one learning approach to the invalidity of another one can be seen as an interesting result in its own right.     

Enforceable component-based realtime contracts

We present enforceable component-based realtime contracts, the first extension of component-based software engineering technology that comprehensively supports adaptive realtime systems from specification all the way to the running system.To provide this support, we have extended component-based interface definition languages (IDLs) and component representations in repositories to express realtime requirements for components. The final software, which is assembled from the components, is then executed on a realtime operating system (RTOS) with the help of a component runtime system. RTOS resource managers and the IDL-extensions are based on the same mathematical foundation. Thus, the component runtime system can use information expressed in a component-oriented manner in the extended IDL to derive parameters for the task-based admission and scheduling in the RTOS. Once basic realtime properties can thus be guaranteed, runtime support can be extended to more elaborate schemes that also support adaptive applications (container-managed quality assurance).We claim that this study convincingly demonstrates how component-based software engineering can be extended to build systems with non-functional requirements.     

A Scalable Farm Skeleton for Hybrid Parallel and Distributed Programming

Multi-core processors and clusters of multi-core processors are ubiquitous. They provide scalable performance yet introducing complex and low-level programming models for shared and distributed memory programming. Thus, fully exploiting the potential of shared and distributed memory parallelization can be a tedious and error-prone task: programmers must take care of low-level threading and communication (e.g. message passing) details. In order to assist programmers in developing performant and reliable parallel applications Algorithmic Skeletons have been proposed. They encapsulate well-defined, frequently recurring parallel and distributed programming patterns, thus shielding programmers from low-level aspects of parallel and distributed programming. In this paper we take on the design and implementation of the well-known Farm skeleton. In order to address the hybrid architecture of multi-core clusters we present a two-tier implementation built on top of MPI and OpenMP. On the basis of three benchmark applications, including a simple ray tracer, an interacting particles system, and an application for calculating the Mandelbrot set, we illustrate the advantages of both skeletal programming in general and this two-tier approach in particular.     

Reengineering component-based software systems with Archimetrix

Many software development, planning, or analysis tasks require an up-to-date software architecture documentation. However, this documentation is often outdated, unavailable, or at least not available as a formal model which analysis tools could use. Reverse engineering methods try to fill this gap. However, as they process the system’s source code, they are easily misled by design deficiencies (e.g., violations of component encapsulation) which leaked into the code during the system’s evolution. Despite the high impact of design deficiencies on the quality of the resulting software architecture models, none of the surveyed related works is able to cope with them during the reverse engineering process. Therefore, we have developed the Archimetrix approach which semiautomatically recovers the system’s concrete architecture in a formal model while simultaneously detecting and removing design deficiencies. We have validated Archimetrix on a case study system and two implementation variants of the CoCoME benchmark system. Results show that the removal of relevant design deficiencies leads to an architecture model which more closely matches the system’s conceptual architecture.     

Design of a mobile,homogeneous, and efficient electromagnet with a large field of view for neonatal low-field MRI

Objective

In this work, a prototype of an effective electromagnet with a field-of-view (FoV) of 140 mm for neonatal head imaging is presented. The efficient implementation succeeded by exploiting the use of steel plates as a housing system. We achieved a compromise between large sample volumes, high homogeneity, high B₀ field, low power consumption, light weight, simple fabrication, and conserved mobility without the necessity of a dedicated water cooling system.

Materials and methods

The entire magnetic resonance imaging (MRI) system (electromagnet, gradient system, transmit/receive coil, control system) is introduced and its unique features discussed. Furthermore, simulations using a numerical optimization algorithm for magnet and gradient system are presented.

Results

Functionality and quality of this low-field scanner operating at 23 mT (generated with 500 W) is illustrated using spin-echo imaging (in-plane resolution 1.6 mm × 1.6 mm, slice thickness 5 mm, and signal-to-noise ratio (SNR) of 23 with a acquisition time of 29 min). B₀ field-mapping measurements are presented to characterize the homogeneity of the magnet, and the B₀ field limitations of 80 mT of the system are fully discussed.

Conclusion

The cryogen-free system presented here demonstrates that this electromagnet with a ferromagnetic housing can be optimized for MRI with an enhanced and homogeneous magnetic field. It offers an alternative to prepolarized MRI designs in both readout field strength and power use. There are multiple indications for the clinical medical application of such low-field devices.

     

Low power SAR ADC switching without the need of precise second reference

In this paper a simple method to reduce the switching energy of capacitive digital-to-analog converters (DACs) in low-power successive approximation register analog-to-digital converters (ADCs) is described. The method is based on the well-known monotonic switching procedure and the use of one intermediate voltage level during switching. Unlike most recently published switching methods the proposed method does not require the intermediate voltage to be accurate. The implementation of digital control and an intermediate voltage-level generator is considered. To evaluate the reduction in switching energy compared to the conventional monotonic switching procedure, the behavioral model of a 10-bit ADC was examined. The additional digital logic, voltage generator, and capacitive DAC were modeled at a transistor level using a 65 nm STM design kit. Simulation results and the subsequent power efficiency gains are presented.     

Wideband impedance spectrum analyzer for process automation applications

For decades impedance spectroscopy is used in technical laboratories and research departments to investigate effects or material characteristics that affect the impedance spectrum of the sensor. Establishing this analytical approach for process automation and stand-alone applications will deliver additional and valuable information beside traditional measurement techniques such as the measurement of temperature, flow rate, and conductivity, among others. As yet, most of the current impedance analysis methods are suited for laboratory applications only since they involve stand-alone network analyzers that are slow, expensive, large, or immobile. Furthermore, those systems offer a large range of functionality that is not being used in process control and other fields of application. We developed a sensor interface based on high speed direct digital signal processing offering wideband impedance spectrum analysis with high resolution for frequency adjustment, excellent noise rejection, very high measurement rate, and convenient data exchange to common interfaces. The electronics has been implemented on two small circuit boards and it is well suited for process control applications such as monitoring phase transitions, characterization of fluidal systems, and control of biological processes. The impedance spectrum analyzer can be customized easily for different measurement applications by adapting the appropriate sensor module. It has been tested for industrial applications, e.g., dielectric spectroscopy and high temperature gas analysis.     

Resonance enhanced dynamic light scattering

We present a novel light scattering setup that enables probing of dynamics near solid surfaces. An evanescent wave generated by a surface plasmon resonance in a metal layer is the incident light field in the dynamic light scattering experiment. The combination of surface plasmon resonance spectroscopy and dynamic light scattering leads to a spatiotemporal resolution extending a few hundred nanometers from the surface and from microseconds to seconds. The comparison with evanescent wave dynamic light scattering identifies the advantages of the presented technique, e.g., surface monitoring, use of metal surfaces, and biorelevant systems. For both evanescent wave geometries, we define the scattering wave vector necessary for the analysis of the experimental relaxation functions.     

Performance of an adaptive liquid microlens controlled by a microcoil actuator

We present an optofluidic system based on electromagnetic manipulation of a ferrofluid to tune a liquid lens. Both studies of the dynamics of fluid transport and of the optical properties of the liquid lens have been carried out. Thermal and magnetic field simulations of the microcoil actuators are presented. Proof-of-principle experiments demonstrating the adaption of the focal length of the lens have been carried out. It is shown that the lens adaption proceeds in a reversible and reproducible manner, given that the ferrofluid plug moves with a speed below a specific threshold value. Furthermore, the time delay between the actuation and the deflection of the lens surface is studied.