The NanoBeamBalance: a passive, tensile-test device for the atomic force microscope

An add-on device is presented, which significantly expands the force measurement capabilities of the atomic force microscope (AFM). The device consists of a completely passive mechanism, which translates the vertical motion of the AFM tip in force measurements into a horizontal motion of two sample support pads. The advantage is that it is much easier to deposit microscopic samples from suspension onto flat surfaces than to attach them reliably between tip and a surface. The working-principle and the design of the device is comprehensively described and demonstrated on the example of collagen fibres with a diameter of a few μm. Well-defined tensile measurements in longitudinal direction were performed, showing that the tensile stiffness of collagen fibres from rat tail tendon decreases by a factor of 5 when rehydrated from a dried sample and slowly increases upon cross-linking with glutaraldehyde.     

0.5 mu m gate length InP/In/sub 0.75/Ga/sub 0.25/As/InP pseudomorphic HEMT with high DC and RF performance

High performance InP/In/sub 0.75/Ga/sub 0.25/As/InP pseudomorphic double heterojunction (DH) HEMTs with a gate length of 0.5 mu m are reported. Both DC and RF characteristics of this new type of Al-free HEMT demonstrate its suitability for microwave applications.<>     

Advances in Windows NT storage management

Windows NT 5.0 introduces fundamental changes to storage management. The new infrastructure in NT 5.0 can adapt to future changes in storage devices and media, brings a more powerful set of management mechanisms, and supports more base services within the system. Most of the changes are transparent to legacy applications and to users, but software producers who want to deploy advanced functionality should realize increased benefits from the underlying infrastructure. Windows NT now supports the dynamic plug-and-play of storage devices and the growth and mounting of storage volumes. It also frees the NT system from drive letter limitations and incorporates several new file system features to aid the development of enterprise-class storage management solutions. The article describes two new mechanisms present in Windows NT 5.0, the reliable change journal and the reparse points. It also presents storage management infrastructure subsystems and services that help administer storage. Both mechanisms are designed to facilitate the robust and efficient administration of an increasing volume of data whose lifetime grows over time     

Entropy based software processes improvement

Actual results of software process improvement projects show different levels of success. Although many software development organisations have adopted improvement models such as CMMI, it appears to be difficult to improve software development processes in the right way, e.g. tuned to the actual needs of the organisation. This paper presents a new approach to determine the direction of improvement for an organisation. This approach is based on an elaboration of the concept of entropy. The approach is empirically validated by carrying out interviews in 11 software development organisations in The Netherlands. The results of the research show that software development organisations can be classified and can be positioned on the basis of their internal and external entropy, c.q. the level of (dis)order in the business system and its environment. Based on a possible out-of-balance situation between the internal and external entropy, directions for software process improvement can be discussed. As such the proposed approach can support the application of current software process improvement methodologies such as the CMMI.

IT Service Management Process Improvement based on ISO/IEC 15504: A systematic review

Context

In recent years, many software companies have considered Software Process Improvement (SPI) as essential for successful software development. These companies have also shown special interest in IT Service Management (ITSM). SPI standards have evolved to incorporate ITSM best practices.

Objective

This paper presents a systematic literature review of ITSM Process Improvement initiatives based on the ISO/IEC 15504 standard for process assessment and improvement.

Method

A systematic literature review based on the guidelines proposed by Kitchenham and the review protocol template developed by Biolchini et al. is performed.

Results

Twenty-eight relevant studies related to ITSM Process Improvement have been found. From the analysis of these studies, nine different ITSM Process Improvement initiatives have been detected. Seven of these initiatives use ISO/IEC 15504 conformant process assessment methods.

Conclusion

During the last decade, in order to satisfy the on-going demand of mature software development companies for assessing and improving ITSM processes, different models which use the measurement framework of ISO/IEC 15504 have been developed. However, it is still necessary to define a method with the necessary guidelines to implement both software development processes and ITSM processes reducing the amount of effort, especially because some processes of both categories are overlapped.     

Evidence for a conjugation-like mechanism of DNA transfer in Helicobacter pylori

Many strains of Helicobacter pylori are naturally competent for transformation in vitro. Since there is a high degree of genetic variation among H. pylori strains, we sought to determine whether mechanisms of DNA exchange other than transformation exist in these organisms. Studies were done with H. pylori cells that each were resistant to two different antibiotics; the procedure used involved mating of cells on plates or in broth, in the absence or presence of DNase. In each experiment, such matings produced progeny with the markers of both parents. Examination of the full resistance profile and random arbitrarily primed DNA PCR (RAPD-PCR) profiles of the progeny indicated that DNA transfer was bidirectional. DNase treatment reduced but did not eliminate transfer; only the presence of both DNase and a membrane separating the cells did so. For progeny derived from matings in the presence of DNase, antibiotic resistance and RAPD profiles indicated that transfer was unidirectional. DNase-treated cell-free supernatants also did not transform, ruling out transduction. These experiments indicate that both a DNase-sensitive mechanism (transformation) and a DNase-resistant conjugation-like mechanism involving cell-to-cell contact may contribute to DNA transfer between H. pylori cells.     

The psychrotrophic bacterium Yersinia enterocolitica requires expression of pnp, the gene for polynucleotide phosphorylase, for growth at low temperature (5 degrees C)

The psychrotrophic bacterium Yersinia enterocolitica is characterized by temperature-dependent adaptations. To investigate Y. enterocolitica genes involved in cold adaptation, a mutant restricted in its ability to grow at 5 degrees C was isolated from a transposon mutant library. The transposon insertion site in this psychrotrophy-defective (PD) mutant mapped 16 bp upstream of an open reading frame whose predicted amino acid sequence showed 93% similarity with the Escherichia coli exoribonuclease polynucleotide phosphorylase (PNPase), encoded by pnp. Expression of this gene was blocked in the PD mutant. However, the introduction of a second copy of pnp, including 0.33 kbp sequences upstream of its coding region, into the chromosome of the PD mutant restored pnp expression as well as the ability to grow at 5 degrees C. Furthermore, the expression of pnp appeared to be temperature dependent: in the parental Y. enterocolitica strain, the levels of both pnp mRNA and PNPase were 1.6-fold higher at 5 degrees C compared with 30 degrees C. A similarly enhanced level of PNPase at 5 degrees C was observed in the merodiploid recombinant strain, which indicates that the 0.33 kbp region upstream of pnp harboured a cold-inducible promoter. A putative cold shock promoter motif (ATTGG) was observed in this region.     

Carrier lifetime measurement in semiconductor lasers usinginjection current pulses of Gaussian shape

The transient optical response of InGaAsP-InP double heterostructure (DH) and InGaAs-InGaAsP separate confinement multiple quantum-well (SC-MQW) lasers emitting at 1.3 μm has been measured using injection current pulses up to 1.5 A of Gaussian shape supplied by an avalanche generator. The method is shown to apply even on broad-area Fabry-Perot cavity devices gives quick access on the dynamic characteristics of novel laser structures. The lasing continuity equation is solved for this type of injection pulse. The comparison of calculated and measured turn-on delay times yields a precise value of the effective carrier lifetime as applicable in very high-bit-rate digital transmission     

Frequency/stress sensitivity of s.a.w. resonators

Surface-acoustic-wave resonators can be used as stress sensors for measuring force and pressure. Experiments at 160 MHz using rotated y-cut substrates indicate that larger linear changes in resonator frequency can be obtained by deforming the substrate. The s.a.w. transducers, besides being small in size, are also stable in frequency.     

Morphology and mechanical stability of amyloid-like peptide fibrils

Synthetic, amyloid-like peptide fibrils have recently attracted interest as a novel, potentially biocompatible material for applications in biotechnology and tissue-engineering. In this paper, we report atomic force microscopy (AFM) studies of the morphology and mechanical stability of fibrils self-assembled in vitro from the short peptide TTR_105–115, which serves as a model system for amyloid fibrils. It forms predominantly straight rods of approximately 1 μm in length and of diameters between 7 nm and 12 nm. We found polymorphism, with some fibrils exhibiting an unstructured morphology and others showing a regular, longitudinal surface pattern of 90 nm periodicity. Contact mode AFM-imaging in air was utilised to perform mechanical tests of individual fibrils on the nanometer scale with a defined, vertical force in the nN-range applied by the AFM-tip. Above 100 nN, all fibrils showed a permanent, mechanical deformation whereas below 40 nN, fibrils remained unaffected. Tapping-mode AFM-imaging in water led to fibril decomposition within 1.5 h whereas tapping-mode imaging in air left fibrils intact. Additional investigations by circular-dichroism spectroscopy showed that dispersed fibrils were structurally stable in aqueous solution between pH 3 and pH 8, and in sodium phosphate buffer of concentration between 50 mM and 1 M.