bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal-on-metal bearings surfaces: Materials, manufacture, design, optimization, and alternatives
Authors: Isaac G H , Thompson J , Williams S , Fisher J
Published: October 2007

When first introduced, total hip replacements offered pain relief and improved mobility in elderly patients. The success of this procedure in terms of long-term durability and restoration of function has led to its use in younger, more active patients. This has resulted in a commensurate increase in patient expectation regarding longevity and the degree to which function and lifestyle is restored.

The bearing surface is a key feature of the performance of replacement joints. It is generally accepted that excessive amounts of wear debris preclude their long-term survivorship and hence there is an ongoing requirement for bearing surfaces which minimize debris generation. The purpose of this paper is to review the factors which affect the performance of so-called metal-on-metal bearings, to compare their performance with that of the other commonly used contemporary alternatives, metal and ceramic articulating against highly cross-linked polyethylene, and ceramic-on-ceramic, and finally to consider the potential solutions offered by new developments such as ceramic-on-metal and coatings applied to metal-on-metal bearings.
Lessons learned from early clinical experience and results of 300 ASR® hip resurfacing implantations
Authors: Siebel T , Maubach S , Morlock M M
Published: October 2007

Between August 2003 and April 2005, 300 ASR® metal-on-metal resurfacing hip endoprostheses were implanted by the first author and a fellow surgeon. The mean age at surgery was 56.8 years (18-75.9 years) and mean body mass index was 27.6 kg/m2 (range, 19-41 kg/m2). The mean follow-up time was 202 days. The mean Harris hip score improved from 44 pre-operatively to 89 at 3 months post-operatively. In total, eight (2.7 per cent) cases [five neck fractures (1.66 per cent) and three cup revisions (1 per cent)] were revised. Two neck fractures occurred within a group of seven cases of femoral neck notching detected postoperatively; one neck fracture occurred out of two cases of incomplete seating of the femoral implant. A significantly higher (p < 0.001) failure rate was observed for patients who had undergone a previous osteosynthesis of the proximal femur (three revisions in a group of 15 patients). Revision cases had a significantly greater body mass index (p = 0.031). A learning curve was evident from the reduction in revisions from 5 in the first 100 surgical procedures to 2 in the next 100 and 1 in the last 100. These results show the importance of accurate surgical technique and careful patient selection for fourth-generation hip resurfacing implants.
Background of metal-on-metal resurfacing
Authors: Amstutz H C , Le Duff M J
Published: October 2007

Hip resurfacing is not a new concept and attempts to treat hip arthritis without resecting the femoral head and neck have been made since the 1950s. The resurgence of new and better-engineered metal-on-metal bearings has provided the means to develop a viable prosthetic solution from a concept that was once abandoned. The lessons drawn from the early resurfacing era led to modern designs all using a cementless fixation of the acetabular component and a short metaphyseal stem designed for component alignment on the femoral side. Currently, only metallic devices can be manufactured with sufficient strength as a thin one-piece shell, combining excellent wear properties for large femoral heads and a bone-conserving device on the acetabular side. The early results of these new designs are extremely encouraging but the rapid development of the procedure needs to be controlled by appropriate training programmes to ensure its future success.
Head replacement, head rotation, and surface damage effects on metal-on-metal total hip replacements: A hip simulator study
Authors: Hardaker C , Dowson D , Isaac G H
Published: October 2007

The possibility of replacing the femoral head alone, in either solid or articular surface replacement form, during revision operations on metal-on-metal total hip replacements remains an attractive feature of such implants. In the present investigation, laboratory simulator studies of the influence upon volumetric wear of inserting a new femoral head, of introducing some head rotation, and of damaging the femoral head by scratches have all been explored.

New and rotated heads both involve an additional running-in period, but the experimental studies show that the volumetric wear associated with this process is less than the initial running-in wear. The beneficial effects upon volumetric wear of small clearances have been confirmed, while the processing of high-carbon Co-Cr-Mo materials appears to be much less influential.

Scratches did not affect wear as much as head replacement or head rotation, but the ongoing wear rates were somewhat higher.
The effect of microstructure on the wear of cobalt-based alloys used in metal-on-metal hip implants
Authors: Varano R , Bobyn J D , Medley J B , Yue S
Published: October 2007

The influence of microstructure on the wear of cobalt-based alloys used in metal-on-metal hip implants was investigated in a boundary lubrication regime designed to represent the conditions that occurred some of the time in vivo. These cobalt-chromium-molybdenum alloys were either wrought, with a total carbon content of 0.05 or 0.23 wt %, cast with a solution-annealing procedure or simply as-cast but not solution annealed. Bars of these different alloy grades were subjected to various heat treatments to develop different microstructures. The wear was evaluated in a linear-tracking reciprocating pin-on-plate apparatus with a 25 per cent bovine serum lubricant. The wear was found to be strongly affected by the dissolved carbon content of the alloys and mostly independent of grain size or the carbide characteristics. The increased carbon in solid solution caused reductions in volumetric wear because carbon helped to stabilize a face-centred cubic crystal structure, thus limiting the amount of strain-induced transformation to a hexagonal close-packed crystal structure. Based on the observed surface twining in and around the contact zone and the potentially detrimental effect of the hexagonal close-packed phase, it was postulated that the wear of cobalt-based alloys in the present study was controlled by a deformation mechanism.
Wear particles from metal-on-metal total hip replacements: Effects of implant design and implantation time
Authors: Catelas I , Campbell P A , Bobyn J D , Medley J B , Huk O L
Published: October 2007

Detailed characterization of wear particles is necessary to understand better the implant wear mechanisms and the periprosthetic tissue response. The purposes of the present study were to compare particle characteristics of current with older designs of metal-on-metal (MM) total hip replacements (THRs), and to determine the effect of implantation time on wear particle characteristics. Metal wear particles isolated from periprosthetic tissues from 19 patients with MM THRs of current and older designs and at different implantation times (very short, longer, and very long) were studied using transmission electron microscopy and energy dispersive X-ray analysis. The particles from the current design implants with implantation times of not more than 15 months (very short term) were almost exclusively round to oval chromium oxide particles. In all other cases, although the predominance was still round to oval chromium oxide particles, greater proportions of cobalt-chromium-molybdenum (Co-Cr-Mo) particles, mainly needle-shaped, were detected. Very long term THRs implanted for more than 20 years had the highest percentage of needle-shaped Co-Cr-Mo particles. Particle lengths were not markedly different between the different designs and implantation times except for the current design implants of not more than 15 months, which had a significantly smaller mean length of 39 nm. In conclusion, the implant design did not seem to have a significant influence on particle characteristics whereas the implantation time appeared to have the most effect on the particles. It should be noted that, because of the limited number of tissue retrievals available, some uncertainty remains regarding the generality of these findings.
Investigation on stick phenomena in metal-on-metal hip joints after resting periods
Authors: Wimmer M A , Nassutt R , Sprecher C , Loos J , Täger G , Fischer A
Published: October 2007

Insufficient understanding of tribological behaviour in total joint arthroplasty is considered as one of the reasons for prosthesis failure. Contrary to the continuous motion input profiles of hip simulators, human locomotion contains motion interruptions. These occurring resting periods can cause stick phenomena in metal-on-metal hip joints. The aim of the present study was to investigate the tribological sensitivity of all-metal bearings to motion interruptions on in vitro test specimens and retrieved implants. Friction and wear with and without resting periods were quantified. Unlike the metal-on-polyethylene joints, the static friction of metal-on-metal joints increased up to μs = 0.3 with rest, while wear appeared to be unaffected. This effect is caused by the interlocking of firmly adhered carbon layers, which were generated from the protein-containing lubricant through tribochemical reactions. Since more than 80 per cent of the retrieved implants exhibited macroscopically visible carbon layers, the increase in friction presumably also occurs under physiological conditions, which is then transferred to the bone-implant interface. These recurrent tangential stress peaks should be considered for the design features of the cup-bone interface, in particular when larger-sized implant heads are used.
The effect of ‘running-in’ on the tribology and surface morphology of metal-on-metal Birmingham hip resurfacing device in simulator studies
Authors: Vassiliou K , D Elfick A P , Scholes S C , Unsworth A
Published: October 2007

It is well documented that hard bearing combinations show a running-in phenomenon in vitro and there is also some evidence of this from retrieval studies. In order to investigate this phenomenon, five Birmingham hip resurfacing devices were tested in a hip wear simulator. One of these (joint 1) was also tested in a friction simulator before, during, and after the wear test and surface analysis was conducted throughout portions of the testing. The wear showed the classical running in with the wear rate falling from 1.84 mm3 per 106 cycles for the first 106 cycles of testing to 0.24 mm3 per 106 cycles over the final 2 × 106 cycles of testing. The friction tests suggested boundary lubrication initially, but at 1 × 106 cycles a mixed lubrication regime was evident. By 2 × 106 cycles the classical Stribeck curve had formed, indicating a considerable contribution from the fluid film at higher viscosities. This continued to be evident at both 3 × 106 and 5 × 106 cycles. The surface study complements these findings.
‘Severe’ wear challenge to ‘as-cast’ and ‘double heat-treated’ large-diameter metal-on-metal hip bearings
Authors: Bowsher J G , Nevelos J , Williams P A , Shelton J C
Published: October 2007

The wear generation of double-heat-treated and as-cast large-diameter metal-on-metal (MOM) hip bearings was investigated using standard- and ‘severe’-gait simulations. The test hypothesis was that double heat treatment would change MOM hip wear compared with the as-cast condition. Two groups of high-carbon MOM bearings of 40 mm diameter were manufactured and subjected to either hot isostatic pressing (HIP) and solution annealing (SA) or no heat treatment (as cast). The results showed no statistical difference between the two groups under both running-in and steady state conditions. Even under the most ‘severe’-gait simulation published to date, the mean volumetric wear rates were 2.9 and 3.9 mm3 per 106 cycles for the HIP-SA and as-cast bearings respectively, showing a ten-fold increase in wear compared with walking. These differences were not statistically different; therefore our hypothesis was negated. Changes in alloy microstructure do not appear to influence the wear behaviour of high-carbon cast MOM articulations with similar chemical compositions. This is in sharp contrast with the published significance of bearing diameter and radial clearance on the wear of MOM hip bearings.
Three-dimensional unsteady investigation of HP turbine stages
Authors: Adami P , Martelli F
Published: October 2007

This article deals with a three-dimensional unsteady numerical simulation of the unsteady rotor—stator interaction in a HP turbine stage. The numerical approach consists of a computational fluid dynamics (CFD) parallel code, based on an upwind total variation diminishing finite volume approach. The computation has been carried out using a sliding plane approach with hybrid unstructured meshes and a two-equation turbulent closure. The turbine rig under investigation is representative of the first stage of aeronautic gas turbine engines. A brief description of the cascade, the experimental setup, and the measuring technique is provided. Time accurate CFD computations of pressure fluctuations and Nusselt number are discussed against the experimental data.
Original design of coal-bed gas/air control units for engine-generator sets
Authors: Qiao An-Ping , Li Yun-Qing , Gao Feng
Published: October 2007

An original air/fuel automatic mixing control unit for a coal-bed gas internal combustion engine and its matching generator, which is different from the conventional one, is introduced. The basic design and calculation method of this novel unit are explained. On the basis of these, the units of the 12V190ZDT type engine-generator sets are calculated and designed, machined, and trial-produced. A year's service-test at the Centre of West Coal Mine Construction shows that the performances of these devices are stable and reliable, and that this method could solve many practical problems that the old unit could not; for instance, working with mid-low concentration of coal-seam gas. They also fill a gap in the field of design, calculation, development, and application of coal-bed gas devices; the economic and social benefits are also truly remarkable. Therefore, the design and calculation method obtained in this article are important for engineering applications. This paper also offers a theoretical basis for the design and development of coal-seam gas engines or sets of engine-generator.
Real-time efficiency index of a steam power plant: A systems approach
Authors: Mohan M , Gandhi O. P. , Agrawal V. P.
Published: October 2007

The present system of recording efficiency parameters under process performance of a steam power plant (SPP) includes specific fuel consumption, auxiliary power consumption, and demineralized water for make-up used during past-specific period, without their integration into a single process performance or efficiency index. For developing integrated efficiency index in real time frame, the use of a process performance digraph (PPD) comprising of P i's as nodes and p ij's as interconnection among the nodes as obtained from the system structure graph (SSG) of SPP has been demonstrated. Each c ij of SSG corresponds to a process, such as air fuel mixing, combustion of mixtuer, generation and expansion of steam and its condensation back into water for recirculation in boiler, etc., taking place in the SPP and corresponds to a P i of PPD. The PPD is then analysed for determining the efficiency of the SPP using matrix method following systems approach.

Variable permanent process performance matrix and its variable permanent function (VPF-p) have been derived from the PPD for the analysis. The real-time efficiency index (RTEI) has been introduced which is the ratio of the values of (VPF-p) in realtime (RT) situation (VPF-p)RT to its achievable design value (VPF-p). It reflects the RT rate of consumption of various inputs like demineralized water make-up, auxiliary power and fuel consumption, etc. It provides a more scientific method for ranking the performance of an SPP. The proposed model is capable of analysing in RT the performance of various systems of the SPP, taking into account simultaneously the failure of various equipments in these systems. A step-by-step procedure for calculation of RTEI has also been suggested and illustrated by giving an example.
Energy and economic assessment of IGCC power plants integrated with DME synthesis processes
Authors: Cocco D , Pettinau A , Cau G
Published: October 2007

The combined production of dimethylether (DME) and electrical energy in Integrated Gasification Combined Cycle (IGCC) power plants is a very attractive option for exploiting the world's huge coal reserves achieving high efficiency and low pollutant emissions, as well as for enhancing the flexibility and economic performance of coal gasification plants. Besides being used for power generation in combined cycle plants, the clean synthesis gas produced by coal gasification processes can also be used as raw material for producing hydrogen, methanol, DME, and other chemicals. In particular, recent studies show the growing interest of DME as a new clean fuel for diesel engines, gas turbines, fuel cells, and household uses.

This article concerns an energy and economic assessment of two different IGCC power plants integrated with a once-through DME synthesis process. In particular, the study has been carried out by examining two different solutions for the gasification process: one based on a dry-fed and the other on a slurry-fed entrained-flow gasifier. The energy assessment has shown that the DME production in IGCC power plants leads to a DME/coal energy conversion of ∼31—32 per cent and an electrical/coal energy conversion of ∼22—25 per cent. Overall, the solution based on the dry-fed gasifier exhibits the best exergy performance (50.8 versus 52.7 per cent). Finally, the economic analysis reveals DME production costs (6—6.5$/GJ) comparable with other premium fuels such as natural gas, liquefied petroleum gases, and so on.
Numerical analysis of a proton exchange membrane fuel cell. Part 1: Model development
Authors: Al-Baghdadi M A R Sadiq , Al-Janabi H A K Shahad
Published: October 2007

A full three-dimensional, non-isothermal computational fluid dynamics model of a proton exchange membrane (PEM) fuel cell with straight flow field channels has been developed. This comprehensive model accounts for the major transport phenomena in a PEM fuel cell: convective and diffusive heat and mass transfer, electrode kinetics, and potential fields. The feature of the algorithm developed in this work is its capability for accurate calculation of the local activation overpotentials, which in turn results in improved prediction of the local current density distribution. Fully three-dimensional results of the velocity flow field, species profiles, temperature distribution, potential distribution, and local current density distribution are presented. The model is shown to be able to understand the many interacting, complex electrochemical and transport phenomena that cannot be studied experimentally.
Numerical analysis of a proton exchange membrane fuel cell. Part 2: Parametric study
Authors: Al-Baghdadi M A R Sadiq , Al-Janabi H A K Shahad
Published: October 2007

The current paper presents the results of a parametric study conducted with a previously described three-dimensional, non-isothermal computational fluid dynamics model of a proton exchange membrane fuel cell, which was developed and discussed in detail in part 1 of this series. The effects of several operating, design, and material parameters on fuel cell performance has been investigated in detail. The results of the current study helped identifying critical parameters and shed insight into the physical mechanisms leading to a fuel cell performance under various operating conditions. Furthermore, the current study demonstrates the use of a comprehensive three-dimensional single-phase model as a design and optimization tool.
A comparison of conjugate heat transfer methods applied to an axial helium turbine
Authors: Verstraete T , Alsalihi Z , Van den Braembussche R. A.
Published: October 2007

The current paper presents a numerical investigation of the conjugate heat transfer (CHT) in an axial helium turbine. The objective is the prediction of the cooling needed to keep the blade temperature below the allowable material limits. The cooling is applied at the hub by means of internal cooling channels.

A CHT solver has been developed for this purpose. It combines a three-dimensional heat conduction calculation inside the blade with a three-dimensional Navier-Stokes flow calculation around the turbine blade. The required cooling at the blade root is calculated by imposing the temperature limit as boundary conditions at the bottom plane.

Various alternative methods to implement the CHT are tested and compared. The results indicate that the so-called h-method is superior both in terms of accuracy and convergence speed.
Experimental and numerical investigation of interaction between turbine stage and exhaust hood
Authors: Fu J , Liu J , Zhou S
Published: October 2007

The current article describes the experimental and numerical studies on the flow field in a coupled turbine stage and exhaust hood model. The low subsonic stage with 22 stator blades and 30 rotor blades is especially designed for the hood model, which is a typical design for a 300/600 MW steam turbine. Velocity distributions at the inlet, outlet, and hood exit stages, in addition to static pressure distributions at the diffuser tip and hub end-walls and at the hood outer casing, are measured and compared with the numerical prediction. The flow details in the exhaust system with the whole annulus stator and rotor blade rows are simulated by employing the computational fluid dynamics software. Good agreements between numerical and experimental results are demonstrated. It is found that the swirl angle profile and total pressure profile due to the upstream turbine stage at the diffuser inlet have an unfavourable effect on the exhaust hood performance.
Modelling the steady-state analysis of a jet pipe electrohydraulic servo valve
Authors: Somashekhar S H , Singaperumal M , Kumar R Krishna
Published: October 2007

In this paper, an attempt has been made to simulate the steady-state operation of a jet pipe electrohydraulic servo valve using the finite element (FE) method. The jet pipe electrohydraulic servo valve is a mechatronic component, used for precise flow control applications in gas turbine engines. It has two assemblies: a first-stage torque motor assembly and a second-stage valve assembly. Between the first and the second stage, there is a mechanical feedback spring assembly to stabilize the valve operation. Each assembly has various delicate and precise components interacting with fluid flows. In the present paper, the structural components were modelled with general-purpose finite elements, e.g. shell, beam, and solid elements, while the fluid cavities were modelled with special-purpose hydrostatic fluid elements. The fluid flows from one fluid cavity to another fluid cavity were modelled with fluid links. The simulation was carried out in a commercially available FE code, ABAQUS, interfaced with user subroutines to form a closed-loop system. The FE simulation clearly showed the dynamics of the jet pipe and spool displacement in achieving the equilibrium position when the applied torque and restoring torques balance, known as steady state. The pressure and flow variations during torque balance are presented. The effect of the feedback loop from the second-stage spool movement to the first-stage jet pipe is seen in the FE results obtained. The theoretical aspects of pressure recovery and flow modelling are presented and used in FE simulation.
Analysis of the dynamics of a defective V-belt and diagnostic possibilities
Authors: Mikalauskas R , Volkovas V
Published: October 2007

To investigate parametrically forced excitation and transverse oscillations of the belt with local heterogeneity, a new dynamic model of a V-belt drive with longitudinal motion has been developed. The model shows that when an appropriate quantitative and qualitative level of local heterogeneity is achieved, the oscillation mode of the belt starts to change, and the belt tensile force developing due to deformation of the belt significantly increases.

Another V-belt drive dynamic model was developed based on the finite element model (FEM) analysis. This was used to examine the interaction of the belt, containing local heterogeneity, with the pulley in the area of contact angle. The natural frequencies of the system were calculated and the system's response to harmonic excitation was established. The correlation between the presence of defects in the belt and vibration activity of the driving pulley bearing housing was established. Using the developed model, the relationship between the defective belt and the dynamic component of the vibration reaction force of the driven pulley was studied. Spectrum components are identified and are used in the belt drive's practical diagnostics.

The method developed based on these models enables non-destructive assessment of the failure state of the mounted belt to be performed in order to assess the failure state of different belt drive types.
An explicit design approach to determine the optimum steady state performance of axial piston motor drives
Authors: Watton J
Published: October 2007

A new non-dimensional approach to the explicit characterization of the non-linear steady state performance of an axial piston motor is presented. The motor is driven by a servovalve and it is shown how the flow characteristics, including losses, may be sufficiently represented by a well-established single equation that may then be used to produce directly usable design equations for speed, efficiency, and power transfer. This has not been previously deduced and the new equations allow direct determination of the conditions for maximum efficiency and power transfer, which leads to the establishment of new conclusions regarding the effect of flow and torque losses for both open-loop and closed-loop operation. The approach is validated by experimental results.
Integrating reliability analysis and diagnostics for complex technical systems
Authors: Snooke N. A. , Price C. J.
Published: October 2007

Creating diagnostic information for complex technical systems has become a very costly and challenging process. Separation of the process of creating diagnostics from the processes of design and of reliability analysis (as is the default in many companies) means that reliability analysis work is often ignored or repeated by engineers creating diagnostics. The current paper explains the basic concepts behind the creation of diagnostic systems, and considers the extent to which reliability analysis results can be used to make the production of diagnostics more efficient. In particular, it considers how the automated production of reliability analyses can be fed into the process of creating diagnostic systems.
A discussion of statistical testing on a safety-related application
Authors: Kuball S , May J. H. R.
Published: October 2007

Safety-critical and safety-related systems are increasingly based, at least partially, on the use of software or logic components. High integrity claims are usually placed on these systems, which means that their probability of failure during operation should be below a specified level in order to ensure that risk of operation is sufficiently low. All this implies that some knowledge needs to be gained on the dependability of these systems or components in actual field use. Dependability assessment methods for software are not as well established as for hardware. Currently, formal proofs and statistical testing methods provide the only methods that have the potential to assess software dependability quantitatively. The present paper explores the applicability of statistical (software) testing (ST) to the example of a real safety-related software application. It discusses the key points arising in this task and highlights the unique and important role ST can play within the wider task of software verification.
Assessment of large automatically generated fault trees by means of binary decision diagrams
Authors: Rauzy A. B. , Gauthier J , Leduc X
Published: October 2007

Dassault Aviation have developed a reliability workbench based on the high-level formal description language AltaRica. The workbench includes a compiler of AltaRica models into fault trees. The fault trees generated for the largest industrial systems involve up to a thousand basic events and several dozen thousand gates; moreover, they are non-coherent. The assessment of such large formulae is challenging, even for binary decision diagrams, the state-of-the-art data structure to encode and to manipulate Boolean functions. This article describes the various heuristics and strategies that were used to make the assessment tractable.
Manipulation of Charge States of Biopolymer Ions by Atmospheric Pressure Ion/Molecule Reactions Implemented in an Extractive Electrospray Ionization Source
Authors: Chen Huanwen , Touboul David , Jecklin Matthias Conradin , Zheng Jian , Luo Mingbiao , Zenobi Renato
Published: October 2007

A home-made extractive electrospray ionization source is coupled to an linear quadrupole ion trap mass spectrometer to investigate ion/molecule reactions of biopolymers at ambient pressure. Multiply charged biopolymers such as peptides and proteins generated in an electrospray are easily reduced to a low charge state by the atmospheric pressure ion/molecule reactions occurring between the multiply charged ions and a strong basic reagent sprayed in neutral form into the electrospray plume. The charge state of the biopolymer ions can be manipulated by controlling the amount of the basic reagent. The production of biopolymer ions with low charge states results in a substantial improvement of sensitivity and reduced spectral congestion in ESI-MS. This is of importance for biopolymer mixture analysis and could have promising applications in proteomics.
Development of a Novel Mass Spectrometer Equipped with an Electron Cyclotron Resonance Ion Source
Authors: Kidera Masanori , Takahashi Kazuya , Enomoto Shuichi , Mitsubori Youhei , Goto Akira , Yano Yasushige
Published: October 2007

The ionization efficiency of an electron cyclotron resonance ion source (ECRIS) is generally high and all elements can be fundamentally ionized by the high-temperature plasma. We focused our attention on the high potentiality of ECRIS as an ion source for mass spectrometers and attempted to customize a mass spectrometer equipped with an ECRIS. Precise measurements were performed by using an ECRIS that was specialized and customized for elemental analysis. By using the charge-state distribution and the isotope ratio, the problem of overlap, such as that observed in the spectra of isobars, could be solved without any significant improvement in the mass resolution. When the isotope anomaly (or serious mass discrimination effect) was not observed in ECR plasma, the system was found to be very effective for isotope analysis. In this paper, based on the spectrum (ion current as a function of an analyzing magnet current) results of low charged state distributions (2+, 3+, 4+, …) of noble gases, we discuss the feasibility of an elemental analysis system employing an ECRIS, particularly for isotopic analysis. The high-performance isotopic analysis obtained from an ECRIS mass spectrometer in this study suggests that it can be widely applied to several fields of scientific study that require elemental or isotopic analyses with high sensitivity.
Alternately spliced WT1 antisense transcripts interact with WT1 sense RNA and show epigenetic and splicing defects in cancer
Authors: Dallosso Anthony R. , Hancock Anne L. , Malik Sally , Salpekar Ashreena , King-Underwood Linda , Pritchard-Jones Kathy , Peters Jo , Moorwood Kim , Ward Andrew , Malik Karim T.A. , Brown Keith W.
Published: October 2007

Many mammalian genes contain overlapping antisense RNAs, but the functions and mechanisms of action of these transcripts are mostly unknown. WT1 is a well-characterized developmental gene that is mutated in Wilms’ tumor (WT) and acute myeloid leukaemia (AML) and has an antisense transcript (WT1-AS), which we have previously found to regulate WT1 protein levels. In this study, we show that WT1-AS is present in multiple spliceoforms that are usually expressed in parallel with WT1 RNA in human and mouse tissues. We demonstrate that the expression of WT1-AS correlates with methylation of the antisense regulatory region (ARR) in WT1 intron 1, displaying imprinted monoallelic expression in normal kidney and loss of imprinting in WT. However, we find no evidence for imprinting of mouse Wt1-as. WT1-AS transcripts are exported into the cytoplasm and form heteroduplexes with WT1 mRNA in the overlapping region in WT1 exon 1. In AML, there is often abnormal splicing of WT1-AS, which may play a role in the development of this malignancy. These results show that WT1 encodes conserved antisense RNAs that may have an important regulatory role in WT1 expression via RNA:RNA interactions, and which can become deregulated by a variety of mechanisms in cancer.
Multisite and bidirectional exonic splicing enhancer in CD44 alternative exon v3
Authors: Vela Elena , Hilari Josep M. , Roca Xavier , Muñoz-Mármol Ana M. , Ariza Aurelio , Isamat Marcos
Published: October 2007

The human CD44 gene encodes multiple isoforms of a transmembrane protein that differ in their extracellular domains as a result of alternative splicing of its variable exons. Expression of CD44 is tightly regulated according to the type and physiological status of a cell, with expression of high molecular weight isoforms by inclusion of variable exons and low molecular weight isoforms containing few or no variable exons. Human CD44 variable exon 3 (v3) can follow a specific alternative splicing route different from that affecting other variable exons. Here we map and functionally describe the splicing enhancer element within CD44 exon v3 which regulates its inclusion in the final mRNA. The v3 splicing enhancer is a multisite bipartite element consisting of a tandem nonamer, the XX motif, and an heptamer, the Y motif, located centrally in the exon. Each of the three sites of this multisite enhancer partially retains its splicing enhancing capacity independently from each other in CD44 and shows full enhancing function in gene contexts different from CD44. We further demonstrate that these motifs act cooperatively as at least two motifs are needed to maintain exon inclusion. Their action is differential with respect to the splice-site target abutting v3. The first X motif acts on the 3′ splice site, the second X motif acts on both splice sites (as a bidirectional exonic splicing enhancer), and the Y motif acts on the 5′ splice site. We also show that the multisite v3 splicing enhancer is functional irrespective of flanking intron length and spatial organization within v3.
Expression and Localization of Aquaporins in the Kidney of the Musk Shrew (Suncus murinus)
Authors: Maeda Seishi , Kuwahara Sachi , Ito Hisao , Tanaka Koichi , Hayakawa Tetsu , Seki Makoto
Published: October 2007

Expression and localization of members of the aquaporin (AQP) family (AQP1, 2, 3, 4, and 5) in the kidney of the musk shrew ( Suncus murinus) was examined by immunohistochemistry. AQP1 was expressed in the proximal tubules and in the thin limb of the loops of Henle. AQP1 was the only water channel expressed in the proximal nephron examined, indicating that AQP1 may be an independent water transporter in the proximal nephron. AQP2 and AQP5 were localized to the apical cytoplasm of the cortical to medullary collecting duct (CD) cells and AQP3 and AQP4 were localized to the basal aspect of the cortical to medullary CD cells. AQP3 expression was weaker in the cortical cells compared with the medullary cells, whereas AQP4 was strongly positive throughout the CD. These indicate that the CD is the main water reabsorption segment of the nephron and is regulated by AQPs. Indeed, apical water transport of CD cells of the musk shrew may be controlled by both AQP2 and AQP5. The characteristic expression pattern of the AQPs in this animal provides a novel animal model for elucidating the regulation of water reabsorption by AQPs in the mammalian kidney.
LPS-induced IL-6, IL-8, VCAM-1, and ICAM-1 Expression in Human Lymphatic Endothelium
Authors: Sawa Yoshihiko , Ueki Takeshi , Hata Minoru , Iwasawa Kana , Tsuruga Eichi , Kojima Hiroshi , Ishikawa Hiroyuki , Yoshida Shigemitsu
Published: October 2007

We have previously reported the TLR4 expression inhuman intestinal lymphatic vessels. In the study here, microarray analysis showed the expression of the TLR4, MD-2, CD14, MyD88, TIRAP, TRAM, IRAK1, and TRAF6 genes in cultured human neonatal dermal lymphatic microvascular endothelial cells (LEC). The microarray analysis also showed that LEC expressed genes of IL-6, IL-8, VCAM-1, and ICAM-1, and the real-time quantitative PCR analysis showed that mRNA production was increased by lipopolysaccharide (LPS). The LPS-induced IL-6, IL-8, VCAM-1, and ICAM-1 production in LEC was suppressed by the introduction of TLR4-specific small interfering RNA, and also by anti-TLR4, nobiletin, and CAPE pretreatment. These findings suggest that LEC has TLR4-mediated LPS recognition mechanisms that involve at least activation of NF-κB, resulting in increased expression of IL-6, IL-8, VCAM-1, and ICAM-1. Both the LPS effect on the gene expression and also the suppression by nobiletin and CAPE pre-treatment on the protein production were larger in IL-6 and in VCAM-1 than in IL-8 and in ICAM-1 in LEC. The signal transduction of NF-κB and AP-1-dependent pathway may be more critical for the expression of IL-6 and VCAM-1 than that of IL-8 and ICAM-1 in LEC.
Pax7 Reveals a Greater Frequency and Concentration of Satellite Cells at the Ends of Growing Skeletal Muscle Fibers
Authors: Allouh Mohammed Z. , Yablonka-Reuveni Zipora , Rosser Benjamin W. C.
Published: October 2007

The main sites of longitudinal growth in skeletal muscle are the ends of the fibers. This study tests the hypothesis that satellite cells (SCs) are at a greater frequency (#SC nuclei/all nuclei within basal laminae) and concentration (closer together) within growing fiber ends of posthatch chicken pectoralis. SCs were localized by their Pax7 expression, and fiber ends were identified by their retention of neonatal myosin heavy chains and small cross-sectional profiles. Whereas SC frequency decreased from about 20% at 9 days posthatch to <5% at 115 days, fiber ends retained a frequency of ∼16%. Calculated mean area of sarcolemma per SC revealed higher concentrations of SCs at fiber ends. There was also a strong inverse correlation between SC frequency and fiber profile cross-sectional size throughout development. This study suggests that SCs at fiber ends play a key role in the longitudinal growth of muscle fibers, and that fiber profile size may impact SC distribution.
Osteopontin Expression in Normal Skin and Non-melanoma Skin Tumors
Authors: Chang Pi-Ling , Harkins Louie , Hsieh Yu-Hua , Hicks Patricia , Sappayatosok Kraisorn , Yodsanga Somchai , Swasdison Somporn , Chambers Ann F. , Elmets Craig A. , Ho Kang-Jey
Published: October 2007

Osteopontin (OPN) is an adhesive, matricellular glycoprotein, whose expression is elevated in many types of cancer and has been shown to facilitate tumorigenesis in vivo. To understand the role of OPN in human skin cancer, this study is designed to determine whether OPN is expressed in premalignant [solar/actinic keratosis (AK)] and in malignant skin lesions such as squamous cell carcinomas (SCC) and basal cell carcinomas (BCC), as well as in normal skin exposed or not exposed to sunlight. Immunohistochemical analyses showed that OPN is expressed in SCC (20/20 cases) and in AK (16/16 cases), which are precursors to SCC, but is absent or minimally expressed in solid BCC (17 cases). However, positive staining for OPN was observed in those BCC that manifest differentiation toward epidermal appendages such as keratotic BCC. In sunlight-exposed normal skin, OPN is minimally expressed in the basal cell layer, but in contrast to those not exposed to sunlight, OPN is more prominent in the spinous cell layer with increasing intensity toward the granular cell layer. Additionally, OPN is expressed in the hair follicles, sebaceous glands, and sweat glands of normal skin. In conclusion, these data suggest that OPN is associated with keratinocyte differentiation and that it is expressed in AK and SCC, which have metastatic potential, but minimally expressed in solid BCC.
Towards understanding selenocysteine incorporation into bacterial proteins
Authors: Fischer Niels , Paleskava Alena , Gromadski Kirill B. , Konevega Andrey L. , Wahl Markus C. , Stark Holger , Rodnina Marina V.
Published: October 2007

In bacteria, UGA stop codons can be recoded to direct the incorporation of selenocysteine into proteins on the ribosome. Recoding requires a selenocysteine incorporation sequence (SECIS) downstream of the UGA codon, a specialized translation factor SelB, and the non-canonical Sec-tRNASec, which is formed from Ser-tRNASec by selenocysteine synthase, SelA, using selenophosphate as selenium donor. Here we describe a rapid-kinetics approach to study the mechanism of selenocysteine insertion into proteins on the ribosome. Labeling of SelB, Sec-tRNASec and other components of the translational machinery allows direct observation of the formation or dissociation of complexes by monitoring changes in the fluorescence of single dyes or fluorescence resonance energy transfer between two fluorophores. Furthermore, the structure of SelA was studied by electron cryomicroscopy (cryo-EM). We report that intact SelA from the thermophilic bacterium Moorella thermoacetica (mthSelA) can be vitrified for cryo-EM using a controlled-environment vitrification system. Two-dimensional image analysis of vitrified mthSelA images shows that SelA can adopt the wide range of orientations required for high-resolution structure determination by cryo-EM. The results indicate that mthSelA forms a homodecamer that has a ring-like structure with five bilobed wings, similar to the structure of the E. coli complex determined previously.
Selenium in mammalian spermiogenesis
Authors: Flohé Leopold
Published: October 2007

The role of selenium in male fertility is reviewed with special emphasis on selenoprotein P and phospholipid hydroperoxide glutathione peroxidase (GPx4) in spermiogenesis. Inverse genetics reveal that selenoprotein P is required for selenium supply to the testis. GPx4 is abundantly synthesized in spermatids. As a moonlighting protein it is transformed in the later stages of spermiogenesis from an active selenoperoxidase into a structural protein that becomes a constituent of the mitochondrial sheath of spermatozoa. The transformation is paralleled by loss of glutathione. Mechanistically, the process is an alternate substrate inactivation of GPx4 resulting from reactions of its selenenic form with thiols of GPx4 itself and other proteins. Circumstantial evidence and ongoing experimental genetics indicate that the mitochondrially expressed form of the GPx4 gene is the most relevant one in spermiogenesis, with the nuclear form being dispensable for fertility and the role of cytosolic GPx4 remaining unclear. Clinical data reveal a strong association of low sperm GPx4 with infertility. Thus, impaired GPx4 biosynthesis, due to selenium deficiency or to genetic defects in gpx4 itself or in proteins involved in Se distribution and selenoprotein biosynthesis, causes male infertility, but can also be an epiphenomenon due to any perturbation of testicular function.
Influence of pH and flanking serine on the redox potential of S-S and S-Se bridges of Cys-Cys and Cys-Sec peptides
Authors: Schneider Alex , Brandt Wolfgang , Wessjohann Ludger A.
Published: October 2007

In selenocysteine (Sec, U)-containing proteins the selenenylsulfide bridge and its reduced thiol-selenol counterpart are usually the significant species. An important role for serine as flanking amino acid in the redox potential of S-S and S-Se bridges was proposed for some thioredoxin reductases. To check the generality of this proposal, model tetrapeptides (GCCG, SCCG, GCCS, SCCS, GCUG, SCUG, GCUS, SCUS) were synthesized, including the GCUG sequence of human thioredoxin reductase. The influence on the redox potential of S-Se and S-S bridges as a function of pH and of serine at different positions reveals (i) a strong general pH dependence, and (ii) a significant influence of flanking serine on disulfide only at basic pH.
Effect of age on sexually dimorphic selenoprotein expression in mice
Authors: Schomburg Lutz , Riese Cornelia , Renko Kostja , Schweizer Ulrich
Published: October 2007

Clinical data suggest that selenium (Se) supplementation decreases disease predisposition and severity and accelerates recovery in a variety of pathologies. Pre-supplementation Se levels and sex represent important determinants of these Se-dependent health effects. Accordingly, we previously reported on sexually dimorphic expression patterns of Se-dependent glutathione peroxidase 1, type I deiodinase, and selenoprotein P in young mice. In the present study we investigated whether these differences vary with age. The strong sexual dimorphic expression of hepatic type I deiodinase that was observed in young mice vanished both at the mRNA and enzyme activity level by 1 year of age. In contrast, the strong sex-specific differences in renal type I deiodinase mRNA expression were sustained with age. Accordingly, deiodinase enzymatic activities differed in male and female kidneys, largely independent of age [average of 6.8 vs. 15.7 pmol/(min mg) in males vs. females]. In parallel, hepatic Se concentrations and glutathione peroxidase activities increased in female mice compared to male littermates, establishing a new sexual dimorphism in liver. Thus, age represents another important modifier of the dynamic sex- and tissue-specific selenoprotein expression patterns. These data highlight again the unique physiological regulatory mechanisms that have evolved to control Se metabolism according to the actual needs of the organism.
Effect of selenium on thioredoxin reductase activity in Txnrd1 or Txnrd2 hemizygous mice
Authors: Kiermayer Claudia , Michalke Bernhard , Schmidt Jörg , Brielmeier Markus
Published: October 2007

Thioredoxin reductase 1 (Txnrd1) and thioredoxin reductase 2 (Txnrd2) are selenoproteins whose expression and function depends on adequate supply of the trace element selenium (Se). As homozygous (-/-) knockout of both Txnrd1 and Txnrd2 is embryonically lethal, we investigated the effect of their hemizygosity (+/-) alone and in combination with dietary Se on enzymatic activity in various tissues. To assess the overall health of the corresponding mice, the growth, viability and fertility of the different experimental groups were also compared. Se depletion led to a marked decrease in Se organ contents. Se depletion was most prominent in lung, followed by liver, kidney, heart, muscle and brain. We found no major effect of Txnrd1 or Txnrd2 hemizygosity and/or Se on male fertility and the viability of offspring. A gene dose effect under Se-adequate conditions for Txnrd1 and Txnrd2 in all organs was observed. Haploid insufficiency decreased Txnrd activity to an extent that can be further decreased by Se deficiency, but not to levels below those observed for Se depletion alone. The only exception was Txnrd2 activity in kidney, heart and muscle, where we found an additive effect.