High-speed capillary zone electrophoresis with online photolytic optical injection

We report an online, optical injection interface for capillary zone electrophoresis (CZE) based upon photophysical activation of a caged, fluorogenic label covalently attached to the target analyte. This injection interface allows online analysis of biomolecular systems with high temporal resolution and high sensitivity. Samples are injected onto the separation capillary by photolysis of a caged-fluorescein label using the 351-364 nm irradiation of an Ar+ laser. Following injection, the sample is separated and detected via laser-induced fluorescence detection at 488 nm. Detection limits for online analysis of arginine, glutamic acid, and aspartic acid were less than 1 nM with separation times less than 5 s and separation efficiencies exceeding 1,000,000 plates/m. Rapid injection of proteins was demonstrated with migration times less than 500 ms and 0.5 nM detection limits. Online monitoring was performed with response times less than 20 s, suggesting the feasibility of this approach for online, in vivo analysis for a range of biologically relevant analytes.     

The influence of cutter orientation and workpiece angle on machinability when high-speed milling Inconel 718 under finishing conditions

The paper details results from a comprehensive series of experiments on the effects of key operating variables; cutter orientation and workpiece tilt angle, on tool life/length cut, cutting force, workpiece surface roughness (R_a), subsurface microstructure/microhardness and residual stress, when high-speed milling under finishing conditions. In terms of length cut, the 8 mm diameter coated (TiAlCrN multi-layer) carbide ball nose end mills achieved tool life values approaching 200 m. Life results for the horizontal downwards orientation when cutting with a workpiece tilt angle of 45° were similar to those when operating with the workpiece mounted horizontally, however, cutting forces were significantly higher in the latter case. Evidence of tool chatter was also observed from cutting force signatures with the horizontal upwards mode. Mean compressive surface residual stresses up to −850 MPa measured parallel to the feed direction were obtained when machining using worn tools with a 0° workpiece inclination, while tensile stresses were obtained when machining with horizontal downwards orientation.     

Identification of a leader exon and a core promoter for the rat tuberous sclerosis 2 (Tsc2) gene and structural comparison with the human homolog

Hereditary renal carcinoma in the Eker rat is an excellent example of predisposition to a specific cancer being transmitted as a dominant trait. Recently, we identified a germline mutation of the tuberous sclerosis 2 (Tsc2) gene in the Eker rat. In the present study, we analyzed the upstream region of the Tsc2 gene. A novel leader exon (exon 1a) in a CpG island was found, and core promoter activity was identified in a 242-bp region of this island. Exon 1a and the promoter region were conserved in the human TSC2 gene. In addition, a rat homolog of a gene found upstream of TSC2 in human has been identified, indicating that the genomic organization around Tsc2/TSC2 is conserved between the two species. Characterization of the 5' region of Tsc2 and TSC2 will facilitate studies of the regulation of the gene and its disregulation in tumorigenesis.     

The effect of machined topography and integrity on fatigue life

The paper reviews published data which address the effect of machining (conventional and non-conventional processes) and the resulting workpiece surface topography/integrity on fatigue performance, for a variety of workpiece materials. The effect of post-machining surface treatments, such as shot peening, are also detailed. The influence of amplitude height parameters (Ra, Rt), amplitude distribution (Rsk) and shape (Rku) parameters, as well as spatial (Std, Sal) and hybrid (Ssc) measures, are considered.There is some disagreement in the literature about the correlation between workpiece surface roughness and fatigue life. In most cases, it has been reported that lower roughness results in longer fatigue life, but that for roughness values in the range 2.5–5 μm Ra it is primarily dependent on workpiece residual stress and surface microstructure, rather than roughness. In the absence of residual stress, machined surface roughness in excess of 0.1 μm Ra has a strong influence on fatigue life. Temperatures above 400 °C reduce the effects of both residual stress and surface roughness on fatigue, due to stress relieving and the change in crack initiation from the surfaces to internal sites. The presence of inclusions an order of magnitude larger than the machined surface roughness generally overrides the effect of surface topography.     

Review on ultrasonic machining

Ultrasonic machining is of particular interest for the cutting of non-conductive, brittle workpiece materials such as engineering ceramics. Unlike other non-traditional processes such as laser beam, and electrical discharge machining, etc., ultrasonic machining does not thermally damage the workpiece or appear to introduce significant levels of residual stress, which is important for the survival of brittle materials in service. The fundamental principles of ultrasonic machining, the material removal mechanisms involved and the effect of operating parameters on material removal rate, tool wear rate and workpiece accuracy are reviewed, with particular emphasis on the machining of engineering ceramics. The problems of producing complex 3-D shapes in ceramics are outlined.     

The Machining of γ-TiAI Intermetallic Alloys

Titanium intermetallic materials are likely to play a significant role in the production of future aeroengines. The paper details the machinabilty of a range of gamma titanium aluminide (γ-TiAl) intermetallic alloys when turning, grinding, HSM, drilling, EDM and ECM. Comprehensive literature review data is augmented with experimental results for turning, turn-milling and temperature measurement when high speed milling. Despite the ability to produce crack free surfaces when grinding and HSM, turning and drilling remain problematic. Turned surfaces are in general characterised by workpiece smearing, numerous arc shaped cracks, subsurface lamellae deformation and significant strain hardening, although the use of PCD tooling and ultrasonic assisted cutting has been shown to minimise these effects.     

Oxygen microsensor and its application to single cells and mouse pancreatic islets.

An oxygen microsensor with a < 3-micron tip diameter was developed for monitoring oxygen levels at single cells and mouse pancreatic islets. The sensor was fabricated by electrochemically recessing an etched Pt wire inside a pulled glass micropipet and then coating with cellulose acetate. This fabrication process was found to be simpler than previous oxygen electrode designs of comparable size. The microsensors had a average sensitivity of 0.59 +/- 0.29 pA/mmHg (mean +/- SD, n = 42), signals that were minimally perturbed by convection, and response times of < 1 s. The electrode was used to measure the oxygen gradient around and inside single mouse islets. The measurements demonstrate that oxygen levels within even the largest islets at maximal glucose stimulation are 67 +/- 1.6 mmHg (mean +/- SD, n = 5), indicating that islets have adequate oxygen supplies by diffusion under tissue culture conditions to support insulin secretion. The electrode was also used to record the dynamics of oxygen level at single islets as a function of glucose concentration. As glucose level was changed from 3 to 10 mM, oxygen level decreased by 15.8 +/- 2.3 mmHg (mean +/- SEM, n = 6) and oscillations with a period of 3.3 +/- 0.6 min (mean +/- SEM, n = 6) appeared in the oxygen level. In islets bathed in quiescent solutions containing 10 mM glucose, similar oscillations could be observed. In addition, in the quiet solutions it was possible to detect faster oscillations with a period of 12.1 +/- 1.7 s (mean +/- SEM, n = 6) superimposed on the slower oscillations. Oxygen consumption could also be observed at single insulinoma cells using the electrode. Individual cells also showed oscillations in oxygen consumption with a period of a few seconds. The results demonstrate that the electrode can be used for dynamic oxygen level recordings in biological microenvironments.     

Effect of laminate configuration and feed rate on cutting performance when drilling holes in carbon fibre reinforced plastic composites

Composites use in the aerospace industry is expanding, in particular carbon fibre reinforced plastics (CFRP) for structural components. Machinability can however be problematic especially when drilling, due to CFRP's inherent anisotropy/in-homogeneity, limited plastic deformation and abrasive characteristics. Following a brief review on composites development and associated machining, the paper outlines experimental results when twist drilling 1.5 mm diameter holes in 3 mm thick CFRP laminate using tungsten carbide (WC) stepped drills. The control variables considered were prepreg type (3 types) and form (unidirectional (UD) and woven), together with drill feed rate (0.2 and 0.4 mm/rev). A full factorial experimental design was used involving 12 tests. Response variables included the number of drilled holes (wear criterion VB_Bmax ≤ 100 μm), thrust force and torque, together with entry and exit delamination (conventional and adjusted delamination factor values calculated) and hole diameter. Best results were obtained with woven MTM44-1/HTS oven cured material (3750 holes) while the effect of prepreg form on tool life was evident only when operating at the higher level of feed rate. Thrust forces were typically under 125 N with torque values generally below 65 Nmm over the range of operating parameters employed. Finally, the delamination factor (F_d) measured at hole entry and exit ranged between ～1.2–1.8 and 1.0–2.1 respectively.     

Creep feed grinding of gamma titanium aluminide and burn resistant titanium alloys using SiC abrasive

Following a brief introduction to titanium alloys and their machinability, the cutting performance of a gamma titanium aluminide intermetallic (γ-TiAl) alloy: Ti–45Al–8Nb–0.2C wt% and a burn resistant titanium (BuRTi) alloy: Ti–25V–15Cr–2Al–0.2C wt%, is compared with creep feed grinding using SiC abrasive. The work utilised 2 separate L9 Taguchi fractional factorial arrays. Typically G-ratios were a factor of 10× greater for γ-TiAl than BuRTi, with on average 10% lower maximum power and 25% lower maximum specific energy for the γ-TiAl alloy. A combination of a moderately high wheel speed: 35 m/s, low depth of cut: 1.25 mm and low feed rate: 150 mm/min, produced the lowest average workpiece surface roughness (Ra1.4 μm). Workpiece surface integrity evaluation indicated that with lower operating parameter levels, in particular a wheel speed of 15 m/s, surfaces free of burn and cracks could be produced, while at higher wheel speeds: 35 m/s, extensive workpiece surface burn was evident, with the γ-TiAl alloy suffering extensive cracking. Microhardness measurements showed in some instances slightly increased workpiece surface hardness of around 50–60HK_0.025 for the BuRTi alloy and 200HK_0.025 for the γ-TiAl material over respective bulk hardness values of 375HK_0.025 and 400HK_0.025.     

The application of polycrystalline diamond (PCD) tool materials when drilling and reaming aluminium based alloys including MMC

Following a review of metal matrix composite (MMC) materials and production methods, the paper outlines the development and application of PCD cutting tools. Experimental data are presented for the drilling and single blade reaming of aluminium-silicon alloys containing 7% and 13% silicon and aluminium 2618 MMC alloy reinforced with 15 vol% silicon carbide (SiC) particulate. Though initially aimed only at aerospace and defence products, MMCs have progressively moved into higher volume applications and are currently under evaluation for volume automotive components. Compared with standard hypoeutectic and hypereutectic cast aluminium-silicon alloys, tool wear when machining MMC is shown to be up to seven times more severe. Tools used for drilling include HSS-M2, diamond plated HSS, WC, TiN coated WC and PCD. Other than when using PCD drills, tool life was extremely short due to the abrasive nature of the (SiC) reinforcement. Similarly, results from PCD reaming tests confirmed that diamond tooling provides the only realistic tooling option.