Improvement of Thermal Stability via Outer-Loop Ion Pair Interaction of Mutated T1 Lipase from Geobacillus zalihae Strain T1

Mutant D311E and K344R were constructed using site-directed mutagenesis to introduce an additional ion pair at the inter-loop and the intra-loop, respectively, to determine the effect of ion pairs on the stability of T1 lipase isolated from Geobacillus zalihae. A series of purification steps was applied, and the pure lipases of T1, D311E and K344R were obtained. The wild-type and mutant lipases were analyzed using circular dichroism. The Tm for T1 lipase, D311E lipase and K344R lipase were approximately 68.52 °C, 70.59 °C and 68.54 °C, respectively. Mutation at D311 increases the stability of T1 lipase and exhibited higher Tm as compared to the wild-type and K344R. Based on the above, D311E lipase was chosen for further study. D311E lipase was successfully crystallized using the sitting drop vapor diffusion method. The crystal was diffracted at 2.1 Å using an in-house X-ray beam and belonged to the monoclinic space group C2 with the unit cell parameters a = 117.32 Å, b = 81.16 Å and c = 100.14 Å. Structural analysis showed the existence of an additional ion pair around E311 in the structure of D311E. The additional ion pair in D311E may regulate the stability of this mutant lipase at high temperatures as predicted in silico and spectroscopically

Magnetic Imaging of Corrosion under Insulation using Quantum Well Hall Effect Sensors

Corrosion Under Insulation (CUI) is one of the most pressing issues facing industries that make use of cladded steel pipes, costing companies trillions of dollars every year to maintain them. Currently while there are few devices capable of detecting corrosion under insulation, they remain expensive, bulky, and difficult to utilise over kilometres of cladded steel pipe [1]. This research presents a prototype device using novel Quantum Well Hall Effect (QWHE) sensors. These sensors are physically small (70-micron square), made on Gallium Arsenide substrates, capable of measuring magnetic fields in the tens of nanotesla, and have a linear response ideally suited to imaging applications [2], [3]. This prototype is capable of scanning insulated or cladded steel pipes. It can detect manufactured wall thickness loss of 1mm, 2mm, and 3mm, in a 10mm thick pipe, which represent 10%, 20%, and 30% loss respectively as far as 95mm from the surface with micron level resolution. The research presented here focuses on demonstrating the accuracy of the QWHE sensor-based prototype system by comparing the measured magnetic data to a scan of the same machined pipe acquired with a high precision laser. Together these two different scans demonstrate the possibility of using a QWHE sensor in future designs aimed at tackling the pressing issue of CUI.</p

Two stage lock in amplification for improving magnetic data acquisition systems using Quantum Well Hall Effect sensors

Quantum Well Hall Effect (QWHE) sensors are a type of magnetic field sensor with previously demonstrated applications in NDT imaging systems. These sensors are typically biased in the 10-100kHz frequency range to avoid both 1/f noise and magnetic pickup. The signal is then further amplitude modulated by the measured magnetic field. Traditionally, this magnetic signal's amplitude is then extracted through Fast Fourier Transforms (FFT). With this traditional method however, most of the measured signal consists of unwanted pick up, and large unchanging offset values resulting from both the circuit and any measurements, with the actual measured signal making up less than 1% of the ADC dynamic range. By designing a two-stage lock in amplifier, the signal is demodulated with respect to both the biasing signal and the AC magnetic signal, leaving only the DC component corresponding to the amplitude of the magnetic signal. The offset from this can then be subtracted, and further gain can be applied, allowing the full dynamic range of the measurement ADC to be utilised, while only measuring the changes in magnetic field strength resulting from the presence of any flaws in the measurement sample. This theoretically allows for smaller signals to be measured than is possible with the FFT method, provided that the signals are not lower than the noise floor of the measurement circuitry. An example of both FFT and early prototype lock in amplifier demodulation is demonstrated in this work. This method of signal demodulation also has the added benefit of decoupling the measurement parameters from the frequencies used in the biasing and magnetic signals, allowing for arbitrarily slow sample rates to be used in measurement.</p