Optimization for continuous-wave terahertz reflection imaging for biological tissues

Continuous-wave terahertz reflection imaging is a potential tool for biological tissues. Based on our home-made continuous-wave terahertz reflection imaging system, the effect of both polarization mode and reflection window on the imaging performance is studied theoretically and experimentally, showing good agreement. By taking obtaining sample information and image contrast into consideration, p-polarized terahertz waves are recommended. Moreover, considering the sample boundary identification and the image contrast, selection criteria for reflection window are proposed. This work will help to improve the performance of continuous-wave terahertz reflection imaging and accelerate the THz imaging in biological application.     

The AC conductivity of human sweat ducts as the dominant factor in the sub-THz reflection coefficient of skin

The helical nature of human sweat ducts, combined with the morphological and dielectric properties of skin, suggests electromagnetic activity in the sub-THz frequency band. A detailed electromagnetic simulation model of the skin, with embedded sweat ducts, was created. The model includes realistic dielectric properties based on the measured water content of each layer of skin, derived from Raman Spectroscopy. The model was verified by comparing it to measurements of the reflection coefficient of the palms of 13 volunteers in the frequency band 350–410 GHz. They were subjected to a measurement protocol intended to induce mental stress, thereby also activating the sweat glands. The Galvanic Skin Response was concurrently measured. Using the simulation model the optimal ac-conductivity for each measurement was found. The range of variation for all subjects was found to be from 100 S/m to a maximum value of 6000 S/m with averages of 1000 S/m. These are one order of magnitude increase from the accepted values for water at these frequencies (~100 s/m at 100 GHz). Considering the known biochemical mechanism for inducing perspiration, we conclude that these ac-conductivity levels are probably valid, even though the real time measurements of sweat ac-conductivity levels inside the duct are inaccessible.     

DNA sliding and loop formation by E. coli SMC complex: MukBEF

SMC (structural maintenance of chromosomes) complexes share conserved architectures and function in chromosome maintenance via an unknown mechanism. Here we have used single-molecule techniques to study MukBEF, the SMC complex in Escherichia coli. Real-time movies show MukB alone can compact DNA and ATP inhibits DNA compaction by MukB. We observed that DNA unidirectionally slides through MukB, potentially by a ratchet mechanism, and the sliding speed depends on the elastic energy stored in the DNA. MukE, MukF and ATP binding stabilize MukB and DNA interaction, and ATP hydrolysis regulates the loading/unloading of MukBEF from DNA. Our data suggests a new model for how MukBEF organizes the bacterial chromosome in vivo; and this model will be relevant for other SMC proteins.     

Cobalt-chromium-molybdenum but not titanium-6aluminium-4vanadium alloy discs inhibit human t cell activation in vitro

This study describes the effect of the presence of cobalt-chromium-molybdenum (CoCrMo) and titanium-6aluminium-4vanadium (Ti6AL4V) disc samples on the CD3-mediated in vitro response of human peripheral blood T lymphocyt es. Lymphocyte proliferation in the presence and absence of these metal alloy discs was measured by [³H]thymidine incorporation. Inhibition of lymphocyte proliferation was observed in the presence of CoCrMo disc samples. In contrast, the presence of the Ti6AL4V metal alloy discs had no effect on T cell proliferation. Ultrastructural studies using scanning electron microscopy revealed that the differences in the number of blast cells on uncoated CoCrMo and Ti6AL4V discs from a 4 day culture were consistent with the results observed in the proliferation experiments, i.e. fewer blast cells were seen on the CoCrMo than on the Ti6AL4V discs. In addition, a quantitative analysis of trace elements using total reflection X-ray fluorescence spectrometry in supernatants from 68 h in vitro cultures containing Ti6AL4V or CoCrMo disc samples was performed, revealing differences in the relative metal concentrations in the culture conditions tested. These differences point to the presence of cobalt in the supernatants as a possible determining factor of the inhibition observed. Because cell viability did not appear to change, a more complex mechanism involving the interaction of metals with T lymphocytes may account for the results obtained.