We have developed hybrid light responsive TiO2 nanoparticles electronically linked to PNA oligonucleotides that site specifically bind to double stranded target DNA. This opens a new opportunity for the development of a highly efficient "artificial restriction enzyme" whose activity can be controlled by using light. The work focuses on the use of TiO2 nanocomposites as analogs of restriction enzymes with unique specificity that does not exist in current biological approaches. TiO2 nanoparticles electronically linked to DNA or PNA adapters have been site-specifically attached along double stranded λ DNA vectors. Illumination of this assembly results in selective oxidation of DNA at the deepest "thermodynamic traps" located closest to the nanoparticle surface, causing DNA cleavage. We investigate the effect of the sequence and length of DNA and PNA adapters on the specificity of DNA cleavage. Related to this issue, the potential use of TiO2/DNA nanocomposites as "rare cutters" that cleave DNA in the places not achieved with existing protein-based enzymes is investigated.
We have demonstrated that a newly developed, ultrafast x-ray streak camera is sensitive to single x-ray pulses of highly monochromatic and unfocused synchrotron radiation at 8 keV. The high sensitivity was achieved by using CsI as the photocathode material. The individually measured x-ray pulses revealed that the bunch length was 120 ps long (full-width-at-half-maximum) and about 20-30 photon events were registered by streak camera in each pulse at the experimental conditions. The results demonstrated the feasibility of using this streak camera for single-shot experiments and using single x-ray pulses from the third-generation synchrotron sources with microfocused and/or polychromatic beams.
The detailed analysis of the fuel sprays has been well recognized as an important step for optimizing the operation of internal-combustion engines to improve efficiency and reduce emissions. However, the structure and dynamics of highly transient fuel sprays have never been visualized or reconstructed in three dimensions (3D) previously due to numerous technical difficulties. By using an ultrafast x-ray detector and intense monochromatic x-ray beams from synchrotron radiation, the fine structures and dynamics of 1-ms direct-injection gasoline fuel sprays were elucidated for the first time by a newly developed, ultrafast computed microtomography technique. Due to the time-resolved nature and the intensive data analysis, the Fourier transform algorithm was used to achieve an efficient reconstruction process. The temporal and spatial resolutions of the current measurement are 5.1 μs and 150 μm, respectively. Many features associated with the transient liquid flows are readily observable in the reconstructed spray. Furthermore, an accurate 3D fuel density distribution was obtained as the result of the computed tomography in a time-resolved manner. These results not only reveal the characteristics of automotive fuel sprays with unprecedented details, but will also facilitate realistic computational fluid dynamic simulations in highly transient, multiphase systems.
We demonstrated that the shot-to-shot timing jitter of a streak camera is reduced to 30 fs when it is triggered by a standard kilohertz laser with 1.2% RMS fluctuation. Such small jitter was obtained by improving the response time of deflection plates and the rise-time of a ramp pulse generated by a photoconductive switch, and by operating the photoconductive switch at the optimum working condition. The temporal resolution of the x-ray streak camera operating in accumulation mode is better than 600 femtosecond that is not limited by the timing jitter.
An x-ray streak camera operating in accumulation mode was developed for studying ultrafast dynamics at synchrotron facilities. A laser-triggered photoconductive switch was used as a sweeping unit to obtain low timing jitter. The fast rise time of the ramp pulse generated by the switch (90 ps) combined with the fast response of the traveling wave deflection plates (150 ps) significantly reduced the jitter caused by the shot-to-shot laser fluctuation. At ~1% rms (root mean square) laser energy fluctuation, the resolution of the camera is 1.1 ps when over 5000 laser shots were accumulated. This is two times better than that of the previous design with slower response (300 ps) deflection plates.
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