Joule-class THz pulses from microchannel targets

Inference of joule-class THz radiation sources from microchannel targets driven with hundreds of joule, picosecond lasers is reported. THz sources of this magnitude are useful for nonlinear pumping of matter and for charged-particle acceleration and manipulation. Microchannel targets demonstrate increased laser-THz conversion efficiency compared to planar foil targets, with laser energy to THz energy conversion up to ∼0.9% in the best cases.

Development of a hardened THz energy meter for use on the kilojoule-scale, short-pulse OMEGA EP laser

A highly adaptable and robust terahertz (THz) energy meter is designed and implemented to detect energetic THz pulses from high-intensity (>10¹⁸ W/cm²) laser-plasma interactions on the OMEGA EP. THz radiation from the laser driven target is detected by a shielded pyrometer. A second identical pyrometer is used for background subtraction. The detector can be configured to detect THz pulses in the 1 mm to 30 μm (0.3- to 10-THz) range and pulse energies from joules to microjoules via changes in filtration, aperture size, and position. Additional polarization selective filtration can also be used to determine the THz pulse polarization. The design incorporates significant radiation and electromagnetic pulse shielding to survive and operate within the OMEGA EP radiation environment. We describe the design, operational principle, calibration, and testing of the THz energy meter. The pyrometers were calibrated using a benchtop laser and show linear sensitivity to up to 1000 nJ of absorbed energy. The initial results from four OMEGA EP THz experiments detected up to ∼15μJ at the detector, which can correspond to hundreds of mJ depending on THz emission and reflection models.

The evaluation of whitening efficacy of cosmetic products using a human skin pigmentation spot model

BACKGROUND

To establish a pigmentation spot model on human skin and to assess whitening efficacy for whitening products by this established pigmentation spot model.

METHODS

Twenty subjects between 20 and 45 years old with skin phototype III or IV were selected. Three consecutive daily UV exposures were performed on buttocks of the subjects as follows: Day 1=1 minimal erythema dose (MED), Day 2=0.5 MED and Day 3=0.5 MED. After the first UV exposure, a selected whitening product was applied to the subjects twice a day on UV exposure area. The application of the whitening product to subjects on the exposed areas was continued till Day 27. CM2500d chromameter, Maxmeter MX18 and visual evaluation were used to assess changes of skin color.

RESULTS

A pigmentation spot model after UV exposure was established. The measurement of the pigment spot showed that L* value declined abruptly at Day 3 and then slowly reached to a lowest point at Day 6. L* value of the pigment spot almost remained at the same level until Day 20, thereafter increased slowly. The a* value showed an abrupt increase at Day 3 and slowly reached to a maximal level at Day 6. The a* value slowly declined toward its baseline level. Likewise, the erythema index also increased significantly at Day 3, and reached to a maximal level at Day 6 and then slowly declined. However, L*, a* and erythema indices did not return to their baseline levels during the 27-day period of this study. On the other hand, b* value started to increase from Day 3 and such increase was observed continuously to Day 27. Melanin index also showed a slow increase during the first 3 days. It started to increase rapidly from Day 3 and a to maximal level at Day 9 and maintain at a plateau till Day 27 (with an exception at Day 13). To assess the whitening product by this pigmentation spot model, DeltaL, Deltab*, and DeltaM values were analyzed. It showed that absolute DeltaL value and Deltab*value of whitening products were lower than those values of the vehicle of the whitening product at each checkpoint, while DeltaM value of the whitening product was lower only at Day 9 and Day 20, although no statistically significant differences was found. The visual results also strongly supported that the whitening product enhanced the decrease of pigmentation.

CONCLUSION

This study showed that repeated UV exposure was able to induce a long extensive period of pigment formation. The resulted pigmentation spot was able to maintain at an elevated level till Day 20. Clinical subjective evaluations together with combined objective instrument measurements were still important to assess whitening and spot-removing ability of a material due to the instrument limitation for color differentiations. This kind of pigmentation spot model can be used to assess whitening efficacy for whitening or spot-removing products. In addition, the combinations of subjective and objective methods were able to serve as advisable references to assess the whitening efficacy of products.

Construction of trypanosome artificial mini-chromosomes

We report the preparation of two linear constructs which, when transformed into the procyclic form of Trypanosoma brucei, become stably inherited artificial mini-chromosomes. Both of the two constructs, one of 10 kb and the other of 13 kb, contain a T.brucei PARP promoter driving a chloramphenicol acetyltransferase (CAT) gene. In the 10 kb construct the CAT gene is followed by one hygromycin phosphotransferase (Hph) gene, and in the 13 kb construct the CAT gene is followed by three tandemly linked Hph genes. At each end of these linear molecules are telomere repeats and subtelomeric sequences. Electroporation of these linear DNA constructs into the procyclic form of T.brucei generated hygromycin-B resistant cell lines. In these cell lines, the input DNA remained linear and bounded by the telomere ends, but it increased in size. In the cell lines generated by the 10 kb construct, the input DNA increased in size to 20-50 kb. In the cell lines generated by the 13 kb constructs, two sizes of linear DNAs containing the input plasmid were detected: one of 40-50 kb and the other of 150 kb. The increase in size was not the result of in vivo tandem repetitions of the input plasmid, but represented the addition of new sequences. These Hph containing linear DNA molecules were maintained stably in cell lines for at least 20 generations in the absence of drug selection and were subsequently referred to as trypanosome artificial mini-chromosomes, or TACs.

Structure of a frequently rearranged rRNA-encoding chromosome in Giardia lamblia

It has been shown previously that the rRNA encoding chromosomes in Giardia lamblia undergo frequent rearrangements with an estimated rate of approximately 1% per cell per division (Le Blancq et al., 1992, Nucleic Acids Res., 17, 4539-4545). Following these observations, we searched for highly recombinogenic regions in one of the frequently rearranged rRNA encoding chromosomes, that is chromosome 1, a small, 1.1 Mb chromosome. Chromosome 1 undergoes frequent rearrangements that result in size variation of 5-20%. We analyzed the structure of chromosome 1 in clonal lineages from the WB strain. The two ends of chromosome 1 comprise telomere repeat [TAGGG] arrays joined to a truncated rRNA gene and a sequence referred to as '4e', respectively. Comparison of the structure of four polymorphic versions of chromosome 1, resulting from independent rearrangement events in four cloned lines, located a single polymorphic region to the variable rDNA-telomere domain. Chromosome 1 is organized into two domains: a core region spanning approximately 850 kb that does not exhibit size heterogeneity among different chromosome 1 and a variable region that spans 185-450 kb and includes the telomeric rRNA genes, referred to as the variable rDNA-telomere domain. The core region contains a conserved region, spanning approximately 550 kb adjacent to the telomeric 4e sequence, which is only present in the 4e containing chromosomes and a 300 kb region of repetitive sequences that are also components of other chromosomes as well. Changes in the number of rDNA repeats accounted for some, but not all, of the size variation. Since there are four chromosomes that share the core region of chromosome 1, we suggest that the genome is tetraploid for this chromosome.