On the Formation Age of the First Planetary System

Recently, it has been observed the extreme metal-poor stars in the Galactic halo, which must be formed just after Pop III objects. On the other hand, the first gas clouds of mass $\sim 10^6 M_{\odot}$ are supposed to be formed at $z \sim$ 10, 20, and 30 for the $1\sigma$, $2\sigma$ and $3\sigma$, where the density perturbations are assumed of the standard $\Lambda$CDM cosmology. If we could apply this gaussian distribution to the extreme small probability, the gas clouds would be formed at $z \sim$40, 60, and 80 for the $4\sigma$, $6\sigma$, and $8\sigma$. The first gas clouds within our galaxy must be formed around $z\sim 40$. Even if the gas cloud is metal poor, there is a lot of possibility to form the planets around such stars. The first planetary systems could be formed within $\sim 6\times 10^7$ years after the Big Bang in the universe. Even in our galaxies, it could be formed within $\sim 1.7\times 10^8$ years. It is interesting to wait the observations of planets around metal-poor stars. For the panspermia theory, the origin of life could be expected in such systems.Comment: 5 pages,Proceedings IAU Symposium No. 249, 2007, Exoplanets:Y-S. Sun, S. Ferraz-Mello and J.-L, Zhou, eds. (p325

Hopping conduction in sizecontrolled Si nanocrystals

We investigate the temperature dependence of conduction in size-controlled silicon nanocrystals. The nanocrystals are ϳ8 nm in diameter, covered by ϳ1.5 nm thick SiO 2 shells. In 300 nm thick films for temperatures T from 30 to 200 K, the conductivity follows a ln͑͒ vs 1 / T 1/2 dependence. This may be associated with either percolation-hopping conductance or Efros-Shklovskii variable range hopping. Assuming hopping sites only on the nanocrystals, the data agree well with the percolation model

Annual direct cost of dry eye in Japan

Yoshinobu Mizuno, Masakazu Yamada, Chika ShigeyasuDivision for Vision Research, National Institute of Sensory Organs, National Tokyo Medical Center, Tokyo, JapanOn behalf of The Dry Eye Survey Group, National Hospital Organization of JapanBackground: This study was performed to estimate the annual direct cost incurred by dry eye patients, which includes expenses for treatment and drugs, as well as the cost of punctal plugs.Methods: The study group consisted of 118 dry eye patients aged 20 years or older who visited any of the 15 medical care facilities that participated in this prospective cohort dry eye study. We estimated annual direct costs from outpatient medical records and survey questionnaires obtained from patients. Results: Of the total patients enrolled, 10 were men and 108 women, and their average age was 64.1 ± 11.2 years. The number of hospital visits made by patients was 5.8 ± 3.6 per year. Among those who used ophthalmic solutions, the numbers of bottles used per year were as follows: 32.1 ± 20.8 bottles of hyaluronic acid ophthalmic solution (87 patients), 53.1 ± 42.2 bottles of artificial tears (40 patients), and 33.2 ± 23.2 bottles of over-the-counter eyedrops (15 patients). In patients with punctal plugs, 4.1 ± 3.9 plugs were used annually. The annual drug cost was 32,000 ± 21,675 Japanese yen (323 ± 219 US dollars). The clinical cost was 16,318 ± 9961 Japanese yen (165 ± 101 US dollars). The total direct costs including punctal plug treatment amounted to 52,467 ± 38,052 Japanese yen (530 ± 384 US dollars). Conclusion: Although treatment modalities for dry eye in Japan were different from those in the US and in European countries, the direct cost of dry eye patients in Japan was comparable with that reported in those countries. Considering the high prevalence of dry eye, the direct cost of this chronic condition may be significant.Keywords: burden of disease, cost, dry eye, eyedrops, quality of lif