Genomic insight into the population history of Central Han Chinese.

BACKGROUND: In recent decades, considerable attention has been paid to exploring the population genetic characteristics of Han Chinese, mainly documenting a north-south genetic substructure. However, the central Han Chinese have been largely underrepresented in previous studies. AIM: To infer a comprehensive understanding of the homogenisation process and population history of Han Chinese. SUBJECTS AND METHODS: We collected samples from 122 Han Chinese from seven counties of Hubei province in central China and genotyped 534,000 genome-wide SNPs. We compared Hubei Han with both ancient and present-day Eurasian populations using Principal Component Analysis, ADMIXTURE, f statistics, qpWave and qpAdm. RESULTS: We observed Hubei Han Chinese are at a genetically intermediate position on the north-south Han Chinese cline. We have not detected any significant genetic substructure in the studied groups from seven different counties. Hubei Han show significant evidence of genetic admixture deriving about 63% of ancestry from Tai-Kadai or Austronesian-speaking southern indigenous groups and 37% from Tungusic or Mongolic related northern populations. CONCLUSIONS: The formation of Han Chinese has involved extensive admixture with Tai-Kadai or Austronesian-speaking populations in the south and Tungusic or Mongolic speaking populations in the north. The convenient transportation and central location of Hubei make it the key region for the homogenisation of Han Chinese.

Disparity between online and offline tests in accelerated aging tests of LED lamps under electric stress.

The accelerated aging tests under electric stress for one type of LED lamp are conducted, and the differences between online and offline tests of the degradation of luminous flux are studied in this paper. The transformation of the two test modes is achieved with an adjustable AC voltage stabilized power source. Experimental results show that the exponential fitting of the luminous flux degradation in online tests possesses a higher fitting degree for most lamps, and the degradation rate of the luminous flux by online tests is always lower than that by offline tests. Bayes estimation and Weibull distribution are used to calculate the failure probabilities under the accelerated voltages, and then the reliability of the lamps under rated voltage of 220 V is estimated by use of the inverse power law model. Results show that the relative error of the lifetime estimation by offline tests increases as the failure probability decreases, and it cannot be neglected when the failure probability is less than 1%. The relative errors of lifetime estimation are 7.9%, 5.8%, 4.2%, and 3.5%, at the failure probabilities of 0.1%, 1%, 5%, and 10%, respectively.

Analysis of junction temperature and modification of luminous flux degradation for white LEDs in a thermal accelerated reliability test.

An accelerated aging test is the main method in evaluation of the reliability of light-emitting diodes (LEDs), and the first goal of this study is to investigate how the junction temperature (Tj) of the LED varies during accelerated aging. The Tj measured by the forward voltage method shows an upward trend over the aging time, which gives a variation about 6°C-8°C after 3,000 h of aging under an ambient temperature of 80°C. The second goal is to investigate how the variation of Tj affects the lifetime estimation. It is verified that at a certain aging stage, as Tj increases, the normalized luminous flux linearly decreases with variation rate of microns (µ) (1/°C). Then, we propose a method to modify the luminous flux degradation with the Tj and µ to meet the requirements of a constant degradation rate in the data fitting. The experimental results show that with the proposed method, the accelerated lifetimes of samples are bigger than that of the current method with increment values from 8.8% to 21.4% in this research.

Pdx1 protein induces human embryonic stem cells into the pancreatic endocrine lineage.

Success in generating insulin-producing cells (IPCs) from human embryonic stem (hES) cells by genetic manipulation has recently revealed a new therapeutic potential for diabetes. However, clinical application has been hampered by the viral genome integration and the risk of insertion mutagenesis that are entailed. Herein, we report the induction of hEC into IPCs by direct delivery of human Pdx1 proteins per se. Recombinant human Pdx1 proteins (hPdx1), which have an Antennapedia-like protein transduction domain sequence in their structure, can be efficiently translocated into hES cells and function as pancreatic transcription factor. hPdx1 protein activates a group of genes related to pancreatic beta-cell lineage development in hES cells, including NeuroD1, Nkx2.2, Pax4, Pax6, Nkx6.1 and Isl-1. hPdx1-treated hES cells synthesise and release insulin in response to glucose challenge. Therefore, this study constitutes a proof-of-concept demonstration of protein-mediated pancreatic specific differentiation of the hES cells by exploiting specific intrinsic properties of the hPdx1 protein.