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  • 1
    Publikationsdatum: 2011-12-14
    Beschreibung: Sporadic E (Es) can have dramatic effects on communications in the HF and low VHF range, producing over-the-horizon propagation for signals normally restricted to line-of-sight, and sometimes blocking F region propagation of signals in the lower HF range. Measuring the E region winds believed to produce Es is difficult, and no practical means of predicting Es occurrence currently exists other than statistical models. We describe a low-cost observing network based on software-controlled receivers that continuously watches for Es in near-real time using oblique HF propagation from existing transmitters. Results from an 11-day pilot campaign in July 2008 demonstrated that even a limited number of receivers in the network can readily determine the presence and extent of Es patches. These observations indicate that Es often develops quickly over regions of several hundred kilometers rather than gradually drifting across an area. These widespread Es “blooms” have been observed near winter solstice and occasionally at other times of the year; their lifetime depends on the season but can be several hours during the summer. The current network allows the extent of Es in portions of North America to be evaluated: the geographical distribution of Es and bounds on the density of the layer are inferred from its effects on the ionospheric maximum usable frequency (MUF). This study demonstrates quantitatively that Es mapping can provide information about Es layer geographical growth and decay. The observed sudden widespread Es blooms are space weather events that can have significant impact on HF/lower VHF communications and propagation model predictions.
    Print ISSN: 1539-4964
    Digitale ISSN: 1542-7390
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2009-12-23
    Beschreibung: Reprogramming of somatic cell nuclei to yield induced pluripotent stem (iPS) cells makes possible derivation of patient-specific stem cells for regenerative medicine. However, iPS cell generation is asynchronous and slow (2-3 weeks), the frequency is low (〈0.1%), and DNA demethylation constitutes a bottleneck. To determine regulatory mechanisms involved in reprogramming, we generated interspecies heterokaryons (fused mouse embryonic stem (ES) cells and human fibroblasts) that induce reprogramming synchronously, frequently and fast. Here we show that reprogramming towards pluripotency in single heterokaryons is initiated without cell division or DNA replication, rapidly (1 day) and efficiently (70%). Short interfering RNA (siRNA)-mediated knockdown showed that activation-induced cytidine deaminase (AID, also known as AICDA) is required for promoter demethylation and induction of OCT4 (also known as POU5F1) and NANOG gene expression. AID protein bound silent methylated OCT4 and NANOG promoters in fibroblasts, but not active demethylated promoters in ES cells. These data provide new evidence that mammalian AID is required for active DNA demethylation and initiation of nuclear reprogramming towards pluripotency in human somatic cells.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2906123/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2906123/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bhutani, Nidhi -- Brady, Jennifer J -- Damian, Mara -- Sacco, Alessandra -- Corbel, Stephane Y -- Blau, Helen M -- AG009521/AG/NIA NIH HHS/ -- AG024987/AG/NIA NIH HHS/ -- AI007328/AI/NIAID NIH HHS/ -- R01 AG009521/AG/NIA NIH HHS/ -- R01 AG009521-25/AG/NIA NIH HHS/ -- R01 AG024987/AG/NIA NIH HHS/ -- R01 AG024987-05/AG/NIA NIH HHS/ -- T32 AI007328/AI/NIAID NIH HHS/ -- U01 HL100397/HL/NHLBI NIH HHS/ -- England -- Nature. 2010 Feb 25;463(7284):1042-7. doi: 10.1038/nature08752.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Baxter Laboratory for Stem Cell Biology, Institute for Stem Cell Biology and Regenerative Medicine, Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305-5175, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20027182" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Animals ; Cell Division ; Cell Fusion ; Cell Line ; Cells, Cultured ; Cellular Reprogramming/genetics/*physiology ; Chromatin Immunoprecipitation ; Cytidine Deaminase/deficiency/genetics/*metabolism ; DNA/chemistry/genetics/metabolism ; *DNA Methylation ; DNA Replication ; Embryonic Stem Cells/cytology/metabolism ; Fibroblasts/cytology/metabolism ; Gene Expression Regulation ; Gene Knockdown Techniques ; Homeodomain Proteins/genetics ; Humans ; Induced Pluripotent Stem Cells/*cytology/enzymology/*metabolism ; Lung/cytology/embryology ; Mice ; Models, Biological ; Octamer Transcription Factor-3/genetics ; Promoter Regions, Genetic/genetics ; Time Factors
    Print ISSN: 0028-0836
    Digitale ISSN: 1476-4687
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Standort Signatur Erwartet Verfügbarkeit
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