755 research outputs found
Limitations to THz generation by optical rectification using tilted pulse fronts
Terahertz (THz) generation by optical rectification (OR) using
tilted-pulse-fronts is studied. One-dimensional (1-D) and 2-D spatial models,
which simultaneously account for (i) the nonlinear coupled interaction of the
THz and optical radiation, (ii) angular and material dispersion, (iii)
absorption, iv) self-phase modulation and (v) stimulated Raman scattering are
presented. We numerically show that the large experimentally observed cascaded
frequency down-shift and spectral broadening (cascading effects) of the optical
pump pulse is a direct consequence of THz generation. In the presence of this
large spectral broadening, the phase mismatch due to angular dispersion is
greatly enhanced. Consequently, this cascading effect in conjunction with
angular dispersion is shown to be the strongest limitation to THz generation in
lithium niobate for pumping at 1 micron. It is seen that the exclusion of these
cascading effects in modeling OR, leads to a significant overestimation of the
optical-to-THz conversion efficiency. The simulation results are supported by
experiments
Cpeb4-Mediated Translational Regulatory Circuitry Controls Terminal Erythroid Differentiation
While we have considerable understanding of the transcriptional networks controlling mammalian cell differentiation, our knowledge of posttranscriptional regulatory events is very limited. Using differentiation of primary erythroid cells as a model, we show that the sequence-specific mRNA-binding protein Cpeb4 is strongly induced by the erythroid-important transcription factors Gata1 and Tal1 and is essential for terminal erythropoiesis. By interacting with the translation initiation factor eIF3, Cpeb4 represses the translation of a large set of mRNAs, including its own mRNA. Thus, transcriptional induction and translational repression combine to form a negative feedback loop to control Cpeb4 protein levels within a specific range that is required for terminal erythropoiesis. Our study provides an example of how translational control is integrated with transcriptional regulation to precisely control gene expression during mammalian cell differentiation.Life Sciences Research Foundation (Merck Fellow)National Institutes of Health (U.S.) (Pathway to Independence Award (1K99HL118157))National Institutes of Health (U.S.) (NIH grant R01DK068348)National Institutes of Health (U.S.) (NIH grant 5P01HL066105
Terahertz-driven linear electron acceleration
The cost, size and availability of electron accelerators is dominated by the
achievable accelerating gradient. Conventional high-brightness radio-frequency
(RF) accelerating structures operate with 30-50 MeV/m gradients. Electron
accelerators driven with optical or infrared sources have demonstrated
accelerating gradients orders of magnitude above that achievable with
conventional RF structures. However, laser-driven wakefield accelerators
require intense femtosecond sources and direct laser-driven accelerators and
suffer from low bunch charge, sub-micron tolerances and sub-femtosecond timing
requirements due to the short wavelength of operation. Here, we demonstrate the
first linear acceleration of electrons with keV energy gain using
optically-generated terahertz (THz) pulses. THz-driven accelerating structures
enable high-gradient electron or proton accelerators with simple accelerating
structures, high repetition rates and significant charge per bunch. Increasing
the operational frequency of accelerators into the THz band allows for greatly
increased accelerating gradients due to reduced complications with respect to
breakdown and pulsed heating. Electric fields in the GV/m range have been
achieved in the THz frequency band using all optical methods. With recent
advances in the generation of THz pulses via optical rectification of slightly
sub-picosecond pulses, in particular improvements in conversion efficiency and
multi-cycle pulses, increasing accelerating gradients by two orders of
magnitude over conventional linear accelerators (LINACs) has become a
possibility. These ultra-compact THz accelerators with extremely short electron
bunches hold great potential to have a transformative impact for free electron
lasers, future linear particle colliders, ultra-fast electron diffraction,
x-ray science, and medical therapy with x-rays and electron beams
miR-590-3p protects against ischaemia/reperfusion injury in an oxygen-glucose deprivation and reoxygenation cellular model by regulating HMGB1/TLR4/MyD88/NF-κB signalling
miR-590-3p has been reported to be reduced in myocardial ischaemia-reperfusion (I/R) injury, but its specific role in cerebral I/R injury is still uncertain. Thus, we explored the function and mechanism of miR590-3p in cerebral I/R injury using a cellular model. miR-590-3p, high mobility group Box 1 (HMGB1), and signalling-related factor levels were assessed using qPCR or a western blot analysis. Cell apoptosis was measured by flow cytometry. Inflammatory factors were detected by ELISA. The target of miR-590-3p was confirmed by dual-luciferase reporter assay and western blot analysis. We found that miR-590-3p was decreased and HMGB1 was increased in the OGD/R model. Upregulation of miR-590-3p reduced cell apoptosis and inflammation in the OGD/R model, and the TLR4/MyD88/NF-κB signalling pathway was suppressed. However, inhibition of miR-590-3p showed the opposite effects. Moreover, HMGB1 was verified as a target gene of miR-590-3p. HMGB1 reversed the decrease in apoptosis and inflammation caused by overexpression of miR590-3p, and the TLR4/MyD88/NF-κB signalling pathway was activated. Our results suggest that miR-590-3p regulates the TLR4/MyD88/NF-κB pathway by interacting with HMGB1 to protect against OGD/R-induced I/R injury. Thus, miR-590-3p may serve as a potential therapeutic target in cerebral I/R repair
SOAPsplice: Genome-Wide ab initio Detection of Splice Junctions from RNA-Seq Data
RNA-Seq, a method using next generation sequencing technologies to sequence the transcriptome, facilitates genome-wide analysis of splice junction sites. In this paper, we introduce SOAPsplice, a robust tool to detect splice junctions using RNA-Seq data without using any information of known splice junctions. SOAPsplice uses a novel two-step approach consisting of first identifying as many reasonable splice junction candidates as possible, and then, filtering the false positives with two effective filtering strategies. In both simulated and real datasets, SOAPsplice is able to detect many reliable splice junctions with low false positive rate. The improvement gained by SOAPsplice, when compared to other existing tools, becomes more obvious when the depth of sequencing is low. SOAPsplice is freely available at http://soap.genomics.org.cn/soapsplice.html
The Cost of Clearing Fragmentation
Fragmenting clearing across multiple central counterparties (CCPs) is costly because global dealers cannot net positions across CCPs. They have to collateralize both the short position in one CCP and an offsetting long position in another CCP. This, coupled with a structural net order imbalance across CCPs, can cause prices to persistently differ across them ("the CCP basis"). Tests based on unique CCP data for interest-rate derivatives (IRDs), yield broad empirical support for this intuition and suggest that the clearing friction costs sellers clearing in LCH, the largest European CCP for IRDs, $80 million daily
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