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  • 1
    Electronic Resource
    Electronic Resource
    Telomerase down-regulation does not mediate PC12 pheochromocytoma cell differentiation induced by NGF, but requires MAP kinase signalling (2005)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 95 (2005), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Telomerase is a ribonucleoprotein complex that maintains chromosomal telomere homeostasis and underlies continuous renewal of stem cells and immortalization of neoplastic cells. Telomerase is down-regulated during cell differentiation, but the mechanisms of down-regulation are largely unknown. Here, we examined roles of mitogen-activated protein (MAP) kinase and phosphatidylinositol-3 (PI3) kinase signalling pathways in telomerase down-regulation triggered by nerve growth factor (NGF), and the role of telomerase down-regulation in NGF-induced neural differentiation in PC12 cells. We report that NGF-induced telomerase down-regulation requires MAP kinase signalling. While mutations of all putative Akt phosphorylation sites in telomerase reverse transcriptase (TERT) has no effect on telomerase activity, inhibition of MAP kinase signalling by PD98059 or U0126 abolishes NGF-induced telomerase down-regulation in a concentration-dependent manner. Reversal of NGF-induced telomerase down-regulation by TERT overexpression does not prevent NGF-induced neural differentiation. Down-regulation of telomerase by silencing TERT gene expression does not trigger cell differentiation in the absence of NGF, nor enhances NGF-induced differentiation. Thus, telomerase, withdraws by a mechanism at TERT gene transcription level involving MAP kinase signalling while cells cease proliferation and undergo differentiation. The withdrawal of telomerase is not required to mediate NGF-induced PC12 cell differentiation and re-establishment of telomerase activity at significant levels does not inhibit differentiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.2005.03439.x
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    Paper (German National Licenses)
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  • 2
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    Parameter study for enhanced high gain harmonic generation scheme (2011)
    Institute of Physics (IOP)
    Details
    Publication Date: 2011-09-17
    Description: An easy-to-implement scheme called Enhanced High Gain Harmonic Generation is expected to be able to significantly enhance the performance of HG-FEL. In this paper we investigate the effects of the system parameters in the new scheme, including the electron energy detuning, initial electron-beam energy spread, seeding laser power, dispersive field strength and amount of the phase shift, etc. The numerical results from GENESIS (3D-code) are presented and show that the new scheme has acceptable parameters tolerance requirements and is no more or even less sensitive to the system parameters than that of the existing scheme; With the electron energy above the resonance, the efficiency is enhanced for both the new scheme and the existing scheme compared with the resonant energy case.
    Print ISSN: 1674-1137
    Topics: Physics
    Published by Institute of Physics (IOP)
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  • 3
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    Harmonics suppression effect of the quasi-periodic undulator in SASE free-electron-laser (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-06-22
    Description: In this paper, the harmonics suppression effect of quasi-periodic undulators (QPUs) in self-amplified spontaneous emission free-electron laser (SASE FEL) is investigated. The numerical results show that the harmonics power is reduced by using QPUs, but the fundamental radiation power also has a pronounced decrease as the saturation length gets very long. The cases of employing QPUs as parts of undulators are studied. The calculations show that if the fraction of QPUs and their offgap are appropriate in an undulator system, the harmonics radiation could be suppressed remarkably, meanwhile the fundamental saturation length does not increase too much.
    Print ISSN: 1674-1137
    Topics: Physics
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  • 4
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    Optimization of single-step tapering amplitude and energy detuning for high-gain FELs (2015)
    Institute of Physics (IOP)
    Details
    Publication Date: 2015-01-15
    Description: We put forward a method to optimize the single-step tapering amplitude of undulator strength and initial energy tuning of electron beam to maximize the saturation power of high gain free-electron lasers (FELs), based on the physics of longitudinal electron beam phase space. Using the FEL simulation code GENESIS, we numerically demonstrate the accuracy of the estimations for parameters corresponding to the linac coherent light source and the Tesla test facility.
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  • 5
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    Enhanced high gain harmonic generation scheme with negative dispersion (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-02-22
    Description: The enhanced high gain harmonic generation (EHGHG) scheme has been proposed and shown to be able to significantly enhance the performance of HGHG FEL. In this paper we investigate the EHGHG scheme with negative dispersion. The bunching factor at the entrance of the radiator is analyzed, which indicates that the scheme with negative dispersion can further weaken the negative effect of the dispersive strength on the energy spread correction factor. The numerical results from GENESIS (3D-code) are presented, and are in good agreement with our analysis. Then we comparatively study the effects of the initial beam energy spread and the relative phase shift on the radiation power. The results show that the EHGHG scheme with negative dispersion has a larger tolerance on the initial beam energy spread and a nearly equal wide good region of the relative phase shift compared with the case of positive dispersion.
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    Topics: Physics
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  • 6
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    Physical design of a wavelength tunable fully coherent VUV source using a self-seeding free electron laser (2014)
    Institute of Physics (IOP)
    Details
    Publication Date: 2014-05-14
    Description: In order to meet the requirements of the synchrotron radiation users, a fully coherent VUV free electron laser (FEL) has been preliminarily designed. One important goal of this design is that the radiation wavelength can be easily tuned in a broad range (70–170 nm). In the light of the users' demand and our actual conditions, the self-seeding scheme is adopted for this proposal. Firstly, we attempted to fix the electron energy and only changed the undulator gap to vary the radiation wavelength; however, our analysis implies that this is difficult because of the great difference of the power gain length and FEL efficiency at different wavelengths. Therefore, we have considered dividing the wavelength range into three subareas. In each subarea, a constant electron energy is used and the wavelength tuning is realized only by adjusting the undulator gap. The simulation results show that this scheme has an acceptable performance.
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    Topics: Physics
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  • 7
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    Performance study of the neutron-TPC (2017)
    Institute of Physics (IOP)
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    Publication Date: 2017-02-21
    Description: Fast neutron spectrometers will play an important role in the future of the nuclear industry and nuclear physics experiments, in tasks such as fast neutron reactor monitoring, thermo-nuclear fusion plasma diagnostics, nuclear reaction cross-section measurement, and special nuclear material detection. Recently, a new fast neutron spectrometer based on a GEM (Gas Electron Multiplier amplification)-TPC (Time Projection Chamber), named the neutron-TPC, has been under development at Tsinghua University. It is designed to have a high energy resolution, high detection efficiency, easy access to the medium material, an outstanding n/ γ suppression ratio, and a wide range of applications. This paper presents the design, test, and experimental study of the neutron-TPC. Based on the experimental results, the energy resolution (FWHM) of the neutron-TPC can reach 15.7%, 10.3% and 7.0% with detection efficiency higher than 10 −5 for 1.2 MeV, 1.81 MeV and 2.5 MeV neutrons respe...
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  • 8
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    Study of influence of radial matcher section end shape on RFQ cavity frequency (2014)
    Institute of Physics (IOP)
    Details
    Publication Date: 2014-07-24
    Description: To investigate the feasibility of using a form cutter to machine the Radial Matcher Section (RMS) of the Radio Frequency Quadrupole (RFQ) for the Accelerator Driven System (ADS) project at Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS), the influence of RMS end shape on the RFQ cavity frequency is studied. The results indicate that using a form cutter to machine the RMS of an RFQ will indeed influence the cavity frequency. The RMS end shape will give more influence to a shorter RFQ cavity. For the 4.2 m ADS RFQ, the influence is negligible, which means that a form cutter can be used to machine the RMS.
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  • 9
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    Calculation and analysis of the magnetic field of a linearly tapered undulator (2015)
    Institute of Physics (IOP)
    Details
    Publication Date: 2015-08-06
    Description: There is an empirical formula describing the relationship between the peak magnetic field and the undulator structure parameters for a uniform-parameter hybrid undulator. In this paper, we investigate the relationship for a linearly tapered undulator through numerical calculation by using the code RADIA, and check it with the empirical formula. The results imply that this empirical formula is also effective for linearly tapered undulators at a big enough scope for the requirements of normal FEL experiments. Therefore, for a linearly tapered undulator, we can use the empirical formula to design the variation of the undulator gap. For the tapering rate demanded by normal FEL experiments, the gap of a linearly tapered undulator increases almost linearly, and the tapering rate will keep constant while adjusting the undulator gap with the same variation for each undulator period.
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    Topics: Physics
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  • 10
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    Recent progress in AMS measurement of 182 Hf at the CIAE (2012)
    Institute of Physics (IOP)
    Details
    Publication Date: 2012-12-01
    Description: In order to improve the accuracy of accelerator mass spectrometry (AMS) measurement for 182 Hf/ 180 Hf, a series of measurements have been taken in the AMS laboratory at the China Institute of Atomic Energy (CIAE). The major ones include the instantaneous monitoring of 180 HfF − 5 current, testing the stability of transmission, the alternate measurements of an unknown sample and standard, and the origin identification and minimization of background 182 W. The experimental details and the improvement in the measurement accuracy, as well as some useful suggestions for better satisfying the requirements of certain practical applications, are presented in this paper.
    Print ISSN: 1674-1137
    Topics: Physics
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