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Integral Neutronics Experiment with a Mock-up of the European HCLL-TBM for ITER
A. Klix,U. Fischer,D. Lebrun-Grandie,P. Batistoni,S. Villari,R. Bottger,K. Fleischer,J. Henniger,D. Gehre,M. Sommer 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
An ITER TBM mock-up made of lithium-lead and sheets of EUROFER was irradiated with short pulses of DT neutrons from the neutron generator at TU Dresden, and time-of-arrival spectra of the slow neutron flux were measured by means of a ^3He counter in two regions inside the mock-up. Fast neutron spectra were obtained by continuous irradiation of the mock-up with DT neutrons and application of a NE-213 spectrometer. The same mock-up was also irradiated at the Frascati Neutron Generator and tritium production rates were measured by means of Li_2CO_3 pellet detectors and LiF thermoluminescense detectors (TLD) inserted into the mock-up. In case of the first type of detectors, the accumulated tritium activity was measured while with the LiF TLD the tritium production rate was obtained from the dose deposited in the detector by the tritium-producing reactions. The Calculation/Experiment ratio for the TPR measurement was nearly 1.0 with an uncertainty of approximately 7.4%. Preliminary results from calculations with FENDL-2.1 and JEFF-3.1.1 suggest a good agreement between experiment and calculation.
The nELBE Neutron Time of Flight Facility
A. R. Junghans,E. Altstadt,R. Beyer,E. Birgersson,T. Cowan,A. Ferrari,R. Hannaske,A. Matic,K. D. Schilling,R. Schlenk,S. Schneider,R. Schwengner,A. Wagner,F. -P. Weiss,D. Gehre,E. Grosse 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
At the superconducting electron linear accelerator ELBE at Forschungszentrum Dresden-Rossendorf the neutron time-of-flight facility nELBE has become operational. Fast neutrons in the energy range from 200 keV to 10 MeV are produced by the pulsed electron beam from ELBE impinging on a liquid lead circuit as a radiator. The short beam pulses of 10 ps provide the basis for an excellent time resolution for neutron time-of-flight experiments, giving an energy resolution of about <1% at 1 MeV with a short flight path of 5 m. The neutron intensity on target is ∼4·10^4 n/(cm^2 s) using an electron bunch charge of 77 pC and 100 kHz pulse repetition rate. The energy range of the neutrons produced is well suited for neutron cross section measurements relevant for the development of Generation IV reactor systems and for the transmutation of nuclear waste. First measurements of inelastic neutron scattering cross sections have been performed and will be presented.
Tunable optical time delay of quantum signals using a prism pair
Gehring, George M.,Shin, Heedeuk,Boyd, Robert W.,Kim, Chil-Min,Ham, Byoung S. The Optical Society 2010 Optics express Vol.18 No.18
<P>We describe a compact, tunable, optical time-delay module that functions by means of total internal reflection within two glass prisms. The delay is controlled by small mechanical motions of the prisms. The device is inherently extremely broad band, unlike time delay modules based on 'slow light' methods. In the prototype device that we fabricated, we obtain time delays as large as 1.45 ns in a device of linear dimensions of the order of 3.6 cm. We have delayed pulses with a full width at half-maximum pulse duration of 25 fs, implying a delay bandwidth product (measured in delay time divided by the FWHM pulse width) of 5.8x10(4). We also show that the dispersion properties of this device are sufficiently small that quantum features of a light pulse are preserved upon delay.</P>
R. Kern,N. Gehring,J. Deutscher,M. Meißner 제어로봇시스템학회 2018 제어로봇시스템학회 국제학술대회 논문집 Vol.2018 No.10
This paper considers the model-based control of a pneumatic system, where a tank is connected to a valve via a long tube. Due to the significant distance between the control input and the pressure in the tank to be controlled, a distributed-parameter model is used for the tube, involving quasilinear hyperbolic partial differential equations. In contrast, the tank is modelled by ordinary differential equations. Experimental data verifies the validity of the corresponding quasilinear system model. Based on a less accurate, linear PDE-ODE system model, derived there upon, both, a backstepping controller and a backstepping observer are designed. The resulting output feedback controller is augmented by a flatness-based feedforward controller. Experimental results for tube lengths of approximately five and twenty meters show that this controller allows to track fast pressure changes in the tank almost perfectly.
Acoustic phonon lifetimes limit thermal transport in methylammonium lead iodide
Gold-Parker, Aryeh,Gehring, Peter M.,Skelton, Jonathan M.,Smith, Ian C.,Parshall, Dan,Frost, Jarvist M.,Karunadasa, Hemamala I.,Walsh, Aron,Toney, Michael F. National Academy of Sciences 2018 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.115 No.47
<▼1><P><B>Significance</B></P><P>Hybrid organic–inorganic perovskites are a promising class of materials for efficient and low-cost solar cells. Unlike conventional inorganic semiconductors such as silicon and gallium arsenide, hybrid perovskites feature significant dynamic disorder in their crystal structure. This dynamic disorder can be broadly classified into lattice vibrations (phonons) and molecular rotations. Phonons interact with charge carriers through electron–phonon coupling, which has substantial impacts on the operation of solar cells. Our study shows that acoustic phonons, the type responsible for transmitting heat in conventional semiconductors, have extraordinarily short lifetimes in the archetypal hybrid perovskite methylammonium lead iodide. These short lifetimes have direct implications on the cooling and transport of electrons and reflect a key difference between hybrid perovskites and conventional photovoltaic semiconductors.</P></▼1><▼2><P>Hybrid organic–inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications. Electron–phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. We report high-precision momentum-resolved measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high-energy resolution and fully deuterated single crystals to reduce incoherent scattering from hydrogen. Our measurements reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths and demonstrating that acoustic phonons are unable to dissipate heat efficiently. Lattice-dynamics calculations using ab initio third-order perturbation theory indicate that the short lifetimes stem from strong three-phonon interactions and a high density of low-energy optical phonon modes related to the degrees of freedom of the organic cation. Such short lifetimes have significant implications for electron–phonon coupling in MAPI and other HOIPs, with direct impacts on optoelectronic devices both in the cooling of hot carriers and in the transport and recombination of band edge carriers. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors and demonstrate the importance of understanding lattice dynamics in the effort to develop metal halide perovskite optoelectronic devices.</P></▼2>
Optimization of single-gate carbon-nanotube field-effect transistors
Ungersboeck, E.,Pourfath, M.,Kosina, H.,Gehring, A.,Cheong, Byoung-Ho,Park, Wan-Jun,Selberherr, S. IEEE 2005 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol.4 No.5
The performance of Schottky-barrier carbon-nanotube field-effect transistors (CNTFETs) critically depends on the device geometry. Asymmetric gate contacts, the drain and source contact thickness, and inhomogenous dielectrics above and below the nanotube influence the device operation. An optimizer has been used to extract geometries with steep subthreshold slope and high I<SUB>on</SUB>/I<SUB>off</SUB> ratio. It is found that the best performance improvements can be achieved using asymmetric gates centered above the source contact, where the optimum position and length of the gate contact varies with the oxide thickness. The main advantages of geometries with asymmetric gate contacts are the increased I<SUB>on</SUB>/I<SUB>off</SUB> ratio and the fact that the gate voltage required to attain minimum drain current is shifted toward zero, whereas symmetric geometries require V<SUB>g</SUB>=V<SUB>d</SUB>/2. Our results suggest that the subthreshold slope of single-gate CNTFETs scales linearly with the gate-oxide thickness and can be reduced by a factor of two reaching a value below 100 mV/dec for devices with oxide thicknesses smaller than 5 nm by geometry optimization.
AMPK Promotes Aberrant PGC1β Expression To Support Human Colon Tumor Cell Survival
Fisher, Kurt W.,Das, Binita,Kim, Hyun Seok,Clymer, Beth K.,Gehring, Drew,Smith, Deandra R.,Costanzo-Garvey, Diane L.,Fernandez, Mario R.,Brattain, Michael G.,Kelly, David L.,MacMillan, John,White, Mic American Society for Microbiology 2015 Molecular and cellular biology Vol.35 No.22
<P>A major goal of cancer research is the identification of tumor-specific vulnerabilities that can be exploited for the development of therapies that are selectively toxic to the tumor. We show here that the transcriptional coactivators peroxisome proliferator-activated receptor gamma coactivator 1β (PGC1β) and estrogen-related receptor α (ERRα) are aberrantly expressed in human colon cell lines and tumors. With kinase suppressor of Ras 1 (KSR1) depletion as a reference standard, we used <U>fu</U>nctional <U>si</U>gnature <U>on</U>tology (FUSION) analysis to identify the γ1 subunit of AMP-activated protein kinase (AMPK) as an essential contributor to PGC1β expression and colon tumor cell survival. Subsequent analysis revealed that a subunit composition of AMPK (α2β2γ1) is preferred for colorectal cancer cell survival, at least in part, by stabilizing the tumor-specific expression of PGC1β. In contrast, PGC1β and ERRα are not detectable in nontransformed human colon epithelial cells, and depletion of the AMPKγ1 subunit has no effect on their viability. These data indicate that Ras oncogenesis relies on the aberrant activation of a PGC1β-dependent transcriptional pathway via a specific AMPK isoform.</P>