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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>
Complex Multicolor Tilings and Critical Phenomena in Tetraphilic Liquid Crystals
Zeng, X.,Kieffer, R.,Glettner, B.,Nurnberger, C.,Liu, F.,Pelz, K.,Prehm, M.,Baumeister, U.,Hahn, H.,Lang, H.,Gehring, G. A.,Weber, C. H. M.,Hobbs, J. K.,Tschierske, C.,Ungar, G. American Association for the Advancement of Scienc 2011 Science Vol.331 No.6022
<P>T-shaped molecules with a rod-like aromatic core and a flexible side chain form liquid crystal honeycombs with aromatic cell walls and a cell interior filled with the side chains. Here, we show how the addition of a second chain, incompatible with the first (X-shaped molecules), can form honeycombs with highly complex tiling patterns, with cells of up to five different compositions ('colors') and polygonal shapes. The complexity is caused by the inability of the side chains to separate cleanly because of geometric frustration. Furthermore, a thermoreversible transition was observed between a multicolor (phase-separated) and a single-color (mixed) honeycomb phase. This is analogous to the Curie transition in simple and frustrated ferro- and antiferromagnets; here spin flips are replaced by 180° reorientations of the molecules.</P>
Effect of chronic lead intoxication on the distribution and elimination of amoxicillin in goats
Ahmed M. Soliman,Ehab A. Abu-Basha,Salah A. H. Youssef,Aziza M. Amer,Patricia A. Murphy,Catherine C. Hauck,Ronette Gehring,Walter H. Hsu 대한수의학회 2013 Journal of Veterinary Science Vol.14 No.4
A study of amoxicillin pharmacokinetics was conducted in healthy goats and goats with chronic lead intoxication. The intoxicated goats had increased serum concentrations of liver enzymes (alanine aminotransferase and γ-glutamyl transferase),blood urea nitrogen, and reactivated δ-aminolevulinic acid dehydratase compared to the controls. Following intravenous amoxicillin (10 mg/kg bw) in control and lead-intoxicated goats,elimination half-lives were 4.14 and 1.26 h, respectively. The volumes of distribution based on the terminal phase were 1.19and 0.38 L/kg, respectively, and those at steady-state were 0.54and 0.18 L/kg, respectively. After intramuscular (IM)amoxicillin (10 mg/kg bw) in lead-intoxicated goats and control animals, the absorption, distribution, and elimination of the drug were more rapid in lead-intoxicated goats than the controls. Peak serum concentrations of 21.89 and 12.19 μg/mL were achieved at 1 h and 2 h, respectively, in lead-intoxicated and control goats. Amoxicillin bioavailability in the lead-intoxicated goats decreased 20% compared to the controls. After amoxicillin, more of the drug was excreted in the urine from lead-intoxicated goats than the controls. Our results suggested that lead intoxication in goats increases the rate of amoxicillin absorption after IM administration and distribution and elimination. Thus, lead intoxication may impair the therapeutic effectiveness of amoxicillin.