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  • American Institute of Physics (AIP)  (3)
  • Nature Publishing Group (NPG)  (2)
  • 1
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    Non-blinking semiconductor nanocrystals (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-05-12
    Description: The photoluminescence from a variety of individual molecules and nanometre-sized crystallites is defined by large intensity fluctuations, known as 'blinking', whereby their photoluminescence turns 'on' and 'off' intermittently, even under continuous photoexcitation. For semiconductor nanocrystals, it was originally proposed that these 'off' periods corresponded to a nanocrystal with an extra charge. A charged nanocrystal could have its photoluminescence temporarily quenched owing to the high efficiency of non-radiative (for example, Auger) recombination processes between the extra charge and a subsequently excited electron-hole pair; photoluminescence would resume only after the nanocrystal becomes neutralized again. Despite over a decade of research, completely non-blinking nanocrystals have not been synthesized and an understanding of the blinking phenomenon remains elusive. Here we report ternary core/shell CdZnSe/ZnSe semiconductor nanocrystals that individually exhibit continuous, non-blinking photoluminescence. Unexpectedly, these nanocrystals strongly photoluminesce despite being charged, as indicated by a multi-peaked photoluminescence spectral shape and short lifetime. To model the unusual photoluminescence properties of the CdZnSe/ZnSe nanocrystals, we softened the abrupt confinement potential of a typical core/shell nanocrystal, suggesting that the structure is a radially graded alloy of CdZnSe into ZnSe. As photoluminescence blinking severely limits the usefulness of nanocrystals in applications requiring a continuous output of single photons, these non-blinking nanocrystals may enable substantial advances in fields ranging from single-molecule biological labelling to low-threshold lasers.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wang, Xiaoyong -- Ren, Xiaofan -- Kahen, Keith -- Hahn, Megan A -- Rajeswaran, Manju -- Maccagnano-Zacher, Sara -- Silcox, John -- Cragg, George E -- Efros, Alexander L -- Krauss, Todd D -- England -- Nature. 2009 Jun 4;459(7247):686-9. doi: 10.1038/nature08072.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, University of Rochester, Rochester, New York 14627, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19430463" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
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    Small molecule inhibition of the KRAS-PDEdelta interaction impairs oncogenic KRAS signalling (2013)
    Nature Publishing Group (NPG)
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    Publication Date: 2013-05-24
    Description: The KRAS oncogene product is considered a major target in anticancer drug discovery. However, direct interference with KRAS signalling has not yet led to clinically useful drugs. Correct localization and signalling by farnesylated KRAS is regulated by the prenyl-binding protein PDEdelta, which sustains the spatial organization of KRAS by facilitating its diffusion in the cytoplasm. Here we report that interfering with binding of mammalian PDEdelta to KRAS by means of small molecules provides a novel opportunity to suppress oncogenic RAS signalling by altering its localization to endomembranes. Biochemical screening and subsequent structure-based hit optimization yielded inhibitors of the KRAS-PDEdelta interaction that selectively bind to the prenyl-binding pocket of PDEdelta with nanomolar affinity, inhibit oncogenic RAS signalling and suppress in vitro and in vivo proliferation of human pancreatic ductal adenocarcinoma cells that are dependent on oncogenic KRAS. Our findings may inspire novel drug discovery efforts aimed at the development of drugs targeting oncogenic RAS.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zimmermann, Gunther -- Papke, Bjorn -- Ismail, Shehab -- Vartak, Nachiket -- Chandra, Anchal -- Hoffmann, Maike -- Hahn, Stephan A -- Triola, Gemma -- Wittinghofer, Alfred -- Bastiaens, Philippe I H -- Waldmann, Herbert -- England -- Nature. 2013 May 30;497(7451):638-42. doi: 10.1038/nature12205. Epub 2013 May 22.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemical Biology, Max Planck Institute of Molecular Physiology, D-44227 Dortmund, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23698361" target="_blank"〉PubMed〈/a〉
    Keywords: Adenocarcinoma/drug therapy/genetics/metabolism ; Animals ; Benzimidazoles/*chemistry/metabolism/*pharmacology/therapeutic use ; Binding Sites ; Carcinoma, Pancreatic Ductal/drug therapy/genetics/metabolism ; Cell Line ; Cell Line, Tumor ; Cell Proliferation/drug effects ; Cyclic Nucleotide Phosphodiesterases, Type 6/antagonists & ; inhibitors/chemistry/*metabolism ; Dogs ; Humans ; Hydrogen Bonding ; MAP Kinase Signaling System/drug effects ; Mice ; Mice, Nude ; Mitogen-Activated Protein Kinases/metabolism ; Models, Molecular ; Molecular Conformation ; Neoplasm Transplantation ; Oncogene Protein p21(ras)/*antagonists & inhibitors/genetics/*metabolism ; Protein Binding/drug effects ; Signal Transduction/*drug effects
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-03-10
    Description: Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by American Institute of Physics (AIP)
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  • 4
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    The cryogenic storage ring CSR (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-06-17
    Description: An electrostatic cryogenic storage ring, CSR, for beams of anions and cations with up to 300 keV kinetic energy per unit charge has been designed, constructed, and put into operation. With a circumference of 35 m, the ion-beam vacuum chambers and all beam optics are in a cryostat and cooled by a closed-cycle liquid helium system. At temperatures as low as (5.5 ± 1) K inside the ring, storage time constants of several minutes up to almost an hour were observed for atomic and molecular, anion and cation beams at an energy of 60 keV. The ion-beam intensity, energy-dependent closed-orbit shifts (dispersion), and the focusing properties of the machine were studied by a system of capacitive pickups. The Schottky-noise spectrum of the stored ions revealed a broadening of the momentum distribution on a time scale of 1000 s. Photodetachment of stored anions was used in the beam lifetime measurements. The detachment rate by anion collisions with residual-gas molecules was found to be extremely low. A residual-gas density below 140 cm −3 is derived, equivalent to a room-temperature pressure below 10 −14 mbar. Fast atomic, molecular, and cluster ion beams stored for long periods of time in a cryogenic environment will allow experiments on collision- and radiation-induced fragmentation processes of ions in known internal quantum states with merged and crossed photon and particle beams.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    A technique for verifying the input response function of neutron time-of-flight scintillation detectors using cosmic raysa) (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-07
    Description: An accurate interpretation of DD or DT fusion neutron time-of-flight (nTOF) signals from current mode detectors employed at the Z-facility at Sandia National Laboratories requires that the instrument response functions (IRF’s) be deconvolved from the measured nTOF signals. A calibration facility that produces detectable sub-ns radiation pulses is typically used to measure the IRF of such detectors. This work, however, reports on a simple method that utilizes cosmic radiation to measure the IRF of nTOF detectors, operated in pulse-counting mode. The characterizing metrics reported here are the throughput delay and full-width-at-half-maximum. This simple approach yields consistent IRF results with the same detectors calibrated in 2007 at a LINAC bremsstrahlung accelerator (Idaho State University). In particular, the IRF metrics from these two approaches and their dependence on the photomultipliers bias agree to within a few per cent. This information may thus be used to verify if the IRF for a given nTOF detector employed at Z has changed since its original current-mode calibration and warrants re-measurement.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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