63 research outputs found
Apparent giant dielectric constants, dielectric relaxation, and ac-conductivity of hexagonal perovskites La1.2Sr2.7BO7.33 (B = Ru, Ir)
We present a thorough dielectric investigation of the hexagonal perovskites
La1.2Sr2.7IrO7.33 and La1.2Sr2.7RuO7.33 in a broad frequency and temperature
range, supplemented by additional infrared measurements. The occurrence of
giant dielectric constants up to 10^5 is revealed to be due to electrode
polarization. Aside of dc and ac conductivity contributions, we detect two
intrinsic relaxation processes that can be ascribed to ionic hopping between
different off-center positions. In both materials we find evidence for charge
transport via hopping of localized charge carriers. In the infrared region,
three phonon bands are detected, followed by several electronic excitations. In
addition, these materials provide further examples for the occurrence of a
superlinear power law in the broadband ac conductivity, which recently was
proposed to be a universal feature of all disordered matter.Comment: 8 pages, 7 figure
The proton radius puzzle
High-precision measurements of the proton radius from laser spectroscopy of
muonic hydrogen demonstrated up to six standard deviations smaller values than
obtained from electron-proton scattering and hydrogen spectroscopy. The status
of this discrepancy, which is known as the proton radius puzzle will be
discussed in this paper, complemented with the new insights obtained from
spectroscopy of muonic deuterium.Comment: Moriond 2017 conference, 8 pages, 4 figure
Séparations mécaniques fluide/solide
Licencedécantation gravitaire ; centrifugations (décantation centrifuge et cyclones) ; filtrations (sur support et en profondeur
Ruthenium-based PACT agents based on bisquinoline chelates: synthesis, photochemistry, and cytotoxicity
The known ruthenium complex [Ru(tpy)(bpy)(Hmte)](PF6)(2) ([1](PF6)(2), where tpy = 2,2':6',2 ''-terpyridine, bpy = 2,2'-bipyridine, Hmte = 2-(methylthio)ethanol) is photosubstitutionally active but non-toxic to cancer cells even upon light irradiation. In this work, the two analogs complexes [Ru(tpy)(NN)(Hmte)](PF6)(2), where NN = 3,3'-biisoquinoline (i-biq, [2](PF6)(2)) and di(isoquinolin-3-yl)amine (i-Hdiqa, [3](PF6)(2)), were synthesized and their photochemistry and phototoxicity evaluated to assess their suitability as photoactivated chemotherapy (PACT) agents. The increase of the aromatic surface of [2](PF6)(2) and [3](PF6)(2), compared to [1](PF6)(2), leads to higher lipophilicity and higher cellular uptake for the former complexes. Such improved uptake is directly correlated to the cytotoxicity of these compounds in the dark: while [2](PF6)(2) and [3](PF6)(2) showed low EC50 values in human cancer cells, [1](PF6)(2) is not cytotoxic due to poor cellular uptake. While stable in the dark, all complexes substituted the protecting thioether ligand upon light irradiation (520 nm), with the highest photosubstitution quantum yield found for [3](PF6)(2) (phi([3]) = 0.070). Compounds [2](PF6)(2) and [3](PF6)(2) were found both more cytotoxic after light activation than in the dark, with a photo index of 4. Considering the very low singlet oxygen quantum yields of these compounds, and the lack of cytotoxicity of the photoreleased Hmte thioether ligand, it can be concluded that the toxicity observed after light activation is due to the photoreleased aqua complexes [Ru(tpy)(NN)(OH2)](2+), and thus that [2](PF6)(2) and [3](PF6)(2) are promising PACT candidates.[GRAPHICS].Metals in Catalysis, Biomimetics & Inorganic Material
Improved X-ray detection and particle identification with avalanche photodiodes
Avalanche photodiodes are commonly used as detectors for low energy x-rays.
In this work we report on a fitting technique used to account for different
detector responses resulting from photo absorption in the various APD layers.
The use of this technique results in an improvement of the energy resolution at
8.2 keV by up to a factor of 2, and corrects the timing information by up to 25
ns to account for space dependent electron drift time. In addition, this
waveform analysis is used for particle identification, e.g. to distinguish
between x-rays and MeV electrons in our experiment.Comment: 6 pages, 6 figure
Colossal dielectric constants in transition-metal oxides
Many transition-metal oxides show very large ("colossal") magnitudes of the
dielectric constant and thus have immense potential for applications in modern
microelectronics and for the development of new capacitance-based
energy-storage devices. In the present work, we thoroughly discuss the
mechanisms that can lead to colossal values of the dielectric constant,
especially emphasising effects generated by external and internal interfaces,
including electronic phase separation. In addition, we provide a detailed
overview and discussion of the dielectric properties of CaCu3Ti4O12 and related
systems, which is today's most investigated material with colossal dielectric
constant. Also a variety of further transition-metal oxides with large
dielectric constants are treated in detail, among them the system La2-xSrxNiO4
where electronic phase separation may play a role in the generation of a
colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in
the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator
Transitions and Ordering of Microscopic Degrees of Freedom
A tale of two worlds:assessing the vulnerability of enclave shielding runtimes
status: publishe
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