160 research outputs found
Luminescent Complexes of Europium (III) with 2-(Phenylethynyl)-1,10-phenanthroline: The Role of the Counterions
New antenna ligand, 2-(phenylethynyl)-1,10-phenanthroline (PEP), and its luminescent Eu
(III) complexes, Eu(PEP)2Cl3 and Eu(PEP)2
(NO3
)3
, are synthesized and characterized. The synthetic
procedure applied is based on reacting of europium salts with ligand in hot acetonitrile solutions in
molar ratio 1 to 2. The structure of the complexes is refined by X-ray diffraction based on the single
crystals obtained. The compounds [Eu(PEP)2Cl3
]·2CH3CN and [Eu(PEP)2
(NO3
)3
]·2CH3CN crystal ize in monoclinic space group P21/n and P21/c, respectively, with two acetonitrile solvent molecules.
Intra- and inter-ligand π-π stacking interactions are present in solid stat and are realized between
the phenanthroline moieties, as well as between the substituents and the phenanthroline units. The
optical properties of the complexes are investigated in solid state, acetonitrile and dichloromethane
solution. Both compounds exhibit bright red luminescence caused by the organic ligand acting as
antenna for sensitization of Eu (III) emission. The newly designed complexes differ in counter ions
in the inner coordination sphere, which allows exploring their influence on the stability, molecular
and supramolecular structure, fluorescent properties and symmetry of the Eu (III) ion. In addition,
molecular simulations are performed in order to explain the observed experimental behavior of the
complexes. The discovered structure-properties relationships give insight on the role of the counter
ions in the molecular design of new Eu (III) based luminescent materials
Spiky strings and single trace operators in gauge theories
We consider single trace operators of the form O_{m_1 ... m_n} = tr D_+^{m_1}
F ... D_+^{m_n} F which are common to all gauge theories. We argue that, when
all m_i are equal and large, they have a dual description as strings with
cusps, or spikes, one for each field F. In the case of N=4 SYM, we compute the
energy as a function of angular momentum by finding the corresponding solutions
in AdS_5 and compare with a 1-loop calculation of the anomalous dimension. As
in the case of two spikes (twist two operators), there is agreement in the
functional form but not in the coupling constant dependence. After that, we
analyze the system in more detail and find an effective classical mechanics
describing the motion of the spikes. In the appropriate limit, it is the same
(up to the coupling constant dependence) as the coherent state description of
linear combinations of the operators O_{m_1 ... m_n} such that all m_i are
equal on average. This agreement provides a map between the operators in the
boundary and the position of the spikes in the bulk. We further suggest that
moving the spikes in other directions should describe operators with
derivatives other than D_+ indicating that these ideas are quite generic and
should help in unraveling the string description of the large-N limit of gauge
theories.Comment: 23 pages, 5 figures. v2: References and comments adde
UV and EUV Instruments
We describe telescopes and instruments that were developed and used for
astronomical research in the ultraviolet (UV) and extreme ultraviolet (EUV)
regions of the electromagnetic spectrum. The wavelength ranges covered by these
bands are not uniquely defined. We use the following convention here: The EUV
and UV span the regions ~100-912 and 912-3000 Angstroem respectively. The
limitation between both ranges is a natural choice, because the hydrogen Lyman
absorption edge is located at 912 Angstroem. At smaller wavelengths,
astronomical sources are strongly absorbed by the interstellar medium. It also
marks a technical limit, because telescopes and instruments are of different
design. In the EUV range, the technology is strongly related to that utilized
in X-ray astronomy, while in the UV range the instruments in many cases have
their roots in optical astronomy. We will, therefore, describe the UV and EUV
instruments in appropriate conciseness and refer to the respective chapters of
this volume for more technical details.Comment: To appear in: Landolt-Boernstein, New Series VI/4A, Astronomy,
Astrophysics, and Cosmology; Instruments and Methods, ed. J.E. Truemper,
Springer-Verlag, Berlin, 201
Finite-Size Corrections to Anomalous Dimensions in N=4 SYM Theory
The scaling dimensions of large operators in N=4 supersymmetric Yang-Mills
theory are dual to energies of semiclassical strings in AdS(5)xS(5). At one
loop, the dimensions of large operators can be computed with the help of Bethe
ansatz and can be directly compared to the string energies. We study
finite-size corrections for Bethe states which should describe quantum
corrections to energies of extended semiclassical strings.Comment: 10 page
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Design and Analysis of Cognitive Interviews for Comparative Multinational Testing
This article summarizes the work of the Comparative Cognitive Testing Workgroup, an international coalition of survey methodologists interested in developing an evidence-based methodology for examining the comparability of survey questions within cross-cultural or multinational contexts. To meet this objective, it was necessary to ensure that the cognitive interviewing (CI) method itself did not introduce method bias. Therefore, the workgroup first identified specific characteristics inherent in CI methodology that could undermine the comparability of CI evidence. The group then developed and implemented a protocol addressing those issues. In total, 135 cognitive interviews were conducted by participating countries. Through the process, the group identified various interpretive patterns resulting from sociocultural and language-related differences among countries as well as other patterns of error that would impede comparability of survey data
Engagement in entrepreneurship in emerging economies: interactive effects of individual-level factors and institutional conditions
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Pyruvate kinase M2 activators promote tetramer formation and suppress tumorigenesis
Cancer cells engage in a metabolic program to enhance biosynthesis and support cell proliferation. The regulatory properties of pyruvate kinase M2 (PKM2) influence altered glucose metabolism in cancer. PKM2 interaction with phosphotyrosine-containing proteins inhibits enzyme activity and increases availability of glycolytic metabolites to support cell proliferation. This suggests that high pyruvate kinase activity may suppress tumor growth. We show that expression of PKM1, the pyruvate kinase isoform with high constitutive activity, or exposure to published small molecule PKM2 activators inhibit growth of xenograft tumors. Structural studies reveal that small molecule activators bind PKM2 at the subunit interaction interface, a site distinct from that of the endogenous activator fructose-1,6-bisphosphate (FBP). However, unlike FBP, binding of activators to PKM2 promotes a constitutively active enzyme state that is resistant to inhibition by tyrosine-phosphorylated proteins. These data support the notion that small molecule activation of PKM2 can interfere with anabolic metabolism
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