828 research outputs found
Parity-violating asymmetry in with a pionless effective theory
Nuclear parity violation is studied with polarized neutrons in the
photodisintegration of the deuteron at low energies. A pionless effective field
theory with di-baryon fields is used for the investigation. Hadronic weak
interactions are treated by parity-violating di-baryon-nucleon-nucleon
vertices, which have undetermined coupling contants. A parity-violating
asymmetry in the process is calculated for the incident photon energy up to 30
MeV. If experimental data for the parity-violating asymmetry become available
in the future, we will be able to determine the unknown coupling contants in
the parity-violating vertices.Comment: 4 pages. A contribution to APFB2011, August 22-26, 2011, Seoul, Kore
Escherichia coli K1 RS218 Interacts with Human Brain Microvascular Endothelial Cells via Type 1 Fimbria Bacteria in the Fimbriated State
Escherichia coli K1 is a major gram-negative organism causing neonatal meningitis. E. coli K1 binding to and invasion of human brain microvascular endothelial cells (HBMEC) are a prerequisite for E. coli penetration into the central nervous system in vivo. In the present study, we showed using DNA microarray analysis that E. coli K1 associated with HBMEC expressed significantly higher levels of the fim genes compared to nonassociated bacteria. We also showed that E. coli K1 binding to and invasion of HBMEC were significantly decreased with its fimH deletion mutant and type 1 fimbria locked-off mutant, while they were significantly increased with its type 1 fimbria locked-on mutant. E. coli K1 strains associated with HBMEC were predominantly type 1 fimbria phase-on (i.e., fimbriated) bacteria. Taken together, we showed for the first time that type 1 fimbriae play an important role in E. coli K1 binding to and invasion of HBMEC and that type 1 fimbria phase-on E. coli is the major population interacting with HBMEC
Dynamical fluctuations in classical adiabatic processes: General description and their implications
Dynamical fluctuations in classical adiabatic processes are not considered by
the conventional classical adiabatic theorem. In this work a general result is
derived to describe the intrinsic dynamical fluctuations in classical adiabatic
processes. Interesting implications of our general result are discussed via two
subtopics, namely, an intriguing adiabatic geometric phase in a dynamical model
with an adiabatically moving fixed-point solution, and the possible "pollution"
to Hannay's angle or to other adiabatic phase objects for adiabatic processes
involving non-fixed-point solutions.Comment: 19 pages, no figures, discussion significantly expanded, published
versio
Rhenium complex as emitting material in highly efficient phosphorescent organic light-emitting diodes
Interest in luminescent materials able to efficiently emit in the solid state is continuously
growing, because in most applications the dyes are used as solid films. This is the case of the
Organic Light Emitting Diodes (OLEDs), where electroluminescent
metal complexes have been widely investigated as dopants, able to
increase their performances [1]. We present here a dinuclear Re(I)
complexes (1, see Scheme 1) whose emission is higher in solid state
and in PMMA matrix than in solution and is used as dopant in
OLEDs.
This complex belong to the family of neutral Re(I) complexes
with general formula [Re2(CO)6(\u3bc-1,2-diazine)(\u3bc-X)2], where X is halogen. Some of them
have recently gained interest for their intense yellow/green emission, occurring from triplet
metal-to-ligand charge transfer (3MLCT) states [2], showing a modulation effect of the
diazine substituents on wavelengths, lifetimes and quantum yields of the emission. \u3a6 up to
0.53 has been measured for the di-chloro complexes containing diazines bearing alkyl groups
in both the \u3b2 positions [3]. At variance with the chloro derivatives, the bromo analogue 1 is
almost not-emitting in solution (\u3a6em 0.002 in deareated toluene). We have now found that in
the solid state 1 shows intense yellow-orange emission (\u3a6em 0.50 in neat powder), blue
shifted with respect to the solution (560 nm vs. 620 nm). The emission is intense also in
PMMA matrix (\u3a6em 0.19 in PMMA at 10% w/w, 556 nm).
This very high aggregated emission here is discussed in terms of the restriction of the
intramolecular roto-vibrational motions of the \u201cRe2(CO)6(\u3bc-Br)2\u201d scaffold imposed by the
rigid environment, as evidenced by the strong decrease of the knr. Moreover a parallel increase
of kr is noticed, which clearly shows the influence of the halides in determining not only the
energy of the excited state, but also the nature of the lowest (emitting) state.
These properties allowed its successful use as a phosphorescent dopant in OLEDs and
here we report the performances of OLED devices prepared both by solution- and vacuumprocessing.
The values of the external quantum efficiency are 1.7% (4.3 cd/A and 1.7 lm/W)
and 10% (29.1 cd/A and 22.1 lm/W) respectively and are the highest ever reported for
rhenium-based devices, comparable to state-of-the-art devices employing Ir(III)- and Pt(II)-
based metal complexes. The combination of synthetic strategy and encouraging results in
potential OLEDs applications should make these dinuclear Re(I) complexes highly attractive
to a broad spectrum of research fields.
1. \u201cHighly efficient OLEDs with Phosphorescent Materials\u201d H. Yersin Ed. Wiley-VCH, (2008).
2. D. Donghi, G. D\u2019Alfonso, M. Mauro, M. Panigati, P. Mercandelli, A. Sironi, P. Mussini, L. D\u2019Alfonso, Inorg.
Chem. 28 (2008) 4243-4255.
3. M. Mauro, E. Quartapelle Procopio, Y. Sun, C. H. Chien, D. Donghi, M. Panigati, P. Mercandelli, P. Mussini,
G. D\u2019Alfonso, L. De Cola, Adv. Funct. Mater. 19 (2009) 2607-2614
Parity nonconservation in deuteron photoreactions
We calculate the asymmetries in parity nonconserving deuteron
photodisintegration due to circularly polarized photons gamma+d to n+p with the
photon laboratory energy ranging from the threshold up to 10 MeV and the
radiative capture of thermal polarized neutrons by protons n+p to gamma+d. We
use the leading order electromagnetic Hamiltonian neglecting the smaller
nuclear exchange currents. Comparative calculations are done by using the
Reid93 and Argonne v18 potentials for the strong interaction and the DDH and
FCDH "best" values for the weak couplings in a weak one-meson exchange
potential. A weak NDelta transition potential is used to incorporate also the
Delta(1232)-isobar excitation in the coupled-channels formalism.Comment: 14 pages, 13 figures (18 eps files), LaTeX2
Thinning leads to calving-style changes at Bowdoin Glacier, Greenland
This research has been supported by the Alfred and Flora Spälti Fund and the ETH Zurich Foundation (Sun2ice; grant no. ETH-12 16-2); the Swiss National Science Foundation (grant nos. 200021-153179/1 and PP00P2_183719); the SPI Exploratory Grants 2018 awarded to Fabian Walter and Guillaume Jouvet; the Japanese Ministry of Education, Culture, Sports, Science and Technology through the GRENE Arctic Climate Research Project and the Arctic Challenge for Sustainability (ArCS) project; and by NERC (CALISMO: Calving Laws for Ice Sheet Models; grant no. NE/P011365/1).Ice mass loss from the Greenland ice sheet is the largest single contributor to sea level rise in the 21st century. The mass loss rate has accelerated in recent decades mainly due to thinning and retreat of its outlet glaciers. The diverse calving mechanisms responsible for tidewater glacier retreat are not fully understood yet. Since a tidewater glacier's sensitivity to external forcings depends on its calving style, detailed insight into calving processes is necessary to improve projections of ice sheet mass loss by calving. As tidewater glaciers are mostly thinning, their calving styles are expected to change. Here, we study calving behaviour changes under a thinning regime at Bowdoin Glacier, north-western Greenland, by combining field and remote-sensing data from 2015 to 2019. Previous studies showed that major calving events in 2015 and 2017 were driven by hydro-fracturing and melt-undercutting. New observations from uncrewed aerial vehicle (UAV) imagery and a GPS network installed at the calving front in 2019 suggest ungrounding and buoyant calving have recently occurred as they show (1) increasing tidal modulation of vertical motion compared to previous years, (2) absence of a surface crevasse prior to calving, and (3) uplift and horizontal surface compression prior to calving. Furthermore, an inventory of calving events from 2015 to 2019 based on satellite imagery provides additional support for a change towards buoyant calving since it shows an increasing occurrence of calving events outside of the melt season. The observed change in calving style could lead to a possible retreat of the terminus, which has been stable since 2013. We therefore highlight the need for high-resolution monitoring to detect changing calving styles and numerical models that cover the full spectrum of calving mechanisms to improve projections of ice sheet mass loss by calving.Publisher PDFPeer reviewe
Apparatus for a Search for T-violating Muon Polarization in Stopped-Kaon Decays
The detector built at KEK to search for T-violating transverse muon
polarization in K+ --> pi0 mu+ nu (Kmu3) decay of stopped kaons is described.
Sensitivity to the transverse polarization component is obtained from
reconstruction of the decay plane by tracking the mu+ through a toroidal
spectrometer and detecting the pi0 in a segmented CsI(Tl) photon calorimeter.
The muon polarization was obtained from the decay positron asymmetry of muons
stopped in a polarimeter. The detector included features which minimized
systematic errors while maintaining high acceptance.Comment: 56 pages, 30 figures, submitted to NI
On the effects of the magnetic field and the isotopic substitution upon the infrared absorption of manganites
Employing a variational approach that takes into account electron-phonon and
magnetic interactions in perovskites with , the
effects of the magnetic field and the oxygen isotope substitution on the phase
diagram, the electron-phonon correlation function and the infrared absorption
at are studied. The lattice displacements show a strong correlation
with the conductivity and the magnetic properties of the system. Then the
conductivity spectra are characterized by a marked sensitivity to the external
parameters near the phase boundary.Comment: 10 figure
A straw drift chamber spectrometer for studies of rare kaon decays
We describe the design, construction, readout, tests, and performance of
planar drift chambers, based on 5 mm diameter copperized Mylar and Kapton
straws, used in an experimental search for rare kaon decays. The experiment
took place in the high-intensity neutral beam at the Alternating Gradient
Synchrotron of Brookhaven National Laboratory, using a neutral beam stop, two
analyzing dipoles, and redundant particle identification to remove backgrounds
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