929 research outputs found
Spin relaxation dynamics of radical-pair processes at low magnetic fields
We report measurements of room-temperature spin-relaxation times and
of charge-carrier spins in a -conjugated polymer thin film under
bipolar injection and low (1\mbox{ mT}\lesssim B_0\lesssim 10\mbox{ mT})
static magnetic fields, using electrically detected magnetic resonant Hahn-echo
and inversion-recovery pulse sequences. The experiments confirm the correlation
between the magnetic-field sensitive observables of radical-pair processes,
which include both the spin-dependent recombination currents in organic
semiconductors and the associated spin-relaxation times when random local
hyperfine fields and external magnetic fields compete in magnitude. Whereas a
striking field dependence of spin-lattice relaxation exists in the low-field
regime, the apparent spin decoherence time remains field independent as the
distinction between the two is lifted at low fields.Comment: Manuscript: 14 pages, 4 figures; Supplemental Material: 13 pages, 7
figure
Morphology effects on spin-dependent transport and recombination in polyfluorene thin films
We have studied the role of spin-dependent processes on conductivity in
polyfluorene (PFO) thin films by conducting continuous wave (c.w.) electrically
detected magnetic resonance (EDMR) spectroscopy at temperatures between 10 K
and 293 K using microwave frequencies between about 100 MHz and 20 GHz as well
as pulsed EDMR at X-band. Variable frequency EDMR allows us to establish the
role of spin-orbit coupling in spin-dependent processes, pulsed EDMR probes
coherent spin motion effects. We used PFO for this study in order to allow for
the investigation of the effects of microscopic morphological ordering since
this material can adopt two distinct intrachain morphologies: an amorphous
(glassy) phase, and an ordered (beta) phase. In thin films of organic
light-emitting diodes (OLEDs) the appearance of a particular phase can be
controlled by deposition parameters, and is verified by electroluminescence
spectroscopy. We conducted multi-frequency c.w. EDMR, electrically detected
Rabi spinbeat experiments, Hahn-echo and inversion-recovery measurements.
Coherent echo spectroscopy reveals electrically detected electron spin-echo
envelope modulation (ESEEM) due to the precession of the carrier spins around
the protons. Our results demonstrate that while conformational disorder can
influence the observed EDMR signals, including the sign of the current changes
on resonance as well as the magnitudes of local hyperfine fields and charge
carrier spin-orbit interactions, it does not qualitatively affect the nature of
spin-dependent transitions in this material. At 293 K and 10 K, polaron-pair
recombination through weakly spin-spin coupled intermediate charge carrier pair
states is dominant, while at low temperatures, additional signatures of
spin-dependent charge transport through the interaction of polarons with
triplet excitons are seen in the half-field resonance of a triplet spin-1
species.Comment: 27 pages, 2 tables, 11 figures, full abstract in articl
PCN47 CHANGE OF ANTIFUNGAL TREATMENT PATTERNS AND ASSOCIATED COSTS IN PATIENTS WITH ACUTE MYELOGENOUS LEUKEMIA (AML) AFTER CHEMOTHERAPY IN A GERMAN HOSPITAL FROM 2004 TO 2006
Non-Bloch-Siegert-type power-induced shift of two-photon electron paramagnetic resonances of charge-carrier spin states in an OLED
We present Floquet theory-based predictions and electrically detected
magnetic resonance (EDMR) experiments scrutinizing the nature of two-photon
magnetic resonance shifts of charge-carrier spin states in the perdeuterated
-conjugated polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene
vinylene] (d-MEH-PPV) under strong magnetic resonant drive conditions
(radiation amplitude ~ Zeeman field ). Numerical calculations show
that the two-photon resonance shift with power is nearly drive-helicity
independent. This is in contrast to the one-photon Bloch-Siegert shift that
only occurs under non-circularly polarized strong drive conditions. We
therefore treated the Floquet Hamiltonian analytically under arbitrary
amplitudes of the co- and counter-rotating components of the radiation field to
gain insight into the nature of the helicity dependence of multi-photon
resonance shifts. In addition, we tested Floquet-theory predictions
experimentally by comparing one-photon and two-photon charge-carrier spin
resonance shifts observed through room-temperature EDMR experiments on
d-MEH-PPV-based bipolar injection devices [i.e., organic light emitting diode
structures (OLEDs)]. We found that under the experimental conditions of strong,
linearly polarized drive, our observations consistently agree with theory,
irrespective of the magnitude of , and therefore underscore the robustness
of Floquet theory in predicting nonlinear magnetic resonance behaviors.Comment: 22 pages, 5 figure
GeneXpert—A Game-Changer for Tuberculosis Control?
Carlton Evans considers whether the new tuberculosis diagnostic test, GeneXpert, is the solution for TB control that it's said to be
An integrated approach to coastal and biological observations
Maritime economy, ecosystem-based management and climate change adaptation and mitigation raise emerging needs on coastal ocean and biological observations. Integrated ocean observing aims at optimizing sampling strategies and cost-efficiency, sharing data and best practices, and maximizing the value of the observations for multiple purposes. Recently developed cost-effective, near real time technology such as gliders, radars, ferrybox, and shallow water Argo floats, should be used operationally to generate operational coastal sea observations and analysis. Furthermore, value of disparate coastal ocean observations can be unlocked with multi-dimensional integration on fitness-for-the-purpose, parameter and instrumental. Integration of operational monitoring with offline monitoring programs, such as those for research, ecosystem-based management and commercial purposes, is necessary to fill the gaps. Such integration should lead to a system of networks which can deliver data for all kinds of purposes. Detailed integration activities are identified which should enhance the coastal ocean and biological observing capacity. Ultimately a program is required which integrates physical, biogeochemical and biological observation of the ocean, from coastal to deep-sea environments, bringing together global, regional, and local observation efforts
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