4,556 research outputs found
'Hole-digging' in ensembles of tunneling Molecular Magnets
The nuclear spin-mediated quantum relaxation of ensembles of tunneling
magnetic molecules causes a 'hole' to appear in the distribution of internal
fields in the system. The form of this hole, and its time evolution, are
studied using Monte Carlo simulations. It is shown that the line-shape of the
tunneling hole in a weakly polarised sample must have a Lorentzian lineshape-
the short-time half-width in all experiments done so far should be
, the half-width of the nuclear spin multiplet. After a time
, the single molecule tunneling relaxation time, the hole width begins
to increase rapidly. In initially polarised samples the disintegration of
resonant tunneling surfaces is found to be very fast.Comment: 4 pages, 5 figure
Coherence Window in the dynamics of Quantum Nanomagnets
Decoherence in many solid-state systems is anomalously high, frustrating
efforts to make solid-state qubits. We show that in nanomagnetic insulators in
large transverse fields, there can be a fairly narrow field region in which
both phonon and nuclear spin-mediated decoherence are drastically reduced. As
examples we calculate decoherence rates for the -8 nanomolecule, for
particles, and for ions in . The reduction in the
decoherence, compared to low field rates, can exceed 6 orders of magnitude. The
results also give limitations on the observability of macroscopic coherence
effects in magnetic systems.Comment: 5 LaTeX pages, 3 figure
Electrospun amplified fiber optics
A lot of research is focused on all-optical signal processing, aiming to
obtain effective alternatives to existing data transmission platforms.
Amplification of light in fiber optics, such as in Erbium-doped fiber
amplifiers, is especially important for an efficient signal transmission.
However, the complex fabrication methods, involving high-temperature processes
performed in highly pure environment, slow down the fabrication and make
amplified components expensive with respect to an ideal, high-throughput and
room temperature production. Here, we report on near infrared polymer fiber
amplifiers, working over a band of about 20 nm. The fibers are cheap, spun with
a process entirely carried out at room temperature, and show amplified
spontaneous emission with good gain coefficients as well as low optical losses
(a few cm^-1). The amplification process is favoured by the high fiber quality
and low self-absorption. The found performance metrics promise to be suitable
for short-distance operation, and the large variety of commercially-available
doping dyes might allow for effective multi-wavelength operation by electrospun
amplified fiber optics.Comment: 27 pages, 8 figure
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Development and validation of verbal emotion vignettes in Portuguese, English, and German
Everyday human social interaction involves sharing experiences verbally and these experiences often include emotional content. Providing this context generally leads to the experience of emotions in the conversation partner. However, most emotion elicitation stimulus sets are based on images or film-sequences providing visual and/or auditory emotion cues. To assimilate what occurs within social interactions, the current study aimed at creating and validating verbal emotion vignettes as stimulus set to elicit emotions (anger, disgust, fear, sadness, happiness, gratitude, guilt, and neutral). Participants had to mentally immerse themselves in 40 vignettes and state which emotion they experienced next to the intensity of this emotion. The vignettes were validated on a large sample of native Portuguese-speakers (N = 229), but also on native English-speaking (N = 59), and native German-speaking (N = 50) samples to maximise applicability of the vignettes. Hierarchical cluster analyses showed that the vignettes mapped clearly on their target emotion categories in all three languages. The final stimulus sets each include 4 vignettes per emotion category plus 1 additional vignette per emotion category which can be used for task familiarisation procedures within research. The high agreement rates on the experienced emotion in combination with the medium to large intensity ratings in all three languages suggest that the stimulus sets are suitable for application in emotion research (e.g., emotion recognition or emotion elicitation)
Quantum nanomagnets and nuclear spins: an overview
This mini-review presents a simple and accessible summary on the fascinating
physics of quantum nanomagnets coupled to a nuclear spin bath. These chemically
synthesized systems are an ideal test ground for the theories of decoherence in
mesoscopic quantum degrees of freedom, when the coupling to the environment is
local and not small. We shall focus here on the most striking quantum
phenomenon that occurs in such nanomagnets, namely the tunneling of their giant
spin through a high anisotropy barrier. It will be shown that perturbative
treatments must be discarded, and replaced by a more sophisticated formalism
where the dynamics of the nanomagnet and the nuclei that couple to it are
treated together from the beginning. After a critical review of the theoretical
predictions and their experimental verification, we continue with a set of
experimental results that challenge our present understanding, and outline the
importance of filling also this last gap in the theory.Comment: 14 pages, 3 figures. Chapter in the Proceedings of the 2006 Les
Houches summer school "Quantum Magnetism", ed. B. Barbara & Y. Imry, Springer
(2007
Study of and and
We study the decays of and to the final states
and based on a single
baryon tag method using data samples of
and events collected with
the BESIII detector at the BEPCII collider. The decays to
are observed for the first time. The
measured branching fractions of and
are in good agreement with, and much
more precise, than the previously published results. The angular parameters for
these decays are also measured for the first time. The measured angular decay
parameter for , , is found to be negative, different to the other
decay processes in this measurement. In addition, the "12\% rule" and isospin
symmetry in the and and
systems are tested.Comment: 11 pages, 7 figures. This version is consistent with paper published
in Phys.Lett. B770 (2017) 217-22
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