16,241 research outputs found
A Birkhoff connection between quantum circuits and linear classical reversible circuits
Birkhoff's theorem tells how any doubly stochastic matrix can be decomposed as a weighted sum of permutation matrices. Similar theorems on unitary matrices reveal a connection between quantum circuits and linear classical reversible circuits. It triggers the question whether a quantum computer can be regarded as a superposition of classical reversible computers
Modulation of galactic protons in the heliosphere during the unusual solar minimum of 2006 to 2009
The last solar minimum activity period, and the consequent minimum modulation
conditions for cosmic rays, was unusual. The highest levels of galactic protons
were recorded at Earth in late 2009 in contrast to expectations. Proton spectra
observed for 2006 to 2009 from the PAMELA cosmic ray detector on-board the
Resurs-DK1 satellite are presented together with the solutions of a
comprehensive numerical model for the solar modulation of cosmic rays. The
model is used to determine what mechanisms were mainly responsible for the
modulation of protons during this period, and why the observed spectrum for
2009 was the highest ever recorded. From mid-2006 until December 2009 we find
that the spectra became significantly softer because increasingly more low
energy protons had reached Earth. To simulate this effect, the rigidity
dependence of the diffusion coefficients had to decrease significantly below ~3
GeV. The modulation minimum period of 2009 can thus be described as relatively
more "diffusion dominated" than previous solar minima. However, we illustrate
that drifts still had played a significant role but that the observable
modulation effects were not as well correlated with the waviness of the
heliospheric current sheet as before. Protons still experienced global gradient
and curvature drifts as the heliospheric magnetic field had decreased
significantly until the end of 2009, in contrast to the moderate decreases
observed during previous minimum periods. We conclude that all modulation
processes contributed to the observed increases in the proton spectra for this
period, exhibiting an intriguing interplay of these major mechanisms
Structure, Organization, and Expression of the lct Gene for Lacticin 481, a Novel Lantibiotic Produced by Lactococcus lactis
The structural gene for the lactococcal lantibiotic lacticin 481 (lct) has been identified and cloned using a degenerated 20-mer DNA oligonucleotide based on the amino-terminal 7 amino acid residues of the purified protein. The transcription of the lct gene was analyzed, and its promoter was mapped. DNA sequence analysis of the lct gene revealed an open reading frame encoding a peptide of 51 amino acids. Comparison of its deduced amino acid sequence with the amino-terminal sequence and the amino acid composition of lacticin 481 indicates that the 61-residue peptide is prelacticin 481, containing a 27-residue carboxyl-terminal propeptide and a 24-residue amino-terminal leader peptide which lacks the properties of a typical signal sequence and which is significantly different from the leaders of other lantibiotics. The predicted amino acid sequence of prolacticin 481 contains 3 cysteines, 2 serines, and 2 threonines which were not detectable in amino acid analyses of mature lacticin 481. Based on these results and on characterization by two-dimensional NMR techniques, a structural model is proposed in which 2 cysteine residues are involved in lanthionine and one in β-methyllanthionine formation, and a 4th threonine residue is dehydrated. This model predicts a molecular mass for lacticin 481 of 2,901, which is in excellent agreement with that obtained from mass spectrometry.
Inhibited spontaneous emission of quantum dots observed in a 3D photonic band gap
We present time-resolved emission experiments of semiconductor quantum dots
in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study
is made of crystals with a range of pore radii to tune the band gap relative to
the emission frequency. The decay rates averaged over all dipole orientations
are inhibited by a factor of 10 in the photonic band gap and enhanced up to 2?
outside the gap, in agreement with theory. We discuss the effects of spatial
inhomogeneity, nonradiative decay, and transition dipole orientations on the
observed inhibition in the band gap.Comment: 5 figures, update author lis
A precise characterisation of the top quark electro-weak vertices at the ILC
Top quark production in the process at a future linear
electron positron collider with polarised beams is a powerful tool to determine
indirectly the scale of new physics. The presented study, based on a detailed
simulation of the ILD detector concept, assumes a centre-of-mass energy of
GeV and a luminosity of
equally shared between the incoming beam polarisations of . Events are selected in which the top pair
decays semi-leptonically and the cross sections and the forward-backward
asymmetries are determined. Based on these results, the vector, axial vector
and tensorial conserving couplings are extracted separately for the photon
and the component. With the expected precision, a large number of models
in which the top quark acts as a messenger to new physics can be distinguished
with many standard deviations. This will dramatically improve expectations from
e.g. the LHC for electro-weak couplings of the top quark.Comment: This work is an update of arXiv:1307.8102, minor changes w.r.t. v1
(typos, wrong grammar, incomplete sentences etc.
Linking travel behavior and tourism literature: Investigating the impacts of travel satisfaction on destination satisfaction and revisit intention
This study aims to link two closely related domains in literature – travel behavior and tourism. Travel behavior studies partly aim to improve travel satisfaction by exploring its relationships with overall and domain-specific life satisfaction. Tourism studies, on the other hand, focus on improving the attraction and sustainability of tourism destinations and often investigate the factors affecting destination satisfaction and revisit intention. The present study uncovers the interconnections between travel behavior and tourism by investigating the impacts of travel satisfaction on destination satisfaction and revisit intention. An online survey of 696 visitors to national parks in the US conducted in the Summer of 2022 was analyzed using a structural equation modeling approach. Analysis results show that travel satisfaction has a direct impact on destination satisfaction and both direct and indirect (through destination satisfaction) impacts on revisit intention. Also, interestingly, results reveal that travel satisfaction has a stronger impact on revisit intention than destination satisfaction. These results offer an important implication to the tourism destination managers that investing in destination attributes alone might not be sufficient to attain the desired level of tourism for the destination. Thus, an area to be focused on is improving the satisfaction and experiences of travelers on the way to their destination. This could be achieved by investing in transportation infrastructures, networks, facilities, and services connecting major tourism destinations and city centers
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