229 research outputs found
Continuous Symmetry Breaking in a Trapped-Ion Spin Chain
One-dimensional systems exhibiting a continuous symmetry can host quantum
phases of matter with true long-range order only in the presence of
sufficiently long-range interactions. In most physical systems, however, the
interactions are short-ranged, hindering the emergence of such phases in one
dimension. Here we use a one-dimensional trapped-ion quantum simulator to
prepare states with long-range spin order that extends over the system size of
up to spins and is characteristic of the continuous symmetry-breaking
phase of matter. Our preparation relies on simultaneous control over an array
of tightly focused individual-addressing laser beams, generating long-range
spin-spin interactions. We also observe a disordered phase with frustrated
correlations. We further study the phases at different ranges of interaction
and the out-of-equilibrium response to symmetry-breaking perturbations. This
work opens an avenue to study new quantum phases and out-of-equilibrium
dynamics in low-dimensional systems
The Kinetics and Mechanism of the Organo-Iridium-Catalysed Enantioselective Reduction of Imines
The iridium complex of pentamethylcyclopentadiene and (S,S)-1,2-diphenyl-N′-tosylethane- 1,2-diamine is an effective catalyst for the asymmetric transfer hydrogenation of imine substrates under acidic conditions. Using the Ir catalyst and a 5:2 ratio of formic acid: triethylamine as the hydride source for the asymmetric transfer hydrogenation of 1-methyl-3,4- dihydroisoquinoline and its 6,7-dimethoxy substituted derivative, in either acetonitrile or dichloromethane, shows unusual enantiomeric excess (ee) profiles for the product amines. The reactions initially give predominantly the (R) enantiomer of the chiral amine products with >90% ee but which then decreases significantly during the reaction. The decrease in ee is not due to racemisation of the product amine, but because the rate of formation of the (R)- enantiomer follows first-order kinetics whereas that for the (S)-enantiomer is zero-order. This difference in reaction order explains the change in selectivity as the reaction proceeds - the rate formation of the (R)-enantiomer decreases exponentially with time while that for the (S)- enantiomer remains constant. A reaction scheme is proposed which requires rate-limiting hydride transfer from the iridium hydride to the iminium ion for the first-order rate of formation of the (R)-enantiomer amine and rate-limiting dissociation of the product for the zero-order rate of formation of the (S)-enantiomer
Application of proline-functionalised 1,2-diphenylethane-1,2-diamine (DPEN) in asymmetric transfer hydrogenation of ketones
A series of enantiomerically pure ligands containing a combination of proline and DPEN groups have been prepared and employed in the asymmetric transfer hydrogenation of ketones. In the case of cyclic ketones, alcohols with ee values of up to 98 % were obtained
The search for transient astrophysical neutrino emission with IceCube-DeepCore
We present the results of a search for astrophysical sources of brief transient neutrino emission using IceCube and DeepCore data acquired between 2012 May 15 and 2013 April 30. While the search methods employed in this analysis are similar to those used in previous IceCube point source searches, the data set being examined consists of a sample of predominantly sub-TeV muon-neutrinos from the Northern Sky (-5 degrees < delta < 90 degrees) obtained through a novel event selection method. This search represents a first attempt by IceCube to identify astrophysical neutrino sources in this relatively unexplored energy range. The reconstructed direction and time of arrival of neutrino events are used to search for any significant self-correlation in the data set. The data revealed no significant source of transient neutrino emission. This result has been used to construct limits at timescales ranging from roughly 1 s to 10 days for generic soft-spectra transients. We also present limits on a specific model of neutrino emission from soft jets in core-collapse supernovae
Search for non-relativistic Magnetic Monopoles with IceCube
The IceCube Neutrino Observatory is a large Cherenkov detector instrumenting
of Antarctic ice. The detector can be used to search for
signatures of particle physics beyond the Standard Model. Here, we describe the
search for non-relativistic, magnetic monopoles as remnants of the GUT (Grand
Unified Theory) era shortly after the Big Bang. These monopoles may catalyze
the decay of nucleons via the Rubakov-Callan effect with a cross section
suggested to be in the range of to
. In IceCube, the Cherenkov light from nucleon decays
along the monopole trajectory would produce a characteristic hit pattern. This
paper presents the results of an analysis of first data taken from May 2011
until May 2012 with a dedicated slow-particle trigger for DeepCore, a
subdetector of IceCube. A second analysis provides better sensitivity for the
brightest non-relativistic monopoles using data taken from May 2009 until May
2010. In both analyses no monopole signal was observed. For catalysis cross
sections of the flux of non-relativistic
GUT monopoles is constrained up to a level of at a 90% confidence level,
which is three orders of magnitude below the Parker bound. The limits assume a
dominant decay of the proton into a positron and a neutral pion. These results
improve the current best experimental limits by one to two orders of magnitude,
for a wide range of assumed speeds and catalysis cross sections.Comment: 20 pages, 20 figure
Use of triazole-ring formation to attach a Ru/TsDPEN complex for asymmetric transfer hydrogenation to a soluble polymer
The cycloaddition of a chiral ligand containing a terminal alkyne to a soluble polymer containing an azide provides a convenient means for the attachment of an asymmetric transfer hydrogenation catalyst to a soluble polymer support. Using these ligands in complexes with Ru(II), gave good results in terms of conversion and enantioselectivity (up to 95% ee) in ketone reduction reactions
Determining neutrino oscillation parameters from atmospheric muon neutrino disappearance with three years of IceCube DeepCore data
We present a measurement of neutrino oscillations via atmospheric muon
neutrino disappearance with three years of data of the completed IceCube
neutrino detector. DeepCore, a region of denser instrumentation, enables the
detection and reconstruction of atmospheric muon neutrinos between 10 GeV and
100 GeV, where a strong disappearance signal is expected. The detector volume
surrounding DeepCore is used as a veto region to suppress the atmospheric muon
background. Neutrino events are selected where the detected Cherenkov photons
of the secondary particles minimally scatter, and the neutrino energy and
arrival direction are reconstructed. Both variables are used to obtain the
neutrino oscillation parameters from the data, with the best fit given by
and
(normal mass hierarchy assumed). The
results are compatible and comparable in precision to those of dedicated
oscillation experiments.Comment: 10 pages, 7 figure
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