12,922 research outputs found
Dicarba-closo-dodecarborane-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium : biological relevance and synthetic strategies
This review describes how the incorporation of dicarba-closo-dodecarboranes into half-sandwich complexes of ruthenium, osmium, rhodium and iridium might lead to the development of a new class of compounds with applications in medicine. Such a combination not only has unexplored potential in traditional areas such as Boron Neutron Capture Therapy agents, but also as pharmacophores for the targeting of biologically important proteins and the development of targeted drugs. The synthetic pathways used for the syntheses of dicarba-closo-dodecarboranes-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium are also reviewed. Complexes with a wide variety of geometries and characteristics can be prepared. Examples of addition reactions on the metal centre, B–H activation, transmetalation reactions and/or direct formation of metal–metal bonds are discussed (103 references)
Single-particle dispersion in stably stratified turbulence
We present models for single-particle dispersion in vertical and horizontal
directions of stably stratified flows. The model in the vertical direction is
based on the observed Lagrangian spectrum of the vertical velocity, while the
model in the horizontal direction is a combination of a continuous-time
eddy-constrained random walk process with a contribution to transport from
horizontal winds. Transport at times larger than the Lagrangian turnover time
is not universal and dependent on these winds. The models yield results in good
agreement with direct numerical simulations of stratified turbulence, for which
single-particle dispersion differs from the well studied case of homogeneous
and isotropic turbulence
qTorch: The Quantum Tensor Contraction Handler
Classical simulation of quantum computation is necessary for studying the
numerical behavior of quantum algorithms, as there does not yet exist a large
viable quantum computer on which to perform numerical tests. Tensor network
(TN) contraction is an algorithmic method that can efficiently simulate some
quantum circuits, often greatly reducing the computational cost over methods
that simulate the full Hilbert space. In this study we implement a tensor
network contraction program for simulating quantum circuits using multi-core
compute nodes. We show simulation results for the Max-Cut problem on 3- through
7-regular graphs using the quantum approximate optimization algorithm (QAOA),
successfully simulating up to 100 qubits. We test two different methods for
generating the ordering of tensor index contractions: one is based on the tree
decomposition of the line graph, while the other generates ordering using a
straight-forward stochastic scheme. Through studying instances of QAOA
circuits, we show the expected result that as the treewidth of the quantum
circuit's line graph decreases, TN contraction becomes significantly more
efficient than simulating the whole Hilbert space. The results in this work
suggest that tensor contraction methods are superior only when simulating
Max-Cut/QAOA with graphs of regularities approximately five and below. Insight
into this point of equal computational cost helps one determine which
simulation method will be more efficient for a given quantum circuit. The
stochastic contraction method outperforms the line graph based method only when
the time to calculate a reasonable tree decomposition is prohibitively
expensive. Finally, we release our software package, qTorch (Quantum TensOR
Contraction Handler), intended for general quantum circuit simulation.Comment: 21 pages, 8 figure
On the bounded cohomology of semi-simple groups, S-arithmetic groups and products
We prove vanishing results for Lie groups and algebraic groups (over any
local field) in bounded cohomology. The main result is a vanishing below twice
the rank for semi-simple groups. Related rigidity results are established for
S-arithmetic groups and groups over global fields. We also establish vanishing
and cohomological rigidity results for products of general locally compact
groups and their lattices
On the flux phase conjecture at half-filling: an improved proof
We present a simplification of Lieb's proof of the flux phase conjecture for
interacting fermion systems -- such as the Hubbard model --, at half filling on
a general class of graphs. The main ingredient is a procedure which transforms
a class of fermionic Hamiltonians into reflection positive form. The method can
also be applied to other problems, which we briefly illustrate with two
examples concerning the model and an extended Falicov-Kimball model.Comment: 23 pages, Latex, uses epsf.sty to include 3 eps figures, to appear in
J. Stat. Phys., Dec. 199
Structure characterization of hard sphere packings in amorphous and crystalline states
The channel size distribution in hard sphere systems, based on the local
neighbor correlation of four particle positions, is investigated for all volume
fractions up to jamming. For each particle, all three particle combinations of
neighbors define channels, which are relevant for the concept of caging. The
analysis of the channel size distribution is shown to be very useful in
distinguishing between gaseous, liquid, partially and fully crystallized, and
glassy (random) jammed states. A common microstructural feature of four
coplanar particles is observed in crystalline and glassy jammed states,
suggesting the presence of "hidden" two-dimensional order in three-dimensional
random close packings.Comment: 5 pages, 5 figure
Temporal multimode storage of entangled photon pairs
Multiplexed quantum memories capable of storing and processing entangled
photons are essential for the development of quantum networks. In this context,
we demonstrate the simultaneous storage and retrieval of two entangled photons
inside a solid-state quantum memory and measure a temporal multimode capacity
of ten modes. This is achieved by producing two polarization entangled pairs
from parametric down conversion and mapping one photon of each pair onto a
rare-earth-ion doped (REID) crystal using the atomic frequency comb (AFC)
protocol. We develop a concept of indirect entanglement witnesses, which can be
used as Schmidt number witness, and we use it to experimentally certify the
presence of more than one entangled pair retrieved from the quantum memory. Our
work puts forward REID-AFC as a platform compatible with temporal multiplexing
of several entangled photon pairs along with a new entanglement certification
method useful for the characterisation of multiplexed quantum memories
Afterlife: the post-research affect and effect of software
Software plays an important role in contemporary research. Aside from its use for administering traditional instruments like surveys and in data analysis, the widespread use of mobile and web apps for social, medical and lifestyle engagement has led to software becoming a research intervention in its own right. For example, it is not unusual to find apps being studied for their utility as interventions in health and social life. Since the software may persist in use beyond the life of an investigation, this raises questions as to the extent of ethical duties for researchers involved in its production and/or study towards the participants involved. Key factors identified include the extent of affect created by the software, the effect it has on a participant’s life, the length of investigation, cost of maintenance and participant agency. In this article we discuss the issues raised in such situations, considering them in the context of post-research duties of care and suggesting strategies to balance the burden on researchers with the need for ongoing participant support
Doped coupled frustrated spin-1/2 chains with four-spin exchange
The role of various magnetic inter-chain couplings is investigated by
numerical methods in doped frustrated quantum spin chains. A non-magnetic
dopant introduced in a gapped spin chain releases a free spin-1/2 soliton. The
formation of a local magnetic moment is analyzed in term of soliton
confinement. A four-spin coupling which might originate from cyclic exchange is
shown to produce such a confinement in contrast to transverse magnetic
exchange. Dopants on different chains experience an effective space-extended
non-frustrating pairwise spin interaction.Comment: Few modifications and references added. Submitted to PR
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