5,316 research outputs found
Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)
We thank ORSAS (GS) and the EPSRC (DE and DMcK supported by project EP/E02971X/1, WYM supported by project EP/I031545/1) for funding.Examples of singly-metallated derivatives of 1,1[prime or minute]-bis(o-carborane) have been prepared and spectroscopically and structurally characterised. Metallation of [7-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-7,8-nido-C2B9H10]2- with a {Ru(p-cymene)}2+ fragment affords both the unisomerised species [1-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-3-(p-cymene)-3,1,2-closo-RuC2B9H10] (2) and the isomerised [8-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-2-(p-cymene)-2,1,8-closo-RuC2B9H10] (3), and 2 is easily transformed into 3 with mild heating. Metallation with a preformed {CoCp}2+ fragment also affords a 3,1,2-MC2B9-1[prime or minute],2[prime or minute]-C2B10 product [1-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-3-Cp-3,1,2-closo-CoC2B9H10] (4), but if CoCl2/NaCp is used followed by oxidation the result is the 2,1,8-CoC2B9-1[prime or minute],2[prime or minute]-C2B10 species [8-(1[prime or minute]-1[prime or minute],2[prime or minute]-closo-C2B10H11)-2-Cp-2,1,8-closo-CoC2B9H10] (5). Compound 4 does not convert into 5 in refluxing toluene, but does do so if it is reduced and then reoxidised, perhaps highlighting the importance of the basicity of the metal fragment in the isomerisation of metallacarboranes. A computational study of 1,1[prime or minute]-bis(o-carborane) is in excellent agreement with a recently-determined precise crystallographic study and establishes that the {1[prime or minute],2[prime or minute]-closo-C2B10H11} fragment is electron-withdrawing compared to H.Publisher PDFPeer reviewe
Transition Metal-free Methylation of Amines with Formaldehyde as the Reductant and Methyl Source
A simple transition metal-free procedure using formal dehyde for the N,N-dimethylation and N-methylation of primary and secondary anilines is reported. The reaction showed limitations on sterically hindered and electron-withdrawing anilines, but is successful on amines
with electron-donating substituents. Formaldehyde acts as both the reducing agent and the carbon source in the reaction
Quantum broadcast communication
Broadcast encryption allows the sender to securely distribute his/her secret
to a dynamically changing group of users over a broadcast channel. In this
paper, we just consider a simple broadcast communication task in quantum
scenario, which the central party broadcasts his secret to multi-receiver via
quantum channel. We present three quantum broadcast communication schemes. The
first scheme utilizes entanglement swapping and Greenberger-Horne-Zeilinger
state to realize a task that the central party broadcasts his secret to a group
of receivers who share a group key with him. In the second scheme, based on
dense coding, the central party broadcasts the secret to multi-receiver who
share each of their authentication key with him. The third scheme is a quantum
broadcast communication scheme with quantum encryption, which the central party
can broadcast the secret to any subset of the legal receivers
A Simultaneous Quantum Secure Direct Communication Scheme between the Central Party and Other M Parties
We propose a simultaneous quantum secure direct communication scheme between
one party and other three parties via four-particle GHZ states and swapping
quantum entanglement. In the scheme, three spatially separated senders, Alice,
Bob and Charlie, transmit their secret messages to a remote receiver Diana by
performing a series local operations on their respective particles according to
the quadripartite stipulation. From Alice, Bob, Charlie and Diana's Bell
measurement results, Diana can infer the secret messages. If a perfect quantum
channel is used, the secret messages are faithfully transmitted from Alice, Bob
and Charlie to Diana via initially shared pairs of four-particle GHZ states
without revealing any information to a potential eavesdropper. As there is no
transmission of the qubits carrying the secret message in the public channel,
it is completely secure for the direct secret communication. This scheme can be
considered as a network of communication parties where each party wants to
communicate secretly with a central party or server.Comment: 4 pages, no figur
Tree species composition, growing space and management in Hong Kong’s commercial sky gardens
Sky gardens, a type of above-ground urban green space, have been increasingly welcomed and installed in cities. However, few studies have assessed tree planting, management and health in high-rise greenery. This study investigated tree species composition, planting space design and management, and their relationships with tree health in sky gardens in 15 commercial sky gardens with 480 trees in Hong Kong. We assessed the differences between old and new sites regarding tree species, height, crown diameter, and health. We also evaluated selected planting and management factors, including planter type, distance to neighbor trees, root-growth obstacles, canopy barriers, canopy overlap and topping history. Tree species selection in commercial sky gardens was substantially different from public and private residential green spaces. Older sky gardens had more palm trees by species and tree counts. Newer gardens had increased adoption of broadleaf and conifer species with high ornamental value and compact form but fewer native tree species and lower species diversity. The widely planted Ficus spp. had created long-term management issues. Trees were often densely planted, particularly in newer sky gardens. The common practice of topping indicates poor species selection and mismanagement. Planter types with insufficient growing space had dampened tree health. Our findings reveal the trend of tree species adoption, narrower planting spaces and wider adoption of the sunken planter. Improvements in species selection, growing space design and management practices could promote healthy, stable and safe trees in sky gardens with contributions to biodiversity and other ecosystem services
An Assessment of Risk of Iodine Deficiency Among Pregnant Women in Sarawak, Malaysia
Previous findings from a state-wide Iodine Deficiency Disorders (IDD) study among pregnant women (PW) in Sarawak indicated that PW are at risk of IDD and further assessment is needed. This paper describes the methodology used in conducting this study for an assessment of risk of iodine deficiency among pregnant women in Sarawak, Malaysia. A total of 30 maternal child health care clinics (MCHCs) were selected using probability proportional to population size (PPS) sampling technique. The PW sample size was calculated based on 95% confidence interval (CI), relative precision of 5%, design effect of 2, anticipated IDD prevalence of 65.0% and non-response rate of 20%. Thus, the total sample size required was 750 (25 respondents per selected MCHC). The WHO Expanded Programme on Immunization (EPI) surveys approach was used to randomly select the first respondent and subsequent respondents were chosen until the required number of PW was met. The required data were obtained through: face-to-face interviews (socio-demographic and food frequency questionnaire), clinical assessments (thyroid size, and hyper/hypothyroidism) and biochemical analysis (urine and blood serum). A total of 677 PW responded in the study with a response rate of 90.2%. Majority of the PW were at second gravida, aged 25-29 years old and of Malay ethnicity. The methodology used in this study was based on International guidelines which may provide state's estimates. All the necessary steps were taken into consideration to ensure valid and reliable findings on current iodine status among PW
Probabilistic teleportation of unknown two-particle state via POVM
We propose a scheme for probabilistic teleportation of unknown two-particle
state with partly entangled four-particle state via POVM. In this scheme the
teleportation of unknown two-particle state can be realized with certain
probability by performing two Bell state measurements, a proper POVM and a
unitary transformation.Comment: 5 pages, no figur
Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbour interactions
By using the method of density-matrix renormalization-group to solve the
different spin-spin correlation functions, the nearest-neighbouring
entanglement(NNE) and next-nearest-neighbouring entanglement(NNNE) of
one-dimensional alternating Heisenberg XY spin chain is investigated in the
presence of alternating nearest neighbour interactions of exchange couplings,
external magnetic fields and next-nearest neighbouring interactions. For
dimerized ferromagnetic spin chain, NNNE appears only above the critical
dimerized interaction, meanwhile, the dimerized interaction effects quantum
phase transition point and improves NNNE to a large value. We also study the
effect of ferromagnetic or antiferromagnetic next-nearest neighboring (NNN)
interactions on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction
increases and shrinks NNE below and above critical frustrated interaction
respectively, while the antiferromagnetic NNN interaction always decreases NNE.
The antiferromagnetic NNN interaction results to a larger value of NNNE in
comparison to the case when the NNN interaction is ferromagnetic.Comment: 13 pages, 4 figures,. accepted by Chinese Physics B 2008 11 (in
press
Multiparty simultaneous quantum identity authentication based on entanglement swapping
We present a multiparty simultaneous quantum identity authentication protocol
based on entanglement swapping. In our protocol, the multi-user can be
authenticated by a trusted third party simultaneously
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