2,429 research outputs found
Iron(III)-catalyzed chlorination of activated arenes
A general and regioselective method for the chlorination of activated arenes has been developed. The transformation uses iron(III) triflimide as a powerful Lewis acid for the activation of N-chlorosuccinimide and the subsequent chlorination of a wide range of anisole, aniline, acetanilide and phenol derivatives. The reaction was utilized for the late-stage mono- and di-chlorination of a range of target compounds such as the natural product nitrofungin, the antibacterial agent chloroxylenol and the herbicide chloroxynil. The facile nature of this transformation was demonstrated with the development of one-pot tandem iron-catalyzed dihalogenation processes allowing highly regioselective formation of different carbon-halogen bonds. The synthetic utility of the resulting dihalogenated aryl compounds as building blocks was established with the synthesis of natural products and pharmaceutically relevant targets
Excited-State Solvation Structure of Transition Metal Complexes from Molecular Dynamics Simulations and Assessment of Partial Atomic Charge Methods
In this work, we investigate the excited-state solute and solvation structure
of , ,
and
(bpy=2,2'-pyridine; bmip=2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine;
phen=1,10-phenanthroline) transition metal complexes (TMCs) in terms of
solute-solvent radial distribution functions (RDFs) and evaluate the
performance of some of the most popular partial atomic charge (PAC) methods for
obtaining these RDFs by molecular dynamics (MD) simulations. To this end, we
compare classical MD of a frozen solute in water and acetonitrile (ACN) with
quantum mechanics/molecular mechanics Born-Oppenheimer molecular dynamics
(QM/MM BOMD) simulations. The calculated RDFs show that the choice of a
suitable PAC method is dependent on the coordination number of the metal,
denticity of the ligands, and type of solvent. It is found that this selection
is less sensitive for water than ACN. Furthermore, a careful choice of the PAC
method should be considered for TMCs that exhibit a free direct coordination
site, such as . The results of this work show that
fast classical MD simulations with ChelpG/RESP or CM5 PACs can produce RDFs
close to those obtained by QM/MM MD and thus, provide reliable solvation
structures of TMCs to be used, e.g. in the analysis of scattering data
Measurement-induced state transitions in a superconducting qubit: Beyond the rotating wave approximation
Many superconducting qubit systems use the dispersive interaction between the
qubit and a coupled harmonic resonator to perform quantum state measurement.
Previous works have found that such measurements can induce state transitions
in the qubit if the number of photons in the resonator is too high. We
investigate these transitions and find that they can push the qubit out of the
two-level subspace, and that they show resonant behavior as a function of
photon number. We develop a theory for these observations based on level
crossings within the Jaynes-Cummings ladder, with transitions mediated by terms
in the Hamiltonian that are typically ignored by the rotating wave
approximation. We find that the most important of these terms comes from an
unexpected broken symmetry in the qubit potential. We confirm the theory by
measuring the photon occupation of the resonator when transitions occur while
varying the detuning between the qubit and resonator
Moisture susceptibility of high and low compaction dry process crumb rubber modified asphalt mixtures
The field performance of dry process crumb rubber-modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures
Cyber security fear appeals:unexpectedly complicated
Cyber security researchers are starting to experiment with fear appeals, with a wide variety of designs and reported efficaciousness. This makes it hard to derive recommendations for designing and deploying these interventions. We thus reviewed the wider fear appeal literature to arrive at a set of guidelines to assist cyber security researchers. Our review revealed a degree of dissent about whether or not fear appeals are indeed helpful and advisable. Our review also revealed a wide range of fear appeal experimental designs, in both cyber and other domains, which confirms the need for some standardized guidelines to inform practice in this respect. We propose a protocol for carrying out fear appeal experiments, and we review a sample of cyber security fear appeal studies, via this lens, to provide a snapshot of the current state of play. We hope the proposed experimental protocol will prove helpful to those who wish to engage in future cyber security fear appeal research
Are direct photons a clean signal of a thermalized quark gluon plasma?
Direct photon production from a quark gluon plasma (QGP) in thermal
equilibrium is studied directly in real time. In contrast to the usual S-matrix
calculations, the real time approach is valid for a QGP that formed and reached
LTE a short time after a collision and of finite lifetime ( as expected at RHIC or LHC). We point out that during such
finite QGP lifetime the spectrum of emitted photons carries information on the
initial state. There is an inherent ambiguity in separating the virtual from
the observable photons during the transient evolution of the QGP. We propose a
real time formulation to extract the photon yield which includes the initial
stage of formation of the QGP parametrized by an effective time scale of
formation . This formulation coincides with the S-matrix approach
in the infinite lifetime limit. It allows to separate the virtual cloud as well
as the observable photons emitted during the pre- equilibrium stage from the
yield during the QGP lifetime. We find that the lowest order contribution
which does \emph{not} contribute to the S-matrix
approach, is of the same order of or larger than the S-matrix contribution
during the lifetime of the QGP for a typical formation time . The yield for momenta features a
power law fall-off and is larger than that obtained
with the S-matrix for momenta . We provide a
comprehensive numerical comparison between the real time and S-matrix yields
and study the dynamics of the build-up of the photon cloud and the different
contributions to the radiative energy loss. The reliability of the current
estimates on photon emission is discussed.Comment: 31 pages, 12 eps figures, version to appear in PR
Vitamin D in the general population of young adults with autism in the Faroe Islands
Vitamin D deficiency has been proposed as a possible risk factor for developing autism spectrum disorder (ASD). 25-Hydroxyvitamin D3 (25(OH)D3) levels were examined in a cross-sectional population-based study in the Faroe Islands. The case group consisting of a total population cohort of 40 individuals with ASD (aged 15–24 years) had significantly lower 25(OH)D3 than their 62 typically-developing siblings and their 77 parents, and also significantly lower than 40 healthy age and gender matched comparisons. There was a trend for males having lower 25(OH)D3 than females. Effects of age, month/season of birth, IQ, various subcategories of ASD and Autism Diagnostic Observation Schedule score were also investigated, however, no association was found. The very low 25(OH)D3 in the ASD group suggests some underlying pathogenic mechanism
Influence of Er, Cr: YSGG (2780 nm) and Nanosecond Nd: YAG Laser (1064 nm) Irradiation on Enamel Acid Resistance: Morphological and Elemental Analysis
BACKGROUND: Enamel demineralisation is an initial step of the serious dental problem including dental caries, white spot lesions and dental erosion.
AIM: Compare the effect of Er, Cr: YSGG (λ = 2780 nm) and nanosecond Nd: YAG (λ = 1064 nm) laser on enamel acid resistance.
MATERIAL AND METHODS: Thirty non-carious human premolars, extracted for orthodontic reasons, were used. The experimental groups (n = 10 each group) were: Group I, untreated (control); Group II, Er,Cr:YSGG laser irradiation (0.75 W, 20 Hz, 140 μs, 10 s); Group III, nanosecond pulsed Nd:YAG laser irradiation (0.8 W, 10 Hz, 7 ns, 10 s). Scanning electron microscope and Energy Dispersive X-ray Spectroscopy (EDX) were used to assess acquired enamel resistance to PH cycling.
RESULTS: After subjecting the three experimental groups to PH cycling, scanning electron microscopic examination revealed irregular porous dissoluted enamel surface in group I. However, groups II and III demonstrated partially dissoluted enamel surface. EDX analysis demonstrated the lowest mean percentage decrease in calcium and phosphorus content in group II followed by group III, then the highest mean percentage decrease was observed in untreated group I. One-way ANOVA revealed significant differences (p < 0.0001) between the tested groups.
CONCLUSIONS: Both Er, Cr: YSSG and nanosecond Nd: YAG laser irradiation were able to improve the acid resistance of enamel. However, enamel surface treated with Er, Cr: YSSG laser showed the lowest mean percentage decrease of calcium and phosphorus (highest acid resistance)
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