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https://www.readbyqxmd.com/read/28938135/bang-bang-optimal-control-of-large-spin-systems-enhancement-of-13-c-13-c-singlet-order-at-natural-abundance
#1
Deepak Khurana, T S Mahesh
Using a bang-bang optimal control technique, we transfer polarization from a set of abundant high-γ nuclei directly to singlet order of a low-γ spin-pair. This approach is analogous to algorithmic cooling (AC) procedure used in quantum state purification. Specifically, we apply this method for enhancing the singlet order in a natural abundant (13)C- (13)C spin pair by exploiting nine equivalent protons of an 11-spin system. Compared to the standard method not involving polarization transfer, we find an enhancement of singlet order by about 3...
September 14, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28937970/spectroscopy-and-enhanced-frequency-upconversion-in-nd-3-yb-3-codoped-tpo-glasses-energy-transfer-and-nir-to-visible-upconverter
#2
Mohd Azam, Vineet Kumar Rai, Deepak Kumar Mohanty
TeO2-Pb3O4 (TPO) glasses codoped with Nd(3+) and Yb(3+) ions have been fabricated by conventional melting technique. The absorption, emission and excitation spectra of the samples have been recorded. The optical band gap in both the doped/codoped glasses is found to be ∼3.31 eV. Judd-Ofelt analysis has been carried out by using the absorption spectrum of 0.8 mol% Nd(3+) doped glass to determine the radiative properties viz radiative transition probabilities, branching ratios, radiative lifetimes, quality factor and emission cross sections of some emitting levels for Nd(3+) ions...
September 22, 2017: Methods and Applications in Fluorescence
https://www.readbyqxmd.com/read/28937772/terahertz-light-matter-interaction-beyond-unity-coupling-strength
#3
Andreas Bayer, Marcel Pozimski, Simon Schambeck, Dieter Schuh, Rupert Huber, Dominique Bougeard, Christoph Lange
Achieving control over light-matter interaction in custom-tailored nanostructures is at the core of modern quantum electrodynamics. In strongly and ultrastrongly coupled systems, the excitation is repeatedly exchanged between a resonator and an electronic transition at a rate known as the vacuum Rabi frequency ΩR. For ΩR approaching the resonance frequency ωc, novel quantum phenomena including squeezed states, Dicke superradiant phase transitions, the collapse of the Purcell effect, and a population of the ground state with virtual photon pairs are predicted...
September 22, 2017: Nano Letters
https://www.readbyqxmd.com/read/28937762/projected-commutator-diis-method-for-accelerating-hybrid-functional-electronic-structure-calculations
#4
Wei Hu, Lin Lin, Chao Yang
The commutator direct inversion of the iterative subspace (commutator DIIS or C-DIIS) method developed by Pulay is an efficient and the most widely used scheme in quantum chemistry to accelerate the convergence of self consistent field (SCF) iterations in Hartree-Fock theory and Kohn-Sham density functional theory. The C-DIIS method requires the explicit storage of the density matrix, the Fock matrix and the commutator matrix. Hence the method can only be used for systems with a relatively small basis set, such as the Gaussian basis set...
September 22, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28937699/electron-transfer-dynamics-from-single-near-infrared-emitting-lead-sulfide-cadmium-sulfide-nanocrystals-to-titanium-dioxide
#5
Huidong Zang, Prahlad K Routh, Qingping Meng, Mircea Cotlet
In this study we report the first successful demonstration of electron transfer between single near infrared emitting PbS/CdS nanocrystals and an external acceptor, titanium dioxide (TiO2). We demonstrate distance-dependent electron transfer from single nanocrystals to TiO2 and explore the effect of this process on the photoluminescence dynamics of these nanocrystals. Isolated PbS/CdS QDs are found to exhibit blinking dynamics similar to other nanocrystals like CdSe/ZnS; however, their photoluminescence follows a quasi two-state pattern with heterogeneous photoluminescence lifetimes which may be the result of their emission originating from different energy states...
September 22, 2017: Nanoscale
https://www.readbyqxmd.com/read/28937675/coherent-singlet-fission-activated-by-symmetry-breaking
#6
Kiyoshi Miyata, Yuki Kurashige, Kazuya Watanabe, Toshiki Sugimoto, Shota Takahashi, Shunsuke Tanaka, Jun Takeya, Takeshi Yanai, Yoshiyasu Matsumoto
Singlet fission, in which a singlet exciton is converted to two triplet excitons, is a process that could be beneficial in photovoltaic applications. A full understanding of the dynamics of singlet fission in molecular systems requires detailed knowledge of the relevant potential energy surfaces and their (conical) intersections. However, obtaining such information is a nontrivial task, particularly for molecular aggregates. Here we investigate singlet fission in rubrene crystals using transient absorption spectroscopy and state-of-the-art quantum chemical calculations...
October 2017: Nature Chemistry
https://www.readbyqxmd.com/read/28937670/feshbach-resonances-in-the-exit-channel-of-the-f%C3%A2-%C3%A2-ch3oh%C3%A2-%C3%A2-%C3%A2-hf%C3%A2-%C3%A2-ch3o-reaction-observed-using-transition-state-spectroscopy
#7
Marissa L Weichman, Jessalyn A DeVine, Mark C Babin, Jun Li, Lifen Guo, Jianyi Ma, Hua Guo, Daniel M Neumark
The transition state governs how chemical bonds form and cleave during a chemical reaction and its direct characterization is a long-standing challenge in physical chemistry. Transition state spectroscopy experiments based on negative-ion photodetachment provide a direct probe of the vibrational structure and metastable resonances that are characteristic of the reactive surface. Dynamical resonances are extremely sensitive to the topography of the reactive surface and provide an exceptional point of comparison with theory...
October 2017: Nature Chemistry
https://www.readbyqxmd.com/read/28937481/optimization-of-computed-tomography-coronary-angiography-for-improved-plaque-detection
#8
Hany Kashani, Graham Wright, Ali Ursani, Garry Liu, Masoud Hashemi, Narinder S Paul
OBJECTIVE: The study aims to optimize visualization of the coronary wall during computed tomography coronary angiography. METHODS: A coronary plaque phantom was scanned on a wide-volume computed tomography scanner. Spatial resolution, contrast resolution, and vessel wall thickness were measured at different x-ray tube currents and voltages. RESULTS: Spatial resolution ranged from 0.385 to 0.625 mm and was significantly lower at higher currents...
September 20, 2017: Journal of Computer Assisted Tomography
https://www.readbyqxmd.com/read/28937175/chiral-six-coordinate-dy-iii-and-tb-iii-complexes-of-an-achiral-ligand-structure-fluorescence-and-magnetism
#9
Mei-Jiao Liu, Juan Yuan, Yi-Quan Zhang, Hao-Ling Sun, Cai-Ming Liu, Hui-Zhong Kou
Two new chiral six-coordinate lanthanide complexes (1 for Dy and 2 for Tb) have been synthesized using the achiral flexible ligand H2L (2,2'-[1,2-ethanediylbis[(methylimino)methylene]]bis[4,5-dimethylphenol]). Both complexes crystallize in the chiral P1 group space, and the enantiomers [Zn(L)Cl]3Dy·MeOH·0.5H2O (Λ-1), [Zn(L)Cl]3Dy·1.5H2O (Δ-1), [Zn(L)Cl]3Tb·1.5H2O (Λ-2) and [Zn(L)Cl]3Tb·H2O (Δ-2) are isolated in the reaction. Three [Zn(L)Cl](-) anions coordinate to the central lanthanide ion using two phenoxo oxygen atoms of L(2-), and the lanthanide ion has the coordination geometry of D3...
September 22, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28936984/what-makes-the-universe-accelerate-a-review-on-what-dark-energy-could-be-and-how-to-test-it
#10
Philippe Brax
Explaining the origin of the acceleration of the expansion of the Universe remains as challenging as ever. In this review, we present different approaches from dark energy to modified gravity. We also emphasize the quantum nature of the problem and the need for an explanation which should violate Weinberg's no go theorem. This might involve a self-tuning mechanism or the acausal sequestering of the vacuum energy. Laboratory tests of the coupling to matter of nearly massless scalar fields, which could be one of the features required to explain the cosmic acceleration, are also reviewed...
September 22, 2017: Reports on Progress in Physics
https://www.readbyqxmd.com/read/28936785/ligand-capped-cdte-quantum-dots-as-a-fluorescent-nanosensor-for-detection-of-copper-ions-in-environmental-water-sample
#11
Hamideh Elmizadeh, Majid Soleimani, Farnoush Faridbod, Ghasem Rezanejade Bardajee
In this work, as a novel fluorescent nano-sensor, a ligand-capped CdTe QDs (CdTe-L QDs) was designed for the detection and quantification of Cu(2+) ions in environmental water samples. The synthesized QDs were characterized by transmission electron microscopy (TEM), thermo-gravimetric (TG) analysis, Fourier transform infrared (FTIR), UV-Vis spectrophotometry and fluorescence spectroscopy. Optical properties of the produced nanosensor were monitored by UV-Vis and fluorescence spectrophotometry. It was observed that fluorescence intensity of the produced nano-sensor selectively quenched by adding Cu(2+) ions in comparison to other metal ions tested...
September 21, 2017: Journal of Fluorescence
https://www.readbyqxmd.com/read/28936529/high-performance-flexible-inverted-organic-light-emitting-diodes-by-exploiting-mos2-nanopillar-arrays-as-electron-injecting-and-light-coupling-layers
#12
Kunping Guo, Changfeng Si, Ceng Han, Saihu Pan, Guo Chen, Yanqiong Zheng, Wenqing Zhu, Jianhua Zhang, Chang Sun, Bin Wei
Inverted organic light-emitting diodes (IOLEDs) on plastic substrates have great potential application in flexible active-matrix displays. High energy consumption, instability and poor electron injection are key issues limiting the commercialization of flexible IOLEDs. Here, we have systematically investigated the electrooptical properties of molybdenum disulfide (MoS2) and applied it in developing highly efficient and stable blue fluorescent IOLEDs. We have demonstrated that MoS2-based IOLEDs can significantly improve electron-injecting capacity...
September 22, 2017: Nanoscale
https://www.readbyqxmd.com/read/28936520/copper-mediated-phospha-annulation-to-attain-water-soluble-polycyclic-luminophores
#13
Andrey Belyaev, Yi-Ting Chen, Shih-Hao Su, Yu-Jui Tseng, Antti J Karttunen, Sergey P Tunik, Pi-Tai Chou, Igor O Koshevoy
A 6-membered P-heterocycle has been fused with a polyaromatic framework through intramolecular transformation of anthracene-based phosphine induced by CuCl2. The resulting water soluble phosphonium fluorophores exhibit extremely high quantum efficiency along with prominent stability and low toxicity that make them suitable for one- and two-photon imaging purposes.
September 22, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28936514/on-the-elusive-nature-of-oxygen-binding-at-coordinatively-unsaturated-3d-transition-metal-centers-in-metal-organic-frameworks
#14
Mali H Rosnes, Denis Sheptyakov, Alexandra Franz, Matthias Frontzek, Pascal D C Dietzel, Peter A Georgiev
Using gas sorption measurements at ambient temperatures and in situ neutron powder diffraction methods, we have studied the interaction strengths and coordination geometries of O2 and N2 near the non-occupied coordination site (open metal site) in the isostructural MOF structures of the CPO-27-M/M-MOF-74 series (with M = Co, Ni, Mn and Cu). Our experimental observations are compared to periodic quantum chemical model calculations. Contrary to recent computational studies, our results, both experimental and theoretical, unequivocally suggest rather weak interactions between the M(ii) coordinatively unsaturated centers and the adsorbate molecules, being mainly dispersive and electrostatic in nature...
September 22, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28936513/solar-cells-with-pbs-quantum-dot-sensitized-tio2-multiwalled-carbon-nanotube-composites-sulfide-titania-gel-and-tin-sulfide-coated-c-fabric
#15
Ramesh K Kokal, Melepurath Deepa, Ankarao Kalluri, Shrishti Singh, Isaac Macwan, Prabir K Patra, Jeff Gilarde
Novel approaches to boost quantum dot solar cell (QDSC) efficiencies are in demand. Herein, three strategies are used: (i) a hydrothermally synthesized TiO2-multiwalled carbon nanotube (MWCNT) composite instead of conventional TiO2, (ii) a counter electrode (CE) that has not been applied to QDSCs until now, namely, tin sulfide (SnS) nanoparticles (NPs) coated over a conductive carbon (C)-fabric, and (iii) a quasi-solid-state gel electrolyte composed of S(2-), an inert polymer and TiO2 nanoparticles as opposed to a polysulfide solution based hole transport layer...
September 22, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28936504/single-quantum-dot-based-nanosensor-for-rapid-and-sensitive-detection-of-terminal-deoxynucleotidyl-transferase
#16
Li-Juan Wang, Ming-Li Luo, Qianyi Zhang, Bo Tang, Chun-Yang Zhang
We developed a simple and rapid method for terminal deoxynucleotidyl transferase (TdT) assay on the basis of the polymerization-directed exonuclease-assisted construction of a single quantum dot (QD)-based fluorescence resonance energy transfer (FRET) nanosensor. This method is very sensitive with a detection limit as low as 1 × 10(-6) U μL(-1), and it can be used for the screening of TDT inhibitors and accurate quantification of TdT activity even in 5 cancer cells.
September 22, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28936503/why-different-ligands-can-control-stereochemistry-selectivity-of-ni-catalyzed-suzuki-miyaura-cross-coupling-of-benzylic-carbamates-with-arylboronic-esters-a-mechanistic-study
#17
Hujun Xie, Yang Li, Lihong Wang, Jian Kuang, Qunfang Lei, Wenjun Fang
Quantum chemistry calculations have been employed to study the mechanisms of nickel-catalyzed Suzuki-Miyaura cross-coupling reactions of benzylic carbamates with arylboronic esters, and the energy profiles have been computed to evaluate possible origins for the generation of different stereochemistry products. It has been demonstrated that the mechanism can be divided into three steps: oxidative addition, transmetallation and reduction elimination. Transmetallation is the rate-limiting step for the whole reaction cycle, and oxidative addition controls the stereoselectivity of the resulting products...
September 22, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28936331/double-c-h-bond-activation-of-acetylene-by-atomic-boron-in-forming-aromatic-cyclic-hbc2bh-in-solid-neon
#18
Jiwen Jian, Wei Li, Xuan Wu, Mingfei Zhou
The organo-boron species formed from the reactions of boron atoms with acetylene in solid neon are investigated using matrix isolation infrared spectroscopy with isotopic substitutions as well as quantum chemical calculations. Besides the previously reported single C-H bond activation species, a cyclic-HBC2BH diboron species is formed via double C-H bond activation of acetylene. It is characterized to have a closed-shell singlet ground state with planar D2h symmetry. Bonding analysis indicates that it is a doubly aromatic species involving two delocalized σ electrons and two delocalized π electrons...
June 1, 2017: Chemical Science
https://www.readbyqxmd.com/read/28935985/polarization-entangled-photon-generation-using-partial-spatially-coherent-pump-beam
#19
Yaseera Ismail, Stuti Joshi, Francesco Petruccione
The generation of two photon fields, to date, has been demonstrated utilizing a fully coherent pump beam. In this paper we demonstrate, the theoretical and experimental generation of polarization entangled single photon pairs by varying the spatial coherence of the pump beam. The effect of the pump beam spatial coherence on the visibility of a polarization-entangled single photon source is investigated. A comparison of the visibility measurements using a fully coherent and partially coherent pump beam is performed...
September 21, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28935981/deterministic-optical-polarisation-in-nitride-quantum-dots-at-thermoelectrically-cooled-temperatures
#20
Tong Wang, Tim J Puchtler, Saroj K Patra, Tongtong Zhu, John C Jarman, Rachel A Oliver, Stefan Schulz, Robert A Taylor
We report the successful realisation of intrinsic optical polarisation control by growth, in solid-state quantum dots in the thermoelectrically cooled temperature regime (≥200 K), using a non-polar InGaN system. With statistically significant experimental data from cryogenic to high temperatures, we show that the average polarisation degree of such a system remains constant at around 0.90, below 100 K, and decreases very slowly at higher temperatures until reaching 0.77 at 200 K, with an unchanged polarisation axis determined by the material crystallography...
September 21, 2017: Scientific Reports
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