474 research outputs found
Charge-transfer in time-dependent density-functional theory via spin-symmetry-breaking
Long-range charge-transfer excitations pose a major challenge for
time-dependent density functional approximations. We show that
spin-symmetry-breaking offers a simple solution for molecules composed of
open-shell fragments, yielding accurate excitations at large separations when
the acceptor effectively contains one active electron. Unrestricted
exact-exchange and self-interaction-corrected functionals are performed on
one-dimensional models and the real LiH molecule within the pseudopotential
approximation to demonstrate our results.Comment: 5 pages, 4 figure
Acid/base-triggered switching of circularly polarized luminescence and electronic circular dichroism in organic and organometallic helicenes.
Electronic circular dichroism and circularly polarized luminescence acid/base switching activity has been demonstrated in helicene-bipyridine proligand 1 a and in its “rollover” cycloplatinated derivative 2 a. Whereas proligand 1 a displays a strong bathochromic shift (>160 nm) of the nonpolarized and circularly polarized luminescence upon protonation, complex 2 a displays slightly stronger emission. This strikingly different behavior between singlet emission in the organic helicene and triplet emission in the organometallic derivative has been rationalized by using quantum-chemical calculations. The very large bathochromic shift of the emission observed upon protonation of azahelicene-bipyridine 1 a has been attributed to the decrease in aromaticity (promoting a charge-transfer-type transition rather than a π–π* transition) as well as an increase in the HOMO–LUMO character of the transition and stabilization of the LUMO level upon protonation
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Tetraphenylpentalenide organolanthanide complexes
The D2h symmetrical 1,3,4,6-tetraphenylpentalenide is an excellent ligand for the stabilisation of strongly coloured bis(pentalenide) LnIII sandwich complexes. These easily accessible compounds complement previously reported lanthanide organometallics and provide new opportunities to understand the roles of the f-orbitals in electronic structure and bonding
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A diuranium carbide cluster stabilized inside a C80 fullerene cage.
Unsupported non-bridged uranium-carbon double bonds have long been sought after in actinide chemistry as fundamental synthetic targets in the study of actinide-ligand multiple bonding. Here we report that, utilizing Ih(7)-C80 fullerenes as nanocontainers, a diuranium carbide cluster, U=C=U, has been encapsulated and stabilized in the form of UCU@Ih(7)-C80. This endohedral fullerene was prepared utilizing the Krätschmer-Huffman arc discharge method, and was then co-crystallized with nickel(II) octaethylporphyrin (NiII-OEP) to produce UCU@Ih(7)-C80·[NiII-OEP] as single crystals. X-ray diffraction analysis reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unexpectedly short uranium-carbon distances (2.03 Å) indicative of covalent U=C double-bond character. The quantum-chemical results suggest that both U atoms in the UCU unit have formal oxidation state of +5. The structural features of UCU@Ih(7)-C80 and the covalent nature of the U(f1)=C double bonds were further affirmed through various spectroscopic and theoretical analyses
Acid/base-triggered switching of circularly polarized luminescence and electronic circular dichroism in organic and organometallic helicenes
Electronic circular dichroism and circularly polarized luminescence acid/base switching activity has been demonstrated in helicene-bipyridine proligand 1 a and in its “rollover” cycloplatinated derivative 2 a. Whereas proligand 1 a displays a strong bathochromic shift (>160 nm) of the nonpolarized and circularly polarized luminescence upon protonation, complex 2 a displays slightly stronger emission. This strikingly different behavior between singlet emission in the organic helicene and triplet emission in the organometallic derivative has been rationalized by using quantum-chemical calculations. The very large bathochromic shift of the emission observed upon protonation of azahelicene-bipyridine 1 a has been attributed to the decrease in aromaticity (promoting a charge-transfer-type transition rather than a π–π* transition) as well as an increase in the HOMO–LUMO character of the transition and stabilization of the LUMO level upon protonation
Проектирование системы электроснабжения цементного завода
Цель работы: разработка системы электроснабжения промышленного предприятия.
В процессе исследования произведен выбор метода расчета, осуществлён расчет электрических нагрузок завода и рассматриваемого цеха, произведён выбор оборудования и его проверка при различных режимах работы.
В результате исследования была спроектирована модель электроснабжения промышленного предприятия, представлена ее техническая целесообразность и безопасность для окружающей среды.
Основные конструктивные, технологические и технико-эксплуатационные характеристики: исследуемый завод состоит из двадцати цехов, из них шесть цехов относятся ко второй категории по надежности электроснабжения; напряжение питающей линии 110 кВ; рабочие напряжения внутри завода: 10/0,4 кВ; схема электроснабжения цеха - магистральная.Objective: Development of power supply system of the industrial enterprise.
In the research process there was chosen the method of calculation, calculation of electrical loads of the enterprise, selection of equipment and it's verification under various operationg conditions.
In the result of the research the model of electrical supply system has been designed. Also there are economical effectiveness and environmental security.
Basic constructive, technological and operational characteristics: there are twenty departments, six of them belong to the second power supply reliability category; voltage of the feeding line is the 110 kV; operating voltages within the plant: 6, 0.4 kV; power supply of consumers of mechanical-repair shop is carried out by trunk power supply network
The Transcription Factor T-bet Regulates Mucosal T Cell Activation in Experimental Colitis and Crohn's Disease
The balance between pro and antiinflammatory cytokines secreted by T cells regulates both the initiation and perpetuation of inflammatory bowel diseases (IBD). In particular, the balance between interferon (IFN)-γ/interleukin (IL)-4 and transforming growth factor (TGF)-β activity controls chronic intestinal inflammation. However, the molecular pathways that evoke these responses are not well understood. Here, we describe a critical role for the transcription factor T-bet in controlling the mucosal cytokine balance and clinical disease. We studied the expression and function of T-bet in patients with IBD and in mucosal T cells in various T helper (Th)1- and Th2-mediated animal models of chronic intestinal inflammation by taking advantage of mice that lack T-bet and retroviral transduction techniques, respectively. Whereas retroviral transduction of T-bet in CD62L+ CD4+ T cells exacerbated colitis in reconstituted SCID mice, T-bet–deficient T cells failed to induce colitis in adoptive transfer experiments suggesting that overexpression of T-bet is essential and sufficient to promote Th1-mediated colitis in vivo. Furthermore, T-bet–deficient CD62L− CD4+ T cells showed enhanced protective functions in Th1-mediated colitis and exhibited increased TGF-β signaling suggesting that a T-bet driven pathway of T cell activation controls the intestinal balance between IFN-γ/IL-4 and TGF-β responses and the development of chronic intestinal inflammation in T cell–mediated colitis. Furthermore, TGF-β was found to suppress T-bet expression suggesting a reciprocal relationship between TGF-β and T-bet in mucosal T cells. In summary, our data suggest a key regulatory role of T-bet in the pathogenesis of T cell–mediated colitis. Specific targeting of this pathway may be a promising novel approach for the treatment of patients with Crohn's disease and other autoimmune diseases mediated by Th1 T lymphocytes
Time dependent density functional theory calculation of van der Waals coefficient C of alkali-metal atoms Li, Na, K, alkali dimers Li, Na, K and sodium clusters Na
In this paper we employ all-electron time dependent density functional theory
(TDDFT) to calculate the long range dipole-dipole dispersion coefficient (van
der Waals coefficient) of alkali-metal atoms Li, Na, K, alkali-metal
atom dimers Li, Na, K and sodium clusters containing even
number of atoms ranging from 2 to 20 atoms. The dispersion coefficients are
obtained via Casimir-Polder expression which relates it to the frequency
dependent linear polarizabilty at imaginary frequencies. The frequency
dependent polarizabilities are calculated by employing TDDFT--based complete
sum-over-states expressions for the atoms, and direct TDDFT linear response
theory for the closed shell dimers and clusters.Comment: 14 pages of text and 4 figure
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