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991.
Dóra Rédei Norbert Kúsz Tímea Rafai Anita Bogdanov Katalin Burián Attila Csorba Attila Mándi Tibor Kurtán Andrea Vasas Judit Hohmann 《Tetrahedron》2019,75(10):1364-1370
Two new 14-noreudesmane sesquiterpenes, one new phenylpropane heterodimer, caulilexin C, and uvaol were isolated from the 70% MeOH extract of the fruit peel of Elaeagnus rhamnoides. The structures of the compounds were elucidated by HRESIMS and advanced NMR methods. The absolute configuration of (R)-6,9-dihydroxy-1-oxo-14-noreudesm-5,7,9-triene was determined by the TDDFT-ECD method. The new compounds, together with structurally similar naphthalenes (musizin, musizin-8-O-glucoside, torachrysone-8-O-glucoside) and 1,4-naphthoquinone (2-methylstipandrone), isolated previously from Rumex aquaticus, were investigated for their antiviral activity against Herpes simplex virus type 2 (HSV-2) using two different methods. Applying the traditional virus yield reduction test, (R)-6,9-dihydroxy-1-oxo-14-noreudesm-5,7,9-triene, 1-[3-methoxy-4-(2-methoxy-4-(1E)-propenyl-phenoxy)-phenyl]-propane-1,2-diol, and musizin caused a 2.00 log10, 3.49 log10, and 2.33 log10 reduction of HSV-2 yield, respectively, at a concentration of 12.5?μM. 2-Hydroxy-1-methoxy-6,9-dioxo-14-noreudesm-1,3,5(10),7-tetraene exhibited an antiviral effect at concentration of 50?μM only. Similar results were obtained when the qPCR method was used to test the antiviral activity of the compounds. 相似文献
992.
Debasish Manna Basudeb Maji Soumyashree A. Gangopadhyay Kurt J. Cox Qingxuan Zhou Benjamin K. Law Ralph Mazitschek Amit Choudhary 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(19):6351-6355
Several genome engineering applications of CRISPR‐Cas9, an RNA‐guided DNA endonuclease, require precision control of Cas9 activity over dosage, timing, and targeted site in an organism. While some control of Cas9 activity over dose and time have been achieved using small molecules, and spatial control using light, no singular system with control over all the three attributes exists. Furthermore, the reported small‐molecule systems lack wide dynamic range, have background activity in the absence of the small‐molecule controller, and are not biologically inert, while the optogenetic systems require prolonged exposure to high‐intensity light. We previously reported a small‐molecule‐controlled Cas9 system with some dosage and temporal control. By photocaging this Cas9 activator to render it biologically inert and photoactivatable, and employing next‐generation protein engineering approaches, we have built a system with a wide dynamic range, low background, and fast photoactivation using a low‐intensity light while rendering the small‐molecule activator biologically inert. We anticipate these precision controls will propel the development of practical applications of Cas9. 相似文献
993.
The phase structure of hadronic matter at high density relevant to the physics of compact stars and relativistic heavy-ion collisions is studied in a low-energy effective quark theory. The relevant phases that figure are (1) chiral condensation, (2) diquark color condensation (color superconductivity) and (3) induced Lorentz-symmetry breaking (“ISB”). For a reasonable strength for the effective four-Fermi current–current interaction implied by the low-energy effective quark theory for systems with a Fermi surface we find that the “ISB” phase sets in together with chiral symmetry restoration (with the vanishing quark condensate) at a moderate density while color superconductivity associated with scalar diquark condensation is pushed up to an asymptotic density. Consequently, color superconductivity seems rather unlikely in heavy-ion collisions although it may play a role in compact stars. Lack of confinement in the model makes the result of this analysis only qualitative but the hierarchy of the transitions we find seems to be quite robust. 相似文献
994.
Christina Kjær Dr. Henriette Lissau Nina Katharina Gravesen Salinas Andreas Østergaard Madsen Dr. Mark H. Stockett Freja E. Storm Thomas Holm Hansen Prof. Jens Ulrik Andersen Prof. Bo W. Laursen Prof. Kurt V. Mikkelsen Prof. Mogens Brøndsted Nielsen Prof. Steen Brøndsted Nielsen 《Chemphyschem》2019,20(4):533-537
Being alone or together makes a difference for the photophysics of dyes but for ionic dyes it is difficult to quantify the interactions due to solvent screening and nearby counter ions. Gas-phase luminescence experiments are desirable and now possible based on recent developments in mass spectrometry. Here we present results on tailor-made rhodamine homodimers where two dye cations are separated by methylene linkers, (CH2)n. In solution the fluorescence is almost identical to that from the monomer whereas the emission from bare cation dimers redshifts with decreasing n. In the absence of screening, the electric field from the charge on one dye is strong enough to polarize the other dye, both in the ground state and in the excited state. An electrostatic model based on symmetric dye responses (equal induced-dipole moments in ground state) captures the underlying physics and demonstrates interaction even at large distances. Our results have possible implications for gas-phase Förster Resonance Energy Transfer. 相似文献
995.
We consider a class of stochastic electromagnetic beams, and we show both analytically and by numerical examples that coherence properties of the electromagnetic field in the source plane affect the polarization properties of the radiated beam. 相似文献
996.
In this paper we develop the ergodic theory for a horseshoe map f which is uniformly hyperbolic, except at one parabolic fixed point ω and possibly also on W
s
(ω). We call f a parabolic horseshoe map. In order to analyze dynamical and geometric properties of such horseshoes, by making use of induced
maps, we establish, in the context of σ-finite measures, an appropriate version of the variational principle for continuous potentials with mild distortion defined
on subshifts of finite type. Staying in this setting, we propose a concept of σ-finite equilibrium states (each classical probability equilibrium state is a σ-finite equilibrium state). We then study the unstable pressure function , the corresponding finite and σ-finite equilibrium states and their associated conditional measures. The main idea is to relate the pressure function to
the pressure of an embedded parabolic iterated function system and to apply the developed theory of the symbolic σ-finite thermodynamic formalism. We prove, in particular, an appropriate form of the Bowen-Ruelle-Manning-McCluskey formula,
the existence of exactly two σ-finite ergodic conservative equilibrium states for the potential –t
u
log |Df|E
u
| (where t
u
denotes the unstable dimension), one of which is the Dirac δ-measure supported at the parabolic fixed point and the other being non-atomic. We also show that the conditional measures
of this non-atomic equilibrium state on unstable manifolds, are equivalent to (finite and positive) packing measures, whereas
the Hausdorff measures vanish. As an application of our results we obtain a classification for the existence of a generalized
physical measure, as well as a criteria implying the non-existence of an ergodic measure of maximal dimension.
The research of the first author was supported in part by the NSF Grant DMS 0400481.
The research of the second author was supported in part by the National Science Foundation under Grant No. EPS-0236913 and
matching support from the State of Kansas through Kansas Technology Enterprise Corporation. 相似文献
997.
We investigate the possibility of dividing quantum channels into concatenations of other channels, thereby studying the semigroup
structure of the set of completely-positive trace-preserving maps. We show the existence of ‘indivisible’ channels which can not be written as non-trivial products of other channels and study the set of ‘infinitesimal divisible’ channels which are elements of continuous completely positive evolutions. For qubit channels we obtain a complete characterization
of the sets of indivisible and infinitesimal divisible channels. Moreover, we identify those channels which are solutions
of time-dependent master equations for both positive and completely positive evolutions. For arbitrary finite dimension we
prove a representation theorem for elements of continuous completely positive evolutions based on new results on determinants
of quantum channels and Markovian approximations. 相似文献
998.
Lestinsky M Lindroth E Orlov DA Schmidt EW Schippers S Böhm S Brandau C Sprenger F Terekhov AS Müller A Wolf A 《Physical review letters》2008,100(3):033001
Term energies for dielectronic-recombination Rydberg resonances below 0.07 eV are determined for Sc18+ with absolute accuracies below 0.0002 eV by electron collision spectroscopy in an ion storage ring, using the twin-electron-beam technique and a cryogenic photocathode. The lithiumlike 2s_{1/2}-2p_{3/2} transition energy for Z=21 is determined to 4.6 ppm, less than 1% of the few-body effects on radiative corrections. Features from the hyperfine structure of the 2s state could be resolved in the dielectronic-recombination spectrum. 相似文献
999.
Quadrature demodulation-based phase rotation beamforming (QD-PRBF) is commonly used to support dynamic receive focusing in medical ultrasound systems. However, it is computationally demanding since it requires two demodulation filters for each receive channel. To reduce the computational requirements of QD-PRBF, we have previously developed two-stage demodulation (TSD), which reduces the number of lowpass filters by performing demodulation filtering on summation signals. However, it suffers from image quality degradation due to aliasing at lower beamforming frequencies. To improve the performance of TSD-PRBF with reduced number of beamforming points, we propose a new adaptive field-of-view (AFOV) imaging method. In AFOV imaging, the beamforming frequency is adjusted depending on displayed FOV size and the center frequency of received signals. To study its impact on image quality, simulation was conducted using Field II, phantom data were acquired from a commercial ultrasound machine, and the image quality was quantified using spatial (i.e., axial and lateral) and contrast resolution. The developed beamformer (i.e., TSD-AFOV-PRBF) with 1024 beamforming points provided comparable image resolution to QD-PRBF for typical FOV sizes (e.g., 4.6% and 1.3% degradation in contrast resolution for 160 mm and 112 mm, respectively for a 3.5 MHz transducer). Furthermore, it reduced the number of operations by 86.8% compared to QD-PRBF. These results indicate that the developed TSD-AFOV-PRBF can lower the computational requirement for receive beamforming without significant image quality degradation. 相似文献
1000.
In vivo determination of the time and location of mucoadhesive drug delivery systems disintegration in the gastrointestinal tract 总被引:1,自引:0,他引:1
Kremser C Albrecht K Greindl M Wolf C Debbage P Bernkop-Schnürch A 《Magnetic resonance imaging》2008,26(5):638-643
OBJECTIVE: The objective of this study was to use magnetic resonance imaging (MRI) to detect the time when and the location at which orally delivered mucoadhesive drugs are released. MATERIALS AND METHODS: Drug delivery systems comprising tablets or capsules containing a mucoadhesive polymer were designed to deliver the polymer to the intestine in dry powder form. Dry Gd-DTPA [diethylenetriaminepentaacetic acid gadolinium(III) dihydrogen salt hydrate] powder was added to the mucoadhesive polymer, resulting in a susceptibility artifact that allows tracking of the application forms before their disintegration and that gives a strong positive signal on disintegration. Experiments were performed with rats using T(1)-weighted spin-echo imaging on a standard 1.5-T MRI system. RESULTS: The susceptibility artifact produced by the dry Gd-DTPA powder in tablets or capsules was clearly visible within the stomach of the rats and could be followed during movement towards the intestine. Upon disintegration, a strong positive signal was unambiguously observed. The time between ingestion and observation of a positive signal was significantly different for different application forms. Quantification of the remaining mucoadhesive polymer in the intestine 3 h after observed release showed significant differences in mucoadhesive effectiveness. CONCLUSION: MRI allows detection of the exact time of release of the mucoadhesive polymer in vivo, which is a prerequisite for a reliable quantitative comparison between different application forms. 相似文献