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排序方式: 共有364条查询结果,搜索用时 31 毫秒
61.
62.
Christopher Knie Manuel Utecht Fangli Zhao Hannes Kulla Sergey Kovalenko Prof. Albert M. Brouwer Prof. Peter Saalfrank Prof. Stefan Hecht Dr. David Bléger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16492-16501
Improving the photochemical properties of molecular photoswitches is crucial for the development of light‐responsive systems in materials and life sciences. ortho‐Fluoroazobenzenes are a new class of rationally designed photochromic azo compounds with optimized properties, such as the ability to isomerize with visible light only, high photoconversions, and unprecedented robust bistable character. Introducing σ‐electron‐withdrawing F atoms ortho to the N?N unit leads to both an effective separation of the n→π* bands of the E and Z isomers, thus offering the possibility of using these two transitions for selectively inducing E/Z isomerizations, and greatly enhanced thermal stability of the Z isomers. Additional para‐electron‐withdrawing groups (EWGs) work in concert with ortho‐F atoms, giving rise to enhanced separation of the n→π* transitions. A comprehensive study of the effect of substitution on the key photochemical properties of ortho‐fluoroazobenzenes is reported herein. In particular, the position, number, and nature of the EWGs have been varied, and the visible light photoconversions, quantum yields of isomerization, and thermal stabilities have been measured and rationalized by DFT calculations. 相似文献
63.
Hannes Junginger-Gestrich Enrico Valdinoci 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2009,61(3):393-401
Using theorems of Bangert, we prove a rigidity result which shows how a question raised by Bangert for elliptic integrands
of Moser type is connected, in the case of minimal solutions without self-intersections, to a famous conjecture of De Giorgi
for phase transitions.
The work of Enrico Valdinoci was supported by MIUR Variational Methods and Nonlinear Differential Equations. Diese Zusammenarbeit
wurde bei einem sehr angenehmen Besuch von EV in Freiburg begonnen. 相似文献
64.
On the distribution of penalized maximum likelihood estimators: The LASSO, SCAD, and thresholding 总被引:1,自引:0,他引:1
We study the distributions of the LASSO, SCAD, and thresholding estimators, in finite samples and in the large-sample limit. The asymptotic distributions are derived for both the case where the estimators are tuned to perform consistent model selection and for the case where the estimators are tuned to perform conservative model selection. Our findings complement those of Knight and Fu [K. Knight, W. Fu, Asymptotics for lasso-type estimators, Annals of Statistics 28 (2000) 1356–1378] and Fan and Li [J. Fan, R. Li, Variable selection via non-concave penalized likelihood and its oracle properties, Journal of the American Statistical Association 96 (2001) 1348–1360]. We show that the distributions are typically highly non-normal regardless of how the estimator is tuned, and that this property persists in large samples. The uniform convergence rate of these estimators is also obtained, and is shown to be slower than n−1/2 in case the estimator is tuned to perform consistent model selection. An impossibility result regarding estimation of the estimators’ distribution function is also provided. 相似文献
65.
66.
Rocío García-Vzquez Umberto M. Battisti Jesper T. Jrgensen Vladimir Shalgunov Lars Hvass Daniel L. Stares Ida N. Petersen Franois Crestey Andreas Lffler Dennis Svatunek Jesper L. Kristensen Hannes Mikula Andreas Kjaer Matthias M. Herth 《Chemical science》2021,12(35):11668
Pretargeted imaging can be used to visualize and quantify slow-accumulating targeting vectors with short-lived radionuclides such as fluorine-18 – the most popular clinically applied Positron Emission Tomography (PET) radionuclide. Pretargeting results in higher target-to-background ratios compared to conventional imaging approaches using long-lived radionuclides. Currently, the tetrazine ligation is the most popular bioorthogonal reaction for pretargeted imaging, but a direct 18F-labeling strategy for highly reactive tetrazines, which would be highly beneficial if not essential for clinical translation, has thus far not been reported. In this work, a simple, scalable and reliable direct 18F-labeling procedure has been developed. We initially studied the applicability of different leaving groups and labeling methods to develop this procedure. The copper-mediated 18F-labeling exploiting stannane precursors showed the most promising results. This approach was then successfully applied to a set of tetrazines, including highly reactive H-tetrazines, suitable for pretargeted PET imaging. The labeling succeeded in radiochemical yields (RCYs) of up to approx. 25%. The new procedure was then applied to develop a pretargeting tetrazine-based imaging agent. The tracer was synthesized in a satisfactory RCY of ca. 10%, with a molar activity of 134 ± 22 GBq μmol−1 and a radiochemical purity of >99%. Further evaluation showed that the tracer displayed favorable characteristics (target-to-background ratios and clearance) that may qualify it for future clinical translation.A simple, scalable and reliable direct 18F-labeling procedure has been developed and applied to obtain a pretargeting tetrazine-based imaging agent with favorable in vivo characteristics. 相似文献
67.
68.
Oyer AJ Carrillo JM Hire CC Schniepp HC Asandei AD Dobrynin AV Adamson DH 《Journal of the American Chemical Society》2012,134(11):5018-5021
Applications requiring pristine graphene derived from graphite demand a solution stabilization method that utilizes an easily removable media. Using a combination of molecular dynamics simulations and experimental techniques, we investigate the solublization/suspension of pristine graphene sheets by an equimolar mixture of benzene and hexafluorobenzene (C(6)H(6)/C(6)F(6)) that is known to form an ordered structure solidifying at 23.7 °C. Our simulations show that the graphene surface templates the self-assembly of the mixture into periodic layers extending up to 30 ? from both sides of the graphene sheet. The solvent structuring is driven by quadrupolar interactions and consists of stacks of alternating C(6)H(6)/C(6)F(6) molecules rising from the surface of the graphene. These stacks result in density oscillations with a period of about 3.4 ?. The high affinity of the 1:1 C(6)H(6)/C(6)F(6) mixture with graphene is consistent with observed hysteresis in Wilhelmy plate measurements using highly ordered pyrolytic graphite (HOPG). AFM, SEM, and TEM techniques verify the state of the suspended material after sonication. As an example of the utility of this mixture, graphene suspensions are freeze-dried at room temperature to produce a sponge-like morphology that reflects the structure of the graphene sheets in solution. 相似文献
69.
Bernien H Childress L Robledo L Markham M Twitchen D Hanson R 《Physical review letters》2012,108(4):043604
We report on the observation of quantum interference of the emission from two separate nitrogen vacancy (NV) centers in diamond. Taking advantage of optically induced spin polarization in combination with polarization filtering, we isolate a single transition within the zero-phonon line of the nonresonantly excited NV centers. The time-resolved two-photon interference contrast of this filtered emission reaches 66%. Furthermore, we observe quantum interference from dissimilar NV centers tuned into resonance through the dc Stark effect. These results pave the way towards measurement-based entanglement between remote NV centers and the realization of quantum networks with solid-state spins. 相似文献
70.
Recently, the scaling result z=d for the dynamic critical exponent at the Bose glass to superfluid quantum phase transition has been questioned both on theoretical and numerical grounds. This motivates a careful evaluation of the critical exponents in order to determine the actual value of z. We study a model of quantum bosons at T=0 with disorder in 2D using highly effective worm Monte?Carlo simulations. Our data analysis is based on a finite-size scaling approach to determine the scaling of the quantum correlation time from simulation data for boson world lines. The resulting critical exponents are z=1.8±0.05, ν=1.15±0.03, and η=-0.3±0.1, hence suggesting that z=2 is not satisfied. 相似文献