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排序方式: 共有1113条查询结果,搜索用时 15 毫秒
111.
Dr. Jiawen Fang Prof. Dr. Yiou Wang Mariam Kurashvili Dr. Sebastian Rieger Dr. Wiktor Kasprzyk Qingli Wang Prof. Dr. Jacek K. Stolarczyk Prof. Dr. Jochen Feldmann Dr. Tushar Debnath 《Angewandte Chemie (International ed. in English)》2023,62(33):e202305817
Photocatalytic water splitting is a promising approach to generating sustainable hydrogen. However, the transport of photoelectrons to the catalyst sites, usually within ps-to-ns timescales, is much faster than proton delivery (∼μs), which limits the activity. Therefore, the acceleration of abstraction of protons from water molecules towards the catalytic sites to keep up with the electron transfer rate can significantly promote hydrogen production. The photobasic effect that is the increase in proton affinity upon excitation offers means to achieve this objective. Herein, we design photobasic carbon dots and identify that internal pyridinic N sites are intrinsically photobasic. This is supported by steady-state and ultrafast spectroscopic measurements that demonstrate proton abstraction within a few picoseconds of excitation. Furthermore, we show that in water, they form a unique four-level lasing scheme with optical gain and stimulated emission. The latter competes with photocatalysis, revealing a rather unique mechanism for efficiency loss, such that the stimulated emission can act as a toggle for photocatalytic activity. This provides additional means of controlling the photocatalytic process and helps the rational design of photocatalytic materials. 相似文献
112.
Matthias Mawick Carolin Jaworski Jens Bittermann Dr. Ljuba Iovkova Yinglan Pu Prof. Dr. Carmen Wängler Prof. Dr. Björn Wängler Prof. Dr. Klaus Jurkschat Prof. Dr. Norbert Krause Prof. Dr. Ralf Schirrmacher 《Angewandte Chemie (International ed. in English)》2023,62(50):e202309002
The ring-opening Si-fluorination of a variety of azasilole derivatives cyclo-1-(iPr2Si)−4-X−C6H3−2-CH2NR ( 4 : R=2,6-iPr2C6H3, X=H; 4 a : R=2,4,6-Me3C6H2, X=H; 9 : R=2,6-iPr2C6H3, X=tBuMe2SiO; 10 : R=2,6-iPr2C6H3, X=OH; 13 : R=2,6-iPr2C6H3, X=HCCCH2O; 22 : R=2,6-iPr2C6H3, X=tBuMe2SiCH2O) with different 19F-fluoride sources was studied, optimized and the experience gained was used in a translational approach to create a straightforward 18F-labelling protocol for the azasilole derivatives [18F] 6 and [18F] 14 . The latter constitutes a potential clickable CycloSiFA prosthetic group which might be used in PET tracer development using Cu-catalysed triazole formation. Based on our findings, CycloSiFA has the potential to become a new entry into non-canonical labelling methodologies for radioactive PET tracer development. 相似文献
113.
石膏在我国储量丰富,应用广泛,快速准确分析其成分含量对石膏资源的综合利用具有重要意义。针对酸溶法无法测定SiO2,碱熔法无法测定K2O、Na2O的问题,本文建立一种偏硼酸锂-四硼酸锂熔融-电感耦合等离子体发射光谱法同时测定石膏中CaO、SO3、Al2O3、Fe2O3、MgO、TiO2、K2O、Na2O、SiO2含量。实验优化了熔剂用量、熔融温度,结果表明采用试样与偏硼酸锂-四硼酸锂混合熔剂质量比例1:5,在铂金坩埚中1000 ℃熔融10 min,在超声条件下,于50 mL 10 %盐酸中浸取熔融物,能够有效分解试样而浸取待测组分。向标准溶液系列中加入偏硼酸锂-四硼酸锂-盐酸基体溶液以消除基体对测试结果的影响。各待测组分的校准曲线的相关性系数均大于0.9990,方法检出限在3~292 μg/g范围内;采用实验方法分别对国家一级标准物质GBW03109a、GBW03110和实际样品进行测定,标准物质的5次平行测试的相对标准偏差在0.14 %~8.86 %之间,测定结果的相对误差在0.03~8.75 %之间,测试结果与标准值无显著性差异;实际样品中各成分测定值的RSD(n=5)为0.24~8.80 %。该方法操作简单、准确度高、精密度好、检出限低,可以同时测定石膏中的多组分含量,能够为石膏资源综合利用调查评价提供一定的技术支撑 。 相似文献
114.
115.
在理论上通过推导首次得出了Black-Litterman模型(B-L模型)最优权重与信心水平的公式.在各资产收益不相关及单一绝对观点的假设下,得出各资产的B-L模型最优权重与信心水平的简化表达式.借助于此,还对信心水平与最优权重公式的进一步理论分析,并以光大证券的"乌龙指"做实证,详细分析投资者在没有市场观点、拥有内幕信息、以及信心水平在某范围变化时,其所持各投资品权重的特点. 相似文献
116.
Optimal trading strategies are found for an insider who is trading in two convergent stocks and is bound by margin constraints. 相似文献
117.
本文构建了电力供应链网络均衡模型,网络中包含三级决策主体,分别是:发电厂、电力服务商和用电市场.在分析各级决策者行为的基础上,得到了基于变分不等式的均衡条件,研究了针对发电厂的排污权交易政策设计问题.研究发现:排污交易政策实施后,总排污量不会超过给定的排污权总量;发电厂清洁生产能力的差异对排污权交易政策影响显著. 相似文献
118.
ABSTRACTWe compare optimal liquidation policies in continuous time in the presence of trading impact using numerical solutions of Hamilton–Jacobi–Bellman (HJB) partial differential equations (PDEs). In particular, we compare the time-consistent mean-quadratic-variation strategy with the time-inconsistent (pre-commitment) mean-variance strategy. We show that the two different risk measures lead to very different strategies and liquidation profiles. In terms of the optimal trading velocities, the mean-quadratic-variation strategy is much less sensitive to changes in asset price and varies more smoothly. In terms of the liquidation profiles, the mean-variance strategy is much more variable, although the mean liquidation profiles for the two strategies are surprisingly similar. On a numerical note, we show that using an interpolation scheme along a parametric curve in conjunction with the semi-Lagrangian method results in significantly better accuracy than standard axis-aligned linear interpolation. We also demonstrate how a scaled computational grid can improve solution accuracy. 相似文献
119.
Optimal Security Liquidation Algorithms 总被引:1,自引:0,他引:1
Sergiy Butenko Alexander Golodnikov Stanislav Uryasev 《Computational Optimization and Applications》2005,32(1-2):9-27
This paper develops trading strategies for liquidation of a financial security, which maximize the expected return. The problem is formulated as a stochastic programming problem that utilizes the scenario representation of possible returns. Two cases are considered, a case with no constraint on risk and a case when the risk of losses associated with trading strategy is constrained by Conditional Value-at-Risk (CVaR) measure. In the first case, two algorithms are proposed; one is based on linear programming techniques, and the other uses dynamic programming to solve the formulated stochastic program. The third proposed algorithm is obtained by adding the risk constraints to the linear program. The algorithms provide path-dependent strategies, i.e., the fraction of security sold depends upon price sample-path of the security up to the current moment. The performance of the considered approaches is tested using a set of historical sample-paths of prices. 相似文献
120.
The purpose of this paper is to present a general stochastic calculus
approach to insider trading. We consider a market driven by a standard Brownian
motion $B(t)$ on a filtered probability space $\displaystyle
(\Omega,\F,\left\{\F\right\}_{t\geq 0},P)$ where the coefficients are
adapted to a filtration ${\Bbb G}=\left\{\G_t\right\}_{0\leq t\leq T}$,
with $\F_t\subset\G_t$ for all $t\in [0,T]$, $T>0$ being a fixed terminal time.
By
an {\it insider} in this market we
mean a person who has access to a filtration (information)
$\displaystyle{\Bbb H}=\left\{\H_t\right\}_{0\leq t\leq T}$ which is strictly
bigger than the filtration
$\displaystyle{\Bbb G}=\left\{\G_t\right\}_{0\leq t\leq T}$.
In this context an insider strategy is represented by an
$\H_t$-adapted process
$\phi(t)$ and we interpret all anticipating integrals as
the forward integral defined in
[23] and [25].
We consider an optimal portfolio problem with
general utility for an insider with access to a general information
$\H_t \supset\G_t$ and show that if
an optimal insider portfolio $\pi^*(t)$ of this problem exists, then
$B(t)$ is an $\H_t$-semimartingale, i.e. the enlargement
of filtration property holds. This is a converse of previously
known results in this field.
Moreover, if $\pi^*$ exists
we obtain an explicit expression in terms of $\pi^*$ for the
semimartingale decomposition of $B(t)$ with respect to $\H_t$.
This is a generalization
of results in [16], [20] and [2]. 相似文献