Hydrolysis and retro‐aldol cleavage of ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate: competing reactions

The hydrolysis of ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate ( 1 ) and the parent ester ethyl 3‐hydroxybutyrate ( 4 ) has been studied experimentally and computationally. In the hydrolysis of threo‐ester 1 with 2 M NaOH, predominantly retro‐aldol product was observed, whereas the hydrolyzed product was present in a minor amount. When the reaction is carried out under the same conditions with the parent ester ethyl 3‐hydroxybutyrate ( 4 ), hydrolyzed product is exclusively observed. The competitive pathways, namely hydrolysis and the retro‐aldol reaction for 1 and 4 were investigated using DFT calculations in the both gas and solvent phase. The calculated results in the solvent phase at B3LYP/6–31 + G* level revealed that the formation of retro‐aldol products is kinetically preferred over the hydrolysis of threo‐ester 1 in the presence of a base. However, the parent ester 4 showed that the retro‐aldol process is less favored than the hydrolysis process under similar conditions. The steric effect imposed by the bulky adamantyl group to enhance the activation barriers for the hydrolysis of the ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate ( 1 ) was further supported by the calculations performed with tert‐butyl group at the α‐carbon atom of ethyl 3‐hydroxybutyrate ( 7 ). Copyright © 2010 John Wiley & Sons, Ltd.     

基于窄带多区域水平集方法的遥感图像分割

由于遥感图像存在边缘混叠等问题,经典的C-V模型会产生大量的冗余轮廓,而且无法分割多个同质区域的目标.为此,提出了基于C-V模型的窄带多区域水平集图像分割方法,采用N-1个水平集函数将图像分割成N(N＞1)个区域,每个水平集函数表达一个区域.该方法一方面通过建立独立多区域水平集模型可以消除多余的轮廓,避免分割区域的重叠...     

Plasmonic crystal waveguides

We study the properties of electromagnetic waves propagating along the waveguides with a periodic core created by alternating metal and dielectric layers, the so-called quasi-one-dimensional plasmonic crystal waveguides. Such waveguides can be symmetric or asymmetric, depending on the cladding or substrate material properties, as well as on the termination of the periodic structure. We analyze the dispersion characteristics as well as the profiles of the guided modes for several types of waveguide structure.     

On managerial risk-taking incentives when compensation may be hedged against

We consider a continuous time principal-agent model where the principal/firm compensates an agent/manager who controls the output’s exposure to risk and its expected return. Both the firm and the manager have exponential utility and can trade in a frictionless market. When the firm observes the manager’s choice of effort and volatility, there is an optimal contract that induces the manager to not hedge. In a two factor specification of the model where an index and a bond are traded, the optimal contract is linear in output and the log return of the index. We also consider a manager who receives exogenous share or option compensation and illustrate how risk taking depends on the relative size of the systematic and firm-specific risk premia of the output and index. Whilst in most cases, options induce greater risk taking than shares, we find that there are also situations under which the hedging manager may take less risk than the non-hedging manager.     

Nonmyopic optimal portfolios in viable markets

We provide a representation for the nonmyopic optimal portfolio of an agent consuming only at the terminal horizon when the single state variable follows a general diffusion process and the market consists of one risky asset and a risk-free asset. The key term of our representation is a new object that we call the “rate of macroeconomic fluctuation” whose properties are fundamental for the portfolio dynamics. We show that, under natural cyclicality conditions, (i) the agent’s hedging demand is positive (negative) when the product of his prudence and risk tolerance is below (above) two and (ii) the portfolio weights decrease in risk aversion. We apply our results to study a general continuous-time capital asset pricing model and show that under the same cyclicality conditions, the market price of risk is countercyclical and the price of the risky asset exhibits excess volatility.     

Optimal contracting with effort and misvaluation

We propose a new continuous-time contracting model, in which the firm value process can only be observed with noise, and there are two sources of moral hazard: the agent’s effort and misvaluation. The principal can induce the agent to alter the perceived fundamental value of the firm through misvaluation, thus changing the market estimate of that value. We consider two cases in detail: the one in which the market correctly anticipates only the effort, and the other in which it correctly anticipates both the effort and the amount of misvaluation. In the first case, we find that it is optimal for the principal to induce the agent to apply a non-zero amount of misvaluation. Using calculus of variation techniques, we find the optimal pay-per-performance sensitivity (PPS) of the contract and optimal effort and misvaluation amount, by means of solving of a second order ordinary differential equation. In the second case, which can be viewed as an extension of the seminal Holmstrom-Milgrom model to the case of noisy observations, we find that the optimal misvaluation value is zero, and we compare the resulting optimal contract to the Holmstrom-Milgrom contract.     

Influence of UV irradiation and subsequent chemical grafting on the surface properties of cellulose

Cellulose - This work is devoted to the study of surface properties of cellulose before and after a surface modification. Surface modification of polymeric materials was carried out in two steps:...     

Homological Algebra for Persistence Modules

Foundations of Computational Mathematics - We develop some aspects of the homological algebra of persistence modules, in both the one-parameter and multi-parameter settings, considered as either...     

An extension of the Landau-Kolmogorov inequality. Solution of a problem of Erdös

For any fixed finite interval [a, b] on the real line, an arbitrary natural numberr and σ>0, we describe the extremal function to the problem $\left\| {f^{(k)} } \right\|L_p \left[ {a,b} \right]^{ \to \sup } \left( {1 \leqslant k \leqslant r - 1, 1 \leqslant p< \infty } \right)$ over all functionsf ∈W _∞ ^r such that |f ^(r)(x)| ≤σ, |f(x)|≤1 on (?∞, ∞). Similarly, we solve the problem, raised by Paul Erdös, of characterizing the trigonometric polynomial of fixed uniform norm whose graph has maximal arc length over [a, b].