Complexation of 2,6-bis(acylamino)pyridines with dipyridin-2-ylamine and 4,4-dimethylpiperidine-2,6-dione

Intermolecular hydrogen bonds between 2,6-bis(acylamino)pyridines and dipyridin-2-ylamine as well as 4,4-dimethylpiperidine-2,6-dione are responsible for relatively strong interactions between these species. Association has been found to be significantly affected by the size of acyl substituent (chemical shift of the NH proton was used as the main probe in determination of the association constants). Calculations at the DFT level of theory are in line with the experimentally observed results. Calculated energies of the interactions between the complex congeners also show the size of the substituent to affect the association. Conformational changes in the dipyridin-2-ylamine molecule are shown to adapt a geometry suitable for formation of efficient hydrogen bonding.     

GTPP: General Truncated Pyramid Peer-to-Peer Architecture over Structured DHT Networks

Hierarchical Distributed Hash Table (DHT) architectures have been among the most interesting research topics since the birth of flat DHT architecture. However, most of the previous work has merely focused on the two-tier hierarchy. In this paper, we study and analyze General Truncated Pyramid Peer-to-Peer (GTPP) architecture, the generalized version of Partially Vertical Hierarchical Architecture (PV-HA). The idea is to study whether added tiers of hierarchy can provide added value in performance and functionality. Through mathematical analysis, we demonstrate performance results in comparison to flat architecture, which helps understanding the typical characteristics of hierarchical architectures. Firstly, GTPP has slightly higher expected lookup hop count, although it can be decreased with optimizing the sub-overlay setup. However, GTPP significantly decreases the expected lookup routing latency. Secondly, GTPP has clearer and more reasonable traffic distribution among all the peers from different tiers of sub-overlays, and can work with slightly lower maintenance traffic. Thirdly, our studies indicate that two to three tiers are most suitable in most cases for GTPP, considering all the parameters.     

Influence of Modified Terminal Segments on Dynamic Modulus and Viscosity of Dendrimer

Theoretical studies of the influence of modified terminal segments (TSs) on the relaxation spectrum of a dendrimer and dendrimer mechanical properties such as dynamic viscosity, η(ω), the elastic, G′(ω), and loss, G″(ω), moduli have been carried out by the Rouse model. Two major types of modified TS have been studied: (i) TS with an attached rigid massive group (i.e., TSs with additional friction) and (ii) TSs with a length different from the length of an inner segment. In the low‐frequency region, G′(ω), G″(ω), and η(ω) increase with the rise of friction of TS. In the high‐frequency region, dynamic moduli and viscosity depend on the length of TS. In the intermediate region, the moduli and viscosity are determined by a combined parameter: the characteristic time of TS, τ_end, which depends on the friction and length of TS. For both types of TSs, the position of the G″(ω) maximum, ω_max, depends on τ_end. In most of the considered cases, the linear dependence of ω_max on τ_end has been found. The method, which takes into account a deceleration of TS mobility with the rise in the number of generations, n, has been proposed. It was supposed that the effect of the deceleration corresponds to the forming of a dense surface shell with the rise of n, but similar behavior can also be caused by other reasons. In this case, ω_max shifts to the low‐frequency region with an increase in the number of generations. The conclusions of the theory developed in this paper are in agreement with results of the experiment, in which G′(ω) and G″(ω) were obtained for polyamidoamine dendrimers.

     

Controllability method for acoustic scattering with spectral elements

We formulate the Helmholtz equation as an exact controllability problem for the time-dependent wave equation. The problem is then discretized in time domain with central finite difference scheme and in space domain with spectral elements. This approach leads to high accuracy in spatial discretization. Moreover, the spectral element method results in diagonal mass matrices, which makes the time integration of the wave equation highly efficient. After discretization, the exact controllability problem is reformulated as a least-squares problem, which is solved by the conjugate gradient method. We illustrate the method with some numerical experiments, which demonstrate the significant improvements in efficiency due to the higher order spectral elements. For a given accuracy, the controllability technique with spectral element method requires fewer computational operations than with conventional finite element method. In addition, by using higher order polynomial basis the influence of the pollution effect is reduced.     

Overcoming the Cut‐Off Charge Transfer Bandgaps at the PbS Quantum Dot Interface

Light harvesting from large size of semiconductor PbS quantum dots (QDs) with a bandgap of less than 1 eV is one of the greatest challenges precluding the development of PbS QD‐based solar cells because the interfacial charge transfer (CT) from such QDs to the most commonly used electron acceptor materials is very inefficient, if it occurs at all. Thus, an alternative electron‐accepting unit with a new driving force for CT is urgently needed to harvest the light from large‐sized PbS QDs. Here, a cationic porphyrin is utilized as a new electron acceptor unit with unique features that bring the donor–acceptor components into close molecular proximity, allowing ultrafast and efficient electron transfer for QDs of all sizes, as inferred from the drastic photoluminescence quenching and the ultrafast formation of the porphyrin anionic species. The time‐resolved results clearly demonstrate the possibility of modulating the electron transfer process between PbS QDs and porphyrin moieties not only by the size quantization effect but also by the interfacial electrostatic interaction between the positively charged porphyrin and the negatively charged QDs. This approach provides a new pathway for engineering QD‐based solar cells that make the best use of the diverse photons making up the Sun's broad irradiance spectrum.     

Classification accuracy and correlation: LDA in failure prediction

The relationship between canonical correlation and classification accuracy in linear discriminant analysis is explored mathematically. The discriminant score is assumed to conform to a uniform distribution on the interval (0, 1]. This distribution is used as a reference distribution to extract a minimum correlation for certain classification accuracy. Four different cases are analyzed. First, a case for equal group size is considered for an overall accuracy of 100%. Second, the results are generalized for unequal group size. Third, existence of discordant observations is allowed. Fourth, the effect of concentration is analyzed for the first case. The results are demonstrated by numerical examples. In addition, a sample of 2092 default and 63,072 non-default Finnish firms are used to empirically illustrate the results in the context of failure prediction. The results show that group size of default firms, number of discordant observations, and bipolar concentration of observations strongly affect both canonical correlation and classification accuracy.     

Deleting-Inserting Theorem for smooth actions of finite nonsolvable groups on spheres

The paper presents a method which allows to construct smooth finite nonsolvable group actions on spheres with prescribed fixed point data. The idea is to consider an action on a disk with the required fixed point data, and then to apply equivariant surgery to the equivariant double of the disk to remove the second copy of the fixed point data. In this paper, the method is applied to construct smooth group actions on spheres with exactly one fixed point, and more general actions with fixed point set diffeomorphic to any given closed stably parallelizable smooth manifold. The method is expected to be useful for constructions of smooth group actions on spheres with more complicated fixed point data. 1991Mathematics Subject Classification: 57S17, 57S25, 57R67, 57R85.     

Succinobucol's new coat--conjugation with steroids to alter its drug effect and bioavailability

Synthesis, detailed structural characterization (X-ray, NMR, MS, IR, elemental analysis), and studies of toxicity, antioxidant activity and bioavailability of unique potent anti-atherosclerotic succinobucol-steroid conjugates are reported. The conjugates consist of, on one side, the therapeutically important drug succinobucol ([4-{2,6-di-tert-butyl-4-[(1-{[3-tert-butyl-4-hydroxy-5-(propan-2-yl)phenyl]sulfanyl}ethyl)sulfanyl]phenoxy}-4-oxo-butanoic acid]) possessing an antioxidant and anti-inflammatory activity, and on the other side, plant stanol/sterols (stigmastanol, β-sitosterol and stigmasterol) possessing an ability to lower the blood cholesterol level. A cholesterol-succinobucol prodrug was also prepared in order to enhance the absorption of succinobucol through the intestinal membrane into the organism and to target the drug into the place of lipid metabolism-The enterohepatic circulation system. Their low toxicity towards mice fibroblasts at maximal concentrations, their antioxidant activity, comparable or even higher than that of ascorbic acid as determined by direct quenching of the DPPH radical, and their potential for significantly altering total and LDL cholesterol levels, suggest that these conjugates merit further studies in the treatment of cardiovascular or other related diseases. A brief discussion of succinobucol's ability to quench the radicals, supported with a computational model of the electrostatic potential mapped on the electron density surface of the drug, is also presented.