New Triterpenoid Saponins from Achyrantes aspera Linn.

Two new bisdesmosidic triterpenoid saponins, i.e. 1 and 2 , were isolated, besides the three known saponins 3 – 5 , from the MeOH extract of the aerial parts of Achyranthes aspera Linn. (Amaranthaceae). Their structures were elucidated as β‐D ‐glucopyranosyl 3β‐[O‐α‐L ‐rhamnopyranosyl‐(1→3)‐O‐β‐D ‐glucopyranuronosyloxy]machaerinate ( 1 ) and β‐D ‐glucopyranosyl 3β‐[O‐β‐D ‐galactopyranosyl‐(1→2)‐O‐α‐D ‐glucopyranuronosyloxy]machaerinate ( 2 ) by NMR spectroscopy, including 2D‐NMR experiments (machaerinic acid=3β,21β‐dihydroxyolean‐12‐en‐28‐oic acid). The other saponins were identified as β‐D ‐glucopyranosyl 3β[O‐α‐L ‐rhamnopyranosyl‐(1→3)‐O‐β‐D ‐glucopyranuronosyloxy]oleanolate ( 3 ), β‐D ‐glucopyranosyl 3‐β‐[O‐β‐D ‐galactopyranosyl‐(1→2)‐O‐β‐D ‐glucopyranuronosyloxy]oleanolate ( 4 ), and β‐D ‐glucopyranosyl 3β‐[O‐β‐D ‐glucopyranuronosyloxy]oleanolate ( 5 ) (oleanolic acid=3β‐hydroxyolean‐12‐en‐28‐oic acid).     

Membrane distillation operated at high seawater concentration factors: Role of the membrane on CaCO3 scaling in presence of humic acid

This study aims at investigating the kinetics of calcium carbonate precipitation (scaling), that occurs in the form of vaterite, when treating seawater by direct contact membrane distillation (DCMD) operated at high concentration factors (from 4 to 6). Induction time measurements carried out by dynamic light scattering (DLS) allowed to identify the shifting between homogeneous and heterogeneous nucleation mechanisms as a function of supersaturation. CaCO₃ interfacial energy, evaluated for concentrated seawater solutions as 45 mJ/m², increased by 7% as a consequence of the inhibition effect of humic acid, and it was reduced to 32 mJ/m² in correspondence of heterogeneous nucleation occurring on microporous polypropylene membranes. Gibbs free energy barrier to the formation of critical nuclei was predicted with good accuracy as a function of physico-chemical properties of the membrane (porosity: 0.70, contact angle: 115 ± 2°).     

Simulation-based evolution of resupply and routing policies in rich vendor-managed inventory scenarios

Vendor managed inventory combines inventory management and transportation. Compared to classical inventory management approaches, this strategy offers various degrees of freedom for the vendor while providing a certain service quality level for the customers. To capture the characteristics of rich real-world scenarios, our problem formulation consists of multiple customers, many products and stochastic product usages. Additionally, we also consider mixed formulations, where only a certain part of the customers is switched to a vendor managed inventory to allow a stepwise transition. We show that resupply and routing policies can be evolved autonomously for those scenarios using a simulation-based optimization approach. By combining inventory management and routing, the resulting policies aim to minimize costs and to maximize resource usage while maintaining a given service level. In order to validate our approach, we perform case studies and apply the evolved rules on a large-scale vendor managed inventory scenario for supermarkets. Furthermore, we show that our methodology can be used to perform a sensitivity analysis by considering the influence of exogenous and endogenous factors on the decision process, if a customer base should be transitioned to a vendor managed inventory.     

Analysis of a map-based neuronal model

ABSTRACT

Subthreshold oscillations in neurons are those oscillations which do not attain the critical value of the membrane's voltage needed for triggering an action potential (a spike). Their contribution to the forming of action potentials in neurons is a current field of research in biology. The present work approaches this subject using tools from mathematical modelling, more exactly, a neuronal non-smooth map-based model is proposed and studied. The behaviour of the model in a noisy medium is also studied.     

Direct arylation polymerization toward a narrow bandgap donor–acceptor conjugated polymer of alternating 5,6‐difluoro‐2,1,3‐benzothiadiazole and alkyl‐quarternarythiophene: From synthesis,optoelectronic properties to devices

ABSTRACT: Direct arylation polymerization (DAP) enabled facile synthesis of a narrow bandgap donor–acceptor conjugated polymer (PDFBT‐Th₄) composed of alternating 5,6‐difluoro‐2,1,3‐benzothiadiazole and alkyl‐quaternarythiophene. The optimized reaction condition of DAP catalyzed with Pd(OAc)₂/(o‐MeOPh)₃P/PivOH/K₂CO₃ in o‐xylene led to the target polymer with a number‐average molecular weight (M_n) of 14.6 kDa without noticeable homocoupling or β‐branching defects. UV‐vis absorption spectra of PDFBT‐Th₄ indicate strong interchain aggregation in films. While the C‐H selectivity and the alternating polymer structure of PDFBT‐Th₄ synthesized via DAP are comparable to those of the same type polymers synthesized via Stille coupling, the batch of PDFBT‐Th₄ synthesized via optimal DAP, despite its lower M_n, showed higher hole mobility in field effect transistors and larger power conversion efficiency in organic solar cell devices. These results further demonstrate the promising potential of DAP for efficient synthesis of high‐performance D‐A conjugated polymers for broad optoelectronic applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1869–1879     

Effects on the x-ray spectra of metals due to final-state interactions with effective barriers and shape resonances

Model calculations of X-ray absorption, emission, and photoemission spectral lineshapes are reported for intrinsic and extrinsic core excitations in metals with final-state interactions that can be represented by a central attractive potential surrounded by an effective barrier on its periphery. Some of the calculated spectra exhibit novel features: XPS lineshapes with multi-electron shake-off sidebands and features characteristic of resonances and anti-resonances, and X-ray absorption and emission spectra with (i) edges that are apparently peaked (on a moderate energy scale) when the X-ray edge singularity causes them to be, in fact, suppressed on a fine scale, (ii) edges that are markedly rounded, and (iii) gross spectral features that are influenced greatly by the electronic structure of the iniial state of the Fermi sea, and only weakly by the final-state.     

Decision Trees with Continuous Distribution

Decision trees are often used as a convenient way to visualize, and then solve, a decision problem. A standard problem approached in this way is a decision as to whether or not to sample, followed by a decision whether or not to engage in an activity. This approach has been limited to a small number of sample outcomes to be practical. This paper develops an approach which permits a continuous distribution of sample outcomes to be used. A new distribution, the "skewed parabolic distribution" is introduced as a flexible way of representing the judgemental (probabilistic) beliefs of the assessor. This new distribution is compared with the beta distribution. An algorithm, which is easily programmed and is practical for hand computation with a calculator and logarithm tables, is developed for the complete solution of a decision tree problem using this skewed parabolic distribution. An example is given. It is concluded that the skewed parabolic distribution makes use of continuous distributions practical for decision trees, and has advantages over the beta for this purpose.     

Direct arylation polymerization toward efficient synthesis of benzo[1,2-c:4,5-c'] dithiophene-4,8-dione based donor-acceptor alternating copolymers for organic optoelectronic applications

Wide-bandgap π-conjugated donor-acceptor (D-A) alternating copolymers consisting of benzo[1,2-c:4,5-c']dithiophene-4,8-dione (BDTD) as the electron-accepting building block have demonstrated outstanding performances in organic bulk heterojunction (BHJ) solar cell devices. But the synthesis of these polymers has been largely limited to conventional polymerization techniques, particularly Stille-coupling based polycondensations, which often involve tedious preactivation of C-H bonds using highly flammable reagents such as butyl lithium and highly toxic reagents such as trialkyl tin chlorides. Herein, we report a “greener” synthetic route of direct arylation polymerization to a series of wide bandgap D-A copolymers with a common acceptor building block of BDTD. The structure–property relationship in these polymers is characterized. We also present the device performances of these polymers in both thin-film field-effect transistors and organic BHJ solar cells involving the BDTD-based polymers as the electron donors and fullerene derivatives as the electron acceptors. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2554–2564     

ENERGY TRANSFER AND ENERGY LOSSES IN BILAYER MEMBRANE VESICLES (LIPOSOMES)

Abstract. The efficiency of singlet-singlet energy transfer was studied in bilayer lipid membrane vesicles (liposomes) for the following donor-acceptor systems: (1) p -terphenyl (TP) and diphenyloctatetraene (DPO); (2) DPO and chlorophyll a (Chl a ); and (3) β-carotene and Chl a. The energy transfer efficiency φ_DA was measured by sensitized fluorescence of the acceptor. Fractional quenching of the donor φ_Q was found from the donor fluorescence in absence and presence of the acceptor. For TP-DPO and for DPO-Chl a , the transfer efficiency increased with increasing acceptor concentration but was essentially independent of the donor concentration. No energy transfer from β-carotene to Chl a could be detected. In liposomes, φ_DA differed only slightly from φ_Q at all donor and acceptor concentrations, thus demonstrating the absence of any appreciable energy losses. For solutions of the same donor-acceptor pairs in cyclohexane φ_Q was considerably larger than φ_DA. The difference represents energy lost, principally by internal conversion, due to collisional quenching. The principal function of the lipid membrane appears to be the suppression of such losses. In addition, the rate of energy transfer in lipid membranes is about double that in solutions (at the same intermolecular distance) due to more favorable orientation.