34 research outputs found

    Calculation of Infrared/Raman Spectra and Dielectric Properties of Various Crystalline Poly(lactic acid)s by Density Functional Perturbation Theory (DFPT) Method

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    We calculated infrared (IR) and Raman spectra of poly­(lactic acid) (PLA) polymorphs by employing density functional perturbation theory (DFPT) and a plane wave basis set. Significant different characteristics are found in the calculated spectra of poly­(l-lactic acid) (PLLA) α-form and PLLA/poly­(d-lactic acid) (PDLA) stereocomplex (sc) form. Particularly in the carbonyl stretching region, there is only one sharp peak in the sc-form while there are five peaks in the PLLA α-form. A low wavenumber (65 cm<sup>–1</sup>) vibration band of α-PLLA observed in a previous terahertz time-domain spectroscopy study was reproduced in the calculated solid-state PLLA spectra. This band could not be obtained by using DFT (B3LYP/6-31G*) simulation on a single PLA oligomer chain and had been attributed to lattice vibrations in the crystal. The permittivity and polarizability tensors of PLA single crystals were also obtained using the DFPT method and were found to be anisotropic

    Graphene-like Molecules Based on Tetraphenylethene Oligomers: Synthesis, Characterization, and Applications

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    Graphene-like molecules were prepared by oxidative cyclodehydrogenation of tetraphenylethene­(TPE) oligomers using iron­(III) chloride as the catalyst under mild conditions. All the oxidized samples can be separated effectively from the stepwise ring-closing reaction that highly related to the reaction time. For example, the model compounds obtained from the stepwise cyclization reaction show a regular red-shift in UV/vis absorption and photoluminescence (PL) spectra. This result reveals that the molecular conjugation length will extend with the stepwise ring-closing reaction going on. Interestingly, we successfully obtained a series of colorful luminogens with blue, cyan, and green emission during this stepwise and accurate ring closing process. Cyclic voltammetry measurements taken give the corresponding band gap, which supports the results obtained from optical spectroscopy. For the strong intermolecular interaction, our graphene molecules can self-assemble to form a red-colored and hexagonal fiber. Furthermore, some molecules exhibit piezochromic luminescence. The PL emission of the molecules before and after oxidation can be dramatically quenched by picric acid through the electron transfer and/or energy transfer mechanism, enabling them to function as chemosensors for explosive detection. In addition, fluorescence cell imaging studies proved their potential biological application

    Origin of Near-Infrared Absorption for Azulene-Containing Conjugated Polymers upon Protonation or Oxidation

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    A series of azulene-containing conjugated polymers were studied to elucidate their tunable absorption properties in near-infrared (NIR) regions (i.e., 1.2–2.5 μm) upon protonation/oxidation. Density function theory (DFT) revealed that protonation-induced intramolecular charge transfer (ICT) in the polymer backbone lead to strong NIR absorption. Distinct spectral change was observed when tiny amount of peroxide was added to the protonated polymer in trifluoroacetic acid/chloroform solution. Electron paramagnetic resonance (EPR) study confirmed the presence of radical cation, which results in the occurrence of newly formed absorption band after the addition of peroxide. The spectro-electrochemical results and DFT study indicate that polarons and polaron pairs were formed during p-doping process, and both the chemical oxidation and electrochemical oxidation could be facilitated by TFA protonation. This represents the first reported mechanisms of NIR absorption under various protonation/oxidation conditions in a single polymer system

    Primary causes of smallholders’ land use changes in tea plantation.

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    Primary causes of smallholders’ land use changes in tea plantation.</p

    Image_2_The consistent background color preference highlights the personality in the lined seahorse, Hippocampus erectus.tif

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    Background color in aquaculture has been paid more attention due to the effect on fish growth, survival, health, and reproduction. In the present study, we evaluated the background color preference of the lined seahorse (Hippocampus erectus) and its relationship with personality. Preference was assessed over 10 consecutive days through allowing the lined seahorse to freely choose six different colored compartments, i.e., white, red, green, black, yellow, and blue backgrounds. To minimize the spurious preference response, the individual preference index (PI) was applied to calculate the preference intensity of the background colors. Preference reliability was further verified by a binary choice test through the choice for the most preferred or non-preferred color. Preference consistency under stress situation was assessed by a “knock-at-the-door” test as confining the seahorse in a transparent circle after a 30-s air exposure and measuring the proportion of knock toward different colored backgrounds. The personality was conjointly analyzed by new environment test and novel object test. Overall, the lined seahorse showed a general preference for white and blue while avoidance of black and red backgrounds at either unstressed or stressed situations. The shyer the seahorse was, the more preference for white background it displayed. Thus, white and blue background colors are recommended for culturing the lined seahorse. Furthermore, white color preference is a potential indicator in personality study of the lined seahorse.</p

    Survey data.

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    Landscape changes driven by cash crop plantations have been prevalent in tropical and subtropical regions worldwide in recent decades. Investigating the landscape changes and concluding livelihood outcomes are fundamental to figure out the solutions for rural sustainability. This paper examined the landscape changes which was caused by land use changes in tea plantations as well as investigated the resultant livelihood impacts, based on a case study in Fuding City, Southeast China. A questionnaire survey of 114 rural households in four sampled villages was conducted. Results demonstrated that expansion and intensification of tea plantations were two major proximate causes of landscape changes in recent decade. Our survey indicated that some existing intensively-managed tea plantations had derived from intensification and expansion of tea plantations, respectively. We identified four underlying driving forces of landscape changes, including economic benefit, governmental policies, wildlife destruction on grain crops, and rural return migration. Our study confirmed that landscape changes have significant positive effects on farmers’ livelihoods, including increasing employment and incomes, raising living standards, enhancing livelihood assets and livelihood sustainability. Especially, the aged rural populations could have a relatively decent living standard. Meanwhile, the excessive expansion of tea plantations may impair livelihood resilience. Lastly, three policy suggestions based on different time scales have been put forward to promote rural households’ livelihood sustainability and resilience.</div
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