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
We calculated infrared (IR) and Raman spectra of polyÂ(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 polyÂ(l-lactic acid)
(PLLA) α-form and PLLA/polyÂ(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
Graphene-like
molecules were prepared by oxidative cyclodehydrogenation
of tetraphenyletheneÂ(TPE) oligomers using ironÂ(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
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.
Primary causes of smallholders’ land use changes in tea plantation.</p
Livelihood improvement attributed to tea plantation.
Livelihood improvement attributed to tea plantation.</p
Trends of tea price in Fuding City, Southeast China.
Trends of tea price in Fuding City, Southeast China.</p
Causes and livelihood outcomes of landscape changes.
Causes and livelihood outcomes of landscape changes.</p
Image_2_The consistent background color preference highlights the personality in the lined seahorse, Hippocampus erectus.tif
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.
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
The distribution of respondents in Fuding City, Fujian Province, China.
The distribution of respondents in Fuding City, Fujian Province, China.</p