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In this short review, we discuss the molecular shapes of monosubstituted polyacetylenes (MSPAs) in their liquid crystalline (LC) phases. Their rigid backbone with high stereoregularity can endow MSPAs with significant shape persistency, which largely determines their LC structures. Helical cis-cisoidal and cis-transoidal MSPAs render rod-like shapes and can form columnar LC (Phi) phases. In the smectic LC (Sm) phases of MSPAs with mesogenic side-chains, the main chain, with trans-cisoidal, trans-transoidal or extended cis-transoidal conformation, is in fact largely coplanar with the side-chains, resulting in a sheet-like molecular shape. From a simple geometric point of view, the rod- or sheet-like MSPA molecules serve as the building block of their LC phases.

An optically active poly(phenylacetylene), poly{2-(R)-methyl-2-[4 0 -(tetradecyloxy)biphenyl-4-yloxy]propyl 4-ethynylbenzoate} (P1) is synthesized in a high yield with a high molecular weight (1.3 � 10 6 g/ mol) by [Rh(nbd)Cl]2 catalyst. The chemical structure of the polymer is characterized by IR and NMR spectroscopies with satisfactory analysis data. The polymer is soluble in many common organic solvents. It shows circular dichroism (CD) band in the absorption region of the polyacetylene backbone, indicating that P1 is chiroptical owing to the formation of helical conformation with an excess screw sense. Combining the results of CD and light scattering experiments, we find that addition of poor solvent can induce the neighboring helical segments within a single polymer strand to become closer, resulting in exciton coupling prior to polymer precipitation. The exciton coupling can be kept in the solid state after solvent evaporation.

The phase structures and transition behaviors of a series of side-chain liquid crystalline (LC) polymethacrylates based on p-methoxyazobenzene (PMnAzs, n ¼ 6, 8, 10, 12) were studied using differential scanning calorimetry, one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction, and Fourier transform infrared spectroscopic experiments. The LC phase transition of PMnAz follows the sequence of smectic A (SmA)4 nematic (N)4 isotropic (I). For PM10Az and PM12Az, the transition of SmA-to-N is not complete upon heating. In the low-temperature SmA phase, the polymers adopt a fully interdigitated side-chain packing with the smectic layer period almost identical to the side-chain length. For all the four samples, the first-order diffraction of the SmA structure only renders when the temperature approaches the transition of SmA 4 N, with the intensity much lower than that of the second-order diffraction. The absence of the first-order diffraction at low temperatures is ascribed to the possible matching of the electron densities between the center portion of the side-chain sublayer and the main-chain sublayer of the SmA structure. Since only the mesogens from the same main-chain sublayer can stack parallel together, the distribution of the azobenzene domains may cause some sort of density undulation within the smectic layer. Among the samples, PM6Az presents the strongest undulation with some additional orders. We also examined the annealing effect on the H-aggregation of PMnAzs. It is found that isothermal annealing at a temperature slightly higher than the T g of PM8Az and PM10Az can significantly enhance

Self-assembly behaviors of a series of hydrophobic side-chain liquid crystalline (LC) polyacetylenes, namely, poly(5-{((4'-alkoxy-4-biphenylyl)carbonyl)oxy}-1-pentyne)s (P-3,m (m ) 5, 7, 9)), were studied in dilute solutions. The assembly was induced by tuning the solvent property to be selective for the alkyl tails on the side chains, with the processes characterized by turbidity, dynamic light scattering, 1 H NMR, and excitation fluorescence anisotropy measurements. The morphology and structure of the P-3,m aggregates formed in the solutions were investigated using atomic force microscopy and wide-angle X-ray diffraction. The experimental results indicate that the P-3,m polymers can form monolayer lamellae in selective solvents. In the lamella, the P-3,m molecules are sheetlike and pack parallel to each other with their backbones located in the lamellar center and their alkyl tails covering the top and bottom lamellar surfaces. The lamellar thickness is largely determined by the width of the molecular sheet. When the solvent becomes selective for the tails, the P-3,m chains may undergo shape stiffening to become more sheetlike.

The recognition of impassable terrain plays a vital role in the motionplanning of a mobile robot, which generally relies on expensive sensors such as stereovision cameras. This paper proposes a rapid impassable terrain recognition algorithmbased on hypotheses testing theory using low-cost range finders with different diffusionangles. In this algorithm, a slope estimation model using two range finders mountedon different heights is first established, where the influence of the diffusion angle ofthe range sensor is considered. To deal with inaccurate measuring from low costrange finders, the hypothesis testing theory is then applied to judge whether there isan impassible terrain approaching, where the historical slope estimation results aretreated as a sample set of the same slope, and the judgement of impassible terrainis then made based on the sampling set rather than the concurrent slope estimation.So the robot is only required to count the number of slope estimation that supportthe determination of a terrain as being impassible, and the judgement is confirmedonly when that number is larger than a precisely designed threshold value. Thenthe stable recognition for impassable terrain would be acquired while the risk ofwrong judgement is limited. The experiments’ results indicate that this algorithmcan provide a reliable recognition of impassable terrain using lower cost range finderswith different diffusion angles with minimal computation.

The present study seeks to detect oxidative damage and to compare anti-oxidative responses among liver, gills and brain of adult zebrafish that were cooled from 28 °C (control) to 12 °C (treatment) for 0-24 h. The lipid peroxidation of liver, gill and brain tissues significantly increased at 1h after transfer, but reactive oxygen species in the treatment group increased significantly after 24 h as compared to the control. The fish were found to develop a cascading anti-oxidative mechanism beginning with an increase in Cu/Zn-SOD levels, followed by increased CAT and GPx mRNA expressions in the three tissue types. Both smtB and mt2 mRNAs increased in the hepatic and brain tissues following 1h of cold stress, but only smtB exhibited a significant increase in the gills at 1 h and 6 h after transfer to 12 °C. Furthermore, cellular apoptosis in the brain was not evident after cold shock, but liver and gills showed cellular apoptosis at 1-3 h, with another peak in the liver at 6 h after cold shock. The results suggest that the cold shock induced oxidative stress, and the enzymatic (SOD, GPx and CAT) and non-enzymatic (mt-2 and smt-B) mRNA expressions all play a role in the resulting anti-oxidation within 1-6 h of cold shock. A functional comparison showed that the brain had the most powerful antioxidant defense system of the three tissue types since it had the highest smtB mRNA expression and a lower level of cell apoptosis than the liver and gills after exposure to cold stress.

This paper addresses the problem of fast semantic segmentation on compressed video. Unlike most prior works for video segmentation, which perform feature propagation based on optical flow estimates or sophisticated warping techniques, ours takes advantage of block motion vectors in the compressed bitstream to propagate the segmentation of a keyframe to subsequent non-keyframes. This approach, however, needs to respect the inter-frame prediction structure, which often suggests recursive, multi-step prediction with error propagation and accumulation in the temporal dimension. To tackle the issue, we refine the motion-compensated segmentation using inpainting. Our inpainting network incorporates guided non-local attention for long-range reference and pixel-adaptive convolution for ensuring the local coherence of the segmentation. A fusion step then follows to combine both the motion-compensated and inpainted segmentations. Experimental results show that our method outperforms the state-of-the-art baselines in terms of segmentation accuracy. Moreover, it introduces the least amount of network parameters and multiply-add operations for non-keyframe segmentation.