FTIR studies of TiO2

PhD ThesisA novel method (in-situ quantitative infrared spectroscopy of evolved C02) for studying photo-degradation has been developed and applied to the study of several different polymers including a series of polyethylene and poly (vinyl chloride) samples containing Ti02 pigments with different photo-activitics. Infrared (IR) analysis was used to monitor carbon dioxide emitted from samples exposed to ultraviolet irradiation (UV) in atmospheres of differing composition. The experiments were conducted in a specially constructed cell that permits simultaneous UV exposure of the sample and IR interrogation of the vapour in the cell. It has been demonstrated that the in-situ gas-phase method permits a fast and convenient way of assessing the durability of pigmented and unpigmented polymer. A single test on one material occupied about 7 hours - very much less than conventional artificial weathering exposures. Excellent correlation between the C02 method and the conventional method for measuring carbonyl groups in the polyethylene films has been demonstrated, The Ti02 pigments used included anatase and rutiles with different surface treatments. Anatase-pigmented material gave significantly higher C02 emission than unpigmented polyethylene. The rutile-pigmented polyethylenes either gave reduced C02 emission or enhanced emission, according to the surface treatment. The ranking of the pigments as protectants or pro-degradants coincided with that obtained from much more time consuming laboratory testing and field experience. Similar results were obtained for the poly (vinyl chloride). The CO2 method is a convenient way to study the factors (humidity, oxygen concentration and UV intensity or wavelength), which influence the rate of carbon dioxide evolution i. e. the rate of photo-oxidation of the polymers. Blown polyethylene(PE) film was exposed to UV irradiation while held under tensile stress in a specially designed metal frame. The chemical degradation was followed using the FTIR carbonyl index. Tests were conducted on unpigmented PE and on a series of five PEs containing TiO2 pigments with different photo-activities. The yield strengths measured in tensile tests on unexposed films were typically 10 % greater in the longitudinal( machine)direction than in the transverse direction. UV exposures were conducted with stress applied both parallel and transverse to the machine direction.For all six materials, tensile stress accelerated carbonyl group development, Some samples cracked during UV exposure in tension and did so in a shorter time if the stress was applied in the machine direction than if it was transverse to it. The carbonyl index at the onset of cracking was lower for longitudinal samples than for transverse samples. Unpigmented PE was slightly more sensitive to transverse strain and the anatasepigmented PE slightly more sensitive to longitudinal strain.Huntsman Tioxid

FTIR studies of TiO₂ : pigmented polymer photodegradation

A novel method (in-situ quantitative infrared spectroscopy of evolved C02) for studying photo-degradation has been developed and applied to the study of several different polymers including a series of polyethylene and poly (vinyl chloride) samples containing Ti02 pigments with different photo-activitics. Infrared (IR) analysis was used to monitor carbon dioxide emitted from samples exposed to ultraviolet irradiation (UV) in atmospheres of differing composition. The experiments were conducted in a specially constructed cell that permits simultaneous UV exposure of the sample and IR interrogation of the vapour in the cell. It has been demonstrated that the in-situ gas-phase method permits a fast and convenient way of assessing the durability of pigmented and unpigmented polymer. A single test on one material occupied about 7 hours - very much less than conventional artificial weathering exposures. Excellent correlation between the C02 method and the conventional method for measuring carbonyl groups in the polyethylene films has been demonstrated, The Ti02 pigments used included anatase and rutiles with different surface treatments. Anatase-pigmented material gave significantly higher C02 emission than unpigmented polyethylene. The rutile-pigmented polyethylenes either gave reduced C02 emission or enhanced emission, according to the surface treatment. The ranking of the pigments as protectants or pro-degradants coincided with that obtained from much more time consuming laboratory testing and field experience. Similar results were obtained for the poly (vinyl chloride). The CO2 method is a convenient way to study the factors (humidity, oxygen concentration and UV intensity or wavelength), which influence the rate of carbon dioxide evolution i. e. the rate of photo-oxidation of the polymers. Blown polyethylene(PE) film was exposed to UV irradiation while held under tensile stress in a specially designed metal frame. The chemical degradation was followed using the FTIR carbonyl index. Tests were conducted on unpigmented PE and on a series of five PEs containing TiO2 pigments with different photo-activities. The yield strengths measured in tensile tests on unexposed films were typically 10 % greater in the longitudinal( machine)direction than in the transverse direction. UV exposures were conducted with stress applied both parallel and transverse to the machine direction.For all six materials, tensile stress accelerated carbonyl group development, Some samples cracked during UV exposure in tension and did so in a shorter time if the stress was applied in the machine direction than if it was transverse to it. The carbonyl index at the onset of cracking was lower for longitudinal samples than for transverse samples. Unpigmented PE was slightly more sensitive to transverse strain and the anatasepigmented PE slightly more sensitive to longitudinal strain.EThOS - Electronic Theses Online ServiceHuntsman TioxideGBUnited Kingdo

Fermions and bosons in nonsymmorphic PdSb2 with sixfold degeneracy

PdSb2 is a candidate for hosting 6-fold-degenerate exotic fermions (beyond Dirac and Weyl fermions).The nontrivial band crossing protected by the nonsymmorphic symmetry plays a crucial role in physical properties. We have grown high-quality single crystals of PdSb2 and characterized their physical properties under several stimuli (temperature, magnetic field, and pressure). While it is a diamagnetic Fermi-liquid metal under ambient pressure, PdSb2 exhibits a large magnetoresistance with continuous increase up to 14 T, which follows the Kohler's scaling law at all temperatures. This implies one-band electrical transport, although multiple bands are predicted by first principles calculations. By applying magnetic field along the [111] direction, de Haas-van Alphen oscillations are observed with frequency of 102 T. The effective mass is nearly zero (0.045m0) with the Berry phase close to {\pi}, confirming that the band close to the R point has a nontrivial character. Under quasihydrostatic pressure (p), evidence for superconductivity is observed in the resistivity below the critical temperature Tc. The dome-shaped Tc versus p is obtained with maximum Tc~2.9 K. We argue that the formation of Cooper pairs (bosons) is the consequence of the redistribution of the 6-fold-degenerate fermions under pressure

Edge-Mediated Skyrmion Chain and Its Collective Dynamics in a Confined Geometry

The emergence of a topologically nontrivial vortex-like magnetic structure, the magnetic skyrmion, has launched new concepts for memory devices. There, extensive studies have theoretically demonstrated the ability to encode information bits by using a chain of skyrmions in one-dimensional nanostripes. Here, we report the first experimental observation of the skyrmion chain in FeGe nanostripes by using high resolution Lorentz transmission electron microscopy. Under an applied field normal to the nanostripes plane, we observe that the helical ground states with distorted edge spins would evolves into individual skyrmions, which assemble in the form of chain at low field and move collectively into the center of nanostripes at elevated field. Such skyrmion chain survives even as the width of nanostripe is much larger than the single skyrmion size. These discovery demonstrates new way of skyrmion formation through the edge effect, and might, in the long term, shed light on the applications.Comment: 7 pages, 3 figure

A mutation degree model for the identification of transcriptional regulatory elements

<p>Abstract</p> <p>Background</p> <p>Current approaches for identifying transcriptional regulatory elements are mainly via the combination of two properties, the evolutionary conservation and the overrepresentation of functional elements in the promoters of co-regulated genes. Despite the development of many motif detection algorithms, the discovery of conserved motifs in a wide range of phylogenetically related promoters is still a challenge, especially for the short motifs embedded in distantly related gene promoters or very closely related promoters, or in the situation that there are not enough orthologous genes available.</p> <p>Results</p> <p>A mutation degree model is proposed and a new word counting method is developed for the identification of transcriptional regulatory elements from a set of co-expressed genes. The new method comprises two parts: 1) identifying overrepresented oligo-nucleotides in promoters of co-expressed genes, 2) estimating the conservation of the oligo-nucleotides in promoters of phylogenetically related genes by the mutation degree model. Compared with the performance of other algorithms, our method shows the advantages of low false positive rate and higher specificity, especially the robustness to noisy data. Applying the method to co-expressed gene sets from Arabidopsis, most of known <it>cis</it>-elements were successfully detected. The tool and example are available at <url>http://mcube.nju.edu.cn/jwang/lab/soft/ocw/OCW.html</url>.</p> <p>Conclusions</p> <p>The mutation degree model proposed in this paper is adapted to phylogenetic data of different qualities, and to a wide range of evolutionary distances. The new word-counting method based on this model has the advantage of better performance in detecting short sequence of <it>cis</it>-elements from co-expressed genes of eukaryotes and is robust to less complete phylogenetic data.</p

Local atomic and magnetic structure of dilute magnetic semiconductor (Ba,K)(Zn,Mn)2_2As2_2

We have studied the atomic and magnetic structure of the dilute ferromagnetic semiconductor system (Ba,K)(Zn,Mn)$_2$As$_2$ through atomic and magnetic pair distribution function analysis of temperature-dependent x-ray and neutron total scattering data. We detected a change in curvature of the temperature-dependent unit cell volume of the average tetragonal crystallographic structure at a temperature coinciding with the onset of ferromagnetic order. We also observed the existence of a well-defined local orthorhombic structure on a short length scale of $\lesssim 5$ \AA, resulting in a rather asymmetrical local environment of the Mn and As ions. Finally, the magnetic PDF revealed ferromagnetic alignment of Mn spins along the crystallographic $c$-axis, with robust nearest-neighbor ferromagnetic correlations that exist even above the ferromagnetic ordering temperature. We discuss these results in the context of other experiments and theoretical studies on this system