4,797 research outputs found
Effects of zinc oxide filler on the curing and mechanical response of alkyd coatings
The mechanical properties of an alkyd resin filled with zinc oxide pigment were studied at different concentrations over a wide range of time scales using dynamic mechanical analysis, quartz crystal rheometry and nanoindentation. The motivation for this work stems from the interest in accessing the long-term properties of paint coatings by studying the mechanical properties of historic paints. In this foundational work, we compare three different modalities of mechanical measurements and systematically determine the effect of pigment filler loading on the measured properties. Quantitative agreement between the methods is obtained when the characteristic time scales of each of the methods is taken into account. While nanoindentation is the technique most readily applied to historic paint samples, the rheometric quartz crystal microbalance (rheo-QCM) is the best suited for obtaining mechanistic information from measurements of paint properties over time, provided that appropriate thin-film samples can be produced. In these studies we find that ZnO increases the rate of oxidation of the alkyd during the initial stages of cure by an amount that depends on the ZnO content
Alternating-Spin Ladders
We investigate a two-leg spin ladder system composed of alternating-spin
chains with two-different kind of spins. The fixed point properties are
discussed by using spin-wave analysis and non-linear sigma model techniques.
The model contains various massive phases, reflecting the interplay between the
bond-alternation and the spin-alternation.Comment: 6 pages, revtex, to appear in PR
Temperature Dependence of Extended and Fractional SU(3) Monopole Currents
We examine in pure SU(3) the dependence of extended monopole current k and
cross-species extended monopole current k^{cross} on temperature t, monopole
size L, and fractional monopole charge 1/q. We find that features of both k and
k^{cross} are sensitive to t for a range of L and q. In particular, the
spatial-temporal asymmetry ratios of both k and k^{cross} are sensitive over a
range of L and q to the SU(3) deconfinement transition. The motivation for
studying cross, extended, and fractional monopoles in SU(3) is given.Comment: 15 pages (archiving final publication version; very minor revisions
Towards an Abelian Formulation of Lattice QCD Confinement
We probe for operators occurring in the APQCD(``abelian-projected QCD'')
action by evaluating abelian-projected -plaquette spectral densities in pure
gauge fixed to maximal abelian gauge. Couplings are
extracted from the spectral densities for each representation ,
plaquette. While APQCD is dominated by a resonance, we also find
evidence for weakly coupled plaquettes. Moreover, since even if , plaquettes must be
significant since APQCD is confining.Comment: 1+11 pages, fixed minor postscript erro
Zero mode in the time-dependent symmetry breaking of theory
We apply the quartic exponential variational approximation to the symmetry
breaking phenomena of scalar field in three and four dimensions. We calculate
effective potential and effective action for the time-dependent system by
separating the zero mode from other non-zero modes of the scalar field and
treating the zero mode quantum mechanically. It is shown that the quantum
mechanical properties of the zero mode play a non-trivial role in the symmetry
breaking of the scalar theory.Comment: 10 pages, 3 figure
A canonical FtsZ protein in Verrucomicrobium spinosum, a member of the Bacterial phylum Verrucomicrobia that also includes tubulin-producing Prosthecobacter species
BACKGROUND: The origin and evolution of the homologous GTP-binding cytoskeletal proteins FtsZ typical of Bacteria and tubulin characteristic of eukaryotes is a major question in molecular evolutionary biology. Both FtsZ and tubulin are central to key cell biology processes – bacterial septation and cell division in the case of FtsZ and in the case of tubulins the function of microtubules necessary for mitosis and other key cytoskeleton-dependent processes in eukaryotes. The origin of tubulin in particular is of significance to models for eukaryote origins. Most members of domain Bacteria possess FtsZ, but bacteria in genus Prosthecobacter of the phylum Verrucomicrobia form a key exception, possessing tubulin homologs BtubA and BtubB. It is therefore of interest to know whether other members of phylum Verrucomicrobia possess FtsZ or tubulin as their FtsZ-tubulin gene family representative. RESULTS: Verrucomicrobium spinosum, a member of Phylum Verrucomicrobia of domain Bacteria, has been found to possess a gene for a protein homologous to the cytoskeletal protein FtsZ. The deduced amino acid sequence has sequence signatures and predicted secondary structure characteristic for FtsZ rather than tubulin, but phylogenetic trees and sequence analysis indicate that it is divergent from all other known FtsZ sequences in members of domain Bacteria. The FtsZ gene of V. spinosum is located within a dcw gene cluster exhibiting gene order conservation known to contribute to the divisome in other Bacteria and comparable to these clusters in other Bacteria, suggesting a similar functional role. CONCLUSION: Verrucomicrobium spinosum has been found to possess a gene for a protein homologous to the cytoskeletal protein FtsZ. The results suggest the functional as well as structural homology of the V. spinosum FtsZ to the FtsZs of other Bacteria implying its involvement in cell septum formation during division. Thus, both bacteria-like FtsZ and eukaryote-like tubulin cytoskeletal homologs occur in different species of the phylum Verrucomicrobia of domain Bacteria, a result with potential major implications for understanding evolution of tubulin-like cytoskeletal proteins and the origin of eukaryote tubulins
The level of Marzano higher-order thinking skills among polytechnic students
This study aims to identify polytechnic students' level of Marzano Higher-Order Thinking Skills (HOTS) based on
two dimensions, 'Extension and Refinement of Knowledge' and 'Meaningful Use of Knowledge,' and to analyze the
difference in the students' level of Marzano HOTS based on these two dimensions depending on the students'
demographic factors. This study design was a survey using quantitative methods. A total of 313 students were
randomly selected as the survey sample. A questionnaire in the form of closed-ended questions was used as the
research instrument. Data were analyzed using frequency percentage and MANOVA test. The findings showed no
significant differences in the eight HOTS in the dimension of 'Extension and Refinement of Knowledge' with the
gender and socio-economic status (SES) factors. However, there were significant differences in the eight HOTS
with the academic achievement factor. Meanwhile, based on the dimension of 'Meaningful Use of Knowledge,' the
findings showed no significant differences in the five HOTS in this dimension with the gender and academic
achievement factors. The paper includes implications of the Higher-Order Thinking Skills (HOTS) for students to
improve their academic performance. In future research, the authors can further identify university students' HOTS
levels in the technical area
Monoclinic and Correlated Metal Phase in VO_2 as Evidence of the Mott Transition: Coherent Phonon Analysis
In femtosecond pump-probe measurements, the appearance of coherent phonon
oscillations at 4.5 THz and 6.0 THz indicating the rutile metal phase of VO_2
does not occur simultaneously with the first-order metal-insulator transition
(MIT) near 68^oC. The monoclinic and correlated metal(MCM) phase between the
MIT and the structural phase transition (SPT) is generated by a photo-assisted
hole excitation which is evidence of the Mott transition. The SPT between the
MCM phase and the rutile metal phase occurs due to subsequent Joule heating.
The MCM phase can be regarded as an intermediate non-equilibrium state.Comment: 4 pages, 2 figure
Effects of zinc oxide filler on the curing and mechanical response of alkyd coatings
The mechanical properties of an alkyd resin filled with zinc oxide pigment were studied at different concentrations over a wide range of time scales using dynamic mechanical analysis, quartz crystal rheometry and nanoindentation. The motivation for this work stems from the interest in accessing the long-term properties of paint coatings by studying the mechanical properties of historic paints. In this foundational work, we compare three different modalities of mechanical measurements and systematically determine the effect of pigment filler loading on the measured properties. Quantitative agreement between the methods is obtained when the characteristic time scales of each of the methods is taken into account. While nanoindentation is the technique most readily applied to historic paint samples, the rheometric quartz crystal microbalance (rheo-QCM) is the best suited for obtaining mechanistic information from measurements of paint properties over time, provided that appropriate thin-film samples can be produced. In these studies we find that ZnO increases the rate of oxidation of the alkyd during the initial stages of cure by an amount that depends on the ZnO content
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