14,213 research outputs found
Classical solutions for Yang-Mills-Chern-Simons field coupled to an external source
We find wide class of exact solutions of Yang-Mills-Chern-Simons theory
coupled to an external source, in terms of doubly periodic Jacobi elliptic
functions. The obtained solutions include localized solitons, trigonometric
solutions, pure cnoidal waves, and singular solutions in certain parameter
range. Furthermore, it is observed that these solutions exist over a nonzero
background.Comment: 5 page
Deficiency of RgpG causes major defects in cell division and biofilm formation, and deficiency of LytR-CpsAPsr family proteins leads to accumulation of cell wall antigens in culture medium by Streptococcus mutans
ABSTRACT
Streptococcus mutans
is known to possess rhamnose-glucose polysaccharide (RGP), a major cell wall antigen.
S. mutans
strains deficient in
rgpG
, encoding the first enzyme of the RGP biosynthesis pathway, were constructed by allelic exchange. The
rgpG
deficiency had no effect on growth rate but caused major defects in cell division and altered cell morphology. Unlike the coccoid wild type, the
rgpG
mutant existed primarily in chains of swollen, “squarish” dividing cells. Deficiency of
rgpG
also causes significant reduction in biofilm formation (
P
< 0.01). Double and triple mutants with deficiency in
brpA
and/or
psr
, genes coding for the LytR-CpsA-Psr family proteins BrpA and Psr, which were previously shown to play important roles in cell envelope biogenesis, were constructed using the
rgpG
mutant. There were no major differences in growth rates between the wild-type strain and the
rgpG brpA
and
rgpG psr
double mutants, but the growth rate of the
rgpG brpA psr
triple mutant was reduced drastically (
P
< 0.001). Under transmission electron microscopy, both double mutants resembled the
rgpG
mutant, while the triple mutant existed as giant cells with multiple asymmetric septa. When analyzed by immunoblotting, the
rgpG
mutant displayed major reductions in cell wall antigens compared to the wild type, while little or no signal was detected with the double and triple mutants and the
brpA
and
psr
single mutants. These results suggest that RgpG in
S. mutans
plays a critical role in cell division and biofilm formation and that BrpA and Psr may be responsible for attachment of cell wall antigens to the cell envelope.
IMPORTANCE
Streptococcus mutans
, a major etiological agent of human dental caries, produces rhamnose-glucose polysaccharide (RGP) as the major cell wall antigen. This study provides direct evidence that deficiency of RgpG, the first enzyme of the RGP biosynthesis pathway, caused major defects in cell division and morphology and reduced biofilm formation by
S. mutans
, indicative of a significant role of RGP in cell division and biofilm formation in
S. mutans
. These results are novel not only in
S. mutans
, but also other streptococci that produce RGP. This study also shows that the LytR-CpsA-Psr family proteins BrpA and Psr in
S. mutans
are involved in attachment of RGP and probably other cell wall glycopolymers to the peptidoglycan. In addition, the results also suggest that BrpA and Psr may play a direct role in cell division and biofilm formation in
S. mutans
. This study reveals new potential targets to develop anticaries therapeutics.
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Warm-Mix Asphalt Study: Test Track Construction and FirstLevel Analysis of Phase 3b HVS and Laboratory Testing (Rubberized Asphalt, Mix Design #2)
This is one of two reports describing the third phase of a warm-mix asphalt study that compares the performance of two rubberized asphalt control mixes with that of seven mixes produced with warm-mix technologies. The control mixes were produced and compacted at conventional hot-mix asphalt temperatures (>300 F [150°C]), while the warm-mixes were produced and compacted at temperatures between 36°F (20°C) and 60°F (35°C) lower than the controls. The mixes, test track, Heavy Vehicle Simulator (HVS) and laboratory testing are discussed. Key findings from the study include: Adequate compaction can be achieved on rubberized warm-mixes at lower temperatures. Optimal compaction temperatures will differ. Equal and potentially better rutting performance can be achieved provided that standard specified limits for hot-mix asphalt are met. Test results indicate that use of the warm-mix technologies did not significantly influence performance when compared to control specimens. However, the mixes produced with chemical surfactant technologies did appear to be influenced in part by the lower mix production and construction temperatures, which would have resulted in less oxidation of the binder and consequent lower stiffness of the mix. Rutting performance, fatigue performance and moisture sensitivity did not appear to be affected. The warm-mixes produced using water-foaming technologies appeared to have lower moisture resistance compared to the other warm-mixes. Smoke and odors are significantly reduced on warm-mixes compared to hot-mixes, while workability is considerably better on warm-mixes compared to hot-mixes. The HVS and laboratory testing completed in this phase have provided no results to suggest that warm-mix technologies should not be used in rubberized asphalt in California
An efficient human body contour extraction method for mobile apps.
With the increasing prevalence of powerful mobile technology, many applications involve human body measurements, such as online cloth shopping. Aiming at the application of non contact human body measurement and modeling system, this paper presents a new method for extracting human contours in complex background environment. Since the H component on the HSV color space is independent of the light changes, the hair and the lower garment can be divided. Therefore, a method of using the elliptical skin model on YCbCr color space is proposed to detect the skin color, then, automatically extract the skin samples to determine the threshold segmentation range. The combination of the two improves the skin color point recognition rate, gradually separating the body skin, clot and the hair by using these binary values of the linear fusion operation to get the final body contours. Our experiments demonstrates that this algorithm effectively reduces constraints on background environment when extracting contours
Effect of bias voltage on the tribological and sealing properties of rubber seals modified by DLC films
Diamond-like carbon (DLC) films were deposited on nitrile butadiene rubber (NBR) by the DC magnetron sputtering under different bias voltages. Raman spectra revealed that the variation of bias voltage could tune the carbon bond structure in DLC films. Both the hardness and Young's modulus increased with the increasing bias voltage. Tribological tests revealed that the DLC-coated NBR prepared at the bias voltage of -200 V exhibited low wear rate due to its high hardness. The sealing property was studied by evaluating the leakage rate of volatile liquid in a simple apparatus. All DLC films resulted in less leakage rate as compared to the raw rubber under large stress. The lowest leakage rate occurred in the DLC-coated NBR prepared with a bias voltage of -200 V, which was associated with the theoretical calculations (Persson's theory). It was attributed to the synergetic effects of the variations of the Young's modulus and root-mean-square (Rms) roughness. The low Young's modulus and Rms, controlled by regulating bias voltage, could enhance actual contact area and reduce the leakage rate
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