202 research outputs found
Microbial Succession and Nitrogen Cycling in Cultured Biofilms as Affected by the Inorganic Nitrogen Availability
Biofilms play important roles in nutrients and energy cycling in aquatic ecosystems. We hypothesized that as eutrophication could change phytoplankton community and decrease phytoplankton diversity, ambient inorganic nitrogen level will affect the microbial community and diversity of biofilms and the roles of biofilms in nutrient cycling. Biofilms were cultured using a flow incubator either with replete inorganic nitrogen (N-rep) or without exogenous inorganic nitrogen supply (N-def). The results showed that the biomass and nitrogen and phosphorous accumulation of biofilms were limited by N deficiency; however, as expected, the N-def biofilms had significantly higher microbial diversity than that of N-rep biofilms. The microbial community of biofilms shifted in composition and abundance in response to ambient inorganic nitrogen level. For example, as compared between the N-def and the N-rep biofilms, the former consisted of more diazotrophs, while the latter consisted of more denitrifying bacteria. As a result of the shift of the functional microbial community, the N concentration of N-rep medium kept decreasing, while that of N-def medium showed an increasing trend in the late stage. This indicates that biofilms can serve as the source or the sink of nitrogen in aquatic ecosystems, and it depends on the inorganic nitrogen availability.</p
QCD quark cyclobutadiene and light tetraquark spectrum
The QCD quark cyclobutadiene (ring-like), a new color structure of tetraquark
system, is proposed and studied in the flux tube model with multi-body
confinement potential. The QCD quark cyclobutadiene and other flux tube
structures of tetraquark states have similar energies and they can be regarded
as QCD isomeric compounds. The light tetraquark spectra ( only) with
ring-like and diquark-antidiquark structures are calculated in the flux tube
model. The results show that many experimental states have the masses close to
the calculated values if they are taken as tetraquark states. The isotensor
states with and are studied and predicted that
the masses are around 1500 MeV. The multi-body interaction plays a important
role to reduce the energy of the multiquark state.Comment: 10 pages, 4 figures, Some statements are change
Quantum chromodynamics quark benzene
A six-quark state with the benzene-like structure is proposed and studied
based on color string model. The calculation with the quadratic confinement
show that such structure has the lowest energy among the various hidden color
six-quark structures proposed so far. Its possible effect on scattering is
discussed.Comment: 5 pages, 7 figure
Systematic study of pentaquark states: configuration
Group theoretic method for the systematic study of five-quark states with
meson-baryon () configuration is developed. The calculation of
matrix elements of many body Hamiltonian is simplified by transforming the
physical bases (meson-baryon quark cluster bases) to symmetry bases (group
chain classified bases), where the fractional parentage expansion method can be
used. Three quark models, the naive Glashow-Isgur model, Salamanca chiral quark
model and quark delocalization color screening model, are used to show the
general applicability of the method and general results of constituent quark
models for five-quark states are given. The method can also be useful in the
calculation of meson-baryon scattering and the study of the five-quark
components effect in baryon structure. The physical contents of different model
configurations for the same multi-quark system can also be compared through the
transformation between different physical bases to the same set of symmetry
bases.Comment: 30 pages, 8 figure
Cationic Polybutyl Cyanoacrylate Nanoparticles for DNA Delivery
To enhance the intracellular delivery potential of plasmid DNA using nonviral vectors, we used polybutyl cyanoacrylate (PBCA) and chitosan to prepare PBCA nanoparticles (NPs) by emulsion polymerization and prepared NP/DNA complexes through the complex coacervation of nanoparticles with the DNA. The object of our work is to evaluate the characterization and transfection efficiency of PBCA-NPs. The NPs have a zeta potential of 25.53 mV at pH 7.4 and size about 200 nm. Electrophoretic analysis suggested that the NPs with positive charges could protect the DNA from nuclease degradation and cell viability assay showed that the NPs exhibit a low cytotoxicity to human hepatocellular carcinoma (HepG2) cells. Qualitative and quantitative analysis of transfection in HepG2 cells by the nanoparticles carrying plasmid DNA encoding for enhanced green fluorescent protein (EGFP-N1) was done by digital fluorescence imaging microscopy system and fluorescence-activated cell sorting (FACS). Qualitative results showed highly efficient expression of GFP that remained stable for up to 96 hours. Quantitative results from FACS showed that PBCA-NPs were significantly more effective in transfecting HepG2 cells after 72 hours postincubation. The results of this study suggested that PBCA-NPs have favorable properties for nonviral delivery
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