63 research outputs found
Gene silencing and large-scale domain structure of the E. coli genome
The H-NS chromosome-organizing protein in E. coli can stabilize genomic DNA
loops, and form oligomeric structures connected to repression of gene
expression. Motivated by the link between chromosome organization, protein
binding and gene expression, we analyzed publicly available genomic data sets
of various origins, from genome-wide protein binding profiles to evolutionary
information, exploring the connections between chromosomal organization,
genesilencing, pseudo-gene localization and horizontal gene transfer. We report
the existence of transcriptionally silent contiguous areas corresponding to
large regions of H-NS protein binding along the genome, their position
indicates a possible relationship with the known large-scale features of
chromosome organization
The effect of demographic stochasticity on predatory-prey oscillations
The ecological dynamics of interacting predator and prey populations can
display sustained oscillations, as for instance predicted by the
Rosenzweig-MacArthur predator-prey model. The presence of demographic
stochasticity, due to the finiteness of population sizes, alters the amplitude
and frequency of these oscillations. Here we present a method for
characterizing the effects of demographic stochasticity on the limit cycle
attractor of the Rosenzweig-MacArthur. We show that an angular Brownian motion
well describes the frequency oscillations. In the vicinity of the bifurcation
point, we obtain an analytical approximation for the angular diffusion
constant. This approximation accurately captures the effect of demographic
stochasticity across parameter values
Emergence of global synchronization in directed excitatory networks of type I neurons
The collective behaviour of neural networks depends on the cellular and
synaptic properties of the neurons. The phase-response curve (PRC) is an
experimentally obtainable measure of cellular properties that quantifies the
shift in the next spike time of a neuron as a function of the phase at which
stimulus is delivered to that neuron. The neuronal PRCs can be classified as
having either purely positive values (type I) or distinct positive and negative
regions (type II). Networks of type 1 PRCs tend not to synchronize via mutual
excitatory synaptic connections. We study the synchronization properties of
identical type I and type II neurons, assuming unidirectional synapses.
Performing the linear stability analysis and the numerical simulation of the
extended Kuramoto model, we show that feedforward loop motifs favour
synchronization of type I excitatory and inhibitory neurons, while feedback
loop motifs destroy their synchronization tendency. Moreover, large directed
networks, either without feedback motifs or with many of them, have been
constructed from the same undirected backbones, and a high synchronization
level is observed for directed acyclic graphs with type I neurons. It has been
shown that, the synchronizability of type I neurons depends on both the
directionality of the network connectivity and the topology of its undirected
backbone. The abundance of feedforward motifs enhances the synchronizability of
the directed acyclic graphs
A Mandibular First Molar with Three Distal Canals: A Case Report and Literature Review
For a successful root canal treatment, it is critical for a clinician to have complete knowledge of the root canal morphology. There are numerous cases in literature concerning the unusual anatomy of mandibular first molars. This report presents a case of a mandibular first molar with three distal canals. An overview of the types and numbers of the common anatomic forms of this tooth also is presented, as is a summary of published anomalies.Key words: Distal Root; Mandibular First Molar; Root Canal Anatom
A New Approach to Root Formation
In endodontics, treatment of an open apex tooth with necrotic pulp is a problem. It seems that with promotion of remnants of Hertwig’s epithelial sheath or rest of malassez accompany with a good irrigation of root canal we can expect root formation
External root resorption: Arrested or progressing?
External root resorption may be an uncontrolled phenomenon, and the most known interventions have no effect. Even progressive external root resorption may not be controlled by long term Ca(OH)2 therapy. Currently, there are no treatment options for vital tooth that suffer from root resorption. This invasive resorption can lead to extraction of the tooth. The use of new technologies such as low power laser may control this type of resorption
Subcutaneous Connective Tissue Reaction to a New Nano Zinc-Oxide Eugenol Sealer in Rat Model
Introduction: The aim of this animal study was to evaluate the histological response of the new nano zinc-oxide eugenol (NZOE) sealer in comparison with Pulp Canal Sealer (ZOE based) and AH-26 (epoxy resin sealer). Methods and Materials: A total of 27 Wistar rats were used. Four polyethylene tubes were implanted in the back of each rat (three tubes containing the test materials and an empty tube as a control). Then, 9 animals were sacrificed at each interval of 15, 30 and 60 days, and the implants were removed with the surrounding tissues.Samples were evaluated for the presence of inflammatory cell (mononuclear cell), vascular changes, fibrous tissue formation and present of giant cell. Comparisons between groups and time-periods were performed using the Kruskal-Wallis and Mann-Whitney U non-parametric tests. The level of significance was set at 0.05. Results: No significant difference was observed in tissue reactions and biocompatibility pattern of three sealers during 3 experimental periods (P<0.05). In all groups the tissue behavior showed tendency to decrease the irritation effect over time. Conclusion: The new nano zinc-oxide eugenol sealer has histocompatibility properties comparable to conventional commercial sealers.Keywords: Biocompatibility; Nanoparticle; Tissue Reaction; Zinc-Oxide Eugeno
In Vitro Cytotoxicity of a New Nano Root Canal Sealer on Human Gingival Fibroblasts
Introduction: The aim of this in vitro study was to evaluate the cytotoxicity of a new nano zinc-oxide eugenol (NZOE) sealer on human gingival fibroblasts (HGFs) compared with Pulpdent (micro-sized ZOE sealer) and AH-26 (resin-based sealer). Methods and Materials: The Pulpdent, AH-26, and NZOE sealers were prepared and exposed to cell culture media immediately after setting, and 24 h and one week after setting. Then, the primary cultured HGFs were incubated for 24 h with different dilutions (1:1 to 1:32) of each sealer extract. Cell viability was evaluated by methyl thiazolyl diphenyl tetrazolium bromide (MTT) assay. The results were compared using two-way analysis of variance followed by Tukey’s post hoc test. The level of significance was set at 0.05. Results: All sealer extracts, up to 32 times dilutions, showed cytotoxicity when exposed to HGF immediately after setting. The extracts obtained 24 h or one week after setting showed lower cytotoxicity than extracts obtained immediately after setting. At all setting times, NZOE showed lower cytotoxicity than Pulpdent and AH-26. While one-week extracts of NZOE had no significant effect on the viability of HGF at dilutions 1:4 to 1:32, both Pulpdent and AH-26 decreased the cell viability at dilutions of 1:4 and 1:8. Conclusion: NZOE exhibited lower cytotoxicity compared to Pulpdent and AH-26 on HGF and has the potential to be considered as a new root canal filling material.Keywords: Cytotoxicity; Human Gingival Fibroblast; MTT assay; Nano; Seale
Intertwined Hamiltonians in Two Dimensional Curved Spaces
The problem of intertwined Hamiltonians in two dimensional curved spaces is
investigated. Explicit results are obtained for Euclidean plane,Minkowski
plane, Poincar{\' e} half plane (), de Sitter Plane (), sphere,
and torus. It is shown that the intertwining operator is related to the Killing
vector fields and the isometry group of corresponding space. It is shown that
the intertwined potentials are closely connected to the integral curves of the
Killing vector fields. Two problems of considered as applications of the
formalism presented in the paper. The first one is the problem of Hamiltonians
with equispaced energy levels and the second one is the problem of Hamiltonians
whose spectrum are like the spectrum of a free particle.Comment: To appear in Annals of Physic
Cytotoxicity of a New Nano Zinc-Oxide Eugenol Sealer on Murine Fibroblasts
Introduction: The aim of this study was to evaluate the cytotoxicity of a new nano zinc-oxide eugenol (NZOE) sealer in comparison with AH-26 and Pulpdent root canal sealers. Methods and Materials: The L929 mouse fibroblast cells were cultivated and incubated for 24, 48 or 72 h with different dilutions (1/1, 1/2, 1/4, 1/8, 1/16 and 1/32) of culture media previously exposed to either of the test sealers naming NZOE, AH-26 or Pulpdent. At the end of incubation period, the effect of sealers on cell viability was evaluated using Mosmann’s Tetrazolium Toxicity (MTT) colorimetric assay. The data was compared using the one-way analysis of variance (ANOVA) followed by the Tukey’s post hoc test for multiple comparisons. Results: After 24, 48 or 72 h, both NZOE and Pulpdent sealers inhibited cell viability at 1/1, 1/2 and 1/8 dilutions. Within the 24 and 48 h, the AH-26 sealer reduced the cell viability at all dilutions except the 1/32 solution; however after 72 h even the 1/32 dilution was cytotoxic. Conclusion: The biocompatibility of the nano zinc-oxide eugenol sealer was comparable to Pulpdent sealer and lower than AH-26.Keywords: Cytotoxicity; MTT Assay; Nanoparticles; Root Canal Sealer; Zinc-Oxide Eugenol
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