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(color online). Comparison of Berendsen and NoséHoover thermostat for NF e = 50 at 400 K for ∆t = 1 fs: temperature dispersion for Nosé-Hoover is closer to the canonical dispersion. Inset shows the distribution of instantaneous kinetic temperature for Berendsen thermostat for ∆t/τ = 0.1, Nosé-Hoover thermostat for τ = 25 fs, and the canonical distribution.
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The thermal behavior of free and alumina-supported iron-carbon nanoparticles is investigated via molecular-dynamics simulations, in which the effect of the substrate is treated with a simple Morse potential fitted to ab initio data. We observe that the presence of the substrate raises the melting temperature of medium and large Fe1−xCx nanoparticle...
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... Dynamics Simulations. MD simulations are carried in the N V T ensemble using the Verlet al- gorithm [66,67] with a time step ∆t = 1.0 fs. Of the several methods developed for controlling the temper- ature in MD simulations [68,69,70,71,72], Berend- sen and Nosé-Hoover thermostats are most commonly used. In Fig. 4 we compare the temperature disper- sion ∆T of the two thermostats with respect to that of the canonical distribution ∆T canonical [73] at T = 400 K for small nanoparticles (N F e = 50). We observe that the widely used Berendsen thermostat is more sensitive to the choice of the coupling constant. Inset in Figure 4 shows the distribution ...
Context 2
... observe that the widely used Berendsen thermostat is more sensitive to the choice of the coupling constant. Inset in Figure 4 shows the distribution of instantaneous kinetic tem- perature for Berendsen thermostat for the typical value of ∆t/τ = 0.1 [74], the Nosé-Hoover thermostat for τ = 25 fs, and the canonical distribution at T = 400 K. The Nosé-Hoover thermostat (σ T ∼ 47 K) reproduces the canonical distribution(σ T ∼ 46 K) much better than the Berendsen thermostat (σ T ∼ 17 K), making it a bet- ter choice for our constant temperature simulations. ...
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Nanotechnology and nanoparticle (NPs) research has attracted a lot
of interest in recent decades, and there is growing attention to find more
effective ways for their synthesis. The use of biological organism as
bionanofactories provides a clean and promising alternative process for
the fabrication of silver nanoparticles. This study was aimed to
biosynthesized silver nanoparticles (SNPs) by using cell free filtrate of
the fungus Aspergillus niger and evaluate the antifungal effects of
biosynthesized silver.
The study was conducted in the period between March /2016 and
January/ 2017 in the microbiology laboratory of the Medicine College /
University of Al-Qadisiyah.
A reference strain of Aspergillus niger was used in present study for
biosynthesis of SNPs. While the reference strains of dermatophytes
namely, Trichophyton rubrum, Trichophyton mentagrophytes
,Trichophyton interdigitale, Epidermophyton floccosum, Microsporum
canis and Candida albicans were used for testing their susceptibility to
bio-prepared SNPs.
The biosynthesized SNPs were characterized by means of several
techniques. The UV-visible spectrophotometric showed characteristic
absorption peak at 420 nm. The presence of proteins as viable reducing
agents for the formation and stability of SNPs was recorded using Fourier
transform infrared spectroscopic analysis (FTIR). Further scanning
electron microscopy (SEM) and transmission electron microscopy (TEM)
micrographs showed the formation of spherical, mono-dispersed
nanoparticles with size ranging between 15 and 60 nm in diameter.
Optimization results showed that the optimum condition for
biosynthesis of SNPs were the use of Potato dextrose broth medium at pH
9, 30°C for 120 h with 1mM silver nitrate.
The MIC and MFC recorded 0.313 and 2.5 µg/mL in the case of
Trichophyton rubrum (the most susceptible species), 5 and 14.14 μg/ml
for Microsporum canis (the most tolerant species), respectively. The
biosynthesized SNPs displayed nearly similar antifungal effect to that
obtained by Miconazole, while it exhibited a higher effect in comparison
to Fluconazole. SNPs had pronounced and significant (P < 0.05) spore
germination inhibition effect on all the tested dermatophytes but this
effect was variable depending on the fungal isolates. A decrease in
keratinase activity in the presence of SNPs was also reported.
Epidermophyton floccosum showed higher enzyme reduction in the
presence of SNPs (47.41%) compared to other dermatophytes .While the
effect of Miconazole on it was 28.30 %. However Fluconazole had no
effect on the tested dermatophytes except on Trichophyton interdigitale.
The biosynthesized SNPs exerted pronounced morphological alteration
in the fungal mycelia; Main morphological changes include swelling,
presence of large vacuoles, wall disorganization and loss of integrity of
their biological membranes indicating extensive cellular death.
SNPs significantly reduced the adhesion and biofilm formation of
C.albicans in a dose-dependent manner. The highest reduction was
observed at 2 X MIC which reached to 51% and 36.1% for adherence and
biofilm formation, respectively. Whereas the Miconazole had lower effect
with reduction percentage of 43% and 31.1% for adherence and biofilm
formation, respectively. SNPs were completely prevented the development of germ tube with
a percentage of inhibition 100%. Similar results were obtained with
Miconazole
The antifungal activities of Fluconazole and Miconazole were
increased in the presence of SNPs. The highest enhancing effect was
observed for Fluconazole against all resistant strains with fold increase
100%. An antagonism effect was observed when a combination of SNPs
and Miconazolre was applied against Microsporum canis.
In conclusion, the obtained results established the fact that SNPs can be
synthesized in inexpensive and promising technique by fungal isolate of
A.niger, and the qualities of these NPs. can be controlled by monitoring
the environmental factors. In addition biosynthesized SNPs have
considerable antifungal activity comparison with other antifungal drugs.
