Casimir forces are of fundamental interest because they originate from quantum fluctuations of the electromagnetic field. Apart from controlling this force via the optical properties of materials, a ...number of novel geometries have been proposed to generate repulsive and/or non-monotonic Casimir forces between bodies separated by vacuum gaps. Experimental realization of these geometries, however, is hindered by the difficulties in alignment when the bodies are brought into close proximity. Here, using an on-chip platform with integrated force sensors and actuators, we circumvent the alignment problem and measure the Casimir force between two surfaces with nanoscale protrusions. We demonstrate that the force depends non-monotonically on the displacement. At some displacements, the Casimir force leads to an effective stiffening of the nanomechanical spring. Our findings pave the way for exploiting the Casimir force in nanomechanical systems using structures of complex and non-conventional shapes.
The aim of this work was to synthesize semiconducting oxide nanoparticles using a simple method with low production cost to be applied in natural sunlight for photocatalytic degradation of pollutants ...in waste water. Iron titanate (Fe
TiO
) nanoparticles with an orthorhombic structure were successfully synthesized using a modified sol-gel method and calcination at 750°C. The as-prepared Fe
TiO
nanoparticles exhibited a moderate specific surface area. The mesoporous Fe
TiO
nanoparticles possessed strong absorption in the visible-light region and the band gap was estimated to be around 2.16 eV. The photocatalytic activity was evaluated by the degradation of methylene blue under natural sunlight. The effect of parameters such as the amount of catalyst, initial concentration of the dye and pH of the dye solution on the removal efficiency of methylene blue was investigated. Fe
TiO
showed high degradation efficiency in a strong alkaline medium that can be the result of the facilitated formation of OH radicals due to an increased concentration of hydroxyl ions.
Dextran sulphate stabilized silver nanoparticles (AgNPs - DS) were synthesized from aqueous solution of silver nitrate (AgNO3) and dextran sulphate sodium salt (DS). The characterization of AgNPs - ...DS was performed by ultraviolet–visible spectroscopy (UV-VIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and antimicrobial activity. The formation of AgNPs - DS was monitored by colour changes of the reaction mixture from yellowish to brown and by measuring the surface plasmon resonance absorption peak in UV-VIS spectra at 420 nm. The SEM analysis was used for size and shape determination of AgNPs - DS. The presence of elemental silver and its crystalline structure in AgNPs - DS were confirmed by EDX and XRD analyses. The possible functional groups of DS responsible for the reduction and stabilization of AgNPs were determinated by FTIR spectroscopy. The AgNPs - DS showed strong antibacterial activity against Staphylococcus aureus ATCC 25923, Bacillus cereus ATCC 11778, Bacillus luteus in haus strain, Bacillus subtilis ATTC 6633, Listeria monocytogenes ATCC 15313, Escherichia coli ATTC 25922, Pseudomonas aeruginosa ATTC 27853, Klebsiella pneumoniae ATTC 700603, Proteus vulgaris ATTC 8427, and antifungal activity against Candida albicans ATTC 2091.
•Dextran sulphate stabilized silver nanoparticles (AgNPs-DS), were synthesized by using a chemical reduction green synthetic method, which involve the application of non-toxic and biodegradable agents such as polysaccharides for the reduction and stabilization of AgNPs.•Nanoparticles, spherical in shape, were characterized by UV-VIS, SEM, XRD, FTIR and EDX methods.•The AgNPs – DS nanoparticles showed strong antibacterial activity against and antifungal activity against.
Polycyclic aromatic hydrocarbons (PAH) have been listed by the United States Environmental Protection Agency (US EPA) and by the European Community as priority environmental pollutants. The removal ...of PAHs from soils, sediments and waste water has attracted attention of scientists and engineers for several decades. Electrochemical oxidation of PAH compounds in water, is receiving increasing attention, due to its convenience and simplicity. In this study we performed electrochemical oxidation of 16 EPA PAHs mixture in 10% NaCl aqueous solution in potentiostatic conditions, at voltage 1 V. Decrease of concentration of some individual PAHs, up to 70% referred to their starting concentration, after 60 min of electrolysis, was confirmed by UPLC/PDA analysis. In further work investigation was extrapolated to in situ removal of PAHs from concrete, as the medium where, to our knowledge, such way of PAH removal has not been investigated before.
High concentrations of PAH contamination occurred in the concrete structure of the residential buildings in Belgrade in 2014. Application of DC voltage of 50 V between nickel and stainless steel electrodes packed in the concrete wall, moisturized with the 10% NaCl solution, led to considerable removal of the pollutants by oxidation process throughout the concrete.
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•Concrete pollution with PAHs determined.•Electrochemical oxidation of PAH water solution examined.•Substantial oxidation of PAH in concrete achieved.
Application of DC voltage between electrodes packed in the concrete wall, led to considerable removal of the pollutants by oxidation process throughout the concrete.
In this paper we study several temperature sensing techniques using the same thermographic phosphor: luminescence intensity ratio, lifetime, rise time. Moreover, we analyze some recently presented ...techniques, based on host luminescence intensity ratio method and delayed gate intensity ratio technique. We have selected YVO4:Eu3+ nano powder as an appropriate material for this study, because it has easily detectable luminescence rise time and host luminescence. The material was prepared using simple solution combustion synthesis. The time resolved analysis of emission spectra was achieved using the streak camera system. We present a very detailed analysis of measured lifetimes and rise times of all emission lines and their temperature dependence. We propose a multi-mode temperature sensing technique based on the concept of luminescence detection part of the temperature sensor capable of switching between several measurements modes to obtain the best sensitivity in desired range of operation.
•Concrete pollution with PAHs determined.•Analytical method of PAH determination developed.•FHO3AOP method of PAH removal.•Substantial and uniform oxidation of PAH in concrete achieved.•The FHO3AOP ...method is feasible, economically viable and environmentally acceptable.
Polycyclic aromatic hydrocarbons (PAHs) are denoted by International Agency for Research on Cancer as mutagens, teratogens and carcinogenic to humans. In 2013, Vinča Institute of Nuclear Sciences was hired to determine whether PAHs are present in significant quantities in the concrete walls of newly built residential buildings (about 15,000m2 of apartments), and to propose appropriate technical solution for PAH removal in this case. As PAH occurrence, determination and remediation in concrete is, to our knowledge, a completely new field, it was necessary to face a number of challenges, including lack of regulations considering contents of PAHs in concrete, investigation of the origin of PAH contamination in concrete (if established), as well as finding feasible and non-expensive remediation method, which would be appropriate for residential space. In first part of this study, a markedly high concentrations of 5PAHs were detected by UPLC/PDA analysis in samples of both concrete walls and mineral oil used for coating of planks during formwork, while control concrete and mineral oil, taken from independent construction site, were taken as a reference. Such coincidence, as well as the fact that mineral oil has penetrated into the concrete which is proven by ASAP/MS analysis, pointed to the mineral oil as the most probable source of PAH contamination of the concrete. In the second part, an efficient and easy-applicable method for PAH oxidation in concrete (called FHO3AOP), using UV light, H2O2 and ozone, was presented and discussed in terms of previous literature data.
Although recent studies report on the benefits of blended learning in improving medical student education, there is still no empirical evidence on the relative effectiveness of blended over ...traditional learning approaches in medical statistics. We implemented blended along with on-site (i.e. face-to-face) learning to further assess the potential value of web-based learning in medical statistics.
This was a prospective study conducted with third year medical undergraduate students attending the Faculty of Medicine, University of Belgrade, who passed (440 of 545) the final exam of the obligatory introductory statistics course during 2013-14. Student statistics achievements were stratified based on the two methods of education delivery: blended learning and on-site learning. Blended learning included a combination of face-to-face and distance learning methodologies integrated into a single course.
Mean exam scores for the blended learning student group were higher than for the on-site student group for both final statistics score (89.36±6.60 vs. 86.06±8.48; p = 0.001) and knowledge test score (7.88±1.30 vs. 7.51±1.36; p = 0.023) with a medium effect size. There were no differences in sex or study duration between the groups. Current grade point average (GPA) was higher in the blended group. In a multivariable regression model, current GPA and knowledge test scores were associated with the final statistics score after adjusting for study duration and learning modality (p<0.001).
This study provides empirical evidence to support educator decisions to implement different learning environments for teaching medical statistics to undergraduate medical students. Blended and on-site training formats led to similar knowledge acquisition; however, students with higher GPA preferred the technology assisted learning format. Implementation of blended learning approaches can be considered an attractive, cost-effective, and efficient alternative to traditional classroom training in medical statistics.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The antiradical activity of phytol was evaluated by electron paramagnetic resonance towards hydroxyl radical (√OH), superoxide anion radical (
), methoxy radical (√CH
2
OH), carbon-dioxide anion ...radical (
), as well as towards nitric-oxide radical (√NO) and 2,2-diphenyl-1-picrylhydrazyl (√DPPH) radical. It reduced the production of all tested radicals showing more promising activity against
, √CH
2
OH and √DPPH radicals (56%, 50% and 48%, respectively) in comparison with √NO,
and √OH radicals (38%, 23% and 15%, respectively). The antimicrobial activity of phytol was evaluated by the microdilution method against eight bacterial and eight fungal strains. To varying degrees, it was proven to be active against all tested bacteria and fungi (MIC 0.003-0.038 mg/mL and MBC 0.013-0.052 mg/mL, MIC 0.008-0.016 mg/mL and MFC 0.090-0.520 mg/mL, respectively). According to the obtained results, medical foods containing phytol may support development of new therapies for heart disease.
The single phase nanocrystalline boehmite is obtained for the first time at room temperature by a facile hydrolysis of Bayer liquor. Mesoporosity in boehmite powders was constructed using the glucose ...as a template. As-synthesized boehmite powders have high surface area (above 350 m2/g) and the average crystallite size less than 5 nm. Through the thermal dehydration at 500 °C, boehmite isomorphously transforms to γ-alumina retaining the lamellar morphology and mesoporosity of the parent phase.
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