The effects of gold nanoparticles size and concentration on viscosity, flow activation energy, dielectric and optical properties

This study was carried out to investigate viscosity in relation with the temperature, flow activation energy and dielectric properties for 10, 20 and 50 nm gold nanoparticles size (GNPs) in addition to absorption and fluorescence spectra at different concentrations (0.2 × 10-3 to 1 × 10-2%) in an attempt to cover and understand the toxicity and potential role of their therapeutic and diagnostic use in medical applications. 10, 20 and 50 nm GNPs dissolved in aqueous solution were purchased (Product MKN-Au, Canada) and used in this study. Mechanical parameters were measured using Brookfield LVDV-III Programmable rheometer with temperature bath controlled by a computer. 0.5 ml of each GNP size in aqueous solution was poured in the sample chamber of the rheometer. The spindle was immersed and rotated in these gold nanofluids in the speed range from 50 to 250 rpm in steps of 20 min. Viscosity of GNPs was measured at temperature of 37°C and at a gradually increase of temperature to 42ºC. UV–Visible characterization of GNPs at different concentrations from 0.2 × 10-3 to 1 × 10-2 % was performed using UV-1601 PC, UV-Visible spectrophotometer. The absorbance measurements were made over the wavelength range of 250 to 700 nm using 1 cm path length quartz cuvettes. Fluorescence characterization of GNPs was performed over the wavelength range of 250 to 700 nm using FluoroMax-2 JOBIAN YVON-SPEX. The measured viscosities for all GNP sizes decreased with increasing the temperatures from 37 to 42°C. The GNPs with larger size (50 nm) exhibited higher viscosity values compared with 10 and 20 nm GNPs. The flow activation energies (kJ/mol) for 10, 20 and 50 nm GNPs were 332.55, 415.4 and 182.2 kJ/mol, respectively. The optical properties such as absorption maxima and the absorption intensity are particle size-dependent. The fluorescence emission band for GNPs with an excitation wavelength of 308 nm and photoluminescence (PL) band centre appeared at 408 nm. With the increase of GNPs concentration at a fixed GNP size of 20 nm, the intensity of emission band positioned increased, and the trend was consistent with the changes of the corresponding surface plasmon resonance (SPR) of GNPs. The presented dielectric data indicates that GNPs have strong dielectric dispersion corresponding to the alpha relaxation region in the frequency range of 20 Hz to 100 kHz which was identified as anomalous frequency dispersion. At a constant GNP size, the absorbance was found to be proportional to the concentration of gold. This is due to the increase in the number of GNPs as well as the increase in the SPR of GNPs. An intense absorption peak was observed at wavelength of 517 nm which is generally attributed to the surface plasmon excitation of the small spherical GNPs. The incident light at 308 nm will lead to excitation of the surface plasmon coherent electronic motion as well as the d electrons. This study suggests that the relaxation of these electronic motions followed by the recombination of the sp electrons with holes in the d band leads to the fluorescence emission. These results indicate that the intensity of fluorescence emission band of GNPs was dependent on the concentration of GNPs. A rapid decrease in the dielectric constant may be attributed to the tendency of dipoles in GNPs to orient themselves in the direction of the applied field in the low-frequency range. However, in the high-frequency range, the dipoles will hardly be able to orient themselves in the direction of the applied field and hence the value of the dielectric constant is nearly constant.Key words: Gold nanoparticles, viscosity, size, temperature, dielectric, absorption, fluorescence

The mini-bestest can predict parkinsonian recurrent fallers : a 6-month prospective study

2012-2013 > Academic research: refereed > Publication in refereed journalVersion of RecordSelf-fundedPublishe

Evaluation of Rice Germplasm under Salt Stress at the Seedling Stage through SSR Markers

Twenty eight rice germplasms were used for identification of salt tolerant rice genotypes at the seedling stage at the experimental farm and Biotechnology laboratory of the Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh during February 2009 to October 2009. Phenotyping for salinity screening of the rice genotypes was done using salinized (EC level 12 dS m-1) nutrient solution in hydroponic system. Genotypes were evaluated for salinity tolerance on 1-9 scale based on seedling growth parameters following modified Standard Evaluation Scoring (SES) of IRRI. Phenotypically, on the basis of SES and % total dry matter (TDM) reduction of the genotypes viz. PBSAL-614, PBSAL-613, PBSAL-730, Horkuch, S-478/3 Pokkali and PBSAL (STL)-15 were found to be salt tolerant; on the other hand Iratom-24, S-653/32, S-612/32, S-604/32, S-633/32, Charnock (DA6), BINA Dhan-6 and S-608/32 were identified as salt susceptible. For genotyping, ten SSR markers were used for polymorphism, where 3 primers (RM127, RM443 and RM140) were selected for evaluation of salt tolerance. In respect of Primer RM127, 7 lines were found salt tolerant and 11 lines were moderately tolerant and 10 lines were susceptible. Nine tolerant, 9 moderately tolerant and 10 susceptible lines were found when the primer RM140 was used and primer RM443 identified 8 lines as tolerant, 9 lines as moderately tolerant and 11 lines as susceptible. Thus, the salt tolerant lines can be used in further evaluation for salinity tolerance and the SSR markers used in this study are proving valuable for identifying salt tolerant genes in marker assisted breeding. Int. J. Agril. Res. Innov. & Tech. 3 (1): 52-59, June, 2013 DOI: http://dx.doi.org/10.3329/ijarit.v3i1.1609

Altered profile of circulating endothelial progenitor cells in obstructive sleep apnea

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Sudanese Medical Students and Scientific Research

Background: Most of developing countries face problems in assessment of their public health practices. Gain of this knowledge is orchestrated by  research. Medical students can play an essential role in improving public database.Objective: to explore knowledge, attitude and skills of medical students in the Faculty of Medicine and Health Sciences (FMHS), Omdurman Islamic University (OIU) towards research.Materials and Methods: This is a descriptive, analytical, cross-sectional, institution-based study. A total of 442 students, equally from each batch participated in the study. Equal numbers of male andfemale were considered to eliminate gender and seniority bias. Structured pretested questionnaire was used for data collection. Data collected were fed to Statistical Package for Social Sciences(SPSS) version 15. Means, standard deviation and correlations were done where appropriate. Statistical  significance was taken at P =0.05.Results: The mean knowledge score was 37% and attitude was positive in 77.1% of the students. Only 18.3% had attended research methodology workshop. The rate of internet navigation is directly proportional to the social class. Only 14.7% knew the engines used for finding medical literature.Conclusion: The low knowledge score is due to lack of application of research in the academic curriculum; however, the students have a fairly positive attitude. The knowledge is expected to improve with the intended policy to include practical research in the curriculum.Key Words: Public health, academic curriculum, Suda

Strategic Digitalization of UMKM Business as an Alternative to Survive the COVID - 19 Pandemic

The purpose of this study is to implement a business digitalization strategy so that micro, small and medium enterprises (UMKM) can survive the Covid 19 pandemic. This research method is descriptive qualitative based on UMKM survey data from the Katadata Insight Center (KIC) June 2020 in the Jabotabek area. From the results of this study it appears that UMKM business activities carried out with a conventional strategy (Offline System) contributed to a decrease in sales turnover by more than 30%. Meanwhile, UMKM business activities carried out with the strategy of digitalization UMKM (Online System) businesses such as Smart phones (PCs or lap tops) connected to the Internet only amounted to 3.8% of UMKM which experienced an increase in sales turnover. For this reason, it is necessary to build an infrastructure that supports the digitalization of UMKM in terms of online marketing of UMKM products

Neurogenesis Drives Stimulus Decorrelation in a Model of the Olfactory Bulb

The reshaping and decorrelation of similar activity patterns by neuronal networks can enhance their discriminability, storage, and retrieval. How can such networks learn to decorrelate new complex patterns, as they arise in the olfactory system? Using a computational network model for the dominant neural populations of the olfactory bulb we show that fundamental aspects of the adult neurogenesis observed in the olfactory bulb -- the persistent addition of new inhibitory granule cells to the network, their activity-dependent survival, and the reciprocal character of their synapses with the principal mitral cells -- are sufficient to restructure the network and to alter its encoding of odor stimuli adaptively so as to reduce the correlations between the bulbar representations of similar stimuli. The decorrelation is quite robust with respect to various types of perturbations of the reciprocity. The model parsimoniously captures the experimentally observed role of neurogenesis in perceptual learning and the enhanced response of young granule cells to novel stimuli. Moreover, it makes specific predictions for the type of odor enrichment that should be effective in enhancing the ability of animals to discriminate similar odor mixtures

Magnetic Control of Valley Pseudospin in Monolayer WSe2

Local energy extrema of the bands in momentum space, or valleys, can endow electrons in solids with pseudo-spin in addition to real spin. In transition metal dichalcogenides this valley pseudo-spin, like real spin, is associated with a magnetic moment which underlies the valley-dependent circular dichroism that allows optical generation of valley polarization, intervalley quantum coherence, and the valley Hall effect. However, magnetic manipulation of valley pseudospin via this magnetic moment, analogous to what is possible with real spin, has not been shown before. Here we report observation of the valley Zeeman splitting and magnetic tuning of polarization and coherence of the excitonic valley pseudospin, by performing polarization-resolved magneto-photoluminescence on monolayer WSe2. Our measurements reveal both the atomic orbital and lattice contributions to the valley orbital magnetic moment; demonstrate the deviation of the band edges in the valleys from an exact massive Dirac fermion model; and reveal a striking difference between the magnetic responses of neutral and charged valley excitons which is explained by renormalization of the excitonic spectrum due to strong exchange interactions

Interval estimation and optimal design for the within-subject coefficient of variation for continuous and binary variables

BACKGROUND: In this paper we propose the use of the within-subject coefficient of variation as an index of a measurement's reliability. For continuous variables and based on its maximum likelihood estimation we derive a variance-stabilizing transformation and discuss confidence interval construction within the framework of a one-way random effects model. We investigate sample size requirements for the within-subject coefficient of variation for continuous and binary variables. METHODS: We investigate the validity of the approximate normal confidence interval by Monte Carlo simulations. In designing a reliability study, a crucial issue is the balance between the number of subjects to be recruited and the number of repeated measurements per subject. We discuss efficiency of estimation and cost considerations for the optimal allocation of the sample resources. The approach is illustrated by an example on Magnetic Resonance Imaging (MRI). We also discuss the issue of sample size estimation for dichotomous responses with two examples. RESULTS: For the continuous variable we found that the variance stabilizing transformation improves the asymptotic coverage probabilities on the within-subject coefficient of variation for the continuous variable. The maximum like estimation and sample size estimation based on pre-specified width of confidence interval are novel contribution to the literature for the binary variable. CONCLUSION: Using the sample size formulas, we hope to help clinical epidemiologists and practicing statisticians to efficiently design reliability studies using the within-subject coefficient of variation, whether the variable of interest is continuous or binary