Explicit Determinations of the Colebrook Equation for the Flow Friction Factor by Statistical Analysis

The implicit Colebrook equation is considered as a fundamental equation for estimating the friction factor for turbulent flows in pipes. A large number of simple and accurate explicit approximations cover just a limited area of turbulent regime inside rough or smooth pipes. Here, three explicit approximations of the friction factor were determined. The friction factor data were fitted into polynomials using the response surface design of Minitab® software. To reduce the relative error of the first approximation compared with the implicit Colebrook equation, the domain was divided into two regions based on the Reynolds number (Re). To compare the accuracy and complexity of the approximations with existing relations, advanced comparison analysis based on the relative error was performed. The second set of approximations defined in two ranges of Re demonstrated high accuracy and a satisfying complexity index.     

Physical investigation of ZnSe QDs synthesized by polyol method at 200 °C

In this paper, zinc selenide nanoparticles powder was successfully synthesized using rapid polyol method. The preparation method was changed by using new Se solvents in the final stage to delete seleniums which have not participated in reaction product. This change in the preparation method increased the purity of final product (92 %); and using selenium’s solvents as detergents caused the production of ZnSe with roughly 100 % purity. X-ray diffractions showed that the samples had a cubic structure with lattice constant equalling 5.6699 Å and with 5.5 nm for crystallite size. Atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) images showed that the particles were almost spherical and well crystallized ZnSe nanoparticles were formed. The average sizes of nanoparticles were 15 and 16.4 nm for AFM and HRTEM, respectively. Absorption Spectra of all samples showed a blue shift in comparison with bulk ZnSe. It showed low absorption in a wide range of wavelengths. Band gap energy of the pure ZnSe nanoparticles was found to be 4.51 eV, which is higher than that of the bulk value of ZnSe (2.67 eV). Photoluminescence spectra of the samples showed emission at 450–500 nm wavelengths at room temperature which are useful for the application of solar cells, quantum dot light-emitting diodes and blue organic light-emitting diodes devices.     

Decay Rate of an Excited Atom in Dispersive and Dissipative Plasma Media

Calculations of decay rates of an excited atom embedded in a dispersive and dissipative plasma medium are presented in this paper. The usual expression for decay rate of an initially excited atom in dipole approximation is given by Fermi’s golden rule. The electric field correlation function is related to the imaginary part of the potential Green’s function along with the fluctuation of dissipation theorem and Kubo’s formula. Using the Green’s function technique offers possibilities of closed function representations. It is applicable to evaluate the decay rate of an excited atom that allows us to understand the particular structure of the vacuum state of the electromagnetic field. In this paper, the decay rate of an excited atom in dispersive and dissipative media is estimated.     

Synthesis,Characterization, and Cesium Sorption Performance of Potassium Nickel Hexacyanoferrate-Loaded Granular Activated Carbon

GAC has been modified by loading of potassium nickel hexacyanoferrate (KNiCF) as a new adsorbent for cesium adsorption. The potassium nickel hexacyanoferrate-loaded granular activated carbon (KNiCF-GAC) was characterized using powder x-ray diffraction (XRD) and nitrogen adsorption-desorption isotherm data, infrared spectroscopy, and its cesium adsorption performance in aqueous solution was investigated. The effect of the various parameters such as initial pH value of the solution, contact time, temperature, and initial concentration of the cesium ion on the adsorption efficiencies of KNiCF-GAC have been studied systematically by batch experiments. The adsorption isotherm of KNiCF-GAC was studied and the fitted results indicated that the Langmuir model could well represent the adsorption process. The maximum adsorption capacity of Cs⁺ onto KNiCF-GAC was found to be 163.9 mg · g^?1.     

Synthesis and characterization of PbTe micro/nanostructures through hydrothermal method by using a novel capping agent

For the first time, a Schiff base compound derived from 1,8-diamino-3,6-dioxaoctane and 2-hydroxybenzophenone marked as (2-HBP)-(DaDo) was synthesized, characterized and then used as capping agent for the preparation of PbTe micro/nanostructures. Besides the as-synthesized Schiff base compound, Pb(NO₃)₂ and Te powders were applied as lead and telluride precursors. In addition, effect of preparation parameters like reaction time and temperature in hydrothermal synthesis on the morphology of the final products was tested. The products were analysed with the aid of SEM, XRD, FT-IR and EDS. Based on the obtained results, it was found that pure cubic phased PbTe has been obtained by this method. According to SEM images, it was found that uniform PbTe micro/nanocubes have been obtained at 180 °C for 12 h. On the other hand, by increasing the reaction temperature from 3 to 24 h, the production of cubic-like shapes increased.     

Thermodynamics of the Spin-1/2 Two-Leg Ladder Compound (C_5H_{12}N)_2CuBr_4

The thermodynamic behavior of the spin \(S=1/2\) antiferromagnetic two-leg ladder compound (C \(_5\) H \(_{12}\) N) \(_{2}\) CuBr \(_{4}\) in a uniform magnetic field is studied using numerical and analytical approaches. The entropy \(S(H,T)\) and specific heat \(C(H,T)\) are calculated. The specific heat shows various behaviors in different regions of the magnetic field. The field dependence of the specific heat is almost symmetric about the average of quantum critical fields in complete agreement with experimental results. In addition, it is found that during an adiabatic demagnetization process, temperature drops in the vicinity of the field induced zero-temperature quantum phase transitions.     

Dominant role of drivers’ attitude in prevention of road traffic crashes: A study on knowledge,attitude, and practice of drivers in Iran

Objective

Evaluating the relation between Iranian drivers’ knowledge, attitude, and practice (KAP) regarding traffic regulations, and their deterministic effect on road traffic crashes (RTCs).

Setting

Two cities of Tehran and Zahedan, Iran.

Methods

A cross-sectional study was designed. Using a simplified cluster sampling design, 2200 motor vehicle drivers including 1200 in Tehran and 1000 in Zahedan were selected. Sixty locations in Tehran and 50 in Zahedan were chosen. In each pre-identified location, 20 adult drivers were approached consecutively. A questionnaire developed by researchers was filled by each participant. The questionnaire had four sections including items assessing the demographics, knowledge, attitude and practice of drivers toward traffic regulations. Logistic regression analysis was used to evaluate the relationship between the RTCs and KAP variables.

Results

The study sample consisted of 619 (28.1%) occupational and 1580 (71.8%) private drivers. Among them, 86.4% were male. The median age was 33.6 ± 10.83. Drivers in Tehran and Zahedan had no significant differences between their mean scores of KAP items of the questionnaire. Higher knowledge, safer attitude, and safer practice were associated with a decreased number of RTC. After adjusting for possible confounders, increase of one standard deviation in attitude and practice scores (but not knowledge) resulted in 26.4% and 18.5% decrease in RTC, respectively. Finally, considering knowledge, attitude and practice of drivers in one model to assess their mutual effect, it was shown that only attitude is significantly associated with a decrease of RTC (OR = 0.76, P = 0.007).

Conclusion

Increase in attitude and practice accompanied with decreased number of RTCs in Iranian drivers. Specifically, drivers’ attitude had the crucial effect. It is not knowledge and standard traffic education; rather it is how such education is registered as an attitude that translates what is being learned into actions. Without safer attitude, even safer self-reported practice will not result in lower RTCs.