Neck,shoulder and low back pain in secondary schoolchildren in relation to schoolbag carriage: Should the recommended weight limits be gender-specific?

The occurrence of neck, shoulder and low back complaints in relation to schoolbag carriage and other potential risk factors were investigated in a cross-sectional study of 586 Iranian schoolchildren aged 12–14 years. The average load carried by schoolchildren was 2.8 kg. Neck, shoulder and low back complaints during the preceding month were reported by 35.3%, 26.1% and 33% of the students, respectively. Gender was an independent factor predicting musculoskeletal symptoms in schoolchildren. Girls were more likely than boys to suffer from neck, shoulder and low back complaints, although there was no significant difference between genders in terms of schoolbag carriage variables. The findings suggest that the recommended weight limit for schoolbag carriage may need to differ between boys and girls. The associations between schoolbag variables and reported symptoms are also discussed. The results provide evidence that the current weight limit should consider a broader combination of factors that influence the use of schoolbags.     

Prediction of the condensed phase heat of formation of energetic compounds

A new reliable simple model is presented for estimating the condensed phase heat of formation of important classes of energetic compounds including polynitro arene, polynitro heteroarene, acyclic and cyclic nitramine, nitrate ester and nitroaliphatic compounds. For CHNO energetic compounds, elemental compositions as well as increasing and decreasing energy content parameters are used in the new method. The novel correlation is tested for 192 organic compounds containing complex molecular structures with at least one nitro, nitramine or nitrate energetic functional groups. This work improves the predictive ability of previous empirical correlations for a wide range of energetic compounds. For those energetic compounds where group additivity method can be applied and outputs of quantum mechanical computations were available, it is shown that the root mean square (rms) deviation of the new method is lower.     

Design of a perfect black absorber at visible frequencies using plasmonic metamaterials

The design and fabrication of a plasmonic black absorber with almost 100% absorbance spanning a broad range of frequencies from ultraviolet (UV) to the near infrared (NIR) is demonstrated. The perfect plasmonic absorber is achieved by a combination of a metal film with suitable metal/dielectric nanocomposites. Our fabrication technique is simple, versatile, cost-effective, and compatible with current industrial methods for solar absorber production.     

A new approach to predict the strength of high energy materials

This paper presents a new approach to predict the strength of energetic compounds in which there are important classes of high explosives including nitroaromatics, acyclic and cyclic nitramines, nitrate esters and nitroaliphatics. For C(a)H(b)N(c)O(d) compounds, the ratio of carbon to oxygen atoms and the predicted heat of detonation on the basis of the H(2)O-CO(2) arbitrary have been used to calculate the strength of an explosive. The new model can give good predictions for mentioned energetic compounds as determined by the Trauzl test. The novel correlation will be useful in predicting the strength or power of a new energetic compound that has significant potential in the field of explosives and propellants.     

Heats of sublimation of nitramines based on simple parameters

In this work, a simple procedure is introduced to determine heats of sublimation of nitramines as an important class of explosives. Molecular weight and one structural parameter of nitramines would be needed in the new method. Calculated heats of sublimation for well-known explosives such as HMX [1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane], RDX [1,3,5-trinitro-1,3,5-triazacyclohexane] and TETRYL [1-(methylnitramino)-2,4,6-trinitrobenzene] as well as new nitramines CL-20 [2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane] and TNAZ [1,3,3-trinitroazatidine] show good agreement with experimental data. R-squared value or the coefficient of determination of new correlation is 0.945. The root-mean-square deviation (RMS) from experiment for the predicted heats of sublimation by new method is 10.10 kJ/mol.     

Assessing the effect of surface chemistry on gold nanorod uptake, toxicity, and gene expression in mammalian cells

Through the use of various layer-by-layer polyelectrolyte (PE) coating schemes, such as the common poly(diallyldimethylammonium chloride)-poly(4-styrenesulfonic acid) (PDADMAC-PSS) system, the mammalian cellular uptake of gold nanorods can be tuned from very high to very low by manipulating the surface charge and functional groups of the PEs. The toxicity of these nanorods is also examined. Since the PE coatings are individually toxic, the toxicity of nanorods coated in these PEs is measured and cells are found to be greater than 90% viable in nearly all cases, even at very high concentrations. This viability assay may not be a complete indicator of toxicity, and thus gene-expression analysis is used to examine the molecular changes of cells exposed to PDADMAC-coated nanorods, which enter cells at the highest concentrations. Indicators of cell stress, such as heat-shock proteins, are not significantly up- or down-regulated following nanorod uptake, which suggests that PDADMAC-coated gold nanorods have negligible impact on cell function. Furthermore, a very low number of genes experience any significant change in expression (0.35% of genes examined). These results indicate that gold nanorods are well suited for therapeutic applications, such as thermal cancer therapy, due to their tunable cell uptake and low toxicity.     

Pullout behavior of polymeric strip in compacted dry granular soil under cyclic tensile load conditions

Assessment of the reinforcement behavior of soil under cyclic and monotonic loads is of great importance in the safe design of mechanically stabilized earth walls. In this article, the method of conducting a multistage pullout (MSP) test on the polymeric strip (PS) is presented. The post-cyclic behavior of the reinforcement can be evaluated using a large-scale pullout apparatus adopting MSP test and one-stage pullout (OSP) test procedures. This research investigates the effects of various factors including load amplitude, load frequency, number of load cycles and vertical effective stress on the peak apparent coefficient of friction mobilized at the soil-PS interface and the pullout resistance of the PS buried in dry sandy soil. The results illustrate that changing the cyclic tensile load frequency from 0.1 Hz to 0.5 Hz does not affect the pullout resistance. Moreover, the influence of increasing the number of load cycles from 30 to 250 on the peak pullout resistance is negligible. Finally, the effect of increasing the cyclic tensile load amplitude from 20% to 40% on the monotonic pullout resistance can be ignored. The peak apparent coefficient of friction mobilized at the soil-PS interface under monotonic and cyclic load conditions decreases with the increase in vertical effective stress.     

Thermochemical,Sensitivity and Detonation Characteristics of New Thermally Stable High Performance Explosives

The M06‐2X/6‐311G(d,p) and B3LYP/6‐311G(d,p) density functional methods and electrostatic potential analysis were used for calculation of enthalpy of sublimation, crystal density and enthalpy of formation of some thermally stable explosives in the gas and solid phases. These data were used for prediction of their detonation properties including heat of detonation, detonation pressure, detonation velocity, detonation temperature, electric spark sensitivity, impact sensitivity and deflagration temperature using appropriate methods. The range of different properties for these compounds are: crystal density 1.51–2.01 g cm⁻³, enthalpy of sublimation 346.4–424.7 kJ mol⁻¹, the solid phase enthalpy of formation 500.4–860.6 kJ mol⁻¹, heat of detonation 13.64–17.57 kJ g⁻¹, detonation pressure 33.0–37.0 GPa, detonation velocity 8.5–9.5 km s⁻¹, detonation temperature 5488–6234 K, electric spark sensitivity 7.89–9.47 J, impact sensitivity 21–38 J, deflagration temperature 560–586 K and power [%TNT] 207–276. The results show that two novel energetic compounds N,N′‐(diazene‐1,2‐diylbis(2,3,5,6‐tetranitro‐4,1‐phenylene))bis(5‐nitro‐4H‐1,2,4‐triazol‐3‐amine) (DDTNPNT3A) and 1,1′‐(diazene‐1,2‐diylbis(2,3,5,6‐tetranitro‐4,1‐phenylene))bis(3‐nitro‐1H‐1,2,4‐triazol‐5‐amine) (DDTNPNT5A) can be introduced as thermally explosives with high detonation performance.