The effect of macroeconomic variables on the stock market index of the Tehran stock exchange

This paper examines the relationship between stock market index and macroeconomic policies (Fiscal and Monetary) on Iran's economy using quarterly data in the period 1999-2013. This study employed cointegration test and vector autoregressive models (VAR) to examine relationships between the stock market index and the macroeconomic variables. The empirical results reveal that a positive money shock can increase stocks return. According to impulse responses, the government expenditure had a slight impact on stocks return in the short term. But the government expenditure has a positive effect on exchange index in long run. Also the effect of taxes on the stock's price index is negative, so that it reaches its maximum level after the third lag and then alleviates. The GDP shock has positive effect on the stock's price index. Increase in production level leads to increase in earnings and profitability, leading to a positive response from stocks index. Therefore the results showed that the macroeconomic variables such as inflation, exchange rate and GDP have significant effects on Tehran exchange price index. So the hypothesis that the improving economic factors can have a useful role in the booming capital market is confirmed. Also the effect of fiscal policy factors such as tax revenues and government expenditures is more than monetary policy factors on stock returns

Intumescent flame retardant polyurethane/reduced graphene oxide composites with improved mechanical, thermal, and barrier properties

Intumescent flame retardant polyurethane (IFRPU) composites were prepared in the presence of reduced graphene oxide (rGO) as synergism, melamine, and microencapsulated ammonium polyphosphate. The composites were examined in terms of thermal stability (both under nitrogen and air), electrical conductivity, gas barrier, flammability, mechanical, and rheological properties. Wide-angle X-ray scattering and scanning electron microscopy indicated that rGO are well-dispersed and exfoliated in the IFRPU composites. The limiting oxygen index values increased from 22.0 to 34.0 with the addition of 18wt% IFR along with 2wt% rGO. Moreover, the incorporation of rGO into IFRPU composites exhibited excellent antidripping properties as well as UL-94 V0 rating. The thermal stability of the composites enhanced. This was attributed to high surface area and good dispersion of rGO sheets induced by strong interactions between PU and rGO. The oxygen permeability, electrical, and viscoelasticity measurements, respectively, demonstrated that rGO lead to much more reduction in the gas permeability (by ~90%), high electrical conductivity, and higher storage modulus of IFRPU composites. The tensile strength, modulus, and shore A remarkably improved by the incorporation of 2.0wt% of rGO as well

Surface forces in the presence of multivalent ions and polyelectrolytes

Colloids and interfaces interacting through polar media such as water often carry electric charges and thus Columbic forces play a dominant role in these systems. Presence of the ions carrying multiple charges strongly modifies these forces and the overall behavior of the colloidal dispersions. This thesis focuses on the surface forces between charged interfaces in the presence of the multivalent ions and polyelectrolytes. This is done through comprehensive force measurements by means of Atomic Force Microscopy (AFM). Specifically, colloidal probe AFM is used to study the impact of organic multivalent ions and polyelectrolytes on surface forces between different charged colloidal particles

Colloidal Stability of Graphene Oxide: Aggregation in Two Dimensions

Colloidal stability of graphene oxide (GO) is studied in aqueous and organic media accompanied by an improved aggregation model based on Derjaguin-Landau-Verwey- Overbeek (DLVO) theory for ultrathin colloidal flakes. It is found that both magnitude and scaling laws for the van der Waals forces are affected significantly by the two-dimensional (2D) nature of GO. Experimental critical coagulation concentrations (CCC) of GO in monovalent salt solutions concur with DLVO theory prediction. The surface charge density of GO is largely affected by pH. However, theoretical calculations and experimental observations show that the colloidal stability of the 2D colloids is less sensitive to the changes in the surface charge density compared to the classical picture of 3D colloids. The DLVO theory also quantitatively predicts the colloidal stability of reduced GO (rGO). The origin of lower stability of rGO compared to GO is rooted in the higher van der Waals forces among rGO sheets, and particularly, in the removal of negatively charged groups, and possibly formation of some cationic groups during reduction. GO also exfoliates in the polar organic solvents and results in stable dispersions. However, addition of nonpolar solvents perturbs the colloidal stability at a critical volume fraction. Analyzing the aggregation of GO in mixtures of different nonpolar solvents and <i>N</i>-methyl-2-pyrrolidone proposed that the solvents with dielectric constants of less than 24 are not able to host stable colloids of GO. However, dispersions of GO in very polar solvents shows unexpected stability at high concentration (>1 M) of salts and acids. The origin of this stability is most probably solvation forces. A crucial parameter affecting the ability of polar solvents to impart high stability to GO is their molecular size: the bigger they are, the higher the chance for stabilization

Depletion and double layer forces acting between charged particles in solutions of like-charged polyelectrolytes and monovalent salts

Interaction forces between silica particles were measured in aqueous solutions of the sodium salt of poly(styrene sulphonate) (PSS) and NaCl using the colloidal probe technique based on an atomic force microscope (AFM). The observed forces can be rationa lized through a superposit ion of damped oscillatory forces and double layer forces quantitatively. The doubl e layer forces are modeled using Poisson–Boltzmann (PB) theory for a mixture of a monovalent symmetric electrolyte and a highly asymmetric electrolyte, whereby the multivalent coions represent the polyelectr olyte chains. The effective charge of the polyelectro- lyte is found to be smaller than the bare number of charged groups residing on one polyelectrolyte molecule. This effect can be explained by counterion condensation. The interplay between depletion and double layer forces can be further used to predict the phase of the depletion force oscillations. However, this picture holds only at not too elevated concentrations of the polyelectrolyte and salt. At higher salt concentrations, attractive van der Waals forces become important, while at higher polyelectrolyte concentrations, the macromolecules adsorb onto the like-charged silica interface

Lightweight flexible polyurethane/reduced ultralarge graphene oxide composite foams for electromagnetic interference shielding

Multifunctional flexible polyurethane (PU)/reduced ultralarge graphene oxide (rUL-GO) composite foams with low density in the range of similar to 53-92 kg m(-3) were fabricated through the in situ polymerization of PU in the presence of rUL-GO. The incorporation of 1 wt% rUL-GO gave the insular flexible PU composite foams a high electrical conductivity of 4.04 S m(-1), and an excellent electromagnetic interference (EMI) shielding efficiency of similar to 253 dB (g(-1) cm(-3)) at 8-12 GHz. Achieving such a high specific EMI shielding efficiency as well as a low percolation threshold, combined with the method of foam preparation, results in a uniform dispersion and very high aspect ratio (>20 000) for the rUL-GO nanosheets. Furthermore, by the introduction of rUL-GO, the Young's modulus and tensile strength of the PU composite foams also improved significantly without reducing the flexibility. TGA experiments also indicated the enhanced thermal stability of the composite foams

Nanometer-ranged attraction induced by multivalent ions between similar and dissimilar surfaces probed using an atomic force microscope (AFM)

Direct force measurements between positively charged amidine latex (AL) and negatively charged sulfate latex (SL) particles are carried out using an atomic force microscope (AFM). Forces between three different pairs, namely AL–AL, AL–SL, and SL–SL, are measured in solutions containing multivalent cationic aliphatic hexamines (N6) and in simple monovalent KCl solutions. The classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) can rationalize the observed force profiles very well, provided the PB equation is solved for the appropriate asymmetric electrolyte and charge regulation effects are included in the analysis. However, the DLVO description is typically valid only at distances beyond several nanometers. At shorter distances, a short-ranged non-DLVO attraction is present, which can be modeled with an exponential force profile. In KCl solutions, the range of this attraction is around 0.3 nm. In N6 solutions, the range of this attraction is about 1.0 nm in the SL–SL system, 0.6 nm in the AL–SL system, and 0.3 nm in the AL–AL system