Sharif Digital Repository

Optical tweezers are proven and indispensable micro-manipulation tools. It is very common to use an immersion-assisted high NA objective for optical trapping of micrometer-sized beads. However, such objectives suffer from low working depth range. Here we show, both by theory and experiment, that a dry objective can be utilized for optimal trapping of even sub-micrometer objects. For the first time, to the best of our knowledge, we were able to stably trap polystyrene beads with radii of 270 and 175 nm in 3D using an objective with numerical aperture of 0.9. © 2022 Optica Publishing Group  

Metallic nanoparticles (NPs) have not been effective in improving the overall performance of the cells with micrometer-thick absorbing layers mainly due to the parasitic optical dissipation in the metal. Here, using both experiment and theory, we demonstrate that aggregates of metallic NPs enhance the light absorption of dye-sensitized solar cells of a few micrometer-thick light absorbing layers. The composite electrode containing the optimal concentration of 5 wt% Au@SiO2 aggregates shows the enhancement of 80% and 52% in external quantum efficiency and photocurrent density, respectively. The superior performance of the aggregates relative to NP is attributed to their larger scattering... 

The aim of this research was to synthesize barium sulfate nanoparticles using a spinning disk reactor. Barium sulfate was produced by continuously pumping two aqueous solutions of BaCl2 and Na2SO 4, respectively, into the chamber of spinning disk reactor, where a liquid-liquid reaction took place to form BaSO4. The influences of various operating and design parameters such as the initial supersaturation, disk rotation speed, free ion ratio, and the disk diameter on the size of barium sulfate nanoparticles were carefully investigated. By varying the supersaturation and disk rotation speed, a broad range of particle size ranging from micrometer sizes down to nanoparticles smaller than 100 nm... 

In this work, the magnetic and transport properties of micro and nanometer-sized samples of La0.9Ba0.1MnO3 manganite have been studied. The temperature variation of ac susceptibility of the nanometer-sized sample shows one transition at high temperature (265 K). On the contrary, the ac susceptibility of the micrometer-sized sample shows two transitions with a high-temperature transition occurring at 240 K and low-temperature transition around 100 K. The high-temperature transition corresponds to the paramagnetic-ferromagnetic (PM–FM) transition (Tc) and is independent of frequency, while the low-temperature transition is frequency-dependent and shifts toward high temperatures by increasing... 

Natural nanochannels and those used for applied purposes are often several nanometers in diameter and have lengths up to micrometer scales. Since normally no pressure gradient, mechanical force or electrical field is exerted on fluids in these situations, the fluid flow within them is not single-file and can be bidirectional. For this reason, studying the behavior of bidirectional flows in the channels is of paramount importance. In this study, a comprehensive investigation on the straight and non-straight bidirectional water transfer through carbon nanotubes is conducted via extensive molecular dynamics simulations. The results indicate that by changing the length, the diameter and the... 

In this work, we used λ-DNA to produce metallic DNA samples and we investigated the stabilization time of their impedances. This is in order to show that the DNA molecules can possibly be utilized as a frame for assembling the nanocircuits and as an electronic element as well, in nanoelectric devices. It has been shown that metallic DNA has lower stabilization time than natural DNA. As expected, it is shown that making the bundled DNA oriented, impacts their impedance stabilization. In order to find the characteristic impedance of the DNA molecules under direct current, we designed and made patterned electrodes to make electrical connections between the DNAs and the used current source. The... 

The properties of W-15 wt.%Cu composites were investigated by preparing two distinct composites of micrometer and nanoscale structures. Micrometer composite was produced by mixing elemental W and Cu powders and nanometer one was synthesized through a mechanochemical reaction between WO3 and CuO powders. Subsequent compaction and sintering process was performed to ensure maximum possible densification at 1000-1200 °C temperatures. Finally, the behavior of produced samples including relative density, hardness, compressive strength, electrical conductivity, coefficient of thermal expansion (CTE) and room temperature corrosion resistance were examined. Among the composites, nano-structured... 

Producing mature and functional cardiomyocytes (CMs) by in vitro differentiation of induced pluripotent stem cells (iPSCs) using only biochemical cues is challenging. To mimic the biophysical and biomechanical complexity of the native in vivo environment during the differentiation and maturation process, polydimethylsiloxane substrates with 3D topography at the micrometer and sub-micrometer levels are developed and used as cell-culture substrates. The results show that while cylindrical patterns on the substrates resembling mature CMs enhance the maturation of iPSC-derived CMs, sub-micrometer-level topographical features derived by imprinting primary human CMs further accelerate both the... 

Two-step sintering (TSS) was applied to suppress the accelerated grain growth of sub-micron (∼150 nm) alumina powder. The application of an optimum TSS regime led to a remarkable decrease of grain size down to ∼500 nm; while the grain size of the full-dense structures produced by conventional sintering ranged between 1 and 2 μm. To find how important the temperatures at sintering steps might be, several TSS regimes were conducted. The results showed that the temperatures at both sintering steps play vital roles in densification and grain growth of the alumina compacts. Based on the results, the optimum regime consisted of heating the green bodies up to 1250 °C (first step) and then holding...