Sharif Digital Repository

A method is developed for in situ generation of 1,3-dioxan-5-one derivatives 2. These compounds are simple precursors for accessing carbohydrate structures and previously had to be produced via stepwise procedures using excessive amounts of reagents. In the present work, three different derivatives of 2 were synthesized via the reaction of trialkoxyalkanes with dihydroxyacetone dimer 1 in the presence of acetic acid as the catalyst. In the same pot, derivatives of 2 were reacted with aromatic aldehydes and 30 mol% of pyrrolidine to obtain high yields of the respective bischalcones 3 within short time periods. © 2019 M. Javad Poursharifi et al., published by De Gruyter 2019  

Tapered circular cylinders are employed in a variety of ocean engineering applications. While being geometrically simple, this configuration creates a complex flow pattern in the near wake of the structure. Most previous experimental studies on tapered circular cylinders were dealing with stationary cylinders to explore the wake flow field and vortex shedding patterns past the cylinder. Few studies paid attentions to the vortex induced vibration of the tapered cylinders. This paper reports some results from in-water towing-tank experiments on the vortex-excited vibrations of tapered circular cylinders in a uniform flow. Cylinders with different mean diameters (28 and 78 mm), mass ratios (6.1... 

In this study the authors present an in-depth study, analysis and discussion on maximum likelihood (ML)-based receiver for a typical spectrally encoded spread-time CDMA in the presence of multiple narrowband interference (NBI) signals in an additive white Gaussian noise channel. Furthermore, the authors demonstrate that by combining useful properties of ML-based receiver and three-level codes, that is, codes with values of -1, 0, +1, the authors can introduce a new strategy in which superior performance with respect to previous receiver structure based on two-level codes, that is, codes with values of -1, +1, can be attained. With the help of an example, the authors drive, first, the... 

A high-order accurate implicit operator scheme is used to solve steady incompressible slip flow and heat transfer in 2D microchannels. The present methodology considers the solution of the Navier-Stokes equations using the artificial compressibility method with employing the Maxwell and Smoluchowski boundary conditions to model the slip flow and temperature jump on the walls in microchannels. Since the slip and temperature jump boundary conditions contain the derivatives of the velocity and temperature profiles, using the compact method the boundary conditions can be easily and accurately implemented. The computations are performed for a 2D microchannel and a 2D backward facing step in the... 

This study aimed to identify the influence of workplace cyber ostracism on employee online work engagement and employee mental well-being with the mediating roles of remote work challenges such as loneliness, procrastination, work-home interference, and ineffective communication. As amidst lockdown due to COVID-19, the data was collected from 303 respondents through an online questionnaire that was distributed in virtual groups among friends, relatives, and other fellows who were working in the private sector organizations of Pakistan. The hypotheses were tested using the partial least square structural equation modeling PLS-SEM technique. The findings of this study showed that workplace... 

Betaine-based natural deep eutectic solvents (NADESs), a new class of green solvents, were immobilized into a porous polyvinylidene fluoride (PVDF) support and evaluated for the separation of CO2 from CO2/N2 and CO2/CH4 mixtures. Two types of NADESs were synthesized by mixing betaine (hydrogen bond acceptor-HBA) with malic acid and tartaric acid (hydrogen bond donors-HBD) respectively. FTIR and Raman spectroscopy were studied to confirm the synthesis and purity of the NADESs. The thermal strength of the NADESs was investigated using thermogravimetric analysis. The gas permeation results of the fabricated NADES-based-supported liquid membranes (NADES-SLMs) showed that the permeability of CO2... 

This study focuses on a forward looking approach in which deep eutectic solvents (DESs), a new class of designer solvents, were impregnated into micro porous polyvinylidene fluoride (PVDF) membrane for the separation of CO2 from CH4. Three types of DESs were prepared by mixing and heating of hydrogen bond acceptor (choline chloride) with either malic acid, tartaric acid or oxalic acid as hydrogen bond donor. The Fourier transform infrared spectroscopy confirmed the hydrogen bond interactions in the resulting DES. Thermal gravimetric analysis (TGA) was used to evaluate the thermal stability of the prepared membranes. The DES based supported liquid membranes were investigated systematically to... 

This study demonstrates a new strategy in which deep eutectic solvents (DES), a new class of sustainable organic solvents, were impregnated into micro porous polymer support for separation of CO2 from CH4. Three different types of DESs were prepared by mixing and subsequent heating of betaine as hydrogen bond acceptor (HBA) in combination with either glycerol (G), ethylene glycol (EG) or urea (U) as hydrogen bond donors (HBD) in 1:3 stoichiometric mole ratio. The Fourier transform infrared (FTIR) spectroscopy was performed to confirm the formation of DESs. The gas permeation results showed that permeability of CO2 increased from 31.23 to 35.67 Barrer on substitution of HBD from glycerol to... 

This article focuses on the study of potassium carbonate (PC) based deep eutectic solvents based supported liquid membranes (DES-SLMs) for CO2 separation. Two types of DESs were synthesized by mixing and subsequently heating PC with glycerol or ethylene glycol separately. The mechanism of interaction was inferred from the spectral analysis (FTIR) whereas thermal study (TGA) was performed to analyze the stability of the membrane. Experiments were carried out to analyze the permeability and separation factor of the membranes. The PC-Glycerol based SLM reported permeability of 34 Barrer and ideal selectivity of 59 while PC-Ethylene Glycol based SLM showed permeability of 20 Barrer and... 

In this study, we discuss the postural stability of a nonprehensile manipulation problem, which deals with multibody objects. As a metric for postural stability, we define PRI. Then, the system is posturally stable, if PRI is inside the convex hull of the object-manipulator contact surface. We then discuss that dynamic biped locomotion is a special case of dynamic nonprehensile manipulation in all aspects; we prove that ZMP (zero-moment point) and FRI (zoot rotation indicator) are special cases of PRI (palm rotation indicator). Simulations and experiments corresponding to simple examples support the results