Turbulent Convective Heat Transfer and Pressure Drop of Graphene–Water Nanofluid Flowing Inside a Horizontal Circular Tube

Turbulent convective heat transfer of graphene–water nanofluids with various concentrations inside a uniformly heated circular tube is studied experimentally. For this purpose, experiments are conducted to measure thermal conductivity, viscosity, pressure drop, and heat transfer coefficient. Results show enhancement of thermal conductivity and moderate increment of viscosity with addition of low amounts of nanoparticles. Moreover, heat transfer coefficient shows relatively high augmentation, and pressure drop remains unchanged. The maximum enhancements are 10.30%, 4.95%, and 6.04% for thermal conductivity, viscosity, and heat transfer coefficient, respectively. UV–Vis spectroscopy results show that the nanofluids are highly stable.     

AB-Contexts and Stability for Gorenstein Flat Modules with Respect to Semidualizing Modules

We investigate the properties of categories of G _C -flat R-modules where C is a semidualizing module over a commutative noetherian ring R. We prove that the category of all G _C -flat R-modules is part of a weak AB-context, in the terminology of Hashimoto. In particular, this allows us to deduce the existence of certain Auslander-Buchweitz approximations for R-modules of finite G _C -flat dimension. We also prove that two procedures for building R-modules from complete resolutions by certain subcategories of G _C -flat R-modules yield only the modules in the original subcategories.     

Gravitational collapse: expanding and collapsing regions

We investigate the expanding and collapsing regions by taking two well-known spherically symmetric spacetimes. For this purpose, the general formalism is developed by using Israel junction conditions for arbitrary spacetimes. This has been used to obtain the surface energy density and the tangential pressure. The minimal pressure provides the gateway to explore the expanding and collapsing regions. We take Minkowski and Kantowski-Sachs spacetimes and use the general formulation to investigate the expanding and collapsing regions of the shell.     

Modeling of the power oscillation observed in single mode intracavity absorption of CO2 laser lines

Single mode intracavity absorption is investigated from an analytical point of view in order to explain the periodical modulation of the power observed in intracavity absorption of CO₂ laser lines by CFC gases. Intracavity absorption is incorporated into the laser rate equations in form of an additional broadband loss. Detuning due to changes in the refractive index with increase in absorber pressure is accounted for by considering the impact of the frequency shift of the oscillating mode on the effective pump rate and the population densities of the laser upper and lower levels. The steady state solution of the rate equations leads to an analytical formula, which fits the measured intracavity absorption curves with only two fit parameters being adjusted to the actual values of the absorption cross section and the mean linear polarizability of the absorber molecule. The formula is applied to analyze the intracavity absorption of the CO₂ 10R lines by CFC-11. The obtained results are in reasonable agreement with the values available in the literature.     

Investigating the interactions of the first 17 amino acid residues of Huntingtin with lipid vesicles using mass spectrometry and molecular dynamics

The first 17 amino acid residues of Huntingtin protein (Nt17 of htt) are thought to play an important role in the protein's function; Nt17 is one of two membrane binding domains in htt. In this study the binding ability of Nt17 peptide with vesicles comprised of two subclasses of phospholipids is studied using electrospray ionization ‐ mass spectrometry (ESI‐MS) and molecular dynamics (MD) simulations. Overall, the peptide is shown to have a greater propensity to interact with vesicles of phosphatidylcholine (PC) rather than phosphatidylethanolamine (PE) lipids. Mass spectra show an increase in lipid‐bound peptide adducts where the ordering of the number of such specie is 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) > 1‐palmitoyl‐2‐oleoyl‐glycero‐3‐phosphocholine (POPC) > 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3 phosphoethanolamine (POPE). MD simulations suggest that the compactness of the bilayer plays a role in governing peptide interactions. The peptide shows greater disruption of the DOPC bilayer order at the surface and interacts with the hydrophobic tails of lipid molecules via hydrophobic residues. Conversely, the POPE vesicle remains ordered and lipids display transient interactions with the peptide through the formation of hydrogen bonds with hydrophilic residues. The POPC system displays intermediate behavior with regard to the degree of peptide‐membrane interaction. Finally, the simulations suggest a helix stabilizing effect resulting from the interactions between hydrophobic residues and the lipid tails of the DOPC bilayer.     

A Short and Elegant Synthesis of (±)‐Streptopyrrolidine

A brief and efficient approach for the synthesis of (±)‐5‐benzyl‐4‐hydroxy‐2‐pyrrolidine ( 1 ) from phenylalanine racemate is described. The key step is the stereocontrolled reduction of the keto functionality of benzylated pyrrolidinone intermediate ( 6 ) via sodium borohydride in carboxylic acid medium furnishing both (R,R)‐ and (S,S)‐configured diastereomers. The natural (R,R) enantiomer ( 2 ), however, crystallized out from its racemic mixture. Structure of 2 was confirmed by NMR, IR, elemental analyzer, and single crystal X‐ray crystallographic techniques.     

A new signal processing method to observe weak P and O NMR peaks

In NMR spectroscopy, situations may arise where sample concentrations are below the threshold for FT NMR detection, or sample lability constrains allowable acquisition times. In ³¹P NMR, for example, observation of ¹³C satellites may not be practical under given conditions. For ¹⁷O NMR, which is useful to characterize ¹⁷O-labeled phosphate derivatives, similar considerations may apply, and added factors are the cost of isotopically enriched samples and the requirement to obtain spectra at relatively high temperatures if narrow spectral peak line widths are desired. We report here application of a new signal processing method [S.D. Kunikeev, H.S. Taylor, J. Phys. Chem. A 108, 2004 743] to observation of weak ³¹P and ¹⁷O NMR peaks.     

Simultaneous determination of potassium clavulanate and cefixime in synthetic mixtures by high-performance liquid chromatography

A simple, precise, and sensitive high-performance liquid chromatographic method was developed and validated for the simultaneous determination of potassium clavulanate and cefixime in synthetic mixture form. The analytes were separated on a C18 column by using 0.03 M disodium hydrogen phosphate buffer (pH 6.5)-methanol (84 + 16, v/v) as the mobile phase with detection at 220 nm. The method exhibited high sensitivity and good linearity in the concentration ranges of 12.5-62.5 and 20-100 microg/mL for potassium clavulanate and cefixime, respectively. The total run time for the 2 components was <8 min, and the average recovery was >101.5% with a relative standard deviation of <1.0%. The proposed method was validated according to guidelines of the International Conference on Harmonization by evaluation of linearity, recovery, selectivity, robustness, limits of detection and quantitation, and within- and between-day precision. The results obtained for the synthetic mixture show that the method is highly precise and accurate for the simultaneous determination of potassium clavulanate and cefixime.     

Chaos and complexity in mine grade distribution series detected by nonlinear approaches

In this article, the underlying dynamics of treating grade distribution is interpreted as a chaotic system instead of a stochastic system for a better understanding. Here, we study the behavior of grade distribution spatial series acquired at the Chadormalu mine in Bafgh city of Iran to distinguish the possible existence of low‐dimensional deterministic chaos. This work applies a variety of nonlinear techniques for detecting the chaotic nature of the grade distribution spatial series and adopts a nonlinear prediction method for predicting the future of the grade distributions. First, the delay time dimension is computed using auto mutual information function to reconstruct the strange attractors. Then, the dimensionality of the trajectories is obtained using Cao's method and, correspondingly, the correlation dimension method is adopted to quantify the embedding dimension. The low embedding dimensions achieved from these methods show the existence of low dimensional chaos in the mining data. Next, the high sensitivity to initial conditions is evaluated using the maximal Lyapunov exponent criterion. Positive Lyapunov exponents obtained demonstrate the exponential divergence of the trajectories and hence the unpredictability of the data. Afterward, the nonlinear surrogate data test is done to further verify the nonlinear structure of the grade distribution series. This analysis provides considerable evidence for the being of low‐dimensional chaotic dynamics underlying the mining spatial series. Lastly, a nonlinear prediction scheme is carried out to predict the grade distribution series. Some computer simulations are presented to illustrate the efficiency of the applied nonlinear tools. © 2016 Wiley Periodicals, Inc. Complexity 21: 355–369, 2016     

Lanthanide complexes with pyridine-2,6-dicarboxylic acid: synthesis,crystal structure,thermal and magnetic properties of [LnPDA)2(PDAH2)] · (DMAH2)2(DMAH0.5)2

Mild solvothermal synthesis, structures, thermal and magnetic properties of coordination complexes [Ln(PDA)₂(PDAH₂)] · (DMAH₂)₂(DMAH_0.5)₂(I–IV) (PDA = pyrdine-2,6-dicarboxylate anion, DMAH = dimethylamine, Ln = Ce, Nd, Sm, and Ho) are described. The DMAH molecules in I–IV, generated in situ from hydrolysis of N,N-dimethylformamide, are responsible to assemble three dimensional coordination polymers through N–H···O and C–H···O hydrogen bonds. Distorted tricapped trigonal prismatic LnO₆N₃ geometry having 14 triangular faces is attributed to mean deviation of dihedral angles while nitrogen shows fairly triangular faces having dihedral angle close to 60°C (CIF files CCDC nos. 872065 (I), 872070 (II), 872069 (III), and 872066 (IV)). Curie–Weiss law and the overall magnetic behavior are typical for the presence of antiferromagnetic exchange coupling interactions between lanthanide. Thermal decomposition analyses reveal removal of ammonia and resultant complexes showthermal stability. Complexes have been further characterized by using elemental analyzer and FT-IR spectroscopy.