Analytical study of the water surface fluctuations induced by grid-stirred turbulence

The free surface dynamics excited by grid stirred turbulence is analysed with a Lagrangian approach, with the analytical model calibrated by using experimental results. The Lagrangian model for free surface oscillations has been developed by assuming that coherent structures in the water layer close to the free interface have the shape of blobs and are mobilized by a periodic force. The blobs are assumed to behave like nonlinear oscillators with different spring stiffness in upwelling and downwelling and neglecting viscosity as first approximation. In order to calibrate the model, a set of experiments in a grid stirred tank was used where free surface elevation time series were measured and all the necessary variables were computed.Through calibration and with some working assumptions, the radius of the blobs is shown to be of the order of the integral vertical length scale of turbulence. The forced oscillations are analysed by the method of Rauscher (1938) [1] to predict the amplitude of the oscillations, possible resonances and discontinuities in the amplitude–frequency space. If the forcing term has multiple harmonics, in some cases a blow up of the oscillator is forecast. Some tests including a small damping, in order to evaluate the effects of viscosity, show that a jump is expected in the amplitude–frequency diagram and a range of unstable frequency. The presence of a small damping should also prevent the blow up for multiple harmonics in the forcing term.     

Tunable visible photoluminescence of powdered silica glass

Intense photoluminescence in the visible region was observed at room temperature in standard soda-lime-silica glass powder, mechanically milled in a high-energy attrition mill. The emission band maximum shows an interesting dependence on the exciting wavelength, suggesting the possibility to tune the PL emission. These findings indicate that the photoluminescence may be directly related to unsatisfied chemical bonds correlated with the high surface area. The Raman scattering and ultraviolet–visible optical reflectance measurements corroborate this assertion. Transmission electron microscopy measurements indicate that samples milled more than 10 h present the formation of nanocrystallites with about 10–20 nm.     

Quantum mechanical modeling of Zn-based spinel oxides: Assessing the structural,vibrational, and electronic properties

The structural, electronic, and vibrational properties of two leading representatives of the Zn-based spinel oxides class, normal ZnX₂O₄ (X = Al, Ga, In) and inverse Zn₂MO₄ (M = Si, Ge, Sn) crystals, were investigated. In particular, density functional theory (DFT) was combined with different exchange-correlation functionals: B3LYP, HSE06, PBE0, and PBESol. Our calculations showed good agreement with the available experimental data, showing a mean percentage error close to 3% for structural parameters. For the electronic structure, the obtained HSE06 band-gap values overcome previous theoretical results, exhibiting a mean percentage error smaller than 10.0%. In particular, the vibrational properties identify the significant differences between normal and inverse spinel configurations, offering compelling evidence of a structure-property relationship for the investigated materials. Therefore, the combined results confirm that the range-separated HSE06 hybrid functional performs the best in spinel oxides. Despite some points that cannot be directly compared to experimental results, we expect that future experimental work can confirm our predictions, thus opening a new avenue for understanding the structural, electronic, and vibrational properties in spinel oxides.     

Direct flow injection profiling of acyl glycerols from food products using isopropanol as solvent

This work proposes a novel method for the direct flow injection profiling of acylglycerols in edible oils and fats without preliminary extraction and consequent reconstitution in the injection solvent. The work exploits the outstanding performance of high‐resolution mass spectrometry to target unique elemental compositions even in the most complex matrices. The performance of isopropanol as the unique solvent for both the solubilization and analysis of acylglycerols was investigated in comparison with other classical methods involving preliminary extractions, sample recovery, and analysis. The calibrations of two triglyceride standards (triolein and trilinolenin) were successfully performed in presence and absence of oil matrix. As final application, the effects on the acylglycerol fraction of a heat treatment on three different fat samples (extra virgin olive oil, lard oil, and fat from dry cured ham—speck) were monitored. The proposed method is therefore suitable for a rapid evaluation of acylglycerol fractions in food lipid samples.     

Disambiguation of Isomeric Procyanidins with Cyclic B-Type and Non-cyclic A-Type Structures from Wine and Peanut Skin with HPLC-HDX-HRMS/MS

Hydrogen/deuterium exchange coupled with high-resolution mass spectrometry was successfully applied for the identification of A-type tetrameric, pentameric, and hexameric procyanidins in peanut skin. This extended a previous study on isomeric cyclic B-type unconventional tetramer, pentamer, and hexamer procyanidins found in wine and cranberries. Not only had the method successfully identified the procyanidins with a single A-linkage (e.g., tetrameric m/z 1153.2608) by means of distinguishing them from their isomeric cyclic B-type analogues, but this method also worked for procyanidins with two or more A-linkages (such as the tetrameric m/z 1151.2452). As a further consequence, B-type cyclic pentamers and hexamers in wine have been elucidated with hydrogen/deuterium exchange (HDX) for the first time.

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Screening and identification of major phytochemical compounds in seeds,sprouts and leaves of Tuscan black kale Brassica oleracea (L.) ssp acephala (DC) var. sabellica L.

We report the spectrophotometric determination of total polyphenols, flavonoids, glucosinolates and antioxidant activity in seeds, seedlings and leaves of Tuscan black kale. The highest content of phytochemicals was observed in 10 days sprouts and antioxidant activity was maximum in 2, 4 days seedlings. Identification and characterisation of phytochemicals were performed by mass spectrometry (MS), high resolution and tandem MS with electrospray ionisation mode. Low-molecular-weight metabolites were evidenced in seeds while metabolites at high m/z range were detected in cotyledons and leaves. MS spectra evidenced different phenolic compounds (flavonoid caffeoyl glucose, hydroxycinnamic acid sinapine) and glucosinolates (glucoerucin, glucobrassicin and glucoraphanin) in function of developmental stage; galactolipids ω3 and ω6 were observed in leaves. Identification of stages with the highest phytochemicals content encourages the consumption of black kale sprouts and young leaves. Our research can support food and pharmaceutical industries for production of health promoting products from black kale.     

Influence of the dissolution rate on the collapse and shedding behavior of monostearin/monopalmitin-rich coated microbubbles

A low cost food grade emulsifier (a mixture of monoglycerides, diglycerides, and sodium stearoyl lactylate) in combination with polyethylene glycol-40 stearate (PEG-40S) was used as an alternative to pure saturated phospholipids to form the thin shell of a microbubble. To investigate the stability of these microbubbles in a water system over time, their dissolution behavior was studied at various degas factors and at two percentages of PEG-40S. It was found that the favored shell collapse/shedding mechanism switched, as the dissolution rate increased (degas factor decreased), from folding with a smooth surface contour to buckling accompanied by surface folding/expulsion with a cyclic buckled-smooth surface contour. The compositional change that we made played a more minor role, mainly controlling the resistance to mass transfer of the microbubble shell and again modifying the mechanism-determinant dissolution rate. The shell resistance behavior for these microbubbles varied from that of previous lipid/PEG-40S-coated microbubbles by the presence of a maximum in shell resistance during dissolution. We hypothesize that the dominance of one collapse mechanism over another for these compositions is related to the time scales of two competing processes, fold nucleation and area compression. For these mixtures at room temperature, we estimate that the maximum area compression rate for folding as the major collapse mechanism is approximately 0.2 s (-1), a rate unattainable in a traditional Langmuir trough but achievable by the use of a dissolving microbubble.     

A New Recurrence Relation and Related Determinantal form for Binomial Type Polynomial Sequences

For polynomial sequence of binomial type we propose a new recurrence formula equivalent to a determinantal form of the sequence, from which known and unknown properties are deducted. Relationships whit \({\delta}\)–functionals, \({\delta}\)–operators and generating function are pointed out. Finally, some classical examples are studied, highlighting interesting determinantal identities.     

Revisiting the concept of the (a)synchronicity of diels‐alder reactions based on the dynamics of quasiclassical trajectories

A number of model Diels‐Alder (D‐A) cycloaddition reactions (H₂C?CH₂ + cyclopentadiene and H₂C?CHX + 1,3‐butadiene, with X = H, F, CH₃, OH, CN, NH₂, and NO) were studied by static (transition state ‐ TS and IRC) and dynamics (quasiclassical trajectories) approaches to establish the (a)synchronous character of the concerted mechanism. The use of static criteria, such as the asymmetry of the TS geometry, for classifying and quantifying the (a)synchronicity of the concerted D‐A reaction mechanism is shown to be severely limited and to provide contradictory results and conclusions when compared to the dynamics approach. The time elapsed between the events is shown to be a more reliable and unbiased criterion and all the studied D‐A reactions, except for the case of H₂C?CHNO, are classified as synchronous, despite the gradual and quite distinct degrees of (a)symmetry of the TS structures. © 2015 Wiley Periodicals, Inc.     

On-chip generation of microbubbles as a practical technology for manufacturing contrast agents for ultrasonic imaging

This paper presents a new manufacturing method to generate monodisperse microbubble contrast agents with polydispersity index (sigma) values of <2% through microfluidic flow-focusing. Micron-sized lipid shell-based perfluorocarbon (PFC) gas microbubbles for use as ultrasound contrast agents were produced using this method. The poly(dimethylsiloxane) (PDMS)-based devices feature expanding nozzle geometry with a 7 microm orifice width, and are robust enough for consistent production of microbubbles with runtimes lasting several hours. With high-speed imaging, we characterized relationships between channel geometry, liquid flow rate Q, and gas pressure P in controlling bubble sizes. By a simple optimization of the channel geometry and Q and P, bubbles with a mean diameter of <5 microm can be obtained, ideal for various ultrasonic imaging applications. This method demonstrates the potential of microfluidics as an efficient means for custom-designing ultrasound contrast agents with precise size distributions, different gas compositions and new shell materials for stabilization, and for future targeted imaging and therapeutic applications.