The unbearable heaviness of colloids: facts, surprises, and puzzles in sedimentation

Sedimentation has played a key role in the development of colloid science. In fact, it is because of the celebrated experiments by Perrin, yielding a concrete demonstration of molecular reality and giving strong support to Einstein's theory of Brownian motion, that colloids enter the realm of basic physics. Subsequent investigations have shown that a lot more can be learnt both from sedimentation equilibrium and from particle settling dynamics. These advances, together with new experimental approaches, will be reviewed in this paper. Yet, we shall also show that inquiring about gravity settling is far from being a closed matter: for instance, the concept of buoyancy for a settling colloidal mixture is far from being obvious. Moreover, sedimentation holds novel surprises, such as colloidal inflations and settling disasters, showing that a simple external field like gravity may induce mind-boggling, and theoretically challenging effects.     

Single-fiber diffuse optical time-of-flight spectroscopy

We demonstrate interstitial diffuse optical time-of-fight spectroscopy based on a single fiber for both light delivery and detection. Detector saturation due to the massive short-time reflection is avoided by ultrafast gating of a single photon avalanche diode. We show that the effects of scattering and absorption are separable and that absorption can be assessed independently of scattering. Measurements on calibrated liquid phantoms and subsequent Monte Carlo-based evaluation illustrate that absorption coefficients can be accurately assessed over a wide range of medically relevant optical properties. Our findings pave the way to simplified and less invasive interstitial in vivo spectroscopy.     

Characterization of HDPE /Polyamide 6/ Nanocomposites Using Scanning-and Transmission Electron Microscopy

Summary: Preparation and morphology of high density polyethylene (HDPE)/ polyamide 6 (PA 6)/modified clay nanocomposites were studied. The ability of PA 6 in dispersing clays was used to prepare modified delaminated clays, which were then mixed with HDPE. Mixing was performed using melt processing in a torque rheometer equipped with roller rotors. After etching the materials with boiling toluene and formic acid at room temperature, the morphology was examined by SEM analyses, showing that the PA 6 formed the continuous phase and HDPE the dispersed phase. X-ray diffraction patterns show that the (001) peak of the clay is dramatically decreased and shifted to lower angles, indicating that intercalated/exfoliated nanocomposites are obtained. TEM analyses confirmed the typical structure of exfoliated nanocomposites. A scheme for the mechanism of exfoliation and/or intercalation of these HDPE /PA 6/ /organoclay nanocomposites is proposed.     

Characterization and Valorization of the Agricultural Waste Obtained from Lavandula Steam Distillation for Its Reuse in the Food and Pharmaceutical Fields

The main focus of the current research was the characterization of the by-products from the steam distillation of Lavandula angustifolia Mill. (LA) and Lavandula x intermedia Emeric ex Loisel (LI) aerial parts, as they are important sources of bioactive compounds suitable for several applications in the food, cosmetic, and pharmaceutical industries. The oil-exhausted biomasses were extracted and the total polyphenol and flavonoid contents were, respectively, 19.22 ± 4.16 and 1.56 ± 0.21 mg/g for LA extract and 17.06 ± 3.31 and 1.41 ± 0.10 mg/g for LI extract. The qualitative analysis by liquid chromatography-electrospray tandem mass spectrometry (HPLC-ESI-MS) revealed that both the extracts were rich in phenolic acids and glycosylated flavonoids. The extracts exhibited radical scavenging, chelating, reducing activities, and inhibitory capacities on acetylcholinesterase and tyrosinase. The IC50 values against acetylcholinesterase and tyrosinase were, respectively, 5.35 ± 0.47 and 5.26 ± 0.02 mg/mL for LA, and 6.67 ± 0.12 and 6.56 ± 0.16 mg/mL for LI extracts. In conclusion, the oil-exhausted biomasses demonstrated to represent important sources of bioactive compounds, suitable for several applications in the food, cosmetic, and pharmaceutical industries.     

Exploring the Porosity in Ceramics at the nm Scale: From Understanding Historical Ceramics to Innovative Materials Design

Ceramics are complex objects and a rich source of information: they constitute a large part of the staple memory of past and present human activities. A deep understanding of traditional ceramics is an essential key to designing new ceramic materials. The demanding synthesis of ceramics with fine-tuned properties, such as enhanced mechanical, electrical, optical or magnetic characteristics, must be associated with cutting-edge analysis procedures in order to improve the engineering process. In this context, we describe a neutron-based non-destructive approach to investigating the nanoporosity of an historical pottery matrix as an effective investigation technique for exploring both traditional and advanced ceramic materials.     

Spin transresistivity—a probe of the opposite-spin correlations in an electron system

We investigate the spin drag effect in spin polarized transport beyond the random phase approximation by considering an effective scattering potential that incorporates self-consistently the effects of the short range Coulomb interaction through momentum dependent local field corrections. We find that the first order many-body correction to the spin transresistivity is determined by the local field factor for opposite-spin correlations.     

Influence of the Mn(II) and CH4 on the evolution of light induced radicals in chloroplasts

The photochemical activity of the leaves and chloroplasts of several species of plants developed in gaseous hydrocarbon environments (C_nH_2n+2) was investigated by the EPR method. The influence of different concentrations of paramagnetic ions [Mn(II), Cu(II) and VO(II), respectively] on the plants grown in dietary media containing these ions was also followed by EPR spectroscopy. The contents of paramagnetic ions, lower than 0.1%, in the nutritive solutions, are the most suitable in the biosynthesis of chlorophyll-like pigments containing paramagnetic ions in their porphyrine ring. The changes in the form, structure and photosensibility of the EPR signals corresponding to the free radicals, as well as the properties of the pheophytins containing paramagnetic ions, such as: Mn(II), Cu(II) and VO(II), were related to the photochemical synthesis in gaseous hydrocarbon environments.     

Pair potentials and structure factors of liquid alkali metals

Summary Measured structure factors of liquid alkali metals are examined in the framework of screened pair potential theory. Information on the main attractive well in the effective pair potential is obtained from the structural data by an approximate method stemming from an optimized random-phase treatment of the indirect ion-ion attraction. The results are compared with a variety of theoretical pair potentials in the cases of sodium and potassium, after a test of the method against computer simulation data on a model for rubidium. Results for the other alkali metals are also given and discussed. The small-angle scattering region is then examined in considerable detail, with special attention to the possibility of a linear term in a series expansion of the structure factor at very small momentum transfer. Although sensitivity to both the bare electron-ion coupling and the local field factor in the screening function is demonstrated and analysed, no linear term of the magnitude reported in recent X-ray diffraction experiments is found in the present theoretical framework.

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Riassunto Il lavoro discute i fattori di struttura misurati nei metalli alcalini liquidi nell'àmbito della teoria di potentiziali di coppia schermati. L'inversione dei dati strutturali permette di ottenere informazioni sulla buca attrattiva nel potenziale, che è confrontata con potenziali teorici dopo un controllo del metodo d'inversione su dati di simulazione. Si analizza quindi il comportamento del fattore di struttura a piccoli numeri d'onda, in relazione all'osservazione di un termine lineare nella figura di diffrazione di raggi X.

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Резюме Измеренные структурные факторы жидких щелочных металлов исследуются в рамках теории экранированных парных потенциалов. Из структурных данных получается информация об основной яме притяжения в эффективном парном потенциале. Полученные результаты сравниваются с целым рядом теоретических парных потенциалов в случаях натрия и калия. Предложенный метод проверяется посредством компьютерного моделирования для рубидия. Также приводятся и обсуждаются результаты для других щело ных металлов. Подробно исследуется область малоуглового рассеяния, уделяя особое внимание возможности существования линейного члена в степенном разложении структурного фактора при очень малых передаваемых импульсах. Анализируется чувствительность предложенного подхода в связи с обнаружением линейного члена в экспериментах по дифракции рентгеновских лучей.

     

Decay of correlations and related sum rules in a layered classical plasma

Summary The asymptotic behaviours of particle correlation functions and the related sum rules are discussed for a layered classical plasma withe ²/r interactions in the fluid state, in dependence on the number of layers. These properties derive from consistency conditions imposed by screening on the hierarchical equations, as already treated by A. Alastuey and P. A. Martin (J. Stat. Phys.,39, 405 (1985)) for various Coulomb fluids. The main results concern i) the type of clustering of correlations needed for the validity of multipolar sum rules at various orders, ii) the proof that the pair correlation function in a finite multilayer may carry an electric dipole moment and the calculation of its partioning among the layers, and iii) the dimensionality crossover in an infinitely extended or periodically repeated multiplayer with varying interlayer spacing and wave vector.     

Molecular associations of [2.2]paracyclophanearylhydrazones with organic acceptors,VIII

Summary Molecular complexes of mono and disubstituted [2.2]paracyclophanehydrazones with organic acceptors have been studied by means of thermodynamic and spectroscopic properties. Furthermore, the enhancement of the donor strength, induced by the hydrazono group, is viewed in the light of substituent as well as transannular effects.

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Molekulare Assoziation von [2.2]Paracyclophanarylhydrazonen mit organischen Akzeptoren, 8. Mitt.

Zusammenfassung Es wurden Molekülkomplexe von mono- und disubstituierten [2.2]Paracyclophanarylhydrazonen mit organischen Akzeptoren mittels thermodynamischer und spektroskopischer Methoden untersucht. Zusätzlich wird der Anstieg in der Donorstärke, der von der Hydrazonogruppe induziert wird, im Hinblick auf Substituenten- und auch transannulare Effekte diskutiert.