An overview on the appearance of the Sommerfeld effect and saturation phenomenon in non-ideal vibrating systems (NIS) in macro and MEMS scales

This paper was written in honor of Prof. Viktor Olimpanovich Kononenko from Ukraine and takes into account reports of recent progress about non-ideal vibrating systems (NIS) published in the period from 2004 to 2017. New and old studies of NIS, with limited power supply (small DC motors or electrodynamical shakers), are usually used in laboratory tests, and therefore, the investigation of mutual interactions of driven and driving sub-system is very important. In this paper, main properties of NIS have been reviewed, such as the Sommerfeld effect, i.e., jump phenomena and the increase in power supply that is required by an excitation source operating near resonance; the possibility of saturation phenomenon occurrence, i.e., the transference of energy from higher frequency and lower amplitude to lower frequency and higher amplitude mode; and the existence of regular (periodic motion) and irregular (chaotic motion) behaviors, depending on the value of control parameters (voltage of a DC motor). This paper is divided into two goals: on the one hand will be treated about NIS and on the other hand will be provided an overview of the main engineering applications, analyzing their physical phenomena involved and the adequate methodologies to deal with them.     

Theoretical-experimental study of formic acid photofragmentation in the valence region

Photoionization and photofragmentation studies of formic acid (HCOOH) are performed for the valence shell electron ionization process. The total and partial ion yield of gaseous HCOOH were collected as a function of photon energy in the ultraviolet region, between 11.12 and 19.57 eV. Measurements of the total and partial ion yield of gaseous formic acid molecule are performed with a time-of-flight mass spectrometer at the Synchrotron Light Brazilian Laboratory. Density functional theory and time dependent density functional theory are employed to calculate the ground and excited electronic state energies of neutral and ionic formic acid as well as their fragments and normal vibration modes. The ionization potential energies, the stability of electronic excited states of HCOOH(+), and the energies of opening fragmentation channels are estimated from theoretical-experimental analysis. Additionally, the main formic acid photofragmentation pathways by exposition of photons within that energy range are determined experimentally. These produced ions primarily have the following mass/charge ratios: 46 (HCOOH(+)), 45 (COOH(+)), 29 (HCO(+)), and 18 (H(2)O(+)).     

Antibacterial activity of glutathione-coated silver nanoparticles against Gram positive and Gram negative bacteria

In the present paper, we study the mechanism of antibacterial activity of glutathione (GSH) coated silver nanoparticles (Ag NPs) on model Gram negative and Gram positive bacterial strains. Interference in bacterial cell replication is observed for both cellular strains when exposed to GSH stabilized colloidal silver in solution, and microbicidal activity was studied when GSH coated Ag NPs are (i) dispersed in colloidal suspensions or (ii) grafted on thiol-functionalized glass surfaces. The obtained results confirm that the effect of dispersed GSH capped Ag NPs (GSH Ag NPs) on Escherichia coli is more intense because it can be associated with the penetration of the colloid into the cytoplasm, with the subsequent local interaction of silver with cell components causing damages to the cells. Conversely, for Staphylococcus aureus, since the thick peptidoglycan layer of the cell wall prevents the penetration of the NPs inside the cytoplasm, the antimicrobial effect is limited and seems related to the interaction with the bacterial surfaces. Experiments on GSH Ag NPs grafted on glass allowed us to elucidate more precisely the antibacterial mechanism, showing that the action is reduced because of GSH coating and the limitation of the translational freedom of NPs.     

Optical method for predicting the composition of self-assembled monolayers of mixed thiols on surfaces coated with silver nanoparticles

With a simple optical method, based on UV-vis absorption spectra on glass slides, it is possible to predict the composition of self-assembled monolayers of mixed thiols, grafted on monolayers of silver nanoparticles. Glass slides are modified with the layer-by-layer technique, first forming a monolayer of mercaptopropyltrimethoxysilane, then grafting a monolayer of silver nanoparticles on it. These surfaces are further coated by single or mixed thiol monolayers, by dipping the slides in toluene solutions of the chosen thiols. Exchange constants are calculated for the competitive deposition between the colorless 1-dodecanethiol or PEG5000 thiol and BDP-SH, with the latter being a thiol-bearing molecule containing the strongly absorbing BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety, synthesized on purpose. The constants are calculated by determining the fraction of BDP-SH deposited on the surface from a solution with a given molar fraction, directly measuring the absorption spectra of BDP-SH on the slides. Then, the exchange constant for the competitive deposition between 1-dodecanethiol and PEG5000 thiol is calculated by combining their exchange constants with BDP-SH. This allows to predict the fraction of the two colorless thiols coating the silver nanoparticles slides obtained from a toluene solution with a given molar fraction, for example, of PEG5000 thiol. The correctness of the calculated surface fraction is verified by studying the coating competition between 1-dodecanethiol and a PEG5000 thiol remotely modified with a strongly absorbing fluorescein fragment.     

Spartium junceum aromatic water: chemical composition and antitumor activity

The purpose of this study was to analyse the chemical composition of Spartium junceum L. (also known as Spanish Broom) aromatic water and to evaluate its cytotoxic activity against a series of human cancer cell lines (melanoma: RPMI 7932; leukemia: K562; breast cancer cell: MCF7-Bart and MCF7-ICLC, colon adenocarcinoma: SW480). The results show that the aromatic water was cytotoxic toward the tumor cell lines analyzed (RPMI 7932, K562, MCF7-Bart, MCF7-ICLC, SW480), while it did not appreciably alter the viability of normal keratinocytes (NCTC 2544) suggesting its potential use as an antitumor agent for cancer treatment and/or prevention.     

The emergence of deontological codes in public administration

We study a model of the evolutionary selection of social standards of behavior in a large public organization, in terms of the propensity to bribery of the organization's rent-seeking officers. We examine several scenarios, allowing for the existence of various types of anti-corruption sanctioning mechanisms, for the role of pro-social, interiorized value systems, for the impact of informational costs on the viability of "informationally sophisticated" players. The conditions under which corruption is eventually eliminated or at least kept under control in the various scenarios are derived and discussed.     

General Wentzell Boundary Conditions and Analytic Semigroups on W 1, p (0, 1)

We are concerned with the analyticity of the (C ₀) semigroups generated by the realizations of the Laplacian Δu:=u″ in the spaces C[0, 1] and W ^{1, p} (0, 1) with the general Wentzell boundary conditions Δu(j)+β ^ju″(j)+γ _ju(j)=0 for j=0,1. Here 1<p<∞ and β _j , γ _j are arbitrary complex numbers for j=0,1.     

Identification and characterization of new Fusarium masked mycotoxins, T2 and HT2 glycosyl derivatives, in naturally contaminated wheat and oats by liquid chromatography-high-resolution mass spectrometry

The presence of glucoside derivatives of T-2 and HT-2 toxins (type A trichothecene mycotoxins) in naturally contaminated wheat and oats is reported for the first time. The use of advanced high-resolution mass spectrometry based on Orbitrap technology allowed to obtain molecular structure details by measuring exact masses of main characteristic fragments, with mass accuracy lower than 2.8?ppm (absolute value). A monoglucoside derivative of T-2 toxin and two monoglucoside derivatives of HT-2 toxin were identified and characterized. The analysis of their fragmentation patterns provided evidence for glucosylation at C-3 position for T-2 toxin and at C-3 or C-4 position for HT-2 toxin. A screening for the presence of these new masked forms of mycotoxins was carried out on a set of naturally contaminated wheat and oats samples. On the basis of peak area ratio between glucoside derivatives and free T-2 and HT-2 toxins, the presence of glucoside derivatives was more likely in wheat than in oats samples. The present work confirms the widespread occurrence of trichothecene glucosides in cereal grains naturally contaminated with the relevant unconjugated toxins, thus suggesting the importance of developing suitable analytical methods for their detection. Besides toxicity studies, tracking down these new masked forms of trichothecenes along the food/feed chain would enable to collect information on their relevance in human/animal exposure to mycotoxin risk.