In situ examination of the protonation behavior of fulvic acids using differential absorbance spectroscopy

The effects of pH changes on the absorbance spectra of fulvic acids, which constitute a major part of natural organic matter (NOM) were examined based primarily on the example of standard Suwannee River fulvic acid (SRFA). Differential absorbance spectra of SRFA generated at varying pH values were determined to be rich in features that are absent in the conventional spectra. Analysis of the differential absorbance revealed the existence of two predominant types of pH-active chromophores which produced features that emerged in the pH ranges associated with carboxylic and phenolic functional groups of fulvic acids. Comparison of the differential absorbance spectra of SRFA and those of the fraction of hydrophobic acids of South Platte River fulvic acid show the existence of differences indicative of fulvic acids's site-specificity. The evolution of the pH-differential spectra of fulvic acids was in accord with predictions made based on the NICA-Donnan theory. These results show that pH-differential absorbance spectroscopy can be used to quantify in situ the protonation and site-specificity of fulvic acids.     

Regiospecifity-driven self-assembly of methyl substituted quaterthiophenes at surface

A study on the self-assembly of regiochemically differentiated methyl substituted quaterthiophenes is presented. Hierarchical self-assembly of 5,4′,3″,5?-tetramethyl-2,2′:5′,2″:5″,2?-quaterthiophene molecule, 7 leads to unprecedented fluorescent superstructures on glass and mica surfaces made by reiteration of a peculiar V-shaped recurring motif that extended at least for three generations.     

Fast Regime Fluidized Bed Machining (FR-FBM) of Thermally Sprayed Coatings

Finishing of thermally sprayed metallic, ceramic, and cermet coatings is required to meet tolerances and requirements on surface roughness in most industrial applications. Conventional machining is a costly and time-consuming process, and is difficult to automate. Therefore, this study investigates and develops a new technique highly amenable for automation: fast regime—fluidized bed machining (FR-FBM). Atmospheric plasma sprayed TiO₂, Cr₂O₃, and HVOF-sprayed WC-17%Co and Tribaloy-800 coatings, deposited on AISI 1040 steel substrates, were subjected to FR-FBM treatment. The effects of the leading operational parameters, namely, abrasive size, jet pressure, and processing time, were evaluated on all coatings by using a two/three-levels full factorial design of experiments. The FR-FBM treated surfaces were observed by FE-SEM and their surface finishing was evaluated by contact profilometry. Significant improvements in surface finishing of all the machined thermally sprayed coatings can always be detected, with FR-FBM being able to guarantee the precision and to ensure the closest geometrical tolerances.     

Heparin induces an accumulation of atherogenic lipoproteins during hemodialysis in normolipidemic end‐stage renal disease patients

Dyslipidemias may account for the excess of cardiovascular mortality in end‐stage renal disease (ESRD). Lipoprotein studies in ESRD patients are usually relative to prehemodialysis samples even if significative changes may occur after dialysis. In this study, we aimed to investigate the effects of ESRD on triglyceride‐rich lipoproteins (TRL) subpopulations distribution and acute change following hemodialytic procedures, including the relative contribution of heparin administration. We selected a group of normolipidemic male middle‐aged ESRD patients free of any concomitant disease affecting lipoprotein remnant metabolism compared with controls. We separated TRL subfractions according to density and apoE content and evaluated the changes of these particles after hemodialytic procedures with or without heparin. ESRD subjects had higher TRL subfractions, with the exception of apoE‐rich particles, lower high‐density lipoprotein (HDL) largest subclasses, and a smaller low‐density lipoprotein peak particle size than controls. After a hemodialytic standard procedure with heparin, we demonstrated a significant reduction of triglyceride, an increase of HDL‐cholesterol levels, and a raise of small very‐low‐density lipoprotein, intermediate‐density lipoproteins (IDL), apoE‐rich particles, and non‐HDL‐cholesterol levels. When hemodialysis was performed without heparin, no significant changes were observed. In the absence of concomitant hyperlipidemic triggers, ESRD patients show significant lipoprotein abnormalities before dialysis, but without any increased remnant particles concentrations. We speculate that hemodialysis, in particular heparin administration during this procedure, leads to a massive atherogenic TRLs production because of the acute stimulation of the dysfunctional lipolytic system not followed by an efficient removal, determining a recurrent lipoprotein remnant accumulation.     

Multi-rate group-orthogonal OFDMA-CDMA for broadband mobile transmission

In this work, the problem of multi-rate Multi-Carrier (MC) Code Division Multiple Access (CDMA) wireless transmission is addressed. In particular, we investigated the possibility of exploiting subcarrier grouping, already considered in literature for constant bit-rate MC-CDMA, in order to reduce mutual interference among different rate users and to allow the use of theoretically-optimum Maximum-Likelihood Multi-User Detection (ML-MUD) with affordable computational burden. We propose a multi-code Group Orthogonal (GO) OFDMA-CDMA system where the available subcarriers are subdivided into fixed-cardinality orthogonal subcarrier groups. The user’s data stream is selectively multiplexed into a variable number of substreams, which depends on the data-rate. Then, these substreams are transmitted over an orthogonal subcarrier group, univocally assigned to a user rate class. Experimental results obtained by adopting linear multi-user detection show that the proposed GO-OFDMA-CDMA outperforms state-of-the-art Variable Spreading Length (VSL) and multi-code MC-CDMA as far as higher data rate users are concerned. On the other hand, BER performance of lowest-rate users is slightly worse. Orthogonal subcarrier grouping allows to greatly increasing BER performance when using ML-MUD operated over small subcarrier groups. In such a case, the tradeoff to be managed is between achievable performance and computational complexity.     

Growth of A1N piezoelectric film on diamond for high-frequency surface acoustic wave devices

Diamond films are very desirable for application to SAW devices because of their high acoustic wave velocity, which allows the extending of the frequency limit of operation at a given interdigital transducer line-width resolution. Use of high-quality AIN as the piezoelectric layer in conjunction with diamond is also desirable because of its high SAW velocity--the highest among all piezoelectric materials--together with its excellent electrical, mechanical, and chemical properties. The problems arising in the growth of A1N films on diamond have prevented, until now, the use of this combination of materials. In this paper we present recent results on the growth of highly oriented, low-stressed A1N films on diamond. SAW propagation on A1N/diamond has been theoretically investigated together with electromechanical coupling for both the Rayleigh and the Sezawa modes. The theoretical calculations show that high SAW velocities are achievable with good coupling efficiencies. Under proper conditions very large piezoelectric couplings are predicted--k2 = 2.2 and 4% for the Rayleigh and the Sezawa wave, respectively--comparable to those observed in strongly piezoelectric single crystals such as LiNbO3, but with SAW velocities approximately two-fold higher. Experiments performed on A1N/diamond/Si SAW test devices have shown good agreement between experimental results and theoretical predictions and demonstrate the feasibility of SAW devices based on this technology.     

Experimental evaluation of the strain field history during plastic progressive folding of aluminium circular tubes

The axisymmetric collapse by plastic progressive folding of a circular tube submitted to axial loading is considered by an experimental approach. The strain field history is measured by means of electric strain gages properly placed on the external surface of the tube so that more than one fold is covered and both axial and circumferential strains are measured. The measured strains are examined both as time-histories and as a deformation field. The formation and development of circumferential plastic hinges are pointed out. The strain histories, reported as a function of the displacement of the testing machine cross-head, are then correlated with the crushing force diagram, leading to a better understanding of the folding mechanics. In particular, the formation of each fold develops through three subsequent phases: the initialization at the closure of the previous fold, the flattening of the upper conical surface, and the flattening of the lower conical surface. While most of the tube wall is pushed outwards of the original cylindrical surface, a portion is pushed inwards of that surface. Moreover, there is a small portion of the wall that is pulled inward during the fold initialization and then pushed outward during the fold closure. The analysis of these histories lead to the validation of the basic assumption of our and other recent kinematical models of the plastic progressive folding.