Aqueous Free-Radical Polymerization of Non-Ionized and Fully Ionized Methacrylic Acid

Water-soluble, carboxylic acid monomers are known to exhibit peculiar kinetics when polymerized in aqueous solution. Namely, their free-radical polymerization rate is affected by several parameters such as monomer concentration, ionic strength, and pH. Focusing on methacrylic acid (MAA), even though this monomer has been largely addressed, a systematic investigation of the effects of the above-mentioned parameters on its polymerization rate is missing, in particular in the fully ionized case. In this work, the kinetics of non-ionized and fully ionized MAA are characterized by in-situ nuclear magnetic resonance (NMR). Such accurate monitoring of the reaction rate enables the identification of relevant but substantially different effects of the monomer and electrolyte concentration on polymerization rate in the two ionization cases. For non-ionized MAA, the development of a kinetic model based on literature rate coefficients allows us to nicely simulate the experimental data of conversion versus time at a high monomer concentration. For fully ionized MAA, a novel propagation rate law accounting for the electrostatic interactions is proposed: the corresponding model is capable of predicting reasonably well the electrolyte concentration effect on polymerization rate. Nevertheless, further kinetic information in a wider range of monomer concentrations would be welcome to increase the reliability of the model predictions

On the Use of Quantum Chemistry for the Determination of Propagation, Copolymerization, and Secondary Reaction Kinetics in Free Radical Polymerization

Throughout the last 25 years, computational chemistry based on quantum mechanics has been applied to the investigation of reaction kinetics in free radical polymerization (FRP) with growing interest. Nowadays, quantum chemistry (QC) can be considered a powerful and cost-effective tool for the kinetic characterization of many individual reactions in FRP, especially those that cannot yet be fully analyzed through experiments. The recent focus on copolymers and systems where secondary reactions play a major role has emphasized this feature due to the increased complexity of these kinetic schemes. QC calculations are well-suited to support and guide the experimental investigation of FRP kinetics as well as to deepen the understanding of polymerization mechanisms. This paper is intended to provide an overview of the most relevant QC results obtained so far from the investigation of FRP. A comparison between computational results and experimental data is given, whenever possible, to emphasize the performances of the two approaches in the prediction of kinetic data. This work provides a comprehensive database of reaction rate parameters of FRP to assist in the development of advanced models of polymerization and experimental studies on the topic

Interferometric length metrology for the dimensional control of ultra-stable Ring Laser Gyroscopes

We present the experimental test of a method for controlling the absolute length of the diagonals of square ring laser gyroscopes. The purpose is to actively stabilize the ring cavity geometry and to enhance the rotation sensor stability in order to reach the requirements for the detection of the relativistic Lense-Thirring effect with a ground-based array of optical gyroscopes. The test apparatus consists of two optical cavities 1.32 m in length, reproducing the features of the ring cavity diagonal resonators of large frame He-Ne ring laser gyroscopes. The proposed measurement technique is based on the use of a single diode laser, injection locked to a frequency stabilized He-Ne/Iodine frequency standard, and a single electro-optic modulator. The laser is modulated with a combination of three frequencies allowing to lock the two cavities to the same resonance frequency and, at the same time, to determine the cavity Free Spectral Range (FSR). We obtain a stable lock of the two cavities to the same optical frequency reference, providing a length stabilization at the level of 1 part in $10^{11}$, and the determination of the two FSRs with a relative precision of 0.2 ppm. This is equivalent to an error of 500 nm on the absolute length difference between the two cavities

Modeling, estimation and control of ring laser gyroscopes for the accurate estimation of the earth rotation

He − Ne ring lasers gyroscopes are, at present, the most precise devices for absolute angular velocity measurements. Limitations to their performances come from the non-linear dynamics of the laser. Accordingly to the Lamb semi-classical theory of gas lasers, a model can be applied to a He–Ne ring laser gyroscope to estimate and remove the laser dynamics contribution from the rotation measurements. We find a set of critical parameters affecting the long term stability of the system. We propose a method for estimating the long term drift of the laser parameters, and for filtering out the laser dynamics effects, e.g. the light backscattering. The intensities of the counterpropagating laser beams exiting one cavity mirror are continuously measured, together with the monitor of the laser population inversion. These quantities, once properly calibrated with a dedicated procedure, allow us to estimate cold cavity and active medium parameters of the Lamb theory. Our identification procedure, based on the perturbative solutions of the laser dynamics, allow us for the application of the Kalman Filter theory for the estimation of the angular velocity. The parameter identification and backscattering subtraction procedure has been verified by means of a Monte Carlo studies of the system, and then applied to the experimental data of the ring lasers G-PISA and G-WETTZELL. After the subtraction of laser dynamics effects by Kalman filter, the relative systematic error of G-PISA reduces from 50 to 5 parts in 103, and it can be attributed to the residual uncertainties on geometrical scale factor and orientation of the ring. We also report that after the backscattering subtraction, the relative systematic errors of G-WETTZELL are reduced too. Conversely, in the last decade an increasing attention was drawn to high precision optical experiments, e.g. ring laser experiments, which combine high sensitivity, accuracy and long term stability. Due to the experimental requirements, position and orientation of optical elements and laser beams formation must be controlled in the field of nano-positioning and ultra-precision instruments. Existing methods for beam direction computing in resonators, e.g. iterative ray tracing or generalized ray transfer matrices, are either computationally expensive or rely on overparametrized models of optical elements. By exploiting the Fermat’s principle, we develop a novel method to compute the beam directions in resonant optical cavities formed by spherical mirrors, as a function of mirror positions and curvature radii. The proposed procedure is based on the geometric Newton method on matrix manifold, a tool with second order convergence rate that relies on a second order model of the cavity optical length. As we avoid coordinates to parametrize the beam position on mirror surfaces, the computation of the second order model does not involve the second derivatives of the parametrization. With the help of numerical tests, we show that the convergence properties of our procedure hold for non-planar polygonal cavities, and we assess the effectiveness of the geometric Newton method in determining their configurations with an high degree of accuracy and negligible computational effort. We also presents a method to account for the (ring laser) cavity deformations due to mirrors displacement, seen as the residual motions of the mirrors centers after the removal of rigid body motions. Having the cavity configuration and the model to account for mirrors movements, the calibration and active control of the optical cavity can be addressed as a control problem. In fact, our results are of some importance not only for the design and simulation of ring laser gyroscopes, but also for the active control of the optical cavities. In the final part of this work we detail a complete model including the simulation of the physical processes of interest in the operation of a ring laser gyroscope. Simulation results for the application of the model to the ring laser GP2 are presented and discusse

Development of a droplet digital PCR assay to detect illicit glucocorticoid administration in bovine

Glucocorticoids are often used illegally in food-producing animals for the growth promotion of livestock animals. In accordance to official chemical methods for glucocorticoid detection, an animal is declared as non-compliant when a residue is identified in the sample. Neverthless, growth promoting molecules can often escape identification due to their rapid elimination or due to the use of non-detectable new generation drugs. Therefore, an indirect screening method able to detect the biological effect of long-term administration of low doses of dexamethasone and prednisolone on livestock has been developed to support official methods. As already described, FKBP5 (FKBP prolyl isomerase 5) expression in bovine thymus is regulated by glucocorticoids, and this specific regulation can be exploited in an indirect screening assay. In the present study, male veal calves and young bulls were considered in three different trials in which estradiol, dexamethasone, and prednisolone were administered alone or in combination with Revalor-200 subcutaneous pellets. Thoracic thymus was sampled from all animals and molecular analysis was performed. A duplex droplet digital PCR assay with EvaGreen(®) was employed to detect the target gene expression using absolute quantification. The developed droplet digital PCR assay was precise, showing intra- and inter-assay mean coefficient of variation values of about 6.16% and 3.17%, respectively. It was also highly specific (100%) with Youden’s index of 76.92% and 53.57% applied to veal calves and young bulls, respectively. The lowest detection limit in which the target gene expression level was kept constant, was 0.05 ng/μl of cDNA with 1 copies/μL and 0.5 copies/μL for target and reference gene, respectively. This study establishes the basis for using a digital PCR-based assay as an efficient test to identify animals illegally treated with glucocorticoids

MALDI-TOF mass spectrometry profiling of bovine skim milk for subclinical mastitis detection

INTRODUCTION: Mastitis is one of most impacting health issues in bovine dairy farming that reduces milk yield and quality, leading to important economic losses. Subclinical forms of the disease are routinely monitored through the measurement of somatic cell count (SCC) and microbiological tests. However, their identification can be tricky, reducing the possibilities of early treatments. In this study, a MALDI-TOF mass spectrometry approach was applied to milk samples collected from cows classified according to the SCC, to identify differences in polypeptide/protein profiles. MATERIALS AND METHODS: Twenty-nine raw milk samples with SCC >200,000 cell/ml (group H) and 91 samples with SCC lower than 200,000 (group L) were randomly collected from 12 dairy farms. Spectral profiles from skim milk were acquired in the positive linear mode within the 4,000–20,000 m/z mass acquisition range. RESULTS AND DISCUSSION: Based on signal intensity, a total of 24 peaks emerged as significant different between the two groups. The most discriminant signals (4,218.2 and 4,342.98 m/z) presented a ROC curve with AUC values higher than 0.8. Classification algorithms (i.e., quick classifier, genetic algorithm, and supervised neural network) were applied for generating models able to classify new spectra (i.e., samples) into the two classes. Our results support the MALDI-TOF mass spectrometry profiling as a tool to detect mastitic milk samples and to potentially discover biomarkers of the disease. Thanks to its rapidity and low-cost, such method could be associated with the SCC measurement for the early diagnosis of subclinical mastitis

Characterization of the virulence, growth temperature and antibiotic resistance of the Campylobacter jejuni IAL 2383 strain isolated from humans

The objective of this study was to characterize the C. jejuni IAL2383 strain isolated from humans in Brazil. Transcripts for the racR, dnaJ and ciaB genes were found and flaA, plda and cadF genes were present in the genome and bacteria was sensitive to most of the important antimicrobials used to treat humans. C. jejuni IAL2383 is a good experimental model to analyze the interactions with cells