Laser-generated liquid microjets: correlation between bubble dynamics and liquid ejection

Laser-based techniques provide excellent means for liquid microprinting, with several advantages over other more conventional printing techniques, such as being nozzle-free (as opposed to inkjet, for instance) or requiring minimal engineering of the liquid properties in the pre-printing stage. In such techniques, the transfer is usually mediated by liquid jets that contact a receiver substrate placed nearby the liquid source, leading to the deposition of a small droplet. The main cause of jetting lies in a laser-generated bubble produced inside the liquid, whose dynamics dictates the evolution of liquid ejection. However, the detailed relationship between the bubble and the jet is not completely understood, as the studies carried out so far have been mostly focused on the jetting dynamics taking place above the liquid free-surface, without access to the liquid interior and therefore to the behavior of the bubble. In this work, we analyze through time-resolved imaging the film-free laser printing of an aqueous solution by simultaneously visualizing both the bubble evolution and the liquid ejection dynamics, thus making possible the correlation between the two phenomena. We find that the pulsating behavior of the bubble leads to successive jetting events with different jet morphologies arising from the particular geometries that the bubble acquires during its evolution. Finally, we find good agreement between our results and those from studies analyzing the dynamics of cavitation bubbles near the free-surface of a liquid through numerical solution of the fluid dynamics equations.     

Homogeneous Catalyzed Ozone Decomposition in the Presence of Co(II).

The homogeneous decomposition of ozone in the presence of a Co(II) catalyst has been investigated in aqueous solution. Under the conditions investigated (Co(II) concentration: 0.0 – 2.0?ppm, pH: 1.6- 8.4, O₃ concentration: 5 10^?5 – 2.0 10⁴?M) the process can be assumed to follow pseudo first order kinetics with respect to ozone. Cobalt concentration dependency also obeys first order kinetics although it may be considered to reach a steady state concentration. pH exerts a positive influence on the decomposition rate from 1.6 to 7.1, the process leveling off at pH 8.4. An Arrhenius analysis of the temperature effect gave a moderate activation energy of the global reaction (E=10917?cal mol^?1). A more detailed radical mechanism than a simple pseudo first order reaction can be postulated for simulation purposes. By numerical optimization of some unknown kinetic constants the influence of several operating variables can be adequately predicted.     

Zinc nutrition in young Chilean adults

To evaluate the effect of dietary factors on plasma zinc levels, dietary zinc intake was estimated and plasma levels were measured in 37 healthy young adults of low and middle socioeconomic status. Our study included 16 males aged 29 +/- 7 and 21 females aged 26 +/- 6 years. Dietary intake of zinc and protein was determined from a 24-hour dietary recall survey. Plasma zinc was measured by atomic absorption spectrophotometry. Alkaline phosphatase (AP) in plasma was also measured and the weight/height percentage for each subject calculated according to Jelliffe's standards. The average diet was composed of cereals, legumes, eggs, bread and noodles, caloric intake was 2051 +/- 154 kcal/day for men and 1767 +/- 158 (x +/- SD) kcal/day for women. The daily intake of zinc was 8.3 +/- 3.0 mg/day for males, and 9.7 +/- 2.0 mg/day for females. Cereals were the main source of zinc for men, while egg and dairy products were for women. Plasma zinc values were 82 +/- 22 micrograms/dl for men and 94 +/- 19 micrograms/dl for women (p less than 0.01). For the whole group plasma zinc concentration was 89 +/- 21 micrograms/dl. Seven males and two females had low plasma zinc values (70 micrograms/dl or less). Alkaline phosphatase (AP) levels were 110 +/- 10 IU for males and 71 +/- 4 IU for females (p less than 0.001). These values did not correlate with the zinc levels. Average weight/height was 99 +/- 18 for men, and 108 +/- 18 for females. Results indicate that on the average, in our study group plasma zinc levels were within the normal range, although they were significantly lower in men. Dietary intake of zinc was below the recommendations, being higher for women as related to values presented by men. The observed low plasma levels of zinc may be caused by a low intake, and/or poor bioavailability.     

Influence of anionic form on thermooxidation of TMAHP–cellulose

With the help of DTA, DTG elementary analysis of carbonized residues and ESR spectroscopy the influence of anionic form on thermooxidation of trimethylammoniumhydroxyprophyl (TMAHP)–cellulose was studied. At 300°C the percentage of carbon in carbonized residue thermolyzed in oxidative atmosphere is higher than for the sample degraded in inert atmosphere. The percentage of hydrogen decreases simultaneously. The concentration of free radicals in thermolyzed residue also increases due to the presence of oxygen. We propose that oxygen is abstracting the hydrogen atoms from polysaccharide and unpaired electrons on carbon atoms are produced. At 400°C the percentage of carbon in residues prepared at inert atmosphere is higher than for residue formed at oxidative atmosphere. Also the concentration of free radicals in thermolyzed residues obtained in inert atmosphere is greater than for those from oxidative ones. That is why suppose that at this temperature oxygen is bonded to polysaccharide residue and free radicals are terminated. From the semiquantitative DTA we can make the following sequence of samples according to their increasing thermooxidative effect: unmodified cellulose < A–HSO < A–Br^? < A–I^? < A–NO < A–H₂PO < A–CH₃COO^? < A–HCO < A–F^? < A–Cl^?1 < A–OH^p?.     

Effect of temperature on the separation of some Δ9-cis-trans isomers of methyl esters of fatty acids by open tubular gas chromatography

The influence of temperature on the gas chromatographic separation ofcis-trans isomers of the methyl esters of some monounsaturated fatty acids was studied on capillary columns coated with Apiezon L, BDS and DEGS. As far as methyl oleate and methyl elaidate are concerned, the separation is better at lower temperatures on Apiezon L (180–210 C) and at higher temperatures on polyester phases (BDS, DEGS; 150–180 C). The influence of temperature on the separation ofcis-trans isomers on the three stationary phases under study is explained by the higher values of δECL/δt forcis isomers. The variation of the equivalent carbon chain length with temperature can be used for the identification ofcis-trans isomers in natural mixtures.     

Influence of maize kernel hardness on flour hydration and cooking properties

Knowledge of the association between cooking properties and endosperm hardness may help nutritionist and processors to select raw materials for preparing maize based food products, particularly those eaten as cooked dispersions. Seven commercial maize cultivars differing in hardness were selected to evaluate endosperm hardness on the kernels and some characteristics such as composition and hydration and cooking properties on the grits obtained from those maizes. Results show that the differences in endosperm hardness (directly related to grits protein content) can explain the differences in swelling and amylographic consistencies values. Cultivars with the hardest endosperm show the lowest values at high temperature. They also show the lowest amylographic consistencies. On the other hand softer endosperms present the highest swelling power and the highest amylographic consistencies. These differences are attributed to the restriction for starch swelling caused by the protein matrix. Endosperm hardness measurements and swelling power at 95 degrees C, can be useful to select cultivars that are going to be used to prepare maize based foods like atoles, polenta, etc.     

The potentiometric behaviour of copolymers of methacrylic acid in water-ethanol solutions

Summary The synthesis is reported of copolymers of styrene with methacrylic acid and of methyl methacrylate with methacrylic acid by radical copolymerization, of copolymers of methyl methacrylate with methacrylic acid by partial alkaline hydrolysis of poly(methyl methacrylate), and of block copolymers of styrene with methacrylic acid. Modified titration curves of all these copolymers were recorded in water and water-ethanol solutions. In a solution containing 50 mass.% ethanol, only small differences could be observed between the potentiometric behaviour of the individual copolymers and polymethacrylic acid. Also, there were no essential differences in any of the solvents used between the potentiometric behaviour of block copolymers of styrene with methacrylic acid, on the one hand, and polymethacrylic acid, on the other. On the contrary, maxima and minima were always observed on the modified titration curves of statistical copolymers with a higher content of the hydrophobic comonomer in solutions with a high water content. Thus, using the modified titration curves, it is possible to decide whether a given copolymer is of the block or statistical type.     

Investigation of Flow Patterns in Continuous‐flow Stirred Vessels by Laser Doppler Velocimetry

The flow structure of a continuous‐flow reactor stirred by a Rushton turbine was investigated by laser Doppler velocimetry for two different mean residence time‐mixing time ratios. Velocity measurements were obtained for two inlet locations, corresponding to the incoming liquid stream being fed co‐currently or counter‐currently to the flow discharged by the turbine. In all investigated configurations and for all operating conditions, it was found that the flow disruption caused by the incoming liquid stream was observable mainly in the first vessel quarter, which followed the feed‐tube plane. From comparison of the velocities encountered in the various planes in the continuous‐flow reactor to the velocities of the batch reactor, it was also concluded that it may be possible to intensify the usage of the turbine‐stirred vessel by decreasing the characteristic times ratio, without considerable flow by‐pass and/or short‐circuiting problems.     

Coordinate descent with arbitrary sampling I: algorithms and complexity†

We study the problem of minimizing the sum of a smooth convex function and a convex block-separable regularizer and propose a new randomized coordinate descent method, which we call ALPHA. Our method at every iteration updates a random subset of coordinates, following an arbitrary distribution. No coordinate descent methods capable to handle an arbitrary sampling have been studied in the literature before for this problem. ALPHA is a very flexible algorithm: in special cases, it reduces to deterministic and randomized methods such as gradient descent, coordinate descent, parallel coordinate descent and distributed coordinate descent—both in nonaccelerated and accelerated variants. The variants with arbitrary (or importance) sampling are new. We provide a complexity analysis of ALPHA, from which we deduce as a direct corollary complexity bounds for its many variants, all matching or improving best known bounds.