A variational approach has been recently employed to determine the ideal time-dependent injection rate Q(t) that minimizes fingering formation when a fluid is injected in a Hele-Shaw cell filled with another fluid of much greater... more
A variational approach has been recently employed to determine the ideal time-dependent injection rate Q(t) that minimizes fingering formation when a fluid is injected in a Hele-Shaw cell filled with another fluid of much greater viscosity. However, such a calculation is approximate in nature, since it has been performed by assuming a high capillary number regime. In this work, we go one step further, and utilize a Hamiltonian formulation to obtain an analytical exact solution for Q(t), now valid for arbitrary values of the capillary number. Moreover, this Hamiltonian scheme is applied to calculate the corresponding injection rate that minimizes fingering formation in a uniform three-dimensional porous media. An analysis of the improvement offered by these exact injection rate expressions in comparison with previous approximate results is also provided.
When a ferrofluid drop is trapped in a horizontal Hele-Shaw cell and subjected to a vertical magnetic field, a fingering instability results in the droplet evolving into a complex branched structure. This fingering instability depends on... more
When a ferrofluid drop is trapped in a horizontal Hele-Shaw cell and subjected to a vertical magnetic field, a fingering instability results in the droplet evolving into a complex branched structure. This fingering instability depends on the magnetic field ramp rate but also depends critically on the initial state of the droplet. Small perturbations in the initial droplet can have a large influence on the resulting final pattern. By simultaneously applying a stabilizing (horizontal) azimuthal magnetic field, we gain more control over the mode selection mechanism. We perform a linear stability analysis that shows that any single mode can be selected by appropriately adjusting the strengths of the applied fields. This offers a unique and accurate mode selection mechanism for this confined magnetic fluid system. We present the results of numerical simulations that demonstrate that this mode selection mechanism is quite robust and "overpowers" any initial perturbations on the droplet. This provides a predictable way to obtain patterns with any desired number of fingers.
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The Saffman-Taylor viscous fingering instability occurs when a less viscous fluid displaces a more viscous one between narrowly spaced parallel plates in a Hele-Shaw cell. Experiments in radial and rectangular flow geometries form... more
The Saffman-Taylor viscous fingering instability occurs when a less viscous fluid displaces a more viscous one between narrowly spaced parallel plates in a Hele-Shaw cell. Experiments in radial and rectangular flow geometries form finger-like patterns, in which fingers of different lengths compete, spread and split. Our weakly nonlinear analysis of the instability predicts these phenomena, which are beyond the scope of linear stability theory. Finger competition arises through enhanced growth of sub-harmonic perturbations, while spreading and splitting occur through the growth of harmonic modes. Nonlinear mode-coupling enhances the growth of these specific perturbations with appropriate relative phases, as we demonstrate through a symmetry analysis of the mode coupling equations. We extend our mode coupling theory to include the situation in which one of the fluids is a ferrofluid and a magnetic field is applied normal to the Hele-Shaw cell. Our analysis indicates that the onset of interface symmetry breaking observed in experiments involving ferrofluids depends on viscosity contrast, not on the applied magnetic field. We also show how magnetic fields lead to finger tip-splitting.
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The alternate current biosusceptometry (ACB) is a biomagnetic technique used to study some physiological parameters associated with gastrointestinal (GI) tract. For this purpose it applies an AC magnetic field and measures the response... more
The alternate current biosusceptometry (ACB) is a biomagnetic technique used to study some physiological parameters associated with gastrointestinal (GI) tract. For this purpose it applies an AC magnetic field and measures the response originating from magnetic marks or tracers. This paper presents an equipment based on the ACB which uses anisotropic magnetoresistive (AMR) sensors and an inexpensive electronic support. The ACB-AMR developed consists of a square array of 6×6 sensors arranged in a first-order gradiometer configuration with one reference sensor. The equipment was applied to capture magnetic images of different phantoms and to acquire gastric contraction activity of healthy rats. The results show a reasonable sensitivity and spatial-temporal resolution, so that it may be applied for imaging of phantoms and signal acquisition of the GI tract of small animals.
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To correlate gastric contractility, gastrointestinal transit, and hormone levels in non-pregnant (estrous cycle) and pregnant rats using noninvasive techniques. Female rats (n = 23) were randomly divided into (1) non-pregnant,... more
To correlate gastric contractility, gastrointestinal transit, and hormone levels in non-pregnant (estrous cycle) and pregnant rats using noninvasive techniques. Female rats (n = 23) were randomly divided into (1) non-pregnant, (contractility, n = 6; transit, n = 6); and (2) pregnant (contractility, n = 5; transit, n = 6). In each estrous cycle phase or at 0, 7, 14, and 20 d after the confirmation of pregnancy, gastrointestinal transit was recorded by AC biosusceptometry (ACB), and gastric contractility was recorded by ACB and electromyography. After each recording, blood samples were obtained for progesterone and estradiol determination. In the estrous cycle, despite fluctuations of sex hormone levels, no significant changes in gastrointestinal motility were observed. Days 7 and 14 of pregnancy were characterized by significant changes in the frequency of contractions (3.90 ± 0.42 cpm and 3.60 ± 0.36 cpm vs 4.33 ± 0.25 cpm) and gastric emptying (168 ± 17 min and 165 ± 15 min vs 113 ...
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A fingering instability occurs when a drop of liquid in a Hele-Shaw cell is rotated at a constant angular velocity. If this liquid is a ferrofluid, this fingering instability can be suppressed by the application of an azimuthally applied... more
A fingering instability occurs when a drop of liquid in a Hele-Shaw cell is rotated at a constant angular velocity. If this liquid is a ferrofluid, this fingering instability can be suppressed by the application of an azimuthally applied magnetic field. We have studied this situation analytically and computationally and have observed a number of interesting behaviors, including what we refer to as a ``diamond ring'' instability. This magnetic damping can also be used to reduce the instabilities in other systems, such as the fingering that results when a ferrofluid drop in a Hele-Shaw cell is subjected to a transverse magnetic field.
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A variabilidade espacial da rugosidade superficial do solo foi estudada a partir de uma grade de dados pontuais medidos com instrumentos de diferentes graus de precisão. Para a medição da rugosidade utilizou-se um rugosímetro laser, em... more
A variabilidade espacial da rugosidade superficial do solo foi estudada a partir de uma grade de dados pontuais medidos com instrumentos de diferentes graus de precisão. Para a medição da rugosidade utilizou-se um rugosímetro laser, em condições de laboratório, sendo as ...
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One efficient way of determining the bond strength of adhesives is to measure the force or the work required to separate two surfaces bonded by a thin adhesive film. We consider the case in which the thin film is not a conventional... more
One efficient way of determining the bond strength of adhesives is to measure the force or the work required to separate two surfaces bonded by a thin adhesive film. We consider the case in which the thin film is not a conventional adhesive material but a high viscosity ferrofluid confined between two narrowly spaced parallel flat plates subjected to an external magnetic field. Our theoretical results demonstrate that both the peak adhesive force and the separation energy are significantly influenced by the action and symmetry properties of the applied field. Specifically, we show that the adhesive strength of a ferrofluid is reduced if the applied magnetic field is perpendicular to the plates or if the applied field is in plane and exhibits azimuthal symmetry. Conversely, the adhesive strength can be either enhanced or reduced if the applied field is in plane and is directed radially outward. This establishes an interesting connection between adhesion and ferrohydrodynamic phenomena, allowing the control of important adhesive properties by magnetic means.
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We perform a detailed analytic and numerical study of the evolution of a ferrofluid drop confined to a rotating Hele-Shaw cell in the presence of an azimuthal magnetic field. Our results demonstrate that the centrifugally driven... more
We perform a detailed analytic and numerical study of the evolution of a ferrofluid drop confined to a rotating Hele-Shaw cell in the presence of an azimuthal magnetic field. Our results demonstrate that the centrifugally driven interfacial instabilities can be simply controlled with the use of a current-carrying wire. We compare an analytic linear analysis to our computational results and show that a number of observed features cannot be explained by linear theory alone, including a "diamond ring" instability that results when a droplet is nearly stabilized.
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A pair of concentric spheres separated by a small gap form a spherical Hele-Shaw cell. In this cell an interfacial instability arises when two immiscible fluids flow. We derive the equation of motion for the interface perturbation... more
A pair of concentric spheres separated by a small gap form a spherical Hele-Shaw cell. In this cell an interfacial instability arises when two immiscible fluids flow. We derive the equation of motion for the interface perturbation amplitudes, including both pressure and gravity drivings, using a mode coupling approach. Linear stability analysis shows that mode growth rates depend upon interface perimeter and gravitational force. Mode coupling analysis reveals the formation of fingering structures presenting a tendency toward finger tip-sharpening.
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We revisit the radial viscous fingering problem in a Hele-Shaw cell, and consider the action of viscous stresses originated from velocity gradients normal to the fluid-fluid interface. The evolution of the interface during linear and... more
We revisit the radial viscous fingering problem in a Hele-Shaw cell, and consider the action of viscous stresses originated from velocity gradients normal to the fluid-fluid interface. The evolution of the interface during linear and weakly nonlinear stages is described analytically through a mode-coupling approach. We find that the introduction of normal stresses influences the stability and the ultimate morphology of the emerging patterns. Although at early stages normal stresses tend to stabilize the interface, they act to favor the development of tip-splitting phenomena at the weakly nonlinear regime. We have also verified that finger competition events are only significantly affected by normal stresses for circumstances involving the development of a large number of interfacial fingers.
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We analyze the Saffman-Taylor viscous fingering problem in rectangular geometry. We investigate the onset of nonlinear effects and the basic symmetries of the mode coupling equations, highlighting the link between interface asymmetry and... more
We analyze the Saffman-Taylor viscous fingering problem in rectangular geometry. We investigate the onset of nonlinear effects and the basic symmetries of the mode coupling equations, highlighting the link between interface asymmetry and viscosity contrast. Symmetry breaking occurs through enhanced growth of sub-harmonic perturbations. Our results explain the absence of finger tip-splitting in the early flow stages, and saturation of growth rates compared with the predictions of linear stability.
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When a ferrofluid is trapped in a Hele-Shaw cell and subjected to a perpendicular magnetic field a fingering instability results in the droplet evolving into a complex branched structure. This fingering instability depends on the magnetic... more
When a ferrofluid is trapped in a Hele-Shaw cell and subjected to a perpendicular magnetic field a fingering instability results in the droplet evolving into a complex branched structure. This fingering instability depends on the magnetic field ramp rate but it also depends critically on the initial state of the droplet. Small perturbations in the initial droplet can have a large influence on the resulting final pattern. By simultaneously applying a stabilizing azimuthal magnetic field, we gain more control over the mode selection mechanism. In fact, a linear stability analysis predicts that any mode can be selected by appropriately adjusting the strengths of the applied fields. We present the results of numerical simulations that demonstrate that this mode-selection mechanism is quite robust and ``overpowers'' any initial perturbations on the droplet. This provides a predicable way to obtain patterns with any number of fingers whatsoever.
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Research Interests: Imaging, Pharmacokinetics, Pharmaceutical Chemistry, Dosage Form, Humans, and 12 moreAnimals, Solubility, European, Intestinal absorption, Electromagnetic phenomena, Gastrointestinal Tract, Gastrointestinal motility, Ionizing Radiation, Dosage Forms, Transit Time, Gastric Emptying, and Pharmaceutical preparations
N3-Alkylation of 1-(pivaloyloxymethyl)-1,2,3-triazoles with alkyl triflates carrying latent "click" functionality, followed by a nucleophile-promoted N1-dealkylation of the resulting strongly electrophilic intermediate... more
N3-Alkylation of 1-(pivaloyloxymethyl)-1,2,3-triazoles with alkyl triflates carrying latent "click" functionality, followed by a nucleophile-promoted N1-dealkylation of the resulting strongly electrophilic intermediate triazolium salts, provides an efficient route to 1,5-disubstituted 1,2,3-triazoles. The azide and alkyne groups incorporated by N-alkylation can be submitted to further copper-catalyzed azide-alkyne and Huisgen cycloadditions to provide bis(1,2,3-triazoles) with unprecedented 1,5/1,4 substitution patterns.
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Elastic fingering supplements the already interesting features of the traditional viscous fingering phenomena in Hele-Shaw cells with the consideration that the two-fluid separating boundary behaves like an elastic membrane. Sophisticated... more
Elastic fingering supplements the already interesting features of the traditional viscous fingering phenomena in Hele-Shaw cells with the consideration that the two-fluid separating boundary behaves like an elastic membrane. Sophisticated numerical simulations have shown that under maximum viscosity contrast the resulting patterned shapes can exhibit either finger tip-splitting or side-branching events. In this work, we employ a perturbative mode-coupling scheme to get important insights into the onset of these pattern formation processes. This is done at lowest nonlinear order and by considering the interplay of just three specific Fourier modes: a fundamental mode n and its harmonics 2n and 3n. Our approach further allows the construction of a morphology diagram for the system in a wide range of the parameter space without requiring expensive numerical simulations. The emerging interfacial patterns are conveniently described in terms of only two dimensionless controlling quantitie...
Polarized ferrofluids, lipid monolayers, and magnetic bubbles form domains with deformable boundaries. Stability analysis of these domains depends on a family of nontrivial integrals. We present a closed-form evaluation of these integrals... more
Polarized ferrofluids, lipid monolayers, and magnetic bubbles form domains with deformable boundaries. Stability analysis of these domains depends on a family of nontrivial integrals. We present a closed-form evaluation of these integrals as a combination of Legendre functions. This result allows exact and explicit formulas for stability thresholds and growth rates of individual modes. We also evaluate asymptotic behavior in several interesting limits.
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One of the best examinations used routinely to detect gastro-oesophageal reflux (GOR) is scintigraphy and attempts are continuously being made to improve the performance of the test. We have tested a new manoeuvre to improve the results.... more
One of the best examinations used routinely to detect gastro-oesophageal reflux (GOR) is scintigraphy and attempts are continuously being made to improve the performance of the test. We have tested a new manoeuvre to improve the results. Three hundred and twenty eight patients (190 males and 138 females, aged 1 month to 84 years, average 4.47 years) were studied after a 12 h fast period with 100 MBq of 99Tcm-phytate, 50 ml volume, directly delivered into the stomach in a mixture of orange juice. All patients were strongly suspected of having GOR. Conventional acquisition was done for 20 min, at a rate of one frame every 20 s. In the middle of the examination, small children were put in the upright position and held there for a few seconds or released in a way that allowed movement; adults were asked to stand up and walk a few metres. The test was then continued for the remaining 10 min. The global index of positivity was 64.6% (76 positive cases in the first half of the examination and 134 positive cases only after the manoeuvre). The mean of GOR episodes observed in the positive cases without the manoeuvre was 0.5 per patient, significantly different from the mean of 1.59 noted after the manoeuvre (P<0.01). In 28 cases the manoeuvre increased either the intensity or the frequency of reflux previously detected without it. We believe that this manoeuvre should be performed in all scintigraphic tests aiming to detect GOR. In the present series, the manoeuvre increased the frequency of GOR episodes.
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A growing number of experimental and theoretical works have been addressing various aspects of the viscous fingering formation in rotating Hele-Shaw cells. However, only a few of them consider the influence of Coriolis forces. The studies... more
A growing number of experimental and theoretical works have been addressing various aspects of the viscous fingering formation in rotating Hele-Shaw cells. However, only a few of them consider the influence of Coriolis forces. The studies including Coriolis effects are mostly restricted to the high-viscosity-contrast limit and rely on either purely linear stability analyses or intensive numerical simulations. We approach the problem analytically and use a modified Darcy's law including the exact form of the Coriolis effects to execute a mode-coupling analysis of the system. By imposing no restrictions on the viscosity contrast A (dimensionless viscosity difference) we go beyond linear stages and examine the onset of nonlinearities. Our results indicate that when Coriolis effects are taken into account, an interesting interplay between the Reynolds number Re and A arises. This leads to important changes in the stability and morphological features of the emerging interfacial patterns. We contrast our mode-coupling approach with previous theoretical models proposed in the literature.
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We investigate a quasi-two-dimensional system composed of an initially circular ferrofluid droplet surrounded by a nonmagnetic fluid of higher density. These immiscible fluids flow in a rotating Hele-Shaw cell, under the influence of an... more
We investigate a quasi-two-dimensional system composed of an initially circular ferrofluid droplet surrounded by a nonmagnetic fluid of higher density. These immiscible fluids flow in a rotating Hele-Shaw cell, under the influence of an in-plane radial magnetic field. We focus on the situation in which destabilizing bulk magnetic field effects are balanced by stabilizing centrifugal forces. In this framing, we consider the interplay of capillary and magnetic normal traction effects in determining the fluid-fluid interface morphology. By employing a vortex-sheet formalism, we have been able to find a family of exact stationary N-fold polygonal shape solutions for the interface. A weakly nonlinear theory is then used to verify that such exact interfacial solutions are in fact stable.
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4-Alkynyl-1,2,3-triazolium cations undergo thermal [3 + 2] cycloaddition reactions with azides roughly 50- to 100-fold faster than comparable noncharged alkynes. Further, the reaction is highly 1,4-regioselective (dr up to 99:1) owing to... more
4-Alkynyl-1,2,3-triazolium cations undergo thermal [3 + 2] cycloaddition reactions with azides roughly 50- to 100-fold faster than comparable noncharged alkynes. Further, the reaction is highly 1,4-regioselective (dr up to 99:1) owing to the selective stabilization of 1,4-TS transition states via conjugative π-acceptor assistance of the alkyne triazolium ring. The novel cationic triazolium alkynes also accelerate the CuAAC reaction to provide bis(1,2,3-triazoles) in an "ultrafast" way (<5 min).
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When a ferrofluid is trapped in a Hele-Shaw cell and subjected to a perpendicular magnetic field, a fingering instability results in the droplet evolving into a complex branched structure. We report here on some preliminary results of a... more
When a ferrofluid is trapped in a Hele-Shaw cell and subjected to a perpendicular magnetic field, a fingering instability results in the droplet evolving into a complex branched structure. We report here on some preliminary results of a study in which perpendicular and azimuthal magnetic fields are applied simultaneously. The azimuthal field acts as a stabilizing influence and thus allows some control over the fingering instability. A linear stability analysis shows that the field strengths can be manipulated to allow any single mode to be unstable while all others are stable. This is confirmed through numerical simulations that demonstrate the ability to ``pick out'' a particular mode for growth.
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It is well known that the constant injection rate flow in radial Hele-Shaw cells leads to the formation of highly branched patterns, where finger tip-splitting events are plentiful. Different kinds of patterns arise in the lifting... more
It is well known that the constant injection rate flow in radial Hele-Shaw cells leads to the formation of highly branched patterns, where finger tip-splitting events are plentiful. Different kinds of patterns arise in the lifting Hele-Shaw flow problem, where the cell's gap width grows linearly with time. In this case, the morphology of the emerging structures is characterized by the strong competition among inward moving fingers. By employing a mode-coupling theory we find that both finger tip-splitting and finger competition can be restrained by properly adjusting the injection rate and the time-dependent gap width, respectively. Our theoretical model approaches the problem analytically and is capable of capturing these important controlling mechanisms already at weakly nonlinear stages of the dynamics.
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ABSTRACT
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The use of medicated feed is a common practice in animal food production to improve animal health. Tetracyclines and β-Lactams are the groups that are most frequently added to this type of feed. The measurement of the concentration of the... more
The use of medicated feed is a common practice in animal food production to improve animal health. Tetracyclines and β-Lactams are the groups that are most frequently added to this type of feed. The measurement of the concentration of the analytes in these types of samples is sometimes due to the matrix characteristic, and manufacturers are demanding fast, precise and reproducible methods. A rapid confirmatory method based on a simple extraction protocol using acidified methanol and followed by high performance liquid chromatography coupled to a tandem mass spectrometer for the quantification of four tetracyclines in feed is presented. Validation was performed following the guidelines of Decision 2002/657/EC. Results indicated that the four tetracyclines can be identified and quantified in a concentration range between 50 and 500 mg/kg with recoveries between 84% and 109% and RSD for precision under reproducible conditions between 12% and 16%. Satisfactory results were also obtained with interlaboratory studies and by comparing the method with an HPLC-Fluorescent method.
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... While previous reports have described the advantages of the application of slurry ice systems to farmed sea bream (Huidobro, Mendes, & Nunes, 2001) and turbot (Rodrı´guez, Barros-Velázquez, Piñeiro, Gallardo,... more
... While previous reports have described the advantages of the application of slurry ice systems to farmed sea bream (Huidobro, Mendes, & Nunes, 2001) and turbot (Rodrı´guez, Barros-Velázquez, Piñeiro, Gallardo, & Aubourg, 2006) and to wild albacore (Price, Melvin, & ...
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The interfacial morphologies of an extremely thin layer of ferrofluid droplet under a constant perpendicular magnetic field are investigated. Striking patterns consisting of numerous sub-scale droplets that develop from Rosensweig... more
The interfacial morphologies of an extremely thin layer of ferrofluid droplet under a constant perpendicular magnetic field are investigated. Striking patterns consisting of numerous sub-scale droplets that develop from Rosensweig instability are observed. For a dry plate the breaking pattern of sub-scale droplets can be characterized by a dimensionless magnetic Bond number, Bom. In general, a more pronounced instability, which
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A modified version of the usual viscous fingering problem in a radial Hele-Shaw cell with immiscible fluids is studied by intensive numerical simulations. We consider the situation in which the fluids involved are miscible, so that the... more
A modified version of the usual viscous fingering problem in a radial Hele-Shaw cell with immiscible fluids is studied by intensive numerical simulations. We consider the situation in which the fluids involved are miscible, so that the diffusing interface separating them can be driven unstable through the injection or suction of the inner fluid. The system is allowed to rotate in such a way that centrifugal and Coriolis forces come into play, imposing important changes on the morphology of the arising patterns. In order to bridge from miscible to immiscible pattern forming structures, we add the surface tensionlike effects due to Korteweg stresses. Our numerical experiments reveal a variety of interesting fingering behaviors, which depend on the interplay between injection (or suction), diffusive, rotational, and Korteweg stress effects. Whenever possible the features of the simulated miscible fronts are contrasted to existing experiments and other theoretical or numerical studies, usually resulting in close agreements. A number of additional complex morphologies, whose experimental realization is still not available, are predicted and discussed.
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ABSTRACT
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Social and sexual contact networks between men who have sex with men (MSM) play an important role in understanding the transmission of HIV and other sexually transmitted infections (STIs). In Salvador (Bahia State, Brazil), one of the... more
Social and sexual contact networks between men who have sex with men (MSM) play an important role in understanding the transmission of HIV and other sexually transmitted infections (STIs). In Salvador (Bahia State, Brazil), one of the cities in the survey Behavior, Attitudes, Practices, and Prevalence of HIV and Syphilis among Men Who Have Sex with Men in 10 Brazilian Cities, data were collected in 2008/2009 from a sample of 383 MSM using Respondent Driven Sampling (RDS). Network analysis was used to study friendship networks and sexual partner networks. The study also focused on the association between the number of links (degree) and the number of sexual partners, in addition to socio-demographic characteristics. The networks’ structure potentially facilitates HIV transmission. However, the same networks can also be used to spread messages on STI/HIV prevention, since the proximity and similarity of MSM in these networks can encourage behavior change and positive attitudes towards...
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Unsymmetrically... more
Unsymmetrically 1,1'-disubstituted 4,4'-bis-1H-1,2,3-triazoles 4 have been prepared from 4-ethynyl-1,2,3-triazoles 5 and azides. Following a "double-click" strategy, two complementary approaches were implemented for the preparation of the key 4-ethynyltriazole intermediates 5: (a) the stepwise Swern oxidation/Ohira-Bestman alkynylation of readily available 4-hydroxymethyl-1,2,3-triazoles 8 and (b) the stepwise cycloaddition of TMS-1,4-butadiyne 9. The method is highlighted by its compatibility with orthogonally protected and functionalized saccharide-peptide hybrids and its ability to be extended to the trisubstituted counterparts 12.
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During the dry season, the quantity and quality of pastures decrease causing low milk production. Corn silage is a good alternative to feed the herd during this time due to its high energy content and fiber quality. Also, besides the high... more
During the dry season, the quantity and quality of pastures decrease causing low milk production. Corn silage is a good alternative to feed the herd during this time due to its high energy content and fiber quality. Also, besides the high productivity of corn, it goes easily through fermentation, is well appreciated by animals and has high digestibility. Although nutritive
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Little information is currently available about the content of different elements in wheat samples from the Republic of Kazakhstan. The concentrations of toxic (As, Cd, Cr, Hg, Pb, and U) and essential (Co, Cu, Fe, Mn, Ni, Se, and Zn)... more
Little information is currently available about the content of different elements in wheat samples from the Republic of Kazakhstan. The concentrations of toxic (As, Cd, Cr, Hg, Pb, and U) and essential (Co, Cu, Fe, Mn, Ni, Se, and Zn) elements in 117 sampled wheat grains from the Republic of Kazakhstan were measured. The results indicated that the mean and maximum concentrations of most investigated elements (As, Cd, Co, Cr, Mn, Se, Pb, and U) were higher in samples collected from southern Kazakhstan. The mean and maximum concentrations of toxic elements such as As, Cd, Hg, and Pb did not exceed levels specified by European, FAO, or Kazakh legislation, although the hazard quotient (HQ) values for Co, Cu, Mn, and Zn were higher than 1 and the hazard index (HI) was higher than 1 for samples collected from all areas of Kazakhstan. This indicates that there should be concern about the potential hazards of the combination of toxic elements in Kazakh wheat.
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Mixing at low Reynolds numbers, especially in the framework of confined flows occurring in Hele-Shaw cells, porous media, and microfluidic devices, has attracted considerable attention lately. Under such circumstances, enhanced mixing is... more
Mixing at low Reynolds numbers, especially in the framework of confined flows occurring in Hele-Shaw cells, porous media, and microfluidic devices, has attracted considerable attention lately. Under such circumstances, enhanced mixing is limited due to the lack of turbulence, and absence of sizable inertial effects. Recent studies, performed in rectangular Hele-Shaw cells, have demonstrated that the combined action of viscous fluid fingering and alternating injection can dramatically improve mixing efficiency. In this work, we revisit this important fluid mechanical problem, and analyze it in the context of radial Hele-Shaw flows. The development of radial fingering instabilities under alternating injection conditions is investigated by intensive numerical simulations. We focus on the impact of the relevant physical parameters of the problem (Péclet number Pe, viscosity contrast A, and injection time interval Δt) on fluid mixing performance.
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A central topic in Hele-Shaw flow research is the inclusion of physical effects on the interface between fluids. In this context, the addition of surface tension restrains the emergence of high interfacial curvatures, while consideration... more
A central topic in Hele-Shaw flow research is the inclusion of physical effects on the interface between fluids. In this context, the addition of surface tension restrains the emergence of high interfacial curvatures, while consideration of kinetic undercooling effects inhibits the occurrence of high interfacial velocities. By connecting kinetic undercooling to the action of the dynamic contact angle, we show in a quantitative manner that the kinetic undercooling contribution varies as a linear function of the normal velocity at the interface. A perturbative weakly nonlinear analysis is employed to extract valuable information about the influence of kinetic undercooling on the shape of the emerging fingered structures. Under radial Hele-Shaw flow, it is found that kinetic undercooling delays, but does not suppress, the development of finger tip-broadening and finger tip-splitting phenomena. In addition, our results indicate that kinetic undercooling plays a key role in determining t...
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The specific surface area is an attribute known to characterize the soil ability to retain and transport nutrients and water. A number of studies have shown that specific surface area correlates cation exchange capacity, organic matter... more
The specific surface area is an attribute known to characterize the soil ability to retain and transport nutrients and water. A number of studies have shown that specific surface area correlates cation exchange capacity, organic matter content, water retention, aggregate stability and clay swelling. In the past fractal theory has been widely used to study different gas adsorption isotherms like
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Despite their practical and academic relevance, studies of interfacial pattern formation in confined magnetorheological (MR) fluids have been largely overlooked in the literature. In this work, we present a contribution to this soft... more
Despite their practical and academic relevance, studies of interfacial pattern formation in confined magnetorheological (MR) fluids have been largely overlooked in the literature. In this work, we present a contribution to this soft matter research topic and investigate the emergence of interfacial instabilities when an inviscid, initially circular bubble of a Newtonian fluid is surrounded by a MR fluid in a Hele-Shaw cell apparatus. An externally applied, in-plane azimuthal magnetic field produced by a current-carrying wire induces interfacial disturbances at the two-fluid interface, and pattern-forming structures arise. Linear stability analysis, weakly nonlinear theory, and a vortex sheet approach are used to access early linear and intermediate nonlinear time regimes, as well as to determine stationary interfacial shapes at fully nonlinear stages.
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ABSTRACT The present study provides a first approach on the employment of an icing medium including Fucus spiralis, an alga exhibiting antimicrobial and antioxidant activities, for the preservation of fish quality during chilled storage.... more
ABSTRACT The present study provides a first approach on the employment of an icing medium including Fucus spiralis, an alga exhibiting antimicrobial and antioxidant activities, for the preservation of fish quality during chilled storage. For it, two different concentrations of a F. spiralis extract (0.67 and 2.50 g lyophilized alga L-1 aqueous solution; F-1 and F-2 batches, respectively) were tested as icing medium for the chilled storage of megrim (Lepidorhombus whiffiagonis) for 14 days. The effects of the alga were compared with a counterpart batch stored in traditional ice prepared only from water (F-0 batch). A significant (p<0.05) inhibition of microbial activity (aerobes, psychrotrophs, proteolytic bacteria, lipolytic bacteria; pH and trimethylamine formation) in F-1 batch and, especially in F-2 batch, was concluded. Concerning lipid oxidation development, a significantly (p<0.05) lower formation of interaction compounds (fluorescence assessment) in samples corresponding to the F-2 batch was also observed, proving the inhibitory effect of F. spiralis on the formation of tertiary lipid oxidation compounds in chilled megrim. The icing medium proposed in this study may open the way to the development of a natural biopreservation strategy for chilled seafood based on algae.