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Search Results: 1 - 10 of 12785 matches for " Marcelo Dapino "
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Magnetostrictive Actuation of a Bone Loading Composite for Accelerated Tissue Formation
Stephen Hart,Ryan Bucio,Marcelo Dapino
Smart Materials Research , 2012, DOI: 10.1155/2012/258638
Abstract: When bone is dynamically loaded it adapts its shape to better support the load. We have developed a magnetostrictive composite consisting of Terfenol-D particles encapsulated in an epoxy resin that changes length when exposed to magnetic fields. When bonded to the surface of a porcine tibia ex vitro, the composite produces surface strains greater than 900?με at a frequency of 30?Hz and magnetic field of 170?kA/m. This is more than sufficient strain magnitude and frequency to promote cortical bone growth in both rats and turkeys and to maintain cortical bone structure in humans. Key advantages of the composite over conventional electromechanical or thermomechanical actuators are its simplicity, compact size, and remote actuation. A mathematical model describing the strains and stresses in the bone is presented. 1. Introduction Bone structure continuously evolves by building new bone and resorbing old bone [1]. The dynamic property of bone remodeling allows bone tissue to adapt to changes in its loading environment [2]. Although the exact mechanism explaining bone remodeling remains elusive, interstitial fluid flow around a particular subset of bone cells called osteocytes is thought to be essential [3]. Eccentric loading of a long bone creates a bending moment and causes the bone to curve. This creates a region of tension on one side of the bone and a region of compression on the opposite side. As the load is cycled, interstitial fluid flows around osteocytes from regions of compression to regions of tension resulting in shear stress on the cell walls. Shear stress is thought to incite a molecular cascade resulting in new bone growth [4, 5]. In humans, strains below 200?με do not stimulate cortical bone remodeling [6]. Strain values between 200 and 2000?με represent physiological levels of strain on the human skeleton. Above 2000?με, the rate of bone formation exceeds the rate of bone resorption, and growth is observed [7]. Studies involving turkeys have shown that a 30?Hz, 100?με signal is sufficient to maintain bone mass [8], and studies involving rats have shown that a 2?Hz, 930?με signal is sufficient to produce bone growth [9]. Along with strain magnitude, the strain rate plays an important role in new bone formation [10]. Based on a compilation of previous studies where animal bones were subjected to mechanical loads in vivo, Turner [11] and Burr et al. [12] concluded that the strain rate and magnitude are related to the strain stimulus by where is the strain stimulus, is a proportionality constant, is the strain magnitude, and is the strain
Effect of heparin on in vitro capacitation of boar sperm
DAPINO,DORA G; MARINI,PATRICIA E; CABADA,MARCELO O;
Biological Research , 2006, DOI: 10.4067/S0716-97602006000500006
Abstract: chlortetracycline (ctc) fluorescent pattern, the ability to undergo acrosome reaction (ar) upon exposure to 10 μm calcium ionophore a23187 and vitality estimation were used to investigate the effect of the sulfated glycosaminoglycan heparin on the in vitro capacitation of porcine spermatozoa. sperm incubation in capacitating medium (cm) supplemented with 10 mm heparin for up to 120 min, showed an increase in the number of capacitated sperm (b pattern) and acrosome reacted sperm (ar pattern), without affecting their viability. in this condition, spermatozoa were incubated in cm depleted of albumin, calcium, bicarbonate or combinations, in the presence of heparin. in either calcium or bicarbonate-free media, capacitation was only basal and did not show variations in the presence of heparin. in absence of albumin the presence of calcium and bicarbonate stimulated capacitation, which was further increased by the addition of heparin. these results suggest that heparin enhances in vitro capacitation of porcine sperm only under capacitating conditions. additionally, when sperm were incubated with 100 μg/ml biotinylated heparin in the presence or absence of unlabeled heparin, we observed that heparin binding sites were located mostly on the acrosomal region of boar sperm in an specific and saturable manner. the in vitro effect of heparin described in this work indicates that sulfated glycosaminoglycans, which are normally present in the female reproductive tract, might play an important role in the fertilization process in porcines.
Effect of heparin on in vitro capacitation of boar sperm
DORA G DAPINO,PATRICIA E MARINI,MARCELO O CABADA
Biological Research , 2006,
Abstract: Chlortetracycline (CTC) fluorescent pattern, the ability to undergo acrosome reaction (AR) upon exposure to 10 μM calcium ionophore A23187 and vitality estimation were used to investigate the effect of the sulfated glycosaminoglycan heparin on the in vitro capacitation of porcine spermatozoa. Sperm incubation in capacitating medium (CM) supplemented with 10 mM heparin for up to 120 min, showed an increase in the number of capacitated sperm (B pattern) and acrosome reacted sperm (AR pattern), without affecting their viability. In this condition, spermatozoa were incubated in CM depleted of albumin, calcium, bicarbonate or combinations, in the presence of heparin. In either calcium or bicarbonate-free media, capacitation was only basal and did not show variations in the presence of heparin. In absence of albumin the presence of calcium and bicarbonate stimulated capacitation, which was further increased by the addition of heparin. These results suggest that heparin enhances in vitro capacitation of porcine sperm only under capacitating conditions. Additionally, when sperm were incubated with 100 μg/ml biotinylated heparin in the presence or absence of unlabeled heparin, we observed that heparin binding sites were located mostly on the acrosomal region of boar sperm in an specific and saturable manner. The in vitro effect of heparin described in this work indicates that sulfated glycosaminoglycans, which are normally present in the female reproductive tract, might play an important role in the fertilization process in porcines.
Porcine oviduct sperm binding glycoprotein and its deleterious effect on sperm: a mechanism for negative selection of sperm?
Teijeiro,Juan M; Dapino,Dora G; Marini,Patricia E;
Biological Research , 2011, DOI: 10.4067/S0716-97602011000400003
Abstract: in their journey through the oviduct some subpopulations of sperm are preserved in a reservoir, while others are negatively selected. sperm binding glycoprotein (sbg) is a pig oviductal epithelial cell glycoprotein that produces, under capacitating conditions, acrosome alteration, p97 tyrosine-phosphorylation and reduction of the motility of sperm. in this paper, we show that sbg is accessible at the extracellular surface of the oviductal epithelial cells, supporting a sperm interaction biological role in situ. we analyze the possible dependence of the tyrosine-phosphorylation of p97 on the pka mechanism, finding that apparently it is not pka dependent. also, after sbg treatment the phosphorylated proteins locate mainly at the detached periacrosomal region and at the tail of sperm; the latter may be related to sbg's motility reduction effect. the study of the time course effect of sbg on sperm as detected by chlortetracycline (ctc) staining and of its binding to sperm by immunodetection in conjunction with ctc, shows results in agreement with the hypothesis that this glycoprotein is involved in the alteration of acrosomes in a specific sperm subpopulation. the results suggest that sbg may be part of a mechanism for negative selection of sperm.
Porcine oviduct sperm binding glycoprotein and its deleterious effect on sperm: a mechanism for negative selection of sperm?
Juan M Teijeiro,Dora G Dapino,Patricia E Marini
Biological Research , 2011,
Abstract: In their journey through the oviduct some subpopulations of sperm are preserved in a reservoir, while others are negatively selected. Sperm binding glycoprotein (SBG) is a pig oviductal epithelial cell glycoprotein that produces, under capacitating conditions, acrosome alteration, p97 tyrosine-phosphorylation and reduction of the motility of sperm. In this paper, we show that SBG is accessible at the extracellular surface of the oviductal epithelial cells, supporting a sperm interaction biological role in situ. We analyze the possible dependence of the tyrosine-phosphorylation of p97 on the PKA mechanism, finding that apparently it is not PKA dependent. Also, after SBG treatment the phosphorylated proteins locate mainly at the detached periacrosomal region and at the tail of sperm; the latter may be related to SBG's motility reduction effect. The study of the time course effect of SBG on sperm as detected by chlortetracycline (CTC) staining and of its binding to sperm by immunodetection in conjunction with CTC, shows results in agreement with the hypothesis that this glycoprotein is involved in the alteration of acrosomes in a specific sperm subpopulation. The results suggest that SBG may be part of a mechanism for negative selection of sperm.
Clinical Psychophysical Assessment of the ON- and OFF-Systems of the Magnocellular and Parvocellular Visual Pathways  [PDF]
Marcelo Fernandes Costa
Neuroscience & Medicine (NM) , 2011, DOI: 10.4236/nm.2011.24043
Abstract: We developed a psychophysical paradigm for the clinical assessment of the contrast sensitivity (CS) mediated by the ON- and OFF-systems of the Magnocellular and Parvocellular pathways. We designed a stimulus considering two dimensions: two spatial frequencies (0.5 and 4.5 cpd) and two temporal rates of flicker (33 ms and 1500 ms). To evidence the ON- and OFF responses, the CS was measured for two polarities of light with luminance changes of 0.6 dB steps above and below the medium luminance grey background. We tested 38 healthy volunteers. The results shows that Magnocellular contrast sensitivity was higher than Parvocellular for the 33 ms flickering stimulus and the Parvocellular contrast sensitivity was higher than Magnocellular for 1500 ms stimuli. The reliability of the test was checked and confirmed. We concluded that the test performs a rapid measurement of the CS mediated by the ON and OFF systems of Magnocellular and Parvocellular pathways. It is useful in clinical protocols due to its high sensitivity and good reliability.
Heat Flow as Origin of Dark Energy  [PDF]
Marcelo Samuel Berman
Journal of Modern Physics (JMP) , 2013, DOI: 10.4236/jmp.2013.410175
Abstract:

We first introduce entropy according to University Physics textbooks, then, briefly discuss it, and then we prove by a general relativistic derivation that the Universe has entropy growth, like a white-hole, that it is R2-dependent, and that dark energy, represented by a cosmological constant, is caused by heat flow, and provides for entropy growth.

Titanium Oxide Nanorods pH Sensors: Comparison between Voltammetry and Extended Gate Field Effect Transistor Measurements  [PDF]
Elidia Maria Guerra, Marcelo Mulato
Materials Sciences and Applications (MSA) , 2014, DOI: 10.4236/msa.2014.57049
Abstract:
In recent years there has increased interest in the characterization of titanium oxide nanorods for application in analytical devices. The titanium oxide nanorods (NRTiO) were obtained by hydrothermal reaction with a NaOH solution heated in the autoclave at 150°C for up to 50 h. Experimental data indicate that the prepared nanorods consist of anatase and rutile phases, with a possible interlayer structure. The NRTiO was investigated as pH sensor in the pH range 2 - 12, and the extended gate field effect transistor (EGFET) configuration presented a sensitivity of 49.6 mV/pH. Voltammetric data showed a sensitivity of 47.8 mV/pH. These results indicate that the material is a promising candidate for applications as an EGFET-pH sensor and as a disposable biosensor in the future.
Positive solutions of higher order quasilinear elliptic equations
Marcelo Montenegro
Abstract and Applied Analysis , 2002, DOI: 10.1155/s1085337502204030
Abstract: The higher order quasilinear elliptic equation −Δ(Δp(Δu))=f(x,u) subject to Dirichlet boundaryconditions may have unique and regular positive solution. If thedomain is a ball, we obtain a priori estimate to the radialsolutions via blowup. Extensions to systems and general domainsare also presented. The basic ingredients are the maximumprinciple, Moser iterative scheme, an eigenvalue problem, apriori estimates by rescalings, sub/supersolutions, andKrasnosel'skiĭ fixed point theorem.
Producir para el agro en un entorno turbulento: El caso de una fábrica de cosechadoras en la Argentina
Rougier,Marcelo;
Mundo agrario , 2007,
Abstract: the production of rural machines in argentina has its beginning very early, stimulated by the great opportunities that gave the cereal production. a remarkable trait of this sector is the tradition of technological innovation encouraged without any doubt by the specific nature of the agricultural production in our country and the high cost of the imported machinery. this tradition of innovation and the land tapestry will be the key to understand the development of a firm of harvest machines in the south of santa fe since the fifties. we can identify four moments in roque vassalli s.a.'s trajectory, each one is presented in this work in a chronological order that emphasises some aspect of the enterprises dynamic that explains the productive development and the financial-economic evolution of the firm in that period. on a first moment we will see the innovative disposition of the founder partner, his relationship with the public policies to promote the sector and the strong will to create a web of distributors; these are the key factors to the consolidation of this enterprise in the internal market. instead, in a second place we emphasize the problems that it had in the agricultural machinery commerce on the second half of the seventies that ended up affecting its productive and financial situation. on the third part this work focalises on the variables that let us explain the recovery of the enterprise, mainly in the important dynamic of the internal market but also in the commercialization strategies and the capture of the wide external markets. finally, the analysis on the fourth part remarks the thin limits that had the macroeconomic conjuncture over the entrepreneur negotiation, which ended up with the selling of the firm.
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