Técnicas de caracterização para investigar interações no nível molecular em filmes de Langmuir e Langmuir-Blodgett (LB)

This paper discusses fundamental concepts for the characterization of Langmuir monolayers and Langmuir-Blodgett (LB) films, with emphasis on investigations of material properties at the molecular level. By way of illustration, results for phospholipid monolayers interacting with the drug dipyridamole are highlighted. These results were obtained with several techniques, including in situ grazing incidence X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, fluorescence microscopy, in addition to surface pressure and surface potential isotherms. Also mentioned are the difficulties in producing Langmuir and LB films from macromolecules, and how molecular-level interactions in mixed polymer LB films can be exploited in sensors.

Allelic Diversity at the Merozoite Surface Protein-1 (MSP-1) Locus in Natural Plasmodium falciparum Populations: a Brief Overview

The merozoite surface protein-1 (MSP-1) locus of Plasmodium falciparum codes for a major asexual blood-stage antigen currently proposed as a major malaria vaccine candidate. The protein, however, shows extensive polymorphism, which may compromise its use in sub-unit vaccines. Here we compare the patterns of allelic diversity at the MSP-1 locus in wild isolates from three epidemiologically distinct malaria-endemic areas: the hypoendemic southwestern Brazilian Amazon (n = 54), the mesoendemic southern Vietnam (n = 238) and the holoendemic northern Tanzania (n = 79). Fragments of the variable blocks 2, 4a, 4b and 6 or 10 of this single-copy gene were amplified by the polymerase chain reaction, and 24 MSP-1 gene types were defined as unique combinations of allelic types in each variable block. Ten different MSP-1 types were identified in Brazil, 23 in Vietnam and 13 in Tanzania. The proportion of genetically mixed infections (isolates with parasites carrying more than one MSP-1 version) ranged from 39% in Brazil to 44% in Vietnam and 60% in Tanzania. The vast majority (90%) of the typed parasite populations from Brazil and Tanzania belonged to the same seven most frequent MSP-1 gene types. In contrast, these seven gene types corresponded to only 61% of the typed parasite populations from Vietnam. Non-random associations were found between allelic types in blocks 4a and 6 among Vietnamese isolates, the same pattern being observed in independent studies performed in 1994, 1995 and 1996. These results suggest that MSP-1 is under selective pressure in the local parasite population. Nevertheless, the finding that similar MSP-1 type frequencies were found in 1994 and 1996 argues against the prominence of short-term frequency-dependent immune selection of MSP-1 polymorphisms. Non-random associations between MSP-1 allelic types, however, were not detected among isolates from Brazil and Tanzania. A preliminary analysis of the distribution of MSP-1 gene types per host among isolates from Tanzania, but not among those from Brazil and Vietnam, shows significant deviation from that expected under the null hypothesis of independent distribution of parasites carrying different gene types in the human hosts. Some epidemiological consequences of these findings are discussed

Energetic efficiency of an agricultural tractor in function of tire inflation pressure

The tire inflation pressure, among other factors, determines the efficiency in which a tractor can exert traction. It was studied the effect of using two tire inflation pressures, 110.4 kPa in the front and rear wheels, 124.2 kPa in the front wheel and 138 kPa in the rear wheels, the energetic efficiency of an agricultural tractor of 147 kW of engine power, in the displacement speed of 6.0 km.h-1, on track with firm surface, with the tractor engine speed of 2000 rpm. For each condition of the tire pressure, the tested tractor was subjected to constant forces in the drawbar of 45 kN and 50 kN, covering 30 meters. It was used a randomized complete block with a 2x2 factorial arrangement (tire pressure and drawbar power) with four replications, totaling 16 experimental units. Data were subjected to analysis of variance, using the Tukey test at 5% probability for comparison averages. The lowest hourly and specific fuel consumption, the lowest slippage of the wheelsets and the highest efficiency in the drawbar was obtained with the tire inflation pressure of 110.4 kPa in the front and rear tires of the tractor, highlighting that lower pressures improve energetic and operational performance of the tractor.

Backpressure effects on the flow-pressure relation of driplines

ABSTRACT For drip irrigation design and management, it is necessary to know the relation between flow and pressure acting on emitters. In the case of subsurface drip irrigation, the backpressure phenomenon may change the hydraulic characteristics of emitters. Thus, this study aimed at determining such relationship between flow and pressure of different driplines in surface and subsurface conditions; aiming to find possible differences in hydraulic behavior. We tested four emitter types; two pressure compensating (D5000 and Hydro PCND) and two non-pressure compensating (TalDrip and Jardiline). Emitter flow rates were attained in atmospheric conditions and submerged in water, in which submergence levels represented backpressure. Assays were performed using inlet pressures of 80, 100, 120, and 150 kPa for the Hydro PCND dripline and 25, 50, 100, and 150 kPa for the other ones; the backpressures were of 0.49, 1.47, 2.45, 4.41 and 6.37 kPa with four replications. The emitters had their proportionality constants and discharge exponents changed in submerged applications, representing backpressure effect. Non-pressure compensating emitters had their discharge exponent decreased, while in pressure compensating ones, it was increased. Backpressure reduced emitter flow rates at all evaluated pressures.

Turbulent heat transfer and pressure drop in pinned annular regions

Experiments were performed to determine average heat transfer coefficients and friction factors for turbulent flow through annular ducts with pin fins. The measurements were carried out by means of a double-pipe heat exchanger. The total number of pins attached to the inner wall of the annular region was 560. The working fluids were air, flowing in the annular channel, and water through the inner circular tube. The average heat transfer coefficients of the pinned air-side were obtained from the experimental determination of the overall heat transfer coefficients of the heat exchanger and from the knowledge of the average heat transfer coefficients of the circular pipe (water-side), which could be found in the pertinent literature. To attain fully developed conditions, the heat exchanger was built with additional lengths before and after the test section. The inner circular duct of the heat exchanger and the pin fins were made of brass. Due to the high thermal conductivity of the brass, the small tube thickness and water temperature variation, the surface of the internal tube was practically isothermal. The external tube was made of an industrial plastic which was insulated from the environment by means of a glass wool batt. In this manner, the outer surface of the annular channel can be considered adiabatic. The results are presented in dimensionless forms, in terms of average Nusselt numbers and friction factors as functions of the flow Reynolds number, ranging from 13,000 to 80,000. The pin fin efficiency, which depends on the heat transfer coefficient, is also determined as a function of dimensionless parameters. A comparison of the present results with those for smooth sections (without pins) is also presented. The purpose of such a comparison is to study the influence of the presence of the pins on the pressure drop and heat transfer rate.

Surface Tension Implementation for Gensmac2d

In the present work we describe a method which allows the incorporation of surface tension into the GENSMAC2D code. This is achieved on two scales. First on the scale of a cell, the surface tension effects are incorporated into the free surface boundary conditions through the computation of the capillary pressure. The required curvature is estimated by fitting a least square circle to the free surface using the tracking particles in the cell and in its close neighbors. On a sub-cell scale, short wavelength perturbations are filtered out using a local 4-point stencil which is mass conservative. An efficient implementation is obtained through a dual representation of the cell data, using both a matrix representation, for ease at identifying neighbouring cells, and also a tree data structure, which permits the representation of specific groups of cells with additional information pertaining to that group. The resulting code is shown to be robust, and to produce accurate results when compared with exact solutions of selected fluid dynamic problems involving surface tension.

Respiratory effects of kynurenic acid microinjected into the ventromedullary surface of the rat

Several studies demonstrate that, within the ventral medullary surface (VMS), excitatory amino acids are necessary components of the neural circuits involved in the tonic and reflex control of respiration and circulation. In the present study we investigated the cardiorespiratory effects of unilateral microinjections of the broad spectrum glutamate antagonist kynurenic acid (2 nmol/200 nl) along the VMS of urethane-anesthetized rats. Within the VMS only one region was responsive to this drug. This area includes most of the intermediate respiratory area, partially overlapping the rostral ventrolateral medulla (IA/RVL). When microinjected into the IA/RVL, kynurenic acid produced a respiratory depression, without changes in mean arterial pressure or heart rate. The respiratory depression observed was characterized by a decrease in ventilation, tidal volume and mean inspiratory flow and an increase in respiratory frequency. Therefore, the observed respiratory depression was entirely due to a reduction in the inspiratory drive. Microinjections of vehicle (200 nl of saline) into this area produced no significant changes in breathing pattern, blood pressure or heart rate. Respiratory depression in response to the blockade of glutamatergic receptors inside the rostral VMS suggests that neurons at this site have an endogenous glutamatergic input controlling the respiratory cycle duration and the inspiratory drive transmission.

The effect of hydrostatic pressure on membrane-bound proteins

Many cellular proteins are bound to the surfaces of membranes and participate in various cell signaling responses. Interactions between this group of proteins are in part controlled by the membrane surface to which the proteins are bound. This review focuses on the effects of pressure on membrane-associated proteins. Initially, the effect of pressure on membrane surfaces and how pressure may perturb the membrane binding of proteins is discussed. Next, the effect of pressure on the activity and lateral association of proteins is considered. We then discuss how pressure can be used to gain insight into these types of proteins.