The objective was to study the flow pattern in a plate heat exchanger (PHE) through residence time distribution (RTD) experiments. The tested PHE had flat plates and it was part of a laboratory scale pasteurization unit. Series flow and parallel flow configurations were tested with a variable number of passes and channels per pass. Owing to the small scale of the equipment and the short residence times, it was necessary to take into account the influence of the tracer detection unit on the RID data. Four theoretical RID models were adjusted: combined, series combined, generalized convection and axial dispersion. The combined model provided the best fit and it was useful to quantify the active and dead space volumes of the PHE and their dependence on its configuration. Results suggest that the axial dispersion model would present good results for a larger number of passes because of the turbulence associated with the changes of pass. This type of study can be useful to compare the hydraulic performance of different plates or to provide data for the evaluation of heat-induced changes that occur in the processing of heat-sensitive products. (C) 2011 Elsevier Ltd. All rights reserved.; FAPESP (The State of Sao Paulo Research Foundation); CAPES (Coordination for the Improvement of Higher Education Personnel); AEP (Association of Polytechnic Engineers)
Os aspectos que envolvem a discussão acerca da diminuição da fome e da miséria em todo o mundo passam pelo entendimento de como se comportam os produtores de alimentos e, por consequência, da sua manutenção no campo. Em se tratando de produtores de alimentos, o entendimento de como se estruturam os canais de distribuição se faz importante à compreensão de como se organiza o poder econômico nessas configurações inter-organizacionais e, por conseguinte, as consequências sociais daí depreendidas. Considerando a cultura da maçã dentre as mais importantes produções de frutas in natura do estado do Rio Grande do Sul e das mais consumidas no Brasil e no mundo, vislumbrar essa estrutura do canal de distribuição e o modo como está estruturado e composto mostrou-se o desafio a ser vencido na pesquisa realizada. Para tanto, o uso e aplicação de métodos de pesquisa que passam desde questionários até entrevistas não-estruturadas permitiu, a partir de uma concepção inicial da estrutura de um canal de comercialização genérico, buscar um desenho e o entendimento das relações entre os players do canal de distribuição da maçã produzida no município de Vacaria (maior produtor gaúcho de maçã e entre os maiores do Brasil). Os resultados indicaram que as relações entre os membros do canal são estabelecidas uma a uma e foram se fortalecendo ao longo dos anos para aqueles players que conseguiram manter-se no mercado. A substituição e renovação daqueles que não conseguiram se manter fortes economicamente aparentaram ser efetivos...
The terminal nephron segment, the inner medullary collecting duct (IMCD), absorbs Na+ by an electrogenic process that involves the entry through an apical (luminal) membrane Na+ channel. To understand the nature of this Na+ channel, we employed the patch clamp technique on the apical membrane of primary cultures of rat IMCD cells grown on permeable supports. We found that all ion channels detected in the cell-attached configuration were highly selective for Na+ (Li+) over K+. The open/closed transitions showed slow kinetics, had a slope conductance of 6-11 pS, and were sensitive to amiloride and benzamil. Nonselective cation channels with a higher conductance (25-30 pS), known to be present in IMCD cells, were not detected in the cell-attached configuration, but were readily detected in excised patches. The highly selective channels had properties similar to the recently described rat epithelial Na+ channel complex, rENaC. We therefore asked whether rENaC mRNA was present in the IMCD. We detected mRNA for all three rENaC subunits in rat renal papilla and also in primary cultures of the IMCD. Either glucocorticoid hormone or mineralocorticoid hormone increased the amount of alpha-rENaC subunit mRNA but had no effect on the mRNA level of the beta-rENaC or gamma-rENaC subunits. From these data...
Plantago media L. and Plantago maritima L. differ in their strategy toward salt stress, a major difference being the uptake and distribution of ions. Patch clamp techniques were applied to root cell vacuoles to study the tonoplast channel characteristics. In both species the major channel found was a 60 to 70 picosiemens channel with a low ion selectivity. The conductance of this channel for Na+ was the same as for K+, PK+/PNa+ = 1, whereas the cation/anion selectivity (PK+/Pc1−) was about 5. Gating characteristics were voltage and calcium dependent. An additional smaller channel of 25 picosiemens was present in P. maritima. In the whole vacuole configuration, the summation of the single channel currents resulted in slowly activated inward currents (t½ = 1.2 second). Inwardly directed, ATP-dependent currents could be measured against a ΔpH gradient of 1.5 units over the tonoplast. This observation strongly indicated the physiological intactness of the used vacuoles. The open probability of the tonoplast channels dramatically decreased when plants were grown on NaCl, although single channel conductance and selectivity were not altered.
1. Single-channel studies were performed to clarify how tonic changes in intracellular Ca2+ concentrations ([Ca2+]i) modulate cardiac L-type Ca2+ channels. Currents were recorded from fura-2-loaded guinea-pig ventricular myocytes in the cell-attached configuration. Fura-2 fluorescence signals were recorded simultaneously during pulses to elicit channel activity. 2. The myocyte [Ca2+]i was altered through changes in bath Ca2+ concentration during K+ depolarization. When [Ca2+]i exceeded approximately 2 times the resting level (estimated [Ca2+]i around 180-400 nM), the activity of Ca2+ channels was reversibly potentiated without changes in unitary current amplitudes. 3. Increased channel open probability during Ca(2+)-dependent potentiation resulted from increased availability and increased open probability during non-blank sweeps. Closed time analysis revealed a distribution best fitted with two exponentials. Increased [Ca2+]i reduced the longer time constant, but had no effect on the shorter time constant. The open time constant was unchanged in most cases. Current records occasionally included sweeps with long openings (approximately 10 ms or more), whose appearance increased during potentiation. 4. When [Ca2+]i was increased after cAMP-dependent upregulation of Ca2+ channels...
1. The rat brain type IIA Na+ channel alpha-subunit was stably expressed in Chinese hamster ovary (CHO) cells. Current through the expressed Na+ channels was studied using the whole-cell configuration of the patch clamp technique. The transient Na+ current was sensitive to TTX and showed a bell-shaped peak current vs. membrane potential relation. 2. Na+ current inactivation was better described by the sum of two exponentials in the potential range -30 to + 40 mV, with a dominating fast component and a small slower component. 3. The steady-state inactivation, h infinity, was related to potential by a Boltzmann distribution, underlying three states of the inactivation gate. 4. Recovery of the channels from inactivation at different potentials in the range -70 to -120 mV were characterized by an initial delay which decreased with hyperpolarization. The time course was well fitted by the sum of two exponentials. In this case the slower exponential was the major component, and both time constants decreased with hyperpolarization. 5. For a working description of the Na+ channel inactivation in this preparation, with a minimal deviation from the Hodgkin-Huxley model, a three-state scheme of the form O<-->I1<-->I2 was proposed, replacing the original two-state scheme of the Hodgkin-Huxley model...
1. A voltage-independent K+ channel was characterized and effects of muscarine were studied in cultured bullfrog sympathetic ganglion cells using the cell-attached patch-clamp configuration. 2. Three types of single-channel current were recorded from 2- to 10-day-old cultured cells in the presence of tetraethylammonium (2-20 mM), tetrodotoxin (1-2 microM), Cd2+ (0.1 mM) and apamin (20 nM). 3. The most frequently observed channel was a voltage-independent K+ channel which was open at the resting membrane potential and had a conductance of 52.6, 78.9 and 114.9 pS at a [K+]o of 2, 40 and 100 mM, respectively. This channel was designated background K+ channel. 4. Two other channel types were observed less frequently. One had a conductance of 26 pS (external K+, 118 mM) and a long open time of several seconds at the resting membrane potential. The second channel had a smaller conductance (20 pS) and displayed a voltage-dependent activation. 5. The open probability of the background K+ channel varied between patches, ranging from 0.0005 to 0.486. The open time distribution was fitted by a single exponential with a time constant of 0.51 ms. Both of these parameters were independent of the membrane potential. The closed time distribution consisted of at least four exponentials having time constants of 0.17...
1. A patch of plasma membrane was excised, in the inside-out configuration, from the outer segment tip of a catfish cone and recorded electrically with a patch pipette. A solution of 118 mM-NaCl was present on both sides of the membrane. 2. With the solution outside the pipette containing a low concentration (typically several micromoles per litre) of cyclic GMP and the membrane potential held at a non-zero level, brief steps of current indicative of the openings of single ion channels could be detected. There was no sign of desensitization to the ligand over a period of tens of seconds. 3. The prominent openings were associated with a conductance near 50 pS and an open-time constant of 0.5 ms or less. There was also an indication of sub-state openings. 4. The conductance of the large openings appeared to be invariant between -50 mV and +50 mV. However, the macroscopic current-voltage relation measured at a saturating concentration of cyclic GMP showed a slight upward curvature, which we attribute to a voltage dependence in the open probability of the fully liganded channel. 5. The relation between mean current and cyclic GMP concentration had an average Hill coefficient of about 2.4. The Hill coefficient was not affected by membrane voltage...
1. The kinetic properties of T-type Ca2+ channels were examined in single ventricular cells from guinea-pig hearts using the cell-attached configuration of the patch-clamp technique. 2. T-type Ca2+ channel activity has been observed in 44 out of 139 patches. The density of these channels was estimated at 0.1-0.3 micron-2. The T-type Ca2+ channel responds to a depolarizing voltage step either with a burst of openings which appears with a distinct delay or with no openings at all. The mean number of bursts per record for the records showing channel activity is 1.1. The probability of observing a blank sweep is high and amounts to 0.65 +/- 0.02 (n = 26). 3. With 110 mM-Ca2+ in the pipette solution, the slope conductance calculated from the current-voltage relationship of the single-channel current in the range between -50 and +10 mV is 6.8 pS. 4. Openings to a subconductance level of about 50% of the main level could be resolved. All possible transitions between the subconductance and the main level were observed, indicating that the cardiac T-type Ca2+ channel possesses a substate. 5. The macroscopic steady-state activation and inactivation, as determined from ensemble-averaged currents, could be described by Boltzmann functions. Half-maximal activation and inactivation occur at -14 and -60.7 mV...
Based on a homology model of the Kv1.3 potassium channel, the recognitions of the six scorpion toxins, viz. agitoxin2, charybdotoxin, kaliotoxin, margatoxin, noxiustoxin, and Pandinus toxin, to the human Kv1.3 potassium channel have been investigated by using an approach of the Brownian dynamics (BD) simulation integrating molecular dynamics (MD) simulation. Reasonable three-dimensional structures of the toxin-channel complexes have been obtained employing BD simulations and triplet contact analyses. All of the available structures of the six scorpion toxins in the Research Collaboratory for Structural Bioinformatics Protein Data Bank determined by NMR were considered during the simulation, which indicated that the conformations of the toxin significantly affect both the molecular recognition and binding energy between the two proteins. BD simulations predicted that all the six scorpion toxins in this study use their β-sheets to bind to the extracellular entryway of the Kv1.3 channel, which is in line with the primary clues from the electrostatic interaction calculations and mutagenesis results. Additionally, the electrostatic interaction energies between the toxins and Kv1.3 channel correlate well with the binding affinities (−logKds)...
We have developed a simple dye transfer method that allows quantification of the gap-junction permeability of small cultured cells. Fluorescent dyes (calcein and Lucifer yellow) were perfused into one cell of an isolated cell pair using a patch-type micropipette in the tight-seal whole cell configuration. Dye spreading into the neighboring cells was monitored using a low-light charge-coupled device camera. Permeation rates for calcein and Lucifer yellow were then estimated by fitting the time course of the fluorescence intensities in both cells. For curve fitting, we used a set of model equations derived from a compartment model of dye distribution. The permeation rates were correlated to the total ionic conductance of the gap junction measured immediately after the perfusion experiment. Assuming that dye permeation is through a unit-conductance channel, we were then able to calculate the single-channel permeance for each tracer dye. We have applied this technique to HeLa cells stably transfected with rat-Cx46 and Cx43, and to BICR/M1Rk cells, a rat mammary tumor cell line that has very high dye coupling through endogenous Cx43 channels. Scatter plots of permeation rates versus junctional conductance did not show a strictly linear correlation of ionic versus dye permeance...
The responses of single-channel currents to capsaicin were recorded using the giga-seal patch-clamp technique in cell-attached and excised (inside-out/outside-out) patches from embryonic rat dorsal root ganglion (DRG) neurones in culture and in Xenopus oocytes heterologously expressing the rat vanilloid receptor (rVR1). Native and cloned vanilloid receptor (VR)-mediated currents exhibited outward rectification. In both the DRG neurones and oocytes expressing VR1, the chord conductances at −60 and +60 mV were ≈50 and ≈100 pS, respectively. At positive potentials, the channel exhibited a single conductance state. In contrast, at negative potentials, brief sojourns to subconductance states were apparent. The probability of the channel being open (Po) was dependent on the transmembrane voltage and the patch configuration (i.e. cell-attached vs. excised). In both DRG neurones and oocytes, the Po was greater at positive (+60 mV) than at negative (-60 mV) potentials. In cell-attached patches, the Po was approximately twofold higher, regardless of the applied potential. Most likely, the outward rectification observed in whole-cell currents is due to the voltage dependence of single-channel conductance and Po. The open-time distributions of single-channel currents recorded from native and cloned VRs in the presence of low agonist concentrations (0.01-0.03 μm) were best fitted with three exponential components. The closed-time distributions were best fitted by five exponential components. At higher concentrations (0.5-1 μm)...
Traditional macro and micro-electroporation devices utilize facing electrodes, which generate electric fields inversely proportional to their separation distance. Although the separation distances in micro-electroporation devices are significantly smaller than those in macro-electroporation devices, they are limited by cell size. Because of this, significant potential differences are required to induce electroporation. These potential differences are often large enough to cause water electrolysis, resulting in electrode depletion and bubble formation, both of which adversely affect the electroporation process. Here, we present a theoretical study of a novel micro-electroporation channel composed of an electrolyte flowing over a series of adjacent electrodes separated by infinitesimally small insulators. Application of a small, non-electrolysis inducing potential difference between the adjacent electrodes results in radially-varying electric fields that emanate from these insulators, causing cells flowing through the channel to experience a pulsed electric field. This eliminates the need for a pulse generator, making a minimal power source (such as a battery) the only electrical equipment that is needed. A non-dimensional primary current distribution model of the novel micro-electroporation channel shows that decreasing the channel height results in an exponential increase in the electric field magnitude...
Ever since the development of liquid rocket engine, there has been a need to predict the peak heat flux that affects the engine material and thus to control the
wall thermal behavior of rocket engine. To prevent thermal failure, the engine is generally cooled by means of a coolant that flows in passages that line the
hottest part of the engine (i.e., combustion chamber and nozzle wall). This is the fluid-cooling system. If the coolant is one of the propellants, once it passes through the cooling circuit, it can be injected into the combustion chamber or it can be dumped overboard. The former case is referred to as
Regenerative cooling system while the latter as dump cooling system. In case of high performance cryogenic rocket engine (such as
LO2/hydrogen and LO2/methane engines) the coolant working pressure is supercritical and thus it behaves far from a liquid or a perfect gas. The fluid-cooling system (often referred to regenerative cooling because of the limited application of the dump cooling) of cryogenic rocket engines, is the technological background of this Ph.D. thesis.
It is common and well confirmed practice in industry to analyze wall thermal behaviour of liquid rocket engine by means of simple and fast tools based on semi-empirical relationships. These relationships are generally calibrated by means of data collected in experimental tests of subscale engines. Industrial
tools provide reasonable results but they are not able to accurately describe many phenomena that occur in the hot-wall/coolant environment...
This work is a study of the size, dynamics and morphological consequences of large-scale horizontal coherent structures (HCS's) in a deep open-channel flow. The study has the following three objectives: 1- to assert the existence of HCS's in a deep open-channel flow and establish their characteristic times and lengths; 2- to penetrate the dynamics of the life cycle of HCS's in such a flow; and 3- to gain insight into why the bed forms known as alternate bars disappear in such flows, even though meandering can still occur. The study is intended as an extension of previous work carried out at Queen's University and focusing on a shallow, alternate bar inducing flow.
For the present purposes, six series of flow velocity measurements were carried out in a 21 m long, 1 m wide straight channel, conveying a 0.14 m deep flow. The bed surface consisted of a silica sand having an average grain size of 2 mm; its surface was flat. The bed slope was such that the bed shear stress was substantially below the threshold for the initiation of motion. The measurements were carried out with the aid of 16 MHz 2D Son Tek Micro-ADV's.
The presence of HCS's affecting (or occupying) the entire body of fluid was unambiguously revealed by the present measurements. The average horizontal burst length and period of the measured flow were found to be equal to 5.5 m. The results of a quadrant analysis of the joint behaviour of the longitudinal and transversal components of fluctuating velocity...
Ao longo do tempo a configuração do canal de distribuição de automóveis novos passou por alterações. De início os distribuidores atuavam de forma isolada, representando somente um fabricante. Após a abertura do mercado brasileiro ao exterior, no início dos anos 90, verificou-se tendência para a formação de grupos de distribuição, representando uma ou várias marcas. Assim, esta tese busca propor um modelo explicativo para a configuração do canal de distribuição de automóveis novos no Brasil. Para isto foi feito estudo de caso de natureza exploratório-conceitual por meio de recursos qualitativos. Verificou-se na limitada bibliografia sobre distribuição de bens especiais, em material de divulgação do setor de distribuição de automóveis e em entrevistas realizadas com representantes de distribuidoras e montadoras, a presença de três variáveis que podem constituir o modelo. Estas três variáveis são: porte dos distribuidores, comportamento do consumidor e ambiente legal. A partir disto construiu-se um modelo que apresenta como resultado três configurações de canal possíveis aos distribuidores: isolado e monomarca, grupo e monomarca e grupo e multimarcas. Dessa forma, espera-se com esta tese contribuir para o entendimento da evolução histórica do setor...
1. Pinched-off cholinergic nerve terminals (synaptosomes) prepared from the electric organ of Torpedo ocelata were fused into large structures (greater than 20 microns) using dimethyl sulphoxide and polyethylene glycol 1500, as previously described for synaptic vesicles from the same organ. 2. The giant fused synaptosomes were easily amenable to the patch clamp technique and 293 seals with a resistance greater than 4 G omega were obtained in the 'cell-attached' configuration. In a large fraction of the experiments, an 'inside-out' patch configuration was achieved. 3. Several types of unitary ionic currents were observed. This study describes the most frequently observed single-channel activity which was found in 247 out of the 293 membrane patches (84.3%). 4. The single-channel current-voltage relation was linear between -60 and 20 mV and showed a slope conductance of 23.8 +/- 1.3 pS when the pipette contained 350-390 mM-Na+ and the bath facing the inside of the synaptosomal membrane contained 390 mM-K+. 5. From extrapolated reversal potential measurements, it was concluded that this channel has a large selectivity for K+ over Na+ (70.4 +/- 11.5, mean +/- S.E.M.). Chloride ions are not transported significantly through this potassium channel. 6. This potassium channel has a low probability of opening. The probability of being in the open state increases upon depolarization and reaches about 1% when the inside of the patch is 20 mV positive compared to the pipette side. 7. The mean channel open time increases with depolarization; thus the product current x time (= charge) also increases upon depolarization...
Confined suspensions of active particles show peculiar dynamics characterized
by wall accumulation, as well as upstream swimming, centerline depletion and
shear-trapping when a pressure-driven flow is imposed. We use theory and
numerical simulations to investigate the effects of confinement and non-uniform
shear on the dynamics of a dilute suspension of Brownian active swimmers by
incorporating a detailed treatment of boundary conditions within a simple
kinetic model where the configuration of the suspension is described using a
conservation equation for the probability distribution function of particle
positions and orientations, and where particle-particle and particle-wall
hydrodynamic interactions are neglected. Based on this model, we first
investigate the effects of confinement in the absence of flow, in which case
the dynamics is governed by a swimming Peclet number, or ratio of the
persistence length of particle trajectories over the channel width, and a
second swimmer-specific parameter whose inverse measures the strength of
propulsion. In the limit of weak and strong propulsion, asymptotic expressions
for the full distribution function are derived. For finite propulsion,
analytical expressions for the concentration and polarization profiles are also
obtained using a truncated moment expansion of the distribution function. In
agreement with experimental observations...
We perform quantum key distribution (QKD) in the presence of 4 classical
channels in a C-band dense wavelength division multiplexing (DWDM)
configuration using a commercial QKD system. The classical channels are used
for key distillation and 1 Gbps encrypted communication, rendering the entire
system independent from any other communication channel than a single dedicated
fibre. We successfully distil secret keys over fibre spans of up to 50 km. The
separation between quantum channel and nearest classical channel is only 200
GHz, while the classical channels are all separated by 100 GHz. In addition to
that we discuss possible improvements and alternative configurations, for
instance whether it is advantageous to choose the quantum channel at 1310 nm or
to opt for a pure C-band configuration.; Comment: 9 pages, 7 figures
We investigate the average velocity of Brownian particles driven by a
constant external force when constrained to move in two-dimensional,
weakly-corrugated channels. We consider both the geometric confinement of the
particles between solid walls as well as the soft confinement induced by a
periodic potential. Using perturbation methods we show that the leading order
correction to the marginal probability distribution of particles in the case of
soft confinement is equal to that obtained in the case of geometric
confinement, provided that the (configuration) integral over the cross-section
of the confining potential is equal to the width of the solid channel. We then
calculate the probability distribution and average velocity in the case of a
sinusoidal variation in the width of the channels. The reduction on the average
velocity is larger in the case of soft channels at small P\'eclet numbers and
for relatively narrow channels and the opposite is true at large P\'eclet
numbers and for wide channels. In the limit of large P\'eclet numbers the
convergence to bulk velocity is faster in the case of soft channels. The
leading order correction to the average velocity and marginal probability
distribution agree well with Brownian Dynamics simulations for the two types of
confinement and over a wide range of P\'eclet numbers.