Changes In Transfer Efficiency Research Articles

Investigations on dynamic failure behaviors and energy transfer efficiency of heat-treated high-performance concrete under multiaxial constraints

In order to explore the internal relationship between the energy transfer efficiency and the dynamic mechanical response of thermal damage concrete under the coupling action of multi-axial stress constraint and high strain rate, the dynamic compression test of high performance concrete is carried out by using the true triaxial Hopkinson pressure bar test system and the combined effects of high temperature, multi-axial stress constraint and impact velocity are fully considered. The temperature effect and strain rate effect of the dynamic failure mechanical behavior of concrete under biaxial stress constraint are analyzed, and the influence mechanism of temperature, prestress and impact velocity on the energy transfer efficiency of the failure process of concrete samples is discussed. The research results show that the dynamic strength of concrete under biaxial stress constraint has both the strengthening effect of loading rate and the hardening and weakening effect of temperature. The dynamic failure of concrete subjected to different degrees of thermal damage under biaxial stress constraint changes from brittleness to plasticity (with 300 °C as the turning point). Under the biaxial stress constraint, the energy absorptivity and reflectivity decrease with the increase of the intermediate principal stress, while the transmittivity shows the opposite trend. When the biaxial stress constraint state is changed to true triaxial constraint state, the energy transfer efficiency changes abruptly along the original evolution trend. The sensitivity of high temperature and stress constraint on the energy transfer efficiency of concrete during dynamic compression is more significant than that of impact velocity. The effects of temperature and stress constraint state (change of intermediate principal stress) on energy dissipation density are positively correlated. The energy dissipation density has an exponential function growth relationship with the dynamic strength and a linear growth relationship with the strain rate.

Effect of Dimples/Protrusion Concavity on Heat Transfer Performance of Rotating Channel

The continuing increase in gas turbine inlet temperature requires additional heat transfer at the trailing edge. Therefore, a large amount of research has been carried out to find a highly efficient cooling process for gas turbine blades. Pin-fins have been widely used in the trailing edge of gas turbines to enhance heat transfer performance. Pin-fins also strengthen the structure between the inlet and outlet faces of the gas turbine. According to previous research, the flow structure and heat transfer characteristics are influenced by many parameters of the pin-fin array, especially the pin-fin shape, height, diameter as well as layout. In this study, instead of changing the structure of the pin-fin array, the work focused on the design of protrusion/dimple points on the leading and trailing edges. Numerical simulations using the SST (Shear Stress Transport) turbulence model were performed to investigate the effect of dimple/protrusion concavity on flow structure and heat transfer characteristics in a rotating channel with pin-fin array. The pin-fins are arranged staggered to each other. The results show that when changing the dimple/protrusion concavity on the leading and trailing edges combined with the rotation speed, the heat transfer efficiency changes positively.

Performance assessment for a novel supersonic turbine engine with variable geometry and fuel precooled: From feasibility, exergy, thermoeconomic perspectives

Aiming at the problem of turbine engine insufficient thrust caused by low efficiency at high Mach number, a three-axis variable geometry dual-mode turbine engine scheme based on ammonia and n-decane equivalent dual fuel precooling and adjustable low-pressure (LP) turbine guide vane is proposed, and parameters such as specific thrust price, relative thrust economic ratio, volumetric specific fuel consumption are defined to scientifically evaluate the feasibility of the scheme. The ammonia and n-decane dual fuel method is used to expand the efficient working range of the precooler. On the one hand, in the low speed section, the engine operates in the turbofan mode, adjusting the LP turbine guide vane can offset the adverse impact of the precooler low efficiency on the engine thrust performance under the low inlet total temperature, and improve the engine economy. On the other hand, the high speed section operates in the turbojet mode, and the equivalent fuel precooling combined with the LP turbine guide vane adjustment is conducive to improving the working efficiency and thrust performance of the turbojet engine. Feasibility, exergy and thermoeconomic analysis indicate that under different operating modes, due to different control plans, the influence of fuel ratio and heat transfer efficiency changes of dual fuel precooler on engine performance is opposite. For the typical climbing process with H = 0, Ma = 0 to H = 30 km, Ma = 5, this scheme can significantly increase the engine thrust, with a maximum increase of about 41%, but it increases the volume fuel consumption, reduces the engine exergy efficiency, exergy sustainability, and thermoeconomic under the turbofan mode. Therefore, the variable geometry turbine engine scheme based on dual fuel precooling and adjustable LP turbine guide vane has high application potential in supersonic commercial flight under the premise of slightly losing economy.

Trophic interactions regulate microbial responses to environmental conditions and partially counteract nitrogen transformation potential in urban river bends

River bends are distinguished by high biodiversity and elevated rates of biogeochemical activities due to complex hydromorphological processes that form diverse geomorphic units, making it challenging to elucidate the impact of trophic interactions on community assembly and biogeochemical processes. Here, we clarify the effect of trophic interactions in determining the assembly of multi-trophic microbial communities and the impact on nitrogen transformation potential by distinguishing the direct and cascading effects of environmental conditions based on 32 samples collected from a typical urban river bends. It was found that both bacterial and micro-eukaryotic communities were determined by homogeneous selection (indicated by β-nearest taxon index, accounted for 85% and 48.3%, respectively), whereas the dominant environmental factors were different, being sediment particle size (P < 0.05) and nitrogen (P < 0.05), respectively. Both the microbial co-occurrence network and the significant association (P < 0.05) between β-nearest taxon index and trophic transfer efficiency changes showed that the trophic interactions strongly shaped microbial communities in the urban river bends. The path modeling suggested that environmental conditions resulted in an increase in abundance of multi-trophic microbial communities via direct effects (mean standardized effects = 0.21), but reductions in abundance of bacteria via cascading effects, i.e., trophic interaction (mean standardized effects = −0.1). When considering direct and cascading effects together, environmental conditions in urban river bends were found to enhance the abundance of microbial communities, with decreasing magnitude at the higher trophic level. Analogously, the path modeling also indicated the nitrogen transformation potential enhanced by environmental conditions via direct effects, but partly counteracted by trophic interactions via cascading effects. The obtained results could provide a theoretical basis for the regulation and restoration of urban rivers.

Multi-parameter heat transfer analysis of molten PCM in an inclined enclosure

• The natural convective heat transfer characters of molten phase change material (mPCM) in an inclined enclosure with forced convection boundary condition on one side and constant heat flux on another side is numerical studied, which is rare in previous literatures. • Heat transfer characters of two side walls and the whole enclosure are investigated separately. • Effects of Reynolds number, Rayleigh number aspect ratio and tilt angles on natural convection inside the enclosure are analyzed, and their influence on heat transfer are compared by quantifying. • A series of dimensionless parameters are conducted to quantitatively evaluate the heat transfer performance of mPCM. The efficiency of the photovoltaic (PV) panel would drop significantly as the absorbed solar radiation converts into heat. To improve the performance of PV, a novel cooling system with phase change material (PCM) and air forced convection cooling is developed, the flow and heat transfer of molten PCM (mPCM) under flow boundary is focused and investigated through numerical method. Three Rayleigh numbers for heat flux boundary (10 4 , 10 5 , and 10 6 ), five Reynolds numbers for forced convection boundary (1 × 10 4 , 1.5 × 10 4 , 2 × 10 4 , 3 × 10 4 and 4 × 10 4 ), three aspect ratios (5, 8, and 10) and tilt angles (30°, 45°, and 60°) for design parameters are considered. A group of dimensionless numbers is performed to describe heat transfer characteristics. It is concluded that different boundary conditions would cause different flow and heat transfer characteristics in the enclosure. Especially for the forced convection boundary, increasing Reynolds number can improve the heat transfer efficiency and reduce the temperature at the same time. Further, the influence of each factor on heat transfer is quantified, as the Rayleigh number increases by two orders of magnitude, Reynolds number increases by 33.33%, aspect ratio enlarged by double variation and tile angle varied by 50%, the heat transfer efficiency changes by 36.53%, 10.76%, 28.45% and 20.34%, respectively.

Adaptive Impedance Matching Scheme for Magnetic MIMO Wireless Power Transfer System

In coupled magnetic resonance (CMR) wireless energy transfer systems, the energy transfer power is low and the power transfer efficiency changes with the coil position. One reason for this reduction in power and efficiency is the impedance mismatching (IM) between the Tx and Rx coils; achieving impedance matching for multiple-input multiple-output (MIMO) CMR IM wireless power transmission (WPT) is quite complex due to the uncertainty in the number of coils and the interaction between coils. In this paper, we provide an analytical model of MIMO CMR which fully formulates the complex relationship between multiple Tx and Rx channels. Then, we design an impedance matching network (IMN) for MIMO CMR and derive an optimal IM solution. Base on this solution, we also develop an adaptive impedance matching scheme to control IMN, based on an automatic analysis of MIMO CMR system; the resulting control scheme achieves optimal values for transmission power and efficiency through IMN and coil selection. The simulation results indicate that the scheme is able to automatically adjust the impedance matching network according to the changes of the relative positions between Tx and Rx coils to achieve high energy transfer power and efficiency.

Testing Maximum Power Point Tracking Controller for PV System

Recently, the demand for renewable energy sources, in particular solar, has been increasing. This is due to declining demand for other fuels due to the poor reputation, waste of nuclear energy and limited fossil resources such as coal. The growing popularity of silicon significantly reduces the cost and increases the availability of solar energy. The main technique of increasing efficiency of the converter is to find maximum power point tracking (MPPT) that addressing problem of efficiency of power transfer from the solar cell depends on both the amount of sunlight falling on the solar panels and the electrical characteristics of the load. As the amount of sunlight varies, the load characteristic that gives the highest power transfer efficiency changes, so that the efficiency of the system is optimized when the load characteristic changes to keep the power transfer at highest efficiency. This load characteristic is called the maximum power point and MPPT is the process of finding this point and keeping the load characteristic there. Electrical circuits can be designed to present arbitrary loads to the photovoltaic cells and then convert the voltage, current, or frequency to suit other devices or systems, and MPPT solves the problem of choosing the best load to be presented to the cells in order to get the most usable power out.This article considers the construction of MPPT controller of solar panel, which must operate at up to 60W power of solar panel and up to 30V of output battery voltage. Given the structure of the system and the necessary operating parameters, for its construction it is necessary to take into account various circuit solutions for the power unit, as well as methods for finding the point of maximum power for the control circuit.The design and construction of the MPPT controller of the photovoltaic system and testing for different irradiation values is considered. Various circuit design solutions and algorithms for the operation of the MPPT controller were analyzed and a two-switch buck-boost circuit and a perturb and observe algorithm were selected. After making the system task is at general checking of possible operating in a given range of current and voltage, as well as the ability to respond to changes in current and voltage values and some external conditions that directly affect the work of a solar panel. The algorithm of work, formulas for emulation and an example of system work were given. The algorithm of work, formulas for emulation and an example of system work were given. The time diagrams of the control signals of the transistors at the time of switching from buck mode to boost mode are shown. A step-by-step description of the changes that occur in the system during the change of parameters and how the feedback stabilizes the operation of the device to maintain the maximum power of the system.After the developed experiment, the workability of the layout was checked and various variants of operation of the device for different lighting conditions were simulated. A conclusion was drawn on the potential for further development of the proposed solution. The circuit used operates at a given power and the proposed idea has the potential for further development and experimenting.

Charge Transfer from Lead Sulfide Quantum Dots to MoS2 Nanoplatelets

The research interest in the transition metal dichalcogenides (TMD) has been reborn a few years ago. This had happened due to the remarkable properties of monolayered TMD (e.g., high carrier mobility and high exciton binding energy) and due to the development of the exfoliation methods. Photoconductive MoS2-based devices spectral range can be expanded to the NIR by coupling them with PbS QDs. However, this requires extensive knowledge about the charge and energy transfer processes in such systems. In this paper, we investigate charge transfer between PbS QDs and MoS2 nanoplatelets (NPls). Using the PL decay analysis, we show how the charge transfer efficiency changes with the distance between the QDs and NPls, as well as with QD size. Last, we demonstrate that the addition of the MoS2 NPLs increases the photoconductive response for up to an order of magnitude, as compared to the bare QD.

Charge Transfer from Lead Sulfide Quantum Dots to MoS-=SUB=-2-=/SUB=- Nanoplatelets-=SUP=-*-=/SUP=-

The research interest in the transition metal dichalcogenides (TMD) has been reborn a few years ago. This had happened due to the remarkable properties of monolayered TMD (e. g. high carrier mobility and high exciton binding energy) and due to the development of the exfoliation methods. Photoconductive MoS2-based devices spectral range can be expanded to the NIR by coupling them with PbS QDs. However, this requires extensive knowledge about the the charge and energy transfer processes in such systems. In this paper, we investigate charge transfer between PbS QDs and MoS2 nanoplatelets (NPls). Using the PL decay analysis, we show how the charge transfer efficiency changes with the distance between the QDs and NPls, as well as with QD size. Last, we demonstrate that the addition of the MoS2 NPLs increases the photoconductive response for up to an order of magnitude, as compared to the bare QD. Keywords: transition metal dichalcogenides, quantum dots, charge transfer, lead sulfide, molybdenum disulfide.

α-Synuclein transfer between neurons and astrocytes indicates that astrocytes play a role in degradation rather than in spreading.

Recent evidence suggests that disease progression in Parkinson's disease (PD) could occur by the spreading of α-synuclein (α-syn) aggregates between neurons. Here we studied the role of astrocytes in the intercellular transfer and fate of α-syn fibrils, using in vitro and ex vivo models. α-Syn fibrils can be transferred to neighboring cells; however, the transfer efficiency changes depending on the cell types. We found that α-syn is efficiently transferred from astrocytes to astrocytes and from neurons to astrocytes, but less efficiently from astrocytes to neurons. Interestingly, α-syn puncta are mainly found inside the lysosomal compartments of the recipient cells. However, differently from neurons, astrocytes are able to efficiently degrade fibrillar α-syn, suggesting an active role for these cells in clearing α-syn deposits. Astrocytes co-cultured with organotypic brain slices are able to take up α-syn fibrils from the slices. Altogether our data support a role for astrocytes in trapping and clearing α-syn pathological deposits in PD.

Particle transport simulation and effect analysis of CCD irradiated by protons

Monte Carlo method is used to calculate the energy deposition of proton-irradiated scientific CCD (charge coupled device) structure, and the radiation damage mechanism of the device is analyzed by combining the proton irradiation with the annealing experiments. The ionizing dose in gate oxide layer and the displacement damage dose in silicon deposition are simulated. During irradiation and annealing experiments two main parameters, dark signal and charge transfer efficiency, are investigated. Results show that variations of dark signal and charge transfer efficiency are the same as those with ionizing dose and displacement damage dose. During irradiation, dark signal rises obviously as the fluence of 10 MeV proton increases. Defects and their annealing temperature:the divacancy levels show little annealing effect below 300℃, while the oxygen-vacancy complex is stable up to 350℃, and the phosphorous-vacancy has a characteristic annealing temperature of 150℃. Interface states are annealed totally at 175℃. So the annealing only affects oxide-trapped-charges. Dark signal is greatly reduced after annealing, this phenomenon means that the dark signal is mainly affected by ionization. The surface dark signal proportion of the total dark signal can be calculated by the reduction of dark signal during annealing and this is at least 80% or more. As the fluence of 10 MeV proton increases, the charge transfer efficiency reduces obviously. After annealing, the recovery of charge transfer efficiency changes very little, so the charge transfer efficiency is unaffected by oxide-trapped-charges, since it is reduced due mainly to bulk defects. The final device damage will always be proportional to the amount of initial damage and also to the electrical effect on the device. Hence NIEL scaling implies a universal relation:device damage=kdamage×displacement damage dose, where kdamage is a damage constant depending on the device and the parameter affected, and the displacement damage dose (DD) is the product of the NIEL and the particle fluence. MULASSIS is used to calculate the displacement damage dose in depletion area of P-area and deduce kdamage by combining with the experimental value of charge transfer efficiency; kdamage is calculated to be about 3.50×10-14. The formula for degradation degree of charge transfer efficiency is CTEafter irradiated = 1-Dd×kdamage, this formula is used to estimated CTE and the result is compared with the value from experiment. It is shown that the simulated data is in agreement with the experimental data.

Nanophotonic Control of the Förster Resonance Energy Transfer Efficiency

We have studied the influence of the local density of optical states (LDOS) on the rate and efficiency of Förster resonance energy transfer (FRET) from a donor to an acceptor. The donors and acceptors are dye molecules that are separated by a short strand of double-stranded DNA. The LDOS is controlled by carefully positioning the FRET pairs near a mirror. We find that the energy transfer efficiency changes with LDOS, and that, in agreement with theory, the energy transfer rate is independent of the LDOS, which allows one to quantitatively control FRET systems in a new way. Our results imply a change in the characteristic Förster distance, in contrast to common lore that this distance is fixed for a given FRET pair.

Mass transport of deposited particles by surface-to-surface contact

The spread of particle-borne contamination by surface-to-surface contact and its implications for exposures within the indoor environment have been observed – largely qualitatively. The present study was conducted with the aim of quantifying the mass transfer efficiency (TE) of deposited aerosol particles when selected soft and hard surfaces come in contact. The surfaces used were 100% cotton, synthetic fleece, plastic laminate and brass. Contact transfer efficiencies ranging from 2 to 45% were observed; these are very significant numbers in terms of hazardous aerosol transport in the environment. Other observations include an increase in the mass transferred with increased surface roughness. An increase in the applied pressure between the two surfaces in contact leads to a step change in transfer efficiency, so that two pressure regimes can be identified, with a transition pressure between them that depends on surface type. Time of contact appears to have little to no effect on the mass transfer efficiency for the surfaces studied, while contaminant loading has some effect that is not systematic.

Spectroscopy studies of methyl orange on silver colloids: pH and Cl－ effects

The UV-Vis absorption and photoluminescence spectral signals of silver colloids and methyl orange (MO) in different pH systems before and after adding Cl- were studied. It was found that the energy transfer efficiency changes with the pH value, i.e., the fluorescence quenching at 428 nm and photoluminescence enhancement at 560 nm was greatly strenthened with the increase of pH of the system. After adding Cl-, dense adsorption layer was formed, leading to stronger spectral signals associated with surface enhancement. On the other hand, because of the decrease of incident light to the inside of Ag-MO complex, energy transfer channel may be suffocated to some extent, the quenching amplitude of 428 nm fluorescence band decreased. Compared with these notable phenomena and discussed with correlative theoretic analysis, it's clear that different molecular structures and adsorption models of MO onto Ag surfaces exist with the changing of pH and the adding of Cl-, which give rise to the different phenomena observed.

Efficiency of Energy Transfer in a Small Plasma Focus Device

A study of energy transfer in a small plasma focus device has been carried out during its axial phase. The snow-plough model has been used in the simulation as a basic model for the calculation of plasma dynamics. The energy transferred to the plasma is calculated by considering the work done by the electromagnetic piston during the axial phase. It was found that the plasma energy calculated by this model agrees well with the experimental data within the pressure range of 1 mbar to 4 mbar if the mass shedding effect is included in the model. According to the present computation, the energy transferred into the plasma, in the case of a plasma focus with 2.3 kJ initial energy operated with nitrogen gas within the pressure range of 1 to 4 mbar, is between 224 J to 250 J. This corresponds to energy transfer efficiency of 9.6% to 10.7%. The mass shedding factor decreases from 0.23 to 0.069 with increasing pressure. Correspondingly, the energy transfer efficiency changes slightly at a higher pressure.

Ca 2+-Induced Movement of Tropomyosin in Skeletal Muscle Thin Filaments Observed by Multi-Site FRET

To obtain information on Ca 2+-induced tropomyosin (Tm) movement in Ca 2+-regulated muscle thin filaments, frequency-domain fluorescence energy transfer data were collected between 5-(2-iodoacetyl-amino-ethyl-amino)naphthalene-1-sulfonic acid at Cys-190 of Tm and phalloidin-tetramethylrhodamine B isothiocyanate bound to F-actin. Two models were used to fit the experimental data: an atomic coordinate (AC) model coupled with a search algorithm that varies the position and orientation of Tm on F-actin, and a double Gaussian distance distribution (DD) model. The AC model showed that little or no change in transfer efficiency is to be expected between different sites on F-actin and Tm if Ca 2+ causes azimuthal movement of Tm of the magnitude suggested by structural data (C. Xu, R. Craig, L. Tobacman, R. Horowitz, and W. Lehman. 1999. Biophys. J. 77:985–992). However, Ca 2+ produced a small but significant change in our phase/modulation versus frequency data, showing that changes in lifetime decay can be detected even when a change of the steady-state transfer efficiency is very small. A change in Tm azimuthal position of 17° on the actin filament obtained with the AC model indicates that solution data are in reasonable agreement with EM image reconstruction data. In addition, the data indicate that Tm also appears to rotate about its axis, resulting in a rolling motion over the F-actin surface. The DD model showed that the distance from one of the two chains of Tm to F-actin was mainly affected, further verifying that Ca 2+ causes Tm to roll over the F-actin surface. The width of the distance distributions indicated that the position of Tm in absence and in presence of Ca 2+ is well defined with appreciable local flexibility.

The Transfer of Trichloroethyene (TCE) from a Shower to Indoor Air: Experimental Measurements and Their Implications

Experiments were performed to measure the transfer of trichloroethylene (TCE), a volatile organic compound (VOC), from tap water in showers to indoor air. In these experiments, the loss of TCE from tap water in the shower is based on the difference between influent and effluent concentrations. We have developed and previously published a three-compartment model, which we use to simulate the 24-h concentration history of VOCs in the shower, bathroom, and remaining household volumes resulting from the use of contaminated tap water. An important input to this model is the transfer efficiency of the VOC from water to air. The experiments reveal that the transfer efficiency of TCE from shower water to air has an arithmetic mean value of 61 percent and an arithmetic standard deviation of 9 percent. Analysis of the results shows that there is no statistically significant difference between the transfer efficiency measured with hot (37 degrees C) or cold (22 degrees C) shower water and that there is no statistically significant change in transfer efficiency with time during a 20-min shower. The implications for exposure assessment are considered.

The Transfer of Trichloroethyene (TCE) from a Shower to Indoor Air: Experimental Measurements and Their Implications

Experiments were performed to measure the transfer of trichloroethylene (TCE), a volatile organic compound (VOC), from tap water in showers to indoor air. In these experiments, the loss of TCE from tap water in the shower is based on the difference between influent and effluent concentrations. We have developed and previously published a three-compartment model, which we use to simulate the 24-h concentration history of VOCs in the shower, bathroom, and remaining household volumes resulting from the use of contaminated tap water. An important input to this model is the transfer efficiency of the VOC from water to air. The experiments reveal that the transfer efficiency of TCE from shower water to air has an arithmetic mean value of 61 percent and an arithmetic standard deviation of 9 percent. Analysis of the results shows that there is no statistically significant difference between the transfer efficiency measured with hot (37 degrees C) or cold (22 degrees C) shower water and that there is no statistically significant change in transfer efficiency with time during a 20-min shower. The implications for exposure assessment are considered.

Resonance energy transfer between points in a reconstituted skeletal muscle thin filament

The spatial relationships between Lys-61, Cys-374 on actin or SH1 on myosin subfragment-1 (S1) and Cys-190 on tropomyosin or Cys-133 on troponin-I (TnI) in a reconstituted thin filament were studied by fluorescence resonance energy transfer. 5-(2-Iodoacetylaminoethyl)aminonaphthalene 1-sulfonic acid (IAEDANS) attached to Lys-190 on tropomyosin or to Cys-133 on TnI was used as a donor. Fluorescein 5-isothiocyanate (FITC) attached to Lys-61 or 5-(iodoacetoamido)fluorescein (IAF) attached to Cys-374 on actin and 4-dimethylaminophenyl-azophenyl 4'-maleimide (DABMI) attached to SH1 on S1 were used as an acceptor. The transfer efficiency between AEDANS attached to Cys-190 on tropomyosin and FITC attached to Lys-61 on actin was 0.42 in the absence of troponin, 0.46 in the presence of troponin and Ca2+ and 0.55 in the presence of troponin and absence of Ca2+. The corresponding distances between the probes were calculated to be 4.7 nm, 4.6 nm and 4.3 nm respectively, assuming a random orientation factor K2 = 2/3. A large difference in the transfer efficiency from AEDANS attached to Cys-133 on TnI to FITC attached to Lys-61 on actin was observed between in the presence (0.52) and absence (0.70) of Ca2+. The corresponding distances between the probes were calculated to be 4.5 nm in the presence of Ca2+ and 3.9 nm in the absence of Ca2+. The distance between Cys-190 on tropomyosin and Cys-374 on actin was measured to be 5.1 nm and the transfer efficiency (0.35) did not change upon addition of troponin whether Ca2+ is present or not, in agreement with the previous report [Tao, T., Lamkin, M. & Lehrer, S. S. (1983) Biochemistry 22, 3059-3064]. The distance between Cys-133 on TnI and Cys-374 on actin was measured to be 4.4 nm. No detectable change in transfer efficiency (0.58) was observed between values in the presence and absence of Ca2+. These results suggest that a relative movement of the two domains of actin monomer in a reconstituted thin filament occurs in response to a change in Ca2+ concentration. The transfer efficiencies between DABMI attached to SH1 on S1 and AEDANS attached to Cys-190 on tropomyosin or Cys-133 on TnI were too small (less than 2%) for an accurate estimation of the distances, suggesting the distances are longer than 7.3 nm.

Use of resonance energy transfer to monitor membrane fusion.

An assay for vesicle--vesicle fusion involving resonance energy transfer between N-(7-nitro-2,1,3-benzoxadiazol-4-yl), the energy donor, and rhodamine, the energy acceptor, has been developed. The two fluorophores are coupled to the free amino group of phosphatidylethanolamine to provide analogues which can be incorporated into a lipid vesicle bilayer. When both fluorescent lipids are in phosphatidylserine vesicles at appropriate surface densities (ratio of fluorescent lipid to total lipid), efficient energy transfer is observed. When such vesicles are fused with a population of pure phosphatidylserine vesicles by the addition of calcium, the two probes mix with the other lipids present to form a new membrane. This mixing reduces the surface density of the energy acceptor resulting in a decreased efficiency of resonance energy transfer which is measured experimentally. These changes in transfer efficiency allow kinetic and quantitative measurements of the fusion process. Using this system, we have studied the ability of phosphatidylcholine, phosphatidylserine, and phosphatidylcholine--phosphatidylserine (1:1) vesicles to fuse with cultured fibroblasts. Under the conditions employed, the majority of the cellular uptake of vesicle lipid could be attributed to the adsorption of intact vesicles to the cell surface regardless of the composition of the vesicle bilayer.