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Статті в журналах з теми "Resistance to enthalpy transfer"
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LEE, EUL-JONG, JUNG-PYO LEE, HYUN-MIN SIM, and NAE-HYUN KIM. "MODELING AND VERIFICATION OF HEAT AND MOISTURE TRANSFER IN AN ENTHALPY EXCHANGER MADE OF PAPER MEMBRANE." International Journal of Air-Conditioning and Refrigeration 20, no. 03 (September 2012): 1250015. http://dx.doi.org/10.1142/s2010132512500150.
Повний текст джерелаАнотація:
In this study, heat and moisture transfer model of an enthalpy exchanger is proposed. With separately measured sorption constant and diffusion coefficient, the model predicts the heat and moisture transfer effectiveness of an enthalpy exchanger. Two sample enthalpy exchangers were tested at a KS condition to verify the model. The model predicts the heat transfer effectiveness within 4%, and the moisture transfer effectiveness within 10%. Pressure drop is predicted within 6%. The spacer fin efficiency for heat transfer was 0.11 to 0.13. The fin efficiency for moisture transfer, however, was negligibly small. For heat transfer, the conduction resistance to total thermal resistance was less than 1%. For moisture transfer, however, membrane resistance was dominant to convective moisture transfer resistance.
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Zhang, L. Z., and J. L. Niu. "Effectiveness Correlations for Heat and Moisture Transfer Processes in an Enthalpy Exchanger With Membrane Cores." Journal of Heat Transfer 124, no. 5 (September 11, 2002): 922–29. http://dx.doi.org/10.1115/1.1469524.
Повний текст джерелаАнотація:
The performance correlations for the effectiveness of heat and moisture transfer processes in an enthalpy exchanger with membrane cores are presented. The physical phenomena relevant to the heat and moisture transfer in these devices have been used to develop a novel set of correlations based on the relevant dimensionless parameters. The total enthalpy effectiveness can be calculated from sensible effectiveness, latent effectiveness, and the ratio of latent to sensible energy differences across the unit. Studies show that the sensible effectiveness is a function of NTU, the number of transfer units for heat; while the latent effectiveness is a function of NTUL, the number of transfer units for moisture. The relations between NTUL and NTU are derived and studied with the proper separation of moisture resistance for membranes. This newly developed dimensionless parameter, NTUL, is to summarize the sorption characteristics of membrane material, the exchanger configurations, as well as the operating conditions. A number of experimental results on an enthalpy exchanger with novel hydrophilic membrane cores has been used to valid these correlations.
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Li, Yong An, Xue Lai Liu, Jia Jia Yan, and Teng Xing. "Research on Wet Thermal Recovery Plant Used by Air Conditioning." Advanced Materials Research 424-425 (January 2012): 1155–58. http://dx.doi.org/10.4028/www.scientific.net/amr.424-425.1155.
Повний текст джерелаАнотація:
Based on the simulation Computational Fluid Dynamics method, in view of air conditioning with wet thermal recovery plant for heat and mass transfer characteristic, establishes air channels in three-dimensional laminar flow and heat transfer, mass transfer coupling process of mathematical physics model, discusses the air conditioning with wet thermal recovery plant air channels in temperature, concentration and pressure parameters such as distribution, application enthalpy efficiency analysis method to the heat transfer performance is evaluated. The results indicate that structure parameters of wet thermal recovery plant used by air conditioning play important influence for the heat transfer performance and flow resistance performance. The research conclusion provides guidance for air conditioning with wet thermal recovery plant of optimization.
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El-Dessouky, H. T. A., A. Al-Haddad, and F. Al-Juwayhel. "A Modified Analysis of Counter Flow Wet Cooling Towers." Journal of Heat Transfer 119, no. 3 (August 1, 1997): 617–26. http://dx.doi.org/10.1115/1.2824150.
Повний текст джерелаАнотація:
The paper describes a theoretical investigation for the steady-state counter flow wet cooling tower with modified definitions for both the number of transfer units and the tower thermal effectiveness. The modified number of transfer units is dependent on both air and water heat capacity. The effectiveness is defined by the tower cooling range and the approach to equilibrium. A new expression relating the tower effectiveness to the modified number of transfer units and the capacity rate ratio has been developed. The model considered the resistance to heat transfer in the water film, the nonunity of the Lewis number, and the curvature of the saturated air enthalpy curve. A procedure for implementing the model in designing or rating cooling towers has been outlined and demonstrated through illustrative examples. The model compares very satisfactorily with other methods such as Logarithmic Mean Enthalpy Difference (LMED) and conventional effectiveness—NTU. Within the ranges used, the obtained results showed that substantial errors varied from +4.289 to −2.536 percent can occur in calculating the cooled water outlet temperature, and errors from +42.847 to −16.667 percent can occur in estimating the tower thermal characteristics.
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Kurose, Ryoichi, Naohisa Takagaki, Atsushi Kimura, and Satoru Komori. "Direct numerical simulation of turbulent heat transfer across a sheared wind-driven gas–liquid interface." Journal of Fluid Mechanics 804 (September 13, 2016): 646–87. http://dx.doi.org/10.1017/jfm.2016.554.
Повний текст джерелаАнотація:
Turbulent heat transfer across a sheared wind-driven gas–liquid interface is investigated by means of a direct numerical simulation of gas–liquid two-phase turbulent flows under non-breaking wave conditions. The wind-driven wavy gas–liquid interface is captured using the arbitrary Lagrangian–Eulerian method with boundary-fitted coordinates on moving grids, and the temperature fields on both the gas and liquid sides, and the humidity field on the gas side are solved. The results show that although the distributions of the total, latent, sensible and radiative heat fluxes at the gas–liquid interface exhibit streak features such that low-heat-flux regions correspond to both low-streamwise-velocity regions on the gas side and high-streamwise-velocity regions on the liquid side, the similarity between the heat-flux streak and velocity streak on the gas side is more significant than that on the liquid side. This means that, under the condition of a fully developed wind-driven turbulent field on both the gas and liquid sides, the heat transfer across the sheared wind-driven gas–liquid interface is strongly affected by the turbulent eddies on the gas side, rather than by the turbulent eddies and Langmuir circulations on the liquid side. This trend is quite different from that of the mass transfer (i.e. $\text{CO}_{2}$ gas). This is because the resistance to heat transfer is normally lower than the resistance to mass transfer on the liquid side, and therefore the heat transfer is controlled by the turbulent eddies on the gas side. It is also verified that the predicted total heat, latent heat, sensible heat and enthalpy transfer coefficients agree well with previously measured values in both laboratory and field experiments. To estimate the heat transfer coefficients on both the gas and liquid sides, the surface divergence could be a useful parameter, even when Langmuir circulations exist.
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Gallardo, Andres, and Umberto Berardi. "A simple method for validating a simulation model of a radiant ceiling panel with thermal energy storage." Journal of Physics: Conference Series 2069, no. 1 (November 1, 2021): 012119. http://dx.doi.org/10.1088/1742-6596/2069/1/012119.
Повний текст джерелаАнотація:
Abstract This paper focuses on validating a simulation model of a radiant ceiling panel (RCP) incorporating phase change materials (PCM) for heating and cooling applications in buildings. The development of an RCP with thermal energy storage capacity aims to encourage high thermal mass radiant systems in existing buildings to replace the traditional all-air HVAC system. First, a heat flow meter (HFM) is used to perform enthalpy measurements at a product scale (macro-encapsulated PCM). Then, a small test chamber is constructed to measure the dynamic thermal performance of an RCP with PCM under well-known and realistic boundary conditions. A known thermal resistance is used to establish a realistic heat transfer coefficient between room air (represented by the temperature of a temperature-controlled metal plate) and ceiling. The results show that HFM enthalpy measurements of products incorporating PCM are within ± 2% of manufacturers’ data. Additionally, results indicate that a test chamber can be used for validating a dynamic simulation model of the RCP with PCM installed in a room. The proposed method can be helpful during the system optimization phase, as many conditions and sample configurations can be tested without spending too much time or money on test rooms or real building monitoring.
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Mahir, Maha, Anas El Maakoul, Ismail Khay, Said Saadeddine, and Mohamed Bakhouya. "An Investigation of Heat Transfer Performance in an Agitated Vessel." Processes 9, no. 3 (March 5, 2021): 468. http://dx.doi.org/10.3390/pr9030468.
Повний текст джерелаАнотація:
Agitated vessels (or mechanically stirred reactors) are heat exchange devices that are most widely used in many chemical and biochemical process industries, such as anaerobic digestion process. The mixing and heat transfer performances in these vessels are of crucial importance for increasing the energy efficiency in both batch and continuous processes. In this paper, a series of experiments were conducted to investigate heat transfer performance in agitated vessels for various configurations. In fact, this study examines the effects of heat transfer geometry (wall jacket and helical coils), heating power, and stirring speed, on the heating performance of two stirred fluids—water alone and a mixture of water and food waste. The experiments were conducted using a jacketed insulation tank with a helical coil and a propeller agitator. In each experiment, a transient method, based on measuring the temperature dependency on time, and solving the unsteady enthalpy balance, was used to determine the overall heat transfer coefficients between the agitated fluid and the heating surface. Finally, an extensive analysis of the reduced data was conducted based on temperature, heating time, heat transfer rate, heat transfer coefficient, and thermal resistance. The main finding was that the presence of food waste in agitated vessels reduces the heat rate of the agitated fluid with an average of 18.13% and 49.51%, respectively, for the case of JHX and CHX, and creates additional fouling, which further limits the heat transfer.
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Khan, Zakir, and Zulfiqar Ahmad Khan. "Performance Evaluation of Coupled Thermal Enhancement through Novel Wire-Wound Fins Design and Graphene Nano-Platelets in Shell-and-Tube Latent Heat Storage System." Energies 14, no. 13 (June 22, 2021): 3743. http://dx.doi.org/10.3390/en14133743.
Повний текст джерелаАнотація:
Technological development in latent heat storage (LHS) systems is essential for energy security and energy management for both renewable and non-renewable sources. In this article, numerical analyses on a shell-and-tube-based LHS system with coupled thermal enhancement through extended fins and nano-additives are conducted to propose optimal combinations for guaranteed higher discharging rate, enthalpy capacity and thermal distribution. Transient numerical simulations of fourteen scenarios with varied combinations are investigated in three-dimensional computational models. The shell-and-tube includes paraffin as phase change material (PCM), longitudinal, radial and wire-wound fins and graphene nano-platelets (GNP) as extended fins and nano-additives, respectively. The extended fins have demonstrated better effectiveness than nano-additives. For instance, the discharging durations for paraffin with longitudinal, radial and wire-wound fins are shortened by 88.76%, 95.13% and 96.44% as compared to 39.33% for paraffin with 2.5% GNP. The combined strengths of extended fins and nano-additives have indicated further enhancement in neutralising the insulative resistance and stratification of paraffin. However, the increase in volume fraction from 1% to 3% and 5% is rather detrimental to the total enthalpy capacity. Hence, the novel designed wire-wound fins with both base paraffin and paraffin with 1% GNP are proposed as optimal candidates owing to their significantly higher heat transfer potentials. The proposed novel designed configuration can retrieve 11.15 MJ of thermal enthalpy in 1.08 h as compared to 44.5 h for paraffin in a conventional shell-and-tube without fins. In addition, the proposed novel designed LHS systems have prolonged service life with zero maintenance and flexible scalability to meet both medium and large-scale energy storage demands.
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Núñez González, J., A. Beltrán Morales, M. Rivero Corona, and J. Vega Munguía. "Numerical simulation of a polymer melting process using solar energy." Suplemento de la Revista Mexicana de Física 1, no. 2 (July 16, 2020): 18–24. http://dx.doi.org/10.31349/suplrevmexfis.1.2.18.
Повний текст джерелаАнотація:
In this work, the melting process of a polymeric material is numerically investigated. In general, the heat required for melting plastics is obtained throughout electrical resistances or by burning fossil fuels. The heat transfer mechanisms of these common practices correspond to conduction and convection, respectively. This work explores the feasibility of using radiation as the primary mechanism of energy supply, which has not been widely studied. The energy to achieve the phase change from solid to liquid can be obtained by concentrated solar energy radiation. The total energy required is calculated solving the energy equation using the enthalpy formulation. An explicit formulation with an enthalpy linearization was implemented in the Mathematica programming language and compared with the solution in the commercial softwares Ansys Fluent and COMSOL Multiphysics showing a good agreement. Based upon numerical predictions, it is examined the effects of the relevant parameters, such as incident radiation and convective heat transfer coefficient, on the melting process. It is observed that under weather conditions commonly attained in different cities worldwide, with a radiation of 1000 W/m$^2$ and low convective losses with $h=8$ W/m$^2\cdot$K, the melting process of a cylindrical rod of 3/4 inches diameter can be carried out in around 2 hours.
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Ceglia, Francesca, Adriano Macaluso, Elisa Marrasso, Maurizio Sasso, and Laura Vanoli. "Modelling of Polymeric Shell and Tube Heat Exchangers for Low-Medium Temperature Geothermal Applications." Energies 13, no. 11 (May 29, 2020): 2737. http://dx.doi.org/10.3390/en13112737.
Повний текст джерелаАнотація:
Improvements in using geothermal sources can be attained through the installation of power plants taking advantage of low and medium enthalpy available in poorly exploited geothermal sites. Geothermal fluids at medium and low temperature could be considered to feed binary cycle power plants using organic fluids for electricity “production” or in cogeneration configuration. The improvement in the use of geothermal aquifers at low-medium enthalpy in small deep sites favours the reduction of drilling well costs, and in addition, it allows the exploitation of local resources in the energy districts. The heat exchanger evaporator enables the thermal heat exchange between the working fluid (which is commonly an organic fluid for an Organic Rankine Cycle) and the geothermal fluid (supplied by the aquifer). Thus, it has to be realised taking into account the thermodynamic proprieties and chemical composition of the geothermal field. The geothermal fluid is typically very aggressive, and it leads to the corrosion of steel traditionally used in the heat exchangers. This paper analyses the possibility of using plastic material in the constructions of the evaporator installed in an Organic Rankine Cycle plant in order to overcome the problems of corrosion and the increase of heat exchanger thermal resistance due to the fouling effect. A comparison among heat exchangers made of commonly used materials, such as carbon, steel, and titanium, with alternative polymeric materials has been carried out. This analysis has been built in a mathematical approach using the correlation referred to in the literature about heat transfer in single-phase and two-phase fluids in a tube and/or in the shell side. The outcomes provide the heat transfer area for the shell and tube heat exchanger with a fixed thermal power size. The results have demonstrated that the plastic evaporator shows an increase of 47.0% of the heat transfer area but an economic installation cost saving of 48.0% over the titanium evaporator.
Дисертації з теми "Resistance to enthalpy transfer"
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Tseitlin, Musii, and Valentina Raiko. "Ratio between heat and mass transfer when concentrating the solution in a cooling tower." Thesis, Lviv Polytechnic National University, 2019. http://repository.kpi.kharkov.ua/handle/KhPI-Press/42106.
Повний текст джерелаАнотація:
The ratio between the intensity of the mass transfer in gas and the heat transfer in liquid during the evaporative solution concentration has been studied. It was determined that the share of liquid resistance in the total resistance to enthalpy transfer increases in the temperature range from 30 to 50°C by almost 2 times, and reaches 40 %. The technique has been developed for the separate determination of the mass transfer coefficients in gas and heat transfer in liquid.Досліджено співвідношення між інтенсивністю масопереносу в газі та передачею тепла в рідині під час концентрації випарного розчину. Встановлено, що частка опору рідини в загальному опорі переносу ентальпії зростає в діапазоні температур від 30 до 50 ° С майже в 2 рази, досягає 40%. Розроблена методика для окремого визначення коефіцієнтів масопереносу в газі і теплопередачі в рідині.
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Jeong, Dahai. "Laboratory Measurements of the Moist Enthalpy Transfer Coefficient." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_theses/145.
Повний текст джерелаАнотація:
The enthalpy (sensible and latent heat) exchange processes within the surface layers at an air-water interface have been examined in 15-m wind-wave tunnel at the University of Miami. Measurements yielded 72 mean values of fluxes and bulk variables in the wind speed (referred to 10 m) range form 0.6 to 39 m/s, covering a full range of aerodynamic conditions from smooth to fully rough. Meteorological variables and bulk enthalpy transfer coefficients, measured at 0.2-m height, were adjusted to neutral stratification and 10-m height following the Monin-Obukhov similarity approach. The ratio of the bulk coefficients of enthalpy and momentum was estimated to evaluate Emanuel's (1995) hypothesis. Indirect "Calorimetric" measurements gave reliable estimates of enthalpy flux from the air-water interface, but the moisture gained in the lower air from evaporation of spray over the rough water remained uncertain, stressing the need for flux measurements along with simultaneous spray data to quantify spray's contribution to the turbulent air-water enthalpy fluxes.
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Staton, JoAnna Christen II. "Heat and Mass Transfer Characteristics of Desiccant Polymers." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/9785.
Повний текст джерелаАнотація:
Desiccant-enhanced air conditioning equipment has exhibited both the capability to improve humidity control and the potential to save energy costs by lowering the latent energy requirement of the supply air stream. The resulting increasing popularity of desiccant-enhanced air conditioning systems has sparked new interest in the search for a better, more efficient desiccant material. The ultimate goal of this research was to develop a material that, when applied to an existing air-to-air heat exchanger, would achieve the necessary heat and mass transfer in a single process, thus transforming a sensible heat exchanger into a total enthalpy exchanger.
This study focuses on the development and determination of appropriate polymeric desiccant materials for use in different heat and mass transfer applications. Various candidate materials were initially studied. It was decided that polyvinyl alcohol best met the pre-determined selection criteria. After the focus material was chosen, numerical models representing two heat and mass transfer applications were created. One-dimensional numerical models were developed for the performance studies of a rotary wheel total enthalpy exchanger. A two-dimensional numerical model was developed for the performance studies of a fixed plate total enthalpy exchanger as well. Material characterization tests were performed to collect material property information required by the numerical models.
Sensible, latent, and total efficiencies gathered from both the rotary wheel total enthalpy exchanger and the fixed plate total enthalpy exchanger models indicate potential uses for some candidate polyvinyl alcohol materials.Master of Science
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Maza, William Antonio. "Reaction Enthalpy and Volume Profiles for Excited State Reactions Involving Electron Transfer and Proton-Coupled Electron Transfer." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4539.
Повний текст джерелаАнотація:
Electron transfer, ET, and proton-coupled electron transfer, PCET, reactions are central to biological reactions involving catalysis, energy conversion and energy storage. The movement of electrons and protons in either a sequential or concerted manner are coupled in a series of elementary reaction steps in respiration and photosynthesis to harvest and convert energy consumed in foodstuffs or by absorption of light into high energy chemi-cal bonds in the form of ATP. These electron transfer processes may be modulated by conformational dynamics within the protein matrix or at the protein-protein interface, the energetics of which are still not well understood. Photoacoustic calorimetry is an estab-lished method of obtaining time-resolved reaction enthalpy and volume changes on the nanosecond to microsecond timescale. Photoacoustic calorimetry is used here to probe 1) the energetics and volume changes for ET between the self-assembled anionic uroporphy-rin:cytochrome c complex and the role of the observed volume changes in modulating ET within the complex, 2) the enthalpy and volume change for the excited state PCET reac-tion of a tyramine functionalized ruthenium(II) bis-(2,2'-bipyridine)(4-carboxy-4'-methyl-2,2'-bipyrine) meant to be a model for the tyrosine PCET chemistry carried out by cyto-chrome c oxidase and photosystem II, 3) the enthalpy and volume changes related to car-bon monoxide and tryptophan migration in heme tryptophan catabolic enzyme indoleam-ine 2,3-dioxygenase.
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Mondragon, Camacho Ricardo. "Non-physical enthalpy method for phase change modelling in the solidification process." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/nonphysical-enthalpy-method-for-phase-change-modelling-in-the-solidification-process(2ab7597c-eaaa-44d8-abb8-0bf49e413c76).html.
Повний текст джерелаАнотація:
This research is concerned with the development of a mathematical approach for energy and mass transport in solidification modelling involving a control volume (CV) technique and finite element method (FEM) and incorporating non-physical variables in its solution. The former technique is used to determine an equivalent capacitance to describe energy transport whilst the latter technique provides temperatures over the material domain. The numerical solution of the transport equations is achieved by the introduction of two concepts, i.e. weighted transport equations and non-physical variables. The main aim is to establish equivalent transport equations that allow exact temporal integration and describe the behaviour of non-physical variables to replace the original governing transport equations. The variables defined are non-physical in the sense that they are dependent on the velocity of the moving CV. This dependence is a consequence of constructing transport equations that do not include flux integrals. The form of the transport equations facilitate the construction of a FEM formulation that is applicable to heat and mass transport problems and caters for singularities arising from phase-change, which can prove difficult to model. However, applying the non-physical enthalpy method (NEM) any singularity involved in the solidification process is precisely identified and annihilated.
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Alamaro, Moshe 1948. "Wind wave tank for experimental investigation of momentum and enthalpy transfer from the ocean surface at high wind speed." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/51587.
Повний текст джерелаАнотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001.Includes bibliographical references (leaves 77-79).
Thermodynamic analysis and numerical modeling of hurricane intensity has shown that its is controlled by the enthalpy transfer from the ocean surface and by drag. Direct measurements of drag, evaporation, and sensible heat transfer are not easily performed on the high seas. Therefore, a wind wave tank has been constructed in which a few aspects of a tropical storm are simulated. The air velocity inside the annular tank is comparable to that of hurricane. However, the three dimensionality of the tank obscures the quantitative comparison between experiments and actual conditions over the surface of the ocean at high wind speeds. The design of the wind wave tank and the initial experiments create a foundation for future and more comprehensive experimental programs. This thesis focuses mainly on the design and engineering of the tank, and on the fluid mechanics of the rotational flow in the tank. It also provides preliminary experimental data on the drag at high wind speeds obtained by using spindown experiments.
by Moshe Alamaro.
S.M.
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Stanczak-Mrozek, Kinga Izabela. "Antimicrobial resistance gene transfer between MRSA from colonized patients." Thesis, St George's, University of London, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687072.
Повний текст джерелаАнотація:
Methicillin-resistant Staphylococcus aureus (MRSA) are opportunistic commensal bacteria that are evolving to become increasingly resistant to antimicrobial agents. Resistance is due to acquisition of resistance genes encoded by mobile genetic elements (MGEs) but little is known about the gene transfer and conditions influencing this process in clinically important MRSA isolates. In this thesis I showed that populations of MRSA colonizing isolates vary phenotypically in antimicrobial resistance (AMR) and genotypically in MGE profiles. A potential mechanism of horizontal gene transfer (HGT) in colonized patients is generalized transducing bacteriophage and we detected free bacteriophage in nasal swabs. AMR and genetic variability have implications for diagnostics, epidemiology, antimicrobial stewardship and selective pressures driving evolution of MRSA populations. All clinical strains harbour at least one prophage which are potentially capable of HGT. Bacteriophage are thought to be induced by environmental conditions including exposure to antibiotics, and 30% of hospitalized patients who are carriers are prescribed antibiotics. Exposure of clinical MRSA isolates to sub-inhibitory concentration of range of anti microbials resulted in increased phage induction and resistance gene transfer, however the ratio of virulent particles to transducing particles differed for each antimicrobial using the new technology of droplet digital peR. Exposure of colonizing MRSA strains to specific antimicrobials may lead to enhanced horizontal transfer of antimicrobial resistance potentially leading to fully resistant MRSA. MRSA isolates collected from patient admitted to St Georges NHS Healthcare Trust between 1999-2003 versus 2012-2013 showed that the recent isolates more easily induced phages and transferred resistance genes more effectively, especially upon induction with ciprofloxacin, suggesting that MRSA is evolving over time to transfer AMR genes more effectively. I developed a new in vitro model mimicking in vivo colonization conditions in the human host by co-culturing two distinct isolates from MRSA carriers in human plasma. Transfer of DNA via HGT occurred at high frequency in plasmas from all 8 donors. However, the presence of certain resistance genes had a fitness cost in some plasma but not others. Frequent horizontal transfer of antimicrobial resistance and other genes between isolates during colonization may play an important role in host-pathogen adaptation and evolution.
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Wang, Lin. "Mass Transfer and GDL Electric Resistance in PEM Fuel Cells." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/486.
Повний текст джерелаАнотація:
Many modeling studies have been carried out to simulate the current distribution across the channel and shoulder direction in a proton exchange membrane (PEM) fuel cell. However the modeling results do not show agreement on the current density distribution. At the same time, no experimental measurement result of current density distribution across the channel and the shoulder direction is available to testify the modeling studies. Hence in this work, an experiment was conducted to separately measure the current densities under the channel and the shoulder in a PEM fuel cell by using the specially designed membrane electrode assemblies. The experimental results show that the current density under the channel is lower than that under the shoulder except when the fuel cell load is high. Afterwards two more experiments were carried out to find out the reason causing the higher current density under the shoulder. The effects of the electric resistance of gas diffusion layer (GDL) in the lateral and through-plane directions on the current density distribution were studied respectively. The experimental results show that it is the through-plane electric resistance that leads to the higher current density under the shoulder. Moreover, a three-dimensional fuel cell model is developed using FORTRAN. A new method of combining the thin-film model and homogeneous model is utilized to model the catalyst layer. The model is validated by the experimental data. The distribution of current density, oxygen concentration, membrane phase potential, solid phase potential and overpotential in a PEM fuel cell have been studied by the model. The modeling results show that the new modeling method provides better simulations to the actual transport processes and chemical reaction in the catalyst layer of a PEM fuel cell.
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Barbosa, Teresa Maria Leite Martins. "Tetracycline resistance transfer among obligate anaerobes from the ruminant gut." Thesis, University of Aberdeen, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286850.
Повний текст джерелаАнотація:
The main aim of this work was to investigate the nature, distribution and transmissibility of tetracycline resistance (TcR) genes among ruminant anaerobic bacteria. Two TcR rumen strains of Butyrivibrio fibrisolvens, 1.230 and 1.23, were able to transfer the resistance phenotype to the type strain, 2221R although a third TcR strain, 1.210, could not. PCR amplification of 16S rDNA sequences showed that the three isolates were phylogenetically distinct from the recipient strain, but related to each other. Hybridisation work suggested the presence of two chromosomal TcR determinants among the B. fibrisolvens isolates. All three strains contained a non-transferable tet(O) gene, 100% identical at the nucleotide level with tet(O) from S. pneumoniae. The mobile TcR determinant present in strains 1.230 and 1.23, proved to be a novel ribosome protection tet gene, tet(V), whose gene product shares only 68% amino acid identity with its closest relatives, TetO/TetM and has G+C content considerably higher than that of other B. fibrisolvens genes. tet(V) was also identified in two Australian rumen B. fibrisolvens strains, in the rumen anaerobes Selenomonas ruminantium and Mitsuokella multiacidus, and in a pig isolate of M. multiacidus. These results provide evidence for gene transfer between obligate and facultative anaerobes from different gut ecosystems and different geographical locations. PFGE demonstrated that mobile chromosomal elements 40-50 kb in size, TnB1230 and TnB123, with preferred insertion sites in the recipient genome mediated the transfer of tet(V) in B. fibrisolvens. No homology was found between TnB1230 and regions from Tn916 and Tn5253. TnB1230 is not associated with tet(V) in the other bacterial strains, suggesting that a diverse range of elements carry the gene in different bacteria. Although tet(V) is chromosomally encoded in the majority of the strains examined, there is some evidence that the gene may be located in a plasmid in S. ruminantium FB32 and FB34.
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Barnard, Danielle. "Conjugative Transfer Pathways of High-Level Mupirocin Resistance and Conjugative Transfer Genes in Staphylococcus." Digital Commons @ East Tennessee State University, 2006. https://dc.etsu.edu/etd/2188.
Повний текст джерелаАнотація:
To combat widespread infections caused by Staphylococcus aureus, mupirocin was introduced at the Veterans Affairs Medical Center, Mountain Home, Tennessee. Soon after introduction, high-level mupirocin-resistance emerged. The rapid emergence was hypothesized to be due to conjugative transfer of the mupA resistance gene from S. epidermidis to S. aureus. Results have shown that transfer of high-level mupirocin-resistance from S. aureus donors commonly occurs. However, transfer from naturally-occurring S. epidermidis donors was not attainable. Staphylococcus epidermidis transconjugants, however, were capable of serving as donors. Further examination of non-transmissibility included PCR analysis of conjugative transfer genes (tra genes) in capable and non-capable donors. Results confirmed that capable donors possess full-length copies of selected transfer genes. Non-capable donors varied in the presence/absence of full-length copies of transfer genes, but none had all three genes. The genetic differences among non-capable donors suggest that non-transmissibility has arisen independently in different strains via gene deletions and recombinations.
Книги з теми "Resistance to enthalpy transfer"
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Salyers, Abigail A. Antibiotic resistance transfer in the mammalian intestinal tract. New York: Springer, 1995.
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Lai, Chan Ji. Flow resistance, discharge capacity and momentum transfer in smooth compound closed ducts. Birmingham: University of Birmingham, 1986.
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Pioro, I. L. Heat transfer and hydraulic resistance at supercritical pressures in power engineering applications. New York: ASME Press, 2007.
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Barrington, Frank. Conjugative transfer of high-level gentamicin resistance in clinical and community isolates of enterococci. [S.l: The Author], 1993.
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Thomas, Barbara Ruth. Guidelines for seed transfer of western white pine in B.C. based on frost hardiness. [Victoria, B.C.]: Forestry Canada, 1993.
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Sjödin, Christina. Transfer of resistance against Phoma lingam to Brassica napus L. via somatic hybridization in combination with in vitro selection. Uppsala [Sweden]: Dept. of Plant Breeding, Institutionen för Växtförädling, Swedish University of Agricultural Sciences, 1989.
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Yuen, Wai-hong Kenneth. A study of boundary shear stress, flow resistance and momentum transfer in open channels with simple and compound trapezoidal cross section. Birmingham: University of Birmingham, 1989.
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Karhumäki, Eliisa. Modulation of infection resistance of mice with dialysates containing transfer factor-like activity derived from leukocytes of man and other mammalia. Tampere: University of Tampere, 1988.
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Nielsen, C. V. Modeling of Thermo-Electro-Mechanical Manufacturing Processes: Applications in Metal Forming and Resistance Welding. London: Springer London, 2013.
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National Heat Transfer Conference (24th 1987 Pittsburgh, Pa.). Fundamentals of conduction and recent developments in contact resistance: Presented at the 24th National Heat Transfer Conference and Exhibition, Pittsburg, Pennsylvania, August 9-12, 1987 ; sponsored by the Heat Transfer Division, ASME ; edited by M. Imber, G.P. Peterson ; with M.M. Yovanovich. New York, N.Y. (345 E. 47th St. New York 10017): American Society of Mechanical Engineers, 1987.
Знайти повний текст джерелаЧастини книг з теми "Resistance to enthalpy transfer"
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Tacke, K. H., and Α. Harnisch. "Finite Difference Enthalpy Methods for Dendritic Growth." In Heat Transfer, edited by L. C. Wrobel and C. A. Brebbia, 165–76. Berlin, Boston: De Gruyter, 1991. http://dx.doi.org/10.1515/9783110853209-012.
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Gooch, Jan W. "Resistance Transfer Factor (RTF)." In Encyclopedic Dictionary of Polymers, 920. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_14682.
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Saharan, Govind Singh, Naresh K. Mehta, and Prabhu Dayal Meena. "Transfer of Disease Resistance." In Genomics of Crucifer’s Host-Resistance, 265–357. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-0862-9_4.
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Gong, Z. X., Y. F. Zhang, and A. S. Mujumdar. "An Efficient Finite Element Procedure for the Solution of Enthalpy Model for Phase Change Heat Conduction Problems." In Heat Transfer, edited by L. C. Wrobel and C. A. Brebbia, 93–104. Berlin, Boston: De Gruyter, 1991. http://dx.doi.org/10.1515/9783110853209-007.
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Kayser, F. H., and B. Berger-Bächi. "Transposon Transfer of Drug Resistance." In Perspectives in Antiinfective Therapy, 109–14. Wiesbaden: Vieweg+Teubner Verlag, 1989. http://dx.doi.org/10.1007/978-3-322-86064-4_15.
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Kayser, F. H., and B. Berger-Bächi. "Transposon Transfer of Drug Resistance." In Perspectives in Antiinfective Therapy, 177–85. Berlin, Heidelberg: Springer Berlin Heidelberg, 1989. http://dx.doi.org/10.1007/978-3-642-46666-3_16.
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Roy, Paul H., and Sally R. Partridge. "Genetic Mechanisms of Transfer of Drug Resistance." In Antimicrobial Drug Resistance, 61–76. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-46718-4_5.
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Roy, Paul H. "Genetic Mechanisms of Transfer of Drug Resistance." In Antimicrobial Drug Resistance, 53–64. Totowa, NJ: Humana Press, 2009. http://dx.doi.org/10.1007/978-1-59745-180-2_5.
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Sasoh, A., X. Chang, T. Murayama, and T. Fujiwara. "Radiative heat transfer from non-equilibrium high-enthalpy shock layers." In Shock Waves, 723–26. Berlin, Heidelberg: Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-77648-9_113.
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Budak-Alpdogan, Tulin, and Joseph R. Bertino. "Chemoprotection by Transfer of Resistance Genes." In Gene Therapy of Cancer, 661–704. Totowa, NJ: Humana Press, 2009. http://dx.doi.org/10.1007/978-1-59745-561-9_34.
Повний текст джерелаТези доповідей конференцій з теми "Resistance to enthalpy transfer"
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Krishnan, Shankar, Jayathi Y. Murthy, and Suresh V. Garimella. "A Two-Temperature Model for Solid/Liquid Phase Change in Metal Foams." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56337.
Повний текст джерелаАнотація:
Transient solid/liquid phase change occurring in metal foams impregnated with phase change material (PCM) is investigated. Natural convection in the melt is considered. Volume-averaged mass and momentum equations are employed, with the Brinkman-Forchheimer extension to the Darcy law to model the porous resistance. Owing to the difference in the thermal diffusivities between the metal foam and the PCM, local thermal equilibrium between the two is not assured. Assuming equilibrium melting at the pore scale, separate volume-averaged energy equations are written for the solid metal foam and the PCM, and are closed using an interstitial heat transfer coefficient. The enthalpy method is employed to account for phase change. The governing equations are solved implicitly using a finite volume method on a fixed grid. The influence of Rayleigh number, Stefan number, and interstitial Nusselt number on the temporal evolution of the melt front location, temperature differentials between the solid and fluid, and the melting rate is documented and discussed. The merits of incorporating metal foam for improving effective thermal conductivity of thermal storage systems are discussed.
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Hawkes, Grant, and Russell Jones. "CFD Model of a Planar Solid Oxide Electrolysis Cell: Base Case and Variations." In ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32310.
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A three-dimensional computational fluid dynamics (CFD) model has been created to model high-temperature steam electrolysis in a planar solid oxide electrolysis cell (SOEC). The model represents a single cell, as it would exist in an electrolysis stack. Details of the model geometry are specific to a stack that was fabricated by Ceramatec, Inc. and tested at the Idaho National Laboratory. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A solid-oxide fuel cell (SOFC) module adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, activation over-potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Mean model results are shown to compare favorably with experimental results obtained from an actual ten-cell stack tested at INL. Mean per-cell area-specific-resistance (ASR) values decrease with increasing current density, consistent with experimental data. Predicted mean outlet hydrogen and steam concentrations vary linearly with current density, as expected. Effects of variations in operating temperature, gas flow rate, cathode and anode exchange current density, and contact resistance from the base case are presented. Discussion of thermal neutral voltage, enthalpy of reaction, hydrogen production, cell thermal efficiency, cell electrical efficiency, and Gibbs free energy are discussed and reported herein.
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Fronk, Brian M., and Srinivas Garimella. "Heat Transfer and Pressure Drop During Condensation of Ammonia in Microchannels." In ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/mnhmt2012-75265.
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An experimental investigation of condensation heat transfer and pressure drop of ammonia flowing through a single, circular, microchannel (D = 1.435 mm) was conducted. The use of ammonia in thermal systems is attractive due to its high latent heat, favorable transport properties, zero ozone depletion (ODP), and zero global warming potential (GWP). At the same time, microchannel condensers are also being adopted to increase heat transfer performance to reduce component size and improve energy efficiency. While there is a growing body of research on condensation of conventional refrigerants (i.e., R134a, R404A, etc.) in microchannels, there are few data on condensation of ammonia at the microscale. Ammonia has significantly different fluid properties than synthetic HFC and HCFC refrigerants. For example, at Tsat = 60°C, ammonia has a surface tension 3.2 times and an enthalpy of vaporization 7.2 times greater than those of R134a. Thus, models validated with data for synthetic refrigerants may not predict condensation of ammonia with sufficient accuracy. The test section consisted of a stainless steel tube-in-tube heat exchanger with ammonia flowing through a microchannel inner tube and cooling water flowing through the annulus in counterflow. A high flow rate of water was maintained to provide an approximately isothermal heat sink and to ensure the condensation thermal resistance dominated the heat transfer process. Data were obtained at mass fluxes of 75 and 150 kg m−2 s−1, multiple saturation temperatures, and in small quality increments (Δx∼15–25%) from 0 to 1. Trends in heat transfer coefficients and pressure drops are discussed and the results are used to assess the applicability of models developed for both macro and microscale geometries for predicting the condensation of ammonia.
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Wang, Han, Qincheng Bi, Linchuan Wang, Haicai Lv, and Laurence K. H. Leung. "Experimental Study of Heat Transfer to Supercritical Pressure Water Flowing in a 2×2 Rod Bundle." In 2014 22nd International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icone22-30313.
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An experiment has recently been performed at Xi’an Jiaotong University to study the wall temperature and pressure drop at supercritical pressures with upward flow of water inside a 2×2 rod bundle. A fuel-assembly simulator with four heated rods was installed inside a square channel with rounded corner. The outer diameter of each heated rod is 8 mm with an effective heated length of 600 mm. Experimental parameters covered the pressure of 23–28 MPa, mass flux of 350–1000 kg/m2s and heat flux on the rod surface of 200–1000 kW/m2. According to the experimental data, it was found that the circumferential wall temperature distribution of a heated rod is not uniform. The temperature difference between the maximum and the minimum varies with heat flux and/or mass flux. Heat transfer characteristics of supercritical water in bundle were discussed with respect to various heat fluxes. The effect of heat flux on heat transfer in rod bundles is similar with that in tubes or annuli. In addition, flow resistance reflected in the form of pressure loss has also been studied. Experimental results showed that the total pressure drop increases with bulk enthalpy and mass flux. Four heat transfer correlations developed for supercritical pressures water were compared with the present test data. Predictions of Jackson correlation agrees closely with the experimental data.
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deBock, Peter, Rinaldo Miorini, Cathleen Hoel, Darin Sharar, and Bryan Whalen. "Experimental Characterization of Heat Transfer and Thermal Energy Storage Capability Using Swirling Two-Phase Flow in the Package Integrated Cyclone COoler (PICCO)." In ASME 2020 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ipack2020-2606.
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Abstract The increasing demand for high power density wide-bandgap power electronics has propelled heat transfer research leading to a constant increase in the thermal performance of cold plates and heat sinks. Most of this research has focused on reducing thermal resistance of the package which can have a detrimental effect on transient thermal performance if thermal capacitance is reduced. In order to provide both a low thermal resistance and a higher thermal capacitance integrated into the package and near the thermal junction, a new cold plate called the Package Integrated Cyclone COoler (PICCO) was developed. GE Research and the US Army Research Lab collaborated to explore and validate the potential of this concept. The PICCO coldplate, which is enabled by 3D printing, establishes a swirling coolant flow field to remove heat. The swirling flow is anticipated to significantly aid in vapor removal from the surface and hence allow for the fluid to provide thermal capacitance through two-phase heat transfer efficiently. This paper describes the experiment design and development for thermal storage and cooling performance characterization of PICCO. The test rig includes a high-pressure capability gear pump moving fluid first through a Coriolis flowmeter and then through PICCO, where the fluid is accelerated in the cyclone and heated by miniaturized ceramic heaters, simulating SiC power electronics. The coolant releases the accumulated enthalpy to a plate-fin heat exchanger that is connected to a chiller. Several absolute and differential pressure transducers and thermocouples monitor the state of FC-72. The experiments will provide empirical transfer functions characterizing the PICCO pressure drop, heat transfer coefficient, critical heat flux and thermal energy storage capability.
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Randle, Lindsey V., and Brian M. Fronk. "Investigation of Buoyancy Effects in Asymmetrically Heated Near-Critical Flows of Carbon Dioxide in Horizontal Microchannels Using Infrared Thermography." In ASME 2021 Heat Transfer Summer Conference collocated with the ASME 2021 15th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/ht2021-63004.
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Abstract In this study, we use infrared thermography to calculate local heat transfer coefficients of top and bottom heated flows of near-critical carbon dioxide in an array of parallel microchannels. These data are used to evaluate the relative importance of buoyancy for different flow arrangements. A Joule heated thin wall made of Inconel 718 applies a uniform heat flux either above or below the horizontal flow. A Torlon PAI test section consists of three parallel microchannels with a hydraulic diameter of 923 μm. The reduced inlet temperature (TR = 1.006) and reduced pressure (PR = 1.03) are held constant. For each heater orientation, the mass flux (520 kgm−2s−2 ≤ G ≤ 800 kgm−2s−2) and heat flux (4.7 Wcm−2 ≤ q″ ≤ 11.1 Wcm−2) are varied. A 2D resistance network analysis method calculates the bulk temperatures and heat transfer coefficients. In this analysis, we divide the test section into approximately 250 segments along the stream-wise direction. We then calculate the bulk temperatures using the enthalpy from the upstream segment, the heat flux in a segment, and the pressure. To isolate the effect of buoyancy, we screen the data to omit conditions where flow acceleration may be important or where relaminarization may occur. In the developed region of the channel, there was a 10 to 15 percent reduction of the local heat transfer coefficients for the upward heating mode compared to downward heating with the same mass and heat fluxes. Thus buoyancy effects should be considered when developing correlations for these types of flow.
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Tomm, Uwe, Sascha Weiske, Ahmet Coksen, Youness Rafaa, and Stefan Münz. "Validation of a Heat Transfer Prediction Approach Inside Turbochargers and its Application on Turbocharged Engine Performance Analysis." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63195.
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In the present study, the entire energy balance of a turbocharger is investigated applying an experimentally validated numerical approach with the intention of examining the heat transfer mechanism inside the turbo. The heat transfer results thus obtained are used amongst others to determine the diabatic effects on the turbine and compressor flow resulting in heat-transfer corrected performance maps. These maps are applied as matching data to 1D engine performance calculation and are utilized in the engine process simulation procedure with GT Power™. In detail, the numerical approach of the entire energy balance is based on a thermal network model (RC-resistance / capacity) where the 3D geometry of the turbocharger is subdivided into segments. These segments are defined as lumped mass elements of the thermal network. The entire energy balance of the modeled turbo is fulfilled by coupling the thermal network of the structure to the enthalpy flows of the turbine, compressor, oil circuit, and water coolant as well as the heat losses to ambient. The heat transfer between the structure and the enthalpy flows, respectively, is achieved by using heat transfer coefficients (HTC) performed in accordance with Nusselt-No. laws. Heat loss to ambient is expressed by natural convection and radiation. In general it would be possible to perform the energy balance of the turbo model in the steady state or transient regime. A time-governed finite volume calculation scheme is used for the solution algorithms. The code of the turbo heat transfer approach (THT) is written in Matlab™, something which facilitates flexible adjustments on the algorithm and good post-processing capabilities. Two routes are resorted to for validating the THT approach. Gas stand tests with instrumented turbochargers using thermocouples and pressure sensors are conducted in the first assignment for generating the essential experimental data. Segmentation of the 3D turbocharger geometry into discrete elements is accomplished in the second assignment by means of CAD technology and used for both, the setup of the THT thermal network model and in parallel for the generation of an AnsysCFX™ 3D CAE model. The same HTC thermal boundary conditions are applied to both models which is favorable in as far as it provides a one-to-one comparison of the heat flux and mean temperature in each segment of the two models, Matlab™ THT and CFX™. Ansys™ model heat flux and mean segment temperature results are validated by the measured experimental temperature data. The THT network model properties such as segment volume, areas, volume, and element distances are calibrated applying the results of the 3D CAD and CAE Ansys™ model. The results of the two numerical models are compared with each other, thus demonstrating the qualitative and quantitative level of agreement. The THT approach that has been developed is successfully applied to GT Power™ gasoline engine model. A thermal network model of that applied turbocharger was setup and validated by gas-stand and engine data obtained on an experimental basis with an instrumented turbo. Finally it was possible to demonstrate that the heat-transfer corrected turbocharger performance map data which was provided utilizing the THT model approach brings about a significant benefit to the determination process aimed at achieving a tailored turbocharger thermodynamic layout.
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Saha, Sudipta, Amitav Tikadar, Jamil Khan, and Tanvir Farouk. "Numerical Analysis on Evaporation Assisted Convective Cooling: Effect of Surface Morphology." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-11065.
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Abstract With an escalating need to find ways to reduce the water consumption in industrial cooling system, on-demand hybrid cooling has been a topic of great interest. The main concept of this cooling method is centered upon the utilization of huge exchange of enthalpy associated with phase change process in a conventional convective cooling system. In this study, a multidimensional multi-physics model has been employed to study a system that undergoes this dual mode cooling process where both convection and evaporation contribute to the heat transfer process. The computational domain considered is comprised of a thin liquid film that undergoes evaporation with constant heat flux provided from the bottom and a convective loading of laminar air flow above it. Evaporation takes place at the liquid-gas interface and the evaporated mass is being carried away by the incoming air, hence augmenting the convective cooling through the phase change process. This is an extension of our prior work where the surface structure modification (i.e. undulated surface) on the performance of this proposed hybrid cooling method is numerically investigated. Array of hemispherical structures have been introduced as the surface introducing the heat flux to the liquid film. The objective is to increase the surface to volume ratio and decrease the thermal resistance across the liquid film. The predictions indicate that with the increase in the height of the undulated surface the thermal resistance across the liquid film tends to decrease. Results from these simulations show that a ∼50% reduction in the thermal resistance can be achieved by the surface structure modification while the net evaporation flux can be doubled compared to a flat film configuration.
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Krishnan, Shankar, Jayathi Y. Murthy, and Suresh V. Garimella. "Analysis of Solid-Liquid Phase Change Under Pulsed Heating." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-82553.
Повний текст джерелаАнотація:
Solid/liquid phase change occurring in a rectangular container with and without metal foams subjected to periodic pulsed heating is investigated. Natural convection in the melt is considered. Volume-averaged mass and momentum equations are employed, with the Brinkman-Forchheimer extension to Darcy’s law to model the porous-medium resistance. A local thermal non-equilibrium model, assuming equilibrium melting at the pore scale, is employed for energy transport through the metal foams and the interstitial phase change material (PCM). Separate volume-averaged energy equations for the foam and the PCM are written and are closed using a heat transfer coefficient. The enthalpy method is employed to account for phase change. The governing equations for the PCM without foam are derived from the porous medium equations. The governing equations are solved implicitly using a finite volume method on a fixed grid. The coupled effect of pulse width and natural convection in the melt is found to have a profound effect on the overall melting behavior. The influence of pulse width, Stefan number, Rayleigh number and interstitial Nusselt number on the temporal evolution of the melt front location and the melting rate for both the cases with and without metal foams is investigated.
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Pasandideh-Fard, M., and J. Mostaghimi. "Droplet Impact and Solidification in a Thermal Spray Process: Droplet-Substrate Interactions." In ITSC 1996, edited by C. C. Berndt. ASM International, 1996. http://dx.doi.org/10.31399/asm.cp.itsc1996p0637.
Повний текст джерелаАнотація:
Abstract Experiments have shown that the mechanical properties of plasma-sprayed coatings depend to a large extent on the details of the spraying process, in particular, they are strongly dependent on the details of the solidification and deformation history of the individual droplets which are in turn highly affected by the substrate conditions such as its temperature, material, and surface thermal contact resistance. In this study, droplet-substrate interactions are investigated through a complete numerical solution of droplet impact and solidification for a typical thermal spray process. The energy equation is numerically solved for both droplet and substrate regions; the solution is based on the Enthalpy Method for the liquid and solidified parts of the droplet, and the conduction heat transfer in the substrate. The numerical solution for the complete Navier-Stokes equations is based on the modified SOLA-VOF method using rectangular mesh in axisymmetric geometry. The developed model is suited for investigating droplet impact and simultaneous solidification permitting any desired condition at the substrate. The splat shape, the solidification front, and the temperature profile in the entire droplet and substrate regions are obtained at any desired time elapsed after the impact. Through these results, the nucleation and growth of solidification and droplet-substrate interactions are extensively studied.
Звіти організацій з теми "Resistance to enthalpy transfer"
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Rich, J. W., Walter R. Lempert, and Igor V. Adamovich. Energy Transfer Processes Among Electrons and Vibrationally Excited Air Species in High Enthalpy Flows. Fort Belvoir, VA: Defense Technical Information Center, February 2007. http://dx.doi.org/10.21236/ada478735.
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Haus, Brian K., and Mark A. Donelan. Enthalpy Flux in Extreme Winds and the Roles of Sensible, Latent and Spray Heat Transfer Processes. Fort Belvoir, VA: Defense Technical Information Center, September 2007. http://dx.doi.org/10.21236/ada573403.
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Zelcer, Aaron, and George Bates. Asymmetric hybridization in crop plants: studies on cellular and genetic mechanisms and transfer of viral resistance. United States Department of Agriculture, January 1995. http://dx.doi.org/10.32747/1995.7604276.bard.
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Gera, Abed, Abed Watad, P. Ueng, Hei-Ti Hsu, Kathryn Kamo, Peter Ueng, and A. Lipsky. Genetic Transformation of Flowering Bulb Crops for Virus Resistance. United States Department of Agriculture, January 2001. http://dx.doi.org/10.32747/2001.7575293.bard.
Повний текст джерелаАнотація:
Objectives. The major aim of the proposed research was to establish an efficient and reproducible genetic transformation system for Easter lily and gladiolus using either biolistics or Agrobacterium. Transgenic plants containing pathogen-derived genes for virus resistance were to be developed and then tested for virus resistance. The proposal was originally aimed at studying cucumber mosaic virus (CMV) resistance in plants, but studies later included bean yellow mosaic virus (BYMV). Monoclonal antibodies were to be tested to determine their effectiveness in interning with virus infection and vector (aphid) transmission. Those antibodies that effectively interfered with virus infection and transmission were to be cloned as single chain fragments and used for developing transgenic plants with the potential to resist virus infection. Background to the topic. Many flower crops, as lily and gladiolus are propagated vegetatively through bulbs and corms, resulting in virus transmission to the next planting generation. Molecular genetics offers the opportunity of conferring transgene-mediated disease resistance to flower crops that cannot be achieved through classical breeding. CMV infects numerous plant species worldwide including both lilies and gladioli. Major conclusions, solutions and achievements. Results from these for future development of collaborative studies have demonstrated the potential transgenic floral bulb crops for virus resistance. In Israel, an efficient and reproducible genetic transformation system for Easter lily using biolistics was developed. Transient as well as solid expression of GUS reporter gene was demonstrated. Putative transgenic lily plantlets containing the disabled CMV replicase transgene have been developed. The in vitro ability of monoclonal antibodies (mAbs) against CMV to neutralize virus infectivity and block virus transmission by M. persicae were demonstrated. In the US, transgenic Gladiolus plants containing either the BYMV coat protein or antisense coat protein genes have been developed and some lines were found to be virus resistant. Long-term expression of the GUS reporter gene demonstrated that transgene silencing did not occur after three seasons of dormancy in the 28 transgenic Gladiolus plants tested. Selected monoclonal antibody lines have been isolated, cloned as single chain fragments and are being used in developing transgenic plants with CMV resistance. Ornamental crops are multi-million dollar industries in both Israel and the US. The increasing economic value of these floral crops and the increasing ban numerous pesticides makes it more important than ever that alternatives to chemical control of pathogens be studied to determine their possible role in the future. The cooperation resulted in the objectives being promoted at national and international meetings. The cooperation also enabled the technology transfer between the two labs, as well as access to instrumentation and specialization particular to the two labs.
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Hansen, Peter J., and Amir Arav. Embryo transfer as a tool for improving fertility of heat-stressed dairy cattle. United States Department of Agriculture, September 2007. http://dx.doi.org/10.32747/2007.7587730.bard.
Повний текст джерелаАнотація:
The overall objective of the current proposal is to develop procedures to improve the pregnancy rate achieved following transfer of fresh or cryopreserved embryos produced in the laboratory into heat-stress recipients. The overall hypothesis is that pregnancy rate in heat-stressed lactating cows can be improved by use of embryo transfer and that additional gains in pregnancy rate can be achieved through development of procedures to cryopreserve embryos, select embryos most likely to establish and maintain pregnancy after transfer, and to enhance embryo competence for post-transfer survival through manipulation of culture conditions. The original specific objectives were to 1) optimize procedures for cryopreservation (Israel/US), 2) develop procedures for identifying embryos with the greatest potential for development and survival using the remote monitoring system called EmbryoGuard (Israel), 3) perform field trials to test the efficacy of cryopreservation and the EmbryoGuard selection system for improving pregnancy rates in heat-stressed, lactating cows (US/Israel), 4) test whether selection of fresh or frozen-thawed blastocysts based on measurement of group II caspase activity is an effective means of increasing survival after cryopreservation and post-transfer pregnancy rate (US), and 5) identify genes in blastocysts induced by insulin-like growth factor-1 (IGF-1) (US). In addition to these objectives, additional work was carried out to determine additional cellular determinants of embryonic resistance to heat shock. There were several major achievements. Results of one experiment indicated that survival of embryos to freezing could be improved by treating embryos with cytochalasin B to disrupt the cytoskeleton. An additional improvement in the efficacy of embryo transfer for achieving pregnancy in heat-stressed cows follows from the finding that IGF-1 can improve post-transfer survival of in vitro produced embryos in the summer but not winter. Expression of several genes in the blastocyst was regulated by IGF-1 including IGF binding protein-3, desmocollin II, Na/K ATPase, Bax, heat shock protein 70 and IGF-1 receptor. These genes are likely candidates 1) for developing assays for selection of embryos for transfer and 2) as marker genes for improving culture conditions for embryo production. The fact that IGF-1 improved survival of embryos in heat-stressed recipients only is consistent with the hypothesis that IGF-1 confers cellular thermotolerance to bovine embryos. Other experiments confirmed this action of IGF-1. One action of IGF-1, the ability to block heat-shock induced apoptosis, was shown to be mediated through activation of the phosphatidylinositol 3-kinase pathway. Other cellular determinants of resistance of embryos to elevated temperature were identified including redox status of the embryo and the ceramide signaling pathway. Developmental changes in embryonic apoptosis responses in response to heat shock were described and found to include alterations in the capacity of the embryo to undergo caspase-9 and caspase-3 activation as well as events downstream from caspase-3 activation. With the exception of IGF-1, other possible treatments to improve pregnancy rate to embryo transfer were not effective including selection of embryos for caspase activity, treatment of recipients with GnRH.and bilateral transfer of twin embryos. In conclusion, accomplishments achieved during the grant period have resulted in methods for improving post-transfer survival of in vitro produced embryos transferred into heat-stressed cows and have lead to additional avenues for research to increase embryo resistance to elevated temperature and improve survival to cryopreservation. In addition, embryo transfer of vitrified IVF embryos increased significantly the pregnancy rate in repeated breeder cows.
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Sink, Ken, Shamay Izhar, and Abraham Nachmias. Asymmetric Somatic Hybridization: Developing a Gene Transfer System for Solanaceous Vegetable Crops. United States Department of Agriculture, February 1996. http://dx.doi.org/10.32747/1996.7613010.bard.
Повний текст джерелаАнотація:
Highly asymmetric somatic hybrid plants were obtained by PEG/DMSO fusion of gamma irradiated (100, 250, 7500 and 1000 Gy) protoplasts of a (KmR-) interspecific hybrid Lycopersicon esculentum x L. pennellii (EP) with protoplasts of eggplant (E). Somatic hybrid calli were selected based on kanamycin resistance and verified by PCR of the NptII gene, RAPD's and Southern's using potato rDNA pTHG2 probes. Flow cytometry indicated all hybrid calli that did not regenerate shoots were 5-9n. Three asymmetric plants regenerated only from callus close to 4n and such calli oly occurred when EP received 100 Gy. The asymmetric plants had eggplant morphology and regenerated from one hybrid callus with 6.29 average size tomato chromosomes. Limited amounts of EP DNA were found in the three somatic hybrid plants H18-1 to -3 by dot-blot hybridization with probe pTHG2, to be equivalent to 6.23, 5.41, and 5.95 % EP, respectively. RFLP analysis of Lycopersicon esculentum and L. pennellii specific chromosomes revealed that only fragments of 8 to 10 out of the 24 EP chromosomes are present in the asymmetric plants. Transgenic plants 2-3, 2-4 and 10-3 were found resistant to verticillium; suggesting successful transfer of the Ve complex from S. torvum to eggplant.
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Perl, Avichai, Bruce I. Reisch, and Ofra Lotan. Transgenic Endochitinase Producing Grapevine for the Improvement of Resistance to Powdery Mildew (Uncinula necator). United States Department of Agriculture, January 1994. http://dx.doi.org/10.32747/1994.7568766.bard.
Повний текст джерелаАнотація:
The original objectives are listed below: 1. Design vectors for constitutive expression of endochitinase from Trichoderma harzianum strain P1. Design vectors with signal peptides to target gene expression. 2. Extend transformation/regeneration technology to other cultivars of importance in the U.S. and Israel. 3. Transform cultivars with the endochitinase constructs developed as part of objective 1. A. Characterize foliar powdery mildew resistance in transgenic plants. Background of the topic Conventional breeding of grapevines is a slow and imprecise process. The long generation cycle, large space requirements and poor understanding of grapevine genetics prevent rapid progress. There remains great need to improve existing important cultivars without the loss of identity that follows from hybridization. Powdery mildew (Uncinula necator) is the most important fungal pathogen of grapevines, causing economic losses around the world. Genetic control of powdery mildew would reduce the requirement for chemical or cultural control of the disease. Yet, since the trait is under polygenic control, it is difficult to manipulate through hybridization and breeding. Also, because grapevines are heterozygous and vegetatively propagated cultivar identity is lost in the breeding process. Therefore, there is great need for techniques to produce transgenic versions of established cultivars with heterologous genes conferring disease resistance. Such a gene is now available for control of powdery mildew of grapevines. The protein coded by the Endochitinase gene, derived from Trichoderma harzianum, is very effective in suppressing U. necator growth. The goal of this proposal is to develop transgenic grapevines with this antifungal gene, and to test the effect of this gene on resistance to powdery mildew. Conclusions, achievements and implications Gene transfer technology for grape was developed using commercial cultivars for both wine and table grapes. It paved the way for a new tool in grapevine genetic studies enabling the alteration of specific important traits while maintaining the essential features of existing elite cultivars. Regeneration and transformation technologies were developed and are currently at an advanced stage for USA wine and Israeli seedless cultivars, representing the cutting edge of grape genetic engineering studies worldwide. Transgenic plants produced are tested for powdery mildew resistance in greenhouse and field experiments at both locations. It is our ultimate goal to develop transgenic grapes which will be more efficient and economical for growers to produce, while also providing consumers with familiar products grown with reduced chemical inputs.
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Sessa, Guido, та Gregory Martin. MAP kinase cascades activated by SlMAPKKKε and their involvement in tomato resistance to bacterial pathogens. United States Department of Agriculture, січень 2012. http://dx.doi.org/10.32747/2012.7699834.bard.
Повний текст джерелаАнотація:
The research problem: Pseudomonas syringae pv. tomato (Pst) and Xanthomonas campestrispv. vesicatoria (Xcv) are the causal agents of tomato bacterial speck and spot diseases, respectively. These pathogens colonize the aerial parts of the plant and cause economically important losses to tomato yield worldwide. Control of speck and spot diseases by cultural practices or chemicals is not effective and genetic sources of resistance are very limited. In previous research supported by BARD, by gene expression profiling we identified signaling components involved in resistance to Xcvstrains. Follow up experiments revealed that a tomato gene encoding a MAP kinase kinase kinase (MAPKKKe) is required for resistance to Xcvand Pststrains. Goals: Central goal of this research was to investigate the molecular mechanisms by which MAPKKKεand associated MAP kinase cascades regulate host resistance. Specific objectives were to: 1. Determine whether MAPKKKεplays a broad role in defense signaling in plants; 2. Identify components of MAP kinase cascades acting downstream of MAPKKKε; 3. Determine the role of phosphorylation-related events in the function of MAPKKKε; 4. Isolate proteins directly activated by MAPKKKε-associatedMAPK modules. Our main achievements during this research program are in the following major areas: 1. Characterization of MAPKKKεas a positive regulator of cell death and dissection of downstream MAP kinase cascades (Melech-Bonfil et al., 2010; Melech-Bonfil and Sessa, 2011). The MAPKKKεgene was found to be required for tomato resistance to Xcvand Pstbacterial strains and for hypersensitive response cell death triggered by different R gene/effector gene pairs. In addition, overexpression analysis demonstrated that MAPKKKεis a positive regulator of cell death, whose activity depends on an intact kinase catalytic domain. Epistatic experiments delineated a signaling cascade downstream of MAPKKKεand identified SIPKK as a negative regulator of MAPKKKε-mediated cell death. Finally, genes encoding MAP kinase components downstream of MAPKKKεwere shown to contribute to tomato resistance to Xcv. 2. Identification of tomato proteins that interact with MAPKKKεand play a role in plant immunity (Oh et al., 2011). We identified proteins that interact with MAPKKKε. Among them, the 14-3-3 protein TFT7 was required for cell death mediated by several R proteins. In addition, TFT7 interacted with the MAPKK SlMKK2 and formed homodimersin vivo. Thus, TFT7 is proposed to recruit SlMKK2 and MAPKKK client proteins for efficient signal transfer. 3. Development of a chemical genetic approach to identify substrates of MAPKKKε-activated MAP kinase cascades (Salomon et al., 2009, 2011). This approach is based on engineering the kinase of interest to accept unnatural ATP analogs. For its implementation to identify substrates of MAPKKKε-activated MAP kinase modules, we sensitized the tomato MAP kinase SlMPK3 to ATP analogs and verified its ability to use them as phosphodonors. By using the sensitized SlMPK3 and radiolabeled N6(benzyl)ATP it should be possible to tag direct substrates of this kinase. 4. Development of methods to study immunity triggered by pathogen-associated molecular patterns (PAMPs) in tomato and N. benthamiana plants (Kim et al., 2009; Nguyen et al. 2010). We developed protocols for measuring various PTI-associatedphenotypes, including bacterial populations after pretreatment of leaves with PAMPs, induction of reporter genes, callose deposition at the cell wall, activation of MAP kinases, and a luciferase-based reporter system for use in protoplasts. Scientific and agricultural significance: Our research activities discovered and characterized a signal transduction pathway mediating plant immunity to bacterial pathogens. Increased understanding of molecular mechanisms of immunity will allow them to be manipulated by both molecular breeding and genetic engineering to produce plants with enhanced natural defense against disease. In addition, we successfully developed new biochemical and molecular methods that can be implemented in the study of plant immunity and other aspects of plant biology.
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Watad, Abed A., Paul Michael Hasegawa, Ray A. Bressan, Alexander Vainstein, and Yigal Elad. Osmotin and Osmotin-Like Proteins as a Novel Source for Phytopathogenic Fungal Resistance in Transgenic Carnation and Tomato Plants. United States Department of Agriculture, January 2000. http://dx.doi.org/10.32747/2000.7573992.bard.
Повний текст джерелаАнотація:
The goal of this project is to enhance fungal resistance of carnation and tomato through the ectopic expression of osmotin and other pathogenesis-related (PR) proteins. The research objectives were to evaluate in vitro antifungal activity of osmotin and osmotin and other PR protein combinations against phytopathogens (including Fusarium oxysporum, Verticillium dahliae, Botrytus cinerea or Phytophthora infestans), develop protocols for efficient transformation of carnation and tomato, express PR proteins in transgenic carnation and tomato and evaluate fungal resistance of transgenic plants. Protocols for microprojectile bombardment and Agrobacterium-mediated transformation of carnation were developed that are applicable for the biotechnology of numerous commercial cultivars. Research established an efficient organogenetic regeneration system, optimized gene delivery and transgene expression and defined parameters requisite to the high frequency recovery of transgenic plants. Additionally, an efficient Agrobacterium-mediated transformation protocol was developed for tomato that is applicable for use with numerous commercial varieties. Rigorous selection and reducing the cytokinin level in medium immediately after shoot induction resulted in substantially greater frequency of adventitious shoots that developed defined stems suitable for rooting and reconstitution of transgenic plants. Transformation vectors were constructed for co-expression of genes encoding osmotin and tobacco chitinase Ia or PR-1b. Expression of osmotin, PR-1 and/or chitinase in transgenic carnation mediated a high level resistance of cv. White Sim (susceptible variety) to F. oxysporum f. sp. dianthi, race 2 in greenhouse assays. These plants are being evaluated in field tests. Comprehensive analysis (12 to 17 experiments) indicated that germination of B. cinerea conidia was unaffected by PR protein expression but germ tube elongation was reduced substantially. The disease severity was significantly attenuated by PR protein expression. Constitutive expression of osmotin in transgenic tomato increased resistance to B. cinerea, and P. infestans. Grey mold and late blight resistance was stable through the third selfed generation. The research accomplished in this project will have profound effects on the use of biotechnology to improve carnation and tomato. Transformation protocols that are applicable for efficient stable gene transfer to numerous commercial varieties of carnation and tomato are the foundation for the capacity to bioengineer these crops. The research further establishes that PR proteins provide a measure of enhanced disease resistance. However, considerations of PR protein combinations and conditional regulation and targeting are likely required to achieve; sustained level of resistance.
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Linker, Raphael, Murat Kacira, Avraham Arbel, Gene Giacomelli, and Chieri Kubota. Enhanced Climate Control of Semi-arid and Arid Greenhouses Equipped with Fogging Systems. United States Department of Agriculture, March 2012. http://dx.doi.org/10.32747/2012.7593383.bard.
Повний текст джерелаАнотація:
The main objectives were (1) to develop, implement and validate control procedures that would make it possible to maintain year-round air temperature and humidity at levels suitable for crop cultivation in greenhouses operating in arid and semi-arid regions and (2) to investigate the influence of the operational flexibility of the fogging system on the performance of the system. With respect to the development of climate controllers, we developed a new control approach according to which ventilation is used to maintain the enthalpy of the greenhouse air and fogging is used to adjust the humidity ratio inside the greenhouse. This approach is suitable mostly for greenhouses equipped with mechanized ventilation, and in which the air exchange rate can be controlled with enough confidence. The development and initial validation of the controllers were performed in a small experimental greenhouses located at the Agricultural Research Organization and very good tracking were obtained for both air temperature and relative humidity (maximum mean deviations over a 10-min period with constant setpoints lower than 2.5oC and 5% relative humidity). The robust design approach used to develop the controllers made it possible to transfer successfully these controllers to a much larger semi-commercial greenhouse located in the much drier Arava region. After only minimal adjustments, which did not require lengthy dedicated experiments, satisfactory tracking of the temperature and humidity was achieved, with standard deviation of the tracking error lower than 1oC and 5% for temperature and relative humidity, respectively. These results should help promote the acceptance of modern techniques for designing greenhouse climate controllers, especially since given the large variety of greenhouse structures (shape, size, crop system), developing high performance site-specific controllers for each greenhouse is not feasible. In parallel to this work, a new cooling control strategy, which considers the contribution of humidification and cooling from the crop, was developed for greenhouses equipped with natural ventilation. Prior to the development of the cooling strategy itself, three evapotranspiration models were compared in terms of accuracy and reliability. The cooling strategy that has been developed controls the amount of fog introduced into the greenhouse as well as the percentage of vent openings based on the desired vapor pressure deficit (VPD) and enthalpy, respectively. Numerical simulations were used to compare the performance of the new strategy with a constant fogging rate strategy based on VPD, and on average, the new strategy saved 36% water and consumed 30% less electric energy. In addition, smaller air temperature and relative humidity fluctuations were achieved when using the new strategy. Finally, it was demonstrated that dynamically varying the fog rate and properly selecting the number of nozzles, yields additional water and electricity savings.