Establishment of pluripotent cell lines from vertebrate species - Present status and future prospects

Pluripotent embryonic stem (ES) cells are undifferentiated cell lines derived from early embryos and are capable of unlimited undifferentiated proliferation in vitro. They retain the ability to differentiate into all cell types including germ cells in chimeric animals in vivo, and can be induced to form derivatives of all three germ layers in vitro. Mouse ES cells represent one of the most important tools in genetic research. Major applications include the targeted mutation of specific genes by homologous recombination and the discovery of new genes by gene trap strategies. These applications would be of high interest for other model organisms and also for livestock species, However, in spite of tremendous research activities, no proven ES cells colonizing the germ line have been established for vertebrate species other than mouse a nd chicken thus far. This review summarizes the current status of deriving pluripotent embryonic stem cell lines from vertebrates and recent developments in nuclear transfer technology, which may provide an alternative tool for genetic modification of livestock animals. Copyright (C) 1999 S. Karger AG, Basel

Automatic Semantic Role Annotation for Spanish

Proceedings of the 17th Nordic Conference of Computational Linguistics NODALIDA 2009. Editors: Kristiina Jokinen and Eckhard Bick. NEALT Proceedings Series, Vol. 4 (2009), 215-218. © 2009 The editors and contributors. Published by Northern European Association for Language Technology (NEALT) http://omilia.uio.no/nealt . Electronically published at Tartu University Library (Estonia) http://hdl.handle.net/10062/9206

Locating Star-Forming Regions in Quasar Host Galaxies

We present a study of the morphology and intensity of star formation in the host galaxies of eight Palomar-Green quasars using observations with the Hubble Space Telescope. Our observations are motivated by recent evidence for a close relationship between black hole growth and the stellar mass evolution in its host galaxy. We use narrow-band [O II] $\lambda$3727, H$\beta$, [O III] $\lambda$5007 and Pa$\alpha$ images, taken with the WFPC2 and NICMOS instruments, to map the morphology of line-emitting regions, and, after extinction corrections, diagnose the excitation mechanism and infer star-formation rates. Significant challenges in this type of work are the separation of the quasar light from the stellar continuum and the quasar-excited gas from the star-forming regions. To this end, we present a novel technique for image decomposition and subtraction of quasar light. Our primary result is the detection of extended line-emitting regions with sizes ranging from 0.5 to 5 kpc and distributed symmetrically around the nucleus, powered primarily by star formation. We determine star-formation rates of order a few tens of M$_\odot$/yr. The host galaxies of our target quasars have stellar masses of order $10^{11}$ M$_\odot$ and specific star formation rates on a par with those of M82 and luminous infrared galaxies. As such they fall at the upper envelope or just above the star-formation mass sequence in the specific star formation vs stellar mass diagram. We see a clear trend of increasing star formation rate with quasar luminosity, reinforcing the link between the growth of the stellar mass of the host and the black hole mass found by other authors.Comment: Accepted for publication in M.N.R.A.

Development and Validation of a Mechanistic Vapor-Compression Cycle Model

Detailed models are crucial tools for engineers in designing and optimizing systems. In particular, mechanistic modeling of vapor compression systems for accurate performance predictions at both full- and part-load conditions have been improved significantly in the past decades. Yet, fully deterministic models present still challenges in estimating charge inventory in order to optimize the performance. In this work, a generalized framework for simulating vapor compression cycles (VCC) has been develvoped with emphasis on a charge-sensitive model. In order to illustrate the capabilities of the tool, a direct–expansion (DX) cycle has been considered. In the cycle model, the compressor was mapped by employing the ANSI/AHRI 540 10-coefficient correlation, the evaporator and the condenser were constructed based on the ACHP models (Bell, 2010). Furthermore, a TXV model was implemented based on Li and Braun (2008) formulation. With respect to the charge inventory estimation, the two-point regression model proposed by Shen et al. (2009) was used to account for inaccurate estimation of refrigerant volumes, ambiguous flow patterns for two-phase flow, and amount of refrigerant dissolved in the oil. The solution scheme required manufacturer input data for each component as well as the amount of refrigerant charge. Hence, the degree of superheating at the evaporator outlet, the subcooling at the condenser outlet and the perfromance parameters of the VCC system can be predicted. The model was validated with available experimental and numerical data available in literature. The simulation results demonstrated that the proposed model is more accurate and more generic than other methods presented in the literature

Validation of a Charge-Sensitive Vapor-Injected Compression Cycle Model with Economization

In recent years, research on economized vapor injected (EVI) compression systems showed potential improvements to both cooling capacity and coefficient of performance (COP). In addition, the operating range of compressors can be extended by reducing the discharge temperature. However, the optimum operation of such systems is directly related to the amount of refrigerant charge, which often is not optimized. Therefore, an accurate charge estimation methodology is required to further improve the operation of EVI compression systems. In this paper, a detailed cycle model has been developed for the economized vapor injected (EVI) compression system. The model aims to predict the performance of EVI systems by imposing the amount of required refrigerant charge as an input. In the cycle model, the EVI compressor was mapped based on the correlation of Tello-Oquendo et al. (2017), whereas evaporator, condenser and economizer heat exchanger models were constructed based on the available ACHP models (Bell, 2010). With respect to charge inventory, the 2-point regression model from Shen et al. (2009) was used to account for inaccurate estimation of refrigerant volumes, ambiguity in slip flow model, solubility of refrigerant in the lubricating oil, among others. The cycle model has been validated with experimental performance data taken with a 5-ton Environmental Control Unit (ECU) that utilizes EVI technology. The developed cycle model showed very good agreement with the data with a MAE in COP of less than 4%. Furthermore, the estimated charge inventory has been compared to the one-point regression model. Results showed that the former method allowed to predict the charge inventory with an MAE of less than 0.5%

Stratified Flow Model to Predict Oil Retention in Horizontal Refrigerant Gas Lines of Unitary Split Systems Running R410A and POE32

Most air conditioning and refrigeration systems that employ the vapor compression cycle rely on oil circulating with refrigerant to lubricate the bearings and other contact surfaces in the compressor. The lubricant acts as a sealant to reduce leakage losses during the compression process and it also helps to absorb some of the excess heat that is generated in the compression chamber. However, this oil circulation results in oil retention in various other components outside the compressor depending on the physical interaction between lubricant and refrigerant and their transport properties. Other factors, such as geometry and orientation of connecting lines and system operating conditions (e.g., refrigerant flow rate and oil circulation ratio), also impact the oil retention. As a result of oil retention, the oil level in the compressor reduces, which may ultimately affect its efficiency and life span. In addition, the pressure drop across the system increases and the efficiency of heat exchangers (evaporators and condensers) decreases with oil retention. The current line sizing rules reported in the ASHRAE Handbook Refrigeration have only limited consideration of the effects of oil in the system. With the increasing development of variable speed systems as well as future use of newer refrigerants, there is a need in the industry for upgrading the line sizing recommendations to consider the effects of oil retention, especially the connecting gas lines of unitary split systems. To address this issue, a physics based model has been developed to predict oil retention in horizontal lines. The model is validated using experimental data collected for R410A-POE32. The developed model will be a backbone of a design tool, which will provide more information on oil retention in refrigerant gas lines of the commonly used refrigerant-lubricant combinations in the HVAC&R industry

Performance Testing of a Vapor Injection Scroll Compressor with R407C

Current studies indicate that the method of economized vapor injection (EVI) increases both cooling capacity and coefficient of performance (COP) of vapor compression systems and enlarges the operating range of compressors by reducing the discharge temperature. The design and analysis of EVI systems require comprehensive and comparable performance data of the compressor. In this work, a thermodynamic model was developed to simulate the potential benefit of EVI systems. Furthermore, the performance of a vapor injection (VI) scroll compressor has been experimentally investigated using a modified compressor calorimeter and the refrigerant mixture R407C. During the experiments, the injection flow was regulated by controlling the injection superheat. The experimental results confirm the predicted tendencies of the EVI model. The investigation also reveals that the injection pressure affects the VI compressor performance and needs to be included in the compressor performance evaluation

Enhancing the Performance of a Transportable Environmental Control Unit (ECU) Operated in High-Temperature Climates

Numerous people live or venture into environments, such as the Middle East, where the temperatures can skyrocket as high as 54°C. This leaves many air conditioners unable to operate efficiently. Although much research has been conducted for incorporating vapor injection processes into refrigeration systems, such as ones used in supermarkets, little has been researched regarding the application in extreme heat environments. While most basic air conditioning units do not require the addition of a vapor injection process along with an economizer, this project requires the air conditioning (AC) unit to operate under extreme high temperature conditions. The project investigates the addition of a vapor injection process and an economizer on the performance of a transportable Environmental Control Unit (ECU), operating with refrigerant R-407C, running under ambient temperatures as high as 51.7°C (125°F) and an indoor temperature of 32.2°C (90°F), and using a single injection port scroll compressor. The retrofitted AC unit was compared to a baseline cycle without vapor injection. Results for fixed injection vapor superheat at 7°C show that the cooling capacity increased for all test conditions from 6.7% to 15%. Due to the high compression ratio, the compressor discharge temperature relatively increased for the extreme test conditions. In addition, the compressor power consumption increased by up to 18%, while the COP of the system increased by 1%. Furthermore, the second law of thermodynamics analysis showed that the compressor had the largest irreversibilities, with the condenser and evaporator showing significant irreversibilities as well. Future work includes optimizing each component to improve the system’s COP