A new look at the long-term performance of general solar thermal systems

This work addresses the problem of evaluating the long-term performance of solar thermal systems, which is quantified through the monthly or seasonal/annual solar fraction. It is shown that for a general solar system it may be expressed as a function of monthly utilizabilities, calculated for two different temperature (radiation) levels, which correspond to minimum and maximum operating temperatures. Both systems without storage and with storage are considered. Examples for solar cooling and solar cogeneration systems are shown.     

A Direct Solver for 2D Non-Stationary Boltzmann-Poisson Systems for Semiconductor Devices: A MESFET Simulation by WENO-Boltzmann Schemes

We present preliminary results of a high order WENO scheme applied to deterministic computations for two dimensional formulation of the transients for the Boltzmann-Poisson system describing electron transport in semiconductor devices. The collisional term models optical-phonon interactions which become dominant under strong energetic conditions corresponding to nanoscale active regions under applied bias. We treat the Boltzmann Transport equation in a spherical coordinate system for the wave-vector space. The problem is three dimensional in the wave-vector space and two dimensional in the physical space, plus the time variable driving to steady states. The new formulation avoids the singularity due to the spherical coordinate system.     

Analysis of the T cell receptor repertoire in rheumatoid arthritis

BACKGROUND AND AIMS OF THE STUDY: Valve repair, where suitable, is the preferred option in patients who require mitral surgery. A number of studies have shown excellent long-term results, but most were undertaken in tertiary referral centers with a high throughput of patients. METHODS: We present our experience in 60 patients, aged 60 +/- 14 years, undergoing repair between 1984 and 1993. Most patients (83%) were in New York Heart Association (NYHA) class II or III at the time of surgery; 27% had concomitant ischemic heart disease. Almost all (98%) had posterior leaflet repair and 18% had anterior leaflet repair. Eight surgeons each performed a mean of 7.5 operations during this period. RESULTS: The 30-day mortality rate was 3.3%. There were seven late deaths. Five patients underwent reoperation for mitral regurgitation (two early, three late). At six years, 60% of patients were alive, or free of stroke or reoperation. Late follow up was obtained in 45 of 47 surviving patients: 95% were in NYHA class I or II; one-third were on anticoagulants for atrial fibrillation; 90% had mild (or less) mitral regurgitation on echocardiography. CONCLUSIONS: These data show that most patients have a very good outcome from valve repair surgery and encourage the trend towards operating earlier in the course of the disease. Adverse outcomes occurred mainly in patients who were highly symptomatic at the time of surgery. The high proportion of patients on postoperative anticoagulants underscores the importance of operating before atrial fibrillation becomes permanent.     

Performance of several Cr and Yb analytical techniques applied to samples of different biological origin (digesta or faeces)

This paper compares the performance, in terms of Cr (liquid phase marker) and Yb (solid phase marker) recovery from spiked samples, of five mineralization procedures applied to faeces, whole duodenal digesta, particulate and liquid phases of duodenal digesta, whole ruminal digesta and ruminal fluid from cattle. Two Holstein–Friesian heifers, fitted with permanent ruminal and duodenal cannulae, and fed twice daily on barley straw and a concentrate (15:85), were used as sample donors. Cr and Yb were added to the samples at 5, 25, 125 and 625 µg g^?1 dry matter, and analyzed by atomic absorption spectrometry. There were differences in marker recovery (p = 0.0481) depending on the mineralization procedure utilized but their performance was not affected by marker type (p = 0.6143). The interaction between type of sample and digestion procedure was statistically significant (p = 0.0290) and the results showed that homogeneous samples (whole duodenal digesta, the particulate phase of duodenal digesta and faeces) allowed the more even distribution of the marker and an easier and more complete mineralization. In contrast, heterogeneous samples (whole rumen digesta and rumen fluid) resulted in either a lesser attachment of markers to the particles and/or incomplete mineralization of the samples, which resulted in a higher variability between procedures. The interaction between type of sample and marker was also significant (p = 0.0426), with Cr recovery being more affected by type of sample than Yb. Copyright © 2004 Society of Chemical Industry     

Isolation and Structural Elucidation of Antiproliferative Compounds of Lipidic Fractions from White Shrimp Muscle (Litopenaeus vannamei)

Shrimp is one of the most popular seafood items worldwide, and has been reported as a source of chemopreventive compounds. In this study, shrimp lipids were separated by solvent partition and further fractionated by semi-preparative RP-HPLC and finally by open column chromatography in order to obtain isolated antiproliferative compounds. Antiproliferative activity was assessed by inhibition of M12.C3.F6 murine cell growth using the MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide) assay. The methanolic fraction showed the highest antiproliferative activity; this fraction was separated into 15 different sub-fractions (M1–M15). Fractions M8, M9, M10, M12, and M13 were antiproliferative at 100 µg/mL and they were further tested at lower concentrations. Fractions M12 and M13 exerted the highest growth inhibition with an IC₅₀ of 19.5 ± 8.6 and 34.9 ± 7.3 µg/mL, respectively. Fraction M12 was further fractionated in three sub-fractions M12a, M12b, and M12c. Fraction M12a was identified as di-ethyl-hexyl-phthalate, fraction M12b as a triglyceride substituted by at least two fatty acids (predominantly oleic acid accompanied with eicosapentaenoic acid) and fraction M12c as another triglyceride substituted with eicosapentaenoic acid and saturated fatty acids. Bioactive triglyceride contained in M12c exerted the highest antiproliferative activity with an IC₅₀ of 11.33 ± 5.6 µg/mL. Biological activity in shrimp had been previously attributed to astaxanthin; this study demonstrated that polyunsaturated fatty acids are the main compounds responsible for antiproliferative activity.     

Evaluation of a solar thermal system using building louvre shading devices

External louvres are increasingly used to provide solar protection for building glazed surfaces. The integration of collectors into the external louvres of buildings offers a means of reducing system cost as well as providing architects with more freedom to integrate the technology into their designs. This work concerns the modification of existing louvre designs to integrate a solar collector in the shading device. The evaluation of a thermal solar system for water heating is assessed in this paper. A numerical model for the integrated solar collector was developed for different configurations and the collector efficiency is quantified for each configuration. System thermal performance was obtained for the climatic conditions of Lisbon (Portugal) and Tenerife (Spain). Economic and environmental viability of the system is assessed.     

Methodology for third-order astigmatism compensation in off-axis spherical reflective systems

The main constraint of classical off-axis reflecting systems is the primary astigmatism that has long been a research topic of interest. This astigmatism in off-axis spherical reflective imaging systems can be eliminated by using the proper configuration. These configurations could be derived from the marginal ray fans equation, and they are valid for small angles of incidence. The conditions for the astigmatism compensation in configurations with two and three off-axis mirrors have been derived and analyzed, which have not been reported previously. The expression that defines the conditions for primary astigmatism compensation in a four-mirror system is presented. This shows that the marginal ray fan equation can be used to obtain the condition for astigmatism compensation of a reflective system with any number of mirrors. The developed methodology is verified by ray-tracing analysis of some examples.     

Optical spectroscopy of single Cd0.6Zn0.4Te/ZnTe quantum dots on Si substrate

Microphotoluminescence (μ-PL) measurements were carried out to investigate the optical properties of single Cd_0.6Zn_0.4Te/ZnTe quantum dots (QDs) grown on Si (001) substrate by using molecular beam epitaxy. The high quality of single Cd_0.6Zn_0.4Te/ZnTe QDs is witnessed by resolution-limited emission, negligible background and absence of measurable spectral jitter or blinking. Polarization-dependent and power-dependent μ-PL spectroscopy measurements were performed to identify the exciton, the biexciton, and the charged exciton in the emission spectra of single QDs. Furthermore a weak linearly polarized line is observed on the low energy side of the neutral exciton and is ascribed to dark exciton recombination.     

A matrix model for the flow of control in prolog programs with applications to profiling

In Prolog the flow of control is relatively complex; four counts (which we call currents)—call, fail, succeed and redo—and two intrinsic properties—the failure and the ‘alternative’ probabilities—can be associated with every literal in a clause body. In this work we describe a new matrix model where those currents and properties are related at the literal, clause and predicate definition levels. This model is useful for predicate classification, execution profiling and program debugging. The application to profilers is discussed in detail.     

Chemical pathways for the polymerization of enines

AM1 calculations are reported for enines with aromatic substituents. It was found that the position of the unsaturated bonds in each molecule may account for the reactivity of each isomer via different polymerization pathways. The resonant structure of the charged form of one of the molecules allowed speculation about the observed inhibition of the polymerization reaction.