bluuebunny/crossref_metadata_2025 huggingface dataset:
UPTAKE OF CADMIUM BY FRESHWATER GREEN ALGAE: EFFECTS OF PH AND AQUATIC HUMIC SUBSTANCES1
Authors: Vigneault Bernard , Campbell Peter G. C.
Published: February 2005

The effects of humic substances and low pH on short‐term Cd uptake by Pseudokirchneriella subcapitata (Korshikov) Hindak and Chlamydomonas reinhardtii Dang were investigated under defined exposure conditions. The uptake experiments were run in the presence of either a synthetic organic ligand (nitrilotriacetate) or natural organic ligands (Suwannee River fulvic or humic acid). An ion‐exchange method was used to measure the free Cd2+ concentrations in the exposure solutions. At pH 5, measured free Cd2+ concentrations agreed with estimations made using the geochemical equilibrium model WHAM, but at pH 7 the model overestimated complexation by both Suwannee River fulvic and humic acids compared with the ion‐exchange measurements. Consistent with the metal internalization step being rate limiting for overall short‐term uptake, intracellular Cd uptake was linear for exposure times less than 20 min at pH 5 or pH 7 for both algal species. After taking into account complexation of Cd in solution, Suwannee River humic substances had no additional effects on cadmium uptake at pH 7, as would be predicted by the free ion model. This absence of effects other than complexation persisted at pH 5, where the tendency of humic substances to adsorb to the algal cell surface is favored. Changes in pH strongly influenced Cd uptake, with the intracellular flux of Cd being at least 20 times lower at pH 5 than at pH 7 for P. subcapitata. Our results support models such as the free ion model or the biotic ligand model, in which humic substances act indirectly on Cd uptake by reducing the bioavailability of Cd by complexation in solution.
RAPID ASSEMBLY OF A WOUND PLUG: STAGE ONE OF A TWO‐STAGE WOUND REPAIR MECHANISM IN THE GIANT UNICELLULAR CHLOROPHYTE DASYCLADUS VERMICULARIS (CHLOROPHYCEAE)1
Authors: Ross Cliff , Vreeland Valerie , Herbert Waite J. , Jacobs Robert S.
Published: February 2005

Upon injury, selected coenocytic algae are capable of forming temporary wound plugs to prevent detrimental cytoplasmic loss. Wound plugs of Dasycladus vermicularis ([Scropoli] Krasser) were harvested 5 min post‐injury and dried. The plug material contained 94% water and can be considered a hydrogel. The gel plug extended several millimeters from the cut end and filled the space inside the cell wall, which resulted from cytoplasmic retraction. Total organic carbon included 55% sugars, 5%–15% protein, and 0.18% lipids. The major sugars were glucose, galactose, mannose, and galacturonic acid. Fluorescein isothiocyanate‐lectins specific for these sugars were localized around the plug matrix. Sulfur content calculated as sulfate corresponded to 17% of the carbohydrate by weight, and sulfated material was detected in plugs by Alcian Blue staining. Formation of the initial plug occurred within 1 min of injury and was not significantly perturbed by the addition of ionic, antioxidant, or chelating agents to the seawater medium. However, addition of exogenous d(+)‐galactose and d(+)‐glucose prevented formation of the nascent gel plug. Wound plugs that were allowed to form from 10 min up until 24 h post‐injury were isolated and incubated with selected biochemical probes to identify the biochemical processes involved in plug formation. The operative strategy in Dasycladus to prevent “cytoplasmic hemorrhage” required availability of sequestered carbohydrate and lectin precursor components throughout the thallus for plug assembly. Once the initial assembly had commenced, additional biochemical interactions were initiated (as a function of time) to promote structural integrity.
MORPHOMETRIC TAXONOMY OF SIPHONOUS GREEN ALGAE: A METHODOLOGICAL STUDY WITHIN THE GENUS HALIMEDA (BRYOPSIDALES)1
Authors: Verbruggen Heroen , De Clerck Olivier , Cocquyt Ellen , Kooistra Wiebe H. C. F. , Coppejans Eric
Published: February 2005

Species‐level taxonomy of Bryopsidalean genera is often based on quantifiable morphological characters. Yet there are relatively few examples of statistically founded morphometric studies within this group of siphonous algae and macroalgae in general. Molecular phylogenetic studies have revealed cases of cryptic diversity in several Bryopsidalean genera and call for new approaches toward taxonomy. We present a combined molecular and morphometric approach toward Halimeda taxonomy using a selection of specimens representing the five natural lineages within the genus. A phylogeny was inferred from partial nuclear rDNA sequences (3′ end of small subunit, internal transcribed spacer region 1, 5.8S, internal transcribed spacer region 2, and 5′ end of large subunit) from our and previously studied specimens. Segment size and shape descriptors were acquired using different techniques, including landmark analysis and elliptic Fourier analysis. A broad range of anatomical structures was measured. Taxonomic utility of the different methods and characters was assessed using predictive discriminant analysis. Molecular data were used to delimit species groups. Segment morphological characters proved fairly good predictors for species membership, but anatomical variables yielded the best results. The good performance of morphometric taxon predictors offers perspectives, not only for future taxonomic case studies within problematic species complexes, but also for thorough examinations of the rich fossil record of Halimeda. Statistically founded morphometric studies can probably help elucidate taxonomic issues within other Bryopsidalean genera as well.
CHARACTERIZATION OF DIATOM (BACILLARIOPHYCEAE) NITRATE REDUCTASE GENES AND THEIR DETECTION IN MARINE PHYTOPLANKTON COMMUNITIES1
Authors: Allen Andrew E. , Ward Bess B. , Song Bongkeun
Published: February 2005

The complete assimilatory nitrate reductase (NR) gene from the pennate diatom Phaeodactylum triconutum Bohlin was sequenced from cDNA and compared with NR sequences from fungi, green algae, vascular plants, and the recently sequenced genome of the centric diatom Thalassiosira pseudonana Hasle and Heimdal CCMP1335. In all the major eukaryotic nitrate reductase (Euk‐NR) functional domains, diatom NR gene sequences are generally 50%–60% identical to plant and alga sequences at the amino acid level. In the less conserved N‐terminal, hinge 1, and hinge 2 regions, homology to other NR sequences is weak, generally<30%. Two PCR primer sets capable of amplifying Euk‐NR from plants, algae, and diatoms were designed. One primer set was used to amplify a 750‐base pair (bp) NR fragment from the cDNA of five additional diatom strains. The PCR amplicon spans part of the well‐conserved dimer interface region, the more variable hinge 1 region, and part of the conserved cytochrome b heme binding region. The second primer set, targeted to the dimer region, was used to amplify an approximately 400‐bp fragment of the NR gene from DNA samples collected in Monterey Bay, California and in central New Jersey inner continental shelf (LEO‐15 site) waters. Only diatom‐like NR sequences were recovered from Monterey Bay samples, whereas LEO‐15 samples yielded NR sequences from a range of photosynthetic eukaryotes. The prospect of using DNA‐ and RNA‐based methods to target the NR genes of diatoms specifically is a promising approach for future physiological and ecological experiments.
GENETIC PATTERNS IN THE CALCIFIED TROPICAL SEAWEEDS HALIMEDA OPUNTIA, H. DISTORTA, H. HEDERACEA, AND H. MINIMA (BRYOPSIDALES, CHLOROPHYTA) PROVIDE INSIGHTS IN SPECIES BOUNDARIES AND INTEROCEANIC DISPERSAL1
Authors: Kooistra Wiebe H. C. F. , Verbruggen Heroen
Published: February 2005

The section Opuntia within the green seaweed genus Halimeda includes sprawling and pendant thalli composed of strongly calcified segments. Within this section, identification of Atlantic material is straightforward, but Indo‐Pacific material is often difficult to key out. This is particularly true for specimens resembling H. opuntia, H. distorta, and H. hederacea; many specimens do not fit any type or are morphologically intermediate. The goals of the present study are to define morphologically and genetically distinct groups among such specimens and to assess phylogeographic patterns within these groups. Specimens were collected throughout the geographical and morphological range. Sequences of H. minima and H. gracilis were included as outgroups. Two morphological groups were discerned within the ingroup; the first fit H. opuntia, whereas most specimens in the second group, referred to as the distorta–hederacea complex, did not fit any species description unambiguously. The latter were subdivided into two subgroups corresponding more or less to H. hederacea and H. distorta, yet intermediates between these morphs existed. A phylogeny inferred from partial nuclear rDNA sequences showed one lineage with H. opuntia and a second one containing the distorta–hederacea complex, thus corroborating the two major morphological groups. The distorta–hederacea complex contained two clades that show only partial correspondence with the morphological subgroups. Therefore, H. hederacea is synonymized with H. distorta. Phylogeographic structure within H. opuntia indicated that this species dispersed from the Indo‐Pacific into the Atlantic. Fossil records of the species also show occurrence at Pacific sites throughout the last 105 years and a sudden appearance in the Caribbean and Bahamas during the last millennium.
CLONING AND FUNCTIONAL CHARACTERIZATION OF AMMONIUM TRANSPORTERS FROM THE MARINE DIATOM CYLINDROTHECA FUSIFORMIS (BACILLARIOPHYCEAE)1
Authors: Hildebrand Mark
Published: February 2005

The general preference of phytoplankton for ammonium over nitrate as a nitrogen source has long been established, but the underlying molecular mechanisms controlling the uptake and utilization of these nutrients, and the preference for one over the other, are poorly understood. Insights are to be gained by cloning genes involved in nitrogen uptake and metabolism and characterizing the expression of these genes and their encoded proteins. I report the first cloning and characterization of ammonium transporter genes (AMT) from a marine diatom, Cylindrotheca fusiformis Reimann and Lewin. Two distinct types of AMT were isolated, which differed in their encoded amino acid sequences by 5%. A cDNA and genomic copy of AMT1 and three genomic copies of AMT2 were isolated. Analysis of mRNA levels in C. fusiformis cultures grown with different nitrogen sources revealed that AMT1 levels were much higher than AMT2 under all conditions. Highest mRNA levels were detected in nitrogen‐starved cells, followed by nitrate‐grown and then ammonium‐grown cells. A substantial amount of mRNA degradation was observed, suggesting that transcripts for the AMTs are turned over rapidly, which may be a regulatory mechanism over their expression. Transporters AMT1 and 2 were cloned into a Saccharomyces cerevisiae expression vector, and each was able to complement a yeast mutant that lacked all three of its native ammonium transporters. In addition to showing that the AMTs were functional, the data indicated that AMT1 was a much more efficient transporter than AMT2.
RESPONSE OF GLUTAMINE SYNTHETASE GENE TRANSCRIPTION AND ENZYME ACTIVITY TO EXTERNAL NITROGEN SOURCES IN THE DIATOM SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1
Authors: Takabayashi Misaki , Wilkerson Frances P. , Robertson Deborah
Published: February 2005

To understand the enhanced ability of marine diatoms to assimilate nitrogen (N), we measured changes in the transcript abundance and enzyme activity of glutamine synthetase (GS), one of the key enzymes that link carbon (C) and N metabolism, in the common diatom Skeletonema costatum (Greville) Cleve. Transcript abundance of glnII (the gene that encodes the GSII isoenzyme), measured by quantitative reverse transcriptase‐PCR, and total GS activity increased 2 to 3.5 times above background in the cells taking up nitrate (NO3−) but not the cells taking up ammonium (NH4+). A background level of glnII mRNA was maintained at a steady level up to 15 days of N starvation before decreasing to below detection after 21 days. These results confirm that transcription of glnII is induced to assimilate NH4+ derived from reduction of NO3−. Because of this role of GSII in diatoms assimilating NH4+ derived from NO3− reduction rather than from the environmental NH4+, quantification of glnII mRNA promises to be a useful indication of new production by phytoplankton.
SEX‐SPECIFIC CELL SURFACE STRUCTURE OF ANISOGAMETES: MORPHOLOGICAL CHANGES DURING FERTILIZATION OF BRYOPSIS MAXIMA (ULVOPHYCEAE, CHLOROPHYTA) REVEALED BY ULTRA–HIGH‐RESOLUTION FIELD EMISSION SEM1
Authors: Miyamura Shinichi , Sakaushi Shinji , Hori Terumitsu , Mitsuhashi Fusako , Nagumo Tamotsu
Published: February 2005

Cell surfaces of biflagellate gametes and their morphological changes during fertilization of Bryopsis maxima Okamura were observed using a high‐resolution field emission scanning electron microscope. Male gametes have broad and narrow faces, which are divided into at least five morphologically distinct regions: 1) the apical plate is a plate‐like structure that is approximately 380–530 nm long and approximately 190 nm wide, in the center of the papilla and slightly protruded from the plasma membrane; 2) strips are smooth materials on ridges that originate from the basal part of the papilla and extend downward; 3) the lateral belt is a belt‐shaped structure on the center of the narrower faces; 4) the flagellar surface; and 5) the other region of the cell body has a fine‐grained appearance. In contrast, the entire female gamete surface is rough because of many granular or amorphous cell coats on the plasma membrane. When both gametes were mixed together, the initial fusion proceeded between the broader face of the male gamete and the anterior side of the female one near the basal bodies. Morphology of the male gamete's cell surface changed gradually as fusion proceeded and was covered by the granular materials; that surface closely resembled those of female gametes except for the apical plate. It was present until the planozygote attached itself to the substrate by the papilla. It finally disappeared after settlement. Therefore, these results indicate that gametes of B. maxima have sex‐specific surface structures that change their morphology during fertilization and settlement.
Mechanism study on solid‐state reduction in the Fe2O3–NiO–Cr2O3–C system using thermal analyses
Authors: Ma Ping , Lindblom Bo , Björkman Bo
Published: February 2005

In order to clarify the interactions among metal oxides during reduction of pickling sludge, the reduction mechanism of the metal oxide mixture, Fe2O3–NiO–Cr2O3, which simulates the composition of these metal oxides in pickling sludge, was studied using graphite as a reductant, by means of thermal analysis techniques. X‐ray diffraction analysis was used for characterization of reduction products. In addition to the reduction test on the metal oxide mixture mentioned above, for comparison, separate tests on the reduction of Fe2O3, NiO and Cr2O3 were also conducted. The results demonstrate that through formation of a transitional compound ‘FeCr2O4’, Fe2O3 promotes the complete reduction of Cr2O3 at a temperature lower than that required for reducing pure Cr2O3. On the other hand, Cr2O3 hinders the reduction of Fe2O3 at lower temperatures. The whole reduction process may be classified as five distinguishable reduction stages in which possible reactions were proposed to represent the reduction mechanism. The reduced metals in the final product exist primarily in the form of solid solutions, such as ‘Cr–Fe–Ni’, which mainly containing ‘(Fe,Ni)’ and ‘(Fe,Cr)’, and small amounts of carbides, such as (Cr,Fe)7C3 and/or Cr7C3.
Experimental studies on solid‐state reduction of pickling sludge generated in the stainless steel production
Authors: Ma Ping , Lindblom Bo , Björkman Bo
Published: February 2005

Neutralized pickling sludge generated during stainless steel production contains large amounts of calcium fluoride, water and a relatively low metal content, which makes it difficult to directly recycle back to the steelmaking process. It would also pose a potential environmental problem if deposited outdoors over a long term. However, metals such as iron, nickel and chromium, in the form of oxides and/or hydroxides, as well as calcium fluoride in the sludge, are of economic concern to stainless steel makers. Therefore, to develop an economically and technically suitable recycling process, a comparison study on reducing both pickling sludge and mixtures of metal oxides, using petroleum coke (P‐coke) and graphite as reductant, respectively, was carried out at temperatures up to 1400°C using thermogravimetric (TG) analysis. Meanwhile, laboratory‐scale tests on reducing pickling sludge, using P‐coke as reductant, were also conducted in a Tammann furnace at 800–1200°C. Results of the comparison study by TG demonstrate that the reduction behaviour of pickling sludge may be approached by the reduction behaviour of the metal oxide mixture having the same composition as those in the pickling sludge. Results of the Tammann furnace tests show that temperature has a significant influence on reduction. The reduced metals in the reduction products exist mostly in the form of alloys such as ‘(Fe,Ni)’ and ‘Cr–Fe–Ni’.
PALM OIL CRYSTALLIZATION: EFFECTS OF COOLING TIME AND OIL CONTENT
Authors: MISKANDAR M.S. , CHE MAN Y.B. , ABDUL RAHMAN R. , NOR AINI I. , YUSOFF M.S.A.
Published: February 2005

Isothermal crystallization behavior of fluid shortening formulation from blends of palm oil and palm olein was investigated. The oil blends filled in nuclear magnetic resonance (NMR) tubes to a height of 2.5 cm were melted at 70C for 30 min crystallization time. A set of 11 tubes for each temperature was placed at selected crystallizing time and the solid fat content (SFC) measured in a Bruker pulse NMR spectrometer. Crystal distribution of the same blend was observed under polarized microscope at the same time interval. A correlation was developed between SFC and crystal distribution. The crystallization curves demonstrated two distinct steps corresponding to two crystallization stages as a result of the occurrence of mixed crystallization. Crystallization was selective to the high melting triacylglycerols (TAG) at all temperatures as shown by shorter induction periods in blends with more than 41.8% palmitic acid. High melting TAG crystallized first and acted as nuclei for recrystallization of the low melting TAG. However, the low melting TAG at the same time could also solubilize the formed crystals. The average SFC as a function of time was 50% lower than the SFC profile. Slow crystallization temperature was able to promote large crystal formation that influences SFC of palm‐based shortenings. Blends of 40–60% palm oil showed promising formulations of stable fluid palm‐based shortening.
ANTIOXIDANT ACTIVITY OF COMMON BEANS (PHASEOLUS VULGARIS L.)
Authors: MADHUJITH TERRENCE , NACZK MARIAN , SHAHIDI FEREIDOON
Published: February 2005

Four bean varieties with different hull colors (white, red, brown and black) were extracted with 80% acetone and evaluated for their total, hydrophobic and hydrophilic phenolics as well as tannin contents. The tannin content was measured using three different methods. Antioxidant capacity of the extracts was assessed using β‐carotene/linoleate and bulk corn oil model systems. The content of hydrophobic antioxidants was higher compared with the hydrophilic fraction in all tested bean types. Evaluation of antioxidant activity in a β‐carotene model system revealed that red, brown and black whole bean extracts were capable of inhibiting oxidation (33–52%) of β‐carotene as compared with the control when used at 100 p.p.m. level as catechin equivalents. In the corn oil model system, red, brown and black bean extracts inhibited the formation of conjugated dienes (CD; 20–28%), thiobarbituric acid reactive substances (TBARS; 44–52%) and hexanal (68–84%) when used at 100 p.p.m. level as catechin equivalents. The results of this study demonstrated that colored beans possess superior antioxidative activity compared with white beans.
PERFORMANCE OF SOME EDIBLE OILS DURING HEATING IN A STEAM PRESSURE COOKER
Authors: ULUSOY BARAN ÖNAL , KARABULUT İHSAN , TURAN SEMRA
Published: February 2005

The performance of corn, soybean and hazelnut oils was investigated over a 60‐min period in a steam pressure cooker at 121C and 1.1 atm pressure. These conditions are typical of Turkish domestic cooking. In this study, the oxidative stability of the three oils was compared using peroxide value (PV), conjugated diene (CD) value and free fatty acid (FFA) content. Fatty acid composition of oils was also determined. Heating of oils for 60 min caused a significant increase in peroxide value (P < 0.05), but PV of hazelnut oil was lower than those of soybean and corn oils (P < 0.05). FFA and CD values of soybean and hazelnut oils showed an insignificant increase (P > 0.05), while the increase in corn oil was significant (P < 0.05). Minor differences existed between the fatty acids, except for linolenic acid, at the begining and at the end of the process.
LIPID EVALUATION OF SOME TUNISIAN CITRUS SEEDS
Authors: SAÏDANI M. , DHIFI W. , MARZOUK B.
Published: February 2005

Seeds from five varieties of Tunisian Citrus fruits, namely blood orange (Citrus sinensis), sweet orange (Citrus sinensis), lemon (Citrus limon L.), bergamot (Citrus bergamia) and bitter orange (Citrus aurantium), were examined for their composition of lipid classes and fatty acids. In addition, the oil yield, total fatty acids, palmitic, oleic and linoleic acids were determined. Petroleum ether‐extracted oils of these Citrus seeds amounted to more than 78% in the case of lemon seeds. The Citrus seed oils had three lipid classes as determined by thin‐layer chromatography. Triacylglycerols were the major oil class in all varieties. Gas chromatographic analyses revealed that the main fatty acids were palmitic, oleic and linoleic acids.
Thermal Performance of a Large Low Flow Solar Heating System With a Highly Thermally Stratified Tank
Authors: Furbo Simon , Vejen Niels Kristian , Shah Louise Jivan
Published: February 2005

In year 2000 a 336 m2 solar domestic hot water system was built in Sundparken, Elsinore, Denmark. The solar heating system is a low flow system with a 10000 l hot-water tank. Due to the orientation of the buildings half of the solar collectors are facing east, half of the solar collectors are facing west. The collector tilt is 15° from horizontal for all collectors. Both the east-facing and the west-facing collectors have their own solar collector loop, circulation pump, external heat exchanger and control system. The external heat exchangers are used to transfer the heat from the solar collector fluid to the domestic water. The domestic water is pumped from the bottom of the hot-water tank to the heat exchanger and back to the hot-water tank through stratification inlet pipes. The return flow from the DHW circulation pipe also enters the tank through stratification inlet pipes. The tank design ensures an excellent thermal stratification in the tank. The solar heating system was installed in May 2000. The thermal performance of the solar heating system has been measured in the first two years of operation. Compared to other large Danish solar domestic hot water systems the system is performing well in spite of the fact that the solar collectors are far from being orientated optimally. The utilization of the solar radiation on the collectors is higher, 46% in the second year of operation, than for any other system earlier investigated in Denmark, 16%–34%. The reason for the good thermal performance and for the excellent utilization of the solar radiation is the high hot-water consumption and the good system design making use of external heat exchangers and stratification inlet pipes.
Solar Thermal Water Pumps: A Preliminary Analysis of the Working Process
Authors: Mahkamov K. , Orda E. P.
Published: February 2005

Solar thermal water pumps are low cost and low maintenance devices with a pumping capacity of 0.2-1m3/hour at a dynamic head of 1.5–5 m. The working fluid in the thermodynamic cycle is an air-steam mixture. In this paper we suggest a simple mathematical model to numerically simulate the internal processes in such a pump and determine the performance and physical dimensions of a preliminary design. The proposed mathematical model has been calibrated against experimental data and it provides the numerical simulation of the processes which occur in the cycle within an acceptable degree of accuracy for engineering purposes. The results of the analysis show that the performance of the solar water pump is mainly determined by the “steam” fraction of the cycle. The power of the solar thermal water pump increases with an increase in the maximum temperature in the cycle, while the indicated efficiency reduces because of the increase in the heat loss due to water vaporization and condensation processes.
An Efficient Method for Assessing the Quality of Large Solar Irradiance Datasets
Authors: Claywell R. , Muneer T. , Asif M.
Published: February 2005

There has been an enormous increase in the use of solar heating and photovoltaic systems worldwide. Building professionals to better design buildings, windows and other solar related constructs require current and accurate compilations of solar irradiance data. Frequently, enough care is not exercised with respect to quality of the measurements. Traditionally, researchers have used several methods for the quality assessment of solar irradiance data. This article addresses two of those methods, visual and quartile analysis, often used to identify “outliers” in the large datasets typically found in solar energy related research. The present work introduces another method for identification of erroneous data, based on standard deviations, using the clearness index and the diffuse ratio. This method is highly efficient in terms of its algorithmic approach.
Study of a Solar Booster Assisted Ejector Refrigeration System With R134a
Authors: Herna´ndez Jorge I. , Best Roberto , Dorantes Rube´n J. , Estrada Claudio A.
Published: February 2005

The studies of ejector refrigeration systems employing refrigerant R134a for air conditioning are scarce and nonexistent for ice making when its potential application in developing countries will lessen their refrigeration needs. So, a parametric study for an ice making solar booster assisted ejector refrigeration system operating with R134a is carried out. System energy and exergy efficiencies as well as ejector efficiency are presented as a function of generator and condenser temperatures and booster discharge pressure. A discussion on maximum ejector efficiency and its effect in system behavior is also carried out. With results indicating that for an evaporator temperature of −10°C, the system can operate at a generator temperature of 85°C with average energy efficiencies between 0.21 and 0.58, depending on the condenser temperature. Consequently, these systems could be a solution for solar refrigeration using off-the-shelf components.
A Model-Based Feed-Forward Controller Scheme for Accurate Chilled Water Temperature Control of Inlet Guide Vane Centrifugal Chillers
Authors: Jia Yongzhong , Reddy T. Agami
Published: February 2005

Capacity control in most commercial centrifugal chillers is achieved by inlet guide vanes which are activated by the leaving chilled water temperature sensor. Due to mechanical reasons, vane control is done discretely, and not continuously. The control module compares the value provided by the temperature sensor to pre-set control band values, and if those bands are exceeded, it sends a signal to the vane control motor to adjust the vane position by one step which could be upwards or downwards. The advantage of this type of discrete control method is its simplicity. Normally, the accuracy in the outlet chilled water temperature is of the order of 0.5°C, which is acceptable for normal cooling plants such as used in office buildings. However, there are applications such as in pharmaceutical processes, mechanics labs, or instances in chemical processes where more accurate control is required (sometimes as low as 0.05°C). This paper proposes a simple method to achieve such tight control without any hardware modifications. The basis of this method is a transient physical inverse model of the refrigerant boiling process in the evaporator, in conjunction with a feed-forward control scheme. The model parameters need to be identified from monitored data since they are chiller-specific. This paper describes the model, and applies it to one-minute monitored data from an actual chiller plant of 1580 kW (450 Tons). It is demonstrated that for this specific chiller such a control scheme has the potential to improve control accuracy by about 28% as compared to the traditional control method.
Scaling in Polymer Tubes and Interpretation for Use in Solar Water Heating Systems
Authors: Wang Yana , Davidson Jane , Francis Lorraine
Published: February 2005

An experimental study of the growth of scale on copper, nylon 6,6, semiaromatic high temperature nylon, polypropylene, polybutylene, and Teflon tubes exposed to hard water is presented. Results provide qualitative information on the scaling of polymer tubes in nonisothermal, flowing conditions expected in heat exchangers and solar absorbers. The 89-cm-long tubes were placed in tube-in-shell heat exchangers. The tubes were exposed to flowing water for 1660 h, a 1120-h pretreatment phase using tap water adjusted to supersaturation of about 2 and pH of 8, followed by a 540-h acceleration phase using tap water with an adjusted total calcium concentration of 4×10−3M, and a pH of 9. Flow rate was 4 cm/s. A 50% propylene glycol solution at 60°C was maintained on the shell side of the heat exchanger. Sections of the tubes were removed periodically to determine the extent of scaling. Results include scanning electron microscope images of the tube surfaces before and after exposure to the flowing water, x-ray diffraction to determine the crystalline phase content of the observed deposits, and chemical analysis to estimate the mass of calcium carbonate per unit surface area. A model of the scaling process is presented to help interpret the data. The data show conclusively that polymer tubes are prone to scaling. With the exception of nylon 6,6, the scaling rate on the polymers is about the same as that on copper. The nylon 6,6 substrate appears to enhance scaling. The enhancement is attributed to hydrolysis of the substrate.
A Numerical and Experimental Investigation of Low-conductivity Unglazed, Transpired Solar Air Heaters
Authors: Gawlik Keith , Christensen Craig , Kutscher Charles
Published: February 2005

The performance of low-conductivity unglazed, transpired solar collectors was determined numerically and experimentally. The numerical work consisted of modeling flow conditions, plate geometries, and plate conductivities with modified commercial computational fluid dynamics software, and the experimental work compared the performance of two plate geometries made with high and low conductivity materials under a variety of flow conditions. Good agreement was found between the numerical and experimental results. The results showed that for practical low-conductivity materials, performance differed little from the equivalent plate geometry in high-conductivity material.
Studies of Heat Pumps Using Direct Expansion Type Solar Collectors
Authors: Ito Sadasuke , Miura Naokatsu , Takano Yasushi
Published: February 2005

An aluminum roll-bond panel with a photovoltaic module on the surface was developed recently for use as an evaporator of a heat pump for residential hot water supply and room heating [Proceedings of the JSES/JWEA Joint Conference, Okinawa, pp. 305–308 (in Japanese)]. In the present study, the panel was modified to reduce the large pressure loss of the refrigerant flow at the evaporator. Total area of the panels was 1.9m2 and the rated capacity of the compressor was 250 W. A collector efficiency factor of 0.9 was obtained for the evaporator. The effect of the location of the feeler bulb on performance of the heat pump was also examined.
Energy Performance Analysis of Coupled-Control Units With Both Thermostat and Humidistat
Authors: Liu Mingsheng , Wang Jinrong
Published: February 2005

Coupled control units typically condition a single zone with constant air volume. A thermostat controls the heating valve or cooling valve when the room relative humidity is below the set point. When the room relative humidity is higher than the set point, a humidistat controls the cooling coil to dehumidify air and the thermostat controls the heating coil to maintain room temperature. Theoretical modeling is performed to investigate the energy performance of coupled control units and potential improvement measures. The study shows that the annual thermal energy consumption of the coupled-control units is up to four times higher than the optimal thermal energy consumption. Thermal energy consumption can be reduced by (a) eliminating excessive airflows, (b) minimizing valve leakages, and (c) modulating airflows with a zone sensible load. This paper presents the simulation models and results and discusses improvement measures.
Monte Carlo Radiative Transfer Modeling of a Solar Chemical Reactor for The Co-Production of Zinc and Syngas
Authors: Kra¨upl Stefan , Steinfeld Aldo
Published: February 2005

Radiation heat transfer within a solar chemical reactor for the co-production of zinc and syngas is analyzed by the Monte Carlo ray-tracing method. The reactor is treated as a 3D nonisothermal cavity-receiver lined with ZnO particles that are directly exposed to concentrated solar irradiation and undergo endothermic reduction by CH4 at above 1300 K. The analysis includes coupling to conduction/convection heat transfer and chemical kinetics. A calculation of the apparent absorptivity indicates the cavity’s approach to a blackbody absorber, for either diffuse or specular reflecting inner walls. Numerically calculated temperature distributions, zinc production rates, and thermal efficiencies are validated with experimental measurements in a solar furnace with a 5-kW prototype reactor. At 1600 K, the zinc production rate reached 0.12 mol/min and the reactor’s thermal efficiency exceeded 16%. Scaling up the reactor to power levels of up to 1 MW while keeping constant the relative geometrical dimensions and the solar power flux at 2000 suns results in thermal efficiencies of up to 54%.
Thermal Characterization of Prototypical Integral Collector Storage Systems With Immersed Heat Exchangers
Authors: Liu W. , Davidson J. H. , Kulacki F. A.
Published: February 2005

Natural convection is measured in an enclosure that represents an integral collector storage system (ICS) with an immersed tube-bundle heat exchanger. Heat transfer coefficients for bundles of 240 tubes contained in a thin enclosure of aspect ratio of 9.3:1 and inclined at 30 deg to the horizontal are obtained for a range of transient operating modes and pitch-to-diameter ratios of 1.5, 2.4, and 3.3. Results for isothermal and stratified enclosures yield a correlation for the overall Nusselt number NuD=2.45±0.03RaD0.188,230⩽RaD⩽9800. The characteristic temperature difference in the Rayleigh number is that between the average water temperature within the bundle and the tube wall temperature. Nusselt numbers are three times larger than those for a similarly configured single-tube and an eight-tube bundle. This increase is attributed to stronger fluid motion within the bundle and higher overall large scale circulation rates in the enclosure.
Photogrammetry: A Powerful Tool for Geometric Analysis of Solar Concentrators and Their Components
Authors: Pottler Klaus , Lu¨pfert Eckhard , Johnston Glen H. G. , Shortis Mark R.
Published: February 2005

Digital close range photogrammetry has proven to be a precise and efficient measurement technique for the assessment of shape accuracies of solar concentrators and their components. The combination of high quality mega-pixel digital still cameras, appropriate software, and calibrated reference scales in general is sufficient to provide coordinate measurements with precisions of 1:50,000 or better. The extreme flexibility of photogrammetry to provide high accuracy 3D coordinate measurements over almost any scale makes it particularly appropriate for the measurement of solar concentrator systems. It can also provide information for the analysis of curved shapes and surfaces, which can be very difficult to achieve with conventional measurement instruments. The paper gives an overview of quality indicators for photogrammetric networks, which have to be considered during the data evaluation to augment the measurement precision. A selection of measurements done on whole solar concentrators and their components are presented. The potential of photogrammetry is demonstrated by presenting measured effects arising from thermal expansion and gravitational forces on selected components. The measured surface data can be used to calculate slope errors and undertake ray-trace studies to compute intercept factors and assess concentrator qualities.
Parametric Analysis of Active and Passive Building Thermal Storage Utilization*
Authors: Zhou Guo , Krarti Moncef , Henze Gregor P.
Published: February 2005

Cooling of commercial buildings contributes significantly to the peak demand placed on an electrical utility grid. Time-of-use electricity rates encourage shifting of electrical loads to off-peak periods at night and on weekends. Buildings can respond to these pricing signals by shifting cooling-related thermal loads either by precooling the building’s massive structure or by using active thermal energy storage systems such as ice storage. While these two thermal batteries have been engaged separately in the past, this paper investigates the merits of harnessing both storage media concurrently in the context of optimal control for a range of selected parameters. A parametric analysis was conducted utilizing an EnergyPlus-based simulation environment to assess the effects of building mass, electrical utility rates, season and location, economizer operation, central plant size, and thermal comfort. The findings reveal that the cooling-related on-peak electrical demand and utility cost of commercial buildings can be substantially reduced by harnessing both thermal storage inventories using optimal control for a wide range of conditions.
Predictive Models of Web-to-Roller Traction
Authors: Rice Brian S. , Gans Roger F.
Published: February 2005

We studied the traction developed between a thin, flexible web and a rotating circumferentially grooved cylindrical roller. We have developed a new two-dimensional analytic model that couples air film pressure, web deflection, and asperity contact to predict traction for circumferentially grooved rollers with arbitrary wrap angles. The entrance effects are incorporated into our new traction model by adapting the squeeze film concept using the distance from the entrance as a surrogate for time. We have verified this model experimentally on a series of 14 rollers and 19 webs. We tested both nongrooved and circumferentially grooved rollers. We showed experimentally that rough, ungrooved rollers that have their low areas unconnected produce significantly lower traction and do not fit the model introduced here. Such rollers should be avoided where traction is important. We introduce dimensionless groups that the roller designer can use to quantitatively assess the interactions of process variables (e.g., speed, tension, etc.) with design variables (e.g., groove depth, groove pitch, roughness, etc.) over the full range of practical wrap angles.
Two-Dimensional CFD-Analysis of Micro-Patterned Surfaces in Hydrodynamic Lubrication
Authors: Sahlin Fredrik , Glavatskih Sergei B. , Almqvist Torbjo¨rn , Larsson Roland
Published: February 2005

Results of a numerical study of the influence of micro-patterned surfaces in hydrodynamic lubrication of two parallel walls are reported. Two types of parameterized grooves with the same order of depth as the film thickness are used on one stationary wall. The other wall is smooth and is sliding with a specified tangential velocity. Isothermal incompressible two dimensional full film fluid flow mechanics is solved using a Computational Fluid Dynamics method. It is shown that, by introducing a micro-pattern on one of two parallel walls, a net pressure rise in the fluid domain is achieved. This produces a load carrying capacity on the walls which is mainly contributed by fluid inertia. The load carrying capacity increases with Reynolds number. The load carrying capacity is reported to increase with groove width and depth. However, at a certain depth a vortex appears in the groove and near this value the maximum load carrying capacity is achieved. It is shown that the friction force decreases with deeper and wider grooves. Among all geometries studied, optimum geometry shapes in terms of hydrodynamic performance are reported.
Understanding Friction Factor Behavior in Liquid Annular Seals With Deliberately Roughened Surfaces
Authors: Villasmil Larry A. , Childs Dara W. , Chen Hamn-Ching
Published: February 2005

Multistage centrifugal pumps and compressors are among the most widely used pieces of rotating machinery in industry. A typical application demands the arrangement of several impellers or wheels mounted on a shaft that spins within a stationary case. Annular seals are the most common sealing devices used in this type of machinery. The annular seal design affects both (i) machinery performance in terms of energy conversion efficiency, and (ii) stability due to the interaction within the rotor and the stator through the fluid flow within the seals. Traditionally, the “bulk-flow” theory due to Hirs (ASME J. Lubrication Technol., pp. 137–146) has been used to estimate annular seals leakage and dynamic coefficients. To predict the flow behavior through the seal, this theory relies on empirical friction factor correlations. While leakage is well predicted, the dynamic coefficients are not. The discrepancy is attributed to the friction factor model. Several experiments have produced seal leakage data indicating that friction factor increases as the seal clearance is increased, contradicting predictions based on Moody’s pipe-friction model. A Computational Fluid Dynamics (CFD) commercial code was used to simulate flat-plate-channel-flow experimental tests of water flowing with deliberately roughened surfaces, showing an increase of friction factor with clearance increase. The higher friction factor characteristics of these deliberately roughened surfaces are governed by their ability to develop a high static pressure in the trailing face of each roughness cavity, while the wall shear stresses on the smooth land play a secondary role. In a certain Reynolds number range, the maximum friction factor observed on a specific roughness pattern size is independent of the actual clearance, which we have referred to as the friction-factor-to-clearance indifference behavior. This phenomenon is found to be related to the roughness cavity size and its length-to-clearance ratio.
Survey and Performance Assessment of Solution Methods for Elastic Rough Contact Problems
Authors: Allwood Julian
Published: February 2005

Recent developments in the solution of models of rough contact have demonstrated the advantages of fast matrix multiplication methods in increasing the size of problem that can usefully be solved. However, to date, no attempt has been made to compare these methods with existing approaches. In this paper a survey of solution methods reveals that three main classes of solution method have been developed: active set methods with direct matrix solution; active set methods with iterative matrix solvers; iterative methods based on fast matrix multiplications. The best features of each class are assembled from the literature and combined to formulate a “best-possible” algorithm in each class. These algorithms are implemented and compared, with emphasis on their solution speed, accuracy and memory requirements. For smaller problems with fewer than 2000 grid points in contact, the direct matrix solution method proves to be most efficient, and is always the most accurate. However, the method is limited by memory requirements as the contact region increases. For large problems with more than 2000 grid points in contact, the multilevel multisummation approach requires less memory, and performs faster, but gives errors in predicted pressure and contact region of approximately 0.5%. The active set method with iterative matrix solver requires less memory than direct matrix solution, is more accurate than the multilevel multisummation approach, but is always slower than one of the other methods.
On Three-Dimensional Flat-Top Defects Passing Through an EHL Point Contact: A Comparison of Modeling with Experiments
Authors: Fe´lix-Quin˜onez A. , Ehret P. , Summers J. L.
Published: February 2005

A direct comparison between experimental and numerical results for the passage of an array of 3D flat-top, square shaped surface features through an EHL point contact is presented. Results for pure rolling conditions show that the features’ deformation in the high-pressure region is governed by their ability to entrap lubricant both underneath and in the grooves during their passage through the inlet zone. Film perturbations associated with each defect occur as locally enhanced regions of lubricant and film thickness micro-constrictions. Under sliding conditions the features sustain further deformations as they traverse the high-pressure conjunction and meet the highly viscous lubricant entrapped in the grooves, which moves at a different velocity. Lubricant is also seen to accumulate just in front or behind the features depending on the slide-to-roll ratio. Overall, the results highlight the importance of understanding the effects of the defects structure and the lubricant rheology on the film thickness to unravel the effects of real roughness patterns.
Squeeze-Film Lubrication of the Human Ankle Joint Subjected to the Cyclic Loading Encountered in Walking
Authors: Hlava´cˇek Miroslav
Published: February 2005

Squeeze-film lubrication of the human ankle joint during walking is numerically analyzed, the effect of surface sliding being neglected at this stage. Biphasic mixture models are considered for synovial fluid (an ideal and viscous fluid phases) and for articular cartilage (an ideal interstitial fluid and an elastic porous matrix). In the model, the ideal fluid phase passes through the articular surface and matrix pores. The cartilage matrix is considered both normal and pathological (with primary osteoarthrosis). Calculations show that water and small solutes of synovial fluid imbibe into the articular cartilage during the stance period, while the interstitial fluid of the cartilage exudes and enriches the lubricant during the swing period in a central part of the contact at each step. Soon after the onset of walking, repeatedly near the load culmination of each step, the synovial fluid should be turned into a synovial gel and, shortly after, changed back again into a fluid there. In the pathological case, the protective synovial gel layer is quickly depleted after several steps and the surfaces may come briefly into contact in each cycle. With normal cartilage, however, the protective intermittent gel film (formed briefly at each step) maintains its thickness for a longer time. Normal cartilage also behaves more favorably, when a long walk is broken and then resumed shortly afterwards. With normal articular cartilage, maintenance of a lubricating fluid film is much aided by the cyclic nature of the loading encountered in walking, compared with the steady loading in standing where the fluid film is quickly filtered out into a protective permanent gel film.