Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Terms modified by MW

  • mw cm
  • mw distribution
  • mw fraction
  • mw irradiation
  • mw m
  • mw power

  • Selected Abstracts

    Effects of earthquake and cyclone sequencing on landsliding and fluvial sediment transfer in a mountain catchment

    Guan-Wei Lin
    Abstract Patterns and rates of landsliding and fluvial sediment transfer in mountain catchments are determined by the strength and location of rain storms and earthquakes, and by the sequence in which they occur. To explore this notion, landslides caused by three tropical cyclones and a very large earthquake have been mapped in the Chenyoulan catchment in the Taiwan Central Range, where water and sediment discharges and rock strengths are well known. Prior to the MW 7·6 Chi-Chi earthquake in 1999, storm-driven landslide rates were modest. Landslides occurred primarily low within the landscape in shallow slopes, reworking older colluvial material. The Chi-Chi earthquake caused wide-spread landsliding in the steepest bedrock slopes high within the catchment due to topographic focusing of incoming seismic waves. After the earthquake landslide rates remained elevated, landslide patterns closely tracking the distribution of coseismic landslides. These patterns have not been strongly affected by rock strength. Sediment loads of the Chenyoulan River have been limited by supply from hillslopes. Prior to the Chi-Chi earthquake, the erosion budget was dominated by one exceptionally large flood, with anomalously high sediment concentrations, caused by typhoon Herb in 1996. Sediment concentrations were much higher than normal in intermediate size floods during the first 5 years after the earthquake, giving high sediment yields. In 2005, sediment concentrations had decreased to values prevalent before 1999. The hillslope response to the Chi-Chi earthquake has been much stronger than the five-fold increase of fluvial sediment loads and concentrations, but since the earthquake, hillslope sediment sources have become increasingly disconnected from the channel system, with 90 per cent of landslides not reaching into channels. Downslope advection of landslide debris associated with the Chi-Chi earthquake is driven by the impact of tropical cyclones, but occurs on a time-scale longer than this study. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Scale-up development of high-performance polymer matrix for DNA sequencing analysis

    ELECTROPHORESIS, Issue 19 2006
    Fen Wan
    Abstract Linear polyacrylamide (LPA) has been widely used as a replaceable separation matrix in CE. An increase in the molecular weight of the separation medium favors the separation of larger DNA fragments. In order to obtain ultrahigh-molecular-weight (UHMW) LPA, a "frozen" method was developed to synthesize the LPA homopolymer. This approach has three major advantages when compared with other existing routes of LPA synthesis: (i),long LPA chains could be obtained easily, with their average molecular weight (MW) being in the high 10,MDa range; (ii),the desired MW could be adjusted over a broad range by controlling the temperature and the concentration of initiators during synthesis; (iii),the product solution contains only a tiny amount of impurity besides the solvent and LPA. Both static and dynamic laser light scattering measurements were carried out to characterize the synthesized LPA in the buffer solution. The DNA sequencing matrix prepared from LPA using this method was studied and the results were compared with the newly developed commercial product POP7 from Applied Biosystems. It should be noted that this approach can be applied to synthesize other water-soluble polymers, resulting in UHMW products because the chain transfer constant is smaller at lower temperatures. [source]

    Narrow-band fractionation of proteins from whole cell lysates using isoelectric membrane focusing and nonporous reversed-phase separations

    ELECTROPHORESIS, Issue 7-8 2004
    Yi Zhu
    Abstract Preparative isoelectric focusing (PIEF) is used to achieve narrow-band fractionation of proteins from whole cell lysates of Escherichia coli (E. coli). Isoelectric membranes create well-defined pH ranges that fractionate proteins by isoelectric point (pI) upon application of an electric potential. A commercial IsoPrime device (Amersham-Pharmacia BioTech) is modified for the PIEF separation to lessen run volumes significantly. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) analysis of chamber contents indicates that excellent pH fractionation is achieved with little overlap between chambers. PIEF pH fractions are further separated using nonporous reversed-phase high-performance liquid chromatography (NPS-RP-HPLC) and HPLC eluent is analyzed on-line by electrospray ionization-time of flight-mass spectrometry (ESI-TOF-MS) for intact protein molecular weight (MW) analysis. The result is a pI versus MW map of bacterial protein content. IEF fractionation down to 0.1 pH units combined with intact protein MW values result in a highly reproducible map that can be used for comparative analysis of different E. coli strains. [source]

    Antioxidative activity of water extracts from the yam (Dioscorea opposita Thunb.) tuber mucilage tororo

    Takeshi Nagai
    Abstract A water extract as a viscous solution was obtained from the yam Dioscorea opposita tuber mucilage tororo, and its functional properties were demonstrated. The protein content was about 280,,g/mL extract, and the main protein bands with an MW of ,33,kDa without 2-mercaptoethanol (2-ME) and ,31,kDa with 2-ME were detected by SDS-PAGE. The water extract possessed high antioxidative activity and scavenging activities against superoxide anion and hydroxyl radicals. However, it showed no inhibitory activity against angiotensin,I-converting enzyme. The yam tuber contains relatively high contents of vitamins, different micro- and macroelements, enzymes, and dietary fibers. The yam D.,opposita tuber will be increasingly regarded as a health-promoting food. [source]

    Temperature-Resolved Local and Macroscopic Charge Carrier Transport in Thin P3HT Layers,

    Patrick Pingel
    Abstract Previous investigations of the field-effect mobility in poly(3-hexylthiophene) (P3HT) layers revealed a strong dependence on molecular weight (MW), which was shown to be closely related to layer morphology. Here, charge carrier mobilities of two P3HT MW fractions (medium-MW: Mn,=,7,200 g mol,1; high-MW: Mn,=,27,000 g mol,1) are probed as a function of temperature at a local and a macroscopic length scale, using pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) and organic field-effect transistor measurements, respectively. In contrast to the macroscopic transport properties, the local intra-grain mobility depends only weakly on MW (being in the order of 10,2 cm2 V,1 s,1) and being thermally activated below the melting temperature for both fractions. The striking differences of charge transport at both length scales are related to the heterogeneity of the layer morphology. The quantitative analysis of temperature-dependent UV/Vis absorption spectra according to a model of F. C. Spano reveals that a substantial amount of disordered material is present in these P3HT layers. Moreover, the analysis predicts that aggregates in medium-MW P3HT undergo a "pre-melting" significantly below the actual melting temperature. The results suggest that macroscopic charge transport in samples of short-chain P3HT is strongly inhibited by the presence of disordered domains, while in high-MW P3HT the low-mobility disordered zones are bridged via inter-crystalline molecular connections. [source]

    Lateral Inhomogeneity in the Electronic Structure of a Conjugated Poly(3-hexylthiophene) Thin Film

    Kaname Kanai
    Abstract How annealing influences the morphology of a highly regioregular poly(3-hexylthiophene) (RR-P3HT) film at the substrate interface as well as the lateral inhomogeneity in the electronic structure of the film are elucidated. Whereas previous studies have reported that high-molecular-weight (MW) RR-P3HT films tend to show low crystallinity even after annealing, it is found that high-MW RR-P3HT does show high crystallinity after annealing at high temperature for a long time. Photoemission electron microscopy (PEEM), X-ray photoemission spectroscopy, and ultraviolet photoemission spectroscopy results clearly resolve a considerable lateral inhomogeneity in the morphology of RR-P3HT film, which results in a variation of the electronic structure depending on the local crystallinity. The PEEM results show how annealing facilitates crystal growth in a high-MW RR-P3HT film. [source]

    Bacterial quorum sensing and nitrogen cycling in rhizosphere soil

    Kristen M. DeAngelis
    Abstract Plant photosynthate fuels carbon-limited microbial growth and activity, resulting in increased rhizosphere nitrogen (N) mineralization. Most soil organic nitrogen is macromolecular (chitin, protein, nucleotides); enzymatic depolymerization is likely rate limiting for plant nitrogen accumulation. Analyzing Avena (wild oat) planted in microcosms containing sieved field soil, we observed increased rhizosphere chitinase and protease-specific activities, bacterial cell densities, and dissolved organic nitrogen (DON) compared with bulk soil. Low-molecular-weight (MW) DON (<3000 Da) was undetectable in bulk soil but comprised 15% of rhizosphere DON. Extracellular enzyme production in many bacteria requires quorum sensing (QS), cell-density-dependent group behavior. Because proteobacteria are considered major rhizosphere colonizers, we assayed the proteobacterial QS signals N -acyl-homoserine lactones (AHLs), which were significantly increased in the rhizosphere. To investigate the linkage between soil signaling and nitrogen cycling, we characterized 533 bacterial isolates from Avena rhizosphere: 24% had chitinase or protease activity and AHL production; disruption of QS in seven of eight isolates disrupted enzyme activity. Many Alphaproteobacteria were newly found with QS-controlled extracellular enzyme activity. Enhanced specific activities of nitrogen-cycling enzymes accompanied by bacterial density-dependent behaviors in rhizosphere soil gives rise to the hypothesis that QS could be a control point in the complex process of rhizosphere nitrogen mineralization. [source]

    Hydrographic features and seabird foraging in Aleutian Passes

    Abstract Strong tidal currents crossing over the abrupt topography of the Aleutian Passes result in regions with high horizontal property gradients. These frontal regions vary with the tidal cycle and form the boundary between vertically mixed and stratified regions. Concentrations of seabirds were associated with convergence zones in the mixed water (MW) and with the front between North Pacific (NP) water and MW. Species that were foraging by picking at prey from the surface were associated with surface convergences that appeared to be associated with Langmuir circulation cells or tidal features (all fulmar aggregations) in the central passes (Samalga, Seguam). In contrast, subsurface foraging puffins and small alcids were mostly observed in areas of turbulent, well-mixed water near the shallow regions of the passes. Short-tailed shearwater flocks that were plunge-diving for prey were associated with the front between the NP water and MW in the passes. On our transects, we observed no significant aggregations of seabirds associated with Bering Sea water or NP water away from the frontal zones. The interaction of strong currents with bathymetric features results in zones of vertical advection, mixing, and surface convergences that make island passes attractive foraging regions for seabirds. Deep passes lacking these features, such as many of the passes in the western Aleutian Archipelago, are not as likely to facilitate trophic transfer to top predators as shallow passes, such as those found in the eastern Aleutian Islands. [source]

    A comparative proteome analysis of human metaphase chromosomes isolated from two different cell lines reveals a set of conserved chromosome-associated proteins

    GENES TO CELLS, Issue 3 2007
    Hideaki Takata
    A comparative proteome analysis of human metaphase chromosomes between a typical epithelial-like cell, HeLa S3, and a lymphoma-type cell, BALL-1, was performed. One-dimensional (1-D) SDS-PAGE and radical-free and highly reducing two-dimensional electrophoresis (RFHR 2-DE) detected more than 200 proteins from chromosomes isolated from HeLa S3 cells, among which 189 proteins were identified by mass spectrometry (MS). Consistent with our recent four-layer structural model of a metaphase chromosome, all the identified proteins were grouped into four distinct levels of abundance. Both HeLa S3 and BALL-1 chromosomes contained specific sets of abundant chromosome structural and peripheral proteins in addition to less abundant chromosome coating proteins (CCPs). Furthermore, titin array analysis and a proteome analysis of the ultra-high molecular mass region indicated an absence of titin with their molecular weight (MW) more than 1000 kDa. Consequently, the present proteome analyses together with previous information on chromosome proteins provide the comprehensive list of proteins essential for the metaphase chromosome architecture. [source]

    Cell cycle mechanisms of sister chromatid separation; Roles of Cut1/separin and Cut2/securin

    GENES TO CELLS, Issue 1 2000
    Mitsuhiro Yanagida
    The correct transmission of chromosomes from mother to daughter cells is fundamental for genetic inheritance. Separation and segregation of sister chromatids in growing cells occurs in the cell cycle stage called ,anaphase'. The basic process of sister chromatid separation is similar in all eukaryotes: many gene products required are conserved. In this review, the roles of two proteins essential for the onset of anaphase in fission yeast, Cut2/securin and Cut1/separin, are discussed with regard to cell cycle regulation, and compared with the postulated roles of homologous proteins in other organisms. Securin, like mitotic cyclins, is the target of the anaphase promoting complex (APC)/cyclosome and is polyubiquitinated before destruction in a manner dependent upon the destruction sequence. The anaphase never occurs properly in the absence of securin destruction. In human cells, securin is an oncogene. Separin is a large protein (MW ,180 kDa), the C-terminus of which is conserved, and is thought to be inhibited by association with securin at the nonconserved N-terminus. In the budding yeast, Esp1/separin is thought to be a component of proteolysis against Scc1, an essential subunit of cohesin which is thought to link duplicated sister chromatids up to the anaphase. Whether fission yeast Cut1/separin is also implicated in proteolysis of cohesin is discussed. [source]

    On the Synthesis of Carbon Nanofibers and Nanotubes by Microwave Irradiation: Parameters, Catalysts, and Substrates

    Tamara Druzhinina
    Abstract The microwave (MW)-assisted synthesis of one dimensional carbon systems is introduced as a promising approach to improve the speed and cost-effectiveness of the fabrication process. Improved reaction conditions are generated by direct MW heating and synthesis under advanced reaction conditions. The influence of the reaction conditions is investigated and the importance of individual process parameters on the synthesis is discussed. Temperature and pressure data recorded during the irradiation process are analyzed in detail and allow the determination of essential process parameters. This leads to improved reaction conditions, better control of the one-dimensional carbon nanosystems by tuning the catalyst materials, and allows expanding this approach to initiate the synthesis on a variety of different substrates, such as quartz glass and mica. [source]

    Tapovan-Vishnugad hydroelectric power project , experience with TBM excavation under high rock cover / . Tapovan-Vishnugad Wasserkraftwerk , Erfahrungen mit TBM-Vortrieb bei hoher Überlagerung

    Johann Brandl
    Mechanised tunnelling - Maschineller Vortrieb; Hydro power plants - Wasserkraftanlagen Abstract NTPC Ltd. of India is presently constructing the 520 MW (4 x 30 MW) Tapovan-Vishnugad hydroelectric power plant in Uttarakhand in the Himalayas. As part of this project, an approximately 12.1 km head race tunnel (HRT) is to be constructed, of which approximately 8.6 km are being excavated by DS-TBM with an excavation diameter of 6.575 m. Construction of this HRT has been awarded to a Joint Venture (JV) of Larsen, Toubro Ltd., India, and Alpine, Austria. Geoconsult ZT GmbH is acting as a Consultant to NTPC Ltd. for the TBM part of the HRT. The overburden above the tunnel is up to 1, 100 m with the result that knowledge of the geology along the HRT alignment could only be based on projections made from surface exposures available in the area. Basically, the ground consists of jointed quartzite, gneiss and schist. Excavation of the HRT started in October 2008 and excavation rates of over 500 m per month were achieved in November 2009. However, in December 2009 the TBM encountered a fault zone along with high-pressure water inflow and became trapped. This paper outlines the present status of HRT construction and describes in particular the difficulties encountered during TBM excavation in fault zones with large high-pressure water inflows and how these problems are being dealt with. Die indische Firma NTPC Ltd. errichtet derzeit das 520 MW (4 x 130 MW) Tapovan-Vishnugad Wasserkraftwerk in Uttarakhand, Himalaya. Als Teil dieses Projekts wird ein ungefähr 12,1 km langer Triebwasserstollen (TWS) errichtet, wobei rund 8,6 km davon mittels einer DS-TBM mit einem Ausbruchdurchmesser von 6.575 m aufgefahren werden. Der Bau dieses Triebwasserstollens wurde an die Arbeitsgemeinschaft Larsen, Toubro Ltd., Indien, und Alpine, Österreich vergeben. Geoconsult ZT GmbH fungiert als Berater von NTPC Ltd. für den TBM-Teil des TWS. Aufgrund der Überlagerung des Tunnels von bis zu 1,100 m konnte die Geologie entlang des Triebwasserstollens nur durch Projektion von vorhandenen Oberflächenaufschlüssen aus der Umgebung bestimmt werden. Das Gebirge besteht hauptsächlich aus geklüftetem Quarzit, Gneis und Schiefer. Der Ausbruch des TWS begann im Oktober 2008. Im November 2009 wurde eine Vortriebsgeschwindigkeit von über 500 m pro Monat erreicht. Im Dezember 2009 jedoch fuhr die TBM eine Störzone mit einem Hochdruckwassereinbruch an, wodurch die TBM stecken blieb. Dieser Artikel skizziert den derzeitigen Stand des TWS und legt besonderes Augenmerk auf die Schwierigkeiten beim Auffahren der Störzone inklusive Hochdruckwassereinbruch mit einer TBM. Darüber hinaus wird gezeigt, wie sich die auftretenden Probleme lösen lassen. [source]

    Disruption of the hyaluronan-based extracellular matrix in spinal cord promotes astrocyte proliferation

    GLIA, Issue 1 2005
    Jaime Struve
    Abstract Astrocyte proliferation is tightly controlled during development and in the adult nervous system. In the present study, we find that a high-molecular-weight (MW) form of the glycosaminoglycan hyaluronan (HA) is found in rat spinal cord tissue and becomes degraded soon after traumatic spinal cord injury. Newly synthesized HA accumulates in injured spinal cord as gliosis proceeds, such that high-MW HA becomes overabundant in the extracellular matrix surrounding glial scars after 1 month. Injection of hyaluronidase, which degrades HA, into normal spinal cord tissue results in increased numbers of glial fibrillary acidic protein (GFAP)-positive cells that also express the nuclear proliferation marker Ki-67, suggesting that HA degradation promotes astrocyte proliferation. In agreement with this observation, adding high- but not low-MW HA to proliferating astrocytes in vitro inhibits cell growth, while treating confluent, quiescent astrocyte cultures with hyaluronidase induces astrocyte proliferation. Collectively, these data indicate that high-MW HA maintains astrocytes in a state of quiescence, and that degradation of HA following CNS injury relieves growth inhibition, resulting in increased astrocyte proliferation. © 2005 Wiley-Liss, Inc. [source]

    Back to the Future: Middle Molecules, High Flux Membranes, and Optimal Dialysis

    Raymond C. Vanholder
    Middle molecules can be defined as compounds with a molecular weight (MW) above 500 Da. An even broader definition includes those molecules that do not cross the membranes of standard low-flux dialyzers, not only because of molecular weight, but also because of protein binding and/or multicompartmental behavior. Recently, several of these middle molecules have been linked to the increased tendency of uremic patients to develop inflammation, malnutrition, and atheromatosis. Other toxic actions can also be attributed to the middle molecules. In the present publication we will consider whether improved removal of middle molecules by large pore membranes has an impact on clinical conditions related to the uremic syndrome. The clinical benefits of large pore membranes are reduction of uremia-related amyloidosis; maintenance of residual renal function; and reduction of inflammation, malnutrition, anemia, dyslipidemia, and mortality. It is concluded that middle molecules play a role in uremic toxicity and especially in the processes related to inflammation, atherogenesis, and malnutrition. Their removal seems to be related to a better outcome, although better biocompatibility of membranes might be a confounding factor. [source]

    Estimation of rainfall from infrared-microwave satellite data for basin-scale hydrologic modelling

    Oscar Anthony Kalinga
    Abstract The infrared-microwave rainfall algorithm (IMRA) was developed for retrieving spatial rainfall from infrared (IR) brightness temperatures (TBs) of satellite sensors to provide supplementary information to the rainfall field, and to decrease the traditional dependency on limited rain gauge data that are point measurements. In IMRA, a SLOPE technique (ST) was developed for discriminating rain/no-rain pixels through IR image cloud-top temperature gradient, and 243K as the IR threshold temperature for minimum detectable rainfall rate. IMRA also allows for the adjustment of rainfall derived from IR-TB using microwave (MW) TBs. In this study, IMRA rainfall estimates were assessed on hourly and daily basis for different spatial scales (4, 12, 20, and 100 km) using NCEP stage IV gauge-adjusted radar rainfall data, and daily rain gauge data. IMRA was assessed in terms of the accuracy of the rainfall estimates and the basin streamflow simulated by the hydrologic model, Sacramento soil moisture accounting (SAC-SMA), driven by the rainfall data. The results show that the ST option of IMRA gave accurate satellite rainfall estimates for both light and heavy rainfall systems while the Hessian technique only gave accurate estimates for the convective systems. At daily time step, there was no improvement in IR-satellite rainfall estimates adjusted with MW TBs. The basin-scale streamflow simulated by SAC-SMA driven by satellite rainfall data was marginally better than when SAC-SMA was driven by rain gauge data, and was similar to the case using radar data, reflecting the potential applications of satellite rainfall in basin-scale hydrologic modelling. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    A carbohydrate neoepitope that is up-regulated on human mononuclear leucocytes by neuraminidase treatment or by cellular activation

    IMMUNOLOGY, Issue 2 2001
    Mark T. Quinn
    Summary The expression of cell-surface antigens can delineate specific leucocyte developmental or functional stages. For example, certain membrane glycoproteins are expressed selectively on leucocyte subsets only after activation. Leucocyte activation can also induce changes in carbohydrate epitopes expressed on surface antigens. In the present studies, we report on a novel monoclonal immunoglobulin M antibody (mAb 13.22) that recognizes a unique carbohydrate epitope expressed on human leucocyte membrane proteins. Characterization of mAb 13.22 specificity by immunoblotting showed that it recognized proteins of MW ,95 000 and 150 000, including both CD18 and CD11b. The mAb 13.22 epitope was removed by N -glycosidase F but not by endoglycosidase H or fucosidase, demonstrating that it is an N-linked carbohydrate antigen. Interestingly, immunoblot staining was enhanced after neuraminidase treatment, suggesting that the antibody epitope might also be partially masked by sialic acid. In resting leucocytes, the mAb 13.22 antigen was expressed strongly on neutrophils, while dull staining was present on monocytes, and no lymphocyte staining was observed. In marked contrast, treatment of leucocytes with neuraminidase resulted in exposure of a mAb 13.22 neoepitope on a subset of lymphocytes (primarily T lymphocytes and natural killer cells) as well as up-regulated staining more than 18-fold on monocytes. Activation of lymphocytes in culture with phytohaemagglutinin or concanavalin A also unmasked the mAb 13.22 neoepitope on ,37% of the CD45RO+ lymphocytes. Furthermore, analysis of leucocytes collected from the synovial fluid of patients with rheumatoid arthritis showed that ,18% of the lymphocytes present expressed the mAb 13.22 neoepitope. Taken together, our results suggest that the mAb 13.22 carbohydrate neoepitope could represent a physiologically relevant marker that is up-regulated on leucocyte subsets during the inflammatory response. [source]

    The Rubino test for leprosy is a ,2 -glycoprotein 1-dependent antiphospholipid reaction

    IMMUNOLOGY, Issue 1 2000
    A. Panunto-Castelo
    Summary We describe the isolation and identification of three components required for the Rubino reaction (RR), which is the rapid sedimentation of formalinized sheep red-blood cells (SRBC) initiated by serum from leprosy patients with defective Mycobacterium leprae -specific cell immunity. The Rubino reaction factor (RRF) required for this phenomenon, previously identified as an immunoglobulin M (IgM), was purified from leprosy patient serum by adsorption to formalinized SRBC. Purified RRF IgM, when added to formalinized SRBC, did not produce a positive RR. However, when the contact was carried out in the presence of normal human serum (NHS), cells rapidly sedimented. The purified cofactor from NHS contained two components of 70 000 and 50 000 molecular weight (MW), as determined by sodium dodecyl sulphate,polyacrylamide gel electrophoresis (SDS,PAGE). The latter was recognized by the RRF IgM on immunoblot and its N-terminal sequence indicated that it was ,2 -glycoprotein 1 (,2 -GP1), an anionic phospholipid-binding protein. Methanol-treated formalinized SRBC did not support the RR. Thin-layer chromatography of an extract of membranes indicated that the SRBC ligand was a cell-surface phospholipid. Cardiolipin inhibited the RR. These data demonstrate that the RR involves a trimolecular interaction in which IgM, ,2 -GP1 and an SRBC phospholipid participate. By analogy with the antiphospholipid antibodies (anti-PL) that occur in autoimmune processes, serum samples from 29 systemic lupus erythematosus patients with high levels of anticardiolipin antibodies were submitted to the RR. A positive RR was obtained for 45% (13 of 29 patients). These results modify the paradigm of the absolute specificity of the RR for leprosy and demonstrate that RRF IgM is a ,2 -GP1-dependent anti-PL. [source]

    Emulsion as a Means of Controlling Electrospinning of Polymers

    ADVANCED MATERIALS, Issue 18 2009
    Jay C. Sy
    A generalized approach to attain spinnability in polymer solutions in electrospinning using emulsions is described. By using emulsions, low-molecular weight (MW) polymer solutions that tend to electrospray can be spun into nanofibers. Additionally, control over fiber properties independent of polymer solution viscosity and MW is achieved, with an order of magnitude reduction in fiber diameter upon emulsification. Nanofibrous sheets obtained demonstrate excellent cellular biocompatibility and are suitable for tissue contacting applications. [source]

    Prevalence of yeasts in saliva and root canals of teeth associated with apical periodontitis

    M. W. Egan
    Abstract Egan MW, Spratt DA, Ng Y-L, Lam JM, Moles DR, Gulabivala K. Prevalence of yeasts in saliva and root canals of teeth associated with apical periodontitis. International Endodontic Journal, 35, 321,329, 2002. Aims To determine: (i) the relative prevalence and diversity of yeasts in salivary and root canal samples from the same patients; and (ii) the clinical factors associated with their presence in saliva and root canals. Methodology Sixty root canal samples from teeth associated apical periodontitis and the corresponding whole unstimulated saliva samples were obtained from 55 patients. The medical history including antibiotic therapy and clinical/radiographic data on the teeth were recorded. The samples were serially diluted and cultured on yeast & fungi-selective sabouraud dextrose agar. Isolates were characterized and speciated by the germ tube formation test, hyphal morphology and a commercial biochemical test kit (Rapid ID32C® system). Results Twenty-three yeast isolates were recovered from 19 saliva samples and eight isolates from six root canal samples. Candida albicans (17/23 & 3/8) and Rodotorula mucilaginosa (2/23 & 4/8) were the most prevalent isolates from saliva and root canal samples. It was significantly (13.8 times) more probable that yeasts would be recovered from root canals when they were also present in the saliva (P = 0.021). The effect of coronal restoration leakage (P = 0.08) and previous root canal treatment (P = 0.123) were equivocal. The history of antibiotic therapy had no association with the presence of yeasts in saliva (OR = 1.1). Conclusions Yeasts occurred relatively infrequently (10%) in root canals. Their presence in root canals was significantly associated with their presence in saliva. The role of yeasts in the initiation and perpetuation of periapical disease remains to be determined. [source]

    Development of hydrogel patch for controlled release of alpha-hydroxy acid contained in tamarind fruit pulp extract

    J. Viyoch
    Synopsis The aim of this study was to develop hydrogel patch using crosslinked chitosan,starch as polymeric matrix for controlling the release of the natural alpha-hydroxy acid (AHA) contained in the extract of tamarind's fruit pulp. The chitosan (MW 100 000) was blended with corn, tapioca or rice starch in various ratios and then crosslinked with glutaraldehyde. The physical characteristics, mechanical resistance, bio-adhesion property and surface morphology of the prepared hydrogel patches with and without the extract were investigated. The release patterns of the hydrogel patches containing the extract were investigated by measuring the amount of tartaric acid, a major AHA present in the tamarind's fruit pulp extract, accumulated in the receptor medium of the vertical diffusion cell at various time intervals over a period of 6 h. The results indicated that the formulations of chitosan : corn starch 4.5 : 0.5 with glutaraldehyde 0.02% w/w (C4.5C0.5G0.02) or 0.04% w/w (C4.5C0.5G0.04), chitosan : tapioca starch 4.5 : 0.5 with glutaraldehyde 0.04% w/w (C4.5T0.5G0.04) or 0.05% w/w (C4.5T0.5G0.05), and chitosan : rice starch 4.5 : 0.5 with glutaraldehyde 0.04% w/w (C4.5R0.5G0.04) and chitosan : rice starch 4.0 : 1.0 with glutaraldehyde 0.03% w/w (C4.0R1.0G0.03) provided the flexible and elastic patches with good bio-adhesive property. The tensile strength values ranged from 5 to15 N mm,2 and the elasticity ranged from 30 to 60%. The addition of the extract in these formulations significantly increased the tensile strength values of the obtained patches. The patch of C4.0R1.0G0.03 formulation containing the extract showed relatively highest porosity, corresponding to its highest amount (12.02 ± 0.33 mg) and rate (0.452 ± 0.012 mg mm,2 min,1/2) of tartaric acid released. The amounts of tartaric acid released from the developed hydrogel patches were proportional to a square root of time (Higuchi's model), particularly the release from C4.0R1.0G0.03 (R2, 0.9978 ± 0.0020) and C4.5R0.5G0.04 (R2, 0.9961 ± 0.0024) patches. Résumé Le but de cette étude était de développer un patch hydrogel en utilisant, en tant que matrice polymère, un mélange chitosane/amidon réticulé pour le contrôle du relargage d', -hydroxyacide naturel contenu dans l'extrait de la pulpe du fruit du tamarinier. Du chitosane (MW 100 000) a été mélangéà des farines de maïs, de tapioca ou de riz dans différentes proportions, les mélanges ont été réticulés avec du glutaraldéhyde. Les caractéristiques physiques, résistance mécanique, propriétés de bio adhésion et morphologie de surface des patchs hydrogels préparés avec et sans extrait ont étéétudiées. Le profil de relargage des patchs hydrogels contenant l'extrait a étéétudié en mesurant la quantité d'acide tartarique, , -aminoacide majoritaire présent dans l'extrait, accumulé dans le milieu récepteur d'une cellule à diffusion verticale en fonction du temps sur une période de 6 heures. Les résultats ont montré que les formulations contenant: ,,un mélange chitosane/amidon de maïs dans un rapport 4.5 : 0.5 réticulé avec 0.02% ou 0.04% poids/poids de glutaraldéhyde (respectivement C4.5C0.5G0.02 et C4.5 C0.5 G0.04) ou ,,un mélange de chitosane/amidon de tapioca dans un rapport 4.5 : 0.5 réticulé avec 0.04% ou 0.05% poids/poids de glutaraldéhyde (C4.5T0.5 G0.04ou C4.5 T0.5 G0.05) ,,ainsi que le mélange chitosane/amidon de riz dans un rapport 4.5 : 0.5 réticulé avec 0.04% poids/poids de glutaraldehyde (C4.5R0.5 G0.04) ,,et le mélange chitosane/amidon de riz dans un rapport 4.0 : 1.0 réticulé avec 0,03% poids/poids de glutaraldehyde (C4.0 R1.0 G0.03) conduisaient à des patchs flexibles et élastiques avec de bonnes propriétés bio adhésives. Leur résistance mécanique varie de 5 à 15 N/m2 et leur élasticité de 30 à 60%. L'addition de l'extrait de fruit à ces formules augmente significativement la résistance mécanique des patchs. Le patch C4.0R1.0 G0.03 contenant l'extrait montre la plus grande porosité correspondant à la quantité d'acide tartarique relargué la plus élevée (12.02 ± 0.33 mg), ainsi qu'à la plus grande vitesse de relargage (0.452 ± 0.012 mg mm- 2 mn- 1/2). Les quantités d'acide tartarique relarguées à partir de patchs hydrogels développés sont proportionnelles à la racine carrée du temps (modèle d'Higuchi), en particulier pour les patchs C4.0 R1.0G0.03 (R2, 0.9978 ± 0.0020) et C4.5R0.5 C0.004 (R2, 0.9061 ± 0.0024). [source]

    Eco-friendly methodologies for the synthesis of some aromatic esters, well-known cosmetic ingredients

    C. Villa
    Synopsis Solid,liquid solvent-free phase transfer catalysis (PTC) and acidic catalysis in dry media were applied, with noticeable improvement and simplification over classical procedures in a Green Chemistry context, to the synthesis of some aromatic esters useful as cosmetic ingredients: 3-methylbutyl 4-methoxycinnamate, 2-ethylhexyl 4-methoxycinnamate, 2-ethylhexyl 4-(dimethylamino)benzoate and 2-ethylhexyl salicylate, well-known ultraviolet B sunscreen filters; 4-isopropylbenzyl salicylate, UV absorber and cutaneous antilipoperoxidant; propyl 4-hydroxybenzoate and butyl 4-hydroxybenzoate (parabens), antimicrobial agents. The reactions were performed under microwave (MW) activation and conventional heating. The best results for the synthesis of cinnamic, salicylic and 4-(dimethylamino)benzoic esters were achieved by in situ preformed carboxylates alkylation with alkyl bromides using PTC. The 4-hydroxybenzoates were obtained in good yields by classical esterification of the acid with alcohols using a simple heterogeneous mixture of reagents with catalytic amounts of p -toluenesulfonic acid (PTSA). The comparisons of yields and thermal profiles under either MW or conventional heating were studied and reported. Résumé La catalyse par transfert de phase (CTP) solide-liquide sans solvant et l'estérification acido-catalysée en ,,milieu sec'' ont été appliquées, dans le cadre de la ,,chimie verte'', avec des nettes améliorations et simplifications par rapport aux méthodes classiques, à la synthèse de certains esters aromatiques, ingrédients cosmétiques: 3-methylbutyl 4-méthoxycinnamate, 2-éthylhéxyl 4-méthoxycinnamate, 2-éthylhéxyl 4-(diméthylamino) benzoate et 2-éthylhéxyl salicylate, filtres solaires UVB bien connus; 4-isopropylbenzyl salicylate, filtre UV et antilipopéroxydant cutané; propyl 4-hydroxybenzoate et butyl 4-hydroxybenzoate (parabens), agents antimicrobien. Les réactions ont été procédées sous irradiation micro-onde et par chauffage classique. Pour la synthèse des esters dérivés de l'acide cinnamique, salicylique et 4-(diméthylamino)benzoïque les meilleurs résultats ont été obtenus grâce à la CTP par alkylation des carboxylates (préformés in situ) avec des bromures d'alkyle. Les esters de l'acide 4-hydroxybenzoique ont été obtenus avec de bons rendements par simple mélange hétérogène des réactifs et d'acide p-toluènesulfonique (PTSA) comme catalyseur. Les rendements et les profils de montée en température sous micro-ondes et par chauffage classique ont été comparés. [source]

    Dynamic energy and exergy analyses of an industrial cogeneration system

    Yilmaz Yoru
    Abstract The study deals with the energetic and exergetic analyses of a cogeneration (combined heat and power, CHP) system installed in a ceramic factory, located in Izmir, Turkey. This system has three gas turbines with a total capacity of 13,MW, six spray dryers and two heat exchangers. In the analysis, actual operational data over one-month period are utilized. The so-called CogeNNexT code is written in C++ and developed to analyze energetic and exergetic data from a database. This code is also used to analyze turbines, spray dryers and heat exchangers in this factory. Specifications of some parts of system components have been collected from the factory. Based on the 720,h data pattern (including 43,200 data), the mean energetic and exergetic efficiency values of the cogeneration system are found to be 82.3 and 34.7%, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Energy, exergy and exergoeconomic analysis of a steam power plant: A case study

    Mohammad Ameri
    Abstract The objective of this paper is to perform the energy, exergy and exergoeconomic analysis for the Hamedan steam power plant. In the first part of the paper, the exergy destruction and exergy loss of each component of this power plant is estimated. Moreover, the effects of the load variations and ambient temperature are calculated in order to obtain a good insight into this analysis. The exergy efficiencies of the boiler, turbine, pump, heaters and the condenser are estimated at different ambient temperatures. The results show that energy losses have mainly occurred in the condenser where 306.9,MW is lost to the environment while only 67.63,MW has been lost from the boiler. Nevertheless, the irreversibility rate of the boiler is higher than the irreversibility rates of the other components. It is due to the fact that the combustion reaction and its high temperature are the most significant sources of exergy destruction in the boiler system, which can be reduced by preheating the combustion air and reducing the air,fuel ratio. When the ambient temperature is increased from 5 to 24°C, the irreversibility rate of the boiler, turbine, feed water heaters, pumps and the total irreversibility rate of the plant are increased. In addition, as the load varies from 125 to 250,MW (i.e. full load) the exergy efficiency of the boiler and turbine, condenser and heaters are increased due to the fact that the power plant is designed for the full load. In the second part of the paper, the exergoeconomic analysis is done for each component of the power plant in order to calculate the cost of exergy destruction. The results show that the boiler has the highest cost of exergy destruction. In addition, an optimization procedure is developed for that power plant. The results show that by considering the decision variables, the cost of exergy destruction and purchase can be decreased by almost 17.11%. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Exergoeconomic optimization of a 1000,MW light water reactor power generation system

    Hoseyn Sayyaadi
    Abstract A typical 1000,MW pressurized water reactor nuclear power plant is considered for optimization. The thermodynamic modeling is performed based on the energy and exergy analysis, while an economic model is developed according to the total revenue requirement method. The objective function based on the exergoeconomic analysis is obtained. The exergoeconomic optimization process with 10 decision variables is performed using a hybrid stochastic/deterministic search algorithm namely as genetic algorithm. The results that are obtained using optimization process are compared with the base case system and the discussion is presented. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Status and development of PEM fuel cell technology

    F. Barbir
    Abstract Fuel cells are an emerging technology with applications in transportation, stationary and portable power generation, with outputs ranging from mW to MW. The most promising and most widely researched, developed and demonstrated type of fuel cells is proton exchange membrane (PEM) fuel cell. State of the art in PEM fuel cell technology and challenges in their development and widespread applications are discussed. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Comparison of evaporative inlet air cooling systems to enhance the gas turbine generated power

    Mohammad Ameri
    Abstract The gas turbine performance is highly sensitive to the compressor inlet temperature. The output of gas turbine falls to a value that is less than the rated output under high temperature conditions. In fact increase in inlet air temperature by 1°C will decrease the output power by 0.7% approximately. The solution of this problem is very important because the peak demand season also happens in the summer. One of the convenient methods of inlet air cooling is evaporating cooling which is appropriate for warm and dry weather. As most of the gas turbines in Iran are installed in such ambient conditions regions, therefore this method can be used to enhance the performance of the gas turbines. In this paper, an overview of technical and economic comparison of media system and fog system is given. The performance test results show that the mean output power of Frame-9 gas turbines is increased by 11 MW (14.5%) by the application of media cooling system in Fars power plant and 8.1 MW (8.9%) and 9.5 MW (11%) by the application of fog cooling system in Ghom and Shahid Rajaie power plants, respectively. The total enhanced power generation in the summer of 2004 was 2970, 1701 and 1340 MWh for the Fars, Ghom and Shahid Rajaie power plants, respectively. The economical studies show that the payback periods are estimated to be around 2 and 3 years for fog and media systems, respectively. This study has shown that both methods are suitable for the dry and hot areas for gas turbine power augmentation. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    The lignite electricity-generating sector in Greece: Current status and future prospects

    N. Koukouzas
    Abstract Lignite plays an important role in Greece's energy sector as it satisfies over 70% of country's needs in electric power. The extraction of lignite takes place mainly in three regions of Greece, namely Ptolemais-Amyndeon, Megalopolis and Florina. The annual production of lignite is around 60 million tons, out of which 48 million tons derive from the coal fields of northern Greece (Ptolemais-Amyndeon and Florina). Almost the entire lignite production is consumed for electricity generation, while small amounts of lignite are used for briquettes and other applications. The Greek coal-fired power plants, which are about 4500 MW, use conventional technology and they are old (an average of 30 years). In the coming years new coal fields will be exploited in Florina,another 2.5 million tons of coal,in order to satisfy the currently under construction 365 MW plant located at Meliti, Florina, Northern Greece. Even though the lignite reserves are widespread in Greece and other areas such as Elassona and Drama could possibly host power plants, it is expected that the Florina power plant will be the last coal-fired plant to be build in the country. Lignite has to compete with natural gas,the construction of the main gas pipeline network has been completed,imported oil and renewable energy sources. The new EU regulations on power plant emissions raise obstacles for the firing of lignite, although it is low in sulphur. It must be shown that lignite produces low cost electricity in a environmentally friendly manner. The utilization of fly ash and land reclamation can improve the situation in lignite mining. In particular, specific attention was paid to further research and potential use of fly ash in road construction, the production of bricks and concrete, and the production of zeolites from lignitic fly ash. The use of clean coal technologies in power plants can solve many emission problems. Specific measures to increase the efficiency of lignite-fired power units might include: identification of the loss sources of every unit, improvement of the cold end of the steam turbines, optimization of the beater wheel mills operation, and the combination of natural gas-fired turbines with the existing boilers. The liberalization of the electricity market needs to be considered seriously from the lignite industry, since the potential electricity producers can freely choose from all kinds of fuels, such as imported coal, oil, gas and renewables. However, Greek lignite meets the requirements for the security of supply, as indicated in the EU's Green Paper. It needs only to be competitive in the new energy sector by improving mining and combustion conditions. Further research on these topics, through the European Commission's ECSC and Framework Programmes, as well as the national programmes, is required. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    The performance of natural draft dry cooling towers under crosswind: CFD study

    Rafat Al-Waked
    Abstract The thermal performance of a natural draft dry cooling tower (NDDCT) under a crosswind has been investigated using a general-purpose CFD code. A three-dimensional study using the standard k,, turbulence model to simulate airflow in and around an NDDCT has been conducted. A parametric study has been carried out to examine the effect of crosswind velocity profile and air dry-bulb temperature on the thermal performance of an NDDCT. Two approaches have been considered in this study to quantify the crosswind effect. Firstly, simulations have been conducted at the nominal conditions and crosswind effect has been represented by thermal effectiveness parameter. Secondly, the ejected heat from the NDDCT has been maintained at a constant value (285 MW) and the crosswind effect has been represented by the change in the cooling tower approach parameter. After quantifying the effect of the crosswind on the thermal performance, windbreak walls have been introduced as a means of reducing this effect. The results in this paper show the importance of considering the crosswind velocity profile. Moreover, the introduction of windbreak walls has indicated an improvement in reducing the thermal performance losses due to the crosswind. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Power sector development in India with CO2 emission targets: Effects of regional grid integration and the role of clean technologies

    A. K. Srivastava
    Abstract The power sector in India at present comprises of five separate regional electricity grids having practically no integrated operation in between them. This study analyses the utility planning, environmental and economical effects of integrated power sector development at the national level in which the regional electric grids are developed and operated as one integrated system. It also examines the effects of selected CO2 emission reduction targets in the power sector and the role of renewable power generation technologies in India. The study shows that the integrated development and operation of the power system at the national level would reduce the total cost including fuel cost by 4912 million $, total capacity addition by 2784 MW, while the emission of CO2, SO2 and NOx would be reduced by 231.6 (1.9%), 0.8 (0.9%), 0.4 (1.2%) million tons, respectively, during the planning horizon. Furthermore, the study shows that the expected unserved energy, one of the indices of generation system reliability, would decrease to 26 GWh under integrated national power system from 5158 GWh. As different levels of CO2 emission reduction targets were imposed, there is a switching of generation from conventional coal plants to gas fired plants, clean coal technologies and nuclear based plants. As a result the capacity expansion cost has increased. It was found that wind power plant is most attractive and economical in the Indian perspective among the renewable options considered (Solar, wind and biomass). Copyright © 2003 John Wiley & Sons, Ltd. [source]

    On the use of reactive power as an endogenous variable in short-term load forecasting

    P. Jorge Santos
    Abstract In the last decades, short-term load forecasting(STLF) has been the object of particular attention in the power systems field. STLF has been applied almost exclusively to the generation sector, based on variables, which are transversal to most models. Among the most significant variables we can find load, expressed as active power (MW), as well as exogenous variables, such as weather and economy-related ones; although the latter are applied in larger forecasting horizons than STLF. In this paper, the application of STLF to the distribution sector is suggested including inductive reactive power as a forecasting endogenous variable. The inclusion of this additional variable is mainly due to the evidence that correlations between load and weather variables are tenuous, due to the mild climate of the actual case-study system and the consequent feeble penetration of electrical heating ventilation and air conditioning loads. Artificial neural networks (ANN) have been chosen as the forecasting methodology, with standard feed forward back propagation algorithm, because it is a largely used method with generally considered satisfactory results. Usually the input vector to ANN applied to load forecasting is defined in a discretionary way, mainly based on experience, on engineering judgement criteria and on concern about the ANN dimension, always taking into consideration the apparent (or actually evaluated) correlations within the available data. The approach referred in the paper includes pre-processing the data in order to influence the composition of the input vector in such a way as to reduce the margin of discretion in its definition. A relative entropy analysis has been performed to the time series of each variable. The paper also includes an illustrative case study. Copyright © 2003 John Wiley & Sons, Ltd. [source]