Multiphase Current Controlled Buck Converter with energy recycling Output Impedance Correction Circuit (OICC)

This work is related to the output impedance improvement of a Multiphase Buck converter with Peak Current Mode Control (PCMC) by means of introducing an additional power path that virtually increases the output capacitance during transients. Various solutions that can be employed to improve the dynamic behavior of the converter system exist, but nearly all solutions are developed for a Single Phase Buck converter with Voltage Mode Control (VMC), while in the VRM applications, due to the high currents, the system is usually implemented as a Multiphase Buck Converter with Current Mode Control. The Output Impedance Correction Circuit (OICC) is used to inject or extract a current n-1 times larger than the output capacitor current, thus virtually increasing n times the value of the output capacitance during the transients. Furthermore, this work extends the OICC concept to a Multiphase Buck Converter system while comparing proposed solution with the system that has n times bigger output capacitor. In addition, the OICC is implemented as a Synchronous Buck Converter with PCMC, thus reducing its influence on the system efficiency

Factors impacting the market share of Construction and Demolition (C&D) Waste recycling solutions

Current EU Directives force the Member States to assure by 2020 that 70% of the Construction and Demolition (C&D) waste is recovered instead of landfilled. While some countries have largely achieved this target, others still have a long way to go. For better understanding the differences arising from local disparities, six factors related to technical, economic, legislative and environmental aspects have been identified as crucial influences in the market share of C&D waste recycling solutions. These factors are able to identify the causes that limit the recycling rate of a certain region. Moreover, progress towards an efficient waste management can vary through the improvement of a single factor. This study provides the background for further fine-tuning the factors and their combination into a mathematical model for assessing the market share of C&D recycling solutions.

New Plaster Composite with Mineral Wool Fibres from CDW Recycling

Over the last decade the intense activity of the building sector has generated large quantities of construction and demolition waste (CDW). In particular, in Europe around 890 million tons of CDW is generated every year; however, only 50% of them are recycled. In Spain, over the last years 40 millions of tons of construction and demolition waste have been generated. On the other hand, since the implementation of the Technical Building Code regulation the use of mineral wools as building insulation materials has become a widespread solution in both rehabilitation and new construction works, and because of that, this kind of insulation waste is increasing. This research analyzes the potential of a new composite (gypsum and fiber waste) including several mineral wools waste into a plaster matrix. For this purpose, an experimental plan, characterizing the physical and mechanical behaviour as well as the Shore C hardness of the new composite, was elaborated fulfilling UNE Standards.

Optically enhanced photon recycling in mechanically stacked multijunction solar cells

Multijunction solar cells can be fabricated by mechanically bonding together component cells that are grown separately. Here, we present four-junction four-terminal mechanical stacks composed of GaInP/GaAs tandems grown on GaAs substrates and GaInAsP/GaInAs tandems grown on InP substrates. The component cells were bonded together with a low-index transparent epoxy that acts as an angularly selective reflector to the GaAs bandedge luminescence, while simultaneously transmitting nearly all of the subbandgap light. As determined by electroluminescence measurements and optical modeling, the GaAs subcell demonstrates a higher internal radiative limit and, thus, higher subcell voltage, compared with GaAs subcells without the epoxy reflector. The best cells demonstrate 38.8 ± 1.0% efficiency under the global spectrum at 1000 W/m2 and ~ 42% under the direct spectrum at ~100 suns. Eliminating the series resistance is the key challenge for further improving the concentrator cells.

RGS-r, a retinal specific RGS protein, binds an intermediate conformation of transducin and enhances recycling

G proteins regulate intracellular signaling by coupling a cycle of guanine nucleotide binding and hydrolysis to transient changes of cellular functions. The mechanisms that control the recycling of transducin, the “pace-setting” G protein that regulates mammalian phototransduction, are unclear. We show that a novel retinal specific RGS-motif protein specifically binds to an intermediate conformation involved in GTP hydrolysis by transducin and accelerates phosphate release and the recycling of transducin. This specific interaction further rationalizes the kinetics of the phototransduction cascade and provides a general hypothesis to explain the mechanism of interaction of RGS proteins with other G proteins.

Association of Rab25 and Rab11a with the Apical Recycling System of Polarized Madin–Darby Canine Kidney Cells

Recent evidence suggests that apical and basolateral endocytic pathways in epithelia converge in an apically located, pericentriolar endosomal compartment termed the apical recycling endosome. In this compartment, apically and basolaterally internalized membrane constituents are thought to be sorted for recycling back to their site of origin or for transcytosis to the opposite plasma membrane domain. We report here that in the epithelial cell line Madin–Darby Canine Kidney (MDCK), antibodies to Rab11a label an apical pericentriolar endosomal compartment that is dependent on intact microtubules for its integrity. Furthermore, this compartment is accessible to a membrane-bound marker (dimeric immunoglobulin A [IgA]) internalized from either the apical or basolateral pole, functionally defining it as the apical recycling endosome. We have also examined the role of a closely related epithelial-specific Rab, Rab25, in the regulation of membrane recycling and transcytosis in MDCK cells. When cDNA encoding Rab25 was transfected into MDCK cells, the protein colocalized with Rab11a in subapical vesicles. Rab25 transfection also altered the distribution of Rab11a, causing the coalescence of immunoreactivity into multiple denser vesicular structures not associated with the centrosome. Nevertheless, nocodazole still dispersed these vesicles, and dimeric IgA internalized from either the apical or basolateral membrane was detected in endosomes labeled with antibodies to both Rab11a and Rab25. Overexpression of Rab25 decreased the rate of IgA transcytosis and of apical, but not basolateral, recycling of internalized ligand. Conversely, expression of the dominant-negative Rab25T26N did not alter either apical recycling or transcytosis. These results indicate that both Rab11a and Rab25 associate with the apical recycling system of epithelial cells and suggest that Rab25 may selectively regulate the apical recycling and/or transcytotic pathways.

Chicken Erythroid AE1 Anion Exchangers Associate with the Cytoskeleton During Recycling to the Golgi

Chicken erythroid AE1 anion exchangers receive endoglycosidase F (endo F)-sensitive sugar modifications in their initial transit through the secretory pathway. After delivery to the plasma membrane, anion exchangers are internalized and recycled to the Golgi where they acquire additional N-linked modifications that are resistant to endo F. During recycling, some of the anion exchangers become detergent insoluble. The acquisition of detergent insolubility correlates with the association of the anion exchanger with cytoskeletal ankyrin. Reagents that inhibit different steps in the endocytic pathway, including 0.4 M sucrose, ammonium chloride, and brefeldin A, block the acquisition of endo F-resistant sugars and the acquisition of detergent insolubility by newly synthesized anion exchangers. The inhibitory effects of ammonium chloride on anion exchanger processing are rapidly reversible. Furthermore, AE1 anion exchangers become detergent insoluble more rapidly than they acquire endo F-resistant modifications in cells recovering from an ammonium chloride block. This suggests that the cytoskeletal association of the recycling anion exchangers occurs after release from the compartment where they accumulate due to ammonium chloride treatment, and prior to their transit through the Golgi. The recycling pool of newly synthesized anion exchangers is reflected in the steady-state distribution of the polypeptide. In addition to plasma membrane staining, anion exchanger antibodies stain a perinuclear compartment in erythroid cells. This perinuclear AE1-containing compartment is also stained by ankyrin antibodies and partially overlaps the membrane compartment stained by NBD C6-ceramide, a Golgi marker. Detergent extraction of erythroid cells in situ has suggested that a substantial fraction of the perinuclear pool of AE1 is cytoskeletal associated. The demonstration that erythroid anion exchangers interact with elements of the cytoskeleton during recycling to the Golgi suggests the cytoskeleton may be involved in the post-Golgi trafficking of this membrane transporter.

Involvement of ATP-dependent Pseudomonas Exotoxin Translocation from a Late Recycling Compartment in Lymphocyte Intoxication Procedure

Pseudomonas exotoxin (PE) is a cytotoxin which, after endocytosis, is delivered to the cytosol where it inactivates protein synthesis. Using diaminobenzidine cytochemistry, we found over 94% of internalized PE in transferrin (Tf) -positive endosomes of lymphocytes. When PE translocation was examined in a cell-free assay using purified endocytic vesicles, more than 40% of endosomal 125I-labeled PE was transported after 2 h at 37°C, whereas a toxin inactivated by point mutation in its translocation domain was not translocated. Sorting of endosomes did not allow cell-free PE translocation, whereas active PE transmembrane transport was observed after > 10 min of endocytosis when PE and fluorescent-Tf were localized by confocal immunofluorescence microscopy within a rab5-positive and rab4- and rab7-negative recycling compartment in the pericentriolar region of the cell. Accordingly, when PE delivery to this structure was inhibited using a 20°C endocytosis temperature, subsequent translocation from purified endosomes was impaired. Translocation was also inhibited when endosomes were obtained from cells labeled with PE in the presence of brefeldin A, which caused fusion of translocation-competent recycling endosomes with translocation-incompetent sorting elements. No PE processing was observed in lymphocyte endosomes, the full-sized toxin was translocated and recovered in an enzymatically active form. ATP hydrolysis was found to directly provide the energy required for PE translocation. Inhibitors of endosome acidification (weak bases, protonophores, or bafilomycin A1) when added to the assay did not significantly affect 125I-labeled PE translocation, demonstrating that this transport is independent of the endosome-cytosol pH gradient. Nevertheless, when 125I-labeled PE endocytosis was performed in the presence of one of these molecules, translocation from endosomes was strongly inhibited, indicating that exposure to acidic pH is a prerequisite for PE membrane traversal. When applied during endocytosis, treatments that protect cells against PE intoxication (low temperatures, inhibitors of endosome acidification, and brefeldin A) impaired 125I-labeled PE translocation from purified endosomes. We conclude that PE translocation from a late receptor recycling compartment is implicated in the lymphocyte intoxication procedure.

Localization and Recycling of gp27 (hp24γ3): Complex Formation with Other p24 Family Members

We report here the characterization of gp27 (hp24γ3), a glycoprotein of the p24 family of small and abundant transmembrane proteins of the secretory pathway. Immunoelectron and confocal scanning microscopy show that at steady state, gp27 localizes to the cis side of the Golgi apparatus. In addition, some gp27 was detected in COPI- and COPII-coated structures throughout the cytoplasm. This indicated cycling that was confirmed in three ways. First, 15°C temperature treatment resulted in accumulation of gp27 in pre-Golgi structures colocalizing with anterograde cargo. Second, treatment with brefeldin A caused gp27 to relocate into peripheral structures positive for both KDEL receptor and COPII. Third, microinjection of a dominant negative mutant of Sar1p trapped gp27 in the endoplasmic reticulum (ER) by blocking ER export. Together, this shows that gp27 cycles extensively in the early secretory pathway. Immunoprecipitation and coexpression studies further revealed that a significant fraction of gp27 existed in a hetero-oligomeric complex. Three members of the p24 family, GMP25 (hp24α2), p24 (hp24β1), and p23 (hp24δ1), coprecipitated in what appeared to be stochiometric amounts. This heterocomplex was specific. Immunoprecipitation of p26 (hp24γ4) failed to coprecipitate GMP25, p24, or p23. Also, very little p26 was found coprecipitating with gp27. A functional requirement for complex formation was suggested at the level of ER export. Transiently expressed gp27 failed to leave the ER unless other p24 family proteins were coexpressed. Comparison of attached oligosaccharides showed that gp27 and GMP25 recycled differentially. Only a very minor portion of GMP25 displayed complex oligosaccharides. In contrast, all of gp27 showed modifications by medial and trans enzymes at steady state. We conclude from these data that a portion of gp27 exists as hetero-oligomeric complexes with GMP25, p24, and p23 and that these complexes are in dynamic equilibrium with individual p24 proteins to allow for differential recycling and distributions.

Fusion of Endosomes Involved in Synaptic Vesicle Recycling

Recycling of vesicles of the regulated secretory pathway presumably involves passage through an early endosomal compartment as an intermediate step. To learn more about the involvement of endosomes in the recycling of synaptic and secretory vesicles we studied in vitro fusion of early endosomes derived from pheochromocytoma (PC12) cells. Fusion was not affected by cleavage of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins synaptobrevin and syntaxin 1 that operate at the exocytotic limb of the pathway. Furthermore, fusion was inhibited by the fast Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid but not by the slow Ca2+ chelator EGTA. Endosome fusion was restored by the addition of Ca2+ with an optimum at a free Ca2+ concentration of 0.3 × 10−6 M. Other divalent cations did not substitute for Ca2+. A membrane-permeant EGTA derivative caused inhibition of fusion, which was reversed by addition of Ca2+. We conclude that the fusion of early endosomes participating in the recycling of synaptic and neurosecretory vesicles is mediated by a set of SNAREs distinct from those involved in exocytosis and requires the local release of Ca2+ from the endosomal interior.

Hydrolysis of GTP on rab11 is required for the direct delivery of transferrin from the pericentriolar recycling compartment to the cell surface but not from sorting endosomes

Rab11 is a small GTP-binding protein that in cultured mammalian cells has been shown to be concentrated in the pericentriolar endosomal recycling compartment and to play a key role in passage of the recycling transferrin receptor through that compartment [Ullrich, O., Reinsch, S., Urbé, S., Zerial, M. & Parton, R. G. (1996) J. Cell Biol. 135, 913–924]. To obtain insights into the site(s) of action of rab11 within the recycling pathway, we have now compared the effects on recycling at 37°C of overexpression of wild-type rab11 and various mutant forms of this protein in cells that had been loaded with transferrin at either 37°C or 16°C. We show that incubation at 16°C blocks passage of endocytosed transferrin into the recycling compartment and that, whereas the rab11 dominant negative mutant form (S25N) inhibits transferrin recycling after interiorization at either temperature, the wild-type rab11 and constitutively active mutant (Q70L) have no inhibitory effect on the recycling of molecules that were interiorized at 16°C. This differential inhibitory effect shows that two distinct pathways for recycling are followed by the bulk of the transferrin molecules interiorized at the two different temperatures. The incapacity of the constitutively active form of rab11 (Q70L) to inhibit recycling of molecules interiorized at 16°C is consistent with their recycling taking place directly from sorting endosomes, in a process that does not require hydrolysis of GTP on rab11. The fact that the dominant negative (S25N) form of rab11 inhibits recycling of molecules interiorized at both temperatures indicates that activation of rab11 by GTP is required for exit of transferrin from sorting endosomes, regardless of whether this exit is toward the recycling compartment or directly to the plasma membrane.

Ascorbate recycling in human neutrophils: Induction by bacteria

Ascorbate (vitamin C) recycling occurs when extracellular ascorbate is oxidized, transported as dehydroascorbic acid, and reduced intracellularly to ascorbate. We investigated microorganism induction of ascorbate recycling in human neutrophils and in microorganisms themselves. Ascorbate recycling was determined by measuring intracellular ascorbate accumulation. Ascorbate recycling in neutrophils was induced by both Gram-positive and Gram-negative pathogenic bacteria, and the fungal pathogen Candida albicans. Induction of recycling resulted in as high as a 30-fold increase in intracellular ascorbate compared with neutrophils not exposed to microorganisms. Recycling occurred at physiologic concentrations of extracellular ascorbate within 20 min, occurred over a 100-fold range of effector/target ratios, and depended on oxidation of extracellular ascorbate to dehydroascorbic acid. Ascorbate recycling did not occur in bacteria nor in C. albicans. Ascorbate did not enter microorganisms, and dehydroascorbic acid entry was less than could be accounted for by diffusion. Because microorganism lysates reduced dehydroascorbic acid to ascorbate, ascorbate recycling was absent because of negligible entry of the substrate dehydroascorbic acid. Because ascorbate recycling occurs in human neutrophils but not in microorganisms, it may represent a eukaryotic defense mechanism against oxidants with possible clinical implications.

A Di-Leucine Sequence and a Cluster of Acidic Amino Acids Are Required for Dynamic Retention in the Endosomal Recycling Compartment of Fibroblasts

Insulin-regulated aminopeptidase (IRAP), a transmembrane aminopeptidase, is dynamically retained within the endosomal compartment of fibroblasts. The characteristics of this dynamic retention are rapid internalization from the plasma membrane and slow recycling back to the cell surface. These specialized trafficking kinetics result in <15% of IRAP on the cell surface at steady state, compared with 35% of the transferrin receptor, another transmembrane protein that traffics between endosomes and the cell surface. Here we demonstrate that a 29-amino acid region of IRAP's cytoplasmic domain (residues 56–84) is necessary and sufficient to promote trafficking characteristic of IRAP. A di-leucine sequence and a cluster of acidic amino acids within this region are essential elements of the motif that slows IRAP recycling. Rapid internalization requires any two of three distinct motifs: M15,16, DED64–66, and LL76,77. The DED and LL sequences are part of the motif that regulates recycling, demonstrating that this motif is bifunctional. In this study we used horseradish peroxidase quenching of fluorescence to demonstrate that IRAP is dynamically retained within the transferrin receptor-containing general endosomal recycling compartment. Therefore, our data demonstrate that motifs similar to those that determine targeting among distinct membrane compartments can also regulate the rate of transport of proteins from endosomal compartments. We propose a model for dynamic retention in which IRAP is transported from the general endosomal recycling compartment in specialized, slowly budding recycling vesicles that are distinct from those that mediate rapid recycling back to the surface (e.g., transferrin receptor-containing transport vesicles). It is likely that the dynamic retention of IRAP is an example of a general mechanism for regulating the distribution of proteins between the surface and interior of cells.

Identification of Discrete Classes of Endosome-derived Small Vesicles as a Major Cellular Pool for Recycling Membrane Proteins

Vesicles carrying recycling plasma membrane proteins from early endosomes have not yet been characterized. Using Chinese hamster ovary cells transfected with the facilitative glucose transporter, GLUT4, we identified two classes of discrete, yet similarly sized, small vesicles that are derived from early endosomes. We refer to these postendosomal vesicles as endocytic small vesicles or ESVs. One class of ESVs contains a sizable fraction of the pool of the transferrin receptor, and the other contains 40% of the total cellular pool of GLUT4 and is enriched in the insulin-responsive aminopeptidase (IRAP). The ESVs contain cellubrevin and Rab4 but are lacking other early endosomal markers, such as EEA1 or syntaxin13. The ATP-, temperature-, and cytosol-dependent formation of ESVs has been reconstituted in vitro from endosomal membranes. Guanosine 5′-[γ-thio]triphosphate and neomycin, but not brefeldin A, inhibit budding of the ESVs in vitro. A monoclonal antibody recognizing the GLUT4 cytoplasmic tail perturbs the in vitro targeting of GLUT4 to the ESVs without interfering with the incorporation of IRAP or TfR. We suggest that cytosolic proteins mediate the incorporation of recycling membrane proteins into discrete populations of ESVs that serve as carrier vesicles to store and then transport the cargo from early endosomes, either directly or indirectly, to the cell surface.