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Letteratura scientifica selezionata sul tema "Urea"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 29 luglio 2024

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Articoli di riviste sul tema "Urea"

Heimer, Susan R., e Harry L. T. Mobley. "Interaction of Proteus mirabilis Urease Apoenzyme and Accessory Proteins Identified with Yeast Two-Hybrid Technology". Journal of Bacteriology 183, n. 4 (15 febbraio 2001): 1423–33. http://dx.doi.org/10.1128/jb.183.4.1423-1433.2001.

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Abstract (sommario):

ABSTRACT Proteus mirabilis, a gram-negative bacterium associated with complicated urinary tract infections, produces a metalloenzyme urease which hydrolyzes urea to ammonia and carbon dioxide. The apourease is comprised of three structural subunits, UreA, UreB, and UreC, assembled as a homotrimer of individual UreABC heterotrimers (UreABC)3. To become catalytically active, apourease acquires divalent nickel ions through a poorly understood process involving four accessory proteins, UreD, UreE, UreF, and UreG. While homologues of UreD, UreF, and UreG have been copurified with apourease, it remains unclear specifically how these polypeptides associate with the apourease or each other. To identify interactions among P. mirabilis accessory proteins, in vitro immunoprecipitation and in vivo yeast two-hybrid assays were employed. A complex containing accessory protein UreD and structural protein UreC was isolated by immunoprecipitation and characterized with immunoblots. This association occurs independently of coaccessory proteins UreE, UreF, and UreG and structural protein UreA. In a yeast two-hybrid screen, UreD was found to directly interact in vivo with coaccessory protein UreF. Unique homomultimeric interactions of UreD and UreF were also detected in vivo. To substantiate the study of urease proteins with a yeast two-hybrid assay, previously described UreE dimers and homomultimeric UreA interactions among apourease trimers were confirmed in vivo. Similarly, a known structural interaction involving UreA and UreC was also verified. This report suggests that in vivo, P. mirabilis UreD may be important for recruitment of UreF to the apourease and that crucial homomultimeric associations occur among these accessory proteins.

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Voland, Petra, David L. Weeks, Elizabeth A. Marcus, Christian Prinz, George Sachs e David Scott. "Interactions among the sevenHelicobacter pyloriproteins encoded by the urease gene cluster". American Journal of Physiology-Gastrointestinal and Liver Physiology 284, n. 1 (1 gennaio 2003): G96—G106. http://dx.doi.org/10.1152/ajpgi.00160.2002.

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Survival of Helicobacter pylori in acid depends on intrabacterial urease. This urease is a Ni2+-containing oligomeric heterodimer. Regulation of its activity and assembly is important for gastric habitation by this neutralophile. The gene complex encodes catalytic subunits ( ureA/B), an acid-gated urea channel ( ureI), and accessory assembly proteins ( ureE–H). With the use of yeast two-hybrid analysis for determining protein-protein interactions, UreF as bait identified four interacting sequences encoding UreH, whereas UreG as bait detected five UreE sequences. These results were confirmed by coimmunoprecipitation and β-galactosidase assays. Native PAGE immunoblotting of H. pylori inner membranes showed interaction of UreA/B with UreI, whereas UreI deletion mutants lacked this protein interaction. Deletion of ureE–H did not affect this interaction with UreI. Hence, the accessory proteins UreE/G and UreF/H form dimeric complexes and UreA/B form a membrane complex with UreI, perhaps enabling assembly of the urease apoenzyme at the membrane surface and immediate urea access to intrabacterial urease to allow rapid periplasmic neutralization.

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Sangari, Félix J., Asunción Seoane, María Cruz Rodríguez, Jesús Agüero e Juan M. García Lobo. "Characterization of the Urease Operon of Brucella abortus and Assessment of Its Role in Virulence of the Bacterium". Infection and Immunity 75, n. 2 (13 novembre 2006): 774–80. http://dx.doi.org/10.1128/iai.01244-06.

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ABSTRACT Most members of the genus Brucella show strong urease activity. However, the role of this enzyme in the pathogenesis of Brucella infections is poorly understood. We isolated several Tn5 insertion mutants deficient in urease activity from Brucella abortus strain 2308. The mutations of most of these mutants mapped to a 5.7-kbp DNA region essential for urease activity. Sequencing of this region, designated ure1, revealed the presence of seven open reading frames corresponding to the urease structural proteins (UreA, UreB, and UreC) and the accessory proteins (UreD, UreE, UreF, and UreG). In addition to the urease genes, another gene (cobT) was identified, and inactivation of this gene affected urease activity in Brucella. Subsequent analysis of the previously described sequences of the genomes of Brucella spp. revealed the presence of a second urease cluster, ure2, in all them. The ure2 locus was apparently inactive in B. abortus 2308. Urease-deficient mutants were used to evaluate the role of urease in Brucella pathogenesis. The urease-producing strains were found to be resistant in vitro to strong acid conditions in the presence of urea, while urease-negative mutants were susceptible to acid treatment. Similarly, the urease-negative mutants were killed more efficiently than the urease-producing strains during transit through the stomach. These results suggested that urease protects brucellae during their passage through the stomach when the bacteria are acquired by the oral route, which is the major route of infection in human brucellosis.

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Yuen, Man Hon, Yu Hang Fong, Yap Shing Nim, Pak Ho Lau e Kam-Bo Wong. "Structural insights into how GTP-dependent conformational changes in a metallochaperone UreG facilitate urease maturation". Proceedings of the National Academy of Sciences 114, n. 51 (4 dicembre 2017): E10890—E10898. http://dx.doi.org/10.1073/pnas.1712658114.

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Abstract (sommario):

The ability of metallochaperones to allosterically regulate the binding/release of metal ions and to switch protein-binding partners along the metal delivery pathway is essential to the metallation of the metalloenzymes. Urease, catalyzing the hydrolysis of urea into ammonia and carbon dioxide, contains two nickel ions bound by a carbamylated lysine in its active site. Delivery of nickel ions for urease maturation is dependent on GTP hydrolysis and is assisted by four urease accessory proteins UreE, UreF, UreG, and UreH(UreD). Here, we determined the crystal structure of the UreG dimer from Klebsiella pneumoniae in complex with nickel and GMPPNP, a nonhydrolyzable analog of GTP. Comparison with the structure of the GDP-bound Helicobacter pylori UreG (HpUreG) in the UreG2F2H2 complex reveals large conformational changes in the G2 region and residues near the 66CPH68 metal-binding motif. Upon GTP binding, the side chains of Cys66 and His68 from each of the UreG protomers rotate toward each other to coordinate a nickel ion in a square-planar geometry. Mutagenesis studies on HpUreG support the conformational changes induced by GTP binding as essential to dimerization of UreG, GTPase activity, in vitro urease activation, and the switching of UreG from the UreG2F2H2 complex to form the UreE2G2 complex with the UreE dimer. The nickel-charged UreE dimer, providing the sole source of nickel, and the UreG2F2H2 complex could activate urease in vitro in the presence of GTP. Based on our results, we propose a mechanism of how conformational changes of UreG during the GTP hydrolysis/binding cycle facilitate urease maturation.

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Scott, David R., Elizabeth A. Marcus, Yi Wen, Siddarth Singh, Jing Feng e George Sachs. "Cytoplasmic Histidine Kinase (HP0244)-Regulated Assembly of Urease with UreI, a Channel for Urea and Its Metabolites, CO2, NH3, and NH4+, Is Necessary for Acid Survival of Helicobacter pylori". Journal of Bacteriology 192, n. 1 (23 ottobre 2009): 94–103. http://dx.doi.org/10.1128/jb.00848-09.

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ABSTRACT Helicobacter pylori colonizes the normal human stomach by maintaining both periplasmic and cytoplasmic pH close to neutral in the presence of gastric acidity. Urease activity, urea flux through the pH-gated urea channel, UreI, and periplasmic α-carbonic anhydrase are essential for colonization. Exposure to pH 4.5 for up to 180 min activates total bacterial urease threefold. Within 30 min at pH 4.5, the urease structural subunits, UreA and UreB, and the Ni2+ insertion protein, UreE, are recruited to UreI at the inner membrane. Formation of this complex and urease activation depend on expression of the cytoplasmic sensor histidine kinase, HP0244. Its deletion abolishes urease activation and assembly, impairs cytoplasmic and periplasmic pH homeostasis, and depolarizes the cells, with an ∼7-log loss of survival at pH 2.5, even in 10 mM urea. Associated with this assembly, UreI is able to transport NH3, NH4 +, and CO2, as shown by changes in cytoplasmic pH following exposure to NH4Cl or CO2. To be able to colonize cells in the presence of the highly variable pH of the stomach, the organism expresses two pH-sensor histidine kinases, one, HP0165, responding to a moderate fall in periplasmic pH and the other, HP0244, responding to cytoplasmic acidification at a more acidic medium pH. Assembly of a pH-regulatory complex of active urease with UreI provides an advantage for periplasmic buffering.

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Kasatkina, Svetlana O., Kirill K. Geyl, Sergey V. Baykov, Mikhail S. Novikov e Vadim P. Boyarskiy. "“Urea to Urea” Approach: Access to Unsymmetrical Ureas Bearing Pyridyl Substituents". Advanced Synthesis & Catalysis 364, n. 7 (8 marzo 2022): 1295–304. http://dx.doi.org/10.1002/adsc.202101490.

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Masepohl, Bernd, Björn Kaiser, Nazila Isakovic, Cynthia L. Richard, Robert G. Kranz e Werner Klipp. "Urea Utilization in the Phototrophic BacteriumRhodobacter capsulatus Is Regulated by the Transcriptional Activator NtrC". Journal of Bacteriology 183, n. 2 (15 gennaio 2001): 637–43. http://dx.doi.org/10.1128/jb.183.2.637-643.2001.

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ABSTRACT The phototrophic nonsulfur purple bacteriumRhodobacter capsulatus can use urea as a sole source of nitrogen. Three transposon Tn5-induced mutations (Xan-9, Xan-10, and Xan-19), which led to a Ure−phenotype, were mapped to the ureF and ureCgenes, whereas two other Tn5 insertions (Xan-20 and Xan-22) were located within the ntrC and ntrB genes, respectively. As in Klebsiella aerogenes and other bacteria, the genes encoding urease (ureABC) and the genes required for assembly of the nickel metallocenter (ureD andureEFG) are clustered in R. capsulatus(ureDABC-orf136-ureEFG). No homologues of Orf136 were found in the databases, and mutational analysis demonstrated that orf136 is not essential for urease activity or growth on urea. Analysis of aureDA-lacZ fusion showed that maximum expression of the ure genes occurred under nitrogen-limiting conditions (e.g., serine or urea as the sole nitrogen source), but ure gene expression was not substrate (urea) inducible. Expression of the ure genes was strictly dependent on NtrC, whereas ς54 was not essential for urease activity. Expression of the ure genes was lower (by a factor of 3.5) in the presence of ammonium than under nitrogen-limiting conditions, but significant transcription was also observed in the presence of ammonium, approximately 10-fold higher than in an ntrC mutant background. Thus, ure gene expression in the presence of ammonium also requires NtrC. Footprint analyses demonstrated binding of NtrC to tandem binding sites upstream of the ureD promoter. Phosphorylation of NtrC increased DNA binding by at least eightfold. Although urea is effectively used as a nitrogen source in an NtrC-dependent manner, nitrogenase activity was not repressed by urea.

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Wen, Yi, Jing Feng, David R. Scott, Elizabeth A. Marcus e George Sachs. "The pH-Responsive Regulon of HP0244 (FlgS), the Cytoplasmic Histidine Kinase of Helicobacter pylori". Journal of Bacteriology 191, n. 2 (31 ottobre 2008): 449–60. http://dx.doi.org/10.1128/jb.01219-08.

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ABSTRACT Helicobacter pylori colonizes the acidic gastric environment, in contrast to all other neutralophiles, whose acid resistance and tolerance responses allow only gastric transit. This acid adaptation is dependent on regulation of gene expression in response to pH changes in the periplasm and cytoplasm. The cytoplasmic histidine kinase, HP0244, which until now was thought only to regulate flagellar gene expression via its cognate response regulator, HP0703, was found to generate a response to declining medium pH. Although not required for survival at pH 4.5, HP0244 is required for survival at pH 2.5 with 10 mM urea after 30 min. Transcriptional profiling of a HP0244 deletion mutant grown at pH 7.4 confirmed the contribution of HP0244 to σ54 activation via HP0703 to coordinate flagellar biosynthesis by a pH-independent regulon that includes 14 flagellar genes. Microarray analysis of cells grown at pH 4.5 without urea revealed an additional 22 genes, including 4 acid acclimation genes (ureA, ureB, ureI, and amiE) that are positively regulated by HP0244. Additionally, 86 differentially expressed genes, including 3 acid acclimation genes (ureF, rocF [arginase], and ansB [asparaginase]), were found in cells grown at pH 2.5 with 30 mM urea. Hence, HP0244 has, in addition to the pH-independent flagellar regulon, a pH-dependent regulon, which allows adaptation to a wider range of environmental acid conditions. An acid survival study using an HP0703 mutant and an electrophoretic mobility shift assay with in vitro-phosphorylated HP0703 showed that HP0703 does not contribute to acid survival and does not bind to the promoter regions of several genes in the HP0244 pH-dependent regulon, suggesting that there is a pathway outside the HP0703 regulon which transduces the acid-responsive signal sensed by HP0244.

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Abdulrahman, Alia Talaat, Shna Ibrahim Ismail, Salar Saadi Hussain, Najat Jabbar Ahmed e Ahmed Nawzad Hassan. "Detection of Helicobacter Pylori’s Virulence Gene (UreA) and its Influence on the Result of Rapid Urease Test (RUT)". Al-Mustansiriyah Journal of Science 33, n. 4 (30 dicembre 2022): 42–48. http://dx.doi.org/10.23851/mjs.v33i4.1152.

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UreA is an important virulence factor of Helicobacter pylori that, along with UreB and UreC, produces urease. Urease enzyme helps the bacterium to colonize the human stomach through metabolizing urea in order to neutralize the gastric environment. The current study aimed to detect the prevalence of the H. pylori’s ureA virulence factor gene, and to investigate the influence of this gene on the result of the rapid urease test (RUT). Eighty stomach biopsy samples were isolated from participants who were suspected to be infected with H. pylori in Erbil city. Participants were 36 males and 44 females, aged between 18 and 67 years. The results showed that 42 (52.5%) of the participants were positive for H. pylori when tested by RUT, while 59 (73.8%) of the patients showed positive H. pylori infection when tested by polymerase chain reaction (PCR) targeting the 16S rRNA gene. The results of the PCR test based on the ureA gene revealed that 42 (52.5%) of the samples were positive. The important finding of this research is the presence of 100% compatibility between positive samples of RUT and ureA genes. It can be concluded from this study that a person may be infected with H. pylori, but the RUT test fails to detect the infection if the bacteria lack the ureA gene, indicating a direct impact of this gene on the result of RUT, which is a defect of RUT.

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Scott, David R., Elizabeth A. Marcus, David L. Weeks, Adrian Lee, Klaus Melchers e George Sachs. "Expression of the Helicobacter pylori ureI Gene Is Required for Acidic pH Activation of Cytoplasmic Urease". Infection and Immunity 68, n. 2 (1 febbraio 2000): 470–77. http://dx.doi.org/10.1128/iai.68.2.470-477.2000.

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ABSTRACT ureI encodes an integral cytoplasmic membrane protein. It is present in the urease gene cluster of Helicobacter pylori and is essential for infection and acid survival, but its role is unknown. To determine the function of UreI protein, we producedH. pylori ureI deletion mutants and measured the pH dependence of urease activity of intact and lysed bacteria and the effect of urea on the membrane potential. We also determinedureI expression, urease activity, and the effect of urea on membrane potential of several gastric and nongastricHelicobacter species. ureI was found to be present in the genome of the gastric Helicobacter species and absent in the nongastric Helicobacter species studied, as determined by PCR. Likewise, Western blot analysis confirmed that UreI was expressed only in the gastric Helicobacterspecies. When UreI is present, acidic medium pH activation of cytoplasmic urease is found, and urea addition increases membrane potential at acidic pH. The addition of a low concentration of detergent raised urease activity of intact bacteria at neutral pH to that of their homogenates, showing that urease activity was membrane limited. No acidic pH activation or urea induced membrane potential changes were found in the nongastric Helicobacter species. The ureI gene product is probably a pH activated urea transporter or perhaps regulates such a transporter as a function of periplasmic pH.

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Più fonti

Tesi sul tema "Urea"

Gray, Lawrence Robert. "Detailed characterization of the urea channel urei from helicobacter pylori". Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3306.

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HpUreI is a pH-gated urea channel found in the pathogenic bacterium Helicobacter pylori. This protein is an essential component of the mechanism of acid acclimation, which allows Helicobacter pylori to survive in the acidic conditions of the stomach. HpUreI conducts urea into the cytoplasm, where it is hydrolyzed by urease into carbon dioxide and ammonia. These products then transit back into the periplasm, where they function as a buffer and proton consumer respectively. HpUreI is an attractive target for small molecule inhibitors for the treatment of H. pylori infections as mutant strains lacking this protein no longer survive under acidic conditions. Despite the importance of HpUreI, it remains biochemically uncharacterized and many questions remain as to how this channel performs its roles. We have solved many of the technical issues regarding the heterologous expression and purification of HpUreI, allowing us to investigate this protein in detail. A robust stopped-flow light-scattering assay was developed which was used to determine the permeability of urea (or other solute) through HpUreI reconstituted proteoliposomes. With slight modifications this assay was be used to measure a wide range of characteristics and variables. Our results show that HpUreI is a hexameric protein that has a relatively weak affinity for urea (˜160mM). Proteoliposome studies indicate that HpUreI is highly selective for urea and hydroxyurea, and is able to conduct water. Interestingly, water and urea conduction is pH-gated, suggesting that both solutes share a common conduction pathway. HpUreI displayed a pH-dependent activity profile with a pH of half maximum activity of ˜5.9. Based on these results an updated mechanism of acid acclimation was proposed. HpUreI is a pH-gated channel; only conducting urea under acidic conditions. The mechanism by which this occurs is not well understood, but can be localized to the periplasmic loops. Chimeric proteins were prepared by swapping the periplasmic loops of HpUreI and StUreI, a pH-independent UreI channel from Streptococcus thermophilus. Our results show that the pH-gating behavior of HpUreI was lost if either periplasmic loop was replaced with the corresponding loop from StUreI. Conversely, pH-gating was gained by StUreI when both periplasmic loops were swapped for those of HpUreI. A model of pH-gating was proposed which takes these findings into account. The mechanism of urea conduction was also examined. The recent crystal structure of HpUreI revealed a ladder of tryptophan residues lining one face of the conduction pathway. Mutation of these residues resulted in lower rates of urea conduction and reduced urea affinity. Our findings indicate that urea interacts directly with the tryptophan residues, via stacking and dipole-dipole interactions, to facilitate urea conduction. These studies have greatly increased our understanding of HpUreI and the role it plays in H. pylori. Further research is required to fully elucidate the mechanisms by which HpUreI operates. However, this is a starting point with which to pursue the ultimate goal of developing small molecule drugs to inhibit HpUreI, culminating in the eradication of H. pylori infections and prevention of gastric cancer.

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Gasparelli, Everton Rogério Ferraz [UNESP]. "Determinação da atividade sérica de enzimas hepáticas e da concentração de uréia, creatinina, cortisol, imunoglobulina G dos valores hemogasométricos de bezerros da raça Nelore oriundos de fertilização in vivo (FV) e fertilização in vitro (FIV)". Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/92203.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Foram acompanhados 310 parturições de receptoras, com embriões fertilizados in vivo (FV) e in vitro (FIV) da raça Nelore, para determinar os índices de partos distócicos em receptoras meio sangue das raças Braford/Nelore, Hereford/Nelore, Simental/Nelore, Red Angus/Nelore, Nelore e anelorados, com idade entre três e seis anos, assim como avaliar o estado de saúde dos bezerros obtidos por intermédio de transferência de embriões, resultantes das técnicas de fertilização in vivo (FV) ou fertilização in vitro (FIV). Observou-se a ocorrência de 38 partos distócicos (38/310) e oito abortos (8/310), dos quais cinco fetos eram oriundos da técnica de fertilização in vivo (FV) e três da técnica de fertilização in vitro (FIV). A taxa de mortalidade em animais neonatos foi de 3,4% (10/290). Os bezerros nascidos de partos distócicos mais duradouros, entre quatro e seis horas, apresentaram os maiores valores médios de freqüência respiratória. A temperatura retal foi mais elevada em animais nascidos de partos laboriosos do que naqueles nascidos de partos normais.
Three hundred and ten parturitions of receivers were accompanied, with Nellore embryos fertilized in vivo (FV) and in vitro (FIV), to determine the indices of dystocic calving in Braford/Nellore, Hereford/Nellore, Simental/Nellore, Red Angus/Nellore, Nellore and Zebu crossbreed recipients cows, aged between three and six years, as well as, to evaluate health condition of calves obtained through embryos transfer, resulting from in vivo fertilization (FV) and in vitro fertilization (FIV) techniques. The occurrence of 38 dystocic calving (38/310) and eight abortions (8/310) were observed, in which five embryos were arisen by in vivo fertilization technique (FV) and three embryos by in vitro fertilization technique (FIV). In neonate animals, the mortality rate was 3,2% (10/310). Calves born by lasting dystocic calving, between four and six hours, presented the biggest average values of respiratory frequency. Animals born by laborious calving showed higher retal temperature than those born by normal calving.

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Gasparelli, Everton Rogério Ferraz. "Determinação da atividade sérica de enzimas hepáticas e da concentração de uréia, creatinina, cortisol, imunoglobulina G dos valores hemogasométricos de bezerros da raça Nelore oriundos de fertilização in vivo (FV) e fertilização in vitro (FIV) /". Araçatuba : [s.n.], 2007. http://hdl.handle.net/11449/92203.

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Orientador: Francisco Leydson Formiga Feitosa
Banca: Alice Maria Melville Paiva Della Libera
Banca: José Jurandir Agliari
Resumo: Foram acompanhados 310 parturições de receptoras, com embriões fertilizados in vivo (FV) e in vitro (FIV) da raça Nelore, para determinar os índices de partos distócicos em receptoras meio sangue das raças Braford/Nelore, Hereford/Nelore, Simental/Nelore, Red Angus/Nelore, Nelore e anelorados, com idade entre três e seis anos, assim como avaliar o estado de saúde dos bezerros obtidos por intermédio de transferência de embriões, resultantes das técnicas de fertilização in vivo (FV) ou fertilização in vitro (FIV). Observou-se a ocorrência de 38 partos distócicos (38/310) e oito abortos (8/310), dos quais cinco fetos eram oriundos da técnica de fertilização in vivo (FV) e três da técnica de fertilização in vitro (FIV). A taxa de mortalidade em animais neonatos foi de 3,4% (10/290). Os bezerros nascidos de partos distócicos mais duradouros, entre quatro e seis horas, apresentaram os maiores valores médios de freqüência respiratória. A temperatura retal foi mais elevada em animais nascidos de partos laboriosos do que naqueles nascidos de partos normais.
Abstract: Three hundred and ten parturitions of receivers were accompanied, with Nellore embryos fertilized in vivo (FV) and in vitro (FIV), to determine the indices of dystocic calving in Braford/Nellore, Hereford/Nellore, Simental/Nellore, Red Angus/Nellore, Nellore and Zebu crossbreed recipients cows, aged between three and six years, as well as, to evaluate health condition of calves obtained through embryos transfer, resulting from in vivo fertilization (FV) and in vitro fertilization (FIV) techniques. The occurrence of 38 dystocic calving (38/310) and eight abortions (8/310) were observed, in which five embryos were arisen by in vivo fertilization technique (FV) and three embryos by in vitro fertilization technique (FIV). In neonate animals, the mortality rate was 3,2% (10/310). Calves born by lasting dystocic calving, between four and six hours, presented the biggest average values of respiratory frequency. Animals born by laborious calving showed higher retal temperature than those born by normal calving.
Mestre

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Wiebler, James. "UREA HYDROLYSIS BY GUT BACTERIA: FIRST EVIDENCE FOR UREA-NITROGEN RECYCLING IN AMPHIBIA". Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami152535331130121.

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Toledo, Paulo Roberto Aparecido Bueno de [UNESP]. "Desenvolvimento de metodologia analítica ambientalmente mais amigável para a determinação de ureía em matrizes diversas". Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/110844.

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Os princípios da Química Verde têm norteado o desenvolvimento de novos procedimentos analíticos que visam reduzir a utilização de substâncias tóxicas e a produção de resíduos que necessitam de tratamento de custo elevado e profissional treinado13. Com base nesses princípios, o presente trabalho propõe o desenvolvimento de uma metodologia ambientalmente mais amigável que possa ser aplicada à análise de ureia em leite e cosméticos.·. A ureia é usada em inúmeros setores industriais para vários usos funcionais como adesivos, pastas, vedadores, resinas, colas, enchimentos, catalisadores, umectantes e agentes desidratantes. Também é usada em suplementos alimentares de animais, fertilizantes e reagentes analíticos. Em produtos de consumo a ureia é encontrada em extensa variedade de amostras comerciais, tais como cosméticos, cremes hidratantes, xampus, condicionadores de cabelo, tinturas de cabelo e removedores de tintura, sabonetes líquidos, detergentes e outros produtos de limpeza, além de ser extensivamente usada em tratamentos para pele ressecada. Em produtos alimentícios como o leite bovino a ureia está presente na concentração media de 160 mg.L-1, porem a adição fraudulenta de ureia no leite para aumento de lucros altera a qualidade do leite em todos os componentes, principalmente os teores de proteína. Esta adulteração influencia diretamente o pagamento do leite por sua qualidade. A metodologia desenvolvida envolve a combinação spot test - espectroscopia de reflectância difusa utilizando dois reagentes cromogênicos diferentes (p-DAB e p-DAC) que reagem com a ureia resultando em um produto colorido. Posteriormente a metodologia foi aplicada para determinação de ureia em formulações dermatologias e leite bovino demonstrando ótimos resultados de precisão e exatidão, evidenciados pela boa recuperação, além de oferecer vantagens como simplicidade de execução...
Green Chemistry principles have guided the development of new analytical procedures aimed at reducing the use of toxic substances and waste production that do not require costly treatment and trained professional13. Based on these principles, this paper proposes the development of a more environmentally friendly method that can be applied to the analysis of urea in milk and cosmetics. Urea is used in numerous industrial sectors for various functional uses as adhesives, binders, sealants, resins, fillers, catalysts, humectants and dehydrating agents. It is also used in supplements for animals, fertilizers and analytical reagents. In consumable products, urea is found in a wide variety of commercial samples such as cosmetics, moisturizers, shampoos, hair conditioners, hair dyes and dye removers, liquid soaps, detergents and other cleaning products, besides being extensively used in treatments for dry skin. In food products, such as cow milk, urea is present in the medium concentration of 160 mg.L-1, but the fraudulent addition of urea in milk to increase profits alters the quality of the milk on all components, especially the milk protein. This tampering directly influences milk payment for their quality. The clean method developed involves combining spot test - diffuse reflectance spectroscopy using two different chromogenic reagents (p-DAB and p-DAC), and was applied for determination of urea in dermatologic formulations and bovine milk, demonstrating great precision and accuracy results, evidenced by good recovery, plus offering advantages such as simplicity of implementation and low reagent consumption, generating minimal amount of waste, speed and security, portability and generating reliable results.

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Toledo, Paulo Roberto Aparecido Bueno de. "Desenvolvimento de metodologia analítica ambientalmente mais amigável para a determinação de ureía em matrizes diversas /". Araraquara, 2014. http://hdl.handle.net/11449/110844.

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Orientador: Leonardo Pezza
Co-orientador: Helena Redigolo Pezza
Banca: Edilene Cristina Ferreira
Banca: Matthieu Tubino
Resumo: Os princípios da Química Verde têm norteado o desenvolvimento de novos procedimentos analíticos que visam reduzir a utilização de substâncias tóxicas e a produção de resíduos que necessitam de tratamento de custo elevado e profissional treinado13. Com base nesses princípios, o presente trabalho propõe o desenvolvimento de uma metodologia ambientalmente mais amigável que possa ser aplicada à análise de ureia em leite e cosméticos.·. A ureia é usada em inúmeros setores industriais para vários usos funcionais como adesivos, pastas, vedadores, resinas, colas, enchimentos, catalisadores, umectantes e agentes desidratantes. Também é usada em suplementos alimentares de animais, fertilizantes e reagentes analíticos. Em produtos de consumo a ureia é encontrada em extensa variedade de amostras comerciais, tais como cosméticos, cremes hidratantes, xampus, condicionadores de cabelo, tinturas de cabelo e removedores de tintura, sabonetes líquidos, detergentes e outros produtos de limpeza, além de ser extensivamente usada em tratamentos para pele ressecada. Em produtos alimentícios como o leite bovino a ureia está presente na concentração media de 160 mg.L-1, porem a adição fraudulenta de ureia no leite para aumento de lucros altera a qualidade do leite em todos os componentes, principalmente os teores de proteína. Esta adulteração influencia diretamente o pagamento do leite por sua qualidade. A metodologia desenvolvida envolve a combinação spot test - espectroscopia de reflectância difusa utilizando dois reagentes cromogênicos diferentes (p-DAB e p-DAC) que reagem com a ureia resultando em um produto colorido. Posteriormente a metodologia foi aplicada para determinação de ureia em formulações dermatologias e leite bovino demonstrando ótimos resultados de precisão e exatidão, evidenciados pela boa recuperação, além de oferecer vantagens como simplicidade de execução...
Abstract: Green Chemistry principles have guided the development of new analytical procedures aimed at reducing the use of toxic substances and waste production that do not require costly treatment and trained professional13. Based on these principles, this paper proposes the development of a more environmentally friendly method that can be applied to the analysis of urea in milk and cosmetics. Urea is used in numerous industrial sectors for various functional uses as adhesives, binders, sealants, resins, fillers, catalysts, humectants and dehydrating agents. It is also used in supplements for animals, fertilizers and analytical reagents. In consumable products, urea is found in a wide variety of commercial samples such as cosmetics, moisturizers, shampoos, hair conditioners, hair dyes and dye removers, liquid soaps, detergents and other cleaning products, besides being extensively used in treatments for dry skin. In food products, such as cow milk, urea is present in the medium concentration of 160 mg.L-1, but the fraudulent addition of urea in milk to increase profits alters the quality of the milk on all components, especially the milk protein. This tampering directly influences milk payment for their quality. The clean method developed involves combining spot test - diffuse reflectance spectroscopy using two different chromogenic reagents (p-DAB and p-DAC), and was applied for determination of urea in dermatologic formulations and bovine milk, demonstrating great precision and accuracy results, evidenced by good recovery, plus offering advantages such as simplicity of implementation and low reagent consumption, generating minimal amount of waste, speed and security, portability and generating reliable results.
Mestre

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Lemos, Evandro Freire. "Uso de fertilizante nitrogenado de liberação lenta na cultura do milho em sistema plantio direto". Universidade Jose do Rosario Vellano, 2011. http://tede2.unifenas.br:8080/jspui/handle/jspui/58.

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The adoption of best practices for use of fertilizers has contributed to the reduction in nutrient losses and the use of protected sources of nitrogen appears to be an interesting alternative.The aim of this study was a technical and economic evaluation of the effects of different nitrogen using slow release urea compared with traditional use of urea. The experimental design was randomized blocks with seven treatments and four replications. It was demonstrated the possibility of reducing nitrogen levels when using the slow release urea can also be applied at planting. Throughout the experiment the use of conventional urea proved more economical. It was concluded that it is necessary to popularize the techniques of protection of urea, thus making the cost of fertilizer more competitive. Treatment 3, which used 100% of the nitrogen in slow release urea at sowing showed the highest yield, and the second treatment, conventional urea applied at planting 30% and 70% coverage (merged) presented the highest net revenue per hectare, considering the costs of fertilizer.
A adoção das boas práticas do uso de fertilizantes tem contribuído para a redução nas perdas de nutrientes, e a utilização de fontes de nitrogênio protegidas parece ser uma alternativa interessante. Sendo assim, o objetivo deste trabalho foi realizar uma avaliação técnica e econômica dos efeitos de diferentes doses de nitrogênio, utilizando ureia de liberação lenta comparado com uso de ureia tradicional na cultura do milho. O delineamento experimental usado foi de blocos casualizados, com sete tratamentos e quatro repetições. Ficou evidenciada a possibilidade de redução da dose de nitrogênio ao se utilizar a ureia de liberação lenta, podendo também a aplicação ser feita toda no plantio, tendo, entretanto, o uso da ureia convencional se mostrado mais econômico. O tratamento 3, em que se utilizou 100% da dose de nitrogênio com ureia de liberação lenta no plantio foi o que apresentou maior produtividade, e o tratamento 2, ureia convencional aplicada 30% no plantio e 70% em cobertura (incorporada), foi o que apresentou maior receita líquida por hectare, considerando os custos da adubação. Pode-se concluir que há necessidade da popularização das técnicas de proteção da ureia, tornando assim o custo do fertilizante mais competitivo em detrimento aos demais nitrogenados.

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Günther, Ulrike, Marcus Hartmann, Siegfried Wartewig e Reinhard Neubert. "Diffusion of urea through membranes". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194383.

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Günther, Ulrike, Marcus Hartmann, Siegfried Wartewig e Reinhard Neubert. "Diffusion of urea through membranes". Diffusion fundamentals 4 (2006) 4, S. 1-5, 2006. https://ul.qucosa.de/id/qucosa%3A14277.

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Park, Yong Hun. "An investigation of urea decomposition and selective non-catalytic removal of nitric oxide with urea". Texas A&M University, 2004. http://hdl.handle.net/1969.1/279.

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The use of urea (NH2CONH2) to remove nitric oxide (NO) from exhaust streams was investigated using a laboratory laminar-flow reactor. The experiments used a number of gas compositions to simulate different combustion exhaust gases. The urea was injected into the gases as a urea-water solution. The decomposition processes of the urea-water solutions and urea powder were examined. For both the nitric oxide removal and the urea decomposition experiments, a Fourier transform infrared (FTIR) spectrometer was used to determine the concentrations of the product species. The products from the decomposition were examined every 50 K from 500 K to 800 K. The dominant products were ammonia (NH3), isocyanuric acid (HNCO) and carbon dioxide (CO2). In case of urea-water solution decomposition, for gas temperatures between 550 and 650 K, the highest concentrations were for NH3 and HNCO. On the other hand, the concentrations of CO2 were highest for gas temperatures of about 500 - 550 K. For temperatures above about 650 K, the amount of these three dominant prod-ucts slightly decreased as temperature increased. ivFor the nitric oxide removal (SNCR) experiments, the gas mixture was heated to temperatures between 800 K and 1350 K. Depending on the temperature, gas composition, residence time, and urea feed rate, removal levels of up to 95% were obtained. Other by-products such as N2O were detected and quantified. The effects of the urea/NO (beta) ratio were determined by varying the urea concentration for a constant NO con-centration of 330 ppm. The effects of the levels of oxygen (O2) in the exhaust gases and the residence time also were investigated. Increasing the urea/NO ratio and residence time resulted in higher NO removal and increased the temperature window of the nitric oxide removal.

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Più fonti

Libri sul tema "Urea"

Canada. Environmental Protection Programs Directorate. Technical Services Branch., a cura di. Urea. Ottawa, Ont: Environmental Protection Service, 1985.

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Yang, Baoxue, e Jeff M. Sands, a cura di. Urea Transporters. Dordrecht: Springer Netherlands, 2014. http://dx.doi.org/10.1007/978-94-017-9343-8.

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Yahya, Noorhana. Green Urea. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-10-7578-0.

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Ritchie, Mark. Biosensors for urea and aspartame. Manchester: UMIST, 1996.

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Canada Mortgage and Housing Corporation., a cura di. Urea-formaldehyde foam insulaton (UFFI). [Ottawa]: Canada Mortgage and Housing Corporation, 2001.

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Massachusetts. Department of Public Health. UFFI (Urea Formaldehyde Foam Insulation). Boston, MA: Massachusetts Dept. of Public Health, 1987.

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United States International Trade Commission. Urea from the German Democratic Republic, Romania, and the Union of Soviet Socialist Republics: Determinations of the Commission in investigations nos. 731-TA-338 through 340 (final) under the Tariff Act of 1930, together with the information obtained in the investigations. Washington, DC: U.S. International Trade Commission, 1987.

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Stuart, Tiernan. Analytical studies into the crease resistant finishing of linen with a bifunctional urea-formaldehyde reagent, dimethylol ethylene urea. [s.l: The Author], 1999.

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Ahmad, Naseem, e Mohammad Faisal, a cura di. Thidiazuron: From Urea Derivative to Plant Growth Regulator. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-10-8004-3.

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Canada. Environmental Protection Service. Technical Services Branch., a cura di. Urea: Environmental and technical information for problem spills. [Ottawa, Ont.]: Environmental Canada, Environmental Protection Service, 1985.

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Capitoli di libri sul tema "Urea"

Bährle-Rapp, Marina. "Urea". In Springer Lexikon Kosmetik und Körperpflege, 574. Berlin, Heidelberg: Springer Berlin Heidelberg, 2007. http://dx.doi.org/10.1007/978-3-540-71095-0_10898.

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Miyakawa, Shin, e Didier Despois. "Urea". In Encyclopedia of Astrobiology, 1721. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-11274-4_1634.

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Wang, Hongkai, Jianhua Ran e Tao Jiang. "Urea". In Subcellular Biochemistry, 7–29. Dordrecht: Springer Netherlands, 2014. http://dx.doi.org/10.1007/978-94-017-9343-8_2.

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Hignett, Travis P. "Urea". In Fertilizer Manual, 109–21. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-017-1538-6_9.

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Gooch, Jan W. "Urea". In Encyclopedic Dictionary of Polymers, 784. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_12387.

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Miyakawa, Shin, e Didier Despois. "Urea". In Encyclopedia of Astrobiology, 2573–74. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-662-44185-5_1634.

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Miyakawa, Shin, e Didier Despois. "Urea". In Encyclopedia of Astrobiology, 1. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-27833-4_1634-3.

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Miyakawa, Shin, e Didier Despois. "Urea". In Encyclopedia of Astrobiology, 1. Berlin, Heidelberg: Springer Berlin Heidelberg, 2022. http://dx.doi.org/10.1007/978-3-642-27833-4_1634-4.

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Miyakawa, Shin, e Didier Despois. "Urea". In Encyclopedia of Astrobiology, 3143–44. Berlin, Heidelberg: Springer Berlin Heidelberg, 2023. http://dx.doi.org/10.1007/978-3-662-65093-6_1634.

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Yahya, Noorhana. "Urea Fertilizer: The Global Challenges and Their Impact to Our Sustainability". In Green Urea, 1–21. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-10-7578-0_1.

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Atti di convegni sul tema "Urea"

Kadu, Sachin, e Harish gangwar. "Urea Quality Sensor Integration in Urea Supply Line / Urea Tank". In SAE 2012 World Congress & Exhibition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2012. http://dx.doi.org/10.4271/2012-01-1086.

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Bose, Asmita, e Karabi Biswas. "Digital Urea Meter for Impedeometric Urea Sensor". In 2019 IEEE International Instrumentation and Measurement Technology Conference (I2MTC). IEEE, 2019. http://dx.doi.org/10.1109/i2mtc.2019.8826918.

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Vicar, Nicoleta, Adina Berbecea, Alina Lato, Liliana Brei e Isidora Raduloiv. "INFLUENCE OF COATED UREA APPLICATION ON SOIL ORGANIC CARBON SEQUESTRATION". In 23rd SGEM International Multidisciplinary Scientific GeoConference 2023. STEF92 Technology, 2023. http://dx.doi.org/10.5593/sgem2023v/4.2/s19.31.

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The application of nitrogen fertilizers in the form of urea tends to increase acidity, especially on low pH soils, and as a result can lead to increased aluminum toxicity, which can adversely affect not only soil properties such as microbial activity, but also productivity. Application of different types of urea with inhibitors to reduce nitrogen losses would result in a different carbon response to fertilizers applications for the same soil type because of differences in soil micro-environment, including microbial biomass and activity. The aim of the study was to determine the influence of applying different forms of urea on the content of total nitrogen, organic carbon, phosphorus and assimilable potassium. The experiment was set up in the Western Plain of Banat, on soil with weak acid pH and medium nitrogen supply. The research was carried out on autumn oilseed rape crops, in the following fertilization variants and application rates: UREE 46% total N; UREE Z 45.7% N total with nitrification inhibitor up to 80%; UREE ZL 45.7% N total with urease inhibitor up to 50%; UREE NDP 45.7% N total with urease inhibitor up to 50% and nitrification inhibitor up to 80%; UREE DMPP 45.7% N total with volatilization reduction up to 95%. For these crops, 300 kg/ha 16:16:16 complex fertilizer and 120 kg/ha UREE were applied, from the described above varieties. There were no significant differences in soil pH and total nitrogen, available potassium increased significantly, and available phosphorus decreased slightly in all treatments. Application of stabilized and coated urea fertilizers resulted in a moderate improvement in soil SOC.

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Ganne, Rajakumar, Kaushal K. Jain, Peter H. Meckl, Harshil Angre e Jagdish R. Hiremath. "Computationally Efficient Urea-Dosing Controllers for Urea-SCR". In ASME 2020 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/dscc2020-3213.

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Abstract This paper presents two non-model-based reference-shaping and a model-based predictive urea-dosing controller for the Urea-SCR system. An ideal urea-dosing controller would minimize both tailpipe NOx and NH3 slip. However, this is not possible because of the trade-off between deNOx and NH3 slip. This trade-off is used to clearly define a control objective in terms of NH3 slip. Three controllers are then developed to meet this control objective such that they are all computationally inexpensive. The three controllers are then tested for three very different drive cycles. Simulation results show that the performance of the non-model based reference-shaping controllers is subjected to manual tuning of their variables. In contrast, the predictive controller, which is the highlight of this paper, can adapt to various drive cycles without compromising on the computational cost.

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Rosker, Mark J. "Recent Developments In Urea". In 30th Annual Technical Symposium, a cura di Larry G. DeShazer. SPIE, 1987. http://dx.doi.org/10.1117/12.939611.

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Jamilova, N. Q., e T. R. Dusiyorov. "UREA FURFUROL RESIN SYNTHESIS". In Теоретические и практические вопросы химической науки и технологий. Улан-Удэ: Восточно-Сибирский государственный университет технологий и управления, 2022. http://dx.doi.org/10.53980/9785907599543_157.

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Ning, Jinbiao, e Fengjun Yan. "Detection of Injected Urea Quantity and Correction for SCR Urea Dosing Control". In SAE 2015 World Congress & Exhibition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2015. http://dx.doi.org/10.4271/2015-01-1038.

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Murugan, M., V. K. Kokate, A. A. Athawale e M. H. M. Alhousami. "Epoxy resin modified urea formaldehyde and silicon urea formaldehyde as microwave absorbers". In 2008 International Conference on Recent Advances in Microwave Theory and Applications (MICROWAVE). IEEE, 2008. http://dx.doi.org/10.1109/amta.2008.4763183.

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Hoeft, Robert G. "Management of Urea Containing Fertilizers". In Proceedings of the 1992 Crop Production and Protection Conference. Iowa State University, Digital Press, 1993. http://dx.doi.org/10.31274/icm-180809-428.

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Yue-Yun Wang, Yu Sun e K. Gady. "Model-based estimation of injected urea quantity and diagnostics for SCR urea injection system". In 2012 American Control Conference - ACC 2012. IEEE, 2012. http://dx.doi.org/10.1109/acc.2012.6314711.

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Rapporti di organizzazioni sul tema "Urea"

Rossiter, Walter J. Urea-formaldehyde foam insulations :. Gaithersburg, MD: National Bureau of Standards, 1985. http://dx.doi.org/10.6028/nbs.tn.1210.

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Strey, Daniel J., e Nick E. Christians. Comparison of Polymer-coated Urea Fertilizers. Ames: Iowa State University, Digital Repository, 2014. http://dx.doi.org/10.31274/farmprogressreports-180814-883.

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Ah Mew, Nicholas, Robert McCarter, Rima Izem, Anne Markus, Maya Gerstein, Katie Rice, Jacqueline Sanz, Cynthia Le Mons, Janice Bartos e Mendel Tuchman. Comparing Treatment Options for Urea Cycle Disorders. Patient-Centered Outcomes Research Institute (PCORI), dicembre 2020. http://dx.doi.org/10.25302/12.20.cer.150227816.

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TRUONG, THANH-TAM. TWO-STEP SYNTHESIS OF POLY (UREA FORMALDEHYDE) MICROCAPSULES. Office of Scientific and Technical Information (OSTI), luglio 2022. http://dx.doi.org/10.2172/1878530.

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Glass, Robert, e Anh Nguyen-Huu. Urea Sensor Final Report CRADA No. TSB-987-94. Office of Scientific and Technical Information (OSTI), marzo 2018. http://dx.doi.org/10.2172/1431006.

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Glass, R. Urea Sensor Final Report CRADA No. TSB-987-94. Office of Scientific and Technical Information (OSTI), settembre 1996. http://dx.doi.org/10.2172/759916.

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Sonder, E., T. C. Quinby e D. L. Kinser. ZnO varistors made from powders produced utilizing a urea process. Office of Scientific and Technical Information (OSTI), settembre 1985. http://dx.doi.org/10.2172/5331308.

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Henning, Stanley, e Russell Doorenbos. Corn Response to Urea-N and Pelletal Limestone in 1999. Ames: Iowa State University, Digital Repository, 2001. http://dx.doi.org/10.31274/farmprogressreports-180814-2371.

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Fujino, Ryusuke, Tetsuya Fujita e Teruo Nakada. Improvement of Urea Spray Characteristics for SCR NOx Aftertreatment System. Warrendale, PA: SAE International, maggio 2005. http://dx.doi.org/10.4271/2005-08-0115.

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Burrows, Elizabeth P. Mass Spectrometric Characterization of N,N-bis(2,4,6-Trichlorophenyl) urea. Fort Belvoir, VA: Defense Technical Information Center, luglio 1991. http://dx.doi.org/10.21236/ada239959.

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