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1.
J Environ Radioact ; 278: 107488, 2024 Jul 04.
Artículo en Inglés | MEDLINE | ID: mdl-38968644

RESUMEN

224Ra (t1/2 = 3.6 d) has been widely used as a tracer in environmental water research. Here, we present a new method for measuring 224Ra in natural waters using a pulsed ionization chamber (PIC)-based radon detector. This method is based on the measurement of the 224Ra daughter isotope 220Rn (thoron) after reaching secular equilibrium within 7 min. Radium isotopes are concentrated on ''Mn-fibers'' before measurement of 220Rn, which can be distinguished from 222Rn by the difference in their half-lives. The measurement efficiency of the method is 0.20 ± 0.01 cps/Bq at an optimum airflow rate of 1.0 L/min and a water/Mn-fiber weight ratio of 1.0. Results from natural water samples obtained by this method agree well with analysis via RaDeCC, an established technique for 224Ra assessments. Since the PIC system is lighter compared to RaDeCC, easier to operate, and does not require the usage of helium carrier gas and desiccant, this method is recommended for in-situ 224Ra measurement in long-term fieldwork with limited logistical support.

2.
J Psychosom Obstet Gynaecol ; 45(1): 2351809, 2024 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-38860635

RESUMEN

OBJECTIVE: In China, there is a unique type of second marriage (SM) family where the woman is remarried, and the man is experiencing his first marriage. Additionally, the woman is older than the man. Therefore, these families experience many challenges: psychological, emotional, and societal pressure. Such family is a typical sample for studying sociocultural and psychological stress influencing on outcome of assisted reproductive technology (ART). This study aimed to investigate the impact of social psychological stress on the live birth outcomes AR. METHODS: In this retrospective cohort, second marriage (SM) families who visited the Second Hospital of Hebei Medical University reproductive center between January 2012 to December 2022 were screened, and 561s marriage families (the SM group) with 5600 first marriage (FM) families (the FM group) were included undergoing their first ART cycles. The primary outcome of this study was the live birth rate (LBR). RESULTS: The live birth rate (LBR) of SM group (30.7%) is lower than that of the FM group (43.6%) (p < 0.01). After adjustment by logistic regression, the second marriage group (OR = 1.269, 95%CI 1.031-1.562, p = 0.025) were independent factors associated with the outcome of live birth. After propensity score matching (PSM), the live birth rate of SM group (28.7%) is lower than the FM group (35.9%) (0 = 0.011). CONCLUSION: The SM family experience higher levels of social and psychological pressure, which lead to lower level of LBR than FM family.


Asunto(s)
Matrimonio , Técnicas Reproductivas Asistidas , Estrés Psicológico , Humanos , Femenino , Técnicas Reproductivas Asistidas/psicología , Adulto , Matrimonio/psicología , Estrés Psicológico/psicología , Estudios Retrospectivos , China , Masculino , Embarazo , Nacimiento Vivo
3.
J Assist Reprod Genet ; 41(2): 363-370, 2024 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-38079076

RESUMEN

OBJECTIVE: In vitro fertilization-embryo transfer (IVF-ET) is a widely used treatment for infertility, with oocyte maturation and quality having a significant impact on oocyte fertilization, embryo development, and fetal growth. Mitochondrial transcription factor A (TFAM) is essential for maintaining the mitochondrial oxidative respiratory chain and supplying energy for oocyte development, fertilization, and embryonic development. In this study, we aimed to examine TFAM expression in women undergoing IVF-ET and assess its impact on the IVF outcomes. METHODS: We recruited 85 women who underwent IVF-ET treatment for infertility. On the date of egg collection, granulosa cells were extracted from the clear follicular fluid of the first mature egg using ultrasound-guided needle aspiration. The collected granulosa cells served three purposes: (1) detecting TFAM gene expression in granulosa cells via immunocytochemistry, (2) determining TFAM mRNA expression using reverse transcription-PCR (RT-PCR), and (3) measuring TFAM protein expression through western blotting. RESULT: Based on the results, we found that TFAM was localized and expressed in the cytoplasm of granulosa cells, whereas no expression was detected in the nucleus. Granulosa cells exhibited a linear correlation between TFAM mRNA and TFAM protein expression. The study participants were divided into three groups using the ternary method based on relative TFAM mRNA expression thresholds of 33% and 76%: the low-expression group (n = 30), the moderate-expression group (n = 27), and the high-expression group (n = 28). When compared to the other two groups, the moderate expression group exhibited a significantly higher egg utilization rate, 2 pronucleus rate, fertilization rate, and clinical pregnancy rate (P < 0.05). CONCLUSION: TFAM was detected in the cytoplasm of human ovarian granulosa cells. Women with moderate TFAM expression demonstrate enhanced outcomes in IVF.


Asunto(s)
Proteínas de Unión al ADN , Fertilización In Vitro , Infertilidad , Proteínas Mitocondriales , Factores de Transcripción , Embarazo , Humanos , Femenino , Células de la Granulosa/metabolismo , Infertilidad/terapia , Oocitos/metabolismo , ARN Mensajero/metabolismo
4.
Bioorg Med Chem Lett ; 97: 129486, 2024 01 01.
Artículo en Inglés | MEDLINE | ID: mdl-37734424

RESUMEN

Antibiotic resistance is a major threat to public health, and Gram-negative bacteria pose a particular challenge due to their combination of a low permeability cell envelope and efflux pumps. Our limited understanding of the chemical rules for overcoming these barriers represents a major obstacle in antibacterial drug discovery. Several recent efforts to address this problem have involved screening compound libraries for accumulation in bacteria in order to understand the structural properties required for Gram-negative permeability. Toward this end, we used cheminformatic analysis to design a library of sulfamidoadenosines (AMSN) having diverse substituents at the adenine C2 position. An efficient synthetic route was developed with installation of a uniform cross-coupling reagent set using Sonogashira and Suzuki reactions of a C2-iodide. The potential utility of these compounds was demonstrated by pilot analysis of selected analogues for accumulation in Escherichia coli.


Asunto(s)
Antibacterianos , Bacterias Gramnegativas , Antibacterianos/química , Descubrimiento de Drogas , Escherichia coli , Permeabilidad/efectos de los fármacos , Adenosina/química , Adenosina/farmacología
5.
Ann Palliat Med ; 12(1): 133-140, 2023 01.
Artículo en Inglés | MEDLINE | ID: mdl-36747387

RESUMEN

BACKGROUND: We investigated the efficacy of progestin-primed ovarian stimulation (PPOS) and minimal stimulation using clomiphene citrate (CC) + gonadotropin (Gn) for in-vitro fertilization-embryo transfer (IVF-ET) in advanced maternal age (AMA) women with poor ovarian response (POR) according to the Patient-Oriented Strategies Encompassing Individualized Oocyte Number (POSEIDON) criteria. METHODS: A retrospective analysis was performed using the data of AMA patients who had received IVF-ET due to a low ovarian reserve. The enrolled patients were screened according to the POSEIDON group 4 criteria. 102 patients were included in the study, including 52 in the PPOS group and 50 in the minimal stimulation group (who received CC + Gn). The duration of Gn administration, Gn dose, estradiol (E2), and luteinizing hormone (LH) levels on the day of trigger, the cancellation rate of the oocyte retrieval cycle, the number of oocytes retrieved, the number of metaphase II (MII) oocytes, and IVF laboratory outcomes during ovarian stimulation were compared between the 2 groups. RESULTS: No significant differences were found in terms of age, infertility, body mass index (BMI), and basal follicle-stimulating hormone, LH, E2, AFC, and AMH between the 2 groups (all P>0.05). The duration of ovarian stimulation [(9.43±2.44) vs. (7.48±3.09) days, P<0.05] was significantly longer and the total Gn dose [(2,423.22±738.66) vs. (1,579.68±728.86) IU, P<0.05] were significantly higher in the PPOS group than the minimal stimulation group. The LH value on the day of trigger in the PPOS group (3.28 mIU/mL) was significantly lower than that in the minimal stimulation group (5.57 mIU/mL) (P<0.05). The number of oocytes retrieved, normal fertilization rate, number of good-quality embryos on day 3, number of transferable embryos, and number of frozen blastocysts did not differ significantly between the 2 groups (all P>0.05). The proportion of MII oocytes was significantly higher in the PPOS group than the minimal stimulation group (94.05% vs. 81.40%, P<0.05). CONCLUSIONS: For patients in the POSEIDON group 4, PPOS effectively blocked the premature LH surge and increased the proportion of mature oocytes. Thus, it is a feasible ovulation stimulation protocol for AMA women with POR.

6.
Antimicrob Agents Chemother ; 67(2): e0137722, 2023 02 16.
Artículo en Inglés | MEDLINE | ID: mdl-36715507

RESUMEN

Gram-negative bacteria are notoriously more resistant to antibiotics than Gram-positive bacteria, primarily due to the presence of the outer membrane and a plethora of active efflux pumps. However, the potency of antibiotics also varies dramatically between different Gram-negative pathogens, suggesting major mechanistic differences in how antibiotics penetrate permeability barriers. Two approaches are used broadly to analyze how permeability barriers affect intracellular accumulation of antibiotics. One compares the antibacterial activities of compounds, while the other measures the total intracellular concentrations of compounds in nongrowing cells, with both approaches using strains harboring wild-type or genetically modified efflux systems and permeability barriers. Whether the two assays provide similar mechanistic insights remains unclear. In this study, we analyzed the intracellular accumulation and antibacterial activities of antibiotics representative of major clinical classes in three Gram-negative pathogens of high clinical importance, Pseudomonas aeruginosa, Escherichia coli, and Acinetobacter baumannii. We found that both assays are informative about properties of permeability barriers, but there is no quantitative agreement between the assays. Our results show that the three pathogens differ dramatically in their permeability barriers, with the outer membrane playing the dominant role in E. coli and P. aeruginosa but efflux dominating in A. baumannii. However, even compounds of the same chemotype may use different permeation pathways depending on small chemical modifications. Accordingly, a classification analysis revealed limited conservation of molecular properties that define compound penetration into the three bacteria.


Asunto(s)
Antibacterianos , Escherichia coli , Antibacterianos/química , Escherichia coli/genética , Escherichia coli/metabolismo , Transporte Biológico , Bacterias Gramnegativas/metabolismo , Permeabilidad , Pruebas de Sensibilidad Microbiana , Pseudomonas aeruginosa/metabolismo
7.
Front Surg ; 9: 1033856, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-36439547

RESUMEN

Introduction: Unilateral biportal endoscopic (UBE) technique can easily decompress the bony spinal canal and accommodate all open surgical instruments under endoscopic guidance. However, indications and reports of this technique have been limited to degenerative and infectious diseases. Methods: We used the UBE technique for the decompression and removal of extradural mass lesions in five patients. Under endoscopic guidance, a unilateral approach was used, and decompression and flavectomy were performed. After decompression, removal of the tumor was performed using various forceps. We evaluated the technical process of the procedure, the patient's pre- and postoperative symptoms, and operative radiology and pathologic results. Results: Postoperative pain and disability improved clinically for all patients. Four patients were confirmed as having an epidural cyst and one patient was diagnosed with hemangioma. During follow-up, no recurrence was observed. Conclusions: We successfully removed five extradural mass lesions using a biportal endoscopic posterior approach without complications. The biportal endoscopic approach may have advantages, such as minimizing trauma to the normal structures, magnified endoscopic view, and early recovery after the surgery. Biportal endoscopy may be used as an alternative surgical treatment for symptomatic intraspinal extradural benign lesions.

8.
Medicine (Baltimore) ; 101(39): e30723, 2022 Sep 30.
Artículo en Inglés | MEDLINE | ID: mdl-36181054

RESUMEN

Bladder cancer (BC) is one of the most common male malignant tumors and the most common urological tumor. However, the molecular mechanism and role of PLK1 on bladder cancer were unclear. Therefore, the study aims to explore the potential part of the overall survival of bladder cancer through bioinformatics analysis. GSE121711 and GSE130598, from the Gene Expression Omnibus database. The GEO2R screened differently expressed genes, and DAVID and Metascape were used for functional annotation. The cytoHubba made hub genes identification and expression. A total of 50 BC participants were recruited. After surgery, 50 BC tumor samples from BC patients and 50 adjacent standard bladder tissue samples were obtained. The RT-qPCR assay was performed to verify the expression of hub genes. The Kaplan-Meier Plotter analyzed the effect of hub gene expression for overall survival of BC. The compulsory module of Molecular Complex Detection tool analysis was shown, which included CDK1, TTK, AURKB, MELK, PLK1, and BUB1. And the six hub genes were up-regulated in the BC compared with the normal tissues. The relative expression levels of CDK1, TTK, AURKB, MELK, PLK1, and BUB1 were significantly higher in BC samples compared with the regular kidney tissue groups. The result demonstrated that CDK1, TTK, AURKB, MELK, PLK1, and BUB1 might be considered biomarkers for BC. Overall survival analysis showed that BC patients with high expression level of PLK1 had poorer overall survival times than those with low expression level (P < .05). The expression levels of CDK1, TTK, AURKB, MELK, and BUB1 was not related to the overall survival of BC patients (P > .05). The PLK1 gene might provide new ideas and evidence for bladder cancer research.


Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Proto-Oncogénicas/metabolismo , Neoplasias de la Vejiga Urinaria , Biomarcadores de Tumor/genética , Biomarcadores de Tumor/metabolismo , Biología Computacional , Perfilación de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Humanos , Masculino , Pronóstico , Proteínas Serina-Treonina Quinasas/genética , Neoplasias de la Vejiga Urinaria/genética , Quinasa Tipo Polo 1
9.
Environ Res ; 207: 112161, 2022 05 01.
Artículo en Inglés | MEDLINE | ID: mdl-34626591

RESUMEN

BACKGROUND: Congenital anomalies (CAs) are the leading causes for children's disabilities and mortalities worldwide. The associations between air pollution and CAs are not fully characterized in fetuses born by in vitro fertilization (IVF) who are at high risk of congenital anomalies. METHODS: We conducted a cross-sectional study including 16,971 IVF cycles from three hospitals in Hebei Province, China, 2014-2019. Air quality data was obtained from 149 air monitoring stations. Individual average daily concentrations of PM2.5, PM10, NO2, SO2, CO, and O3 were estimated by spatiotemporal kriging method. Exposure windows were divided into 5: preantral follicle period, antral follicle period, germinal period, embryonic period and early fetal period. Logistic generalized estimating equations were used to estimate the associations between air pollutants and overall or organ-system specific congenital anomalies. Negative control exposure method was used to detect and reduce bias of estimation. RESULTS: We found increasing levels of PM2.5 and PM10 were associated with higher risk of overall congenital anomalies during early fetal period, equating gestation 10-12 weeks (OR: 1.05, 95% CI: 1.02-1.09, p = 0.013 for a 10 µg/m3 increase of PM2.5; OR: 1.03, 95% CI: 1.01-1.06, p = 0.021 for a 10 µg/m3 increase of PM10). Cleft lip and cleft palate were associated with PM10 in germinal period and early fetal period. The CAs of eye, ear, face and neck were related to CO in preantral follicle stage. We did not find an association between chromosome abnormalities and air pollution exposure. CONCLUSIONS: We concluded that ambient air pollution was a risk factor for congenital anomalies in the fetuses conceived through IVF, especially exposure in early fetal period.


Asunto(s)
Contaminantes Atmosféricos , Contaminación del Aire , Contaminantes Atmosféricos/análisis , Contaminantes Atmosféricos/toxicidad , Contaminación del Aire/análisis , Contaminación del Aire/estadística & datos numéricos , Niño , China/epidemiología , Estudios Transversales , Femenino , Fertilización In Vitro , Humanos , Material Particulado/análisis , Material Particulado/toxicidad , Parto , Embarazo
10.
ACS Catal ; 11(5): 2504-2510, 2021 Mar 05.
Artículo en Inglés | MEDLINE | ID: mdl-34667656

RESUMEN

Using deuterium-labeled stereochemical probes, we show that primary alkyltrifluoroborate nucleophiles undergo transmetalation to palladium exclusively via a stereoretentive pathway and that the resulting stereospecificity is broadly independent of electronic and steric effects. This stands in stark contrast to the stereochemical course of transmetalation for secondary alkyltrifluoroborates, which varies between net stereoretention and net stereoinversion depending upon the electronic properties of the supporting phosphine ligand, the electronic properties of the aryl electrophile, and the steric properties of the alkylboron nucleophile. In this study, we additionally show that the stereochemical course of transmetalation for secondary alkylboron reagents can be under reagent steric control, while no such steric control exists for analogous primary alkylboron nucleophiles. The combined study reveals fundamental mechanistic differences between transmetalations of primary and secondary alkylboron reagents in Pd-catalyzed Suzuki reactions.

11.
Sci Total Environ ; 770: 144845, 2021 May 20.
Artículo en Inglés | MEDLINE | ID: mdl-33736390

RESUMEN

One of the largest "green tide" (Ulva prolifera) outbreaks in the world has occurred every year from 2007 to present in the Southern Yellow Sea, China. Currently, the coastal area around Jiangsu Province (Subei Shoal region) is thought to be the origination point of these giant green tide blooms. The combination of high nutrient demand but low river discharge and other inputs suggests that there is a significant flux of submarine groundwater discharge (SGD) in this area. By using a radium mass balance model, we estimated the SGD flux in the area to be (0.7-1.4) × 109 m3 d-1 (6.1-12 cm d-1), at the high end of SGD fluxes worldwide. Geographically, Subei Shoal is less than 5% of the entire Southern Yellow Sea area, while our calculated SGD flux just for the shoal area is ~3 times larger than previously documented for the whole Southern Yellow Sea. Therefore, Subei Shoal may be considered a SGD hotspot that plays an important role in SGD associated material fluxes. Compared to inputs from local rivers, atmospheric deposition, and anthropogenic activities, SGD-derived nutrients are the main source term that can support the growth of macroalgae. We specifically highlight that this type of areas that are shallow, intensively mixed, anthropogenically polluted, sandy or muddy with heavy bio-irrigation, may have a higher risk of suffering harmful ecological problems, even with limited terrestrial runoff.


Asunto(s)
Monitoreo del Ambiente , Agua Subterránea , China , Nutrientes , Ríos
12.
Nat Chem Biol ; 16(12): 1293-1302, 2020 12.
Artículo en Inglés | MEDLINE | ID: mdl-33199906

RESUMEN

We live in the era of antibiotic resistance, and this problem will progressively worsen if no new solutions emerge. In particular, Gram-negative pathogens present both biological and chemical challenges that hinder the discovery of new antibacterial drugs. First, these bacteria are protected from a variety of structurally diverse drugs by a low-permeability barrier composed of two membranes with distinct permeability properties, in addition to active drug efflux, making this cell envelope impermeable to most compounds. Second, chemical libraries currently used in drug discovery contain few compounds that can penetrate Gram-negative bacteria. As a result of these challenges, intensive screening campaigns have led to few successes, highlighting the need for new approaches to identify regions of chemical space that are specifically relevant to antibacterial drug discovery. Herein we provide an overview of emerging insights into this problem and outline a general approach to addressing it using prospective analysis of chemical libraries for the ability of compounds to accumulate in Gram-negative bacteria. The overall goal is to develop robust cheminformatic tools to predict Gram-negative permeation and efflux, which can then be used to guide medicinal chemistry campaigns and the design of antibacterial discovery libraries.


Asunto(s)
Antibacterianos/farmacología , Membrana Celular/efectos de los fármacos , Quimioinformática/métodos , Bacterias Gramnegativas/efectos de los fármacos , Modelos Estadísticos , Bibliotecas de Moléculas Pequeñas/farmacología , Antibacterianos/química , Transporte Biológico , Membrana Celular/química , Membrana Celular/metabolismo , Permeabilidad de la Membrana Celular , Química Farmacéutica , Simulación por Computador , Descubrimiento de Drogas , Farmacorresistencia Bacteriana Múltiple , Bacterias Gramnegativas/química , Bacterias Gramnegativas/metabolismo , Humanos , Porinas/química , Porinas/metabolismo , Bibliotecas de Moléculas Pequeñas/química , Relación Estructura-Actividad
13.
Biomed Res Int ; 2020: 6954793, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32626756

RESUMEN

BACKGROUND: Clear cell renal cell carcinoma (ccRCC) is the most common subtype of kidney cancer, which represents the 9th most frequently diagnosed cancer. However, the molecular mechanism of occurrence and development of ccRCC is indistinct. Therefore, the research aims to identify the hub biomarkers of ccRCC using numerous bioinformatics tools and functional experiments. METHODS: The public data was downloaded from the Gene Expression Omnibus (GEO) database, and the differently expressed genes (DEGs) between ccRCC and normal renal tissues were identified with GEO2R. Protein-protein interaction (PPI) network of the DEGs was constructed, and hub genes were screened with cytoHubba. Then, ten ccRCC tumor samples and ten normal kidney tissues were obtained to verify the expression of hub genes with the RT-qPCR. Finally, the neural network model was constructed to verify the relationship among the genes. RESULTS: A total of 251 DEGs and ten hub genes were identified. AURKB, CCNA2, TPX2, and NCAPG were highly expressed in ccRCC compared with renal tissue. With the increasing expression of AURKB, CCNA2, TPX2, and NCAPG, the pathological stage of ccRCC increased gradually (P < 0.05). Patients with high expression of AURKB, CCNA2, TPX2, and NCAPG have a poor overall survival. After the verification of RT-qPCR, the expression of hub genes was same as the public data. And there were strong correlations between the AURKB, CCNA2, TPX2, and NCAPG with the verification of the neural network model. CONCLUSION: After the identification and verification, AURKB, CCNA2, TPX2, and NCAPG might be related to the occurrence and malignant progression of ccRCC.


Asunto(s)
Carcinoma de Células Renales , Biología Computacional/métodos , Neoplasias Renales , Biomarcadores de Tumor/genética , Biomarcadores de Tumor/metabolismo , Carcinoma de Células Renales/genética , Carcinoma de Células Renales/metabolismo , Carcinoma de Células Renales/mortalidad , Carcinoma de Células Renales/patología , Progresión de la Enfermedad , Humanos , Neoplasias Renales/genética , Neoplasias Renales/metabolismo , Neoplasias Renales/mortalidad , Neoplasias Renales/patología , Redes Neurales de la Computación , Mapas de Interacción de Proteínas/genética , Transcriptoma/genética
14.
Chem ; 6(3): 781-791, 2020 Mar 12.
Artículo en Inglés | MEDLINE | ID: mdl-32440572

RESUMEN

A novel strategy employing cyclohexyl spectator ligands in Stille cross-coupling reactions has been developed as a general solution to the long-standing challenge of conducting stereospecific cross-coupling reactions at nitrogen-containing stereocenters. This method enables direct access to enantioenriched products that are difficult (or impossible) to obtain via alternative preparative methods. Selective and predictable transfer of a single secondary alkyl unit can be achieved under reaction conditions that exploit subtle electronic differences between activated and unactivated alkyl units. Through this approach, enantioenriched α-stannylated nitrogen-containing stereocenters undergo Pd-catalyzed arylation and acylation reactions with exceptionally high stereofidelity in all instances investigated. We demonstrate this process by using α-stannylated pyrrolidine, azetidine, and open-chain (benzylic and non-benzylic) nucleophiles in stereospecific reactions. This process will facilitate rapid and reliable access to enantioenriched compounds possessing nitrogen-substituted stereocenters, which constitute ubiquitous structural motifs in biologically active compounds emerging from the drug-discovery process.

15.
Sci Total Environ ; 719: 137450, 2020 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-32120100

RESUMEN

The Changjiang (Yangtze) River Estuary (CJE) is one of the largest and most intense seasonal hypoxic zones in the world. Here we examine the possibility that submarine groundwater discharge (SGD) may contribute to the summer hypoxia. Spatial distributions of bottom water 222Rn suggest a hotspot discharge area in the northern section of the CJE. SGD fluxes were estimated based on a 222Rn mass balance model and were found to range from 0.002 ± 0.004 to 0.022 ± 0.011 m3/m2/day. Higher SGD fluxes were observed during summer hypoxia period. The well-developed overlap of the distribution patterns for SGD flux and dissolved oxygen (DO) implies that SGD could be an important contributor to summer hypoxia in the region off the CJE. We suggest that SGD contributes to the seasonal hypoxia either: (1) directly via discharge of anoxic groundwaters together with reducing substances; and/or (2) indirectly by delivering excess nutrients that stimulate primary productivity with consequent consumption of DO during organic matter decomposition.

16.
Chemosphere ; 214: 250-258, 2019 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-30265932

RESUMEN

Radium isotopes are known to be excellent geochemical tracers for study of oceanographic processes. We show here that radium isotopes can also be used to assess adsorption/desorption and transport processes in rivers. The Yellow River (Huanghe), one of the longest, most turbid and heavily regulated rivers in the world, is used as an example. We first investigated the temporal and spatial behavior of radium isotopes (224Ra and 226Ra) in the lower reaches of the river, and found that this zone displayed some of the highest known riverine radium concentrations and fluxes in the world. Suspended particulate matter (SPM) is shown to be the dominant factor controlling radium activities. Laboratory simulation experiments showed that radium desorption from SPM obeys an exponential relationship in fresh water (S = 0). When salinities are >10, the increase in radium concentration follows a linear increase with respect to the amounts of SPM added. Significantly higher radium concentrations (3-5 times), especially for short-lived 224Ra, were observed during the "Water-Sediment Regulation Scheme" (WSRS), an annual management event when ∼15%-55% of the annual water discharge and ∼30%-75% of the annual sediment load are released from a reservoir to control sedimentation in the Yellow River. The radium fluxes during WSRS periods (∼2 weeks long) accounted for more than half of the entire annual load during the periods studied. Sediment erosion and pore water release are also thought to be important processes supplying radium to the river. After a WSRS, Ra desorption from SPM increases and becomes the prevailing process.


Asunto(s)
Radio (Elemento)/análisis , Ríos/química , Contaminantes Radiactivos del Agua/análisis , Monitoreo del Ambiente/métodos , Sedimentos Geológicos/química , Material Particulado/análisis
17.
Science ; 362(6415): 670-674, 2018 11 09.
Artículo en Inglés | MEDLINE | ID: mdl-30237245

RESUMEN

Despite the enormous potential for the use of stereospecific cross-coupling reactions to rationally manipulate the three-dimensional structure of organic molecules, the factors that control the transfer of stereochemistry in these reactions remain poorly understood. Here we report a mechanistic and synthetic investigation into the use of enantioenriched alkylboron nucleophiles in stereospecific Pd-catalyzed Suzuki cross-coupling reactions. By developing a suite of molecular descriptors of phosphine ligands, we could apply predictive statistical models to select or design distinct ligands that respectively promoted stereoinvertive and stereoretentive cross-coupling reactions. Stereodefined branched structures were thereby accessed through the predictable manipulation of absolute stereochemistry, and a general model for the mechanism of alkylboron transmetallation was proposed.

18.
J Am Chem Soc ; 136(40): 14027-30, 2014 Oct 08.
Artículo en Inglés | MEDLINE | ID: mdl-25226092

RESUMEN

We report the development of a Pd-catalyzed process for the stereospecific cross-coupling of unactivated secondary alkylboron nucleophiles and aryl chlorides. This process tolerates the use of secondary alkylboronic acids and secondary alkyltrifluoroborates and occurs without significant isomerization of the alkyl nucelophile. Optically active secondary alkyltrifluoroborate reagents undergo cross-coupling reactions with stereospecific inversion of configuration using this method.


Asunto(s)
Alcanos/química , Derivados del Benceno/química , Boro/química , Cloro/química , Paladio/química , Catálisis , Estereoisomerismo
19.
ScientificWorldJournal ; 2014: 384649, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-25097876

RESUMEN

PURPOSE: Researchers developed evaluation tools measuring employment relevant satisfaction for nursing new graduates. The evaluation tools were designed to be relevant to nursing managers who make employment decisions and nursing new graduates who were just employed. METHODS: In-depth interviews and an expert panel were established to review the activities that evaluate the employee and employer satisfaction of nursing new graduates. Based on individual interviews and literature review, evaluation items were selected. A two-round Delphi study was then conducted from September 2008 to May 2009 with a panel of experts from a range of nursing colleges in China. RESULTS: The response rate was 100% and Kendall's W was 0.73 in the second round of Delphi study. After two rounds of Delphi surveys, a list of 5 employee satisfaction items and 4 employer satisfaction items was identified for nursing new graduates. CONCLUSIONS: The findings of this study identified a different but multidimensional set of factors for employment relevant satisfaction, which confirmed the importance of certain fundamental aspects of practice. We developed the evaluation tools to assess the employer and employee satisfaction of nursing new graduates, which provided a database for further study.


Asunto(s)
Evaluación del Rendimiento de Empleados/métodos , Satisfacción en el Trabajo , Enfermeras y Enfermeros/psicología , China , Educación de Postgrado en Enfermería/normas , Enfermeras y Enfermeros/normas
20.
Med Teach ; 36(11): 973-7, 2014 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-25072750

RESUMEN

In 2008, China established a medical school accreditation process based on international standards and guidelines. Twenty schools had been accredited by 2013 and it is intended to accredit all 137 schools by 2020. To achieve this ambitious aim, Chinese medical educators have entered into collaboration with their Australian counterparts, engendered by mutual membership of the Association for Medical Education in the Western Pacific Region, a regional division of the World Federation for Medical Education. The collaboration began in 2000 as informal discussions at regional meetings and has since developed three major components: workshops held throughout China for potential assessors and for medical schools undergoing accreditation; visits by Chinese accreditors to Australia to observe Australian Medical Council processes; and participation by Australian assessors in the accreditation of Chinese medical schools. The incremental steps that led to this unique bi-national venture are outlined in the context of other international developments in accreditation of medical education. Then, the preparation, piloting and implementation of accreditation standards and guidelines with Chinese specifications are described. Finally, the outcomes achieved thus far and the challenges remaining are discussed.


Asunto(s)
Acreditación/organización & administración , Conducta Cooperativa , Educación Médica/organización & administración , Internacionalidad , Facultades de Medicina/organización & administración , Australia , China , Curriculum , Educación Médica/normas , Humanos , Facultades de Medicina/normas
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