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1.
Curr Microbiol ; 2021 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-33813642

RESUMO

A Gram-stain-negative, yellow-pigmented, rod-shaped, strictly aerobic, non-motile bacterium, designated BDHS18T, was isolated from the sediment of the Hasuhai Lake, China. Phylogenetic analysis based on 16S rRNA gene sequences revealed that this strain belongs to the genus Moheibacter in the family Flavobacteriaceae and its closest relative was Moheibacter sediminis JCM 19634T (96.0%), followed by Moheibacter stercoris DSM 29388T (95.3%). Cells of strain BDHS18T were catalase-positive and oxidase-negative. Strain BDHS18T was found to grow optimally at 28-33 â„ƒ, pH 7.5-8.0, and in the presence of approximately 1.0% (w/v) NaCl. Major cellular fatty acids were iso-C15:0, iso-C17:0 3-OH, Summed feature 4 and Summed feature 9. The predominant respiratory quinone was MK-6. The predominant polar lipids in strain BDHS18T were phosphatidylethanolamine, phosphatidylglycerol, one unidentified aminolipid and one unidentified lipid. The DNA G + C content was 36.9 mol%. According to the phylogenetic analysis, physiological and phenotypic characteristics, strain BDHS18T represents a novel species of the genus Moheibacter, for which the name Moheibacter lacus sp. nov. is proposed. The type strain is BDHS18T (= KCTC 72160T = MCCC 1H00369T).

2.
Arch Microbiol ; 2021 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-33655407

RESUMO

A novel Gram-stain-negative, aerobic, non-flagellated, non-motile, oval-rod-shaped and light pink to light tawny-pigmented bacterial strain (designated 1151T) were isolated from marine green algae obtained from the coastal seawater of Weihai, China. Strain 1151T was found to grow at 15-37 °C (optimum, 33 °C), pH 7.0-9.5 (optimum, 7.5-8.5) and in the presence of 1-6% (w/v) NaCl (optimum, 3%). Cells were oxidase-positive and catalase-positive. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 1151T was a member of the genus Sulfitobacter and exhibited the hightest sequence similarity to Sulfitobacter indolifex DSM 14862T (96.6%), followed by the sequence similarity to Sulfitobacter aestuarii hydD52T (96.5%) and Sulfitobacter profundi SAORIC-263T (96.5%). The average nucleotide identity and digital DDH values between strain 1151T and Sulfitobacter indolifex DSM 14862T were 69.9% and 20.9%, respectively. The average amino acid identity between strain 1151T and Sulfitobacter pontiacus DSM 10014T (type strain of the type species) was 62.3%. Q-10 was detected as the sole respiratory quinone. The dominant cellular fatty acids were sum feature 8 (C18: 1ω7c; 44.1%), C20: 1ω7c (29.7%) and C18: 0 (11.7%). The DNA G + C content of strain 1151T was 51.8 mol%. The polar lipids included phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidylcholine (PC), and three unidentified lipids (L1, L2 and L3). Based on the phylogenetic and phenotypic characteristics, strain 1151T is considered to represent a novel species of the genus Sulfitobacter, for which the name Sulfitobacter algicola sp. nov. is proposed. The type strain is 1151T (= KCTC 72513T = MCCC 1H00384T).

3.
J Biophotonics ; : e202000443, 2021 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-33576160

RESUMO

Motion correction is an important issue in ophthalmic optical coherence tomography (OCT), and can improve the ability of data sets to reflect the physiological structures of tissues and make visualization and subsequent analysis easier. In this study, we present a novel method to correct the cross-sectional motion artifacts in retinal OCT volumes. Motion along the x-direction (fast-scan direction) is corrected through the normalized cross-correlation algorithm, while axial motion compensation is performed using the polynomial fitting method on the inner segment/outer segment (IS/OS) layer segmented by the shortest path faster algorithm (SPFA). The results of volunteers with central serous chorioretinopathy demonstrate that the proposed method effectively corrects motion artifacts in OCT volumes and may have potential application value in the evaluation of ophthalmic diseases such as diabetic retinopathy, glaucoma and age-related macular degeneration.

4.
J Transl Med ; 19(1): 66, 2021 02 12.
Artigo em Inglês | MEDLINE | ID: mdl-33579301

RESUMO

BACKGROUND: Microbes are closely related to human health and diseases. Identification of disease-related microbes is of great significance for revealing the pathological mechanism of human diseases and understanding the interaction mechanisms between microbes and humans, which is also useful for the prevention, diagnosis and treatment of human diseases. Considering the known disease-related microbes are still insufficient, it is necessary to develop effective computational methods and reduce the time and cost of biological experiments. METHODS: In this work, we developed a novel computational method called MDAKRLS to discover potential microbe-disease associations (MDAs) based on the Kronecker regularized least squares. Specifically, we introduced the Hamming interaction profile similarity to measure the similarities of microbes and diseases besides Gaussian interaction profile kernel similarity. In addition, we introduced the Kronecker product to construct two kinds of Kronecker similarities between microbe-disease pairs. Then, we designed the Kronecker regularized least squares with different Kronecker similarities to obtain prediction scores, respectively, and calculated the final prediction scores by integrating the contributions of different similarities. RESULTS: The AUCs value of global leave-one-out cross-validation and 5-fold cross-validation achieved by MDAKRLS were 0.9327 and 0.9023 ± 0.0015, which were significantly higher than five state-of-the-art methods used for comparison. Comparison results demonstrate that MDAKRLS has faster computing speed under two kinds of frameworks. In addition, case studies of inflammatory bowel disease (IBD) and asthma further showed 19 (IBD), 19 (asthma) of the top 20 prediction disease-related microbes could be verified by previously published biological or medical literature. CONCLUSIONS: All the evaluation results adequately demonstrated that MDAKRLS has an effective and reliable prediction performance. It may be a useful tool to seek disease-related new microbes and help biomedical researchers to carry out follow-up studies.

5.
Science ; 371(6529): 589-595, 2021 02 05.
Artigo em Inglês | MEDLINE | ID: mdl-33542130

RESUMO

Iodic acid (HIO3) is known to form aerosol particles in coastal marine regions, but predicted nucleation and growth rates are lacking. Using the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we find that the nucleation rates of HIO3 particles are rapid, even exceeding sulfuric acid-ammonia rates under similar conditions. We also find that ion-induced nucleation involves IO3 - and the sequential addition of HIO3 and that it proceeds at the kinetic limit below +10°C. In contrast, neutral nucleation involves the repeated sequential addition of iodous acid (HIO2) followed by HIO3, showing that HIO2 plays a key stabilizing role. Freshly formed particles are composed almost entirely of HIO3, which drives rapid particle growth at the kinetic limit. Our measurements indicate that iodine oxoacid particle formation can compete with sulfuric acid in pristine regions of the atmosphere.

7.
Nat Commun ; 12(1): 757, 2021 02 03.
Artigo em Inglês | MEDLINE | ID: mdl-33536423

RESUMO

Chordoma is a rare bone tumor with an unknown etiology and high recurrence rate. Here we conduct whole genome sequencing of 80 skull-base chordomas and identify PBRM1, a SWI/SNF (SWItch/Sucrose Non-Fermentable) complex subunit gene, as a significantly mutated driver gene. Genomic alterations in PBRM1 (12.5%) and homozygous deletions of the CDKN2A/2B locus are the most prevalent events. The combination of PBRM1 alterations and the chromosome 22q deletion, which involves another SWI/SNF gene (SMARCB1), shows strong associations with poor chordoma-specific survival (Hazard ratio [HR] = 10.55, 95% confidence interval [CI] = 2.81-39.64, p = 0.001) and recurrence-free survival (HR = 4.30, 95% CI = 2.34-7.91, p = 2.77 × 10-6). Despite the low mutation rate, extensive somatic copy number alterations frequently occur, most of which are clonal and showed highly concordant profiles between paired primary and recurrence/metastasis samples, indicating their importance in chordoma initiation. In this work, our findings provide important biological and clinical insights into skull-base chordoma.


Assuntos
Cordoma/genética , Proteínas de Ligação a DNA/genética , Predisposição Genética para Doença/genética , Proteína SMARCB1/genética , Neoplasias da Base do Crânio/genética , Fatores de Transcrição/genética , Sequenciamento Completo do Genoma/métodos , Adulto , Cordoma/patologia , Variações do Número de Cópias de DNA , Feminino , Genômica/métodos , Humanos , Estimativa de Kaplan-Meier , Masculino , Pessoa de Meia-Idade , Mutação , Recidiva Local de Neoplasia , Neoplasias da Base do Crânio/patologia , Adulto Jovem
8.
Microb Pathog ; 150: 104717, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33421608

RESUMO

Helicobacter pylori (H. pylori) is one of the most important pathogenic bacteria associated with various gastrointestinal diseases. At present, its apoptotic or antiapoptotic mechanism on gastric epithelial cells remains unknown and needs further illustrated. In this study, acute infection model (H. pylori and GES-1 cells were co-cultured for 24 h at a multiplicity of infection MOI of 100:1) and chronic infection model (GES-1 cells were infected repeatedly every 24 h at a multiplicity of infection MOI of 100:1 for approximately 8 weeks) were established, respectively. the chronic H. pylori infected GES-1 cells underwent a typically morphological change and Western Blot results showed that there was slight decrease in expression of E-cadherin, and obvious increase in expression of Vimentin. Apoptosis of these two models were analyzed by flow cytometry compared with the control cells, meanwhile, apoptosis associated markers (Bcl-xL, Bcl-2, Bax, etc) were detected by Western blot, additional in clinical H. pylori-positive gastric cancer tissues. Results showed that compared with the control cells, acute infection of H. pylori significantly accelerated the apoptosis of GES-1, increased the expression of Bax and Cleaved caspase-3, down-regulated expression of Bcl-xL and Bcl-2. Moreover, an opposite result was found in chronic infection of model and clinical gastric cancer tissues, and enhanced expression of NF-κB p65. Taken together, these findings suggest that H. pylori infection plays differential effects on apoptosis of gastric epithelial cells.

9.
J Biophotonics ; : e202000411, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33449425

RESUMO

Blood flow functional imaging is widely applied in biological research to provide vascular morphological and statistical parameters. It relies on the absorption difference and is, therefore, easily affected by complex biological structures, and it cannot accommodate abundant functional information. We propose a full-field multi-functional angiography method to classify arteriovenous vessels and to display flow velocity and vascular diameter distribution simultaneously. Unlike previous methods, an under-sampled laser Doppler acquisition mode is used to record the low-coherence speckle, and multi-functional angiography is achieved by modulating the endogenous hemodynamic characteristics from low-coherence speckle. To demonstrate the combination of classified angiography, blood flow velocity measurement, and vascular diameter measurement realized using our method, we performed experiments on the flow phantom and living chicken embryos and generated multi-functional angiograms. The proposed method can be used as a label-free multi-functional angiography technique in which red blood cells provide a strong endogenous source of naturally hemodynamic characteristics.

10.
Aging Med (Milton) ; 3(3): 159-168, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33103036

RESUMO

Aging is a major risk factor for quintessential cardiovascular diseases, which are closely related to arterial proinflammation. The age-related alterations of the amount, distribution, and properties of the collagen fibers, such as cross-links and degradation in the arterial wall, are the major sequelae of proinflammation. In the aging arterial wall, collagen types I, II, and III are predominant,  and are mainly produced by stiffened vascular smooth muscle cells (VSMCs) governed by proinflammatory signaling, leading to profibrosis. Profibrosis is regulated by an increase in the proinflammatory molecules angiotensin II, milk fat globule-EGF-VIII, and transforming growth factor-beta 1 (TGF-ß1) signaling and a decrease in the vasorin signaling cascade. The release of these proinflammatory factors triggers the activation of matrix metalloproteinase type II (MMP-2) and activates profibrogenic TGF-ß1 signaling, contributing to profibrosis. The age-associated increase in activated MMP-2 cleaves latent TGF-ß and subsequently increases TGF-ß1 activity leading to collagen deposition in the arterial wall. Furthermore, a blockade of the proinflammatory signaling pathway alleviates the fibrogenic signaling, reduces profibrosis, and prevents arterial stiffening with aging. Thus, age-associated proinflammatory-profibrosis coupling is the underlying molecular mechanism of arterial stiffening with advancing age.

11.
J Biophotonics ; : e202000292, 2020 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-33107151

RESUMO

Based on the numerical analysis that covariance exhibits superior statistical precision than cumulant and variance, a new SOFI algorithm by calculating the n orders covariance for each pixel is presented with an almost 2 n -fold resolution improvement, which can be enhanced to 2n via deconvolution. An optimized deconvolution is also proposed by calculating the (n + 1) order SD associated with each n order covariance pixel, and introducing the results into the deconvolution as a damping factor to suppress noise generation. Moreover, a re-deconvolution of the covariance image with the covariance-equivalent point spread function is used to further increase the final resolution by above 2-fold. Simulated and experimental results show that this algorithm can significantly increase the temporal-spatial resolution of SOFI, meanwhile, preserve the sample's structure. Thus, a resolution of 58 nm is achieved for 20 experimental images, and the corresponding acquisition time is 0.8 seconds.

12.
Int J Nanomedicine ; 15: 6593-6603, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32982220

RESUMO

Purpose: Micro-arc oxidation (MAO) is a fast and effective method to prepare nanoporous coatings with high biological activity and bonding strength. Simple micro/nano-coatings cannot fully meet the requirements of osteogenesis. To further improve the biological activity of a titanium surface, we successfully added biological magnesium (Mg2+) to a coating by micro-arc oxidation and evaluated the optimal magnesium concentration in the electrolyte, biocompatibility, cell adhesion, proliferation, and osteogenesis in vitro. Methods: Nanoporous titanium coatings with different concentrations of magnesium were prepared by micro-arc oxidation and characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The Mg2+ release ability of the magnesium-incorporated nanoporous titanium coatings was determined by inductively coupled plasma emission spectrometry (ICP-OES). The cytotoxicity of the magnesium-incorporated nanoporous titanium coatings was detected with live/dead double-staining tests. A CCK-8 assay was employed to evaluate cell proliferation, and FITC-phalloidin was used to determine the structure of the cytoskeleton by staining ß-actin. Alkaline phosphatase (ALP) activity was evaluated by alizarin red S (ARS) staining to determine the effect of the coatings on osteogenic differentiation in vitro. The mRNA expression of osteogenic differentiation-related markers was measured using qRT-PCR. Results: EDS analyses revealed the successful addition of magnesium to the microporous coatings. The best magnesium concentration of the electrolyte for preparing the new coating was determined. The results showed that the nano-coatings prepared using the electrolyte with 2 g/L magnesium acetate best promoted the adhesion, proliferation, and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Conclusion: These results suggest that the new titanium metal coating with a dual effect of promoting bone morphology and supplying the biological ion Mg2+ can be beneficial for rapid osseointegration.

13.
Future Microbiol ; 15: 1101-1107, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32795131

RESUMO

Since December 2019, an outbreak of SARS coronavirus 2 (SARS-CoV-2) began in Wuhan, and has rapidly spread worldwide. Previously, discharged patients with coronavirus disease 2019 (COVID-19) patients met the criteria of China's pneumonia diagnosis and treatment program of novel coronavirus infection (trial version 7) for cure of viral infection. Nevertheless, positive detection of SARS-CoV-2 has been found again in several cured COVID-19 patients, leading to conflicts with current criteria. Here, we report clinically cured cases with positive results only in anal swabs, and investigate the clinical value of anal swabs for SARS-CoV-2 detection.


Assuntos
Canal Anal/virologia , Betacoronavirus/isolamento & purificação , Infecções por Coronavirus/virologia , Pneumonia Viral/virologia , Adulto , Pré-Escolar , Técnicas de Laboratório Clínico/métodos , Infecções por Coronavirus/diagnóstico , Infecções por Coronavirus/diagnóstico por imagem , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Pandemias , Alta do Paciente , Pneumonia Viral/diagnóstico por imagem , Reação em Cadeia da Polimerase em Tempo Real , Adulto Jovem
14.
Future Microbiol ; 15: 981-985, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32815419

RESUMO

Eggerthella lenta is an emerging and uncommon human pathogen that has been under recognized due to the limitations of phenotypic identification. Here we describe two cases of bacteremia caused by E. lenta and summarize the results of antimicrobial susceptibility testing according to some previous literatures, which illustrate the importance of identification and treatment of unusual organisms. The most reliable antibiotic treatment options to E. lenta appear to be metronidazole, amoxicillin-clavulanate, carbapenems, vancomycin, cefoxitin, chloramphenicol and clindamycin.

15.
Sci Rep ; 10(1): 12898, 2020 07 30.
Artigo em Inglês | MEDLINE | ID: mdl-32732891

RESUMO

It is challenging to identify somatic variants from high-throughput sequence reads due to tumor heterogeneity, sub-clonality, and sequencing artifacts. In this study, we evaluated the performance of eight primary somatic variant callers and multiple ensemble methods using both real and synthetic whole-genome sequencing, whole-exome sequencing, and deep targeted sequencing datasets with the NA12878 cell line. The test results showed that a simple consensus approach can significantly improve performance even with a limited number of callers and is more robust and stable than machine learning based ensemble approaches. To fully exploit the multi-callers, we also developed a software package, SomaticCombiner, that can combine multiple callers and integrates a new variant allelic frequency (VAF) adaptive majority voting approach, which can maintain sensitive detection for variants with low VAFs.

16.
Nat Commun ; 11(1): 3096, 2020 06 18.
Artigo em Inglês | MEDLINE | ID: mdl-32555180

RESUMO

Intratumor heterogeneity (ITH) and tumor evolution have been well described for clear cell renal cell carcinomas (ccRCC), but they are less studied for other kidney cancer subtypes. Here we investigate ITH and clonal evolution of papillary renal cell carcinoma (pRCC) and rarer kidney cancer subtypes, integrating whole-genome sequencing and DNA methylation data. In 29 tumors, up to 10 samples from the center to the periphery of each tumor, and metastatic samples in 2 cases, enable phylogenetic analysis of spatial features of clonal expansion, which shows congruent patterns of genomic and epigenomic evolution. In contrast to previous studies of ccRCC, in pRCC, driver gene mutations and most arm-level somatic copy number alterations (SCNAs) are clonal. These findings suggest that a single biopsy would be sufficient to identify the important genetic drivers and that targeting large-scale SCNAs may improve pRCC treatment, which is currently poor. While type 1 pRCC displays near absence of structural variants (SVs), the more aggressive type 2 pRCC and the rarer subtypes have numerous SVs, which should be pursued for prognostic significance.


Assuntos
Carcinoma de Células Renais/genética , Neoplasias Renais/genética , Variações do Número de Cópias de DNA/genética , Epigenômica , Mutação em Linhagem Germinativa/genética , Humanos , Filogenia
17.
Environ Sci Technol ; 54(13): 7911-7921, 2020 07 07.
Artigo em Inglês | MEDLINE | ID: mdl-32515954

RESUMO

To better understand the role of aromatic hydrocarbons in new-particle formation, we measured the particle-phase abundance and volatility of oxidation products following the reaction of aromatic hydrocarbons with OH radicals. For this we used thermal desorption in an iodide-adduct Time-of-Flight Chemical-Ionization Mass Spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-ToF-CIMS). The particle-phase volatility measurements confirm that oxidation products of toluene and naphthalene can contribute to the initial growth of newly formed particles. Toluene-derived (C7) oxidation products have a similar volatility distribution to that of α-pinene-derived (C10) oxidation products, while naphthalene-derived (C10) oxidation products are much less volatile than those from toluene or α-pinene; they are thus stronger contributors to growth. Rapid progression through multiple generations of oxidation is more pronounced in toluene and naphthalene than in α-pinene, resulting in more oxidation but also favoring functional groups with much lower volatility per added oxygen atom, such as hydroxyl and carboxylic groups instead of hydroperoxide groups. Under conditions typical of polluted urban settings, naphthalene may well contribute to nucleation and the growth of the smallest particles, whereas the more abundant alkyl benzenes may overtake naphthalene once the particles have grown beyond the point where the Kelvin effect strongly influences the condensation driving force.


Assuntos
Hidrocarbonetos Aromáticos , Compostos Orgânicos Voláteis , Aerossóis , Gases , Volatilização
18.
Health Sci Rep ; 3(2): e155, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32382660

RESUMO

Background and aims: Guatemala has the highest incidence of hepatocellular carcinoma (HCC) in the Western hemisphere. The major risk factors in Guatemala are not well characterized, but the prevalence of hepatitis B virus (HBV) and hepatitis C virus (HCV) appears to be low, while the prevalence of aflatoxin (AFB1) exposure appears to be high. To examine whether AFB1 may contribute to the elevated incidence of HCC in Guatemala, this study examined the frequency of the AFB1-signature mutation in the TP53 gene (R249S) as well as other somatic mutations. In addition, we assessed whether the frequency of the TP53 mutation differed by sex. Methods: Formalin-fixed, paraffin-embedded (FFPE) HCC tissues were obtained from three hospitals in Guatemala City between 2016 and 2017. In addition, tumor tissues preserved in RNAlater were also obtained. Sociodemographic and clinical information including HBV and HCV status were collected. Targeted sequencing of TP53 was performed in the FFPE samples, and a panel of 253 cancer-related genes was sequenced in the RNAlater samples. Results: Ninety-one FFPE tissues were examined, from 52 men and 39 women. Median (IQR) age at diagnosis was 62 (51-70). Among those with known HBV and HCV status, two were HBV+ and three were HCV+. Overall, 47% of the HCCs had a TP53 mutation. The AFB1-signature R249S mutation was present in 24%. No overlap between the R249S mutation and HBV+ was observed in this cohort. Among 18 RNAlater samples examined, 44% had any TP53 mutation and 33% had the R249S mutation. Other somatic mutations were identified in known HCC driver genes. Conclusions: The presence of the TP53 R249S mutation in the samples studied suggests that AFB1 may contribute to the high incidence of HCC in Guatemala. The proportion of HBV+ tumors was low, suggesting that AFB1 may be associated with HCC in the absence of concomitant HBV infection. Further investigation of AFB1 and other risk factors for HCC in Guatemala is warranted.

19.
Nat Commun ; 11(1): 2459, 2020 05 18.
Artigo em Inglês | MEDLINE | ID: mdl-32424208

RESUMO

Intratumor heterogeneity (ITH) of genomic alterations may impact prognosis of lung adenocarcinoma (LUAD). Here, we investigate ITH of somatic copy number alterations (SCNAs), DNA methylation, and point mutations in lung cancer driver genes in 292 tumor samples from 84 patients with LUAD. LUAD samples show substantial SCNA and methylation ITH, and clonal architecture analyses present congruent evolutionary trajectories for SCNAs and DNA methylation aberrations. Methylation ITH mapping to gene promoter areas or tumor suppressor genes is low. Moreover, ITH composed of genetic and epigenetic mechanisms altering the same cancer driver genes is shown in several tumors. To quantify ITH for valid statistical association analyses, we develope an average pairwise ITH index (APITH), which does not depend on the number of samples per tumor. Both APITH indexes for SCNAs and methylation aberrations show significant associations with poor prognosis. This study further establishes the important clinical implications of genetic and epigenetic ITH in LUAD.


Assuntos
Adenocarcinoma de Pulmão/genética , Heterogeneidade Genética , Neoplasias Pulmonares/genética , Idoso , Idoso de 80 Anos ou mais , Ilhas de CpG/genética , Variações do Número de Cópias de DNA , Metilação de DNA/genética , Epigênese Genética , Evolução Molecular , Feminino , Humanos , Estimativa de Kaplan-Meier , Masculino , Pessoa de Meia-Idade , Mutação/genética , Polimorfismo de Nucleotídeo Único/genética , Resultado do Tratamento
20.
Nature ; 581(7807): 184-189, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32405020

RESUMO

A list of authors and their affiliations appears at the end of the paper New-particle formation is a major contributor to urban smog1,2, but how it occurs in cities is often puzzling3. If the growth rates of urban particles are similar to those found in cleaner environments (1-10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below -15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid-base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from the continental boundary layer and nitric acid is abundant from electrical storms4,5.

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