Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 13 de 13
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Nat Commun ; 15(1): 5783, 2024 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-38987267

RESUMO

Water ice and other volatiles that accumulated in the Moon's polar regions are among the top priority targets for lunar exploration, due to their significances in both lunar geology and extraterrestrial resource utilization. Locating suitable landing sites and determining the provenance of sampled/measured surface materials are critical for future landed missions. Here, we map over 800 sites of plains terrains in the Moon's south polar region, with a total surface area of ~46,000 km2. Orbital measurements and analog studies show that most of these plains have apparently higher albedo and lower iron content than volcanic mare plains, suggesting an origin of ejecta-induced debris flows from distant impact craters, especially from the Schrödinger basin. Our findings suggest that the entire lunar south polar region probably have experienced contributions from distant basin materials. We recommend these plains as priority landing sites for future exploration of lunar polar volatiles and early bombardment history.

2.
Polymers (Basel) ; 16(9)2024 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-38732697

RESUMO

Self-consistent field (SCF) theory serves as a robust tool for unraveling the intricate behavior exhibited by soft polymeric materials. However, the accuracy and efficiency of SCF calculations are crucially dependent on the numerical methods employed for system discretization and equation-solving. Here, we introduce a simple three dimensional SCF algorithm that uses real-space methods and adaptive discretization, offering improved accuracy and efficiency for simulating polymeric systems at surfaces. Our algorithm's efficacy is demonstrated through simulations of two distinct polymeric systems, namely, block copolymer (BCP) films and polymer brushes. By enhancing spatial resolution in regions influenced by external forces and employing finer contour discretization at grafting chain ends, we achieve significantly more accurate results at very little additional cost, enabling the study of 3D polymeric systems that were previously computationally challenging. To facilitate the widespread use of the algorithm, we have made our 1D-3D SCF code publicly available.

3.
Macromolecules ; 57(9): 4629-4634, 2024 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-38765499

RESUMO

Sphere-patterned ultrathin block copolymer films are potentially interesting for a variety of applications in nanotechnology. We use self-consistent field theory to investigate the elastic response of sphere monolayer films with respect to in-plane shear, in-plane extension, compression deformations, and bending. The relations between the in-plane elastic moduli are roughly compatible with the expectations for two-dimensional elastic systems with hexagonal symmetry, with one notable exception: The pure shear and the simple shear moduli differ from each other by roughly 20%. Even more importantly, the bending constants are found to be negative, indicating that free-standing block copolymer membranes made of only a sphere monolayer are inherently unstable above the glass transition. Our results are discussed in view of the experimental findings.

4.
Nano Lett ; 23(4): 1343-1349, 2023 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-36705546

RESUMO

We present a new concept for the separation of DNA molecules by contour length that combines a nanofluidic ratchet, nanopore translocation, and pulsed fields. Using Langevin dynamics simulations, we show that it is possible to design pulsed field sequences to ratchet captured semiflexible molecules in such a way that only short chains successfully translocate, effectively transforming the nanopore process into a low pass molecular filter. We also show that asymmetric pulses can significantly enhance the device efficiency. The process itself can be performed with many pores in parallel, and it should be possible to integrate it directly into nanopore sequencing devices, increasing its potential utility.

5.
Phys Chem Chem Phys ; 24(11): 6444-6452, 2022 Mar 16.
Artigo em Inglês | MEDLINE | ID: mdl-35244666

RESUMO

We investigate the translocation of rods with different charge distributions using hybrid Langevin dynamics and lattice Boltzmann (LD-LB) simulations. Electrostatic interactions are added to the system using the P3M algorithm to model the electrohydrodynamic interactions (EHI). We first examine the free-solution electrophoretic properties of rods with various charge distributions. Our translocation simulation results suggest that the order parameter is asymmetric during the capture and escape processes despite the symmetric electric field lines, while the impacts of the charge distribution on rod orientation are more significant during the capture process. The capture/threading/escape times are under the combined effects of charge screening, rod orientation, and charge distributions. We also show that the mean capture time of a rod is shorter when it is launched near the wall because rods tend to align along the wall and hence with the local field lines. Remarkably, the orientational capture radius we proposed previously for uniformly charged rods is still valid in the presence of EHI.


Assuntos
Nanoporos , Simulação por Computador , Eletroforese , Hidrodinâmica , Eletricidade Estática
6.
Sensors (Basel) ; 21(7)2021 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-33916546

RESUMO

Laboratory simulation is the only feasible way to achieve Martian environmental conditions on Earth, establishing a key link between the laboratory and Mars exploration. The mineral phases of some Martian surface materials (especially hydrated minerals), as well as their spectral features, are closely related to environmental conditions. Therefore, Martian environment simulation is necessary for Martian mineral detection and analysis. A Mars environment chamber (MEC) coupled with multiple in situ spectral sensors (VIS (visible)-NIR (near-infrared) reflectance spectroscopy, Raman spectroscopy, laser-induced breakdown spectroscopy (LIBS), and UV-VIS emission spectroscopy) was developed at Shandong University at Weihai, China. This MEC is a comprehensive research platform for Martian environmental parameter simulation, regulation, and spectral data collection. Here, the structure, function and performance of the MEC and the coupled spectral sensors were systematically investigated. The spectral characteristics of some geological samples were recorded and the effect of environmental parameter variations (such as gas pressure and temperature) on the spectral features were also acquired by using the in situ spectral sensors under various simulated Martian conditions. CO2 glow discharge plasma was generated and its emission spectra were assigned. The MEC and its tested functional units worked well with good accuracy and repeatability. China is implementing its first Mars mission (Tianwen-1), which was launched on 23 July 2020 and successfully entered into a Mars orbit on 10 February 2021. Many preparatory works such as spectral databases and prediction model building are currently underway using MECs, which will help us build a solid foundation for real Martian spectral data analysis and interpretation.

7.
Phys Chem Chem Phys ; 23(2): 1489-1499, 2021 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-33400742

RESUMO

To better understand the capture process by a nanopore, we introduce an efficient Kinetic Monte Carlo (KMC) algorithm that can simulate long times and large system sizes by mapping the dynamic of a point-like particle in a 3D spherically symmetric system onto the 1D biased random walk. Our algorithm recovers the steady-state analytical solution and allows us to study time-dependent processes such as transients. Simulation results show that the steady-state depletion zone near pore is barely larger than the pore radius and narrows at higher field intensities; as a result, the time to reach steady-state is much smaller than the time required to empty a zone of the size of the capture radius λe. When the sample reservoir has a finite size, a second depletion region propagates inward from the outer wall, and the capture rate starts decreasing when it reaches the capture radius λe. We also note that the flatness of the electric field near the pore, which is often neglected, induces a traffic jam that can increase the transient time by several orders of magnitude. Finally, we propose a new proof-of-concept scheme to separate two analytes of the same mobility but different diffusion coefficients using time-varying fields.

8.
Mol Ecol ; 30(1): 297-309, 2021 01.
Artigo em Inglês | MEDLINE | ID: mdl-33135269

RESUMO

Morphological traits have served generations of biologists as a taxonomic indicator, and have been the main basis for defining and classifying species diversity for centuries. A quantitative integration of behavioural characters, such as vocalizations, in studies on biotic differentiation has arisen more recently, and the relative importance of these different traits in the diversification process remains poorly understood. To provide a framework within which to interpret the evolutionary interplay between morphological and behavioural traits, we generated a draft genome of a cryptic Southeast Asian songbird, the limestone wren-babbler Napothera crispifrons. We resequenced whole genomes of multiple individuals of all three traditional subspecies and of a distinct leucistic population. We demonstrate strong genomic and mitochondrial divergence among all three taxa, pointing to the existence of three species-level lineages. Despite its great phenotypic distinctness, the leucistic population was characterized by shallow genomic differentiation from its neighbour, with only a few localized regions emerging as highly diverged. Quantitative bioacoustic analysis across multiple traits revealed deep differences especially between the two taxa characterized by limited plumage differentiation. Our study demonstrates that differentiation in these furtive songbirds has resulted in a complex mosaic of colour-based and bioacoustic differences among populations. Extreme colour differences can be anchored in few genomic loci and may therefore arise and subside rapidly.


Assuntos
Aves Canoras , Animais , Evolução Biológica , Cor , Genoma , Humanos , Filogenia , Aves Canoras/genética
9.
J Chem Phys ; 152(14): 144902, 2020 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-32295359

RESUMO

Both the translational diffusion coefficient D and the electrophoretic mobility µ of a short rod-like molecule (such as dsDNA) that is being pulled toward a nanopore by an electric field should depend on its orientation. Since a charged rod-like molecule tends to orient in the presence of an inhomogeneous electric field, D and µ will change as the molecule approaches the nanopore, and this will impact the capture process. We present a simplified study of this problem using theoretical arguments and Langevin dynamics simulations. In particular, we introduce a new orientational capture radius, which we compare to the capture radius for the equivalent point-like particle, and we discuss the different physical regimes of orientation during capture and the impact of initial orientations on the capture time.

10.
Neurosci Lett ; 716: 134647, 2020 01 18.
Artigo em Inglês | MEDLINE | ID: mdl-31765729

RESUMO

BACKGROUND: This study was to investigate the neuroprotective effect of erythropoietin (EPO) on hippocampal neuronal cell injury in developing rats. METHODS: The hippocampal neurons cells were obtained from SD rats aged 10 days and divided into control, propofol, EPO, and propofol + erythropoietin (E + P) groups. Cell proliferation and apoptosis were measured by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Ki-67 immunofluorescence, and flow cytometry, respectively. The levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1ß, IL-6, IL-4 and IL-10 were detected by enzyme-linked immunosorbent assay (ELISA). Cellular immunohistochemistry was utilized to detect the expression of proliferating cell nuclear antigen (PCNA), nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3). Quantitative real time polymerase chain reaction (qRT-PCR) and western blot were used to detect the expression of Bax, Bcl-2, Caspase-3, toll-like receptor 4 (TLR4) and p65. Furthermore, TLR4 antagonist (TAK-242) and activator (LPS) were used to study the relationship between EPO and TLR4. RESULTS: Propofol treatment caused morphological and structural damage of hippocampal neurons. However, EPO significantly improved this damage, enhanced cell proliferation, decreased apoptosis and pro-inflammatory factor content, up-regulated the expression of Ki-67, PCNA, Bcl-2, NGF, BDNF and NT-3, as well as decreased the expression of Bax, Caspase-3, TLR4 and p65 (p < 0.05). After TAK-242 or LPS treatment, it showed similar results in propofol + TAK-242 (T + P) group and E + P group. CONCLUSION: Erythropoietin could attenuate propofol-induced hippocampal neuronal cell injury in developing rats, which may be related to inhibit TLR4 expression.


Assuntos
Anestésicos Intravenosos/toxicidade , Eritropoetina/farmacologia , Hipocampo/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Propofol/toxicidade , Receptor 4 Toll-Like/efeitos dos fármacos , Animais , Células Cultivadas , Feminino , Hipocampo/metabolismo , Masculino , Neurônios/metabolismo , Fármacos Neuroprotetores/farmacologia , Ratos , Ratos Sprague-Dawley , Receptor 4 Toll-Like/metabolismo
11.
J Chem Phys ; 151(24): 244902, 2019 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-31893914

RESUMO

Analyte translocation involves three phases: (i) diffusion in the loading solution, (ii) capture by the pore, and (iii) threading. The capture process remains poorly characterized because it cannot easily be visualized or inferred from indirect measurements. The capture performance of a device is often described by a capture radius generally defined as the radial distance R* at which diffusion-dominated dynamics cross over to field-induced drift. However, this definition is rather ambiguous and the related models are usually oversimplified and studied in the steady-state limit. We investigate different approaches to defining and estimating R* for a charged particle diffusing in a liquid and attracted to the nanopore by the electric field. We present a theoretical analysis of the Péclet number as well as Monte Carlo simulations with different simulation protocols. Our analysis shows that the boundary conditions, pore size, and finite experimental times all matter in the interpretation and calculation of R*.

12.
Brain Res Bull ; 132: 39-43, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28461186

RESUMO

OBJECTIVE: This study aimed to investigate the impact of apolipoprotein E 4 (APOE4) gene polymorphisms on the expressions of inflammatory factors and the progression of Alzheimer's disease (AD). METHODS: A total of 185 AD patients (the case group, 130 cases from the Han ethnic group and 55 cases from the She ethnic group) and 190 healthy individuals (the control group, 130 cases from the Han ethnic group and 60 cases from the She ethnic group) were recruited for our study. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was conducted to detect APOE4 genotype and allele frequency. Enzyme-linked immunosorbent assay (ELISA) was used to determine the expressions of inflammatory factors in plasma. RESULTS: In both Han and She populations, the frequency of ε3/4 and ε4/4 genotypes and the ε4 allele was significantly higher in the case group than that in the control group. ε3/4 and ε4/4 genotypes and the ε4 allele were the risk factors for AD. In both Han and She populations, the ε2/4, ε3/4 and ε4/4 carriers showed increased levels of TNF-α, IL-6, and IL-1ß when compared with the ε2/2 + ε2/3 + ε3/3 carriers. The TNF-α, IL-6, and IL-1ß levels were higher in the ε4/4 carriers than those in the ε2/4 and ε3/4 carriers, and ε2/4, ε3/4 and ε4/4 carriers in the case group exhibited increased levels of TNF-α, IL-6, and IL-1ß when compared with the control group (P<0.05). Logistic regression analysis indicated that the ε3/4 genotype and TNF-α, IL-6, and IL-1ß levels were associated with the susceptibility to AD in the Han population, while ε3/4 and ε4/4 genotypes and TNF-α, IL-6, and IL-1ß levels were related to the susceptibility to AD in the She population. CONCLUSIONS: The APOE4 ε4 allele may enhance susceptibility to AD and promotes the expressions of inflammatory factors in AD.


Assuntos
Doença de Alzheimer/genética , Doença de Alzheimer/fisiopatologia , Apolipoproteína E4/genética , Predisposição Genética para Doença , Idoso , Idoso de 80 Anos ou mais , Alelos , Doença de Alzheimer/etnologia , Apolipoproteína E3/genética , Povo Asiático/genética , Biomarcadores/sangue , China , Progressão da Doença , Feminino , Frequência do Gene , Heterozigoto , Humanos , Interleucina-1beta/sangue , Interleucina-6/sangue , Masculino , Pessoa de Meia-Idade , Fator de Necrose Tumoral alfa/sangue
13.
Science ; 347(6227): 1226-9, 2015 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-25766228

RESUMO

China's Chang'E-3 (CE-3) spacecraft touched down on the northern Mare Imbrium of the lunar nearside (340.49°E, 44.12°N), a region not directly sampled before. We report preliminary results with data from the CE-3 lander descent camera and from the Yutu rover's camera and penetrating radar. After the landing at a young 450-meter crater rim, the Yutu rover drove 114 meters on the ejecta blanket and photographed the rough surface and the excavated boulders. The boulder contains a substantial amount of crystals, which are most likely plagioclase and/or other mafic silicate mineral aggregates similar to terrestrial dolerite. The Lunar Penetrating Radar detection and integrated geological interpretation have identified more than nine subsurface layers, suggesting that this region has experienced complex geological processes since the Imbrian and is compositionally distinct from the Apollo and Luna landing sites.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...