Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 23
Filtrar
1.
Sensors (Basel) ; 20(4)2020 Feb 23.
Artículo en Inglés | MEDLINE | ID: mdl-32102261

RESUMEN

The tracking accuracy of a traditional Frequency Lock Loop (FLL) decreases significantly in a complex environment, thus reducing the overall performance of a satellite receiver. In order to ensure high tracking accuracy of a receiver in a complex environment, this paper proposes a new tracking loop combining the vector FLL (VFLL) with a robust least squares method, which accurately matches the weights of received signals of different qualities to ensure high positioning accuracy. The weights of received signals are selected at the signal level, not at the observation level. In this paper, the ranges of strong and weak signals of the loop are determined according to the different expressions of the distribution function at different signal strengths, and the concept of loop segmentation is introduced. The segmentation results of the FLL are taken as a basis of the weight selection, and then combined with the Institute of Geodesy and Geophysics (IGGIII) weight function to obtain the equivalent weight matrix; the experiments are conducted to prove the advantages of the proposed method over the traditional methods. The experimental results show that the proposed VFLL tracking method has strong denoising capability under both normal- signal and harsh application environment conditions. Accordingly, the proposed model has a promising application perspective.

2.
Sensors (Basel) ; 20(8)2020 Apr 20.
Artículo en Inglés | MEDLINE | ID: mdl-32325964

RESUMEN

Ground-based synthetic aperture radar interferometry (GB-InSAR) is a valuable tool for deformation monitoring. The 2D interferograms obtained by GB-InSAR can be integrated with a 3D terrain model to visually and accurately locate deformed areas. The process has been preliminarily realized by geometric mapping assisted by terrestrial laser scanning (TLS). However, due to the line-of-sight (LOS) deformation monitoring, shadow and layover often occur in topographically rugged areas, which makes it difficult to distinguish the deformed points on the slope between the ones on the pavement. The extant resampling and interpolation method, which is designed for solving the scale difference between the point cloud and radar pixels, does not consider the local scattering characteristics difference of slope. The scattering difference information of road surface and slope surface in the terrain model is deeply weakened. We propose a differentiated method with integrated GB-InSAR and terrain surface point cloud. Local geometric and scattering characteristics of the slope were extracted, which account for pavement and slope differentiating. The geometric model is based on a GB-InSAR system with linear repeated-pass and the topographic point cloud relative observation geometry. The scattering model is based on k-nearest neighbor (KNN) points in small patches varies as radar micro-wave incident angle changes. Simulation and a field experiment were conducted in an open-pit mine. The results show that the proposed method effectively distinguishes pavement and slope surface deformation and the abnormal area boundary is partially relieved.

3.
Sensors (Basel) ; 19(5)2019 Feb 28.
Artículo en Inglés | MEDLINE | ID: mdl-30823436

RESUMEN

To keep the global navigation satellite system functional during extreme conditions, it is a trend to employ autonomous navigation technology with inter-satellite link. As in the newly built BeiDou system (BDS-3) equipped with Ka-band inter-satellite links, every individual satellite has the ability of communicating and measuring distances among each other. The system also has less dependence on the ground stations and improved navigation performance. Because of the huge amount of measurement data, the centralized data processing algorithm for orbit determination is suggested to be replaced by a distributed one in which each satellite in the constellation is required to finish a partial computation task. In the present paper, the balanced extended Kalman filter algorithm for distributed orbit determination is proposed and compared with the whole-constellation centralized extended Kalman filter, the iterative cascade extended Kalman filter, and the increasing measurement covariance extended Kalman filter. The proposed method demands a lower computation power; however, it yields results with a relatively good accuracy.

4.
Sensors (Basel) ; 19(12)2019 Jun 19.
Artículo en Inglés | MEDLINE | ID: mdl-31248220

RESUMEN

Although there are already several real-time precise positioning service providers, unfortunately, not all users can use the correction information due to either cost of the service and limitation of their equipment or out of the service coverage. An alternative way is to enhance the accuracy of the predicted satellite clocks for precise real-time positioning. Based on the study of existing prediction models, an improved model combing the spectrum analysis (SA) and the generalized regression neural network (GRNN) model is proposed especially for BeiDou satellite navigation system (BDS)-2 satellites. The periodic terms and GRNN-related parameters including length and interval of sample data, as well as a smooth factor, are optimized satellite by satellite to consider satellite-specific characteristics for all the fourteen BDS-2 satellites. The improved model is validated by comparing the predicted clocks of existing models and the improved model with precisely estimated ones. The bias of the predicted clock is within ±0.5 ns over three hours and better than that of the other models and can be used for several real-time precise applications. The clock prediction is further evaluated by applying clock corrections to precise point positioning (PPP) in both static and kinematic mode for eight IGS (International GNSS Service) MGEX (Multi-GNSS Experiment) stations in the Asia-Pacific region. In the static PPP, the improved model is validated to be effective, and position accuracies of some IGS MGEX stations achieve more than 30.0% improvements on average for each component, which enables us to obtain sub-decimeter positioning. In the kinematic PPP, the improved model performs much better than the others in terms of both the convergence time and the position accuracy. The convergence time can be shortened from 1-2 h to 0.5-1 h, while the position accuracy is enhanced by 15.4%, 21.6% and 19.3% on average in east, north and up component, respectively.

5.
Sensors (Basel) ; 19(22)2019 Nov 16.
Artículo en Inglés | MEDLINE | ID: mdl-31744110

RESUMEN

Snow is one of the most critical sources of freshwater, which influences the global water cycle and climate change. However, it is difficult to monitor global snow variations with high spatial-temporal resolution using traditional techniques due to their costly and labor-intensive nature. Nowadays, the Global Positioning System Interferometric Reflectometry (GPS-IR) technique can measure the average snow depth around a GPS antenna using its signal-to-noise ratio (SNR) data. Previous studies focused on the use of GPS data at sites located in flat areas or on very gentle slopes. In this contribution, we propose a strategy called the Tilted Surface Strategy (TSS), which uses the SNR data reflected only from the flat quadrants to estimate the snow depth instead of the conventional strategy, which employs all the SNR data reflected from the whole area around a GPS antenna. Three geodetic GPS sites from the Plate Boundary Observatory (PBO) project were chosen in this experimental study, of which GPS sites p683 and p101 were located on slopes with their gradients up to 18% and the site p025 was located on a flat area. Comparing the snow depths derived with the GPS-IR TSS method with the snow depth results provided with the GPS-PBO, i.e., GPS-IR with the conventional strategy, the Snowpack Telemetry (SNOTEL) network measurements and gridded Snow Data Assimilation System (SNODAS) estimates, it was found that the snow depths derived with the four methods had a good agreement, but the snow depth time series with the GPS-IR TSS method were closer to the SNOTEL measurements and the SNODAS estimates than those with GPS-PBO method. Similar observations were also obtained from the cumulative snowfall time series. Results generally indicated that for those GPS sites located on slopes, the TSS strategy works better.

6.
Sensors (Basel) ; 19(20)2019 Oct 17.
Artículo en Inglés | MEDLINE | ID: mdl-31627473

RESUMEN

A GNSS station, located on the shore of sea and inland waters, and equipped with standard geodetic receivers and antennas, can be used to measure water levels using a technique called GNSS Interferometric Reflectometry (GNSS-IR). The classical GNSS-IR method is based on SNR data and LSP spectrum analysis method. In order to promote the application of GNSS-IR, the accuracy of the results needs to be further improved, and quality control needs to be achieved better. Classical quality control methods include denoising filtering based on data source SNR; post-processing filtering based on results; morphological analysis based on parameters, such as the ratio of the maximum peak value to the background noise mean, the ratio of the maximum peak to the sub-peak, and the amplitude of the maximum peak. All three methods have the problem of correct frequency extraction under multiple approximate peak conditions. This paper focuses on the performance analysis of three methods of quality control for two situations with real examples, summarizes the advantages and disadvantages of each method, and discusses the measures in applications. Considering the limitations in the threshold setting for the third method, a new quality control method combining multiple parameters and external constraints is proposed. This method is more flexible, especially in dealing with a periodogram with multiple similar peaks, breaking through the premise that the frequency corresponding to the maximum peak is the correct frequency, and validated in two different environments. The experimental results show that the proposed method can improve the accuracy of the measured water level while ensuring the amount of the results. It eliminates the gross errors effectively and uses the data efficiently.

7.
Sensors (Basel) ; 15(8): 19416-28, 2015 Aug 07.
Artículo en Inglés | MEDLINE | ID: mdl-26262620

RESUMEN

Monitoring ocean waves plays a crucial role in, for example, coastal environmental and protection studies. Traditional methods for measuring ocean waves are based on ultrasonic sensors and accelerometers. However, the Global Positioning System (GPS) has been introduced recently and has the advantage of being smaller, less expensive, and not requiring calibration in comparison with the traditional methods. Therefore, for accurately measuring ocean waves using GPS, further research on the separation of the wave signals from the vertical GPS-mounted carrier displacements is still necessary. In order to contribute to this topic, we present a novel method that combines complementary ensemble empirical mode decomposition (CEEMD) with a wavelet threshold denoising model (i.e., CEEMD-Wavelet). This method seeks to extract wave signals with less residual noise and without losing useful information. Compared with the wave parameters derived from the moving average skill, high pass filter and wave gauge, the results show that the accuracy of the wave parameters for the proposed method was improved with errors of about 2 cm and 0.2 s for mean wave height and mean period, respectively, verifying the validity of the proposed method.

8.
J Org Chem ; 79(2): 599-607, 2014 Jan 17.
Artículo en Inglés | MEDLINE | ID: mdl-24344740

RESUMEN

Aphadilactones A-D (1-4), four diastereoisomers possessing an unprecedented carbon skeleton, were isolated from the Meliaceae plant Aphanamixis grandifolia. Their challenging structures and absolute configurations were determined by a combination of spectroscopic data, chemical degradation, fragment synthesis, experimental CD spectra, and ECD calculations. Aphadilactone C (3) with the 5S,11S,5'S,11'S configuration showed potent and selective inhibition against the diacylglycerol O-acyltransferase-1 (DGAT-1) enzyme (IC50 = 0.46 ± 0.09 µM, selectivity index > 217) and is the strongest natural DGAT-1 inhibitor discovered to date. In addition, compounds 1-4 showed significant antimalarial activities with IC50 values of 190 ± 60, 1350 ± 150, 170 ± 10, and 120 ± 50 nM, respectively.


Asunto(s)
Antimaláricos/farmacología , Diacilglicerol O-Acetiltransferasa/antagonistas & inhibidores , Diterpenos/farmacología , Inhibidores Enzimáticos/farmacología , Meliaceae/química , Plasmodium falciparum/efectos de los fármacos , Antimaláricos/química , Antimaláricos/aislamiento & purificación , Diacilglicerol O-Acetiltransferasa/metabolismo , Dimerización , Diterpenos/química , Diterpenos/aislamiento & purificación , Relación Dosis-Respuesta a Droga , Inhibidores Enzimáticos/química , Inhibidores Enzimáticos/aislamiento & purificación , Humanos , Conformación Molecular , Pruebas de Sensibilidad Parasitaria , Proteínas Recombinantes/metabolismo , Relación Estructura-Actividad
9.
Sci Bull (Beijing) ; 68(24): 3240-3251, 2023 Dec 30.
Artículo en Inglés | MEDLINE | ID: mdl-37980171

RESUMEN

Reducing soil salinization of croplands with optimized irrigation and water management is essential to achieve land degradation neutralization (LDN). The effectiveness and sustainability of various irrigation and water management measures to reduce basin-scale salinization remain uncertain. Here we used remote sensing to estimate the soil salinity of arid croplands from 1984 to 2021. We then use Bayesian network analysis to compare the spatial-temporal response of salinity to water management, including various irrigation and drainage methods, in ten large arid river basins: Nile, Tigris-Euphrates, Indus, Tarim, Amu, Ili, Syr, Junggar, Colorado, and San Joaquin. In basins at more advanced phases of development, managers implemented drip and groundwater irrigation and thus effectively controlled salinity by lowering groundwater levels. For the remaining basins using conventional flood irrigation, economic development and policies are crucial for establishing a virtuous circle of "improving irrigation systems, reducing salinity, and increasing agricultural incomes" which is necessary to achieve LDN.

10.
Yao Xue Xue Bao ; 47(7): 966-8, 2012 Jul.
Artículo en Zh | MEDLINE | ID: mdl-22993866

RESUMEN

The paper is to report the establishment of three methods for determination of methyl salicylate-2-O-beta-D-galactopyranoside (1-4)-beta-D-glucopyranoside (MSG) by HPLC, UV or potentiometric titration. The results determined by the three methods turned out to be of no significant difference (P>0.05). The method was chosen according to MSG difference test demands.


Asunto(s)
Antiinflamatorios/análisis , Cromatografía Líquida de Alta Presión/métodos , Glicósidos/análisis , Potenciometría/métodos , Salicilatos/análisis , Espectrofotometría Ultravioleta/métodos , Antiinflamatorios/química , Glicósidos/química , Estructura Molecular , Reproducibilidad de los Resultados , Salicilatos/química , Sensibilidad y Especificidad
11.
Sci Rep ; 12(1): 4465, 2022 Mar 16.
Artículo en Inglés | MEDLINE | ID: mdl-35296746

RESUMEN

Despite the extensive investigation on the stress and displacement distributions in tunnels, few have considered the influences of the damaged zone around a tunnel on the strength and stiffness parameters of the surrounding rock, including the gradual variation in the damaged factor D and dimensionless damaged radius [Formula: see text], under the effect of excavation disturbance. In this paper, a numerical solution is presented for the stresses and displacement of a circular tunnel excavated in a Hoek-Brown rock mass considering the progressive destruction of the damaged zone. First, the results obtained using the proposed algorithm are compared with those obtained using other numerical solutions, demonstrating a high degree of accuracy through some examples. Second, the influences of the damaged factor [Formula: see text] and dimensionless damaged radius [Formula: see text] on the stresses, radial displacement, plastic radii, and ground response curve are investigated. The results show that, as the damaged factor D increases, the radial displacement and plastic radius increase, whereas the tangential stress decreases. Both the plastic radius and displacement decrease with decreasing [Formula: see text]. This shows that the damaged factor D has a significant effect on tunnel convergence.

12.
Bioorg Med Chem Lett ; 21(1): 125-9, 2011 Jan 01.
Artículo en Inglés | MEDLINE | ID: mdl-21131198

RESUMEN

Five new ring A-seco triterpenoids, dysoxyhainic acids F-J (1-5), along with a known ring A-seco triterpenoid koetjapic acid (6) were isolated from the twigs and leaves of Dysoxylum hainanense. Their structures were established on the basis of extensive spectroscopic analysis. Antimicrobial activity of all the compounds against fungi and bacteria were tested. Compounds 2-4 and 6 exhibited significant antimicrobial activity against Gram-positive bacteria, and the antibacterial SAR (structure-activity relationship) was also briefly discussed.


Asunto(s)
Antibacterianos/química , Meliaceae/química , Triterpenos/química , Antibacterianos/aislamiento & purificación , Antibacterianos/farmacología , Bacterias Grampositivas/efectos de los fármacos , Espectroscopía de Resonancia Magnética , Pruebas de Sensibilidad Microbiana , Conformación Molecular , Hojas de la Planta/química , Relación Estructura-Actividad , Triterpenos/aislamiento & purificación , Triterpenos/farmacología
13.
Planta Med ; 77(14): 1617-22, 2011 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-21472647

RESUMEN

Three new limonoids (toonaciliatins N-P, 1-3)and four new pimaradiene-type diterpenoids(toonacilidins A-D, 4-7) were isolated from the leaves and twigs of Toona ciliata Roem. var. yunnanensis.Their structures were elucidated on the basis of spectroscopic methods. Toonacilidin B(5)showed moderate inhibitory activity against H. pylori-SS1 with an MIC of 50 µg/mL.


Asunto(s)
Antiinfecciosos/química , Diterpenos/química , Helicobacter pylori/efectos de los fármacos , Limoninas/química , Meliaceae/química , Extractos Vegetales/química , Antiinfecciosos/aislamiento & purificación , Diterpenos/aislamiento & purificación , Limoninas/aislamiento & purificación , Pruebas de Sensibilidad Microbiana , Estructura Molecular
14.
J Nat Prod ; 73(1): 45-50, 2010 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-20038159

RESUMEN

Two new sesquiterpenes, sarcandralactones A (1) and B (2), and five new dimeric sesquiterpenoids, sarcandrolides A-E (3-7), along with 10 known compounds were isolated from the whole plants of Sarcandra glabra. Their structures were elucidated on the basis of spectroscopic analysis. Some of the new isolates exhibit significant cytotoxicities when tested against a small panel of tumor cell lines.


Asunto(s)
Antineoplásicos Fitogénicos/aislamiento & purificación , Medicamentos Herbarios Chinos/aislamiento & purificación , Magnoliaceae/química , Sesquiterpenos/aislamiento & purificación , Antineoplásicos Fitogénicos/química , Antineoplásicos Fitogénicos/farmacología , Ensayos de Selección de Medicamentos Antitumorales , Medicamentos Herbarios Chinos/química , Medicamentos Herbarios Chinos/farmacología , Células HL-60 , Humanos , Concentración 50 Inhibidora , Estructura Molecular , Sesquiterpenos/química , Sesquiterpenos/farmacología
15.
J Nat Prod ; 73(8): 1344-9, 2010 Aug 27.
Artículo en Inglés | MEDLINE | ID: mdl-20614901

RESUMEN

Ten new limonoids, namely, mesendanins A-J (1-10), together with 14 known compounds, have been isolated from the leaves and twigs of Melia toosendan. Their structures were established on the basis of spectroscopic data analysis.


Asunto(s)
Medicamentos Herbarios Chinos/aislamiento & purificación , Limoninas/aislamiento & purificación , Melia/química , Medicamentos Herbarios Chinos/química , Limoninas/química , Estructura Molecular , Resonancia Magnética Nuclear Biomolecular , Hojas de la Planta/química , Tallos de la Planta/química
16.
Sci Rep ; 10(1): 9568, 2020 06 12.
Artículo en Inglés | MEDLINE | ID: mdl-32533037

RESUMEN

Increasing organic fertilizer application can improve the sustainability of soil productivity, but the effects of increased organic fertilizer application with reduced chemical fertilizer application over different time periods on chemical properties and bacterial community of grape rhizosphere soil in an arid region are not clear. In this study, three years of fixed-point field tests were used to compare the effects of various fertilization treatments on the soil properties and bacterial community in the grape rhizosphere. The results showed that (1) T1 and T2 significantly increased SOM, AN, AP and AK contents in grape rhizosphere soil. TN, TP and TK contents in grape leaves of T2 were the highest of those in five fertilization treatments. (2) The abundances of Proteobacteria and Bacteroidetes phyla and especially of Arthrobacter, Pseudomonas, Nitrosopira and Bacillus genera were higher in T2 than in the other samples. (3) SOM, AP and AN contents in soil were the main factors affecting soil bacterial community and mineral element contents in grape leaves and roots according to an RDA analysis. In summary, the application of organic fertilizer with reduced chemical fertilizer for two years had the greatest impact on the soil properties and bacterial community of the grape rhizosphere soil.


Asunto(s)
Bacterias/crecimiento & desarrollo , Fertilizantes/análisis , Rizosfera , Microbiología del Suelo , Suelo/química , Vitis/crecimiento & desarrollo , Agricultura , Bacterias/clasificación , Bacterias/efectos de los fármacos , Bacterias/genética , ARN Ribosómico 16S , Vitis/efectos de los fármacos , Vitis/microbiología
17.
J Agric Food Chem ; 67(42): 11710-11717, 2019 Oct 23.
Artículo en Inglés | MEDLINE | ID: mdl-31600058

RESUMEN

Lactuca sativa L. var. augustana has a basmati rice-like odor with a green note in the background. This typical odor is due to the release of 2-acetyl-1-pyrroline (2-AP) after heating, which is confirmed by volatile analysis. Recent metabolomic and genomic studies of different rice varieties highlighted that the presence of 2-AP was linked to the accumulation of γ-aminobutyraldehyde; genome-wide association studies also indicated that acyltransferases were involved. These results prompted us to analyze nonvolatile compound precursors in L. sativa L. var. augustana (celtuce) to search for compound derivatives with a 4,5-dioxohexan alkyl amine-like structure. Hypothetical synthetic compounds were prepared from a reductive amination between 4,5-dioxohexanal and glycine, alanine, aspartic acid, and glutamic acid to give 2-(2-acetylpyrrolidin-1-yl) alkanoic acid. We proved that 2-(2-acetylpyrrolidin-1-yl) propionic acid is present in L. sativa, which, when thermally treated, released 2-AP. Other 2-AP precursors occurring in this plant are discussed.


Asunto(s)
Lactuca/química , Extractos Vegetales/química , Pirroles/química , Genoma de Planta , Lactuca/genética , Espectrometría de Masas , Odorantes/análisis
18.
Zhongguo Zhong Yao Za Zhi ; 31(1): 21-3, 2006 Jan.
Artículo en Zh | MEDLINE | ID: mdl-16548160

RESUMEN

OBJECTIVE: To select a proper Ganoderma luciderm strain for the fruiting body production. METHOD: The strains were cultivated on the agar media and in the liquid media, respectively. Then the strains were inoculated onto the solid medium made from agricultural products (such as wheat bran, corn powder, wood meal, etc.) and cultured for a certain period. RESULT: Strains, which were easier to produce polyporic tissues at the vegetative growth stage, would be more quickly to form fruiting body with high quality and yield of the spores. CONCLUSION: Appearance of the polyporic tissues at the mycelium vegetative growth stage could be used as a marker for the strain selection for the G. luciderm substituted cultivation.


Asunto(s)
Cuerpos Fructíferos de los Hongos/crecimiento & desarrollo , Ganoderma/crecimiento & desarrollo , Micelio/crecimiento & desarrollo , Reactores Biológicos , Medios de Cultivo , Triticum , Zea mays
19.
Org Lett ; 12(6): 1168-71, 2010 Mar 19.
Artículo en Inglés | MEDLINE | ID: mdl-20148570

RESUMEN

Three highly oxygenated new diterpenes, trigochinins A-C (1-3) were isolated from Trigonostemon chinensis. Their structures with the absolute configuration were determined by a spectroscopic method, X-ray crystallography, and CD analysis. This study suggested the revision of the C-6 stereochemistry of trigonothyrins A-C reported quite recently. Compound 3 showed significant inhibition against MET tyrosine kinase activity with a IC(50) value of 1.95 microM.


Asunto(s)
Diterpenos/química , Euphorbiaceae/química , Inhibidores de Proteínas Quinasas/química , Cristalografía por Rayos X , Diterpenos/aislamiento & purificación , Diterpenos/farmacología , Modelos Moleculares , Conformación Molecular , Hojas de la Planta/química , Tallos de la Planta/química , Inhibidores de Proteínas Quinasas/aislamiento & purificación , Inhibidores de Proteínas Quinasas/farmacología , Proteínas Tirosina Quinasas/antagonistas & inhibidores , Proteínas Tirosina Quinasas/metabolismo , Estereoisomerismo
20.
Org Lett ; 11(18): 4080-3, 2009 Sep 17.
Artículo en Inglés | MEDLINE | ID: mdl-19702252

RESUMEN

Trigochilides A (1) and B (2), two highly modified daphnane-type diterpenoids with 12-carbon-containing polyketide appendages at C-16 forming a macro-lactone with C-3, were isolated from the twigs and leaves of Trigonostemon chinensis. Their structures were elucidated by spectroscopic analysis. Trigochilides A (1) showed modest cytotoxicity against two tumor cell lines.


Asunto(s)
Antineoplásicos/uso terapéutico , Diterpenos/uso terapéutico , Ensayos de Selección de Medicamentos Antitumorales , Euphorbiaceae/química , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Diterpenos/clasificación , Medicamentos Herbarios Chinos/química , Células HeLa , Humanos , Células K562 , Lactonas/farmacología , Hojas de la Planta/química , Relación Estructura-Actividad , Células Tumorales Cultivadas
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA