综合资源展示 综合资源展示

最小化 最大化
英文(1855)
Elsevier(1855)
其他(1855)
略(1855)
 
 
 
 
 
   

1 Effect of different types of surfactants on the microstructure of methyltrimethoxysilane-derived silica aerogels: A combined experimental and computational approach 2017-10-19             

HTML   |   详细信息   |  

Publication date: 15 February 2018
Source:Journal of Colloid and Interface Science, Volume 512

Author(s): João P. Vareda, Pedro Maximiano, Luís P. Cunha, André F. Ferreira, Pedro N. Simões, Luísa Durães

Hypothesis Surfactants interfere with sol-gel particle/pore growth, influencing the structure and properties of silica aerogels. Their ability to induce microscopic changes in the aerogel’s structure may be useful to improve/control the thermal insulation performance of aerogels. Experiments The influence of different types of surfactants (anionic, cationic and non-ionic) on the microstructural arrangement and macroscopic properties of methyltrimethoxysilane (MTMS)-based aerogels was evaluated for the first time, using an experimental and computational comparative approach. Molecular dynamics simulations were performed based on two representative silica molecular structures derived from MTMS, while the experimentally-obtained silica aerogels were characterized in terms of chemical/structural/mechanical/thermal insulation properties. Findings The use of both hexadecyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) led to a decrease in bulk density, thermal conductivity and average pore size of the aerogels, with notorious increase of their flexibility. The observed changes were due to microstructural arrangements, as evidenced by scanning electron microscopy (SEM). However, the non-ionic surfactant, Pluronic F-127, did not have a positive impact on the desired properties. Globally, the simulation results support the experimental findings, suggesting differentiated microstructural changes induced by the use of cationic or anionic surfactants. The addition of CTAB and SDS generally resulted in smaller or larger silica aggregates, respectively.

Graphical abstract

image




2 Wavelet-based coupling of leaf and canopy reflectance spectra to improve the estimation accuracy of foliar nitrogen concentration 2017-10-19             

HTML   |   详细信息   |  

Publication date: 15 January 2018
Source:Agricultural and Forest Meteorology, Volume 248

Author(s): Junjie Wang, Yiyun Chen, Fangyuan Chen, Tiezhu Shi, Guofeng Wu

The leaf or canopy reflectance spectra of vegetation have been widely employed in estimating foliar nitrogen (N) concentration; however, they alone may not actually reflect the spectral and detailed information at a sampling plot. In this study, the potential spectral details of Carex (C. cinerascens) at a plot scale were derived using discrete wavelet transform, in which a simple operation of addition was employed to combine the reconstructed leaf and canopy reflectance at the fourth decomposition level (named “leaf-canopy d4 reflectance”). Partial least squares regression (PLSR), successive projections algorithm-based multiple linear regression (SPA-MLR) and random forest regression (RFR) models with leaf, canopy and leaf-canopy d4 reflectance were established and validated for foliar N estimation, respectively. The results showed that the PLSR (R2 CV =0.718, determination coefficient of cross-validation; R2 Val =0.743, determination coefficient of independent validation; RPD=1.91, residual prediction deviation), SPA-MLR (R2 CV =0.709, R2 Val =0.747, RPD=1.97) and RFR (R2 CV =0.714, R2 Val =0.783, RPD=2.16) models with leaf-canopy d4 reflectance outperformed their corresponding models with leaf or canopy reflectance. We conclude that the wavelet-based coupling of leaf and canopy reflectance spectra has great potential in the accurate estimation of foliar N concentration. This proposed strategy helps to understand the spectral details of vegetation at a plot scale, providing the potential for improving the plot-based estimation of plant nutrients in grassland, precision agriculture or forestry.





3 Lab-on-a-chip systems for photodynamic therapy investigations 2017-10-19             

HTML   |   详细信息   |  

Publication date: 15 March 2018
Source:Biosensors and Bioelectronics, Volume 101

Author(s): Michał Chudy, Katarzyna Tokarska, Elżbieta Jastrzębska, Magdalena Bułka, Sławomir Drozdek, Łukasz Lamch, Kazimiera A. Wilk, Zbigniew Brzózka

In recent years photodynamic therapy (PDT) has received widespread attention in cancer treatment due to its smaller surgical trauma, better selectivity towards tumor cells, reduced side effects and possibility of repeatable treatment. Since cancer is the second cause of death worldwide, scientists constantly seek for new potential therapeutic agents including nanotechnology-based photosensitizers used in PDT. The new-designed nanostructures must be carefully studied and well characterized what require analytically useful and powerful tools that enable real progress in nanoscience development. This review describes the current status of PDT investigations using microfluidic Lab-on-a-Chip systems, including recent developments of nanoparticle-based PDT agents, their combinations with different drugs, designs and examples of in vitro applications. This review mainly lays emphasis on biological evaluation of FDA approved photosensitizing agents as well as newly designed nanophotosensitizers. It also highlights the analytical performances of various microfluidic Lab-on-a-chip systems for PDT efficacy analysis on 3D culture and discusses microsystems designs in detail.





4 Exploiting chaos-based compressed sensing and cryptographic algorithm for image encryption and compression 2017-10-19             

HTML   |   详细信息   |  

Publication date: 1 February 2018
Source:Optics & Laser Technology, Volume 99

Author(s): Junxin Chen, Yu Zhang, Lin Qi, Chong Fu, Lisheng Xu

This paper presents a solution for simultaneous image encryption and compression. The primary introduced techniques are compressed sensing (CS) using structurally random matrix (SRM), and permutation-diffusion type image encryption. The encryption performance originates from both the techniques, whereas the compression effect is achieved by CS. Three-dimensional (3-D) cat map is employed for key stream generation. The simultaneously produced three state variables of 3-D cat map are respectively used for the SRM generation, image permutation and diffusion. Numerical simulations and security analyses have been carried out, and the results demonstrate the effectiveness and security performance of the proposed system.





5 On the Potential Role of MRI Biomarkers of COPD to Guide Bronchoscopic Lung Volume Reduction 2017-10-17             

HTML   |   详细信息   |  

Publication date: Available online 16 October 2017
Source:Academic Radiology

Author(s): Colin J. Adams, Dante P.I. Capaldi, Robert Di Cesare, David G. McCormack, Grace Parraga

Rationale and Objectives In patients with severe emphysema and poor quality of life, bronchoscopic lung volume reduction (BLVR) may be considered and guided based on lobar emphysema severity. In particular, x-ray computed tomography (CT) emphysema measurements are used to identify the most diseased and the second–most diseased lobes as BLVR targets. Inhaled gas magnetic resonance imaging (MRI) also provides chronic obstructive pulmonary disease (COPD) biomarkers of lobar emphysema and ventilation abnormalities. Our objective was to retrospectively evaluate CT and MRI biomarkers of lobar emphysema and ventilation in patients with COPD eligible for BLVR. We hypothesized that MRI would provide complementary biomarkers of emphysema and ventilation that help determine the most appropriate lung lobar targets for BLVR in patients with COPD. Materials and Methods We retrospectively evaluated 22 BLVR-eligible patients from the Thoracic Imaging Network of Canada cohort (diffusing capacity of the lung for carbon monoxide = 37 ± 12%predicted, forced expiratory volume in 1 second = 34 ± 7%predicted, total lung capacity = 131 ± 17%predicted, and residual volume = 216 ± 36%predicted). Lobar CT emphysema, measured using a relative area of <−950 Hounsfield units (RA950) and MRI ventilation defect percent, was independently used to rank lung lobe disease severity. Results In 7 of 22 patients, there were different CT and MRI predictions of the most diseased lobe. In some patients, there were large ventilation defects in lobes not targeted by CT, indicative of a poorly ventilated lung. CT and MRI classification of the most diseased and the second–most diseased lobes showed a fair-to-moderate intermethod reliability (Cohen κ = 0.40–0.59). Conclusions In this proof-of-concept retrospective analysis, quantitative MRI ventilation and CT emphysema measurements provided different BLVR targets in over 30% of the patients. The presence of large MRI ventilation defects in lobes next to CT-targeted lobes might also change the decision to proceed or to guide BLVR to a different lobar target.





6 Development of web-based WERM-S module for estimating spatially distributed rainfall erosivity index (EI30) using RADAR rainfall data 2017-10-17             

HTML   |   详细信息   |  

Publication date: February 2018
Source:CATENA, Volume 161

Author(s): Avay Risal, Kyoung Jae Lim, Rabin Bhattarai, Jae E. Yang, Huiseong Noh, Rohit Pathak, Jonggun Kim

Despite technological advances, soil erosion modeling is a very complicated process as the amount and rate of soil erosion vary considerably over space and time. Universal Soil Loss Equation (USLE) is one of the oldest and popular models used for soil loss estimation worldwide. USLE R-factor is one of the six input parameters accounting for the impact of rainfall amount and intensity on soil erosion in USLE. The USLE R factor is calculated by averaging annual long time rainfall erosivity index (EI30) values, computed by multiplying maximum rainfall intensity during 30min periods and the kinetic energy of the rainfall. The gage rainfall data are used for the determination of such EI30 index, and one representative value is given for the entire area. Due to the spatial and temporal variability of rainfall pattern, the value may vary considerably over space and time. It is required to obtain the rainfall data over a surface (heterogeneous) rather than at a point (homogeneous) so that spatially distributed erosivity index values can be calculated. Even though RADAR can provide spatially and temporally distributed rainfall data, the process of manual erosivity index calculation for each raster pixel is very tedious, time-consuming and practically not feasible. To overcome these limitations, the web-based WERM-S module was developed to compute a spatial EI30 index from the 10-min interval spatial rainfall data. The WERM-S consists of three different Fortran modules (Convert Module, R-factor calculation module, and R-factor ASCII module). The Jaun-ri watershed was selected as the study area to test the module since the RADAR rainfall data was available for 2015. June, July, and August were found to be the months receiving the maximum amount of rainfall and the average erosivity indices for June, July and August were found to be 2096, 1002, and 993MJ·mm/ha-hr-month, respectively. The maximum erosivity index for a pixel within the study area was observed to be 9821MJ·mm/ha-hr-month for June 4382MJ·mm/ha-hr-month for July and 6093MJ·mm/ha-hr-month for August respectively. The higher value of standard deviations of 1850, 950 and 1115MJ·mm/ha-hr-month for June, July, and August were observed respectively representing that the erosivity index of individual space widely deviated from the mean monthly erosivity index. Thus spatial erosivity index is suggested to be used over average annual R factor values to calculate soil loss using USLE. Furthermore, the WERM-S module can be a very useful tool to automatically calculate the spatially distributed rainfall erosivity index from 10-min interval RADAR rainfall data.





7 Ultrafast Laplace NMR with hyperpolarized xenon gas 2017-10-17             

HTML   |   详细信息   |  

Publication date: Available online 16 October 2017
Source:Microporous and Mesoporous Materials

Author(s): Otto Mankinen, Julia Hollenbach, Susanna Ahola, Jörg Matysik, Ville-Veikko Telkki

Laplace NMR, consisting of diffusion and relaxation experiments, provides detailed information about dynamics of fluids in porous materials. Recently, we showed that two-dimensional Laplace NMR experiments can be carried out with a single scan based on spatial encoding. The method shortens the experiment time by one to three orders of magnitude, and therefore it is called ultrafast Laplace NMR. Furthermore, the single-scan approach facilitates significantly the use of nuclear spin hyperpolarization for boosting the sensitivity of the experiment, because a laborious hyperpolarization procedure does not need to be repeated. Here, we push the limits of the ultrafast Laplace NMR method by applying it, for the first time, in the investigation of a gas phase substance, namely hyperpolarized xenon gas. We show that, regardless of the fast diffusion of gas, layer-like spatial encoding is feasible, and an ultrafast diffusion – T 2 relaxation correlation experiment reveals significantly different signals of free gas and gas adsorbed in a mesoporous controlled pore glass (CPG). The observed diffusion coefficients are many orders of magnitude larger than those detected earlier from liquid phase substances, emphasizing the extended application range of the method. The challenges in the methodology, caused by the fast diffusion, are also discussed.

Graphical abstract

image




8 Ultrafast 2D NMR: Methods and Applications 2017-10-17             

HTML   |   详细信息   |  

Publication date: Available online 16 October 2017
Source:Annual Reports on NMR Spectroscopy

Author(s): Boris Gouilleux, Laetitia Rouger, Patrick Giraudeau

Multidimensional NMR (nD NMR) has become one of the most powerful spectroscopic tools to deliver diverse structural and functional insights into organic and biomolecules as well as on raw materials. A long-standing concern of nD NMR is related to its long experiment duration, arising from the need to sample the indirect dimension(s) in a multistep fashion. For decades, the NMR community has been developing numerous strategies to speed up nD NMR experiments and therefore extend their scope of applications. Among them is the ultrafast (UF) NMR methodology, capable of delivering arbitrary homo- or heteronuclear multidimensional spectra in a single scan. Since the initial concept was published in 2002, the performance of this subsecond 2D NMR approach has been greatly improved so that UF NMR is nowadays a relevant analytical tool used in broad variety of situations whereby the experiment duration is crucial. Following a description of the principles of UF NMR, the present review aims at emphasizing the numerous methodological developments that this approach has undergone so far in 2017. Thereafter, the high versatility of UF NMR is highlighted through the review of the applications that have been reported in a variety of settings and disciplines, in isotropic as well as anisotropic media.





9 Crystal field distortion of La3+ ion-doped Mn-Cr ferrite 2017-10-17             

HTML   |   详细信息   |  

Publication date: 1 February 2018
Source:Journal of Magnetism and Magnetic Materials, Volume 447

Author(s): M.H. Abdellatif, G.M. El-Komy, A.A. Azab, M. Salerno

Ion doping in crystals can result in lattice modifications triggering interesting magnetic and optical properties of the material, understood as a compensation of the crystal deformation and microstrain. We investigated the spinel structure of Mn-Cr ferrite after doping with La3+ ions. The structure was first characterized by X-ray diffraction and high-resolution transmission electron microscopy. Raman scattering spectra were taken that could also be interpreted in terms of crystal field distortion due to La3+ ion doping. On assessing the magneto-impedance of the doped ferrite, it showed giant magneto-impedance behavior, with a strong drop of over 50%. The saturation magnetization was characterised by vibrating sample magnetometer and was found to be 20.25emu/g with remnant magnetization of 1.47emu/g.

Graphical abstract

image




10 Stimuli responsive ion gels based on polysaccharides and other polymers prepared using ionic liquids and deep eutectic solvents 2017-10-17             

HTML   |   详细信息   |  

Publication date: 15 January 2018
Source:Carbohydrate Polymers, Volume 180

Author(s): Kamalesh Prasad, Dibyendu Mondal, Mukesh Sharma, Mara G. Freire, Chandrakant Mukesh, Jitkumar Bhatt

Ion gels and self-healing gels prepared using ionic liquids (ILs) and deep eutectic solvents (DESs) have been largely investigated in the past years due to their remarkable applications in different research areas. Herewith we provide an overview on the ILs and DESs used for the preparation of ion gels, highlight the preparation and physicochemical characteristics of stimuli responsive gel materials based on co-polymers and biopolymers, with special emphasis on polysaccharides and discuss their applications. Overall, this review summarizes the fundamentals and advances in ion gels with switchable properties prepared using ILs or DESs, as well as their potential applications in electrochemistry, in sensing devices and as drug delivery vehicles.





 
共计:1855条记录 页次:1/186    下一页 末页   跳转到第 页  
您还没有登录。 请先登录再使用本系统。
您还没有登录。 请先登录再使用本系统。