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Case study of spatial and temporal variability of snow cover, grain size, albedo and radiative forcing in the Sierra Nevada and Rocky Mountain snowpack derived from imaging spectroscopy
摘要： Quantifying the spatial distribution and temporal change in mountain snow cover, microphysical and optical properties is important to improve our understanding of the local energy balance and the related snowmelt and hydrological processes. In this paper, we analyze changes of snow cover, optical-equivalent snow grain size (radius), snow albedo and radiative forcing by light-absorbing impurities in snow and ice (LAISI) with respect to terrain elevation and aspect at multiple dates during the snowmelt period. These snow properties are derived from the NASA/JPL Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data from 2009 in California’s Sierra Nevada and from 2011 in Colorado’s Rocky Mountains, USA.
关键词： snow cover,grain size,Sierra Nevada,Rocky Mountains,imaging spectroscopy,radiative forcing,albedo
更新于2025-09-04 15:30:14
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Encyclopedia of Spectroscopy and Spectrometry || Spectroscopy of Ions ☆
摘要： Ions and radicals are transient species which are not readily accessible to conventional spectroscopic characterization. There are essentially three problems to be overcome – the production in sufficient concentration, the availability of a sensitive technique enabling their IR or electronic spectra to be recorded and the ability to identify the observed spectral features. The involvement of mass-selection not only leads to the solution of the last problem, but enables methods based on particle detection – fragment ions, electrons and photons – to be incorporated. The aim of the spectroscopic studies is, on the one hand, to provide a fingerprint of the species by its vibrational or electronic spectrum, enabling its identification in various terrestrial and space environments, and on the other hand, the spectroscopic analysis leads to information on geometric structures, force fields and fundamental interactions.
关键词： Electronic spectra,Ions,Spectroscopy,IR spectra,Mass-selection
更新于2025-09-04 15:30:14
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Construction of Ce-MOF@COF hybrid nanostructure: Label-free aptasensor for the ultrasensitive detection of oxytetracycline residues in aqueous solution environments
摘要： Porous organic framework (COF) nanomaterials have drawn increasing attention and showed promising potential in the applications of various fields. Nevertheless, its applications in biosensing or biomedical fields are still in the early stage. In this work, we designed and synthesized a series of nanohybrids of COF and Ce-based metal organic framework (Ce-MOF) for the first time as label-free bioplatforms for a sensitive electrochemical aptasensor to detect oxytetracycline (OTC). A novel kinds of Ce-MOF@COF hybrids were prepared by adding different dosages of COF, into the preparation system of Ce-MOF, for which COF was synthesized using melamine and cyanutic acidmonomers through polycondensation (represented by MCA). Basic characterizations revealed that Ce-MOF@MCA nanohybrids not only remained their orignal crystal and chemical structure and features, such as different Ce species containing in Ce-MOF (Ce3+ and Ce4+), various functional amino-groups of MCA, and individual frameworks, but also showed a large specific surface area and interpenetrated morphologies. As a result, the Ce-MOF@MCA hybrid with high content of MCA exhibited high bioaffinity toward the OTC-targeted aptamer, further leading to the incremental detection effect for OTC detection. Among different hybrid-based aptasensors, the Ce-MOF@MCA-based one with an MCA dosage of 500 mg exhibited the lowest limit of detection at 17.4 fg?mL-1 within a wider linearity of the OTC concentration within 0.1–0.5 ng?mL-1. Additionally, the fabricated aptasensor displayed excellent analytical performance with great reproducibility, high selectivity and stability, and acceptable applicability for detecting OTC in various aqueous solutions, including milk, wastewater, and urine samples. This new Ce-MOF@MCA hybrid will become an excellent aptasensors platform for detecting various analytes, such as antibiotics, heavy metal ions, or cancer markers, and it have shown the promissing application potentials in the fields of biomedicine, food safety and environmental monitoring.
关键词： Ce-based metal organic frameworks,Aptamer sensor,Detection of oxytetracycline,Electrochemical impedance spectroscopy,Covalent organic frameworks
更新于2025-09-04 15:30:14
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[Topics in Current Chemistry Collections] Multidimensional Time-Resolved Spectroscopy || Electronic Couplings in (Bio-) Chemical Processes
摘要： During the last two decades, 2D optical techniques have been extended to the visible range, targeting electronic transitions. Since the report of the very first 2D electronic measurement (Hybl et al. in J Chem Phys 115:6606–6622, [2001]), two-dimensional electronic spectroscopy (2DES) has allowed fundamentally new insights into the structure and dynamics of condensed-phase systems (Ginsberg et al. in Acc Chem Res 42:1352–1363, 2009; Jonas in Annu Rev Phys Chem 54:425–463, 2003), producing experiments that measure correlations among electronic states of an absorbing species within complex systems. 2DES is used to investigate photophysical phenomena involving electronic or vibrational couplings in multi-chromophoric systems [energy transfer in photosynthesis is one great example of how 2DES can disentangle various energy transfer pathways (Brixner et al. in Nature 625–628, 2005; Engel et al. in Nature 446:782–786, 2007; Collini et al. in Nature 463:644–647, 2010)], but also ultrafast photochemical processes in which the tracked molecules change permanently or are heterogeneous (Ruetzel et al. in Proc Natl Acad Sci 111:4764–4769, 2014; Consani et al. in Science 339:1586–1589, 2013). We divide this chapter according to some of the major areas that have been established thanks to 2DES in the following fields: heterogeneity of systems, excitation energy transfer mechanisms, photo-induced coherent oscillations associated with electronic and vibrational couplings, and complex chemical reactions (Fig. 1).
关键词： Energy transfer,Vibronic coupling,Two-dimensional electronic spectroscopy,Photoreactivity,Heterogeneity
更新于2025-09-04 15:30:14
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[Topics in Current Chemistry Collections] Multidimensional Time-Resolved Spectroscopy || Towards Accurate Simulation of Two-Dimensional Electronic Spectroscopy
摘要： We introduce the basic concepts of two-dimensional electronic spectroscopy (2DES) and a general theoretical framework adopted to calculate, from first principles, the nonlinear response of multi-chromophoric systems in realistic environments. Specifically, we focus on UV-active chromophores representing the building blocks of biological systems, from proteins to nucleic acids, describing our progress in developing computational tools and protocols for accurate simulation of their 2DUV spectra. The roadmap for accurate 2DUV spectroscopy simulations is illustrated starting with benchmarking of the excited-state manifold of the chromophoric units in a vacuum, which can be used for building exciton Hamiltonians for large-scale applications or as a reference for first-principles simulations with reduced computational cost, enabling treatment of minimal (still realistic) multi-chromophoric model systems. By adopting a static approximation that neglects dynamic processes such as spectral diffusion and population transfer, we show how 2DUV is able to characterize the ground-state conformational space of dinucleosides and small peptides comprising dimeric chromophoric units (in their native environment) by tracking inter-chromophoric electronic couplings. Recovering the excited-state coherent vibrational dynamics and population transfers, we observe a remarkable agreement between the predicted 2DUV spectra of the pyrene molecule and the experimental results. These results further led to theoretical studies of the excited-state dynamics in a solvated dinucleoside system, showing that spectroscopic fingerprints of long-lived excited-state minima along the complex photoinduced decay pathways of DNA/RNA model systems can be simulated at a reasonable computational cost. Our results exemplify the impact of accurate simulation of 2DES spectra in revealing complex physicochemical properties of fundamental biological systems and should trigger further theoretical developments as well as new experiments.
关键词： Aromatic amino acids,DNA/RNA nucleobases,Theoretical simulations,QM/MM computations,Wavefunction methods,Nonlinear electronic spectroscopy
更新于2025-09-04 15:30:14
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Transmission Spectroscopy in Noninvasive Blood Glucose Measurement
摘要： The use of laser diodes and photodiodes in transmission spectroscopy has some effects (temperature, time, spectral, and spatial) reducing the accuracy of glucose measurement. These effects can be reduced by using a (1600 ± 3) nm laser in combination with fixation and occlusion of the tissue area under examination. In this work, a method is suggested that allows spatial displacements of the system to be taken into account. A number of methods for reducing the effect of the thermal drift of the diodes are also suggested. A portable noninvasive optical glucose meter implemented using these methods provides high clinical performance: more than 97% of the measurements are in the A and B zones of the Parkes error grid.
关键词： photodiodes,transmission spectroscopy,noninvasive blood glucose measurement,laser diodes,thermal drift,spatial displacements
更新于2025-09-04 15:30:14
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Methane on Mars: New insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration
摘要： The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5 × 5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.
关键词： NOMAD,Instrumentation,Infrared spectroscopy,Mars atmosphere,Methane
更新于2025-09-04 15:30:14
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Fabrication and electrical characterization of (Bi0.49Na0.49Ba0.02)TiO3-PVDF thin film composites
摘要： The barium doped bismuth sodium titanate (i.e., Bi0.49Na0.490.98Ba0.02)TiO3 (BNBT) powder was prepared by a conventional ceramic processing route. The thin film composites of BNBT- PVDF (polyvinylidene fluoride) were fabricated via a solution casting route. The scanning electron micrographs of the thin film samples show the homogenous distribution of grains with absence of cracks/pores. It is observed that with the increase of BNBT content in PVDF leads to enhancement in the dielectric permittivity and the reduction in the dissipation factor (tangent loss). The various electrical properties of the thin film samples were studied in the frequency range of 1 kHz to 1 MHz at different temperature between 25 and 100 °C. The prepared composite films have been used to study the (a) relationship between properties and crystal structure and (b) relaxation and conduction mechanism through the complex modulus and impedance spectroscopy. The contribution of grains was analyzed in the composite films by the fitting of equivalent circuit with the experimental data. An existence of the non-Debye type of dielectric relaxation was indicated by studying of the impedance and modulus parameters. The calculated activation energy from the temperature dependence of AC conductivity depicts hopping nature of charge carriers, which further explain the conduction process and mechanism in the prepared composites.
关键词： Impedance spectroscopy,Dielectric,Ceramic-polymer composites
更新于2025-09-04 15:30:14
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Structural, Linear and Third Order Nonlinear Optical Properties of Sol-Gel Grown Ag-CdS Nanocrystalline Thin Films
摘要： Pure and Ag doped CdS nanocrystalline ?lms with different Ag doping concentrations were successfully grown on glass substrates by a sol-gel spin coating method. Ag doping was performed using silver acetate aqueous solution with 0.01, 0.02 and 0.03 M concentrations via ion exchange. The in?uences of Ag doping on structural, vibrational, morphological, linear and third order nonlinear optical properties of CdS nanocrystalline ?lms were studied. The x-ray diffraction patterns of the ?lms exhibited a broad peak centered at an angle 2h = 26.5(cid:2) along the (111) plane, which con?rms the cubic structure and formation of nanocrystalline ?lms. Raman spectra of ?lms demonstrate a shift in longitudinal optical phonon vibrations as compared to the bulk counterpart. Pure CdS ?lm shows high transmittance (83%) in the visible and near infrared (NIR) regions. With Ag doping, a signi?cant red shift in the band edge and reduction in the transmittance of the ?lms in visible and NIR regions were observed. However, the ?lms doped with Ag showed appreciable transmittance in visible region for window layer applications. A signi?cant effect on optical parameters such as absorption index, refractive index, and optical dielectric constant was observed after Ag doping. The nonlinear optical properties of ?lms were enhanced with incorporation of Ag atoms into the CdS binary system. The values of nonlinear optical susceptibility v(3) and refractive index n2 were found to increase with increasing Ag concentration and were estimated to be in the range of 2.92 9 10(cid:2)10 (cid:2) 1910(cid:2)7 esu and 1.00 9 10(cid:2)9 2.00 9 10(cid:2)7 esu, respectively. These values suggest that these ?lms can be potential candidates for nonlinear optical device applications.
关键词： structural properties,optical properties,surface morphology,Ag-CdS,Raman spectroscopy
更新于2025-09-04 15:30:14
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The study on negative dielectric properties of Al/PVA (Zn-doped)/p-Si (MPS) capacitors
摘要： In this research, PVA (doped with 7% Zn) was sandwiched between Al and p-Si as a polymer interfacial layer. Voltage and frequency effect on the real and imaginary components of complex dielectric constant (e0 and e00), electric modulus (M0 and M00), loss tangent (tan d) and electrical conductivity (r) of the MPS-type capacitor has been studied. Impedance spectroscopy method was used between 5 and 5000 kHz at room temperature. Almost all frequency-related parameters were found as quite susceptible, especially in the accumulation and depletion regions. These changes in real and imaginary components of dielectric properties in depletion region were attributed to the interface layer and dipole polarization, the existence of surface states (Nss) and their relaxation time (s), especially at low frequencies. But these changes in the accumulation region were attributed to the existence of interfacial layer and series resistance (Rs) of the capacitor owing to the voltage divided between them and capacitor. As a result, frequency, applied biases, interfacial polymer layer, polarization processes, Nss and Rs of the capacitor are more effective on the values of e0, e00, tan d, M0, M00 and r. Therefore, the effects of them must be considered in determining the dielectric parameters, electric modulus, conductivity and conduction mechanisms in the capacitors with and without an interfacial layer such as insulator/oxide, polymer, ferroelectric materials.
关键词： Electric modulus,Impedance spectroscopy method,Electrical conductivity,Negative dielectric properties
更新于2025-09-04 15:30:14