Excellent Spectral Quality Research Articles

Solution-state nuclear magnetic resonance spectroscopy of crystalline cellulosic materials using a direct dissolution ionic liquid electrolyte.

Owing to its high sustainable production capacity, cellulose represents a valuable feedstock for the development of more sustainable alternatives to currently used fossil fuel-based materials. Chemical analysis of cellulose remains challenging, and analytical techniques have not advanced as fast as the development of the proposed materials science applications. Crystalline cellulosic materials are insoluble in most solvents, which restricts direct analytical techniques to lower-resolution solid-state spectroscopy, destructive indirect procedures or to 'old-school' derivatization protocols. While investigating their use for biomass valorization, tetralkylphosphonium ionic liquids (ILs) exhibited advantageous properties for direct solution-state nuclear magnetic resonance (NMR) analysis of crystalline cellulose. After screening and optimization, the IL tetra-n-butylphosphonium acetate [P4444][OAc], diluted with dimethyl sulfoxide-d6, was found to be the most promising partly deuterated solvent system for high-resolution solution-state NMR. The solvent system has been used for the measurement of both 1D and 2D experiments for a wide substrate scope, with excellent spectral quality and signal-to-noise, all with modest collection times. The procedure initially describes the scalable syntheses of an IL, in 24-72 h, of sufficient purity, yielding a stock electrolyte solution. The dissolution of cellulosic materials and preparation of NMR samples is presented, with pretreatment, concentration and dissolution time recommendations for different sample types. Also included is a set of recommended 1D and 2D NMR experiments with parameters optimized for an in-depth structural characterization of cellulosic materials. The time required for full characterization varies between a few hours and several days.

Self-Assembly of Solvent-Stabilized Au Nanocluster as Efficient Förster Resonance Energy-Transfer Initiator for White Light Generation.

Aggregation-induced enhancement (AIE) in the photoluminescence quantum yield (PLQY) from 12.5 to 51% in the N,N-dimethylformamide (DMF)-stabilized Au nanocluster (AuNC) system is reported here. The self-assembling of AuNC has been achieved via hydrogen bonding interaction, which is further utilized in designing the AuNC_DCM system for realizing a Förster resonance energy transfer (FRET)-based white LED (WLED), having CIE coordinates of (0.35, 0.29). The solution-processed fabrication strategy used, has given us the liberty to optimize its components for optimal full-spectrum light output. The CIE coordinates of the designed WLED have been improved further to (0.33, 0.32), with a high color rendering index of 93 and correlated color temperature of 5620 K by incorporating a green emitter, namely nitrogen-doped graphene quantum dots (NGQD), in the AuNC_DCM system. The excellent spectral quality of the as-designed WLED and the repeatability of the proposed fabrication method will make the developed AuNCs_DCM FRET conjugate useful in practical photonic applications.

Emission Spectrochemical Analysis of Soft Samples Including Raw Fish by Employing Laser-Induced Breakdown Spectroscopy with a Subtarget at Low-Pressure Helium Gas.

Laser-induced breakdown spectroscopy (LIBS) to detect the light elements such as lithium (Li) and boron (B) and heavy elements such as copper (Cu) and lead (Pb) in raw fish samples is reported in this work. This is made possible by understanding that the soft target absorbs recoil energy and as a result, the ablated atoms gushing from the soft target do not acquire sufficient speed to form a shock wave. In order to overcome this problem, we set a subtarget on the back of the soft target so as to produce the repulsion force by which the gushing speed of the ablated atoms is increased, yielding a sufficiently high plasma temperature or sufficiently large thermal energy needed for the excitation of the ablated atoms. Excellent spectral qualities of various soft samples such as margarine, butter, peanut butter, strawberry jam, raw tuna, raw gindara, and raw salmon are presented. Furthermore, a linear calibration curve with a zero intercept is also obtained for Li, Cu, and Pb. The detection limit of Li, Cu, and Pb is found to be around 0.1 mg/L. This modification of LIBS for soft samples by using a subtarget effect clearly promises a rapid and in situ soft sample analysis since there is practically no sample digestion in the analysis.

Extraction of high-quality genomic DNA and identification of different DNA barcoding markers for chickpea (Cicer arietinum L.)

The genetic studies of individual plants, especially self-pollinated species like chickpea need to be evaluated at the DNA level with the help of molecular markers for identifying genetic variations among the plants. High-quality DNA extraction is a prerequisite for genetic studies. Extraction of intact genomic DNA with high – molecular mass is essential for the study of many molecular biology applications like Polymerase Chain Reaction, endonuclease restriction digestion, southern blot analysis, and also for the construction of a genomic library. Several plant DNA extraction methods are available, even though the DNA isolation methods that give good yield employing both quantity and quality is quite difficult especially for self-pollinated crops like a chickpea. This work was focused on developing a standard protocol for the extraction of genomic DNA and identifying different barcoding markers. The result revealed that the CTAB extraction method with slight modification in protocol had been optimized for DNA isolation. The purified DNA, which was isolated through the CTAB method, had excellent spectral qualities and is efficiently digested by a restriction endonuclease, and is found to be more suitable for long-fragment PCR amplification. DNA barcoding is considered as a promising tool because it provides a practical and standard identification of plants. The isolated DNA sample was processed with a classical DNA barcoding approach by amplifying and sequencing with a universal primer. According to the result, among the different barcoding markers studied, the RbcL and Mat K were found to given the best result for molecular species identification in chickpea.

68 MHz Fundamental Repetition Rates for Mode-Locked Erbium Doped Fiber Laser based Carbon Nanotube Saturable Absorber

A carbon nanotube thin film as saturable absorber in a cavity design of mode-locked fiber laser is reported in this work. Measured by power dependent absorption setup, 22% modulation depth of the saturable absorber is estimated which is ideal for stabilizing the mode-locked operation. Based on the scanning image from atomic force microscope (AFM), Single wall carbon nanotube components are identified existed in the thin film. The laser cavity employed a ~40 cm long erbium doped fiber as a gain medium which corresponds to the laser wavelength of 1550 nm (telecommunication wavelength region). Total length cavity of the fiber laser is about 3.1 m where shorter cavity design is required for higher repetition rate. This proposed system result in a firm soliton spectrum at centre wavelength of ~1561 nm with ~0.7 mW average output power and pulse duration of 410 fs. The pulses are generated at fundamental repetition rate of 68 MHz without any distortion and excellent spectral quality.

Performance of Spatial Frequency Discrete Wavelet Transform Based Remote Sensing Image Fusion Algorithm

The high sensor cost for producing images with superior spectral and spatial qualities in remote sensing application have led to the development of image fusion algorithms. Image fusion technique combines a Panchromatic image and a Multispectral image with an aim to produce images with excellent spatial and spectral qualities. One of the major factors that affect the performance of any image fusion algorithm is the capability of the algorithm in extracting the spatial and spectral data from the respective images and how effective the so extracted information is blended together. One of the recently developed spectral domain algorithm to perform image fusion in remote sensing applications is Spatial Frequency Discrete Wavelet Transform abbreviated as SFDWT. The excellence of SFDWT image fusion algorithm is already proven better than the prevailing algorithms based on Discrete Wavelet Transform. This paper is coined with an eye to realize the performance of SFDWT based image fusion algorithm with respect to IHS-DWT, which being an enhanced form of a typical DWT based image fusion algorithm. The performance of SFDWT and IHS-DWT based image fusion algorithms will be evaluated by applying both techniques in the fusion of urban images received from Pléiades sensors with 1:4 resolution ratio using qualitative and quantitative image quality assessment methods. The consequence of varying the decomposition level on the quality of the images produced using SFDWT image fusion technique and three variants of IHS-DWT techniques based on substitution, averaging and maximum selection will be also evaluated. From the experimental analysis done using MATLAB simulation, it will be vivid that images obtained using image fusion algorithm based on SFDWT are much better than that obtained using IHS-DWT technique with excellent spatial and spectral qualities.

Quantification of rare earth elements with low pressure laser induced breakdown spectroscopy employing subtarget supported micro mesh sample holder

Presented in this paper are the results of practical application of laser-induced breakdown spectroscopy to sensitive detection of rare earth elements (REEs) in trace amounts using a Cu subtarget supported stainless steel micro mesh (SSMM) powder sample holder. Powder samples containing separately a number of REEs (Yb, Y, Eu, and La) are measured using the SSMM sample holder and a 68 mJ ns Nd:YAG laser with −5 mm defocused irradiation in 1.3 kPa ambient air. All the resulted emission spectra are shown to exhibit excellent spectral quality featuring well resolved sharp spectral lines with low background and without spectral interference from the sample holder. Further measurements of additional powder samples with varied content of REEs are performed to reveal the existence of linear calibration lines with extrapolated zero intercept and well below 100 ppm detection limits promising for practical quantitative REEs analysis, particularly for sensitive field exploration of REEs.

Underlying Physical Process for the Unusual Spectral Quality of Double Pulse Laser Spectroscopy in He Gas.

This study is aimed at elucidating the physical processes responsible for the excellent spectral qualities in terms of full width at half-maximum (fwhm) and signal-to-noise (S/N) ratio shown in a special double pulse laser-induced spectroscopy. Apart from the use of atmospheric He ambient gas, the achievement is due to the first laser for generating He gas plasma and the subsequent use of the second laser pulse for target ablation, in opposite order of the two-laser operations in conventional double pulse LIBS. This setup allows adjustments of the many experimental parameters to yield the optimal condition resulting in 0.03 nm fwhm and around 1000× S/N ratio of Cu I 521.8 nm and far surpasses the spectral qualities obtained by other techniques. This is obtained by allowing the crucial separation of the target plasma from the He gas plasma and thereby enabling the He-assisted excitation (HAE) to play its full and unique role of nonthermal excitation, taking advantage of metastable excited He atoms in the He plasma and the Penning-like energy transfer process. This excellent performance is further verified by its successful application analysis of Cr in low alloy steel samples, with the presence of smooth linear calibration lines, signifying the absence of the self-absorption effect well-known in ordinary LIBS.

Food analysis employing high energy nanosecond laser and low pressure He ambient gas

We report the results of an experimental study of food analysis using Nd:YAG nanosecond (ns) laser at various pulse energies in atmospheric ambient air and He ambient gas at different pressures. In contrary to previous results indicating the unfavorable applications of LIBS to food analysis using lower pulse energies and atmospheric ambient air, this study demonstrates clearly the excellent spectral quality obtained from a number of food samples of different hardnesses with high energy (132 mJ) ns laser pulses and 20 Torr He ambient gas. A series of energy dependent intensity measurements show that the intensities generally increase with higher laser energies and harder samples which can be attributed to the generation of stronger shock wave plasma and the subsequently induced He assisted excitation (HAE) mechanism which is responsible for the sharp emission lines and the very low spectral background. Using mochi samples with different Cu impurity contents, this experiment further reveals the existence of a linear calibration line and a detection limit of sub ppm level. The results of this study have thus suggested the promising development of low cost and practical technique for quantitative food analysis in place of more expensive and bulkies picosecond laser used before.

Poly-γ-p-Biphenylmethyl-Glutamate as Enantiodifferentiating Alignment Medium for NMR Spectroscopy with Temperature-Tunable Properties.

The use of anisotropic NMR parameters-especially residual dipolar couplings (RDCs)-offers access to additional structural information and, therefore, alignment media required for this approach are under a continuous development. Here, we present poly-γ-p-biphenylmethyl-glutamate (PBPMG) as a new versatile enantiodifferentiating alignment medium. The thermoresponsive properties of this polymer allowed for RDC measurements of more than one orientation within the same sample at different temperatures. Moreover, the outstanding enantiodifferentiation along with excellent spectral quality even offered the opportunity to differentiate enantiomers in mixtures.

Shock wave plasma generation in low pressure ambient gas from powder sample using subtarget supported micro mesh as a sample holder and its potential applications for sensitive analysis of powder samples

We present in this report the results of experimental study on the spectrochemical analysis of powder samples using subtarget supported micro mesh (SSMM) sample holder in low pressure ambient gases. The study is substantiated by establishing the analyte excitation mechanism with the evidence of shock wave plasma generation and the high temperature induced subsequently required for the thermal excitation and emission of the ablated atoms. The application of SSMM sample holder using Cu subtarget and stainless steel micro mesh to a number of powder samples in low pressure ambient gases are shown to produce generally sharp emission lines with low background, without suffering from intensity reduction and matrix effect commonly found in the use of pelletized powder samples. The same excellent spectral quality is demonstrated by its application to the analysis of rice samples which is the major staple diets in a large number of countries. In particular the analysis of Zn in rice is shown to exhibit a linear calibration line with extrapolated zero intercept and a detection limit of <0.87 μg/g which is promising for quantitative analysis.

Graphene-based optical fiber ammonia gas sensor

ABSTRACTTo precisely monitor and forecast harmful gases in the air, a high-performance fiber gas sensor based on graphene nanometer-functional materials is proposed and experimentally demonstrated. The sensing area of the proposed sensor was a graphene-wrapped fiber which was cascaded between a down-taper and an up-taper. The graphene wrapping on the subuliform fiber sensing area substantially increased the evanescent field which transmits along the surface of fiber and will have a significant sensitization effect on the gas sensing. At the same time, the gas molecules adsorbed by graphene lead to changes of the effective refractive index of the composite waveguide, which causes corresponding wavelength drift and attenuation. By detecting the change of the output optical signal, the concentration of gas molecules was detected. Based on this principle, the sensor realized a gas sensitivity of 0.015 nm/ppm. The research shows that the sensing structure has the advantages of small volume, good mechanical strength, excellent spectral quality, and high sensitivity.

A New Geometry Enforcing Variational Model for Pan-Sharpening

In this paper, a new variational method for pan-sharpening is proposed to obtain a high-resolution multispectral (MS) image from a low-resolution MS image and a high-resolution panchromatic (PAN) image. In addition to using the data generative fidelity term and wavelet-based spectral information preserving term, we also associate the Hessian structural information of the PAN image with the desired pan-sharpened MS image to enforce geometry correspondence in the fusion process. More specifically, we introduce a new geometry enforcing term called “vectorial Hessian feature consistence” and combine it with the data generative fidelity term and wavelet-based spectral information preserving term to form an unified variational model for pan-sharpening. Then, the optimal solution of the proposed variational pan-sharpening model is effectively obtained using the fast iterative shrinkage thresholding algorithm (FISTA) method. In addition to well preserving spectral information, our algorithm is also able to eliminate some undesired blocky or blurry artifacts by incorporating the curvature information. Experimental results demonstrate that the proposed method outperforms various well-known pan-sharpening methods in terms of both excellent spatial and spectral qualities.

Software reconfigurable highly flexible gain switched optical frequency comb source

The authors present the performance and noise properties of a software reconfigurable, FSR and wavelength tunable gain switched optical frequency comb source. This source, based on the external injection of a temperature tuned Fabry-Pérot laser diode, offers quasi-continuous wavelength tunability over the C-band (30nm) and FSR tunability ranging from 6 to 14GHz. The results achieved demonstrate the excellent spectral quality of the comb tones (RIN ~-130dB/Hz and low phase noise of 300kHz) and its outstanding stability (with fluctuations of the individual comb tones of less than 0.5dB in power and 5pm in wavelength, characterized over 24hours) highlighting its suitability for employment in next generation flexible optical transmission networks.

Excitation mechanisms in 1 mJ picosecond laser induced low pressure He plasma and the resulting spectral quality enhancement

We report in this paper the results of an experimental study on the spectral and dynamical characteristics of plasma emission induced by 1 mJ picoseconds (ps) Nd-YAG laser using spatially resolved imaging and time resolved measurement of the emission intensities of copper sample. This study has provided the experimental evidence concerning the dynamical characteristics of the excitation mechanisms in various stages of the plasma formation, which largely consolidate the basic scenarios of excitation processes commonly accepted so far. However, it is also clearly shown that the duration of the shock wave excitation process induced by ps laser pulses is much shorter than those observed in laser induced breakdown spectroscopy employing nanosecond laser at higher output energy. This allows the detection of atomic emission due exclusively to He assisted excitation in low pressure He plasma by proper gating of the detection time. Furthermore, the triplet excited state associated with He I 587.6 nm is shown to be the one most likely involved in the process responsible for the excellent spectral quality as evidenced by its application to spectrochemical analysis of a number of samples. The use of very low energy laser pulses also leads to minimal destructive effect marked by the resulted craters of merely about 10 μm diameter and only 10 nm deep. It is especially noteworthy that the excellent emission spectrum of deuterium detected from D-doped titanium sample is free of spectral interference from the undesirable ubiquitous water molecules without a precleaning procedure as applied previously and yielding an impressive detection limit of less than 10 μg/g. Finally, the result of this study also shows a promising application to depth profiling of impurity distribution in the sample investigated.

Evaluation of 2D spatially selective MR spectroscopy using parallel excitation at 7 T.

In this work, two-dimensional (2D) spatially selective magnetic resonance spectroscopy (MRS) was evaluated in both phantom and human brain using 8-channel parallel excitation (pTX) at 7 T and compared to standard STEAM. A 2D spiral excitation k-space trajectory was segmented into multiple individual segments to increase the bandwidth. pTX was used to decrease the number of segments by accelerating the trajectory. Different radio frequency (RF) shim settings were used for refocusing, water suppression and fat saturation pulses. Phantom experiments demonstrate that, although segmented 2D excitation provided excellent spatial selectivity and spectral quality, STEAM outperformed it in terms of outer volume suppression with 0.6% RMSD compared to 1.7%, 2.5%, 3.9% and 5.5% RMSDs for acceleration factors of R=1, 2, 3 and 4, respectively. Seven major metabolites [choline (Cho), creatine (Cr), phosphocreatine (PCr), glutamate (Glu), glutamine (Gln), glutathione (GSH) and N-acetylaspartate (NAA)] were detected with sufficient accuracy [Cramér-Rao lower bounds (CRLBs) <20%] from the in vivo spectra of both methods. Conservative RF power limits resulted in reduced SNR for 2D selective MR spectra (SNR 131 and 82 for R=1 and 2, respectively) compared to the reference STEAM spectrum (SNR 199). Single voxel spectra acquired using 2D selective MRS with and without pTX showed very good agreement with the reference STEAM spectrum. Efficient SAR management of the 2D selective MRS sequence would potentially improve the SNR of spectra.

NMR Structural Studies of the Binding of Activating Mamba Toxin Tx7335 on the Potassium Channel KcsA

We have recently identified a novel 63 amino acid residue three-finger toxin (called Tx7335) from eastern green mamba snake (Dendroaspis angusticeps) which interacts with KcsA and induces an increase in frequency and duration of individual channel openings when added to the outside of the channel. The toxin exerts this activating effect both on wild-type KcsA as well as on an agitoxin2-sensitive mutant form of the channel, indicating a mode of action and binding site that are different from the classic pore-blocker toxins. We are currently using NMR spectroscopy to unravel the structural underpinnings of this mechanism of action. High yield of purified 15N labeled KcsA and excellent NMR spectral quality have been achieved. Currently the characterization of toxin binding using 1H15N correlation spectra of 15N labeled KcsA in the absence and presence of toxin is ongoing. Experiments are conducted in different membrane mimetics including DMPC/DHPC bicelles and DPC or DM micelles at different pH, temperature and salt concentration. Some chemical shifts and peak intensity changes upon toxin addition have been observed. Continuing NMR structural studies will further elucidate the mechanism of how Tx7335 interacts with KcsA and shed light on the conformational and dynamic changes of C-type inactivation in KcsA and on a novel mechanism of ion channel regulation.

A New Pansharpening Algorithm Based on Total Variation

In this letter, we present a new method for the pansharpening of multispectral satellite imagery. Pansharpening is the process of synthesizing a high spatial resolution multispectral image from a low spatial resolution multispectral image and a high-resolution panchromatic (PAN) image. The method uses total variation to regularize an ill-posed problem dictated by a widely used explicit image formation model. This model is based on the assumptions that a linear combination of the bands of the pansharpened image gives the PAN image and that a decimation of the pansharpened image gives the original multispectral image. Experimental results are based on two real datasets and the quantitative quality of the pansharpened images is evaluated using a number of spatial and spectral metrics, some of which have been recently proposed and do not need a reference image. The proposed method compares favorably to other well-known methods for pansharpening and produces images of excellent spatial and spectral quality.

Real-time motion- and B0-correction for LASER-localized spiral-accelerated 3D-MRSI of the brain at 3 T

The full potential of magnetic resonance spectroscopic imaging (MRSI) is often limited by localization artifacts, motion-related artifacts, scanner instabilities, and long measurement times.Localized adiabatic selective refocusing (LASER) provides accurate B1-insensitive spatial excitation even at high magnetic fields. Spiral encoding accelerates MRSI acquisition, and thus, enables 3D-coverage without compromising spatial resolution. Real-time position- and shim/frequency-tracking using MR navigators correct motion- and scanner instability-related artifacts. Each of these three advanced MRI techniques provides superior MRSI data compared to commonly used methods.In this work, we integrated in a single pulse sequence these three promising approaches. Real-time correction of motion, shim, and frequency-drifts using volumetric dual-contrast echo planar imaging-based navigators were implemented in an MRSI sequence that uses low-power gradient modulated short-echo time LASER localization and time efficient spiral readouts, in order to provide fast and robust 3D-MRSI in the human brain at 3T.The proposed sequence was demonstrated to be insensitive to motion- and scanner drift-related degradations of MRSI data in both phantoms and volunteers. Motion and scanner drift artifacts were eliminated and excellent spectral quality was recovered in the presence of strong movement.Our results confirm the expected benefits of combining a spiral 3D-LASER-MRSI sequence with real-time correction. The new sequence provides accurate, fast, and robust 3D metabolic imaging of the human brain at 3T. This will further facilitate the use of 3D-MRSI for neuroscience and clinical applications.

How the Saint Santin incoherent scatter system paved the way for a French involvement in EISCAT

Abstract. This paper relates the development of a French incoherent scatter system which started its operations in 1965. This development took place several years after the initial implementation of such systems in the United States, in Peru and in the United Kingdom. The French system, owing to its bistatic configuration and the use of continuous waves, differed from the previous ones. These characteristics yielded signals of excellent spectral quality, unravelling the possibility of inferring physical parameters (Doppler shift, average ion mass) out of reach, at that time, of other systems. The possibility of making ion drift vector measurements led to extend the system into a quadristatic configuration. The multiple capabilities offered by the incoherent scatter technique, notably as concerns the thermodynamical properties of the ionosphere and of the thermosphere, led further the French community to a project of embarking an incoherent scatter radar on board a ship. Taking account of a project of a Scandinavian auroral zone radar and of the considerable interest of the study of auroral zone electrodynamics, the French community abandoned the idea of the ship and expressed an interest in joining the Scandinavian project in conjunction with Germany and the United Kingdom.