scholarly journals Spatial and spectral features of the luminescence of liquid nitrogen stimulated by infrared lasers

2021 ◽  
Vol 2056 (1) ◽  
pp. 012038
Author(s):  
N V Klassen ◽  
P V Provotorov
Keyword(s):  
Liquid Nitrogen ◽  
Femtosecond Lasers ◽  
Spectral Characteristics ◽  
Average Power ◽  
Visible Region ◽  
Spectral Lines ◽  
Spectral Features ◽  
Nanosecond Lasers ◽  
Spectral Bands ◽  
Cryogenic Liquids

Abstract Spectral features of cryogenic liquids, especially nitrogen, seem to be clearly investigated due to the wide application in science. On the other hand, material properties can really be different under intensive laser irradiation. During irradiation of liquid nitrogen with pulsed (pulse duration 20 ns) YaG: Nd 1064 nm laser with average power of 0.3 W we have found bright luminescence in the visible region with five narrow spectral lines. This phenomenon can be explained by the multiphoton excitation of nitrogen molecules and ions with infrared photons. Its spatial and spectral characteristics are attributed to Amplified Spontaneous Emission. The main features include super-linear dependence of the emission intensity on the intensity of the excitation radiation, limited amount of narrow spectral bands and conical geometry of the emission with the clear separation of the cones in correspondence with the spectral lines of the emission. This phenomenon manifests liquid nitrogen as the convenient substance of Kerr type for studies of various non-linear optical processes by means of nanosecond lasers instead of femtosecond lasers applied usually for these purposes.

Reflectance characteristics of cumulative defoliation of balsam fir

1988 ◽  
Vol 18 (8) ◽  
pp. 1008-1016 ◽  
Author(s):  
D. G. Leckie ◽  
P. M. Teillet ◽  
G. Fedosejevs ◽  
D. P. Ostaff
Keyword(s):  
Near Infrared ◽  
Spectral Characteristics ◽  
Broad Band ◽  
Integrating Sphere ◽  
Simple Relationship ◽  
Spectral Bands ◽  
Infrared Wavelengths ◽  
Remote Sensing Techniques ◽  
Middle Infrared ◽  
Airborne Sensors

Knowledge of the spectral characteristics of trees with varying degrees of needle loss is essential for developing remote sensing techniques for assessing defoliation. Spectra covering the range 400–2400 nm were acquired for single tree crowns suffering varying degrees of cumulative defoliation due to the spruce budworm (Choristoneurafumiferana (Clem.)), using a spectrometer mounted in the bucket of a boom truck. Spectra over the range 360–1100 nm were also obtained for the components of defoliated trees (i.e., needles, bare branches, and lichen), using a separate spectrometer and integrating sphere. Estimates of defoliation symptoms of each tree were made from the ground and above the tree. Changes in reflectance had a close and simple relationship with the defoliation symptoms measured. The spectral differences due to cumulative defoliation that were observed were broad-band features. The best spectral regions for differentiating levels of cumulative defoliation symptoms were the blue, red, shorter near-infrared wavelengths, and middle-infrared. Although currently available satellite and airborne sensors operate in these spectral regions, defoliation assessment may be improved by the use of optimized spectral bands.

scholarly journals How Sensitive are EEG Results to Preprocessing Methods: A Benchmarking Study

2020 ◽  
Author(s):  
Kay A. Robbins ◽  
Jonathan Touryan ◽  
Tim Mullen ◽  
Christian Kothe ◽  
Nima Bigdely-Shamlo
Keyword(s):  
Best Practices ◽  
General Structure ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Spectral Features ◽  
Eeg Analysis ◽  
Research Reporting ◽  
Automated Processing ◽  
Open Question

AbstractAlthough several guidelines for best practices in EEG preprocessing have been released, even those studies that strictly adhere to those guidelines contain considerable variation in the ways that the recommended methods are applied. An open question for researchers is how sensitive the results of EEG analyses are to variations in preprocessing methods and parameters. To address this issue, we analyze the effect of preprocessing methods on downstream EEG analysis using several simple signal and event-related measures. Signal measures include recording-level channel amplitudes, study-level channel amplitude dispersion, and recording spectral characteristics. Event-related methods include ERPs and ERSPs and their correlations across methods for a diverse set of stimulus events. Our analysis also assesses differences in residual signals both in the time and spectral domains after blink artifacts have been removed. Using fully automated pipelines, we evaluate these measures across 17 EEG studies for two ICA-based preprocessing approaches (LARG, MARA) plus two variations of Artifact Subspace Reconstruction (ASR). Although the general structure of the results is similar across these preprocessing methods, there are significant differences, particularly in the low-frequency spectral features and in the residuals left by blinks. These results argue for detailed reporting of processing details as suggested by most guidelines, but also for using a federation of automated processing pipelines and comparison tools to quantify effects of processing choices as part of the research reporting.

scholarly journals Mass spectral characterization of primary emissions and implications in source apportionment of organic aerosol

2020 ◽  
Vol 13 (6) ◽  
pp. 3205-3219 ◽  
Author(s):  
Weiqi Xu ◽  
Yao He ◽  
Yanmei Qiu ◽  
Chun Chen ◽  
Conghui Xie ◽  
...  
Keyword(s):  
Source Apportionment ◽  
Spectral Characteristics ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Spectral Characterization ◽  
Rural Site ◽  
Spectral Features ◽  
Mass Spectral ◽  
Spectral Profiles ◽  
Primary Emissions

Abstract. Source apportionment of organic aerosol (OA) from aerosol mass spectrometer (AMS) or aerosol chemical speciation monitor (ACSM) measurements relies largely upon mass spectral profiles from different source emissions. However, the changes in mass spectra of primary emissions from AMS–ACSM with the newly developed capture vaporizer (CV) are poorly understood. Here we conducted 21 cooking, crop straw, wood, and coal burning experiments to characterize the mass spectral features of OA and water-soluble OA (WSOA) using SV-AMS and CV-ACSM. Our results show overall similar spectral characteristics between SV-AMS and CV-ACSM for different primary emissions despite additional thermal decomposition in CV, and the previous spectral features for diagnostics of primary OA factors are generally well retained. However, the mass spectral differences between OA and WSOA can be substantial for both SV-AMS and CV-ACSM. The changes in f55 (fraction of m∕z 55 in OA) vs. f57, f44 vs. f60, and f44 vs. f43 in CV-ACSM are also observed, yet the evolving trends are similar to those of SV-AMS. By applying the source spectral profiles to a winter CV-ACSM study at a highly polluted rural site in the North China Plain, the source apportionment of primary OA was much improved, highlighting the two most important primary sources of biomass burning and coal combustion (32 % and 21 %). Considering the rapidly increasing deployments of CV-ACSM and WSOA studies worldwide, the mass spectral characterization has significant implications by providing essential constraints for more accurate source apportionment and making better strategies for air pollution control in regions with diverse primary emissions.

scholarly journals Detection of Magnesite and Associated Gangue Minerals using Hyperspectral Remote Sensing—A Laboratory Approach

2020 ◽  
Vol 12 (8) ◽  
pp. 1325
Author(s):  
Baru Chung ◽  
Jaehyung Yu ◽  
Lei Wang ◽  
Nam Hoon Kim ◽  
Bum Han Lee ◽  
...  
Keyword(s):  
Logistic Regression ◽  
Random Forest ◽  
Mineral Composition ◽  
Regression Models ◽  
Spectral Characteristics ◽  
Random Forest Algorithm ◽  
Band Ratio ◽  
Logistic Regression Models ◽  
Spectral Bands ◽  
Absorption Features

This study introduced a detection method for magnesite and associated gangue minerals, including dolomite, calcite, and talc, based on mineralogical, chemical, and hyperspectral analyses using hand samples from thirteen different source locations and Specim hyperspectral short wave infrared (SWIR) hyperspectral images. Band ratio methods and logistic regression models were developed based on the spectral bands selected by the random forest algorithm. The mineralogical analysis revealed the heterogeneity of mineral composition for naturally occurring samples, showing various carbonate and silicate minerals as accessory minerals. The Mg and Ca composition of magnesite and dolomite varied significantly, inferring the mixture of minerals. The spectral characteristics of magnesite and associated gangue minerals showed major absorption features of the target minerals mixed with the absorption features of accessory carbonate minerals and talc affected by mineral composition. The spectral characteristics of magnesite and dolomite showed a systematic shift of the Mg-OH absorption features toward a shorter wavelength with an increased Mg content. The spectral bands identified by the random forest algorithm for detecting magnesite and gangue minerals were mainly associated with spectral features manifested by Mg-OH, CO3, and OH. A two-step band ratio classification method achieved an overall accuracy of 92% and 55.2%. The classification models developed by logistic regression models showed a significantly higher accuracy of 98~99.9% for training samples and 82–99.8% for validation samples. Because the samples were collected from heterogeneous sites all over the world, we believe that the results and the approach to band selection and logistic regression developed in this study can be generalized to other case studies of magnesite exploration.

Numerical analysis of factors influencing thermal effects generated by cavitation flow of cryogenic fluids

2020 ◽  
Vol 34 (17) ◽  
pp. 2050184 ◽  
Author(s):  
Suguo Shi ◽  
Guoyu Wang
Keyword(s):  
Thermal Effect ◽  
Liquid Nitrogen ◽  
Thermal Effects ◽  
Dynamic Pressure ◽  
Density Ratio ◽  
Cavitation Flow ◽  
Cryogenic Fluids ◽  
Factors Influencing ◽  
Fluid Properties ◽  
Cryogenic Liquids

Thermal effects dramatically impact on the cavitation dynamics of cryogenic fluids. Thus, to study the thermal effect factors influencing cryogenic cavitation, numerical simulations were conducted considering an axisymmetric ogive and a 2D quarter caliber hydrofoil in liquid nitrogen and hydrogen, respectively. The modified Merkle cavitation model and filter-based turbulence model were applied to account for the thermodynamic properties of the fluid. The energy equation was modified considering the cavitation phase change effects. Compared to the experimental data, the numerical method satisfactorily predicts the cryogenic cavitation flows. Based on the numerical results, the thermal effect characteristics in the cavitation flow of cryogenic fluids were investigated. The thermal effects in cryogenic cavitation is obvious when vapor content in constant location is considerably low, where the cavity becomes more porous and the interface becomes less distinct. The factors influencing the thermal effects in cavitation such as the temperature, fluid type and velocity were analyzed. Findings showed that thermal effects of cavitation were prominent around the critical temperature of cryogenic liquids. Compared to the thermal effects in liquid nitrogen, those in liquid hydrogen were more distinct because of the changes in the density ratio, vapor pressure and other fluid properties. When the flow velocity is higher, the thermal effects of cavitation are suppressed as the pressure depression caused by evaporation is much smaller than the dynamic pressure.

scholarly journals The Value of Sentinel-2 Spectral Bands for the Assessment of Winter Wheat Growth and Development

2019 ◽  
Vol 11 (17) ◽  
pp. 2050 ◽  
Author(s):  
Andrew Revill ◽  
Anna Florence ◽  
Alasdair MacArthur ◽  
Stephen Hoad ◽  
Robert Rees ◽  
...  
Keyword(s):  
Winter Wheat ◽  
Chlorophyll Content ◽  
Management Practices ◽  
Near Infrared ◽  
Spectral Characteristics ◽  
Crop Management ◽  
Area Index ◽  
Spectral Bands ◽  
The Mean ◽  
Sentinel 2

Leaf Area Index (LAI) and chlorophyll content are strongly related to plant development and productivity. Spatial and temporal estimates of these variables are essential for efficient and precise crop management. The availability of open-access data from the European Space Agency’s (ESA) Sentinel-2 satellite—delivering global coverage with an average 5-day revisit frequency at a spatial resolution of up to 10 metres—could provide estimates of these variables at unprecedented (i.e., sub-field) resolution. Using synthetic data, past research has demonstrated the potential of Sentinel-2 for estimating crop variables. Nonetheless, research involving a robust analysis of the Sentinel-2 bands for supporting agricultural applications is limited. We evaluated the potential of Sentinel-2 data for retrieving winter wheat LAI, leaf chlorophyll content (LCC) and canopy chlorophyll content (CCC). In coordination with destructive and non-destructive ground measurements, we acquired multispectral data from an Unmanned Aerial Vehicle (UAV)-mounted sensor measuring key Sentinel-2 spectral bands (443 to 865 nm). We applied Gaussian processes regression (GPR) machine learning to determine the most informative Sentinel-2 bands for retrieving each of the variables. We further evaluated the GPR model performance when propagating observation uncertainty. When applying the best-performing GPR models without propagating uncertainty, the retrievals had a high agreement with ground measurements—the mean R2 and normalised root-mean-square error (NRMSE) were 0.89 and 8.8%, respectively. When propagating uncertainty, the mean R2 and NRMSE were 0.82 and 11.9%, respectively. When accounting for measurement uncertainty in the estimation of LAI and CCC, the number of most informative Sentinel-2 bands was reduced from four to only two—the red-edge (705 nm) and near-infrared (865 nm) bands. This research demonstrates the value of the Sentinel-2 spectral characteristics for retrieving critical variables that can support more sustainable crop management practices.

scholarly journals Photo-ionized neon plasmas induced by radiation pulses of a laser-plasma EUV source and a free electron laser FLASH

2013 ◽  
Vol 31 (2) ◽  
pp. 195-201 ◽  
Author(s):  
A. Bartnik ◽  
R. Fedosejevs ◽  
P. Wachulak ◽  
H. Fiedorowicz ◽  
C. Serbanescu ◽  
...  
Keyword(s):  
Free Electron ◽  
Free Electron Laser ◽  
Extreme Ultraviolet ◽  
Spectral Characteristics ◽  
Emission Spectra ◽  
Spectral Lines ◽  
Plasma Radiation ◽  
Beam Radiation ◽  
Radiation Beam ◽  
Ionized Plasmas

AbstractIn this work, a laser-produced plasma extreme ultraviolet source and a free electron laser were used to create Ne photo-ionized plasmas. In both cases, a radiation beam was focused onto a gas stream injected into a vacuum chamber synchronously with the radiation pulse. Extreme ultraviolet radiation from the plasma spanned a wide spectral range with pronounced maximum centered at λ = 11 ± 1 nm while the free electron laser pulses were emitted at a wavelength of 32 nm. The power density of the focused plasma radiation was approximately 2 × 107 W/cm2 and was seven orders of magnitude lower compared with the focused free electron laser beam. Radiation fluences in both experimental conditions were comparable. Despite quite different spectral characteristics and extremely different power densities, emission spectra of both photo-ionized plasmas consist of the same spectral lines within a wavelength range of 20 to 50 nm, however, with different relative intensities of the corresponding lines. The dominating spectral lines originated from singly charged ions (Ne II); however, Ne III lines were also detected. Additionally, computer simulations of the emission spectra, obtained for photo-ionized plasmas, driven by the plasma extreme ultraviolet source, were performed. The corresponding measured and calculated spectra are presented. An electron temperature and ionic composition were estimated. Differences between the experimental spectra, obtained for both irradiation conditions, were analyzed. The differences were attributed mainly to different energies of driving photons.

Metal deep engraving with high average power femtosecond lasers

2015 ◽  
Author(s):  
M. Faucon ◽  
G. Mincuzzi ◽  
F. Morin ◽  
C. Hönninger ◽  
E. Mottay ◽  
...  
Keyword(s):  
Femtosecond Lasers ◽  
Average Power ◽  
High Average Power

Development of an Electrohydrodynamic Injection Micropump for Cryogenic Cooling

2003 ◽  
Author(s):  
J. Darabi ◽  
H. Wang
Keyword(s):  
Experimental Investigation ◽  
Liquid Nitrogen ◽  
Pressure Head ◽  
Cryogenic Cooling ◽  
Maximum Pressure ◽  
Base Length ◽  
Inhomogeneous Electric Field ◽  
Cooling Systems ◽  
Pumping System ◽  
Cryogenic Liquids

Cryogenic cooling has become a widely adopted technique to improve the performance of electronics and sensors. A potential application of an electrohydrodynamic (EHD) pumping system is its use in pumping fluids in cryogenic cooling systems. In this paper we present the results of a theoretical/experimental investigation to study the feasibility of using an EHD injection micropump for pumping liquid nitrogen. First, the mechanisms of charge transport and ionization phenomenon in cryogenic liquids are discussed. Next, the design and fabrication of an EHD injection micropump that employs an array of interdigitated saw-tooth/plane electrodes are described. Finally, experimental results and observations are presented. An asymmetric saw-tooth/plane geometry was designed to achieve strong inhomogeneous electric field. Each saw-tooth had a base length of 10 μm with a tip angle of 60°. The gap between emitter and collector electrodes was 20 μm and the distance between each stage (a pair of emitter and collector electrodes) from neighboring stage was 40 μm. The dimensions of the patterned area were 10 mm by 20 mm allowing approximately 300 stages to be fabricated along the length of the micropump. The maximum pressure head achieved by this micropump was 550 Pa and 205 Pa for HFE-7100 and liquid nitrogen, respectively.

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