Laboratory Spectroscopy Research Articles

Laboratory spectroscopy of allylimine and tentative detection towards the G+0.693-0.027 molecular cloud

Context. Substituted methanimines and ethylenes have been identified in the interstellar medium. Therefore, allylimine (CH2 =CH–CH=NH) represents a promising candidate for a new interstellar detection. Aims. The goal of the present work is to perform a comprehensive laboratory investigation of the rotational spectrum of allylimine in its ground vibrational state in order to obtain a highly precise set of rest frequencies to assist its search for astronomical sources. Methods. The rotational spectra of the two most stable trans–anti and trans–syn geometrical isomers of allylimine were recorded in the laboratory in the 84–300 GHz frequency interval. Measurements were performed using a source-modulation millimetre-wave spectrometer equipped with a pyrolysis system for the production of unstable species. High-level ab initio calculations were performed to assist the analysis and to obtain reliable estimates for an extended set of spectroscopic parameters. Guided by new laboratory data, allylimine was searched for in space using a sensitive spectral survey of the G+0.693-0.027 molecular cloud, located at the Galactic centre. Results. Almost 1000 rotational transitions have been recorded for trans–anti and trans–syn allylimine. These new data have enabled the determination of a very accurate set of spectroscopic parameters including rotational, quartic and sextic centrifugal distortion con-stants, as well as nuclear quadrupole coupling constants. The improved spectral data allowed us to report a tentative detection for both allylimine isomers in the G+0.693-0.027 molecular cloud, located at the Galactic centre.

AOTF-based spectro-polarimeter for observing Earth as an exoplanet

Earth is the only known habitable planet and it serves as a testbed to benchmark the observations of temperate and more Earth-like exoplanets. It is required to observe the disk-integrated signatures of Earth for a large range of phase angles, resembling the observations of an exoplanet. In this work, an acousto-optic tunable filter (AOTF)-based experiment is designed to observe the spectro-polarimetric signatures of Earth. The results of spectroscopic and polarimetric laboratory calibration are presented here along with a brief overview of a possible instrument configuration. Based on the results of the spectro-polarimetric calibration, simulations are carried out to optimize the instrument design for the expected signal levels for various observing conditions. The usefulness of an AOTF-based spectro-polarimeter is established from this study, and it is found that, in the present configuration, the instrument can achieve a polarimetric accuracy of <0.3 % for linear polarization for an integration time of 100 ms or larger. The design configuration of the instrument and the planning of conducting such observations from Lunar orbit are discussed.

Dedication to Professor Jūras Banys

This year, on 30 December, is the 60th anniversary of the outstanding physicist, Vilnius University professor, academician, president of the Lithuanian Academy of Sciences Jūras Banys. J. Banys graduated with honours from the Faculty of Physics of Vilnius University in 1985, defended his doctoral thesis in 1990. In 1989–1990, he worked at a professor Mike Glazer’s laboratory at the University of Oxford (UK), studying the structural properties of ferroelectric crystals using X-ray diffraction methods. In 1993–1995, after receiving Alexander von Humboldt scholarship, he worked at the University of Leipzig, where he studied the local dynamics of phase transitions using electron paramagnetic spectroscopy. After returning to his Alma Mater, J. Banys took charge of the Laboratory of Microwave Spectroscopy, turning it into a modern centre for the study of the dielectric properties of ferroelectric materials. Over the years, he assembled here a group of highly qualified scientists who perform scientific experiments using unique materials developed in well-known foreign and Lithuanian laboratories. In 2000, J. Banys successfully defended his habilitation thesis, and in 2003 the title of Vilnius University professor was awarded to him.

Laboratory spectroscopy of theoretical ices: Predictions for JWST and test for astrochemical models

Context. The pre-stellar core L1544 has been the subject of several observations conducted in the past years, complemented by modelling studies focused on its gas and ice-grain chemistry. The chemical composition of the ice mantles reflects the environmental physical changes along the temporal evolution, such as density and temperature. The investigation outcome hints at a layered structure of interstellar ices with abundance of H2O in the inner layers and an increasing concentration of CO near the surface. The morphology of interstellar ice analogues can be investigated experimentally assuming a composition derived from chemical models. Aims. This research presents a new approach of a three-dimensional fit where observational results are first fitted with a gas-grain chemical model predicting the exact ice composition including infrared (IR) inactive species. Then the laboratory IR spectra are recorded for interstellar ice analogues whose compositions reflect the obtained numerical results, in a layered and in a mixed morphology. These results could then be compared with the results of James Webb Space Telescope (JWST) observations. Special attention is paid to the inclusion of IR inactive species whose presence is predicted in the ice, but is typically omitted in the laboratory obtained data. This stands for N2, one of the main possible constituents of interstellar ice mantles, and O2. Methods. Ice analogue spectra were recorded at a temperature of 10 K using a Fourier transform infrared spectrometer. In the case of layered ice we deposited a H2O-CO-N2-O2 mixture on top of a H2O-CH3OH-N2 ice, while in the case of mixed ice we examined a H2O-CH3OH-N2-CO composition. The selected species are the four most abundant ice components predicted by the chemical model. Results. Following the changing composition and structure of the ice, we find differences in the absorption bands for most of the examined vibrational modes. The extent of observed changes in the IR band profiles will allow us to analyse the structure of ice mantles in L1544 from future observations by the JWST. Conclusions. Our spectroscopic measurements of interstellar ice analogues predicted by our well-received gas-grain chemical codes of pre-stellar cores will allow detailed comparison with upcoming JWST observations. This is crucial in order to put stringent constraints on the chemical and physical structure of dust icy mantles just before the formation of stars and protoplanetary disks, and to explain surface chemistry.

Soil order knowledge as a driver in soil properties estimation from Vis-NIR spectral data – Case study from northern Karnataka (India)

Visible and near-infrared (Vis-NIR, 350–2500 nm) laboratory spectroscopy has been proven to provide soil properties estimations, such as clay or organic carbon (OC). However, the performances of such estimations may be dependent on pedological and spectral similarities between calibration and validation datasets. The objective of this study was to analyze how the soil order knowledge can be used to increase regression models performance for soil properties estimation. For this purpose, Random Forest regression models were calibrated and validated from both regional database (called regional models) and subsets stratified by soil order from the regional database (called soil-order models). The regional database contained 482 soil samples belonging to four soil orders (Alfisols, Vertisols, Inceptisols and Entisols) and associated with Vis-NIR laboratory spectra and six soil properties: OC, sand, silt, clay, cation exchange capacity (CEC) and pH. First, regional models provided i) high accuracy of some soil properties estimations when considering the regional strategy in the validation step (e.g., R2val of 0.74, 0.76 and 0.74 for clay, CEC and sand, respectively) but ii) modest accuracy of these same soil properties when considering subsets stratified by soil order from the regional database in validation step (e.g., R2val of 0.48, 0.58 and 0.38 over Vertisol for clay, CEC and sand, respectively). So the estimation accuracy appreciation is highly depending on the validation database as there is a risk of over-appreciated prediction accuracies at the soil-order scale when figures of merit are based on a regional validation dataset. Second, this work highlighted that the benefit of a soil-order model compared to a regional model for calibration depends on both soil property and soil order. So no recommendations for choosing between both models for calibration may be given. Finally, while Vis-NIR laboratory spectroscopy is becoming a popular way to estimate soil physicochemical properties worldwide, this work highlights that this technique may be used discreetly depending on the targeted scale and targeted soil type.

From Light-Powered Motors, to Micro-Grippers, to Crawling Caterpillars, Snails and Beyond-Light-Responsive Oriented Polymers in Action.

"How would you build a robot, the size of a bacteria, powered by light, that would swim towards the light source, escape from it, or could be controlled by means of different light colors, intensities or polarizations?" This was the question that Professor Diederik Wiersma asked PW on a sunny spring day in 2012, when they first met at LENS-the European Laboratory of Nonlinear Spectroscopy-in Sesto Fiorentino, just outside Florence in northern Italy. It was not just a vague question, as Prof. Wiersma, then the LENS director and leader of one of its research groups, already had an idea (and an ERC grant) about how to actually make such micro-robots, using a class of light-responsive oriented polymers, liquid crystal elastomers (LCEs), combined with the most advanced fabrication technique-two-photon 3D laser photolithography. Indeed, over the next few years, the LCE technology, successfully married with the so-called direct laser writing at LENS, resulted in a 60 micrometer long walker developed in Prof. Wiersma's group (as, surprisingly, walking at that stage proved to be easier than swimming). After completing his post-doc at LENS, PW returned to his home Faculty of Physics at the University of Warsaw, and started experimenting with LCE, both in micrometer and millimeter scales, in his newly established Photonic Nanostructure Facility. This paper is a review of how the ideas of using light-powered soft actuators in micromechanics and micro-robotics have been evolving in Warsaw over the last decade and what the outcomes have been so far.

Coherent Optical-Fiber Link Across Italy and France

The dissemination of atomic clocks with fiber-based techniques finds application in the fields of metrology, fundamental physics, navigation, and spectroscopy but is a challenge in terms of reliability, maintenance, and performance. Here, we describe the realization of a 1023-km-long fiber link between the metrological institutes of Italy and France that shares the infrastructure with the Internet traffic and exploits segmentation in shorter, cascaded spans to fight optical losses exceeding 280 dB. With four months of quasicontinuous operation of this link, we compared the $\mathrm{Cs}$, $\mathrm{Rb}$, and $\mathrm{Yb}$ atomic clocks at our laboratories, highlighting the potential of this tool to assess the clock uncertainty budgets, characterize advanced satellite techniques, and develop optical timescales. The integration of the metrological, fiber-based infrastructures in the two countries, connecting photonics and spectroscopy laboratories as well as telescope facilities, provides the research community with a physical layer over which applications can be built on.

Spectral assessment of soil properties in semi-arid tropical regions of southern Karnataka Plateau

ABSTRACT The present study assessed the visible and short wave infrared (VNIR-SWIR) laboratory spectroscopy coupled random forest regression (RF) technique for predicting soil properties in the southern Karnataka Plateau, India. The spectral data acquired for about 228 profile samples were used to predict key soil properties. The RF model fits well for the spectral prediction of clay (R2 = 0.65), sand (R2 = 0.60), cation exchange capacity (R2 = 0.74), field capacity (R2 = 0.65) and permanent wilting point (R2 = 0.72). Wherein soil organic carbon was poorly predicted with an R2 of 0.22 and RPD of 1.2 due to its lower content and narrow range (0.8 to 20 g kg−1). The spectral assessment by PCA showed that the first (50%) and third (34%) components had high spectral variation and significantly correlated with soil properties such as pH, CEC, clay, FC, and PWP related to wavelengths indicating clay minerals and iron oxides. However, the second component had less spectral variation (13%) that is related to wavelengths indicating various organic components and correlated well with SOC. Thus, the VNIR-SWIR spectroscopy could be a suitable supplementary method for rapidly predicting soil properties related to clay minerals and iron oxides.

Linking remote sensing, in situ and laboratory spectroscopy for a Ryugu analog meteorite sample

In 2022 JAXA issued an Announcement of Opportunity (AO) for receiving Hayabusa2 samples returned to Earth. We responded to the AO submitting a proposal based on using a multi-prong approach to achieve two main goals. The first goal is to address the subdued contrast of remote-sensing observations compared to measurements performed under laboratory conditions on analog materials. For this we will link the hyperspectral and imaging data collected from the spacecraft and the in-situ observations from the MASCOT lander instruments (MARA and MASCam) with laboratory-based measurements of Hayabusa2 samples using bi-directional reflectance spectroscopy under simulated asteroid surface conditions from UV to MIR/FIR achieved using three Bruker Vertex 80 V spectrometers in the Planetary Spectroscopy Laboratory. The second goal is the investigation of the mineralogy and organic matter of the samples collected by Hayabusa2, to better understanding the evolution of materials characterizing Ryugu and in general of protoplanetary disk and organic matter, investigating the aqueous alteration that took place in the parent body, and comparing the results with data collected from pristine carbonaceous chondrite analog meteorites. Spectral data will be complemented by Raman spectroscopy under simulated asteroid surface conditions, X-ray diffraction, would also allow us to define the bulk mineralogy of the samples as well as investigate the presence and nature of organic matter within the samples. In situ mineralogical and geochemical characterization will involve a pre-characterization of the sample fragments through scanning electron microscopy low voltage electron dispersive X-ray (EDX) maps, and micro IR analyses of the fragments. If allowed, a thin section of one grain will be used for electron microprobe analyses to geochemically characterize its mineralogical composition. To train our data collection and analysis methods on a realistic sample, we selected a piece of the Mukundpura meteorite, as one of the closer analogs to Ryugu’s surface (Ray et al., Planetary and Space Science, 2018, 151, 149–154). The Mukundpura chunk we selected for this study measures 3 mm in its maximum dimension, and we chose it so to have a test sample of the same size as the Hayabusa2 grain we requested in our proposal to JAXA’s AO. The test gave us confidence that we can measure with good SNR measurements in bi-directional reflectance for samples around 3 mm in size (see Figures 3, 4 below). To address our second goal the spectral data was complemented by Raman spectroscopy measured again under simulated asteroid surface conditions in our Raman Mineralogy and Biodetection Laboratory at DLR.

Experimental Study of Determining Technique for Table Grape Qualities using Visible Wavelength of Imaging and Spectroscopy

Imaging and spectroscopy are non-destructive techniques for determining fruit qualities. The qualities of table grapes (Vitis vinifera) such as soluble solids content (SSC), pH, fi rmness and seedlessness are key parameters. This research was focused on comparison between imaging and spectroscopy in laboratory and fi eld. The results of Partial least squares regression (PLSR) showed that the best coeffi cient of determination (R2) for prediction (R2 pred) on SSC for laboratory was 0.8085, for fi eld was 0.8169, and for imaging was 0.7994. The best R2 pred on fi rmness for laboratory was 0.6925, for fi eld was 0.5737, and for imaging was 0.6216. The best R2 pred on pH for laboratory was 0.6820, for fi eld was 0.7101 and for imaging was 0.6494. Partial least squares discriminant analysis (PLS-DA) was analyzed the successful percentage of seedlessness classifi cation: 89.66%, 93.10% and 81.25% for spectroscopy in laboratory, fi eld and imaging, respectively. The results of SSC and seedlessness in fi eld are almost same effi cient as in laboratory. That means farmer can do spectroscopy on SSC and seedlessness anywhere and non-destructively. By the way, we can use both techniques as effi cient non-destructive techniques for determining these key parameters of table grape qualities.

Searching for biosignatures by their rotational spectrum: global fit and methyl group internal rotation features of dimethylsulphoxide up to 116 GHz

AbstractThe identification and quantification of molecules in interstellar space and atmospheres of planets in the solar systems and in exoplanets rely on spectroscopic methods and laboratory work is essential to provide the community with the spectral features needed to analyse cosmological observations. Rotational spectroscopy in particular, with its intrinsic high resolution, allows the unambiguous identification of biomolecular building blocks and biosignature gases which can be correlated with the origin of life or the identification of habitable planets. We report the extension of the measured rotational transition frequencies of dimethylsulphoxide and its 34S and 13C isotopologues in the millimetre wave range (59.6–78.4 GHz) by use of an absorption spectrometer based on the supersonic expansion technique. Hyperfine patterns related to the methyl group internal rotation were analysed in the microwave range region (6–18 GHz) with a Pulsed Jet Fourier Transform spectrometer at extremely high resolution (2 kHz) and reliable predictions up to 116 GHz are provided. The focus on sulphur-bearing molecules is motivated by the fact that sulphur is largely involved in the intra- and inter-molecular hydrogen bonds in proteins and although it is the 10th most abundant element in the known Universe, understanding its chemistry is still a matter of debate. Moreover, sulphur-bearing molecules, in particular dimethylsulphoxide, have been indicated as possible biosignature gases to be monitored in the search of habitable exoplanets.

Bridging the gap between soil spectroscopy and traditional laboratory: Insights for routine implementation

We need innovative solutions to help laboratories to rapidly characterize the soils and adopt internal quality controls with lower costs and ecosystem impacts. Soil spectroscopy emerged as an alternative to wet chemistry. However, soil laboratories still do not widely use this technology in their routines, mainly due to the lack of: i) standards and protocols, ii) spectral libraries, iii) capacity in spectral methods, and iv) professionals with expertise in chemometrics. Therefore, we aimed to provide basic guidelines for the use of soil spectra in laboratory routines regarding internal quality control and samples selection for analysis and prediction. We used 350–2500 nm spectra and unsupervised random forests to compute proximity matrices and cluster spectrally similar soil samples for outlier detection using an adjusted method for skewed distribution, which allowed us to establish an internal quality control. Then, we used the most important wavelengths from unsupervised random forest to order soil samples by laboratory and subset them into different set sizes for training and testing prediction models for clay, sand, organic matter cation exchange capacity and base saturation. Our results indicated that internal quality control based on soil spectra and unsupervised analysis can be implemented for laboratory routines. Spectra-based soil samples selection and attributes predictions can reduce the need for laboratory analysis by half. Soil spectroscopy can become an important alternative to improve traditional analytical results, save time, reduce costs, and mitigate environmental impact with acceptable accuracy. Soil data and full codes from this study are publicly available at https://github.com/raulpoppiel/urssa.

Helium nanodroplet isolation spectroscopy in an undergraduate teaching laboratory

A home-built helium nanodroplet isolation spectrometer has been utilized by undergraduate students in course-based experiments to investigate the rovibrational dynamics of small molecules. Helium nanodroplets are a versatile medium that simplifies the spectroscopy of embedded molecules owing to their low temperature (0.4 K) and weakly interacting nature. In the infrared spectral region, this often results in a small number of rotationally resolved lines that can be observed and analyzed within several lab periods. We demonstrate the advantages of using this well-established technique in an upper-level undergraduate chemistry course for which the laser spectroscopy of helium solvated 13C-labelled formic acid was investigated for the first time.

THE SPECTRUM LENGTH METHOD IN QUANTITATIVE INTERPRETATION OF SELECTED OPTICAL SPECTRA

Different algorithms are used for the quantitative interpretation of optical spectra. Regression methods e.g CLS (Classical Least Squares) or PLS (Partial Least Squares) are often used in typical problems of laboratory spectroscopy. The spectra analysis is generally a multi-step process, in which, depending on the spectra type, modification of individual regression methods or special dedicated methods are applied. For example, contour length method or spectra length algorithm are used in this purpose. The basic version of the algorithm is very simple in terms of mathematics. It has been proposed for the analysis of spectra in the OP-FTIR open path spectroscopy, where there are significant fluctuations in the spectrum baseline. The spectrum length is a parameter closely related to the content of the analyzed gas component. Independently of spectral length algorithm, a method has been developed in which difference length of two spectra (measured and reference) is used to compare the spectra. The minimum length of the spectral difference is an indicator of their best fitting. The article presents two ways of using the spectrum length: as a direct and indirect parameter indicating the measured quantity on the basis of the spectrum. There were performed the spectrum length algorithm as a digital differentiating filter with a specific frequency response. There were also analyzed more advanced differentiating filter and the possibility of frequency spectrum filter design used in an analysis of optical spectral signal. There were performed the analysis of the spectrum length method in the case of the synthetic calibration involving the use of model spectra from simulations realized by HITRAN database. There were analyzed numerically the problem of the Instrument Line Shape influence on the synthetic spectra and results of the determining the content of components by the minimizing the difference of spectral length.

Soil Order-Land Use Index Using Field-Satellite Spectroradiometry in the Ecuadorian Andean Territory for Modeling Soil Quality

Land use conversion is the main cause for soil degradation, influencing the sustainability of agricultural activities in the Ecuadorian Andean region. The possibility to identify the quality based on the spectral properties allows remote sensing methods to offer an alternative form of monitoring the environment. This study used laboratory spectroscopy and multi-spectral images (Sentinel 2) with environmental covariates (physicochemical parameters) to find an affordable method that can be used to present spatial prediction models as a tool for the evaluation of the quality of Andean soils. The models were developed using statistical techniques of logistic regression and linear discriminant analysis to generate an index based on soil order and three indexes based on the combination of soil order and land use. This combined approach offers an effective method, relative to traditional laboratory methods, to derive estimates of the content and composition of soil constituents, such as electrical conductivity (CE), organic matter (OM), pH, and soil moisture (HU). For Mollisol index.3 with Páramo land use, a value of organic matter (OM) ≥8.6% was obtained, whereas for Mollisol index.4 with Shrub land use, OM was ≥6.1%. These results reveal good predictive (estimation) capabilities for these soil order–land use groups. This provides a new way to monitor soil quality using remote sensing techniques, opening promising prospects for operational applications in land use planning.

Identifying Shocked Feldspar on Mars Using Perseverance Spectroscopic Instruments: Implications for Geochronology Studies on Returned Samples

The Perseverance rover (Mars 2020) mission, the first step in NASA’s Mars Sample Return (MSR) program, will select samples for caching based on their potential to improve understanding Mars’ astrobiological, geological, geochemical, and climatic evolution. Geochronologic analyses will be among the key measurements planned for returned samples. Assessing a sample’s shock history will be critical because shock metamorphism could influence apparent sample age. Shock effects in one Mars-relevant mineral class, plagioclase feldspar, have been well-documented using various spectroscopy techniques (thermal infrared reflectance, emission, and transmission spectroscopy, Raman, and luminescence). A subset of these data will be obtained with the SuperCam and SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instruments onboard Perseverance to inform caching decisions for MSR. Here, we review shock indicators in plagioclase feldspar as revealed in Raman, luminescence, and IR spectroscopy lab data, with an emphasis on Raman spectroscopy. We consider how this information may inform caching decisions for selecting optimal samples for geochronology measurements. We then identify challenges and make recommendations for both in situ measurements performed with SuperCam and SHERLOC and for supporting lab studies to enhance the success of geochronologic analyses after return to Earth.

Dos and don'ts tutorial for sample alignment in sum frequency generation spectroscopy.

This Tutorial aims to provide a concise yet practical guideline for different scenarios that one may face in a sum frequency generation (SFG) spectroscopy laboratory, especially when it comes to sample alignment. The effort is made to reconstruct the real and often challenging sample alignment conditions for a broad range of liquid or solid samples interfacing solid, liquid, or gas phases, with a pedagogical approach. Both newcomer operators of an SFG setup without a strong experience in nonlinear spectroscopy and the more experienced SFG users can utilize the approaches that are provided in this Tutorial for an easier and more reliable sample alignment in their SFG laboratories.

Chronic Musculoskeletal Pain Moderates the Association between Sleep Quality and Dorsostriatal-Sensorimotor Resting State Functional Connectivity in Community-Dwelling Older Adults

Aging is associated with poor sleep quality, and greater chronic pain prevalence with age-related changes in brain function as potential underlying mechanisms. The following cross-sectional study aimed to determine whether self-reported chronic musculoskeletal pain in community-dwelling older adults moderates the association between sleep quality and resting state functional brain connectivity (rsFC). Community-dwelling older individuals (mean age=73.29 years) part of the NEPAL study who completed the Pittsburg Sleep Quality Index (PSQI) and an rsFC scan were included (n=48) in the present investigation. To that end, we tested the effect of chronic pain-by-PSQI interaction on rsFC among atlas-based brain regions-of-interest, controlling for age and sex. A significant network connecting the bilateral putamen and left caudate with bilateral precentral gyrus, postcentral gyrus and juxtapositional lobule cortex, survived global multiple comparisons (FDR; q<0.05) and threshold-free network-based-statistics. Greater PSQI scores were significantly associated with greater dorsostriatal-sensorimotor rsFC in the no-pain group, suggesting that a state of somatomotor hyperarousal may be associated with poorer sleep quality in this group. However, in the pain group greater PSQI scores were associated with less dorsostriatal-sensorimotor rsFC, possibly due to a shift of striatal functions toward regulation sensorimotor aspects of the pain experience, and/or aberrant cortico-striatal loops in the presence of chronic pain. This preliminary investigation advances knowledge about the neurobiology underlying the associations between chronic pain and sleep in community-dwelling older adults that may contribute to the development of effectitractve therapies to decrease disability in geriatric populations. This work was supported by the National Institutes of Aging (NIAK01AG048259, R01AG059809, R01AG067757, and T32AG049673). A portion of this work was performed in the McKnight Brain Institute at the National High Magnetic Field Laboratory's Advanced Magnetic Resonance Imaging and Spectroscopy (AMRIS) Facility, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and DMR-1157490, and the State of Florida and the University of Florida Claude D. Pepper Older Americans Independence Center.

The Brazilian Program of soil analysis via spectroscopy (ProBASE): Combining spectroscopy and wet laboratories to understand new technologies

Spectroscopy has been extensively used in soil analysis. However, users, such as commercial laboratories, still do not know the application, potential, and limitations of this technique. This paper aims to present a given course going from theory to practice for end-users regarding spectroscopy technique. The paper combines the use of soil spectroscopy and wet laboratories to perform a scientific-teaching dynamic using their own data, allowing for a better understanding of the technique. The course is denominated ProBASE (The Brazilian Program of Soil Analysis via Spectroscopy). Soil samples from 35 laboratories were sent (34 from Brazil and 1 from Paraguay) to a central spectroscopy laboratory. Samples were measured for visible-near-short-wave-infrared, Vis-NIR (400–2500 nm), and mid-infrared, MIR (3000–25000 nm) ranges and by portable X-ray Fluorescence (pXRF) sensor. We also used the Brazilian Soil Spectral Library (BSSL) dataset (Vis-NIR). We performed three different population models with Vis-NIR as follows: a) using the dataset of each laboratory (Local), b) using the entire ProBASE-dataset (Regional), and c) using the BSSL (Country). Afterward, we developed spectral models using the other spectral ranges for comparison. We also used a qualitative approach to detect errors from the wet laboratory analyses using Vis-NIR data and evaluated their impact on spectral modeling. The models that used Local samples had the best performance, with R2 in validation reaching up to 0.93 for clay, 0.92 for sand, 0.86 for P, 0.82 for pH, 0.81 for organic matter (OM), 0.75 for Ca2+, 0.72 for cation exchange capacity (CEC), 0.71 for aluminum saturation, 0.71 for Al3+, 0.70 for Mg2+, 0.64 for base saturation (V%), and 0.56 for K+. However, the base saturation presented greater variation from good to poor results. For the comparison dataset, the results can be summarized as follows: a) pXRF was better for P, Ca2+ B, V% and Mn; b) MIR was better for clay, sand, OM, pH, Mg2+, CEC and Mn; c) Vis-NIR was better for H + Al; d) the three spectral ranges had good performance for OM, sand, silt and clay. In addition, our findings indicate that all spectral ranges are useful for a wet laboratory, where each model has advantages and limitations, but they can be used complementary to each other. Spectroscopy can detect inconsistencies of the wet laboratory analyses, affecting thus the quality of the results. The commercial laboratory community viewed the techniques positively. The results indicate the viability to create a hybrid laboratory, combining both wet and dry (soil spectroscopy) chemistry.

Fermi polarons at finite temperature: Spectral function and rf spectroscopy

We present a systematic study of a mobile impurity immersed in a three-dimensional Fermi sea of fermions at finite temperature, by using the standard non-self-consistent many-body $T$-matrix theory that is equivalent to a finite-temperature variational approach with the inclusion of one-particle-hole excitation. The impurity spectral function is determined in the real-frequency domain, avoiding any potential errors due to the numerical analytic continuation in previous $T$-matrix calculations and the small spectral broadening parameter used in variational calculations. In the weak-coupling limit, we find that the quasiparticle decay rate of both attractive and repulsive polarons does not increase significantly with increasing temperature, and therefore Fermi polarons may remain well-defined far above Fermi degeneracy. In contrast, near the unitary limit with strong coupling, the decay rate of Fermi polarons rapidly increase and the quasiparticle picture breaks down close to the Fermi temperature. We analyze in detail the recent ejection and injection radio-frequency (rf) spectroscopy measurements, performed at Massachusetts Institute of Technology (MIT) and at European Laboratory for Non-Linear Spectroscopy (LENS), respectively. We show that the momentum average of the spectral function, which is necessary to account for the observed rf-spectroscopy, has a sizable contribution to the width of the quasiparticle peak in spectroscopy. As a result, the measured decay rate of Fermi polarons could be significantly larger than the calculated quasiparticle decay rate at zero momentum. By take this crucial contribution into account, we find that there is a reasonable agreement between theory and experiment for the lifetime of Fermi polarons in the strong-coupling regime, as long as they remain well-defined.