Conventional Reference Method Research Articles

Structures, energies and vibrational frequencies of the X and A states of haloacetylene cations, HCCX+ (X = F, Cl, Br, I)

Modeling charge migration resulting from the coherent superposition of cation ground and excited states requires information about the potential energy surfaces of the relevant cation states. Since these states are often of the same electronic symmetry as the ground state of the cation, conventional single reference methods such as coupled cluster cannot be used for the excited states. The EOMCCSD-IP (equation of motion coupled cluster with single and double excitations and ionization) is a convenient and reliable “black-box” method that can be used for the ground and excited states of cations, yielding results of CCSD (coupled cluster with singles and double excitation) quality. Charge migration in haloacetylene cations arises from the superposition of the X and A states of HCCX+ (X = F, Cl, Br and I). The geometries, ionization potentials and vibrational frequencies have been calculated by CCSD/cc-pVTZ for neutral HCCX and the X state of HCCX+ and by EOM CCSD-IP/cc-pVTZ for the X and A states of HCCX+. The results agree very well with each other and with experiment. The very good agreement between CCSD and EOMCCSD-IP for the X states demonstrates that EOMCCSD-IP is a suitable method for calculating the structure and properties of ground and excited states for the HCCX cations.

Mueller-Gabor holographic microscopy

Despite the emergence of various methods for Mueller matrix recovery, achieving complete volumetric Mueller matrix retrieval remains a challenge. An alternative approach that leverages in-line Gabor holography to comprehensively extract polarization information from volumetric samples is introduced in this context. The proposed polarization-sensitive in-line Gabor holographic setup enables the recovery of the complete Mueller matrix of three-dimensional (3D) samples after the numerical repropagation of the holographically rendered complex field to various sample planes. This proposal is validated using a calibrated birefringent polarization test target, a sample of Calcium Oxalate crystals, and a volumetric sample containing microplastics, providing the 3D measurement of polarimetric parameters such as diattenuation, polarizance, depolarization, and retardance. The results agree with those obtained through reference methods based on image-plane brightfield polarimetry. The in-line Gabor holographic system proposed is sensitive to the axial variations in polarimetric information within volumetric samples without any mechanical movement nor optical adjustments— an accomplishment that remains elusive to conventional image-plane reference methods and non-holographic/interferometric systems. These findings emphasize the versatility and potential of this alternative approach in recovering the intricate polarization characteristics of 3D specimens, offering the first in-line holographic Mueller imaging to the best of the authors' knowledge.

Application of near-infrared hyperspectral imaging for determination of cheese chemical composition

Cheeses vary in chemical composition as they have different applications according to the technological features; some hard cheeses are consumed fresh while melting is a desirable characteristic for others. The conventional reference methods for determination of cheese composition and quality are accurate, but include physical-chemical analyses that are time-consuming and require use of chemical reagents. The objective of this work was to apply near-infrared hyperspectral imaging (NIR-HSI) as a fast method for prediction and visualization of spatial distribution of chemical composition of different types of cheeses (mozzarela, requeijão do norte, minas meia cura, coalho, prato). Moisture, fat, protein, and free oil were measured, and used as reference for prediction models, while spectral information extracted from images in the range of 928–2524 nm were used as predictors. Partial Least Squares (PLS) regression models were built with full spectra and using only few selected regions with higher importance, which were applied to the images to build chemical maps and visualize the spatial variation of the cheese composition. The regression models were able to predict moisture (R2P = 0.92, RMSEP = 1.1%); fat (R2P = 0.84, RMSEP = 1.5%); protein (R2P = 0.80, RMSEP = 1.8%); and free oil (R2P =0.64, RMSEP = 0.5%) for an external set of samples, while requiring a small number of latent variables (LVs) (between 3 and 4). The chemical maps allowed visualization of the spatial distribution for each attribute, demonstrating that the composition may vary within sample. The study demonstrated the potential of NIR-HSI for the determination of cheese composition and possible application to cheese quality control.

A microfluidic chip-based multiplex PCR-reverse dot blot hybridization technique for rapid detection of enteropathogenic bacteria

Diarrhea caused by enteropathogenic bacteria is a major public health issue worldwide, especially in developing countries. In this study, a microfluidic chip-based multiplex polymerase chain reaction (PCR)-reverse dot blot hybridization technology for the rapid and simultaneous detection of 11 enteropathogenic bacteria was developed and the entire process was completed within 3–4 h. The specificity of this method was analyzed using 11 types of pure target bacterial colonies and another 7 types of pure bacterial colonies, and its sensitivity was evaluated with the serial 10-fold dilution of 11 types of pure target bacterial colonies. The detection limit of this method was as low as 103–102 CFU/mL, and it exhibited high specificity for enteropathogenic bacteria. A total of 60 clinical diarrheal fecal samples were detected using this method, the results of which were compared with those of the conventional reference method, which resulted in a positive coincident rate of 100% and a negative coincident rate of 93.75%. Based on the findings, it could be concluded that multiplex PCR-reverse dot blot hybridization based on the microfluidic chip is a rapid, economical, sensitive, specific, and high-throughput method for detecting enteropathogenic bacteria.

MALDI-TOF MS-Based Approaches for Direct Identification of Gram-Negative Bacteria and BlaKPC-Carrying Plasmid Detection from Blood Cultures: A Three-Year Single-Centre Study and Proposal of a Diagnostic Algorithm.

The rapid identification of pathogens of bloodstream infections (BSIs) and the detection of antibiotic resistance markers are critically important for optimizing antibiotic therapy and infection control. The purpose of this study was to evaluate two approaches based on MALDI-TOF MS technology for direct identification of Gram-negative bacteria and automatic detection of Klebsiella pneumoniae carbapenemase (KPC) producers using the Bruker MBT Subtyping IVD Module in a large routine laboratory over a three-year period. MALDI-TOF MS analysis was performed directly from blood culture (BC) bottles following bacterial pellet recovery by Rapid MBT Sepsityper® Kit and on blood agar 4-h subcultures. Automated detection of blaKPC-carrying pKpQIL-plasmid by Bruker MBT Subtyping Module was evaluated in BCs tested positive to K. pneumoniae or E. coli. The results were compared with those obtained with conventional reference methods. Among the 2858 (93.4%) monomicrobial BCs, the overall species identification rates of the Rapid Sepsityper and the short-term subculture protocols were 84.5% (n = 2416) and 90.8% (n = 2595), respectively (p < 0.01). Excellent specificity for KPC-producers identification were observed for both MALDI-TOF MS protocols. The pKpQIL plasmid-related peak was detected in overall 91 of the 120 (75.8%) KPC-producing isolates. Notably, 14 out of the 17 (82.3%) K. pneumoniae isolates carrying blaKPC variants associated with ceftazidime/avibactam resistance and tested negative by the immunocromatography assay, were correctly identified as KPC-producers by MALDI-TOF MS. In conclusion, combination of both Rapid Sepsityper and short-term subculture protocols may represent an optimal solution to promptly identify more than 95% of Gram-negative bacteria causing BSIs. MALDI Biotyper® platform enabled a reliable and robust automated detection of KPC producers in parallel with species identification. However, integration of molecular or immunocromatographic assays are recommended according to local epidemiology.

Absolute Quantification of Total Hemoglobin in Whole Blood by High-Performance Liquid Chromatography Isotope Dilution Inductively Coupled Plasma-Mass Spectrometry.

Accurate and traceable measurement of hemoglobin (HGB) is of great importance in clinical testing. Although the HiCN method is the internationally accepted conventional reference method for this biomarker and frequently used in clinical routine diagnostics, the HiCN method cannot be traceable to the International System of Units (SI) and thus does not meet highest metrological demands. In this study, an absolute quantitative approach for total HGB in a whole blood sample is proposed based on the determination of natural Fe and S present in the heme-group of HGB by HPLC isotope dilution ICP-MS. IRMM/IFCC-467 is used for method validation, and then clinical blood samples are measured by the established strategy and HiCN method. The measurable ranges of total HGB were 10.0-240.0 g L-1. Limits of detection via Fe and S were 0.01 and 0.07 g L-1, respectively. The intra-assay imprecision CVs via Fe and S were 0.89-1.35 and 0.99-1.56%, and the interassay CVs were 1.19-2.15 and 1.55-2.55%, respectively. Good agreement was achieved in the method validation. In the comparison with HiCN experiments, the ID-ICP-MS assays via Fe and S showed correlations of r2 = 0.991 and 0.970 against HiCN methods. Moreover, the concentration of transferrin (Tf) was also simultaneously measured. This strategy has potential to serve as a reference measurement procedure for total HGB in whole blood, which could be traceable to SI and does not require toxic derivation reagent.

The Effects of Different Reference Methods on Decision-Making Implications of Auditory Brainstem Response.

Hearing loss is a common disease affecting public health all around the world. In clinic, auditory brainstem response (ABR) has been widely used for the detection of hearing loss based on its convenience and accuracy. The different reference methods directly influence the quality of the ABR waveform which in turn affects the ABR-based diagnosis. Therefore, in this study, a reference electrode standardization technique (REST) was adopted to systematically investigate and evaluate the effect of different reference methods on the quality of ABR waveform in comparison with the conventional average reference (AR) and mean mastoid (MM) methods. In this study, ABR signals induced by click stimulus were acquired via an EEG electrode cap arrays, and those located on the six channels along the midline were compared systemically. The results showed that, when considering the different channels, the ABR in the Cz channel showed the best morphology. Then, the ABR waveforms acquired via the REST method possessed better morphologies with large amplitude (0.06 ± 0.02 μV for wave I, 0.07 ± 0.02 μV for wave III, and 0.21 ± 0.04 μV for wave V) when compared with the traditional method. Summarily, we found that the REST and MM methods improved the quality of ABR on both amplitude and morphology under different stimulation rates and levels without changing the latencies of ABR when compared with the conventional AR method, suggesting that the REST and MM methods have the potential to help physicians with high accurate ABR-based clinical diagnosis. Moreover, this study might also provide a theoretic basis of reference methods on the acquisition of electroencephalogram over public health issues.

Technical challenges for complete implementation of automated growth-based methods for microbiological examination of advanced therapy medicinal products. What's wrong with Candida albicans?

BackgroundAutomated growth-based methods for sterility testing of cell-therapy products should be qualified to demonstrate that they are equivalent to, or better than, the conventional reference method. The aim of the present study was to assess the ability of the BACTEC FX40 system to detect low microbial contamination and to confirm the suitability of the method in the presence of seven different human mesenchymal cell–based products, according to Ph. Eur. 2.6.27. Additionally, a study to select the best vial to detect fungus contamination was performed. MethodsMicroorganisms representing Gram-negative, Gram-positive, aerobic, anaerobic, spore-forming, slow-growing bacteria, yeast and mold were prepared in either Dulbecco's PBS or seven biological matrices containing approximately 5, 10, and 15 colony-forming units (CFU) per sample. These preparations were inoculated to the specific media required for each test method: (i) BACTEC aerobic and anaerobic vials; (ii) aerobic and anaerobic media for direct inoculation; and (iii) Trypcase soy 3P or Brucella blood agar plates. Colonies from cultures were identified using MALDI-TOF mass spectrometry. ResultsThe BACTEC FX40 system, in both Dulbecco's PBS and the biological matrices with a 5-CFU inoculum, detected most of the microorganisms significantly faster than the conventional method, despite the presence of a matrix containing gentamicin and several matrices containing 10% DMSO. Conversely, it showed an extremely delayed detection of Candida albicans compared with the conventional method. The addition of a Mycosis IC/F (MYC) vial decreased radically the time to detection (TTD) of C. albicans (28.2 ± 1.8 h) compared with the conventional method (36 h). ConclusionsWhen a MYC vial was added to the standard aerobic and anaerobic vials to test each sample, BACTEC FX40 was shown to be a superior alternative sterility method for cell-therapy products contaminated with low inocula, with a faster TTD for microbial growth compared with the conventional method (5 versus 14 days). The studies were carried out in different cell-based matrices with sensitivities and specificities of 100% for all the tested strains at 15-, 10- and 5-CFU inoculum, with the exception of Kocuria rhizophila at 5 CFU (90.48% sensitivity and 100% specificity).

Dopaminergic Activity in Antipsychotic-Naïve Patients Assessed With Positron Emission Tomography Before and After Partial Dopamine D2 Receptor Agonist Treatment: Association With Psychotic Symptoms and Treatment Response

BackgroundDopamine activity has been associated with the response to antipsychotic treatment. Our study used a four-parameter model to test the association between the striatal decarboxylation rate of 18F-DOPA to 18F-dopamine (k3) and the effect of treatment on psychotic symptoms in antipsychotic-naïve patients with first-episode psychosis. We further explored the effect of treatment with a partial dopamine D2 receptor agonist (aripiprazole) on k3 and dopamine synthesis capacity (DSC) determined by the four-parameter model and by the conventional tissue reference method. MethodsSixty-two individuals (31 patients and 31 control subjects) underwent 18F-DOPA positron emission tomography at baseline, and 15 patients were re-examined after 6 weeks. Clinical re-examinations were completed after 6 weeks (n = 28) and 6 months (n = 15). Symptoms were evaluated with the Positive and Negative Syndrome Scale. ResultsHigh baseline decarboxylation rates (k3) were associated with more positive symptoms at baseline (p < .001) and with symptom improvement after 6 weeks (p = .006). Subregion analyses showed that baseline k3 for the putamen (p = .003) and nucleus accumbens (p = .013) and DSC values for the nucleus accumbens (p = .003) were associated with psychotic symptoms. The tissue reference method yielded no associations between DSC and symptoms or symptom improvement. Neither method revealed any effects of group or treatment on average magnitudes of k3 or DSC, whereas changes in dopamine synthesis were correlated with higher baseline values, implying a potential effect of treatment. ConclusionsStriatal decarboxylation rate at baseline was associated with psychotic symptoms and treatment response. The strong association between k3 and treatment effect potentially implicate on new treatment strategies.

Magnetotelluric multi-reference array data processing algorithm

Rational use of multiple remote reference data is an important way to improve the data quality of MT method. Based on the electromagnetic array data processing model, a data processing algorithm with multiple reference stations is proposed. Firstly, reference channels are selected from multiple remote stations to construct the natural field dominated reference data array; then the polarization parameters of natural sources are extracted from the reference data array by robust principal component analysis method; the parameters are then applied to the target array, which constructed by data from the stations to be processed, to estimate the target tensor impedances by robust estimation method. Finally, the effectiveness of the proposed algorithm is discussed by comparing it with the robust least squares and conventional remote reference methods, using a case study in east China. The results show that the new scheme is an effective strategy by using the multiple reference channel data, which can improve the quality of MT data processing in noisy environment and provide a reasonable correction for MT “dead band” distortions.

An accurate instantaneous angular speed estimation method based on a dual detector setup

Instantaneous angular speed (IAS), or ‘true IAS’, is an inherent signature directly related to the mechanical dynamics of rotor systems and has been employed extensively in different rotating machines. Due to various uncertainties, such as manufacturing error or the inaccurate installation of encoders, the acquired IAS signals often contains significant contents of ‘false IAS’ which can mask the small variations of IAS, lead to low accuracy and consequently affect the understanding of the dynamic behaviour of a rotor system. This study proposes a dual detector method to minimize the influence of encoder errors and hence obtain more accurate IAS estimation. Through theoretical study, it is proved that the false IAS induced by encoder errors from the two detectors have the same amplitudes but with a phase difference, whereas the true IAS components from the two detectors are identical. On this basis, an algorithm is developed firstly to acquire the encoder errors through a phase alignment operation and then estimate the true IAS after removing the estimated encoder errors. The proposed method is evaluated by both numerical simulations and experimental studies. The results show that the proposed method can more significantly suppress the encoder errors associated with encoder eccentricities in comparison with conventional reference methods, thereby yielding an accurate true IAS from the measurement. The proposed method can be particularly effective when the encoder has very low accuracy, allowing a more cost-effective IAS monitoring system to be achieved.

Evaluation of drug susceptibility profile of Mycobacterium tuberculosis Lineage 1 from Brazil based on whole genome sequencing and phenotypic methods.

BACKGROUND The evaluation of procedures for drug susceptibility prediction of Mycobacterium tuberculosis based on genomic data against the conventional reference method test based on culture is realistic considering the scenario of growing number of tools proposals based on whole-genome sequences (WGS).OBJECTIVES This study aimed to evaluate drug susceptibility testing (DST) outcome based on WGS tools and the phenotypic methods performed on isolates of M. tuberculosis Lineage 1 from the state of Pará, Brazil, generally associated with low levels of drug resistance.METHODOLOGY Culture based DST was performed using the Proportion Method in Löwenstein-Jensen medium on 71 isolates that had been submitted to WGS. We analysed the seven main genome sequence-based tools for resistance and lineage prediction applied to M. tuberculosis and for comparison evaluation we have used the Kappa concordance test.FINDINGS When comparing the WGS-based tools against the DST, we observed the highest level of agreement using TB-profiler. Among the tools, TB-profiler, KvarQ and Mykrobe were those which identified the largest number of TB-MDR cases. Comparing the four most sensitive tools regarding resistance prediction, agreement was observed for 43 genomes.MAIN CONCLUSIONS Drug resistance profiling using next-generation sequencing offers rapid assessment of resistance-associated mutations, therefore facilitating rapid access to effective treatment.

How to measure coating thickness of tablets: Method comparison of optical coherence tomography, near-infrared spectroscopy and weight-, height- and diameter gain

Film coating of pharmaceutical dosage forms, such as tablets and pellets, can be used to tailor the drug release profile. With that regard, a uniform coating thickness of a single tablet (intra-tablet), all tablets (inter-tablet) and subsequent batches (inter-batch) is crucial. We present a method comparison between in-line (optical coherence tomography and near-infrared spectroscopy) and well-established off-line (height-, weight- and diameter-gain) approaches to determining the coating thickness of tablets. We used single tablets drawn during a commercial coating process. Comparing the low intra- and high inter-tablet coating variability indicated that the tablets had a broad distribution of spray zone passes but at a random tablet orientation. Even at the end of the coating process at a mean coating thickness of about 70 µm, the inter-tablet standard deviation was about 9 µm or 13% relative standard deviation. Determining correlations between the methods identified the factors that contribute to the measurement uncertainty and bias for each method. Ultimately, we aimed to establish that in-line methods match or even surpass the conventional off-line reference methods in terms of accuracy and precision of coating thickness measurement.

Performance assessment of SVM-based classification techniques for the detection of artificial debondings within pavement structures from stepped-frequency A-scan radar data

Owing to traffic and weather conditions, pavement structures may suffer from horizontal and vertical cracks that shorten the overall lifetime of roadways. In this paper, we focus on the detection of the horizontal subsurface cracks (debondings) occurring between the first two pavement layers from Stepped-frequency Radar (SFR) data. The processing of radar data requires some refined signal analysis to detect constructive interference between overlapping echoes. It is performed from timely data by a supervised machine learning method namely, Support Vector Machines (SVM) and compared to the conventional reference method, namely, the Amplitude Ratio Test (ART), which is routinely performed at the operational level. Besides, the straightforward application of SVM on raw data is compared to the solution using physical signal features (global and local) that reduces the computational burden. Performance assessment and comparison of the processing methods are conducted on data collected on a specific test-site with three different types of artificial debondings.

Multicenter study establishing the clinical validity of a nucleic-acid amplification–based assay for the diagnosis of bacterial vaginosis

The present study sought to validate the clinical performance of a previously described PCR-based assay for the diagnosis of bacterial vaginosis (BV). A total of 1579 patients were enrolled in 5 locations; samples were classified as BV positive (n=538) or negative (n=1,041) based on an algorithm utilizing quantitative Gram-stain analysis of vaginal discharge and clinical evaluation (Amsel criteria); a next-generation sequencing (NGS) approach to determining diversity of vaginal microbiota was used to resolve discordant results between BV-PCR and Nugent/Amsel. BV-PCR demonstrated a sensitivity of 96.0% (483/503) and a specificity of 90.2% (885/981) when measured against the conventional test standard, with 95 samples (6.0%) being classified as indeterminate. After resolution of discordant results by NGS, including elimination of the PCR indeterminate category, the resolved sensitivity, specificity, and positive and negative predictive values of the BV-PCR assay were 98.7%, 95.9%, 92.9%, and 96.9%, respectively. The results of this study conclusively demonstrate that a relatively simple, 3-biomarker, molecular amplification construct can effectively diagnose BV in symptomatic women. Results generated using this assay were congruent with those obtained using conventional and molecular reference methods.

Performance of Xpert MTB/RIF for detection of Mycobacterium tuberculosis and rifampicin resistance in pus aspirates

IntroductionWHO endorsed Xpert MTB/RIF assay has proven to be rapid with results obtained within 2h. The evidence base regarding the use of Xpert MTB/RIF in pulmonary TB is strong. Relatively few performance data have been published to date on detection of Mycobacterium tuberculosis in aspirated pus specimens from abscesses. ObjectivesThe aim of the study was to determine the sensitivity and specificity of Xpert MTB/RIF assay for the detection of M. tuberculosis and rifampicin resistance in aspirated pus specimens using culture on Lowenstein Jensen (LJ) medium and economic variant of proportion method (PM) for drug susceptibility testing (DST) as the reference standard. ResultsXpert MTB/RIF assay in comparison to conventional reference method showed sensitivity and specificity of 76.19% and 68.75% for detection of M. tuberculosis and 71.4% and 100% for detection of rifampicin resistance respectively. ConclusionThe simplicity, sensitivity, speed and automation makes this assay a very promising diagnostic test for detection of M. tuberculosis and rifampicin resistance in aspirated pus specimens.

Cardiopulmonary signal acquisition from different regions using video imaging analysis

Activity of the cardiovascular and respiratory systems causes some imperceptible physiological and physical effects in different regions of the human body, which can be highly informative in clinical and biomedical settings, where physiological signs and lifestyle indicators are required to be measured remotely. The possibility of extracting cardiopulmonary signals from many different ROIs (face, forehead, head, palm, wrist, arm, neck, leg and chest), based on cost effective systems without any biological effects on humans, has been investigated in this paper using different image and signal processing techniques. The experimental results of all proposed systems (the colour-based method and the motion-based method) approved their effectiveness, high correlation coefficients (PCC = 0.98 for cardiac measurements and 0.93 for respiratory measurements) and low error rates (RMSE = 1.97 beats/min for cardiac measurements and 1.98 breaths/min for respiratory measurements) in comparison with those obtained from conventional reference methods. Therefore, the proposed systems in this paper may be of value for upcoming non-contact monitoring systems in the diagnostic and health care applications.

The Rate of Success of the Accelerated Solvent Extraction (Ase) of Fat and Organochlorine Pesticides from Dried Fish Meat Samples

The replacement of conventional sample preparation techniques with newer techniques which are automated, faster and more eco-friendly, is nowadays desired in every analytical laboratory. One of the techniques with the attributes mentioned above is the Accelerated Solvent Extraction. In order to evaluate how successful this method is for the extraction of fat and organochlorine pesticides (OCPs) from dried fish meat samples, we have tested two series of diverse fish using Dionex™ 350 ASE provided by Thermo Scientific™ (Germany). For a more interesting approach, we added to our investigation 7 polychlorinated biphenyl (PCBs), 3 thricholorobenzenes, 2 tetrachlorobenzenes, 1 pentachlorobenzenes and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The study focused on comparing the recoveries of these analytes from different fish samples, after replacing the conventional reference method of the laboratory with ASE. The ASE parameters tested were previously used for the extraction of fat and polybrominated diphenyl ethers (PBDE) from fish samples: temperature: 120 ° C; static time: 5 min; number of cycles: 3; flushing volume: 25%; rinse with nitrogen: 90 s; solvent: cyclohexane/ethyl acetate (ratio 1:1). The ASE method provided similar and in some cases better results when compared to the standard reference method, more rapidly, eco-friendly and safer. Any high or low recoveries of the analytes taken into study are attributed to random or systematic errors during the Clean-up step of the extracts and the quantification with Gas Chromatography coupled with Tandem Mass-Spectrometry (GC MS/MS).

Assessing the distinguishable cluster approximation based on the triple bond-breaking in the nitrogen molecule.

Obtaining the correct potential energy curves for the dissociation of multiple bonds is a challenging problem for ab initio methods which are affected by the choice of a spin-restricted reference function. Coupled cluster (CC) methods such as CCSD (coupled cluster singles and doubles model) and CCSD(T) (CCSD + perturbative triples) correctly predict the geometry and properties at equilibrium but the process of bond dissociation, particularly when more than one bond is simultaneously broken, is much more complicated. New modifications of CC theory suggest that the deleterious role of the reference function can be diminished, provided a particular subset of terms is retained in the CC equations. The Distinguishable Cluster (DC) approach of Kats and Manby [J. Chem. Phys. 139, 021102 (2013)], seemingly overcomes the deficiencies for some bond-dissociation problems and might be of use in quasi-degenerate situations in general. DC along with other approximate coupled cluster methods such as ACCD (approximate coupled cluster doubles), ACP-D45, ACP-D14, 2CC, and pCCSD(α, β) (all defined in text) falls under a category of methods that are basically obtained by the deletion of some quadratic terms in the double excitation amplitude equation for CCD/CCSD (coupled cluster doubles model/coupled cluster singles and doubles model). Here these approximate methods, particularly those based on the DC approach, are studied in detail for the nitrogen molecule bond-breaking. The N2 problem is further addressed with conventional single reference methods but based on spatial symmetry-broken restricted Hartree-Fock (HF) solutions to assess the use of these references for correlated calculations in the situation where CC methods using fully symmetry adapted SCF solutions fail. The distinguishable cluster method is generalized: 1) to different orbitals for different spins (unrestricted HF based DCD and DCSD), 2) by adding triples correction perturbatively (DCSD(T)) and iteratively (DCSDT-n), and 3) via an excited state approximation through the equation of motion (EOM) approach (EOM-DCD, EOM-DCSD). The EOM-CC method is used to identify lower-energy CC solutions to overcome singularities in the CC potential energy curves. It is also shown that UHF based CC and DC methods behave very similarly in bond-breaking of N2, and that using spatially broken but spin preserving SCF references makes the CCSD solutions better than those for DCSD.

Mid-Infrared and Total X-Ray Fluorescence Spectroscopy Complementarity for Assessment of Soil Properties

Diffuse reflectance Fourier transformed mid-infrared (DRIFT-MIR) spectroscopy can predict many soil properties but extractable nutrients are often predicted poorly. This paper tested the combined DRIFT-MIR and total X-ray fluorescence (TXRF) spectroscopy analysis for prediction of soil properties related to soil fertility. A total of 700 soil samples from 44 stratified randomly located 100-km2 sentinel sites distributed across Sub-Saharan Africa (SSA) were analyzed for physicochemical composition using conventional reference methods, and compared with MIR and TXRF spectra using Random Forests (RF) regression algorithm and an internal out-of-bag (OOB) validation. Mid-infrared spectra resulted in good prediction models (R2 > 0.80) for organic C and total N, Mehlich-3 Ca and Al, and pH. Moderately predicted (R2 > 0.60) were extractable Mg, P sorption index, sand, silt, and clay. Models were less satisfactory (R2 < 0.60) for Mehlich-3 extractable K, Mn, Fe, Cu, B, Zn, P, S, and Na, exchangeable acidity and electrical conductivity (Ecd). Inclusion of total element concentration data from TXRF analysis in the MIR RF models significantly reduced root mean square error of prediction by 70% for Ecd, 66% for Mehlich-3 Na, 61% for Mehlich-3 S, and 50% for Mehlich-3 B due to detection by TXRF of some saline soils that were not well predicted by MIR. Overall, both methods predicted soil properties that relate to nutrient buffering capacity, including some exchangeable bases, pH, P sorption capacity, clay content, and organic matter content, and fingerprint basic soil mineralogy. Thus, further research should test whether MIR and TXRF fingerprinting could better predict soil nutrient supply capacity, as determined by crop nutrient uptake potential, than conventional soil P, K and micronutrient tests.