Direct Calibrations Research Articles

A multi-instrumental approach for calibrating real-time mass spectrometers using high-performance liquid chromatography and positive matrix factorization

Abstract. Obtaining quantitative information for molecular species present in aerosols from real-time mass spectrometers such as an extractive electrospray time-of-flight mass spectrometer (EESI) and an aerosol mass spectrometer (AMS) can be challenging. Typically, molecular species are calibrated directly through the use of pure standards. However, in some cases (e.g., secondary organic aerosol (SOA) formed from volatile organic compounds (VOCs)), direct calibrations are impossible, as many SOA species can either not be purchased as pure standards or have ambiguous molecular identities. In some cases, bulk OA sensitivities are used to estimate molecular sensitivities. This approach is not sufficient for EESI, which measures molecular components of OA, because different species can have sensitivities that vary by a factor of more than 30. Here, we introduce a method to obtain EESI calibration factors when standards are not available, and we provide a thorough analysis of the feasibility, performance, and limitations of this new technique. In this method, complex aerosol mixtures were separated with high-performance liquid chromatography (HPLC) followed by aerosol formation via atomization. The separated aerosols were then measured by an EESI and an AMS, which allowed us to obtain sensitivities for some species present in standard and SOA mixtures. Pure compounds were used to test the method and characterize its uncertainties, and obtained sensitivities were consistent within ±20 % when comparing direct calibrations vs. HPLC calibrations for a pure standard and within a factor of 2 for a standard mixture. In some cases, species were not completely resolved by chromatography, and positive matrix factorization (PMF) of AMS data enabled further separation. This method should be applicable to other real-time MS techniques. Improvements in chromatography are possible that would allow better separation in complex mixtures.

PSX-2 Data Analytics of a Global Nirs Database of Soybean Meal Nutrient Content

Abstract The nutrient and energy content of soybean meal (SBM) is variable due to genetics, country of origin, agronomic conditions, and to a lesser extent, the solvent-extraction process. The analytical variability among and within-labs can increase the difficulty of detecting differences among sources and establish nutrient interrelationships to estimate some nutrients based on others that are less variable. Near-infrared reflectance spectroscopy (NIRS) can reduce laboratory analytical inconsistencies and increase the sample size for feedstuff evaluation enhancing feed formulation accuracy. The PNE system (Adisseo) has unique NIRS curves based on direct calibrations generated with in vivo data of standard chicken metabolizable energy (AME and AMEn) and amino acid (AA) digestibility methods. This study evaluated the relationship between AA concentrations and crude protein (CP) and among proximate parameters (CP, crude fiber, ether extract, nitrogen-free extract, and ash), AA concentrations, and digestibilities with AME AMEn. The PNE database used contained 77,573 samples of SBM from Argentina (9,684), Brazil (62,322), and the U.S. (5,567) scanned in diverse countries worldwide between 2018 and 2021. Correlation and regression analyses between AA and CP were conducted. The pairwise correlations (P < 0.001) between AA and CP ranged between 0.34 and 0.82. Concentrations of all AAs in SBM can be predicted (P < 0.001) from the positive linear relationships with CP content. However, all coefficients of determination (R2) were low (0.11 to 0.68). The SBM country of origin was a significant factor and interacted with CP (P < 0.001), but R2 improved only slightly when included in these linear models. Multiple linear regression (MLR) and neural networks (NN) analyses were conducted to estimate AME and AMEn based on proximate values, AA concentrations and digestibility, and country of origin. All factors were significant (P < 0.001) in the MLR models for AME (R2 = 0.78, AICc = 643,940.6) and AMEn (R2 = 0.77, AICc = 642,785). Additionally, to have R2 below 0.80, the MLR models had collinearity for digestibility data and branched-chain AAs concentrations. The NN models had a better fit for training and validation datasets for AME (R2 = 0.88, RASE = 39.96) and AMEn (R2 = 0.87, RASE = 37.21). The NN models allowed us to visualize the greater importance of AA digestibility coefficients (His, Val, Trp, Cys, Arg, Leu, Thr) than the concentration of AAs or proximate values to estimate SBM energy values. In conclusion, AA concentrations of SBM cannot be accurately predicted from its CP content. The AA content of SBM varies by country of origin and may vary independently of CP content. The energy value of SBM may depend more on AA digestibility than proximate parameters. Data analytics of NIRS databases with direct calibration of in vivo parameters of energy utilization and AA digestibility elucidates relevant nutritional factors.

PSX-1 Data Analytics of a Global Nirs Database of Corn Nutrient Content

Abstract Corn is the primary energy source for livestock and poultry. Corn nutrient composition and energy value vary due to genetics, country of origin, agronomic, harvest, and storage conditions. Analytical variability among and within-labs makes it more difficult to detect differences among sources and establish nutrient interrelationships to estimate amino acid (AA) content based on crude protein (CP), which is less variable. Near-infrared reflectance spectroscopy (NIRS) can standardize feedstuff evaluation and increase the sample size. The PNE system (Adisseo) has distinctive NIRS curves created using direct calibrations with in vivo data of standard chicken metabolizable energy (AME and AMEn) and AA digestibility studies. This study assessed the link between AA concentrations and CP and among proximate parameters (CP, crude fiber, ether extract, nitrogen-free extract, and ash), starch, AA concentrations and digestibilities with AME and AMEn. The PNE database used includes 84,331samples of maize scanned in diverse countries between 2018 and 2021 that came from Argentina (7,654), Brazil (49,672), Indonesia (18,072), Philippines (4,747), and the United States (4,186). Correlation and regression analyses between AA and CP were performed. The pairwise correlations (P < 0.001) observed between AA and CP ranged between 0.52 and 0.90. The positive linear associations with CP content can be used to predict the concentrations of all AAs in corn (P < 0.001). However, coefficients of determination (R2) ranged from 0.27 (Trp) to 0.80 (Val) or 0.81 (Phe). Prediction equations for Lys, sulfur AAs had lower R2 values (0.37 to 0.47). Although the country of origin and CP interacted (P < 0.001), R2 modestly increased when added to these models. The estimation of AME and AMEn based on proximate values, starch, amylose, amylose:amylopectin, AA concentrations, AA digestibility, and country of origin was done using multiple linear regression (MLR) and neural networks (NN) analysis. All factors were significant (P < 0.001), and MLR models including starch and amylopectin, had the best fit for AME (R2 = 0.87, AICc = 149,635) and AMEn (R2 = 0.87, AICc = 149,543). The NN models had a better fit for training and validation datasets for AME (R2 = 0.95, RASE = 15.18) and AMEn (R2 = 0.95, RASE = 15.23). The NN models helped to visualize the greater importance of starch, AA concentration (Trp, Ile, Thr), and Leu digestibility. In summary, some corn AA concentrations (Val, Phe, Ile) may be predicted from their CP content; other AA concentrations may be more difficult to predict. Corn AA content varies by country of origin and independent of CP content. Starch content, AA concentration, and AA digestibility are essential factors in determining energy value of corn. Relevant nutritional aspects were elucidated by data analytics of a NIRS database with direct calibration of in vivo parameters of energy utilization and AA digestibility.

Evaluating on-board kVCT- and MVCT-based dose calculation accuracy using a thorax phantom for helical tomotherapy treatments

Purpose. To evaluate the impact of CT number calibration and imaging parameter selection on dose calculation accuracy relative to the CT planning process in thoracic treatments for on-board helical CT imaging systems used in helical tomotherapy. Methods and Materials. Direct CT number calibrations were performed with appropriate protocols for each imaging system using an electron density phantom. Large volume and SBRT treatment plans were simulated and optimized for planning CT scans of an anthropomorphic thorax phantom and transferred to registered kVCT and MVCT scans of the phantom as appropriate. Relevant DVH metrics and dose-difference maps were used to evaluate and compare dose calculation accuracy relative to the planning CT based on a variation in imaging parameters applied for the on-board systems. Results. For helical kVCT scans of the thorax phantom, median differences in DVH parameters for the large volume treatment plan were less than ±1% with dose to the target volume either over- or underestimated depending on the imaging parameters utilized for CT number calibration and thorax phantom acquisition. For the lung SBRT plan calculated on helical kVCT scans, median dose differences were up to –2.7% with a more noticeable dependence on parameter selection. For MVCT scans, median dose differences for the large volume plan were within +2% with dose to the target overestimated regardless of the imaging protocol. Conclusion. Accurate dose calculations (median errors of <±1%) using a thorax phantom simulating realistic patient geometry and scatter conditions can be achieved with images acquired with a helical kVCT system on a helical tomotherapy unit. This accuracy is considerably improved relative to that achieved with the MV-based approach. In a clinical setting, careful consideration should be made when selecting appropriate kVCT imaging parameters for this process as dose calculation accuracy was observed to vary with both parameter selection and treatment type.

Calibration of an airborne HO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; instrument using the All Pressure Altitude-based Calibrator for HO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; Experimentation (APACHE)

Abstract. Laser-induced fluorescence (LIF) is a widely used technique for both laboratory-based and ambient atmospheric chemistry measurements. However, LIF instruments require calibrations in order to translate instrument response into concentrations of chemical species. Calibration of LIF instruments measuring OH and HO2 (HOx) typically involves the photolysis of water vapor by 184.9 nm light, thereby producing quantitative amounts of OH and HO2. For ground-based HOx instruments, this method of calibration is done at one pressure (typically ambient pressure) at the instrument inlet. However, airborne HOx instruments can experience varying cell pressures, internal residence times, temperatures, and humidity during flight. Therefore, replication of such variances when calibrating in the lab is essential to acquire the appropriate sensitivities. This requirement resulted in the development of the APACHE (All Pressure Altitude-based Calibrator for HOx Experimentation) chamber to characterize the sensitivity of the airborne LIF-FAGE (fluorescence assay by gas expansion) HOx instrument, HORUS, which took part in an intensive airborne campaign, OMO-Asia 2015. It utilizes photolysis of water vapor but has the additional ability to alter the pressure at the nozzle of the HORUS instrument. With APACHE, the HORUS instrument sensitivity towards OH (26.1–7.8 cts s−1 pptv−1 mW−1, ±22.6 % 1σ; cts stands for counts by the detector) and HO2 (21.2–8.1 cts s−1 pptv−1 mW−1, ±22.1 % 1σ) was characterized to the external pressure range at the instrument nozzle of 227–900 mbar. Measurements supported by a computational fluid dynamics model, COMSOL Multiphysics, revealed that, for all pressures explored in this study, APACHE is capable of initializing a homogenous flow and maintaining near-uniform flow speeds across the internal cross section of the chamber. This reduces the uncertainty regarding average exposure times across the mercury (Hg) UV ring lamp. Two different actinometrical approaches characterized the APACHE UV ring lamp flux as 6.37×1014(±1.3×1014) photons cm−2 s−1. One approach used the HORUS instrument as a transfer standard in conjunction with a calibrated on-ground calibration system traceable to NIST standards, which characterized the UV ring lamp flux to be 6.9(±1.1)×1014 photons cm−2 s−1. The second approach involved measuring ozone production by the UV ring lamp using an ANSYCO O3 41 M ozone monitor, which characterized the UV ring lamp flux to be 6.11(±0.8)×1014 photons cm−2 s−1. Data presented in this study are the first direct calibrations of an airborne HOx instrument, performed in a controlled environment in the lab using APACHE.

Reconsideration of seawater surfactant activity analysis based on an inter-laboratory comparison study

Surfactants, or surface-active substances (SAS), are amphipathic organic substances that adsorb on aquatic phase boundaries, including the air-sea interface that covers ~70% of Earth's surface. SAS thus mediate all mass transfer across the air-sea interface and are central to planetary scale biogeochemical processes. SAS are routinely quantified in seawater and freshwater in terms of total surfactant activity (SA), using alternating current (AC) out-of-phase voltammetry with a hanging mercury drop electrode (HMDE). Although this technique is well established, method modifications have been implemented and differing calibration procedures adopted in individual research laboratories. Increasing interest in the environmental roles of SAS prompts a timely inter-comparison of these varying analytical approaches. Using sea-surface microlayer (SML: uppermost 80 μm layer sampled) and sub-surface (SSW: 1 m depth sampled) seawater from Jade Bay (south-eastern North Sea), we carried out the first inter-laboratory comparison for SA, using methods and calibration protocols previously established in three participating laboratories. The internal calibration protocol follows direct calibrations of individual samples against the model surfactant Triton-X-100 during analysis, whereas external calibration produces independent Triton-X-100 calibration curves; both protocols express SAS concentrations in Triton-X-100 equivalents (T-X-100 eq.). There was no significant difference between SA derived via internal or external calibration protocols, or by using different analytical instruments (range in Kruskall-Wallis and Dunn-Bonferroni post-hoc test p-values: 0.062–1.000), except where freeze/thaw degradation was suspected to have occurred during transit (p < .001). We recommend using discrete calibration standards during external calibration. Irrespective of any differences in SA determined by the three laboratories, the SA enrichment factor (EF: =SASML/SASSW) was not affected for any sample; the root mean square error (±one standard deviation) between all laboratories was 0.156 ± 0. 226 (n = 45). We present and discuss recommendations for a standard analytical protocol to ensure the inter-laboratory compatibility of SAS measurements into the future.

OA028] On the potential of direct MV calibration of ionization chambers by secondary standards laboratories

Purpose The IAEA protocol (TRS-398) for absorbed dose to water measurements in therapeutic MV photon beams, recommends that ionization chambers be calibrated directly in MV accelerator photon beams rather than in cobalt-60 combined with generic beam quality correction factors ( k Q ) tabulated in the protocol. The purpose of this work was to study the feasibility for secondary standards laboratories to provide direct MV calibrations for hospitals and to evaluate the benefit of such calibrations versus conventional cobalt calibrations. Methods A laboratory with the potential to provide direct MV calibrations was established. It includes both a cobalt irradiator and a linear accelerator with the following MV beams: 4, 6, 10, 15, and 18 MV with flattening filter and 6 and 10 MV without flattening filter. Procedures were designed for accurate positioning of ionization chambers, beam output monitoring and relevant ionization chamber correction factors. Over a two-month period, k Q -factors were measured in all beams for seven nominally identical chambers (IBA FC65G) covering a wide range of serial numbers. Traceability to primary standards were established using transfer chambers. The results were compared with published k Q -factors from TRS-398. Results The monitoring of beam output using an external monitor chamber was found to be essential for calibration purposes: The raw accelerator output changed systematically by 0.4% over the measurement period. However, with an external monitor chamber, the output variability was reduced to less than 0.05% (1 sd). For each beam quality, the relative standard deviation for the measured k Q factors for the seven ionization chambers was about 0.07%. Conclusions The study demonstrates the feasibility of highly reproducible MV calibrations at the level of a secondary standards laboratory, and the closeness of agreement (sd k Q -factors may be adequate for the tested ionization chamber model. Ongoing work focuses on characterization of additional ionization chambers models (PTW30013, PTW31021, and NE2571) and on an improved estimation of the uncertainty related to establishing traceability to primary standards. The latter work includes direct use of water calorimetry in the specific accelerator beams of the laboratory.

Direct and indirect predictions of enteric methane daily production, yield, and intensity per unit of milk and cheese, from fatty acids and milk Fourier-transform infrared spectra

Mitigating the dairy chain's contribution to climate change requires cheap, rapid methods of predicting enteric CH4 emissions (EME) of dairy cows in the field. Such methods may also be useful for genetically improving cows to reduce EME. Our objective was to evaluate different procedures for predicting EME traits from infrared spectra of milk samples taken at routine milk recording of cows. As a reference method, we used EME traits estimated from published equations developed from a meta-analysis of data from respiration chambers through analysis of various fatty acids in milk fat by gas chromatography (FAGC). We analyzed individual milk samples of 1,150 Brown Swiss cows from 85 farms operating different dairy systems (from very traditional to modern), and obtained the cheese yields of individual model cheeses from these samples. We also obtained Fourier-transform infrared absorbance spectra on 1,060 wavelengths (5,000 to 930 waves/cm) from the same samples. Five reference enteric CH4 traits were calculated: CH4 yield (CH4/DMI, g/kg) per unit of dry matter intake (DMI), and CH4 intensity (CH4/CM, g/kg) per unit of corrected milk (CM) from the FAGC profiles; CH4 intensity per unit of fresh cheese (CH4/CYCURD, g/kg) and cheese solids (CH4/CYSOLIDS, g/kg) from individual cheese yields (CY); and daily CH4 production (dCH4, g/d). Direct infrared (IR) calibrations were obtained by BayesB modeling; the determination coefficients of cross-validation varied from 0.36 for dCH4 to 0.57 for CH4/CM, and were similar to the coefficient of determination values of the equations based on FAGC used as the reference method (0.47 for CH4/DMI and 0.54 for CH4/CM). The models allowed us to select the most informative wavelengths for each EME trait and to infer the milk chemical features underlying the predictions. Aside from the 5 direct infrared prediction calibrations, we tested another 8 indirect prediction models. Using IR-predicted informative fatty acids (FAIR) instead of FAGC, we were able to obtain indirect predictions with about the same precision (correlation with reference values) as direct IR predictions of CH4/DMI (0.78 vs. 0.76, respectively) and CH4/CM (0.82 vs. 0.83). The indirect EME predictions based on IR-predicted CY were less precise than the direct IR predictions of both CH4/CYCURD (0.67 vs. 0.81) and CH4/CYSOLIDS (0.62 vs. 0.78). Four indirect dCH4 predictions were obtained by multiplying the measured or IR-predicted daily CM production by the direct or indirect CH4/CM. Combining recorded daily CM and predicted CH4/CM greatly increased precision over direct dCH4 predictions (0.96-0.96 vs. 0.68). The estimates obtained from the majority of direct and indirect IR-based prediction models exhibited herd and individual cow variability and effects of the main sources of variation (dairy system, parity, days in milk) similar to the reference data. Some rapid, cheap, direct and indirect IR prediction models appear to be useful for monitoring EME in the field and possibly for genetic/genomic selection, but future studies directly measuring CH4 with different breeds and dairy systems are needed to validate our findings.

Calibration of Ultraviolet, Mid-infrared, and Radio Star Formation Rate Indicators

Abstract We present calibrations for star formation rate (SFR) indicators in the ultraviolet, mid-infrared, and radio-continuum bands, including one of the first direct calibrations of 150 MHz as an SFR indicator. Our calibrations utilize 66 nearby star-forming galaxies with Balmer-decrement-corrected luminosities, which span five orders of magnitude in SFR and have absolute magnitudes of . Most of our photometry and spectrophotometry are measured from the same region of each galaxy, and our spectrophotometry has been validated with SDSS photometry, so our random and systematic errors are small relative to the intrinsic scatter seen in SFR indicator calibrations. We find that the Wide-field Infrared Space Explorer W4 (22.8 μm), Spitzer 24 μm, and 1.4 GHz bands have tight correlations with the Balmer-decrement-corrected Hα luminosity, with a scatter of only 0.2 dex. Our calibrations are comparable to those from the prior literature for L ∗ galaxies, but for dwarf galaxies, our calibrations can give SFRs that are far greater than those derived from most previous literature.

A Low Nonlinearity, Missing-Code Free Time-to-Digital Converter Based on 28-nm FPGAs With Embedded Bin-Width Calibrations

This paper presents a low nonlinearity, missing-code free, time-to-digital converter (TDC) implemented in a 28-nm field programmable gate array (FPGA) device (Xilinx Virtex 7 XC7V690T) with novel direct bin-width calibrations. We combine the tuned tapped delay lines (TDLs) and a modified direct-histogram architecture to correct the nonuniformity originated from carry chains, and use a multiphase sampling structure to minimize the skews of clock routes. Results of code density tests show that the proposed TDC has much better linearity performances than previously published TDCs. Moreover, our TDC does not generate missing codes. For a single TDL, the differential nonlinearity (DNL) is within [−0.38, 0.87] LSB (the least significant bit: 10.5 ps) with $\sigma _{\mathrm {DNL}} = 0.20$ LSB, and the integral nonlinearity (INL) is within [−1.23, 1.02] LSB with $\sigma _{\mathrm {INL}} = 0.50$ LSB. Based on the modified direct-histogram architecture, a direct bin-width calibration method was implemented and verified in the FPGA. By implementing embedded bin-width calibrations, the histogram data of TDCs can be calibrated on the fly. After the calibration, the DNL $_{\mathrm {pk-pk}}$ (peak-to-peak DNL) and INL $_{\mathrm {pk-pk}}$ (peak-to-peak INL) can be reduced to 0.08 LSB with $\sigma _{\mathrm {DNL}} = 0.01$ and 0.13 LSB with $\sigma _{\mathrm {INL}} = 0.02$ LSB, respectively.

Millimeter-Wave On-Wafer TRL Calibration Employing 3-D EM Simulation-Based Characteristic Impedance Extraction

In this paper, we propose a method based on 3-D electromagnetic simulations, for the characteristic impedance extraction of transmission lines employed in TRL calibration, focusing on lines integrated in silicon technologies. The accuracy achieved with TRL calibrations using the proposed characteristic impedance extraction is benchmarked versus conventional approaches, with an emphasis on aluminum pads structures operating in the (sub) millimeter-wave range. The proposed method proves to be insensitive to common sources of error (i.e., large pad capacitance and inductive pad-to-line transitions), which affect the accuracy of characteristic impedance extraction based on measurements, especially as the testing frequency increases. First, direct on-wafer TRL calibrations are performed on uniform CPWs (i.e., with no pads discontinuities) to demonstrate how the proposed method performs as good as the calibration comparison method and outperforms calibration transfer approaches. Finally, the method is applied to a nonuniform CPW-based calibration kit, demonstrating how the proposed method provides accurate results, improving the calibration quality that can be achieved using the calibration comparison method when inductive pad-to-line transitions are present.

Au Fixed Point Development at NRC

Two Au fixed points filled using metal of different nominal purities in carbon crucibles have been developed at the National Research Council Canada (NRC). The primary motivation behind this project was to provide the means for direct thermocouple calibrations at the Au freezing point (\(1064.18~^\circ \hbox {C}\)). Using a Au fixed point filled with the metal of maximum available purity [99.9997 % pure according to glow discharge mass spectroscopy (GDMS)], multiple freezing plateaus were measured in a commercial high-temperature furnace. Four Pt/Pd thermocouples constructed and calibrated in-house were used to measure the freezing plateaus. From the calibration at Sn, Zn, Al and Ag fixed points, the linear deviation function from the NIST-IMGC reference function (IEC 62460:2008 Standard) was determined and extrapolated to the freezing temperature of Au. For all the Pt/Pd thermocouples used in this study, the measured EMF values agree with the extrapolated values within expanded uncertainty, thus substantiating the use of 99.9997 % pure Au fixed point cell for thermocouple calibrations at NRC. Using the Au fixed point filled with metal of lower purity (99.99 % pure according to GDMS), the effect of impurities on the Au freezing temperature measured with Pt/Pd thermocouple was further investigated.

Using albedo to reform wind erosion modelling, mapping and monitoring

Wind erosion and dust emission models are used to assess the impacts of dust on radiative forcing in the atmosphere, cloud formation, nutrient fertilisation and human health. The models are underpinned by a two-dimensional geometric property (lateral cover; L) used to characterise the three-dimensional aerodynamic roughness (sheltered area or wakes) of the Earth’s surface and calibrate the momentum it extracts from the wind. We reveal a fundamental weakness in L and demonstrate that values are an order of magnitude too small and significant aerodynamic interactions between roughness elements and their sheltered areas have been omitted, particularly under sparse surface roughness. We describe a solution which develops published work to establish a relation between sheltered area and the proportion of shadow over a given area; the inverse of direct beam directional hemispherical reflectance (black sky albedo; BSA). We show direct relations between shadow and wind tunnel measurements and thereby provide direct calibrations of key aerodynamic properties. Estimation of the aerodynamic parameters from albedo enables wind erosion assessments over areas, across platforms from the field to airborne and readily available satellite data. Our new approach demonstrated redundancy in existing wind erosion models and thereby reduced model complexity and improved fidelity. We found that the use of albedo enabled an adequate description of aerodynamic sheltering to characterise fluid dynamics and predict sediment transport without the use of a drag partition scheme (Rt) or threshold friction velocity (u∗t). We applied the calibrations to produce global maps of aerodynamic properties which showed very similar spatial patterns to each other and confirmed the redundancy in the traditional parameters of wind erosion modelling. We evaluated temporal patterns of predicted horizontal mass flux at locations across Australia which revealed variation between land cover types that would not be detected using traditional models. Our new approach provided new opportunities to investigate the dynamics of wind erosion in space and time and elucidate aeolian processes across scales.

Traceability of solar UV measurements using the Qasume reference spectroradiometer.

One major objective of the European Joint Research Project "Traceability for surface spectral solar ultraviolet (UV) radiation" was to reduce the uncertainty of spectral UV measurements. The measurement instrument used for this work was the portable UV European reference spectroradiometer Qasume. The calibration uncertainty of this instrument was decreased and validated by a comparison of direct calibrations against a primary standard for spectral irradiance, a high temperature blackbody radiator, and against a reference detector using a spectrally tunable laser as a monochromatic source. The spectral irradiance responsivity of the reference detector is traceable to the primary standard of optical power, realized through a cryogenic radiometer, and to the SI unit of meter. The measuring technique was improved by the construction of a new reference spectroradiometer, QasumeII. An improved input optics removes the dependences of the measured solar irradiance on the angle of incident for solar zenith angle smaller than 75deg. Moreover, a hybrid photon detection system enables continuous tracking of the instrument's responsivity changes. For both spectroradiometer systems an uncertainty budget was calculated. The improvements have reduced the measurement uncertainties of solar spectral UV irradiance measurements from 4.8% in 2005 to 2.0% (k=2) in the spectral region above 310nm. The largest sources of uncertainty were the absolute spectral irradiance responsivity calibration, the angular response uncertainty, and the instrument stability using the hybrid detector, which were reduced from 3.6% to 1.1%, from 1.2% to 0.6%, and from 0.65% to 0.4%, with respect to the situation prior to the project. The new instrument was validated during a four month intercomparison relative to the Qasume reference. The mean ratio of the solar irradiance scans between the two reference spectroradiometers has an offset of +0.7% and a standard deviation of ±1.5% for a wavelength greater than 305nm, which is well within the combined uncertainty of 3.7% calculated from the uncertainties of the two systems.

Point/Counterpoint. Calibration of radiotherapy ionization chambers using Co-60 is outdated and should be replaced by direct calibration in linear accelerator beams.

Point/Counterpoint. Calibration of radiotherapy ionization chambers using Co-60 is outdated and should be replaced by direct calibration in linear accelerator beams.

A simple, projection-based geometric model for several linear pretreatment and calibration methods

A general model is proposed for the explanation of several linear methods used for quantification. A first projection approach concerns pretreatments and calibrations. It consists of an oblique projection of the spectral data onto a subspace containing useful information for calibrations or detrimental information for pretreatments. Corrected spectra and scores are obtained for pretreatments and calibrations, respectively. A second projection approach concerns only calibrations. The regression vector is deduced after an orthogonal projection of the reference values onto the scores previously obtained. Several pretreatments, and direct and indirect (inverse) calibrations also called regressions are reviewed according to this model. The methods described are focused on spectroscopic applications. Some are very specific to spectroscopy; however, most of them also can be applied in other situations.

In situ calibration using univariate analyses based on the onboard ChemCam targets: first prediction of Martian rock and soil compositions

Curiosity rover landed on August 6th, 2012 in Gale Crater, Mars and it possesses unique analytical capabilities to investigate the chemistry and mineralogy of the Martian soil. In particular, the LIBS technique is being used for the first time on another planet with the ChemCam instrument, and more than 75,000 spectra have been returned in the first year on Mars. Curiosity carries body-mounted calibration targets specially designed for the ChemCam instrument, some of which are homgeneous glasses and others that are fine-grained glass-ceramics. We present direct calibrations, using these onboard standards to infer elements and element ratios by ratioing relative peak areas. As the laser spot size is around 300μm, the LIBS technique provides measurements of the silicate glass compositions representing homogeneous material and measurements of the ceramic targets that are comparable to fine-grained rock or soil. The laser energy and the auto-focus are controlled for all sequences used for calibration. The univariate calibration curves present relatively to very good correlation coefficients with low RSDs for major and ratio calibrations. Trace element calibration curves (Li, Sr, and Mn), down to several ppm, can be used as a rapid tool to draw attention to remarkable rocks and soils along the traverse. First comparisons to alpha-particle X-ray spectroscopy (APXS) data, on selected targets, show good agreement for most elements and for Mg# and Al/Si estimates. SiO2 estimates using univariate cannot be yet used. Na2O and K2O estimates are relevant for high alkali contents, but probably under estimated due to the CCCT initial compositions. Very good results for CaO and Al2O3 estimates and satisfactory results for FeO are obtained.

Direct reference air-kerma rate calibration of 192Ir for a thimble-type ionization chamber in a cylindrical solid phantom

International and national reports strongly recommend experimental verification of the calibration of new HDR 192Ir sources prior to their clinical application for afterloading brachytherapy. To guarantee traceability, calibrated transfer standards are used, e.g. the recommended well-type ionization chambers (WIC) or certain detector–phantom arrangements (DPA) consisting of a thimble-type ionization chamber with a solid phantom. In Germany, direct calibrations for 192Ir were only provided for WICs. In June 2010, the PTB directly calibrated a DPA-transfer standard in the quantity reference air-kerma rate (RAKR) for 192Ir photons for the University Hospital Tübingen. This direct calibration provides the advantage that the comprehensive RAKR 192Ir calibration coefficient already takes all influence quantities into account—their correction factors are thus unified—except for the air-density correction kρ. The DPA-transfer standard described above and a WIC used as a reference were compared for acceptance tests of three GammaMedplus HDR 192Ir afterloading sources. The measurement uncertainty of the WIC and of the DPA-transfer standard were ±2.6%(k = 2) and ±2.8%(k = 2) respectively. A strong correlation was found between these measurement results with a coefficient of determination of r2 = 0.9998.Determining the RAKR of an HDR 192Ir afterloading source is as simple with the DPA as it is with WIC. The direct 192Ir calibrated DPA-transfer standard can therefore be used alternatively in future with the same measurement uncertainty if no WIC is available.

Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas

The semiaquatic platypus and terrestrial echidnas (spiny anteaters) are the only living egg-laying mammals (monotremes). The fossil record has provided few clues as to their origins and the evolution of their ecological specializations; however, recent reassignment of the Early Cretaceous Teinolophos and Steropodon to the platypus lineage implies that platypuses and echidnas diverged >112.5 million years ago, reinforcing the notion of monotremes as living fossils. This placement is based primarily on characters related to a single feature, the enlarged mandibular canal, which supplies blood vessels and dense electrosensory receptors to the platypus bill. Our reevaluation of the morphological data instead groups platypus and echidnas to the exclusion of Teinolophos and Steropodon and suggests that an enlarged mandibular canal is ancestral for monotremes (partly reversed in echidnas, in association with general mandibular reduction). A multigene evaluation of the echidna-platypus divergence using both a relaxed molecular clock and direct fossil calibrations reveals a recent split of 19-48 million years ago. Platypus-like monotremes (Monotrematum) predate this divergence, indicating that echidnas had aquatically foraging ancestors that reinvaded terrestrial ecosystems. This ecological shift and the associated radiation of echidnas represent a recent expansion of niche space despite potential competition from marsupials. Monotremes might have survived the invasion of marsupials into Australasia by exploiting ecological niches in which marsupials are restricted by their reproductive mode. Morphology, ecology, and molecular biology together indicate that Teinolophos and Steropodon are basal monotremes rather than platypus relatives, and that living monotremes are a relatively recent radiation.

Electron density estimations derived from spacecraft potential measurements on Cluster in tenuous plasma regions

Spacecraft potential measurements by the EFW electric field experiment on the Cluster satellites can be used to obtain plasma density estimates in regions barely accessible to other type of plasma experiments. Direct calibrations of the plasma density as a function of the measured potential difference between the spacecraft and the probes can be carried out in the solar wind, the magnetosheath, and the plasmashere by the use of CIS ion density and WHISPER electron density measurements. The spacecraft photoelectron characteristic (photoelectrons escaping to the plasma in current balance with collected ambient electrons) can be calculated from knowledge of the electron current to the spacecraft based on plasma density and electron temperature data from the above mentioned experiments and can be extended to more positive spacecraft potentials by CIS ion and the PEACE electron experiments in the plasma sheet. This characteristic enables determination of the electron density as a function of spacecraft potential over the polar caps and in the lobes of the magnetosphere, regions where other experiments on Cluster have intrinsic limitations. Data from 2001 to 2006 reveal that the photoelectron characteristics of the Cluster spacecraft as well as the electric field probes vary with the solar cycle and solar activity. The consequences for plasma density measurements are addressed. Typical examples are presented to demonstrate the use of this technique in a polar cap/lobe plasma.