Default Instrument Research Articles

Revisiting Dissolved Organic Matter Analysis Using High-Resolution Trapped Ion Mobility and FT-ICR Mass Spectrometry.

The molecular level characterization of complex mixtures remains an analytical challenge. We have shown that the integration of complementary, high-resolution, gas-phase separations allows for chemical formula level isomeric content description. In the current work, we revisited the current challenges associated with the analysis of dissolved organic matter using high-resolution trapped ion mobility separation (TIMS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In particular, we evaluated the separation capabilities provided by TIMS-MS compared to MS alone, the use of ICR complementary data acquisition (DAQ) systems and transient processing strategies, ICR cell geometries (e.g., Infinity cell vs harmonized cell), and magnetic field strengths (7 T vs 9.4 T vs 21 T) for the case of a Harney River DOM sample. Results showed that the external high-performance DAQ enables direct representation of mass spectra in absorption mode FT (aFT), doubling the MS resolution compared to the default magnitude mode FT (mFT). Changes between half- vs full-apodization result in greater MS signal/noise vs superior MS resolving power (RP); in the case of DOM analysis, a 45% increase in assigned formulas is observed when employing the DAQ half (Kaiser-type)-apodization window and aFT when compared to the default instrument mFT. Results showed the advantages of reprocessing 2D-TIMS-FT-ICR MS data with higher RP and magnetic field chemical formulas generated list acquired (e.g., 21 T led to a 24% increase in isomers reported) or the implementation of alternative strategies.

Simulation-aided characterization of a versatile water-based condensation particle counter for atmospheric airborne research

Abstract. Capturing the vertical profiles and horizontal variations of atmospheric aerosols often requires accurate airborne measurements. With the advantage of avoiding health and safety concerns related to the use of butanol or other chemicals, water-based condensation particle counters have emerged to provide measurements under various environments. However, airborne deployments are relatively rare due to the lack of instrument characterization under reduced pressure at flight altitudes. This study investigates the performance of a commercial “versatile” water-based condensation particle counter (vWCPC, model 3789, TSI, Shoreview, MN, USA) under various ambient pressure conditions (500–920 hPa) with a wide range of particle total number concentrations (1500–70 000 cm−3). The effect of conditioner temperature on vWCPC 3789 performance at low pressure is examined through numerical simulation and laboratory experiments. We show that the default instrument temperature setting of 30 ∘C for the conditioner is not suitable for airborne measurement and that the optimal conditioner temperature for low-pressure operation is 27∘. Under the optimal conditioner temperature (27∘), the 7 nm cut-off size is also maintained. Additionally, we show that insufficient droplet growth becomes more significant under the low-pressure operation. The counting efficiency of the vWCPC 3789 can vary up to 20 % for particles of different chemical compositions (e.g., ammonium sulfate and sucrose particles). However, such variation is independent of pressure.

Accuracies and detection limits of major, minor, and trace element quantification in rocks by portable laser-induced breakdown spectroscopy

The recent manufacture of portable laser-induced breakdown spectroscopy (pLIBS) instruments has permitted widespread applications of an established analytical technique for in situ geochemical quantifications. This novelty has created a need for investigations comparing the default univariate pLIBS calibration accuracies to custom instrument calibrations based on geological samples and to other modeling methods. Previous research has shown that multivariate models can mitigate some of the matrix effects that cause intensity and concentration non-linearity within LIBS plasmas of rocks. This study thus makes two pLIBS calibration comparisons: one compares partial least squares (PLS) multivariate regression to univariate instrument models, while the other compares the default instrument calibration, intended for general industrial use, to a custom instrument calibration based on rock standards. Both comparisons use root mean squared errors (RMSE) between model-predicted and true standard values of the major oxides Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O, P2O5, SiO2, and TiO2, and minor and trace elements Ba, Cr, Cu, H2O, Li, Ni, Pb, S, and Zn to test calibration accuracies. pLIBS spectra from 2007 diverse rock standards were used for the PLS versus univariate model comparison, while 89 publicly-available geochemical standards were used to compare the default and custom instrument calibrations. PLS models give test accuracies for major elements of ±8.61 wt% for SiO2, ±3.38 for Al2O3, ±0.77 for TiO2, ±3.84 for Fe2O3, ±4.41 wt% for MgO, ±3.08 wt% for CaO, ±1.09 wt% for Na2O, and ±1.52 wt% for K2O. Quantification of trace and minor elements was more accurate with multivariate regression than with univariate instrument models, and the new custom instrument calibration had lower prediction errors for these elements than those of the default models. However, minor and trace element errors from all three calibrations were often greater than the average concentration of the test standards, which suggests that these substances are not well quantified in rocks by pLIBS instruments.

Government Equity Investments in Coronavirus Rescues: Why, How, When?

Governments around the world are attempting to support individuals’ incomes, rescue distressed businesses, and preserve employer-employee relationships damaged in the coronavirus pandemic by adopting fiscal stimulus programs of unprecedented scale. Although the bulk of this spending will involve direct payments to individuals or some type of direct lending or loan guarantees to businesses, large sums will (and should) take the form of government purchases of equity in distressed firms — either by direct purchase or by exercising warrants attached to rescue loans. We discuss why we think these equity injections will be necessary, but only in a limited number of cases; how they should be structured; when investments should be made and, almost as important, exited. We summarize (and tabulate) both the modest recent history of governments rescuing non-financial firms with equity injections and the voluminous research examining the efficacy of governments rescuing failing banks using equity investments. We highlight the dangers that would likely arise if governments permanently retain and vote the equity stakes purchased during the current crisis. Where equity investments must be made, we argue that these should: (1) be effective, in being large enough to be decisive; (2) be passive after the initial injection, when some financial restrictions should be imposed; (3) be temporary and preferably self-liquidating through open-market sales or redemptions; (4) provide taxpayers an upside claim if and when the rescued firm recovers; (5) be restricted to exchange-listed companies in all but extreme cases; and (6) be timely, as speed is crucial. In most cases, the default instrument to employ should be either non-voting preferred stock or warrants that convert into immediately marketable common shares, and we present a numerical example of how a preferred stock-with-warrants equity investment could pay off handsomely for taxpayers if rescued companies recover even partially.

How Reliable Are Enantiomeric Excess Measurements Obtained By Chiral HPLC?

AbstractUncertainties and errors in enantiomeric excess determinations obtained by high performance liquid chromatography (HPLC) with a chiral column are evaluated with different peak resolutions and elution orders using (R)‐ and (S)‐ibuprofen standards. Five injections of each sample were made to reduce the variability in the data and each chromatogram was monitored at multiple wavelengths to facilitate the detection of chemical impurities. Using appropriate sample concentrations, the most favorable detection wavelengths, and default instrument parameters led to large errors (>10 %) whereas properly set integration values gave impressive reproducibilities (±0.5 % or better) and accuracies (<1 %) in the most favorable situations. Uncertainties and errors of up to±2.0 % and 5.2 % ee, respectively were also observed under separation conditions routinely reported in chemistry journals. This study aims to provide a practical guide to the accuracy and precision that can be achieved with HPLC, and suggestions for obtaining reliable results.

The Determinants of Market-Implied Recovery Rates

In the presence of recovery risk, the recovery rate is a random variable whose risk-neutral expectation can be inferred from the prices of defaultable instruments. I extract market-implied recovery rates from the term structures of credit default swap spreads for a sample of 497 United States (U.S.) corporate issuers over the 2005–2014 period. I analyze the explanatory factors of market-implied recovery rates within a linear regression framework and also within a Tobit model, and I compare them with the determinants of historical recovery rates that were previously identified in the literature. In contrast to their historical counterparts, market-implied recovery rates are mostly driven by macroeconomic factors and long-term, issuer-specific variables. Short-term financial variables and industry conditions significantly impact the slope of market-implied recovery rates. These results indicate that the design of a recovery risk model should be based on specific market factors, not on the statistical evidence that is provided by historical recovery rates.

Pricing of Fixed-Strike Lookback Options on Assets with Default Risk

In over-the-counter markets, many options on defaultable instruments are influenced by default risks emanating from the possibility that the option writer may not fulfill its contractual obligations. In this paper, we investigate the valuation of fixed-strike lookback options based on the issuer’s credit risk. Using double Mellin transforms and the method of images, we have a closed-form solution to fixed-strike lookback options with a default risk. Furthermore, we analyze the values of the vulnerable fixed-strike lookback options with respect to the model parameters and also show that the Monte Carlo simulations and the Implicit Finite Difference Method converge to the closed-form solutions and this verifies the correctness of our formulas.

Market implied volatilities for defaultable bonds

Typically, implied volatilities for defaultable instruments are not available in the financial market since quotations related to options on defaultable bonds or on credit default swaps are usually not quoted by brokers. However, an estimate of their volatilities is needed for pricing purposes. In this paper, we provide a methodology to infer market implied volatilities for defaultable bonds using equity implied volatilities and CDS spreads quoted by the market in relation to a specific issuer. The theoretical framework we propose is based on the Merton’s model under stochastic interest rates where the short rate is assumed to follow the Hull–White model. A numerical analysis is provided to illustrate the calibration process to be performed starting from financial market data. The market implied volatility calibrated according to the proposed methodology could be used to evaluate options where the underlying is a risky bond, i.e. callable bond or other types of credit-risk sensitive financial instruments.

Preliminary Analysis of the Potential and Limitations of MICAP for the Retrieval of Sea Surface Salinity

A new payload concept has been proposed: the microwave imager combined active/passive (MICAP). MICAP is a combined one-dimensional microwave interferometric radiometer that operates at 1.4, 6.9, 18.7, and 23.8 GHz and L-band (1.26 GHz) scatterometer. It has the capability to simultaneously remotely sense sea surface salinity (SSS), sea surface temperature (SST), and wind speed. MICAP will be a candidate payload onboard the Ocean Salinity Satellite led by the State Oceanic Administration of China to monitor SSS and reduce geophysical errors caused by surface roughness and SST. To provide an “all-weather” estimation of SSS with high accuracy from space, the errors of the simultaneous retrieval of multiparameters using MICAP are analyzed, and noise levels and stability requirements of instruments are estimated. Preliminary analysis shows that MICAP can provide SSS with an accuracy of 1 psu for single measurement and 0.1 psu over the global ocean for 200 × 200 km resolution pixels and one month at middle and low latitudes with default instrument noises (0.1 K, 0.3 K and 0.3 K for the L, C, and K band radiometers, respectively, and 0.1 dB for the L-band scatterometer) while uncertainties of the drift corrections are less than the radiometer sensitivities.

Improvement of Engine Exhaust Particle Sizer (EEPS) size distribution measurement – I. Algorithm and applications to compact-shape particles

Comparisons between the Engine Exhaust Particle Sizer Spectrometer (EEPS) and scanning mobility particle sizers (SMPS) have shown that the EEPS underestimates size and concentration of particles >~75nm and that the discrepancies vary by particle type. This paper describes the development of a new EEPS instrument matrix to improve size distribution measurements for compact-shape particles. Both the operating principle and the mathematical model of the EEPS data inversion are described. Monodisperse and polydisperse sucrose, poly-α-olefin oil (PAO), and sodium chloride (NaCl) particles were used for calibration. A new instrument matrix was developed and implemented for data inversion. This study confirms the literature findings that the geometric mean diameter, geometric standard deviation, and total number concentration by EEPS with the default instrument matrix (referred to as IM-2004) agrees with SMPS within ±20% for compact-shape particles <~75nm. However, EEPS with IM-2004 underestimates geometric mean diameters by 20–40% for larger particles. The revised instrument matrix improves the size agreement with the SMPS to within ±14% across the entire size range.

Numerical performance analysis of acoustic Doppler velocity profilers in the wake of an axial-flow marine hydrokinetic turbine

The use of acoustic Doppler current profilers (ADCPs) for the characterization of flow conditions in the vicinity of both experimental and full scale marine hydrokinetic (MHK) turbines is becoming increasingly prevalent. The computation of a three dimensional velocity measurement from divergent acoustic beams requires the assumption that the flow conditions are homogeneous among all beams at a particular axial distance from the instrument.In the near wake of MHK devices, the mean fluid motion is observed to be highly spatially variable as a result of torque generation and energy extraction. We examine the performance of ADCP measurements through modeling of a virtual ADCP (VADCP) instrument in the wake of an MHK turbine resolved using unsteady computational fluid dynamics (CFD). This is achieved by sampling the CFD velocity field at equivalent locations to the sample bins of an ADCP, and performing the coordinate transformation from beam coordinates to instrument coordinates, and finally to global coordinates.The stream-wise velocity deficit and tangential swirl velocity caused by the moving rotor lead to significant misrepresentation of the true flow velocity profiles by the VADCP. The most significant errors were observed in the transverse (cross-flow) velocity direction, with a relative error of 17% of the incident velocity. The relative RMS error over the rotor plane was calculate to be less than 2% of the incident velocity by a distance of x/D⩾2,x/D⩾1 and x/D⩾6 for the stream-wise, transverse and vertical directions, respectively. For the default instrument orientation, A maximum error in the V-velocity occurs when the instrument is located directly behind the turbine, and a maximum W-velocity error is found at a lateral offset y/D=0.20. For an instrument directly behind the MHK device, the maximum error in the U-velocity and V-velocity occurs at a yaw angle of ϕ≈30° and ϕ≈60°.

Ratings-based credit risk modelling: An empirical analysis

Banks have recently developed new techniques for gauging the credit risk associated with portfolios of illiquid and defaultable instruments. These techniques could revolutionise banks' management of credit risk and could in the longer term serve as a more risk-sensitive basis for calculating regulatory capital on banks' loan books than in Basel 2, the new regulatory capital framework. In this paper we implement a popular credit risk model that exploits the information in credit ratings to determine a portfolio's value-at-risk. Using price data on large eurobond portfolios, we assess, on an out-of-sample basis, how well the model tracks the risks it is supposed to measure.

Identification of Apolipoprotein A-I as a “STOP” Signal for Myopia

Good visual acuity requires that the axial length of the ocular globe is matched to the refractive power of the cornea and lens to focus the images of distant objects onto the retina. During the growth of the juvenile eye, this is achieved through the emmetropization process that adjusts the ocular axial length to compensate for the refractive changes that occur in the anterior segment. A failure of the emmetropization process can result in either excessive or insufficient axial growth, leading to myopia or hyperopia, respectively. Emmetropization is mainly regulated by the retina, which generates two opposite signals: "GO/GROW" signals to increase axial growth and "STOP" signals to block it. The presence of GO/GROW and STOP signals was investigated by a proteomics analysis of the retinas from chicken with experimental myopia and hyperopia. Of 18 differentially expressed proteins that were identified, five displayed an expression profile corresponding to GO/GROW signals, and two corresponded to STOP signals. Western blotting confirmed that apolipoprotein A-I (apoA-I) has the characteristics of a STOP signal both in the retina as well as in the fibrous sclera. In accordance with this, intraocular application of the peroxisome proliferator-activated receptor alpha agonist GW7647 resulted in up-regulation of apoA-I levels and in a significant reduction of experimental myopia. In conclusion, using a comprehensive functional proteomics analysis of chicken ocular growth models we identified targets for ocular growth control. The correlation of elevated apoA-I levels with reduced ocular axial growth points toward a functional relationship with the observed morphological changes of the eye.