Spurious Values Research Articles

Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust

Combined whole-rock and zircon MC-ICP-MS Lu–Hf isotope data are reported for a large collection of Archean granitoids belonging to typical tonalite–trondhjemite–granodiorite (TTG) suites. Our data demonstrate that the time-integrated Lu/Hf of the mantle source of TTGs has not significantly changed over the last 4Gy. Continents therefore most likely grew from nearly primordial unfractionated material extracted from the deep mantle via rising plumes that left a depleted melt residue in the upper mantle. The deep mantle could retain its primitive relative element abundances over time because sinking plates are largely stripped barren of their oceanic and continental crust components at subduction zones; this process results in only small proportions (<15–25%) of present-day continental mass getting recycled to great depths. Zircon populations extracted from the analyzed TTGs have Hf isotopic compositions broadly consistent with those of their host whole-rocks, whereas the U–Pb system in the same grains is often disturbed, causing a discrepancy that creates spurious initial εHf values. This problem is endemic to the Archean detrital zircon record and consistent with experimental results bearing on the relative retentivity of Hf vs. U and Pb in zircon. We argue that this behavior biases the Archean zircon record toward negative εHf values, which are at odds with the present TTG data set. If Hadean Jack Hills zircons are considered in light of these results, the mantle source of continents has remained unchanged for the last 4.3Gy.

Influence of the materials magnetic state on the accurate determination of the magnetocaloric effect

In this paper, we report a detailed study of the magnetocaloric effect (MCE) in different first order magnetic transition (FOMT) materials with different situation of the magnetic state (magnetic order). For this purpose, R-Co2, MnAs based compounds were considered in this study. The MCE is discussed in terms of Maxwell relation (MR) and Clausius-Clapeyron (C-C) equation. The deviation observed between both methods is discussed and analyzed. On the other hand, practically all the reported data of the MCE in the literature are associated to the applied external magnetic field and have not been corrected taking into account the demagnetization effect related to the materials shape. The obtained results demonstrate that this phenomenon can alter drastically the MCE values by cancelling out a large part of the external field, resulting in spurious values of the measured MCE. The effect of the demagnetization field on the magnetocaloric performances is also the subject of this paper.

Initiation and progress of breakdown in the range to the left of the paschen minimum

Mechanisms of gas breakdown initiation and development in the range to the left of the Paschen minimum are investigated in this paper. Experiments were conducted for gas pressures from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> bar and inter-electrode gaps from 0.1 to 1 mm. The obtained results were subjected to the Chauvenet's criterion for discarding spurious values, the U-test for checking if they belonged to a common statistical distribution, and the chisquared test for testing their adherence to one of the considered theoretical distributions (normal, Weibull or double-exponential). The statistical analysis shows that the region left of the Paschen minimum can be divided into three subregions. It is established that the so called anomalous Paschen effect refers to breakdown occuring by way of the edge mechanisms in the first subregion, just next to the Paschen minimum. In the second subregion, breakdown emerges through the vacuum avalanche mechanism, and in the third subregion it occurs through the vacuum cathode emission mechanism.

Vitamin B12 absorption judged by measurement of holotranscobalamin, active vitamin B12: evaluation of a commercially available EIA kit

Active vitamin B12 absorption is followed by an increase in holotranscobalamin (holoTC) upon loading with a high physiological dose of the vitamin (the CobaSorb test). This study evaluates the use of a newly launched EIA kit for measurement of holoTC (active B12) in relation to the CobaSorb test. Intra-assay imprecision and linearity of the EIA kit was examined, employing serum pools of increasing holoTC concentrations. For the CobaSorb test, holoTC was measured before and after loading with 3-times 9 μg of vitamin B12 employing both the in-house ELISA and the EIA kit (n=25). The EIA kit showed an intra-assay CV between 2.2% and 5.8% for holoTC values ranging from 21 to 80 pmol/L. Employing diluted serum samples resulted in spurious high values of holoTC. The EIA kit performed well in relation to the CobaSorb test and classified the patients studied as capable of absorbing vitamin B12 (n=10) or not (n=15), as did the in-house ELISA. The Active B12 (holoTC) EIA kit proved suitable for use with the CobaSorb test, but not for analysis of diluted serum samples.

A comparison of algorithms to automatically extract vowel formants and nasal poles from tagged vowels in PRAAT.

The goal of the present research was to develop an easy-to-use PRAAT script yielding robust measurements of acoustic correlates of vowel quality and vowel nasality. Several algorithms were scripted in PRAAT and evaluated on two corpora. The first was the Hillenbrand corpus, containing /hVd/ words in isolation, spoken by 50 men, 50 women, 29 boys, and 21 girls, where vowels have been hand-tagged by experts. The best performing algorithm yielded extremely high correlations with the expert-measured F1 and F2 frequencies (r&amp;gt;0.95). The second corpus consisted of spontaneous speech by American English and Canadian French women, addressing either their infant or an adult, and where several types of vowels had been hand-tagged (including point vowels /i,a,u/, frequently used to assess vowel space size; and contrasts of vowel tenseness, likely involving F1 and F2 frequencies; and vowel nasality, correlated with F1 bandwidth, as well as its amplitude in relation to the nasal poles P0 and P1). Although, even the best algorithm yielded spurious F2 values for infant-directed /u/'s, measures were robust indicators of vowel quality and nasality in non-back vowels across the different speakers, languages, and registers. Thus, this script may be useful, particularly for non-specialists, since it only requires vowel-tagging.

Sea State Bias in Radar Altimetry Revisited

Sea state bias (SSB) is calculated anew for each radar altimeter. The input data are sea surface height (h) differences, separated in time by at most one repeat cycle, or the difference between measured h and a time-mean sea surface, an approach called here “differences from the mean” (DFM). In order to release data to users soon, early estimates of SSB are computed from short time series. This work has three objectives: 1) show that the DFM approach introduces spurious values in the estimated SSB, 2) quantify the SSB error caused by short time series, and 3) estimate SSB for OSTM.

Wavelet Functions for Rejecting Spurious Values

Wavelet Functions for Rejecting Spurious Values

Comparison between QuikSCAT and buoy wind data in the Ligurian Sea

Wind above sea surface plays an important role in the Mediterranean Sea for a large variety of scientific applications (i.e., climatological, meteorological and oceanographic studies). In this work we compare wind vectors obtained from the SeaWinds scatterometer on board the National Aeronautics and Space Administration (NASA) QuikSCAT satellite with wind data measured in situ by an anemometer mounted on the offshore ODAS Italia 1 buoy. This platform is moored in the Central Ligurian Sea, a basin where the wind field is highly variable both in time and space due to the orographic constraints and the thermal contrast between land and sea that give rise to specific local effects. The work covers the period from July 2006 to June 2007. The comparison confirms that the QuikSCAT wind vectors satisfy the accuracy requirements for high wind speeds, but, QuikSCAT skill is less for low wind speed, especially for the direction assessment. These results are in agreement with those of previous investigations but the analysis evidences some issues mistreated until now. The most relevant is the scarceness of data. The satellite passes over the Ligurian Sea only twice a day and data taken under rainy condition and with wind speed lower than 3 ms − 1 are not valid. Thus, the temporal sampling may be not adequate to monitor wind fields and their evolution over this basin where calm condition often occurs and strong perturbations are generally associated to rain. Furthermore, the comparison shows that it may be difficult to recognize spurious values obtained from QuikSCAT when the true wind speed is lower than 3 ms − 1 without a reference at sea.

QUASI-NONUNIQUENESS IN THE SCATTERED FIELD OF A DIELECTRIC CIRCULAR CYLINDER

It is well known that the scattered field of a z polarized plane wave incident on a dielectric circular cylinder can be expanded as an infinite series involving Hankel functions. From numerical calculations of this expansion, Lam and Yedlin [5] observed that the mean square measure, over all space, of the difference of the scattered fields from two or more distinct values of the dielectric constant of the cylinder can take very small values, thereby almost contradicting the uniqueness property. We investigate this phenomenon rigorously using uniform asymptotic expansions of Bessel functions, and from our analysis we determine the spurious values of the dielectric constant which lead to this quasi-nonuniqueness.

A Forward Modeling Approach for Interpreting Impeller Flow Logs

A rigorous and practical approach for interpretation of impeller flow log data to determine vertical variations in hydraulic conductivity is presented and applied to two well logs from a Chalk aquifer in England. Impeller flow logging involves measuring vertical flow speed in a pumped well and using changes in flow with depth to infer the locations and magnitudes of inflows into the well. However, the measured flow logs are typically noisy, which leads to spurious hydraulic conductivity values where simplistic interpretation approaches are applied. In this study, a new method for interpretation is presented, which first defines a series of physical models for hydraulic conductivity variation with depth and then fits the models to the data, using a regression technique. Some of the models will be rejected as they are physically unrealistic. The best model is then selected from the remaining models using a maximum likelihood approach. This balances model complexity against fit, for example, using Akaike's Information Criterion.

DFasArt: Dynamic neural processing in FasArt model

The temporal character of the input is, generally, not taken into account in the neural models. This paper presents an extension of the FasArt model focused on the treatment of temporal signals. FasArt model is proposed as an integration of the characteristic elements of the Fuzzy System Theory in an ART architecture. A duality between the activation concept and membership function is established. FasArt maintains the structure of the Fuzzy ARTMAP architecture, implying a static character since the dynamic response of the input is not considered. The proposed novel model, dynamic FasArt (dFasArt), uses dynamic equations for the processing stages of FasArt: activation, matching and learning. The new formulation of dFasArt includes time as another characteristic of the input. This allows the activation of the units to have a history-dependent character instead of being only a function of the last input value. Therefore, dFasArt model is robust to spurious values and noisy inputs. As experimental work, some cases have been used to check the robustness of dFasArt. A possible application has been proposed for the detection of variations in the system dynamics.

The impact of global signal regression on resting state correlations: Are anti-correlated networks introduced?

Low-frequency fluctuations in fMRI signal have been used to map several consistent resting state networks in the brain. Using the posterior cingulate cortex as a seed region, functional connectivity analyses have found not only positive correlations in the default mode network but negative correlations in another resting state network related to attentional processes. The interpretation is that the human brain is intrinsically organized into dynamic, anti-correlated functional networks. Global variations of the BOLD signal are often considered nuisance effects and are commonly removed using a general linear model (GLM) technique. This global signal regression method has been shown to introduce negative activation measures in standard fMRI analyses. The topic of this paper is whether such a correction technique could be the cause of anti-correlated resting state networks in functional connectivity analyses. Here we show that, after global signal regression, correlation values to a seed voxel must sum to a negative value. Simulations also show that small phase differences between regions can lead to spurious negative correlation values. A combination breath holding and visual task demonstrates that the relative phase of global and local signals can affect connectivity measures and that, experimentally, global signal regression leads to bell-shaped correlation value distributions, centred on zero. Finally, analyses of negatively correlated networks in resting state data show that global signal regression is most likely the cause of anti-correlations. These results call into question the interpretation of negatively correlated regions in the brain when using global signal regression as an initial processing step.

Statistical pre-processing and analyses of hydro-meteorological time series in a geologic clay site (methodology and first results for Mont Terri’s PP experiment)

This article presents a set of statistical methods for pre-processing (or pre-conditioning) and analyzing multivariate hydro-geologic time series, such as pore pressures and atmospheric pressure (temporal structures). The pre-processing methods are necessary to enhance or complete the signals due to defects in the observed time series (data gaps, spurious values, variable time steps). The statistical analyses aim, in fine, at characterizing the hydraulic behaviour of a clayey formation in the context of deep geologic disposal of radioactive waste. Pore water and atmospheric pressure time series from the Mont Terri rock laboratory (BPP-1 borehole) are taken as an example.

Quantifying Spurious Free T4 Results Attributable to Thyroxine-Binding Proteins in Serum Dialysates and Ultrafiltrates

Direct equilibrium dialysis and direct ultrafiltration free thyroxine (T(4)) assays rely on semipermeable membranes to exclude T(4)-binding serum proteins from dialysates and ultrafiltrates. The presence of these proteins in dialysates or ultrafiltrates will yield spuriously high free T(4) values when free T(4) is quantified by RIA. We used a nonanalog free T(4) RIA that detects and quantifies dialyzable and ultrafilterable serum free T(4) to detect T(4)-binding serum proteins. Two equilibrium dialysis devices and 3 ultrafiltration devices were used to illustrate this application. Displacements of [(125)I]T(4) from anti-T(4) by various concentrations of T(4)-depleted thyroxine-binding globulin, albumin, and serum total protein were compared to displacements by various concentrations of free T(4). Both dialysis devices excluded detectable T(4)-binding serum proteins from dialysates. Two of 3 ultrafiltration devices excluded detectable T(4)-binding serum proteins from ultrafiltrates. One did not, and its ultrafiltrate yielded spurious free T(4) values that correlated directly with serum protein concentrations. The presence or absence of T(4)-binding proteins in dialysates and ultrafiltrates and the spurious free T(4) values that these proteins cause can be documented using a nonanalog free T(4) RIA.

Evaluating digital elevation models for glaciologic applications: An example from Nevado Coropuna, Peruvian Andes

This paper evaluates the suitability of readily available elevation data derived from recent sensors – the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) – for glaciological applications. The study area is Nevado Coropuna (6426 m), situated in Cordillera Ampato of Southern Peru. The glaciated area was 82.6 km 2 in 1962, based on aerial photography. We estimate the glacier area to be ca. 60.8 km 2 in 2000, based on analysis of the ASTER L1B scene. We used two 1:50,000 topographic maps constructed from 1955 aerial photography to create a digital elevation model with 30 m resolution, which we used as a reference dataset. Of the various interpolation techniques examined, the TOPOGRID algorithm was found to be superior to other techniques, and yielded a DEM with a vertical accuracy of ± 14.7 m. The 1955 DEM was compared to the SRTM DEM (2000) and ASTER DEM (2001) on a cell-by-cell basis. Steps included: validating the DEM's against field GPS survey points on rock areas; visualization techniques such as shaded relief and contour maps; quantifying errors (bias) in each DEM; correlating vertical differences between various DEM's with topographic characteristics (elevation, slope and aspect) and subtracting DEM elevations on a cell-by-cell basis. The RMS error of the SRTM DEM with respect to GPS points on non-glaciated areas was 23 m. The ASTER DEM had a RMS error of 61 m with respect to GPS points and displayed 200–300 m horizontal offsets and elevation ‘spikes’ on the glaciated area when compared to the DEM from topographic data. Cell-by-cell comparison of SRTM and ASTER-derived elevations with topographic data showed ablation at the toes of the glaciers (− 25 m to − 75 m surface lowering) and an apparent thickening at the summits. The mean altitude difference on glaciated area (SRTM minus topographic DEM) was − 5 m, pointing towards a lowering of the glacier surface during the period 1955–2000. Spurious values on the glacier surface in the ASTER DEM affected the analysis and thus prevented us from quantifying the glacier changes based on the ASTER data.

Atmospheric CO 2 measurements and error analysis on seasonal air–sea CO 2 fluxes in the Bay of Biscay

Atmospheric molar fraction of CO 2 ( xCO 2 atm) measurements obtained on board of ships of opportunity are used to parameterize the seasonal cycle of atmospheric xCO 2 ( xCO 2 atm) in three regions of the eastern North Atlantic (Galician and French offshore and Bay of Biscay). Three selection criteria are established to eliminate spurious values and identify xCO 2 atm data representative of atmospheric background values. The filtered data set is fitted to seasonal curve, consisting of an annual trend plus a seasonal cycle. Although the fitted curves are consistent with the seasonal evolution of xCO 2 atm data series from land meteorological stations, only ship-board measurements can report the presence of winter xCO 2 atm minimum on Bay of Biscay. Weekly air–sea CO 2 flux differences (mmol C·m − 2 day − 1 ) produced by the several options of xCO 2 atm usually used (ship-board measurements, data from land meteorological stations and annually averaged values) were calculated in Bay of Biscay throughout 2003. Flux error using fitted seasonal curve relative to on board measurements was minimal, whereas land stations and annual means yielded random (− 0.2 ± 0.3 mmol C·m − 2 ·day − 1 ) and systematic (− 0.1 ± 0.4 mmol C·m − 2 day − 1 ), respectively. The effect of different available sources of sea level pressure, wind speed and transfer velocity were also evaluated. Wind speed and transfer velocity parameters are found as the most critical choice in the estimate of CO 2 fluxes reaching a flux uncertainty of 7 mmol C·m − 2 ·day − 1 during springtime. The atmospheric pressure shows a notable relative effect during summertime although its influence is quantitatively slight on annual scale (0.3 ± 0.2 mmol C·m − 2 ·day − 1 ). All results confirms the role of the Bay of Biscay as CO 2 sink for the 2003 with an annual mean CO 2 flux around − 5 ± 5 mmol C m − 2 day − 1 .

Why perfusion in neonates with congenital heart defects is negative — Technical issues related to pulsed arterial spin labeling

Pulsed arterial spin labeling (PASL) perfusion MRI has unique advantages for measuring cerebral blood flow (CBF) in the pediatric population. In neonates with congenital heart defects (CHDs), however, a considerable number of negative CBF values were observed in PASL perfusion images. A set of specific physiological and biophysical conditions were proposed as plausible explanations for this phenomenon, including small body size, low blood flow, prolonged tracer life time (blood T1) and the "shunt" between pulmonary and systemic circulations in CHD. An optimized PASL scheme with a restricted label volume was proposed, and experimental data demonstrated reduced spurious negative values and lower intersubject variability of perfusion measurements in neonates with CHD as compared to standard PASL sequences.

The approximation of the Maxwell eigenvalue problem using a least-squares method

In this paper we consider an approximation to the Maxwell's eigenvalue problem based on a very weak formulation of two div-curl systems with complementary boundary conditions. We formulate each of these div-curl systems as a general variational problem with different test and trial spaces, i.e., the solution space is L 2 (Ω) ≡ (L 2 (Ω)) 3 and components in the test spaces are in subspaces of H 1 (Ω), the Sobolev space of order one on the computational domain Q. A finite-element least-squares approximation to these variational problems is used as a basis for the approximation. Using the structure of the continuous eigenvalue problem, a discrete approximation to the eigenvalues is set up involving only the approximation to either of the div-curl systems. We give some theorems that guarantee the convergence of the eigenvalues to those of the continuous problem without the occurrence of spurious values. Finally, some results of numerical experiments are given.

Secure program execution via dynamic information flow tracking

We present a simple architectural mechanism called dynamic information flow tracking that can significantly improve the security of computing systems with negligible performance overhead. Dynamic information flow tracking protects programs against malicious software attacks by identifying spurious information flows from untrusted I/O and restricting the usage of the spurious information.Every security attack to take control of a program needs to transfer the program's control to malevolent code. In our approach, the operating system identifies a set of input channels as spurious, and the processor tracks all information flows from those inputs. A broad range of attacks are effectively defeated by checking the use of the spurious values as instructions and pointers.Our protection is transparent to users or application programmers; the executables can be used without any modification. Also, our scheme only incurs, on average, a memory overhead of 1.4% and a performance overhead of 1.1%.

Secure program execution via dynamic information flow tracking

We present a simple architectural mechanism called dynamic information flow tracking that can significantly improve the security of computing systems with negligible performance overhead. Dynamic information flow tracking protects programs against malicious software attacks by identifying spurious information flows from untrusted I/O and restricting the usage of the spurious information.Every security attack to take control of a program needs to transfer the program's control to malevolent code. In our approach, the operating system identifies a set of input channels as spurious, and the processor tracks all information flows from those inputs. A broad range of attacks are effectively defeated by checking the use of the spurious values as instructions and pointers.Our protection is transparent to users or application programmers; the executables can be used without any modification. Also, our scheme only incurs, on average, a memory overhead of 1.4% and a performance overhead of 1.1%.