Incomplete Samples Research Articles

Determination of the number of sapwood annual rings in oak in the region of southern Moravia

The paper deals with the determination of the number of sapwood annual rings in oak (Quercus sp.) in relation to altitude, locality and stand age. Several different groups of samples were used from two localities of southern Moravia. The results of the study demonstrate the effects of site water regime and age on the growth of sapwood annual rings. On the other hand, the effect of altitude was not proved. The information can be of crucial importance for the dendrochronological dating of an incomplete sample for particular regions where sapwood is partly or totally missing.

Discrimination of Observations into One of Two Elliptic Populations based on Monotone Training Samples

In this paper we deal with the problem of classifying a p-dimensional random vector into one of two elliptically contoured populations with unknown and distinct mean vectors and a common, but unknown, scale matrix. The classification procedure is based on two-step monotone training samples, one from each population, with the same monotone pattern. Our aim is to extend the classification procedure, which proposed recently by Chung and Han (Ann Ins Stat Math 52:544–556, 2000). This procedure is a linear combination of two discriminant functions, one based on the complete samples and the other on the incomplete samples. The performance of the proposed classification rule is compared with the plug-in method, this means with the classification rule which arises if the unknown parameters are substituted, into the usual classification rule, by their estimators. In order to apply the plug-in method, the MLE of the location parameters and of the common scale matrix of g ≥ 2 elliptically contoured populations are analytically obtained on the basis of two-step monotone training samples.

Reaction mechanism of the nitridation of α-gallium oxide to gallium nitride under a flow of ammonia

The reaction mechanism of nitridation of α-gallium oxide (α-Ga2O3) to gallium nitride (GaN) under a flow of ammonia was deduced by observing the change in morphology of α-Ga2O3 powder coated with silicon substrate at an increasing reaction temperature. Upon their complete nitridation to GaN below 1000 °C, the morphology of α-Ga2O3 powder was retained. This strongly indicates that the conversion of α-Ga2O3 to GaN does not proceed through any gaseous intermediate but solid-state intermediates of gallium oxynitrides (GaOxNy). The occurrence of the intermediates was also evidenced by the change in weights of products with increasing the reaction temperature and by comparison of XRD patterns and 71Ga magic-angle spinning (MAS) NMR spectra of incomplete nitrided samples before and after oxidation.

Robust uncertainty principles: exact signal reconstruction from highly incomplete frequency information

This paper considers the model problem of reconstructing an object from incomplete frequency samples. Consider a discrete-time signal f/spl isin/C/sup N/ and a randomly chosen set of frequencies /spl Omega/. Is it possible to reconstruct f from the partial knowledge of its Fourier coefficients on the set /spl Omega/? A typical result of this paper is as follows. Suppose that f is a superposition of |T| spikes f(t)=/spl sigma//sub /spl tau//spl isin/T/f(/spl tau/)/spl delta/(t-/spl tau/) obeying |T|/spl les/C/sub M//spl middot/(log N)/sup -1/ /spl middot/ |/spl Omega/| for some constant C/sub M/>0. We do not know the locations of the spikes nor their amplitudes. Then with probability at least 1-O(N/sup -M/), f can be reconstructed exactly as the solution to the /spl lscr//sub 1/ minimization problem. In short, exact recovery may be obtained by solving a convex optimization problem. We give numerical values for C/sub M/ which depend on the desired probability of success. Our result may be interpreted as a novel kind of nonlinear sampling theorem. In effect, it says that any signal made out of |T| spikes may be recovered by convex programming from almost every set of frequencies of size O(|T|/spl middot/logN). Moreover, this is nearly optimal in the sense that any method succeeding with probability 1-O(N/sup -M/) would in general require a number of frequency samples at least proportional to |T|/spl middot/logN. The methodology extends to a variety of other situations and higher dimensions. For example, we show how one can reconstruct a piecewise constant (one- or two-dimensional) object from incomplete frequency samples - provided that the number of jumps (discontinuities) obeys the condition above - by minimizing other convex functionals such as the total variation of f.

NMR Diffusometry and Dynamic Light Scattering Studies of Amylopectin: Effect of Shearing and Heating on the Size Distribution and Diffusion Behaviour

AbstractThe influence of different factors on the diffusion behaviour of cationized potato amylopectin (CAP) in water was investigated by NMR Diffusometry and Dynamic Light Scattering (DLS). The sample preparation procedure was found to have a fundamental influence on the size and size distribution evolution of the different samples, whereas the addition of NaN3 or the replacement of CAP by non‐cationic potato amylopectin (PAP) did not influence the diffusion behaviour. NMR samples were prepared by re‐dissolving a freeze‐dried CAP sample in D2O at ambient temperature or by heating. Some samples were sheared, reducing their average aggregate size by a factor of 40. The unheated samples had a large average molecular size, indicating incomplete aggregate dissolution. The single‐fit average diffusion coefficient Dav,init showed a strong time evolution for the unheated samples, increasing with a factor of 1000 over 20 days for both sheared and unsheared samples. This effect was mainly attributed to incomplete sample dissolution, leading to a time evolution of the molecular size and size distribution. For heated samples, Dav,init oscillated around a much higher value indicating the occurrence of sub‐molecular sized fragments and possibly also a time‐coherent rearrangement of the sample. The size distribution was very large for both heated and unheated samples, with σlnD values of up to 2.5 and diffusion coefficients ranging from 10‐14 to 10‐11 m2/s in the same sample. DLS measurements corroborated the conclusions drawn from the results found by NMR diffusometry, but the complementary use of DLS and NMR diffusometry also highlighted the difference between the two methods for size determination. With NMR diffusometry, the proportion of small molecules may be slightly exaggerated, whereas the scattering methods mostly used in previous studies may underestimate their importance, resulting in a larger mean aggregate size than may actually be the case. This study thus draws the attention to the importance of the analysis method for the size and size distribution of amylopectin samples.

Model selection for incomplete and design-based samples

The Akaike information criterion, AIC, is one of the most frequently used methods to select one or a few good, optimal regression models from a set of candidate models. In case the sample is incomplete, the naive use of this criterion on the so-called complete cases can lead to the selection of poor or inappropriate models. A similar problem occurs when a sample based on a design with unequal selection probabilities, is treated as a simple random sample. In this paper, we consider a modification of AIC, based on reweighing the sample in analogy with the weighted Horvitz-Thompson estimates. It is shown that this weighted AIC-criterion provides better model choices for both incomplete and design-based samples. The use of the weighted AIC-criterion is illustrated on data from the Belgian Health Interview Survey, which motivated this research. Simulations show its performance in a variety of settings.

Hybrid color filter array demosaicking for effective artifact suppression

Color filter array (CFA) demosaicking is an essential process for restoring full-color images from incomplete color samples acquired by single-sensor digital cameras. We present two main contributions to CFA demosaicking. First, we analyze the causes of two main types of CFA demosaicking artifacts and examine the schemes that are effective in suppressing them, respectively. Second, by combining and extending the core merits of the schemes examined, we compose a new CFA demosaicking algorithm to suppress as many demosaicking artifacts as possible and obtain full-color images of high quality. Experiments using a large variety of test images have been conducted, and the results show that the proposed method outperforms the existing state-of-the-art methods both visually and in terms of peak signal-to-noise ratio.

Limited sample recovery in coupled methods of high-performance liquid chromatography of synthetic polymers

AbstractComplex polymer systems, which exhibit multiple distributions in their molecular parameters can be characterized by coupled liquid chromatographic methods. The latter combine entropic (exclusion) and enthalpic (interaction) retention mechanisms. However, recent experimental results suggest that some coupled liquid chromatographic methods may suffer from incomplete sample recovery. This refers, for example, to liquid chromatography under critical conditions of enthalpic interactions and to eluent gradient liquid chromatography. Sample recovery in both latter methods was investigated for selected model systems applying adsorption retention mechanism. Reduced sample recovery was confirmed for both methods. It was revealed that even very high final strength of mobile phase may be insufficient for complete elution of polymer samples in eluent gradient polymer liquid chromatography.

Increased instrument intelligence--can it reduce laboratory error?

Recent literature has focused on the reduction of laboratory errors and the potential impact on patient management. This study assessed the intelligent, automated preanalytical process-control abilities in newer generation analyzers as compared with older analyzers and the impact on error reduction. Three generations of immuno-chemistry analyzers were challenged with pooled human serum samples for a 3-week period. One of the three analyzers had an intelligent process of fluidics checks, including bubble detection. Bubbles can cause erroneous results due to incomplete sample aspiration. This variable was chosen because it is the most easily controlled sample defect that can be introduced. Traditionally, lab technicians have had to visually inspect each sample for the presence of bubbles. This is time consuming and introduces the possibility of human error. Instruments with bubble detection may be able to eliminate the human factor and reduce errors associated with the presence of bubbles. Specific samples were vortexed daily to introduce a visible quantity of bubbles, then immediately placed in the daily run. Errors were defined as a reported result greater than three standard deviations below the mean and associated with incomplete sample aspiration of the analyte of the individual analyzer Three standard deviations represented the target limits of proficiency testing. The results of the assays were examined for accuracy and precision. Efficiency, measured as process throughput, was also measured to associate a cost factor and potential impact of the error detection on the overall process. The analyzer performance stratified according to their level of internal process control The older analyzers without bubble detection reported 23 erred results. The newest analyzer with bubble detection reported one specimen incorrectly. The precision and accuracy of the nonvortexed specimens were excellent and acceptable for all three analyzers. No errors were found in the nonvortexed specimens. There were no significant differences in overall process time for any of the analyzers when tests were arranged in an optimal configuration. The analyzer with advanced fluidic intelligence demostrated the greatest ability to appropriately deal with an incomplete aspiration by not processing and reporting a result for the sample. This study suggests that preanalytical process-control capabilities could reduce errors. By association, it implies that similar intelligent process controls could favorably impact the error rate and, in the case of this instrument, do it without negatively impacting process throughput. Other improvements may be realized as a result of having an intelligent error-detection process including further reduction in misreported results, fewer repeats, less operator intervention, and less reagent waste.

Binary formation within globular clusters: X-ray clues

We have investigated the effect of the number of primordial binaries on the relationship between the total number of detected binaries within globular cluster and its collision rate. We have used simulated populations of binary stars in globular clusters : primordial binaries and binaries formed through gravitational interactions. We show that the initial number of primordial binaries influences the relationship between the number of detected sources and the collision rate, which we find to be a power law. We also show that observing an incomplete sample provides the same results as those obtained with a complete sample. We use observations made by XMM-Newton and Chandra to constrain the formation mechanism of sources with X-ray luminosities larger than 10^{31} erg/s, and show that some of the cataclysmic variables within globular clusters should be primordial objects. We point out a possibly hidden population of neutron stars within high mass globular clusters with a low collision rate.

Hf isotopic measurements on Barberton komatiites: effects of incomplete sample dissolution and importance for primary and secondary magmatic signatures

Komatiites from a single lava flow, Carl's Flow, in the Schapenburg Greenstone Remnant, near Barberton in South Africa, yielded very different Hf isotope compositions, depending on the manner in which the samples were treated analytically. Data from samples dissolved in Savillex beakers define a statistically significant (MSWD=0.77) isochron with an age of 3.4±0.2 Ga, which is identical within error to the probable eruption age, and an initial ε Hf of −1.3. Analyses of samples dissolved in bombs, on the other hand, plot on a linear array which, if interpreted as an isochron, gives an age of 2.9 Ga. Their initial 176Hf/ 177Hf, calculated using the probable eruption age of 3.45 Ga, are positive and variable, ranging from ε Hf of +1.3 to +6.3. Hf contents are much lower and Lu/Hf ratios systematically higher in the Savillex beaker-dissolved batch of komatiites, indicating that a Hf-rich phase (zircon or baddeleyite?) remained undissolved in these samples. The negative ε Hf of the Savillex beaker-dissolved samples is attributed to interaction with crust-derived fluids that affected the komatiite soon after its eruption. The anomalously low isochron age of the bomb-dissolved samples is due to the presence of a single olivine cumulate sample that appears to have lost Hf during post-emplacement alteration. Without this sample, initial ε Hf values cover a much narrower range between +4.3 and +6.3, which is believed to be that of the mantle source of the komatiites. The combination of highly positive ε Hf and lower-than-chondritic Lu/Hf indicates that the mantle source of the Carl's Flow was garnet-enriched for a substantial period of time prior to komatiite formation and that garnet was retained in the source during the melting event that eventually produced the komatiite magma.

Distribution of mutual information from complete and incomplete data

Mutual information is widely used, in a descriptive way, to measure the stochastic dependence of categorical random variables. In order to address questions such as the reliability of the descriptive value, one must consider sample-to-population inferential approaches. This paper deals with the posterior distribution of mutual information, as obtained in a Bayesian framework by a second-order Dirichlet prior distribution. The exact analytical expression for the mean, and analytical approximations for the variance, skewness and kurtosis are derived. These approximations have a guaranteed accuracy level of the order O( n −3), where n is the sample size. Leading order approximations for the mean and the variance are derived in the case of incomplete samples. The derived analytical expressions allow the distribution of mutual information to be approximated reliably and quickly. In fact, the derived expressions can be computed with the same order of complexity needed for descriptive mutual information. This makes the distribution of mutual information become a concrete alternative to descriptive mutual information in many applications which would benefit from moving to the inductive side. Some of these prospective applications are discussed, and one of them, namely feature selection, is shown to perform significantly better when inductive mutual information is used.

L'archéologie à la conquête de l'espace : les « cartes à pois » et le poids des cartes, de la carte archéologique au système d'information géographique

The scatter of points on an archaeological distribution map is not an end in itself, although it does provide solid information. Are we ready to concede that scientific proof can be obtained from a graphic document ? Are we able to reconstitute the organisation of a given territory from an incomplete sample of the sites it once contained ? Examples are presented from an experiment conducted on data from Iron Age and Roman Berry. Together with statistics and mathematical calculations, spatial analysis and the graphical manipulation of data can provide all the elements needed for a scientific hypothesis to be demonstrated. To identify the outcomes of spatial analyses and to sustain them as proof of particular past circumstances requires both the serious study of cartography and collaboration with geographers. Archaeological distribution maps have always been developed in parallel with the standard mapping of any given region. The juxtaposition of archaeological data with other layers of information (e.g. pedology, natural environment, present-day settlement) in a GIS system, allows the archaeological distribution patterns to be critically examined, and enables the historic landscape to be either simulated or modelled. Superposing and juxtaposing the different georeferenced data sets presently available allows the elimination of those biases which affect the distributions that we presently know.

Inefficiency, Subsample Selection Bias, and Nonrobustness

This article responds to Peterson and Howell’s (PH’s) defense of their voucher research. We show that PH’s rationales for excluding some 815 students—more than 40% of their sample—because they lacked baseline data in a randomized experiment are unconvincing. For example, PH’s assertion that students with missing baseline scores had a greater risk of mismatch is based on a misunderstanding of the way the experiment was conducted; the organization that conducted the experiment believes the procedures actually used precluded such a problem. Including students with missing baseline data renders the effect of vouchers insignificant for Black students, even using PH’s nonstandard racial classification scheme. PH also give the misleading impression that our reanalysis shows their results to be robust. In fact, only 7 out of the 27 of our estimates that did not simply reuse PH’s original, incomplete sample of Black students are positive and statistically significant.

Estimating Diversity in Unsampled Habitats of a Biogeographical Province

Abstract: Estimating the number of species in a biogeographical province can be problematic. A number of methods have been developed to overcome sample‐size limits within a single habitat. We evaluated six of these methods to see whether they could also compensate for incomplete habitat samples. We applied them to the butterfly species of the 110 ecoregions of Canada and the United States. Two of the methods use the frequency of species that occur in a few of the sampled ecoregions. These two methods did not work. The other four methods estimate the asymptote of the species‐accumulation curve ( the graph of “number of species in a set of samples” versus “number of species occurrences in those samples” ). The asymptote of this curve is the actual number of species in the system. Three of these extrapolation estimators produced good estimates of total diversity even when limited to 10% of the ecoregions. Good estimates depend on sampling ecoregions that are hyperdispersed in space. Clustered sampling designs ruin the usefulness of the three successful methods. To ascertain their generality, our results must be duplicated at other scales and for other taxa and in other provinces.

Exact credal treatment of missing data

This paper proposes an exact, no-assumptions approach to dealing with incomplete sets of multivariate categorical data. An incomplete data set is regarded as a finite collection of complete data sets, and a joint distribution is obtained from each of them, at a descriptive level. The tools to simultaneously treat all the possible joint distributions compatible with an incomplete set of data are given. In particular, a linear description of the set of distributions is formulated, and it is shown that the computation of bounds on the expectation of real-valued functions under such distributions is both possible and efficient, by means of linear programming. Specific algorithms are also developed whose complexity grows linearly in the number of observations. An analysis is then carried out to estimate population probabilities from incomplete multinomial samples. The descriptive tool extends in a straightforward way to the inferential problem by exploiting Walley's imprecise Dirichlet model.

A 'periodic table' for protein structures.

Current structural genomics programs aim systematically to determine the structures of all proteins coded in both human and other genomes, providing a complete picture of the number and variety of protein structures that exist. In the past, estimates have been made on the basis of the incomplete sample of structures currently known. These estimates have varied greatly (between 1,000 and 10,000; see for example refs 1 and 2), partly because of limited sample size but also owing to the difficulties of distinguishing one structure from another. This distinction is usually topological, based on the fold of the protein; however, in strict topological terms (neglecting to consider intra-chain cross-links), protein chains are open strings and hence are all identical. To avoid this trivial result, topologies are determined by considering secondary links in the form of intra-chain hydrogen bonds (secondary structure) and tertiary links formed by the packing of secondary structures. However, small additions to or loss of structure can make large changes to these perceived topologies and such subjective solutions are neither robust nor amenable to automation. Here I formalize both secondary and tertiary links to allow the rigorous and automatic definition of protein topology.

The Distances of Planetary Nebulae: A Scale Based upon Nearby Sources

The statistical distances of planetary nebulae (PNe) are known to be notoriously uncertain, differing from each by factors approaching ~2, and also from more reliable distances based upon trigonometric and spectroscopic parallaxes, expansion distances, and so forth. We point out that many of these problems arise from the use of inappropriate relations between surface brightness and nebular radius; of incomplete samples of standard sources; and the use of indirect (and/or inaccurate) methods for the evaluation of distances. Many of these problems can be side-stepped, however, where the standard sources are confined to nearby nebulae; planetaries whose distances are less than ~0.7 kpc or so. We have, using such sources, undertaken a detailed revision of the surface brightness-radius calibration, and thereby defined a new statistical scale which is consistent with the most direct, recent, and reliable distance measures. This scale is used to determine distances to 448 Population I Galactic planetary nebulae, and the results are compared to alternative statistical scales. It is shown that much of the disparity between the present distance scale and that of Zhang is likely to arise through differences in calibration source distances. It does not (as supposed by previous authors) appear to be a product of selection effects within the nebular samples. A disparity with the van de Steene & Zijlstra distances may arise from differences between Galactic bulge and disk nebulae, while the scales of Daub and Cahn et al. appear to be based upon inappropriate trends between surface brightness and radius. Finally, we discuss the implications of these results for the formation rates of planetary nebulae and determine a galaxy-wide total of PNe NT = 3.0 × 104. The luminosity specific formation rate χL ~ 3 × 10-11 L appears ~2.5 times larger than determined in previous analyses, while the rate per unit area of Galactic disk [χA(PNe) ~ 1.6 × 10-3 yr-1 kpc-2] is comparable to the value deduced for white dwarfs.

Generalizing Molecular Results Arising from Incomplete Biological Samples:: Expected Bias and Unexpected Findings

PURPOSE: In molecular epidemiology, obtaining biological samples for all subjects targeted for study is frequently hampered by ethical, clinical, and logistic factors. The extent to which the incompleteness of biological samples could cause bias is rarely analyzed in depth. Here we report some expected bias and some unexpected findings during a study on mutations in the K- ras gene in exocrine pancreatic cancer (EPC). METHODS: In this case–case study, all patients registered with EPC between 1980 and 1990 at two general hospitals were retrospectively identified from the hospital tumor registries. Their clinical records were abstracted and paraffin-embedded samples retrieved from pathology records. DNA was amplified, and mutations in codon 12 of the K- ras gene were detected using the artificial RFLP technique. RESULTS: Results on the mutations (RM) were obtained for 51 of the 149 cases of EPC (34.2%). There were no significant differences on the availability of RM by age, gender, and tumor stage at diagnosis, but RM were over five times more likely to be available from one of the hospitals. Subjects with RM were more likely to have received a treatment with curative intent (OR = 11.56, 95% CL: 2.88–46.36). The existence of RM was positively associated with the availability of information on alcohol use and family history of cancer. Subjects with RM tended to belong to higher occupational groups and to smoke less than subjects without RM. Unexpectedly—given that in EPC K- ras mutations have consistently been found unrelated to age, gender, tumor stage, and other clinical factors—, cases with a K- ras mutation were more likely than wild-type cases to have information on tobacco and alcohol use (OR = 3.29, p = .21), medical history (OR = 4.46, p = .41), and family history of cancer (OR = 4.80, p = .01). The relationship between completeness of clinical records and K- ras mutations among cases with RM could not be accounted by age, gender, and occupational group. CONCLUSIONS: Simple tests of age and gender distributions among subjects with and without available clinical information and molecular results may not rule out selection and information bias. Studies using biologic specimens are even more in need than classic studies to explain clearly the process followed to include and exclude subjects. Additional caution is needed when generalizing molecular results arising from incomplete biological specimens.

Inhomogeneous flow in a micellar solution of a diblock copolymer: creep rheometry experiments

The flow behaviour of a solution of a poly(oxyethylene)-poly(oxybutylene) diblock copolymer in water forming a body-centred cubic micellar phase is studied via creep rheometry. This indicates a plateau in a plot of stress versus shear rate, suggesting an inhomogeneous flow mechanism, possibly shear banding. Creep recovery measurements are performed as a function of stress, which reveals partial recovery at low stress but no recovery and purely viscous flow at large stress. The creep response of as-mounted (unoriented) and pre-sheared (oriented) samples is compared. The flow behaviour is identical for stresses above the plateau value, but differs at lower stresses due to incomplete sample alignment. At low stresses, shear thinning is observed for samples pre-oriented by shear at a stress above the plateau value. However, shear thickening is observed in creep curves at small stresses for samples pre-oriented at the same stress, suggesting micellar association occurs under these conditions. Small-angle X-ray scattering reveals that flow in the plateau region is in {110} planes oriented normal to the neutral direction with a close-packed 111 direction along the shear direction. However, at higher shear rates flow occurs in {110} and {211} planes oriented in the shear plane. The proportion of flow in the latter planes is observed to increase with shear rate, even though outside the plateau regime, suggesting that the high shear rate branch of the flow curve does not correspond to a unique orientation state of the bcc structure.