Multivariate control charts: Control charts for calibration curves

The proposed multivariate control charts for p-dimensional vectors are an extension of the conventional control charts for one variable. The controlling quantity is the Mahalanobis distance of vector x from the central value vector x..: D=(x-x..)^T-1.(x-x..), where is the covariance matrix estimate. The quantity D has Hotelling's T² distribution. A PC program was set up for the automatic graphical construction of such charts. The program draws the sequential chart of the quantity D as well as the position of the vectors x in the p dimensional control ellipsoid in the axes of the principal components. In this way a control chart was developed for the calibration curve in the photometric determination of Fe³⁺ with sulfosalicylic acid. Vector x was formed by absorbance values for the calibration curve points (p=5). The chart can assist in detection of even small disturbances of the calibration curve.     

Spectra and eigenspaces of arbitrary lifts of graphs

Journal of Algebraic Combinatorics - We describe, in a very explicit way, a method for determining the spectra and bases of all the corresponding eigenspaces of arbitrary lifts of graphs (regular...     

Effect of different dimethylphenols on the interactions with Ni2+-exchanged montmorillonite

The influence of different steric and electronic properties of 2,4-; 2,5-; and 3,5- dimethylphenols (2,4-; 2,5-; and 3,5- DMP, respectively) on Ni²⁺-montmorillonite (Ni²⁺-MMT) (I) were studied. The results of X-ray diffraction show that the observed changes of the basal spacing were due to the intercalation of phenol derivatives into the interlayer space of montmorillonite. The existence of one peak at ~1,633 cm^?1 in the IR spectra of sample Ni²⁺-MMT + 2,4-DMP (II) and Ni²⁺-MMT + 2,5-DMP (III) and shift of this peaks to higher frequency indicate that 2,4-DMP and 2,5-DMP exist in the interlayer space of Ni²⁺-MMT in the protonated form. The two bands at ~1,622 and 1,597 cm^?1 in the sample Ni²⁺-MMT + 3,5-DMP (IV) indicate that 3,5-DMP may be also directly coordinated to Ni²⁺ cations. The different interactions of phenol derivatives in the silicate interlayers will be connected with different position of methyl groups on the phenol ring.     

Comparison of aqua regia and HNO3-H2O2 procedures for extraction of Tl and some other elements from soils

The relationship between aqua regia (ISO 11466) and HNO(3)-H(2)O(2) (ISO/CD 20279) extraction procedures for atomic emission spectrometric (ICP/OES and ICP/MS) determinations of Tl, P, Mn, Fe, Mg, Ca, Sr, Al, K, As, Bi, Zn, Pb, Co, Cd, Ni, V, Be, Cu and Cr was investigated. Soil samples (155) representing areas with different contents of the elements were selected for the comparison. Tl was the element of the highest interest and therefore the sampling sites were chosen to achieve as wide range of Tl contents as possible. Both extraction procedures are comparable in results (differences lower than 10% for the most of the elements) for all the tested elements. Statistically non-significant differences between the two extraction procedures were found for P, Zn, V and K (the slope was very close to 1 and the intercept included zero). Statistically significant values of intercepts were found for Fe, Al, Ca, Cd, Sr and Ni. Significantly higher results for aqua regia were found for Cu (12%), Pb (17%), Mn (11%) and lower results by aqua regia were found for Mg (4%), As (13%), Co (20%), Be (11%), Cr (4%) and Bi (6%). The results for Tl, the element of the highest interest, after HNO(3)-H(2)O(2) extraction procedure, were approximately 6% higher than the results after aqua regia extraction. Content of Tl in the soil samples was from 0.08 to 2.8 mg kg(-1). A highly significant linear relationship was found (R(2)=0.97).     

Nickel(II) hexamethyleneiminedithiocarbamate complexes with triphenylphosphine or tributylphosphine

A series of square-planar nickel(II) hexamethylenedithiocarbamate complexes with heterogeneous coordination spheres of composition [NiX(hmidtc)Y] · nCHCl₃ [X = Cl, Br, I or NCS; hmi = C₆H₁₂, dtc = S₂CN^–; Y = PPh₃ or PBu₃, n = 0,1] have been synthesized and characterized by elemental analyses, i.r. and u.v.–v.i.s. spectroscopy, magnetochemical and conductivity measurements, and by thermal analysis. X-ray structures of [NiCl(hmidtc)(PPh₃)] · CHCl₃ and [NiBr(hmidtc)(PPh₃)] · CHCl₃ have been determined.     

Comparison of mild extraction procedures for determination of plant-available arsenic compounds in soil

In this work three mild extraction agents for determination of plant-available fractions of elements in soil were evaluated for arsenic speciation in soil samples. Pepper (Capsicum annum, L.) var. California Wonder was cultivated in pots, and aqueous solutions of arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid, at a concentration of 15 mg As kg^–1 soil, were added at the beginning of the experiment. Control pots (untreated) were also included. Deionized water, 0.01 mol L^–1 CaCl₂, and 0.05 mol L^–1 (NH₄)₂SO₄ were used to extract the plant-available fraction of the arsenic compounds in soil samples collected during the vegetation period of the plants. Whereas in control samples the extractable arsenic fraction did not exceed 1% of total arsenic content, soil amendment by arsenic compounds resulted in extraction of larger amounts, which varied between 1.4 and 8.1% of total arsenic content, depending on soil treatment and on the extracting agent applied. Among arsenic compounds determined by HPLC–ICPMS arsenate was predominant, followed by small amounts of arsenite, methylarsonic acid, and dimethylarsinic acid, depending on the individual soil treatment. In all the experiments in which methylarsonic acid was added to the soil methylarsonous acid was detected in the extracts, suggesting that the soil bacteria are capable of reducing methylarsonic acid before a further methylation occurs. No significant differences were observed between analytical data obtained by using different extraction procedures.     

On the inverse and the dual index of a tree

The inverse of a graph with the spectrum λ ₁, λ ₁, …λ _n (λ ₁≠0) is a graph with the spectrum 1/λ₁,1/λ₂,…,1/λ _n ,.We present a purely graph-theoretic construction of the inverse ol a tree with a perfect matening. We apply this method for deriving results concerning the least nonnegative eigenvalue of a tree (called the dual index of a tree), including the best possible upper bound for the dual index of a tree in terms of a the number of its vertices.     

Experimental Test of the Evans’ <Emphasis Type="Italic">B</Emphasis>(3)-Field: Measuring the Interaction with Free Electrons

During the past decade, M.W. Evans and his coworkers have been developing so-called “Evans” or “ECE theory” that intends to serve as an unified field theory. One of its predictions is an existence of a radiation magnetic field called a “B(3)-field” which should accompany a circularly polarized electromagnetic radiation. This field should affect free electrons in two ways: (1) the electrons should behave in the B(3)-field in the same way as in a classical magnetic field (i.e., Larmor precession) and moreover, (2) the electrons should undergo quantum interaction with the B(3)-field with the formation of a spin connection resonance. This paper presents an experimental test of the B(3)-field existence by observing the changes in trajectories of free electrons in special detector, when strong (up to 200 W/m²) continuous circularly polarized microwave radiation of a frequency of 2.45 GHz is applied. We have not detected any sign of B(3)-field in presented experiment. It follows that if the B(3)-field really exists, it should be at least 4 orders of magnitude smaller than the Evans’ theory predicts.