Unto Tapper

Analysis of different modes of factor analysis as least squares fit problems

Abstract Paatero, P. and Tapper, U., 1993. Analysis of different modes of factor analysis as least squares fit problems. Chemometrics and intelligent Laboratory Systems , 18: 183–194. It is shown that each mode of principal component analysis or ‘factor analysis’ is equivalent to solving a certain least squares problem where certain error estimators σ ij are assumed for the measured data matrix X ij . Selecting the mode (e.g. Q-mode) implicitly selects a scaling transformation as a preparatory step. Each scaling corresponds optimally to a certain σ . It is shown that the customary modes (Q-mode and R-mode) corresponds to such error estimates which do not normally occur in chemistry or physics. The best posssible scaling (‘optimal scaling’) and a near-optimal scaling are introduced. The Quail Roost II air pollution simulation data sets are studied as examples: it is shown that the X 2 values produced by the new alternatives are smaller by a a factor of 10. Thus one would also expect that the factors are more precise. However, the values of the factors are not monitored in the present work.

Source identification of bulk wet deposition in Finland by positive matrix factorization

Abstract A new variant of factor analysis (positive matrix factorization, PMF) is applied to a Finnish data set (18 years, 15 locations) of monthly bulk wet deposition concentrations of strong acids, SO4, NO3, NH4, total nitrogen (Ntot), total phosphorus (Ptot), Ca, K, Mg, Na, Cl, and total organic carbon (TOC). PMF produces strictly nonnegative factors, optimally based on error estimates of data values, with almost no rotational ambiguity. The application of PMF to environmental data is outlined: handling of outliers and missing values, determination of error estimates, interpretation of results. The results are displayed in different ways: (1) seasonal profiles of factors; (2) factor compositions by absolute value; (3) factor compositions scaled by their importance in explaining the variation of data. For most compounds 90–95% of the total weighted variation is explained by four factors. Each of the 15 data matrices is analysed with four factors. Different types of factors are characterized by the following five key elements: strong acids (H+), nitrogen compounds (N), Cl, TOC and P. Likely main sources for factors are discussed. A high degree of neutralization is observed at all inland stations. Only at four stations the acidity-related substances—SO4 and NO3—are mainly explained by the H-factor. The neutralization caused by the Estonian oil-shale industry is detected at one station. The N-factor is the major anthropogenic factor associating acidic anions SO4 and NO3 together with NH4. Some features of the factors H and N seem to be connected with degradation processes during the collection period of one month. The marine source creates a well-defined Cl-factor at five stations. The annual cycle of the TOC-factor and its association with Ca and K could be connected to airborne particulate matter, such as soil dust. The seasonal behaviour and elemental concentrations of the P-factor suggest a biological origin: pollen, spores, plant debris. The anion-cation balance is shown for all factors and it is mostly good.

A novel cement-based hybrid material

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are known to possess exceptional tensile strength, elastic modulus and electrical and thermal conductivity. They are promising candidates for the next-generation high-performance structural and multi-functional composite materials. However, one of the largest obstacles to creating strong, electrically or thermally conduc- tive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps of purifica- tion and functionalization of the carbon nanomaterial are required. We propose a new approach to grow CNTs/CNFs directly on the surface of matrix particles.

Single-electron transistor made of multiwalled carbon nanotube using scanning probe manipulation

We positioned semiconducting multiwalled carbon nanotube, using an atomic force microscope, between two gold electrodes at SiO2 surface. Transport measurements exhibit single-electron effects with a charging energy of 24 K. Using the Coulomb staircase model, the capacitances and resistances between the tube and the electrodes can be characterized in detail.

Thin multilayer CdS/ZnS films grown by SILAR technique

Abstract Multilayer ZnS/CdS thin films were grown on glass, ITO-covered glass and (100)GaAs substrates by successive ionic layer adsorption and reaction (SILAR) technique at room temperature and ambient pressure. The layers in multilayer thin film structures were nominally 1–6 nm thick and the amount of layers varied so that the total thickness of 100–120 nm was achieved. The films were polycrystalline according to X-ray diffraction analysis and scanning electron microscopy. The interfaces between the separate cadmium sulfide (CdS) and zinc sulfide (ZnS) layers were not sharp, but contained thin Cd x Zn 1− x S solid solution layers. Annealing enhanced the mixing of the different layers and after 50 h at 300°C no separate CdS and ZnS X-ray reflections could be detected. About 20 nm thick layers could be detected as separate fields by scanning electron microscopy.

A size selective nanoparticle collection device based on diffusion and thermophoresis

There is a growing industry fabricating products that are based on nanoparticles (particle diameter dp≤100 nm). The production of these particles requires detection, classification and characterisation of even smaller particles because of, e.g. preventing unwanted particle emissions from the processes and health issues. Monitoring of the processes is needed on one hand for product quality determinations, on the other hand to ensure safe and particle-free working conditions. Thus simple, fast and reliable measurement devices are needed for particle characterisation.

Aerosol synthesis of Ti–O powders via in-droplet hydrolysis of titanium alkoxide

Abstract A method to produce Ti–O powders by an in-droplet hydrolysis of metal alkoxide precursor is presented. Titanium n -tetrabutoxide, hydrolysis water, and acetic acid were included in the ethanolic precursor solution that was nebulized. The resulting aerosol was transported to a tubular flow reactor where the ethanol evaporation initiated a polycondensation reaction and solid particles were formed starting from droplet surface. Titanium hydrous oxide particles were obtained at 200°C in atmospheric pressure of nitrogen and air. The collected powders were characterized by XRD, TG–SDTA, BET, SEM, TEM, and IR- spectroscopy, as well as with aerosol impactor. The as-produced powder particles were amorphous, smooth on the surface, and either spherical or deflated in shape. Aerodynamic mass mean diameter was 2.7 μm. Nanocrystalline TiO 2 was obtained after thermal post-annealing for one hour. An expected tendency to convert to anatase crystalline phase up to 500°C and subsequently to rutile phase up to 900°C in the annealing was observed. The results show that the in-droplet hydrolysis is a viable method in preparing fine Ti–O powder particles with controlled properties.

On the transport and speciation of ruthenium in high temperature oxidising conditions

Summary In this paper, the transport and speciation of ruthenium under conditions simulating an air ingress accident was studied. Ruthenium dioxide was exposed to an oxidising environment at high temperatures (>1200 °C) in a tubular flow furnace. At these conditions, volatile ruthenium species were formed. A major part of the released ruthenium was deposited in the tube as RuO2. Depending on the experimental conditions, 12–35 wt. % of the released ruthenium was trapped in the outlet filter as RuO2 particles. At completely dry conditions using stainless steel tubes, only 0.1–0.2 wt. % of the released ruthenium reached the trapping bottle as gaseous RuO4. However, when alumina was applied as tube material or the atmosphere contained some water vapour and silver seed particles, the fraction of gaseous ruthenium reaching the trapping bottle increased to 5 wt. % which is close to thermodynamic equilibrium. This indicates that RuO2 does not catalyse the decomposition of RuO4.

Trace and heavy metal analyses of a skeletal population representing the town people in Turku (Åbo), Finland in the 16th–17th centuries: with special reference to gender, age and social background

The Julin site in the city of Turku, Finland, was excavated in 1964, 1983-1985 and 1987. On this site are the remains of the church of the Holy Spirit with its cemetery. The burial period of the excavated skeletons lasted most probably from the 1580s to the 1650s. Sodium, phosphorus, calcium, manganese, iron, copper, zinc, bromine, strontium and lead concentrations of ribs from skeletal remains of 141 individuals were analyzed. The main finding is that the concentrations of Sr and Zn in younger women tend to be lower than that in men of a corresponding age, and in older people both the strontium and zinc values tend to be higher in women than men. On the basis of this study the Pb exposure in the early modern population in Finland was at a very low level. We conclude that the role of migration and the source of grain supply on the variation of the elemental values are more difficult to evaluate than the role of diagenesis.

Mobility size development and the crystallization path during aerosol decomposition synthesis of TiO2 particles

Abstract Size and morphology transformation as well as the crystallization path of monodisperse titanium dioxide particles were studied in aerosol flow reactor. Solid, hydrated titanium oxide particles were prepared from titanium alkoxide by a droplet hydrolysis and a subsequent size classification. The particles were carried to a reactor in air at temperature range of 20–1500°C. The inlet particle size of 100 and 200 nm gradually decreased 40% with increasing temperature as investigated by a tandem differential mobility analyzer (TDMA) system. The decrease was due to decomposition of the hydrated Ti–O particles, densification of the forming TiO2 particles, and a phase change from anatase to rutile. Above 1000°C the mobility size increased due to crystal-habit formation that created faceted, elongated particles and consequently an increased dynamic shape factor. Microstructure investigations with a transmission electron microscope (TEM) showed that nanocrystalline anatase particles were present at 600°C and transformed to rutile up to 1100°C with simultaneous crystallite growth. Single-crystal rutile particles were observed at temperatures with the increased mobility diameters.