Heikki Häkkänen - Academia.edu (original) (raw)

Papers by Heikki Häkkänen

In: Lindblom, J., 2005, Mineralogical Studies on Luminescence in Diamond, Quartz and Corundum. Tu... more In: Lindblom, J., 2005, Mineralogical Studies on Luminescence in Diamond, Quartz and Corundum. Turun Yliopiston Julkaisuja Annales Universitatis Turkuensis, Sarja - Ser. AII Vol. 183, pp. 1-26.

Acta biomaterialia, Jan 18, 2015

Bioactive glasses are known for their ability to induce osteogenic differentiation of stem cells.... more Bioactive glasses are known for their ability to induce osteogenic differentiation of stem cells. To elucidate the mechanism of the osteoinductivity in more detail, we studied whether ionic extracts prepared from a commercial glass S53P4 and from three experimental glasses (2-06, 1-06 and 3-06) are alone sufficient to induce osteogenic differentiation of human adipose stem cells. Cells were cultured using basic medium or osteogenic medium as extract basis. Our results indicate that cells stay viable in all the glass extracts for the whole culturing period, 14 days. At 14 days the mineralization in osteogenic medium extracts was excessive compared to the control. Parallel to the increased mineralization we observed a decrease in the cell amount. Raman and Laser Induced Breakdown Spectroscopy analyses confirmed that the mineral consisted of calcium phosphates. Consistently, the osteogenic medium extracts also increased osteocalcin production and collagen Type-I accumulation in the ext...

Minerals Engineering, 2003

ABSTRACT Sulfide minerals in rock samples were identified with laser-induced plasma spectroscopy ... more ABSTRACT Sulfide minerals in rock samples were identified with laser-induced plasma spectroscopy (LIPS) in the near vacuum ultraviolet spectral region. Reference spectra of pyrite, pyrrhotite, chalcopyrite, sphalerite, barite, calcite and dolomite were applied to classification of minerals in sulfur-bearing drill core samples. On the basis of the results mineral distributions in the sample were estimated. The potential of the LIPS method for in situ analysis is discussed.

Journal of Virology, 2014

In recent decades, Raman spectroscopy has entered the biological and medical fields. It enables n... more In recent decades, Raman spectroscopy has entered the biological and medical fields. It enables nondestructive analysis of structural details at the molecular level and has been used to study viruses and their constituents. Here, we used Raman spectroscopy to study echovirus 1 (EV1), a small, nonenveloped human pathogen, in two different uncoating states induced by heat treatments. Raman signals of capsid proteins and RNA genome were observed from the intact virus, the uncoating intermediate, and disrupted virions. Transmission electron microscopy data revealed general structural changes between the studied particles. Compared to spectral characteristics of proteins in the intact virion, those of the proteins of the heat-treated particles indicated reduced α-helix content with respect to β-sheets and coil structures. Changes observed in tryptophan and tyrosine signals suggest an increasingly hydrophilic environment around these residues. RNA signals revealed a change in the environment of the genome and in its conformation. The ionized-carbonyl vibrations showed small changes between the intact virion and the uncoating intermediate, which points to cleavage of salt bridges in the protein structure during the uncoating process. In conclusion, our data reveal distinguishable Raman signatures of the intact, intermediate, and disrupted EV1 particles. These changes indicate structural, chemical, and solute-solvent alterations in the genome and in the capsid proteins and lay the essential groundwork for investigating the uncoating of EV1 and related viruses in real time. In order to combat virus infection, we need to know the details of virus uncoating. We present here the novel Raman signatures for opened and intact echovirus 1. This gives hope that the signatures may be used in the near future to evaluate the ambient conditions in endosomes leading to virus uncoating using, e.g., coherent anti-Stokes Raman spectroscopy (CARS) imaging. These studies will complement structural studies on virus uncoating. In addition, Raman/CARS imaging offers the possibility of making dynamic live measurements in vitro and in cells which are impossible to measure by, for example, cryo-electron tomography. Furthermore, as viral Raman spectra can be overwhelmed with various contaminants, our study is highly relevant in demonstrating the importance of sample preparation for Raman spectroscopy in the field of virology.

Spectrochimica Acta Part B: Atomic Spectroscopy, 2007

Laser-induced breakdown spectroscopy (LIBS) has been applied to the direct analysis of powdered t... more Laser-induced breakdown spectroscopy (LIBS) has been applied to the direct analysis of powdered tungsten carbide hard-metal precursors and cemented tungsten carbides. The aim of this work was to examine the possibility of quantitative determination of the niobium, titanium, tantalum and cobalt. The investigated samples were in the form of pellets, pressed with and without binder (powdered silver) and in the form of cemented tungsten carbides. The pellets were prepared by pressing the powdered material in a hydraulic press. Cemented tungsten carbides were embedded in resin for easier manipulation.

Spectrochimica Acta Part B: Atomic Spectroscopy, 2001

Material distributions in paper and paper coatings are important factors which determine the char... more Material distributions in paper and paper coatings are important factors which determine the characteristics and Ž . quality of paper. We have used laser-induced plasma spectroscopy LIPS to determine various properties of coated and uncoated papers. Depth profiles of double coated papers were determined. Microscopic variations of pigments in a double-coated paper were analyzed. It was observed, that the two coating layers can be distinguished, if they differ enough in composition. Filler distributions of uncoated copier papers were determined. The surface of the paper was studied for five samples containing different amounts of binder in the coating. Lateral contamination in paper analysis i.e. splash over effect of ablation was studied by varying the sampling distance and number of laser pulses used for ablation. Influence of splash over effect on lateral analysis is briefly discussed. ᮊ 2001 Published by Elsevier Science B.V.

Optical Materials, 2003

Laser-excited time-resolved and UV-excited static photoluminescence (PL) as well as cathodolumine... more Laser-excited time-resolved and UV-excited static photoluminescence (PL) as well as cathodoluminescence (CL) techniques were applied to identify the origin of diamonds. Samples represented natural faced and rough diamonds from diamond market and different kimberlites as well as the most common high pressure-high temperature (HPHT) and as-grown synthetic diamonds. The time-resolved PL spectra of natural and synthetic diamonds display clear mutual differences. The static PL and CL spectra of natural diamonds revealed emission bands caused by complex nitrogenvacancy (N-V)-aggregates whereas the bands of synthetic diamonds reflect simple N-V-aggregates and nickel-containing defects. The luminescence properties depended on the excitation method and also changed during the excitation. The study of PL colors revealed information about the emission distribution of the PL spectra giving possibilities for future applications. The results indicated the sensitivity of luminescence techniques and revealed interesting structural information about diamond materials.

Journal of Analytical Atomic Spectrometry, 2004

Several solid organic compounds containing bromine and chlorine were analyzed with laser-induced ... more Several solid organic compounds containing bromine and chlorine were analyzed with laser-induced plasma spectroscopy. Emission lines were detected in the near vacuum ultraviolet spectral region by using a gas-purged spectrograph and an intensified charge-coupled device detector. The performance of this setup in the determination of the halides in the organic samples was evaluated. Carbon emission lines in the near vacuum ultraviolet were used as internal standards for the measurement of chlorine and bromine. Linear correlation was found between the carbon and halogen emission signal ratio and the corresponding atomic ratio of the compound. 4 7 4 J . A n a l . A t . S p e c t r o m . , 2 0 0 4 , 1 9 , 4 7 4 -4 7 8 T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

Drying Technology, 2003

ABSTRACT The aim of this study was to find out what will happen to paper coating quality and mate... more ABSTRACT The aim of this study was to find out what will happen to paper coating quality and material gradients if coating is dried in one air dryer at a high convection rate (150 kg/mh). Different printing papers were coated, calendered and printed with pilot machines. The binder and pigment gradients of the coated, and also printed, samples were analyzed with LIPS (Laser Induced Plasma Spectrometry). It was found that drying affects the migration of starch, but not latex. Total air drying can be used to dry printing papers, if air temperature, velocity and moisture content can be separately controlled. The control of web temperature is more important for paper quality formation in a coater drying section than that of evaporation rate.

Applied Spectroscopy, 1993

ABSTRACT Laser-induced fluorescence imaging has been used to study the microstructure of paper su... more ABSTRACT Laser-induced fluorescence imaging has been used to study the microstructure of paper surfaces. Pulses from a XeCl-excimer laser, 10 ns in duration at 308 nm, were used for excitation, and fluorescence was collected at 420 nm. The excitation spot diameter was approximately 20 μm, and the sampling interval 0.15 mm. Within an area of 5*5 mm2, 1023 sampling points were recorded to generate 3D fluorescence maps of paper surfaces. Papers containing fluorescence whitening agents (FWAs) gave the highest average fluorescence signals. Coated papers with no FWAs show weaker signals than the base sheet. For some thirty different paper samples, an obvious correlation between the amount of coating and the average intensity of the fluorescence signal was observed. Signal fluctuations around the average intensity values were sensitive to (1) the chemical pulp content in super calantered (SC) paper, (2) the amount of recycled fiber in newsprint, and (3) the amount of coating on the light-weight coated (LWC) paper surface. An effort was made to correlate fluorescence imaging results to predict mottling (diffusion of printing ink after printing) in various paper brands.

Applied Optics, 2003

An experimental setup is described for measuring laser-induced plasma emission spectra in the nea... more An experimental setup is described for measuring laser-induced plasma emission spectra in the near vacuum UV with a Czerny-Turner spectrograph and intensified charge-coupled device under atmospheric pressure. With a simple gas-purge technique, emission lines down to 130 nm could be recorded. The strongest emission lines of bromine, chlorine, and iodine in the near vacuum UV are easily detected.

Analytical Chemistry, 1998

ABSTRACT Laser-induced plasma emission spectroscopy (LIPS) has been used to study inorganic pigme... more ABSTRACT Laser-induced plasma emission spectroscopy (LIPS) has been used to study inorganic pigment and organic binder distributions in paper coatings, which are inhomogeneous and porous materials. The plasma was generated by focusing a pulsed XeCl excimer laser beam (diameter 100 μm, irradiance 0.3 GW/cm2) on the sample surface at atmospheric pressure. A gated intensified CCD detector was used to record time-delayed emission spectra. Linear correlations between the LIPS signals and the coat weight and the binder content of the coatings studied were obtained. Emission line intensities from ionic and neutral magnesium atoms were used to evaluate plasma temperature corrections in determining silicon and calcium in coatings. Self-absorption of the Ca(I) 423-nm line in air was observed for the coatings containing calcium carbonate. In an argon buffer, self-absorption was not present. Pigment and binder depth profiles of the coatings were studied for several coated paper samples. All samples studied indicated binder enrichment on the top layer of the coating.

Applied Spectroscopy, 1995

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