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Dive into the research topics where Primož Oven is active.

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Featured researches published by Primož Oven.


Wood Science and Technology | 2007

Regular cambial activity and xylem and phloem formation in locally heated and cooled stem portions of Norway spruce

Jožica Gričar; Martin Zupančič; Katarina Čufar; Primož Oven

The effect of heating (23–25°C) and cooling (9–11°C) on regular cambial activity and xylem and phloem formation in the stem portion of Norway spruce was investigated. Adult trees were sampled at 21-day intervals during the 2005 vegetation period. Continuously elevated temperatures increased the rate of cell division in the first part of the growing season, but did not significantly prolong cambial activity at the end of the vegetation period in the heated tree. Low-temperature treatments shortened regular cambial activity and slowed down cell production. The xylem growth ring was wider in the heated sample and narrower in the cooled sample compared to the control. The temperature in the cambial region was only negligibly transferred along the stem from the site of its application. In general, the temperature in the cambium was affected by a long-term rise or drop in air temperatures. Both experiments affected the structure and width of phloem growth increments. The tangential band of the axial parenchyma was not continuous in the cooled sample. The number of late phloem cells was reduced in the cool-treated sample and increased in the heat-treated sample. Our experiments confirmed the effect of constantly increased or decreased temperatures on regular cambial activity in Norway spruce.


Trees-structure and Function | 2009

The climate sensitivity of Norway spruce [Picea abies (L.) Karst.] in the southeastern European Alps

Tom Levanič; Jožica Gričar; Mary Gagen; Risto Jalkanen; Neil J. Loader; Danny McCarroll; Primož Oven; Iain Robertson

To investigate the potential of Norway spruce (Picea abies L. Karst) as a palaeoclimate archive in the southeastern European Alps, tree ring chronologies were developed from trees growing at two sites in Slovenia which differed in their ecological and climatological characteristics. Ring width, maximum latewood density, annual height increment and latewood cellulose carbon isotope composition were determined at both sites and the resulting time-series compared with and verified against instrumental climate data for their common period (AD 1960–AD 2002). Results indicate that ring width sensitivity to summer temperature is very site-dependent, with opposing responses at alpine and lowland sites. Maximum density responds to September temperatures, indicating lignification after cell division has ceased. Stable carbon isotopes have most potential, responding strongly to summer temperature in both alpine and lowland stands. Height increment appears relatively insensitive to climate, and is likely to be dominated by local stand dynamics.


Holzforschung | 2009

A single point NMR method for an instantaneous determination of the moisture content of wood

Maks Merela; Primož Oven; Igor Serša; Urša Mikac

Abstract Nuclear magnetic resonance (NMR) enables an instantaneous determination of the proton density in liquids and is thus convenient for determining the moisture content (MC) of wood. We demonstrated that the MC of a wood sample can be determined instantaneously on the basis of its mass (m) and the amplitude of its NMR free-induction-decay (FID) signal. The measurement is based on the assumption that the only liquid in the wood is water and that the relationship between the amplitude of the FID signal (S) and the mass of the water (m w ) in the sample is linear, i.e., S=k m w +k′ (m-m w ), and can be precisely calibrated for a given NMR probe and NMR spectrometer setup (in our case k=105 AU g-1 and k/k′ =34). With the FID signal converted into the mass of water, the MC is calculated as: MC=(S-m k′)/(m k-S). After the initial calibration of the FID signal with respect to the content of water, the correctness of the method was verified on samples of different wood species with various MCs. The results confirmed that the proposed method is comparable in terms of accuracy and reliability to the gravimetric method, regardless of the species of wood. As the method is instantaneous, it might become the method of choice in applications where a short measurement time combined with a high accuracy is demanded.


Ultrasonics Sonochemistry | 2016

Fabrication of bacterial cellulose thin films self-assembled from sonochemically prepared nanofibrils and its characterization

Dimitrios Tsalagkas; Rastislav Lagaňa; Ida Poljanšek; Primož Oven; Levente Csoka

Bacterial cellulose (BC) film formation could be a critical issue in nanotechnology applications such as biomedical or smart materials products. In this research, purified pretreated BC was subjected to high intensity ultrasound (HIUS) and was investigated for the development of BC films. The morphological, structural and thermal properties of the obtained films were studied by using FE-SEM, AFM, FT-IR, XRD, TGA and DSC characterizations. Results showed that the most favorable purification treatment was the 0.01 M NaOH at 70°C for 2h under continuous stirring. The most suitable ultrasound operating conditions were found to be, 1cm distance of ultrasonic probe from the bottom of the beaker, submerged in cold water bath cooling around 12 ± 2°C. The power (25 W/cm(2)), time (30 min), BC concentration (0.1%w/w), amplitude (20 μm) and frequency (20 kHz) were maintained constant.


Flora | 1999

The formation of a ligno-suberised layer and necrophylactic periderm in beech bark (Fagus sylvatica L.)

Primož Oven; Niko Torelli; Walter C. Shortle; Martin Zupančič

Beech (Fagus sylvatica L.) bark was wounded in early April of 1993 and tissue changes followed on days 7, 14, 21, 28, 35, 42, 49, 56, 84, 112, and 140. In 7 days, tissue at the wound surface became necrotic and discoloured. In 14 days the walls of the parenchyma cells immediately underneath the necrotic tissue became thickened and after 21 days became lignified. In 28 days these lignified cells showed intracellular-suberisation. In 42 days the ligno-suberised layer was continuous with the phellem of the superficial periderm. In 35 days we first noted differentiation of the necrophylactic phellogen under the ligno-suberised layer. In 49 days suberised phellem of the necrophylactic periderm differentiated. At 112 days the phellem of the necrophylactic periderm had coalesced with that of the surface periderm. In I40 days abscission of the wound rhytidome began.


Holzforschung | 2014

Morphological, thermal, and structural aspects of dried and redispersed nanofibrillated cellulose (NFC)

Vesna Žepič; Erika Š. Fabjan; Marta Kasunič; Romana Cerc Korošec; Aleš Hančič; Primož Oven; Lidija S. Perše; Ida Poljanšek

Abstract The effects of various drying techniques, such as air, oven, freeze, and spray drying, on the morphological, thermal, and structural behaviors of two different nanofibrillated cellulose (NFC) materials were investigated. Field emission scanning electron microscopy (FE-SEM) observations indicated an interlaced network formation of predominantly in-plane fibrillar orientation for air- and oven-dried samples, while freeze and spray drying resulted in the formation of coarse and fine powder fractions. Comparison of redispersed powders obtained by freeze and spray drying indicated that aggregation phenomena are significantly reduced in freeze-dried specimens. Rheological and sedimentation analysis revealed that the freeze-dried NFC powders are more stable than spray-dried NFC powders when redispersed in water. Aggressive dehydration processes, such as freezing or heating, significantly influence the thermal stability of the dried cellulose samples. On the contrary, the crystallinity properties of dried NFC materials are very similar regardless of the drying treatment.


Magnetic Resonance Materials in Physics Biology and Medicine | 2005

Three-dimensional in vivo magnetic resonance microscopy of beech (Fagus sylvatica L.) wood

Maks Merela; Primož Oven; A. Sepe; I. Serša

Spatial structure and water distribution in branch tissues after mechanical injury were investigated in vivo by three-dimensional (3D) magnetic resonance (MR) microscopy. On a beech tree (Fagus sylvatica L.), transplanted in a portable pot, a branch was topped and then MR imaged. High-resolution 3D MR images revealed structures which could not be identified by conventional MR images or by light microscopy. MR measurements confirmed our assumption that moisture content is decreasing towards the wounded part of the branch. This indicates that quick moisture loss from mechanically wounded tissues represents the initial passive response of compromised tissue.


Holzforschung | 2008

3D magnetic resonance microscopy of a wounded beech branch

Primož Oven; Maks Merela; Urša Mikac; Igor Serša

Abstract The pruned part of a beech (Fagus sylvatica) branch was imaged by a 3D spin-echo magnetic resonance imaging (MRI) technique to visualize change in structure and water content in the tissues. Proton density-weighted MR images of intact tissues confirmed high moisture content (MC) associated with high MRI signal in the pith, xylem rays and earlywood vessels, as well as in the cambial zone with current annual xylem and phloem increment. MRI images derived from the 3D datasets showed a previously unreported moisture-related structural response of the beech branch to wounding. An extensive wound tissue with a high MRI signal at the wound edge was a conspicuous new structure clearly visualized by 3D MRI. MRI revealed that the xylem at the wound was dehydrated in a cone-shaped pattern extending approximately 4.5 mm deep into the branch. Dehydration was delimited from the underlying sound wood by a layer, corresponding to the reaction zone, of tissue with a high MRI signal and hence high moisture content. Moisture content of these reaction zones in beech determined by MRI were greater than in healthy wood by factors of 1.3–1.8. Accordingly, in the margins of wounded beech wood not only cell wall alterations can be observed, but also an intensive water accumulation, which is probably an integral part of the protective mechanism for the underlying sound wood.


Holzforschung | 1998

Electric Current Density Imaging of Pedunculate Oak (Quercus Robur L.) Twigs by Magnetic Resonance Imaging

Katarina Beravs; Primož Oven; Igor Serša; Niko Torelli; Franci Demsar

The use of Electric Current Density Imaging (CDI) technique to map spatial distribution of induced electric currents through two years old twigs of pedunculate oak (Quercus robur L.) is presented. Specifically, this magnetic resonance technique was implemented to image conductivity contrast in different tree tissues. Imaged electric conductivity distributions of pith, wood, and phloem together with cambial zone and undifferentiated xylem were compared with flame atomic absorption spectrometry measurements of potassium. Good correlation was observed. The undifferentiated xylem + cambial zone + complete phloem showed higher electrical conductivity and normalized potassium values than both differentiated xylem and pith. By a novel magnetic resonance imaging technique it is demonstrated that the path of least resistance to an electric current was along tissues of maximum free potassium concentration.


Holzforschung | 2013

Evaluation of selective extraction methods for recovery of polyphenols from pine

Wenwen Fang; Jarl Hemming; Markku Reunanen; Patrik Eklund; Enma Conde Pineiro; Ida Poljanšek; Primož Oven; Stefan Willför

Abstract The extraction conditions have been evaluated concerning the recovery of specific polyphenols from Scots pine (Pinus sylvestris) knots by means of an accelerated solvent extractor. The composition of the extracts was determined by gas chromatography, gas chromatography-mass spectrometry, and high-performance size-exclusion chromatography. The main phenolic compounds are the stilbenes pinosylvin and its monomethyl ether and the lignan nortrachelogenin (NTG), and their amounts vary a lot from sample to sample. The sequential extraction with a nonpolar solvent as a first step for removing the lipophilic compounds was the most efficient approach for the recovery of both pinosylvins and NTG. For food applications, hot water and 85% aqueous ethanol were good solvents for the production of the substances in focus. An industrial knotwood sample from a pulp mill was sequentially extracted with cyclohexane and ethanol/water (95:5) in a large-scale Soxhlet equipment. The results show that the industrial production of pinosylvins and NTG from knots is feasible.

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Niko Torelli

University of Ljubljana

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Viljem Vek

University of Ljubljana

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Maks Merela

University of Ljubljana

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Igor Serša

University of Ljubljana

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Miha Humar

University of Ljubljana

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Tom Levanič

University of Ljubljana

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