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Wojno, S., Ahlinder, A., Altskär, A., Stading, M., Abitbol, T. & Kádár, R. (2023). Percolation and phase behavior in cellulose nanocrystal suspensions from nonlinear rheological analysis. Carbohydrate Polymers, 308, Article ID 120622.
Open this publication in new window or tab >>Percolation and phase behavior in cellulose nanocrystal suspensions from nonlinear rheological analysis
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2023 (English)In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 308, article id 120622Article in journal (Refereed) Published
Abstract [en]

We examine the influence of surface charge on the percolation, gel-point and phase behavior of cellulose nanocrystal (CNC) suspensions in relation to their nonlinear rheological material response. Desulfation decreases CNC surface charge density which leads to an increase in attractive forces between CNCs. Therefore, by considering sulfated and desulfated CNC suspensions, we are comparing CNC systems that differ in their percolation and gel-point concentrations relative to their phase transition concentrations. The results show that independently of whether the gel-point (linear viscoelasticity, LVE) occurs at the biphasic - liquid crystalline transition (sulfated CNC) or at the isotropic - quasi-biphasic transition (desulfated CNC), the nonlinear behavior appears to mark the existence of a weakly percolated network at lower concentrations. Above this percolation threshold, nonlinear material parameters are sensitive to the phase and gelation behavior as determined in static (phase) and LVE conditions (gel-point). However, the change in material response in nonlinear conditions can occur at higher concentrations than identified through polarized optical microscopy, suggesting that the nonlinear deformations could distort the suspensions microstructure such that for example a liquid crystalline phase (static) suspension could show microstructural dynamics similar to a biphasic system.

Place, publisher, year, edition, pages
Elsevier Ltd, 2023
Keywords
Cellulose nanocrystal suspensions, Fourier-transform rheology, Percolation, Self-assembly phases, Stress decomposition, Cellulose, Cellulose derivatives, Gelation, Nanocrystals, Nonlinear optics, Solvents, Suspensions (fluids), Cellulose nanocrystal suspension, Gel phasis, Gel point, Linear viscoelasticity, Material response, Rheological analysis, Self-assembly phase, Stress decompositions, Self assembly, Behavior, Dispersions, Phase Transition
National Category
Engineering and Technology
Identifiers
urn:nbn:se:ri:diva-64094 (URN)10.1016/j.carbpol.2023.120622 (DOI)2-s2.0-85147603169 (Scopus ID)
Note

Correspondence Address: Abitbol T, RISE, Sweden;  Funding details: BASF; Funding details: Wallenberg Wood Science Center, WWSC; Funding text 1: SW and RK are grateful for the financial support of the Wallenberg Wood Science Centre (WWSC) and of the Chalmers Area of Advance Materials Science. The Chair of Sustainable Packaging within the Institute of Materials at EPFL, co-funded by BASF, Logitech, Nestlé and SIG, is acknowledged by TA. A.Ah, A.A. and M.S. are grateful for the financial support from KP Nanocellulose platform at RISE AB.; Funding text 2: SW and RK are grateful for the financial support of the Wallenberg Wood Science Centre (WWSC) and of the Chalmers Area of Advance Materials Science. The Chair of Sustainable Packaging within the Institute of Materials at EPFL, co-funded by BASF, Logitech, Nestlé and SIG, is acknowledged by TA. A.Ah, A.A. and M.S. are grateful for the financial support from KP Nanocellulose platform at RISE AB.

Available from: 2023-02-28 Created: 2023-02-28 Last updated: 2023-10-06Bibliographically approved
Sharafi, N., Sepehri, S., Andersson, J., Lopez-Sanchez, P., Schaller, V., Altskär, A., . . . Johansson, C. (2020). Nanorheological analysis of xanthan/water solutions using magnetic nanoparticles with different particle sizes. Annual Transactions of the Nordic Rheology Society, 28, 147
Open this publication in new window or tab >>Nanorheological analysis of xanthan/water solutions using magnetic nanoparticles with different particle sizes
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2020 (English)In: Annual Transactions of the Nordic Rheology Society, Vol. 28, p. 147-Article in journal (Refereed) Published
Abstract [en]

We have studied nanorheological properties (viscosity and shear moduli) of aqueous xanthan solutions, in the oscillation frequency range up to 10 kHz by using magnetic particles that undergo Brownian relaxation and frequency dependent AC susceptibility (ACS). We used two magnetic nanoparticle (MNP) systems with different mean particle sizes of 80 nm and 100 nm. The determined viscosity and shear modulus of the diluted xanthan solutions from the ACS measurement of the two particle systems agree with traditional oscillatory rheological measurements. However, there is a particle size dependency that could be explained by comparing particles sizes with the xanthan microstructure

National Category
Physical Chemistry
Identifiers
urn:nbn:se:ri:diva-58463 (URN)
Available from: 2022-01-31 Created: 2022-01-31 Last updated: 2023-10-06Bibliographically approved
Hagsten, C., Altskär, A., Gustafsson, S., Loren, N., Trägårdh, C., Innings, F., . . . Nylander, T. (2019). Structural and compositional changes during UHT fouling removal—Possible mechanisms of the cleaning process. Food Structure, 21, Article ID 100118.
Open this publication in new window or tab >>Structural and compositional changes during UHT fouling removal—Possible mechanisms of the cleaning process
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2019 (English)In: Food Structure, ISSN 2213-3291, Vol. 21, article id 100118Article in journal (Refereed) Published
Abstract [en]

Ultra-high temperature (UHT) treatment of milk forms a deposit or fouling in the processing equipment that is mineral-based with an enclosed protein network. This study addresses the fundamental mechanisms that control the removal of this deposit. For this purpose, the structural and compositional changes during the cleaning process have been studied. The structure analysis was performed with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) on samples that were quenched at different stages of the cleaning process. It was found for acid cleaning that the mineral content is rapidly decreasing in the fouling layer as the cleaning continues, but there is still an intact protein structure with the similar thickness as the original fouling. For alkali cleaning, part of the protein structure was subsequently removed from the outside towards the stain-less steel as a function of time, while the mineral structure was mostly remaining. The break-up of the organic network structure, which likely involves depolymerization of protein aggregates, were found to control the cleaning efficiency. The weakening of the protein network facilitates the removal of the UHT fouling layer during the acid cleaning step and allow for an efficient cleaning cycle. The chemical reactions that occur within the fouling layer between the hydroxyl ions and the protein network was modeled according to a depolymerization reaction and a mechanistic model of the cleaning process is presented. © 2019

Place, publisher, year, edition, pages
Elsevier Ltd, 2019
Keywords
Cleaning, Fouling structure, Mechanistic model, Milk fouling, Mineral deposit, Protein depolymerization, Protein net-work
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-39449 (URN)10.1016/j.foostr.2019.100118 (DOI)2-s2.0-85067823105 (Scopus ID)
Note

Funding details: Svenska Forskningsrådet Formas; Funding text 1: We acknowledge the financial support of TvärLivs , which is a cooperative venture between The Swedish Research Council Formas, The Swedish Farmers Foundation for Agricultural Research (SLF), the Swedish Governmental Agency for Innovation Systems Vinnova, Livsmedelsföretagen, and Svensk Dagligvaruhandel, as well as Tetra Pak Processing Systems and Arla Foods. Appendix A

Available from: 2019-07-08 Created: 2019-07-08 Last updated: 2023-10-06Bibliographically approved
Lopez-Sanchez, P., Fredriksson, N., Larsson, A., Altskär, A. & Ström, A. (2018). High sugar content impacts microstructure, mechanics and release of calcium-alginate gels. Food Hydrocolloids, 84, 26-33
Open this publication in new window or tab >>High sugar content impacts microstructure, mechanics and release of calcium-alginate gels
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2018 (English)In: Food Hydrocolloids, ISSN 0268-005X, E-ISSN 1873-7137, Vol. 84, p. 26-33Article in journal (Refereed) Published
Abstract [en]

The use of calcium-alginate gels as carriers of food and pharmaceutical compounds is of great interest due the versatile properties of such systems. In this work, we investigated the influence of sugars (glucose:fructose) as co-solutes (15–60% (wt)) on the physico-chemical properties of calcium-alginate gel particles. Sugar concentrations above 15% (wt) reduced extensibility of alginate molecules, as shown by intrinsic viscosity measurements, and lead to a more open or less connected gel network with aggregated alginate strands. Furthermore, it is shown for the first time that sugar impacted swelling-deswelling ability of calcium alginate gels under simulated gastric (pH 1.2) and intestinal (pH 6.6) conditions. Release of sugar from calcium alginate gels with 15% (wt) and 30% (wt) sugar was close to Fickian diffusion mechanism, in both simulated gastric and intestinal fluid, with diffusion coefficient close to that previously reported for calcium-alginate gels with lower sugar contents. However, release from 60% (wt) gels in gastric fluid was slower than for 15 and 30% (wt) and, there was a drastic shrinkage of the gels under acid conditions. In intestinal fluid 60% (wt) gels showed slower release than gels with lower sugar content, this was hypothesised to be due to the lower surface area of these gels. Understanding the structure-function relationship of these gels is key to the successful design of delivery systems for food and biotechnological applications.

Keywords
Alginate, Intrinsic viscosity, Microstructure, Release, Solvent quality, Sugar
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-36430 (URN)10.1016/j.foodhyd.2018.05.029 (DOI)2-s2.0-85056323909 (Scopus ID)
Note

 Funding details: VINNOVA

Available from: 2018-11-22 Created: 2018-11-22 Last updated: 2023-10-06Bibliographically approved
Lopez-Sanches, P., Fredriksson, N., Larsson, A., Altskär, A. & Ström, A. K. (2018). High sugar content impacts microstructure, mechanics and release of calcium-alginate gels. Food Hydrocolloids, 84, 26-33
Open this publication in new window or tab >>High sugar content impacts microstructure, mechanics and release of calcium-alginate gels
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2018 (English)In: Food Hydrocolloids, ISSN 0268-005X, E-ISSN 1873-7137, Vol. 84, p. 26-33Article in journal (Refereed) Published
Abstract [en]

The use of calcium-alginate gels as carriers of food and pharmaceutical compounds is of great interest due the versatile properties of such systems. In this work, we investigated the influence of sugars (glucose:fructose) as co-solutes (15–60% (wt)) on the physico-chemical properties of calcium-alginate gel particles. Sugar concentrations above 15% (wt) reduced extensibility of alginate molecules, as shown by intrinsic viscosity measurements, and lead to a more open or less connected gel network with aggregated alginate strands. Furthermore, it is shown for the first time that sugar impacted swelling-deswelling ability of calcium alginate gels under simulated gastric (pH 1.2) and intestinal (pH 6.6) conditions. Release of sugar from calcium alginate gels with 15% (wt) and 30% (wt) sugar was close to Fickian diffusion mechanism, in both simulated gastric and intestinal fluid, with diffusion coefficient close to that previously reported for calcium-alginate gels with lower sugar contents. However, release from 60% (wt) gels in gastric fluid was slower than for 15 and 30% (wt) and, there was a drastic shrinkage of the gels under acid conditions. In intestinal fluid 60% (wt) gels showed slower release than gels with lower sugar content, this was hypothesised to be due to the lower surface area of these gels. Understanding the structure-function relationship of these gels is key to the successful design of delivery systems for food and biotechnological applications.

Keywords
Alginate, Intrinsic viscosity, Microstructure, Release, Solvent quality, Sugar
National Category
Engineering and Technology
Identifiers
urn:nbn:se:ri:diva-44984 (URN)10.1016/j.foodhyd.2018.05.029 (DOI)2-s2.0-85056323909 (Scopus ID)
Available from: 2020-05-18 Created: 2020-05-18 Last updated: 2023-10-06Bibliographically approved
Longfils, M., Röding, M., Altskär, A., Schuster, E., Loren, N., Sarkka, A. & Rudemo, M. (2018). Single particle raster image analysis of diffusion for particle mixtures. Journal of Microscopy, 269(3), 269-281
Open this publication in new window or tab >>Single particle raster image analysis of diffusion for particle mixtures
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2018 (English)In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 269, no 3, p. 269-281Article in journal (Refereed) Published
Abstract [en]

Recently we complemented the raster image correlation spectroscopy (RICS) method of analysing raster images via estimation of the image correlation function with the method single particle raster image analysis (SPRIA). In SPRIA, individual particles are identified and the diffusion coefficient of each particle is estimated by a maximum likelihood method. In this paper, we extend the SPRIA method to analyse mixtures of particles with a finite set of diffusion coefficients in a homogeneous medium. In examples with simulated and experimental data with two and three different diffusion coefficients, we show that SPRIA gives accurate estimates of the diffusion coefficients and their proportions. A simple technique for finding the number of different diffusion coefficients is also suggested. Further, we study the use of RICS for mixtures with two different diffusion coefficents and investigate, by plotting level curves of the correlation function, how large the quotient between diffusion coefficients needs to be in order to allow discrimination between models with one and two diffusion coefficients. We also describe a minor correction (compared to published papers) of the RICS autocorrelation function. Lay description Diffusion is a key mass transport mechanism for small particles. Efficient methods for estimating diffusion coefficients are crucial for analysis of microstructures, for example in soft biomaterials. The sample of interest may consist of a mixture of particles with different diffusion coefficients. Here, we extend a method called Single Particle Raster Image Analysis (SPRIA) to account for particle mixtures and estimation of the diffusion coefficients of the mixture components. SPRIA combines elements of classical single particle tracking methods with utilizing the raster scan with which images obtained by using a confocal laser scanning microscope. In particular, single particles are identified and their motion estimated by following their center of mass. Thus, an estimate of the diffusion coefficient will be obtained for each particle. Then, we analyse the distribution of the estimated diffusion coefficients of the population of particles, which allows us to extract information about the diffusion coefficients of the underlying components in the mixture. On both simulated and experimental data with mixtures consisting of two and three components with different diffusion coefficients, SPRIA provides accurate estimates and, with a simple criterion, the correct number of mixture components is selected in most cases.

Keywords
Bootstrap; Confocal laser scanning microscopy; Diffusion; Fluorescent beads; Maximum likelihood; Particle mixtures; Single particle tracking
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-33367 (URN)10.1111/jmi.12625 (DOI)2-s2.0-85041951653 (Scopus ID)
Available from: 2018-03-05 Created: 2018-03-05 Last updated: 2023-10-06Bibliographically approved
Malmgren, B., Ardö, Y., Langton, M., Altskär, A., Bremer, M. G. .., Dejmek, P. & Paulsson, M. (2017). Changes in proteins, physical stability and structure in directly heated UHT milk during storage at different temperatures. International Dairy Journal, 71, 60-75
Open this publication in new window or tab >>Changes in proteins, physical stability and structure in directly heated UHT milk during storage at different temperatures
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2017 (English)In: International Dairy Journal, ISSN 0958-6946, E-ISSN 1879-0143, Vol. 71, p. 60-75Article in journal (Refereed) Published
Abstract [en]

Changes occurring in directly heated UHT milk were studied during storage at 5, 22, 30 and 40 °C. Industrially produced UHT milk samples were analysed for changes in enzymatic activity, protein modification, destabilisation of casein micelles and relocation of milk proteins in relation to sedimentation and gel formation. Sedimentation occurred at all temperatures, and the protein composition of the sediments reflected the composition of its liquid phase; however, there was no α-lactalbumin, β-lactoglobulin or κ-casein present in sediments. Tendrils composed of β-lactoglobulin and κ-casein were seen on casein micelles after UHT treatment and grew in length prior to gelation. High degrees of lactosylation of proteins and peptides were clearly correlated with the absence of gelation and long tendrils. Gelled samples showed complete hydrolysis of intact β-casein, and limited lactosylation of β-lactoglobulin and κ-casein.

National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-29264 (URN)10.1016/j.idairyj.2017.03.002 (DOI)2-s2.0-85016613718 (Scopus ID)
Available from: 2017-04-07 Created: 2017-04-07 Last updated: 2023-10-06Bibliographically approved
Gmoser, R., Bordes, R., Nilsson, G., Altskär, A., Stading, M., Loren, N. & Berta, M. (2017). Effect of dispersed particles on instant coffee foam stability and rheological properties. European Food Research and Technology, 243(1), 115-121
Open this publication in new window or tab >>Effect of dispersed particles on instant coffee foam stability and rheological properties
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2017 (English)In: European Food Research and Technology, ISSN 1438-2377, E-ISSN 1438-2385, Vol. 243, no 1, p. 115-121Article in journal (Refereed) Published
Abstract [en]

Properties of instant coffee foam constitute the focus of this study. The coffee, obtained from commercial sources, was dispersed in water at a concentration in the range of standard use. The resulting solution contained a substantial amount of micron and submicron size particles that were filtered with membranes having difference size cut-offs in order to investigate the relationship foam properties—particles size. The foams produced from these solutions have been imaged by confocal laser scanning microscopy, and their moduli and stability have been measured by oscillatory rheology, using an in-house developed rheometric set-up. The results show that particles larger than 0.8 µm have little effect on the reduction of drainage while a clear strengthening effect on the foam was evident. This was a result of their diffusion to the lamellae borders, which increases the viscosity of the liquid–air interface. Particles smaller than 0.2 µm affect bubble coarsening and likely hinder the migration of soluble surface active species to the bubble surface. Particles also participate in the stabilization of the air–water interface, and this affects both the foam stability and mechanical properties. Established models developed for ideal foam systems containing particles are difficult to apply due to the complexity of the system studied. Despite this limitation, these results provide increased understanding of the effect of particles on instant coffee foams.

Keywords
Foam microscopy, Foamability, Instant coffee, Particles, Rheology, Surface tension, Elasticity, Elementary particles, Stabilization, Confocal laser scanning microscopy, Dispersed particle, Oscillatory rheologies, Rheological property, Strengthening effect, Sub-micron size particles, Surface active species, Phase interfaces
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-27645 (URN)10.1007/s00217-016-2728-7 (DOI)2-s2.0-84975221929 (Scopus ID)
Available from: 2016-12-22 Created: 2016-12-21 Last updated: 2023-10-06Bibliographically approved
Hamngren Blomqvist, C., Gebäck, T., Altskär, A., Hermansson, A.-M., Gustafsson, S., Loren, N. & Olsson, E. (2017). Interconnectivity imaged in three dimensions: Nano-particulate silica-hydrogel structure revealed using electron tomography. Micron, 100, 91-105
Open this publication in new window or tab >>Interconnectivity imaged in three dimensions: Nano-particulate silica-hydrogel structure revealed using electron tomography
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2017 (English)In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, Vol. 100, p. 91-105Article in journal (Refereed) Published
Abstract [en]

We have used Electron Tomography (ET) to reveal the detailed three-dimensional structure of particulate hydrogels, a material category common in e.g. controlled release, food science, battery and biomedical applications. A full understanding of the transport properties of these gels requires knowledge about the pore structure and in particular the interconnectivity in three dimensions, since the transport takes the path of lowest resistance. The image series for ET were recorded using High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM). We have studied three different particulate silica hydrogels based on primary particles with sizes ranging from 3.6 nm to 22 nm and with pore-size averages from 18 nm to 310 nm. Here, we highlight the nanostructure of the particle network and the interpenetrating pore network in two and three dimensions. The interconnectivity and distribution of width of the porous channels were obtained from the three-dimensional tomography studies while they cannot unambiguously be obtained from the two-dimensional data. Using ET, we compared the interconnectivity and accessible pore volume fraction as a function of pore size, based on direct images on the nanoscale of three different hydrogels. From this comparison, it was clear that the finest of the gels differentiated from the other two. Despite the almost identical flow properties of the two finer gels, they showed large differences concerning the accessible pore volume fraction for probes corresponding to their (two-dimensional) mean pore size. Using 2D pore size data, the finest gel provided an accessible pore volume fraction of over 90%, but for the other two gels the equivalent was only 10–20%. However, all the gels provided an accessible pore volume fraction of 30–40% when taking the third dimension into account.

Keywords
Accessible volume fraction, Colloidal silica gel, Electron tomography, Interconnectivity, Porous soft materials, Silica nanoparticle gel, Electric impedance tomography, Electrons, High resolution transmission electron microscopy, Medical applications, Pore size, Scanning electron microscopy, Silica, Silica gel, Tomography, Transmission electron microscopy, Volume fraction, Accessible volume, Colloidal silica, Silica nanoparticles, Soft material, Hydrogels
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-30813 (URN)10.1016/j.micron.2017.04.012 (DOI)2-s2.0-85019875116 (Scopus ID)
Available from: 2017-08-23 Created: 2017-08-23 Last updated: 2023-10-06Bibliographically approved
Qasi, W., Wiklund, J., Ekberg, O., Altskär, A. & Stading, M. (2017). Shear and extensional rheology of commercial thickeners used for dysphagia management. Journal of texture studies, 48(6), 507-517
Open this publication in new window or tab >>Shear and extensional rheology of commercial thickeners used for dysphagia management
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2017 (English)In: Journal of texture studies, ISSN 0022-4901, E-ISSN 1745-4603, Vol. 48, no 6, p. 507-517Article in journal (Refereed) Published
Abstract [en]

People who suffer from swallowing disorders, commonly referred to as dysphagia, are often restricted to a texture-modified diet. In such a diet, the texture of the fluid is modified mainly by the addition of gum or starch-based thickeners. For optimal modification of the texture, tunable rheological parameters are shear viscosity, yield stress, and elasticity. In this work, the flow properties of commercial thickeners obtained from major commercial suppliers were measured both in shear and extensional flow using a laboratory viscometer and a newly developed tube viscometry technique, termed Pulsed Ultrasound Velocimetry plus Pressure Drop (PUV+PD). The two methods gave similar results, demonstrating that the PUV+PD technique can be applied to study flow during the swallowing process in geometry similar to that of the swallowing tract. The thickeners were characterized in relation to extensional viscosity using the Hyperbolic Contraction Flow (HCF) method, with microscopy used as a complementary method for visualization of the fluid structure. The gum-based thickeners had significantly higher extensional viscosities than the starch-based thickeners. The rheological behavior was manifested in the microstructure as a hydrocolloid network with dimensions in the nanometer range for the gum-based thickeners. The starch-based thickeners displayed a granular structure in the micrometer range. In addition, the commercial thickeners were compared to model fluids (Boger, Newtonian and Shear-thinning) set to equal shear viscosity at 50s−1 and it was demonstrated that their rheological behavior could be tuned between highly elastic, extension-thickening to Newtonian. This article is protected by copyright. All rights reserved.

Keywords
Dysphagia, thickeners, extensional viscosity, fluid elasticity, microstructure, velocity profile
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-29262 (URN)10.1111/jtxs.12264 (DOI)2-s2.0-85018743329 (Scopus ID)
Available from: 2017-04-07 Created: 2017-04-07 Last updated: 2023-10-06Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0009-0000-1671-4583

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