| 1. |
- Braide, M, et al.
(författare)
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Migration of human granulocytes in filters: effects of gravity and movable gradients of f-MLP
- 1994
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Ingår i: Biorheology. - THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD, ENGLAND OX5 1GB : PERGAMON-ELSEVIER SCIENCE LTD. - 0006-355X .- 1878-5034. ; 31:6, s. 617-630
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Tidskriftsartikel (refereegranskat)abstract
- The Boyden chamber technique for chemotaxis uses a mesh filter that constitutes a matrix for cell locomotion and, at the same time, creates a local restriction for convective fluid movements that allows the establishment of a diffusive concentration gradient of chemotactic substance in the filter. In the present study, the Boyden chamber was modified by the introduction of a filter sandwich that allowed cell migration both upwards and downwards and by the use of a fluid density gradient controlling cell buoyancy and mechanically supporting a movable chemotactic gradient. This method was used to study chemotaxis and random migration of human granulocytes under the influence of gravitational forces and movable gradients of f-MLP. The results show that gravity affected cell motion significantly during random migration but not during chemotaxis. The rate of chemotactic migration was dependent on the steepness of the spatio-temporal f-MLP gradients. A stationary spatial gradient produced less migration than a gradient that was slowly moved through the filter sandwich in a direction opposite to that of the cell migration. The presence of f-MLP at constant concentration caused a minor, statistically insignificant, increase of the rate of random migration.
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| 2. |
- Ebrahimzadeh, PR, et al.
(författare)
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A model of the dynamic mechanical responses of wood, paper and some polymers to moisture changes
- 1998
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Ingår i: Journal of Materials Science. - SPUIBOULEVARD 50, PO BOX 17, 3300 AA DORDRECHT, NETHERLANDS : KLUWER ACADEMIC PUBL. - 0022-2461 .- 1573-4803. ; 33:5, s. 1201-1209
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic mechanical responses of Scots pine, paper, PA6, cellophane, PVAc and PUR samples subjected to changes in the relative humidity of the surrounding air from 5 to 85% and vice versa have been analysed semiquantitatively on the basis of coupled non-linear rate equations for the moisture concentration in the sample as a function of the time. Important characteristics of the diffusion of moisture into and out of the samples have been studied by measuring the sample weight as a function of time. Moisture sorption results in sample swelling in Scots pine, paper, PA6, cellophane and PUR, for all of which mechanical loss peaks were detected. For PVAc, which does not bind moisture at load-bearing hydrogen bonding sites, no mechanical loss peak could be found. Characteristic of the mechanical loss at low vibration frequencies (0.01 to 1 Hz) is a peak immediately following a change in relative humidity for all studied sample materials except PVAc. This peak is almost certainly due to modulation of the number of load-bearing hydrogen bonds in the material. The relation between the width of the mechanical loss peak and the duration of the moisture sorption and desorption processes is interpreted according to an accepted model of two water molecule binding modes, one in which load-bearing hydrogen bonds are broken unimolecularly by water molecules and one in which further water molecules form clusters on the already unimolecularly bound water. (C) 1998 Chapman & Hall.
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| 3. |
- Ebrahimzadeh, PR, et al.
(författare)
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A subpopulation analysis of f-MLP stimulated granulocytes migrating in filters
- 1996
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Ingår i: Biorheology. - : IOS Press. - 0006-355X .- 1878-5034. ; 33:3, s. 231-250
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Tidskriftsartikel (refereegranskat)abstract
- Leukocyte migration in vitro has been studied extensively during many years without providing satisfactory theoretical models for the different migratory behaviors (chemotaxis and chemokinesis) of leukocyte populations. The present study utilized the fluid gradient chamber, which is a new method to study leukocyte migration in filters. Human neutrophils were applied between two stacked filters and migrated in all directions under the influence of constant concentrations or chemotactic gradients of f-MLP, maintained in fluid phase density gradients. The distributions of the granulocytes over filter depth were fitted to theoretical functions composed by 1-3 Gaussian distributions, representing subpopulations. The results showed that the neutrophils migrated as two discrete subpopulations during chemokinetic stimulation (a constant concentration of f-MLP). One of the subpopulations showed less active and passive (slow sedimentation under the influence of gravity) translocation. The most mobile subpopulation was divided into two new subpopulations when exposed to chemotactic stimulation (concentration gradient of f-MLP), one of which responded chemotactically and one of which migrated in random directions. The properties of the different subpopulations where characterized in terms of diffusion coefficient (random migration), convection velocity (chemotactic migration) and sedimentation coefficient (passive translocation).
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| 4. |
- Ebrahimzadeh, PR, et al.
(författare)
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Dynamic mechanical characterization of mechanosorptive effects in wood and paper
- 1996
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Ingår i: European Journal of Wood and Wood Products. - 0018-3768 .- 1436-736X. ; 54:4, s. 263-271
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic mechanical studies in dual cantilever and tensile stretching mode of Scots pine veneer, birch veneer and paper under stepwise humidity changes between 5% and 85% relative humidity are reported. The loss tangent (tan delta) shows a transient peak every time the relative humidity of the surrounding atmosphere is changed. In the bending mode a clamping arrangement that is freely movable in the longitudinal direction gives more distinct damping peaks than does a static fixture.There is a close relationship between the rate of sorption/desorption and the shape of the tan delta peak. In response to reduction of the rate of humidity change the damping transients slowly disappear. They also diminish in strength as the temperature is raised toward 60 degrees C. Their strengths increase as the measuring frequency is lowered toward 0.01 Hz. Also, when the samples are highly compressed or prestressed with static loads the peak heights are greatly reduced. The tans peaks become less distinct and eventually disappear when the amplitude of the vibration increases. Long time testing results in significant changes in the shapes of the tan delta versus time data.A working hypothesis is that these phenomena are closely related to molecular diffusion of water through the sample material. Simple estimates show that the relaxation time for a diffusion related process should be of the order of a minute.
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| 5. |
- Ebrahimzadeh, PR
(författare)
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Effect of impregnation on mechanosorption in wood and paper studied by dynamic mechanical analysis
- 1998
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Ingår i: Wood Science and Technology. - 175 FIFTH AVE, NEW YORK, NY 10010 USA : SPRINGER VERLAG. - 0043-7719 .- 1432-5225. ; 32:2, s. 101-118
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Tidskriftsartikel (refereegranskat)abstract
- The results of dynamic mechanical measurements in dual cantilever and uniaxial tension of untreated Scots pine veneer and unbleached sulphate paper under stepwise changes in the relative humidity of the surrounding atmosphere between 5% and 85% are compared to corresponding results for acetylated samples and samples treated by impregnation with poly(ethylene oxide) (PEO), glycerol or melamine formaldehyde resin. The treatments resulted in significant reductions in the transient mechanical losses associated with stepwise humidity changes. Although acetylation of wood and impregnation with PEO or glycerol both result in greatly improved dimensional stability with respect to humidity changes, the two types of treatment appear to be fundamentally different in terms of the models used here to interpret the results. We find that it is helpful to consider the dynamic process of moisture sorption/ desorption in these samples in terms of two coupled processes: the diffusion of moisture into or out of the sample, with a characteristic diffusion time given approximately by t* = (pi/16)h(2)/D where h is the sample thickness and D a characteristic diffusion constant for the moisture in the material, and the attachment/detachment of (clusters of) water molecules to binding sites in the samples, apparently with characteristic "chemical" relaxation times of the order of seconds or minutes. Clearly, when the sample thickness is quite small, 0.8 mm in our case, and the diffusion coefficient of the order of 50 x 10(-8) cm(2)/s, then the characteristic diffusion time is about 40 minutes, already for these small dimensions more than an order of magnitude larger than the characteristic "chemical" relaxation time. By varying the frequency of the dynamic mechanical measurements these characteristic processes for untreated and treated samples can be probed in some detail.
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| 6. |
- Ebrahimzadeh, PR, et al.
(författare)
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EFFECTS OF HUMIDITY CHANGES ON DAMPING AND STRESS-RELAXATION IN WOOD
- 1993
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Ingår i: Journal of Materials Science. - 2-6 BOUNDARY ROW, LONDON, ENGLAND SE1 8HN : CHAPMAN HALL LTD. - 0022-2461 .- 1573-4803. ; 28:20, s. 5668-5674
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical damping (tan delta) and stress relaxation on pine veneer samples under stepwise humidity changes were investigated. The loss factor shows a transient peak every time the relative humidity (RH) of the surrounding atmosphere is changed, The effect appears to be associated with the diffusion of water molecules into or out of the material, the peaks being observed both when the sample is humidified (5%-85% RH) or subjected to drying. The results are supplemented by stress relaxation data obtained on similar specimens. Also in this case a higher relaxation rate is observed when the RH level around the sample is changed, the total stress decrease after several cycles being significantly larger than the corresponding value observed after the same period at the higher RH level.
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| 7. |
- Ebrahimzadeh, PR, et al.
(författare)
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Mechanosorptive effects in cellophane, polyamide 6 and some other polymers studied by dynamic mechanical analysis
- 1997
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Ingår i: Journal of Materials Science. - 2-6 BOUNDARY ROW, LONDON, ENGLAND SE1 8HN : CHAPMAN HALL LTD. - 0022-2461 .- 1573-4803. ; 32:16, s. 4227-4235
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic mechanical data obtained in the tensile mode with cellophane, polyamide 6, PEG, PVAc and PUR foam (compression) subjected to stepwise humidity changes between 5% and 85% relative humidity are reported. With the exception of PVAc, the loss tangent, tan delta, shows a transient peak every time the relative humidity of the surrounding atmosphere is changed. The strength of the tan delta transients increases when the measuring frequency is lowered. The tan delta transients slowly disappear in response to reduction of the rate of humidity change. High amplitude and prestress with static load reduce the height of the transient peaks. Long-term testing results in relatively small changes in the shape of the loss tangent versus time data. For PA6 a narrowing of the loss tangent peaks with diminishing specimen thickness was observed.
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