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- Al-Manasir, Nodar, et al.
(författare)
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Effects of Temperature and pH on the Contraction and Aggregation of Microgels in Aqueous Suspensions
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:32, s. 11115-11123
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Tidskriftsartikel (refereegranskat)abstract
- Chemically cross-linked poly(N-isopropylacrylamide) (PNIPAM) microgels and PNIPAM with different amounts of acrylic acid groups (PNIPAM-co-PAA) were synthesized and the temperature-induced aggregation behaviors of aqueous suspensions of these microgels were investigated mainly with the aid of dynamic light scattering (DLS) and turbidimetry. The DLS results show that the particles at all conditions shrink at temperatures up to approximately the lower critical solution temperature (LCST), but the relative contraction effect is larger for the microgels without acid groups or for microgels with added anionic surfactant (SDS). A significant depression of the cloud point is found in suspensions of PNIPAM with very low concentrations of SDS. The compression of the microgels cannot be traced from the turbidity results, but rather the values of the turbidity increase in this temperature interval. This phenomenon is discussed in the framework of a theoretical model. At temperatures above LCST, the size of the microgels without attached charged groups in a very dilute suspension is unaffected by temperature, while the charged particles (pH 7 and 11) continue to collapse with increasing temperature over the entire domain. In this temperature range, low-charged particles of higher concentration and particles containing acrylic acid groups at low pH (pH 2) aggregate, and macroscopic phase separation is approached at higher temperatures. This study demonstrates how the stabilization of microgels can be affected by factors such as polymer concentration, addition of ionic surfactant to particles without charged acid groups, amount of charged groups in the polymer, and pH.
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| 2. |
- Nyström, Henrik, 1977, et al.
(författare)
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Platelet-derived growth factor B retention is essential for development of normal structure and function of conduit vessels and capillaries
- 2006
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Ingår i: Cardiovasc Res. - : Oxford University Press (OUP). - 0008-6363. ; 71:3, s. 557-65
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Extracellular retention of PDGF-B has been proposed to play an important role in PDGF-B signalling. We used the PDGF-B retention motif knockout mouse (RetKO) to study the effects of retention motif deletion on development of micro- and macrovascular structure and function. METHODS: Passive and active properties of conduit vessels were studied using myograph techniques and histological examination. Capillary structure and function was studied using measurements of capillary density in skeletal muscle and by assessing aerobic physical performance in a treadmill setup. Cardiac function was assessed using echocardiography. RESULTS: Myograph experiments revealed an increased diameter and stiffness of the aorta in RetKO. Histological examination showed increased media collagen content and a decreased number of aortic wall layers, however with a similar number of vascular smooth muscle cells. This outward eutrophic remodelling of the aorta was accompanied by endothelial dysfunction. RetKO showed decreased capillary density in skeletal muscle and signs of a defective delivery of capillary oxygen to skeletal muscle, as shown by a decreased physical performance. In RetKO mice, echocardiography revealed an adaptive eccentric cardiac hypertrophy. CONCLUSION: We conclude that retention of PDGF-B during development is essential for a normal conduit vessel function in the adult mouse. Furthermore, PDGF-B retention is also necessary for the development of an adequate capillary density, and thereby for a normal oxygen delivery to skeletal muscle. The lack of primary effects on cardiac function supports the redundant role of PDGF-B in cardiac development.
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| 3. |
- Nyström, Henrik, 1977, et al.
(författare)
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Short-term administration of growth hormone (GH) lowers blood pressure by activating eNOS/nitric oxide (NO)-pathway in male hypophysectomized (Hx) rats
- 2005
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Ingår i: BMC Physiol. - : Springer Science and Business Media LLC. - 1472-6793. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The aim of the study was to evaluate the acute and continuous (up to 14 days of treatment) effect of growth hormone (GH) on blood pressure (BP) regulation and to investigate the interplay between GH, nitric oxide (NO) and BP. In un-supplemented and GH supplemented hypophysectomized (Hx) male rats as well as intact rats, continuous resting mean arterial blood pressure (MAP) was measured using telemetry. Baroreceptor activity and the influences of NO on BP control were assessed during telemetric measurement. Furthermore, basal plasma and urine nitrate levels and aortic endothelial nitric oxide synthase (eNOS) expression were analysed. Endothelial function as well as vascular structure in the hindquarter vascular bed was estimated using an in vivo constant-flow preparation. RESULTS: Hypophysectomy was associated with decreased MAP (Hx: 83 +/- 3 vs Intact: 98 +/- 6 mmHg, p < 0.05) and heart rate (HR) (Hx: 291 +/- 4 vs Intact: 351 +/- 7 beat/min, p < 0.05). Endothelial dysfunction and reduced vasculature mass in the hindquarter vascular bed was found in Hx rats. GH substitution caused a further transient decrease in MAP and a transient increase in HR (14% and 16% respectively, p < 0.05). The reduction in MAP appeared to be NO dependent. Aortic eNOS expression was unchanged. GH substitution resulted in an impaired baroreceptor function. Two weeks of GH treatment did not normalise the BP, vascular structure and the endothelial function in the resistance vessels. CONCLUSION: GH substitution seems to have a short lasting effect on lowering blood pressure via activation of the NO-system. An interaction between GH, NO-system and BP regulation can be demonstrated.
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| 9. |
- Nyström, Marcus, et al.
(författare)
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Semantic override of low-level features in image viewing - both initially and overall
- 2008
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Ingår i: Journal of Eye Movement Research. - 1995-8692. ; 2:2, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Guidance of eye-movements in image viewing is believed to be controlled by stimulus driven factors as well as viewer dependent higher level factors such as task and memory. It is currently debated to what proportions these factors contribute to gaze guidance, and also how they vary over time after image onset. Overall, the unanimity regarding these issues is surprisingly low and there are results supporting both types of factors as being dominant in eye-movement control under certain conditions. We investigate in this paper how low, and high level factors influence eye guidance by manipulating contrast statistics on images from three different semantic categories and measure how this affects fixation selection. Our results show that the degree to which contrast manipulations affect fixation selection heavily depends on an image’s semantic content, and how this content is distributed over the image. Over the three image categories, we found no systematic differences between contrast and edge density at fixated location compared to control locations, neither during the initial fixation nor over the whole time course of viewing. These results suggest that cognitive factors easily can override low-level factors in fixation selection, even when the viewing task is neutral.
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| 10. |
- Nyström, Marcus, et al.
(författare)
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Variable resolution images and their effects on eye-movements during free-viewing
- 2007
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6492, s. 49216-49216
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Konferensbidrag (refereegranskat)abstract
- Earlier studies have shown that while free-viewing images people tend to gaze at regions with a high local density of bottom up features such as contrast and edge density. In particular, this tendency seems to be more emphasized during the first few fixations after image onset. In this paper, we present a new method to investigate how gaze locations are chosen by introducing varying image resolution, and measure how it affects eye-movement behavior during free viewing. Results show that gaze density overall is shifted toward regions presented in high resolution over those degraded in resolution. However, certain image regions seem to attract early fixations regardless of display resolution. These results suggest that top-down control of gaze guidance may be the dominant factor early in visual processing. © 2007 SPIE-IS and T.
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