| 1. |
- Tonpheng, Bounphanh, 1959-, et al.
(författare)
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Tensile strength and young's modulus of polyisoprene/single-wall carbon nanotube composites increased by high pressure cross-linking
- 2010
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 43:18, s. 7680-7688
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Tidskriftsartikel (refereegranskat)abstract
- High-viscosity liquid cis-1,4 polyisoprene (PI), with up to 20 wt % single-wall carbon nanotubes (SWCNTs), has been cross-linked by high pressure and high temperature (HP&HT) treatment at 513 K and pressures in the range 0.5 to 1.5 GPa to yield densified network polymer composites. A composite with 5 wt % SWCNTs showed 2.2 times higher tensile strength σUTS (σUTS = 17 MPa), 2.3 times higher Young’s modulus E (E = 220 MPa) and longer extension at break than pure PI. The improvement is attributed to SWCNT reinforcement and improved SWCNT−PI interfacial contact as a result of the HP&HT cross-linking process, and reduced brittleness despite a higher measured cross-link density than that of pure PI. The latter may originate from an effect similar to crazing, i.e., bridging of microcracks by polymer fibrils. We surmise that the higher cross-link densities of the composites are due mainly to physical cross-links/constraints caused by the SWCNT−PI interaction, which also reflects the improved interfacial contact, and that the CNTs promote material flow by disrupting an otherwise chemically cross-linked network. We also deduce that the PI density increase at HP&HT cross-linking is augmented by the presence of CNTs.
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| 2. |
- Andersson, Bengt Olof, et al.
(författare)
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The reference step method for DC voltage at 1 mV and 10 mV
- 2014
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Ingår i: CPEM Digest (Conference on Precision Electromagnetic Measurements). - : Institute of Electrical and Electronics Engineers Inc.. - 9781479952052 ; , s. 520-521
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Konferensbidrag (refereegranskat)abstract
- We have investigated the performance of a method called the Reference Step Method at low voltage levels. The method has been evaluated earlier at voltage levels from 0.1 V to 1 kV with excellent results. The advantages of this method are that it uses commonly available equipment and can be fully automated. We have made comparisons with three other low-voltage methods and the differences show that the uncertainties can be less than 30 μV/V at 1 mV and 3 μV/V at 10 mV, making it possible to use this method to perform automated calibration of calibrators with sufficient accuracy for calibration of high-end instruments.
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| 3. |
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| 4. |
- Andersson, Ove, et al.
(författare)
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Effect of pressure on thermal conductivity and pressure collapse of ice in a polymer-hydrogel and kinetic unfreezing at 1 GPa
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:12, s. 124903-
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Tidskriftsartikel (refereegranskat)abstract
- We report a study of aqueous solutions of poly(vinylalcohol) and its hydrogel by thermal conductivity,κ, and specific heat measurements. In particular, we investigate (i) the changes in the solution and the hydrogel at 0.1 MPa observed in the 350-90 K range and of the frozen hydrogel at 130 K observed in the range from 0.1 MPa to 1.3 GPa, and (ii) the nature of the pressure collapse of ice in the frozen hydrogel and kinetic unfreezing on heating of its high density water at 1 GPa. The water component of the polymer solution on cooling either first phase separates and then freezes to hexagonal ice or freezes without phase separation and the dispersed polymer chains freeze-concentrate in nanoscopic and microscopic regions of the grain boundaries and grain junctions of the ice crystals in the frozen state of water in the hydrogel. The change in κ with temperature at 1 bar is reversible with some hysteresis, but not reversible with pressure after compression to 0.8 GPa at 130 K. At high pressures the crystallized state collapses showing features of. and specific heat characteristic of formation of high density amorphous solid water. The pressure of structural collapse is 0.08 GPa higher than that of ice at 130 K. The slowly formed collapsed state shows kinetic unfreezing or glass-liquid transition temperature at 140 K for a time scale of 1 s. Comparison with the change in the properties observed for ice shows that κ decreases when the polymer is added.
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| 5. |
- Andersson, Ove, et al.
(författare)
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Effects of pressure and temperature on the thermal conductivity of Sn2P2S6
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:13
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity kappa of the ferroelectric, paraelectric, and incommensurate phases of polycrystalline Sn2P2S6 has been measured in the 0.1-0.7 GPa range. The thermal conductivity kappa of the ferroelectric phase decreases with increasing pressure p. This unusual behavior, which is found in only a few other phases, is attributed to a negative Gruneisen parameter. The temperature T dependence of kappa for the ferroelectric phase (kappa similar to T-1) is well described by the Debye model for kappa, with three-phonon Umklapp scattering serving as the dominant scattering mechanism near and above the Debye temperature (similar to 100 K) up to a few tenths of degrees below the ferro- to paraelectric phase transition, where kappa(T) gradually changes and becomes temperature independent upon further heating. The thermal conductivity of the paraelectric and incommensurate phases was temperature independent and indistinguishable. Possible causes for the unusually weak T dependence at high temperatures and implications of the p dependence of kappa are discussed.
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| 6. |
- Andersson, Ove
(författare)
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Glass-liquid transition of water at high pressure
- 2011
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:27, s. 11013-11016
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Tidskriftsartikel (refereegranskat)abstract
- The knowledge of the existence of liquid water under extreme conditions and its concomitant properties are important in many fields of science. Glassy water has previously been prepared by hyperquenching micron-sized droplets of liquid water and vapor deposition on a cold substrate (ASW), and its transformation to an ultraviscous liquid form has been reported on heating. A densified amorphous solid form of water, high-density amorphous ice (HDA), has also been made by collapsing the structure of ice at pressures above 1 GPa and temperatures below approximately 140 K, but a corresponding liquid phase has not been detected. Here we report results of heat capacity C(p) and thermal conductivity, in situ, measurements, which are consistent with a reversible transition from annealed HDA to ultraviscous high-density liquid water at 1 GPa and 140 K. On heating of HDA, the Cp increases abruptly by (3.4 ± 0.2) J mol-1 K-1 before crystallization starts at (153 ± 1) K. This is larger than the Cp rise at the glass to liquid transition of annealed ASW at 1 atm, which suggests the existence of liquid water under these extreme conditions.
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| 7. |
- Andersson, Ove, et al.
(författare)
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Glass Transitions in Pressure-Collapsed Ice Clathrates and Implications for Cold Water
- 2012
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Ingår i: Journal of Physical Chemistry Letters. - Washington : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 3:15, s. 1951-1955
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Tidskriftsartikel (refereegranskat)abstract
- Ice is known to collapse to amorphous ice upon pressurization at low temperatures and shows the unusual feature of multiple distinct solid amorphous water states, which have inspired models of liquid water’s structure and unusual properties.Here, we use heat capacity Cp measurements to show that similarly collapsed ice clathrates display identical glass behavior as amorphous ice but that crystallization above the glass transition temperature Tg of ∼140 K at 1 GPa is inhibited. This effect of the homogeneously distributed “guest molecules” in water reveals a relatively strong reversible Cp increase above Tg but no further transition before crystallization at ∼190 K.This is consistent with a glass−liquid transition of water at Tg, which suggests a new path to study an ultraviscous liquid water network and evaluate water models
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| 8. |
- Andersson, Ove, et al.
(författare)
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Phase coexistence and hysteresis effects in the pressure-temperature phase diagram of NH3BH3
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:2, s. 024115-
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Tidskriftsartikel (refereegranskat)abstract
- The potential hydrogen storage compound NH3BH3 has three known structural phases in the temperature and pressure ranges 110–300 K and 0–1.5 GPa, respectively. We report here the boundaries between, and the ranges of stability of, these phases. The phase boundaries were located by in situ measurements of the thermal conductivity, while the actual structures in selected areas were identified by in situ Raman spectroscopy and x-ray diffraction. Below 0.6 GPa, reversible transitions involving only small hysteresis effects occur between the room-temperature tetragonal plastic crystal I4mm phase and the low-temperature orthorhombic Pmn21 phase. Transformations of the I4mm phase into the high-pressure orthorhombic Cmc21 phase, occurring above 0.8 GPa, are associated with very large hysteresis effects, such that the reverse transition may occur at up to 0.5 GPa lower pressures. Below 230 K, a fraction of the Cmc21 phase is metastable to atmospheric pressure, suggesting the possibility that dense structural phases of NH3BH3, stable at room temperature, could possibly be created and stabilized by alloying or by other methods. Mixed orthorhombic Pmn21/Cmc21 phases were observed in an intermediate pressure-temperature range, but a fourth structural phase predicted by Filinchuk et al. [ Phys. Rev. B 79 214111 (2009)] was not observed in the pressure-temperature ranges of this experiment. The thermal conductivity of the plastic crystal I4mm phase is about 0.6 W m−1 K−1 and only weakly dependent on temperature, while the ordered orthorhombic phases have higher thermal conductivities limited by phonon-phonon scattering.
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| 9. |
- Andersson, Ove, et al.
(författare)
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Thermal Properties and Transition Behavior of Host –Guest Compounds under High Pressure
- 2014
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Ingår i: Current inorganic chemistry. - : Bentham Science Publishers Ltd.. - 1877-9441. ; 4:1, s. 2-18
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The thermal properties and transition behavior of the host-guest inclusion compounds: urea, thiourea, Dianin’s compound, clathrate hydrates and hydroquinone have been reviewed. In particular, we summarize their thermal conductivities, heat capacities and transitions at high pressures. Two of the systems: urea inclusion compounds and clathrate hydrates, show unusual glass-like thermal conductivity k, i.e. their k is low and only weakly dependent on temperature despite their crystalline structure. Moreover, results for k of Dianin’s compound with guests such as ethanol and CCl4 indicate a change from glass-like k at atmospheric pressure to crystalline-like k at elevated pressure, whereas k of hydroquinone and thiourea inclusion compounds appears not to have been studied. Despite the technological and fundamental importance of the unusual glass-like k, e.g. the use of inclusion compounds as structural model systems for finding improved thermoelectrical materials, the origin of the glass-like k is not established. More specifically, the commonly employed rattling model, in which rattling guest motions cause resonance scattering of the acoustic host phonons, has recently been challenged, and we discuss alternative models. Heat capacity studies of these compounds reveal numerous transitions, which are associated with guest and host disorder-order transitions upon cooling and pressurization. A transition in hydroquinone may be of second order, or have only a small first-order component, which can explain discrepancies in the observed transition behavior. On pressurization at low temperatures, clathrate hydrates collapse to an amorphous state, which appears to be a glassy state of a water solution with perfectly spaced solute molecules.
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| 10. |
- Andersson, Sten-Ove, et al.
(författare)
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Doctors’ and Nurses’ Perceptions of Military Pre-hospital Emergency Care
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study was to identify physicians’ and nurses’ perceptions of military prehospital emergency care before and after an international mission. A qualitative empirical study with a phenomenographic approach was used. The aim is to identify the area of knowledge, pre-hospital care in a military environment, in terms of expressions from doctors and nurses focussing on the variation in how learning of pre-hospital care is perceived. The result of the study is a set of descriptive categories on a collective level, showing the variation in how doctors and nurses perceived the phenomenon of military pre-hospital emergency care. The results after predeployment training can be categorized as (1) to learn military medicine, (2) to take care of the casualty and (3) to have safety awareness. The results after an international mission can be categorized as (1) to collaborate with others, (2) to deliver general health care, and (3) to improve competence in military medicine. Possible implications of the results from the present study are the following; (I) better conditions for doctors and nurses to provide appropriate military medical care by clarification and better understanding of professions in the mission area (doctors, nurses, officers), since they may have different goals for their actions, (II) to pay attention to all aspects of military health care during predeployment training, including general health care in the mission area, (III) to implement new knowledge in military medicine in the predeployment training, and (IV) to train for the reality all doctors and nurses are about to meet. These results indicate that the training should be developed in order to optimize the prepare physicians and nurses for international assignments. This may result in increased safety for the provider of care, while at the same time minimizing suffering and enhancing the possibility of survival of the injured.
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