8 research outputs found
Structural Changes in Cylinder-Forming PS-b-PB Thin Films During Solvent Vapor Annealing
No full textThe orientational changes of cylinders in Polystyrene-b-Polybutadiene (PS-b-PB) diblock copolymer thin films during solvent vapor annealing (SVA) was investigated using White- Light Interferometry (WLI) and time-resolved grazing-incidence small-angle x-ray scattering (GISAXS). The SVA procedure was performed with three different solvents of varying selec- tivity to the two blocks: Ethyl Acetate (EAC), Toluene (TOL) and Cyclohexane (CHX). A change from standing to lying cylinders was found using all three solvents. The orientational change appears to depend on the minimal polymer volume fraction phi_min of the film, and different threshold values were found for each solvent: phi_min,EAC = 0.66, phi_min,TOL = 0.63, phi_min,CHX = 0.49. In one experiment with CHX, the switch from standing to lying cylin- ders happens through a disordered phase spanning 15 minutes. This, along with other circumstantial evidence, hints at the timescales of structural changes.The orientational changes of cylinders in Polystyrene-b-Polybutadiene (PS-b-PB) diblock copolymer thin films during solvent vapor annealing (SVA) was investigated using White- Light Interferometry (WLI) and time-resolved grazing-incidence small-angle x-ray scattering (GISAXS). The SVA procedure was performed with three different solvents of varying selec- tivity to the two blocks: Ethyl Acetate (EAC), Toluene (TOL) and Cyclohexane (CHX). A change from standing to lying cylinders was found using all three solvents. The orientational change appears to depend on the minimal polymer volume fraction phi_min of the film, and different threshold values were found for each solvent: phi_min,EAC = 0.66, phi_min,TOL = 0.63, phi_min,CHX = 0.49. In one experiment with CHX, the switch from standing to lying cylin- ders happens through a disordered phase spanning 15 minutes. This, along with other circumstantial evidence, hints at the timescales of structural changes
Allergivenligt GMO-Græs?: Using GMO-grass to aid allergic patients?
No full textRapporten giver et indblik i, hvilke muligheder der er for at genmodificere græs til glæde for allergikere. Gennem beskrivelse og analyse af igangværende projekter prøver rapporten at diskutere og perspektivere aspekterne i problemstillingen. Diskussionen tager udgangspunkt i de naturvidenskabelige problemer i at udvikle og produdere af et eventuelt produkt, mens perspektiveringen inddrager de politiske og etiske sider af sagen. Analyse gennemgås ved hjælp af en række emner. Under emnet allergi bliver der taget fat i ting som IgE-respons og en beskrivelse af allergener og epitoper. Under emnet genteknologi beskrives anti-sense, shotgun-metoden og revers transkriptase. Derudover er der også eksempler på brug af λ-fag-vira og E. coli-bakterier til indsættelse gener. Rapporten sluttes af med et forsøg på at finde en optimal løsning på problemstillingen.Rapporten giver et indblik i, hvilke muligheder der er for at genmodificere græs til glæde for allergikere. Gennem beskrivelse og analyse af igangværende projekter prøver rapporten at diskutere og perspektivere aspekterne i problemstillingen. Diskussionen tager udgangspunkt i de naturvidenskabelige problemer i at udvikle og produdere af et eventuelt produkt, mens perspektiveringen inddrager de politiske og etiske sider af sagen. Analyse gennemgås ved hjælp af en række emner. Under emnet allergi bliver der taget fat i ting som IgE-respons og en beskrivelse af allergener og epitoper. Under emnet genteknologi beskrives anti-sense, shotgun-metoden og revers transkriptase. Derudover er der også eksempler på brug af λ-fag-vira og E. coli-bakterier til indsættelse gener. Rapporten sluttes af med et forsøg på at finde en optimal løsning på problemstillingen
Solvent Vapor Annealing of a Diblock Copolymer Thin Film with a Nonselective and a Selective Solvent:Importance of Pathway for the Morphological Changes
No full textDiblock copolymer thin films of polystyrene-block-poly(dimethyl siloxane)(PS-b-PDMS) featuring PDMS cylinders in a PS matrix are investigated duringsolvent vapor annealing with mixtures of n-heptane (which is strongly selectivefor PDMS) and toluene (which is close to nonselective for both blocks).Swelling in the vapor of one of the pure solvents and exchanging it stepwise bythe vapor of the other solvent is compared to swelling in a given binary solventvapor mixture for a prolonged time. The resulting structural changes, such asordering of the cylinders on a hexagonal lattice and their transition into lamellae, are followed using in situ, real-time grazing-incidence small-angle X-ray scattering (GISAXS). In three runs, the sequence of solvent vapor swelling and vapor exchange is varied. Compiling the resulting morphologies in a diagram of states in dependence on the solvent content in the film and in the minority nanodomains allows insight into the role of the glass transition of the PS matrix for the ordering processes and their time scales. Based on these findings, a protocol is suggested to efficiently obtain an order-to-order transition from the cylindrical morphology with random domain orientation to the oriented lamellar state.Diblock copolymer thin films of polystyrene‐block‐poly(dimethyl siloxane) (PS‐b‐PDMS) featuring PDMS cylinders in a PS matrix are investigated during solvent vapor annealing with mixtures of n‐heptane (which is strongly selective for PDMS) and toluene (which is close to nonselective for both blocks). Swelling in the vapor of one of the pure solvents and exchanging it stepwise by the vapor of the other solvent is compared to swelling in a given binary solvent vapor mixture for a prolonged time. The resulting structural changes, such as ordering of the cylinders on a hexagonal lattice and their transition into lamellae, are followed using in situ, real‐time grazing‐incidence small‐angle X‐ray scattering (GISAXS). In three runs, the sequence of solvent vapor swelling and vapor exchange is varied. Compiling the resulting morphologies in a diagram of states in dependence on the solvent content in the film and in the minority nanodomains allows insight into the role of the glass transition of the PS matrix for the ordering processes and their time scales. Based on these findings, a protocol is suggested to efficiently obtain an order‐to‐order transition from the cylindrical morphology with random domain orientation to the oriented lamellar state
Vidensproduktionens Udvikling: Grundforskning vs Anvendt Forskning: The Progress of Knowledge Production – Basic Research vs. Applied Research
No full textFormålet med dette projekt er at finde ud af, hvordan vidensproduktionen har ændret sig i forhold til anvendt forskning og grundforskning. Motivationen udspringer fra den nye universitetsreform, som derfor beskrives sammen med en række sociologiske tekster med udgangspunkt i Modus 2-begrebet. På denne baggrund belyses to naturvidenskabelige cases ud fra tre parametre - forskningsstrategi, midler og publikationer. Ved en analyse af de offentlige midler finder man indikationer på, at der generelt bliver bedre vilkår for anvendte forskningsprojekter. En kvantitativ analyse af publikationer i tidsskriftet »Science« viser, at forskningen i perioden 1999-2005 er blevet mere tværfaglig, og udføres i større grupper. Disse analyser suppleres med interviews af henholdsvis forsker og forskningsleder i hver af vores to cases for at give en ide, om hvor vidensproduktionen er på vej hen. Disse parametre peger i retning af, at vidensproduktionen fortsat bevæger sig mod en større anvendelse og kontekst i samfundet. Grundforskningen får dårligere kår, og den internationale disciplinære forskning nedprioriteres i Danmark.Formålet med dette projekt er at finde ud af, hvordan vidensproduktionen har ændret sig i forhold til anvendt forskning og grundforskning. Motivationen udspringer fra den nye universitetsreform, som derfor beskrives sammen med en række sociologiske tekster med udgangspunkt i Modus 2-begrebet. På denne baggrund belyses to naturvidenskabelige cases ud fra tre parametre - forskningsstrategi, midler og publikationer. Ved en analyse af de offentlige midler finder man indikationer på, at der generelt bliver bedre vilkår for anvendte forskningsprojekter. En kvantitativ analyse af publikationer i tidsskriftet »Science« viser, at forskningen i perioden 1999-2005 er blevet mere tværfaglig, og udføres i større grupper. Disse analyser suppleres med interviews af henholdsvis forsker og forskningsleder i hver af vores to cases for at give en ide, om hvor vidensproduktionen er på vej hen. Disse parametre peger i retning af, at vidensproduktionen fortsat bevæger sig mod en større anvendelse og kontekst i samfundet. Grundforskningen får dårligere kår, og den internationale disciplinære forskning nedprioriteres i Danmark
Multiple scattering camouflaged as magnetic stripes in single crystals of superconducting (La,Sr)<sub>2</sub>CuO<sub>4</sub>
No full textNeutron diffraction has been a very prominent tool to investigate high-temperature superconductors, in particular through the discovery of an incommensurate magnetic signal known as stripes. We here report the findings of a neutron diffraction experiment on the superconductor (La,Sr)2CuO4, where a spurious signal appeared to be magnetic stripes. The signal strength was found to be strongly dependent on the neutron energy, peaking at E = 4.6 meV. We therefore attribute the origin of this signal to be a combination of multiple scattering and crystal twinning. A forward calculation of the scattering intensity including these two effects almost completely recovers our experimental observations. We emphasize the need for employing such analysis when searching for ways to avoid spurious scattering signals.</p
Gradual emergence of superconductivity in underdoped LSCO
No full textWe present triple-axis neutron scattering studies of low-energy magnetic
fluctuations in strongly underdoped LaSrCuO with ,
and , providing quantitative evidence for a direct competition
between these fluctuations and superconductivity. At dopings and
, three-dimensional superconductivity is found, while only a very weak
signature of two-dimensional superconductivity residing in the CuO planes
is detectable for . We find a surprising suppression of the low-energy
fluctuations by an external magnetic field at all three dopings. This implies
that the response of two-dimensional superconductivity to a magnetic field is
similar to that of a bulk superconductor. Our results provide direct evidence
of a very gradual onset of superconductivity in cuprates.Comment: 5 pages, 4 figures, and supplementary materia
Magnetic structure and excitations of the topological semimetal YbMnBi2
No full textWe investigated the magnetic structure and dynamics of YbMnBi2, with elastic and inelastic neutron
scattering, to shed light on the topological nature of the charge carriers in the antiferromagnetic phase. We
confirm C-type antiferromagnetic ordering of the Mn spins below TN = 290 K and determine that the spins
point along the c axis to within about 3◦. The observed magnon spectrum can be described very well by the
same effective spin Hamiltonian that was used previously to model the magnon spectrum of CaMnBi2. Our
results show conclusively that the creation of Weyl nodes in YbMnBi2 by the time-reversal symmetry-breaking
mechanism can be excluded in the bulk
Nature of the magnetic stripes in fully oxygenated La<sub>2</sub>CuO<sub>4+y</sub>
No full textWe present triple-axis neutron scattering studies of static and dynamic magnetic stripes in an optimally oxygen-doped cuprate superconductor, La2CuO4+y, which exhibits a clean superconducting transition at Tc=42K. Polarization analysis reveals that the magnetic stripe structure is equally represented along both of the tetragonal crystal axes and that the fluctuating stripes display significant weight for in-plane as well as out-of-plane spin components. Both static magnetic order as well as low-energy fluctuations are fully developed in zero applied magnetic field and the low-energy spin fluctuations at ω=0.3-10meV intensify on cooling. We interpret this as an indication that superconductivity and low-energy spin fluctuations coexist microscopically in spatial regions which are separated from domains with static magnetic order. </p
