1,060 research outputs found
Quantum Correlated Interstitials and the Hall Resistivity of the Magnetically Induced Wigner Crystal
We study a trial wavefunction for an interstitial in a Wigner crystal. We
find that the electron correlations, ignored in a conventional Hartree-Fock
treatment, dramatically lower the interstitial energy, especially at fillings
close to an incompressible liquid state. The correlation between the
interstitial electron and the lattice electrons at is introduced by
constructing a trial wave- function which bears a Jastrow factor of a Laughlin
state at . For fillings close to but just below , we find
that a perfect Wigner crystal becomes unstable against formation of such
interstitials. It is argued that conduction due to correlated interstitials in
the presence of weak disorder leads to the {\it classical} Hall resistivity, as
seen experimentally.Comment: 10 pages, RevTe
Wigner Crystals Phases in Bilayer Quantum Hall Systems
(This is a substantially shortened version of the original abstract:)
The Wigner crystal phase diagram of the bilayer systems have been studied
using variational methods. Five crystal phases are obtained. As the layer
spacing increases, the system will undergo a sequence of phase transitions. A
common feature of most bilayer Wigner crystals is that they have mixed
(pseudo-spin) ferromagnetic and antiferromagnetic order.Comment: 19 figures. Figures will be provided upon request. Submitted in PRB
in Nov 94
Oil-in-oil pickering emulsions stabilized by diblock copolymer nanoparticles
Hypothesis
Diblock copolymer nanoparticles have been shown to be Pickering emulsifiers for both oil-in-water and water-in-oil emulsions. Recently, we reported the preparation of sterically-stabilized diblock copolymer spheres in a low-viscosity silicone oil (Macromolecules 53 (2020) 1785–1794). We hypothesized that such spheres could be used as a Pickering emulsifier for a range of oil-in-oil emulsions comprising droplets of a bio-sourced oil dispersed in silicone oil.
Experiments
Diblock copolymer spheres were prepared via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate in silicone oil and characterized by dynamic light scattering and transmission electron microscopy. These spheres were evaluated as Pickering emulsifiers for a series of oil-in-oil Pickering emulsions. The influence of both sphere size and core-forming block composition was investigated.
Findings
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Optimization of the nanoparticle size and core-forming block composition enabled stable bio-sourced oil-in-silicone emulsions to be obtained for nine out of the ten bio-sourced oils investigated. These emulsions were characterized in terms of their mean droplet size by optical microscopy
New insulating phases of two-dimensional electrons in high Landau levels: observation of sharp thresholds to conduction
The intriguing re-entrant integer quantized Hall states recently discovered
in high Landau levels of high-mobility 2D electron systems are found to exhibit
extremely non-linear transport. At small currents these states reflect
insulating behavior of the electrons in the uppermost Landau level. At larger
currents, however, a discontinuous and hysteretic transition to a conducting
state is observed. These phenomena, found only in very narrow magnetic field
ranges, are suggestive of the depinning of a charge density wave state, but
other explanations can also be constructed.Comment: 5 pages, 5 figure
The dual-acting chemotherapeutic agent Alchemix induces cell death independently of ATM and p53
YesTopoisomerase inhibitors are in common use as chemotherapeutic agents although they can display reduced efficacy in chemotherapy-resistant tumours, which have inactivated DNA damage response (DDR) genes, such as ATM and TP53. Here, we characterise the cellular response to the dual-acting agent, Alchemix (ALX), which is a modified anthraquinone that functions as a topoisomerase inhibitor as well as an alkylating agent. We show that ALX induces a robust DDR at nano-molar concentrations and this is mediated primarily through ATR- and DNA-PK- but not ATM-dependent pathways, despite DNA double strand breaks being generated after prolonged exposure to the drug. Interestingly, exposure of epithelial tumour cell lines to ALX in vitro resulted in potent activation of the G2/M checkpoint, which after a prolonged arrest, was bypassed allowing cells to progress into mitosis where they ultimately died by mitotic catastrophe. We also observed effective killing of lymphoid tumour cell lines in vitro following exposure to ALX, although, in contrast, this tended to occur via activation of a p53-independent apoptotic pathway. Lastly, we validate the effectiveness of ALX as a chemotherapeutic agent in vivo by demonstrating its ability to cause a significant reduction in tumour cell growth, irrespective of TP53 status, using a mouse leukaemia xenograft model. Taken together, these data demonstrate that ALX, through its dual action as an alkylating agent and topoisomerase inhibitor, represents a novel anti-cancer agent that could be potentially used clinically to treat refractory or relapsed tumours, particularly those harbouring mutations in DDR genes
Synthesis of crystallizable poly(behenyl methacrylate)-based block and statistical copolymers and their performance as wax crystal modifiers
Two series of behenyl methacrylate-based diblock and statistical copolymers have been prepared by reversible addition–fragmentation chain transfer (RAFT) solution polymerization in n-dodecane and evaluated as additives for the crystal habit modification of a model wax (n-octacosane). DSC studies indicated that each statistical copolymer exhibited a significantly lower crystallization temperature (Tc) and melting temperature (Tm) for the semi-crystalline behenyl methacrylate component than the corresponding diblock copolymer of almost identical overall composition. Temperature-dependent turbidimetry studies were conducted for each copolymer using a series of solutions of 5.0% w/w n-octacosane dissolved in n-dodecane to determine Tcool, which is the temperature at which zero transmittance is first observed owing to wax crystallization. At a constant molar copolymer concentration of 0.26 mM, each of the eight copolymers produced a reduction in Tcool of approximately 3–5 °C. Scanning electron microscopy (SEM) studies confirmed that the presence of such copolymers led to a reduction in the overall size and/or a higher crystal aspect ratio. The diblock and statistical copolymers were similar in their performance as potential wax crystal modifiers. However, the statistical copolymers were easier to prepare and did not suffer from any homopolymer contamination. Moreover, optical microscopy and SEM studies revealed that needle-like crystals were formed instead of platelets when employing behenyl methacrylate-rich statistical copolymers
A Theory for High- Superconductors Considering Inhomogeneous Charge Distribution
We propose a general theory for the critical and pseudogap
temperature dependence on the doping concentration for high- oxides,
taking into account the charge inhomogeneities in the planes. The well
measured experimental inhomogeneous charge density in a given compound is
assumed to produce a spatial distribution of local . These differences
in the local charge concentration is assumed to yield insulator and metallic
regions, possibly in a stripe morphology. In the metallic region, the
inhomogeneous charge density yields also spatial distributions of
superconducting critical temperatures and zero temperature gap
. For a given sample, the measured onset of vanishing gap
temperature is identified as the pseudogap temperature, that is, , which
is the maximum of all . Below , due to the distribution of
's, there are some superconducting regions surrounded by insulator or
metallic medium. The transition to a superconducting state corresponds to the
percolation threshold among the superconducting regions with different
's. To model the charge inhomogeneities we use a double branched
Poisson-Gaussian distribution. To make definite calculations and compare with
the experimental results, we derive phase diagrams for the BSCO, LSCO and YBCO
families, with a mean field theory for superconductivity using an extended
Hubbard Hamiltonian. We show also that this novel approach provides new
insights on several experimental features of high- oxides.Comment: 7 pages, 5 eps figures, corrected typo
"Forbidden" transitions between quantum Hall and insulating phases in p-SiGe heterostructures
We show that in dilute metallic p-SiGe heterostructures, magnetic field can
cause multiple quantum Hall-insulator-quantum Hall transitions. The insulating
states are observed between quantum Hall states with filling factors \nu=1 and
2 and, for the first time, between \nu=2 and 3 and between \nu=4 and 6. The
latter are in contradiction with the original global phase diagram for the
quantum Hall effect. We suggest that the application of a (perpendicular)
magnetic field induces insulating behavior in metallic p-SiGe heterostructures
in the same way as in Si MOSFETs. This insulator is then in competition with,
and interrupted by, integer quantum Hall states leading to the multiple
re-entrant transitions. The phase diagram which accounts for these transition
is similar to that previously obtained in Si MOSFETs thus confirming its
universal character
Topological Defects, Orientational Order, and Depinning of the Electron Solid in a Random Potential
We report on the results of molecular dynamics simulation (MD) studies of the
classical two-dimensional electron crystal in the presence disorder. Our study
is motivated by recent experiments on this system in modulation doped
semiconductor systems in very strong magnetic fields, where the magnetic length
is much smaller than the average interelectron spacing , as well as by
recent studies of electrons on the surface of helium. We investigate the low
temperature state of this system using a simulated annealing method. We find
that the low temperature state of the system always has isolated dislocations,
even at the weakest disorder levels investigated. We also find evidence for a
transition from a hexatic glass to an isotropic glass as the disorder is
increased. The former is characterized by quasi-long range orientational order,
and the absence of disclination defects in the low temperature state, and the
latter by short range orientational order and the presence of these defects.
The threshold electric field is also studied as a function of the disorder
strength, and is shown to have a characteristic signature of the transition.
Finally, the qualitative behavior of the electron flow in the depinned state is
shown to change continuously from an elastic flow to a channel-like, plastic
flow as the disorder strength is increased.Comment: 31 pages, RevTex 3.0, 15 figures upon request, accepted for
publication in Phys. Rev. B., HAF94MD
Jekyll and Hyde: men's constructions of feminism and feminists
Research and commentary on men's responses to feminism has demonstrated the range of ways in which men have mobilised both against and for feminist principles. This paper argues that further analyses of men's responses require a sophisticated theory of discourse acknowledging the fragmented and contradictory nature of representation. A corpus of men's talk on feminism and feminists was studied to identify the pervasive patterns in men's accounting and regularities in rhetorical organisation. Material from two samples of men was included: a sample of white middle-class 17-18 year old school students and a sample of 60 interviews with a more diverse sample of older men aged 20 to 64. Two interpretative repertoires of feminism and feminists were identified. These set up a 'Jekyll and Hyde' binary and positioned feminism along with feminists very differently as reasonable versus extreme and monstrous. Both repertoires tended to be deployed together and the paper explores the ideological and interactional consequences of typical deployments along with the identity work accomplished by the men as they positioned themselves in relation to these
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