999 research outputs found
Using level-2 fuzzy sets to combine uncertainty and imprecision in fuzzy regions
In many applications, spatial data need to be considered but are prone to uncertainty or imprecision. A fuzzy region - a fuzzy set over a two dimensional domain - allows the representation of such imperfect spatial data. In the original model, points of the fuzzy region where treated independently, making it impossible to model regions where groups of points should be considered as one basic element or subregion. A first extension overcame this, but required points within a group to have the same membership grade. In this contribution, we will extend this further, allowing a fuzzy region to contain subregions in which not all points have the same membership grades. The concept can be used as an underlying model in spatial applications, e.g. websites showing maps and requiring representation of imprecise features or websites with routing functions needing to handle concepts as walking distance or closeby
Fuzzy regions: adding subregions and the impact on surface and distance calculation
In the concept of fuzzy regions we introduced before, a region was considered to be a fuzzy set of points, each having its own membership grade. While this allows the modelling of regions in which points only partly belong to the region, it has the downside that all the points are considered independently, which is too loose a restriction for some situations. The model is not able to support the fact that some points may be linked together. In this contribution, we propose an extension to the model, so that points can be made related to one another. It will permit the user to, for instance, specify points or even (sub)regions within the fuzzy region that are linked together: they all belong to the region to the same extent at the same time. By letting the user specify such subregions, the accuracy Of the model can be increased: the model can match the real situation better; while at the same time decreasing the fuzziness: if points are known to be related, there is no need to consider them independently. As an example, the use of such a fuzzy region to represent a lake with a variable water level can be considered: as the water level rises, a set of points will become flooded; it is interesting to represent this set of points as a. subset of the region, as these points are somewhat related (the same can be done for different water levels). The impact of this extension to the model on both surface area calculation an distance measurement are considered, and new appropriate definitions are introduced
Topological nature of spinons and holons: Elementary excitations from matrix product states with conserved symmetries
We develop variational matrix product state (MPS) methods with symmetries to
determine dispersion relations of one dimensional quantum lattices as a
function of momentum and preset quantum number. We test our methods on the XXZ
spin chain, the Hubbard model and a non-integrable extended Hubbard model, and
determine the excitation spectra with a precision similar to the one of the
ground state. The formulation in terms of quantum numbers makes the topological
nature of spinons and holons very explicit. In addition, the method also
enables an easy and efficient direct calculation of the necessary magnetic
field or chemical potential required for a certain ground state magnetization
or particle density.Comment: 13 pages, 4 pages appendix, 8 figure
Nonlocal resources in the presence of Superselection Rules
Superselection rules severely alter the possible operations that can be
implemented on a distributed quantum system. Whereas the restriction to local
operations imposed by a bipartite setting gives rise to the notion of
entanglement as a nonlocal resource, the superselection rule associated with
particle number conservation leads to a new resource, the \emph{superselection
induced variance} of local particle number. We show that, in the case of pure
quantum states, one can quantify the nonlocal properties by only two additive
measures, and that all states with the same measures can be asymptotically
interconverted into each other by local operations and classical communication.
Furthermore we discuss how superselection rules affect the concepts of
majorization, teleportation and mixed state entanglement.Comment: 4 page
Minimally Entangled Typical Thermal State Algorithms
We discuss a method based on sampling minimally entangled typical thermal
states (METTS) that can simulate finite temperature quantum systems with a
computational cost comparable to ground state DMRG. Detailed implementations of
each step of the method are presented, along with efficient algorithms for
working with matrix product states and matrix product operators. We furthermore
explore how properties of METTS can reveal characteristic order and excitations
of systems and discuss why METTS form an efficient basis for sampling. Finally,
we explore the extent to which the average entanglement of a METTS ensemble is
minimal.Comment: 18 pages, 14 figure
Fermionic concurrence in the extended Hubbard dimer
In this paper, we introduce and study the fermionic concurrence in a two-site
extended Hubbard model. Its behaviors both at the ground state and finite
temperatures as function of Coulomb interaction (on-site) and
(nearest-neighbor) are obtained analytically and numerically. We also
investigate the change of the concurrence under a nonuniform field, including
local potential and magnetic field, and find that the concurrence can be
modulated by these fields.Comment: 5 pages, 7 figure
Cross-linked cationic diblock copolymer worms are superflocculants for micrometer-sized silica particles
A series of linear cationic diblock copolymer nanoparticles are prepared by polymerization-induced self-assembly (PISA) via reversible additionâfragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) using a binary mixture of non-ionic and cationic macromolecular RAFT agents, namely poly(ethylene oxide) (PEO113, Mn = 4400 g molâ1; Mw/Mn = 1.08) and poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) (PQDMA125, Mn = 31 800 g molâ1, Mw/Mn = 1.19). A detailed phase diagram was constructed to determine the maximum amount of PQDMA125 stabilizer block that could be incorporated while still allowing access to a pure worm copolymer morphology. Aqueous electrophoresis studies indicated that zeta potentials of +35 mV could be achieved for such cationic worms over a wide pH range. Core cross-linked worms were prepared via statistical copolymerization of glycidyl methacrylate (GlyMA) with HPMA using a slightly modified PISA formulation, followed by reacting the epoxy groups of the GlyMA residues located within the worm cores with 3-aminopropyl triethoxysilane (APTES), and concomitant hydrolysis/condensation of the pendent silanol groups with the secondary alcohol on the HPMA residues. TEM and DLS studies confirmed that such core cross-linked cationic worms remained colloidally stable when challenged with either excess methanol or a cationic surfactant. These cross-linked cationic worms are shown to be much more effective bridging flocculants for 1.0 ÎŒm silica particles at pH 9 than the corresponding linear cationic worms (and also various commercial high molecular weight water-soluble polymers.). Laser diffraction studies indicated silica aggregates of around 25â28 ÎŒm diameter when using the former worms but only 3â5 ÎŒm diameter when employing the latter worms. Moreover, SEM studies confirmed that the cross-linked worms remained intact after their adsorption onto the silica particles, whereas the much more delicate linear worms underwent fragmentation under the same conditions. Similar results were obtained with 4 ÎŒm silica particles
Entanglement and bifurcations in Jahn-Teller models
We compare and contrast the entanglement in the ground state of two
Jahn-Teller models. The system models the coupling of a
two-level electronic system, or qubit, to a single oscillator mode, while the
models the qubit coupled to two independent, degenerate
oscillator modes. In the absence of a transverse magnetic field applied to the
qubit, both systems exhibit a degenerate ground state. Whereas there always
exists a completely separable ground state in the system, the
ground states of the model always exhibit entanglement. For
the case we aim to clarify results from previous work, alluding
to a link between the ground state entanglement characteristics and a
bifurcation of a fixed point in the classical analogue. In the
case we make use of an ansatz for the ground state. We
compare this ansatz to exact numerical calculations and use it to investigate
how the entanglement is shared between the three system degrees of freedom.Comment: 11 pages, 9 figures, comments welcome; 2 references adde
Stimulus-responsive non-ionic diblock copolymers: protonation of a tertiary amine end-group induces vesicle-to-worm or vesicle-to-sphere transitions
A well-defined poly(glycerol monomethacrylate) (PGMA) macromolecular chain transfer agent (macroCTA) with a mean degree of polymerisation (DP) of 43 was prepared by reversible additionâfragmentation chain transfer (RAFT) polymerisation using a morpholine-functionalised trithiocarbonate-based chain transfer agent (MPETTC). Chain extension of this macro-CTA by RAFT aqueous dispersion polymerisation of 2-hydroxypropyl methacrylate (HPMA) at pH 7.0â7.5 produced a series of four MPETTC-PGMA43- PHPMAy vesicles (where y = 190, 200, 220 or 230). Protonation of the morpholine end-group increases the hydrophilic character of the PGMA stabiliser block, which leads to a reduction in the packing parameter for the diblock copolymer chains. However, such pH-responsive behaviour critically depends on the value of y. For y = 190 or 200, lowering the solution pH to pH 3 induces a vesicle-to-worm transition at 20 °C according to dynamic light scattering, aqueous electrophoresis, transmission electron microscopy and turbidimetry studies. This orderâorder transition is suppressed in the presence of added electrolyte, which screens the cationic end-groups. In addition, no change in copolymer morphology was observed on lowering the solution temperature at neutral pH, regardless of the y value. The diblock copolymer nano-objects obtained at pH 3 were also cooled to 4 °C to examine their dual stimulusresponsive behaviour to both pH and temperature triggers. In all four cases, a change in morphology from either worms or vesicles to afford spheres (or spheres plus relatively short worms) was observed. Temperature-dependent oscillatory rheology experiments performed on cationic worms at pH 3 indicated a worm-to-sphere transition on cooling from 20 °C to 4 °C, which leads to reversible degelation. In summary, spheres, worms or vesicles can be obtained for MPETTC-PGMA-PHPMA diblock copolymers on first lowering the solution pH to pH 3, followed by cooling from 20 °C to 4 °C
Violation of area-law scaling for the entanglement entropy in spin 1/2 chains
Entanglement entropy obeys area law scaling for typical physical quantum
systems. This may naively be argued to follow from locality of interactions. We
show that this is not the case by constructing an explicit simple spin chain
Hamiltonian with nearest neighbor interactions that presents an entanglement
volume scaling law. This non-translational model is contrived to have couplings
that force the accumulation of singlet bonds across the half chain. Our result
is complementary to the known relation between non-translational invariant,
nearest neighbor interacting Hamiltonians and QMA complete problems.Comment: 9 pages, 4 figure
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