270 research outputs found
Coherent chemical kinetics as quantum walks II: Radical-pair reactions in Arabidopsis thaliana
We apply the quantum-walk approach recently proposed in
arXiv:quant-ph-1506.04213 to a radical-pair reaction where realistic estimates
for the intermediate transition rates are available. The well-known average
hitting time from quantum walks can be adopted as a measure of how quickly the
reaction occurs and we calculate this for varying degrees of dephasing in the
radical pair. The time for the radical pair to react to a product is found to
be independent of the amount of dephasing introduced, even in the limit of no
dephasing where the transient population dynamics exhibit strong coherent
oscillations. This can be seen to arise from the existence of a rate-limiting
step in the reaction and we argue that in such examples, a purely classical
model based on rate equations can be used for estimating the timescale of the
reaction but not necessarily its population dynamics
Re-entrant ferroelectricity in liquid crystals
The ferroelectric (Sm C) -- antiferroelectric (Sm C) -- reentrant
ferroelectric (re Sm C) phase temperature sequence was observed for system
with competing synclinic - anticlinic interactions. The basic properties of
this system are as follows (1) the Sm C phase is metastable in temperature
range of the Sm C stability (2) the double inversions of the helix
handedness at Sm C -- Sm C and Sm C% -- re-Sm C phase
transitions were found (3) the threshold electric field that is necessary to
induce synclinic ordering in the Sm C phase decreases near both Sm
C -- Sm C and Sm C -- re-Sm C phase boundaries, and it has
maximum in the middle of the Sm C stability region. All these properties
are properly described by simple Landau model that accounts for nearest
neighboring layer steric interactions and quadrupolar ordering only.Comment: 10 pages, 5 figures, submitted to PR
The electroclinic effect and modulated phases in smectic liquid crystals
We explore the possibility that the large electroclinic effect observed in
ferroelectric liquid crystals arises from the presence of an ordered array of
disclination lines and walls. If the spacing of these defects is in the
subvisible range, this modulated phase would be similar macroscopically to a
smectic A phase. The application of an electric field distorts the array,
producing a large polarization, and hence a large electroclinic effect. We show
that with suitable elastic parameters and sufficiently large chirality, the
modulated phase is favored over the smectic A and helically twisted smectic C*
phases. We propose various experimental tests of this scenario.Comment: 9 pages, 7 figures; new version includes dipolar interactions and
bend-twist couplin
Short-range smectic fluctuations and the flexoelectric model of modulated nematic liquid crystals
We show that the flexoelectric model of chiral and achiral modulated nematics predicts the compression modulus that is by orders of magnitude lower than the measured values. The discrepancy is much larger in the chiral modulated nematic phase, in which the measured value of the compression modulus is of the same order of magnitude as in achiral modulated nematics, even though the heliconical pitch is by an order of magnitude larger. The relaxation of a one-constant approximation in the biaxial elastic model used for chiral modulated nematics does not solve the problem. Therefore, we propose a structural model of the modulated nematic phase, which is consistent with the current experimental evidence and can also explain large compression modulus: the structure consists of short-range smectic clusters with a fourfold symmetry and periodicity of two molecular distances. In chiral systems, chiral interactions lead to a helicoidal structure of such clusters
Linguistics
Contains table of contents for Section 4, an introduction and abstracts for three doctoral dissertations
Hydrogen bonding and the design of twist-bend nematogens
Acknowledgements The work was supported by the National Science Centre (Poland) under the grant no. 2016/22/A/ST5/00319. RW gratefully thanks the Carnegie Trust for the Universities of Scotland for the award of a PhD Scholarship (2015-2018). The Erasmus programme is thanked for supporting a study visit for CAC to Warsaw. Declaration of competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author statement Rebecca Walker: Investigation, Formal analysis, Validation, Visualisation, Writing – Original Draft, Writing – Reviewing and Editing Damian Pociecha: Visualisation, Investigation, Formal analysis Catriona Crawford: Investigation, Formal analysis John MD Storey: Resources, Supervision Ewa Gorecka: Investigation, Formal analysis, Resources, Supervision Corrie T Imrie: Conceptualization, Supervision, Resources, Writing – Reviewing and EditingPeer reviewedPostprin
Critical behavior of the optical birefringence at the nematic to twist bend nematic phase transition
This research was supported by the National Science Centre (Poland) under the grant no. 2016/22/A/ST5/00319. NV acknowledges the support of the Slovenian Research Agency (ARRS), through the research programme P1-0055.Peer reviewedPublisher PD
Induced Anticlinic Ordering and Nanophase Segregation of Bow-Shaped Molecules in a Smectic Solvent
Recent experiments indicate that doping low concentrations of bent-core
molecules into calamitic smectic solvents can induce anticlinic and biaxial
smectic phases. We have carried out Monte Carlo (MC) simulations of mixtures of
rodlike molecules (hard spherocylinders with length/breadth ratio ) and bow- or banana-shaped molecules (hard spherocylinder dimers
with length/breadth ratio or 2.5 and opening angle ) to
probe the molecular-scale organization and phase behavior of rod/banana
mixtures. We find that a low concentration (3%) of dimers
induces anticlinic (SmC) ordering in an untilted smectic (SmA) phase for
. For smaller , half of each bow-shaped
molecule is nanophase segregated between smectic layers, and the smectic layers
are untilted. For , no tilted phases are induced. However,
with decreasing we observe a sharp transition from {\sl intralamellar}
nanophase segregation (bow-shaped molecules segregated within smectic layers)
to {\sl interlamellar} nanophase segregation (bow-shaped molecules concentrated
between smectic layers) near . These results demonstrate that
purely entropic effects can lead to surprisingly complex behavior in rod/banana
mixtures.Comment: 5 pages Revtex, 7 postscript figure
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