201 research outputs found
Photonic gaps in cholesteric elastomers under deformation
Cholesteric liquid crystal elastomers have interesting and potentially very
useful photonic properties. In an ideal monodomain configuration of these
materials, one finds a Bragg-reflection of light in a narrow wavelength range
and a particular circular polarization. This is due to the periodic structure
of the material along one dimension. In many practical cases, the cholesteric
rubber possesses a sufficient degree of quenched disorder, which makes the
selective reflection broadband. We investigate experimentally the problem of
how the transmittance of light is affected by mechanical deformation of the
elastomer, and the relation to changes in liquid crystalline structure. We
explore a series of samples which have been synthesized with photonic stop-gaps
across the visible range. This allows us to compare results with detailed
theoretical predictions regarding the evolution of stop-gaps in cholesteric
elastomers
Morphological variation and sensitivity to frequency of forms among native speakers of Czech
This article looks at inter-speaker variation in two environments: the genitive and locative singular cases of masculine âhard inanimateâ nouns in Czech, using a large-scale survey of native speakers that used two tasks to test their preferences for certain forms (acceptability) and their choices (gap filling). Our hypothesis that such variation exists was upheld, but only within limited parameters. Most biographical data (age, gender, education) played no role in respondentsâ choices or preferences. Their region of origin played a small but significant role, although not the one expected. Relating the two types of tasks to each other, we found that respondentsâ use of the ratings scale did not correlate to their choice of forms, but their overall strength of preference for one form over another did correlate with their choices. Inter-speaker variation does thus go some way to explaining the persistent diversity in this paradigm and arguably may contribute to its maintenance
Phase chirality and stereo-selective swelling of cholesteric elastomers
Cholesteric elastomers possess a macroscopic ``phase chirality'' as the
director n rotates in a helical fashion along an optical axis and can be
described by a chiral order parameter. This parameter can be tuned by changing
the helix pitch p and/or the elastic properties of the network. The
cholesterics also possess a local nematic order, changing with temperature or
during solvent swelling. In this paper, by measuring the power of optical
rotation, we discover how these two parameters vary as functions of temperature
or solvent adsorbed by the network. The main result is a finding of pronounced
stereo-selectivity of cholesteric elastomers, demonstrating itself in the
retention of the ``correct'' chirality component of a racemic solvent. It has
been possible to quantify the amount of such stereo-separation, as the basic
dynamics of the effect
Thermal Equilibrium as an Initial State for Quantum Computation by NMR
We present a method of using a nuclear magnetic resonance computer to solve
the Deutsch-Jozsa problem in which: (1) the number of molecules in the NMR
sample is irrelevant to the number of qubits available to an NMR quantum
computer, and (2) the initial state is chosen to be the state of thermal
equilibrium, thereby avoiding the preparation of pseudopure states and the
resulting exponential loss of signal as the number of qubits increases. The
algorithm is described along with its experimental implementation using four
active qubits. As expected, measured spectra demonstrate a clear distinction
between constant and balanced functions.Comment: including 4 figure
Do usersâ reading skills and difficulty ratings for texts affect choices and evaluations?
In our contribution, we consider how corpus data can be used as a proxy for the written language environment around us in constructing offline studies of native-speaker intuition and usage. We assume a broadly emergent perspective on language: in other words, the linguistic competence of individuals is not identical or hardwired but forms gradually through exposure and coalescence of patterns of production and reaction. We hypothesize that while users presumably all in theory have access to the same linguistic material, their actual exposure to it and their ability to interpret it may differ, which will result in differing judgments and choices. Our study looks at the interaction between corpus frequency and two possible indicators of individual difference: attitude towards reading tasks and performance on reading tasks. We find a small but consistent effect of task performance on respondentsâ judgments but do not confirm any effects on respondentsâ production tasks
Tailoring optical nonlinearities via the Purcell effect
We predict that the effective nonlinear optical susceptibility can be
tailored using the Purcell effect. While this is a general physical principle
that applies to a wide variety of nonlinearities, we specifically investigate
the Kerr nonlinearity. We show theoretically that using the Purcell effect for
frequencies close to an atomic resonance can substantially influence the
resultant Kerr nonlinearity for light of all (even highly detuned) frequencies.
For example, in realistic physical systems, enhancement of the Kerr coefficient
by one to two orders of magnitude could be achieved
Sensorimotor Cortex Gamma-Aminobutyric Acid Concentration Correlates with Impaired Performance in Patients with MS
ABSTRACT BACKGROUND AND PURPOSE: Abnormalities in GABA concentration [GABA] have been associated with several neuropsychiatric disorders, and research has suggested that GABA may play a role in sensorimotor cortex function. We sought to determine whether identifying a change in [GABA] within the sensorimotor cortex of patients with MS has any effect on motor function and would provide information about the adaptive/compensatory mechanisms involved in the attempt to maintain motor function during disease progression
13C-direct detected NMR experiments for the sequential J-based resonance assignment of RNA oligonucleotides
We present here a set of 13C-direct detected NMR experiments to facilitate the resonance assignment of RNA oligonucleotides. Three experiments have been developed: (1) the (H)CC-TOCSY-experiment utilizing a virtual decoupling scheme to assign the intraresidual ribose 13C-spins, (2) the (H)CPC-experiment that correlates each phosphorus with the C4Ⲡnuclei of adjacent nucleotides via J(C,P) couplings and (3) the (H)CPC-CCH-TOCSY-experiment that correlates the phosphorus nuclei with the respective C1â˛,H1Ⲡribose signals. The experiments were applied to two RNA hairpin structures. The current set of 13C-direct detected experiments allows direct and unambiguous assignment of the majority of the hetero nuclei and the identification of the individual ribose moieties following their sequential assignment. Thus, 13C-direct detected NMR methods constitute useful complements to the conventional 1H-detected approach for the resonance assignment of oligonucleotides that is often hindered by the limited chemical shift dispersion. The developed methods can also be applied to large deuterated RNAs
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