14,419 research outputs found
Biaxial order parameter in the homologous series of orthogonal bent-core smectic liquid crystals
The fundamental parameter of the uniaxial liquid crystalline state that governs nearly all of its physical properties is the primary orientational order parameter (S) for the long axes of molecules with respect to the director. The biaxial liquid crystals (LCs) possess biaxial order parameters depending on the phase symmetry of the system. In this paper we show that in the first approximation a biaxial orthogonal smectic phase can be described by two primary order parameters: S for the long axes and C for the ordering of the short axes of molecules. The temperature dependencies of S and C are obtained by the Haller's extrapolation technique through measurements of the optical birefringence and biaxiality on a nontilted polar antiferroelectric (Sm-APA) phase of a homologous series of LCs built from the bent-core achiral molecules. For such a biaxial smectic phase both S and C, particularly the temperature dependency of the latter, are being experimentally determined. Results show that S in the orthogonal smectic phase composed of bent cores is higher than in Sm-A calamatic LCs and C is also significantly large
Precise Charm- and Bottom-Quark Masses: Theoretical and Experimental Uncertainties
Recent theoretical and experimental improvements in the determination of
charm and bottom quark masses are discussed. A new and improved evaluation of
the contribution from the gluon condensate to the
charm mass determination and a detailed study of potential uncertainties in the
continuum cross section for production is presented, together with a
study of the parametric uncertainty from the -dependence of our
results. The final results, MeV and
MeV, represent, together with a closely related lattice
determination MeV, the presently most precise
determinations of these two fundamental Standard Model parameters. A critical
analysis of the theoretical and experimental uncertainties is presented.Comment: 12 pages, presented at Quarks~2010, 16th International Seminar of
High Energy Physics, Kolomna, Russia, June 6-12, 2010; v2: references adde
Observation of quantum interference in the plasmonic Hong-Ou-Mandel effect
We report direct evidence of the bosonic nature of surface plasmon polaritons
(SPPs) in a scattering-based beamsplitter. A parametric down-conversion source
is used to produce two indistinguishable photons, each of which is converted
into a SPP on a metal-stripe waveguide and then made to interact through a
semi-transparent Bragg mirror. In this plasmonic analog of the Hong-Ou-Mandel
experiment, we measure a coincidence dip with a visibility of 72%, a key
signature that SPPs are bosons and that quantum interference is clearly
involved.Comment: 5 pages, 3 figure
Overview of Actual Methods for Characterization of Ash Depostion
Utility operation with frequent fuel switching is a common practice, forced by cheaper coal availability in the international market. Additionally, a substitution of coal by cheaper local secondary fuels, ranging from forest wood to sewage sludge and industrial or domestic residues, is gaining importance. Switching between different fuels, even if these do not differ much from the design coal, enhances operational problems arising from ash deposition. In order to prevent operational problems, through comprehension of the phenomena taking place within the furnace, appropriate sampling and characterization of the deposits are necessary. Methods commonly used for analysis of ash deposits and their characterization are summarized in this paper. The goals of the experimental work at the Institute of Process Engineering and Power Plant Technology (IVD) are then summarized. Finally, work on modeling the slagging and fouling phenomena or their characterization is presented
Attosecond tracking of light absorption and refraction in fullerenes
The collective response of matter is ubiquitous and widely exploited, e.g. in
plasmonic, optical and electronic devices. Here we trace on an attosecond time
scale the birth of collective excitations in a finite system and find distinct
new features in this regime. Combining quantum chemical computation with
quantum kinetic methods we calculate the time-dependent light absorption and
refraction in fullerene that serve as indicators for the emergence of
collective modes. We explain the numerically calculated novel transient
features by an analytical model and point out the relevance for ultra-fast
photonic and electronic applications. A scheme is proposed to measure the
predicted effects via the emergent attosecond metrology.Comment: 11 pages, 3 figures, accepted in Phys. Rev.
Intercalation-enhanced electric polarization and chain formation of nano-layered particles
Microscopy observations show that suspensions of synthetic and natural
nano-layered smectite clay particles submitted to a strong external electric
field undergo a fast and extended structuring. This structuring results from
the interaction between induced electric dipoles, and is only possible for
particles with suitable polarization properties. Smectite clay colloids are
observed to be particularly suitable, in contrast to similar suspensions of a
non-swelling clay. Synchrotron X-ray scattering experiments provide the
orientation distributions for the particles. These distributions are understood
in terms of competing (i) homogenizing entropy and (ii) interaction between the
particles and the local electric field; they show that clay particles polarize
along their silica sheet. Furthermore, a change in the platelet separation
inside nano-layered particles occurs under application of the electric field,
indicating that intercalated ions and water molecules play a role in their
electric polarization. The resulting induced dipole is structurally attached to
the particle, and this causes particles to reorient and interact, resulting in
the observed macroscopic structuring. The macroscopic properties of these
electro-rheological smectite suspensions may be tuned by controlling the nature
and quantity of the intercalated species, at the nanoscale.Comment: 7 pages, 5 figure
Magnetic Reversal in Nanoscopic Ferromagnetic Rings
We present a theory of magnetization reversal due to thermal fluctuations in
thin submicron-scale rings composed of soft magnetic materials. The
magnetization in such geometries is more stable against reversal than that in
thin needles and other geometries, where sharp ends or edges can initiate
nucleation of a reversed state. The 2D ring geometry also allows us to evaluate
the effects of nonlocal magnetostatic forces. We find a `phase transition',
which should be experimentally observable, between an Arrhenius and a
non-Arrhenius activation regime as magnetic field is varied in a ring of fixed
size.Comment: RevTeX, 23 pages, 7 figures, to appear in Phys. Rev.
Direct measurement of plasmon propagation lengths on lithographically defined metallic waveguides on GaAs
We present optical investigations of rectangular surface plasmon polariton
waveguides lithographically defined on GaAs substrates. The plasmon propagation
length is directly determined using a confocal microscope, with independent
polarization control in both excitation and detection channels. Surface plasmon
polaritons are launched along the waveguide using a lithographically defined
defect at one end. At the remote end of the waveguide they scatter into the
far-field, where they are imaged using a CCD camera. By monitoring the length
dependence of the intensity of scattered light from the waveguide end, we
directly extract the propagation length, obtaining values ranging from LSPP =
10-40 {\mu}m depending on the waveguide width (w=2-5 {\mu}m) and excitation
wavelength (760-920 nm). Results are in good accord with theoretical
expectations demonstrating the high quality of the lithographically defined
structures. The results obtained are of strong relevance for the development of
future semiconductor based integrated plasmonic technologies
Physiological parameter estimation from multispectral images unleashed
Multispectral imaging in laparoscopy can provide tissue reflectance measurements for each point in the image at multiple wavelengths of light. These reflectances encode information on important physiological parameters not visible to the naked eye. Fast decoding of the data during surgery, however, remains challenging. While model-based methods suffer from inaccurate base assumptions, a major bottleneck related to competing machine learning-based solutions is the lack of labelled training data. In this paper, we address this issue with the first transfer learning-based method to physiological parameter estimation from multispectral images. It relies on a highly generic tissue model that aims to capture the full range of optical tissue parameters that can potentially be observed in vivo. Adaptation of the model to a specific clinical application based on unlabelled in vivo data is achieved using a new concept of domain adaptation that explicitly addresses the high variance often introduced by conventional covariance-shift correction methods. According to comprehensive in silico and in vivo experiments our approach enables accurate parameter estimation for various tissue types without the need for incorporating specific prior knowledge on optical properties and could thus pave the way for many exciting applications in multispectral laparoscopy
Lifting of nodes by disorder in extended- state superconductors: application to ferropnictides
We show, using a simple model, how ordinary disorder can gap an extended-
() symmetry superconducting state with nodes. The concommitant
crossover of thermodynamic properties, particularly the -dependence of the
superfluid density, from pure power law behavior to an activated one is
exhibited. We discuss applications of this scenario to experiments on the
ferropnictide superconductors.Comment: 9 page
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