5,273 research outputs found
Diamagnetic repulsion of particles for multilaminar flow assays
© The Royal Society of Chemistry. We demonstrate diamagnetic repulsion forces for performing continuous multilaminar flow assays on particles based on their intrinsic properties and with a simple setup. The platform could be applied to sandwich assays on polystyrene particles, and to cell-based assays via their suspension in biologically benign magnetic media
Correlation effects in quasi one dimensional electron wires
We explore the role of electron correlation in quasi one dimensional quantum
wires as the range of the interaction potential is changed and their thickness
is varied by performing exact quantum Monte Carlo simulations at various
electronic densities. In the case of unscreened interactions with a long range
1/x tail there is a crossover from a liquid to a quasi Wigner crystal state as
the density decreases. When this interaction is screened, quasi long range
order is prevented from forming, although a significant correlation with 4 k_F
periodicity is still present at low densities. At even lower electron
concentration, exchange is suppressed and the spin-dependent interactions
become negligible, making the electrons behave like spinless fermions. We show
that this behavior is shared by the long range and screened interactions by
studying the spin and charge excitations of the system in both cases. Finally,
we study the effect of electron correlations in the double quantum wire
experiment [Steinberg et al., Phys. Rev. B 77, 113307 (2006)], by introducing
an accurate model for the screening in the experiment and explicitly including
the finite length of the system in our simulations. We find that decreasing the
electron density drives the system from a liquid to a state with quite strong 4
k_F correlations. This crossover takes place around , the
density where the electron localization occurs in the experiment. The charge
and spin velocities are also in remarkable agreement with the experimental
findings in the proximity of the crossover. We argue that correlation effects
play an important role at the onset of the localization transition.Comment: minor improvements, 13 pages, 12 figure
Hybridization gap versus hidden order gap in URuSi as revealed by optical spectroscopy
We present the in-plane optical reflectance measurement on single crystals of
URuAs. The study revealed a strong temperature-dependent spectral
evolution. Above 50 K, the low frequency optical conductivity is rather flat
without a clear Drude-like response, indicating a very short transport life
time of the free carriers. Well below the coherence temperature, there appears
an abrupt spectral weight suppression below 400 cm, yielding evidence
for the formation of a hybridization energy gap arising from the mixing of the
conduction electron and narrow f-electron bands. A small part of the suppressed
spectral weight was transferred to the low frequency side, leading to a narrow
Drude component, while the majority of the suppressed spectral weight was
transferred to the high frequency side centered near 4000 cm. Below the
hidden order temperature, another very prominent energy gap structure was
observed, which leads to the removal of a large part of the Drude component and
a sharp reduction of the carrier scattering rate. The study revealed that the
hybridization gap and the hidden orger gap are distinctly different: they occur
at different energy scales and exhibit completely different spectral
characteristics.Comment: 5 page
Optically-ambidextrous circularly-polarised reflection from the chiral cuticle of the scarab beetle Chrysina resplendens
This is the author accepted manuscript. The final version is available from Royal Society via the DOI in this record.The evolution of structural colour mechanisms in biological
systems has given rise to many interesting optical effects in
animals and plants. The instance of the scarab beetle Chrysina
resplendens is particularly distinctive. Its exoskeleton has a
bright, golden appearance and reflects both right-handed and
left-handed circularly-polarized light concurrently. The chiral
nanostructure responsible for these properties is a helicoid, in
which birefringent dielectric planes are assembled with an
incremental rotation. This study correlates details of the
beetle’s circularly-polarized reflectance spectra directly with
physical aspects of its structural morphology. Electron
micrography is used to identify and measure the physical
dimensions of the key constituent components. These include
a chiral multilayer configuration comprising two chirped, lefthanded
helicoids that are separated by a birefringent retarder.
A scattering matrix technique is used to simulate the system’s
optical behaviour in which the roles of each component of the
morphological substructure are elucidated by calculation of
the fields throughout its depth.This work was supported by AFOSR grant number FA9550-10-1-
0020
Circularly polarized reflection from the scarab beetle Chalcothea smaragdina: light scattering by a dual photonic structure
Helicoidal architectures comprising various polysaccharides, such as chitin and cellulose, have been reported in biological systems. In some cases, these architectures exhibit stunning optical properties analogous to ordered cholesteric liquid crystal phases. In this work, we characterize the circularly polarized reflectance and optical scattering from the cuticle of the beetle Chalcothea smaragdina (Coleoptera: Scarabaeidae: Cetoniinae) using optical experiments, simulations and structural analysis. The selective reflection of left-handed circularly polarized light is attributed to a Bouligand-type helicoidal morphology within the beetle's exocuticle. Using electron microscopy to inform electromagnetic simulations of this anisotropic stratified medium, the inextricable connection between the colour appearance of C. smaragdina and the periodicity of its helicoidal rotation is shown. A close agreement between the model and the measured reflectance spectra is obtained. In addition, the elytral surface of C. smaragdina possesses a blazed diffraction grating-like surface structure, which affects the diffuse appearance of the beetle's reflected colour, and therefore potentially enhances crypsis among the dense foliage of its rainforest habitat
Charge-monopole versus Gravitational Scattering at Planckian Energies
The amplitude for the scattering of a point magnetic monopole and a point
charge, at centre-of-mass energies much larger than the masses of the
particles, and in the limit of low momentum transfer, is shown to be
proportional to the (integer-valued) monopole strength, assuming the Dirac
quantization condition for the monopole-charge system. It is demonstrated that,
for small momentum transfer, charge-monopole electromagnetic effects remain
comparable to those due to the gravitational interaction between the particles
even at Planckian centre-of-mass energies.Comment: 9 pages, revtex, IMSc/93-4
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