193 research outputs found
The possible evolution of pitch angles of spiral galaxies
The origin and maintenance of spiral structure in galaxies, the correlation
between different types of spiral structure and several proposed mechanisms for
their generation, and the evolution of spiral arms of galaxies with time are
questions that are still controversial. In this note we study the spiral
structure in a sample of distant galaxies in order to infer the evolution of
spiral arm characteristics with redshift. We considered a sample of 171 face-on
spiral galaxies in the Hubble Space Telescope COSMOS (The Cosmic Evolution
Survey) field. The galaxies are distributed up to with a mean
value of 0.44. For all galaxies, we determined the pitch angles of the spiral
arms and analysed their dependence on redshift; a total of 359 arms were
measured. Analyses of our measurements combined with the literature data
suggest a possible evolution of the pitch angles of spiral galaxies: by the
modern epoch the spiral pattern, on average, becomes more tightly wound. This
may be a consequence of the general evolution of the structure of galaxies as
galaxies become more massive over time and their bulges grow. In addition, the
distribution of the cotangent of pitch angle of galaxies indicates the
possibility that the dominant mechanism of spiral pattern generation changes
over time.Comment: 5 pages, accepted for publication on Astronomy & Astrophysics Letter
The C-type natriuretic peptide induces thermal hyperalgesia through a noncanonical Gβγ-dependent modulation of TRPV1 channel
Natriuretic peptides (NPs) control natriuresis and normalize changes in blood pressure. Recent studies suggest that NPs are also involved in the regulation of pain sensitivity, although the underlying mechanisms remain largely unknown. Many biological effects of NPs are mediated by guanylate cyclase (GC)-coupled NP receptors, NPR-A and NPR-B, whereas the third NP receptor, NPR-C, lacks the GC kinase domain and acts as the NP clearance receptor. In addition, NPR-C can couple to specific Gα(i)-βγ-mediated intracellular signaling cascades in numerous cell types. We found that NPR-C is co-expressed in TRPV1-expressing mouse DRG neurons. NPR-C can be co-immunoprecipitated with Gα(i), and CNP treatment induced translocation of PKCε to the plasma membrane of these neurons, which was inhibited by pertussis toxin pre-treatment. Application of CNP potentiated capsaicin- and proton-activated TRPV1 currents in cultured mouse DRG neurons, and increased neuronal firing frequency, an effect that was absent in DRG neurons from TRPV1(−/−) mice. CNP-induced sensitization of TRPV1 activity was attenuated by pre-treatment of DRG neurons with the specific inhibitors of Gβγ, PLCβ or PKC, but not of PKA, and was abolished by mutations at two PKC phosphorylation sites in TRPV1. Further, CNP injection into mouse hind paw led to the development of thermal hyperalgesia that was attenuated by administration of specific inhibitors of Gβγ or TRPV1, and was also absent in TRPV1(−/−) mice. Thus, our work identifies the Gβγ-PLCβ-PKC-dependent potentiation of TRPV1 as a novel signaling cascade recruited by CNP in mouse DRG neurons that can lead to enhanced nociceptor excitability and thermal hypersensitivity
A pulsed source of continuous variable polarization entanglement
We have experimentally demonstrated polarization entanglement using
continuous variables in an ultra-short pulsed laser system at telecommunication
wavelengths. Exploiting the Kerr-nonlinearity of a glass fibre we generated a
polarization squeezed pulse with S2 the only non-zero Stokes parameter thus S1
and S3 being the conjugate pair. Polarization entanglement was generated by
interference of the polarization squeezed field with a vacuum on a 50:50 beam
splitter. The two resultant beams exhibit strong quantum noise correlations in
S1 and S3. The sum noise signal of S3 was at the respective shot noise level
and the difference noise signal of S1 fell 2.9dB below this value
Polarization quantum properties in type-II Optical Parametric Oscillator below threshold
We study the far field spatial distribution of the quantum fluctuations in
the transverse profile of the output light beam generated by a type II Optical
Parametric Oscillator below threshold, including the effects of transverse
walk-off. We study how quadrature field correlations depend on the
polarization. We find spatial EPR entanglement in quadrature-polarization
components: For the far field points not affected by walk-off there is almost
complete noise suppression in the proper quadratures difference of any
orthogonal polarization components. We show the entanglement of the state of
symmetric intense, or macroscopic, spatial light modes. We also investigate
nonclassical polarization properties in terms of the Stokes operators. We find
perfect correlations in all Stokes parameters measured in opposite far field
points in the direction orthogonal to the walk-off, while locally the field is
unpolarized and we find no polarization squeezing.Comment: 16 pages, 18 figure
Polarization squeezing and continuous-variable polarization entanglement
The Stokes-parameter operators and the associated Poincare sphere, which
describe the quantum-optical polarization properties of light, are defined and
their basic properties are reviewed. The general features of the Stokes
operators are illustrated by evaluation of their means and variances for a
range of simple polarization states. Some of the examples show polarization
squeezing, in which the variances of one or more Stokes parameters are smaller
than the coherent-state value. The main object of the paper is the application
of these concepts to bright squeezed light. It is shown that a light beam
formed by interference of two orthogonally-polarized quadrature-squeezed beams
exhibits squeezing in some of the Stokes parameters. Passage of such a primary
polarization-squeezed beam through suitable optical components generates a pair
of polarization-entangled light beams with the nature of a two-mode squeezed
state. The use of pairs of primary polarization-squeezed light beams leads to
substantially increased entanglement and to the generation of EPR-entangled
light beams. The important advantage of these nonclassical polarization states
for quantum communication is the possibility of experimentally determining all
of the relevant conjugate variables of both squeezed and entangled fields using
only linear optical elements followed by direct detection.Comment: 27 pages, including 10 figure
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Ice imaging in aircraft anti-icing fluid films using polarized light
Article presents how to enhance ice contrast in the visible spectrum by using ice birefringence and polarized light reflection. The method can be used for both visual inspection and automatic ice detection systems
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