1,739 research outputs found
Infrared astronomy research and high altitude observations
Highlights are presented of studies of the emission mechanisms in the 4 to 8 micron region of the spectrum using a circular variable filter wheel spectrometer with a PbSnTe photovoltaic detector. Investigations covered include the spectroscopy of planets, stellar atmospheres, highly obscured objects in molecular clouds, planetary nebulae, H2 regions, and extragalactic objects
Spitzer Mid-Infrared Imaging of Nearby Ultraluminous Infrared Galaxies
We have observed 14 nearby (z<0.16) Ultraluminous Infrared Galaxies (ULIRGs)
with Spitzer at 3.6-24 microns. The underlying host galaxies are well-detected,
in addition to the luminous nuclear cores. While the spatial resolution of
Spitzer is poor, the great sensitivity of the data reveals the underlying
galaxy merger remnant, and provides the first look at off-nuclear mid-infrared
activity.Comment: To appear in the conference proceedings for Spitzer New Views of the
Universe, held Nov. 2004 in Pasadena, C
Boost regulator design and development
Design criteria for pulse and frequency modulated boost regulato
Sorting photons by radial quantum number
The Laguerre-Gaussian (LG) modes constitute a complete basis set for
representing the transverse structure of a {paraxial} photon field in free
space. Earlier workers have shown how to construct a device for sorting a
photon according to its azimuthal LG mode index, which describes the orbital
angular momentum (OAM) carried by the field. In this paper we propose and
demonstrate a mode sorter based on the fractional Fourier transform (FRFT) to
efficiently decompose the optical field according to its radial profile. We
experimentally characterize the performance of our implementation by separating
individual radial modes as well as superposition states. The reported scheme
can, in principle, achieve unit efficiency and thus can be suitable for
applications that involve quantum states of light. This approach can be readily
combined with existing OAM mode sorters to provide a complete characterization
of the transverse profile of the optical field
Star-Like Micelles with Star-Like Interactions: A quantitative Evaluation of Structure Factor and Phase Diagram
PEP-PEO block copolymer micelles offer the possibility to investigate phase
behaviour and interactions of star polymers (ultra-soft colloids). A star-like
architecture is achieved by an extremely asymmetric block ratio (1:20).
Micellar functionality f can be smoothly varied by changing solvent composition
(interfacial tension). Structure factors obtained by SANS can be quantitatively
described in terms of an effective potential developed for star polymers. The
experimental phase diagram reproduces to a high level of accuracy the predicted
liquid/solid transition. Whereas for intermediate f a bcc phase is observed,
for high f the formation of a fcc phase is preempted by glass formation.Comment: 5 pages, 4 figures, PRL in pres
Using all transverse degrees of freedom in quantum communications based on a generic mode sorter
The dimension of the state space for information encoding offered by the
transverse structure of light is usually limited by the finite size of
apertures. The widely used orbital angular momentum (OAM) number of
Laguerre-Gaussian (LG) modes in free-space communications cannot achieve the
theoretical maximum transmission capacity unless the radial degree of freedom
is multiplexed into the protocol. While the methodology to sort the radial
quantum number has been developed, the application of radial modes in quantum
communications requires an additional ability to efficiently measure the
superposition of LG modes in the mutually unbiased basis. Here we develop and
implement a generic mode sorter that is capable of sorting the superposition of
LG modes through the use of a mode converter. As a consequence, we demonstrate
an 8-dimensional quantum key distribution experiment involving all three
transverse degrees of freedom: spin, azimuthal, and radial quantum numbers of
photons. Our protocol presents an important step towards the goal of reaching
the capacity limit of a free-space link and can be useful to other applications
that involve spatial modes of photons
Photoionenspektroskopie an Schwefelchloridpentafluorid SF5Cl, das lonisationspotential von Schwefelpentafluorid SF5
The appearance potentials of fragment ions from SF5Cl have been measured in the energy range 12 - 20 eV by means of photoionization mass spectrometry. From these data, the ionization potential of SF5 comes to 9.65 eV
Performance analysis of d-dimensional quantum cryptography under state-dependent diffraction
Standard protocols for quantum key distribution (QKD) require that the sender
be able to transmit in two or more mutually unbiased bases. Here, we analyze
the extent to which the performance of QKD is degraded by diffraction effects
that become relevant for long propagation distances and limited sizes of
apertures. In such a scenario, different states experience different amounts of
diffraction, leading to state-dependent loss and phase acquisition, causing an
increased error rate and security loophole at the receiver. To solve this
problem, we propose a pre-compensation protocol based on pre-shaping the
transverse structure of quantum states. We demonstrate, both theoretically and
experimentally, that when performing QKD over a link with known,
symbol-dependent loss and phase shift, the performance of QKD will be better if
we intentionally increase the loss of certain symbols to make the loss and
phase shift of all states same. Our results show that the pre-compensated
protocol can significantly reduce the error rate induced by state-dependent
diffraction and thereby improve the secure key rate of QKD systems without
sacrificing the security.Comment: 10 pages, 6 figure
Dynamic Response of Block Copolymer Wormlike Micelles to Shear Flow
The linear and non-linear dynamic response to an oscillatory shear flow of
giant wormlike micelles consisting of Pb-Peo block copolymers is studied by
means of Fourier transform rheology. Experiments are performed in the vicinity
of the isotropic-nematic phase transition concentration, where the location of
isotropic-nematic phase transition lines is determined independently. Strong
shear-thinning behaviour is observed due to critical slowing down of
orientational diffusion as a result of the vicinity of the isotropic- nematic
spinodal. This severe shear-thinning behaviour is shown to result in gradient
shear banding. Time-resolved Small angle neutron scattering experiments are
used to obtain insight in the microscopic phenomena that underly the observed
rheological response. An equation of motion for the order-parameter tensor and
an expression of the stress tensor in terms of the order-parameter tensor are
used to interpret the experimental data, both in the linear and non-linear
regime. Scaling of the dynamic behaviour of the orientational order parameter
and the stress is found when critical slowing down due to the vicinity of the
isotropic-nematic spinodal is accounted for.Comment: Accepted by J. Phys.: Condens. Matter, CODEF II Special Issue. 20
pages, 9 figure
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