7,633 research outputs found
Thermal Properties of a Simulated Lunar Material in Air and in Vacuum
Thermal properties of simulated lunar material in air and in vacuu
Selective detection of gaseous ammonia with specifically functionalized silicon photonic microring resonator: towards low cost and portable breath monitoring
We demonstrate a selective ammonia sensor based on a silicon photonic microring resonator functionalized with nanoporous silicate films. The potential of this sensor as a low cost, portable and real-time medical breath monitoring device is discussed
Onderzoek naar de effecten op het milieu bij het terugstorten van baggerspecie in de Beneden-Zeeschelde. Bijlagerapport
Onderzoek naar de effecten op het milieu bij het terugstorten van baggerspecie in de Beneden-Zeeschelde. Hoofdrapport
Exact Results for the Kuramoto Model with a Bimodal Frequency Distribution
We analyze a large system of globally coupled phase oscillators whose natural
frequencies are bimodally distributed. The dynamics of this system has been the
subject of long-standing interest. In 1984 Kuramoto proposed several
conjectures about its behavior; ten years later, Crawford obtained the first
analytical results by means of a local center manifold calculation.
Nevertheless, many questions have remained open, especially about the
possibility of global bifurcations. Here we derive the system's complete
stability diagram for the special case where the bimodal distribution consists
of two equally weighted Lorentzians. Using an ansatz recently discovered by Ott
and Antonsen, we show that in this case the infinite-dimensional problem
reduces exactly to a flow in four dimensions. Depending on the parameters and
initial conditions, the long-term dynamics evolves to one of three states:
incoherence, where all the oscillators are desynchronized; partial synchrony,
where a macroscopic group of phase-locked oscillators coexists with a sea of
desynchronized ones; and a standing wave state, where two counter-rotating
groups of phase-locked oscillators emerge. Analytical results are presented for
the bifurcation boundaries between these states. Similar results are also
obtained for the case in which the bimodal distribution is given by the sum of
two Gaussians.Comment: 28 pages, 7 figures; submitted to Phys. Rev. E Added comment
Solar Coronal Structures and Stray Light in TRACE
Using the 2004 Venus transit of the Sun to constrain a semi-empirical
point-spread function for the TRACE EUV solar telescope, we have measured the
effect of stray light in that telescope. We find that 43% of 171A EUV light
that enters TRACE is scattered, either through diffraction off the entrance
filter grid or through other nonspecular effects. We carry this result forward,
via known-PSF deconvolution of TRACE images, to identify its effect on analysis
of TRACE data. Known-PSF deconvolution by this derived PSF greatly reduces the
effect of visible haze in the TRACE 171A images, enhances bright features, and
reveals that the smooth background component of the corona is considerably less
bright (and hence much more rarefied) than commonly supposed. Deconvolution
reveals that some prior conlclusions about the Sun appear to have been based on
stray light in the images. In particular, the diffuse background "quiet corona"
becomes consistent with hydrostatic support of the coronal plasma; feature
contrast is greatly increased, possibly affecting derived parameters such as
the form of the coronal heating function; and essentially all existing
differential emission measure studies of small features appear to be affected
by contamination from nearby features. We speculate on further implications of
stray light for interpretation of EUV images from TRACE and similar
instruments, and advocate deconvolution as a standard tool for image analysis
with future instruments such as SDO/AIA.Comment: Accepted by APJ; v2 reformatted to single-column format for online
readabilit
Macroscopic effects in attosecond pulse generation
We examine how the generation and propagation of high-order harmonics in a
partly ionized gas medium affect their strength and synchronization. The
temporal properties of the resulting attosecond pulses generated in long gas
targets can be significantly influenced by macroscopic effects, in particular
by the intensity in the medium and the degree of ionization. Under some
conditions, the use of gas targets longer than the absorption length can lead
to the generation of self-compressed attosecond pulses. We show this effect
experimentally, using long argon-filled gas cells as generating medium.Comment: 5 pages 4 figure
Self-heating Effect in Silicon-Photomultipliers
The main effect of radiation damage in a Silicon-Photolumtiplier (SiPM) is a
dramatic increase in the dark current. The power dissipated, if not properly
cooled, heats the SiPM, whose performance parameters depend on temperature.
Heating studies were performed with a KETEK SiPM, glued on an AlO
substrate, which is either directly connected to the temperature-controlled
chuck of a probe station, or through layers of material with well-known thermal
resistance. The SiPM is illuminated by a LED operated in DC-mode. The SiPM
current is measured and used to determine the steady-state temperature as a
function of power dissipated in the multiplication region of the SiPM and
thermal resistance, as well as the time dependencies for heating and cooling.
This information can be used to correct the parameters determined for
radiation-damaged SiPM for the effects of self-heating. The method can also be
employed for packaged SiPMs with unknown thermal contact to a heat sink. The
results presented in this paper are preliminary
On Non-Abelian Symplectic Cutting
We discuss symplectic cutting for Hamiltonian actions of non-Abelian compact
groups. By using a degeneration based on the Vinberg monoid we give, in good
cases, a global quotient description of a surgery construction introduced by
Woodward and Meinrenken, and show it can be interpreted in algebro-geometric
terms. A key ingredient is the `universal cut' of the cotangent bundle of the
group itself, which is identified with a moduli space of framed bundles on
chains of projective lines recently introduced by the authors.Comment: Various edits made, to appear in Transformation Groups. 28 pages, 8
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