1,710 research outputs found
Characterization of Zero-Bias Microwave Diode Power Detectors at Cryogenic Temperature
We present the characterization of commercial tunnel diode low-level
microwave power detectors at room and cryogenic temperatures. The sensitivity
as well as the output voltage noise of the tunnel diodes are measured as
functions of the applied microwave power, the signal frequency being 10 GHz. We
highlight strong variations of the diode characteristics when the applied
microwave power is higher than few microwatt. For a diode operating at K,
the differential gain increases from V/W to about V/W when
the power passes from dBm to dBm. The diode present a white
noise floor equivalent to a NEP of pW/ and
pW/ at 4 K and 300 K respectively. Its flicker noise is
equivalent to a relative amplitude noise power spectral density
~dB/Hz at K. Flicker noise is 10 dB
higher at room temperature.Comment: 8 pages and 16 figure
The cosmic evolution of massive black holes in the Horizon-AGN simulation
We analyse the demographics of black holes (BHs) in the large-volume
cosmological hydrodynamical simulation Horizon-AGN. This simulation
statistically models how much gas is accreted onto BHs, traces the energy
deposited into their environment and, consequently, the back-reaction of the
ambient medium on BH growth. The synthetic BHs reproduce a variety of
observational constraints such as the redshift evolution of the BH mass density
and the mass function. Strong self-regulation via AGN feedback, weak supernova
feedback, and unresolved internal processes result in a tight BH-galaxy mass
correlation. Starting at z~2, tidal stripping creates a small population of BHs
over-massive with respect to the halo. The fraction of galaxies hosting a
central BH or an AGN increases with stellar mass. The AGN fraction agrees
better with multi-wavelength studies, than single-wavelength ones, unless
obscuration is taken into account. The most massive halos present BH
multiplicity, with additional BHs gained by ongoing or past mergers. In some
cases, both a central and an off-centre AGN shine concurrently, producing a
dual AGN. This dual AGN population dwindles with decreasing redshift, as found
in observations. Specific accretion rate and Eddington ratio distributions are
in good agreement with observational estimates. The BH population is dominated
in turn by fast, slow, and very slow accretors, with transitions occurring at
z=3 and z=2 respectively.Comment: Accepted for publication in MNRA
Tests of Sapphire Crystals Produced with Different Growth Processes for Ultra-stable Microwave Oscillators
We present the characterization of 8-12 GHz whispering gallery mode
resonators machined in high-quality sapphire crystals elaborated with different
growth techniques. These microwave resonators are intended to constitute the
reference frequency of ultra-stable Cryogenic Sapphire Oscillators. We
conducted systematic tests near 4 K on these crystals to determine the unloaded
Q-factor and the turnover temperature for whispering gallery modes in the 8-12
GHz frequency range. These characterizations show that high quality sapphire
crystals elaborated with the Heat Exchange or the Kyropoulos growth technique
are both suitable to meet a fractional frequency stability better than 1x10-15
for 1 s to 10.000 s integration times.Comment: 7 figure
Process Optimization and Downscaling of a Single Electron Single Dot Memory
This paper presents the process optimization of a single-electron nanoflash
electron memory. Self-aligned single dot memory structures have been fabricated
using a wet anisotropic oxidation of a silicon nanowire. One of the main issue
was to clarify the process conditions for the dot formation. Based on the
process modeling, the influence of various parameters (oxidation temperature,
nanowire shape) has been investigated. The necessity of a sharp compromise
between these different parameters to ensure the presence of the memory dot has
been established. In order to propose an aggressive memory cell, the
downscaling of the device has been carefully studied. Scaling rules show that
the size of the original device could be reduced by a factor of 2. This point
has been previously confirmed by the realization of single-electron memory
devices
Model Assisted Creativity Sessions for the Design of Mixed Interactive Systems: a Protocol Analysis
Part 1: Long and Short Papers (Continued)International audienceTo help designers face the complexity of mixed interaction and identifying original and adapted solutions, we developed and evaluated an original approach to interaction design. This approach, called MACS, aims to combine the best elements of both a model of mixed interaction, and a collaborative and creative session. The objective is twofold: to support the exploration of the design space, and to establish a common language between participants. To assess the viability of this approach, we relied on a protocol analysis technique on the verbal recordings of two existing design situations. Results show that the model has a strong impact on the generation of ideas and that participants use the model concepts to share their thoughts during the session
Caught in the rhythm: how satellites settle into a plane around their central galaxy
Using the cosmological hydrodynamics simulation Horizon-AGN, we investigate
the spatial distribution of satellite galaxies relative to their central
counterpart in the redshift range between 0.3 and 0.8. We find that, on
average, these satellites tend to be located on the galactic plane of the
central object. This effect is detected for central galaxies with a stellar
mass larger than 10^10 solar masses and found to be strongest for red passive
galaxies, while blue galaxies exhibit a weaker trend. For galaxies with a minor
axis parallel to the direction of the nearest filament, we find that the
coplanarity is stronger in the vicinity of the central galaxy, and decreases
when moving towards the outskirts of the host halo. By contrast, the spatial
distribution of satellite galaxies relative to their closest filament follows
the opposite trend: their tendency to align with them dominates at large
distances from the central galaxy, and fades away in its vicinity. Relying on
mock catalogs of galaxies in that redshift range, we show that massive red
centrals with a spin perpendicular to their filament also have corotating
satellites well aligned with both the galactic plane and the filament. On the
other hand, lower-mass blue centrals with a spin parallel to their filament
have satellites flowing straight along this filament, and hence orthogonally to
their galactic plane. The orbit of these satellites is then progressively bent
towards a better alignment with the galactic plane as they penetrate the
central region of their host halo. The kinematics previously described are
consistent with satellite infall and spin build-up via quasi-polar flows,
followed by a re-orientation of the spin of massive red galaxies through
mergers.Comment: 26 pages, 28 figures, 2 tables, submitted to A&
Caught in the rhythm II: Competitive alignments of satellites with their inner halo and central galaxy
The anisotropic distribution of satellites around the central galaxy of their
host halo is well-documented. However the relative impact of baryons and dark
matter in shaping this distribution is still debated. Using the simulation
Horizon-AGN, the angular distribution of satellite galaxies with respect to
their central counterpart and halo is quantified. Below one Rvir, satellites
cluster more strongly in the plane of the central, rather than merely tracing
the shape of their host halo. This is due to the increased isotropy of inner
haloes acquired through their inside-out assembly in vorticity-rich flows along
the cosmic web. While the effect of centrals decreases with distance, halos'
triaxiality increases, impacting more and more the satellite's distribution.
Effects become comparable just outside one virial radius. Above this scale, the
filamentary infall also impacts the satellites distribution, dominating above
two virial radii. The central's morphology plays a governing role: the
alignment w.r.t. the central plane is four times stronger in haloes hosting
stellar discs than in spheroids. But the impact of the galactic plane decreases
for lower satellite-to-central mass ratios, suggesting this might not hold for
dwarf satellites of the Local group. The orientation of the Milky-Way's
satellites traces their cosmic filament, their level of coplanarity is
consistent with systems of similar mass and cosmic location in Horizon-AGN.
However, the strong impact of galactic planes in massive groups and clusters
bounds the likelihood of finding a relaxed region where satellites can be used
to infer halo shape. The minor-to-major axis ratios for haloes with
log(M0/Msun)>13.5 is underestimated by 10%. This error soars quickly to 30-40%
for individual halo measurements.Comment: 30 pages, 28 figures, submitted to A&
- âŠ