The architecture of microalgae biofilms has been poorly investigated, in particular with respect to shear stress, which is a crucial factor in biofilm-based reactor design and operation. To ...investigate how microalgae biofilms respond to different hydrodynamic regimes, the architecture and cohesion of Chlorella vulgaris biofilms were studied in flow-cells at three shear stress: 1.0, 6.5 and 11.0 mPa. Biofilm physical properties and architecture dynamics were monitored using a set of microscopic techniques such as, fluorescence recovery after photobleaching (FRAP) and particle tracking. At low shear, biofilms cohesion was heterogeneous resulting in a strong basal (close to the substrate) layer and in more loose superficial ones. Higher shear (11.0 mPa) significantly increased the cohesion of the biofilms allowing them to grow thicker and to produce more biomass, likely due to a biological response to resist the shear stress. Interestingly, an acclimation strategy seemed also to occur which allowed the biofilms to preserve their growth rate at the different hydrodynamic regimes. Our results are in accordance with those previously reported for bacteria biofilms, revealing some general physical/mechanical rules that govern microalgae life on substrates. These results may bring new insights about how to improve productivity and stability of microalgae biofilm-based systems.
Available commercial piezoelectric pressure sensors are not able to accurately reproduce the ultra-fast transient pressure occurring during an air blast experiment. In this communication a new ...pressure sensor prototype based on a miniature silicon membrane and piezoresistive gauges is reported for significantly improving the performances in terms of time response. Simulation results demonstrate the feasibility of a pressure transducer having a fundamental resonant frequency almost ten times greater than the commercial piezoelectric sensors one. The sensor uses a 5μm-thick SOI membrane and four P-type silicon gauges (doping level ≅ 1019 at/cm3) in Wheatstone bridge configuration. To obtain a good trade-off between the fundamental mechanical resonant frequency and pressure sensitivity values, the typical dimension of the rectangular membrane is fixed to 30μm x 90μm with gauge dimension of 1μm x 5μm. The achieved simulated mechanical resonant frequency of these configuration is greater than 40MHz with a sensitivity of 0.04% per bar.
Pluto and its satellite, Charon (discovered in 1978; ref. 1), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about ...one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities. Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius, which was later refined to 601.5 km (ref. 4). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, RC = 603.6 ± 1.4 km (1σ), and a density of ρ = 1.71 ± 0.08 g cm-3. This occultation also provides upper limits of 110 and 15 (3σ) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
During the 2014–2015 mutual events season, the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE), Paris, France, and the Sternberg Astronomical Institute (SAI), Moscow, ...Russia, led an international observation campaign to record ground-based photometric observations of Galilean moon mutual occultations and eclipses. We focused on processing the complete photometric observations data base to compute new accurate astrometric positions. We used our method to derive astrometric positions from the light curves of the events. We developed an accurate photometric model of mutual occultations and eclipses, while correcting for the satellite albedos, Hapke's light scattering law, the phase effect, and the limb darkening. We processed 609 light curves, and we compared the observed positions of the satellites with the theoretical positions from IMCCE NOE-5-2010-GAL satellite ephemerides and INPOP13c planetary ephemeris. The standard deviation after fitting the light curve in equatorial positions is ±24 mas, or 75 km at Jupiter. The rms (O−C) in equatorial positions is ±50 mas, or 150 km at Jupiter.
The main contribution of this study is to propose time-resolved measurements to determine temperature with a novel source of continuous excitation for an induced fluorescence technique with laser ...diagnosis based on tracer-induced fluorescence, which has become a major tool for experimental studies of fluid dynamics in reaction flows. We use a Hg (Xe) arc lamp as a continuous light source that has a wide range of emissions in wavelength. With this setup, one can reach high spatial and temporal resolution (temperature, pressure, species concentration, and velocity) to acquire quantitative data for the control of fluid thermal systems, such as engines, combustion chambers, furnaces, and reactors. A fluorescence study was performed on various tracers and their configurations. We focus on an anisole tracer using a broad wavelength of excitations. We propose a calibration to achieve temperature measurements in the range of 493–773 K and from 0.2 to 3.5 MPa of pressure. The temperature-dependent fluorescence is based on a two-line technique. The results give a better understanding of the influence of temperature and pressure in a nitrogen bath gas on the fluorescence photophysics in the UV domain. High temporal resolution was acquired using a high-speed intensified camera setup. The application of the photomultipliers manages the time-scale evolution of the flow in continuous emission and this eliminates the signal-to-noise ratio impact.
This paper addresses the measurement of incident pressure in air blast experiment using wireless pressure sensors. The analysis of the proposed wireless system is presented and measurement results ...obtained during an air blast event are reported. The proposed approach offers a very attractive solution in terms of cost, size and power consumption for transmitting and analyzing sensor data in harsh environment.
Context. Aims.We present evidence that four minor planets of the main belt are binary systems. Methods.These discoveries are based on CCD photometric measurements made by many observers coordinated ...in a network of observatories. Results.Orbital and physical properties are derived from a total of 134 partial light curves involving 26 stations. (854) Frostia, (1089) Tama, (1313) Berna, and (4492) Debussy show mutual eclipses features on their light curves. In all cases, rotation and revolution are synchronous. Synodic periods are 37.728, 16.444, 25.464 and 26.606 h respectively. From a simple model, we have derived their bulk densities as follows: 0.89 ± 0.14, 2.52 ± 0.30, 1.22 ± 0.15 and 0.91 ± 0.10 g cm-3 respectively. Uncertainties in the bulk densities, arising from scattering and shadow effects are not taken into account. These could increase the density estimates by a factor up to 1.6. Our method of determining bulk density is completely independent of their mass and their diameter estimates. The low rotational periods and the low bulk densities clearly imply a collisional process to explain this kind of binary asteroid. Based on our database of a few thousand light curves of minor planets, the population of similar-sized objects in the main belt is estimated to $6\pm 3$ percent in the 10–50 km diameter class. Conclusions.
Core level photoelectron spectromicroscopy in laboratory conditions (XPS imaging) with standard Al Kα
1 excitation (1486.6
eV), either in scanning or parallel imaging mode, is currently limited to a ...spatial resolution of ∼4
μm. Using energy-filtered X-ray photoelectron emission microscopy (XPEEM) and a bright monochromated Al Kα source (photon flux ∼10
12
photons/(s
mm
2)), we demonstrate refined results regarding lateral and energy resolutions on cross-sectioned epitaxial Si/SiGe layers imaged with photoelectrons of 266.4
eV energy referred to the Fermi level of the sample (Ge 2p
3/2 transition). Despite an elemental contrast of only 50%, XPS imaging performed this way has an edge lateral resolution of 480
nm and an energy resolution of 0.56
eV, the spectroscopic information being available at the decanometric scale. Since the lateral resolution is only limited by the counting statistics due to a modest illumination flux, this method paves the way to laterally resolved XPS and UPS in the 100
nm range.
On September 8, 2001 around 2 h UT, the largest uranian moon, Titania, occulted Hipparcos star 106829 (alias SAO 164538, a
V
=
7.2
, K0 III star). This was the first-ever observed occultation by this ...satellite, a rare event as Titania subtends only 0.11 arcsec on the sky. The star's unusual brightness allowed many observers, both amateurs or professionals, to monitor this unique event, providing fifty-seven occultations chords over three continents, all reported here. Selecting the best 27 occultation chords, and assuming a circular limb, we derive Titania's radius:
R
T
=
788.4
±
0.6
km
(
1
-
σ
error bar). This implies a density of
ρ
=
1.711
±
0.005
g
cm
−3
using the value
G
M
=
(
2.343
±
0.006
)
×
10
11
m
3
s
−2
derived by Taylor Taylor, D.B., 1998. Astron. Astrophys. 330, 362–374. We do not detect any significant difference between equatorial and polar radii, in the limit
r
eq
−
r
po
=
−
1.3
±
2.1
km
, in agreement with
Voyager limb image retrieval during the 1986 flyby. Titania's offset with respect to the DE405 + URA027 (based on GUST86 theory) ephemeris is derived:
Δ
α
T
cos
(
δ
T
)
=
−
108
±
13
mas and
Δ
δ
T
=
−
62
±
7
mas (ICRF J2000.0 system). Most of this offset is attributable to a Uranus' barycentric offset with respect to DE405, that we estimate to be:
Δ
α
U
cos
(
δ
U
)
=
−
100
±
25
mas
and
Δ
δ
U
=
−
85
±
25
mas at the moment of occultation. This offset is confirmed by another Titania stellar occultation observed on August 1st, 2003, which provides an offset of
Δ
α
T
cos
(
δ
T
)
=
−
127
±
20
mas and
Δ
δ
T
=
−
97
±
13
mas for the satellite. The combined ingress and egress data do not show any significant hint for atmospheric refraction, allowing us to set surface pressure limits at the level of 10–20 nbar. More specifically, we find an upper limit of 13 nbar (
1
-
σ
level) at 70 K and 17 nbar at 80 K, for a putative isothermal CO
2 atmosphere. We also provide an upper limit of 8 nbar for a possible CH
4 atmosphere, and 22 nbar for pure N
2, again at the
1
-
σ
level. We finally constrain the stellar size using the time-resolved star disappearance and reappearance at ingress and egress. We find an angular diameter of
0.54
±
0.03
mas (corresponding to
7.5
±
0.4
km
projected at Titania). With a distance of
170
±
25
parsecs, this corresponds to a radius of
9.8
±
0.2
solar radii for HIP 106829, typical of a K0 III giant.
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