114 research outputs found
Torsion pendulum facility for direct force measurements of LISA GRS related disturbances
A four mass torsion pendulum facility for testing of the LISA GRS is under
development in Trento. With a LISA-like test mass suspended off-axis with
respect to the pendulum fiber, the facility allows for a direct measurement of
surface force disturbances arising in the GRS. We present here results with a
prototype pendulum integrated with very large-gap sensors, which allows an
estimate of the intrinsic pendulum noise floor in the absence of sensor related
force noise. The apparatus has shown a torque noise near to its mechanical
thermal noise limit, and would allow to place upper limits on GRS related
disturbances with a best sensitivity of 300 fN/Hz^(1/2) at 1mHz, a factor 50
from the LISA goal. Also, we discuss the characterization of the gravity
gradient noise, one environmental noise source that could limit the apparatus
performances, and report on the status of development of the facility.Comment: Submitted to Proceedings of the 6th International LISA Symposium, AIP
Conference Proceedings 200
Thermal gradient-induced forces on geodetic reference masses for LISA
The low frequency sensitivity of space-borne gravitational wave observatories
will depend critically on the geodetic purity of the trajectories of orbiting
test masses. Fluctuations in the temperature difference across the enclosure
surrounding the free-falling test mass can produce noisy forces through several
processes, including the radiometric effect, radiation pressure, and
outgassing. We present here a detailed experimental investigation of thermal
gradient-induced forces for the LISA gravitational wave mission and the LISA
Pathfinder, employing high resolution torsion pendulum measurements of the
torque on a LISA-like test mass suspended inside a prototype of the LISA
gravitational reference sensor that will surround the test mass in orbit. The
measurement campaign, accompanied by numerical simulations of the radiometric
and radiation pressure effects, allows a more accurate and representative
characterization of thermal-gradient forces in the specific geometry and
environment relevant to LISA free-fall. The pressure dependence of the measured
torques allows clear identification of the radiometric effect, in quantitative
agreement with the model developed. In the limit of zero gas pressure, the
measurements are most likely dominated by outgassing, but at a low level that
does not threaten the LISA sensitivity goals.Comment: 21 pages, 16 figures, submitted to Physical Review
An examination of targeted gene neighborhoods in strawberry
<p>Abstract</p> <p>Background</p> <p>Strawberry (<it>Fragaria </it>spp.) is the familiar name of a group of economically important crop plants and wild relatives that also represent an emerging system for the study of gene and genome evolution. Its small stature, rapid seed-to-seed cycle, transformability and miniscule basic genome make strawberry an attractive system to study processes related to plant physiology, development and crop production; yet it lacks substantial genomics-level resources. This report addresses this deficiency by characterizing 0.71 Mbp of gene space from a diploid species (<it>F. vesca</it>). The twenty large genomic tracks (30-52 kb) captured as fosmid inserts comprise gene regions with roles in flowering, disease resistance, and metabolism.</p> <p>Results</p> <p>A detailed description of the studied regions reveals 131 Blastx-supported gene sites and eight additional EST-supported gene sites. Only 15 genes have complete EST coverage, enabling gene modelling, while 76 lack EST support. Instances of microcolinearity with <it>Arabidopsis thaliana </it>were identified in twelve inserts. A relatively high portion (25%) of targeted genes were found in unanticipated tandem duplications. The effectiveness of six FGENESH training models was assessed via comparisons among <it>ab initio </it>predictions and homology-based gene and start/stop codon identifications. Fourteen transposable-element-related sequences and 158 simple sequence repeat loci were delineated.</p> <p>Conclusions</p> <p>This report details the structure and content of targeted regions of the strawberry genome. The data indicate that the strawberry genome is gene-dense, with an average of one protein-encoding gene or pseudogene per 5.9 kb. Current overall EST coverage is sparse. The unexpected gene duplications and their differential patterns of EST support suggest possible subfunctionalization or pseudogenization of these sequences. This report provides a high-resolution depiction of targeted gene neighborhoods that will aid whole-genome sequence assembly, provide valuable tools for plant breeders and advance the understanding of strawberry genome evolution.</p
Brownian force noise from molecular collisions and the sensitivity of advanced gravitational wave observatories
We present an analysis of Brownian force noise from residual gas damping of
reference test masses as a fundamental sensitivity limit in small force
experiments. The resulting acceleration noise increases significantly when the
distance of the test mass to the surrounding experimental apparatus is smaller
than the dimension of the test mass itself. For the Advanced LIGO
interferometric gravitational wave observatory, where the relevant test mass is
a suspended 340 mm diameter cylindrical end mirror, the force noise power is
increased by roughly a factor 40 by the presence of a similarly shaped reaction
mass at a nominal separation of 5 mm. The force noise, of order 20 fN\rthz\ for
Pa of residual H gas, rivals quantum optical
fluctuations as the dominant noise source between 10 and 30 Hz. We present here
a numerical and analytical analysis for the gas damping force noise for
Advanced LIGO, backed up by experimental evidence from several recent
measurements. Finally, we discuss the impact of residual gas damping on the
gravitational wave sensitivity and possible mitigation strategies.Comment: 13 pages with 9 figures (fixed typos found in proofs
Transport of Po Valley aerosol pollution to the northwestern Alps – Part 1: Phenomenology
Mountainous regions are often considered pristine environments;
however they can be affected by pollutants emitted in more populated and
industrialised areas, transported by regional winds. Based on experimental
evidence, further supported by modelling tools, here we demonstrate and quantify
the impact of air masses transported from the Po Valley, a European
atmospheric pollution hotspot, to the northwestern Alps. This is achieved
through a detailed investigation of the phenomenology of near-range (a few
hundred kilometres), trans-regional transport, exploiting synergies of
multi-sensor observations mainly focussed on particulate matter. The explored
dataset includes vertically resolved data from atmospheric profiling
techniques (automated lidar ceilometers, ALCs), vertically integrated aerosol
properties from ground (sun photometer) and space, and in situ measurements
(PM10 and PM2.5, relevant chemical analyses, and aerosol
size distribution). During the frequent advection episodes from the Po basin,
all the physical quantities observed by the instrumental setup are found to
significantly increase: the scattering ratio from ALC reaches values >30,
aerosol optical depth (AOD) triples, surface PM10 reaches
concentrations >100 µg m−3 even in rural areas, and
contributions to PM10 by secondary inorganic compounds such as
nitrate, ammonium, and sulfate increase up to 28 %, 8 %, and 17 %,
respectively. Results also indicate that the aerosol advected from the Po
Valley is hygroscopic, smaller in size, and less light-absorbing compared to
the aerosol type locally emitted in the northwestern Italian Alps. In this
work, the phenomenon is exemplified through detailed analysis and discussion
of three case studies, selected for their clarity and relevance within the
wider dataset, the latter being fully exploited in a companion paper
quantifying the impact of this phenomenology over the long-term
(Diémoz et al., 2019). For the three case studies investigated, a high-resolution
numerical weather prediction model (COSMO) and a Lagrangian tool (LAGRANTO)
are employed to understand the meteorological mechanisms favouring
transport and to demonstrate the Po Valley origin of the air masses. In
addition, a chemical transport model (FARM) is used to further support the
observations and to partition the contributions of local and non-local
sources. Results show that the simulations are important to the understanding
of the phenomenon under investigation. However, in quantitative terms,
modelled PM10 concentrations are 4–5 times lower than the ones
retrieved from the ALC and maxima are anticipated in time by 6–7 h.
Underestimated concentrations are likely mainly due to deficiencies in the
emission inventory and to water uptake of the advected particles not fully
reproduced by FARM, while timing mismatches are likely an effect of
suboptimal simulation of up-valley and down-valley winds by COSMO. The
advected aerosol is shown to remarkably degrade the air quality of the Alpine
region, with potential negative effects on human health, climate, and
ecosystems, as well as on the touristic development of the investigated area.
The findings of the present study could also help design mitigation
strategies at the trans-regional scale in the Po basin and suggest an
observation-based approach to evaluate the outcome of their implementation.</p
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