239 research outputs found
Lunar laser ranging in infrfared at hte Grasse laser station
For many years, lunar laser ranging (LLR) observations using a green
wavelength have suffered an inhomogeneity problem both temporally and
spatially. This paper reports on the implementation of a new infrared detection
at the Grasse LLR station and describes how infrared telemetry improves this
situation. Our first results show that infrared detection permits us to densify
the observations and allows measurements during the new and the full Moon
periods. The link budget improvement leads to homogeneous telemetric
measurements on each lunar retro-reflector. Finally, a surprising result is
obtained on the Lunokhod 2 array which attains the same efficiency as Lunokhod
1 with an infrared laser link, although those two targets exhibit a
differential efficiency of six with a green laser link
ASTROD and ASTROD I -- Overview and Progress
In this paper, we present an overview of ASTROD (Astrodynamical Space Test of
Relativity using Optical Devices) and ASTROD I mission concepts and studies.
The missions employ deep-space laser ranging using drag-free spacecraft to map
the gravitational field in the solar-system. The solar-system gravitational
field is determined by three factors: the dynamic distribution of matter in the
solar system; the dynamic distribution of matter outside the solar system
(galactic, cosmological, etc.) and gravitational waves propagating through the
solar system. Different relativistic theories of gravity make different
predictions of the solar-system gravitational field. Hence, precise
measurements of the solar-system gravitational field test all these. The tests
and observations include: (i) a precise determination of the relativistic
parameters beta and gamma with 3-5 orders of magnitude improvement over
previous measurements; (ii) a 1-2 order of magnitude improvement in the
measurement of G-dot; (iii) a precise determination of any anomalous, constant
acceleration Aa directed towards the Sun; (iv) a measurement of solar angular
momentum via the Lense-Thirring effect; (v) the detection of solar g-mode
oscillations via their changing gravity field, thus, providing a new eye to see
inside the Sun; (vi) precise determination of the planetary orbit elements and
masses; (viii) better determination of the orbits and masses of major
asteroids; (ix) detection and observation of gravitational waves from massive
black holes and galactic binary stars in the frequency range 0.05 mHz to 5 mHz;
and (x) exploring background gravitational-waves.Comment: 17 pages, 6 figures, presented to The Third International ASTROD
Symposium on Laser Astrodynamics, Space Test of Relativity and
Gravitational-Wave Astronomy, Beijing, July 14-16, 2006; International
Journal of Modern Physics D, in press (2008
Velocity measurements for a solar active region fan loop from Hinode/EIS observations
The velocity pattern of a fan loop structure within a solar active region
over the temperature range 0.15-1.5 MK is derived using data from the EUV
Imaging Spectrometer (EIS) on board the Hinode satellite. The loop is aligned
towards the observer's line-of-sight and shows downflows (redshifts) of around
15 km/s up to a temperature of 0.8 MK, but for temperatures of 1.0 MK and above
the measured velocity shifts are consistent with no net flow. This velocity
result applies over a projected spatial distance of 9 Mm and demonstrates that
the cooler, redshifted plasma is physically disconnected from the hotter,
stationary plasma. A scenario in which the fan loops consist of at least two
groups of "strands" - one cooler and downflowing, the other hotter and
stationary -- is suggested. The cooler strands may represent a later
evolutionary stage of the hotter strands. A density diagnostic of Mg VII was
used to show that the electron density at around 0.8 MK falls from 3.2 x 10^9
cm^-3 at the loop base, to 5.0 x 10^8 cm^-3 at a projected height of 15 Mm. A
filling factor of 0.2 is found at temperatures close to the formation
temperature of Mg VII (0.8 MK), confirming that the cooler, downflowing plasma
occupies only a fraction of the apparent loop volume. The fan loop is rooted
within a so-called "outflow region" that displays low intensity and blueshifts
of up to 25 km/s in Fe XII 195.12 A (formed at 1.5 MK), in contrast to the
loop's redshifts of 15 km/s at 0.8 MK. A new technique for obtaining an
absolute wavelength calibration for the EIS instrument is presented and an
instrumental effect, possibly related to a distorted point spread function,
that affects velocity measurements is identified.Comment: 42 pages, 15 figures, submitted to Ap
Features of the ancestral bilaterian inferred from Platynereis dumerilii ParaHox genes
Background The ParaHox gene cluster is the evolutionary sister to the Hox cluster. Whilst the role of the Hox cluster in patterning the anterior-posterior axis of bilaterian animals is well established, and the organisation of vertebrate Hox clusters is intimately linked to gene regulation, much less is known about the more recently discovered ParaHox cluster. ParaHox gene clustering, and its relationship to expression, has only been described in deuterostomes. Conventional protostome models (Drosophila melanogaster and Caenorhabditis elegans) are secondarily derived with respect to ParaHox genes, suffering gene loss and cluster break-up. Results We provide the first evidence for ParaHox gene clustering from a less-derived protostome animal, the annelid Platynereis dumerilii. Clustering of these genes is thus not a sole preserve of the deuterostome lineage within Bilateria. This protostome ParaHox cluster is not entirely intact however, with Pdu-Cdx being on the opposite end of the same chromosome arm from Pdu-Gsx and Pdu-Xlox. From the genomic sequence around the P. dumerilii ParaHox genes the neighbouring genes are identified, compared with other taxa, and the ancestral arrangement deduced. Conclusion We relate the organisation of the ParaHox genes to their expression, and from comparisons with other taxa hypothesise that a relatively complex pattern of ParaHox gene expression existed in the protostome-deuterostome ancestor, which was secondarily simplified along several invertebrate lineages. Detailed comparisons of the gene content around the ParaHox genes enables the reconstruction of the genome surrounding the ParaHox cluster of the protostome-deuterostome ancestor, which existed over 550 million years ago.Publisher PDFPeer reviewe
Look ahead to improve QoE in DASH streaming
[EN] When a video is encoded with constant quality, the resulting bitstream will have variable bitrate due to the inherent nature of the video encoding process. This paper proposes a video Adaptive Bitrate Streaming (ABR) algorithm, called Look Ahead, which takes into account this bitrate variability in order to calculate, in real time, the appropriate quality level that minimizes the number of interruptions during the playback. The algorithm is based on the Dynamic Adaptive Streaming over HTTP (DASH) standard for on-demand video services. In fact, it has been implemented and integrated into ExoPlayer v2, the latest version of the library developed by Google to play DASH contents. The proposed algorithm is compared to the Müller and Segment Aware Rate Adaptation (SARA) algorithms as well as to the default ABR algorithm integrated into ExoPlayer. The comparison is carried out by using the most relevant parameters that affect the Quality of Experience (QoE) in video playback services, that is, number and duration of stalls, average quality of the video playback and number of representation switches. These parameters can be combined to define a QoE model. In this sense, this paper also proposes two new QoE models for the evaluation of ABR algorithms. One of them considers the bitrate of every segment of each representation, and the second is based on VMAF (Video Multimethod Assessment Fusion), a Video Quality Assessment (VQA) method developed by Netflix. The evaluations presented in the paper reflect: first, that Look Ahead outperforms the Müller, SARA and the ExoPlayer ABR algorithms in terms of number and duration of video playback stalls, with hardly decreasing the average video quality; and second, that the two QoE models proposed are more accurate than other similar models existing in the literature.This work is supported by the PAID-10-18 Program of the Universitat Politecnica de Valencia (Ayudas para contratos de acceso al sistema espanol de Ciencia, Tecnologia e Innovacion, en estructuras de investigacion de la Universitat Politecnica de Valencia) and by the Project 20180810 from the Universitat Politecnica de Valencia ("Tecnologias de distribucion y procesado de informacion multimedia y QoE").Belda Ortega, R.; De Fez Lava, I.; Arce Vila, P.; Guerri Cebollada, JC. (2020). Look ahead to improve QoE in DASH streaming. Multimedia Tools and Applications. 79(33-34):25143-25170. https://doi.org/10.1007/s11042-020-09214-9S25143251707933-34Akhshabi S, Narayanaswamy S, Begen AC, Dovrolis C (2012) An experimental evaluation of rate-adaptive video players over HTTP. Signal process. Image Commun 27(4):271–287. https://doi.org/10.1016/j.image.2011.10.003Android Developers webpage, ExoPlayer. Available online at: https://developer.android.com/guide/topics/media/exoplayer.html . Accessed: Jun. (2019)Bampis CG, Li Z, Bovik AC (2018) SpatioTemporal feature integration and model fusion for full reference video quality assessment. IEEE Trans on Circuits and Syst for Video Tech 29:2256–2270. https://doi.org/10.1109/TCSVT.2018.2868262Barman N, Martini MG (2019) QoE modeling for HTTP adaptive video streaming - a survey and open challenges. IEEE Access 7:30831–30859. https://doi.org/10.1109/ACCESS.2019.2901778Belda R (2013) Algoritmo de adaptación DASH: Look Ahead. Master Thesis. Universitat Politècnica de València. http://hdl.handle.net/10251/33359 .Belda R, de Fez I, Arce P, Guerri J C (2018) Look ahead: a DASH adaptation algorithm. Proc. of the IEEE Int. Symp. On broadband multimed. Syst. And broadcast., Valencia, Spain: article no. 158. https://doi.org/10.1109/BMSB.2018.8436718 .Blender Foundation webpage. Available online at: https://www.blender.org/foundation . Accessed: Jun. (2019).Cortes C, Vapnik V (1995) Support-vector networks. Mach Learn 20-3:273–297. https://doi.org/10.1023/A:1022627411411DASH Industry forum webpage. Available online at: http://dashif.org . Accessed: Jun. (2019)Ghadiyaram D, Pan J, Bovik AC (2019) A subjective and objective study of stalling events in mobile streaming videos. IEEE Trans on Circuits and Syst for Video Technol 29(1):183–197. https://doi.org/10.1109/TCSVT.2017.2768542Ghent University. 4G/LTE bandwidth logs. Available online at: http://users.ugent.be/~jvdrhoof/dataset-4g . Accessed: Jun. (2019).Github webpage. A DASH segment size aware rate adaptation model for DASH. Available online at: https://github.com/pari685/AStream . Accessed: Jun. (2019)GitHub website. Dashgen, Multimedia Communications Group. Available online at: https://github.com/comm-iteam/dashgen . Accessed: Jun. (2019).van der Hooft J, Petrangeli S, Wauters T, Huysegems R, Alface PR, Bostoen T, De Turck F (2016) HTTP/2-based adaptive streaming of HEVC video over 4G/LTE networks. IEEE Commun Lett 20(1):2177–2180. https://doi.org/10.1109/LCOMM.2016.2601087Huang TY, Johari R, McKeown N, Trunnell M, Watson M (2014) A buffer-based approach to rate adaptation: evidence from a large video streaming service. Proc. of the 2014 ACM Conf. On SIGCOMM, Chicago, IL, USA: 187-198. https://doi.org/10.1145/2619239.2626296Institute of Telecommunications and Multimedia Applications website. Look Ahead Demo. Available online at: https://lookahead.iteam.upv.es . Accessed: Jun. (2019)ISO/IEC 23009–1:2014 (2014) Dynamic adaptive streaming over HTTP (DASH) - Part 1: media presentation description and segment formats.Juluri P, Tamarapalli V, Medhi D (2015) SARA: segment aware rate adaptation algorithm for dynamic adaptive streaming over HTTP. Proc. of the IEEE Int. Conf. On Commun. Workshop (ICCW), London, UK: 1765-1770. https://doi.org/10.1109/ICCW.2015.7247436 .Juluri P, Tamarapalli V, Medhi D (2016) QoE management in DASH systems using the segment aware rate adaptation algorithm. Proc. of the IEEE/IFIP Netw. Oper. And Manag. Symp. (NOMS), Istanbul, Turkey: 129-136. https://doi.org/10.1109/NOMS.2016.7502805 .Kua J, Armitage G, Branch P (2017) A survey of rate adaptation techniques for dynamic adaptive streaming over HTTP. IEEE Commun Surv & Tutor 19(3):1842–1866. https://doi.org/10.1109/COMST.2017.2685630Lee S, Youn K, Chung K (2015) Adaptive video quality control scheme to improve QoE of MPEG DASH. Proc. of IEEE Int. Conf. On Consum. Electron. (ICCE), Las Vegas, NV, USA: 126-127. https://doi.org/10.1109/ICCE.2015.7066348 .Li S, Zhang F, Ma L, Ngan K (2011) Image quality assessment by separately evaluating detail losses and additive impairments. IEEE Trans. on Multimed. 13-5:935–949. https://doi.org/10.1109/TMM.2011.2152382Liu C, Bouazizi I, Gabbouj M (2011) Rate adaptation for adaptive HTTP streaming. Proc. of the second annual ACM Conf. On multimed. Syst. (MMSys), San Jose, CA, USA: 169-174. https://doi.org/10.1145/1943552.1943575 .Medium webpage (2016) Toward a practical perceptual video quality metric. Available online at: https://medium.com/netflix-techblog/toward-a-practical-perceptual-video-quality-metric-653f208b9652 . Accessed: Jun. 2019.Mobile Video Service Performance Study (2015) HUAWEI white paper. Available online at: http://www.ctiforum.com/uploadfile/2015/0701/20150701091255294.pdf .Mok RKP, Luo X, Chan EWW, Chang RKC (2012) QDASH: a QoE-aware DASH system. Proc. of multim. Syst. Conf. (MMSys), Chapel Hill, NC, USA: 11-22. https://doi.org/10.1145/2155555.2155558Moldovan C, Hagn K, Sieber C, Kellerer W, Hoßfeld T (2017) Keep calm and don’t switch: about the relationship between switches and quality in HAS. Proc. of the Int. Teletraffic Congr. (ITC), Genoa, Italy: pp. 1-6. https://doi.org/10.23919/ITC.2017.8065802Müller C, Lederer S, Timmerer C (2012) An evaluation of dynamic adaptive streaming over HTTP in vehicular environments. Proc. of the 4th workshop on mob. Video (MoVid), Chapel Hill, NC, USA: 37-42. https://doi.org/10.1145/2151677.2151686Nguyen T, Vu T, Nguyen DV, Ngoc NP, and Thang TC (2015) QoE optimization for adaptive streaming with multiple VBR videos. Proc. of the Int. Conf. On comp., Manag. And Telecommun. (ComManTel), DaNang, Vietnam: 189-193. https://doi.org/10.1109/ComManTel.2015.7394285 .Qin Y, H. Shuai, Pattipati K R, Qian F, Sen S, Wang B, Yue C (2018) ABR Streaming of VBR-encoded videos: characterization, challenges, and solutions. 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IEEE Journal on Select Areas in Commun 34-8:2141–2153. https://doi.org/10.1109/JSAC.2016.2577361Yarnagula H K, Juluri P, Mehr S K, Tamarapalli V, Medhi D (2019) QoE for Mobile clients with segment-aware rate adaptation algorithm (SARA) for DASH video streaming. ACM trans. On multimed. Comput., Commun., and Appl. (TOMM) 15(2):article no. 36 https://doi.org/10.1145/3311749 .Yin X, Sekar V, Sinopoli B (2014) Toward a principled framework to design dynamic adaptive streaming algorithms over HTTP. Proc. of the 13th ACM workshop on hot topics in Netw. (HotNets), Los Angeles, CA, USA: 1-7. https://doi.org/10.1145/2670518.2673877 .YouTube webpage (2019) Youtube press. Available online at: https://www.youtube.com/yt/about/press . Accessed: Jun. 2019.Youtube webpage, Google I/O ‘18: Building feature-rich media apps with ExoPlayer. Available online at: https://youtu.be/svdq1BWl4r8?t=2m . Published: May (2018)Yu L, Tillo T, Xiao J (2017) QoE-driven dynamic adaptive video streaming strategy with future information. IEEE Trans on Broadcast 63-3:523–534. https://doi.org/10.1109/TBC.2017.2687698Zhao S, Li Z, Medhi D, Lai P, Liu S (2017) Study of user QoE improvement for dynamic adaptive streaming over HTTP (MPEG-DASH). Proc. of the Int. Conf. On Comput., network. And Commun. (ICNC): multimed. Comput. And Commun., Santa Clara, CA, USA: 566-570. https://doi.org/10.1109/ICCNC.2017.7876191 .Zhou Y, Duan Y, Sun J, Guo Z (2014) Towards a simple and smooth rate adaption for VBR video in DASH. Proc. of the IEEE Vis. Commun. and Image Process. Conf, Valletta, pp 9–12. https://doi.org/10.1109/VCIP.2014.7051491Zhou C, Lin C-W, Guo Z (2016) mDASH: a Markov decision-based rate adaptation approach for dynamic HTTP streaming. IEEE Trans. on Multimed 18(4):738–751. https://doi.org/10.1109/TMM.2016.252265
A Mission to Explore the Pioneer Anomaly
The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep
space to date. These spacecraft had exceptional acceleration sensitivity.
However, analysis of their radio-metric tracking data has consistently
indicated that at heliocentric distances of astronomical units,
the orbit determinations indicated the presence of a small, anomalous, Doppler
frequency drift. The drift is a blue-shift, uniformly changing with a rate of
Hz/s, which can be interpreted as a
constant sunward acceleration of each particular spacecraft of . This signal has become known as the Pioneer
anomaly. The inability to explain the anomalous behavior of the Pioneers with
conventional physics has contributed to growing discussion about its origin.
There is now an increasing number of proposals that attempt to explain the
anomaly outside conventional physics. This progress emphasizes the need for a
new experiment to explore the detected signal. Furthermore, the recent
extensive efforts led to the conclusion that only a dedicated experiment could
ultimately determine the nature of the found signal. We discuss the Pioneer
anomaly and present the next steps towards an understanding of its origin. We
specifically focus on the development of a mission to explore the Pioneer
Anomaly in a dedicated experiment conducted in deep space.Comment: 8 pages, 9 figures; invited talk given at the 2005 ESLAB Symposium
"Trends in Space Science and Cosmic Vision 2020", 19-21 April 2005, ESTEC,
Noordwijk, The Netherland
Fundamental Physics with the Laser Astrometric Test Of Relativity
The Laser Astrometric Test Of Relativity (LATOR) is a joint European-U.S.
Michelson-Morley-type experiment designed to test the pure tensor metric nature
of gravitation - a fundamental postulate of Einstein's theory of general
relativity. By using a combination of independent time-series of highly
accurate gravitational deflection of light in the immediate proximity to the
Sun, along with measurements of the Shapiro time delay on interplanetary scales
(to a precision respectively better than 0.1 picoradians and 1 cm), LATOR will
significantly improve our knowledge of relativistic gravity. The primary
mission objective is to i) measure the key post-Newtonian Eddington parameter
\gamma with accuracy of a part in 10^9. (1-\gamma) is a direct measure for
presence of a new interaction in gravitational theory, and, in its search,
LATOR goes a factor 30,000 beyond the present best result, Cassini's 2003 test.
The mission will also provide: ii) first measurement of gravity's non-linear
effects on light to ~0.01% accuracy; including both the Eddington \beta
parameter and also the spatial metric's 2nd order potential contribution (never
measured before); iii) direct measurement of the solar quadrupole moment J2
(currently unavailable) to accuracy of a part in 200 of its expected size; iv)
direct measurement of the "frame-dragging" effect on light by the Sun's
gravitomagnetic field, to 1% accuracy. LATOR's primary measurement pushes to
unprecedented accuracy the search for cosmologically relevant scalar-tensor
theories of gravity by looking for a remnant scalar field in today's solar
system. We discuss the mission design of this proposed experiment.Comment: 8 pages, 9 figures; invited talk given at the 2005 ESLAB Symposium
"Trends in Space Science and Cosmic Vision 2020," 19-21 April 2005, ESTEC,
Noodrwijk, The Netherland
Discovery of a sol–gel reinforcing the strength of hair structure: mechanisms of action and macroscopic effects on the hair
Recommended from our members
Multi-scale sensible heat fluxes in the urban environment from large aperture scintillometry and eddy covariance
Sensible heat fluxes (QH) are determined using scintillometry and eddy covariance over a suburban area. Two large aperture scintillometers provide spatially integrated fluxes across path lengths of 2.8 km and 5.5 km over Swindon, UK. The shorter scintillometer path spans newly built residential areas and has an approximate source area of 2-4 km2, whilst the long path extends from the rural outskirts to the town centre and has a source area of around 5-10 km2. These large-scale heat fluxes are compared with local-scale eddy covariance measurements. Clear seasonal trends are revealed by the long duration of this dataset and variability in monthly QH is related to the meteorological conditions. At shorter time scales the response of QH to solar radiation often gives rise to close agreement between the measurements, but during times of rapidly changing cloud cover spatial differences in the net radiation (Q*) coincide with greater differences between heat fluxes. For clear days QH lags Q*, thus the ratio of QH to Q* increases throughout the day. In summer the observed energy partitioning is related to the vegetation fraction through use of a footprint model. The results demonstrate the value of scintillometry for integrating surface heterogeneity and offer improved understanding of the influence of anthropogenic materials on surface-atmosphere interactions
Space-QUEST: Experiments with quantum entanglement in space
The European Space Agency (ESA) has supported a range of studies in the field
of quantum physics and quantum information science in space for several years,
and consequently we have submitted the mission proposal Space-QUEST (Quantum
Entanglement for Space Experiments) to the European Life and Physical Sciences
in Space Program. We propose to perform space-to-ground quantum communication
tests from the International Space Station (ISS). We present the proposed
experiments in space as well as the design of a space based quantum
communication payload.Comment: 4 pages, 1 figure, accepted for the 59th International Astronautical
Congress (IAC) 200
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