53,005 research outputs found
On the consequences of a fragmentation due to a NEO mitigation strategy
The fragmentation of an Earth threatening asteroid as a result of a hazard mitigation mission is examined in
this paper. The minimum required energy for a successful impulsive deflection of a threatening object is
computed and compared with the energy required to break-up a small size asteroid. The fragmentation of an asteroid that underwent an impulsive deflection such as a kinetic impact or a nuclear explosion is a very plausible outcome in the light of this work. Thus a model describing the stochastic evolution of the cloud of fragments is described. The stochasticity of the fragmentation is given by a Gaussian probability distribution that
describes the initial relative velocities of each fragment of the asteroid, while the size distribution is expressed
through a power law function. The fragmentation model is applied to Apophis as illustrative example. If a barely
catastrophic disruption (i.e. the largest fragment is half the size the original asteroid) occurs 10 to 20 years prior
to the Earth encounter only a reduction from 50% to 80% of the potential damage is achieve for the Apophis test
case
The use of tethers for payload orbital transfer. Continuation of investigation of electrodynamic stabilization and control of long orbiting tethers, volume 2
The SKYHOOK program was used to do simulations of two cases of the use of the tether for payload orbital transfer. The transport of a payload along the tether from a heavy lower platform to an upper launching platform is considered. A numerical example of the Shuttle launching a payload using an orbital tether facility is described
Constraining the Warm Dark Matter Particle Mass through Ultra-Deep UV Luminosity Functions at z=2
We compute the mass function of galactic dark matter halos for different
values of the Warm Dark Matter (WDM) particle mass m_X and compare it with the
abundance of ultra-faint galaxies derived from the deepest UV luminosity
function available so far at redshift z~2. The magnitude limit M_UV=-13 reached
by such observations allows us to probe the WDM mass functions down to scales
close to or smaller than the half-mass mode mass scale ~10^9 M_sun. This
allowed for an efficient discrimination among predictions for different m_X
which turn out to be independent of the star formation efficiency adopted to
associate the observed UV luminosities of galaxies to the corresponding dark
matter masses. Adopting a conservative approach to take into account the
existing theoretical uncertainties in the galaxy halo mass function, we derive
a robust limit m_X>1.8 keV for the mass of thermal relic WDM particles when
comparing with the measured abundance of the faintest galaxies, while m_X>1.5
keV is obtained when we compare with the Schechter fit to the observed
luminosity function. The corresponding lower limit for sterile neutrinos
depends on the modeling of the production mechanism; for instance m_sterile > 4
keV holds for the Shi-Fuller mechanism. We discuss the impact of observational
uncertainties on the above bound on m_X. As a baseline for comparison with
forthcoming observations from the HST Frontier Field, we provide predictions
for the abundance of faint galaxies with M_UV=-13 for different values of m_X
and of the star formation efficiency, valid up to z~4.Comment: 14 pages, 3 figures. Accepted for publication in The Astrophysical
Journa
Electrospun fibrinogen-PLA nanofibres for vascular tissue engineering
Here we report on the development of a new type of hybrid fibrinogen–polylactic acid (FBG–PLA) nanofibres (NFs) with improved stiffness, combining the good mechanical properties of PLA with the excellent cell recognition properties of native FBG. We were particularly interested in the dorsal and ventral cell response to the nanofibres' organization (random or aligned), using human umbilical endothelial cells (HUVECs) as a model system. Upon ventral contact with random NFs, the cells developed a stellate-like morphology with multiple projections. The well-developed focal adhesion complexes suggested a successful cellular interaction. However, time-lapse analysis shows significantly lowered cell movements, resulting in the cells traversing a relatively short distance in multiple directions. Conversely, an elongated cell shape and significantly increased cell mobility were observed in aligned NFs. To follow the dorsal cell response, artificial wounds were created on confluent cell layers previously grown on glass slides and covered with either random or aligned NFs. Time-lapse analysis showed significantly faster wound coverage (within 12 h) of HUVECs on aligned samples vs. almost absent directional migration on random ones. However, nitric oxide (NO) release shows that endothelial cells possess lowered functionality on aligned NFs compared to random ones, where significantly higher NO production was found. Collectively, our studies show that randomly organized NFs could support the endothelization of implants while aligned NFs would rather direct cell locomotion for guided neovascularization
Highlights and Conclusions of the Chalonge 14th Paris Cosmology Colloquium 2010: `The Standard Model of the Universe: Theory and Observations'
The Chalonge 14th Paris Cosmology Colloquium was held on 22-24 July 2010 in
Paris Observatory on the Standard Model of the Universe: News from WMAP7,
BICEP, QUAD, SPT, AMI, ACT, Planck, QUIJOTE and Herschel; dark matter (DM)
searches and galactic observations; related theory and simulations. %aiming
synthesis, progress and clarification. P Biermann, D Boyanovsky, A Cooray, C
Destri, H de Vega, G Gilmore, S Gottlober, E Komatsu, S McGaugh, A Lasenby, R
Rebolo, P Salucci, N Sanchez and A Tikhonov present here their highlights of
the Colloquium. Inflection points emerged: LambdaWDM (Warm DM) emerges
impressively over LambdaCDM whose galactic scale problems are ever-increasing.
Summary and conclusions by H. J. de Vega, M. C. Falvella and N. G. Sanchez
stress among other points: (i) Primordial CMB gaussianity is confirmed.
Inflation effective theory predicts a tensor to scalar ratio 0.05-0.04 at
reach/border line of next CMB observations, early fast-roll inflation provides
lowest multipoles depression. SZ amplitudes are smaller than expected: CMB and
X-ray data agree but intracluster models need revision and relaxed/non-relaxed
clusters distinction. (ii) cosmic ray positron excess is explained naturally by
astrophysical processes, annihilating/decaying dark matter needs growing
tailoring. (iii) Cored (non cusped) DM halos and warm (keV scale mass) DM are
increasingly favored from theory and observations, naturally producing observed
small scale structures, wimps turn strongly disfavoured. LambdaWDM 1 keV
simulations well reproduce observations. Evidence that LambdaCDM does not work
at small scales is staggering. P Biermann presents his live minutes of the
Colloquium and concludes that a keV sterile neutrino is the most interesting DM
candidate. Photos of the Colloquium are included.Comment: 58 pages, 20 figures. Three contributions added: G. Gilmore, S.
Gottlober and E. Komats
Towards the Chalonge 16th Paris Cosmology Colloquium 2012: Highlights and Conclusions of the Chalonge 15th Paris Cosmology Colloquium 2011
The Chalonge 15th Paris Cosmology Colloquium 2011 was held on 20-22 July in
the historic Paris Observatory's Perrault building, in the Chalonge School
spirit combining real cosmological/astrophysical data and hard theory
predictive approach connected to them in the Warm Dark Matter Standard Model of
the Universe: News and reviews from Herschel, QUIET, Atacama Cosmology
Telescope (ACT), South Pole Telescole (SPT), Planck, PIXIE, the JWST, UFFO,
KATRIN and MARE experiments; astrophysics, particle and nuclear physics warm
dark matter (DM) searches and galactic observations, related theory and
simulations, with the aim of synthesis, progress and clarification. Philippe
Andre, Peter Biermann, Pasquale Blasi, Daniel Boyanovsky, Carlo Burigana,
Hector de Vega, Joanna Dunkley, Gerry Gilmore, Alexander Kashlinsky, Alan
Kogut, Anthony Lasenby, John Mather, Norma Sanchez, Alexei Smirnov, Sylvaine
Turck-Chieze present here their highlights of the Colloquium. Ayuki Kamada and
Sinziana Paduroiu present here their poster highlights. LambdaWDM (Warm Dark
Matter) is progressing impressively over LambdaCDM whose galactic scale crisis
and decline are staggering. The International School Daniel Chalonge issued an
statement of strong support to the James Webb Space Telescope (JSWT). The
Daniel Chalonge Medal 2011 was awarded to John C. Mather, Science PI of the
JWST. Summary and conclusions are presented by H. J. de Vega, M. C. Falvella
and N. G. Sanchez. Overall, LambdaWDM and keV scale DM particles deserve
dedicated astronomical and laboratory experimental searches, theoretical work
and simulations. KATRIN experiment in the future could perhaps adapt its set-up
to look to keV scale sterile neutrinos. It will be a a fantastic discovery to
detect dark matter in a beta decay. Photos of the Colloquium are included.
(Abridged)Comment: 65 pages, 21 figure
Towards the Chalonge 17th Paris Cosmology Colloquium 2013: highlights and conclusions of the Chalonge 16th Paris Cosmology Colloquium 2012
LWDM (Warm Dark Matter) is progressing impressively.The galactic scale crisis
and decline of LCDM+baryons are staggering. The 16th Paris Chalonge Colloquium
2012 combined real cosmological/astrophysical data and hard theory predictive
approach in the LWDM Standard Model. News and reviews from
ACT,WMAP,SPT,QUIET,Planck,Herschel,JWST,UFFO,KATRIN and MARE experiments;
astrophysics, particle and nuclear physics WDM searches, galactic observations,
related theory and simulations, with the aim of synthesis and clarification.
Here highlights by P Biermann, C Burigana, C Conselice, A Cooray, H de Vega, C
Giunti & M Laveder, J Kormendi & K Freeman, E Ma, J Mather, L Page, G Smoot, N
Sanchez. Summary and conclusions by de Vega, Falvella and Sanchez. Data confirm
primordial CMB gaussianity. Effective (Ginsburg-Landau) Inflation theory
predicts r about 0.04-0.05, negligeable running of ns, the inflation energy
scale (GUT scale) and the set of CMB observables in agreement with the data.
WMAP9 and Planck measurements are compatible with one or two Majorana sterile
neutrinos in the eV mass scale. Cored (non cusped) DM halos and keV WDM are
strongly favored by theory and observations, Wimps are strongly disfavoured.
LambdaCDM with baryons do not work at small scales. Inside galaxy cores,
quantum WDM effects are important. Quantum WDM calculations (Thomas-Fermi)
provide galaxy masses, velocity dispersions and cored profiles and their sizes
in agreement with observations. A WDM fermion of about 2 keV naturally
reproduces galaxy, large scale and cosmological observations. WDM keV particles
deserve dedicated astronomical and laboratory searches, theoretical work and
numerical simulations. KATRIN can be adapted to look to keV scale sterile
neutrinos. It will be a fantastic discovery to detect dark matter in beta
decay. Photos of the Colloquium are includedComment: 58 pages, 15 figures. arXiv admin note: substantial text overlap with
arXiv:1203.3562, arXiv:1305.7452, arXiv:1009.3494, arXiv:1304.075
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