349 research outputs found
Photometry of comet 9P/Tempel 1 during the 2004/2005 approach and the Deep Impact module impact
The results of the 9P/Tempel 1 CARA (Cometary Archive for Amateur
Astronomers) observing campaign is presented. The main goal was to perform an
extended survey of the comet as a support to the Deep Impact (DI) Mission. CCD
R, I and narrowband aperture photometries were used to monitor the
quantity. The observed behaviour showed a peak of 310 cm 83 days before
perihelion, but we argue that it could be distorted by the phase effect, too.
The phase effect is roughly estimated around 0.0275 mag/degree, but we had no
chance for direct determination because of the very similar geometry of the
observed apparitions. The log-slope of was around -0.5 between about
180--100 days before the impact but evolved near the steady-state like 0 value
by the impact time. The DI module impact caused an about 60%{} increase in the
value of and a cloud feature in the coma profile which was observed
just after the event. The expansion of the ejecta cloud was consistent with a
fountain model with initial projected velocity of 0.2 km/s and =0.73.
Referring to a 25~000 km radius area centered on the nucleus, the total cross
section of the ejected dust was 8.2/ km 0.06 days after the impact, and
1.2/ km 1.93 days after the impact ( is the dust albedo). 5 days
after the event no signs of the impact were detected nor deviations from the
expected activity referring both to the average pre-impact behaviour and to the
previous apparitions ones.Comment: 25 pages (including cover pages), 9 figures, 1 table, accepted by
Icarus DI Special Issu
Gauge-Invariant Quasi-Free States on the Algebra of the Anyon Commutation Relations
Let and let , . For and from , we define a function to be equal to if , and to if . Let , () be operator-valued distributions such that is the adjoint of . We say that , satisfy the anyon commutation relations (ACR) if for and for . In particular, for , the ACR become the canonical commutation relations and for , the ACR become the canonical anticommutation relations. We define the ACR algebra as the algebra generated by operator-valued integrals of , . We construct a class of gauge-invariant quasi-free states on the ACR algebra. Each state from this class is completely determined by a positive self-adjoint operator on the real space which commutes with any operator of multiplication by a bounded function . In the case ), we discuss the corresponding particle density . For , using a renormalization, we rigorously define a vacuum state on the commutative algebra generated by operator-valued integrals of . This state is given by a negative binomial point process. A scaling limit of these states as gives the gamma random measure, depending on parameter
Aharonov-Bohm Physics with Spin II: Spin-Flip Effects in Two-dimensional Ballistic Systems
We study spin effects in the magneto-conductance of ballistic mesoscopic
systems subject to inhomogeneous magnetic fields. We present a numerical
approach to the spin-dependent Landauer conductance which generalizes recursive
Green function techniques to the case with spin. Based on this method we
address spin-flip effects in quantum transport of spin-polarized and
-unpolarized electrons through quantum wires and various two-dimensional
Aharonov-Bohm geometries. In particular, we investigate the range of validity
of a spin switch mechanism recently found which allows for controlling spins
indirectly via Aharonov-Bohm fluxes. Our numerical results are compared to a
transfer-matrix model for one-dimensional ring structures presented in the
first paper (Hentschel et al., submitted to Phys. Rev. B) of this series.Comment: 29 pages, 15 figures. Second part of a series of two article
Quasars and their host galaxies
This review attempts to describe developments in the fields of quasar and
quasar host galaxies in the past five. In this time period, the Sloan and 2dF
quasar surveys have added several tens of thousands of quasars, with Sloan
quasars being found to z>6. Obscured, or partially obscured quasars have begun
to be found in significant numbers. Black hole mass estimates for quasars, and
our confidence in them, have improved significantly, allowing a start on
relating quasar properties such as radio jet power to fundamental parameters of
the quasar such as black hole mass and accretion rate. Quasar host galaxy
studies have allowed us to find and characterize the host galaxies of quasars
to z>2. Despite these developments, many questions remain unresolved, in
particular the origin of the close relationship between black hole mass and
galaxy bulge mass/velocity dispersion seen in local galaxies.Comment: Review article, to appear in Astrophysics Update
Multiwavelength observations of the obscuring wind in the radio-quiet quasar MR 2251-178
High Energy Astrophysic
Psicoanalisi e prospettive evoluzionistiche dell'attaccamento: un progetto di prevenzione per la tutela della salute mentale perinatale
GIBBERELLIC ACID REDUCES FLOWERING AND TIME OF MANUAL THINNING IN ‘MACIEL’ PEACH TREES
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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