487 research outputs found
A method for handlebars ballast calculation in order to reduce vibrations transmissibility in walk behind tractors
Walk behind tractors have some advantages over other agricultural machines, such as the cheapness and the easy to use, however the driver is exposed to high level of vibrations transmitted from handles to hand-arm system and to shoulders. The vibrations induce discomfort and early fatigue to the operator. In order to control the vibration transmissibility, a ballast mass may be added to the handles. Even if the determination of the appropriate ballast mass is a critical point in the handle design. The aim of this research was to study the influence of the handle mass modification, on the dynamic structure behaviour. Modal frequencies and subsequent transmissibility calculated by using an analytical approach and a finite elements model, were compared. A good agreement between the results obtained by the two methods was found (average percentage difference calculated on natural frequencies equal to 5.8\ub13.8%). Power tillers are made generally by small or medium-small size manufacturers that have difficulties in dealing with finite element codes or modal analysis techniques. As a consequence, the proposed analytical method could be used to find the optimal ballast mass in a simple and economic way, without experimental tests or complex finite element codes. A specific and very simple software or spreadsheet, developed on the base of the analytical method here discussed, could effectively to help the manufacturers in the handlebar design phase. The choice of the correct elastic mount, the dimensioning of the guide members and the ballast mass could be considerably simplified
Probing the end of reionization with the near zones of z ≳ 6 QSOs
QSO near zones are an important probe of the ionization state of the intergalactic medium (IGM) at z ∼ 6-7, at the end of reionization. We present here high-resolution cosmological 3D radiative transfer simulations of QSO environments for a wide range of host halo masses, 1010-12.5 M⊙. Our simulated near zones reproduce both the overall decrease of observed near-zone sizes at 6 7 QSOs will provide important constraints on the evolution of the neutral hydrogen fraction and thus on how late reionization end
First Results from Viper: Detection of Small-Scale Anisotropy at 40 GHZ
Results of a search for small-scale anisotropy in the cosmic microwave
background (CMB) are presented. Observations were made at the South Pole using
the Viper telescope, with a .26 degree (FWHM) beam and a passband centered at
40 GHz. Anisotropy band-power measurements in bands centered at l = 108, 173,
237, 263, 422 and 589 are reported. Statistically significant anisotropy is
detected in all bands.Comment: 5 pages, 4 figures, uses emulateapj.sty, submitted to ApJ Letter
Probing the AGN Unification Model at redshift z 3 with MUSE observations of giant Ly nebulae
A prediction of the classic active galactic nuclei (AGN) unification model is
the presence of ionisation cones with different orientations depending on the
AGN type. Confirmations of this model exist for present times, but it is less
clear in the early Universe. Here, we use the morphology of giant Ly
nebulae around AGNs at redshift z3 to probe AGN emission and therefore
the validity of the AGN unification model at this redshift. We compare the
spatial morphology of 19 nebulae previously found around type I AGNs with a new
sample of 4 Ly nebulae detected around type II AGNs. Using two
independent techniques, we find that nebulae around type II AGNs are more
asymmetric than around type I, at least at radial distances ~physical kpc
(pkpc) from the ionizing source. We conclude that the type I and type II AGNs
in our sample show evidence of different surrounding ionising geometries. This
suggests that the classical AGN unification model is also valid for
high-redshift sources. Finally, we discuss how the lack of asymmetry in the
inner parts (r30 pkpc) and the associated high values of the HeII to
Ly ratios in these regions could indicate additional sources of (hard)
ionizing radiation originating within or in proximity of the AGN host galaxies.
This work demonstrates that the morphologies of giant Ly nebulae can be
used to understand and study the geometry of high redshift AGNs on
circum-nuclear scales and it lays the foundation for future studies using much
larger statistical samples.Comment: 15 pages, 13 figures, accepted for publication in MNRA
Induction of interferon-stimulated genes by Simian virus 40 T antigens
AbstractSimian virus 40 (SV40) large T antigen (TAg) is a multifunctional oncoprotein essential for productive viral infection and for cellular transformation. We have used microarray analysis to examine the global changes in cellular gene expression induced by wild-type T antigen (TAgwt) and TAg-mutants in mouse embryo fibroblasts (MEFs). The expression profile of approximately 800 cellular genes was altered by TAgwt and a truncated TAg (TAgN136), including many genes that influence cell cycle, DNA-replication, transcription, chromatin structure and DNA repair. Unexpectedly, we found a significant number of immune response genes upregulated by TAgwt including many interferon-stimulated genes (ISGs) such as ISG56, OAS, Rsad2, Ifi27 and Mx1. Additionally, we also observed activation of STAT1 by TAgwt. Our genetic studies using several TAg-mutants reveal an unexplored function of TAg and indicate that the LXCXE motif and p53 binding are required for the upregulation of ISGs
Detection of dark galaxies and circum-galactic filaments fluorescently illuminated by a quasar at z=2.4
A deep narrow-band survey for Ly-alpha emission carried out on the VLT-FORS2
has revealed 98 Ly-alpha candidates down to a flux limit of 4.e-18 erg/s/cm^2
in a volume of 5500 comoving Mpc^3 at z=2.4 centered on the hyperluminous
quasar HE0109-3518. The properties of the detected sources in terms of their i)
equivalent width distribution, ii) luminosity function, and iii) the average
luminosity versus projected distance from the quasar, all suggest that a large
fraction of these objects have been fluorescently "illuminated" by HE0109-3518.
This conclusion is supported by comparison with detailed radiative transfer
simulations of the effects of the quasar illumination. 18 objects have a
rest-frame Equivalent Width (EW0) larger than 240A, the expected limit for
Ly-alpha emission powered by Population II star formation and 12 sources among
these do not have any continuum counterpart in a deep V-band imaging of the
same field. For these, a stacking analysis indicates EW0>800A, effectively
ruling out Ly-alpha powered by internal star formation. These sources are thus
the best candidates so far for proto-galactic clouds or "dark" galaxies at
high-redshift, whose existence has recently been suggested by several
theoretical studies. Assuming they are mostly ionized by the quasar radiation,
we estimate that their gas masses would be about 10^9 Msun implying that their
star formation efficiencies (SFE) are less than 1.e-11 yr^-1 several times
below the SFE of the most gas-rich dwarf galaxies locally, and five hundred
times lower than typical massive star-forming galaxies at z~2. We have also
discovered extended, filamentary gas, also likely illuminated by the quasar,
around some of the brightest continuum-detected sources with EW0>240A. This
emission is compatible with the expectations for circum-galactic cold streams
but other origins, including tidal stripping, are also possible.Comment: 26 pages, 16 figures; MNRAS in press (accepted 2012 Jun 15); minor
changes from previous version, typos corrected, references adde
Galaxy Formation with local photoionisation feedback I. Methods
We present a first study of the effect of local photoionising radiation on
gas cooling in smoothed particle hydrodynamics simulations of galaxy formation.
We explore the combined effect of ionising radiation from young and old stellar
populations. The method computes the effect of multiple radiative sources using
the same tree algorithm used for gravity, so it is computationally efficient
and well resolved. The method foregoes calculating absorption and scattering in
favour of a constant escape fraction for young stars to keep the calculation
efficient enough to simulate the entire evolution of a galaxy in a cosmological
context to the present day. This allows us to quantify the effect of the local
photoionisation feedback through the whole history of a galaxy`s formation. The
simulation of a Milky Way like galaxy using the local photoionisation model
forms ~ 40 % less stars than a simulation that only includes a standard uniform
background UV field. The local photoionisation model decreases star formation
by increasing the cooling time of the gas in the halo and increasing the
equilibrium temperature of dense gas in the disc. Coupling the local radiation
field to gas cooling from the halo provides a preventive feedback mechanism
which keeps the central disc light and produces slowly rising rotation curves
without resorting to extreme feedback mechanisms. These preliminary results
indicate that the effect of local photoionising sources is significant and
should not be ignored in models of galaxy formation.Comment: Accepted for Publication in MNRAS, 13 pages, 13 figure
Characterizing the Circumgalactic Medium of Quasars at z 2.2 through H and Ly Emission
The discovery of giant quasar Ly nebulae at has opened up the
possibility to directly study in emission the Circumgalactic and Intergalactic
Medium (CGM/IGM). However, the resonant nature of the Ly line and its
different emission mechanisms hamper the ability to constrain both the
kinematics and physical properties of the CGM/IGM. Here, we present results of
a pilot project aiming at the detection of CGM H emission, a line which
does not suffer from these limitations. To this end, we first used KCWI to
detect Ly emission around three bright quasars with , a
range which is free from bright IR sky lines for H, and then selected
the most extended nebula for H follow-up with MOSFIRE. Within the
MOSFIRE slit, we detected H emission extending up to 20 physical kpc
with a total H flux of F=(9.5 0.9)
10 erg s cm. Considering the Ly flux in the same
region, we found F/F=3.7 0.3
consistent with that obtained for the Slug Nebula at z and with
recombination radiation. This implies high densities or a very broad density
distribution within the CGM of high-redshift quasars. Moreover, the H
line profile suggests the presence of multiple emitting components overlapping
along our line-of-sight and relatively quiescent kinematics, which seems
incompatible with either quasar outflows capable of escaping the potential well
of the host halo or disk-like rotation in a massive halo
(M).Comment: 15 pages, 12 figures, 2 table
A Joint Sunyaev-Zel'dovich Effect and X-ray Analysis of Abell 3667
We present a 40GHz (7.5 mm) raster scan image of a 3.6x2 degree region
centered on the low redshift (z=0.055) cluster of galaxies Abell 3667. The
cluster was observed during the Antarctic winter of 1999 using the Corona
instrument (15.7' FWHM beam) on the Viper Telescope at the South Pole. The
Corona image of A3667 is one of the first direct (i.e. rather than
interferometer) thermal Sunyaev-Zel'dovich effect images of a low redshift
cluster. The brightness temperature decrement at the X-ray centroid (20h 12m
28.9s, -56 49 51 J2000) was measured to be . We
have used the 40GHz map of A3667 in conjunction with a deep ROSAT PSPC (X-ray)
image of the cluster, to make a measurement of the Hubble Constant. We find
km s Mpc (68% confidence interval). Our
calculation assumes that the cluster can be described using an
isothermal, tri-axial ellipsoidal, -model and includes several new
analysis techniques including an automated method to remove point sources from
X-ray images with variable point spread functions, and an efficient method for
determining the errors in multi-parameter maximum likelihood analyzes. The
large errors on the measurement are primarily due to the statistical
noise in the Corona image. We plan to increase the precision of our measurement
by including additional clusters in our analysis and by increasing the
sensitivity of the Viper SZE maps.Comment: 15 pages, 4 figures, submitted to ApJ (count rate units corrected in
Table 1 and Figure 4
How neutral is the intergalactic medium surrounding the redshift z=7.085 quasar ULAS J1120+0641?
The quasar ULAS J1120+0641 at redshift z=7.085 has a highly ionised near zone
which is smaller than those around quasars of similar luminosity at z~6. The
spectrum also exhibits evidence for a damping wing extending redward of the
systemic Lya redshift. We use radiative transfer simulations in a cosmological
context to investigate the implications for the ionisation state of the
inhomogeneous IGM surrounding this quasar. Our simulations show that the
transmission profile is consistent with an IGM in the vicinity of the quasar
with a volume averaged HI fraction of f_HI>0.1 and that ULAS J1120+0641 has
been bright for 10^6--10^7 yr. The observed spectrum is also consistent with
smaller IGM neutral fractions, f_HI ~ 10^-3--10-4, if a damped Lya system in an
otherwise highly ionised IGM lies within 5 proper Mpc of the quasar. This is,
however, predicted to occur in only ~5 per cent of our simulated sight-lines
for a bright phase of 10^6--10^7 yr. Unless ULAS J1120+0641 grows during a
previous optically obscured phase, the low age inferred for the quasar adds to
the theoretical challenge of forming a 2x10^9 M_sol black hole at this high
redshift.Comment: 5 pages, 4 figures, accepted to MNRAS letter
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