Radiative non-isothermal Bondi accretion onto a massive black hole

In this paper, we present the classical Bondi accretion theory for the case of non-isothermal accretion processes onto a supermassive black hole (SMBH), including the effects of X-ray heating and the radiation force due to electron scattering and spectral lines. The radiation field is calculated by considering an optically thick, geometrically thin, standard accretion disk as the emitter of UV photons and a spherical central object as a source of X-ray emission. In the present analysis, the UV emission from the accretion disk is assumed to have an angular dependence, while the X-ray/central object radiation is assumed to be isotropic. This allows us to build streamlines in any angular direction we need to. The influence of both types of radiation is evaluated for different flux fractions of the X-ray and UV emissions with and without the effects of spectral line driving. We find that the radiation emitted near the SMBH interacts with the infalling matter and modifies the accretion dynamics. In the presence of line driving, a transition resembles from pure type 1 & 2 to type 5 solutions (see Fig2.1 of Frank etal. 2002), which takes place regardless of whether or not the UV emission dominates over the X-ray emission. We compute the radiative factors at which this transition occurs, and discard type 5 solution from all our models. Estimated values of the accretion radius and accretion rate in terms of the classical Bondi values are also given. The results are useful for the construction of proper initial conditions for time-dependent hydrodynamical simulations of accretion flows onto SMBH at the centre of galaxies.Comment: 10 pages, 10 figures, Accepted to be published in A&

Tunability experiments at the FERMI@Elettra free-electron laser

FERMI@Elettra is a free electron-laser (FEL)-based user facility that, after two years of commissioning, started preliminary users' dedicated runs in 2011. At variance with other FEL user facilities, FERMI@Elettra has been designed to deliver improved spectral stability and longitudinal coherence. The adopted scheme, which uses an external laser to initiate the FEL process, has been demonstrated to be capable of generating FEL pulses close to the Fourier transform limit. We report on the first instance of FEL wavelength tuning, both in a narrow and in a large spectral range (fine- and coarse-tuning). We also report on two different experiments that have been performed exploiting such FEL tuning. We used fine-tuning to scan across the 1s–4p resonance in He atoms, at ≈23.74 eV (52.2 nm), detecting both UV–visible fluorescence (4p–2s, 400 nm) and EUV fluorescence (4p–1s, 52.2 nm). We used coarse-tuning to scan the M4,5 absorption edge of Ge (∼29.5 eV) in the wavelength region 30–60 nm, measured in transmission geometry with a thermopile positioned on the rear side of a Ge thin foil

Breast cancer stem cells: implications for therapy of breast cancer

The concept of cancer stem cells responsible for tumour origin, maintenance, and resistance to treatment has gained prominence in the field of breast cancer research. The therapeutic targeting of these cells has the potential to eliminate residual disease and may become an important component of a multimodality treatment. Recent improvements in immunotherapy targeting of tumour-associated antigens have advanced the prospect of targeting breast cancer stem cells, an approach that might lead to more meaningful clinical remissions. Here, we review the role of stem cells in the healthy breast, the role of breast cancer stem cells in disease, and the potential to target these cells

Protostellar collapse models of prolate molecular cloud cores

The continued detection of binary systems among pre-main-sequence stars suggests that fragmentation is a very frequent process during the early stages of star formation. However, the fragmentation hypothesis rests only upon the results of three-dimensional hydrodynamics code calculations. The validity of isothermal fragmentation calculations was questioned by the results of Truelove et al. (1997), and more recently, of Boss et al. (2000), who found, working at very high spatial resolution, that a particular Gaussian cloud model collapsed isothermally to form a singular filament rather than a binary or quadruple protostellar system as predicted by previous calculations. Sufficiently high spatial resolution is necessary to resolve the Jeans length and hence avoid artificial fragmentation in isothermal collapse calculations. Here we use an adaptive, spherical-coordinate hydrodynamics code based on the "zooming" coordinates to investigate the isothermal collapse of centrally condensed (Gaussian), prolate (2:1 axial ratio) cloud core models, with thermal energy $\alpha\approx 0.22$ and varied rotational energy ($0.246\leq\beta\leq 0.00025$), to discern whether they will still undergo fragmentation into a protostellar binary system, as found in most previous prolate cloud collapse calculations, or condense all the way into a thin filament, as suggested by the linear analysis of Inutsuka & Miyama (1992) and the findings of Truelove et al. and Boss et al. for the spherical, Gaussian cloud model. The prolate clouds all collapsed self-similarly to produce an intermediate barlike core, which then shrank indefinetely into a singular filament without fragmenting. Collapse of the bar into a thin filament also occurred self-similarly, with the forming filaments being much longer than the Jeans length. Since the filaments form at maximum densities that are typical of the transition from the isothermal to the nonisothermal phase, gradual heating may retard the collapse and allow fragmentation of the filament into a binary or multiple protostellar core, as required to explain the high frequency of binary stars

Dynamics of solar coronal loops

Observations in X-ray and EUV of the solar corona reveal the existence of very complex and dynamic structures made of plasma magnetically confined in loops. These structures can be studied by means of one-dimensional hydrodynamical loop models. Here we use a Lagrangian-remap code to simulate the dynamics of solar coronal loops with the purpose of quantifying the effects of varying the initial distribution of energy along the loop, the amount of input heating (h0), the total loop length ($2L$) and including/excluding the solar gravity term. In particular, the model calculations with no gravity are compared with the results obtained from previous isobaric, time-dependent models. Using a heat function that depends on distance along the loop and temperatures at the base of the loop typical of the solar corona, we find that in the non-gravity cases the plasma is allowed to cool down to chromospheric temperatures only when the decay length of the heating is below a certain critical value ($s_{H}/L=0.043$). For the same initial parameters, the inclusion of gravity produces final equilibrium states which are considerably hotter than those obtained when gravity is neglected and lowers the critical value of the decay length of the heating for which a cool condensation forms. In all cases, the outcome of the evolution can be predicted by a diagnostic diagram which describes the location of possible solutions for thermal equilibrium models

Gravitational collapse of nonsingular logatropic spheres

We present the results of high-resolved, hydrodynamic calculations of the spherical gravitational collapse and subsequent accretion of nonsingular subcritical and critical $A=0.2$ logatropes, starting with initial configurations close to hydrostatic equilibrium. Two sequences of models with varying masses and the same central temperature $T_{\rm c}=10$ K are defined, which differ only in the fiducial value of the truncation pressure ($p_{\rm s}/k=1.3\times 10^{5}$ cm-3 K and $1.0\times 10^{7}$ cm-3 K). In all cases, we follow the calculations until the central protostar has accreted 99% of the total available mass. Thus, the models may be indicative of early evolution from the Class 0 to the Class I protostellar phase. We find that the approach to the singular density profile is never entirely subsonic. In the lower ps sequence, about 6% of the mass collapses supersonically in a $1~M_{\odot}$ sphere, while only ∼0.02% behaves this way in a critical ($\approx$92.05 $M_{\odot}$) logatrope. In the high ps sequence the same trend is observed, with ∼0.7% of the mass now infalling supersonically at the time of singularity formation in a $1~M_{\odot}$ sphere. Immediately after singularity formation, the accretion rate rises steeply in all cases, reaching a maximum value when the central protostar has accreted ∼40% of its final mass. Thereafter, it decreases monotonically for the remainder of the evolution. Our models predict peak values of ${\dot M}_{\rm acc}$ as high as ∼ $5 {-} 6\times 10^{-5}~M_{\odot}$ yr-1 for logatropes close to the critical mass. In contrast, a subcritical $1~M_{\odot}$ logatrope reaches a maximum value of ∼ $8\times 10^{-7}~M_{\odot}$ yr-1 for the lower ps sequence compared to ~$5\times 10^{-6}~M_{\odot}$ yr-1 for the higher ps case. The results also imply that the accretion lifetimes are longer in logatropes with lower ps, consistent with the observational evidence that star formation in clumped regions occurs on shorter timescales compared to more isolated environments