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Modern Lattice Boltzmann methods for multiphase micro-flows
This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.During the last decade, the Lattice Boltzmann (LB) method has captured an increasing attention as an efficient tool for the numerical simulation of complex
fluids, particularly multi-phase and multi-component flows. In this paper, we revisit the basic features of two modern variants of lattice Boltzmann models for non-ideal
fluids, which offer promising perspectives for the numerical simulation of complex micro-
flows.This study is funded from the European Project INFLUS, NMP3-CT-2006-031980
SAXJ1712.6-3739: a persistent hard X-ray source as monitored with INTEGRAL
The X-ray source SAXJ1712.6-3739 is a very weak Low Mass X-ray Binary
discovered in 1999 with BeppoSAX and located in the Galactic Center. This
region has been deeply investigated by the INTEGRAL satellite with an
unprecedented exposure time, giving us an unique opportunity to study the hard
X-ray behavior also for weak objects. The spectral results are based on the
systematic analysis of all INTEGRAL observations covering the source position
performed between February 2003 and October 2006. SAXJ1712.6-3739 did not shows
any flux variation along this period as well as compared to previous BeppoSAX
observation. Hence, to better constrain the physical parameters we combined
both instrument data. Long INTEGRAL monitoring reveals, for the first time,
that this X-ray burster is a weak persistent source, displaying a X-ray
spectrum extended to high energy and spending most of the time in a low
luminosity hard state. The broad-band spectrum is well modeled with a simple
Comptonized model with a seed photons temperature of ~0.5keV and an electron
temperature of ~24keV. The low mass accretion rate (~2x10^{-10} Msun/yr), the
long bursts recurrence time, the small sizes of the region emitting the seed
photons consisting with the inner disk radius and the high luminosity ratio in
the 40-100keV and 20-40keV band, are all features common to the Ultra Compact
source class.Comment: accepted A&
FERMI transient J1544-0649: a flaring radio-weak BL Lac
On May 15th, 2017, the \emph{FERMI}/LAT gamma-ray telescope observed a
transient source not present in any previous high-energy catalogue: J1544-0649.
It was visible for two consecutive weeks, with a flux peak on May 21st.
Subsequently observed by a \emph{Swift}/XRT follow-up starting on May 26, the
X-ray counterpart position was coincident with the optical transient
ASASSN-17gs = AT2017egv, detected on May 25, with a potential host galaxy at
=0.171. We conducted a 4-months follow-up in radio (Effelsberg-100m) and
optical (San Pedro M\'artir, 2.1m) bands, in order to build the overall
Spectral Energy Distribution (SED) of this object. The radio data from 5 to 15
GHz confirmed the flat spectrum of the source, favoring a line of sight close
to jet axis, not showing significant variability in the explored post-burst
time-window. The Rx ratio, common indicator of radio loudness, gives a value at
the border between the radio-loud and radio-quiet AGN populations. The
Ca H\&K break value (0.290.05) is compatible with the range
expected for the long-sought intermediate population between BL Lacs and FRI
radio galaxies. An overall SED fitting from Radio to -ray band shows
properties typical of a low-power BL Lac. As a whole, these results suggest
that this transient could well be a new example of the recently discovered
class of radio-weak BL Lac, showing for the first time a flare in the
gamma/X-ray bands.Comment: Accepted for publication in ApJ Letter
An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544-0639
Fermi J1544-0639/ASASSN-17gs/AT2017egv was identified as a gamma-ray/optical
transient on May 15, 2017. Subsequent multiwavelength observations suggest that
this source may belong to the new class of radio-weak BL Lacs. We studied the
X-ray spectral properties and short-term variability of Fermi J1544-0639 to
constrain the X-ray continuum emission mechanism of this peculiar source. We
present the analysis of an XMM-Newton observation, 56 ks in length, performed
on February 21, 2018. The source exhibits strong X-ray variability, both in
flux and spectral shape, on timescales of ~10 ks, with a harder-when-brighter
behaviour typical of BL Lacs. The X-ray spectrum is nicely described by a
variable broken power law, with a break energy of around 2.7 keV consistent
with radiative cooling due to Comptonization of broad-line region photons. We
find evidence for a `soft excess', nicely described by a blackbody with a
temperature of ~0.2 keV, consistent with being produced by bulk Comptonization
along the jet.Comment: 11 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
INTEGRAL/IBIS search for e-e+ annihilation radiation from the Galactic Center Region
Electron-positron annihilation radiation from the Galactic Center region has
been detected since the seventies, but its astrophysical origin is still a
topic of a scientific debate. We have analyzed data of the gamma-ray imager
IBIS/ISGRI onboard of ESA's INTEGRAL platform in the ee line.
During the first year of the missions Galactic Center Deep Exposure no evidence
for point sources at 511 keV has been found in the ISGRI data; the
upper limit for resolved single point sources is estimated to be .Comment: 6 pages, 3 figures; Cospar 2004. To be published in: Advances in
Space Researc
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