190 research outputs found
Intestinal perforation after surgical treatment for incisional hernia. iatrogenic or idiopathic?
Intestinal perforation (IP) is a life-threatening gastroenterological condition requiring urgent surgical care, which may present itself as an uncommon complication following incisional hernia repair surgery, most often because of iatrogenic traumatism occurring during the procedure. However, we report a case where a spontaneous onset can be hypothesised. A 60-years-old patient underwent repair of an abdominal laparocele, through rectus abdominis muscle plasty, 5Â years after development of an incisional hernia due to exploratory laparotomy for the treatment of acute appendicitis. Xipho-pubic scar was excised and umbilicus and supra-umbilical hernia sac dissected, a linear median incision was performed along the sub-umbilical linea alba, reaching preperitoneal plane to assess any intestinal loop adherence to the abdominal wall. After limited viscerolysis, abdominal wall defect was corrected by 'rectus abdominis muscle plasty' and umbilicus reconstruction by Santanelli technique. Postoperative course was uneventful until Day 29, with sudden onset of epigastric pain, fever and bulge. Sixty cubic centimeter pus was drained percutaneously and cavity was rinsed with a 50% H2O2 and H2O V-V solution until draining clear fluid. Symptoms recurred two days later, while during rinsing presented dyspnoea. X-Ray and CT scan diagnosed IP, and she underwent under emergency an exploratory laparotomy, leading to right hemicolectomy extended to last ileal loops and middle third of the transverse, right monolateral salpingo-ovariectomy and a temporary ileostomy by general surgeon. Twenty-three days later an ileostomy reversal surgery was performed and 8 days after she was discharged. At latest follow-up patient showed fair conditions, complaining abdominal pain and diarrhoea, attributable to the extensive intestinal resection. IP following incisional hernia repair, is reported as uncommon and early postoperative complication. In our case, the previous regular postoperative course with late onset lead us to hypothesise a possible idiopathic etiopathogenesis, because of a strangulation followed by gangrene and abscess formation, which might begin before the incisional hernia repair and unnoticed at the time surgery was performed
Long Gamma-Ray Bursts as standard candles
As soon as it was realized that long GRBs lie at cosmological distances,
attempts have been made to use them as cosmological probes. Besides their use
as lighthouses, a task that presents mainly the technological challenge of a
rapid deep high resolution follow-up, researchers attempted to find the Holy
Grail: a way to create a standard candle from GRB observables. We discuss here
the attempts and the discovery of the Ghirlanda correlation, to date the best
method to standardize the GRB candle. Together with discussing the promises of
this method, we will underline the open issues, the required calibrations and
how to understand them and keep them under control. Even though GRB cosmology
is a field in its infancy, ongoing work and studies will clarify soon if and
how GRBs will be able to keep up to the promises.Comment: To appear in the proceedings of the 16th Annual October Astrophysics
Conference in Maryland "Gamma Ray Bursts in the Swift Era", eds. S. Holt, N.
Gehrels & J. Nouse
The effects of Non-Gaussian initial conditions on the structure and substructure of Cold Dark Matter halos
We study the structure and substructure of halos obtained in N-body
simulations for a Lambda Cold Dark Matter (LCDM) cosmology with non-Gaussian
initial conditions (NGICs). The initial statistics are lognormal in the
gravitational potential field with positive (LNp) and negative (LNn) skewness;
the sign of the skewness is conserved by the density field, and the power
spectrum is the same for all the simulations. Our aim is not to test a given
non-Gaussian statistics, but to explore the generic effect of positive- and
negative-skew statistics on halo properties. From our low-resolution
simulations, we find that LNp (LNn) halos are systematically more (less)
concentrated than their Gaussian counterparts. This result is confirmed by our
Milky Way- and cluster-sized halos resimulated with high-resolution. In
addition, they show inner density profiles that depend on the statistics: the
innermost slopes of LNp (LNn) halos are steeper (shallower) than those obtained
from the corresponding Gaussian halos. A subhalo population embedded in LNp
halos is more susceptible to destruction than its counterpart inside Gaussian
halos. On the other hand, subhalos in LNn halos tend to survive longer than
subhalos in Gaussian halos. The spin parameter probability distribution of LNp
(LNn) halos is skewed to smaller (larger) values with respect to the Gaussian
case. Our results show how the statistics of the primordial density field can
influence some halo properties, opening this the possibility to constrain,
although indirectly, the primordial statistics at small scale.Comment: 15 pages, 8 figures. Slight corrections after referee report. To
appear in ApJ, v598, November 20, 200
The dependence on environment of Cold Dark Matter Halo properties
High-resolution LCDM cosmological N-body simulations are used to study the
properties of galaxy-size dark halos in different environments (cluster, void,
and "field"). Halos in clusters and their surroundings have a median spin
parameter ~1.3 times lower, and tend to be more spherical and to have less
aligned internal angular momentum than halos in voids and the field. For halos
in clusters the concentration parameters decrease on average with mass with a
slope of ~0.1; for halos in voids these concentrations do not change with mass.
For masses <5 10^11 M_sh^-1, halos in clusters are on average ~30-40% more
concentrated and have ~2 times higher central densities than halos in voids.
When comparing only parent halos, the differences are less pronounced but they
are still significant. The Vmax-and Vrms-mass relations are shallower and more
scattered for halos in clusters than in voids, and for a given Vmax or Vrms,
the mass is smaller at z=1 than at z=0 in all the environments. At z=1, the
differences in the halo properties with environment almost dissapear,
suggesting this that the differences were stablished mainly after z~1. The
halos in clusters undergo more dramatic changes than those in the field or the
voids. The differences with environment are owing to (i) the dependence of halo
formation time on environment, and (ii) local effects as tidal stripping and
the tumultuos histories that halos suffer in high-density regions. We calculate
seminumerical models of disk galaxy evolution in halos with the properties
found for the different environments. For a given disk mass, the galaxy disks
have higher surface density, larger Vd,max and secular bulge-to-disk ratio,
lower gas fraction, and are redder as one goes from cluster to void
environments, in rough agreement with observations. (abridged)Comment: 28 pages, 13 figures included. To appear in The Astrophysical Journa
Turbulent dissipation in the ISM: the coexistence of forced and decaying regimes and implications for galaxy formation and evolution
We discuss the dissipation of turbulent kinetic energy Ek in the global ISM
by means of 2-D, MHD, non-isothermal simulations in the presence of model
radiative heating and cooling. We argue that dissipation in 2D is
representative of that in three dimensions as long as it is dominated by shocks
rather than by a turbulent cascade. Energy is injected at a few isolated sites
in space, over relatively small scales, and over short time periods. This leads
to the coexistence of forced and decaying regimes in the same flow. We find
that the ISM-like flow dissipates its turbulent energy rapidly. In simulations
with forcing, the input parameters are the radius l_f of the forcing region,
the total kinetic energy e_k each source deposits into the flow, and the rate
of formation of those regions, sfr_OB. The global dissipation time t_d depends
mainly on l_f. In terms of measurable properties of the ISM, t_d >= Sigma_g
u_rms^2/(e_k sfr_OB), where Sigma_g is the average gas surface density and
u_rms is the rms velocity dispersion. For the solar neighborhood, t_d >=
1.5x10^7 yr. The global dissipation time is consistently smaller than the
crossing time of the largest energy-containing scales. In decaying simulations,
Ek decreases with time as t^-n, where n~0.8-0.9. This suggests a decay with
distance d as Ek\propto d^{-2n/(2-n)} in the mixed forced+decaying case. If
applicable to the vertical direction, our results support models of galaxy
evolution in which stellar energy injection provides significant support for
the gas disk thickness, but not models of galaxy formation in which this energy
injection is supposed to reheat an intra-halo medium at distances of up to
10-20 times the optical galaxy size, as the dissipation occurs on distances
comparable to the disk height.Comment: 23 pages, including figures. To appear in ApJ. Abstract abridge
Structure and Subhalo Population of Halos in a Self-Interacting Dark Matter Cosmology
We study the structure of Milky Way (MW)- and cluster-sized halos in a Lambda
Cold Dark Matter (CDM) cosmology with self-interacting (SI) dark particles. The
cross section per unit of particle mass has the form sigma =
sig_0(1/v_100)^alpha, where sig_0 is a constant in units of cm^2/gr and v_100
is the relative velocity in units of 100 km/s. Different values for sigma with
alpha= 0 or 1 were used. For small values of sigma = const. (sig_0<0.5), the
core density of the halos at z=0 is typically higher at a given mass for lower
values of sig_0 or, at a given sig_0, for lower masses. For values of sig_0 as
high as 3.0, the halos may undergo the gravothermal catastrophe before z=0.
When alpha = 1, the core density of cluster- and MW-sized halos is similar.
Using sigma = 0.5-1.0x(1/v_100), our predictions agree with the central
densities and the core scaling laws of halos both inferred from the
observations of dwarf and LSB galaxies and clusters of galaxies. The cumulative
Vmax-functions of subhalos in MW-sized halos with (sig_0,alpha) = (0.1,0.0),
(0.5,0.0) and (0.5,1.0) agree roughly with observations (luminous satellites)
for Vmax > 30 km/s, while at Vmax = 20 km/s the functions are a factor 5-8
higher, similar to the CDM predictions. The halos with SI have slightly more
specific angular momentum at a given mass shell and are rounder than their CDM
counterparts. We conclude that the introduction of SI particles with sigma
\propto 1/v_100 may remedy the cuspy core problem of the CDM cosmogony, while
the subhalo population number remains similar to that of the CDM halos.Comment: To appear in ApJ, December 20, 2002. We added plots showing the
evolution of the heat capacity profile for halos in the core expansion and
gravothermal catastrophe phases. Minor changes in the text were introduce
On the future of Gamma-Ray Burst Cosmology
With the understanding that the enigmatic Gamma-Ray Burts (GRBs) are beamed
explosions, and with the recently discovered ``Ghirlanda-relation'', the dream
of using GRBs as cosmological yardsticks may have come a few steps closer to
reality. Assuming the Ghirlanda-relation is real, we have investigated possible
constraints on cosmological parameters using a simulated future sample of a
large number of GRBs inspired by the ongoing SWIFT mission. Comparing with
constraints from a future sample of Type Ia supernovae, we find that GRBs are
not efficient in constraining the amount of dark energy or its equation of
state. The main reason for this is that very few bursts are available at low
redshifts.Comment: 5 pages, 2 figures, matches version accepted for publication in JCA
Extending the Hubble diagram by gamma ray bursts
A new method to constrain the cosmological equation of state is proposed by
using combined samples of gamma-ray bursts (GRBs) and supernovae (SNeIa). The
Chevallier-Polarski-Linder parameterization is adopted for the equation of
state in order to find out a realistic approach to achieve the
deceleration/acceleration transition phase of dark energy models. We find that
GRBs, calibrated by SNeIa, could be good distance indicators capable of
discriminating between cosmological models and CDM model at high
redshift.Comment: 5 pages, 5 figures, to appear in Astron. & Astrop
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