923 research outputs found
Research on the organic binders in archaeological wall paintings
Wall painting realized using organic binders is the oldest form of parietal painting and precedes the birth of the affresco by about 20,000 years. This paper reports the results obtained from the main studies in the field of archaeological wall paintings. The attention was paid to the study of organic binders used for the application of the color, as well as on the instrumental techniques chosen to obtain such information. Different techniques can be used for the study of organic material in archeological paintings: non-destructive techniques, which can be applied directly in situ without sampling, and laboratory micro-invasive techniques for a more in-depth characterization. Among these, the chromatographic techniques represent a potential tool to acquire as much information as possible about chemical composition of binders
Gas and Dust in the Taffy Galaxies: Ugc12914/15
We present a comprehensive study of the dust and gas properties in the
after-head-on-collision UGC12914/15 galaxy system using multi-transition CO
data and SCUBA sub-mm continuum images at both 450 and 850m. CO(3-2) line
emission was detected in the disks of UGC 12914 and UGC 12915 as well as in a
bridge connecting the two galaxies. Dust emission at 450m was detected for
the first time in the two galactic disks and in the connecting bridge. Using an
LVG excitation analysis model we have obtained good estimates of the physical
parameters in different regions of this system and the amount of molecular gas
was found to be 3-4 times lower than that estimated by other investigators
using the standard Galactic CO-to-H2 conversion factor. Comparing with the dust
mass derived from the SCUBA data, we found that the gas-to-dust ratio was
comparable to the Galactic value in the two galaxy disks but a factor of ~3
higher in the bridge. The physical condition of the molecular gas in the bridge
is comparable to that in the diffuse clouds in our Galaxy. Our result is
consistent with the scenario that the bridge molecular gas originated from the
disk molecular clouds and has been drawn out of the galactic disks due to
direct cloud-cloud collision.
Our data indicate that the global star formation efficiency (SFE) in UGC
12915 is comparable to that of normal spiral galaxies, and the SFE is 40% lower
in UGC 12914 than in UGC 12915. Little star formation activity was found in the
bridge except in an HII region adjacent to the disk of UGC 12915.Comment: Accepted by AJ. 45 pages, 10 figures (Fig 1-5 and Fig 7 in gif
format
Where is the Molecular Hydrogen in Damped Lyman-Alpha Absorbers?
We show in this paper why molecular millimeter absorption line searches in
DLAs have been unsuccessful. We use CO emission line maps of local galaxies to
derive the H2 column density distribution function f(N_H2) at z=0. We show that
it forms a natural extension to f(N_HI): the H2 distribution exceeds f(N_HI) at
N_H ~ 10^22 cm^-2 and exhibits a power law drop-off with slope ~ -2.5.
Approximately 97% of the H2 mass density rho_H2 is in systems above N_H2=10^21
cm^-2. We derive a value rho_H2 = 1.1 x 10^7 h_70 M_sun Mpc^-3, which is ~25%
the mass density of atomic hydrogen. Yet, the redshift number density of H2
above this N_H2 limit is only ~3 x 10^-4, a factor 150 lower than that for HI
in DLAs at z=0. Furthermore, we show that the median impact parameter between a
N_H2>10^21 cm^-2 absorber and the centre of the galaxy hosting the H2 gas is
only 2.5 kpc. Based on arguments related to the Schmidt law, we argue that H2
gas above this column density limit is associated with a large fraction of the
integral star formation rate density. Even allowing for an increased molecular
mass density at higher redshifts, the derived cross-sections indicate that it
is very unlikely to identify the bulk of the molecular gas in present quasar
absorption lines samples. We discuss the prospects for identifying this
molecular mass in future surveys.Comment: 6 pages, 4 figures. Accepted for publication in the Astrophysical
Journa
First Interferometric Observations of Molecular Gas in a Polar Ring: The Helix Galaxy NGC 2685
We have detected four Giant Molecular cloud Associations (GMAs) (sizes <
6.6'' ~ 430 pc) in the western and eastern region of the polar ring in NGC2685
(the Helix galaxy) using the Owens Valley Radio Observatory (OVRO) millimeter
interferometer. Emission from molecular gas is found close to the brightest
Halpha and HI peaks in the polar ring and is confirmed by new IRAM 30m single
dish observations. The CO and HI line velocities are very similar, providing
additional kinematic confirmation that the CO emission emerges from the polar
ring. For the first time, the total molecular mass within a polar ring is
determined (M_H2~(8-11)x10^6 M_sol, using the standard Galactic conversion
factor). We detect about M_H2~4.4x10^6 M_sol in the nuclear region with the
single dish. Our upper limit derived from the interferometric data is lower
(M_H2<0.7x10^6 M_sol) suggesting that the molecular gas is distributed in an
extended (< 1.3 kpc) diffuse disk. These new values are an order of magnitude
lower than in previous reports. The total amount of molecular gas and the
atomic gas content of the polar ring are consistent with formation due to
accretion of a small gas-rich object, such as a dwarf irregular. The properties
of the NGC2685 system suggest that the polar ring and the host galaxy have been
in a stable configuration for a considerable time (few Gyr). The second (outer)
HI ring within the disk of NGC2685 is very likely at the outer Lindblad
resonance (OLR) of the ~ 11 kpc long stellar bar.Comment: 8 pages, 4 figures, accepted by ApJ Letter
Atomic Carbon in Galaxies
We present new measurements of the ground state fine-structure line of atomic
carbon at 492 GHz in a variety of nearby external galaxies, ranging from spiral
to irregular, interacting and merging types. In comparison with CO(1-0), the
CI(1-0) intensity stays fairly comparable in the different environments, with
an average value of the ratio of the line integrated areas in Kkm/s of
CI(1-0)/CO(1-0) = 0.2 +/- 0.2. However, some variations can be found within
galaxies, or between galaxies. Relative to CO lines, CI(1-0) is weaker in
galactic nuclei, but stronger in disks, particularly outside star forming
regions. Also, in NGC 891, the CI(1-0) emission follows the dust continuum at
1.3mm extremely well along the full length of the major axis where molecular
gas is more abundant than atomic gas. Atomic carbon therefore appears to be a
good tracer of molecular gas in external galaxies, possibly more reliable than
CO. Atomic carbon can contribute significantly to the thermal budget of
interstellar gas. Cooling due to C and CO amounts typically to 2 x 10^{-5} of
the FIR continuum or 5% of the CII line. However, C and CO cooling reaches 30%
of the gas total, in Ultra Luminous InfraRed Galaxies, where CII is abnormally
faint. Together with CII/FIR, the emissivity ratio CI(1-0)/FIR can be used as a
measure of the non-ionizing UV radiation field in galaxies.Comment: 26 pages, 8 figure
A Search for H2O in the Strongly Lensed QSO MG 0751+2716 at z=3.2
We present a search for 183 GHz H_2O(3_13-2_20) emission in the
infrared-luminous quasar MG 0751+2716 with the NRAO Very Large Array (VLA). At
z=3.200+/-0.001, this water emission feature is redshifted to 43.6 GHz. As
opposed to the faint rotational transitions of HCN (the standard high-density
tracer at high-z), H_2O(3_13-2_20) is observed with high maser amplification
factors in Galactic star-forming regions. It therefore holds the potential to
trace high-density star-forming regions in the distant universe. If indeed all
star-forming regions in massively star-forming galaxies at z>3 have similar
physical properties as e.g. the Orion or W49N molecular cloud cores, the flux
ratio between the maser-amplified H_2O(3_13-2_20) and the thermally excited
CO(1-0) transitions may be as high as factor of 20 (but has to be corrected by
their relative filling factor). MG 0751+2716 is a strong CO(4-3) emitter, and
therefore one of the most suitable targets to search for H_2O(3_13-2_20) at
cosmological redshifts. Our search resulted in an upper limit in line
luminosity of L'(H_2O) < 0.6 x 10^9 K km/s pc^2. Assuming a brightness
temperature of T_b(H_2O) ~= 500 K for the maser emission and CO properties from
the literature, this translates to a H_2O(3_13-2_20)/CO(4-3) area filling
factor of less than 1%. However, this limit is not valid if the H_2O(3_13-2_20)
maser emission is quenched, i.e. if the line is only thermally excited. We
conclude that, if our results were to hold for other high-z sources, H_2O does
not appear to be a more luminous alternative to HCN to detect high-density gas
in star-forming environments at high redshift.Comment: 6 pages, 1 figure, to appear in ApJ (accepted May 19, 2006
Spin configurations in hard-soft coupled bilayer systems: from rigid magnet to exchange spring transitions
We investigate equilibrium properties of an exchange-spring magnetic system
constituted of a soft layer (e.g. Fe) of a given thickness on top of a hard
magnetic layer (e.g. FePt). The magnetization profile M(z) as a function of the
atomic position ranging from the bottom of the hard layer to the top of the
soft layer is obtained in two cases with regard to the hard layer: i) in the
case of a rigid interface (the FePt layer is a single layer), the profile is
obtained analytically as the exact solution of a sine-Gordon equation with
Cauchy's boundary conditions. Additional numerical simulations also confirm
this result. Asymptotic expressions of M(z) show a linear behavior near the
bottom and the top of the soft layer. In addition, a critical value of the
number of atomic planes in the soft layer, that is necessary for the onset of
spin deviations, is obtained in terms of the anisotropy and exchange coupling
between the adjacent plane in the soft layer. ii) in the case of a relaxed
interface (the FePt layer is a multilayer), the magnetization profile is
obtained numerically for various Fe and FePt films thicknesses and applied
field.Comment: 10 pages, 9 figures, PRB submitted (12-07-2010
Effect of Udder Health Status and Lactation Phase on the Characteristics of Sardinian Ewe Milk
Mammary involution and inflammation are known to negatively affect milk quality. A trial was carried out to elucidate the mechanism by which udder health status and lactational phase determine compositional modifications in ovine milk. A total of 60 individual milk samples was collected from a group of 20 pluriparous Sardinian ewes from mid to late lactation. Each sample was assessed for its chemical characteristics, quantitative distribution of casein fractions, lactodynamographic characteristics, and enzymatic activity. Udders were classed as healthy, doubtful, or infected on the basis of repeated somatic cell counts, and samples were grouped in 3 classes of days in milk. Results indicated that both udder inflammation and mammary involution can increase plasmin (PL) activity (15.6 vs. 18.4 U/mL in healthy vs. infected udders; 14.0 vs. 20.2 U/mL in phase 1 vs. 3), which is responsible for an evident protein breakdown in milk. Significant differences between groups were observed for several characteristics. With regard to udder heath status, casein index was lower in the infected vs. healthy udders (74.8 vs. 76.6%), and beta(tot)-casein showed a similar trend (43.9 vs. 46.6%). As a consequence of protein degradation, gamma-casein (5.78 vs. 2.82%) and proteolysis index (7.60 vs. 3.82) increased in the infected group with respect to the healthy group. Udder health status also affected milk technological traits. Udder inflammation resulted in longer clotting time (20.7 vs. 16.5 min for infected vs. healthy, respectively) and in poorer curd firmness (35.6 vs. 47.6 mm for infected vs. healthy, respectively). Frequency of samples reactive to rennet was 100, 93, and 67%, respectively, for healthy, doubtful, and infected groups. With regard to lactational phase, a decrease in alpha(s1)-casein (39.13 vs. 29.36%) and beta(1)-casein (23.41 vs. 19.36%) occurred during phase 1 vs. 3, whereas kappa + alpha(s2)-casein increased (12.30 vs. 21.56%, phase 1 vs. 3). Correlation coefficients confirmed the role of PL in protein degradation. It was concluded that PL activity was strongly affected by both lactational phase and udder health status and, in turn, could be an important agent enhancing milk quality detriment
High spatial resolution photo mosaicking for the monitoring of coralligenous reefs
AbstractCoralligenous reefs are characterized by large bathymetric and spatial distribution, as well as heterogeneity; in shallow environments, they develop mainly on vertical and sub-vertical rocky walls. Mainly diver-based techniques are carried out to gain detailed information on such habitats. Here, we propose a non-destructive and multi-purpose photo mosaicking method to study and monitor coralligenous reefs developing on vertical walls. High-pixel resolution images using three different commercial cameras were acquired on a 10 m2 reef, to compare the effectiveness of photomosaic method to the traditional photoquadrats technique in quantifying the coralligenous assemblage. Results showed very high spatial resolution and accuracy among the photomosaic acquired with different cameras and no significant differences with photoquadrats in assessing the assemblage composition. Despite the large difference in costs of each recording apparatus, little differences emerged from the assemblage characterization: through the analysis of the three photomosaics twelve taxa/morphological categories covered 97–99% of the sampled surface. Photo mosaicking represents a low-cost method that minimizes the time spent underwater by divers and capable of providing new opportunities for further studies on shallow coralligenous reefs
The HI Content of Local Late-Type Galaxies
We present a solid relationship between the neutral hydrogen (HI) disk mass
and the stellar disk mass of late-type galaxies in the local universe. This
relationship is derived by comparing the stellar disk mass function from the
Sloan Digital Sky Survey and the HI mass function from the HI Parkes All Sky
Survey (HIPASS). We find that the HI mass in late-type galaxies tightly
correlates with the stellar mass over three orders of magnitude in stellar disk
mass. We cross-check our result with that obtained from a sample of HIPASS
objects for which the stellar mass has been obtained by inner kinematics. In
addition, we derive the HI versus halo mass relationship and the dependence of
all the baryonic components in spirals on the host halo mass. These
relationships bear the imprint of the processes ruling galaxy formation, and
highlight the inefficiency of galaxies both in forming stars and in retaining
their pristine HI gas.Comment: 6 pages, 5 figures. Match to the published version. References
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