792 research outputs found
Evidence of anomalous dispersion of the generalized sound velocity in glasses
The dynamic structure factor, S(Q,w), of vitreous silica, has been measured
by inelastic X-ray scattering in the exchanged wavevector (Q) region Q=4-16.5
nm-1 and up to energies hw=115 meV in the Stokes side. The unprecedented
statistical accuracy in such an extended energy range allows to accurately
determine the longitudinal current spectra, and the energies of the vibrational
excitations. The simultaneous observation of two excitations in the acoustic
region, and the persistence of propagating sound waves up to Q values
comparable with the (pseudo-)Brillouin zone edge, allow to observe a positive
dispersion in the generalized sound velocity that, around Q=5 nm-1, varies from
6500 to 9000 m/s: this phenomenon was never experimentally observed in a glass.Comment: 5 pages, 3 figures. To appear in Phys. Rev.
Growth, carcass and meat quality of Casertana, Italian Large White and Duroc x (Landrace x Italian Large White) pigs reared outdoors
To compare growth, skeletal development,
carcass traits and meat quality of different
genotypes, 10 Casertana (CT), 10 Italian Large
White (LW) and 10 Duroc x (Landrace x Italian
Large White) (DU) crosses, barrows of 90 days
of age, were allotted to the same outdoor rearing
and feeding conditions. Live weight was
recorded and average daily gain (ADG) was
calculated. At slaughter (330-day-old) dressing
and lean percentages were determined; backfat
thickness and loin eye depth were measured.
Carcasses were dissected into commercial
cuts. Water holding capacity, pH and colour
(45 min and 24 h post-mortem) were measured.
Longissimus lumborum muscle samples
were collected for cholesterol, \u3b1-tochopherol
and intramuscular collagen (IMC) analyses.
CT compared to DU and LW had the lowest
growth rate and skeletal development.
Casertana showed higher backfat thickness,
lower lean cut/fatty cut ratio and less lean
meat (P<0.05). Loin eye depth differed among
genotypes with LW>DU>CT (P<0.05). CT
showed higher red colour of the meat than DU
and LW (P<0.05). CT compared to LW had the
highest hydroxylysylpiridinoline (HLP)
crosslink concentration and HLP/IMC ratio,
and a lower IMC amount (P<0.05). Casertana
pigs produced meat that could be tougher than
that from the improved breed, but more acceptable
from the technological point of view.
At eleven months of age bone weight, length
and diameter were clearly genetic type-related;
differently, the bone maturit
Maintenance of the virulence plasmid in Shigella flexneri is influenced by Lon and two functional partitioning systems
Members of the genus Shigella carry a large plasmid, pINV, which is essential for virulence. In Shigella flexneri, pINV harbours three toxin -antitoxin (TA) systems, CcdAB, GmvAT and VapBC that promote vertical transmission of the plasmid. Type II TA systems, such as those on pINV, consist of a toxic protein and protein antitoxin. Selective degradation of the antitoxin by proteases leads to the unopposed action of the toxin once genes encoding a TA system have been lost, such as following failure to inherit a plasmid harbouring a TA system. Here, we investigate the role of proteases in the function of the pINV TA systems and demonstrate that Lon, but not ClpP, is required for their activity during plasmid stability. This provides the first evidence that acetyltransferase family toxin -antitoxin systems, such as GmvAT, can be regulated by Lon. Interestingly, Shigella flexneri pINV also harbours two putative partitioning systems, ParAB and StbAB. We show that both systems are functional for plasmid maintenance although their activity is masked by other systems on pINV . Using a model vector based on the pINV replicon, we observe temperature -dependent differences between the two partitioning systems that contribute to our understanding of the maintenance of virulence in Shigella species
Frustration and sound attenuation in structural glasses
Three classes of harmonic disorder systems (Lennard-Jones like glasses,
percolators above threshold, and spring disordered lattices) have been
numerically investigated in order to clarify the effect of different types of
disorder on the mechanism of high frequency sound attenuation. We introduce the
concept of frustration in structural glasses as a measure of the internal
stress, and find a strong correlation between the degree of frustration and the
exponent alpha that characterizes the momentum dependence of the sound
attenuation . In particular, alpha decreases from
about d+1 in low-frustration systems (where d is the spectral dimension), to
about 2 for high frustration systems like the realistic glasses examined.Comment: Revtex, 4 pages including 4 figure
- âŠ