1,453 research outputs found
Tracking the phase-transition energy in disassembly of hot nuclei
In efforts to determine phase transitions in the disintegration of highly
excited heavy nuclei, a popular practice is to parametrise the yields of
isotopes as a function of temperature in the form
, where 's are the measured yields
and and are fitted to the yields. Here would be
interpreted as the phase transition temperature. For finite systems such as
those obtained in nuclear collisions, this parametrisation is only approximate
and hence allows for extraction of in more than one way. In this work we
look in detail at how values of differ, depending on methods of
extraction. It should be mentioned that for finite systems, this approximate
parametrisation works not only at the critical point, but also for first order
phase transitions (at least in some models). Thus the approximate fit is no
guarantee that one is seeing a critical phenomenon. A different but more
conventional search for the nuclear phase transition would look for a maximum
in the specific heat as a function of temperature . In this case is
interpreted as the phase transition temperature. Ideally and would
coincide. We invesigate this possibility, both in theory and from the ISiS
data, performing both canonical () and microcanonical ()
calculations. Although more than one value of can be extracted from the
approximate parmetrisation, the work here points to the best value from among
the choices. Several interesting results, seen in theoretical calculations, are
borne out in experiment.Comment: Revtex, 10 pages including 8 figures and 2 table
Dynamics of 8CB confined into porous silicon probed by incoherent neutron backscattering experiments
Confinement in the nanochannels of porous silicon strongly affects the phase
behavior of the archetype liquid-crystal 4-n-octyl-4-cyanobiphenyl (8CB). A
very striking phenom- enon is the development of a short-range smectic order,
which occurs on a very broad temperature range. It suggests in this case that
quenched disorder effects add to usual finite size and surface interaction
effects. We have monitored the temperature variation of the molecular dynamics
of the confined fluid by incoherent quasielastic neutron scat- tering. A
strongly reduced mobility is observed at the highest temperatures in the liquid
phase, which suggests that the interfacial molecular dynamics is strongly
hindered. A continuously increasing slowdown appears on cooling together with a
progressive growth of the static correlation lengt
Differences in daptomycin and vancomycin ex vivo behaviour can lead to false interpretation of negative blood cultures
AbstractIn clinical studies on bacteraemia, the negativity of blood cultures is an important endpoint for comparing the efficacy of different therapeutic regimens. In FAN° anaerobic blood culture medium (BacT/ALERT system), daptomycin displayed increased MIC against Staphylococcus aureus and improved abolishment of its carryover effect in charcoal when compared with vancomycin. Differences between these two drugs can lead to a false interpretation of negative blood cultures. To compare different antibiotic regimens for the treatment of bacteraemia, preliminary studies are mandatory to ensure that ex vivo antibiotic behaviour is similar in the blood-culture system used
A detailed study of the diastereoselective catalytic hydrogenation of 6-hydroxytetrahydroisoquinoline-(3R)-carboxylic ester intermediates
A key step towards a highly-selective antagonist of ionotropic glutamate receptors entails the diastereoselective arene hydrogenation of an enantiopure tetrahydroisoquinoline. An extensive screen using parallel reactors was conducted and led to the discovery of several Pd/C catalysts giving high yield and improved diastereoselectivity from 75 : 25 to 95 : 5. A detailed kinetic study of the best system was performed and supports the reduction occuring in two-steps.
Prevention of antigen-induced bronchial hyperreactivity and airway inflammation in sensitized guinea-pigs by tacrolimus.
We examined the effect of the immunosuppressive agent, tacrolimus (FK506), on antigen-induced bronchial hyperreactivity to acetylcholine and leukocyte infiltration into the airways of ovalbumin-challenged guinea-pigs. Subcutaneous injection of 0.5 mg/kg of FK506, 1 h before and 5 h after intra-nasal antigen challenge prevented bronchial hyperreactivity to aerosolized acetylcholine, eosinophilia in bronchoalveolar lavage (BAL) fluid and bronchial tissue and the invasion of the bronchial wall by CD4+ T-lymphocytes. FK506 also suppressed ovalbumin-induced increase in the number of leukocytes adhering to the pulmonary vascular endothelium and expressing alpha4-integrins. Inhibition by FK506 of antigen-induced bronchial hyperreactivity in sensitized guinea-pigs may thus relate to its ability to prevent the emergence of important inflammatory components of airway inflammation, such as eosinophil accumulation, as well as CD4+ T-lymphocyte infiltration into the bronchial tissue
Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solutions nanoconfined in porous silicon
Glycerol and trehalose-glycerol binary solutions are glass-forming liquids
with remarkable bioprotectant properties. Incoherent quasielastic neutron
scattering (QENS) is used to reveal the different effects of nanoconfinement
and addition of trehalose on the molecular dynamics in the normal liquid and
supercooled liquid phases, on a nanosecond timescale. Confinement has been
realized in straight channels of diameter D=8 nm formed by porous silicon. It
leads to a faster and more inhomogeneous relaxation dynamics deep in the liquid
phase. This confinement effect remains at lower temperature where it affects
the glassy dynamics. The glass transitions of the confined systems are shifted
to low temperature with respect to the bulk ones. Adding trehalose tends to
slow down the overall glassy dynamics and increases the non-exponential
character of the structural relaxation. Unprecedented results are obtained for
the binary bioprotectant solution, which exhibits an extremely non-Debye
relaxation dynamics as a result of the combination of the effects of
confinement and mixing of two constituents
Ruthenacycles and Iridacycles as Catalysts for Asymmetric Transfer Hydrogenation and Racemisation
Ruthenacycles, which are easily prepared in a single step by reaction between enantiopure aromatic amines and [Ru(arene)Cl2]2 in the presence of NaOH and KPF6, are very good asymmetric transfer hydrogenation catalysts. A range of aromatic ketones were reduced using isopropanol in good yields with eeâs up to 98%. Iridacycles, which are prepared in similar fashion from [IrCp*Cl2]2 are excellent catalysts for the racemisation of secondary alcohols and chlorohydrins at room temperature. This allowed the development of a new dynamic kinetic resolution of chlorohydrins to the enantiopure epoxides in up to 90% yield and 98% enantiomeric excess (ee) using a mutant of the enzyme Haloalcohol dehalogenase C and an iridacycle as racemisation catalyst.
Excitation and decay of projectile-like fragments formed in dissipative peripheral collisions at intermediate energies
Projectile-like fragments (PLF:15<=Z<=46) formed in peripheral and
mid-peripheral collisions of 114Cd projectiles with 92Mo nuclei at E/A=50 MeV
have been detected at very forward angles, 2.1 deg.<=theta_lab<=4.2 deg.
Calorimetric analysis of the charged particles observed in coincidence with the
PLF reveals that the excitation of the primary PLF is strongly related to its
velocity damping. Furthermore, for a given V_PLF*, its excitation is not
related to its size, Z_PLF*. For the largest velocity damping, the excitation
energy attained is large, approximately commensurate with a system at the
limiting temperatureComment: 5 pages, 6 figure
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