1,183 research outputs found
Does shade improve light interception efficiency? A comparison among seedlings from shade-tolerant and -intolerant temperate deciduous tree species
âą Here, we tested two hypotheses: shading increases light interception efficiency (LIE) of broadleaved tree seedlings, and shade-tolerant species exhibit larger LIEs than do shade-intolerant ones. The impact of seedling size was taken into account to detect potential size-independent effects on LIE. LIE was defined as the ratio of mean light intercepted by leaves to light intercepted by a horizontal surface of equal area. âą Seedlings from five species differing in shade tolerance (Acer saccharum, Betula alleghaniensis, A. pseudoplatanus, B. pendula, Fagus sylvatica) were grown under neutral shading nets providing 36, 16 and 4% of external irradiance. Seedlings (1- and 2-year-old) were three-dimensionally digitized, allowing calculation of LIE. âą Shading induced dramatic reduction in total leaf area, which was lowest in shade-tolerant species in all irradiance regimes. Irradiance reduced LIE through increasing leaf overlap with increasing leaf area. There was very little evidence of significant size-independent plasticity of LIE. âą No relationship was found between the known shade tolerance of species and LIE at equivalent size and irradiance
Photon Physics in Heavy Ion Collisions at the LHC
Various pion and photon production mechanisms in high-energy nuclear
collisions at RHIC and LHC are discussed. Comparison with RHIC data is done
whenever possible. The prospect of using electromagnetic probes to characterize
quark-gluon plasma formation is assessed.Comment: Writeup of the working group "Photon Physics" for the CERN Yellow
Report on "Hard Probes in Heavy Ion Collisions at the LHC", 134 pages. One
figure added in chapter 5 (comparison with PHENIX data). Some figures and
correponding text corrected in chapter 6 (off-chemical equilibrium thermal
photon rates). Some figures modified in chapter 7 (off-chemical equilibrium
photon rates) and comparison with PHENIX data adde
Emission patterns of neutral pions in 40 A MeV Ta+Au reactions
Differential cross sections of neutral pions emitted in 181Ta + 197Au
collisions at a beam energy of 39.5A MeV have been measured with the photon
spectrometer TAPS. The kinetic energy and transverse momentum spectra of
neutral pions cannot be properly described in the framework of the thermal
model, nor when the reabsorption of pions is accounted for in a
phenomenological model. However, high energy and high momentum tails of the
pion spectra can be well fitted through thermal distributions with unexpectedly
soft temperature parameters below 10 MeV.Comment: 16 pages (double-spaced), 5 figures; corrections after referee's
comments and suggestion
Thermal bremsstrahlung probing the thermodynamical state of multifragmenting systems
Inclusive and exclusive hard-photon (E 30 MeV) production in five
different heavy-ion reactions (Ar+Au, Ag, Ni,
C at 60{\it A} MeV and Xe+Sn at 50{\it A} MeV) has been
studied coupling the TAPS photon spectrometer with several charged-particle
multidetectors covering more than 80% of 4. The measured spectra, slope
parameters and source velocities as well as their target-dependence, confirm
the existence of thermal bremsstrahlung emission from secondary nucleon-nucleon
collisions that accounts for roughly 20% of the total hard-photon yield. The
thermal slopes are a direct measure of the temperature of the excited nuclear
systems produced during the reaction.Comment: 4 pages, 3 figures, Proceedings CRIS 2000, 3rd Catania Relativistic
Ion Studies, "Phase Transitions in Strong Interactions: Status and
Perspectives", Acicastello, Italy, May 22-26, 2000 (to be published in Nuc.
Phys. A
HEAVY ION SECONDARY BEAMS
The possibility of producing secondary beams of radioactive nuclei is an interesting application of medium and high energy heavy ion beams. After a first attempt at CERN (1) , two experiments have been performed at GANIL, using 44 MeV/u 40Ar (2) and 65 MeV/u 180 projectiles. This paper recalls the results of the Ar experiment, and presents new data obtained with the 180 beam
New quinoxaline derivatives as potential MTâ and MTâ receptor ligands.
Ever since the idea arose that melatonin might promote sleep and resynchronize
circadian rhythms, many research groups have centered their efforts on obtaining new
melatonin receptor ligands whose pharmacophores include an aliphatic chain of variable
length united to an N-alkylamide and a methoxy group (or a bioisostere), linked to a central
ring. Substitution of the indole ring found in melatonin with a naphthalene or quinoline
ring leads to compounds of similar affinity. The next step in this structural approximation
is to introduce a quinoxaline ring (a bioisostere of the quinoline and naphthalene rings) as
the central nucleus of future melatoninergic ligand
Emotional memory impairments in a genetic rat model of depression : involvement of 5-HT/MEK/Arc signaling in restoration
Cognitive dysfunctions are common in major depressive disorder, but have been difficult to recapitulate in animal models. This study shows that Flinders sensitive line (FSL) rats, a genetic rat model of depression, display a pronounced impairment of emotional memory function in the passive avoidance (PA) task, accompanied by reduced transcription of Arc in prefrontal cortex and hippocampus. At the cellular level, FSL rats have selective reductions in levels of NMDA receptor subunits, serotonin 5-HT(1A) receptors and MEK activity. Treatment with chronic escitalopram, but not with an antidepressant regimen of nortriptyline, restored memory performance and increased Arc transcription in FSL rats. Multiple pharmacological manipulations demonstrated that procognitive effects could also be achieved by either disinhibition of 5-HT(1A)R/MEK/Arc or stimulation of 5-HT(4)R/MEK/Arc signaling cascades. Taken together, studies of FSL rats in the PA task revealed reversible deficits in emotional memory processing, providing a potential model with predictive and construct validity for assessments of procognitive actions of antidepressant drug therapies. Molecular Psychiatry advance online publication, 18 January 2011; doi:10.1038/mp.2010.131
An insulating grid spacer for large-area MICROMEGAS chambers
We present an original design for large area gaseous detectors based on the MICROMEGAS technology. This technology incorporates an insulating grid, sandwiched between the micro-mesh and the anode-pad plane, which provides an uniform 200 m amplification gap. The uniformity of the amplification gap thickness has been verified under several experimental conditions. The gain performances of the detector are presented and compared to the values obtained with detectors using cylindrical micro spacers. The new design presents several technical and financial advantages
Quasi-fission reactions as a probe of nuclear viscosity
Fission fragment mass and angular distributions were measured from the
^{64}Ni+^{197}Au reaction at 418 MeV and 383 MeV incident energy. A detailed
data analysis was performed, using the one-body dissipation theory implemented
in the code HICOL. The effect of the window and the wall friction on the
experimental observables was investigated. Friction stronger than one-body was
also considered. The mass and angular distributions were consistent with
one-body dissipation. An evaporation code DIFHEAT coupled to HICOL was
developed in order to predict reaction time scales required to describe
available data on pre-scission neutron multiplicities. The multiplicity data
were again consistent with one-body dissipation. The cross-sections for touch,
capture and quasi-fission were also obtained.Comment: 25 pages REVTeX, 3 tables, 13 figures, submitted to Phys. Rev
Melatonin receptors in GtoPdb v.2021.3
Melatonin receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Melatonin Receptors [40]) are activated by the endogenous ligands melatonin and clinically used drugs like ramelteon, agomelatine and tasimelteon
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