20,470 research outputs found
Correlation effects and orbital magnetism of Co clusters
Recent experiments on isolated Co clusters have shown huge orbital magnetic
moments in comparison with their bulk and surface counterparts. These clusters
hence provide the unique possibility to study the evolution of the orbital
magnetic moment with respect to the cluster size and how competing interactions
contribute to the quenching of orbital magnetism. We investigate here different
theoretical methods to calculate the spin and orbital moments of Co clusters,
and assess the performances of the methods in comparison with experiments. It
is shown that density functional theory in conventional local density or
generalized gradient approximations, or even with a hybrid functional, severely
underestimates the orbital moment. As natural extensions/corrections we
considered the orbital polarization correction, the LDA+U approximation as well
as the LDA+DMFT method. Our theory shows that of the considered methods, only
the LDA+DMFT method provides orbital moments in agreement with experiment, thus
emphasizing the importance of dynamic correlations effects for determining
fundamental magnetic properties of magnets in the nano-size regime
Study of Beam Losses at Injection in the CERN Proton Synchrotron
The maximum intensity the CERN PS has to deliver is continuously increasing. In particular, during the next years, one of the most intense beams ever produced in the PS, with up to 3000 1010 proton per pulse, should be delivered on a regular basis for the CNGS physics program. It is now known that the existing radiation shielding of the PS in some places is too weak and constitutes a major limitation due to large beam losses in specific locations of the machine. This is the case for the injection region: losses appear on the injection septum when the beam is injected in the ring and during the first turn, due to an optical mismatch between the injection line and the PS. This paper presents the experimental studies and the simulations which have been made to understand the loss pattern in the injection region. Possible solutions to reduce the beam losses will be described, including the computation of a new injection optics
Statistical mechanics in the context of special relativity
In the present effort we show that is the unique existing entropy obtained
by a continuous deformation of the Shannon-Boltzmann entropy and preserving unaltered its fundamental properties of concavity,
additivity and extensivity. Subsequently, we explain the origin of the
deformation mechanism introduced by and show that this deformation
emerges naturally within the Einstein special relativity. Furthermore, we
extend the theory in order to treat statistical systems in a time dependent and
relativistic context. Then, we show that it is possible to determine in a self
consistent scheme within the special relativity the values of the free
parameter which results to depend on the light speed and reduces
to zero as recovering in this way the ordinary statistical
mechanics and thermodynamics. The novel statistical mechanics constructed
starting from the above entropy, preserves unaltered the mathematical and
epistemological structure of the ordinary statistical mechanics and is suitable
to describe a very large class of experimentally observed phenomena in low and
high energy physics and in natural, economic and social sciences. Finally, in
order to test the correctness and predictability of the theory, as working
example we consider the cosmic rays spectrum, which spans 13 decades in energy
and 33 decades in flux, finding a high quality agreement between our
predictions and observed data.
PACS number(s): 05.20.-y, 51.10.+y, 03.30.+p, 02.20.-aComment: 17 pages (two columns), 5 figures, RevTeX4, minor typing correction
PHYLOGENETICS OF ELONGATION FACTOR-G MITOCHONDRIAL PROTEIN GENE (GFM1) IN TEN SELECTED SPECIES
The second stage of protein synthesis is elongation. One of the elongation factors in the elongation cycle of protein synthesis is the elongation factor-G (GFM1). GFM1 is an ancient translational GTPase (trGTPase); the bacterial homolog of eukaryotic eEF2 and archaeal aEF2, respectively. It may interact with the transcriptional apparatus as a positive regulator of RNA synthesis in various species. Genetic variations in GFM1 gene of ten species including cattle, human, chicken, mouse, rat, horse, zebra fish, honeybee, pig and rabbit based on availability were investigated using bioinformatic approach. Using a comparative genomic approach, 4,442 base pairs (bp) of the GFM1 sequences were obtained. Alignment of the sequences within the region of 3,626 bp and containing 816 gaps was carried out using Clustal W software. A very close relationship between rabbit and pig was observed in the phylogenetic tree of GFM1 gene which showed that the comparability of GFM1 gene sequence was highest between the two species and they evolved from a most recent common ancestor with respect to GFM1 gene. Cattle, human, rat and zebra fish were closest by their genetic distances to the ancestor, while mouse, horse, chicken, rabbit and honeybee were distant from the common ancestor. However, close phylogenetic relationship among species might be as a result of conservation of the sequence in the various species.Â
Ultrafast Molecular Imaging by Laser Induced Electron Diffraction
We address the feasibility of imaging geometric and orbital structure of a
polyatomic molecule on an attosecond time-scale using the laser induced
electron diffraction (LIED) technique. We present numerical results for the
highest molecular orbitals of the CO2 molecule excited by a near infrared
few-cycle laser pulse. The molecular geometry (bond-lengths) is determined
within 3% of accuracy from a diffraction pattern which also reflects the nodal
properties of the initial molecular orbital. Robustness of the structure
determination is discussed with respect to vibrational and rotational motions
with a complete interpretation of the laser-induced mechanisms
Effects of light colour and oscillator frequency on earthworm bioactivity
An experiment was conducted at the Zoology Laboratory of the Olabisi Onabanjo University, Nigeria to
evaluate the suitability of different light colours. Being generated from 15-watt, low-heat, or frequencygenerated
flourescent tubes as stimulants to enhance, major cast productivity of the earthworm
species Hyperiodrilus africanus. The aim was to determine if exposure to the different light colours
would improve the cast productivity of the worms and show whether H. africanus would show
preference for any particular light colour, in terms of mass of cast produced and rates of emigration.
The earthworms were kept in cylindrical plastic containers and put in different cubicles on a wooden
shelf, where they are subjected to different light colours that is, white, dark (control), green, blue, and
red. Results indicated that the red light colour was the most suitable in terms of cast productivity, as
casting was highest (11.96 g/worm), followed by blue (10.66 g/worm), green (9.49 g/worm), dark (7.2
g/worm) and white (4.86 g/worm), respectively. Least emigration was recorded under the control (dark) ,
followed by red, white, blue and green respectively, which indicated that the worms were probably more
‘comfortable’ in the dark and the red light than the other light colours tested. Results suggest that if
red light is introduced to a farm, casting activities can be increased and therefore, soil fertility can be
improved
The calibration of photographic and spectroscopic films: Reciprocity failure and thermal responses of IIaO film at liquid nitrogen temperatures
Reciprocity failure was examined for IIaO spectroscopic film. The results indicate reciprocity failure occurs at three distinct minimum points in time; 15 min, 30 min and 90 min. The results are unique because theory suggests only one minimum reciprocity failure point should occur. When incubating 70mm IIaO film for 15 and 30 min at temperatures of 30, 40, 50, and 60 C and then placing in a liquid nitrogen bath at a temperature of -190 C the film demonstrated an increase of the optical density when developed at a warm-up time of 30 min. Longer warm-up periods of 1, 2 and 3 hrs yield a decrease in optical density of the darker wedge patterns; whereas, shorter warm-up times yield an overall increase in the optical densities
The SILCC (SImulating the LifeCycle of molecular Clouds) project: I. Chemical evolution of the supernova-driven ISM
The SILCC project (SImulating the Life-Cycle of molecular Clouds) aims at a
more self-consistent understanding of the interstellar medium (ISM) on small
scales and its link to galaxy evolution. We simulate the evolution of the
multi-phase ISM in a 500 pc x 500 pc x 10 kpc region of a galactic disc, with a
gas surface density of .
The Flash 4.1 simulations include an external potential, self-gravity, magnetic
fields, heating and radiative cooling, time-dependent chemistry of H and CO
considering (self-) shielding, and supernova (SN) feedback. We explore SN
explosions at different (fixed) rates in high-density regions (peak), in random
locations (random), in a combination of both (mixed), or clustered in space and
time (clustered). Only random or clustered models with self-gravity (which
evolve similarly) are in agreement with observations. Molecular hydrogen forms
in dense filaments and clumps and contributes 20% - 40% to the total mass,
whereas most of the mass (55% - 75%) is in atomic hydrogen. The ionised gas
contributes <10%. For high SN rates (0.5 dex above Kennicutt-Schmidt) as well
as for peak and mixed driving the formation of H is strongly suppressed.
Also without self-gravity the H fraction is significantly lower (
5%). Most of the volume is filled with hot gas (90% within 2 kpc).
Only for random or clustered driving, a vertically expanding warm component of
atomic hydrogen indicates a fountain flow. Magnetic fields have little impact
on the final disc structure. However, they affect dense gas () and delay H formation. We highlight that individual chemical
species, in particular atomic hydrogen, populate different ISM phases and
cannot be accurately accounted for by simple temperature-/density-based phase
cut-offs.Comment: 30 pages, 23 figures, submitted to MNRAS. Comments welcome! For
movies of the simulations and download of selected Flash data see the SILCC
website: http://www.astro.uni-koeln.de/silc
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