4,623 research outputs found
Bonding in doped gallium nanoclusters: Insights from regional DFT
The molecular nature (Ga2)n of gallium makes this an interesting metal to investigate for the development of novel nano-materials. However, establishment of a targeted approach to manipulating the properties of gallium clusters requires a detailed understanding of how doping affects the bonding in these species. In this study, the bonding of gallium nanoclusters has been investigated using electron deformation densities and Regional Density Functional Theory (RDFT). Bonding throughout Ga12X clusters is generally intermediate between covalent and metallic. However, the presence of Ga2 subunits is clearly identified in clusters with endohedral dopants (Ga12X, X = Al, Si, P, Ga, Ge, As). Although there is evidence of Ga2 subunits in exohedral doped clusters, localised bonding to the dopant generally leads to significant disruption to the cluster framework. Maps of electronic chemical potential provide understanding for the observed differences in regioselectivity for hydrogen adsorption
The Cosmic Neutrino Background and the Age of the Universe
We discuss the cosmological degeneracy between the age of the Universe, the
Hubble parameter and the effective number of relativistic particles N_eff. We
show that independent determinations of the Hubble parameter H(z) as those
recently provided by Simon,Verde, Jimenez (2006), combined with other
cosmological data sets can provide the most stringent constraint on N_eff,
yielding N_eff=3.7 (-1.2) (+1.1) at 95% confidence level. A neutrino background
is detected with high significance: N_eff >1.8 at better than 99% confidence
level. Constraints on the age of the universe in the framework of an extra
background of relativistic particles are improved by a factor 3.Comment: JCAP, in pres
Electronic stress tensor analysis of hydrogenated palladium clusters
We study the chemical bonds of small palladium clusters Pd_n (n=2-9)
saturated by hydrogen atoms using electronic stress tensor. Our calculation
includes bond orders which are recently proposed based on the stress tensor. It
is shown that our bond orders can classify the different types of chemical
bonds in those clusters. In particular, we discuss Pd-H bonds associated with
the H atoms with high coordination numbers and the difference of H-H bonds in
the different Pd clusters from viewpoint of the electronic stress tensor. The
notion of "pseudo-spindle structure" is proposed as the region between two
atoms where the largest eigenvalue of the electronic stress tensor is negative
and corresponding eigenvectors forming a pattern which connects them.Comment: 22 pages, 13 figures, published online, Theoretical Chemistry
Account
The Hubble constant and dark energy from cosmological distance measures
We study how the determination of the Hubble constant from cosmological
distance measures is affected by models of dark energy and vice versa. For this
purpose, constraints on the Hubble constant and dark energy are investigated
using the cosmological observations of cosmic microwave background, baryon
acoustic oscillations and type Ia suprenovae. When one investigates dark
energy, the Hubble constant is often a nuisance parameter, thus it is usually
marginalized over. On the other hand, when one focuses on the Hubble constant,
simple dark energy models such as a cosmological constant and a constant
equation of state are usually assumed. Since we do not know the nature of dark
energy yet, it is interesting to investigate the Hubble constant assuming some
types of dark energy and see to what extent the constraint on the Hubble
constant is affected by the assumption concerning dark energy. We show that the
constraint on the Hubble constant is not affected much by the assumption for
dark energy. We furthermore show that this holds true even if we remove the
assumption that the universe is flat. We also discuss how the prior on the
Hubble constant affects the constraints on dark energy and/or the curvature of
the universe.Comment: 45 pages, 15 figure
Neutrino mass constraint from CMB and its degeneracy with other cosmological parameters
We show that the cosmic microwave background (CMB) data of WMAP can give
subelectronvolt limit on the neutrino mass: m_nu < 0.63 eV (95% CL). We also
investigate its degeneracy with other cosmological parameters. In particular,
we show the Hubble constant derived from the WMAP data decreases considerably
when the neutrino mass is a few times 0.1 eV.Comment: 3 pages, 2 figures, prepared for the TAUP2007 Proceeding
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