8,831 research outputs found
Surface excitations in the modelling of electron transport for electron- beam-induced deposition experiments
The aim of the present overview article is to raise awareness of an essential
aspect that is usually not accounted for in the modelling of electron transport
for focused-electron-beam-induced deposition (FEBID) of nanostructures: surface
excitations are on the one hand responsible for a sizeable fraction of the
intensity in reflection-electron-energy-loss spectra for primary electron
energies of up to a few keV and, on the other hand, they play a key role in the
emission of secondary electrons from solids, regardless of the primary energy.
In this overview work we present a general perspective of recent works on the
subject of surface excitations and on low-energy electron transport,
highlighting the most relevant aspects for the modelling of electron transport
in FEBID simulations.Comment: 17 pages, 5 figure
WISeREP - An Interactive Supernova Data Repository
We have entered an era of massive data sets in astronomy. In particular, the
number of supernova (SN) discoveries and classifications has substantially
increased over the years from few tens to thousands per year. It is no longer
the case that observations of a few prototypical events encapsulate most
spectroscopic information about SNe, motivating the development of modern tools
to collect, archive, organize and distribute spectra in general, and SN spectra
in particular. For this reason we have developed the Weizmann Interactive
Supernova data REPository - WISeREP - an SQL-based database (DB) with an
interactive web-based graphical interface. The system serves as an archive of
high quality SN spectra, including both historical (legacy) data as well as
data that is accumulated by ongoing modern programs. The archive provides
information about objects, their spectra, and related meta-data. Utilizing
interactive plots, we provide a graphical interface to visualize data, perform
line identification of the major relevant species, determine object redshifts,
classify SNe and measure expansion velocities. Guest users may view and
download spectra or other data that have been placed in the public domain.
Registered users may also view and download data that are proprietary to
specific programs with which they are associated. The DB currently holds >8000
spectra, of which >5000 are public; the latter include published spectra from
the Palomar Transient Factory, all of the SUSPECT archive, the
Caltech-Core-Collapse Program, the CfA SN spectra archive and published spectra
from the UC Berkeley SNDB repository. It offers an efficient and convenient way
to archive data and share it with colleagues, and we expect that data stored in
this way will be easy to access, increasing its visibility, usefulness and
scientific impact.Comment: To be published in PASP. WISeREP:
http://www.weizmann.ac.il/astrophysics/wiserep
An almost nilpotent variety of exponent 2
We construct a non-associative algebra A over a field of characteristic zero with the following properties: if V is the variety generated by A, then V has exponential growth but any proper subvariety of V is nilpotent.
Moreover, by studying the asymptotics of the sequence of codimensions of A we deduce that exp(V) = 2
An uncountable family of almost nilpotent varieties of polynomial growth
A non-nilpotent variety of algebras is almost nilpotent if any proper subvariety is nilpotent. Let the base field be of characteristic zero. It has been shown that for associative or Lie algebras only one such variety exists. Here we present infinite families of such varieties. More precisely we shall prove the existence of. 1) a countable family of almost nilpotent varieties of at most linear growth and. 2) an uncountable family of almost nilpotent varieties of at most quadratic growth
SN/GRB connection: a statistical approach with BATSE and Asiago Catalogues
Recent observations suggest that some types of GRB are physically connected
with SNe of type Ib/c. However, it has been pointed out by several authors that
some GRBs could be associated also with other types of core-collapse SNe (type
IIdw/IIn). On the basis of a comphrensive statistical study, which has made use
of the BATSE and Asiago catalogues, we have found that: i) the temporal and
spacial distribution of SNe-Ib/c is marginally correlated with that of the
BATSE GRBs; ii) we do not confirm the existence of an association between GRBs
and SNe-IIdw/IIn.Comment: Proceeding of the 4th workshop on Gamma Ray Bursts in the Afterglow
Era, Rome, 2004; 4 page
Varieties with at most cubic growth
Let V be a variety of non necessarily associative algebras over a field of characteristic zero. The growth of V is determined by the asymptotic behavior of the sequence of codimensions c(n) (V),n = 1,2,..., and here we study varieties of polynomial growth. We classify all possible growth of varieties V of algebras satisfying the identity x(yz) equivalent to 0 such that c(n) (V) < C-n(alpha) with 1 <= alpha < 3, for some constant C. We prove that if 1 <= alpha < 2 then c(n) (V) <= C-1n, and if 2 <= alpha < 3, then c(n)(V) <= C(2)n(2), for some constants C-1, C-2
Origin of the insulating state in honeycomb iridates and rhodates
A burning question in the emerging field of spin-orbit driven insulating
iridates, such as Na2IrO3 and Li2IrO3 is whether the observed insulating state
should be classified as a Mott-Hubbard insulator derived from a half-filled
relativistic j_eff=1/2 band or as a band insulator where the gap is assisted by
spin-orbit interaction, or Coulomb correlations, or both. The difference
between these two interpretations is that only for the former, strong
spin-orbit coupling (lambda >~ W, where W is the band width) is essential. We
have synthesized the isostructural and isoelectronic Li2RhO3 and report its
electrical resistivity and magnetic susceptibility. Remarkably it shows
insulating behavior together with fluctuating effective S=1/2 moments, similar
to Na2IrO3 and Li2IrO3, although in Rh4+ (4d5) the spin-orbit coupling is
greatly reduced. We show that this behavior has non-relativistic one-electron
origin (although Coulomb correlations assist in opening the gap), and can be
traced down to formation of quasi-molecular orbitals, similar to those in
Na2IrO3.Comment: 7 pages, 7 figure
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