648 research outputs found
On Generating Binary Words Palindromically
We regard a finite word up to word isomorphism as an
equivalence relation on where is equivalent to if
and only if Some finite words (in particular all binary words) are
generated by "{\it palindromic}" relations of the form for some
choice of and That is to say,
some finite words are uniquely determined up to word isomorphism by the
position and length of some of its palindromic factors. In this paper we study
the function defined as the least number of palindromic relations
required to generate We show that every aperiodic infinite word must
contain a factor with and that some infinite words have
the property that for each factor of We obtain a
complete classification of such words on a binary alphabet (which includes the
well known class of Sturmian words). In contrast for the Thue-Morse word, we
show that the function is unbounded
Radio continuum imaging of the R CrA star-forming region with the ATCA
The aim of this study is to investigate the nature of radio sources
associated with young stellar objects (YSOs) belonging to the R CrA cluster. By
combining the centimetre radio data with the wealth of shorter wavelength data
accumulated recently we wish to refine estimates of the evolutionary stages of
the YSOs. Fluxes and spectral indices for the brightest radio sources were
derived from the observations at 3, 6, and 20 cm using the ATCA. Seven of
detected sources can be assigned to YSOs, which have counterparts in the
X-rays, infrared or submm. One of the YSOs, Radio Source 9, is a Class 0
candidate, and another, IRS 7B, is suggested to be in the Class 0/I transition
stage. IRS 7B is associated with extended radio lobes at 6 and 20 cm. The lobes
may have a gyrosynchrotron emission component, which could be understood in
terms of Fermi accleration in shocks. The Class I objects detected here seem to
be a mixed lot. One of these, the wide binary IRS 5, shows a negative spectral
index, rapid variability, and a high degree of circular polarisation with
% on one of the days of observation. These signs of magnetic
activity suggest that at least one of the binary components has advanced beyond
the Class I stage. The radio source without YSO assigment, Radio Source 5, has
been suggested to be a brown dwarf. The radio properties, in particular its
persistent strong emission, do not support this classification. The radio
characteristics of the detected YSOs roughly agree with the scheme where the
dominant emission mechanism changes with age. The heterogeneity of the Class I
group can possibly be explained by a drastic decline in the jet activity during
this stage, which also changes the efficiency of free-free absorption around
the protostar.Comment: Accepted for publication in A&A (8 pages, 4 figures, 4 tables
Far-infrared spectra of lateral quantum dot molecules
We study effects of electron-electron interactions and confinement potential
on the magneto-optical absorption spectrum in the far-infrared range of lateral
quantum dot molecules. We calculate far-infrared (FIR) spectra for three
different quantum dot molecule confinement potentials. We use accurate exact
diagonalization technique for two interacting electrons and calculate
dipole-transitions between two-body levels with perturbation theory. We
conclude that the two-electron FIR spectra directly reflect the symmetry of the
confinement potential and interactions cause only small shifts in the spectra.
These predictions could be tested in experiments with nonparabolic quantum dots
by changing the number of confined electrons. We also calculate FIR spectra for
up to six noninteracting electrons and observe some additional features in the
spectrum.Comment: For better quality Figs download manuscript from
http://www.fyslab.hut.fi/~mma/FIR/Helle_qdmfir.ps.g
Ground-state of two-dimensional finite electron systems in the Quantum Hall regime
We study electronic structures of quasi-two-dimensional finite electron
systems in high magnetic fields. The solutions in the fractional quantum Hall
regime are interpreted as quantum liquids of electrons and off-electron
vortices. The ground states are classified according to the number of vortices
inside the electron droplet. The theory predicts observable effects due to
vortex formation in the chemical potentials and magnetization of electron
droplets. We compare the transitions in the theory to those found in electron
transport experiments on a quantum dot device and find significant
correspondence.Comment: 4 pages, 4 figures (3 in colour), revised in response to referees'
comments, to appear in Phys. Rev. let
Influence of the Catalyst Particle Size on the Aqueous Phase Reforming of n-Butanol Over Rh/ZrO2
Butanol is a by-product obtained from biomass that can be valorized through aqueous phase reforming. Rh/ZrO2 catalysts were prepared and characterized, varying the size of the support particles. The results showed a relatively mild effect of internal mass transport on butanol conversion. However, the influence of internal transport limitations on the product distribution was much stronger, promoting consecutive reactions, i.e., dehydrogenation, hydrogenolysis, and reforming of propane and ethane. Hydrogen consuming reactions, i.e., hydrogenolysis, were more strongly enhanced than hydrogen producing reactions due to internal concentration gradients. Large support particles deactivated faster, attributed to high concentrations of butyraldehyde inside the catalyst particles, enhancing deposit formation via aldol condensation reactions. Consequently, also the local butyric acid concentration was high, decreasing the local pH, enhancing Rh leaching. The influence of internal transfer limitation on product distribution and stability is discussed based on a reaction scheme with three main stages, i.e., (1) formation of liquid intermediates via dehydrogenation, (2) formation of gas via decarbonylation/decarboxylation reactions, and (3) hydrocarbon hydrogenolysis/reforming/dehydrogenation
Search for grain growth towards the center of L1544
In dense and cold molecular clouds dust grains are surrounded by thick icy
mantles. It is however not clear if dust growth and coagulation take place
before the switch-on of a protostar. This is an important issue, as the
presence of large grains may affect the chemical structure of dense cloud
cores, including the dynamically important ionization fraction, and the future
evolution of solids in protoplanetary disks. To study this further, we focus on
L1544, one of the most centrally concentrated pre-stellar cores on the verge of
star formation, and with a well-known physical structure. We observed L1544 at
1.2 and 2 mm using NIKA, a new receiver at the IRAM 30 m telescope, and we used
data from the Herschel Space Observatory archive. We find no evidence of grain
growth towards the center of L1544 at the available angular resolution.
Therefore, we conclude that single dish observations do not allow us to
investigate grain growth toward the pre-stellar core L1544 and high sensitivity
interferometer observations are needed. We predict that dust grains can grow to
200 m in size toward the central ~300 au of L1544. This will imply a dust
opacity change by a factor of ~2.5 at 1.2 mm, which can be detected using the
Atacama Large Millimeter and submillimeter Array (ALMA) at different
wavelengths and with an angular resolution of 2".Comment: 12 pages, 14 figures. Accepted for publication in A&
Glutathione s-transferase omega in the lung and sputum supernatants of COPD patients
BACKGROUND: The major contribution to oxidant related lung damage in COPD is from the
oxidant/antioxidant imbalance and possibly impaired antioxidant defence. Glutathione (GSH) is one
of the most important antioxidants in human lung and lung secretions, but the mechanisms
participating in its homeostasis are partly unclear. Glutathione-S-transferase omega (GSTO) is a
recently characterized cysteine containing enzyme with the capability to bind and release GSH in
vitro. GSTO has not been investigated in human lung or lung diseases.
METHODS: GSTO1-1 was investigated by immunohistochemistry and Western blot analysis in 72
lung tissue specimens and 40 sputum specimens from non-smokers, smokers and COPD, in
bronchoalveolar lavage fluid and in plasma from healthy non-smokers and smokers. It was also
examined in human monocytes and bronchial epithelial cells and their culture mediums in vitro.
RESULTS: GSTO1-1 was mainly expressed in alveolar macrophages, but it was also found in airway
and alveolar epithelium and in extracellular fluids including sputum supernatants, bronchoalveolar
lavage fluid, plasma and cell culture mediums. The levels of GSTO1-1 were significantly lower in the
sputum supernatants (p = 0.023) and lung homogenates (p = 0.003) of COPD patients than in nonsmokers.
CONCLUSION: GSTO1-1 is abundant in the alveolar macrophages, but it is also present in
extracellular fluids and in airway secretions, the levels being decreased in COPD. The clinical
significance of GSTO1-1 and its role in regulating GSH homeostasis in airway secretions, however,
needs further investigations
C18O (3-2) observations of the Cometary Globule CG 12: a cold core and a C18O hot spot
The feasibility of observing the C18O (3-2) spectral line in cold clouds with
the APEX telescope has been tested. As the line at 329.330 GHz lies in the wing
of a strong atmospheric H2O absorption it can be observed only at high altitude
observatories. Using the three lowest rotational levels instead of only two
helps to narrow down the physical properties of dark clouds and globules. The
centres of two C18O maxima in the high latitude low mass star forming region CG
12 were mapped in C18O (3-2) and the data were analyzed together with spectral
line data from the SEST. The T_MB(3-2)/T_MB(2-1) ratio in the northern C18O
maximum, CG 12 N, is 0.8, and in the southern maximum, CG 12 S, ~2. CG 12 N is
modelled as a 120'' diameter (0.4pc) cold core with a mass of 27 Msun. A small
size maximum with a narrow, 0.8 kms-1, C18O (3-2) spectral line with a peak
temperature of T_MB ~11 K was detected in CG 12 S. This maximum is modelled as
a 60'' to 80'' diameter (~0.2pc) hot (80 K < Tex < 200 K) ~1.6 Msun clump. The
source lies on the axis of a highly collimated bipolar molecular outflow near
its driving source. This is the first detection of such a compact, warm object
in a low mass star forming region.Comment: APEX A&A special issue, accepte
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