2,811 research outputs found
Carbonized spent bleaching earth as a sorbent for some organic dyes
The potential of carbonized spent bleaching earth (CSBE) to remove/reduce acid and basic dyes in aqueous solution was investigated. Results show that CSBE was more effective in removing basic dyes. Parameters like pH, initial concentration, agitation rate, contact time and temperature which affect the sorption process were studied. As determined from Langmuir isotherms the maximum sorption capacities of CSBE for Basic Blue 3 and Methylene Blue were 102.6 and 94.5 mg/g respectively. Hence CSBE could be a useful sorbent in the treatment of baisc dyes in wastewater
Scaling and non-Abelian signature in fractional quantum Hall quasiparticle tunneling amplitude
We study the scaling behavior in the tunneling amplitude when quasiparticles
tunnel along a straight path between the two edges of a fractional quantum Hall
annulus. Such scaling behavior originates from the propagation and tunneling of
charged quasielectrons and quasiholes in an effective field analysis. In the
limit when the annulus deforms continuously into a quasi-one-dimensional ring,
we conjecture the exact functional form of the tunneling amplitude for several
cases, which reproduces the numerical results in finite systems exactly. The
results for Abelian quasiparticle tunneling is consistent with the scaling
anaysis; this allows for the extraction of the conformal dimensions of the
quasiparticles. We analyze the scaling behavior of both Abelian and non-Abelian
quasiparticles in the Read-Rezayi Z_k-parafermion states. Interestingly, the
non-Abelian quasiparticle tunneling amplitudes exhibit nontrivial k-dependent
corrections to the scaling exponent.Comment: 16 pages, 4 figure
Star count analysis of the interstellar matter in the region of L1251
We studied the ISM distribution in and around the star forming cloud L1251
with optical star counts. A careful calculation with a maximum likelihood based
statistical approach resulted in B,V,R,I extinction distributions from the star
count maps. A distance of 330+/-30 pc was derived. The extinction maps revealed
an elongated dense cloud with a bow shock at its eastern side. We estimated a
Mach number of M~2 for the bow shock. A variation of the apparent dust
properties is detected, i.e. the Rv=Av/E{B-V} total to selective extinction
ratio varies from 3 to 5.5, peaking at the densest part of L1251. The spatial
structure of the head of L1251 is well modelled with a Schuster-sphere (i.e.
n=5 polytropic sphere). The observed radial distribution of mass fits the model
with high accuracy out to 2.5pc distance from the assumed center. Unexpectedly,
the distribution of NH3 1.3 cm line widths is also well matched by the Schuster
solution even in the tail of the cloud. Since the elongated head-tail structure
of L1251 is far from the spherical symmetry the good fit of the linewidths in
the tail makes it reasonable to assume that the present cloud structure has
been formed by isothermal contraction.Comment: 9 pages, 9 figures, accepted in Astronomy & Astrophysic
Molecular Line Observations of the Small Protostellar Group L1251B
We present molecular line observations of L1251B, a small group of pre- and
protostellar objects, and its immediate environment in the dense C18O core
L1251E. These data are complementary to near-infrared, submillimeter and
millimeter continuum observations reported by Lee et al. (2006, ApJ, 648, 491;
Paper I). The single-dish data of L1251B described here show very complex
kinematics including infall, rotation and outflow motions, and the
interferometer data reveal these in greater detail. Interferometer data of N2H+
1-0 suggest a very rapidly rotating flattened envelope between two young
stellar objects, IRS1 and IRS2. Also, interferometer data of CO 2-1 resolve the
outflow associated with L1251B seen in single-dish maps into a few narrow and
compact components. Furthermore, the high resolution data support recent
theoretical studies of molecular depletions and enhancements that accompany the
formation of protostars within dense cores. Beyond L1251B, single-dish data are
also presented of a dense core located ~150" to the east that, in Paper I, was
detected at 850 micron but has no associated point sources at near- and
mid-infrared wavelengths. The relative brightness between molecules, which have
different chemical timescales, suggests it is less chemically evolved than
L1251B. This core may be a site for future star formation, however, since line
profiles of HCO+, CS, and HCN show asymmetry with a stronger blue peak, which
is interpreted as an infall signature.Comment: 46 pages, 18 figures. Accepted for publication in Ap
Disordered Fe vacancies and superconductivity in potassium-intercalated iron selenide (K2-xFe4+ySe5)
The parent compound of an unconventional superconductor must contain unusual
correlated electronic and magnetic properties of its own. In the high-Tc
potassium intercalated FeSe, there has been significant debate regarding what
the exact parent compound is. Our studies unambiguously show that the
Fe-vacancy ordered K2Fe4Se5 is the magnetic, Mott insulating parent compound of
the superconducting state. Non-superconducting K2Fe4Se5 becomes a
superconductor after high temperature annealing, and the overall picture
indicates that superconductivity in K2-xFe4+ySe5 originates from the Fe-vacancy
order to disorder transition. Thus, the long pending question whether magnetic
and superconducting state are competing or cooperating for cuprate
superconductors may also apply to the Fe-chalcogenide superconductors. It is
believed that the iron selenides and related compounds will provide essential
information to understand the origin of superconductivity in the iron-based
superconductors, and possibly to the superconducting cuprates
Branching, Capping, and Severing in Dynamic Actin Structures
Branched actin networks at the leading edge of a crawling cell evolve via
protein-regulated processes such as polymerization, depolymerization, capping,
branching, and severing. A formulation of these processes is presented and
analyzed to study steady-state network morphology. In bulk, we identify several
scaling regimes in severing and branching protein concentrations and find that
the coupling between severing and branching is optimally exploited for
conditions {\it in vivo}. Near the leading edge, we find qualitative agreement
with the {\it in vivo} morphology.Comment: 4 pages, 2 figure
Spitzer Observations of IC 2118
IC 2118, also known as the Witch Head Nebula, is a wispy, roughly cometary,
~5 degree long reflection nebula, and is thought to be a site of triggered star
formation. In order to search for new young stellar objects (YSOs), we have
observed this region in 7 mid- and far-infrared bands using the Spitzer Space
Telescope and in 4 bands in the optical using the U. S. Naval Observatory
40-inch telescope. We find infrared excesses in 4 of the 6 previously-known T
Tauri stars in our combined infrared maps, and we find 6 entirely new candidate
YSOs, one of which may be an edge-on disk. Most of the YSOs seen in the
infrared are Class II objects, and they are all in the "head" of the nebula,
within the most massive molecular cloud of the region.Comment: Accepted to Ap
Triggered Star Formation by Massive Stars
We present our diagnosis of the role that massive stars play in the formation
of low- and intermediate-mass stars in OB associations (the Lambda Ori region,
Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars
and Herbig Ae/Be stars tend to line up between luminous O stars and
bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively
younger they are. Our positional and chronological study lends support to the
validity of the radiation-driven implosion mechanism, where the Lyman continuum
photons from a luminous O star create expanding ionization fronts to evaporate
and compress nearby clouds into bright-rimmed or comet-shaped clouds. Implosive
pressure then causes dense clumps to collapse, prompting the formation of
low-mass stars on the cloud surface (i.e., the bright rim) and
intermediate-mass stars somewhat deeper in the cloud. These stars are a
signpost of current star formation; no young stars are seen leading the
ionization fronts further into the cloud. Young stars in bright-rimmed or
comet-shaped clouds are likely to have been formed by triggering, which would
result in an age spread of several megayears between the member stars or star
groups formed in the sequence.Comment: 2007, ApJ, 657, 88
Extending the limits of globule detection -- ISOPHOT Serendipity Survey Observations of interstellar clouds
A faint MJysr bipolar globule was discovered with the
ISOPHOT 170 m Serendipity Survey (ISOSS). ISOSS J 20246+6541 is a cold
( K) FIR source without an IRAS pointsource counterpart.
In the Digitized Sky Survey B band it is seen as a 3\arcmin size bipolar
nebulosity with an average excess surface brightness of
mag/\arcsec . The CO column density distribution determined by
multi-isotopic, multi-level CO measurements with the IRAM-30m telescope agrees
well with the optical appearance. An average hydrogen column density of
cm was derived from both the FIR and CO data. Using a
kinematic distance estimate of 400 pc the NLTE modelling of the CO, HCO,
and CS measurements gives a peak density of cm. The
multiwavelength data characterise ISOSS 20246+6541 as a representative of a
class of globules which has not been discovered so far due to their small
angular size and low 100m brightness. A significant overabundance of
CO is found . This is likely due to
isotope selective chemical processes.Comment: 5 pages, 3 figure
Quasiparticle transport and localization in high-T_c superconductors
We present a theory of the effects of impurity scattering in d_{x^2-y^2}
superconductors and their quantum disordered counterparts, based on a
non-linear sigma model formulation. We show the existence, in a
quasi-two-dimensional system, of a novel spin-metal phase with a non-zero spin
diffusion constant at zero temperature. With decreasing inter-layer coupling,
the system undergoes a quantum phase transition (in a new universality class)
to a localized spin-insulator. Experimental implications for spin and thermal
transport in the high-temperature superconductors are discussed.Comment: 4 pages, 1 figur
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