130 research outputs found
Strong vs. Weak Coupling Duality and Coupling Dependence of the Kondo Temperature in the Two-Channel Kondo Model
We perform numerical renormalization group (NRG) as well as analytical
calculations for the two-channel Kondo model to obtain the dependence of the
Kondo temperature on the dimensionless (bare) spin exchange coupling
over the complete parameter range from to . We show that there
exists a duality between the regimes of small and large coupling. It is unique
for the two-channel model and enables a mapping between the strong and the weak
coupling cases via the identification , implying an
exponential dependence of on and , respectively, in the two
regimes. This agrees quantitatively with our NRG calculations where we extract
over the complete parameter range and obtain a non-monotonous
dependence, strongly peaked at the 2CK fixed point coupling . These
results may be relevant for resolving the long-standing puzzle within the 2CK
interpretation of certain random defect systems, why no broad distribution of
is observed in those systems.Comment: 6 pages, 3 figures; PRB published version, shortened, nomenclature
clarifie
Comment on "Fano Resonance for Anderson Impurity Systems"
In a recent Letter, Luo et al. (Phys. Rev. Lett. 92, 256602 (2004)) analyze
the Fano line shapes obtained from scanning tunneling spectroscopy (STS) of
transition metal impurities on a simple metal surface, in particular of the
Ti/Au(111) and Ti/Ag(100) systems. As the key point of their analysis, they
claim that there is not only a Fano interference effect between the impurity
d-orbital and the conduction electron continuum, as derived in Ujsaghy et al.
(Phys. Rev. Lett. 85, 2557 (2000)), but that the Kondo resonance in the
d-electron spectral density has by itself a second Fano line shape, leading to
the experimentally observed spectra. In the present note we point out that this
analysis is conceptually incorrect. Therefore, the quantitative agreement of
the fitted theoretical spectra with the experimental results is meaningless.Comment: 1 page, no figures. Accepted for publication in PRL; revised version
uploaded on November 18th, 200
Experimental results on strangeness production in proton-proton collisions at COSY
The production of K+ and K- mesons in elementary proton-proton collision has
been investigated at the Cooler Synchrotron COSY in Juelich. A high quality
proton beam with low emittance and small momentum spread permitted to study the
creation of these mesons very close to the kinematical threshold. The energy
dependence of the total cross section is investigated using internal beam
facilities providing a high accuracy particle momentum determination as well as
an external non-magnetic detection setup with a large geometrical acceptance.
The determination of the four-momentum vectors for all ejectiles of each
registered event gives the complete kinematical information allowing to study
the interaction of the outgoing particles. Results on the performed studies of
the pp --> pp K+ K-, pp --> p Lambda K+ and pp --> p Sigma0 K+ reactions will
be presented and their relevance to the interpretation of heavy ion collisions
will be discussed.Comment: 8 pages, 6 figures, plenary talk at 6th International Conference On
Strange Quarks in Matter: '2001 - A Flavorspace Odyssey' (SQM2001),
Frankfurt, Germany, September 25-29, 2001, to be published in J. Phys. G:
Nucl. Part. Phy
Drift chamber with a c-shaped frame
We present the construction of a planar drift chamber with wires stretched
between two arms of a c-shaped aluminium frame. The special shape of the frame
allows to extendthe momentum acceptance of the COSY-11 detection system towards
lower momenta without suppressing the high momentum particles. The proposed
design allows for construction of tracking detectors covering small angles with
respect to the beam, which can be installed and removed without dismounting the
beam-pipe. For a three-dimensional track reconstruction a computer code was
developed using a simple algorithm of hit preselection.Comment: submitted to Nucl. Instr. & Meth
Cadmium accumulation and interactions with zinc, copper, and manganese, analysed by ICP-MS in a long-term Caco-2 TC7 cell model
The influence of long-term exposure to cadmium (Cd) on essential minerals was investigated using a Caco-2
TC7 cells and a multi-analytical tool: microwave digestion and inductively coupled plasma mass spectrometry.
Intracellular levels, effects on cadmium accumulation, distribution, and reference concentration
ranges of the following elements were determined: Na, Mg, Ca, Cr, Fe, Mn, Co, Ni, Cu, Zn, Mo, and Cd.
Results showed that Caco-2 TC7 cells incubated long-term with cadmium concentrations ranging from 0 to
10 lmol Cd/l for 5 weeks exhibited a significant increase in cadmium accumulation. Furthermore, this
accumulation was more marked in cells exposed long-term to cadmium compared with controls, and that
this exposure resulted in a significant accumulation of copper and zinc but not of the other elements
measured. Interactions of Cd with three elements: zinc, copper, and manganese were particularly studied.
Exposed to 30 lmol/l of the element, manganese showed the highest inhibition and copper the lowest on
cadmium intracellular accumulation but Zn, Cu, and Mn behave differently in terms of their mutual
competition with Cd. Indeed, increasing cadmium in the culture medium resulted in a gradual and significant
increase in the accumulation of zinc. There was a significant decrease in manganese from 5 lmol
Cd/l exposure, and no variation was observed with copper.
Abbreviation: AAS – Atomic absorption spectrometry; CRM– Certified reference material; PBS – Phosphate
buffered saline without calcium and magnesium; DMEM – Dubelcco’s modified Eagle’s medium
On the close to threshold meson production in neutron-neutron collisions
A method of measuring the close to threshold meson production in
neutron-neutron collisions is described where the momenta of the colliding
neutrons can be determined with the accuracy obtainable for the proton-proton
reaction. The technique is based on the double quasi-free nn --> nn X^0
reaction, where deuterons are used as a source of neutronsComment: 6 pages, 2 figures, to be published in Phys. Lett.
Derivation of Chondrogenically-Committed Cells from Human Embryonic Cells for Cartilage Tissue Regeneration
Background: Heterogeneous and uncontrolled differentiation of human embryonic stem cells (hESCs) in embryoid bodies (EBs) limits the potential use of hESCs for cell-based therapies. More efficient strategies are needed for the commitment and differentiation of hESCs to produce a homogeneous population of specific cell types for tissue regeneration applications. Methodology/Principal Findings: We report here that significant chondrocytic commitment of feeder-free cultured human embryonic stem cells (FF-hESCs), as determined by gene expression and immunostaining analysis, was induced by coculture with primary chondrocytes. Furthermore, a dynamic expression profile of chondrocyte-specific genes was observed during monolayer expansion of the chondrogenically-committed cells. Chondrogenically-committed cells synergistically responded to transforming growth factor-b1 (TGF-b1) and b1-integrin activating antibody by increasing tissue mass in pellet culture. In addition, when encapsulated in hydrogels, these cells formed cartilage tissue both in vitro and in vivo. In contrast, the absence of chondrocyte co-culture did not result in an expandable cell population from FF-hESCs. Conclusions/Significance: The direct chondrocytic commitment of FF-hESCs can be induced by morphogenetic factor
Zfp521 controls bone mass by HDAC3-dependent attenuation of Runx2 activity
Zfp521 regulates osteoblast development during lineage commitment and osteoblast maturation by suppressing Runx2 transcriptional activity
Analysing power A_y in the reaction p(pol) p --> p p eta close to threshold
Measurements of the eta meson production with a polarised proton beam in the
reaction p(pol) p --> p p eta have been carried out at an excess energy of Q =
40 MeV. The dependence of the analysing power A_y on the polar angle theta^*_q
of the eta meson in the center of mass system (CMS) has been studied. The data
indicate the possibility of an influence of p- and d-waves to the close to
threshold eta production.Comment: 6 pages, 5 figures, in section 3.1 the formula of vec(p) containing
fatal typos was removed, and the values in table were correcte
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