3,731 research outputs found
The linewidth of a non-Markovian atom laser
We present a fully quantum mechanical treatment of a single mode atom laser
including pumping and output coupling. By ignoring atom-atom interactions, we
have solved this model without making the Born-Markov approximation. We find
substantially less gain narrowing than is predicted under that approximation.Comment: 4 pages, 1 encapsulated postscript figur
Detuning effects in the one-photon mazer
The quantum theory of the mazer in the non-resonant case (a detuning between
the cavity mode and the atomic transition frequencies is present) is written.
The generalization from the resonant case is far from being direct. Interesting
effects of the mazer physics are pointed out. In particular, it is shown that
the cavity may slow down or speed up the atoms according to the sign of the
detuning and that the induced emission process may be completely blocked by use
of a positive detuning. It is also shown that the detuning adds a potential
step effect not present at resonance and that the use of positive detunings
defines a well-controlled cooling mechanism. In the special case of a mesa
cavity mode function, generalized expressions for the reflection and
transmission coefficients have been obtained. The general properties of the
induced emission probability are finally discussed in the hot, intermediate and
cold atom regimes. Comparison with the resonant case is given.Comment: 9 pages, 8 figure
Laser-induced collective excitations in a two-component Fermi gas
We consider the linear density response of a two-component (superfluid) Fermi
gas of atoms when the perturbation is caused by laser light. We show that
various types of laser excitation schemes can be transformed into linear
density perturbations, however, a Bragg spectroscopy scheme is needed for
transferring energy and momentum into a collective mode. This makes other types
of laser probing schemes insensitive for collective excitations and therefore
well suited for the detection of the superfluid order parameter. We show that
for the special case when laser light is coupled between the two components of
the Fermi gas, density response is always absent in a homogeneous system.Comment: 6 pages, no figure
Non-diagonal solutions of the reflection equation for the trigonometric vertex model
We obtain a class of non-diagonal solutions of the reflection equation for
the trigonometric vertex model. The solutions can be expressed
in terms of intertwinner matrix and its inverse, which intertwine two
trigonometric R-matrices. In addition to a {\it discrete} (positive integer)
parameter , , the solution contains {\it continuous}
boundary parameters.Comment: Latex file, 14 pages; V2, minor typos corrected and a reference adde
Twisted algebra R-matrices and S-matrices for affine Toda solitons and their bound states
We construct new and invariant
-matrices and comment on the general construction of -matrices for
twisted algebras. We use the former to construct -matrices for
affine Toda solitons and their bound states, identifying the lowest breathers
with the particles.Comment: Latex, 24 pages. Various misprints corrected. New section added
clarifying relationship between R-matrices and S-matrice
Comparison of gene expression profile between human chondrons and chondrocytes: a cDNA microarray study
SummaryObjectiveThe chondron is a basic unit of articular cartilage that includes the chondrocyte and its pericellular matrix (PCM). This current study was designed to investigate the effects of the chondron PCM on the gene expression profile of chondrocytes.DesignChondrons and chondrocytes were enzymatically isolated from human articular cartilage, and maintained in pellet culture. Pellets of chondrons or chondrocytes were collected at days 1, 3 and 5 for cDNA microarray analysis.ResultsIn comparison with chondrocytes alone, chondrons had 258 genes, in a broad range of functional categories, either up- or downregulated at the three time points tested. At day 1, 26 genes were significantly upregulated in chondrons and four downregulated in comparison to chondrocytes. At day 3, the number of upregulated chondron genes was 97 and the number downregulated was 43. By day 5, there were more downregulated genes (56) than upregulated genes (32) in chondrons. Upregulation of a group of heat shock proteins (HSPA1A, HSPA2 and HSPA8) in chondrons was validated by real time reverse transcription polymerase chain reaction (RT-PCR). Genes related to chondrocyte hypertrophy and dedifferentiation such as SSP1 and DCN were downregulated in chondrons as compared to the expression in chondrocytes.ConclusionThe presence of the PCM in chondrons has a profound influence on chondrocyte gene expression. Upregulation of the heat shock protein 70 may contribute to the robustness and active matrix production of chondrons. The intact PCM may further stabilize the phenotype of chondrocytes within chondrons
Comparison of gene expression profile between human chondrons and chondrocytes: a cDNA microarray study
OBJECTIVE: The chondron is a basic unit of articular cartilage that includes the chondrocyte and its pericellular matrix (PCM). This current study was designed to investigate the effects of the chondron PCM on the gene expression profile of chondrocytes. DESIGN: Chondrons and chondrocytes were enzymatically isolated from human articular cartilage, and maintained in pellet culture. Pellets of chondrons or chondrocytes were collected at days 1, 3 and 5 for cDNA microarray analysis. RESULTS: In comparison with chondrocytes alone, chondrons had 258 genes, in a broad range of functional categories, either up- or downregulated at the three time points tested. At day 1, 26 genes were significantly upregulated in chondrons and four downregulated in comparison to chondrocytes. At day 3, the number of upregulated chondron genes was 97 and the number downregulated was 43. By day 5, there were more downregulated genes (56) than upregulated genes (32) in chondrons. Upregulation of a group of heat shock proteins (HSPA1A, HSPA2 and HSPA8) in chondrons was validated by real time reverse transcription polymerase chain reaction (RT-PCR). Genes related to chondrocyte hypertrophy and dedifferentiation such as SSP1 and DCN were downregulated in chondrons as compared to the expression in chondrocytes. CONCLUSION: The presence of the PCM in chondrons has a profound influence on chondrocyte gene expression. Upregulation of the heat shock protein 70 may contribute to the robustness and active matrix production of chondrons. The intact PCM may further stabilize the phenotype of chondrocytes within chondrons
Chemicals from lignin by diol-stabilized acidolysis:Reaction pathways and kinetics
The product selectivity, production rates and the required process conditions are important for technology development. Selective lignin depolymerisation on the prime β-O-4 motif provides an opportunity to obtain valuable functionalized phenolic monomers. Diol-stabilized acidolysis of lignin with sulfuric acid, triflic acid or triflate salts is a proven β-O-4 cleavage methodology that forms acetals by trapping of released reactive aldehydes. For future scale-up, a better understanding of the prime reaction pathways and how these can be controlled upon changing reaction parameters is required. By using β-O-4 model compounds and ytterbium(iii) triflate as catalyst, starting material conversion and product formation including two key intermediates, the diol adducts (in this study, ethylene glycol as the diol) and the vinyl ethers, were accurately monitored, allowing for detailed kinetic modelling. Over the selected temperature range (80-150 °C), higher temperatures led to higher overall carbon balance and selectivity for the main desired acetal product. The kinetic modelling allowed for establishing a detailed reaction network with activation energies and rate constants. These collectively led to new insights into the key steps involved in the diol-stabilized β-O-4 motif acidolysis and how the reaction selectivity can be manipulated by controlling the reaction temperature, and the ethylene glycol and water content. The elucidation on reaction kinetics and networks constitutes a further step in the design of a diol-stabilized lignin acidolysis process
The steady state quantum statistics of a non-Markovian atom laser
We present a fully quantum mechanical treatment of a single-mode atomic
cavity with a pumping mechanism and an output coupling to a continuum of
external modes. This system is a schematic description of an atom laser. In the
dilute limit where atom-atom interactions are negligible, we have been able to
solve this model without making the Born and Markov approximations. When
coupling into free space, it is shown that for reasonable parameters there is a
bound state which does not disperse, which means that there is no steady state.
This bound state does not exist when gravity is included, and in that case the
system reaches a steady state. We develop equations of motion for the two-time
correlation in the presence of pumping and gravity in the output modes. We then
calculate the steady-state output energy flux from the laser.Comment: 14 pages (twocloumn), 6 figure
Ground State and Spectral Properties of a Quantum Impurity in d-Wave Superconductors
The variational approach of Gunnarsson and Sch\"onhammer to the Anderson
impurity model is generalized to study d-wave superconductors in the presence
of dilute spin-1/2 impurities. We show that the local moment is screened when
the hybridization exceeds a nonzero critical value at which the ground state
changes from a spin doublet to a spin singlet. The electron spectral functions
are calculated in both phases. We find that while a Kondo resonance develops
above the Fermi level in the singlet phase, the spectral function exhibits a
low-energy spectral peak below the Fermi level in the spin doublet phase. The
origin of such a ``virtual Kondo resonance'' is the existence of low-lying
collective excitations in the spin-singlet sector. We discuss our results in
connection to recent spectroscopic experiments on Zn doped high-T
superconductors.Comment: 5 pages, 4figures, revised versio
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