16 research outputs found
Effects of arbitrarily directed field on spin phase oscillations in biaxial molecular magnets
Quantum phase interference and spin-parity effects are studied in biaxial
molecular magnets in a magnetic field at an arbitrarily directed angle. The
calculations of the ground-state tunnel splitting are performed on the basis of
the instanton technique in the spin-coherent-state path-integral
representation, and complemented by exactly numerical diagonalization. Both the
Wentzel-Kramers-Brillouin exponent and the preexponential factor are obtained
for the entire region of the direction of the field. Our results show that the
tunnel splitting oscillates with the field for the small field angle, while for
the large field angle the oscillation is completely suppressed. This distinct
angular dependence, together with the dependence of the tunnel splitting on the
field strengh, provide an independent test for spin-parity effects in biaxial
molecular magnets. The analytical results for the molecular Fe magnet,
are found to be in good areement with the numerical simulations, which suggests
that even the molecular magnet with total spin S=10 is large enough to be
treated as a giant spin system.Comment: 19 pages, 5 figure
Macroscopic quantum coherence in antiferromagnetic molecular magnets
The macroscopic quantum coherence in a biaxial antiferromagnetic molecular
magnet in the presence of magnetic field acting parallel to its hard anisotropy
axis is studied within the two-sublattice model. On the basis of instanton
technique in the spin-coherent-state path-integral representation, both the
rigorous Wentzel-Kramers-Brillouin exponent and preexponential factor for the
ground-state tunnel splitting are obtained. We find that the quantum
fluctuations around the classical paths can not only induce a new quantum phase
previously reported by Chiolero and Loss (Phys. Rev. Lett. 80, 169 (1998)), but
also have great influnence on the intensity of the ground-state tunnel
splitting. Those features clearly have no analogue in the ferromagnetic
molecular magnets. We suggest that they may be the universal behaviors in all
antiferromagnetic molecular magnets. The analytical results are complemented by
exact diagonalization calculation.Comment: 6 pages, 1 figur
Low energy exciton states in a nanoscopic semiconducting ring
We consider an effective mass model for an electron-hole pair in a simplified
confinement potential, which is applicable to both a nanoscopic self-assembled
semiconducting InAs ring and a quantum dot. The linear optical susceptibility,
proportional to the absorption intensity of near-infrared transmission, is
calculated as a function of the ring radius . Compared with the
properties of the quantum dot corresponding to the model with a very small
radius , our results are in qualitative agreement with the recent
experimental measurements by Pettersson {\it et al}.Comment: 4 pages, 4 figures, revised and accepted by Phys. Rev.
Energy levels and far-infrared spectroscopy for two electrons in a semiconductor nanoring
The effects of electron-electron interaction of a two-electron nanoring on
the energy levels and far-infrared (FIR) spectroscopy have been investigated
based on a model calculation which is performed within the exactly numerical
diagonalization. It is found that the interaction changes the energy spectra
dramatically, and also shows significant influence on the FIR spectroscopy. The
crossings between the lowest spin-singlet and triplet states induced by the
coulomb interaction are clearly revealed. Our results are related to the
experiment recently carried out by A. Lorke et al. [Phys. Rev. Lett. 84, 2223
(2000)].Comment: 17 pages, 6 figures, revised and accepted by Phys. Rev. B (Dec. 15
A phase II trial of gemcitabine plus carboplatin in advanced transitional cell carcinoma of the urothelium
<p>Abstract</p> <p>Background</p> <p>Recent studies have demonstrated the effectiveness of cisplatin-based combinations in patients with advanced transitional cell carcinoma(TCC) of the urothelium. Concern over cisplatin toxicity instigated a search for alternative regimens. The aim of the study was to evaluate the activity and tolerability of gemcitabine plus carboplatin combination as first-line treatment in patients with advanced transitional cell carcinoma of the urothelium.</p> <p>Methods</p> <p>Patients with advanced TCC were treated with gemcitabine 1200 mg/m<sup>2 </sup>on days 1 and 8 and carboplatin area under the concentration-time curve(AUC) 5 on day 1 every 21 days.</p> <p>Results</p> <p>Out of 41 patients, thirty-nine were evaluable for efficacy and 41 for toxicity. A median of 5 cycles (range 1–6) was administered. Overall response rate was 46.2% (95% confidence interval: 32–65%) including 10.3% complete responses and 35.9% partial responses. The median time to progression and median overall survival were 7.5 months (95% confidence interval: 6.6–8.4 months) and 13.6 months (95% confidence interval: 10.2–17.0 months), respectively. Grade 3/4 neutropenia, anemia and thrombocytopenia were observed in 36.6%, 26.8, and 24.4% of patients, respectively. Non-hematological toxicity was generally mild. Grade 3 vomiting occurred in 1 (2.4%) patients.</p> <p>Conclusion</p> <p>The gemcitabine plus carboplatin combination is active in advanced TCC with acceptable toxicity and needs to be evaluated further and compared with other non-cisplatin-containing regimens.</p> <p>Trial registration</p> <p>ISRCTN88259320</p
Aharonov-Bohm effect of excitons in nano-rings
The magnetic field effects on excitons in an InAs nano-ring are studied theoretically. By numerically diagonalizing the effective-mass Hamiltonian of the problem, which can be separated into terms in centre-of-mass and relative coordinates, we calculate the low-lying exciton energy levels and oscillator strengths as a function of the width of the ring and the strength of the external magnetic field. The analytical results are obtained for a narrow-width nanoring in which the radial motion is the fastest one and adiabatically decoupled from the azimuthal motions. It is shown that in the presence of Coulomb correlation, the so called Aharonov-Bohm effect of excitons exists in a finite (but small) width nano-ring. However, when the ring width becomes large, the non-simply-connected geometry of nano-rings is destroyed and in turn yields the suppression of Aharonov-Bohm effect. The conditional probability distribution calculated for the low-lying exction states allows identification of the presence of Aharonov-Bohm effect. The linear optical susceptibility is also calculated as a function of the magnetic field, to be confronted with the future measurements of optical emission experiments on InAs nano-rings. PACS numberes: 73.20.Dx, 71.35.-y, 03.65.Bz, 78.66.Fd I