Resolution of the A- and B-site hyperfine fields of the spinel system Mg1+t Fe2(1−t ) Ti t O4 in the spin-glass-like state

Spectra for three members of the spinel system Mg_1+t Fe_2(1−t)Ti _t O₄, witht=0.5, 0.6 and 0.7, all showing re-entrant spin-glass-like behavior, were collected at temperatures down to 1.6 K and decomposed in A- and B-site components, both having a broad distribution of hyperfine fields. The numerical results suggest a more pronounced spin canting on A sites as compared to B sites. From spectra recorded at 4.2 K in an applied field of 6 T, and analysed with a sum of two bi-dimensional distributions of hyperfine fields and canting angles, the existence of reversed A-site spins is evidenced. The number of such spins increases with increasing magnetic dilution. Senior Research Associate at the National Fund for Scientific Research, Belgium     

Measurement and analysis of optical gain spectra in 1.6 to 1.8 μm InAs/InP (100) quantum-dot amplifiers

Small signal modal gain measurements have been performed on two-section ridge waveguide InAs/InP (100) quantum-dot amplifiers that we have fabricated with a peak gain wavelength around 1.70 μm. The amplifier structure is suitable for monolithic active-passive integration, and the wavelength region and wide gain bandwidth are of interest for integrated devices in biophotonic applications. A 65 nm blue shift of the peak wavelength in the gain spectrum has been observed with an increase in injection current density from 1,000 to 3,000 A/cm². The quantum-dot amplifier gain spectra have been analyzed using a quantum-dot rate-equation model that considers only the carrier dynamics. The comparison between measured and simulated spectra shows that two effects in the quantum-dot material introduce this large blue shift in the gain spectrum. The first effect is the carrier concentration dependent state filling with carriers of the bound excited and ground states in the dots. The second effect is the decrease in carrier escape time from the dots to the wetting layer with decreasing dot size.     

Gamow-Teller strength in the exotic odd-odd nuclei 138La and 180Ta and its relevance for neutrino nucleosynthesis

The Gamow-Teller strength distributions below the particle threshold in 138La and 180Ta, deduced from high-resolution measurements of the (3He,t) reaction at 0 degrees, allow us to evaluate the role of charged-current reactions for the production of these extremely rare nuclides in neutrino-nucleosynthesis models. The analysis suggests that essentially all 138La in the Universe can be made that way. Neutrino nucleosynthesis also contributes significantly to the abundance of 180Ta but the magnitude depends on the unknown branching ratio for population of the long-lived isomer.     

Fine structure of the isoscalar giant quadrupole resonance in Ca due to Landau damping?

The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in ⁴⁰Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at Ep=200 MeV$E_{\mathrm{p}}=200\text{MeV}$. Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon–nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for ⁴⁰Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle–two-hole (2p–2h) states.     

Modeling of integrated extended cavity InP/InGaAsP semiconductor modelocked ring lasers

In this paper a model and simulation results of integrated semiconductor passively modelocked ring lasers are presented. The model includes nonlinear effects such as two-photon absorption and a non-linear refractive index, a logarithmic gain-carrier relation, and concentration dependent radiative and non-radiative carrier recombination rates. The optical bandwidth of the system is controlled by a digital filter. The model has been used to simulate two geometries of ring modelocked lasers. The first is a symmetric design, where the two counter propagating pulses in the cavity experience the same amplification and absorption. The second is an asymmetric design where the differences for the two directions of pulse propagation are maximised. Simulation results show that a symmetrical cavity shows a several times wider window for its operating parameters for stable modelocking.     

The use of poly(L-lactide-co-caprolactone) as a scaffold for adipose stem cells in bone tissue engineering: application in a spinal fusion model

Since the early 1990s, tissue engineering has been heralded as a strategy that may solve problems associated with bone grafting procedures. The original concept of growing bone in the laboratory, however, has proven illusive due to biological, logistic, and regulatory problems. Fat-derived stem cells and synthetic polymers open new, more practicable routes for bone tissue engineering. In this paper, we highlight the potential of poly(L-lactide-co-caprolactone) (PLCL) to serve as a radiolucent scaffold in bone tissue engineering. It appears that PLCL quickly and preferentially binds adipose stem cells (ASCs), which proliferate rapidly and eventually differentiate into the osteogenic phenotype. An in vivo spinal fusion study in a goat model provides a preclinical proof-of-concept for a one-step surgical procedure with ASCs in bone tissue engineering.