Philips

About: Philips is a company organization based out in Vantaa, Finland. It is known for research contribution in the topics: Signal & Layer (electronics). The organization has 68260 authors who have published 99663 publications receiving 1882329 citations. The organization is also known as: Koninklijke Philips Electronics N.V. & Royal Philips Electronics.

Functional cardiac MR imaging with steady-state free precession (SSFP) significantly improves endocardial border delineation without contrast agents.

Abstract: Contrast between blood and myocardium in standard turbo gradient echo MR techniques (TFE) used routinely in clinical practice is mainly caused by unsaturated inflowing blood. Steady-state free precession (SSFP) has excellent contrast even in the absence of inflow effects. In 45 subjects cardiac cine loops in two long axis projections were acquired using TFE and compared with SSFP. A visual score (range 0 worst – 3 best) was assigned for endocardial border delineation for six myocardial segments in two long axis views. Endocardial border delineation score for TFE was 1.3 ± 0.3 per segment and 2.4 ± 0.3 for SSFP (P < 0.0001). Signal intensity blood/signal intensity myocardium was 1.5 ± 0.4 at enddiastole and 1.4 ± 0.3 at systole for TFE and 3.5 ± 1.1 and 3.2 ± 1.3 for SSFP, respectively (P < 0.0001). SSFP increases contrast between blood and myocardium more than twofold, resulting in an improved endocardial border definition. This may reduce variability for the determination of cardiac volumes and ejection fraction. J. Magn. Reson. Imaging 2001;14:362–367. ©2001 Wiley-Liss, Inc.

Size Dependence of the Dissolution of ZnO Nanoparticles

Abstract: ZnO nanoparticles of about 30−60 A size in ethanolic solution were etched by addition of anhydrous acetic acid. Upon dissolution, the volume-weighted particle size decreased by about 10%. The polydispersity increased slightly. The dissolution rate was strongly dependent on particle size, and size selective etching of a mixture of ZnO particles was demonstrated. The change of the particle size during etching can be modeled adequately by a Monte Carlo simulation, in which the known degree of polydispersity and the size dependence of the etch rate are taken into account. On the basis of a comparison with work on the dissolution of silica nanoparticles and oxidic thin films, and on the etching of single-crystal ZnO, it is proposed that the size dependence is caused by variations of the chemical reactivity of the nanoparticles related to, for example, the concentration of defects and kink sites. Thus, dissolution provides a convenient method to investigate size-dependent chemical properties.

Quantum ballistic and adiabatic electron transport studied with quantum point contacts

Abstract: We present an experimental and theoretical study of quantum ballistic transport in single quantum point contacts (QPC's), defined in the two-dimensional electron gas (2DEG) of a high-mobility GaAs/${\mathrm{Al}}_{0.33}$${\mathrm{Ga}}_{0.67}$As heterojunction. In zero magnetic field the conductance of quantum point contacts shows the formation of quantized plateaus at multiples of 2${\mathit{e}}^{2}$/h. The experimental results are explained with a simple model. Deviations from ideal quantization are discussed. The experimental results are compared with model calculations. Energy averaging of the conductance has been studied, both as a function of temperature and voltage across the device. The application of a magnetic field leads to the magnetic depopulation of the one-dimensional subbands in the QPC. It is shown that the zero-field quantization and quantization in high magnetic fields are two limiting cases of a more general quantization phenomenon. We use quantum point contacts to study the high-magnetic-field transport in a 2DEG. Quantum point contacts are used to selectively populate and detect edge channels. The experiments show that scattering between adjacent edge channels can be very weak, under certain circumstances even on length scales longer than 200 \ensuremath{\mu}m. This adiabatic transport has resulted in the observation of an anomalous integer quantum Hall effect, in which the quantization of the Hall conductance is not determined by the number of Landau levels in the bulk 2DEG, but by the number of Landau levels in the QPC's instead. Related effects are the anomalous quantization of the longitudinal resistance and the adiabatic transport through QPC's in series. A theoretical description for transport in the presence of Shubnikov--de Haas (SdH) backscattering is given. This model explains the experimentally observed suppression of the SdH oscillations due to the selective population or detection of edge channels. Finally, we demonstrate that the combination of a QPC and a bulk Ohmic contact can act as a controllable edge-channel mixer.