W line shape in the resistively detected nuclear magnetic resonance.

The resistively detected nuclear magnetic resonance (RDNMR) performed on a two-dimensional electron gas is known to exhibit a peculiar 'dispersive' line shape at some filling factors, especially around ν = 1. Here, we study in detail the inversion of the dispersive line shape as a function of the filling factor from ν = 1 to 2/3. The RDNMR spectra show a new characteristic W line shape in the longitudinal resistance, whereas dispersive lines detected in the Hall resistance remain unchanged. This W resonance, like the dispersive line, can be fitted correctly by a model of two independent response functions, which are the signatures of polarized and unpolarized electronic sub-systems.

Measuring placental transfusion for term births: weighing babies with cord intact.

OBJECTIVE: To estimate the volume and duration of placental transfusion at term. DESIGN: Prospective observational study. SETTING: Maternity unit in Bradford, UK. POPULATION: Twenty-six term births. METHODS: Babies were weighed with umbilical cord intact using digital scales that record an average weight every 2 seconds. Placental transfusion was calculated from the change in weight between birth and either cord clamping or when weighing stopped. Start and end weights were estimated using both a B-spline and inspection of graphs. Weight was converted to volume, 1 ml of blood weighing 1.05 g. MAIN OUTCOME MEASURES: Volume and duration of placental transfusion. RESULTS: Twenty-six babies were weighed. Start weights were difficult to determine because of artefacts in the data as the baby was placed on the scales and wrapped. The mean difference in weight was 116 g [95% confidence interval (CI), 72-160 g] using the B-spline and 87 g (95% CI, 64-110 g) using inspection. Converting this to the mean volume of placental transfusion gave 110 ml (95% CI, 69-152 ml) and 83 ml (95% CI, 61-106 ml), respectively. Placental transfusion was usually complete by 2 minutes, but sometimes continued for up to 5 minutes. Based on the B-spline, placental transfusion contributed 32 ml (95% CI, 30-33 ml) per kilogram of birth weight to blood volume, but 24 ml (95% CI, 19-32 ml) based on inspection. This equates to 40% (95% CI, 37-42%) and 30% (24-40%), respectively, of total potential blood volume. CONCLUSION: Inspection of the graphs probably underestimates placental transfusion. For term infants, placental transfusion contributes between one-third and one-quarter of total potential blood volume at birth.

Fock-Darwin-like quantum dot states formed by charged Mn interstitial ions.

We report a method of creating electrostatically induced quantum dots by thermal diffusion of interstitial Mn ions out of a p-type (GaMn)As layer into the vicinity of a GaAs quantum well. This approach creates deep, approximately circular, and strongly confined dotlike potential minima in a large (200 microm) mesa diode structure without need for advanced lithography or electrostatic gating. Magnetotunneling spectroscopy of an individual dot reveals the symmetry of its electronic eigenfunctions and a rich energy level spectrum of Fock-Darwin-like states with an orbital angular momentum component |lz| from 0 to 11.

Magnetic-field-induced suppression of electronic conduction in a superlattice.

We use a magnetic field applied along the axis of a semiconductor superlattice (SL) as a controllable means of creating a one-dimensional band structure. We demonstrate that the current flow through the SL is strongly suppressed when the electron motion perpendicular to the SL axis is strongly confined by the quantizing magnetic field. By modeling this behavior using semiclassical and nonequilibrium Green's function methods, we show that the observed quenching arises from a qualitative change in electron dynamics caused by increasing quantum confinement.

High temperature gate control of quantum well spin memory.

Time-resolved optical measurements in (110)-oriented GaAs/AlGaAs quantum wells show a tenfold increase of the spin-relaxation rate as a function of applied electric field from 20 to 80 kV cm(-1) at 170 K and indicate a similar variation at 300 K, in agreement with calculations based on the Rashba effect. Spin relaxation is almost field independent below 20 kV cm(-1) reflecting quantum well interface asymmetry. The results indicate the achievability of a voltage-gateable spin-memory time longer than 3 ns simultaneously with a high electron mobility.

Magnetotunneling spectroscopy of dilute Ga(AsN) quantum wells.

We use magnetotunneling spectroscopy to explore the admixing of the extended GaAs conduction band states with the localized N-impurity states in dilute GaAs(1-y)N(y) quantum wells. In our resonant tunneling diodes, electrons can tunnel into the N-induced E- and E+ subbands in a GaAs(1-y)N(y) quantum well layer, leading to resonant peaks in the current-voltage characteristics. By varying the magnetic field applied perpendicular to the current direction, we can tune an electron to tunnel into a given k state of the well; since the applied voltage tunes the energy, we can map out the form of the energy-momentum dispersion curves of E- and E+. The data reveal that for a small N content (approximately 0.1%) the E- and E+ subbands are highly nonparabolic and that the heavy effective mass E+ states have a significant Gamma-conduction band character even at k=0.

Detrusor contraction strength in men undergoing prostatectomy.

Elective prostatectomy is a frequently performed operation but the outcome may not always be satisfactory. This is probably because a significant number of men, despite subjective symptoms, are not urodynamically obstructed before operation and the preoperative assessment of obstruction is not easy using conventional urodynamic criteria. We have calculated detrusor contraction strength (WF) in men before and after prostatectomy. Our aim was to determine its relationship with symptomatic and urodynamic findings before and after prostatectomy and whether it was associated with clinical outcome. One hundred and twenty nine men listed for operation because of symptoms and low urinary flow rates were studied by means of urodynamic investigation and symptom scoring both before and 6 months after prostatectomy. A significant association was found between persistent obstructive symptoms after operation and a low WF before operation (P = 0.01), suggesting that weak detrusor function before operation was the cause of persistent symptoms afterwards. A significant correlation was also found between a high pre-operative WF and a high post-operative urinary flow rate; (P = 0.003); men with high detrusor power achieving the better flow rates after operation. Despite this relationship, the overall subjective clinical outcome was not strongly associated with WF and WF was no better than simple measurement of voiding pressure in predicting outcome in a multivariate analysis. The measurement of detrusor contraction strength provides some insight into the relationship between bladder function and clinical outcome after prostatectomy, but we have found it unable to predict outcome for the individual patient.