Experimental study of weak antilocalization effect in a high mobility InGaAs/InP quantum well

The magnetoresistance associated with quantum interference corrections in a high mobility, gated InGaAs/InP quantum well structure is studied as a function of temperature, gate voltage, and angle of the tilted magnetic field. Particular attention is paid to the experimental extraction of phase-breaking and spin-orbit scattering times when weak anti- localization effects are prominent. Compared with metals and low mobility semiconductors the characteristic magnetic field $B_{tr} = \hbar/4eD \tau$ in high mobility samples is very small and the experimental dependencies of the interference effects extend to fields several hundreds of times larger. Fitting experimental results under these conditions therefore requires theories valid for arbitrary magnetic field. It was found, however, that such a theory was unable to fit the experimental data without introducing an extra, empirical, scale factor of about 2. Measurements in tilted magnetic fields and as a function of temperature established that both the weak localization and the weak anti-localization effects have the same, orbital origin. Fits to the data confirmed that the width of the low field feature, whether a weak localization or a weak anti-localization peak, is determined by the phase-breaking time and also established that the universal (negative) magnetoresistance observed in the high field limit is associated with a temperature independent spin-orbit scattering time.Comment: 13 pages including 10 figure

Comparison of steer feedlot performance and carcass trait uniformly by method of sorting

Long yearling steers (n=997) of various biological types from two origins were used to test performance and carcass trait uniformity of unsorted cattle, visually sorted cattle, and cattle sorted by ultrasound and hip height. No significant differences (P> .05) in initial backfat uniformity were identified between sorted and unsorted groups; however, very little variation existed across all treatments (.17±.033 in.). Initial backfat had positive linear relationships with initial weight and carcass backfat and negative linear relationships with days on feed and daily gain (P<.05). These data indicate a reliable measurement of initial backfat could be useful for predicting days on feed and/or carcass backfat in long yearling steers, but economic usefulness will depend upon the variability of the cattle and the method of grouping

Factors influencing first-service conception and overall pregnancy rates in commercial beef heifers

Commercial beef heifers (n=1863) from 16 different sources were used to evaluate the influence of management practices and biological traits on first-service conception and overall pregnancy rates. Frame score, initial weight, overall ADG, body condition score, reproductive tract score, source, AI technician, and AI sire significantly influenced first-service conception. Overall pregnancy rates were influenced by frame score, body weight, and ADG

Si1-xGex critical thickness for surface wave generation during UHV-CVD growth at 525\ub0C

Several Si1-xGex/Si heterostructures were grown at 525\ub0C using a commercially available UHV-CVD reactor. Layers with a germanium fraction ranging from 0.15 to 0.5 were examined by means of cross-sectional transmission electron microscopy and atomic force microscopy. Surface waves were found in layers with a thickness above a critical value which decreases rapidly as the Ge fraction is increased. Both experimental and modeling results show that surface waves are generated before misfit dislocations for Ge fractions above 0.3.Peer reviewed: YesNRC publication: Ye