29 research outputs found
Transverse Magnetoresistance of GaAs/AlGaAs Heterojunctions in the Presence of Parallel Magnetic Fields
We have calculated the resistivity of a GaAs\slash AlGaAs heterojunction in
the presence of both an in--plane magnetic field and a weak perpendicular
component using a semiclassical Boltzmann transport theory. These calculations
take into account fully the distortion of the Fermi contour which is induced by
the parallel magnetic field. The scattering of electrons is assumed to be due
to remote ionized impurities. A positive magnetoresistance is found as a
function of the perpendicular component, in good qualitative agreement with
experimental observations. The main source of this effect is the strong
variation of the electronic scattering rate around the Fermi contour which is
associated with the variation in the mean distance of the electronic states
from the remote impurities. The magnitude of the positive magnetoresistance is
strongly correlated with the residual acceptor impurity density in the GaAs
layer. The carrier lifetime anisotropy also leads to an observable anisotropy
in the resistivity with respect to the angle between the current and the
direction of the in--plane magnetic field.Comment: uuencoded file containing a 26 page RevTex file and 14 postscript
figures. Submitted to Phys. Rev.
Anomalous Hall effect in paramagnetic two dimensional systems
We investigate the possibility of observing the anomalous Hall effect (AHE)
in two dimensional paramagnetic systems. We apply the semiclassical equations
of motion to carriers in the conduction and valence bands of wurtzite and
zincblende quantum wells in the exchange field generated by magnetic impurities
and we calculate the anomalous Hall conductivity based on the Berry phase
corrections to the carrier velocity. We show that under certain circumstances
this conductivity approaches one half of the conductance quantum. We consider
the effect of an external magnetic field and show that for a small enough field
the theory is unaltered.Comment: 9 pages, 10 figures, 2 table
Influence of the postoperative inflammatory response on cognitive decline in elderly patients undergoing on-pump cardiac surgery: a controlled, prospective observational study
BACKGROUND: The role of non-infective inflammatory response (IR) in the aetiology of postoperative cognitive dysfunction (POCD) is still controversial. The aim of this controlled, prospective observational study was to assess the possible relationship between the grade of IR, defined by procalcitonin (PCT) changes, and development of POCD related to cardiac surgery. METHODS: Forty-two patients, who were >/= 60 years of age and scheduled for elective cardiac surgery, were separated into the low inflammatory (LIR) and high inflammatory (HIR) response groups based on their PCT levels measured on the first postoperative day. A matched normative control group of 32 subjects was recruited from primary care practice. The PCT and C-reactive protein (CRP) levels were monitored daily during the first five postoperative days. The cognitive function and mood state were preoperatively tested with a set of five neurocognitive tests and two mood inventories and at the seventh postoperative day. The Reliable Change Index modified for practice (RCIp) using data from normative controls was applied to determine the significant decline in test performance. RESULTS: The LIR (n = 20) and HIR (n = 22) groups differed significantly in the PCT (p 0.05). Additionally, there was no difference in the mood states, anxiety levels and perioperative parameters known to influence the development of POCD. CONCLUSIONS: In this study, the magnitude of the non-infective inflammatory response generated by on-pump cardiac surgery did not influence the development of POCD in the early postoperative period in elderly patients