All-electric quantum point contact spin-polarizer.

The controlled creation, manipulation and detection of spin-polarized currents by purely electrical means remains a central challenge of spintronics. Efforts to meet this challenge by exploiting the coupling of the electron orbital motion to its spin, in particular Rashba spin-orbit coupling, have so far been unsuccessful. Recently, it has been shown theoretically that the confining potential of a small current-carrying wire with high intrinsic spin-orbit coupling leads to the accumulation of opposite spins at opposite edges of the wire, though not to a spin-polarized current. Here, we present experimental evidence that a quantum point contact -- a short wire -- made from a semiconductor with high intrinsic spin-orbit coupling can generate a completely spin-polarized current when its lateral confinement is made highly asymmetric. By avoiding the use of ferromagnetic contacts or external magnetic fields, such quantum point contacts may make feasible the development of a variety of semiconductor spintronic devices.

Effects of electromagnetic fields and gender on neurotransmitters and amino acids in rats.

Epidemiological studies have linked electromagnetic field (EMF) exposure to certain forms of cancer, however only limited laboratory evidence supports a connection between EMF and biological effects. In the present study we exposed male and female rats to low level, 1000 milli-Gauss (mGs), direct current EMF generated with Helmholtz coils for 1 mo or 4 mo. The effects of these EMF exposures on regional brain neurotransmitter metabolism and circulating amino acid concentrations were determined. After 1 mo of EMF exposure the concentration of serotonin was elevated in the hypothalamus of male rats. Levels of the dopamine metabolite, 3-methoxytyramine, were increased in the corpus striatum of male and female rats that were exposed to EMF for 1 mo. Hypothalamic concentration of norepinephrine was elevated in both groups of male rats, as compared to respective female groups, but was not affected by EMF. Similarly, levels of tyrosine were increased in hypothalamus, corpus striatum and nucleus accumbens of male rats, but were not affected by EMF exposure. Following 4 mo of EMF exposure, no significant effect of EMF was observed. Significant sex differences in plasma amino acid concentrations were observed in both studies, with female rats exhibiting decreases in a majority of the amino acids measured. These results are suggestive that short-term exposure may cause small alterations in neurotransmitter metabolism and in circulating amino acids, which dissipate when exposure duration is increased.

Carbon dioxide lasers for otosclerosis.

Over the past eight years, the senior author (SGL) has sought the ideal microsurgical laser for otosclerosis surgery. This quest required learning the principles of laser physics and of the interactions of light with matter. Rather simple thermocouple experiments were performed in the laboratories of the Midwest Ear Foundation (MEF) to confirm some of what was predicted from these principles. More sophisticated transmission spectroscopy experiments were performed at the Massachusetts Institute of Technology (MIT) to evaluate which electromagnetic wavelengths are best absorbed by collagen and bone. MIT's spectroscopy studies paralleled MEF's thermocouple data. CO2 laser energy (10.6 microns) is nearly completely absorbed by collagen and bone, whereas visible argon and KTP laser energy (0.5 micron) is poorly absorbed. Despite the better optical precision of visible lasers, the author chose the CO2 laser for stapedectomy revision and stapedotomy, because long infrared electromagnetic energy has vastly superior tissue absorption characteristics for these procedures. With the development of I. L. Med's Unilase, the otologic surgeon now has a CO2 laser with optical precision and convenience approaching that of visible lasers. Clinical studies of 102 consecutive CO2 laser stapedectomy revisions show that in 92% of patients, hearing was significantly improved with the new CO2 laser revision techniques. Nearly half of these patients had undergone one or more previous, unsuccessful, nonlaser revisions. For primary otosclerosis, CO2 laser stapedotomy has simplified a technically difficult operation while significantly reducing mechanical trauma to the inner ear. Most gratifying to the senior author is that after approximately 450 consecutive CO2 laser operations for otosclerosis, no patient has experienced significant postoperative sensorineural hearing loss (greater than 15 dB; mean 500, 1000, 2000, 3000 Hz). This fact alone has justified our theoretical and laboratory efforts to find the safest laser for otosclerosis surgery.