Synchronous Spin-Exchange Optical Pumping

We demonstrate a new approach to precision NMR with hyperpolarized gases designed to mitigate NMR shifts due to the alkali spin-exchange field. The NMR bias field is implemented as a sequence of alkali (Rb) 2π pulses, allowing the Rb polarization to be optically pumped transverse to the bias field. When the Rb polarization is modulated at the noble-gas (Xe) NMR resonance, spin-exchange collisions buildup a precessing transverse Xe polarization. We study and mitigate novel NMR broadening effects due to the oscillating spin-exchange field. Spin-exchange frequency shifts are suppressed 2500×, and Rb magnetometer gain measurements project photon shot-noise limited NMR frequency uncertainties below 10  nHz/sqrt[Hz].

Suppression of spin-exchange relaxation using pulsed parametric resonance

We demonstrate that spin-exchange dephasing of Larmor precession at near-Earth-scale fields is effectively eliminated by dressing the alkali-metal atom spins in a sequence of ac-coupled 2π pulses, repeated at the Larmor precession frequency. The contribution of spin-exchange collisions to the spectroscopic linewidth is reduced by a factor of the duty cycle of the pulses. We experimentally demonstrate resonant transverse pumping in magnetic fields as high as 0.1 G, present experimental measurements of the suppressed spin-exchange relaxation, and show enhanced magnetometer response relative to a light-narrowed scalar magnetometer.

Injuries from antipersonnel mines: the experience of the International Committee of the Red Cross

OBJECTIVE

To describe and quantify patterns of injury from antipersonnel mines in terms of distribution of injury, drain on surgical resources, and residual disability.

DESIGN

Retrospective analysis.

SETTING

Two hospitals for patients injured in war.

SUBJECTS

757 patients with injuries from antipersonnel mines.

MAIN OUTCOME MEASURES

Distribution and number of injuries; number of blood transfusions; number of operations; disability.

RESULTS

Pattern 1 injury results from standing on a buried mine. These patients usually sustain traumatic amputation of the foot or leg; they use most surgical time and blood and invariably require surgical amputation of one or both lower limbs. Pattern 2 injury is a more random collection of penetrating injuries caused by multiple fragments from a mine triggered near the victim. The lower limb is injured but there is less chance of traumatic amputation or subsequent surgical amputation. Injuries to the head, neck, chest, or abdomen are common. Pattern 3 injury results from handling a mine: the victim sustains severe upper limb injuries with associated face injuries. Eye injuries are common in all groups.

CONCLUSIONS

Patients who survive standing on a buried mine have greatest disability. Non-combatants are at risk from these weapons; in developing countries their social and economic prospects after recovery from amputation are poor.