July 2012 Greenland melt extent enhanced by low-level liquid clouds.

Melting of the world's major ice sheets can affect human and environmental conditions by contributing to sea-level rise. In July 2012, an historically rare period of extended surface melting was observed across almost the entire Greenland ice sheet, raising questions about the frequency and spatial extent of such events. Here we show that low-level clouds consisting of liquid water droplets ('liquid clouds'), via their radiative effects, played a key part in this melt event by increasing near-surface temperatures. We used a suite of surface-based observations, remote sensing data, and a surface energy-balance model. At the critical surface melt time, the clouds were optically thick enough and low enough to enhance the downwelling infrared flux at the surface. At the same time they were optically thin enough to allow sufficient solar radiation to penetrate through them and raise surface temperatures above the melting point. Outside this narrow range in cloud optical thickness, the radiative contribution to the surface energy budget would have been diminished, and the spatial extent of this melting event would have been smaller. We further show that these thin, low-level liquid clouds occur frequently, both over Greenland and across the Arctic, being present around 30-50 per cent of the time. Our results may help to explain the difficulties that global climate models have in simulating the Arctic surface energy budget, particularly as models tend to under-predict the formation of optically thin liquid clouds at supercooled temperatures--a process potentially necessary to account fully for temperature feedbacks in a warming Arctic climate.

Siblings as therapists: a behavioral approach.

Although many family therapy programs have taught behavior modification techniques to parents, few have involved siblings as therapeutic agents in the treatment of retarded, emotionally disturbed, or physically handicapped children. The authors describe their experiences with two families in which siblings were taught to use simple procedures to encourage desired behaviors in a disturbed brother or sister. They conclude that further investigation is needed to refine sibling training techniques and suggest that involvement in treatment programs may have beneficial influences on the normal siblings of disturbed children.

The effects of a pre-time-out stimulus on matching-to-sample of humans.

In each of two experiments human subjects were intermittently reinforced with money on a fixed-ratio schedule for emitting correct matching responses. A pre-time-out stimulus which signaled removal of positive reinforcement was periodically superimposed. In the first experiment the superimposed pre-time-out stimulus was paired with a 1-min or 4-min response-independent time out. In the second experiment the pre-time-out stimulus was paired with a 1-min or 4-min time out contingent on the incorrect responses. The pre-time-out stimulus did not markedly influence performance when the time out was response independent. In contrast, the pre-time-out stimulus markedly suppressed incorrect responding when the time out was contingent on the incorrect responses. When duration of this time-out was increased from 1-min to 4-min, suppression of incorrect responding increased and correct responding was suppressed. Therefore, behavioral suppression by a pre-time-out stimulus was obtained only when the signaled aversive event-time out-was response produced. In this case, suppression was influenced by time-out duration.

Distortions of ultrasonic field introduced by the rib cage in echocardiography.

In ultrasonic examination of the heart, the anatomy and motion of heart structures can be observed by placing the ultrasonic transducer over an intercostal window adjacent to the sternum. The ultrasonic beam may be reflected, refracted, or scattered from its path by the ribs and soft tissues before reaching the target of interest. This interaction between the tissues and ultrasound beam, which introduces significant changes in ultrasonic beam characteristics, may result in considerable degradation of the lateral resolution of the ultrasonic system, determined largely by the beam width. In this paper, the effect of rib cage on the beam characteristics is examined. It is shown that the rib cage can produce severe distortions of the ultrasonic beam, namely, asymmetry in beam cross-section, alteration in beam diameter, and deflection of the beam from its central path. It is also demonstrated that this distortion is dependent upon transducer diameter, width of the intercostal window, and transducer angulation relative to the breast plate.