Current photon counting x-ray detector (PCD) technology faces limitations associated with spectral fidelity and photon starvation. One strategy for addressing these limitations is to supplement PCD data with high-resolution, low-noise data acquired with an energy-integrating detector (EID). In this work, we propose an iterative, hybrid reconstruction technique which combines the spectral properties of PCD data with the resolution and signal-to-noise characteristics of EID data. Our hybrid reconstruction technique is based on an algebraic model of data fidelity which substitutes the EID data into the data fidelity term associated with the PCD reconstruction, resulting in a joint reconstruction problem. Within the split Bregman framework, these data fidelity constraints are minimized subject to additional constraints on spectral rank and on joint intensity-gradient sparsity measured between the reconstructions of the EID and PCD data. Following a derivation of the proposed technique, we apply it to the reconstruction of a digital phantom which contains realistic concentrations of iodine, barium, and calcium encountered in small-animal micro-CT. The results of this experiment suggest reliable separation and detection of iodine at concentrations ! 5 mg/ml and barium at concentrations ! 10 mg/ml in 2-mm features for EID and PCD data reconstructed with inherent spatial resolutions of 176 μm and 254 μm, respectively (point spread function, FWHM). Furthermore, hybrid reconstruction is demonstrated to enhance spatial resolution within material decomposition results and to improve low-contrast detectability by as much as 2.6 times relative to reconstruction with PCD data only. The parameters of the simulation experiment are based on an in vivo micro-CT experiment conducted in a mouse model of soft-tissue sarcoma. Material decomposition results produced from this in vivo data demonstrate the feasibility of distinguishing two K-edge contrast agents with a spectral separation on the order of the energy resolution of the PCD hardware.

During long-term studies of the numbers of non-swarming C. terminifera, it was noted frequently that sudden changes in distribution and population densities occurred after storms. In most instances no flight was observed during the day rain fell or on the following day, but light trapping revealed considerable flight activity on nights after storms. Examples of night flight and associated changes in density are presented. It seems possible that C. terminifera requires higher humidities than those generally prevailing in the areas where it occurs, in order to undertake sustained flights. Hence there is an association between storms and night flights. The temperature threshold for flight is approximately 70�F. The airspeed of free flying C. terminifera in still air is 10 ft/sec and it is suggested that at night, in the absence of visual clues from the ground, flying locusts are likely to drift downwind at wind speeds well below their own airspeed. Drift of night-flying locusts in the air flowing behind fronts or flight activity in the zone of more humid air flowing from convective thunderstorms to places beyond the areas of rain are suggested to account for the occurrence of higher numbers of locusts in areas where rain has fallen.

Phaulacridium vittatum is a very abundant grasshopper in pastures in the Southern Tablelands area of New South Wales. It has a single generation per year, the active stages of which are present from late spring until mid-autumn of the following year. In grazed pastures female grasshoppers lay their egg pods in bare spaces between plants and there is a close correlation between the density distribution of egg pods and that of adults of the parent generation. An egg diapause occurs and mortality of eggs is relatively low. The first-instar nymph of P. vittatum feeds on prostrate and rosette-forming plants. However, irrespective of their abundance it is unable to locate these plants where grasses form the dominant plant cover and so fails to survive. Heavy spring rains which produce an abundance of annual and perennial grasses limit the amount of favourable space where the young nymphs can locate suitable food plants and thus result in high mortality. Heavy grazing and the introduction of mat-forming Trifolium subterraneum (L.) maintain open low pastures and favour survival of first-instar nymphs. When hatching has been relatively late, the seasonal drying off of annuals, particularly T. subterraneum, which is a favoured food plant of P. vittatum, results in heavy mortality of the early-instar stages. In most instances, populations have reached the fourth-instar stage by the time that the annuals dry out and dispersal then occurs. Frequently, dispersal consists merely of movement from sites where survival was high after hatching into areas in which the cover was initially unfavourable for post-hatching survival. However, where conditions were uniformly favourable for hatchling survival, mass movement of the grasshoppers to trees may occur. Under average rainfall and evaporation rates in summer very little plant growth occurs, so that to develop from the fourth instar to the sexually immature adult stage, the grasshoppers depend on the foliage accumulated by broad-leafed plants during the spring. As the numbers of fourth-instar nymphs are usually excessive in relation to the amounts of food accumulated during the spring growing period, heavy depletion of food occurs and numbers fall simultaneously. However, development of the grasshoppers is not interrupted by food shortage and, on reaching the sexually immature adult stage, numbers become stable. The persistence of populations under conditions of limited food is attributed to poor discrimination between favourable plants and those unfavourable for development or survival, the restriction of the movements of individuals to ambits or "home ranges" of limited area, an apparent inability of individuals to locate food plants when they wander away from their ambits in search of food and cannibalism of weakened individuals. In contrast to nymphs, adults can survive for prolonged periods in the sexually immature condition on a diet consisting exclusively of the fresh growth of those shallow-rooted perennial grasses which respond to light falls of rain. They do not become sexually mature under these conditions, but reproduce when sufficient rain falls to induce renewed growth of broad-leafed plants.

Adult C. terminifera take off shortly after sunset, climb steeply into the air, and fly out of sight. This steep take-off differs from that of locusts that take flight during the day. One important factor which induces take-off appears to be decreasing light intensity. Take-off has been recorded at air temperatures as low as 17*5"C, relative humidities that ranged from 9 to 70%, and surface wind speeds (at 2 m) which varied from 1 .7 to 21 -2 ft/sec. Initially the locusts take off into wind. At low surface wind speeds individuals subsequently fly out of sight, dispersing in various directions, but at winds in excess of 6 ftlsec the locusts orient and fly downwind. Hundreds of individuals were seen flying away from concentrations of sexually immature adults on successive evenings in 1969. It appears that flight occurs on practically every evening when temperatures are suitable. Significant numbers of C. terminifera appear at lights during the night only during disturbed weather caused by the approach and passage of depressions. In view of the random orientation of flying locusts with respect to wind at low wind speeds, it is suggested that under dry anticyclonic conditions with slight pressure gradients flights after sunset would lead to widespread dispersal, i.e. scattering of individuals over large areas. The downwind orientation at higher wind speeds, which would result in greater displacement, is associated with the approach and passage of depressions (low pressure systems) and the development of storms. In addition to this the increased turbulence of the winds accelerating ahead of the depression (mainly northerlies) and the convergent air flow from the opposite quarter behind the depression would lead to concentration of the locusts in flight. The hypothesis outlined above would explain the striking changes in distribution and densities that frequently occur among populations of adult C. terminifera. Dispersal under dry anticyclonic conditions, and concentration and mass displacement during periods of disturbed weather during which rain-storms may produce conditions favourable for breeding, play an important part in the survival of C. terminifera. In the major part of its distribution area the probability of effective rain in any particular locality is low.

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