Quantifying crater production and regolith overturn on the Moon with temporal imaging

Random bombardment by comets, asteroids and associated fragments form and alter the lunar regolith and other rocky surfaces. The accumulation of impact craters over time is of fundamental use in evaluating the relative ages of geologic units. Crater counts and radiometric ages from returned samples provide constraints with which to derive absolute model ages for unsampled units on the Moon and other Solar System objects. However, although studies of existing craters and returned samples offer insight into the process of crater formation and the past cratering rate, questions still remain about the present rate of crater production, the effect of early-stage jetting during impacts and the influence that distal ejecta have on the regolith. Here we use Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) temporal ('before and after') image pairs to quantify the contemporary rate of crater production on the Moon, to reveal previously unknown details of impact-induced jetting, and to identify a secondary impact process that is rapidly churning the regolith. From this temporal dataset, we detected 222 new impact craters and found 33 per cent more craters (with diameters of at least ten metres) than predicted by the standard Neukum production and chronology functions for the Moon. We identified broad reflectance zones associated with the new craters that we interpret as evidence of a surface-bound jetting process. We also observe a secondary cratering process that we estimate churns the top two centimetres of regolith on a timescale of 81,000 years-more than a hundred times faster than previous models estimated from meteoritic impacts (ten million years).

Torsional power study using CENTURION phacoemulsification technology

BACKGROUND

To evaluate the effect of varying levels of power on phacoemulsification efficiency using the CENTURION Vision System.

METHODS

Formalin-soaked porcine lenses were divided into 2-mm cubes; 0.9-mm, balanced tips were used. Torsional power levels were tested from 10% to 100% at 10% intervals. Vacuum was set to 550 mmHg, aspiration to 50 ml/min, and intraocular pressure at 50 mmHg. Efficiency (time to lens removal) and chatter (number of lens fragment repulsions from the tip) were determined.

RESULTS

Increasing torsional power up to 60% increased efficiency. This effect was linear from 30 to 60% power (R²  = .90; P < 0.05). There were no significant differences in efficiency past 60%. Chatter was highest at 10% power and decreased linearly (R²  = .87; P = 0.007) as power was increased up to 60% power, and chatter did not improve above this power level.

CONCLUSIONS

Power improved efficiency only up to a 60% power level, and then was negligible. Chatter correlated well with power up to the 60% level, so that as power was increased, chatter decreased. Because there are no additional benefits in efficiency past 60% power, and because chatter is minimal at 60% power, we recommend torsional ultrasound at 60% as the optimal power setting for using the CENTURION System for phacoemulsification.l.

The clementine mission to the moon: scientific overview

In the course of 71 days in lunar orbit, from 19 February to 3 May 1994, the Clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths. These data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side. In addition, laser-ranging measurements provided the first view of the global topographic figure of the moon. The topography of many ancient impact basins has been measured, and a global map of the thickness of the lunar crust has been derived from the topography and gravity.

Evolution of the Rembrandt impact basin on Mercury

MESSENGER's second Mercury flyby revealed a ~715-kilometer-diameter impact basin, the second-largest well-preserved basin-scale impact structure known on the planet. The Rembrandt basin is comparable in age to the Caloris basin, is partially flooded by volcanic plains, and displays a unique wheel-and-spoke-like pattern of basin-radial and basin-concentric wrinkle ridges and graben. Stratigraphic relations indicate a multistaged infilling and deformational history involving successive or overlapping phases of contractional and extensional deformation. The youngest deformation of the basin involved the formation of a approximately 1000-kilometer-long lobate scarp, a product of the global cooling and contraction of Mercury.

Reticulated platelets

Young or reticulated platelets contain some residual mRNA, which is rapidly degraded after platelet release into the circulation. They can be easily detected either with supravital dye staining (e.g. new methylene blue) on blood films, or more commonly with fluorescent dyes (e.g thiazole orange) and flow cytometry. Using the latter technique many different groups have demonstrated that the measurement of reticulated platelets has much clinical potential. It is apparent that the level of reticulated platelets gives a relatively simple and non-invasive measurement of the rate of thrombopoiesis in an analogous fashion to the red cell reticulocyte count. Many research groups are currently measuring reticulated platelets but with wide variation in data and methods. An international platelet panel has begun to develop protocols and between laboratory comparisons, which will result in the standardization of the procedure. Platelet reticulocyte analysis should thus become part of accepted haematological practice and provide useful clinical information for the investigation and monitoring of platelet production in various thrombocytopenic conditions. In particular, measurement of reticulated platelets will provide an excellent and simple means for monitoring the response of chemotherapy and transplant patients to growth factors (e.g. thrombopoietin) resulting in a decrease in the demand for platelet transfusion.

Seismic resurfacing by a single impact on the asteroid 433 Eros

Impact cratering creates a wide range of topography on small satellites and asteroids. The population of visible craters evolves with impacts, and because there are no competing endogenic processes to modify the surface, determining the various ways younger craters add to or subtract from the population is a fundamental aspect of small-body geology. Asteroid 433 Eros, the most closely studied small body, has regions of substantially different crater densities that remain unexplained. Here we show that the formation of a relatively young crater (7.6 km in diameter) resulted in the removal of other craters as large as 0.5 km over nearly 40 percent of the asteroid. Burial by ejecta cannot explain the observed pattern of crater removal. The limitation of reduced crater density to a zone within a particular straight-line distance through the asteroid from the centre of the large crater suggests degradation of the topography by seismic energy released during the impact. Our observations indicate that the interior of Eros is sufficiently cohesive to transmit seismic energy over many kilometres, and the outer several tens of metres of the asteroid must be composed of relatively non-cohesive material.

Constant illumination at the lunar north pole

Images returned by the spacecraft Clementine have been used to produce a quantitative illumination map of the north pole of the Moon, revealing the percentage of time that points on the surface are illuminated during the lunar day. We have used this map to identify areas that are constantly illuminated during a lunar day in summer and which may therefore be in permanent sunlight. All are located on the northern rim of Peary crater, close to the north pole. Permanently sunlit areas represent prime locations for lunar outpost sites as they have abundant solar energy, are relatively benign thermally (when compared with equatorial regions), and are close to permanently shadowed regions that may contain water ice.

Adaptins

Clathrin has long been known to provide the structural basis for vesicle budding from the plasma membrane during endocytosis, but how is clathrin targeted specifically to some cellular membranes and not others? The answer seems to lie in the adaptors--protein complexes whose shape resembles the head of Mickey Mouse--which seem to be required both for clathrin-coat assembly and for sequestering specific receptors by interacting with their cytoplasmic domains. In this article, Margaret Robinson describes what is currently known about these versatile proteins.

GGAs: roles of the different domains and comparison with AP-1 and clathrin

We have previously identified a novel family of proteins called the GGAs (Golgi-localized, gamma-ear-containing, ADP-ribosylation factor-binding proteins). These proteins consist of an NH(2)-terminal VHS domain, followed by a GAT domain, a variable domain, and a gamma-adaptin ear homology domain. Studies from our own laboratory and others, making use of both yeast and mammals cells, indicate that the GGAs facilitate trafficking from the trans-Golgi network to endosomes. Here we have further investigated the function of the GGAs. We find that GGA-deficient yeast are not only defective in vacuolar protein sorting but they are also impaired in their ability to process alpha-factor. Using deletion mutants and chimeras, we show that the VHS domain is required for GGA function and that the VHS domain from Vps27p will not substitute for the GGA VHS domain. In contrast, the gamma-adaptin ear homology domain contributes to GGA function but is not absolutely required, and full function can be restored by replacing the GGA ear domain with the gamma-adaptin ear domain. Deleting the gamma-adaptin gene together with the two GGA genes exacerbates the phenotype in yeast, suggesting that they function on parallel pathways. In mammalian cells, the association of GGAs with the membrane is extremely unstable, which may account for their absence from purified clathrin-coated vesicles. Double- and triple-labeling immunofluorescence experiments indicate that the GGAs and AP-1 are associated with distinct populations of clathrin-coated vesicles budding from the trans-Golgi network. Together with results from other studies, our findings suggest that the GGAs act as monomeric adaptors, with the four domains involved in cargo selection, membrane localization, clathrin binding, and accessory protein recruitment.

The nature of ponded deposits on Eros

One of the surprises of the NEAR-Shoemaker mission was that Eros's surface exhibits a wide variety of landforms, which are indicative of a global covering of loose fragmental debris. At one extreme in roughness is the Shoemaker Regio area, which is characterized by a high density of boulders up to 100 m across, slumps, slides, and finer blanketing material. At the other extreme are distinctive, flat deposits that appear smooth down to a resolution of 1.2 cm per pixel. Here we report the results of global mapping and colour analysis of these smooth deposits. They have formed most efficiently in restricted areas, and appear to be the result of deposition of finer material sorted from the upper portion of the asteroid's regolith. The smooth deposits constitute a family of features with a range of morphologies, but all appear to be the result of sedimentation. The geography of the deposits is consistent with some predicted aspects of photoelectric sorting, but these exotic transport and depositional mechanisms are not well understood. Deposits with the properties seen on Eros have no obvious analogues in previous lunar or asteroid data.

Shoemaker crater as the source of most ejecta blocks on the asteroid 433 Eros

The loose material--regolith--on the surfaces of asteroids is thought to represent ballistically emplaced ejecta from impacts but the identification of source craters and the detailed study of the regolith modification have been hampered by the limited spatial resolution and area coverage of the few asteroids imaged by spacecraft. Here we report the results of global mapping of the asteroid 433 Eros from high-resolution images obtained by the NEAR-Shoemaker spacecraft. Based on the images and ejecta-emplacement models, we suggest that most large ejecta blocks on Eros originate from a relatively young 7.6-km-diameter crater. A large fraction of the ejecta from impacts pre-dating that crater has apparently been buried or eroded. The images also show evidence for the action of a variety of sorting environments for regolith particles after they are deposited on the surface.

Adaptor-related proteins

Two new adaptor-related protein complexes, AP-3 and AP-4, have recently been identified, and both have been implicated in protein sorting at the trans-Golgi network (TGN) and/or endosomes. In addition, two families of monomeric proteins with adaptor-related domains, the GGAs and the stoned B family, have also been identified and shown to act at the TGN and plasma membrane, respectively. Together with the two conventional adaptors, AP-1 and AP-2, these proteins may act to direct different types of cargo proteins to different post-Golgi membrane compartments.

Platelet reactivity in acute coronary syndromes: evidence for differences in platelet behaviour between unstable angina and myocardial infarction

Previous work has shown that P-selectin and mean platelet volume, two markers associated with platelet reactivity, are elevated in acute coronary syndromes. This study investigated the possibility that these markers may define unstable angina (UA) and acute myocardial infarction (MI) as two separate conditions based on platelet behaviour. Mean platelet volume (MPV) was higher in UA patients (n = 15) than in those diagnosed with MI (n = 15) (10.7 +/- 0.25 fL, vs. 9.8 +/- 0.27 fL, P = 0.005). Platelet count was lower in UA than in MI (215 +/- 13 x 10(9)/L vs. 271 +/- 20 x 10(9)/L, P = 0.03). The percentage of platelets expressing P-selectin was higher in MI than in UA (9.1 +/- 1.9% vs. 4.2 +/- 0.85%, P = 0.03). This parameter was positively correlated with MPV in UA (r = 0.5, P = 0.04) but negatively correlated in MI (r = -0.6, P = 0.01), with no correlation for ACS as a whole (r = -0.32, P = 0.1). Our results suggest that in MI there is an acute process of generalised platelet activation that is unrelated to changes in MPV, whereas in UA there is an ongoing process of platelet consumption that leads to an increase in platelet size to compensate for a persistent decrease in platelet count. This study suggests that there is a fundamental difference in platelet biology between these two diseases.

The Temple-Wisconsin Cognitive Vulnerability to Depression Project: lifetime history of axis I psychopathology in individuals at high and low cognitive risk for depression

The authors tested the cognitive vulnerability hypotheses of depression with a retrospective behavioral high-risk design. Individuals without current Axis I diagnoses who exhibited either negative or positive cognitive styles were compared on lifetime prevalence of depressive and other disorders and the clinical parameters of depressive episodes. Consistent with predictions, cognitively high-risk participants had higher lifetime prevalence than low-risk participants of major and hopelessness depression and marginally higher prevalence of minor depression. These group differences were specific to depressive disorders. The high-risk group also had more severe depressions than the low-risk group, but not longer duration or earlier onset depressions. The risk group differences in prevalence of depressive disorders were not mediated by current depressive symptoms.

Interconnection of a two-dimensional array of vertical-cavity surface-emitting lasers to a receiver array by means of a fiber image guide

The implementation of a 10-channel parallel optical interconnect consisting of a two-dimensional array of vertical-cavity surface-emitting lasers, a 1.35-m fiber image guide, and a metal-semiconductor-metal receiver array is described. Transmission rates of 250 Mbits/s per channel are demonstrated with an optical cross talk of less than -27 dB and a loss of -3 dB. Coupling issues associated with image guides are analyzed and discussed.