Water ice cloud formation on Mars is more difficult than presumed: Laboratory studies of ice nucleation on surrogate materials

The role of water ice clouds in the martian water cycle and climate depends on cloud properties such as particle size and number distribution. These properties, in turn, depend on heterogeneous nucleation parameters which are poorly understood. Here we report laboratory experiments performed under martian temperature and water partial pressure conditions (158–185 K, 9 × 10⁻⁷–1 × 10⁻⁴ Torr H₂O) to determine the critical saturation ratio for ice onset, S_crit, as a function of temperature and dust composition. Using infrared spectroscopy to monitor ice nucleation and growth, we find a significant barrier to ice formation, with a pronounced temperature dependence. Even on clay minerals which show uptake of non-crystalline water before ice nucleation, we find a saturation ratio of 2.5 or more (RH_ice > 250%) is needed to begin ice growth at temperatures near 160 K. These results could lead to changes of four orders of magnitude in the nucleation rate relative to the presumptions used currently in Mars microphysical models, which commonly set the contact parameter, m, to a single value of 0.95. Our results range from m = 0.84 to m = 0.98. For ice nucleation on Arizona Test Dust, the temperature dependence is described by m = 0.0046 * T_nucl + 0.1085, while m = 0.0055 * T_nucl + 0.0003 on a smectite-rich clay sample. Our findings suggest that cloud formation will be more difficult than previously thought, potentially leading to areas of increased near-surface humidity but generally drier conditions in the atmosphere of Mars, overall.     

The development of integrated terrestrial and marine pathways in the Argo-Saronic region,Greece

Least cost path applications can be a powerful tool for understanding connectivity across a landscape. A limitation to this method is its difficulty in integrating terrestrial, marine, and cultural factors – all of which would have been at play in the prehistoric Aegean. This study looks at a method of modeling pathways that integrates major factors (land, sea, and culture) that would be in play while considering medium- to long-distance travel in the Aegean. This test case explores the possible relationships between proposed routes for communication and identified coastal sites with parameters modeled in geographic information system that affect travel in cultural, marine, and terrestrial contexts. The methods presented have significance beyond the Late Bronze Age Aegean. The development of a methodology that incorporates marine, cultural, and terrestrial environments provides a mechanism by which specific hypotheses regarding complex communication routes may be addressed in regions of the world where there is an intensive interplay between terrestrial and marine geographies.     

A geoinformatic approach to the collection of archaeological survey data

This article explores the integration of GIS technology with archaeological survey, focusing primarily on two case studies from central Anatolia, the Göksu Archaeological Project and the Avkat Archaeological Project. The methodology employed allows for expediency and accuracy in data recording, which enables refined analyses of anthropogenic and environmental phenomena. The approaches outlined in this article allowed the investigators to move from field observation to publication quality results within a single field day, usually within a four-hour window from initial field observation. The techniques described in the article are some of the geoinformatic applications that classical archaeology is implementing increasingly to develop a robust archaeoinformatic tool kit.     

Re-Os同位素定年方法进展及ICP-MS精确定年测试关键技术

本文介绍了Re-Os同位素定年的基本原理、技术发展及应用现状;综述了样品分解和Re-Os分离富集的主要方法,重点对ICP-MS法进行Re-Os同位素定年做了较详尽的介绍,包括质量分馏校正、干扰校正、含量初测、取样量的确定、稀释剂的稀释比及稀释剂加入量等,以确保高精度测试;评述了ICP-MS最常见的测定对象-辉钼矿中Re-Os的失耦现象及降低其对Re-Os同位素定年影响的对策,文中描述了由测定同位素比值计算含量时的误差传递公式并重申了最佳稀释比。最后,指出了Re-Os同位素定年方法研究中应该关注的工作方向。