The First Half Billion Years (z > 9): Results from the Frontier Fields

The First Four Billion Years

Life: the first two billion years.

Microfossils, stromatolites, preserved lipids and biologically informative isotopic ratios provide a substantial record of bacterial diversity and biogeochemical cycles in Proterozoic (2500-541 Ma) oceans that can be interpreted, at least broadly, in terms of present-day organisms and metabolic processes. Archean (more than 2500 Ma) sedimentary rocks add at least a billion years to the recorded...

The first billion years: new insights from geochemistry

Prologue: (V)ast globes. . . after reaching the last stages of ebullition, were coveredwith scoriae like bubbling foam. And the crust which covered the molten matter of the globe and which hardened from the fused condition would be like scoria, as happens with metals in the furnace. If then the great framework of the earth, the exposed rocks, the imperishable silicates, are almost entirely vitr...

Two and a Half Billion Years of Distance Research

In a seminal paper published in 1946, Erdős initiated the investigation of the distribution of distances generated by point sets in metric spaces. In spite of some spectacular partial successes and persistent attacks by generations of mathematicians, most problems raised in Erdős’ paper are still unsolved. Given a set of n points in Rd, let d1 > d2 > d3 > · · · denote the sequence of all distan...

the effect of traffic density on the accident externality from driving the case study of tehran

در این پژوهش به بررسی اثر افزایش ترافیک بر روی تعداد تصادفات پرداخته شده است. به این منظور 30 تقاطع در شهر تهران بطور تصادفی انتخاب گردید و تعداد تصادفات ماهیانه در این تقاطعات در طول سالهای 89-90 از سازمان کنترل ترافیک شهر تهران استخراج گردید و با استفاده از مدل داده های تابلویی و نرم افزار eviews مدل خطی و درجه دوم تخمین زده شد و در نهایت این نتیجه حاصل شد که تقاطعات پر ترافیک تر تعداد تصادفا...