Daily Archives March 14, 2016
By the turn of the millennium in 1000 ad, the population was still rising and a statue-carving culture had developed. The statues were carved in Easter Island’s lone quarry and then transported to desired locations using logs as rollers. The forest stock would have been down to perhaps two-thirds of its original level and the islanders probably would have regarded as apocryphal any claims that the island was once fully forested. However, this much loss of forest cover would have begun to reduce rainfall (because low clouds could pass overhead more easily) and would also have reduced the capacity of the soil to retain water. These trends continued for the next several hundred years...Read More
Although there is some uncertainty about dates, it now seems that Easter Island was first discovered by a small group of Polynesians sometime between 400 and 700
ad. The striking surprise that emerged from analysis of core samples is that Easter Island was at this time covered by a dense forest of Jubaea chilensis (the Chilean wine palm). This particular palm is a large, slow-growing tree that grows in temperate climates.
Following first discovery of Easter Island, the new inhabitants developed an economy based on the wine palm...Read More
First European contact with Easter Island occurred on Easter Day of 1722, when three Dutch ships under the command of Jacob Rogaveen stopped for a 1-day visit at the very isolated South Pacific island, just over 3000 km west of Chile. The visitors observed a small, treeless island populated by what they thought were about 3000 islanders and, to their surprise, by a large number of giant statues. The outside world had no previous knowledge of Easter Island and the islanders apparently had no awareness of the outside world. The visit must have been a shock to the Easter Islanders, but no systematic account of their reaction survives and no further contact with Europeans occurred until 1770, when a Spanish vessel made a brief stop.
The first systematic study of East...Read More
JAMES A. BRANDER
University of British Columbia Vancouver, British Columbia, Canada
1. The Mystery of Easter Island
2. First Discovery and Early History
3. Resource Depletion and Collapse
4. Malthusian Population Dynamics
5. A Predator-Prey System with Unfortunate Parameter Values
6. The Role of Property Rights and Open Access
8. Lessons of Easter Island
core sample A specimen obtained in a long cylinder, taken from a physical site for subsequent study; used in many fields, including oil exploration and archaeology. In archaeology, elements in the core sample can be carbon dated, allowing a reconstruction of the implicit historical record.
Malthusian population dynamics A demographic theory originated by Thomas Malthus, suggesting that the human population has a nat...Read More
Ground-coupled and groundwater (often called ground-source or geothermal) heat pump systems are being installed in great numbers in the United States, Sweden, Switzerland, and Germany. Groundwater aquifers and soil temperatures in the range of 5-30°C are being used in these systems. Ground – source heat pumps utilize groundwater in wells or by direct ground coupling with vertical heat exchangers (Fig. 16). Nearly every state in the United States, especially in the midwestern and eastern states,
FIGURE 16 Typical ground-source heat pump installation.
utilizes these systems, which are in part subsidized by public and private utilities...Read More
The fluid state in transmission lines of direct-use projects can be liquid water, steam vapor, or a two – phase mixture. These pipelines carry fluids from the wellhead to either a site of application or a steam – water separator. Thermal expansion of pipelines heated rapidly from ambient to geothermal fluid temperatures (which may vary from 50 to 200°C) causes stress that must be accommodated by careful engineering design.
The cost of transmission lines and the distribution networks in direct-use projects is significant. This is especially true when the geothermal resource is located a great distance from the main load center; however, transmission distances of up to 60 km have proven economical for hot water (e. g...Read More
Unless the well is artesian, downhole pumps are needed, especially in large-scale, direct utilization systems. Downhole pumps may be installed not only to lift fluid to the surface but also to prevent the release of gas and the resultant scale formation. The two most common types are lineshaft pump systems and submersible pump systems.
The lineshaft pump system (Fig. 10) consists of a multistage downhole centrifugal pump, a surface – mounted motor, and a long driveshaft assembly extending from the motor to the pump. Most are enclosed, with the shaft rotating within a lubrication column, which is centered in the production tubing. This assembly allow the bearings to be lubricated by oil since hot water may not provide adequate lubrication...Read More
Changes in climate have occurred in the distant past as the distribution of continents and their landscapes have changed, as the so-called Milanko – vitch changes in the orbit of the earth and the earth’s tilt relative to the ecliptic plane have varied the insolation received on earth, and as the composition of the atmosphere has changed, all through natural processes. Recent evidence obtained from ice cores drilled through the Greenland ice sheet indicates that changes in climate may often have been quite rapid and major and not associated with any known external forces.
Observations of surface temperature show a global mean warming of approximately 0.7°C during the past 100 years...Read More