A malthusian model for all seasons

An issue often discussed in relation to agricultural development is the effect on agricultural labour productivity of more intensive land-use. Introducing aspects of seasonality into a stylized Malthusian model, we unify two diverging views by showing that labour productivity may go up or down with agricultural intensification, depending on whether technological progress emerges in relation to cultivation or harvesting activities. Our result rests on evidence reported by Boserup (1965) and others, which suggests that harvest seasons in traditional agriculture are characterized by severe labour shortage.Agricultural Intensification, Boserup, Labour Surplus, Malthus, Seasonality

A Malthusian model for all seasons?

An issue often discussed in relation to agricultural development is the effect on agricultural labour productivity of more intensive land-use. Introducing aspects of seasonality into a stylized Malthusian model, we unify two diverging views by showing that labour productivity may go up or down with agricultural intensification, depending on whether technological progress emerges in relation to cultivation or harvesting activities. Our result rests on evidence reported by Boserup (1965) and others, which suggests that harvest seasons in traditional agriculture are characterized by severe labour shortage.agricultural intensification ; Boserup ; labour surplus ; Malthus ; seasonality

Studies in upper and lower atmosphere coupling

The theoretical and data-analytic work on upper and lower atmosphere coupling performed under a NASA Headquarters contract during the period April 1978 to March 1979 are summarized. As such, this report is primarily devoted to an overview of various studies published and to be published under this contract. Individual study reports are collected as exhibits. Work performed under the subject contract are in the following four areas of upper-lower atmosphere coupling: (1) Magnetosphere-ionosphere electrodynamic coupling in the aurora; (2) Troposphere-thermosphere coupling; (3) Ionosphere-neutral-atmosphere coupling; and (4) Planetary wave dynamics in the middle atmosphere

A Malthusian model for all seasons?

An issue often discussed in relation to agricultural development is the effect on agricultural labour productivity of more intensive land-use. Introducing aspects of seasonality into a stylized Malthusian model, we unify two diverging views by showing that labour productivity may go up or down with agricultural intensification, depending on whether technological progress emerges in relation to cultivation or harvesting activities. Our result rests on evidence reported by Boserup (1965) and others, which suggests that harvest seasons in traditional agriculture are characterized by severe labour shortage.Une question souvent discutée par rapport au développement agricole est l'effet sur la productivité agricole de méthodes plus intensives d'utilisation de la terre. En présentant des éléments de saisonnalité dans un modèle malthusien stylisé, nous unifions deux vues divergentes en montrant que la productivité du travail peut augmenter ou diminuer avec l'intensification agricole, selon que le progrès technologique est concentré sur les activités de culture ou de récolte. Notre résultat repose sur des observations rapportées par Boserup (1965) et d'autres auteurs qui suggèrent que dans l'agriculture traditionnelle les saisons de récolte sont caractérisées par une pénurie sévère de travail

A mechanical, thermal and electrical packaging design for a prototype power management and control system for the 30 cm mercury ion thruster

A prototype electric power management and thruster control system for a 30 cm ion thruster is described. The system meets all of the requirements necessary to operate a thruster in a fully automatic mode. Power input to the system can vary over a full two to one dynamic range (200 to 400 V) for the solar array or other power source. The power management and control system is designed to protect the thruster, the flight system and itself from arcs and is fully compatible with standard spacecraft electronics. The system is easily integrated into flight systems which can operate over a thermal environment ranging from 0.3 to 5 AU. The complete power management and control system measures 45.7 cm (18 in.) x 15.2 cm (6 in.) x 114.8 cm (45.2 in.) and weighs 36.2 kg (79.7 lb). At full power the overall efficiency of the system is estimated to be 87.4 percent. Three systems are currently being built and a full schedule of environmental and electrical testing is planned

On the theory of resonant scattering of gamma rays by nuclei bound in crystals

An attempt is made in the present paper to give a physical description of the process in which a gamma quantum is resonantly scattered or absorbed by nuclei bound in a crystal structure. The discussion includes a description of the time development of these processes as well as a critical study of the limits imposed upon such a description by the laws of quantum mechanics.(1

Extreme Precision Antenna Reflector Study Results

Thermal and mechanical distortion degrade the RF performance of antennas. The complexity of future communications antennas requires accurate, dimensionally stable antenna reflectors and structures built from materials other than those currently used. The advantages and disadvantages of using carbon fibers in an epoxy matrix are reviewed as well as current reflector fabrications technology and adjustment. The manufacturing sequence and coefficient of thermal expansion of carbon fiber/borosilicate glass composites is described. The construction of a parabolic reflector from this material and the assembling of both reflector and antenna are described. A 3M-aperture-diameter carbon/glass reflector that can be used as a subassembly for large reflectors is depicted. The deployment sequence for a 10.5M-aperture-diameter antenna, final reflector adjustment, and the deployment sequence for large reflectors are also illustrated

The swept angle retarding mass spectrometer: Initial results from the Michigan auroral probe sounding rocket

Data from a sounding rocket flight of the swept angle retarding ion mass spectrometer (SARIMS) are presented to demonstrate the capability of the instrument to make measurements of thermal ions which are differential in angle, energy, and mass. The SARIMS was flown on the Michigan auroral probe over regions characterized first by discrete auroral arcs and later by diffuse precipitation. The instrument measured the temperature, densities, and flow velocities of the ions NO(+) and O(+). Measured NO(+) densities ranged from 10 to the 5th power up to 3 x 10 to the 5th power ions/cu cm, while the measured O(+) densities were a factor of 5-10 less. Ion temperatures ranged from 0.15 up to 0.33 eV. Eastward ion flows approximately 0.5 km/sec were measured near the arcs, and the observed flow magnitude decreased markedly inside the arcs

Estimating translational selection in Eukaryotic Genomes

Natural selection on codon usage is a pervasive force that acts on a large variety of prokaryotic and eukaryotic genomes. Despite this, obtaining reliable estimates of selection on codon usage has proved complicated, perhaps due to the fact that the selection coefficients involved are very small. In this work, a population genetics model is used to measure the strength of selected codon usage bias, S, in 10 eukaryotic genomes. It is shown that the strength of selection is closely linked to expression and that reliable estimates of selection coefficients can only be obtained for genes with very similar expression levels. We compare the strength of selected codon usage for orthologous genes across all 10 genomes classified according to expression categories. Fungi genomes present the largest S values (2.24–2.56), whereas multicellular invertebrate and plant genomes present more moderate values (0.61–1.91). The large mammalian genomes (human and mouse) show low S values (0.22–0.51) for the most highly expressed genes. This might not be evidence for selection in these organisms as the technique used here to estimate S does not properly account for nucleotide composition heterogeneity along such genomes. The relationship between estimated S values and empirical estimates of population size is presented here for the first time. It is shown, as theoretically expected, that population size has an important role in the operativity of translational selection

Quantifying argonaute proteins in and out of GW/P-bodies: Implications in microRNA activities

MicroRNAs (miRNAs) are a class of ∼22nt non-coding RNAs that regulate the translational potential and stability of mRNAs. Though constituting only 1-4% of human genes, miRNAs are predicted to regulate more than 60% of all mRNAs. The action of miRNAs is mediated through their associations with Argonaute proteins and mRNA targets. Previous studies indicated that though the majority of Argonaute proteins is diffusely distributed in the cytoplasm, a small fraction is consistently observed to be concentrated in a cytoplasmic compartment called GW/P-bodies. In this chapter, we will provide a quantitative and dynamic view of the subcellular localization of miRNA function, followed by a discussion on the possible roles of PBs in miRNA silencing.National Institutes of Health (U.S.) (Grant R01-CA133404)National Cancer Institute (U.S.) (Grant P01-CA42063)National Cancer Institute (U.S.) (Grant P30-CA14051