Partial Specialization and Heterogeneous Task Assignments

I analyze the impact of industrial robots on the employment of natives and immigrants in US local labor markets between 1990 and 2014. The proposed mechanism, through which robot adoption affects the employment of natives and immigrants differentially, is based on two facts: first, robots tend to displace workers based on the task content of occupations, and second, natives and immigrants in the US differ in their task specialization. Therefore, robots should affect their employment unequally. Exploiting plausibly exogenous variation in robot exposure across US local labor markets over time, I test this mechanism and find that the effect on immigrants is roughly 1.76 times greater than that observed for natives. Specifically, I find that one more robot per thousand workers reduces the employment-to-population ratio of natives and immigrants by 0.38 and 0.67 percentage points, respectively. I attribute these results to the fact that immigrants specialize in jobs or tasks at risk of being automated.

There is a need for rapid methods of assessing changes in the quality of agricultural soils because of the need to monitor such changes under different land management practices. For example, the increasing interest in use of agricultural lands for application of coal combustion byproducts, such as fluidized bed ash, has led to concern that such use may be detrimental to the quality of soil organic matter. Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) techniques hold promise as rapid procedures for detecting changes in the organic matter composition of soils, which contrasts with the often laborious chemical methods used commonly for analyzing soil organic matter. To evaluate Py-GC/MS for this use, we characterized changes in the organic matter composition of bed ash-amended soils by both chemical and pyrolytic analyses. The chemical analysis of the soil samples had shown substantial degradation and loss of organic matter as a result of the ash amendments, and the pyrolytic analyses reflected these losses of soil organic matter by decreases in the total peak areas within the total ion chromatogram. Information on the changes in composition of soil organic matter was reflected by changes in peak area for individual pyrolytic products, and the identity of more than 40 pyrolytic products was determined from their mass spectral data. This permitted identification of various pyrolytic signature products for the protein, carbohydrate, and humic fractions of soil organic matter. The change in peak areas of these different signature products could be correlated with changes in the content of different constituents in the soil organic matter as measured by chemical analysis. The pyrolysis product furfural was correlated with changes in carbohydrate content. Changes in production of 2-methoxyphenol, guaiacol, vinylphenol, vinylguaiacol, and isoeugenol represented changes within the humic fraction. Nitrile and propane pyrolysis products were correlated with changes in protein content. The good agreement between classical chemical analysis and pyrolytic analysis indicates that Py-GC/MS can be used to monitor changes in the organic matter composition of agricultural soils subjected to environmental stress.

Exposure of plants to biotic and abiotic stress agents causes changes in the composition and content of metabolites of different chemical nature, including lipophilic compounds. One of the ways to simulate a stress situation is plant treatment with exogenous phytohormones. This work deals with investigation of organ specificity of composition of lipophilic compounds and changes in their content in wheat Triticum aestivum L. seedlings treated with exogenous stress hormones: abscisic acid (ABA), salicylic acid (SA), and methyl jasmonate (MeJA). It was found that roots and leaves of wheat seedlings have identical composition of lipophilic compounds but their content considerably differed. In the leaves, the quantity of hydrocarbons, including squalene, as well as triterpenes, sterols, and phosphatidyl choline, was much greater than in the roots. In the leaves, glycoceramides of type 1 containing a FA residue with -hydroxyl group predominated; on the contrary, glycoceramides of type 2 whose FA residues lack -hydroxyl group prevailed in the roots. Moreover, lipid extracts from the leaves contain lipophilic pigments (chlorophylls a and b and carotenoids) and hydrophobic phenolic compounds in the form of hydroxycinnamic acids. Treatment with stress phytohormones brings about considerable changes in growth characteristics, the rate of photosynthesis, and the profile of lipophilic compounds in wheat seedlings depending on the plant organ and the chemical nature of the phytohormone. In the case of ABA and MeJA, the growth of roots and leaves was suppressed, the level of nonphotochemical quenching rose, and the content of photosynthetic pigments changed. An unexpected effect was observed upon treatment with MeJA that raised the level of cholesterol and phosphatidyl serine. SA was notable for organ-specific changes in the content of products of mevalonate pathway, triterpenes, and sterols. Thus, the simulation of stress conditions by means of treatment of wheat seedlings with exogenous phytohormones strongly affected the composition of lipophilic compounds. Specific changes in lipid composition induced by hormones may contribute to adaptive structural transformations of cellular membranes, whereas changes in the content of hydrophobic phenolic metabolites and photosynthetic pigments may reinforce antioxidant defense of plants under stress conditions.

We provide a unifying framework to quantify the impact of several determinants of changes in US between-group inequality. We use an assignment framework with many labor groups, equipment types, and occupations in which changes in inequality are driven by changes in workforce composition, occupation demand, computerization, and labor productivity. We parameterize the model using direct measures of computer usage within labor group-occupation pairs and quantify the impact of each shock for various dimensions of between-group inequality between 1984 and 2003. We find, for example, that computerization and shifts in occupation demand jointly account for roughly 80 percent of the rise in the skill premium, with computerization alone accounting for roughly 60 percent. In an open-economy extension of the model, we show how computerization and changes in occupation demand can be caused by changes in the extent of international trade and perform counterfactual exercises to quantify these effects. (JEL D63, J16, J22, J23, J24, J31)

We perform a quantitative analysis of observed changes in U.S. between-group inequality between 1984 and 2003. We use an assignment framework with many labor groups, equipment types, and occupations in which changes in inequality are caused by changes in workforce composition, occupation demand, computerization, and labor productivity. We parameterize our model using direct measures of computer usage within labor group-occupation pairs and quantify the impact of each shock for various measures of between-group inequality. We find, for instance, that the combination of computerization and shifts in occupation demand account for roughly 80% of the rise in the skill premium, with computerization alone accounting for roughly 60%. We show theoretically how computerization and changes in occupation demand may be caused by international trade and quantify the impact of trade in computers on U.S. inequality.

This paper aims to inform policies facilitating job-to-job transitions triggered by changes in the task content of occupations and in job demand. It assesses the distances existing between occupations in terms of cognitive skills and of skills as they emerge from the tasks performed on the job, and the training needs that moving between occupations entails. Skill “shortages” and “excesses” calculated on data for 31 countries and aggregated over 127 occupations are used to estimate the training efforts required to meet the skills requirements of the destination job. Distances in cognitive skills are found to be higher among low-skilled or from mid- to high-skilled occupations than among higher-skilled occupations. Conversely, distances in task-related skills are higher within high-skilled than low-skilled occupations. These results call for policies aimed at developing general cognitive skills complemented by task-related skills for workers in low-skilled occupations, and on-the-job training options for workers in high-skilled occupations.

The Distribution of the Gender Wage Gap

The Distribution of the Gender Wage Gap

The ecological success of social insects is often attributed to their complex social organization and division of labor. Much previous work has investigated the extent to which individual workers within colonies specialize on certain tasks, which presumably increases colony efficiency. Fewer studies have investigated the extent to which individual biases for multiple related tasks adaptively shape division of labor. Here, we focus on honey bee (Apis mellifera) workers that perform hygienic behavior, the detection and removal of diseased larvae in order to reduce pathogen transmission within the hive. We individually marked workers observed performing this rare task and tracked their behavior over three days to fully characterize their task repertoires. We then compared the task repertoires of workers who specialized on hygienic behavior to generalist workers who occasionally perform hygienic behavior to identify additional task biases in hygienic specialists. We show that workers specialized in hygienic behavior are much more likely to also specialize in removing dead adult bodies from the hive, a task that is also associated with colony defense against disease. Our results demonstrate that individual specialization in one task can predict specialization in another related task. We argue these associations represent a type of specialization in multiple tasks that may be an important aspect of how insect colonies adaptively allocate their workers. Any animal group that divides up work among individuals faces the challenge of figuring out the best way to allocate workers towards certain tasks. One mechanism by which large groups can increase their efficiency is by utilizing specialized workers dedicated to a single task. However, it has also been suggested that if multiple tasks require similar skills or are spatially associated with one another, then group efficiency can be further increased by using the same set of workers to perform those tasks as well. Here, we show that honey bee workers specialized in removing dead larvae from the brood zone of the hive are much more likely than bees of the same age to also specialize in removing dead adults from the bottom of the hive. We suggest that this task association has implications for colony fitness and exemplifies an understudied component of how social insect colonies allocate their workers.

The composition of the cell wall of the cotton fiber (Gossypium hirsutum L. Acala SJ-1) has been studied from the early stages of elongation (5 days postanthesis) through the period of secondary wall formation, using cell walls derived both from fibers developing on the plant and from fibers obtained from excised, cultured ovules. The cell wall of the elongating cotton fiber was shown to be a dynamic structure. Expressed as a weight per cent of the total cell wall, cellulose, neutral sugars (rhamnose, fucose, arabinose, mannose, galactose, and noncellulosic glucose), uronic acids, and total protein undergo marked changes in content during the elongation period. As a way of analyzing absolute changes in the walls with time, data have also been expressed as grams component per millimeter of fiber length. Expressed in this way for plant-grown fibers, the data show that the thickness of the cell wall is relatively constant until about 12 days postanthesis; after this time it markedly increases until secondary wall cellulose deposition is completed. Between 12 and 16 days postanthesis increases in all components contribute to total wall increase per millimeter fiber length. The deposition of secondary wall cellulose begins at about 16 days postanthesis (at least 5 days prior to the cessation of elongation) and continues until about 32 days postanthesis. At the time of the onset of secondary wall cellulose deposition, a sharp decline in protein and uronic acid content occurs. The content of some of the individual neutral sugars changes during development, the most prominent change being a large increase in noncellulosic glucose which occurs just prior to the onset of secondary wall cellulose deposition. Methylation analyses indicate that this glucose, at least in part, is 3-linked. In contrast to the neutral sugars, no significant changes in cell wall amino acid composition are observed during fiber development.Compositional analyses of cell walls derived from culture-grown fibers indicate that these walls are remarkably similar to those derived from fibers grown on the plant, both in terms of composition and in terms of relative changes in composition during development.A comparison of our results on total cell wall composition and linkages of sugars as determined by a preliminary methylation analysis of unfractionated fiber walls indicates that the primary cell wall of cotton fibers is similar to that of primary cell walls of other dicotyledons and of gymnosperms as reported in the literature.

A number of mechanisms contribute to the gender earnings gap – both its level and trends in it. We focus on three of them: occupational demand, the cumulation of disadvantage that originates in the unequal domestic division of labour, and labour market statuses which also may originate in the domestic division of labour. We show that changes in occupational demand associated with the dot-com boom and what followed it have caused substantial shifts in the relative earnings of young male and female university graduates. We provide evidence of how one consequence of the domestic division of labour – differences in hours worked by gender - contribute to the size and growth of the female earnings disadvantage. And, even in our generally young sample, human capital accumulation is more likely to be disrupted for women than for men. We identify several methodological and substantive implications of our results.

The purpose of this study was to investigate the stability of aggregate national residential electricity demand coefficients over time. The hypothesis is maintained that the aggregate residential demand is the sum of various end-use demand components. Since the end-use composition changes over time, the demand relationship may change as well. Since the end-use composition differs among regions, the results obtained from this study can be used for making inferences about regional differences in electricity demand relationships. There are two additional sources for a possible structural change. One is that consumers may react differently to declining and rising prices, secondly, the impact of the 1973 oil embargo may have shifted demand preferences. The electricity demand model used for this study is presented. A moving regression method was employed to investigate changes in residential electricity demand over time. The statistical results show a strikingly consistent pattern of change for most of the structural variables. The most important finding of this study is that the estimated structure of residential electricity demand changes systematically over time as a result of changes in the characteristics (both durability and saturation level) of the stock of appliances. Furthermore, there is not strong evidence that the structural changes in demand occurred due to either the reversal of the declining trend of electricity prices or the impact of the 1973 oil embarge. (LCL)

The articular cartilage from nineteen osteoarthritic and fourteen normal control adult human knee joints was analyzed for changes in water content, proteoglycan composition and structure, glycosaminoglycan synthesis rates, and cell content. We found no significant differences between visually intact cartilage from osteoarthritic knee joints and cartilage from control joints for any of the parameters studied. In osteoarthritic specimens in which the cartilage surface was not intact the biochemical changes depended on the degree of fibrillation. Surface-fibrillated specimens had a higher water content in the surface layers but no change in the content or synthesis rate of glycosaminoglycan. Deeply fibrillated cartilage, however, had an increased water content through its full depth, and there was a decrease in both the rate of synthesis and the content of glycosaminoglycans. The results of this study suggest that degenerative changes in osteoarthritic knees are focal in origin and that corrective osteotomy or unicompartmental joint replacement might be rational procedures for knees in which the cartilage in all of one compartment is visually intact.

Phospholipid biosynthesis in health and disease

We studied the changes with time in the composition of leaves of different age, with particular attention given to the youngest leaves, because relatively little is known of the effect of iron chlorosis on the elemental composition of groundnut leaves (Arachis hypogaea L.). For cultivar TMV2 and a number of breeder's lines, the development of chlorosis did not cause a consistent change in nutrient content of the leaves, but marked changes in content were associated with leaf age independent of chlorosis susceptibility. Concentrations of N, P, K, Cu, Mn, and Zn in the leaves of TMV2 generally decreased with increasing age; N, Zn, and Mn concentrations decreased from the unfolded buds to the second unfolded leaf (L2), but thereafter did not decrease. The concentrations of Ca increased markedly with leaf age and Mg concentrations tended to increase. These results indicate that while iron chlorosis did not cause any consistent changes in the elemental composition of groundnut leaves, marked changes in content were associated with leaf age.