Job search by employed workers : the effects of restrictions

Within the framework of a general equilibrium search model, the authors study the effect of institutional restrictions on workers'job mobility. The model generates endogenuous job searches on the job and off the job with two forms of labor contracts emerging and coexisting in equilibrium. One form of contract involves the workers'long-term commitment to the firm ("reversed tenure"): some firms offer high wages in return for their workers'commitment not to search for better jobs. The other is a short-term contract requiring no such commitment: some firms that cannot afford to pay wages that guarantee lifetime attachment pay lower wages, have lower turn-over costs, but impose no restrictions on searches for better jobs. The authors study the effects on employment of exogenous restrictions on mobility - in the form of a transfer from the quitting worker, made either to the employer or to a third party. These transfers, the separation bonds, are typically the benefits lost by the quitting worker, such as vested pension. Restrictions of this type, by crowding out the firms that allow on-the-job searches for employment directly increase unemployment. When restrictions on workers'mobility take the form of a zero-sum transfer, there is no real effect so long as the transfer is below some bound - the worker loses nothing. When the separation bond is prohibitively large, or when it is forfeited to a third party, employment among all types of workers falls.Health Monitoring&Evaluation,Health Economics&Finance,Environmental Economics&Policies,Economic Theory&Research,Labor Markets

Exploring the Prokaryotic Community Associated With the Rumen Ciliate Protozoa Population

Ciliate protozoa are an integral part of the rumen microbiome and were found to exert a large effect on the rumen ecosystem itself as well as their host animal physiology. Part of these effects have been attributed to their ability to harbor a diverse ecto- and endo-symbiotic community of prokaryotic cells. Studies on the relationship between the protozoa population and their associated prokaryotic community in the rumen mainly focused on the methanogens, revealing that protozoa play a major role in enhancing methanogenesis potential. In contrast, little is known about the composition and function of the bacteria associated with rumen protozoa and the extent of this association. In this study, we characterize the prokaryotic communities associated with different protozoa populations and compare their structure to the free-living prokaryotic population residing in the cow rumen. We show that the overall protozoa associated prokaryotic community structure differs significantly compared to the free-living community in terms of richness and composition. The methanogens proportion was significantly higher in all protozoa populations compared to the free-living fraction, while the Lachnospiraceae was the most prevalent bacterial family in the protozoa associated bacterial communities. Several taxa not detected or detected in extremely low abundance in the free-living community were enriched in the protozoa associated bacterial community. These include members of the Endomicrobia class, previously identified as protozoa symbionts in the termite gut. Our results show that rumen protozoa harbor prokaryotic communities that are compositionally different from their surroundings, which may be the result of specific tropism between the prokaryotic community and protozoa

Development of one-part geopolymers based on industrial waste

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Near-IR wide field-of-view Huygens metalens for outdoor imaging applications

The ongoing effort to implement compact and cheap optical systems is the main driving force for the recent flourishing research in the field of optical metalenses. Metalenses are a type of metasurface, used for focusing and imaging applications, and are implemented based on the nanopatterning of an optical surface. The challenge faced by metalens research is to reach high levels of performance, using simple fabrication methods suitable for mass-production. In this paper we present a Huygens nanoantenna based metalens, designed for outdoor photographic/surveillance applications in the near-infra-red. We show that good imaging quality can be obtained over a field-of-view (FOV) as large as +/-15 degrees. This first successful implementation of metalenses for outdoor imaging applications is expected to provide insight and inspiration for future metalens imaging applications

How good is your metalens? Experimental verification of metalens performance criterion

A metric for evaluation of overall metalens performance is presented. It is applied to determination of optimal operating spectral range of a metalens, both theoretically and experimentally. This metric is quite general and can be applied to the design and evaluation of future metalenses, particularly achromatic metalenses

Sensors for Cure Monitoring of Composite Materials

Monitoring and control of the integrity and properties of materials at all stages of structural life, from cradle to retirement, is a growing NDE field. A typical system consists of a sensor, data acquisition, processing and control setup with a host personal computer. For composites, the stage of cure is the only time when an adequate actuation can easily affect the cause of unacceptable characteristics or possibly eliminate the formation of defects. Real-time monitoring of the cure process of plastic-reinforced composites can prevent overbleeding, minimize trapped volatiles, alert of vacuum leak, indicate cure rate and optimize the material properties. For many years, the process of curing composites has been an empirical science and has evolved through a trial-and-error approach. In recent years, significant progress has been made towards understanding the process as a result of data accumulation and progress in mathematical modelling of the composite cure process. Computer science is increasingly applied to support the process analysis using artificial intelligence and knowledge base systems

Human Dental Microwear From Ohalo II (22,500–23,500 cal BP), Southern Levant

Dietary hardness and abrasiveness are inferred from human dental microwear at Ohalo II, a late Upper Palaeolithic site (22,500–23,500 cal BP) in the southern Levant. Casts of molar grinding facets from two human skeletons were examined with a scanning electron microscope. The size and frequency of microwear was measured, counted, and compared to four prehistoric human groups from successive chronological periods in the same region: pre-pottery Neolithic A, Chalcolithic (this study); Natufian, pre-pottery Neolithic B (Mahoney: Am J Phys Anthropol 130 (2006) 308–319). The Ohalo molars had a high frequency of long narrow scratches, and a few small pits, suggesting a tough abrasive diet that required more shearing rather than compressive force while chewing. These results imply that the diet of the two late Upper Palaeolithic hunter-gatherers did not focus on very hard foods. Aquatic foods with adherent contaminants, as well as grit from plant grinding tools seemed likely causal agents. The size of the pits and scratches on the Ohalo molars were most similar to microwear from the pre-pot- tery Neolithic A period, though they also compared well to the Chalcolithic period. These results contrasted with the larger pits and scratches from the Natufian hunter-gath- erers and pre-pottery Neolithic B farmers, implying that there is no simple increase or decrease in dietary hard- ness and abrasiveness across the late Upper Palaeolithic to Chalcolithic development in the Southern Levant