Jeans instability criterion modified by external tidal field

The well-known Jeans criterion describes the onset of instabilities in an infinite, homogeneous, self-gravitating medium supported by pressure. Most realistic astrophysical systems, however, are not isolated - instead they are under the influence of an external field such as the tidal field due to a neighbour. Here, we do a linear perturbation analysis for a system in an external field and obtain a generalized dispersion relation that depends on the wavenumber, the sound speed and also the magnitude of the tidal field. A typical, disruptive tidal field is shown to make the system more stable against perturbations, and results in a higher effective Jeans wavelength. The minimum mass that can become unstable is then higher (super-Jeans) than the usual Jeans mass. Conversely, in a compressive tidal field, perturbations can grow even when the mass is lower (sub-Jeans). This approach involving the inclusion of tidal field opens up a new way of looking at instabilities in gravitating systems. The treatment is general and the simple analytical form of the modified Jeans criterion obtained makes it easily accessible.

星系螺旋结构三维密度波的流体动力学理论(Ⅰ)——局部解及局部Jeans稳定性的讨论

本文是作者的盘状星系三维密度波工作的第一部分.文中给出了在厚度参数ε及准单色波参数ε_

Vida y Muerte Empresarial. Caso de estudio Jeans and Jackets.

Dentro de este estudio de caso se busca identificar las posibles causas por las cuales una empresa de alto prestigio y reconocimiento por los consumidores colombianos, como lo era Jeans and Jackets, luego de treinta (30) años de funcionamiento se vio en la necesidad de acogerse a la Ley de Reestructuración Económica (Ley 550 de 1999) con el fin de reestructurar sus pasivos en un momento de crisis global que fue impredecible para muchas compañías. Desde el principio, el “Core Business” de Jeans and Jackets era la venta de prendas sofisticadas y de alta calidad a los jóvenes, especialmente en la capital de la República, con el fin de convertirse en la marca líder de este segmento de la industria. Este estudio de caso pretende identificar cuáles fueron las decisiones estratégicas implementadas por parte de la alta gerencia de la compañía en el contexto mencionado anteriormente que llevaron a la empresa a una crisis de liquidez. La metodología utilizada para el desarrollo de este estudio de caso se basa en variables cualitativas que permitan realizar un análisis profundo y la indagación sobre el fenómeno de morbilidad empresarial; De la misma manera se utilizan variables cuantitativas para observar la situación de la empresa financieramente y el desempeño económico de la misma.

Del Gossypium las blue jeans. L'an??lisi. L'h??bit de concloure. 'Del Gossypium a los blue jeans. El an??lisis. El h??bito de concluir'

Desarrollo de un cr??dito del ??rea de Tecnolog??a para el ??ltimo curso del ciclo 12-16. La tem??tica presentada permite hacer una valoraci??n de una secuencia de un proceso y de la evoluci??n tecnol??gica del textil. Estructura los contenidos en los temas: fibras textiles, hilatura, tejidos y confecci??n. Para cada tema describe los contenidos conceptuales, de procedimiento y actitudinales, los objetivos did??cticos y las actividades de aprendizaje y evaluaci??n. Presenta el material de soporte planteado para el desarrollo de las veintid??s actividades de aprendizaje.

Reúso de água no processamento de jeans na indústria têxtil

This study aims to assess the potential for industrial reuse of textile wastewater, after passing through a physical and chemical pretreatment, into denim washing wet processing operations in an industrial textile laundry, with no need for complementary treatments and dilutions. The methodology and evaluation of the proposed tests were based on the production techniques used in the company and upgraded for the experiments tested. The characterization of the treated effluent for 16 selected parameters and the development of a monitoring able to tailor the treated effluent for final disposal in accordance with current legislation was essential for the initiation of testing for reuse. The parameters color, turbidity, SS and pH used were satisfactory as control variables and presents simple determination methods. The denim quality variables considered were: color, odor, appearance and soft handle. The tests were started on a pilot scale following complexity factors attributed to the processes, in denim fabric and jeans, which demonstrated the possibility of reuse, because there was no interference in the processes and at quality of the tested product. Industrial scale tests were initiated by a step control that confirmed the methodology efficiency applied to identify the possibility of reuse by tests that precede each recipe to be processed. 556 replicates were performed in production scale for 47 different recipes of denim washing. The percentage of water reuse was 100% for all processes and repetitions performed after the initial adjustment testing phase. All the jeans were framed with the highest quality for internal control and marketed, being accepted by contractors. The full-scale use of treated wastewater, supported by monitoring and evaluation and control methodology suggested in this study, proved to be valid in textile production, not given any negative impact to the quality the produced jeans under the presented conditions. It is believed that this methodology can be extrapolated to other laundries to determine the possibility of reuse in denim washing wet processing with the necessary modifications to each company.

Modello iperbolico del fluido perfetto barotropico e il problema dell'instabilita gravitazionale secondo Jeans

In questa tesi proponiamo una rivisitazione del classico criterio di Jeans per l'instabilità gravitazionale di una nube di gas autogravitante, tenendo conto anche degli effetti viscosi e della presenza di una forza di Coriolis. Si dimostra che l'aggiunta di tali presenze, pur non alterando la soglia critica di Jeans, è generalmente stabilizzante. Infine si evidenzia un'interessante analogia, per modellamento matematico, tecniche e terminologie, fra il collasso gravitazionale e quello chemiotattico

A water footprint assessment of a pair of jeans: the influence of agricultural policies on the sustainability of consumer products.

This study reports the results of a water footprint (WF) assessment of five types of textiles commonly used for the production of jeans, including two different fibres (cotton and Lyocell fibre) and five corresponding production methods for spinning, dyeing and weaving. The results show that the fibre production is the stage with the highest water consumption, being cotton production particularly relevant. Therefore, the study pays particular attention to the water footprint of cotton production and analyses the effects of external factors influencing the water footprint of a product, in this case, the incentives provided by the EU Common Agricultural Policy (CAP), and the relevance of agricultural practices to the water footprint of a product is emphasised. An extensification of the crop production led to higher WF per unit, but a lower overall pressure on the basins water resources. This study performs a sustainability assessment of the estimated cotton WFs with the water scarcity index, as proposed by Hoekstra et al. (2011), and shows their variations in different years as a result of different water consumption by crops in the rest of the river basin. In our case, we applied the assessment to the Guadalquivir, Guadalete and Barbate river basins, three semi-arid rivers in South Spain. Because they are found to be relevant, the available water stored in dams and the outflow are also incorporated as reference points for the sustainability assessment. The study concludes that, in the case of Spanish cotton production, the situation of the basin and the policy impact are more relevant for the status of the basin s water resources than the actual WF of cotton production. Therefore, strategies aimed at reducing the impact of the water footprint of a product need to analyse both the WF along the value chain and within the local context.