Jet Collimation by Small-Scale Magnetic Fields

A popular model for jet collimation is associated with the presence of a large-scale and predominantly toroidal magnetic field originating from the central engine (a star, a black hole, or an accretion disk). Besides the problem of how such a large-scale magnetic field is generated, in this model the jet suffers from the fatal long-wave mode kink magnetohydrodynamic instability. In this paper we explore an alternative model: jet collimation by small-scale magnetic fields. These magnetic fields are assumed to be local, chaotic, tangled, but are dominated by toroidal components. Just as in the case of a large-scale toroidal magnetic field, we show that the ``hoop stress'' of the tangled toroidal magnetic fields exerts an inward force which confines and collimates the jet. The magnetic ``hoop stress'' is balanced either by the gas pressure of the jet, or by the centrifugal force if the jet is spinning. Since the length-scale of the magnetic field is small (< the cross-sectional radius of the jet << the length of the jet), in this model the jet does not suffer from the long-wave mode kink instability. Many other problems associated with the large-scale magnetic field are also eliminated or alleviated for small-scale magnetic fields. Though it remains an open question how to generate and maintain the required small-scale magnetic fields in a jet, the scenario of jet collimation by small-scale magnetic fields is favored by the current study on disk dynamo which indicates that small-scale magnetic fields are much easier to generate than large-scale magnetic fields.Comment: 14 pages, no figur

Modelling of epitaxial film growth with a Ehrlich-Schwoebel barrier dependent on the step height

The formation of mounded surfaces in epitaxial growth is attributed to the presence of barriers against interlayer diffusion in the terrace edges, known as Ehrlich-Schwoebel (ES) barriers. We investigate a model for epitaxial growth using a ES barrier explicitly dependent on the step height. Our model has an intrinsic topological step barrier even in the absence of an explicit ES barrier. We show that mounded morphologies can be obtained even for a small barrier while a self-affine growth, consistent with the Villain-Lai-Das Sarma equation, is observed in absence of an explicit step barrier. The mounded surfaces are described by a super-roughness dynamical scaling characterized by locally smooth (faceted) surfaces and a global roughness exponent $\alpha>1$. The thin film limit is featured by surfaces with self-assembled three-dimensional structures having an aspect ratio (height/width) that may increase or decrease with temperature depending on the strength of step barrier.Comment: To appear in J. Phys. Cond. Matter; 3 movies as supplementary materia

The linear growth rate of structure in Parametrized Post Friedmannian Universes

A possible solution to the dark energy problem is that Einstein's theory of general relativity is modified. A suite of models have been proposed that, in general, are unable to predict the correct amount of large scale structure in the distribution of galaxies or anisotropies in the Cosmic Microwave Background. It has been argued, however, that it should be possible to constrain a general class of theories of modified gravity by focusing on properties such as the growing mode, gravitational slip and the effective, time varying Newton's constant. We show that assuming certain physical requirements such as stability, metricity and gauge invariance, it is possible to come up with consistency conditions between these various parameters. In this paper we focus on theories which have, at most, 2nd derivatives in the metric variables and find restrictions that shed light on current and future experimental constraints without having to resort to a (as yet unknown) complete theory of modified gravity. We claim that future measurements of the growth of structure on small scales (i.e. from 1-200 h^{-1} Mpc) may lead to tight constraints on both dark energy and modified theories of gravity.Comment: 15 Pages, 11 Figure

Measuring quality of life in the speaker with dysarthria: reliability and validity of the european portuguese version of the QoL-DyS

Background: The impact of acquired dysarthria on the person’s life and social participation is well recognized and is the key to the process of rehabilitation. Evaluation of the effectiveness of an intervention that addresses this impact is a challenge for clinicians and researchers. Objectives: The purpose of this study was to evaluate the validity and reliability of the European Portuguese version of the Quality of Life in the Speaker with Dysarthria (QoL-DyS). Methods: This research was conducted in three phases: (i) cultural and linguistic adaptation; (ii) feasibility and reliability; and (iii) validity. The sample was composed of 105 subjects with dysarthria and 103 healthy subjects. The QAD (Quick Assessment for Dysarthria), PEAT10 (Portuguese Eating Assessment Tool), and EQ-5D (EuroQol five-dimension scale) were used for validity and reliability. Results and Conclusion: The QoL-DyS correlated positively with the QAD, PEAT-10, and EQ5D. Cronbach’s ? was 0.973, and it remained excellent when any item was deleted. The QoL-DyS score mean difference between the non-dysarthric cohort and the dysarthric cohort was also significant. Confirmatory factor analysis did not validate the original 40-item scale but a 33-item scale maintaining the four domains of the original version. A significantly higher perception of QoL was found in the non-dysarthric group. The results indicate that the European Portuguese version of the QoL-DyS is a reliable and valid tool to assess QoL in patients with dysarthria and may be used for screening in clinical practice and in research.info:eu-repo/semantics/acceptedVersio

Desempenho do feijoeiro comum em primeira safra e severidade de doenças em sistema agroecológico no Cerrado Goiano.

O presente trabalho teve por objetivos avaliar a produção de massa seca e quantidade de N produzidas por plantas de cobertura do solo, bem como seus efeitos, e de sistemas de manejo do solo, sobre a severidade de doenças e desempenho agronômico da cultura do feijoeiro comum de primeira safra

Improved image analysis procedures for monitoring activated sludge systems with filamentous bulking

Activated sludge systems are frequently used in wastewater treatment plant. This process is the most suitable and studied system. However, several problems are being always detected, such as filamentous bulking. Filamentous bulking is typically caused by an overabundance of filamentous organisms that interfere with the settling and compaction process. This phenomenon can be studied and related with settling parameters by automated image analysis using different microscopy acquisitions. However, by using these standard image analysis procedures some relevant information about the state of the sludge is enclosed. Conventional routines, using monochrome images are not suitable to detect the filamentous bacteria which are gram-positive or gram-negative. Moreover, the traditional image acquisition methodologies are not capable to detect both viable and damaged bacteria present within the sludge. Presently, the gram-stain evaluation is performed by visual inspection and manual counting using a microscope which is a tedious procedure. Also, to overcome the lack of viability information, an epifluorescence staining method composed with two nucleic acid-binding stains can be used. For this study, a lab-scale activated sludge reactor was monitored during 100 days through image analysis information and the operational parameters were modified inducing filamentous bulking. Morphological changes were investigated by using new acquisition methods such as epifluorescence staining LIVE/DEAD® BacLight™ Bacterial Viability Kit, the LIVE BacLight™ Bacterial Gram Stain Kit and the traditional bright field. The overall results revealed an improvement of the sludge morphological characterisation, combining these new image analysis procedures with the conventional routines

Monitoring filamentous bulking and pin-point flocs in a lab-scale activated sludge system using image analysis

Activated sludge processes are the most frequently used techniques regarding biological wastewater treatment. However, depending on the process operation conditions, several malfunctions could take place, in which filamentous bulking and deflocculation processes, such as pin-point flocs, are the most common problems, causing the sludge settling ability decrease and effluent quality deterioration. Bright field Image analysis is nowadays considered a powerful tool to quantitatively characterize aggregated and filamentous bacteria. Furthermore, the use of epifluorescent staining techniques, coupled to image analysis, presents a promising method to determine bacteria gram nature and viability. Encouraged by the success of image analysis procedures over the last years, the present work studied a lab-scale activated sludge system, under operation conditions causing filamentous bulking and pin-point flocs phenomena. Sludge settling ability and turbidity values were measured verifying the nature of the settling problem. COD contents, as well as nitrogen contents, in terms of N-NH4+, N-NO3- and N-NO2-, were surveyed in the feeding effluent, reactor bulk and settler. Regarding the biomass characterization, four major morphological descriptors groups were studied, covering free filamentous bacteria contents, aggregates contents, aggregates size and aggregates morphology. With respect to the aggregates characterization, these were divided in 3 classes (large, intermediate and small aggregates) according to their size. Percentages of gram-positive bacteria, gram-negative bacteria, viable and damaged bacteria were also evaluated based on fluorescent image analysis. Finally, the raw resulting data was fed into a multivariate statistical analysis, in order to enlighten the relationships between the obtained image analysis information and operational parameters. An improvement of the sludge morphological characterisation was found by combining fluorescent and bright field image analysis procedures. Furthermore, the results obtained during the monitoring period indicate that automated image analysis can help clarifying the nature of the events within the aeration tank, when the system is submitted to disturbances