2,231 research outputs found
Signatures of Relativistic Helical Motion in the Rotation Measures of AGN Jets
Polarization has proved an invaluable tool for probing magnetic fields in
relativistic jets. Maps of the intrinsic polarization vectors have provided the
best evidence to date for uniform, toroidally dominated magnetic fields within
jets. More recently, maps of the rotation measure (RM) in jets have for the
first time probed the field geometry of the cool, moderately relativistic
surrounding material. In most cases, clear signatures of toroidal magnetic
field are detected, corresponding to gradients in RM profiles transverse to the
jet. However, in many objects these profiles also display marked asymmetries
which are difficult to explain in simple helical jet models. Furthermore, in
some cases the RM profiles are strongly frequency and/or time dependent. Here
we show that these features may be naturally accounted for by including
relativistic helical motion in the jet model. In particular, we are able to
reproduce bent RM profiles observed in a variety of jets, frequency dependent
RM profile morphologies and even the time dependence of the RM profiles of
knots in 3C 273. Finally, we predict that some sources may show reversals in
their RM profiles at sufficiently high frequencies, depending upon the the
ratio of the components of jet sheath velocity transverse and parallel to the
jet. Thus, multi-frequency RM maps promise a novel way in which to probe the
velocity structure of relativistic outflows.Comment: 5 pages, 4 figures, submitted to ApJ
Effect of Plasma Composition on the Interpretation of Faraday Rotation
Faraday rotation (FR) is widely used to infer the orientation and strength of
magnetic fields in astrophysical plasmas. Although the absence of
electron-positron pairs is a plausible assumption in many astrophysical
environments, the magnetospheres of pulsars and black holes and their
associated jets may involve a significant pair plasma fraction. This motivates
being mindful of the effect of positrons on FR. Here we derive and interpret
exact expressions of FR for a neutral plasma of arbitrary composition. We focus
on electron-ion-positron plasmas in which charge neutrality is maintained by an
arbitrary combination of ions and positrons. Because a pure electron-positron
plasma has zero FR, the greater the fraction of positrons the higher the field
strength required to account for the same FR. We first obtain general formulae
and then specifically consider parameters relevant to active galctic nuclei
(AGN) jets to illustrate the significant differences in field strengths that FR
measurements from radio frequency measurements. Complementarily, using galaxy
cluster core plasmas as examples, we discuss how plasma composition can be
constrained if independent measurements of the field strength and number
density are available and combined with FR.Comment: Submitted to MNRA
Leveling the Fields for Migrant Farmworkers: Developing Human Rights Public Policies Using Human Rights-Based Approach
This paper identifies the shortfalls of United States policy regarding migrant agricultural workers and proposes several courses of action for the federal government. Analysis of current U.S. policy and practices reveals serious human rights violations toward migrant agricultural workers by various U.S. entities, including the U.S. Department of Homeland Security, the U.S. Department of Labor, and the state of Arizona. Human rights violated include freedom from discrimination, equality before the law, the right to marriage and a family, the right to work, and the right to adequate living standards, including food, shelter, and health. These breaches find ground in both the international arena through international treaties and in the domestic sphere through the U.S. Constitution and other established laws.
In order to overcome these problems, the best course of action would be to promote ratification of international treaties regarding the rights of relevant vulnerable groups, including the Convention on the Protection of the Rights of All Migrant Workers and Members of Their Families. This would set the foundation for future U.S. policy-making standards regarding migrant workers. In addition, the federal government should focus on amending current policies based on the recommendations of the U.N. Special Rapporteur on the Rights of Migrants and the Working Group in the Universal Periodic Review
Are emotional states based in the brain? A critique of affective brainocentrism from a physiological perspective
This is the final version. Available on open access from Springer via the DOI in this recordWe call affective brainocentrism the tendency to privilege the brain over other parts of the
organism when defining or explaining emotions. We distinguish two versions of this tendency.
According to brain-sufficient, emotional states are entirely realized by brain processes.
According to brain-master, emotional states are realized by both brain and bodily processes,
but the latter are entirely driven by the brain: the brain is the master regulator of bodily
processes. We argue that both these claims are problematic, and we draw on physiological
accounts of stress to make our main case. These accounts illustrate the existence of complex
interactions between the brain and endocrine systems, the immune system, the enteric
nervous system, and even gut microbiota. We argue that, because of these complex brainbody interactions, the brain cannot be isolated and identified as the basis of stress. We also
mention recent evidence suggesting that complex brain-body interactions characterize the
physiology of depression and anxiety. Finally, we call for an alternative dynamical, systemic,
and embodied approach to the study of the physiology of emotions that does not privilege the
brain, but rather aims at understanding how mutually regulating brain and bodily processes
jointly realize a variety of emotional states
Oscillation arrest in the mouse somitogenesis clock presumably takes place via an infinite period bifurcation
This is the author accepted manuscript available from arXiv.org via the DOI in this record.In this work we address the question of how oscillations are arrested in the
mouse somitogenesis clock when the determination front reaches presomitic
cells. Based upon available experimental evidence we hypothesize that the
mechanism underlying such a phenomenon involves the interaction between
a limit cycle (originated by a delayed negative feedback loop) and a bistable
switch (originated by a positive feedback loop). With this hypothesis in mind
we construct the simplest possible model comprising both negative and positive
feedback loops and show that (with a suitable choice of paremeters):
1) it can show an oscillatory behavior, 2) oscillations are arrested via an
infinite-period bifurcation whenever the different gene-expression regulatorinputs
act together in an additive rather than in a multiplicative fashion,
and 3) this mechanism for oscillation arrest is compatible whit plentiful experimental
observations
The long and viscous road: uncovering nuclear diffusion barriers in closed mitosis.
This is the final version of the article. Available from Public Library of Science via the DOI in this record.Diffusion barriers are effective means for constraining protein lateral exchange in cellular membranes. In Saccharomyces cerevisiae, they have been shown to sustain parental identity through asymmetric segregation of ageing factors during closed mitosis. Even though barriers have been extensively studied in the plasma membrane, their identity and organization within the nucleus remains poorly understood. Based on different lines of experimental evidence, we present a model of the composition and structural organization of a nuclear diffusion barrier during anaphase. By means of spatial stochastic simulations, we propose how specialised lipid domains, protein rings, and morphological changes of the nucleus may coordinate to restrict protein exchange between mother and daughter nuclear lobes. We explore distinct, plausible configurations of these diffusion barriers and offer testable predictions regarding their protein exclusion properties and the diffusion regimes they generate. Our model predicts that, while a specialised lipid domain and an immobile protein ring at the bud neck can compartmentalize the nucleus during early anaphase; a specialised lipid domain spanning the elongated bridge between lobes would be entirely sufficient during late anaphase. Our work shows how complex nuclear diffusion barriers in closed mitosis may arise from simple nanoscale biophysical interactions.OIST funding
Delays induce novel stochastic effects in negative feedback gene circuits
AbstractStochastic models of reaction networks are widely used to depict gene expression dynamics. However, stochastic does not necessarily imply accurate, as subtle assumptions can yield erroneous results, masking key discrete effects. For instance, transcription and translation are not instantaneous processes—explicit delays separate their initiation from the appearance of their functional products. However, delays are often ignored in stochastic, single-gene expression models. By consequence, effects such as delay-induced stochastic oscillations at the single-cell level have remained relatively unexplored. Here, we present a systematic study of periodicity and multimodality in a simple gene circuit with negative feedback, analyzing the influence of negative feedback strength and transcriptional/translational delays on expression dynamics. We demonstrate that an oscillatory regime emerges through a Hopf bifurcation in both deterministic and stochastic frameworks. Of importance, a shift in the stochastic Hopf bifurcation evidences inaccuracies of the deterministic bifurcation analysis. Furthermore, noise fluctuations within stochastic oscillations decrease alongside increasing values of transcriptional delays and within a specific range of negative feedback strengths, whereas a strong feedback is associated with oscillations triggered by bursts. Finally, we demonstrate that explicitly accounting for delays increases the number of accessible states in the multimodal regime, and also introduces features typical of excitable systems
Political conservatism, need for cognitive closure and intergroup hostility
Two studies examined the interaction of political conservatism and the need for cognitive closure in predicting aggressiveness in intergroup conflict and hostility toward out-groups. In the first study, Polish participants indicated their preference for coercive conflict strategies in the context of a real-life intergroup conflict. Only among participants who identify themselves as conservative, need for cognitive closure was positively and significantly related to preference for aggressive actions against the out-group. In the second study, the predicted interaction was investigated in the context of the terrorist threat in Poland. The findings indicated that high in need for closure conservatives showed greater hostility against Arabs and Muslims only when they believed that Poland was under threat of terrorist attacks inspired by Islamist fundamentalism
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