This review discusses the physics of magnetic reconnection—a process in which the magnetic field topology changes and magnetic energy is converted to kinetic energy—in pair plasmas in the ...relativistic regime. We focus on recent progress in the field driven by theory advances and the maturity of particle-in-cell codes. This work shows that fragmentation instabilities at the current sheet can play a critical role in setting the reconnection speed and affect the resulting particle acceleration, anisotropy, bulk flows, and radiation. Then, we discuss how this novel understanding of relativistic reconnection can be applied to high-energy astrophysical phenomena, with an emphasis on pulsars, pulsar wind nebulae, and active galactic nucleus jets.
Visual information is conveyed to the brain by axons of >30 retinal ganglion cell (RGC) types. Characterization of these types is a prerequisite to understanding visual perception. Here, we identify ...a family of RGCs that we call F-RGCs on the basis of expression of the transcription factor Foxp2. Intersectional expression of Foxp1 and Brn3 transcription factors divides F-RGCs into four types, comprising two pairs, each composed of closely related cells. One pair, F-miniON and F-miniOFF, shows robust direction selectivity. They are among the smallest RGCs in the mouse retina. The other pair, F-midiON and F-midiOFF, is larger and not direction selective. Together, F-RGCs comprise >20% of RGCs in the mouse retina, halving the number that remain to be classified and doubling the number of known direction-selective cells. Co-expression of Foxp and Brn3 genes also marks subsets of RGCs in macaques that could be primate homologs of F-RGCs.
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•Foxp2 expression marks F-RGCs, two mini and two midi types comprising two pairs•Intersectional expression of Foxp and Brn3 genes uniquely identifies each F-RGC type•The two F-mini RGC types are unusually small, abundant, and direction selective•Combinatorial expression of Foxp and Brn3 genes also marks RGC types in macaque retina
The visual system depends upon the functioning of >30 retinal ganglion cell (RGC) types, many of which remain poorly characterized. Using intersectional labeling techniques in mouse and primate retina, Rousso et al. identify F-RGCs: two pairs of related cells that vary in size, distribution, and selectivity to directional motion.
Electrochemically-propelled nanomotors offer considerable promise for developing new and novel bioanalytical and biosensing strategies based on the direct isolation of target biomolecules or changes ...in their movement in the presence of target analytes. For example, receptor-functionalized nanomotors offer direct and rapid target isolation from raw biological samples without preparatory and washing steps. Microtube engines functionalized with ss-DNA, aptamer or antibody receptors are particularly useful for the direct isolation of nucleic acids, proteins or cancer cells, respectively. A new nanomotor-based signal transduction involving measurement of speed and distance travelled by nanomotors, offers highly sensitive, rapid, simple and low cost detection of target biomarkers, and a new dimension of analytical information based on motion. The resulting distance signals can be easily visualized by optical microscope (without any sophisticated analytical instrument) to reveal the target presence and concentration. The attractive features of the new micromachine-based target isolation and signal transduction protocols reviewed in this article offer numerous potential applications in biomedical diagnostics, environmental monitoring, and forensic analysis.
Supernovae are thought to arise from two different physical processes. The cores of massive, short-lived stars undergo gravitational core collapse and typically eject a few solar masses during their ...explosion. These are thought to appear as type Ib/c and type II supernovae, and are associated with young stellar populations. In contrast, the thermonuclear detonation of a carbon-oxygen white dwarf, whose mass approaches the Chandrasekhar limit, is thought to produce type Ia supernovae. Such supernovae are observed in both young and old stellar environments. Here we report a faint type Ib supernova, SN 2005E, in the halo of the nearby isolated galaxy, NGC 1032. The ‘old’ environment near the supernova location, and the very low derived ejected mass (∼0.3 solar masses), argue strongly against a core-collapse origin. Spectroscopic observations and analysis reveal high ejecta velocities, dominated by helium-burning products, probably excluding this as a subluminous or a regular type Ia supernova. We conclude that it arises from a low-mass, old progenitor, likely to have been a helium-accreting white dwarf in a binary. The ejecta contain more calcium than observed in other types of supernovae and probably large amounts of radioactive 44Ti.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Synesthesia is an unusual condition in which stimulation of one modality evokes sensation or experience in another modality. Although discussed in the literature well over a century ago, synesthesia ...slipped out of the scientific spotlight for decades because of the difficulty in verifying and quantifying private perceptual experiences. In recent years, the study of synesthesia has enjoyed a renaissance due to the introduction of tests that demonstrate the reality of the condition, its automatic and involuntary nature, and its measurable perceptual consequences. However, while several research groups now study synesthesia, there is no single protocol for comparing, contrasting and pooling synesthetic subjects across these groups. There is no standard battery of tests, no quantifiable scoring system, and no standard phrasing of questions. Additionally, the tests that exist offer no means for data comparison. To remedy this deficit we have devised the Synesthesia Battery. This unified collection of tests is freely accessible online (
http://www.synesthete.org). It consists of a questionnaire and several online software programs, and test results are immediately available for use by synesthetes and invited researchers. Performance on the tests is quantified with a standard scoring system. We introduce several novel tests here, and offer the software for running the tests. By presenting standardized procedures for testing and comparing subjects, this endeavor hopes to speed scientific progress in synesthesia research.
In this paper questions of the existence of non-trivial pseudocharacters for different classes of groups and the most important applications of pseudocharacters are considered. We review the results ...obtained for non-trivial pseudocharacters of free group constructions. Pseudocharacter is the real functions
f
on a group
G
such that 1) |
f
(
ab
) −
f
(
a
) −
f
(
b
)| ≤ ε for some ε > 0 and for any
a, b
∈
G
and 2)
f
(
x
n
) =
nf
(
x
) ∀
n
∈ Z, ∀
x
∈
G
. Existence of non-trivial pseudocharacters implies the results for second group of bounded cohomologies and the width of verbal subgroups. Results of R.I. Grigorchuk, V.G. Bardakov, V.A. Fayziev and author on this topic are examined. Theorems about conditions of the existence of non-trivial pseudocharacters on such group objects as free products with amalgamation, HNN-extensions, group with one defining relation, anomalous products are given in the article.
The problem concerning existence conditions for nontrivial pseudocharacters on one-relator groups with nontrivial centre is completely solved. It is proved that a nontrivial pseudocharacter exists on ...a group of this type if and only if the group is nonamenable. A pseudocharacter is a real function on a group for which the set is bounded and for all and . The existence of pseudocharacters is related to many important characteristics and properties of groups, such as the cohomology groups and the width of verbal subgroups. From our results for pseudocharacters we obtain corollaries concerning the width of verbal subgroups and the second bounded cohomology group for the one-relator groups with nontrivial centre. Bibliography: 21 titles.
I began this review with three objectives: (a) to determine whether recent learning-to-teach studies form a coherent body of literature, (b) to use any common themes that emerged from these studies ...to construct a model of professional growth for novice and beginning teachers, and (c) to draw inferences from the model concerning the nature of preservice teacher education programs likely to promote growth by capitalizing on naturally occurring processes and stages. I review 40 learning-to-teach studies published or presented between 1987 and 1991: 27 deal with preservice teachers, 13 with first-year or beginning teachers. All were naturalistic and qualitative in methodology. Studies within each of those divisions are clustered and summarized according to major themes that emerged from findings. The model I ultimately infer from the 40 studies confirms, explicates, and integrates Fuller's (Fuller & Bown, 1975) developmental model of teacher concerns and Berliner's (1988) model of teacher development based on cognitive studies of expertise. Preservice and first-year teaching appears to constitute a single developmental stage during which novices accomplish three primary tasks: (a) acquire knowledge of pupils; (b) use that knowledge to modify and reconstruct their personal images of self as teacher; and (c) develop standard procedural routines that integrate classroom management and instruction. In general, preservice programs fail to address these tasks adequately.
We show that the general class of Double Beltrami (DB) states, which are the lowest energy equilibria of Hall magnetohydrodynamics, can have characteristics similar to those of active regions in the ...solar corona and is capable of undergoing a catastrophe that can cause a solar eruption, such as a flare or coronal mass ejection (CME). We then show that the qualitative evolution of the DB state is consistent with that of a solar eruption. Finally, we make two quantitative comparisons of DB states to CMEs, which are the simplest result of the catastrophe. First, we show that the DB expansion by a factor of 1–2 before the catastrophe is consistent with the increase in the height of the leading edges of Large-Angle Spectrometric Coronagraph (LASCO C1) CMEs in the quasi-equilibrium stage. Secondly, we use the assumption that DB states are randomly chosen from the allowed phase space of coronal structures to predict that the probability of a coronal structure erupting is 0.046. Identifying active regions with DB states and using observational constraints to estimate that the state is replaced every 60 min by emerging loops results in a CME rate of 11 d−1, which is in reasonable agreement with the actual rate of about 6 d−1 at solar maximum.
Recent literature suggests that functional treatment of acute non-insertional Achilles tendon ruptures yields outcomes (re-rupture and function) similar to those of surgery, but does not address the ...unique issues in treating high performance athletes or other high demand patients.
Decision analysis was used to develop an estimate of outcome utility for both types of treatment using published Costs and Quality-Adjusted Life Years (QALYs) values. The expected value for either treatment was then calculated for high, intermediate, and normal demand patients, using the specific functional needs of the patients.
Nonoperative treatment is the preferred management for normal demand patients, while high and intermediate demand patients are more likely to experience better expected functional outcomes from surgery.
The combination of a decision analysis and expected value analysis provides evidence-based support for the existing intuitive recommendations that favor surgical treatment in elite athletes and other high demand patients.
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