3,223 research outputs found
The diameter of the set of boundary slopes of a knot
Let K be a tame knot with irreducible exterior M(K) in a closed, connected,
orientable 3--manifold Sigma such that pi_1(Sigma) is cyclic. If infinity is
not a strict boundary slope, then the diameter of the set of strict boundary
slopes of K, denoted d_K, is a numerical invariant of K. We show that either
(i) d_K >= 2 or (ii) K is a generalized iterated torus knot. The proof combines
results from Culler and Shalen [Comment. Math. Helv. 74 (1999) 530-547] with a
result about the effect of cabling on boundary slopes.Comment: This is the version published by Algebraic & Geometric Topology on 29
August 200
Multiple moonlighting functions of mycobacterial molecular chaperones
Molecular chaperones and protein folding catalysts are normally thought of as intracellular proteins involved in protein folding quality control. However, in the mycobacteria there is increasing evidence to support the hypothesis that molecular chaperones are also secreted intercellular signalling molecules or can control actions at the cell wall or indeed control the composition of the cell wall. The most recent evidence for protein moonlighting in the mycobacteria is the report that chaperonin 60.2 of Mycobacterium tuberculosis is important in the key event in tuberculosis - the entry of the bacterium into the macrophage. This brief overview highlights the potential importance of the moonlighting functions of molecular chaperones in the biology and pathobiology of the mycobacteria. © 2010 Elsevier Ltd. All rights reserved
The Antarctic ozone hole during 2015 and 2016
We reviewed the 2015 and 2016 Antarctic ozone holes, making use of a variety of ground-based and spacebased measurements of ozone and ultraviolet radiation, supplemented by meteorological reanalyses. The ozone hole of 2015 was one of the most severe on record with respect to maximum area and integrated deficit and was notably longlasting, with many values above previous extremes in October, November and December. In contrast, all assessed metrics for the 2016 ozone hole were at or below their median values for the 37 ozone holes since 1979 for which adequate satellite observations exist. The 2015 ozone hole was influenced both by very cold conditions and enhanced ozone depletion caused by stratospheric aerosol resulting from the April 2015 volcanic eruption of Calbuco (Chile)
The Antarctic ozone hole during 2014
We review the 2014 Antarctic ozone hole, making use of a variety of ground-based and space-based measurements of ozone and ultra-violet radiation, supplemented by meteorological reanalyses. Although the polar vortex was relatively stable in 2014 and persisted some weeks longer into November than was the case in 2012 or 2013, the vortex temperature was close to the long-term mean in September and October with modest warming events occurring in both months, preventing severe depletion from taking place. Of the seven metrics reported here, all were close to their respective median values of the 1979â2014 record, being ranked between 16th and 21st of the 35 years for which adequate satellite observations exist
The Landscape of Particle Production: Results from PHOBOS
Recent results from the PHOBOS experiment at RHIC are presented, both from
Au+Au collisions from the 2001 run and p+p and d+Au collisions from 2003. The
centrality dependence of the total charged particle multiplicity in p+p and
d+Au show features, such as Npart-scaling and limiting fragmentation, similar
to p+A collisions at lower energies. Multiparticle physics in Au+Au is found to
be local in (pseudo)rapidity, both when observed by HBT correlations and by
forward-backward pseudorapidity correlations. The shape of elliptic flow in
Au+Au, measured over the full range of pseudorapidity, appears to have a very
weak centrality dependence. Identified particle ratios in d+Au reactions show
little difference between the shape of proton and anti-proton spectra, while
the absolute yields show an approximate m_T scaling.Comment: 8 Pages, 11 Figures, Plenary talk at Quark Matter 2004, Oakland, CA,
January 11-18, 200
Job Strain, Health and Sickness Absence: Results from the Hordaland Health Study
MW and SBH are funded by NSW Health. M. Henderson and M. Hotopf were supported by the NIHR Biomedical Research Centre for Mental Health at the South London and Maudsley NHS Foundation Trust and Institute of Psychiatry, Kingâs College London. AM and SO were funded by the Norwegian Research Council
Proteolytic processing of the L-type Ca2+Â channel alpha11.2 subunit in neurons [version 2; referees: 3 approved]
Background: The L-type Ca2+ channel Cav1.2 is a prominent regulator of neuronal excitability, synaptic plasticity, and gene expression. The central element of Cav1.2 is the pore-forming α11.2 subunit. It exists in two major size forms, whose molecular masses have proven difficult to precisely determine. Recent work suggests that α11.2 is proteolytically cleaved between the second and third of its four pore-forming domains (Michailidis et al,. 2014). Methods: To better determine the apparent molecular masses (MR)of the α11.2 size forms, extensive systematic immunoblotting of brain tissue as well as full length and C-terminally truncated α11.2 expressed in HEK293 cells was conducted using six different regionâspecific antibodies against α11.2. Results: The full length form of α11.2 migrated, as expected, with an apparent MR of ~250 kDa. A shorter form of comparable prevalence with an apparent MR of ~210 kDa could only be detected in immunoblots probed with antibodies recognizing α11.2 at an epitope 400 or more residues upstream of the C-terminus. Conclusions: The main two size forms of α11.2 are the full length form and a shorter form, which lacks ~350 distal C-terminal residues. Midchannel cleavage as suggested by Michailidis et al. (2014) is at best minimal in brain tissue
The Holy Grail: A road map for unlocking the climate record stored within Mars' polar layered deposits
In its polar layered deposits (PLD), Mars possesses a record of its recent climate, analogous to terrestrial ice sheets containing climate records on Earth. Each PLD is greater than 2 âkm thick and contains thousands of layers, each containing information on the climatic and atmospheric state during its deposition, creating a climate archive. With detailed measurements of layer composition, it may be possible to extract age, accumulation rates, atmospheric conditions, and surface activity at the time of deposition, among other important parameters; gaining the information would allow us to âreadâ the climate record. Because Mars has fewer complicating factors than Earth (e.g. oceans, biology, and human-modified climate), the planet offers a unique opportunity to study the history of a terrestrial planetâs climate, which in turn can teach us about our own planet and the thousands of terrestrial exoplanets waiting to be discovered.
During a two-part workshop, the Keck Institute for Space Studies (KISS) hosted 38 Mars scientists and engineers who focused on determining the measurements needed to extract the climate record contained in the PLD. The group converged on four fundamental questions that must be answered with the goal of interpreting the climate record and finding its history based on the climate drivers.
The group then proposed numerous measurements in order to answer these questions and detailed a sequence of missions and architecture to complete the measurements. In all, several missions are required, including an orbiter that can characterize the present climate and volatile reservoirs; a static reconnaissance lander capable of characterizing near surface atmospheric processes, annual accumulation, surface properties, and layer formation mechanism in the upper 50 âcm of the PLD; a network of SmallSat landers focused on meteorology for ground truth of the low-altitude orbiter data; and finally, a second landed platform to access ~500 âm of layers to measure layer variability through time. This mission architecture, with two landers, would meet the science goals and is designed to save costs compared to a single very capable landed mission. The rationale for this plan is presented below.
In this paper we discuss numerous aspects, including our motivation, background of polar science, the climate science that drives polar layer formation, modeling of the atmosphere and climate to create hypotheses for what the layers mean, and terrestrial analogs to climatological studies. Finally, we present a list of measurements and missions required to answer the four major questions and read the climate record.
1. What are present and past fluxes of volatiles, dust, and other materials into and out of the polar regions?
2. How do orbital forcing and exchange with other reservoirs affect those fluxes?
3. What chemical and physical processes form and modify layers?
4. What is the timespan, completeness, and temporal resolution of the climate history recorded in the PLD
Universal Behavior of Charged Particle Production in Heavy Ion Collisions
The PHOBOS experiment at RHIC has measured the multiplicity of primary
charged particles as a function of centrality and pseudorapidity in Au+Au
collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV. Two kinds of universal
behavior are observed in charged particle production in heavy ion collisions.
The first is that forward particle production, over a range of energies,
follows a universal limiting curve with a non-trivial centrality dependence.
The second arises from comparisons with pp/pbar-p and e+e- data.
N_tot/(N_part/2) in nuclear collisions at high energy scales with sqrt(s) in a
similar way as N_tot in e+e- collisions and has a very weak centrality
dependence. This feature may be related to a reduction in the leading particle
effect due to the multiple collisions suffered per participant in heavy ion
collisions.Comment: 4 Pages, 5 Figures, contributed to the Proceedings of Quark Matter
2002, Nantes, France, 18-24 July 200
- âŠ