Local manifestations of cometary activity

Comets are made of volatile and refractory material and naturally experience various degrees of sublimation as they orbit around the Sun. This gas release, accompanied by dust, represents what is traditionally described as activity. Although the basic principles are well established, most details remain elusive, especially regarding the mechanisms by which dust is detached from the surface and subsequently accelerated by the gas flows surrounding the nucleus. During its 2 years rendez-vous with comet 67P/Churyumov-Gerasimenko, ESA's Rosetta has observed cometary activity with unprecedented details, in both the inbound and outbound legs of the comet's orbit. This trove of data provides a solid ground on which new models of activity can be built. In this chapter, we review how activity manifests at close distance from the surface, establish a nomenclature for the different types of observed features, discuss how activity is at the same time transforming and being shaped by the topography, and finally address several potential mechanisms.Comment: This paper is a review chapter in the upcoming book "Comets: Post 67P Perspectives" edited by ISSI and Space Science Reviews. Accepted on 08 April 201

On exact categories and applications to triangulated adjoints and model structures

We show that Quillen's small object argument works for exact categories under very mild conditions. This has immediate applications to cotorsion pairs and their relation to the existence of certain triangulated adjoint functors and model structures. In particular, the interplay of different exact structures on the category of complexes of quasi-coherent sheaves leads to a streamlined and generalized version of recent results obtained by Estrada, Gillespie, Guil Asensio, Hovey, J{\o}rgensen, Neeman, Murfet, Prest, Trlifaj and possibly others.Comment: 38 pages; version 2: major revision, more explanation added at several places, reference list updated and extended, misprints correcte

Propriétés technologiques du bois de cèdre de l'Atlas (Cedrus atlantica Manetti)

Certaines propriétés importantes du bois de cèdre de l'Atlas et leur variabilité ont été étudiées à partir d'échantillonnages non destructifs prélevés dans des peuplements au Maroc et en France. Les caractéristiques pris en considération sont les suivantes : l'anatomie, la vitesse de croissance, la densité, le retrait, la couleur et la duraminisation, la teneur en résine et d'extraits à l'eau. Elles ont été étudiées en fonction du type de substrat, du traitement sylvicole, de l'intensité des éclaircies

MAC layer functions for SLEF

We develop three functions around the MAC layer: (1) Pseudo broadcast is a technique used to improve throughput of broadcast transmissions in case of congested networks. The mechanism consists in sending a packet in unicast to a station using RTS/CTS. Other stations will receive the packet by capturing all the frames that are transmitted on the network, even if they are not directed to them. (2) The injection rate of packets in the MAC layer has to be controlled. The application must not be allowed to deliver to the MAC layer more packets than the number that can be sent by the network adapter. It is also necessary to know the nominal rate of the network. (3) An indication of activity on the network has to be provided. This function has to detect the activity of other SLEF stations in the neighborhood. The address of the last transmitting station and the time of transmission have to be provided. The implementation is carried out using JAVA and native native code and it is portable across all operating systems and wireless cards

CenomanianTuronian transition in a shallow water sequence of the Sinai, Egypt

Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, δ13C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanianearly Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, low-oxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak δ13C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the δ13C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the δ13C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first δ13C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous δ13C shift, but delayed effects of OAE2 dependent on water depth

Morphine Exacerbates HIV-1 Tat-Induced Cytokine Production in Astrocytes through Convergent Effects on [Ca2+]i, NF-κB Trafficking and Transcription

Astroglia are key cellular sites where opiate drug signals converge with the proinflammatory effects of HIV-1 Tat signals to exacerbate HIV encephalitis. Despite this understanding, the molecular sites of convergence driving opiate-accelerated neuropathogenesis have not been deciphered. We therefore explored potential points of interaction between the signaling pathways initiated by HIV-1 Tat and opioids in striatal astrocytes. Profiling studies screening 152 transcription factors indicated that the nuclear factor-kappa B (NF-κB) subunit, c-Rel, was a likely candidate for Tat or Tat plus opiate-induced increases in cytokine and chemokine production by astrocytes. Pretreatment with the NF-κB inhibitor parthenolide provided evidence that Tat±morphine-induced release of MCP-1, IL-6 and TNF-α by astrocytes is NF-κB dependent. The nuclear export inhibitor, leptomycin B, blocked the nucleocytoplasmic shuttling of NF-κB; causing p65 (RelA) accumulation in the nucleus, and significantly attenuated cytokine production in Tat±morphine exposed astrocytes. Similarly, chelating intracellular calcium ([Ca2+]i) blocked Tat±morphine-evoked MCP-1 and IL-6 release, while artificially increasing the concentration of extracellular Ca2+ reversed this effect. Taken together, these results demonstrate that: 1) exposure to Tat±morphine is sufficient to activate NF-κB and cytokine production, 2) the release of MCP-1 and IL-6 by Tat±morphine are highly Ca2+-dependent, while TNF-α appears to be less affected by the changes in [Ca2+]i, and 3) in the presence of Tat, exposure to opiates augments Tat-induced NF-κB activation and cytokine release through a Ca2+-dependent pathway

Case study in six sigma methadology : manufacturing quality improvement and guidence for managers

This article discusses the successful implementation of Six Sigma methodology in a high precision and critical process in the manufacture of automotive products. The Six Sigma define–measure–analyse–improve–control approach resulted in a reduction of tolerance-related problems and improved the first pass yield from 85% to 99.4%. Data were collected on all possible causes and regression analysis, hypothesis testing, Taguchi methods, classification and regression tree, etc. were used to analyse the data and draw conclusions. Implementation of Six Sigma methodology had a significant financial impact on the profitability of the company. An approximate saving of US$70,000 per annum was reported, which is in addition to the customer-facing benefits of improved quality on returns and sales. The project also had the benefit of allowing the company to learn useful messages that will guide future Six Sigma activities

High frequency diffraction of an electromagnetic plane wave by an imperfectly conducting rectangular cylinder

Copyright @ 2011 IEEEWe shall consider the the problem of determining the scattered far wave field produced when a plane E-polarized wave is incident on an imperfectly conducting rectangular cylinder. By using the the uniform asymptotic solution for the problem of the diffraction of a plane wave by a right-angled impedance wedge, in conjunction with Keller's method, the a high frequency far field solution to the problem is given

Composite-pulse magnetometry with a solid-state quantum sensor

The sensitivity of quantum magnetometers is challenged by control errors and, especially in the solid-state, by their short coherence times. Refocusing techniques can overcome these limitations and improve the sensitivity to periodic fields, but they come at the cost of reduced bandwidth and cannot be applied to sense static (DC) or aperiodic fields. Here we experimentally demonstrate that continuous driving of the sensor spin by a composite pulse known as rotary-echo (RE) yields a flexible magnetometry scheme, mitigating both driving power imperfections and decoherence. A suitable choice of RE parameters compensates for different scenarios of noise strength and origin. The method can be applied to nanoscale sensing in variable environments or to realize noise spectroscopy. In a room-temperature implementation based on a single electronic spin in diamond, composite-pulse magnetometry provides a tunable trade-off between sensitivities in the microT/sqrt(Hz) range, comparable to those obtained with Ramsey spectroscopy, and coherence times approaching T1

Neuronal activity moves protein palmitoylation into the synapse

Many neuronal proteins undergo lipid modification that regulates their function and subcellular localization. One such modification is palmitoylation, which is mediated by a large class of protein palmitoyl acyltransferases (PATs). Now, a paper in this issue (Noritake et al. 2009. J. Cell Biol. doi:10.1083/jcb.200903101) demonstrates that the localization of the PAT DHHC2 is regulated by neuronal activity and thereby selectively controls the palmitoylation and subsequent accumulation of specific proteins in the synapse