204 research outputs found
The X-ray and radio-emitting plasma lobes of 4C23.56: further evidence of recurrent jet activity and high acceleration energies
New Chandra observations of the giant (0.5 Mpc) radio galaxy 4C23.56 at z =
2.5 show X-rays in a linear structure aligned with its radio emission, but
anti-correlated with the detailed radio structure. Consistent with the
powerful, high-z giant radio galaxies we have studied previously, X-rays seem
to be invariably found where the lobe plasma is oldest even where the radio
emission has long since faded. The hotspot complexes seem to show structures
resembling the double shock structure exhibited by the largest radio quasar
4C74.26, with the X-ray shock again being offset closer to the nucleus than the
radio synchrotron shock. In the current paper, the offsets between these shocks
are even larger at 35kpc. Unusually for a classical double (FRII) radio source,
there is smooth low surface-brightness radio emission associated with the
regions beyond the hotspots (further away from the nucleus than the hotspots
themselves), which seems to be symmetric for the ends of both jets. We consider
possible explanations for this phenomenon, and conclude that it arises from
high-energy electrons, recently accelerated in the nearby radio hotspots that
are leaking into a pre-existing weakly-magnetized plasma that are symmetric
relic lobes fed from a previous episode of jet activity. This contrasts with
other manifestations of previous epochs of jet ejection in various examples of
classical double radio sources namely (1) double-double radio galaxies by e.g.
Schoenmakers et al, (2) the double-double X-ray/radio galaxies by Laskar et al
and (3) the presence of a relic X-ray counter-jet in the prototypical classical
double radio galaxy, Cygnus A by Steenbrugge et al. The occurrence of
multi-episodic jet activity in powerful radio galaxies and quasars indicates
that they may have a longer lasting influence on the on-going structure
formation processes in their environs than previously presumed.Comment: Accepted by MNRAS; 6 page
Titania-doped tantala/silica coatings for gravitational-wave detection
Reducing thermal noise from optical coatings is crucial to reaching the required sensitivity in next generation interferometric gravitational-wave detectors. Here we show that adding TiO2 to Ta2O5 in Ta2O5/SiO2 coatings reduces the internal friction and in addition present data confirming it reduces thermal noise. We also show that TiO2-doped Ta2O5/SiO2 coatings are close to satisfying the optical absorption requirements of second generation gravitational-wave detectors
Young Planetary Nebulae: Hubble Space Telescope Imaging and a New Morphological Classification System
Using Hubble Space Telescope images of 119 young planetary nebulae, most of
which have not previously been published, we have devised a comprehensive
morphological classification system for these objects. This system generalizes
a recently devised system for pre-planetary nebulae, which are the immediate
progenitors of planetary nebulae (PNs). Unlike previous classification studies,
we have focussed primarily on young PNs rather than all PNs, because the former
best show the influences or symmetries imposed on them by the dominant physical
processes operating at the first and primary stage of the shaping process.
Older PNs develop instabilities, interact with the ambient interstellar medium,
and are subject to the passage of photoionization fronts, all of which obscure
the underlying symmetries and geometries imposed early on. Our classification
system is designed to suffer minimal prejudice regarding the underlying
physical causes of the different shapes and structures seen in our PN sample,
however, in many cases, physical causes are readily suggested by the geometry,
along with the kinematics that have been measured in some systems. Secondary
characteristics in our system such as ansae indicate the impact of a jet upon a
slower-moving, prior wind; a waist is the signature of a strong equatorial
concentration of matter, whether it be outflowing or in a bound Keplerian disk,
and point symmetry indicates a secular trend, presumably precession, in the
orientation of the central driver of a rapid, collimated outflow.Comment: (to appear in The Astronomical Journal, March 2011.) The quality of
the figures as it appears in the arXiv pdf output is not up-to-par; the full
ms with high-quality figures is available by anonymous FTP at
ftp://ftp.astro.ucla.edu/pub/morris/sahai_AJ_360163.pd
Is There an Upper Limit to Genome Size?
O.H. was supported by the Marie SkĆodowska Curie Action Individual Fellowship program (CAPITULA, grant agreement 657918
Quantum state preparation and macroscopic entanglement in gravitational-wave detectors
Long-baseline laser-interferometer gravitational-wave detectors are operating
at a factor of 10 (in amplitude) above the standard quantum limit (SQL) within
a broad frequency band. Such a low classical noise budget has already allowed
the creation of a controlled 2.7 kg macroscopic oscillator with an effective
eigenfrequency of 150 Hz and an occupation number of 200. This result, along
with the prospect for further improvements, heralds the new possibility of
experimentally probing macroscopic quantum mechanics (MQM) - quantum mechanical
behavior of objects in the realm of everyday experience - using
gravitational-wave detectors. In this paper, we provide the mathematical
foundation for the first step of a MQM experiment: the preparation of a
macroscopic test mass into a nearly minimum-Heisenberg-limited Gaussian quantum
state, which is possible if the interferometer's classical noise beats the SQL
in a broad frequency band. Our formalism, based on Wiener filtering, allows a
straightforward conversion from the classical noise budget of a laser
interferometer, in terms of noise spectra, into the strategy for quantum state
preparation, and the quality of the prepared state. Using this formalism, we
consider how Gaussian entanglement can be built among two macroscopic test
masses, and the performance of the planned Advanced LIGO interferometers in
quantum-state preparation
Searching for a Stochastic Background of Gravitational Waves with LIGO
The Laser Interferometer Gravitational-wave Observatory (LIGO) has performed
the fourth science run, S4, with significantly improved interferometer
sensitivities with respect to previous runs. Using data acquired during this
science run, we place a limit on the amplitude of a stochastic background of
gravitational waves. For a frequency independent spectrum, the new limit is
. This is currently the most sensitive
result in the frequency range 51-150 Hz, with a factor of 13 improvement over
the previous LIGO result. We discuss complementarity of the new result with
other constraints on a stochastic background of gravitational waves, and we
investigate implications of the new result for different models of this
background.Comment: 37 pages, 16 figure
Recommended from our members
Pre- and Post-entry, Descent and Landing Assessment of the Martian Atmosphere for the Mars 2020 Rover
This review provides an analysis of activities undertaken by the Mars 2020 Council of Atmospheres (CoA) in support of the entry, descent, and landing (EDL) of the Mars 2020 rover Perseverance in Jezero crater, Mars. The activities of the CoA were designed to evaluate the safety of early-stage landing site candidates and, later, to constrain the range of plausible conditions expected at Jezero crater during the early northern spring season of EDL, following the successful blueprint of similar councils for prior landed Mars missions. The multiyear effort of the CoA involved using a combination of numerical modeling of the local Martian atmosphere with limited-domain mesoscale models and atmospheric reanalysis using data assimilation techniques, along with atmospheric observations from multiple orbiting assets, to generate an atmospheric âforecastâ for the day of landing. Here we present an overview of these activities, focusing in greater detail on those elements that depart from prior CoA activities as performed for Mars Phoenix, Mars Science Laboratory, and the InSight lander. Following the successful landing of Perseverance on 2021 February 18, reconstruction and reassessment activities were performed and are presented here, comparing prelanding predictions with actual, as-flown conditions
Serotonin inhibits axonal regeneration of identifiable descending neurons after a complete spinal cord injury in lampreys
Classical neurotransmitters are mainly known for their roles as neuromodulators, but they also play important roles in the control of developmental and regenerative processes. Here, we used the lamprey model of spinal cord injury to study the effect of serotonin in axon regeneration at the level of individually identifiable descending neurons. Pharmacological and genetic manipulations after a complete spinal cord injury showed that endogenous serotonin inhibits axonal regeneration in identifiable descending neurons through the activation of serotonin 1A receptors and a subsequent decrease in cyclic adenosine monophosphate (cAMP) levels. RNA sequencing revealed that changes in the expression of genes that control axonal guidance could be a key factor determining the serotonin effects during regeneration. This study provides new targets of interest for research in non-regenerating mammalian models of traumatic central nervous system injuries and extends the known roles of serotonin signalling during neuronal regeneration.
This article has an associated First Person interview with the first author of the paper
Evidence for Extended Hydrogen-Poor CSM in the Three-Peaked Light Curve of Stripped Envelope Ib Supernova
We present multi-band ATLAS photometry for SN 2019tsf, a stripped-envelope
Type Ib supernova (SESN). The SN shows a triple-peaked light curve and a late
(re-)brightening, making it unique among stripped-envelope systems. The
re-brightening observations represent the latest photometric measurements of a
multi-peaked Type Ib SN to date. As late-time photometry and spectroscopy
suggest no hydrogen, the potential circumstellar material (CSM) must be H-poor.
Moreover, late (>150 days) spectra show no signs of narrow emission lines,
further disfavouring CSM interaction. On the contrary, an extended CSM
structure is seen through a follow-up radio campaign with Karl G. Jansky Very
Large Array (VLA), indicating a source of bright optically thick radio emission
at late times, which is highly unusual among H-poor SESNe. We attribute this
phenomenology to an interaction of the supernova ejecta with
spherically-asymmetric CSM, potentially disk-like, and we present several
models that can potentially explain the origin of this rare Type Ib supernova.
The warped disc model paints a novel picture, where the tertiary companion
perturbs the progenitors CSM, that can explain the multi-peaked light curves of
SNe, and here we apply it to SN 2019tsf. This SN 2019tsf is likely a member of
a new sub-class of Type Ib SNe and among the recently discovered class of SNe
that undergo mass transfer at the moment of explosionComment: 23 pages, Comments are welcome, Submitted to Ap
Biological membranes in EV biogenesis, stability, uptake, and cargo transfer: an ISEV position paper arising from the ISEV membranes and EVs workshop
Paracrine and endocrine roles have increasingly been ascribed to extracellular vesicles (EVs) generated by multicellular organisms. Central to the biogenesis, content, and function of EVs are their delimiting lipid bilayer membranes. To evaluate research progress on membranes and EVs, the International Society for Extracellular Vesicles (ISEV) conducted a workshop in March 2018 in Baltimore, Maryland, USA, bringing together key opinion leaders and hands-on researchers who were selected on the basis of submitted applications. The workshop was accompanied by two scientific surveys and covered four broad topics: EV biogenesis and release; EV uptake and fusion; technologies and strategies used to study EV membranes; and EV transfer and functional assays. In this ISEV position paper, we synthesize the results of the workshop and the related surveys to outline important outstanding questions about EV membranes and describe areas of consensus. The workshop discussions and survey responses reveal that while much progress has been made in the field, there are still several concepts that divide opinion. Good consensus exists in some areas, including particular aspects of EV biogenesis, uptake and downstream signalling. Areas with little to no consensus include EV storage and stability, as well as whether and how EVs fuse with target cells. Further research is needed in these key areas, as a better understanding of membrane biology will contribute substantially towards advancing the field of extracellular vesicles.Fil: Russell, Ashley E.. University Johns Hopkins; Estados UnidosFil: Sneider, Alexandra. University Johns Hopkins; Estados UnidosFil: Witwer, Kenneth W.. University Johns Hopkins; Estados UnidosFil: Bergese, Paolo. UniversitĂ Degli Studi Di Brescia; ItaliaFil: Bhattacharyya, Suvendra N.. Indian Institute of Chemical Biology; IndiaFil: Cocks, Alexander. Cardiff University; Reino UnidoFil: Cocucci, Emanuele. Ohio State University; Estados UnidosFil: ErdbrĂŒgger, Uta. University of Virginia; Estados UnidosFil: Falcon Perez, Juan M.. Ikerbasque Basque Foundation for Science; EspañaFil: Freeman, David W.. National Institute On Aging National Institute for Helth ; Estados UnidosFil: Gallagher, Thomas M.. Loyola University Of Chicago; Estados UnidosFil: Hu, Shuaishuai. Technological University Dublin; IrlandaFil: Huang, Yiyao. University Johns Hopkins; Estados Unidos. Southern Medical University; ChinaFil: Jay, Steven M.. University of Maryland; Estados UnidosFil: Kano, Shin-ichi. The University of Alabama at Birmingham School of Medicine; Estados UnidosFil: Lavieu, Gregory. Institut Curie; FranciaFil: Leszczynska, Aleksandra. University of California at San Diego; Estados UnidosFil: Llorente, Alicia M.. Oslo University Hospital; NoruegaFil: Lu, Quan. Harvard University. Harvard School of Public Health; Estados UnidosFil: Mahairaki, Vasiliki. University Johns Hopkins; Estados UnidosFil: Muth, Dillon C.. University Johns Hopkins; Estados UnidosFil: Noren Hooten, Nicole. National Institute On Aging National Institute for Helth ; Estados UnidosFil: Ostrowski, Matias. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones BiomĂ©dicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones BiomĂ©dicas en Retrovirus y Sida; ArgentinaFil: Prada, Ilaria. Consiglio Nazionale delle Ricerche; ItaliaFil: Sahoo, Susmita. Icahn School of Medicine at Mount Sinai ; Estados UnidosFil: SchĂžyen, Tine Hiorth. Uit The Arctic University Of Norway; Noruega. University Johns Hopkins; Estados UnidosFil: Sheng, Lifuy. University of Washington. School of Medicine; Estados UnidosFil: Tesch, Deanna. Shaw University; Estados UnidosFil: Van Niel, Guillaume. No especifĂca;Fil: Vandenbroucke, Roosmarijn E.. University of Ghent; BĂ©lgicaFil: Verweij, Frederik J.. No especifĂca;Fil: Villar, Ana V.. Universidad de Cantabria; EspañaFil: Wauben, Marca. University of Utrecht; PaĂses BajosFil: Wehman, Ann M.. UniversitĂ€t WĂŒrzburg; AlemaniaFil: Ardavan, Arzhang. Peking University; ; ChinaFil: Carter, David Raul Francisco. Oxford Brookes University; Reino UnidoFil: Vader, Pieter. University Medical Center Utrecht; PaĂses Bajo
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