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Articles de revues sur le sujet "Pulsars: individual"
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Fierro, J. M., Z. Arzoumanian, M. Bailes, J. F. Bell, D. L. Bertsch, K. T. S. Brazier, J. Chiang et al. « EGRET High-Energy gamma -Ray Pulsar Studies. II. Individual Millisecond Pulsars ». Astrophysical Journal 447 (juillet 1995) : 807. http://dx.doi.org/10.1086/175919.
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Manchester, R. N. « Finding Pulsars at Parkes ». Publications of the Astronomical Society of Australia 18, no 1 (2001) : 1–11. http://dx.doi.org/10.1071/as01002.
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AbstractThere are many reasons why it is important to increase the number of known pulsars. Not only do pulsar searches continue to improve statistical estimates of, for example, pulsar birthrates, lifetimes and the Galactic distribution, but they continue to turn up interesting and, in some cases, unique individual pulsars. In the early days of pulsar astronomy, the Molonglo radio telescope led the world as a pulsar detection instrument. However, the Parkes radio telescope, with its frequency versatility and greater tracking ablility, combined with sensitive receivers and powerful computer detection algorithms, is now the world’s most successful telescope at finding pulsars. The Parkes multibeam survey, begun in 1997, by itself will come close to doubling the number of known pulsars. Parkes has also been very successful at finding millisecond pulsars (MSPs), especially in globular clusters. One third of the known MSPs have been found in just one cluster, 47 Tucanae.
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Lynch, Ryan S. « The hunt for new pulsars with the Green Bank Telescope ». Proceedings of the International Astronomical Union 8, S291 (août 2012) : 41–46. http://dx.doi.org/10.1017/s1743921312023113.
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AbstractThe Green Bank Telescope (GBT) is the largest fully steerable radio telescope in the world and is one of our greatest tools for discovering and studying radio pulsars. Over the last decade, the GBT has successfully found over 100 new pulsars through large-area surveys. Here I discuss the two most recent—the GBT 350 MHz Drift-scan survey and the Green Bank North Celestial Cap survey. The primary science goal of both surveys is to find interesting individual pulsars, including young pulsars, rotating radio transients, exotic binary systems, and especially bright millisecond pulsars (MSPs) suitable for inclusion in Pulsar Timing Arrays, which are trying to directly detect gravitational waves. These two surveys have combined to discover 85 pulsars to date, among which are 14 MSPs and many unique and fascinating systems. I present highlights from these surveys and discuss future plans. I also discuss recent results from targeted GBT pulsar searches of globular clusters and Fermi sources.
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Wu, Xinji, et Wen Xu. « A Determination of Pulsar Emission Geometry from Polarization Observations ». International Astronomical Union Colloquium 128 (1992) : 400–403. http://dx.doi.org/10.1017/s0002731600155623.
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AbstractOne of the important problems in pulsar studies is to determine the magnetic inclination angle α, the intrinsic width of the radiation beam (2ρ) and the angle (α + β) between the observer's direction and the rotation axis. In this paper we solve this problem for individual pulses by using the observed pulse width (2Δ𝜙), the swing of polarization angle (2Δψ), and its central gradient (dψ/d𝜙)max.From the polar cap model we establish three basic geometrical relations, a complete set of equations from which explicit solutions can be obtained using the observed data. This is the first time that the orientation of pulsar emission is solved analytically solely on the basis of a geometrical model. However, the results are shown to be sensitively connected to the polarization-angle swing (2Δψ), which is not well measured for most pulsars. So the number of pulsars to which our method can be applied is limited. The importance of the measurement of Δψ is seen from our method. To ensure the credibility of our results, we have discussed the conditions to be satisfied by all reliable pulsar measurements. Our method is shown to be more favorable for pulsars with large pulse width 2Δ𝜙, large central gradient (dψ/d𝜙)max and large magnetic inclination angle α. Out of 120 pulsars (from Lyne and Manchester 1988), 40 are solvable, and 7 are believed to be reliable. We discuss our method for the determination of pulsar geometry in comparison with other methods.
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Suleymanova, S. A., V. A. Izvekova et V. D. Pugachev. « Individual Pulse Polarization of Pulsars at Low Frequencies ». International Astronomical Union Colloquium 160 (1996) : 257–60. http://dx.doi.org/10.1017/s0252921100041646.
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AbstractThis paper presents the results of the measurements of linear polarization characteristics of individual pulses at frequencies 40, 60 and 103 MHz for 10 strong pulsars. We have measured total intensity, linear polarization percentage and angle along the pulse window and obtained distribution displays for these data.Two orthogonal polarization modes are common features in the radiation of pulsars at low frequency. The energy ratio of these two modes can change significantly between different frequencies. The linear polarisation percentage has a general tendency to increase at low frequencies, but by very different factors for different components of the integrated intensity profile. The relationship between the polarization properties of PSR 0943+10 and its mode changing behaviour was studied. It is shown that the energy ratio and the frequency of occurence of two polarization modes change simultaneously with changes in the integrated intensity profile.
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Joshi, B. C., M. Kramer, A. G. Lyne, M. A. McLaughlin et I. H. Stairs. « Giant Pulses in Millisecond Pulsars ». Symposium - International Astronomical Union 218 (2004) : 319–20. http://dx.doi.org/10.1017/s0074180900181252.
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Giant pulses (GPs), occasional individual pulses with an intensity 100 times the average intensity, have been detected in four pulsars to date. Their origin is not well understood, but studies suggest a connection between the strength of magnetic field at the light cylinder Blc and the existence of GPs. Here, we report on detection of significant Large Amplitude Pulses (LAPs) in two more pulsars with high values of Blc, PSRs J0218+4232 and B1957+20, observed using Giant Meterwave Radio Telescope (GMRT).
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Nowakowski, Leszek A. « Finding Pulsar Emission Heights from Dual–Frequency Observations ». International Astronomical Union Colloquium 177 (2000) : 219–20. http://dx.doi.org/10.1017/s0252921100059510.
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AbstractWe present a method that allows to find the radial separation of regions emitting individual components of pulsar average profiles at two radio frequencies. It may also be used for single–frequency observations in pulsars that have intensity–dependent average profiles and/or mode–switching. Preliminary results for three radio pulsars are presented, obtained using average profiles from non-simultaneous observations.
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Basu, A., B. Shaw, D. Antonopoulou, M. J. Keith, A. G. Lyne, M. B. Mickaliger, B. W. Stappers, P. Weltevrede et C. A. Jordan. « The Jodrell bank glitch catalogue : 106 new rotational glitches in 70 pulsars ». Monthly Notices of the Royal Astronomical Society 510, no 3 (25 novembre 2021) : 4049–62. http://dx.doi.org/10.1093/mnras/stab3336.
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ABSTRACT Pulsar glitches are rapid spin-up events that occur in the rotation of neutron stars, providing a valuable probe into the physics of the interiors of these objects. Long-term monitoring of a large number of pulsars facilitates the detection of glitches and the robust measurements of their parameters. The Jodrell Bank pulsar timing programme regularly monitors more than 800 radio pulsars and has accrued, in some cases, over 50 yr of timing history on individual objects. In this paper, we present 106 new glitches in 70 radio pulsars as observed up to the end of 2018. For 70 per cent of these pulsars, the event we report is its only known glitch. For each new glitch, we provide measurements of its epoch, amplitude, and any detected changes to the spin-down rate of the star. Combining these new glitches with those listed in the Jodrell Bank glitch catalogue, we analyse a total sample of 543 glitches in 178 pulsars. We model the distribution of glitch amplitudes and spin-down rate changes using a mixture of two Gaussian components. We corroborate the known dependence of glitch rate and activity on pulsar spin-down rates and characteristic ages, and show that younger pulsars tend to exhibit larger glitches. Pulsars with spin-down rates between 10−14 and 10−10.5 Hz s−1 show a mean reversal of 1.8 per cent of their spin-down as a consequence of glitches. Our results are qualitatively consistent with the superfluid vortex unpinning models of pulsar glitches.
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Lu, T., P. C. Zhu et J. S. Kui. « Does the Radio Luminosity of Pulsar Grow up in its Later Stage ? » Symposium - International Astronomical Union 125 (1987) : 50. http://dx.doi.org/10.1017/s007418090016036x.
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In usual statistical analyses, because of diversities of proper parameters of pulsars, some interesting features might be smeared. In order to remove these diversities, we use the mean values for all quantities of pulsars, instead of values of individual pulsar, to do statistical analyses. logP/P3 - log τ and logL - logτ have been plotted, here τ P/2P and L denote the characteristic time scale and the radio luminosity of pulsars respectively. The most striking feature is that after its initial dropping to a dip at about τ∼106 yrs, the radio luminosity of pulsar appears to grow up evidently and then redrop again. This feature is difficult to be understood in usual models. However, two tentative interpretations have been given in this paper.
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Hobbs, George. « Pulsars and Gravitational Wave Detection ». Publications of the Astronomical Society of Australia 22, no 3 (2005) : 179–83. http://dx.doi.org/10.1071/as04063.
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AbstractThe number of known millisecond pulsars has dramatically increased in the last few years. Regular observations of these pulsars may allow gravitational waves with frequencies ∼10−9 Hz to be detected. A ‘pulsar timing array’ is therefore complimentary to other searches for gravitational waves using ground-based or space-based interferometers that are sensitive to much higher frequencies. In this review we describe (1) the basic methods for using an array of pulsars as a gravitational wave detector, (2) the sources of the potentially detectable waves, (3) current limits on individual sources and a stochastic background, and (4) the new project recently started using the Parkes radio telescope.
Thèses sur le sujet "Pulsars: individual"
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PAPITTO, ALESSANDRO. « Analysis of the rotational behaviour and evolutionary scenarios of Accreting Millisecond Pulsars ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/812.
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In questo studio viene presentata un'analisi
dell'evoluzione rotazionale ed orbitale delle Pulsar X al millisecondo (AMSP). Queste sorgenti sono delle stelle di neutroni (NS) che emettono energia in raggi X accrescendo la materia trasferita da una stella compagna, tramite un disco di accrescimento. Poichè le AMSP poseggono una magnetosfera che interrompe il flusso di materia nel disco prima della superficie, concentrando l'accrescimento nelle vicinanze dei poli magnetici, l'emissione X è pulsata al periodo di rotazione della stella, che è di qualche millisecondo per una AMSP.
Il mio progetto di ricerca si basa sull'utilizzo di questa proprietà fondamentale per valutare la reazione della NS all'accrescimento di materia. Infatti le particelle di un disco di accrescimento posseggono un elevato momento angolare specifico, specialmente nelle vicinanze della NS; quando la materia viene accresciuta il suo momento angolare viene rilasciato alla stella, che tende quindi ad accellerare. E' proprio questo meccanismo che ha condotto le AMSP alla estrema velocità di rotazione attuale (un decimo della velocità della luce). Avendo a disposizione un tale orologio solidale alla stella, ho utilizzato le pulsazioni X provenienti dalla superficie per misurare le piccole variazioni della frequenza di rotazione della NS mentre accresce massa. Se ne trae quindi una misura delle coppie che agiscono su di essa e la stima delle grandezze che le regolano, principalmente il tasso di accrescimento di massa e l'intensità del campo magnetico della NS.
Tali misure sono estremamente delicate, specialmente nel caso delle AMSP. Infatti queste sorgenti accrescono massa al più per qualche mese ed, a causa dell'elevata inerzia di una NS, la variazione di frequenza attesa è solamente di poche parti su dieci miliardi. Innanzi tutto le tecniche standard di timing sono state quindi adattate al caso particolare di questi oggetti, permettendo per la prima volta una misura affidabile del loro stato rotazionale. Sono state prese in considerazione sei delle dieci AMSP scoperte sin ora. In particolare, le due alle quali mi sono dedicato maggiormente mostrano adeguatamente come il semplice schema di accellerazione della NS delineato sopra non valga in ogni caso, e come una AMSP possa anche decelerare durante l'accrescimento. La causa di tale decelerazione è individuata dalla teoria dell'accrescimento nell'interazione tra il campo magnetico e il disco di accrescimento, interazione che può quindi rallentare la stella specialmente se questa ruota molto rapidamente. In questo lavoro mostro come questi rallentamenti vengono effettivamente osservati e come consentano di ottenere stime del campo magnetico della NS.
Gli elementi basilari delle teorie dell'accrescimento su un rotatore veloce sono stati testati non solo sulla base dei risultati dell'analisi temporale. Si mostra infatti come le attese teoriche siano supportate anche alla luce dell'informazione spettrale. In particolare l'osservazione di una AMSP mostra la presenza di una riga del ferro molto larga nel suo spettro in raggi X. Essendo la regione interna del disco di accrescimento l'unica possibile regione di formazione di una riga così larga, è stato possibile misurare, per la prima volta nel caso di una pulsar, l'estensione del bordo interno del disco. Il valore misurato è perfettamente in accordo con il ristretto intervallo permesso dalla teoria, rappresentando così una verifica fondamentale della sua consistenza.
L'analisi temporale consente inoltre di valutare l'evoluzione orbitale del sistema binario al quale appartiene la NS. Nell'unico caso di un sistema che abbia mostrato più di un episodio di attività, si è trovata evidenza di una evoluzione molto più rapida di quella attesa. Questo comportamento può essere spiegato solo in termini di rilevanti perdite di massa, massa che porta con sé la quantità di momento angolare necessaria per rendere conto dell'evoluzione misurata. Ciò supporta inoltre l'ipotesi che tali perdite di massa siano dovute all'accensione di una pulsar alimentata dalla rotazione durante le sue fasi di quiete del sistema. Questo può in definitiva essere considerato uno dei pochi casi astrofisici in cui viene osservata in tempo reale un'evoluzione altamente non conservativa.
I risultati presentati in questa tesi coprono quindi molti aspetti della fisica di questi sistemi, mostrando come l'unione dell'analisi temporale e spettrale possa fornire una gran quantità di informazioni su questi sistemi estremi e per certi versi sconcertanti. In definitiva sono state confermate le attese teoriche di base sull'accrescimento su NS veloci, ma si aprono anche diverse questioni che promettono di gettare maggiore luce sulla fisica dell'ambiente immediatamente circostante la stella e sull'effettiva linea evolutiva delle AMSP.I present in this study an analysis of the spin and orbital evolution of Accreting Millisecond Pulsars (AMSP). These sources are neutron stars (NS) emitting X-rays because of the accretion of mass transferred by a nearby companion star through an accretion disc. As AMSP owns a magnetosphere that truncates the disc before the NS, thus channelling accreted matter in the vicinity of the magnetic poles, their X-ray emission is pulsed at the NS spin period, which is of few milliseconds in an AMSP. My scientific project relies on the use this invaluable property to evaluate the rotational reaction of the NS to the accretion of mass. As a matter of fact, mass orbiting in an accretion disc has a large specific angular momentum especially close to the NS; when this matter is accreted, it releases its angular momentum to the NS that is therefore expected to accelerate. It is indeed through this mechanism that AMSP have been spun up to their extreme rotational velocities (up to 0.1 times the speed of light in vacuum). I therefore used the X-ray pulsations coming from the NS surface as a clock to precisely measure the tiny variations of the accretor spin frequency as it accretes. This is ultimately a measure of the accretion torques acting on the NS and allows a model dependent estimate of the physical quantities regulating these torques, mainly the rate at which mass is accreted on the NS and the magnetic field straight. Such measurements can be very tricky especially for AMSP. They accrete mass for at most few months, and because of to the large inertia of a NS, the expected frequency variations are of only few parts on ten billions. Standard timing techniques were therefore first tailored to the particular case of these sources, allowing for the first time reliable estimates of their spin state. Six among the ten AMSP discovered so far are considered in this work. In particular, the two sources I focused on the most show how the simple picture of the NS spin-up outlined above does not hold in every case, as the outcome of the accretion can also be the deceleration of the NS. The reason for this behaviour is interpreted by the accretion theory in terms of the interaction between the magnetic field and the accretion disc. This interaction may then brake of the compact object especially if it is very fast. I show in this work how these spin-down are effectively observed and how this allows an estimate of the NS magnetic field. The basics of the accretion picture onto a fast object are tested not only on the basis of a temporal analysis. I show in fact how the spectral information also supports the theoretical expectations. In particular a high spectral resolution observation of a AMSP shows the presence of a broadened iron line in its X-ray spectrum. The only viable location for the formation of a line so broadened is the inner part of the accretion disc, thus allowing for the first time the measure of the size of the inner disc rim of a pulsar. This measure is perfectly consistent with the small range allowed by theory, thus representing a fundamental test of their consistency. Temporal analysis also allows to enlighten the evolution of the binary system the NS belongs to. In the only case of a system which recurred more than once, we could find evidence of a faster than expected evolution. We interpret such behaviour as an indication of relevant mass lost which carries away the angular momentum needed to match the observations. This supports the hypothesis that a rotation powered pulsar switches on during the quiescent phases of the binary. Moreover, this observation can be considered as one of the few astrophysical cases in which a highly non conservative evolution was directly observed. The results presented in this thesis cover many aspects of the physics of these fast accretors, and show how X-ray temporal and spectral analysis can jointly supply a wealth of information on the physical state of these extreme and puzzling systems. These results confirm the basic theoretical expectations but open also several issues which are very promising to shed some light in particular on the environment surrounding these fast rotating NS and on their actual evolutionary progeny.
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RIGOSELLI, MICHELA. « X-ray emission from the magnetic polar caps of old rotation-powered pulsars ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/277373.
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Le stelle di neutroni sono il risultato dell'evoluzione di stelle massive dopo l'esplosione di supernova. Il progetto di questa Tesi di PhD consiste nello studio dell'emissione di raggi X da parte di stelle di neutroni isolate di età superiore a 100000 anni. Sono stati analizzati dati provenienti dal satellite XMM-Newton (ESA). Per estrarre la miglior informazione possibile dai dati, ho implementato un metodo di maximum likelihood (ML) e l'ho utilizzato per estrarre spettri e profili pulsati di pulsar vecchie in banda X, che poi sono stati analizzati con raffinati di emissione.
La Tesi è strutturata come segue: nei primi tre capitoli illustro le proprietà principali delle stelle di neutroni, con particolare attenzione ai processi termici e non termici che producono raggi X. I raggi X non termici sono prodotti da particelle relativistiche accelerate da campi elettromagnetici; una frazione di queste particelle viene accelerata verso la superficie della stella, e riscalda le zone delle calotte polari magnetiche. La componente termica, che può essere prodotta dall'intera superficie o da una parte, viene solitamente descritta come un corpo nero; tuttavia, la presenza di intensi campi magnetici superficiali influenza le proprietà della materia, e la radiazione emessa è ampiamente anisotropa.
Nel Capitolo 4 descrivo come ho generato spettri e profili pulsati sintetici, utilizzando modelli di emissione che considerano calotte polari ricoperte di un'atmosfera di idrogeno magnetizzata. Mi sono basata su un software esistente che, dato un certo set di parametri relativi alle proprietà fisiche della stella, stima l'intensità della radiazione prodotta. Successivamente, esso somma i contributi degli elementi di superficie che sono visibili all'osservatore alle differenti fasi di rotazione. Quindi, nel Capitolo 5 descrivo come ho implementato un software di analisi che si basa sul metodo di ML. Dato un certo modello, esso stima i parametri più probabili che ricostruiscono i dati osservati, nella fattispecie il numero di conteggi relativo alla sorgente e al background. Ho validato il metodo e dimostrato che esso è particolarmente efficace per sorgenti deboli, quali sono la maggior parte delle pulsar vecchie.
Successivamente, ho applicato i metodi finora descritti ad alcune pulsar vecchie. Nel Capitolo 6 riporto l'analisi di PSR J0726-2612, una pulsar radio che ha alcune delle caratteristiche delle XDINSs: un periodo di rotazione lungo, un intenso campo magnetico, ed emissione X termica. Grazie ad un'analisi congiunta dello spettro e del profilo pulsato, ho mostrato che la presenza di impulsi radio in PSR J0726-2612, così come la loro assenza nelle XDINSs, potrebbe essere dovuta ad un'orientazione differente rispetto all'osservatore. Nel Capitolo 7 presento il caso di PSR B0943+10, una pulsar con emissione X sia termica sia non termica ma che, nonostante sia un rotatore allineato, ha una grande frazione pulsata. Sono riuscita a riappacificare i due diversi aspetti grazie ad un'attenta analisi di ML e all'intrinseca anisotropia dell'emissione termica prodotta da un'atmosfera magnetizzata. Nel Capitolo 8 ho invece applicato il metodo di ML su sette pulsar poco brillanti, delle quali quattro avevano diverse analisi già pubblicate in letteratura, ma con risultati discordanti, mentre le altre tre non erano ancora state rivelate in banda X. Ho trovato tracce evidenti di emissione termica solo in due oggetti, più un accenno nello spettro pulsato di un terzo oggetto.
Infine, ho considerato tutte le pulsar vecchie che emettono raggi X termici e ho confrontato le misure di temperatura, raggio e luminosità alle aspettative dei modelli teorici. In particolare, ho scoperto che le aree di emissione sono generalmente in accordo con quelle previste dal modello di dipolo magnetico rotante, purché vengano considerati anche effetti di proiezione geometrica e modelli di emissione realistici, quali appunto i modelli di atmosfera magnetizzata.Neutron stars are the remnants of massive stars whose cores collapse during the supernova explosions. The project of this PhD Thesis consisted in the study of the X-ray emission from isolated neutron stars older than about 100000 years. The work was based mainly on data obtained with the XMM-Newton satellite (ESA). To extract the best possible information from the data, I implemented a maximum likelihood (ML) technique and used it to derive the X-ray spectra and pulse profiles of several old pulsars, that were then studied with state-of-the-art models of X-ray emission. The Thesis is structured as follows: in the first three chapters I outline the main properties of neutron stars, with a major focus on the thermal and nonthermal processes that produce X-rays. The nonthermal X-rays are produced by relativistic particles accelerated by rotation-induced electric fields and moving along the magnetic field lines. A fraction of these particles is accelerated backward and returns on the stellar surface, heating the magnetic polar caps. The thermal component, that can be produced by the whole stellar surface or by small hot spots, can be described, in a first approximation, by a blackbody. However, the presence of intense surface magnetic fields strongly affects the properties of matter, and the emergent radiation is widely anisotropic. In Chapter 4, I describe how I generated synthetic spectra and pulse profiles using thermal emission models that consider polar caps covered by a magnetized hydrogen atmosphere or with a condensed iron surface. I relied on an existing software that, given a set of stellar parameters, evaluates the emerging intensity of the radiation. A second software, which I adapted on the sources I analyzed in the Thesis, collects the contribution of surface elements which are in view at different rotation phases from a stationary observer. Then, in Chapter 5, I describe how I implemented an analysis software that relies on the ML method. It estimates the most probable number of source and background counts by comparing the spatial distribution of the observed counts with the expected distribution for a point source plus an uniform background. I demonstrated that the ML method is particularly effective for dim sources, as most old pulsars are. Subsequently, I applied the methods described above to some old pulsars. In Chapter 6, I report the analysis of PSR J0726-2612, a radio pulsars that shares some properties with the radio-silent XDINSs, as the long period, the high magnetic field, and the thermal X-ray emission from the cooling surface. Thanks to an in-depth analysis of the combined spectrum and pulse profile, I showed that the presence of radio pulses from PSR J0726-2612, as well as the absence from the XDINSs, might simply be due to different viewing geometries. In Chapter 7, I present the case of PSR B0943+10, a pulsar with a nonthermal and thermal X-ray spectrum but that, despite being an aligned rotator, has a large pulsed fraction. I could reconcile the two opposite properties analyzing with the ML the spectrum and the pulse profile, and considering the magnetic beaming of a magnetized atmosphere model, that well fits the thermal component. In Chapter 8, I applied the ML method to seven old and dim pulsars, of which four had controversial published results, and three were so far undetected. I found convincing evidence of thermal emission only in the phase-averaged spectrum of two of them, plus a hint for a thermal pulsed spectrum in a third object. Finally, I considered all the old thermal emitters and I compared their observed temperatures, radii and luminosities to the expectations of the current theoretical models for these objects. In particular, I found that the emitting area are generally in agreement with the polar cap regions evaluated in a dipole approximation, if the combined effects of geometry projections plus realistic thermal models (as the magnetic atmosphere) are taken into account.
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Venter, Christo. « Millisecond pulsars and pulsar wind nebulae as sources of gamma rays and cosmic rays / C. Venter ». Thesis, North-West University, 2008. http://hdl.handle.net/10394/2067.
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Bock, Douglas Carl-Johan. « Wide Field Aperture Synthesis Radio Astronomy ». University of Sydney. Physics, 1998. http://hdl.handle.net/2123/377.
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This thesis is focussed on the Molonglo Observatory Synthesis Telescope (MOST), reporting on two primary areas of investigation. Firstly, it describes the recent upgrade of the MOST to perform an imaging survey of the southern sky. Secondly, it presents a MOST survey of the Vela supernova remnant and follow-up multiwavelength studies. The MOST Wide Field upgrade is the most significant instrumental upgrade of the telescope since observations began in 1981. It has made possible the nightly observation of fields with area ~5 square degrees, while retaining the operating frequency of 843 MHz and the pre-existing sensitivity to point sources and extended structure. The MOST will now be used to make a sensitive (rms approximately 1 mJy/beam) imaging survey of the sky south of declination -30°. This survey consists of two components: an extragalactic survey, which will begin in the south polar region, and a Galactic survey of latitudes |b| < 10°. These are expected to take about ten years. The upgrade has necessitated the installation of 352 new preamplifiers and phasing circuits which are controlled by 88 distributed microcontrollers, networked using optic fibre. The thesis documents the upgrade and describes the new systems, including associated testing, installation and commissioning. The thesis continues by presenting a new high-resolution radio continuum survey of the Vela supernova remnant (SNR), made with the MOST before the completion of the Wide Field upgrade. This remnant is the closest and one of the brightest SNRs. The contrast between the structures in the central pulsar-powered nebula and the synchrotron radiation shell allows the remnant to be identified morphologically as a member of the composite class. The data are the first of a composite remnant at spatial scales comparable with those available for the Cygnus Loop and the Crab Nebula, and make possible a comparison of radio, optical and soft X-ray emission from the resolved shell filaments. The survey covers an area of 50 square degrees at a resolution of 43" x 60", while imaging structures on scales up to 30'. It has been used for comparison with Wide Field observations to evaluate the performance of the upgraded MOST. The central plerion of the Vela SNR (Vela X) contains a network of complex filamentary structures. The validity of the imaging of these filaments has been confirmed with Very Large Array (VLA) observations at 1.4 GHz. Unlike the situation in the Crab Nebula, the filaments are not well correlated with H-alpha emission. Within a few parsec of the Vela pulsar the emission is much more complex than previously seen: both very sharp edges and more diffuse emission are present. It has been postulated that one of the brightest filaments in Vela X is associated with the X-ray feature (called a `jet') which appears to be emanating from the region of the pulsar. However, an analysis of the MOST and VLA data shows that this radio filament has a flat spectral index similar to another more distant filament within the plerion, indicating that it is probably unrelated to the X-ray feature.
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Bock, Douglas Carl-Johan. « Wide Field Aperture Synthesis Radio Astronomy ». Thesis, The University of Sydney, 1997. http://hdl.handle.net/2123/377.
Texte intégralRésumé :
This thesis is focussed on the Molonglo Observatory Synthesis Telescope (MOST), reporting on two primary areas of investigation. Firstly, it describes the recent upgrade of the MOST to perform an imaging survey of the southern sky. Secondly, it presents a MOST survey of the Vela supernova remnant and follow-up multiwavelength studies. The MOST Wide Field upgrade is the most significant instrumental upgrade of the telescope since observations began in 1981. It has made possible the nightly observation of fields with area ~5 square degrees, while retaining the operating frequency of 843 MHz and the pre-existing sensitivity to point sources and extended structure. The MOST will now be used to make a sensitive (rms approximately 1 mJy/beam) imaging survey of the sky south of declination -30°. This survey consists of two components: an extragalactic survey, which will begin in the south polar region, and a Galactic survey of latitudes |b| < 10°. These are expected to take about ten years. The upgrade has necessitated the installation of 352 new preamplifiers and phasing circuits which are controlled by 88 distributed microcontrollers, networked using optic fibre. The thesis documents the upgrade and describes the new systems, including associated testing, installation and commissioning. The thesis continues by presenting a new high-resolution radio continuum survey of the Vela supernova remnant (SNR), made with the MOST before the completion of the Wide Field upgrade. This remnant is the closest and one of the brightest SNRs. The contrast between the structures in the central pulsar-powered nebula and the synchrotron radiation shell allows the remnant to be identified morphologically as a member of the composite class. The data are the first of a composite remnant at spatial scales comparable with those available for the Cygnus Loop and the Crab Nebula, and make possible a comparison of radio, optical and soft X-ray emission from the resolved shell filaments. The survey covers an area of 50 square degrees at a resolution of 43" x 60", while imaging structures on scales up to 30'. It has been used for comparison with Wide Field observations to evaluate the performance of the upgraded MOST. The central plerion of the Vela SNR (Vela X) contains a network of complex filamentary structures. The validity of the imaging of these filaments has been confirmed with Very Large Array (VLA) observations at 1.4 GHz. Unlike the situation in the Crab Nebula, the filaments are not well correlated with H-alpha emission. Within a few parsec of the Vela pulsar the emission is much more complex than previously seen: both very sharp edges and more diffuse emission are present. It has been postulated that one of the brightest filaments in Vela X is associated with the X-ray feature (called a `jet') which appears to be emanating from the region of the pulsar. However, an analysis of the MOST and VLA data shows that this radio filament has a flat spectral index similar to another more distant filament within the plerion, indicating that it is probably unrelated to the X-ray feature.
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Yukita, M., A. Ptak, A. E. Hornschemeier, D. Wik, T. J. Maccarone, K. Pottschmidt, A. Zezas et al. « Identification of the Hard X-Ray Source Dominating the E > ; 25 keV Emission of the Nearby Galaxy M31 ». IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623858.
Texte intégralRésumé :
We report the identification of a bright hard X-ray source dominating the M31 bulge above 25 keV from a simultaneous NuSTAR-Swift observation. We find that this source is the counterpart to Swift J0042.6+4112, which was previously detected in the Swift BAT All-sky Hard X-ray Survey. This Swift BAT source had been suggested to be the combined emission from a number of point sources; our new observations have identified a single X-ray source from 0.5 to 50 keV as the counterpart for the first time. In the 0.5-10 keV band, the source had been classified as an X-ray Binary candidate in various Chandra and XMM-Newton studies; however, since it was not clearly associated with Swift J0042.6+4112, the previous E < 10 keV observations did not generate much attention. This source has a spectrum with a soft X-ray excess (kT similar to 0.2 keV) plus a hard spectrum with a power law of Gamma similar to 1 and a cutoff around 15-20 keV, typical of the spectral characteristics of accreting pulsars. Unfortunately, any potential pulsation was undetected in the NuSTAR data, possibly due to insufficient photon statistics. The existing deep HST images exclude high-mass (> 3 M-circle dot) donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass (< 3 M-circle dot) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.
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Venter, Christo. « The effect of general relativistic frame dragging on millisecond pulsar visibility for the H.E.S.S. telescope / C. Venter ». Thesis, North-West University, 2004. http://hdl.handle.net/10394/215.
Texte intégralRésumé :
It has been noted by several authors that General Relativistic frame dragging in rotating
neutron stars is a first order effect which has to be included in a self-consistent model of pulsar
magnetospheric structure and associated radiation and transport processes. To this end, I
undertook the present study with the aim of investigating the effect of General Relativity
(GR) on millisecond pulsar (MSP) visibility.
I developed a numerical code for simulating a pulsar magnetosphere, incorporating the
GR-corrected expressions for the electric potential and field. I included curvature radiation
(CR) due to primary electrons accelerated above the stellar surface, as well as inverse Compton
scattering (ICS) of thermal X-ray photons by these electrons. I then applied the model to
PSR J0437-4715, a prime candidate for testing the GR-Electrodynamic theory, and examined
its visibility for the H.E.S.S. telescope. I also considered the question of whether magnetic
photon absorption would take place for this particular pulsar. In addition, I developed a
classical model for comparison with the GR results.
I found that the typical electron energies and associated CR photon energies are functions
of position above the polar cap (PC). These energies are also quite smaller in the GR case
than in the classical case due to the different functional forms of the GR and classical electric
fields. I found the CR energy cut-off to be ~ 4 GeV compared to the well-known classical
value of ~ 100 GeV. Since the H.E.S.S. energy threshold is ~ 100 GeV, it seems as though
the CR component will not be visible, contrary to wide-held opinion. However, the ICS
component seems to be well in excess of the H.E.S.S. energy threshold and is expected to be
visible. I also found that no pair production will take place for PSR J0437-4715.
Hopefully, forthcoming H.E.S.S. observations will provide validation of these results.
KEY WORDS: General relativistic frame dragging, GR electrodynamics, millisecond pulsar
visibility, non-thermal radiation processes, pair production, H.E.S.S., individual pulsars:
PSR J0437-4715.Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.
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Füßling, Matthias. « Search for VHE gamma-ray emission from the direction of the two millisecond pulsars PSR J0437-4715 and PSR J1824-2452 and the composite supernova remnant Kes 75 with H.E.S.S ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16852.
Texte intégralRésumé :
Diese Arbeit berichtet über die Suche nach gepulster und ungepulster hochenergetischer (VHE) Gammastrahlung mit dem High Energy Stereoscopic System (H.E.S.S.) im Energiebereich von 100 GeV bis 100 TeV von drei Pulsaren. Gepulste VHE Gammastrahlung wurde bisher nur fuer den jungen Krebspulsar gefunden. Eine besondere Gruppe von Pulsarwindnebeln (PWN) sind die zusammengesetzten Supernovaüberreste (SNR), bei denen sich ein PWN im Zentrum einer expandierenden SNR Schale befindet. Die Resultate der Suche nach gepulster und ungepulster VHE Gammastrahlung von zwei Millisekundenpulsaren, PSR J0437-4715 und PSR J1824-2452, werden im ersten Teil dieser Arbeit vorgestellt. Teile der Beobachtungen wurden in einer speziellen Triggerkonfiguration (dem Topologischen Trigger mit konvergenter Ausrichtung) durchgeführt, um die Energieschwelle des Instruments zu senken. Kein Hinweis auf gepulste oder ungepulste Emission wurde gefunden und obere Grenzen auf den gepulsten und ungepulsten Fluss wurden bestimmt. Die oberen Grenzen auf den gepulsten Fluss werden mit bestehenden Modellvorhersagen verglichen und erlauben für PSR J1824-2452 den Bereich möglicher Geometrien in einigen Modellen einzuschränken. Die Resultate der Suche nach gepulster und ungepulster VHE Gammastrahlung aus der Richtung des zusammengesetzten SNR Kes 75 werden im zweiten Teil dieser Arbeit präsentiert. Der PWN im Zentrum von Kes 75 wird von einem sehr jungen und energiereichen Pulsar, PSR J1846-0258, angetrieben, der ein aussergewöhnlich starkes Magnetfeld besitzt. Während kein Hinweis auf gepulste Strahlung gefunden wurde, konnte ungepulste Emission von VHE Gammastrahlung von einer Punktquelle mit einer statistischen Signifikanz von 10 sigma nachgewiesen werden. Die VHE Gammastrahlung ist räumlich koinzident mit dem PWN und mit der SNR Schale. Beide werden als mögliche Quelle für die beobachtete Emission diskutiert. Der Pulsar von Kes 75 wäre der jüngste bisher bekannte Pulsar, der einen Pulsarwindnebel antreibt.This work reports on the search for pulsed and steady very-high energy (VHE) gamma-ray emission in the energy range extending from 100 GeV up to 100 TeV from the direction of three pulsars with the High Energy Stereoscopic System (H.E.S.S.). Pulsed gamma-ray radiation from pulsars with energies beyond 100 GeV was found thus far only for the young and energetic Crab pulsar. A special class of pulsar wind nebulae (PWNe) is associated with composite supernova remnants (SNRs) where the PWN is centered in an expanding SNR shell. In the first part of this thesis, the results on the search for pulsed and steady VHE gamma-ray emission from the two millisecond pulsars, PSR J0437-4715 and PSR J1824-2452, are presented. Parts of the observations were conducted in a special trigger setup (the topological trigger with convergent pointing) to reduce the energy threshold of the instrument. No signal of pulsed or steady emission is found and upper limits on the pulsed and steady gamma-ray flux are derived. The upper limits on the pulsed gamma-ray flux are compared to existing model predictions and, in the case of PSR J1824-2452, allow the range of possible viewing geometries in some models to be constrained. In the second part of this work, results on the search for pulsed and steady VHE gamma-ray emission from the direction of the composite SNR Kes 75 are presented. The PWN in the center of Kes 75 is powered by a very young and powerful pulsar, PSR J1846-0258, that has an exceptionally high magnetic field. While no hint for pulsed emission is found, steady VHE gamma-ray emission is detected with a statistical significance of 10 sigma from a point-like source. The VHE gamma-ray emission is spatially coincident with the PWN and the SNR shell. Both are discussed as a possible origin for the observed emission. The pulsar of Kes 75 would be the youngest pulsar known to date to power a VHE PWN.
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Schlenker, Stefan. « Very high energy gamma rays from the binary pulsar PSR B1259-63 ». Doctoral thesis, [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976502267.
Texte intégral
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Guimarães, Margarete Cristina. « Estudo de desempenho de dosimétros eletrônicos em feixes de raios X contínuos e pulsados ». CNEN - Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, 2014. http://www.bdtd.cdtn.br//tde_busca/arquivo.php?codArquivo=313.
Texte intégralRésumé :
A monitoração individual é um procedimento básico de verificação da obediência às
diretrizes regulatórias de proteção radiológica. Dosímetros eletrônicos com detectores
de estado sólido (DE) têm sido amplamente usados para dosimetria pessoal, inclusive
em feixes pulsados de radiação onde a resposta deles ainda não é conhecida e falhas têm
sido registradas. Neste trabalho, condições de radiação para testar a resposta de DE em
feixes contínuos e pulsados foram estudadas na máquina de raios X de potencial
constante Seifert-Pantak HS320 e na máquina de raios X médico VMI Pulsas 800 Plus.
Os feixes foram caracterizados em termos de tensão no tubo, camada semirredutora,
energia média e taxa de kerma no ar. A coerência metrológica do detector Xi R/F
Unfors usado como referência nas medidas de kerma no ar foi verificada contra câmaras
de ionização Radcal 10X6-6 a RC-6. Dosímetros eletrônicos RADOS Rad-60, Aloka
PDM-111 Thermoelectron e EPD MK2 foram testados quanto ao erro intrínseco
relativo e dependência energética em radiações similares às qualidades RQR e RQA da
IEC e série N da ISO. Os resultados demonstraram a confiabilidade do dosímetro de
estado sólido Unfors Xi R/F, embora sua resposta mostrasse ser afetada em feixes
altamente filtrados. Os testes nos DE mostraram que alguns erros intrínsecos relativos
em termos de equivalente de dose pessoal, Hp(10), foram maiores que os valores
estabelecidos em normas para feixes contínuos. Em feixes pulsados, alguns DE não
responderam adequadamente à radiação e apresentaram erros intrínsecos relativos bem
altos. Este trabalho ressaltou a necessidade de testes adicionais nos DE, além de
limitada calibração em feixes de 137Cs, antes de usá-los em feixes pulsados de raios X.Personal radiation monitoring is a basic procedure to verify the compliance to regulatory requirements for radiological protection. Electronic personal dosimeters (EPD) based on solid state detectors have largely been used for personnel monitoring; including for pulsed radiation beams where their responses are not well known and deficiencies have been reported. In this work, irradiation conditions for testing the response of EPDs in both continuous and pulsed X-ray beams were studied to be established in a constant potential Seifert-Pantak and in a medical Pulsar 800 Plus VMI X-ray machines. Characterization of X-ray beams was done in terms of tube voltage, half-value layer, mean energy and air kerma rate. A Xi R/F Unfors solid state dosimeter used as reference for air kerma measurements was verified against a RC-6 and 10X6-6 Radcal ionization chambers as far its metrological coherence. Rad-60 RADOS, PDM- 11 Aloka and EPD MK2 Thermoelectron EPDs were selected to be tested in terms of relative intrinsic error and energy response in similar to IEC RQR, IEC RQA and ISO N reference radiations. Results demonstrated the reliability of the solid state Xi R/F Unfors dosimeter to be as reference dosimeter although its response was affected by heavily filtered beams. Results also showed that relative intrinsic errors in the response of the EPDs in terms of personal dose equivalent, Hp(10), were higher than the requirement established for continuous beams. In pulsed beams, some EPDs showed inadequate response and high relative intrinsic errors. This work stressed the need of performing additional checks for EPDs, besides the limited 137Cs beam calibration, before using them in pulsed X-ray beams.
Livres sur le sujet "Pulsars: individual"
1
Moore, Michael R., et Ehab Farag. Unstable Cervical Spine and Airway Management. Sous la direction de David E. Traul et Irene P. Osborn. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780190850036.003.0012.
Texte intégralRésumé :
In patients with cervical myelopathy, the spinal cord is already compromised to a point at which there is little reserve for surgical maneuvers and the slightest adverse action can result in dramatic consequences. Awake fiberoptic intubation and neurological assessment before induction of anesthesia could be the safest way to avoid waking up the patient before proceeding with surgery in the case of absent motor evoke potentials (MEPs) in spite of increasing the stimulating voltage together with increasing the rate of stimulating pulses. Hypotension is an additional factor, which may lead to irreversible neurologic deficit in a partially compressed but functionally intact spinal cord. Intraoperative neurophysiologic monitoring for cervical myelopathy should include somatosensory evoked potentials, transcranial electric MEPs, and electromyography to provide complementary information and monitor different spinal cord tracts and individual nerve roots.
2
Andrews, Rob, et Clare England. Poor diets. Sous la direction de Patrick Davey et David Sprigings. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780199568741.003.0335.
Texte intégralRésumé :
Apart from breast milk, no single food contains all the essential nutrients the body needs to be healthy and function efficiently. The nutritional value of a person’s diet depends on the overall balance of foods eaten over a period of time, as well as on the needs of the individual. Over the last 60 years, there has been increasing agreement about the balance of nutrients and foods that make up a ‘good’ diet. This consists primarily of wholegrains (i.e. cereal grains, or foods made from them, containing bran, germ, and endosperm, e.g. wholemeal breads, oatmeal, and dark rye); vegetables and fruit, including nuts and pulses; moderate amounts of fish and low-fat dairy foods; and limited amounts of meat. The consumption of saturated fat should be low, with saturated fat being replaced by mono- and polyunsaturated vegetable fats and fish oils. Trans-fatty acids should be minimized, and added sugar should provide no more than 10% of energy intake. However, as omnivores, humans can survive on a wide range of different foods, and many people worldwide eat diets that fall far short of this ideal.
Chapitres de livres sur le sujet "Pulsars: individual"
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Tanyag, Rico Mayro P., Bruno Langbehn, Thomas Möller et Daniela Rupp. « X-Ray and XUV Imaging of Helium Nanodroplets ». Dans Topics in Applied Physics, 281–341. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-94896-2_7.
Texte intégralRésumé :
AbstractX-ray and extreme ultraviolet (XUV) coherent diffractive imaging (CDI) have the advantage of producing high resolution images with current spatial resolution of tens of nanometers and temporal resolution of tens of femtoseconds. Modern developments in the production of coherent, ultra-bright, and ultra-short X-ray and XUV pulses have even enabled lensless, single-shot imaging of individual, transient, non-periodic objects. The data collected in this technique are diffraction images, which are intensity distributions of the scattered photons from the object. Superfluid helium droplets are ideal systems to study with CDI, since each droplet is unique on its own. It is also not immediately apparent what shapes the droplets would take or what structures are formed by dopant particles inside the droplet. In this chapter, we review the current state of research on helium droplets using CDI, particularly, the study of droplet shape deformation, the in-situ configurations of dopant nanostructures, and their dynamics after being excited by an intense laser pulse. Since CDI is a rather new technique for helium nanodroplet research, we also give a short introduction on this method and on the different light sources available for X-ray and XUV experiments.
2
Singh, Pradeep, et Sujith Kumar Appikatla. « Epileptic Seizure Detection From EEG Signals Using Bagged Ensemble Approach ». Dans Handbook of Research on Advancements of Artificial Intelligence in Healthcare Engineering, 67–79. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-7998-2120-5.ch004.
Texte intégralRésumé :
Seizures are caused by irregular electrical pulses in the brain. Epileptic seizure detection on EEG signals is a long process, which is done manually by epileptologists. The aim of the study is automatically detecting the seizures of the brain, given the electroencephalogram signals by feature extraction and processing through different machine learning algorithms. Machines can be trained to do this type of observation and predict the output with high accuracy. In this chapter, the classification study of individual and ensemble classifier is performed for epileptic seizure detection. The proposed method consists of two phases: extraction of data from EEG signals and development of an individual and ensemble models. Bagging ensemble is developed to achieve better results. The development of the ensemble using various classification algorithms contributes towards increasing the diversity of the ensemble. An extensive comparative study with existing benchmark algorithm is performed for epileptic seizure detection.
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Madhushri, Priyanka, et Emil Jovanov. « Long-Term Synchronization of Hybrid Sensors Networks ». Dans Sensor Technology, 1178–92. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-7998-2454-1.ch056.
Texte intégralRésumé :
This article presents synchronization of a hybrid distributed sensor network with wired and wireless sensors. Authors present an implementation of a sleep monitoring system as a hybrid sensor network that combines wireless inertial sensors controlled by a custom smartphone application as an extension of the polysomnographic (PSG) monitor to improve user's comfort. The authors developed an original method of synchronization of wireless sensor data with the PSG records using an auxiliary audio synchronization signal generated by the smartphone. The timestamps on the smartphone are synchronized with the timestamps from inertial sensors, and time of generated synchronization pulses recorded by the PSG. The individual data streams were synchronized using the Dynamic Time Warping (DTW) mechanism. Authors present the system organization and the results of analysis of the whole night monitoring, including the analysis of channel reliability and clock drift. Clock drift has been reduced from 10-30 seconds to 5.1± 3 milliseconds which is with an improved accuracy as compare to existing methods.
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Rampino, Michael R. « Does the Earth have a pulse ? Evidence relating to a potential underlying ~26–36-million-year rhythm in interrelated geologic, biologic, and astrophysical events ». Dans From the Guajira Desert to the Apennines, and from Mediterranean Microplates to the Mexican Killer Asteroid : Honoring the Career of Walter Alvarez. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.2557(17).
Texte intégralRésumé :
ABSTRACT The existence of an ~26–36 m.y. rhythm in interrelated global tectonism, sea-level oscillations, climate, and resulting sedimentation patterns during Phanerozoic time (the last 541 m.y.) has long been suspected. A similar underlying ~26.4–27.5 m.y. cycle was reported independently in episodes of extinctions of marine and non-marine species. Subsequent spectral analyses of individual geologic events of the last 260 m.y., including changes in seafloor spreading and subduction, times of hotspot initiation and intraplate volcanism, eruptions of Large Igneous Provinces (LIPs), tectonic events, sea-level fluctuations, oceanic anoxia, atmospheric carbon dioxide levels, and global climate have revealed evidence for the 26–36 m.y. cycle and the temporal association of events with an apparent overall periodicity of ~27.5 m.y. modulated by an ~8–9 m.y. cycle. The proposed episodes of geologic activity and environmental and biotic change may result from cyclical internal Earth processes that affect changes in mantle convection, plate motions, intraplate stresses, and/or periodic pulses of mantle-plume activity. Recently, the ~30 m.y. cycle has been linked to Earth’s long-term orbital changes within the Solar System, and it may also affect tectonism and climate. I also note considerable evidence for a similar ~30 m.y. cycle in the ages of terrestrial impact craters, which suggests possible astronomical connections. The shared geologic cycle time, formally ranging from ~26 to 36 m.y. (depending partly on varying data sets, geologic timescales, and statistical techniques utilized) is close to the estimated interval (~32 ± 3 m.y.) between our cyclical crossings of the crowded mid-plane region of the Milky Way Galaxy. Here I outline a proposed astrophysical pacing for the apparent pulses of both impact cratering and rhythmic geological episodes.
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« Conservation, Ecology, and Management of Catfish : The Second International Symposium ». Dans Conservation, Ecology, and Management of Catfish : The Second International Symposium, sous la direction de MICHAEL L. FINE, EDWARD N. SISMOUR, SCOTT H. NEWTON, BISHOP T. BOSHER, AMANDA DH SULLIVAN, JOSEPH PAUL MIANO, ZACHARY N. GHAHRAMANI, YASHA J. MOHAJER et SHELLEY C. NELLIS. American Fisheries Society, 2011. http://dx.doi.org/10.47886/9781934874257.ch63.
Texte intégralRésumé :
<em>Abstract</em>.—We have been examining proximate (functional morphology) and ultimate factors (survival from predation) relating to the pectoral spine in channel catfish <em>Ictalurus punctatus</em>. We briefly review functional morphology of the spine in channel catfish and then add new data on morphology in other ictalurids, including interpretation of the relatively smooth anterior and armored posterior profiles of the spine, functions of the various pectoral spine muscles, and new details about the mechanism of stridulatory sound production. Binding, locking, and production of stridulation sounds by the spine utilize derived processes on the spine base (dorsal, anterior, and ventral processes) that mate with counterparts within the pectoral girdle. Stridulation sounds are produced as a series of individual pulses during a forward pectoral fin sweep (abduction), and we provide evidence that each pulse is produced by a small amplitude forward movement, a slip-stick movement similar to bowing a violin. An anti-predator adaptation can work as a deterrent that reduces the probability of attack and as a defense that reduces the risk of mortality. Previous work indicated that the spine functions in defense. Intact channel catfish have a threefold greater chance of surviving a session with a largemouth bass <em>Micropterus salmoides</em> predator as comparably sized individuals with clipped spines. The question of whether the spine reduces the probability of attack had not been investigated. We presented bluegills <em>Lepomis macrochirus</em> and channel catfish to largemouth bass and found that largemouth bass consume more bluegills than channel catfish in a choice situation. Thus, experience with the pectoral spines likely deters attack, particularly if other species are available, and the spine increases the probability of surviving attack by complicating ingestion and possibly by the production of distress calls. Survival advantages accruing from the spine appear to have lead to the evolution of complex adaptations that permit locking and sound production.
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Chen, Yu-Luen, Walter Chang et Te-Son Kuo. « Sensors in Assistive Technology ». Dans Handbook of Research on Personal Autonomy Technologies and Disability Informatics, 224–32. IGI Global, 2011. http://dx.doi.org/10.4018/978-1-60566-206-0.ch014.
Texte intégralRésumé :
This chapter reports on the development of an eyeglass-type infrared-controlled computer interface for the disabled. This system may serve to assist those who suffer from spinal cord injuries or other handicaps to operate a computer. This system is comprised of three major components: (A) an infrared transmitting module; (B) an infrared receiving / signal-processing module; and (C) a main controller, the Intel-8951 microprocessor. The infrared transmitting module utilizes tongue-touch circuitry which is converted to an infrared beam and a low power laser (<0.1mW) beam. The infrared receiving / signal-processing module, receives the infrared beam and fine tunes the unstable infrared beam into standard pulses which are used as control signals. The main controller is responsible for detecting the input signals from the infrared receiving / signal-processing module and verifying these signals with the mapping table in its memory. After the signal is verified, it is released to control the keys of the computer keyboard and mouse interface. This design concept was mainly based on the idea that the use of an infrared remote module fastened to the eyeglasses could allow the convenient control of the input motion on the keys of a computer keyboard and mouse which are all modified with infrared receiving / signal-processing modules. The system is designed for individuals with spinal cord injuries and disabled in which the subjects’ movement are severely restricted. The infrared transmitting module can be easily mounted on eyeglasses or artificial limbs.
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Farne, Hugo, Edward Norris-Cervetto et James Warbrick-Smith. « Chest pain ». Dans Oxford Cases in Medicine and Surgery. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780198716228.003.0015.
Texte intégralRésumé :
A good way to come up with a list of causes is to visualize the anatomy of the affected area and think of what could go wrong. Thus, in chest pain, there may be pathology of the heart, aorta, lungs, pulmonary vessels, oesophagus, stomach, thoracic nerves, thoracic muscles, or ribs. The main causes of acute chest pain in an individual aged over 60 include are listed in Figure 9.1. A younger patient is less likely to be suffering from diseases of old age, such as: • Acute coronary syndrome • Stable angina • Myopericarditis (usually post-infarction) • Thoracic aortic dissection • Thoracic aortic aneurysm A younger female patient on the combined oral contraceptive pill is more likely to be suffering from: • PE (the combined oral contraceptive pill is thrombogenic) • Pneumothorax (especially if tall and thin) • Cocaine-induced coronary spasm (still rare, but particularly unusual in older people). The following diagnoses require immediate management and should be kept in mind: • Acute coronary syndrome (unstable angina, or myocardial infarction (MI)) • Aortic dissection • Pneumothorax • PE • Boerhaave’s perforation The key features of each are listed below. 1 Features of acute coronary syndrome ■ History of sudden-onset, central, crushing chest pain radiating to either/both arms, neck or jaw, usually lasting a few minutes to half an hour (longer if there is ongoing infarction). Have a higher index of suspicion in those with a previous history of angina on exertion or MI and/or cardiovascular risk factors (smoking, hypertension, hypercholesterolaemia, diabetes mellitus, family history). ■ Signs of hypercholesterolaemia: cholesterol deposits in small skin lumps on the back of the hand or bony prominences like elbows (xanthomata), in creamy spots around the eyelids (xanthelasma), or a creamy ring around the cornea (arcus). Note that arcus is a normal finding in older people. ■ Signs of peripheral (atherosclerotic) vascular disease: weak pulses, peripheral cyanosis, cool peripheries, atrophic skin, ulcers, bruits on auscultation of carotids. ■ Signs of brady- or tachyarrhythmia. An arrhythmia is relevant for two reasons.
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Koch, Christof. « Beyond Hodgkin and Huxley : Calcium and Calcium-Dependent Potassium Currents ». Dans Biophysics of Computation. Oxford University Press, 1998. http://dx.doi.org/10.1093/oso/9780195104912.003.0015.
Texte intégralRésumé :
The cornerstone of modern biophysics is the comprehensive analysis by Hodgkin and Huxley (1952a,b,c,d) of the generation and propagation of action potentials in the squid giant axon. The basis of their model is a fast sodium current INa and a delayed potassium current IK (which here we also refer to as IDR)- The last 40 years of research have shown that impulse conduction along axons can be successfully analyzed in terms of one or both of these currents. Nonetheless, their equations do not capture—nor were they intended to capture—a number of important biophysical phenomena, such as adaptation of the firing frequency to long-lasting stimuli or bursting, that is, the generation of two to five spikes within 5-20 msec. Moreover, the transmission of electrical signals within and between neurons involves more than the mere circulation of stereotyped pulses. These impulses must be set up and generated by subthreshold processes. The differences between the firing behavior of most neurons and the squid giant axon reflect the roles of other voltage-dependent ionic conductances than the two described by Hodgkin and Huxley. Over the last two decades, more than several dozen membrane conductances have been characterized (Hagiwara, 1983; Llinás, 1988; Hille, 1992). They differ in principal carrier, voltage, and time dependence, dependence on the presence of intracellular calcium and on their susceptibility to modulation by synaptic inputs and second messengers. Our knowledge of these conductances and the role they play in impulse formation has accelerated rapidly in recent years as a result of various technical innovations such as single-cell isolation, patch clamping, and molecular techniques. We will here describe the most important of these conductances and briefly characterize each one. In order to understand more completely the functional role of these conductances in determining the response of the cell to input, empirical equations that approximate their behavior under physiological conditions must be developed and compared against the physiological preparations. In a remarkable testimony to the power and the generality of the Hodgkin-Huxley approach, the majority of such phenomenological models has used their methodology of describing individual ionic conductances in terms of activating and inactivating particles with first-order kinetics (see Chap. 6).
Actes de conférences sur le sujet "Pulsars: individual"
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McKinnon, M. M., Manuel de León, D. M. de Diego et R. M. Ros. « Directional Statistics for Polarization Observations of Individual Pulses from Radio Pulsars ». Dans MATHEMATICS AND ASTRONOMY : A JOINT LONG JOURNEY : Proceedings of the International Conference. AIP, 2010. http://dx.doi.org/10.1063/1.3506055.
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Petrova, S. A. « Manifestations of propagation effects in the individual pulse polarization of radio pulsars ». Dans ASTROPHYSICAL SOURCES OF HIGH ENERGY PARTICLES AND RADIATION. AIP, 2005. http://dx.doi.org/10.1063/1.2141881.
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Prokopovich, I. P., et Justin Peatross. « Generation of high-intensity individual attosecond pulses ». Dans XVII International Conference on Coherent and Nonlinear Optics (ICONO 2001), sous la direction de Vyacheslav M. Gordienko, Anatoly A. Afanas'ev et Vladimir V. Shuvalov. SPIE, 2002. http://dx.doi.org/10.1117/12.469117.
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Wenger, Jérôme, Rosa Brouri et Philippe Grangier. « Non-Gaussian statistics from individual pulses of squeezed light ». Dans International Quantum Electronics Conference. Washington, D.C. : OSA, 2004. http://dx.doi.org/10.1364/iqec.2004.itug1.
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Jing Yong Ye, Christine Tse, Marwa J. Zohdy, Kyle Hollman, Lajos Balogh, Theodore B. Norris et Matthew O'Donnell. « Generating controllable microbubbles inside individual cells using femtosecond laser pulses ». Dans 2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference. IEEE, 2006. http://dx.doi.org/10.1109/cleo.2006.4628302.
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Rettich, Florian, Nico Vieweg, Oleg Cojocari et Anselm Deninger. « Detection of individual terahertz pulses at 80 MHz repetition rate ». Dans 2015 40th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz). IEEE, 2015. http://dx.doi.org/10.1109/irmmw-thz.2015.7327693.
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Malinowski, A., K. T. Vu, K. K. Chen, P. Horak et D. J. Richardson. « Selective Generation of Individual Raman Stokes Wavelengths using Shaped Optical Pulses ». Dans 2008 Conference on Optical Fiber Communication - OFC 2008 Collocated National Fiber Optic Engineers. IEEE, 2008. http://dx.doi.org/10.1109/ofc.2008.4528569.
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Wilson, Emma, Emiliano Rustighi, Philip L. Newland et Brian R. Mace. « A Model of Force Generation by Locust Skeletal Muscle in Response to Individual Stimuli ». Dans ASME 2009 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/detc2009-86620.
Texte intégralRésumé :
A mathematical model of the locust hind leg extensor muscle is presented. The model accounts for the force response of the muscle due to individual stimuli under isometric conditions. Experimental data was collected by stimulating the muscle directly and force measured at the tibia. Joint dimensions were calculated, enabling tibial force to be converted into muscle force. In developing a model it was assumed that the response to a single isolated stimulus was linear, but no assumptions were made about the model order. Models of various order were fitted using time and frequency domain methods to data obtained from well-separated input pulses. The response could be approximated as an impulse response, with the response to each stimulus best described by a linear third-order system. Responses where input pulses were not well-separated, so that summation of subsequent pulses occurred, were also investigated. As has been observed in mammalian muscle, both facilitation and force depression were evident in locust muscle. The linear third-order model was found to provide an adequate fit to data in which depression and facilitation were evident if the parameters describing the system were allowed to vary between each response.
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Park, Doo Jae, Björn Piglosiewicz, Slawa Schmidt et Christoph Lienau. « Strong field acceleration of Attosecond Electron Pulses emitted by an individual Metallic Nanostructure ». Dans Quantum Electronics and Laser Science Conference. Washington, D.C. : OSA, 2012. http://dx.doi.org/10.1364/qels.2012.qth1f.3.
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Monserud, Nils, Bruno Langbehn, Mario Sauppe, Julian Zimmermann, Annabelle Spanier, Pablo Nuñez von Voigt, Bernd Schütte et al. « Single-shot diffractive imaging of individual helium nanodroplets with intense multicolor XUV pulses ». Dans High Intensity Lasers and High Field Phenomena. Washington, D.C. : OSA, 2018. http://dx.doi.org/10.1364/hilas.2018.hw2a.3.
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