Статті в журналах з теми "Cosmic-ray phenomenology"

Galactic winds constitute a primary feedback process in the ecology and evolution of galaxies. They are ubiquitously observed and exhibit a rich phenomenology, whose origin is actively investigated both theoretically and observationally. Cosmic rays have been widely recognized as a possible driving agent of galactic winds, especially in Milky–Way like galaxies. The formation of cosmic ray-driven winds is intimately connected with the microphysics of the cosmic ray transport in galaxies, making it an intrinsically non-linear and multiscale phenomenon. In this complex interplay, the cosmic ray distribution affects the wind launching and, in turns, is shaped by the presence of winds. In this review, we summarize the present knowledge of the physics of cosmic rays involved in the wind formation and of the wind hydrodynamics. We also discuss the theoretical difficulties connected with the study of cosmic ray-driven winds and possible future improvements and directions.

AbstractThe Cosmic Ray (CR) physics has entered a new era driven by high precision measurements coming from direct detection (especially AMS-02 and PAMELA) and also from gamma-ray observations (Fermi-LAT). In this review we focus our attention on how such data impact the understanding of the supernova remnant paradigm for the origin of CRs. In particular we discuss advancement in the field concerning the three main stages of the CR life: the acceleration process, the escape from the sources and the propagation throughout the Galaxy. We show how the new data reveal a phenomenology richest than previously thought that could even challenge the current understanding of CR origin.

Context. Recent observations of unexpected structures in the Galactic cosmic ray (GCR) spectrum and composition, as well as growing evidence for episodes of intense dynamical activity in the inner regions of the Galaxy, call for an evaluation of the high-energy particle acceleration associated with such activity and its potential impact on the global GCR phenomenology. Aims. We investigate whether particles accelerated during high-power episodes around the Galactic centre can account for a significant fraction of the observed GCRs, or, conversely, what constraints can be derived regarding their Galactic transport if their contributions are negligible. Methods. Particle transport in the Galaxy is described with a two-zone analytical model. We solved for the contribution of a Galactic centre cosmic-Ray (GCCR) source using Green functions and Bessel expansion, and discussed the required injection power for these GCCRs to influence the global GCR phenomenology at Earth. Results. We find that, with standard parameters for particle propagation in the galactic disk and halo, the GCCRs can make a significant or even dominant contribution to the total CR flux observed at Earth. Depending on the parameters, such a source can account for both the observed proton flux and boron-to-carbon ratio (in the case of a Kraichnan-like scaling of the diffusion coefficient), or potentially produce spectral and composition features. Conclusions. Our results show that the contribution of GCCRs cannot be neglected a priori, and that they can influence the global GCR phenomenology significantly, thereby calling for a reassessement of the standard inferences from a scenario where GCRs are entirely dominated by a single type of sources distributed throughout the Galactic disk.

At high energies the Pomeron plays a crucial part in describing the soft interactions. In the light of LHC (Large Hadron Collider) data we perform a detailed analysis of proton-proton ([Formula: see text]) and antiproton-proton ([Formula: see text]) forward scattering data in order to determine the intercept and the slope of the soft Pomeron trajectory. This analysis is performed based on Regge theory using Born-level amplitudes. We investigate the role of the proton-Pomeron vertex form and of the nearest [Formula: see text]-channel singularity. We give predictions for the total cross section and the ratio of the real part to the imaginary part of the elastic amplitude in [Formula: see text] collisions at LHC and cosmic-ray energies.

The logical inconsistency of quantum mechanics and general relativity can be avoided if the relativity principle fails for length scales smaller than the quantum coherence length for the vacuum state. This has dramatic consequences for the phenomenology of compact astrophysical objects. If we assume that at the Planck scale elementary particles interact via a universal four-point interaction and baryon number conservation is violated, then nucleons approaching an event horizon surface can disintegrate into gamma rays and high energy leptons. Integrating the Altarelli–Parisi equations to find the Planck scale parton distribution function for a nucleon, we find that nucleon decays produce a fluorescence gamma ray spectrum strikingly similar to that observed for cosmic gamma ray bursts.

Abstract Galactic cosmic rays (CRs) are accelerated at the forward shocks of supernova remnants (SNRs) via diffusive shock acceleration (DSA), an efficient acceleration mechanism that predicts power-law energy distributions of CRs. However, observations of nonthermal SNR emission imply CR energy distributions that are generally steeper than E −2, the standard DSA prediction. Recent results from kinetic hybrid simulations suggest that such steep spectra may arise from the drift of magnetic structures with respect to the thermal plasma downstream of the shock. Using a semi-analytic model of nonlinear DSA, we investigate the implications that these results have on the phenomenology of a wide range of SNRs. By accounting for the motion of magnetic structures in the downstream, we produce CR energy distributions that are substantially steeper than E −2 and consistent with observations. Our formalism reproduces both modestly steep spectra of Galactic SNRs (∝E −2.2) and the very steep spectra of young radio supernovae (∝E −3).

We review the phenomenology of relativistic nuclear collisions in the light of ultra-high energy cosmic ray physics. A novel phase of quantum chromodynamics called quark-gluon plasma is expected to appear in nuclear collisions at high energies. The produced hot matter is found to be well-described as a relativistic fluid with small viscosity. We show that the transport coefficient can be quantitatively extracted by comparing theoretical estimations of viscous hydrodynamic models to experimental data.

We propose that the effective dimensionality of the space we live in depends on the length scale we are probing. As the length scale increases, new dimensions open up. At short scales the space is lower dimensional; at the intermediate scales the space is three-dimensional; and at large scales, the space is effectively higher dimensional. This setup allows for some fundamental problems in cosmology, gravity, and particle physics to be attacked from a new perspective. The proposed framework, among the other things, offers a new approach to the cosmological constant problem and results in striking collider phenomenology and may explain elongated jets observed in cosmic-ray data.

We review a few topics in Planck-scale physics, with emphasis on possible manifestations in relatively low energy. The selected topics include quantum fluctuations of spacetime, their cumulative effects, uncertainties in energy–momentum measurements, and low energy quantum-gravity phenomenology. The focus is on quantum-gravity-induced uncertainties in some observable quantities. We consider four possible ways to probe Planck-scale physics experimentally: (i) looking for energy-dependent spreads in the arrival time of photons of the same energy from GRBs; (ii) examining spacetime fluctuation-induced phase incoherence of light from extragalactic sources; (iii) detecting spacetime foam with laser-based interferometry techniques; (iv) understanding the threshold anomalies in high energy cosmic ray and gamma ray events. Some other experiments are briefly discussed. We show how some physics behind black holes, simple clocks, simple computers, and the holographic principle is related to Planck-scale physics. We also discuss a formulation of the Dirac equation as a difference equation on a discrete Planck-scale spacetime lattice, and a possible interplay between Planck-scale and Hubble-scale physics encoded in the cosmological constant (dark energy).

Preamble: Medium/Format/Marker Medium/Format/Marker (M/F/M) was a visual-aural improvisational performance involving myself, and musicians Joe Sorbara, and Ben Grossman. It was formed through my work as a PhD candidate at the Improvisation, Community, and Social Practice research initiative at the University of Guelph. This performance was conceived as an attempted intervention against the propensity to reify the “new.” It also sought to address the proliferation of the screen and question how the increased presence of screens in everyday life has augmented the way in which an audience is conceived and positioned. This conception is in direct conversation with my thesis, which is a practice-based research project exploring what the experimental combination of intermediality, improvisation, and the cinema might offer towards developing a reflexive approach to "new" media, screen culture, and expanded cinemas. One of the ways I chose to explore this area involved developing an interface that allowed an audio-visual ensemble to improvise with a film's audio-visual projection. I experimented with different VJ programs. These programs often utilize digital filters and effects to alter images through real-time mixing and layering, much like a DJ does with sound. I found a program developed by Chicago-based artist Ontologist called Ontoplayer, which he developed out of his practice as an improvisational video artist. The program works through a dual-channel interface where two separate digital files could be augmented, with their projected tempo capable of being determined by musicians through a MIDI interface. I conceptualized the performance around the possibility of networking myself with two other musicians via this interface. I approached percussionist Joe Sorbara and multi-instrumentalist Ben Grossman with the idea to use Ontoplayer as a means to improvise with Chris Marker's La Jetée (1962, 28 mins). The film itself would be projected simultaneously in four different formats: 16mm celluloid, VHS, Blu-ray, and Standard Definition video (the format the ensemble improvised with) projected onto four separate screens. From left to right, the first screen contained the projected version of La Jetée that we improvised with, next to it was its Blu-ray format, next to that, a degraded VHS copy of the film, and next to that, the 16mm print. The performance materialized through performing a number of improvisatory experiments. A last minute experiment conceived a few hours before the performance involved placing contact microphones overtop of the motor on a Bell & Howell 16mm projector. The projector was tested in the days leading up to the performance and it ran as smoothly as could be expected. It had a nice cacophonous hum that Ben Grossman intended to improvise with using some contact mics attached directly over the projector’s motor, a $5 iPad app, and his hurdy-gurdy. Fifteen minutes before the performance began, the three of us huddled to discuss how long we'd like to go. We had met briefly the day before to discuss the technical setup of the performance but not its execution and length. I hadn't considered duration. Joe broke the silence by asking if we'd be "finding beginnings and endings." I didn't know what that entailed, but nodded. We started. I turned on the projector and it immediately started to cough and chew on the 40 year old 16mm print I found online. My first impulse was to intervene, to try to save it. The film continued and I sat frozen for a moment. Joe started playing and Ben, expecting me to send him the audio track from La Jetée, prompted me to do so. I let the projector go and began. Joe had a digital kick-drum and two contact mics on his drum kit hooked into a MIDI hub, while Ben's hurdy-gurdy had a contact mic inside it, wired into the hub. The hub hooked into my laptop and allowed for an intermedial conversation to emerge between the three of us. While the 16mm, VHS, and Blu-Ray formats proceeded relatively unimpeded alongside each other on their respective screens, the fourth screen was where this conversation took place. I digitally reordered different image sequences from La Jetée. The fact that it’s a film (almost) comprised entirely of still images made this reordering intriguing in that I was able control the speed of progressing from each image to the next. The movement from image to image was structured between Ben and Joe’s improvisations and the kind of effects and filters I had initialized. Ontoplayer has a number of effects and filters that push the base image into more abstract territories (e.g.: geometric shapes, over pixelation) I was uninterested in exploring. I utilized effects that to some degree still kept the representational content of the image intact. The degree to which these effects took hold of the image were determined by whether or not Ben and Joe decided to use the part of their instrument that would trigger them. The decision to linger on an image, colour it differently, or skip ahead in the film’s real-time projection destabilized my sense of where I was in the film. It became an event in the sense that each movement, both visual and aural was happening with an indeterminate duration. La Jetée opens with the narrator proclaiming: “this is the story of a man marked by an image from his childhood.” The story itself is situated around a man in a post-apocalyptic world, haunted by the persistent memory of a woman he saw as a child while standing on the jetty at Orly Airport in Paris. The man was a soldier, now captured, and imprisoned in an underground camp. The prison guards have been conducting experiments on the prisoners, attempting to use the prisoner’s memories as a mechanism to send them backwards and forwards in time. The narrator explains, “with the surface of the planet irradiated … The human race was doomed. Space was off limits. The only link with survival passed through time … The purpose of the experiments was to throw emissaries into time to call the past and future to the aid of the present.” La Jetée is visually structured as a photomontage, with voice-over narration, diegetic and non-diegetic sound existing as component parts to the whole film. I decided to separate these components for the sake of isolating them before the performance as instruments of the film to be improvisationally deployed through the intermedial connection between Ben, Joe, and myself. The resulting projections that emerged from our interface became a kind of improvised "grooving" to La Jetée that restricted the impulse to discriminately place sound beneath and behind the image. I selected images from different points in the film that felt "timely" given the changing dynamic between the three of us. I remember lingering on an image of the woman's face, her hand against her mouth, her hair being blown back by the wind. I looked and listened for the moment when the film would catch and then catch fire. It never came. We let the reel run to the end and continued on improvising until we found an ending. But the sound of that film catching but never breaking, the intention and tension of the film being near death the entire time made everything we did more precious, teetering on the brink of failure. We could never have predicted that, and it gave us something I continue to ponder and be thankful for. Celluloid junkies in the room commented on how precipitous the whole thing was, given how rare it is to encounter the sound of celluloid film travelling through a projector inside a cinematic space. An audiophile mused over how there wasn’t any document, his mind adequately blown by how “funky” the projector sounded. With there being no document of the performance, I'm left with my own memories. In mining the aftermath of this performance, I hope to find an addendum that considers how improvisation might negotiate with augmentation in ways that speak to Walter Benjamin's assertion that the "camera, the film, on the one hand, extends our comprehension of the necessities which rule our lives; on the other hand, it manages to assure us of an immense and unexpected field of action” (Benjamin 236-7).Images to be Determined I got a job working in a photo lab eight years ago, right around the time digital cameras started becoming not only affordable, but technologically-comparable alternatives to film cameras. The photo printer in the lab was setup to scan and digitize celluloid filmstrips to allow for digital “touchups” by the technician. It was also hooked into touchscreen media stations that accepted a variety of memory card formats so that customers could “touchup” their own images. Celluloid film meant that as long as their format was chemical, touching up their images remained the task of the technician. Against the urging of the lab’s manager, I resisted altering other people’s images. It felt like a violation, despite the fact that almost every customer was unaware of this process. They assumed a degree of responsibility for a chemically-exposed image. I still got blamed for a lot of bad photography, but an image chemically under or overexposed was irreparable. Digital cameras changed all of that. I still preferred an evenly exposed celluloid print to a digital, but the allure was the ability for these images to be augmented. Augmentation is synonymous with "enhancement," "prosthesis," "addition," "amplification," "enrichment," "expansion,” and "extension" (to name a few). For the purpose of this essay, I am situating augmentation as an agential act engaging with a static form to purposefully alter its aesthetic and political relation to a reality. To what extent can we say that the digital image is itself, an augmentation? If Instagram is any indication, the digital image's existence is bound by its perpetual augmentation. A digital image is only as good as its capacity to be worked on. The ubiquity of digitally applying lomographic filters to digital images, as a defining step in their distributive chain, is indicative of the discursive impact remediating the old into the new has on digital forms. These digitally-coded filters used to augment “clear” digital images are comprised of exaggerated imperfections that existed to varying degrees, as unforeseen side effects of working with comparatively more unstable celluloid textures. The filtered images themselves are digital distortions of a digital original. The filters augment this original through obscuring one or a number of components. Some filters might exaggerate the green values or sharpen a particular quadrant within the frame that might coincide with the look of a particular film stock from the past. The discourse of “film” and “vintage” photography has become a synonymous component of the digital aesthetic, discursively warming up what is often considered to be a cold, and disembodied medium. Augmentation works to re-establish a congruous relationship between the filmic and the digital, attempting to reconcile the aesthetic distance between granularity and pixelation. This is ironic because this process is encapsulated through digitally encoding and applying these filters for the sake of obscuring clarity. Thus, the object is both hailed as clear and clearly manipulable. Another example a bit closer to the cinema is the development of digital video cameras offering RAW, or minimally compressed file formats for the sole purpose of augmenting the initial recording in post-production workflows in an attempt to minimize degradation in the image. The colour values and dynamic range of these images are muted, or flattened so that the human can control their elevation after the fact. To some degree the initial image, in itself, is an augmentation of its filmic relative. From early experiments with video synthesizers to the present digital coding of film effects, digital images have tantalized video artists and filmmakers with possibility shrouded in instantaneity and malleability. A key problem with this structure remains the unbridled proliferation and expansion of the digital image, set free for the sake of newness. How might improvisation work towards establishing an ethics of augmentation? An ethics of this kind must disrupt the popular notion of the digital image existing beyond analogical constraints. The belief that “if you can imagine it, you can do it” obfuscates the reality that to work with images, whatever their texture, is a negotiation with constraint. Part of M/F/M’s fruition emerged from a conversation I'd had with Canadian Animator Pierre Hébert last summer. Now obvious, but for Hébert, the first obstacle he needed to overcome as an improviser was developing an instrument that he could gig with. Through the act of designing an instrument I immediately became aware of what wasn't possible, and so the work leading up to the performance involved attempting to expand the possibilities of that instrument. How might I conceive of my own treatment of images simultaneously treated by Joe and Ben as a kind of cinematic extended technique we collaboratively bring into being? Constraint necessitates the need for extension, for finding new ways to sound and appear. Constraint is also consistently conceived as shackling progress. In scientific methodologies it is often arbitrarily imposed to steer an experiment into a desired direction. This sort of experimental methodology is in the business of presupposing outcomes, which I feel is often the case with what ultimately becomes the essay of end result in Humanities research. Constraint is an important imposition in improvisation only if the parties involved are willing to find new ways to move in consort with it. The act of improvisation is thus an engagement with the spatio-temporal constraints of performance, politics, memory, texture, and difference. My conception of the cinema is that of an instrument, whose past is what I work with to better understand its future. Critic Gene Youngblood, in his landmark book, Expanded Cinema, theorized a new conception of the cinema as a global planetary phenomenon suffused inside a space of intermedia, where immersive, interactive, and interconnected realms necessitated the need to critically conceptualise the cinema in cosmic terms. At around the time of Youngblood's writing, another practitioner of the cosmic way, improviser and composer Sun Ra was staking a similar claim for music's ability to uplift the species cosmically. Ra's popular line “If we came from nowhere here, why can’t we go somewhere there?” (Heble 125), articulated the problematic racial politics in post-WWII America, that fixed African-American identity into a static domain with little room to move upward. The "somewhere there" to Ra was a non-space, created from "a desire to opt out of the very codes of representation and intelligibility, the very frameworks of interpretation and assumption which have legitimated the workings of dominant culture" (Heble 125). Though Youngblood's and Ra's intellectual and creative impulses formed from differing political circumstances, the work and thinking of these two figures remain significant articulations of the need to work from and towards the cosmic. In 2003, Youngblood published a follow-up essay in a reprint of Expanded Cinema entitled Cinema and the Code. In it, he defines cinema as a “phenomenology of the moving image.” Rather than conceiving of it through any of its particular media, Youngblood advocates for a segregated conception of the cinema: Just as we separate music from its instruments. Cinema is the art of organizing a stream of audiovisual events in time. It is an event-stream, like music. There are at least four media through which we can practice cinema – film, video, holography, and structured digital code—just as there are many instruments through which we can practice music. (Youngblood cited in Marchessault and Lord 7) Music and cinema are thus conceived as the exterior consequences of creative and co-creative instrumental experimentation. For Ra and Youngblood, the planetary stakes of this project are infused with the need to manufacture and occupy an imaginative space (if only for a moment) outside of the known. This is not to say that the action itself is transcendental. But rather this outside is the planetary. For the past year I've been making a documentary with Joe Sorbara on the free improv scene in Toronto. Listening to musicians talk about improvisation in expansive terms, as this ethereal and ephemeral experience, that exists on the brink of failure, that is as much an act of memory as renewal, reverberated with my own feelings surrounding the cinema. Improvisation, to philosopher Gary Peters, is the "entwinement of preservation and destruction", that "invites us to make a transition from a closed conception of the past to one that re-thinks it as an endlessly ongoing event or occurrence whereby tradition is re-originated (Benjamin) or re-opened (Heidegger)” (Peters 2). This “entwinement of preservation and destruction” takes me back to my earlier discussion of the ways in which digital photography, in particular lomographically filtered snapshots, is structured through preserving the discursive past of film while destroying its standard. The performance of M/F/M attempted to connect the augmentation of the digital image and the impact this augmentation had on conceptualizing the past through an improvisational approach to intermediality. The issue I have with the determination of images concerns their technological standardization. As long as manufacturers and technicians control this process then the practice of gathering, projecting, and experiencing digital images is predetermined by their commercial obligation. It assures that augmenting the “immense and unexpected field of action” comprising the domain of images is itself a predetermination. References Benjamin, Walter. Illuminations. New York: Schocken Books, 1985. Heble, Ajay. Landing on the Wrong Note. London: Routledge, 2000. Marker, Chris, dir. La Jetée. Argos Films. 1962. Marchessault, Janine, and Susan Lord. Fluid Screens, Expanded Cinema. Toronto: University of Toronto Press, 2007. Peters, Gary. The Philosophy of Improvisation. Chicago: University of Chicago Press, 2009.