372 research outputs found
Chandra HETGS Multiphase Spectroscopy Of The Young Magnetic O Star Theta(1) Orionis C
We report on four Chandra grating observations of the oblique magnetic rotator theta(1) Ori C (O5.5 V), covering a wide range of viewing angles with respect to the star\u27s 1060 G dipole magnetic field. We employ line-width and centroid analyses to study the dynamics of the X-ray - emitting plasma in the circumstellar environment, as well as line-ratio diagnostics to constrain the spatial location, and global spectral modeling to constrain the temperature distribution and abundances of the very hot plasma. We investigate these diagnostics as a function of viewing angle and analyze them in conjunction with new MHD simulations of the magnetically channeled wind shock mechanism on theta(1) Ori C. This model fits all the data surprisingly well, predicting the temperature, luminosity, and occultation of the X-ray - emitting plasma with rotation phase
The Benefits and Harms of Transmitting Into Space
Deliberate and unintentional radio transmissions from Earth propagate into
space. These transmissions could be detected by extraterrestrial watchers over
interstellar distances. Here, we analyze the harms and benefits of deliberate
and unintentional transmissions relevant to Earth and humanity. Comparing the
magnitude of deliberate radio broadcasts intended for messaging to
extraterrestrial intelligence (METI) with the background radio spectrum of
Earth, we find that METI attempts to date have much lower detectability than
emissions from current radio communication technologies on Earth. METI
broadcasts are usually transient and several orders of magnitude less powerful
than other terrestrial sources such as astronomical and military radars, which
provide the strongest detectable signals. The benefits of radio communication
on Earth likely outweigh the potential harms of detection by extraterrestrial
watchers; however, the uncertainty regarding the outcome of contact with
extraterrestrial beings creates difficulty in assessing whether or not to
engage in long-term and large-scale METI.Comment: Published in Space Polic
Color television study Final report, Nov. 1965 - Mar. 1966
Color television camera for transmission from lunar and earth orbits and lunar surfac
Oversampling Increases the Pre-Log of Noncoherent Rayleigh Fading Channels
We analyze the capacity of a continuous-time, time-selective, Rayleigh
block-fading channel in the high signal-to-noise ratio (SNR) regime. The fading
process is assumed stationary within each block and to change independently
from block to block; furthermore, its realizations are not known a priori to
the transmitter and the receiver (noncoherent setting). A common approach to
analyzing the capacity of this channel is to assume that the receiver performs
matched filtering followed by sampling at symbol rate (symbol matched
filtering). This yields a discrete-time channel in which each transmitted
symbol corresponds to one output sample. Liang & Veeravalli (2004) showed that
the capacity of this discrete-time channel grows logarithmically with the SNR,
with a capacity pre-log equal to . Here, is the number of
symbols transmitted within one fading block, and is the rank of the
covariance matrix of the discrete-time channel gains within each fading block.
In this paper, we show that symbol matched filtering is not a
capacity-achieving strategy for the underlying continuous-time channel.
Specifically, we analyze the capacity pre-log of the discrete-time channel
obtained by oversampling the continuous-time channel output, i.e., by sampling
it faster than at symbol rate. We prove that by oversampling by a factor two
one gets a capacity pre-log that is at least as large as . Since the
capacity pre-log corresponding to symbol-rate sampling is , our result
implies indeed that symbol matched filtering is not capacity achieving at high
SNR.Comment: To appear in the IEEE Transactions on Information Theor
'Don't box me in': Blurred lines in 'Waking Life' and 'A Scanner Darkly'
This is the author's accepted manuscript. The final published article is available from the link below.This article seeks to evaluate the visual style of Waking Life and A Scanner Darkly, predominantly through an analysis of the filmsâ aesthetics. The use of Rotoshop as an expressive means to illustrate character and theme, where identity becomes sketched and multi-faceted rather than fixed or stable is explored here. Yet this aesthetic play with borders has a greater resonance than simply a means by which to delineate thematic preoccupations with troubled identity. While such representations are indeed key to these two films, the darkly outlined contours of character borders, which move and slide incessantly, also comment on the blurred divide between live action and animation. Central to the argument is the use of the animated line in understanding these two films; the line provides impetus for exploring several issues raised by the films and the use of Rotoshop. This article explores the following key ideas: the animated line and aesthetic analysis; Rotoshop technology; the representation of fragmentary identity; and the relationship between photo-real cinema and animation, with a particular focus on narrative and spectacle. The author addresses Rotoshop within the context of technology and spectacle; taking industry practices into account allows for an appreciation of how a technological innovation such as Rotoshop can change the shape of live-action cinema
Competing orders in one-dimensional half-filled multicomponent fermionic cold atoms: The Haldane-charge conjecture
We investigate the nature of the Mott-insulating phases of half-filled
2N-component fermionic cold atoms loaded into a one-dimensional optical
lattice. By means of conformal field theory techniques and large-scale DMRG
calculations, we show that the phase diagram strongly depends on the parity of
. First, we single out charged, spin-singlet, degrees of freedom, that carry
a pseudo-spin allowing to formulate a Haldane conjecture: for
attractive interactions, we establish the emergence of Haldane insulating
phases when is even, whereas a metallic behavior is found when is odd.
We point out that the cases do \emph{not} have the generic properties
of each family. The metallic phase for odd and larger than 1 has a
quasi-long range singlet pairing ordering with an interesting edge-state
structure. Moreover, the properties of the Haldane insulating phases with even
further depend on the parity of N/2. In this respect, within the low-energy
approach, we argue that the Haldane phases with N/2 even are not topologically
protected but equivalent to a topologically trivial insulating phase and thus
confirm the recent conjecture put forward by Pollmann {\it et al.} [Pollmann
{\it et al.}, arXiv:0909.4059 (2009)].Comment: 25 pages, 20 figure
Treatise on Hearing: The Temporal Auditory Imaging Theory Inspired by Optics and Communication
A new theory of mammalian hearing is presented, which accounts for the
auditory image in the midbrain (inferior colliculus) of objects in the
acoustical environment of the listener. It is shown that the ear is a temporal
imaging system that comprises three transformations of the envelope functions:
cochlear group-delay dispersion, cochlear time lensing, and neural group-delay
dispersion. These elements are analogous to the optical transformations in
vision of diffraction between the object and the eye, spatial lensing by the
lens, and second diffraction between the lens and the retina. Unlike the eye,
it is established that the human auditory system is naturally defocused, so
that coherent stimuli do not react to the defocus, whereas completely
incoherent stimuli are impacted by it and may be blurred by design. It is
argued that the auditory system can use this differential focusing to enhance
or degrade the images of real-world acoustical objects that are partially
coherent. The theory is founded on coherence and temporal imaging theories that
were adopted from optics. In addition to the imaging transformations, the
corresponding inverse-domain modulation transfer functions are derived and
interpreted with consideration to the nonuniform neural sampling operation of
the auditory nerve. These ideas are used to rigorously initiate the concepts of
sharpness and blur in auditory imaging, auditory aberrations, and auditory
depth of field. In parallel, ideas from communication theory are used to show
that the organ of Corti functions as a multichannel phase-locked loop (PLL)
that constitutes the point of entry for auditory phase locking and hence
conserves the signal coherence. It provides an anchor for a dual coherent and
noncoherent auditory detection in the auditory brain that culminates in
auditory accommodation. Implications on hearing impairments are discussed as
well.Comment: 603 pages, 131 figures, 13 tables, 1570 reference
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