48 research outputs found
Environment-Induced Decoherence and the Transition From Quantum to Classical
We study dynamics of quantum open systems, paying special attention to those
aspects of their evolution which are relevant to the transition from quantum to
classical. We begin with a discussion of the conditional dynamics of simple
systems. The resulting models are straightforward but suffice to illustrate
basic physical ideas behind quantum measurements and decoherence. To discuss
decoherence and environment-induced superselection einselection in a more
general setting, we sketch perturbative as well as exact derivations of several
master equations valid for various systems. Using these equations we study
einselection employing the general strategy of the predictability sieve.
Assumptions that are usually made in the discussion of decoherence are
critically reexamined along with the ``standard lore'' to which they lead.
Restoration of quantum-classical correspondence in systems that are classically
chaotic is discussed. The dynamical second law -it is shown- can be traced to
the same phenomena that allow for the restoration of the correspondence
principle in decohering chaotic systems (where it is otherwise lost on a very
short time-scale). Quantum error correction is discussed as an example of an
anti-decoherence strategy. Implications of decoherence and einselection for the
interpretation of quantum theory are briefly pointed out.Comment: 80 pages, 7 figures included, Lectures given by both authors at the
72nd Les Houches Summer School on "Coherent Matter Waves", July-August 199
Detecting violations of temporal regularities in waking and sleeping two-month-old infants
Correctly processing rapid sequences of sounds is essential for developmental milestones, such as language acquisition. We investigated the sensitivity of two-month-old infants to violations of a temporal regularity, by recording event-related brain potentials (ERP) in an auditory oddball paradigm from 36 waking and 40 sleeping infants. Standard tones were presented at a regular 300 ms inter-stimulus interval (ISI). One deviant, otherwise identical to the standard, was preceded by a 100 ms ISI. Two other deviants, presented with the standard ISI, differed from the standard in their spectral makeup. We found significant differences between ERP responses elicited by the standard and each of the deviant sounds. The results suggest that the ability to extract both temporal and spectral regularities from a sound sequence is already functional within the first few months of life. The scalp distribution of all three deviant-stimulus responses was influenced by the infants‟ state of alertness
Scalar field "mini--MACHOs": a new explanation for galactic dark matter
We examine the possibility that galactic halos are collisionless ensembles of
scalar field ``massive compact halo objects'' (MACHOs). Using mass constraints
from MACHO microlensing and from theoretical arguments on halos made up of
massive black holes, as well as demanding also that scalar MACHO ensambles of
all scales do not exhibit gravothermal instability (as required by consistency
with observations of LSB galaxies), we obtain the range: m\alt 10^{-7}
M_\odot or 30 M_\odot\alt m\alt 100 M_\odot. The rather narrow mass range of
large MACHOs seems to indicate that the ensambles we are suggesting should be
probably made up of scalar MACHOs in the low mass range (``mini--MACHOs''). The
proposed model allows one to consider a non--baryonic and non--thermal
fundamental nature of dark matter, while at the same time keeping the same
phenomenology of the CDM paradigm.Comment: 5 pages, 1 eps figure. RevTex 4 style. To appear in Physical Review
The evolution of language: a comparative review
For many years the evolution of language has been seen as a disreputable topic, mired in fanciful "just so stories" about language origins. However, in the last decade a new synthesis of modern linguistics, cognitive neuroscience and neo-Darwinian evolutionary theory has begun to make important contributions to our understanding of the biology and evolution of language. I review some of this recent progress, focusing on the value of the comparative method, which uses data from animal species to draw inferences about language evolution. Discussing speech first, I show how data concerning a wide variety of species, from monkeys to birds, can increase our understanding of the anatomical and neural mechanisms underlying human spoken language, and how bird and whale song provide insights into the ultimate evolutionary function of language. I discuss the ‘‘descended larynx’ ’ of humans, a peculiar adaptation for speech that has received much attention in the past, which despite earlier claims is not uniquely human. Then I will turn to the neural mechanisms underlying spoken language, pointing out the difficulties animals apparently experience in perceiving hierarchical structure in sounds, and stressing the importance of vocal imitation in the evolution of a spoken language. Turning to ultimate function, I suggest that communication among kin (especially between parents and offspring) played a crucial but neglected role in driving language evolution. Finally, I briefly discuss phylogeny, discussing hypotheses that offer plausible routes to human language from a non-linguistic chimp-like ancestor. I conclude that comparative data from living animals will be key to developing a richer, more interdisciplinary understanding of our most distinctively human trait: language
Long term treatment with clonidine during the development of hypertension in spontaneously hypertensive rats.
Chronic administration of clonidine in the drinking water of spontaneously hypertensive (SH) rats from 11 through 17 weeks of age prevented the further development of hypertension in this model. A dosage adjustment (from about 0.1 to 0.5 mg/kg) was required to maintain a stable systolic pressure of about 200 mmHg. After six weeks of treatment clonidine was withheld for 48 hrs during which time blood pressure increased to a level similar to that of untreated controls