257 research outputs found
Models of the Knee in the Energy Spectrum of Cosmic Rays
The origin of the knee in the energy spectrum of cosmic rays is an
outstanding problem in astroparticle physics. Numerous mechanisms have been
proposed to explain the structure in the all-particle spectrum. In the article
basic ideas of several models are summarized, including diffusive acceleration
of cosmic rays in shock fronts, acceleration via cannonballs, leakage from the
Galaxy, interactions with background particles in the interstellar medium, as
well as new high-energy interactions in the atmosphere. The calculated energy
spectra and mean logarithmic masses are compiled and compared to results from
direct and indirect measurements.Comment: 30 pages, 20 figures accepted by Astroparticle Physics captions of
figures 1-3 clarified, references adde
High Resolution Intravital Imaging of Subcellular Structures of Mouse Abdominal Organs Using a Microstage Device
Intravital imaging of brain and bone marrow cells in the skull with subcellular resolution has revolutionized neurobiology, immunology and hematology. However, the application of this powerful technology in studies of abdominal organs has long been impeded by organ motion caused by breathing and heartbeat. Here we describe for the first time a simple device designated ‘microstage’ that effectively reduces organ motions without causing tissue lesions. Combining this microstage device with an upright intravital laser scanning microscope equipped with a unique stick-type objective lens, the system enables subcellular-level imaging of abdominal organs in live mice. We demonstrate that this technique allows for the quantitative analysis of subcellular structures and gene expressions in cells, the tracking of intracellular processes in real-time as well as three-dimensional image construction in the pancreas and liver of the live mouse. As the aforementioned analyses based on subcellular imaging could be extended to other intraperitoneal organs, the technique should offer great potential for investigation of physiological and disease-specific events of abdominal organs. The microstage approach adds an exciting new technique to the in vivo imaging toolbox
Effective Hadron Dynamics: From Meson Masses to the Proton Spin Puzzle
We construct a three flavor chiral Lagrangian of pseudoscalars and vectors
with special emphasis on the symmetry breaking terms. Comparing tree level two
and three point functions with experiment allows us to first, fix the
parameters of the model (including the light quark mass ratios) and second, to
predict and
. The last mentioned quantities come
out reasonably well, in contrast to an ``ordinary" treatment. For this
purpose we need ``second order" symmetry breakers involving the vector fields
analogous to those needed for the chiral perturbation theory program with only
pseudoscalars. An improved description of the system is also
given. We then use the soliton sector of this improved chiral Lagrangian to
investigate some aspects of baryon physics which are especially sensitive to
symmetry breaking. For this purpose a fairly elaborate ``cranking" techinque is
employed in connection with the collective Hamiltonian. In addition to the
``strong" baryon mass spectrum a careful investigation is made of the
non-electromagnetic part of the neutron-proton mass difference. This work is
needed to improve our previous estimates concerning the two component approach
to the ``proton spin" puzzle. We find that both the ``matter" and ``glue"
contributions are small but they do tend to cancel each other.Comment: 33 pages, LaTe
A study on the sharp knee and fine structures of cosmic ray spectra
The paper investigates the overall and detailed features of cosmic ray (CR)
spectra in the knee region using the scenario of nuclei-photon interactions
around the acceleration sources. Young supernova remnants can be the physical
realities of such kind of CR acceleration sites. The results show that the
model can well explain the following problems simultaneously with one set of
source parameters: the knee of CR spectra and the sharpness of the knee, the
detailed irregular structures of CR spectra, the so-called "component B" of
Galactic CRs, and the electron/positron excesses reported by recent
observations. The coherent explanation serves as evidence that at least a
portion of CRs might be accelerated at the sources similar to young supernova
remnants, and one set of source parameters indicates that this portion mainly
comes from standard sources or from a single source.Comment: 13 pages, 4 figures, accepted for publication in SCIENCE CHINA
Physics, Mechanics & Astronomy
Cosmic-ray composition and its relation to shock acceleration by supernova remnants
An overview is given on the present status of the understanding of the origin
of galactic cosmic rays. Recent measurements of charged cosmic rays and photons
are reviewed. Their impact on the contemporary knowledge about the sources and
acceleration mechanisms of cosmic rays and their propagation through the Galaxy
is discussed. Possible reasons for the knee in the energy spectrum and
scenarios for the end of the galactic cosmic-ray component are described.Comment: Invited talk given at the 36th COSPAR Scientific Assembly Beijing,
China, 16 -- 23 July 2006 - submitted to Advances in Space Research -
comments are welcom
The effect of dopamine agonists on adaptive and aberrant salience in Parkinson's disease
Clinical evidence suggests that after initiation of dopaminergic medications some patients with Parkinson's disease (PD) develop psychotic symptoms, such as hallucinations and delusions. Here, we tested the hypothesis that the neurocognitive basis of this phenomenon can be defined as the formation of arbitrary and illusory associations between conditioned stimuli and reward signals, called aberrant salience. Young, never-medicated PD patients and matched controls were assessed on a speeded reaction time task in which the probe stimulus was preceded by conditioned stimuli that could signal monetary reward by color or shape. The patients and controls were re-evaluated after 12 weeks during which the patients received a dopamine agonist (pramipexole or ropinirole). Results indicated that dopamine agonists increased both adaptive and aberrant salience in PD patients, that is, formation of real and illusory associations between conditioned stimuli and reward, respectively. This effect was present when associations were assessed by means of faster responding after conditioned stimuli signaling reward (implicit salience) and overt rating of stimulus-reward links (explicit salience). However, unusual feelings and experiences, which are subclinical manifestations of psychotic-like symptoms, were specifically related to irrelevant and illusory stimulus-reward associations (aberrant salience) in PD patients receiving dopamine agonists. The learning of relevant and real stimulus-reward associations (adaptive salience) was not related to unusual experiences. These results suggest that dopamine agonists may increase psychotic-like experiences in young patients with PD, possibly by facilitating dopaminergic transmission in the ventral striatum, which results in aberrant associations between conditioned stimuli and reward
Cosmic ray acceleration at oblique shocks
We show that the diffusion approximation breaks down for particle
acceleration at oblique shocks with velocities typical of young supernova
remnants. Higher order anisotropies flatten the spectral index at
quasi-parallel shocks and steepen the spectral index at quasi-perpendicular
shocks. We compare the theory with observed spectral indices.Comment: 11 pages, 4 figures, 1 table. Accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Captivating behaviour: mouse models, experimental genetics and reductionist returns in the neurosciences
This a post-print, author-produced version of an article accepted for publication in The Sociological Review. Copyright © 2010 Wiley Blackwell. The definitive version is available at www3.interscience.wiley.comNo Abstract availabl
Cosmic Rays from the Knee to the Highest Energies
This review summarizes recent developments in the understanding of
high-energy cosmic rays. It focuses on galactic and presumably extragalactic
particles in the energy range from the knee (10^15 eV) up to the highest
energies observed (>10^20 eV). Emphasis is put on observational results, their
interpretation, and the global picture of cosmic rays that has emerged during
the last decade.Comment: Invited review, submitted to Progress in Particle and Nuclear Physic
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