354 research outputs found
The Pioneer Anomaly and a Machian Universe
We discuss astronomical and astrophysical evidence, which we relate to the
principle of zero-total energy of the Universe, that imply several relations
among the mass M, the radius R and the angular momentum L of a "large" sphere
representing a Machian Universe. By calculating the angular speed, we find a
peculiar centripetal acceleration for the Universe. This is an ubiquituous
property that relates one observer to any observable. It turns out that this is
exactly the anomalous acceleration observed on the Pioneers spaceships. We have
thus, shown that this anomaly is to be considered a property of the Machian
Universe. We discuss several possible arguments against our proposal.Comment: 6 pages including front page. Publishe
On the tree-transformation power of XSLT
XSLT is a standard rule-based programming language for expressing
transformations of XML data. The language is currently in transition from
version 1.0 to 2.0. In order to understand the computational consequences of
this transition, we restrict XSLT to its pure tree-transformation capabilities.
Under this focus, we observe that XSLT~1.0 was not yet a computationally
complete tree-transformation language: every 1.0 program can be implemented in
exponential time. A crucial new feature of version~2.0, however, which allows
nodesets over temporary trees, yields completeness. We provide a formal
operational semantics for XSLT programs, and establish confluence for this
semantics
Spin-trapping and Human Neutrophils: Limits of detection of hydroxyl radical
Using the spin trap, 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and an excess of dimethyl sulfoxide, we previously reported that in the absence of an exogenous iron catalyst, human neutrophils will not generate hydroxyl radical, manifested as the catalyse-inhibitable methyl radical spin-trapped adduct, 2,2,5-trimethyl-1-pyrrolidinyloxy (DMPO-CH3) (Britigan, B.E., Rosen, G.M., Chai, Y., and Cohen, M.S. (1986) J. Biol. Chem. 261, 4426-4431). However, superoxide destroys the preformed hydroxyl radical spin-trapped adduct, 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxy (DMPO-OH), and DMPO-CH3. The present study was undertaken to better resolve the limits of sensitivity of the spin-trapping method. Photolytically generated DMPO-CH3 and DMPO-OH slowly decomposed in the presence of a low flux (1 μM/min) of enzymatically (xanthine/xanthine oxidase)-generated superoxide, but more rapid decomposition of these adducts occurred with higher superoxide flux (5 μM/min). Inclusion of cysteine markedly increased the rate of DMPO-OH and DMPO-CH3 decomposition, masking the effects of superoxide alone. The addition of varying concentrations of superoxide dismutase did not lead to increased formation of DMPO-OH or DMPO-CH3, as should have occurred if these adducts were being destroyed by superoxide. As a positive control, we employed an iron-supplemented system with phorbol 12-myristate 13-acetate-stimulated neutrophils or xanthine/xanthine oxidase to generate DMPO-CH3. Addition of superoxide dismutase increased the magnitude of DMPO-CH3, primarily by increasing the rate of hydrogen peroxide formation, and to a lesser extent by prolonging the half-life of DMPO-CH3. Although spin-trapped adducts can be destroyed by a high concentration of superoxide, or by lower concentrations of superoxide in the presence of thiol-containing compounds, our results demonstrate that such decomposition does not interfere with the ability of the spin-trapping method to detect hydroxyl radical generated by human neutrophils. These data do not support the capacity of neutrophils to generate hydroxyl radical in the absence of an exogenous Haber-Weiss catalyst
Conformally coupled dark matter
Dark matter is obtained from a scalar field coupled conformally to
gravitation; the scalar being a relict of Dirac's gauge function. This
conformally coupled dark matter includes a gas of very light () neutral bosons having spin 0, as well as a
time-dependent global scalar field, both pervading all of the cosmic space. The
time-development of this dark matter in the expanding F-R-W universe is
investigated, and an acceptable cosmological behaviour is obtained.Comment: LaTEX File 10 pages, no figure
Stimulated human neutrophils limit iron-catalyzed hydroxyl radical formation as detected by spin-trapping techniques
Neutrophils stimulated with phorbol myristate acetate (PMA) in the presence of the spin trap 5,5-dimethyl-1-pyrroline 1-oxide (DMPO), dimethyl sulfoxide, and diethylenetriaminepentaacetic acid (DETAPAC) fail to generate hydroxyl radical (.OH), detected as the methyl spin-trapped adduct of DMPO (2,2,5-trimethyl-1-pyrrolidinyloxyl, DMPO-CH3), unless ferric salts (Fe3+) are also added (Britigan, B.E., Rosen, G.M., Chai, Y., and Cohen, M.S. (1986) J. Biol. Chem. 261, 4426-4431). Even then, .OH formation wanes in spite of ongoing superoxide (O2̇-) production. In contrast, ferric salt supplementation of a hypoxanthine/xanthine oxidase O2̇- generating system containing DETAPAC produces continual .OH, suggesting that neutrophils limit the formation of this free radical. To evaluate this hypothesis, neutrophil cytoplasts (largely devoid of granules but able to generate O2̇-) were stimulated with PMA in the presence of Fe3+, DETAPAC, dimethyl sulfoxide, and DMPO. This resulted in continual production of DMPO-CH3. In the presence of dimethyl sulfoxide, HL-60 (promyelocytic) cells differentiate into cells similar in morphology and O2̇- generating capacity to neutrophils. However, their granules lack the iron-binding protein lactoferrin (LF). Ferric salt supplementation of HL-60 cells stimulated with PMA yielded an EPR spectrum similar to cytoplasts. Supernatant obtained following PMA-induced neutrophil degranulation (which releases LF extracellularly) suppressed DMPO-CH3 formation by the hypoxanthine/xanthine oxidase/Fe3+/DETAPAC system. Anti-LF antibody, but not anti-transferrin antibody, prevented stimulated neutrophil supernatant inhibition of hypoxanthine/xanthine oxidase/Fe3+/DETAPAC-mediated .OH formation. Similarly, neutrophils stimulated with PMA in the presence of Fe3+, DETAPAC, and anti-LF antibody (but not anti-transferrin antibody) demonstrated continual formation of .OH. Neutrophil degranulation of LF limits Fe3+-catalyzed .OH formation which in vivo could protect tissue from possible .OH-mediated injury
Discrete Symmetries and Generalized Fields of Dyons
We have studied the different symmetric properties of the generalized
Maxwell's - Dirac equation along with their quantum properties. Applying the
parity (\mathcal{P}), time reversal (\mathcal{T}), charge conjugation
(\mathcal{C}) and their combined effect like parity time reversal
(\mathcal{PT}), charge conjugation and parity (\mathcal{CP}) and \mathcal{CP}T
transformations to varius equations of generalized fields of dyons, it is shown
that the corresponding dynamical quantities and equations of dyons are
invariant under these discrete symmetries.
Abstract Key words- parity, time reversal, charge-conjugation, dyons
Abstract PACS No.- 14.80 Hv
Adiabatic following criterion, estimation of the nonadiabatic excitation fraction and quantum jumps
An accurate theory describing adiabatic following of the dark, nonabsorbing
state in the three-level system is developed. An analytical solution for the
wave function of the particle experiencing Raman excitation is found as an
expansion in terms of the time varying nonadiabatic perturbation parameter. The
solution can be presented as a sum of adiabatic and nonadiabatic parts. Both
are estimated quantitatively. It is shown that the limiting value to which the
amplitude of the nonadiabatic part tends is equal to the Fourier component of
the nonadiabatic perturbation parameter taken at the Rabi frequency of the
Raman excitation. The time scale of the variation of both parts is found. While
the adiabatic part of the solution varies slowly and follows the change of the
nonadiabatic perturbation parameter, the nonadiabatic part appears almost
instantly, revealing a jumpwise transition between the dark and bright states.
This jump happens when the nonadiabatic perturbation parameter takes its
maximum value.Comment: 33 pages, 8 figures, submitted to PRA on 28 Oct. 200
A review of diagnostic and functional imaging in headache
The neuroimaging of
headache patients has revolutionised
our understanding of the pathophysiology
of primary headaches and provided
unique insights into these syndromes.
Modern imaging studies
point, together with the clinical picture,
towards a central triggering
cause. The early functional imaging
work using positron emission
tomography shed light on the genesis
of some syndromes, and has
recently been refined, implying that
the observed activation in migraine
(brainstem) and in several trigeminal-autonomic headaches (hypothalamic
grey) is involved in the pain
process in either a permissive or
triggering manner rather than simply
as a response to first-division nociception
per se. Using the advanced
method of voxel-based morphometry,
it has been suggested that there
is a correlation between the brain
area activated specifically in acute
cluster headache — the posterior
hypothalamic grey matter — and an
increase in grey matter in the same
region. No structural changes have
been found for migraine and medication
overuse headache, whereas
patients with chronic tension-type
headache demonstrated a significant
grey matter decrease in regions
known to be involved in pain processing.
Modern neuroimaging thus
clearly suggests that most primary
headache syndromes are predominantly
driven from the brain, activating
the trigeminovascular reflex and
needing therapeutics that act on both
sides: centrally and peripherally
Low-field MRI: a report on the 2022 ISMRM workshop
In March 2022, the first ISMRM Workshop on Low-Field MRI was held virtually. The goals of this workshop were to discuss recent low field MRI technology including hardware and software developments, novel methodology, new contrast mechanisms, as well as the clinical translation and dissemination of these systems. The virtual Workshop was attended by 368 registrants from 24 countries, and included 34 invited talks, 100 abstract presentations, 2 panel discussions, and 2 live scanner demonstrations. Here, we report on the scientific content of the Workshop and identify the key themes that emerged. The subject matter of the Workshop reflected the ongoing developments of low-field MRI as an accessible imaging modality that may expand the usage of MRI through cost reduction, portability, and ease of installation. Many talks in this Workshop addressed the use of computational power, efficient acquisitions, and contemporary hardware to overcome the SNR limitations associated with low field strength. Participants discussed the selection of appropriate clinical applications that leverage the unique capabilities of low-field MRI within traditional radiology practices, other point-of-care settings, and the broader community. The notion of "image quality" versus "information content" was also discussed, as images from low-field portable systems that are purpose-built for clinical decision-making may not replicate the current standard of clinical imaging. Speakers also described technical challenges and infrastructure challenges related to portability and widespread dissemination, and speculated about future directions for the field to improve the technology and establish clinical value.Radiolog
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
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