1,959 research outputs found
Analytic perturbation theory in QCD and Schwinger's connection between the beta-function and the spectral density
We argue that a technique called analytic perturbation theory leads to a
well-defined method for analytically continuing the running coupling constant
from the spacelike to the timelike region, which allows us to give a
self-consistent definition of the running coupling constant for timelike
momentum. The corresponding -function is proportional to the spectral
density, which confirms a hypothesis due to Schwinger.Comment: 11 pages, 2 figure
P38 MAP Kinase inhibition promotes primary tumour growth via VEGF independent mechanism
<p>Abstract</p> <p>Background</p> <p>The surgical insult induces an inflammatory response that activates P38 MAP kinases and solid tumours can also release cytokines. Therfore inhibition of these pathways may reduce tumour growth We set out to examine the effects of P38-MAPK inhibition on apoptosis, proliferation, VEGF release and cell cycle effects <it>in-vitro </it>and on primary tumour growth <it>in-vivo</it>.</p> <p>Methods</p> <p>4T-1 cells (2 × 10<sup>5</sup>cells/well) were incubated, in 24 well plates with control, 25, 50 or 100 ng/ml of SB-202190 for 24 hours. Cells were subsequently asessed for apoptosis, proliferation, VEGF release and cell cycle analysis. Balb-c mice each received 1 × 10<sup>6 </sup>4T1 cells subcutaneously in the flank and were then randomised to receive control or SB202190 (2.5 μM/kg) by intraperitoneal injection daily. Tumour size was measured alternate days and at day 24 animals were sacrificed and serum VEGF assessed.</p> <p>Results</p> <p>P38-MAPK inhibition <it>in-vitro </it>resulted in a significant reduction in proliferation (75.2 ± 8.4% vs. 100 ± 4.3%, p < 0.05) and G<sub>1 </sub>cell cycle phase(35.9 ± 1.1% vs. 32.5 ± 0.6%, p < 0.05) but no significant changes in apoptosis or VEGF levels. <it>In-vivo</it>, P38-MAPK inhibition resulted in an increase in primary tumour growth (155.6 ± 34.9 vs. 86.7 ± 18.2 mm<sup>3</sup>, p < 0.05). P38-MAPK inhibition also lowered circulating VEGF levels but this difference was not significant (101.9 ± 27.1 ηg/ml compared to 158.6 ± 27.1 ηg/ml)</p> <p>Conclusion</p> <p>These findings demonstrate that P38-MAPK inhibition in-vitro reduces proliferation and G<sub>1 </sub>cell cycle phase as well as promoting primary tumour growth in-vivo. These effects would appear to be independent of VEGF.</p
The role of endotoxin/lipopolysaccharide in surgically induced tumour growth in a murine model of metastatic disease
Surgical removal of a primary tumour is often followed by rapid growth of previously dormant metastases. Endotoxin or lipopolysaccharide, a cell wall constituent of Gram-negative bacteria, is ubiquitously present in air and may be introduced during surgery. BALB/c mice received a tail vein injection of 105 4T1 mouse mammary carcinoma cells. Two weeks later, animals were subjected to surgical trauma or an intraperitoneal injection of endotoxin (10 μg per animal). Five days later, animals which underwent open surgery, laparoscopy with air sufflation or received an endotoxin injection displayed increased lung metastasis compared to anaesthetic controls. These increases in metastatic tumour growth were reflected in increased tumour cell proliferation and decreased apoptosis within lung metastases. Circulating levels of the angiogenic cytokine, vascular endothelial growth factor (VEGF), were also elevated in these groups and correlated with increased plasma levels of endotoxin. Endotoxin treatment for 18 h (>10 ng ml–1) directly up-regulated VEGF production by the 4T1 tumour cells in vitro. Metastatic tumour growth in mice undergoing carbon dioxide laparoscopy, where air is excluded, was similar to anaesthetic controls. These data indicate that endotoxin introduced during surgery is associated with the enhanced growth of metastases following surgical trauma, by altering the critical balances governing cellular growth and angiogenesis. © 1999 Cancer Research Campaig
Computer recommendations for an automatic approach and landing system for V/STOL aircraft. Volume 2 - Equations
Automatic approach and landing system for V/STOL aircraf
Dirac Cat States in Relativistic Landau Levels
We show that a relativistic version of Schrodinger cat states, here called
Dirac cat states, can be built in relativistic Landau levels when an external
magnetic field couples to a relativistic spin 1/2 charged particle. Under
suitable initial conditions, the associated Dirac equation produces unitarily
Dirac cat states involving the orbital quanta of the particle in a well defined
mesoscopic regime. We demonstrate that the proposed Dirac cat states have a
purely relativistic origin and cease to exist in the non-relativistic limit. In
this manner, we expect to open relativistic quantum mechanics to the rich
structures of quantum optics and quantum information.Comment: Revtex4, color figures, submitted for publicatio
Differential effects of lower limb revascularisation on organ injury and the role of the amino acid taurine
Lower torso revascularisation following ischaemia results in a systemic inflammatory response. Endothelial barrier function is disrupted by neutrophil-derived proteases and oxidants. Taurine, an amino acid found in large quantities in neutrophils, is a powerful endogeneous anti-oxidant. The aims of this study were to investigate the systemic effects of reperfusion following lower limb revascularisation and to evaluate the role of taurine administration in preventing this injury. A rat model of aortic occlusion (30 min) followed by 2 h of reperfusion was used. Animals were randomised to one of three groups (n = 10 per group): control; ischaemia reperfusion untreated (IR) and taurine-treated. Taurine (4% solution) was administrated orally for 48 h prior to the experiment. Neutrophil infiltration and microvascular permeability were assessed by measuring tissue myeloperoxidase activity and wet/dry weights respectively in lung, liver, kidney, and in cardiac and skeletal muscle. Statistical analysis was by means of analysis of variance (ANOVA). Reperfusion resulted in pulmonary and renal microvascular injury as assessed by organ oedema. Hepatic tissue, skeletal and cardiac muscle were unaffected by lower limb revascularisation. Taurine was effective in preventing neutrophil-mediated pulmonary but not renal microvascular injury. These data suggest that, whilst reperfusion-induced pulmonary injury is predominantly neutrophilmediated, agents other than neutrophil-derived oxidative metabolites, capable of independently causing organ injury through direct endothelial damage, are produced during reperfusion
Uncovering the Neural Signature of Lapsing Attention: Electrophysiological Signals Predict Errors up to 20 s before They Occur
The extent to which changes in brain activity can foreshadow human error is uncertain yet has important theoretical and practical implications. The present study examined the temporal dynamics of electrocortical signals preceding a lapse of sustained attention. Twenty-one participants performed a continuous temporal expectancy task, which involved continuously monitoring a stream of regularly alternating patterned stimuli to detect a rarely occurring target stimulus whose duration was 40% longer. The stimulus stream flickered at a rate of 25 Hz to elicit a steady-state visual-evoked potential (SSVEP), which served as a continuous measure of basic visual processing. Increasing activity in the band (8 –14 Hz) was found beginning20 s before a missed target. This was followed by decreases in the amplitude of two event-related components over a short pretarget time frame: the frontal P3 (3– 4 s) and contingent-negative variation (during the target interval). In contrast, SSVEP amplitude before hits and misses was closely matched, suggesting that the efficacy of ongoing basic visual processing was unaffected. Our results show that the specific neural signatures of attentional lapses are registered in the EEG up to 20 s before an error
Taming Landau singularities in QCD perturbation theory: The analytic approach 2.0
The aim of this topical article is to outline the fundamental ideas
underlying the recently developed Fractional Analytic Perturbation Theory
(FAPT) of QCD and present its main calculational tools together with key
applications. For this, it is first necessary to review previous methods to
apply QCD perturbation theory at low spacelike momentum scales, where the
influence of the Landau singularities becomes inevitable. Several concepts are
considered and their limitations are pointed out. The usefulness of FAPT is
discussed in terms of two characteristic hadronic quantities: the
perturbatively calculable part of the pion's electromagnetic form factor in the
spacelike region and the Higgs-boson decay into a pair in the
timelike region. In the first case, the focus is on the optimization of the
prediction with respect to the choice of the renormalization scheme and the
dependence on the renormalization and the factorization scales. The second case
serves to show that the application of FAPT to this reaction reaches already at
the four-loop level an accuracy of the order of 1%, avoiding difficulties
inherent in the standard perturbative expansion. The obtained results are
compared with estimates from fixed-order and contour-improved QCD perturbation
theory. Using the brand-new Higgs mass value of about 125 GeV, measured at the
Large Hadron Collider (CERN), a prediction for is extracted.Comment: v3: 23 pages, 7 figures, Invited topical article published in
Particles and Nuclei with update using the CERN Higgs discovery. Abridged
version presented as plenary talk at International Conference on
Renormalization Group and Related Topics (RG 2008), Dubna, Russia, September
1 - 5, 2008. v4 typo in Eq. (3) correcte
A differential identity for Green functions
If P is a differential operator with constant coefficients, an identity is
derived to calculate the action of exp(P) on the product of two functions. In
many-body theory, P describes the interaction Hamiltonian and the identity
yields a hierarchy of Green functions. The identity is first derived for scalar
fields and the standard hierarchy is recovered. Then the case of fermions is
considered and the identity is used to calculate the generating function for
the Green functions of an electron system in a time-dependent external
potential.Comment: 14 page
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