8,972 research outputs found
The Cosmic Microwave Background Spectrum and a Determination of Fractal Space Dimensionality
The possibility to constrain fractal space dimensionality from Astrophysics
and other areas is briefly reviewed. Assuming such dimensionality to be , a limit to can be inferred from COBE satellite data. The
available data for the cosmic microwave background radiation spectrum are
fitted by a Planck's radiation distribution generalized to non integer space
dimensionality. Our analysis shows that the shape of the CMBR spectrum, which
does not depend on the absolute normalization, is correctly described from this
distribution provided the absolute temperature is equal to 2.726
K and .
This value for is shown to be consistent with what is found on a
very different spatial scale based on a quantum field phenomenon. The
is interpreted as an upper limit for how much space dimensionality
could have deviated from three. In other words, this is the maximum fluctuation
space dimensionality should have experienced in a spatial and temporal scale
compared to that of the decoupling era.Comment: 6 pages, 2 figure
Book Reviews
We develop a first-principles approach based on many-body perturbation theory to investigate the effects of the interaction between electrons and carrier plasmons on the electronic properties of highly doped semiconductors and oxides. Through the evaluation of the electron self-energy, we account simultaneously for electron-plasmon and electron-phonon coupling in theoretical calculations of angle-resolved photoemission spectra, electron linewidths, and relaxation times. We apply this methodology to electron-doped anatase TiO2 as an illustrative example. The simulated spectra indicate that electron-plasmon coupling in TiO2 underpins the formation of satellites at energies comparable to those of polaronic spectral features. At variance with phonons, however, the energy of plasmons and their spectral fingerprints depends strongly on the carrier concentration, revealing a complex interplay between plasmon and phonon satellites. The electron-plasmon interaction accounts for approximately 40% of the total electron-boson interaction strength, and it is key to improve the agreement with measured quasiparticle spectra
Comparison of LPS-stimulated release of cytokines in punch versus transwell tissue culture systems of human gestational membranes
Abstract Background Cytokine signaling within the amnionic, chorionic and decidual extraplacental gestational membranes plays an important role in membrane rupture and the timing of birth. The predominant in vitro explant culture system for evaluating cytokine induction in human gestational membranes has been the free-floating biopsy punch culture. Punch systems have been used to investigate the impact of various toxicants, pharmaceuticals and genetic variation on expression of pro-inflammatory cytokines. More recently, a dual compartment transwell culture system has been developed that more closely mimics the intrauterine compartment. The current study compares these two systems with respect to release of pro- and anti-inflammatory cytokines in response to lipopolysaccharide (LPS), a model stimulant. Methods Tissue samples were exposed to 100 ng/ml LPS for 12 h and cytokines were measured by ELISA. Data are expressed as increase relative to non-treated controls. Results Levels of interleukin-6 increased in punch culture medium samples to a significantly greater extent (34.2 fold) compared with medium from transwell cultures in the amnion (6.6 fold) or choriodecidual (7.1 fold) compartments. Interleukin-8 also showed a significantly greater induction in punch (4.8 fold) than transwell amnion (1.6 fold) or choriodecidual (1.7 fold) samples. The anti-inflammatory interleukin-10 showed a significant difference between punch (36.5 fold) and transwell amnion (15.4 fold) samples, but no difference was observed between punch and transwell choriodecidual (28.5 fold) samples. Neither interleukin-1beta nor tumor necrosis factor-alpha (TNF-alpha) showed a significant difference between the punch and transwell samples. Conclusions These results indicate that the pattern of LPS-stimulated cytokine release from gestational membranes in vitro depends on the culture system used, confounding comparisons of studies that use different gestational membrane culture systems to study inflammatory responses.http://deepblue.lib.umich.edu/bitstream/2027.42/78253/1/1477-7827-8-121.xmlhttp://deepblue.lib.umich.edu/bitstream/2027.42/78253/2/1477-7827-8-121.pdfPeer Reviewe
Off-diagonal helicity density matrix elements for vector mesons produced in polarized e+e- processes
Final state quark-antiquark interactions give origin to non zero values of
the off-diagonal element rho_{1,-1} of the helicity density matrix of vector
mesons produced in e+e- annihilations, as confirmed by recent OPAL data on Phi,
D^* and K^*'s. New predictions are given for rho_{1,-1} of several mesons
produced at large x_E and small p_T -- i.e. collinear with the parent jet -- in
the annihilation of polarized e+ and e-; the results depend strongly on the
elementary dynamics and allow further non trivial tests of the Standard Model.Comment: LaTeX, 20 pages, 6 ps figures, uses epsfig.st
Giant enhanced optical nonlinearity of colloidal nanocrystals with a graded-index host
The effective linear and third-order nonlinear optical properties of metallic
colloidal crystal immersed in a graded-index host fluid are investigated
theoretically. The local electric fields are extracted self-consistently based
on the layer-to-layer interactions, which are readily given by the Lekner
summation method. The resultant optical absorption and nonlinearity enhancement
show a series of sharp peaks, which merge in a broadened resonant band. The
sharp peaks become a continuous band for increasing packing density and number
of layers. We believe that the sharp peaks arise from the in-plane dipolar
interactions and the surface plasmon resonance, whereas the continuous band is
due to the presence of the gradient in the host refractive index. These results
have not been observed in homogeneous and randomly-dispersed colloids, and thus
would be of great interest in optical nanomaterial engineering.Comment: Submitted to Applied Physics Letter
- âŠ