226 research outputs found
Problems in relativity theory and relativistic cosmology
The thesis consists of the following three parts: PART I. Chapter I: MOLLER'S THEORY ON ENERGY AND ITS LOCALIZATION AND ITS APPLICATION TO STATIC FIELDS. The difficulties of the Einstein canonical momentum-energy pseudo-tensor are discussed. Moller's new theory on the concept of energy and its localization in general relativity is summarized (and its application by Moller criticized)and applied to find that the energy of the Schwarzschild fields is equal to the gravitational mass of, and resides inside, the material system associated with the fields. Chapter II: THE ELECTROMAGNETIC ENERGY AND THE GRAVITATIONAL MASS OF A CHARGED PARTICLE IN GENERAL RELATIVITY. The electromagnetic energy of the field of a charged particle is calculated using Moller's new theory.The contribution of to the gravitational mass of the particle is investigated. Contrary to currently accepted ideas it is shown that increases the (newtonian) gravitational mass of the particle by an amount which is precisely the mass-equivalence of PART II. ENERGY IN PLANE GRAVITATIONAL WAVES OF FINITE DURATION. The result that the passage of plane gravitational waves impart a relative velocity to test particlesoriginally at relative rest, first obtained by Bondi. Pirani and Robinson using groups of motions, is obtained here by more direct and mathematically easier methods using only the geodesic equations. This effect shows that these waves must carry energy.Moller's result that these waves carry no energy is discussed. PART III. OBSERVABLE RELATIONS IN RELATIVISTIC COSMOLOGY. A new observational criterion likely to solve the " cosmological problem" is formulated. It incorporates the fundamental property that an evolving expanding universe must be more congested at great distances than it is in the cosmic neighbourhood of the observer, while a steady-state universe must exhibit the same congestion at all distances. It is shown that this congestion, measured in suitable statistical terms by the ratio of the angular separation of galaxies from their neighbour galaxies to the angular diameter of the galaxies themselves, is proportional to in an evolving universe; it is independent of Z, the red-shift, ina steady-state universe.The applicability of the criterion and the angular diameter of a galaxy in special relativity are also discussed. <p
Variation in Interleukin 6 Receptor Gene Associates with Risk of Crohn’s Disease and Ulcerative Colitis
Interleukin 6 (IL6) is an inflammatory cytokine; signaling via its receptor (IL6R) is believed to contribute to development of inflammatory bowel diseases (IBD). The single nucleotide polymorphism rs2228145 in IL6R associates with increased levels of soluble IL6R (s-IL6R), as well as reduced IL6R signaling and risk of inflammatory disorders; its effects are similar to those of a therapeutic monoclonal antibody that blocks IL6R signaling. We used the effect of rs2228145 on s-IL6R level as an indirect marker to investigate whether reduced IL6R signaling associates with risk of ulcerative colitis (UC) or Crohn’s disease (CD). In a genome-wide meta-analysis of 20,550 patients with CD, 17647 patients with UC, and more than 40,000 individuals without IBD (controls), we found that rs2228145 (scaled to a 2-fold increase in s-IL6R) was associated with reduced risk of CD (odds ratio, 0.876; 95% CI, 0.822–0.933; P=.00003) or UC (odds ratio, 0.932; 95% CI, 0.875–0.996; P=.036). These findings indicate that therapeutics designed to block IL6R signaling might be effective in treatment of IBD
An unexpected cubic symmetry in group IV alloys prepared using pressure and temperature
The cubic diamond (Fd-3m) group IVA element Si has been the material driver of the electronics industry since its inception. We report synthesis of a new cubic (Im-3m) group IVA material, a GeSn solid solution, upon heating Ge and Sn at pressures from 13 to 28 GPa using double-sided diamond anvil laser-heating and large volume press methods. Both methods were coupled with in-situ angle dispersive X-ray diffraction characterization. The new material substantially enriches the seminal group IVA alloy materials landscape by introducing an eightfold coordinated cubic symmetry, which markedly expands on the conventional tetrahedrally coordinated cubic one. This cubic solid solution is formed, despite Ge never adopting the Im-3m symmetry, melting inhibiting subsequent Im-3m formation and reactant Ge and Sn having unlike crystal structures and atomic radii at all these pressures. This is hence achieved without adherence to conventional formation criteria and routes to synthesis. This advance creates fertile avenues for new materials development
Dense SixGe1-x (0 <x <1) Materials Landscape Using Extreme Conditions and Precession Electron Diffraction
Order parameter model for unstable multilane traffic flow
We discuss a phenomenological approach to the description of unstable vehicle
motion on multilane highways that explains in a simple way the observed
sequence of the phase transitions "free flow -> synchronized motion -> jam" as
well as the hysteresis in the transition "free flow synchronized motion".
We introduce a new variable called order parameter that accounts for possible
correlations in the vehicle motion at different lanes. So, it is principally
due to the "many-body" effects in the car interaction, which enables us to
regard it as an additional independent state variable of traffic flow. Basing
on the latest experimental data (cond-mat/9905216) we assume that these
correlations are due to a small group of "fast" drivers. Taking into account
the general properties of the driver behavior we write the governing equation
for the order parameter. In this context we analyze the instability of
homogeneous traffic flow manifesting itself in both of the mentioned above
phase transitions where, in addition, the transition "synchronized motion ->
jam" also exhibits a similar hysteresis. Besides, the jam is characterized by
the vehicle flows at different lanes being independent of one another. We
specify a certain simplified model in order to study the general features of
the car cluster self-formation under the phase transition "free flow
synchronized motion". In particular, we show that the main local parameters of
the developed cluster are determined by the state characteristics of vehicle
motion only.Comment: REVTeX 3.1, 10 pages with 10 PostScript figure
Theoretical determination of the Raman spectra of MgSiO3 perovskite and post-perovskite at high pressure
We use the density functional perturbation theory to determine for the first
time the pressure evolution of the Raman intensities for a mineral, the two
high-pressure structures of MgSiO3 perovskite and post-perovskite. At high
pressures, the Raman powder spectra reveals three main peaks for the perovskite
structure and one main peak for the post-perovskite structure. Due to the large
differences in the spectra of the two phases Raman spectroscopy can be used as
a good experimental indication of the phase transition.Comment: 16 pages, submitted to Geophysical Research Letter
Unconventional Route to High-Pressure and -Temperature Synthesis of GeSn Solid Solutions
Ge and Sn are unreactive at ambient conditions. Their significant promise for optoelectronic applications is thus largely confined to thin film investigations. We sought to remove barriers to reactivity here by accessing a unique pressure, 10 GPa, where the two elements can adopt the same crystal structure (tetragonal, /) and exhibit compatible atomic radii. The route to GeSn solid solution, however, even under these directed conditions, is different. Reaction upon heating at 10 GPa occurs between unlike crystal structures (Ge, and Sn, 4/), which also have highly incompatible atomic radii. They should not react, but they do. A reconstructive transformation of 4/ into the 4/ solid solution then follows. The new tetragonal GeSn solid solution (4/ = 5.280(1) Ã…, c = 2.915(1) Ã…, Z = 4 at 9.9 GPa and 298 K) also constitutes the structural and electronic bridge between 4-fold and newly prepared 8-fold coordinated alloy cubic symmetries. Furthermore, using this high-pressure route, bulk cubic diamond-structured GeSn alloys can now be obtained at ambient pressure. The findings here remove confining conventional criteria on routes to synthesis. This opens innovative avenues to advanced materials development
- …