41,531 research outputs found
Metal (2) 4,4',4",4'" phthalocyanine tetraamines as curing agents for epoxy resins
Metal, preferably divalent copper, cobalt or nickel, phthalocyanine tetraamines are used as curing agents for epoxides. The resulting copolymers have high thermal and chemical resistance and are homogeneous. They are useful as binders for laminates, e.g., graphite cloth laminate
Metal phthalocyanine intermediates for the preparation of polymers
Metal 4, 4', 4"",-tetracarboxylic phthalocyanines (MPTC) are prepared by reaction of trimellitic anhydride, a salt or hydroxide of the desired metal (or the metal in powdered form), urea and a catalyst. A purer form of MPTC is prepared than heretofore. These tetracarboxylic acids are then polymerized by heat to sheet polymers which have superior heat and oxidation resistance. The metal is preferably a divalent metal having an atomic radius close to 1.35A
Metal phthalocyanine polymers
Metal 4, 4', 4", 4"'=tetracarboxylic phthalocyanines (MPTC) are prepared by reaction of trimellitic anhydride, a salt or hydroxide of the desired metal (or the metal in powdered form), urea and a catalyst. A purer form of MPTC is prepared than heretofore. These tetracarboxylic acids are then polymerized by heat to sheet polymers which have superior heat and oxidation resistance. The metal is preferably a divalent metal having an atomic radius close to 1.35A
Relation Between Einstein And Quantum Field Equations
We show that there exists a choice of scalar field modes, such that the
evolution of the quantum field in the zero-mass and large-mass limits is
consistent with the Einstein equations for the background geometry. This choice
of modes is also consistent with zero production of these particles and thus
corresponds to a preferred vacuum state preserved by the evolution. In the
zero-mass limit, we find that the quantum field equation implies the Einstein
equation for the scale factor of a radiation-dominated universe; in the
large-mass case, it implies the corresponding Einstein equation for a
matter-dominated universe. Conversely, if the classical radiation-dominated or
matter-dominated Einstein equations hold, there is no production of scalar
particles in the zero and large mass limits, respectively. The suppression of
particle production in the large mass limit is over and above the expected
suppression at large mass. Our results hold for a certain class of conformally
ultrastatic background geometries and therefore generalize previous results by
one of us for spatially flat Robertson-Walker background geometries. In these
geometries, we find that the temporal part of the graviton equations reduces to
the temporal equation for a massless minimally coupled scalar field, and
therefore the results for massless particle production hold also for gravitons.
Within the class of modes we study, we also find that the requirement of zero
production of massless scalar particles is not consistent with a non-zero
cosmological constant. Possible implications are discussed.Comment: Latex, 24 pages. Minor changes in text from original versio
Populations of Pear Thrips, \u3ci\u3eTaeniothrips Inconsequens\u3c/i\u3e (Thysanoptera: Thripidae) in Sugar Maple Stands in Vermont: 1989-2005
Development of an effective IPM strategy for pear thrips, Taeniothrips inconsequens (Uzel) (Thysanoptera: Thripidae), a pest of sugar maple, Acer saccharum Marshall, demands an understanding of their population fluctuations over time. Pear thrips populations were monitored using a standardized soil sampling method every fall from 1989 – 2005 in 14 counties of Vermont (U.S.). Data from individual sites were combined into north, central and south regions. High numbers of thrips emerged from soil sampled in 1989, 1990, 1993 and 2001, particularly in the north region (Washington, Lamoille, and Franklin counties). The central and south regions had lower pear thrips populations over all years. These results provide, for the first time, fundamental knowledge of pear thrips populations across a wide geographical area of Vermont and will assist in the design of suitable control strategies for pear thrips in the future
Instability of Rotationally Tuned Dipolar Bose-Einstein Condensates
The possibility of effectively inverting the sign of the dipole-dipole
interaction, by fast rotation of the dipole polarization, is examined within a
harmonically trapped dipolar Bose-Einstein condensate. Our analysis is based on
the stationary states in the Thomas-Fermi limit, in the corotating frame, as
well as direct numerical simulations in the Thomas-Fermi regime, explicitly
accounting for the rotating polarization. The condensate is found to be
inherently unstable due to the dynamical instability of collective modes. This
ultimately prevents the realization of robust and long-lived rotationally tuned
states. Our findings have major implications for experimentally accessing this
regime.Comment: 9 pages with 5 figure
Observing collapse in two colliding dipolar Bose-Einstein condensates
We study the collision of two Bose-Einstein condensates with pure dipolar
interaction. A stationary pure dipolar condensate is known to be stable when
the atom number is below a critical value. However, collapse can occur during
the collision between two condensates due to local density fluctuations even if
the total atom number is only a fraction of the critical value. Using full
three-dimensional numerical simulations, we observe the collapse induced by
local density fluctuations. For the purpose of future experiments, we present
the time dependence of the density distribution, energy per particle and the
maximal density of the condensate. We also discuss the collapse time as a
function of the relative phase between the two condensates.Comment: 6 pages, 7 figure
Next-to-leading term of the renormalized stress-energy tensor of the quantized massive scalar field in Schwarzschild spacetime. The back reaction
The next-to-leading term of the renormalized stress-energy tensor of the
quantized massive field with an arbitrary curvature coupling in the spacetime
of the Schwarzschild black hole is constructed. It is achieved by functional
differentiation of the DeWitt-Schwinger effective action involving coincidence
limit of the Hadamard-Minakshisundaram-DeWitt-Seely coefficients and
The back reaction of the quantized field upon the Schwarzschild black
hole is briefly discussed
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