12,073 research outputs found
A study of high frequency nonlinear combustion instability in baffled annular liquid propellant rocket motors
Computer program contains mathematical model which provides relationship between engine gas dynamics and combustion processes. Mathematically simulated explosions initiate gas disturbances. Design methods for damping disturbances can be studied to prevent future engine shutdown or destruction
Comment on decay puzzle
We analize the current data on -lepton decays and show that they are
consistent with the Standard ModelComment: 5 pages, 1 figure (available from de authors), Latex, preprint
IFT-P.022/9
Inclusive Quark Production in -Annihilation - A Path Integral Approach
The single-particle inclusive differential cross-section for a reaction
is written as imaginary part of a correlation function in a
forward scattering amplitude for in a modified effective theory.
In this modified theory the interaction Hamiltonian equals
of the original theory up to a certain time. Then there is a sign change and
becomes nonlocal. This is worked out in detail for scalar field
models and for QED plus the abelian gluon model. A suitable path integral for
direct calculations of inclusive cross sections is presented.Comment: Latex, 5 pages, 2 figures, talk given at the QCD 00 Euroconference,
Montpellier, 6-13 July 200
Mearsurement of and the function with the DELPHI detector at LEP
Event shape distributions in annihilation are determined from the
DELPHI data taken between 183 and 207\gev. From these the strong coupling
is extracted with several techniques. Together with the results from
other LEP2 energies and at about this allows both, a combined measurement
of and a test of the scale dependence of the strong interaction.
Alternatively the renormalisation group invariant (RGI) perturbation theory is
applied to measure the function of strong interaction. The results are
good agreement with the QCD expectation and allow to exclude the existence of
light gluinos with a mass below 30\gev in a model independent way.Comment: Talk presented at the QCD02 conference, Montpellier 200
The Noncommutative Doplicher-Fredenhagen-Roberts-Amorim Space
This work is an effort in order to compose a pedestrian review of the
recently elaborated Doplicher, Fredenhagen, Roberts and Amorim (DFRA)
noncommutative (NC) space which is a minimal extension of the DFR space. In
this DRFA space, the object of noncommutativity () is a
variable of the NC system and has a canonical conjugate momentum. The DFRA
formalism is constructed in an extended space-time with independent degrees of
freedom associated with the object of noncommutativity . A
consistent algebra involving the enlarged set of canonical operators is
described, which permits one to construct theories that are dynamically
invariant under the action of the rotation group. A consistent classical
mechanics formulation is analyzed in such a way that, under quantization, it
furnishes a NC quantum theory with interesting results. The Dirac formalism for
constrained Hamiltonian systems is considered and the object of
noncommutativity plays a fundamental role as an independent
quantity. It is also explained about the generalized Dirac equation issue, that
the fermionic field depends not only on the ordinary coordinates but on
as well. The dynamical symmetry content of such fermionic
theory is discussed, and we show that its action is invariant under . In the last part of this work we analyze the complex scalar fields using
this new framework. As said above, in a first quantized formalism,
and its canonical momentum are seen as
operators living in some Hilbert space. In a second quantized formalism
perspective, we show an explicit form for the extended Poincar\'e generators
and the same algebra is generated via generalized Heisenberg relations. We also
consider a source term and construct the general solution for the complex
scalar fields using the Green function technique
Entangling power of baker's map: Role of symmetries
The quantum baker map possesses two symmetries: a canonical "spatial"
symmetry, and a time-reversal symmetry. We show that, even when these features
are taken into account, the asymptotic entangling power of the baker's map does
not always agree with the predictions of random matrix theory. We have verified
that the dimension of the Hilbert space is the crucial parameter which
determines whether the entangling properties of the baker are universal or not.
For power-of-two dimensions, i.e., qubit systems, an anomalous entangling power
is observed; otherwise the behavior of the baker is consistent with random
matrix theories. We also derive a general formula that relates the asymptotic
entangling power of an arbitrary unitary with properties of its reduced
eigenvectors.Comment: 5 page
Uptake of uranium by lettuce (Lactuca sativa L.) in natural uranium contaminated soils in order to assess chemical risk for consumers
Uranium mining activity in Cunha Baixa
(Portugal) village has left a legacy of polluted soils
and irrigation water. A controlled field experiment
was conducted with lettuce (Lactuca sativa L.) in an
agricultural area nearby the abandoned mine in order
to evaluate uranium uptake and distribution in roots
and leaves as well as ascertain levels of uranium
intake by the local inhabitants from plant consuming.
Two soils with different average uranium content (38
and 106 mg/kg) were irrigated with non-contaminated
and uranium contaminated water (100 μg/l).
A non-contaminated soil irrigated with local tap water
(<1 μg/l uranium) was also used as a control. Uranium
in lettuce tissues was positively correlated with soil
uranium content, but non-significant differences were
obtained from contaminated soils irrigated with different water quality. Uranium in plants (dry weight)
growing in contaminated soils ranged from 0.95 to
6 mg/kg in roots and 0.32 to 2.6 mg/kg in leaves.
Lettuce bioconcentration is more related to available
uranium species in water than to its uranium concentration.
Translocated uranium to lettuce leaves corresponds
to 30% of the uranium uptake whatever the soil
or irrigation water quality. A maximum uranium daily
intake of 0.06 to 0.12 μg/kg bodyweight day was
estimated for an adult assuming 30 to 60 g/day of
lettuce is consumed. Although this value accounts
for only 10% to 20% of the recommended Tolerable
Daily Intake for ingested uranium, it still provides
an additional source of the element in the local
inhabitants’ die
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