3,726 research outputs found
Arithmetic progressions consisting of unlike powers
In this paper we present some new results about unlike powers in arithmetic
progression. We prove among other things that for given and
there are only finitely many arithmetic progressions of the form
with
gcd and for Furthermore, we
show that, for L=3, the progression is the only such progression
up to sign.Comment: 16 page
Renormalised nonequilibrium quantum field theory: scalar fields
We discuss the renormalisation of the initial value problem in quantum field
theory using the two-particle irreducible (2PI) effective action formalism. The
nonequilibrium dynamics is renormalised by counterterms determined in
equilibrium. We emphasize the importance of the appropriate choice of initial
conditions and go beyond the Gaussian initial density operator by defining
self-consistent initial conditions. We study the corresponding time evolution
and present a numerical example which supports the existence of a continuum
limit for this type of initial conditions.Comment: 18 pages in revtex4, 5 figure
Out of Equilibrium Non-perturbative Quantum Field Dynamics in Homogeneous External Fields
The quantum dynamics of the symmetry broken lambda (Phi^2)^2 scalar field
theory in the presence of an homogeneous external field is investigated in the
large N limit. We choose as initial state the ground state for a constant
external field J .The sign of the external field is suddenly flipped from
J to - J at a given time and the subsequent quantum dynamics calculated.
Spinodal instabilities and parametric resonances produce large quantum
fluctuations in the field components transverse to the external field. This
allows the order parameter to turn around the maximum of the potential for
intermediate times. Subsequently, the order parameter starts to oscillate near
the global minimum for external field - J, entering a novel quasi-periodic
regime.Comment: LaTex, 30 pages, 12 .ps figures, improved version to appear in Phys
Rev
A strengths-based case management service for people with serious mental illness in Israel: A randomized controlled trial
Case management services for people with serious mental illness are generally found to be effective, but controlled and randomized studies assessing such services are scarce. The aim of the present study was to assess the effectiveness of a new strengths-based case management (SBCM) service in Israel, using a randomized controlled approach. The sample consisted of 1276 individuals with serious mental illness, who consume psychiatric rehabilitation services (PRS) in the community, and were randomly assigned to receive or not to receive the SBCM service in addition to treatment-as-usual PRS. Quality of life, goal setting and attainment, unmet needs, self-efficacy, interpersonal relationships, symptom severity, and service utilization were assessed by clients at onset and after 20 months. Results show that SBCM participants improved in self-efficacy, unmet needs, and general quality of life, and set more goals than the control group. SBCM participants also consumed fewer services at follow-up. Results suggest that SBCM services are effective in helping individuals with serious mental illness set personal goals and use PRS in a better and more focused manner
Green's function for a Schroedinger operator and some related summation formulas
Summation formulas are obtained for products of associated Lagurre
polynomials by means of the Green's function K for the Hamiltonian H =
-{d^2\over dx^2} + x^2 + Ax^{-2}, A > 0. K is constructed by an application of
a Mercer type theorem that arises in connection with integral equations. The
new approach introduced in this paper may be useful for the construction of
wider classes of generating function.Comment: 14 page
Self-adjoint Lyapunov variables, temporal ordering and irreversible representations of Schroedinger evolution
In non relativistic quantum mechanics time enters as a parameter in the
Schroedinger equation. However, there are various situations where the need
arises to view time as a dynamical variable. In this paper we consider the
dynamical role of time through the construction of a Lyapunov variable - i.e.,
a self-adjoint quantum observable whose expectation value varies monotonically
as time increases. It is shown, in a constructive way, that a certain class of
models admit a Lyapunov variable and that the existence of a Lyapunov variable
implies the existence of a transformation mapping the original quantum
mechanical problem to an equivalent irreversible representation. In addition,
it is proved that in the irreversible representation there exists a natural
time ordering observable splitting the Hilbert space at each t>0 into past and
future subspaces.Comment: Accepted for publication in JMP. Supercedes arXiv:0710.3604.
Discussion expanded to include the case of Hamiltonians with an infinitely
degenerate spectru
Semigroup evolution in Wigner Weisskopf pole approximation with Markovian spectral coupling
We establish the relation between the Wigner-Weisskopf theory for the
description of an unstable system and the theory of coupling to an environment.
According to the Wigner-Weisskopf general approach, even within the pole
approximation (neglecting the background contribution) the evolution of a total
system subspace is not an exact semigroup for the multi-channel decay, unless
the projectors into eigesntates of the reduced evolution generator are
orthogonal. In this case these projectors must be evaluated at different pole
locations . Since the orthogonality relation does not
generally hold at different values of , for example, when there is symmetry
breaking, the semigroup evolution is a poor approximation for the multi-channel
decay, even for a very weak coupling. Nevertheless, there exists a possibility
not only to ensure the orthogonality of the projectors regardless the
number of the poles, but also to simultaneously suppress the effect of the
background contribution. This possibility arises when the theory is generalized
to take into account interactions with an environment. In this case , and
hence its eigenvectors as well, are {\it independent} of , which corresponds
to a structure of the coupling to the continuum spectrum associated with the
Markovian limit.Comment: 9 pages, 3 figure
The cultural and geopolitical dimensions of nation-building in the Ukraine
Ukraine belongs among those young countries where the beginnings of democratisation and nation-building approximately coincided. While the development of nation states in Central Europe was usually preceded by the development of nations, the biggest dilemma in the Ukraine is whether a nation-state programme — parallel to the aim of state-building — is able to bring unfinished nation-building to completion. Ukraine sways between the EU and Russia with enormous amplitude. The alternating orientation between the West and the East can be ascribed to superpower ambitions reaching beyond Ukraine. Eventually, internal and external determinants are intertwined and mutually interact with one another. The aim of the paper is to explain the dilemmas arising from identity problems behind the Ukraine’s internal and external orientation
Pressure dependence of the spin gap in BaVS_3
We carried out magnetotransport experiments under hydrostatic pressure in
order to study the nature of the metal-insulator transition in BaVS.
Scaling relations for are established and the pressure dependence
of the spin gap is determined. Our new results, in conjunction with a
re-analysis of earlier specific heat and susceptibility data, demonstrate that
the transition is weakly second order. The nature of the phase diagram in the
---- space is discussed.Comment: 5 pages, 5 figures, submitted to PRB Rap. Co
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