7,692 research outputs found
Vertical pairing of identical particles suspended in the plasma sheath
It is shown experimentally that vertical pairing of two identical
microspheres suspended in the sheath of a radio-frequency (rf) discharge at low
gas pressures (a few Pa), appears at a well defined instability threshold of
the rf power. The transition is reversible, but with significant hysteresis on
the second stage. A simple model, which uses measured microsphere resonance
frequencies and takes into account besides Coulomb interaction between
negatively charged microspheres also their interaction with positive ion wake
charges, seems to explain the instability threshold quite well.Comment: 4 pages, 6 figures. to appear in Phys. Rev. Lett. 86, May 14th (2001
Interaction between dust grains near a conducting wall
The effect of the conducting electrode on the interaction of dust grains in a
an ion flow is discussed. It is shown that two grains levitating above the
electrode at the same height may attract one another. This results in the
instability of a dust layer in a plasma sheath.Comment: 9 pages. 3 figures. Submitted to Plasma Physics Report
Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution
A self-consistent, mean-field model of charge-carrier injection and unipolar
transport in an organic semiconductor diode is developed utilizing the
effective transport energy concept and taking into account a realistic
density-of-states distribution as well as the presence of trap states in an
organic material. The consequences resulting from the model are discussed
exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic
conductor structure. A comparison of the theory to experimental data of a
unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.Comment: 6 pages, 2 figures; to be published in Journal of Applied Physic
The Many Faces of a Character
We prove an identity between three infinite families of polynomials which are
defined in terms of `bosonic', `fermionic', and `one-dimensional configuration'
sums. In the limit where the polynomials become infinite series, they give
different-looking expressions for the characters of the two integrable
representations of the affine algebra at level one. We conjecture yet
another fermionic sum representation for the polynomials which is constructed
directly from the Bethe-Ansatz solution of the Heisenberg spin chain.Comment: 14/9 pages in harvmac, Tel-Aviv preprint TAUP 2125-9
Exceptional structure of the dilute A model: E and E Rogers--Ramanujan identities
The dilute A lattice model in regime 2 is in the universality class of
the Ising model in a magnetic field. Here we establish directly the existence
of an E structure in the dilute A model in this regime by expressing
the 1-dimensional configuration sums in terms of fermionic sums which
explicitly involve the E root system. In the thermodynamic limit, these
polynomial identities yield a proof of the E Rogers--Ramanujan identity
recently conjectured by Kedem {\em et al}.
The polynomial identities also apply to regime 3, which is obtained by
transforming the modular parameter by . In this case we find an
A_1\times\mbox{E}_7 structure and prove a Rogers--Ramanujan identity of
A_1\times\mbox{E}_7 type. Finally, in the critical limit, we give
some intriguing expressions for the number of -step paths on the A
Dynkin diagram with tadpoles in terms of the E Cartan matrix. All our
findings confirm the E and E structure of the dilute A model found
recently by means of the thermodynamic Bethe Ansatz.Comment: 9 pages, 1 postscript figur
Self-consistent analytical solution of a problem of charge-carrier injection at a conductor/insulator interface
We present a closed description of the charge carrier injection process from
a conductor into an insulator. Common injection models are based on single
electron descriptions, being problematic especially once the amount of
charge-carriers injected is large. Accordingly, we developed a model, which
incorporates space charge effects in the description of the injection process.
The challenge of this task is the problem of self-consistency. The amount of
charge-carriers injected per unit time strongly depends on the energy barrier
emerging at the contact, while at the same time the electrostatic potential
generated by the injected charge- carriers modifies the height of this
injection barrier itself. In our model, self-consistency is obtained by
assuming continuity of the electric displacement and the electrochemical
potential all over the conductor/insulator system. The conductor and the
insulator are properly taken into account by means of their respective density
of state distributions. The electric field distributions are obtained in a
closed analytical form and the resulting current-voltage characteristics show
that the theory embraces injection-limited as well as bulk-limited
charge-carrier transport. Analytical approximations of these limits are given,
revealing physical mechanisms responsible for the particular current-voltage
behavior. In addition, the model exhibits the crossover between the two
limiting cases and determines the validity of respective approximations. The
consequences resulting from our exactly solvable model are discussed on the
basis of a simplified indium tin oxide/organic semiconductor system.Comment: 23 pages, 6 figures, accepted to Phys.Rev.
Nonlinear vertical oscillations of a particle in a sheath of a rf discharge
A new simple method to measure the spatial distribution of the electric field
in the plasma sheath is proposed. The method is based on the experimental
investigation of vertical oscillations of a single particle in the sheath of a
low-pressure radio-frequency discharge. It is shown that the oscillations
become strongly nonlinear and secondary harmonics are generated as the
amplitude increases. The theory of anharmonic oscillations provides a good
qualitative description of the data and gives estimates for the first two
anharmonic terms in an expansion of the sheath potential around the particle
equilibrium.Comment: 11 pages, 4 figure
Continued Fractions and Fermionic Representations for Characters of M(p,p') minimal models
We present fermionic sum representations of the characters
of the minimal models for all relatively prime
integers for some allowed values of and . Our starting point is
binomial (q-binomial) identities derived from a truncation of the state
counting equations of the XXZ spin chain of anisotropy
. We use the Takahashi-Suzuki method to express
the allowed values of (and ) in terms of the continued fraction
decomposition of (and ) where stands for
the fractional part of These values are, in fact, the dimensions of the
hermitian irreducible representations of (and )
with (and We also establish the duality relation and discuss the action of the Andrews-Bailey transformation in the
space of minimal models. Many new identities of the Rogers-Ramanujan type are
presented.Comment: Several references, one further explicit result and several
discussion remarks adde
Stationary Velocity and Charge Distributions of Grains in Dusty Plasmas
Within the kinetic approach velocity and charge distributions of grains in
stationary dusty plasmas are calculated and the relations between the effective
temperatures of such distributions and plasma parameters are established. It is
found that the effective temperature which determines the velocity grain
distribution could be anomalously large due to the action of accelerating ionic
bombarding force. The possibility to apply the results obtained to the
explanation of the increasing grain temperature in the course of the
Coulomb-crystal melting by reduction of the gas pressure is discussed. This
paper was received by Phys.Rev.Lett. on 11 August 1999. As potential referees
the authors offered to Editor the following persons: V.N.Tsytovich, Russia;
R.Bingham, UK; D.Resendes, Portugal; G.Morfill, P.Shukla, Y.M.Yu., Germany.Comment: 8 pages, no figure
Charge carrier injection into insulating media: single-particle versus mean-field approach
Self-consistent, mean-field description of charge injection into a dielectric
medium is modified to account for discreteness of charge carriers. The improved
scheme includes both the Schottky barrier lowering due to the individual image
charge and the barrier change due to the field penetration into the injecting
electrode that ensures validity of the model at both high and low injection
rates including the barrier dominated and the space-charge dominated regimes.
Comparison of the theory with experiment on an unipolar ITO/PPV/Au-device is
presented.Comment: 32 pages, 9 figures; revised version accepted to PR
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