7,538 research outputs found
A simultaneous spin/eject mechanism for aerospace payloads
A simultaneous spin/eject mechanism was developed for aerospace applications requiring a compact, passive device which would accommodate payload support and controlled-release functions, and which would provide a highly accurate spin-ejection motion to the payload. The mechanism satisfied the requirements and is adaptable to other deployment applications
A note on Gauge Theories Coupled to Gravity
We analyze the bound on gauge couplings , suggested by
Arkani-Hamed et.al. We show this bound can be derived from simple
semi-classical considerations and holds in spacetime dimensions greater than or
equal to four. Non abelian gauge symmetries seem to satisfy the bound in a
trivial manner. We comment on the case of discrete symmetries and close by
performing some checks for the bound in higher dimensions in the context of
string theory.Comment: 15 pages, 1 figure, Late
Twisted supersymmetry and the topology of theory space
We present examples of four dimensional, non-supersymmetric field theories in
which ultraviolet supersymmetry breaking effects, such as bose-fermi splittings
and the vacuum energy, are suppressed by , where
is a weak coupling factor and can be made arbitrarily large. The particle
content and interactions of these models are conveniently represented by a
graph with sites and links, describing the gauge theory space structure. While
the theories are supersymmetric ``locally'' in theory space, supersymmetry can
be explicitly broken by topological obstructions.Comment: 9 pages, revtex
Breaking the Rayleigh-Plateau instability limit using thermocavitation within a droplet
We report on the generation of liquid columns that extend far beyond the traditional Rayleigh-Plateau instability onset. The columns are driven by the acoustic pressure wave emitted after bubble collapse. A high-speed video imaging device, which records images at a rate of up to 105 fps, was employed to follow their dynamics. These bubbles, commonly termed thermocavitation bubbles, are generated by focusing a midpower (275 mW) continuous wavelength laser into a highly absorbing liquid droplet. A simple model of the propagation of the pressure wavefront emitted after the bubble collapse shows that focusing the pressure wave at the liquid-air interface drives the evolution of the liquid columns. Control over the aspect ratio of the liquid column is realized by adjusting the cavitation bubble's size, beam focus position, and droplet volume. © 2013 by Begell House, Inc
Interacting Strings in Matrix String Theory
It is here explained how the Green-Schwarz superstring theory arises from
Matrix String Theory. This is obtained as the strong YM-coupling limit of the
theory expanded around its BPS instantonic configurations, via the
identification of the interacting string diagram with the spectral curve of the
relevant configuration. Both the GS action and the perturbative weight
, where is the Euler characteristic of the world-sheet
surface and the string coupling, are obtained.Comment: 11 pages, no figures, two references adde
Vertex Operators in 2K Dimensions
A formula is proposed which expresses free fermion fields in 2K dimensions in
terms of the Cartan currents of the free fermion current algebra. This leads,
in an obvious manner, to a vertex operator construction of nonabelian free
fermion current algebras in arbitrary even dimension. It is conjectured that
these ideas may generalize to a wide class of conformal field theories.Comment: Minor change in notation. Change in references
Ten Dimensional Black Hole and the D0-brane Threshold Bound State
We discuss the ten dimensional black holes made of D0-branes in the regime
where the effective coupling is large, and yet the 11D geometry is unimportant.
We suggest that these black holes can be interpreted as excitations over the
threshold bound state. Thus, the entropy formula for the former is used to
predict a scaling region of the wave function of the latter. The horizon radius
and the mass gap predicted in this picture agree with the formulas derived from
the classical geometry.Comment: 11 pages, harvmac; v2: typos corrected, argument for the convergence
of two integrals improved, v3: one ref. adde
Origin of the approximate universality of distributions in equilibrium correlated systems
We propose an interpretation of previous experimental and numerical
experiments, showing that for a large class of systems, distributions of global
quantities are similar to a distribution originally obtained for the
magnetization in the 2D-XY model . This approach, developed for the Ising
model, is based on previous numerical observations. We obtain an effective
action using a perturbative method, which successfully describes the order
parameter fluctuations near the phase transition. This leads to a direct link
between the D-dimensional Ising model and the XY model in the same dimension,
which appears to be a generic feature of many equilibrium critical systems and
which is at the heart of the above observations.Comment: To appear in Europhysics Letter
D-branes, String Cosmology and Large Extra Dimensions
D-branes are fundamental in all scenarios where there are large extra
dimensions and the string scale is much smaller than the four-dimensional
Planck mass. We show that this current picture leads to a new approach to
string cosmology where inflation on our brane is driven by the large extra
dimensions and the issue of the graceful exit becomes inextricably linked to
the problem of the stabilization of the extra dimensions, suggesting the
possibility of a common solution. We also show that branes may violently
fluctuate along their transverse directions in curved spacetime, possibly
leading to a period of brane-driven inflation. This phenomenon plays also a
crucial role in many other cosmological issues, such as the smoothing out of
the cosmological singularities and the generation of the baryon asymmetry on
our three brane.Comment: LaTeX file, 4 page
Zerobrane Matrix Mechanics, Monopoles and Membrane Approach in QCD
We conjecture that a T-dual form of pure QCD describes dynamics of point-like
monopoles. T-duality transforms the QCD Lagrangian into a matrix quantum
mechanics of zerobranes which we identify with monopoles. At generic points of
the monopole moduli space the SU(N) gauge group is broken down to
reproducing the key feature of 't Hooft's Abelian projection. There are certain
points in the moduli space where monopole positions coincide, gauge symmetry is
enhanced and gluons emerge as massless excitations. We show that there is a
linearly rising potential between zerobranes. This indicates the presence of a
stretched flux tube between monopoles. The lowest energy state is achieved when
monopoles are sitting on top of each other and gauge symmetry is enhanced. In
this case they behave as free massive particles and can condense. In fact, we
find a constant eigenfunction of the corresponding Hamiltonian which describes
condensation of monopoles. Using the monopole quantum mechanics, we argue that
large QCD in this T-dual picture is a theory of a closed bosonic membrane
propagating in {\em five} dimensional space-time. QCD point-like monopoles can
be regarded in this approach as constituents of the membrane.Comment: 16 pages, new section and references adde
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