20,329 research outputs found

### The effect of circumferential distortion on fan performance at two levels of blade loading

Single stage fans designed for two levels of pressure ratio or blade loading were subjected to screen-induced circumferential distortions of 90-degree extent. Both fan rotors were designed for a blade tip speed of 425 m/sec, blade solidity of 1.3 and a hub-to-tip radius ratio of 0.5. Circumferential measurements of total pressure, temperature, static pressure, and flow angle were obtained at the hub, mean and tip radii at five axial stations. Rotor loading level did not appear to have a significant influence on rotor response to distorted flow. Losses in overall pressure ratio due to distortion were most severe in the stator hub region of the more highly loaded stage. At the near stall operating condition tip and hub regions of (either) rotor demonstrated different response characteristics to the distorted flow. No effect of loading was apparent on interactions between rotor and upstream distorted flow fields

### Interpolation and harmonic majorants in big Hardy-Orlicz spaces

Free interpolation in Hardy spaces is caracterized by the well-known Carleson
condition. The result extends to Hardy-Orlicz spaces contained in the scale of
classical Hardy spaces $H^p$, $p>0$. For the Smirnov and the Nevanlinna
classes, interpolating sequences have been characterized in a recent paper in
terms of the existence of harmonic majorants (quasi-bounded in the case of the
Smirnov class). Since the Smirnov class can be regarded as the union over all
Hardy-Orlicz spaces associated with a so-called strongly convex function, it is
natural to ask how the condition changes from the Carleson condition in
classical Hardy spaces to harmonic majorants in the Smirnov class. The aim of
this paper is to narrow down this gap from the Smirnov class to ``big''
Hardy-Orlicz spaces. More precisely, we characterize interpolating sequences
for a class of Hardy-Orlicz spaces that carry an algebraic structure and that
are strictly bigger than $\bigcup_{p>0} H^p$. It turns out that the
interpolating sequences are again characterized by the existence of
quasi-bounded majorants, but now the weights of the majorants have to be in
suitable Orlicz spaces. The existence of harmonic majorants in such Orlicz
spaces will also be discussed in the general situation. We finish the paper
with an example of a separated Blaschke sequence that is interpolating for
certain Hardy-Orlicz spaces without being interpolating for slightly smaller
ones.Comment: 19 pages, 2 figure

### Electromagnetic Interaction in the System of Multimonopoles and Vortex Rings

Behavior of static axially symmetric monopole-antimonopole and vortex ring
solutions of the SU(2) Yang-Mills-Higgs theory in an external uniform magnetic
field is considered. It is argued that the axially symmetric
monopole-antimonopole chains and vortex rings can be treated as a bounded
electromagnetic system of the magnetic charges and the electric current rings.
The magnitude of the external field is a parameter which may be used to test
the structure of the static potential of the effective electromagnetic
interaction between the monopoles with opposite orientation in the group space.
It is shown that for a non-BPS solutions there is a local minimum of this
potential.Comment: 10 pages, 12 figures, some minor corrections, version to appear in
Phys. Rev.

### On Which Length Scales Can Temperature Exist in Quantum Systems?

We consider a regular chain of elementary quantum systems with nearest
neighbor interactions and assume that the total system is in a canonical state
with temperature $T$. We analyze under what condition the state factors into a
product of canonical density matrices with respect to groups of $n$ subsystems
each, and when these groups have the same temperature $T$. While in classical
mechanics the validity of this procedure only depends on the size of the groups
$n$, in quantum mechanics the minimum group size $n_{\text{min}}$ also depends
on the temperature $T$! As examples, we apply our analysis to different types
of Heisenberg spin chains.Comment: To appear in: Proceedings of the SPQS conference, J. Phys. Soc. Jpn.
74 (2005) Supp

### Environment-Mediated Quantum State Transfer

We propose a scheme for quantum state transfer(QST) between two qubits which
is based on their individual interaction with a common boson environment. The
corresponding single mode spin-boson Hamiltonian is solved by mapping it onto a
wave propagation problem in a semi-infinite ladder and the fidelity is
obtained. High fidelity occurs when the qubits are equally coupled to the boson
while the fidelity becomes smaller for nonsymmetric couplings. The complete
phase diagram for such an arbitrary QST mediated by bosons is discussed.Comment: 6 pages and 5 figure

### Ground-State and Domain-Wall Energies in the Spin-Glass Region of the 2D $\pm J$ Random-Bond Ising Model

The statistics of the ground-state and domain-wall energies for the
two-dimensional random-bond Ising model on square lattices with independent,
identically distributed bonds of probability $p$ of $J_{ij}= -1$ and $(1-p)$ of
$J_{ij}= +1$ are studied. We are able to consider large samples of up to
$320^2$ spins by using sophisticated matching algorithms. We study $L \times L$
systems, but we also consider $L \times M$ samples, for different aspect ratios
$R = L / M$. We find that the scaling behavior of the ground-state energy and
its sample-to-sample fluctuations inside the spin-glass region ($p_c \le p \le
1 - p_c$) are characterized by simple scaling functions. In particular, the
fluctuations exhibit a cusp-like singularity at $p_c$. Inside the spin-glass
region the average domain-wall energy converges to a finite nonzero value as
the sample size becomes infinite, holding $R$ fixed. Here, large finite-size
effects are visible, which can be explained for all $p$ by a single exponent
$\omega\approx 2/3$, provided higher-order corrections to scaling are included.
Finally, we confirm the validity of aspect-ratio scaling for $R \to 0$: the
distribution of the domain-wall energies converges to a Gaussian for $R \to 0$,
although the domain walls of neighboring subsystems of size $L \times L$ are
not independent.Comment: 11 pages with 15 figures, extensively revise

### Statistics of lowest excitations in two dimensional Gaussian spin glasses

A detailed investigation of lowest excitations in two-dimensional Gaussian
spin glasses is presented. We show the existence of a new zero-temperature
exponent lambda describing the relative number of finite-volume excitations
with respect to large-scale ones. This exponent yields the standard thermal
exponent of droplet theory theta through the relation, theta=d(lambda-1). Our
work provides a new way to measure the thermal exponent theta without any
assumption about the procedure to generate typical low-lying excitations. We
find clear evidence that theta < theta_{DW} where theta_{DW} is the thermal
exponent obtained in domain-wall theory showing that MacMillan excitations are
not typical.Comment: 4 pages, 3 figures, (v2) revised version, (v3) corrected typo

### On the merit of a Central Limit Theorem-based approximation in statistical physics

The applicability conditions of a recently reported Central Limit
Theorem-based approximation method in statistical physics are investigated and
rigorously determined. The failure of this method at low and intermediate
temperature is proved as well as its inadequacy to disclose quantum
criticalities at fixed temperatures. Its high temperature predictions are in
addition shown to coincide with those stemming from straightforward appropriate
expansions up to (k_B T)^(-2). Our results are clearly illustrated by comparing
the exact and approximate temperature dependence of the free energy of some
exemplary physical systems.Comment: 12 pages, 1 figur

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