29,459 research outputs found
The noncommutative harmonic oscillator in more than one dimensions
The noncommutative harmonic oscillator in arbitrary dimension is examined. It
is shown that the -genvalue problem can be decomposed into separate
harmonic oscillator equations for each dimension. The noncommutative plane is
investigated in greater detail. The constraints for rotationally symmetric
solutions and the corresponding two-dimensional harmonic oscillator are solved.
The angular momentum operator is derived and its -genvalue problem is
shown to be equivalent to the usual eigenvalue problem. The -genvalues
for the angular momentum are found to depend on the energy difference of the
oscillations in each dimension. Furthermore two examples of assymetric
noncommutative harmonic oscillator are analysed. The first is the
noncommutative two-dimensional Landau problem and the second is the
three-dimensional harmonic oscillator with symmetrically noncommuting
coordinates and momenta.Comment: 12 page
Pressure-Temperature Phase Diagram of Multiferroic
The pressure-temperature phase diagram of multiferroic is
investigated for hydrostatic pressures up to 2 GPa. The stability range of the
ferroelectric phase associated with the incommensurate helical spin order is
reduced by pressure and ferroelectricity is completely suppressed at the
critical pressure of 1.64 GPa at 6.2 K. Thermal expansion measurements at
ambient pressure show strong step-like anomalies of the lattice parameters
associated with the lock-in transition into the commensurate paraelectric
phase. The expansion anomalies are highly anisotropic, the related volume
change is consistent with the high-pressure phase diagram
Symplectic Quantization of Open Strings and Noncommutativity in Branes
We show how to translate boundary conditions into constraints in the
symplectic quantization method by an appropriate choice of generalized
variables. This way the symplectic quantization of an open string attached to a
brane in the presence of an antisymmetric background field reproduces the non
commutativity of the brane coordinates.Comment: We included a comparison with previous results obtained from Dirac
quantization, emphasizing the fact that in the symplectic case the boundary
conditions, that lead to the non commutativity, show up from the direct
application of the standard method. Version to appear in Phys. Rev.
Improving Effective Surgical Delivery in Humanitarian Disasters: Lessons from Haiti
Kathryn Chu and colleagues describe the experiences of Médecins sans Frontières after the 2010 Haiti earthquake, and discuss how to improve delivery of surgery in humanitarian disasters
Novel Field-Induced Phases in HoMnO3 at Low Temperatures
The novel field-induced re-entrant phase in multiferroic hexagonal HoMnO3 is
investigated to lower temperatures by dc magnetization, ac susceptibility, and
specific heat measurements at various magnetic fields. Two new phases have been
unambiguously identified below the Neel transition temperature, TN=76 K, for
magnetic fields up to 50 kOe. The existence of an intermediate phase between
the P[6]_3[c]m and P[6]_3c[m] magnetic structures (previously predicted from
dielectric measurements) was confirmed and the magnetic properties of this
phase have been investigated. At low temperatures (T<5 K) a dome shaped phase
boundary characterized by a magnetization jump and a narrow heat capacity peak
was detected between the magnetic fields of 5 kOe and 18 kOe. The transition
across this phase boundary is of first order and the magnetization and entropy
jumps obey the magnetic analogue of the Clausius-Clapeyron relation. Four of
the five low-temperature phases coexist at a tetracritical point at 2 K and 18
kOe. The complex magnetic phase diagram so derived provides an informative
basis for unraveling the underlying driving forces for the occurrence of the
various phases and the coupling between the different orders.Comment: 14 pages, 14 figure
Plasma-Like Negative Capacitance in Nano-Colloids
A negative capacitance has been observed in a nano-colloid between 0.1 and
10^-5 Hz. The response is linear over a broad range of conditions. The
low-omega dispersions of both the resistance and capacitance are consistent
with the free-carrier plasma model, while the transient behavior demonstrates
an unusual energy storage mechanism. A collective excitation, therefore, is
suggested.Comment: 3 pages, 3 figure
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