7,998 research outputs found
Programmable physiological infusion
A programmable physiological infusion device and method are provided wherein a program source, such as a paper tape, is used to actuate an infusion pump in accordance with a desired program. The system is particularly applicable for dispensing calcium in a variety of waveforms
Programmed physiological infusion system
Infusion system delivers incremental volumes from a reservoir with a piston pump at a rate that varies in time and follows the envelope of a preprogrammed curve
Temperature dependence of the spin and orbital magnetization density in around the spin-orbital compensation point
Non-resonant ferromagnetic x-ray diffraction has been used to separate the
spin and orbital contribution to the magnetization density of the proposed
zero-moment ferromagnet . The alignment of the
spin and orbital moments relative to the net magnetization shows a sign
reversal at 84K, the compensation temperature. Below this temperature the
orbital moment is larger than the spin moment, and vice versa above it. This
result implies that the compensation mechanism is driven by the different
temperature dependencies of the spin and orbital moments. Specific heat
data indicate that the system remains ferromagnetically ordered throughout
Calculation and spectroscopy of the Landau band structure at a thin and atomically precise tunneling barrier
Two laterally adjacent quantum Hall systems separated by an extended barrier
of a thickness on the order of the magnetic length possess a complex Landau
band structure in the vicinity of the line junction. The energy dispersion is
obtained from an exact quantum-mechanical calculation of the single electron
eigenstates for the coupled system by representing the wave functions as a
superposition of parabolic cylinder functions. For orbit centers approaching
the barrier, the separation of two subsequent Landau levels is reduced from the
cyclotron energy to gaps which are much smaller. The position of the
anticrossings increases on the scale of the cyclotron energy as the magnetic
field is raised. In order to experimentally investigate a particular gap at
different field strengths but under constant filling factor, a GaAs/AlGaAs
heterostructure with a 52 Angstrom thick tunneling barrier and a gate electrode
for inducing the two-dimensional electron systems was fabricated by the cleaved
edge overgrowth method. The shift of the gaps is observed as a displacement of
the conductance peaks on the scale of the filling factor. Besides this effect,
which is explained within the picture of Landau level mixing for an ideal
barrier, we report on signatures of quantum interferences at imperfections of
the barrier which act as tunneling centers. The main features of the recent
experiment of Yang, Kang et al. are reproduced and discussed for different gate
voltages. Quasiperiodic oscillations, similar to the Aharonov Bohm effect at
the quenched peak, are revealed for low magnetic fields before the onset of the
regular conductance peaks.Comment: 8 pages, 10 figures, 1 tabl
Size-dependent fine-structure splitting in self-organized InAs/GaAs quantum dots
A systematic variation of the exciton fine-structure splitting with quantum
dot size in single InAs/GaAs quantum dots grown by metal-organic chemical vapor
deposition is observed. The splitting increases from -80 to as much as 520
eV with quantum dot size. A change of sign is reported for small quantum
dots. Model calculations within the framework of eight-band k.p theory and the
configuration interaction method were performed. Different sources for the
fine-structure splitting are discussed, and piezoelectricity is pinpointed as
the only effect reproducing the observed trend.Comment: 5 pages, 5 figure
Curie-like paramagnetism due to incomplete Zhang-Rice singlet formation in La2-xSrxCuO4
In an effort to elucidate the origin of the Curie-like paramagnetism that is
generic for heavily-overdoped cuprates, we have performed high transverse-field
muon spin rotation (TF-muSR) measurements of La2-xSrxCuO4 single crystals over
the Sr content range 0.145 < x < 0.33. We show that the x-dependence of the
previously observed field-induced broadening of the internal magnetic field
distribution above the superconducting transition temperature Tc reflects the
presence of two distinct contributions. One of these becomes less pronounced
with increasing x and is attributed to diminishing antiferromagnetic
correlations. The other grows with increasing x, but decreases above x ~ 0.30,
and is associated with the Curie-like term in the bulk magnetic susceptibility.
In contrast to the Curie-like term, however, this second contribution to the
TF-muSR line width extends back into the underdoped regime. Our findings imply
a coexistence of antiferromagnetically correlated and paramagnetic moments,
with the latter becoming dominant beyond x ~ 0.185. This suggests that the
doped holes do not neutralize all Cu spins via the formation of Zhang-Rice
singlets. Moreover, the paramagnetic component of the TF-muSR line width is
explained by holes progressively entering the Cu 3d_{x^2-y^2} orbital with
doping.Comment: 8 pages, 7 figure
Oxygen minimum zone: An important oceanographic habitat for deep-diving northern elephant seals, Mirounga angustirostris.
Little is known about the foraging behavior of top predators in the deep mesopelagic ocean. Elephant seals dive to the deep biota-poor oxygen minimum zone (OMZ) (>800 m depth) despite high diving costs in terms of energy and time, but how they successfully forage in the OMZ remains largely unknown. Assessment of their feeding rate is the key to understanding their foraging behavior, but this has been challenging. Here, we assessed the feeding rate of 14 female northern elephant seals determined by jaw motion events (JME) and dive cycle time to examine how feeding rates varied with dive depth, particularly in the OMZ. We also obtained video footage from seal-mounted videos to understand their feeding in the OMZ. While the diel vertical migration pattern was apparent for most depths of the JME, some very deep dives, beyond the normal diel depth ranges, occurred episodically during daylight hours. The midmesopelagic zone was the main foraging zone for all seals. Larger seals tended to show smaller numbers of JME and lower feeding rates than smaller seals during migration, suggesting that larger seals tended to feed on larger prey to satisfy their metabolic needs. Larger seals also dived frequently to the deep OMZ, possibly because of a greater diving ability than smaller seals, suggesting their dependency on food in the deeper depth zones. Video observations showed that seals encountered the rarely reported ragfish (Icosteus aenigmaticus) in the depths of the OMZ, which failed to show an escape response from the seals, suggesting that low oxygen concentrations might reduce prey mobility. Less mobile prey in OMZ would enhance the efficiency of foraging in this zone, especially for large seals that can dive deeper and longer. We suggest that the OMZ plays an important role in structuring the mesopelagic ecosystem and for the survival and evolution of elephant seals
Linear-response theory of the longitudinal spin Seebeck effect
We theoretically investigate the longitudinal spin Seebeck effect, in which
the spin current is injected from a ferromagnet into an attached nonmagnetic
metal in a direction parallel to the temperature gradient. Using the fact that
the phonon heat current flows intensely into the attached nonmagnetic metal in
this particular configuration, we show that the sign of the spin injection
signal in the longitudinal spin Seebeck effect can be opposite to that in the
conventional transverse spin Seebeck effect when the electron-phonon
interaction in the nonmagnetic metal is sufficiently large. Our linear-response
approach can explain the sign reversal of the spin injection signal recently
observed in the longitudinal spin Seebeck effect.Comment: Proc. of ICM 2012 (Accepted for publication in J. Korean Phys. Soc.),
typos correcte
Calculation of pure dephasing for excitons in quantum dots
Pure dephasing of an exciton in a small quantum dot by optical and acoustic
phonons is calculated using the ``independent boson model''. Considering the
case of zero temperature the dephasing is shown to be only partial which
manifests itself in the polarization decaying to a finite value. Typical
dephasing times can be assigned even though the spectra exhibits strongly
non-Lorentzian line shapes. We show that the dephasing from LO phonon
scattering, occurs on a much larger time scale than that of dephasing due to
acoustic phonons which for low temperatures are also a more efficient dephasing
mechanism. The typical dephasing time is shown to strongly depend on the
quantum dot size whereas the electron phonon ``coupling strength'' and external
electric fields tend mostly to effect the residual coherence. The relevance of
the dephasing times for current quantum information processing implementation
schemes in quantum dots is discussed
Cu-spin dynamics in the overdoped regime of La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ probed by muon spin relaxation
Muon-spin-relaxation measurements have been performed for the partially
Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with y=0-0.10 in the overdoped
regime up to x=0.30. In the 3 % Zn-substituted samples up to x=0.27,
exponential-like depolarization of muon spins has been observed at low
temperatures, indicating Zn-induced slowing-down of the Cu-spin fluctuations.
The depolarization rate decreases with increasing x and almost no fast
depolarization of muon spins has been observed for x=0.30 where
superconductivity disappears. The present results suggest that the dynamical
stripe correlations exist in the whole superconducting regime of
La_2-x_Sr_x_CuO_4_ and that there is no quantum critical point at x~0.19.Comment: 6 pages, 5 figure
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