7,465 research outputs found
Singlet oxygen generator for a solar powered chemically pumped iodine laser
The potential of solid phase endoperoxides as a means to produce single-delta oxygen in the gas phase in concentrations useful to chemical oxygen-iodine lasers was investigated. The 1,4 - endoperoxide of ethyl 3- (4-methyl - 1-naphthyl) propanoate was deposited over an indium-oxide layer on a glass plate. Single-delta oxygen was released from the endoperoxide upon heating the organic film by means of an electrical discharge through the conductive indium oxide coating. The evolution of singlet-delta oxygen was determined by measuring the dimol emission signal at 634 nm. Comparison of the measured signal with an analytic model leads to two main conclusions: virtually all the oxygen being evolved is in the singlet-delta state and in the gas phase, and there is no significant quenching other than energy pooling on the time scale of the experiment (approximately 10 msec). The use of solid phase endoperoxide as a singlet-delta oxygen generator for an oxygen-iodine laser appears promising
The structure of classical extensions of quantum probability theory
On the basis of a suggestive definition of a classical extension of quantum mechanics in terms of statistical models, we prove that every such classical extension is essentially given by the so-called Misra–Bugajski reduction map. We consider how this map enables one to understand quantum mechanics as a reduced classical statistical theory on the projective Hilbert space as phase space and discuss features of the induced hidden-variable model. Moreover, some relevant technical results on the topology and Borel structure of the projective Hilbert space are reviewed
Quantum reservoirs with ion chains
Ion chains are promising platforms for studying and simulating quantum
reservoirs. One interesting feature is that their vibrational modes can mediate
entanglement between two objects which are coupled through the vibrational
modes of the chain. In this work we analyse entanglement between the transverse
vibrations of two heavy impurity defects embedded in an ion chain, which is
generated by the coupling with the chain vibrations. We verify general scaling
properties of the defects dynamics and demonstrate that entanglement between
the defects can be a stationary feature of these dynamics. We then analyse
entanglement in chains composed of tens of ions and propose a measurement
scheme which allows one to verify the existence of the predicted entangled
state.Comment: 14 pages, 12 figure
Tumbleweeds and airborne gravitational noise sources for LIGO
Gravitational-wave detectors are sensitive not only to astrophysical
gravitational waves, but also to the fluctuating Newtonian gravitational forces
of moving masses in the ground and air around the detector. This paper studies
the gravitational effects of density perturbations in the atmosphere, and from
massive airborne objects near the detector. These effects were previously
considered by Saulson; in this paper I revisit these phenomena, considering
transient atmospheric shocks, and the effects of sound waves or objects
colliding with the ground or buildings around the test masses. I also consider
temperature perturbations advected past the detector as a source of
gravitational noise. I find that the gravitational noise background is below
the expected noise floor even of advanced interferometric detectors, although
only by an order of magnitude for temperature perturbations carried along
turbulent streamlines. I also find that transient shockwaves in the atmosphere
could potentially produce large spurious signals, with signal-to-noise ratios
in the hundreds in an advanced interferometric detector. These signals could be
vetoed by means of acoustic sensors outside of the buildings. Massive
wind-borne objects such as tumbleweeds could also produce gravitational signals
with signal-to-noise ratios in the hundreds if they collide with the
interferometer buildings, so it may be necessary to build fences preventing
such objects from approaching within about 30m of the test masses.Comment: 15 pages, 10 PostScript figures, uses REVTeX4.cls and epsfig.st
The Uniqueness Problem of Sequence Product on Operator Effect Algebra
A quantum effect is an operator on a complex Hilbert space that satisfies
. We denote the set of all quantum effects by . In
this paper we prove, Theorem 4.3, on the theory of sequential product on which shows, in fact, that there are sequential products on which are not of the generalized L\"{u}ders form. This result answers a
Gudder's open problem negatively
Approximate joint measurement of qubit observables through an Arthur-Kelly type model
We consider joint measurement of two and three unsharp qubit observables
through an Arthur-Kelly type joint measurement model for qubits. We investigate
the effect of initial state of the detectors on the unsharpness of the
measurement as well as the post-measurement state of the system. Particular
emphasis is given on a physical understanding of the POVM to PVM transition in
the model and entanglement between system and detectors.Two approaches for
characterizing the unsharpness of the measurement and the resulting measurement
uncertainty relations are considered.The corresponding measures of unsharpness
are connected for the case where both the measurements are equally unsharp. The
connection between the POVM elements and symmetries of the underlying
Hamiltonian of the measurement interaction is made explicit and used to perform
joint measurement in arbitrary directions. Finally in the case of three
observables we derive a necessary condition for the approximate joint
measurement and use it show the relative freedom available when the observables
are non-orthogonal.Comment: 22 pages; Late
Sharp crossover from composite fermionization to phase separation in mesoscopic mixtures of ultracold bosons
We show that a two-component mixture of a few repulsively interacting
ultracold atoms in a one-dimensional trap possesses very different quantum
regimes and that the crossover between them can be induced by tuning the
interactions in one of the species. In the composite fermionization regime,
where the interactions between both components are large, none of the species
show large occupation of any natural orbital. Our results show that by
increasing the interaction in one of the species, one can reach the
phase-separated regime. In this regime, the weakly interacting component stays
at the center of the trap and becomes almost fully phase coherent, while the
strongly interacting component is displaced to the edges of the trap. The
crossover is sharp, as observed in the in the energy and the in the largest
occupation of a natural orbital of the weakly interacting species. Such a
transition is a purely mesoscopic effect which disappears for large atom
numbers.Comment: 5 pages, 3 figure
Quantum correlations and spatial localization in one-dimensional ultracold bosonic mixtures
We present the complete phase diagram for one-dimensional binary mixtures of
bosonic ultracold atomic gases in a harmonic trap. We obtain exact results with
direct numerical diagonalization for small number of atoms, which permits us to
quantify quantum many-body correlations. The quantum Monte Carlo method is used
to calculate energies and density profiles for larger system sizes. We study
the system properties for a wide range of interaction parameters. For the
extreme values of these parameters, different correlation limits can be
identified, where the correlations are either weak or strong. We investigate in
detail how the correlation evolve between the limits. For balanced mixtures in
the number of atoms in each species, the transition between the different
limits involves sophisticated changes in the one- and two-body correlations.
Particularly, we quantify the entanglement between the two components by means
of the von Neumann entropy. We show that the limits equally exist when the
number of atoms is increased, for balanced mixtures. Also, the changes in the
correlations along the transitions among these limits are qualitatively
similar. We also show that, for imbalanced mixtures, the same limits with
similar transitions exist. Finally, for strongly imbalanced systems, only two
limits survive, i.e., a miscible limit and a phase-separated one, resembling
those expected with a mean-field approach.Comment: 18 pages, 8 figure
"Tolerization" of human T-helper cell clones by chronic exposure to alloantigen
Induction of clonal anergy in T-helper (Th) cells may have a role in regulating immune responses. A model system for studying Th cell tolerization at the clonal level in vitro could be useful for investigating the mechanisms involved. Accordingly, alloreactive helper cells were maintained in culture with interleukin 2 (IL 2) by intermittent stimulation with specific antigen. Regardless of the frequency of antigen stimulation, clones of age less than ca. 35 population doublings (PD) were found to undergo antigen-specific autocrine clonal expansion in the absence of exogenous IL 2. Such young clones (designated as phase I) could therefore not be "tolerized" by frequent exposure to antigen. In contrast, most clones of age greater than ca. 35 PD could be tolerized by frequent exposure to antigen (designated as phase II clones). Their autocrine proliferation was then blocked, although they still recognized antigen specifically as shown by their retained ability to secrete interferon-gamma (IFN-gamma) and granulocyte-macrophage colony stimulating factor (GM-CSF). The mechanism of response failure involved both an inability to upregulate IL 2 receptors in the absence of exogenous IL 2, as well as an inability to secrete IL 2. These defects were not overcome by stimulation with mitogens or calcium ionophore and phorbol esther in place of alloantigen. T-cell receptor, alpha, beta, and gamma-chain gene rearrangements remained identical in phase I and phase II clones. Tolerization of phase II clones could be avoided by increasing the period between antigen exposures. Despite this, whether or not phase II cells were capable of autocrine proliferation, they were found to have acquired the novel function of inducing suppressive activity in fresh lymphocytes. Suppressor-induction was blocked by the broadly reactive MHC class II-specific monoclonal antibody (moAb) TU39, but not by moAb preferentially reacting only with HLA-DR, DQ, or DP. Sequential immunoprecipitation on T-cell clones showed the presence of a putative non-DR, DQ, DP, TU39+ molecule on phase II clones. However, this molecule was also found on phase I clones. The nature of the TU39-blockable suppressor-inducing determinant present on phase II but not on (most) phase I clones thus remains to be clarified. In addition to suppressor-induction activity, phase II clones also acquired lytic potential as measured in a lectin approximation system. Cytotoxic (CTX) potential was also not influenced by the frequency of antigenic stimulation and could be viewed as a constitutive modulation of clonal functio
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