657 research outputs found
Interactions between vaccinia virus and sensitized macrophages in vitro
The action of peritoneal exudate cells (PEC) from normal and vaccinia virus infected mice on infectious vaccinia virus particles was investigatedin vitro. PEC from immune mice showed a significantly higher infectivity titre reduction (virus clearance, VC) than normal cells. This effect could be clearly attributed to the macrophage. Vaccinia virus multiplied in PEC from normal animals while there was no virus propagation in cells from immunized mice. The release of adsorbed or engulfed virus was reduced significantly in PEC from immunized animals. Anti-vaccinia-antibodies seem to activate normal macrophages to increased virus clearance. This stimulating effect was demonstrable only in the IgG fraction of the antiserum.
The activity of macrophages from mice injected three times over a period of 14 days with vaccinia virus could be entirely blocked with anti-mouse-IgG, while PEC from mice injected one time six days previously were not inhibited
Wavefunction considerations for the central spin decoherence problem in a nuclear spin bath
Decoherence of a localized electron spin in a solid state material (the
``central spin'' problem) at low temperature is believed to be dominated by
interactions with nuclear spins in the lattice. This decoherence is partially
suppressed through the application of a large magnetic field that splits the
energy levels of the electron spin and prevents depolarization. However,
dephasing decoherence resulting from a dynamical nuclear spin bath cannot be
removed in this way. Fluctuations of the nuclear field lead to uncertainty of
the electron's precessional frequency in a process known as spectral diffusion.
This article considers the effect of the electron's wavefunction shape upon
spectral diffusion and provides wavefunction dependent decoherence time
formulas for free induction decay as well as spin echoes and concatenated
dynamical decoupling schemes for enhancing coherence. We also discuss dephasing
of a qubit encoded in singlet-triplet states of a double quantum dot. A central
theoretical result of this work is the development of a continuum approximation
for the spectral diffusion problem which we have applied to GaAs and InAs
materials specifically
Low-frequency noise as a source of dephasing of a qubit
With the growing efforts in isolating solid-state qubits from external
decoherence sources, the material-inherent sources of noise start to play
crucial role. One representative example is electron traps in the device
material or substrate. Electrons can tunnel or hop between a charged and an
empty trap, or between a trap and a gate electrode. A single trap typically
produces telegraph noise and can hence be modeled as a bistable fluctuator.
Since the distribution of hopping rates is exponentially broad, many traps
produce flicker-noise with spectrum close to 1/f. Here we develop a theory of
decoherence of a qubit in the environment consisting of two-state fluctuators,
which experience transitions between their states induced by interaction with
thermal bath. Due to interaction with the qubit the fluctuators produce
1/f-noise in the qubit's eigenfrequency. We calculate the results of qubit
manipulations - free induction and echo signals - in such environment. The main
problem is that in many important cases the relevant random process is both
non-Markovian and non-Gaussian. Consequently the results in general cannot be
represented by pair correlation function of the qubit eigenfrequency
fluctuations. Our calculations are based on analysis of the density matrix of
the qubit using methods developed for stochastic differential equations. The
proper generating functional is then averaged over different fluctuators using
the so-called Holtsmark procedure. The analytical results are compared with
simulations allowing checking accuracy of the averaging procedure and
evaluating mesoscopic fluctuations. The results allow understanding some
observed features of the echo decay in Josephson qubits.Comment: 18 pages, 8 figures, Proc. of NATO/Euresco Conf. "Fundamental
Problems of Mesoscopic Physics: Interactions and Decoherence", Granada,
Spain, Sept.200
Tactical Athletes: An Integrated Approach to Understanding and Enhancing the Health and Performance of Firefighters-in-Training
International Journal of Exercise Science 8(4): 341-357, 2015. In an effort to reduce the rates of firefighter fatality, injury, and workplace stress, there has been a call for research to advance knowledge of firefighting performance and injury prevention. Physical and psychological variables important to firefighter health and performance have been identified, yet the interrelated nature of these variables has been overlooked. Given the overlap between the physical and psychological demands of firefighting and sport, and given that an integrated framework has been used in the sport domain to guide athlete health and performance research and practice, firefighter organizations could benefit from adopting a sport-based, integrated model of firefighter training and performance management. Guided by the Meyer Athlete Performance Management Model (MAPM), the purposes of the current study were to: (a) describe the physical and psychological characteristics of firefighters-in-training (i.e., cadets and recruits), and (b) explore relationships between the physical and psychological variables associated with health and performance. Firefighters-in-training employed by a Midwestern area fire department in the United States (N = 34) completed a battery of physical and psychological assessments at the department’s Fire and Safety Academy building. Results of the current study revealed significant correlations between several of the physical and psychological characteristics of firefighters-in-training. These results, along with the multidimensional data set that was also established in the current study, provide preliminary evidence for the use of a sport-based integrated performance model such as the MAPM to guide training and performance research in firefighter populations
Theory of the ground state spin of the NV- center in diamond: I. Fine structure, hyperfine structure, and interactions with electric, magnetic and strain fields
The ground state spin of the negatively charged nitrogen-vacancy center in
diamond has been the platform for the recent rapid expansion of new frontiers
in quantum metrology and solid state quantum information processing. In ambient
conditions, the spin has been demonstrated to be a high precision magnetic and
electric field sensor as well as a solid state qubit capable of coupling with
nearby nuclear and electronic spins. However, in spite of its many outstanding
demonstrations, the theory of the spin has not yet been fully developed and
there does not currently exist thorough explanations for many of its
properties, such as the anisotropy of the electron g-factor and the existence
of Stark effects and strain splittings. In this work, the theory of the ground
state spin is fully developed for the first time using the molecular orbital
theory of the center in order to provide detailed explanations for the spin's
fine and hyperfine structures and its interactions with electric, magnetic and
strain fields.Comment: 12 pages, 3 figures, 3 table
Electron spin as a spectrometer of nuclear spin noise and other fluctuations
This chapter describes the relationship between low frequency noise and
coherence decay of localized spins in semiconductors. Section 2 establishes a
direct relationship between an arbitrary noise spectral function and spin
coherence as measured by a number of pulse spin resonance sequences. Section 3
describes the electron-nuclear spin Hamiltonian, including isotropic and
anisotropic hyperfine interactions, inter-nuclear dipolar interactions, and the
effective Hamiltonian for nuclear-nuclear coupling mediated by the electron
spin hyperfine interaction. Section 4 describes a microscopic calculation of
the nuclear spin noise spectrum arising due to nuclear spin dipolar flip-flops
with quasiparticle broadening included. Section 5 compares our explicit
numerical results to electron spin echo decay experiments for phosphorus doped
silicon in natural and nuclear spin enriched samples.Comment: Book chapter in "Electron spin resonance and related phenomena in low
dimensional structures", edited by Marco Fanciulli. To be published by
Springer-Verlag in the TAP series. 35 pages, 9 figure
Decay of Rabi oscillations induced by magnetic dipole interactions in diluted paramagnetic solids
Decay of Rabi oscillations of equivalent spins diluted in diamagnetic solid
matrix and coupled by magnetic dipole interactions is studied. It is shown that
these interactions result in random shifts of spin transient nutation
frequencies and thus lead to the decay of the transient signal. Averaging over
random spatial distribution of spins within the solid and over their spectral
positions within magnetic resonance line, we obtain analytical expressions for
the decay of Rabi oscillations. The rate of the decay in the case when the
half-width of magnetic resonance line exceeds Rabi frequency is found to depend
on the intensity of resonant microwave field and on the spin concentration. The
results are compared with the literature data for E1' centers in glassy silica
and [AlO4] centers in quartz.Comment: 14 pages, 3 figure
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