1,134 research outputs found
Non-linear amplification of small spin precession using long range dipolar interactions
In measurements of small signals using spin precession the precession angle
usually grows linearly in time. We show that non-linear interactions between
particles can lead to an exponentially growing spin precession angle, resulting
in an amplification of small signals and raising them above the noise level of
a detection system. We demonstrate amplification by a factor of greater than 8
of a spin precession signal due to a small magnetic field gradient in a
spherical cell filled with hyperpolarized liquid Xe. This technique can
improve the sensitivity in many measurements that are limited by the noise of
the detection system, rather then the fundamental spin-projection noise.Comment: 4 pages, 4 figure
Electron Spin-Lattice Relaxation of doped Yb3+ ions in YBa2Cu3Ox
The electron spin-lattice relaxation (SLR) times T1 of Yb3+‡ ions were
measured from the temperature dependence of electron spin resonance linewidth
in Y0.99Yb0.01Ba2Cu3Ox with different oxygen contents. Raman relaxation
processes dominate the electron SLR. Derived from the temperature dependence of
the SLR rate, the Debye temperature (Td) increases with the critical
temperature Tc and oxygen content x. Keywords: EPR; ESR; Electron spin-lattice
relaxation; Debye temperature; Critical temperatureComment: 5 Pages 4 Figure
Electron Shock Waves with a Large Current Behind the Shock Front
The propagation of breakdown waves in a gas, which is primarily driven by electron gas pressure, is described by a one-dimensional, steady-state, three-component (electrons, ions, and neutral particles) fluid model. We consider the electron gas partial pressure to be much larger than that of the other species and the waves to have a shock front. Our set of equations consists of the equations of conservation of the flux of mass, momentum, and energy coupled with Poisson’s equation. This set of equations is referred to as the electron fluid dynamical equations. In this study we are considering breakdown waves propagating in the opposite direction of the electric field force on electrons (return stroke in lightning) and moving into a neutral medium. For Breakdown waves with a significant current behind the shock front, the set of electron fluid dynamical equations and also the boundary condition on electron temperature need to be modified. For a range of experimentally observed current values and also some larger current values which few experimentalists have been able to observe, we have been able to solve the set of electron fluid dynamical equations through the dynamical transition region of the wave. Some experimentalists have reported the existence of a relationship between return stroke lightning wave speed and current behind the shock front; however, some others are skeptical of the existence of such a relationship. Our solutions to the set of electron fluid dynamical equations within the dynamical transition region of the wave confirm the existence of such a relationship. We will present the method of solution of the set of electron fluid dynamical equations through the dynamical transition region of the wave and also the wave profile for electric field, electron velocity, electron temperature and electron number density, within the dynamical transition region of the wave
Detection of radio frequency magnetic fields using nonlinear magneto-optical rotation
We describe a room-temperature alkali-metal atomic magnetometer for detection
of small, high frequency magnetic fields. The magnetometer operates by
detecting optical rotation due to the precession of an aligned ground state in
the presence of a small oscillating magnetic field. The resonance frequency of
the magnetometer can be adjusted to any desired value by tuning the bias
magnetic field. We demonstrate a sensitivity of in a 3.5 cm diameter, paraffin coated cell. Based
on detection at the photon shot-noise limit, we project a sensitivity of
.Comment: 6 pages, 6 figure
Physical properties of thermoelectric zinc antimonide using first-principles calculations
We report first principles calculations of the structural, electronic,
elastic and vibrational properties of the semiconducting orthorhombic ZnSb
compound. We study also the intrinsic point defects in order to eventually
improve the thermoelectric properties of this already very promising
thermoelectric material. Concerning the electronic properties, in addition to
the band structure, we show that the Zn (Sb) crystallographically equivalent
atoms are not exactly equivalent from the electronic point of view. Lattice
dynamics, elastic and thermodynamic properties are found to be in good
agreement with experiments and they confirm the non equivalency of the zinc and
antimony atoms from the vibrational point of view. The calculated elastic
properties show a relatively weak anisotropy and the hardest direction is the y
direction. We observe the presence of low energy modes involving both Zn and Sb
atoms at about 5-6 meV, similarly to what has been found in Zn4Sb3 and we
suggest that the interactions of these modes with acoustic phonons could
explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the
most stable defects and this explains the intrinsic p-type conductivity of
ZnSb.Comment: 33 pages, 8 figure
Influence of white and gray matter connections on endogenous human cortical oscillations
Brain oscillations reflect changes in electrical potentials summated across neuronal populations. Low- and high-frequency rhythms have different modulation patterns. Slower rhythms are spatially broad, while faster rhythms are more local. From this observation, we hypothesized that low- and high-frequency oscillations reflect white- and gray-matter communications, respectively, and synchronization between low-frequency phase with high-frequency amplitude represents a mechanism enabling distributed brain-networks to coordinate local processing. Testing this common understanding, we selectively disrupted white or gray matter connections to human cortex while recording surface field potentials. Counter to our original hypotheses, we found that cortex consists of independent oscillatory-units (IOUs) that maintain their own complex endogenous rhythm structure. IOUs are differentially modulated by white and gray matter connections. White-matter connections maintain topographical anatomic heterogeneity (i.e., separable processing in cortical space) and gray-matter connections segregate cortical synchronization patterns (i.e., separable temporal processing through phase-power coupling). Modulation of distinct oscillatory modules enables the functional diversity necessary for complex processing in the human brain
Nonlinear magneto-optical rotation with frequency-modulated light in the geophysical field range
Recent work investigating resonant nonlinear magneto-optical rotation (NMOR)
related to long-lived (\tau\ts{rel} \sim 1 {\rm s}) ground-state atomic
coherences has demonstrated potential magnetometric sensitivities exceeding
for small () magnetic
fields. In the present work, NMOR using frequency-modulated light (FM NMOR) is
studied in the regime where the longitudinal magnetic field is in the
geophysical range (), of particular interest for many
applications. In this regime a splitting of the FM NMOR resonance due to the
nonlinear Zeeman effect is observed. At sufficiently high light intensities,
there is also a splitting of the FM NMOR resonances due to ac Stark shifts
induced by the optical field, as well as evidence of alignment-to-orientation
conversion type processes. The consequences of these effects for FM-NMOR-based
atomic magnetometry in the geophysical field range are considered.Comment: 8 pages, 8 figure
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