1,503 research outputs found
Construct validity of multiple achievement goals: A multitrait-multimethod approach
The aim of this study was to examine three different instruments which have been used in research conducted in the physical domain to measure mastery, performance-approach, and performance-avoidance goals. The construct validity of the assessment tools, including a determination of their convergent and discriminant validity as well as a method effect, was tested via several confirmatory factor analyses. Four hundred and fifty athletes from different sport clubs were involved in the present study. Participants were asked to fill out three different multiple achievement goal instruments as well as two external criteria scales. The results based on CFA showed that all of the three instruments measured the same latent construct of multiple achievement goals. The convergent validity as well as the discriminant validity was supported. Evidence for a limited method effect in terms of the different measures was also provided
Using Abrupt Changes in Magnetic Susceptibility within Type-II Superconductors to Explore Global Decoherence Phenomena
A phenomenon of a periodic staircase of macroscopic jumps in the admitted
magnetic field has been observed, as the magnitude of an externally applied
magnetic field is smoothly increased or decreased upon a superconducting (SC)
loop of type II niobium-titanium wire which is coated with a
non-superconducting layer of copper. Large temperature spikes were observed to
occur simultaneously with the jumps, suggesting brief transitions to the normal
state, caused by en masse motions of Abrikosov vortices. An experiment that
exploits this phenomenon to explore the global decoherence of a large
superconducting system will be discussed, and preliminary data will be
presented. Though further experimentation is required to determine the actual
decoherence rate across the superconducting system, multiple classical
processes are ruled out, suggesting that jumps in magnetic flux are fully
quantum mechanical processes which may correspond to large group velocities
within the global Cooper pair wavefunction.Comment: 13 pages, 4 figures, part of proceedings for FQMT 2011 conference in
Prague, Czech Republi
Quantum Noise and Superluminal Propagation
Causal "superluminal" effects have recently been observed and discussed in
various contexts. The question arises whether such effects could be observed
with extremely weak pulses, and what would prevent the observation of an
"optical tachyon." Aharonov, Reznik, and Stern (ARS) [Phys. Rev. Lett., vol.
81, 2190 (1998)] have argued that quantum noise will preclude the observation
of a superluminal group velocity when the pulse consists of one or a few
photons. In this paper we reconsider this question both in a general framework
and in the specific example, suggested by Chiao, Kozhekin, and Kurizki [Phys.
Rev. Lett., vol. 77, 1254 (1996)], of off-resonant, short-pulse propagation in
an optical amplifier. We derive in the case of the amplifier a signal-to-noise
ratio that is consistent with the general ARS conclusions when we impose their
criteria for distinguishing between superluminal propagation and propagation at
the speed c. However, results consistent with the semiclassical arguments of
CKK are obtained if weaker criteria are imposed, in which case the signal can
exceed the noise without being "exponentially large." We show that the quantum
fluctuations of the field considered by ARS are closely related to
superfluorescence noise. More generally we consider the implications of
unitarity for superluminal propagation and quantum noise and study, in addition
to the complete and truncated wavepackets considered by ARS, the residual
wavepacket formed by their difference. This leads to the conclusion that the
noise is mostly luminal and delayed with respect to the superluminal signal. In
the limit of a very weak incident signal pulse, the superluminal signal will be
dominated by the noise part, and the signal-to-noise ratio will therefore be
very small.Comment: 30 pages, 1 figure, eps
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Passive wireless antenna sensor for strain, temperature, crack and fatigue measurement
An apparatus and method is provided for monitoring a condition of a structure using a passive wireless antenna sensor having a known resonant frequency when mounted on the structure. A series of radio frequency signals are transmitted with sweeping frequencies around the known resonant frequency to the passive wireless antenna sensor. The passive wireless antenna sensor includes a dielectric substrate disposed between an antenna pattern and a ground plane such that a change in the condition of the structure will cause a change in one or more characteristics of the passive wireless sensor. A signal is received from the passive wireless antenna sensor and a resonant frequency of the passive wireless antenna sensor is determined based on the received signal. The determined resonant frequency is then compared to the known resonant frequency, whereby a change in the resonant frequency indicates a change in the condition of the structure.Board of Regents, University of Texas Syste
Effective photon-photon interaction in a two-dimensional "photon fluid"
We formulate an effective theory for the atom-mediated photon-photon
interactions in a two-dimensional ``photon fluid'' confined in a Fabry-Perot
resonator. With the atoms modelled by a collection of anharmonic Lorentz
oscillators, the effective interaction is evaluated to second order in the
coupling constant (the anharmonicity parameter). The interaction has the form
of a renormalized two-dimensional delta-function potential, with the
renormalization scale determined by the physical parameters of the system, such
as density of atoms and the detuning of the photons relative to the resonance
frequency of the atoms. For realistic values of the parameters, the
perturbation series has to be resummed, and the effective interaction becomes
independent of the ``bare'' strength of the anharmonic term. The resulting
expression for the non-linear Kerr susceptibility, is parametrically equal to
the one found earlier for a dilute gas of two-level atoms. Using our result for
the effective interaction parameter, we derive conditions for the formation of
a photon fluid, both for Rydberg atoms in a microwave cavity and for alkali
atoms in an optical cavity.Comment: 25 pages (revtex4), including 2 figure
Signal velocity, causality, and quantum noise in superluminal light pulse propagation
We consider pulse propagation in a linear anomalously dispersive medium where
the group velocity exceeds the speed of light in vacuum (c) or even becomes
negative. A signal velocity is defined operationally based on the optical
signal-to-noise ratio, and is computed for cases appropriate to the recent
experiment where such a negative group velocity was observed. It is found that
quantum fluctuations limit the signal velocity to values less than c.Comment: 4 Journal pages, 3 figure
Vacuum field energy and spontaneous emission in anomalously dispersive cavities
Anomalously dispersive cavities, particularly white light cavities, may have
larger bandwidth to finesse ratios than their normally dispersive counterparts.
Partly for this reason, their use has been proposed for use in LIGO-like
gravity wave detectors and in ring-laser gyroscopes. In this paper we analyze
the quantum noise associated with anomalously dispersive cavity modes. The
vacuum field energy associated with a particular cavity mode is proportional to
the cavity-averaged group velocity of that mode. For anomalously dispersive
cavities with group index values between 1 and 0, this means that the total
vacuum field energy associated with a particular cavity mode must exceed . For white light cavities in particular, the group index approaches
zero and the vacuum field energy of a particular spatial mode may be
significantly enhanced. We predict enhanced spontaneous emission rates into
anomalously dispersive cavity modes and broadened laser linewidths when the
linewidth of intracavity emitters is broader than the cavity linewidth.Comment: 9 pages, 4 figure
Transparent Anomalous Dispersion and Superluminal Light Pulse Propagation at a Negative Group Velocity
Anomalous dispersion cannot occur in a transparent passive medium where
electromagnetic radiation is being absorbed at all frequencies, as pointed out
by Landau and Lifshitz. Here we show, both theoretically and experimentally,
that transparent linear anomalous dispersion can occur when a gain doublet is
present. Therefore, a superluminal light pulse propagation can be observed even
at a negative group velocity through a transparent medium with almost no pulse
distortion. Consequently, a {\it negative transit time} is experimentally
observed resulting in the peak of the incident light pulse to exit the medium
even before entering it. This counterintuitive effect is a direct result of the
{\it rephasing} process owing to the wave nature of light and is not at odds
with either causality or Einstein's theory of special relativity.Comment: 12 journal pages, 9 figure
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