80 research outputs found
Testing Einstein's time dilation under acceleration using M\"ossbauer spectroscopy
The Einstein time dilation formula was tested in several experiments. Many
trials have been made to measure the transverse second order Doppler shift by
M\"{o}ssbauer spectroscopy using a rotating absorber, to test the validity of
this formula. Such experiments are also able to test if the time dilation
depends only on the velocity of the absorber, as assumed by Einstein's clock
hypothesis, or the present centripetal acceleration contributes to the time
dilation. We show here that the fact that the experiment requires -ray
emission and detection slits of finite size, the absorption line is broadened;
by geometric longitudinal first order Doppler shifts immensely. Moreover, the
absorption line is non-Lorenzian. We obtain an explicit expression for the
absorption line for any angular velocity of the absorber.
The analysis of the experimental results, in all previous experiments which
did not observe the full absorption line itself, were wrong and the conclusions
doubtful. The only proper experiment was done by K\"{u}ndig (Phys. Rev. 129
(1963) 2371), who observed the broadening, but associated it to random
vibrations of the absorber. We establish necessary conditions for the
successful measurement of a transverse second order Doppler shift by
M\"{o}ssbauer spectroscopy. We indicate how the results of such an experiment
can be used to verify the existence of a Doppler shift due to acceleration and
to test the validity of Einstein's clock hypothesis.Comment: 11 pages, 4 figure
Unusual Response to a Localized Perturbation in a Generalized Elastic Model
The generalized elastic model encompasses several physical systems such as
polymers, membranes, single file systems, fluctuating surfaces and rough
interfaces. We consider the case of an applied localized potential, namely an
external force acting only on a single (tagged) probe, leaving the rest of the
system unaffected. We derive the fractional Langevin equation for the tagged
probe, as well as for a generic (untagged) probe, where the force is not
directly applied. Within the framework of the fluctuation-dissipation
relations, we discuss the unexpected physical scenarios arising when the force
is constant and time periodic, whether or not the hydrodynamic interactions are
included in the model. For short times, in case of the constant force, we show
that the average drift is linear in time for long range hydrodynamic
interactions and behaves ballistically or exponentially for local hydrodynamic
interactions. Moreover, it can be opposite to the direction of external
disturbance for some values of the model's parameters. When the force is time
periodic, the effects are macroscopic: the system splits into two distinct
spatial regions whose size is proportional to the value of the applied
frequency. These two regions are characterized by different amplitudes and
phase shifts in the response dynamics
Correlations in a Generalized Elastic Model: Fractional Langevin Equation Approach
The Generalized Elastic Model (GEM) provides the evolution equation which
governs the stochastic motion of several many-body systems in nature, such as
polymers, membranes, growing interfaces. On the other hand a probe
(\emph{tracer}) particle in these systems performs a fractional Brownian motion
due to the spatial interactions with the other system's components. The
tracer's anomalous dynamics can be described by a Fractional Langevin Equation
(FLE) with a space-time correlated noise. We demonstrate that the description
given in terms of GEM coincides with that furnished by the relative FLE, by
showing that the correlation functions of the stochastic field obtained within
the FLE framework agree to the corresponding quantities calculated from the
GEM. Furthermore we show that the Fox -function formalism appears to be very
convenient to describe the correlation properties within the FLE approach
Space-Time Approach to Scattering from Many Body Systems
We present scattering from many body systems in a new light. In place of the
usual van Hove treatment, (applicable to a wide range of scattering processes
using both photons and massive particles) based on plane waves, we calculate
the scattering amplitude as a space-time integral over the scattering sample
for an incident wave characterized by its correlation function which results
from the shaping of the wave field by the apparatus. Instrument resolution
effects - seen as due to the loss of correlation caused by the path differences
in the different arms of the instrument are automatically included and analytic
forms of the resolution function for different instruments are obtained. The
intersection of the moving correlation volumes (those regions where the
correlation functions are significant) associated with the different elements
of the apparatus determines the maximum correlation lengths (times) that can be
observed in a sample, and hence, the momentum (energy) resolution of the
measurement. This geometrical picture of moving correlation volumes derived by
our technique shows how the interaction of the scatterer with the wave field
shaped by the apparatus proceeds in space and time. Matching of the correlation
volumes so as to maximize the intersection region yields a transparent,
graphical method of instrument design. PACS: 03.65.Nk, 3.80 +r, 03.75, 61.12.BComment: Latex document with 6 fig
A Derivation of Three-Dimensional Inertial Transformations
The derivation of the transformations between inertial frames made by
Mansouri and Sexl is generalised to three dimensions for an arbitrary direction
of the velocity. Assuming lenght contraction and time dilation to have their
relativistic values, a set of transformations kinematically equivalent to
special relativity is obtained. The ``clock hypothesis'' allows the derivation
to be extended to accelerated systems. A theory of inertial transformations
maintaining an absolute simultaneity is shown to be the only one logically
consistent with accelerated movements. Algebraic properties of these
transformations are discussed. Keywords: special relativity, synchronization,
one-way velocity of light, ether, clock hypothesis.Comment: 16 pages (A5), Latex, one figure, to be published in Found. Phys.
Lett. (1997
A Review of One-Way and Two-Way Experiments to Test the Isotropy of the Speed of Light
As we approach the 125th anniversary of the Michelson-Morley experiment in
2012, we review experiments that test the isotropy of the speed of light.
Previous measurements are categorized into one-way (single-trip) and two-way
(round-trip averaged or over closed paths) approaches and the level of
experimental verification that these experiments provide is discussed. The
isotropy of the speed of light is one of the postulates of the Special Theory
of Relativity (STR) and, consequently, this phenomenon has been subject to
considerable experimental scrutiny. Here, we tabulate significant experiments
performed since 1881 and attempt to indicate a direction for future
investigation.Comment: Updated Fig. 7 and references; Revised sections 3.2 and 4. Accepted
in the Indian Journal of Physics on March 30, 201
Efficient Olfactory Coding in the Pheromone Receptor Neuron of a Moth
The concept of coding efficiency holds that sensory neurons are adapted, through both evolutionary and developmental processes, to the statistical characteristics of their natural stimulus. Encouraged by the successful invocation of this principle to predict how neurons encode natural auditory and visual stimuli, we attempted its application to olfactory neurons. The pheromone receptor neuron of the male moth Antheraea polyphemus, for which quantitative properties of both the natural stimulus and the reception processes are available, was selected. We predicted several characteristics that the pheromone plume should possess under the hypothesis that the receptors perform optimally, i.e., transfer as much information on the stimulus per unit time as possible. Our results demonstrate that the statistical characteristics of the predicted stimulus, e.g., the probability distribution function of the stimulus concentration, the spectral density function of the stimulation course, and the intermittency, are in good agreement with those measured experimentally in the field. These results should stimulate further quantitative studies on the evolutionary adaptation of olfactory nervous systems to odorant plumes and on the plume characteristics that are most informative for the ‘sniffer’. Both aspects are relevant to the design of olfactory sensors for odour-tracking robots
Evidence of coexistence of change of caged dynamics at Tg and the dynamic transition at Td in solvated proteins
Mossbauer spectroscopy and neutron scattering measurements on proteins
embedded in solvents including water and aqueous mixtures have emphasized the
observation of the distinctive temperature dependence of the atomic mean square
displacements, , commonly referred to as the dynamic transition at some
temperature Td. At low temperatures, increases slowly, but it assume
stronger temperature dependence after crossing Td, which depends on the
time/frequency resolution of the spectrometer. Various authors have made
connection of the dynamics of solvated proteins including the dynamic
transition to that of glass-forming substances. Notwithstanding, no connection
is made to the similar change of temperature dependence of obtained by
quasielastic neutron scattering when crossing the glass transition temperature
Tg, generally observed in inorganic, organic and polymeric glass-formers.
Evidences are presented to show that such change of the temperature dependence
of from neutron scattering at Tg is present in hydrated or solvated
proteins, as well as in the solvents used unsurprisingly since the latter is
just another organic glass-formers. The obtained by neutron scattering at
not so low temperatures has contributions from the dissipation of molecules
while caged by the anharmonic intermolecular potential at times before
dissolution of cages by the onset of the Johari-Goldstein beta-relaxation. The
universal change of at Tg of glass-formers had been rationalized by
sensitivity to change in volume and entropy of the beta-relaxation, which is
passed onto the dissipation of the caged molecules and its contribution to
. The same rationalization applies to hydrated and solvated proteins for
the observed change of at Tg.Comment: 28 pages, 10 figures, 1 Tabl
The Confrontation between General Relativity and Experiment
The status of experimental tests of general relativity and of theoretical
frameworks for analysing them is reviewed. Einstein's equivalence principle
(EEP) is well supported by experiments such as the Eotvos experiment, tests of
special relativity, and the gravitational redshift experiment. Future tests of
EEP and of the inverse square law are searching for new interactions arising
from unification or quantum gravity. Tests of general relativity at the
post-Newtonian level have reached high precision, including the light
deflection, the Shapiro time delay, the perihelion advance of Mercury, and the
Nordtvedt effect in lunar motion. Gravitational-wave damping has been detected
in an amount that agrees with general relativity to better than half a percent
using the Hulse-Taylor binary pulsar, and other binary pulsar systems have
yielded other tests, especially of strong-field effects. When direct
observation of gravitational radiation from astrophysical sources begins, new
tests of general relativity will be possible.Comment: 89 pages, 8 figures; an update of the Living Review article
originally published in 2001; final published version incorporating referees'
suggestion
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