3,643 research outputs found
Efficient qubit detection using alkali earth metal ions and a double STIRAP process
We present a scheme for robust and efficient projection measurement of a
qubit consisting of the two magnetic sublevels in the electronic ground state
of alkali earth metal ions. The scheme is based on two stimulated Raman
adiabatic passages (STIRAP) involving four partially coherent laser fields. We
show how the efficiency depends on experimentally relevant parameters: Rabi
frequencies, pulse widths, laser linewidths, one- and two-photon detunings,
residual laser power, laser polarization and ion motion.Comment: 14 pages, 15 figure
On the Possibility of Measuring the Abraham Force using Whispering Gallery Modes
Critical experimental tests of the time-dependent Abraham force in
phenomenological electrodynamics are scarce. In this paper we analyze the
possibility of making use of intensity-modulated whispering gallery modes in a
microresonator for this purpose. Systems of this kind appear attractive, as the
strong concentration of electromagnetic fields near the rim of the resonator
serves to enhance the Abraham torque exerted by the field. We analyze mainly
spherical resonators, although as an introductory step we consider also the
cylinder geometry. The order of magnitude of the Abraham torques are estimated
by inserting reasonable values for the various input parameters. As expected,
the predicted torques turn out to be very small, although probably not beyond
any reach experimentally. Our main idea is essentially a generalization of the
method used by G. B. Walker et al. [Can. J. Phys. 53, 2577] for low-frequency
fields, to the optical case.Comment: 6 pages, no figures. Minor typos corrected, acknowledgment added. To
appear in Phys. Rev.
On the sizes of z>2 Damped Lyman-alpha Absorbing Galaxies
Recently, the number of detected galaxy counterparts of z > 2 Damped
Lyman-alpha Absorbers in QSO spectra has increased substantially so that we
today have a sample of 10 detections. M{\o}ller et al. in 2004 made the
prediction, based on a hint of a luminosity-metallicity relation for DLAs, that
HI size should increase with increasing metallicity. In this paper we
investigate the distribution of impact parameter and metallicity that would
result from the correlation between galaxy size and metallicity. We compare our
observations with simulated data sets given the relation of size and
metallicity. The observed sample presented here supports the metallicity-size
prediction: The present sample of DLA galaxies is consistent with the model
distribution. Our data also show a strong relation between impact parameter and
column density of HI. We furthermore compare the observations with several
numerical simulations and demonstrate that the observations support a scenario
where the relation between size and metallicity is driven by feedback
mechanisms controlling the star-formation efficiency and outflow of enriched
gas.Comment: Accepted for publishing in MNRAS lette
Influence of gas flow rate on liquid distribution in trickle-beds using perforated plates as liquid distributors
Two wire mesh tomography devices and a liquid collector were used to study
the influence of the gas flow rate on liquid distribution when fluids
distribution on top of the reactor is ensured by a perforated plate. In
opposition to most of the studies realized by other authors, conditions in
which the gas has a negative impact in liquid distribution were evidenced.
Indeed, the obtained results show that the influence of gas flow rate depends
on the quality of the initial distribution, as the gas forces the liquid to
"respect" the distribution imposed at the top of the reactor. Finally, a
comparison between the two measuring techniques shows the limitations of the
liquid collector and the improper conclusions to which its use could lead
On quasi-local charges and Newman--Penrose type quantities in Yang--Mills theories
We generalize the notion of quasi-local charges, introduced by P. Tod for
Yang--Mills fields with unitary groups, to non-Abelian gauge theories with
arbitrary gauge group, and calculate its small sphere and large sphere limits
both at spatial and null infinity. We show that for semisimple gauge groups no
reasonable definition yield conserved total charges and Newman--Penrose (NP)
type quantities at null infinity in generic, radiative configurations. The
conditions of their conservation, both in terms of the field configurations and
the structure of the gauge group, are clarified. We also calculate the NP
quantities for stationary, asymptotic solutions of the field equations with
vanishing magnetic charges, and illustrate these by explicit solutions with
various gauge groups.Comment: 22 pages, typos corrected, appearing in Classical and Quantum Gravit
New positive small vacuum region gravitational energy expressions
We construct an infinite number of new holonomic quasi-local gravitational
energy-momentum density pseudotensors with good limits asymptotically and in
small regions, both materially and in vacuum. For small vacuum regions they are
all a positive multiple of the Bel-Robinson tensor and consequently have
positive energy.Comment: 4 page
An analytical treatment of the Clock Paradox in the framework of the Special and General Theories of Relativity
In this paper we treat the so called clock paradox in an analytical way by
assuming that a constant and uniform force F of finite magnitude acts
continuously on the moving clock along the direction of its motion assumed to
be rectilinear. No inertial motion steps are considered. The rest clock is
denoted as (1), the to-and-fro moving clock is (2), the inertial frame in which
(1) is at rest in its origin and (2) is seen moving is I and, finally, the
accelerated frame in which (2) is at rest in its origin and (1) moves forward
and backward is A. We deal with the following questions: I) What is the effect
of the finite force acting on (2) on the proper time intervals measured by the
two clocks when they reunite? Does a differential aging between the two clocks
occur, as it happens when inertial motion and infinite values of the
accelerating force is considered? The Special Theory of Relativity is used in
order to describe the hyperbolic motion of (2) in the frame I II) Is this
effect an absolute one, i.e. does the accelerated observer A comoving with (2)
obtain the same results as that in I, both qualitatively and quantitatively, as
it is expected? We use the General Theory of Relativity in order to answer this
question.Comment: LaTex2e, 19 pages, no tables, no figures. Rewritten version, it
amends the previous one whose results about the treatment with General
Relativity were wrong. References added. Eq. (55) corrected. More refined
version. Comments and suggestions are warmly welcom
Second order perturbation theory for embedded eigenvalues
We study second order perturbation theory for embedded eigenvalues of an
abstract class of self-adjoint operators. Using an extension of the Mourre
theory, under assumptions on the regularity of bound states with respect to a
conjugate operator, we prove upper semicontinuity of the point spectrum and
establish the Fermi Golden Rule criterion. Our results apply to massless
Pauli-Fierz Hamiltonians for arbitrary coupling.Comment: 30 pages, 2 figure
Galaxy Counterparts of metal-rich Damped Lyman-alpha Absorbers - I: The case of the z=2.35 DLA towards Q2222-0946
We have initiated a survey using the newly commissioned X-shooter
spectrograph to target candidate relatively metal-rich damped Lyman-alpha
absorbers (DLAs). The spectral coverage of X-shooter allows us to search for
not only Lyman-alpha emission, but also rest-frame optical emission lines. We
have chosen DLAs where the strongest rest-frame optical lines ([OII], [OIII],
Hbeta and Halpha) fall in the NIR atmospheric transmission bands. In this first
paper resulting from the survey, we report on the discovery of the galaxy
counterpart of the z_abs = 2.354 DLA towards the z=2.926 quasar Q2222$-0946.
This DLA is amongst the most metal-rich z>2 DLAs studied so far at comparable
redshifts and there is evidence for substantial depletion of refractory
elements onto dust grains. We measure metallicities from ZnII, SiII, NiII, MnII
and FeII of -0.46+/-0.07, -0.51+/-0.06, -0.85+/-0.06, -1.23+/-0.06, and
-0.99+/-0.06, respectively. The galaxy is detected in the Lyman-alpha, [OIII]
lambda4959,5007 Halpha emission lines at an impact parameter of about 0.8
arcsec (6 kpc at z_abs = 2.354). We infer a star-formation rate of 10 M_sun
yr^-1, which is a lower limit due to the possibility of slit-loss. Compared to
the recently determined Halpha luminosity function for z=2.2 galaxies the
DLA-galaxy counterpart has a luminosity of L~0.1L^*_Halpha. The emission-line
ratios are 4.0 (Lyalpha/Halpha) and 1.2 ([OIII]/Halpha). The Lyalpha line shows
clear evidence for resonant scattering effects, namely an asymmetric,
redshifted (relative to the systemic redshift) component and a much weaker
blueshifted component. The fact that the blueshifted component is relatively
weak indicates the presence of a galactic wind. The properties of the galaxy
counterpart of this DLA is consistent with the prediction that metal-rich DLAs
are associated with the most luminous of the DLA-galaxy counterparts.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
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