6,720 research outputs found
Selecting molecules in the vibrational and rotational ground state by deflection
A beam of diatomic molecules scattered off a standing wave laser mode splits
according to the rovibrational quantum state of the molecules. Our numerical
calculation shows that single state resolution can be achieved by properly
tuned, monochromatic light. The proposed scheme allows for selecting
non-vibrating and non-rotating molecules from a thermal beam, implementing a
laser Maxwell's demon to prepare a rovibrationally cold molecular ensemble.Comment: 11 pages, LaTeX. To appear in the European Physical Journal
Generalized Kac's Lemma for Recurrence Time in Iterated Open Quantum Systems
We consider recurrence to the initial state after repeated actions of a
quantum channel. After each iteration a projective measurement is applied to
check recurrence. The corresponding return time is known to be an integer for
the special case of unital channels, including unitary channels. We prove that
for a more general class of quantum channels the expected return time can be
given as the inverse of the weight of the initial state in the steady state.
This statement is a generalization of the Kac lemma for classical Markov
chains
Quantized recurrence time in iterated open quantum dynamics
The expected return time to the original state is a key concept
characterizing systems obeying both classical or quantum dynamics. We consider
iterated open quantum dynamical systems in finite dimensional Hilbert spaces, a
broad class of systems that includes classical Markov chains and unitary
discrete time quantum walks on networks. Starting from a pure state, the time
evolution is induced by repeated applications of a general quantum channel, in
each timestep followed by a measurement to detect whether the system has
returned to the original state. We prove that if the superoperator is unital in
the relevant Hilbert space (the part of the Hilbert space explored by the
system), then the expectation value of the return time is an integer, equal to
the dimension of this relevant Hilbert space. We illustrate our results on
partially coherent quantum walks on finite graphs. Our work connects the
previously known quantization of the expected return time for bistochastic
Markov chains and for unitary quantum walks, and shows that these are special
cases of a more general statement. The expected return time is thus a
quantitative measure of the size of the part of the Hilbert space available to
the system when the dynamics is started from a certain state
Discovery of the spectroscopic binary nature of six southern Cepheids
We present the analysis of photometric and spectroscopic data of six bright
Galactic Cepheids: GH Carinae, V419 Centauri, V898 Centauri, AD Puppis, AY
Sagittarii, and ST Velorum. Based on new radial velocity data (in some cases
supplemented with earlier data available in the literature), these Cepheids
have been found to be members in spectroscopic binary systems. V898 Cen turned
out to have one of the largest orbital radial velocity amplitude (> 40 km/s)
among the known binary Cepheids. The data are insufficient to determine the
orbital periods nor other orbital elements for these new spectroscopic
binaries.
These discoveries corroborate the statement on the high frequency of
occurrence of binaries among the classical Cepheids, a fact to be taken into
account when calibrating the period-luminosity relationship for Cepheids.
We have also compiled all available photometric data that revealed that the
pulsation period of AD Pup, the longest period Cepheid in this sample, is
continuously increasing with Delta P = 0.004567 d/century, likely to be caused
by stellar evolution. The wave-like pattern superimposed on the parabolic O-C
graph of AD Pup may well be caused by the light-time effect in the binary
system. ST Vel also pulsates with a continuously increasing period. The other
four Cepheids are characterised with stable pulsation periods in the last half
century.Comment: accepted by the MNRAS, 11 pages, 16 figures, 18 tables, a part of the
data can be downloaded from the online version of this articl
Parametric amplification of the mechanical vibrations of a suspended nanowire by magnetic coupling to a Bose-Einstein condensate
We consider the possibility of parametric amplification of a mechanical
vibration mode of a nanowire due to its interaction with a Bose-Einstein
condensate (BEC) of ultracold atoms. The magneto-mechanical coupling is
mediated by the vibrationally modulated magnetic field around the
current-carrying nanowire, which can induce atomic transitions between
different hyperfine sublevels. We theoretically analyze the limitations arising
from the fact that the spin inverted atomic medium which feeds the mechanical
oscillation has a finite bandwidth in the range of the chemical potential of
the condensate
New iron-based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties
The present work reports on the new soft ferromagnetic Heusler phases
Fe2NiGe, Fe2CuGa, and Fe2CuAl, which in previous theoretical studies have been
predicted to exist in a tetragonal regular Heusler structure. Together with the
known phases Fe2CoGe and Fe2NiGa these materials have been synthesized and
characterized by powder XRD, 57 Fe M\"ossbauer spectroscopy, SQUID and EDX
measurements. In particular M\"ossbauer spectroscopy was used to monitor the
degree of local atomic order/disorder and to estimate magnetic moments at the
Fe sites from the hyperfine fields. It is shown that in contrast to the
previous predictions all the materials except Fe2NiGa basically adopt the
inverse cubic Heusler (X-) structure with differing degrees of disorder. The
disorder is more enhanced in case of Fe2NiGa, which was predicted as an inverse
Heusler phase. The experimental data are compared with results from ab-inito
electronic structure calculations on LDA level incorporating the effects of
atomic disorder by using the coherent potential approximation (CPA). A good
agreement between calculated and experimental magnetic moments is found for the
cubic inverse Heusler phases. Model calculations on various atomic
configurations demonstrate that antisite disorder tends to enhance the
stability of the X-structure. Given the fundamental scientific and
technological importance of tetragonal Heusler phases the present results call
for further investigations to unravel the factors stabilizing tetragonal
Heusler materials
The Clinical Significance of the Primary Malignant Melanoma of the Lower Respiratory Tract and/or Lung Based on the Analysis of Published Case Reports and of Two Patients
Considering the data and including two patients of the authors, there exist only 18 authentic cases of primary malignant melanoma of the lower respiratory tract and/or the lung. The tumor was localized
in the endobronchial space in 7 cases and only once in the trachea. Endobronchial localization, together
with the involvement of the surrounding lung tissue, was found in two cases, whereas in 8 patients,
the tumor was found exclusively in the lung parenchyma. Successful resection could be
performed in 14 of the 18 cases. Survival was influenced primarily by operability, and on actual size
and extension. The authors question the role of the obduction in the diagnostic criteria, because most
of the survivors, even up to ten years postsurgery were considered primary. Apart from the various
imaging methods, diagnostic endoscopy (i.e., bronchoscopy) and the histology of the biopsy material
are major aides in the diagnosis of primary character, location, and operability, as well as in the
elaboration of the surgical plans, than it is usual in cases of other tumors
Discovery of the spectroscopic binary nature of three bright southern Cepheids
We present an analysis of spectroscopic radial velocity and photometric data
of three bright Galactic Cepheids: LR Trianguli Australis (LR TrA), RZ Velorum
(RZ Vel), and BG Velorum (BG Vel). Based on new radial velocity data, these
Cepheids have been found to be members of spectroscopic binary systems.
The ratio of the peak-to-peak radial velocity amplitude to photometric
amplitude indicates the presence of a companion for LR TrA and BG Vel. IUE
spectra indicate that the companions of RZ Vel and BG Vel cannot be hot stars.
The analysis of all available photometric data revealed that the pulsation
period of RZ Vel and BG Vel varies monotonically, due to stellar evolution.
Moreover, the longest period Cepheid in this sample, RZ Vel, shows period
fluctuations superimposed on the monotonic period increase. The light-time
effect interpretation of the observed pattern needs long-term photometric
monitoring of this Cepheid. The pulsation period of LR TrA has remained
constant since the discovery of its brightness variation.
Using statistical data, it is also shown that a large number of spectroscopic
binaries still remain to be discovered among bright classical Cepheids.Comment: 9 pages, 14 figure
N=4 Supergravity with Antisymmetric Tensor in Central Charge Superspace
A concise geometrical formulation of N=4 supergravity containing an
antisymmetric tensor gauge field is given in central charge superspace:
graviphotons are identified in the super-vielbein on the same footing as the
vierbein and the Rarita-Schwinger fields. As a consequence of superspace
soldering, Chern-Simons terms in the fieldstrength of the antisymmetric tensor
arise as an intrinsic property of superspace with central charge coordinates.Comment: Latex, 13 pages, minor clarification about a referenc
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