6,671 research outputs found
Human-like machines: Transparency and comprehensibility [Commentary]
AbstractArtificial intelligence algorithms seek inspiration from human cognitive systems in areas where humans outperform machines. But on what level should algorithms try to approximate human cognition? We argue that human-like machines should be designed to make decisions in transparent and comprehensible ways, which can be achieved by accurately mirroring human cognitive processes.</jats:p
High-pressure transport properties of CeRu_2Ge_2
The pressure-induced changes in the temperature-dependent thermopower S(T)
and electrical resistivity \rho(T) of CeRu_2Ge_2 are described within the
single-site Anderson model. The Ce-ions are treated as impurities and the
coherent scattering on different Ce-sites is neglected. Changing the
hybridisation \Gamma between the 4f-states and the conduction band accounts for
the pressure effect. The transport coefficients are calculated in the
non-crossing approximation above the phase boundary line. The theoretical S(T)
and \rho(T) curves show many features of the experimental data. The seemingly
complicated temperature dependence of S(T) and \rho(T), and their evolution as
a function of pressure, is related to the crossovers between various fixed
points of the model.Comment: 9 pages, 10 figure
Measurements of thermodynamic and transport properties of EuC: a low-temperature analogue of EuO
EuC is a ferromagnet with a Curie-temperature of K. It
is semiconducting with the particularity that the resistivity drops by about 5
orders of magnitude on cooling through , which is therefore called a
metal-insulator transition. In this paper we study the magnetization, specific
heat, thermal expansion, and the resistivity around this ferromagnetic
transition on high-quality EuC samples. At we observe well defined
anomalies in the specific heat and thermal expansion data.
The magnetic contributions of and can satisfactorily be
described within a mean-field theory, taking into account the magnetization
data. In zero magnetic field the magnetic contributions of the specific heat
and thermal expansion fulfill a Gr\"uneisen-scaling, which is not preserved in
finite fields. From an estimation of the pressure dependence of via
Ehrenfest's relation, we expect a considerable increase of under applied
pressure due to a strong spin-lattice coupling. Furthermore the influence of
weak off stoichiometries in EuC was studied. It is
found that strongly affects the resistivity, but hardly changes the
transition temperature. In all these aspects, the behavior of EuC strongly
resembles that of EuO.Comment: 7 pages, 6 figure
Evidence for Heating of Neutron Stars by Magnetic Field Decay
We show the existence of a strong trend between neutron star surface
temperature and the dipolar component of the magnetic field extending through
three orders of field magnitude, a range that includes magnetars, radio-quiet
isolated neutron stars, and many ordinary radio pulsars. We suggest that this
trend can be explained by the decay of currents in the crust over a time scale
of few Myr. We estimate the minimum temperature that a NS with a given magnetic
field can reach in this interpretation.Comment: 4 pages, 1 figures, version accepted for publication in Phys. Rev.
Let
Are We Seeing Magnetic Axis Reorientation in the Crab and Vela Pulsars?
Variation in the angle between a pulsar's rotational and magnetic
axes would change the torque and spin-down rate. We show that sudden increases
in , coincident with glitches, could be responsible for the persistent
increases in spin-down rate that follow glitches in the Crab pulsar. Moreover,
changes in at a rate similar to that inferred for the Crab pulsar
account naturally for the very low braking index of the Vela pulsar. If
increases with time, all pulsar ages obtained from the conventional
braking model are underestimates. Decoupling of the neutron star liquid
interior from the external torque cannot account for Vela's low braking index.
Variations in the Crab's pulse profile due to changes in might be
measurable.Comment: 14 pages and one figure, Latex, uses aasms4.sty. Accepted to ApJ
Letter
Antiferroquadrupolar Order in the Magnetic Semiconductor TmTe
The physical properties of the antiferroquadrupolar state occurring in TmTe
below TQ=1.8 K have been studied using neutron diffraction in applied magnetic
fields. A field-induced antiferromagnetic component k = (1/2,1/2,1/2) is
observed and, from its magnitude and direction for different orientations of H,
an O(2,2) quadrupole order parameter is inferred. Measurements below TN ~= 0.5
K reveal that the magnetic structure is canted, in agreement with theoretical
predictions for in-plane antiferromagnetism. Complex domain repopulation
effects occur when the field is increased in the ordered phases, with
discontinuities in the superstructure peak intensities above 4 T.Comment: 6 pages, 6 figures, Presented at the International Conference on
Strongly Correlated Electrons with Orbital Degrees of Freedom (ORBITAL 2001),
September 11-14, 2001 (Sendai, JAPAN). To appear in: Journal of the Physical
Society of Japan (2002
Structures and orientational transitions in thin films of tilted hexatic smectics
We present detailed systematic studies of structural transformations in thin
liquid crystal films with the smectic-C to hexatic phase transition. For the
first time all possible structures reported in the literature are observed for
one material (5 O.6) at the variation of temperature and thickness. In unusual
modulated structures the equilibrium period of stripes is twice with respect to
the domain size. We interpret these patterns in the frame work of
phenomenological Landau type theory, as equilibrium phenomena produced by a
natural geometric frustration in a system having spontaneous splay distortion.Comment: 7 pages, 6 figure
The Crustal Rigidity of a Neutron Star, and Implications for PSR 1828-11 and other Precession Candidates
We calculate the crustal rigidity parameter, b, of a neutron star (NS), and
show that b is a factor 40 smaller than the standard estimate due to Baym &
Pines (1971). For a NS with a relaxed crust, the NS's free-precession frequency
is directly proportional to b. We apply our result for b to PSR 1828-11, a 2.5
Hz pulsar that appears to be precessing with period 511 d. Assuming this 511-d
period is set by crustal rigidity, we show that this NS's crust is not relaxed,
and that its reference spin (roughly, the spin for which the crust is most
relaxed) is 40 Hz, and that the average spindown strain in the crust is 5
\times 10^{-5}. We also briefly describe the implications of our b calculation
for other well-known precession candidates.Comment: 44 pages, 10 figures, submitted to Ap
Search for T Violation in Charm Meson Decays
Using data from the FOCUS (E831) experiment, we have searched for T violation
in charm meson decays using the four-body decay channels , , and . The T violation asymmetry is obtained using triple-product
correlations and assuming the validity of the CPT theorem. We find the
asymmetry values to be
,
, and
.
Each measurement is consistent with no T violation. New measurements of the
CP asymmetries for some of these decay modes are also presented.Comment: 17 pages,6 figures,submitted to Phys.Lett.
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