5,396 research outputs found
Dark Energy Evolution and the Curvature of the Universe from Recent Observations
We discuss the constraints on the time-varying equation of state for dark
energy and the curvature of the universe using observations of type Ia
supernovae from Riess et al. and the most recent Supernova Legacy Survey
(SNLS), the baryon acoustic oscillation peak detected in the SDSS luminous red
galaxy survey and cosmic microwave background. Due to the degeneracy among the
parameters which describe the time dependence of the equation of state and the
curvature of the universe, the constraints on them can be weakened when we try
to constrain them simultaneously, in particular when we use a single
observational data. However, we show that we can obtain relatively severe
constraints when we use all data sets from observations above even if we
consider the time-varying equation of state and do not assume a flat universe.
We also found that the combined data set favors a flat universe even if we
consider the time variation of dark energy equation of state.Comment: 17 pages, 12 figures, references adde
The Dwarf Nova Outbursts of Nova Her 1960 (=V446 Her)
V446 Her is the best example of an old nova which has developed dwarf nova
eruptions in the post-nova state. We report on observed properties of the
long-term light curve of V446 Her, using photometry over 19 years. Yearly
averages of the outburst magnitudes shows a decline of ~0.013 mag/yr,
consistent with the decline of other post-novae that do not have dwarf nova
outbursts. Previous suggestions of bimodal distributions of the amplitudes and
widths of the outbursts are confirmed. The outbursts occur at a mean spacing of
18 days but the range of spacings is large (13-30 days). From simulations of
dwarf nova outbursts it has been predicted that the outburst spacing in V446
Her will increase as M-dot from the red dwarf companion slowly falls following
the nova; however the large intrinsic scatter in the spacings serves to hide
any evidence of this effect. We do find a systematic change in the outburst
pattern in which the brighter, wider type of outbursts disappeared after late
2003, and this phenomenon is suggested to be due to falling M-dot following the
nova.Comment: To appear at the Astronomical Journal; 7 pages, 1 table, 11 figure
Revisiting the Constraint on the Helium Abundance from CMB
We revisit the constraint on the primordial helium mass fraction Yp from
observations of cosmic microwave background (CMB) alone. By minimizing chi
square of recent CMB experiments over 6 other cosmological parameters, we
obtained rather weak constraints as 0.17 < Yp < 0.52 at 1 sigma C.L. for a
particular data set. We also study the future constraint on cosmological
parameters when we take account of the prediction of the standard big bang
nucleosynthesis (BBN) theory as a prior on the helium mass fraction where Yp
can be fixed for a given energy density of baryon. We discuss the implications
of the prediction of the standard BBN on the analysis of CMB.Comment: 15 pages, 5 figures, published versio
Outcome Independence of Entanglement in One-Way Computation
We show that the various intermediate states appearing in the process of
one-way computation at a given step of measurement are all equivalent modulo
local unitary transformations. This implies, in particular, that all those
intermediate states share the same entanglement irrespective of the measurement
outcomes, indicating that the process of one-way computation is essentially
unique with respect to local quantum operations.Comment: 6 pages, 4 figure
Cluster formations in deformed states for Si and S
We study cluster formation in strongly deformed states for Si and
S using a macroscopic-microscopic model. The study is based on
calculated total-energy surfaces, which are the sums of deformation-dependent
macroscopic-microscopic potential-energy surfaces and rotational-energy
contributions. We analyze the angular-momentum-dependent total-energy surfaces
and identify the normal- and super-deformed states in Si and S,
respectively. We show that at sufficiently high angular momenta strongly
deformed minima appear. The corresponding microscopic density distributions
show cluster structure that closely resemble the O+C and
O+O configurations. At still higher deformations, beyond the
minima, valleys develop in the calculated surfaces. These valleys lead to mass
divisions that correspond to the target-projectile configurations for which
molecular resonance states have been observed. We discuss the relation between
the one-body deformed minima and the two-body molecular-resonance states.Comment: 6 pages, 7 figure
Evaluating the effectiveness of physical shape-change for in-pocket mobile device notifications
Audio and vibrotactile output are the standard mechanisms mobile devices use to attract their owner's attention. Yet in busy and noisy environments, or when the user is physically active, these channels sometimes fail. Recent work has explored the use of physical shape-change as an additional method for conveying notifications when the device is in-hand or viewable. However, we do not yet understand the effectiveness of physical shape-change as a method for communicating in-pocket notifications. This paper presents three robustly implemented, mobile-device sized shape-changing devices, and two user studies to evaluate their effectiveness at conveying notifications. The studies reveal that (1) different types and configurations of shape-change convey different levels of urgency and; (2) fast pulsing shape-changing notifications are missed less often and recognised more quickly than the standard slower vibration pulse rates of a mobile device
The contrasting fission potential-energy structure of actinides and mercury isotopes
Fission-fragment mass distributions are asymmetric in fission of typical
actinide nuclei for nucleon number in the range
and proton number in the range . For somewhat
lighter systems it has been observed that fission mass distributions are
usually symmetric. However, a recent experiment showed that fission of
Hg following electron capture on Tl is asymmetric. We calculate
potential-energy surfaces for a typical actinide nucleus and for 12 even
isotopes in the range Hg--Hg, to investigate the similarities
and differences of actinide compared to mercury potential surfaces and to what
extent fission-fragment properties, in particular shell structure, relate to
the structure of the static potential-energy surfaces. Potential-energy
surfaces are calculated in the macroscopic-microscopic approach as functions of
fiveshape coordinates for more than five million shapes. The structure of the
surfaces are investigated by use of an immersion technique. We determine
properties of minima, saddle points, valleys, and ridges between valleys in the
5D shape-coordinate space. Along the mercury isotope chain the barrier heights
and the ridge heights and persistence with elongation vary significantly and
show no obvious connection to possible fragment shell structure, in contrast to
the actinide region, where there is a deep asymmetric valley extending from the
saddle point to scission. The mechanism of asymmetric fission must be very
different in the lighter proton-rich mercury isotopes compared to the actinide
region and is apparently unrelated to fragment shell structure. Isotopes
lighter than Hg have the saddle point blocked from a deep symmetric
valley by a significant ridge. The ridge vanishes for the heavier Hg isotopes,
for which we would expect a qualitatively different asymmetry of the fragments.Comment: 8 pages, 9 figure
Accelerator modes of square well system
We study accelerator modes of a particle, confined in an one-dimensional
infinite square well potential, subjected to a time-periodic pulsed field.
Dynamics of such a particle can be described by one generalization of the
kicked rotor. In comparison with the kicked rotor, this generalization is shown
to have a much larger parametric space for existence of the modes. Using this
freedom we provide evidence that accelerator mode assisted anomalous transport
is greatly enhanced when low order resonances are exposed at the border of
chaos. We also present signature of the enhanced transport in the quantum
domain.Comment: 7 pages, 5 figures, revtex
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