1,700 research outputs found
Saddlepoint approximation for Student's t-statistic with no moment conditions
A saddlepoint approximation of the Student's t-statistic was derived by
Daniels and Young [Biometrika 78 (1991) 169-179] under the very stringent
exponential moment condition that requires that the underlying density function
go down at least as fast as a Normal density in the tails. This is a severe
restriction on the approximation's applicability. In this paper we show that
this strong exponential moment restriction can be completely dispensed with,
that is, saddlepoint approximation of the Student's t-statistic remains valid
without any moment condition. This confirms the folklore that the Student's
t-statistic is robust against outliers. The saddlepoint approximation not only
provides a very accurate approximation for the Student's t-statistic, but it
also can be applied much more widely in statistical inference. As a result,
saddlepoint approximations should always be used whenever possible. Some
numerical work will be given to illustrate these points.Comment: Published at http://dx.doi.org/10.1214/009053604000000742 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Necessity for quantum coherence of nondegeneracy in energy flow
In this work, we show that the quantum coherence among non-degenerate energy
subspaces (CANES) is essential for the energy flow in any quantum system. CANES
satisfies almost all of the requirements as a coherence measure, except that
the coherence within degenerate subspaces is explicitly eliminated.We show that
the energy of a system becomes frozen if and only if the corresponding CANES
vanishes, which is true regardless of the form of interaction with the
environment. However, CANES can remain zero even if the entanglement changes
over time. Furthermore, we show how the power of energy flow is bounded by the
value of CANES. An explicit relation connecting the variation of energy and
CANES is also presented. These results allow us to bound the generation of
system-environment correlation through the local measurement of the system's
energy flow
Incompatibility of Observables as State-Independent Bound of Uncertainty Relations
For a pair of observables, they are called "incompatible", if and only if the
commutator between them does not vanish, which represents one of the key
features in quantum mechanics. The question is, how can we characterize the
incompatibility among three or more observables? Here we explore one possible
route towards this goal through Heisenberg's uncertainty relations, which
impose fundamental constraints on the measurement precisions for incompatible
observables. Specifically, we quantify the incompatibility by the optimal
state-independent bounds of additive variance-based uncertainty relations. In
this way, the degree of incompatibility becomes an intrinsic property among the
operators, but not on the quantum state. To justify our case, we focus on the
incompatibility of spin systems. For an arbitrary setting of two or three
linearly-independent Pauli-spin operators, the incompatibility is analytically
solved, the spins are maximally incompatible if and only if they are orthogonal
to each other. On the other hand, the measure of incompatibility represents a
versatile tool for applications such as testing entanglement of bipartite
states, and EPR-steering criteria.Comment: Comments are welcom
A Comet Active Beyond the Crystallization Zone
We present observations showing in-bound long-period comet C/2017 K2
(PANSTARRS) to be active at record heliocentric distance. Nucleus temperatures
are too low (60 K to 70 K) either for water ice to sublimate or for amorphous
ice to crystallize, requiring another source for the observed activity. Using
the Hubble Space Telescope we find a sharply-bounded, circularly symmetric dust
coma 10 km in radius, with a total scattering cross section of 10
km. The coma has a logarithmic surface brightness gradient -1 over much of
its surface, indicating sustained, steady-state dust production. A lack of
clear evidence for the action of solar radiation pressure suggests that the
dust particles are large, with a mean size 0.1 mm. Using a coma
convolution model, we find a limit to the apparent magnitude of the nucleus 25.2 (absolute magnitude 12.9). With assumed geometric albedo =
0.04, the limit to the nucleus circular equivalent radius is 9 km.
Pre-discovery observations from 2013 show that the comet was also active at
23.7 AU heliocentric distance. While neither water ice sublimation nor
exothermic crystallization can account for the observed distant activity, the
measured properties are consistent with activity driven by sublimating
supervolatile ices such as CO, CO, O and N. Survival of
supervolatiles at the nucleus surface is likely a result of the comet's recent
arrival from the frigid Oort cloud.Comment: 20 pages, 3 figures, 2 tables, published on Astrophysical Journal
Letters, 847:L19 (5pp), 2017 October
- …