15,080 research outputs found
A Criterion for Comparing Measurement Results and Determining Conformity with Specifications
In this paper a new criterion for comparing measurement results and determining conformity with specifications is proposed, which essentially is a strategy of estimating the empirical relationships of objects. Comparing with traditional methods given in GUM: 2008 and ISO 14253-1, this criterion improves the resolution of comparison by reducing the sizes of the coverage intervals to be compared. Interval order (a binary relation) is used for comparing the coverage intervals of the measurand and represents the empirical relations. The systematic effects of measurement are classified into two types: monotonic and non-monotonic effects, so that, without correcting the monotonic effects, a biased measurand can be specified to represent the empirical relations. Thereby the uncertainty components arising from the monotonic effects can be removed from the combined uncertainty. A strategy is given for determining the relationships among measurement results and specification limits. An example is given to demonstrate the application of the criterion
Cosmological dynamics of scalar fields with O(N) symmetry
In this paper, we study the cosmological dynamics of scalar fields with O(N)
symmetry in general potentials. We compare the phase space of the dynamical
systems of the quintessence and phantom and give the conditions for the
existence of various attractors as well as their cosmological implications. We
also show that the existence of tracking attractor in O(N) phantom models
require the potential with , which makes the models with
exponential potential possess no tracking attractor.Comment: 9 pages, 4 figures; Replaced with the version to be published in
Classical and Quantum Gravity. Reference adde
Observation of an in-plane magnetic-field-driven phase transition in a quantum Hall system with SU(4) symmetry
In condensed matter physics, the study of electronic states with SU(N)
symmetry has attracted considerable and growing attention in recent years, as
systems with such a symmetry can often have a spontaneous symmetry-breaking
effect giving rise to a novel ground state. For example, pseudospin quantum
Hall ferromagnet of broken SU(2) symmetry has been realized by bringing two
Landau levels close to degeneracy in a bilayer quantum Hall system. In the past
several years, the exploration of collective states in other multi-component
quantum Hall systems has emerged. Here we show the conventional pseudospin
quantum Hall ferromagnetic states with broken SU(2) symmetry collapsed rapidly
into an unexpected state with broken SU(4) symmetry, by in-plane magnetic field
in a two-subband GaAs/AlGaAs two-dimensional electron system at filling factor
around . Within a narrow tilting range angle of 0.5 degrees, the
activation energy increases as much as 12 K. While the origin of this puzzling
observation remains to be exploited, we discuss the possibility of a
long-sought pairing state of electrons with a four-fold degeneracy.Comment: 13 pages, 4 figure
The Properties of H{\alpha} Emission-Line Galaxies at z = 2.24
Using deep narrow-band and -band imaging data obtained with
CFHT/WIRCam, we identify a sample of 56 H emission-line galaxies (ELGs)
at with the 5 depths of and (AB)
over 383 arcmin area in the ECDFS. A detailed analysis is carried out
with existing multi-wavelength data in this field. Three of the 56 H
ELGs are detected in Chandra 4 Ms X-ray observation and two of them are
classified as AGNs. The rest-frame UV and optical morphologies revealed by
HST/ACS and WFC3 deep images show that nearly half of the H ELGs are
either merging systems or with a close companion, indicating that the
merging/interacting processes play a key role in regulating star formation at
cosmic epoch z=2-3; About 14% are too faint to be resolved in the rest-frame UV
morphology due to high dust extinction. We estimate dust extinction from SEDs.
We find that dust extinction is generally correlated with H luminosity
and stellar mass (SM). Our results suggest that H ELGs are
representative of star-forming galaxies (SFGs). Applying extinction correction
for individual objects, we examine the intrinsic H luminosity function
(LF) at , obtaining a best-fit Schechter function characterized by a
faint-end slope of . This is shallower than the typical slope of
in previous works based on constant extinction correction.
We demonstrate that this difference is mainly due to the different extinction
corrections. The proper extinction correction is thus key to recovering the
intrinsic LF as the extinction globally increases with H luminosity.
Moreover, we find that our H LF mirrors the SM function of SFGs at the
same cosmic epoch. This finding indeed reflects the tight correlation between
SFR and SM for the SFGs, i.e., the so-called main sequence.Comment: 15 pages, 12 figures, 2 tables, Received 2013 October 11; accepted
2014 February 13; published 2014 March 18 by Ap
CMBR Constraint on a Modified Chaplygin Gas Model
In this paper, a modified Chaplygin gas model of unifying dark energy and
dark matter with exotic equation of state
which can also explain the recent accelerated expansion of the universe is
investigated by the means of constraining the location of the peak of the CMBR
spectrum. We find that the result of CMBR measurements does not exclude the
nonzero value of parameter , but allows it in the range .Comment: 4 pages, 3 figure
Resolving and Tuning Mechanical Anisotropy in Black Phosphorus via Nanomechanical Multimode Resonance Spectromicroscopy
Black phosphorus (P) has emerged as a layered semiconductor with a unique
crystal structure featuring corrugated atomic layers and strong in-plane
anisotropy in its physical properties. Here, we demonstrate that the crystal
orientation and mechanical anisotropy in free-standing black P thin layers can
be precisely determined by spatially resolved multimode nanomechanical
resonances. This offers a new means for resolving important crystal orientation
and anisotropy in black P device platforms in situ beyond conventional optical
and electrical calibration techniques. Furthermore, we show that
electrostatic-gating-induced straining can continuously tune the mechanical
anisotropic effects on multimode resonances in black P electromechanical
devices. Combined with finite element modeling (FEM), we also determine the
Young's moduli of multilayer black P to be 116.1 and 46.5 GPa in the zigzag and
armchair directions, respectively.Comment: Main Text: 13 Pages, 4 Figures; Supplementary Information: 5 Pages, 2
Figures, 2 Table
First-principles study of native point defects in Bi2Se3
Using first-principles method within the framework of the density functional
theory, we study the influence of native point defect on the structural and
electronic properties of BiSe. Se vacancy in BiSe is a double
donor, and Bi vacancy is a triple acceptor. Se antisite (Se) is always
an active donor in the system because its donor level ((+1/0))
enters into the conduction band. Interestingly, Bi antisite(Bi) in
BiSe is an amphoteric dopant, acting as a donor when
0.119eV (the material is typical p-type) and as an acceptor when
0.251eV (the material is typical n-type). The formation energies
under different growth environments (such as Bi-rich or Se-rich) indicate that
under Se-rich condition, Se is the most stable native defect independent
of electron chemical potential . Under Bi-rich condition, Se vacancy
is the most stable native defect except for under the growth window as
0.262eV (the material is typical n-type) and
-0.459eV(Bi-rich), under such growth windows one
negative charged Bi is the most stable one.Comment: 7 pages, 4 figure
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