1,730 research outputs found
-optimal saturated designs: a simulation study
In this work we focus on saturated -optimal designs. Using recent results,
we identify -optimal designs with the solutions of an optimization problem
with linear constraints. We introduce new objective functions based on the
geometric structure of the design and we compare them with the classical
-efficiency criterion. We perform a simulation study. In all the test cases
we observe that designs with high values of -efficiency have also high
values of the new objective functions.Comment: 8 pages. Preliminary version submitted to the 7th IWS Proceeding
Markov basis and Groebner basis of Segre-Veronese configuration for testing independence in group-wise selections
We consider testing independence in group-wise selections with some
restrictions on combinations of choices. We present models for frequency data
of selections for which it is easy to perform conditional tests by Markov chain
Monte Carlo (MCMC) methods. When the restrictions on the combinations can be
described in terms of a Segre-Veronese configuration, an explicit form of a
Gr\"obner basis consisting of moves of degree two is readily available for
performing a Markov chain. We illustrate our setting with the National Center
Test for university entrance examinations in Japan. We also apply our method to
testing independence hypotheses involving genotypes at more than one locus or
haplotypes of alleles on the same chromosome.Comment: 25 pages, 5 figure
Koszul binomial edge ideals
It is shown that if the binomial edge ideal of a graph defines a Koszul
algebra, then must be chordal and claw free. A converse of this statement
is proved for a class of chordal and claw free graphs
Evidence for Strong-coupling S-wave Superconductivity in MgB2 :11B NMR Study
We have investigated a gap structure in a newly-discovered superconductor,
MgB2 through the measurement of 11B nuclear spin-lattice relaxation rate,
^{11}(1/T_1). ^{11}(1/T_1) is proportional to the temperature (T) in the normal
state, and decreases exponentially in the superconducting (SC) state, revealing
a tiny coherence peak just below T_c. The T dependence of 1/T_1 in the SC state
can be accounted for by an s-wave SC model with a large gap size of 2\Delta
/k_BT_c \sim 5 which suggests to be in a strong-coupling regime.Comment: 2 pages with 1 figur
Multigap Superconductivity in YC: A C-NMR Study
We report on the superconducting (SC) properties of YC with a
relatively high transition temperature K investigated by
C nuclear-magnetic-resonance (NMR) measurements under a magnetic field.
The C Knight shift has revealed a significant decrease below , suggesting a spin-singlet superconductivity. From an analysis of the
temperature dependence of the nuclear spin-lattice relaxation rate in
the SC state, YC is demonstrated to be a multigap superconductor that
exhibits a large gap at the main band and a
small gap at other bands. These results have
revealed that YC is a unique multigap s-wave superconductor similar to
MgB.Comment: 4 pages, 5 figure
Infrared/optical - X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506
We investigate the origin of short X-ray flares which are occasionally
observed in early stages of afterglows of gamma-ray bursts (GRBs). We observed
two events, GRB 071112C and GRB 080506, before the start of X-ray flares in the
optical and near-infrared (NIR) bands with the 1.5-m Kanata telescope. In
conjunction with published X-ray and optical data, we analyzed densely sampled
light curves of the early afterglows and spectral energy distributions (SEDs)
in the NIR-X-ray ranges. We found that the SEDs had a break between the optical
and X-ray bands in the normal decay phases of both GRBs regardless of the model
for the correction of the interstellar extinction in host galaxies of GRBs. In
the X-ray flares, X-ray flux increased by 3 and 15 times in the case of GRB
071112C and 080506, respectively, and the X-ray spectra became harder than
those in the normal decay phases. No significant variation in the optical-NIR
range was detected together with the X-ray flares. These results suggest that
the X-ray flares were associated with either late internal shocks or external
shocks from two-component jets.Comment: 10 pages, 5 figures, accepted to Astronomy and Astrophysic
Toric rings, inseparability and rigidity
This article provides the basic algebraic background on infinitesimal
deformations and presents the proof of the well-known fact that the non-trivial
infinitesimal deformations of a -algebra are parameterized by the
elements of cotangent module of . In this article we focus on
deformations of toric rings, and give an explicit description of in
the case that is a toric ring.
In particular, we are interested in unobstructed deformations which preserve
the toric structure. Such deformations we call separations. Toric rings which
do not admit any separation are called inseparable. We apply the theory to the
edge ring of a finite graph. The coordinate ring of a convex polyomino may be
viewed as the edge ring of a special class of bipartite graphs. It is shown
that the coordinate ring of any convex polyomino is inseparable. We introduce
the concept of semi-rigidity, and give a combinatorial description of the
graphs whose edge ring is semi-rigid. The results are applied to show that for
, is not rigid while for , is
rigid. Here is the complete bipartite graph with one
edge removed.Comment: 33 pages, chapter 2 of the Book << Multigraded Algebra and
Applications>> 2018, Springer International Publishing AG, part of Springer
Natur
Nuclear spin-spin coupling in La_{2-x}Sr_{x}CuO_{4} studied by stimulated echo decay
We have performed copper NQR experiments in high temperature superconductors
YBa_{2}Cu_{4}O_{8}, YBa_{2}Cu_{3}O_{7}, and La_{2-x}Sr_{x}CuO_{4} (x=0.12 and
0.15), using the stimulated echo technique. The stimulated echo intensity is
analyzed by a model that includes the spin-lattice relaxation process (T_ {1
}-process) and the fluctuating local field due to nuclear spin-spin coupling.
The model gives quantitative account of the experimental results in Y-based
compounds using the known values of 1/T_{1} and 1/T_{2G}, the gaussian decay
rate of the spin echo intensity. The same model applied to LSCO enables us to
extract the value of T_{2G}. Our results indicate that T_{1}T/T_{2G} is
independent of temperature, implying that the dynamic exponent is one in
La_{2-x}Sr_{x}CuO_{4}.Comment: 14 pages, 11 fugures, The bibliography field is correcte
Antiferromagnetic phase transition in four-layered high-T_c superconductors Ba_2Ca_3Cu_4O_8(F_yO_{1-y})_2 with T_c=55-102 K: Cu- and F-NMR studies
We report on magnetic characteristics in four-layered high-T_c
superconductors Ba_2Ca_3Cu_4O_8(F_yO_{1-y})_2 with apical fluorine through Cu-
and F-NMR measurements. The substitution of oxygen for fluorine at the apical
site increases the carrier density (N_h) and T_c from 55 K up to 102 K. The NMR
measurements reveal that antiferromagnetic order, which can uniformly coexist
with superconductivity, exists up to N_h = 0.15, which is somewhat smaller than
N_h = 0.17 being the quantum critical point (QCP) for five-layered compounds.
The fact that the QCP for the four-layered compounds moves to a region of lower
carrier density than for five-layered ones ensures that the decrease in the
number of CuO_2 layers makes an interlayer magnetic coupling weaker.Comment: 7 pages, 6 gigures, Submitted to J. Phys. Soc. Jp
Experimental Evidence for a Glass forming "Stripe Liquid" in the Magnetic Ground State of La1.65Eu0.2Sr0.15CuO4
We report measurements of the longitudinal () and transverse
() decay rates of the magnetization of La nuclei
performed in a high quality single crystal of
LaEuSrCuO. We observe a dramatic slowing of the
Cu 3d spins manifested as a sharp increase of both and
below 30 K. We find that in this temperature range the
fluctuations involve a unique time scale which diverges as with K. This behavior is distinct from
the continuous freezing observed in underdoped LaSrCuO which
involves a distribution of energy barriers. By contrast, in
LaEuSrCuO, the freezing below 30K is intrinsic
to its magnetic ground state and the observed power law supports the existence
of a glass forming "charge stripe liquid".Comment: 5 pages, 3 Figures. Revised version, resubmitte
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