224,273 research outputs found
Real-time representations of the output gap
Methods are described for the appropriate use of data obtained and analysed in real time to represent the output gap. The methods employ cointegrating VAR techniques to model real-time measures and realizations of output series jointly. The model is used to mitigate the impact of data revisions; to generate appropriate forecasts that can deliver economically meaningful output trends and that can take into account the end-of-sample problems encountered in measuring these trends; and to calculate probability forecasts that convey in a clear way the uncertainties associated with the gap measures. The methods are applied to data for the United States 1965q4–2004q4, and the improvements over standard methods are illustrated
Compensated Half-metallicity in the Trigonally Distorted Perovskite-type NiCrO
Using first principles calculations, we investigate the electronic and
magnetic properties of the trigonally distorted (R-3c) perovskite-derived
NiCrO. Within the local spin density approximation (LSDA), our calculations
show that this system is an exactly compensated half-metal (CHM). The local
spin moments of Cr 2.04, and antialigned Ni -1.41 and three oxygens -0.63 (in
the units of ), indicate high spin S=3/2 Cr and S=3/2
(NiO) units. Considering reasonable values of the on-site Coulomb
repulsion U on both Ni and Cr ions with LDA+U approach, this system becomes an
insulator (as reported by Chamberland and Cloud) having a narrow gap in the
spin-up channel, whereas the other channel has a large gap of ~3 eV. Although
inclusion of U seemingly leads to the transition Ni^{3+}_3$ and provide another route to search for
CHM, which is a property sought by many.Comment: 5 pages, 5 embedded figures, (To be published in PRB rapid Commun.
Real-time imaging of pulvinus bending in Mimosa pudica
Mimosa pudica is a plant that rapidly shrinks its body in response to external stimuli. M. pudica does not perform merely simple movements, but exhibits a variety of movements that quickly change depending on the type of stimuli. Previous studies have investigated the motile mechanism of the plants from a biochemical perspective. However, an interdisciplinary study on the structural characteristics of M. pudica should be accompanied by biophysical research to explain the principles underlying such movements. In this study, the structural characteristics and seismonastic reactions of M. pudica were experimentally investigated using advanced bio-imaging techniques. The results show that the key factors for the flexible movements by the pulvinus are the following: bendable xylem bundle, expandable/shrinkable epidermis, tiny wrinkles for surface modification, and a xylem vessel network for efficient water transport. This study provides new insight for better understanding the M. pudica motile mechanism through structural modification.open1111Nsciescopu
Charge and Spin Ordering in Insulating NaCoO: Effects of Correlation and Symmetry
Ab initio band theory including correlations due to intra-atomic repulsion is
applied to study charge disproportionation and charge- and spin-ordering in
insulating NaCoO. Various ordering patterns (zigzag and two
striped) for four-Co supercells are analyzed before focusing on the observed
"out-of-phase stripe" pattern of antiferromagnetic Co spins along
charge-ordered stripes. This pattern relieves frustration and shows distinct
analogies with the cuprate layers: a bipartite lattice of antialigned spins,
with axes at 90 degree angles. Substantial distinctions with cuprates are also
discussed, including the tiny gap of a new variant of "charge transfer" type
within the Co 3d system.Comment: 5 pages, 3 figure
A Chemical turnstile
A chemical turnstile is a device for transporting small, well-characterised
doses of atoms from one location to another. A working turnstile has yet to be
built, despite the numerous technological applications available for such a
device. The key difficulty in manufacturing a chemical turnstile is finding a
medium which will trap and transport atoms. Here we propose that ferroelastic
twin walls are suitable for this role. Previous work shows that twin walls can
act as two-dimensional trapping planes within which atomic transport is fast.
We report simulations showing that a stress-induced reorientation of a twin
wall can occur. This behaviour is ideal for chemical turnstile applications.Comment: 2 pages, 3 figure
Dyons in N=4 Supersymmetric Theories and Three-Pronged Strings
We construct and explore BPS states that preserve 1/4 of supersymmetry in N=4
Yang-Mills theories. Such states are also realized as three-pronged strings
ending on D3-branes. We correct the electric part of the BPS equation and
relate its solutions to the unbroken abelian gauge group generators. Generic
1/4-BPS solitons are not spherically symmetric, but consist of two or more
dyonic components held apart by a delicate balance between static
electromagnetic force and scalar Higgs force. The instability previously found
in three-pronged string configurations is due to excessive repulsion by one of
these static forces. We also present an alternate construction of these 1/4-BPS
states from quantum excitations around a magnetic monopole, and build up the
supermultiplet for arbitrary (quantized) electric charge. The degeneracy and
the highest spin of the supermultiplet increase linearly with a relative
electric charge. We conclude with comments.Comment: 33 pages, two figures, LaTex, a footnote added, the figure caption of
Fig.2 expanded, one more referenc
Charge Disproportionation and Spin Ordering Tendencies in Na(x)CoO2
The strength and effect of Coulomb correlations in the (superconducting when
hydrated) x~1/3 and ``enhanced'' x~2/3 regimes of Na(x)CoO2 are evaluated using
the correlated band theory LDA+U method. Our results, neglecting quantum
fluctuations, are: (1) allowing only ferromagnetic order, there is a critical
U_c = 3 eV, above which charge disproportionation occurs for both x=1/3 and
x=2/3, (2) allowing antiferromagnetic order at x=1/3, U_c drops to 1 eV for
disproportionation, (3) disproportionation and gap opening occur
simultaneously, (4) in a Co(3+)-Co(4+) ordered state, antiferromagnetic
coupling is favored over ferromagnetic, while below U_c ferromagnetism is
favored. Comparison of the calculated Fermi level density of states compared to
reported linear specific heat coefficients indicates enhancement of the order
of five for x~0.7, but negligible enhancement for x~0.3. This trend is
consistent with strong magnetic behavior and local moments (Curie-Weiss
susceptibility) for x>0.5 while there no magnetic behavior or local moments
reported for x<0.5. We suggest that the phase diagram is characterized by a
crossover from effective single-band character with U >> W for x>0.5 into a
three-band regime for x U_eff <= U/\sqrt(3) ~ W and
correlation effects are substantially reduced.Comment: 10 pages, 8 figures, corrected a few typos and changed reference
Chemical Differences between K and Na in Alkali Cobaltates
KCoO shares many similarities with NaCoO, as well as some
important differences (no hydration-induced superconductivity has been
reported). At =20 K, KCoO becomes an insulator with a tiny
optical gap as happens in NaCoO at 52 K. This similarity, with a
known common structure, enables direct comparisons to be made. Using the
K-zigzag structure recently reported and the local density approximation, we
compare and contrast these cobaltates at x=0.5. Although the electronic
structures are quite similar as expected, substantial differences are observed
near the Fermi level. These differences are found to be attributable mostly to
the chemical, rather than structural difference: although Na is normally
considered to be fully ion, K has somewhat more highly ionic character than
does Na in these cobaltates.Comment: 5 paper
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