628 research outputs found
Collisional shifts in optical-lattice atom clocks
We theoretically study the effects of elastic collisions on the determination
of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom
clocks. Interparticle interactions of bosonic atoms in multiply-occupied
lattice sites can cause a linear frequency shift, as well as generate
asymmetric Ramsey fringe patterns and reduce fringe visibility due to
interparticle entanglement. We propose a method of reducing these collisional
effects in an optical lattice by introducing a phase difference of
between the Ramsey driving fields in adjacent sites. This configuration
suppresses site to site hopping due to interference of two tunneling pathways,
without degrading fringe visibility. Consequently, the probability of double
occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure
Late Pleistocene-Holocene productivity record of benthic foraminifera from the Iceland Plateau (Core PS1246-2)
Benthic foraminiferal assemblage patterns in Core PS 1246-2 from the Iceland Plateau are
examined as they relate to annual productivity and seasonal productivity changes during the
Late Pleistocene glacial (23,000-11,000 yrs B.P.), Younger Dryas cool period (11,000-10,000 yrs B.P.) and Holocene (10,000-2,900 yrs B.P.). Abundance fluctuations of Cibicidoides wuellerstorji, a suspension-feeder, are used as the proxy for annual productivity, while fluctuations of the phytodetritus-exploiting species Epistoininclln r ~ i p r a E, ponides tlinzid~illisa nd GloDocossidlrliiia strbglobosa are used as the indicators of seasonal productivity.
These records show seasonal productivity began to increase around 22,500 yrs B.P. and
experienced three subsequent peaks in the glacial, while annual productivity increased around 16,000 yrs B.P. and shows only one peak in the glacial. The Younger Dryas shows a decrease in
both seasonal and annual productivity records. Seasonal productivity in the early Holocene is
much higher than during the glacial, yet appears more extreme. The Holocene record of annualproductivity continues to show a strong general increase in intensity
Last interglacial ocean changes in the Bahamas: climate teleconnections between low and high latitudes
Paleorecords and modeling studies suggest that instabilities in
the Atlantic Meridional Overturning Circulation (AMOC) strongly affect the
low-latitude climate, namely via feedbacks on the Atlantic Intertropical
Convergence Zone (ITCZ). Despite the pronounced millennial-scale overturning and
climatic variability documented in the subpolar North Atlantic during the
last interglacial period (MISÂ 5e), studies on cross-latitudinal
teleconnections remain very limited. This precludes a full understanding of
the mechanisms controlling subtropical climate evolution across the last
warm cycle. Here, we present new planktic foraminiferal assemblage data
combined with δ18O values in surface and thermocline-dwelling
foraminifera from the Bahamas, a region ideally suited to studying past
changes in the subtropical ocean and atmosphere. Our data reveal that the peak
sea surface warmth during early MISÂ 5e was intersected by an abrupt
millennial-scale cooling/salinification event, which was possibly associated
with a sudden southward displacement of the mean annual ITCZ position. This
atmospheric shift is, in turn, ascribed to the transitional climatic regime
of early MISÂ 5e, which was characterized by persistent ocean freshening in the high
latitudes and an unstable AMOC mode.</p
Photoemission induced gating of topological insulator
The recently discovered topological insulators exhibit topologically
protected metallic surface states which are interesting from the fundamental
point of view and could be useful for various applications if an appropriate
electronic gating can be realized. Our photoemission study of Cu intercalated
Bi2Se3 shows that the surface states occupancy in this material can be tuned by
changing the photon energy and understood as a photoemission induced gating
effect. Our finding provides an effective tool to investigate the new physics
coming from the topological surface states and suggests the intercalation as a
recipe for synthesis of the material suitable for electronic applications.Comment: + resistivity data and some discussio
Combinatorial identities for binary necklaces from exact ray-splitting trace formulae
Based on an exact trace formula for a one-dimensional ray-splitting system,
we derive novel combinatorial identities for cyclic binary sequences (P\'olya
necklaces).Comment: 15 page
Green's function for the Relativistic Coulomb System via Sum Over Perturbation Series
We evaluate the Green's function of the D-dimensional relativistic Coulomb
system via sum over perturbation series which is obtained by expanding the
exponential containing the potential term in the path integral
into a power series. The energy spectra and wave functions are extracted from
the resulting amplitude.Comment: 13 pages, ReVTeX, no figure
Interplay between Static and Dynamic Properties of Semifluxons in YBa2Cu3O7−δ 0−π Josephson Junctions
We have investigated the static and dynamic properties of long YBa2Cu3O7-delta 0-pi Josephson junctions and compared them with those of conventional 0 junctions. Scanning SQUID microscope imaging has revealed the presence of a semifluxon at the phase discontinuity point in 0-pi Josephson junctions. Zero field steps have been detected in the current-voltage characteristics of all junctions. Comparison with simulation allows us to attribute these steps to fluxons traveling in the junction for conventional 0 junctions and to fluxon-semifluxon interactions in the case of 0-pi Josephson junctions
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