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 $\pi$ 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

Collapse of thermal activation in moderately damped Josephson junctions

We study switching current statistics in different moderately damped Josephson junctions: a paradoxical collapse of the thermal activation with increasing temperature is reported and explained by interplay of two conflicting consequences of thermal fluctuations, which can both assist in premature escape and help in retrapping back into the stationary state. We analyze the influence of dissipation on the thermal escape by tuning the damping parameter with a gate voltage, magnetic field, temperature and an in-situ capacitor.Comment: 4 pages, 4 figure

Theory of two-dimensional macroscopic quantum tunneling in a Josephson junction coupled with an LC circuit

We investigate classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a Josephson junction coupled with an LC circuit theoretically. The TA and MQT escape rate are calculated analytically by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling gives rise to slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in grain boundary YBCO Josephson junctions.Comment: 4 pages, 1 figure, Proceedings of LT2

Possible observation of energy level quantization in an intrinsic Josephson junction

Energy level quantization (ELQ) is studied to clarify the macroscopic quantum dynamics of the d-wave Josephson junction (JJ). The influences of the nodal quasiparticles of d-wave superconductivity on the damping effect are numerically evaluated on the basis of a phenomenological model. The calculation, based on realistic parameters for a Bi2Sr2CaCu2O8+d (Bi2212) intrinsic JJ, shows that the observation of ELQ is possible when the sweep rate of the bias current exceeds 10 A/sec. High-sweep- rate measurements (121A/sec) performed on a Bi2212 intrinsic JJ result in the appearance of multiple peaks in the switching current distribution suggesting the realization of ELQ in the d-wave JJ.Comment: 5 pages, 3 figure

The Impact of Oil Prices on the U.S. Economy

Nine of the ten recessions since WWII have been preceded by relatively large and sudden increases in the price of oil. In this paper, I use time series analysis to forecast GDP growth using oil prices. I use the methodology from Hamilton (2009), and extend the dataset through 2010. Impulse response functions are used to analyze the historical performance of the model’s one-year-ahead forecasts. In April, 2011, the International Monetary Fund changed its forecast of 2011 GDP growth in the U.S. from 3.0% to 2.8% largely due to persistently high oil prices. My model suggests that the price increase in 2011Q1 will lead to growth of 2% in 2011. Furthermore, my model predicts that a 54% increase in crude oil prices during the second quarter of 2011 will lead the U.S. into a double dip recession

Biomass production and mineral element supply of selected useful tropical plants.

This current investigation is part of a cooperative project of CPAA-Manaus and Hamburg University entitled "Recultivation of degraded and abandoned monocultures instable mixed cultures with special reference to soil biological factors". In this study the biomass product and the mineral element supply of selected useful tropical plants will be determined. Parallel to it the availability of nutrient element in the soil will be analyzed. These experiments may allow an evaluation, in which way a sustainable growth of the suggested plant system under the prevailing site conditions is possible.Poster 11

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