Scanning Tunneling Spectroscopy of Bi2Sr2CuO6+d: New Evidence for the Common Origin of the Pseudogap and Superconductivity

Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped Bi2Sr2CuO6+δ between 275 mK and 82 K. Below Tc = 10 K, the spectra show a gap with well-defined coherence peaks at ±Δp≃12 meV, which disappear at Tc. Above Tc, the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at T*≃68 K. The comparison with Bi2Sr2CaCu2O8+δ demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin

Far-infrared absorption and the metal-to-insulator transition in hole-doped cuprates

By studying the optical conductivity of BSLCO and YCBCO, we show that the metal-to-insulator transition (MIT) in these hole-doped cuprates is driven by the opening of a small gap at low T in the far infrared. Its width is consistent with the observations of Angle-Resolved Photoemission Spectroscopy in other cuprates, along the nodal line of the k-space. The gap forms as the Drude term turns into a far-infrared absorption, whose peak frequency can be approximately predicted on the basis of a Mott-like transition. Another band in the mid infrared softens with doping but is less sensitive to the MIT.Comment: To be published on Physical Review Letter

Comparison of Three Gravimetric-Geometric Geoid Models for Best Local Geoid Model of Benin City, Nigeria

International audienceThe conversion of geometric as well as ellipsoidal heights from GNSS observations to practical heights for engineering constructions has necessitated the determination of the local geoid model of areas. Benin City is a developing area which requires a local geoid model for conversion of geometric heights to orthometric heights for physical developments in the area. This paper is on the best local geoid model of Benin City, Nigeria by comparing three gravimetric-geometric geoid models of the study area. GNSS and gravimetric observations were carried out on 49 points to respectively obtain their coordinates and absolute gravity values. The theoretical gravity values of the points were computed on the Clarke 1880 ellipsoid, subtracted from the absolute gravity values and corrected for the air (free air) to obtain the free air gravity anomalies of the points. The computed free air gravity anomalies were applied to compute the geoid heights of the points using the integration of the modified Stokes integral. Three geometric geoid surfaces (plane, second degree and third degree surfaces) were fitted to the computed gravimetric geoid heights using the least squares technique to obtain the gravimetric-geometric geoid models of the study area. The RMSE of the three gravimetric-geometric geoid models were computed to determine their (the models) accuracy. The three gravimetric-geometric geoid models were compared using their accuracy to obtain the most suitable geoid model of the study area. The results of the comparison showed that the third degree gravimetric-geometric geoid model is most suitable for application in the study area. It is recommended that ellipsoidal heights obtained from GNSS observation within Benin City, Nigeria should be converted to orthometric heights using the third degree geoid model

Determination of effective microscopic models for the frustrated antiferromagnets Cs2_2CuCl4_4 and Cs2_2CuBr4_4 by density functional methods

We investigate the electronic and magnetic properties of the frustrated triangular-lattice antiferromagnets Cs$_2$CuCl$_4$ and Cs$_2$CuBr$_4$ in the framework of density functional theory. Analysis of the exchange couplings J and J' using the available X-ray structural data corroborates the values obtained from experimental results for Cs$_2$CuBr$_4$ but not for Cs$_2$CuCl$_4$. In order to understand this discrepancy, we perform a detailed study of the effect of structural optimization on the exchange couplings of Cs$_2$CuCl$_4$ employing different exchange-correlation functionals. We find that the exchange couplings depend on rather subtle details of the structural optimization and that only when the insulating state (mediated through spin polarization) is present in the structural optimization, we do have good agreement between the calculated and the experimentally determined exchange couplings. Finally, we discuss the effect of interlayer couplings as well as longer-ranged couplings in both systems.Comment: Phys. Rev. B in pres

Practical Local Geoid Model Determination for Mean Sea Level Heights of Surveys and Stable Building Projects

A local geoid model for Evboriaria, Benin City using the geometric (GPS/Levelling) method was determined for calculation of mean sea level heights. Fifty points were established for the model and ten points were used for interpolation. The geoid heights were determined by finding the difference between the observed orthometric heights and the ellipsoidal heights. The polynomial regression model D was used for the interpolation of the orthometric heights. The computed mean standard deviation between the observed orthometric heights and the interpolated orthometric heights was ± 21cm. A mean geoidal undulation of 28.410m was computed using the gravimetric method. The computed orthometric heights using the gravimetry mean geoidal undulation were compared with the observed orthometric heights and seen to be identical. It is recommended that orthometric heights of project areas should be determined from GPS observations with the local geoid model of the area also determined

ARCHITECTURAL AND PSYCHOLOGICAL ASPECTS IN OPTIMIZED RADIATION SHIELDING DESIGN FOR SPACE APPLICATIONS

NewSpace bears all the hallmarks of past revolutions in technology. Since we have other examples of exponential growth of specific technologies, we should maximize the economic and engineering potential of this movement by expanding the envelopes for long term crewed habitats in deep space. We should also take an approach that minimizes waste in both design and fabrication as these bases expand. This paper provides a systematic approach to habitats optimized for volume, radiation protection, crew psychology, reusability, affordability, crowd-sourced subsystem design, and expansion. These habitats and systems are designed to be as “future proof” as possible to allow rapid and safe technological advancement within the structures. One of major “showstoppers” of human space exploration is cosmic and solar events radiation. It is a serious problem that may cause cancer and other types of tissue damage and equipment malfunction. It has to be addressed in space vehicles design especially for long-term space exploration missions and future Moon or Mars surface settlements. This paper discusses a unique layered system incorporated into a habitat structure, which may help to reduce the radiation hazard to the crew and interior equipment and systems. The paper also argues that a successful mitigation of radiation impact on human health should be based on a multidisciplinary methodology that also includes psychophysiological approach to the problem. Multiple techniques and practices to minimize psychological stress that may suppress immune system and reduce resistance to cancer, are presented and compared. Conclusions are drawn upon results of those comparisons and a multidisciplinary design concept is proposed to be applied both in long-duration human space exploration missions and in radioactive environment on Earth

High-temperature optical spectral weight and Fermi liquid renormalization in Bi-based cuprates

The optical conductivity and the spectral weight W(T) of two superconducting cuprates at optimum doping, Bi2Sr2-xLaxCuO6 and Bi2Sr2CaCu2O8, have been first measured up to 500 K. Above 300 K, W(T) deviates from the usual T2 behavior in both compounds, even though the zero-frequency extrapolation of the optical conductivity remains larger than the Ioffe-Regel limit. The deviation is surprisingly well described by the T4 term of the Sommerfeld expansion, but its coefficients are enhanced by strong correlation. This renormalization is due to strong correlation, as shown by the good agreement with dynamical mean field calculations.Comment: 5 pages, 3 figures, Physical Review Letters in pres

Analisis Alternatif Strategi Pengembangan Koperasi Produksi Susu

The objective of the research is to analyze the strategic alternative to be implemented in the Bogor development of milk production cooperation. The analysis covered descriptive analysis, Internal Factor Evaluation (IFE), External Factor Evaluation (EFE), Internal-External (IE) matrix analysis, Strengths, Weaknesses, Opportunities and Threat (SWOT). The results showed that the position of the cooperatives in quadrants V of the Internal-Eksternal (IE) matrix, the strategy of the cooperative should be hold and maintain where a strategy that is widely used in these cells is market penetration and product development. Managerial implication of alternative strategy that can be immplemented in the milk production cooperatives are improve the competitiveness of products, products promotion, promotion activities by socializing the importance of drinking milk, product diversification, improve the quality of milk, strengthening the modal through loan with the financial intitutions, coordinating with the government to get assistance in strengthening the cooperation and breeder, increasing the population of cattle through joint venture, expanding markets, improve production facilities, improve technology, develop the healthy partnership, improve the management of the maintenance of dairy cows