Exclusive B−−>πℓ+ℓ−B --> \pi \ell^+ \ell^- and B−−>ρℓ+ℓ−B --> \rho \ell^+ \ell^- Decays in the Universal Extra Dimension

We investigate the influence of the universal extra dimension on the branching ratio in the $B \to \pi(\rho) \ell^+ \ell^-$ decay. Taking $1/R\sim \{200-1000\}$GeV with one universal extra spatial dimension, which is consistent with the experimental data for ${\cal B}(B \to X_s \gamma)$, ${\cal B}(B \to K^\ast \mu^+\mu^-$) and the electroweak precision tests, we obtain that for both ($\mu,\tau$) channels the branching ratio strongly depends on the compactification radius 1/R.Comment: 14 pages, 4 figure

Kondo correlation and spin-flip scattering in spin-dependent transport through a quantum dot coupled to ferromagnetic leads

We investigate the linear and nonlinear dc transport through an interacting quantum dot connected to two ferromagnetic electrodes around Kondo regime with spin-flip scattering in the dot. Using a slave-boson mean field approach for the Anderson Hamiltonian having finite on-site Coulomb repulsion, we find that a spin-flip scattering always depresses the Kondo correlation at arbitrary polarization strength in both parallel and antiparallel alignment of the lead magnetization and that it effectively reinforces the tunneling related conductance in the antiparallel configuration. For systems deep in the Kondo regime, the zero-bias single Kondo peak in the differential conductance is split into two peaks by the intradot spin-flip scattering; while for systems somewhat further from the Kondo center, the spin-flip process in the dot may turn the zero-bias anomaly into a three-peak structure.Comment: 4 pages, 2 figure

Long-term stability of GaAs/AlAs terahertz quantum-cascade lasers

We have investigated high-performance GaAs/AlAs terahertz (THz) quantum-cascade lasers (QCLs) with respect to the long-term stability of their operating parameters. The output power of lasers that contain an additional, thick AlAs refractive-index contrast layer underneath the cascade structure decreases after three months by about 35%. The deterioration of these lasers is attributed to the oxidation processes in this contrast layer starting from the facets. However, GaAs/AlAs THz QCLs with an Al0.9Ga0.1As refractive-index contrast layer exhibit long-term stability of the operating parameters over many years even when they are exposed to atmospheric conditions. Therefore, these lasers are promising high-power radiation sources in the terahertz spectral region for commercial applications

Soil moisture and land use are major determinants of soil microbial community composition and biomass at a regional scale in northeastern China

Global environmental factors impact soil microbial communities and further affect organic matter decomposition, nutrient cycling and vegetation dynamic. However, little is known about the relative contributions of climate factors, soil properties, vegetation types, land management practices and spatial structure (which serves as a proxy for underlying effects of temperature and precipitation for spatial variation) on soil microbial community composition and biomass at large spatial scales. Here, we compared soil microbial communities using phospholipid fatty acid method across 7 land use types from 23 locations at a regional scale in northeastern China (850 × 50 km). The results showed that soil moisture and land use changes were most closely related to microbial community composition and biomass at the regional scale, while soil total C content and climate effects were weaker but still significant. Factors such as spatial structure, soil texture, nutrient availability and vegetation types were not important. Higher contributions of gram-positive bacteria were found in wetter soils, whereas higher contributions of gram-negative bacteria and fungi were observed in drier soils. The contributions of gram-negative bacteria and fungi were lower in heavily disturbed soils than historically disturbed and undisturbed soils. The lowest microbial biomass appeared in the wettest and driest soils. In conclusion, dominant climate and soil properties were not the most important drivers governing microbial community composition and biomass because of inclusion of irrigated and managed practices, and thus soil moisture and land use appear to be primary determinants of microbial community composition and biomass at the regional scale in northeastern China

Magnetic-field induced resistivity minimum with in-plane linear magnetoresistance of the Fermi liquid in SrTiO3-x single crystals

We report novel magnetotransport properties of the low temperature Fermi liquid in SrTiO3-x single crystals. The classical limit dominates the magnetotransport properties for a magnetic field perpendicular to the sample surface and consequently a magnetic-field induced resistivity minimum emerges. While for the field applied in plane and normal to the current, the linear magnetoresistance (MR) starting from small fields (< 0.5 T) appears. The large anisotropy in the transverse MRs reveals the strong surface interlayer scattering due to the large gradient of oxygen vacancy concentration from the surface to the interior of SrTiO3-x single crystals. Moreover, the linear MR in our case was likely due to the inhomogeneity of oxygen vacancies and oxygen vacancy clusters, which could provide experimental evidences for the unusual quantum linear MR proposed by Abrikosov [A. A. Abrikosov, Phys. Rev. B 58, 2788 (1998)].Comment: 5 pages, 4 figure

f(R) Gravities, Killing Spinor Equations, "BPS" Domain Walls and Cosmology

We derive the condition on f(R) gravities that admit Killing spinor equations and construct explicit such examples. The Killing spinor equations can be used to reduce the fourth-order differential equations of motion to the first order for both the domain wall and FLRW cosmological solutions. We obtain exact "BPS" domain walls that describe the smooth Randall-Sundrum II, AdS wormholes and the RG flow from IR to UV. We also obtain exact smooth cosmological solutions that describe the evolution from an inflationary starting point with a larger cosmological constant to an ever-expanding universe with a smaller cosmological constant. In addition, We find exact smooth solutions of pre-big bang models, bouncing or crunching universes. An important feature is that the scalar curvature R of all these metrics is varying rather than a constant. Another intriguing feature is that there are two different f(R) gravities that give rise to the same "BPS" solution. We also study linearized f(R) gravities in (A)dS vacua.Comment: 37 pages, discussion on gravity trapping in RSII modified, typos corrected, further comments and references added; version to appear in JHE

A phytoplankton bloom caused by the super cyclonic storm Amphan in the central Bay of Bengal

The super cyclonic storm Amphan originated in the central Bay of Bengal (BoB) in May 2020, and a phytoplankton bloom occurred in the upper ocean that was devoid of background nutrients. The dynamic mechanism of the chlorophyll a (Chl a) bloom was researched based on reanalysis data, remote sensing and Argo float data. During the passage of Amphan, an inertial oscillation with a 2 d period appeared in the thermocline and lasted for approximately 2 weeks. After the passage of Amphan, a cyclonic eddy with a maximum vorticity of approximately 0.36 s−1 formed in the study area (Box A). Additionally, horizontal transport of Chl a also occurred when the maximum inlet fluxes through the western and northern sides of Box A were 0.304 and −0.199 mg m−2 s−1, respectively. With the weakened thermocline and thinner barrier layer thickness (BLT), nitrate and Chl a were uplifted to the upper ocean by upwelling. Then, with the high photosynthetically available radiation (PAR) in the upper ocean, a phytoplankton bloom occurred. This study provides new insights into the biological responses in the BoB during the passage of tropical cyclones (TCs).</p

Carrier freeze-out induced metal-insulator transition in oxygen deficient SrTiO3 films

We report the optical, electrical transport, and magnetotransport properties of high quality oxygen deficient SrTiO3 (STO) single crystal film fabricated by pulsed laser deposition and reduced in the vacuum chamber. The oxygen vacancy distribution in the thin film is expected to be uniform. By comparing the electrical properties with oxygen deficient bulk STO, it was found that the oxygen vacancies in bulk STO is far from uniform over the whole material. The metal-insulator transition (MIT) observed in the oxygen deficient STO film was found to be induced by the carrier freeze-out effect. The low temperature frozen state can be re-excited by an electric field, Joule heating, and surprisingly also a large magnetic field.Comment: 5 pages, 5 figure