Reflectance in the Red and Near Infra-Red Ranges of the Spectrum as Tool for Remote Chlorophyll Estimation in Inland Waters: Lake Kinneret Case Study

Signature analysis of reflectance spectra was used for the selection of the most suitable spectral bands for remote sensing of chlorophyll in inland waters. The parameters of the reflectance peak near 700 nm were employed for construction of algorithms for chlorophyll determination. The best model, validated by independent data sets, enabled estimation of chlorophyll concentration with an error \u3c 0.6 mg/m3 for period of low Chl concentration and \u3c 6.5 mg/m3 for period of the phytoplankton bloom. For the purpose of chlorophyll mapping in Lake Kinneret, the use of three relatively narrow spectral bands was sufficient. Radiometric data were also used to simulate radiances in the channels of TM Landsat and to find algorithm for chlorophyll assessment. The ratio (TM2-TM3)/TMl was used to retrieve chlorophyll in the range 3-10 mg/m3 with an error of \u3c 1 mg.m-3; the ratio TM4/TM3 was used to map chlorophyll in the range 10-200 mg/m3 with 10 gradations

Method of Estimating the Incompressible-flow Pressure Distribution of Compressor Blade Sections at Design Angle of Attack

A method was devised for estimating the incompressible-flow pressure distribution over compressor blade sections at design angle of attack. The theoretical incremental velocities due to camber and thickness of the section as an isolated airfoil are assumed proportional to the average passage velocity and are modified by empirically determined interference factors. Comparisons were made between estimated and test pressure distributions of NACA 65-series sections for typical conditions. Good agreement was obtained

NIR-red reflectance-based algorithms for chlorophyll-a estimation in mesotrophic inland and coastal waters: Lake Kinneret case study

A variety of models have been developed for estimating chlorophyll-a (Chl-a) concentration in turbid and productive waters. All are based on optical information in a few spectral bands in the red and near-infra-red regions of the electromagnetic spectrum. The wavelength locations in the models used were meticulously tuned to provide the highest sensitivity to the presence of Chl-a and minimal sensitivity to other constituents in water. But the caveat in these models is the need for recurrent parameterization and calibration due to changes in the biophysical characteristics of water based on the location and/or time of the year. In this study we tested the performance of NIR-red models in estimating Chl-a concentrations in an environment with a range of Chl-a concentrations that is typical for coastal and mesotrophic inland waters. The models with the same spectral bands as MERIS, calibrated for small lakes in the Midwest U.S., were used to estimate Chla concentration in the subtropical Lake Kinneret (Israel), where Chl-a concentrations ranged from 4 to 21 mgm-3 during four field campaigns. A two-band model without reparameterization was able to estimate Chl-a concentration with a root mean square error less than 1.5 mgm-3. Our work thus indicates the potential of the model to be reliably applied without further need of parameterization and calibration based on geographical and/or seasonal regimes

Nature of the Ferroelectric Phase Transition in PbTiO₃

We have measured quantitatively the temperature dependence of the local distortions of PbTiO3 crystals below and above the structural ferroelectric phase transition, using x-ray absorption fine-structure (XAFS) measurements. Two probe atoms, Pb and Ti, were used. The results were analyzed by fitting parametrized theoretical XAFS spectra to the experimental results. These measurements provide quantitative distortion parameters defined as the difference between the distance of the probe to its nearest neighbor measured in the actual structure and that in a centrosymmetric structure with the same unit cell dimensions. At low temperatures the Pb-edge spectra were fit using four shells and included single, double, and triple scattering configurations. The high-temperature fits included only two shells. The Ti-edge spectra were fitted with the first shell only. The Pb and Ti distortions vary relatively little with temperature below the transition and decrease faster near the transition temperature. Above the transition temperature, the Pb and Ti distortions at the peaks of their distortion distribution function (DDFs) are both more than 70% of the corresponding low-temperature values. These results show that an essential element of order-disorder is present even in this nominally pure ferroelectric crystal which displays a soft mode and a dielectric constant typical of displacive-type ferroelectrics. The presence of the local distortions suggests that the displacements should have at least two correlation length scales, one associated with the local distortions, the other with the order parameter

Current oscillations in a metallic ring threaded by a time-dependent magnetic flux

We study a mesoscopic metallic ring threaded by a magnetic flux which varies linearly in time PhiM(t)=Phi t with a formalism based in Baym-Kadanoff-Keldysh non-equilibrium Green functions. We propose a method to calculate the Green functions in real space and we consider an experimental setup to investigate the dynamics of the ring by recourse to a transport experiment. This consists in a single lead connecting the ring to a particle reservoir. We show that different dynamical regimes are attained depending on the ratio hbar Phi/Phi0 W, being Phi0=h c/e and W, the bandwidth of the ring. For moderate lengths of the ring, a stationary regime is achieved for hbar Phi/Phi0 >W. In the opposite case with hbar Phi/Phi0 < W, the effect of Bloch oscillations driven by the induced electric field manifests itself in the transport properties of the system. In particular, we show that in this time-dependent regime a tunneling current oscillating in time with a period tau=2piPhi0/Phi can be measured in the lead. We also analyze the resistive effect introduced by inelastic scattering due to the coupling to the external reservoir.Comment: 17 pages, 13 figure

Threshold features in transport through a 1D constriction

Suppression of electron current $\Delta I$ through a 1D channel of length $L$ connecting two Fermi liquid reservoirs is studied taking into account the Umklapp electron-electron interaction induced by a periodic potential. This interaction causes Hubbard gaps $E_H$ for $L \to \infty$. In the perturbative regime where $E_H \ll v_c/L$ ($v_c:$ charge velocity), and for small deviations $\delta n$ of the electron density from its commensurate values $- \Delta I/V$ can diverge with some exponent as voltage or temperature $V,T$ decreases above $E_c=max(v_c/L,v_c \delta n)$, while it goes to zero below $E_c$. This results in a nonmonotonous behavior of the conductance.Comment: Final variant published in PRL, 79, 1714; minor correction

The State of Addis Ababa 2021: Towards a Healthier City

The 'State of Addis Vol. II: Toward a healthier city' was written by an international multidisciplinary team, as the pandemic was unfolding. The report assesses the relationship between urban form and function and the spread of the COVID-19 pandemic, in Addis Ababa. It explores what is meant by a healthy city, and why planning for and investing in a healthy city, matters to Addis Ababa. It goes on to investigate the state of health, urban infrastructure and social services in the city. The socio-economic and health impacts of the pandemic are also explored further, together with the institutional response to the public health emergency. The findings provide insights on the role of urban form and infrastructure to urban health and urban resilience. Finally, the authors highlight a post-pandemic agenda for a healthier, more resilient city

Kondo resonance effect on persistent currents through a quantum dot in a mesoscopic ring

The persistent current through a quantum dot inserted in a mesoscopic ring of length L is studied. A cluster representing the dot and its vicinity is exactly diagonalized and embedded into the rest of the ring. The Kondo resonance provides a new channel for the current to flow. It is shown that due to scaling properties, the persistent current at the Kondo regime is enhanced relative to the current flowing either when the dot is at resonance or along a perfect ring of same length. In the Kondo regime the current scales as $L^{-1/2}$, unlike the $L^{-1}$ scaling of a perfect ring. We discuss the possibility of detection of the Kondo effect by means of a persistent current measurement.Comment: 11 pages, 3 Postscript figure

A science based approach to topical drug classification system (TCS).

The Biopharmaceutics Classification System (BCS) for oral immediate release solid drug products has been very successful; its implementation in drug industry and regulatory approval has shown significant progress. This has been the case primarily because BCS was developed using sound scientific judgment. Following the success of BCS, we have considered the topical drug products for similar classification system based on sound scientific principles. In USA, most of the generic topical drug products have qualitatively (Q1) and quantitatively (Q2) same excipients as the reference listed drug (RLD). The applications of in vitro release (IVR) and in vitro characterization are considered for a range of dosage forms (suspensions, creams, ointments and gels) of differing strengths. We advance a Topical Drug Classification System (TCS) based on a consideration of Q1, Q2 as well as the arrangement of matter and microstructure of topical formulations (Q3). Four distinct classes are presented for the various scenarios that may arise and depending on whether biowaiver can be granted or not

Bias and temperature dependence of the 0.7 conductance anomaly in Quantum Point Contacts

The 0.7 (2e^2/h) conductance anomaly is studied in strongly confined, etched GaAs/GaAlAs quantum point contacts, by measuring the differential conductance as a function of source-drain and gate bias as well as a function of temperature. We investigate in detail how, for a given gate voltage, the differential conductance depends on the finite bias voltage and find a so-called self-gating effect, which we correct for. The 0.7 anomaly at zero bias is found to evolve smoothly into a conductance plateau at 0.85 (2e^2/h) at finite bias. Varying the gate voltage the transition between the 1.0 and the 0.85 (2e^2/h) plateaus occurs for definite bias voltages, which defines a gate voltage dependent energy difference $\Delta$. This energy difference is compared with the activation temperature T_a extracted from the experimentally observed activated behavior of the 0.7 anomaly at low bias. We find \Delta = k_B T_a which lends support to the idea that the conductance anomaly is due to transmission through two conduction channels, of which the one with its subband edge \Delta below the chemical potential becomes thermally depopulated as the temperature is increased.Comment: 9 pages (RevTex) with 9 figures (some in low resolution