Papers by MR ahmed Kenawy
Electronic transport through single-molecule devices is a powerful spectroscopic tool to probe va... more Electronic transport through single-molecule devices is a powerful spectroscopic tool to probe various degrees of freedom at the nanoscopic level. Among these degrees of freedom, molecular vibrations are of particular relevance since they can result in drastic effects such as transport blockade. While the effect of the interaction between the molecular charge and vibrations on transport through a single magnetic molecule has already been characterized, additional research, especially from the theoretical perspective, is still required to examine the vibrations’ coupling to the molecular spin and its impact on the magnetic anisotropy. For this reason, the aim of this thesis is to provide and scrutinize a theoretical model for transport through a single magnetic molecule that takes into account the threefold interplay between charge, spin and molecular vibrations. For a quantum mechanical treatment, the real-time diagrammatic technique is employed to study transport in the sequential ...
Bulletin of the American Physical Society, 2019
13 The performance of the Tropical Rainfall Measuring Mission (TRMM) version 3B42 V7 product 14 i... more 13 The performance of the Tropical Rainfall Measuring Mission (TRMM) version 3B42 V7 product 14 is validated over north-eastern Iberia, a region with considerable topographical gradients and 15 complexity. Precipitation characteristics from a dense network of 656 rain gauges, spanning the 16 period from 1998 to 2009, are used to evaluate the TRMM 3B42 estimates on a daily scale. A set 17 of accuracy estimators, including the relative bias, mean absolute error (MAE), root mean square 18 error (RMSE) and Spearman rho coefficient were used to evaluate the results. The assessment 19 indicates that the TRMM 3B42 product is capable of describing the seasonal characteristics of 20 the observed precipitation over most of the study domain. In particular, TRMM 3B42 21 precipitation agrees well with in situ measurements, with MAE less than 2.5 mm.day-1, RMSE of 22 6.4 mm.day-1 and rho correlation coefficients generally above 0.6. TRMM 3B42 provides 23 improved accuracies in winter and summer, ...
Superconductor Science and Technology, 2020
Quantum phase slips represent a coherent mechanism to couple flux states of a superconducting loo... more Quantum phase slips represent a coherent mechanism to couple flux states of a superconducting loop. Since their first direct observation, there have been substantial developments in building charge-insensitive quantum phase-slip circuits. At the heart of these devices is a weak link, often a nanowire, interrupting a superconducting loop. Owing to the very small cross-sectional area of such a nanowire, quantum phase slip rates in the gigahertz range can be achieved. Instead, here we present the use of a bias voltage across a superconducting loop to electrostatically induce a weak link, thereby amplifying the rate of quantum phase slips without physically interrupting the loop. Our simulations reveal that the bias voltage modulates the free energy barrier between subsequent flux states in a very controllable fashion, providing a route towards a phase-slip flux qubit with a broadly tunable transition frequency.
AIP Advances, 2019
Over the past few decades, superconducting circuits have been used to realize various novel elect... more Over the past few decades, superconducting circuits have been used to realize various novel electronic devices such as quantum bits, SQUIDs, parametric amplifiers, etc. One domain, however, where superconducting circuits fall short is information storage. Superconducting memories are based on the quantization of magnetic flux in superconducting loops. Standard implementations store information as magnetic flux quanta in a superconducting loop interrupted by two Josephson junctions (i.e., a SQUID). However, due to the large inductance required, the size of the SQUID loop cannot be scaled below several micrometers, resulting in low-density memory chips. Here, we propose a scalable memory consisting of a voltage-biased superconducting ring threaded by a half-quantum flux bias. By numerically solving the time-dependent Ginzburg-Landau equations, we show that applying a time-dependent bias voltage in the microwave range constitutes a writing mechanism to change the number of stored flux quanta within the ring. Since the proposed device does not require a large loop inductance, it can be scaled down, enabling a high-density memory technology.
Physical Review B, 2018
We theoretically analyze the spectrum of a magnetic molecule when its charge and spin can couple ... more We theoretically analyze the spectrum of a magnetic molecule when its charge and spin can couple to the molecular vibrations. More specifically, we show that the interplay between charge-vibron and spin-vibron coupling leads to a renormalization of the magnetic anisotropy parameters of the molecule. This effect is discussed for a model device consisting of an individual magnetic molecule embedded in a junction. We study the transport properties of the device and illustrate how the differential conductance is affected by the vibrationally induced renormalization of the magnetic anisotropy. Depending on the total molecular spin and the bare (intrinsic) magnetic anisotropy, the induced modulation can lead to visible shifts and crossings in the spectrum, and it can even be the cause of a transport blockade. It is therefore of particular interest to use mechanically controllable break junctions, since in such a case, the relevant coupling between the molecular spin and vibrations can be controlled via deformations of the molecule when stretching or compressing the junction.
AIP Advances, 2017
The effect of molecular vibrations on the tunnel magnetoresistance (TMR) of a magnetic tunnel jun... more The effect of molecular vibrations on the tunnel magnetoresistance (TMR) of a magnetic tunnel junction with a single spin-anisotropic molecule interconnecting its electrodes is investigated theoretically. We demonstrate that if these vibrations couple at the same time to the charge of tunneling electrons and to the spin of the molecule, the spin anisotropy of such a molecule becomes enhanced. This has, in turn, a profound impact on the TMR of such a device showing that molecular vibrations lead to a significant change of spin-polarized transport, differing for the parallel and antiparallel magnetic configuration of the junction.
Recently a new drought indicator, the Standardised Precipitation-Evapotranspiration Index (SPEI),... more Recently a new drought indicator, the Standardised Precipitation-Evapotranspiration Index (SPEI), has been proposed to quantify the drought condition over a given area. The SPEI considers not only precipitation but also evapotranspiration (PET) data on its calculation, allowing for a more complete approach to explore the effects of climate change on drought conditions. The SPEI can be calculated at several time scales to adapt to the characteristic times of response to drought of target natural and economic systems, allowing determining their resistance to drought. Following the formulation of the SPEI a global dataset, the SPEIbase, has been made available to the scientific community. The dataset covers the period 1901-2006 with a monthly frequency, and offers global coverage at a 0.5 degrees resolution. The dataset consists on the monthly values of the SPEI at the time scales from 1 to 48 months. A description of the data and metadata, and links to download the files, are provided...
International Journal of Climatology, 2015
Many arid and semi-arid regions have sparse precipitation observing networks, which limits the ca... more Many arid and semi-arid regions have sparse precipitation observing networks, which limits the capacity for detailed hydrological modeling, water resources management and flood forecasting efforts. The objective of this work is to evaluate the utility of relatively high-spatial resolution rainfall products to reproduce observed multi-decadal rainfall characteristics such as climatologies, anomalies and trends over Saudi Arabia. Our study compares the statistical characteristics of rainfall from 53 observatories over the reference period 1965-2005, with rainfall data from six widely used gauge-based products, including APHRODITE, GPCC, PRINCETON, UDEL, CRU, and PREC/L. In addition, the performance of three Global Climate Models (GCMs), including CCSM4, EC-EARTH, and MRI-I-CGCM3, integrated as part of the Fifth Coupled Model Intercomparison Project (CMIP5), was also evaluated. Results indicate that the gauge-based products were generally skillful in reproducing rainfall characteristics in Saudi Arabia. In most cases, the gauge-based products were also able to capture the annual cycle, anomalies and climatologies of observed data, although significant inter-product variability was observed, depending on the assessment metric being used. In comparison, the GCM-based products generally exhibited poor performance, with larger biases and very weak correlations, particularly during the summertime. Importantly, all products generally failed to reproduce the observed long-term seasonal and annual trends in the region, particularly during the dry seasons (summer and autumn). Overall, this work suggests that selected gauge-based products with daily (APHRODITE and 2 PRINCETON) and monthly (GPCC and CRU) resolutions show superior performance relative to other products, implying that they may be the most appropriate data source from which multi-decadal variations of rainfall can be investigated at the regional scale over Saudi Arabia. Discriminating these skillful products is important not only for reducing uncertainty in climate, hydrological, and environmental assessments, but also for advancing model developments in the region.
Remote Sensing, 2015
We analyzed potential land degradation processes in semiarid regions worldwide using long time se... more We analyzed potential land degradation processes in semiarid regions worldwide using long time series of remote sensing images and the Normalized Difference Vegetation Index (NDVI) for the period 1981 to 2011. The objectives of the study were to identify semiarid regions showing a marked decrease in potential vegetation activity, indicative of the occurrence of land degradation processes, and to assess the possible influence of the observed drought trends quantified using the Standardized Precipitation Evapotranspiration Index (SPEI). We found that the NDVI values recorded during the period of maximum vegetation activity (NDVImax) predominantly showed a positive
Recently a new drought indicator, the Standardised Precipitation-Evapotranspiration Index (SPEI),... more Recently a new drought indicator, the Standardised Precipitation-Evapotranspiration Index (SPEI), has been proposed to quantify the drought condition over a given area. The SPEI considers not only precipitation but also evapotranspiration (PET) data on its calculation, allowing for a more complete approach to explore the effects of climate change on drought conditions. The SPEI can be calculated at several time
Fluxes in eutrophication status in Lake Manzala, the largest freshwater lake in Egypt, were inves... more Fluxes in eutrophication status in Lake Manzala, the largest freshwater lake in Egypt, were investigated based on comparison of multiparameter data. Eutrophication maps were undertaken for each parameter using Carlson trophic indices. In addition, Kriging method of interpolation was effectively performed to identify the spatial patterns of all measured parameters. Spherical model was applied to fit all experimental variograms. It was shown that all eutrophication variables were significantly located along SE – NW and E – W directions.The investigation indicates that the lake has dramatically experienced accelerated eutrophication (71.14 % and 27.73% of the lake were eutrophic and hypertrophic respectivel). In conjunction with excessive eutrophication in the lake, an overall move towards urbanization and increasing the cultivated land was detected in the catchment. An integrated approach should be adopted to attain the lake restoration and enhance truly sustainable development of water. This approach should chiefly be based on a comprehensive range of policies such as building capacity and increasing environmental awareness in the local community.
Climate impact studies are more profoundly associated with changes in intensity and frequency of ... more Climate impact studies are more profoundly associated with changes in intensity and frequency of extreme events rather than changes in mean values. Long-term changes and spatial variability of extreme temperature were investigated in Northeastern Spain based on a daily dataset of 128 quality controlled and homogenized series spanning the period from 1960 to 2006. Extreme temperature was defined in terms of 20 indices recommended by the World Meteorological Organization. These indices included, for example, cold nights (TN10), warm nights (TN90), cold days (TX10), total number of frost days, intra-annual extreme temperature range and Diurnal temperature range. The magnitude of the trends and their statistical significance were determined using the nonparametric Kendall tau test at the 95% level of significance. A clear positive trend was exhibited across the region for summer days (SU25), warm days (TX90), and tropical nights (TR20). This closely matches the general observed warming trend of daily maximum temperature. Conversely, a negative trend was marked for ice days, cold days, cold nights and the Diurnal temperature range.
High resolution climatology-towards climate change services
2013 The International Conference on Technological Advances in Electrical, Electronics and Computer Engineering (TAEECE), 2013
ABSTRACT This paper proposes a methodology for calculating the energy consumption and the through... more ABSTRACT This paper proposes a methodology for calculating the energy consumption and the throughput of a Wireless Sensor Network (WSN) taking into account retransmissions and data dropped due to collisions. For various scenarios, simulations are conducted using OPNET and utilizing off-the-shelf wireless communications standards such as ZigBee, Low-Power Wi-Fi and Wi-Fi. A figure of merit is then introduced for a fair comparison between the mentioned standards.
Hydrological, Socioeconomic and Ecological Impacts of the North Atlantic Oscillation in the Mediterranean Region, 2011
When considering 100% renewable scenarios, backup generation is needed for stabilizing the networ... more When considering 100% renewable scenarios, backup generation is needed for stabilizing the network when Climate Related Energy (CRE) such as wind, solar or run-of-the river hydropower are not sufficient for supplying the load. Several studies show that, over relatively short time period (less than 10 years), backup generation needs are reduced by dissipating power densities either in space through grids or time through storage. This study looks at the impact of low time frequency variations of CRE with a specific focus on the time variability induced by the North Atlantic Oscillation (NAO) teleconnection pattern during winter season. A set of eleven regions in Europe and Tunisia is used for highlighting space variability of the winter NAO's impact. For each of these regions, we combine data from the Weather Research and Forecasting Model and the European Climate Assessment & Dataset for estimating solarpower, wind-power, run-of-the-river hydro-power and the energy load over the 1980e2012 time period. Results show that NAO's impact on winter penetration rate depends on both the considered energy source and the location. They also highlight a non-linear relation between the NAO's impact on CRE penetration rates and the level of equipment used for harvesting the CRE sources.
Theoretical and Applied Climatology, 2009
Page 1. ORIGINAL PAPER Temperature trends in Libya over the second half of the 20th century Ahmed... more Page 1. ORIGINAL PAPER Temperature trends in Libya over the second half of the 20th century Ahmed M. El Kenawy & Juan I. López-Moreno & Sergio M. Vicente-Serrano & Mohammed S. Mekld Received: 7 August 2008 /Accepted ...
Journal of Hydrometeorology, 2010
A monthly global dataset of a multiscalar drought index is presented and compared in terms of spa... more A monthly global dataset of a multiscalar drought index is presented and compared in terms of spatial and temporal variability with the existing continental and global drought datasets based on the Palmer drought severity index (PDSI). The presented dataset is based on the standardized precipitation evapotranspiration index (SPEI). The index was obtained using the Climatic Research Unit (CRU) TS3.0 dataset at a spatial resolution of 0.5°. The advantages of the new dataset are that (i) it improves the spatial resolution of the unique global drought dataset at a global scale; (ii) it is spatially and temporally comparable to other datasets, given the probabilistic nature of the SPEI; and, in particular, (iii) it enables the identification of various drought types, given the multiscalar character of the SPEI. The dataset is freely available on the Web page of the Spanish National Research Council (CSIC) in three different formats [network Common Data Form (netCDF), binary raster, and p...
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Papers by MR ahmed Kenawy