33 research outputs found
Carbon Nanotube Ultracapacitor Characteristics and Cell Design
A model of carbon nanotube (CNT) ultracapacitor (CNU) as a high-performance energy storage device is developed based on simulations of electrolyte ion motions between cathode and anode. Using a molecular dynamics (MD) approach, the equilibrium positions of electrode charges interacting through Coulomb potential are determined, which in turn yield the equipotential surface and electric field associated with the capacitor. With an applied AC voltage, the current is computed from the nanotube and electrolyte particle distribution and interaction, resulting in a frequency-dependent CNU impedance. From the current and impedance profiles, the Nyquist and Cyclic Voltammetry plots are then extracted. Results of these calculations compare well with existing experimental data. A lumped-element equivalent circuit for the CNU is proposed and the impedance computed from this circuit correlates well with the simulated and measured impedances.
Further, a methodology is developed to optimize vertically grown carbon nanotube CNU geometrical features such as CNT length, electrode-to-electrode separation, and CNT packing density. The electric field and electrolyte ionic motion within the CNU are critical in determining device performance. Using a particle-based model (PBM) based on MD techniques, developed for this purpose, the electric field in the device is computed, the electrolyte ionic motion in the device volume is tracked, and the CNU electrical performance as a function of the aforementioned geometrical features is determined. Interestingly, the PBM predicts an optimal CNT packing density for the UC electrodes. Electrolyte ionic trapping occurs in the high CNT density regime, which limits the electrolyte ions from forming a double layer capacitance. In this regime, the CNU capacitance does not increase with the CNT packing density as expected, but decreases significantly. The results compare well with existing experimental data and the PBM methodology can be applied to an ultracapacitor built from any metallic electrode materials, as well as vertically aligned CNTs studied here
A statistical analysis of sounding derived indices and parameters for extreme and non-extreme thunderstorm events over Cyprus
The main purpose of this study is to provide a simple
statistical analysis of several stability indices and
parameters for extreme and non-extreme thunderstorm events
during the period 1997 to 2001 in Cyprus. For this study,
radiosonde data from Athalassa station (35°1´ N,
33°4´ E) were analyzed during the aforementioned
period. The stability indices and parameters set under study
are the K index, the Total Totals (TT) index, the Convective
Available Potential Energy related parameters such as
Convective Available Potential Energy (CAPE),
Downdraft CAPE (DCAPE) and the Convective Inhibition (CIN), the Vorticity
Generator Parameter (VGP), the Bulk Richardson Number (BRN),
the BRN Shear and the Storm Relative Helicity (SRH). An
event is categorized as extreme, if primarily, CAPE was non
zero and secondary, if values of both the K and the
TotalTotals (TT) indices exceeded 26.9 and 50, respectively.
The cases with positive CAPE but lower values of the other
indices, were identified as non-extreme. By calculating the
median, the lower and upper limits, as well as the lower and
upper quartiles of the values of these indices, the main
characteristics of their distribution were determined
The cold frontal depression that affected the area of Cyprus between 28 and 29 January 2008
The baroclinic depression that affected the area of Cyprus during the cold period, between 28 and 29 January 2008 was thoroughly studied and is presented in the present paper. A small perturbation on a northwesterly flow to the north of Cyprus has initiated the generation of the depression and in 24 h this developed into a deep baroclinic system. This depression was associated with intense weather phenomena, such as heavy thunderstorms with hail and near gale force winds. Strong cold advection resulted in a significant temperature decrease; precipitation even in lower altitudes was in the form of snow, while the accumulated rainfall corresponded to the 25% of the monthly normal. January 2008 is considered as a dry month, despite the fact that, on the average, January is considered as the wettest month of the year. In this study, the evolution and development of the depression was investigated from synoptic, dynamic, energetic and thermodynamic perspectives, in order to enhance our knowledge on the life cycle and behaviour of similar depressions over the area with extreme characteristics
Synoptic, thermodynamic and agroeconomic aspects of severe hail events in Cyprus
Hail is a hazardous weather element often accompanying a thunderstorm, as a result of either thermal instability or instability associated with baroclinic synoptic-scale systems (i.e. frontal depressions). Nevertheless, instability of any kind and thunderstorm activity does not always lead to the formation of hail of adequate size to reach the ground. The broader the knowledge concerning hail events the better the understanding of the underlying thermodynamic and dynamic mechanisms, as well as the physical processes associated with its formation. <br><br> In the present study, the severe hail events that were recorded in Cyprus during the ten-year period from 1996 until 2005 were examined, first by grouping them into two clusters, namely, the "thermal instability cluster" and the "frontal depression cluster". Subsequently, the spatial and temporal evolution of the synoptic, dynamic and thermodynamic characteristics of these hail events was studied in depth. Also, the impact of hailstorms on the local economy of the island is presented in terms of the compensations paid by the Agricultural Insurance Organization of the country
Preliminary verification results of the DWD limited area model LME and evaluation of its storm forecasting skill over the area of Cyprus
A preliminary verification and evaluation is made of the forecast fields of the non-hydrostatic limited area model LME of the German Weather Service (DWD), for a recent three month period. For this purpose, observations from two synoptic stations in Cyprus are utilized. In addition, days with depressions over the area were selected in order to evaluate the model's forecast skill in storm forecasting
DeepCare: A Deep Dynamic Memory Model for Predictive Medicine
Personalized predictive medicine necessitates the modeling of patient illness
and care processes, which inherently have long-term temporal dependencies.
Healthcare observations, recorded in electronic medical records, are episodic
and irregular in time. We introduce DeepCare, an end-to-end deep dynamic neural
network that reads medical records, stores previous illness history, infers
current illness states and predicts future medical outcomes. At the data level,
DeepCare represents care episodes as vectors in space, models patient health
state trajectories through explicit memory of historical records. Built on Long
Short-Term Memory (LSTM), DeepCare introduces time parameterizations to handle
irregular timed events by moderating the forgetting and consolidation of memory
cells. DeepCare also incorporates medical interventions that change the course
of illness and shape future medical risk. Moving up to the health state level,
historical and present health states are then aggregated through multiscale
temporal pooling, before passing through a neural network that estimates future
outcomes. We demonstrate the efficacy of DeepCare for disease progression
modeling, intervention recommendation, and future risk prediction. On two
important cohorts with heavy social and economic burden -- diabetes and mental
health -- the results show improved modeling and risk prediction accuracy.Comment: Accepted at JBI under the new name: "Predicting healthcare
trajectories from medical records: A deep learning approach
Report on the CyCAT winter school on fairness, accountability, transparency and ethics (FATE) in AI
The first FATE Winter School, organized by the Cyprus Center for Algorithmic Transparency (CyCAT) provided a forum for both students as well as senior researchers to examine the complex topic of Fairness, Accountability, Transparency and Ethics (FATE). Through a program that included two invited keynotes, as well as sessions led by CyCAT partners across Europe and Israel, participants were exposed to a range of approaches on FATE, in a holistic manner. During the Winter School, the team also organized a hands-on activity to evaluate a tool-based intervention where participants interacted with eight prototypes of bias-aware search engines. Finally, participants were invited to join one of four collaborative projects coordinated by CyCAT, thus furthering common understanding and interdisciplinary collaboration on this emerging topic
Preface "10th EGU Plinius Conference on Mediterranean Storms (2008)"
No abstract available
Tropopause and jetlet characteristics in relation to thunderstorm development over Cyprus
In the present study, the monthly statistical
characteristics of jetlet and tropopause in relation to the development of
thunderstorms over Cyprus are examined. For the needs of the study the 12:00 UTC
radiosonde data obtained from the Athalassa station (33.4° E,
35.1° N) for an 11-year period, from 1997 till 2007, were employed. On the basis
of this dataset, the height and the temperature of the tropopause, as well
as the height, wind direction and speed of the jetlet were estimated.
Additionally, the days in the above period with observed thunderstorms were
selected and the aforementioned characteristics of the jetlet and tropopause
were noted. The two data sets were subsequently contrasted in an attempt to
identify possible relations between thunderstorm development, on the one
hand, and tropopause and jetlet characteristics, on the other hand