Ph. Tsalides

Stochastic simulation model of hourly total solar radiation

Abstract A stochastic simulation model of hourly global solar radiation is presented in this paper. It is developed by introducing the concept of “time dependent frequency distribution” (TDFD) of hourly insolation values. In this model the two most critical aspects of time series simulation, i.e., the reproduced time series values which have the appropriate time dependent frequency distribution for the parameter being simulated and the correlation between successive values, are taken into account. The elimination of the TDFD of the data and the transformation of the data distribution to a Gaussian distribution (required for the stationary time series analysis) were carried out using a mapping technique. The autocorrelation function of the transformed data showed that the produced time series is stationary. Then, an antimapping coefficient matrix is developed, which provides a simple yet an effective simulation device. The described model has been applied in Athens (Greece) where hourly insolation data covering a period of two years are used. The theoretical results obtained using this simulation model, regarding both the TDFD and the correlation, are in agreement with the measured data.

A cellular automaton model for the study of DNA sequence evolution

Cellular automata are introduced as a model for DNA structure, function and evolution. DNA is modeled as a one-dimensional cellular automaton with four states per cell. These states are the four DNA bases A, C, T and G. The four states are represented by numbers of the quaternary number system. Linear evolution rules, represented by square matrices, are considered. Based on this model a simulator of DNA evolution is developed and simulation results are presented. This simulator has a user-friendly input interface and can be used for the study of DNA evolution.

Loss-of-load probability and related parameters in optimum computer-aided design of stand-alone photovoltaic systems

Abstract Loss-of-load probability (LOLP) and related parameters are presented as a technique, based on an hour-by-hour approach, for optimum computer-aided design of stand-alone photovoltaic (PV) systems. The minimum, and hence economically optimum, size of a PV system of a specified degree of reliability is determined mathematically as a function of the array orientation. Also, the dependence of unserved energy (as a measure complementary to LOLP) on array tilt angle and/or orientation for a given PV system is determined. The technique is applied in the design of a stand-alone PV system in a remote and isolated village in northern Greece. For a given array orientation, the optimum array tilt angle (which minimizes the size of the PV system) is independent of the chosen values of LOLP. The unserved energy increases linearly with array area for a given battery capacity, decreases with increasing battery capacity and array off-south orientation, and increases with increasing values of LOLP. The minimum values of unserved energy for a given battery capacity and a given orientation correspond to the optimum array tilt angle. The dependence on LOLP of the total life-cycle cost (TLC) of a PV system having the optimum size for the desired degree of reliability, for a range of LOLP values comparable to the range of reliability levels of traditional systems, is rather weak. The TLC of an optimum system increases with array off-south orientation, particularly for angles greater than ±30° .

Direct computation of the array optimum tilt angle in constant-tilt photovoltaic systems

Abstract In this paper a general method is presented for the direct determination of the optimum tilt angle of solar photovoltaic arrays, taking into account the latitude of the place, the local climatological and insolation conditions and the orientation of the photovoltaic arrays, independently of the particular application. The optimization method is based on the minimization of the relative error (with respect to the annual mean insolation on a tilted surface for each tilt angle of a given orientation) in the average monthly insolation on the tilted surface for those months for which this insolation is less than the annual mean. In this process the optimum tilt angle is selected so that it leads to the maximum degree of uniformity of insolation throughout the year and hence to the photovoltaic system with the smallest installed peak power and battery capacity required for any given application. The method has been applied to obtain optimum tilt angles for south-facing as well as off-south-facing modules for a number of different places in Greece. The optimum tilt angles of photovoltaic arrays for the azimuthal angles in the range from 0° to ±60° studied were found always to be greater than the latitude of the site by about 40% – 60%, and to be constant for azimuthal angles of up to ±30° . The array optimum tilt angle was found to be a linear function of the clearness factor at the particular location. The values of the optimum tilt angles obtained directly using this method are in excellent agreement with those obtained indirectly using the method of selecting the “optimum” photovoltaic system.

A low-cost fiber optic force sensor

A transducer that uses an intensity-modulated optical method to measure force is described in this paper. The method relies on the additional optical power loss induced by the compression of a fiber optic loop. The sensor is shown to exhibit long-term stability. Using a simple recalibration procedure, a repeatability of /spl plusmn/0.5% was obtained.

Digital ultrasonic scanning system for positioning underwater remotely operated vehicles

The design of a digital ultrasonic scanning system for positioning underwater remotely operated vehicles (UROVs) is presented in this paper. Its principle of operation is based on ultrasonic distance measurements (by determining the time of flight) and mechanical scanning. Ultrasonic imaging is used to construct the 3-D image of the environment surrounding the vehicle. The image is then used, in combination with signals coming from a gyroscope, to estimate the actual distances of the vehicle from the objects in the vicinity of the vehicle. The system consists of a 200 KHz point transducer, a scanning transmitter-receiver unit and a computer for image reconstruction and control of the UROV. The main advantages of this system are its simplicity and its accurate large scale measurement capability. The design of the system was carried out in order to conform directly with the computer controlling the UROV, and its operation was experimentally demonstrated.

An intelligent image sensor based on two-dimensional cellular automata

The design of an intelligent image sensor based on two-dimensional cellular automata is presented. This intelligent sensor performs simple first-stage preprocessing of the image in parallel with the sensing operation. The sensor acts, in parallel with the sensing operation and that of thresholding, as a spatial low-pass filter on the image. A photodiode is used as a sensing element. The thresholding circuit is simply an inverter. The low-pass filtering operates to remove bright spikes, which would incorrectly appear in the thresholded image. This is performed by each pixel cell according to a local transition function, which takes into account the majority of the values of its four nearest-neighbour pixel cells. The sensor is addressable like a dynamic memory, and hence techniques such as windowing can be performed rapidly without the large data redundancy that occurs with serially addressed sensors.<<ETX>>

The HCUAV project: Electronics and software development for medium altitude remote sensing

The continuous increase of illegal migration flows to southern European countries has been recently in the spotlight of European Union due to numerous deadly incidents. Another common issue that the aforementioned countries share is the Mediterranean wildfires which are becoming more frequent due to the warming climate and increasing magnitudes of droughts. Different ground early warning systems have been funded and developed across these countries separately for these incidents, however they have been proved insufficient mainly because of the limited surveyed areas and challenging Mediterranean shoreline and landscape. In 2011, the Greek Government along with European Commission, decided to support the development of the first Hellenic Civil Unmanned Aerial Vehicle (HCUAV), which will provide solutions to both illegal migration and wildfires. This paper presents the challenges in the electronics and software design, and especially the under development solutions for detection of human and fire activity, image mosaicking and orthorectification using commercial off-the-shelf sensors. Preliminary experimental results of the HCUAV medium altitude remote sensing algorithms, show accurate and adequate results using low cost sensors and electronic devices.

A new ASIC for the measurement of appearance

This paper presents the design and VLSI implementation of a new color space converter chip which performs the conversion, in real-time, of the X, Y and Z color coordinates to the CIE L*u*v* perceptually uniform color space. The high speed of operation is achieved by pipelining the data in a vector fashion. The module is implemented using a DLM, 0.7 /spl mu/m, N-well, CMOS technology process and it occupies a silicon area of 5.73 mm/spl times/5.59 mm 32.03 mm/sup 2/. Its maximum speed of operation is 20 MHz and its throughput rate of operation is 200 MIPS. Targeted applications include display device modelling (matching of computer image processing to human sensing), device independent color reproduction, colorimetry instrumentation, and color machine vision applications.

Image enhancement using colour information

Abstract A new image enhancement technique using the Intensity, Hue and Saturation (lIHS) colour space is presented in this letter Experimental results illustrating the enhancement capabilities of the proposed technique are given. Comparative examples of the proposed technique to the grey level histogram equalisation technique are also included.