3,037 research outputs found
An assessment of the impact of possible CAP reform scenarios on Romanian agriculture
Get PDFUsing a simplified model, with key-variable the prices of two different possible scenarios of CAP reform after 2013 (moderate and radical), this paper present a comparison between the price effects of implementation of each reform scenario at 2015 horizon on Romanian agriculture. This short analysis shows that, under the presented hypotheses, the net welfare effect, due to the price changes, for the selected products, is positive in both reform scenarios, yet greater in the case of the radical reform. Integrated in the large context of Romanian development, it seems that the influence of CAP reform upon agriculture and rural areas will be most likely a gradual one: an interpenetration between the two scenarios is foreseeable, starting with the moderate reform that will dominate the period around 2013, the reform measures acquiring a more radical character afterwards.CAP reform, Romania, welfare effects, Agricultural and Food Policy,
Rich, Sturmian, and trapezoidal words
Get PDFIn this paper we explore various interconnections between rich words, Sturmian words, and trapezoidal words. Rich words, first introduced by the second and third authors together with J. Justin and S. Widmer, constitute a new class of finite and infinite words characterized by having the maximal number of palindromic factors. Every finite Sturmian word is rich, but not conversely. Trapezoidal words were first introduced by the first author in studying the behavior of the subword complexity of finite Sturmian words. Unfortunately this property does not characterize finite Sturmian words. In this note we show that the only trapezoidal palindromes are Sturmian. More generally we show that Sturmian palindromes can be characterized either in terms of their subword complexity (the trapezoidal property) or in terms of their palindromic complexity. We also obtain a similar characterization of rich palindromes in terms of a relation between palindromic complexity and subword complexity
Time-Frequency Analysis of a Thermally Induced Pulsating Slug Flow
Get PDFThe thermofluidic operation of two-phase heat transfer devices is affected by thermally induced fluid oscillations of unknown frequency and amplitude. In line with previous studies, the time-frequency analysis of experimental signals is performed to investigate the existence of local characteristic frequencies. This work applies the wavelet transform to the evaporator fluid pressure signal of a passive two-phase heat transfer which can work as a Thermosyphon or as a Pulsating Heat Pipe, depending on the gravity acceleration. The results, obtained by means of a parabolic flight campaign, shows that the local characteristic frequencies are present only during the microgravity phase and in a frequency range from 0.8 to 2 Hz. Understanding the complex phenomena related to thermally induced oscillation is essential for the development of reliable heat transfer models and robust design tools for Pulsating Heat Pipes
Machine Learning Algorithms for Flow Pattern Classification in Pulsating Heat Pipes
Get PDFData Availability Statement: Not applicableCopyright: © 2022 by the authors. Owing to their simple construction, cost effectiveness, and high thermal efficiency, pulsating heat pipes (PHPs) are growing in popularity as cooling devices for electronic equipment. While PHPs can be very resilient as passive cooling systems, their operation relies on the establishment and persistence of slug/plug flow as the dominant flow regime. It is, therefore, paramount to predict the flow regime accurately as a function of various operating parameters and design geometry. Flow pattern maps that capture flow regimes as a function of nondimensional numbers (e.g., Froude, Weber, and Bond numbers) have been proposed in the literature. However, the prediction of flow patterns based on deterministic models is a challenging task that relies on the ability of explaining the very complex underlying phenomena or the ability to measure parameters, such as the bubble acceleration, which are very difficult to know beforehand. In contrast, machine learning algorithms require limited a priori knowledge of the system and offer an alternative approach for classifying flow regimes. In this work, experimental data collected for two working fluids (ethanol and FC-72) in a PHP at different gravity and power input levels, were used to train three different classification algorithms (namely K-nearest neighbors, random forest, and multilayer perceptron). The data were previously labeled via visual classification using the experimental results. A comparison of the resulting classification accuracy was carried out via confusion matrices and calculation of accuracy scores. The algorithm presenting the highest classification performance was selected for the development of a flow pattern map, which accurately indicated the flow pattern transition boundaries between slug/plug and annular flows. Results indicate that, once experimental data are available, the proposed machine learning approach could help in reducing the uncertainty in the classification of flow patterns and improve the predictions of the flow regimes.EPSRC grant HyHP (EP/P013112/1); European Space Agency MAP projects TOPDESS; Hexxcell Ltd
Time-Frequency Analysis of a Pulsating Heat Pipe in Microgravity Environment
No full textThe thermofluidic operation of Pulsating Heat Pipe is affected by thermally induced fluid oscillations of unknown frequency and amplitude. In line with previous studies, the time-frequency analysis of experimental signals is performed to investigate the existence of local characteristic frequencies. The spectral analysis of PHPs by means of Fast Fourier Transforms (FFT) performed so far in the literature, shows contradictory results. Since it is expected that the flow signal parameters may vary in time, the time frequency analysis seems a more suitable tool for catching the local dominant frequencies. This work applies the wavelet transform to the evaporator and condenser fluid pressure signal of a passive two-phase heat transfer which can work as a Thermosyphon or as a Pulsating Heat Pipe, depending on the gravity acceleration. The results, obtained by means of a parabolic flight campaign, shows that the local characteristic frequencies are present only during the microgravity phase and in a frequency range from 0.8 to 2 Hz. Understanding the complex phenomena related to thermally induced oscillation is essential for the development of reliable heat transfer models and robust design tools for Pulsating Heat Pipes
Characterization Results for the Poset Based Representation of Topological Relations - I: Introduction and Models
No full text@article{DBLP:journals/informaticaSI/ForlizziN99,
author = {Luca Forlizzi and
Enrico Nardelli},
title = {Characterization Results for the Poset Based Representation
of Topological Relations - I: Introduction and Models.},
journal = {Informatica (Slovenia)},
volume = {23},
number = {2},
year = {1999},
bibsource = {DBLP, http://dblp.uni-trier.de}
Characterization Results for the Poset Based Representation of Topological Relations - II: Intersection and Union
No full text@article{DBLP:journals/informaticaSI/ForlizziN00,
author = {Luca Forlizzi and
Enrico Nardelli},
title = {Characterization Results for the Poset Based Representation
of Topological Relations - II: Intersection and Union.},
journal = {Informatica (Slovenia)},
volume = {24},
number = {1},
year = {2000},
bibsource = {DBLP, http://dblp.uni-trier.de}
System-on-chip Computing and Interconnection Architectures for Telecommunications and Signal Processing
No full textThis dissertation proposes novel architectures and design techniques targeting SoC building blocks for telecommunications and signal processing applications.
Hardware implementation of Low-Density Parity-Check decoders is approached at both the algorithmic and the architecture level. Low-Density Parity-Check codes are a promising coding scheme for future communication standards due to their outstanding error correction performance.
This work proposes a methodology for analyzing effects of finite precision arithmetic on error correction performance and hardware complexity. The methodology is throughout employed for co-designing the decoder. First, a low-complexity check node based on the P-output decoding principle is designed and characterized on a CMOS standard-cells library. Results demonstrate implementation loss below 0.2 dB down to BER of 10^{-8} and a saving in complexity up to 59% with respect to other works in recent literature. High-throughput and low-latency issues are addressed with modified single-phase decoding schedules. A new "memory-aware" schedule is proposed requiring down to 20% of memory with respect to the traditional two-phase flooding decoding. Additionally, throughput is doubled and logic complexity reduced of 12%. These advantages are traded-off with error correction performance, thus making the solution attractive only for long codes, as those adopted in the DVB-S2 standard. The "layered decoding" principle is extended to those codes not specifically conceived for this technique. Proposed architectures exhibit complexity savings in the order of 40% for both area and power consumption figures, while implementation loss is smaller than 0.05 dB.
Most modern communication standards employ Orthogonal Frequency Division Multiplexing as part of their physical layer. The core of OFDM is the Fast Fourier Transform and its inverse in charge of symbols (de)modulation. Requirements on throughput and energy efficiency call for FFT hardware implementation, while ubiquity of FFT suggests the design of parametric, re-configurable and re-usable IP hardware macrocells. In this context, this thesis describes an FFT/IFFT core compiler particularly suited for implementation of OFDM communication systems. The tool employs an accuracy-driven configuration engine which automatically profiles the internal arithmetic and generates a core with minimum operands bit-width and thus minimum circuit complexity. The engine performs a closed-loop optimization over three different internal arithmetic models (fixed-point, block floating-point and convergent block floating-point) using the numerical accuracy budget given by the user as a reference point. The flexibility and re-usability of the proposed macrocell are illustrated through several case studies which encompass all current state-of-the-art OFDM communications standards (WLAN, WMAN, xDSL, DVB-T/H, DAB and UWB). Implementations results are presented for two deep sub-micron standard-cells libraries (65 and 90 nm) and commercially available FPGA devices. Compared with other FFT core compilers, the proposed environment produces macrocells with lower circuit complexity and same system level performance (throughput, transform size and numerical accuracy).
The final part of this dissertation focuses on the Network-on-Chip design paradigm whose goal is building scalable communication infrastructures connecting hundreds of core. A low-complexity link architecture for mesochronous on-chip communication is discussed. The link enables skew constraint looseness in the clock tree synthesis, frequency speed-up, power consumption reduction and faster back-end turnarounds. The proposed architecture reaches a maximum clock frequency of 1 GHz on 65 nm low-leakage CMOS standard-cells library. In a complex test case with a full-blown NoC infrastructure, the link overhead is only 3% of chip area and 0.5% of leakage power consumption.
Finally, a new methodology, named metacoding, is proposed. Metacoding generates correct-by-construction technology independent RTL codebases for NoC building blocks. The RTL coding phase is abstracted and modeled with an Object Oriented framework, integrated within a commercial tool for IP packaging (Synopsys CoreTools suite). Compared with traditional coding styles based on pre-processor directives, metacoding produces 65% smaller codebases and reduces the configurations to verify up to three orders of magnitude
Towards the Development of Flow Pattern Maps for Thermally-Induced Pulsating Two-Phase Flows
No full textFlow boiling instabilities affect the operating range of two-phase thermal management systems. Flow pattern transitions, as a form of instability, has been extensively mapped under conditions of controlled mass flow rate and velocity. In case of a chaotic pulsating flow, like in Pulsating Heat Pipes, the conventional maps present applicability limitations. In this work, flow pattern transitions and bubble break-up events have been investigated in a single loop Pulsating Heat Pipe. Modified Froude, Weber and Bond numbers have been introduced, considering the actual acceleration of the fluid and the length of the bubble as main controlling factors for the transitions. Finally, based on the modified non-dimensional analysis, a novel flow pattern map, valid for a pulsating flow and obtained under the three different gravity levels (from parabolic flight), has been proposed. This new map will be useful to the development of comprehensive designing tools for passive two-phase devices
Wavelet Analysis of the Pressure Signal in a Pulsating Heat Pipe
Get PDFThermally induced oscillations in two phase slug flow may largely affect the design heat transfer in microchannel heat exchangers and in passive wickless two-phase systems, i.e. Pulsating Heat Pipes (PHPs). The occurrence of flow instabilities and how and when possible dominant frequencies appear during the device operation are still open issues in the scientific community and, most important, are not known a priori, neither can be derived only from physical and analytical considerations. In the literature, studies about different types of time-frequency analyses on the fluid pressure, the fluid and wall temperature, the liquid slug velocity and the vapor plugs displacement signals can be found. The results are incomplete because the link between frequencies and device performance is still not clear. In this work the time-frequency analysis has been applied to the evaporator and condenser pressure signals of a Pulsating Heat Pipe and individually analyzed to investigate the existence of dominant frequencies. Data recording is performed varying the heat power input at the evaporator zone, ranging from 68 W to 146 W. To characterize the signal in the frequency domain and identify the time interval in which the dominant frequency occurs the selected tool is the Wavelet Transform, a good compromise between resolution and complexity of implementation. During the slug-plug flow regime, the results show that the dominant frequencies always fall in the range 0.6 - 0.9 Hz, with an increasing trend with the heat input level. Moreover, the two signals at the evaporator and at the condenser were compared through the Wavelet Cross-Correlation, identifying the dominant frequency common to both signals and the phase angle 〖10〗^o 〖-20〗^o. The understanding of the complex phenomena related to the thermally induced oscillations is essential for the development of reliable heat transfer models and robust design tools for Pulsating heat pipes
- …
