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Investigation of Noise and Reliability of White Light-emitting Diodes Used in LCD Monitors
No full textŠio darbo tikslai yra pagaminti stendą skirtą šviesos diodų elektrinių ir optinių triukšmų matavimo darbams, susipažinti su šviesos diodų triukšmų matavimo metodika, ištirti šviesos diodus triukšmų koreliacijos metodu, bei įvertinti jų triukšmų charakteristikų kitimą diodams senstant.White light-emitting diodes were analyzed using noise correlation method. Samples were divided by the manufacturer into test samples to be analyzed and standard samples that were to be used for comparison. Electrical and optical fluctuations were measured at forward current range from 0,05 mA to 21 mA. Special attention was paid to the measurement of simultaneous correlation coefficient between electrical and optical fluctuations. Correlation coefficient was measured not only over the frequency range of 10 Hz to 20 kHz, but also in every one-octave frequency band. Analysis showed that at aging time t=0 h both samples had relatively the same amount of noise sources, however in the test sample a larger part of those noise sources were in the active layer of LED. Samples were then aged for 234 hours at forward current of 20 mA. At aging time t=234 h test sample’s noise level has increased to immeasurable levels. After aging standard sample retained the same amount of noise sources, however a part of those noise sources migrated from the peripheral layers into the active region of the LED
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Factors of thermodynamical approach to buildings life cycle/Pastato gyvavimo ciklo termodinaminio vertinimo veiksniai
No full textThe article suggests that non-industrial buildings in Lithuania consume half the final energy including appr.70% heat produced in electric power plants and boiler-houses. In order to ensure standard heating and ventilation conditions for these buildings in terms of climate parameters of a normal year it would require heat consumption of some 22 TWh. However, the energy is required not only for operation and maintenance of the building (for active microclimatic conditioning systems—AMCS), but also for setting up the building (for passive microclimatic conditioning systems—PMCS). The above input is therefore determined by technological level in the building and building materials industries. Rather exact evaluations show that in the course of several next years already, primary energy consumption used for a building maintenance shall be equal to that used while construction thereof. In terms of a building life cycle, this is a fairly short term. Therefore these buildings in terms of energetic approach make an intensive energy-consumption system. It is hereby suggested to apply an exergic analysis for a life cycle of a building under certain climatic conditions and PMCS and AMCS combinations defined by the local produce technology level. Using solely economical (both direct or derived) criteria for this intention is therefore insufficient, because the reliability of economic forecasts for longer prospect falls below any other forecasts of physical quantities. As an example for this, a globally-ecological evaluation of energetic systems based on thermodynamics is therefore presented, and is characterised by thermo-economic and exergo-economic criteria.
Further, the article provides formulas and indices for thermodynamic evaluation of climatic conditions which indicate minimum requirements of exergy for operation of AMCS. Furthermore, MCS operating points and zones characteristic of different climatic regions are provided. Tasks for MCS thermodynamic analysis have been formulated to include the processes of production of building and insulation materials, and construction erection process. These should be considered the first three stages of the above task:
• indices of present exergic input in production of materials;
• forecast of potential exergic input in production of materials;
• thermodynamic optimisation of technological processes and equipment of building materials.
It is therefore considered, that the integration of separate exergic loss components of building life cycle into a general optimisation task shall enable establishment of thermodynamically-optimum combination of exergic use in the buildings under concrete climatic conditions. This would launch, apart from economic, social and ecological aspects, an approach for handling strategic issues of construction and energetic interaction.
First Published Online: 26 Jul 201
ORO PARUOŠIMO ĮRENGINIO SU DVIEM PRIEŠPRIEŠINIŲ SRAUTŲ ŠILUMOGRĄŽIAIS EFEKTYVUMO TYRIMAS
No full textStraipsnyje nagrinėjamas oro paruošimo įrenginys (OPĮ), su dviem priešpriešinių srautų šilumogrąžiais (PSŠ), esantis Vil-niaus Gedimino technikos universiteto (VGTU) 8 aukšte Pastato energetinių ir mikroklimato sistemų (PEMS) laboratorijos patalpose. Tyrimo metu buvo išmatuotos efektyvumui nustatyti reikalingos į PSŠ įtekančio bei ištekančio oro temperatūros bei tiekiamo ir šalinamo oro srautai. Eksperimento metu išmatuoti duomenys buvo naudojami nustatant PSŠ1, PSŠ2 bei bendrą abiejų šilumokaičių temperatūros efektyvumą PSŠ. Priklausomai nuo į pirmąjį PSŠ įtekančios oro temperatūros (t1) sudarytas temperatūros efektyvumo kitimo grafikas. Įvertinus išmatuotas t1 temperatūros trukmes, sudaryta kumuliacinė kreivė bei PSŠ efektyvumo kitimo nuo t1 temperatūrų trukmės grafikas. Gauti duomenys parodė, jog PSŠ1 (85,8 – 94,4 %) temperatūrinis efektyvumas viso tyrimo metu buvo didesnis už PSŠ2 (73,7 – 86,0 %). Bendras abiejų šilumogrąžių efektyvumas kito nuo 93,8 iki 97,8 %.</jats:p
The demand for exergy during the life cycle of dwelling houses/Tipinių daugiabučių pastatų gyvavimo ciklo eksergijos poreikių įvertinimas
No full textThe heat demand for heating and ventilation of dwelling houses depends on the climate and thermal characteristics of buildings. Energy is consumed not only in the process of maintenance of a building, but also for constructing it. The aim of current research is to assess the needs of a building life cycle (constructing, maintenance, demolition) expressed in energy units.
In order to determine the energy demand of the building life cycle, lasting from a few decades to a century, the thermodynamic methodology is used. The chosen method is based on a systematic approach, applying analysis through combination of approaches such as thermodynamics exergic approach and method of an economic life cycle. The exergic method describes the energy of different types not only by its quantity, but also by the quality, ie it evaluates different forms of energy and its sources by the same quality criteria.
According to the design data of four main types of blocks of flats, based on splitting the thermodynamic model into special stages and analysing data of the primary energy consumption of material processing, and the stages of it, the comparative primary energy consumption levels are defined for the principal building material production and the construction process.
Primary energy consumption for typical block of flats construction material processing (forming construction goals, planning, research, coordination, designing, management of the construction process, labour force costs, service costs, transportation, use of machinery, energy and fuel consumption) is different as regards the design variations and construction work technology. For the concrete panel five-storey building it amounts to 4,42 kWh/m2, for a nine-storey building 4,36 kWh/m2, for a five-storey brick house 6,35 kWh/m2, and 11,59 kWh/m2for a nine-storey building.
Regular primary energy consumption needs (maintenance and repairs) for a concrete panel five-storey building are 35,45 kWh/m2, for a nine-storey building 39,77 kWh/m2, for a five-storey brick house 44,83 kWh/m2, and 52,54 kWh/m2 for a nine-storey building. 40 per cent of the consumed energy is used for heating and ventilation, the rest of it is used for hot water preparation, lighting, home appliances and repairs. Two renovations and demolition of a building (manufacture of materials and products for renovation, research, designing, realization of the projects, demolition of the building, regeneration of the territory and the waste, systemating the data, development of a new technology) need within the building life cycle from 5 to 12 kWh/m2 of energy.
In the existing blocks of flats almost three fourths of energy are used for microclimate and comfort systems, whereas heating and conditioning require one third of primary energy used within the building life cycle. The main strategy for diminishing the level of primary energy consumption in dwelling houses is aimed at developing of technical, mostly thermodynamic, features of heating systems and considering nominal power of those systems and the heating characteristics of exterior surfaces, the optimal coordination of building life cycle energy demands.
First Published Online: 26 Jul 201
Energy for buildings
No full text„Energy for buildings" Journal of Civil Engineering and Management, 12(1), p. 1-2
First Published Online: 14 Oct 201
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