1,720,960 research outputs found
Modeling of melt flow influence on zone shape during the industrial floating zone crystal growth process
No full textDarbā tiek modelēts silīcija monokristālu audzēšanas process ar peldošās zonas adatas acs metodi, izmantojot specializētu programmu fZone, kas ir verificēta liela diametra (4''-8'') kristālu audzēšanai ar ātrumiem līdz 4 mm/min. Atbilstoši Berlīnē veiktajai eksperimentu sērijai tiek veikti kausējuma zonas formas skaitliskie aprēķini relatīvi mazai 2'' sistēmai ar lieliem augšanas ātrumiem 5-8 mm/min gan neņemot, gan ņemot vērā kausējuma kustības ietekmi uz zonas formu. Analizējot HD ietekmi, tiek parādīts, ka konvektīvā siltuma pārnese kausējumā var būtiski ietekmēt temperatūras lauku un fāzu robežu formu. Aprēķinos iegūtie kristalizācijas frontes dziļumi tiek salīdzināti ar eksperimentālajiem mērījumiem, tiek parādīta divu skaitlisko atrisinājumu iespēja.In the current work the floating zone growth of silicon crystals with the needle-eye technique is modeled using a specialized program fZone. So far the program has been verified for crystals of large diameters (4''-8'') and growth rates up to 4 mm/min. In the present work numerical calculations of the shape of phase boundaries have been carried out for relatively small 2'' system for large growth rates (5-8 mm/min) according to the series of experiments in Berlin. The calculations were performed with and without taking into account the melt motion. It is shown that convective heat transfer in melt can noticeably affect the temperature field and the shape of the phase boundaries. The calculated deflections of crystallization interface are compared with the experimental measurements, and the possibility of two numerical solutions is shown
Modelins of the influence of gas flow on the zone shape and dopant transport in floating zone process
No full textElektroniskā versija nesatur pielikumusDarbā tiek veikta silīcija monokristālu audzēšanas ar peldošās zonas metodi matemātiskā modelēšana. Izveidotais matemātiskais modelis ļauj aprēķināt gāzes plūsmu un tās radīto papildus dzesēšanu uz silīcija virsmām. Tāpat ir izveidots vienots modelis piemaisījumu pārnesei gāzē un kausējumā, kas apraksta piemaisījumu ievadīšanu no atmosfēras.
Jaunizveidotie modeļi tika sajūgti ar esošo modeļu sistēmu. Modeļu kopums realizēts datorprogrammu veidā, galvenokārt uz atvērtā koda bibliotēkas OpenFOAM bāzes. Tika veikti peldošās zonas procesa skaitliskie aprēķini, kuros pētīta gāzes un kausējuma plūsma un to ietekme uz silīcija fāzu robežvirsmām, kā arī piemaisījumu pārnese gāzē un kausējumā.In the present work mathematical modeling of floating zone silicon single crystal growth is carried out. The developed mathematical model allows to calculate the gas flow and additional cooling at silicon surfaces caused by it. Additionally, a unified model of the dopant transport in the gas and melt is developed, which describes doping from the atmosphere.
The developed models have been coupled with the existing system of models. The set of models is implemented in computer programs, mainly based on the open source library OpenFOAM. Numerical calculations of the floating zone process have been carried out in which gas and melt flow and their influence on the silicon phase boundaries as well as dopant transport in the gas and melt was investigated
Validation of CZ-Trans simulation software for LiBr crystal growth using Czochralski method
No full textMaģistra darbā tiek pētīts litija bromīda kristālu audzēšanas process ar Čohraļska metodi. Tiek veikti pieejamās Čohraļska iekārtas uzlabojumi un temperatūras lauka mērījumi. Tiek iegūti eksperimentālie dati kristalizācijas frontes formai dažādos kristāla augšanas posmos un kristāla rādiusa vērtībai gan manuālā režīmā, gan izmantojot PID kontroli. Veiktie eksperimenti ir atkārtojami, kas līdz šim nebija izdarāms. Izmantojot papildu siltuma plūsmas blīvumu uz kristalizācijas frontes un P1 aproksimāciju, tiek veikti skaitliskie aprēķini ar iepriekš izstrādātu CZ-Trans programmatūru. Tiek iegūts nestacionārs temperatūras sadalījums, kristāla rādiuss un kristalizācijas frontes forma. Lai validētu CZ-Trans, simulācijas tiek salīdzinātas ar eksperimentālajiem datiem.The master’s thesis studies the process of growing lithium bromide crystals using the Czochralski method. Improvements to the available Czochralski furnace are conducted, temperature field measurements are performed. Experimental data are obtained for the shape of the crystallization front at different stages of crystal growth and for the value of the crystal radius in manual mode and using PID control. Experiments performed are repeatable, which was not possible until now. Using additional heat flux density on crystallization front and P1 approximation, numerical calculations are performed with the previously developed CZ-Trans software. Non-stationary temperature distribution, crystal radius, and shape of the crystallization front are obtained. Simulations are compared with experimental data to validate CZ-Trans
3D mathematical modelling of dopant transport in melt for Si floating zone single crystal growth process
No full textDarbs ir veltīts silīcija monokristāla audzēšanas peldošās zonas procesa, izmantojot adatas acs tehniku, skaitliskajai modelēšanai. Pamatojoties uz to, ka uz atklātās kušanas frontes eksistē plāns šķidrā silīcija slānis, kas ieplūst kausējumā pa kakliņa ārējo daļu, un ka piemaisījumu ievadīšana notiek caur argona atmosfēru, tiek ievesti precizēti robežnosacījumi kausējuma ātrumam un piemaisījumu koncentrācijai, un tiek pētīta to ietekme uz piemaisījumu koncentrācijas sadalījumu kausējumā. Aprēķini tiek veikti ar iepriekš izstrādātām programmām FZone un FZSiFOAM (uz atvērtā koda bibliotēkas OpenFOAM bāzes), tiek iegūti īpatnējās pretestības radiālie sadalījumi izaudzētajā monokristālā, un veikts to salīdzinājums ar eksperimentu (Leibniz Institute for Crystal Growth, Berlīne).Present work is devoted to the numerical modelling of silicon single crystal growth with floating zone method, using needle-eye technique. Because of thin liquid silicon film, which flows into melt along the outer part of the neck, and because of doping from argon atmosphere, precised boundary conditions for melt velocity and dopant concentration are introduced. The influence of them on the distribution of dopants in the melt is investigated. Calculations are performed with pre-developed programs FZone and FZSiFOAM (on the base of open-source code library OpenFOAM), radial distributions of single crystal resistivity are obtained and compared with experimental data (Leibniz Institute for Crystal Growth, Berlin)
Experimental and numerical investigation of LiBr crystal growth using laboratory Czochralski furnace
No full textDarbā tiek veikti laboratorijas LiBr kristālu audzēšanas eksperimenti, izmantojot Čohraļska metodi. Eksperimenti tiek veikti manuālā režīmā, kā arī izmantojot PID kontroli. Izmantojot iepriekš izstrādātu simulācijas programmatūru CZ-Trans, tiek meklētas optimālas PID kontroles parametru vērtības, lai uzlabotu kristāla rādiusa kontroli. Atrastās parametru vērtības tiek pārbaudītas eksperimentāli un secināts, ka vilkšanas ātruma un sprieguma fluktuācijas ir pārāk stipras, tāpēc jāizmanto mazāka laika konstante D daļai. Veikts skaitlisko aprēķinu rezultātu salīdzinājums ar eksperimentiem, iegūstot apmierinošu sakritību.Laboratory experiments for growing LiBr crystals are being carried out in the present work using the Czochralski method. The experiments are performed in manual mode, as well as utilizing PID control. Using the previously developed CZ-Trans simulation software, optimal PID control parameter values are being searched to improve crystal radius control. The found parameter values are tested experimentally, and it is concluded that the fluctuations in pulling speed and voltage are too strong, therefore, a smaller time constant needs to be used for the D control part. A comparison was made between the results of numerical calculations and experiments, resulting in a satisfactory agreement
Airflow and aerosol transport modeling with applications to Covid-19 aerosol reduction indoors
No full textPēdējo pāris gadu laikā Covid-19 infekcijas slimība ir izraisījusi lielu kaitējumu cilvēkiem visā pasaulē, kas ir licis zinātniskajai kopienai apsvērt pieejas infekcijas mazināšanai, tostarp skaitliskās modelēšanas pieejas. Šī darba mērķis ir modelēt Covid-19 aerosola pārnesi un tā samazināšanu iekštelpās. Skaitliskās hidrodinamikas risināšanai tiek izmantota Reinoldsa vidējotā Navjē Stoksa modelēšanas pieeja kopā ar turbulentās difūzijas modeli aerosola pārnesei. Darbs sākas ar konkrētas telpas gaisa plūsmas modelēšanu un skaitlisko aprēķina parametru izpēti. Nākamajā daļā tiek izveidots gaisa attīrīšanas iekārtas matemātiskais modelis, kas tiek skaitliski ieviests un pārbaudīts izmantojot skaitliskās hidrodinamikas rīkkopu OpenFOAM. Aerosola koncentrācijas aprēķina rezultāti liek secināt, ka stacionārajā RANS modelī iekštelpu gaisa plūsmu gadījumā turbulentā koncentrācijas izkliede netiek korekti aprakstīta, tāpēc nākotnē modeli nepieciešams pilnveidot.Over the past few years, the Covid-19 infection disease has caused great harm to humans worldwide, which has led the scientific community to consider various approaches to mitigate the infection, including numerical modelling approaches. The aim of this work is to model the aerosol transmission of Covid-19 and its reduction in an indoor environment. The Reynolds averaged Navier Stokes approach is used in the computational fluid dynamics model along with a turbulent diffusion model for the aerosol transport. The work starts off with the indoor airflow modeling of specific room, for which the numerical parameters are studied. In the next part a mathematical model of an air purifier is develped, which is numerically implemented and verified using the computational fluid dynamics toolbox OpenFOAM. The results of the aerosol concentration calculation suggest that the stationary RANS model does not correctly describe the turbulent concentration dispersion in the case of indoor air flows, which is cause to improve the model in the future
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
