1,720,979 research outputs found
Kapljični mikroresonatorji za preučevanje mehkih in bioloških sistemov
No full textDroplet microresonators can support whispering gallery mode (WGM) optical resonances, which are highly dependent on the size and shape of the droplet. Even small perturbations in these two parameters cause distinct changes in the droplet\u27s WGM spectra, providing a precise optomechanical sensing platform. Relying on the spectroscopy of WGMs we developed WGM tensiometry, a method for measuring interfacial tension (IFT) of the interface between the droplet microresonator and the surrounding liquid, and WGM elastometry, a method for measuring local stress and Young\u27s modulus of a soft matrix surrounding the droplet.
WGM tensiometry involves generating a dye-doped microdroplet of an optically clear liquid attached to the end of a glass microcapillary that can support WGMs while submerged in an immiscible continuous liquid phase. The size changes of the droplet are monitored via WGMs while applying finely tunable pressure through the microcapillary. The IFT is determined from the droplet size and the equilibrium pressure. This method allows the use of droplets as small as 8μm, requiring minimal sample volumes. Compared to other tensiometry methods, WGM tensiometry does not require the densities of the two liquids to be known in advance. Additionally, IFT measurements can be performed in non-equilibrium states when the droplet size or the chemical composition of the continuous phase changes over time.
WGM elastometry is based on the elastocapillary interaction between the droplets and the surrounding soft matrix. We used gelatin hydrogel and mouse tissues as examples. The matrix was controllably deformed and the deformation response of the droplets was measured via modification of the WGM spectrum to determine the local anisotropic stresses, which could be as small as a few pN/μm^2. Additionally, Young\u27s modulus of the matrix in the range 1kPa to 35 kPa, which covers most human soft tissues, could be measured.
The developed methods enable precise determination of the mechanical properties of fluids and soft materials, relevant to a wide range of applications, including the study of biological processes.Mikroresonatorji na osnovi kapljic lahko podpirajo ``whispering gallery\u27\u27 (WGM) optične resonance, ki so močno odvisne od velikosti in oblike kapljice. Tudi najmanjše spremembe v teh dveh parametrih povzročijo znatne spremembe v WGM spektru kapljice, kar je osnova za natančno optomehansko senzoriko. Z uporabo WGM spektroskopije smo razvili metodo imenovano WGM tenziometrija, za merjenje površinske napetosti na stiku med kapljičnim mikroresonatorjem in okoliško tekočino, ter metodo, imenovana WGM elastometrija, za merjenje lokalne napetosti in Youngovega modula mehke matrike, ki obdaja kapljico.
WGM tenziometrija vključuje generiranje in kontroliranje velikosti fluorescentno obarvane mikrokapljice narejene iz optično čiste tekočine, ki je pritrjena na konico steklene mikrokapilare in potopljena v okoliško tekočino. Mikrokapljice lahko podpirajo WGM načine, s katerimi spremljamo spreminjanje velikosti kapljice, medtem ko skozi mikrokapilaro apliciramo natančno nastavljiv tlak. Površinsko napetost se določi na podlagi velikosti kapljice in ravnovesnega tlaka. Ta metoda omogoča uporabo kapljic velikih le 8μm in zahteva minimalne količine vzorca. V primerjavi z drugimi metodami tenziometrije pri WGM tenziometriji ni potrebno vnaprej poznati gostote obeh tekočin. Poleg tega se lahko meritve površinske napetosti izvajajo v neravnovesnih stanjih, ko se velikost kapljice ali kemijska sestava okoliške tekočine s časom spreminjata.
WGM elastometrija temelji na elastokapilarni interakciji med kapljicami in okoliško mehko matriko, pri čemer sta bila uporabljena hidrogel iz želatine in mišja tkiva. Matrika je bila nadzorovano deformirana, odziv kapljic pa merjen prek WGM-jev, kar je omogočilo določanje lokalnih anizotropnih napetosti, ki so lahko velikostnega reda le nekaj pN/μm^2. Poleg tega metoda omogoča meritev Youngovega modula matrike v območju 1kPa do 35kPa, kar zajema večino mehkih tkiv pri ljudeh.
Razvite metode omogočajo natančnejšo določitev mehanskih lastnosti tekočin in mehkih materialov, kar je pomembno za širok spekter aplikacij, vključno s preučevanjem bioloških procesov
Generation and characterization of entangled photons from a liquidcrystal
No full textNapredek v kvantni optiki je v zadnjih letih povečal potrebo po boljših izvorih
prepletenih fotonov. Kot obetavni materiali za tvorbo prepletenih fotonskih parov
preko spontane parametrične pretvorbe navzdol (SPDC) so se pred kratkim izka-
zali feroelektrični nematski tekoči kristali (FNLC). Zaradi polarne urejenosti lahko
v njih potekajo nelinearni optični pojavi drugega reda, kamor spada tudi SPDC.
Za opazovanje in zaznavanje fotonskih parov smo sestavili lastno eksperimentalno
postavitev. Z njo je mogoče spreminjati polarizacijo črpalnega žarka, ki vpada na
vzorec. Nastalo svetlobo skolimiramo ter do detektorjev prepustimo zgolj fotone z
določeno polarizacijo. Iz časovnega zamika med posameznimi zaznanimi dogodki
lahko izluščimo SPDC signal. Merjenje različnih polarizacijskih stanj nam omogoča
izvedbo polarizacijske tomografije, s čimer dobimo informacijo o celotnem polariza-
cijskem stanju nastalih fotonskih parov. Poleg tega je postavitvi dodan še del za
mikroskopijo ter merjenje signala optičnega frekvenčnega podvajanja (SHG).
Delovanje in ustreznost postavitve za merjenje SPDC signala smo preverili na
vzorcu kristala litijevega niobata. Ker so se rezultati meritev ujemali z rezultati iz
literature, smo nadaljevali z merjenjem na tekočih kristalih. Razmerje med tokom
nastalih fotonskih parov in ozadjem je bilo v skladu s teoretično napovedjo obratno
sorazmerno z močjo črpalnega žarka. Ugotovili smo, da je koherenčna razdalja
približno trikrat manjša od pričakovane teoretične vrednosti.
Ker je namen SPDC običajno tvorba prepletenih parov fotonov, sem se v drugem
delu magistrske naloge osredotočila na odvisnost prepletenosti fotonskih stanj od la-
stnosti tekočekristalne celice in polarizacije črpalnega žarka. S teoretičnim modelom,
ki sta ga razvila Kavčič in Sultanov [1], sem tako izračunala odvisnost prepletenosti
od debeline tekočekristalne celice ter polarizacije črpalnega žarka. Rezultati modela
so napovedali, da je prepletenost blizu 1 mogoče dobiti le pri zelo tankih celicah.
Posledično smo zato meritve izvedli pri najmanjših debelinah naše klinaste tekoče-
kristalne celice, ki so znašale približno 1.8 μm. Prepletenost fotonskega para smo
spreminjali s polarizacijo črpalnega žarka. Med drugim smo tako ustvarili pare foto-
nov z nizko prepletenostjo C = 0.12 ± 0.2 ter prepletene fotonske pare z zelo visoko
stopnjo prepletenosti C = 0.98 ± 0.07. Po nam znanih informacijah smo bili s tem
prvi v Sloveniji, ki nam je uspelo ustvariti prepletene fotone.Developments in the field of quantum optics have led to an increased demand for
better sources of entangled photons. Recently discovered ferroelectric nematic liq-
uid crystals (FNLCs) have emerged as promising materials for generating entangled
photon pairs via spontaneous parametric down-conversion (SPDC). Their polar or-
dering leads to second-order nonlinear optical phenomena, such as SPDC. To observe
and detect photon pairs, we assembled a custom experimental setup. With it, we
can adjust the polarization of the pump beam incident on the sample. The resulting
photon pairs are collimated, and only those with a certain polarization are transmit-
ted to the detectors. From the time delay between individual detected events, we
can extract the SPDC signal. Measuring various polarization states enables us to
perform polarization tomography, providing information on the overall polarization
state of the generated photon pairs. Additionally, the setup includes a camera for
microscopy and a part for measuring second harmonic generation (SHG).
The performance and suitability of the setup for measuring the SPDC signal
was verified using a lithium niobate crystal. As the measurement results were con-
sistent with the results from literature, we proceeded with measurements on liquid
crystals. The ratio between the flux of generated photon pairs and the background
was inversely proportional to the pump beam power, which is in accordance with
theoretical predictions. We determined that the coherence length is approximately
three times smaller than the expected theoretical value.
Since the purpose of SPDC is typically to generate entangled photon pairs, I
focused in the second part of my thesis on how the photon entanglement depends
on the properties of the liquid crystal cell and the polarization of the pump beam.
With the simulation developed by Kavčič and Sultanov [1], I examined the theo-
retical dependence of entanglement on the thickness of the liquid crystal cell and
the polarization of the pump beam. The model predicted that entanglement close
to 1 could be achieved only with very thin cells. Consequently, measurements were
conducted at the smallest thicknesses of our wedge-shaped liquid crystal cell, which
was at approximately 1.8 μm. The entanglement of the photon pair was controlled
by the polarization of the pump beam. Among other results, we generated photon
pairs with low entanglement C = 0.12 ± 0.2 and also photon pairs with very high
entanglement C = 0.98 ± 0.07. To the best of our knowledge, we were the first in
Slovenia to have succeeded in creating entangled photons
Emission of laser light from smectic and soap bubbles
No full textMilni mehurčki so na prvi pogled preprosti objekti, vendar imajo mnogo zanimivih lastnosti, ki pritegnejo pozornost tako širše kot tudi strokovne javnosti. Preučevali so jih že iz različnih vidikov, med drugim njihove interferenčne barve in tvorjenje minimalnih površin, še nikoli pa niso bili uporabljeni kot optični resonatorji. V okviru tega dela smo pokazali, da milni mehurčki in mehurčki iz smektičnih tekočih kristalov, z dodanimi fluorescenčnimi barvili, oddajajo lasersko svetlobo, če jih vzbujamo z zunanjim laserjem. Laserji narejeni iz mehurčkov delujejo na principu ojačanja optičnih resonanc, ki jim pravimo whispering gallery modes (WGM). Nastanejo, ko je svetloba ujeta v resonatorju krogelne oblike zaradi večkratnega totalnega odboja na meji med resonatorjem in okoliškim zrakom ter zato kroži blizu površine resonatorja. Predvsem so zanimivi smektični mehurčki, ki imajo izredno tanko steno, ki je lahko popolnoma enakomerne debeline, tipično ⠼100nm. Posledično podpirajo le en optični način razširjanja svetlobe, zaradi česar je spekter laserske svetlobe zelo lep. Sestavljen je iz več sto enakomerno razmaknjenih vrhov, ki spominjajo na frekvenčni glavnik. Na podlagi spektra oddane laserske svetlobe in njegovega spreminjanja v času smo lahko izmerili tudi le 10nm velike spremembe velikosti milimetrskega mehurčka. To nam omogoča uporabo smektičnih mehurčkov kot zelo občutljivih senzorjev električnega polja in tlaka. Smektične mehurčke smo preizkusili
kot senzorje električnega polja in dobili izjemno občutljivost z najmanjšim merljivim električnim poljem 0.35V/mm. Z mehurčki je mogoče meriti spremembe zunanjega tlaka do 100 bar z natančnostjo 1.5Pa, kar ustreza izjemno visokemu dinamičnemu razponu 10^7. Ker so mehurčki pritrjeni na konec kapilare, je mogoče z dodatnim fiksnim volumnom zraka v kapilari poljubno povečati natančnost meritve tlaka in hkrati ohraniti visoko vrednost dinamičnega razpona. Milni in smektični mehurčki, ki oddajajo lasersko svetlobo, so edinstven tip mikroresonatorjev. So eni najboljših mikrosenzorjev električnega polja in tlaka razvitih do zdaj, v prihodnosti pa bi jih lahko uporabili tudi za preučevanje tankih filmov in optomehaniko resonančnih votlin.Soap bubbles are simple but very fascinating objects for both researchers and the general public. Several of their properties have been studied, including interference colors and the formation of minimal surfaces, but until now they have not been used as optical cavities. In this work, we have demonstrated that dye doped soap bubbles and smectic liquid crystal bubbles emit laser light when pumped with an external laser. Soap bubble lasers operate on the principle of whispering gallery mode resonances, which form when light circulates in a spherical resonator due to multiple total internal reflections. Smectic bubbles are particularly interesting because they have a very thin and uniform wall, typically ⠼100nm thick. For this reason, they support only one optical mode, which results in the laser spectrum consisting of hundreds of regularly spaced peaks, resembling a frequency comb. Using the spectrum of the emitted light captured in time, we were able to measure size changes as small as 10nm of a millimeter-sized bubble. This allows us to use smectic bubbles as very sensitive electric field and pressure sensors. Using the bubbles, we measured the electric field with an exceptional sensitivity with a minimal measurable electric field of 0.35V/mm. They also enable measurement of pressures up to 100 bar with a resolution of 1.5Pa, resulting in a dynamic range of nearly 10^7. Since the bubbles were attached to one end of the capillary, an additional fixed volume allowed for arbitrarily high sensitivity while maintaining excellent dynamic range. Soap and smectic bubble lasers are a very unique type of microresonators as well as one of the best electric field and pressure sensors to date. In the future, they could be used to study thin fluid films and cavity optomechanics
Microscopy and sensing through scattering tissues using optical microresonators
No full textV večini bioloških tkiv močno sipanje svetlobe omejuje uporabo standardne mikroskopije. Tako so v zadnjem obdobju bile razvite številne nove metode in pristopi, ki se osredotočajo na premostitev omenjene težave. V okviru tega dela smo razvili novo metodo za globinsko slikanje ter senzoriko v tkivih, ki izkorišča optične WGM (ang. whispering gallery mode) mikroresonatorje in njihove značilnosti. Lastnosti kot so ozka spektralna emisija in velika občutljivost na spremembe okolja so ključna prednost WGM mikroresonatorjev v primerjavi s standardnimi fluorescentnimi označevalci, ki se tipično uporabljajo v bioloških raziskavah. WGM mikroresonatorje, ki se nahajajo pod oziroma znotraj sipalnega medija, lahko lokaliziramo z veliko natančnostjo s pomočjo dekompozicije zajetega spektralnega signala na prispevke posameznih mikroresonatorjev. To je možno doseči zaradi izrazitih WGM resonanc, ki navkljub potovanju svetlobe preko sipajočega medija ostanejo praktično nespremenjene. WGM mikroresonatorje zaznamujejo edinstvene spektralne lastnosti. Njihovi spektri so medsebojno razločljivi v kolikor se njihove velikosti komaj znatno razlikujejo, kar dodatno omogoča označevanje, identificiranje in spremljanje individualnih celic, medtem ko analiza izsevanih spektrov omogoča zaznavanje oziroma senzoriko številnih parametrov kot so lomni količnik, pH ali temperatura okolice. Razvita metoda s sposobnostjo simultane lokalizacije ter senzorike predstavlja vsestransko orodje na področju globinskega slikanja v tkivih.In most biological tissues, strong scattering of visible light limits the use of standard microscopy. New approaches and methods that focus on overcoming this particular problem have been developing recently. In this work, we have developed a novel technique for deep tissue imaging and sensing that utilizes optical WGM (whispering gallery mode) microresonators and their properties. The properties of spectrally narrow emission and high sensitivity to the environment make WGM microresonators superior to the standard fluorescent probes typically used in biological research. WGM microresonators placed under scattering materials or embedded inside them can be localized with high precision by decomposing the acquired spectral signal into contributions from individual microresonators. This is possible due to the fact that strong WGM resonances are mainly unaffected when propagating through a scattering medium. The spectral characteristics of each WGM microresonator are unique as long as they differ in size by only a very small margin. This can further be used to tag, identify and track individual cells. Additionally, sensing of different parameters such as refractive index, pH or temperature of the surroundings is also possible by analyzing the spectra. Simultaneous sensing and localization capabilities make the developed method a versatile tool in the field of deep tissue imaging
Biocompatible microlasers as sensors of glucose concentration and temperature
Get PDFV zadnjih letih se vedno več študij ukvarja z bio laserji, ki so namenjeni uporabi znotraj bioloških sistemov. Sipanje in absorpcija svetlobe znotraj tkiv sta glavni problem pri detekciji svetlobe. Zato imajo laserji v primerjavi s fluorescenco veliko prednostiglavne lastnosti laserske svetlobe so ozke emisijske črte, visoka koherenca in velika intenziteta.
Glavna motivacija tega magistrskega dela je bila študija potencialno možnih aplikacij biokompatibilnih mikro laserjev za namen biosenzorike. Mikro laserje lahko vgradimo v biološko tkivo in merimo fiziološke parametre, kot sta koncentracija glukoze in temperatura, v realnem času. Za namene biosenzorike znotraj bioloških tkiv je potrebno razviti laserje iz biokompatibilnih snovi, ki so tudi biorazgradljive. Biokompatibilna snov ne povzroči imunskih reakcij in omogoča nemoteno delovanje telesa. Hkrati morajo biti laserji dovolj občutljivi na zunanje spremembe, ki so v območju fizioloških vrednosti.
Razvili smo postopek izdelave mikro laserjev iz biokompatibilnih materialov, ki so tudi biorazgradljivi in dovoljeni za uporabo v medicinske namene. Vsak laser ima tri glavne sestavne dele: optični resonator, ki ujame svetlobo, ojačevalni medij, ki ojačuje svetlobo v resonatorju in črpalni mehanizem, ki ustvarja obrnjeno zasedenost v ojačevalnem mediju.
Izdelali smo dva tipa mikro laserjev glede na način delovanja. Prvi tip je Whispering Gallery Mode (WGM) mikro laser. Izdelan je iz biokompatibilnega polimera Poly(L-lactic acid) (PLLA), dopiranega s fluorescentnim barvilom. Drugi tip mikro laserja je Braggov mikro laser, izdelan iz holesteričnih tekočih kristalov, estrov holesterola, ki so že naravno prisotni v človeškem telesu, in dopiran s fluorescentnim barvilom. Najprej smo predstavili lastnosti delovanja klasičnih laserjev, ključne lastnosti WGM in Braggovih resonatorjev ter princip njihovega delovanja. WGM mikro laserji temeljijo na večkratnem popolnem odboju svetlobe znotraj resonatorja, ki je dielektrična sfera, katere lomni količnik je večji od lomnega količnika v okoliškem mediju. Braggovi mikro laserji se zaradi samo urejene periodične strukture obnašajo kot fotonski kristali s prepovedanim pasom za fotone. Svetloba se selektivno odbija na periodični strukturi v skladu z Braggovim zakonom.
V drugem delu smo natančno opisali materiale in postopke izdelave mikro laserjev ter eksperimentalne metode, ki smo jih uporabili. V tretjem delu so predstavljeni rezultati in diskusija. Demonstrirali smo lasersko delovanje WGM mikro laserja znotraj biološkega tkiva na globini . Testirali smo možnosti uporabe biokompatibilnih WGM mikro laserjev kot senzorjev spremembe lomnega količnika okoliškega medija in posledično koncentracije glukoze. Pri tem smo naleteli na težave in eksperimentalne omejitve, ki smo jih predstavili. Rezultati so dokaj obetavni, vendar bo potrebno razrešiti še nekaj eksperimentalnih problemov. Holesterične mikro laserje smo uporabili kot senzorje temperature. Izkazali so se kot zelo stabilen senzor temperature, saj so ti mikro laserji manj občutljivi na ostale zunanje dejavnike.In the past few years there has been an increasing number of studies focusing on biolasers, which are used in biological systems. Scattering and absorption of light inside tissues are two main problems of light detection. This is why lasers have many benefits compared to only fluorescencelaser light has high coherence, high intensity and narrow emission spectrum.
The main motivation of this master thesis was the study of potential applications of biocompatible microlasers as biosensors. Microlasers can be implanted in a biological tissue where we can measure physiological parameters such as concentration of glucose and temperature in real time. If we want to use microlasers inside a biological tissue, they must be made of biocompatible materials which are also biodegradable. Biocompatible material does not cause any immune reactions and allow body to function normally. At the same time it is important that lasers are sensitive enough to environmental changes in the range of physiological values.
We developed a procedure for production of microlasers from biocompatible and biodegradable materials which have already been used for medical applications. There are three main components of every laser system: optical resonator that confines light, gain medium and pumping system which provides an inverted population. We produced two different types of biocompatible microlasers regarding the principle of how it works. The first type is Whispering Gallery Mode (WGM) microlaser. It is made of a biocompatible polymer Poly(L-lactic acid) (PLLA), doped with a fluorescent dye. The second type of a microlaser is so called Bragg microlaser, made of a cholesteric liquid crystals which are cholesterol-derivatives, naturally presented in the body. They are also doped with a fluorescent dye. In the first part we present the characteristic of a classical laser, the main features of WGM and Bragg resonators and their principle of how they work. WGM microlasers are based on a multiple total internal reflections inside a resonator which is a dielectric sphere with a refractive index greater than the surrounding medium. If the circulating light circles the resonator with an integer number of wavelengths and returns to the same point, a constructive interference occurs. Bragg microlasers have self-assembled periodical structure which acts as a photonic crystal with a photonic band gap. Light is selectively reflected on a periodic structure in accordance with Bragg law. In the second part we describe in details materials and procedures for production of both kinds of microlasers and the used experimental methods. In the third part our results and discussion are shown. We demonstrated lasing of a WGM microlaser inside a biological tissue at a depth of approximately . We tested possibilities of using WGM microlasers as sensors of changing refractive index of the surrounding medium and consequently glucose concentration. We found many experimental limitations and problems which we discuss. We used Bragg microlasers as sensors of temperature. They are an accurate temperature sensor, mainly due to lower sensitivity to other external factors
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
Potential wood biomass for energy purposes in Slovenia
Get PDFSlovenija je ena najbolj gozdnatih držav v Evropinjena pokritost z gozdom je več kot 57 %. To zagotavlja velik potencial lesne biomase, ki bi ga lahko bolj učinkovito in v večjem obsegu izkoristili tudi v energetske namene. Les je pomembna surovina v lesno obdelovalni industriji, gradbeništvu, energetiki in celulozni industriji. Njegova poraba se že nekaj časa zmanjšuje, saj ga kot surovino, predvsem v energetiki in gradbeništvu, izpodrivajo drugi materialito pa ima negativen vpliv na okolje in družbo. Celovitejše izkoriščanje lesa iz naših gozdov bi imelo pozitiven vpliv tako v lesni obdelovalni industriji kot energetiki. Omogočilo bi večjo rast prihodka, odpiranje novih delovnih mest, zmanjševanje emisij toplogrednih plinov in večjo samooskrbo s toplotno energijo. V Sloveniji se les kot biomasa v energetske namene uporablja predvsem na podeželjuskupno pa se z lesom ogreva približno 30 % prebivalstva. V zadnjem obdobju se zaradi sodobnih tehnologij pridobivanja, predelave in rabe lesa, kot tudi zaradi sodobnih sistemov kurjenja z visokimi energijskimi izkoristki, opaza povečanje uporabe lesne biomase kot goriva.Slovenia is one of the most forested countries in Europe. More than 57 % of its surface is covered with forests, securing a large potential, which could be used more efficiently, and in greater extend also for energy purposes. Wood is an important raw material in wood industry, in civil engineering, in energy and cellulose industry. Wood usage has been reduced. As a raw material it has been superseded by other materials, especially in energy and civil engineeringthis having a bad influence for environment and society. Better exploitation of wood from our forests would have better influence on wood industry, as well on energy. It would enable to rise revenues, new employments, as well at reduce emission from greenhouse gases and bigger self-sufficiency with heat energy. In Slovenia, wood as biomass is used especially in the country30 % of population use it. In the last period, the interest to use wood biomass increased, especially because of contemporary technology of acquiring, processing and using wood, as well as because of contemporary systems of heating with good energy results
Variations on the Author
Get PDF“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
Get PDFWe 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
- …
