Graphs Encoded by Regular Expressions

In the conversion of finite automata to regular expressions, an exponential blowup in size can generally not be avoided. This is due to graph-structural properties of automata which cannot be directly encoded by regular expressions and cause the blowup combinatorially. In order to identify these structures, we generalize the class of arc-series-parallel digraphs to the acyclic case. The resulting digraphs are shown to be reversibly encoded by linear-sized regular expressions. We further derive a characterization of our new class by a finite set of forbidden minors and argue that these minors constitute the primitives causing the blowup in the conversion from automata to expressions

Radiografska analiza odnosa lateralnog interkondilarnog grebena s Blumensaatovom linijom i tangentom stražnjeg femoralnog kortikalisa

The aim of this study is to determine the radiographic position of the lateral intercondylar ridge (LIR) and its relationship with the Blumensaat line (BL) and the tangent to the posterior cortex (PCT) of the distal femur. On 35 femur specimens, the LIR was labeled by using a 1 gauge wire. A true lateral view with the distal femur was taken. On the taken plain radiographs, we measured angles that close between BL and LIR, PCT and LIR. We also measured the ratio in which LIR crosses the BL. The mean angle between BL and LIR was 70,130 (SD 12,690), and the mean angle that BL closes with PCT was 143,610 (SD 7,910). The point where LIR intersects the BL divides it in a 1:6 ratio. Using these radiological measurements will allow surgeons to quickly estimate the position of the LIR and also allow quick and convenient preoperative planning, intraoperative tunnel placement as well as postoperative analysis.Cilj ove studije je odrediti radiografski položaj lateralnog interkondilarnog grebena (LIR) u odnosu na Blumensaatovu liniju (BL) i tangentu stražnjeg kortikalisa (PCT) femura. Na 35 preparata femura lateralni interkondilarni greben označili smo bakrenom žicom debljine 1 mm. Na pravim postraničnim radiografskim snimkama femura odredili smo kut koji zatvaraju BL i LIR, te LIR i PCT. Također smo izračunali omjer u kojem LIR dijeli BL. Prosječni kut koji zatvaraju BL i LIR iznosi 70,130 (SD 12,690), a prosječan kut između BL i PCT 143,610 (SD 7,910). Točka u kojoj LIR sječe BL dijeli liniju u omjeru 1:6. Predloženom radiografskom metodom moguće je pouzdano odrediti položaj LIR-a što će omogućiti lakše planiranje zahvata, lakše i točnije postavljenje femoralnog tunela kao i poslijeoperacijsku analizu

Femoral Neck Anteversion: Values, Development, Measurement, Common Problems

The femoral neck anteversion angle is an important factor for hip stability and normal walking. It is multifactoral result of evolution, heredity, fetal development, intrauterine position, and mechanical forces. Abnormal FNA sometimes can be associated with many clinical problems ranging from harmless intoeing gait in the early childhood, to disabling osteoarthritis of the hip and the knee in the adults. In most cases is associated with minor functional problems in children during growth, but cause a concern in parents for children future. The child must be examined carefully and an accurate diagnosis must be established. The most important part of care is observation of the children. If abnormal femoral neck anteversion produces severe functional disability, derotational osteotomy should be done, but delayed until late childhoo

The Canal Fill Ratio as a Factor Influencing the Aseptic Loosening of the Müller-Type Cemented Stem – Preliminary Report

The Müller type cemented hip prosthesis, also called self-locking prosthesis, is one of the most extensively copied and utilized hip prostheses. Considering the implantation of the cemented stem, the author originally suggested achieving a press fit between the stem and endostal cortex by implanting a prosthesis of the largest possible size. Analyzing our group of patients who undergo aseptic stem revision, we try to quantify the term „press fit“ by measuring the filling of the femoral canal by the metal stem, the so-called canal-fill ratio. Our preliminary results suggest that press-fit is achieved when the stem occupies more than 90% of the canal diameter in the anterior-posterior projection

The role of context in Müller-Lyer illusion: The case of negative Müller-Lyer illusion

The Müller-Lyer illusion is one of the most prominent geometrical-optical illusions that have been the subjectof experimental investigation throughout a century. Like most optical illusions the Müller-Lyer illusion is causedby an appropriate context - inward or outward fins that act in a specific manner. These fins either prolong or shortenthe central line placed between the fins. In this study, we manipulated the context by varying the presentation ofthe illusion parts, which led to the negative effect of Müller-Lyer illusion. Here we disassociated the context, i.e.,the fins that create the illusion, from the lines the length of which needed to be assessed. Firstly, the fins were presentedalone for 10 seconds, than the line would appear alone for 100 ms. In such situations the phenomenon ofillusion emerges in an opposite direction: the line that temporally succeeded the inward fins seemed longer, whilethe line succeeding the outward fins seemed shorter. An experiment with three experimental situations was carriedout. Twenty participants took part in the experiment, in three different experimental situations. The size of the illusionwas measured using the method of constant stimuli, which was also used to determine the point of subjectiveequality. The analysis confirmed the described effect which was found to be significant when compared to two othersituations: the control situation and the standard Müller-Lyer illusion situation. The negative Müller-Lyer illusionis possibly caused by a kind of after effect, which occurred by prolonged gazing at the fins and/or by fatigue of theappropriate selective angle sensitive cells. Such findings implicate that angle sensitive cells might be active in theemergence of the standard Müller-Lyer illusion

Numeričko istraživanje efekata poroznih svojstava i debljine sloja na performance protonske izmjenjivačke membrane gorive ćelije

In this study, fluid flow and concentration distribution on the cathode side of a Proton Exchange Membrane Fuel Cell were numerically analyzed. The problem domain consists of a cathode gas flow channel, cathode gas diffusion layer and cathode catalyst layer. The governing equations, continuity, momentum and concentration equations were discritized by the control volume method and solved using a computer program based on SIMPLE algorithm. Simulations were made for different values of gas diffusion layer porosity, catalyst layer porosity and the ratio of the cathode gas diffusion layer thickness to the gas flow channel height. Using the results of these simulations, the effects of these parameters on flow, oxygen concentration and current density distribution were analyzed. It is observed that increasing the porosities of the gas diffusion layer and catalyst layer increases the current and power densities. The increase in the porosity of the gas diffusion layer also increases the oxygen concentration in both gas diffusion and catalyst layers but decreases the oxygen concentration in gas flow channel. Simulations also showed that increasing porosity of the catalyst layer increases the oxygen concentration in a catalyst layer but decreases the oxygen concentration in a gas flow channel and gas diffusion layer. It is also seen that the effect of the gas diffusion layer porosity is more dominant on cell performance compared to the catalyst layer porosity. The analysis of the effect of the ratio of the cathode gas diffusion layer thickness to the gas flow channel height on the cell performance showed that the increasing ratio of the cathode gas diffusion layer thickness to the gas flow channel height decreases the current and power densities. An analysis of the data obtained from simulations also shows that increasing the ratio of the cathode gas diffusion layer thickness to the gas flow channel height increases the oxygen concentration in the gas flow channel but decreases the oxygen concentration in both gas diffusion and catalyst layers.U ovom radu je numerički analizirano strujanje fluida i raspodjela koncentracije protonske izmjenjivačke membrane na katodnoj strani gorive ćelije. Problemska domena se sastoji od kanala katode kroz koji struji plin, difuznog sloja plina na strani katode kao i katodnog katalitičkog sloja. Generalne jednadžbe, jednadžbe kontinuiteta, jednadžbe količine gibanja i jednadžbe koncentracije su diskretizirane metodom kontrolnog volumena i riješene koristeći računarski program koji je baziran na algoritmu SIMPLE. Simulacije su napravljene za različite vrijednosti poroznosti difuzijskog sloja na strani plina, poroznosti katalitičkog sloja i omjera debljine difuzijskog sloja na strani plina i visine kanala kroz koji struji plin. Koristeći rezultate ovih simulacija, analizirani su efekti ovih parametara na strujanje, koncentraciju kisika i raspodjelu gustoće struje. Uočeno je da se s povećavanjem poroznosti difuzijskog sloja na strani plina i katalitičkog sloja, povećava se jakost struje i snage. Povećavanjem poroznosti difuzijskog sloja na strani plina, povećava se i koncentracija kisika i u difuzijskom sloju na strani plina i u katalitičkom sloju, ali se smanjuje koncentracija kisika u kanalu kroz koji struji plin. Simulacije su također pokazale da povećavanjem poroznosti u katalitičkom sloju povećavaju u njemu koncentraciju kisika, ali smanjuje se koncentracija kisika u kanalu strujanja plina kao i u difuzijskom sloju na strani plina. Također je uočeno da je efekt poroznosti u difuzijskom sloju na straniplina bitno utjecajniji na performanse gorive ćelije od poronosti kataltičkog sloja. Analiza efekta omjera debljine difuzijskog sloja na strani plina na katodi i visine kanala kroz koji struji plin na performance gorive ćelije je pokazala da se povećavanjem debljine difuzijskog sloja plina na katodi u odnosu na visinu kanala, smanjuje jakost struje i gustoću snage. Analiza podataka dobivena simulacijom također pokazuje da se povećavanjem omjera debljine difuzijskog sloja plina na strani katode prema visini kanala, povećava koncentraciju kisika u kanalu strujanja plina ali smanjuje koncentraciju kisiku i u dufuzijskom sloju plina i katalitičkom sloju

Numeričko istraživanje efekata poroznih svojstava i debljine sloja na performance protonske izmjenjivačke membrane gorive ćelije

In this study, fluid flow and concentration distribution on the cathode side of a Proton Exchange Membrane Fuel Cell were numerically analyzed. The problem domain consists of a cathode gas flow channel, cathode gas diffusion layer and cathode catalyst layer. The governing equations, continuity, momentum and concentration equations were discritized by the control volume method and solved using a computer program based on SIMPLE algorithm. Simulations were made for different values of gas diffusion layer porosity, catalyst layer porosity and the ratio of the cathode gas diffusion layer thickness to the gas flow channel height. Using the results of these simulations, the effects of these parameters on flow, oxygen concentration and current density distribution were analyzed. It is observed that increasing the porosities of the gas diffusion layer and catalyst layer increases the current and power densities. The increase in the porosity of the gas diffusion layer also increases the oxygen concentration in both gas diffusion and catalyst layers but decreases the oxygen concentration in gas flow channel. Simulations also showed that increasing porosity of the catalyst layer increases the oxygen concentration in a catalyst layer but decreases the oxygen concentration in a gas flow channel and gas diffusion layer. It is also seen that the effect of the gas diffusion layer porosity is more dominant on cell performance compared to the catalyst layer porosity. The analysis of the effect of the ratio of the cathode gas diffusion layer thickness to the gas flow channel height on the cell performance showed that the increasing ratio of the cathode gas diffusion layer thickness to the gas flow channel height decreases the current and power densities. An analysis of the data obtained from simulations also shows that increasing the ratio of the cathode gas diffusion layer thickness to the gas flow channel height increases the oxygen concentration in the gas flow channel but decreases the oxygen concentration in both gas diffusion and catalyst layers.U ovom radu je numerički analizirano strujanje fluida i raspodjela koncentracije protonske izmjenjivačke membrane na katodnoj strani gorive ćelije. Problemska domena se sastoji od kanala katode kroz koji struji plin, difuznog sloja plina na strani katode kao i katodnog katalitičkog sloja. Generalne jednadžbe, jednadžbe kontinuiteta, jednadžbe količine gibanja i jednadžbe koncentracije su diskretizirane metodom kontrolnog volumena i riješene koristeći računarski program koji je baziran na algoritmu SIMPLE. Simulacije su napravljene za različite vrijednosti poroznosti difuzijskog sloja na strani plina, poroznosti katalitičkog sloja i omjera debljine difuzijskog sloja na strani plina i visine kanala kroz koji struji plin. Koristeći rezultate ovih simulacija, analizirani su efekti ovih parametara na strujanje, koncentraciju kisika i raspodjelu gustoće struje. Uočeno je da se s povećavanjem poroznosti difuzijskog sloja na strani plina i katalitičkog sloja, povećava se jakost struje i snage. Povećavanjem poroznosti difuzijskog sloja na strani plina, povećava se i koncentracija kisika i u difuzijskom sloju na strani plina i u katalitičkom sloju, ali se smanjuje koncentracija kisika u kanalu kroz koji struji plin. Simulacije su također pokazale da povećavanjem poroznosti u katalitičkom sloju povećavaju u njemu koncentraciju kisika, ali smanjuje se koncentracija kisika u kanalu strujanja plina kao i u difuzijskom sloju na strani plina. Također je uočeno da je efekt poroznosti u difuzijskom sloju na straniplina bitno utjecajniji na performanse gorive ćelije od poronosti kataltičkog sloja. Analiza efekta omjera debljine difuzijskog sloja na strani plina na katodi i visine kanala kroz koji struji plin na performance gorive ćelije je pokazala da se povećavanjem debljine difuzijskog sloja plina na katodi u odnosu na visinu kanala, smanjuje jakost struje i gustoću snage. Analiza podataka dobivena simulacijom također pokazuje da se povećavanjem omjera debljine difuzijskog sloja plina na strani katode prema visini kanala, povećava koncentraciju kisika u kanalu strujanja plina ali smanjuje koncentraciju kisiku i u dufuzijskom sloju plina i katalitičkom sloju

Periprosthetic Infections after Total Hip and Knee Arthroplasty – A Review

Periprosthetic joint infections (PJI) in orthopedic surgery are considered to be very serious and dangerous complications of total joint arthroplasty. PJI becomes a long-lasting medical problem and a heavy burden on patient and his family. Patients with such a complication are a signifi cant fi nancial burden for the health care system. Recognizing this issue, investing in scientifi c research and simultaneously developing technologies in medicine are efforts taken to increase successfulness in preventing and treating PJI. Each year the number of total joint arthroplasties increases which entails a rise in the number of complications among which infections are the leading ones. Sometimes, in the worst case scenarios, infections can endanger patients’ lives. New procedural algorithms and new diagnostic possibilities help us make accurate and early diagnoses of postoperative PJI with a great degree of certainty. These diagnostic methods include laboratory tests, imaging, histopathology and microbiological analyses. Treatment options depend on many factors which include the onset of symptoms, patients’ general physical condition and type of pathogen. The approach to treating PJI is complex and it requires a multidisciplinary approach in order to ensure the most successful treatment possible. For adequate and successful treatment we need to take into account antibiotic therapy, one-stage or two-stage revision, Girdlestone operation, athrodesis and amputation. In this review we will try to sum up all relevant fi ndings and suggest further steps in management of PJI