Analysis of heat losses of operated heat exchangers

Předložená bakalářská práce se zabývá výpočtem a analýzou tepelných ztrát provozovaných výměníků tepla používaných pro potravinářské aplikace. V úvodní části práce je představena problematika tepelných výměníků, jejich využití a členění podle základních kritérií, a také problematika jejich izolace, která je doplněna o výčet nejčastěji používaných druhů tepelné izolace. V druhé části práce je představeno zadání a popis řešeného průmyslového případu a je zde prezentována rovněž poskytnutá výkresová dokumentace a naměřená vstupní data nezbytná pro výpočet tepelných ztrát. V poslední části práce je představen použitý postup stanovení ztrátového tepelného toku výměníkové konstrukce, dosažené výsledky a jejich diskuse.The proposed bachelor’s thesis deals with calculation and analysis of heat losses of operated heat exchangers used for food applications. In the first part of the thesis, general problematics of heat exchangers is introduced, including their use and breakdown by basic categories, as well as problematics of insulation, which is supplemented by a list of the most commonly used types of insulation. Another chapter is devoted both to the assignment and description of the industrial case; drawing documentation and measured input data necessary for the calculation of heat losses are also presented. The last part of the thesis introduces the used method of assessment of heat losses of the heat exchanger network, achieved results and their discussion.

Voltammetric determination of cholecalciferol at glassy carbon electrode performed in water ethanol mixture

To confirm or disprove previous hypotheses, cyclic voltammetry of 0.5 mM cholecalciferol (vitamin D3) at glassy carbon electrode (GCE) and platinum disk electrode (PtE) in pure acetonitrile and water‑ethanol mixture at 50 mV·s‑1 has been used to investigate the oxidation mechanism. The oxidation occurs in two one-electrone steps. According to calculation of the highest electron density in cholecalciferol molecule which is evidently delocalized over carbon atoms of the three conjugated double bonds (C19, C10, C5-C8) points to part of the molecule involved in oxidation processes. An oxidation peak (at +0.925 V vs. Ag/AgCl) was used to develop direct voltammetric method based on differential pulse voltammetry for the vitamin D3 determination at GCE performed in 40% ethanol containing 0.1 M LiClO4. Under optimization of analytical procedure, it was found that a composition of the supporting electrolyte used significantly affects a current response of oxidation peak obtained. Satisfactory sensitivity was achieved in the 1:1 water‑ethanol mixture containing 0.05 M lithium perchlorate as as supporting electrolyte. The linear range for vitamin D3 determination was2.4 × 10-6 - 3.5 × 10-4 M with the detection limit of 8.0 × 10-7 M. This work demonstrates a fact that the GCE is suitable electroanalytical device for analysis of various food supplements and medicaments

Electrochemical Study and Determination of All-trans-Retinol at Carbon Paste Electrode Modified by a Surfactant

U radu je cikličkom voltametrijom istražen mehanizam oksidacije trans-retinola (vitamina A1) i nekoliko njegovih estera u organskom otapalu, miješanoj otopini voda/organsko otapalo i vodenoj otopini. Proces oksidacije odvijao se u nekoliko ireverzibilnih koraka. Najveća gustoća elektrona u retinoidnoj molekuli delokaliziranih oko ugljikovih atoma vezanih s pet konjugiranih dvostrukih veza (C5-C14) pronađena je u dijelu molekule koji sudjeluje u oksidaciji. Najviši oksidacijski pik (na +0.8 V prema Ag/AgCl elektrodi) korišten je za određivanje retinola diferencijalnom pulsnom voltametrijom pomoću elektrode od ugljikove paste modificirane površinski aktivnom tvari (natrijev dodecil-sulfat). Rezultati pokazuju da je s dodatkom 30 % (po masi) natrijeva dodecil-sulfata dobivena optimalna osjetljivost elektrode i optimalan oblik voltamograma. U usporedbi s uobičajenom elektrodom od staklastog ugljika, elektroda od ugljikove paste modificirane pomoću natrijeva dodecil-sulfata bitno je pospješila elektroanalizu retinola. Linearan odziv modificirane elektrode od ugljikove paste bio je u rasponu od 1,5·10^−6–1,8·10^−4 M retinola s limitom detekcije 1,3·10^−6 M, dok je elektroda od staklastog ugljika imala linearni raspon 4,4·10^−6–7,0·10^−4 M i limit detekcije 4,6·10^−7 M.The oxidation mechanism of all-trans-retinol (vitamin A1) and its several esters in non-aqueous, aqueous organic mixture, and pure aqueous media was investigated by cyclic voltammetry. The oxidation occurred in several irreversible steps. The calculated highest density of electrons in retinoid molecules which are delocalized over carbon atoms of the five conjugated double bonds (C5-C14) was found in the part of the molecule involved in oxidation processes. The most sensitive oxidation peak (at +0.8 V vs. Ag/AgCl) was used for development of new direct voltammetric method based on differential pulse voltammetry for the determination of retinol at carbon paste electrode modified with surfactant sodium dodecyl sulfate (CPE/SDS). The results show that 30 % (by mass) of modifier SDS exhibited optimal sensitivity and shape of voltammograms. Compared to commonly used glassy carbon electrode (GCE), the CPE/SDS showed significant progress in the retinol electroanalysis. The linear ranges for retinol determination were 1.5·10^−6–1.8·10^−4 M for CPE/SDS and 4.4·10^−6–7.0·10^−4 M for GCE with the detection limits of 1.3·10^−6 and 4.6·10^−7 M, respectively

Special Issue on Cryptology : Guest Editorial

This special issue brings selected papers from the 2019 Central European Conference on Cryptology, held in Telč, June 12-14, 2019

Application of the Enzymatic Electrochemical Biosensors for Monitoring Non-Competitive Inhibition of Enzyme Activity by Heavy Metals

The inhibition effect of the selected heavy metals (Ag+, Cd2+, Cu2+, and Hg2+) on glucose oxidase (GOx) enzyme from Aspergillus niger (EC 1.1.3.4.) was studied using a new amperometric biosensor with an electrochemical transducer based on a glassy carbon electrode (GCE) covered with a thin layer of multi-wall carbon nanotubes (MWCNTs) incorporated with ruthenium(IV) oxide as a redox mediator. Direct adsorption of multi-wall carbon nanotubes (MWCNTs) and subsequent covering with Nafion((R)) layer was used for immobilization of Gox. The analytical figures of merit of the developed glucose (Glc) biosensor are sufficient for determination of Glc in body fluids in clinical analysis. From all tested heavy metals, mercury(II) has the highest inhibition effect. However, it is necessary to remember that cadmium and silver ions also significantly inhibit the catalytic activity of Gox. Therefore, the development of Gox biosensors for selective indirect determination of each heavy metal still represents a challenge in the field of bioelectroanalysis. It can be concluded that amperometric biosensors, differing in the utilized enzyme, could find their application in the toxicity studies of various poisons

Bis(2,2-bipyridil)Copper(II) Chloride Complex: Tyrosinase Biomimetic Catalyst or Redox Mediator?

In this article, construction of amperometric sensor(s) based on screen-printed carbon electrodes covered by thin layers of two types of carbon nanomaterials serving as amplifiers, and containing [Cu(bipy)(2)Cl]Cl center dot 5H(2)O complex is reported. Their performance and biomimetic activity towards two selected neurotransmitters (dopamine and serotonin) was studied mainly using flow injection analysis (FIA). The important parameters of FIA such as working potential, flow rate, and pH were optimized. The mechanism of the catalytic activity is explained and experimentally confirmed. It reveals that presence of hydrogen peroxide plays a crucial role which leads to answer the title question: can presented complex really be considered as a tyrosinase biomimetic catalyst or only as a redox mediator

Determination of trolox equivalent antioxidant capacity in berries using amperometric tyrosinase biosensor based on multi-walled carbon nanotubes

In this contribution, Trolox equivalent antioxidant capacity (TEAC) was determined in various berries using carbon paste tyrosinase biosensor with multi-walled carbon nanotubes (MWCNTs), coated with Nafion((R)) layer. Electrochemical behaviour of the biosensor and influence of MWCNTs on carbon paste surface were studied with respect to the sensitive amperometric detection of total content of phenolic compounds in berries, expressed as concentration equivalent of Trolox. After optimization of key instrumental and electroanalytical parameters, the biosensor was used for determination of TEAC in blackberries, blueberries, cranberries, raspberries and strawberries by method of multiple standard additions. Electrochemical TEAC assays corresponded well with results obtained by spectrophotometric 1,1-diphenyl-2-picrylhydrazyl radical method, known as DPPH assay. Obtained values were compared with those listed in the National Nutrient Database for additional antioxidant capacity assays as well

Extensive profiling of three varieties of Opuntia spp. fruit for innovative food ingredients

[EN] Consumer interest in the use of natural ingredients is creating a growing trend in the food industry, leading to research into the development of natural products such as colorants, antimicrobials and antioxidant compounds. This work involves an extensive morphological (using physico-chemical assays), chemical (antioxidant activity assays) and microbiological (Gram-positive and negative strains) characterization of prickly peras (Opuntia ficusindica (OFI) var. sanguigna, gialla and Opuntia engelmannii) fruits. Through chromatographic assays, these species have shown interesting contents of hydrophilic (sugars, organic acids and betalains) and lipophilic (tocopherols and fatty acids) compounds. While Opuntia engelmannii exhibited higher content of betacyanins and mucilage, OFI varieties sanguigna and gialla displayed greater organic acid content. The sanguigna variety also showed the highest ¿-tocopherol content. All this compounds could be the responsible of enhancing the bioactivity of this variety, which can be observed in its antimicrobial potential, tested in the studied strains too. Results revealed that Opuntia spp. could be used as a nutraceutical and/or food additive, maintaining and promoting health and life quality.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2013) and L. Barros contract. This work is funded by the European Structural and Investment Funds (FEEI) through the Regional Operational Program North 2020, within the scope of Project NORTE-01-0145-FEDER-023289 (DeCodE) and ValorNatural (R). B. Melgar (No. 329930) also thanks CONACyT for his grant. The authors are grateful for a grant from the Serbian Ministry of Education, Sciences and Technological Development (no. 173032). The authors would also like to thank Dr. Carlos Aguiar for the botanical identification of these species.Melgar-Castañeda, B.; Pereira, E.; Oliveira, MBP.; Garcia-Castello, EM.; Rodríguez López, AD.; Sokovic, M.; Barros, L.... (2017). Extensive profiling of three varieties of Opuntia spp. fruit for innovative food ingredients. Food Research International. 101:259-265. https://doi.org/10.1016/j.foodres.2017.09.024S25926510

Emotional montage and its principles

Bakalářská práce se zabývá filmem dánského režiséra Larse von Triera "Prolomit vlny" dokončeného roku 1996. Koncentruje se na jeho velice nevšední a pokrokovou práci s filmovými výrazovými prostředky, především pak se střihovou skladbou. Práce definuje a podrobně vysvětluje tři hlavní principy tzv. "EMOCIONÁLNÍ MONTÁŽE": 1. PREFERUJ EMOCI, NE INFORMACI 2. NARUŠUJ KONTINUITU 3. DBEJ NA SVOJI INTUICI Tvůrci této teorie, která se vyznačuje především schopností kondenzovat emoci, jsou Lars von Trier a střihač filmu Anders Refn. Jejich přínos je dodnes aktuální a přispěl ke vzniku hnutí Dogme95. Pojem Emocionální montáž zavádí autor práce (tedy já), který celý film podrobuje osobní analýze