The Role of Online Shopping in the Republic of Serbia During COVID‐19

This paper investigates the role of online shopping during severe COVID-19. The main aim is to see whether this virus and implemented measures of reducing the spread of contagion brought by the Government of the Republic of Serbia, resulted with changes in consumer behaviour. The data was collected from 408 respondents from the Republic of Serbia using an online questionnaire. The questionnaire lasted from 07th April until 04th May. Data were analysed using the Chi-Square test. Results of this study revealed that there is a significant association between purchasing online before and after the appearance of the COVID-19. Also, the authors conclude that there is no significant association between gender and the decision to purchase after the appearance of the COVID-19. The main three motives for online shopping in the period during COVID-19 were that too many stores are working only online, reducing health risk, and saving time. The most frequently online bought products by the respondents, were food (groceries), medicines and books (magazines, newspapers). The contribution of this paper, even though the analysed sample is not national representative, lays in the fact that there is almost none research of this topic in our country

Variable Neighborhood Search Approach for Solving Roman and Weak Roman Domination Problems on Graphs

In this paper Roman and weak Roman domination problems on graphs are considered. Given that both problems are NP hard, a new heuristic approach, based on a Variable Neighborhood Search (VNS), is presented. The presented algorithm is tested on instances known from the literature, with up to 600 vertices. The VNS approach is justified since it was able to achieve an optimal solution value on the majority of instances where the optimal solution value is known. Also, for the majority of instances where optimization solvers found a solution value but were unable to prove it to be optimal, the VNS algorithm achieves an even better solution value

Radioactive Contamination of the Soil: Assessments of Pollutants Mobility with Implication to Remediation Strategies

Accidental releases, nuclear weapons testing, and inadequate practices of radioactive waste disposal are the principal human activities responsible for radioactive contamination as a new and global form of soil degradation. Understanding the radionuclide distribution, mobility and bioavailability, as well as the changes caused by the variation of environmental conditions, is essential for soil rehabilitation. This chapter aims to highlight the importance of evaluating radionuclide distribution, for the selection of proper in situ or ex situ remediation strategy. Attention was focused onto remediation methods based on radioactive pollutants redistribution, for enhanced separation (chemical extraction) or containment (in situ immobilization). When the excavation and off-site leaching treatments are uneconomic, impractical, or unnecessary, in situ stabilization by the addition of appropriate reactive materials is an alternative approach. The optimization of factors in control of chemical leaching methods, selection of cost-effective immobilization agents, especially among suitable wastes and by-products, and verification of long-term effects of remediating actions are the major challenges for future investigation in this field. Furthermore, the improvement and standardization of the methods for radionuclide speciation are necessary to enable comparison between studies and monitoring of the effects achieved by the soil treatments

Trust between friends of different genders and sexual orientation in the context of adaptive reproductive behavior

Premda se čini kako je potreba za povjerljivim, toplim prijateljskim odnosom u današnjem, sve otuđenijem i manipulativnijem društvu potrebnija no ikada, evolucijski korijeni ove potrebe su jasni: optimalni interpersonalni odnosi našim precima bili su od izuzetne važnosti u preživljavanju i reprodukciji. Od svih „miješanih“ prijateljstava s obzirom na spol i seksualnu orijentaciju prijatelja, posebno su intrigantna ona između homoseksualaca i heteroseksualki te se čine najadaptivnijima za obje strane u kontekstu evolucijske psihologije, posebno kad ih se usporedi s ostalim prijateljskim dijadama. Naime, budući da su homoseksualci muškarci, ispunjavaju ženama potrebu za sigurnošću i zaštitom kao nježnijem spolu. Daju im informacije o muškom svijetu, a da pritom izostaju seksualne tenzije - koje takav odnos s hetero prijateljima kvare te s njima ostvaruju intiman, blizak i podržavajući odnos. Drugim riječima, zbog izostanka interspolnih i intraspolnih obmanjujućih strategija koje su prisutne u prijateljstvima žena s hetero prijateljima i prijateljicama, žene u takvom, seksualno nenabijenom odnosu, osjećaju veću dobronamjernost, tj. više vjeruju homoseksualcima. U online eksperimentu sudjelovale su sudionice isključivo heteroseksualne orijentacije, koje su s obzirom na spol i seksualnu orijentaciju Vanje, virtualnog prijatelja/ice razvrstane u tri nezavisne skupine - Vanja kao heteroseksualac (N=85), homoseksualac (N=74) ili heteroseksualka (N=92). Sve su sudionice procjenjivale dobronamjernost Vanjinih savjeta u dvjema ženama relevantnim domenama, udvaranje i akademska pitanja. Dobiveni rezultati pokazuju da žene općenito više vjeruju savjetima za udvaranje nego akademskim, neovisno o tipu prijatelja te da homoseksualcima više vjeruju nego hetero prijateljima/icama, glede udvaranja, što je očekivano, no homoseksualcima više vjeruju i glede akademskih savjeta, što nije u skladu s polaznom hipotezom. Sve navedeno je objašnjeno u kontekstu evolucijski adaptivnog ponašanja, uz dodatna pojašnjenja relativne popularnosti homoseksualaca kao savjetodavaca, čak i u neseksualnom kontekstu.Although the need for a confidential, warm friendships in today's increasingly alienated and manipulative society is needed, the evolutionary roots of this need are clear: the optimum interpersonal relationships in our ancestors lives were of outstanding importance in survival and reproduction. Of all the "mixed" friendships with regard to the sex and sexual orientation, those between homosexual men and heterosexual women are particularly intriguing and are the most adaptive for both sides in the context of evolutionary psychology, especially when they are compared with other friendship dyads. Namely, since homosexuals are men, they satisfy women's need for security and protection as a gentler sex, they are informative about the male world without sexual tensions. In other words, due to the lack of intersexual and intrasexual conciliating strategies that are present in the friendships of women with heterosexuals, women in this sexually uncharged relationship feel more benevolence and believe more homosexuals. The online experiment involved three independent groups of exclusively heterosexual women, with regard to gender and orientation of Vanja, virtual FB friends: Vanja as heterosexual male (N=85), homosexual male (N=74), heterosexual female (N=92). All participants were estimating benevolence of his mating / academic advices. The results indicate that women trust more in mating advices rather than academic, regardless of the friend, and homosexuals are more trusted, regardless of advice type. All these results are explained in the terms of evolutionary adaptive behavior, with additional explanations of relative popularity of homosexuals as advisors, even in nonsexual context

Модел за детекцију и анализу узрока кашњења на пројектима базиран на подацима издвојеним из неструктурираних извора

Прекорачење рокова на грађевинским пројектима представља глобални феномен који се истражује већ деценијама. Традиционални приступ детекцији и анализи узрока кашњења најчешће подразумева прикупљање искустава експерата везано за групе сродних пројеката (по врсти или географској локацији). Резултат таквог приступа је листа узрока кашњења хијерархијски поређана према њиховом значају. Таква емпиријска истраживања су неминовно обојена субјективизмом и пристрасношћу експерата и не доводе до утврђивања који су то базни узроци кашњења (root causes of delay) на нивоу појединачног пројекта. У циљу приказа наведених слабости традиционалног приступа, као и због стварања основе за дефинисање и каснију валидацију новог приступа, прикупљени су подаци са 75 пројеката путне инфраструктуре који су реализовани у Србији у периоду од 2004. до 2021. године и формирана је одговарајућа база података. Резултати истраживања и анализе података из базе указују да је преко 80% пројеката имало кашњење док је просечно прекорачење износило више од 90% уговореног трајања. На основу спроведене анкете кључних учесника на пројектима из базе, формирана је листа узрока која не одступа у односу на већину студија. При томе, добијене су ниске вредности Spearman-овог ранга корелације (0,204 - 0,565) између ставова различитих учесника, што потврђује значајно присуство субјективизма и пристрасности у спроведеним емпиријским истраживањима (анкетама). Главни циљ докторске дисертације је формирање новог модела за непристрасно откривање базних узрока кашњења на нивоу појединачног пројекта и његових физичких целина, применом машинског учења на неструктурираној текстуалној документацији са пројекта. Изабрани текстуални документи за развој модела су записници са састанака (Minutes of Meetings), зато што они садрже свеобухватне информације о кашњењима, настале у време настанка проблема и то са прецизном временском одредницом. Технике машинског учења, користећи Transformer језичке моделе, омогућавају аутоматску детекцију узрока кашњења. Фокусирано експертско знање се користи за додатно непристрасно обучавање модела за изабрани домен путне инфраструктуре, повезивањем делова текста са узроцима кашњења из претходно дефинисане листе. Препознате физичке целине путних инфраструктурних пројеката су: тунел, траса и мост. Комбинујући наведене елементе, у дисертацији је развијен аналитички Модел за детекцију и анализу узрока кашњења на грађевинским пројектима путне инфраструктуре, назван DREAM (Delay Root-causes Extraction and Analysis Model). У првој фази, DREAM аутоматски генерише листу детектованих узрока кашњења по пројектним целинама, засновану на учесталости њиховог viii појављивања у записницима са састанака. Резултати показују да је модел у стању да детектује узроке кашњења са задовољавајућим вредностима одзива (recall =0,69, за најучесталије узроке кашњења). У другој фази, DREAM, захваљујући временској компоненти записника, омогућава потпуно нову и јединствену функционалност - графичку презентацију временске дистрибуције узрока кашњења током пројекта. Квалитативном анализом информативних графикона који показују учесталост и интензитет појединачних узрока кашњења, стручњаци могу да разумеју природу проблема и открију базне узроке кашњења (root causes of delay), што је кључни циљ свих истраживања о кашњењима на грађевинским пројектима. Спроведено истраживање пружа научни и стручни допринос. Предложен је нов приступ идентификацији и анализи узрока кашњења, кроз развијен аналитички модел базиран на текстуалним подацима, машинском учењу и фокусираној употреби експертског знања. DREAM превазилази недостатке традиционалног приступа приликом формирања листе узрока кашњења, и омогућава откривање базних узрока кашњења применом јединствене функционалности – временске дистрибуције узрока кашњења. У стручном смислу, предложени модел пружа непристрасну помоћ при реконструкцији догађаја који су проузроковали кашњење на нивоу појединачног пројекта и његових целина, што доприноси смањењу спорова између уговорних страна и помажу приликом интелигентног доношења одлука на будућим пројектима

Influence of thermodynamic parameters on the synthesis of porous silicate materials and their functional application

Glavni cilj ove doktorske disertacije je sinteza poroznog aluminosilikatnog materijala za potencijalnu primenu u oblasti zaštite životne sredine. Aluminosilikatni materijali ekološki su prihvatljivi u smislu energetske efiksanosti i male potrošnje energije za sintezu. Sinteza ovakvih materijala podrazumeva i smanjenje proizvodnje gasova sa efektom staklene bašte, odnosno CO2. U prvom delu doktorske disertacije ispitivane su termodinamičke karakteristike homogenih rastvora alkalnih aktivatora na osnovu kojih se mogu tumačiti molekulske interakcije unutar rastvora. Ispraćena je promena termodinamičkih parametara (gustine, viskoznosti, indeksa refrakcije i brzine zvuka) u zavisnosti od temperature. Porozni silikatni materijali sintetisani su od polazne komponente (metakaolin-MK), alkalnog aktivatora koji se sastoji od rastvora NaOH različitih koncentracija (2M-16M NaOH) i natrijum silikata. Potencijalna primena usmerena je na ispitivanje adsorpcionih karakteristika ovih materijala za adsorpciju teških metala i ispitane su mehaničke osobine materijala radi potencijalne primene u građevinarstvu. Umrežena je i organska faza (poli(vinil-alkohol)-(PVA)) radi poboljšanja karakteristika sintetisanog materijala. Različitim metodama (rendgenska difrakciona analiza (XRD), Furijeova transformacija infracrvena spektroskopija (FTIR), Raman spektorskopija, Skenirajuća elektronska mikroskopija, (SEM)) analizirane su promene strukture sintetisanog materijala kao i morfologije čestica prahova prekursora i mikrostruktura sintetisanih uzoraka. Rendgenskom flurescentnom analizom (XRF) određen je hemijski sastav polaznih sirovina i sintetisanog materijala. XRD analizom i Raman spektroskopijom izvršena je identifikacija faza i praćenje veličina kristalita i udela amorfne faze u sintetisanom poroznom silikatnom materijalu. SEM metodom je ispitana morfologija čestica prahova prekursora, veličina i oblik pora sintetisanih poroznih materijala, a metodom energetske disperzione spektroskopije (EDS) utvrđen je sastav čestica prahova i faza kako prekursora, tako i sintetisanih materijala. Veličina čestica sintetisanih materijala praćena je laserskom metodom za određivanje veličine čestica. Određena je specifična površina i poroznost sintetisanog materijala pomoću BET metode. Ispraćen je proces polimerizacije alkalno-aktiviranog materijala (AAM) XRD i FTIR analizom. MALDI-TOF metodom potvrđeni su sintetisani polimerni materijali. Ispitana je i prirodna radioaktivnost materijala polazne sirovine, metafaze i polimernog materijala. Urađena je i termička analiza pomoću TGA/DTA metode. Takođe je urađena i karakterizacija termički tretiranih uzoraka kao i rendgenska fotoelektronska spektroskopija (XPS)The main goal of this doctoral dissertation is the synthesis of porous aluminosilicate materials for potential application in the field of environmental protection. Aluminosilicate materials are environmentally friendly in terms of energy efficiency and low energy consumption for synthesis. The synthesis of such materials implies a reduction in the production of greenhouse gases, i.e., CO2. In the first part of the doctoral dissertation, the thermodynamic characteristics of homogeneous solutions of alkaline activators were examined, on the basis of which molecular interactions within the solution can be interpreted. The change of thermodynamic parameters (density, viscosity, refractive index and speed of sound) depending on temperature was monitored. Porous silicate materials were synthesized from the starting component (metakaolin-MK), an alkaline activator consisting of a solution of NaOH of different concentrations (2M-16M NaOH) and sodium silicate. The potential application is aimed at testing the adsorption properties of these materials for adsorption of heavy metals and the mechanical properties of the materials for potential application in construction have been examined. The organic phase (Poly(vinyl alcohol) (PVA)) was also crosslinked to improve the characteristics of the synthesized material. Changes in the structure of the synthesized material as well as the morphology of the precursor powder particles and the microstructure of the synthesized samples were analyzed by various methods (X - ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, Scanning electron microscopy (SEM)). The chemical composition of the starting materials and the synthesized material was performed by X - ray fluorescence analysis (XRF). XRD and Raman spectroscopy identified the phases and monitored the crystallite size and the proportion of the amorphous phase in the synthesized porous silicate material. SEM examined the morphology of precursor powder particles, pore size and shape of synthesized porous materials, and the composition of powder particles and phases of both precursors and synthesized materials was determined by energy dispersion spectroscopy (EDS). The particle size of the synthesized materials was monitored by the laser method for determining the particle size. The specific surface area and porosity of the synthesized material were determined using the BET method. The polymerization process of alkali-activated material (AAM) was monitored by XRD and FTIR method. The synthesized polymeric materials were confirmed by the MALDI-TOF method. The natural radioactivity of the raw material, metaphase and polymeric material was also examined. Thermal analysis was performed using the TGA / DTA method. Characterization of thermally treated samples as well as X-ray photoelectron spectroscopy (XPS) was also performed

Investigation of mass transfer phenomenna during sorption of Cu (II)-ions onto inorganic sorbents

Predmet rada ove doktorske disertacije je bio ispitivanje sorpcije Cu (II)- jona sintetičkim HAP-om i prirodnim sorbentima zeolitom, glinom i dijatomitom, u cilju definisanja ravnoteže i kinetike procesa pri različitim uslovima. Fizičko-hemijska karakterizacija je pokazala da se sintetički HAP sastoji od čistog nestehiometrijskog, kalcijum deficitarnog, kalcijum-hidroksiapatita, zeolit od klinoptilolita, dok je glina kompozit ilita, kaolinita i montmorilonita. Glavna faza u dijatomitu je amorfni silicijum-dioksid. Takođe, HAP i zeolit su okarakterisani kao mezoporozni sorbenti specifičnih površina 58 m2/g i 23 m2/g, redom, dok su se glina i dijatomit pokazali neporozni, nižih specifičnih površina od 8 m2/g i 5 m2/g. Definisana je pHPZC koja iznosi 6,6 za HAP, glinu i dijatomit, dok je kod zeolita nešto viša i iznosi 7,5. Dobijene vrednosti pHPZC HAP-a, gline i zeolita su u dobroj saglasnosti sa literaturom, dok pHPZC dijatomita do sada nije objavljena. Ispitivanjem uticaja inicijalne pH vrednosti rastvora na ravnotežu, pokazano je da se finalne pH vrednosti razlikuju u zavisnosti od ispitivanog sorbenta. Generalno, ravnotežne pH vrednosti najviše rastu sa porastom inicijalnih pH rastvora u oblasti 2 - 4. Oblast platoa, u kome su finalne pH vrednosti nezavisne od inicijalnih i koja ukazuje na puferska svojstva sorbenata, zavisi od vrste sorbenta i koncentracije jona metala u rastvoru. Dalje povećanje polaznih pH prouzrokuje porast i finalnih. Krive zavisnosti sorbovane količine od inicijalnih pH su istog oblika kao i krive pH finalno-pH inicijalno, što se objašnjava povećanom rastvorljivoću sorbenata ili njihovih komponenti i kompeticijom Cu(II) i H+ jona u jako kiselim rastvorima. Porast finalnih pH iznad 6 dovodi do precipitacije bakar – hidroksida što rezultira 100% uklanjanjem jona metala iz rastvora. Maksimalni sorpcioni kapaciteti prema Cu(II)- jonima, na sobnoj temperaturi, opadaju u nizu: HAP (0,585 mmol/g) > zeolit (0,128 mmol/g) > glina (0,098 mmol/g) > dijatomit (0,047 mmol/g). U datim eksperimentima je utvrđen pad pH vrednosti rastvora u odnosu na početnu, što ukazuje na postojanje mehanizma specifične sorpcije, koji je najdominantniji tokom sorpcije na dijatomitu. Za vezivanje jona metala ispitivanim materijalima, odgovoran je i mehanizam jonske izmene, gde se Cu(II)- joni izmenjuju sa Ca2+ jonima sa površine HAP-a, odnosno sa jonima Na+, K+, Ca2+, Mg2+ sa površine prirodnih sorbenata. Stabilnost sistema sorbent/jon metala je ispitana u kiselom rastvoru za izluživanje i zavisi od vrste sorbenta, kao i prethodno sorbovane količine Cu(II)- jona. Sa porastom sorbovane količine na uzorcima HAP-a i dijatomejske zemlje, raste i procenat desorbovane količine, dok desorpcija sa zeolita i gline pokazuje suprotan trend - u kiseloj sredini su stabilniji uzorci sa većom sorbovanom količinom jona metala. Ako posmatramo desorbovanu količinu izraženu u mmol/g ili mg/g, ona je veća na uzorcima koji su više zasićeni, nezavisno od vrste sorbenta. Kinetika procesa je ispitana u različitim šaržnim sistemima. Prvi sistem su pojedinačne šarže sa mešanjem na horizontalnom šejkeru, gde je proces sorpcije ispitan u funkciji od početne koncentracije Cu(II)- jona na svim ispitanim sorbentima. Drugi šaržni sistem je sud sa mešalicom u kom je ispitana kinetika procesa sorpcije HAP-om i zeolitom u funkciji od koncentracije sorbata, mase sorbenta, brzine mešanja, a za zeolit i od granulacije sorbenta. Pokazano je da je sorpcija glinom i dijatomitom, kao neporoznim sorbentima, limitirana otporom u filmu fluida. Nasuprot tome, difuzija u filmu fluida tokom sorpcije na šejkeru HAP-om i zeolitom je značajna na početku procesa, tokom prvih 15 minuta. Vrednosti zapreminskog koeficijenta prenosa mase su izračunate Boyd-ovim modelom. Dobijene vrednosti kf·a su nezavisne od početne koncentracije Cu(II)- jona u rastvoru i variraju oko srednje vrednosti 0,046 1/min za HAP, 0,023 1/min za zeolit, 0,017 1/min za glinu i 0,031 1/min za dijatomit. Iz prethodno navedenog proizilazi da je kf·a kod neporoznih sorbenata funkcija veličine čestica, tj. najveći je za najsitnije čestice jer je i specifična površina veća. Primenom jednačina za difuziju u porama, pokazano je da efektivne difuzivnosti blago opadaju sa porastom c0 za sorpciju HAP-om, dok za sorpciju zeolitom Deff nije funkcija c0. Zavisnost Deff od c0 i nezavisnost kfa od c0 kod HAP-a može se objasniti suprotnostrujnom difuzijom odlazećih katjona sa površine sorbenta, kao i elektrostatičkim odbijanjem istoimenih naelektrisanja koji su zanemarljivi u masi fluida, ali se ne mogu zanemariti u unutrašnjosti pora. Analizom rezultata sorpcije HAP-om u sudu sa mešanjem, dobijeno je da kf·a za prvih 10 minuta procesa ne zavisi od mase sorbenta i brzine mešanja, a blago opada sa porastom početne koncentracije metala u rastvoru, što je najverovatnije uslovljeno postojanjem otpora difuzije u porama. Nasuprot tome, kf·a izračunat za zeolit ne zavisi od mase sorbenta, kao ni početne koncentracije, ali raste sa porastom brzine mešanja i padom veličine čestica sorbenta. Efektivne difuzivnosti i kod HAP-a i kod zeolita ne zavise od mase sorbenta, kao ni brzine mešanja. Deff opada sa porastom c0 usled postojanja suprotnostrujne difuzije u porama, a raste sa porastom veličine čestica. Kao krajnji zaključak, može se izvesti da je za procese sorpcije HAP-om i zeolitom na šejkeru u prvih 15 minuta limitirajući otpor u filmu fluida, a zatim difuzija u porama sorbenta, pri čemu se dešava sorpcija u mezoporama. Takođe, šejker ne obezbeđuje dovoljno efikasno mešanje, te su vrednosti kfa i Deff značajno niže od vrednosti dobijenih za sud sa mešanjem. Sorpcija HAP-om u sudu sa mešanjem je limitirana samo difuzijom u porama jer se difuzija u filmu fluida i zasićenje površine dešava skoro trenutno. Tokom sorpcije zeolitom u sudu sa mešanjem, prvih 10 minuta procesa značajan je otpor u filmu, a nakon toga otpor u porama sorbenta.The subject of the work presented in this dissertation was to investigate the sorption of Cu (II)- ions onto synthetic hydroxyapatite (HAP)-and natural sorbents: zeolite, clay and diatomite, in order to define process equilibrium and kinetics under different conditions. Physico-chemical characterization showed that synthetic HAP was consisted of pure non-stoichiometric, calcium deficient, calcium hydroxyapatite, zeolite of clinoptilolite, while clay was the composite of illite, kaolinite and montmorillonite. The main phase of diatomite was amorphous silicon dioxide. Also, HAP and zeolite were characterized as a mesoporous sorbents with specific surface areas of 58 m2 / g and 23 m2 / g, respectively, while the clay and diatomite were non-porous, with low specific surface areas of 8 m2/g and 5 m2 / g. pHPZC of 6.6 was defined for HAP, clay and diatomite, while higher value of 7.5 was obtained for zeolite. Obtained results for pHPZC for HAP, clay and zeolite are in good agrement with literature, while pHPZC of diatomite has not been published. The investigation of influence of initial solution pH in the range of 2 - 10 on equilibrium showed that the final pH values varied depending on the tested sorbent. In general, final pH values increased the most in pH range 2 – 4. Areas of the plateau, where the final pH values were independent on the initial pH indicating the buffering properties of sorbents, were dependent on the sorbent and the concentration of metal ions in solution. Further increase of initial pH caused increase of final pH values. The plots of sorbed amounts vs. initial pH were of the same shape as plots pH final vs. pH initial, which can be explained with higher solubility of sorbents and their components and competition between Cu(II) and H+ ions in the strong acidic media. The final pH increase above 6 caused copper hydroxide precipitation and 100 % removal of metal ions from solution. The maximal sorption capacities at room temperature decreased in the order: HAP (0,585 mmol/g) > zeolite (0,128 mmol/g) > clay (0,098 mmol/g) > diatomite (0,047 mmol/g). In these experiments pH drop was observed, signifying the existence of specific cation sorption mechanism which was the most dominant during the sorption onto diatomite. Also, ion-exchange mechanism between Cu(II)- ions and Ca2+ ions from HAP surface was responsible for metal bonding, as well as ion-exchange with Na+, K+, Ca2+, Mg2+ from surfaces of natural mineral sorbents. The stability of system sorbent/ metal was investigated in acidic leaching solution and it was dependant on sorbent type, as well as on the previously loaded amounts. With increase of loaded metal amounts onto HAP and diatomite, the percentages of desorption also increased, while the opposite was observed for desorption from zeolite and clay- the samples with higher loadings were more stable in the acidic media. The desorbed amounts expressed in mmol/g or mg/g were higher for the more saturated samples, independent of sorbent type. The process kinetics was investigated as a function of initial metal concentration in batch system, on horizontal shaker. It was shown that the sorption onto non-porous sorbents, clay and diatomite was limited with diffusion film resistance. Contrary, the film diffusion was significant only during the first 15 minutes of process onto HAP and zeolite. The values of volumetric mass transfer coefficient kf·a were calculated using Boyd model. The values of kf·a were independent on initial concentration, and varied around averaged value of: 0,046 1/min for HAP, 0,023 1/min for zeolite, 0,017 1/min for clay and 0,031 1/min for diatomite. According to this it can be concluded that kf·a was a function of particle size for nonporous sorbents, i.e. it was highest for the smallest particles because specific surface area was higher. The obtained values for kf·a decreased in the order: HAP>diatomite>zeolite>clay, but probably this order would be different if the zeolite particles were smaller, where value for kf·a onto zeolite would be higher. Using pore diffusion models, it was shown that the effective diffusivities slightly decreased with c0 increase, while for sorption onto zeolite Deff was independent on c0. Dependence of Deff on c0 and independence of kfa on c0 can be explained by counter diffusion of cations released from sorbent surface, as well as with electrostatic repulsion of positive charged particles. These phenomena can be neglected in the fluid mass, but not inside the pores. From the analysis of results obtained for sorption onto HAP in the agitated vessel, it was observed that kf·a calculated for the first 10 minutes of the process was independent on sorbent mass and agitation speed, but slightly decreased with initial metal concentration increase, which was probably caused by the existence of pore diffusion resistance. Contrary, kf·a calculated for zeolite was independent on metal concentration and sorbent mass, but increased with agitation speed increase and particle size decrease. Effective diffusivities for sorption onto HAP and zeolite were independent on sorbent mass and agitation speed. Deff decreased with c0 increase because of counter diffusion inside the pores, but increased with particle size increase. Finally, it can be concluded that for the first 15 minutes of the sorption onto HAP and zeolite using shaker, the limiting step was film diffusion, and after that the pore diffusion, where sorption occurred inside the mesopores. Also, the mixing using shaker was not good enough, thus the obtained values for kfa and Deff were significantly lower than the values obtained for the sorption in the agitated vessel. The sorption onto HAP in the agitated vessel was limited only by pore diffusion because the film diffusion and surface saturation occurred almost instantaneously. The sorption onto zeolite in agitated vessel was governed by film diffusion during the first 10 minutes, whereas after that by diffusion inside the pores

Impact of Corporate Social Responsibility on the Competitiveness of Multinational Corporations

AbstractCurrent development trends, at the global level, caused fundamental transformation in doing business in modern economy, and at the same time, set a request to change the dominant business strategies and policies by which companies achieve their goals. The liberalization of international trade and investment flows has contributed to the spread of the effects of technological progress and influenced development in many countries, but also raised a number of limitations in opportunities for achieving sustainable development. Decade of the nineties of the twentieth century can be characterized as a period of increasing pressure on the environment, the direct recipient of pollutants, resulting from the use of dirty manufacturing processes and production techniques, as well as the space through which manufactured products are distributed, used and postponed. The uncontrolled use of natural resources, especially non-renewable, has led to the endangerment of existential prerequisite for the maintenance of a healthy environment, as well as deterioration of environmental quality and escalating environmental problems on a global level.Under pressure from institutional factors, multinational corporations (MNCs), as motor of developments in the world economy, today pay more attention to the integration of the dimensions of sustainability in its own operations. Involving aspects of managing the impacts of corporate activities on social development and the environment is in the function of sustainable business. Development of key competences in the area of addressing social and environmental issues is a prerequisite of achieving and sustaining competitive advantage of MNCs in the modern market. In addition, long-term negligence of the non-financial aspects of the business can make multiple negative effects on the financial performance and the reduction of corporate reputation among key stakeholders, thereby reducing its competitive advantage.Great impact on the rise of social-economic consciousness of MNCs was made by a bulk of problems caused by negative consequences of their activities, which gave rise to boycott of consumers and other stakeholders. This resulted in the decrease of enterprise credibility, ruin of their reputation, built in years, and failure in competitiveness. An MNC management team has realized that un-responsible behavior towards environment could have a “boomerang effect” to it. On the other hand, responsible behavior of enterprises towards stakeholders, society, and environment could contribute to achievement of competitive advantage. For example, by ensuring good working conditions to employees, by instigation of non-discrimination, by respecting of human rights, and by offering a possibility of advancement, MNC become attractive for new employees, especially most talented people. By insuring transparency towards shareholders, and respect of their rights, by continuous reporting, and risk management, MNC become attractive for new investments. By offering quality, healthy, and safe products, and by performing promises about after-sale services, enterprises become attractive for consumers. Talented employees, substantial capital, and safe market are the key conditions for achieving MNC competitive advantage. Hence, it is obvious that social responsible behavior of MNC becomes important factor of their survival and success. By explaining the impact of corporate social responsibility on the competitiveness of MNCs, the aim of this paper is to highlight the importance of such practice for the competitiveness of MNCs

Influence of bentonite and zeolite on Cs+ and Co2+ cement matrix leaching phenomena

The probability of Cs+ and Co2+ ions retention by immobilization processes in the cement matrix was determinate as the subject of analyses: matrix design, water/cement ratio, and structure porosity. Comparison of experimental results was accomplished by Hespe standard leaching method. Diffusion and semi-empirical models were used for the assessment of the washing rate as a function of time. The higher value of cement matrix mechanical resistance corresponds to a lower value of Co2+ and Cs+ ions leaching. The Co2+ leaching level was more than two orders of magnitude less than the leaching level of Cs+. The influence of bentonite and zeolite on Co2+ leaching reduction was significantly smaller in comparison with Cs+, while zeolite had a higher Cs+ and Co2+ sorption ability than bentonite. Under static leaching conditions, the contribution of diffusion to the total transport of ions in the matrix porous medium was dominant. The contribution of matrix dissolution was insignificant concerning the dominant contribution of diffusion and surface washing. The semi-empirical model showed a better approximation of the Co2+ and Cs+ ions laboratory leaching process

Digital Competences Performance of Serbian Female Entrepreneurs

This paper aims to examine Serbian female entrepreneurs’ performance related to digital competences based on real-life scenario questions. The research was conducted on a sample of 114 female entrepreneurs. The method used for collecting data was an online survey (Google form). The survey questions were based on Digital Competence Framework (DigComp) focusing on the first two areas, “Information and data literacy” and “Communication and collaboration”. The results showed that the female entrepreneurs in Serbia achieved better performance (i.e., answered the questions correctly) in the area “Information and data literacy” especially in the segment “Browsing, searching, and filtering data, information and digital content”. On the other side, lower performance of Serbian female entrepreneurs was achieved in the area “Communication and collaboration”, where nine questions from thirteen were not answered correctly. Segments “Engaging in citizenship through digital technologies”, “Collaborating through digital technologies” and “Netiquette” were identified as the most problematic because there was no correct answer. The authors can conclude that skills incorporated in the segments of the second area need to be improved and boosted to be in line with market demands