Mreža bežičnih senzora za merenje vibracija na građevinskim objektima

Nedestruktivno praćenje stanja građevinskih objekata se bazira na merenju vibracija objekata pri dinamičkim ispitivanjima ili u toku njihove eksploatacije. U ovu svrhu se sve više koriste mreže bežičnih senzora (WSN) koje čine fleksibilan i jeftin merni sistem, jer nema razvlačenja kablova velikih dužina za povezivanje senzora. U ovom radu je ukratko prikazan sadašnji stepen razvoja i primene WSN i opisan je sistem za bežično merenje vibracija na objektima razvijen na Građevinskom fakultetu u Beogradu. Predstavljeni su struktura i karakteristike mernog sistema baziranog na elektronskim komponentama male potrošnje i originalnom softveru

SIMULTANEOUS MEASUREMENT OF OPTICAL AND DYNAMIC MECHANICAL PROPERTIES OF PLASTIC OPTICAL FIBERS

Dynamic mechanical analysis (DMA) is one of the most powerful tools to study the behavior of plastic and polymer composite materials and it is a potentially very useful tool to simulate behavior of plastic optic fibers (POF) in real appli¬cations. The possibility of simultaneous measurements of some optical proper¬ties during DMA would significantly upgrade investigations of POF alone or embedded in some materials. In this work, single cantilever DMA of the POFs that was done simultaneously with measuring the transmitted optical signal in¬tensity is described and discussed. In order to compare mechanical results of the same material for cylindrical and rectangular specimens, rectangular plates were prepared by melting POFs and the same kind of tests were performed. It is shown that changes of the optical signal intensity correspond to the changes of storage modulus of the POF during DMA, and the maximums in optical sig¬nals intensity indicate the beginning of glass transition processes in the POF materia

Comparison between Carotid Artery Wall Thickness Measured by Multidetector Row Computed Tomography Angiography and Intimae-Media Thickness Measured by Sonography

The increased thickness of the carotid wall >1 mm is a significant predictor of coronary and cerebrovascular diseases. The purpose of our study was to assess the agreement between multidetector row computed tomography angiography (MDCTA) in measuring carotid artery wall thickness (CAWT) and color Doppler ultrasound (CD-US) in measuring intimae-media thickness (IMT). Eighty-nine patients (aged 35–81) were prospectively analyzed using a 64-detector MDCTA and a CD-US scanner. Continuous data were described as the mean value ± standard deviation, and were compared using the Mann–Whitney U test. A p value <0.05 was considered significant. Bland–Altman statistics were employed to measure the agreement between MDCTA and CD-US. CAWT ranged from 0.62 to 1.60 mm, with a mean value of 1.09 mm. IMT ranged from 0.60 to 1.55 mm, with a mean value of 1.06 mm. We observed an excellent agreement between CD-US and MDCTA in the evaluation of the common carotid artery thickness, with a bias between methods of 0.029 mm (which is a highly statistically important difference of absolute values [t = 43.289; p < 0.01] obtained by paired T test), and limits of agreement from 0.04 to 0.104. Pearson correlation coefficient was 0.9997 (95% CI 0.9996–0.9998; p < 0.01). We conclude that there is an excellent correlation between CAWT and IMT measurements obtained with the MDCTA and CD-US

Ispitivanje vremenske sinhronizovanosti mernih signala snimljenih MEMS akcelerometrima

U radu je opisano ispitivanje sinhronizovanosti podataka koji su uzorkovani putem odvojenih MEMS akcelerometara. Korišćeni su bežični senzorski uređaji razvijeni na Građevinskom fakultetu u Beogradu, namenjeni merenju vibracija građevinskih objekata. Poznato je da ovi uređaji mogu da postignu tačnost vremenskog označavanja uzoraka reda veličine10 μs za kraće merne periode (ispodminuta). Ovo znači da je greška koju elektronika unosi zanemarljiva za merenje mehaničkih veličina sa frekvencijom uzorkovanja reda veličine kHz. Analizirane su varijacije u fazi izlaznih signala različitih senzora prilikom identične pobude. Problem je ograničena mogućnost ostvarivanja identične mehaničke pobude na različitim mestima u prostoru, te je bez savršene opreme nemoguće razgraničiti koliki deo greške potiče od nepoklapanja ulaznih signala, a koliki od nesavršenosti senzorskog aparata. Pokazano je da je moguće dobiti standardnu devijaciju vremenskog ofseta između snimljenih signala reda veličine milisekunde

Passive and active shielding against electromagnetic radiation

In nuclear physics experiments, it is very important to isolate the measured quantities from electromagnetic noise. Without this possibility, it is impossible to obtain usable experimental results since natural electromagnetic noise can be several orders of magnitude larger than the measured magnitude. In order to enable such measurements, it is necessary to eliminate electromagnetic noise from the experimental procedure. This is achieved by shielding against electromagnetic radiation. In this paper, experiments were performed to protect a room from electromagnetic noise. By applying all known methods of shielding against electromagnetic radiation, it was concluded that the room can be protected from the electrical component, but it is impossible to protect it from the magnetic component of electromagnetic radiation

Impact of adverse childhood experiences on alcohol use in emerging adults in Montenegro and Romania

Aiming at generating evidence for formulating targeted and cost-effective public health interventions for the effective control of alcohol use (AU) in emerging adults in South Eastern Europe. The study's objective was to assess if alcohol users experience adverse childhood experiences (ACE) more often than non-users, and to identify which ACE victims are the most vulnerable to AU. The data was collected in 2010-2012 in two cross-sectional studies conducted in university settings in Montenegro and Romania (overall response rate 89.1%). In the present study, 3,283 students were included. The international ACE Study Questionnaires were used as a base for study instruments for collecting information on ACEs, health behaviours, and socio-economic factors. The association between AU and individual ACEs, adjusted to background factors, was assessed by using logistic regression. From the child maltreatment group, three ACEs were included in the final model as statistically significantly associated with AU, all of them from physical neglect/abuse types: frequently being hit so hard to have marks or being injured (OR=1.68; p=0.012), frequently being spanked (OR=1.38; p=0.012), and frequently having no person to take to the doctor if necessary (OR=0.58; p=0.031). From the household dysfunction group, two ACEs were included in the final model: exposure to mental health problems in the household (OR=2.85; p<0.001), and living with a problematic drinker/alcoholic (OR=1.51; p=0.019). The effect of exposure to ACEs on AU persists into emerging adulthood. This should be considered when developing cost-effective response to AU burden through targeted interventions, in particular in settings with scarce resources

Identification of adverse childhood experiences strongly predicting suicidal behaviour among emerging adults in Montenegro and Romania: A new way to targeted cost-effective prevention

Introduction. Aiming at generating evidence for cost-effective public health (PH) interventions for suicidal behaviour (SB) prevention in South Eastern Europe, the objective was to identify adverse childhood experiences (ACEs) most strongly predicting SB in emerging adults. Methods. Survey data of 3283 students aged 18-29 from Montenegro and Romania were analysed by logistic regression. Based on estimation of risk-for-SB, the profiles with the highest values were identified. Results. The SB odds were the highest in respondents, experienced a suicide attempt in the household (OR: 13.81; p < 0.001), and whose primary family was not complete, in particular in those with the foster family background (OR: 18.30; p = 0.001). Conclusions. Magnitude of impact on emerging adults' mental health vulnerability tends to vary considerably with individual ACEs. This should be considered carefully when developing cost-effective response to SB burden through PH interventions in particular at the times of financial crises and in scarce resources settings

Fiberoptički i grafitni senzori za detektovanje pukotina u betonu

Praćenje pojave i prostiranja pukotina u betonu ima veliki značaj u građevinarstvu. U našoj laboratoriji su razvijene dve vrste senzora za detekciju pukotina, fiberoptički i grafitni. Da bi se ispitale mogućnosti njihovog korišćenja sa jedne strane i uporedile teorijski dobijene vrednosti parametara mehanike loma u betonu sa druge, ovi senzori su ugrađeni u osam betonskih greda. Grede su izlagane povišenom opterećenju i praćen je način nastajanja i prostiranja pukotina. U ovom radu su opisane karakteristike razvijenih senzora, kao i kompletan merni sistem koji je korišćen za detekciju pukotina u gredama i rezultati su analizirani

Jedan metod za merenje i akviziciju relativne vlažnosti vazduha od značaja za građevinsku struku

Prilikom projektovanja građevinskih objekata različite namene, kao i projektovanja termičkih i klima uređaja, sa aspekta uštede energije i ugodnog osećaja boravka ljudi, posebnu pažnju treba obratiti na neke parametre vazduha, a naročito na vrednosti temperature i vlažnosti vazduha. U tom cilju, u okviru ovog rada opisan je uređaj koji je razvijen za merenje relativne vlažnosti vazduha sa kapacitivnim senzorom, ugrađenim u astabilnom multivibratorskom mostu. Preko AD/DA kartice, personalnog računara i posebno razvijenog softvera, moguće je u realnom vremenu registrovati izlazni signal srazmeran relativnoj vlažnosti vazduha