Mathematical modelling and experimental validation of electrostatic sensors for rotational speed measurement

Recent research has demonstrated that electrostatic sensors can be applied to the measurement of rotational speed with excellent repeatability and accuracy under a range of conditions. However, the sensing mechanism and fundamental characteristics of the electrostatic sensors are still largely unknown and hence the design of the sensors is not optimised for rotational speed measurement. This paper presents the mathematical modelling of strip electrostatic sensors for rotational speed measurement and associated experimental studies for the validation of the modelling results. In the modelling, an ideal point charge on the surface of the rotating object is regarded as an impulse input to the sensing system. The fundamental characteristics of the sensor, including spatial sensitivity, spatial filtering length and signal bandwidth, are quantified from the developed model. The effects of the geometric dimensions of the electrode, the distance between the electrode and the rotor surface and the rotational speed being measured on the performance of the sensor are analyzed. A close agreement between the modelling results and experimental measurements has been observed under a range of conditions. Optimal design of the electrostatic sensor for a given rotor size is suggested and discussed in accordance with the modelling and experimental results

The use of plants, including trees, to remediate oil-contaminated soils : a review and empirical study

Soil contamination can result in soil degradation, bring great loss to agricultural production and pose threat to human health. Many of the soil contaminants are petroleum hydrocarbons (PHCs) derived from crude oil or refined petroleum products. Phytoremediation which relies on plants and their associated microorganisms to remove contaminants is cost-effective and applicable to treat a wide variety of soil contaminants. Besides trees, herbaceous plants are widely and effectively used in the remediation of PHC contaminated soils. Greenhouse studies have found that Galega orientalis co-inoculated with Rhizobium galegae and plant growth promoting bacteria (PGPB) benefiting soil with nitrogen fixation is able to remediate PHC contaminated soils. The FP7 ‘‘Legume-Futures’’ remediation field experiment was established at Viikki experimental farm, University of Helsinki in 2009 in order to test the practical applicability of the greenhouse results in a field scale. In a split-plot design, crop (Galega orientalis, Bromus inermis, Galega orientalis + Bromus inermis, bare soil control) treatments were designated the main factor, oil (±) and PGPB (±) the sub-factors in factorial combination with four replicates. Soil samples were taken at four time points from July 2009 to May 2011. Soil total solvent extractable material (TSEM) was extracted and measured by the gravimetrical method as a direct indicator of oil content. Physiochemical properties (pH, EC, total C and N and C/N ratio) of soil samples (taken in July 2009 and Nov. 2010) were determined. The losses of total C and TSEM between July 2009 and Nov. 2010 were calculated to estimate the differences crops and PGPB brought in oil treated plots. Crop dry matter yields were determined. The changes of soil microbial population, bacterial diversity and community structures were studied by the 16S rRNA gene based community fingerprinting method LH-PCR. Bioremediation and physical removal were the main processes of oil removal in our experiment. Climate factors (e.g. temperature and precipitation) had an overriding influence on the removal of oil in our study. Soil condition with a neutral pH and C/N ratio in our field was optimal for biodegradation of hydrocarbons. The changes in soil microbial total DNA, diversity and community structure were sensitive indicators of soil contamination and recovery. Crop (Galega orientalis and Bromus inermis) and PGPB treatment had no significant effect on soil physiochemical and microbiological properties nor on the removal of oil in our experiment, which largely differed from our hypothesis. Resource competition between crops and microorganisms might have resulted in the better oil remediation in bare soils than in vegetated soils. Nevertheless, crops were found to have a high tolerance to oil contamination and surprisingly, the oil contamination seemed to increase the growth of both crop species. Bromus in mixture plots (without commercial nitrogen fertilization) had better yield than in pure plots (with commercial nitrogen fertilization) as a result of biological nitrogen fixation of Galega orientalis and Rhizobium galegae. Therefore the mixture of galega and bromus can be suggested to be applied in future phytoremediation projects

Bacterial community dynamics and perennial crop growth in motor oil-contaminated soil in a boreal climate

Soil pollution by petroleum hydrocarbons (PHCs) as a result of anthropogenic activities poses significant threats in the environment. In particular, used motor oil that contains high concentrations of aliphatics, polycyclic aromatic hydrocarbons (PAHs) and heavy metals (e.g. lead, zinc, chromium, barium and arsenic) contribute to chronic hazards including carcinogenicity. Microorganisms are able to degrade and utilize many recalcitrant compounds as carbon and energy sources in a natural attenuation process. However, in boreal regions this process is limited by the cool climate. The main goal of most bioremediation designs should be an optimization of environmental conditions for microbial growth and metabolic activities. Plant growth can stimulate the activities of soil microflora in the rhizosphere, thus enhancing the bioremediation of oil-polluted soil. Nitrogen deficiency is a frequent limiting factor of biomediation in oil-contaminated soils. Legumes that form symbiotic association with N-fixing bacteria are able to assist the biodegradation of PHCs. The planting of oil-tolerant perennial crops, especially legumes, in oil-contaminated soil holds promise for great economic benefits for bioenergy production while accelerating the oil degradation process. Fodder galega (Galega orientalis Lam.), a perennial forage legume, and smooth brome (Bromus inermis L.), a cool-season perennial sod-forming grass, are both persistent in boreal zones and have been shown to grow well together in crop mixtures without N-fertilizer supply. The oil tolerance and oil-rhizoremediation potential of G. orientalis and its microsymbiont Neorhizobium galegae have been demonstrated at microcosm and mesocosm scales. Plant growth promoting bacteria (PGPB) have potential to increase nodulation of galega, mitigate plant stress response and increase the bioavailability of soil contaminants, therefore enhancing the degradation of contaminants. These components can form a powerful combination to be used for bioremediation of oil-contaminated soil. However, the competitiveness and effectiveness of the crop- and PGPB-assisted bioremediation system need to be evaluated in field conditions. To date, there were no systematically described studies on bioremediation of oil-contaminated soil combined with crop biomass production in boreal regions. This multidisciplinary research project was conducted to fill this knowledge gap by evaluating the sustainability of the legume-cropping bioremediation system economically in terms of crop yield, and environmentally in terms of oil degradation rate and the dynamics of bacterial communities. To reach these aims, we established a multi-year bioremediation field experiment at the Viikki Experimental Farm, University of Helsinki, Finland (60°14'N, 25°01'E, 8 m AMSL) with crop treatments (brome grass, fodder galega, their mixture and bare fallow) as the main plots in four replicated blocks, and used motor oil treatments (7000 ppm +/-) and PGPB (+/-) treatments as the sub-plot factors. Soil samples were taken from the top 20 cm layer at six time points (July 2009, May 2010, November 2010, May 2011, May 2012 and October 2012). Soil chemical properties e.g. pH, electrical conductivity (EC), total C, total N and C:N ratio of three sample sets (July 2009, November 2010 and May 2012) were measured. Oil concentration was determined based on the difference of total solvent extractable material (TSEM) concentration between the oil-spiked plot and the average of control plots at each sampling time using the gravimetrical method. Crop physiological properties e.g. annual DM yield, total C, total N, C: N ratio, chlorophyll and BNF of the legume were measured. Soil-borne bacterial communities were investigated using i) LH-PCR community fingerprinting technique (all samples) and ii) Illumina s MiSeq sequencing (spring-summer samples). Oil contamination had a significant impact on soil chemical properties, e.g. pH, EC, total C and C:N ratio. The oil degradation was incomplete 40 months after the oil spike, with a dissipation of 73% - 92% of oil concentration (Paper I). As the field soil condition was good for oil degradation, the advantage of using crops to assist oil degradation was not evident. The oil degradation followed firstorder kinetics with the reduction rates decreasing as follows: bare fallow > galega-brome grass mixture > brome grass > galega. Oil, surprisingly, increased crop dry matter and nitrogen yield, particularly in the fourth year (Paper I). The legume-grass mixture produced significantly higher crop dry biomass than the pure stands. For instance, the unfertilized galega-brome grass mixture out-yielded the Nfertilized pure grass swards over years by an average of 32% (Paper I), suggesting that the inoculated galega could fully replace N-fertilizer for brome grass. PGPB enhanced the efficiency of biological nitrogen fixation of the legume, especially in legume-grass mixture plots (Paper I). The LH-PCR community fingerprinting technique produced similar results as the 16S rRNA gene amplicon sequencing. Both time and oil contamination were the main drivers of bacterial community dynamics (Papers II and III). The effect of oil was initially negative on overall bacterial diversity (Papers II and III), but variable on the diversity of bacterial sub-communities (Paper III). The bacterial communities responded quickly to oil contamination, but the effect of oil on community composition was recoverable over time (Papers II and III). Crop cultivation had a small impact on the composition of bacterial community (Paper III). The oil-favored taxa that discriminated bacterial communities between oil-contaminated and non-contaminated soils were mainly assigned to the two prevalent phyla Actinobacteria and Proteobacteria (Paper III). The operational taxonomic units (OTUs) with significantly different oil-specific abundance changes over time were all favored by oil; therefore, these oil-specific taxa were suggested as suitable bio-indicators to monitor the ecological impact of oil contamination (Paper III). Besides oil concentration, the changes in soil chemical properties, e.g. soil pH and EC, significantly affected bacterial community structure (Paper II and III). To summarize, oil contamination affected soil chemical and biological properties (e.g. crop growth and bacterial community), but the impact of oil decreased with time. The cultivation of oil-tolerant perennial crops, especially galega-brome grass mixture, in oil-contaminated soil can hopefully produce considerable biomass for bioenergy industry. Bacterial communities underwent a significant time- and season-dependent succession, regardless of oil contamination. Therefore, studies restricted to a single snapshot of time without any non-contaminated samples as reference cannot reveal oil contaminationrelated changes in the dynamic patterns of bacterial communities in the field soil. With the development and decreasing cost of high-throughput sequencing (NGS), NGS-based metagenomics analysis has become the mainstream method in microbial ecology research, providing in-depth view on bacterial populations at different taxonomic levels in the community. However, the LH-PCR technique is still suggested as a cost-effective method to monitor microbial community dynamics for assessing the ecological impact of oil contamination. Oil degradation was rather slow in the boreal climate. Long-term stimulation and monitoring of soil chemical properties, oil concentration, crop growth and microbial community are still needed for risk control. All these suggestions can be applied to soil contaminated by PHC contaminants other than used motor oil, despite hydrocarbon compositional differences.Maaperän saastuminen öljyhiilivedyillä aiheuttaa vakavia ympäristöongelmia. Erityisesti moottoriöljyjäte aiheuttaa suuria riskejä, sillä se sisältää alifaattisten ja polyaromaattisten öljyhiilivetyjen lisäksi raskasmetalleja, kuten lyijyä, sinkkiä, kromia, bariumia ja arseenia. Maaperän mikrobit ovat tärkeässä roolissa öljyhiilivedyillä saastuneen maan ennallistamisessa. Bioremediaatiossa, mikrobien suorittamassa ennallistamisessa, mikrobit käyttävät öljyn vaikeasti hajoavia yhdisteitä hiilen ja energian lähteenä. Boreaalisella vyöhykkeellä, kuten esimerkiksi Suomessa, bioremediaatio on hidasta kylmän ilmaston vuoksi. Bioremediaatiossa pitäisi pyrkiä optimoimaan olosuhteita suotuisiksi mikrobien kasvulle ja metaboliselle aktiivisuudelle. Kasvit voivat edistää öljyllä saastuneen maan bioremediaatiota stimuloimalla maan mikrobien aktiivisuutta kasvien juuriston välittömässä läheisyydessä eli ritsosfäärissä. Typen puute rajoittaa usein bioremediaatiota. Palkokasvien symbioosi typpeä sitovien bakteerien eli ritsobien kanssa voi kohottaa maan typpipitoisuutta ja edistää öljyhiilivetyjen bioremediaatiota. Öljyä sietävien monivuotisten kasvien, erityisesti palkokasvien, käyttö bioremediaatiossa on lupaava menetelmä, missä saastuneen maan ennallistamista voidaan nopeuttaa ja samalla kasvattaa biomassaa bioenergian tuottoon. Boreaaliselle vyöhykkeelle sopivia monivuotisia kasveja ovat esimerkiksi palkokasvi rehuvuohenherne (Galega orientalis Lam.) ja heinäkasvi rehukattara (Bromus inermis L.). Rehuvuohenherneen ja sen ritsobisymbiontin Neorhizobium galegae öljynsietokykyä ja bioremediaatiopotentiaalia on tutkittu mikro- ja mesokosmeissa. Lisäksi kasvien kasvua edistävien bakteerien (PGPB) käyttö saattaa lisätä palkokasvien ritsobinystyröiden määrää, vaimentaa kasvien stressivasteita ja lisätä saasteyhdisteiden saatavuutta, mikä edistää yhdisteiden hajoamista. Kasvit ja bakteerit voivat muodostaa tehokkaan yhdistelmän öljyllä saastuneen bioremediaatioon. Kasvien ja bakteerien käyttöön perustuvan bioremediaatiomenetelmän kilpailukyky ja tehokkuus on arvioitava kenttäolosuhteissa. Ennen tätä työtä öljyllä saastuneen maan ennallistamista kasvien ja bakteerien avulla yhdistettynä biomassan tuottoon ei ollut tutkittu boreaalisella vyöhykkeellä. Tämän monitieteisen työn tavoitteena oli arvioida palko- ja heinäkasvien sekä bakteerien käyttöön perustuvan bioremediaatiomenetelmän kestävyyttä sekä taloudellisin (sadon määrä) että ympäristöllisin (öljyn hajotusnopeus, bakteeriyhteisöjen dynamiikka) kriteerein. Tavoitteen saavuttamiseksi Helsingin yliopiston Viikin koetilalle perusteettiin kenttäkoe, jossa oli neljä kasvikäsittelyä (rehukattara, rehuvuohenherne, edellisten sekaviljelmä ja avokesanto), kaksi öljykäsittelyä (0 ppm, 7000 ppm) ja PGPB-käsittely (+/-). Rehuvuohenherne ympättiin Neorhizobium galegae ritsobilla. Koekentältä otettiin maanäytteet kuutena ajankohtana (heinäkuu 2009-lokakuu 2012). Maasta määritettiin pH, sähkönjohtokyky, hiili- ja typpipitoisuus sekä öljypitoisuus. Kasveista määritettiin vuotuinen kuiva-ainesato, hiili- ja typpipitoisuus, lehtivihreäpitoisuus sekä biologisesti sidotun typen määrä. Bakteeriyhteisöjä tutkittiin käyttämällä sormenjälkitekniikkaa (LH-PCR) ja bakteerispesifisen markkerigeenin sekvensointia. Öljyllä saastuminen vaikutti merkitsevästi maan ominaisuuksiin. Neljäkymmentä kuukautta kokeen aloittamisen jälkeen öljystä oli hajonnut 73 - 92 % (Julkaisu 1). Kasvikäsittelyjen vaikutus öljyn hajoamisnopeuteen ei ollut merkitsevä. Yllättäen öljyllä saastuneessa maassa kasvien kuiva-ainesadot ja typpipitoisuus olivat suuremmat kuin saastumattomassa maassa (Julkaisu 1). Sekaviljelmien kuiva-ainesadot olivat suurimmat. Lannoittamattoman sekaviljelmän kuiva-ainesato oli keskimäärin 32 % suurempi kuin rehukattaran (Julkaisu 1), mistä voidaan päätellä, että ympätty rehuvuohenherne voi täysin korvata typpilannoitteen rehukattaran sekaviljelyssä. PGPB lisäsi biologisesti sidotun typen määrää (Julkaisu 1). Sekä LH-PCR- että sekvensointitulosten mukaan aika ja maan öljypitoisuus olivat merkittävimmät tekijät mikrobiyhteisöjen muutoksessa (Julkaisut II ja III). Myös maan pH ja sähkönjohtokyky selittivät osan bakteeriyhteisöjen muutoksesta (Julkaisut II ja III).Bakteeriyhteisöt reagoivat nopeasti öljykontaminaatioon, mutta toipuivat ajan myötä (Julkaisut II ja III). Öljykontaminaation jälkeen bakteeriyhteisön diversiteetti oli pienimmillään (Julkaisut II ja III), vaikkakin vaikutus eri alayhteisöihin oli vaihteleva (Julkaisu III). Kasvien vaikutus bakteeriyhteisöihin oli pieni (Julkaisu III). Actinobacteria ja Proteobacteria olivat kaikkein runsaimmat bakteeripääjaksot, ja erot saastuneen ja puhtaan maan bakteeriyhteisöissä näkyivät selvimmin näihin pääjaksoihin kuuluvissa bakteereissa (Julkaisu III). Kaikki bakteeritaksonit (OTU), joiden runsaus muuttui merkittävästi öljykontaminaation ja ajan funktiona, olivat runsaampia saastuneessa maassa; näiden taksonien voi olettaa olevan sopivia bioindikaattoreita, joiden avulla öljykontaminaation ekologisia vaikutuksia voi seurata (Julkaisu III). Lyhyesti sanottunat öljykontaminaatio vaikutti maan kemiallisiin ja biologisiin ominaisuuksiin, mutta kontaminaation vaikutus pieneni ajan myötä. Monivuotisten, öljyä sietävien kasvien kasvatus saastuneessa maassa tuotti biomassaa, jota voi käyttää bioenergian tuottoon. Bakteeriyhteisöt muuttuivat ajan ja vuodenajan mukaan sekä saastuneessa että puhtaassa maassa. Bakteeriyhteisöjä saastuneessa maassa tulisi seurata useana ajankohtana ja verrata puhtaan maan yhteisöihin, jotta kontaminaation aiheuttamat muutokset yhteisöissä saadaan selville. Sekvensointitekniikoiden kehityksen ja halpenemisen myötä sekvensointipohjaiset menetelmät ovat yleistyneet mikrobiekologiassa. Sekvensointimenetelmät mahdollistavat bakteeriyhteisöjen tarkan analyysin eri taksonomisilla tasoilla. Sormenjälkimenetelmä LH-PCR on silti suositeltava, kustannustehokas menetelmä, joka sopii yhteisöjen muutosten tiheään seurantaan. Öljyn hajoaminen boreaalisessa ilmastossa oli hidasta. Maan kemiallisten ominaisuuksien, öljyn pitoisuuden, kasvien kasvun ja bakteeriyhteisöjen pitkäaikainen seuranta ovat tarpeellisia saastumisen riskejä arvioidessa. Nämä suositukset soveltuvat moottoriöljyjätteellä saastuneen maan lisäksi muilla öljypohjaisten saastumisten arviointiin

Non-Contact Vibration Monitoring of Power Transmission Belts Through Electrostatic Sensing

On-line vibration monitoring plays an important role in the fault diagnosis and prognosis of industrial belt drive systems. This paper presents a novel measurement technique based on electrostatic sensing to monitor the transverse vibration of power transmission belts in an on-line, continuous, and non-contact manner. The measurement system works on the principle that variations in the distance between a strip-shaped electrode and the naturally electrified dielectric belt give rise to a fluctuating current output. The response of the sensor to a belt moving both axially and transversely is numerically calculated through finite-element modeling. Based on the sensing characteristics of the sensor, the transverse velocity of the belt is characterized through the spectral analysis of the sensor signal. Experiments were conducted on a two-pulley belt drive system to verify the validity of the sensing technique. The belt vibration at different axial speeds was measured and analyzed. The results show that the belt vibrates at well-separated modal frequencies that increase with the axial speed. A closer distance between the electrode and the belt makes higher order vibration modes identifiable, but also leads to severer signal distortion that produces higher order harmonics in the signal. On-line vibration monitoring plays an important role in the fault diagnosis and prognosis of industrial belt drive systems. This paper presents a novel measurement technique based on electrostatic sensing to monitor the transverse vibration of power transmission belts in an on-line, continuous, and non-contact manner. The measurement system works on the principle that variations in the distance between a strip-shaped electrode and the naturally electrified dielectric belt give rise to a fluctuating current output. The response of the sensor to a belt moving both axially and transversely is numerically calculated through finite-element modeling. Based on the sensing characteristics of the sensor, the transverse velocity of the belt is characterized through the spectral analysis of the sensor signal. Experiments were conducted on a two-pulley belt drive system to verify the validity of the sensing technique. The belt vibration at different axial speeds was measured and analyzed. The results show that the belt vibrates at well-separated modal frequencies that increase with the axial speed. A closer distance between the electrode and the belt makes higher order vibration modes identifiable, but also leads to severer signal distortion that produces higher order harmonics in the signal

SIFT Saliency Analysis for Matching Repetitive Structures

The ambiguity resulting from repetitive structures in a scene presents a major challenge for image matching. This paper proposes a matching method based on SIFT feature saliency analysis to achieve robust feature matching between images with repetitive structures. The feature saliency within the reference image is estimated by analyzing feature stability and dissimilarity via Monte-Carlo simulation. In the proposed method, feature matching is performed only within the region of interest to reduce the ambiguity caused by repetitive structures. The experimental results demonstrate the efficiency and robustness of the proposed method, especially in the presence of respective structures

Radial Vibration Measurement of Rotary Shafts through Electrostatic Sensing and Hilbert-Huang Transform

Radial vibration measurement of rotary shafts plays a significant part in condition monitoring and fault diagnosis of rotating machinery. This paper presents a novel method for radial vibration measurement through electrostatic sensing and HHT (Hilbert-Huang Transform) signal processing. The foundational characteristics of the electrostatic sensor in the vicinity of a drifting shaft are studied through Finite Element Modelling. Experimental tests were conducted on a purpose-built test rig to characterize the operating condition of the rotor at different rotational speeds (400 rpm and 600 rpm). A normal working shaft and an eccentric shaft were tested and the output signals from the electrostatic sensors were analyzed. Through empirical mode decomposition (EMD) on the electrostatic signals, the intrinsic mode functions (IMF) including the vibration information of the shaft are identified and further analyzed in the time-frequency domain. Experimental results suggest that the electrostatic sensing technique in conjunction with HHT provides a simple and cost-effective approach to radial vibration measurement of rotary shafts

Bacterial community changes in response to oil contamination and perennial crop cultivation

We investigated bacterial community dynamics in response to used motor oil contamination and perennial crop cultivation by 16S rRNA gene amplicon sequencing in a 4-year field study. Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, and Gemmatimonadetes were the major bacterial phyla, and Rhodococcus was the most abundant genus. Initially, oil contamination decreased the overall bacterial diversity. Actinobacteria, Betaproteobacteria, and Gammaproteobacteria were sensitive to oil contamination, exhibiting clear succession with time. However, bacterial communities changed over time, regardless of oil contamination and crop cultivation. The abundance difference of most OTUs between oil-contaminated and non-contaminated plots remained the same in later sampling years after the initial abundance difference induced by oil spike. The abundances of three oil-favored actinobacteria (Lysinimonas, Microbacteriaceae, and Marmoricola) and one betaproteobacterium (Aquabacterium) changed in different manner over time in oil-contaminated and non-contaminated soil. We propose that these taxa are potential bio-indicators for monitoring recovery from motor oil contamination in boreal soil. The effect of crop cultivation on bacterial communities became significant only after the crops achieved stable growth, likely associated with plant material decomposition by Bacteroidetes, Armatimonadetes and Fibrobacteres.Peer reviewe