2021, Vol. 19, Special Issue 1

Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/6909

Sirvi

Nüüd näidatakse 1 - 20 24

Use of principal component analysis to evaluate thermal properties and combustibility of coffee-pine wood briquettes
(2021) Mendoza Martinez, C.L.; Sermyagina, E.; Silva de Jesus, M.; Vakkilainen, E.
The coffee production chain is a potential source of residual biomass inherent to the high productivity that can contribute to the generation of value-added products. The residues from the coffee sector are typically disposed to landfill without treatment causing potential environmental inconveniences. Briquetting presents an alternative process to produce a uniform fuel with high energy density. Briquettes facilitates easy transportation, enables better handling and storage of biomass residues. Properties such as low equilibrium moisture content, high energy density and compressive strength were reported for different coffee-pine wood briquettes treatments. Moreover, understanding of the thermal properties of the briquettes during combustion is crucial to evaluate their final application. This research is the first study that investigates the combustibility properties and kinetic parameters of the thermal decomposition of briquettes from coffee-pine wood using differential and integral thermal analysis under non-isothermal conditions. Multivariate analysis of the collected parameters through principal components analysis (PCA), was implemented to reduce the dimensionality of the data. The desired profile in the combustibility is directly related to high temperatures and long burning times, thus, the tested briquettes displayed a significant combustibility potential, reporting peak temperatures and burnout times around 600 °C and 27 minutes, respectively. Activation energy kinetic parameter in the range of 12–42 kJ mol-1 and average reactivity of 0.14–0.22 min-1 , were also found. The results revealed the not thermally hard material to degrade when compared to biomasses typically used for combustion.
Improving ecological safety of agricultural off-road machines operating of sloped ground
(2021) Rédl, J.; Findura, P.
The goal of this article is the analysis of the specific technical properties of the agricultural machinery to prevent the ecological impacts on nature in case of a machine accident. The loss of stability and overturning of the machine is an important part of the farm safety code of practice document and the source of the ground contamination with fuel and no-bio lubricants. The main work is oriented to determine and derive the steps of prevention or prediction of dangerous states of the agricultural off-road vehicle operating on sloped ground and even applicable for heavy trucks. These steps are based on the experimental measurement of accelerations functions and implementing these into the mathematical model and following the European Union Regulations. The recommended simulation and obtained results can tell the engineers in the design process of the prototype how to accurate the technical parameters to keep the machine in a safe state while the machine is under acting the dynamic loads. Optimization of specific dimensions in the process of design can help to improve the ecological safety of the agricultural machines operating on sloped ground. Some theoretical methods are based on the Slovak National Standard STN 47 0170.
Carbon balance of biogas production from maize in Latvian conditions
(2021) Bumbiere, K.; Gancone, A.; Pubule, J.; Blumberga, D.
Production of biogas using bioresources of agricultural origin plays an important role in Europe’s energy transition to sustainability. However, many substrates have been denounced in the last years as a result of differences of opinion on its impact on the environment, while finding new resources for renewable energy is a global issue. The aim of the study is to use a carbon balance method to evaluate the real impact on the atmosphere by carrying out a carbon balance to objectively quantify naturally or anthropogenically added or removed carbon dioxide from the atmosphere. This study uses Latvian data to determine the environmental impact of biogas production depending on the choice of substrate, in this case from specially grown maize silage. GHG emissions from specially grown maize use and cultivation (including the use of diesel fuel, crop residue and nitrogen fertilizer incorporation, photosynthesis), biogas production leaks, as well as digestate emissions (including digestate emissions and also saved nitrogen emissions by the use of digestate) are taken into account when compiling the carbon balance of maize. The results showed that biogas production from specially grown maize can save 1.86 kgCO2eq emissions per 1 m3 of produced biogas.
Prospect on agro-industrial residues usage for biobutanol production
(2021) Raita, S.; Spalvins, K.; Blumberga, D.
Climate changes, environmental pollution and resource depletion are one of the numerous major problems humanity faces. United Nations sustainable development goals are aimed at solving these problems. The requirement for affordable, renewable, sustainable, biodegradable and environmentally friendly fossil fuel alternative sources is prompted by the development and advancement of biofuel production technologies. Of the various biofuel alternatives, biobutanol has increased the interests of researchers due to its desirable characteristics such as hydrophobicity, relatively high heating value and energy density, relatively low vapour pressure, etc. Nowadays, sustainable production of the biobutanol depends on the used feedstock source and its pre-treatment method, selected enhancing microorganism strain, acetone–butanol–ethanol fermentation effectiveness and titer of biobutanol. The main research challenges in biobutanol production are an improvement of production efficiency and increasing the financial viability of the technology. This review summarizes the latest results of lignocellulosic components content and fermentable sugars composition in different agro-industrial residues; biobutanol production depending on the Clostridium enhancing strategy, process optimization and selection of substrate. Such analysis provides a better perception of the capability of using agro-industrial residues for biobutanol production efficiency.
Packing materials for biotrickling filters used in biogas upgrading – biomethanation
(2021) Kusnere, Z.; Spalvins, K.; Blumberga, D.; Veidenbergs, I.
One of the promising methods of biogas upgrading is biological methanation (biomethanation). During biomethanation process hydrogenotrophic microorganisms use carbon dioxide from biogas and added hydrogen to generate biomethane. Application of biotrickling filter reactors is one of the prospective biotechnologies for methanation where hydrogenotrophic methanogens are immobilized over a material that is used in reactor. Packing materials for biomethanation are critical in terms of hydrogenotrophic methanogens immobilization on the surface of packing material. It acts as support for biofilm growth. Therefore, characteristics of filter material are important parameters that influence the growth of microorganisms and methane production. Factors, such as optimal specific surface area and porosity are important to sustain growth and activity of microorganisms. Optimal particle size and capability to mechanically resist compaction ensures avoiding high pressure drop. Optimal particle size also ensures uniform gas flow as gases distribute through the packing material. This review paper summarizes and compare the characteristics of different packing materials important for biomethanation through ex-situ biotrickling filter reactor systems.
Comparison of physical composition of municipal solid waste in Czech municipalities and their potential in separation
(2021) Zhao, S.; Altmann, V.; Richterova, L.; Vitkova, V.
Czech Republic has been moving from landfill-based waste system toward resourcebased waste management system with an increasing rate of recyclable waste in the last years (38.6% of recycling by material and 11.7% of energy recovery in 2018). However, landfill is still a popular way of mixed municipal solid waste (MMSW) disposal due to the low tax. In the Czech Republic, MMSW is collected from households by door-to-door system or recovery operations (Household Waste Recycling Centre) and only should consists of everyday items, which are further non-recyclable and non-reusable. However, a significant amount of recyclable waste can still be found in MMSW. Therefore, a good knowledge of the physical composition of MMSW is required to define strategy plans and improve waste management in municipalities. This work is aimed at comparing the physical composition of MMSW in the Czech Republic with small municipalities up to 2,999 inhabitants and big municipalities from 3,000 inhabitants to recognize the share of recyclable and non-recyclable waste in MSW and designate the potential of separation at source. Composition of MMSW was determined by a physical evaluation of waste collected from households in target municipalities which consists in a detailed manual sorting of waste into 13 specific groups according to their types, and weighting by a scale. We found that the real proportion of MMSW that could no longer be reused or recycled was much less than the amount disposed of in the municipal waste bins. A large part of MMSW consisted of organic waste together with food waste. This type of waste is especially useful when people turn it into compost to prevent the production of waste and it returns the nutrients back to the soil, closing the circle. The rate of recyclable waste was also high in many municipalities covered by our analyses, which indicated a lower rate of separation and reflected an insufficient sorting system in municipality and insufficient education of inhabitants. On the other hand, it points to the larger space of separation potential in households. In conclusion the evaluation emphasizes the improper proportion of MMSW in Czech municipalities. A lot of waste can be recycled but once it is thrown into black bins as MMSW, there is no chance that it will be reused/recycled. It therefore calls for measures to improve sorting at source, which will benefit municipal authorities in term of increasing recycle rates in order to comply with regulations and make a profit. We found the analysis of the physical composition of MMSW as a fundamental method for municipalities to verify the separation rate at the source, and it is recommended to conduct this analysis regularly and monitor developments.
Solar electric tricycle development and research
(2021) Berjoza, D.; Jurgena, I.; Bergspics, D.
Due to the fact that the world's energy resources are declining, various alternative energy sources are being sought. One such source of energy is solar energy. However, due to the large size of solar photovoltaic panels, solar energy is not widely used in mobile vehicles. In some electric automobiles, solar energy is used as an additional energy source, yet usually the sun is not able to provide more than 15–20% of the energy needed for their propulsion. There are some experimental design solutions for water vessels that are propelled by solar energy only. A recumbent electric tricycle was designed, constructed and tested within the present research. The recumbent electric tricycle used a 330 W solar battery, which was designed as a tricycle roof. During the tests with the solar battery, the electric tricycle reached a maximum speed of 32 km h -1 . On a sunny day in May under the conditions in Latvia, a distance of 50.20 km was experimentally covered without battery recharging, compared with a distance of 17.14 km covered without the use of a solar battery. By skilfully operating the solar electric tricycle and limiting the speed to 20 km h -1 on a sunny day, the expected distance covered could be unlimited. The acceleration and braking parameters of the solar electric tricycle were identified by using a scientific radar Stalker ATS.
Comparative analysis of the use of biostimulants on the main types of soil
(2021) Chernikova, O.; Mazhaysky, Yu.; Buryak, S.; Seregina, T.; Ampleeva, L.
A plant requires certain physiological conditions for normal and productive development. The determining vital factor is the nutritional status of the soil and the environment. At present, the biologization of agriculture is becoming increasingly important. The use of biostimulants is one of the rapidly developing areas in the world practice of crop production and, in the cultivation of agricultural crops, contributes to the production of environmentally friendly products and the improvement of the environment.Such substances can be metal nanoparticles, as well as preparations with a high level of biogenicity, nutritional value and physiology,they are used to improve the growth and development of plants, as well as to activate soil-microbiological processes, which is a liquid-phase biological product (LPBP). The purpose of this work is to identify the effectiveness of the use of a liquid-phase biological product and cobalt nanoparticles in pre-sowing seed treatment against the background of a minimum dose of organic fertilizers, the effect on the productivity and quality indicators of green mass when growing a grass mixture with over-sowing oats on three main types of soil: sod-podzolic, gray forest and black soil.Used cobalt nanoparticles have the following characteristics 40–60 nm, phase composition - Co - 100%. A suspension of nanoparticles was obtained by dispersing with ultrasound in an aqueous solution. LPBP is a dark brown liquid with a specific odor, pH =6.5–7.5, contains N, C, P, K, Ca, Mg, tryptophan, microorganisms. Cobalt nanopowder in solution contained 0.01 g per hectare seeding rate; LPBP concentration was 1%. The seeds were soaked 30 min before sowing in double distilled water (control), in a suspension of nanoparticles and LPBP. The research was carried out according to generally accepted methods. Presowing seed treatment in combination with organic fertilizers in minimal doses provided an increase in yield on soddy-podzolic soil - by 5.69–21.71%, gray forest soil - 2.64–7.50%, black soil - 9.18–18.28%, while no decrease in nutritional value was observed: metabolizable energy, feed units, digestible protein. It is noted that the use of cobalt nanoparticles leads to an increase in the carotene content.
An overview of measurement standards for power quality
(2021) Shabbir, Noman; Kütt, Lauri; Jarkovoi, Marek; Iqbal, Muhammad Naveed; Rassõlkin, Anton; Daniel, Kamran
Power Quality (PQ) is a vital aspect of electrical power systems, which cannot be neglected anymore, as an ample PQ guarantees the essential compatibility between consumer equipment and the electricity network. The analysis of electrical parameters related to distributing electricity is recognized as a complex engineering problem. It remains a critical task to maintain and improve PQ in modern evolving networks as the overall system performance highly depends on it. Future smart grids will also require a further increase in PQ levels in terms of observability, affordability, data exchange, flexibility, and net metering, thus making the network much more complex as it will be featuring a large amount of variable renewable-based distributed generation. This will further require the need for the introduction of novel, efficient and intelligent monitoring, control, and communication systems with various demand manageable resources. In this paper, a review and comparisons have been made for different IEEE and IEC measurement standards that are used for PQ with a specific focus on harmonic distortion as it is one of the most important parameters in PQ and some guidelines have been suggested for future electricity networks.
New device for air disinfection with a shielded UV radiation and ozone
(2021) Martinovs, A.; Mezule, L.; Revalds, R.; Pizica, V.; Denisova, V.; Skudra, A.; Kolcs, G.; Zaicevs, E.; Juhna, T.
Indoor air disinfection has become particularly relevant recently because of the Covid-19 pandemics. A shielded device for air and surface disinfection with UV radiation and ozone has been developed. It contains 28 low intensity (11 W) UV lamps (254 nm) in a specially designed three-dimensional grid to provide a large flow cross-sectional area and long path for the air particles to be irradiated. The device can be used in medical institutions, veterinary clinics, manufacturing plants, public premises, poultry, and livestock farms. It does not generate air-ions and ozone concentrations do not exceed the allowed 8-hour average values. The large number of UV lamps and powerful fans ensure air disinfection in large rooms in a relatively short time (400 m3 h -1 ). Simultaneously, the floor surface under the appliance is disinfected. Disinfection efficiency tests demonstrated 99.9999% reduction for Escherichia coli, Staphylococcus aureus and Pseudomonas phage Φ6 aerosols within a single transfer through the system (10 seconds of treatment). The housing of the device protects from direct UV radiation; therefore, people can be in the room during the operation of the device.
Effects of storage on the properties of rapeseed oil and alcohol blends
(2021) Nuortila, C.; Heikkilä, S.; Help, R.; Suopanki, H.; Sirviö, K.; Niemi, S.
Kinematic viscosity and density are important fuel properties because they influence fuel atomisation during injection into the engine cylinder. The viscosity and density of neat vegetable oils usually are too high to allow optimal use of these oils in compression ignition engines. Blending vegetable oils with alcohols can improve these properties, but it is not known whether the blend properties remain stable during storage. This study measured kinematic viscosity (at 40 °C), density (at 15 °C) and surface tension of rapeseed oil-alcohol blends that had been stored in closed borosilicate glass bottles at room temperature in the dark for 49 weeks. The values were compared with those of the fresh blends. Further measurements of oxidation stability for the rapeseed oil and the blends were taken after 72 weeks of storage. The blends consisted of rapeseed oil with ethanol at 5 vol–%, and rapeseed oil with 1–butanol at 5 vol–%, 10 vol–%, 20 vol–% and 30 vol–%. All in all, the observed changes during storage were small. Density values deviated by less than 1%, surface tension by no more than 3% and kinematic viscosity differed from the fresh blends’ values by 1% to 8%. Surface tension had increased in some blends and decreased in others. Kinematic viscosity rose in all blends, with the smallest increase measured for the rapeseed oil–butanol 30 vol–% blend. This blend also showed the best oxidation stability, which was close to six hours.
Influence of different methods of treating natural açai fibre for mortar in rural construction
(2021) Rocha, D.L.; Azevedo, A.R.G.; Marvila, M.T.; Cecchin, D.; Alexandre, J.; Carmo, D.F.; Ferraz, P.F.P.; Conti, L.; Rossi, G.
Açai is a typical Amazonian fruit that has enormous potential for use in medicines and foods, whose consumption has been growing year after year. One of the major environmental impacts related to Açai is the generation of agro-industrial wastes, which are disposed of in landfills. One of the major problems related to the reuse of natural fibres in cementitious materials is related to their durability due to the alkalinity of the matrix. Thus, the objective of this work was to evaluate three different methodologies for surface treatment of Açai fibre, by immersion in NaOH, KOH and Ca(OH)2 solution to mortar application in rural construction. After the treatments, the fibres were added in a proportion of 2.5 and 5.0% in relation to the cement mass, in addition to the reference mortar (without fibre) in the making of the prismatic specimens (40×40×160 mm) and cured for 28 days in room temperature. Right after the curing period, the specimens were evaluated according to the mechanical strength of flexion and compression, workability, water absorption by capillarity and mass density in the hardened state of each methodology. The results showed that the best treatment methodology is with NaOH solution, with the addition of 5% Açai fibre in relation to the cement mass, producing a suitable mortar for use in rural buildings.
Approach to a classification of construction typologies of pig facilities: case study Antioquia – Colombia
(2021) Castrillón, N.; Gonzalez, V.; Osorio, J.A.
Pig facilities foro confined production in tropical countries such as Colombia does not specify, in the present moment a typological classification that allows researchers to carry out evaluations related to animal comfort and environmental impacts according to the type of accommodation. To achieve the objective of this research were developed a survey to a panel of experts, a decision sensitivity analysis and the hierarchical analytical method AHP. Parameters that allowed to describe the concept of a technified pig farm were obteined, where the most relevant were: biosecurity measures, measurement of zootechnical parameters, training for workers and legal fulfilment. Additionally, ranges were defined to establish the production size in small, medium and large according to the number of animals. The results obtained per group were: 1) breeding small (50–200), medium (201–1,000) and large (1,001–5,000); 2) growth small (60–200), medium (201–800) and large (801–5000); and 3) finishing stage small (50–500), medium (501–1,000) and large (2,001–5,000). A total of 948 typological combinations were initially determined. Finally, the construction characteristics with the greatest technical and operational feasibility were prioritized for each group achieving 36 typologies that can represent the typological pig facilities not only in the state of Antioquia but also in many others states in Colombia.
Waste fish oil as an alternative renewable fuel for IC engines
(2021) Hissa, M.; Niemi, S.; Ovaska, T.; Niemi, A.
Bio-oils are potential fuels for internal combustion engines because of they have advantageous properties such as biodegradability, renewability, high oxygen content and low sulphur. However, the high viscosity, surface tension, and density of crude bio-oils pose challenges for engine use. Those properties affect fuel spray characteristics, mixture formation and combustion. In turn, these impact engine, efficiency, power and emissions. This study investigated the use of crude fish oil (FO) at medium and low engine-loads at two engine speeds in an off-road engine. The injectors had 6-hole high flow rate tips. The results were compared with those of fossil diesel fuel oil (DFO). Fish oil increased hydrocarbon (HC), carbon monoxide (CO) and partly oxides of nitrogen (NOx) emissions. Smoke number, however, decreased. Crude fish oil also showed lowered total particle number (TPN) at low load at low engine-speed compared with DFO.
Productive efficiency and density and viscosity studies of biodiesels from vegetable oil mixtures
(2021) Correia, R.C.B.; Silva, F.C.; Barros, M.M.; Maria, A.C.L.; Cecchin, D.; Souza, L.A.; Carmo, D.F.
Currently in Brazil the minimum content of biodiesel in mixtures is 11% and, according to Brazilian laws, the goal is to reach 15% in volume in diesel fuel available for final consumers by 2023. Therefore, studies about different matrices of biodiesel and distinct mixtures are essential. The present work had two goals, the first one was to analyse physico-chemical properties of 16 biofuels produced from soybean and cotton oils, using S10 diesel, in mixtures B8, B10, B20 and B30. The second goal was to verify the vantages and disadvantages of biodiesel production through prior mixing of the oils, before and after the transesterification process. All biofuels produced presented results of specific mass values at 20 °C and kinematic viscosity at 40 °C within the limits established by ANP Resolution no 30/2016 and International Resolutions. The soybean B20 biofuel showed the best overall results, with the second highest production yield of 65.36%, the fifth lowest kinematic viscosity with 3.48 mm s -1 . The mixture of soybean and cotton oils before the transesterification process presented the highest production yield when compared with the production from a single oil or biodiesel mixtures. The results found proved to be satisfactory and corroborate to continue with the increase of biodiesel in the mixture with diesel to B15 until 2023 and support the possibility of planning for a gradual increase of this mixture in the following years.
Evaluation of passive cooling system in plywood enclosure for agricultural robot prototype
(2021) Galins, J.; Osadcuks, V.; Pecka, A.
The use of autonomous robots in agriculture has been increasing rapidly in recent years, but is hampered by the complexity of data recording and processing. The prototyping process involves many changes to the housing design during development. Using laser cutting to make a housing is more convenient, faster and cheaper than milling or casting if only one body needs to be made. To speed up the production of autonomous robot prototypes, the body was made of birch plywood using laser-cut parts. The study analyses the efficiency of passive cooling to make sure that birch wood plywood is suitable for the production of a robotic body for outdoor use in agriculture. Under laboratory conditions, temperature measurements were made inside and outside the housing to determine how the heat released by the electronic components dissipates into the environment. An exponential model with a static coefficient and a time constant can be used to determine the recommended operating time at different ambient temperatures when the allowable operating temperature of the component is known. Air flow and heat transfer simulations were performed to represent heat dissipation. Birch plywood can be used for the production of prototype enclosures for agricultural robots, but the design must provide technological solutions for heat dissipation to prevent overheating of electronic components.
Research into engineering and operation parameters of mineral fertiliser application machine with new fertiliser spreading tools
(2021) Bulgakov, V.; Adamchuk, O.; Pascuzzi, S.; Santoro, F.; Olt, Jüri; Estonian University of Life Sciences. Institute of Technology
The output capacity of the machine for top spreading the soil with solid mineral fertilisers can be raised by means of increasing its working width. The authors have carried out field trials and field experiment investigations with the MVU-8 granulated mineral fertilizer spreading machine equipped with two prototype units of the centrifugal fertiliser spreading tool, in which the axis can be tilted at different angles to the vertical line. In accordance with the results of the completed investigations, it has been established that setting the axial tilt angle of the centrifugal operating device in the fertiliser spreading tool within the range of 25–30° provides for achieving a productivity of the combined tractor-implement unit for applying mineral fertilisers at a level of 35–40 ha per working shift hour. The best performance in the fertiliser application with regard to both the working width and the fertiliser placing distribution uniformity is ensured at angles of inclination of the disc in the fertiliser spreading tool with respect to the horizontal plane within the range of 25–30°. At these angles, the uneven distribution of the fertiliser over the working width is equal to 19.2%, the uneven distribution of the fertiliser along the unit’s line of travel is equal to 8.9%, while the deviation in the dosage of the applied fertilisers from the set value is equal to 7.5%.
Compositional evaluation of hot-pressed rapeseed cake for the purpose of bioplastic production
(Estonian University of Life Sciences, 2021) Jõgi, Katrin; Malenica, Dunja; Jõudu, Ivi; Bhat, Rajeev; ERA-Chair for Food (By-) Products Valorisation Technologies of the Estonian University of Life Sciences (VALORTECH). Estonian University of Life Sciences; Chair of Food Science and Technology. Institute of Veterinary Medicine and Animal Sciences. Estonian University of Life Science
Rapeseed is widely cultivated for biodiesel or food-grade oil production. As the oil production process generates huge amounts of wastes and by-products (e.g. oil press cake and meal) that have relatively high crude protein content, valorisation as input material for proteinbased bioplastics has a lot of potential. There is a limited number of studies undertaken on using rapeseed cake directly (without prior protein extraction) for biomaterial production, but the initial results have been very promising. As rape and turnip rapeseeds are also some of the most harvested crops in Estonia, the rapeseed oil press cake as a by-product is also available from local food-grade rapeseed oil production. In this regard, we investigated locally available rapeseed oil press cake for chemical composition and explored suitability for bioplastic production. The results indicate suitability for direct biomaterial production, meaning properties for biomaterial formation could be further explored.
Operation of the photovoltaic system in Prague and data evaluation
(2021) Šafránková, J.; Petrík, T.; Libra, M.; Beránek, V.; Poulek, V.; Belza, R.; Sedláček, J.
The on-grid photovoltaic system was installed at the Faculty of Engineering in 2015. The monitoring system developed in our laboratory monitors data and can also detect failure and type of failure. The evaluation of the data shows that the amount of electricity produced slightly exceeds the expected values predicted by the internationally used internet application PVGIS. The effect of the aging of PV panels has so far had a minimal effect on the electricity produced. Immediate output power is affected by multiple parameters. Higher temperatures reduce the efficiency of energy conversion, so in summer the instantaneous power may be lower even at higher radiation intensity and smaller angle of incidence.
Thermo mechanical vibration of single wall carbon nanotube partially embedded into soil medium
(2021) Hossain, Mainul; Lellep, Jaan
Single wall carbon nanotube is one of the promising forms of carbon nanocomposite. Due to its high strength and stiffness, carbon nanotube is potentially used in various nanoscale structures. In this paper, dynamic behaviour of single wall carbon nanotube partially embedded into elastic soil medium is modelled by the Euler-Bernoulli beam theory and nonlocal theory of elasticity. Analytical solution technique is employed to solve these governing differential equations of nanotube. Analysing the effects of temperature, nonlocal parameter, coefficients of elastic medium on dynamic behaviour of nanotube are our main concern. The results reveal that the effects of temperature, nonlocal parameter and coefficients of elastic medium are very significant on the natural frequency of nanotube.

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