771 research outputs found
Cluster emission under femtosecond laser ablation of silicon
Rich populations of clusters have been observed after femtosecond laser
ablation of bulk silicon in vacuum. Size and velocity distributions of the
clusters as well as their charge states have been analyzed by reflectron
time-of-flight mass spectrometry. An efficient emission of both neutral silicon
clusters Sin (up to n = 6) and their cations Sin+ (up to n = 10) has been
observed. The clusters are formed even at very low laser fluences, below
ablation threshold, and their relative yield increases with fluence. We show
the dependencies of the cluster yield as well as the expansion dynamics on both
laser wavelength and laser fluence. The mechanisms of the cluster formation are
discussed
Mathematical model of the movement of a potato body along the surface of a spiral separator
The potato is grown in over one hundred countries spread over all latitudes, with the most diverse climatic conditions, from the areas near the Arctic Circle to the southern end of the South American continent. The potato is an irreplaceable component of the food tradition of many countries and is the most cultivated species after cereals (wheat, rice and corn). The authors set up and developed a new clod and rubbish spiral separator for potatoes, which is protected by the patent of Ukraine. The operation modalities of this machine are briefly described in the paper. The aim of this study is the development of a mathematical model concerning the movement of a potato body along the surface the spiral separator. In particular, equations are found for determining the coordinates of the position of a potato tuber on the surface of a spiral separator depending on the parameters of the spiral (spiral line) and the size of the tuber. Furthermore, the velocity of tuber movement in the stream formed by the surfaces of two neighboring spirals in the direction of the horizontal, vertical and longitudinal axis are determined. The results of this study will be used in the future to analytically considering the dynamics of movement of a potato tuber on the surface of a spiral separator, taking into account the conditions that exclude its damage
The theory of sifting the soil mass when cleaning potatoes on a spiral separator
The removal of soil and impurities is an important problem when harvesting potatoes. and the main reason for this problem is due to the modalities employed to carry out the potatoes mechanical harvesting. The equipments currently implemented on potato harvesters do not always allow to obtain high levels of soil and impurities separation, mainly due to the gluing of the moist soil to the surfaces of the separating organs. The authors have developed a spiral separator of soil clods from potatoes heaps, patented in Ukraine. The purpose of this paper has been to analyze the theory of sifting the soil mass when a spiral separator is used. A mathematical model of the motion of an elementary body along the spiral surface of a potato heap separator has been built. The numerical solution of the model has highlighted that the lowest angular speed (10 rad s-1) of the cleaning rollers allows the greatest amount of sifted soil mass. Field tests carried out confirmed that the developed spiral separator is able to perform the task achieving meaningful values of the efficiency of separation and heap purity. Further field and laboratory tests will be executed in order to improve the set up mathematical model
Experimental research into new harrowing unit based on gantry agricultural implement carrier
Received: October 6th, 2020 ; Accepted: December 11th, 2020 ; Published: December 16th, 2020 ; Correspondence: [email protected] the point of view of energy saving, research into agricultural gantry units equipped
with new implements specially adapted for operation in such systems and capable of efficiently
functioning in controlled traffic (permanent lane) and wide span (gantry) systems is an important
and topical issue in soil tillage science. The range of wide span systems includes harrowing units
for fallow land tillage. This paper describes the experimental determination of the operating
characteristics of the harrowing unit, in which a gantry implement carrier propels harrows for fallow
land tillage, for the purpose of establishing the compliance of their parameters with the fundamental
principles of the effective implementation of the controlled traffic and wide span soil management.
The experimental investigations were done using strain-gauge and control-and-measuring
equipment with analogue-to-digital conversion of the signals received from the sensing elements.
An agricultural wide span unit with a track width of 3.5 m and harrows for fallow land tillage were
investigated. The results show the harrowing unit is well adapted to operation in controlled traffic
and wide span soil tillage systems and delivers high quality performance of the harrowing process.
The latter effect is also due to the fact that the gantry travels on the compacted tracks which have a
few surface irregularities compared to cultivated soil. The coefficient of variation of the draught
force applied to the hook of the gantry during harrowing operations did not exceed 10%. This is
evidence of the high stability (low variability) of the harrowing process, which has a positive effect
on the motion stability of the harrowing unit based on the gantry tractor
Intensification of rapeseed drying process through the use of infrared emitters
ArticleThe theoretical basis of the agricultural material drying techniques has been formed in
the world for two and a half centuries. Nevertheless, despite the multitude of studies well
presented in the literature, the i
ndustry still lacks universally recognized methods of design
calculation for the majority of drying problems. Presumably, this is due to the fact that the
dehydration of foodstuffs is one of the most energy
-
intensive and complicated work processes.
In the
process of thermal treatment during the drying, the physical state of the water in the treated
item changes, the properties of the item itself are altered.
Recently, the drying of foodstuffs by means of infrared (IR) radiation has been gaining ever wider
a
cceptance. At the same time, the technologies for dehydrating foodstuffs and materials are now
far ahead of the theory of drying. Not only the classical literature on the drying problems, but
even special studies on the subject cannot provide any specific
recommendations for the design
of installations with the electro
-
magnetic principle of energy input. Whereas that is exactly the
type of installations that are now actively making headway, while offering serious challenges in
their modelling. For that reas
on, experimenting has until now been the only reliable way of their
studying. Despite the available extensive scientific literature on the drying, including works on
IR units, the practical issues of engineering IR driers have not been tackled. All the exi
sting
studies consider solely particular cases.
This study discusses the process of drying the fixed bed
of rapeseeds with the use of the electromagnetic infrared emitter. The energy intensity of the
process and the optimum thickness of the product bed are
determined.
The aim of the paper is to
examine the effect that the operating condition
parameter
s (energy input intensity, temperature,
grain bed thickness) have on the drying kinetics and the energy characteristics of the process. The
methods of research
are based on the thermophysical analysis of the material’s structure. The
experimental studies were carried out with the use of monitoring and measuring equipment, up
-
to
-
date methods and instruments, including solutions developed by the authors. The analy
tical
treatment was performed with the use of the software packages: MathCAD, Excel. The sample
testing and examination took place in the laboratory and the methods were in compliance with
the applicable standards. A comprehensive experimental
investigatio
n
of the effect that the
operating
parameter
s (specific load and power) have on the rape seed IR
-
drying kinetics had been
accomplished
The theory of cleaning the crowns of standing beet roots with the use of elastic blades
ArticleA standing beet root crown cleaner has been designed. The design comprises the
vertical drive shaft that carries two flat elastic cleaning blades installed on axes and connected
through the articulated connection. The aim of the study was to develop the new theory of
cleaning the crowns of standing roots with the use of an elastic blade installed on the vertical
drive shaft in order to determine its optimal design and kinematic parameters. The first step was
to design an equivalent schematic model of the interaction between the elastic cleaning blade
installed on the vertical drive shaft and the spherical surface of the beet root fixed in the soil. The interaction between the blade and the root's crown took place at the point, where all the forces that can arise during such interaction are applied. A three-dimensional coordinate system was set
and the design and kinematic parameters of the considered interaction were designated. Using the
original differential equations projected on the set coordinate axes, the system of four nonlinear
differential equations of the three-dimensional motion of the elastic cleaning blade on the
spherical surface of the root crown was set up, then it was transformed into the system of two
differential equations in the normal form. Further, to determine the force that strips off the
remaining haulm, which is part of the obtained system of differential equations, the problem of
its analytical determination was solved separately. Also, the additional equivalent schematic
model of the interaction between the elastic blade as a cantilever beam and the root's crown was designed, the differential equation of the beam's deflection curve (taking into account the beam's simultaneous bending and twisting) was set up and, on the basis of it, the projections of the
stripping force on the coordinate axes were found. The values of the force were substituted in the
earlier obtained system of differential equations
Research in dynamic transitional processes of functioning of combine harvester hydraulic drives
An analysis of perspective methods is made for diagnosing hydraulic drives, based on the on-board automated tools. Prospects are substantiated for the development of technical diagnostics of agricultural machinery on the basis of on-board electronic means. Special attention is paid to the need for significant research in the direction of creating new diagnostic parameters, adapted to these means, and methods of their measurement. The parameters of the characteristics of changes in the pressure of the working fluid in the hydraulic aggregates in transitional modes of operation of the hydraulic drives are advisable to be used as diagnostic, since the veracity (accuracy) of the parameters, based on them, is not less than 95%. As an example, a method of diagnosing on dynamic transitional modes of operation of the hydraulic drives is given, which is the basis for the development and use of built-in and portable electronic means for conducting CIP diagnostics, which will provide 2-3 times decrease in the labour intensity and the cost of work with at least 85% veracity of diagnosis and the permissible error measurements no more than ± 4%. The novelty of this work lies in the method we have developed for diagnosing the dynamic transient modes of operation of hydraulic drives
A mathematical model of the plane-parallel movement of an asymmetric machine-and-tractor aggregate
Technological peculiarities of cultivation and harvesting of some agricultural crops make it necessary to use asymmetric machine-and-tractor aggregates. However, for the time being there is no sufficiently complete, analytical study of the steady movement of such machine-and-tractor aggregates. This necessitates the development of a theory of stable movement of the aggregates which would allow choosing their optimal kinematic and design parameters. On the basis of the results of mathematical simulation, a system of linear differential equations of the second order is obtained describing transverse displacement of the center of masses of the aggregating wheeled tractor and turning of its longitudinal axis of symmetry by some angle around the indicated center of mass, as well as the deviation angle of the rear-trailed harvester from the longitudinal axis of the tractor at any arbitrary moment of time. This system of differential equations can be applied for numerical calculations on the PC, which will make it possible to evaluate the stability of the movement of the asymmetric machine-and-tractor aggregate when it performs the technological process
Synthesis and Laser Processing of ZnO Nanocrystalline Thin Films
We present the results of experiments on synthesis of ZnO nanoclusters by
reactive pulsed laser deposition (PLD). The nanoclusters were formed and
crystallized in the gas phase and deposited on SiO2 substrates. The
nanostructured films were characterized by conventional photoluminescence (PL).
The PL spectra consist of a narrow UV excitonic band and a broad visible band
related to defects in the film. The film preparation conditions such as the
substrate temperature, ambient gas nature and pressure, were optimized in order
to increase the intensity of excitonic emission and prevent the formation of
defects. A post-growth annealing by UV laser radiation improved the optical
quality of the deposited films. The photoluminescence intensity was found to be
dependent significantly on the laser fluence and on the number of shots per
site. The nature of the defects responsible for the observed luminescence in a
visible range is discussed
Investigations about the impact of the sowing time and rate of the biomass yield and quality of industrial hemp
ArticleThe aim of this study was to find the optimum sowing rate of industrial hemp
(Cannabis sativa L.) and to clarify the impact of the sowing rate on the production of biofuel
from hemp biomass in Latvia. Field trials were carried out at the Research and Study Farm
‘Pēterlauki’ of the Latvia University of Agriculture in 2012–2014. The industrial hemp (Cannabis
sativa L.) ‘Futura 75’ was sown in a Luvic Endogleyic Stagnosol soil: pHKCl 6.7; P – 52 mg kg-1
;
K – 128 mg kg-1
; the organic matter content – 21–25 g kg-1
. Hemp was sown in 10-m2 plots,
triplicate, on May 8 and 17. The total sowing rate was 20 (100), 30 (150), 40 (200), 50 (250),
60 (300), 70 (350), 80 (400), 90 (450), and 100 (500) kg ha-1
(germinating seeds per 1 m2
). The
plots were fertilised as follows: N – 120 kg ha-1
; P2O5 – 80 kg ha-1
; and K2O – 112 kg ha-1
. Hemp
was harvested when the first matured seeds appeared. The biometrical indices (height and stem
diameter), harvesting time, the amount of fresh and dry biomass, and the fibre content were
evaluated. Depending on the sowing rate, the yield of dry matter was on average 9.2–12.1 t ha-1
when hemp was sown at the beginning of May, and 7.9–10.0 t ha-1 when hemp was sown in the
middle of May
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