Small-scale Components Research Articles

Discussions on Tritiated Water Treatment for Fukushima Daiichi Nuclear Power Station

A series of discussions on tritiated water of the Fukushima Daiichi Nuclear Power Station (FD-NPS) was carried out. A large amount of contaminated water has been generated in FD-NPS. Radioisotopes in the contaminated water have been removed except tritium, and thus, tritiated water has been left and stored. As of March 2019, 1 126 500 m3 of tritiated water has been stored in tanks. The average tritium concentration in the tritiated water is 1000 Bq/cm3. Various options for handling the tritiated water, such as discharge into the sea, geosphere injection, underground burial, and vapor or hydrogen release with and without pretreatment, were discussed on the basis that there is no scientific impact on people. Through the discussions, 11 options for handling tritiated water were summarized. At the same time, some experimental tests of tritium separation (with small-scale and/or full-scale component test stands) were also carried out. As a result, it was concluded that the tested separation technologies could not yet be applied to the case of FD-NPS. No selection from the 11 options has yet been recommended, and further discussions for the tritiated water have continued with public hearings.

Vector Field Decompositions Using Multiscale Poisson Kernel.

Extraction of multiscale features using scale-space is one of the fundamental approaches to analyze scalar fields. However, similar techniques for vector fields are much less common, even though it is well known that, for example, turbulent flows contain cascades of nested vortices at different scales. The challenge is that the ideas related to scale-space are based upon iteratively smoothing the data to extract features at progressively larger scale, making it difficult to extract overlapping features. Instead, we consider spatial regions of influence in vector fields as scale, and introduce a new approach for the multiscale analysis of vector fields. Rather than smoothing the flow, we use the natural Helmholtz-Hodge decomposition to split it into small-scale and large-scale components using progressively larger neighborhoods. Our approach creates a natural separation of features by extracting local flow behavior, for example, a small vortex, from large-scale effects, for example, a background flow. We demonstrate our technique on large-scale, turbulent flows, and show multiscale features that cannot be extracted using state-of-the-art techniques.

Generation of Solenoidal Modes and Magnetic Fields in Turbulence Driven by Compressive Driving

Abstract We perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic (MHD) turbulence driven by compressive driving, to study the generation of solenoidal velocity components and the small-scale magnetic field. We mainly focus on the effects of mean magnetic field (B 0) and the sonic Mach number (M s ). The dependence of solenoidal ratio (i.e., ratio of solenoidal to kinetic energies) and magnetic energy density on M s in compressively driven turbulence is already established, but that on B 0 is not yet. We also consider two different driving schemes in terms of the correlation timescale of forcing vectors: a finite-correlated driving and a delta-correlated driving. Our findings are as follows. First, when we fix the value of B 0, the solenoidal ratio after saturation increases as increases. A similar trend is observed for generation of magnetic field when B 0 is small. Second, when we fix the value of , HD and MHD simulations result in similar solenoidal ratios when B 0 is not strong (say, M A ≳ 5, where M A is Alfvén Mach number). However, the ratio increases when M A ≲ 5. Roughly speaking, the magnetic energy density after saturation is a linearly increasing function of B 0 irrespective of M s . Third, generation of the solenoidal velocity component is not sensitive to numerical resolution, but that of magnetic energy density is mildly sensitive. Finally, when initial conditions are same, the finite-correlated driving always produces more solenoidal velocity and small-scale magnetic field components than the delta-correlated driving. We additionally analyze the vorticity equation to understand why higher and B 0 yield a larger quantity of the solenoidal velocity component.

Tracer-based estimates of eddy-induced diffusivities

This study provides estimates of the mean eddy-induced diffusivities of passive tracers in a three-layer, double-gyre quasigeostrophic (QG) simulation. A key aspect of this study is the use of a spatial filter to separate the flow and tracer fields into small-scale and large-scale components, and we compare results with those obtained using Reynolds temporal averaging. The eddy tracer flux is related to a rank-2 diffusivity tensor via the flux-gradient relation, which is solved for a pair of tracers with misaligned large-scale gradients. We concentrate on the symmetric part of the resulting diffusivity tensor which represents irreversible mixing processes. The eigenvalues of the symmetric tensor exhibit complicated behaviour, but a particularly dominant and robust feature is the positive/negative eigenvalue pairs, which physically represent filamentation of the tracer concentration. The large off-diagonal diffusivity tensor component is the primary contributor to the eigenvalue polarity, and since this is such a prevalent feature we argue that the (horizontal) eddy-induced diffusivity should always be treated as a full 2×2 tensor. Diffusivity magnitudes are largest in the upper layer and in the eastward jet region, where the eddying flow is strongest. After removing the rotational part of the eddy tracer flux, typical mean diffusivities (eigenvalues) in the upper-layer are on the order of 103 m2 s−1 in the jet region and 102 m2 s−1 elsewhere. We also confirm that the time-mean of the diffusivity calculated from instantaneous fluxes is not the same as the diffusivity associated with the time-mean fluxes.

Hidden magnetic fields of young suns

Global magnetic fields of active solar-like stars are, nowadays, routinely detected with spectropolarimetric measurements and are mapped with Zeeman Doppler imaging (ZDI). However, due to the cancellation of opposite field polarities, polarimetry only captures a tiny fraction of the magnetic flux and cannot assess the overall stellar surface magnetic field if it is dominated by a small-scale component. The analysis of Zeeman broadening in high-resolution intensity spectra can reveal these hidden complex magnetic fields. Historically, there were very few attempts to obtain such measurements for G dwarf stars due to the difficulty of disentangling the Zeeman effect from other broadening mechanisms affecting spectral lines. Here, we developed a new magnetic field diagnostic method based on relative Zeeman intensification of optical atomic lines with different magnetic sensitivity. By using this technique, we obtained 78 field strength measurements for 15 Sun-like stars, including some of the best-studied young solar twins. We find that the average magnetic field strengthBfdrops from 1.3−2.0 kG in stars younger than about 120 Myr to 0.2−0.8 kG in older stars. The mean field strength shows a clear correlation with the Rossby number and with the coronal and chromospheric emission indicators. Our results suggest that magnetic regions have roughly the same local field strengthB ≈ 3.2 kG in all stars, with the filling factorfof these regions systematically increasing with stellar activity. In comparing our results with the spectropolarimetric analyses of global magnetic fields in the same stars, we find that ZDI recovers about 1% of the total magnetic field energy in the most active stars. This figure drops to just 0.01% for the least active targets.

Critical Review on Factors Determining High Performance Organizations within Small-Scale Plastic Components Manufacturing Industry in India

Critical Review on Factors Determining High Performance Organizations within Small-Scale Plastic Components Manufacturing Industry in India

Factors Determining High Performance Organizations within Small-scale Plastic Components Manufacturing Industry in India

Factors Determining High Performance Organizations within Small-scale Plastic Components Manufacturing Industry in India

A Fast Tunable Blurring Algorithm for Scattered Data

A blurring algorithm with linear time complexity can reduce the small-scale content of data observed at scattered locations in a spatially extended domain of arbitrary dimension. The method works by forming a Gaussian interpolant of the input data, and then convolving the interpolant with a multiresolution Gaussian approximation of the Green's function to a differential operator whose spectrum can be tuned for problem-specific considerations. Like conventional blurring algorithms, which the new algorithm generalizes to data measured at locations other than a uniform grid, applications include deblurring and separation of spatial scales. An example illustrates a possible application toward enabling importance sampling approaches to data assimilation of geophysical observations, which are often scattered over a spatial domain, since blurring observations can make particle filters more effective at state estimation of large scales. Another example, motivated by data analysis of dynamics like ocean eddies that have strong separation of spatial scales, uses the algorithm to decompose scattered oceanographic float measurements into large-scale and small-scale components.

Unified Deep Learning Architecture for the Detection of All Catenary Support Components

With the rapid development of deep learning technologies, researchers have begun to utilize convolutional neural network (CNN)-based object detection methods to detect multiple catenary support components (CSCs). The literature has focused on the detection of specified large-scale CSCs. Additionally, CNN architectures have faced difficulties in identifying overlapping CSCs, especially small-scale components. In this paper, a unified CNN architecture is proposed for detecting all components at various scales of CSCs. First, a detection network for CSCs with large scales is proposed by optimizing and improving Faster R-CNN. Next, a cascade network for the detection of CSCs with small scales is proposed and is integrated into the detection network for CSCs with large scales to construct the unified network architecture. The experimental results demonstrate that the detection accuracy of the proposed CNN architecture can reach 92.8%; hence, it outperforms the popular CNN architectures.

The impact of non-dipolar magnetic fields in core-collapse supernovae

ABSTRACT The magnetic field is believed to play an important role in at least some core-collapse supernovae (CCSN) if its magnitude reaches $10^{15}\, \rm {G}$, which is a typical value for a magnetar. In the presence of fast rotation, such a strong magnetic field can drive powerful jet-like explosions if it has the large-scale coherence of a dipole. The topology of the magnetic field is, however, probably much more complex with strong multipolar and small-scale components and the consequences for the explosion are so far unclear. We investigate the effects of the magnetic field topology on the dynamics of CCSN and the properties of the forming proto-neutron star (PNS) by comparing pre-collapse fields of different multipolar orders and radial profiles. Using axisymmetric special relativistic MHD simulations and a two-moment neutrino transport, we find that higher multipolar magnetic configurations lead to generally less energetic explosions, slower expanding shocks, and less collimated outflows. Models with a low order multipolar configuration tend to produce more oblate PNS, surrounded in some cases by a rotationally supported toroidal structure of neutron-rich material. Moreover, magnetic fields which are distributed on smaller angular scales produce more massive and faster rotating central PNS, suggesting that higher order multipolar configurations tend to decrease the efficiency of the magnetorotational launching mechanism. Even if our dipolar models systematically display a far more efficient extraction of the rotational energy of the PNS, fields distributed on smaller angular scales are still capable of powering magnetorotational explosions and shape the evolution of the central compact object.

The potential added value of Regional Climate Models in South America using a multiresolution approach

This paper aims to identify those regions within the South American continent where the Regional Climate Models (RCMs) have the potential to add value (PAV) compared to their coarser-resolution global forcing. For this, we used a spatial-scale filtering method based on the wavelet theory to distinguish the regional climatic signal present in atmospheric surface fields from observed data (CPC and TRMM) and 6 RCM simulations belonging to the CORDEX Project. The wavelet used for filtering was Haar wavelet, but a comparative analysis with Daubechies 4 wavelet indicated that meteorological fields or regional indices were not very sensitive to the wavelet selected. Once the longer wavelengths were filtered, we focused on analyzing the spatial variability of extreme rainfall and the spatiotemporal variability of maximum and minimum surface air temperature on a daily basis. The results obtained suggest essential differences in the spatial distribution of the small-scale signal of extreme precipitation between TRMM and regional models, together with a large dispersion between models. While TRMM and CPC register a large signal throughout the continent, the RCMs place it over the Andes Cordillera and some over tropical South America. PAV signal for surface air temperature was found over the Andes Cordillera and the Brazilian Highlands, which are regions characterized by complex topography, and also on the coasts of the continent. The signal came specially from the small-scale stationary component. The transient part is much smaller than the stationary one, except over la Plata Basin where they are of the same order of magnitude. Also, the RCMs and CPC showed a large spread between them in representing this transient variability. The results confirm that RCMs have the potential to add value in the representation of extreme precipitation and the mean surface temperature in South America. However, this condition is not applicable throughout the whole continent but is particularly relevant in those terrestrial regions where the surface forcing is strong, such as the Andes Cordillera or the coasts of the continent.

Deciphering the Role of Small-Scale Inhomogeneity on Geophysical Flow Structuration: A Stochastic Approach

AbstractAn important open question in fluid dynamics concerns the effect of small scales in structuring a fluid flow. In oceanic or atmospheric flows, this is aptly captured in wave–current interactions through the study of the well-known Langmuir secondary circulation. Such wave–current interactions are described by the Craik–Leibovich system, in which the action of a wave-induced velocity, the Stokes drift, produces a so-called “vortex force” that causes streaking in the flow. In this work, we show that these results can be generalized as a generic effect of the spatial inhomogeneity of the statistical properties of the small-scale flow components. As demonstrated, this is well captured through a stochastic representation of the flow.

THE THESIS SUMMARIZES THEORETICAL-METHODOLOGICAL AND METHODICAL BASES TO EXPLORE REGULARITIES OF CHANNEL WAY FORMATION IN THE RIVER SYSTEM OF THE PISTYNKA - LUCHKA - SOPIVKA

Geological-geomorphologic conditions within the basin of the Upper Prut and the history of development of its river-lowland system were put under thorough analysis.The territorial division of the modern river-valley systems is an urgent task both theoretically and practically. On the basis of the homogeneous sections of the river valleys bottoms as well as homogeneous sections of the river-beds and flood-lands, the landscapes, ecosystems and social-natural geo-systems are developing.The systems of river-valley bottoms are central and most important components of the basin systems where different natural and anthropogenic pressures are concentrated. In modern conditions, the question the formation of appropriate geo informational systems, the usage of the GIS method in the research, the development of supervision and cadaster is raised.The signified major trunk section of the modern river-valley system of the Upper Prut reflect the most important features of the geological and geomorphological structure of the territory, the history of the valley development and the corresponding history of functioning of the system «stream-river bad».Our following objective is to find morphometrically integral, homogeneous territorial units, give their description and develop the corresponding data base of GIS. Meanwhile, we would like to point out that beyond our investigation we have left minor, small-scale components of the river-valley system which we have related to the typical ones.These are the valleys of the 1st -4th quantities. By analogy with the term «small river», they can be defined as small river-valley systems. They include primary and more developed links. For their investigation, a different method should be wed. it can be a typological research when the specific features of different geomorphological districts will be taken into consideration.When studying the processes and patterns of the formation of the rivers of the Ukrainian Carpathians, it is necessary to take into account the features of the development of their hydrographic network. The predominant pattern of the network in the Pistynka-Lyuchka-Lyuchka Sopivka channel system is the radial one, which is due to the orographic structure of Rungurska Sloboda.The modern system of the hydrographic network of Pistynka-Lucki-Lucki Sopovka, as part of the Upper Prut basin, has undergone two stages of development: emergence and formation. Some rivers have ancient valleys, others have formed their valleys relatively recently, as evidenced by a slight erosion cut. Hydro network is a polysynthetic formation formed on the basis of numerous changes in its configuration due to the active erosion-accumulation activity of rivers and economic activity of man. The decisive factor in the formation and development of the hydrographic network is neotectonics. The unevenness of the earth's crust raised contributed to the expansion of the catchment area, the formation of a series of basement terraces and epigenetic valleys, the formation of a peculiar pattern of the network.Significant changes in the hydrographic network of the study area are happening nowadays. Comparison of topographic maps (Polish for 1931-1933 and Soviet for 1978, 1992) showed that in 50-60 years the total number of rivers decreased by about 20%. The vast majority of extinct rivers have 1 order. Depending on the location of the river and the type of hydrographic network, the number of tributaries that have disappeared or appeared varies significantly. The largest inflow disappeared in the Lyuchki Basin (65 small rivers) and only 6 appeared. It is mainly directly its tributaries, or tributaries of the rivers Accra, Lucha, Lunga (all flowing within the inner valley). The total comparison is 156/97. In our opinion, the reason for such changes is anthropogenic factor: the direct or indirect impact of human economic activity on the catchment area. Climate change in the region is also likely to play a role.

Characteristics of large- and small-scale structures in the turbulent boundary layer over a drag-reducing riblet surface

Riblet is one of the most promising passive drag reduction techniques in turbulent flows. In this paper, hot-wire measurements on a turbulent boundary layer perturbed by a drag-reducing riblet surface are carried out to further understand the riblet effects on the turbulent flows and the drag reduction mechanism. Compared with the smooth case, different energy variations in the near-wall region and the logarithmic region are observed over riblets. Then, by using a spectral filter of a given wavelength, the time series of the hot-wire data are decomposed into large- and small-scale components. It is indicated that large-scale structures in the logarithmic region impose a footprint (amplitude modulating effect) on the near-wall small-scale structures. By quantifying this footprint, it is found that the interactions between large- and small-scale structures over riblets are weakened in the near-wall region. Furthermore, the bursting process of large and small scales is studied. For both large- and small-scale structures, a shorter bursting duration and a higher bursting frequency are observed over the riblet surface, which indicates that riblets impede the formation of large- and small-scale bursting events. The flow physics behind these phenomena are also discussed in detail.

EVIDENCES FOR STRONG MIXED-POLARITY MAGNETIC FIELDS IN AREA OF A SEISMIC SOURCE ASSOCIATED WITH LARGE PROTON SOLAR FLARE

We present in a concise statement the new results based on spectral-polarization measurements of magnetic fields in an extremely powerful proton solar flare on October 28, 2003 of X17.2 / 4B class. The observation material was obtained with Echelle spectrograph of HST AO KNU, which makes it possible to analyze the spectral manifestations of the Zeeman effect in very many lines of the visible region of the spectrum, including the photospheric and chromospheric lines. The I ± V and V profiles of about ten FeI and FeII lines, as well as the Hα, Hβ, Hγ, and Hδ lines were studied in a area of the seismic source of the flare, which was localized in the sunspot penumbra of S magnetic polarity. In this flare, we found an unprecedented Balmer decrement of intensities of Hα and Hβ lines which corresponds to ratio I (Hβ) / I (Hα) = 1.68. In the FeI 5434.5 line with very low Lande factor (g eff = –0.014), a reliable splitting of emission peaks was found, which could indicate superstrong magnetic fields (about 50 kG) of N polarity. Indications for magnetic fields with intensity ≈ 12 kG of S polarity were found too. These indications are based on the study of the Stokes V profile of FeII 5234.6 line. In this line, there were two positive and two negative peaks of profile V, indicating a two- component structure of the magnetic field. According to the simulation data, the small-scale component with the above-mentioned superstrong magnetic field had a filling factor about 0.1 and had narrow (about twice) the half- widths of the line profiles. The close contact of subtelescopic magnetic fields of different magnetic polarity, but of lower intensity (B ≈ 1 kG) was also indicated by the comparison of the half-widths of the FeI 5247.1 and 5250.2 lines. In general, it can be concluded that the necessary conditions for the reconnection of magnetic lines were fulfilled even at the photospheric level, rather than in the corona or chromosphere, as suggested by theoretical models of solar flares.

The Doppler Spectrum of the Microwave Radar Signal Backscattered From the Sea Surface in Terms of the Modified Bragg Scattering Model

Significant progress has been made in the study of electromagnetic wave scattering from the sea surface. Essential results were obtained in solving applied problems, but there are still unsolved problems in the scattering theory. The radar backscatter cross section is usually used to solve remote sensing tasks, although the Doppler spectrum (DS) of the scattered microwave signal contains more information about sea waves. The concept of a two-scale model of the scattering surface is used in this article. Correct allowance for large-scale waves, in comparison with radar wavelength, in deriving theoretical formulas enabled us to develop a modified Bragg scattering model. It is based on the previously developed scattering model that is refined here to take into account the contribution of the horizontal component of the orbital velocity to the DS. It is shown that allowance for large-scale waves limits the growth of the radar cross section of the Bragg component with a decrease in the incidence angle, which allows using the resonant scattering model at small incidence angles. An additional result is that the modified model of the DS can also be used in the range of middle incidence angles because it takes into account the contribution of the horizontal component of the orbital velocity. It is shown that if the correlation between large-scale and small-scale components of sea waves is neglected, the new formulas pass into the known formulas for the DS within the framework of the Bragg scattering model.

Диамагнитные структуры — основа квазистационарного медленного солнечного ветра

The results presented in this review reflect the fundamentals of the modern understanding of the nature of the structure of the slow solar wind (SW) along the entire length from the Sun to the Earth's orbit. It is known that the source of the slow quasi-stationary SW on the Sun is the belt and the chains of coronal streamers The streamer belt encircles the entire Sun as a wave-like surface (skirt), representing a sequence of pairs of rays with increased brightness (plasma density) or two lines of rays located close to each other. Neutral line of the radial component of the solar global magnetic field goes along the belt between the rays of each of these pairs. The streamer belt extends in the heliosphere is as the heliospheric plasma sheet (HPS). Detailed analysis of data from Wind and IMP-8 satellites showed that HPS sections on the Earth orbit are registered as a sequence of diamagnetic tubes with high density plasma and low interplanetary magnetic field. They represent an extension of rays with increased brightness of the streamer belt near the Sun. Their angular size remains the same over the entire way from the Sun to the Earth's orbit. Each HPS diamagnetic tube has a fine internal structure on several scales, or fractality. In other words, diamagnetic tube is a set of nested diamagnetic tubes, whose angular size can vary by almost two orders of magnitude. These sequences of diamagnetic tubes that form the base of slow SW on the Earth's orbit has a more general name — diamagnetic structures (DS). In the final part of this article, a comparative analysis of several events was made, based on the results of this review. He made it possible to find out the morphology and nature of the origin of the new term “diamagnetic plasmoids” SW (local amplifications of plasma density), which appeared in several articles published during 2012–2018. The analysis carried out at the end of this article, for the first time, showed that the diamagnetic plasmoids SW are the small-scale component of the fractal diamagnetic structures of the slow SW, considered in this review.

Diamagnetic structures as a basis of quasi-stationary slow solar wind

The results presented in this review reflect the fundamentals of the modern understanding of the nature of the structure of the slow solar wind (SW) along the entire length from the Sun to the Earth's orbit. It is known that the source of the slow quasi-stationary SW on the Sun is the belt and the chains of coronal streamers The streamer belt encircles the entire Sun as a wave-like surface (skirt), representing a sequence of pairs of rays with increased brightness (plasma density) or two lines of rays located close to each other. Neutral line of the radial component of the solar global magnetic field goes along the belt between the rays of each of these pairs. The streamer belt extends in the heliosphere is as the heliospheric plasma sheet (HPS). Detailed analysis of data from Wind and IMP-8 satellites showed that HPS sections on the Earth orbit are registered as a sequence of diamagnetic tubes with high density plasma and low interplanetary magnetic field. They represent an extension of rays with increased brightness of the streamer belt near the Sun. Their angular size remains the same over the entire way from the Sun to the Earth's orbit. Each HPS diamagnetic tube has a fine internal structure on several scales, or fractality. In other words, diamagnetic tube is a set of nested diamagnetic tubes, whose angular size can vary by almost two orders of magnitude. These sequences of diamagnetic tubes that form the base of slow SW on the Earth's orbit has a more general name — diamagnetic structures (DS). In the final part of this article, a comparative analysis of several events was made, based on the results of this review. He made it possible to find out the morphology and nature of the origin of the new term “diamagnetic plasmoids” SW (local amplifications of plasma density), which appeared in several articles published during 2012–2018. The analysis carried out at the end of this article, for the first time, showed that the diamagnetic plasmoids SW are the small-scale component of the fractal diamagnetic structures of the slow SW, considered in this review.

A High-Precision Positioning Approach for Catenary Support Components With Multiscale Difference

The catenary support components (CSCs) are the most important devices in high-speed railways to support contact lines for powering trains. To estimate the states of CSCs, it is very necessary to locate their positions in a monitoring system based on computer vision. Considering the application scenarios and characteristics of CSCs, an automatic and quick positioning system is designed in this paper to simultaneously position the multiscale CSCs with 12 categories. In the system, an effective framework called CSCs network (CSCNET) is presented, which cascades the coarse positioning network and the fine positioning network to reduce multiscale differences between different CSCs. In the coarse positioning network, a new unsupervised clustering algorithm based on the relative positioning information is proposed to classify the catenary images. Then, a convolutional neural network (CNN) classification network is trained to extract the structural features of catenary images and generate the proposal regions with labels. In the fine positioning network, a modified CNN positioning framework is applied to obtain the accurate positions of CSCs based on the coarse positioning results. Due to the special lightweight structure with a classification network, the relative position information is applied and makes the CSCNET sensitive to small-scale components. The experimental results from some high-speed railway lines in China show that the proposed system has obvious advantages in the CSCs positioning. The mean average precision and frames per second of CSCNET reach 0.837 and 2.17, respectively. Compared with some popular convolutional networks [faster region-based CNN (Faster R-CNN), etc.] and a typical positioning method, the proposed system significantly improves the AP without increasing the computational time.

Effectiveness of a community-based water, sanitation, and hygiene (WASH) intervention in reduction of diarrhoea among under-five children: Evidence from a repeated cross-sectional study (2007-2015) in rural Bangladesh.

Diarrhoea, the most common disease directly related to water, sanitation, and hygiene (WASH), still remains one of the most significant health problems among children under-five worldwide. In this reality, BRAC, the largest NGO in the world initiated a comprehensive WASH intervention in 50 upazilas (sub-districts) of Bangladesh in 2007 which was later scaled up to cover 150 upazilas in two subsequent phases. The intervention period of the programme was 2007-2011. The present study encompassed 30 upazilas of the first phase of intervention. The aim of the study was to investigate the effectiveness of this intervention on reduction of diarrhoea among under-five children, and to identify the factors associated with childhood diarrhoea. A repeated cross-sectional study design was followed, and a population-based survey was carried out on four occasions: baseline (2007), midline (2009), endline (2011), and post-endline (2015) among 4,775 households. This analysis considers only households having at least one under-five children. Absence of handwashing practice with soap after defecation and before eating food, unclean latrine condition, and unsafe disposal of child faeces were identified as significant risk factors associated with under-five diarrhoea from Log-binomial regression. The prevalence of under-five diarrhoea within the past 2 weeks of the survey declined from 13.7% at baseline to 3.6% at end-line (p < 0.001) in the WASH intervention area. However, the progress seemingly stalled after 2011, which may have occurred due to the lack of improvement in unsafe disposal of child faeces and unclean latrine condition after the intervention period. Study findings suggest that, to reduce the prevalence of childhood diarrhoea it is important to promote safe disposal of child faeces, maintaining cleanliness of latrines, and washing hand with soap at critical times, beyond merely increasing the sanitation coverage. Findings also underline the necessity of maintaining a small-scale monitoring component involving local community, such as a WatSan committee (a local committee comprising the user communities for supervising WASH related activities) for periodic monitoring at household level for a certain period after the program intervention works to make the behavioural change more sustainable and to keep the reduction rate of under-five diarrhoeal prevalence steady.