Browsing Research articles (Dept of Physics) by Title
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Kumar, P.; Sathiaraj, T.S.; Thangaraj, R. (Taylor & Francis, NaN, 2010)[more][less]
Abstract: The measurements and analysis of optical transmission and far-infrared (IR) reflectivity spectra of thermally evaporated Sb2Se3:Sn films are reported. The refractive index and film thickness have been determined from the upper and lower envelopes of the transmission spectra (Swanepoel’s standard envelope method), measured at normal incidence, in the spectral range from 800 to 2500 nm. Values of the refractive index fit well to Cauchy’s dispersion relation. The optical gap decreases with an increase in the Sn content, while a maximum in the tailing parameter and Urbach’s energy occurs with only a small amount ( 1 at %) of this additive. Characteristic vibrational bands for SbSe3 structural units are revealed in the far-IR spectrum with no additional ones arising from the Sn additive. The Kramers–Kronig analysis has been used to calculate the dielectric constants and hence the longitudinal optic and transverse optic splitting for various compositions. The inclusion of Sn as a charged entity along with the Coulomb interactions which serve to polarize the glass medium is found to be responsible for these results. URI: http://hdl.handle.net/10311/547 Files in this item: 1
Optical properties.pdf (1.116Mb) -
Ringrose, S.; Kampunzu, A.B.; Vink, B.W.; Matheson, W.; Downey, W.S. (John Wiley & Sons, Ltd. http://www3.interscience.wiley.com/journal/117935722/grouphome/home.html, NaN, 2002)[more][less]
Abstract: Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an 'upper surface (1095 m) containing abundant sil-calcrete, an intermediate surface (1085 m) in which sil-calcrete underlies nodular calcrete and lower (1075 m) surface in which sil-calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing Si02 content (and increasing CaC03 content) with depth from the highest to the lowest surface levels. The calcretes and sil-calcretes represent modifications of pre-existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++ -rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying-induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid-Pleistocene age for sil-calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late st~ge dissolution of CaC03 from pre-existing surface calcretes or sil-calcretes led to the formation of pedogenic case-hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. URI: http://hdl.handle.net/10311/310 Files in this item: 1
Ringrose_ESPL_2002.pdf (3.095Mb) -
Kumar, J.; Ahmad, M.; Chander, R.; Thangaraj, R.; Sathiaraj, T.S. (EDP Sciences, NaN, 2008)[more][less]
Abstract: Effect of Pb substitution on the amorphous-crystalline transformation temperature, optical band gap and crystalline structure of Ge2Sb2Te5 has been studied. In Pb:GeSbTe chalcogenide films prepared by thermal evaporation, an amorphous to crystallization transition is observed at 124, 129, 136 and 138 ◦C in Pb0Ge20Sb24Te56, Pb1.6Ge19Sb26Te54, Pb3Ge17Sb28Te53 and Pb5Ge12Sb28Te55 respectively. XRD investigations of annealed samples reveal that Pb substitution retains NaCl type crystalline structure of GST but expands the lattice due to large atomic radii. The increase in amorphous-crystalline transformation temperature is followed with the increase in phase segregation. The optical gap shows marginal variations with composition. URI: http://hdl.handle.net/10311/531 Files in this item: 1
Phase segregation.pdf (573.5Kb) -
Kumar, J.; Ahmad, M.; Chander, R.; Thangaraj, R.; Sathiaraj, T.S. (EDP Sciences. http://www.epjap.org/, NaN, 2008)[more][less]
Abstract: Effect of Pb substitution on the amorphous-crystalline transformation temperature, optical band gap and crystalline structure of Ge2Sb2Te5 has been studied. In Pb:GeSbTe chalcogenide films prepared by thermal evaporation, an amorphous to crystallization transition is observed at 124, 129, 136 and 138 ◦C in Pb0Ge20Sb24Te56, Pb1.6Ge19Sb26Te54, Pb3Ge17Sb28Te53 and Pb5Ge12Sb28Te55 respectively. XRD investigations of annealed samples reveal that Pb substitution retains NaCl type crystalline structure of GST but expands the lattice due to large atomic radii. The increase in amorphous-crystalline transformation temperature is followed with the increase in phase segregation. The optical gap shows marginal variations with composition. URI: http://hdl.handle.net/10311/278 Files in this item: 1
Kumar_EPJAP41_2008.pdf (796.1Kb) -
Nijegorodov, N.; Zvolinski, V.; Luhanga, P.V.C.; Mabbs, R.; Ahmad, J. (Elsevier Ltd. www.elsevier.com/locate/saa, NaN, 2006)[more][less]
Abstract: The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293 K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6-5.2 kcal mol-1 in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha-Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed. URI: http://hdl.handle.net/10311/176 Files in this item: 2
license.txt (1.998Kb) -
Nijegorodov, N; Zvolinski, V; Luhanga, P V C; Mabbs, R; Ahmad, J (Elsevier Science Ltd. www.elsevier.com/locate/saa, NaN, 2006)[more][less]
Abstract: The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6–5.2 kcal mol−1 in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha–Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed. URI: http://hdl.handle.net/10311/247 Files in this item: 2
license.txt (1.998Kb)Nijegorodov_SAa65_2006.pdf (2.225Mb) -
Murty, V.R.K.; Devan, K.R.S. (Elsevier Science Ltd. www.elsevier.com/locate/radphyschem, NaN, 2004)[more][less]
Abstract: The interaction of photons with matter has been extensively studied over the past several decades in view of its importance in basic radiation physics research, medical, industrial and other applied fields. Large amounts of data have been complied on photon cross sections mostly in tabular and graphical forms (Hubbell, 1999, 1994; Berger and Hubbell, 1987). A careful survey of the latest bibliography (Hubbell, 1994) of experimental investigations shows gaps in the cross section data, especially in certain low-Z elements. These are mainly attributed to the difficulty in procuring thin absorbers in suitable form for low energy experiments. It was also evident from the bibliography that the cross section data was sparse for elements Mg and V, especially, using high resolution solid state detectors in the photon energy region below 100 keV. URI: http://hdl.handle.net/10311/266 Files in this item: 1
Murty_RPC_2004.pdf (191.6Kb) -
Nijegorodov, N.; Zvolinsky, V.; Luhanga, P.V.C. (Elsevier Science Ltd. www.elsevier.com/locate/jphotochem, NaN, 2008)[more][less]
Abstract: Intramolecular processes and fluorescence properties of 32 specially chosen aromatic molecules, different in degrees of planarity and rigidity, but family related in -structure are experimentally and theoretically (using the PPP-method) studied at room temperature (293 K). The quantum yields of fluorescence , and decay times τf, of deaerated and non-deaerated cyclohexane solutions are measured. The oscillator strength fe, the fluorescence rate constants kf, the natural lifetimes τT o , and the intersystem crossing rate constants kST, are calculated. The investigations showed the following differences in the behaviour of the fluorescence parameters in transition from the non-planar molecule to the planar and more rigid-type: the value of the symmetry line wave-number υ00 (the frequency of the S0→S1 * transition) and the Stokes shift υST, decrease. The oscillator strength and fluorescence constant, normally decrease. The change in the quantum yield of the fluorescence depends upon the changes in the kf and kST values. Furthermore, the intersystem crossing rate constant generally decreases, sometimes very significantly. However, there are some interesting exceptions. For example, the kST value of the non-planar molecule of 9,10-diphenylanthracene is less than the kST value of the planar and very rigid molecule of anthracene. This important phenomenon is explained. The differences of the intramolecular processes of planar and non-planar molecules are discussed. The photochemical stability of planar and non-planar molecules is studied. The effect of planarity, rigidity and molecular symmetry upon laser properties is also traced. URI: http://hdl.handle.net/10311/367 Files in this item: 1
Nijegorodov_JPPaC196_2008.pdf (1.901Mb) -
Mphale, K.M.; Heron, M.L. (Elsevier Science Ltd. www.elsevier.com/locate/jastp, NaN, 2007)[more][less]
Abstract: The flames of wildfires are weakly ionized gas. The ionization is mainly due to omnipresent alkali and alkaline earth metal species that are emitted from thermally decomposing plant structure into the flame during a wildfire. The amount of ionization in flames with alkali impurities is a factor of both the temperature and the quantity of the emitted alkali species in vegetation. Assuming a Maxwellian velocity distribution of flame particles and collision frequencies much higher than plasma frequencies, the propagation of radio waves through wildfires is predicted to have attenuation and phase shift. A theoretical model has been developed to predict propagation characteristics of HF–VHF radio signals at normal incidence to a high intensity wildfire fuel–flame interface. At the interface, the flame medium is modelled by a series of mini-slabs, each with a different but fixed electron density and dielectric permittivity governed by the Rayleigh distribution of temperature. Electron density in each mini-slab is calculated from thermal ionization of alkali species assuming the existence of thermal equilibrium. The model predicts average electron densities ranging from 10¹4 to 10¹7m–³ for fuel–flame interfaces with maximum temperatures from 900 to 1200 K. Specific attenuation and phase shift for propagation in the ionized gas are calculated from the predicted average electron density and collision frequency. At collision frequency of 10¹¹ s–¹, radio signal specific attenuation for the simulated grassfires range from 0.001 to 0.49 dBm–¹ while specific phase shift ranged from 0.0002 to 152°m–¹ for the maximum temperature range of 900–1150 K. URI: http://hdl.handle.net/10311/269 Files in this item: 1
Mphale_JASTP69_2007.pdf (2.265Mb) -
Kwadiba, M.T.O.G.; Wright, C.; Kgaswane, E.M.; Simon, R.E.; Nguuri, T.K. (Elsevier Science Ltd. www.elsevier.com/locate/lithos, NaN, 2003)[more][less]
Abstract: Pn arrivals from mining-induced earthquakes on the edge of the Witwatersrand basin show that the P wavespeeds in the uppermost mantle are almost constant throughout most of the Kaapvaal craton. The presence of only small wavespeed variations allows the use of a simple method of estimating crustal thicknesses below the stations of the Kaapvaal broad-band network using Pn times that has been compared with results from receiver functions. One thousand three hundred thirty-seven Pn arrivals were used to derive crustal thicknesses at 46 stations on the Kaapvaal craton. The average crustal thicknesses for 19 centrally located stations on each of the northern and southern regions of the craton that yielded well-constrained thicknesses were 50.52 ± 0.88 km and 38.07 ± 0.85 km, respectively. In contrast, the corresponding average thicknesses determined from receiver functions were 43.58 ± 0.57 km and 37.58 ± 0.70 km, respectively. The systematically lower values for receiver functions in the northern part of the Kaapvaal craton that was affected by the Bushveld magmatism at 2.05 Ga, suggest that the receiver functions do not enable the petrological crust mantle boundary to be reliably resolved due to variations in composition and metamorphic grade in a mafic lower crust. The Pn times also suggest pervasive azimuthal anisotropy with maximum wavespeeds of about 8.40 km/s at azimuths of about 15° and 217° in the northern and southern regions of the craton, respectively, and minimum wavespeeds of about 8.25 km/s. URI: http://hdl.handle.net/10311/281 Files in this item: 1
Kwadiba_L71_2003.pdf (2.747Mb) -
Jain, P.K.; Lungu, E.M.; Mogotsi, B. (Elsevier Science Ltd. http://www.sciencedirect.com/science/journal/09601481, January NaN, 2002)[more][less]
Abstract: Lack of trained manpower for repair and maintenance of solar energy devices in Botswana has resulted in failure of devices, loss of revenue, and dwindling of consumer faith in solar technologies. The government of Botswana commissioned a study to assess the needs for trained manpower in New and Renewable Sources of Energy (NRSE) technologies, to identify the required training programs and their levels, and the facilities that need to be upgraded and/or created for the implementation of such training programs at the existing technical and educational institutions within the country. The paper presents the findings of the study, and the recommendations made. The study proposed seven training programs at progressively increasing skills and expertise levels that include two certificate courses in each of the solar water heating and photovoltaic technologies for maintenance personnel, a national craft certificate program in solar energy technologies, a higher diploma in energy technologies for supervisory personnel, and a short course for upper management personnel in decision-making positions in order to raise their skills in the procurement of equipment and services, and to provide overall effective leadership. A short course to upgrade the skills of the present maintenance personnel to alleviate the immediate problems is also proposed. Required upgrading of existing technical training facilities, the creation of new facilities and estimated budgetary requirements constitute some of the recommendations. The recommendations have gone through various channels of discussions, and have been accepted in principle. The report is currently under consideration for implementation by relevant government departments. URI: http://hdl.handle.net/10311/137 Files in this item: 2
license.txt (1.998Kb) -
Masale, M. (Elsevier Science Ltd. http://www.elsevier.com/locate/physb, NaN, 2004)[more][less]
Abstract: The energy spectrum of an electron confined near a current-carrying core is obtained as a function of the azimuthal applied magnetic field within the effective-mass approximation. The double degeneracy of the non-zero electron's axial wave number (kz) states is lifted by the current-induced magnetic field while that of the non-zero azimuthal quantum number (m) states is preserved. A further analysis is the evaluations of the oscillator strengths for optical transitions involving the lowest-order pair of the electron's energy subbands within the dipole approximation. The radiation field is taken as that of elliptically polarized light incident along the core axis. In this polarization and within the dipole approximation, the allowed transitions are only those governed by the following specific selection rules. The azimuthal quantum numbers of the initial and final states must differ by unity while the electron's axial wave number is conserved. The azimuthal magnetic field is also found to lift the multiple degeneracies of the kz=0 interaction integrals as well as those of the oscillator strengths for optical transitions. URI: http://hdl.handle.net/10311/244 Files in this item: 2
license.txt (1.998Kb)Masale_PB_2004.pdf (1.197Mb) -
Wright, C.; Kgaswane, E.M.; Kwadiba, M.T.O.; Simon, R.E.; Nguuri, T.K.; McRae-Samuel, R. (Elsevier Science Ltd. www.elsevier.com/locate/lithos, NaN, 2003)[more][less]
Abstract: Events induced by deep gold-mining activity on the edge of the Witwatersrand basin dominate the seismicity of South Africa. The deployment of 54 broad-band seismic stations at 84 separate locations across southern Africa between April 1997 and April 1999 (Kaapvaal network) enabled the seismicity of South Africa to be better defined over a 2-year period. Seismic events located by the South African national network, and by localized seismic networks deployed in mines or across goldmining areas, were used to evaluate earthquake location procedures and to show that the Kaapvaal network locates mininginduced tremors with an average error of 1.56 ± 0.10 km compared with 9.50 ± 0.36 km for the South African network. Travel times of seismic events from the mines recorded at the Kaapvaal network indicate regional variations in the thickness of the crust but no clearly resolved variations in seismic wavespeeds in the uppermost mantle. Greater average crustal thicknesses (48–50 km compared with 41–43 km) are observed in the northern parts of the Kaapvaal craton that were affected by the Bushveld magmatism at 2.05 Ga. Estimates of average crustal thickness for the southern part of the Kaapvaal craton from receiver functions (38 km) agree well with those from refracted arrivals from mining-induced earthquakes if the crustal thicknesses below the sources are assumed to be 40–43 km. In contrast, the average crustal thickness inferred from refracted arrivals for the northern part of the Kaapvaal craton is larger by about 7 km (51 km) than that inferred from receiver functions (44 km), suggesting a thick mafic lower crust of variable seismic properties due to variations in composition and metamorphic grade. Pn wavespeeds are high (8.3–8.4 km/s), indicating the presence of highly depleted magnesium-rich peridotite throughout the uppermost mantle of the craton. Seismic Pg and Sg phases indicate that the upper crust around the Witwatersrand basin is comparatively uniform in composition when averaged over several kilometres. URI: http://hdl.handle.net/10311/280 Files in this item: 1
Wright_L71_2003.pdf (3.483Mb) -
Jain, P.K.; Lungu, E.M. (Elsevier Science Ltd: http://www.elsevier.com/wps/find/journaldescription.cws_home/969/description#description, NaN, 2002)[more][less]
Abstract: Abstract Harmonic analysis of sunshine duration and solar irradiation measured at Sebele, Botswana is carried out. The data used consists of the monthly averages and the Julian-days averages of sunshine duration and solar irradiation sequences. This study involves splitting the time series into deterministic and stochastic components, and determining the proportion of the variance explained by each component. The stochastic component is analyzed for persistence using the Box and Jenkins technique. It is found that the stochastic component for monthly averages solar radiation series is best described by the second-order autoregressive Markov process, while that for Julian-days averages series has no memory. URI: http://hdl.handle.net/10311/138 Files in this item: 2
license.txt (1.998Kb) -
Masale, M. (Elsevier Science Ltd. www.elsevier.com/locate/physb, February NaN, 2002)[more][less]
Abstract: The experimental techniques of attenuated total reflection and grating-coupling were originally employed separately as probes for surface polaritons. However, as far back as the mid-1970s, some value was found in actually combining them into a single tool for probing elementary surface excitations. In this article, the theory of the two methods combined into one probe for surface polaritons is presented. The main results of the calculations, here, are the firstorder diffuse reflectivities, which arise due to the presence of a classical grating. For the ease of presentation, only a semi-infinite specimen is considered and the grating is thought to be deposited only on one interface. The discussion highlights the advantages the combined technique has over either of the two methods when each is employed on its own. URI: http://hdl.handle.net/10311/195 Files in this item: 2
license.txt (1.998Kb) -
Masale, M. (Elsevier Science Ltd. http://www.elsevier.com/wps/find/journaldescription.cws_home/505712/description#description, NaN, 2003)[more][less]
Abstract: The experimental techniques of attenuated total reflection (ATR) and grating coupling were originally employed separately as probes for polaritons. The combined technique of these methods into a single probe is a very versatile tool for probing elementary surface excitations. A theoretical investigation of this single probe for surface polaritons, ATRgrating coupling, is undertaken. The emphasis is on the calculations of first-order diffuse reflectivities, which arise due to the presence of a classical grating. More specifically, the ATR set-up in the Otto configuration is considered and for ease of presentation of the results, a classical grating is thought to be deposited on only one interface of a surface-active thin-film specimen. The discussion highlights the advantages the combined technique has over either of the two methods when each is employed on its own. URI: http://hdl.handle.net/10311/233 Files in this item: 2
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Thermal annealing dependence of some physical propertiesof Bi-substituted Sn–Sb–Se glassy thin filmsAhmad, M.; Thangaraj, R.; Sathiaraj, T.S. (EDP Sciences, NaN, 2009)[more][less]
Abstract: Bulk glasses of the Sn10Sb20−xBixSe70 (0 x 8) system were prepared by the conventional melt quenching technique. Thin films were prepared by the thermal evaporation technique on glass substrates. Appearance of some crystalline phases is observed from the X-ray diffractograms after heat treatment below the glass transition temperature for 1 h. Scanning electron microscopy studies also show the presence of microcrystalline phases in the amorphous matrix after annealing for 1 h. The effect of Bi concentration and heat treatment on the optical gap and activation energy for dark conductivity were also investigated for the pristine as well as annealed films. The results are discussed on the basis of models related to the presence of defect states in chalcogenide materials. URI: http://hdl.handle.net/10311/534 Files in this item: 1
Thermal annealing dependence.pdf (822.7Kb) -
Masale, M. (Elsevier Science Ltd. www.elsevier.com/locate/physc, January NaN, 2003)[more][less]
Abstract: The problem of a type II superconducting disk in a spatially inhomogeneous magnetic field is considered. The aim of the investigations undertaken here is to evaluate the effects of the spatial inhomogeneity of the parallel component of the applied magnetic field on the nature of the superconducting nucleation of a short cylinder. Full numerical solutions of the linearized Ginzburg-Landau equation for the order parameter, taking into account only the parallel component of the field, are presented in the case of a solid disk;free-standing and in a metallic matrix. In the case of a mesoscopic system, only the limiting form of the critical temperature is obtained. The temperature-field (e-f) curves are characterized by flux-entry points at each of which the azimuthal quantum number decreases by unity. The quasi-period of the flux-entry points increases in f with the increasing strength of the spatial inhomogeneity of the applied field. The increased effect of coating the superconductor with a suitable normal metal leads to the well known suppression of the critical temperature as well as smoothing out of flux entries. It is predicted that the wiping out of surface nucleation is effected with relative ease when the applied magnetic field is uniform than when it posseses a degree of spatial inhomogeneity. URI: http://hdl.handle.net/10311/197 Files in this item: 2
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Otiti, T.; Ekosse, G-I.; Stephen, S.T. (Bioline International. http://www.ajol.info/journal_index.php?jid=90, June NaN, 2007)[more][less]
Abstract: Normal, helical and zigzag deposited Ni films were produced by letting a vapour stream of source material impinge on Corning 1737 glass substrates at oblique incidence while rotating the substrate during deposition. Films produced by glancing angle deposition (GLAD) technique while rotating the substrate. The microstructures of these Ni films were studied using X-ray diffractometry technique. The X-ray diffraction (XRD) patterns depicted 100% and 42% relative intensity (RI) peaks identified for normal and helical deposited Ni films but none for the zigzag deposited Ni film. Higher degree of crystallinity of Ni was demonstrated by the helical thin film sample having 200 nm thickness (sample Ni40) compared to the normal thin film which had only the 100% RI peak defined. Should an application therefore require Ni thin films of high crystallinity, it would be the film prepared with helical microstructure of 200 nm thickness that will be employed. URI: http://hdl.handle.net/10311/353 Files in this item: 2
license.txt (1.998Kb)Otiti_JASEM11_2007.pdf (451.5Kb)
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