X-ray spectroscopic study of chemical bonding in NiSe and NiSe2

The K absorption spectra of nickel and selenium have been recorded photographically in the pure metals and the compounds NiSe and NiSe₂. It has been observed that the Ni discontinuity shifts toward the high energy side with respect to that in the pure metal by about 5.0 eV for NiSe and about 6.7 eV for NiSe₂. The Se edge in both these compounds is found to shift by about 2.6 eV toward the low energy side with respect to that in pure selenium. From these results it is possible to obtain the bonding pictures for the compounds. The compound NiSe appears to have resonating p³ type of bonding. For NiSe₂ the orbitals involved in the bonding are d²sp³ for the metal atom and sp³ for the metalloid atom. The electrical behaviour of the compounds has been explained on the basis of these bonding pictures.     

X-ray spectroscopic study of chemical bonding in MnSe2 and CoSe2

X-ray absorption study of two intermetallic compounds MnSe₂ and CoSe₂ has been carried out using a Cauchois type bent crystal spectrograph. The metal K absorption edges in both the compounds are found to shift toward the high energy side with respect to the discontinuities in the pure metals. On the other hand, the Se K absorption edge in both these compounds is found to shift toward the lower energies. Emission study of the compound MnSe₂ has shown that the Mn Kβ ₅ band in this compound is shifted toward the high energy side with respect to that in the pure metal. From the magnetic data and the results obtained in this work it is possible to obtain the chemical bonding pictures in these compounds. For MnSe₂ the bondings sp ³ d ² for the metal atom andsp ³ for the metalloid atom have been suggested. For CoSe₂ the bondings appear to bed ² sp ³ for the metal atom andsp ³ for the metalloid atom. These bondings are compatible with the pyrite type structure of these compounds. It is possible to explain the electrical behaviour of the compounds on the basis of these bonding pictures.     

The shapes of the LIII X-ray absorption discontinuity of rhenium in compounds

The X-ray L_III absorption edge of rhenium in the pure metal and in two compounds, namely, K₂ReCl₆ and KReO₄ has been studied using a Cauchois type bent crystal spectrograph of 40 cm diameter. The splitting of the main absorption discontinuity has been observed for the first time in the compounds. This splitting and the edge structure of the Re L_III discontinuity in the compounds have been interpreted on the basis of molecular orbital diagrams. The crystal field splitting, Δ, has been determined experimentally in both the compounds in the solid state.     

Angle- and time-resolved mass spectrometric study on pulsed laser ablation of an La-Ca-Mn-O target

Pulsed laser ablation (PLA) of an La₂O₃-CaO-MnO₂ target at 532 nm has been investigated by angle- and time-resolved quadrupole mass spectrometry. The results show that different kinds of metal oxides as well as metal ions and atoms are produced during the ablation at high laser fluence. The measured TOF spectra are fitted by multicomponent Maxwell-Boltzmann distribution with a stream velocity, which gives the translational energy of 6.34 and 0.43 eV for Mn⁺ ions and Mn atoms, respectively. It implies that ablated ions are mainly formed via a nonthermal process, while the neutral atoms mainly via a thermal one. The angular distributions of Mn + ions and Mn atoms can be described by a cos ⁿ θ and a bicosine function a cosθ+ (1-a)cos ⁿ θ, respectively. Possible mechanisms of laser ablation of La-Ca-Mn-0 are discussed. Project supported by the National Natural Science Foundation of China (Grant No. 29683001).     

The growth and decay of sonic waves in a radiating gas at high temperature

The propagation of a sonic discontinuity in an optically thick gray gas at temperature 10⁵°K or higher has been studied. The effects of radiation pressure and radiation energy density have been taken into account, while the profiles structured by radiant heat transfer are imbedded in the discontinuities under high temperature conditions of an optically thick medium. When the sonic discontinuity is propagating into a gas at rest, its velocity of propagation is found to be a constant which is the effective speed of sound in a radiating gas. The fundamental differential equations governing the growth of the sonic discontinuity are obtained and solved. It is concluded that if the sonic discontinuity is a compressive wave of order 1, then it terminates into a shock wave after a critical timet _c which has been determined. But on the other hand, when the sonic discontinuity is an expansion wave of order 1, then it will decay and will vanish ultimately. Particular cases of interest have been studied in details.     

Ag/Si multilayers with nanometer sized particles of silver during annealing process

Thein situ low angle X-ray diffraction and transmission electron microscopy were used to monitor the interdiffusion characteristics as well as the microstructure in Ag/Si multilayers with modulated wavelength 7. 64 nm when annealing from 323 to 573 K. The interdiffusion mechanism of Ag/Si multilayers with immiscibility is different from that of other metal/Si multilayers which are miscible. Phase separation takes place at 323 K, then silicon atoms diffuse into silver sublayers through silver grain boundaries and separate silver sublayers into nanometer sized silver particles gradually at higher temperature. The mean size of silver particles is about 5 nm. The activation energy and frequency factor are determined to be 0.24 eV and 2.02 x⁻²⁰m²/s, respectively. An erratum to this article is available at .     

Optical properties of nanocrystalline silicon embedded in SiO2

Nanocrystalline silicon embedded SiO₂ matrix has been formed by annealing the a-SiO_x films fabricated by plasma enhanced chemical vapor deposition technique. Absorption and photoluminescence spectra of the films have been studied in conjunction with micro-Raman scattering spectra. It is found that absorption presents an exponential dependence of absorption coefficient to photon energy in the range of 1.5–3.0 eV, and a sub-band appears in the range of 1.0–1.5 eV. The exponential absorption is due to the indirect band-to-band transition of electrons in silicon nanocrys-tallites, while the sub-band absorption is ascribed to transitions between surfaces and/or defect states of the silicon nanocrystallites. The existence of Stokes shift between absorption and photoluminescence suggests that the phonon-assisted luminescence would be enhanced due to the quantum confinement effects.     

γ-rays from discrete radio sources

The fluxes of low energy (～100 MeV) and high energy (～5×10¹² eV)γ-rays from intense radio sources have been calculated under the hypothesis that radio electrons are continuously produced through nuclear collisions. The effect of expansion of the source which gives rise to a decrease in production rate with time has been taken into account in these calculations. It is found that the fluxes expected from nuclear collision process are generally higher than the fluxes from other processes like bremstrahlung and inverse compton scattering by factors of 10 or more. While the calculated fluxes ofγ-rays of energy >100 MeV are less than the observed upper limits for all the processes, the fluxes calculated for nuclear collision process for E>5×10¹² eV, exceed the experimental upper limits for Crab, Cas A and the jet in Virgo A. More sensitive experiments should be able to decide whether the nuclear collision process is ruled out for low energies as well: in this respect Cas A seems to be the most promising source.     

Full-potential LMTO study on the electronic structure of heavy-fermion compound LiV2O4

The electronic structure of heavy fermion compound LiV₂O₄ has been calculated using a self-consistent full-potential LMTO method. The results show that the conduction bands in this compound are formed from V 3 d states with a bandwidth of 2.5 eV. The symmetric characteristics of conduction bands are of t_2g in principle. The energy gap between conduction bands and fully occupied oxygen 2p bands is 1.9 eV. The band dispersions near Fermi energy display complicated structures. Furthermore, the N( E_F) and y_cal are 11.1 (states/eV/f.u.) and 26.7 mJ/mol.K₂ determined numerically by LDA calculation, respectively. It is insufficient to clarify the origin of local moment in LiV₂O₄ from plain LDA calculations. In addition to the above LDA calculation, we also found a LSDA solution of LiV₂O₄ that is lower in total energy than that of LDA calculation. Similarly, LSDA + GGA calculation yields almost the identical result as that in LSDA. We conclude that the mechanism responsible for heavy fermion properties in LiV₂O₄ might be somewhat different from the plain Kondo mechanism in conventional 4f and 5f heavy fermion compounds and perhaps the quantum transition might play an adequate role in heavy-ferrnion behaviors in LiV₂O₄.     

X-ray spectroscopic study of the thiomalic acid complex of cobalt

The cobalt K absorption spectrum has been studied in thiomalic acid complex of cobalt using a bent crystal X-ray spectrograph. It has been observed that the position of the absorption discontinuity taken with the freshly prepared complex differs from that of the discontinuity obtained with the complex kept in air for about 24 hours. It has been shown that this shift of the absorption edge is due to the change in valency of cobalt in the complex. The shape of the absorption discontinuity has revealed that the complex has an octahedral structure with the hybridizationsp ³ d ². On the molecular orbital theory the electronic configuration in this complex can be described asa _1g ^Emphasis>2 t _1u ^Emphasis>6 e _g ^Emphasis>4 t _2g ^Emphasis>4 e _g ^Emphasis>*2 .     

Full-potential LMTO study on the electronic structure of heavy-fermion compound LiV2O4

The electronic structure of heavy fermion compound LiV2O4 has been calculated using a self-consistent full-potential LMTO method. The results show that the conduction bands in this com pound are formed from V 3 d states with a bandwidth of 2.5 eV. The symmetric characteristics of con duction bands are of t2g in principle. The energy gap between conduction bands and fully occupied oxygen 2 p bands is 1.9 eV. The band dispersions near Fermi energy display complicated structures.Furthermore, the N(EF) and γcal are 11.1 (states/eV/f. u. ) and 26.7 mJ/mol@ K2 determined numer ically by LDA calculation, respectively. It is insufficient to clarify the origin of local moment in LiV2O4 from plain LDA calculations. In addition to the above LDA calculation, we also found a LSDA solution of LiV2O4 that is lower in total energy than that of LDA calculation. Similarly, LSDA + GGA calculation yields almost the identical result as that in LSDA. We conclude that the mechanism responsible for heavy fermion properties in LiV2O4 might be somewhat different from the plain Kondo mechanism in conventional 4 f and 5 f heavy fermion compounds and perhaps the quantum transition might play an adequate role in heavy-fermion behaviors in LiV2O4.     

Spectrophotometric study of the uranyl-streptomycin complex

Spectrophotometric studies of the yellow coloured complex of uranyl ion with streptomycin have been carried out. The complex absorbs maximum at 420 mµ and at a pH value of 3·5. The composition of the complex has been ascertained employing Job’s method, mole ratio method and slope ratio method and found to be 1:1. The apparent stability constant (logK) and free energy of formation (ΔF) of the complex at 40° C have been found to be 3·37 and ?4·83K cal per mole respectively.     

Ratio of pions to protons and ratio of neutral to charged interacting particles at mountain altitude of 800 gm/cm2

Using a combined set-up of a multiplate cloud chamber, an air Cerenkov counter and a total absorption spectrometer, the ratio of pions to protons not associated with large air showers has been determined to be 0·50 ± ·07 in the energy region 20–40 GeV at an altitude of 800 gm/cm². In the same energy region the ratio of neutral to charged particles is found to be 0·66 ± ·07. From the ratio of neutrons to protons deduced from these measurements (i.e., 0·99 ± ·11), it is concluded that most of the charge excess of nuclear active particles of energies > 20 GeV at mountain altitudes and sea-level is due to pions.     

Recent observations on cosmic electrons and their consequences on different cosmic ray models and related astrophysical quantities

An experiment has been carried out to study the electron component of the primary cosmic radiation at energies >12 GeV using a hypersensitised nuclear emulsion stack, flown oriented in the east-west plane over Hyderabad, India. The results of this experiment, on the basis of 28 identified electrons of energy above 12 GeV are: (i) the integral flux of electrons above an effective energy of 16 GeV is 0·51±·10 per m.² sec. sr.; (ii) the differential energy spectrum between 12 and 300 GeV can be represented as N(E)dE=12·7 E^?2.1±·2 dE m.^?2 sec.^?1 sr.^?1; and (iii) the fraction of positrons among the total electrons in the energy region 12 to 30 GeV has been discussed. A critical study has been made on the applicability of different cosmic ray models by making use of the observed differential energy spectrum of electrons and the relevant astrophysical parameters associated with the confinement regions. The confinement regions considered are: (i) the universe as a whole, (ii) the super cluster to which our galaxy belongs, (iii) the galactic halo and (iv) the galactic disc. The consequences of the recently postulated universal black body radiation at 3° K. on the cosmic ray models have also been considered. Some of the crucial experiments needed to set more stringent constrains on the models which would then permit meaningful interpretation, are enumerated.     

Ordinals and scattered compact ordered spaces

Scattered Compact Ordered Spaces (SCOS) are studied with respect to their well ordered images and preimages. Typical results:

1. A SCOS is homeomorphic to an ordinal iff it has no pit point (a pit in an ordered space is one with infinite left and right cofinalities, one of which is uncountable).
2. A SCOS of characteristic <μ,m> is mappable onto and includes ω^μ·m+1; it is also an image of ω^μ·(2m)+1. The SCOSs are characterized by: Theorem 5: Let K be a Hausdorff space. The following conditions are equivalent:
3. K is homeomorphic to a compact scattered ordered space.
4. K is an order-two image of a compact ordinal. A.M.S. (MOS) Subject Classification: Primary: 54F05, 54F65, 06A45 Secondary: 54D30.

     

Spectrophotometric studies of copper (II)—bis-2-pyridyl glycol complex

An aqueous solution ofbis-2-pyridyl glycol forms a deep blue water-soluble complex with an aqueous solution of copper (II) salts. The complex has an absorption maximum at 600–650 mµ between pH range 3·0–8·7. The complex is stable for four days and obeys Lambert-Beer’s law in the concentration range of 5·08–50·80 ppm. of copper (II) in solution. The optical density of the complex remains constant between pH 3·8–5·9. The molar composition as determined by the method of continuous variation and by the slope ratio method has been found to be 1:1. The limits of interference due to some foreign ions during the estimation of copper (II) have been determined.     

A possible cosmic ray primary particle energy spectrum above 104 GeV and its astrophysical implications

A primary cosmic ray particle energy specturm of Galactic origin with a sharp cut-off at an energy per nucleon of 3 × 10⁴ GeV for protons and 5 × 10⁴ GeV for heavier particles and extending only upto energies ～ 10¹⁵ eV is deduced in part from the observed cosmic ray phenomena at the highest energies. It appears that the cut off is not due to the magnetic rigidity of the particles in the Galaxy but due to a cut off in or near the sources themselves. In particular, it is pointed out that Fermi type of acceleration is unlikely to be important in the production of energetic cosmic ray particles in the Galaxy. A pedestal in the energy spectrum from an extra Galactic component upto a maximum energy per nucleon ～ 10⁷ GeV with an upper limit of total energies ～ 10¹⁸ eV has been added.     

Studies in the hydrolysis of metal ions

The hydrolysis of cupric ion has been studied at various ionic strengths (0·01, 0·05, 0·1 and 0·5 M). The results are analyzed employing ‘core + links’ theory, log-log plot, normalization plot, and extrapolation method for obtaining the pure mononuclear curve. The stability constants of Cu₂(OH) ₂ ⁺⁺ , Cu₃(OH) ₄ ⁺⁺ , Cu(OH)⁺ and Cu(OH)₂ have been reported.     

Titrimetric determination of manganese and its separation from iron using pyridine and thiocyanate

The method describes the indirect estimation of manganese volumetrically using thiocyanate and pyridine. In a standard measuring flask a known aliquot of manganese solution is taken to which is added pyridine and an excess of a standard thiocyanate solution. Manganese gets precipitated as Mn Py₄ (SCN)₂. The solution is filtered and the measured aliquot of the filtrate, after acidifying, is treated with an excess of standard silver nitrate solution. The excess of silver nitrate is then back-titrated with standard thiocyanate solution using ferric alum as the indicator. In the separation of Mn from Fe, the latter is quantitatively precipitated as hydroxide by treatment with slight excess of pyridine. The precipitated iron is removed by filtration and the manganese in the filtrate is estimated as described above. Quantitative results for Mn are obtained by double precipitation.     

Estimation of the quality of adhesion of a metallic coating to a polymer film using the scratch method

A method of determining the quality of adhesion of a metallic coating to a polymer film at coating thicknesses of 1000–3000 Å and film thicknesses of 10–100 µ using the scratch method is described. The results of testing various aluminized polyethylene terephthalate and polyethylene film specimens, differing with respect to the treatment of the polymer surface before deposition of the metal, are presented. The aluminization vacuum was 5 · 10^?4 or 9 · 10^?3 mm Hg.