bluuebunny/crossref_metadata_2025 huggingface dataset:
Genome‐wide transcriptomic and proteomic analysis of the primary response to phosphate limitation in Streptomyces coelicolor M145 and in a ΔphoP mutant
Authors: Rodríguez‐García Antonio , Barreiro Carlos , Santos‐Beneit Fernando , Sola‐Landa Alberto , Martín Juan F.
Published: July 2007

Phosphate limitation in Streptomyces and in other bacteria triggers expression changes of a large number of genes. This response is mediated by the two‐component PhoR–PhoP system. A Streptomyces coelicolor ΔphoP mutant (lacking phoP) has been obtained by gene replacement. A genome‐wide analysis of the primary response to phosphate limitation using transcriptomic and proteomic studies has been made in the parental S. coelicolor M145 and in the ΔphoP mutant strains. Statistical analysis of the contrasts between the four sets of data generated (two strains under two phosphate conditions) allowed the classification of all genes into 12 types of profiles. The primary response to phosphate limitation involves upregulation of genes encoding scavenging enzymes needed to obtain phosphate from different phosphorylated organic compounds and overexpression of the high‐affinity phosphate transport system pstSCAB. Clear interactions have been found between phosphate metabolism and expression of nitrogen‐regulated genes and between phosphate and nitrate respiration genes. PhoP‐dependent repressions of antibiotic biosynthesis and of the morphological differentiation genes correlated with the observed ΔphoP mutant phenotype. Bioinformatic analysis of the presence of PHO boxes (PhoP‐binding sequences) in the upstream regions of PhoP‐controlled genes were validated by binding of PhoP, as shown by electrophoretic mobility shift assays.
Proteome analysis and characterization of phenotypes of lesion mimic mutantspotted leaf 6in rice
Authors: Kang Sang Gu , Matin Mohammad Nurul , Bae Hanhong , Natarajan Savithiry
Published: July 2007

Ricespotted leaf 6(spl6) mutant produces lesions caused by spontaneous cell death in the absence of pathogenic infection. Expression of this genetic trait was developmentally programmed. After the tillering stage, small red and brown lesions were initiated in groups on the leaf blade. Eventually, the lesions formed parallel lines along the midrib of the leaf. Under light and transmission electron microscopy, we observed that thylakoid membranes of mesophyll chloroplasts were progressively damaged in the nonspotted section of the mutant leaf. However, chloroplasts were absent in the mesophyll cells of the spotted area of thespl6mutant. These results indicated that lesion formation of thespl6mutant might be caused by oxidative burst. Proteome analysis revealed that 159 protein spots were up or downregulated in comparison between spotted leaves of thespl6mutant plants and normal leaves of the wild type. Among them, protein disulfide isomerase (PDI), transketolase, thioredoxin peroxidase (TPX), ATP synthase, RuBisCO large subunit, and RuBisCO activase small subunit were not identified in thespl6mutant but were abundant in the wild type. Especially, the absence of TPX and PDI might be the cause of the failure to protect cells against oxidative burst resulting in degradation of the thylakoid membranes and leading to programmed cell death and lesion development.
Proteomic analysis of plasma membrane lipid rafts of HL‐60 cells
Authors: Yanagida Mitsuaki , Nakayama Hitoshi , Yoshizaki Fumiko , Fujimura Tsutomu , Takamori Kenji , Ogawa Hideoki , Iwabuchi Kazuhisa
Published: July 2007

Neutrophils acquire phagocytic activity as they differentiate. Recently, plasma membrane lipid rafts have been shown to play important roles in the process of phagocytosis in neutrophils. To characterize the proteins involved in phagocytosis and to elucidate the process by which they acquire phagocytic activity, we investigated by nano‐LC‐MS/MS analysis the changes in protein composition of plasma membrane lipid rafts during DMSO‐induced differentiation of the human leukemia cell line HL‐60 cells into neutrophilic lineage. Based on the spectrum counts of 147 proteins identified, 25 proteins were upregulated and 49 were downregulated by DMSO treatment. CD11b/CD18 subunits of β2‐integrin Mac‐1, CD35, and GPI‐80, which are known to be upregulated during differentiation, were dominantly detected in the lipid rafts of DMSO‐treated cells. Many known membrane proteins, G proteins, and cytoskeletal proteins were also detected and they showed characteristic distributions. Absolute quantification of nine proteins in the lipid rafts using internal standard peptides labeled with stable isotopes showed that the amount of protein almost corresponded to the results obtained by spectrum count. Identified proteins, expression of which was altered by DMSO treatment, are expected to be candidate proteins involved in differentiation and functions of neutrophils.
Proteomics of nipple aspirate fluid, breast cyst fluid, milk, and colostrum
Authors: Ruhlen Rachel L. , Sauter Edward R.
Published: July 2007

Proteomic analysis of breast fluids has wide‐ranging clinical applications. Protein expression in nipple aspirate fluid and breast cyst fluid may prove valuable for the detection and monitoring of breast cancer, but has been hampered by the lack of a single marker with sufficient breast cancer sensitivity and specificity to be clinically useful. The assessment of multiple proteins may offer a more powerful cancer detection tool. Breast cancer is particularly difficult to detect in women who are lactating. The identification of cancer predicting proteins in milk may prove very helpful in an early cancer detection in this group of women. A better understanding of the protein composition of milk and colostrum should improve infant care and nutrition, and lead to alternatives for individuals with milk allergies.
Common conformational changes in flavodoxins induced by FMN and anion binding: The structure of Helicobacter pylori apoflavodoxin
Authors: Martínez‐Júlvez Marta , Cremades Nunilo , Bueno Marta , Pérez‐Dorado Inmaculada , Maya Celia , Cuesta‐López Santiago , Prada Diego , Falo Fernando , Hermoso Juan A. , Sancho Javier
Published: July 2007

Flavodoxins, noncovalent complexes between apoflavodoxins and flavin mononucleotide (FMN), are useful models to investigate the mechanism of protein/flavin recognition. In this respect, the only available crystal structure of an apoflavodoxin (that from Anabaena) showed a closed isoalloxazine pocket and the presence of a bound phosphate ion, which posed many questions on the recognition mechanism and on the potential physiological role exerted by phosphate ions. To address these issues we report here the X‐ray structure of the apoflavodoxin from the pathogen Helicobacter pylori. The protein naturally lacks one of the conserved aromatic residues that close the isoalloxazine pocket in Anabaena, and the structure has been determined in a medium lacking phosphate. In spite of these significant differences, the isoallozaxine pocket in H. pylori apoflavodoxin appears also closed and a chloride ion is bound at a native‐like FMN phosphate site. It seems thus that it is a general characteristic of apoflavodoxins to display closed, non‐native, isoalloxazine binding sites together with native‐like, rather promiscuous, phosphate binding sites that can bear other available small anions present in solution. In this respect, both binding energy hot spots of the apoflavodoxin/FMN complex are initially unavailable to FMN binding and the specific spot for FMN recognition may depend on the dynamics of the two candidate regions. Molecular dynamics simulations show that the isoalloxazine binding loops are intrinsically flexible at physiological temperatures, thus facilitating the intercalation of the cofactor, and that their mobility is modulated by the anion bound at the phosphate site. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Protonation state and substrate binding to B2 metallo‐β‐lactamase CphA from Aeromonas hydrofila
Authors: Simona F. , Magistrato A. , Vera D. M. A. , Garau G. , Vila A. J. , Carloni P.
Published: July 2007

The zinc enzymes metallo β‐lactamases counteract the beneficial action of β‐lactam antibiotics against bacterial infections, by hydrolyzing their β‐lactam rings. To understand structure/function relationships on a representative member of this class, the B2 MβL CphA, we have investigated the H‐bond pattern at the Zn enzymatic active site and substrate binding mode by molecular simulation methods. Extensive QM calculations at the DFT‐BLYP level on eleven models of the protein active site, along with MD simulations of the protein in aqueous solution, allow us to propose two plausible protonation states for the unbound enzyme, which are probably in equilibrium. Docking procedures along with MD simulations and QM calculations suggest that in the complex between the enzyme and its substrate (biapenem), the latter is stable in only one of the two protonation states, in addition it exhibits two different binding modes, of which only one agrees with previous proposals. In both cases, the substrate is polarized as in aqueous solution. We conclude that addressing mechanistic issues on this class of enzymes requires a careful procedure to assign protonation states and substrate docking modes. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Substrate polarization in enzyme catalysis: QM/MM analysis of the effect of oxaloacetate polarization on acetyl‐CoA enolization in citrate synthase
Authors: van der Kamp Marc W. , Perruccio Francesca , Mulholland Adrian J.
Published: July 2007

Citrate synthase is an archetypal carbon–carbon bond forming enzyme. It promotes the conversion of oxaloacetate (OAA) to citrate by catalyzing the deprotonation (enolization) of acetyl‐CoA, followed by nucleophilic attack of the enolate form of this substrate on OAA to form a citryl‐CoA intermediate and subsequent hydrolysis. OAA is strongly bound to the active site and its α‐carbonyl group is polarized. This polarization has been demonstrated spectroscopically, [(Kurz et al., Biochemistry 1985;24:452–457; Kurz and Drysdale, Biochemistry 1987;26:2623–2627)] and has been suggested to be an important catalytic strategy. Substrate polarization is believed to be important in many enzymes. The first step, formation of the acetyl‐CoA enolate intermediate, is thought to be rate‐limiting in the mesophilic (pig/chicken) enzyme. We have examined the effects of substrate polarization on this key step using quantum mechanical/molecular mechanical (QM/MM) methods. Free energy profiles have been calculated by AM1/CHARMM27 umbrella sampling molecular dynamics (MD) simulations, together with potential energy profiles. To study the influence of OAA polarization, profiles were calculated with different polarization of the OAA α‐carbonyl group. The results indicate that OAA polarization influences catalysis only marginally but has a larger effect on intermediate stabilization. Different levels of treatment of OAA are compared (MM or QM), and its polarization in the protein and in water analyzed at the B3LYP/6‐31+G(d)/CHARMM27 level. Analysis of stabilization by individual residues shows that the enzyme mainly stabilizes the enolate intermediate (not the transition state) through electrostatic (including hydrogen bond) interactions: these contribute much more than polarization of OAA. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Structural assessment of glycyl mutations in invariantly conserved motifs
Authors: Prakash Tulika , Sandhu Kuljeet Singh , Singh Nitin Kumar , Bhasin Yasha , Ramakrishnan C. , Brahmachari Samir K.
Published: July 2007

Motifs that are evolutionarily conserved in proteins are crucial to their structure and function. In one of our earlier studies, we demonstrated that the conserved motifs occurring invariantly across several organisms could act as structural determinants of the proteins. We observed the abundance of glycyl residues in these invariantly conserved motifs. The role of glycyl residues in highly conserved motifs has not been studied extensively. Thus, it would be interesting to examine the structural perturbations induced by mutation in these conserved glycyl sites. In this work, we selected a representative set of invariant signature (IS) peptides for which both the PDB structure and mutation information was available. We thoroughly analyzed the conformational features of the glycyl sites and their local interactions with the surrounding residues. Using Ramachandran angles, we showed that the glycyl residues occurring in these IS peptides, which have undergone mutation, occurred more often in the L‐disallowed as compared with the L‐allowed region of the Ramachandran plot. Short range contacts around the mutation site were analyzed to study the steric effects. With the results obtained from our analysis, we hypothesize that any change of activity arising because of such mutations must be attributed to the long‐range interaction(s) of the new residue if the glycyl residue in the IS peptide occurred in the L‐allowed region of the Ramachandran plot. However, the mutation of those conserved glycyl residues that occurred in the L‐disallowed region of the Ramachandran plot might lead to an altered activity of the protein as a result of an altered conformation of the backbone in the immediate vicinity of the glycyl residue, in addition to long range effects arising from the long side chains of the new residue. Thus, the loss of activity because of mutation in the conserved glycyl site might either relate to long range interactions or to local perturbations around the site depending upon the conformational preference of the glycyl residue. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Truncated prolyl oligopeptidase from Pyrococcus furiosus
Authors: Juhász Tünde , Szeltner Zoltán , Polgár László
Published: July 2007

The peptidase domain of prolyl oligopeptidase is covered by a propeller domain, which excludes large peptides and proteins from the catalytic triad. Previous studies indicated that some amino acids of the N‐terminal region constitute a part of the substrate entrance to the active site. To investigate the catalytic role of the N‐terminus, we removed the residues 1–32 from the enzyme and examined the kinetic, thermodynamic, and structural consequences of the deletion, using the thermophile Pyrococcus furiosus prolyl oligopeptidase. An about threefold decrease in the catalytic activity along with a 20°C reduction in the temperature optimum was observed. The pH‐rate profile, the rate‐limiting step, and the activation parameters did not change significantly. However, a substantial decrease was observed in the stability of the protein as demonstrated by circular dichroism and differential scanning calorimetry measurements, and by denaturation with guanidinium chloride. It was concluded that the N‐terminal segment did not facilitate the substrate binding, independent of the size of the substrate, but contributed principally to the protein stability required for the formation of the proper active site. Proteins 2007. © 2007 Wiley‐Liss, Inc.
The Heat Capacity of Solid CF4
Authors: Bagatskii M. I. , Manzhelii V. G. , Popov V. A.
Published: July 2007

The heat capacity of solid tetrafluoromethane has been measured in the temperature range 2 to 20 °K. The analysis of the results of this paper and literature data on the heat capacity allow to make conclusions about the character of the heat motion of the molecules in crystalline CF4. An “extra” heat capacity of CF4 near the phase transformation temperature Tλ = 76.09 °K is due to orientational disordering. The temperature dependence of the “extra” heat capacity ΔCor is well described by the logarithmic function ΔCor ∼ lg ∼|–T|Tλ|.
Mössbauer Effect Study of the Structure of Inorganic Glasses
Authors: Bartenev G. M. , Suzdalev I. P. , Tsyganov A. D.
Published: July 2007

The structure of inorganic glasses and glass fibres has been investigated by means of the Mössbauer effect. According to Mössbauer effect data the microstructure of glass differs considerably from that of the glass fibre. The polymeric constitution of the glass is observed to undergo certain structural orientation during drawing of glass fibres which is indicated by the presence of an axially symmetrical molecular field, asymmetry of atom oscillations, and considerably lower degree of microheterogeneities. Heat treatment of glass fibres removes structural orientation. Tin ions, like other elements of the IVth group of the Mendeleev periodic table, can act as well as a glass former.
On Acoustic Attenuation in Dielectric Solids
Authors: Ožvold M.
Published: July 2007

Starting from the general equation of motion for the atoms of the primitive lattice and using the Green function method the sound absorption coefficient is derived in the three‐phonon approximation. The here derived results hold for transverse waves in the whole frequency region and for longitudinal ones in the high frequency region (Ω τ > 1). The frequency and temperature dependence of the absorption coefficient are discussed for the high and low frequencies (Ω τ 1 and Ω τ 1). Using the dispersion relation, the change of elastic constants due to the three‐phonon processes is determined.
The Order — Disorder Transformation in Fe3Al Alloys
Authors: Lesoille M. R. , Gielen P. M.
Published: July 2007

A Mössbauer investigation in FeAl alloys ranging from 20 to 28 at% Al has been performed. In the disordered spectra, which were computer analyzed, a very slight mean electric quadrupole interaction has been measured, which may be due to some directional order, while in the ordered spectra two ordered phases were observed for a composition around 25 at% Al: the DO3‐type of ordered structure, in which each Al atom has eight Fe nearest neighbours and six Fe next‐nearest neighbours, and another phase with a structure similar to Cu3Au, in which each Al atom has 12 Fe nearest neighbours and six Al next‐nearest neighbours. Both phases are ferromagnetic. In the Cu3Au‐type structure a strong electric quadrupole interaction has been measured, which is the same as in the Fe3AlC compound. The quadrupole effect does not appear in the DO3‐type structure probably because of special relationships between the easy axis of magnetization and the electric field gradient tensor. Measurements of quadrupole effects show that Al should be strongly ionized when alloyed with Fe. This gives a clue to understand the physical reasons why order‐disorder transitions appear in such alloys. Below the transition temperature, each Al gets better surrounded exclusively by Fe atoms in order to minimize the Coulomb interaction energy with its neighbours.
Symmetry Properties of the Clebsch‐Gordan Coefficients of Space Groups
Authors: Cornwell J. F.
Published: July 2007

The symmetry properties of the Clebsch‐Gordan coefficients of space groups are described. The connection with time‐reversal symmetry is studied in an appendix.
Spezifische Wärme und Debyetemperatur von AgCl zwischen 2 und 12 °K
Authors: Donecker J.
Published: July 2007

Die spezifische Wärme wurde zwischen 2 und 12 °K gemessen. Die zugehörigen Debyetemperaturen werden angegeben und die Koeffizienten von ω2 und ω4 in der Entwicklung des Gitterspektrums für niedrige Frequenzen abgeschätzt. Für T → 0 ergibt sich eine Debyetemperatur von 162 (± 3) °K, die mit der elastischen Debyetemperatur Θel = 161,6 °K übereinstimmt. ΘC(T) hat in der Nähe von 10 °K ein Minimum. Das kann durch ein einfaches Modell für das Gitterspektrum erklärt werden, das eine Häufung von Moden bei ω ≈ 6,5 × 1012 s−1 enthält, die wahrscheinlich auf eine starke Dispersion transversaler akustischer Schwingungen zurückzuführen ist.
Second Harmonic Generation in Anisotropic Semiconductors Using DC Electric Fields
Authors: Sodha M. S. , Gupta B. M.
Published: July 2007

An analytical investigation is made of the use of dc electric fields of arbitrary strength for the generation of second harmonic of high frequency electromagnetic waves in anisotropic semiconductors. The acoustical phonon, non‐polar optical phonon, and intervalley scattering are assumed to be the dominant type of scattering. It is seen that for the frequency of wave much greater than the effective collision frequency (i.e. the IR region), the generated second harmonic is proportional to the applied dc field. This is in contrast to the case of microwave frequencies where the generation is most efficient at some optimum dc field. The calculations of the anisotropy and the magnitude of the second harmonic generated are reported for [100], [110], and [111] directions of the combined wave and dc field for the case of n‐Ge.
Elastic Diffusion Relaxation
Authors: Alefeld G. , Völkl J. , Schaumann G.
Published: July 2007

A theory for relaxation strength and relaxation time of the elastic diffusion relaxation is derived. Strain relaxation, stress relaxation, and internal friction are considered. Interaction between the diffusing particles is taken into account. The behaviour of relaxation strength and relaxation time in the region of a critical point has been discussed. It is shown that at a critical point the static compressibility of the host lattice approaches infinity. Furthermore it is suggested, that the orientation and diffusion relaxation processes may cause strong dispersion and damping of phonons close to the Brillouin zone boundary.
Many‐Particle Approach to the Optical Absorption of the Alkali Metals
Authors: Stolz H.
Published: July 2007

The influence of the electron‐electron interaction on the optical absorption of the alkali metals is calculated in the ladder‐approximation for the Bethe‐Salpeter equation and in the nearly‐free‐electron approximation of the single‐particle functions. With a suitable approximation of the interaction matrix element the summation of an infinite number of ladder graphs is achieved. The resulting enhancement of the interband absorption — about 33% for sodium and 35% for potassium — is non‐resonant and there are no anomalous structures below the interband threshold.
On the Faraday Effect of Hot Electrons in Many‐Valley Semiconductors
Authors: Asche M.
Published: July 2007

For the calculation of the Faraday effect of hot electrons in many‐valley semiconductors the ellipsoidal form of the constant energy surfaces can be taken into account, if scattering between valleys on axes with different orientations to the applied fields is weak in comparison with other collision processes. In the case of small losses the rotation of the polarization plane and the ellipticity of radiation are discussed with respect to the electric de field as functions of mean carrier energies and electron redistribution among the valleys, considering interaction with acoustical and optical phonons as well as ionized impurities.
Energy Bands in β′‐PdIn
Authors: Cho S. J.
Published: July 2007

The energy bands for ordered β′‐PdIn have been calculated by the augmented‐plane‐wave (APW) method. The results are similar to those for β′‐CuZn except near R. The theoretical extremal Fermi surface cross‐sections are reasonably in agreement with those obtained by the de Haas‐van Alphen studies. The possible open orbits have also been studied. The electronic density of states curve has been obtained from the energy bands. The electronic specific heat coefficient, the magnetic susceptibility and the cyclotron effective masses have also been estimated. Comparisons have been made between our results and optical data.
Lattice Distortion in Uranium Dioxide near 30 °K
Authors: Pirie J. D. , Smith T.
Published: July 2007

Uranium dioxide is an antiferromagnetic below 30.8 °K. It has been suggested that there may be a displacement of the uranium ions associated with the magnetic phase transition. X‐ray measurements show that provided the antiferromagnetic domains are sufficiently large (several hundred Å) a possible uranium movement in the 〈100〉 directions is less than 0.0076 Å.
The Magnetic Behaviour of FeAl Alloys of B2‐Structure Investigated by Mössbauer Spectroscopy
Authors: Hergt R. , Wieser E. , Gengnagel H. , Gladun A.
Published: July 2007

FeAl alloys in the concentration range 25 to 50 at% Al were investigated between 1.3 °K and room temperature by Mössbauer spectroscopy and magnetic measurements. These alloys are characterized by the simultaneous appearance of Fe atoms in two kinds of very different neighbourhood: 8 nn Fe and 4 or less nn Fe. This fact causes the appearance of strong fluctuation effects observed above 30 at% Al. At 33 at% Al two kinds of domains coexist, such which order magnetically above room temperature (“Fe3Al”) and other with a magnetic transition temperature of about 100 °K (“FeAl”). The concentration dependence of the observed hyperfine fields and the magnetic transition temperature is explained by the decrease of the iron magnetic moment with increasing Al‐content, which in this concentration range is not correlated to the number of next nearest neighbour Fe atoms but seems to be determined by the absolute Al‐content.
Contribution to the Quantum Theory of the Seond‐Harmonic Generation in a Molecular Crystal
Authors: Lebon F.
Published: July 2007

The quantum theory of the second‐harmonic generation is developed for diamagnetic molecules through a variational perturbation method. The advantage of this method is that it requires only to know the wave function Ψ of the ground state of the non‐perturbed molecule; thus, the coefficient characterizing the second‐harmonic generation can be expressed as a function of the wave function Ψ and of vectors determined by a variation calculus; so this coefficient can be computed numerically. This calculation is achieved for the hexamethylene‐tetramine crystal.
The Effect of Concentration Gradients of Impurities on the Temperature Dependence of the Spin—Lattice Relaxation Time in Lithium and Beryllium
Authors: Orchard‐Webb J. H. , Watts A. J. , Smithard M. A. , Cousins J. E.
Published: July 2007

Measurements are presented of the conduction electron spin resonance linewidths for various samples of lithium and beryllium at frequencies of 9.27 GHz and 33 and 80 MHz, the samples having dimensions which are large compared with the appropriate skin depth. An increase in the linewidths and certain line shape anomalies as measured at 9.27 GHz at low temperatures, are discussed in terms of relaxation in an impure surface layer. A value of χs = 1.6 × 10−7 c.g.s. units has been deduced for the spin susceptibility of beryllium.
Acousto‐Electric Phonon Distributions Measured by X‐Ray Brillouin Scattering
Authors: Lemke H. , Müller G. O. , Schnürer E.
Published: July 2007

Evaluation of phonon distributions from satellites of X‐ray Bragg reflections is complicated by convolutions with spectral and angular distributions of the primary beam. Assuming only first‐order processes an integral equation fitting the experimental situation is derived and numerically solved. First results indicate higher phonon frequencies than previously obtained by optical Brillouin scattering on different samples and expected from Hutson and White [3] gain and McFee and Bateman [9] losses.
Interpretation of Positron Annihilation Curves for Lithium by Mijnarends' Method. Has the Fermi Surface of Lithium a Neck?
Authors: Stachowiak H.
Published: July 2007

The positron annihilation curves of Donaghy and Stewart for lithium have been reinterpreted using Mijnarends' method. In this way it has been possible to split the total number of counts into two parts, one corresponding to electron momenta inside the main Fermi surface, the other arising from higher momentum components of the conduction electron wave functions and core annihilation. Evidence is found for the possible existence of a neck in the Fermi surface in the (110) direction with a radius of the order of 13% of the free electron sphere radius. The need for more detailed experimental investigations of positron annihilation in lithium is emphasized.
Invariant Piezoelectric Coefficients for Crystals
Authors: Srinivasan T. P.
Published: July 2007

In writing out tensors which represent physical properties of crystals, it is customary to choose a Cartesian frame of reference which has a specific orientation with respect to the crystallographic axes. A new formulation is proposed in which the physical properties (in particular the piezoelectric property) of crystals can be specified without reference to any coordinate system.
Calculation of ϵ2‐Spectra for Amorphous Selenium, Germanium, and Silicon Using the Non‐Direct Transition Model with Energy Dependent Matrix Elements
Authors: Maschke K. , Thomas P.
Published: July 2007

The non‐direct transition model for calculation of amorphous ϵ2‐spectra is considered with respect to energy dependent matrix elements. It is shown how these amorphous matrix elements may be obtained from the crystalline matrix elements. The model is discussed for amorphous Selenium, Germanium, and Silicon.
Optical Study of the Crystal Field Splitting of Excited 5d States of Ce3+:YPO4
Authors: Briffaut J. P. , Denis J. P.
Published: July 2007

Fluorescence and absorption ultraviolet spectra of Ce3+: YPO4 are reported. They appear as bands which are assigned to 4f ↔ 5d transitions. From fluorescence quantum efficiency measurements the values of the parameters A (9014 cm−1), A (45320 cm−1), and A (5406 cm−1) characterizing the crystal field acting on the 5d states of Ce3+:YPO4 are obtained.
Two‐Photon Absorption of CaF2:Eu2+
Authors: Bayer E. , Schaack G.
Published: July 2007

The technique of two‐photon‐absorption spectroscopy with polarized laser‐light is applied to localized excitations of 4f‐electrons in crystals. The relevant selection rules are discussed. A method is outlined for the unique determination of the relative magnitude of partial transition‐probabilities with different types of symmetry using linear and circular polarization of the incident light. The anisotropy of the two‐photon absorption has been measured in single crystals of cubic CaF2:Eu2+ at five different wavenumbers. The relative intensities of transitions belonging to the three different types of symmetry active in two‐photon absorption are constant in the range of the e‐band (26,000 to 29,000 cm−1) but differ from these values at 37,700 cm−1 in the range between the e‐ and the t‐band. This result is discussed in the frame of existing interpretations of the 4f65d‐configuration of Eu2+ in CaF2.
On the Theory of Cooperative Luminescence
Authors: Shekhtman V. L. , Trifonov E. D.
Published: July 2007

The effect of the cumulation of the energy of two impurity ions on one of them is considered. The stationary equations for the density matrix of a pair of ions are derived and an estimate of the cumulation probability for the dipole—dipole interaction between ions is obtained.
Calculation of the Coulomb Integral for Ni, Co, Fe
Authors: Galperin F.M , Amelin I.I , Yorkin V.M
Published: July 2007

For the calculation of the Coulomb interaction between 3d‐electrons of a metal atom the authors have used the Slater radial wave function. The Coulomb integral calculated by the Hartree method is KAB = 2.62Z* (eV), where Z* is the effective charge. Substituting Z* = 9/R, into this integral, where R, previously calculated by one of the authors, is the effective radius of the 3d‐electrons of the metal atom, we find KAB = 9.1; 9.85; 10.3 eV for Fe, Co, Ni, respectively. Exactly the same values are afforded by the empirical formula suggested here KAB = [C + m/(2 MB)] eV, where C is the number of electrons outside the argon shell of the free atom in the ground state, m is the atomic magnetic moment of a pure ferromagnetic metal in Bohr magnetons MB.
Light scattering and ionic conductivity in NaCl:Ba and NaCl:Cd single crystals
Authors: Baltog I. , Ghit̃ă C. , Giurgea M.
Published: July 2007

Simultaneous measurements are made of light scattering and ionic conductivity as a function of temperature in the range 20 to 650°C on Ba‐ and Cd‐doped NaCl single crystals submitted to different heat treatments. In case of Ba‐doped crystals, the results are interpreted by changes in the decoration of the precipitates with cation vacancies; in case of Cd‐doped crystals by dissolution and reformation of the precipitates as a consequence of appropriate heat treatments.
Splitting of superdislocations in ordered CuAu‐type structure
Authors: Greenberg B. A.
Published: July 2007

The various splittings of superdislocations in an ordered CuAu‐Type structure have been investigated. A new possible type of superdislocations has been considered. Such a type of superdislocations are sessile configurations arising from glissile configurations as already known due to certain transformations. It has been shown that under definite conditions the sessile configurations are energetically more favourable as compared with glissile configurations. The features of the transformations of the glissile configurations into the sessile ones and the reverse transformations have been investigated. A new model of twin nucleation has been proposed which is associated with the possibility of the transformations considered.
Zur nichtlinearen Antworttheorie quantenmechanischer Systeme
Authors: Fick E. , Sauermann G.
Published: July 2007

In diesem Beitrag zur nichtlinearen Antworttheorie werden für die Erwartungswerte von Observablen exakte Integralgleichungen hergeleitet. Man erhält aus ihnen, selbst in der niedrigsten Näherung für die Kerne, eine Antwort, die nichtlineare Effekte enthält. Als Beispiel für die Theorie werden zwei Probleme der magnetischen Relaxation behandelt: Das Einschalten eines Magnetfeldes h0 θ(t) und ein periodisches Störfeld h0 cos ω t mit nicht kleinen Amplituden h0.
Vibronic spectra of crystals at arbitrary shifts of the atomic equilibrium positions in the molecules
Authors: Davydov A. S. , Serikov A. A.
Published: July 2007

The vibronic spectra of molecular crystals are investigated for the case of a combination of the electronic excitation with the totally symmetrical intramolecular vibration at arbitrary shifts ξ of the atomic equilibrium positions in molecules. It is shown that three types of excitations can correspond to the vibronic excitations of molecules in the crystal: a) the vibronic excitons, i.e. the one‐particle excitations with definite value of the wave vector; b) the two‐particle excitations corresponding to a simultaneous formation of free excitons and intramolecular vibrations in the crystal; c) the unstable one‐particle excitations decaying into free excitons and intramolecular vibrations. The relative disposition of the corresponding absorption bands and their intensities depend on the three parameters ξ2, ΔΩ and L.
Optical absorption in crystals containing impurities
Authors: Hacker K.
Published: July 2007

A model calculation is made of the optical absorption coefficient for semiconductors containing impurities with short‐range potentials. An averaged Green's function method, developed by Yonezawa [1, 2] and Soven [3, 4] is used. Results are given for impurities with the same and with different valencies as the host crystal and for different temperatures.
Zero‐field splitting of the R‐centre ground state in KCl
Authors: Lehmberg H. , von der Osten W. , Weber J.
Published: July 2007

From optical investigations of the R2 zero‐phonon absorption line in γ‐ and X‐irradiated KCl under uniaxial stress at low temperatures the 2E ground state of the R‐centre is suggested to be split without external field. Measuring the changes of integral absorption and of energetic position of the line for stress along 〈100〉, a zero‐field splitting of 2 Z = 0.9 cm−1 is found. This result is confirmed from studying the spectral shift of the line when the crystal is cooled from 4.2 to 1.5 °K. The results are analysed using the zeroth and first moments of the line. The origin of the zero‐field splitting is discussed.
ESR and ENDOR investigation of interstitial hydrogen atoms in alkali halides
Authors: Spaeth J. M. , Sturm M.
Published: July 2007

We report on the results of ESR and ENDOR investigations of H centres in KF, NaCl, KCl, RbCl, NaBr, KBr, and RbBr. New ESR results were obtained for KF, NaBr, and RbCl. The g‐factor and the proton hyperfine constant for all mentioned alkali halides have been measured precisely. In addition to the previously published ENDOR results in KCl and RbCl we obtained well resolved ENDOR spectra in NaCl and KBr. All superhyperfine and quadrupole constants known at present for H centres in alkali halides are given and compared.
On the strain‐enhanced diffusion of α‐iron
Authors: Watanabe T. , Karashima S.
Published: July 2007

In order to explain the origin of strain‐enhanced diffusion in α‐iron, the concentration of excess vacancies generated by non‐conservative motion of jogs on screw dislocations during creep deformation was estimated under various creep conditions. In the estimation the values of activation volume for high temperature creep obtained by the stress‐relaxation test during creep were used. It was concluded that the reported strain‐enhanced diffusion is well explained by the excess vacancies due to the non‐conservative motion of jogs on screw dislocations.
Luminescence decay and delayed spectra of CaWO4 single crystals
Authors: Scharmann A. , Schwarz G.
Published: July 2007

Luminescence decay and delayed spectra of single crystals have been measured under 15 keV electron pulse excitation. Significant differences in the spectral decay for temperatures below and above Debye temperature are observed. For low temperatures (T < θD) the delayed spectra show a pronounced red shift during decay. The results are discussed in the model of the “small polaron”.
Kramers‐Kronig analysis of exciton spectra in case of spatial resonance dispersion
Authors: Skettrup T.
Published: July 2007

The reflection spectrum of excitons exhibiting spatial resonance dispersion yields in a Kramers‐Kronig analysis values for the optical constants that deviate from the ones determined directly by transmission measurements. This is due to the extra polariton mode present in case of spatial resonance dispersion. In spite of this discrepancy, these values permit to derive sufficiently accurate the resonance frequencies, oscillator strengths, and background dielectric constants. The damping constant obtained in this way contains a mass‐dependent term in addition to the true damping of the excitons. We derive a necessary condition for the observation of spatial dispersion effects. An estimate for the exciton masses of some II–VI compounds is obtained from their low temperature reflection spectra.
Experimental phonon frequencies and widths of lead at 5, 80, and 290 °K
Authors: Furrer A. , Hälg W.
Published: July 2007

The phonon frequencies and lifetimes of lead have been measured in a (110) plane at 5, 80, and 290 °K using the neutron inelastic scattering technique. The importance of special conditions required to minimize the experimental error is pointed out. The phonon lifetimes do not show anomalies which could be presumed in consequence of the strong phonon‐electron interaction in lead. The phonon widths and frequency shifts have been analysed on the basis of anharmonic effects taking account of phonon‐phonon and phonon‐electron scattering processes.
Détermination microcalorimétrique de l'énergie et de l'entropie de formation des lacunes dans l'or
Authors: Moya G. , Lagarde L.
Published: July 2007

L'énergie dégagée, au cours de revenus, par des défauts bloqués après trempe a été mesurée au moyen d'un microcalorimètre différentiel de grande précision. L'évaluation précise de la chaleur restituée, pour différentes températures de trempe, fournit des résultats sur l'énergie de formation (Ef= (0,92 ± 0,04)eV), l'entropie de formation (Sf ≈︁ 0,4 k) et sur les concentrations des monolacunes. Ces valeurs sont discutées.
On the Calculation of the Complex Susceptibility of a Heisenberg Ferromagnet in the Vicinity of the Curie Point
Authors: Potapkov N. A. , Shelkov N. V.
Published: July 2007

The behaviour of the Fourier component of a longitudinal spin pair correlation function near the Curie point is considered on the base of results of [1, 2]. It is shown, that in the small wave vectors limit when T → Tc the results of [1] and [2] are equal. The formula obtained is substituted in the general expressions for the r.f. susceptibility and the width of the resonance line.
Measurement of Stabilization Fields for 180° and 90° Bloch Walls in Iron Single Crystals Containing Solute Nitrogen Atoms
Authors: Tahara Y. , Sugeno T.
Published: July 2007

In order to ascertain Néel's prediction stabilization fields were measured for 180° and 90° Bloch walls using iron single crystals containing solute nitrogen atoms. Initial magnetization curves were measured when solute nitrogen atoms were distributed in a uniform or equilibrium state. The observed stabilization field for 180° walls showed a sharp maximum in low induction region and tended to zero for large induction. That for 90° walls, however, didn't show such a maximum but approached asymptotically to a finite value. These results support qualitatively Néel's theory. The coefficient w of the interaction energy between nitrogen atoms and the spontaneous magnetization is found to be 9.0 × 10−16 erg per atom for solute nitrogen atoms in α‐iron.
Temperature Dependence of Defect Production in KBr and KCl (II)
Authors: Comins J. D.
Published: July 2007

Studies of the growth of F‐centres in Harshaw KBr and KCl during X‐irradiation as a function of temperature show that the “late‐stage” production rate progressively decreases as the temperature of irradiation T is increased above ≈ 195 °K for KBr and above ≈ 213 °K for KCl. Various mechanisms are examined to explain this effect. The results are found to be in semi‐quantitative agreement with the predictions of the excitonic mechanism of defect production, but arguments are presented to show that the mechanism of suppression involving mobile vacancies makes some contribution. The V‐bands formed in the range investigated (195 °K < T < 298 °K) show a continuing progressive change in shape and peak position with increasing temperature of irradiation. Their growth behaviour becomes increasingly non‐proportional to F‐centre growth as T increases, but nevertheless the overall “late‐stage” rate decreases in a manner comparable with that found for F‐centres, and provides evidence that they are of an interstitial nature. The growth of the 213 nm band shows a two‐stage behaviour, the first resulting from decomposition of OH− centres to form the U‐band, while the later stage is considered to be due to the formation of V3‐centres.
Dielectric and Anelastic Relaxation in Ca‐Doped Cerium Dioxide
Authors: Lay K. W. , Whitmore D. H.
Published: July 2007

Measurements of dielectric losses and internal friction in Ca‐doped CeO2 have been made over the temperature range 253 to 573 °K on specimens with up to 2.5% of the Ce4+ ions replaced by Ca2+ ions. The observed internal friction and dielectric loss peaks have relaxation times which are in close accord with the predictions of an eight‐position, nearest‐neighbor model, namely, that the relaxation time for electrically‐active modes is equal to twice that for mechanically‐active modes. These relaxations occur because of the redistribution of oxygen vacancies (bound to substitutional Ca2+ ions) among eight sites which are initially equivalent, but which become inequivalent in the presence of the external electric or mechanical stress field. From the temperature dependence of the relaxation times and the peak shape, the activation energy required for such oxygen vacancy jumps is calculated to be 0.86 eV, with the pre‐exponential factor estimated to be 2.4 × 1014 s−1.
Effect of Hydrostatic Pressure on the Diffusion of Silver in Indium
Authors: Ott A.
Published: July 2007

The pressure effect on the silver impurity diffusion has been measured parallel and perpendicular to the tetragonal axis in single crystals of indium metal. A thin film radioactive tracer deposition and sectioning method was used. The experiments were performed at 96.1 and 112.3 °C, and at hydrostatic pressures varying from 0.9 to 7.7 kbar. The diffusion rate was observed to decrease with increasing pressure and the activation volume for the diffusion process was determined to (6.4 ± 0.6) cm3/mol, with no detectable dependence on either temperature or crystallographic orientation. Comparison with systematics and theoretical arguments suggests interstitial diffusion.
X‐Ray Spectra and Energy Band Structure of Some Noble and Transition Metal Aluminides
Authors: Nemnonov S. A. , Zyryanov V. G. , Minin V. I. , Sorokina M. F.
Published: July 2007

The Al L2,3 and Kβ emission bands of noble and several transition metal aluminides have been investigated. In the spectra of the alloys long‐wavelength intensity peaks are observed which are not present in the spectrum of pure aluminium. The appearance of these peaks is associated with the energy bands originating from the d‐states of the noble and transition metal atoms. For the Al bands in CuAl2, Cu2Al, and PdAl3 the position of the long‐wave‐length peaks relative to short‐wavelength edges is found to correspond approximately to the position of the copper and palladium L2,3‐band peaks with respect to the absorption edges. It is assumed that the energy region of the d‐like bands in the vicinity of aluminium atoms contains an appreciable amount of states arising from the s and p aluminium atom states. This is suggested to be the reason for the long‐wavelength intensity peaks to appear in the Al L2,3‐and Kβ‐bands of the alloys.
Mössbauer Study of Isomorphous Substitution in Ilvaite
Authors: Borshagovskii B. V. , Marfunin A. S. , Mkrtchyan A. R. , Nagyaryan G. N. , Stukan R. A.
Published: July 2007

The isomorphous substitution of manganese for Fe in ilvaite has been studied. It has been found that in the absence of manganese or at low manganese content (up to 4.5%) the spectrum consists of two doublets, corresponding to bivalent and trivalent iron. When the degree of substitution increases the spectrum becomes complex. For a manganese content above 12%, hyperfine structure is observed. Values of Heff have been determined. Heff of Fe2+ is equal to (210 ± 7) kOe, Heff of Fe3+ –(340 ± 7) kOe. The low value of Heff of Fe3+ is accounted for by the fact that the temperature at which the experiment was carried out is close to the Curie point. The value ΔEQ derived from magnetic spectra is less than half the value derived from paramagnetic samples. This can be attributed to the existence of an angle between the direction of the magnetic field and the main axis of the electric field gradient tensor of the iron ions.
Temperature Dependence of Non‐Resonance Energy Migration in Solids
Authors: Nagibarova I. A. , Shegeda A. M.
Published: July 2007

The non‐resonance energy migration by means of the electrical multipole‐multipole interactions modulated by the lattice vibrations is considered. The consideration is made with regard for the temperature dependence of the line width.
A Method for Computation of Equilibrium Dislocation Configurations
Authors: Shtolberg A. A.
Published: July 2007

A numerical method for the solution of non‐linear integro‐differential equations typical for problems on equilibrium dislocation configurations is developed which makes it possible to pass to the ordinary differential equations at every step of the iterative procedure. The presented method contrary to the existing ones provides automatic computation of the equilibrium dislocation shapes and guarantees the equilibrium (with given precision) of all the points of the dislocation line. As an example a problem has been solved which is of importance for the dislocation theory of dispersion strengthening, concerning a dislocation breaking through an array of obstacles. The dependence of the critical applied stress (at which the dislocation becomes unstable) both on the concentration of obstacles and their size is obtained, which is in accordance with the experimental data. In conclusion possible applications and modifications of the method are discussed, which can be used in different (not only dislocation) problems.