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1.
  • Abreu, P., et al. (författare)
  • Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP
  • 2001
  • Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 15-28
  • Tidskriftsartikel (refereegranskat)abstract
    • Muon pair production in the process e+e- → e+e- μ+μ- is studied using the data taken at LEP1 (√s ≃ mz) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb-1. The QED predictions have been tested over the whole Q2 range accessible at LEP1 (from several GeV2/c4 to several hundred GeV2/c4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function Fγ 2. Azimuthal correlations are used to obtain information on additional structure functions, Fγ A and Fγ B, which originate from interference terms of the scattering amplitudes. The measured ratios Fγ A/Fγ 2 and FγB/Fγ 2 are significantly different from zero and consistent with QED predictions.
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2.
  • Abreu, P., et al. (författare)
  • Search for sleptons in e+e- collisions at √s = 183 to 189 GeV
  • 2001
  • Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 29-42
  • Tidskriftsartikel (refereegranskat)abstract
    • Data taken by the DELPHI experiment at centre-of-mass energies of 183 GeV and 189 GeV with a total integrated luminosity of 212 pb-1 have been used to search for the supersymmetric partners of the electrons, muons, and taus in the context of the Minimal Supersymmetric Standard Model (MSSM). The decay topologies searched for were the direct decay (ℓ̃ → ℓx̃), producing acoplanar lepton pairs plus missing energy, and the cascade decay (ℓ → ℓx̃0 2 → ℓγx̃0 1), producing acoplanar lepton and photon pairs plus missing energy. The observed number of events is in agreement with Standard Model predictions. The 95% CL excluded mass limits for selectrons, smuons and staus are mẽ ≤ 87 GeV/c2, mμ̃ ≤ 80 GeV/c2 and mτ̃ 75 GeV/c2, respectively, for values of μ=-200 GeV/c2 and tanβ=1.5.
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3.
  • Beral, V, et al. (författare)
  • Alcohol, tobacco and breast cancer - collaborative reanalysis of individual data from 53 epidemiological studies, including 58515 women with breast cancer and 95067 women without the disease
  • 2002
  • Ingår i: British Journal of Cancer. - : Springer Science and Business Media LLC. - 1532-1827 .- 0007-0920. ; 87, s. 1234-45
  • Tidskriftsartikel (refereegranskat)abstract
    • Alcohol and tobacco consumption are closely correlated and published results on their association with breast cancer have not always allowed adequately for confounding between these exposures. Over 80% of the relevant information worldwide on alcohol and tobacco consumption and breast cancer were collated, checked and analysed centrally. Analyses included 58515 women with invasive breast cancer and 95067 controls from 53 studies. Relative risks of breast cancer were estimated, after stratifying by study, age, parity and, where appropriate, women's age when their first child was born and consumption of alcohol and tobacco. The average consumption of alcohol reported by controls from developed countries was 6.0 g per day, i.e. about half a unit/drink of alcohol per day, and was greater in ever-smokers than never-smokers, (8.4 g per day and 5.0 g per day, respectively). Compared with women who reported drinking no alcohol, the relative risk of breast cancer was 1.32 (1.19 - 1.45, P < 0.00001) for an intake of 35 - 44 g per day alcohol, and 1.46 (1.33 - 1.61, P < 0.00001) for greater than or equal to 45 g per day alcohol. The relative risk of breast cancer increased by 7.1% (95% CI 5.5-8.7%; P<0.00001) for each additional 10 g per day intake of alcohol, i.e. for each extra unit or drink of alcohol consumed on a daily basis. This increase was the same in ever-smokers and never-smokers (7.1 % per 10 g per day, P < 0.00001, in each group). By contrast, the relationship between smoking and breast cancer was substantially confounded by the effect of alcohol. When analyses were restricted to 22 255 women with breast cancer and 40 832 controls who reported drinking no alcohol, smoking was not associated with breast cancer (compared to never-smokers, relative risk for ever-smokers= 1.03, 95% CI 0.98 - 1.07, and for current smokers=0.99, 0.92 - 1.05). The results for alcohol and for tobacco did not vary substantially across studies, study designs, or according to 15 personal characteristics of the women; nor were the findings materially confounded by any of these factors. If the observed relationship for alcohol is causal, these results suggest that about 4% of the breast cancers in developed countries are attributable to alcohol. In developing countries, where alcohol consumption among controls averaged only 0.4 g per day, alcohol would have a negligible effect on the incidence of breast cancer. In conclusion, smoking has little or no independent effect on the risk of developing breast cancer; the effect of alcohol on breast cancer needs to be interpreted in the context of its beneficial effects, in moderation, on cardiovascular disease and its harmful effects on cirrhosis and cancers of the mouth, larynx, oesophagus and liver. (C) 2002 Cancer Research UK.
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5.
  • Hillier, Ladeana W, et al. (författare)
  • Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution
  • 2004
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 432:7018, s. 695-716
  • Tidskriftsartikel (refereegranskat)abstract
    • We present here a draft genome sequence of the red jungle fowl, Gallus gallus. Because the chicken is a modern descendant of the dinosaurs and the first non-mammalian amniote to have its genome sequenced, the draft sequence of its genome--composed of approximately one billion base pairs of sequence and an estimated 20,000-23,000 genes--provides a new perspective on vertebrate genome evolution, while also improving the annotation of mammalian genomes. For example, the evolutionary distance between chicken and human provides high specificity in detecting functional elements, both non-coding and coding. Notably, many conserved non-coding sequences are far from genes and cannot be assigned to defined functional classes. In coding regions the evolutionary dynamics of protein domains and orthologous groups illustrate processes that distinguish the lineages leading to birds and mammals. The distinctive properties of avian microchromosomes, together with the inferred patterns of conserved synteny, provide additional insights into vertebrate chromosome architecture.
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6.
  • Asmolov, V.G., et al. (författare)
  • Partitioning of Zr, U and FP between Molten Oxidic and Metallic Corium
  • 2004
  • Ingår i: Proceeding of MASCA Seminar.
  • Konferensbidrag (refereegranskat)abstract
    • Interaction of molten corium and liquid iron/stainless steel has been studied in different tests of theMASCA-1 program. These tests utilized the technology of induction melting in a cold crucible. Themasses of tested corium were approximately 0.5, 2 and 100 kg. Representative quantities of Mo, Ru,SrO, BaO, CeO2 and La2O3 served as fission product simulants.After the suboxidized melt - steel interaction U and Zr have been found in the metallic phase.To quantify the partitioning of Zr, U and fission products an extensive experimental program has beenperformed. The following key parameters have been identified: oxygen potential in the melt (degree ofZr-oxidation), the corium/steel mass ratio and U/Zr ratio. The paper discusses the influence of theseparameters on the partitioning of the main species.
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8.
  • Svensson, C. E., et al. (författare)
  • Collective rotational motion in the N=Z nucleus 36Ar
  • 2001
  • Ingår i: Nuclear Physics A. - 0375-9474. ; 682:1-4, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • A superdeformed rotational band has been identified in the N = Z nucleus 36Ar, firmly linked to known low-spin states, and observed to its high-spin termination at Iπ = 16+. Lifetime measurements by the Doppler shift attenuation method establish a large low-spin deformation (β2 ≈ 0.46) and a decrease in the collectivity as the band approaches termination. Comparisons with cranked Nilsson-Strutinsky and large-scale spherical shell model calculations lead to a consistent description of the band based on a configuration in which four particles are promoted to the pf shell. With two major shells active for both protons and neutrons, yet a valence space dimension small enough to be approached from the shell model perspective, this band offers an excellent opportunity to investigate the microscopic structure of collective rotational motion in nuclei.
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9.
  • Svensson, C. E., et al. (författare)
  • Superdeformation in the N = z Nucleus 36Ar : Experimental, deformed mean field, and spherical shell model descriptions
  • 2000
  • Ingår i: Physical Review Letters. - 0031-9007. ; 85:13, s. 2693-2696
  • Tidskriftsartikel (refereegranskat)abstract
    • A superdeformed rotational band has been identified in 36Ar, linked to known low-spin states, and observed to its high-spin termination at Iπ = 16+. Cranked Nilsson-Strutinsky and spherical shell model calculations assign the band to a configuration in which four pf-shell orbitals are occupied, leading to a low-spin deformation β2 ≈ 0.45. Two major shells are active for both protons and neutrons, yet the valence space remains small enough to be confronted with the shell model. This band thus provides an ideal case to study the microscopic structure of collective rotational motion.
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10.
  • Andreoiu, Corina, et al. (författare)
  • Yrast Superdeformed Band in 59Cu
  • 2000
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 62:5, s. 513011-513015
  • Tidskriftsartikel (refereegranskat)abstract
    • High-spin states in 59Cu were populated using the fusion-evaporation reactions 28Si+40Ca at a beam energy of 125 MeV and 36Ar+28Si at a beam energy of 143 MeV. The Gammasphere array in conjunction with ancillary detector systems allowed for the identification of a superdeformed rotational band in 59Cu, which was firmly linked to low-spin yrast states. Using directional correlations of oriented states, a spin-parity assignment of Iπ = 25/2+ to the band head was possible. The average quadrupole moment of the band is measured to be Qt = (2.24±0.40) e b. The characteristics of the band are compared to neighboring nuclei and predictions of different mean-field theories.
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11.
  • Asztalos, S. J., et al. (författare)
  • Isotopic yields of neutron-rich nuclei from deep-inelastic reactions
  • 2000
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 6101:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We follow up on our earlier work involving a light projectile (Ca-48) to populate high spin states in neutron-rich nuclei with results from experiments involving a heavier projectile (Sm-154) fur the purposes of studying isotopic yields. These yields, which in some cases were mensurable down to a level of 0.1 of the total reaction cross section, are presented from three separate reactions. A trend in the isotopic yields towards N/Z equilibration is observed in one experiment having a large disparity in N/Z ratios between the projectile and target. In the two other reactions, where the N/Z driving force is less pronounced, the yields are instead clustered around the projectile and target nuclei. We present correlated projectilelike and targetlike fragment isotopic yields derived from gamma-gamma coincidences, a technique that enables one to partition the yield of an isotope according to the amount of neutron evaporation. Using this method we find that for the zero-neutron evaporation channel transfer occurs predominantly into the light fragment, consistent with the nature of the deep-inelastic mechanism. We further find that multiple-neutron evaporation contributes substantially to the yields of the isotopes.
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12.
  • Azevedo, G D, et al. (författare)
  • Direct evidence of defect annihilation during structural relaxation of amorphous indium phosphide
  • 2003
  • Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:11: 115204
  • Tidskriftsartikel (refereegranskat)abstract
    • Extended x-ray absorption fine structure measurements have been used to characterize the low-temperature, thermally induced structural relaxation of amorphous InP. We show reductions in both chemical and structural disorder associated with homopolar and heteropolar bonding, respectively, are operative during structural relaxation of this amorphous compound semiconductor. The latter is analogous to that observed in the amorphous elemental semiconductors Ge and Si. Though a reduction in homopolar bonding accompanies structural relaxation, the fully relaxed, minimum-energy configuration of the amorphous phase still retains chemical disorder.
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15.
  • Johansson, DM, et al. (författare)
  • Influence of polymerization temperature on molecular weight, photoluminescence, and electroluminescence for a phenyl-substituted poly(p-phenylenevinylene)
  • 2001
  • Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 34:11, s. 3716-3719
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the synthesis and characterization of poly(2-(2",5'-bis(2"-ethylhexyloxy)phenyl)-1,4-phenylenevinylene) (BEHP-PPV) polymerized at different temperatures. The photoluminescence efficiencies in the solid state of BEHP-PPV obtained at 144 and 0 degreesC are 28% and 60%, respectively. H-1 NMR measurements showed a lower concentration of structural defects for BEHP-PPV obtained at lower temperatures, which can explain the increased photoluminescence efficiencies for these polymers. Polymerization temperatures below 0 degreesC decrease the molecular weight without changing the photoluminescence efficiency to any large extent. The electroluminescence efficiencies follow the trend in the photoluminescence efficiencies.
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16.
  • Johansson, D.M., et al. (författare)
  • Synthesis and characterization of highly soluble phenyl-substituted poly(p-phenylenevinylenes)
  • 2000
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:7, s. 2525-2529
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the synthesis and characterization of soluble, high molecular weight phenyl-substituted poly(p-phenylenevinylenes). The studied polymers are poly(2-(2',5'-bis(2?-ethylhexyloxy)phenyl)- 1,4-phenylenevinylene) (BEHP-PPV) and copolymers of BEHP-PPV and poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). Their photoluminescence and electroluminescence have been examined as well as their stability to air and light. The polymers emitted green and yellow light. Stability measurements showed increased stability compared to some previously known substituted PPVs.
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17.
  • Johansson, DM, et al. (författare)
  • Synthesis of soluble phenyl-substituted poly(p-phenylenevinylenes) with a low content of structural defects
  • 2002
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:13, s. 4997-5003
  • Tidskriftsartikel (refereegranskat)abstract
    • The synthesis and characterization of two new soluble poly(p-phenylenevinylenes) (PPVs) are reported. The polymers are poly(2-2',5'-bis(octyloxy)benzene)-1,4-phenylenevinylene) (BOP-PPV) and poly(2-(2',5'-bis(octyloxy)benzene)-5-methoxy-1,4-phenylenevinylene) (BOPM-PPV). Both polymers have been polymerized at high and low temperatures to study the formation of structural defects. It is shown that both methoxy groups as side chains and low polymerization temperatures decrease the content of defects in the final polymer. As a consequence, the polymers with lower concentration of defects exhibit higher electroluminescence yields in light-emitting diodes. In addition to this, the polymers with a low content of defects exhibited longer operational lifetimes in these devices. The highest photoluminescence quantum yield in the solid state and electroluminescence efficiency were found to be 72% and 1.74%, respectively.
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18.
  • Karger, E M, et al. (författare)
  • Dysfunctionality of a tobacco mosaic virus movement protein mutant mimicking threonine 104 phosphorylation.
  • 2003
  • Ingår i: J Gen Virol. - 0022-1317. ; 84:Pt 3, s. 727-32
  • Tidskriftsartikel (refereegranskat)abstract
    • Replication of tobacco mosaic virus (TMV) is connected with endoplasmic reticulum (ER)-associated membranes at early stages of infection. This study reports that TMV movement protein (MP)-specific protein kinases (PKs) associated with the ER of tobacco were capable of phosphorylating Thr(104) in TMV MP. The MP-specific PKs with apparent molecular masses of about 45-50 kDa and 38 kDa were revealed by gel PK assays. Two types of mutations were introduced in TMV MP gene of wild-type TMV U1 genome to substitute Thr(104) by neutral Ala or by negatively charged Asp. Mutation of Thr(104) to Ala did not affect the size of necrotic lesions induced by the mutant virus in Nicotiana tabacum Xanthi nc. plants. Conversely, mutation of Thr to Asp mimicking Thr(104) phosphorylation strongly inhibited cell-to-cell movement. The possible role of Thr(104) phosphorylation in TMV MP function is discussed.
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20.
  • Maksimov, Igor S., et al. (författare)
  • Low-Temperature Magnetoresistive Effect in Bulk La0.7Ca0.3-xSrxMnO3 Perovskites.
  • 2001
  • Ingår i: Materials Science Forum volumes 373-376. - Zürich : Trans Tech Publications. - 9780878498802 ; , s. 585-588
  • Konferensbidrag (refereegranskat)abstract
    • The temperature and field dependencies of the magnetoresistivity (MR) were studied and analysed for two series of polycrystalline samples of La0.7Ca0.3-xSrxMnO3 (0
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21.
  • Ward, D., et al. (författare)
  • Band Structure of 68Ge
  • 2001
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 63:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The nucleus Ge-68 has been studied by gamma-ray spectroscopy following its population at high spin in the reaction Ca-40(S-32,4p) Ge-68. The reaction channel was selected with the Microball array and gamma rays were detected with the Gammasphere array. The level scheme is very complex, reflecting the many different, and presumably mixed, excitation modes in this nucleus. Nevertheless, there appear to be some simplifications in the spin range above 18 (h) over bar where we have identified a superdeformed band and several terminating bands. The results are compared with a cranked Nilsson-Strutinsky model without pairing.
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22.
  • Yu, H.Y., et al. (författare)
  • Current enhancement with alternating gate voltage in the Coulomb blockade regime of a single wall carbon nanotube
  • 2004
  • Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 79, s. 1613-1615
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated the current–voltage characteristics of a carbon nanotube in a single electron transistor structure with alternating gate voltage. A continuous current enhancement effect with increasing frequency of the applied gate voltage up to 13 MHz is reported. Assuming that I=nef, more than 1000 electrons are driven to flow across the source–drain channel at VDS=100 mV, 13 MHz of gate voltage (Vp-p=2 V) and T=1.8 K. The continuous current enhancement is explained by the broadening effect of the discrete energy levels of the finite-length carbon nanotube.
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27.
  • Brage, C., et al. (författare)
  • Tar evolution profiles obtained from gasification of biomass and coal
  • 2000
  • Ingår i: Biomass and Bioenergy. - 0961-9534 .- 1873-2909. ; 18:1, s. 87-91
  • Tidskriftsartikel (refereegranskat)abstract
    • The tar content of the product gases from gasification of biomass is one of the major factors affecting the subsequent process stages. In this work, evolution profiles of the main tar constituents, i.e. benzene, toluene, indene, naphthalene and phenol were obtained during about 1 h gasification runs of biomass and coal in a pressurised fluidised-bed at 700 and 900 degrees C, 0.4 MPa. Sampling and analysis was achieved, using the solid-phase adsorption (SPA) method, previously developed in our laboratory. Our main objectives were: (1) to illustrate the usefulness of the SPA method; (2) to shed new light on the main factors governing tar evolution. It was found that temperature and the type of feedstock used mainly affected tar yields. For both biomass and coal the concentration of tar products decreased with increasing run time at a rate that was fastest initially. This behaviour, which was much more pronounced for coal, provides evidence that char catalytically affects tar evolution. Accordingly, char accumulates in the bed to a various extent depending on fuel and gradually approaching steady state. Biomass char, contrary to coal char, is readily oxidised during gasification, and thus only small steady-state amounts are available to catalyse tar cracking reactions.
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28.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Control of spin functionality in ZnMnSe-based structures : Spin switching versus spin alignment
  • 2003
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:11, s. 1700-
  • Tidskriftsartikel (refereegranskat)abstract
    •  The ability of attaining desired spin functionality by adjusting structural design is demonstrated in diluted magnetic semiconductor (DMS) quantum structures based on II-VI semiconductors. The following spin enabling functions are achieved by tuning the ratio between the rates of exciton spin relaxation within the DMS and exciton escape from it to an adjacent nonmagnetic spin detector. Spin switching is realized when using a thin layer of Zn0.95Mn0.05Se as a spin manipulator and is attributed to a fast exciton escape from the DMS preceding the spin relaxation. Spin alignment is accomplished in tunneling structures where the presence of an energy barrier inserted between a spin manipulator (a DMS-based superlattice) and a spin detector ensures a slow escape rate from the DMS layer.
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  • Buyanova, Irina, 1960-, et al. (författare)
  • On the Origin of Light Emission in GaNxP1-x
  • 2002
  • Konferensbidrag (refereegranskat)abstract
    •  Temperature dependent photoluminescence (PL) and absorption measurements are employed to clarify mechanism for light emission in GaNP alloys with low (< 4.1) nitrogen content. The PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent red shift of the PL maximum position. On the other hand, band-to-band recombination in the alloy remains predominantly non-radiative presumably due to the presence of a large number of competing recombination channels.
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31.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Radiative recombination mechanism in GaNxP1-x alloys
  • 2002
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80, s. 1740-
  • Tidskriftsartikel (refereegranskat)abstract
    •  Based on the results of temperature-dependent photoluminescence (PL) and absorption measurements, the PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures with N composition up to 4% is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition, these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent redshift of the PL maximum position.
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32.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Resonant suppression of exciton spin relaxation in Zn0.96Mn0.04Se/CdSe superlattices
  • 2003
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:10, s. 7352-
  • Tidskriftsartikel (refereegranskat)abstract
    •  Spin relaxation processes in strained Zn0.96Mn0.04Se/CdSe superlattices are studied in detail by using hot photoluminescence combined with tunable excitation spectroscopy. A drastic enhancement in occupation of the upper-lying |+1/2,-3/2> state of the heavy-hole excitons is observed when excitation photon energy is resonantly tuned near an integer number of the LO phonon energy above the |+1/2,-3/2> state. Assuming the Boltzmann distribution between the excitonic states, the spin temperature of the excitons is deduced to be as high as 85 K, well above the lattice temperature of 2 K. The observed behavior provides experimental evidence for a surprisingly strong suppression of spin relaxation from the upper spin-split excitonic branch for small values of wave vector.
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33.
  • Caballero, O L, et al. (författare)
  • "Complete" High-Spin Structure of 57Co
  • 2003
  • Ingår i: Physical Review C: covering nuclear physics. ; 67
  • Tidskriftsartikel (refereegranskat)abstract
    • A comprehensive high-spin decay scheme has been deduced for 57Co using the Gammasphere Germanium detector array coupled to the 4π charged-particle detector system Microball. Following the fusion-evaporation reaction of 28Si(36Ar,1α3p)57Co at 136 MeV beam energy about 90 excited states have been observed in 57Co, which are connected by some 230 γ-ray transitions. The proposed level scheme reaches 16 MeV excitation energy at a spin of 17ħ–18ħ. With its complexity the level scheme of 57Co appears to be “complete” up to 1 or 2 MeV above the yrast line. This aspect is further investigated through a comparison of the data with spherical shell-model calculations.
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36.
  • Godlewski, M., et al. (författare)
  • Mn2+ intra-shell recombination in bulk and quantum dots of II-VI compounds
  • 2002
  • Ingår i: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 341:1-2
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Origin of a fast component of the photoluminescence (PL) decay of Mn 2+ intra-shell 4T1 ? 6A 1 transition in bulk and quantum dot structures is discussed based on the results of PL, PL kinetics and optically detected magnetic resonance experiments. It is demonstrated that a fast component of the PL decay, reported previously for quantum dot structure and related to quantum confinement effects, is also observed in bulk samples and is very much enhanced upon generation of free carriers. The appearance of this fast component of the PL decay is related to a very efficient spin cross-relaxation between localized spins of Mn ions and spins of free carriers. © 2002 Elsevier Science B.V. All rights reserved.
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37.
  • Grippa, Alexander Yu, et al. (författare)
  • Crystal Structure of BaNb0.9S3
  • 2001
  • Ingår i: Crystallography Reports. - : American Institute of Physics. - 1063-7745. ; 46:3, s. 373-376
  • Tidskriftsartikel (refereegranskat)abstract
    • Single crystals of the composition BaNb[sub 0.9]S[sub 3] have been synthesized from the BaS, Nb, and S mixture and the BaCl[sub 2] flux at 900°C. The BaNb[sub 0.9]S[sub 3] structure was refined by X-ray single-crystal and electron diffraction data. The compound is crystallized in the sp. gr P6[sub 3]/mmc (z = 2) with the unit-cell parameters a = 6.839(1) Å and c = 5.745(1) Å. It was established that the cationic vacancies in the niobium positions are statistically distributed over the structure.
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38.
  • Grippa, Alexander Yu, et al. (författare)
  • New strontium and rare earth-based mixed niobium misfit sulfides
  • 2003
  • Ingår i: Solid State Sciences. - : Elsevier. ; 5:3, s. 495-502
  • Tidskriftsartikel (refereegranskat)abstract
    • New niobium-based misfit sulfides [(Ln1/3Sr2/3S)1.5]1.15NbS2 (Ln=Sm, Tb) have been synthesized from a mixture of SrS, Ln2S3, Nb(m), and S in evacuated and sealed silica tubes by annealing at 1000 °C for 144 h under a sulfur partial pressure of 49.3 kPa. The compounds have been characterized by EDX analysis, X-ray single crystal and powder diffraction, electron diffraction, and magnetic susceptibility measurements. Both sulfides have misfit structures with orthorhombic symmetry for the (Ln1/3Sr2/3S)1.5 (Ln=Sm, Tb) and NbS2 subsystems. The lattice parameters for the different subsystems are: for the Sm-based sulfide [(Sm1/3Sr2/3S)1.5]: a=5.7953(9) Å, b=5.8007(5) Å, c=14.957(2) Å and [NbS2]: a=3.3420(7) Å, b=5.8008(5) Å, c=14.955(2) Å, and for the Tb-based sulfide [(Tb1/3Sr2/3S)1.5]: a=5.769(2) Å, b=5.7766(7) Å, c=14.906(2) Å and [NbS2]: a=3.340(1) Å, b=5.7769(8) Å, c=14.905(2) Å. The [(Sm1/3Sr2/3S)1.5]1.15NbS2 crystal structure has been refined from X-ray single crystal data. It belongs to the 1.5Q/1H homologue type where the (Sm1/3Sr2/3S)1.5 part is a three-atoms-thick slab. Sr-cations are mainly located at the exterior of the slab whereas Sm preferably occupy the positions at its center. Both compounds exhibit paramagnetic temperature dependence down to 2 K.
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39.
  • Hermann, G, et al. (författare)
  • Platform-to-platform sample transfer, distribution, dilution, and dosing via electrothermal vaporization and electrostatic deposition
  • 2004
  • Ingår i: Spectrochimica Acta Part B: Atomic Spectroscopy. - : Elsevier BV. - 0584-8547. ; 59:5, s. 737-48
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel system for solid sample pretreatment, handling and dosing for analytical atomic spectrometry is described. A primary solid or liquid sample is vaporized in a graphite furnace and then condensed in a specially designed condensation zone. On the further transport path, the analyte aerosol can be diluted and distributed in pre-set ratios in the laboratory made flow control system. Applying a corona discharge, aerosol particulates are then quantitatively re-collected by means of intra-furnace electrostatic precipitation on the platform of another graphite furnace or by external precipitation on one or a set of platforms. This makes possible to produce a set of secondary platforms with equal analyte compositions from one individual primary sample. Such multitudes allow sequential multi-element determinations with single-element instrumentation or comparative measurements with different techniques. Furthermore, the described procedure allows external thermal sample pretreatment with preceding pyrolysis and additional vaporization, condensation, and re-precipitation that significantly reduces or removes the sample matrix. Owing to different losses, transport efficiencies of electrothermal vaporization (ETV) instrumentation depend on analyte element, matrix, vaporization temperature, ramp rate, and tube history. In order to reduce the losses and therewith such dependencies of the losses, new laboratory constructed ETV unit with analyte condensation in an axially focusing upstream convection zone has been constructed. Analytical performance of the new setup is compared with the performance of a commercial end-on flow-through ETV unit when analyzing both liquid dosed samples and certified solid reference materials. The new system shows much higher transport efficiencies that are, in addition, more uniform for elements of different volatility. The effects of chemical sample modifiers and elements supporting analyte condensation are studied. Most of the analytical measurements were carried out with a continuum source coherent forward scattering multi-element spectrometer. Comparative measurements were also carried out independently in the co-authors’ laboratories with atomic absorption and inductively coupled plasma mass spectrometry techniques.
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43.
  • Khasanova, Nellie R., et al. (författare)
  • A New Structure Type of the Ternary Sulfide Eu1.3Nb1.9S5
  • 2002
  • Ingår i: Journal of Solid State Chemistry. - : Elsevier. - 1095-726X .- 0022-4596. ; 164:2, s. 345-353
  • Tidskriftsartikel (refereegranskat)abstract
    • The structure model for the Eu1.3Nb1.9S5 compound is determined based on high-resolution electron microscopy evidence. This compound crystallizes in a hexagonal unit cell with a=8.8732(8) Å and c=23.45(1) Å. Its structure is built up as an alternating sequence of trigonal-prismatic NbS2 layers of formula [Nb7S14] and [Nb(Eu3S4)2] slabs along the c-direction. In the [Nb(Eu3S4)2] block the stacking of two close-packed (Eu3S4) layers creates octahedral interstices formed by S atoms; these cavities are occupied by Nb cations. The model is compared with structures of other Eu-containing niobium sulfides, such as Eu0.167NbS2 and the misfit compound [(EuS)1.5]1.15NbS2.
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44.
  • Lipoglavsek, M., et al. (författare)
  • First Observation of Excitation Across the 100Sn Core
  • 2001
  • Ingår i: Nuclear Physics, Section A. - 0375-9474. ; 682, s. 399-403
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states of nuclei near the doubly-magic nucleus Sn-100 were studied with the Ni-58+Cr-50 reaction. The experimental setup consisted of the GAMMASPHERE array augmented with light charged-particle and neutron detectors. Excited states were identified for the first time in the proton emitting nucleus Sb-105. Excitations across the N=Z=50 doubly closed shell were observed in Cd-99 and In-101. Some results of large-scale shell-model calculations are discussed.
  •  
45.
  • Litvinenko, Yu.A., et al. (författare)
  • Control of spanwise flow instability of a swept wing by suction
  • 2003
  • Ingår i: Thermophysics and Aeromechanics. ; 10:4, s. 541-548
  • Tidskriftsartikel (refereegranskat)abstract
    • The experimental results on control by disturbances development in a swept wing boundary layer by means of localized and distributed suction are presented. The control by spanwise flow stationary vortices and secondary periodical disturbances generated at late stages of these vortices development was studied. It is shown that the distributed suction is a simple way to suppress the secondary vortex instability of a spanwise flow as compared with a localized suction. It was shown that the localized suction through a small diameter hole may cause generation of additional stationary vortices in the boundary layer. In this case complex nonlinear interactions between both controlled and controlling disturbances take place. The distributed suction effect through a group of holes is similar to the slot suction and it introduces much less disturbances of vorticity into the boundary layer.
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46.
  • Litvinenko, Yu.A., et al. (författare)
  • Experimental investigation of a streaky structure varicose instability in a swept wing boundary layer
  • 2004
  • Ingår i: Thermophysics and Aeromechanics. ; 11:1, s. 13-22
  • Tidskriftsartikel (refereegranskat)abstract
    • The investigation results of the controlled experiment of a streaky structure varicose instability in a swept wing boundary layer are presented. The picture of a streaky structure spatial evolution and secondary high-frequency disturbances generated on it is obtained using hot-wire measurements. It is shown that exactly a varicose instability is realized. It has been found that the secondary disturbance increases owing to instability of mean velocity distribution on normal to the wall caused by the streaky structure development. The following features of a varicose breakdown of a longitudinal stationary streaky structure are presented: structure modulation in the longitudinal direction by a secondary disturbance frequency, downstream excitation of new streaky structures, formation and development of nonstationary structures localized in space. In contrast to the boundary layer flow of the unswept wing models, where these structures resemble classical horseshoe structures or lambda-vortices, only one vortex remains on a swept wing from the two making the vortex structure because of the crossflow.
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47.
  • Litvinenko, Yu.A., et al. (författare)
  • Nonlinear sinusoidal and varicose instability in the boundary layer (review)
  • 2004
  • Ingår i: Thermophysics and Aeromechanics. ; 11:3, s. 329-354
  • Tidskriftsartikel (refereegranskat)abstract
    • Results of studying sinusoidal and varicose instabilities of streaky structures at the nonlinear stage of the laminar-turbulent process in shear flows are presented. The flow behavior in the course of spatial evolution of streaky structures with a secondary high-frequency disturbance generated on them is discussed. Various scenarios of origination and development of coherent vortex structures examined in physical and numerical experiments are considered. Specific features of the development of sinusoidal and varicose cases of destruction of the steady streamwise streaky structure are demonstrated, such as transverse and streamwise modulation of the structure by the secondary-disturbance frequency, appearance of new streaky structures in the downstream direction, and emergence and evolution of unsteady Λ-type structures localized in space in both cases.
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