¹⁵C(d,p)¹⁶C reaction and exotic behavior in ¹⁶C

We have studied the 1?C(d,p)1?C reaction in inverse kinematics using the Helical Orbit Spectrometer at Argonne National Laboratory. Prior studies of electromagnetic-transition rates in 1?C suggested an exotic decoupling of the valence neutrons from the core in that nucleus. Neutron-adding spectroscopic factors give a different probe of the wave functions of the relevant states in 1?C. Shell-model calculations reproduce both the present transfer data and the previously measured transition rates, suggesting that 1?C may be described without invoking very exotic phenomena.     

Righi-Leduc Effect in InSb between 25°C and 300°C

The Righi-Leduc effect has been measured for n-type InSb crystals of various mobilities and was found to increase with temperature in a manner to indicate that the unipolar contribution is prevalent over the bipolar part of the effect. The experimental values measured over the temperature range between 25°C and 300°C agree well withPutley's theory. The Righi-Leduc coefficient was also determined as a function of the magnetic field and the strong decrease observed is explained in terms of the magnetoresistance.     

Low-Energy 12C States in Three-α Model

Cross sections for three-α photodisintegration process of the¹²C nucleus are calculated by a Faddeev formalism, from which 0⁺- and 2⁺ low-lying resonant ¹²C states are studied. The triple-alpha reaction rate is evaluated from the calculated cross sections of the disintegration process.     

Theoretical prediction of new C–Si alloys in C2/m-20 structure

We study structural,mechanical,and electronic properties of C_(20),Si_(20) and their alloys(C_(16)Si_4,C_(12)Si_8,C_8Si_(12),and C_4Si_(16)) in C2/m structure by using density functional theory(DFT) based on first-principles calculations.The obtained elastic constants and the phonon spectra reveal mechanical and dynamic stability.The calculated formation enthalpy shows that the C-Si alloys might exist at a specified high temperature scale.The ratio of BIG and Poisson's ratio indicate that these C-Si alloys in C2/m-20 structure are all brittle.The elastic anisotropic properties derived by bulk modulus and shear modulus show slight anisotropy.In addition,the band structures and density of states are also depicted,which reveal that C_(20),C_(16)Si_4,and Si_(20) are indirect band gap semiconductors,while C_8Si_(12) and C_4Si_(16) are semi-metallic alloys.Notably,a direct band gap semiconductor(C_(12)Si_8) is obtained by doping two indirect band gap semiconductors(C_(20) and Si_(20)).     

Relaxation Processes and Coherent Spin Manipulations for Triplet Si–C Divacancies in Silicon Carbide Enriched Tenfold in the 13C Isotope

JETP Letters - Coherent spin manipulations of ensembles of color centers in the form of neutral VSi–VC divacancies with the spin $$S = 1$$ in hexagonal silicon carbide 6H–SiC enriched...     

Spectral editing for in vivo ¹³C magnetic resonance spectroscopy

In vivo detection of carboxylic/amide carbons is a promising technique for studying cerebral metabolism and neurotransmission due to the very low RF power required for proton decoupling. In the carboxylic/amide region, however, there is severe spectral overlap between acetate C1 and glutamate C5, complicating studies that use acetate as an astroglia-specific substrate. There are no known in vivo MRS techniques that can spectrally resolve acetate C1 and glutamate C5 singlets. In this study, we propose to spectrally separate acetate C1 and glutamate C5 by a two-step J-editing technique after introducing homonuclear (13)C-(13)C scalar coupling between carboxylic/amide carbons and aliphatic carbons. By infusing [1,2-(13)C(2)]acetate instead of [1-(13)C]acetate the acetate doublet can be spectrally edited because of the large separation between acetate C2 and glutamate C4 in the aliphatic region. This technique can be applied to studying acetate transport and metabolism in brain in the carboxylic/amide region without spectral interference.     

Structural changes in austenitic steel in contact with solid oxide electrolyte at 950°C

Changes in the structure and redistribution of alloying elements in 10Kh23N18 austenitic steel after operating at 950°C for 8800 h in contact with La-Sr-Mn-O electrolyte are investigated to establish the reasons for the degrading of the surface layer of a current collector in a solid-oxide fuel cell over long periods of service. It is established that the degradation of the surface layer of steel is associated with the formation of a network of silicon and aluminum oxides along grain boundaries and the considerable discrepancy between the linear thermal expansion coefficients of steel and the solid electrolyte.     

New algebraic structures in the Cλ-extended Hamiltonian system

A realization of various algebraic structures in terms of the C_λ-extended oscillator algebras is introduced. In particular, the C_λ-extended oscillator algebras realization of the Fairlie–Fletcher–Zachos (FFZ) algebra is given. This latter lead easily to the realization of the quantum U_t(sl(2)) algebra. The new deformed Virasoro algebra is also presented.     

Electronic Transport in Molecular Junction Based on C20 Cages

Choosing closed-ended armchair （5, 5） single-wall carbon nanotubes （CCNTs） as electrodes, we investigate the electron transport properties across an all-carbon molecular junction consisting of C20 molecules suspended between two semi-infinite carbon nanotubes. It is shown that the conductances are quite sensitive to the number of C20 molecules between electrodes for both configuration CF1 and double-bonded models： the conductances of C20 dimers are markedly smaller than those of monomers. The physics is that incident electrons easily pass the C20 molecules and are predominantly scattered at the C20-C20 junctions. Moreover, we study the doping effect of such molecular junction by doping nitrogen atoms substitutionally. The bonding property of the molecular junction with configuration CF1 has been analysed by calculating the Mulliken atomic charges. Our results have revealed that the C atoms in N-doped junctions are more ionic than those in pure-carbon ones, leading to the fact that N-doped junctions have relatively large conductance.     

π0-production in12C+12C at 800 and 1000 MeV/u

⁰-production in the system¹²C+¹²C was studied with the two-arm photon spectrometer TAPS at projectile energies of 800 and 1000 MeV/u. The experiments focus on the determination of the cross sections and the correspondingp _t -distributions. The results will extend the existing systematics of ⁰-production in heavy-ion collisions to a system with small mass.Presented at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.     

Structural phase transitions in ‘hcp’ C70 single-crystals

The thermal expansion of vapor-grownC ₇₀ single crystals ahs been investigated using high-resolution capacitance dilatometry from 5–380 K. Measurements were made both parallel and perpendicular to the hexagonalc-axis. Three first-order phase transitions which we associate with the consecutive disordering of theC ₇₀ molecules are observed upon heating at 280 K (long-axis spinning), 300 K (long-axis precession) and 355 K (quasi-free rotation), respectively. The highest-temperature transition exhibits a very large (50 K) thermal hysteresis. Powder and single-crystal X-ray diffraction show that the crystals are predominantly hexagonal-close-packed (HCP) with an idealc/a1.63 above 360 K andc/a1.84 at 295 K.     

First-principles study of He trapping in η-Fe_2C

The distribution of He in η-Fe_2C has been studied by first-principles calculations.The formation energies of interstitial He and substitutional He(replacing Fe) are 3.76 eV and 3.49 eV,respectively,which are remarkably smaller than those in bcc Fe,indicating that He is more soluble in η-Fe_2C than in bcc Fe.The binding potencies of both a substitutionalinterstitial He pair(1.28 eV) and a substitutional-substitutional He pair(0.76 eV) are significantly weaker than those in bcc Fe.The binding energy between the two He atoms in an interstitial-interstitial He pair(0.31 eV) is the same as that in bcc Fe,but the diffusion barrier of interstitial He(0.35 eV) is much larger than that in bcc Fe,suggesting that it is more difficult for the interstitial He atom to agglomerate in η-Fe_2C than in bcc Fe.Thus,self-trapping of He in η-Fe_2C is less powerful than that in bcc Fe.As a consequence,small and dense η-Fe_2C particles in ferritic steels might serve as scattered trapping centers for He,slow down He bubble growth at the initial stage,and make the steel more swelling resistant.     

Selective homonuclear Hartmann–Hahn for 13C→13C polarization transfer in solution state NMR

Polarization transfer has become a commonplace technique for the enhancement of a variety of nuclei in high field nuclear magnetic resonance (NMR). In this paper the homonuclear Hartmann-Hahn method for polarization transfer is revisited and it is shown that a 90% transfer of polarization can be achieved experimentally between a pair of scalar coupled ¹³C nuclei in a sample of isotopically enriched glycine. This may show particular utility in the field of dynamic nuclear polarization (DNP) and could be used as an addendum to already established DNP techniques allowing the favourable enhancement to be ‘stored’ on long-lived nuclei and subsequently transferred to shorter-lived nuclei prior to observation.     

Electrochemistry of NaK2C12 in lithium-containing electrolytes and its use in lithium-ion cells☆

The electrochemistry of NaK₂C₁₂ in 1 M LiClO₄ EC-DMC solutions has been studied. The results show that, upon oxidation, NaK₂C₁₂ irreversibly releases one mole of potassium ions. The resulting composite electrode, that appears to be a mixture of graphite and Na–K alloy, is capable to reversibly intercalate lithium up to LiC₆ with fast rate. The compound can be used in lithium-ion cells with partially lithiated cathodes such as LiMn₂O₄, resulting in a two plateaus cell operating in the Li_1+xMn₂O₄ and Li_1−xMn₂O₄ regions.     

Radiation defects in germanium. radiation defects annealed at ∼260°C in n-type germanium

Abstract

Point defects produced by neutron, electron or γ-ray irradiation were studied by electrical measurements. The defect levels were analyzed by DLTS technique. Annealing of radiation induced defects at about 260°C was obtained in 20 min isochronal annealings. Annealed fraction of the 260°C stage was obtained to be 85% in arsenic-doped crystals and independent of the species of irradiating particle. The value in antimony-doped and oxygen-doped specimens were 25 and 70%, respectively. The activation energy was found to be 1.6 eV and the annealing kinetics were first order. A tentative model for the defect responsible at the 260°C stage is a vacancy complex.     

Symmetry breaking and electron correlation in C603− fullerene anions

Effects of electron interactions in electronic states of C₆₀³⁻ with a rigid icosahedral nuclear skeleton are considered. Under a transition of the Hubbard potential to a long-range e-e potential within the Hartree-Fock approach, the minimum energy state with broken symmetry bifurcates from the symmetry state ⁴A_u, which is shown to be closely related to the electron correlation. The multiconfigurational structure of C₆₀³⁻ electronic states is calculated using analytical expressions derived for Cl matrix elements. The validity of the common one-electron-band approach for fullerides is discussed.     

Limitations of the Quantification of Organic Carbon in Sediment from C–H Stretching Vibrations in DRIFT Spectra

Abstract

The limitations of quantifying organic carbon (OC) or various organic substances in sediment from the integration of infrared C–H stretching bands using diffuse reflectance infrared Fourier transform (DRIFT) spectra are pointed out, both from theoretical arguments and by presenting experimental data. Such determinations are inaccurate and imprecise because (i) the band at 2930 cm^?1 is not exclusively due to CH₂ groups; (ii) there is a spectral interference from CO₃ ^2? absorption; and (iii) the proportion of CH₂ groups in organic matter varies for different sediments. The measurement of aliphatic C–H stretching band areas only provides an approximate measurement of aliphatic carbon bonded to hydrogen, which turns out to be a factor of about 3 to 3.5 times smaller than the OC content for Hong Kong marine sediments, depending on their nature and origin.     

A rotating α-chain in the nucleus ~(12)C

<正>Because of the strong nuclear force among protons and neutrons,α-particles form a stable configuration not only in free space, but also in very light nuclei. Even in unstable configurations of heavy and super-heavy nuclei,α-decay is often observed. Obviously there is a high probability for the formation of anα-particle in such systems, which tunnels through the Coulomb barrier as a combined particle. There