Extra Splitting Research Articles

Pressure-induced band-gap energy increase in a metal iodate

A wide band gap is one of the essential requirements for metal iodates to be used as nonlinear optical materials. Usually, the band gap of these materials decreases under the application of pressure. Herein, we introduce a case in which the band-gap energy of a hydrated metal iodate, namely $\mathrm{Ca}{({\mathrm{IO}}_{3})}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{H}}_{2}\mathrm{O}$, has been successfully increased, from 4.52 to 4.92 eV, by applying external pressure without showing signs of saturation upon increasing pressure. The pressure-induced nonlinear band-gap opening correlates with the pressure-induced shortening of the I-O bond distances, as obtained from x-ray diffraction measurements. In addition, two pressure-induced isostructural phase transitions are observed in the pressure regions of 6.6--8.0 and 13.0--15.5 GPa. These two isostructural phase transitions cause a nonlinear pressure-induced evolution of the band-gap energy and crystal lattice parameters, as well as the occurrence of several extra peaks and peak splitting in Raman spectra.

Structures and manifestation of ortho-, meta-, and para-NH2-substitution in the optical spectra of europium and terbium aminobenzoates

Four pairs of isostructural europium and terbium ortho-, meta, and para-aminobenzoates ([Ln(2-ABenz)3(H2O)], [Ln(3-ABenz)3(H2O)3], [Ln(3-ABenz)3(H2O)3]·3H2O, [Ln(4-ABenz)3(H2O)], (Ln = Eu, Tb; ABenz – aminobenzoate anion)) were investigated using X-ray diffraction and optical spectroscopy (luminescence and luminescence excitation spectra, as well as vibrational IR and Raman spectra). The crystal structures of [Tb(2-ABenz)3(H2O)], [Eu(3-ABenz)3(H2O)3], [Eu(3-ABenz)3(H2O)3]·3H2O, and [Eu(4-ABenz)3(H2O)] were determined by single crystal X-ray analysis. The [Eu(3-ABenz)3(H2O)3] structure constitutes a new type of lanthanide m-aminobenzoate in the R3 space group. The Ln3+ coordination polyhedron formed by three bidentate chelate carboxylic groups and three terminal water molecules in both structures of m-aminobenzoate can be described as a distorted three-capped trigonal prism. The influence of the incorporation of three solvate outer-sphere H2O molecules in the crystal lattice of m-aminobenzoate on the Eu3+ luminescence center was analyzed. Restructuring of the LnO9 coordination polyhedron results in a decrease in the distortions of the crystal field that appears as a loss of extra splitting of the Ln3+ electronic levels in [Ln(3-ABenz)3(H2O)3]·3H2O. The effect of the electron-donating NH2 group located in different positions on the benzene ring on process of the excitation energy transfer to Ln3+ ion is examined. The hypsochromic shift of an intense interligand charge transfer (ILCT) band in the Tb3+ excitation spectra of the sequence of o-, m-, and p-NH2-substituted compounds is observed. This shift is the consequence of the different electron density distribution depending on the NH2 position in the ligands. The predominant role of low-energy ligand–metal charge transfer (LMCT) states in the quenching of the luminescence of the europium o- and p-aminobenzoates in contrast with the europium m-aminobenzoates is discussed. Compounds including a supplementary Cl substituent on the benzene ring [Ln(2-A-5-Cl-Benz)3(H2O)n] (Ln = Eu, Tb) and [Eu(4-A-2-Cl-Benz)3(H2O)n] are also under consideration.

Influence of outer-sphere anions in europium tetrahydrofuran-2-carboxylates on the Eu3+ luminescence center, analyzed by methods of X-ray diffraction and optical spectroscopy

Five new lanthanide tetrahydrofuran-2-carboxylate (THFC) complexes [Ln(THFC)2(H2O)2]·L·H2O (Ln=Eu; L=Cl−, Br−, NO3− and Ln=Tb; L=Cl−, NO3−) have been synthesized. The crystal structures of four compounds were solved by the X-ray diffraction method. The Ln3+ ions are coordinated to eight oxygen atoms: six oxygen atoms are provided by two tridentate bridging-cyclic THFC ligands, and the other two by water molecules. The Ln3+ coordination polyhedron can be described as a distorted square antiprism. The structures consist of planar layers linked by hydrogen bonds through outer-sphere L anions and H2O molecules. The influence of the L anion on the Eu3+ luminescence center is analyzed with the help of luminescence and IR vibrational spectroscopy. The distortions of the square antiprism increase with the size of the L outer-sphere anions. Consequently, the lowering of the symmetry of the crystal field around the Eu3+ ion appears as an extra splitting of the 7FJ levels under the influence of the crystal field components of the second and fourth ranks.

Exact wave functions for atomic electron interacting with photon fields

Many nonlinear quantum optical physics phenomena need more accurate wave functions and corresponding energy or quasienergy levels to account for. An analytic expression of wave functions with corresponding energy levels for an atomic electron interacting with a photon field is presented as an exact solution to the Schrodinger-like equation involved with both atomic Coulomb interaction and electron-photon interaction. The solution is a natural generalization of the quantum-field Volkov states for an otherwise free electron interacting with a photon field. The solution shows that an Nlevel atom in light form stationary states without extra energy splitting in addition to the Floquet mechanism. The treatment developed here with computing codes can be conveniently transferred to quantum optics in classical-field version as research tools to benefit the whole physics community.

Separated Unicast/Multicast Splitter-and-Delivery Switch and Its Use in Multicasting-Capable Optical Cross-Connect

We propose a novel separated unicast/multicast splitter-and-delivery (SUM-SaD) switch for mixed unicast and multicast traffic. Only multicast connections undergo extra splitting loss but are compensated by incorporated optical amplifiers. A typical multicasting-capable optical cross-connect is constructed by using the proposed SUM-SaDs. Theoretically, we prove that it is strictly nonblocking for both unicast and multicast connections if d=N/2, where N and d are the dimension of SUM-SaD and the number of SaD input ports, respectively. Therefore, d means the maximum accommodated trees in the SUM-SaD. To save cost, d can be less than N/2 , and the throughput performance is investigated by simulation. The results show that the throughput is improved when d increases. In the experiment, we construct a 4 times 4 SUM-SaD prototype and measure the bit-error rate (BER) of unicast connection, multicast connection with or without optical amplifier. There is no clear BER difference between them for the small dimensional SUM-SaD switch.

Experimental Demonstration of a SAC-OCDMA PON With Burst-Mode Reception: Local Versus Centralized Sources

In this paper, we demonstrate experimentally the uplink of a 7 times 622 Mb/s incoherent spectral amplitude coded optical code-division multiple access (SAC-OCDMA) passive optical network (PON) with burst-mode reception. We consider two network architectures: local sources (LS) at each optical network unit (ONU) versus a single source located at the central office. We examine both architectures over a 20-km optical link, as well as a reference back-to-back configuration. Our architectures can adopt two-feeder and single-feeder topologies; however, we only test the two-feeder topology and therefore the effect of Rayleigh backscattering is neglected. We also study the relative merits (cost and performance) of local sources versus centralized architectures. A penalty of less than 2 dB between the LS and the centralized light sources (CLS) architectures was measured at a bit error rate (BER) of 10-9 under certain assumptions on the relative power of the sources. The power budget in the CLS architectures is more critical than in the LS architectures; extra splitting and propagation losses exist as the uplink travels through the network back and forth. Doubling the number of users while maintaining the same distance and source power in LS architectures imposes 3-dB additional losses, whereas for CLS architectures, there are 6-dB extra losses. CLS architectures can overcome these penalties using amplification at the central office. Alternately, central office amplification can be used to more than double the number of users in LS SAC-OCDMA PONs. A standalone (no global clock) burst-mode receiver with clock and data recovery (CDR), clock and phase alignment (CPA), and Reed-Solomon RS(255,239) forward-error correction (FEC) decoder is demonstrated. A penalty of less than 0.25 dB due to the nonideal sampling of the CDR is reported. The receiver also provides an instantaneous phase acquisition time for any phase step between consecutive packets, and a good immunity to silence periods. A coding gain of more than 2.5 dB was reported for a single-user system, and BER floors were completely eliminated. Error-free transmission (BER < 10-9 ) for a fully loaded PON was achieved for the LS architecture as well as the CLS architecture. Continuous and bursty upstream traffic were tested. Due to the CPA algorithm, even with zero preamble bits we report a zero packet loss ratio (PLR) for up to four simultaneous users in case of bursty traffic, and more than two orders of magnitude improvement in the PLR for fully loaded PON systems.

EELS study of interfaces in magnetoresistive LSMO/STO/LSMO tunnel junctions

A magnetic tunnel junction consists of two ferromagnetic conducting electrodes separated by an insulating thin layer. The performance of such a system strikingly depends on the last conducting atomic layers in contact with the insulator. Consequently, the present paper reports a nanoscale electron energy loss spectroscopy (EELS) study, which has been performed across a couple of La0.66Sr0.33MnO3,/SrTiO3/La0.66Sr0.33MnO3 tunnel junctions with different barrier thickness es (1.5 nm and 5 nm respectively). It aims at determining not only the chemical composition in the interface areas, but also the effect of the neighbouring atoms on their electronic structure. Using recent improvements in the STEM-EELS data acquisition and processing techniques (systematic use of spectrum-line and spectrum-image modes, multivariate statistical analysis, 2D energy deconvolution schemes, etc.), the local chemical information is better extracted with shorter acquisition times, while the large increase of the data set contributes to validate the results. Within the accuracy level of these measurements, the elemental composition of the different phases remains stable up to the interfaces with no evidence of extra doping. Furthermore, weak changes on the Mn-2p edge fine structures (weak shift to lower energy loss values and extra splitting on the top of the Mn L3 line are observed on all the interfaces. They are interpreted as a consequence of a slight reduction of the local Mn valence likely accompanied by a strain induced change in local symmetry. The discussion is focussed on all spectral changes identified at a (sub)nanometer scale and their potential effects on the degradation of magnetic and transport properties measured, close to room temperature, at a macroscopic level.

Magnetic resonance investigation of gold-doped and gold-hydrogen-doped silicon

Three paramagnetic centers related to gold have been observed in gold-doped and gold-doped hydrogenated silicon by magnetic resonance. One spectrum, labeled Si-NL62, corresponding to a center with monoclinic-I symmetry, presents fourfold splitting due to the hyperfine interaction with one gold atom and further hyperfine interaction with two silicon nearest-neighbor atoms. After being diffused with hydrogen in a wet atmosphere of water vapor at 1300 \ifmmode^\circ\else\textdegree\fi{}C for about 30 min, a second electron paramagnetic resonance spectrum, labeled Si-NL63, is detected, also of the monoclinic-I symmetry. The spectrum of the center is characterized by a complex hyperfine structure, in which, depending on magnetic field orientation, a sevenfold splitting with the intensities 1:2:3:4:3:2:1, a fourfold splitting 4:4:4:4, and other more arbitrary structures are observed. Extra small splitting is observed in the sample diffused with deuterium, indicating hydrogen involvement in the microscopic structure of the Si-NL63 center. Under band gap illumination the third center of a one-gold--two-hydrogen complex is observed. The center, labeled Si-NL64, has low triclinic symmetry and features the hyperfine interactions with one gold and two nearly equivalent hydrogen atoms. This results in a (1:2:1):(1:2:1):(1:2:1):(1:2:1) structure of each group of spectral lines. Spin-Hamiltonian parameters for the three spectra are determined and microscopic models are discussed.

Chemical effects in rare gas adsorption: FLAPW calculations forAg(001)c(2×2)−Xe

In order to investigate postulated chemical effects in adsorption of heavy rare gas atoms, we investigate the $\mathrm{Ag}(001)c(2\ifmmode\times\else\texttimes\fi{}2)$-Xe system using the full-potential linearized augmented plane-wave method. Adsorption in the on-top site is found to be favored by 8.6 meV---adsorption in this site suggests that there is a chemical contribution to the bonding. The topology of the charge density associated with the Xe 5$p$ states clearly shows that these states are involved in a bonding interaction with the substrate states. We also show that the extra splitting of the ${5p}_{3/2}$ orbitals arises from adsorbate-adsorbate interactions. It is observed that the spin-orbit interaction drastically alters the electronic, but not geometric, properties of the system.

Odd-even input-buffered multicast switch

An input buffered packet switch called the odd-even multicast switch is proposed. The packet splitting probability of the proposed switch is derived and the packet output contention is resolved using the cyclic-priority reservation (CPR) algorithm. The throughput and mean packet delay of the proposed switch are compared with a simple input buffered switch. It is found that the proposed switch gives a significant performance improvement at the expense of extra packet splitting overhead.

Zeise's salt studied by high resolution solid state 13C CPMAS and 1H SPEDA NMR spectroscopy

Polycrystalline Zeise's salt ( K(CH 2 CH 2 PtCl 3⊎x H 2 O ) was investigated by high resolution solid state 13C CPMAS (cross polarization magic-angle spinning) and 1H SPEDA (single pulse excitation with delayed acquisation) NMR spectroscopies using different rotor spinning speeds. Though the 13C and 1H nuclei are respectively two and three bond lengths separated from the 35 37 Cl nuclei, both the 13C and 1H spectral lineshapes are influenced by the second and higher order dipolar couplings between 13C and 1H and the quadrupole spins 35 37 Cl . An extra splitting or broadening resulting from the coupling between 13C and 195Pt is also found. The high resolution 1H spectrum is also influenced by 1H 195Pt coupling. A computer program was developed to simulate theoretically the observed 13C and 1H NMR spectral lineshapes.

Thermal annealing of defects in highly defective NiO nanoparticles studied by X-ray and electron spectroscopies

We studied the electronic structure of highly defective NiO nanoparticles using X-ray and electron spectroscopies. The spectra of NiO nanoparticles exhibit splittings which are not present in the spectra of bulk NiO. These extra splittings are attributed to changes in the crystal field caused by both adsorbates and defects. Thermal annealing of the nanoparticles reduces the splittings observed in the spectra. The changes observed in the spectra up to 300°C are attributed mostly to the desorption of various adsorbates. The changes observed above 300°C are attributed to the annealing out of defects. The spectra annealed at higher temperatures approach the spectra of bulk NiO. We suggest that the defects are unsaturated NiO bonds at the surface of the nanoparticles.

Modes of electron loss from triphenul phosphonium bromide: an unusual structural switch

The exposure of dilute solutions of triphenyl phosphonium bromide in CFCl 3 to ionizing radiation at 77 K gave a species whose ESR spectrum was characteristic of the phosphoryl radical, Ph 3P +, with a small extra doublet splitting assigned to the HBr proton. On annealing, these features were lost irreversibly and replaced by new features with large splitting from 31P and an extra quartet splitting from bromine without any resolved proton splitting. This change comprises the movement of a proton out of the  … HBr δ region, whilst remaining bound to bromine (spin density on bromine: only ca. 25%).

Low-energy excitations and the electronic specific heat of YbBiPt.

Neutron scattering data from the cubic heavy-fermion compound YbBiPt are presented, along with an interpretation in terms of strongly broadened crystal-field levels. To first order, the ground state is sixfold degenerate, consisting of a doublet ({Gamma}{sub 7}) and quartet ({Gamma}{sub 8}). Integration over these levels reproduces the observed linear specific-heat coefficient {gamma} of 8 J mol{sup {minus}1} K{sup {minus}2} to within {plus_minus}20%. At the lowest temperatures, an extra symmetry-forbidden splitting is observed.

Distribution of Electron Trapping in DNA: Protonation of One-Electron Reduced Cytosine

Electron spin resonance was employed to study one-electron reduced cytosine stabilized in glasses at low temperatures. In a LiCl/H2O glass, deoxycytidine gives an extra approximately 1 mT splitting that is not observed in oligomers. To better understand the source of the extra splitting, 1-methylcytosine (1mC) and N,N-dimethyldeoxycytidine (dmC) were examined in an HCl/H2O glass. The spectrum of 1mC is a quartet and the spectrum of dmC is a triplet. A probable explanation for this is that in both cases N4 is fully protonated prior to electron addition. In the LiCl/H2O glass, monomeric cytosine, after one-electron reduction, appears to protonate at N4. However, oligomeric cytosine, after one-electron reduction, does not protonate at N4 and therefore must protonate at N3. This could be due to the exclusion of Li+ coordination at N3 and/or the constraining of N4 to a planar configuration via stacking interactions. These findings provide additional insight into why cytosine is the major site of electron capture in DNA. Proton transfer across the N1-H...N3 hydrogen bond is expected to stabilize electron addition to cytosine preferentially.

Factors controlling the site of protonation of the one-electron adduct of cytosine and its derivatives

Exposure of cytosine and derivatives thereof to 60Co γ-rays at 77 K in a range of aqueous solutions (H2O or D2O) at 77 K gave EPR spectra assigned to the corresponding radical anions. These spectra comprise either doublet or triplet hyperfine features due to one or two protons. Triplet features observed using H2O media become doublets using D2O media. Well defined triplet spectra were observed using lithium chloride glasses and methanol–water glasses. Using frozen aqueous solutions which give phase-separated solids, spectra ranging from doublets via mixtures to triplets were obtained, depending on the derivative used. It is suggested that the first formed radical anions are rapidly protonated either on the ring nitrogen [N(3)] or on the amino nitrogen. In the former, there is no extra splitting from the added proton and a major doublet is observed because of hyperfine coupling to the C(6) proton [C(6)–H]. In the latter case, the proton is thought to add along a path normal to the plane of the ring so that overlap with the SOMO is maximised, and there is a large hyperfine coupling. Coupling to the other two amino protons is too small to resolve under these conditions. The fact that the –N(CH3)2 derivative gives a doublet rather than a triplet supports the postulate that the –NH2 group is indeed protonated in the triplet species. For the aqueous-methanol glasses, on annealing, this extra doublet splitting is lost irreversibly, probably because rotation of the –NH+3 group sets in, making the three protons equivalent.As has been shown by Bernhard and co-workers, certain oligomers which give C·– centres on irradiation give rise to doublets only in H2O glasses. Hence N(3)-protonation is favoured in polymeric systems. Reasons for these differences, and the importance of these results in relation to DNA are discussed.

SOLID-STATE CARBON-13 CP/MAS NMR SPECTRA OF 2, 2'-BI-1H-IMIDAZOLE

Solid-state carbon-13 NMR spectra have been measured for 2, 2'-bi-1H-imidazole to study with its proton exchange tautomerism in solid. The CP/MAS NMR spectra showed four peaks for the 4, 4', 5, and 5' carbons in the solid state in contrast to the single peak assigned to these carbons in solution. Therefore, the tautomerism was proved to be frozen in the solid state. A crystal field effect was considered to cause the extra splittings in these peaks.

Variation in the normalized tetanic force of single frog muscle fibres.

1. The forces produced in maximal fixed-end tetani of single fibres isolated from the anterior tibialis muscle of the frog Rana temporaria have been measured at sarcomere lengths of 2.2 microns and temperatures near 0 and 10 degrees C. 2. When normalized by either cross-sectional area or dry weight per unit length at a sarcomere length of 2.2 microns, the forces vary over a twofold range. 3. The normalized force is not significantly correlated with the velocity of unloaded shortening or the twitch characteristics of the fibres. Lack of variability of these two quantities (together with histochemical evidence) suggest that only one fibre type is present in the experimental sample. 4. The steady rate of energy liberation (stable, heart rate) of the fibres during isometric tetani is positively correlated with the normalized force, indicating that extra ATP splitting is required to produce higher forces. 5. Fibres with a higher ratio of dry weight per unit length to cross-sectional area ('dry density') show a higher force when normalized by area, but not when normalized by dry weight per unit length. 6. Fibres with a more circular cross-sectional profile produce more force when normalized by either cross-sectional area or dry weight per unit length. The significance of this correlation is unclear. 7. The contribution of various sources to the total overall variation in normalized force is assessed. It is suggested that a diffusible substance or substances may be involved in modulating fibre force.

Identification of resonances from an oncogenic activating locus of human N-RAS-encoded p21 protein using isotope-edited NMR.

A sample of Escherichia coli-expressed human N-RAS-encoded p21, a 21-kDa protein, was selectively labeled with 15N at each of the 14 glycine amide positions. Two-dimensional proton-observe 15N correlation spectra showed one peak for each glycine residue. Five glycine resonances were identified with residues near the nucleotide binding site and provide useful reporters of several oncogene-activating positions. Three of these resonances were assigned to residues 10, 15, and 115 from the spectrum of a sample that was also labeled with [13C]valine. These resonances showed extra splitting or broadening due to the 13C label, which could be eliminated by 13C decoupling. Two other peaks were unambiguously identified as Gly-12 and Gly-13 using a one-dimensional edited nuclear Overhauser experiment and by spectral comparison with an Asp-12 mutant. These assignments have provided several site-specific probes of critical domains in p21.

N.m.r. spectroscopic and X-ray crystallographic studies on some o-NO2substituted aromatic sulphur amides

Solid state 13C c.p.-m.a.s. and solution 13C, 15N, 14N, and 17O n.m.r. spectra have been measured for N,N-dimethyl-o-nitrobenzenesulphenamide, o-nitrobenzenesulphenamide, and N,N-dimethyl-onitrobenzenesulphonamide. The 13C c.p.-m.a.s. n.m.r. resonance signals of the methyl carbon atoms bonded to nitrogen show a characteristic doublet pattern. In addition, like the signal of N,N-dimethyltoluene-p-sulphonamide, the N-methyl resonance signal of N,N-dimethyl-o-nitrobenzenesulphenamide shows extra splitting. In the solution spectra the 15N nuclei of the amide group of the sulphonamides are considerably less shielded than those of the corresponding sulphenamides. The nitro-substituent of the aromatic ring has hardly any effect on the electron density of the nitrogen atom of the sulphonamide group.The crystal structures of N,N-dimethyl-o-nitrobenzenesulphenamide (1) and N,N-dimethyl-o-nitrobenzenesulphonamide (2) have been determined by the single crystal X-ray diffraction technique and refined to final R values 0.043 and 0.049, respectively. The configurations of these sulphur(II) and sulphur(VI) amides, with respect to the geometry around the sulphur atom and the orientation of the substituents in the phenyl ring, are different. The sulphenamide adopts crystallographic σ symmetry, with all atoms except the methyl groups lying in the crystallographic mirror plane. N,N-Dimethyl-o-nitrobenzenesulphonamide has no high molecular symmetry and there is clear steric repulsion between the NO2 group and the oxygen atoms of the SO2N group. The nitro group is rotated 53.5(2)° relative to the plane through the phenyl group. The amide nitrogen displays a pseudo-trigonal arrangement in both compounds.