Center Defects Research Articles

Effects of γ-radiation on Yb-doped fiber

Yb-doped double-clad fibers are prepared through a conventional modified chemical-vapor deposition technique and solution doping method: each fiber contains a core of around 10 μm in diameter. These fibers are divided into groups under 60Co γ radiations of different doses, and we investigate the fiber absorption spectra and laser spectral properties before and after irradiation. Experimental results show that with increasing the irradiation dose the absorption of the fiber after irradiation increases significantly in the visible region, we believe that the enhancement of optical fiber absorption in the visible region may be due to the color center defects existing already in the fiber (such ODC (Ⅱ)) and the color center defects produced by the irradiation (E'center, POR and Yb2+ions). We also analyze slope efficiencies, bare efficiencies, and transmission characteristics of the fiber before and after laser irradiation. Finally, we use the power-law to fit the radiation-induced losses of the fiber under different radiation doses, and the results obtained in this paper provide a theoretical basis for studying the anti-radiation of optical fibers.

Effect of Stress Field on Closure of Center Defects in Symmetric Rolling and Asymmetric Rolling of Round Billets

Although the closure of defects at the center of billets on rolling such billets is an important subject, a method of quantity evaluation for such closure has not yet been clarified. Therefore, to establish a method for such quantity evaluation, we study such defects using experiments and finite element analysis including asymmetric rolling, especially with respect to the integration of the hydrostatic stress Gm. The results showed that stress was widely distributed, as determined in the experiment and in the FEM analysis of rolling at the edge around an artificial central hole in which defects were simulated. Therefore, it was suggested that, to evaluate the behavior of defect closure, the size of defects and the shape of the grooved roll used should be taken into account. [doi:10.2320/matertrans.P-M2014837]

Substrate crystal recovery for homoepitaxial diamond synthesis

Abstract Homoepitaxial chemical vapor deposition (CVD) of diamond requires high quality substrate crystals. This paper describes the process of diamond substrate crystal recovery so that the original substrate can be reused for multiple synthesis processes. A three-stage treatment is applied after homoepitaxial CVD growth. First the original substrate is separated by laser cutting, then the cut surface is mechanically polished, and finally polycrystalline material at the edges of the recovered seed plate is laser trimmed. This recovery process yields reusable diamond substrates that do not differ appreciably from their original state in terms of stresses and impurity concentrations. While the recovery process was demonstrated using HPHT seed substrates the process can also be applied to the as-grown CVD diamond plates. Infrared absorption spectral analysis, surface profilometry, birefringence imaging and Raman spectroscopy are performed after each processing step to monitor crystal quality. The nitrogen concentration in the substrate crystal remains constant throughout CVD and recovery processes. When using HPHT type Ib substrates the detected nitrogen concentration is 110–180 ppm. The nitrogen is mainly incorporated in form of C center defects and no transformation to other forms of defect centers occurs during the CVD process. Birefringence imaging showed a low level of internal stress within the HPHT crystals. No change is observed during CVD growth and recovery processes. It is shown that the polycrystalline rim removal is essential for repeatable CVD deposition on the same seed substrate. Substrate crystal recovery allows growth of up to 20 crystals from one original seed.

Somatic and germ‐line mosaicism of deletion 15q11.2–q13 in a mother of dyzigotic twins with Angelman syndrome

Angelman syndrome (AS, OMIM105830) is a neurogenetic disorder caused by different genetic mechanisms. Determining the genetic mechanism is essential to establish the recurrence risk and the accuracy of genetic/reproductive counseling. The majority of AS patients present with a deletion of the 15q11.2-q13 region on the maternally derived chromosome. The other genetic mechanisms are: paternal disomy of chromosome 15, imprinting center defects, and mutations in the ubiquitin-protein ligase E3A gene (UBE3A). Different recurrence risks are associated with each specific genetic mechanism involved. We report on the study of dizygotic twins with classic phenotypic AS due to deletion of the same maternally derived chromosome 15. The mother presented with hypopigmented macular lesions on the inner side of both arms. Fibroblast culture studies of the maternal hypopigmented skin areas from both arms showed mosaicism for a normal cell line and for a second cell line with a 15q11.2-q13 deletion. This family represents the first demonstrated case of maternal somatic and germ line mosaicism for 15q11.2-q13 deletion as the cause of AS.

Structural studies and optical properties of pearl nucleus irradiated by γ-ray

The effect of γ-ray irradiation on the color and structure of the nucleus and cultured pearl nucleus is studied experimentally. By using a (60Co) γ-ray irradiator, the nucleus originating from freshwater shell is irradiated. Consequently, the color of the nucleus is altered from white to blackish brown or gray by an increase in the irradiation dose treatments. The structural identification of all samples has been confirmed using X-ray diffraction. It is clearly found that all the samples are composed of aragonite, a common phase of the mineral CaCO3. A slight change in the crystallinity of the sample is observed when irradiated with high dose of radiation. Scanning electron microscopy images show that there are no morphological changes by irradiation. UV–Vis spectroscopic measurement is used to distinguish and analyze the change of color due to different irradiation doses. With an increase in the γ-ray radiation doses, a red shift in the absorption edge of the optical spectra of pearl nucleus is observed. Electron spin resonance signal shows mainly the presence of radiation-induced radicals as color center defects within the samples. An increase in the defects with a gradual increase in the radiation dose depicts that the defect-level transition is the dominant mechanism for the color change in the pearl nucleus.

Photoluminescence in amorphous MgSiO$\boldsymbol {_{3}}$ silicate

Samples of amorphous MgSiO_3 annealed at temperature steps leading up to their crystallisation temperature show a rise in photoluminescence activity, peaking at ~450C. The photoluminescence band has a main peak at 595nm and a weaker peak at 624nm. We present laboratory data to show that the maximum in photoluminescence activity is related to substantial structural reordering that occurs within a relatively narrow temperature range. We attribute the origin of the photoluminescence to non-bridging oxygen hole centre defects, which form around ordered nano-sized domain structures as a result of the breakup of tetrahedral connectivity in the disordered inter-domain network, aided by the loss of bonded OH. These defects are removed as crystallisation progresses, resulting in the decrease and eventual loss of photoluminescence. Thermally processed hydrogenated amorphous silicate grains could therefore represent a potential carrier of extended red emission.

Epilepsy in Prader–Willi syndrome: experience of a national referral centre

The aim of the study was to characterize epilepsy, febrile seizures, electrographic features, and brain abnormalities in a large, national cohort of individuals with Prader-Willi syndrome (PWS). This was an observational cohort study. Clinic charts of 126 individuals (63 males, 63 females) with genetically confirmed PWS (due to a deletion in 72 cases, to uniparental disomy [UPD] in 51 cases, and to an imprinting centre defect in two cases), aged from 1 month to 48 years (mean age 13y), were reviewed and 119 interviews conducted. Information regarding seizures, medication, imaging studies, and family history of seizures was collected. Ninety-five individuals (aged 1mo-48y) underwent electroencephalography (EEG). Five individuals had epilepsy (4.0%), three of whom had major cerebral findings on imaging, and eight others had febrile seizures (6.4%). Of the three genetic abnormalities, deletion was associated with seizures. Focal epileptiform abnormalities were found in 12 out of 94 individuals, and five out of these 12 had a frank electrographic seizure pattern. Epileptogenic EEG abnormalities were associated with young age. The risk of epilepsy and febrile seizures in PWS is significantly lower than in Angelman syndrome and is associated with brain abnormalities. Electrographic seizures and focal epileptiform activity were present in 5% of individuals and were associated with young age. The underpinnings of epileptiform abnormalities in PWS and how they differ from those of the Angelman syndrome should be studied further.

Thermal conductance calculations of silicon nanowires: comparison with diamond nanowires

We present phonon thermal conductance calculations for silicon nanowires (SiNWs) with diameters ranging from 1 to 5 nm with and without vacancy defects by the non-equilibrium Green’s function technique using the interatomic Tersoff-Brenner potentials. For the comparison, we also present phonon thermal conductance calculations for diamond nanowires. For two types of vacancy defects in the SiNW, a ‘center defect’ and a ‘surface defect’, we found that a center-defect reduces thermal conductance much more than a surface defect. We also found that the thermal conductance changes its character from the usual behavior, in proportion to the square of diameter (the cross-sectional area) for over 100 and 300 K, to the unusual one, not dependent on its diameter at all at low temperature. The crossover is attributed to the quantization of thermal conductance.

Point-defect optical transitions and thermal ionization energies from quantum Monte Carlo methods: Application to theF-center defect in MgO

We present an approach to calculation of point-defect optical and thermal ionization energies based on the highly accurate quantum Monte Carlo methods. The use of an inherently many-body theory that directly treats electron correlation offers many improvements over the typically employed density functional theory Kohn-Sham description. In particular, the use of quantum Monte Carlo methods can help overcome the band-gap problem and obviate the need for ad hoc corrections. We demonstrate our approach to the calculation of the optical and thermal ionization energies of the $F$-center defect in magnesium oxide, and obtain excellent agreement with experimental and/or other high-accuracy computational results.

Electron Tomography Reveals Novel Microtubule Lattice and Microtubule Organizing Centre Defects in +TIP Mutants

Mal3p and Tip1p are the fission yeast (Schizosaccharomyces pombe) homologues of EB1 and CLIP-170, two conserved microtubule plus end tracking proteins (+TIPs). These proteins are crucial regulators of microtubule dynamics. Using electron tomography, we carried out a high-resolution analysis of the phenotypes caused by mal3 and tip1 deletions. We describe the 3-dimensional microtubule organization, quantify microtubule end structures and uncover novel defects of the microtubule lattices. We also reveal unexpected structural modifications of the spindle pole bodies (SPBs), the yeast microtubule organizing centers. In both mutants we observe an increased SPB volume and a reduced number of MT/SPB attachments. The discovered defects alter previous interpretations of the mutant phenotypes and provide new insights into the molecular functions of the two protein families.

Follicular T-helper cell recruitment governed by bystander B cells and ICOS-driven motility

Germinal centres support antibody affinity maturation and memory formation. Follicular T-helper cells promote proliferation and differentiation of antigen-specific B cells inside the follicle. A genetic deficiency in the inducible co-stimulator (ICOS), a classic CD28 family co-stimulatory molecule highly expressed by follicular T-helper cells, causes profound germinal centre defects, leading to the view that ICOS specifically co-stimulates the follicular T-helper cell differentiation program. Here we show that ICOS directly controls follicular recruitment of activated T-helper cells in mice. This effect is independent from ICOS ligand (ICOSL)-mediated co-stimulation provided by antigen-presenting dendritic cells or cognate B cells, and does not rely on Bcl6-mediated programming as an intermediate step. Instead, it requires ICOSL expression by follicular bystander B cells, which do not present cognate antigen to T-helper cells but collectively form an ICOS-engaging field. Dynamic imaging reveals ICOS engagement drives coordinated pseudopod formation and promotes persistent T-cell migration at the border between the T-cell zone and the B-cell follicle in vivo. When follicular bystander B cells cannot express ICOSL, otherwise competent T-helper cells fail to develop into follicular T-helper cells normally, and fail to promote optimal germinal centre responses. These results demonstrate a co-stimulation-independent function of ICOS, uncover a key role for bystander B cells in promoting the development of follicular T-helper cells, and reveal unsuspected sophistication in dynamic T-cell positioning in vivo.

Thermal annealing of femtosecond laser written structures in silica glass

We have investigated the thermal stability of femtosecond laser modification inside fused silica. Raman and FL spectroscopy show that fs-laser induced non-bridging oxygen hole center (NBOHC) defects completely disappear at 300 °C, whereas changes in Si-O ring structures only anneal out after heat treatment at 800-900 °C. After annealing at 900 °C optical waveguides written inside the glass had completely disappeared whereas more significant damage induced in the glass remained. The results are related to different types of bond rearrangements in the glass network.

The proportion of uniparental disomy is increased in Prader–Willi syndrome due to an advanced maternal childbearing age in Korea

Prader-Willi syndrome (PWS) is a genetic disorder caused by the absence of expression of the paternal copy of maternally imprinted genes in chromosome region 15q11-13. The genetic subtypes of PWS are classified into deletion (~70%), maternal uniparental disomy (mUPD; 25-30%), imprinting center defects (3-5%) and rare unbalanced translocations. Recently, Matsubara et al. reported a significantly higher maternal age in a trisomy rescue (TR) or gamete complementation (GC) by nondisjunction at maternal meiosis 1 (M1) group than in a deletion group. In the present study, we try to confirm their findings in an ethnically different population. A total of 97 Korean PWS patients were classified into deletional type (n=66), TR/GC (M1) (n=15), TR/GC by nondisjunction at maternal meiosis 2 (n=2), monosomy rescue or postfertilization mitotic nondisjunction (n=4) and epimutation (n=2). Maternal ages at birth showed a significant difference between the deletion group (median age of 29, interquartile range (IQR)=(27,31)) and the TR/GC (M1) group (median age of 35, IQR=(31,38)) (P<0.0001). The relative birth frequency of the TR/GC (M1) group has substantially increased since 2006 when compared with the period before 2005. These findings support the hypothesis that the advanced maternal age at childbirth is a predisposing factor for the development of mUPD because of increased M1 errors.

Optical single sideband modulation of 60-GHz radio over fiber (ROF) system using ultra compact photonic crystal ring-shaped channel drop filter

An ultra compact photonic crystal (PC) ring-shaped channel drop filter (RSCDF) is proposed to generate single side band (SSB) signal for 60GHz ROF system. This PC-RSCDF contains a bus waveguide, a resonant cavity, a ring-shaped waveguide (RSW) and a coupled cavity output waveguide. The notch depth and notch bandwidth of CDF can get 98% and 0.4nm respectively by inducing RSW and shifting the center defect rod of cavity and the rod around the cavity. Then, a method of fine tuning the resonant frequency of PC-RSCDF is proposed by adjusting the radius of insensitive rods which have weak coupling interaction with the light and the sensitivity of structure can be decreased, and the resonant frequency can be shifted to the sideband frequency of double side band (DSB) signal accurately. Finally, a 60GHz ROF SSB modulation system is demonstrated by using designed PC-RSCDF that can filter lower or upper sideband by changing its structure parameters. The extinction ratio (ER) of lower and upper sideband can get 20.9dB and 18.6dB respectively.

Photonic crystal multi-channel drop filters with Fabry–Pérot microcavity reflection feedback

We have designed a multi-port channel-drop filter (MCDF) based on a two-dimensional photonic crystal (PhC) with a Fabry–Pérot reflector at the end of the bus waveguide. The conditions to achieve 100% drop efficiency at the resonance frequency were derived through the coupled mode theory in time and the transmission properties for such structure were calculated by finite-difference time-domain (FDTD) method. The results show that the light with different wavelengths can be successfully filtered to different ports by setting different radii of the center defect rods in the drop waveguides and high drop efficiency can be achieved by means of reflection feedback. The MCDF we designed can easily separate the light with five different wavelengths simultaneously with high drop efficiency. Among them are the wavelengths of 1.31 and 1.55μm which are two main communication wavelengths. It is superior than the MCDFs reported before and can be used extensively in optical communication systems.

Structure dependent photoluminescence of nanoporous amorphous anodic aluminium oxide membranes: Role of F+ center defects

The origin of photoluminescence (PL) of the anodic aluminium oxide (AAO) membranes synthesized by electrochemical anodization of aluminium by using oxalic, phosphoric and sulfuric acid electrolytes for different anodization time duration have been investigated. All the as prepared AAO membranes exhibit strong visible blue luminescence around 410–430nm at room temperature. The mechanism of the visible light emission in AAOs has been explained by correlating the structural studies of the membranes with the PL and electron paramagnetic resonance (EPR) spectroscopy measurements. It is found that the AAO membranes are amorphous in nature (XRD and HRTEM study) and they contain large concentration of structural of defects (HRTEM study). The extensive PL and EPR investigations have indicated the presence of singly ionized oxygen vacancy related defects (F+ center defects) in AAO membranes. Based on the experimental evidences, the F+ center defects are attributed to the visible blue light emission from the AAOs.

고온고압법에 의한 Type II, Type I aB 갈색 다이아몬드의 색향상

It is possible to enhance the color of the natural diamond with a high pressure high temperature(HPHT) process. We employed a pyrophyllite tube cell and cubic press apparatus for HPHT treatment on the brown colored Type Ⅱ (5.6 ㎬/ 1700℃/ 52 min), and Type Ⅰ aB(5.6 ㎬/ 1650℃/ 30 min) diamond samples. We investigated the microstructure, Types, fluorescence, properties of the diamonds with an optical microscopy, FT-IR, photoluminescence(PL) spectroscopy, Diamond-View, and micro-Raman spectroscopy. Two tinted brown diamonds changed into colorless just after the HPHT process. Optical microscopy showed that no crack and significant inclusion evolution occurred during the HPHT process except the small graphite spot appeared in Type Ⅰ aB sample. FTIR spectrum confirmed that no Type, amber center, and platelet defect change with the HPHT treatment. Diamond-View could not distinguish the HPHT treated diamonds from the naturals. PL spectroscopy showed that N3 and H3 color centers remained even after HPHT process. Consequently, we successfully changed the color of diamonds into colorless by 5.6 ㎬ HPHT process.

Barrier Evaluation by Linearly Increasing Voltage Technique Applied to Si Solar Cells and Irradiated Pin Diodes

Technique for barrier evaluation by measurements of current transients induced by linearly increasing voltage pulse based on analysis of barrier and diffusion capacitance changes is presented. The components of the barrier capacitance charging and generation/recombination currents are discussed. Different situations of the impact of deep center defects on barrier and diffusion capacitance changes are analyzed. Basics of the profiling of layered junction structures using the presented technique are discussed. Instrumentation for implementation of this technique and for investigations of the steady-state bias infra-red illumination and temperature dependent variations of the barrier capacitance charging and generation/recombination currents are described. Applications of this technique for the analysis of barrier quality in solar cells and particle detectors fabricated on silicon material are demonstrated.

B-cell replication history and somatic hypermutation status identify distinct pathophysiologic backgrounds in common variable immunodeficiency

AbstractCommon variable immunodeficiency disorder (CVID) is the most prevalent form of primary idiopathic hypogammaglobulinemia. Identification of genetic defects in CVID is hampered by clinical and immunologic heterogeneity. By flow cytometric immunophenotyping and cell sorting of peripheral B-cell subsets of 37 CVID patients, we studied the B-cell compartment at the B-cell subset level using the κ-deleting recombination excision circle assay to determine the replication history and the Igκ-restriction enzyme hot-spot mutation assay to assess the somatic hypermutation status. Using this approach, 5 B-cell patterns were identified, which delineated groups with unique replication and somatic hypermutation characteristics. Each B-cell pattern reflected an immunologically homogenous patient group for which we proposed a different pathophysiology: (1) a B-cell production defect (n = 8, 18%), (2) an early peripheral B-cell maturation or survival defect (n = 4, 11%), (3) a B-cell activation and proliferation defect (n = 12, 32%), (4) a germinal center defect (n = 7, 19%), and (5) a postgerminal center defect (n = 6, 16%). The results of the present study provide for the first time insight into the underlying pathophysiologic background in 5 immunologically homogenous groups of CVID patients. Moreover, this study forms the basis for larger cohort studies with the defined homogenous patient groups and will facilitate the identification of underlying genetic defects in CVID.

Dependence of gamma-ray dose on annihilation processes of irradiation defects in Li 2TiO 3

Dependence of gamma-ray dose on formation and annihilation behaviors of irradiation defects was studied by means of ESR. In the formation behavior of irradiation defects, the amount of irradiation defects and ratio of O 2 −-center to O −-center increased as the in gamma-ray dose increased. The annealing experiments showed that the amounts of E′-center and O-related defects which are the Frenkel pair decreased in the two temperature ranges of 300–400 and 550–650 K. The first and second stages were identified to reactions between E′-center and O −-center and E′-center and O 2 −-center, respectively. By comparing annihilation with formation behaviors of irradiation defects, it was revealed that the activation energy of annihilation for irradiation defects was influenced by the ratio of O 2 −-center and O-related defects. Therefore, the annihilation process of irradiation defects was dominated by pyrolysis of O 2 −-center.