Structural hierarchy of chromatin in chicken erythrocyte nuclei based on small-angle neutron scattering: Fractal nature of the large-scale chromatin organization

The chromatin organization in chicken erythrocyte nuclei was studied by small-angle neutron scattering in the scattering-vector range from 1.5 × 10^?1 to 10^?4 Å^?1 with the use of the contrast-variation technique. This scattering-vector range corresponds to linear dimensions from 4 nm to 6 μm and covers the whole hierarchy of chromatin structures, from the nucleosomal structure to the entire nucleus. The results of the present study allowed the following conclusions to be drawn: (1) both the chromatin-protein structure and the structure of the nucleic acid component in chicken erythrocyte nuclei have mass-fractal properties, (2) the structure of the protein component of chromatin exhibits a fractal behavior on scales extending over two orders of magnitude, from the nucleosomal size to the size of an entire nucleus, and (3) the structure of the nucleic acid component of chromatin in chicken erythrocyte nuclei is likewise of a fractal nature and has two levels of organization or two phases with the crossover point at about 300–400 nm.     

Larmor procession reflectometry for studying multilayers

A new experimental method (angular encoding) based on the combination of reflectometry and neutron spin-echo methods, which makes it possible to use widely collimated neutron beams and provides an angular resolution of about 0.01°, has been proposed. It was used to study magnetic thin films. In particular, the effect of Larmor pseudoprecession of neutron polarization upon reflection from a ⁵⁷Fe film with a thickness of about 100 nm was investigated, and it was shown that this method allows one to determine the absolute magnetization direction; this cannot be done using conventional reflectometry.     

Measurement of Singlet Exciton Diffusion Coefficient in the C′-Direction in Crystalline Naphthalene

Abstract

The diffusion coefficient of singlet excitons in the c¹ direction in crystalline naphthalene has been deduced from the temporal analysis of fluorescence quenching at the surface by an Al layer, D_C ¹ = 5 × 10^?5 cm² s^?l, corresponding to a diffusion length A_C ¹ = 230 Å.     

Synthesis,crystal structure,magnetic characterization and spectroscopic properties of a new dinuclear iron(III) complex asymmetrically bridged by a phenoxo and methoxo groups

Dinuclear iron(III) derivative of Fe₂L¹(OCH₃)Cl₂ (L¹=1,3‐bis[N‐(5‐bromo‐2‐hydroxybenzylidene)‐2‐aminoethyl]‐2‐(5‐bromo‐2‐hydroxyphenyl)imidazolidine) has been synthesized, its crystal structure determined and magnetically characterized. The title compound crystallizes in orthorhombic space group Pbcn with cell parameters a = 12.9770(10), 18.7930(10), 25.2950(10) Å, V = 6168.9(6)ų, Z = 8, D_cal = 1.951 Mg/m³. The two iron(III) ions are asymmetrically bridged by a phenoxo and methoxo groups in the compound. The iron(III) centers are separated by 3.166(3) Å. Magnetic susceptibilities of the complex were measured over the range 5 – 298 K and the observed data were successfully simulated by the equation based on the spin‐Hamiltonian operator. Magnetic susceptibility measurements indicate very weak antiferromagnetic coupling between the iron(III) ions with J = – 11.5 cm^‐1. The comparison of the magnetic and structural parameters of the investigated compound is given and the nature of the magnetic super‐exchange interaction of the title compound is compared with similar dinuclear iron(III) complexes. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Feasibility of study magnetic proximity effects in bilayer “superconductor/ferromagnet” using waveguide-enhanced polarized neutron reflectometry

A resonant enhancement of the neutron standing waves is proposed to use in order to increase the magnetic neutron scattering from a “superconductor/ferromagnet” (S/F) bilayer. The model calculations show that usage of this effect allows to increase the magnetic scattering intensity by factor of hundreds. Aspects related to the growth procedure (order of deposition, roughness of the layers etc.) as well as experimental conditions (resolution, polarization of the neutron beam, background etc) are also discussed. Collected experimental data for the S/F heterostructure Cu(32 nm)/V(40 nm)/Fe(1 nm)/MgO confirmed the presence of a resonant 60-fold amplification of the magnetic scattering.     

Dispersion of acoustic-like and optic-like vibrational excitations in Ni2B metallic glass

The dynamic structure factor S(Q, E) of Ni₂B metallic glass was studied by inelastic neutron scattering in the ranges of momentum transfers 0.7 < ?Q/Å^?1 < 7, and energy, 2 < E/meV < 70, transfers. The measurements were performed with the IN4 spectrometer (Institut Laue-Langevin (ILL), Grenoble, France) on three samples of the same chemical composition but with different contents of Ni and B isotopes, as a result of which partial contributions were determined. The cuts through S(Q, E) for different values of E and Q demonstrated a characteristic behavior indicating that vibrational excitations, similar to acoustic and optical phonon excitations in crystals, propagate in an amorphous medium in a certain energy and momentum range.     

Structural studies of lead aluminate glasses

Lead aluminate melts were quenched rapidly with a roller quencher and bulk glasses were formed over a composition range from 72.5 to 80.0 mol% PbO. Pulsed neutron diffraction, ²⁷Al MAS NMR and Raman spectroscopy were used to study the structure of a series of these glasses. The results show that in the glasses the aluminium is four coordinated by oxygen across the compositional range, with a bond length of about 1.76 Å. The Pb–O peak in the neutron correlation function is asymmetric, and it can be modelled in terms of two bond lengths of ∼2.25 Å and ∼2.47 Å, with the majority of the coordination at the shorter distance. There is evidence that most or all of the lead ions are on asymmetric sites, coordinated by three oxygens in a trigonal pyramid arrangement. Both the neutron diffraction and Raman results indicate that the Pb–O bond lengths become shorter with increasing lead content.     

Long Range Correlations in Polymeric Fluids

We shall review structural aspects of intermediate length scale correlations in fluids. In particular, we shall discuss the application of low angle x-ray and neutron scattering to spatial correlations in the 10Å - 10⁴Å range, intermediate between the atomic and macroscopic domains. Polymer solutions, blends and colloidal suspensions will serve as examples.     

High field effects in amorphous germanium

Measurements of high field current have been made on amorphous Ge (a-Ge) films over the temperature range from 100 to 300 K. Non-ohmic conduction in a-Ge occurs at electric fields greater than 1–2 × 10⁴ V/cm. Field dependence of the conductivity has been explained in terms of the enhanced emission probability of carriers from the screened coulombic trap centers. Assuming the optical dielectric constant for a-Ge films, the screening length of the trap centers and the density of states at the Fermi level are estimated to be 12 Å and ～6.1 × 10²⁰ cm^?3 eV^?1, respectively.     

Metamorphic InAs(Sb)/InGaAs/InAlAs nanoheterostructures grown on GaAs for efficient mid-IR emitters

High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5?μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1?Å are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ～8?μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic In_xAl_1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded In_xAl_1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6?μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T?=?10–300?K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As₄/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3?×?10⁷ cm^?2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300?nm, the extremely low surface roughness with the RMS value of 1.6–2.4?nm, measured by AFM, as well as rather high 3.5?μm-PL intensity at temperatures up to 300?K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform.     

Organic Light-Emitting Diodes based on Benzo[q]quinoline Derivatives

Abstract

In this study, we synthesized two emitting materials based on benzo[q]quinoline derivatives. OLED devices using these materials were facricated in the following sequence;ITO(180nm)/4,4',4''-Tris[2-naphthyl(phenyl)amino]triphenylamine(2-TNATA)(30nm)/N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine(NPB)(20nm)/Emitting materials(30nm)/4,7-diphenyl-1,10-phenanthroline (Bphen)(30nm)/Liq(2nm)/Al(100nm). Particularly, a device using 2,4-di(naphtalene-1-yl)benzo[q]quinoline as an emitter exhibited the efficient emission with a luminous efficiency, a power efficiency, and exteranl quantum efficiency of, and the CIE coordinates of 2.91cd/A, 0.99lm/W, 0.90% at 20mA/cm², and (0.33, 0.55) at 1000cd/m², respectively. Interestingly, emissions from electromers and electroplexes were shown to be crucial role in electroluminescences from benzo[q]quinoline derivatives     

X-ray crystal structural analysis of 1,2-dihydro-3-methylpyrazole-5-one

The title compound 1,2-dihydro-3-methylpyrazole-5-one was determined by X-ray crystal structural analysis. The crystals are monoclinic, with space group P2(1)/n with a = 7.968(7), b = 6.502(6), c = 9.986(10) Å, α = 90°, β = 109.995(15)°, γ = 90°, V = 486.1(8) ų, Z = 4, F(000) = 208, D_c = 1.340 g cm^–3, μ = 0.100 mm^?1, and the final R = 0.0373 and wR = 0.0961. A total of 4776 reflections were collected, of which 1148 were independent (R_int = 0.0589). In the crystal packing diagram, intermolecular N?H···O hydrogen bonds and π?π stacking interactions stabilize the solid state of the title compound.     

Fast X-ray scattering measurements on high temperature levitated liquids

We describe a new high temperature environment based on aerodynamic levitation and CO₂ laser heating designed for high energy X-ray diffraction at the ID11 beamline at ESRF. The use of two lasers simultaneously provides a homogeneous temperature and makes it possible to explore the supercooled state with a high degree of control (about 500 °C below the melting point in this work) and to work very close to T_g. The scattered beam is measured over a relatively wide Q-range of 0.5–19 Å^?1 with the ESRF Frelon 2D CDD camera. Using 1-min measurements we obtained good quality structure factors at various temperatures in the liquid and supercooled state of CaAl₂O₄. We also performed time-resolved measurements using an acquisition time of 100 ms and we obtained good statistics even at large Q. The Al–O and Ca–O bond lengths and coordination numbers derived from the calculated pair distribution functions are in good agreement with our previous X-ray and neutron works.     

Investigation of the ultrasonic wave influence on magnetic ordering in a 20 × [Fe(20 Å)/Cr(12 Å)]/MgO layered structure

A 20 × [Fe(20 Å)/Cr (12 Å)]/MgO structure excited by an ultrasonic wave was investigated by polarized neutron reflectometry. It was found that magnetic domains oscillate and their effective size decreases in weak magnetic fields. In close-to-saturation fields, a magnetic lattice is formed in the layered structure; the interplanar spacings in this lattice change with an increase in the field strength and as a result of the excitation of the structure by an ultrasonic wave.     

Investigation of the tripoli porous structure by small-angle neutron scattering

The characteristics of the tripoli porous structure have been investigated by small-angle neutron scattering (SANS). Tripoli is a finely porous sedimentary rock formed by small spherical opal particles. Its main component is aqueous silica SiO₂ · nH₂O (80–90%). Tripoli is widely used in practice as a working medium for sorption filters and in some other commercial and construction technologies. The shape of the experimental SANS curves indicates the presence of small and large pores in tripoli. The small-pore size was estimated to be ～100 Å. The size of large pores turned out to be beyond the range of neutron wave vector transfers Q that are available for the instrument used; however, their size was indirectly estimated to be ～(2000–2500) Å. The pores of both groups behave as surfacetype fractal scatterers with the fractal dimension D ～ 2.2‐2.6. The densities of pores of these two groups differ by approximately three orders of magnitude (～10¹⁶ and ～10¹³ cm^?3 for small and large pores, respectively); the fraction of large pores amounts to 70–80% of the total pore volume. The found pore characteristics (their densities, sizes, and relative volumes) are in satisfactory agreement (when a comparison is possible) with the absorption data.     

Molecular structure of [(tBu)2Al(3,5-Me2py)]2(μ-O): Preferential hydrolysis of an aluminum-aryl over an aluminum-alkyl

The structure of [(^tBu)₂Al(3,5-Me₂py)]₂(μ-O) has been determined as a consequence of the preferential hydrolytic cleavage of an Al–O versus an Al–C bond from the hydrolysis of the quinone bridged compound, [(^tBu)₂Al(3,5-Me₂py)]₂(μ-OC₆H₄O). The Al–O distance is 1.710(1) Å and the Al–O–Al angle is 180° because of crystallographic symmetry. Crystal data: triclinic, P $\overline 1$ , a = 9.334(2) Å, b = 10.639(2) Å, c = 10.661(2) Å, α = 112.65(3)°, β = 93.84(3)°, γ = 115.84(3)°, V = 843.4(3) ų, Z = 1, R = 0.0581, R _w = 0.1674.     

Study by x-ray and neutron diffraction of the structure of ex-carbonyl amorphous iron

Ex-carbonyl amorphous iron is a heterogeneous finely powdered material. Its texture established by standard physico-chemical analysis is compatible with the diffraction data: two phases have been identified, an amorphous ferromagnetic phase homogeneous up to 300 Å containing less than 1% carbon in solution and an unstable phase coming from a part of the CO from the decomposition of carbonyl and representing 7.2% by weight. The pair distances from both X-ray and neutron diffraction spectra are identical after taking into account measurement error: the shorter pair distances are those already found in icosahedral structures, the higher distances, identified up to 19 Å^?1, are simple exact combinations of the shorter ones.     

X-ray crystal structural analysis of dicyclohexylthiocarbamide

The title compound dicyclohexylthiocarbamide has been determined by single crystal X-ray crystal diffraction analysis. The crystals are monoclinic, space group P2(1)/c with a = 12.5908(9), b = 11.2158(9), c = 10.4255(8) Å, α = 90, β = 110.7360(10), γ = 90°, V = 1376.88(18) ų, Z = 4, F(000) = 528, D_c = 1.160 g/cm³, μ = 0.214 mm^?1, the final R = 0.0381 and wR = 0.1030. A total of 6836 reflections were collected, of which 2423 were independent (R_int = 0.0154). In the crystal packing diagram, intermolecular N?H···S hydrogen bonds stabilize the solid state of the title compound.     

Solution-Processable Low Voltage Organic Transistors of Thieno[3,2-b]thiophene-Based Conducting Polymer

A low-operating voltage and high performance polymeric field effect transistors using octadecylphosphonic acid-treated high-k AlOx and HfO₂ hybrid dielectrics were demonstrated. High-k metal oxide hybrid dielectrics were prepared by oxygen plasma treatment of deposited Al film for AlOx and by spin coating of solution-processable HfO₂ sol-gel solution for HfO₂ in combination with phosphoric acid-based self-assembled monolayer (SAM), resulting in high capacitance (10 nF/cm² for SiO₂, 600 nF/cm² for AlOx and 580 nF/cm² for HfO₂). With phosphoric acid-based SAM on high-k metal oxide and thermal annealing of thieno[3,2-b]thiophene-based conducting polymer, the device performance was significantly enhanced. The highest mobility of the transistors using ODPA-treated AlOx as a gate dielectric is 2.3 × 10^?2 cm² V^?1 s^?1 in the saturation region with the source-drain of ?2 V. In ODPA-treated HfO₂ hybrid dielectric, the saturated mobility is 1.1 × 10^?2 cm² V^?1 s^?1 and the threshold voltage was measured to be ?0.31 V, which is at least one order lower than SiO₂ hybrid dielectric (?3 V).     

Synthesis,conductivity, and the crystal structure of a new stable metal, β″-(<Emphasis Type="Italic">DOEO</Emphasis>)<Subscript>2</Subscript>HSeO<Subscript>4</Subscript> · H<Subscript>2</Subscript>O

The stable metal β″-(DOEO)₂HSeO₄ · H₂O I) based on a new donor compound, 3,4-(1,4-dioxanediyl-2,3-dithio)-3′,4′-ethylenedioxo-2,5,2′,5′-tetrathiafulvalene] (DOEO), is synthesized and structurally characterized for the first time. The synthesis is performed by the electrocrystallization technique (direct current density j = 2 × 10^?6 A/cm²). The crystals are triclinic, and the unit cell parameters are as follows: a = 5.495(1) Å, b = 9.715(2) Å, c = 16.878(3) Å, α = 83.52(3)°, β = 82.54(3)°, γ = 73.51(3)°, Z = 1, and space group \(P\bar 1\). The salt has a layered structure. The DOEO^1/2+ radical cation layers are aligned parallel to the ab planes. The HS_eO ₄ ^? · H₂O solvated anions are located in channels along the a axis and are disordered over two positions near the center of symmetry (1/2 0 0) with a probability of 50%. The conductivity of the salt is equal to 300–400 Ω^?1 cm^?1 at room temperature and increases upon cooling to the boiling point of liquid helium (4.2 K) by a factor of 100–200 depending on the sample.