TOWARDS DEEP AND SIMPLE UNDERSTANDING OF THE TRANSCENDENTAL EIGENPROBLEM OF STRUCTURAL VIBRATIONS

When using exact methods for undamped free vibration problems the generalized linear eigenvalue problem (K−ω²M) D=0 of approximate methods, e.g., finite elements, is replaced by the transcendental eigenvalue problem K (ω) D=0. Here ω is the circular frequency; D is the displacement amplitude vector; M and K are the mass and static stiffness matrices; and K (ω) is the dynamic stiffness matrix, with coefficients which include trigonometric and hyperbolic functions involving ω and mass because elements (for example, bars or beams) are analyzed exactly by solving their governing differential equations. The natural frequencies of this transcendental eigenvalue problem are generally found by the Wittrick-Williams algorithm which gives the number of natural frequencies below ω_t, a trial value of ω, as ∑J_m+s{K (ω_t)} wheres {} denotes the readily computed sign count property of K (ω) and the summation is over the clamped-clamped natural frequencies of all elements of the structure. Understanding the alternative solution forms of the transcendental eigenvalue problem is important both to accelerate convergence to natural frequencies, e.g., by plotting ∣K (ω)∣, and to improve the mode calculations, which lack the complete reliability of natural frequencies obtained by using the Wittrick-Williams algorithm. The three solution forms are: ∣K (ω)∣=0; D=0 with ∣K (ω)∣→∞; and ∣K (ω)∣≠0 with D≠0. The literature covers the first two forms thoroughly but the third form has been almost totally ignored. Therefore, it is now examined thoroughly, principally by analytical studies of simple bar structures and also by confirmatory numerical results for a rigidly jointed plane frame. Although structures are unlikely to have exactly the properties giving this form, it needs to be understood, particularly because ill-conditioning can occur for structures approximating those for which it occurs.     

Synthesis of 2,3-dimorpholino-6-aminoquinoxaline derivatives and application to a new intramolecular fluorescent probe

Two fluorescent monomers having a quinoxaline skeleton, N-(2,3-dimorpholinoquinoxalin-6-yl)acrylamide (QxA) and N-(1-(2,3-dimorpholinoquinoxalin-6-ylamino)prop-2-yl)methacrylamide (QxAlaMA), were synthesized. Thermo-responsive copolymers of N-isopropylacrylamide (NIPAM) and a small amount of a fluorescent monomer were synthesized and their fluorescence properties investigated. The fluorescent monomers showed intense solvatochromism in their fluorescence. The wavelength at the maximum fluorescence intensity of the QxAlaMA-labeled PNIPAM dramatically blue-shifted and the fluorescence intensity of the QxA-labeled PNIPAM significantly increased around the transition temperature. It was found that these fluorescent dyes can sense and report the thermo-responsive behavior of the PNIPAM in water. Both QxAlaMA and QxA were demonstrated to be applicable to new intramolecular fluorescent probes.     

Surface-modification of TiO2 with new metalloporphyrins and their photocatalytic activity in the degradation of 4-notrophenol

A new mono-functionalized porphyrin derivative, 5-mono-[4-(2-(4-hydroxy)-phenoxy)ethoxy]-10,15,20-triphenylporphyrin (3) and its Cu(II) (3a), Zn(II) (3b) and Ni(II) (3c) metalloporphyrins were synthesized and characterized by using various spectroscopic techniques. The corresponding 3a, 3b, 3c-TiO₂ photocatalysts were then prepared and characterized by means of FT-IR and diffused reflectance spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activities of 3a, 3b, 3c-TiO₂ were investigated by testing the photodegradation of 4-nitrophenol (4-NP) in aqueous solution under the halogen lamp irradiation. The results indicated that all the 3a, 3b, 3c enhanced the photocatalytic efficiency of bare TiO₂ in photodegrading the 4-NP, and 3a-TiO₂ exhibited the highest photocatalytic activity. The result is considered a combined action of potential match of 3a with TiO₂ CB and effective impregnated of 3a onto the surface of TiO₂.     

Three-dimensional magnetic properties of soft magnetic composite materials

A three-dimensional (3-D) magnetic property measurement system, which can control the three components of the magnetic flux density B vector and measure the magnetic field strength H vector in a cubic sample of soft magnetic material, has been developed and calibrated. This paper studies the relationship between the B and H loci in 3-D space, and the power losses features of a soft magnetic composite when the B loci are controlled to be circles with increasing magnitudes and ellipses evolving from a straight line to circle in three orthogonal planes. It is found that the B and H loci lie in the same magnetization plane, but the H loci and power losses strongly depend on the orientation, position, and process of magnetization. On the other hand, the H vector evolves into a unique locus, and the power loss approaches a unique value, respectively, when the B vector evolves into the round locus with the same magnitude from either a series of circles or ellipses.     

Surface-enhanced Raman scattering studies on bombesin, its selected fragments and related peptides adsorbed at the silver colloidal surface

SERS studies presented in this work on BN^8-14, [d-Phe⁶,β-Ala¹¹,Phe¹³,Nle¹⁴]BN^6-14, [d-Tyr⁶,β-Ala¹¹,Phe¹³,Nle¹⁴]BN^6-14, BN and its modified analogues, as well as NMB, NMC, and PG-L show that these molecules at pH 8.3 bind to a colloidal silver surface mainly through Trp⁸ and Met¹⁴ residues. Trp⁸ adsorbs at the surface almost perpendicularly. Met¹⁴ appears on the surface mainly as a P_C-G conformer. His¹², as is evident from the spectra, practically does not take part in the adsorption process. Substitution of l-leucine at the 13 position of amino acid sequence with l-phenylalanine does not change substantially the pattern of the adsorption mechanism; however, substitution of phenylalanine at the 12 position (instead of l-histidine) causes changes in the SERS spectra that show that Phe¹² takes parallel orientation to the surface upon adsorption of [d-Phe¹²]BN, while in the case of [Tyr⁴,d-Phe¹²]BN this residue is perpendicular to the surface and influences the orientation of the bound Trp⁸. On the other hand, substitution of Asn with Tyr in the 6 position in nonapeptide fragment causes changes in the adsorption mechanism. In this case, the discussed fragment binds to the silver colloidal surface by Tyr⁶, Trp⁸, and Met¹⁴. The SERS spectrum of NMC is very similar to that of BN; although it differs by the binding orientation of the amide bond towards the surface. Appearance of Phe¹³ in NMB and PG-L causes that this residue competes successfully with Trp⁸ forcing it to take tilted orientation. As seen from the enhancement of the characteristic Phe vibrations this moiety in NMB and PG-L adsorbs on the silver surface in a tilted fashion. This arrangements cause that the 8-14 peptide chain in all these studied compounds takes almost a parallel orientation to the surface while the 1-5 fragment of the peptide chain is removed from the silver surface vicinity.     

Eu(III) and Tb(III) luminescent lanthanide systems derived from DTPA-bisamide and DTTA-based ligands incorporating bipyridine antenna

Four new polycarboxylate ligands H₃Lⁿ have been synthesized by the attachment of two or one 2,2′-bipyridine subunits onto a diethylenetriamine pentacarboxylic acid (DTPA-bisamide derivatives: H₃L¹, H₃L²) or a diethylenetriamine tricarboxylic acid (DTTA derivatives: H₃L³, H₃L⁴) core. The neutral Eu^III and Tb^III complexes of these chelates have been prepared and studied from their UV-vis and luminescence data. The main photophysical characteristics of these complexes, i.e. the absorption and luminescence spectra, the metal-centred lifetimes and the overall luminescence yields (Φ) were measured in buffered aqueous solutions. In addition the role played by non-radiative paths (vibrational energy transfer involving coordinated water molecules, involvement of ligand-to-metal charge-transfer excited states, or metal→ligand back-transfer) was investigated. In all complexes, we found that the bidentate bipyridine chromophore is not coordinated to the lanthanide ion, allowing one (LnL¹, LnL²) or two (LnL³, LnL⁴) water molecules to penetrate the first coordination sphere of the metal. Although the bipyridine chromophore behaves as remote (from the binding site) light-harvesting unit for the lanthanide ion in these systems, a sizeable sensitization of the Eu- and Tb-centred luminescence can be effective (LnL², LnL³, Φ=16-19% in aerated D₂O solutions). Our photophysical investigations show that overall non-radiative deactivation is not dependant of thermally activated non-radiative channels but the efficiency of the ligand→Ln intramolecular energy transfer has to be taken into account to explain the obtained results.     

Adsorption mechanism of physiologically active l-phenylalanine phosphonodipeptide analogues: Comparison of colloidal silver and macroscopic silver substrates

Here we present SERS spectra of several l-phenylalanine (Phe) phosphonodipeptides, i.e., l-Phe-l-Ala-PO₃H₂ (MD1), l-Phe-l-Val-PO₃H₂ (MD2), l-Phe-β-Ala-CH(OH)-PO₃H₂ (MD3), l-Phe-l-Ala-CH(OH)-PO₃H₂ (MD4), l-Ala-(3,4-dimethoxy)-l-Phe-PO₃H₂ (MD5), and l-Ala-(3,4-dimethoxy)-(des-CH₂)-l-Phe-PO₃H₂ (MD6), immobilized on electrochemically roughened silver electrodes. These spectra are analyzed by theoretical calculations using density functional theory (DFT) at the B3LYP level with 6-31++G∗∗ basis set. In addition, these spectra are compared with SERS spectra of these species adsorbed on a colloidal silver surface. We showed that on the macroscopic silver substrate, the Phe aromatic ring of MD3 and MD4 is oriented vertically, while for MD1 it almost “stands up” on this surface. In the other three cases, the Phe ring adopts a tilted orientation in regard to the substrate. We also find that the phosphonate , methyl/methane, or dimethoxy groups of MD1, MD2, MD3, MD5, and MD6 are involved in the interaction of these phosphonodipeptides with the electrochemically roughened surface. This phenomenon is clearly seen for -CH₂-/-CH₃/-OCH₃ moieties as well as for the group that adsorbs on the macroscopic silver substrates mainly via the PO fragment. We also showed that MD4 binds to the macroscopic silver substrate through the hydroxyl, amine, and phosphonate groups, while the methylene/methane moieties are remote from this surface. We found that studied phosphonodipeptides often adsorb differently on the macroscopic silver substrate and on the colloidal silver nanoparticles. For example, MD1 adopts an almost vertical orientation on the electrochemically roughened silver substrate and is tilted or close to flat on the silver nanoparticles.     

The CRESST dark matter search

The aim of CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) is to search for particle dark matter via elastic scattering off nuclei. The experiment is located at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, and it uses low-background cryogenic detectors with superconducting phase-transition thermometers for the direct detection of WIMP-nucleus scattering events.     

Indium-induced superstructures formed on Si(1 1 0) surfaces

Si(1 1 0) surfaces covered with small amounts of In deposit and then annealed at high temperature were investigated by RHEED, and two kinds of superstructures with A = 3a and B = −a + 4b, and A = 3a − 2b and B = −2a + 4b as primitive translational vectors are reported to form on the surfaces.     

Self-consistent treatment of spin and magnetization dynamic effect in spin transfer switching

The effect of itinerant spin moment (m) dynamic in spin transfer switching has been ignored in most previous theoretical studies of the magnetization (M) dynamics. Thus in this paper, we proposed a more refined micromagnetic model of spin transfer switching that takes into account in a self-consistent manner of the coupled m and M dynamics. The numerical results obtained from this model further shed insight on the switching profiles of m and M, both of which show particular sensitivity to parameters such as the anisotropy field, the spin torque field, and the initial deviation between m and M.     

Aliphatic dithiocarboxylic acids: New adsorbates for soft lithographic patterning

This paper describes an initial evaluation of the use of aliphatic dithiocarboxylic acids (ADTCAs) as transient protecting agents in soft lithographic patterning, also known as microcontact printing (μCP). Surfaces micropatterned using ADTCA-based inks (C10-C16) were compared to that patterned using a standard hexadecanethiol ink. The patterns were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Etch-removal studies of SAM-coated gold substrates found that the longer chain-length ADTCAs (C13-C16) provide better protection against etching than the shorter chain-length ADTCAs (C10-C12). These studies demonstrate that ADTCA-derived SAMs can be used as effective resists for soft lithographic applications.     

Self-assembly of bipyridine derivatives at solid/liquid interface: Effects of the number of peripheral alkyl chains and metal coordination on the two-dimensional structures

Self-assembled two-dimensional structures of bipyridine derivatives (bpys) were observed by scanning tunneling microscopy at HOPG/1-phenyloctane interface. Two types of bpy molecules were used in this study. One is bpy 1, which has two alkyl chains on each end, and the other is bpy 2, which holds single alkyl chain on each end. The bpy 1 formed a monolayer, which is composed of a bent molecular structure with interdigitated alkyl chains. In the case of bpy 2, the structure exhibited pm plane group symmetry. A pair of molecules formed a columnar structure, and the alkyl chains aligned in a tail-to-tail orientation. Metal coordination of both bpy samples increased the intermolecular distance at the π-conjugated units, resulting in the formation of lamellar structure. Although both bpys showed straight form, the alkyl chain unit of complexed bpy 1 was not interdigitated, whereas that of complexed bpy 2 was interdigitated. Thus, the metal-metal distances could be tuned by changing the number of alkyl chain unit.     

Organic radical molecular solids based on [(TCNQ)n] (n=1 or 2): Syntheses, crystal structures, magnetic properties and DFT analyses

Four molecular solids consisting of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical and benzylpyridinium or benzylquinolinium derivatives with molar ratios of 1:1 (1-3) and 2:1 (4) have been prepared and characterized. In the crystals of 1 and 3, TCNQ⁻ monoanions and the corresponding cations form segregated stacks, which are regular in 1 but irregular in 3. Instead of segregated stacks, TCNQ⁻ monoanions in 2 form isolated π-dimers. In the crystals of 4, two crystallographic independent TCNQ species possess almost equal fractional negative charge (ca. −0.5). Two types of TCNQ species form a tetrad, these tetrads make a TCNQ stack with the pattern …BAAB…BAAB… along the crystallographic a-b direction. The magnetisms for 1-4 can be simply explained by the formation of singlet spin state. A broken symmetry approach in a density functional theory framework at the ub3lyp/6-31 g level was used to calculate the magnetic exchange constants in 1-4. The results qualitatively demonstrate the observed magnetic properties.     

The molecular vibration-rotation kinetic-energy operator for general internal coordinates

The molecular kinetic-energy operator for general internal coordinates is formulated in terms of simple generalisations of the matrices A, B, α, and β of Crawford. A new matrix γ of the gradients of the translational and rotational constraints facilitates the calculation of the β matrix. It is shown that the kinetic pseudo-potential U is most conveniently calculated as an atomic sum, and results are given for valence coordinates in various types of molecules.     

The synthesis and photophysical properties of novel cationic tetra pyridiloxy substituted aluminium, silicon and titanium phthalocyanines in water

This work reports on the synthesis, characterisation and photophysical properties of new unquaternized β-2,(3)-tetra-(2 pyridiloxy) aluminium(III) (3a), silicon(IV) (3b), titanium(IV) (3c) phthalocyanines and their water-soluble quaternized counterparts, 4a, 4b and 4c, respectively. The water-soluble silicon(IV) (4b) and titanium(IV) (4c) phthalocyanine derivatives were found to be aggregated in aqueous media but were partially or fully disaggregated in the presence of a surfactant Cremophor^® EL (CEL). The photophysical properties of aggregated complexes were investigated both in the presence of CEL and in pH 11 alone. Low triplet and fluorescence yield were obtained in pH 11 but an improvement was achieved upon addition of CEL for the aggregated complexes. The unquaternized silicon(IV) phthalocyanine complex (3b) gave the highest triplet quantum yield of 0.77 in DMF followed by its quaternized derivative (4b) with triplet yield of 0.73 in pH 11 plus CEL. The highest triplet lifetime of 220 μs was obtained for 4b in the presence of CEL. Higher fluorescence yields of 0.23 were obtained for quaternized water-soluble aluminium(III) phthalocyanine derivative (4a) in the presence of CEL.     

Cubic helimagnets in magnetic field and at pressure

Cubic helimagnets with B20 structure display several unusual properties such as anisotropy of the spin-wave spectrum al small momenta q, rotation of the helix vector k in magnetic field and quantum phase transition at pressure. We demonstrate that first two phenomena are a result of umklapp processes mixing excitations with momenta q, q+k and q−k. At very low magnetic field perpendicular to k the helical structure remains stable due to spin-wave gap Δ. Its square is sum of two parts. The first one is a result of the magnon interaction and the second negative part stems from magneto-elastic interaction. It is suggested that competition between these parts leads to the quantum phase transition observed in MnSi and FeGe. For MnSi from rough estimations at ambient pressure was shown that both parts are comparable with the experimentally observed gap. The magneto-elastic interaction is also responsible for 2k modulation of the lattice and contributes to the magnetic anisotropy. Experimental observation by X-ray and neutron scattering of this lattice modulation allows to determine the strength of the magneto-elastic interaction responsible for above phenomena and the lattice helicity.     

Photophysical characteristics of 4,4′-bis(N-carbazolyl)tolan derivatives and their application in organic light emitting diodes

4,4′-bis(N-carbazolyl)tolan (BCT) and 4,4′-bis[N-(3,6-di-t-butyl)carbazolyl]tolan (BCT-t-Bu) were synthesized as π-expanded analogs of 4,4′-bis(N-carbazolyl)biphenyl. Their photophysical characteristics both in solution and films were thoroughly investigated. Interestingly, the phosphorescence spectrum of BCT was significantly medium-dependent, and the emission maximum was red-shifted by 131 nm from 489 nm in solution at 77 K to 620 nm in a deposited film at 5 K, suggesting the presence of strong intermolecular interactions in the film. BCT and BCT-t-Bu were found to be useful as host materials for fluorescence-based organic light emitting diodes (OLEDs). However, their low triplet energy levels in films negated their potential to act as hosts in phosphorescence-based OLEDs.     

Luminescence and crystal-field fitting of two optical isomeric complexes of europium

FT-IR and Raman vibrational spectra and electronic emission spectra have been recorded for enantiomers of europium complexes with DBM: dibenzoylmethanate 1,2, and TTFA: 2-thenoyltrifluoroacetonate 3,4, employing the chiral ligands L_SS(+)- and L_RR(-)-4,5-pinene bipyridine. Contrary to the previously published X-ray data, where geometrical differences were stated to occur for particular enantiomers, the vibrational (and the emission) spectra of the individual optical isomers of a complex are not distinguishable. Using excitation into the Eu³⁺⁵D₂ multiplet term, the emission intensity is weak from ⁵D₁, whereas a complex structure is observed for the ⁵D₀→⁷F_J transitions. Features in the vibronic sidebands exhibit similar derived vibrational energies to those observed in the Raman spectra. Fittings of 25 4f⁶ crystal-field energy levels of 2 and 4 have been attempted with some approximations concerning the local Eu³⁺ environments. The ⁵D₀ emission lifetimes are monoexponential and are 0.5 (1,2) and 0.9 ms (3,4) at room temperature.     

Adsorption of parent nitrosamine on the nanocrystaline H-zeolite: A theoretical study

Adsorption of parent nitrosamine (NA) on 5T and 10T cluster models of H-ZSM-5 catalyst has been theoretically investigated using quantum chemical B3LYP and MP2 methods. Three stable complexes (A-C) were found on the potential energy surface of interaction between NA and cluster models of H-ZSM-5. NA can interact not only with acidic site of zeolite via the lone electron pair on nitrogen and oxygen atoms (O(N)?H_ZO) but also with the oxygen atoms of the framework via the hydrogen atoms of NH₂ group (NH?O) as well. However, the Lewis acidity of zeolite framework is the dominating factor in the interaction between NA and zeolite. The calculated adsorption enthalpy of NA on 5T and 10T clusters of H-ZSM-5 catalyst at ONIOM(MP2/6-311++G(d,p):HF/6-31+G(d)) level ranges from −19.73 to −40.33 and −63.81 to −73.73 kJ/mol, respectively. Adsorption energy for A-C complexes increases in going from B3LYP method to MP2 one. The results of atoms in molecules (AIM) calculations showed that NH5?O interactions have electrostatic character, whereas O(N)?H_Z interactions have partially covalent nature. The results of natural bond orbital (NBO) analysis showed that charge transfer occurs from NA to H-zeolite cluster.     

Nonlinear optical absorption and fluorescence of phosphine-substituted bithiophenes in the violet-blue spectral region

The nonlinear optical absorptions of two 5,5′-bis(diphenylphosphino)-2,2′-bithiophene derivatives, Ph₂(X)P(C₄H₂S)₂P(X)Ph₂ (X = O, 1; S, 2), have been investigated by direct transmission measurement with both picosecond and nanosecond laser pulses from 420 nm to 480 nm. Saturated dichloromethane solutions of 1 and 2 exhibit strong nonlinear optical absorptions in this violet-blue spectral region with that of 2 being stronger at all wavelengths. In the picosecond regime, at 420 nm, the transmittance rapidly falls to 50% when the incident fluence is 0.22 J/cm² for 1 and 0.11 J/cm² for 2. Two-photon absorption appears to be the primary mechanism for this nonlinear absorption. The two-photon absorption coefficients β for 1 (2.1 cm/GW) and 2 (4.4 cm/GM) were obtained by fitting the measurement of transmittance as the function of incident beam intensity at 420 nm. These β values are comparable with some of the best results obtained for organic materials in the green, red and infrared spectral region. Both compounds also show fluorescence with an emission peak at 390 nm for 1 and 400 nm for 2. The fluorescence of 1 is considerably stronger than is that of 2. The combination of the wide band gap and strong fluorescence emission of 1 makes it a promising candidate as a host material for blue organic light emitting diodes.