Resonance method for IR sensing

A highly sensitive method for infrared radiation detection based on thermal resonance in an active bolometer is set forth. An active bolometer is a self-oscillating system consisting of an IR-sensitive cell in a feedback circuit of an adjustable proportional controller. The analysis of an active bolometer autonomous (dark) dynamics reveals that with a generalized gain factor A variation the system evolves from relaxation type towards oscillating and self-oscillating type. When A=A_c, where A_c is a critical value of the generalized gain factor A, the steady state loses stability through self-excited thermal oscillations. The resonance in a system weakly perturbed by IR radiation modulated at self-oscillation frequency q₀[1+exp(iω_ct)] is considered. It is shown that in a small precritical vicinity =(A−A_c)/A_c of the gain factor the amplitude of forced thermal oscillations is proportional to q₀/A_c. The D^* calculation reveals that the detection power of a passive (A=0) bolometer increases with feedback introduction by a factor of 1/||. The detection powers of feasible versions of an active bolometer are compared.     

Measurement of the Strong Interaction Shift and Width of the Ground State of Pionic Hydrogen

Hyperfine Interactions - An experiment to measure the strong interaction width (Γ1s ) and shift (ε1s ) of the ground state of pionic hydrogen (π?p), in order to determine the...     

A new proof for Rockafellar's characterization of maximal monotone operators

We provide a new and short proof for Rockafellar's characterization of maximal monotone operators in reflexive Banach spaces based on S. Fitzpatrick's function and a technique used by R. S. Burachik and B. F. Svaiter for proving their result on the representation of a maximal monotone operator by convex functions.

     

Field theory of mesoscopic fluctuations in superconductor/normal-metal systems

The thermodynamic and transport properties of normal disordered conductors are strongly influenced by the proximity of a superconductor. A cooperation between mesoscopic coherence and Andreev scattering of particles from the superconductor generates new types of interference phenomena. A field theoretic approach is introduced which is capable of exploring both the averaged properties and mesoscopic fluctuations of superconductor/normal-metal systems. As an example the method is applied to the study of the level statistics of a SNS junction. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 1, 21–26 (10 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Aufbau und Zunderverhalten von Niob-Bor-Silicium-Legierungen

Zusammenfassung Der Aufbau des Dreistoffes Niob-Bor-Silicium wird bei 1600° C mit Hilfe röntgenographischer und mikroskopischer Methoden ermittelt. Die T 2-Phase sowie die ternäre D 8₈-Phase besitzen einen ausgedehnten homogenen Bereich. Während Silicium in T 2 durch Bor bis annähernd Nb₅SiB₂ substituiert wird, besteht beim D 8₈-Typ eine Gitterauffüllung gemäß Nb₅Si₃B. Oxydationsversuche im Bereich von 400 bis 1200° C zeigen vor allem die Selektivität, indem Nb–Mk bzw. die Nb-Boride bevorzugt in Pentoxyd übergehen. Silicium übt einen stabilisierenden Einfluß auch auf das Bestehen von -Nb₂O₅ aus. -Nb₂O₅ tritt als Mischphase mit Anionendefekt auf, wodurch die sogenannte scharfe und diffuse Form erklärt wird. Die Umwandlungstemperatur - wird teilweise erheblich oberhalb der vonGoldschmidt angegebenen beobachtet. Die -Form wird als M-Modifikation nachBrauer identifiziert und relativ häufig nachgewiesen. Die -Form erweist sich alsBrauersche H-Modifikation und entsteht offensichtlich stufenweise (fast kontinuierlich) aus -Nb-Oxyd. Auf die Anionendefekt-Bildung wird nachdrücklich hingewiesen.Mit 3 Abbildungen     

A theoretical study of the structure and bonding of UOX4 (X = F, Cl, Br, I) molecules: the importance of inverse trans influence.

During nitroxide-mediated polymerization (NMP) in the presence of a nitroxide R2(R1)NO*, the reversible formation of N-alkoxyamines [P-ON(R1)R2] reduces significantly the concentration of polymer radicals (P*) and their involvement in termination reactions. The control of the livingness and polydispersity of the resulting polymer depends strongly on the magnitude of the bond dissociation energy (BDE) of the C-ON(R1)R2 bond. In this study, theoretical BDEs of a large series of model N-alkoxyamines are calculated with the PM3 method. In order to provide a predictive tool, correlations between the calculated BDEs and the cleavage temperature (T(c)), and the dissociation rate constant (k(d)), of the N-alkoxyamines are established. The homolytic cleavage of the N-OC bond is also investigated at the B3P86/6-311++G(d,p)//B3LYP/6-31G(d), level. Furthermore, a natural bond orbital analysis is carried out for some N-alkoxyamines with a O-C-ON(R1)R2 fragment, and the strengthening of their C-ON(R1)R2 bond is interpreted in terms of stabilizing anomeric interactions.     

Boundary phase stability and critical phenomena in higher order solid solution systems II

The thermodynamic treatment of double-pseudobinary solutions of the type (A _xB_y) _{r o}(M _uN_v) _{s o} presented in a preceding publication was extended to include the conditions defining the critical points for the asymmetric case (r _os _o) and approximations for the spinodal and binodal surface near the critical solution point.Closed solutions for the coordinates of the critical points were obtained only for systems with ideal mixing behavior, and the isothermal binodal and spinodal near the critical solution point in such systems are adequately approximated by circles and ellipses, respectively. An axes ratio of is nearly independent of the relative sublattice abundance and the major effect of changes in the ratios _o/r _o is a rotation of the binodal by an angle tg .The principal features of nonideal regular systems for temperatures close to the critical solution point are described by expressions derived from small term expansions of the conditional equations, but generalizations are not possible to the same extent as for the case with ideal boundary systems. The results are discussed and the application of the equations demonstrated on model examples.Mit 6 Abbildungen     

Probing the glycosidic linkage: UV and IR ion-dip spectroscopy of a lactoside

The beta(1-->4) glycosidic linkage found in lactose is a prevalent structural motif in many carbohydrates and glycoconjugates. Using UV and IR ion-dip spectroscopies to probe benzyl lactoside isolated in the gas phase, we find that the disaccharide unit adopts only a single, rigid structure. Its fully resolved infrared ion-dip spectrum is in excellent agreement with that of the global minimum structure computed ab initio. This has glycosidic torsion angles of phi(H) (H1-C1-O-C4') approximately 180 degrees and psi(H) (C1-O-C4'-H4') approximately 0 degrees which correspond to a rotation of approximately 150 degrees about the glycosidic bond compared to the accepted solution-phase conformation. We discuss the biological implications of this discovery and the generality of the strategies employed in making it.     

The coupled-cluster method with a multiconfiguration reference state

The coupled-cluster approach to obtaining the bond-state wave functions of many-electron systems is extended, with a set of physically reasonable approximations, to admit a multiconfiguration reference state. This extension permits electronic structure calculations to be performed on correlated closed- or open-shell systems with potentially uniform precision for all molecular geometries. Explicit coupled cluster working equations are derived using a multiconfiguration reference state for the case in which the so-called cluster operator is approximated by its one- and two-particle components. The evaluation of the requisite matrix elements is facilitated by use of the unitary group generators which have recently received wide attention and use in the quantum chemistry community.