Predicting the Normal Temperature Depression in Boiling of Complex Aqueous Solutions of Nonvolatile Substances

An equation for predicting the normal temperature depression in boiling of complex aqueous solutions of nonvolatile substances is considered. The constants of the equation are tabulated. The equation is compared with experimental data for a binary solution of caustic soda and sodium chloride.     

Matrix-isolated monomeric tryptophan: electrostatic interactions as nontrivial factors stabilizing conformers

An extensive analysis of the conformational space of tryptophan (Trp) was performed at the B3LYP/6-311++G(d,p) level and verified by comparison with the infrared spectra of the compound isolated in low-temperature argon and xenon matrixes. Different types of conformers have been unequivocally identified in the matrixes. Type I exhibits the trans arrangement of the carboxylic group and is stabilized by an O-H...N intramolecular H-bond. Types II and III have the carboxylic group in the cis conformation and feature N-H...O=C and N-H...O-C hydrogen bonds, respectively. Three individual conformers of type I were identified in the matrixes. Other conformational degrees of freedom are related with the Calpha-Cbeta-Cgamma=C and C1-Calpha-Cbeta-Cgamma angles (chi1 and chi2, respectively). In proteins, these two dihedral angles define the conformations of the amino acid residues. In monomeric Trp, chi1 adopts the "+" (ca. +90 degrees ) and "-" (ca. -90 degrees ) orientations, while average values of -67.4, 170.5, and 67.6 degrees ("a", "b", and "c", respectively) were found for chi2. Theoretical analysis revealed two important factors in stabilizing the structures of the Trp conformers: the H-bond type and electrostatic interactions. Classified by the H-bond type, the most stable are forms I, followed by II and III. Out of possible combinations of the chi1 and chi2 dihedral angles, "a+", "b+", and "c-" were theoretically found more stable than their "a-", "b-", and "c+" counterparts. Thus, the stabilizing effect of interactions involving the pyrrole ring (which are possible in Ia+, Ib+, and Ic- conformers) is considerably higher compared to those in which the phenyl ring is engaged (existing in the Ia-, Ib-, and Ic+ forms).     

The Absolute Instability of Thin Wakes in an Incompressible/Compressible Fluid

RID="ID=" Communicated by P. HallAbstract:The absolute/convective instability of two-dimensional wakes forming behind a flat plate and near the trailing-edge of a thin wedge-shaped aerofoil in an incompressible/compressible fluid is investigated. The mean velocity profiles are obtained by solving numerically the classical compressible boundary-layer equations with a negative pressure gradient for the flat plate case, and the incompressible triple-deck equations for a thin wedge-shaped trailing-edge. In addition for a Joukowski aerofoil the incompressible mean boundary-layer flow in the vicinity of the trailing-edge is also calculated by solving the interactive boundary-layer equations. A linear stability analysis of the boundary-layer profiles shows that a pocket of absolute instability occurs downstream of the trailing-edge with the extent of the instability region increasing with more adverse pressure gradients. The region of absolute instability persists along the near-wake axis, while the majority of the wake is convectively unstable. For a thin wedge-shaped trailing-edge in an incompressible fluid, a similar stability analysis of the velocity profiles obtained via a composite expansion, also shows the occurrence of absolute instability behind the trailing-edge for a wedge angle greater than a critical value. For increasing values of the wedge angle and for thicker aerofoils, separation takes place near the trailing-edge and the extent of absolute instability increases. Calculations also show that for insulated plates compressibility has a stabilizing effect but cooling the wall destabilizes the flow unlike wall heating.} Received 11 May 1998 and accepted 25 February 1999     

4×288 readouts and FPAs properties

Analysis of four types 4×288 designed and manufactured readouts is presented. All the readouts have the direct injection input circuit with the circuits incorporated that allows testing procedure of readouts without the photodiodes attached to readout circuits. TDI registers have three delay elements between neighbouring inputs. Some characteristics of 4×288 FPAs with mercury-cadmium-telluride (MCT) arrays are presented too. Analysis have shown that in spite of different constructions of four readout types, different numbers of outputs and external service, rather similar parameters of FPAs have been obtained. Detectivity values measured for all 4×288 FPAs at operation temperature T ≈ 78 K with skimming mode included and background temperature T_b ≈295 K were in the range D*_λ ≅ (1.2−1.7)×10¹¹ cmHz^1/2/W.     

Intermolecular interactions in acetonitrile in a liquid and in a low-temperature argon matrix

IR spectra of acetonitrile embedded in an argon matrix and in a liquid are recorded. IR spectra of specimens obtained with different concentrations of acetonitrile in argon are analyzed. The spectral region of C≡N vibrations of 2200–2300 cm⁻¹ with bands of monomers and possible associates is investigated. Overlap with the band of a hot transition on the low-frequency side is responsible for the pronounced asymmetry of the band ν(C≡N). To whom correspondence should be addressed. St. Petersburg State Institute of Precision Mechanics and Optics (Technical University), 14, Sablinskaya Str., St. Petersburg, 197101, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 627–631, September–October, 1999.     

Accelerator mass spectrometer for the Siberian Branch of the Russian Academy of Sciences

A concept of an accelerator mass spectrometer intended for the Siberian Branch of the Russian Academy of Sciences is suggested. Preliminary tests have been conducted, and a carbon isotope having a mass of 14 amu has been detected in a charcoal sample.     

Adsorption activity of carbon nanotubes formed from brown sphagnum moss in mechanical activation

Carbon nanotubes have been formed as a result of mechanical activation of amorphous carbon obtained after the pyrolytic treatment of brown sphagnum moss. The yield of nanotubes grows from 8 to 75 wt % with increasing the time of mechanical activation from 4 to 27 h. An integrated study of the adsorption properties of carbon materials obtained from sphagnum moss is presented. It is shown that the capability of the oxidative modification of carbon nanotubes depends on the parameters of the formation process, and the efficiency of adsorption capacity is a function of the storage time of the carbon material. The potential of carbon materials obtained from sphagnum moss as enterosorbents is considered.     

Dynamical model for a plane manipulator with rotary kinematic couples and rigid links

A system of differential equations is obtained for an N-link plane manipulator with rotary kinematic couples. The problem of the optimal design of manipulators with hydraulically driven links is considered. The optimal parameters of the mechanism are computed for a specific example.Translated fromVychislitel'naya i Prikladnaya Matematika, No. 69, pp. 105–110, 1989.     

EUV observations of the solar corona with superhigh spatial resolution in the ARCA project

Observing the Sun’s hot corona with sub-second spatial resolution is important in solving a number of basic solar physics problems. The new ARCA satellite observatory under development at the Lebedev Physical Institute, Russian Academy of Sciences, will be first to provide images of the hot solar corona with a spatial resolution of about 0.18 arcsec. Scientific and technical features of the observatory are discussed.