Absorption anisotropy of cubic or randomly oriented chromophores in anisotropic solvents. Dispersion induced linear dichroism (DILD)

A new mechanism through which cubic or orientationally averaged solutes could gain absorption anisotropy (linear dichroism) in the presence of an anisotropic (oriented) solvent medium is proposed. Transitions of the unoriented species exhibit a dispersion induced linear dichroism (DILD) as a result of dispersive coupling to the transitions of the oriented system. The phenomenon depends on the nature of the angular distribution of solute molecules about a particular solvent species, being maximised for a cylindrical distribution around a polymer, but still yielding a measurable DILD for spherical distributions of the solute. It is also shown that the LD of non-cubic or oriented solutes in anisotropic media should be corrected for a significant DILD contribution.     

A problem on heat conduction in an insulated wire solved by numerical inverse Laplace transform

A problem of transient heat conduction in an insulated wire is solved by use of Laplace transform and numerical inversion. The problem is solved for the radiation boundary condition and also for the boundary condition of no heat flux through the outer surface of the insulation. The results are presented both numerically with four significant figures and graphically. Asymptotic expansions are derived for small and large values of the time variable. The numerical inversion of the Laplace transform is checked by comparison with the asymptotic expansions and with the numerical results obtained by a numerical inversion formula utilizing one more abscissa than the previous one.     

Cooling of a cylindrical container blasted into the rock

An upright cylindrical container blasted into the rock is filled instantaneously with a warm liquid. Heat is transferred from the liquid into the surrounding rock and the open air. The temperature of the liquid and the surrounding rock is determined as a function of time.The differential equation and the auxiliary conditions of the transient heat conduction problem are Laplace transformed, the subsidiary equations are solved by two-dimensional relaxation, and the resulting temperature is obtained by means of numerical inversion of the Laplace transform.The results are presented numerically and graphically.     

On transient heat conduction in the walls of a rectangular gas channel

In this paper a problem on transient heat conduction in the walls of a gas channel with a rectangular cross-section is solved. The temperature of the gas flow in the channel rises linearly while the temperature of the surrounding open air is constant.The differential equation and its auxiliary conditions are Laplace transformed, the subsidiary equations are solved by a method resembling the two-dimensional relaxation method for steady state heat conduction problems, and the resulting temperatures are obtained by numerical inversion.Numerical results are presented at the end of the paper.     

Was natural β radioactivity of carbon-14 the origin of optical one-handedness in life?

¹⁴C labelled solid D- and L-leucine decomposes with significantly different rates by auto-radiolysis. The -decarboxylation ratio (10³xCO₂%)_D/(10³xCO₂%)_L was found to be (2.3±0.2)/(1.2±0.2)= 1.9±0.5 for samples kept in evacuated tubes at room temperature for 1 year /sp. activity: 0.9 MBq g^–1; -dose: 224 Gy/. EPR indicates a 10% higher radical concentration in the stored solid D-leucine samples than in L-leucine. The relevance of these results to the question of origin of optical onehandedness in life, is discussed.     

Seasonal temperature variation of soil

The surface temperature of the ground is a periodic function of time. The summer temperature of the surface can be approximated by a harmonic function, and the winter temperature, due to an insulating layer of snow, can be assumed constant. In this paper the temperature of the ground was determined as a function of depth and time.The ground temperature variation was solved by means of the Laplace transformation; the analytic solution was calculated numerically for different soil types and air temperatures. The results are presented numerically and graphically.     

Observation of polarization in bottomonium production at square root of s = 38.8 GeV

We present a measurement of the polarization observed for bottomonium states produced in p-Cu collisions at square root of s = 38.8 GeV. The angular distribution of the decay dimuons of the Upsilon(1S) state shows no polarization at small values of the fractional longitudinal momentum x(F) and transverse momentum p(T) but significant positive transverse production polarization for either p(T)>1.8 GeV/c or for x(F)>0.35. The Upsilon(2S+3S) (unresolved) states show a large transverse production polarization at all values of x(F) and p(T) measured. These observations challenge NRQCD calculations of the polarization expected in the hadronic production of bottomonium states.     

Enantioselective DNA threading dynamics by phenazine-linked.

The interactions between the stereoisomers of the chiral bis-intercalator [mu-C4(cpdppz)(2)-(phen)(4)Ru(2)](4+) and DNA reveal interesting dynamic discrimination properties. The two enantiomers Delta-Delta and Lambda-Lambda both form very strong complexes with calf thymus DNA with similar thermodynamic affinities. By contrast, they display considerable variations in their binding kinetics. The Delta-Delta enantiomer has higher affinity for calf thymus DNA than for [poly(dA-dT)](2), and the association kinetics of the dimer to DNA, as well as to polynucleotides, requires a multiexponential fitting function. The dissociation reaction, on the other hand, could be described by a single exponential for [poly(dA-dT)](2), whereas two exponentials were required for mixed-sequence DNA. To understand the key mechanistic steps of the reaction, the kinetics was studied at varied salt concentration for different choices of DNA and chirality of the threading complex. The enantiomers were found to have markedly different dissociation rates, the Lambda-Lambda enantiomer dissociating about an order of magnitude faster than the Delta-Delta enantiomer. Also, the salt dependence of the dissociation rate constants differed between the enantiomers, being stronger for the Lambda-Lambda enantiomer than for the Delta-Delta enantiomer. Since the dissociation reaction requires unthreading of bulky parts of the bis-intercalator through the DNA helix, a considerable conformational change of the DNA must be involved, possibly defining the rate-limiting step.     

A new highly adaptable design of shear-flow device for orientation of macromolecules for Linear Dichroism (LD) measurement

This article presents a new design of flow-orientation device for the study of bio-macromolecules, including DNA and protein complexes, as well as aggregates such as amyloid fibrils and liposome membranes, using Linear Dichroism (LD) spectroscopy. The design provides a number of technical advantages that should make the device inexpensive to manufacture, easier to use and more reliable than existing techniques. The degree of orientation achieved is of the same order of magnitude as that of the commonly used concentric cylinders Couette flow cell, however, since the device exploits a set of flat strain-free quartz plates, a number of problems associated with refraction and birefringence of light are eliminated, increasing the sensitivity and accuracy of measurement. The device provides similar shear rates to those of the Couette cell but is superior in that the shear rate is constant across the gap. Other major advantages of the design is the possibility to change parts and vary sample volume and path length easily and at a low cost.