Curious Behavior Research Articles

A unified approach to spin polarization (CIDEP) and relaxation by Heisenberg spin exchange. I. Generalized equations for reactive radicals

A theory of Heisenberg spin exchange (HSE) has been formulated in this and the following paper to consider the processes of chemically induced dynamic electron polarization (CIDEP) and relaxation. The framework, which includes all the spin states of a radical pair (RP), relies on an exact transient solution of the encounter RP density matrix. To aid in interpreting time-resolved ESR studies of these effects, a nonphenomenological formulation of Bloch-type equations is explicitly derived for the ⋅RH and ⋅RH2 radical spin systems as well as for general radical systems in terms of their n-line ESR spectra. The longitudinal and transverse relaxation rates and the frequency shifts are calculated for conditions spanning the weak to the strong exchange limit under a wide range of viscosities. The normally slight frequency shifts are shown to be strongly enhanced by CIDEP although not to an extent that is easily observable. Aside from the usual degeneracy effects, a curious HSE relaxation behavior is predicted for ESR lines that exhibit multiplet CIDEP, wherein the observed longitudinal relaxation rate can appear faster than the transverse rate by an amount that depends on the degeneracy of the line vs the total number of transitions of the radical. The present theory is formulated to be descriptive of time-resolved ESR experiments. Implications to reactive radicals are discussed and the solutions of the modified Bloch equations are presented to consider (i) instantaneous, geminate, and diffusive RP CIDEP, (ii) coupled and time dependent relaxation by HSE, and (iii) second-order chemical decay.

Possible antiferromagnetic interactions in NdRh 3B 2 and CeRh 3B 2

The magnetic phase transition and spin arrangement in the ordered phase of NdRh 3 B 2 and CeRh 3 B 2 have been studied by measurements of magnetic susceptibility and heat capacity of the isostructural compounds RRh 3 B 2 ( R: La, Ce, Nd, Gd). The existence of small antiferromagnetic interactions between R ions ( R = Nd, Ce) on the neighbouring ferromagnetic chains along the c-axis has been suggested. This model gives another aspect to explain the origin of the anomalous magnetism of CeRh 3 B 2 such as the small value of magnetic moment in the ordered state and the curious behaviour of susceptibility. The magnitude of the effective moment of Ce has been estimated for the consumption of magnetic entropy of the Ce compound.

The differential permeation rate measurement of gases in PVAc

AbstractThe temperature dependence of the CO2 permeability coefficient in poly(vinyl acetate) (PVAc) was measured continuously by a differential permeation rate method. Tg was changed at upstream pressure in PVAc/CO2 system, and curious behavior of Ar was observed after CO2 conditioning. The differential permeation rate experiment successfully exhibits the effects of continuous temperature change for membranes with different histories.

The rigid body dynamics of unidirectional spin

A toy consists of a boat-shaped body showing great preference for spin in one direction only. Its sophisticated rigid body dynamics is examined in some detail, and fully accounts for this curious behaviour.

Information theoretical approach to noisy dynamics

The information theoretical structure of a noisy one-dimensional dynamics is investigated. The framework of mutual information and the information flow is given, and the mutual information is calculated in the BZ (Belousov-Zhabotinskii) reaction map and the logistic map. The computational results show the real mechanism of a curious behaviour of noisy dynamics.

Low-Energy nuclear reactions with hydrogen isotopes

Using the Los Alamos Low-Energy Fusion Cross-Section Facility (LEFCS), we have completed the study of the D(t, α)n reaction from E t = 12.5–117 keV, and now have measured angular distributions of the reactions D(d, p)T and D(d, 3He)n from E d= 20–117 keV. The experimental equipment features a windowless cryogenic target, a precision beam-intensity calorimeter, a 10 to 120 keV accelerator producing negative tritium ions, an accurate target gas-flow and temperature system, and a tritium gas-handling system. Most of the quite anisotropic angular distributions of the D+D reactions have relative errors of about 1% and the integrated cross-sections have absolute errors of about 1.5%. Astrophysical S functions extracted from the data and also from a least-squares fit of a+ b cos 2 θ to the data show a curious behavior with energy. The cross-sections, which agree with previous but less accurate data, are compared with R-matrix calculations. We also show preliminary results for alpha-particle spectra of the T(t, α)nn reaction. A feature of this experiment is the flow through our windowless target of 1.5 standard liters of tritium gas per day.

Macromolecular structure and liquid crystallinity.

The relationship between low-molar-mass or monomeric liquid crystals and polymeric liquid crystals is explored by examining the historical development of experimental and theoretical aspects of the latter materials. Polymeric liquid crystals are initially contrasted with conventional, non-mesogenic, flexible polymer chains (random coils), and then semiflexible and rigid-rod polymers are examined. Both thermotropic and lyotropic phases are described, with emphasis placed on the former; in particular, the relationship between dimers and polymers belonging to the semi-flexible category: [graphic omitted](mesogenic core)—(flexible spacer)[graphic omitted]n. The review concludes by drawing attention to the curious behaviour of polypeptide liquid crystals (cholesteric compensation). The underlying theme of the lecture is the need to recognize the synergism and affinity that characterizes research on monomeric and polymeric liquid crystals.

New wine in old bottles

By taking a natural science perspective, it is possible to think about different ways of understanding this curious behavior–play–and to think of different ways of probing the phenomenon to determine whether it will behave as expected.

Learning and courtship in Drosophila: two stories with mutants.

Victorian ladies and gentlemen cultivated waltzing mice and tumbling pigeons as parlor pets. They derived mild social amusement from the inbred animals' curious behavior, unmindful of the hereditary ataxias and seizures that caused it. Present day fanciers of behavioral mutants continue to be amused by their organisms, but as biologists they are concerned above all with the etiology of curious behavior. Other things have changed as well. Simple organisms bear­ ing single gene mutations have replaced complex, inbred strains, and the emphasis is on using these new mutants to dissociate complex behaviors and the neuronal processes that underlie them. Recently, the cumulative effect of many experiments with many mutations, brought to bear on a few well-defined questions, has helped promote some of these studies from promising curiosities to coherent stories. Here we concen­ trate on two of these, in the organism we know best. In one case, mutations that perturb learning and memory in well-defined ways have led directly to the underlying biochemistry. In another, mutations and mosaics in combination with behavioral studies have resolved an ethologically complex behavior in unprecedented detail, showing the brain regions, sensory cues, and experiential determinants of many of its steps. For more comprehensive reviews, see Hall and colleagues (1982) and Hall (1982).

High electric-field hall effect measurements onn-type InSb at 77 K

Pulsed Hall-effect experiments onn-type InSb at 77 K, with nanosecond time resolution, at magnetic inductions down to 2 mT and for electric field strengths up into the avalanche regime are reported. Results on mobility are compared with previous experimental data and various theoretical calculations. For the first time also results on the scattering factor as a function of electric field are given. A curious time dependent behaviour of the transverse voltage under avalanche conditions is reported. Along with the development of the avalanche the transverse voltage decreases and may even change sign. This phenomenon is qualitatively explained in terms of the magnetoconcentration effect and the change of contact properties under avalanche conditions.

Wave-theory peaks in range-averaged channels of uniform sound velocity

Even in isovelocity water the wave or modal nature of the sound propagation causes special effects at four particular depths. Thus, the range-averaged level shows a zero at the free surface, a maximum at the source depth, and effects of uncertain sign at the bottom and near the source complementary depth. These peaks show further curious behavior, akin to interference, as source depth is varied. The present source depth peaking is a wave effect in isovelocity water, in contrast with the flux-theory infinities predicted for refracting conditions. For large numbers of modes, the present source depth peak is normally 50% above the average, and this anticipates a similar wave-theory result for refracting conditions.

The response of sheared turbulence to additional distortion

In unidirectional flows, the ratios of Reynolds shear stress to total intensity (except near positions of zero stress) remain remarkably constant from one flow to another, but curvature or strong divergence of the mean flow causes very considerable changes in the stress ratios. A scheme for calculating the changes is described, based on the rapid-distortion approximation of the equations of motion. The results depend to some extent on the effective history of distortion of the turbulence and on the magnitude of an eddy viscosity that models the effect of nonlinear transfer of energy to smaller eddies of the dissipation sequence, but the correspondence with measured values in a distorted wake and in a curved mixing layer is fairly good. In particular, the curious behaviour of stress ratios in the curved mixing-layer can be reproduced qualitatively without any difficulty. Small perturbations of wall turbulence provide a simple application, and earlier calculations of the energy transfer between wind and water waves have been repeated including the changes in the stress ratios predicted by the scheme. In the latter case, very large changes in the distributions of pressure and shear stress are found, and the rates of energy transfer are much larger and in better agreement with observations.

X heterochromatin subdivision and cytogenetic analysis in Sciara coprophila (diptera, sciaridae)

The so-called controlling element (CE), which normally programs the curious behavior of the sex chromosome in this genus, has been localized in the short right arm of the polytene X in S. coprophila. The localization was accomplished by use of five X-autosome translocations whose break points define three blocks of heterochromatin (“heterochromomeres”) extending from the X centromere to the very end (right) of the chromosome. The behavior of the translocation chromosomes at the crucial second spermatocyte division was examined and the “precocious” chromosome identified in all five cases. Then, knowing the heterochromomere make-up of each chromosome, the position of the CE could be mapped; it is located in heterochromomere H2, the same block of heterochromatin that contains 50% of the ribosomal RNA cistrons. — The question of whether the CE can manipulate any centromere in the nucleus has been only partially answered. It can manipulate translocation chromosomes which possess the centromere of the metacentric autosome (salivary chromosome IV) or that of the shorter rod (salivary chromosome II); but the longer rod (salivary chromosome III) whose proximal end, as seen in the polytene nucleus, is heavily laden with heterochromatin of its own, has not been brought under CE control. — In one of the translocations, T23, the precocious chromosome is a very large metacentric chromosome which resembles the “peculiar” V-shaped X of S. pauciseta. This peculiarity is not observed in the J-shaped precocious chromosome of T29. These points are discussed.

On exhibiting reptiles

Herpetology may not be the biological discipline of highest esteem in the public view but, among zoo animals, reptiles clearly rank near the top in their attractiveness. The snake that lost its limbs after misleading Eve, the asp that permitted Cleopatra to terminate her spectacular career, the house snake of Greek mythology, and Sherlock Holmes’ speckled band all manifest the intrinsic fascination and aura of danger accompanying modern snakes. The fascination of other reptiles is Werent but as profound as that of snakes. The iguana, slunk and crocodile share affinities with the dragon, and the shell of the tortoise reminds students of Hindu and other eastern mythology that a large turtle supports the foundations of the earth. Perhaps the scaly skin and ‘cold blood‘ induce curiosity, whereas the fear of venom, the odd shape and the curious behaviour increase the interest. The intrinsic attractiveness of reptiles as exhibit animals is clear. Most zoos capitdise upon this, and the present volume contains a collection of reports deahg with some by-products of such exhibit programmes. It seems useful, as part of its introduction, to consider some, more general aspects regardmg the philosophy and requirements of reptilian ehbition, about the place of zoos in the conservation scheme, about reptilian adaptations, and about the place of research or organised discovery in an exhibit park. Although opposing views are alluded to, what follows is primarily a personal statement, based upon some decades of interaction with the various amateur and professional publics faced by a herpetologist, and presumably tinted quite strongly by the biases of a long-time afkionado of reptiles.

An aspect of the low temperature dielectric behaviour of Saran and the nature of molecular relaxation

A curious behaviour of the low temperature dielectric loss in a PVC—PVDC copolymer (Saran) is reported: below 270 K the loss, tan δ, is essentially independent of both the temperature and the frequency in the range 100 Hz to 100 kHz. An analysis of the experimental data leads to the inference that dielectric relation is possibly a critical phenomenon, in which the reorientation polarization, and thus the dipolar loss arising from it, vanish at some finite temperature T o, such as 270 K for the loss curve at 100 Hz and 290 K for the loss curve at 100 kHz.

Lagrangian–Eulerian relation and the independence approximation

The relation between Lagrangian and Eulerian functions is basic to the understanding of turbulent diffusion. To explore this relation, the independence approximation was suggested by Corrsin and used by Saffman. Here, a theoretical investigation is made of the Lagrangian–Eulerian relation and the validity of the independence approximation. A renormalized expansion is introduced for this purpose. It is shown that the independence approximation is the first term in a systematic expansion of the Lagrangian function, and is valid when an explicit condition on the turbulence spectrum is satisfied. Correction terms to the independence approximation are derived. The Lagrangian function is then related to the Eulerian function by an integral equation. This equation justifies a result previously derived by Saffman, and is a little more general. In addition, a calculation is made of the probability distribution of a particle displacement, including non-Gaussian corrections. These corrections are consistent with the non-Gaussian form found in numerical simulations by Peskin, and may explain the observation of a curious behavior concerning the independence approximation. Within the context of the independence approximation, it is seen that the Lagrangian correlation time is less than or equal to the Eulerian correlation time.

Quasi-elastic behavior of solutions of viral capsid and RNA at very low shearing stresses.

By the application of shearing stresses on the order of 10(-3) dyne cm-2 (10(-2) muN cm-2), via the magnetic viscodensimeter, extremely high relative viscosities (greater than 500) were observed when turnip yellow mosaic virus was degraded in alkali into its capsid and RNA. The solutions, however, possessed a watery consistency at this stage and exhibited a quasi-elastic character by rotor-recoil experiments. The development of this curious behavior was concentration and temperature dependent; it was not seen less than 0.5% nor at 8 degrees, and appeared sooner at 30 degrees than at 20 degrees. The time of appearance was delayed as the pH was lowered; however, the effect was still observed when the pH was as low as 9. Whereas reversibility was demonstrated when the shearing stresses exceeded the elastic resistance [0.17 dyne cm-2 (1.7 muN CM-2)], thorough mixing usually resulted in a normal behavior of the solutions thereafter. Values for the modulus of rigidity at 20 degrees for about 1% virus concentration was less than 2 X 10(-2) dyne cm-2 rad-1 (0.2 muN cm-2 rad-1), which, while extremely small, was reproducible. A porous structure, possibly involving a capsid and RNA complex, is envisioned.

The Oxidation of Thin Single Crystals of Iron

Single crystal (001) films of iron treated with mixtures of oxygen and nitrogen at 10−7 Torr and 700°C form individual oxide grains observable in transmission electron microscopy. The three reaction products all have a fixed epitaxy with (001) parallel to the iron film. The grain size and distribution of the product phases are reported as well as a curious growth behavior of .

Linear viscous stability analysis of the stratified Bickley jet

The stability of the stably stratified Bickley jet to small disturbances in a viscous, heat conducting fluid is explored by numerical integration of the governing differential equation. Curves of neutral stability are presented in the α-R plane and the parametric dependence of these curves upon Richardson number and Prandtl number is examined. The results show a curious bimodal behavior of the curve of neutral stability for small Richardson numbers. In addition, closed neutral curves are found for Richardson numbers in excess of the critical value for the inviscid flow. The unstable regions in the interior of these curves increase with decreasing Prandtl number. Energy balances are computed which show the relative magnitude of the Reynolds stress production, buoyancy dissipation, and viscous dissipation terms across the flow. As the thermal diffusivity becomes large compared with the kinematic viscosity, the buoyancy term is suppressed and the thermal stratification becomes irrelevant.

“Fourth sound” in helium‐three confirms superfluidity

An experiment at the University of California at La Jolla, based on the propagation of fourth sound, appears to provide the first really direct evidence for superfluidity in He3. Over the past two years (PHYSICS TODAY, October 1972, page 17 and July 1973, page 17), a variety of experiments have studied the curious behavior of He3 below a few millidegrees Kelvin, where it undergoes two transitions, both in the liquid—“A” near 2.6 mK and “B” near 2.0 mK (at a melting pressure near 34.4 bar). These experiments measured various properties characteristic of a superfluid, ranging from nuclear magnetic resonance to viscosity.