Search for free quark production at the CERN SPS collider

No experiment has found convincing evidence for free quarks [1, 2]. A possible explanation for this non-observation in accelerator experiments is that their cross-section for interaction with matter is much larger than those of hadrons [3], and hence they are scattered and/or absorbed by material between their production point and the detector. We have examined this possibility by exposing 1/4 mm diameter steel balls near an intersection point of the CERN SPS \(p\bar p\) collider beams. These balls have been subsequently examined for the presence of fractional charge, using the Rutherford Laboratory room temperature magnetic levitation system [4]. None of the 60 balls tested to date shows evidence of fractional charge.     

Adsorption reactions of alkali-halide nanocrystals: Identification of an important surface defect

The adsorption reactions of alkali-halide clusters have been investigated on a size-selected basis using flow-reactor methods. The reactivity of larger sodium-fluoride clusters [Na_nF_n?1]⁺ toward polar molecules NH₃ and H₂O shows a distinctive pattern as a function ofn at ambient temperature. Comparison with computed structures shows that aparticular kind of defect greatly facilitates the initial adsorption process. This defect can be formed by removal of an ion-pair from the face of an otherwise perfect nanocrystal, to create a basket-like opening for the adsorbed molecule. It is shown that this kind of defect occurs as a most stable low-temperature structure only to a certain size, after which a less reactive defect takes its place. The implications of these findings for the adsorption reactivity of the surfaces of ionic solids are briefly discussed.     

Chaos and algorithmic complexity

Our aim is to discover whether the notion of algorithmic orbit-complexity can serve to define chaos in a dynamical system. We begin with a mostly expository discussion of algorithmic complexity and certain results of Brudno, Pesin, and Ruelle (BRP theorems) which relate the degree of exponential instability of a dynamical system to the average algorithmic complexity of its orbits. When one speaks of predicting the behavior of a dynamical system, one usually has in mind one or more variables in the phase space that are of particular interest. To say that the system is unpredictable is, roughly, to say that one cannot feasibly determine future values of these variables from an approximation of the initial conditions of the system. We introduce the notions of restrictedexponential instability and conditionalorbit-complexity, and announce a new and rather general result, similar in spirit to the BRP theorems, establishing average conditional orbit-complexity as a lower bound for the degree of restricted exponential instability in a dynamical system. The BRP theorems require the phase space to be compact and metrizable. We construct a noncompact kicked rotor dynamical system of physical interest, and show that the relationship between orbit-complexity and exponential instability fails to hold for this system. We conclude that orbit-complexity cannot serve as a general definition of chaos.     

DIETARY FAT MODULATES IMMUNORESPONSIVENESS IN UV-IRRADIATED MICE

Previous studies have shown that a high level of dietary lipid (corn oil) exacerbates UV-carcinogenic expression in hairless mice. Furthermore, it was demonstrated that this effect occurs at the postinitiation, or promotion, stage of UV-carcinogenesis-a stage believed to be modulated immunologically. Thus, we sought to examine the influence of dietary lipid on specific immune parameters at various times within a UV-carcinogenic protocol, with the purpose of detecting potential relationships to UV carcinogenesis. Hairless mice were fed either a high- (12%, wt/wt, corn oil) or low-fat (0.75%, wt/wt, corn oil) diet for 2 weeks prior to start of the UV or experimental protocols. Animals were sensitized to dinitrochlorobenzene (DNCB) hapten and delayed-type hypersensitivity (DTH) was assessed. Delayed-type hypersensitivity was significantly suppressed (P= 0.01) in the high-fat group, even before UV irradiation. Although both groups exhibited UV-induced suppression of this response, the high-fat group was totally suppressed after 3 weeks of UV, whereas the low-fat group exhibited reactivity through week 8. The splenic T-lymphocyte (Thy 1.2⁺) population had declined by about 50% at the time of UV termination (11 weeks). Dietary lipid exerted no apparent influence upon this T-cell population. However, after 6 weeks of UV, I-J⁺ cells (a marker shown to be acquired adaptively by suppressor T lymphocytes) began to increase. By week 15 (4 weeks post-UV) I-J⁺ cells had increased by about 65% in the high-fat group, twice the % increase that occurred in the low-fat group. When UV-induced tumors were transplanted to recipient animals receiving various periods (0, 6, 11 weeks) of UV irradiation, no significant differences in median tumor rejection times between the two dietary groups occurred at 0 or 6 weeks. After 11 weeks of UV, the low-fat group exhibited a tumor rejection time that was comparable to that of nonirradiated animals, i.e. 21 days. However, median tumor rejection time for the high-fat group was greater than 63 days, significantly (P= 0.01) longer than that of the low-fat group. Thus, suppression of tumor rejection by high fat occurred at a time when high fat had been shown to exacerbate carcinogenic expression and when I-J⁺ cells had markedly increased. These data demonstrate that level of dietary lipid modulates immunoresponsiveness in UV-irradiated animals and is compatible with the thesis that immune suppression may account for the exacerbation of carcinogenic expression elicited by high dietary fat.     

STUDIES ON THE PHOTOPROTECTIVE MECHANISM OF BUTYLATED HYDROXYTOLUENE

Abstract It has been suggested that butylated hydroxytoluene (BHT) ^‡ , a phenolic antioxidant that conveys photoprotective properties to skin, may act by altering epidermal parameters that influence the level of ultraviolet light (UV) reaching critical target sites. The potential diminution of effective UV dose could account for the observed inhibition of UV-induced ornithine decarboxylase (ODC). Thus studies were conducted to examine the possibility that BHT was capable of promoting epidermal proliferation, just as others have shown with lung epithelial cells. UV-induction of ODC, in unrestrained Skh-Hr-I mice irradiated with Westinghouse FS–20 lamps, was shown to be linearly responsive from 0.3 to 0.6, J/cm²/dose. The degree of inhibition afforded by dietary BHT was approximately constant over this dose range. In addition, intraperitoneal administration of BHT (400 mg/kg) inhibited UV-induced ODC as greatly as when provided dietarily. Greatest inhibition occurred when BHT was administered at least 46 h prior to UV exposure, with the inhibitory event(s) requiring over 20 h to become effective. However, BHT had no effect, during this time interval, upon the incorporation of [³H]thymidine or leucine into DNA and protein, respectively. Nor were BHT effects reflected in the epidermal labeling index. These data suggest that BHT does not induce epidermal proliferation. An alternate explanation, in which the antioxidant properties of BHT play a major role, is proposed.     

The evolving,flowless drainhole: A nongravitating-particle model in general relativity theory

Nonstationary, spherically symmetric solutions of the coupled field equationsR =2,, and =0, in which the coupling polarity is opposite to the orthodox, are derived. The basic solution, termed the evolving, flowless drainhole manifold, has these properties: (1) geodesic completeness; (2) a topological hole that shrinks to a point at a singular event and immediately begins to expand back to infinite size; (3) multiple branching of geodesics that arrive at the singular event; (4) asymptotic flatness at spatial infinity, luminal infinity, and temporal infinity; (5) isometric symmetry under time reversal and under space reflection through the drainhole; (6) conformal symmetry under space-time dilatations that leave the singular event fixed, and also under space-time inversions that interchange the singular event and a point at infinity. An earlier, static drainhole solution of the same equations was able to represent an ordinary star's external field or to serve as a model of a simple gravitating or nongravitating particle, replacing in these capacities the Kruskal-Fronsdal-Schwarzschild black-hole manifolds. The evolving, flowless drainhole can be thought of as modeling the death and rebirth of a scalar particle that is infinitely large in the infinite past and the infinite future. This particle does not gravitate, for the ether flow whose spatial variations in the static drainhole solution are identified with gravitation is removed from consideration in the evolving, flowless drainhole solution by being turned off at the outset. What is left is space alone, evolving dynamically in accordance with the field equations.Presented at the Seventh International Conference on Gravitation and Relativity (GR7), Tel Aviv, Israel, 23–28 June 1974.     

A computer simulation study of imaging flexural inhomogeneities using plate-wave diffraction tomography

This paper investigates the feasibility of plate-wave diffraction tomography for the reconstruction of flexural inhomogeneities in plates using the results of computer simulation studies. The numerical implementation of the fundamental reconstruction algorithm, which has recently been developed by Wang and Rose [C.H. Wang, L.R.F. Rose, Plate-wave diffraction tomography for structural health monitoring, Rev. Quant. Nondestr. Eval. 22 (2003) 1615-1622] is investigated addressing the essential effects of applying the discrete form of the Fourier diffraction theorem for solving the inverse problem as discussed by Kak and Slaney [A.C. Kak, M. Slaney, Principles of Computerized Tomographic Imaging, IEEE Press, New York, 1988] for the acoustic case, viz. diffraction limited sensitivity, influence of weak scatterer assumption, damage location and scatter field data processing in time and Fourier space as well as experimental limitations such as finite receiver length and limited views. The feasibility of the imaging technique is investigated for cylindrical inhomogeneities of various severities and relative position within the interrogation space and a normal incident interrogation configuration. The results show that plate-wave diffraction tomography enables the quantitative reconstruction of location, size and severity of plate damage with excellent sensitivity and offers the potential for detecting corrosion thinning, disbonds and delamination damage in structural integrity management applications.     

Landau-level lifetimes in PbTe nipi superlattices, PbTe/PbEuTe and InAs/AlSb quantum wells

Landau-level lifetimes are determined from saturation cyclotron resonance (CR) in wide parabolic wells, quantum wells and bulk PbTe–Pb_1−xEu_xTe systems. These narrow gap structures exhibit strong band non-parabolicity necessary to terminate the normally equi-spaced Landau-level ladder. It was not possible to saturate the bulk sample, but short lifetimes, of between 1.5 and 8 ps, were obtained for the wide parabolic well and the quantum well, respectively, utilising a multi-level rate equation model. We also report the first pump–probe cyclotron resonance result in an InAs–AlSb quantum structure. The pump–probe experiment provides a direct determination of the lifetime, giving τ=40 ps in this InAs–AlSb sample. This shows good agreement with an 8×8k·p calculation.