ALBERT

Notes: Abstract Type I hypersensitivity, which functions to protect the organism from parasites, is caused by binding of antigen to IgE antibodies pre-attached to the cell surface of tissue mast cells and their circulating counterparts, the basophils. In “allergy,” type I hypersensitivity is inappropriately induced by protein-based foreign substances (such as pollen) or protein components of insect stings, which in the normal course of events would be cleared from the organism without causing any damage. Paradoxically, a successful clinical treatment of allergy involves repeated immunization of allergic persons with low doses of the allergen—immunotherapy. Investigation of the available experimental evidence leads to the conclusion that the phenomena of immunotherapy are best addressed in terms of the interplay among the mechanism(s) of immune memory—Th1/Th2 cross-regulation—and the physical compart-mentalization of the immune system. These conclusions are illustrated with a numerical simulation.

Notes: Abstract The T helper (Th) phenotypes, Th1/Th2, are acquired upon interaction of a naive T helper cell and an antigen presenting cell (APC). Naive T helper cells may differentiate into either phenotype, and the actual outcome is determined by the density and avidity of the antigenic determinants presented by the APC, and the APCs inherent costimulatory properties. Until recently it was thought that differentiation is further affected by cytokines. However, Murphy et al. (1996, J. Exp. Med. 183, 901) have demonstrated that the experimental results, formerly interpreted as Th1/Th2 differentiation, in effect comprise an observation of two consecutive processes. (i) An interaction between naive T cells and APC creates a mixture of mature cells irreversibly committed to Th1 or Th2 phenotype. (ii) Subsequent addition of regulatory cytokines, promotes expansion of one phenotype while suppressing the other. The consequent shift in the per culture production of marker cytokines mimics the appearance of a cellular phenotype switch. We present and analyse a mathematical model that extrapolates these experimental facts into systemic behavior during an immune response. Despite the fact that differentiation produces cells of Th1 and Th2 phenotypes with the same receptor specificity, our results indicate that competition for antigenic stimulation, mediated by the APCs, combines with cytokine mediated cross-suppression between phenotypes to yield a response that is eventually dominated by T helper cells that are uniform in both receptor specificity (clonotype) and in cytokine secretion phenotype.

Notes: The growing importance and effectiveness of the Global Positioning System (GPS) in positioning geophysical surveys is now well established. In Ecuador's Amazon basin the use of GPS was the determining factor in the successful completion of a gravity survey carried out in 1994. Over 500 gravity stations, spaced from 1 to 5 km apart and positioned by GPS, were collected in the jungle environment in the country's southeast, where the preexisting data, of variable and unknown quality, were mostly confined to areas along the major rivers. This station densification, which includes the reoccupation of selected points, contributed to increase the gravity coverage; it also allowed us to evaluate and correct 1100 preexisting data points in the area, so that the different surveys can be merged. The composite data set is used for a geologic analysis of the study area, where previously unknown structures are discovered. © 1999 John Wiley & Sons, Inc.

Notes: Abstract This paper describes a method of sampling from the Poisson distribution on a computer that appears to be less costly than a recently suggested method in [1]. The proposed method relies on a conventional search using the inverse transform approach for nonintegral μ〈7, on a modification of the inverse transform approach that begins the search at the mode for integral μ, and on a combination of these two approaches for nonintegral μ〉7. For large μ the sampling cost is proportional to μ1/2. The paper also shows that for μ≥15 an incidental error occurs by using max (0, [μ+Yμ1/2+0.5]) whereY is fromN(0,1). Since the sampling cost ofY is a constant, this approach places an upper bound on the cost of generating a Poisson variate.

Notes: Conclusions 1. Analysis of the studies and computations suggests that loss of stability due to shearing is characteristic for concrete gravity dams constructed only on extremely weak rock and semirock foundations. On sound rock and rock of medium soundness, concrete dams form a strong contact with the foundation and lose their stability if there is compressive failure of the foundation with rotation about a pivot center located beneath the foundation surface. Rock foundations for which limiting rotation of the structure is the basic type of failure are characterized by a critical shear coefficient tan ψcr≥1.0#x2013;1.1. 2. It is recommended that gravity dams and their foundations be designed on the basis of two limiting states: on the condition of limiting rotation, which corresponds to the dam's loss of stability and is referred to as the first group of limiting states, and on the condition of incipient rotation for which the local strength of the rock foundation is exceeded; the latter is referred to as the second group of limiting states. 3. The initial stage of rotation (incipient rotation) is accompanied by crack formation in the rock foundation in the region of the upstream face after attaining the ultimate, tensile strength (Rt) with the smallest principal stresses. The final stage of rotation (limiting rotation) is accompanied by failure of the rock mass beneath the downstream face of the structure with the smallest principal stresses that are attained for the ultimate compressive strength (Rc) of the rock mass. It is recommended that the stability and strength of the rock foundations of concrete dams be computed from the conditions of incipient and limiting rotation, using these characteristics of the tensile Rt and compressive Rc strengths of the rock mass, which have a clear-cut physical meaning. 4. Stability computations performed for gravity dams on the basis of the condition of limiting rotation yield safety factors for stability, which correspond, to actual fracture kinematics and are therefore more reliable. 5. Conversion to dam-stability computations based on the conditions of limiting and incipient, rotation make it possible to: a) utilize the additional bearing capacity of sound and medium-sound foundation rocks; b) estblish grounds for economical gravity dams of reduced size, using engineering measures that ensure their adaptability to normal operations as cracks form in the foundation; c) reduce the, depth of the cut formed in rock foundations for dams, assuming that rock characterized by the parameter tan ω≥1.0–1.1 can remain, in the foundation, since in this case loss of stability occurs not as a result of sheart, but due to rotation of the structure, which is characterized by high stability safety factors; d) use engineering methods correctly and efficiently, to increase the stability of dams, such as, for example, their anchorage in the rock foundation, which creates a significant restraining moment that is not considered in computing the shear resistance of the dams. 6. The method proposed to compute the stability and strength of rock foundations of gravity dams can also be expanded to buttress dams and retaining walls.

Notes: Conclusions 1. It was experimentally established that depending on the strength and level of normal stresses at the contact of a concrete structure with a rock foundation two modes of loss of stability can occur: shear (sliding) at small values of the shear parameters tan ϕ and c and normal stresses σ and tilting (crushing of the foundation under the downstream face) at large values of the indicated parameters and small value of the crushing strength Rcr. 2. In the case of shear the ultimate shear strength (bearing capacity) does not depend on the moment created by external forces. In the case of failure of the system in the form of tilting the bearing capacity of the foundation substantially depends on the scheme of applying the loads (moment of external forces), which must be taken into account in calculations of the stability of structures. 3. The Eqs. (6)–(10) given in the article make it possible to establish criteria determining the boundary between the two modes of failure and to select the appropriate method of calculating the stability of concrete structures on rock foundations [Eqs. (2) and (4), (5)].

Notes: Conclusions 1. The erection of coffer dams in two stages with overtopping at an intermediate elevation removes the existing limitations in the time of erection and permits increasing the total height of the coffer dams, thus decreasing the sizes of diversion structures, and often shortening the construction time of hydrocenters. 2. In the case of the Toktogul’sk HES the decision to pass the flood through the tunnel and over the crest of a partially erected earth coffer dam made it possible to dam up the Naryn River at the beginning of 1966, and thereby to begin preparatory work in the pit of the dam one year ahead of time. 3. The earthen 30-m high Stage I coffer dam, through which a discharge (600 m3/sec) exceeding the design value by 30% was passed, withstood the flood without any damage. This shows the dependability of the adopted design of the spillway coffer dam and the good quality of the work. 4. The successful passage of the flood at the Toktogul’sk through the partially erected earth coffer dam makes it possible to recommend this method for other projects. The maximum effect can be expected in the construction of earth or rock-filled dams, where the coffer dam, as a rule, becomes part of the dam. 5. The 1966 flood at the Toktogul’sk HES passed with discharges exceeding those of the design and with heads lower than the design; this requires a special analysis of the discharge capacity of tunnels and pipes of large cross sections.