Fabrication and performance of low loss optical components made byion exchange in glass

Passive optical components made by photolithography with ion exchange in glass have been developed. The technology used to fabricate these components is described, and their performance characterization is discussed. It is shown that this technique produces highly uniform low-loss devices     

Fairness and the axioms of control predicates

Many recent axiomatic definitions for structured programming languages include control predicates,at(S), in(S), andafter(S), which are an abstraction of location counters. The usual axioms identify control locations so as to imply that no time (i.e., no state transition) is needed to pass from the end of one statement to the next, and in particular from the end of a loop body back to the test at the head of the loop. Here, an axiomatic framework for control predicates is examined. It is shown that if all the axioms are to be maintained with common representation mappings, there are difficult new requirements which need to be satisfied by an implementation for fair concurrent models of computation. Several approaches to resolving the difficulty are considered, and in particular it is suggested to replace some axioms of the formPQ byPeventually(Q), whereP andQ are control predicates, thereby separating control states previously identified.The North has receded, but the South has not yet arrived.-Reuven Miran, 42 Degrees in the Shade Every three lines intersect at a point, if the point is thick enough.-Folk theoremNote: A talk based on this paper was presented at the Colloquium on Temporal Logic and Specification, Altrincham, Cheshire, April 1987.C.R. Categories: D.3.1 [Programming languages] Formal definitions and theory: semantics; D..3.3 [Programming languages] Language constructs: control structures; F.3.1. [Logics and meanings of programs] Specifying and verifying and reasoning about programs.     

Detecting unknown computer worm activity via support vector machines and active learning

To detect the presence of unknown worms, we propose a technique based on computer measurements extracted from the operating system. We designed a series of experiments to test the new technique by employing several computer configurations and background application activities. In the course of the experiments, 323 computer features were monitored. Four feature-ranking measures were used to reduce the number of features required for classification. We applied support vector machines to the resulting feature subsets. In addition, we used active learning as a selective sampling method to increase the performance of the classifier and improve its robustness in the presence of misleading instances in the data. Our results indicate a mean detection accuracy in excess of 90?%, and an accuracy above 94?% for specific unknown worms using just 20 features, while maintaining a low false-positive rate when the active learning approach is applied.     

Effect of subclinical intramammary infection on somatic cell counts, NAGase activity and gross composition of goats' milk

The study was aimed at identifying the pathogens causing subclinical udder infections in representative Israeli dairy goat herds and determining their effect on milk quality. Five hundred goats in ten flocks of various breeds and crossbreeds were surveyed. Of the 500 goats, 13.4% were in their first lactation, 36.4% were in their second lactation and 50.2% were in their third or higher lactation. Percentages of udder halves with subclinical intramammary infection in the flocks ranged from 35 to 71%. The effect of the bacteriological infection on somatic cells count (SCC) was significant (P<0.001). Various species of coagulase-negative staphylococci (CNS), mainly Staphylococcus caprae and Staphylococcus epidermidis, were the main pathogens in infected udder halves. Lactation number did not significantly influence either infection rate of udder halves or SCC, although the percentage of udder halves with no bacteriological findings was higher at the first lactation than at the third lactation. Milk composition (fat, protein and lactose) varied among flocks, with lower mean total protein in uninfected halves than in infected ones and higher lactose in uninfected than infected halves.     

A logic-based approach to program flow analysis

A formalism is presented for tracking assertions which hold universally, i.e., at the end of all the execution paths to a given program point, and assertions which hold existentially, i.e., at the end of some execution paths. In the formalism, the assertions which hold at a given execution path are uniformly defined by an entry environment which contains the assertions which hold when the execution of the program begins and an environment transformer for every program construct. The novel aspect of our formalism is that Horn clauses are used to specify the consistent environments and the meaning of program constructs. The best iterative algorithm (a notion defined by P. Cousot and R. Cousot) for tracking universal and existential assertions simultaneously is given. Conditions are presented under which the best iterative algorithm can be efficiently implemented. The formalism is applied to the pointer equality problem in Pascal. It is shown that universal pointer equalities may be used to reduce the number of superfluous existential equalities, and that existential equalities may be used to obtain more universal equalities. Recent empirical results indicate that tracking the combination of may and must equalities leads to substantial improvements in the result of the analysis. For programs without recursively defined records, the best iterative algorithm can be effectively implemented. These results apply to multiple levels of pointers and can be extended to handle possibly recursive procedures. However, for programs with recursively defined data types further approximations are necessary, e.g., by using a finite graph to model all the possible pointer equalities. For simplicity, this paper does not present an analysis algorithm for this case. Received: 2 September 1991 / 25 June 1997     

Similarity preservation in default logic

The paper identifies a problem in default reasoning in Reiter’s Default Logic and related systems: elements which are similar given the axioms only, become distinguishable in extensions. We explain why, sometimes, this is considered undesirable. Two approaches are presented for guaranteeing similarity preservation: One approach formalizes a way of uniformly applying the defaults to all similar elements by introducing generic extensions, which depend only on similarity types of objects. According to the second approach, for a restricted class of default theories, a default theory is viewed as a “shorthand notation” to what is “really meant” by its formulation. In this approach we propose a rewriting of defaults in a form that guarantees similarity preservation of the modified theory. It turns out that the above two approaches yield the same result. This revised version was published online in June 2006 with corrections to the Cover Date.     

Small-focus integral fiber lenses: modeling with the segmented beam-propagation method and near-field characterization

Tapered- and straight-core fiber microlenses of hyperbolic shape are studied with the segmented beam propagation method (Se-BPM). This new formulation extends to a large scale the finite-difference time-domain method for calculating propagation of the wave field in guiding systems. It is based on partitioning an entire computational domain into subdomains along the direction of propagation. The Helmholtz equation can be solved directly for each subdomain, and an iterative procedure is used to propagate the field from one subdomain to another. The Se-BPM is compared with other approaches that are commonly used to analyze straight-core fiber microlen devices in the paraxial approximation. We deal mainly with small-spot-size fiber microlenses where this approximation does not apply. We show that the emergent beam is not Gaussian in the far field. Instead of the usual far-field characterization we propose a near-field characterization of the fiber microlens. This is possible with the near-field scanning optical microscopy technique.     

Backtracking in recursive computations

Summary A mathematical (denotational) semantics is constructed for a formalism of recursive equations with the Alternative operator. This formalism enables the combination of recursion and backtracking. The semantics is defined by applying fixpoint theory to set valued functions. We introduce the notion of strategy to produce subsets of the result. Two implementations are suggested using an auxiliary stack, that trade off recomputation time with space in the auxiliary stack. The concept of a sub-fixpoint is introduced, and the implementations are shown to be incomplete even w.r.t. sub-fixpoint values. One special strategy, the leftmost strategy, which stems from problems such as pattern matching or parsing, is discussed.