The JEM-X monitor provides X-ray spectra and imaging with arcminute angular resolution in the 3 to 35 keV band. The good angular resolution and the low energy response of JEM-X plays an important role in the identification of gamma ray sources and in the analysis and scientific interpretation of the combined X-ray and gamma ray data. JEM-X is a coded aperture instrument consisting of two identical, coaligned telescopes. Each of the detectors has a sensitive area of 500 cm 2 , and views the sky through its own coded aperture mask. The two coded masks are inverted with respect to each other and provides an angular resolution of 3 0 across an eective field of view of about 10 diameter.

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JEM-X: The X-ray monitor aboard INTEGRAL ?

Introduction to BIBDs.- Symmetric BIBDs.- Difference sets and automorphisms.- Hadamard matrices and designs.- Resolvable BIBDs.- Steiner triple systems.- Mutually orthogonal Latin squares.- Pairwise balanced designs.- t-designs.- Orthogonal arrays and codes.- Index.

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Combinatorial Designs: Constructions and Analysis

A table of binary constant weight codes of length nl28 is presented. Explicit constructions are given for most of the 600 codes in the table; the majority of these codes are new. The known techniques for constructing constant weight codes are surveyed, and a table of (unrestricted) binary codes of length nl28 is given

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A new table of constant weight codes

Coded aperture imaging in high energy astronomy represents an important technical advance in instrumentation over the full energy range from X- to γ-rays and is playing a unique role in those spectral ranges where other techniques become ineffective or impracticable due to limitations connected to the physics of interactions of photons with matter. The theory underlying this method of indirect imaging is of strong relevance both in design optimization of new instruments and in the data analysis process. The coded aperture imaging method is herein reviewed with emphasis on topics of mainly practical interest along with a description of already developed and forthcoming implementations.

Coded aperture imaging in X- and gamma-ray astronomy

This paper first considers several types of additive bases. A typical problem is to find $n_\gamma ( k )$, the largest n for which there exists a set $\{ 0 = a_1 < a_2 < \cdots < a_k \}$ of distinct integers modulo n such that each r in the range $0\leqq r \leqq n - 1$ can be written at least once as $r \equiv a_i + a_j $ (modulo n) with $i < j$. For example, $n_\gamma ( 8 ) = 24$, as illustrated by the set {0, 1, 2, 4, 8, 13, 18, 22}. The other problems arise if at least is changed to at most, or $i < j$ to $i\leqq j$, or if the words modulo n are omitted. Tables and bounds are given for each of these problems. Then a closely related graph labeling problem is studied. A connected graph with n edges is called harmonious if it is possible to label the vertices with distinct numbers (modulo n) in such a way that the edge sums are also distinct (modulo n). Some infinite families of graphs (odd cycles, ladders, wheels, $ \cdots $) are shown to be harmonious while others (even cycles, most complete or complete...

On Additive Bases and Harmonious Graphs

Existence questions.- Multipliers and constructive existence tests.- Difference sets of special type.- Families of difference sets.- Miscellany.

Leonard D. Baumert

Papers

Cyclic difference sets