Summary We present a formulation for a fractal fracture network embedded into a Euclidean matrix. Single-phase flow in the fractal object is described by an appropriate modification of the diffusivity equation. The system's pressure-transient response is then analyzed in the absence of matrix participation and when both the fracture network and the matrix participate. participate. The results obtained extend previous pressure-transient and well-testing methods to reservoirs of arbitrary (fractal) dimensions and provide a unified description for both single- and dual-porosity systems. provide a unified description for both single- and dual-porosity systems. Results may be used to identify and model naturally fractured reservoirs with multiple scales and fractal properties. Introduction Fractured reservoirs have received considerable attention over the past few decades. Naturally fractured reservoirs typically are represented by the two-scale (fracture/matrix) model of Warren and Root. The fracture network is assumed to be connected and equivalent to a homogeneous medium of Euclidean geometry. Alternatives must be sought, however, for reservoirs with multiple property scales and a non-Euclidean fracture network. Fractal geometry is a natural candidate for the representation of such systems. Naturally and artificially fractured systems (e.g., carbonate reservoirs and stimulated wells) have been actively investigated. The following key concepts are typically applied in conventional models. Premise 1. There are two media (matrix/fracture network) with two distinctly different flow-conductivity (permeability) and storage (porosity) scales. Premise 2. The matrix is a Euclidean object (i.e., of dimension D = 2 for cylindrical-symmetry reservoirs) within which the fracture network is embedded. The fracture network is also Euclidean with dimension D = 2 in the dual-porosity case, or D = 1 in the single-fracture case. Premise 3. The matrix is not interconnected; thus fluid flow to and from wells occurs only through the perfectly connected fracture network. These premises are reflected in the pressure-transient response models. Thus, the dual-porosity system exhibits the asymptotic behavior, pertinent to flow in a system with D = 2 and cylindrical symmetry, while the single-fracture system response is at early times and at later times, suggesting linear (D = 1) and bilinear (D = 3/2) flow geometry, respectively. Note with the singular exception of 2D cylindrical geometry, the asymptotic pressure response generally is the power-law type . Although various improvements and modifications of the original model have been proposed (see Ref. 4 for a rigorous analysis), they all pertain to the well-ordered but rather restricted structure described above. Recognizing the need for further extension, Abdassah and Ershaghi recently proposed a triple-porosity model that relaxes Premise 1 by considering an proposed a triple-porosity model that relaxes Premise 1 by considering an additional scale. While this incremental approach may be adequate in several cases, it is less applicable to systems exhibiting a large number of different scales, poor fracture connectivity, and disordered spatial distribution. An alternative formulation for these systems is desirable. Several naturally fractured reservoirs share many such features, notably a large variability in scales and fracture density and extent. These features are induced by the fracturing process in conjunction with the initial brittleness of the material. While such relations are actively researched, evidence increasingly points out that fracturing processes may lead to the creation of fractal objects. Examples range from Monte Carlo simulations to field observations and modeling. Fractal properties have been variously assigned to fracture perimeter, fracture-system mass, or the fracture-size density function.

Public Health Biiefs reports to the NMHED. The high rates of reporting of laboratory-confirmed cases documented in this study demonstrate that the system is working efficiently.Connell, etal, have described the opportunities and hazards in the use for research of datasets designed and compiled for other purposes.6 Our study exemplifies such limitations. Although ICD-9-CM code assignments were not sensitive for detection and surveillance ofthe notifiable infectious diseases we chose for this study, they were congruent with the clinical picture and may have identified potential cases not detected by laboratorybased surveillance. Conditions whose diagnoses rely predominantly on clinical evidence (e.g., injuries) are likely to be more accurately identified by ICD-9-CM code surveillance. Although further studies on the feasibility of inpatient and outpatient data systems for surveillance are needed, access to a dataset combining laboratory, inpatient, and outpatient information holds potential for disease surveillance. O

No abstract

The magnitude of the lung cancer risk from radon levels commonly found in U.S. dwellings appears low.

No abstract

No abstract

A case-control study of lung cancer was conducted to evaluate the relationship between lung cancer histologic types and occupation, adjusted for smoking. A total of 4,431 white male cases and 11,326 cancer controls, diagnosed between 1980 and 1985, were identified through the Missouri Cancer Registry. For all histologic types combined, excess risk was observed among many a priori suspected high-risk occupations. Lung cancer was elevated among men employed as insulators (odds ratio [OR] = 6.0; 95% confidence interval [CI] = 0.7, 137.8), carpenters (OR = 1.3; 95% CI = 1.0, 1.7), painters, plasterers, and wallpaper hangers (OR = 2.0; 95% CI = 1.2,3.3), structural metal workers (OR = 1.9; 95% CI = 0.6,6.0), mechanics and repairers (OR = 1.3; 95% CI = 1.0,1.7), motor vehicle drivers (OR = 1.5; 95% CI = 1.2,1.8), police and firefighters (OR = 1.6; 95% CI = 1.1,2.3), and food service personnel (OR = 1.8; 95% CI = 1.0,3.5). A deficit of lung cancer was observed among farmers (OR = 0.9; 95% CI = 0.7,1.0). Adenocarcinoma of the lung was elevated among carpenters (OR = 1.6; 95% CI = 1.0,2.5) and cabinet and furniture makers (OR = 2.0; 95% CI = 0.4,8.1), which is interesting because of the previous reports of excess adenocarcinoma of the nasal cavity associated with wood dust exposure. Adenocarcinomas were also elevated among plumbers (OR = 2.0; 95% CI = 1.0,3.8) and printers (OR = 1.8; 95% CI = 0.7,4.2). Electricians were at slightly increased risk for adenocarcinoma (OR = 1.5; 95% CI = 0.7,2.8) and "other" or mixed cell types of lung cancer (OR = 1.5; 95% CI = 0.8,2.9) but at decreased risk for small cell (OR = 0.8; 95% CI = 0.3,2.0) and squamous cell (OR = 0.8; 95% CI = 0.4,1.6) tumors. Among welders, adenocarcinoma (OR = 1.7; 95% CI = 0.7,3.8) and squamous cell (OR = 1.7; 95% CI = 0.9,3.3) cancers were elevated, but small cell and "other" lung cancers were not. Despite the limitations of the Cancer Registry data, some interesting associations were observed that merit further study, particularly the association between lung adenocarcinoma and occupational exposure to wood and wood dust.

We evaluated the risks of brain cancer in relation to employment history in a case-control study of 312 cases and 1,248 cancer controls. Subjects were identified through the Missouri Cancer Registry for the period 1984 through 1988. Job classification was based on data routinely abstracted from hospital records. Elevated risks were identified for certain white collar occupations: for men employed in engineering, the odds ratio (OR) = 2.1; 95% confidence interval (CI) = 0.4, 10.3; for social science professionals, the OR = 6. 1; 95% CI = 1.5, 26.1. Among occupations with potential exposure to occupational carcinogens, increased risks were ob-