Subspace-based signal analysis using singular value decomposition

A unified approach is presented to the related problems of recovering signal parameters from noisy observations and identifying linear system model parameters from observed input/output signals, both using singular value decomposition (SVD) techniques. Both known and new SVD-based identification methods are classified in a subspace-oriented scheme. The SVD of a matrix constructed from the observed signal data provides the key step in a robust discrimination between desired signals and disturbing signals in terms of signal and noise subspaces. The methods that are presented are distinguished by the way in which the subspaces are determined and how the signal or system model parameters are extracted from these subspaces. Typical examples, such as the direction-of-arrival problem and system identification from input/output measurements, are elaborated upon, and some extensions to time-varying systems are given     

Nanocell logic gates for molecular computing

Molecular electronics seeks to build electrical devices to implement computation - logic and memory - using individual or small collections of molecules. These devices have the potential to reduce device size and fabrication costs, by several orders of magnitude, relative to conventional CMOS. However, the construction of a practical molecular computer will require the molecular switches and their related interconnect technologies to behave as large-scale diverse logic, with input/output wires scaled to molecular dimensions. It is unclear whether it is necessary or even. possible to control the precise regular placement and interconnection of these diminutive molecular systems. This paper describes genetic algorithm-based simulations of molecular device structures in a nanocell where placement and connectivity of the internal molecular switches are not specifically directed and the internal topology is generally disordered. With some simplifying assumptions, these results show that it is possible to use easily fabricated nanocells as logic devices by setting the internal molecular switch states after the topological molecular assembly is complete. Simulated logic devices include an inverter, a NAND gate, an XOR gate and a 1-bit adder. Issues of defect and fault tolerance are addressed.     

The Generic Bilinear Calibration-Estimation Problem

We identify a very general, recurring pattern in a number of well known problems in biological and machine vision. Many problems are of a peculiar double-sided nature: One attempts to estimate certain properties of the environment using a certain type of equipment and simultaneously one attempts to calibrate the same equipment on the structure of the environment. At first sight this appears the kind of the chicken and the egg problem that might well prove to be insoluble. However, due to basic constraints that universally apply (e.g., the world is only three-dimensional), a solution—up to a certain class of ambiguity transformations—often exists. The more complicated the problem is, the less important the remaining ambiguity will be, at least in a relative sense. Many well known problems are special in that they can be cast in bilinear form, sometimes after transformation or the introduction of dummy variables. Instances include photometric stereo, photometric estimations (e.g., of lightness), local (differential) image operators, a variety of photogrammetric problems, etc. It turns out that many of these problems—and together these make up a large fraction of the generic problems in machine vision today—can be cast in a simple universal framework. This framework enables one to handle arbitrarily large (that is, not minimal, consistent configurations), noisy (thus inconsistent) date sets automatically. The level at which prior information (either of a deterministic or a statistical nature) is used (assumptions such as constant albedo, rigidity, uniform distributions, etc.) is clearly separated as an additional, typically nonlinear, stage.     

Miscellaneous lesions of bone

There are several tumors and tumorlike entities of bone that do not easily fit into the specific classifications provided elsewhere in this issue. In this article, several seemingly unrelated entities are discussed, including cystic diseases of bone (simple bone cysts and aneurysmal bone cysts), Langerhans' cell histiocytosis, benign and malignant vascular tumors of bone, and adamantinoma of long bone and its relationship to osteofibrous dysplasia.     

Acute aortic outflow obstruction by diminution of bulboventricular foramen size after volume unloading in univentricular physiology

A young child with [S, L, L] segmental anatomy, double-inlet left ventricle, transposition of the great arteries, rudimentary right ventricle, and mildly restrictive bulboventricular foramen is reported, in whom intraoperative temporary snaring of the modified Blalock-Taussig shunt resulted in instantaneous and dramatic volume contraction of the left ventricle, decrease in bulboventricular foramen size, and increase of the gradient across the latter from 10 mm Hg preoperatively to 50 mm Hg. A modified Damus-Stansel-Kaye procedure using autogenous aortic tissue resulted in unobstructed aortic outflow; in addition, a bidirectional cavopulmonary shunt was performed. The importance of early relief of actual or potential aortic outflow obstruction in hearts with restrictive bulboventricular foramen is emphasized.     

Fetal lung growth after tracheal ligation is not solely a pressure phenomenon

We investigated cell proliferation and cell death in the olfactory epithelium (OE) of mice from birth to maturity using bromodeoxyuridine and terminal deoxynucleotidyl transferase nick end labeling. We show that cell death events and proliferative activity diminish concomitantly with age in the OE. Thus, the age-dependent and coordinate diminution in cell proliferative activity and cell death events may serve to maintain the thickness of the OE as mice mature and age.     

Virulence of Aspergillus fumigatus double mutants lacking restriction and an alkaline protease in a low-dose model of invasive pulmonary aspergillosis

To investigate the pathogenicity of Aspergillus fumigatus mutants lacking putative virulence factors, we have developed a new murine model of invasive pulmonary aspergillosis based on neutropenia, the major factor predisposing patients to this infection. Mice were treated with cyclophosphamide and inoculated by the intranasal route with 5 x 10(3) conidia, a significant reduction from inoculum levels used in previous models. Evidence for the production of the extracellular alkaline protease (Alp) in lung tissue was obtained by using a fungal transformant harboring an alp::lacZ reporter gene fusion. The pathogenicities of single mutant strains lacking either Alp or the ribotoxin restrictocin and of a double mutant strain lacking both proteins were assessed in this infection model. There were no significant differences between the mutant and the wild-type strains in terms of mortality or histological-features. Inoculations with mixtures of conidia showed that the double mutant strain is slightly less virulent than the wild-type strain. We conclude that Alp and restrictocin are not important virulence determinants in pulmonary infection.     

Pertussis in Massachusetts, 1981-1991: incidence, serologic diagnosis, and vaccine effectiveness

Massachusetts provides diphtheria-tetanus toxoid-pertussis (DTP) vaccine, and since 1980 has monitored pertussis with a statewide diagnostic service. The incidence of bacteriologically confirmed pertussis was 104.5 per 100,000 person-years in 1-month-old infants and declined progressively thereafter. Infants < 6 months old experienced disproportionate morbidity: 44% of bacteriologically confirmed pertussis, 64% of hospitalizations, and 71% of hospital days. Most children with pertussis had received < 3 DTP doses during childhood, whereas 87% of adolescents with pertussis had received > or = 4 doses. Serodiagnosis by single serum anti-pertussis toxin antibody ELISA increased the incidence of confirmed pertussis in persons 11-19 years old from 3.0 to 12.9 per 100,000 and in persons > or = 20 years old from 0.16 to 0.56 per 100,000. Bacteriologic methods underestimate pertussis incidence, but a single serum anti-pertussis toxin antibody ELISA is a practical method for population-based diagnosis in adolescents and adults.     

Efficacy of surgical treatment in traumatic central cord syndrome

BACKGROUND: Controversy surrounds the treatment of traumatic central cord syndrome (TCCS), as there are strong advocates for nonsurgical treatment for most patients. However, conservative treatment has been shown to yield a longer period of discomfort from pain and weakness in certain cases. METHODS: In a retrospective review of 114 patients presenting with acute or chronic TCCS from 1988-94, four different age groups were separately observed under different treatments. Motor and sensory recovery were assessed. RESULTS: Better results were achieved in younger patients, with or without radiographic abnormalities, and in patients with clinically correlated encroaching cord lesions who received early surgical decompression. CONCLUSIONS: Surgical intervention for TCCS must be addressed with careful clinical and radiographic survey. Removal of offending lesions in the subacute period results in significant motor and sensory improvement in short-term and long-term follow-up.     

Assessing multidisciplinary areas of science and technology: A synthetic bibliometric study of Dutch nuclear energy research

This paper presents a selection of results of a comprehensive quantitative, research literature-based study of Dutch energy research. The primary goal of this paper is to provide an overview of what bibliometric data from ISI and non-ISI databases may offer to describe the state of affairs in a scientific field. It illustrates the added value of combining bibliometric indicators of publication output, international visibility, international co-operation, and interdisciplinarity in a study of nuclear energy research in the 1980's when its budget decreased dramatically.