Eric R. Craine

The Mass-Radius(-Rotation?) Relation for Low-Mass Stars

The fundamental properties of low-mass stars are not as well understood as those of their more massive counterparts. The best method for constraining these properties, especially masses and radii, is to study eclipsing binary systems, but only a small number of late-type (≥M0) systems have been identified and well characterized to date. We present the discovery and characterization of six new M dwarf eclipsing binary systems. The 12 stars in these eclipsing systems have masses spanning 0.38-0.59 M_⊙ and orbital periods of 0.6-1.7 days, with typical uncertainties of ~0.3% in mass and ~0.5%-2.0% in radius. Combined with six known systems with high-precision measurements, our results reveal an intriguing trend in the low-mass regime. For stars with M = 0.35-0.80 M_⊙, components in short-period binary systems (P ≲ 1 day; 12 stars) have radii which are inflated by up to 10% (μ = 4.8% ± 1.0%) with respect to evolutionary models for low-mass main-sequence stars, whereas components in longer-period systems (> 1.5 days; 12 stars) tend to have smaller radii (μ = 1.7% ± 0.7%). This trend supports the hypothesis that short-period systems are inflated by the influence of the close companion, most likely because they are tidally locked into very high rotation speeds that enhance activity and inhibit convection. In summary, very close binary systems are not representative of typical M dwarfs, but our results for longer-period systems indicate that the evolutionary models are broadly valid in the M ~ 0.35-0.80 M_⊙ regime.

A Clinical System For Digital Imaging Colposcopy

We have developed a prototype digital imaging colposcope system for use in clinical, research and teaching environments. A goal of this system is to aid in earlier detection of cervical pathology and to assist in more precise site directed biopsies. The system is expected to provide a valuable research and teaching tool, as well as a mechanism for including colposcopic images in proposed medical Picture Archiving and Communications Systems (PACS). The system consists of a charge coupled device (CCD) imager attached to the camera port of a conventional photocolposcope, a microcomputer host and a software package for processing of the resultant digital images. It is envisioned that this basic system could eventually be reconfigured to accommodate advantages to be derived from an integrated expert system. We discuss the hardware and software system, review some of the analysis algorithms used for this application and present preliminary results of clinical use of the system.

The First MOTESS-GNAT Variable-Star Survey

We present the results of the first MOTESS-GNAT variable-star survey, a deep, wide-field variability survey conducted over 2 yr with a total sky coverage of 300 deg2. In this survey, we identified 26,042 variable-star candidates with magnitudes R = 13-19, including 5271 that are periodic at the 99% confidence level. We recovered 59 out of 68 members of the General Catalogue of Variable Stars (GCVS) that are in this brightness range. We discuss the implications for completeness and accuracy for both this survey and the GCVS; the implied completeness for distinctly classifiable variable stars in our survey is ~85%-90%. We also discuss some of the caveats of our survey results. We conclude that this instrument design is ideal for an inexpensive, longitudinally distributed telescope network that could be used to study faint or rare transient phenomena in a previously unexplored regime of parameter space.

A Digital Optically Multiplexed Charge Coupled Device (CCD) Based Deoxyribonucleic Acid (DNA) Sequence Reader

We have developed a unique prototype solid state digital imaging system for use in the analysis of one dimensional deoxyribonucleic acid (DNA) sequencing gels. The system can be used to digitize, interpret and store DNA sequence information directly from an autoradiogram. The system consists of a two dimensional charge coupled device (CCD) imager, a multiplexing optical front end for reformatting of the gel image, a microcomputer host and a software package for reconstruction of the gel image and analysis of the DNA sequence.

Cervical surface shape recovery using digital imaging colposcopy

A common application of digital imaging colposcopy in cervical examinations is the measurement of lesion dimensions and areas. Typically this is done by interactively marking the region of interest on a cervix image, calculating the corresponding pixel dimensions and then scaling to the colposcope optics. Until now no one has suggested a solution to the effects of the cervical surface slant on these measurements. Away from the cervical os the surface slant is large and lesion dimensions there will be underestimated, possibly leading to a misinterpretation of the lesions progression. In this paper we discuss a noninvasive method for determining the surface geometry of the cervix using digital imaging colposcopy. The method is an application of shape-from-shading techniques used to determine the surface slant at all points in the cervix image. From the surface slant we can calculate area corrections to measurements made on the image. In our initial investigations we have applied this method to area measurements of circular regions drawn on spherical test targets. Our results indicate that we can obtain improvements in area measurement errors of factors between 3 and 6, resulting in relative errors of a few percent.

Role of color and spatial resolution in digital imaging colposcopy

We have developed a practical digital imaging colposcope for use in research on early detection of cancerous and pre-cancerous tissue in the cervix. Several copies of the system have now been used in a variety of clinical and research environments. Two issues of considerable interest which emerged early in our work involved the roles of color and spatial resolution as they applied to digital imaging colposcopy. In each instance these qualities potentially have a significant impact on the diagnostic efficacy of the system. In order to evaluate the role of these parameters we devised and conducted a receiver operating characteristic (ROC) evaluation of the system. It is apparent from these tests that a spatial resolution of 512 x 480 pixel with 7 or 8 bits of contrast is adequate for the task. The more interesting result arises from the study of the use of color in these examinations; it appears that in general, contrary to the widely held perception of the physicians involved, color apparently provides the clinician with little or no diagnostic information. Indeed, in some instances, access to color seemed to confuse the physician and resulted in an elevated rate of false positives. Results of the ROC tests are presented in this paper along with their implications for further development of this imaging modality.

Digital and optically filtered clinical colposcopic images

We have begun experimentation with a variety of digital and optical filters used in conjunction with a digital imaging colposcope system of our design. We have successfully implemented a number of different filtering techniques and now see potential applications of multispectral imaging in colposcopic examination. We discuss some of the methodology relevant to acquisition of multispectral images. Analysis of the scope of application of this imaging to colposcopic diagnosis is an interesting problem requiring further study.

GNAT—A Global Network of Small Astronomical Telescopes

New generation small telescopes are powerful tools for astronomical research and for educational outreach. GNAT, the Global Network of Astronomical Telescopes, is a non-profit organization whose goals are to implement and operate a global network of relatively small telescopes. GNAT should have nearly infinite upside potential for astronomers and students everywhere. Its Value Per Cost Ratio is enormous.

Three-dimensional induced errors in digital imaging colposcopy

The new technology of digital imaging colposcopy is the subject of experimentation by a number of physicians, some of them working in clinical environments. One of the interesting applications of digital imaging colposcopy is the quantitative measurement of areas of dysplasia, or of anatomical features, on the cervix. It has been suggested that patient care can be managed in response to findings based on these area measurements. We call attention to several sources of error which may not be immediately apparent to users of these systems and which may have implications for the clinical utility of these measurements. We suggest guidelines for the measurement protocols which should be a minimum requirement for use of the systems, and indicate new directions for research to improve the efficacy of this important new technology.

Blink comparison techniques applied to medical images

There are numerous instances in which it is desirable to compare similar, but subtly different, images in an effort to detect important temporal or spectral changes. In practice there are several approaches to addressing this problem, each with its own advantages and disadvantages. Simple image comparison techniques borrowed from observational astronomy are readily implemented now in very modest microcomputer systems. The advantages of the so-called blink comparison technique are dramatic, particularly when comparing complex or crowded scenes. We have implemented a video image blink system in hardware and software which has been used in several medical applications, including colposcopy, dermatological monitoring, x-ray comparisons and various biotechnology projects. To better understand the potential advantages of this methodology we have performed an ROC analysis of a series of synthetic images presented in a conventional photographic display mode and as a set of video blink pairs. The mechanics of implementing this type of visual image display, and the consequences of its availability, are discussed.