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Biomedical subjects

J Ennis

Publications and source records attributed to J Ennis.

At least 19 recordsLinked to original sources
PubMed2000

Dynamic Mobility of Two Spherical Particles with Thick Double Layers.

The dynamic electrophoretic mobility of a pair of nearby spherical particles is analyzed in the case when the thickness of the electrical double layer around each particle is comparable to the particle radius. By means of an integral reciprocal relation, a formal expression is obtained for the force and torque on N spheres subject to an oscillating electric field which may be spatially varying. Upon linearizing in the surface potential, this expression is shown to depend upon a set of purely hydrodynamic problems involving N neutral spheres, the calculation of the electric field around N neutral spheres, and the equilibrium charge distribution around N charged spheres. In the case of a single particle, the known analytic formula for the dynamic mobility is recovered. For a pair of identical particles, the dynamic mobility is calculated numerically, using known solutions to the required subproblems. An analytical expression for the mobility of a pair of widely separated spheres is also obtained by a method of reflections, and this is in excellent agreement with the numerical results outside the range of double layer overlap. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Dynamic Mobility of Particles with Thick Double Layers in a Nondilute Suspension.

The dynamic mobility of a nondilute suspension of spherical particles is investigated in the case where the thickness of the electrical double layer around each particle is comparable to the particle radius. A formula is obtained for the O(φ) correction in a random suspension of particles with volume fraction φ, involving an integral over the dynamic mobility of a pair of spheres. This formula is then evaluated using both analytical approximations and numerical results previously obtained for the pair mobilities and valid for low surface potentials. The effect of double-layer thickness on the O(φ) coefficient is most pronounced at low frequencies, and lessens once the hydrodynamic penetration depth is smaller than the particle radius. Various approximations are considered that use the O(φ) result to predict the dynamic mobility in concentrated suspensions, and at high frequencies these approximations are shown to give results qualitatively different from those of recent cell models. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Fibromyalgia: can one distinguish it from simulation? An observer-blind controlled study.

OBJECTIVE: A randomized controlled trial was conducted to assess reliability and accuracy in identification of fibromyalgia (FM), motivated simulation, and normal controls. METHODS: Eight female subjects with chronic FM were age matched with 19 healthy female volunteers. The volunteers were randomized to a financially motivated "simulator" group who were paid to simulate FM, or to a "normal control" group. Examiners under blinded conditions rated tender and control points, and illness behavior. Intraclass correlation coefficients and F values showed that counts of tender points significantly discriminated the 3 groups. Variance was mostly due to experimental groups and not to observer or error factors. In this study, simulators could not be discriminated from normals or FM subjects on the basis of tenderness at "control points." Examiner ratings of illness behavior (UAB), and subjects' self-ratings for pain showed that FM subjects had the highest scores, normals the lowest, and simulators had mean scores midway between the mean FM and simulator. On grip strength, the normals obtained the highest scores, the simulators the lowest, and the FM subjects had scores midway between those of the other 2 groups. Diagnostic accuracy of the blinded examiners in distinguishing FM from simulators and from normals was 80%, and for correct diagnosis the kappa value was significant at 0.69. Despite this, simulators were misidentified as FM in 1/3 of judgments, and FM was misidentified as simulators in 1/5 of judgments. CONCLUSION: Under randomized blinded conditions, examiners using the American College of Rheumatology criteria for FM and other bedside observations are able to distinguish chronic FM, normal individuals, and motivated simulators with 80% accuracy, with a good level of agreement and reliability in tender point counts. Our results do not provide a "test for malingering," and it is likely that an important minority of motivated simulators and of FM subjects will be misidentified.

Adult↗
PubMed1999

Surface Electrical Properties of Polystyrene Latex.

A polystyrene latex suspended in HCl has been studied by dielectric response and dynamic mobility measurements. The aim was to see if these data, along with previous results from other techniques, could be interpreted in a consistent way within the standard electrokinetic model to yield information about the surface electrical properties of the latex. It was found that the zeta-potentials deduced from dynamic mobility and conductivity measurements were reasonably consistent, but did not agree well with those deduced from the electrophoretic mobility. The use of a dynamic Stern layer did not improve the agreement to any great extent. It is conjectured that differences in the methods of preparation, in particular the use of centrifugation, may be responsible for some of the disagreement. The pH-dependence of the dynamic mobility was also investigated and found to be weak. The dielectric response measurements showed significant discrepancies from the predictions of the standard electrokinetic model in the kHz regime, and the dynamic Stern layer model with realistic parameters could not improve the agreement very much. However the experimental relaxation frequencies were in good agreement with the predictions of the theory. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Compression of a polymer chain by a small obstacle: the effect of fluctuations on the escape transition.

We describe the escape transition of an ideal chain compressed between finite-sized obstacles. Three different theoretical methods are used and each provides a similar description of the escape transition, as predicted by earlier and less detailed mean-field theories. The first two methods show that thermal fluctuations near the transition can blur what was previously described as a sharp transition. The last method is an exact calculation of the partition function that shows unambiguously the character of the escape transition. This exact calculation overcomes the inherent uncertainties associated with previous theory and computer simulation.

Journal Article↗
PubMed1997

Boundary Effects on Electrophoretic Motion of Spherical Particles for Thick Double Layers and Low Zeta Potential

The electrophoretic motion of a charged sphere in the presence of a rigid boundary is analyzed for low surface zeta potentials but arbitrary kappaa, where a is the particle radius and kappa is the inverse Debye length. The boundary configurations considered are a single flat wall, a slit, and a long cylindrical tube. Using a method of reflections, we obtain the particle velocity for a constant applied electric field in powers of lambda up to O(lambda6), where lambda is the ratio of the particle radius to the distance from the boundary. This analysis is valid as long as the double layer around the particle does not overlap significantly with the double layer at the boundary. The effect of finite kappaa is to enhance the viscous retardation of the particle, although for large separations the first effect due to the proximity of the boundary is still at O(lambda3) in all cases. When the applied field is parallel to the boundary, the electrophoretic velocity is not proportional to the difference in zeta potential between the particle and the boundary (as occurs for kappaa --> infinity), and the proximity of the boundary may increase the particle velocity or change its direction. An important result of the analysis is that the hindrance to the electrophoretic velocity of a particle in a cylindrical pore increases significantly as kappaa is reduced below 10.

Journal Article↗
PubMed1997

Electrophoretic Mobility of a Semi-dilute Suspension of Spherical Particles with Thick Double Layers and Low Zeta Potentials

The electrophoretic mobilities of two spherical particles are analyzed for the case where the electrical double layer is no longer thin with respect to the particle sizes, but the zeta potentials on the particles are low. Using a method of reflections, we obtain the mobilities as a power series in 1/r12 up to O(r-1012) (where r12 is the center-to-center separation of the spheres), with the proviso that the double layers on the two particles do not overlap. Unlike the case of thin double layers, there is now a nonzero interaction between identical particles. The first term in the interaction is O(r-312), but the coefficient becomes large for thick double layers. An expression for the average mobility of a mildly polydisperse suspension of spheres with thick double layers is then derived correct to first order in the volume fraction of the spheres. The results of the reflection calculation are then used to obtain an approximate evaluation of this expression. It is found that the first order effect for thick double layers is significantly larger than it is for thin double layers, and that the average effect of polydispersity in size or surface potential is weak unless the double layers are quite thick. For a monodisperse suspension, an expression is obtained for the mean square deviation of the particle velocity from the mean velocity. An approximate evaluation of this expression using the reflection results shows that the magnitude of the mean square fluctuations in the direction of the applied field can be significantly larger than that in the transverse direction.

Journal Article↗
PubMed1995

Prospective evaluation of a composite scoring system for mammographically detected cytologically assessed impalpable breast abnormalities.

The aim of all breast screening programmes is a reduction in deaths from the disease. It is hoped that this can be achieved with minimal intervention in the patient cohort who do not have cancer. In this study we have assessed the efficacy of a combination of mammographic and cytological scoring systems in the evaluation of 208 women with screen-detected non-palpable breast lesions. All mammograms were scored 1-5 and those with a score of 3 or more required needle localization. A cytology score of 1 to 5 was generated for each patient according to a similar system and an aggregate score for each patient was achieved by the addition of the mammographic and cytology score. Ninety-three of the 208 patients had malignancy--the positive predictive value for mammography alone in this series was 45%. All 58 patients who had an aggregate score of 8 or greater had cancer. The 60 patients who had an aggregate score of 4 had benign disease on excision biopsy. We suggest that a 'wait and repeat mammogram' approach is appropriate in patients with grade 3 mammography and benign (grade 1) cytology. Patients with an intermediate aggregate score of 5-7 should have an excision biopsy and those with an aggregate score of 8 could have definitive surgery rather than excision biopsy. Application of this aggregate scoring technique would enhance the delivery of more appropriate surgery to a majority of patients with screen-detected breast abnormalities.

Biopsy↗
PubMed1994

Stereotactic cytology in a regional breast-screening programme.

Stereotactic localization and fine-needle aspiration are new procedures for the management of non-palpable mammographic abnormalities. In this prospective study, stereotactically guided cytology with immediate reporting was performed before biopsy in a consecutive series of 166 patients with screen-detected non-palpable abnormalities. All specimens were obtained by multiple stereotactically guided passes with a 22-G Franzén needle and graded as: 1, acellular or inadequate; 2, benign; 3, atypical, probably benign; 4, probably malignant; or 5, malignant. After definitive surgery all tumours were staged according to the Union Internacional Contra la Cancrum classification. Of 71 patients with malignancy, 56 were correctly diagnosed by cytology before operation. Twelve patients with malignancy had grade 1 cytology and 50 of the 52 with grade 2 cytology had benign disease. This study confirms that stereotactic cytology is a valuable diagnostic test in a breast-screening programme.

Aged↗
PubMed1994

The NHS R&D Information Systems Strategy (ISS).

Following a strategy study which reported in August 1992 the NHS R&D Information Systems Strategy (ISS), a strategic framework for information systems, has been developed to support research and development in the NHS. This paper summarizes its main features, illustrates the benefits which specific information systems will bring, and outlines how the products of the programme are disseminated and accessed.

Cost-Benefit Analysis↗
PubMed1991

Management of reflux oesophagitis: role of weight loss and cimetidine.

A double blind clinical trial was performed to evaluate the effect of weight loss and cimetidine in the treatment of reflux oesophagitis. Thirty-two patients were evaluated by endoscopy, L.O.S.P. determination, oesophageal scintigraphy and ambulatory 24 hour oesophageal pH monitoring. Patients were randomly allocated into treatment using a regimen of placebo/weight loss or cimetidine/weight loss. Assessments were repeated after 8-12 weeks. A similar weight loss and improvement in symptoms and endoscopy appearances was seen in both groups. In contrast there was no significant change in frequency or duration of reflux on 24-hour pH monitoring or oesophageal scintigraphy or L.O.S.P. We conclude that weight loss may have an important role in the treatment of reflux oesophagitis and should be recommended to patients as an early therapeutic intervention. Cimetidine did not confer any additional benefit to that obtained from weight loss alone.

Adult↗
PubMed1991

Magnetic resonance imaging in the assessment of rheumatoid arthritis--a comparison with plain film radiographs.

Conventional radiography lacks sensitivity in early rheumatoid disease. MRI with its advantages of soft tissue discrimination and multiplanar imaging facility might detect earlier disease. This study compares the MR images and conventional radiographs of 11 rheumatoid patients' wrists and carpi. In all cases, erosions were more extensive and numerous on the MR images compared to plain radiographs. MR is useful in detecting early aggressive disease and in monitoring the response to treatments.

Adult↗
PubMed1990

Rewarding medical teaching excellence in a major Canadian teaching hospital.

A major Canadian teaching hospital has developed a program to recognize and reward excellence in medical education. The program includes a system to collect and evaluate feedback from trainees and administrators--with an annual celebration event where awards are presented. Three categories of hospital-wide awards are presented: educational administration, program development, and extraordinary contribution. There are departmental awards for best undergraduate and postgraduate physicians, allied health professional, and house staff/fellow. This program functioned well to evaluate teachers across departments and for all levels of trainees in the hospital and will expand to become part of the ongoing evaluation of teachers in the institution.

Awards and Prizes↗
PubMed1990

The prevalence of cyclothymia in borderline personality disorder.

Sixty patients with personality disorders were evaluated by several different diagnostic instruments to determine the prevalence of cyclothymia in borderline personality disorder (BPD) and in other personality disorders (OPD). Cyclothymia occurred more frequently in BPD than in OPD, regardless of which diagnostic system was used. In contrast, the prevalence of major, minor, and intermittent depression, hypomania, and bipolar disorder was not significantly different in BPD as compared with OPD. Cyclothymic borderlines and noncyclothymic borderlines could not be distinguished on behavioral or functional measures. These results have implications for the diagnostic validity of both BPD and cyclothymia.

Adult↗
PubMed1989

Models of state funding for mental health research.

Twenty-eight of 49 states that responded to a survey supported mental health or substance abuse research through at least one of four funding mechanisms--the joint state-university research unit, research grants, state in-house research, and contracts. The authors illustrate the use of these mechanisms with examples from the states. The events leading to the establishment of the new Oklahoma Mental Health Research Institute are described.

Academic Medical Centers↗
PubMed1989

Depression in self-harm patients.

DSM-III diagnoses and responses to the Beck Depression Inventory (BDI) were examined in 71 consecutive admissions to an in-patient psychiatric crisis service following deliberate self-harm. Although 80% of the admitted patients were moderately or severely depressed according to BDI scores, only 31% were diagnosed with a major depressive episode. While all of the self-harm patients may be viewed as experiencing severe subjective distress, only a minority were shown to suffer from DSM-III depressive illness. The high depression scores on the BDI may be related to the patients' extreme distress preceding a crisis admission and to the high prevalence of personality disorders in this group of patients.

Adolescent↗