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PubMed2003

[Questions about questions: cognitive survey of questionnaire development].

OBJECTIVES: Traditional pretests are used in the development of survey items to identify technical and comprehension problems. Cognitive processes involved in answering survey questions are not the object of this kind of test. METHODS: Cognitive survey methods were used here to test a questionnaire screening for rehabilitation needs in people suffering from back pain. Essential techniques of cognitive testing (think-aloud, probing, confidence ratings) are outlined. We applied these techniques to 20 patients suffering from either acute or chronic back pain in order to test the survey. RESULTS: The main goal, i.e., identifying problems in item formulation by means of cognitive testing, was achieved. Almost one third of the survey questions were rephrased according to the results of the study. Some of the improvements of the questionnaire are illustrated. CONCLUSIONS: The increased effort required to perform cognitive testing as compared to traditional pretesting pays off. The two methods have specific pros and cons and cannot replace one another.

Adult↗

PubMed2007

Optimal planar flow network designs for tissue engineered constructs with built-in vasculature.

Convective delivery of nutrients is important to enhance mass transport within tissue engineered (TE) products. Depending on the target tissue, an ideal TE product will have an integrated microvasculature that will eliminate mass transport limitations that can occur during product growth in vitro and integration in vivo. A synthetic approach to develop microvasculature involves development of network designs with efficient mass transfer characteristics. In this paper, utilizing a planar bifurcating network as a basis, we develop an approach to design optimal flow networks that have maximum mass transport efficiency for a given pressure drop. We formulated the optimization problem for a TE skin product, incorporating two types of duct flow, rectangular and square, and solved using a generalized reduced gradient algorithm. Under the conditions of this study, we found that rectangular ducts have superior mass transport characteristics than square ducts. Microvascular area per volume values obtained in this work are significantly greater than those reported in the literature. We discuss the effect of network variables such as porosity and generations on the optimal designs. This research forms the engineering basis for the rational development of TE products with built-in microvasculature and will pave the way to design complex flow networks with optimal mass transfer characteristics.

Microcirculation↗

PubMed2006

A network flow approach to optimizing hospital bed capacity decisions.

The delivery of cost-effective and quality hospital-based health care remains an important and ongoing challenge for the American health care industry. Despite numerous advances in medical procedures and technologies, a growing array of outpatient health care options, limits on inpatient reimbursements, and almost two decades of hospital contraction and consolidation, annual inpatient admissions in the United States are currently at levels not seen since the early 1980s. This combination of increased demand and diminished resources makes planning for hospital bed capacity a difficult problem for health care decision makers. We examine this problem by developing a network flow model that incorporates facility performance and budget constraints to determine optimal hospital bed capacity over a finite planning horizon. Under modest assumptions, we demonstrate that for realistic sized capacity planning problems, our network formulation is not computationally intensive, and allows us to obtain optimal bed capacity plans quickly.

Decision Making, Organizational↗

PubMed1995

Assessment of hypochondriasis.

This article gives a detailed description of the assessment of hypochondriasis. Other conditions are described in which this type of assessment can be useful. The aims of assessment are outlined, followed by a full description of the information that should be obtained, and methods of assessment used. Information gained at assessment is used to construct a cognitive-behavioural formulation of the problem, emphasising aetiological and maintaining factors, which then can be modified during treatment. Other important aspects of assessment include overcoming problems in the therapeutic relationship, and helping the patient to accept psychological treatment. Other practical difficulties in assessment are described, and some solutions are offered.

Behavior Therapy↗

PubMed1989

Application of the general linear model for smoothing gas exchange data.

The precision of an interpretation of gas exchange records in progressive exercise is limited by the typical breath-to-breath variation in the data. Recently, two procedures have been proposed for minimizing the "noise" in the estimates of alveolar gas exchange time series data. One approach utilizes an estimate of pulmonary blood flow (Q) for smoothing purposes. The other approach utilizes an estimate of effective lung volume (V'L) for smoothing purposes. In this paper, we formulate the smoothing problem as a general linear model and demonstrate the concurrent estimates of both V'L and Q. Furthermore, we investigate the interaction between V'L and Q. Specifically, when a high value of lung volume is used (such as the subject's resting functional residual capacity) in the alveolar gas exchange algorithm, the estimate of Q is biased low and the result is a less effective smoothing of the data. In addition, we demonstrate how the Q estimate can be improved by utilizing more appropriate estimates of arterial carbon dioxide tension.

Algorithms↗

PubMed1978

Survival after right radical nephrectomy and resection of suprarenal vena cava.

The problems relating to injury and the resection of the suprarenal vena cava during a right nephrectomy may well confront every urologic surgeon. Although such a procedure is compatible with survival, postoperative temporary renal dysfunction may occur and a plan to deal with this problem should be formulated.

Adenocarcinoma, Papillary↗

PubMed1989

International migration and real wages: is there any neo-classical ambiguity?

"Recent research has shown that while labor emigration increases the nominal wage rate, the impact on the real wage rate remains quite ambiguous. The present paper reexamines the issue under the standard two-factor, two-commodity international trade model normally employed for this purpose. The principal finding of this paper is that once the problem is correctly formulated and analyzed, introducing utility-maximizing consumers, no such ambiguity exists. Indeed, labor emigration always leads to an increase in the welfare (real wage) of labor in the source country."

Demography↗

PubMed1989

The application of the maximum entropy method to electron microscopic tomography.

The maximum entropy method has been applied to single axis tilt electron microscopic tomography. Its application requires that the problem be correctly formulated and that the model for the noise in electron micrographs be developed. A suitable noise model was determined empirically. The maximum entropy method was applied to a reconstruction of a test object from projections to which noise had been added. These reconstructions were superior to those obtained by reciprocal space weighted back protection. The method was also robust towards the incorrect specification of the noise, the penalty being an increase in the time required for convergence rather than degradation of the quality of the reconstructed image. In the reconstruction of negatively stained chromatin fibres it was possible to obtain satisfactory images utilizing all the information in the projections, in contrast to conventional methods in which high resolution data are removed by the application of Fourier space filters.

Algorithms↗

PubMed1989

A patient with new Q waves: methods for decision making in the individual patient.

Decision analysis, an analytic approach to making decisions when uncertainty is present, has its foundation in probability and utility theory. It provides insights into the trade-offs that are involved when a selection must be made among patient management strategies. In general, several broad steps are involved. The process begins by formulating the clinical problem as a well focused choice among a limited set of clinical etiologies. These strategies are then structured explicitly in a model that depicts the clinical events that may ensue from each option. By assigning probability values to each outcome, the weighted average outcome or expected utility can be calculated for each alternative strategy. The strategy with the highest expected utility is the optimal one. The methods of decision analysis offer a number of distinct advantages. These include: 1) providing a structure with which to simplify and focus clinical dilemmas; 2) providing a forum for discussing clinical reasoning; and 3) developing a consensus among groups of decision makers.

Aged↗

PubMed1991

Culture media for postimplantation embryos.

The search for an effective culture medium for postimplantation mammalian embryos is considered from two viewpoints: identification of the medium that gives the best development in culture and of the problems associated with formulating a fully defined medium for such embryos. The types of media that have been applied to the culture of mammalian embryos are reviewed and their effectiveness assessed. At present, the media that support the best development of explanted embryos are composed partly or wholly of heat-activated rat serum, prepared by centrifugation of blood immediately after withdrawal from the donor. Experimental approaches to elaborating fully defined media are considered, and progress with identifying the nutrient requirements of postimplantation mammalian embryos in culture is reviewed. Particular attention is given to the use of extensively dialysed serum which, when supplemented with glucose, amino acids, and vitamins, supports good development of midgestation rodent embryos in vitro.

Animals↗

PubMed2005

Electrostatics of heterogeneous monolayers. Constitutive equations and mathematical models.

A new approach for modelling the electrochemistry of complex heterogeneous systems, composed of various bulk, surface and line phases, is proposed. A key step in it is the generalization of standard electrostatic boundary conditions, considered as 2D, 1D Poisson-Boltzmann equations. This viewpoint is applied to experimentally studied systems of two co-existing (e.g. liquid expanded, liquid condensed) monolayer phases. Another important feature of the given model is that, at electrochemical equilibrium, like with bulk double layers, surface double layers emerge on both sides of the contact line dividing the surface phases. A general mathematical formulation of the problem is proposed in respect of the electric potential as distributed in the complex heterogeneous system. Comments are also provided on the methods of solving the problem. The example illustrates a simplified system of two semi-infinite surface phases (monolayers) having equivalent parameters and divided by a contact line. The paper discusses the expressions obtained for the electrical potential, electrostatic energy, etc. and their dependence on the parameters of the system. Special focus is taken of the work of contact line formation.

Colloids↗

PubMed2005

Preparation and characterization of nanocrystals for solubility and dissolution rate enhancement of nifedipine.

Poorly water-soluble drugs such as nifedipine (NIF) (approximately 20 microg/ml) offer challenging problems in drug formulation as poor solubility is generally associated to poor dissolution characteristics and thus to poor oral bioavailability. In order to enhance these characteristics, preparation of nifedipine nanoparticles has been achieved using high pressure homogenization. The homogenization procedure has first been optimized in regard to particle size and size distribution. Nanoparticles were characterized in terms of size, morphology and redispersion characteristics following water-removal. Saturation solubility and dissolution characteristics were investigated and compared to the un-milled commercial NIF to verify the theoretical hypothesis on the benefit of increased surface area. Crystalline state evaluation before and following particle size reduction was also conducted through differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) to denote eventual transformation to amorphous state during the homogenization process. Through this study, it has been shown that initial crystalline state is maintained following particle size reduction and that the dissolution characteristics of nifedipine nanoparticles were significantly increased in regards to the commercial product. The method being simple and easily scaled up, this approach should have a general applicability to many poorly water-soluble drug entities.

Calcium Channel Blockers↗

PubMed2006

A robust approach for iterative contaminant source location and release history recovery.

Contamination source identification is a crucial step in environmental remediation. The exact contaminant source locations and release histories are often unknown due to lack of records and therefore must be identified through inversion. Coupled source location and release history identification is a complex nonlinear optimization problem. Existing strategies for contaminant source identification have important practical limitations. In many studies, analytical solutions for point sources are used; the problem is often formulated and solved via nonlinear optimization; and model uncertainty is seldom considered. In practice, model uncertainty can be significant because of the uncertainty in model structure and parameters, and the error in numerical solutions. An inaccurate model can lead to erroneous inversion of contaminant sources. In this work, a constrained robust least squares (CRLS) estimator is combined with a branch-and-bound global optimization solver for iteratively identifying source release histories and source locations. CRLS is used for source release history recovery and the global optimization solver is used for location search. CRLS is a robust estimator that was developed to incorporate directly a modeler's prior knowledge of model uncertainty and measurement error. The robustness of CRLS is essential for systems that are ill-conditioned. Because of this decoupling, the total solution time can be reduced significantly. Our numerical experiments show that the combination of CRLS with the global optimization solver achieved better performance than the combination of a non-robust estimator, i.e., the nonnegative least squares (NNLS) method, with the same solver.

Environmental Restoration and Remediation↗

PubMed2004

Preparing the older adult for surgery and anesthesia.

Life expectancy in the United States has increased significantly over the past 100 years. It has been suggested that by the year 2050, approximately 20% of the population may be over the age of 65. Many of these older adults will undergo surgery and anesthesia. Preadmission testing nurses need to be able to deal with the various challenges that accompany this group of patients. While many of the elderly are quite active, there are others with multiple disease processes that put them at an increased risk over the general population. It will be to the advantage of all involved if health care providers can develop a better understanding and an increased expertise in caring for the geriatric surgical patient. This article describes the importance of the preanesthetic nursing assessment and evaluation in helping to identify potential problems so that a plan of care to prevent those problems can be formulated and communicated to other members of the health care team.

Age Factors↗

PubMedDate not supplied

Maplets for correspondence-based object recognition.

We present a correspondence-based system for visual object recognition with invariance to position, orientation, scale and deformation. The system is intermediate between high- and low-dimensional representations of correspondences. The essence of the approach is based on higher-order links, called here maplets, which are specific to narrow ranges of mapping parameters (position, scale and orientation), which interact cooperatively with each other, and which are assumed to be formed by learning. While being based on dynamic links, the system overcomes previous problems with that formulation in terms of speed of convergence and range of allowed variation. We perform face recognition experiments, comparing ours to other published systems. We see our work as a step towards a reformulation of neural dynamics that includes rapid network self-organization as essential aspect of brain state organization.

Artificial Intelligence↗

PubMed2000

Coupling of hydrodynamic and electric interactions in adsorption of colloidal particles.

The role of the coupling between hydrodynamic and electric interactions in adsorption of colloid particles is reviewed. First the general formulation of the problem of fluid motion connected with the macroscopic suspension flow as well as microscopic particle motion is presented together with the general description of the colloid particle adsorption. Then two limiting cases are considered: motion of uncharged particles and electric interactions of stationary particles. The theoretical consideration are supported by illustrative experimental results. Next the electrokinetic effects in particle adsorption process are considered and the theoretical background for the description of these effects is given. The effect of the electroviscous drag on the particle aggregation and adsorption kinetics is discussed. Also the electrokinetic lift force, which is an example of the non-linear electrokinetic effect, is considered and the possible implications on particle adsorption are examined. In the following part of the review the influence of electro-hydrodynamic coupling on the particle transport to the interface is considered. First the 'inverse salt effect' for the initial adsorption flux when the interface is not covered by adsorbed particles is examined. Then, the electro-hydrodynamic scattering effect which occurs when the interface is partially covered by particles is considered and its experimental evidence concerning the adsorption kinetics and the local structure of adsorbate is considered. Also a novel application of the scattering effect to measure interparticle forces the 'colloid particle collider' is presented and some experimental results obtained using this technique are shown. All results reported in this review suggest strong coupling of the hydrodynamic and electric forces and their pronounced influence on colloid particle adsorption.

Adsorption↗

PubMed1965

The electrical conductance of semipermeable membranes. II. Unipolar flow, symmetric electrolytes.

A general formulation of the problem of stationary ion flow through semipermeable membranes was presented in the first paper of this series. The formalism is applied here to the evaluation of membrane conductance for the special case of unipolar ion flow between symmetric electrolytes. Thus it is assumed that the permeant ions carry one sign of charge only. Furthermore, the valences of all ions in solution on both sides of the membrane are taken to be of equal absolute magnitude. Conductance results obtained by numerical methods are presented for several representative sets of the parameters which characterize the membrane system in equilibrium. These results are discussed qualitatively with emphasis upon the contribution of particular system parameters to the non-linearities observed. Approximate analytic conductance relations, valid for high current levels, are also given.

Cell Membrane↗

PubMed1979

Calculation of the concentrations of free cations and cation-ligand complexes in solutions containing multiple divalent cations and ligands.

The method described permits the computation of the concentrations of free ions and ion-ligand complexes in a solution containing arbitrary numbers of divalent cations and ligands. It is required that the pH be known, along with appropriate sets of ligand-hydrogen and ligand-divalent cation concentration binding constants. It is assumed that these sets of constants are chosen to be consistent with the ionic strength of the complete solution which contains the divalent cations and ligands. The technique is an iterative one which provides upper and lower bounds for the values of the unknowns. The method does not require initial guesses at the values of the unknowns, and it gives correct answers even when the concentrations involved are many orders of magnitude apart. The present formulation of the problem is restricted to the case where only one cation can bind to a given ligand at any one time. The method is applicable to large molecules with multiple "sub-ligands" provided these sub-ligands are independent in their function as ion-binding sites. These sub-ligands need not all have the same properties. It is also shown that a simple modification of the method permits the determination of the subset of total ion concentrations that are required in order to produce a specified subset of free ion concentrations. The modifications required to include monovalent cation binding are presented in outline form.

Adenosine Triphosphate↗