Publications

In clinical notes, physicians commonly describe reasons why certain treatments are given. However, this information is not typically available in a computable form. We describe a supervised learning system that is able to predict whether or not a treatment relation exists between any two medical concepts mentioned in clinical notes. To train our prediction model, we manually annotated 958 treatment relations in sentences selected from 6,864 discharge summaries. The features used to indicate the existence of a treatment relation between two medical concepts consisted of lexical and semantic information associated with the two concepts as well as information derived from the MEDication Indication (MEDI) resource and SemRep. The best F1-measure results of our supervised learning system (84.90) were significantly better than the F1-measure results achieved by SemRep (72.34).

: The objective of this research effort is to construct a purely theoretical foundation for the phenomenon of turbulent heat transfer. In this first annual report, the current methodology of theoretical research is reexamined critically. The report outlines in three self-standing units (papers) the new theoretical viewpoint that turbulence is the result of inviscid flow buckling. This viewpoint leads to first examples of theoretical prediction of turbulence parameters, for instance, the transition to turbulence, the flapping motion of turbulent jets, the frequency of vortex shedding and the meandering and mixing mechanism of thermal plumes. (Author)

This paper documents the convection heat transfer enhancement effect that is associated with the periodic (timewise and spatial) longitudinal stretching of an infinite plane wall bathed by a semi-infinite fluid reservoir. It is shown that the flow field reaches a truly periodic state, and that the temperature field does not. The timedependent heat transfer rate is greater than the classical pure-diffusion limit only when the Reynolds number based on wall speed and wavelength is greater than 1. The enhancement effect becomes pronounced as Re increases above 10. The enhancement effect increases also as the Prandtl number increases, provided Re is greater than 1. The same conclusions apply in the case of convective mass transfer, when a concentration difference is maintained between the flexible wall and the ambient fluid.

This study documents the pressure drop and heat transfer through bundles of parallel cylinders in a domain that has been overlooked, namely, low Reynolds numbers, arrays that are long in the direction of flow such that the flow is hydraulically and thermally fully developed, and cylinders inclined relative to the flow direction. The numerical results cover the range 1 ≤ ReD ≤ 30, 0.72 ≤ Pr ≤ 100, 0.6 ≤ φ ≤ 0.95 and 0° ≤ β ≤ 60°, where φ is the porosity of the bundle as a saturated porous medium, and β is the angle between the verified by means of experimental measurements of the pressure drop across a bundle with 115 cylinders in the flow direction, in the range 8 < ReD < 50, 0.84 ≤ φ ≤ 0.92 and 0° ≤ β ≤ 60°. The results show that significant errrors may occur if the available large-ReD information is extrapolated to the domain covered by this study.

No abstract is provided for this article.

The heat transfer across the air boundary layer that descends along a vertical ice slab causes melting at the surface.

Thermodynamics is a discipline, with unambiguous concepts, words, laws and usefulness. Today it is in danger of becoming a Tower of Babel. Its key words are being pasted brazenly on new concepts, to promote them with no respect for their proper meaning. In this brief Perspective, I outline a few steps to correct our difficult situation.

The aeroelastic flight envelops of flying wing aircraft can be extended with a better flow of stresses in the structure. In the present study, we investigate the effect of cross-section configuration on the stress distribution and aeroelastic behavior of a flying wing aircraft. We invoke the constructal law and the principle; the prevention of stress strangulation leads to a wing design associated with the most stable and lightest structure. We used three computer programs Gmsh, VABS (Variational Asymptotic Beam Sectional Analysis), and NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft) to study stress distribution and stability of the flying wing aircraft. The results indicate that different wing cross-section designs affect stress distribution as well as the aeroelastic stability of the aircraft. Furthermore, the design with less stress strangulation is associated with a higher flutter speed structure.

This paper describes a two-part study of the time-dependent melting of an enclosed phase- change material heated at a constant rate from the side. The first part describes experimental measurements with n-octadeoane conducted in a 74 cm tall enclosure. The heat flux Rayleigh numbers of these experiments are of the order of lo, and the liquid flow pattern is weakly turbulent. The second part of the study describes the liquid-superheat effect analytically, by means of a 'matched boundary layers' solution for the convection regime of the heat transfer and melting process. The predicted overall Nusselt number relation- ship agrees very well with the empirical correlation based on experiments. THIS PAPER describes a two-part study of the process of melting in the presence of natural convection in an enclosure that is being heated at a constant rate. The general subject of natural convection melting in enclosures has received considerable attention, because of its applicability in areas such as thermal energy storage, metallurgy, manufacturing and geo- physics. The existing work, however, is primarily based on the model in which the heating effect is provided by an isothermal side wall the temperature of which remains fixed in time (see, e.g. the two reviews by Viskanta (l, 21). The constant-rate heating mode deserves to be studied because it can serve as a good model for the operation of latent-heat storage devices for solar energy. The first part of the paper (Section 2) describes a series of laboratory experiments conducted in a con- siderably taller enclosure than in the existing exper- imental studies, that is, at high Rayleigh numbers where the flow shows signs of turbulence. The second part of the study consists of a compact boundary layer analysis of the convection-dominated regime. Therefore, in addition to the new focus on the con- stant-rate heating mode, two additional objectives of this study are to extend the high Rayleigh number domain experimentally (Section 2), and to document analytically the effect of liquid superheat in the con- vection regime (Section 3).

In this chapter we discuss a series of developments that point in the direction of applying porous media concepts to the description, simulation, and optimization of compact systems with complex flow structures. Compact and miniaturized heat exchangers are primary...

Objective To evaluate the contribution of the MEDication Indication (MEDI) resource and SemRep for identifying treatment relations in clinical text. Materials and methods We first processed clinical documents with SemRep to extract the Unified Medical Language System (UMLS) concepts and the treatment relations between them. Then, we incorporated MEDI into a simple algorithm that identifies treatment relations between two concepts if they match a medication-indication pair in this resource. For a better coverage, we expanded MEDI using ontology relationships from RxNorm and UMLS Metathesaurus. We also developed two ensemble methods, which combined the predictions of SemRep and the MEDI algorithm. We evaluated our selected methods on two datasets, a Vanderbilt corpus of 6864 discharge summaries and the 2010 Informatics for Integrating Biology and the Bedside (i2b2)/Veteran's Affairs (VA) challenge dataset. Results The Vanderbilt dataset included 958 manually annotated treatment relations. A double annotation was performed on 25% of relations with high agreement (Cohen's κ = 0.86). The evaluation consisted of comparing the manual annotated relations with the relations identified by SemRep, the MEDI algorithm, and the two ensemble methods. On the first dataset, the best F1-measure results achieved by the MEDI algorithm and the union of the two resources (78.7 and 80, respectively) were significantly higher than the SemRep results (72.3). On the second dataset, the MEDI algorithm achieved better precision and significantly lower recall values than the best system in the i2b2 challenge. The two systems obtained comparable F1-measure values on the subset of i2b2 relations with both arguments in MEDI. Conclusions Both SemRep and MEDI can be used to extract treatment relations from clinical text. Knowledge-based extraction with MEDI outperformed use of SemRep alone, but superior performance was achieved by integrating both systems. The integration of knowledge-based resources such as MEDI into information extraction systems such as SemRep and the i2b2 relation extractors may improve treatment relation extraction from clinical text.

Tree-shaped networks are now being considered as small-scale architectures for high-densities in electronics cooling and fuel cells design. This paper documents the optimization of tree-shaped inserts of high thermal conductivity. The new feature is the presence of loops in the tree canopy. Every feature of the tree-with-loops architecture is optimized numerically. Two classes of trees with loops are considered: loops with one size, and loops with two sizes. The performance of trees with loops is compared with that of trees without loops and designs with purely radial inserts. It is shown that dendrites and loops are features that become attractive as scales decrease and complexity increases. In the same direction, the robustness of tree-with-loops architectures increases.

No abstract is provided for this article.

This paper illustrates the method of evolutionary design with freedom by considering the problem of determining the distribution of the thickness of a high-conductivity layer (heat spreader) installed on a conducting wall. Heating comes from a steady line source imposed at t = 0. Heat spreads in time-dependent fashion in two directions: longitudinally by conduction along the layer and the wall, and transversally by conduction through the wall and then by convection into the flow that cools the other side of the wall. The heat spreading has two regimes, which are dictated by the two diffusion time scales along the layer and across the wall. It is shown that the solution to the optimal heat spreader thickness problem is the parabolic profile, and it is the same in both regimes of time-dependent conduction.

This lecture reviews a relatively recent body of heat transfer work that bases on a deterministic (constructal) principle the occurrence of geometric form in systems with internal flows. The same principle of global optimization subject to constraints allow us to anticipate the natural (animate and inanimate) flow architectures that surround us. The lecture starts with the example of the optimal spatial distribution of material (e.g., heat exchanger equipment) in power plants. Similarly, void space can be allocated optimally to construct flow channels in the volume occupied by a heat generating system. The lecture continues with the optimization of the path for heat flow between a volume and one point. It shows that when the heat flow can choose between at least two paths, low conductivity versus high conductivity, the optimal flow structure for minimal global resistance in steady flow is a tree. Nearly the same tree is deduced by minimizing the time of discharge in the flow from a volume to one point. Analogous tree-shaped flows are constructed in pure fluid flows, and in flow through a heterogeneous porous medium. The optimization of trees that combine heat transfer and fluid flow is illustrated by means of two-dimensional trees of plate fins. The method is extended to the superposition of two fluid trees in counterflow, as in vascularized tissues under the skin. The two trees in counterflow are one tree of convective heat currents that effect the loss of body heat. It is shown that the optimized geometry of the tree is responsible for the proportionalities between body heat loss and body size raised to the power 3/4, and between breathing time and body size raised to the power 1/4. The optimized structures are robust with respect to changes in some of the externally specified parameters. When more degrees-of-freedom are allowed, the optimized structure looks more natural. The lecture outlines a unique opportunity for engineers to venture beyond their discipline, and to construct an engineering theory on the origin and workings of naturally organized systems. [S0022-1481(00)02403-8]

This paper shows that the dendritic patterns formed by low-resistance channels in a river drainage basin are reproducible and can be deduced from a single principle that acts at every step in the development of the pattern: the constrained minimization of global resistance in area-to-point flow. The river basin is modeled as a two-dimensional territory with Darcy flow through a saturated heterogeneous porous medium with uniform flow addition per unit area. From one step to the next, small elements of the porous medium are dislodged and removed in ways that minimize the global flow resistance. The removed elements are replaced by channels with lower flow resistance. The channels form a dendritic pattern that is deterministic, not random. The finest details of this structure are sensitive to internal properties and external forcing, i.e. variations in the local properties of the flow medium, and the manner in which the total area-to-point flow rate varies as the structure develops. Remarkably insensitive to such effects are the basic type and rough size of the flow structure (channels versus no channels, dendrite, number of branches) and the minimized global resistance to flow.

The paper presents a theoretical and experimental study of natural convection in a horizontal cavity which communicates laterally with a large reservoir. The cavity walls and the reservoir are at different temperatures. It is shown theoretically that the flow consists of a horizontal counterflow which penetrates the cavity over a distinct length. The penetration length is shown to be proportional to the cavity height and to the square root of the Rayleigh number based on cavity height and cavity-reservoir temperature difference. The validity of the theory is demonstrated on the basis of a flow visualization experiment. It is shown also that the Nusselt number for cavity-reservoir heat exchange is proportional to the square root of the Rayleigh number, and is relatively insensitive to the Prandtl number in the Pr range 0·7 to ∞. The energy-engineering applications of the lateral penetration flow are discussed.