Summary
We assessed the ability of a fracture liaison service (FLS) to directly reduce re-fracture risk. Having a FLS is associated with a ∼40 % reduction in the 3-year risk of major bone and ∼30 % ...of any bone re-fracture. The number needed to treat to prevent a re-fracture is 20.
Introduction
FLS have been promoted as the most effective interventions for secondary fracture prevention, and while there is evidence of increased rate of investigation and treatment at institutions with a FLS, only a few studies have considered fracture outcomes directly. We therefore sought to evaluate the ability of our FLS to reduce re-fracture risk.
Methods
Historical cohort study of all patients ≥50 years presenting over a 6-month period with a minimal trauma fracture (MTF) to the emergency departments of a tertiary hospital with a FLS, and one without a FLS. Baseline characteristics, mortality and MTFs over a 3-year follow-up were recorded.
Results
Five hundred fifteen patients at the FLS hospital and 416 patients at the non-FLS hospital were studied. Over 3 years, 63/515 (12 %) patients at the FLS hospital and 70/416 (17 %) at the non-FLS hospital had a MTF. All patients were analysed in an intention-to-treat analysis regardless of whether they were seen in the FLS follow-up clinic. Statistical analysis using Cox proportional hazard models in the presence of a competing risk of death from any cause was used. After adjustment for baseline characteristics, there was a ∼30 % reduction in rate of any re-fracture at the FLS hospital (hazard ratio (HR) 0.67, confidence interval (CI) 0.47-0.95,
p
value 0.025) and a ∼40 % reduction in major re-fractures (hip, spine, femur, pelvis or humerus) (HR 0.59, CI 0.39-0.90,
p
value 0.013).
Conclusions
We found a ∼30 % reduction in any re-fractures and a ∼40 % reduction in major re-fractures at the FLS hospital compared with a similar non-FLS hospital. The number of patients needed to treat to prevent one new fracture over 3 years is 20.
•Quick estimate of thermal conductivity was proposed for metal frame and prismatic structures.•Summation law was derived for those structures made of the same ligaments.•One-third the solidity law ...was derived for those structures identical in three coordinate directions.•Engineering applications were made to design structures with controlled thermal anisotropy.
Metal frame and prismatic cellular structures are promising candidates for compact heat exchangers and heat sinks with capability of carrying both mechanical and thermal loads. Useful formulas and corresponding laws were analytically derived for quickly estimating the individual effective thermal conductivity components of these structures. Such effective thermal conductivity estimates were made for metal foam structures, cubic cell structures, octet-truss structures, tetrakaidecahedron structures and various architectures of prismatic cellular honeycomb. The estimated values are found to agree well with existing experimental data and those obtained from exhaustive numerical computations. These formulas and laws enable us to design the structures with directionally controlled thermal conductivity, which is quite advantageous for maintaining an optimum temperature range and a uniform temperature distribution in thermal engineering applications such as in electric vehicles, batteries and HVAC industries.
ABSTRACT
Terrestrial planets covered globally with thick oceans (termed ocean planets) in the habitable zone were previously inferred to have extremely hot climates in most cases. This is because H2O ...high-pressure (HP) ice on the seafloor prevents chemical weathering and, thus, removal of atmospheric CO2. Previous studies, however, ignored melting of the HP ice and horizontal variation in heat flux from oceanic crusts. Here, we examine whether high heat fluxes near the mid-ocean ridge melt the HP ice and thereby remove atmospheric CO2. We develop integrated climate models of an Earth-size ocean planet with plate tectonics for different ocean masses, which include the effects of HP ice melting, seafloor weathering, and the carbonate–silicate geochemical carbon cycle. We find that the heat flux near the mid-ocean ridge is high enough to melt the ice, enabling seafloor weathering. In contrast to the previous theoretical prediction, we show that climates of terrestrial planets with massive oceans lapse into extremely cold ones (or snowball states) with CO2-poor atmospheres. Such extremely cold climates are achieved mainly because the HP ice melting fixes seafloor temperature at the melting temperature, thereby keeping a high weathering flux regardless of surface temperature. We estimate that ocean planets with oceans several tens of the Earth’s ocean mass no longer maintain temperate climates. These results suggest that terrestrial planets with extremely cold climates exist even in the habitable zone beyond the Solar system, given the frequency of water-rich planets predicted by planet formation theories.
•An L.T.N.E. integral analysis was made for the thermal entry problem in porous media.•An entire development was captured accounting for both solid and fluid thermal boundary layers.•A set of ...algebraic expressions was derived for accurate estimation of local Nusselt number.•Three distinctive regions, entrance, transition and nearly fully developed regions, were identified.•A region map was constructed, for the first time, to identify the locations of transition from one region to another.
An integral solution procedure has been developed to describe the entire evolution of the thermal boundary layer in a channel filled with a fluid-saturated porous medium. The upper and lower walls are heated under a constant heat flux condition, and local thermal nonequilibrium is assumed to apply. The development of the thermal boundary layer in this channel is divided into three distinctive regions, namely, the entrance, transition and the nearly fully-developed regions, in which separate fluid and solid phase thermal boundary layers develop near heated walls with different growth rates. In this integral analysis, each region is considered in terms of the interactions between the fluid and solid thermal boundary layers; this eventually yields a set of algebraic equations for the easy and accurate estimation of the local Nusselt number. The solutions thus obtained for the three regions are combined to reveal the entire development of the local Nusselt number from the entrance to fully-developed stage. This analytic procedure, for the first time, reveals a complete region map showing the locations of the transition from one region to another, and these depend on the Biot number, the thermal conductivity ratio and the Graetz number in a complex manner.
Effects of tortuosity and dispersion on the effective thermal conductivity of fluid-saturated porous media are investigated analytically with help of a volume averaging theory. Firstly, a general ...expression for the effective stagnant thermal conductivity has been derived using a unit cell model, which consists of rectangular solids with connecting arms in an in-line arrangement. The validity of the expression for the stagnant thermal conductivity has been confirmed comparing the present results with available experimental and theoretical data for packed beds, porous foams and wire screens. Secondly, an general expression for the thermal dispersion conductivity has been sought with help of the two energy equations for solid and fluid phases, derived on the basis of a volume averaging theory. It has been shown that the interstitial heat transfer between the solid and fluid phases is closely associated with the thermal dispersion. The resulting expressions for the longitudinal and transverse thermal dispersion conductivities agree well with available experimental data and empirical correlations.
A volume averaging theory (VAT) established in the field of fluid-saturated porous media has been successfully exploited to derive a general set of bioheat transfer equations for blood flows and its ...surrounding biological tissue. A closed set of macroscopic governing equations for both velocity and temperature fields in intra- and extravascular phases has been established, for the first time, using the theory of anisotropic porous media. Firstly, two individual macroscopic energy equations are derived for the blood flow and its surrounding tissue under the thermal non-equilibrium condition. The blood perfusion term is identified and modeled in consideration of the transvascular flow in the extravascular region, while the dispersion and interfacial heat transfer terms are modeled according to conventional porous media treatments. It is shown that the resulting two-energy equation model reduces to Pennes model, Wulff model and their modifications, under appropriate conditions. Subsequently, the two-energy equation model has been extended to the three-energy equation version, in order to account for the countercurrent heat transfer between closely spaced arteries and veins in the circulatory system and its effect on the peripheral heat transfer. This general form of three-energy equation model naturally reduces to the energy equations for the tissue, proposed by Chato, Keller and Seiler. Controversial issues on blood perfusion, dispersion and interfacial heat transfer coefficient are discussed in a rigorous mathematical manner.
An analytical consideration has been made to explore the velocity, temperature and nanoparticle distributions and heat transfer characteristics associated with thermal dispersion and nanoparticle ...mechanical dispersion within a nanofluid-saturated homogeneous metal foam. A volume-averaging theory was rigorously applied to integrate locally a set of governing equations based on the modified Buongiorno model at the pore scale. Thus, a macroscopic set of volume-averaged governing equations were derived allowing interstitial heat transfer between the nanofluid and metal phases. Unknown terms were modelled mathematically to obtain a closed set of volume-averaged governing equations. Subsequently, a pore-scale analysis was carried out to find possible functional forms for describing thermal dispersion and nanoparticle mechanical dispersion in a nanofluid-saturated metal foam. Using the resulting set of volume-averaged governing equations, forced convective flows in nanofluid-saturated metal foams were analytically investigated for the steady-state case. Eventually, it has been predicted that an unconventionally high level of the heat transfer rate (about 80 times more than the case of base fluid convection without a metal foam) may be achieved by combination of metal foam and nanofluid.
Forced convective heat transfer of nanofluids in a concentric annulus is investigated theoretically to seek possible anomalous heat transfer enhancement associated with nanofluids convection, in ...which the heat transfer rate exceeds the rate expected from the increase in thermal conductivity of nanofluids. The Buongiorno model for convective heat transfer in nanofluids was modified to fully account for the effects of nanoparticle volume fraction distribution on the continuity, momentum and energy equations. The effects of the inner to outer diameter ratio, thermal boundary conditions on the fully developed Nusselt number have been investigated. Anomalous heat transfer enhancement has been captured for the case of the heated outer wall with the inner wall insulated. This anomaly level is found higher when the inner to outer diameter ratio is smaller. The effects of Brownian and thermophoretic diffusivities ratio, bulk mean nanoparticle volume fraction and nanoparticle type on pressure gradient and Nusselt number are discussed in depth for the case of the heated outer wall with the inner wall insulated and fixed inner to outer diameter ratio ζ = 0.5. It has been found that Nusselt number has optimal bulk mean nanoparticle volume fraction value for alumina–water nanofluids, whereas it only increases monotonously with bulk mean nanoparticle volume fraction for titania–water nanofluids.
•We modeled convection of nanofluids with density variation included.•Solutions for nanofluid convective flows in concentric annuli are obtained.•Two distinctive thermal boundary conditions are examined in detail.•Anomalous heat transfer exits for the case of the heated outer wall.•The anomaly level is found higher for the smaller inner to outer diameter ratio.
According to the concept of heat transfer enhancement in the core flow, porous media with a slightly smaller diameter to a tube are developed and inserted in the core of the tube under the constant ...and uniform heat flux condition. The flow resistance and heat transfer characteristics of the air flow for laminar to fully turbulent ranges of Reynolds numbers are investigated experimentally and numerically. There are three different porous media used in the experiments with porosity of 0.951, 0.966 and 0.975, respectively. The effect of porous radius ratio on the heat transfer performance is studied in numerical simulation. Both numerical and experimental results show that the convective heat transfer is considerably enhanced by the porous inserts of an approximate diameter with the tube and the corresponding flow resistance increases in a reasonable extent especially in laminar flow. It shows that the core flow enhancement is an efficacious method for enhancing heat transfer.
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