Prediction of forced convective boiling heat transfer coefficient of pure refrigerants and binary refrigerant mixtures inside a horizontal tube

Forced convective boiling heat transfer coefficients were predicted for an annular flow inside a horizontal tube for pure refrigerants and nonazeotropic binary refrigerant mixtures. The heat transfer coefficients were calculated based on the turbulent temperature profile in liquid film and vapor core considering the composition difference in vapor and liquid phases, and the nonlinearity in mixing rules for the calculation of mixture properties. The heat transfer coefficients of pure refrigerants were estimated within a standard deviation of 14% compared with available experimental data. For nonazeotropic binary refrigerant mixtures, prediction of the heat transfer coefficients was made with a standard deviation of 18%. The heat transfer coefficients of refrigerant mixtures were lower than linearly interpolated values calculated from the heat transfer coefficients of pure refrigerants. This degradation was represented by several factors such as the difference between the liquid and the overall compositions, the conductivity ratio and the viscosity ratio of both components in refrigerant mixtures. The temperature change due to the concentration gradient was a major factor for the heat transfer degradation and the mass flux itself at the interface had a minor effect.     

Cooling characteristics on the forced convection of an array of flat-form electronic components in channel flow

Present study is concerned with forced convective heat transfer of the channel flow with line arrays of heated electronic components mounted on a printed circuit board. For the assessment of thermal performance in channel flows, three separate variables are used:channel spacing, row number of the component, and inlet air velocity. The thermal characteristics of a component due to own power and upstream air heated by components were studied. The experimental results were compared with those of numerical solution for various conditions: surface temperature of the components, adiabatic temperature rise, and heat transfer coefficient. The experimental results agree well with the numerical solutions. The study shows that the adiabatic heat transfer coefficient is significantly affected by the inlet velocity in channel flow and less dependent on the channel spacing and row number, except for the case ofH/B=3.3. While reviewing the previous literatures, it is found that a little difference in the correlation between Nu and Re is due to the different geometric ratio of the packaged components.     

Model validation and controller design for vibration suppression of flexible rotor using AMB

This paper discusses the model validation and vibration suppression of an AMB flexible rotor via additional LQG controller. The main difficulty in the vibration suppression of the flexible rotor using AMB is to realize a controller that can minimize resonance without injuring the stabilized rigid modes. In order to solve this problem, simple scheme for system modeling and controller design are developed. Firstly, the AMB flexible rotor is stabilized with a PID controller, which leads to a new stable rotor-bearing system. Then, authors propose the model validation procedure using measured open-loop frequency responses to obtain an accurate model of the AMB flexible rotor system. After that, LQG controller with modal weighting is designed to suppress resonances of the stable rotor-bearing system. Due to the poor controllability and observability of flexible modes compared to rigid ones, balancing of two Gramians is prerequisite for the fair LQG controller design. Simulation with step disturbance and experimental results of unbalance response up to 10,000 rpm verified the effectiveness of the proposed scheme.     

Using a hash-based method with transaction trimming for miningassociation rules

We examine the issue of mining association rules among items in a large database of sales transactions. Mining association rules means that, given a database of sales transactions, to discover all associations among items such that the presence of some items in a transaction will imply the presence of other items in the same transaction. The mining of association rules can be mapped into the problem of discovering large itemsets where a large itemset is a group of items that appear in a sufficient number of transactions. The problem of discovering large itemsets can be solved by constructing a candidate set of itemsets first, and then, identifying, within this candidate set, these itemsets that meet the large itemset requirement. Generally, this is done iteratively for each large k-itemset in increasing order of k, where a large k-itemset is a large itemset with k items. To determine large itemsets from a huge number of candidate sets in early iterations is usually the dominating factor for the overall data mining performance. To address this issue, we develop an effective algorithm for the candidate set generation. It is a hash-based algorithm and is especially effective for the generation of a candidate set for large 2-itemsets. Explicitly, the number of candidate 2-itemsets generated by the proposed algorithm is, in orders of magnitude, smaller than that by previous methods, thus resolving the performance bottleneck. Note that the generation of smaller candidate sets enables us to effectively trim the transaction database size at a much earlier stage of the iterations, thereby reducing the computational cost for later iterations significantly. The advantage of the proposed algorithm also provides us the opportunity of reducing the amount of disk I/O required. An extensive simulation study is conducted to evaluate performance of the proposed algorithm     

Task Oriented Optimum Positioning of a Mobile Manipulator Base in a Cluttered Environment

A method for generating discrete optimal sequences of base locations for mobile manipulators is presented that considers the task capability of the workspace in a cluttered environment. In implementation, the obstacles and task trajectories are represented by 2ⁿ trees, so that a series of set operations are performed to characterize the manipulators configuration space into topological subspaces. By incorporating trajectory-motion-capable subspaces into the enumeration of the cost function, an optimum search technique is made applicable to the determination of a task feasible location. The method is then extended to a multiple positioning problem by concatenating the single optimization processes into a serial multistage decision making system, for which an optimal set of decisions can be found through a computationally efficient dynamic programming process.The computational paradigm of the present method is coherent with topological workspace analysis, and thus applicable to task trajectories of arbitrary dimensions and shapes. The effectiveness of the presented method is demonstrated through simulation studies performed for a 3-d.o.f. regional manipulator operating under various task conditions.     

Age, gender, and non-modulation. A sexual dimorphism in essential hypertension

The angiotensinogen gene is one of the very few related by linkage analysis to human hypertension, but the linkage has been consistently shown only among males. Moreover, polymorphisms in this gene predict an abnormal renal responsiveness to angiotensin II, a feature of non-modulation, but again, only among males. To pursue these related bridges between genetics and physiology, we evaluated the effects of sex on a second feature of non-modulation, the aldosterone response to infused angiotensin II during low sodium balance. We tested the resultant hypothesis-that non-modulation would be less frequent in women-by conducting identical protocols on 225 hypertensive inpatients (70 women, 155 men). Non-modulation was strikingly less frequent among women (26%; 95% confidence interval, 16% to 37%) than men (49%; 95% confidence interval, 40% to 57% (P = .001). We tested the hypothesis that sex steroids play a role by comparing young, premenopausal women (< 35 years) with women who were perimenopausal (45 to 55 years) and postmenopausal (> 55 years). Among the youngest women, the frequency of non-modulation was only 7%, significantly less than in young men (41%, P = .02). A steady increase in non-modulation frequency accompanied advancing age in women, reaching 47% in those older than 55 years, equal to the fraction of men affected. Age influenced non-modulation frequency in men far less. We conclude that a striking sex difference underlies the non-modulation phenotype and that female sex hormones may confer protection against a genotypic predisposition in women. This "override" of genotype, manifest by a very low frequency of non-modulation in young women, may participate in their known protection against cardiovascular disease.     

Hereditary angio-oedema: new clinical observations and autoimmune screening, complement and kallikrein-kinin analyses

Sinus cavities are often a major obstacle to the placement of dental implants in the posterior maxilla, especially when early tooth loss has occurred. Several grafting procedures aimed at reducing the expanded volume of these pneumatic cavities have been routinely utilized since 1979. Essentially, these techniques have consisted of recreating the necessary viable bone volume at the floor of sinus cavities by placing different bone substitute materials to allow for the insertion of endosseous implant devices. The progress achieved in the refinement of the surgical procedures and the knowledge acquired in the field of patient screening and selection, choice of biomaterials, management of complications, etc., have made sinus graft surgery highly codified and predictable. A comprehensive statistical study by multifactorial procedures was carried out to establish a Burt Contingency Chart. This chart visualizes the frequencies of all the "modality combinations" among the selected "qualitative parameters" and, by a " factorial analysis", the "multiple correlations", so that the "statistical affinities" that may exist among the same variables can be determined. This critical study endeavors to search for and reveal the favorable clinical, biologic and scientific parameters necessary for the success of sinus graft surgery on short-, medium-, and long-term bases (more than nine years). It is a particularly homogenous study, since all the operative procedures have been carried out exclusively by the author under standardized conditions. The wide variety of biomaterials utilized by the author since 1979 shows the development of bone substitute biomaterials as they have been introduced into the market during the past 15 years. The large number of patients treated, the variety of grafting materials, the important success rate obtained, and the long duration of patient follow-up have been instrumental in enabling us to establish scientifically significant results. Autogenous bone and its combinations with calcium- and phosphorus-containing biomaterials remain undoubtedly the best all-purpose biomaterials. The synthetic biomaterials have their own specific indications according to their stable (non-resorbable) or unstable (resorbable) nature and their rates of metabolic "turnover". Differently treated bones from the tissue bank (if not contaminated or immunologically questionable) behave in a fashion not unlike autogenous bone. Root-form implants are by far the best implants in the reconstructed sinus sites, while other implant types (subperiosteal implants, etc.) inserted beneath the reinforced osseous sinus floor, buccal wall, and pyramidal process, also have their indications.     

A new method of acrylic cranioplasty

BACKGROUND: Previous acrylic cranioplasty techniques have relied on wire or suture fixation of the acrylic to the skull. A new methyl methacrylate cranioplasty technique, using acrylic with titanium plating, is described. METHODS: Titanium plates were bent into a "Z" shape and attached to the skull at the perimeter of the skull defect, extending into the defect. The acrylic was then poured into the defect and held in place during setting with a sheet of plastic. The plates are thereby embedded in the acrylic. RESULTS: Standard methyl methacrylate and titanium plates and screws were used to perform a new method of cranioplasty. CONCLUSIONS: A rigid, form-fitting, aesthetic construct can be easily and quickly created. This technique also offers the benefit of allowing secondary craniotomy, if necessary.     

Use of Elastic,Porous, and Ultrathin Co-Culture Membranes to Control the Endothelial Barrier Function via Cell Alignment

Porous membranes used in co-culture enable the in vitro partitioning of cellular microenvironments, while still permitting physical and biochemical crosstalk between cells. Thus, features of the co-culture membrane are crucial for recapitulating the physiological functions of co-cultured cells. This study presents elastic, porous, and ultrathin membranes (EPUMs), which enhance cell–cell interactions and control cell alignment with surface topology created by stretching the membranes. The EPUM is fabricated using poly(lactide-co-caprolactone) as the base material, and the porous feature is endowed by a vapor-induced phase separation process induced by the presence of hygroscopic salt. Owing to its elastic property, the membrane can be stretched, and the deformed porous structures on the membrane surfaces act as nanostructured topographical cues, resulting in cell alignment. By co-culturing human mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells (HUVECs) on the opposite sides of the membrane, rapid endothelialization occurs through the membranes, as compared to the commercial membranes. Furthermore, the stretched membranes induce the alignment of hMSCs and HUVECs and ultimately exhibit enhanced endothelial barrier function. The co-culture membrane developed in this study may provide an effective tool for recapitulating endothelial basement membranes with a controllable endothelial barrier function.     

Buckling Instability Control of 1D Nanowire Networks for a Large‐Area Stretchable and Transparent Electrode

A commonly used strategy to impose deformability on conductive materials is the prestrain method, in which conductive materials are placed on prestretched elastic substrates and relaxed to create wavy or wrinkled structures. However, 1D metallic nanowire (NW) networks typically result in out‐of‐plane buckling defects and NW fractures, due to their rigid and brittle nature and nonuniform load transfer to specific points of NW. To resolve these problems, an alternative method is proposed to control the elastic modulus of 1D NW networks through contact with various solvents during compressive strain. Through solvent contact, the interface interactions between the NWs and between the NW and substrate can be controlled, and it is shown that the surface instability of the 1D random network is formed differently from a uniform bilayer film, which also can vary with the modulus of the network. For modulus values lower than the critical point, slippage and rearrangement of NW strands mainly occur and individual strands in the network show an in‐plane wavy configuration, which is ideal for structural stretchability. Based on the solvent‐assisted prestrain method, letter‐sized, large‐area stretchable, and transparent electrodes with high transparency and conductivity are achieved, and stretchable and transparent alternating current electroluminescent devices for stretchable display applications are also realized.