Differentiation and growth of kype skeletal tissues in anadromous male Atlantic salmon (Salmo salar)

The re-initiation of bone development in adult starving Atlantic salmon (Salmo salar) during their energetically expensive upstream migration is remarkable and deserves closer examination. Dramatic alterations of the skull bones and teeth, most prominently, the development of a kype in males, are widely known but little studied or understood. We describe the microstructure and the cellular processes involved in the formation of the skeletal tissues of the kype. Fresh bone material, obtained from animals migrating upstream was subjected to radiological, histological or histochemical analysis. We show that the kype is, in part, composed of rapidly growing skeletal needles arising at the tip of the dentary. Proximally, the needles anastomose into a spongiosa-like meshwork which retains connective tissue inside bone marrow spaces. Ventrally, the needles blend into Sharpey fiber bone. Skeletal needles and Sharpey fiber bone can be distinguished from the compact bone of the dentary by radiography. Rapid formation of the skeleton of the kype is demonstrated by the presence of numerous osteoblasts, a broad distal osteoid zone, and the appearance of proteoglycans at the growth zone. The mode of bone formation in anadromous males can be described as 'making bone as fast as possible and with as little material as possible'. Unlike the normal compact bone of the dentary, the new skeletal tissue contains chondrocytes and cartilaginous extracellular matrix. Formation of the skeleton of the kype resembles antler development in deer (a form of regeneration), or hyperostotic bone formation in other teleost fishes, rather than periosteal bone growth. The type of boneformation may be understandable in the light of the animals' starvation and the energetic costs of upstream migration. However, the structured and regulated mode of bone formation suggests that the skeleton of the kype has functional relevance and is not a by-product of hormonal alterations or change of habitat

Numerical Analysis of Active Flow Boiling Regime Management Using a Vapor-Compression Cycle Applied to Electronic Processor Cooling

As computing power continues to grow at a rapid rate, the thermal load generated from electronic devices follows. Furthermore, reduced size requirements for electronic devices have driven engineers to produce this increased computing power in smaller packaging than ever before. The combination of these two trends results in high heat flux processors that require innovative cooling techniques. Industry and academia alike have anticipated this trend and have developed several general families of solutions to cooling high-heat flux processors. This work proposes the use of flow boiling in a vapor compression cycle and a spreader to distribute the heat from a high-heat flux source to the evaporator. Specifically, the balance between cycle performance and achievable heat flux is assessed, and operating conditions where the ability of the cycle to control evaporator heat flux and simultaneously achieve a high cycle efficiency are identified. A numerical flow boiling correlation is applied and a microchannel evaporator design model is proposed. Geometric parameters and performance limitations of this technique are analyzed and both quantitative and qualitative results along with future work are presented

Numerical study of scars in a chaotic billiard

We study numerically the scaling properties of scars in stadium billiard. Using the semiclassical criterion, we have searched systematically the scars of the same type through a very wide range, from ground state to as high as the 1 millionth state. We have analyzed the integrated probability density along the periodic orbit. The numerical results confirm that the average intensity of certain types of scars is independent of $\hbar$ rather than scales with $\sqrt{\hbar}$. Our findings confirm the theoretical predictions of Robnik (1989).Comment: 7 pages in Revtex 3.1, 5 PS figures available upon request. To appear in Phys. Rev. E, Vol. 55, No. 5, 199

Experimental Comparison of Cycle Modifications to a Multi-Stage Two-Evaporator Transcritical CO2 Refrigeration Cycle

With increasing awareness of the adverse effects of carbon emissions on the environment, researchers within the heating, ventilation, air conditioning, and refrigeration (HVAC&R) community have been pushing for lower global warming potential (GWP) and natural working fluids as well as systems that are more efficient than the higher-GWP systems they replace. One such working fluid is carbon dioxide (CO2). While CO2 has the advantages of being low-cost, non-flammable, and possessing a high volumetric heat capacity, it has a high critical pressure associated with a low critical temperature, thus often necessitating transcritical operation that requires significant compressor input power. As such, numerous cycle modifications have been proposed that enable the transcritical CO2 cycle to match, and in some cases surpass, the coefficient of performance (COP) of existing hydrofluorocarbon (HFC) cycles under the same operating conditions. This work provides an experimental comparison of four cycle architectures that utilize the same compressors and heat exchangers. This enables a meaningful comparison of these modifications, consisting of open economization with an evaporator bypass, as well as both electronic expansion valve (EXV) and ejector expansion strategies, along with a pump applied between the gas cooler outlet and the ejector motive nozzle inlet for control and increased recoverable pressure differential. Experimental parametric studies were conducted, and comparisons of architecture costs and benefits are presented. Design recommendations are provided along with future work

Experimental and Numerical Optimization of a Variable-Geometry Ejector in a Transcritical CO2 Refrigeration Cycle

Implementation of an ejector for expansion work recovery in transcritical carbon dioxide (CO2) cycles provides an opportunity to improve the efficiency of these environmentally-friendly refrigeration systems. However, literature outlining an approach to ejector design for a given application is lacking. This paper presents a tool to design a complete ejector applied in a vapor compression cycle. In this work, the developed design tool was validated using experimentally-derived polynomials for air-conditioning conditions. Then, constant values for nozzle and mixing section efficiencies were used as inputs into design tool to broaden the analysis outside of the application boundaries of the experimentally-derived polynomials to study a transcritical CO2 system with an ejector operating in the evaporating temperature and gas cooler pressure in the range of -15 °C to 20 °C and 80 bar to 110 bar, respectively. The design tool allows for the calculation of the motive and suction nozzle throat diameters, the mixing section diameter, and the diffuser outlet diameter, as well as the lengths of each section, to output a full internal geometry of the ejector based on performance requirements. Individual component sub-models are presented within the proposed model structure. The model which forms the basis of the design tool was experimentally validated with a mean absolute error (MAE) between 3% to 4%. Additionally, the sensitivity of the ejector geometry and performance to component efficiencies, operating conditions, and component versus system optimization was investigated. The optimization and parametric studies provided novel insights into the impact of desired efficiency and operating conditions on ejector geometry, thus allowing a designer to make decisions based on the tradeoff between ejector size and performance. For example, as the diffuser length increased by 5.1 mm to obtain an efficiency increase, to obtain a further efficiency increase of the same amount would require a 17.1 mm length increase in diffuser length. Potential model improvements and other future work are also discussed

Influence of normal and radial contributions of local current density on local electrochemical impedance spectroscopy.

A new tri-electrode probe is presented and applied to local electrochemical impedance spectroscopy (LEIS) measurements. As opposed to two-probe systems, the three-probe one allows measurement not only of normal, but also of radial contributions of local current densities to the local impedance values. The results concerning the cases of the blocking electrode and the electrode with faradaic reaction are discussed from the theoretical point of view for a disk electrode. Numerical simulations and experimental results are compared for the case of the ferri/ferrocyanide electrode reaction at the Pt working electrode disk. At the centre of the disk, the impedance taking into account both normal and radial contributions was in good agreement with the local impedance measured in terms of only the normal contribution. At the periphery of the electrode, the impedance taking into account both normal and radial contributions differed significantly from the local impedance measured in terms of only the normal contribution. The radial impedance results at the periphery of the electrode are in good agreement with the usual explanation that the associated larger current density is attributed to the geometry of the electrode, which exhibits a greater accessibility at the electrode edge