IJTC2009-15137 PERFORMANCE OPTIMIZATION OF THERMAL NANO-ACTUATOR FOR FLY HEIGHT CONTROL IN DISK DRIVES

ABSTRACT Slider with thermal fly height control (TFC) uses a thermal heater to produce localized thermal protrusion and adjust the vertical position of the read/write head. This paper reports authors' efforts in exploring large protrusion stroke with minimal heater power input whilst preserving heater robustness in the TFC slider, with an optimized thermal nano-actuator design. Effects of both heater line width and line spacing on TFC slider performances are investigated. A novel 'StreamRiver' heater design approach is proposed. Simulation results conclude that the "Stream-River" approach is of both high power-protrusion efficiency and high heater robustness

Single cell transcriptome profiling reveals cutaneous immune microenvironment remodeling by photodynamic therapy in photoaged skin

BackgroundThe immune microenvironment plays a critical role in maintaining skin homeostasis, which is closely related to the dysfunction in photoaged skin such as autoimmunity and tumorigenesis. Several recent studies have demonstrated the efficacy of 5-aminolevulinic acid photodynamic therapy (ALA-PDT) in alleviating photoaging and skin cancer. However, the underlying immune mechanisms and the immune microenvironment change by ALA-PDT remain largely unknown.MethodsTo illustrate the effects of ALA-PDT on immune microenvironment in photoaged skin, single cell RNA sequencing (scRNA-seq) analysis of photoaged skin on the extensor side of the human forearm before and after ALA-PDT was performed. R-packages of Seurat, clusterProfiler, Monocle, CellChat were used for cell clustering, differentially expressed genes analysis, functional annotation, pseudotime analysis and cell-cell communication analysis. The gene sets related to specific functions were extracted from the MSigDB database, which were used to score the functions of immune cells in different states. We also compared our result with published scRNA-seq data of photoaged skin of the eyelids.ResultsThe increase score of cellular senescence, hypoxia and reactive oxygen species pathway in immune cells and the decrease of immune receptor activity function and proportion of naive T cells were found in skin photoaging. Moreover, the function of T cell ribosomal synthesis was also impaired or down regulated and function of G2M checkpoint was up regulated. However, ALA-PDT showed promising results in reversing these effects, as it improved the above functions of T cells. The ratio of M1/M2 and percentage of Langerhans cells also decreased with photoaging and increased after ALA-PDT. Additionally, ALA-PDT restored the antigen presentation and migration function of dendritic cells and enhanced cell-cell communication among immune cells. These effects were observed to last for 6 months.ConclusionALA-PDT has potential to rejuvenate immune cells, partially reversed immunosenescence and improved the immunosuppressive state, ultimately remodelling the immune microenvironment in photoaged skin. These results provide an important immunological basis for further exploring strategies to reverse skin photoaging, chronological aging and potentially systemic aging

Limit and shakedown analysis of tubular joints

Offshore structures are generally constructed as frameworks of tubular members. The inelastic response is significant when considering their ability to resist collapse during extreme events. Hence, their tubular joints should be designed to allow the full post yield capacity of the members.Doctor of Philosophy (CEE

Numerical study on thermal-induced lubricant depletion in laser heat-assisted magnetic recording systems

This paper presents a numerical investigation of heat transfer and lubricant depletion on the hard disk in a heat-assisted magnetic recording (HAMR) system. The heat is induced by a laser pulse shooting down from a slider flying over the disk coated with a thin layer of lubricant. The main mechanisms to cause the lubricant depletion are examined by taking into account of effects associated with evaporation enthalpy, thermal induced surface tension and initial lubricant film thickness. The results show that the evaporation has a dominant effect at a lower evaporation enthalpy, while the thermocapillarity plays a main role at a higher evaporation enthalpy. The lubricant depletion is also found to be affected by the initial thickness of the lubricant film, mainly through the influence on the evaporation rather than on the thermocapillarity. In addition, the effect of lubricant accommodation coefficient on the evaporation has been addressed for the first time in the present study. It is found that a full accommodation assumption adopted in previous numerical studies may overestimate the actual evaporation rate, and a suitable value for the accommodation coefficient between 0 and 1 is required in the prediction in order to yield a good agreement between the simulation results and the experimental data

Numerical study on heat transfer and lubricant depletion in a heat assisted magnetic recording system with multilayer disk structure

Heat transfer and lubricant depletion in a HAMR system with multilayer disk substrate are numerically simulated in this study. Cases under two types of multilayer disk substrates with different materials on the top layer as well as different laser powers are examined. The results show the significant effects of the material property and the laser power. Compared with pure glass disk substrate, larger thermal conductivity of top-layer material in the multilayer disk substrate causes faster heat conduction and thus substantial reductions in the temperature increase and lubricant depletion on the top surface. Hence it is necessary and important to incorporate the real multilayer structure in modeling heat transfer and lubricant depletion in practical HAMR systems

A numerical study on heat transfer and lubricant depletion on an anisotropic multilayer hard disk

This paper presents a numerical investigation on the effect of thermal anisotropy of the top layer alloy on heat transfer and lubricant depletion on the disk surface in a heat-assisted magnetic recording (HAMR) system. The disk consists of multilayer structures and a thin layer of lubricant on the top surface. Cases under different laser powers and initial lubricant film thicknesses are examined. The top-layer alloy thermal anisotropy does show non-negligible effect on the heat transfer and lubricant depletion. With the top-layer alloy being more anisotropic, higher temperature increase and lager lubricant depletion can be observed on the disk surface. The results also show that the thermal anisotropy effect is more significant under a lower laser power but nearly keeps no much difference under different initial lubricant film thicknesses. Thus it is of importance to include the thermal anisotropy effect of the top-layer Co-alloy when simulating the heat transfer and lubricant depletion in practical multilayer HMAR systems, especially for the cases under the condition of lower laser power, as the effect cannot be neglected under such conditions

A model for laser induced lubricant depletion in heat-assisted magnetic recording

The lubricant evaporation caused by the rapid laser heating is always a big concern in heat-assisted magnetic recording. In this article, we develop an empirical equation based on the existing measurement data to describe the relation between the evaporation coefficient of lubricant and temperature on the disk surface. The evaporation coefficient of lubricant is found to decrease from ~1.0 to ~0.003 for the temperature range from 406 to 512 K and follow the trend given by the Arrhenius formula. By incorporating this formula into a previously established evaporation model, we can get a new model, which enables us to predict the lubricant evaporation and depletion caused by the rapid laser heating more accurately than ever