Thermal processes of miniature thermomagnetic generators in resonant self-actuation mode.

This paper presents an investigation of the heat transfer processes in miniature thermomagnetic generators (TMGs) that are based on the recently developed concept of resonant self-actuation of a cantilever enabling efficient conversion of thermal into electrical energy. A lumped element model (LEM) is introduced to describe the dynamics of heat intake during mechanical contact between a thermomagnetic (TM) film and heat source, and of heat dissipation. The key parameters governing heat intake and dissipation are the heat transfer coefficient at contact and the thermal resistance R b of the bonding layer between TM film and cantilever, respectively. The effects of these parameters on the performance metrics are investigated for different heat source temperatures above the Curie temperature of the TM film. LEM simulations reveal critical values of κ and R b , above which stable performance of energy generation occurs characterized by large stroke and frequency resulting in large power.

Lumped Element Model for Thermomagnetic Generators Based on Magnetic SMA Films.

This paper presents a lumped element model (LEM) to describe the coupled dynamic properties of thermomagnetic generators (TMGs) based on magnetic shape memory alloy (MSMA) films. The TMG generators make use of the concept of resonant self-actuation of a freely movable cantilever, caused by a large abrupt temperature-dependent change of magnetization and rapid heat transfer inherent to the MSMA films. The LEM is validated for the case of a Ni-Mn-Ga film with Curie temperature TC of 375 K. For a heat source temperature of 443 K, the maximum power generated is 3.1 µW corresponding to a power density with respect to the active material's volume of 80 mW/cm3. Corresponding LEM simulations allow for a detailed study of the time-resolved temperature change of the MSMA film, the change of magnetic field at the position of the film and of the corresponding film magnetization. Resonant self-actuation is observed at 114 Hz, while rapid temperature changes of about 10 K occur within 1 ms during mechanical contact between heat source and Ni-Mn-Ga film. The LEM is used to estimate the effect of decreasing TC on the lower limit of heat source temperature in order to predict possible routes towards waste heat recovery near room temperature.

AlN formation by an Al/GaN substitution reaction.

Aluminium nitride (AlN) is a promising semiconductor material for use as a substrate in high-power, high-frequency electronic and deep-ultraviolet optoelectronic devices. We study the feasibility of a novel AlN fabrication technique by using the Al/GaN substitution reaction method. The substitution method we propose here consists of an Al deposition process on a GaN substrate by a sputtering technique and heat treatment process. The substitution reaction (Al + GaN = AlN + Ga) is proceeded by heat treatment of the Al/GaN sample, which provides a low temperature, simple and easy process. C-axis-oriented AlN layers are formed at the Al/GaN interface after heat treatment of the Al/GaN samples at some conditions of 1473-1573 K for 0-3 h. A longer holding time leads to an increase in the thickness of the AlN layer. The growth rate of the AlN layer is controlled by the interdiffusion in the AlN layer.

Study of solidification pathway of a MoSiBTiC alloy by optical thermal analysis and in-situ observation with electromagnetic levitation.

MoSiBTiC alloys are promising candidates for next-generation ultrahigh-temperature materials. However, the phase diagram of these alloys has been unknown. We have developed an ultrahigh-temperature thermal analyser based on blackbody radiation that can be used to analyse the melting and solidification of the alloy 67.5Mo-5Si-10B-8.75Ti-8.75 C (mol%). Furthermore, electromagnetic levitation (EML) was used for in-situ observation of solidification and microstructural study of the alloy. On the basis of the results, the following solidification pathway is proposed: Mo solid solution (Moss) begins to crystallize out as a primary phase at 1955 °C (2228 K) from a liquid state, which is followed by a (Moss+TiC) eutectic reaction starting at 1900 °C (2173 K). Molybdenum boride (Mo2B) phase precipitates from the liquid after the eutectic reaction; however, the Mo2B phase may react with the remaining liquid to form Moss and Mo5SiB2 (T2) as solidification proceeds. In addition, T2 also precipitates as a single phase from the liquid. The remaining liquid reaches the (Moss + T2 + TiC) ternary eutectic point at 1880 °C (2153 K), and the (Moss + T2 + Mo2C) eutectic reaction finally occurs at 1720 °C (1993 K). This completes the solidification of the MoSiBTiC alloy.

Control Mechanism for Carbon-Chain Length in Polyunsaturated Fatty-Acid Synthases.

Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are essential fatty acids. PUFA synthases are composed of three to four subunits and each create a specific PUFA without undesirable byproducts. However, detailed biosynthetic mechanisms for controlling final product profiles have been obscure. Here, the bacterial DHA and EPA synthases were carefully dissected by in vivo and in vitro experiments. In vitro analysis with two KS domains (KSA and KSC ) and acyl-acyl carrier protein (ACP) substrates showed that KSA accepted short- to medium-chain substrates while KSC accepted medium- to long-chain substrates. Unexpectedly, condensation from C18 to C20 , the last elongation step in EPA biosynthesis, was catalyzed by KSA domains in both EPA and DHA synthases. Conversely, condensation from C20 to C22 , the last elongation step for DHA biosynthesis, was catalyzed by the KSC domain in DHA synthase. KSC domains therefore determine the chain lengths.

NFAM1, an immunoreceptor tyrosine-based activation motif-bearing molecule that regulates B cell development and signaling.

A functional cDNA cloning system was developed by using a retrovirus library encoding CD8-chimeric proteins and a nuclear factor of activated T cells (NFAT)-GFP reporter cell line to identify molecules inducing NFAT activation. By using this strategy, NFAT activating molecule 1 (NFAM1) was cloned as an immunoreceptor tyrosine-based activation motif (ITAM)-bearing cell surface molecule belonging to the Ig superfamily and is predominantly expressed in spleen B and T cells. NFAM1 crosslinking induced ITAM phosphorylation, ZAP-70/Syk recruitment, NFAT activation, and cytokine production. In vivo overexpression of NFAM1 in bone marrow chimeras and transgenic mice induced severe impairment of early B cell development in an ITAM-dependent manner. In NFAM1-expressing B cells, B cell antigen receptor stimulation induced NFAM1 translocation to lipid raft, and NFAM1 co-crosslinking augmented B cell antigen receptor signaling. The results suggest that NFAM1 modulates B cell signaling through its ITAM, which regulates B cell development.