Polydopamine (PDA) is a biopolymer, which can form uniform thin films on almost all solid substrates as well as at the liquid/air interface. Carbonized polydopamine possesses graphite-like structure and exhibits high electrical conductivity, which makes it a potential carbon-based thin film conductor. However, studies on mechanical behavior of PDA and its derived materials are very limited. In this study, PDA samples were synthesized through self-assembly of dopamine in aqueous solution. Elastic modulus of thin films was measured using the nanoindentation technique. It is shown that the Young’s modulus of PDA thin film increased with increasing heat treatment temperature (up to 600°C). Doping with Cu ions also increased the Young’s modulus of PDA. Furthermore, all PDA thin films, with and without Cu, exhibited creep behavior.

The unsteady flow separation of airfoil with a local flexible structure (LFS) is studied numerically in Lagrangian frames in detail, in order to investigate the nature of its high aerodynamic performance. For such aeroelastic system, the characteristic-based split (CBS) scheme combined with arbitrary Lagrangian-Eulerian (ALE) framework is developed firstly for the numerical analysis of unsteady flow, and Galerkin method is used to approach the flexible structure. The local flexible skin of airfoil, which can lead to self-induced oscillations, is considered as unsteady perturbation to the flow. Then, the ensuing high aerodynamic performances and complex unsteady flow separation at low Reynolds number are studied by Lagrangian coherent structures (LCSs). The results show that the LFS has a significant influence on the unsteady flow separation, which is the key point for the lift enhancement. Specifically, the oscillations of the LFS can induce the generations of moving separation and vortex, which can enhance the kinetic energy transport from main flow to the boundary layer. The results could give a deep understand of the dynamics in unsteady flow separation and flow control for the flow over airfoil.

The testosterone-inducible regulator (teiR) gene was cloned from Comamonas testosteroni chromosomal DNA, and introduced into plasmids pKtac2 (containing a tac promoter) and pK18 to yield plasmids pKtac2-teiR and pKteiR100. The recombinant plasmids were transformed into competent Escherichia coli HB101 and total protein was extracted to detect the TeiR protein expression level using enzyme-linked immunosorbent assay (ELISA). E. coli transformed by pKtac2-teiR and pKteiR100 produced 6.65 and 5.93 μg/mg of TeiR protein, respectively. Recombinant plasmids were also co-transformed into competent E. coli HB101 with plasmid p6 [containing hsdA gene (3α-HSD/CR, 3α-hydroxysteroid dehydrogenase/carbonyl reductase encoding gene)] to reveal the relationship between 3α-HSD/CR and TeiR by ELISA. The amounts of TeiR protein expressed by E. coli containing pKtac2-teiR and pKteiR100 were 5.94 μg/mg and 5.33 μg/mg, respectively, and these increased up to 6.81 μg/mg and 6.10 μg/mg after inducing with 1 mmol/l isopropyl-β-d-thiogalactoside (IPTG). Interestingly, 3α-HSD/CR protein expression level, after co-transformation with plasmids pKtac2-teiR and p6, was lower than that observed in the co-transformation with pKteiR100 and p6. The first co-transformation induced 1.20 μg/mg 3α-HSD/CR protein and the second 1.71 μg/mg. These values rose to 1.42 and 1.80 μg/mg, respectively, after treatment with 1 mmol/l IPTG. Our results proved that the tac promoter was more efficient than the lacZ promoter and that the teiR gene could act as an activator for hsdA gene expression.

The U.S. military uses large amounts of fuel during deployments and battlefield operations. Consequently, the U.S. military has a strong need to develop technologies that increase fuel efficiency and minimize fuel requirements all along the logistics trail and in all battlefield operations. There are additional requirements to reduce and minimize the environmental footprint of various military equipment and operations and reduce the need for batteries (non-rechargeable) in battlefield operations. The tri-agency SERDP (Strategic Environmental Research and Development Program) office is sponsoring a challenging, high-payoff project to develop a lightweight, small form-factor, soldier-portable advanced thermoelectric generator (TEG) system prototype to recover and convert waste heat from a variety of deployed equipment with the ultimate purpose of obtaining additional power for soldier battery charging, advanced capacitor charging, and other battlefield power applications. The project seeks to achieve power conversion efficiencies of 10% (double current commercial TE conversion efficiencies) in a system with ˜1.6-kW power output for a spectrum of battlefield power applications. In order to meet this objective, the project is taking on the multi-faceted challenges of tailoring LAST/LASTT-based thermoelectric (TE) materials for the proper temperature ranges (300 K – 700 K), fabricating these materials with cost-effective hot-pressed and sintered processes while maintaining their TE properties, measuring and characterizing their thermal fatigue and structural properties, developing the proper manufacturing processes for the TE materials and modules, designing and fabricating the necessary microtechnology heat exchangers, and fabricating and testing the final TEG system. The ultimate goal is to provide an opportunity to deploy these TEG systems in a wide variety of current military equipment. This would help the Army in achieving one of the Office of Secretary of Defense’s major strategic objectives to maintain and enhance operational effectiveness while reducing total force energy demands. The presentation will review the progress made on 1) the performance of LAST / LASTT TE materials and tailoring their temperature dependency; 2) evaluating the structural (Elastic modulus, Poisson’s ratio and mechanical strength) properties of these materials, 3) development of the necessary LAST/LASTT-based TE modules, 4) development of the required hot- and cold-side microtechnology heat exchangers, and 5) the overall system designs for 30 kW and 60 kW TQG applications and potential performance pathways/differences for these two TQG cases. This work leverages critical fundamental research performed by the Office of Naval Research in developing LAST/LASTT materials.

Copper aluminum oxide (CuAlO2) with delafossite structure is a promising candidate for high temperature thermoelectric applications because of its modest band gap, high stability and low cost. We investigate magnesium doping on the aluminum site as a means of producing higher electrical conductivity and optimized Seebeck coefficient. Powder samples were synthesized using solid-state reaction and bulk samples were prepared using both cold-pressing and hot-pressing techniques. Composition analysis, microstructural examination and transport property measurements were performed, and the results suggest that while hot-pressing can achieve high density samples, secondary phases tend to form and lower the performance of the materials.

Thermoelectric modules are of great interest for power generation applications where temperature gradients of approximately 500K exist, and hot side temperatures near 800K. The fabrication of such modules requires optimization of the material compositions, low contact resistivities, and low thermal loss.

AgPbmSbTe2+m (LAST) and Ag(Pb1-xSnx)m SbTe2+m (LASTT) compounds are among the best known materials appropriate for this temperature range. Various measurement systems have been developed and used to characterize bulk samples in the LAST and LASTT systems within this operating temperature range. From the characterized data, modeling of modules based on these materials and segmented legs using LAST(T) with Bi2Te3 have been used to identify the optimal geometry for the individual legs, and the length of the Bi2Te3 segments. We have segmented LAST(T) with Bi2Te3 and achieved contact resistivities of less than 10 μΩ•cm2.

Here we give a detailed presentation on the procedures used in the fabrication of thermoelectric generators based on LAST, LASTT, and segmented with Bi2Te3 materials. We also present the output data on these generators.

Low electrical contact resistance is essential for the fabrication of high efficiency thermoelectric generators in order to convert heat to electricity. These contacts must be stable to high temperatures and through thermal cycling. A ratio of the contact resistance to the leg resistance below 0.1 is the goal for fabrication of a high efficiency thermoelectric power generation device. Here we present the fabrication procedures and characterization of contacts of metal alloys to Pb-Sb-Ag-Te (LAST) and Pb-Sb-Ag-Sn-Te (LASTT) compounds. Contacts were fabricated and measured for both ingot and hot pressed materials. Stainless steel 316 has shown a low resistance contact to these thermoelectric materials when the proper bonding conditions are used. Different time-temperature-pressure conditions for bonding to n-type and to p-type legs are presented. Contact resistances below 10μΩcm2 have been measured. In addition, break tests have shown bond strengths exceeding the semiconductor fracture strength. One of the considerations used in selecting iron alloys for electrical interconnects is the similarity in the coefficient of thermal expansion to the LAST and LASTT materials which is 18 ppm/°C and relatively temperature insensitive. Contacts to the thermoelectric materials were accomplished by diffusion bonding in a furnace developed in our lab at Michigan State University. The furnace is capable of reaching temperatures of up to 1000°C with a controlled atmosphere of a reducing gas. Fabrication procedures and contact data are presented in this paper.

PbTe-based thermoelectric (TE) materials exhibit promising thermoelectric properties and have potential applications in waste heat recovery from sources such as truck engines and shipboard engines. TE components designed for these applications will be subject to mechanical/thermal loading and vibration as a result from in-service conditions, including mechanical vibration, mechanical and/or thermal cycling, and thermal shock.

In the current study, we present and discuss the mechanical properties of several PbTe-based compositions with different dopants and processing methods, including n-type and p-type specimens fabricated both by casting and by powder processing. Room temperature hardness and Young's modulus are studied by Vickers indentation and nanoindentation while fracture strength is obtained by biaxial flexure testing. Temperature dependent Young's modulus, shear modulus, and Poisson's ratio are studied via resonant ultrasound spectroscopy (RUS).

Effect of electromigration on mechanical shear behavior of flip chip solder joints consisting of 97Pb3Sn and 37Pb63Sn composite solder joints was studied. The under bump metallurgy (UBM) on the chip side was TiW/Cu/electroplated Cu, and the bond pad on the board side was electroless Ni/Au. It was found that the mode of shear failure has changed after electromigration and the mode depends on the direction of electron flow during electromigration. The shear induced fracture occurs in the bulkof 97Pb3Sn solder without current stressing, however, after 10 h current stressing at 2.55 × 104 A/cm2 at 140 °C, it occurs alternately at the cathode interfaces between solder and intermetallic compounds (IMCs). In the downward electron flow, from the chip to substrate, the failure site was at the Cu–Sn IMC/solder interface near the Si chip. However, in the upward electron flow, from the substrate to chip, failure occurred at the Ni–Sn IMC/solder interface near the substrate. The failure mode has a strong correlation to microstructural change in the solder joint. During the electromigration, while Pb atoms moved to the anode side in the same direction as with the electron flow, Sn atoms diffused to the cathode side, opposite the electron flow. In addition, electromigration dissolves and drives Cu or Ni atoms from UBM or bond pad at the cathode side into the solder. These reactions resulted in the large growth of Sn-based IMC at the cathode sides. Therefore, mechanical shear failure occurs predominantly at the cathode interface.

Electromigration in solder joints causes a void formation between intermetallic compounds (IMC) and solder at the cathode. The effect of electromigration in mechanical test of Cu wires joined by solder was performed. The current density of electromigration was 1∼5×103 A/cm2. The working temperature was 100∼150°C. Tensile stress and shear stress were applied either before or after electromigration. The tensile strain rate was 3 μm/min. We observed that, without electromigration, tensile stress caused a ductile break at the middle of solders because the solder was softer. On the other hand, if combined with electromigration, a brittle failure always occurred at the cathodes interface during tensile test. The ultimate tensile strength decreased with longer electromigration time or higher current density. In shear test, the daisy chain of solders failed alternatively at the cathodes after electromigration.

AFLP provides an effective, rapid and economical tool for detecting a large number of polymorphic genetic markers that are highly reliable and reproducible, and are able to be genotyped automatically. The AFLP technique has been used extensively to detect genetic polymorphisms, evaluate and characterize breed resources, construct genetic maps and identify genes. In this paper, we describe the optimization of the AFLP technique for porcine genomic DNA fingerprinting, including the enzyme digestion, adapter ligation, preamplification, selective amplification, denatured PAGE, silver staining and multicolour fluorescent detection. Twenty-eight polymorphic markers were detected in the pooled genomic DNA of 44 pig breeds (populations) by E32/T32 primer combinations.