Voltage-pulse-induced electromigration

We propose and demonstrate a voltage-pulse-induced electromigration technique, in which electromigration in a gold nanowire is induced for a short period of about 10?μs by applying a voltage pulse. A local temperature analysis and a controlled electromigration experiment in the presence of voltage pulses indicate successful control of this voltage-pulsed-induced electromigration. We also measured the current-voltage characteristics of the nanowire after the application of each single voltage pulse to investigate the stochastic behavior of electromigration. A pulse duration shorter than the thermal relaxation time of the nanowire would allow us to separately control the local temperature and driving force for electromigration.     

Evaluation of application timing in fertilizer micro-dosing technology on millet production in Niger,West Africa

Micro-dosing technology has been developed by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and its partners to help subsistence farmers in the Sahel improve inorganic fertilizer application. However, the ICRISAT's recommendations regarding fertilizer application through this technology are only applicable at sowing and do not allow any flexibility in terms of labor and/or capital management. In rural areas, fertilizer cannot always be applied at sowing due to financial and labor constraints. The purpose of this study was to evaluate the effect of the timing of fertilizer application on millet production. A 2-year on-station experiment and a 1-year on-farm field experiment were conducted in the western region of Niger, West Africa. Even under the heterogeneous climatic conditions of the region during our experimental period, the results showed that the trend was the same as observed in previous studies: millet production improved through fertilizer application compared to the control (without fertilizer). The harvest index was also higher compared to that of the control. This increased production was consistently the same for all application timings. The marginal value–cost ratio on the investment calculated using a budgeting analysis for the on-farm experiment showed that – regardless of application timing – millet farmers who fertilized their fields with inorganic fertilizer made more profit than those who did not (control). This was also true for farmers who were unable to fertilize at sowing – delayed application was still the more profitable option relative to the no fertilizer control. Our results indicate that small subsistence farmers can be offered more options for inorganic fertilizer application timing using the micro-dosing technology. Delayed inorganic fertilizer application can help small farmers who are often labor constrained at the sowing period improve their yields as well as their economic returns.

Bulk production of a new form of sp(2) carbon: crystalline graphene nanoribbons

We report the use of chemical vapor deposition (CVD) for the bulk production (grams per day) of long, thin, and highly crystalline graphene ribbons (<20-30 microm in length) exhibiting widths of 20-300 nm and small thicknesses (2-40 layers). These layers usually exhibit perfect ABAB... stacking as in graphite crystals. The structure of the ribbons has been carefully characterized by several techniques and the electronic transport and gas adsorption properties have been measured. With this material available to researchers, it should be possible to develop new applications and physicochemical phenomena associated with layered graphene.     

Condensation experiments for counter-current flow limitation in an inverted U-tube

In this study, we measured counter-current flow limitation (CCFL) characteristics in an inverted U-tube (18.4 mm diameter and 1.0 m straight-part length) simulating steam generator (SG) U-tubes under conditions of steam condensation at pressures of 0.1–0.14 MPa. Differential pressure ΔP between the top of the inverted U-tube and the lower tank was measured, and the flow patterns wave estimated by comparing the waveforms of ΔP with those in air–water experiments. As a result, we classified the flow patterns under CCFL conditions into CCFL-P, CCFL-L and CCFL-T. The falling water flow rate under CCFL conditions slightly increased as the pressure increased and the cooling water temperature decreased (subcooling of cooling water increased). In the case of CCFL-L, CCFL characteristics in the inverted U-tube were between those in air–water and saturated steam–water experiments at 0.1 MPa. Furthermore, we derived a Wallis type CCFL correlation and its uncertainty from CCFL data, including previously measured data, i.e., J*^1/2_G + 0.88J_L*^1/2 = 0.76 ± 0.05.     

Effect of hydrocarbons on the efficiency of catalytic reactor of detritiation system in an event of fire

Detritiation system of a nuclear fusion plant is mandatory to be designed and qualified taking carefully into consideration all the possible extraordinary situations in addition to that in a normal condition. We focused on the change in the efficiency of tritium oxidation of a catalytic reactor in an event of fire where the air accompanied with hydrocarbons, water vapor, and tritium is fed into a catalytic reactor at the same time. Our test results on the effect of these gases on the efficiency of tritium oxidation of the catalytic reactor indicated; (1) tritiated hydrocarbon produces significantly by reaction between tritium and hydrocarbons in a catalytic reactor; (2) there is little possibility of degradation in the detritiation performance because the tritiated hydrocarbons produced in the catalyst reactor are combusted; (3) there is no possibility of uncontrollable rise in the temperature of the catalytic reactor by heat of reactions; and (4) saturated water vapor could temporarily poison the catalyst and degrades the detritiation performance. Our investigation indicated a saturated water vapor condition without hydrocarbons would be the dominant scenario to determine the amount of catalyst for the design of catalytic reactor of the detritiation system.     

Reactive compatibilization of biodegradable poly(lactic acid)/poly(ε‐caprolactone) blends with reactive processing agents

Poly(lactic acid) (PLA) blended with poly(ε‐caprolactone) (PCL) was prepared with various reactive processing agents. Four isocyanates‐lysine triisocyanate (LTI); lysine diisocyanate (LDI); 1,3,5‐tris(6‐isocyanatohexyl)‐1,3,5‐triazinane‐2,4,6‐trione (Duranate TPA‐100); 1,3,5‐tris(6‐isocyanatohexyl)biuret (Duranate 24A‐100)‐and an industrial epoxide‐trimethylolpropane triglycidyl ether (Epiclon 725)‐were used as reactive processing agents. PLA/PCL blended in the presence of LTI had the highest torque in a mixer test. The test specimens were prepared by injection molding. The mechanical properties, thermal properties, molecular weight, melt viscosity, phase behavior, and morphology were investigated using tensile strength, impact strength, differential scanning calorimetry, melt mass‐flow rate measurements, capillary rheometery, gel permeation chromatography, laser scanning confocal microscopy (LSCM), and visco‐elasticity atomic force microscopy (VE‐AFM). The impact strength increased considerably at 20 wt% PCL. The nominal tensile strain of PLA/PCL blended with LTI increased by 270%. The MFR values of PLA/PCL blends decreased with increasing LTI. Similar results were observed for shear viscosity. LSCM measurements showed that the diameters of PCL were dispersed about 0.4 μm in the presence of LTI. VE‐AFM showed that spherical particles with diameters of 50 nm were PCL‐rich domain. These results indicate that isocyanate groups of LTI react with both terminal hydroxyl or carboxyl groups of polymers, and the compatibility of PLA/PCL blends improves with LTI by reactive processing. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

激光诱导自蔓延Ni-Al合金组织性能及掺杂B的影响

在Ni14.3Al5.7中掺杂原子数分数为1.86%的B,将原始粉末压制成坯。采用不同激光点火功率对压坯进行激光诱导自蔓延烧结,利用SEM、XRD及硬度、磨损、耐蚀性测试表征手段,分析研究烧结合金的微观组织结构及宏观性能。结果表明:未添加B,烧结合金物相为Ni3Al、NiAl、Al2O3,合金组织呈网状分布;掺杂B后,烧结产物为Ni3Al、NiAl、Al4B2O9、Al2O3,对产物组织形貌影响较小。当烧结功率为700 W,烧结合金的显微硬度达到381.27HV,维钝电流为0.253 mA/mm2;功率为1 100 W,相对密度达89.3%;功率为900 W,耐磨性最佳,相对质量损失为0.24%。在相同烧结功率下,B提升了烧结合金的相对密度、硬度,但耐磨性、耐蚀性能有所下降。     

Fe40-Al60掺杂钨精矿粉激光自蔓延烧结合金组织及性能研究

采用不同激光输出功率对掺杂一定含量钨精矿粉末Fe40-A60粉末压坯进行激光点燃自蔓延烧结,利用XRD,SEM,硬度、磨损和耐蚀性测试等表征手段,分析研究引燃功率对烧结合金微观组织结构及宏观性能的影响。结果表明：合金组织为条状组织,且随着引燃功率的增加,组织愈加均匀;产物物相主要为AlCrFe2,AlFe,FeAl3,Al86Fe14,Al5Fe2及硬质颗粒相WO3。当引燃功率为1 100 W,合金的烧结密度最大为4.47 g/cm3,孔隙率最低为4.41%;烧结合金的耐蚀性能最佳,合金的致钝电流密度最小为79.8 mA/cm2,维钝电流密度也最小为0.37 mA/cm2;烧结合金硬度达到最大值,a层为1 309.7HK,b层为1 003HK。当引燃功率为1 000 W,烧结合金的a,b两层相对磨损量最低为0.06,0.05 mg/mm2。     

Asymmetric Aldol Reaction of Dichloroacetaldehyde Catalyzed by Diarylprolinol

The asymmetric cross‐aldol reaction of dichloroacetaldehyde with aldehyde pronucleophiles proceeds in the presence of a trifluoromethyl‐substituted diarylprolinol to afford γ,γ‐dichloro‐β‐hydroxy aldehydes in good yield with excellent enantioselectivity. The obtained products are useful synthetic intermediates; they were successfully converted to form chiral alkynes and dichloroalkenes.