Polymerization of acrylonitrile by catalytic systems consisting of triphenylphosphine and a lewis acid

Polymerization of acrylonitrile in the presence of systems that consisted of triphenylphosphine (PPh₃) and a Lewis acid R_mMX_n (ZnCl₂, Me₃Al, Et₃Al, Et₂AlCl, EtAlCl₂, AlCl₃) was studied. The systems that contained Me₃Al and Et₃Al (i.e., Lewis acid of moderate acidity) were the most efficient catalysts. Conductometric measurements carried out in the polymerization systems showed the presence of ions. The presence of phosphonium cation in the polyacrylonitrile chain formed by the PPh₃–R_mMX_n catalytic systems was determined by IR, ¹H-NMR, and ³¹P-NMR spectroscopy. The average molecular weight measurements and kinetic chain lengths of polyacrylonitrile formed within the reaction time in the presence of PPh₃–Et₃Al showed that transfer reactions occur. According to the results obtained, the polymerization reaction of acrylonitrile by PPh₃–R_mMX_n involved a zwitterion formed by the attack of PPh₃ on acrylonitrile complexed by Lewis acid [Ph₃P^⊕? CH₂? C^?H? C?N → MR_mX_n] and the anion [CH₂?C^?? C?N] formed by the proton abstraction from the monomer.     

Mobilization and fractionation of137Cs in calcareous soils

Mobility of¹³⁷Cs was investigated in columns of calcareous loam and clay soils leached under river water, NH₄OAc, KCl, CaCl₂, and EDTA. Fractionation of Cs into ten sequential fractions was accomplished in the leached soils as well as in soil samples received carrier-free¹³⁷Cs and incubated for 60 d. At the end of 90 d of leaching with river water and CaCl₂, the bulk of Cs applied (>97%) was found to remain in the upper 1 cm of soil columns. On the other hand, the reduction in Cs concentration was approximately 30% with NH₄OAc, 18% with KCl, and 10 to 25% with EDTA. The major soil constituents appeared to be responsible for retaining Cs were clay, silt, and Fe oxides. The leaching consistently increased the magnitude of fractions bound to clay minerals and in most cases decreased the fractions of water soluble, exchangeable, carbonate, and organic matter.     

Analysis of natural milk and milk poweder samples by NAA

As a part of the Iraqi Food Analysis Programme /I.F.A.P./ the concentration of Na, Mg, P, Cl, K, Ca, Zn, Se, Br, Rb and I in natural milk collected from different regions of Iraq, and in milk powder samples have been determined by using the NAA technique. It was found that except for the elements I, Rb and Br the concentration of the elements was approximately identical in both the natural milks and milk powders.     

Separation of velocity distribution and diffusion using PFG NMR

Pulsed field gradient (PFG) NMR is applied to investigate flow processes. In this case the NMR signal experiences phase modulation due to flow and signal attenuation due to the distribution of velocities. The velocity distribution consists of one part originating from diffusion and of a second part, the distribution of the directed motion. The usual PFG-experiment in which the gradient strength is incremented cannot distinguish between both. Incrementing velocity at constant gradient strength keeps the contribution from diffusion constant but changes the absolute width of the velocity distribution. So the signal is attenuated again, but only due to the distribution of the directed motion. The phase modulation as a signature of flow is not affected by this strategy, because velocity and gradient strength are Fourier conjugated. The key advantage of this approach is the possibility of measuring very low velocities, which only cause a very slight phase modulation that is easily covered by diffusion. The method is discussed here for very slow flow in a rheometer cell.     

优化功率在便携式应用中的挑战

便携式产品电源管理面临挑战 便携式应用产品的外形尺寸日趋小巧轻薄，但其糅合的功能却愈来愈多。这个趋势所衍生的需求是有效管理功率及减少板上的元件数目。为了应付这个挑战，半导体供应商在这个市场区间担当了不可或缺的角色。半导体供应商必须集成最好的低功率和高功率器件，并致力在低输出功率和待机状态下实现高效率。这种集成可以通过于一块基板或平台上整合所有器件，或者把所有器件集成在一个封装里作为混合电路来实现。由于便携式产品采用的外形尺寸越来越小，开关频率因此不断增加。随着开关频率提高，无源器件的尺寸则会减小。半导体供应商需要好好管理这个高频，正是它才实现了较小型的无源器件使用，从而实现尺寸更小的总体解决方案（其成本也可能更低）。最后，2．5G和3G的RF无线器件是“线性”（linear）的，故在低功率时很容易受低效率影响。由此可见，半导体供应商必需提供能在低功率时增加系统效率的功率管理芯片。     

Alternierende Copolymerisation von CO2 und Propylenoxid in Gegenwart von organometallischen Katalysatoren

Ohne Zusammenfassung     

Perception and cortical neural coding of harmonic fusion in ferrets

This study examined the perception and cortical representation of harmonic complex tones, from the perspective of the spectral fusion evoked by such sounds. Experiment 1 tested whether ferrets spontaneously distinguish harmonic from inharmonic tones. In baseline sessions, ferrets detected a pure tone terminating a sequence of inharmonic tones. After they reached proficiency, a small fraction of the inharmonic tones were replaced with harmonic tones. Some of the animals confused the harmonic tones with the pure tones at twice the false-alarm rate. Experiment 2 sought correlates of harmonic fusion in single neurons of primary auditory cortex and anterior auditory field, by comparing responses to harmonic tones with those to inharmonic tones in the awake alert ferret. The effects of spectro-temporal filtering were accounted for by using the measured spectrotemporal receptive field to predict responses and by seeking correlates of fusion in the predictability of responses. Only 12% of units sampled distinguished harmonic tones from inharmonic tones, a small percentage that is consistent with the relatively weak ability of the ferrets to spontaneously discriminate harmonic tones from inharmonic tones in Experiment 1.     

The metallofullerene Tm@C82: isomer-selective electronic structure

82 using photoemission and electron energy-loss spectroscopy in transmission. In particular, the impact of the isomer symmetry of the C₈₂ cage (C_s or C_3v) on the electronic structure and on the optical properties is analysed in detail. For both isomers, combined XPS and XAS measurements of the Tm 4f and 4d states offer conclusive proof of a divalent encaged Tm ion. No significant change of the valence of the rare earth ion upon changes in the cage symmetry is observed. From the C 1s excitation spectra we find a more pronounced LUMO for the C_3v(8) isomer, as is expected for the higher symmetry of the cage. Additional information about the optical properties was obtained from the low-energy loss function. With use of a Kramers–Kronig analysis, the dielectric function, ε, and the optical conductivity, σ, have been derived. ε(0) and the onset of the spectral weight are found to be 7.7 [12.8] and 0.6 eV [0.8 eV] for the C_s(6) {C_3v(8)} isomer, respectively. Received: 14 October 1997/Accepted: 28 October 1997     

IoT-Solar Energy Powered Smart Farm Irrigation System

As the Internet of things (IoT) technology is evolving, distributed solar energy resources can be operated, monitored, and controlled remotely. The design of an IoT based solar energy system for smart irrigation is essential for regions around the world, which face water scarcity and power shortage. Thus, such a system is designed in this paper. The proposed system utilizes a single board system-on-a-chip controller (the controller hereafter), which has built-in WiFi connectivity, and connections to a solar cell to provide the required operating power. The controller reads the field soil moisture, humidity, and temperature sensors, and outputs appropriate actuation command signals to operate irrigation pumps. The controller also monitors the underground water level, which is essential to prevent the pump motors from burning due to the level in the water well. The proposed system has three modes of operations, i.e. the local control mode, mobile monitoring-control mode, and fuzzy logic-based control mode. For the purpose of the proposed system validation, a prototype was designed, built, and tested.