Miscible-Solvent-Assisted Two-Phase Synthesis of Monolayer-Ligand-Protected Metal Nanoclusters with Various Sizes

Effective yet versatile synthetic strategies for size-tunable metal nanoclusters (NCs) are scarce. This has hampered the development of this unique class of nanomaterials. Here, a general protocol is reported for the synthesis of high-quality metal NCs protected by a variety of organic ligands (e.g., selenolate, thiolate, and phosphine) based on a miscible-solvent-assisted phase transfer between water and organic solution. This method is demonstrated to be facile, rapid (≤3 h), scalable (gram-scale), and versatile. The size of the selenolated and thiolated Au NCs can be tuned from Au₁₀ to Au₆₁ by simply varying the miscible solvent in proportions and types. The advantages of this method, such as quick phase separation and no need for purification treatment, enable real-time monitoring of metal NC growth within the NaBH₄ reduction system. The results show that the size of Au NCs gradually increases with increasing valence electron count by a stepwise 2x e^- hopping mechanism (x = 0–5), i.e., 0 e^- → 2 e^- → 4 e^- → 8 e^- → 18 e^- → 22 e^- → 32 e^-.     

Model simplification of stable discrete‐time systems by the squared magnitude Padé approximation

Abstract

A squared magnitude Padé approximation technique is presented for the model simplification of stable discrete‐time systems. The simplification is started from the squared magnitude function M(e^jTω ) =G(e^jTω )G(e^–jTω ), where G(z) is the z‐transfer function of a given high order discrete‐time system. The method is fully computer‐oriented and leads to a satisfactory approximation while preserving stability and minimum‐phase characteristics.     

Crack velocities in natural rubber

Measurements are reported of the limiting velocity of a running crack in biaxially stretched sheets of unfilled and carbon-black-filled natural rubber. The crack velocity was found to increase with the cleavage strain,e _y , and also with the strain,e _x , parallel to the direction of tearing, reaching values of over 100 m sec^–1 at the highest strain levels employed. These crack velocities are shown to be close to those predicted by Mott's theory, i.e., about one-third of the velocity of sound, when a strong strain-dependence is recognized for the velocity of sound in rubber.     

Nontrivial behavior of the piezoelectric coefficients of 0–3 composites of the modified PbTiO<Subscript>3</Subscript> ceramics-polymer type

Piezoelectric properties of the 0–3 connectivity composites comprising spheroidal inclusions of modified PbTiO₃ ceramics dispersed in a polymer matrix have been studied. Monotonic and nonmonotonic concentration dependences of the effective piezoelectric coefficients e _3j *, d _3j *, h _3j *, and (j=1, 3) of the composites with elongated ferroelectric ceramic (FC) inclusions are analyzed. The observed nontrivial piezoelectric response of the 0–3 composites of the modified PbTiO₃ ceramics-polymer type is determined to a considerable extent by properties of the polymer matrix and by the sign of the e _3j ^(FC) coefficients (e _3j ^(FC) >0).     

A Coefficient Measuring the Goodness of Fit

An “index of discrepancy” is introduced to measure the deviation of an actual population from the population stated as null-hypothesis. The index is estimated by a statistic proportional to the familiar expression Σ(o – e)^2/e , used in chi-square tests, with a subsequent correction for bias. The index can be used for any simple hypothesis and also as a measure of heterogeneity or of association in contingency tables. Asymptotic confidence limits (for large samples) are established on the basis that (under suitable conditions) Σ(o – e)^2/e approaches a non-central chi-square distribution. Nomograms are provided to facilitate the computation of the confidence limits.     

Isoindigo‐Based Polymers with Small Effective Masses for High‐Mobility Ambipolar Field‐Effect Transistors

So far, most of the reported high‐mobility conjugated polymers are p‐type semiconductors. By contrast, the advances in high‐mobility ambipolar polymers fall greatly behind those of p‐type counterparts. Instead of unipolar p‐type and n‐type materials, ambipolar polymers, especially balanced ambipolar polymers, are potentially serviceable for easy‐fabrication and low‐cost complementary metal‐oxide‐semiconductor circuits. Therefore, it is a critical issue to develop high‐mobility ambipolar polymers. Here, three isoindigo‐based polymers, PIID‐2FBT , P1FIID‐2FBT , and P2FIID‐2FBT are developed for high‐performance ambipolar organic field‐effect transistors. After the incorporation of fluorine atoms, the polymers exhibit enhanced coplanarity, lower energy levels, higher crystallinity, and thus increased µ _e. P2FIID‐2FBT exhibits n‐type dominant performance with a µ _e of 9.70 cm² V^?1 s^?1. Moreover, P1FIID‐2FBT exhibits a highly balanced µ _h and µ _e of 6.41 and 6.76 cm² V^?1 s^?1, respectively, which are among the highest values for balanced ambipolar polymers. Moreover, a concept “effective mass” is introduced to further study the reasons for the high performance of the polymers. All the polymers have small effective masses, indicating good intramolecular charge transport. The results demonstrate that high‐mobility ambipolar semiconductors can be obtained by designing polymers with fine‐tuned energy levels, small effective masses, and high crystallinity.     

Modeling Steady Acoustic Fields Bounded in Cavities with Geometrical Imperfections

A mathematical method is derived within the framework of classical Lagrangian field theory, which is suitable for the determination of the eigenstates of acoustic resonators of nearly spherical shape. The method is based on the expansion of the Helmholtz differential operator and the boundary condition in a power series of a small geometrical perturbation parameter e{\epsilon} . The method extends to orders higher than e²{\epsilon^2} the calculation of the perturbed acoustic eigenvalues, which was previously limited by the use of variational formalism and the methods of Morse and Ingard. A specific example is worked out for radial modes of a prolate spheroid, with the frequency perturbation calculated to order e³{\epsilon^3} . A possible strategy to tackle the problem of calculating the acoustic eigenvalues for cavities presenting non-smooth geometrical imperfections is also described.     

Self-driven tunneling crack arrays—a 3D-fracture mechanics bifurcation analysis

Tunneling cracks driven by drying in a ceramic precursor confined between two glass plates represent a simple type of three-dimensional (3D) crack pattern. They arrange themselves via mutual unloading which causes some cracks to stop whereby the remaining ones get the right spacing for further propagation. By extending a 2D-model of self-driven propagation of crack arrays, a fracture mechanical bifurcation analysis for 3D-crack patterns based on calculating the post-critical contour of the alternating bifurcation mode has been developed. Shrinkage due to drying is replaced here by a simplified thermo-mechanical model based on an effective heat flow whose related temperature field and thermal stresses drive crack propagation. By means of the finite element method, the propagation velocity and the minimum spacing between the steady-state parallel tunnelling cracks are determined. Comparison of theory and experiment suggests that propagation may be non-stationary in these experiments. The observed relation between crack spacing and layer thickness, p ~ e ^2/3, follows from a scaling analysis.     

Studying the Properties of Supercooled Strongly-Coupled Plasma Created by Artificial Injection into Space

Attention is drawn to the possibility of creation of the supercooled strongly-coupled (nonideal) plasma by an explosive ejection from spacecraft into vacuum. The values of the Coulomb's coupling parameter *_e=(e²N^1/3)/(k_BT_e) attained in such process can be as large as 3, i.e., considerably greater than in laboratory devices. By using the virial relations and the assumption of ergodicity, we developed an efficient method for reduction of the many-particle distribution function for the system of strongly-coupled electrons to the effective one-particle function, which enabled us to calculate a concentration of free charge carriers. This quantity turns out to be substantially suppressed by the quasi-localization of electrons in the vicinity of nearby ions; and, as a result, an anomalous electrical resistance should be expected.     

Inelastic Interaction of an Electron with a C60 Cluster

The method of intersecting beams of C₆₀ fullerene clusters and of electrons is used to investigate the production of C ₆₀ ⁺ and C ₆₀ ^– ions and the radiation in the wavelength range from 300 to 800 nm for the electron energy E _e ranging from zero to 100 eV. The absolute values of the ionization and electron-attachment cross sections [⁺(E _e ) and ^–(E _e ), respectively] are determined. A maximum of ⁺(E _e ) of 0.53 nm²is observed at E _e = 52 eV. For a C₆₀ cluster excited by electron impact, delayed (150 s) ionization initiated by collision with the surface and ionization due to thermionic emission (its characteristic time at E _e = 60 eV is 6 s) is observed. It is found that, for E _e < 0.4 eV, the formation of C ₆₀ ^– is defined by the polarization capture of an s-electron (^– E _e ^–1 ), and a formula is suggested for determining ^–(E _e ). In the region of E _e from 1 to 6 eV, the cross section ^–(E _e ) shows only slight variations about ^–(E _e ) = 0.36 ± 0.03 nm². For E _e > 7.5 eV, C ₆₀ ^– ions proved to be unstable to electron autodetachment. In the region of intersection of C₆₀ and electron beams, radiation of a quasicontinuous spectrum described by a modified Planck formula for the thermal emission of spherical particles of diameter d is recorded. For E _e > 47 eV, the brightness temperature proved to be 3150 ± 50 K. It is found that this radiation is emitted predominantly by hot C ₆₀ ^+* ions produced as a result of thermionic emission from C ₆₀ ^* . The rate of radiation loss of energy by a C ₆₀ ^+* ion and the cross section for the formation of radiating C ₆₀ ^+* ions are found to be, respectively, 5.5 × 10⁵ eV/s at T = 3150 K and 2 × 10^–2 nm² at E _e = 60 eV.     

Optimal method for changing the number of kanbans in the e -Kanban system and its applications

The Toyota Motor Corporation has recently developed a new kanban system called ‘e-Kanban’, which is a parts ordering information system that operates within the communications network established between Toyota and its suppliers. One of the goals for developing the e-Kanban system was to introduce an efficient means for properly changing the number of kanbans once the required number has been calculated, as changing the number of kanbans in the kanban system directly affects the order quantity. Consequently, it is very important to monitor carefully and control changes in the number of kanbans. The paper investigates and proposes an effective method for changing the number of kanbans using the e-Kanban system. Applying this method to three problems, it is shown that the e-Kanban system can be implemented more efficiently and effectively than the original kanban system.     

破损铝电解槽阴极钢棒的冲击回波法检测

电解槽的寿命及修复关系着整个电解铝行业的经济效益,是不容忽视的技术问题。为能对破损电解槽进行及时修复从而延长电解槽寿命,提出应用冲击回波法对电解槽破损状况进行评估。首先利用数值模拟方法探讨了冲击回波激振源特性对应力波脉冲宽度及应力峰值的影响,得出激振源直径D与脉冲宽度tc呈线性相关：tc=0.004D,且与应力峰值(P)呈指数相关P=2e~8D^{1.928 8},而冲击速度v不改变脉冲宽度tc,但与应力峰值P呈线性相关：P=0.0751v-0.068 6。进而基于数值分析结果,运用冲击回波法检测破损电解槽中的阴极钢棒,通过对检测结果的时频域分析,得出了阴极钢棒的破损状况及位置,并与刨槽后真实的阴极钢棒对比。结果表明：冲击回波法能很好地实现电解槽破损部位的定位,可为电解槽寿命评估与修复提供参考。     

Laminar boundary layers with vectored mass transfer

By using Keller's Box method, the effects of vectored mass transfer with heat transfer on boundary layer flows with variable gas properties, non-unity Prandtl number and non-zero E( = u²_e/2H_e) has been studied. The results have been compared with the results obtained by other investigators and it has been found that the point of inflexion in velocity and total enthalpy profiles responsible for inducing instability in the flows, can be avoided under certain circumstances.     

An equilibrium theory of the dilute solutions of3He in superfluid4He at very low temperatures

An equilibrium theory of the dilute solutions of ³ He in superfluid ⁴ He is derived systematically. The theory is based on a model which (a) goes beyond the parabolic Landau-Pomeranchuk approximation for the ³ He quasiparticle energy by taking into account the fourth-order term in the momentum expansion of this quantity, (b) disregards contributions to the ³ He quasiparticle effective interaction whose order in the momentum is higher than two, and (c) allows the effective interaction to be nonlocal. The simplicity of the model enables the development of a unified parametrization of the various equilibrium properties of the solutions. The expressions obtained for these properties are both easy to apply and highly accurate over a wide temperature range spanning from T=0 to temperatures of the order of the ³ He quasiparticle degeneracy temperature. It is shown that the parameters appearing in the expression for the ³ He quasiparticle effective interaction at fixed ⁴ He number density are replaced in the fixed-pressure, low-temperature expansions of the equilibrium properties by other parameters whose appearance in the theory seems to be due to the renormalization of this interaction by the interactions between the ³ He quasiparticles and the virtual fluctuations of the ⁴ He number density Finally, a comparison is made between theory and experiment. Three quantities are considered in detail : the ³ He osmotic pressure and the ³ He quasiparticle inertial and specific heat effective masses. The analysis of the experimental data makes it possible to determine the parameters associated with the effective interaction at several pressures. It is found that the theory is, in general, in a very good accord with the experimental situation and that, within its framework, the experimental values of the osmotic pressure and the two effective masses are indeed consistent with one another.     

Polarization, piezoelectric properties, and elastic coefficients of In x Ga1−x N solid solutions from first principles

III-nitrides GaN and InN, and In _x Ga_1−x N solid solutions are polarizable semiconductors that crystallize in the prototypical wurtzite (W) structure. We present here the results of a density functional theory study carried out to determine the spontaneous polarization, piezoelectric coefficients, and elastic coefficients of In _x Ga_1−x N alloys as a function of In the concentration x. To calculate these properties, we construct three distinct hexagonal/orthorhombic equivalent In _x Ga_1−x N supercells that are derived from the disordered W unit cell of GaN and InN. These include an ordered W lattice (P6₃ mc/Pmc2₁) and orthorhombic O-16 and O-32 lattices with Pmn2₁/Pna2₁ or P2₁ symmetry, respectively. Depending on the crystal structure, spontaneous polarization as a function of the In concentration x shows a downward bowing (W), a linear interpolation (O-16), and an upward bowing (O-32) between −0.033 C/m² and −0.043 C/m², the spontaneous polarizations of the end components GaN and InN, respectively. The composition dependence of the effective basal plane and out of plane (along the [0001] direction) piezoelectric coefficients (e _// and e ₃₃, respectively) in the W and O-16 structure is non-linear and varies between e _// = −0.287 C/m² and e ₃₃ = 0.598 C/m² for GaN, and e _// = −0.455 C/m² and e ₃₃ = 1.044 C/m² for InN. While the bulk modulus of In _x Ga_1−x N in the W and O-16 structures follows Vegard’s law from 170 GPa (x = 0) to 124 GPa (x = 1), in the O-32 structure it shows a strong downward bowing for compositions 0 < x < 0.5.     

The parameters of laser plasmas formed using polycrystalline CuInS<Subscript>2</Subscript>, copper,and indium targets

We have studied the electron temperature (T _e) and density (N _e) of laser plasmas formed under the action of a neodymium laser in a polycrystalline CuInS₂ target, as well as in pure copper and indium targets. At a laser beam power density of ∼10⁸ W/cm², the average electron temperature of a laser plasma at a distance of r=1 mm from the CuInS₂ target falls within 0.55–0.77 eV, while the laser plasmas of copper and indium are characterized by T _e(Cu)=0.4–1.8 eV and T _e(In)=0.58–2.4 eV, respectively. The average electron density at the core of the laser torch (r=1 mm) at the CuInS₂ target reaches N _e=2.2×10¹⁶ cm⁻³. The results obtained for the polycrystalline target can be used in microelectronics for optimization of the process of laser deposition of thin films for solar cell elements.     

Spin-vortex Superconductivity

We present a theory of superconductivity based on the theoretical prediction that a macroscopic persistent current is generated by spin-vortices. It explains the origin of the phase variable θ that is canonical conjugate to the superfluid density as a Berry phase arising from the spin-vortex formation. This superconductivity does not require Cooper-pairs as charge carriers, thus, is not directly related to the standard theory based on the BCS one; however, it exhibits the flux quantization in the unit Φ ₀=hc/2|e|, where h is Planck’s constant, c the speed of light, and e the electron charge; and the AC Josephson frequency, f _J=2|e|V/h, where V is the voltage of the battery connected to the superconductor–insulator–superconductor junction. In due course, it is found that the standard derivation of the AC Josephson frequency misses a term arising from the flow of particles through the leads connected to the junction. If this contribution is included, the observed f _J indicates that the phase θ is a variable conjugate to the number density of charge e carriers instead of the currently accepted charge 2e carriers. We propose an experiment that discriminates whether it is e or 2e. If the above claim is verified, it means that the BCS theory cannot predict whether a particular compound is a superconductor or not since it does not explain the origin of θ. A connection between the present mechanism and the BCS mechanism is discussed; the fact that the BCS theory gives an excellent estimate of T _c is attributed to the fact that it predicts the temperature at which spin-vortices become long-lived due to the energy gap formation; since the stabilization by the electron-pair formation is compatible with the present mechanism, asymmetries observed in the even and odd number of electron systems are preserved. The most notable difference is that the persistent current generation is formulated in a strictly particle-number-conserving manner. Thus, it does not violate the superselection rule for the total charge.     

Anomalously high charging of dispersed particles by 25-keV electron beam

The phenomenon of ultrahigh charging of dust particles under the action of an electron beam has been studied. The electron energy was 25 keV and the characteristic size of dispersed aluminum oxide micro-particles was about 100 μm. The charge acquired by a dust particle amounted to 5 × 10⁷ e, which corresponds to a charge of 10⁶ e for a micron-sized particle and is greater by at least two orders of magnitude than the characteristic values of charge observed for particles of the same size in low-pressure gas discharge.     

Development and Characterization of Microcalorimeters for a Next Generation 187Re Beta-Decay Experiment

It has been demonstrated in the past that observing the β-decay spectrum of ¹⁸⁷Re with microbolometers provides a suitable method to determine the mass of the electron anti-neutrino from β-endpoint measurements. In a first step, with the experiment MIBETA a sensitivity of m _νe≤15 eV/c² was achieved. To compete with the sensitivity of m _νe≤2.2 eV/c² established by the Mainz/Troitsk tritium β-decay experiment and the limit of m _νe≤0.2 eV/c² aimed at with KATRIN, a new experiment MARE has been initiated. As a first stage (MARE-1), 300 detectors consisting of silicon implanted thermistors, produced by NASA/GSFC, and absorbers of AgReO₄ crystals will be mounted. To optimize the experimental setup, a test array was equipped with 10 AgReO₄ crystals of various size and shape. The influence of the crystal quality as well as of different types of resin on rise time and energy resolution was investigated.      

The velocities of first and second sound in dilute solutions of3He in superfluid4He at very low temperatures

A unified theory of first and second sound in dilute solutions of ³ He in superfluid ⁴ He at very low temperatures is presented. The theory is based on the detailed semimicroscopic model for the ³ He quasiparticle excitations described by Disatnik and Brucker a few years ago. In contrast with Khalatnikov's macroscopic theory, the application of this model enables the derivation of relatively simple expressions for the sound velocities in which no omissions of terms representing contributions due to the thermal expansion are made. The sound velocities are given in the final expressions in terms of various parameters of the ³ He quasiparticle spectrum and effective interaction. These expressions are both highly accurate and easy to use over a wide temperature regime spanning from the quantum limit to temperatures of the order of the ³ He quasiparticle degeneracy temperature. The actual application of the theory to measurements of the sound velocities is described in detail. Numerical values or estimates for various characteristic parameters of the ³ He quasiparticle system, including in particular the ³ He quasiparticle effective mass, are obtained from the comparison between the theory and the experiment. The example of the second sound velocity is used to illustrate a procedure for analyzing data from very low-temperature measurements of the equilibrium properties of the solutions, which is expected to produce meaningful information regarding the parameters of the basic model. In practice, the theory is found to be in a very good accord with the measurements of the sound velocities. The result obtained for the zero concentration limit of the ³ He quasiparticle effective mass (m ₀ =2.19m ₃ ) is somewhat lower than the empirical estimates reported in the past. On the other hand, this result is in very good agreement with variational calculations based on the detailed microscopic theory of the solutions. A discussion of this and other results obtained from the comparison between theory and experiment is included.Work supported in part by the United States-Israel Binational Science Foundation.Killed in action, 16 October 1973.