Pulsed-Field-Gradient Measurements of Time-Dependent Gas Diffusion

Pulsed-field-gradient NMR techniques are demonstrated for measurements of time-dependent gas diffusion. The standard PGSE technique and variants, applied to a free gas mixture of thermally polarized xenon and O₂, are found to provide a reproducible measure of the xenon diffusion coefficient (5.71 × 10⁻⁶m²s⁻¹for 1 atm of pure xenon), in excellent agreement with previous, non-NMR measurements. The utility of pulsed-field-gradient NMR techniques is demonstrated by the first measurement of time-dependent (i.e., restricted) gas diffusion inside a porous medium (a random pack of glass beads), with results that agree well with theory. Two modified NMR pulse sequences derived from the PGSE technique (named the Pulsed Gradient Echo, or PGE, and the Pulsed Gradient Multiple Spin Echo, or PGMSE) are also applied to measurements of time dependent diffusion of laser polarized xenon gas, with results in good agreement with previous measurements on thermally polarized gas. The PGMSE technique is found to be superior to the PGE method, and to standard PGSE techniques and variants, for efficiently measuring laser polarized noble gas diffusion over a wide range of diffusion times.     

A new synthesis of α-amino acids—III: Amidoalkylation of active methylene compounds with glyoxylic acid derivatives

The synthesis of N-acyl derivatives of γ - keto - α - amino acids (3, 4, 5) by the amidoalkylation of 1,3-dicarbonyl compounds with glyoxylic acid-amide adducts (1, 2) is described. The γ - keto - α - amino acid derivatives (4, 5) were further converted to the corresponding butenolides (6, 7) and to pyrazolylglycine (12).     

Aluminum sulfate—an electrolyte for MnO2 hybrid supercapacitor

Journal of Solid State Electrochemistry - Manganese oxide is an important emerging electrode material for use in supercapacitor applications. Herein, we propose a new aqueous electrolyte,...     

Observation of a quantized hall resistivity in the presence of mesoscopic fluctuations

We present an experimental study of mesoscopic, two-dimensional electronic systems at high magnetic fields. Our samples, prepared from a low-mobility InGaAs/InAlAs wafer, exhibit reproducible, sample specific, resistance fluctuations. Focusing on the lowest Landau level, we find that, while the diagonal resistivity displays strong fluctuations, the Hall resistivity is free of fluctuations and remains quantized at its nu=1 value, h/e(2). This is true also in the insulating phase that terminates the quantum Hall series. These results extend the validity of the semicircle law of conductivity in the quantum Hall effect to the mesoscopic regime.     

Novel type of indium oxide thin films sputtering for opto-electronic applications

Transparent conductive oxide (TCO) thin films play a significant role in recent optical technologies. Displays of various types, photovoltaic systems, and opto-electronic devices use these films as transparent signal electrodes. They are used as heating surfaces and active control layers. Oxides of TCO materials such as: tin, indium, zinc, cadmium, titanium and the like, exhibit their properties. However, indium oxide and indium oxide doped with tin (ITO) coatings are the most used in this technology.In this work, we present conductive transparent indium oxide thin films which were prepared using a novel triode sputtering method. A pure In₂O₃ target of 2 in. in diameter was used in a laboratory triode sputtering system. This system provided plane plasma discharge at a relatively low pressure 0.5-5 mTorr of pure argon. The substrate temperature was varied during the experiments from room temperature up to 200 °C. The films were deposited on glass, silicon, and flexible polyimide substrates. The films were characterized for optical and electrical properties and compared with the indium oxide films deposited by magnetron sputtering.     

Artificial solid-electrolyte interphase (SEI) for improved cycleability and safety of lithium–ion cells for EV applications

Since the SEI is one of the most vulnerable factors in the safety of the lithium–ion battery, improvement in the stability of the SEI will result in a safer battery with better performance characteristics. In this work an artificial SEI was formed on graphite and tin–copper anodes by electropainting and vacuum-insertion techniques. The artificial SEI was found to stabilize the structure of the Sn–Cu anode and led to a cycle life for the cell that was longer by a factor of five and irreversible capacity less than half that of the pristine anode.     

Analysis of blank thickening in deep drawing processes using the theory of a Cosserat generalized membrane

This paper analyzes a transient, nonlinear deep drawing process where a circular blank of a rigid-plastic material is forced by a rigid circular punch to deform into a cylindrical cup. Attention is focused on the plastic flow beneath the blank-holder. Using the Cosserat theory of a generalized membrane it is possible to obtain analytical solutions which examine the following two major effects: (a) the importance of added “rim pressure” acting on the outer edge of the blank; and (b) the importance of a controlled moveable blank-holder to allow blank thickening during the drawing process. Guided by these analytical results, a new deep drawing machine was built to exploit these effects and increase the limit drawing ratio (LDR) of the drawing process. Specifically, the LDR (in one stroke) reached the value of 3.16 compared with the value of about 2.0 in the conventional process. Moreover, the analytical prediction of the punch force versus the punch stroke is in good agreement with the experimental data and with simulations using the computer code DYTRAN.     

Modal Analysis of a Servo-Hydraulic High Speed Machine and its Application to Dynamic Tensile Testing at an Intermediate Strain Rate

This paper describes the experimental procedure to identify the predominant frequencies of the high speed testing machine by conducting modal analysis. The effects due to the predominant frequencies of the system and loading rate on the magnitude of system ringing and the flow stress were analyzed by using a single degree-of-freedom (SDOF) spring-mass-damper model. The system was then used to study the dynamic tensile behavior of two engineering materials, i.e., polyethylene (PE) fabric-cement composite and Alkaline Resistant (AR) glass fabrics at an intermediate strain rate. The stress oscillations in the response of these materials due to system ringing were addressed. The failure behavior of each material was studied by examining high speed digital camera images of specimens during the test. The validity of the dynamic tensile tests was investigated by examining the condition of dynamic stress equilibrium—a criterion used in split Hopkinson pressure bar (SHPB) tests. The results show that the quantitative criterion for a valid SHPB test is also applicable to dynamic tensile tests of these materials at the intermediate strain rate.     

Enumeration and randomized constructions of hypertrees

Over 30 years ago, Kalai proved a beautiful d‐dimensional analog of Cayley's formula for the number of n‐vertex trees. He enumerated d‐dimensional hypertrees weighted by the squared size of their (d ? 1)‐dimensional homology group. This, however, does not answer the more basic problem of unweighted enumeration of d‐hypertrees, which is our concern here. Our main result, Theorem 1.4, significantly improves the lower bound for the number of d‐hypertrees. In addition, we study a random 1‐out model of d‐complexes where every (d ? 1)‐dimensional face selects a random d‐face containing it, and show that it has a negligible d‐dimensional homology.     

Box-threshold graphs

A graph is called box-threshold when all pairs of vertices with incomparable neighborhoods have the same degree. Several properties of box-threshold graphs, generalizing properties of threshold graphs, are proved. A transportation model with priority constraints is used to characterize their degree sequences. Further characterizations are given using the concept of the frame of a graph.