Molecular modeling guided isotope separation of gadolinium with strong cation exchange resin using displacement chromatography

Molecular modeling was carried out using DFT to identify the suitable displacing agent for carrying out Gd isotope separation using displacement chromatography. EDTA was identified as the best eluting agent among EDTA, malic acid and citric acid. Displacement chromatography of Gd adsorption band in cation exchange resin was performed to observe the isotope effects in the Gd ion exchange processes involving complex forming reagent – EDTA. The heavier isotope of ¹⁶⁰Gd was found to be enriched at the front boundary of Gd adsorption band, while the lighter isotopes of ¹⁵⁵Gd and ¹⁵⁷Gd were enriched at the rear boundary.     

Structural and Luminescence Studies on Barium Sodium Borosilicate Glasses Containing Uranium Oxides

Barium sodium borosilicate glasses containing different amounts of uranium oxides were prepared by conventional melt quench method and investigated for their structural aspects by ²⁹Si and ¹¹B MAS NMR technique combined with steady‐state luminescence and lifetime measurements. Based on MAS NMR studies, it is confirmed that uranium ions act as network modifier up to 15 wt% and beyond which a separate uranium containing phase is formed. From the luminescence studies, it is inferred that uranyl species is in a highly distorted environment. For more than 15 wt% uranium oxide incorporation, weaker U–O–U linkages are formed at the expense stronger U–O–Si/B linkages, as suggested by the excited state lifetime value of the uranyl species as well as red shift in emission peak maximum. For glass samples containing more than 25 wt% uranium oxides, crystalline barium uranium silicate gets phase separated from glass matrix as confirmed by XRD studies.     

Revisiting the size selective performance of EPA's high-volume total suspended particulate matter (Hi-Vol TSP) sampler

Under the National Ambient Air Quality Standard (NAAQS) for airborne lead, measurements are conducted by means of a high-volume total suspended particulate matter (Hi-Vol TSP) sampler. In the decade between 1973 and 1983, there were 12 publications that explored the sampling characteristics and effectiveness of the Hi-Vol TSP, yet there persists uncertainty regarding its performance. This article presents an overview of the existing literature on the performance of the Hi-Vol TSP, and identifies the reported sampler effectiveness with respect to four factors: particle size (reported effectiveness of 7%–100%), wind speed (?36% to 100%), sampler orientation (7%–100%), and operational state (107%–140%). Effectiveness of the Hi-Vol TSP was evaluated with a solid, polydisperse aerosol in a controlled wind tunnel setting. Isokinetic samplers were deployed alongside the Hi-Vol TSP to investigate three wind speeds (2, 8, and 24 km h^?1), three sampler orientations (0°, 45°, 90°), and two operational states (on, off) for aerosols with aerodynamic diameters from 5 to 35 µm. Results indicate that particle diameter was the largest determining factor of effectiveness followed by wind speed. Orientation of the sampler did not have a significant effect at 2 and 8 km h^?1 but did at 24 km h^?1. In a passive state, the Hi-Vol TSP was collected between 1% and 7% of available aerosol depending on particle size and wind speed. Results of this research do not invalidate results of previous studies but rather contribute to our overall understanding of the Hi-Vol TSP's size-selective performance. While results generally agreed with previous studies, the Hi-Vol TSP was found to exhibit less dependence on these four factors than previously reported.

© 2017 American Association for Aerosol Research     

Tokens vs. Signals: On Conformance between Formal Models of Dataflow and Hardware

Designing hardware often involves several types of modeling and analysis, e.g., in order to check system correctness, to derive performance properties such as throughput, to optimize resource usages (e.g., buffer sizes), and to synthesize parts of a circuit (e.g., control logic). Working directly with low-level hardware models such as finite-state machines (FSMs) to answer such questions is often infeasible, e.g., due to state explosion. Instead, designers often use dataflow models such as SDF and CSDF, which are more abstract than FSMs, and less expensive to use since they come with more efficient analysis algorithms. However, dataflow models are only abstractions of the real hardware, and often omit critical information. This raises the question, when can one say that a certain dataflow model faithfully captures a given piece of hardware? The question is of more than simply academic interest. Indeed, as illustrated in this paper, dataflow-based analysis outcomes may sometimes be defensive (e.g., buffers that are too big) or even incorrect (e.g., buffers that are too small). To answer the question of faithfully capturing hardware using dataflow models, we develop a formal conformance relation between the heterogeneous formalisms of (1) finite-state machines with synchronous semantics, typically used to model synchronous hardware, and (2) asynchronous processes communicating via queues, used as a formal model for dataflow. The conformance relation preserves performance properties such as worst-case throughput and latency.     

Topology optimization for nonlinear dynamic problems: Considerations for automotive crashworthiness

Crashworthiness of automotive structures is most often engineered after an optimal topology has been arrived at using other design considerations. This study is an attempt to incorporate crashworthiness requirements upfront in the topology synthesis process using a mathematically consistent framework. It proposes the use of equivalent linear systems from the nonlinear dynamic simulation in conjunction with a discrete-material topology optimizer. Velocity and acceleration constraints are consistently incorporated in the optimization set-up. Issues specific to crash problems due to the explicit solution methodology employed, nature of the boundary conditions imposed on the structure, etc. are discussed and possible resolutions are proposed. A demonstration of the methodology on two-dimensional problems that address some of the structural requirements and the types of loading typical of frontal and side impact is provided in order to show that this methodology has the potential for topology synthesis incorporating crashworthiness requirements.     

Propagation delay and power dissipation for different aspect ratio of single-walled carbon nanotube bundled TSV

Through-silicon vias (TSVs) have provided an attractive solution for three-dimensional (3D) integrated devices and circuit technologies with reduced parasitic losses and power dissipation, higher input-output (I/O) density and improved system performance. This paper investigates the propagation delay and average power dissipation of single-walled carbon nanotube bundled TSVs having different via radius and height. Depending on the physical configuration, a comprehensive and accurate analytical model of CNT bundled TSV is employed to represent the via (vertical interconnect access) line of a driver-TSV-load (DTL) system. The via radius and height are used to estimate the bundle aspect ratio (AR) and the cross-sectional area. For a fixed via height, the delay and the power dissipation are reduced up to 96.2% using a SWCNT bundled TSV with AR = 300 : 1 in comparison to AR = 6 : 1.     

Admittance Loci Based Design of Plasmonic Sensor Working in Wavelength Interrogation Regime

A prism coupler based plasmonic sensor consisting of a prism, gold (Au) metal film and dielectric sample has been investigated with the use of admittance loci method in wavelength interrogation mode. Prism materials namely fused silica, chalcogenide (2S2G) and silicon have been used to study their effect on surface plasmon sensing in wavelength interrogation mode by admittance loci plots and by corresponding surface plasmon sensing curves. The performance of the plasmonic sensor under wavelength interrogation mode based on the choice of the prism material has been discussed and validated by the dynamic range and sensitivity plots.     

Using light to control the interactions between self-rotating assemblies of active gels

Polymer gels undergoing the oscillating Belousov-Zhabotinsky (BZ) reaction exhibit an autonomous, periodic swelling and deswelling, where the mechanical oscillations are driven by the chemical reaction within the polymer network. Using computer simulations, we show that these BZ gels can undergo a form of auto-chemotaxis, enabling the gels to spontaneously move in response to self-generated chemical gradients. Focusing on four millimeter-sized pieces of these BZ gels, we show that the pieces can organize into self-rotating clusters that resemble a moving pinwheel or gear. By analyzing the factors that promote the formation of a single self-rotating cluster, we attempt to design systems of multiple, interacting gears. We show that light, which suppresses the oscillations of the gels, can be harnessed to promote the formation of two self-rotating clusters. These studies point to a novel form of photo-chemo-mechanical transduction, where light is utilized to control the conversion of chemical and mechanical energy in the system. Moreover, the interaction between the BZ gel gears reveals a new form of entrainment between these moving units. Namely, their coordinated motion is achieved through chemical coupling or communication, rather than a mechanical coupling. These findings can lead to the formation of chemically “communicating” devices that can be programmed to perform autonomous work through the use of light.