Bookermason9207

We conclude that mesoscopic models can reliably describe knots in those melts, where the length scale characterizing polymer stiffness is substantially larger than the size of monomer-monomer excluded volume. In this case, simplified local liquid structure influences knotting properties only marginally. In contrast, mesoscopic models perform poorly in melts with flexible chains. We qualitatively explain our findings through a free energy model of simple knots available in the literature.Block copolymer stars (BCSs) have been demonstrated to constitute versatile, self-assembling building blocks with tunable softness, functionalization, and shape. We investigate the dynamical properties of suspensions of short-arm BCSs under linear shear flow by means of extensive particle-based multiscale simulations. We determine the properties of the system for representative values of monomer packing fraction ranging from semidilute to concentrate regimes. We systematically analyze the formed network structures as a function of both shear rate and packing fraction, the reorganization of solvophobic patches, and the corresponding radial correlation functions. Connecting our findings with rheology, we calculate the viscosity as a function of shear rate and discuss the implications of the found shear thinning behavior.The autumnal leaf color change is a familiar phenomenon to most students living in temperate climate zones. The extraction and analysis of the pigments of the autumn leaves provide an engaging way to study the phenomenon utilizing both simple as well as more sophisticated analytical methods. In this laboratory experiment, students extract the red and yellow pigments, that is, anthocyanins and carotenoids from leaves and separate them from each other by liquid-liquid extractions. From the separated phases, anthocyanin and carotenoid concentrations can be evaluated visually or spectrophotometrically. The anthocyanins are analyzed by a rapid and simple ultra-performance liquid chromatography-tandem mass spectrometry method to discover which of the six most common groups of anthocyanins are present in the sample. The simplicity of the experiment setup allows it to be used as an introduction to mass spectrometry since the results can be easily interpreted without complicated data processing. The experiment provides opportunities for learning outside the classroom, as the samples can be collected from the nearby parks or forests and analyzed using more sophisticated methods on a student visit to a university or other research institution. The sample preparation followed by the visual analyses of the phases is however simple enough to be performed in a regular school laboratory.Tightly packaged receivers pose a challenge for noise measurements. Their only outputs are often diagnostic or benchmark information-"user data" that result from unknown processing. These include data rate test results, signal-to-noise ratio estimated by the receiver, and so on. Some of these are important gauges of communication viability that may be enshrined in performance and conformance specifications. Engineers can estimate these parameters based on standards and simplified system models, but there are few means to validate against physical measurements. We propose here a set of measurement techniques to complement and support models of system noise. The approach is founded on a semiparametric model of the noise response of a full-stack receiver. We probe this response experimentally by systematically perturbing signals and excess noise levels at the receiver input. The resulting technique is blind to protocol and implementation details. We introduce the design and implementation of some novel test capabilities required for these tests a precision programmable excess noise source and a highly directive programmable attenuator. We also introduce a regression procedure to estimate system noise (or NF) from the controlled input conditions and summary statistics of the user data output. We also estimate uncertainty in the measurement by combining traditional methods with a Monte Carlo method that propagates random errors through the regression. selleck products Case studies demonstrate the measurement with consumer wireless networking and geolocation equipment. These include verification by repeatability testing and cross-comparison against Y-factor measurements.A graphene quantized Hall resistance (QHR) device fabricated at the National Institute of Standards and Technology (NIST) was measured alongside a GaAs QHR device fabricated by the National Research Council of Canada (NRC) by comparing them to a 1 kΩ standard resistor using a cryogenic current comparator. The two devices were mounted in a custom developed dual probe that was then assessed for its viability as a suitable apparatus for precision measurements. The charge carrier density of the graphene device exhibited controllable tunability when annealed after Cr(CO)3 functionalization. These initial measurement results suggest that making resistance comparisons is possible with a single probe wired for two types of quantum standards - GaAs, the established material, and graphene, the newer material that may promote the development of more user-friendly equipment.Precision quantum Hall resistance measurements can be greatly improved when implementing new electrical contact geometries made from superconducting NbTiN. The sample designs described here minimize undesired resistances at contacts and interconnections, enabling further enhancement of device size and complexity when pursuing next-generation quantized Hall resistance devices.This work presents one solution for long-term storage of epitaxial graphene (EG) in air, namely through the functionalization of millimeter-scale devices with chromium tricarbonyl - Cr(CO)3. The carrier density may be tuned reproducibly by annealing below 400 K due to the presence of Cr(CO)3. All tuning is easily reversible with exposure to air, with the idle, in-air, carrier density always being close to the Dirac point. Precision measurements in the quantum Hall regime indicate no detrimental effects from the treatment, validating the pursuit of developing air-stable EG-based QHR devices.