Tip Allocation: A Compliance Study tor Restaurants

Survey research of the commercial food service industry with regard to tips and tip allocation revealed that 50 percent of restaurateurs require that employees report a minimum amount or percentage of sales and over 50 percent which allocate tips report them as employee income. The authors discuss these results and point out other problems

Controlling Spatiotemporal Mechanics of Supramolecular Hydrogel Networks with Highly Branched Cucurbit[8]uril Polyrotaxanes

Attempts to rationally tune the macroscopic mechanical performance of supramolecular hydrogel networks through noncovalent molecular interactions have led to a wide variety of supramolecular materials with desirable functions. While the viscoelastic properties are dominated by temporal hierarchy (crosslinking kinetics), direct mechanistic studies on spatiotemporal control of supramolecular hydrogel networks, based on host-guest chemistry, have not yet been established. Here, supramolecular hydrogel networks assembled from highly branched cucurbit[8]uril-threaded polyrotaxanes (HBP-CB[8] ) and naphthyl-functionalized hydroxyethyl cellulose (HECNp) are reported, exploiting the CB[8] host-guest complexation. Mechanically locking CB[8] host molecules onto a highly branched hydrophilic polymer backbone, through selective binary complexation with viologen derivatives, dramatically increases the solubility of CB[8]. Additionally, the branched architecture enables tuning of material dynamics of the supramolecular hydrogel networks via both topological (spatial hierarchy) and kinetic (temporal hierarchy) control. Relationship between macroscopic properties (time- and temperature-dependent rheological properties, thermal stability, and reversibility), spatiotemporal hierarchy, and chain dynamics of the highly branched polyrotaxane hydrogel networks is investigated in detail. Such kind of tuning of material mechanics through spatiotemporal hierarchy improves our understanding of the challenging relationship between design of supramolecular polymeric materials and their complex viscoelasticity, and also highlights a facile strategy to engineer dynamic supramolecular materials.Ministry of Education of Malaysia and Universiti Teknologi MARA, Marie Curie Fellowship. Grant Number: 65836

Three-waveform bidirectional pumping of single electrons with a silicon quantum dot

Semiconductor-based quantum dot single-electron pumps are currently the most promising candidates for the direct realization of the emerging quantum standard of the ampere in the International System of Units. Here, we discuss a silicon quantum dot single-electron pump with radio frequency control over the transparencies of entrance and exit barriers as well as the dot potential. We show that our driving protocol leads to robust bidirectional pumping: one can conveniently reverse the direction of the quantized current by changing only the phase shift of one driving waveform with respect to the others. We anticipate that this pumping technique may be used in the future to perform error counting experiments by pumping the electrons into and out of a reservoir island monitored by a charge sensor.The financial support from the Centre of Excellence in Computational Nanoscience (project 284621 and 251748) by the Academy of Finland (Grant Nos 251748, 135794, 272806, and 276528), the Australian Research Council (Grant Nos DP120104710 and DP160104923), Jenny and Antti Wihuri Foundation, The Finnish Cultural Foundation, and the Australian National Fabrication Facility are acknowledged. A. R. thanks the University of New South Wales Early Career Research Grant scheme for financial support. We acknowledge the provision of facilities and technical support by Aalto University at Micronova Nanofabrication Centre

Nanoscale state-of-charge heterogeneities within polycrystalline nickel-rich layered oxide cathode materials

Nickel-rich cathodes (LiNixMnyCo1-x-yO2, x > 0.6) permit higher energy in lithium-ion rechargeable batteries but suffer from accelerated degradation at potentials above 4.1 V versus Li/Li+. Here, we present a proof-of-concept in situ pouch cell and methodology for correlative 2D synchrotron transmission X-ray microscopy with 3D lab-based micro-CT. XANES analysis of the TXM data enables tracking of Ni edge energy within and between the polycrystalline NMC811 particles embedded in the operating electrode through its initial delithiation. By using edge energy as a proxy, state-of-charge heterogeneities can be tracked at the nanoscale, revealing the role of cracked particles as potential nucleation points for failure and highlighting the challenges in achieving uniform (de-)lithiation. We propose, in future work, to leverage the pouch cell design presented here for longitudinal TXM-XANES studies of nickel-rich cathodes across multiple cycles and operating variables and investigate the effect of dopants and microstructural optimization in mitigating degradation

4D Bragg Edge Tomography of Directional Ice Templated Graphite Electrodes

Bragg edge tomography was carried out on novel, ultra-thick, directional ice templated graphite electrodes for Li-ion battery cells to visualise the distribution of graphite and stable lithiation phases, namely LiC12 and LiC6. The four-dimensional Bragg edge, wavelength-resolved neutron tomography technique allowed the investigation of the crystallographic lithiation states and comparison with the electrode state of charge. The tomographic imaging technique provided insight into the crystallographic changes during de-/lithiation over the electrode thickness by mapping the attenuation curves and Bragg edge parameters with a spatial resolution of approximately 300 µm. This feasibility study was performed on the IMAT beamline at the ISIS pulsed neutron spallation source, UK, and was the first time the 4D Bragg edge tomography method was applied to Li-ion battery electrodes. The utility of the technique was further enhanced by correlation with corresponding X-ray tomography data obtained at the Diamond Light Source, UK

Rapid Preparation of Geometrically Optimal Battery Electrode Samples for Nano Scale X-ray Characterisation

Rechargeable lithium-based batteries are one of the key enabling technologies driving the shift to renewable energy, and research into novel technologies has intensified to meet growing demands in applications requiring higher energy and power density. The mechanisms behind battery degradation can be investigated across multiple length-scales with X-ray imaging methods; at the nanoscale severe constraints are imposed on sample size in order to obtain adequate signal to noise. Here, we present a novel lasermilling technique to prepare geometrically optimal samples for X-ray nano-tomography. Advantages of this technique include significantly reduced sample preparation time, and a suitable geometry for mosaic acquisition, enabling a larger field of view to be captured at high spatial resolution, thus improving statistics. The geometry of the resulting electrode remains highly suitable for nano-tomography, and yet permits in situ and operando experiments to be carried out on standard electrode coatings, providing new insights into transient phenomena whilst closely mimicking standard electrochemical cells

Integrated model for flood forecasting and river inundation in Taiwan

This is the author accepted manuscriptRoyal Societ

Nature of the many-body excitations in a quantum wire: Theory and experiment

The natural excitations of an interacting one-dimensional system at low energy are hydrodynamic modes of Luttinger liquid, protected by the Lorentz invariance of the linear dispersion. We show that beyond low energies, where quadratic dispersion reduces the symmetry to Galilean, the main character of the many-body excitations changes into a hierarchy: calculations of dynamic correlation functions for fermions (without spin) show that the spectral weights of the excitations are proportional to powers of $\mathcal{R}^{2}/L^{2}$, where $\mathcal{R}$ is a length-scale related to interactions and $L$ is the system length. Thus only small numbers of excitations carry the principal spectral power in representative regions on the energy-momentum planes. We have analysed the spectral function in detail and have shown that the first-level (strongest) excitations form a mode with parabolic dispersion, like that of a renormalised single particle. The second-level excitations produce a singular power-law line shape to the first-level mode and multiple power-laws at the spectral edge. We have illustrated crossover to Luttinger liquid at low energy by calculating the local density of state through all energy scales: from linear to non-linear, and to above the chemical potential energies. In order to test this model, we have carried out experiments to measure momentum-resolved tunnelling of electrons (fermions with spin) from/to a wire formed within a GaAs heterostructure. We observe well-resolved spin-charge separation at low energy with appreciable interaction strength and only a parabolic dispersion of the first-level mode at higher energies. We find structure resembling the second-level excitations, which dies away rapidly at high momentum in line with the theoretical predictions here.We acknowledge financial support from the UK EPSRC through Grants No. EP/J01690X/1 and No. EP/J016888/1 and from the DFG through SFB/TRR 49. This research was supported in part by the National Science Foundation under Grant No. NSF PHY11-25915.This is the author accepted manuscript. The final version is available from APS via http://dx.doi.org/10.1103/PhysRevB.93.07514

Identifying the Origins of Microstructural Defects Such as Cracking within Ni‐Rich NMC811 Cathode Particles for Lithium‐Ion Batteries

The next generation of automotive lithium‐ion batteries may employ NMC811 materials; however, defective particles are of significant interest due to their links to performance loss. Here, it is demonstrated that even before operation, on average, one‐third of NMC811 particles experience some form of defect, increasing in severity near the separator interface. It is determined that defective particles can be detected and quantified using low resolution imaging, presenting a significant improvement for material statistics. Fluorescence and diffraction data reveal that the variation of Mn content within the NMC particles may correlate to crystallographic disordering, indicating that the mobility and dissolution of Mn may be a key aspect of degradation during initial cycling. This, however, does not appear to correlate with the severity of particle cracking, which when analyzed at high spatial resolutions, reveals cracking structures similar to lower Ni content NMC, suggesting that the disconnection and separation of neighboring primary particles may be due to electrochemical expansion/contraction, exacerbated by other factors such as grain orientation that are inherent in such polycrystalline materials. These findings can guide research directions toward mitigating degradation at each respective length‐scale: electrode sheets, secondary and primary particles, and individual crystals, ultimately leading to improved automotive ranges and lifetimes