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The β and γ phases of methylammonium chloride CH3NH3Cl and methylammonium bromide CH3NH3Br are identified to be ferroelectric via pyroelectric current and dielectric constant measurements.

In vendor managed inventory (VMI) operations, it is necessary for both the suppliers and the customers to reach an agreement on the maximal and minimal inventory level. In practice, in VMI, inventory levels are decided manually by planning personnel, based on their experience and past operating records. From a system optimization point of view, the determination of the upper and lower inventory levels in storage areas is complicated, necessitating analysis of many factors. Consequently, it may not be possible to obtain the best planning results, to determine and maintain the optimum levels of inventory. In this study, we utilize network flow techniques to build a replenishment model to deal with the upper-and-lower inventory level control problem, with the objective of minimizing the total cost in short-term operations, subject to inventory level control and other operating constraints. The model is formulated as an integer network flow problem with side constraints and is characterized as NP-hard in terms of optimization. To efficiently and effectively solve the large-scale problems that occur in the real world, a solution algorithm is also developed. Finally, numerical tests are conducted using real data from a major retail company in northern Taiwan. The results demonstrate the usefulness of the proposed model and solution algorithm for replenishment planning in actual practice.

We observe sharp step-down discontinuities in the magnetic susceptibility of NH4H2PO4 and NH4H2PO4-d60 (60% deuterated) along the a- and c-axes occurring exactly at their antiferroelectric transiti...

Most ferroelectric crystals have their own set of unique characteristics, and ammonium sulfate (NH4)2SO4 is no exception. We report on two previously unidentified features in ammonium sulfate: (1) ...

Different types of magnetism arise mainly from how electrons move and interact with each other. In this work, we show how protons (H+) also exhibit magnetic behavior. We measured the magnetic susce...

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We observe sharp step-down discontinuities in the magnetic susceptibility of NH

The associated magnetic moments of the periodic rotational motion of methyl groups in hexamethylbenzene C$_6$(CH$_3$)$_6$ were recently identified to contribute to its overall magnetic susceptibility. Those measurements however, were only performed on hydrogenous polycrystalline samples. We report magnetic susceptibility measurements on single crystalline C$_6$(CH$_3$)$_6$ in the cases where the applied magnetic field is parallel and perpendicular to the molecular basal planes. In the former case, metastable behavior near the onset temperature T$_{C-H}$=118 K is identified while in the latter, no anomalous behavior is observed. Similar anomalies are observed in deuterated hexamethylbenzene C$_6$(CD$_3$)$_6$ (where D is deuterium), however, T$_{C-D}$ occurs 14 K higher at 132 K. In addition, a peak anomaly identified near 42 K is suggested to be due to the onset of coherent quantum tunneling of deuterons. The near cubic ground state is proposed to be the result of a more radical form of the Jahn-Teller effect occurring in a molecular solid where the lattice distorts to remove the orbital degeneracies of the protons to lower its energy. The apparent magnetic anisotropy and isotope effect provide evidence that apart from electrons, not only protons, but also deuterons establish strongly correlated behavior., Comment: 21 pages (double spaced), 4 figures + 2 supplementary figures, Just Accepted Manuscript by the Journal of Physical Chemistry C

The polarity of the magnetic susceptibility χ(T) of ammonium alum NH4Al(SO4)2•12H2O single crystals below its ferroelectric Curie temperature TC is identified to depend only on the cooling rate. To explain this, we consider reorienting distorted NH4+ to carry weak magnetic and electric dipole moments that are linearly coupled. Slow cooling allows the dipole moments to align which enhances χ(T) to become positive. However, due to energy degeneracy of rotational motion and geometric frustration of the NH4+, faster cooling rates render the system to become an orientational glass state causing χ(T) to remain negative. Specific heat measurements also show the presence of excess entropy below a negative anomaly near 53 K. Our findings identify a possible new class of non-equilibrium system with potential applications in non-volatile memory devices.

PurposeTo determine the in vitro accuracy, test-retest repeatability, and interplatform reproducibility of T1 quantification protocols used for dynamic contrast-enhanced MRI at 1.5 and 3 T.MethodsA T1 phantom with 14 samples was imaged at eight centers with a common inversion-recovery spin-echo (IR-SE) protocol and a variable flip angle (VFA) protocol using seven flip angles, as well as site-specific protocols (VFA with different flip angles, variable repetition time, proton density, and Look-Locker inversion recovery). Factors influencing the accuracy (deviation from reference NMR T1 measurements) and repeatability were assessed using general linear mixed models. Interplatform reproducibility was assessed using coefficients of variation.ResultsFor the common IR-SE protocol, accuracy (median error across platforms = 1.4-5.5%) was influenced predominantly by T1 sample (P

The types of magnetism known to date are all mainly based on contributions from electron motion. We show how rotational motion of protons (H+) within the methyl groups in hexamethylbenzene (C6(CH3)6) also contribute significantly to the magnetic susceptibility. Starting from below 118 K, as the rotational motion of the methyl groups set in, an associated magnetic moment positive in nature due to charge of the protons renders the susceptibility to become anomalously dependent on temperature. Starting from 20 K, the susceptibility diverges with decreasing temperature indicative of spin–spin interactions between methyl groups aligned in a previously unclassified type of anti-ferromagnetic configuration. Complementary dielectric constant measurements also show the existence of magneto-dielectric coupling. Our findings allow for the study of strongly correlated systems that are based on a species that possesses much slower dynamics.

A linear induction motor system composed of a high– T c superconducting secondary with close-ended coils made of REBCO coated conductor wire was designed and tested experimentally. The measured thrust, normal force and power loss are presented and explained by combining the flux dynamics inside superconductors with existing linear drive theory. It is found that an inherent capacitive component associated to the flux motion of vortices in the Type-II superconductor reduces the impedance of the coils; from such, the associated Lorentz forces are drastically increased. The resulting breakout thrust of the designed linear motor system was found to be extremely high (up to 4.7 kN/m 2 ) while the associated normal forces only a fraction of the thrust. Compared to its conventional counterparts, high- T c superconducting secondaries appear to be more feasible for use in maglev propulsion and electromagnetic launchers.

Epitaxy and misfit strain imposed by underlying substrates have been intensively used to tailor the microstructure and electronic properties of oxide films, but this approach is largely restricted by commercially limited substrates. In contrast to the conventional epitaxial misfit strains with a positive Poisson’s constant, we show here a tunable Poisson’s ratio with anomalous values from negative, zero, to positive. This permits effective control over the out-of-plane lattice parameters that strongly correlate the magnetic and transport properties in perovskite mixed-valence La1–xSrxMnO3 thin films. Our results provide an unconventional approach to better modulation and understanding of elastic-mediated microstructures and physical properties of oxide films by engineering the Poisson’s ratios.

Stochastic disturbances occurring in real world operations could have a significant influence on the planned routing and scheduling results for inter-school buses. An optimal schedule might therefore lose its optimality when applied in actual operations where stochastic disturbances occur. In this study we employ network flow techniques to construct an inter-school bus routing and scheduling model, considering the characteristics of inter-school buses for class attendance, under stochastic travel times. The model is formulated as a special multiple commodity network flow problem which is characterized as NP-hard. To efficiently solve realistically large problems a problem decomposition and variable fixing method, coupled with the use of CPLEX mathematical programming solver, is employed to develop a solution algorithm. Finally, computational tests are performed using data from an allied university system in Taiwan. The test results show that the model and the solution algorithm are good and therefore could be useful for actual operations.

As a follow-up of our previous work on pressure-induced metallization of the 2H_{c}-MoS_{2} [Chi et al., Phys. Rev. Lett. 113, 036802 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.036802], here we extend pressure beyond the megabar range to seek after superconductivity via electrical transport measurements. We found that superconductivity emerges in the 2H_{a}-MoS_{2} with an onset critical temperature T_{c} of ca. 3 K at ca. 90 GPa. Upon further increasing the pressure, T_{c} is rapidly enhanced beyond 10 K and stabilized at ca. 12 K over a wide pressure range up to 220 GPa. Synchrotron x-ray diffraction measurements evidenced no further structural phase transition, decomposition, and amorphization up to 155 GPa, implying an intrinsic superconductivity in the 2H_{a}-MoS_{2}. DFT calculations suggest that the emergence of pressure-induced superconductivity is intimately linked to the emergence of a new flat Fermi pocket in the electronic structure. Our finding represents an alternative strategy for achieving superconductivity in 2H-MoS_{2} in addition to chemical intercalation and electrostatic gating.

The methyl groups in hexamethylbenzene C$_6$(CH$_3$)$_6$ become magnetically ordered at the molecular level below 118 K. This is also near the temperature at which the system structurally transitions from triclinic to a unique near-cubic phase. High-precision measurements of the near-static dielectric constant reveal that the structural phase transition is actually comprised of four successive transformations upon cooling at T$_1$=110.7 K, T$_2$=109.5 K, T$_3$=109.1 K and T$_4$=107.8 K. In contrast to warming, only two transitions occur at T'$_4$=119.2 K and T'$_1$=120.9 K. The methyl groups in the near-cubic phase become slightly distorted according to existing neutron powder diffraction measurements. Analysis of the 2$^6$=64 possible spin orientation configurations of the methyl groups reveal a 20-fold ground state degeneracy presiding in each molecule rendering the system to become highly unstable. From such, it is interpreted that T$_1$ and T$_2$ are temperatures at which the molecules successively lower their symmetry to remove the energy degeneracy which involve methyl group elongation and further out-of-plane tilting. This triggers the system to phase transition into the near-cubic phase which involves a shearing of the molecular planes and partial rotation of the methyl groups at T$_3$ and T$_4$. We interpret the low temperature near-cubic phase to be a manifestation of Jahn-Teller distortions based on energy degeneracies of the orbital motion of protons in each molecule and suggest that the metastable nature of the phase transition originates from the methyl groups requiring a larger amount of energy to order than to disorder. Our findings help explain why many unusual structural phase transitions occur at low temperatures in other molecular crystals possessing periodic motion of protons., Comment: 14 pages (1.5 spaced, 3 figures + 1 'Table of Contents' graphic; accepted (on Dec. 4th, 2018) by the Journal of Physical Chemistry C

As a follow-up of our previous work on pressure-induced metallization of the 2H_{c}-MoS_{2} [Chi et al., Phys. Rev. Lett. 113, 036802 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.036802], here we extend pressure beyond the megabar range to seek after superconductivity via electrical transport measurements. We found that superconductivity emerges in the 2H_{a}-MoS_{2} with an onset critical temperature T_{c} of ca. 3 K at ca. 90 GPa. Upon further increasing the pressure, T_{c} is rapidly enhanced beyond 10 K and stabilized at ca. 12 K over a wide pressure range up to 220 GPa. Synchrotron x-ray diffraction measurements evidenced no further structural phase transition, decomposition, and amorphization up to 155 GPa, implying an intrinsic superconductivity in the 2H_{a}-MoS_{2}. DFT calculations suggest that the emergence of pressure-induced superconductivity is intimately linked to the emergence of a new flat Fermi pocket in the electronic structure. Our finding represents an alternative strategy for achieving superconductivity in 2H-MoS_{2} in addition to chemical intercalation and electrostatic gating.

PURPOSE: To determine the in-vitro accuracy, test-retest repeatability and interplatform reproducibility of T(1) quantification protocols used for DCE-MRI at 1.5T and 3.0T. METHODS: A T(1) phantom with 14 samples was imaged at 8 centers with a common inversion recovery spin echo (IR-SE) protocol and a variable flip angle (VFA) protocol using 7 flip angles (FA), as well as site-specific protocols [VFA with different FA, variable TR (VTR), proton density (PD) and Look-Locker IR]. Factors influencing accuracy (deviation from reference NMR T(1) measurements) and repeatability were assessed using general linear mixed models. Interplatform reproducibility was assessed using coefficients of variation (CV). RESULTS: For the common IR-SE protocol, accuracy (median error across platforms=1.4%–5.5%) was influenced predominantly by T(1) sample (P

H2O is one of the most important substances needed in sustaining life; but yet not much is known about its ground state. Here, a previously unidentified anomaly is identified in the form of a minimum in the imaginary part of the dielectric constant with respect to temperature near 20 K while the real part remains monotonic. Isothermal dispersion and absorption measurements show coinciding results. For the case of heavy ice (D2O), no anomaly was identified confirming an apparent isotope effect. Concerted quantum tunneling of protons is believed to be the main cause behind the reported anomaly. Our findings identify another system that exhibits macroscopic quantum phenomena of which rarely occur in nature., Comment: 12 pages (single column double spaced), 4 figures

From high precision measurements of the complex dielectric constant of H2O ice, we identify the critical temperatures of the phase transition into and out of ice XI from ice Ih to occur at T_Ih-IX=58.9 K and T_IX-Ih=73.4 K. For D2O, T_Ih-IX=63.7 K and T_IX-Ih=78.2 K. A triple point is identified to exist at 0.07 GPa and 73.4 K for H2O and 0.08 GPa and 78.2 K for D2O where ices Ih, II and XI coexist. A first order phase transition with kinetic broadening associated to proton ordering dynamics is identified at 100 K., 11 pages, 5 figures

Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (Tc) of 7 K at around 16.8 GPa, followed by a monotonic decrease in Tc with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in Tc to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides., Tungsten ditelluride has been recently discovered to possess very large and unsaturated magnetoresistance, up to 60 T. Here the authors apply high pressure on this material and observe a dome-shaped superconducting phase transition.

The phase diagram of H2O is extremely complex, in particular, it is believed that a second critical point exists deep below the supercooled water (SCW) region where two liquids of different densities coexist. The problem however, is that SCW freezes at temperatures just above this hypothesized liquid-liquid critical point (LLCP) so direct experimental verification of its existence has yet to be realized. Here, we report two anomalies in the complex dielectric constant during warming in the form of a peak anomaly near Tp=203 K and a sharp minimum near Tm=212 K from ice samples prepared from SCW under hydrostatic pressures up to 760 MPa. The same features were observed about 4 K higher in heavy ice. Tp is believed to be associated to the nucleation process of metastable cubic ice Ic and Tm the transitioning of ice Ic to either ices Ih or II depending on pressure. Given that Tp and Tm are nearly isothermal and present up to at least 620 MPa and ending as a critical point near 33-50 MPa, it is deduced that two types of SCW with different density concentrations exists which affects the surface energy of ice Ic nuclei in the "no man's land" region of the phase diagram. Our results are consistent with the LLCP theory and suggest that a metastable critical point exists in the region of 33-50 MPa and Tc > 212 K., 17 pages (single-columned, double-spaced), 4 figures + ToC graphic, The Journal of Physical Chemistry C, Publication Date (Web): August 18, 2015

Optical and synchrotron x-ray diffraction diamond anvil cell experiments have been combined with first principles theoretical structure predictions to investigate mixed N2 and H2 up to 55 GPa. We found the formation of oligomeric NxH (x>1) compounds using mechano- and photochemistry at pressures above 47 and 10 GPa, respectively, and room temperature. These compounds can be recovered to ambient pressure at T, 26 pages, 12 figures, I table