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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...

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 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.

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.

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

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

Working towards developing lightweight superconducting magnets for future space and other applications, we have successfully fabricated mono-core Ti-sheathed MgB2 wires by the powder-in-tube method. The wires were characterized by magnetization, electrical resistivity, x-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry measurements. The results indicate that the Ti sheath does not react with the magnesium and boron, and the present wire rolling process can produce MgB2 wires with a superconducting volume fraction of at least 64% in the core. Using the Bean model, it was found that at 5 K, the magnetic critical current densities, Jc, measured in magnetic fields of 0, 5, and 8 T are about 4.2 × 105, 3.6 × 104, and 1.4 × 104 A cm−2, respectively. At 20 K and 0 T, the magnetic Jc is about 2.4 × 105 A cm−2. These results show that at zero and low fields, the values of the magnetic Jc for Ti-sheathed MgB2 wires are comparable with the best results available for the Fe-sheathed MgB2 wires. At high fields, however, the Jc for Ti-sheathed MgB2 wires appears higher than that for the Fe-sheathed MgB2 wires.

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

The reaction of mercaptoacetaldehyde dialkyl acetals 1a-c in the presence of sulfuric acid, polyphosphoric acid and zinc chloride is described. Other than the disulfide reported previously, new compounds 1,2-bis-(mercapto)ethylene, 1,2,3-tris-(mercapto)ethane and 1,2-bis-(mercapto)methane have been isolated for the first time.

Polymerization of actin was investigated by a microcalorimetric method at 298.15 K. The calorimetric curves showed that polymerization of actin in the presence of Mg 2+ at the concentration range 1.00–6.00 mM was an exothermic process. There was only one exothermic peak in the thermal curves under each condition. The average molar enthalpy change of actin polymerization was −0.703 kJ mol −1 . It was still exothermic in the presence of K + when the concentration was in the range 25.0–200.0 mM. The average molar enthalpy change of polymerization was −3.03 kJ mol −1 . However, the calorimetric curves contained only one exothermic peak when the K + concentration was lower, in the range 25.0–75.0 mM; there were two peaks, first exothermic and second endothermic, in the calorimetric curves as the K + concentration was higher, in the range 100.0–200.0 mM. The result not only indicated that calorimetric curves of actin polymerization changed with different concentration of K + but also showed that there were some differences between K + - and Mg 2+ -induced polymerization of actin in the presence of 0.1 mM CaCl 2 and 0.2 mM ATP. The ΔG 0 of actin polymerization in each condition was also assayed at 298.15 K and ΔS 0 in the corresponding condition were consequently evaluated from the energy-entropy relation at constant temperature and pressure.

The heat effect produced in the interaction of rabbit muscle F-actin with myosin and its proteolytic fragments (HMM, S 1 ) was measured with an MS-80 Calvet microcalorimeter (Setaram, France). An improved reaction cell of the microcalorimeter was used. There were three thermokinetic peaks in the measured curve of the interaction of myosin with F-actin in the absence of ATP, which were exothermic, endothermic and exothermic in order of appearance. When ATP was added to F-actin before mixing with myosin, the curve remained similar in feature to that in the absence of ATP. But the first peak (exothermic) became smaller and the second and third peaks became larger. There was only one exothermic peak in the measured curve of the interaction between S 1 and F-action. But ATP caused big changes in the curve of their interaction. With addition of ATP to F-action solution before it was mixed with S 1 , there were four thermokinetic peaks in the curve which were endothermic, exothermic, endothermic, and exothermic in order of appearance. The measured curves of interaction between HMM and F-actin in the presence and absence of ATP were quite similar to that of interaction between S 1 and F-action.

Pollen is an excellent source of actin for biochemical and physiological studies of the actomyosin system in higher plants. We have developed an efficient method to prepare relatively high levels of actin from the pollen of maize (Zea mays L.). The procedures of purification include acetone powder preparation, saturated ammonium sulfate fractionation, diethylaminoethyl-cellulose chromatography, a cycle of polymerization-depolymerization, and Sephacryl S-200 gel filtration. The average yield of actin is 19 milligrams per 100 grams of pollen grains extracted. This is comparable with those of Acanthamoeba castellanii and human platelets. The purified pollen actin is electrophoretically homogeneous and its molecular mass is 42 kilodaltons. The amino acid composition and circular dichroism spectrum of pollen actin are identical to those of muscle actin. The actin purified from pollen is able to polymerize to F-actin. The pollen F-actin activated the activity of the muscle myosin ATPase sevenfold.

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

GdFe3(BO3)4 exhibits a structural phase transition at 156 K, antiferromagnetic order of the Fe3+ moments at 36 K followed by a spin reorientation phase transition at 9 K. The reorientation phase transition is studied through dielectric, magnetic and heat capacity measurements under the application of external magnetic fields of up to 7 kOe. The dielectric constant indicates the existence of two distinct anomalies at T_SR = 9 K that separate in temperature under external magnetic fields. The spin rotation phase transition is proven to be of the first-order nature through the magnetic analogue of the Clausius-Clapeyron equation. Magneto-dielectric effect of up to 1% is observed at 8 K and 7 kOe. The uniaxial magnetocaloric effect along the c axis is observed below the spin reorientation phase transition of 9 K., Comment: 11 pages, 7 figures

By using Western blotting, immunofluorescence and immunogold labeling, a novel alpha-actinin-like protein was found in pollen and pollen tubes of Lilium davidii, a model system for cytoskeleton and Golgi apparatus study of plant. As measured by Western blotting, the molecular mass of the a-actinin-like protein was about 80 kDa. Under confocal laser scanning microscopy after immunofluorescence labeling, the distribution of the alpha-actinin-like protein appeared punctated in the cytoplasm of the pollen and pollen tubes. When double labeled, the protein was co-localized with Golgi 58K protein. In addition, some fraction of the alpha-actinin-like protein was found to co-distribute with F-actin bundles in the pollen tubes. Additional studies with immuno-gold labeling and transmission electron microscopy revealed that the alpha-actinin-like protein bound mainly to the membranes of Golgi-associated vesicles. When the pollen tubes were treated with Brefeldin A (BFA), the a-actinin-like proteins were dispersed into the cytoplasm, and the growth of pollen tubes was inhibited. After BFA was removed, the protein was reversibly recovered on the Golgi apparatus. These results suggest that the novel alpha-actinin-like protein is a BFA-sensitive protein on the membranes of Golgi-associated vesicles, and may participate in Golgi-associated vesicles budding and/or sorting, together with actin microfilaments.

Here we describe the in vitro polymerization of actin from maize (Zea mays) pollen. The purified actin from maize pollen reported in our previous paper (X. Liu, L.F. Yen [1992] Plant Physiol 99: 1151-1155) is biologically active. In the presence of ATP, KCl, and MgCl2 the purified pollen actin polymerized into filaments. During polymerization the spectra of absorbance at 232 nm increased gradually. Polymerization of pollen actin was evidently accompanied by an increase in viscosity of the pollen actin solution. Also, the specific viscosity of pollen F-actin increased in a concentration-dependent manner. The ultraviolet difference spectrum of pollen actin is very similar to that of rabbit muscle actin. The activity of myosin ATPase from rabbit muscle was activated 7-fold by the polymerized pollen actin (F-actin). The actin filaments were visualized under the electron microscope as doubly wound strands of 7 nm diameter. If cytochalasin B was added before staining, no actin filaments were observed. When actin filaments were treated with rabbit heavy meromyosin, the actin filaments were decorated with an arrowhead structure. These results imply that there is much similarity between pollen and muscle actin.

It is well known that actomyosin system plays an important role in the maintenance of cell shape and performing cell motility, such as mitosis, cytokinesis, cytoplasmic streaming, organelle movement and amoeboid movement in higher plants (Jackson, 1982). Actin and myosin have been identified in higher plants by many authors with the use of biochemical and immunological methods (Condeelis, 1974; Vahey et al., 1982; Yenet al., 1986; Tang et al., 1989; Ma et al., 1989; Villanueva et al., 1990). But the quantity of actin is too low to be isolated for biochemical and physiological studies. Meagher and McLean (1990) pointed out that the concentrations of actin in any plant tissue are lower than they are even in animal cytoplasmic tissues. However, we found that pollen is an excellent source of actin in higher plants in which the quantity of actin is sufficient to do biochemical investigation.

We present a detailed study of the zone-center phonons and magnetoelectric interactions in Ni3V2O8. Using combined neutron scattering, polarized infrared (IR) measurements and first-principles LDA+U calculations, we successfully assigned all IR-active modes, including eleven B2u phonons which can induce the observed spontaneous electric polarization. We also calculated the Born-effective charges and the IR intensities which are in surprisingly good agreement with the experimental data. Among the eleven B2u phonons, we find that only a few of them can actually induce a significant dipole moment. The exchange interactions up to a cutoff of 6.5 A are also calculated within the LDA+U approach with different values of U for Ni, V and O atoms. We find that LSDA (i.e. U = 0) gives excellent results concerning the optimized atomic positions, bandgap and phonon energies. However, the magnitudes of the exchange constants are too large compared to the experimental Curie–Weiss constant, Θ. Including U for Ni corrects the magnitude of the superexchange constants but opens a too large electronic bandgap. We observe that including correlation at the O site is very important to get simultaneously the correct phonon energies, bandgap and exchange constants. In particular, the nearest and next-nearest exchange constants along the Ni-spine sites result in incommensurate spin ordering with a wavevector that is consistent with the experimental data. Our results also explain how the antiferromagnetic coupling between sublattices in the b and c directions is consistent with the relatively small observed value of Θ. We also find that, regardless of the values of U used, we always get the same five exchange constants that are significantly larger than the rest. Finally, we discuss how the B2u phonons and the spin structure combine to yield the observed spontaneous polarization. We present a simple phenomenological model which shows how trilinear (and quartic) couplings of one (or two) phonons to two spin operators perturbatively affects the magnon (i.e. electromagnon) and phonon energies.

We demonstrate here the presence of actin and myosin in pea (Pisum sativum L.) tendrils. The molecular weight of tendril actin is 43,000, the same as rabbit skeletal muscle actin. The native molecular weight of tendril myosin is about 440,000. Tendril myosin is composed of two heavy chains of molecular weight approximately 165,000 and four (two pairs) light chains of 17,000 and 15,000. At high ionic strength, the ATPase activity of pea tendril myosin is activated by K(+)-EDTA and Ca(2+) and is inhibited by Mg(2+). At low ionic strength, the Mg(2+)-ATPase activity of pea tendril myosin is activated by rabbit skeletal muscle F-actin. Superprecipitation occurred after incubation at room temperature when ATP was added to the crude actomyosin extract. It is suggested that the interaction of actin and myosin may play a role in the coiling movement of pea tendril.