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Long-term facilitation (LTF) of sensory to motor neuron synapses of the gill-withdrawal reflex in Aplysia is synapse-specific that requires local protein synthesis at activated synapses. At molecular and cellular levels, a multi-scale model is proposed to characterize synapse specificity of LTF which integrates transcription and local translation controlled by cytoplasmic polyadenylation element binding protein (CPEB) in presynaptic sensory neuron, and presynaptic membrane action potential with the excitatory postsynaptic potential (EPSP) of a sensory neuron connected with three different motor neurons. Motif of a positive feedback loop involving local protein synthesis exhibits reversible and irreversible bistable switches, and the bistability crucial for LTF induction is robust to variations of parameters in the subsystem of the positive feedback loop. Moreover, the EPSP amplitude increases with level of active protein kinase A (PKA) due to spike broadening of the presynaptic action potential produced by PKA. Simulations through four stimulus protocols in the model verify synapse-specific LTF is established only at activated synapses, based on the bistable switch in the subsystem of the positive feedback loop. The model brings insights into underlying mechanisms of the synapse specificity of LTF in Aplysia , and further understanding of fundamental processes involved in synaptic plasticity and memory formation.

MicroRNAs are able to modulate gene expression at the posttranscriptional level and play an essential role in various biological processes. In this paper, we establish a general model of an miRNA-mediated gene regulatory network motif with extracellular stimulus. Dynamical properties of the regulatory motif without stimulus focus on diverse codimension-1 and codimension-2 bifurcation analyses of two important feedback strengths as the parameters. Under varying levels of stimulus, we further consider stochastic dynamics controlled by crucial behaviors of monostability, bistability, excitability and oscillation in four typical regions on different two-parameter bifurcation diagrams. Furthermore, we apply potential landscapes to characterize global dynamics and stability behind physical properties of the stochastic behaviors. More essentially, our model can qualitatively simulate experimental findings of long-term memory formation in Aplysia.

We report high pressure studies on the C-type antiferromagnetic semiconductor EuTe2 up to 36.0 GPa. A structural transition from the I4/mcm to C2/m space group is identified at ~16 GPa. Superconductivity is discovered above ~5 GPa in both the I4/mcm and C2/m space groups. In the low-pressure phase (< 16 GPa), the antiferromagnetic transition temperature is enhanced with increasing pressure due to the enhanced magnetic exchange interactions. Magnetoresistance measurements indicate an interplay between the local moments of Eu2+ and the conduction electrons of Te 5p orbits. The upper critical field of the superconductivity is well above the Pauli limit. Across the structural transition to the high-pressure phase (> 16 GPa), EuTe2 becomes nonmagnetic and the superconducting transition temperature evolves smoothly with the upper critical field below the Pauli limit. Therefore, the high upper critical field of EuTe2 in the low-pressure phase is due to the exchange field compensation effect of the Eu magnetic order and the superconductivity in both structures may arise in the framework of the BCS theory., 11 pages,5 figures with 8 pages supplementary

The spin dynamics of {Cr8Y8}, a rare example of ferromagnetic molecular rings, has been studied by inelastic neutron scattering (INS) and heat capacity (HC) methods. Clear evidence of low-lying magnetic excitation has been found. Magnetic Schottky anomalies are observed in low-temperature (low-T) HC curves measured under various fields and can be well fitted with a multi-level Schottky term, giving important information on the energy gaps between spin levels. The INS results obtained on TOFTOF and NEAT time-of-flight spectrometers show INS peaks corresponding to the transitions within S = 12 ground states and between the S = 12 ground state and the S = 11 excited state. The single-J model with a unique exchange constant J = 0.151 meV can well reproduce the low-lying energy levels and their Zeeman splitting upon applied magnetic fields. This work shows that the single-J model can be a good approach for the low-T spin dynamics of {Cr8Y8} and may have general significance for other weak ferromagnetic molecular rings. Determination of the Cr3+-Cr3+ exchange constant in {Cr8Y8} will benefit the study on the complicated magnetic interactions in chromium lanthanide complexes. The zero-field splitting which is suggested by HC data still calls for EPR or high-resolution INS technique to verify.

Sensitive and accurate determination of DNA methyltransferase (DNA Mtase) activity is highly pursued for understanding fundamental biological processes related to DNA methylation, clinical disease diagnosis and drug discovery. Herein, we propose a new electrochemical immuno-DNA sensing platform for DNA Mtase activity assay and inhibitor screening. After homogeneous DNA methylation by CpG methyltransferase (M.SssI Mtase), the methylated DNA can be specifically recruited onto an electrode via its immunological binding with the immobilized anti-5-methylcytosine antibody. The recruited methylated DNA was simultaneously used as a substrate to facilitate successive template-free DNA extension and enzyme catalysis for the dual-step signal amplification of DNA Mtase activity. The developed immuno-DNA sensing strategy effectively integrates solution-phase DNA methylation, surface affinity binding recognition, and successive template-free DNA extension and enzyme catalysis-based signal amplification, rendering a highly specific, sensitive and accurate assay of DNA Mtase activity. A low detection limit of 0.039 U mL-1 could be achieved with a high selectivity. It was also applied for efficient evaluation of various inhibitors. Current affinity recognition of the immobilized antibody with methylated DNA switches the sensing platform into a DNA operation interface, facilitating the opportunity for combining various DNA-based signal amplification strategies to improve the detection performance. It would be used as a general strategy for the analysis of DNA Mtase activity, inhibitors and more analytes, and is anticipated to show potential for applications in disease diagnosis and drug discovery.

Comparing with the widely known transitional metal based van der Waals (vdW) materials, rare-earth based ones are rarely explored in the research of intrinsic two-dimensional (2D) magnetism. In this work, we report the physical properties of DyOCl, a rare-earth based vdW magnetic insulator with direct band gap of $\sim 5.72~eV$. The magnetic order of bulk DyOCl is determined by neutron scattering as the $A$-type antiferromagnetic structure below the N\'{e}el temperature $T_N=10~$K. The large magnetic moment near 10.1 $ \mu_{B} $/Dy lies parallel to the $a$-axis with strong uniaxial magnetic anisotropy. At $2~K$, a moderate magnetic field ($\sim 2~T$) applied along the easy axis generates spin-flip transitions and polarizes DyOCl to a ferromagnetic state. Density functional theory calculations reveal an extremely large magnetic anisotropy energy ($-5850~\mu eV/Dy$) for DyOCl, indicating the great potentials to realize magnetism in 2D limit. Furthermore, the mechanical exfoliation of bulk DyOCl single crystals down to seven layers is demonstrated. Our findings suggest DyOCl is a promising material playground to investigate 2D $f$-electron magnetism and spintronic applications at the nanoscale.

Thermoelectric technology allows conversion between heat and electricity. Many good thermoelectric materials contain rare or toxic elements, so developing low-cost and high-performance thermoelectric materials is warranted. Here, we report the temperature-dependent interplay of three separate electronic bands in hole-doped tin sulfide (SnS) crystals. This behavior leads to synergistic optimization between effective mass (m*) and carrier mobility (μ) and can be boosted through introducing selenium (Se). This enhanced the power factor from ~30 to ~53 microwatts per centimeter per square kelvin (μW cm−1 K−2 at 300 K), while lowering the thermal conductivity after Se alloying. As a result, we obtained a maximum figure of merit ZT (ZTmax) of ~1.6 at 873 K and an average ZT (ZTave) of ~1.25 at 300 to 873 K in SnS0.91Se0.09 crystals. Our strategy for band manipulation offers a different route for optimizing thermoelectric performance. The high-performance SnS crystals represent an important step toward low-cost, Earth-abundant, and environmentally friendly thermoelectrics.

The crystal structure, dynamics, magnetic structure and property of orthochromites solid solution Ho1−xYxCrO3 (x = 0, 0.2,…,1.0) were systematically investigated by X-ray diffraction, Raman scattering, magnetometry and neutron powder diffraction. With increasing non-magnetic Y3+-substitution for Ho3+ throughout the whole range, the crystallographic parameters remain almost unchanged, so is Neel temperature (TN ≈ 141 K), which is closely related to the structure in these orthochromites. However, the Raman spectra demonstrates the lattice dynamics is influenced due to the mass difference between Ho3+ and Y3+. Moreover, the spin reorientation property is also strongly affected by Y-substitution revealed by neutron powder diffraction. For the composition of x ≤ 0.6, the magnetism of Cr3+ sublattice adopts Γ2 spin configuration in terms of Bertaut notation from low temperature (10 K) up to Neel temperature. With the doping concentration further increases to x = 0.7 and 0.8, the system exhibits a mixed structure of (Γ2 + Γ4) within a certain temperature range. Beyond and underneath of which, a single spin configuration is identified as Γ4 (GxAyFz) and Γ2 (FxCyGz), respectively. After x = 0.8, only Γ4 (GxAyFz) are observed below TN. These phenomena are attributed to the weakened Ho3+-Cr3+ interaction with Y-substitution, which causes a competition between Γ2 and Γ4 spin configurations.

Protein kinase activity analysis is essential and important for elucidation of many fundamental biological processes, disease diagnosis, and drug discovery. Herein, a novel electrochemical biosensing method for protein kinase (PKA) activity was demonstrated by the use of a reduced graphene oxide-zirconium dioxide–thionine (rGO-ZrO2–Thi) nanocomposite, which interestingly served as an integral phosphopeptide-recognizing, signal amplifying and reporting platform. The ZrO2 nanoparticle-decorated reduced graphene oxide (rGO-ZrO2) was first prepared by a hydrothermal reaction route, and then the thionine was conjugated onto the rGO surface via π–π stacking as an excellent electrochemical probe. The prepared rGO-ZrO2–Thi nanocomposites were well-characterized by various techniques. With the full advantage of specific recognition of ZrO2 nanoparticles for the phosphate group, signal amplification, and transduction of abundant thionines onto the rGO surface, and excellent conductivity of rGO, the rGO-ZrO2–Thi nan...

Noncoding RNAs such as miRNAs and piRNAs have long-lasting effects on the regulation of gene expression involved in long-term synaptic changes. To characterize gene regulation mediated by small noncoding RNAs associated with long-term memory in Aplysia, we consider two noncoding RNAs stimulated by 5-HT into a gene regulatory network motif model, including miR-124 that binds to and inhibits the mRNA of CREB1 and piR-F that facilitates serotonin-dependent DNA methylation to lead to repression of CREB2. Codimension-1 and -2 bifurcation analyses of 5-HT regulating both miR-124 and piR-F and a negative feedback strength for oscillation reveal rich dynamical properties of bistability and oscillations robust to variations in all other parameters. More importantly, we verify three stimulus protocols of 5-HT in experiments by our model and find that application of five pulses of 5-HT leads to a transient decrease of miR-124 but increase of piR-F concentrations, which matters sustained high level of CREB1 concentration associated with long-term memory. Furthermore, we perform bifurcation analyses for the concentrations of miR-124 and piR-F as two parameters to explore dynamical mechanisms underlying the epigenetic regulation in long-term memory formation. This study provides insights into revealing regulatory roles of epigenetic changes in gene expression involving noncoding RNAs associated with synaptic plasticity.

Mn-doped transition metal perovskites have shown versatile magnetic phenomena, and research on these materials has been revived in recent decades. Many controversies over the microscopic spin configuration remain unsolved, presumably due to the complicated spin and orbit interactions, which are strongly coupled with each other and sensitive to structural and chemical modulation. Here, the Mn-doped orthochromite YCrO3 was investigated to shed some light on this issue. The orthochromite YCr1-xMnxO3 (0 ≤ x ≤ 0.6) was synthesized and studied by X-ray diffraction, magnetometry and neutron powder diffraction. For x = 0.2–0.5 samples, the Cr3+ (Mn3+) sublattice adopts a Γ4 (Gx,Ay,Fz) antiferromagnetic structure with a canted ferromagnetic component. Negative magnetization behavior is observed for the x = 0.1 and 0.2 samples, which is suppressed and reversed by the applied magnetic field. As the doping concentration further increases to x = 0.6, the system exhibits a distinct spin-glass behavior below a spin-freezing temperature. These phenomena are attributed to the competition between weakened antiferromagnetic Cr3+-Cr3+ interactions and enhanced ferromagnetic Cr3+-Mn3+ interactions with Mn3+-doping. This work provides deep insights into understanding the complicated magnetic phenomena in Mn-doped correlated transition metal oxides.

The temperature dependent magnetism of Fe-doped rare earth orthochromite HoCr 1-x Fe x O 3 (x = 0, 0.2) was investigated by neutron powder diffraction. It is found that the magnetism of Cr(Fe) 3+ can be well understood within mean field theory, while the ordering of Ho 3+ was induced by the Cr(Fe) 3+ sublattice and can be satisfyingly described by an effective S = 1/2 model. The absences of both the most common G x F z configuration of Cr 3+ and the ordering of Ho 3+ caused by Ho-Ho interaction evidence a strong Ho 3+ -Cr 3+ interaction which dominates this system. On the other hand, a remarkable magnetoelastic strain was observed accompanying the Cr(Fe) 3+ ordering. An analysis based on the equation of state with a Gruneisen approximation was performed and revealed magnetic origin of this strain.

Orthoferrite solid solution HoFe1−xCrxO3 (x=0, 0.2,…,1.0) was synthesized via solid state reaction methods. The crystal structure, magnetism and spin reorientation properties of this system were investigated by X-ray diffraction, neutron powder diffraction and magnetic measurements. For compositions of x≤0.6, the system exhibits similar magnetic properties to HoFeO3. With increasing Cr-doping, the system adopts a Γ4(GxAyFz) magnetic configuration with a decreased Neel temperature from 640 K to 360 K. A Γ42 spin reorientation of Fe(Cr)3+ was also observed in this system with an increase in transition temperature from 56 K to about 200 K due to competition between the Fe(Cr)–Fe(Cr) and Ho–Fe(Cr) interactions. For the x≥0.8, the system behaves more like HoCrO3 which adopts a Γ2(FxCyGz) configuration with no spin reorientation below the Neel temperature TN. Throughout the whole substitution range, we found that the saturated moment of Fe(Cr) was less than the ideal value for a free ion, which implies the existence of spin fluctuation in this system. A systematic magnetic structure variation with Cr-substitution is revealed by Rietveld refinement. A phase diagram combining the results of the magnetic measurements and neutron powder diffraction results was obtained.

Development of simple, convenient, and sensitive assay methods for pyrophosphatase (PPase) activity is of importance, for disease diagnosis and drug discovery. Herein, a simple, rapid, label-free, and sensitive fluorescence sensor for PPase activity assay is developed, using Cu2+ doping-induced quantum dot (QD) photoluminescence as a signal reporter. The Cu2+ doping of ZnSe QD can induce a dopant-dependent emission response, which will be inhibited after the premixing of Cu2+ with pyrophosphate (PPi), to form a Cu2+-PPi complex. Then, the hydrolysis of PPi into phosphate (Pi), specifically catalyzed by PPase, liberates the free Cu2+ to regain the QD doping for the fluorescence response, which is highly dependent on the PPase activity. The PPase can be sensitively and selectively assayed, with a detection limit of 0.1 mU/mL. The developed sensing strategy can be also employed for the PPase inhibitor screening. Thus, the current QD doping-based sensing strategy offers an efficient and promising avenue for Cu2+, PPi, or PPase-related target analysis, and might hold great potential for the further applications in the clinical disease diagnosis.

The development of simple, flexible, cost-effective and sensitive electrochemical methods for protein analysis is of very importance for its potential application in disease diagnosis and biomedicine research. Herein, a new protein binding-induced proximity recognition and polymerase-powered DNA walker strategy was proposed for one-step and sensitive electrochemical quantification of proteins. Two DNA probes were designed with a hairpin-like one immobilized on the electrode and another one used as a DNA walker strand. The protein binding with the recognition elements labeled on these two probes brought their proximity hybridization, accompanied with the annealing of a redox probe-labeled primer strand on the opened immobilization probe. The DNA polymerization of primer strand in the presence of DNA polymerase induced the release of the DNA walker strand, which then walked to the adjacent immobilization probe for the proximity hybridization and progressive polymerase-powered DNA walker operation again. This induced the electrochemical signal reporting and amplifying toward protein quantification. The sensitive and selective detection toward proteins was achieved with the detection limits toward anti-dig antibody and streptavidin as 80 and 16 pM, respectively. Thus, the current study offers a simple, generic, one-step and amplified detection strategy for electrochemical protein quantification.

Cement hydration is a key process to determine most properties of cementitious materials. A deep understanding of cement hydration is thus favourable for the improvement of the overall properties of these materials and for providing solutions to the technique problems for concrete applications in terms of durability and sustainability. The conversion of water states is a fundamental process associated with cement hydration. Quasi-elastic neutron scattering (QENS) has recently emerged as a powerful non-destructive technique for studying the conversion of water states during cement hydration. The free water index and correlation parameters describing the states of the bound water and confined water can be quantitatively given. Compared with conventional methods of cement hydration characterization, QENS has a unique advantage. This paper summarizes the application of QENS for hydration in cement-based materials. In this review, the focus is first placed on the mechanism of the QENS method and the development of QENS spectrum analysis models to provide insight into the new technique. Then, the focus is shifted to its application for hydration and hydration kinetics in cement-based materials. Recent improvements in QENS facilities have allowed unexpected possibilities for studying complex hydration processes in cementitious materials. The potential of this promising technology for further research is outlined.

The ability to form long-term memories is an important function for the nervous system, and the formation process is dynamically regulated through various transcription factors, including CREB proteins. In this paper, we investigate the dynamics of a delay differential equation model for CREB protein activities, which involves two positive and two negative feedbacks in the regulatory network. We discuss the dynamical mechanisms underlying the induction of long-term memory, in which bistability is essential for the formation of long-term memory, while long time delay can destabilize the high level steady state to inhibit the long-term memory formation. The model displays rich dynamical response to stimuli, including monostability, bistability, and oscillations, and can transit between different states by varying the negative feedback strength. Introduction of a time delay to the model can generate various bifurcations such as Hopf bifurcation, fold limit cycle bifurcation, Neimark–Sacker bifurcation of cycles, and period-doubling bifurcation, etc. Increasing the time delay can induce chaos by two routes: quasi-periodic route and period-doubling cascade.

The interplay of small, noncoding microRNAs (miRNAs), mRNAs and proteins plays crucial roles in almost all cellular processes. MiR-124, widely known as a memory-related miRNA, can regulate LTM by binding to the mRNA of CREB1 stimulated with 5-HT. In this paper, we establish a regulatory network model of CREB1 and miR-124 stimulated by 5-HT, in which miR-124 inhibits CREB1, which in turn enhances miR-124. Our model validates three protocols based on 5-HT in experiments on the induction of LTM in Aplysia. A steady-state analysis and numerical bifurcations of the abstracted system beyond memory formation, when the fast reaction has been in the equilibrium, can facilitate more abundant dynamical behaviors such as bistability and oscillation. The original system also exhibits bistability under appropriate feedback strengths, which is relevant to the mechanism of LTM formation. Furthermore, we specifically show a change in the transition from a reversible switch to an irreversible switch via bifurcations of the negative regulation of miR-124 on CREB1, which eventually maintains a high phosphorylated CREB1 level after initially elevated by 5-HT. These findings indicate that miR-124 provides an inhibitory constraint on long-term synaptic plasticity through the regulation of CREB1.

Experiments have demonstrated that in mice, the PVT strongly projects to the CeL and participates in the formation of fear memories by synaptic potentiation in the amygdala. Herein, we propose a mathematical model based on a positive feedback loop of BDNF expression and signaling to investigate PVT manipulation of synaptic potentiation. The model is validated by comparisons with experimental observations. We find that a high postsynaptic firing frequency after stimulation is induced by presynaptic [Formula: see text] when the rates of BDNF secretion from PVT and LA neurons to the CeL are above a threshold value. Moreover, the positive feedback of postsynaptic BDNF production is important for the maintenance of the high excitability of the [Formula: see text] CeL neuron after stimulation. The model brings insight into the underlying mechanisms of PVT modulation of synaptic potentiation at LA-CeL synapses and provides a framework of understanding other similar processes associated with synaptic plasticity.

A Python software package for data reduction and visualization of continuous angle multiple energy analysis (CAMEA) type detector backend MultiFLEXX is presented. The software concept focuses on unambiguous, automated aggregation of experimental data and preservation of raw data structure in graphical representation, enabling on-the-fly analysis of experimental data from MultiFLEXX with minimal amount of user input, reducing confusion and human error in studies involving multiple parameters. The software also provides a set of interfaces for versatile tweaking of graphing parameters, facilitating generation of production-quality graphs for use in publications. The software enhances the role of MultiFLEXX as a swift mapping option available at the cold-neutron triple-axis spectrometer FLEXX. Keywords: Inelastic neutron scattering, Three-axis spectroscopy, Visualization tool

We report a systematic crystal growth and characterization of Ca$_{1-y}$La$_{y}$Fe$_{1-x}$Ni$_{x}$As$_{2}$, the newly discovered 112-type iron-based superconductor. After substituting Fe by a small amount of Ni, bulk superconductivity is successfully obtained in high quality single crystals sized up to 6 mm. Resistivity measurements indicate common features for transport properties in this 112-type iron pnictide, suggest strong scattering from chemical dopants. Together with the superconducting transition temperature $T_c$, and the Neel temperature $T_N$ determined by the elastic neutron scattering, we sketch a three-dimensional phase diagram in the combination of both Ni and La dopings., Comment: 8 pages, 8 figures

The generic phantom bursting model proposed by Bertram et al. can evoke complex bursting oscillations in collaboration with two generic slow variables with different time scales. Two models with the phantom bursting mechanism are suggested, when these two generic slow variables are provided with some specific biological significances by combining slowly varying intracellular Ca2+ concentration of the Chay-Keizer electrical bursting model with two different glycolytic oscillations, respectively. Also, complex dynamic behaviors of different compound bursting occurring in these two models are comprehensively surveyed by two fast/slow analyses for a moderately and a slower slow variable, respectively.

The origin of nematic order remains one of the major debates in iron-based superconductors. In theories based on spin nematicity, one major prediction is that the spin-spin correlation length at (0,π) should decrease with decreasing temperature below the structural transition temperature T_{s}. Here, we report inelastic neutron scattering studies on the low-energy spin fluctuations in BaFe_{1.935}Ni_{0.065}As_{2} under uniaxial pressure. Both intensity and spin-spin correlation start to show anisotropic behavior at high temperature, while the reduction of the spin-spin correlation length at (0,π) happens just below T_{s}, suggesting the strong effect of nematic order on low-energy spin fluctuations. Our results favor the idea that treats the spin degree of freedom as the driving force of the electronic nematic order.

We report a spin reorientation from Γ4(Gx, Ay, Fz) to Γ1(Ax, Gy, Cz) magnetic configuration near room temperature and a re-entrant transition from Γ1(Ax, Gy, Cz) to Γ4(Gx, Ay, Fz) at low temperature in TbFe1−xMnxO3 single crystals by performing both magnetization and neutron diffraction measurements. The Γ4 − Γ1 spin reorientation temperature can be enhanced to room temperature when x is around 0.5 ~ 0.6. These new transitions are distinct from the well-known Γ4 − Γ2 transition observed in TbFeO3, and the sinusoidal antiferromagnetism to complex spiral magnetism transition observed in multiferroic TbMnO3. We further study the evolution of magnetic entropy change (−ΔSM) versus Mn concentration to reveal the mechanism of the re-entrant spin reorientation behavior and the complex magnetic phase at low temperature. The variation of −ΔSM between a and c axes indicates the significant change of magnetocrystalline anisotropy energy in the TbFe1−xMnxO3 system. Furthermore, as Jahn-Teller inactive Fe3+ ions coexist with Jahn-Teller active Mn3+ ions, various anisotropy interactions, compete with each other, giving rise to a rich magnetic phase diagram. The large magnetocaloric effect reveals that the studied material could be a potential magnetic refrigerant. These findings expand our knowledge of spin reorientation phenomena and offer the alternative realization of spin-switching devices at room temperature in the rare-earth orthoferrites.

The origin of nematic order remains one of the major debates in iron-based superconductors. In theories based on spin nematicity, one major prediction is that the spin-spin correlation length at (0,π) should decrease with decreasing temperature below the structural transition temperature T_{s}. Here, we report inelastic neutron scattering studies on the low-energy spin fluctuations in BaFe_{1.935}Ni_{0.065}As_{2} under uniaxial pressure. Both intensity and spin-spin correlation start to show anisotropic behavior at high temperature, while the reduction of the spin-spin correlation length at (0,π) happens just below T_{s}, suggesting the strong effect of nematic order on low-energy spin fluctuations. Our results favor the idea that treats the spin degree of freedom as the driving force of the electronic nematic order.

A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed `spinon'). Here, we report neutron scattering measurements that reveal broad spin excitations covering a wide region of the Brillouin zone in a triangular antiferromagnet YbMgGaO4. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, which is consistent with the particle-hole excitation of a spinon Fermi surface. Our results therefore point to a QSL state with a spinon Fermi surface in YbMgGaO4 that has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids., Comment: 23 pages, 10 figures

Neutron diffraction experiments have been performed to investigate the electronic phase transitions in the Pr-based filled skutterudite PrFe 4 P 12 . This compound undergoes a transition from a characteristic heavy-electron state to a nonmagnetic phase below 6.5 K. Neutron diffraction experiments reveal an antiferromagnetic alignment of the magnetic-field induced dipole moments. The directions of the antiferromagnetic components are considered to be always parallel to the magnetic field applied along either [0 0 1], [1 1 0] or [1 1 1]. This implies that the symmetry of the ordered state can be categorized as Γ 1 . This phenomenon is consistent with the scenario of a scalar-type order parameter for the Pr 4 f electron state.

The cyclic AMP (cAMP)-response element-binding protein (CREB) family of transcription factors is crucial in regulating gene expression required for long-term memory (LTM) formation. Upon exposure of sensory neurons to the neurotransmitter serotonin (5-HT), CREB1 is activated via activation of the protein kinase A (PKA) intracellular signaling pathways, and CREB2 as a transcriptional repressor is relieved possibly via phosphorylation of CREB2 by mitogen-activated protein kinase (MAPK). Song et al. [18] proposed a minimal model with only interlinked positive and negative feedback loops of transcriptional regulation by the activator CREB1 and the repressor CREB2. Without considering feedbacks between the CREB proteins, Pettigrew et al. [8] developed a computational model characterizing complex dynamics of biochemical pathways downstream of 5-HT receptors. In this work, to describe more simply the biochemical pathways and gene regulation underlying 5-HT-induced LTM, we add the important extracellular sensitizing stimulus 5-HT as well as the product Ap-uch into the Song’s minimal model. We also strive to examine dynamical properties of the gene regulatory network under the changing concentration of the stimulus, [5-HT], cooperating with the varying positive feedback strength in inducing a high state of CREB1 for the establishment of long-term memory. Different dynamics including monostability, bistability and multistability due to coexistence of stable steady states and oscillations is investigated by means of codimension-2 bifurcation analysis. At the different positive feedback strengths, comparative analysis of deterministic and stochastic dynamics reveals that codimension-1 bifurcation with respect to [5-HT] as the parameter can predict diverse stochastic behaviors resulted from the finite number of molecules, and the number of CREB1 molecules more and more preferentially resides near the high steady state with increasing [5-HT], which contributes to long-term memory formation.

Electronic state evolution in the metal-non-metal transition of PrRu4P12 has been studied by X-ray and polarized neutron diffraction experiments. It has been revealed that, in the low-temperature non-metallic phase, two inequivalent crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2) ground states are located at Pr1 and Pr2 sites forming the bcc unit cell surrounded by the smaller and larger cubic Ru-ion sublattices, respectively. This modulated electronic state can be explained by the p-f hybridization mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f hybridization effect plays an important role for the electronic energy gain in the metal-non-metal transition originated from the Fermi surface nesting., 5 pages, 5 figures. Accepted by J. Phys. Soc. Jpn

We performed measurements of specific heat and inelastic neutron scattering on Pr(Fe1-xCox)4P12 to investigate the effects of d-electron doping on the heavy fermion (HF) state and non-magnetic order state of PrFe4P12. The ordered state is suppressed by the Co substitution. A Schottky type behavior in the specific-heat appears at 8 K, in contrast with the undoped system. The inelastic neutron spectrum of the Co substituted system is composed of several sharp inelastic peaks, in contrast with the quasi-elastic spectrum in the HF phase of PrFe4P12. The experimental results indicate that the Co substitution induces localized 4f electrons of Pr ions with suppression of the HF state and the exotic ordering.