The Development of Phasemeter for Taiji Space Gravitational Wave Detection

Taiji space gravitational wave detection utilizes the laser interferometer to convert the tiny distance change into the phase fluctuation of the beat note. As to realize the sensitivity of 1 pm/√ Hz, the phasemeter needs to calculate the phase with the precision of 2πμ rad/√ Hz in the frequency range of 0.1 mHz and 1 Hz. In this paper, we report recent progress of the phasemeter for Taiji. Noises which possibly affect the measurement sensitivity are tested and discussed, especially the sampling noise and the frequency jitter. Finally, the accuracy of the phasemeter is calibrated. The result shows that the sensitivity has reached the requirement of Taiji in the frequencies between 0.01 Hz and 1 Hz, 0.1 mHz–1 mHz. Noises in the range of 1 mHz and 0.01 Hz, which have not yet depressed well, are dominated by the clocking jitter and the thermal fluctuation.     

<Emphasis Type="Italic">V</Emphasis><Subscript>N</Subscript>-Mg defect complexes as compensating centers in GaN:Mg

Defect equilibrium diagrams have been constructed for intrinsic and extrinsic defects in GaN:Mg crystals using the quasi-chemical formalism, and the formation of (V _N-Mg_Ga)^× and (V _N-Mg_Ga ^??) defect complexes has been analyzed. The results indicate that, under equilibrium conditions, V _N vacancies in the charge state 3+ and Mg′_Ga impurities form (V _N-Mg_Ga)^?? defect complexes, which compensate acceptors.     

Diagram of the Critical Temperature—Nernst Temperature for the Superconductivity Induced by Modified Electron-Phonon Interaction

We have taken into consideration the Eliashberg equations based on the electron-phonon and the electron-electron-phonon interaction. It has been shown that the Eliashberg equations set generalizes the model based on the canonical transformation, which for the cuprates quantitatively associates with each other the critical temperature (T _C ), the Nernst temperature (T ^??), and the energy gap at 0 K. Next, we have derived the analytical formulas for the basic thermodynamic parameters. The conducted analysis allowed to designate the T _C - T ^?? diagram. Finally, we found the limitation from below for the value of T ^??, occurring for the critical temperature higher than 150 K.     

On VLSI interconnect optimization and linear ordering problem

Some well-known VLSI interconnect optimizations problems for timing, power and cross-coupling noise immunity share a property that enables mapping them into a specialized Linear Ordering Problem (LOP). Unlike the general LOP problem which is NP-complete, this paper proves that the specialized one has a closed-form solution. Let f(x,y):?²→? be symmetric, non-negative, defined for x≥0 and y≥0, and let f(x,y) be twice differentiable, satisfying ? ² f(x,y)/?x?y<0. Let π be a permutation of {1,…,n}. The specialized LOP comprises n objects, each associated with a real value parameter r _i , 1≤i≤n, and a cost f(r _i ,r _j ) associated to any two objects if |π(i)?π(j)|=1,1≤i,j≤n, and f(r _i ,r _j )=0 otherwise. We show that the permutation π which minimizes \(\sum_{i= 1}^{n - 1} f( r_{\pi^{ - 1}( i )},r_{\pi^{ - 1}( i + 1 )} )\), called “symmetric hill”, is determined upfront by the relations between the parameter values r _i .     

Investigation of Magnetic,Magnetocaloric, and Critical Properties of La<Subscript>0.5</Subscript>Ba<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> Manganite

We present an extensive study of the magnetic properties of a novel La_0.5Ba_0.5MnO₃ perovskite material prepared by the hydrothermal method. The explored sample was structurally studied by the x-ray diffraction (XRD) method which confirms the formation of a pure cubic phase of a perovskite structure with Pm3m space group. The magnetic properties were probed by employing temperature M (T) and external magnetic field M (μ_oH) dependence of magnetization measurements. A magnetic phase transition from ferromagnetic to paramagnetic phase occurs at 339 K in this sample. The maximum magnetic entropy change (\(\left | {{\Delta } S}_{M}^{\max } \right |\)) took a value of 1.4 J kg^??1 K^??1 at the applied magnetic field of 4.0 T for the explored sample and has also been found to occur at Curie temperature (T_C). This large entropy change might be instigated from the abrupt reduction of magnetization at T_C. The magnetocaloric effect (MCE) is maximum at T_C as represented by M (μ_oH) isotherms. The relative cooling power (RCP) is 243.2 J kg^??1 at μ_oH =?4.0 T. Moreover, the critical properties near T_C have been probed from magnetic data. The critical exponents δ, β, and γ with values 3.82, 0.42, and 1.2 are close to the values predicted by the 3D Ising model. Additionally, the authenticity of the critical exponents has been confirmed by the scaling equation of state and all data fall on two separate branches, one for T < T_C and the other for T > T_C, signifying that the critical exponents obtained in this work are accurate.     

In-field Conductivity Fluctuations in Ba<Subscript>0.72</Subscript>K<Subscript>0.28</Subscript>Fe<Subscript>2</Subscript>As<Subscript>2</Subscript> Single Crystals

Fluctuations in the conductivity of Ba_0.72K_0.28Fe₂As₂ single crystal are studied systematically by resistance measurements as a function of temperature and magnetic field. A clear Maki?Thompson and Aslamakov?Larkin (MT–AL) two- to three-dimensional (2D–3D) crossover is found on the excess conductivity (Δσ) curves as the temperature approaches the superconducting critical temperature, T _c. 3D fluctuations in superconductivity are realized near T _c that are well fitted to experimental data by the 3D Aslamazov–Larkin theory. The Maki–Thompson model shows a 2D conductivity fluctuation above the 2D-3D temperature transition, T ₀, which depends on magnetic field. Results show that the 2D-3D dimensional crossover moves to lower temperature with increasing magnetic field. The values of the transition temperature and the crossover in the reduced temperature, ln(ε ₀), as functions of magnetic field were used to determine the coherence length and the lifetime, τ _φ , of the fluctuational pairs at the temperature of 35 K. Analysis of the Ba_0.72K_0.28Fe₂As₂ single crystal gives a value of 3.76 × 10^??12 s for the τ _φ in the absence of magnetic field and it decreases to 2.4 × 10^??12 s in magnetic field of 13 T.     

The size and impact of the elite set of publications in scientometric assessments

Several scientometric impact indicators [total citations, h, g, and π-index, percentage rank position (PRP), weighted citation share (WCS)] of 190 elite papers of 15 members of the Hungarian Academy of Sciences active in three different fields were calculated. From the indices the PRP indicator proved to be independent of the citation practices in the fields. The PRP index of a journal paper can be calculated in per cent as unity minus (the rank number of the paper by citation frequency within the publishing journal minus one divided with the total number of papers in the journal) times hundred. The sum of the PRP index of the elite papers of a scientist may characterize his or her total publication performance. The size of the elite set of journal papers within the total was calculated by different methods. The h-index and g-index corresponds to the size of the elite, i.e. number of the elite papers according to the h-statistics and g-statistics, respectively. The number of papers in the π-set is equal to the square root of total papers. The π-index equals to one hundredth of citations to the π-set papers. In the present paper the size of the elite set is determined as the number of papers in the h-set, g-set, or π-set, and as 10 % of total papers, or number of papers cited 2, 3, or 5 times the mean citation rate (MCR) of the publishing journal. The π-citation threshold model is presented for demonstrating how MCR and the distribution of citations over the papers may influence the size of the elite set and the corresponding π-index. It was found that the scientific performances concluded from the π-index obtained from elite sets of different size are in good agreement.     

Spin Dynamics in the Bi-Directional Charge Density Wave State of High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

In this paper, we investigate the dynamical spin susceptibility in the bi-directional charge density wave (BCDW) state by adopting a random-phase approximation. In the BCDW state, we find that no spin resonance exists and only a broad commensurate peak appears for the frequency dependence of the dynamical spin susceptibility at Q = (π,π), though a low-energy spin gap feature can also be found as in the superconducting state. While the “hourglass” type of the dispersion for the BCDW state bears some similarities with that in the superconducting state, the momentum distribution of Im χ ^+?(Q,ω) is just the opposite with the incommensurate peaks lying along the diagonal direction for the energy below ω _c and along the axial direction above ω _c . In the coexistence of SC and BCDW, the frequency dependence of the dynamical spin susceptibility at Q = (π,π) generally shows the two-peak structure, reflecting two energy scales of the spin excitations. These unique features may serve as signatures to verify whether or not the BCDW state is responsible for the formation of the Fermi arcs.     

Effect of manganese doping on conduction in olivine LiFePO<Subscript>4</Subscript>

Lithium ion batteries play a crucial role in terms of good rechargeability, long cycles and higher shelf life. For the fabrication of such a Li ion battery, properties of cathode material can be engineered keeping anode and electrolyte fixed. In the present work, lithium iron phosphate (LiFePO₄) has been utilized as cathode material and the properties of LiFePO₄ have been tuned by doping manganese (Mn). LiFePO₄ and different concentrations of Mn doped LiFePO₄ were prepared by solid state route. X-Ray diffraction and Raman studies were performed to confirm the formation of LiFePO₄ and Mn doped LiFePO₄ in olivine structure. Cyclic voltammetry studies revealed maximum peak oxidation current (2.96 mA) and largest surface coverage (0.066 nanoMoles/cm²) for the LiFePO₄ doped with 15% Mn (LiMn_0.15Fe_0.85PO₄). AC-conductivity study was carried out for different frequencies at room temperature. The conductivity parameters estimated using Almond and West formalism support the cyclic voltammetry results. Ion-hopping rate (ω _p ) and charge carrier concentration (K) maximize for 15% Mn doping (ω _p : 582974.48719 Hz; K: 2.62447?×?10^?6) and drop on either increasing (ω _p : 167134.73521 Hz; K: 1.25647?×?10^?7) or decreasing (ω _p : 130726.49084 Hz; K: 2.52435?×?10^?6) the Mn doping. The increase till 15% Mn doping has been attributed to the increase in unit cell volume with Mn doping while the sudden decrease at 20% Mn doping is due to dominance of back-hopping mechanism. The results clearly indicate that 15% Mn doped LiFePO₄ is the most appropriate for the realization of a cathode for Li-ion battery.     

Mechanism of AC charge transport in TlSb<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>2</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0 and 0.03)

The dielectric properties and ac electrical conductivity of TlSb_1–xGa _x S₂ (x = 0, 0.03) single-crystals have been measured in the frequency range 5 × 10⁴ to 3.5 × 10⁷ Hz. Experimental data on the frequency dispersion of the dielectric coefficients and electrical conductivity of the TlSb_1–xGa _x S₂ (x = 0, 0.03) single crystals have allowed us to identify the nature of the dielectric loss and the mechanism of charge transport and evaluate parameters of localized states in the band gap. The incorporation of gallium atoms into the crystal lattice of TlSbS₂ crystals has been shown to lead to an increase in the Fermi-level density of states and mean hop time and distance.     

Chromium diffusion in GaAs in an open system

We have studied chromium diffusion from a surface layer produced by thermal evaporation into n-type GaAs in a flowing inert-reducing atmosphere. The temperature dependences of the Cr diffusivity and solubility in GaAs are well represented by Arrhenius equations with D ₀ = 1.7 × 10^?2 cm²/s and Q _D = 1.43 eV for the diffusivity and C _Cr ⁰ = 8.9 × 10²¹ cm^?3 and Q _Cr = 1.22 eV for the solubility.     

Field-Controllable Spin Filter Based on Parallel Quantum Dot Systems

In this paper, we investigate the spin-polarized transport through parallel N?dot (N = 1, 2, 3) systems in the strongly correlated regime. We focus our attention on the responses of the N _{t o t} = i n t e g e r states to an increasing magnetic field B, where N _{t o t} is the total charge number on the dots. We show that when the charge level ?? is chosen at the particle-hole (p-h) symmetric case, spin filtering is difficult to occur. While if ?? is beyond the p-h symmetric point, perfect spin-polarized currents could be achieved, and the spin directions can be easily manipulated by tuning external electric and/or magnetic fields, making it easy to be realized in future experiments of the ideas. To approach these problems, the celebrated numerical renormalization group (NRG) technique is implemented, the dynamical properties and the quantum fluctuations are shown.     

Dielectric Properties and Electrical Conductivity of (<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>)TlGaSe<Subscript>2</Subscript> · <Emphasis Type="Italic">x</Emphasis>Tm Crystals

We have synthesized samples based on the layered compound TlGaSe₂ and containing thulium: (1–x)TlGaSe₂ · xTm with x = 0.001, 0.005, 0.01, and 0.02. The polycrystalline samples have been used as charges for growing crystals with the corresponding compositions by the Bridgman method. The phase composition of the (1–x)TlGaSe₂ · xTm samples has been determined by X-ray diffraction analysis. Their dielectric properties have been studied in ac electric fields at frequencies in the range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. We have identified the relaxation character of the dielectric permittivity, the nature of the dielectric loss, and the hopping mechanism of charge transport in the (1–x)TlGaSe₂ · xTm crystals. Our results demonstrate that increasing the thulium concentration in the crystals reduces the mean hop distance and time of charge carriers and increases the ac conductivity and the density of localized states near the Fermi level in the crystals.     

4<Emphasis Type="Italic">H</Emphasis>-SiC Based Subnanosecond (150 ps) High-Voltage (1600 V) Current Breakers

High-voltage (1600 V) diodes based on epitaxial 4H-SiC p⁺⁺–p⁺–n₀–n⁺ structures are tested as fast current breakers included in a special pulsed circuit. The measured current-breakdown time is about 150 ps. This is a record short time for high-voltage (above 1000 V) silicon-carbide diode breakers. The saturated hole-drift velocity in 4H-SiC of p type is experimentally estimated for the first time: v _sp = 3 × 10⁶ cm/s.     

Formation of a periodic diffractive structure based on poly(methyl methacrylate) with ion-implanted silver nanoparticles

We propose to form optical diffractive elements on the surface of poly(methyl methacrylate) (PMMA) by implanting the polymer with silver ions (E = 30 keV; D = 5.0 × 10¹⁴ to 1.5 × 10¹⁷ ion/cm²; I = 2 μA/cm²) through a nickel grid (mask). Ion implantation leads to the nucleation and growth of silver nanoparticles in unmasked regions of the polymer. The formation of periodic surface microstructures during local sputtering of the polymer by incident ions was monitored using an optical microscope. The diffraction efficiency of obtained gratings is demonstrated under conditions of their probing with semiconductor laser radiation in the visible spectral range.     

Preparation and structural study of Mg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> ceramics and their dielectric properties from 1 Hz to 7.7 GHz

A series of Mg_1?x Zn _x TiO₃, x = 0–0.5 (MZT0–MZT0.5) ceramics was synthesised and characterised. The dielectric properties of the samples in the frequency range of 1 Hz–7.7 GHz were explored using three different methods: a contacting electrode method, a parallel-plate method and a perturbed resonator method. The electrical properties in the space charge and dipolar polarisation frequency ranges are discussed in relation to the phase composition and microstructure data. Differences in the zinc substitution divided the dielectrics into two groups, namely MZT0–MZT0.2 and MZT0.3–MZT0.5, each with different amount of a main Mg_1?x Zn _x TiO₃ solid solution phase and a secondary solid solution phase. Zinc substitution promoted the density of the ceramics, improved the purity of the main phase and increased the permittivity for frequencies up to 10⁸ Hz, but reduced the permittivity in the microwave range. In the MZT0.3–MZT0.5 samples, for frequencies less than 1 MHz the quality (Q × f) factors were lower and log σ _a.c, the AC conductivity, was higher than for the MZT0–MZT0.2 samples. Above 10 MHz, the (Q × f) factors and log σ _a.c of the two groups were similar.     

Overlapping Large Polaron Conductivity Mechanism and Dielectric Properties of Al<Subscript>0.2</Subscript>Cd<Subscript>0.8</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> Ferrite Nanocomposite

In this work, the conduction and dielectric properties of Al_0.2Cd_0.8Fe₂O₄ ferrite nanoparticle, which was synthesized by a co-precipitation method, were investigated. Experimental data were taken from 20 Hz to 10 MHz and from 293 to 613 K. AC conductivity of the sample was analyzed within the framework of the overlapping large polaron tunneling (OLPT) mechanism. DC conductivity behavior fits the classical Arrhenius-type conductivity in the examined temperature range. Electrical properties of the material sample have been studied using an impedance spectroscopy technique. The effect of frequency and temperature on dielectric constant (ε ^′), dielectric loss (tan ??), and impedance (Z′ and Z′′) has been discussed in terms of hopping of charge carriers between Fe²⁺ and Fe³⁺ ions. According to results, a relaxation process fits the Cole–Cole model.     

Structure and properties of the layered compound HoBaCuCoO<Subscript>5 + δ</Subscript>

HoBaCuCoO_{5 + δ} has been synthesized, and its crystal structure and physicochemical properties have been studied. It crystallizes in tetragonal symmetry (sp. gr. P4/mmm) with lattice parameters a = 0.3867(2) nm and c = 0.7554(5) nm (V = 113.0(2) × 10^?3 nm³, δ = 0.01) and is a p-type semiconductor. According to dilatometry results, holmium barium cobaltocuprate undergoes no structural phase transitions in the temperature range 300–1100 K. Its linear thermal expansion coefficient is 15.1 × 10^?6K^?1.     

Ionic conductivity of BaF<Subscript>2</Subscript> + ZnF<Subscript>2</Subscript> + CdF<Subscript>2</Subscript> + YbF<Subscript>3</Subscript> optical fluoride ceramic

The electrical conductivity of an optical fluoride ceramic in the quaternary system BaF₂ + ZnF₂ + CdF₂ + YbF₃ has been determined in the temperature range 338–722 K using impedance spectroscopy (5 to 5 × 10⁵ Hz). The 500-K ionic conductivity of the ceramic is σ = 3.3 × 10^–4 S/cm, which corresponds to the electrical characteristics of single crystals of the best conducting nonstoichiometric M_1–x R _x F_{2 + x} (M = Sr, Ba; R = La–Nd; x = 0.3–0.5) fluorite phases. We have observed nonmonotonic variation (breaks) in temperature-dependent σ, which is due to competing fluoride ion transport processes in different parts of the ceramic sample. The highly conductive state of the BaF₂ + ZnF₂ + CdF₂ + YbF₃ fluoride ceramic seems to be due to the formation of structural regions corresponding to a Ba_1–x Yb _x F_{2 + x} solid solution.     

The passive <Emphasis Type="Italic">Q</Emphasis>-switching regime in a solid state laser with a multiloop cavity

A compact, pulsed-periodic YAG: Nd³⁺ laser with self-pumped phase-conjugate multiloop cavity and passive Q-switching by YAG: Cr4+ and GSGG: Cr4+ crystals has been studied. It is established that the energy and temporal parameters of radiation in separate pulses of a periodic train can be controlled almost without changing the pulse train energy. A regime of generating modulated radiation pulses with a peak power of up to 30 MW and a spatial brightness of 1.7 × 10¹⁵ W/(cm² sr) at a radiation beam quality parameter of M ² < 1.2 has been realized in experiment.