An in vitro culture system demonstrating the transitions from megakaryocyte progenitors to functional platelets is described. CD34- selected cells from normal human peripheral blood are cultured under conditions that promote megakaryocyte formation. After 8 to 11 days, enriched populations of mature megakaryocytes are replated under conditions that favor the development of proplatelets. Proplatelets express the platelet-specific proteins, glycoproteins Ib and IIb (GPIb and GPIIb), and fibrinogen and also contain microtubule coils equal in size to those found in plasma-derived platelets. In addition, proplatelets have ultrastructural features in common with plasma- derived platelets. Platelet-sized particles from the proplatelet culture supernatants are examined. Ultrastructurally, these particles are identical to plasma-derived platelets. Functionally, these culture- derived platelets aggregate in response to both thrombin and adenosine diphosphate (ADP) plus fibrinogen. This aggregation is specifically inhibited by the addition of a function-blocking anti-GPIIbIIIa antibody. Culture-derived platelets stimulated with agonists also express the activation-dependent antigens P-selectin and functional fibrinogen receptor. This is the first description of an in vitro culture system that sequentially demonstrates megakaryocyte growth, development, and platelet production.
The longitudinal resistivity ρxx and Hall coefficient RH were measured for MgB2 sintered under high pressure. We found that RH is positive like cuprate high-Tc superconductors, and decreases as temperature increases for 40 K < T < 300 K. The cotangent of Hall angle was found to follow a + bT 2 behavior from Tc to 300 K. At T = 100 K, RH = 4.1 × 10 −11 m 3 /C from which hole carrier density was determined to be 1.5 × 10 23 /cm 3 . This carrier density is 2 -3 orders of magnitude larger than those of Nb3Sn and optimally doped YBa2Cu3Oy superconductors.Recently, MgB 2 was found to be metallic superconductor with transition temperature (T c ) of about 40 K. [1,2], and has provided great scientific interest. Several thermodynamic parameters have been estimated, [3,4] such as a upper critical field H c2 = 13 -18 T, a GinzburgLandau parameter κ ∼ 26, and the critical supercurrent density J c (0) ∼ 10 5 A/cm 2 . In order to probe the nature of gap, tunneling spectroscopy measurements have been reported [5,6], and they observed superconducting energy gap (∆) of 5 -7 meV in the framework of the BCS model. The conventional BCS electron-phonon interaction was proposed as the origin of the superconductivity based on a band calculation. [7] The possible origin of the enhanced T c is suggested to originate from a strong electron-phonon interaction and a enhanced phonon frequency due to the light boron mass in MgB 2 . Most of the charge carrier density at the Fermi level comes from the boron band. Indeed, the boron isotope effect has been reported with an exponent of α B ∼ 0.26. [8] No experimental study on the electronic structure has been reported yet.Another interesting feature concerning the normalstate Hall effect in high-T c cuprates is the universal temperature dependence of the cotangent of the Hall angle (cotθ H ). Anderson [10] and Chien et al. [9] have proposed that the charge transport is governed by two different scattering times with different temperature dependences. In this model, the cotθ H should be proportional to T 2 since the Hall angle is proportional to the inverse of the Hall scattering time τ H (∝ T −2 ), and has been observed for most high-T c superconductors. [11,12] In the mixed-state, the flux-flow Hall effect is also quite interesting. A puzzling sign anomaly has been observed in some conventional superconductors [13,14] as well as in most of high-T c superconductors.[15] Even double [16,17] or triple sign changes [15] have been observed in some high-T c superconductors. Furthermore, a universal scaling behavior between the Hall resistivity and the longitudinal resistivity has attracted much experimental [15][16][17][18] and theoretical interest. [19] However, these Hall effects in the mixed state are not well understood.To understand the superconductivity in MgB 2 , it is essential to know the type of charge carrier and it's density, but these have not been reported yet . Theoretically, Hirsch [20] proposed that the 40 K superconductivity of MgB 2 originates mainly from the hole carriers with bor...
The origin of the spin liquid state in Tb2Ti2O7 has challenged experimentalists and theorists alike for nearly 20 years. To improve our understanding of the exotic magnetism in Tb2Ti2O7, we have synthesized a chemical pressure analog, Tb2Ge2O7. Germanium substitution results in a lattice contraction and enhanced exchange interactions. We have characterized the magnetic ground state of Tb2Ge2O7 with specific heat, ac and dc magnetic susceptibility, and polarized neutron scattering measurements. Akin to Tb2Ti2O7, there is no long-range order in Tb2Ge2O7 down to 20 mK. The Weiss temperature of −19.2(1) K, which is more negative than that of Tb2Ti2O7, supports the picture of stronger antiferromagnetic exchange. Polarized neutron scattering of Tb2Ge2O7 reveals that at 3.5 K liquid-like correlations dominate in this system. However, below 1 K, the liquid-like correlations give way to intense short-range ferromagnetic correlations with a length scale related to the Tb-Tb nearest neighbor distance. Despite stronger antiferromagnetic exchange, the ground state of Tb2Ge2O7 has ferromagnetic character, in stark contrast to the pressure-induced antiferromagnetic order observed in Tb2Ti2O7.Geometrically frustrated pyrochlores, R 2 M 2 O 7 , exhibit a diverse array of exotic magnetic behaviors [1]. The ground states in these materials are dictated by a complex, and often delicate balance of exchange, dipolar, and crystal field energies. Tb 2 Ti 2 O 7 is one of the most remarkable of these frustrated pyrochlores; strong antiferromagnetic exchange and Ising-like spins led to predictions of an antiferromagnetic Néel state below ∼1 K for this material [2]. However, experimental studies revealed a lack of static order or spin freezing in Tb 2 Ti 2 O 7 down to 70 mK [3,4], and more recently 57 mK [5]. Subsequently, enormous efforts have been undertaken to uncover the origin of the spin liquid state in Tb 2 Ti 2 O 7 .A further complication in Tb 2 Ti 2 O 7 is the coupling of magnetic and lattice degrees of freedom [6][7][8][9]. It has been suggested that hybridized magnetoelastic excitations may be responsible for the suppression of magnetic order in Tb 2 Ti 2 O 7 [10]. Another theoretical construct that attempts to account for the lack of static order in Tb 2 Ti 2 O 7 is a quantum spin ice state [11][12][13][14][15]. A third proposed scenario is that the non-Kramers doublet ground state of Tb 2 Ti 2 O 7 is split into two non-magnetic singlets through a symmetry reducing structural distortion [16][17][18].Other studies sought to uncover the origin of the spin liquid state in Tb 2 Ti 2 O 7 by focusing on mechanisms of its destruction, such as: external pressure [19], magnetic fields [18,20,21], and a combination of the two [22]. Partial antiferromagnetic order is induced in Tb 2 Ti 2 O 7 with external hydrostatic pressures of 8.6 GPa, resulting in a 1% compression of the lattice [19]. Another means of destroying the spin liquid state is chemical pressure: substitution of the non-magnetic titanium cation for an iso-electronic cation w...
The remarkably high superconducting transition temperature and upper critical field of iron(Fe)-based layered superconductors, despite ferromagnetic material base, open the prospect for superconducting electronics. However, success in superconducting electronics has been limited because of difficulties in fabricating high-quality thin films.We report the growth of high-quality c-axis-oriented cobalt(Co)-doped SrFe 2 As 2 thin films with bulk superconductivity by using an in-situ pulsed laser deposition technique with a 248-nm-wavelength KrF excimer laser and an arsenic(As)-rich phase target. The temperature and field dependences of the magnetization showing strong diamagnetism and transport critical current density with superior J c -H performance are reported.These results provide necessary information for practical applications of Fe-based superconductors. \pacs{} The classes of Iron (Fe)-based superconductors [1][2][3][4][5][6][7][8] have remarkably high superconducting transition temperatures (T c ) in spite of the ferromagnetic material base; the highest T c is 55 K in LnFeAsO (FeAs-1111, Ln = lanthanide) [2] and 37.5 K in AEFe 2 As 2 (FeAs-122, AE = alkaline-earth element) [7]. The zero-temperature upper critical field (H c2 (0)) was found to be up to 65 T in the FeAs-1111 [9]. The discovery of these new classes of superconductors has regenerated interest in superconductivity because of an opportunity to tune these materials in many ways [10,11]. This potentially allows one to reveal the mechanism of high-temperature superconductors.Ever since discovering these compounds, much progress has been made in measuring the fundamental physical properties in order to understand the superconducting mechanism. However, controversy still exists because the measurements were carried out on bulk polycrystals, except for some works on single crystals [8,[12][13][14][15][16]. Highquality thin films are needed to investigate the physical properties and to develop superconducting electronic devices, such as Josephson junctions. However, controlling the stoichiometry of the FeAs-1111 phase is difficult because the crystal structure contains two different anions [17]. Also, in the FeAs-1111 phase, electrons are doped by partially replacing oxygen ions with fluorine (F), which is easily evaporated in a vacuum chamber at a high temperature because of its very high vapor pressure. These reasons make it difficult to fabricate high-quality thin film [17][18][19].Very recently, Hosono et al. reported success in growing cobalt (Co)-doped SrFe 2 As 2 thin film [18,19]. Even though this compound has a relatively lower T c , Codoping is more suitable for thin film growth than other types of doping (F or potassium (K)) because of the low vapor pressure of Co. Also, SrFe 2 As 2 contains only one anion species. Hosono et al. fabricated the thin films by using pulsed laser deposition (PLD) with a second-harmonic 532-nm-wavelength Nd:YAG laser and a stoichiometric target disk.In general, an ultraviolet (UV) wavelength is known ...
The pyrochlore Ho2Ge2O7 is a new highly correlated spin ice material. Physical property measurements including x-ray diffraction, dc susceptibility and ac susceptibility, confirm that it shares the distinctive characteristics of other known spin ices. Polarized neutron scattering measurements on a powder sample, combined with reverse Monte Carlo (RMC) refinements, give unique information about the spin ice state in Ho2Ge2O7. RMC refinements are used to fit the powder magnetic diffuse scattering and predict the single crystal magnetic scattering of Ho2Ge2O7, demonstrating consistency with spin ice behavior
We have fabricated high-quality FeSe 1−x superconducting films with a bulk T c of 11−12 K on different substrates, Al 2 O 3 (0001), SrTiO 3 (100), MgO(100), and LaAlO 3 (100), by using a pulsed laser deposition technique. All the films were grown at a high substrate temperature of 610 • C, and were preferentially oriented along the (101) direction, the latter being to be a key to fabricating of FeSe 1−x superconducting thin films with high T c . According to the energy dispersive spectroscopy data, the Fe:Se composition ratio was 1:0.90±0.02. The FeSe 1−x film grown on a SrTiO 3 substrate showed the best quality with a high upper critical magnetic field [H c2 (0)] of 56 T.
We investigated thermoelectric power S(T ) of MgB2−xBex (x = 0, 0.2, 0.3, 0.4, and 0.6). S(T ) decreases systematically with x, suggesting that the hole density increases. Our band calculation shows that the increase occurs in the σ-band. With the hole-doping, Tc decreases. Implication of this phenomenon is discussed within the BCS framework. While the Mott formula explains only the linear part of S(T ) at low temperature, incorporation of electron-phonon interaction enables us to explain S(T ) over wide temperature range including the anomalous behavior at high temperature.
The microwave cutoff probe (CP) is an accurate diagnostic technique to measure absolute electron density even in processing gas plasmas. Because this technique needs the installation of two probe tips and a probe body in the plasma chamber, it may cause plasma perturbation in semiconductor plasma processing; this may increase the uncertainty of the measured value. In this work, a flat CP, which is embedded in the substrate chuck or chamber wall, is proposed to measure electron density without plasma perturbation and to monitor processing plasma in real-time. We first evaluated the performance of various types of flat CPs, such as the point CP, ring CP, and bar cutoff probe (BCP), through electromagnetic (EM) field simulation. The BCP showed better performance with clearer cut-off signal characteristics and minimization of noise signals compared with the other probe types. Therefore, we focused on the characteristics of the BCP through experiments and/or EM simulations and concluded the followings: (i) the measured electron densities of the BCP agree well with those of the conventional CP; (ii) the BCP measures the plasma density near the plasma-sheath boundary layer, which is very closely adjacent to the chamber wall or wafer; (iii) it was demonstrated for the first time that the plasma density can be measured, even though the processing wafers such as un-doped silicon, P type silicon, amorphous carbon, or amorphous carbon/SiO2 patterned wafers were placed on the flat CP; and (iv) we performed real-time measurements of the electron density using the BCP covered with the wafers in plasmas with various process gases, such as Ar, NF3, and O2. These results indicate that the chuck-embed-type or wall-type flat CP can be used as a real-time electron density measurement (monitoring) tool during industrial plasma processing, such as during etching, deposition, sputtering or implantation, and the chuck-embed-type flat CP can measure the plasma density impinging on the wafer in real-time without stopping the processing.
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