Showing papers by "Tohoku University published in 1996"

Spectroscopic evidence for a pseudogap in the normal state of underdoped high- T c superconductors

Abstract: IT is well known that BCS mean-field theory is remarkably successful in describing conventional superconductors. A central concept of BCS theory is the energy gap in the electronic excitation spectrum below the superconducting transition temperature, Tc. The gap also serves as the order parameter: quite generally, long-range phase coherence and a non-zero gap go hand-in-hand1. But in underdoped high-Tc superconductors there is considerable evidence that a pseudogap (a suppression of spectral weight) is already formed in the normal state above Tc—first, from studies of the spin excitation spectrum2–5,24, which measure a 'spin gap', and later from a variety of other probes6–10. Here we present a study of underdoped Bi2Sr2CaCu2O8+δ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES), which directly measures the momentum-resolved electron excitation spectrum of the CuO2 planes. We find that a pseudogap with d-wave symmetry opens up in the normal state below a temperature T* > Tc, and develops into the d-wave superconducting gap once phase coherence is established below Tc.

Lepton-flavor violation via right-handed neutrino Yukawa couplings in the supersymmetric standard model.

Abstract: Various lepton-flavor-violating (LFV) processes in the supersymmetric standard model with right-handed neutrino supermultiplets are investigated in detail. It is shown that large LFV rates are obtained when $tan\ensuremath{\beta}$ is large. In the case where the mixing matrix in the lepton sector has a similar structure as the Kobayashi-Maskawa matrix and the third-generation Yukawa coupling is as large as that of the top quark, the branching ratios can be as large as $B(\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma})\ensuremath{\simeq}{10}^{\ensuremath{-}11}$ and $B(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma})\ensuremath{\simeq}{10}^{\ensuremath{-}7}$, which are within the reach of future experiments. If we assume a large mixing angle solution to the atmospheric neutrino problem, the rate for the process $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$ becomes larger. We also discuss the difference between our case and the case of the minimal SU(5) grand unified theory.

Bach proteins belong to a novel family of BTB-basic leucine zipper transcription factors that interact with MafK and regulate transcription through the NF-E2 site.

Abstract: Members of the small Maf family (MafK, MafF, and MafG) are basic region leucine zipper (bZip) proteins that can function as transcriptional activators or repressors. The dimer compositions of their DNA binding forms determine whether the small Maf family proteins activate or repress transcription. Using a yeast two-hybrid screen with a GAL4-MafK fusion protein, we have identified two novel bZip transcription factors, Bach1 and Bach2, as heterodimerization partners of MafK. In addition to a Cap'n'collar-type bZip domain, these Bach proteins possess a BTB domain which is a protein interaction motif; Bach1 and Bach2 show significant similarity to each other in these regions but are otherwise divergent. Whereas expression of Bach1 appears ubiquitous, that of Bach2 is restricted to monocytes and neuronal cells. Bach proteins bind in vitro to NF-E2 binding sites, recognition elements for the hematopoietic transcription factor NF-E2, by forming heterodimers with MafK. Furthermore, a DNA binding complex that contained MafK as well as Bach2 or a protein related closely to Bach2 was found to be present in mouse brain cells. Bach1 and Bach2 function as transcription repressors in transfection assays using fibroblast cells, but they function as a transcriptional activator and repressor, respectively, in cultured erythroid cells. The results suggest that members of the Bach family play important roles in coordinating transcription activation and repression by MafK.

Solar Neutrino Data Covering Solar Cycle 22.

Abstract: Results from 1036 days of solar neutrino data accumulated in the upgraded Kamiokande detector (Kamiokande III) are presented. The $^{8}\mathrm{B}$ solar neutrino flux observed in Kamiokande III is ${2.82}_{\ensuremath{-}0.24}^{+0.25}$ (stat) \ifmmode\pm\else\textpm\fi{} 0.27 (syst) \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ ${\mathrm{cm}}^{\ensuremath{-}2}$${\mathrm{s}}^{\ensuremath{-}1}$; the combined flux from Kamiokande II and III (2079 days in total) is 2.80 \ifmmode\pm\else\textpm\fi{} 0.19 (stat) \ifmmode\pm\else\textpm\fi{} 0.33 (syst) \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ ${\mathrm{cm}}^{\ensuremath{-}2}$${\mathrm{s}}^{\ensuremath{-}1}$, which is 49% to 64% of the standard solar models. These combined data from January 1987 to February 1995, covering an entire period of solar cycle 22, enabled us to study a correlation between the neutrino flux and the solar activity in detail: no strong correlation of the solar neutrino flux with the sunspot numbers was found within experimental errors. The result on a search for the daytime and nighttime flux difference is also reported.

Millisecond X-Ray Variability from an Accreting Neutron Star System

Abstract: We report the detection with the Proportional Counter Array (PCA) on board the Rossi X-Ray Timing Explorer (RXTE) of millisecond variability in the X-ray emission from the low-mass X-ray binary 4U 1728-34. Pulsations at 363 Hz with amplitudes (rms) of 2.5%-10% are present in six of the eight bursts analyzed to date. The strongest were seen in two successive bursts recorded on 1996 February 16 when the quiescent count rate was near the highest seen by PCA. The pulsations during these bursts show frequency changes of 1.5 Hz during the first few seconds but become effectively coherent as the burst decays. We interpret the 363 Hz pulsations as rotationally induced modulations of inhomogeneous burst emission. This represents the first compelling evidence for a millisecond spin period in a low-mass X-ray binary. Complex, intensity-dependent, millisecond X-ray variability is also present in all the quiescent flux intervals we examined. Most interesting was the behavior as the count rate approached its highest observed level. Two quasi-periodic oscillations (QPOs) were simultaneously observed in the 650-1100 Hz range. Both QPOs increased in frequency together, maintaining a nearly constant frequency separation of about 363 Hz, the spin period inferred from the burst oscillations. This phenomenology is strongly suggestive of the magnetospheric beat frequency model proposed for the horizontal-branch oscillations (HBOs) seen in Z sources. We discuss this and several other possible physical interpretations for the observed X-ray variability.

The interleukin-2 receptor gamma chain: its role in the multiple cytokine receptor complexes and T cell development in XSCID.

Abstract: Interleukin 2 (IL-2), a T cell-derived cytokine, targets a variety of cells to induce their growth, differentiation, and functional activation. IL-2 inserts signals into the cells through IL-2 receptors expressed on cell surfaces to induce such actions. In humans, the functional IL-2 receptor consists of the subunit complexes of the alpha, beta and gamma chains, or the beta and gamma chains. The third component, the gamma chain, of IL-2 receptor plays a pivotal role in formation of the full-fledged IL-2 receptor, together with the beta chain, the gamma chain participates in increasing the IL-2 binding affinity and intracellular signal transduction. Moreover, the cytokine receptors for at least IL-2, IL-4, IL-7, IL-9, and IL-15 utilize the same gamma chain as an essential subunit. Interestingly, mutations of the gamma chain gene cause human X-linked severe combined immunodeficiency (XSCID) characterized by a complete or profound T cell defect. Among the cytokines sharing the gamma chain, at least IL-7 is essentially involved in early T cell development in the mouse organ culture system. The molecular identification of the gamma chain brought a grasp of the structures and functions of the cytokine receptor and an in-depth understanding of the cause of human XSCID. To investigate the mechanism of XSCID and development of gene therapy for XSCID, knockout mice for the gamma chain gene were produced that showed similar but not exactly the same phenotypes as human XSCID.

N-body Simulations of the Small Magellanic Cloud and the Magellanic Stream

Abstract: An extensive set of N-body simulations has been carried out on the gravitational interaction of the Small Magellanic Cloud (SMC) with the Galaxy and the Large Magellanic Cloud (LMC). The SMC is assumed to have been a barred galaxy with a disc-to-halo mass ratio of unity before interaction and modelled by a large number of self-gravitating particles, whereas the Galaxy and LMC have been represented by rigid spherical potentials. The best model we have found succeeded in reproducing the Magellanic Stream (MS), as well as a leading counterpart to the Magellanic Stream (the leading arm), on the opposite side of the Magellanic Clouds to the Stream, which mimicks the overall distribution of several neutral hydrogen clumps observed in the corresponding region of the sky. The elongation of the SMC bar along the line-of-sight direction suggested by Cepheid observations has been partially reproduced, alongside its projected appearance on the sky. The model successfully explains some major trends in the kinematics of young populations in the SMC bar and older populations in the `halo' of the SMC, as well as the overall velocity pattern for the gas, young stars, and carbon stars in the inter-Cloud region.

Transgenic plant production mediated by Agrobacterium in indica rice

Abstract: A reproducible system has been developed for the production of transgenic plants in indica rice using Agrobacterium-mediated gene transfer. Three-week-old scutella calli served as an excellent starting material. These were infected with an Agrobacterium tumefaciens strain EHA101 carrying a plasmid pIG121Hm containing genes for β-glucuronidase (GUS) and hygromycin resistnace (HygR). Hygromycin (50 mg/l) was used as a selectable agent. Inclusion of acetosyringone (50μM) in the Agrobacterium suspension and co-culture media proved to be indispensable for successful transformation. Transformation efficiency of Basmati 370 was 22% which was as high as reported in japonica rice and dicots. A large number of morphologically normal, fertile transgenic plants were obtained. Integration of foreign genes into the genome of transgenic plants was confirmed by Southern blot analysis. GUS and HygR genes were inherited and expressed in R1 progeny. Mendelian segregation was observed in some R1 progeny.

Continental Crust, Crustal Underplating, and Low- Q Upper Mantle Beneath an Oceanic Island Arc

Abstract: A detailed structural model of the crust, subducting slab, and underlying upper mantle across the northern Izu-Ogasawara (Bonin) island arc system is derived from a marine seismic reflection and ocean bottom seismographic refraction survey and subsequent forward modeling combined with tomographic inversion. The model indicates that the crust is thickest beneath the presently active rift zone and a granitic crust may have formed in the mid-crust. A highly attenuative mantle (that is, one with low quality Q) seems to be confined mainly beneath the presently active rift zone. In contrast, high P-wave velocity persists in the lower crust between the forearc and eastern margin of the back arc basin, suggesting a large-scale magma input responsible for the arc formation.

Corner Transfer Matrix Renormalization Group Method

Abstract: We propose a new fast numerical renormalization group method – the corner transfer matrix renormalization group (CTMRG) method – which is based on a unified scheme involving Baxter's corner transfer matrix method and White's density matrix renormalization group method. The key point is that a product of four corner transfer matrices coincides with the density matrix. We formulate CTMRG as a renormalization group for 2D classical models.

A method for determining the spring constant of cantilevers for atomic force microscopy

Abstract: Cantilevers fabricated by means of micromachining techniques are usually used for atomic force microscopy. In this paper, the spring constant of an atomic force microscope (AFM) cantilever is determined by using a large-scale cantilever. Since the spring constant of the large-scale cantilever is calibrated accurately, the spring constant of the AFM cantilever is determined precisely by measuring the deflections of both cantilevers simultaneously using heterodyne interferometry. The slope of the force curve gives the spring constant of the AFM cantilever. It is not necessary to measure the dimensions of the AFM cantilever in the proposed method. Although this method is simple, the spring constant of the AFM cantilever is obtained accurately.

Preparation of bulk glassy Pd40Ni10Cu30P20 alloy of 40 mm in diameter by water quenching

Abstract: Cylindrical glassy alloys with diameters up to 40 mm were prepared for a Pd 40 Ni 10 Cu 30 P 20 alloy with a high reduced glass transition temperature (T g /T m ) of 0.71 by water quenching the molten alloy in the quartz tube. The bulk glassy alloy with a diameter of 40 mm exhibits good metallic luster on the outer surface. Neither cavities nor voids are seen over the whole inner region and no contrast revealing a crystalline phase is seen over the transverse cross section. The glass transition temperature (T g ), crystallization temperature (T x ), the temperature interval of the supercooled liquid region (AT x =T x -T g ) and the melting temperature (T m ) are measured to be 575, 95 and 804K, respectively, for the Pd 40 Ni 10 Cu 30 P 20 alloy with a diameter of 40 mm. The deviation of Cu content from 30 at%Cu in the Pd 40 Ni 40-x Cu x P 20 system causes a steep increase in T m and a decrease in T g /T m , leading to the decrease in the glass-forming ability. The successes of finding the new Pd-Cu base alloy composition with the large ΔT x and T g /T m values and preparing the bulk glassy alloy with a diameter of 40 mm are encouraging for the future development of glassy alloys.

Fabrication of bulk glassy Zr55Al10Ni5Cu30 alloy of 30 mm in diameter by a suction casting method

Abstract: A bulk glassy Zr 55 Al 10 Ni 5 Cu 30 alloy in a cylindrical form with a diameter of 30 mm and a length of 50 mm was produced by sucking the molten alloy into a copper mold. The sucking force was generated from the rapid movement (5.0 m/s) of piston with a diameter of 30 mm which was set at the center of the copper hearth. The sucking velocity is evaluated to be as high as 22.1 kg/s. Neither cavity nor hole is seen in the transverse cross section of the bulk glassy alloy. The glass transition temperature (T g ), crystallization temperature (T x ) and supercooled liquid region defined by ΔT x (=T x -T g ) are nearly the same as those for the melt-spun glassy ribbon with a thickness of 30 μm, in spite of the significant difference in sample thickness by three orders. Furthermore, there is no appreciable difference in T g , T x and ΔT x over the whole cast sample. The Vickers hardness number is 523, in agreement with that (=510) for the corresponding melt-spun glassy ribbon and cast bulk glassy cylinders with diameters below 15 nm. Thus, the direct production of the bulk glassy alloy with a diameter of 30 mm by the suction casting method is important for the future development of bulk glassy alloys.

Observation of Spin-Charge Separation in One-Dimensional SrCuO2.

Abstract: Angle-resolved photoemission data from one-dimensional SrCu${\mathrm{O}}_{2}$ compounds are found to be qualitatively different from that of two-dimensional S${\mathrm{r}}_{2}$Cu${\mathrm{O}}_{2}$C${\mathrm{l}}_{2}$. The data can be quantitatively accounted for by the exact diagonalization calculation based on the t-J model. We identify the two underlying bands having approximately 1.2 and 0.3 eV energy dispersion as that of holon and spinon, with their energy scaled by t and J, respectively.

Elves : Lightning-induced transient luminous events in the lower ionosphere

Abstract: Observations of optical phenomena at. high alti- tude a, bove thunderstorms using a multichannel high-speed photometer and image intensified CCD cameras were carried out at Yucca Ridge Field Station (40040 ' N, 104o.56 ' W), Colorado as part of the SPRITES'95 campaign from 15 June to August 6, 1995. These newneasurements indicate that diffuse optical flashes with a duration of < I ms and a hori- zontal scale of-.- 100-300 km occur at 75-105 km altitude in the lower ionosphere just after the onset of cloud-to-ground lightning discharges, but preceding the onset of sprites. Here we designate these events as 'alves" to distinguish them from 'i'ed sprites" . This finding is consistent with the production of diffuse optical emissions due to the heating of the lower ionosphere by electromagnetic pulses generated by lightning discharges as suggested by several authors.

Impaired locomotor activity and exploratory behavior in mice lacking histamine H1 receptors

Abstract: From pharmacological studies using histamine antagonists and agonists, it has been demonstrated that histamine modulates many physiological functions of the hypothalamus, such as arousal state, locomotor activity, feeding, and drinking. Three kinds of receptors (H1, H2, and H3) mediate these actions. To define the contribution of the histamine H1 receptors (H1R) to behavior, mutant mice lacking the H1R were generated by homologous recombination. In brains of homozygous mutant mice, no specific binding of [3H]pyrilamine was seen. [3H]Doxepin has two saturable binding sites with higher and lower affinities in brains of wild-type mice, but H1R-deficient mice showed only the weak labeling of [3H]doxepin that corresponds to lower-affinity binding sites. Mutant mice develop normally, but absence of H1R significantly increased the ratio of ambulation during the light period to the total ambulation for 24 hr in an accustomed environment. In addition, mutant mice significantly reduced exploratory behavior of ambulation and rearings in a new environment. These results indicate that through H1R, histamine is involved in circadian rhythm of locomotor activity and exploratory behavior as a neurotransmitter.

Ets-1 regulates angiogenesis by inducing the expression of urokinase-type plasminogen activator and matrix metalloproteinase-1 and the migration of vascular endothelial cells.

Abstract: The coordinate induction of protease activities and cell migration is a principal feature of endothelial cells (ECs) invading the interstitial space in the initial step of angiogenesis. However, the molecular mechanisms of these events are not fully characterized. Ets-1 is a member of the ets gene family of transcription factors, which binds to the Ets binding motif in the cis-acting elements and regulates the expression of certain genes. Four typical angiogenic growth factors, aFGF, bFGF, VEGF, and EGF, induced the expression of ets-1 mRNA in either human umbilical vein endothelial cells (HUVECs), ECV-304 cells (immortalized HUVECs), or human omental microvascular endothelial cells (HOMECs). The expression of ets-1 reached its maximum at 2 hr after factor addition and then decreased to the basal level by 12 hr. For characterization of the role of Ets-1 in angiogenesis, ets-1 antisense and sense oligodeoxynucleotides (ODNs) were constructed. The ets-1 antisense ODN but not sense ODN efficiently blocked the synthesis of Ets-1 protein by human ECs in response to angiogenic growth factors. Moreover, the ets-1 antisense ODN but not sense ODN almost completely abolished the binding of endothelial cell extract to DNA containing the Ets binding motif. The expression of urokinase-type plasminogen activator and matrix metalloproteinase-1 and the migration of ECs in response to growth factors were significantly inhibited by ets-1 antisense ODN but not by sense ODN. Tube formation by HOMECs in type 1 collagen gel stimulated with EGF was abrogated by ets-1 antisense ODN. Finally, the expression of Ets-1 protein in ECs during angiogenesis in vivo was confirmed by an immunohistochemical analysis using a murine angiogenesis model. These results indicate that the induction of ets-1 mRNA is a mutual phenomenon in ECs stimulated with angiogenic growth factors. Ets-1 appears to play an important role in angiogenesis, regulating the expression of proteases and the migration of ECs.

cDNA cloning and tissue-specific expression of a novel basic helix-loop-helix/PAS factor (Arnt2) with close sequence similarity to the aryl hydrocarbon receptor nuclear translocator (Arnt).

Abstract: We isolated mouse cDNA clones (Arnt2) that are highly similar to but distinct from the aryl hydrocarbon receptor (AhR) nuclear translocator (Arnt). The composite cDNA covered a 2,443-bp sequence consisting of a putative 2,136-bp open reading frame encoding a polypeptide of 712 amino acids. The predicted Arnt2 polypeptide carries a characteristic basic helix-loop-helix (bHLH)/PAS motif in its N-terminal region with close similarity (81% identity) to that of mouse Arnt and has an overall sequence identity of 57% with Arnt. Biochemical properties and interaction of Arnt2 with other bHLH/PAS proteins were investigated by coimmunoprecipitation assays, gel mobility shift assays, and the yeast two-hybrid system. Arnt2 interacted with AhR and mouse Sim as efficiently as Arnt, and the Arnt2-AhR complex recognized and bound specifically the xenobiotic responsive element (XRE) sequence. Expression of Arnt2 successfully rescued XRE-driven reporter gene activity in the Arnt-defective c4 mutant of Hepa-1 cells. RNA blot analysis revealed that expression of Arnt2 mRNA was restricted to the brains and kidneys of adult mice, while Arnt mRNA was expressed ubiquitously. In addition, whole-mount in situ hybridization of 9.5-day mouse embryos showed that Arnt2 mRNA was expressed in the dorsal neural tube and branchial arch 1, while Arnt transcripts were detected broadly in various tissues of mesodermal and endodermal origins. These results suggest that Arnt2 may play different roles from Arnt both in adult mice and in developing embryos. Finally, sequence comparison of the currently known bHLH/PAS proteins indicates a division into two phylogenetic groups: the Arnt group, containing Arnt, Arnt2, and Per, and the AhR group, consisting of AhR, Sim, and Hif-1alpha.

Transcutaneous measurement and spectrum analysis of heart wall vibrations

Abstract: For the noninvasive diagnosis of heart disease based on the acoustic and elastic characteristics of the heart muscle, it is necessary to transcutaneously measure small vibration signals, including components with an amplitude of less than 100 /spl mu/m, from various parts of the heart wall continuously for periods of more than several heartbeats in a wide frequency range up to 1 kHz. Such measurement, however, has not been realized by any ultrasonic diagnostic methods or systems to date. By introducing the constraint least-square approach, this paper proposes a new method for accurately tracking the movement of the heart wall based on both the phase and magnitude of the demodulated signal to determine the instantaneous position of the object so that the vibration velocity of the moving object can be accurately estimated. By this method, small vibrations of the heart wall with small amplitudes less than 100 /spl mu/m on the motion resulting from a heartbeat with large amplitude of 10 mm can be successfully detected with sufficient reproducibility in the frequency range up to several hundred Hertz continuously for periods of about 10 heartbeats. The resultant small vibration is analyzed not only in the time domain, but also in the frequency domain. As confirmed by the preliminary experiments herein reported, the new method offers potential for research in acoustical diagnosis of heart disease.

Inhibition of testicular germ cell apoptosis and differentiation in mice misexpressing Bcl-2 in spermatogonia.

Abstract: During normal spermatogenesis, more than half of the germ cells undergo apoptosis, but the physiological significance and molecular mechanisms of this programmed cell death are largely unknown. Because Bcl-2 functions as a death repressor, we have investigated the effect of misexpressing Bcl-2 in spermatogonia in transgenic mice using the human bcl-2 cDNA under the control of the human polypeptide chain elongation factor 1alpha (EF-1alpha) promoter. In the 2-week-old transgenic testes, exogenous Bcl-2 was expressed in spermatogonia and massive accumulation of spermatogonia was observed in seminiferous tubules by 4 weeks. At this time, only a few spermatocytes were apparent, and the accumulated cells degenerated, leading to vacuolization in some seminiferous tubules by 7 weeks. In older transgenic mice, abnormal accumulation of spermatogonia and degeneration of these germ cells was still observed, but some seminiferous tubules in which the level of Bcl-2 expression was reduced recovered normal spermatogenesis. These observations indicate that spermatogonial apoptosis is part of the normal program of mammalian spermatogenesis and is regulated by a pathway affected by Bcl-2.

Similarity Among the Drosophila (6-4)Photolyase, a Human Photolyase Homolog, and the DNA Photolyase-Blue-Light Photoreceptor Family

Abstract: Ultraviolet light (UV)-induced DNA damage can be repaired by DNA photolyase in a light-dependent manner. Two types of photolyase are known, one specific for cyclobutane pyrimidine dimers (CPD photolyase) and another specific for pyrimidine (6-4) pyrimidone photoproducts [(6-4)photolyase]. In contrast to the CPD photolyase, which has been detected in a wide variety of organisms, the (6-4)photolyase has been found only in Drosophila melanogaster. In the present study a gene encoding the Drosophila (6-4)photolyase was cloned, and the deduced amino acid sequence of the product was found to be similar to the CPD photolyase and to the blue-light photoreceptor of plants. A homolog of the Drosophila (6-4)photolyase gene was also cloned from human cells.

Transforming growth factor beta 1 (TGF beta 1) gene expression by eosinophils in asthmatic airway inflammation.

Abstract: The increase in thickness of bronchial walls by such structural changes as subepithelial fibrosis contributes to the severity and chronicity of asthma by amplifying airway narrowing. However, the pathogenesis of this structural alteration is not known. Transforming growth factor beta 1 (TGF beta 1) is known to have biologic activities relevant to the cellular and molecular events in subepithelial fibrosis, such as the deposition of collagen I and III and the increase of myofibroblasts beneath the epithelial basement membrane. Therefore, we examined TGF beta 1 gene expression in bronchial biopsy tissues from five severe asthmatics, five mild asthmatics, and five normal subjects using in situ hybridization combined with histochemical staining. Cells expressing TGF beta 1 mRNA were detected in tissues from four normal subjects, one mild asthmatic, and five severe asthmatics. The density of positive cells in severe asthmatic tissues (52.1 +/- 22.7, mean +/- SD/mm2) was significantly greater than that in mild ...

Role for cells in the presupplementary motor area in updating motor plans

Abstract: Two motor areas are known to exist in the medial frontal lobe of the cerebral cortex of primates, the supplementary motor area (SMA) and the presupplementary motor area (pre-SMA). We report here on an aspect of cellular activity that characterizes the pre-SMA. Monkeys were trained to perform three different movements sequentially in a temporal order. The correct order was planned on the basis of visual information before its execution. A group of pre-SMA cells (n = 64, 25%) were active during a process when monkeys were required to discard a current motor plan and develop a plan appropriate for the next orderly movements. Such activity was not common in the SMA and not found in the primary motor cortex. Our data suggest a role of pre-SMA cells in updating motor plans for subsequent temporally ordered movements.

Magnetism and structural distortion in the La0.7Sr0.3MnO3 metallic ferromagnet.

Abstract: Neutron scattering studies on a single crystal of the highly correlated electron system, La{sub 1{minus}{ital x}}Sr{sub {ital x}}MnO{sub 3} with {ital x}{approx_equal}0.3, have been carried out elucidating both the spin and lattice dynamics of this metallic ferromagnet. We report a large measured value of the spin wave stiffness constant, which directly shows that the electron transfer energy of the {ital d} band is large. The spin dynamics, including magnetic critical scattering, demonstrate that this material behaves similar to other typical metallic ferromagnets such as Fe or Ni. The crystal structure is rhombohedral, as previously reported, for all temperatures studied (below {approximately}425 K). We have observed superlattice peaks which show that the primary rhombohedral lattice distortion arises from oxygen octahedra rotations resulting in an {ital R}{bar 3}{ital c} structure. The superlattice reflection intensities, which are very sensitive to structural changes, are independent of temperature demonstrating that there is no primary lattice distortion anomaly at the magnetic transition temperature {ital T}{sub {ital C}}=378.1 K; however, there is a lattice contraction. {copyright} {ital 1996 The American Physical Society.}