Showing papers by "Aoyama Gakuin University published in 2015"

Néel-type skyrmion lattice with confined orientation in the polar magnetic semiconductor GaV4S8.

Abstract: Following the early prediction of the skyrmion lattice (SkL)--a periodic array of spin vortices--it has been observed recently in various magnetic crystals mostly with chiral structure. Although non-chiral but polar crystals with Cnv symmetry were identified as ideal SkL hosts in pioneering theoretical studies, this archetype of SkL has remained experimentally unexplored. Here, we report the discovery of a SkL in the polar magnetic semiconductor GaV4S8 with rhombohedral (C3v) symmetry and easy axis anisotropy. The SkL exists over an unusually broad temperature range compared with other bulk crystals and the orientation of the vortices is not controlled by the external magnetic field, but instead confined to the magnetic easy axis. Supporting theory attributes these unique features to a new Neel-type of SkL describable as a superposition of spin cycloids in contrast to the Bloch-type SkL in chiral magnets described in terms of spin helices.

Psychotropic dose equivalence in Japan.

Abstract: Psychotropic dose equivalence is an important concept when estimating the approximate psychotropic doses patients receive, and deciding on the approximate titration dose when switching from one psychotropic agent to another. It is also useful from a research viewpoint when defining and extracting specific subgroups of subjects. Unification of various agents into a single standard agent facilitates easier analytical comparisons. On the basis of differences in psychopharmacological prescription features, those of available psychotropic agents and their approved doses, and racial differences between Japan and other countries, psychotropic dose equivalency tables designed specifically for Japanese patients have been widely used in Japan since 1998. Here we introduce dose equivalency tables for: (i) antipsychotics; (ii) antiparkinsonian agents; (iii) antidepressants; and (iv) anxiolytics, sedatives and hypnotics available in Japan. Equivalent doses for the therapeutic effects of individual psychotropic compounds were determined principally on the basis of randomized controlled trials conducted in Japan and consensus among dose equivalency tables reported previously by psychopharmacological experts. As these tables are intended to merely suggest approximate standard values, physicians should use them with discretion. Updated information of psychotropic dose equivalence in Japan is available at http://www.jsprs.org/en/equivalence.tables/. [Correction added on 8 July 2015, after first online publication: A link to the updated information has been added.].

Mutations in SLC12A5 in epilepsy of infancy with migrating focal seizures

Abstract: The potassium-chloride co-transporter KCC2, encoded by SLC12A5, plays a fundamental role in fast synaptic inhibition by maintaining a hyperpolarizing gradient for chloride ions. KCC2 dysfunction has been implicated in human epilepsy, but to date, no monogenic KCC2-related epilepsy disorders have been described. Here we show recessive loss-of-function SLC12A5 mutations in patients with a severe infantile-onset pharmacoresistant epilepsy syndrome, epilepsy of infancy with migrating focal seizures (EIMFS). Decreased KCC2 surface expression, reduced protein glycosylation and impaired chloride extrusion contribute to loss of KCC2 activity, thereby impairing normal synaptic inhibition and promoting neuronal excitability in this early-onset epileptic encephalopathy.

Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010

Abstract: Context. Because of its proximity, Mrk 421 is one of the best sources on which to study the nature of BL Lac objects. Its proximity allows us to characterize its broadband spectral energy distribution (SED). Aims. The goal is to better understand the mechanisms responsible for the broadband emission and the temporal evolution of Mrk 421. These mechanisms may also apply to more distant blazars that cannot be studied with the same level of detail. Methods. A flare occurring in March 2010 was observed for 13 consecutive days (from MJD 55265 to MJD 55277) with unprecedented wavelength coverage from radio to very high energy (VHE; E > 100 GeV) γ-rays with MAGIC, VERITAS, Whipple, FermiLAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We modeled the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigated the physical parameters, and evaluated whether the observed broadband SED variability can be associated with variations in the relativistic particle population. Results. The activity of Mrk 421 initially was high and then slowly decreased during the 13-day period. The flux variability was remarkable at the X-ray and VHE bands, but it was minor or not significant at the other bands. The variability in optical polarization was also minor. These observations revealed an almost linear correlation between the X-ray flux at the 2–10 keV band and the VHE γ-ray flux above 200 GeV, consistent with the γ-rays being produced by inverse-Compton scattering in the Klein-Nishina regime in the framework of SSC models. The one-zone SSC model can describe the SED of each day for the 13 consecutive days reasonably well, which once more shows the success of this standard theoretical scenario to describe the SEDs of VHE BL Lacs such as Mrk 421. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission, while the other smaller zone, which is spatially separated from the first, contributes to the daily variable emission occurring at X-rays and VHE γ-rays. The second blob is assumed to have a smaller volume and a narrow electron energy distribution with 3×104 < γ < 6×105, where γ is the Lorentz factor of the electrons. Such a two-zone scenario would naturally lead to the correlated variability at the X-ray and VHE bands without variability at the optical/UV band, as well as to shorter timescales for the variability at the X-ray and VHE bands with respect to the variability at the other bands. Conclusions. Both the one-zone and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly with the underlying particle population. This shows that the particle acceleration and cooling mechanism that produces the radiating particles might be the main mechanism responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement with the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by varying the parameters related to the emitting region itself (δ, B and R), in addition to the parameters related to the particle population.

Magnetoelectric domain control in multiferroic TbMnO3

Abstract: The manipulation of domains by external fields in ferroic materials is of major interest for applications In multiferroics with strongly coupled magnetic and electric order, however, the magnetoelectric coupling on the level of the domains is largely unexplored We investigated the field-induced domain dynamics of TbMnO3 in the multiferroic ground state and across a first-order spin-flop transition In spite of the discontinuous nature of this transition, the reorientation of the order parameters is deterministic and preserves the multiferroic domain pattern Landau-Lifshitz-Gilbert simulations reveal that this behavior is intrinsic Such magnetoelectric correlations in spin-driven ferroelectrics may lead to domain wall-based nanoelectronics devices

Unconventional superconductivity in Y5Rh6Sn18 probed by muon spin relaxation

Abstract: Conventional superconductors are robust diamagnets that expel magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high-temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor Y5Rh6Sn18 ( TC= 3.0 K). The electronic heat capacity of Y5Rh6Sn18 shows a T(3) dependence below Tc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu5Rh6Sn18 which is a strong coupling s-wave superconductor. The temperature dependence of the deduced superfluid in density Y5Rh6Sn18 is consistent with a BCS s-wave gap function, while the zero-field muon spin relaxation measurements strongly evidences unconventional superconductivity through a spontaneous appearance of an internal magnetic field below the superconducting transition temperature, signifying that the superconducting state is categorized by the broken time-reversal symmetry.

The 2009 multiwavelength campaign on Mrk 421: variability and correlation studies

Abstract: Aims. We perform an extensive characterization of the broadband emission of Mrk 421, as well as its temporal evolution, during the non-flaring (low) state. The high brightness and nearby location (z = 0.031) of Mrk 421 make it an excellent laboratory to study blazar emission. The goal is to learn about the physical processes responsible for the typical emission of Mrk 421, which might also be extended to other blazars that are located farther away and hence are more difficult to study. Methods. We performed a 4.5-month multi-instrument campaign on Mrk 421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. This extensive radio to very-high-energy (VHE; E> 100 GeV) γ-ray dataset provides excellent temporal and energy coverage, which allows detailed studies of the evolution of the broadband spectral energy distribution. Results. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the X-rays. We determined the power spectral densities (PSD) at most wavelengths and found that all PSDs can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. We observed a harder-when-brighter behavior in the X-ray spectra and measured a positive correlation between VHE and X-ray fluxes with zero time lag. Such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. We also observed an overall anti-correlation between optical/UV and X-rays extending over the duration of the campaign. Conclusions. The harder-when-brighter behavior in the X-ray spectra and the measured positive X-ray/VHE correlation during the 2009 multi-wavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. In particular, this observation supports leptonic scenarios as being responsible for the emission of Mrk 421 during non-flaring activity. Such a temporally extended X-ray/VHE correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. The highest variability is observed in the X-ray band, which, within the one-zone synchrotron self-Compton scenario, indicates that the electron energy distribution is most variable at the highest energies.

Dynamical magnetoelectric phenomena of multiferroic skyrmions

Abstract: Magnetic skyrmions, vortex-like swirling spin textures characterized by a quantized topological invariant, realized in chiral-lattice magnets are currently attracting intense research interest. In particular, their dynamics under external fields is an issue of vital importance both for fundamental science and for technical application. Whereas observations of magnetic skyrmions has been limited to metallic magnets so far, their realization was also discovered in a chiral-lattice insulating magnet Cu2OSeO3 in 2012. Skyrmions in the insulator turned out to exhibit multiferroic nature with spin-induced ferroelectricity. Strong magnetoelectric coupling between noncollinear skyrmion spins and electric polarizations mediated by relativistic spin-orbit interaction enables us to drive motion and oscillation of magnetic skyrmions by application of electric fields instead of injection of electric currents. Insulating materials also provide an environment suitable for detection of pure spin dynamics through spectroscopic measurements owing to the absence of appreciable charge excitations. In this article, we review recent theoretical and experimental studies on multiferroic properties and dynamical magnetoelectric phenomena of magnetic skyrmions in insulators. We argue that multiferroic skyrmions show unique coupled oscillation modes of magnetizations and polarizations, so-called electromagnon excitations, which are both magnetically and electrically active, and interference between the electric and magnetic activation processes leads to peculiar magnetoelectric effects in a microwave frequency regime.

Magnetic control of transverse electric polarization in BiFeO

Abstract: BiFeO3 is one of the most widely studied multiferroic materials, as it offers a strong coupling between magnetism and electric polarization up to room temperature. Here, studying monodomain crystals, the authors find an additional electric polarization component orthogonal to the widely studied one.

Magnetic soliton confinement and discretization effects arising from macroscopic coherence in a chiral spin soliton lattice

Abstract: Understanding the conditions determining the appearance of stable chiral spin topological excitations is a central problem in condensed matter physics and related fields. This work provides the first unambiguous demonstration of discretization due to the macroscopic phase coherence and metastability for chiral topological excitations, and evidence of the mechanisms underlying its appearance. This was achieved through the use of an advanced Lorentz electron microscope with the highest possible resolution imaging of spin textures. The results provide new insights into dynamics in the phase transition of the chiral system, and will raise new questions concerning the mechanisms governing loss of chiral ordering.

Numerical estimation of the thrust performance on a rotating detonation engine for a hydrogen–oxygen mixture

Abstract: The numerical simulations of 2D and 3D rotating detonation engines for a hydrogen–oxygen mixture are performed using a detailed chemistry model. The comparison of 2D/3D flow fields for the same injection conditions indicates that the overall flow structures are in agreement for the two simulations and that both rotating velocities are approximately 96% of the CJ value. However, I sp for the 2D RDE is approximately 10 s larger than I sp for the 3D RDE. The grid resolution study indicates that the higher grid resolution produces detonation cellular structure; however, its effects on I sp are approximately a few seconds. Although I sp in the 2D smallest scale for higher mass flow is approximately 10 s larger than that of the other large scales, I sp for low mass flow is not affected by the scale. However, 3D scale effects are important because the radius of curvature along the circumferential direction changes, which affects the propagation of the rotating detonation. Because I sp and thrust are governed by the stagnation pressure and the micro-nozzle area ratio, the mass flow rate from the injector also depends on these parameters. I sp and thrust for RDE are found to be correlated with the mass flow rate, similar to the case of a conventional rocket engine. This result indicates that the two important parameters, A ∗ / A and p 0 , can be replaced by one parameter, i.e., the mass flow rate.

Broken time-reversal symmetry probed by muon spin relaxation in the caged type superconductor Lu5Rh6Sn18

Abstract: The superconducting state of the caged type compound ${\mathrm{Lu}}_{5}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$ has been investigated by using magnetization, heat capacity, and muon spin relaxation or rotation $(\ensuremath{\mu}\mathrm{SR})$ measurements, and the results interpreted on the basis of the group theoretical classifications of the possible pairing symmetries and a simple model of the resulting quasiparticle spectra. Our zero-field $\ensuremath{\mu}\mathrm{SR}$ measurements clearly reveal the spontaneous appearance of an internal magnetic field below the transition temperature, which indicates that the superconducting state in this material is characterized by broken time-reversal symmetry. Further, the analysis of the temperature dependence of the magnetic penetration depth measured using the transverse-field $\ensuremath{\mu}\mathrm{SR}$ measurements suggests an isotropic $s\ensuremath{-}\text{wave}$ character for the superconducting gap. This is in agreement with the heat capacity behavior, and we show that it can be interpreted in terms of a nonunitary triplet state with point nodes and an open Fermi surface.

Botulinum toxin A complex exploits intestinal M cells to enter the host and exert neurotoxicity.

Abstract: To cause food-borne botulism, botulinum neurotoxin (BoNT) in the gastrointestinal lumen must traverse the intestinal epithelial barrier. However, the mechanism by which BoNT crosses the intestinal epithelial barrier remains unclear. BoNTs are produced along with one or more non-toxic components, with which they form progenitor toxin complexes (PTCs). Here we show that serotype A1 L-PTC, which has high oral toxicity and makes the predominant contribution to causing illness, breaches the intestinal epithelial barrier from microfold (M) cells via an interaction between haemagglutinin (HA), one of the non-toxic components, and glycoprotein 2 (GP2). HA strongly binds to GP2 expressed on M cells, which do not have thick mucus layers. Susceptibility to orally administered L-PTC is dramatically reduced in M-cell-depleted mice and GP2-deficient (Gp2(-/-)) mice. Our finding provides the basis for the development of novel antitoxin therapeutics and delivery systems for oral biologics.

Photochromic Phenoxyl-Imidazolyl Radical Complexes with Decoloration Rates from Tens of Nanoseconds to Seconds

Abstract: We report a novel photochromic molecular system, phenoxyl-imidazolyl radical complex (PIC), in which both a phenoxyl radical site and an imidazolyl radical site are reversibly and simultaneously generated upon UV light irradiation. PIC consists of the three parts: an aromatic linker, a diarylimidazole moiety, and a 4H-cyclohexadienone ring. Upon UV light irradiation, the C–N bond between the 4H-cyclohexadienone ring and the imidazole ring in the colorless closed-ring isomer of PIC undergoes a homolytic cleavage, leading to the formation of the transient colored open-ring isomer. Based on the substituents on the imidazoyl/4H-cyclohexadienone rings and the nature of the aromatic linker, the half-life of the colored open-ring isomer can be varied between tens of nanoseconds and seconds. PIC derivatives containing a 1,2-phenylene linker exhibit high fatigue resistance toward repeated photochromic reactions. Analysis using laser flash photolysis reveals that the absorption spectra of the open-ring isomers are ...

Enhancing Willingness to Communicate: Relative Effects of Visualization and Goal Setting

Abstract: This article examines the relative effects of two treatments-goal setting and visualization-on enhancing Willingness to Communicate (WTC) among a group of 373 Japanese university EFL learners. Although longitudinal studies in both EFL and ESL settings have been conducted to examine the developmental aspect of WTC, no solid results of enhancing WTC through instruction have been found in EFL settings. Based on Dornyei's (2005) concept of the Ideal L2 Self, lessons were designed for the two treatment groups so learners could visualize themselves as future specialists in their field, discussing global issues and presenting their creative ideas for solving these global problems. For the second treatment group, a goal setting activity was introduced in which students articulated their speaking goals in each class. The nontreatment group, the visualization group, and the visualization plus goal setting group had approximately the same amount of communicative activities. The ANCOVA results suggest that the visualization treatment alone was not effective in enhancing learners' L2 WTC over the nontreatment group. However, when visualization was combined with goal setting, the increase in learners' L2 WTC was significantly larger compared to the visualization group, and by implication, significantly larger compared to the nontreatment group. Additionally, the impact of visualization and goal setting on learners' WTC was qualitatively explored. [ABSTRACT FROM AUTHOR]

A Detailed Study of Non-thermal X-Ray Properties and Interstellar Gas toward the γ-Ray Supernova Remnant RX J1713.7-3946

Abstract: We have carried out a spectral analysis of the Suzaku X-ray data in the 0.4-12 keV range toward the shell-type very high-energy γ-ray supernova remnant (SNR) RX J1713.7–3946. The aims of this analysis are to estimate detailed X-rays spectral properties at a high angular resolution up to 2 arcmin and to compare them with the interstellar gas. The X-ray spectrum is non-thermal and used to calculate absorbing column density, photon index, and absorption-corrected X-ray flux. The photon index varies significantly from 2.1 to 2.9. It is shown that the X-ray intensity is well correlated with the photon index, especially in the west region, with a correlation coefficient of 0.81. The X-ray intensity tends to increase with the averaged interstellar gas density while the dispersion is relatively large. The hardest spectra, with photon indexes of less than 2.4, are found outside of the central 10 arcmin of the SNR, from the north to the southeast (~430 arcmin2) and from the southwest to the northwest (~150 arcmin2). The former region shows low interstellar gas density, while the latter shows high interstellar gas density. We present a discussion of possible scenarios that explain the distribution of the photon index and its relationship with the interstellar gas.

The Cognition Hypothesis, second language task demands, and the SSARC model of pedagogic task sequencing

Abstract: This chapter first summarises the basic pedagogic claim of the Cognition Hypothesis, that the cognitive demands of tasks be sequenced from simple to complex for learners, and describes a theoretically motivated model for syllabus designers and teachers to follow in planning and implementing such task sequences. This is followed by a description of the Triadic Componential Framework of task characteristics, which makes distinctions between task complexity, task conditions, and task difficulty. Next, I discuss the extent to which individual differences in cognitive and affective factors may mediate the effects of task complexity and task conditions on learning, interaction, and language production, and I argue for the need to research the interactions between task complexity/condition and task difficulty. The chapter concludes by identifying some points of contrast between the claims of the Cognition Hypothesis and Peter Skehan`s Trade-Off Hypothesis, and the differences in their intended scope of application to pedagogy.

Coverless Information Hiding Method Based on the Chinese Mathematical Expression

Abstract: Recently, many fruitful results have been presented in text information hiding such as text format-based, text image-based method and so on. However, existing information hiding approaches so far have been very difficult to resist the detecting techniques in steganalysis based on statistical analysis. Based on the Chinese mathematical expression, an efficient method of coverless text information hiding is presented, which is a brand-new method for information hiding. The proposed algorithm directly generates a stego-vector from the hidden information at first. Then based on text big data, a normal text that includes the stego-vector will be retrieved, which means that the secret messages can be send to the receiver without any modification for the stego-text. Therefore, this method is robust for any current steganalysis algorithm, and it has a great value in theory and practical significance.

Evidence for Thermal X-Ray Line Emission from the Synchrotron-Dominated Supernova Remnant RX J1713.7-3946

Abstract: We report the first detection of thermal X-ray line emission from the supernova remnant (SNR) RX J1713.7-3946, the prototype of the small class of synchrotron dominated SNRs. A softness-ratio map generated using XMM-Newton data shows that faint interior regions are softer than bright shell regions. Using Suzaku and deep XMM-Newton observations, we have extracted X-ray spectra from the softest area, finding clear line features at 1 keV and 1.35 keV. These lines can be best explained as Ne Ly-alpha and Mg He-alpha from a thermal emission component. Since the abundance ratios of metals to Fe are much higher than solar values in the thermal component, we attribute the thermal emission to reverse-shocked SN ejecta. The measured Mg/Ne, Si/Ne, and Fe/Ne ratios of 2.0-2.6, 1.5-2.0, and <0.05 solar suggest that the progenitor star of RX J1713.7-3946 was a relatively low-mass star (<~20 M_sun), consistent with a previous inference based on the effect of stellar winds of the progenitor star on the surrounding medium. Since the mean blastwave speed of ~6000 km/s (the radius of 9.6 pc divided by the age of 1600 yr) is relatively fast compared with other core-collapse SNRs, we propose that RX J1713.7-3946 is a result of a Type Ib/c supernova whose progenitor was a member of an interacting binary. While our analysis provides strong evidence for X-ray line emission, our interpretation of its nature as thermal emission from SN ejecta requires further confirmation especially through future precision spectroscopic measurements using ASTRO-H.

Self-Contained Photoacid Generator Triggered by Photocyclization of Triangle Terarylene Backbone

Abstract: We herein propose a new type of efficient neutral photoacid generator. A photoinduced 6π-electrocyclization reaction of photochromic triangle terarylenes triggers subsequent release of a Bronsted acid, which took place from the photocyclized form. A H-atom and its conjugate base were introduced at both sides of a 6π-system to form the self-contained photoacid generator. UV irradiation to the 6π-system produces a cyclohexa-1,3-diene part with a H-atom and a conjugate base on the sp3 C-atoms at 5- and 6-positions, respectively, which spontaneously release an acid molecule quantitatively forming a polyaromatic compound. A net quantum yield of photoacid generation as high as 0.52 under ambient conditions and a photoinitiated cationic polymerization of an epoxy monomer are demonstrated.

Temperature dependence of thermal conductivity of VO2 thin films across metal–insulator transition

Abstract: Thermal conductivity of a 300-nm-thick VO2 thin film and its temperature dependence across the metal–insulator phase transition (TMIT) were studied using a pulsed light heating thermoreflectance technique. The VO2 and Mo/VO2/Mo films with a VO2 thickness of 300 nm were prepared on quartz glass substrates: the former was used for the characterization of electrical properties, and the latter was used for the thermal conductivity measurement. The VO2 films were deposited by reactive rf magnetron sputtering using a V2O3 target and an Ar–O2 mixture gas at 645 K. The VO2 films consisted of single phase VO2 as confirmed by X-ray diffraction and electron beam diffraction. With increased temperature, the electrical resistivity of the VO2 film decreased abruptly from 6.3 × 10−1 to 5.3 × 10−4 Ω cm across the TMIT of around 325–340 K. The thermal conductivity of the VO2 film increased from 3.6 to 5.4 W m−1 K−1 across the TMIT. This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann–Franz law.

The JEM-EUSO mission: An introduction

Abstract: The Extreme Universe Space Observatory on board the Japanese Experiment Module of the International Space Station, JEM-EUSO, is being designed to search from space ultra-high energy cosmic rays. These are charged particles with energies from a few 1019 eV to beyond 1020 eV, at the very end of the known cosmic ray energy spectrum. JEM-EUSO will also search for extreme energy neutrinos, photons, and exotic particles, providing a unique opportunity to explore largely unknown phenomena in our Universe. The mission, principally based on a wide field of view (60 degrees) near-UV telescope with a diameter of ∼ 2.5 m, will monitor the earth’s atmosphere at night, pioneering the observation from space of the ultraviolet tracks (290-430 nm) associated with giant extensive air showers produced by ultra-high energy primaries propagating in the earth’s atmosphere. Observing from an orbital altitude of ∼ 400 km, the mission is expected to reach an instantaneous geometrical aperture of A g e o ≥ 2 × 105 km2 sr with an estimated duty cycle of ∼ 20 %. Such a geometrical aperture allows unprecedented exposures, significantly larger than can be obtained with ground-based experiments. In this paper we briefly review the history of space-based search for ultra-high energy cosmic rays. We then introduce the special issue of Experimental Astronomy devoted to the various aspects of such a challenging enterprise. We also summarise the activities of the on-going JEM-EUSO program.

Link-Correlation-Aware Opportunistic Routing in Wireless Networks

Abstract: Recent empirical studies have shown clear evidence that wireless links are not independent and that the packet receptions on adjacent wireless links are correlated. This finding contradicts the widely held link-independence assumption in the calculation of the core metric, i.e., the expected number of transmissions to the candidate forwarder set, in opportunistic routing (OR). The inappropriate assumption may cause serious estimation errors in the forwarder set selection, which further leads to underutilized diversity benefits or extra scheduling costs. We thus advocate that OR should be made aware of link correlation. In this paper, we propose a novel link-correlation-aware OR scheme, which significantly improves the performance by exploiting the diverse low correlated forwarding links. We evaluate the design in a real-world setting with 24 MICAz nodes. Testbed evaluation and extensive simulation show that higher link correlation leads to fewer diversity benefits and that, with our link-correlation-aware design, the number of transmissions is reduced by 38%.

Quantum unidirectional rotation directly imaged with molecules.

Abstract: A gas-phase molecular ensemble coherently excited to have an oriented rotational angular momentum has recently emerged as an appropriate microscopic system to illustrate quantum mechanical behavior directly linked to classical rotational motion, which has a definite direction. To realize an intuitive visualization of such a unidirectional molecular rotation, we report high-resolution direct imaging of direction-controlled rotational wave packets in nitrogen molecules. The rotational direction was regulated by a pair of time-delayed, polarization-skewed laser pulses, introducing the dynamic chirality to the system. The subsequent spatiotemporal propagation was tracked by a newly developed Coulomb explosion imaging setup. From the observed molecular movie, time-dependent detailed nodal structures, instantaneous alignment, angular dispersion, and fractional revivals of the wave packet are fully characterized while the ensemble keeps rotating in one direction. The present approach, providing an accurate view on unidirectional rotation in quantum regime, will guide more sophisticated molecular manipulations by utilizing its capability in capturing highly structured spatiotemporal evolution of molecular wave packets.

Stepwise Two-Photon-Gated Photochemical Reaction in Photochromic [2.2]Paracyclophane-Bridged Bis(imidazole dimer).

Abstract: Stepwise two-photon processes not only have great potential for efficient light harvesting but also can provide valuable insights into novel photochemical sciences. Here we have designed a [2.2]paracyclophane-bridged bis(imidazole dimer), a molecule that is composed of two photochromic units and absorbs two photons in a stepwise manner. The absorption of the first photon leads to the formation of a short-lived biradical species (half-life = 88 ms at 298 K), while the absorption of the additional photon by the biradical species triggers a subsequent photochromic reaction to afford a long-lived quinoid species. The short-lived biradical species and the long-lived quinoid species display significantly different absorption spectra and rates of the thermal back-reaction. The stepwise two-photon excitation process in this photochromic system can be initiated even by incoherent continuous-wave light irradiation, indicating that this two-photon reaction is highly efficient. Our molecule based on the bridged bis(i...

Neighborhood effects and social behavior: The case of irrigated and rainfed farmers in Bohol, the Philippines

Abstract: Artifactual field experiments, spatial econometrics, and household surveys are combined in a single study to investigate the neighborhood effects of social behaviors. The dictator and public goods games are conducted among rice farmers in irrigated and non-irrigated areas in the Philippines. We find the neighborhood effects but the magnitude and statistical significance of endogenous social effects vary with the irrigation availability, type of social behavior, and type of neighborhood. Altruistic and cooperative behaviors are significantly influenced by the behaviors of neighbors only in the irrigated area, where social ties are strengthened through collective irrigation management. Through this effect, irrigated farmers’ social behaviors become similar to those of one another. Neighborhood effects for cooperative behavior are stronger among farm plot neighbors than among residential neighbors, which may reflect their interactions in irrigation management. Although non-dynamic, these findings are consistent with the theory of social norm evolution through common pool resource management.