Point-like Structure Research Articles

Sedenion Algebra Model as an Extension of the Standard Model and Its Link to SU(5)

In the Standard Model, ad hoc hypotheses assume the existence of three generations of point-like leptons and quarks, which possess a point-like structure and follow the Dirac equation involving four anti-commutative matrices. In this work, we consider the sedenion hypercomplex algebra as an extension of the Standard Model and show its close link to SU(5), which is the underlying symmetry group for the grand unification theory (GUT). We first consider the direct-product quaternion model and the eight-element octonion algebra model. We show that neither the associative quaternion model nor the non-associative octonion model could generate three fermion generations. Instead, we show that the sedenion model, which contains three octonion sub-algebras, leads naturally to precisely three fermion generations. Moreover, we demonstrate the use of basis sedenion operators to construct twenty-four 5 × 5 generalized lambda matrices representing SU(5) generators, in analogy to the use of octonion basis operators to generate Gell-Mann’s eight 3 × 3 lambda-matrix generators for SU(3). Thus, we provide a link between the sedenion algebra and Georgi and Glashow’s SU(5) GUT model that unifies the electroweak and strong interactions for the Standard Model’s elementary particles, which obey SU(3)SU(2)U(1) symmetry.

The potential of Co3O4 nanoparticles attached to the surface of MnO2 nanorods as cathode catalyst for single-chamber microbial fuel cell

A simple two-step hydrothermal method was used to prepare the cathode catalyst of microbial fuel cell (MFC). MnO2@Co3O4 composite was successfully prepared by in-situ growth of nano-particle-like Co3O4 on nano-rod-like MnO2. The hybrid products had (121), (310), (311), (400) and (511) crystal planes, rod-like and point-like structures were observed. MnO2@Co3O4 nanohybrids were rich in a variety of metallic elements and provided rich electrochemically active sites. The maximum voltage of MnO2@Co3O4-MFC was 425 mV, the maximum stabilization time was 4 d. The maximum output power was 475 mW/m2, which was 2.24 times that of Co3O4-MFC (212 mW/m2) and 2.63 times of MnO2-MFC (180 mW/m2). The rod-like structure of MnO2 could effectively improve the ion flow efficiency and reduce the transfer resistance, and the point-like structure of Co3O4 can increase the specific surface area of the complex and provide more active sites.

Electromagnetic transition form factors and Dalitz decays of hyperons

Dalitz decays of a hyperon resonance to a ground-state hyperon and an electron-positron pair can give access to some information about the composite structure of hyperons. We present expressions for the multi-differential decay rates in terms of general transition form factors for spin-parity combinations J^P = frac{1}{2}^pm , frac{3}{2}^pm of the hyperon resonance. Even if the spin of the initial hyperon resonance is not measured, the self-analyzing weak decay of the “final” ground-state hyperon contains information about the relative phase between combinations of transition form factors. This relative phase is non-vanishing because of the unstable nature of the hyperon resonance. If all form factor combinations in the differential decay formulae are replaced by their respective values at the photon point, one obtains a QED type approximation, which might be interpreted as characterizing hypothetical hyperons with point-like structure. We compare the QED type approximation to a more realistic form factor scenario for the lowest-lying singly-strange hyperon resonances. In this way we explore which accuracy in the measurements of the differential Dalitz decay rates is required in order to distinguish the composite-structure case from the pointlike case. Based on the QED type approximation we obtain as a by-product a rough prediction for the ratio between the Dalitz decay width and the corresponding photon decay width.

Masses of doubly heavy tetraquarks TQQ′ in a relativized quark model

In the present work, the mass spectra of doubly heavy tetraquarks $T_{QQ^\prime}$ are systematically investigated in a relativized quark model. The four-body systems including the Coulomb potential, confining potential, spin-spin interactions, and relativistic corrections are solved within the variational method. Our results suggest that the $IJ^P=01^+$ $bb \bar u \bar d$ state is 54 MeV below the relevant $\bar B \bar B$ and $\bar B \bar B^*$ thresholds, which indicates that both strong and electromagnetic decays are forbidden, and thus this state can be a stable one. Its large hidden color component and small root mean square radius demonstrate that it is a compact tetraquark rather than a loosely bound molecule or point-like diquark-antidiquark structure. Our predictions of the doubly heavy tetraquarks may provide valuable information for future experimental searches.

Adaptive optics in spectroscopy and densely labeled-fluorescence applications.

Adaptive optics systems have been integrated in many imaging modalities in order to correct for aberrations that are introduced by samples and optical elements. Usually, the optical system has access to a guide star (i.e., a point-like structure that is smaller than the diffraction limit). This guide star can be used as a beacon for adaptive optics enhancement. In contrast, for spectroscopy and densely-labeled fluorescent samples, the signal is diffused throughout the entire beam path and is not confined to a well-defined point-like structure. Here, we show analytically and experimentally that, in these scenarios, adaptive optics systems are expected to yield significantly lower signal enhancement than when a guide star is available. We discuss adaptive optics' performance degradation for different imaging modalities (e.g., confocal, multi-photon microscopy) and identify solutions to overcome low signal enhancements.

Revealing two radio-active galactic nuclei extremely near PSR J0437−4715

Newton's gravitational constant $G$ may vary with time at an extremely low level. The time variability of $G$ will affect the orbital motion of a millisecond pulsar in a binary system and cause a tiny difference between the orbital period-dependent measurement of the kinematic distance and the direct measurement of the annual parallax distance. PSR J0437$-$4715 is the nearest millisecond pulsar and the brightest at radio. To explore the feasibility of achieving a parallax distance accuracy of one light-year, comparable to the recent timing result, with the technique of differential astrometry, we searched for compact radio sources quite close to PSR J0437$-$4715. Using existing data from the Very Large Array and the Australia Telescope Compact Array, we detected two sources with flat spectra, relatively stable flux densities of 0.9 and 1.0 mJy at 8.4 GHz and separations of 13 and 45 arcsec. With a network consisting of the Long Baseline Array and the Kunming 40-m radio telescope, we found that both sources have a point-like structure and a brightness temperature of $\geq$10$^7$ K. According to these radio inputs and the absence of counterparts in the other bands, we argue that they are most likely the compact radio cores of extragalactic active galactic nuclei rather than Galactic radio stars. The finding of these two radio active galactic nuclei will enable us to achieve a sub-pc distance accuracy with the in-beam phase-referencing very-long-baseline interferometric observations and provide one of the most stringent constraints on the time variability of $G$ in the near future.

The Brightest Known H2CO Maser in the Milky Way: G339.88-1.26

Abstract We report the detection of the strongest 6 cm H2CO emission in our Galaxy. The detection toward the massive star-forming region G339.88-1.26 was made using the Shanghai Tianma radio telescope (TMRT). The G339.88-1.26 star formation region hosts one of the strongest 6.7 GHz methanol masers and has an accompanying collimated, ionized jet seen in radio continuum free–free emission. The peak flux density of the detected H2CO emission is ∼19 Jy, one order of magnitude stronger than the nine previously known H2CO maser sources. The corresponding luminosity is also brighter than has been observed in previous H2CO maser sources, even those detected in the Central Molecular Zone of our Galaxy. A TMRT on-the-fly map of the region shows a point-like source structure and this, combined with the spectral characteristics of the H2CO emission (multiple, narrow components), leads us to conclude that the detected H2CO emission is masing (with a brightness temperature in excess of 104 K). The detection of a very strong H2CO maser in G339.88-1.26 suggests that ionized jet/outflow environments might provide efficient maser pumping for this transition, with the ionized jet/outflow-driven shock causing collisional excitation, and are also able to provide additional seed photons for maser amplification of the radio continuum emission.

The LQAC-4, last update of the Large Quasar Astrometric Catalogue

AbstractThanks to their point-like structure and to their lack of significant proper motion, quasars represent the ideal objects for modeling quasi-inertial directions in space. For that reason the present primary conventional reference frame, the ICRF-2, is constructed from the set of the celestial coordinates of a sample of extragalactic objects, whose the very large majority are quasars. Thus any newly discovered quasar must be considered as a potential future ideal astrometric marker. Therefore compiling all the recorded quasars at a given epoch looks as a useful task. This constitutes the aim of the LQAC (Large Quasar Astrometric Catalogue). We present here the contents of the future release of this catalogue quoted as the LQAC-4, insisting on the related strategy of compilation. Preliminary results concerning the cross-identification with the Gaia DR1 catalogue are emphasized

The 2008 outburst in the young stellar system Z CMa

Context. Z CMa is a complex pre-main sequence binary with a current separation of 110 mas, known to consist of an FU Orionis star (SE component) and an embedded Herbig Be star (NW component). Although it represents a well-studied and characterized system, the origin of photometric variabilities, the component properties, and the physical configuration of the system remain mostly unknown. Aims. Immediately when the late-2008 outburst of Z CMa was announced to the community, we initiated a high angular resolution imaging campaign aimed at characterizing the outburst state of both components of the system in the near-infrared. Methods. We used the VLT/NACO and the Keck/NIRC2 near-infrared adaptive optics instrument to monitor the astrometric position and the near-infrared photometry of the Z CMa components during the outburst phase and one year after. The VLT/SINFONI and Keck/OSIRIS integral field spectroscrographs were in addition used to characterize for the first time the resolved spectral properties of the FU Orionis and the Herbig Be component during and after the outburst. Results. We confirm that the NW star dominates the system flux in the 1.1−3.8 μm range and is responsible for the photometric outburst. We extract the first medium-resolution (R ~ 2000−4000) near-infrared (1.1−2.4 μm) spectra of the individual components. The SE component has a spectrum typical of FU Orionis objects. The NW component spectrum is characteristic of embedded outbursting protostars and EX Or objects. It displays numerous emission lines whose intensity correlates with the system activity. In particular, we find a correlation between the Brγ equivalent width and the system brightness. The bluing of the continuum of the NW component along with the absolute flux and color-variation of the system during the outburst suggests that the outburst was caused by a complex interplay between a variation of the extinction in the line of sight of the NW component on one hand, and the emission of shocked regions close to the NW component on the other. We confirm the recently reported wiggling of the SE component jet from [Fe II] line emission. We find a point-like structure associated with a peak emission at 2.098 μm coincidental with the clump or arm seen in broadband polarization differential imaging as well as additional diffuse emission along a PA = 214°. The origin of these two structures is unclear and deserves further investigation.

Base contacts and selective emitters processed by laser doping technique for p-type IBC c-Si solar cells

In this work, we describe a novel fabrication process of p-type interdigitated back contact (IBC) silicon solar developed by means of laser doping and laser firing techniques. We use dielectric layers both as dopant sources to create highly-doped regions and as passivating layers. In particular, we use phosphorus-doped silicon carbide stacks (a-SiCx (n)) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and aluminum oxide (Al2O3) layer deposited by atomic layer deposition (ALD). Emitters were fabricated with a light thermal phosphorus diffusion in order to reduce bulk and surface emitter recombination losses. Highly doped regions n++ (emitter) and p++ (base) were simultaneously created in a point-like structure using a pulsed Nd-YAG 1064nm laser in the nanosecond regime by laser processing the dielectric layers. The results obtained for a cell, 3x3 cm2, are presented. Efficiencies up to 18.1% (Jsc = 39mA/cm2, Voc = 632mV, FF = 73.4%) have been achieved in our fabricated IBC cells.

Wormhole inspired by non-commutative geometry

In the present Letter we search for a new wormhole solution inspired by noncommutative geometry with the additional condition of allowing conformal Killing vectors (CKV). A special aspect of noncommutative geometry is that it replaces point-like structures of gravitational sources with smeared objects under Gaussian distribution. However, the purpose of this letter is to obtain wormhole solutions with noncommutative geometry as a background where we consider a point-like structure of gravitational object without smearing effect. It is found through this investigation that wormhole solutions exist in this Lorentzian distribution with viable physical properties.

Emitter formation using laser doping technique on n- and p-type c-Si substrates

In this work laser doping technique is used to create highly-doped regions defined in a point-like structure to form n+/p and p+/n junctions applying a pulsed Nd-YAG 1064nm laser in the nanosecond regime. In particular, phosphorous-doped silicon carbide stacks (a-SiCx/a-Si:H (n-type)) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and aluminum oxide (Al2O3) layers deposited by atomic layer deposition (ALD) on 2±0.5Ωcm p- and n-type FZ c-Si substrates respectively are used as dopant sources.Laser power and number of pulses per spot are explored to obtain the optimal electrical behavior of the formed junctions. To assess the quality of the p+ and n+ regions, the junctions are electrically contacted and characterized by means of dark J–V measurements. Additionally, a diluted HF treatment previous to front metallization has been explored in order to know its impact on the junction quality. The results show that fine tuning of the energy pulse is critical while the number of pulses has minor effect. In general the different HF treatments have no impact in the diode electrical behavior except for an increase of the leakage current in n+/p junctions.The high electrical quality of the junctions makes laser doping, using dielectric layers as dopant source, suitable for solar cell applications. Particularly, a potential open circuit voltage of 0.64V (1 sun) is expected for a finished solar cell.

Symmetry breaking of magnetic vortices before annihilation

Magnetic vortices in nanoscopic ferromagnetic elements can be treated as solitons that exhibit static and dynamic stability even above room temperature, making them promising for technological applications. Although their properties at low energy configurations have been well studied, the properties of solitons undergoing structural breakdown are poorly understood. Here, we destabilize the soliton through Zeeman and demagnetization interactions and investigate the symmetry breaking of the magnetic vortex state. Using high-resolution Lorentz imaging and numerical simulations, we observe phase transitions of the core from the characteristic point-like structure into distinct extended asymmetric states differentiated by the polarity. The deformations start at intermediate displacements and are traced until the point of annihilation at the disc's edge. We discuss the use of these asymmetric states as a method to determine the core polarity for in-plane magnetic imaging techniques.

Rear Contact Pattern Optimization based on 3D Simulations for IBC Solar Cells with Point-like Doped Contacts

In this work 3D simulations are used to study the impact of technological parameters on device performance of c-Si interdigitated back-contacted IBC solar cells with point-like doped contacts. In these cells, the highly-doped regions are defined in a point-like structure instead of the more classical arrangement of fully doped fingers. Numerical simulations allow us to optimize rear contact geometry, i.e. optimum pitch between contacts, depending on the substrate resistivity and the passivation quality of base contacts. Results show a trade-off between recombination and base resistive losses demonstrating limit efficiencies over 27% for a perfectly passivated structure on p- and n-type substrates. More realistic devices where state-of-the-art surface passivation is considered reach efficiencies beyond 22% on 2 ± 1Ωcm substrates with optimum pitch values of 200 ± 50μm.

Mass-density compensation can improve the performance of a range of different detectors under non-equilibrium conditions

Dosimeters often consist of several components whose mass densities differ substantially from water. These components cause small-field correction factors to vary significantly as lateral electronic equilibrium breaks down. Even amongst instruments designed for small-field dosimetry, inter-detector variation in the correction factors associated with very small (∼0.5 cm) fields can amount to tens of per cent. For a given dosimeter, small-field correction factors vary not only with field size but also with detector azimuthal angle and position within the field. Furthermore the accurate determination of these factors typically requires time-intensive Monte Carlo simulations. Thus, if achievable, ‘correction factor free’ small-field dosimetry would be highly desirable. This study demonstrates that a new generation of mass-density compensated detectors could take us towards this goal. Using a 6 MV beam model, it shows that ‘mass-density compensation’ can be utilized to improve the performance of a range of different detectors under small-field conditions. Non-sensitive material of appropriate mass-density is incorporated into detector designs in order to make the instruments behave as if consisting only of water. The dosimeter perturbative effects are then reduced to those associated with volume averaging. An even better solution—which modifies detectors to obtain profiles that look like those measured by a point-like water structure—is also considered. Provided that adequate sensitivity can be achieved for a small measurement volume, this study shows that it may be possible to use mass-density compensation (and Monte Carlo-driven design) to produce a solid-state dosimeter/ionization chamber with a near-perfect non-equilibrium response.

Multiwavelength VLBI observations of Sagittarius A*

The compact radio source Sgr\,A*, associated with the super massive black hole at the center of the Galaxy, has been studied with VLBA observations at 3 frequencies (22, 43, 86\,GHz) performed on 10 consecutive days in May 2007. The total VLBI flux density of Sgr\,A* varies from day to day. The variability is correlated at the 3 observing frequencies with higher variability amplitudes appearing at the higher frequencies. For the modulation indices, we find 8.4\,% at 22\,GHz, 9.3\,% at 43\,GHz, and 15.5\,% at 86\,GHz. The radio spectrum is inverted between 22 and 86\,GHz, suggesting inhomogeneous synchrotron self-absorption with a turnover frequency at or above 86\,GHz. The radio spectral index correlates with the flux density, which is harder (more inverted spectrum) when the source is brighter. The average source size does not appear to be variable over the 10-day observing interval. However, we see a tendency for the sizes of the minor axis to increase with increasing total flux, whereas the major axis remains constant. Towards higher frequencies, the position angle of the elliptical Gaussian increases, indicative of intrinsic structure, which begins to dominate the scatter broadening. At cm-wavelength, the source size varies with wavelength as $\lambda^{2.12\pm0.12}$, which is interpreted as the result of interstellar scatter broadening. After removal of this scatter broadening, the intrinsic source size varies as $\lambda^{1.4 ... 1.5}$. The VLBI closure phases at 22, 43, and 86\,GHz are zero within a few degrees, indicating a symmetric or point-like source structure. In the context of an expanding plasmon model, we obtain an upper limit of the expansion velocity of about 0.1\,c from the non-variable VLBI structure. This agrees with the velocity range derived from the radiation transport modeling of the flares from the radio to NIR wavelengths.}

Graphene to graphite: electronic changes within DFT calculations

Calculations based on the first-principles pseudopotential plane-wave method and density-functional theory are performed to investigate the electronic properties of graphene, bilayer graphene, multilayer graphene, and graphite. From an analysis of the electronic band structure close to the Fermi level, we have quantified the gradual change in the Fermi surface topology from the point-like structure for graphene to a warped triangular shape for graphite. We have also discussed the gradual change in the electron and hole effective masses and velocities as the system evolves from graphene to graphite.

Gradual changes in electronic properties from graphene to graphite: first-principlescalculations

Calculations based on the first-principles pseudopotential plane-wave method and densityfunctional theory are performed to investigate the electronic properties of graphene, bilayergraphene, multilayer graphene, and graphite. From an analysis of the electronic bandstructure close to the Fermi level, we have quantified the gradual change in the Fermisurface topology from the point-like structure for graphene to a warped triangular shapefor graphite. We have also discussed the gradual change in the electron and holeeffective masses and velocities as the system evolves from graphene to graphite.

Charge-density oscillation on graphite induced by the interference of electron waves

We report on a pronounced redistribution of the local electronic density of states at the graphite surface, which is induced by the presence of low energy hydrogen-ion induced point defects. Scanning tunneling microscopy reveals standing waves in the local density of states, which are due to backscattering of electron wave functions at individual point defects. The superstructure thereby formed is directly related to the pointlike structure of the Fermi surface of graphite. For high defect density interference patterns are observed which sensitively change structure on the relative positions of the defects. These patterns could be reproduced by tight binding simulations of various defect distributions.

A planar microfabricated nanoelectrospray emitter tip based on a capillary slot.

We report on the fabrication and testing of planar nib-like structures for nanoelectrospray ionization-mass spectrometry (nanoESI-MS) applications. The micro-nib structures were fabricated on silicon substrates using the negative photoresist SU-8; they include capillary slots with widths of 8 and 16 microm. A suitable wafer cleaving step made the nib-like structures overhang the edge of a silicon substrate to provide a robust interface for nanoESI-MS applications; this freeing of the nib tip from the wafer surface created a point-like structure that is essential to establish an electrospray. The micro-nib sources were successfully tested on an LCQ Deca XP+ ion trap mass spectrometer using peptide samples at concentrations down to 1 microM. The high voltage was applied using a platinum wire inserted in the sample reservoir upstream to the capillary slot. A Taylor cone was clearly seen at the nib tip. The micro-nibs performed well at voltages as low as 0.8 kV; such performances are state-of-the-art with respect to current micromachined ESI-MS interfaces and are conditions comparable to those used for standard emitter tips. In addition, we clearly observed the influence of the micro-nib slot width on the ionization performances: the narrower the slot, the better the performances.