1,384 research outputs found
Deformation of Schild String
We attempt to construct new superstring actions with a -plet of Majorana
fermions , where is the dimensional space-time
index and is the two dimensional spinor index, by deforming the Schild
action. As a result, we propose three kinds of actions: the first is invariant
under N=1 (the world-sheet) supersymmetry transformation and the
area-preserving diffeomorphism. The second contains the Yukawa type
interaction. The last possesses some non-locality because of bilinear terms of
. The reasons why completing a Schild type superstring action
with is difficult are finally discussed.Comment: 12 pages, Latex, both title and abstract are changed, discussion of
some relations among our results, Nambu-Goto string and super Yang-Mills
theories, added. Results unchange
Hifâ1alpha stabilisation is protective against infection in zebrafish comorbid models
Multiâdrugâresistant tuberculosis is a worldwide problem, and there is an urgent need for hostâderived therapeutic targets, circumventing emerging drug resistance. We have previously shown that hypoxiaâinducible factorâ1α (Hifâ1α) stabilisation helps the host to clear mycobacterial infection via neutrophil activation. However, Hifâ1α stabilisation has also been implicated in chronic inflammatory diseases caused by prolonged neutrophilic inflammation. Comorbid infection and inflammation can be found together in disease settings, and it remains unclear whether Hifâ1α stabilisation would be beneficial in a holistic disease setting. Here, we set out to understand the effects of Hifâ1α on neutrophil behaviour in a comorbid setting by combining two wellâcharacterised in vivo zebrafish models â TB infection (Mycobacterium marinum infection) and sterile injury (tailfin transection). Using a local Mm infection near to the tailfin wound site caused neutrophil migration between the two sites that was reduced during Hifâ1α stabilisation. During systemic Mm infection, wounding leads to increased infection burden, but the protective effect of Hifâ1α stabilisation remains. Our data indicate that Hifâ1α stabilisation alters neutrophil migration dynamics between comorbid sites and that the protective effect of Hifâ1α against Mm is maintained in the presence of inflammation, highlighting its potential as a hostâderived target against TB infection
ROSAT and ASCA observations of the Crab-Like Supernova Remnant N157B in the Large Magellanic Cloud
We report the results of ROSAT and ASCA X-ray observations of the supernova
remnant N157B (or 30 Dor B, SNR 0539-69.1) in the Large Magellanic Cloud. For
comparison, we also briefly describe the results on SNR 0540-69.3, the only
confirmed Crab-like remnant in the Cloud. The X-ray emission from N157B can be
decomposed into a bright comet-shaped feature, superimposed on a diffuse
emission region of a dimension pc. The flat and nearly featureless
spectrum of the remnant is distinctly different from those of young shell-like
remnants, suggesting a predominantly Crab-like nature of N157B. Characterized
by a power law with an energy slope , the spectrum of N157B above
keV is, however, considerably steeper than that of SNR 0540-69.3,
which has a slope of . At lower energies, the spectrum of N157B
presents marginal evidence for emission lines, which if real most likely arise
in hot gas of the diffuse emission region. The hot gas has a characteristic
thermal temperature of 0.4-0.7 keV. No significant periodic signal is detected
from N157B in the period range of s. The pulsed
fraction is (99% confidence) in the keV range. We discuss
the nature of the individual X-ray components. In particular, we suggest that
the synchrotron radiation of relativistic particles from a fast-moving () pulsar explains the size, morphology, spectrum, and energetics
of the comet-shaped X-ray feature. We infer the age of the remnant as yrs. The lack of radio polarization of the remnant may be due to
Faraday dispersion by foreground \ion{H}{2} gas.Comment: To be published in The Astrophysical Journal, 21 pages, plus 11
images in the PS, GIF, or jpeg format. Postscript files of images are
available at http://www.astro.nwu.edu/astro/wqd/paper/n157b
Redshifted emission lines and radiative recombination continuum from the Wolf-Rayet binary theta Muscae: evidence for a triplet system?
We present XMM-Newton observations of the WC binary Theta Muscae (WR 48), the
second brightest Wolf-Rayet binary in optical wavelengths. The system consists
of a short-period (19.1375 days) WC5/WC6 + O6/O7V binary and possibly has an
additional O supergiant companion (O9.5/B0Iab) which is optically identified at
a separation of ~46 mas. Strong emission lines from highly ionized ions of C,
O, Ne, Mg, Si, S, Ar, Ca and Fe are detected. The spectra are fitted by a
multi-temperature thin-thermal plasma model with an interstellar absorption N_H
= 2--3*10**21 cm**-2. Lack of nitrogen line indicates that the abundance of
carbon is at least an order of magnitude larger than that of nitrogen. A
Doppler shift of ~630 km/s is detected for the OVIII line, while similar shifts
are obtained from the other lines. The reddening strongly suggests that the
emission lines originated from the wind-wind shock zone, where the average
velocity is ~600 km/s. The red-shift motion is inconsistent with a scenario in
which the X-rays originate from the wind-wind collision zone in the
short-period binary, and would be evidence supporting the widely separated O
supergiant as a companion. This may make up the collision zone be lying behind
the short-period binary. In addition to the emission lines, we also detected
the RRC (radiative recombination continuum) structure from carbon around 0.49
keV. This implies the existence of additional cooler plasma.Comment: 6 pages, 4 figures, accepted to A&
"Go eat a bat, {Chang!}": {A}n Early Look on the Emergence of Sinophobic Behavior on {Web} Communities in the Face of {COVID}-19
The outbreak of the COVID-19 pandemic has changed our lives in unprecedented ways. In the face of the projected catastrophic consequences, many countries have enacted social distancing measures in an attempt to limit the spread of the virus. Under these conditions, the Web has become an indispensable medium for information acquisition, communication, and entertainment. At the same time, unfortunately, the Web is being exploited for the dissemination of potentially harmful and disturbing content, such as the spread of conspiracy theories and hateful speech towards specific ethnic groups, in particular towards Chinese people since COVID-19 is believed to have originated from China. In this paper, we make a first attempt to study the emergence of Sinophobic behavior on the Web during the outbreak of the COVID-19 pandemic. We collect two large-scale datasets from Twitter and 4chan's Politically Incorrect board (/pol/) over a time period of approximately five months and analyze them to investigate whether there is a rise or important differences with regard to the dissemination of Sinophobic content. We find that COVID-19 indeed drives the rise of Sinophobia on the Web and that the dissemination of Sinophobic content is a cross-platform phenomenon: it exists on fringe Web communities like \dspol, and to a lesser extent on mainstream ones like Twitter. Also, using word embeddings over time, we characterize the evolution and emergence of new Sinophobic slurs on both Twitter and /pol/. Finally, we find interesting differences in the context in which words related to Chinese people are used on the Web before and after the COVID-19 outbreak: on Twitter we observe a shift towards blaming China for the situation, while on /pol/ we find a shift towards using more (and new) Sinophobic slurs
Postmodern String Theory: Stochastic Formulation
In this paper we study the dynamics of a statistical ensemble of strings,
building on a recently proposed gauge theory of the string geodesic field. We
show that this stochastic approach is equivalent to the Carath\'eodory
formulation of the Nambu-Goto action, supplemented by an averaging procedure
over the family of classical string world-sheets which are solutions of the
equation of motion. In this new framework, the string geodesic field is
reinterpreted as the Gibbs current density associated with the string
statistical ensemble. Next, we show that the classical field equations derived
from the string gauge action, can be obtained as the semi-classical limit of
the string functional wave equation. For closed strings, the wave equation
itself is completely analogous to the Wheeler-DeWitt equation used in quantum
cosmology. Thus, in the string case, the wave function has support on the space
of all possible spatial loop configurations. Finally, we show that the string
distribution induces a multi-phase, or {\it cellular} structure on the
spacetime manifold characterized by domains with a purely Riemannian geometry
separated by domain walls over which there exists a predominantly Weyl
geometry.Comment: 24pages, ReVTe
String Propagator: a Loop Space Representation
The string quantum kernel is normally written as a functional sum over the
string coordinates and the world--sheet metrics. As an alternative to this
quantum field--inspired approach, we study the closed bosonic string
propagation amplitude in the functional space of loop configurations. This
functional theory is based entirely on the Jacobi variational formulation of
quantum mechanics, {\it without the use of a lattice approximation}. The
corresponding Feynman path integral is weighed by a string action which is a
{\it reparametrization invariant} version of the Schild action. We show that
this path integral formulation is equivalent to a functional ``Schrodinger''
equation defined in loop--space. Finally, for a free string, we show that the
path integral and the functional wave equation are {\it exactly } solvable.Comment: 15 pages, no figures, ReVTeX 3.
Thermodynamic description of Be(II) solubility and hydrolysis in acidic to hyperalkaline NaCl and KCl solutions
The solubility of Be(II) is investigated in carbonate-free dilute to concentrated HClâNaClâNaOH, KClâKOH, NaOH and KOH solutions. Undersaturation experiments were performed under Ar atmosphere at T= (22 ± 2) °C. XRD, XPS, SEM and quantitative chemical analysis confirm that α-Be(OH)(cr) is the solid phase controlling the solubility in all evaluated systems. No transformation of α-Be(OH)(cr) to ÎČ-Be(OH)(cr) or ternary solid phases Na/KâBe(II)âOH(s) is observed in the investigated systems within the timeframe of this study (t †600 days). An amphoteric solubility behaviour of Be(II) is observed with a solubility minimum at pH â 9.5 (with [Be(II)] â 10M), regardless of the ionic strength. The combination of solubility data determined in acidic pH conditions and the hydrolysis scheme reported in the literature for cationic hydrolysis species of Be(II) is used for the determination of the solubility constant of α-Be(OH)(cr), log *K° = (6.9 ± 0.4). Slope analysis of the solubility data in alkaline to hyperalkaline conditions and Be NMR support the predominance of the monomeric hydrolysis species Be(OH)(aq), Be(OH)â and Be(OH) within the strongly alkaline pH-conditions relevant in cementitious systems. The comprehensive solubility dataset collected within this study in combination with extensive solid and aqueous phase characterization allow the development of a complete chemical, thermodynamic and (SIT) activity model for the system BeâNaâKâHâClâOHâHO(l). This model provides an accurate and robust tool for the evaluation of Be(II) solubility and speciation in a diversity of geochemical conditions, including source term calculations of beryllium in the context of the nuclear waste disposal Safety Case
Open membranes, ribbons and deformed Schild strings
We analyze open membranes immersed in a magnetic three-form field-strength
. While cylindrical membranes in the absence of behave like tensionless
strings, when the flux is present the strings polarize into thin membrane
ribbons, locally orthogonal to the momentum density, thus providing the strings
with an effective tension. The effective dynamics of the ribbons can be
described by a simple deformation of the Schild action for null strings.
Interactions become non-local due to the polarization, and lead to a
deformation of the string field theory, whereby string vertices receive a phase
factor proportional to the volume swept out by the ribbons. In a particular
limit, this reduces to the non-commutative loop space found previously.Comment: revte
Hole distribution for (Sr,Ca,Y,La)_14 Cu_24 O_41 ladder compounds studied by x-ray absorption spectroscopy
The unoccupied electronic structure for the Sr_14Cu_24O_41 family of two-leg
ladder compounds was investigated for different partial substitutions of Sr^2+
by Ca^2+, leaving the nominal hole count constant, and by Y^3+ or La^3+,
reducing the nominal hole count from its full value of 6 per formula unit.
Using polarization-dependent x-ray absorption spectroscopy on single crystals,
hole states on both the chain and ladder sites could be studied. While for
intermediate hole counts all holes reside on O sites of the chains, a partial
hole occupation on the ladder sites in orbitals oriented along the legs is
observed for the fully doped compound Sr_14Cu_24O_41. On substitution of Ca for
Sr orbitals within the ladder planes but perpendicular to the legs receive some
hole occupation as well.Comment: 10 pages RevTeX style with 7 embedded figures + 1 table; accepted by
Phys. Rev.
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