33,581 research outputs found
The Nullity of Bicyclic Signed Graphs
Let \Gamma be a signed graph and let A(\Gamma) be the adjacency matrix of
\Gamma. The nullity of \Gamma is the multiplicity of eigenvalue zero in the
spectrum of A(\Gamma). In this paper we characterize the signed graphs of order
n with nullity n-2 or n-3, and introduce a graph transformation which preserves
the nullity. As an application we determine the unbalanced bicyclic signed
graphs of order n with nullity n-3 or n-4, and signed bicyclic signed graphs
(including simple bicyclic graphs) of order n with nullity n-5
Soft power: Power of attraction or confusion?
Despite its popularity soft power remains power of confusion. The paper examines the concept, with a special focus on the nature and sources of soft power. Nyeâs notion of soft power is largely ethnocentric and based on the assumption that there is a link between attractiveness and the ability to influence others in international relations. This poses two problems: Firstly, a country has many different actors. Some of them like the attraction and others donât. Whether the attraction will lead to the ability to influence the policy of the target country depends on which groups in that country find it attractive and how much control they have on policymaking. Secondly, policymaking at the state level is far more complicated than at the personal level; and has different dynamics that emphasise the rational considerations. This leaves little room for emotional elements thus significantly reducing the effect of soft power. Given the nature of soft power being uncontrollable and unpredictable, it would be impossible to wield soft power in any organised and coordinated fashion as Nye suggested. Furthermore, the relationship between two countries is shaped by many complex factors. It is ultimately decided by the geopolitics and strategic interests of nations, in which soft power may play only a limited role. The paper also discusses the link between soft power and nation branding as both concepts are concerned with a nationâs influence on the world stage. Public diplomacy is a subset of nation branding that focuses on the political brand of a nation; whereas nation branding is about how a nation as whole to reshape the international opinions. A successful nation branding campaign will help create a more favourable and lasting image among the international audience thus further enhancing a countryâs soft power
Is keV ion induced pattern formation on Si(001) caused by metal impurities?
We present ion beam erosion experiments performed in ultra high vacuum using
a differentially pumped ion source and taking care that the ion beam hits the
Si(001) sample only. Under these conditions no ion beam patterns form on Si for
angles below 45 degrees with respect to the global surface normal using 2 keV
Kr ions and fluences of 2 x 10^22 ions/m^2. In fact, the ion beam induces a
smoothening of preformed patterns. Simultaneous sputter deposition of stainless
steel in this angular range creates a variety of patterns, similar to those
previously ascribed to clean ion beam induced destabilization of the surface
profile. Only for grazing incidence with incident angles between 60 degrees and
83 degrees pronounced ion beam patterns form. It appears that the angular
dependent stability of Si(001) against pattern formation under clean ion beam
erosion conditions is related to the angular dependence of the sputtering
yield, and not primarily to a curvature dependent yield as invoked frequently
in continuum theory models.Comment: 15 pages, 7 figures. This is an author-created, un-copyedited version
of an article published in Nanotechnology. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from i
Nonsaturating magnetoresistance and nontrivial band topology of type-II Weyl semimetal NbIrTe4
Weyl semimetals, characterized by nodal points in the bulk and Fermi arc
states on the surface, have recently attracted extensive attention due to the
potential application on low energy consumption electronic materials. In this
report, the thermodynamic and transport properties of a theoretically predicted
Weyl semimetal NbIrTe4 is measured in high magnetic fields up to 35 T and low
temperatures down to 0.4 K. Remarkably, NbIrTe4 exhibits a nonsaturating
transverse magnetoresistance which follows a power-law dependence in B.
Low-field Hall measurements reveal that hole-like carriers dominate the
transport for T 80 K, while the significant enhancement of electron
mobilities with lowering T results in a non-negligible contribution from
electron-like carriers which is responsible for the observed non-linear Hall
resistivity at low T. The Shubnikov-de Haas oscillations of the Hall
resistivity under high B give the light effective masses of charge carriers and
the nontrivial Berry phase associated with Weyl fermions. Further
first-principles calculations confirm the existence of 16 Weyl points located
at kz = 0, 0.02 and 0.2 planes in the Brillouin zone.Comment: 5 figures, 1 tabl
Timing Features of the Accretion--driven Millisecond X-Ray Pulsar XTE J1807--294 in 2003 March Outburst
In order to probe the activity of the inner disk flow and its effect on the
neutron star surface emissions, we carried out the timing analysis of the Rossi
X-Ray Timing Explorer (RXTE) observations of the millisecond X-ray pulsar XTE
J1807--294, focusing on its correlated behaviors in X-ray intensities, hardness
ratios, pulse profiles and power density spectra. The source was observed to
have a serial of broad "puny" flares on a timescale of hours to days on the top
of a decaying outburst in March 2003. In the flares, the spectra are softened
and the pulse profiles become more sinusoidal. The frequency of kilohertz
quasi-periodic oscillation (kHz QPO) is found to be positively related to the
X-ray count rate in the flares. These features observed in the flares could be
due to the accreting flow inhomogeneities. It is noticed that the fractional
pulse amplitude increases with the flare intensities in a range of , comparable to those observed in the thermonuclear bursts of the
millisecond X-ray pulsar XTE J1814--338, whereas it remains at about 6.5% in
the normal state. Such a significant variation of the pulse profile in the
"puny" flares may reflect the changes of physical parameters in the inner disk
accretion region. Furthermore, we noticed an overall positive correlation
between the kHz QPO frequency and the fractional pulse amplitude, which could
be the first evidence representing that the neutron-star surface emission
properties are very sensitive to the disk flow inhomogeneities. This effect
should be cautiously considered in the burst oscillation studies.Comment: Accepted by ApJ, 23 pages, 7 figures, 3 table
A Soluble Free-Fermion Model in d Dimensions
We consider a vertex model in d dimensions characterized by lines which run
in a preferred direction. We show that this vertex model is soluble if the
weights of vertices with intersecting lines are given by a free-fermion
condition, and that a fugacity -1 is associated to each loop of lines. The
solution is obtained by mapping the model into a dimer problem and by
evaluating a Pfaffian. We also determine the critical point and the singular
behavior of the free energy.Comment: 19 pages, REVTEX, 6 figure
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