99 research outputs found
Magnetic Miniband Structure and Quantum Oscillations in Lateral Semiconductor Superlattices
We present fully quantum-mechanical magnetotransport calculations for
short-period lateral superlattices with one-dimensional electrostatic
modulation. A non-perturbative treatment of both magnetic field and modulation
potential proves to be necessary to reproduce novel quantum oscillations in the
magnetoresistance found in recent experiments in the resistance component
parallel to the modulation potential. In addition, we predict oscillations of
opposite phase in the component perpendicular to the modulation not yet
observed experimentally. We show that the new oscillations originate from the
magnetic miniband structure in the regime of overlapping minibands.Comment: 6 pages with 4 figure
Susceptibility of Commercial-Off-The-Shelf Sensors to IEMI using Pulse Modulated Signals
The use of sensors has grown dramatically in recent years and many devices
rely on the information they provide. The lack of proper security mechanisms
available to control the use of sensors and the high degree of integration
make them more vulnerable to Intentional Electromagnetic Interference
(IEMI). The aim of this paper was to investigate the impact of IEMI on
separate sensors with privileged access to the hardware and software to
pursue a deep analysis of the effects of IEMI attacks using pulse modulated
signals. Measurements were carried out in a shielded hall using an open TEM
(Transverse Electromagnetic) waveguide in the 100âMHzâ7.5âGHz frequency
range. A variety of effects were observed and significant differences were
found with pulse modulated signals compared to continuous wave signals.
These results indicate weak points in the sensors hardware leading to
possible hardening measures.</p
Magnetoconductivity of quantum wires with elastic and inelastic scattering
We use a Boltzmann equation to determine the magnetoconductivity of quantum
wires. The presence of a confining potential in addition to the magnetic field
removes the degeneracy of the Landau levels and allows one to associate a group
velocity with each single-particle state. The distribution function describing
the occupation of these single-particle states satisfies a Boltzmann equation,
which may be solved exactly in the case of impurity scattering. In the case
where the electrons scatter against both phonons and impurities we solve
numerically - and in certain limits analytically - the integral equation for
the distribution function, and determine the conductivity as a function of
temperature and magnetic field. The magnetoconductivity exhibits a maximum at a
temperature, which depends on the relative strength of the impurity and
electron-phonon scattering, and shows oscillations when the Fermi energy or the
magnetic field is varied.Comment: 21 pages (revtex 3.0), 5 postscript figures available upon request at
[email protected] or [email protected]
Anisotropic scattering and quantum magnetoresistivities of a periodically modulated 2D electron gas
We calculate the longitudinal conductivities of a two-dimensional
noninteracting electron gas in a uniform magnetic field and a lateral electric
or magnetic periodic modulation in one spatial direction, in the quantum
regime. We consider the effects of the electron-impurity scattering anisotropy
through the vertex corrections on the Kubo formula, which are calculated with
the Bethe-Salpeter equation, in the self-consistent Born approximation. We find
that due to the scattering anisotropy the band conductivity increases, and the
scattering conductivities decrease and become anisotropic. Our results are in
qualitative agreement with recent experiments.Comment: 19 pages, 8 figures, Revtex, to appear in Phys. Rev.
Environmental changes and violent conflict
This letter reviews the scientific literature on whether and how environmental changes affect the risk of violent conflict. The available evidence from qualitative case studies indicates that environmental stress can contribute to violent conflict in some specific cases. Results from quantitative large-N studies, however, strongly suggest that we should be careful in drawing general conclusions. Those large-N studies that we regard as the most sophisticated ones obtain results that are not robust to alternative model specifications and, thus, have been debated. This suggests that environmental changes may, under specific circumstances, increase the risk of violent conflict, but not necessarily in a systematic way and unconditionally. Hence there is, to date, no scientific consensus on the impact of environmental changes on violent conflict. This letter also highlights the most important challenges for further research on the subject. One of the key issues is that the effects of environmental changes on violent conflict are likely to be contingent on a set of economic and political conditions that determine adaptation capacity. In the authors' view, the most important indirect effects are likely to lead from environmental changes via economic performance and migration to violent conflict. © 2012 IOP Publishing Ltd
A critical review of smaller state diplomacy
In The Peloponnesian War, Thucydides (1972: 402) highlights the effects of the general, overall
weakness of smaller states vis-Ă -vis larger, more powerful ones in a key passage, where the
Athenians remind the Melians that:
â⊠since you know as well as we do that, as the world goes, right is only in question
between equals in power. Meanwhile, the strong do what they can and the weak suffer
what they must.â
Concerns about the vulnerability of small, weak, isolated states have echoed throughout history:
from Thucydides, through the review by Machiavelli (1985) of the risks of inviting great powers
to intervene in domestic affairs, through 20th century US-led contemporary political science
(Vital, 1971; Handel, 1990) and Commonwealth led scholarship (Commonwealth Secretariat,
1985). In the context of 20th century âBalkanizationâ, the small state could also prove unstable,
even hostile and uncooperative, a situation tempting enough to invite the intrusion of more
powerful neighbours: a combination, according to Brzezinski (1997: 123-124) of a power
vacuum and a corollary power suction2: in the outcome, if the small state is âabsorbedâ, it would
be its fault, and its destiny, in the grand scheme of things. In an excellent review of small states
in the context of the global politics of development, Payne (2004: 623, 634) concludes that
âvulnerabilities rather than opportunities are the most striking consequence of smallnessâ. It has
been recently claimed that, since they cannot defend or represent themselves adequately, small
states âlack real independence, which makes them suboptimal participants in the international
systemâ (Hagalin, 2005: 1).
There is however, a less notable and acknowledged but more extraordinary strand of
argumentation that considers âthe power of powerlessnessâ, and the ability of small states to
exploit their smaller size in a variety of ways in order to achieve their intended, even if unlikely,
policy outcomes. The pursuance of smaller state goals becomes paradoxically acceptable and
achievable precisely because such smaller states do not have the power to leverage disputants or
pursue their own agenda. A case in point concerns the smallest state of all, the Vatican, whose
powers are both unique and ambiguous, but certainly not insignificant (The Economist, 2007).
Smaller states have âpunched above their weightâ (e.g. Edis, 1991); and, intermittently, political scientists confront their âamazing intractabilityâ (e.g. Suhrke, 1973: 508). Henry Kissinger
(1982: 172) referred to this stance, with obvious contempt, as âthe tyranny of the weakâ3.
This paper seeks a safe passage through these two, equally reductionist, propositions. It
deliberately focuses first on a comparative case analysis of two, distinct âsmall state-big stateâ
contests drawn from the 1970s, seeking to infer and tease out the conditions that enable smaller
âLilliputianâ states (whether often or rarely) to beat their respective Goliaths. The discussion is
then taken forward to examine whether similar tactics can work in relation to contemporary
concerns with environmental vulnerability, with a focus on two other, small island states. Before
that, the semiotics of âthe small stateâ need to be explored, since they are suggestive of the
perceptions and expectations that are harboured by decision makers at home and abroad and
which tend towards the self-fulfilling prophecy.peer-reviewe
Organised crime and international aid subversion: evidence from Colombia and Afghanistan
Scholarly attempts to explain aid subversion in post-conflict contexts frame the challenge in terms of corrupt practices and transactions disconnected from local power struggles. Also, they assume a distinction between organised crime and the state. This comparative analysis of aid subversion in Colombia and Afghanistan reveals the limits of such an approach. Focusing on relations that anchor organised crime within local political, social and economic processes, we demonstrate that organised crime is dynamic, driven by multiple motives, and endogenous to local power politics. Better understanding of governance arrangements around the organised crime-conflict nexus which enable aid subversion is therefore required
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