60,619 research outputs found
Critical magnetic field in AdS/CFT superconductor
We have studied a holographically dual description of superconductor in
(2+1)-dimensions in the presence of applied magnetic field, and observed that
there exists a critical value of magnetic field, below which a charged
condensate can form via a second order phase transition.Comment: 8 pages, 3 figures, REVTeX v4. Typos corrected and Fig.3 replace
Spin chain from marginally deformed AdS_3 x S^3
We derive a spin chain Hamiltonian from a fast spinning string in the
marginally deformed AdS(3)X S(3). This corresponds to a closed trajectory swept
out by the SU(2) or SL(2) spin vector on the surface of one-parameter deformed
two-sphere or hyperboloid in the background of anisotropic magnetic field
interaction. In the limit of small deformation, a class of general
Landau-Lifshitz equation with a nontrivial anisotropic matrix can be derived.Comment: 4 pages, 2 figures, revised for PR
Exploring the rationale of enlightened shareholder value in the realm of UK company law – the path dependence perspective
Despite conventional beliefs in the predominance of shareholder value, a broader agenda of stakeholder consideration has been advocated in the UK by the recently-introduced ESV principle – the overriding corporate objective in the new company law regime. In this paper, the efficiency of this principle in terms of stakeholder enhancement is challenged through an interdisciplinary analysis. Through a critical review of the ESV principle, it is discovered that stakeholder enhancement practices in the context of the 2006 company law regime are still for the fundamental goal of shareholder value maximisation, and that their enlightened impact has been fairly limited in practice. Furthermore, by revisiting the interrelationships between UK economic, political and cultural factors with the predominance objective of shareholder value maximisation in the Companies Act 2006, it is discovered that the enlightened effect of this new approach in the company law regime is in fact impeded by strong, persistent forces deriving from shareholder-oriented particulars. Providing insight into the future direction of corporate governance practice, the paper concludes the rationale behind the shareholder-oriented ESV principle, and further suggests the continuing predominance of shareholder value in UK corporate governance
General theory of feedback control of a nuclear spin ensemble in quantum dots
We present a microscopic theory of the nonequilibrium nuclear spin dynamics
driven by the electron and/or hole under continuous wave pumping in a quantum
dot. We show the correlated dynamics of the nuclear spin ensemble and the
electron and/or hole under optical excitation as a quantum feedback loop and
investigate the dynamics of the many nuclear spins as a nonlinear collective
motion. This gives rise to three observable effects: (i) hysteresis, (ii)
locking (avoidance) of the pump absorption strength to (from) the natural
resonance, and (iii) suppression (amplification) of the fluctuation of weakly
polarized nuclear spins, leading to prolonged (shortened) electron spin
coherence time. A single nonlinear feedback function as a "measurement" of the
nuclear field operator in the quantum feedback loop is constructed which
determines the different outcomes of the three effects listed above depending
on the feedback being negative or positive. The general theory also helps to
put in perspective the wide range of existing theories on the problem of a
single electron spin in a nuclear spin bath.Comment: 20 pages, 7 figure
Stable Direct Adaptive Control of Linear Infinite-dimensional Systems Using a Command Generator Tracker Approach
A command generator tracker approach to model following contol of linear distributed parameter systems (DPS) whose dynamics are described on infinite dimensional Hilbert spaces is presented. This method generates finite dimensional controllers capable of exponentially stable tracking of the reference trajectories when certain ideal trajectories are known to exist for the open loop DPS; we present conditions for the existence of these ideal trajectories. An adaptive version of this type of controller is also presented and shown to achieve (in some cases, asymptotically) stable finite dimensional control of the infinite dimensional DPS
Drag Force, Jet Quenching, and AdS/QCD
In this note, two important transport observables in the RHIC experiment,
relaxation time constant and jet quenching parameter, are calculated from an
AdS/QCD model. A quark moving in the viscous medium such as the
Quark-Gluon-Plasma is modelled by an open string whose end point travels on the
boundary of a deformed AdS_5 black hole. The correction introduced via the
deformed AdS_5 is believed to help us better understand the data which is
expected to be measured in the RHIC.Comment: 13 pages, 4 figures, revised for PRD. Some comments have been added
below Eq.(34) to avoid a misreading in comparison between our result and
CFT'
On the "Security analysis and improvements of arbitrated quantum signature schemes"
Recently, Zou et al. [Phys. Rev. A 82, 042325 (2010)] pointed out that two
arbitrated quantum signature (AQS) schemes are not secure, because an
arbitrator cannot arbitrate the dispute between two users when a receiver
repudiates the integrity of a signature. By using a public board, they try to
propose two AQS schemes to solve the problem. This work shows that the same
security problem may exist in their schemes and also a malicious party can
reveal the other party's secret key without being detected by using the
Trojan-horse attacks. Accordingly, two basic properties of a quantum signature,
i.e. unforgeability and undeniability, may not be satisfied in their scheme
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