17,624 research outputs found
Cerebral and cardiovascular effects of analgesic doses of ketamine during a target controlled general anesthesia: a prospective randomized study
Introduction: Ketamine is increasingly being used in various pain settings. The purpose of this study was to
assess the effect of an analgesic dose of ketamine in the bispectral index (BIS), spectral edge frequency (SEF-95), density spectral array (DSA), cerebral oximetry (rSO2) and mean arterial pressure (MAP) during general
anaesthesia with a target controlled infusion.
Methods: A prospective, single-blinded and randomized study on adult patients scheduled for elective spine
surgery was carried out. After anaesthesia induction with propofol, remifentanil and rocuronium, when a stable BIS
value (45-55) was achieved, an automatic recording of BIS, SEF-95, rSO2 and MAP values during 9 min was
performed to establish patients baseline values. Subsequently, patients were randomly assigned to receive a
ketamine bolus dose of 0.2 mg/kg, 0.5 mg/kg or 1 mg/kg; all variables were recorded for additional 9 min after the
ketamine bolus, in the absence of any surgical stimulus. A p-value <0.05 was considered significant in the statistical
analysis.
Results and discussion: Thirty-nine patients were enrolled in the study. Our results show a dose-related
increase of SEF-95 and BIS values. DSA demonstrate a shift in the frequency range and power distribution towards
higher frequencies. Our results do not show significant differences in MAP and rSO2 values.
Conclusion: When ketamine is used intraoperatively in analgesic doses, the anaesthetist should anticipate an
increase in SEF-95 and BIS values which will not be associated with the level of anaesthesia.info:eu-repo/semantics/publishedVersio
On the renormalization of the electroweak chiral Lagrangian with a Higgs
We consider the scalar sector of the effective non-linear electroweak
Lagrangian with a light "Higgs" particle, up to four derivatives in the chiral
expansion. The complete off-shell renormalization procedure is implemented,
including one loop corrections stemming from the leading two-derivative terms,
for finite Higgs mass. This determines the complete set of independent chiral
invariant scalar counterterms required for consistency; these include bosonic
operators often disregarded. Furthermore, new counterterms involving the Higgs
particle which are apparently chiral non-invariant are identified in the
perturbative analysis. A novel general parametrization of the pseudoescalar
field redefinitions is proposed, which reduces to the various usual ones for
specific values of its parameter; the non-local field redefinitions reabsorbing
all chiral non-invariant counterterms are then explicitly determined. The
physical results translate into renormalization group equations which may be
useful when comparing future Higgs data at different energies
The graphene sheet versus the 2DEG: a relativistic Fano spin-filter via STM and AFM tips
We explore theoretically the density of states (LDOS) probed by an STM tip of
2D systems hosting an adatom and a subsurface impurity,both capacitively
coupled to AFM tips and traversed by antiparallel magnetic fields. Two kinds of
setups are analyzed, a monolayer of graphene and a two-dimensional electron gas
(2DEG). The AFM tips set the impurity levels at the Fermi energy, where two
contrasting behaviors emerge: the Fano factor for the graphene diverges, while
in the 2DEG it approaches zero. As result, the spin-degeneracy of the LDOS is
lifted exclusively in the graphene system, in particular for the asymmetric
regime of Fano interference. The aftermath of this limit is a counterintuitive
phenomenon, which consists of a dominant Fano factor due to the subsurface
impurity even with a stronger STM-adatom coupling. Thus we find a full
polarized conductance, achievable just by displacing vertically the position of
the STM tip. To the best knowledge, our work is the first to propose the Fano
effect as the mechanism to filter spins in graphene. This feature arises from
the massless Dirac electrons within the band structure and allows us to employ
the graphene host as a relativistic Fano spin-filter
Quantum phase transition triggering magnetic BICs in graphene
Graphene hosting a pair of collinear adatoms in the phantom atom
configuration has pseudogap with cubic scaling on energy,
which leads to the appearance of
spin-degenerate bound states in the continuum (BICs) [Phys. Rev. B 92, 045409
(2015)]. In the case when adatoms are locally coupled to a single carbon atom
the pseudogap scales linearly with energy, which prevents the formation of
BICs. In this Letter, we explore the effects of non-local coupling
characterized by the Fano factor of interference tunable by changing
the slope of the Dirac cones in the graphene band-structure. We demonstrate
that three distinct regimes can be identified: i) for (critical
point) a mixed pseudogap appears
yielding a phase with spin-degenerate BICs; ii) near when
the system undergoes a quantum phase
transition in which the new phase is characterized by magnetic BICs and iii) at
a second critical value the cubic scaling of the pseudogap with
energy characteristic to the phantom atom
configuration is restored and the phase with non-magnetic BICs is recovered.
The phase with magnetic BICs can be described in terms of an effective
intrinsic exchange field of ferromagnetic nature between the adatoms mediated
by graphene monolayer. We thus propose a new type of quantum phase transition
resulting from the competition between the states characterized by
spin-degenerate and magnetic BICs
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