48 research outputs found
Self-energy and critical temperature of weakly interacting bosons
Using the exact renormalization group we calculate the momentum-dependent
self-energy Sigma (k) at zero frequency of weakly interacting bosons at the
critical temperature T_c of Bose-Einstein condensation in dimensions 3 <= D <
4. We obtain the complete crossover function interpolating between the critical
regime k << k_c, where Sigma (k) propto k^{2 - eta}, and the short-wavelength
regime k >> k_c, where Sigma (k) propto k^{2 (D-3)} in D> 3 and Sigma (k)
\propto ln (k/k_c) in D=3. Our approach yields the crossover scale k_c on the
same footing with a reasonable estimate for the critical exponent eta in D=3.
From our Sigma (k) we find for the interaction-induced shift of T_c in three
dimensions Delta T_c / T_c approx 1.23 a n^{1/3}, where a is the s-wave
scattering length and n is the density.Comment: 4 pages,1 figur
Deformation of anisotropic Fermi surfaces due to electron-electron interactions
We analyze the deformations of the Fermi surface induced by electron-electron
interactions in anisotropic two dimensional systems. We use perturbation theory
to treat, on the same footing, the regular and singular regions of the Fermi
surface. It is shown that, even for weak local coupling, the self-energy
presents a nontrivial behavior showing momentum dependence and interplay with
the Fermi surface shape. Our scheme gives simple analytical expressions based
on local features of the Fermi surface.Comment: 7 pages, 3 figure
Fermi surface renormalization and confinement in two coupled metallic chains
Using a non-perturbative functional renormalization group approach involving
both fermionic and bosonic fields we calculate the interaction-induced change
of the Fermi surface of spinless fermions moving on two chains connected by
weak interchain hopping t_{bot}. We show that interchain backscattering can
strongly reduce the distance Delta between the Fermi momenta associated with
the bonding and the antibonding band, corresponding to a large reduction of the
effective interchain hopping t_{bot}^{*} A self-consistent one-loop
approximation neglecting marginal vertex corrections and wave-function
renormalizations predicts a confinement transition for sufficiently large
interchain backscattering, where the renormalized t_{bot}^{*} vanishes.
However, a more accurate calculation taking vertex corrections and
wave-function renormalizations into account predicts only weak confinement in
the sense that 0< | t_{bot}^{*} | << | t_{bot} |. Our method can be applied to
other strong-coupling problems where the dominant scattering channel is known.Comment: 15 RevTex pages, 11 figures; final version as published in Phys. Rev.
B; changes: figure with weak coupling RG flow added; more extensive
discussion of previous work added; some references adde
Current Trends in Neuromuscular Blockade, Management, and Monitoring amongst Singaporean Anaesthetists
Introduction. This survey aimed to investigate the attitudes/practice pertaining the use, management, and monitoring of neuromuscular blockade amongst Singaporean anaesthetists. Methods. All specialist accredited anaesthetists registered with the Singapore Medical Council were invited to complete an anonymous online survey. Results. The response rate was 39.5%. Neuromuscular monitoring (NM) was used routinely by only 13.1% despite the widespread availability of monitors. 82% stated residual NMB (RNMB) was a significant risk factor for patient outcome, but only 24% believed NMB monitoring should be compulsory in all paralyzed patients. 63.6% of anaesthetists estimated the risk of RNMB in their own institutions to be <5%. 63.1% always gave reversal. Neostigmine was predominantly used (85.1%), with 28.2% using sugammadex at least sometimes, citing unavailability and high costs. However, 83.8% believed in sugammadex’s benefits for patients’ safety and >50% said such benefits may be able to offset the associated costs. Conclusions. There is a significant need for reeducation about RNMB, studies on local RNMB incidences, and strengthening of current monitoring practices and guidelines. Strategies are discussed. As NM monitors appear widely available and reversal of NMB standard practice, it is hopeful that Singaporean anaesthetists will change and strive for evidence-based best clinical practice to enhance patient safety
Postoperative Residual Neuromuscular Paralysis at an Australian Tertiary Children’s Hospital
Purpose. Residual neuromuscular blockade (RNMB) is known to be a significant but frequently overlooked complication after the use of neuromuscular blocking agents (NMBA). Aim of this prospective audit was to investigate the incidence and severity of RNMB at our Australian tertiary pediatric center. Methods. All children receiving NMBA during anesthesia were included over a 5-week period at the end of 2011 (Mondays to Fridays; 8 a.m.–6 p.m.). At the end of surgery, directly prior to tracheal extubation, the train-of-four (TOF) ratio was assessed quantitatively. Data related to patient postoperative outcome was collected in the postoperative acute care unit. Results. Data of 64 patients were analyzed. Neostigmine was given in 34 cases and sugammadex in 1 patient. The incidence of RNMB was 28.1% overall (without reversal: 19.4%; after neostigmine: 37.5%; n.s.). Severe RNMB (TOF ratio < 0.7) was found in 6.5% after both no reversal and neostigmine, respectively. Complications in the postoperative acute care unit were infrequent, with no differences between reversal and no reversal groups. Conclusions. In this audit, RNMB was frequently observed, particularly in cases where patients were reversed with neostigmine. These findings underline the well-known problems associated with the use of NMBA that are not fully reversed
Exact integral equation for the renormalized Fermi surface
The true Fermi surface of a fermionic many-body system can be viewed as a
fixed point manifold of the renormalization group (RG). Within the framework of
the exact functional RG we show that the fixed point condition implies an exact
integral equation for the counterterm which is needed for a self-consistent
calculation of the Fermi surface. In the simplest approximation, our integral
equation reduces to the self-consistent Hartree-Fock equation for the
counterterm.Comment: 5 pages, 1 figur
On the (anisotropic) uniform metallic ground states of fermions interacting through arbitrary two-body potentials in d dimensions
We demonstrate that the skeleton of the Fermi surface S_{F;s} pertaining to a
uniform metallic ground state (corresponding to fermions with spin index s) is
determined by the Hartree-Fock contribution to the dynamic self-energy. The
Fermi surface S_{F;s} consists of all points which in addition to satisfying
the quasi-particle equation in terms of the Hartree-Fock self-energy, fulfill
the equation S_{s}(k) = 0, where S_{s}(k) is defined in the main text; the set
of k points which satisfy the Hartree-Fock quasi-particle equation but fail to
satisfy S_{s}(k) = 0, constitute the pseudo-gap region of the putative Fermi
surface of the interacting system. We consider the behaviour of the
ground-state momentum-distribution function n_{s}(k) for k in the vicinity of
S_{F;s} and show that whereas for the uniform metallic ground states of the
conventional Hubbard Hamiltonian n_{s}(k) is greater/less than 0.5 for k
approaching S_{F;s} from inside/outside the Fermi sea, for interactions of
non-zero range these inequalities can be violated (without thereby contravening
the condition of the non-negativity of the possible jump in n_{s}(k) on k
crossing S_{F;s} from directly inside to directly outside the Fermi sea). We
discuss, in the light of the findings of the present work, the growing
experimental evidence with regard to the `frustration' of the kinetic energy of
the charge carriers in the normal states of the copper-oxide-based
high-temperature superconducting compounds. [Short abstract]Comment: 30 pages, 3 postscript figures. Brought into conformity with the
published versio
Conserving Gapless Mean-Field Theory for Weakly Interacting Bose Gases
This paper presents a conserving gapless mean-field theory for weakly
interacting Bose gases. We first construct a mean-field Luttinger-Ward
thermodynamic functional in terms of the condensate wave function and
the Nambu Green's function for the quasiparticle field. Imposing its
stationarity respect to and yields a set of equations to
determine the equilibrium for general non-uniform systems. They have a
plausible property of satisfying the Hugenholtz-Pines theorem to provide a
gapless excitation spectrum. Also, the corresponding dynamical equations of
motion obey various conservation laws. Thus, the present mean-field theory
shares two important properties with the exact theory: ``conserving'' and
``gapless.'' The theory is then applied to a homogeneous weakly interacting
Bose gas with s-wave scattering length and particle mass to clarify its
basic thermodynamic properties under two complementary conditions of constant
density and constant pressure . The superfluid transition is predicted
to be first-order because of the non-analytic nature of the order-parameter
expansion near inherent in Bose systems, i.e., the Landau-Ginzburg
expansion is not possible here. The transition temperature shows quite
a different interaction dependence between the -fixed and -fixed cases.
In the former case increases from the ideal gas value as
, whereas it decreases in the latter as
. Temperature dependences of
basic thermodynamic quantities are clarified explicitly.Comment: 19 pages, 8 figure
Anaesthesiological strategies in elective craniotomy: randomized, equivalence, open trial – The NeuroMorfeo trial
<p>Abstract</p> <p>Background</p> <p>Many studies have attempted to determine the <it>"best" </it>anaesthetic technique for neurosurgical procedures in patients without intracranial hypertension. So far, no study comparing intravenous (IA) with volatile-based neuroanaesthesia (VA) has been able to demonstrate major outcome differences nor a superiority of one of the two strategies in patients undergoing elective supratentorial neurosurgery. Therefore, current practice varies and includes the use of either volatile or intravenous anaesthetics in addition to narcotics. Actually the choice of the anaestesiological strategy depends only on the anaesthetists' preferences or institutional policies.</p> <p>This trial, named NeuroMorfeo, aims to assess the equivalence between volatile and intravenous anaesthetics for neurosurgical procedures.</p> <p>Methods/Design</p> <p>NeuroMorfeo is a multicenter, randomized, open label, controlled trial, based on an equivalence design. Patients aged between 18 and 75 years, scheduled for elective craniotomy for supratentorial lesion without signs of intracranial hypertension, in good physical state (ASA I-III) and Glasgow Coma Scale (GCS) equal to 15, are randomly assigned to one of three anaesthesiological strategies (two VA arms, sevoflurane + fentanyl or sevoflurane + remifentanil, and one IA, propofol + remifentanil). The equivalence between intravenous and volatile-based neuroanaesthesia will be evaluated by comparing the intervals required to reach, after anaesthesia discontinuation, a modified Aldrete score ≥ 9 (primary end-point). Two statistical comparisons have been planned:</p> <p>1) sevoflurane + fentanyl vs. propofol + remifentanil;</p> <p>2) sevoflurane + remifentanil vs. propofol + remifentanil.</p> <p>Secondary end-points include: an assessment of neurovegetative stress based on (a) measurement of urinary catecholamines and plasma and urinary cortisol and (b) estimate of sympathetic/parasympathetic balance by power spectrum analyses of electrocardiographic tracings recorded during anaesthesia; intraoperative adverse events; evaluation of surgical field; postoperative adverse events; patient's satisfaction and analysis of costs.</p> <p>411 patients will be recruited in 14 Italian centers during an 18-month period.</p> <p>Discussion</p> <p>We presented the development phase of this anaesthesiological on-going trial. The recruitment started December 4<sup>th</sup>, 2007 and up to 4<sup>th</sup>, December 2008, 314 patients have been enrolled.</p
Mapping the contribution of β3-containing GABA(A )receptors to volatile and intravenous general anesthetic actions
BACKGROUND: Agents belonging to diverse chemical classes are used clinically as general anesthetics. The molecular targets mediating their actions are however still only poorly defined. Both chemical diversity and substantial differences in the clinical actions of general anesthetics suggest that general anesthetic agents may have distinct pharmacological targets. It was demonstrated previously that the immobilizing action of etomidate and propofol is completely, and the immobilizing action of isoflurane partly mediated, by β3-containing GABA(A )receptors. This was determined by using the β3(N265M) mice, which carry a point mutation known to decrease the actions of general anesthetics at recombinant GABA(A )receptors. In this communication, we analyzed the contribution of β3-containing GABA(A )receptors to the pharmacological actions of isoflurane, etomidate and propofol by means of β3(N265M) mice. RESULTS: Isoflurane decreased core body temperature and heart rate to a smaller degree in β3(N265M) mice than in wild type mice, indicating a minor but significant role of β3-containing GABA(A )receptors in these actions. Prolonged time intervals in the ECG and increased heart rate variability were indistinguishable between genotypes, suggesting no involvement of β3-containing GABA(A )receptors. The anterograde amnesic action of propofol was indistinguishable in β3(N265M) and wild type mice, suggesting that it is independent of β3-containing GABA(A )receptors. The increase of heart rate variability and prolongation of ECG intervals by etomidate and propofol were also less pronounced in β3(N265M) mice than in wild type mice, pointing to a limited involvement of β3-containing GABA(A )receptors in these actions. The lack of etomidate- and propofol-induced immobilization in β3(N265M) mice was also observed in congenic 129X1/SvJ and C57BL/6J backgrounds, indicating that this phenotype is stable across different backgrounds. CONCLUSION: Our results provide evidence for a defined role of β3-containing GABA(A )receptors in mediating some, but not all, of the actions of general anesthetics, and confirm the multisite model of general anesthetic action. This pharmacological separation of anesthetic endpoints also suggests that subtype-selective substances with an improved side-effect profile may be developed