493 research outputs found
Influence of central venous pressure upon sinus node responses to arterial baroreflex stimulation in man
Measurements were made of sinus node responses to arterial baroreceptor stimulation with phenylephrine injection or neck suction, before and during changes of central venous pressure provoked by lower body negative pressure or leg and lower truck elevation. Variations of central venous pressure between 1.1 and 9.0 mm Hg did not influence arterial baroreflex mediated bradycardia. Baroreflex sinus node responses were augmented by intravenous propranolol, but the level of responses after propranolol was comparable during the control state, lower body negative pressure, and leg and trunk elevation. Sinus node responses to very brief baroreceptor stimuli applied during the transitions of central venous pressure also were comparable in the three states. The authors conclude that physiological variations of central venous pressure do not influence sinus node responses to arterial baroreceptor stimulation in man
Single crystal investigation of proposed type-II Weyl semimetal CeAlGe
We present details of materials synthesis, crystal structure, and anisotropic
magnetic properties of single crystals of CeAlGe, a proposed type-II Weyl
semimetal. Single-crystal x-ray diffraction confirms that CeAlGe forms in
noncentrosymmetric I4md space group, in line with predictions of
non-trivial topology. Magnetization, specific heat and electrical transport
measurements were used to confirm antiferromagnetic order below 5 K, with an
estimated magnon excitation gap of = 9.11 K from heat capacity and
hole-like carrier density of 1.44 10 cm from Hall effect
measurements. The easy magnetic axis is along the [100] crystallographic
direction, indicating that the moment lies in the tetragonal -plane
below 7 K. A spin-flop transition to less than 1 /Ce is observed to
occur below 30 kOe at 1.8 K in the () data. Small
magnetic fields of 3 kOe and 30 kOe are sufficient to suppress magnetic order
when applied along the - and -axes, respectively, resulting in
a complex phase diagram for and a simpler one for
Single-Crystal Investigation of the Proposed Type-II Weyl Semimetal CeAlGe
We present details of materials synthesis, crystal structure, and anisotropic magnetic properties of single crystals of CeAlGe, a proposed type-II Weyl semimetal. Single-crystal x-ray diffraction confirms that CeAlGe forms in a noncentrosymmetric I41md space group, in line with predictions of nontrivial topology. Magnetization, specific heat, and electrical transport measurements were used to confirm antiferromagnetic order below 5 K, with an estimated magnon excitation gap of Δ = 9.11 K from heat capacity and hole-like carrier density of 1.4 x 1020 cm-3 from Hall effect measurements. The easy magnetic axis is along the [100] crystallographic direction, indicating that the moment lies in the tetragonal ab plane below 7 K. A spin-flop transition to less than 1 μB/Ce is observed to occur below 30 kOe at 1.8 K in the M(H) (H||a) data. Small magnetic fields of 3 and 30 kOe are sufficient to suppress magnetic order when applied along the a and c axes, respectively, resulting in a complex T-H phase diagram for H||a and a simpler one for H||c
Anomalous symmetry breaking in Weyl semimetal CeAlGe
CeAlGe, a proposed type-II Weyl semimetal, orders antiferromagnetically below
5 K. At 2 K, spin-flop and a spin-flip transitions to less than 1 /Ce
are observed in the data below 30 kOe, ( and ,
and 4.3 kOe, , respectively, indicating a four-fold
symmetry of the data along the principal directions in the tetragonal
plane with set of easy directions. However,
anomalously robust and complex twofold symmetry is observed in the angular
dependence of resistivity and magnetic torque data in the magnetically ordered
state once the field is swept in the plane. This twofold symmetry is
independent of temperature and field hystereses and suggests a magnetic phase
transition that separates two different magnetic structures in the
plane. The boundary of this magnetic phase transition and possibly the type of
low-field magnetic structure can be tuned by an Al deficiency
Testing Rotational Mixing Predictions with New Boron Abundances in Main Sequence B-type Stars
(Abridged) New boron abundances for seven main-sequence B-type stars are
determined from HST STIS spectroscopy around the BIII 2066A line. Boron
abundances provide a unique and critical test of stellar evolution models that
include rotational mixing since boron is destroyed in the surface layers of
stars through shallow mixing long before other elements are mixed from the
stellar interior through deep mixing. Boron abundances range from 12+log(B/H) =
1.0 to 2.2. The boron abundances are compared to the published values of their
stellar nitrogen abundances (all have 12+log(N/H) < 7.8, i.e., they do not show
significant CNO-mixing) and to their host cluster ages (4 to 16 Myr) to
investigate the predictions from models of massive star evolution with
rotational mixing effects (Heger & Langer 2000). Only three stars (out of 34)
deviate from the model predictions, including HD36591, HD205021, and HD30836.
These three stars suggest that rotational mixing could be more efficient than
currently modelled at the highest rotation rates.Comment: 10 figures, 7 tables; accepted for publication in the Astrophysical
Journa
Asymptotically stable phase synchronization revealed by autoregressive circle maps
A new type of nonlinear time series analysis is introduced, based on phases,
which are defined as polar angles in spaces spanned by a finite number of
delayed coordinates. A canonical choice of the polar axis and a related
implicit estimation scheme for the potentially underlying auto-regressive
circle map (next phase map) guarantee the invertibility of reconstructed phase
space trajectories to the original coordinates. The resulting Fourier
approximated, Invertibility enforcing Phase Space map (FIPS map) is well suited
to detect conditional asymptotic stability of coupled phases. This rather
general synchronization criterion unites two existing generalisations of the
old concept and can successfully be applied e.g. to phases obtained from ECG
and airflow recordings characterizing cardio-respiratory interaction.Comment: PDF file, 232 KB, 24 pages, 3 figures; cheduled for Phys. Rev. E
(Nov) 200
Quantum Oscillations from Networked Topological Interfaces in a Weyl Semimetal
Layered transition metal chalcogenides are promising hosts of electronic Weyl nodes and topological superconductivity. MoTe2 is a striking example that harbors both noncentrosymmetric Td and centrosymmetric T\u27 phases, both of which have been identified as topologically nontrivial. Applied pressure tunes the structural transition separating these phases to zero temperature, stabilizing a mixed Td–T\u27 matrix that entails a network of interfaces between the two nontrivial topological phases. Here, we show that this critical pressure range is characterized by distinct coherent quantum oscillations, indicating that the difference in topology between topologically nonvtrivial Td and T\u27 phases gives rise to an emergent electronic structure: a network of topological interfaces. A rare combination of topologically nontrivial electronic structures and locked-in transformation barriers leads to this counterintuitive situation, wherein quantum oscillations can be observed in a structurally inhomogeneous material. These results further open the possibility of stabilizing multiple topological phases coexisting with superconductivity
Predicting sudden death in patients with mild to moderate chronic heart failure
Objectives: To explore the relation between non-invasive measures of cardiac function and sudden cardiac death, as well as the development and utility of an index integrating these variables to identify patients at increased risk of this mode of death. Design: UK-HEART (United Kingdom-heart failure evaluation and assessment of risk trial) was a prospective study conducted between December 1993 and April 2000. The study was specifically designed to identify non-invasive markers of death and mode of death among patients with chronic heart failure. Setting: 8 UK general hospitals. Main outcome measures: Death and mode of death. Results: 553 patients aged a mean (SD) of 63 (10) years, in New York Heart Association functional class 2.3 (0.02), recruited prospectively. After 2365 patient-years’ follow up, 201 patients had died (67 suddenly). Predictors of sudden death were greater cardiothoracic ratio, QRS dispersion, QT dispersion corrected for rate (QTc) across leads V1–V6 on the 12 lead ECG, and the presence of non-sustained ventricular tachycardia. The hazard ratio and 95% confidence intervals (CI) of sudden death for a 10% increase in cardiothoracic ratio was 1.43 (95% CI 1.20 to 1.71), for a 10% increase in QRS dispersion 1.11 (95% CI 1.04 to 1.19), for the presence of non-sustained ventricular tachycardia 2.03 (95% CI 1.27 to 3.25), and for a 10% increase in QTc dispersion across leads V1–V6 1.03 (95% CI 1.00 to 1.07) (all p < 0.04). An index derived from these four factors performed well in identifying patients specifically at increased risk of sudden death. Conclusions: Results show that an index derived from three widely available non-invasive investigations has the potential to identify ambulant patients with chronic heart failure at increased risk of sudden death. This predictive tool could be used to target more sophisticated investigations or interventions aimed at preventing sudden death
Interpretation of heart rate variability via detrended fluctuation analysis and alpha-beta filter
Detrended fluctuation analysis (DFA), suitable for the analysis of
nonstationary time series, has confirmed the existence of persistent long-range
correlations in healthy heart rate variability data. In this paper, we present
the incorporation of the alpha-beta filter to DFA to determine patterns in the
power-law behaviour that can be found in these correlations. Well-known
simulated scenarios and real data involving normal and pathological
circumstances were used to evaluate this process. The results presented here
suggest the existence of evolving patterns, not always following a uniform
power-law behaviour, that cannot be described by scaling exponents estimated
using a linear procedure over two predefined ranges. Instead, the power law is
observed to have a continuous variation with segment length. We also show that
the study of these patterns, avoiding initial assumptions about the nature of
the data, may confer advantages to DFA by revealing more clearly abnormal
physiological conditions detected in congestive heart failure patients related
to the existence of dominant characteristic scales.Comment: 18 pages, 14 figure
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