442 research outputs found
Partial pharmacologic blockade shows sympathetic connection between blood pressure and cerebral blood flow velocity fluctuations
Cerebral autoregulation (CA) dampens transfer of blood pressure (BP)-fluctuations onto cerebral blood flow velocity (CBFV). Thus, CBFV-oscillations precede BP-oscillations. The phase angle (PA) between sympathetically mediated low-frequency (LF: 0.03–0.15 Hz) BP- and CBFV-oscillations is a measure of CA quality. To evaluate whether PA depends on sympathetic modulation, we assessed PA-changes upon sympathetic stimulation with and without pharmacologic sympathetic blockade.
In 10 healthy, young men, we monitored mean BP and CBFV before and during 120-second cold pressor stimulation (CPS) of one foot (0 °C ice-water). We calculated mean values, standard deviations and sympathetic LF-powers of all signals, and PAs between LF-BP- and LF–CBFV-oscillations. We repeated measurements after ingestion of the adrenoceptor-blocker carvedilol (25 mg). We compared parameters before and during CPS, without and after carvedilol (analysis of variance, post-hoc t-tests, significance: p < 0.05).
Without carvedilol, CPS increased BP, CBFV, BP-LF- and CBFV-LF-powers, and shortened PA. Carvedilol decreased resting BP, CBFV, BP-LF- and CBFV-LF-powers, while PAs remained unchanged. During CPS, BPs, CBFVs, BP-LF- and CBFV-LF-powers were lower, while PAs were longer with than without carvedilol. With carvedilol, CPS no longer shortened resting PA.
Sympathetic activation shortens PA. Partial adrenoceptor blockade abolishes this PA-shortening. Thus, PA-measurements provide a subtle marker of sympathetic influences on CA and might refine CA evaluation
Delta-Function Potential with a Complex Coupling
We explore the Hamiltonian operator H=-d^2/dx^2 + z \delta(x) where x is
real, \delta(x) is the Dirac delta function, and z is an arbitrary complex
coupling constant. For a purely imaginary z, H has a (real) spectral
singularity at E=-z^2/4. For \Re(z)<0, H has an eigenvalue at E=-z^2/4. For the
case that \Re(z)>0, H has a real, positive, continuous spectrum that is free
from spectral singularities. For this latter case, we construct an associated
biorthonormal system and use it to perform a perturbative calculation of a
positive-definite inner product that renders H self-adjoint. This allows us to
address the intriguing question of the nonlocal aspects of the equivalent
Hermitian Hamiltonian for the system. In particular, we compute the energy
expectation values for various Gaussian wave packets to show that the
non-Hermiticity effect diminishes rapidly outside an effective interaction
region.Comment: Published version, 14 pages, 2 figure
Conceptual Foundations for a Service-oriented Knowledge and Learning Architecture: Supporting Content, Process and Ontology Maturing
Abstract: The knowledge maturing model views learning activities as embedded into, interwoven with, and even indistinguishable from everyday work processes. Learning is understood as an inherently social and collaborative activity. The Knowledge Maturing Process Model structures this process into five phases: expressing ideas, distributing in communities, formalizing, ad-hoc learning and standardization. It is applicable not only for content but also to process knowledge and semantics. In the MATURE IP two toolsets will be develop that support the maturing process: a personal learning environment and an organisation learning environment integrating the levels of individuals, communities and organisation. The development is guided by the SER theory of seeding, evolutionary growth and reseeding and is based on generally applicable maturing services
Norm estimates of complex symmetric operators applied to quantum systems
This paper communicates recent results in theory of complex symmetric
operators and shows, through two non-trivial examples, their potential
usefulness in the study of Schr\"odinger operators. In particular, we propose a
formula for computing the norm of a compact complex symmetric operator. This
observation is applied to two concrete problems related to quantum mechanical
systems. First, we give sharp estimates on the exponential decay of the
resolvent and the single-particle density matrix for Schr\"odinger operators
with spectral gaps. Second, we provide new ways of evaluating the resolvent
norm for Schr\"odinger operators appearing in the complex scaling theory of
resonances
The association between real-life markers of phone use and cognitive performance, health-related quality of life and sleep
INTRODUCTION: The real-life short-term implications of electromagnetic fields (RF-EMF) on cognitive performance and health-related quality of life have not been well studied. The SPUTNIC study (Study Panel on Upcoming Technologies to study Non-Ionizing radiation and Cognition) aimed to investigate possible correlations between mobile phone radiation and human health, including cognition, health-related quality of life and sleep. METHODS: Adult participants tracked various daily markers of RF-EMF exposures (cordless calls, mobile calls, and mobile screen time 4 h prior to each assessment) as well as three health outcomes over ten study days: 1) cognitive performance, 2) health-related quality of life (HRQoL), and 3) sleep duration and quality. Cognitive performance was measured through six "game-like" tests, assessing verbal and visuo-spatial performance repeatedly. HRQoL was assessed as fatigue, mood and stress on a Likert-scale (1-10). Sleep duration and efficiency was measured using activity trackers. We fitted mixed models with random intercepts per participant on cognitive, HRQoL and sleep scores. Possible time-varying confounders were assessed at daily intervals by questionnaire and used for model adjustment. RESULTS: A total of 121 participants ultimately took part in the SPUTNIC study, including 63 from Besancon and 58 from Basel. Self-reported wireless phone use and screen time were sporadically associated with visuo-spatial and verbal cognitive performance, compatible with chance findings. We found a small but robust significant increase in stress 0.03 (0.00-0.06; on a 1-10 Likert-scale) in relation to a 10-min increase in mobile phone screen time. Sleep duration and quality were not associated with either cordless or mobile phone calls, or with screen time. DISCUSSION: The study did not find associations between short-term RF-EMF markers and cognitive performance, HRQoL, or sleep duration and quality. The most consistent finding was increased stress in relation to more screen time, but no association with cordless or mobile phone call time
The dynamical Green's function and an exact optical potential for electron-molecule scattering including nuclear dynamics
We derive a rigorous optical potential for electron-molecule scattering
including the effects of nuclear dynamics by extending the common many-body
Green's function approach to optical potentials beyond the fixed-nuclei limit
for molecular targets. Our formalism treats the projectile electron and the
nuclear motion of the target molecule on the same footing whereby the dynamical
optical potential rigorously accounts for the complex many-body nature of the
scattering target. One central result of the present work is that the common
fixed-nuclei optical potential is a valid adiabatic approximation to the
dynamical optical potential even when projectile and nuclear motion are
(nonadiabatically) coupled as long as the scattering energy is well below the
electronic excitation thresholds of the target. For extremely low projectile
velocities, however, when the cross sections are most sensitive to the
scattering potential, we expect the influences of the nuclear dynamics on the
optical potential to become relevant. For these cases, a systematic way to
improve the adiabatic approximation to the dynamical optical potential is
presented that yields non-local operators with respect to the nuclear
coordinates.Comment: 22 pages, no figures, accepted for publ., Phys. Rev.
Calcium-stimulated calcitonin - The “new standard” in the diagnosis of thyroid C-cell disease - clinically relevant gender-specific cut-off levels for an “old test”
Introduction: Pentagastrin (Pg) stimulated calcitonin (sCT) was used to enhance accuracy in medullary thyroid cancer (MTC) diagnosis. As it is now
unavailable, calcium (Ca) has been recommended as an alternative. The aim of this study was to define gender-specific cut-off values to predict MTC
in patients with elevated basal CT (bCT) following Pg-sCT and Ca-sCT stimulation and to compare the time courses of CT release during stimulation.
Materials and methods: The stimulation tests were applied in 62 consecutive patients with thyroid nodules. Basal calcitonin was measured by
chemiluminescent immunometric assay. All patients underwent thyroidectomy and bilateral central neck dissection. C-cell pathology was confirmed
by histological and immunohistochemical evaluation.
Results: In 39 (0.63) patients MTC was documented while isolated C-cell hyperplasia (CCH) was identified in 23 (0.37) patients. Medullary thyroid
cancer was predicted in males with bCT values > 43 pg/mL or sCT concentrations > 470 pg/mL (Pg-sCT) or > 1500 pg/mL (Ca-sCT), and in females
with bCT concentrations > 23 pg/mL or sCT concentrations > 200 pg/mL (Pg-sCT) or > 780 pg/mL (Ca-sCT), respectively. Pg-sCT correctly predicted
MTC in 16 (0.66) compared to 13 (0.54) after Ca-sCT in males and in 12 (0.80) compared to 11 (0.73) in females; without statistical significance. In
patients with CCH or low tumor burden, there was a tendency of faster CT release after Ca stimulation (CT peak after 3min in > 60%) compared to
patients with advanced MTC (CT peak after 3min in < 10%).
Conclusions: Using gender-specific cut-off values, Ca could replace Pg to predict MTC with similar diagnostic power
Obstructed defaecation syndrome: European consensus guidelines on the surgical management.
Not availabl
- …