30 research outputs found
Explicit schemes for time propagating many-body wavefunctions
Accurate theoretical data on many time-dependent processes in atomic and
molecular physics and in chemistry require the direct numerical solution of the
time-dependent Schr\"odinger equation, thereby motivating the development of
very efficient time propagators. These usually involve the solution of very
large systems of first order differential equations that are characterized by a
high degree of stiffness. We analyze and compare the performance of the
explicit one-step algorithms of Fatunla and Arnoldi. Both algorithms have
exactly the same stability function, therefore sharing the same stability
properties that turn out to be optimum. Their respective accuracy however
differs significantly and depends on the physical situation involved. In order
to test this accuracy, we use a predictor-corrector scheme in which the
predictor is either Fatunla's or Arnoldi's algorithm and the corrector, a fully
implicit four-stage Radau IIA method of order 7. We consider two physical
processes. The first one is the ionization of an atomic system by a short and
intense electromagnetic pulse; the atomic systems include a one-dimensional
Gaussian model potential as well as atomic hydrogen and helium, both in full
dimensionality. The second process is the decoherence of two-electron quantum
states when a time independent perturbation is applied to a planar two-electron
quantum dot where both electrons are confined in an anharmonic potential. Even
though the Hamiltonian of this system is time independent the corresponding
differential equation shows a striking stiffness. For the one-dimensional
Gaussian potential we discuss in detail the possibility of monitoring the time
step for both explicit algorithms. In the other physical situations that are
much more demanding in term of computations, we show that the accuracy of both
algorithms depends strongly on the degree of stiffness of the problem.Comment: 24 pages, 14 Figure
Multiresolution schemes for time-scaled propagation of wave packets
We present a detailed analysis of the time scaled coordinate approach and its
implementation for solving the time-dependent Schr\"odinger equation describing
the interaction of atoms or molecules with radiation pulses. We investigate and
discuss the performance of multi-resolution schemes for the treatment of the
squeezing around the origin of the bound part of the scaled wave packet. When
the wave packet is expressed in terms of B-splines, we consider two different
types of breakpoint sequences: an exponential sequence with a constant density
and an initially uniform sequence with a density of points around the origin
that increases with time. These two multi-resolution schemes are tested in the
case of a one-dimensional gaussian potential and for atomic hydrogen. In the
latter case, we also use Sturmian functions to describe the scaled wave packet
and discuss a multi-resolution scheme which consists in working in a sturmian
basis characterized by a set of non-linear parameters. Regarding the continuum
part of the scaled wave packet, we show explicitly that, for large times, the
group velocity of each ionized wave packet goes to zero while its dispersion is
suppressed thereby explaining why, eventually, the scaled wave packet
associated to the ejected electrons becomes stationary. Finally, we show that
only the lowest scaled bound states can be removed from the total scaled wave
packet once the interaction with the pulse has ceased
Estrous cycle and ovariectomy-induced changes in visceral pain are microbiota-dependent
Visceral hypersensitivity (VH) is a hallmark of many functional gastrointestinal disorders including irritable bowel syndrome and is categorized by a dull, diffuse sensation of abdominal pain. Recently, the gut microbiota has been implicated in VH in male mice, but the effects in females have yet to be explored fully. To this end, we now show that somewhat surprisingly, female germ-free mice have similar visceral pain responses to colorectal distension (CRD) as their conventional controls. However, we show that although sensitivity to CRD is estrous cycle stage-dependent in conventional mice, it is not in germ-free mice. Further, ovariectomy (OVX) induced VH in conventional but not germ-free mice, and induced weight gain regardless of microbiota status. Finally, we show that estrogen-replacement ameliorated OVX-induced VH. Taken together, this study provides evidence for a major role of female sex hormones and the gut microbiota in sensation of visceral pain in females.Funding: This work was funded by Science Foundation Ireland through the Irish Government’s National Development Plan in the form of a center grant (APC Microbiome Institute Grant Number SFI/12/RC/2273_P2)
Albiglutide and cardiovascular outcomes in patients with type 2 diabetes and cardiovascular disease (Harmony Outcomes): a double-blind, randomised placebo-controlled trial
Background:
Glucagon-like peptide 1 receptor agonists differ in chemical structure, duration of action, and in their effects on clinical outcomes. The cardiovascular effects of once-weekly albiglutide in type 2 diabetes are unknown. We aimed to determine the safety and efficacy of albiglutide in preventing cardiovascular death, myocardial infarction, or stroke.
Methods:
We did a double-blind, randomised, placebo-controlled trial in 610 sites across 28 countries. We randomly assigned patients aged 40 years and older with type 2 diabetes and cardiovascular disease (at a 1:1 ratio) to groups that either received a subcutaneous injection of albiglutide (30–50 mg, based on glycaemic response and tolerability) or of a matched volume of placebo once a week, in addition to their standard care. Investigators used an interactive voice or web response system to obtain treatment assignment, and patients and all study investigators were masked to their treatment allocation. We hypothesised that albiglutide would be non-inferior to placebo for the primary outcome of the first occurrence of cardiovascular death, myocardial infarction, or stroke, which was assessed in the intention-to-treat population. If non-inferiority was confirmed by an upper limit of the 95% CI for a hazard ratio of less than 1·30, closed testing for superiority was prespecified. This study is registered with ClinicalTrials.gov, number NCT02465515.
Findings:
Patients were screened between July 1, 2015, and Nov 24, 2016. 10 793 patients were screened and 9463 participants were enrolled and randomly assigned to groups: 4731 patients were assigned to receive albiglutide and 4732 patients to receive placebo. On Nov 8, 2017, it was determined that 611 primary endpoints and a median follow-up of at least 1·5 years had accrued, and participants returned for a final visit and discontinuation from study treatment; the last patient visit was on March 12, 2018. These 9463 patients, the intention-to-treat population, were evaluated for a median duration of 1·6 years and were assessed for the primary outcome. The primary composite outcome occurred in 338 (7%) of 4731 patients at an incidence rate of 4·6 events per 100 person-years in the albiglutide group and in 428 (9%) of 4732 patients at an incidence rate of 5·9 events per 100 person-years in the placebo group (hazard ratio 0·78, 95% CI 0·68–0·90), which indicated that albiglutide was superior to placebo (p<0·0001 for non-inferiority; p=0·0006 for superiority). The incidence of acute pancreatitis (ten patients in the albiglutide group and seven patients in the placebo group), pancreatic cancer (six patients in the albiglutide group and five patients in the placebo group), medullary thyroid carcinoma (zero patients in both groups), and other serious adverse events did not differ between the two groups. There were three (<1%) deaths in the placebo group that were assessed by investigators, who were masked to study drug assignment, to be treatment-related and two (<1%) deaths in the albiglutide group.
Interpretation:
In patients with type 2 diabetes and cardiovascular disease, albiglutide was superior to placebo with respect to major adverse cardiovascular events. Evidence-based glucagon-like peptide 1 receptor agonists should therefore be considered as part of a comprehensive strategy to reduce the risk of cardiovascular events in patients with type 2 diabetes.
Funding:
GlaxoSmithKline
Ionization and excitation of the excited hydrogen atom in strong circularly polarized laser fields
In the recent work of Herath et al. [T. Herath, L. Yan, S. K. Lee, and W. Li, Phys. Rev. Lett. 109, 043004 (2012)PRLTAO0031-900710.1103/PhysRevLett.109.043004] the first experimental observation of a dependence of strong-field ionization rate on the sign of the magnetic quantum number m [of the initial bound state (n,l,m)] was reported. The experiment with nearly circularly polarized light could not distinguish which sign of m favors faster ionization. We perform ab initio calculations for the hydrogen atom initially in one of the four bound substates with the principal quantum number n=2, and irradiated by a short circularly polarized laser pulse of 800nm. In the intensity range of 1012-1013W/cm2 excited bound states play a very important role, but also up to some 1015W/cm2 they cannot be neglected in a full description of the laser-atom interaction. We explore the region that with increasing intensity switches from multiphoton to over-the-barrier ionization and we find, unlike in tunneling-type theories, that the ratio of ionization rates for electrons initially counter-rotating and corotating (with respect to the laser field) may be higher or lower than 1