275 research outputs found
Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer
During the first steps of photosynthesis, the energy of impinging solar photons is transformed into electronic excitation energy of the light-harvesting biomolecular complexes. The subsequent energy transfer to the reaction center is commonly rationalized in terms of excitons moving on a grid of biomolecular chromophores on typical timescales [Formula: see text]100 fs. Today's understanding of the energy transfer includes the fact that the excitons are delocalized over a few neighboring sites, but the role of quantum coherence is considered as irrelevant for the transfer dynamics because it typically decays within a few tens of femtoseconds. This orthodox picture of incoherent energy transfer between clusters of a few pigments sharing delocalized excitons has been challenged by ultrafast optical spectroscopy experiments with the Fenna-Matthews-Olson protein, in which interference oscillatory signals up to 1.5 ps were reported and interpreted as direct evidence of exceptionally long-lived electronic quantum coherence. Here, we show that the optical 2D photon echo spectra of this complex at ambient temperature in aqueous solution do not provide evidence of any long-lived electronic quantum coherence, but confirm the orthodox view of rapidly decaying electronic quantum coherence on a timescale of 60 fs. Our results can be considered as generic and give no hint that electronic quantum coherence plays any biofunctional role in real photoactive biomolecular complexes. Because in this structurally well-defined protein the distances between bacteriochlorophylls are comparable to those of other light-harvesting complexes, we anticipate that this finding is general and directly applies to even larger photoactive biomolecular complexes
Evaluating glucose‐lowering treatment in older people with diabetes : lessons from the IMPERIUM trial
Understanding the benefits and risks of treatments to be used by older individuals (≥65 years old) is critical for informed therapeutic decisions. Glucose‐lowering therapy for older patients with diabetes should be tailored to suit their clinical condition, comorbidities and impaired functional status, including varying degrees of frailty. However, despite the rapidly growing population of older adults with diabetes, there are few dedicated clinical trials evaluating glucose‐lowering treatment in older people. Conducting clinical trials in the older population poses multiple significant challenges. Despite the general agreement that individualizing treatment goals and avoiding hypoglycaemia is paramount for the therapy of older people with diabetes, there are conflicting perspectives on specific glycaemic targets that should be adopted and on use of specific drugs and treatment strategies. Assessment of functional status, frailty and comorbidities is not routinely performed in diabetes trials, contributing to insufficient characterization of older study participants. Moreover, significant operational barriers and problems make successful enrolment and completion of such studies difficult. In this review paper, we summarize the current guidelines and literature on conducting such trials, as well as the learnings from our own clinical trial (IMPERIUM) that assessed different glucose‐lowering strategies in older people with type 2 diabetes. We discuss the importance of strategies to improve study design, enrolment and attrition. Apart from summarizing some practical advice to facilitate the successful conduct of studies, we highlight key gaps and needs that warrant further research
Optimal Time Decay of the Vlasov-Poisson-Boltzmann System in
The Vlasov-Poisson-Boltzmann System governs the time evolution of the
distribution function for the dilute charged particles in the presence of a
self-consistent electric potential force through the Poisson equation. In this
paper, we are concerned with the rate of convergence of solutions to
equilibrium for this system over . It is shown that the
electric field which is indeed responsible for the lowest-order part in the
energy space reduces the speed of convergence and hence the dispersion of this
system over the full space is slower than that of the Boltzmann equation
without forces, where the exact difference between both power indices in the
algebraic rates of convergence is 1/4. For the proof, in the linearized case
with a given non-homogeneous source, Fourier analysis is employed to obtain
time-decay properties of the solution operator. In the nonlinear case, the
combination of the linearized results and the nonlinear energy estimates with
the help of the proper Lyapunov-type inequalities leads to the optimal
time-decay rate of perturbed solutions under some conditions on initial data.Comment: 37 page
Friction force on a vortex due to the scattering of superfluid excitations in helium II
The longitudinal friction acting on a vortex line in superfluid He is
investigated within a simple model based on the analogy between such vortex
dynamics and that of the quantal Brownian motion of a charged point particle in
a uniform magnetic field. The scattering of superfluid quasiparticle
excitations by the vortex stems from a translationally invariant interaction
potential which, expanded to first order in the vortex velocity operator, gives
rise to vortex transitions between nearest Landau levels. The corresponding
friction coefficient is shown to be, in the limit of elastic scattering
(vanishing cyclotron frequency), equivalent to that arising from the Iordanskii
formula. Proposing a simple functional form for the scattering amplitude, with
only one adjustable parameter whose value is set in order to get agreement to
the Iordanskii result for phonons, an excellent agreement is also found with
the values derived from experimental data up to temperatures about 1.5 K.
Finite values of the cyclotron frequency arising from recent theories are shown
to yield similar results. The incidence of vortex-induced quasiparticle
transitions on the friction process is estimated to be, in the roton dominated
regime, about 50 % of the value of the friction coefficient, 8 % of which
corresponds to roton-phonon transitions and 42 % to roton
ones.Comment: 15 pages, 4 figures; typos corrected, to be published in PR
Regularizing effect and local existence for non-cutoff Boltzmann equation
The Boltzmann equation without Grad's angular cutoff assumption is believed
to have regularizing effect on the solution because of the non-integrable
angular singularity of the cross-section. However, even though so far this has
been justified satisfactorily for the spatially homogeneous Boltzmann equation,
it is still basically unsolved for the spatially inhomogeneous Boltzmann
equation. In this paper, by sharpening the coercivity and upper bound estimates
for the collision operator, establishing the hypo-ellipticity of the Boltzmann
operator based on a generalized version of the uncertainty principle, and
analyzing the commutators between the collision operator and some weighted
pseudo differential operators, we prove the regularizing effect in all (time,
space and velocity) variables on solutions when some mild regularity is imposed
on these solutions. For completeness, we also show that when the initial data
has this mild regularity and Maxwellian type decay in velocity variable, there
exists a unique local solution with the same regularity, so that this solution
enjoys the regularity for positive time
Formation and Propagation of Discontinuity for Boltzmann Equation in Non-Convex Domains
The formation and propagation of singularities for Boltzmann equation in
bounded domains has been an important question in numerical studies as well as
in theoretical studies. Consider the nonlinear Boltzmann solution near
Maxwellians under in-flow, diffuse, or bounce-back boundary conditions. We
demonstrate that discontinuity is created at the non-convex part of the grazing
boundary, then propagates only along the forward characteristics inside the
domain before it hits on the boundary again.Comment: 39 pages, 5 Figure
Global existence and full regularity of the Boltzmann equation without angular cutoff
We prove the global existence and uniqueness of classical solutions around an
equilibrium to the Boltzmann equation without angular cutoff in some Sobolev
spaces. In addition, the solutions thus obtained are shown to be non-negative
and in all variables for any positive time. In this paper, we study
the Maxwellian molecule type collision operator with mild singularity. One of
the key observations is the introduction of a new important norm related to the
singular behavior of the cross section in the collision operator. This norm
captures the essential properties of the singularity and yields precisely the
dissipation of the linearized collision operator through the celebrated
H-theorem
Nuclear effects on J/{\psi} production in proton-nucleus collisions
The study of nuclear effects for J/{\psi} production in proton-nucleus
collisions is crucial for a correct interpretation of the J/{\psi} suppression
patterns experimentally observed in heavy-ion collisions. By means of three
representative sets of nuclear parton distribution, the energy loss effect in
the initial state and the nuclear absorption effect in the final state are
taken into account in the uniform framework of the Glauber model. A leading
order phenomenological analysis is performed on J/{\psi} production
cross-section ratios RW/Be(xF) for the E866 experimental data. The J/{\psi}
suppression is investigated quantitatively due to the different nuclear
effects. It is shown that the energy loss effect with resulting in the
suppression on RW/Be(xF) is more important than the nuclear effects on parton
distributions in high xF region. The E866 data in the small xF keep out the
nuclear gluon distribution with a large anti-shadowing effect. However, the new
HERA-B measurement is not in support of the anti-shadowing effect in the
nuclear gluon distribution. It is found that the J/{\psi}-nucleon inelastic
cross section {\sigma} J/{\psi} abs depends on the kinematical variable xF, and
increases as xF in the region xF > 0.2. 1 Introductio
Glycaemic outcomes of an Individualised treatMent aPproach for oldER vulnerable patIents: A randomised, controlled stUdy in type 2 diabetes Mellitus (IMPERIUM).
AIM: To compare the glycaemic outcomes of 2 glucose-lowering treatment strategies in vulnerable (moderately ill and/or frail) patients aged ≥65 years with type 2 diabetes whose individual HbA1c targets were not met with diet/exercise and/or oral antihyperglycaemic medications (OAMs). METHODS: The primary endpoint of this study was a composite of achieving/maintaining individualised HbA1c targets without 'clinically significant' hypoglycaemia (severe hypoglycaemia or repeated hypoglycaemia causing interruption of patients' activities or blood glucose <54 mg/dL). Strategy-A comprised glucose-dependent therapies (N = 99) with a non-sulphonylurea OAM and a glucagon-like peptide-1 receptor agonist as the first injectable. Strategy-B comprised non-glucose-dependent therapies (N = 93) with sulphonylurea as the preferred OAM and insulin glargine as the first injectable. RESULTS: There was no significant difference between Strategies A and B in percentages of patients achieving the primary endpoint (64.5% vs 54.9%; P=0.190). Mean incidences (A vs B) of total (10.2% vs 53.8%), documented symptomatic (5.1% vs 36.6%), and asymptomatic (8.2% vs 32.3%) hypoglycaemia were lower for Strategy-A (P<0.001 each). Proportions of patients achieving/maintaining HbA1c target (A, 63.3% vs B, 55.9%) were similar. CONCLUSIONS: Similar proportions of older, vulnerable aged ≥65 years patients with type 2 diabetes achieved/maintained glycaemic treatment goals without clinically significant hypoglycaemia with Strategies A or B. However, Strategy-A resulted in lower risk of total, documented symptomatic, and asymptomatic hypoglycaemia. These results identify an approach of potential clinical benefit in this age group and will inform future clinical research in older patients with type 2 diabetes. This trial is registered with ClinTrials.gov, number NCT02072096
Single Atom and Two Atom Ramsey Interferometry with Quantized Fields
Implications of field quantization on Ramsey interferometry are discussed and
general conditions for the occurrence of interference are obtained.
Interferences do not occur if the fields in two Ramsey zones have precise
number of photons. However in this case we show how two atom (like two photon)
interferometry can be used to discern a variety of interference effects as the
two independent Ramsey zones get entangled by the passage of first atom.
Generation of various entangled states like |0,2>+|2,0> are discussed and in
far off resonance case generation of entangled state of two coherent states is
discussed.Comment: 20 pages, 5 figures, revised version. submitted to Phys. Rev.
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