3,188 research outputs found
Path Integrals and Alternative Effective Dynamics in Loop Quantum Cosmology
The alternative dynamics of loop quantum cosmology is examined by the path
integral formulation. We consider the spatially flat FRW models with a massless
scalar field, where the alternative quantization inherit more features from
full loop quantum gravity. The path integrals can be formulated in both
timeless and deparameterized frameworks. It turns out that the effective
Hamiltonians derived from the two different viewpoints are equivalent to each
other. Moreover, the first-order modified Friedmann equations are derived and
predict quantum bounces for contracting universe, which coincide with those
obtained in canonical theory.Comment: 8 pages. arXiv admin note: substantial text overlap with
arXiv:1102.475
Measurement-induced disturbance and thermal negativity of qutrit-qubit mixed spin chain
We investigate the quantum correlation in a qutrit-qubit mixed spin chain
based on measurement-induced disturbance (MID) [S. Luo, Phys. Rev. A, 77,
(2008) 022301]. We also compare MID and thermal entanglement measured by
negativity and illustrate their different characteristics.Comment: 1 text and 3 eps figures;accepted by solid state communication
Smooth-AP: Smoothing the Path Towards Large-Scale Image Retrieval
Optimising a ranking-based metric, such as Average Precision (AP), is
notoriously challenging due to the fact that it is non-differentiable, and
hence cannot be optimised directly using gradient-descent methods. To this end,
we introduce an objective that optimises instead a smoothed approximation of
AP, coined Smooth-AP. Smooth-AP is a plug-and-play objective function that
allows for end-to-end training of deep networks with a simple and elegant
implementation. We also present an analysis for why directly optimising the
ranking based metric of AP offers benefits over other deep metric learning
losses. We apply Smooth-AP to standard retrieval benchmarks: Stanford Online
products and VehicleID, and also evaluate on larger-scale datasets: INaturalist
for fine-grained category retrieval, and VGGFace2 and IJB-C for face retrieval.
In all cases, we improve the performance over the state-of-the-art, especially
for larger-scale datasets, thus demonstrating the effectiveness and scalability
of Smooth-AP to real-world scenarios.Comment: Accepted at ECCV 202
Expanding the phenotypic spectrum consequent upon de novo WDR37 missense variants.
Structural eye disorders are increasingly recognised as having a genetic basis, although current genetic testing is limited in its success. De novo missense variants in WDR37 are a recently described cause of a multisystemic syndromic disorder featuring ocular coloboma. This study characterises the phenotypic spectrum of this disorder and reports 2 de novo heterozygous variants (p.Thr115Ile, p.Ser119Tyr) in three unrelated Caucasian individuals. All had a clinical phenotype consisting of bilateral iris and retinal coloboma, developmental delay and additional, variable multisystem features. The variants fall within a highly conserved region upstream of the WD-repeat domains, within an apparent mutation cluster. Consistent with the literature, intellectual disability, structural eye disorders, epilepsy, congenital heart disease, genitorenal anomalies and dysmorphic facial features were observed. In addition, a broader developmental profile is reported with a more specific musculoskeletal phenotype described in association with the novel variant (p.Thr115Ile). We further expand the phenotypic spectrum of WDR37-related disorders to include those with milder developmental delay and strengthen the association of ocular coloboma and musculoskeletal features. We promote the inclusion of WDR37 on gene panels for intellectual disability, epilepsy and structural eye disorders
Creation of quantum correlations between two atoms in a dissipative environment from an initial vacuum state
We have investigated the effect of counter-rotating terms on the dynamics of
entanglement and quantum discord between two identical atoms interacting with a
lossy single mode cavity field for a system initially in a vacuum state. The
counter-rotating terms are found to lead to steady states in the long time
limit which can have high quantum discord, but have no entanglement. The effect
of cavity decay rate on this steady state quantum discord has been also
investigated, surprisingly, the increase in cavity decay rate is found to both
enhance and maximize the steady quantum discord for separable states.Comment: Effects of counter-rotating interaction terms on quantum discor
Frequent burning promotes invasions of alien plants into a mesic African savanna
Fire is both inevitable and necessary for maintaining the structure and functioning of mesic savannas. Without disturbances such as fire and herbivory, tree cover can increase at the expense of grass cover and over time dominate mesic savannas. Consequently, repeated burning is widely used to suppress tree recruitment and control bush encroachment. However, the effect of regular burning on invasion by alien plant species is little understood. Here, vegetation data from a long-term fire experiment, which began in 1953 in a mesic Zimbabwean savanna, were used to test whether the frequency of burning promoted alien plant invasion. The fire treatments consisted of late season fires, lit at 1-, 2-, 3-, and 4-year intervals, and these regularly burnt plots were compared with unburnt plots. Results show that over half a century of frequent burning promoted the invasion by alien plants relative to areas where fire was excluded. More alien plant species became established in plots that had a higher frequency of burning. The proportion of alien species in the species assemblage was highest in the annually burnt plots followed by plots burnt biennially. Alien plant invasion was lowest in plots protected from fire but did not differ significantly between plots burnt triennially and quadrennially. Further, the abundance of five alien forbs increased significantly as the interval (in years) between fires became shorter. On average, the density of these alien forbs in annually burnt plots was at least ten times as high as the density of unburnt plots. Plant diversity was also altered by long-term burning. Total plant species richness was significantly lower in the unburnt plots compared to regularly burnt plots. These findings suggest that frequent burning of mesic savannas enhances invasion by alien plants, with short intervals between fires favouring alien forbs. Therefore, reducing the frequency of burning may be a key to minimising the risk of alien plant spread into mesic savannas, which is important because invasive plants pose a threat to native biodiversity and may alter savanna functioning
Global and local critical current density in superconducting SmFeAsOF measured by two methods
The critical current densities of polycrystalline bulk SmFeAsOF
prepared by the powder-in-tube (PIT) method and by a conventional solid-state
reaction were investigated using the remnant magnetic moment method and
Campbell's method. Two types of shielding current, corresponding to global and
local critical current densities were observed using both
measurement methods. The global and local were on the order of
A/m and A/m at 5 K, respectively. The local decreased slightly with increasing magnetic field. The global
was independent of the preparation method, while the local was
larger for samples prepared by PIT than for those prepared by solid-state
reaction.Comment: 20 pages, 5 figures. to be published in Physica
Conserved presence of G-quadruplex forming sequences in the Long Terminal Repeat Promoter of Lentiviruses
G-quadruplexes (G4s) are secondary structures of nucleic acids that epigenetically regulate cellular processes. In the human immunodeficiency lentivirus 1 (HIV-1), dynamic G4s are located in the unique viral LTR promoter. Folding of HIV-1 LTR G4s inhibits viral transcription; stabilization by G4 ligands intensifies this effect. Cellular proteins modulate viral transcription by inducing/unfolding LTR G4s. We here expanded our investigation on the presence of LTR G4s to all lentiviruses. G4s in the 5'-LTR U3 region were completely conserved in primate lentiviruses. A G4 was also present in a cattle-infecting lentivirus. All other non-primate lentiviruses displayed hints of less stable G4s. In primate lentiviruses, the possibility to fold into G4s was highly conserved among strains. LTR G4 sequences were very similar among phylogenetically related primate viruses, while they increasingly differed in viruses that diverged early from a common ancestor. A strong correlation between primate lentivirus LTR G4s and Sp1/NF\u3baB binding sites was found. All LTR G4s folded: their complexity was assessed by polymerase stop assay. Our data support a role of the lentiviruses 5'-LTR G4 region as control centre of viral transcription, where folding/unfolding of G4s and multiple recruitment of factors based on both sequence and structure may take place
Distinctive aspects of consent in pilot and feasibility studies
Prior to a main randomized clinical trial, investigators often carry out a pilot or feasibility study in order to test certain trial processes or estimate key statistical parameters, so as to optimize the design of the main trial and/or determine whether it can feasibly be run. Pilot studies reflect the design of the intended main trial, whereas feasibility studies may not do so, and may not involve allocation to different treatments. Testing relative clinical effectiveness is not considered an appropriate aim of pilot or feasibility studies. However, consent is no less important than in a main trial as a means of morally legitimizing the investigator's actions. Two misperceptions are central to consent in clinical studies-therapeutic misconception (a tendency to conflate research and therapy) and therapeutic misestimation (a tendency to overestimate possible benefits and/or underestimate possible harms associated with participation). These phenomena may take a distinctive form in pilot and feasibility studies, owing to potential participants' likely prior unfamiliarity with the nature and purposes of such studies. Thus, participants may confuse the aims of a pilot or feasibility study (developing or optimizing trial design and processes) with those of a main trial (testing treatment effectiveness) and base consent on this misconstrual. Similarly, a misunderstanding of the ability of pilot and feasibility studies to provide information that will inform clinical care, or the underdeveloped nature of interventions included in such studies, may lead to inaccurate assessments of the objective possibility of benefit, and weaken the epistemic basis of consent accordingly. Equipoise may also be particularly challenging to grasp in the context of a pilot study. The consent process in pilot and feasibility studies requires a particular focus, and careful communication, if it is to carry the appropriate moral weight. There are corresponding implications for the process of ethical approval
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