1,034 research outputs found
Stochastic niche-based models for the evolution of species
There have been many studies to examine whether one trait is correlated with
another trait across a group of present-day species (for example, do species
with larger brains tend to have longer gestation times. Since the introduction
of the phylogenetic comparative method some authors have argued that it is
necessary to have a biologically realistic model to generate evolutionary trees
that incorporates information about the ecological niche occupied by species.
Price presented a simple model along these lines in 1997. He defined a
two-dimensional niche space formed by two continuous-valued traits, in which
new niches arise with trait values drawn from a bivariate normal distribution.
When a new niche arises, it is occupied by a descendant species of whichever
current species is closest in ecological niche space. In sequence, more species
are then evolved from already-existing species to which they are ecologically
closest.
Here we explore ways of extending Price's adaptive radiation model. One
extension is to increase the dimensionality of the niche space by considering
more than two continuous traits. A second extension is to allow both extinction
of species (which may leave unoccupied niches) and removal of niches (which
causes species occupying them to go extinct). To model this problem, we
consider a continuous-time stochastic process which implicitly defines a
phylogeny. To explore if trees generated under such a model (or under different
parametrizations of the model) are realistic we can compute a variety of
summary statistics that can be compared to those of empirically observed
phylogenies. For example, there are existing statistics that aim to measure:
tree balance, the relative rate of diversification, and phylogenetic signal of
traits.Comment: The Eleventh International Conference on Matrix-Analytic Methods in
Stochastic Models (MAM11), 2022, Seoul, Republic of Kore
Tensions between policy and practice: A qualitative analysis of decisions regarding compulsory admission to psychiatric hospital.
The use of detention for psychiatric treatment is widespread and sometimes necessary. International human rights law requires a legal framework to safeguard the rights to liberty and personal integrity by preventing arbitrary detention. However, research suggests that extra-legal factors may influence decisions to detain. This article presents observational and interview data to describe how decisions to detain are made in practice in one jurisdiction (England and Wales) where a tension between policy and practice has been described. The analysis shows that practitioners mould the law into 'practical criteria' that appear to form a set of operational criteria for identifying cases to which the principle of soft paternalism may be applied. Most practitioners also appear willing, albeit often reluctantly, to depart from their usual reliance on the principle of soft paternalism and authorise detention of people with the capacity to refuse treatment, in order to prevent serious harm. We propose a potential resolution for the tension between policy and practice: two separate legal frameworks to authorise detention, one with a suitable test of capacity, used to enact soft paternalism, and the other to provide legal justification for detention for psychiatric treatment of the small number of people who retain decision-making capacity but nonetheless choose to place others at risk by refusing treatment. This separation of detention powers into two systems, according to the principle that justifies the use of detention would be intellectually coherent, consistent with human rights instruments and, being consistent with the apparent moral sentiments of practitioners, less prone to idiosyncratic interpretations in practice.This study was conducted by EF as a PhD student in the Cambridge Intellectual and Developmental Disabilities Research Group, Department of Psychiatry, University of Cambridge, funded by a Wellcome Trust PhD Studentship in Biomedical Ethics. AJH and ICHC supervised the work, and MR contributed social science expertise to the working group. Cambridgeshire and Peterborough NHS Foundation Trust sponsored the project as a service evaluation study and we thank the participations for their co-operation. The findings, and suggestions for practice, have been fed back to the Trust through internal clinical governance processes. During the preparation of this paper, ICHC and AJH were supported by the NIHR's Collaboration for Leadership in Applied Health Research and Care (CLAHRC) East of England at Cambridgeshire and Peterborough NHS Foundation Trust. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Elsevier
Quantized Dispersion of Two-Dimensional Magnetoplasmons Detected by Photoconductivity Spectroscopy
We find that the long-wavelength magnetoplasmon, resistively detected by
photoconductivity spectroscopy in high-mobility two-dimensional electron
systems, deviates from its well-known semiclassical nature as uncovered in
conventional absorption experiments. A clear filling-factor dependent
plateau-type dispersion is observed that reveals a so far unknown relation
between the magnetoplasmon and the quantum Hall effect.Comment: 5 pages, 3 figure
Running coupling of the sextet composite Higgs model
The scale-dependent renormalized coupling of SU(3) gauge theory coupled to Nf = 2 flavors of massless Dirac flavors in the sextet representation is presented in the range 0 < g2 < 6:5. This range includes the location where the βb-function turns zero in the MS scheme to 3-loop and 4-loop approximations, however our non-perturbative result shows a monotonically increasing β-function. Our lattice calclulations are carried out at several lattice spacings allowing for a controlled continuum extrapolation. We also comment on a recent similar calculation by Hasenfratz et al
The lattice gradient flow at tree-level and its improvement
The Yang-Mills gradient flow and the observable , defined by the square of the field strength tensor at t > 0, are calculated at finite lattice spacing and tree-level in the gauge coupling. Improvement of the flow, the gauge action and the observable are all considered. The results are relevant for two purposes. First, the discretization of the flow, gauge action and observable can be chosen in such a way that O(a(2)), O(a(4)) or even O(a(6)) improvement is achieved. Second, simulation results using arbitrary discretizations can be tree-level improved by the perturbatively calculated correction factor normalized to one in the continuum limit
The effect of volumetric breast density on the risk of screen-detected and interval breast cancers: a cohort study.
BACKGROUND: In the light of the breast density legislation in the USA, it is important to know a woman's breast cancer risk, but particularly her risk of a tumor that is not detected through mammographic screening (interval cancer). Therefore, we examined the associations of automatically measured volumetric breast density with screen-detected and interval cancer risk, separately. METHODS: Volumetric breast measures were assessed automatically using Volpara version 1.5.0 (Matakina, New Zealand) for the first available digital mammography (DM) examination of 52,814 women (age 50 - 75 years) participating in the Dutch biennial breast cancer screening program between 2003 and 2011. Breast cancer information was obtained from the screening registration system and through linkage with the Netherlands Cancer Registry. We excluded all screen-detected breast cancers diagnosed as a result of the first digital screening examination. During a median follow-up period of 4.2 (IQR 2.0-6.2) years, 523 women were diagnosed with breast cancer of which 299 were screen-detected and 224 were interval breast cancers. The associations between volumetric breast measures and breast cancer risk were determined using Cox proportional hazards analyses. RESULTS: Percentage dense volume was found to be positively associated with both interval and screen-detected breast cancers (hazard ratio (HR) 8.37 (95% CI 4.34-16.17) and HR 1.39 (95% CI 0.82-2.36), respectively, for Volpara density grade category (VDG) 4 compared to VDG1 (p for heterogeneity < 0.001)). Dense volume (DV) was also found to be positively associated with both interval and screen-detected breast cancers (HR 4.92 (95% CI 2.98-8.12) and HR 2.30 (95% CI 1.39-3.80), respectively, for VDG-like category (C)4 compared to C1 (p for heterogeneity = 0.041)). The association between percentage dense volume categories and interval breast cancer risk (HR 8.37) was not significantly stronger than the association between absolute dense volume categories and interval breast cancer risk (HR 4.92). CONCLUSIONS: Our results suggest that both absolute dense volume and percentage dense volume are strong markers of breast cancer risk, but that they are even stronger markers for predicting the occurrence of tumors that are not detected during mammography breast cancer screening
Thermopower of a 2D electron gas in suspended AlGaAs/GaAs heterostructures
We present thermopower measurements on a high electron mobility
two-dimensional electron gas (2DEG) in a thin suspended membrane.We show that
the small dimension of the membrane substantially reduces the thermal
conductivity compared to bulk material so that it is possible to establish a
strong thermal gradient along the 2DEG even at a distance of few micrometers.
We find that the zero-field thermopower is significantly affected by the micro
patterning. In contrast to 2DEGs incorporated in a bulk material, the diffusion
contribution to the thermopower stays dominant up to a temperature of 7 K until
the phonon-drag becomes strong and governs the run of the thermopower. We also
find that the coupling between electrons and phonons in the phonon-drag regime
is due to screened deformation potentials, in contrast to piezoelectric
coupling found with bulk phonons.Comment: 7 page
On quantum teleportation with beam-splitter-generated entanglement
Following the lead of Cochrane, Milburn, and Munro [Phys. Rev. A {\bf 62},
062307 (2000)], we investigate theoretically quantum teleportation by means of
the number-sum and phase-difference variables. We study Fock-state entanglement
generated by a beam splitter and show that two-mode Fock-state inputs can be
entangled by a beam splitter into close approximations of maximally entangled
eigenstates of the phase difference and the photon-number sum
(Einstein-Podolsky-Rosen -- EPR -- states). Such states could be experimentally
feasible with on-demand single-photon sources. We show that the teleportation
fidelity can reach near unity when such ``quasi-EPR'' states are used as the
quantum channel.Comment: 7 pages (two-column), 7 figures, submitted to Phys. Rev. A. Text
unmodified, postscript error correcte
Population-based analysis of ocular Chlamydia trachomatis in trachoma-endemic West African communities identifies genomic markers of disease severity.
BACKGROUND: Chlamydia trachomatis (Ct) is the most common infectious cause of blindness and bacterial sexually transmitted infection worldwide. Ct strain-specific differences in clinical trachoma suggest that genetic polymorphisms in Ct may contribute to the observed variability in severity of clinical disease. METHODS: Using Ct whole genome sequences obtained directly from conjunctival swabs, we studied Ct genomic diversity and associations between Ct genetic polymorphisms with ocular localization and disease severity in a treatment-naĂŻve trachoma-endemic population in Guinea-Bissau, West Africa. RESULTS: All Ct sequences fall within the T2 ocular clade phylogenetically. This is consistent with the presence of the characteristic deletion in trpA resulting in a truncated non-functional protein and the ocular tyrosine repeat regions present in tarP associated with ocular tissue localization. We have identified 21 Ct non-synonymous single nucleotide polymorphisms (SNPs) associated with ocular localization, including SNPs within pmpD (odds ratio, OR = 4.07, p* = 0.001) and tarP (OR = 0.34, p* = 0.009). Eight synonymous SNPs associated with disease severity were found in yjfH (rlmB) (OR = 0.13, p* = 0.037), CTA0273 (OR = 0.12, p* = 0.027), trmD (OR = 0.12, p* = 0.032), CTA0744 (OR = 0.12, p* = 0.041), glgA (OR = 0.10, p* = 0.026), alaS (OR = 0.10, p* = 0.032), pmpE (OR = 0.08, p* = 0.001) and the intergenic region CTA0744-CTA0745 (OR = 0.13, p* = 0.043). CONCLUSIONS: This study demonstrates the extent of genomic diversity within a naturally circulating population of ocular Ct and is the first to describe novel genomic associations with disease severity. These findings direct investigation of host-pathogen interactions that may be important in ocular Ct pathogenesis and disease transmission
Stable nondegenerate optical parametric oscillation at degenerate frequencies in Na:KTP
We report the realization of a light source specifically designed for the
generation of bright continuous-variable entangled beams and for
Heisenberg-limited inteferometry. The source is a nondegenerate, single-mode,
continuous-wave optical parametric oscillator in Na:KTP, operated at frequency
degeneracy and just above threshold, which is also of interest for the study of
critical fluctuations at the transition point. The residual
frequency-difference jitter is 150 kHz for a 3 MHz cold cavity half-width
at half maximum. We observe 4 dB of photon-number-difference squeezing at 200
kHz. The Na:KTP crystal is noncritically phase-matched for a 532 nm pump and
polarization crosstalk is therefore practically nonexistent
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