A class of identifiable birth-death models

In a striking result, Louca and Pennell (2020) recently proved that a large class of birth-death models are statistically unidentifiable from lineage-through-time (LTT) data. Specifically, they showed that any pair of sufficiently smooth birth and death rate functions is "congruent" to an infinite collection of other rate functions, all of which have the same likelihood for any LTT vector of any dimension. This fact has distressing implications for the thousands of studies which have utilized birth-death models to study evolution. In this paper, we qualify their finding by proving that an alternative and widely used class of birth-death models is indeed identifiable. Specifically, we show that piecewise constant birth-death models can, in principle, be consistently estimated and distinguished from one another, given a sufficiently large extant time tree and some knowledge of the present day population. Subject to mild regularity conditions, we further show that any unidentifiable birth-death model class can be arbitrarily closely approximated by a class of identifiable models. The sampling requirements needed for our results to hold are explicit, and are expected to be satisfied in many contexts such as the phylodynamic analysis of a global pandemic.

An example regarding Kalton's paper ‘isomorphisms between spaces of vector-valued continuous functions’

The paper alluded to in the title contains the following striking result: Let $I$ be the unit interval and $\Delta$ the Cantor set. If $X$ is a quasi Banach space containing no copy of $c_{0}$ which is isomorphic to a closed subspace of a space with a basis and $C(I,\,X)$ is linearly homeomorphic to $C(\Delta ,\, X)$ , then $X$ is locally convex, i.e., a Banach space. We will show that Kalton result is sharp by exhibiting non-locally convex quasi Banach spaces $X$ with a basis for which $C(I,\,X)$ and $C(\Delta ,\, X)$ are isomorphic. Our examples are rather specific and actually, in all cases, $X$ is isomorphic to $C(K,\,X)$ if $K$ is a metric compactum of finite covering dimension.

Scavenging of "dry" electrons prior to hydration by azide ions: Effect on the formation of H2 in the radiolysis of water by 60Co γ-rays and tritium β-electrons.

In this study, we use Monte Carlo track chemistry simulations to show that "dry" secondary electrons, precursors of the "hydrated" electron (e^-_aq), can be scavenged on the sub-picosecond time scale prior to hydration, by a high concentration (>0.1-1 M) of azide ions (N₃^-) in water irradiated with ⁶⁰Co γ-rays and ³H β-electrons at 25 °C. This is a striking result, as N₃^- is known to react very slowly with e^-_aq. These processes tend to significantly reduce the yields of H₂ as observed experimentally. For both energetic Compton electrons ("linear energy transfer", LET ∼ 0.3 keV/μm), which are generated by the cobalt-60 γ-rays, and ³H β-electrons (LET ∼ 6 keV/μm), our H₂ yield results confirm previous Monte Carlo simulations, which indicated the necessity of including the capture of the precursors to e^-_aq. Interestingly, our calculations show no significant changes in the scavenging of "dry" electrons at high azide concentrations in passing from γ-radiolysis to tritium β-radiolysis (<i>i.e.</i>, with LET). This led us to the conclusion that the higher H₂ yield observed experimentally for ³H β-electrons compared to ⁶⁰Co γ-rays is explained mainly by the difference in the radiation track structures during the chemical stage (>1 ps). The higher LET of tritium β-electrons leads to more molecular products (H₂ in this case) in tritium radiolysis than in γ-radiolysis. Finally, a value of 0.5 nm was derived for the reaction distance between N₃^- and the “dry” electron from the H₂ yields observed in ⁶⁰Co γ-radiolysis at high N₃^- concentrations.

The Physical Metric in General Relativity, Size and Gravitational Lensing of Black Holes and Neutron Stars

The physical metric in general relativity has been introduced by the author as the exact solution of Einstein equation that fits the observation of time delay of the solar system. The necessary and sufficient condition for the physical metric is that the speed of light on the angular direction is unchanged from that of vacuum. A striking result is that the radius size of a black hole and a neutron star (summarized as compact object hereafter) is found to be 2.60 times greater than predicted by the Schwarzschild metric. In this article, the gravitational lensing of the compact object at long distance is absent. In other words, it is a feature result of the physical metric that the effect of the gravitational lensing for compact object by itself disappears at long distance. It will be shown that the recent observations are consistent with the prediction of the physical metric.

Resonant absorption: Transformation of compressive motions into vortical motions

This paper investigates the changes in spatial properties when magnetohydrodynamic (MHD) waves undergo resonant damping in the Alfvén continuum. The analysis is carried out for a 1D cylindrical pressure-less plasma with a straight magnetic field. The effect of the damping on the spatial wave variables is determined by using complex frequencies that arise as a result of the resonant damping. Compression and vorticity are used to characterise the spatial evolution of the MHD wave. The most striking result is the huge spatial variation in the vorticity component parallel to the magnetic field. Parallel vorticity vanishes in the uniform part of the equilibrium. However, when the MHD wave moves into the non-uniform part, parallel vorticity explodes to values that are orders of magnitude higher than those attained by the transverse components in planes normal to the straight magnetic field. In the non-uniform part of the equilibrium plasma, the MHD wave is controlled by parallel vorticity and resembles an Alfvén wave, with the unfamiliar property that it has pressure variations even in the linear regime.

External Stressors and Time Poverty among Online Students: An Exploratory Study

In this exploratory study, we report results from interviews with 49 students at a large public urban university in the US who enrolled in at least one course online. In line with the literature, many students cited work or family reasons for enrolling in an online course. However, when asked at the end of the interview whether there were any other life events that impacted the time and energy that they had for their studies, 73% of the students cited at least one additional external stressor, and many of them cited up to three or four different categories of external stressors. These included illness/disability, death in the family, caretaking responsibilities, and housing instability, among others. One particularly striking result is that 89% of the external stressors reported by students in response to the final questions of the interview had not been volunteered by students when they were originally asked why they enrolled online or what factors impacted their course outcomes – this suggests that the prevalence of these more complex environmental factors may go underreported in studies that do not ask about them explicitly.

Revealing a temporal symmetry/asymmetry dichotomy in a Markovian setting, and a parameterization based on fractional low-order joint moments

&lt;p&gt;We show that &quot;an arrow of time&quot;, which is reflected by the joint distributions of successive variables in a stochastic process, may exist (or not) solely on grounds of marginal probability distributions, without affecting stationarity or involving the structural dependencies within the process. The temporal symmetry/asymmetry dichotomy thus revealed, is exemplified for the simplest case of stably-distributed Markovian recursions, where the lack of Gaussianity, even when the increments of the process are independent and identically distributed (i.i.d.) with symmetric marginal, is generating a break of temporal symmetry. We devise a statistical tool to evidence this striking result, based on fractional low-order joint moments, whose existence is guaranteed even for the case of &quot;fat-tailed&quot; strictly-stable distributions, and is thereby suited for parameterizing structural dependencies within such a process.&lt;/p&gt;

Relationships between metabolic status, seminal adipokines, and reproductive functions in men from infertile couples

Objective Adipokines could be a link between metabolic syndrome (MS) and infertility. While the association between circulating adipokines and fertility has been extensively studied in females, this relationship in males was less investigated, although some adipokines are detectable in seminal plasma (SP). The aim of this study was to determine adipokine levels in blood and SP and to assess the relationships between adipokines, MS and semen parameters in men from infertile couples. Design Male partners of infertile couples referred to four medical French centers were enrolled in years 2013–2016. Methods Subjects (n = 160) aged 18–45 years were assessed for anthropometric, biochemical, sperm, and circulating hormonal parameters. Leptin, adiponectin, resistin, chemerin, visfatin, and IL-6 were measured in serum and SP. Results Infertility duration was higher in men with than without MS. Adipokine concentrations were higher in blood than in SP, except for IL-6 and visfatin. The most striking result was the significant correlation observed between seminal IL-6 and spermatozoid concentration, progressive motility, and sperm vitality. Moreover, while men with MS exhibited an expected lower adiponectinemia, they displayed 2.1-fold higher adiponectin levels in SP than men without MS. Finally, logistic regression analysis showed that BMI, infertility duration, and adiponectin serum/SP ratio were independently associated with MS. Conclusions These results suggest an involvement of seminal adipokines to modulate fertility in men with MS and that seminal IL-6 could play a beneficial role on sperm functionality. Further mechanistic studies are necessary to investigate the precise roles of these adipokines in male reproduction.

ADAM10 is Expressed by Ameloblasts, Cleaves the RELT TNF Receptor Extracellular Domain and Facilitates Enamel Development

MMP20 cleaves cadherins and may facilitate cell movement, however MMP20 is not known to cleave tight junction or desmosome proteins. Ameloblasts had not previously been screened for membrane anchored proteases that could contribute to cell movement. Here we performed a PCR screen for proteolyticlly active A Disintegrin And Metalloproteinase (ADAM) family members. These proteinases are termed sheddases because they have a transmembrane domain and their catalytic domain on the cell surface can function to release anchored proteins. Significantly, ADAMs can be targeted to specific substrates on the cell membrane through their interaction with tetraspanins. Six ADAMs (ADAM8, 9, 10, 15, 17, 19) were expressed in mouse enamel organs. We show that Adam10 expression begins in the apical loop, continues through the secretory stage and abruptly ends at the transition stage when ameloblast migration ceases. ADAM10 cleaves cadherins and tight junction plus desmosome proteins and is well characterized for its role in cell movement. ADAM10 facilitated LS8 cell migration/invasion through a Matrigel coated membrane and we demonstrate that ADAM10, but not ADAM17 cleaves the RELT extracellular domain. This striking result is significant because RELT mutations cause amelogenesis imperfecta (AI) and this directly links ADAM10 to an important role in enamel development.